Modified copolyesters and improved multilayer reflective films

[0001] Field of invention The present invention relates to multilayer optical films having two or more different sets of layers, each set made of a different polyester, and the improved polyester used in these films. [0002] Background of the invention Polymer films are used in a variety of applications. Certain uses of polymer films are mirrors and polarizers that reflect light in a certain polarization and wavelength range. Such reflective films are used, for example, with the backlight of a liquid crystal display to improve brightness and reduce display glare. The polarizing film is placed between the user and the backlight to reduce glare by directing the light towards the user. Further, the mirror film is placed behind the backlight to reflect the light to the user to improve the brightness. Another use of polarizing films is to reduce light intensity and glare in articles such as sunglasses. [0003] Polyester is a type of polymer useful for making polarizers or mirror films. An example of a polyester-based polarizer is the lamination of polyester layers with different compositions. One of the configurations of this laminate is that the first set is a birefringent layer and the second set of layers has an isotropic index of refraction. The second set of layers, alternating with the birefringent layer, forms a series of boundaries for reflecting light. The polarizer may also include one or more non-optical layers, eg, covering at least one surface of the laminate to prevent damage to the laminate during or after treatment. There are other configurations in which a polarizer / mirror film may be used that includes a laminate with two or more different sets of birefringence and / or isotropic layers. [0004] The properties of a given polyester generally depend on the monomer material used to prepare the polyester. Polyesters are one or more different carboxylate monomers (ie, compounds with two or more carboxylic acids or ester functional groups) and one or more different glycol monomers (ie, compounds with two or more hydroxy functional groups). ) Is often prepared by the reaction. Each set of polyester layers in the stack generally has different combinations of monomers to give each type of layer the desired properties. There is a need to develop polyester films used in polarizers and mirrors with improved properties such as physical properties, optical properties and low manufacturing costs. [0005] Outline of the invention The present invention relates to a multilayer polymer film. One embodiment is a multilayer polymer film having a plurality of first layers and a plurality of second layers. The first layer is made of a semi-crystalline, birefringent first copolyester. The first copolyester contains a carboxylate subunit and a glycol subunit, with 70-100 mol% of the carboxylate subunit being the first carboxylate subunit and 0-30 mol% of the carboxylate subunit being the first. 1 comonomer carboxylate subunit, 70-100 mol% of the glycol subunit is the first glycol subunit, 0-30 mol% of the glycol subunit is the first comonomer glycol subunit, the first At least 2.5 mol% of the combination of carboxylate and glycol subunit of copolyester is the first comonomer carboxylate subunit, the first comonomer glycol subunit or a combination thereof. The second layer is made of a second polymer with an in-plane birefringence of about 0.04 or less at 632.8 nm after the multilayer polymer film is formed. [0006] Another embodiment is a multilayer polymer film having a plurality of first layers and a plurality of second layers. The first layer is made of a semi-crystalline, birefringent first copolyester. The first copolyester contains a carboxylate subunit and a glycol subunit, with 70-100 mol% of the carboxylate subunit being the first carboxylate subunit and 0-30 mol% of the carboxylate subunit being the first. 1 comonomer carboxylate subunit, 70-100 mol% of the glycol subunit is the first glycol subunit, 0-30 mol% of the glycol subunit is the first comonomer glycol subunit, the first At least 0.5 mol% of the combination of carboxylate and glycol subunit of copolyester is the first comonomer carboxylate subunit, the first comonomer glycol subunit or a combination thereof. The first copolyester has an in-plane refractive index of 1.83 or less and a difference of 0.2 or more when measured with light of 632.8 nm. The second layer is made of a second polymer with an in-plane birefringence of about 0.04 or less at 632.8 nm after the multilayer polymer film is formed. [0007] A further embodiment is a multilayer polymer film having a plurality of first layers and a plurality of second layers. The first layer is made of a semi-crystalline, birefringent first copolyester. The first copolyester has a carboxylate subunit and a glycol subunit, with 70-100 mol% of the carboxylate subunit being the first carboxylate subunit and 0-30 mol% of the carboxylate subunit. The first comonomer carboxylate subunit, 70-100 mol% of the glycol subunit is the first glycol subunit, 0-30 mol% of the glycol subunit is the first comonomer glycol subunit, the first At least 0.5 mol% of the combination of carboxylate and glycol subunit of 1 copolyester is the first comonomer carboxylate subunit, the first comonomer glycol subunit or a combination thereof. The second layer is made of a second polymer with an in-plane birefringence of about 0.04 or less at 632.8 nm after the multilayer polymer film is formed. Multilayer polymer films are made by stretching the first and second layers at a particular stretch ratio in at least one stretch direction. After stretching the first and second layers, the index of refraction of the first layer of the multilayer polymer film in the stretching direction at 632.8 nm is a similarly constructed polyethylene naphthalate with the same in-plane birefringence and stretch ratio. At least 0.02 units less than the index of refraction in the stretching direction of the layer. [0008] Yet another embodiment is a multilayer polymer film having a plurality of first layers and a plurality of second layers. The first layer is made of a semi-crystalline, birefringent first copolyester. The first copolyester has a carboxylate subunit and a glycol subunit, with 70-100 mol% of the carboxylate subunit being the first carboxylate subunit and 70-99 mol% of the glycol subunit being the first. In 1 glycol subunit, 1-30 mol% of the glycol subunit is the first comonomer glycol subunit. The second layer is made of a second polymer with an in-plane birefringence of about 0.04 or less at 632.8 nm after the multilayer polymer film is formed. [0009] Another embodiment is a multilayer polymer film having a plurality of first layers and a plurality of second layers. The first layer is made of a semi-crystalline, birefringent first copolyester. The second layer is made of a second copolyester with an in-plane birefringence of about 0.04 or less at 632.8 nm after the multilayer polymer film is formed. The second copolyester contains a carboxylate subunit and a glycol subunit, and 0.01 to 2.5 mol% of the combination of the carboxylate and the glycol subunit contains 3 or more compounds having 3 or more carboxylate or ester functional groups. It is derived from a compound having the above hydroxy functional groups or a combination thereof. [0010] A further embodiment is a multilayer polymer film having a plurality of first layers and a plurality of second layers. The first layer is made of a semi-crystalline, birefringent first copolyester. The second layer is made of a second copolyester of polyethylene naphthalate. The second copolyester contains a glycol subunit and a carboxylate subunit, the glycol subunit of which is 70-100 mol% ethylene or butylene subunit and 1,6-hexanediol, trimethylolpropane or neopentyl glycol. 0-30 mol% comonosomal glycol subunits derived from one or more of them, the carboxylate subunits are 20-100 mol% naphthalate subunit and 0-80 mol% terephthalate or isophthalate subunit. Or a mixture of these and a 0-30 mol% comonomer carboxylate subunit derived from phthalic acid, t-butylisophthalic acid, a lower alkyl ester of these acids or a combination thereof, of the second copolyester. At least 0.5 mol% of the carboxylate and glycol subunit combination is the comonomer carboxylate subunit, the comonomer glycol subunit or a combination thereof. [0011] Another embodiment is a polymer that is a copolyester with an intrinsic viscosity of about 0.4 dL / g or higher as measured in a 60/40 wt.% Mixture of phenol / o-dichlorobenzene. This polymer contains glycol subunits and carboxylate subunits, which are 70-99 mol% ethylene or butylene subunits and 1-30 mol% comonomer glycol derived from 1,6-hexanediol. The carboxylate subunits are 5 to 99 mol% naphthalate subunits, 1 to 95 mol% terephthalate or isophthalate subunits or mixtures thereof, and phthalic acid, t-butylisophthalic acid, these. 0-30 mol% comonomer carboxylate subunits derived from lower alkyl esters of the acid or combinations thereof, with at least 3 or more 0.01-2.5 mol% combinations of copolyester carboxylates and glycol subunits. It is derived from a compound having a carboxylate, ester or hydroxy functional group of. [0012] Another embodiment is a multilayer polymer film comprising a plurality of birefringent first layers and a plurality of second layers. The first layer is made of a first copolyester with a naphthalate subunit. The second layer has an intrinsic viscosity of 0.4 to 0.5 dL / g and contains 0.01 to 5 mol% of comonomer subunits derived from a compound having three or more carboxylates, esters or hydroxy functional groups. Made of copolyester. The multilayer polymer film also includes one or more non-optical layers having an intrinsic viscosity of 0.5 dL / g or more. [0013] The above overview of the present invention is not intended to illustrate each of the illustrated embodiments or the respective embodiments of the present invention. These embodiments will be demonstrated in more detail with the following drawings and detailed description. [0014] Detailed explanation The present invention improves the properties of polymer films, particularly multilayer polymer films and comonomer for optics, which improve the properties of polymer films made from polyesters having naphthalate subsystems, including, for example, copolymers of polyethylene naphthalate. Regarding the use of subunits. [0015] FIG. 1 shows, for example, a multilayer polymer film 10 that can be used as an optical polarizer or a mirror. The film 10 includes one or more first optical layers 12, one or more second optical layers 14 and one or more non-optical layers 18. The first optical layer 12 is preferably a uniaxial or biaxially oriented birefringent polymer layer. The second optical layer 14 may also be a birefringent, uniaxial or biaxially oriented polymer layer. However, more generally, the second optical layer 14 has an isotropic refractive index different from that of at least one of the first optical layers 12 after stretching. The manufacturing, usage and design requirements for the multilayer polymer film 10 are described in detail in US Patent Application No. 08 / 402,041 "Multilayer Optical Film" and US Patent Application No. 09 / 006,288 "Process for Making Multilayer Optical Films". ing. The present invention is mainly illustrated by a film 10 having a second optical layer 14 having an isotropic refractive index, but the principles and examples described herein are described in US Patent Application No. 09 / 006,458. It also applies to multilayer polymer films with a second birefringent optical layer 14, as described in "Optical Films and Their Manufacturing Processes". [0016] Similar additional sets of optical layers for the first and second optical layers 12 and 14 may be used for the multilayer polymer film 10. The design principles disclosed herein for the first and second sets of optics can also be applied to additional sets of optics. Further, although FIG. 1 shows only a single laminate 16, it is conceivable that the multilayer polymer film 10 may be formed from a plurality of laminates and later combined to form the film 10. [0017] The optical layers 12, 14 and any one or more non-optical layers 18 are generally arranged on top of the other layers to form a laminate 16. Usually, the optical layers 12 and 14 are configured as alternating pairs, as shown in FIG. 1, to form a series of boundaries between layers with different optical properties. The optical layers 12 and 14 are generally less than 1 μm thick. However, a thicker layer may be used. Further, although only 6 optical layers 12 and 14 are used in FIG. 1, many multilayer polymer films 10 have a large number of optical layers. A typical multilayer polymer film has about 2 to 5000 optical layers, preferably about 25 to 2000 optical layers, more preferably about 50 to 1500 optical layers, and most preferably about 75 to 1000 optical layers. Has a layer. [0018] The non-optical layer 18 is a polymer layer located in and / or on the laminate 16 (see FIG. 1) that protects the optical layers 12 and 14 from damage and assists in the coextrusion process. And / or improve the mechanical properties after processing. The non-optical layer 18 is often thicker than the optical layers 12 and 14. The thickness of the non-optical layer 18 is usually at least 2 times, preferably at least 4 times, more preferably at least 10 times the individual thicknesses of the optical layers 12 and 14. The thickness of the non-optical layer 18 may be varied to create a multilayer polymer film 10 with a particular thickness. Generally, one or more non-optical layers 18 are arranged such that at least part of the light is transmitted, polarized and / or reflected by the optical layers 12 and 14 and passes through the non-optical layers (eg, non-optical layers). The optical layer is placed in the path of light that passes through or is reflected by the optical layers 12 and 14). [0019] The optical layers 12, 14 and the non-optical layers 18 of the multilayer polymer film 10 are generally composed of a polymer such as polyester. Polyester contains carboxylate and glycol subunits and is produced by the reaction of carboxylate monomer molecules with glycol monomer molecules. Each carboxylate monomer molecule has two or more types of carboxylic acid or ester functional groups, and each glycol monomer molecule has two or more types of hydroxy functional groups. The carboxylate monomer molecules may all be the same or may be two or more different types of molecules. The same is true for glycol monomer molecules. The term "polymer" includes both polymers and copolymers, as well as polymers or copolymers formed in miscible blends by reactions, such as coextrusion or, for example, transesterification. [0020] The properties of the polymer layer or film depend on the monomer molecule specially selected. An example of a polyester useful for a multilayer optical film is, for example, polyethylene naphthalate (PEN), which can be produced by the reaction of naphthalenedicarboxylic acid and ethylene glycol. [0021] [0021] Suitable carboxylate monomer molecules for use in the formation of carboxylate subunits in the polyester layer include, for example, 2,6-naphthalenedicarboxylic acid and its isomers; terephthalic acid; isophthalic acid; phthalic acid; azelaic acid; adipic acid. Sevacinic acid; norbornenedicarboxylic acid; bicyclooctanedicarboxylic acid; 1,6-cyclohexanedicarboxylic acid and its isomers; t-butylisophthalic acid, trimeritoic acid, sulfonated sodium isophthalic acid; 2,2'-biphenyldicarboxylic acid and its isomers Heterogeneous; and lower alkyl esters such as methyl and ethyl esters of these acids. The term "lower alkyl" here refers to a straight or branched chain alkyl group from C1 to C10. The term "polyester" also includes polycarbonate derived from the reaction of glycol monomer molecules with carbonic acid esters. [0022] Glycol monomer molecules suitable for use in the formation of glycol subunits in the polyester layer include ethylene glycol; propylene glycol; 1,4-butanediol and its isomers; 1,6-hexanediol; neopentyl glycol; polyethylene glycol. Diethylene glycol; tricyclodecanediol; 1,4-cyclohexanedimethanol and its isomers; norbornandiol; bicyclo-octanediol; trimethylolpropane; pentaerythritol; 1,4-benzenedimethanol and its isomers; bisphenol A; Included are 1,8-dihydroxybiphenyl and its isomers; and 1,3- (bis (2-hydroxyethoxy) benzene). [0023] Non-polyester polymers are also useful in making polarizers or mirror films. For example, a layer made of polyester, such as polyethylene naphthalate, can be combined with a layer made of an acrylic polymer to form a highly reactive mirror film. In addition, polyetherimides may be used with polyesters such as PEN and coPEN to produce multilayer optical films. Other polyester / non-polyester combinations such as polybutylene terephthalate and polyvinyl chloride may be used. [0024] The first optical layer 12 is generally an orientable polymer film such as a polyester film, for example birefringent by stretching the first optical layer 12 in one or more desired directions. be able to. The term "birefringence" means that the indices of refraction in the orthogonal x, y and z directions are not all the same. A simple selection of the x, y and z axes for multiple films or layers in a film is shown in Figure 1. The x and y axes correspond to the length and width of the film or layer, and the x-axis corresponds to the thickness of the layer or film. In the embodiment shown in FIG. 1, the film 10 has several optical layers 12 and 14 laminated on top of the other layers in the z direction. [0025] The first optical layer 12 may be uniaxially oriented, for example, by stretching in a unidirectional direction. The second orthogonal direction may be narrowed to a value less than its original length. In one embodiment, the extension direction essentially corresponds to either the x or y axis shown in FIG. However, other directions may be selected. A birefringent uniaxially oriented layer generally has an incident ray having a plane of polarization parallel to the direction of orientation (ie, the direction of extension) and a plane of polarization parallel to the direction of intersection (ie, the direction orthogonal to the direction of extension). Shows differences in light transmission and / or reflection. For example, stretching an orientable polyester film along the x-axis generally results in n_x n_yThe result is. n_xAnd n_yIs the index of refraction of light polarized in a plane parallel to the "x" and "y" axes, respectively. The degree of change in the index of refraction along the stretching direction depends on factors such as the amount of stretching, the stretching rate, the temperature of the film during stretching, the thickness of the film, the variation in the thickness of the film, and the composition of the film. In general, in-plane birefringence (n) after orientation of the first optical layer 12._x-n_yAbsolute value) is 0.04 or more, preferably about 0.1 or more, and more preferably about 0.2 or more at 632.8 nm. All birefringence and index values are recorded for light at 632.8 nm unless otherwise noted. [0026] Polyethylene naphthalate (PEN) is a useful material for forming the first optical layer 12 because it becomes extremely birefringent after stretching. The index of refraction of PEN for 632.8 nm light polarized in a plane parallel to the stretching direction increases from about 1.62 to about 1.87. Within the visible spectrum, PEN exhibits birefringence of 0.20 to 0.40 over the wavelength range of 400 to 700 nm for general highly oriented elongation (ie, the original dimensions at a temperature of 130 ° C and an initial strain rate of 20% / min). Material stretched more than 5 times. [0027] The birefringence of the material can be increased by increasing the molecular orientation. Many birefringent materials are crystalline or semi-crystalline. The term "crystalline" here refers to both crystalline and semi-crystalline materials. PEN and other crystalline polyesters such as polybutylene terephthalate (PBN), polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are the birefringent film layers often found in the first optical layer 12. This is an example of a crystalline material useful for construction. In addition, copolymers of PEN, PBN, PET and PBT are also crystalline or semi-crystalline. When a comonomer is added to PEN, PBN, PET or PBT, for example, the adhesion to the second optical layer 14 or the non-optical layer 18 and / or the low temperature of the working temperature (ie, the temperature of film extrusion and / or elongation) Other properties of the material, including optics, can be improved. [0028] In certain embodiments, the first optical layer 12 is a semi-crystal of 70-99 mol% of the first carboxylate subunit and 1-30 mol%, preferably 5-15 mol% of comonomer carboxylate subunit. Made from sex, birefringent copolyester. The comonomer carboxylate subunit may be one or more of the above-mentioned subunits. Preferred first carboxylate subunits include naphthalate and terephthalate. [0029] If the polyester material of the first optical layer 12 contains two or more carboxylate subunits, the polyester is a block copolyester and the other layer (ie, the first) made from block copolymers with similar blocks. The adhesion of 2 to the optical layer 14 or the non-optical layer 18) may be improved. Random copolyester may be used. [0030] In another embodiment, the first optical layer 12 is semi-crystalline with 70-99 mol% of the first glycol subunit and 1-30 mol%, preferably 5-30 mol% of comonomer glycol subunit. Made from birefringent copolyol. The comonomer glycol subunit may be one or more of the above-mentioned subunits. The preferred first glycol subunit is derived from the C2-C8 diols. The more preferred first glycol subunit is derived from ethylene glycol or 1,4-butanjir. [0031] Yet another embodiment includes a first optical layer 12 in which both carboxylate and glycol subunits contain comonomer subunits. For these embodiments, generally at least 0.5 mol%, preferably at least 2.5 mol%, of the combination of carboxylate and glycol subunits is the comonomer carboxylate subunit, comonomer glycol subunit, or a combination thereof. [0032] As the addition of comonomer carboxylates and / or glycol subunits increases, the index of refraction in the orientation direction, which is generally the maximum index of refraction, often decreases. Based on such observations, we come to the conclusion that the birefringence of the first optical layer has a proportional effect. However, the refractive index in the cross direction has also been found to decrease with the addition of comonomer subunits. This means that birefringence is essentially maintained. [0033] For example, when 3 mol% isophthalate subunit is added to polyethylene naphthalate, the melting treatment temperature drops to about 280 ° C to about 265 ° C with only 0.02 units of birefringence being lost. Figures 3A and 3B show the glass transition temperature and freezing point for the addition of 3-9 mol% isophthalate (derived from dimethylisophthalate (DMI)) or terephthalate (derived from dimethylterephthalate (DMT)) subunit. Shows a decrease in. In general, the reduction in freezing point is usually greater than the change in glass transition temperature for a given amount of substitution subunits. FIG. 4 shows the average birefringence of low melting point coPEN with 0-9 mol% terephthalate and isophthalate subunits. This low melting point coPEN generally adheres well to a second optical layer made from coPEN containing terephthalate and / or isophthalate subunits due to the presence of common monomer subunits. [0034] In many cases, the multilayer polymer film 10 is a similar multilayer polymer film formed using PEN for the first optical layer and a given stretch ratio (ie, the length of the film in the stretch direction before and after stretching). It is formed using a first optical layer 12 made from coPEN having the same in-plane birefringence. The birefringence value can be adapted by adjusting processing parameters such as processing or stretching temperature. The coPEN optical layer has a refractive index in the stretching direction that is at least 0.02 units less than the refractive index in the stretching direction of the PEN optical layer. Since the refractive index in the non-stretching direction is reduced, birefringence is maintained. [0035] In certain preferred embodiments of the multilayer polymer film, the first optical layer has an in-plane index of refraction (ie, n)._xAnd n_y) Is 1.83 or less, preferably 1.80 or less, and differs by 0.15 units or more, preferably 0.2 units or more when measured using light of 632.8 nm (that is, | n)._x-n_y|) Created from coPEN. PEN often has an in-plane refractive index difference of 1.84 or higher and an in-plane refractive index of about 0.22 to 0.24 when measured using light of 632.8 nm. The difference in in-plane refractive index, or birefringence, of the first optical layer, whether PEN or coPEN, may be reduced to less than 0.2 to improve properties such as interlayer adhesion. Similar comparisons of coPBN and coPET suitable for the first layer can also be made with PBN and PET. [0036] The second optical layer 14 can be made of various polymers. Suitable polymers include vinyl polymers and copolymers made from monomers such as vinylnaphthalene, styrene, maleic anhydride, acrylates and methacrylates. Examples of such polymers include polyacrylates, polymethacrylates such as poly (methylmethacrylate) (PMMA) and isotactic or syndiotactic polystyrene. Other polymers include condensed polymers such as polysulfones, polyamides, polyurethanes, polyamic acids and polyimides. In addition, the second optical layer 14 may be formed from polymers and copolymers such as polyester and polycarbonate. The second optical layer 14 is illustrated below by a polyester copolymer. However, it is understood that other polymers mentioned above can also be used. Similar issues regarding the optical properties of copolyesters also apply to other polymers and copolymers, as described below. [0037] In some embodiments, the second optical layer 14 is uniaxially or biaxially oriented. However, more generally, the second optical layer 14 is not oriented under the treatment conditions used to orient the first optical layer 12. These second optical layers 14 generally retain a relatively isotropic index of refraction, even when stretched. The birefringence of the second optical layer is preferably less than about 0.04 at 632.8 nm, more preferably less than about 0.02. [0038] Suitable materials for the second optical layer 14 include copolymers of PEN, PBN, PET or PBT. Generally, these copolymers have 20-100 mol% of a second carboxylate subunit, such as a naphthalate (for coPEN or coPBN) or terephthalate (for coPET or coPBT) subunits, and a second comonomer carboxy. Contains 0-80 mol% of rate subunits. The copolymer also has 40-100 mol% of second glycol subunits such as ethylene (for coPEN or coPET) or butylene (for coPBN or coPBT) and 0-60 for the second comonomer glycol subunit. Contains mol%. At least about 10 mol% of the combination of carboxylate and glycol subunit is the second comonomer carboxylate or glycol subunit. [0039] An example of polyester used in the second optical layer 14 is low cost coPEN. One coPEN currently in use has a carboxylate subunit of about 70 mol% naphthalate and about 30 mol% isophthalate. The low cost coPEN replaces some or all of the isophthalate subunits with terephthalate subunits. The cost of this polymer is reduced because dimethylisophthalate, a common source of isophthalate subunits, is now significantly more expensive than dimethylterephthalate, the source of terephthalate subunits. Further, as shown in FIG. 5, coPEN having a terephthalate subunit tends to have higher thermal stability than coPEN having an isophthalate subunit. [0040] However, replacing terephthalate with isophthalate increases the birefringence of the coPEN layer. Therefore, a combination of terephthalate and isophthalate is desirable. Low-cost coPEN generally has a carboxylate subunit in which 20-80 mol% of the carboxylate subunit is naphthalate, 10-60 mol% is terephthalate, and 0-50 mol% is isophthalate subunit. .. It is preferred that 20-60 mol% carboxylate subunit is terephthalate and 0-20 mol% is isophthalate. It is preferred that 50-70 mol% carboxylate subunit is naphthalate, 2-50 mol% is terephthalate and 0-10 mol% is isophthalate subunit. [0041] Since coPEN is slightly birefringent and oriented when stretched, it is desirable to produce this birefringent-reduced polyester composition for use in the second optical layer 14. The low birefringence coPEN may be synthesized by the addition of a comonomer material. Examples of birefringent reduced comonomer materials suitable for use in the diol subunit include those derived from 1,6-hexanediol, trimethylolpropane and neopentyl glycol. Examples of birefringent reduced comonomer materials suitable for use in the carboxylate subunit include those derived from t-butyl-isophthalic acid, phthalic acid and their lower alkyl esters. FIG. 6 is a graph showing the decrease in birefringence of coPEN due to the addition of these materials. This reduction is greater than or equal to 0.07 at 632.8 nm when the second optical layer 14 is stretched under high strain conditions (ie, stretching ratio of 5: 1 or greater) or at low stretching temperatures. The addition of comonomer to coPEN also increases the angular gain of the optical polarizer normal. The normal angular gain is a measure of the increase in light emitted from the LCD when the reflected polarizer is used in combination with an absorbent polymer. [0042] Preferred birefringence-reducing comonomer materials are derived from t-butyl-isophthalic acid, its lower alkyl esters and 1,6-hexanediol. Certain preferred comonomer materials are trimethylolpropane and pentaerythritol, which also act as branching agents. The comonomer may be irregularly distributed in the coPEN polyester or may form one or more blocks in the block copolymer. [0043] Examples of low polyrefractive coPENs are 70-100 mol% of C2-C4 diols and about 0-30 mol derived from 1,6-hexanediol or its subunits, trimethylrol propane or neopentyl glycol. Glycol subunits derived from% comonomerdiol subunits and 20-100 mol% naphthalate, 0-80 mol% terephthalate or isophthalate subunits or mixtures thereof, 0-30 mol% phthalic acid, t -Includes carboxylate subunits, which are comonomer carboxylate subunits derived from butyl-isophthalic acid or lower alkyl esters thereof. In addition, the low birefringent coPEN has at least 0.5-5 mol% of the comonomer carboxylate or the combination of the glycol subunit carboxylate and the glycol subunit. [0044] The addition of comonomer subunits derived from compounds with three or more carboxylates, esters or hydroxy functional groups also reduces the birefringence of the copolyester in the second layer. These compounds act as branching agents to form branches or crosslink with other polymer molecules. In certain embodiments of the invention, the copolyester in the second layer contains 0.01-5 mol%, preferably 0.1-2.5 mol% of these branching agents. [0045] Certain polymers include 70-99 mol% C2-C4 diols, about 1-30 mol% comonomer subunits derived from 1,6-hexanediol, and 5-~ Derived from one or more of 99 mol% naphthalate, 1-95 mol% terephthalate, isophthalate or mixtures thereof, 0-30 mol% phthalic acid, t-butyl-isophthalic acid or lower alkyl esters thereof. It has a carboxylate subunit, which is a comonomer carboxylate subunit. In addition, at least 0.01-2.5 mol% of the combination of carboxylate and glycol subunit of this copolyester is the branching agent. [0046] Another useful polyester is the low molecular weight coPEN, as birefringence generally decreases with molecular weight. The intrinsic viscosity of low molecular weight coPEN is 0.4 to 0.5 dL / g. The intrinsic viscosity of the polymer is maintained by adding about 0.5-5 mol% of monomer with 3 or more carboxylates, esters and / or hydroxy groups. These monomers often also act as branching agents. The molecular weight of the polymer is established, for example, by terminating the polymerization at a particular melt viscosity determined by the stretching force of the reaction stirrer, the stirrer speed and the melt temperature. Generally, a non-optical layer with an intrinsic viscosity of 0.5 dL / g or higher is used with this low molecular weight coPEN to provide a structural support. [0047] Suitable branched monomers for use in increasing the melt viscosity of low molecular weight coPENs are alcohols with more than 2 hydroxy functional groups, carboxylic acids with more than 2 carboxylic acid functional groups and their lower alkyls. Esters can be mentioned. Suitable branched monomers include trimethylolpropane, pentaerythritol and trimeritic acid. FIG. 7 shows the decrease in birefringence with the decrease in molecular weight (measured by the decrease in intrinsic viscosity). [0048] Another type of useful copolyester includes cyclohexanedicarboxylate subunits. These copolyesters are particularly useful as low index polymers due to their viscoelastic properties that allow stable multi-layer coextrusion with polyethylene naphthalate in the first optical layer 12. In contrast, other low-refractive-index aliphatic copolyesters do not have the rheological properties required to provide a stable melt flow when co-extruded with polyethylene naphthalates in a multilayer melt manifold. Cyclohexanedicarboxylate also exhibits improved thermal stability during coextrusion over other low index copolyesters. [0049] Tertiary butylisophthalate is a carboxylate subunit that is preferred for use with cyclohexanedicarboxylate in that it effectively improves the tensile stress of copolyesters without essentially increasing the glass transition temperature and refractive index. It is a unit. With the addition of tertiary butylisophthalate, the refractive index of cyclohexanedicarboxylate copolyester is as low as 1.51 at 632.8 nm, and the glass transition temperature exceeds room temperature. Branched monomers such as trimethylolpropane can be used to synthesize high viscosity polymers from these monomers without the need for large amounts of catalyst or long reaction times, improving polymer color and lightness. .. Thus, non-birefringent copolyesters with a low index of refraction are produced by cyclohexanedicarboxylate and tertiary butylisophthalates, which provide carboxylate subunits, and ethylene glycol and trimethylolpropane, which provide glycol subunits. To. These copolyesters are useful for making multilayer optical films that retain their physical properties at room temperature. Copolyesters made using naphthalene dicarboxylate and cyclohexane dicarboxylate as carboxylates can be coextruded with polyethylene naphthalate to form a multilayer polymer film with good interlayer adhesion. [0050] One embodiment of the invention includes a second optical layer made of polyester with a carboxylate subunit derived from cyclohexane dicarboxylate. Preferably, the polyester is a carboxylate subunit derived from 5 to 95 mol% dimethylcyclohexanedicarboxylate and 5 to 95 mol% dimethyl tertiary butylisophthalate, and 85 to 99.99 mol% C2 to C4. And a glycol subunit derived from 0.01-5 mol% trimethylolpropane. More preferably, the polyester is a carboxylate subunit derived from 50-85 mol% dimethylcyclohexanedicarboxylate and 15-50 mol% dimethyl tertiary butylisophthalate, and 98-99.99 mol% C2-. It has a diol of C4 and a glycol subunit derived from 0.01-2 mol% trimethylolpropane. [0051] The non-optical layer 18 may also be made of copolyester using the same material and the same amount of each material as in the second optical layer 14. Further, as described above for the second optical layer 14, other polymers may be used. When coPEN (ie, a copolymer of PEN) or other copolymer material is used in the skin layer (as shown in Figure 1), the layering of the multilayer polymer film (ie, most polymer molecules in strain crystallinity and orientation). It was found that the peeling of the film due to the arrangement of This is because the coPEN orientation of the skin layer is very small when stretched under the conditions used to orient the first optical layer 12. [0052] Preferably, the polyester of the second optical layer 12, the polyester of the second optical layer 14 and the non-optical layer 18 are selected to have similar rheological properties (melt viscosity) so that they can be coextruded. In general, the second optical layer 14 and the non-optical layer 18 have a glass transition temperature that is lower than the glass transition temperature of the first optical layer 12 or higher than the glass transition temperature of the first optical layer 12 by about 40 ° C. Has Tg. The glass transition temperature of the second optical layer 14 and the non-optical layer 18 is preferably lower than the glass transition temperature of the first optical layer 12. [0053] A polarizer is created by combining a uniaxially oriented first optical layer 12 with a second optical layer 14 having an isotropic index of refraction that is approximately equal to one of the in-plane refractive indexes of the oriented layer. You may. Instead, the optical layers 12 and 14 are both formed from the birefringent polymer and oriented by multiple stretching treatments so that the refractive indexes in a single in-plane direction are approximately equal. In each case, a light reflecting surface is formed at the boundary between the two optical layers 12 and 14. Light polarized in a plane parallel to the direction in which the refractive indexes of the two layers are approximately equal is essentially transmitted. Light polarized on planes parallel to different directions of refractive index of the two layers is reflected at least partially. The index of refraction can be increased by increasing the number of layers or by increasing the difference in index of refraction between the first and second layers 12, 14. [0054] In general, the highest reflectance for a particular boundary is obtained at a wavelength that corresponds to twice the optical thickness of the combination of the pair of optical layers 12, 14 that form the boundary. The optical depth of the two layers is n₁d₁+ n₂d₂Represented by, in the formula, n₁, N₂Is the index of refraction of two layers, d₁, D₂Is the thickness of the layer. Layers 12 and 14 each have a quarter wavelength thickness, or layers 12 and 14 have different optical thicknesses as long as the total optical thickness is half (or twice) the wavelength. May have. Films with multiple layers may include layers of different optical thicknesses to increase the reflectance of the film over a wavelength range. For example, the film may include individually tuned pairs of layers for best reflection of light with a particular wavelength. [0055] Alternatively, the first optical layer 12 may be biaxially oriented by stretching in two different directions. Stretching the optical layer 12 in two directions results in a symmetric or asymmetric stretch in the two orthogonal axes of choice. [0056] An example of the formation of a mirror is to combine a biaxially oriented optical layer 22 with a second optical layer 24 having a refractive index different from the in-plane refractive index of both layers of the biaxially oriented layer. Due to the refractive index mismatch between the two optical layers 12 and 14, the mirror works by reflecting either polarized light. Mirrors can also be made by using a combination of uniaxially oriented layers and significantly different in-plane refractive indexes. In another embodiment, the first optical layer 12 is not birefringent, and the mirror is formed by combining the first and second optical layers 12, 14 having significantly different refractive indexes. Reflection occurs without orienting the layers. There are other methods, and a combination of layers known to create a mirror and a polarizer may be used. These particular combinations described above are merely examples. [0057] The second optical layer 14 may be made to have various optical properties, at least in part, depending on the desired action of the film 10. In one embodiment, the second optical layer 14 is made of a polymeric material that is less optically oriented when stretched under the conditions used to orient the first optical layer 12. Such a layer is particularly useful for forming a reflective polarizing film. This is because, for example, when the laminate 16 is formed by coextrusion and then stretched, the second optical layer 14 can orient the first optical layer 12 while remaining relatively isotropic. In general, the index of refraction of the second optical layer 14 is approximately equal to the index of refraction of one of the oriented first optical layers 12 and transmits polarized light in a plane parallel to the direction of the matching refractive index. be able to. The two nearly equal indices of refraction differ at 632.8 nm, preferably by about 0.05 or less, more preferably by about 0.02 or less. In one embodiment, the refractive index of the second optical layer 14 is approximately equal to the refractive index of the first optical layer 12 before stretching. [0058] [0058] In other embodiments, the second optical layer 14 is oriented. In some cases, the second optical layer 14 has one in-plane index of refraction that is essentially the same as the corresponding index of refraction of the first optical layer 12 after the orientation of the two sets of layers 12, 14. On the other hand, the other in-plane refractive index is essentially different from that of the first optical layer 12. In other cases, especially in mirror applications, the in-plane refractive indexes of both optical layers 12 and 14 are essentially different after orientation. [0059] Again, referring to FIGS. 1 and 2, one or more non-optical layers 18 are formed as skin layers on at least one surface of the laminate 16 as shown in FIG. 1, for example during and / or after treatment. Protects optical layers 12 and 14 from physical damage. In addition, one or more non-optical layers 18 are formed in the laminate 16 as shown in FIG. 2, for example, to impart greater mechanical strength to the laminate or to protect the laminate during processing. [0060] It is desirable that the non-optical layer 18 be less involved in determining the optical properties of the multilayer polymer film 10, at least over the wavelength range. The non-optical layer 18 is generally birefringent or non-orientable, but in some cases not necessarily. Generally, when the non-optical layer 18 is used as a skin layer, there is at least some surface reflection. When the multilayer polymer film 10 is used as a polarizer, the non-optical layer preferably has a relatively low refractive index. This reduces the amount of surface reflection. When the multilayer polymer film 10 is used as a mirror, the non-optical layer 18 preferably has a high refractive index in order to increase the reflection of light. [0061] When the non-optical layer 18 is in the stack 16, light is at least slightly polarized or reflected by the non-optical layer 18 along with the optical layers 12 and 14 in close proximity to the non-optical layer 18. However, in general, the thickness of the non-optical layer is such that the light reflected by the non-optical layer 18 in the stack 16 has wavelengths outside the region, for example, wavelengths in the infrared region for visible light polarizers or mirrors. The thickness. [0062] Various functional layers or coatings may be added to the films and optics of the invention, especially along the surface of the film or device, to alter or improve physical or chemical properties. Such layers or coatings include, for example, lubricants, low adhesive backside materials, conductive layers, antistatic coatings or films, barrier layers, flame retardants, UV stabilizers, abrasion resistant materials, optical coatings and / or mechanical. Examples include substrates designed to improve completeness or strength of the film or device. [0063] A skin layer or coating may be added to impart the desired barrier properties to the resulting film or device. Thus, for example, a barrier film or coating may be added as a skin layer, or component within the skin layer, to allow the film or device to permeate liquids such as water and organic solvents, or gases such as oxygen and carbon dioxide. Can be changed. [0064] A skin layer or coating may be added to impart wear resistance to the resulting article or improve the wear resistance of the resulting article. Thus, for example, a skin layer containing silica particles embedded in a polymer matrix, of course, if such a layer does not impair the optical properties required for the intended use of the film. , In addition to the optical film produced according to the present invention, the film may be imparted with abrasion resistance. [0065] A skin layer or coating may be added to impart fracture and / or tear resistance to the resulting article or to improve the fracture and / or tear resistance of the resulting article. Factors to consider when choosing a material for the tear resistance layer are percent elongation at break, Young rate, tear strength, adhesion to the inner layer, percent transmission and absorbance in the electromagnetic band, optical clarity or Haze, index of refraction as a function of frequency, texture and sparseness, thermal stability of melt, molecular weight distribution, melt rhology and coextrusion, mixability and internal diffusion rate between skin and optical layers, viscoelasticity Response, relaxation and crystallization behavior under stretching conditions, thermal stability at operating temperature, wettability, ability to adhere to coatings, and permeability to various gases and solvents. The break or tear resistance layer can be applied during the manufacturing process or during subsequent coating or laminating of the multilayer polymer film 10. Adhesion of these layers to the film during a manufacturing process, such as a coextrusion process, provides the advantage that the film is protected during the manufacturing process. In certain embodiments, one or more fracture or tear resistance layers may be applied in the film alone or in combination with a fracture or tear resistance skin layer. [0066] The films and optics of the present invention can be provided with good sliding properties by treatment with a low friction coating or lubricant, such as coating the surface with polymer beads. Alternatively, the surface morphology of these materials may be modified by manipulating the extrusion conditions to give the film a slippery surface. Such a method of modifying surface morphology is described in US Pat. No. 5,759,467. [0067] In certain applications, such as when the multilayer polymer film 10 of the present invention is used as a component in an adhesive tape, the film is treated with a low adhesive backside (LAB) coating or film, such as based on urethane, silicone or fluorocarbon chemistry. Is desirable. Since the film treated in this way exhibits appropriate peeling properties with respect to the pressure-sensitive adhesive (PSA), it is possible to treat them with an adhesive and wind them on a roll. The adhesive tape thus produced can be used for decorative purposes or for any application where a diffuse or transmissive surface on the tape is desired. [0068] The film and optical device of the present invention may also be provided with one or more conductive layers. Such conductive layers include metals such as silver, gold, copper, aluminum, chromium, nickel, tin and titanium, metal alloys such as silver alloys, stainless steel and inconel, doped and non-doped tin oxide, zinc oxide and It may contain semiconductor metal oxides such as indium tin oxide (ITO). [0069] The films and optical devices of the present invention may also be coated with an antistatic coating or film. Such coatings or films can be, for example, V.₂O₅Includes salts of sulfonic acid polymers, carbon or other conductive metal layers. [0070] The films and devices of the present invention may also be fitted with one or more layers of barrier films or coatings that alter the permeation properties of the film for certain liquids or gases. Thus, for example, the devices and films of the present invention include water vapor, organic solvents, O.₂Or CO₂A film or coating may be applied to prevent permeation through the film. Barrier coatings are especially desirable in high humidity environments where the film or device components are distorted by the permeation of moisture. [0071] The films and optics of the present invention may also be treated with flame retardant materials, especially when used in environments subject to strict fire protection regulations such as aircraft. Suitable flame-retardant materials include aluminum trihydrate, antimony trioxide, antimony pentoxide and flame-retardant organic phosphate compounds. [0072] The films and optics of the present invention may also have an abrasion resistant or hard coating that may be applied as a skin layer. For example, acrylic hard coats available under the trade names Acryloid A-11 and Paraloid K-120N from Rohm & Haas (Philadelphia, PA); for example, those described in US Pat. No. 4,249,011 and Sartomer. Urethane acrylate available from (Westchester, PA); and aliphatic polyisocyanate (available from Miles (Pittsburgh, PA) under the trade name Desmodur N-3300) and polyester (Union Carbide (Texas, Texas). A urethane hard coat obtained from the reaction of Tone Polyol 0305) from Houston) can be mentioned. [0073] The films and optics of the present invention are further laminated to rigid or semi-rigid substrates such as glass, metal, acrylic, polyester and other polymer backings to provide structural rigidity, wettability or manageability. You may. For example, the multilayer polymer film 10 can be laminated to a thin acrylic or metal backing and punched or otherwise molded to maintain the desired shape. For applications such as applying the film to other destructible backings, additional layers may be used, including PET film or fracture-tear resistant film. [0074] The films and optics of the present invention may also be impact resistant films and coatings. Suitable films and coatings for this purpose are described, for example, in EP 592284 and EP 591055 and are commercially available from 3M, Inc. (St. Paul, Minnesota). [0075] Various optical layers, materials and devices may be applied or used together with the films and devices of the present invention for specific applications. Magnetic or magnetic optical coatings or films; LCD panels such as those used for display panels, privacy windows, etc .; photographic emulsions; fabrics; linear Frenel lenses; brightness-enhancing films; holographic films or images; embossable films; anti-tamper films or Coatings; IR transmissive films for low radiation applications; release films or release coated papers; and polarizers or mirrors, but not limited to. [0076] Multiple additional layers can be considered on one or both main surfaces of the multilayer polymer film 10 and can be any combination of the coatings or films described above. For example, when the adhesive is applied to the multilayer polymer film 10, the adhesive may contain a white pigment such as titanium dioxide to increase the overall reflectance, or the reflectance of the multilayer polymer film 10. It may be optically transparent so that the reflectance of the base material can be added to the film. [0077] To improve roll formation and film fluidity, the multilayer polymer films 10 of the present invention may also contain lubricants that are incorporated into the film or added as a separate coating. In most applications, the lubricant is applied to only one side of the film, ideally to the side facing the rigid substrate to minimize haze. [0078] Films and other optical devices made in accordance with the present invention also include, for example, conventional vacuum coated dielectric metal oxide or metal / metal oxide optical films, silica solgel coatings, THV, 3M (St. Paul, Minnesota). ) May include one or more anti-reflection layers or coatings such as a coat or co-extruded anti-reflection layer as derived from a low index fluoropolymer such as extrudable fluoropolymer. .. Such layers or coatings, which may or may not be polarization sensitive, serve to increase transmittance and reduce reflective glare, and by appropriate surface treatments such as coatings and sputter etching, the films of the invention and Applies to optical devices. [0079] Films and other optical devices made in accordance with the present invention may be provided with a film or coating that imparts anti-fog properties. In some cases, the antireflection layer described above serves the dual purpose of imparting both antireflection and antifogging properties to the film or device. Various anti-fog agents are known in the industry. However, in general, these materials include substances such as fatty acid esters that impart hydrophobic properties to the film surface and promote the formation of continuous, less opaque water films. [0080] [0080] Coatings that reduce the tendency of the surface to "cloud" have already been reported by several inventors. For example, US Pat. No. 3,212,909 (Leigh) uses ammonium soaps such as alkylammonium carboxylate in mixtures with surfactants, which are sulfated or sulfonated aliphatic materials, to produce anti-fog compositions. It is disclosed to do. U.S. Pat. No. 3,075,228 (Elias) discloses that salts of sulfated alkylaryloxypolyalkoxy alcohols and alkylbenzene sulfonates are used to produce anti-fog articles that are useful for cleaning and provide anti-fog properties to various surfaces. ing. U.S. Pat. No. 3,819,522 (Zmoda) discloses a combination of surfactants containing derivatives of decinediol and the use of surfactant mixtures containing alkyl ethoxylated sulfates in anti-fog window cleaner surfactant mixtures. There is. Japanese Unexamined Patent Publication No. 6 (1994) No. 41,335 discloses an antifogging and dew-preventing composition containing colloidal alumina, colloidal silica and an anionic surfactant. In US Pat. No. 4,478,909 (Taniguchi et al.), A cured anti-fog coating containing polyvinyl alcohol, fine silica and organosilicon compounds, where the carbon / silicon weight ratio is clearly important for the reported anti-fog properties of the film. The film is disclosed. Various surfactants, including fluorine-containing surfactants, can be used to improve the surface smoothness of the coating. Other anti-fog coatings incorporating surfactants are described in US Pat. Nos. 2,803,552, 3,022,178 and 3,897,356. PCT 96 / 18,691 (Scholtz et al.) Discloses a means by which the coating imparts both anti-fog and anti-reflection properties. [0081] The films and optics of the present invention may also be protected from UV radiation by using UV stabilizing films or coatings. Suitable UV stabilizing films and coatings include, for example, those incorporating a benzotriazole or hindered amine light stabilizer (HALS) available under the trade name Tinuvin 292 from Ciba Geigy, Inc. (Horselone, NY). .. Other suitable UV-stabilized films and coatings include those containing benzophenone or diphenyl acrylates commercially available from BASF (Parsippany, NJ). Such films or coatings are particularly desirable when the films and optics of the invention are used outdoors or in luminaires where the light source emits a large spectrum in the UV region. [0082] The films and optical devices of the present invention may be treated with inks, dyes or pigments to change their appearance or be customized for specific applications. Thus, for example, the film may be treated with ink or other printed signs such as those used to display product identification, advertisements, warnings, decorations or other information. You may print on film using various techniques such as screen printing, typographic printing, offset, flexo printing, stippling, laser printing, etc., one- and two-component inks, oxidative-dried and UV-dried inks, Various types of inks can be used, including molten inks, dispersed inks and 100% inks. In addition, dyes or pigments may be blended into the polymer before or after the formation of layers with the polymer. [0083] The appearance of the multilayer polymer film 10 also pigments one or more materials used to laminate a dyed film onto a multilayer polymer film, apply a pigmented coating to the surface of the film, or make a film. It can be changed by coloring the film, such as by including. [0084] Both visible and near IR dyes and pigments are conceivable in the present invention and include, for example, optical brighteners such as dyes that are absorbed by UV and fluoresce in the visible region of the color spectrum. Other additional layers that may be added to alter the appearance of the optical film include, for example, an opaque (black) layer, a diffuse layer, a holographic image or a holographic diffuser and a metal layer. Each of these may be applied directly to one or both surfaces of the film, or may be a component of a second film or foil structure laminated to the film. Alternatively, components such as opaque or diffusers, or color pigments may be included in the adhesive layer used to laminate the film to another surface. [0085] The films and optical devices of the present invention may also have a metal coating. In this way, for example, the metal layer may be directly attached to the optical film by thermal decomposition, powder coating, vapor deposition, cathode sputtering, ion plating, or the like. A metal foil or rigid metal plate may be laminated to an optical film, a separate polymer film or glass or plastic sheet may first be coated with metal using the techniques described above and then laminated to the films and devices of the invention. May be good. [0086] One method of forming a multilayer polymer film will be briefly described. Details on the processing conditions and points to consider can be found in US Patent Application No. 09 / 006,288, "Manufacturing Process of Multilayer Optical Films". The multilayer polymer film is formed by extruding the polymer used for the first and second optical layers and the non-optical layer. Extrusion conditions are chosen to properly feed, melt, mix and pump the polymeric resin feed stream in a continuous and stable manner. The temperature of the final melt flow is chosen to be in a range that reduces freezing, crystallization or unreasonable high pressure drops in the low end of the range and reduces degradation in the high end of the range. The process of total melt flow of two or more polymers, including film casting on chill rolls, is often referred to as coextrusion. [0087] After extrusion, each melt flow is moved from the neck tube to the gear pump used to control the continuous and uniform speed of the polymer flow. A static mixer may be placed at the end of the neck tube to move the polymer melt flow from the gear pump to a multi-layer feed block with a uniform melt flow temperature. The total melt flow is generally heated as uniformly as possible to improve the uniform flow of the melt flow and reduce deterioration during the melting process. [0088] The multi-layer feed block divides two or more polymer melt streams into many layers, interposing these layers to combine the many layers into a single multi-layer flow. A layer from a given melt flow is created by continuously discharging a portion of the flow from the main flow channel to a secondary channel tube leading to a layer slot in the supply block manifold. The flow of layers is often controlled by the selection made by the machinery and the shape and physical dimensions of the individual side channel tubes and layer slots. [0089] Secondary channel tubes and two or more types of melt flow layer slots are often intervened, for example, to form alternating layers. The manifold on the downstream side of the feed block is often shaped to compress and evenly spread the bonded multi-layered layers so that they intersect. A thick non-optical layer known as the Protective Boundary Layer (PBL) is fed near the manifold wall using or by a separate melt flow of the optical multilayer laminate. As mentioned above, these non-optical layers may be used to protect the thin optical layer from the effects of wall stresses and the resulting flow instability. [0090] The multi-layer laminate ejected from the feed block manifold enters a final molding unit such as a die. Alternatively, the flows may preferably be separated by the normals of the layers being laminated to form two or more multilayer flows that are recombinated by the lamination. The flow may be separated at an angle other than the normal of the layer. A flow channel system that separates and stacks flows is called a multiplier. The width of the separated flows (ie, the sum of the thicknesses of the individual layers) may or may not be equal. The multiplier ratio is defined as the ratio of the wider and narrower flows. The unequal flow widths (ie, the multiplier ratio is greater than the simple substance) are useful for creating a layer thickness gradient. If the flow widths are not equal, the multiplier widens the narrower flow and / or compresses the wider flow that intersects the thickness and flow direction to match the width of the layers during stacking. [0091] Additional non-optical layers can be added to the multi-layer stack before stacking. These non-optical layers function as PBLs within the multiplier. After stacking and stacking, some of these layers form the internal boundary layer between the optical layers and the other layers form the skin layer. [0092] After superposition, point the web towards the final molding unit. The web is cast on a chill roll, sometimes referred to as a casting wheel or casting drum. This casting is often assisted by electrostatic pinning, the details of which are well known in the polymer film manufacturing industry. The web may be cast laterally to a uniform thickness, or the peripheral side surfaces of the web thickness may be cast using die lip control. [0093] The multilayer web is stretched to create the final multilayer optical film. An example of a method for producing a multilayer optical polarizer is to use a single stretching step. This process takes place in a tenter or length orienter. While common tenters stretch in the crossing direction (TD) of the web path, some tenters have a mechanism that stretches or relaxes (contracts) in the film or mechanical direction (MD) of the web path. Thus, in this exemplary method, the film is stretched in one in-plane direction. The second in-plane dimension is kept constant in a normal tenter or narrowed to a smaller width in a length orienter. The amount of narrowing is considerable and the draw ratio increases. [0094] An example of how to make a multilayer mirror is to orient the birefringent material inward on both sides using a two-step stretching process. The stretching process may be a combination of the above-mentioned single-step processes of stretching in two in-plane directions. Further, a tenter that stretches along the MD, that is, a biaxial tenter that can stretch continuously or simultaneously in two directions may be used. In the latter case, a single biaxial stretching process may be used. [0095] In yet other methods of making multilayer polarizers, different layers containing different materials within a single coextruded multilayer film are different from each other using a multilayer stretching process that utilizes the different behaviors of different materials in individual stretching steps. Gives the degree and type of orientation. Mirrors can also be formed in this way. [0096] The intrinsic viscosity of the polyester used in these layers and films is related to the molecular weight of the polymer (because there are no branched monomers). Generally, the intrinsic viscosity of polyester is greater than about 0.4 dL / g. Preferably, the intrinsic viscosity is about 0.4-0.7 dL / g. In this disclosure, unless otherwise specified, the intrinsic viscosity is measured in a phenol / o-dichlorobenzene solvent at 30 ° C., 60/40 wt.%. [0097] The following examples show the manufacture and use of the multilayer polymer film of the present invention. These examples are for illustration purposes only and shall not be construed as limiting the scope of the invention in any way. [0098] Example The monomers, catalysts and stabilizers used to make the polymers in these examples are commercially available from the following vendors: Dimethylnaphthalenedicarboxylate and terephthalic acid from Amoko (Decatur, Alabama), dimethylterephthalate from Hextoceranis (Dallas, Texas), dimethylisophthalate and dimethyl from Morflex (Greensborough, NC) Tertiary butyl isophthalate, ethylene glycol from Union Carbide (Charleston, NC), 1,6-hexanediol from BASF (Charlotte, NC), sebacic acid from Union Camp (Dover, OH), Elf Atchem (Pencilvania) Antimone triacetate from Philadelphia, CA, cobalt acetate and manganese acetate from Whole Chemical (Wickrife, NC), triethylphosphon acetate from Orbright & Wilson (Glenallen, Virginia), Eastman Chemical (Tennessee, Tennessee) Dimethylcyclohexanedicarboxylate from Kingsport) and triethylamine from Air Products (Philipsburg, NA). [0099] In each of the examples below, an 836 layer film is formed. The 836 optical layer structure includes four multi-layer optical stacks with a gradient in layer thickness obtained by doubly superimposing the 209 layer structures from the multi-layer feed block. The optical layer occupies about 50 percent of the thickness of the structure. Each laminate is separated by one layer of three non-optical internal protective boundary layers, which make up about 2% of the total thickness. Ultimately, each side of the film has an outer non-optical skin layer that occupies about 22% of the thickness. [0100] Some of the films of the examples were tested using a "gain tester". A "gain tester" can be manufactured using a spot photometer and a suitable backlight with a polarizer is placed between the two so that only one polarized light from the backlight is measured by this photometer. Suitable spot photometers are Minolta LS-100 and LS-110 (Lamsey, NJ). The absolute value of the gain measured for the backlight used, the orientation of the backlight sample, and the size of the sample. The backlight used in the examples was obtained from a landmark, and the polarizer was a high-brightness display polarizer in which the passing axis of the polarizer was aligned with the long axis of the backlight. The sample was inserted into the tester so that the axis of passage of the sample was aligned with the axis of passage of the high-intensity polarizer. The sample was large enough to cover the entire backlight. [0101] Comparative example Polarizing film with PEN / coPEN (70/0/30) layer As a comparative example, the first optical layer was made of polyethylene naphthalate, and the second optical layer was a carboxylate subunit derived from 70 mol% dimethyl naphthalenedicarboxylate and 30 mol% dimethyl isophthalate. A multilayer reflective polarizer film was constructed from optics (polyethylene naphthalate) having a glycol subunit derived from 100 mol% ethylene glycol. [0102] The polyethylene naphthalate used to form the first optical layer was placed in a batch reactor packed with raw materials consisting of 136 kg of dimethylnaphthalene carboxylate, 73 kg of ethylene glycol, 27 g of manganese acetate, 27 g of cobalt acetate and 48 g of antimony triacetate. Synthesized. 2atm (2x10)⁵N / m²), The mixture was heated to 254 ° C while removing methanol (a by-product of the transesterification reaction). After 35 kg of methanol was removed, the reactor was filled with 49 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.48 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene was produced. [0103] The co (polyethylene naphthalate) used to form the second optical layer consists of 109 kg of dimethylnaphthalene carboxylate, 37 kg of dimethylisophthalate, 79 kg of ethylene glycol, 29 g of manganese acetate, 29 g of cobalt acetate and 58 g of antimony triacetate. Synthesized in a batch reactor packed with raw materials. 2atm (2x10)⁵N / m²), The mixture was heated to 254 ° C while removing methanol. After 41 kg of methanol was removed, the reactor was filled with 52 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.57 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene was produced. [0104] The above-mentioned PEN and coPEN were coextruded from a multilayer molten manifold to prepare a multilayer film having 836 alternating first and second optical layers. The multilayer reflective film also includes an internal protective layer and an external protective layer made of the same material (polyethylene naphthalate) as the second optical layer. These protective layers are introduced into additional melting ports. The cast film was heated in an oven filled with hot air set at 150 ° C. for about 1 minute and uniaxially oriented with a 6: 1 stretch to produce a reflective polarizer film with a thickness of about 125 μm. [0105] Placing this multilayer reflective film in the "gain tester" described above increased the brightness by 58%. This corresponds to a "gain" of 1.58. The increase in brightness is measured as a gain, which is the ratio of the brightness of a tester with a polarizing film to the brightness of a tester without a polarizing film. [0106] The second film was constructed and processed as described above, except that the second film was uniaxially oriented with a 7: 1 stretch. The resulting birefringence of the second film was predicted to be about 0.24 at 632.8 nm. The average gain of the second film was predicted to be about 1.62. [0107] A peeling test was performed. A sample of the second film was cut into 2.54 cm pieces at 45 ° with respect to the reflection and transmission axes (ie, in-plane axes) of the film. A multilayer optical film is adhered to a substrate and a layer of film is peeled at 25 ° C, 50% relative humidity, 90 ° using an Instruments slip / peel tester (Strongsville, Ohio). It was peeled off at an angle of 2.54 cm / sec. Test error is about ± 8x10³It was predicted to be dynes / cm. For this second film, the resistance to delamination between the two sets of optical layers is approximately 1.2x10.⁴It was relatively low at dynes / cm. [0108] Similar to the first two films, except that the third multilayer reflective polarizer film was preheated in a tenter with hot air filled at a temperature of about 160 ° C and stretched with air filled at about 150 ° C. It was configured and processed by the method. The in-plane birefringence of this film was predicted to be about 0.17 for 632.8 nm light. The average gain was predicted to be about 1.53. Peeling resistance is about 6.2x10⁴It was dynes / cm. [0109] Example 1 Polarizing film with PEN / coPEN (90/10/0) / coPEN (55/0/45) layers The first optical layer has a carboxylate subunit derived from 90 mol% dimethyl naphthalenedicarboxylate and 10 mol% dimethyl terephthalate, and a glycol subunit derived from 100 mol% ethylene glycol subunit. The second optical layer was made of co (polyethylene naphthalate) with a carboxylate subunit derived from 55 mol% dimethylnaphthalenedicarboxylate and 45 mol% dimethylisophthalate, and 99.8 mol% ethylene glycol. It is made of co (polyethylene naphthalate) having a glycol subunit derived from 0.2 mol% trimethylol propane to form a multilayer reflective polarizer film. [0110] The raw material (polyethylene naphthalate) used to form the first optical layer is composed of 126 kg of dimethylnaphthalene carboxylate, 11 kg of dimethyl terephthalate, 75 kg of ethylene glycol, 27 g of manganese acetate, 27 g of cobalt acetate and 48 g of antimony triacetate. Is synthesized in a batch reactor filled with. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol. After 36 kg of methanol has been removed, the reactor is filled with 49 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 0.50 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0111] The co (polyethylene naphthalate) used to form the second optical layer was dimethylnaphthalene carboxylate 83 kg, dimethylisophthalate 54 kg, ethylene glycol 79 kg, trimethylolpropane 313 g, manganese acetate 27 g, cobalt acetate 27 g. And in a batch reactor packed with a raw material consisting of 48 g of antimony triacetate. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol. After 39.6 kg of methanol has been removed, the reactor is filled with 49 g of triethylphosphon acetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 0.60 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0112] The coPEN described above is coextruded from a multilayer molten manifold to create a multilayer film with 836 alternating first and second optical layers. This special multilayer reflective film also includes internal and external protective layers made of the same material (polyethylene naphthalate) as the second optical layer. The cast film is heated in an oven filled with hot air set at 145 ° C for about 1 minute and uniaxially oriented with a 6: 1 stretch to produce a reflective polarizer film with a thickness of about 125 Tm. [0113] Example 2 Polarizing film with PEN / coPEN (85/15/0) / coPEN (50/0/50) layers The first optical layer has a carboxylate subunit derived from 85 mol% dimethyl naphthalenedicarboxylate and 15 mol% dimethyl terephthalate, and a glycol subunit derived from 100 mol% ethylene glycol. Polyethylene naphthalate) and the second optical layer is derived from 100 mol% ethylene glycol and a carboxylate subunit derived from 50 mol% dimethyl naphthalenedicarboxylate and 50 mol% dimethyl isophthalate. It was made of co (polyethylene naphthalate) having a glycol subunit to form a multilayer reflective polarizer film. [0114] The raw material (polyethylene naphthalate) used to form the first optical layer is composed of 123 kg of dimethylnaphthalene carboxylate, 17 kg of dimethyl terephthalate, 76 kg of ethylene glycol, 27 g of manganese acetate, 27 g of cobalt acetate and 48 g of antimony triacetate. Was synthesized in a batch reactor packed with. 2atm (2x10)⁵N / m²), The mixture was heated to 254 ° C while removing methanol. After 36 kg of methanol was removed, the reactor was filled with 49 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.51 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene was produced. [0115] The co (polyethylene naphthalate) used to form the second optical layer was dimethylnaphthalene carboxylate 77 kg, dimethylisophthalate 61 kg, ethylene glycol 82 kg, manganese acetate 27 g, cobalt acetate 27 g and antimony triacetate 48 g. It was synthesized in a batch reactor filled with raw materials consisting of. 2atm (2x10)⁵N / m²), The mixture was heated to 254 ° C while removing methanol. After 39.6 kg of methanol was removed, the reactor was filled with 49 g of triethylphosphon acetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.60 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene was produced. [0116] The coPEN described above was coextruded from a multilayer molten manifold to create a multilayer film with 836 alternating first and second optical layers. This special multilayer reflective film also contained internal and external protective layers made of the same material (polyethylene naphthalate) as the second optical layer. The cast film was heated in an oven filled with hot air set at 135 ° C. for about 1 minute and uniaxially oriented with a 6: 1 stretch to produce a reflective polarizer film with a thickness of about 125 Tm. The resulting in-plane birefringence was predicted to be about 0.17 for 632.8 nm light. Inner layer peeling resistance is about 5.9x10⁴It was dynes / cm. [0117] Placing this multilayer reflective film in the "gain tester" described above increased the brightness by 58%. This corresponds to a "gain" of 1.58. The increase in brightness is measured as a gain, which is the ratio of the brightness of a tester with a polarizing film to the brightness of a tester without a polarizing film. [0118] A second film was formed in the same manner except that it was stretched to 129 ° C in filled hot air. The in-plane birefringence of this film was predicted to be about 0.185. The measured gain is 1.58 and the internal layer peeling resistance is about 4.5x10.⁴It was dynes / cm. [0119] Example 3 Polarizing film with coPEN (88/12/0) / coPEN (55/45/0) layers The first optical layer has a carboxylate subunit derived from 88 mol% dimethyl naphthalenedicarboxylate and 12 mol% dimethyl terephthalate, and a glycol subunit derived from 100 mol% ethylene glycol. Polyethylene naphthalate) and a second optical layer with a carboxylate subunit derived from 55 mol% dimethyl naphthalenedicarboxylate and 45 mol% dimethyl terephthalate, 96.8 mol% ethylene glycol and 3.0 mol%. A multilayer reflective polarizer film was constructed from co (polyethylene naphthalate) having a hexanediol of hexane and a glycol subunit derived from 0.2 mol% trimethylol propane. [0120] The co (polyethylene naphthalate) used to form the first optical layer was made as a blend of two polymers, PET (8 wt.%) And coPEN (92 wt.%). The PET used for the blend was synthesized in a batch reactor packed with raw materials consisting of 138 kg of dimethyl terephthalate, 93 kg of ethylene glycol, 27 g of zinc acetate, 27 g of cobalt acetate and 48 g of antimony triacetate. 2atm (2x10)⁵N / m²), The mixture was heated to 254 ° C while removing methanol, a by-product of the transesterification reaction. After 45 kg of methanol was removed, the reactor was filled with 52 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.60 measured in 60 / 40wt.% Phenol / o-dichlorobenzene was produced. [0121] The coPEN used in the blend to form the first optical layer consisted of 97 mol% dimethylnaphthalene carboxylate, 3 mol% dimethyl terephthalate-derived carboxylate subunit, and 100 mol% ethylene glycol. It had an induced glycol subunit. coPEN was synthesized in a batch reactor packed with raw materials consisting of 135 kg of dimethyl naphthalate dicarboxylate, 3.2 kg of dimethyl terephthalate, 75 kg of ethylene glycol, 27 g of manganese acetate, 27 g of cobalt acetate and 48 g of antimony triacetate. 2atm (2x10)⁵N / m²), The mixture was heated to 254 ° C while removing methanol. After 37 kg of methanol was removed, the reactor was filled with 49 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.50 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene was produced. [0122] The co (polyethylene naphthalate) used to form the second optical layer was dimethyl naphthalenedicarboxylate 88.5 kg, dimethyl terephthalate 57.5 kg, ethylene glycol 81 kg, hexanediol 4.7 kg, manganese acetate 15 g, cobalt acetate 22. Synthesized in a batch reactor packed with raw materials consisting of grams, 15 g zinc acetate, 239 g trimethylolpropane and 51 g antimone triacetate. 2atm (2x10)⁵N / m²), The mixture was heated to 254 ° C while removing methanol. After 39.6 kg of methanol was removed, the reactor was filled with 47 g of triethylphosphone acetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.56 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene was produced. [0123] The coPEN described above was coextruded from a multilayer molten manifold to create a multilayer film with 836 alternating first and second optical layers. This special multilayer reflective film also contained internal and external protective layers made of the same material (polyethylene naphthalate) as the second optical layer. The cast film was heated in an oven filled with hot air set at 140 ° C. for about 1 minute and uniaxially oriented with a 6: 1 stretch to produce a reflective polarizer film with a thickness of about 125 Tm. [0124] Placing this multilayer reflective film in the "gain tester" described above increased the brightness by 58%. This corresponds to a "gain" of 1.58. The increase in brightness is measured as a gain, which is the ratio of the brightness of a tester with a polarizing film to the brightness of a tester without a polarizing film. [0125] When the internal layer adhesive strength was measured using a 90 degree tape peeling test, it was approximately 9.5x10⁴It was dynes / cm. [0126] Example 4 Polarizing film with coPEN (85/15/0) / coPEN (55/45/0) layers The first optical layer has a carboxylate subunit derived from 85 mol% dimethyl naphthalenedicarboxylate and 15 mol% dimethyl terephthalate, and a glycol subunit derived from 100 mol% ethylene glycol subunit. The second optical layer was made of co (polyethylene naphthalate) with a carboxylate subunit derived from 55 mol% dimethyl naphthalenedicarboxylate and 45 mol% dimethyl terephthalate, 96.8 mol% ethylene glycol and 3.0. It was made of co (polyethylene naphthalate) having a molar% hexanediol and a glycol subunit derived from 0.2 mol% trimethylol propane to construct a multilayer reflective polarizer film. [0127] The co (polyethylene naphthalate) used to form the first optical layer was synthesized as described in Example 2. [0128] The co (polyethylene naphthalate) used to form the second optical layer was synthesized as described in Example 3. [0129] The coPEN described above was coextruded from a multilayer molten manifold to create a multilayer film with 836 alternating first and second optical layers. This special multilayer reflective film also contained internal and external protective layers made of the same material (polyethylene naphthalate) as the second optical layer. The cast film was heated in an oven filled with hot air set at 135 ° C. for about 1 minute and uniaxially oriented with a 6: 1 stretch to produce a reflective polarizer film with a thickness of about 125 Tm. [0130] Placing this multilayer reflective film in the "gain tester" described above increased the brightness by 58%. This corresponds to a "gain" of 1.58. The increase in brightness is measured as a gain, which is the ratio of the brightness of a tester with a polarizing film to the brightness of a tester without a polarizing film. [0131] Example 5 Polarizing film with coPEN (85/15/0) / coPEN (50/50/0) layers The first optical layer has a carboxylate subunit derived from 85 mol% dimethyl naphthalenedicarboxylate and 15 mol% dimethyl terephthalate, and a glycol subunit derived from 100 mol% ethylene glycol. Polyethylene naphthalate) and a second optical layer with a carboxylate subunit derived from 50 mol% dimethyl naphthalenedicarboxylate and 50 mol% dimethyl terephthalate, 96.8 mol% ethylene glycol and 3.0 mol%. A multilayer reflective polarizer film was constructed from co (polyethylene naphthalate) having a hexanediol of hexane and a glycol subunit derived from 0.2 mol% trimethylol propane. [0132] The co (polyethylene naphthalate) used to form the first optical layer was synthesized as described in Example 2. [0133] The co (polyethylene naphthalate) used to form the second optical layer was dimethylnaphthalene carboxylate 81.4 kg, dimethyl terephthalate 64.5 kg, ethylene glycol 82 kg, hexanediol 4.7 kg, manganese acetate 15 g, cobalt acetate 22 g, It was synthesized in a batch reactor packed with raw materials consisting of 15 g of zinc acetate, 239 g of trimethylolpropane and 48 g of antimony triacetate. 2atm (2x10)⁵N / m²), The mixture was heated to 254 ° C while removing methanol. After 44 kg of methanol was removed, the reactor was filled with 47 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.60 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene was produced. [0134] The coPEN described above was coextruded from a multilayer molten manifold to create a multilayer film with 836 alternating first and second optical layers. This special multilayer reflective film also contained internal and external protective layers made of the same material (polyethylene naphthalate) as the second optical layer. The cast film was heated in an oven filled with hot air set at 135 ° C. for about 1 minute and uniaxially oriented with a 6: 1 stretch to produce a reflective polarizer film with a thickness of about 125 Tm. [0135] Placing this multilayer reflective film in the "gain tester" described above increased the brightness by 58%. This corresponds to a "gain" of 1.58. The increase in brightness is measured as a gain, which is the ratio of the brightness of a tester with a polarizing film to the brightness of a tester without a polarizing film. [0136] Example 6 A polarizing film in which the second optical layer is derived from dimethylcyclohexanedicarboxylate. The first optical layer has a carboxylate subunit derived from 100 mol% dimethyl terephthalate and a glycol subunit derived from 90 mol% 1,4-butanediol and 10 mol% ethylene glycol. It is made of polyester to form a multilayer reflective polarizer film. The second optical layer consists of a carboxylate subunit derived from 50 mol% cyclohexanedicarboxylic acid and 50 mol% terephthalic acid, and a glycol derived from 99.8 mol% ethylene glycol and 0.2 mol% trimethylolpropane. Made from copolyester with subunits. [0137] The poly (butylene terephthalate) used to form the first optical layer was synthesized in a batch reactor packed with raw materials consisting of 127 kg of dimethyl terephthalate, 77 kg of 1,4-butanediol, 9 kg of ethylene glycol and 11 g of tetrabutyl titanate. To do. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol, which is a by-product of the transesterification reaction. After 41 kg of methanol has been removed, the reactor is depressurized to atmospheric pressure to remove excess 1,4-butanediol. A further 22 grams of tetrabutyl titanate is loaded into the reactor and further reduced to 1 torr while heating to 270 ° C. 1,4-Butanediol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 0.85 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. To do. [0138] A batch of copolyester used to form the second optical layer filled with raw materials consisting of 58.6 terephthalic acid, 59.5 kg cyclohexanedicarboxylic acid, 87.7 kg ethylene glycol, 300 g triethylamine, 275 g trimethylolpropane and 82 g antimony triacetate. Synthesize in a reactor. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing water, which is a by-product of the transesterification reaction. After 25.5 kg of water has been removed, the pressure is gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 1.1 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0139] The copolyester described above is coextruded from a multilayer molten manifold to create a multilayer film with 836 alternating first and second optical layers. This special multilayer reflective film also includes an internal and external protective layer made of the same copolyester as the second optical layer. The cast film is heated in an oven filled with hot air set at 65 ° C for about 1 minute and uniaxially oriented with a 6: 1 stretch to produce a reflective polarizer film with a thickness of about 125 Tm. [0140] Example 7 Mirror film in which the second optical layer is derived from dimethylcyclohexanedicarboxylate and tertiary isophthalate The first optical layer is coPEN with a carboxylate subunit derived from 90 mol% dimethylnaphthalene carboxylate and 10 mol% dimethyl terephthalate, and a glycol subunit derived from 100 mol% ethylene glycol. Create to construct a multilayer reflector film. The second optical layer consists of a carboxylate subunit derived from 85 mol% cyclohexanedicarboxylic acid and 15 mol% dimethyl tertiary butylisophthalate, 99.7 mol% ethylene glycol and 0.3 mol% trimethylolpropane. Made from copolyester with glycol subunits derived from. [0141] The coPEN used to form the first optical layer is synthesized as described in Example 1. [0142] The copolyester used to form the second optical layer was dimethyl tertiary butylisophthalate 25.5 kg, cyclohexanedicarboxylic acid 112 kg, ethylene glycol 88 kg, trimethylolpropane 409 g, copper acetate 34 g, manganese acetate 27 g and triacetic acid. It was synthesized in a batch reactor packed with a raw material consisting of 82 g of antimony. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol, which is a by-product of the transesterification reaction. After 43 kg of methanol is removed, gradually reduce the pressure to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 1.2 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0143] The copolyester described above is coextruded from a multilayer molten manifold to create a multilayer film with 836 alternating first and second optical layers. This special multilayer reflective film also includes an internal and external protective layer made of the same copolyester as the second optical layer. This cast film is biaxially oriented. First, the film is heated in an oven filled with hot air set at 120 ° C. for about 1 minute and oriented with a 3.6: 1 stretch. The film is then heated in an oven filled with hot air set at 135 ° C for about 1 minute and oriented in the cross direction with a 4.0: 1 stretch. [0144] Example 8 Polarizing film with PEN optical layer and low intrinsic viscosity coPEN (70/0/30) optical layer and high intrinsic viscosity coPEN (70/0/30) non-optical layer The first optical layer was made of polyethylene naphthalate and the second optical layer was 100 mol% with a carboxylate subunit derived from 70 mol% dimethyl naphthalenedicarboxylate and 30 mol% dimethyl isophthalate. It is made of low viscosity (0.48 dL / g) optics (polyethylene naphthalate) with glycol subunits derived from ethylene glycol to form a multilayer reflective polarizer film. The film is also highly viscous with a carboxylate subunit derived from 70 mol% dimethylnaphthalenedicarboxylate and 30 mol% dimethylisophthalate, and a glycol subunit derived from 100 mol% ethylene glycol. Also includes a non-optical layer made of (0.57dL / g) co (polyethylene naphthalate). [0145] The polyethylene naphthalate used to form the first optical layer was placed in a batch reactor packed with raw materials consisting of 136 kg of dimethylnaphthalene carboxylate, 73 kg of ethylene glycol, 27 g of manganese acetate, 27 g of cobalt acetate and 48 g of antimony triacetate. Synthesize. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol (a by-product of the transesterification reaction). After 35 kg of methanol has been removed, the reactor is filled with 49 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 0.46 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0146] The co (polyethylene naphthalate) used to form the second optical layer consists of 109 kg of dimethylnaphthalene carboxylate, 37 kg of dimethylisophthalate, 79 kg of ethylene glycol, 29 g of manganese acetate, 29 g of cobalt acetate and 58 g of antimony triacetate. Synthesize in a batch reactor filled with raw materials. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol. After 41 kg of methanol has been removed, the reactor is filled with 52 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 0.48 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0147] The raw material (polyethylene naphthalate) used to form the non-optical layer was composed of 109 kg of dimethylnaphthalene carboxylate, 37 kg of dimethylisophthalate, 79 kg of ethylene glycol, 29 g of manganese acetate, 29 g of cobalt acetate and 58 g of antimony triacetate. Synthesize in a packed batch reactor. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol. After 41 kg of methanol has been removed, the reactor is filled with 52 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 0.57 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0148] Regarding the second optical layer The above-mentioned PEN and coPEN are coextruded from a multilayer molten manifold to prepare a multilayer film having alternating first and second optical layers. The multilayer reflective film also includes an internal protective layer and an external protective layer made using high intrinsic viscosity co (polyethylene naphthalate) introduced from an additional melting port. This cast film is heated in an oven filled with hot air set at 145 ° C for about 1 minute and uniaxially oriented with a 6: 1 stretch to produce a reflective polarizer film with a thickness of about 125 m. .. [0149] Example 9 CoPEN (85/15) Optical layer and low intrinsic viscosity coPEN (50/50) Optical layer and high intrinsic viscosity coPEN (50/50) Polarizing film with non-optical layer The first optical layer has a carboxylate subunit derived from 85 mol% dimethyl naphthalenedicarboxylate and 15 mol% dimethyl terephthalate, and a glycol subunit derived from 100 mol% ethylene glycol. The second optical layer was made of polyethylene naphthalate) and the second optical layer was derived from 50 mol% dimethyl naphthalenedicarboxylate and 50 mol% dimethyl terephthalate with a carboxylate subunit, 96.6 mol% ethylene glycol and 3 mol%. Made of low viscosity (0.48 dL / g) co (polyethylene naphthalate) with 1,6-hexanediol of 1,6-hexanediol and a glycol subunit derived from 0.4 mol% trimethylol propane to make a multilayer reflective polarizer film. Configure. The film also contains a carboxylate subunit derived from 50 mol% dimethyl naphthalenedicarboxylate and 50 mol% dimethyl terephthalate, 96.8 mol% ethylene glycol and 3 mol% 1,6-hexanediol and 0.2. It also includes a non-optical layer made of high viscosity (0.56 dL / g) co (polyethylene naphthalate) with glycol subunits derived from mol% trimethylol propane. [0150] The co (polyethylene naphthalate) used to form the first optical layer was filled with 123 kg of dimethylnaphthalene carboxylate, 17 kg of dimethyl terephthalate, 76 kg of ethylene glycol, 27 g of manganese acetate, 27 g of cobalt acetate and 48 g of antimony triacetate. Synthesize in a batch reactor. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol (a by-product of the transesterification reaction). After 36 kg of methanol has been removed, the reactor is filled with 49 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 0.48 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0151] The co (polyethylene naphthalate) used to form the second optical layer was dimethylnaphthalene carboxylate 81.4 kg, dimethyl terephthalate 64.5 kg, ethylene glycol 82 kg, 1,6-hexanediol 4.7 kg, manganese acetate 15 g, Synthesize in a batch reactor packed with 22 g of cobalt acetate, 15 g of zinc acetate, 581 g of trimethylolpropane and 48 g of antimony triacetate. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol. After 44 kg of methanol has been removed, the reactor is filled with 47 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 0.48 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0152] The co (polyethylene naphthalate) used to form the non-optical layer was dimethyl naphthalene carboxylate 81.4 kg, dimethyl terephthalate 64.5 kg, ethylene glycol 82 kg, 1,6-hexanediol 4.7 kg, manganese acetate 15 g, cobalt acetate. Synthesize in a batch reactor packed with raw materials consisting of 22 g, zinc acetate 15 g, trimethylolpropane 290 g and antimone triacetate 48 g. 2atm (2x10)⁵N / m²), The mixture is heated to 254 ° C while removing methanol. After 44 kg of methanol has been removed, the reactor is filled with 47 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, is continuously removed until a polymer with an intrinsic viscosity of 0.56 dL / g measured in 60/40 wt.% Phenol / o-dichlorobenzene is produced. [0153] Co-extruding the above-mentioned coPEN from the multilayer molten manifold for the first and second optical layers to prepare a multilayer film having alternating first and second optical layers. The multilayer reflective film also includes an internal protective layer and an external protective layer made using high intrinsic viscosity co (polyethylene naphthalate) introduced from an additional melting port. This cast film is heated in an oven filled with hot air set at 130 ° C for about 1 minute and uniaxially oriented with a 6: 1 stretch to produce a reflective polarizer film with a thickness of about 125 m. .. [0154] Example 10 The first optical layer was made from 100 mol% naphthalene carboxylate as a carboxylate and 100 mol% ethylene glycol as a diol to form a multilayer reflective polarizer film. The second optical layer consists of 55 mol% naphthalenedicarboxylate and 45 mol% terephthalate as carboxylates, 95.8 mol% ethylene glycol as glycols, 4 mol% hexanediol and 0.2 mol% trimethylolpropane. Made from copolyethylene naphthalate. [0155] The polyethylene naphthalate used to form the first optical layer was synthesized in a batch reactor packed with 136 kg of dimethylnaphthalenedicarboxylate, 73 kg of ethylene glycol, 27 g of manganese acetate, 27 g of cobalt acetate and 48 g of antimony triacetate. Under a pressure of 2 atm, the mixture was heated to 254 ° C while removing methanol, a by-product of the transesterification reaction. After 35 kg of methanol was removed, the reactor was filled with 49 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.48 measured in 60/40 phenol / dichlorobenzene was produced. [0156] The copolyethylene naphthalate used to form the second optical layer was dimethylnaphthalene carboxylate 88.5 kg, dimethyl terephthalate 57.5 kg, ethylene glycol 81 kg, hexanediol 4.7 kg, cobalt acetate 29 g, zinc acetate 29 g, tri. It was synthesized in a batch reactor packed with 239 g of methylolpropane and 51 g of antimony triacetate. Under a pressure of 2 atm, the mixture was heated to 254 ° C while removing methanol, a by-product of the transesterification reaction. After 39.6 kg of methanol was removed, the reactor was filled with 56 g of triethylphosphone acetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.54 measured in 60/40 phenol / dichlorobenzene was produced. [0157] The CoPEN described above was coextruded from a multilayer dimanifold to create a multilayer film with 836 alternating first and second optical layers. This special multilayer reflective film also includes an internal protective layer and an external protective layer composed of the same copolyethylene naphthalate as the second optical layer. The cast film was heated to 163 ° C and then uniaxially oriented by 6: 1 stretching to produce a reflective polarizer film with a thickness of about 125 mm. [0158] Placing the multilayer reflective film described above inside the LCD computer display increased the brightness of the LCD display by 56%. This corresponds to a "gain" of 1.56. The increase in the brightness of the LCD display is measured as a gain, which is the ratio of the brightness of the LCD display with the brightness-enhancing film to the brightness of the LCD display without the brightness-enhancing film. The brightness of the display was measured with an LS-100 or LS-110 luminance meter. The adhesive strength of the inner layer of the above-mentioned multilayer reflector was measured using a standard 90-degree tape peeling test and found to exceed 450 g / inch (180 g / m). [0159] Example 11 The first optical layer was made from 100 mol% naphthalene carboxylate as a carboxylate and 100 mol% ethylene glycol as a diol to form a multilayer reflective polarizer film. The second optical layer consists of 55 mol% naphthalenedicarboxylate and 45 mol% terephthalate as carboxylates, 95.8 mol% ethylene glycol as glycols, 4 mol% hexanediol and 0.2 mol% trimethylolpropane. Made from copolyethylene naphthalate. This special multilayer film is also made from 75 mol% naphthalenedicarboxylate and 25 mol% terephthalate as carboxylates, 95.8 mol% ethylene glycol as glycols and 4 mol% hexanediol and 0.2 mol% trimethylol propane. It also contained an external protective layer made from the composed copolyethylene naphthalate. [0160] The polyethylene naphthalate used to form the first optical layer was synthesized in a batch reactor packed with 136 kg of dimethylnaphthalenedicarboxylate, 73 kg of ethylene glycol, 27 g of manganese acetate, 27 g of cobalt acetate and 48 g of antimony triacetate. did. Under a pressure of 2 atm, the mixture was heated to 254 ° C while removing methanol, a by-product of the transesterification reaction. After 35 kg of methanol was removed, the reactor was filled with 49 g of triethylphosphonoacetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.48 measured in 60/40 phenol / dichlorobenzene was produced. [0161] The copolyethylene naphthalate used to form the second optical layer was dimethylnaphthalene carboxylate 88.5 kg, dimethyl terephthalate 57.5 kg, ethylene glycol 81 kg, hexanediol 6.2 kg, cobalt acetate 29 g, zinc acetate 29 g, tri. It was synthesized in a batch reactor packed with 239 g of methylolpropane and 51 g of antimony triacetate. Under a pressure of 2 atm, the mixture was heated to 254 ° C while removing methanol, a by-product of the transesterification reaction. After 39.6 kg of methanol was removed, the reactor was filled with 56 g of triethylphosphone acetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.54 measured in 60/40 phenol / dichlorobenzene was produced. [0162] The copolyethylene naphthalate used to form the outer protective layer was dimethylnaphthalene carboxylate 114.8 kg, dimethyl terephthalate 30.4 kg, ethylene glycol 75 kg, hexanediol 5.9 kg, cobalt acetate 29 g, zinc acetate 29 g, trimethylol propane. It was synthesized in a batch reactor packed with 200 g and 51 g of antimony triacetate. Under a pressure of 2 atm, the mixture was heated to 254 ° C while removing methanol, a by-product of the transesterification reaction. After 39.6 kg of methanol was removed, the reactor was filled with 56 g of triethylphosphone acetate and gradually reduced to 1 torr while heating to 290 ° C. Ethylene glycol, a by-product of the condensation reaction, was continuously removed until a polymer with an intrinsic viscosity of 0.52 measured in 60/40 phenol / dichlorobenzene was produced. [0163] The CoPEN described above was coextruded from a multilayer dimanifold to create a multilayer film with 836 alternating first and second optical layers. This special multilayer reflective film also includes an internal protective layer composed of the same copolyethylene naphthalate as the second optical layer. After heating this cast film to 160 ° C., it was uniaxially oriented by stretching at 6: 1 to produce a reflective polarizer film having a thickness of about 125 mm. [0164] Placing the multilayer reflective film described above inside the LCD computer display increased the brightness of the LCD display by 58%. This corresponds to a "gain" of 1.58. The increase in the brightness of the LCD display is measured as a gain, which is the ratio of the brightness of the LCD display with the brightness-enhancing film to the brightness of the LCD display without the brightness-enhancing film. The brightness of the display was measured with an LS-100 or LS-110 luminance meter. [0165] The adhesive strength of the inner layer of the above-mentioned multilayer reflector was measured using a standard 90-degree tape peeling test and found to exceed 450 g / inch (180 g / cm). [0166] The present invention is not limited to the specific examples described above, and includes all aspects of the invention as defined in the appended claims. Various modifications, equivalent processes, and various structures to which the present invention can be applied will be apparent to those skilled in the art intended by the present invention in light of the present specification. The claims shall include such modifications and devices. [Simple explanation of drawings] The invention will be more fully understood in light of the following detailed description of the various embodiments of the invention in connection with the accompanying drawings. FIG. 1 is a cross-sectional view of an embodiment of a multilayer polymer film according to the present invention. FIG. 2 is a cross-sectional view of another embodiment of the multilayer polymer film according to the present invention. FIG. 3 Addition of terephthalate (using dimethyl terephthalate (DMT)) and isophthalate (using dimethyl isophthalate (DMI)) subunits to polyethylene naphthalate (PEN) derived from dimethylnaphthalene carboxylate. The graph which shows the decrease of the glass transition temperature (Fig. 3A) and the freezing temperature (Fig. 3B) at that time. FIG. 4 is a graph of average in-plane birefringence of coPEN denatured with terephthalates and isophthalate subunits and oriented at relatively low temperatures. FIG. 5 is a graph of thermal stability of coPEN containing terephthalates and isophthalate subunits. FIG. 6 is a graph showing the reduction of in-plane birefringence of coPEN at 632.8 nm with the addition of comonomer subunits. FIG. 7 is a graph showing the dependence of in-plane birefringence on molecular weight at 632.8 nm. The present invention can be modified to various modifications and variations, and specific examples thereof will be illustrated in the drawings and will be described in detail. However, the present invention is not limited to the specific embodiments described. Conversely, it shall include all modifications, equivalents and modifications contained within the technical ideas and scope of the invention as defined by the accompanying claims.