EP1296831A2

EP1296831A2 - White, sealable, thermodeformable, biaxially oriented and coextruded polyester film containing a cyclooelfin copolymer, method for producing the same and the use thereof

Info

Publication number: EP1296831A2
Application number: EP01964976A
Authority: EP
Inventors: Herbert Peiffer; Holger Kliesch; Gottfried Hilkert; Cynthia Bennett
Original assignee: Mitsubishi Polyester Film GmbH
Current assignee: Mitsubishi Polyester Film GmbH
Priority date: 2000-06-20
Filing date: 2001-06-13
Publication date: 2003-04-02
Also published as: US20030170479A1; WO2001098080A3; KR20030016296A; DE10030235A1; JP2003535732A; US20060127642A1; WO2001098080A2

Abstract

The invention relates to a white, sealable, thermodeformable, biaxially oriented and coextruded polyester film that comprises at least one base layer B and at least one sealable cover layer A, wherein at least the base layer B contains a polyester starting compound and a cycloolefin copolymer (COC). The polyester starting compound should contain an increased amount of diethylene glycol, polyethylene glycol or isophthtalic acid. The invention further relates to a method for producing the inventive polyester film and to the use thereof for thermoformed articles, especially on high-speed machines.

Description

White, sealable, thermoformable, biaxially oriented and coextruded polyester film with cycloolefin copolymer, process for its production and its use

The present invention relates to a white, sealable, thermoformable, biaxially oriented, coextruded polyester film which comprises at least one base layer B and at least one sealable cover layer, at least the base layer B containing a polyester raw material and a cycloolefin copolymer (COC). The invention further relates to a method for producing the polyester film and its use.

White, biaxially oriented polyester films are known in the prior art.

These films, which are known from the prior art, are distinguished either by good producibility or by good optics or by acceptable processing behavior.

DE-A 23 53 347 describes a process for producing a single-layer or multilayer, milky polyester film, which is characterized in that a mixture of particles of a linear polyester with 3 to 27% by weight of a homopolymer or copolymer of Ethylene or

Propylene is produced, the mixture is extruded as a film, the film is quenched and oriented biaxially by stretching in directions perpendicular to one another and the film is heat-set. A disadvantage of the process is that the regrind obtained in the production of the film (essentially a mixture of polyester raw material and ethylene or propylene copolymer) is no longer suitable for the

Production can be used, otherwise the film turns yellow. The process is therefore uneconomical and the yellowish film produced with regenerated material was not able to establish itself on the market. In addition, the film has significantly too high roughness and therefore has a very matt appearance (very low gloss), which is undesirable for many applications. EP-A-0300060 describes a single-layer polyester film which, in addition to polyethylene terephthalate, also contains 3 to 40% by weight of a crystalline propylene polymer and 0.001 to 3% by weight of a surface-active substance. The surface-active substance causes the number of vacuoles in the film to increase and, at the same time, their size to decrease to the desired extent. This results in a higher opacity and a lower density of the film. A further disadvantage of the film is that waste material (essentially a mixture of polyester raw material and propylene homopolymer) which is produced during the production of the film can no longer be used as regenerate, since otherwise the film turns yellow. The process is therefore uneconomical and the film with yellow tint produced with regenerated material was not able to establish itself on the market. In addition, the film has significantly too high roughness and therefore has a very matt appearance (very low gloss), which is undesirable for many applications.

EP-A-0 360201 describes an at least two-layer polyester film which contains a base layer with fine vacuoles, the density of which is between 0.4 and 1.3 kg / dm ³ and has at least one cover layer, the density of which is greater than 1. 3 kg / dm. The vacuoles are achieved by adding 4 to 30% by weight of a crystalline propylene polymer and then biaxially stretching the film. The additional cover layer improves the manufacturability of the film (no streaking on the surface of the film), the surface tension is increased and the roughness of the laminated surface can be reduced. However, it remains disadvantageous that the regrind obtained in the production of the film (essentially a mixture of polyester raw material and propylene homopolymer) can no longer be used for the production process, since otherwise the film turns yellow. The process is therefore uneconomical and the yellow-tinged film produced with regenerated material was not able to establish itself on the market. In addition, the films listed in the examples still have high roughness and thus have a matt appearance (low gloss), which is undesirable for many applications. EP-A-0 795 399 describes an at least two-layer polyester film which contains a base layer with fine vacuoles, the density of which is between 0.4 and 1.3 kg / dm ³ and has at least one cover layer, the density of which is greater than 1 , 3 kg / dm ³ . The vacuoles are achieved by adding 5 to 45% by weight of a thermoplastic polymer to the polyester raw material in the base and then biaxially stretching the film. Polypropylene, polyethylene, polymethylpentene, polystyrene or polycarbonate are mentioned as thermoplastic polymers, polypropylene being the preferred thermoplastic polymer. The additional cover layer improves the manufacturability of the film (no streaking on the surface of the film), increases the surface tension and the roughness of the laminated surface can be adapted to the respective requirements. A further modification of the film in the base layer and / or in the outer layers with white pigments (usually TiO ₂ ) and / or with optical brighteners enables the film properties to be adapted to the respective application requirements. The disadvantage, however, is that waste material produced in the production of the film (essentially a mixture of polyester raw material and the additive raw material) can no longer be used as regrind for the film production, since otherwise the color of the film produced with regrind is changed indefinitely, which is undesirable. The process is therefore uneconomical and the film with discolouration produced with regenerated material was not able to establish itself on the market. In addition, the films listed in the examples still have too high roughness and thus have a matt appearance (low gloss), which is undesirable for many applications.

DE-A 19540277 describes a single-layer or multilayer polyester film which contains a base layer with fine vacuoles, the density of which lies between 0.6 and 1.3 kg / dm ³ and has a birefringence in the plane which is from -0 , 02 is sufficient to 0.04. The vacuoles are achieved by adding 3 to 40% by weight of a thermoplastic resin to the polyester raw material in the base and then biaxially stretching the film. Thermoplastic resins include polypropylene, polyethylene, polymethyl-pentene, cyclic olefin polymers, Polyacrylic resins, polystyrene or polycarbonate called, with polypropylene and polystyrene are preferred raw materials. By adhering to the specified limits for the birefringence of the film, the claimed film is distinguished in particular by a superior tear strength and isotropic properties. The disadvantage, however, is that the regrind produced in the production of the film can no longer be used for film production, since otherwise the color of the film is changed indefinitely, which is undesirable.The process is therefore uneconomical and the discolored film produced with regrind could not prevail on the market. In addition, the films listed in the examples still have too high roughness and thus have a matt appearance (low gloss), which is undesirable for many applications.

Sealable, biaxially oriented polyester films are also known in the prior art. These films, which are known from the prior art, are distinguished either by good sealing behavior or by good optics or by acceptable processing behavior.

GB-A 1 465 973 describes a coextruded, two-layer polyester film, one layer of which consists of copolyesters containing isophthalic acid and terephthalic acid and the other layer of which consists of polyethylene terephthalate. There is no usable information in the script about the sealing behavior of the film. Due to the lack of pigmentation, the film cannot be produced reliably (film cannot be wound) and can only be further processed to a limited extent. In addition, white films are not mentioned in GB-A.

EP-A 0 035 835 describes a coextruded, sealable polyester film which, in order to improve the winding and processing behavior, contains particles in the sealing layer whose average particle size is greater than the layer thickness of the sealing layer. The particulate additives form surface protrusions that prevent unwanted blocking and sticking to rollers or guides. Over the other, not sealable Layer of the film, no further details are given on the incorporation of anti-blocking agents. However, the choice of particles with a larger diameter than the thickness of the sealing layer in the amounts given in the examples deteriorates the sealing behavior of the film. The document does not give any information on the sealing temperature range of the film. The seal seam strength is measured at 140 ° C and is in a range from 63 to 120 N / m (0.97 N / 15 mm to 1.8 N / 15 mm film width). White films are not described in EP-A.

EP-A-0 432 886 describes a coextruded, multilayer polyester film which has a first surface on which a sealable layer is arranged and a second surface on which there is an acrylate layer. The sealable cover layer can also consist of copolyesters containing isophthalic acid and terephthalic acid. The film on the back has improved processing properties. The script does not give any information about the sealing area of the film. The seal seam strength is measured at 140 ° C. A seal seam strength of 761.5 N / m (corresponding to 11.4 N / 15 mm) is specified for an 11 μm thick seal layer. A disadvantage of the acrylic coating on the back is that this side no longer seals against the sealable top layer. The film can therefore only be used to a very limited extent. White foils are not mentioned in the writing.

EP-A-0 515 096 describes a coextruded, multilayer, sealable polyester film which contains an additional additive on the sealable layer. The additive can contain, for example, inorganic particles and is preferably applied to the film in an aqueous layer during its manufacture. As a result, the film should maintain the good sealing properties and be easy to process. The back contains very few particles that get into this layer mainly through regranulate. No information is given in this document on the sealing temperature range of the film. The seal seam strength is measured at 140 ° C and is more than 200 N / m (corresponding to 3 N / 15 mm). For a 3 μm thick sealing layer, there is a sealing seam strength of 275 N / m (corresponding to 4.125 N / 15 mm). However, white foils are not mentioned in the writing.

The object of the present invention was to provide a white, sealable, thermoformable and biaxially oriented polyester film which has a very good sealability and which can be produced with great economy. In particular, it should be ensured that waste material inherent in the manufacturing process can be used as regrind in an amount in the range of 10 to 70% by weight, based on the total weight of the film, for film production without the physical Properties of the film produced with it are significantly negatively affected. In particular, no significant yellowing of the film should occur due to the addition of regenerate.

The object is achieved according to the invention by providing a white, sealable, biaxially oriented, coextruded polyester film with at least one base layer B and one sealable cover layer A, both made of thermoplastic polyester. The characteristic features of this film can be seen in the fact that at least the base layer B contains a cycloolefin copolymer (COC) in addition to polyester raw material in an amount in the range from 2 to 60% by weight, based on the weight of the base layer B, the glass transition temperature T _{g of} the cycloolefin copolymer (COC) is in the range from 70 to 270 ° C., and that the polyester raw material contains an increased amount of diethylene glycol and / or polyethylene glycol and / or isophthalic acid.

• Good stretchability means that the film can be oriented well both lengthways and crossways, and above all without tears. Good thermoformability means that the film can be thermoformed or thermoformed to complex and large-area molded parts on commercially available thermoforming machines without uneconomical pretreatment. To achieve good thermoformability, it is essential that the polyester raw material for the base layer B and for the cover layer A or also for further cover layers contains diethylene glycol (DEG) in an amount of> 0.5% by weight, preferably of> 1, 0% by weight, particularly preferably of> 1.2% by weight, and / or polyethylene glycol (PEG) in an amount of 0,5 0.5% by weight, preferably

> 1.0% by weight, in particular of ≥ 1.2% by weight, and / or isophthalic acid (IPA) in an amount in the range from 3 to 10% by weight.

A white, biaxially oriented polyester film in the sense of the present invention refers to a film which has a degree of whiteness of more than 70%, preferably more than 75% and particularly preferably more than 80%. Furthermore, the opacity of the film according to the invention is more than 55%, preferably more than 60% and particularly preferably more than 65%.

To achieve the desired degree of whiteness of the film according to the invention, the proportion of COC in the base layer B must be greater than 2% by weight, otherwise the degree of whiteness is less than 70%. On the other hand, if the COC content is greater than 60% by weight, the film can no longer be produced economically since it can no longer be stretched in a process-safe manner.

Furthermore, it is necessary that the glass transition temperature T _{g of} the COC used is greater than 70 ° C. Otherwise (at a glass transition temperature T _g of less than 70 ° C) the raw material mixture is difficult to process (difficult to extrude), the desired degree of whiteness is no longer achieved and the regrind used leads to a film which tends to increase its yellowing. On the other hand, if the glass transition temperature T _{g of} the selected COC is greater than 270 ° C, the raw material mixture may no longer be sufficiently homogeneously dispersed in the extruder. This would result in a film with inhomogeneous properties. In the preferred embodiment of the film according to the invention, the glass transition temperature T _{g of} the COCs used is in a range from 90 to 250 ° C. and in the very particularly preferred embodiment in a range from 110 to 220 ° C.

Surprisingly, it was found that a white, opaque film can be produced by adding a COC in the manner described above.

Depending on the amount and type of COC added, the degree of whiteness and also the opacity of the film can be set precisely and adapted to the respective requirements. This measure makes it possible to largely dispense with other common whitening and opaque additives. Completely surprising was the additional effect that the regenerate, like the polymeric additives according to the prior art, does not tend to turn yellow.

All of the benefits described were unpredictable. All the more so since COCs are apparently largely incompatible with polyethylene terephthalate, but are known to be oriented with similar stretching ratios and stretching temperatures as polyethylene terephthalate. Under these conditions, the person skilled in the art would have expected that no white, opaque film could be produced under these manufacturing conditions.

In the preferred and the particularly preferred embodiments, the film according to the invention is characterized by a high / or. through a particularly high degree of whiteness and a high / or. through a particularly high opacity, the color change of the film due to the addition of regenerated material remains extremely low and is therefore highly economical.

The film according to the invention is multilayered. Multi-layer embodiments are at least two-layer and always include the COC-containing base layer B and at least one sealable cover layer A. In a preferred embodiment, the COC-containing layer forms the base layer B of the film at least one sealable cover layer A, it being possible for one or both sides to have intermediate layers. In a further preferred embodiment, the COC-containing layer forms the base layer B of the film with at least one sealable cover layer A and preferably with a further cover layer C, it being possible for one or both sides to have an intermediate layer or layers. In a further possible embodiment, the COC-containing layer also forms an intermediate layer of the multilayer film. Further embodiments with COC-containing intermediate layers have a five-layer structure and, in addition to the COC-containing base layer B, have COC-containing intermediate layers on both sides. In a further embodiment, the COC-containing layer can form a cover layer on the base or intermediate layer in addition to the base layer B. For the purposes of the present invention, the base layer B is that layer whose thickness makes up more than 30 to 99.5%, preferably 60 to 95%, of the total film thickness. The cover layer (s) is / are the layer (s) that form the outer layer (s) of the film.

The optional additional cover layer C can be sealable, like the cover layer A, or it can also contain COC like the base layer B, but it can also contain other equipment features such as e.g. have a matt or particularly rough or particularly smooth surface. It can e.g. also be high gloss.

It has also been found that the film already has a particularly high gloss if the non-sealable cover layer C is constructed in exactly the same way as the base layer B or the base layer B simultaneously (in the case of a two-layer structure) is the non-sealable outer layer. The gloss of the film thus obtained is more than 50, preferably more than 70 and particularly preferably more than 90.

The COC-containing base layer B of the film according to the invention contains a polyester raw material, a COC and optionally further additives in effective amounts. Generally this layer contains at least 20% by weight, preferably 40 to 98% by weight, in particular 70 to 96% by weight, of polyester raw material, based on the weight of the layer.

Suitable thermoplastic polyester raw materials are polyesters from ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), from ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene-2,6-naphthalate, PEN), from 1,4-bis-hydroxymethyl-cyclohexane 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 80 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 the top layer A and / or the top layer C of the multilayer ABC film (B = base layer).

Suitable other aliphatic diols are, for example, diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO- (CH ₂ ) _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) may be mentioned. Suitable other aromatic diols correspond, for example, to the formula HO-C ₆ H ₄ -XC ₆ H ₄ -OH, where X is -CH ₂ -, -C (CH ₃ ) ₂ -, -C (CF ₃ ) -, -O- , -S- or -SO ₂ stands. In addition, bisphenols of the formula HO-C ₆ H -C ₆ H ₄ -OH are also very suitable.

Suitable other aromatic dicarboxylic acids are preferably benzenedicarboxylic acids, naphthalene dicarboxylic acids (for example naphthalene-1,4- or 1,6-dicarboxylic acid), biphenyl-x.x'-dicarboxylic acids (especially 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 (especially cyclohexane-1,4- dicarboxylic acid). Of the aliphatic dicarboxylic acids, the (C ₃ -C ₁₉ ) -alkanedioic acids are particularly suitable, the alkane fraction being straight-chain or branched.

The production of the polyesters can e.g. according to 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. Production can also be carried out using the direct esterification process in the presence of polycondensation catalysts. Here one starts directly from the dicarboxylic acids and the diols.

According to the invention, the COC-containing layer (s) contain a cycloolefin copolymer (COC) in an amount of at least 2.0% by weight, preferably 4 to 50% by weight and particularly preferably 6 to 40% by weight on the weight of the COC-containing layer. It is essential for the present invention that the COC is incompatible with the polyethylene terephthalate and does not form a homogeneous mixture with it.

Cycloolefin polymers are homopolymers or copolymers which contain polymerized cycloolefin units and optionally acyclic olefins as comonomers. Cycloolefin polymers which contain 0.1 to 100% by weight, preferably 10 to 99% by weight, particularly preferably 50 to 95% by weight, based in each case on the total mass of the cycloolefin polymer, of polymerized cycloolefin units are suitable for the present invention. Particularly preferred are polymers which are composed of the monomers of the cyclic olefins of the formulas I, II, III, IV, V or VI:

. C ₃₀ - In these formulas, R ^1, R ^2, R ^3, R ^4, R ^5, R ^6, R ⁷ and R ⁸ independently of one another identical or different and represent a hydrogen atom or a C, are - Hydrocarbon radical; or two or more of the radicals R ¹ to R ⁸ are cyclically linked, the same radicals in the different formulas having the same or different meaning. C ₁ -C ₃₀ -hydrocarbon radicals are preferably linear or branched C ₁ -C ₈ alkyl, ^'C ₆ -C ₁₈ aryl radicals, C ₇ -C ₂₀ -Alkylenarylreste or cyclic C ₃ -C ₂₀ alkyl or acyclic C ₂ - C ₂₀ alkenyl groups.

The cycloolefin polymers can optionally contain 0 to 45% by weight, based on the total mass of the cycloolefin polymer, of polymerized units of at least one monocyclic olefin of the formula VII:

Here n is a number from 2 to 10.

The cycloolefin polymers can optionally contain 0 to 99% by weight, based on the total mass of the cycloolefin polymer, of polymerized units of an acyclic olefin of the formula VIII:

Here R ⁹ , R ¹⁰ , R ¹¹ and R ^{12 are,} independently of one another, the same or different and denote a hydrogen atom or C 1 -C 4 -hydrocarbon radical, preferably a C ₁ -C 4 -alkyl radical or C ₆ -C ₁₄ -aryl radical.

Also suitable in principle are cycloolefin polymers which are obtained by ring-opening polymerization of at least one of the monomers of the formulas I to VI and subsequent hydrogenation. Cycloolefin homopolymers are composed of a monomer of the formulas I to VI. These cycloolefin polymers are less suitable for the purposes of the present invention. For the purposes of the present invention, such cycloolefin copolymers (COC) are suitable which contain at least one cycloolefin of the formulas I to VI and additionally acyclic olefins of the formula VIII as comonomer. Above and below, these cycloolefin copolymers which can be used according to the invention are called COC. Preferred acyclic olefins are those which have 2 to 20 carbon atoms, in particular unbranched acyclic olefins with 2 to 10 carbon atoms, such as, for example, ethylene, propylene and / or butylene. The proportion of polymerized units of acyclic olefins of the formula VIII is up to 99% by weight, preferably 5 to 80% by weight, particularly preferably 10 to 60% by weight, based on the total weight of the respective COC.

Among the COCs described above, those are particularly preferred which contain polymerized units of polycyclic olefins with a norbornene basic structure, particularly preferably norbornene or tetracyclododecene. COCs which contain polymerized units of acyclic olefins, in particular ethylene, are also particularly preferred. Again particularly preferred are norbornene / ethylene and tetracyclododecene / ethylene copolymers which contain 5 to 80% by weight, preferably 10 to 60% by weight (based on the weight of the copolymer).

The COCs generically described above generally have glass transition temperatures T _g between -20 ° C and 400 ° C. COCs can be used for the invention which have a glass transition temperature T _g of greater than 70 ° C., preferably greater than 90 ° C. and in particular greater than 110 ° C. The viscosity number (decalin, 135 ° C, DIN 53 728) is advantageously between 0.1 and 200 ml / g, preferably between 50 and 150 ml / g.

The COCs are produced by heterogeneous or homogeneous catalysis with organometallic compounds and can be found in numerous documents described. Suitable catalyst systems based on mixed catalysts made of titanium or zirconium or vanadium compounds in combination with aluminum organyls are described in DD 109 224, DD 237070 and EP-A-0 156464. EP-A-0 283 164, EP-A-0 407 870, EP-A-0 485 893 and EP-A-0 503 422 describe the preparation of cycloolefin copolymers (COC) with catalysts based on soluble metallocene complexes. Reference is hereby expressly made to the production processes for cycloolefin polymers described in the abovementioned documents.

The COCs are incorporated into the film either as pure granules or as granulated concentrates (masterbatch) by premixing the polyester granules or powder with the COC or the COC masterbatch and then feeding them to the extruder. The components are mixed further in the extruder and heated to processing temperature. It is expedient for the process according to the invention that the extrusion temperature is above the glass transition temperature T _{g of} the COC, generally at least 5 K, preferably 10 to 180 K, in particular 15 to 150 K, above the glass transition temperature T _{g of} the cycloolefin copolymer (COC).

In principle, the same polymers can be used for the intermediate layers and possibly the outer layer C as for the previously described base layer B. In addition, this outer layer C and possibly the intermediate layers can also contain other materials, in which case this outer layer C and possibly the intermediate layers preferably consist of a mixture of polymers, a copolymer or a homopolymer which contain ethylene-2,6-naphthalate units and ethylene terephthalate units.

The sealable outer layer A, which is applied to the base layer B by coextrusion, is based on polyester copolymers and consists essentially of copolyesters, which are predominantly composed of a mixture of isophthalic and terephthalic acid units and of ethylene glycol units. The remaining monomer units come from other aliphatic, cycloali- phatic or aromatic diols or dicarboxylic acids, as they can also occur in the base layer B. The preferred copolyesters which provide the desired sealing properties are those built up from ethylene terephthalate, from ethylene isophthalate units and from ethylene glycol units. The proportion of ethylene terephthalate is 40 to 95 mol% and the corresponding proportion of ethylene isophthalate is 60 to 5 mol%. Preferred are copolyesters in which the proportion of ethylene terephthalate is 50 to 90 mol% and the corresponding proportion of ethylene isophthalate is 50 to 10 mol% and very preferred are copolyesters in which the proportion of ethylene terephthalate is 60 to 85 mol% and the corresponding The proportion of ethylene isophthalate is 40 to 15 mol%.

The total thickness of the film can vary within wide limits and depends on the intended use. The preferred embodiments of the film according to the invention have total thicknesses of 4 to 500 μm, 8 to 300 μm, in particular 10 to 300 μm, being preferred. The thickness of the intermediate layer (s) which may be present is generally in each case 0.5 to 15 μm, independently of one another, with intermediate layer thicknesses of 1 to 10 μm, in particular 1 to 8 μm, being preferred. The values given relate to an intermediate layer. The thickness of the cover layer (s) is selected independently of the other layers and is preferably in the range from 0.1 to 10 μm, in particular 0.2 to 5 μm, preferably 0.3 to 2 μm, with cover layers applied on both sides with regard to thickness and composition can be the same or different. The thickness of the base layer B results accordingly from the difference between the total thickness of the film and the thickness of the applied top and intermediate layer (s) and can therefore vary within wide limits analogously to the total thickness.

It was surprising for the experts that the white, sealable polyester film according to the invention can be produced economically from a polyester raw material with a comparatively enriched amount of DEG and / or PEG and / or IPA as stated above and can then also be produced at conventional low temperatures. drawing systems can be thermoformed without any problems and delivers a surprisingly high level of detail.

The base layer B and the other layers can additionally contain conventional additives, such as stabilizers, antiblocking agents and other fillers. 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, SiO ₂ in colloidal and in chain-like form, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, Aluminum oxide, lithium fluoride, calcium, barium, zinc or manganese salts of the dicarboxylic acids used, carbon black, titanium dioxide, kaolin or crosslinked polymer particles, for example 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 polymers of the individual layers of the film in the respective advantageous amounts, e.g. as a glycolic dispersion during polycondensation or via masterbatches during extrusion. Pigment concentrations of 0 to 25% by weight have proven to be particularly suitable (based on the weight of the respective layer). A detailed description of the antiblocking agents can be found, for example, in EP-A-0 602 964.

To improve the degree of whiteness of the film, the base layer B or the other additional layers can contain further pigmentation. It has proven to be particularly favorable here as additional additives barium sulfate in a grain size in the range from 0.3 to 0.8 μm, preferably from 0.4 to 0.7 μm or titanium dioxide with a grain size of 0.05 to 0.3 μm, measured according to the Sedigraph method. This gives the film a brilliant, white appearance. The amount of barium sulfate is in the range from 1 to 25% by weight, preferably from 1 to 20% by weight, very preferably from 1 to 15% by weight.

The cover layers can in principle contain the above-mentioned additive concentrations according to the invention. However, the following embodiments have proven to be particularly favorable:

The lowest sealing starting temperature and the highest sealing seam strength are achieved if the copolymers described in more detail above are used for the sealable cover layer A. The best sealing properties of the film are obtained if no further additives, in particular no inorganic or organic particles, are added to the copolymer. In this case, the lowest seal starting temperature and the highest seal seam strengths are obtained for a given copolyester. However, the handling of the film is not optimal in this case, since the surface of the sealable cover layer A tends to block.

It has therefore proven to be particularly favorable if the sealable cover layer A is modified in order to improve the handling of the film and the processability. This is preferably done with the aid of suitable antiblocking agents of a selected size, which are added to the sealing layer in a certain amount, in such a way that on the one hand the blocking is minimized and on the other hand the sealing properties are only slightly deteriorated. This desired combination of properties can be achieved if the topography of the sealable cover layer A is preferably characterized by the following set of parameters:

- The roughness of the sealable outer layer, expressed by the R _a -

Value, should be less than 100 nm and preferably <80 nm. Otherwise the sealing properties are negatively influenced in the sense of the present invention.

The measured value of the surface gas flow time should preferably be in the range from 50 to 4000 s. At values below 50 s, the sealing properties are negatively influenced in the sense of the present invention, and at values above 4000 s, the handling of the film becomes poor.

It has proven particularly favorable for the processing behavior if the film additionally has a cover layer C, the topography of which should preferably be characterized by the following set of parameters:

The coefficient of friction (COF) of this side against itself should preferably be less than 0.7 and particularly preferably <0.6. Otherwise the winding behavior and the further processing of the film are less good. - The roughness of the non-sealable top layer, expressed by the

R _a value, should be> 30 nm. Values smaller than 30 nm have negative effects on the winding and processing behavior of the film. The measured value of the surface gas flow time should advantageously be in the range below 500 s. At values of 500 s or more, the winding and processing behavior of the film is adversely affected.

In order to achieve this particularly favorable property profile of the film, the film has a cover layer C which contains a larger amount of pigments (ie higher pigment concentration) than the cover layer A. The pigment concentration in this second top layer C is between 0.1 and 10% by weight, advantageously between 0.12 and 8% by weight and in particular between 0.15 and 6% by weight, based on the weight of this layer. The other sealable cover layer A, opposite the cover layer C, is filled with a smaller amount of inert pigments. The concentration of the inert particles within layer A is advantageously between 0.01 and 0.3% by weight, preferably between 0.015 and 0.2% by weight and in particular between 0.02 and 0.1% by weight, based on the weight of this layer. The invention further relates to a method for producing the white, sealable polyester film according to the invention by the extrusion or coextrusion method known per se.

In this process, the procedure is such that the melts corresponding to the individual layers of the film are co-extruded through a flat die, the film thus obtained is drawn off on one or more rollers for consolidation, the film is then biaxially stretched (oriented), the biaxial stretched film is heat-set and optionally corona or flame treated on a surface layer intended for treatment and then wound up.

Biaxial stretching is generally carried out sequentially. It is preferably stretched first in the longitudinal direction (i.e. in the machine direction, = MD direction) and then in the transverse direction (i.e. perpendicular to the machine direction, = TD direction). If necessary, a further longitudinal stretching can take place after the transverse stretching. The stretching leads to a spatial orientation of the molecular chains of the polyester. The stretching in the longitudinal direction is preferably carried out with the aid of a plurality of rollers rotating at different angular speeds in accordance with the desired stretching ratio. A corresponding tenter frame is generally used for transverse stretching.

The temperature at which the stretching is carried out can vary in a relatively large window 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.

The stretching can also take place in a simultaneous stretching frame (simultaneous stretching), the number of stretching steps and the sequence (longitudinal / transverse) not of is of crucial importance for the property profile of the film. However, stretching temperatures <125 ° C and particularly favorable <115 ° C are favorable here. The stretching ratios correspond to those in the conventional sequential process.

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

To set further desired properties, the film can be chemically treated or also corona or flame treated. The treatment intensity should be set so that the surface tension of the film is generally over 45 mN / m.

The film can also be coated to set further properties. Typical coatings are adhesion-promoting, antistatic, slip-improving or adhesive layers. It is advisable to apply these additional layers to the film using the technique of “in-line coating” by means of aqueous dispersions after the longitudinal stretching and before the transverse stretching.

It was surprising that the film according to the invention can be thermoformed without further pretreatment, in particular without an upstream drying step, so that complex molded parts can be produced therefrom.

Thermoforming generally includes the steps of pre-drying, heating, molding, cooling, demolding, tempering and cooling. During the thermoforming process, it was found that the films according to the invention can be shaped surprisingly well without the pre-drying step. This advantage compared to other thermoformable films made of polycarbonate or polymethyl methacrylate, which, depending on the thickness of the film, require pretreatments at temperatures of 100 to 120 ° C for times in the range of 10 to 15 hours, reduces the costs for thermoforming when using the film according to the invention and for this reason makes the thermoformable film according to the invention particularly economically attractive.

The following particularly suitable process parameters were found in particular for thermoforming the white, sealable polyester film according to the invention:

Process step film according to the invention

Predrying Not necessary

Mold temperature [° C] 100 to 160

Heating time <5 seconds per 10 μm film thickness

Film temperature during forming [° C] 160 to 200 possible deformation factor 1, 5 to 2.0

Good detail reproduction

Shrinkage (shrinkage) <1.5%

The particular advantage of the film according to the invention is expressed by a high degree of whiteness combined with excellent sealability. The degree of whiteness of the film is more than 70%, preferably more than 75% and particularly preferably more than 80%. The opacity of the film according to the invention is more than 55%, preferably more than 60% and particularly preferably more than 65%.

Of particular note, however, is the economically important and particularly surprising advantage, namely that waste material inherent in the production of the film is used again as regrind in an amount in the range from 10 to 70% by weight, based on the total weight of the film, for film production can be made without significantly affecting the physical properties of the film produced in this way. In particular, the regrind (essentially made of polyester raw material and COC) the film does not change its color undefined, which is always the case with the films according to the prior art.

Due to its very good handling and its very good processing properties, the film is particularly suitable for processing on high-speed machines.

The film according to the invention is excellently suitable for the production of thermoformed packaging for light and / or air sensitive food and beverages. In addition, it is also excellent for use in industrial areas, e.g. suitable for the production of stamping foils or as label foils. In addition, the film is of course particularly suitable for the production of thermoformed molded parts of all kinds or for image recording papers, printing sheets, magnetic recording cards, to name just a few possible applications.

In addition, due to its excellent combination of properties, the film is suitable for a variety of different applications, e.g. for interior cladding, for trade fair construction and trade fair items, as displays, for signs, for protective glazing of machines and vehicles, in the lighting sector, in shop and shelf construction, as Promotional item and as a lamination medium.

The table below (Table 1) summarizes the most important film properties according to the invention at a glance.

Table 1: Properties; area according to the invention

The following measurement methods were used to characterize the raw materials and the foils in the context of the present invention:

DEG / PEG / IPA content The amount of DEG, PEG and / or IPA in the polyester is determined by gas chromatography after saponification in methanolic KOH and subsequent neutralization with aqueous hydrochloric acid.

SV value (standard viscosity) The standard viscosity SV (DCE), based on DIN 53726, is measured in dichloroacetic acid.

The intrinsic viscosity (IV) is calculated as follows from the standard viscosity IV (DCE) = 6.67 ^• 10 ^"4 SV (DCE) + 0.118

Friction (COF)

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

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

roughness

The roughness R _{a of} the film was determined according to DIN 4768 with a cut-off of 0.25 mm.

Whiteness and opacity

The degree of whiteness and the opacity are determined with the aid of the electrical reflectance photometer "ELREPHO" from Zeiss, Oberkochem (DE), standard illuminant C, 2 ° normal observer. The opacity is determined in accordance with DIN 53 146. The whiteness is defined as WG = RY + 3RZ - 3RX. WG = whiteness, RY, RZ, RX = corresponding reflection factors when using the Y, Z and X color measurement filter. A barium sulfate pressing (DIN 5033, part 9) is used as the white standard. A detailed description is described, for example, in Hansl Loo's "Color Measurement", Verlag Beruf und Schule, Itzehoe (1989).

Light transmission

The light transmittance is measured based on ASTM-D 1033-77.

Gloss The gloss was determined according to DIN 67 530 at a measuring angle of 60 °. The reflector value was measured as an optical parameter for the surface of a film. 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.

Glass transition temperature T _g

The glass transition temperature T _g was determined on the basis of film samples with the aid of DSC (Differential Scanning Calorimetry) (DIN 73 765). A DSC 1090 from DuPönt was used. The heating rate was 20 K / min and the initial weight was about 12 mg. The glass transition was determined in the first heating process. The samples often showed enthalpy relaxation (a peak) at the beginning of the step-shaped glass transition. The T _g was the temperature at which the step-like change in heat capacity - regardless of the peak-shaped enthalpy relaxation - reached half its height in the first heating process. In all cases, only a single glass transition stage was observed in the thermogram when it was first heated up.

Seal start temperature (minimum seal temperature)

With the sealing device HSG / ET from Brugger, heat-sealed samples (sealing seam 20 mm x 100 mm) are produced, whereby the film with different Temperatures are sealed with the help of two heated sealing jaws at a sealing pressure of 2 bar and a sealing time of 0.5 s. Test strips 15 mm wide were cut from the sealed samples. The T-seal strength was measured as in the determination of the seal strength. The seal start temperature is the temperature at which a seal seam strength of at least 0.5 N / 15 mm is achieved.

Seal strength

To determine the seal seam strength, two 15 mm wide film strips were placed on top of each other and sealed at 130 ° C, a sealing time of 0.5 s and a sealing pressure of 2 bar (device: Brugger type NDS, one-sided heated sealing jaw). The seal seam strength was determined by the T-Peel method.

Surface gas flow time The principle of the measuring method is based on the air flow between a film side and a smooth silicon wafer plate. The air flows from the environment into an evacuated room, the interface between the film and the silicon wafer plate serving as flow resistance.

A round film sample is placed on a silicon wafer plate, in the middle of which a hole ensures the connection to the recipient. The recipient is evacuated to a pressure of less than 0.1 mbar. The time in seconds that the air needs to cause a pressure increase of 56 mbar in the recipient is determined.

Measurement conditions:

Measuring area 45.1 cm ²

Contact weight 1276 g

Air temperature 23 ° C Air humidity 50% relative humidity

Gas collection volume 1, 2 cm ³

Pressure interval 56 mbar example 1

According to the co-extrusion technology, a 23 μm thick multilayer film with the layer sequence AB was produced, where B was the base layer and A was the cover layer. The base layer ^' B was 21.5 μm thick and the top layer A 1.5 μm.

Polyethylene terephthalate chips, which contained an amount of 1.25% by weight of DEG (produced by the transesterification process with Mn as transesterification catalyst, Mn concentration: 100 ppm), were dried at 150 ° C. to a residual moisture content of below 100 ppm and fed to the extruder for the base layer B. In addition, chips made of cycloolefin copolymers (COC) from Ticona: ^® Topas 6015 (COC consisting of 2-norbornene and ethylene, see also W. Hatke: Films made of COC, Kunststoffe 87 (1997) 1, pp. 58-62) a glass transition temperature T _g of 160 ° C also fed to the extruder for the base layer B. The quantitative proportion of COC in the base layer B was 10% by weight.

97% by weight of chips of a linear polyester which consisted of an amorphous copolyester with 78 mol% of ethylene terephthalate and 22 mol% of ethylene isophthalate (produced via the transesterification process with Mn as transesterification catalyst, Mn concentration: 100 ppm) were fed to top layer A , The copolyester was dried at a temperature of 100 ° C. to a residual moisture content of below 200 ppm and fed to the extruder for the sealable outer layer A. In addition, 3% by weight of chips from a masterbatch were fed to the extruder, which in addition to the polyester with a proportion of 1.25% by weight of DEG additionally 10,000 ppm of silicon dioxide ( ^® Sylobloc, Grace, Germany) and 12500 ppm of silicon dioxide ( ^® Aerosil , pyrogenic SiO ₂ from Degussa). These chips were also dried at 100 ° C. to a residual moisture of below 200 ppm.

A white, opaque two-layer film with a total thickness of 23 μm was produced by coextrusion and subsequent stepwise orientation in the longitudinal and transverse directions. Base layer B, mixture of:

90.0% by weight of polyethylene terephthalate homopolymer with 1.25% by weight of DEG

(RT49, Kosa, Germany) 10.0% by weight of cycloolefin polyryrenes (COC) from Ticona, ^® Topas 6015

The manufacturing conditions in the individual process steps were:

Extrusion: Base and top layer temperatures: 280 ° C

! Take-off roller temperature: 30 ° C

Longitudinal stretch: temperature: 80 - 125 ° C

Longitudinal stretch ratio: 4.2

Lateral stretching: temperature: 80 - 135 ° C

Lateral stretch ratio: 4.0

Fixation: temperature: 230 ° C

Duration: 3 s

These process parameters apply to all examples (without comparative examples).

The film had the required good properties and showed the desired handling and processing behavior. The properties achieved in films produced in this way are shown in Tables 2 and 3.

Example 2

In comparison to Example 1, 50% by weight of regenerate was now added to the base layer B. The amount of COC in the base layer B thus produced was again 10% by weight. The process parameters were not changed compared to Example 1. The top layer A remained unchanged. The yellowing of the film was observed visually. Tables 2 and 3 show that hardly any yellow discoloration of the film has become visible. Base layer B, mixture of:

44.7% by weight of polyethylene terephthalate homopolymer with 1.25% by weight of DEG and with an SV value of 800 50.0% by weight of regenerate (polymer content: 90.7% by weight of polyester including isophthalate + 9 , 3% by weight of Topas 6015)

5.3% by weight of cycloolefin copolymers (COC) from Ticona, ^® Topas 6015

Example 3

The base layer B was built up as in Example 1, but was only 40.5 μm thick. The sealable cover layer A had a thickness of 2.5 μm. In addition, a third 2.0 μm thick pigmented top layer C was coextruded (drying like top layer A).

This cover layer C contained: 88% by weight of polyethylene terephthalate homopolymer with 1.25% by weight of DEG and with an SV value of 800 12% by weight of masterbatch made of polyester with 1.25% by weight of DEG and with 10,000 ppm silicon dioxide ( ^® Sylobloc, Grace, Germany) and 12500 ppm silicon dioxide ( ^® Aerosil, pyrogenic SiO ₂ from Degussa)

The other process conditions corresponded to example 1.

The film had the same good properties in terms of whiteness and sealability as the film from Examples 1 and 2, but showed an even better processing behavior. The properties achieved in films produced in this way are shown in Tables 2 and 3.

Example 4

The procedure was as in Example 3, but 50% by weight of own regrind was added to the base layer B. The amount of COC in the base layer B was again 10% by weight. The process parameters were compared to the example

1 not changed. The yellowing of the film was observed visually. The Tables 2 and 3 show that hardly any yellowing of the film has become visible.

Comparative Example 1

A film with a structure as described in Example 3 was produced. The polyester raw material used for all layers A, B and C, however, only had an amount of 0.45% by weight of DEG. The properties of the film are described in Tables 2 and 3. The thermoformability of this film was no longer sufficient.

Comparative Example 2

Example 1 from EP-A-0 300 060 was reworked. In a modification of the example, the film was equipped with a sealable outer layer A, which had a thickness of 2.0 μm, and an additional 50% by weight of regrind was processed for the base layer. Table 2 shows that a clear yellowing of the film has become visible.

Base layer B, mixture of:

45.0% by weight of polyethylene terephthalate homopolymer with 0.6% by weight and with an SV value of 800

50.0% by weight of self-regenerated material (95% by weight of polyester + 5% by weight of polypropylene) 5.0% by weight of polypropylene.

Table 2

Table 3

Explanation of symbols for the yellowness of the films produced:

++ no yellowing can be seen + slight yellowing can be seen clear yellowing can be seen

Claims

claims

1. White, sealable, biaxially oriented, thermoformable and coextruded polyester film comprising at least one base layer B and at least one sealable cover layer A, both made of thermoplastic polyester, characterized in that at least the base layer B in addition to a polyester raw material also contains a cycloolefin copolymer (COC) in an amount Contains range of 2 to 60 wt .-%, based on the weight of the base layer B, wherein the glass transition temperature T _{g of} the cycloolefin copolymer (COC) is in the range of 70 to 270 ° C, and that the polyester raw material an increased amount of diethylene glycol and / or contains polyethylene glycol and / or isophthalic acid.

2. White, sealable polyester film according to claim 1, characterized in that the cycloolefin copolymer (COC) contains polynorbornene, poly-dimethyloctahydronaphthalene, polycyclopentene or poly (5-methyl) norbornene and a glass transition temperature T _g in the range from 90 to 250 ° C. has.

3. White, sealable polyester film according to claim 1 or 2, characterized in that the COC has a glass transition temperature T _g in the range from 110 to 220 ° C and that the polyester raw material for the base layer B and for the outer layer A or for further outer layers of diethylene glycol contains an amount of> 0.5% by weight, preferably of> 1.0% by weight, particularly preferably of> 1.2% by weight, and / or polyethylene glycol in an amount of> 0.5% by weight. %, preferably> 1.0% by weight, in particular of> 1.2% by weight, and / or isophthalic acid in an amount in the range from 3 to 10% by weight.

4. White, sealable polyester film according to one or more of claims 1 to 3, characterized in that the film has a degree of whiteness of more than 70% and an opacity of more than 55%.

5. White, sealable polyester film according to one or more of claims 1 to 4, characterized in that the sealable cover layer A contains a polyester copolymer which contains ethylene terephthalate units in an amount in the range from 40 to 95 mol% and ethylene isophthalate units in one Contains amount of 60 to 5 mol%, based on the total amount of carboxylic acid units, and that the other monomer units come from aliphatic, cycloaliphatic or aromatic diols.

6. White, sealable polyester film according to one or more of claims 1 to 5, characterized in that the sealable cover layer A has a thickness in the range from 0.2 to 5.0 microns and has a seal starting temperature of <200 ° C.

7. White, sealable polyester film according to one or more of claims 1 to 6, characterized in that the film has a total thickness in the range from 4 to 500 μm, preferably from 8 to 300 μm, in particular from 10 to 300 μm.

8. White, sealable polyester film according to one or more of claims 1 to 7, characterized in that the roughness of the sealable cover layer A, expressed by its R _a value, is less than or equal to 100 nm, preferably ≤ 80 nm, and that it Measurement of the surface gas flow time is in the range of 50 to 4000 s.

9. White, sealable polyester film according to one or more of claims 1 to 8, characterized in that an intermediate layer is arranged between the COC-containing base layer B and the sealable cover layer A.

10. White, sealable polyester film according to one or more of claims 1 to 9, characterized in that it contains a further cover layer C, the coefficient of friction (COF) of which is less than 0.7, preferably less than itself

≤ 0.6, whose roughness, expressed by its R _a value, is ≥ 30 nm and whose measured value of the surface gas flow time is in the range below 500 s.

11. White, sealable polyester film according to claim 10, characterized in that the cover layer C contains an amount of pigments in the range between 0.1 and 10% by weight, preferably between 0.12 and 8% by weight, in particular between 0, 15 and 6 wt .-% contains.

12. The method for producing a polyester film according to claim 1, characterized in that the polymer or the polymer mixture of the individual layers are compressed and liquefied in separate extruders, the melts are then pressed simultaneously through a flat die (slot die), the pressed multilayer film is pulled off one or more take-off rolls, the pre-film thus obtained is then biaxially stretched and heat-set and, if appropriate, is corona or flame treated on a surface view provided for the treatment.

13. The method according to claim 13, characterized in that in the production of the film inherent waste material as regrind in an amount in the range of 10 to 70 wt .-%, based on the total weight of the film, is used again for the film production.

14. Use of a white, sealable film according to one or more of claims 1 to 11 for the production of thermoformed packaging for light and / or air-sensitive food and beverages or for the Use in the industrial sector in the manufacture of embossing foils or as a label foil or for the production of thermoformed molded parts of all kinds or for image recording papers, printing sheets or magnetic recording cards.

15. Use of a white, sealable polyester film according to one or more of claims 1 to 11 as interior cladding, for trade fair construction and trade fair items, as a display, for signs, in the lighting sector, in shop and shelf construction, as a promotional item, as a laminating medium, for covers Materials, or in electrical applications, especially on high-speed machines.