DE10030243A1 - White pigmented sealable biaxially oriented coextruded polyester film containing cycloolefin polymer useful for displays, protective glazing of machines and automobiles - Google Patents

Abstract

On addition of a cyclolefin polymer (COC) to a white, sealable biaxially oriented UV stabilized and coextruded polyester film containing at least one thermoplastic base layer B and a sealabled thermoplastic top layer A, in amount 2-60 wt.% relative to the weight of basic layer B, where layer B contains at least one white pigment, a white opaque film can be obtained An Independent claim is included for preparation of the film by coextrusion and liquefying of individual layers of the polymer or polymer mixture, pressing of the melts simultaneously through a flat nozzle (wide slit nozzle), feeding of the pressed multi-layer film to one or more rollers, and biaxial stretching and thermal fixing of the pre-film obtained, which is then subjected optionally to corona or flame treatment. The film is stretched longitudinally at 80-130 deg C and transversely at 90-150 deg C, and the longitudinal stretch ratio is within 2.5:1 to 6:1, preferably 3:1 to 5:1, while the transverse stretch ratio is 3.0:1 to 5.0:1, preferably 3.5:1 to 4.5:1.

Description

The present invention relates to a white, sealable, biaxially oriented, coextruded polyester film, the at least one base layer B and at least one sealable cover layer A, both made of thermoplastic polyester, wherein at least the base layer B is a polyester raw material and a cycloolefin copolymer (COC) and at least one white pigment and optionally an optical brightener. 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 known from the prior art are either characterized by good manufacturability or good optics or acceptable Processing behavior.

DE-A 23 53 347 describes a process for producing one or more layered, milky polyester film described, which is characterized in that a mixture of particles of a linear polyester with 3 to 27 wt .-% of a Homopolymers or copolymers of ethylene or propylene that Extruded mixture as a film, quenching the film and stretching it vertically mutually biaxially oriented directions and heat-set the film. A disadvantage of the method is that it is incurred during the production of the film Regenerate (essentially a mixture of polyester raw material and ethylene or Propylene copolymer) can no longer be used for production because otherwise the film turns yellow. The process is therefore uneconomical and the with Regenerated, yellowish film could not prevail on the market. In addition, the film has significantly too high roughness and therefore has a very high matt appearance (very low gloss), which is undesirable for many applications is.  

EP-A-0 300 060 describes a single-layer polyester film which, apart from Polyethylene terephthalate 3 to 40 wt .-% of a crystalline propylene polymer and Contains 0.001 to 3 wt .-% 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 decreases as desired. This will result in a higher opacity and achieved a lower density of the film. A disadvantage of the film remains that waste material (essentially a mixture made of polyester raw material and propylene homopolymer) no longer used as regrind can become otherwise the film turns yellow. The procedure is however uneconomical and the film produced with regenerated material with a yellow tinge could Don't prevail in the market. In addition, the film has significantly too high roughness and has a very matte appearance (very low gloss), which for many Applications is undesirable.

EP-A-0 360 201 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 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 too 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 film produced with regrind is changed in an undefined way, what is not desired. 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 195 40 277 describes a single-layer or multilayer polyester film which contains a base layer with fine vacuoles, the density of which is between 0.6 and 1.3 kg / dm ³ and has a birefringence in the plane of -0.02 to 0.04 is sufficient. 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, polypropylene and polystyrene being 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. However, it remains disadvantageous 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 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.

Sealable, biaxially oriented polyester films are state of the art also known. These films known from the prior art stand out either by good sealing behavior or by good optics or by a acceptable processing behavior.

GB-A 1 465 973 describes a co-extruded, two-layer polyester film wrote a layer of isophthalic and terephthalic Copolyesters and their other layer consists of polyethylene terephthalate. About the There is no usable information in the script for the sealing behavior of the film. Because of If there is no pigmentation, the film cannot be produced reliably (film is not can be wound) and can only be further processed with restrictions.

EP-A 0 035 835 describes a coextruded, sealable polyester film, to improve the winding and processing behavior in the sealing layer Particles are buried whose average particle size is larger than the layer thickness of the sealing layer. The particulate additives make surfaces projections formed, the unwanted blocking and sticking to rollers or  Prevent guided tours. over the other, non-sealable layer of the film no further details on the incorporation of antiblocking agents made. It remains open whether this layer contains antiblocking agents. By choosing particles with larger Diameter as the sealing layer in the amounts specified in the examples however, the sealing behavior of the film deteriorates. Information about the sealing temperature areas of the film are not made in the script. The seal seam strength is at 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).

EP-A-0 432 886 describes a coextruded, multilayer polyester film described, 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 top layer can also be made of isophthalic acid and copolyesters containing terephthalic acid. Thanks to the coating on the back the film gets an improved processing behavior. Sealing area information the film is not made in the script. The seal seam strength is at 140 ° C measured. For an 11 µm thick sealing layer, a sealing seam strength of 761.5 N / m (corresponding to 11.4 N / 15 mm). A disadvantage of the back Acrylic coating is that this side against the sealable top layer no longer seals. The film can therefore only be used to a very limited extent.

EP-A-0 515 096 describes a coextruded, multilayer, sealable polyester described that contains an additional additive on the sealable layer. The additive can e.g. B. contain inorganic particles and is preferably in one aqueous layer brought to the film during its manufacture. This is supposed to Foil maintain the good sealing properties and be easy to process. The Reverse contains very few particles, mainly via regranulate in this Layer. Information on the sealing temperature range of the film is in this Scripture not made. 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 a seal seam strength of 275 N / m (corresponding to 4.125 N / 15 mm).

The object of the present invention was a white, sealable, and biaxial to provide oriented polyester film which has a very good sealability and which can be manufactured with great economy. In particular, it should be ensured that waste material inherent in the manufacturing process as regrind in an amount in the range of 10 to 70 wt .-%, based on the total weight of the Foil, can be used again for foil production without the physical properties of the film produced with it appreciably negative to be influenced. In particular, the addition of regenerate should not result in any noteworthy The film turns yellow.

The task is solved by a white, pigmented, biaxially oriented, coextruded Polyester film with at least one base layer B and at least one sealable Cover layer A, both made of thermoplastic polyester, the distinctive Features consist in that at least the base layer B additionally has a white pigment ment in an amount of 0.1 to 25 wt .-%, an optical brightener in an amount from 0 to 50,000 ppm and a cycloolefin copolymer (COC) in an amount of 2 to 60% by weight, based on the weight of the base layer B.

Under a white polyester film in the sense of the present invention, such a Understood film that has a whiteness of more than 80%, preferably of more than 85% and particularly preferably of more than 90%. Furthermore, the opacity is inventive film more than 55%, preferably more than 60% and particularly preferably more than 65%.

To achieve the desired opacity of the film according to the invention, the proportion of the cycloolefin copolymer (COC) in the base layer be greater than 2%, otherwise the opacity is less than 65%. Is the cycloolefin copolymer (COC) content  on the other hand, greater than 60%, the film can no longer be produced economically, because 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 yellow more. On the other hand, if the glass transition temperature T _{g of} the selected COC is greater than 270 ° C, the raw material mixture in the extruder will no longer be able to be dispersed sufficiently homogeneously. This then results 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 particularly preferred embodiment in a range from 110 to 220 ° C.

Surprisingly, it was found that the addition of a COC in the above described a white, opaque film can be produced.

According to the amount and type of cycloolefin copolymer (COC) added the degree of whiteness and the opacity of the film can be set precisely and the respective Requirements are adjusted. The additional one was completely surprising Effect that the regenerate does not tend to yellow, like the polymeric additives According to the state of the art.

All of the features described were unpredictable. All the more because While COCs are apparently largely incompatible with polyethylene terephthalate, as is known, but oriented with similar stretching ratios and stretching temperatures like polyethylene terephthalate. Under these conditions, the subject would have  It is expected that under these manufacturing conditions no white, opaque film can be produced.

In the preferred and the particularly preferred embodiments stands out the film of the invention by a particularly high degree of whiteness and particularly high opacity in combination with a good sealability, the Color change of the film due to the addition of regeneration remains extremely small and therefore in is highly economical.

The film according to the invention is multi-layered. Are multi-layer embodiments at least two layers 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 with at least one sealable cover layer A, optionally one-sided or two-sided Intermediate layer (s) may be present. In another preferred In one embodiment, the COC-containing layer also forms the base layer B of the film at least one sealable cover layer A and preferably with another Covering layer C, with one or both sides of an intermediate layer, if necessary can be present. In a further possible embodiment, the COC-containing layer also 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 intermediates on both sides layers. In a further embodiment, the COC-containing layer can additionally to the base layer B, a cover layer on one side on the base or intermediate layer form. For the purposes of the present invention, the base layer B is the layer whose thickness is more than 30 to 99.5%, preferably 60 to 95%, of the total film thickness accounts. The top layer (s) is / are the layers that make up the outer layer (s) the film forms / n.  

The optional additional cover layer C, like the cover layer A, can be sealable or like the base layer B contain COC, but it can also be further equipment features such as B. a matt or particularly rough or particularly smooth surface exhibit. But you can z. B. also be high-gloss.

It has also been found that the film is already a special one has a high gloss if the non-sealable cover layer C is constructed in the same way is like the base layer B or the base layer B at the same time (with a two-layer structure) represents the non-sealable outer layer. The sheen of the so obtained Film 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, preferably a polyester homopolymer, a COC and optionally additional additives in effective amounts. Generally this contains Layer at least 20 wt .-%, preferably 40 to 98 wt .-%, in particular 70 to 96% by weight, polyester raw material, based on the weight of the layer.

The base layer B of the film contains a thermoplastic polyester. Suitable for that are polyesters of 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-hydroximethyl-cyclohexane and terephthalic acid (= poly-1,4-cyclo hexanedimethylene terephthalate, PCDT) and from ethylene glycol, naphthalene-2,6- dicarboxylic acid and biphenyl-4,4'-dicarboxylic acid (= polyethylene-2,6-naphthalate bibenzoate, PENBB). Polyesters which are at least 90 mol% preferred at least 95 mol%, from ethylene glycol and terephthalic acid units or from Ethylene glycol and naphthalene-2,6-dicarboxylic acid units exist. The remaining Monomer units come from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids, as also in the top layer A and / or the top layer C of the multilayer ABC film (B = base layer) can.  

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 ₄ -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), diphenyl acetylene-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 (C ₃ -C ₁₉ ) alkanedioic acids are particularly suitable, it being possible for the alkane portion to be straight-chain or branched.

The production of the polyester can e.g. B. after the transesterification process. It is based on dicarboxylic acid esters and diols, which with the usual Transesterification catalysts such as zinc, calcium, lithium, magnesium and manganese Salt, are implemented. The intermediates then become general in the presence conventional polycondensation catalysts, such as antimony trioxide or titanium salts, polycondensed. The production can just as well after the direct esterification proceed in the presence of polycondensation catalysts. Here you go directly from the dicarboxylic acids and the diols.

According to the invention, the COC-containing layers contain a cycloolefinco polymeric (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, based on the weight of the finished Layer. It is essential to the present invention that the cycloolefinco polymer (COC) is incompatible with and with this polyethylene terephthalate does not form a homogeneous mixture.

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 50-95% by weight, each based 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:

In these formulas, R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ^{8 are} independently the same or different and represent a hydrogen atom or a C ₁ -C ₃₀ 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 meanings. C ₁ -C ₃₀ hydrocarbon radicals are preferably linear or branched C ₁ -C ₈ alkyl radicals, C ₆ -C ₁₈ aryl radicals, C ₇ -C ₂₀ alkylene aryl radicals or cyclic C ₃ -C ₂₀ alkyl radicals 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 ₁₀ hydrocarbon radical, preferably a C ₁ -C ₈ alkyl radical or C ₆ -C ₁₄ aryl radical.

Also suitable in principle are COCs, which are produced by ring-opening polymerization at least one of the monomers of the formulas I to VI and subsequent hydrogenation be preserved.

COCs are made up of a monomer of the formulas I-VI. These COCs are for the Less suitable for purposes of the present invention. For the purposes of the present Invention COCs are suitable which contain at least one cycloolefin of the formulas I to VI and contain acyclic olefins of formula VIII as comonomer. In the above like In the following, these cycloolefinco usable according to the invention called polymers COC. Preferred acyclic olefins are those which 2 have up to 20 carbon atoms, in particular unbranched acyclic olefins with 2 to 10 C atoms such as ethylene, propylene and / or butylene. The amount polymerized units of acyclic olefins of the formula VIII is up to 99% by weight, preferably 5 to 80 wt .-%, particularly preferably 10 to 60 wt .-%, based on the Total weight of the respective cycloolefin copolymer.

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

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 is described in numerous documents. Suitable catalyst systems based on mixed catalysts made of titanium or Zirconium or vanadium compounds in connection with aluminum organyls in DD 109 224, DD 237 070 and EP-A-0 156 464. 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 complex. The manufacturing processes described in the above-mentioned documents cycloolefin polymers are hereby expressly incorporated by reference.

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 can be used for the intermediate layers and, if applicable, the cover layer C. Polymers are used as for the previously described base layer B. In addition can this cover layer C and possibly the intermediate layers also other materials contain, this cover layer C and possibly the intermediate layers being preferred from a mixture of polymers, a copolymer or a homopolymer exist which ethylene-2,6-naphthalate units and ethylene terephthalate units contain.

The sealable cover layer A applied to the base layer B by coextrusion is based on polyester copolymers and consists essentially of Copolyesters consisting predominantly of a mixture of isophthalic acid and Terephthalic acid units and composed of ethylene glycol units. The remaining monomer units come from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids, as also found in the base layer B can occur. The preferred copolyesters that have the desired seals provide, are those made from ethylene terephthalate, from ethylene isophthalate Units and are built up from ethylene glycol units. The proportion of ethylene terephthalate halate is 40 to 95 mol% and the corresponding proportion of ethylene isophthalate is 60 up to 5 mol%. Copolyesters in which the proportion of ethylene terephthalate is preferred 50 to 90 mol% and the corresponding proportion of ethylene isophthalate 50 to 10 mol% is and very preferred are copolyesters in which the proportion of ethylene terephthalate halate 60 to 85 mol% and the corresponding proportion of ethylene isophthalate 40 to 15 mol% is.

The total thickness of the film can vary within wide limits and depends according to the intended use. The preferred embodiments of the films according to the invention have total thicknesses of 4 to 500 μm, 8 to 300 μm, in particular 10 to 300 μm are preferred. The thickness of the existing one Intermediate layer (s) is generally in each case independently of one another 0.5 to 15 µm, with intermediate layer thicknesses of 1 to 10 µm, in particular 1 to 8 µm,  are preferred. The values given relate to an intermediate layer. The thickness of the top layers becomes independent of the other layers selected 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 covering layers applied on both sides with respect 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 be analog of the total thickness vary within wide limits.

According to the invention, the base layer B contains to improve the whiteness of the film and / or possibly another additional layer of at least one white pigment and optionally an optical brightener.

Suitable white pigments are preferably titanium dioxide, barium sulfate, calcium carbonate, kaolin, silicon dioxide, with titanium dioxide and barium sulfate being preferred.

The titanium dioxide particles can consist of anatase or rutile, preferably predominantly made of rutile, which shows a higher opacity compared to anatas. In In a preferred embodiment, the titanium dioxide particles consist of at least 95% by weight. made of rutile. You can by a conventional procedure, e.g. B. after the chloride or the sulfate process. Their amount in the base layer B is expediently 0.1 to 25% by weight, preferably 0.2 to 23% by weight and in particular 0.3 to 22 wt .-%, based on the weight of the base layer B. Die average particle size is relatively small and is preferably in the range from 0.10 to 0.30 µm, measured according to the sedigraph method.

Titanium dioxide of the type described does not produce any within the polymer matrix Vacuoles during film production.  

The titanium dioxide particles can have a coating of inorganic oxides, as is usually used as a coating for TiO ₂ white pigment in papers or paints to improve the lightfastness.

As is well known, TiO ₂ is photoactive. When exposed to UV rays, free radicals form on the surface of the particles. These free radicals can migrate into the polymer matrix, which leads to degradation reactions and yellowing. To avoid this, the TiO ₂ particles can be coated oxidically. The particularly suitable oxides for the coating include the oxides of aluminum, silicon, zinc or magnesium or mixtures of two or more of these compounds. TiO ₂ particles with a coating of several of these compounds are, for. B. in EP-A-0 044 515 and EP-A-0 078 633. Furthermore, the coating can contain organic compounds with polar and non-polar groups. The organic compounds must be sufficiently thermostable in the production of the film by extrusion of the polymer melt. Polar groups are for example -OH; -OR; --COOX; (X = R; H or Na, R = alkyl with 1-34 C atoms). Preferred organic compounds are alkanols and fatty acids with 8-30 C atoms in the alkyl group, in particular fatty acids and primary n-alkanols with 12-24 C atoms, and polydiorganosiloxanes and / or polyorganohydrogensiloxanes such as, for. B. polydimethylsiloxane and polymethyl hydrogensiloxane.

The coating for the titanium dioxide particles usually consists of 1 to 12, in particular 2 to 6 g of inorganic oxides and / or 0.5 to 3, in particular 0.7 to 1.5 g organic compound, based on 100 g of titanium dioxide particles. The cover will usually applied to the particles in aqueous suspension. The inorganic Oxides can be made from water-soluble compounds, e.g. B. alkali, in particular Sodium nitrate, sodium silicate (water glass) or silica in the aqueous Suspension can be precipitated.  

Among inorganic oxides such as Al ₂ O ₃ or SiO ₂ are also the hydroxides or their various dewatering stages such. B. Understanding oxide hydrate without knowing its exact composition and structure. On the TiO ₂ pigment after the annealing and grinding in aqueous suspension, the oxide hydrates such. B. of aluminum and / or silicon, the pigments are then washed and dried. This precipitation can thus take place directly in a suspension, as occurs in the manufacturing process after annealing and the subsequent wet grinding. The oxides and / or oxide hydrates of the respective metals are precipitated from the water-soluble metal salts in the known pH range, for the aluminum, for example, aluminum sulfate in aqueous solution (pH less than 4) is used and in the pH range between by adding aqueous ammonia solution or sodium hydroxide solution 5 and 9, preferably between 7 and 8.5, the oxide hydrate precipitates. Assuming a water glass or alkali aluminate solution, the pH of the TiO ₂ suspension presented should be in the strongly alkaline range (pH greater than 8). The precipitation then takes place by adding mineral acid such as sulfuric acid in the pH range 5 to 8. After the precipitation of the metal oxides, the suspension is stirred for a further 15 minutes to about 2 hours, the precipitated layers undergoing aging. The coated product is separated from the aqueous dispersion and, after washing, is dried at elevated temperature, in particular at 70 to 100 ° C.

The film optionally contains barium sulfate as a pigment instead of titanium dioxide, wherein the concentration of the barium sulfate is preferably between 0.1 and 25% by weight, particularly preferably between 0.2 and 23% by weight, in particular between 0.3 and 22% by weight, based on the total weight of the base layer B. Preferably also the barium sulfate via the so-called masterbatch technology directly at the Film production metered.

In a preferred embodiment, precipitated barium sulfate types are used. Precipitated barium sulfate is obtained from barium salts and sulfates or sulfuric acid as a finely divided, colorless powder whose grain size increases due to the precipitation conditions  control is. Precipitated barium sulfates can be prepared using the usual methods described in Kunststoff-Journal 8, No. 10, 30-36 and No. 11, 36-31 (1974) are described, getting produced.

The average particle size is relatively small and is preferably in the range from 0.1 to 5 μm, particularly preferably in the range from 0.2 to 3 μm, measured by the sedigraph method. The density of the barium sulfate used is between 4 and 5 g / cm ³ .

The film optionally contains an optical brightener, the optical brightener in Quantities from 0 ppm to 50,000 ppm, in particular from 20 ppm to 30,000 ppm, particularly preferably from 50 ppm to 25,000 ppm, based on the weight of the crystallizable polyester is used. Preferably also the optical one Brightener using so-called masterbatch technology directly in film production added.

The optical brighteners according to the invention are able to withstand UV rays in the range absorb from 360 to 380 nm and as longer-wave, visible blue-violet light to deliver again.

Suitable optical brighteners are bis-benzoxazoles, phenylcoumarins and bis sterylbiphenyls, especially phenylcumann, particularly preferred are triazine phenylcumann (®Tinopal, Ciba-Geigy, Basel, Switzerland), ®Hostalux KS (Clariant, Germany) and ®Eastobrite OB-1 (Eastman).

The film according to the invention preferably contains 10 to 50,000 ppm of an optical Brightener, which is soluble in the crystallizable polyester, wherein triazine-phenyl coumarins are particularly preferred.  

If appropriate, in addition to the optical brightener can also be made in polyester soluble blue dyes can be added. Blue dyes have been found to be suitable Cobalt blue, ultramarine blue and anthraquinone dyes, in particular ®Sudan blue 2 (BASF, Ludwigshafen, Federal Republic of Germany).

The blue dyes are used in amounts of 10 ppm to 10,000 ppm, in particular from 20 ppm to 5,000 ppm, particularly preferably from 50 ppm to 1000 ppm on the weight of the crystallizable thermoplastic.

According to the invention, titanium dioxide or the barium sulfate, the optical brightener and if necessary, the blue dye already at the thermoplastic raw material manufacturer be metered in or in the production of foils using masterbatch technology in the Extruder be metered.

The addition of titanium dioxide or barium sulfate is particularly preferred optical brightener and, if necessary, the blue dye via the masterbatch Technology. The additives are fully dispersed in a solid carrier material. As Backing materials come from the thermoplastic itself, such as. B. the polyethylene terephthalate halat or other plastics that are sufficiently compatible with the thermoplastic are in question.

It is important that the grain size and bulk density of the masterbatch (s) are similar is the grain size and the bulk density of the thermoplastic, so that a homogeneous Distribution and thus a homogeneous whiteness and thus a homogeneous opacity can be achieved.

The base layer B and the other layers can additionally conventional additives such as Stabilizers, antiblocking agents and other fillers. You will be functional added to the polymer or the polymer mixture before melting. As  Stabilizers are, for example, phosphorus compounds, such as phosphoric acid or Phosphoric acid ester used.

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, e.g. B. polystyrene or acrylate particles.

Mixtures of two or more different ones can also be used as additives Antiblocking agents or mixtures of antiblocking agents of the same composition, but different particle sizes can be selected. The particles can Polymers of the individual layers of the film in the respective advantageous amounts, e.g. B. as a glycolic dispersion during polycondensation or via masterbatches be added to the extrusion. Pigment has proven particularly suitable concentrations of 0 to 25 wt .-% (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.

The cover layers can in principle be those specified above according to the invention Contain additive concentrations. The following have proven to be particularly cheap Embodiments proved:

The lowest seal starting temperature and the highest seal seam strength will be achieved when the sealable top layer A described above Copolymers are used. The best sealing properties of the film are obtained if the copolymer has no other additives, especially no inorganic ones or organic fillers can be added. In this case you get at  specified copolyester the lowest seal starting temperature and the highest Seal seam strengths. 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, blocking is minimized and, on the other hand, the sealing properties are only insignificantly deteriorated. This desired combination of properties can be achieved if the topography of the sealable outer layer A is preferably characterized by the following set of parameters:

• - The roughness of the sealable top layer, expressed by the R _a value, should be less than 100 nm and preferably ≦ 80 nm. In the other case, the sealing properties are negatively influenced in the sense of the present invention.
• - The measurement value for the surface gas flow time should preferably be in the range from 50 to 4000 s. If the value is less than 50 s, the sealing will start in the sense of the present invention negatively influenced and at values the handling of the film becomes poor above 4000 s.

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

• - The coefficient of friction (COF) of this side against itself should be preferred be less than 0.7 and particularly preferably ≦ 0.6. Otherwise it is Wrapping behavior and 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 measurement value for the surface gas flow time should be favorable in the range are below 500 s. With values from 500 s the winding and negatively affects the processing behavior of the film.

In order to achieve this particularly favorable property profile of the film, the film shows a top layer C containing a larger amount of pigments (i.e. higher pigment concentration) as the cover layer A. The pigment concentration in this second Cover 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. The other, the top layer C opposite, sealable cover layer A, however, is with a smaller amount filled with inert pigments. The concentration of the inert particles in 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.

The invention further relates to a method for producing the invention white, sealable polyester film according to the known extrusion or Coextrusion.

Within the scope of this process, the individual layers are processed in such a way the melt corresponding to the film are co-extruded through a flat die, so the film obtained is removed for solidification on one or more roller (s) The film is then biaxially stretched (oriented), the biaxially stretched film is heat-set and if necessary on a surface layer intended for treatment corona or flame treated and then wound up.

Biaxial stretching is generally carried out sequentially. Doing so preferably only 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) stretched. If necessary, a further longitudinal can be done after the transverse stretching extension. The stretching leads to a spatial orientation of the molecule chain ten of the polyester. The stretching in the longitudinal direction is preferably carried out with the help of several according to the desired stretch ratio with different angles speeds of rotating rollers. For cross-stretching one generally uses one corresponding tenter frame.

The temperature at which the stretching is carried out can be in a relatively large Windows vary and depend on the desired properties of the film. in the in general the longitudinal stretching is at 80 to 130 ° C and the transverse stretching at 90 up to 150 ° C. The aspect ratio is generally in the range of 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), where the number of stretching steps and the sequence (lengthways / crossways) do not differ from ent is of crucial importance for the property profile of the film. However, are cheap here Stretching temperatures ≦ 125 ° C and particularly favorable ≦ 115 ° C. The stretching ratios correspond to those in the conventional sequential process.

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

The film can be chemically treated to set other desired properties be corona or flame treated. The treatment intensity is like this adjust that the surface tension of the film is generally over 45 mN / m lies.  

The film can also be coated to set further properties. Typical coatings are anti-static, anti-slip or anti-slip layers with an adhesive effect. It is advisable to add these additional layers after the Technique of the so-called "in-line coating" by means of aqueous dispersions according to the Apply longitudinal stretching and before transverse stretching on the film.

The particular advantage of the film according to the invention is expressed by a high level Whiteness and excellent sealability. The degree of whiteness of the film is more than 80%, preferably more than 85% and particularly preferably more than 90%. 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 is the economically important and surprising Advantage that in the production of the film inherent waste material as Regenerate in an amount of 10 to 70 wt .-%, based on the total weight of the Film, can be used again for film production, without the physical properties of the film are significantly affected. In particular, the regenerate (essentially made of polyester raw material and Cycloolefin copolymers (COC) consisting of the film is not undefined in color changed what is the case with the films according to the prior art.

The film is suitable because of its very good handling and because of its very good processing properties, especially for processing quickly running machines.

The film is also suitable due to its excellent properties combinations for a variety of different applications, for example for Interior cladding, for stand construction and for the manufacture of trade fair items, as Displays, for signs, for protective glazing of machines and vehicles, in  Lighting sector, in shop and shelf construction, as a 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:

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

SV (standard viscosity)

The standard viscosity SV (DCE) is based on DIN 53 726 in dichloroacetic acid measured.

The intrinsic viscosity (IV) is calculated from the standard viscosity as follows

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 14 days measured after production.

surface tension

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

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 using the electrical "ELREPHO" remission photometer 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. We as the white standard a pellet made of barium sulfate (DIN 5033, part 9) is used. A detailed one Description is z. B. in Hansl Loos "color measurement", publisher occupation and school, Itzehoe (1989).  

Light transmission

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

shine

The gloss was determined in accordance with DIN 67 530 at a measuring angle of 60 °. Measured was the reflector value as an optical parameter for the surface of a film. On The light beam strikes the flat test surface and at the set angle of incidence is reflected or scattered by it. The on the photoelectronic receiver striking light rays are displayed as a proportional electrical quantity. The 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 DuPont 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 the 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 × 100 mm) made, the film at different Temperatures with the help of two heated sealing jaws at a sealing pressure of 2 bar and a sealing time of 0.5 s is sealed. From the sealed samples were Cut test strips 15 mm wide. The T-seal strength was the same as for the Determination of the seal seam strength measured. The seal starting temperature is that  Temperature at which a seal seam strength of at least 0.5 N / 15 mm is reached becomes.

Seal strength

Two 15 mm wide film strips were used to determine the seal seam strength one on top of the other and 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) sealed. 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 one Foil side and a smooth silicon wafer plate. The air flows from the surroundings into an evacuated room, the interface between the film and the silicon wafer Plate serves as a 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 coextrusion technology, a 23 µm thick two-layer film was used the order of layers A-B, where B is the base layer and A the top layer showed. The base layer B was 21.5 µm thick and the top layer 1.5 µm.

Polyethylene terephthalate chips (produced by the transesterification process with Mn as the 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)) with a glass transition temperature T _g of 160 ° C also fed to the extruder for the base layer B. The quantitative proportion of the COC in the base layer was 10% by weight.

In addition, the base layer contained 5% by weight barium sulfate (®Blanc fixe XR-HX, Sachtleben Chemie) and 200 ppm optical brightener (®Tinopal, Ciba-Geigy, Basel). The additives barium sulfate and optical brightener were added as masterbatch 2.

The polyethylene terephthalate used to make the masterbatches had a standard viscosity SV (DCE) in the range of 700 to 1100.

Masterbatch 2 consisted of clear raw material, 50% by weight barium sulfate and 2000 ppm optical brightener together and was dosed with 10 wt .-% in the base layer B.

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 by 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% chips of a masterbatch 1 were fed to the extruder which, in addition to polyester, contained 10,000 ppm silicon dioxide (®Sylobloc, Grace, Germany) and 12,500 ppm silicon dioxide (®Aerosil, pyrogenic SiO ₂ from Degussa, Germany). These chips were also dried at 100 ° C. to a residual moisture of below 200 ppm.

It was made by coextrusion and subsequent gradual orientation in longitudinal and Transversely, a white, opaque two-layer film with a total thickness of 23 microns manufactured.

Base layer B, mixture of:
85.0% by weight of polyethylene terephthalate homopolymer (RT49, Kosa, Germany)
10.0% by weight of cycloolefin copolymers (COC) from Ticona, ®Topas 6015
5% by weight of masterbatch 2

The manufacturing conditions in the individual process steps were:
extrusion:
Base and top layer temperatures: 280 ° C
Take-off roller temperature: 30 ° C
Longitudinal stretching:
Temperature: 80-125 ° C
Longitudinal stretch ratio: 4.2
Transverse 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 one Handling and the desired processing behavior. The properties achieved Films produced in this way are shown in Tables 2 and 3.  

Example 2

In comparison to Example 1, an amount of 50% by weight was now added to the base layer B. Regenerate added. The amount of COC in the base layer B thus produced was again 10% by weight. The process parameters were compared to the example 1 not changed. The top layer A remained unchanged. The yellow discoloration of the Visually observed film. From tables 2 and 3 you can see that hardly any Yellowing of the film has become visible.

Base layer B, mixture of:
42.2% by weight of polyethylene terephthalate homopolymer 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
2.5% by weight of masterbatch 2

Example 3

The base layer B was built up as in Example 1, but was only 20 μm thick. The sealable cover layer A corresponded to example 1 in thickness and composition. In addition, a third 1.5 µm thick top layer C was coextruded (drying like Top layer A).

This top layer C contained:
88% by weight polyethylene terephthalate homopolymer with an SV value of 800
12% by weight of masterbatch 1 made of polyester and 10,000 ppm of silicon dioxide (Sylobloc, Grace, Germany) and 12,500 ppm of 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 on example 1 and 2, but showed better processing behavior. The  Properties achieved in films produced in this way are shown in Tables 2 and 3 shown.

Example 4

Like Example 3, but base layer B became 50% by weight of its own Regenerate added. The amount of COC in the film was again 10% by weight. The process parameters were not changed compared to Example 1. It was visually observed the yellow discoloration of the film. Using tables 2 and 3 you can see that hardly any yellowing of the film has become visible.

Example 5

The composition of cover layers A and C corresponded to the film from Example 3. Die Layer thickness of the sealable top layer A was now 2.5 microns and that of pigmented top layer C was now 2 µm. The film was a total of 96 microns thick and the COC concentration of the base layer was 9% of the other components corresponded to example 1. The process parameters were chosen as in example 1.

The properties achieved in films produced in this way are shown in Tables 2 and 3 shown.

The seal seam strength was significantly increased with good processability.

Example 6

Like example 5, but with 50% by weight of its own regrind in the base layer B. All other parameters as in Example 5. The properties of the film were opposite Example 5 largely unchanged.

The yellowing of the film was observed visually. Using Table 2 and 3 you can see that hardly any yellow discoloration of the film has become visible.  

Comparative Example 1

A white film was produced analogously to example 1 from EP-A 0 300 060 (this was a non-sealable white film). In a modification of this example, the film was additionally provided with a 2 μm thick sealable cover layer A analogous to Example 5. In addition, in a modification of the example in EP-A 0 300 060, 50% by weight of own regrind was added to the base layer. Tables 2 and 3 show that a clear yellowing of the film has become visible. In addition, the roughness of the film is clearly too high for many applications and the gloss of the non-sealable side at 58 (examples 1-6 had gloss values between 116 and 172 on this side) is too low for many applications.
45.0% by weight of polyethylene terephthalate homopolymer with an SV value of 800
50.0% by weight self-regenerated material (95% by weight polyester + 5% by weight polypropylene)
5.0 wt% polypropylene

Claims (15)

1. White, sealable, pigmented biaxially oriented, 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 is a cycloolefin copolymer (COC) in an amount in the range from 2 to 60% by weight, based on the weight of the base layer B, and that the base layer B additionally contains at least one white pigment. 2. White, sealable polyester film according to claim 1, characterized indicates that the base layer B in addition to the white pigment contains optical brighteners. 3. White, sealable polyester film according to claim 1 or 2, characterized notes that the cycloolefin copolymer (COC) polynorbornene, Polydi methyl octahydronaphthalene, polycyclopentene or poly (5-methyl) norbornene contains. 4. White, sealable polyester film according to one or more of claims 1 to 3, characterized in that the COC has a glass transition temperature T _g in the range from 90 to 250 ° C. 5. White, sealable polyester film according to one or more of claims 1 to 4, characterized in that the COC has a glass transition temperature T _g in the range from 110 to 220 ° C. 6. White, sealable polyester film according to one or more of claims 1 to 5, characterized in that the film has a degree of whiteness of more than  80% and that it as a white pigment titanium dioxide and / or barium sulfate and / or contains calcium carbonate and / or kaolin and / or silicon dioxide. 7. White, sealable polyester film according to one or more of claims 1 to 6, characterized in that the film has an opacity of more than 55% having. 8. White, sealable polyester film according to one or more of claims 1 to 7, characterized in that the film has a gloss of more than 50 having. 9. White, sealable polyester film according to one or more of claims 1 to 8, characterized in that the film has at least two layers and the Cover layers do not contain / contain COC. 10. White, sealable polyester film according to claim 9, characterized in that between the COC-containing base layer B and the cover layer A a Intermediate layer is arranged. 11. White, sealable polyester film according to one or more of claims 1 to 10, characterized in that the sealable cover layer A Polyester copolymer contains the ethylene terephthalate units in an amount in the range of 40 to 95 mol% and ethylene isophthalate units in an amount contains from 60 to 5 mol%, based on the total amount of carboxylic acid units, and that the other monomer units from aliphatic, cycloaliphati or aromatic diols. 12. White, sealable polyester film according to one or more of the claims 1 to 11, characterized in that the sealable cover layer A a Thickness in the range of 0.2 to 5.0 microns.   13. Process for producing a white, sealable polyester film according to a of claims 1 to 12, wherein the polymer or the polymer mixture for the individual layers are compressed and liquefied in separate extruders the molten plastics then simultaneously through a flat nozzle (Slot die) are pressed, the pressed multilayer pre-film on one or more take-off rollers is drawn off, the pre-film thus obtained then stretched biaxially, heat-set and optionally on a to Surface treatment provided is corona or flame treated, characterized in that the longitudinal stretching at temperatures in the range from 80 to 130 ° C and the transverse stretching at temperatures in the range of 90 up to 150 ° C and that the longitudinal stretching ratio is within a range from 2.5: 1 to 6: 1, preferably from 3: 1 to 5.5: 1 and the transverse stretch ratio within a range from 3.0: 1 to 5.0: 1, preferably from 3.5: 1 to 4.5: 1. 14. The method according to claim 13, characterized in that in the manufacture Waste material inherent in the film as regrind in a quantity from 10 to 70 wt .-%, based on the total weight of the film, again for the Foil production is used. 15. Use a white, sealable polyester film after one or several of claims 1 to 12 as interior cladding for trade fair construction and for the manufacture of trade fair articles, as a display, for signs, in lighting sector, in shop and shelf construction, as promotional items, as a lamination medium for Covers of materials, or in electrical applications.