Infrared reflective optical interference film

The present invention relates to a multilayer optical interference film, and in more detail relates to an optical interference film that can reflect light in the infrared region of the spectrum and transmit substantially all light in the visible spectrum.

Co-extruded multilayer films including spacer layers with a thickness of 100 nanometers or less, which are mostly composed of two kinds of polymers, have been made. Such a multilayer film is described in, for example, Alfrey et al., US Patent No. 3,711,176. When the selected polymers have a sufficient mismatch in refractive index, these multilayer films cause constructive interference of light. As a result, the film only transmits light of a specific wavelength through the film and reflects light of other wavelengths. The multilayer film can be made of relatively inexpensive, commercially available polymer resins with the required refractive index difference. This film has the further advantage that they can be shaped or formed into other objects.

For a particular film, the reflection and transmission spectra are mainly determined by the optical thickness of each layer, and the optical thickness is defined as the product of the actual thickness of the layer and its refractive index. The film can be designed to reflect infrared, visible, or ultraviolet wavelength light depending on the optical thickness of each layer. When designed to reflect light of infrared wavelengths, the conventional film can also exhibit a higher level of reflection in the visible light range, resulting in an iridescent appearance of the film. The film manufactured according to the Alfrey patent described above shows iridescence and changing colors when the incident light on the film changes.

For some applications, although the reflection of infrared wavelengths is what is needed, the higher level of visible light reflection is not what is desired. For example, infrared reflective films can be laminated on the glass of buildings and automobiles to reduce the load on air conditioning. The film can also be laminated to other substantially transparent plastic materials to reflect infrared wavelengths. However, the film must be substantially transparent to visible light so that the vision through glass or plastic is not impaired.

Some higher-level reflections can be suppressed by appropriately selecting the optical thickness ratio in the two-component multilayer film. See Radford et al.,<u style="single">Reflectiyity of Iridescent Coextruded Multilayered Plastic Films</u>, Polymer Engneering and Science, vol. 13, No. 3, May 1973. However, it is impossible for a two-component film to suppress two consecutive higher-order reflections.

Other workers have designed a layer composed of three or more materials that can suppress specific higher-level reflections. For example, Thelen, US Patent No. 3,247,392 describes a bandpass filter that can be used as a reflection spectrum in the infrared and ultraviolet regions. This coating is taught to suppress the second and third level reflection bands. However, the materials used in the production of the film are metal oxide and halide dielectric materials, and these materials must be deposited in a separate processing step using expensive vacuum deposition techniques. At the same time, once deposited, the film and its attached bottom layer cannot be further shaped. Furthermore, the coating film is susceptible to cutting, scratching, and/or corrosion, so it must be protected. Finally, it is difficult to produce a film covering a large surface area due to the use of vacuum deposition technology.

Rock, US Patent No. 3,432,225 teaches a four-layer anti-reflection coating, which uses the first two layers of a specific thickness to synthesize a layer with an effective refractive index and is located between the two layers. Similarly, Rock utilizes metal halides, oxides, sulfides, and selenides to be deposited in separate processing steps using vacuum deposition techniques.

Similarly, Rancourt et al., US Patent No. 4,229,066 teaches a multilayer coating that utilizes visible light transmission and infrared reflection of metal halides, sulfides, and selenides. These materials have a high or low refractive index and are deposited in separate steps using vacuum deposition techniques. Neither Rock nor Rancourt's patents have been further formed after deposition.

Therefore, an optical interference film that can suppress most or multiple continuous higher-level reflections and can be manufactured using relatively inexpensive materials and then shaped or later formed is still required in this technical field.

The present invention provides an optical interference film made of multiple layers composed of different polymers, which can reflect light of wavelengths in the infrared region of the spectrum and is substantially transparent to light of wavelengths in the visible light spectrum. The term "different" means that the polymeric material does not need to be different in any respect other than the refractive index. Therefore, if such materials have the same refractive index, they are not "different" for the purpose of the invention. The number of layers can vary from a wide range of 50 to 1000 layers.

According to an embodiment of the present invention, an optical interference film including a plurality of spacer layers composed of at least first, second, and third different and substantially transparent polymer materials A, B, and C is provided. The optical thickness is between about 0.09 and 0.45 microns and each polymer material has a different refractive index, n_i. The optical thickness of a special layer can be defined as the physical thickness, d, multiplied by the refractive index of the polymer material, n_i. In addition, the refractive index of the second polymer material is between the respective refractive indices of the first and third polymer materials. In the embodiment of the present invention with a repeating unit ABCB and a plurality of layers with continuous higher-order reflection suppressed, the optical thickness ratio of the first material A, f_AIs 1/3, the optical thickness ratio of the second material B,<i>f</i>_<i>B</i>, Is 1/6, the optical thickness ratio of the third material C,<i>f</i>_<i>C</i>, Is 1/3, and<maths><img file="TW204397B_D0001.tif" /></maths>Where the optical thickness, f_idefined as<maths><img file="TW204397B_D0002.tif" /></maths>And m is the number of layers in the optical repeating unit, n_iIs the refractive index of polymer i, and d_iIs the layer thickness of polymer i. This particular embodiment of the invention produces a thin film in which the second, third and fourth order wavelengths will be suppressed.

In order to make a film with a broad bandwidth wavelength in the infrared range of the sun (e.g. reflection at about 0.7 to 2.0 mm), there may be a gradient in the layer thickness through the film thickness. Therefore, in an embodiment of the present invention, the layer thickness will increase monotonously across the film thickness.

In a preferred embodiment of the present invention, the polymeric material forms a repeating unit ABCB. In order to ensure that the second polymer material has a refractive index between the first and third polymers, any or all of the first, second, or third polymers may be a copolymer or a mixture of polymers Blend. For example, the second polymeric material may be a copolymer or a mixed blend of one of the first and third polymeric materials. By changing the amount of the first and third polymers in the copolymer or blend, the second polymer material can be synthesized to have the required refractive index. Those who are accustomed to this art should also understand that the refractive index of any polymer material, n, can be adjusted according to the method of synthesizing the required refractive index.

Furthermore, the refractive index of the first polymer material and the refractive index of the second polymer material preferably differ by at least about 0.03, and the refractive index of the second polymer material and the third polymer material preferably differ by about 0.03. According to a preferred embodiment, the first polymer material is polystyrene, the second polymer material is a copolymer of styrene and methyl methacrylate, and the third polymer material is polymethyl methacrylate. The optical interference film of the present invention reflects light of wavelengths in the infrared region of the spectrum while suppressing continuous higher-order reflections in the visible light range of two or more in the spectrum.

The optical interference film of the present invention can be used in a range where infrared reflection properties are required. For example, the film of the present invention can be laminated to glass used in buildings or automobiles to reflect infrared radiation, thereby reducing heating load. Furthermore, the film can also be laminated on other transparent plastics to provide infrared reflection properties. For example, the windshield and canopy on special aircraft are made of flexible polymer resin. Laminating or bonding the optical interference film of the present invention to such a polymer resin will provide protection against infrared radiation while still being transparent to light in the visible region of the spectrum, substantially without iridescence or otherwise undesirable The color effect is presented.

Therefore, one item of the present invention is to provide an infrared reflective optical interference film, which can suppress most or multiple continuous higher-level visible light reflections but can still be made of relatively inexpensive materials. Furthermore, an object of the present invention is to provide an optical interference film that can be formed into a variety of useful shapes or can be laminated to other substrates that can be formed or post-cut. These and other objectives and advantages of the present invention can be understood from the following detailed description and the scope of the patent application.

The present invention provides an improved multi-layer optical interference film that has a variety of desirable advantages, including infrared reflectivity of a wide bandwidth in the infrared range, substantial transparency to visible light, and forming ability, or layering and then being formed to form many useful objects. The optical principle of multiple reflections from layers with different refractive indexes confirms the dependence of the effect on the thickness of individual layers and the refractive index of the material. See, Radford et al., "Reflectivity of Iridescent Coextruded Multilayered Plastic Films", Polymer Engineering and Science 13, 3, pg. 216 (1973). The main or first-order reflection wavelength of the two-component multilayer film is determined by the following equation.

λ_I=2(<i>n</i>₁<i>d</i>₁+<i>n</i>₂<i>d</i>₂) Where λ_IIs the first-order reflection wavelength in nanometers, n₁And n₂Is the refractive index of the two polymers, and d₁And d₂It is the layer thickness of the two polymers, also in nanometers.

It can be understood that the first-order reflection wavelength is proportional to the sum of the optical thickness of the two polymers (where the optical thickness, n_id_i, Is the product of layer thickness multiplied by refractive index). Except for the first-order reflection, higher-order reflections occur at the whole fraction of the first-order. The relative intensity of these higher-order reflections depends on the optical thickness of the polymer composition. As taught by Radford et al., by controlling the thickness ratio of the two constituent systems, reflections of different levels can be enhanced while others are suppressed. However, the multiple continuous higher-order reflections in a two-component multilayer polymer system cannot be suppressed.

Therefore, a multilayer optical interference film, which is designed to have a strong reflection in the near-infrared region of the spectrum, also exhibits useless reflection in the visible light region of the spectrum due to this higher level of reflection. Such films typically display a range of iridescent colors. However, according to the present invention, a multilayer optical interference film containing an m-layer repetitive unit, where m is an integer of 4 or greater, is provided to suppress useless higher-order reflections. This film includes at least three different polymer materials in its structure. For this m-layer repeating unit, the first-order reflection will be at a wavelength λ_IOccurs everywhere, where:<maths><img file="TW204397B_D0003.tif" /></maths>N-level reflection will be at a wavelength λ_IHappens everywhere, where,<maths><img file="TW204397B_D0004.tif" /></maths>The relative intensity of higher-order reflection is determined by the ratio of optical thickness, f_iControlled by:<maths><img file="TW204397B_D0005.tif" /></maths>Wait until the number of repeating units m. Because there is more than one optical thickness for this system, this ratio can be adjusted to suppress at least two consecutive higher-level reflections. The actual effect is that for the optical interference film designed to reflect the near-infrared region of the spectrum, it usually appears in the visible light region of the spectrum and the higher-level reflection that causes the film to appear iridescent is suppressed.

In a preferred embodiment of the present invention, the multilayer optical interference film is composed of three different substantially transparent polymer materials A, B and C and has repeating units ABCB. The optical thickness of the layers is between 0.09 and 0.45 microns, and each polymer material has a different refractive index, n_i。

A better relationship of the optical thickness ratio of the polymer makes an optical interference film in which multiple successive higher-order reflections are suppressed. In this embodiment, the optical thickness ratio of the first material A, f_A, Is 1/3, the optical thickness ratio of the second material B, f_B, Is 1/6, the optical thickness of the third material C, f_C, Is 1/3, and<maths><img file="TW204397B_D0006.tif" /></maths>Where the optical thickness, n_id_i, Is as defined above. For this embodiment of the present invention, there is strong reflection at the first order wavelength, and the third and fourth order wavelengths will be suppressed.

In order to make a wide-bandwidth wavelength within the range of reflecting the sun's infrared rays (for example, reflection at about 0.7 to 2.0 microns), there can be a thick gradient through the thickness of the film. Therefore, in one embodiment of the present invention, the layer thickness through the thickness of the film will monotonously increase. As can be seen from the above equation, the change in the thickness of the individual layer, d, has a direct effect on the optical properties of the film.

For the three-component system of the present invention, it is preferable that the refractive index difference between the first polymer material (A) and the second polymer material (B) is at least about 0.03, and the second polymer material (B) and the third polymer material (C) The refractive index difference is at least 0.03, and the refractive index of the second polymer material (B) is between the refractive index of the first (A) and the third (C) polymer material.

Any or all of these polymeric materials can be synthesized using a copolymer or a mixed blend to have the required refractive index. For example, the second polymeric material may be a copolymer or a mixed blend of the first and third polymeric materials. By changing the relative amount of the monomers in the copolymer or the polymer in the blend, any one of the first, second, or third materials can be adjusted so that the relation of the refractive index is<maths><img file="TW204397B_D0007.tif" /></maths>Those who are accustomed to this art will understand that the optical thickness discussed above can be used to calculate the required relationship between materials, refractive index, and layer thickness.

The preferred polymer materials used in the practice of the present invention include styrene, methyl methacrylate, acrylonitrile, polycarbonate, butadiene, poly(ethylene-2,6-naphthalate), and methylene tetraethylene dicarboxylate. Alcohol thermoplastic polyurethane. The aforementioned and other copolymers that can be used in the practice of the present invention include, for example, copolymers of styrene methyl methacrylate, copolymers of styrene and acrylonitrile, and copolymers of styrene and butadiene. Other copolymers include the copolycarbonate of 4,4-benzenethiodiol and bisphenol A and the copolymer of glutarimide and methyl methacrylate (KAMAX resin, sold by Rohm and Haas).

For example, the first polymer material may be polystyrene, the second polymer material may be a copolymer of styrene and methyl methacrylate, and the third polymer material may be polymethyl methacrylate. Alternatively, phase-mixed blends of polymers can also be used to form any of the first, second, or third polymeric materials by mixing them in the correct ratio of the required refractive index. Examples of suitable phase blend blends include polymethyl methacrylate and polyvinylidene fluoride, and polycarbonate blends with the following: Saron, polyesters and copolyesters, polycaprolactone, Poly (1,4-butene adipate), poly 1,4-cyclohexane dimethyl succinate), and a 1,4-cyclohexane dimethyl terephthalate.

Other suitable thermoplastic resins that can be used in the practice of the present invention, along with their representative refractive index, include but are not limited to: perfluoroalkoxy resin (refractive index = 1.35), polytetrafluoroethylene (1.35), fluorinated ethylene-propylene Copolymer (1.34), silicone resin (1.41), polyvinylidene fluoride (1.42), polychlorodifluoroethylene (1.42), epoxy resin (1.45), poly(butyl acrylate) (1.46), poly(4) -Methylpentene-1) (1.46), polyvinyl acetate (1.47), ethyl cellulose (1.47), polyoxymethylene (1.48), polyisobutyl methacrylate (1.48), polymethyl acrylate ( 1.48), polypropyl methacrylate (1.48), polyether block amide (1.49), polymethyl methacrylate (1.49), cellulose ester (1.49), cellulose propionate (1.49) , Polybutene (1.50), ionomer resins such as Surlyn (trademark) (1.51), low density polyethylene (1.51), polyacrylonitrile (1.51), polyisobutylene (1.51), thermoplastic polyesters such as Ecdel (trademark) (1.52), polybutadiene (1.52), nylon (1.53), polypropylene imide (1.53), poly(chlorinated vinyl acetate) (1.554), polyvinyl chloride (1.54), high-density polyethylene (1.54), copolymer of methyl methacrylate and styrene (1.54), transparent acrylonitrile-butadiene-styrene terpolymer (1.54), allyl diethylene glycol resin (1.55), polyvinylidene chloride Blends of ethylene and polyvinyl chloride such as Saron resin (trademark) (1.55), poly-α-methylstyrene (1.56), styrene-butadiene latex such as Dow512-K (1.56), polyurethane Esters (1.56), chloroprene rubber (1.56), copolymers of styrene and acrylonitrile such as Tyril resin (trademark) (1.57), copolymers of styrene and butadiene (1.57), polycarbonate (1.59) , Other thermoplastic polyesters such as polyethylene terephthalate and polyethylene terephthalate (1.60), polystyrene (1.60), polyimide (1.61), polyvinyl chloride (1.61), Polydichlorostyrene (1.62), poly (1.63), polyether (1.65), polyether amide (1.66). Other polymers and their respective indices are recorded in J. Brandrup and E. 1mmergut, Polymer Handbook,

Preferably the polymer has compatible coextrusion rheological properties. That is, a preferred method for forming a multilayer film is coextrusion technology, and the melt viscosity of the polymer must be reasonably matched to prevent the instability or inhomogeneity of the layer. The polymer used must also have sufficient interfacial adhesion to prevent the film from delamination.

The multilayer optical interference film of the present invention has several outstanding advantages over the conventional techniques using expensive metal and dielectric vapor deposition techniques. The films of the present invention can be customized to reflect infrared light in a wide bandwidth; they can be easily co-extruded and can have a large surface area; and they can be shaped and formed into many useful structures after co-extrusion.

The multilayer body according to the present invention preferably uses a multilayer co-extrusion device as described in US Patent Nos. 3,773,882 and 3,884,606, the disclosures of which are incorporated herein for reference. This device provides a thermoplastic material for preparing multiple layers and extruding at the same time, each layer of which has a substantially uniform thickness. It is best to use a series of multilayered devices described in US Patent No. 3,759,647, the disclosure of which is also incorporated herein for reference.

The feeding carriage of the co-extrusion device receives different streams of thermoplastic polymer materials from a source such as a thermoplastic extruder. The resin material flow passes through a mechanical operating part in the feed sled. This part can rearrange the original liquid flow into a multilayered liquid flow with the required number of layers for the final product body. Optionally, this multilayered liquid stream can then be passed through a series of multilayered devices to further increase the number of layers in the final product.

The multi-layered liquid flow is then passed to an extrusion die which is constructed and arranged to maintain the laminar liquid flow in it. This extrusion device is described in US Patent No. 3,557,265, and the disclosure of the case is incorporated herein for reference. The resulting product is extruded to form a multilayer body, where each layer is substantially parallel to the main surface of the adjacent layer.

The structure of the extrusion die can be changed and the thickness and size of each layer can be reduced. The precise reduction degree of the layer thickness sent by the mechanical orientation part, the structure of the mold, and the mechanical processing of the multilayer body after extrusion all affect the thickness of the individual layers of the final product body.

The optical interference film of the present invention can have many applications. For example, they have applications in fields that require infrared reflective properties. The film of the present invention can be laminated to glass used in buildings and automobiles to reflect infrared radiation, thereby reducing heating load. Furthermore, the film can also be laminated to other substantially transparent plastics to provide infrared reflection properties. For example, windshields and canopies on special aircraft. Laminating or bonding the optical interference film of the present invention to such a polymer resin can provide protection against infrared radiation while being substantially transparent to light in the visible region of the spectrum.

The film itself and the plastic laminated on the film can be formed or later formed into a variety of useful objects. Since the film is transparent to light in the visible light region of the spectrum, there is substantially no iridescence or other undesirable color effects.

In addition to sheets and films of polymeric materials, there are many different contours that can be extruded. The profile mentioned here refers to the multilayer body 1) formed into a sheet, groove, lens-shaped cross-section, circular or elliptical tube, and a blank in a forming mold, or 2) outside a mold in a post-forming process Formed. A tube-shaped mold is used to make a multilayer tube. This tubular extrusion die can also be used to make bottles and containers that can be blow molded. Since the materials used in the film composition can be selected for special needs, if elastic resin is used, the final film or article can be flexible or elastic.

In order to make the present invention easier to understand, the following examples can be referred to. These examples are intended to illustrate the invention and not to limit its scope.

<u style="single">Example 1</u>

Using the device described in US Patent Nos. 3,773,882 and 3,759,647, a three-component multilayer optical interference film is made. The film reflects in the infrared region of the spectrum and suppresses the second and third in the visible region of the spectrum. And the fourth level of reflection, creating a visually transparent film that reflects solar infrared radiation. The co-extruded film is composed of the following three polymer components: Component A has a refractive index of 1057 and a density of 1.08, a styrene methyl methacrylate copolymer sold under the trade name of P-359 by Richardson Polymer Corporation Component B is a methyl methacrylate styrene copolymer with a refractive index of 1.53 and a density of 1.13, sold under the trade name of RPC-440 by Richardson Polymer Corporation; and Component C is a refractive index of 1.49 and a density of 1.20, produced by Rohm and Haas is a polymethyl methacrylate sold under the trade name of VS-100.

The skin layer of polycarbonate is provided on the surface of the two films and is sufficient to avoid surface instability and provide mechanical properties. The three components were co-extruded into a 165-layer film with ABCB repeating units. The three-component feeding trolley has 42 feeding channels for component A, 82 feeding channels for component B, and 41 feeding channels for component C. Three separate extruders used 8.5 kg/hr (18.8 lb/hr) component A, 9.0 kg/hr (19.7 lb/hr) component B, and 9.8 kg/hr (155 lb/hr) component C The rate at which the individual polymer components are fed to the charging trolley. In addition, 6.8 kg/hr (15 lb/hr) of polycarbonate was extruded to form the skin layers on both sides of the film. The extension of the film is adjusted to show a strong first-order reflection at 1400 nm when the film thickness is about 0.9 mil.

This produces a single layer of component A that is 148.6 nanometers thick, and the individual layer of component B is 76.3 nanometers thick. And the individual layers of component C are 156.6 nanometers thick. Therefore, the optical thickness ratio of the first component A, f_A, Is 1/3, the optical thickness ratio of the second component B, f_B, Is 1/6, the optical thickness ratio of the third component C, f_C, Is 1/3, and<maths><img file="TW204397B_D0008.tif" /></maths>Where the optical thickness, f, is defined as:<maths><img file="TW204397B_D0009.tif" /></maths>And n_iIs the refractive index of polymer i, and d_iIs the layer thickness of polymer i.

This film was found to have a wavelength λ in the near-infrared region of the spectrum_IThere is a strong first-order reflection at 1400nm. Secondary, tertiary, and fourth-level reflections are suppressed in this system. Therefore, the secondary radiation at 700 nm in the red range of the visible light spectrum, λ_I/2, the third level reflection at 467nm in the blue range of the visible light spectrum, λ_I/3, and the fourth-order reflection λ in the long ultraviolet range of the spectrum_I/4 are suppressed.

<u style="single">Example 2</u>

A solar infrared reflective film can be designed to reflect the wavelength of 0.75 to 2.0 microns and is substantially transparent to the wavelength of visible light (0.4 to 0.7 microns). The secondary, tertiary, and fourth-order reflections occurring in the wavelength bands of 0.375-1.0 microns, 0.25-0.667 microns, and 0.188-0.5 microns, respectively, are suppressed. The five-stage reflection of this system is in the wavelength band of 0.15-0.4 microns in the ultraviolet range.

A three-component film with polymer repeating units of ABCB can be fabricated as in Example 1. The first component, A, is a copolymer of 75-25 mole percent of 4,4-benzenethiodiol and bisphenol A with a refractive index of 1.636. The second component, B, is a copolymer of pentadiimide and methyl methacrylate (KAMAX T-260 resin, sold by Rohm and Haas), with a refractive index of 1.54.

The third component, C, must have a refractive index of 1.45 to meet the following requirements<maths><img file="TW204397B_D0010.tif" /></maths>A blend of 55 percent by weight of polyvinylidene fluoride (PVDF) and 45 percent of polymethyl methacrylate (PMMA) was used.

A relatively thick polycarbonate and/or polymethyl methacrylate skin layer is provided on the second surface of the film. The thickness of the skin layer is sufficient to avoid instability and/or provide mechanical strength. The polymer used is selected according to the mechanical properties and the conditions of the substrate on which the film will be laminated.

The ABCB repeat unit is given a thickness gradient in its film thickness to provide reflectivity in the range of 0.75 microns (minimum cut-off wavelength) to 2.0 microns (maximum cut-off wavelength). The layer thickness of the ABCB repeat unit will be d at the minimum cut-off wavelength at a wavelength of 0.75 microns_A=0.0765 microns, d_B=0.0405 microns, d_C=0.086 microns, and d_B= 0.0405 micron change to the maximum cut-off wavelength d at the wavelength of 2.0 micron_A=0.202 microns, d_C=0.230 microns, and d_B=0.108 microns. The co-extrusion feeding carriage can be adjusted to provide 842 layers with a 2.67:1 layer thickness gradient of the repeating unit.

The extrusion rates of polymers A, B, and C were set to provide a repetitive unit volume composition ratio of 31.4%, 33.2%, and 35.4%, respectively. The film thickness is reduced by speed to obtain a first-order reflection between 0.75 and 2.0 microns. The total film thickness depends on the amount of skin layer polymer provided and the layer thickness gradient pattern used.

This example illustrates the use of a blend of two different copolymers and polymers to adjust the refractive index. The calculated spectrum of a 420-layer film shows a cut-off wavelength at 0.742.0 and microns, respectively, and the average reflectance is about 75%. The layer thickness gradient of the optical repeating unit can be obtained by co-extrusion with a monotonously increasing layer thickness or other distribution that can provide sufficient reflectivity in the range of 0.75 to 2.0 microns. Alternatively, several films reflecting different parts of this range can be laminated together to achieve the same result.

Although the present invention has been described in terms of specific representative embodiments and details, those skilled in the art will understand that the methods and devices disclosed herein can make various changes without departing from the scope of the present invention defined in the scope of the appended patent application. The change.

Infrared reflective optical interference layer film