Matt coextruded polyester foil, method of manufacture and use

The invention relates to a biaxially oriented polyester film with a base layer which consists of at least 80% by weight of a thermoplastic polyester and at least one matt cover layer which contains a mixture or a blend of two polyester components I and II. The invention further relates to a method for producing the film and its use.

The packaging industry has a high demand for transparent, high-gloss plastic films, such as biaxially oriented polypropylene or biaxially oriented polyester films. In addition, there is an increasing need for such transparent films in which at least one surface layer is not high-gloss but is characterized by a characteristic matt appearance, and thereby, for example gives the packaging a special, attractive and therefore effective advertising appearance.

EP 346 647 describes a biaxially oriented polyester film which contains at least one cover layer which contains a filler in a concentration of 0.5 to 50%, the diameter of this filler being in a specific ratio to the layer thickness of the cover layer. Furthermore, the cover layer has a certain thickness and a certain degree of crystallization, which is determined with the aid of Raman spectroscopy.

In US 4,399,179 a coextruded biaxially oriented polyester film is described, which consists of a transparent base layer and at least one matt layer, which consists essentially of a certain polyethylene terephthalate copolymer and also internal particles with a diameter of 0.3 to 20 microns in one Contains a concentration of 3 to 40%. The special copolymer is a processing aid by which the viscosity of the melt containing the inner particles is reduced, so that a perfect extrusion of this layer is possible. The mattness of the film is achieved by adding the inner particles to the corresponding layer.

EP 0 144 978 describes a self-supporting oriented film made of thermoplastic material which has a continuous polyester coating on at least one of its two surfaces, which is applied as an aqueous dispersion to the film before the last stretching step. The polyester coating consists of a condensation product of various monomers or of their derivatives capable of forming polyesters, such as isophthalic acid, aliphatic dicarboxylic acid, sulfomonomers and aliphatic or cycloaliphatic glycol.

In the cases described, there is no indication of how the film can be given a low gloss, at least on a film surface, while the film is still highly transparent.

The object of the present invention was therefore to provide a coextruded biaxially oriented and transparent polyester film with at least one matt cover layer which can be produced simply and economically, which has the good physical properties of the known films and does not cause any disposal problems.

The object is achieved by a coextruded and biaxially oriented polyester film of the type mentioned, the distinguishing features of which are that the matt cover layer contains a mixture or a blend of two components I and II.

Component I of the mixture or blend is preferably a polyethylene terephthalate homopolymer or polyethylene terephthalate copolymer or a mixture of polyethylene terephthalate homo- or copolymers.

Component II of the copolymer or of the mixture or of the blend consists of a condensation product of the following monomers or their derivatives capable of forming polyesters:<ul id="ul0001" list-style="none" compact="compact"><li>A) 65 to 95 mol% isophthalic acid;</li><li>B) 0 to 30 mol% of at least one aliphatic dicarboxylic acid having the formula HOOC (CH₂)_nCOOH, where n ranges from 1 to 11;</li><li>C) 5 to 15 mol% of at least one sulfomonomer containing an alkali metal sulfonate group on the aromatic part of a dicarboxylic acid;</li><li>D) the stoichiometric amount of a copolymerizable aliphatic or cycloaliphatic glycol having 2 to 11 carbon atoms necessary to form 100 mol% condensate;</li></ul> the percentages are based in each case on the total amount of the monomers forming component II.

Mixtures for the purposes of the present invention are understood to mean mechanical mixtures which are produced from the individual components. For this purpose, the individual constituents are generally poured together as pressed molded articles of small size, for example lenticular or spherical granules, and mechanically mixed with one another using a suitable vibrating device. Another possibility for the preparation of the mixture is that the respective components I and II in granulate form are fed separately to the extruder for the top layer according to the invention and the mixture is carried out in the extruder or in the subsequent melt-carrying systems.

A blend in the sense of the present invention is an alloy-like composite of the individual components I and II, which can no longer be broken down into the original components. A blend has properties like a homogeneous substance and can be characterized accordingly by suitable parameters.

The subclaims indicate preferred embodiments of the invention, which are additionally explained below.

According to the invention, the film has at least two layers. It then comprises as layers a layer B and the cover layer A according to the invention. In a preferred embodiment of the invention, the film is constructed in three layers and has cover layer A on one side of layer B (= base layer) and one on the other side of layer B. another layer C. In this case, the two layers A and C form the outer layers A and C.

The cover layer according to the invention is characterized by a characteristic matt surface or optics and is well suited for use as packaging film or for applications in the industrial sector.

The <b>Base layer</b> B of the film preferably consists of at least 90% by weight of a thermoplastic polyester. Polyesters of ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), of ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene-2,6-naphthalate, PEN), of 1,4-bis-hydroxymethylcyclohexane and terephthalic acid [= Poly (1,4-cyclohexanedimethylene terephthalate, PCDT) as well as from ethylene glycol, naphthalene-2,6-dicarboxylic acid and biphenyl-4,4'-dicarboxylic acid (= polyethylene-2,6-naphthalate bibenzoate, PENBB). Particularly preferred are polyesters which consist of at least 90 mol%, preferably at least 95 mol%, of ethylene glycol and terephthalic acid units or of ethylene glycol and naphthalene-2,6-dicarboxylic acid units. The remaining monomer units originate from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids, as can also occur in layer A (or layer C).

Suitable other aliphatic diols are, for example, diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO- (CH₂)_n-OH, where n represents an integer from 3 to 6 (in particular propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol and hexane-1,6-diol) or branched aliphatic Glycols with up to 6 carbon atoms. Of the cycloaliphatic diols, cyclohexanediols (in particular cyclohexane-1,4-diol) can be mentioned. Suitable other aromatic diols correspond, for example, to the formula HO-C₆H₄-XC₆H₄-OH, where X is for -CH₂-, -C (CH₃)₂-, -C (CF₃)₂-, -O-, -S- or -SO₂- stands. In addition, bisphenols of the formula HO-C are also₆H₄-C₆H₄-OH well suited.

Other aromatic dicarboxylic acids are preferably benzenedicarboxylic acids, naphthalenedicarboxylic acids (for example naphthalene-1,4- or 1,6-dicarboxylic acid), biphenyl-x, x'-dicarboxylic acids (in particular biphenyl-4,4'-dicarboxylic acid), diphenylacetylene-x, x ' -dicarboxylic acids (especially diphenylacetylene-4,4'-dicarboxylic acid) or stilbene-x, x'-dicarboxylic acids. Of the cycloaliphatic dicarboxylic acids, cyclohexanedicarboxylic acids (in particular cyclohexane-1,4-dicarboxylic acid) should be mentioned. Of the aliphatic dicarboxylic acids, the (C₃-C₁₉) Alkanedioic acids are particularly suitable, the alkane fraction being straight-chain or branched.

The polyester can be produced, for example, by the transesterification process. The starting point is dicarboxylic acid esters and diols, which are reacted with the usual transesterification catalysts, such as zinc, calcium, lithium, magnesium and manganese salts. The intermediates are then polycondensed in the presence of generally customary polycondensation catalysts, such as antimony trioxide or titanium salts. The preparation can also be carried out by the direct esterification process in the presence of polycondensation catalysts. Here one starts directly from the dicarboxylic acids and the diols.

At least one <b>Top layer</b> The multilayer film according to the invention contains a mixture or a blend of two components I and II, which are described in more detail below, and optionally added additives.

Component I of the cover layer mixture or of the blend is generally a thermoplastic polyester, in particular a polyester as was described in more detail for the base layer. For the production of high degrees of matting, it has proven to be advantageous if the polyester polymer for component I of the top layer according to the invention has a comparatively low viscosity per se. A modified solvent viscosity (SV value or "solution viscosity") is used to describe the viscosities of the melts. For commercially available polyethylene terephthalates, which are suitable for the production of biaxially oriented films, the SV values ​​are in the range from 500 to 1200. In order to achieve a high mattness of the film in the sense of the present invention, it has proven to be advantageous if the SV value of the polymers for component I of the top layer according to the invention is in the range from 500 to 800, preferably in the range from 500 to 750. are particularly preferably in the range from 500 to 700. However, component I is preferably a PET homo- or copolymer or a mixture thereof.

Component II of the top layer mixture is, as already stated, by polycondensation of A) isophthalic acid, B) an aliphatic dicarboxylic acid with the formula         HOOC (CH₂)_nCOOH, in which    n is in the range from 1 to 11, C) a sulfomonomer containing an alkali metal sulfonate group on the aromatic part of an aromatic dicarboxylic acid and D) at least one aliphatic or cycloaliphatic alkylene glycol having about 2 to 11 carbon atoms. The total acid equivalents present should essentially correspond on a molar basis to the total glycol equivalents present.

Dicarboxylic acids suitable as component B) of the copolyester are, for example, malonic, adipic, azelaic, glutaric, sebacic, cork, succinic and brassylic acid as well as mixtures of these acids or their derivatives capable of forming polyesters. Of the acids mentioned, sebacic acid is preferred.

Examples of sulfomonomers which contain an alkali metal sulfonate group on the aromatic part of an aromatic dicarboxylic acid (component C) are those monomers which correspond to the following general formula:<chemistry id="chem0001" num="0001"><img file="EP0976548A2_D0001.tif" /></chemistry>

In this formula is<ul id="ul0002" list-style="none" compact="compact"><li>M is a monovalent cation of an alkali metal,</li><li>Z is a trivalent aromatic radical, and</li><li>X and Y are carboxyl groups or polyester-forming equivalents.</li></ul>

Monomers of this type are described in U.S. Patents 3,563,942 and 3,779,993. Examples of such monomers are sodium sulphoterephthalic acid, sodium 5-sulfoisophthalic acid, sodium sulfophthalic acid, 5- (p-sodium sulfophenoxy) isophthalic acid, 5- (sodium sulfopropoxy) isophthalic acid and the like monomers and their derivatives capable of forming polyesters, such as eg the dimethyl esters. M is preferably Na⁺, Li⁺ or K⁺.

The term “derivatives capable of forming polyesters” here means reaction participants with groups which are capable of condensation reactions, in particular transesterification reactions, of forming polyester bonds. Such groups include carboxyl groups and their lower alkyl esters, for example dimethyl terephthalate, diethyl terephthalate and numerous other esters, halides or salts. The acid monomers are preferably used as dimethyl esters, since the condensation reaction can be better controlled in this way.

Glycols suitable as component D) are, for example, ethylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,10-decanediol, cyclohexane-dimethanol and similar substances. Ethylene glycol is preferably used.

The copolyesters can be made by known polymerization techniques. In general, the procedure is such that the acid components are brought together with glycol and heated in the presence of an esterification catalyst, followed by the addition of a polycondensation catalyst.

It has been shown that the relative proportions of components A, B, C and D, which are used to produce the mixtures according to the invention, are decisive for achieving the matt top layer. For example, at least about 65 mol% of isophthalic acid (component A) must be present as the acid component. Component A is preferred as pure isophthalic acid, which is present in an amount of about 70 to 95 mol%.

For component B it applies that any acid with the formula mentioned gives satisfactory results, with adipic acid, azelaic acid, sebacic acid, malonic acid, succinic acid, glutaric acid and mixtures of these acids being preferred. The desired amount within the specified range is preferably 1 to 20 mol%, based on the acid components of mixture I, if component B is contained in the composition.

The glycol component is present in an approximately stoichiometric amount.

The copolyesters suitable for the purposes of the invention are furthermore distinguished by the fact that they have an acid number below 10, preferably from 0 to 3, an average molar weight below approximately 50,000 and an SV value in the range from approximately 30 to 700, preferably approximately 350 to 650.

The ratio (weight ratio) of the two components I and II of the cover layer mixture or of the blend can vary within wide limits and depends on the intended use of the multilayer film. The ratio of components I and II is preferably in a range from I: II = 10: 90 to I: II = 95: 5, preferably between I: II = 20:80 to I: II = 95: 5 and in particular between I. : II = 30: 70 to I: II = 95: 5.

The base layer and the top layer (s) can additionally contain conventional additives, such as stabilizers and antiblocking agents. They are expediently added to the polymer or the polymer mixture before the melting. For example, phosphorus compounds such as phosphoric acid or phosphoric acid esters are used as stabilizers. Typical antiblocking agents (also referred to as pigments in this context) are inorganic and / or organic particles, for example calcium carbonate, amorphous silica, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, LiF, calcium, barium , Zinc or manganese salts of the dicarboxylic acids used, carbon black, titanium dioxide, kaolin or crosslinked polystyrene or acrylate particles.

Mixtures of two or more different antiblocking agents or mixtures of antiblocking agents of the same composition but different particle size can also be selected as additives. The particles can be added to the individual layers in the usual concentrations, for example as a glycolic dispersion during polycondensation or via masterbatches during extrusion. Pigment concentrations of 0.0001 to 10% by weight have proven to be particularly suitable. By adding these particles into the top layer A according to the invention, there is a further advantageous possibility of varying the degree of matting of the film. As a rule, the increase in pigment concentration is also associated with an increase in the degree of mattness of the film. A detailed description of the antiblocking agents can be found, for example, in EP-A 0 602 964.

The present invention also relates to a method for producing this film. It includes that<ul id="ul0003" list-style="none" compact="compact"><li>a) producing a film from the base and top layer (s) by coextrusion,</li><li>b) biaxial stretching of the film and</li><li>c) heat setting of the stretched film.</li></ul>

To produce the cover layer according to the invention, granules from mixture component I and granules from mixture component II are expediently fed directly to the extruder in the desired mixing ratio. It has proven to be expedient to use a twin-screw extruder for the extrusion of the matt cover layer according to the invention, as is used, for example, in<b>EP 0 826 478</b> is described. The two materials can be melted and extruded at about 300 ° C. and with a residence time of about 5 minutes. Under these conditions, transesterification reactions can take place in the extruder, in which further copolymers can form from the homopolymers and the copolymers.

The polymers for the base layer are expediently fed in via a further extruder. Any foreign bodies or impurities that may be present can be filtered off from the polymer melt before extrusion. The melts are then formed into flat melt films in a multi-layer nozzle and layered one on top of the other. The multilayer film is then pulled off and solidified with the aid of a cooling roller and, if appropriate, further rollers.

Biaxial stretching is generally carried out sequentially or simultaneously. In sequential stretching, stretching is preferably carried out first in the longitudinal direction (ie in the machine direction) and then in the transverse direction (ie perpendicular to the machine direction). This leads to an orientation of the molecular chains. The stretching in the longitudinal direction can be carried out with the aid of two rolls running at different speeds in accordance with the desired stretching ratio. A corresponding tenter frame is generally used for transverse stretching. With simultaneous stretching, the film is stretched simultaneously in the longitudinal and transverse directions in a tenter frame.

The temperature at which the stretching is carried out can vary within a relatively wide range and depends on the desired properties of the film. In general, the longitudinal stretching is carried out at 80 to 130 ° C and the transverse stretching at 90 to 150 ° C. The longitudinal stretching ratio is generally in the range from 2.5: 1 to 6: 1, preferably from 3: 1 to 5.5: 1. The transverse stretching ratio is generally in the range from 3.0: 1 to 5.0: 1, preferably from 3.5: 1 to 4.5: 1. If desired, a longitudinal stretching and even a further transverse stretching can follow the transverse stretching.

In the subsequent heat setting, the film is held at a temperature of 150 to 250 ° C. for about 0.1 to 10 s. The film is then wound up in the usual way.

The film can also be coated on at least one of its surfaces, so that the coating on the finished film has a thickness of 5 to 100 nm, preferably 20 to 70 nm, in particular 30 to 50 nm. The coating is preferably applied in-line, ie during the film production process, expediently before transverse stretching. Application by means of the “reverse gravure-roll coating” method is particularly preferred, in which the coatings can be applied extremely homogeneously in the layer thicknesses mentioned. The coatings are preferably applied as solutions, suspensions or dispersions, particularly preferably as an aqueous solution, suspension or dispersion. The coatings mentioned give the film surface an additional function, for example. this makes the film sealable, printable, metallizable, sterilizable, antistatic or, for example, improve the aroma barrier or enable adhesion to materials that would otherwise not adhere to the film surface (eg photographic emulsions). Examples of substances / compositions that provide additional functionality:

Acrylates as described, for example, in WO 94/13476, ethylene vinyl alcohols (EVA), PVDC, water glass (Na₂SiO),₄ hydrophilic polyesters (5-nasulfoisophthalic acid-containing PET / IPA polyesters as described, for example, in EP-A-0 144 878, US-A-4,252,885 or EP-A-0 296 620, vinyl acetates as described, for example, in WO 94/13481, polyvinyl acetates, polyurethanes, alkali or alkaline earth salts from C₁₀-C₁₈-Fatty acids, butadiene copolymers with acrylonitrile or methyl methacrylate, methacrylic acid, acrylic acid or their esters.

The substances / compositions mentioned are applied as a dilute solution, emulsion or dispersion, preferably as an aqueous solution, emulsion or dispersion, to one or both film surfaces and the solvent is then volatilized. If the coatings are applied in-line before the transverse stretching, the heat treatment in the transverse stretching and subsequent heat setting is usually sufficient to volatilize the solvent and to dry the coating. The dried coatings then have the desired layer thicknesses mentioned above.

Furthermore, the films can - preferably in an off-line process with metals such as aluminum or ceramic materials such as SiO_x or Al_xO_y be coated. This improves their gas barrier properties in particular.

The polyester film according to the invention preferably also contains a second cover layer C. The structure, thickness and composition of a second cover layer can be selected independently of the cover layer already present, the second cover layer likewise containing the polymers or polymer mixtures already mentioned for the base layer or the first cover layer according to the invention can, which do not have to be identical to those of the first cover layer. The second cover layer can also contain other common cover layer polymers.

There may also be an intermediate layer between the base layer and the cover layer (s). It can consist of the polymers described for the base layers. In a particularly preferred embodiment, it consists of the polyester used for the base layer. It can also contain the usual additives described. The thickness of the intermediate layer is generally greater than 0.3 μm and is preferably in the range from 0.5 to 15 μm, in particular 1.0 to 10 μm.

The thickness of the cover layer (s) is generally greater than 0.1 μm and is preferably in the range from 0.2 to 6 μm, in particular 0.3 to 5.5 μm, in particular 0.4 to 4.5 μm, the cover layers can be the same or different thickness.

The total thickness of the polyester film according to the invention can vary within wide limits and depends on the intended use. It is preferably 4 to 300 μm, in particular 5 to 250 μm, preferably 6 to 200 μm, the base layer preferably having a share of approximately 40 to 90% of the total thickness.

Another advantage is that the production costs of the film according to the invention are only slightly above those of a film made from standard polyester raw materials. The other processing and use-relevant properties of the film according to the invention remain essentially unchanged or are even improved. In addition, the manufacture of the film ensures that the regenerate can be reused in a proportion of up to 50% by weight, preferably 10 to 50% by weight, based in each case on the total weight of the film, without the physical Properties of the film are significantly negatively affected.

The film is ideal for packaging light and / or air sensitive food and beverages. It is particularly suitable for the production of packaging for coffee, in particular ground coffee.

In summary, the film according to the invention is characterized by a low gloss, in particular a low gloss on the film surface A, and by a comparatively low haze. It also has good winding and processing behavior. It is also worth mentioning that the top layer according to the invention can be easily written on with a ballpoint pen, felt-tip pen or fountain pen.

The gloss of the film surface A is less than 70. In a preferred embodiment, the gloss of this side is less than 60 and in a particularly preferred embodiment less than 50. This film surface thus conveys a particularly high advertising effect and is therefore particularly suitable as an external surface a packaging.

The haze of the film is less than 40%. In a preferred embodiment the haze of the film is less than 35% and in a particularly preferred embodiment less than 30%. Due to the comparatively low cloudiness of the film (compared to a matt mono film, see comparative example), the film can be printed, for example, in reverse printing or viewing windows can be installed, through which, for example, the contents can be recognized very well.

Further areas of application are the use for the production of labels, as a release film for the production of GRP semi-finished products, as an embossing film or in-mold labeling.

The table below (Table 1) summarizes the most important film properties according to the invention.<tables id="tabl0001" num="0001"><img file="EP0976548A2_D0002.tif" /></tables>

The following methods were used to characterize the raw materials and the foils:

To determine the SV value (SV = solvent viscosity), a polyester sample was dissolved in a solvent (dichloroacetic acid) (1% by weight solution). The viscosity of this solution and the viscosity of the pure solvent were measured in an Ubbelohde viscometer. The quotient (= relative viscosity η_rel) determined, subtracted 1,000 from this and multiplied this value by 1,000. The result was the SV value ("solution viscosity").

The friction was determined according to DIN 53 375. The sliding friction number was measured 14 days after production.

The surface tension was determined using the so-called ink method (DIN 53 364).

The haze of the film was measured according to ASTM-D 1003-52. The haze measurement according to Hölz ​​was determined based on ASTM-D 1003-52, however, in order to utilize the optimal measuring range, measurements were taken on four layers of film lying one above the other and a 1 ° slit diaphragm was used instead of a 4 ° perforated diaphragm.

The gloss was determined in accordance with DIN 67 530. The reflector value was measured as an optical parameter for the surface of a film. Based on the standards ASTM-D 523-78 and ISO 2813, the angle of incidence was set at 20 ° or 60 °. A light beam hits the flat test surface at the set angle of incidence and is reflected or scattered by it. The light rays striking the photoelectronic receiver are displayed as a proportional electrical quantity. The measured value is dimensionless and must be specified with the angle of incidence.

The roughness R_a the film was determined according to DIN 4768 with a cut-off of 0.25 mm.

The following examples illustrate the invention.

example 1

<ul id="ul0004" list-style="none"><li>a) Preparation of component II for the top layer mixture according to the invention. A copolyester with approx. 90 Mol% of isophthalic acid and 10 mol% of the sodium salt of 5-sulfoisophthalic acid as the acid component and 100 mol% of ethylene glycol as the glycol component were prepared by the following procedure: A 2 liter stainless steel reaction vessel equipped with an anchor stirrer, a thermocouple to measure the temperature of the vessel contents, an 18 inch Claisen / Vigreux distillation column with a cooler and receiver, an inlet opening and a heating jacket was preheated to 190 ° C , flushed with nitrogen and filled with 1065.6 g of dimethyl isophthalate, 180.6 g of dimethyl 5-sulfoisophthalate sodium salt and 756.9 g of ethylene glycol. In addition, a buffer (Na₂CO₃• 10 hours₂O-0.439 g) and a transesterification catalyst (Mn (OAC)₂ · 4 h₂O - 0.563 g) was added to the reaction vessel. The mixture was heated with stirring, with methanol distilling off. During the distillation, the temperature in the vessel was gradually raised to 250 ° C. When the weight of the distillate corresponded to the theoretical yield of methanol, an ethylene glycol solution containing 0.188 g of phosphorous acid was added. The distillation column was replaced with a curved steam outlet with template. 20 g of pure ethylene carbonate were added to the reaction mixture, and violent gas evolution (CO₂) a. The CO₂-Development subsided after about 10 minutes. A vacuum of 240 mm Hg was then drawn and the polycondensation catalyst (0.563 g Sb₂O₃) in an ethylene glycol slurry) added. The reaction mixture was stirred for 10 min while maintaining the negative pressure of 240 mm Hg, after which the pressure was reduced further in steps of 10 mm Hg / min from 240 mm Hg to 20 mm Hg. As soon as the vacuum in the system was reduced to 20 mm Hg, the vessel temperature was raised from 250 ° C to 290 ° C at a rate of 2 ° C / min. At a temperature of 290 ° C in the vessel, the stirrer speed was reduced and the pressure was reduced to a maximum of 0.1 mm Hg. At this point an ammeter reading of the stirrer motor was carried out. The viscosity of the polymer was controlled by letting the polycondensation proceed according to fixed values ​​for the change in the amperage of the stirrer motor of (in each case) 2.3 A. When the desired molecular weight was reached, the vessel was pressurized with nitrogen to force the liquid polymer from the bottom plug of the vessel into a quench bath of ice water.</li><li>B) Mixture preparation for the cover layer A according to the invention 80% by weight of component I (polyethylene terephthalate with an SV value of 680) and 20% by weight of component II were fed to the hopper of a twin-screw extruder and the two components were extruded together at about 300 ° C. and the top layer channel A one Multi-layer nozzle supplied.</li></ul>

At the same time, chips made of polyethylene terephthalate were dried at 160 ° C. to a residual moisture content of less than 50 ppm and fed to the extruder for the base layer. Chips of polyethylene terephthalate and a filler were also fed to the extruder for the cover layer C. A transparent three-layer film with ABC structure and a total thickness of 12 µm was then produced by coextrusion and subsequent stepwise orientation in the longitudinal and transverse directions. The cover layers each had a thickness of 1.5 µm. <tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col2" align="left">Base layer B:</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">95 % By weight</entry><entry namest="col2" nameend="col2" align="left">Polyethylene terephthalate (RT 49 from Hoechst AG) with an SV value of 800 and</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">5 % By weight</entry><entry namest="col2" nameend="col2" align="left">Masterbatch made from 99% by weight of polyethylene terephthalate and 1.0% by weight of silica particles (®Sylobloc 44 H from Grace) with an average particle size of 4.5 µm.</entry></row></tbody></tgroup></table></tables><tables id="tabl0003" num="0003"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col2" align="left">Top layer A:</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">80 % By weight</entry><entry namest="col2" nameend="col2" align="left">Component I and</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">20 % By weight</entry><entry namest="col2" nameend="col2" align="left">Component II.</entry></row></tbody></tgroup></table></tables><tables id="tabl0004" num="0004"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col2" align="left">Top layer C:</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">90 % By weight</entry><entry namest="col2" nameend="col2" align="left">Polyethylene terephthalate (RT 49 from Hoechst AG) with an SV value of 800 and</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">10th % By weight</entry><entry namest="col2" nameend="col2" align="left">Masterbatch made from 99% by weight of polyethylene terephthalate and 1.0% by weight of silica particles (®Sylobloc 44 H from Grace) with an average particle size of 4.5 µm.</entry></row></tbody></tgroup></table></tables>

The individual process steps were: <tables id="tabl0005" num="0005"><table frame="all"><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" colsep="1" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Extrusion</entry><entry namest="col2" nameend="col2" align="left">Temperatures</entry><entry namest="col3" nameend="col3" align="left">Top layer</entry><entry namest="col4" nameend="col4" align="center">300 ° C</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="left">Base layer</entry><entry namest="col4" nameend="col4" align="center">300 ° C</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">Pull roller temperature</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">30th ° C</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">Nozzle gap width</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">1 mm</entry></row><row><entry namest="col1" nameend="col1" align="left">Longitudinal extension</entry><entry namest="col2" nameend="col2" align="left">temperature</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">85-135 ° C</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">Longitudinal stretch ratio</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">4,0 : 1</entry></row><row><entry namest="col1" nameend="col1" align="left">Transverse stretching</entry><entry namest="col2" nameend="col2" align="left">temperature</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">85-135 ° C</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">Cross stretch ratio</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">4,0 : 1</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Fixation</entry><entry namest="col2" nameend="col2" align="left">temperature</entry><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" align="center">230 ° C</entry></row></tbody></tgroup></table></tables>

Example 2

Analogously to Example 1, a three-layer film with a total thickness of 12 μm was produced by coextrusion. Only the composition of top layer A was changed:<tables id="tabl0006" num="0006"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col2" align="left">Top layer A:</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">75 % By weight</entry><entry namest="col2" nameend="col2" align="left">Component I and</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">25th % By weight</entry><entry namest="col2" nameend="col2" align="left">Component II.</entry></row></tbody></tgroup></table></tables>

Example 3

A coextruded film with the formulation according to Example 1, in which the top layer A was composed as follows: <tables id="tabl0007" num="0007"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">70 % By weight</entry><entry namest="col2" nameend="col2" align="left">Component I and</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">30th % By weight</entry><entry namest="col2" nameend="col2" align="left">Component II.</entry></row></tbody></tgroup></table></tables>

Example 4

A coextruded film with the formulation according to Example 1, in which the top layer A was composed as follows: <tables id="tabl0008" num="0008"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">60 % By weight</entry><entry namest="col2" nameend="col2" align="left">Component I and</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">40 % By weight</entry><entry namest="col2" nameend="col2" align="left">Component II.</entry></row></tbody></tgroup></table></tables>

Comparative example

A monofilm was produced which was composed like the cover layer A from Example 3. The film surfaces had the required mattness, but the film did not meet the requirements because it was too cloudy. It was also very difficult to process the film reliably and therefore economically.<tables id="tabl0009" num="0009"><table frame="all"><title>Table 2</title><tgroup cols="8" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="19.68mm" /><colspec colnum="2" colname="col2" colwidth="19.68mm" /><colspec colnum="3" colname="col3" colwidth="19.68mm" /><colspec colnum="4" colname="col4" colwidth="19.68mm" /><colspec colnum="5" colname="col5" colwidth="19.68mm" /><colspec colnum="6" colname="col6" colwidth="19.68mm" /><colspec colnum="7" colname="col7" colwidth="19.68mm" /><colspec colnum="8" colname="col8" colwidth="19.68mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" rowsep="0" align="left">Example No.</entry><entry namest="col2" nameend="col2" rowsep="0" align="left">Mixing ratio KI: K II of the top layer A</entry><entry namest="col3" nameend="col3" rowsep="0" align="left">Film n-thickness (µm)</entry><entry namest="col4" nameend="col4" rowsep="0" align="left">Cover layer thickness A / C (µm)</entry><entry namest="col5" nameend="col5" rowsep="0" align="left">Foil structure</entry><entry namest="col6" nameend="col7" align="left">Gloss (60 ° measuring angle)</entry><entry namest="col8" nameend="col8" rowsep="0" align="left">Cloudiness</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" /><entry namest="col6" nameend="col6" align="left">A-side</entry><entry namest="col7" nameend="col7" align="left">C side</entry><entry namest="col8" nameend="col8" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="center">1</entry><entry namest="col2" nameend="col2" align="center">80:20</entry><entry namest="col3" nameend="col3" align="center">12</entry><entry namest="col4" nameend="col4" align="left">1,5/1,5</entry><entry namest="col5" nameend="col5" align="left">ABC</entry><entry namest="col6" nameend="col6" align="center">65</entry><entry namest="col7" nameend="col7" align="center">175</entry><entry namest="col8" nameend="col8" align="center">25</entry></row><row><entry namest="col1" nameend="col1" align="center">2</entry><entry namest="col2" nameend="col2" align="center">75:25</entry><entry namest="col3" nameend="col3" align="center">12</entry><entry namest="col4" nameend="col4" align="left">1,5/1,5</entry><entry namest="col5" nameend="col5" align="left">ABC</entry><entry namest="col6" nameend="col6" align="center">55</entry><entry namest="col7" nameend="col7" align="center">175</entry><entry namest="col8" nameend="col8" align="center">26</entry></row><row><entry namest="col1" nameend="col1" align="center">3</entry><entry namest="col2" nameend="col2" align="center">70:30</entry><entry namest="col3" nameend="col3" align="center">12</entry><entry namest="col4" nameend="col4" align="left">1,5/1,5</entry><entry namest="col5" nameend="col5" align="left">ABC</entry><entry namest="col6" nameend="col6" align="center">45</entry><entry namest="col7" nameend="col7" align="center">175</entry><entry namest="col8" nameend="col8" align="center">28</entry></row><row><entry namest="col1" nameend="col1" align="center">4</entry><entry namest="col2" nameend="col2" align="center">60:40</entry><entry namest="col3" nameend="col3" align="center">12</entry><entry namest="col4" nameend="col4" align="left">1,5/1,5</entry><entry namest="col5" nameend="col5" align="left">ABC</entry><entry namest="col6" nameend="col6" align="center">35</entry><entry namest="col7" nameend="col7" align="center">175</entry><entry namest="col8" nameend="col8" align="center">30</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="center">VB</entry><entry namest="col2" nameend="col2" align="center">70:30</entry><entry namest="col3" nameend="col3" align="center">12</entry><entry namest="col4" nameend="col4" /><entry namest="col5" nameend="col5" align="left">A</entry><entry namest="col6" nameend="col6" align="center">35</entry><entry namest="col7" nameend="col7" align="center">160</entry><entry namest="col8" nameend="col8" align="center">70</entry></row></tbody></tgroup></table></tables>