DE10026167A1 - Glossy, white, opaque, UV-stabilized polyester laminate film, useful e.g. in packaging foodstuffs, comprising base layer(s) containing cycloolefin copolymer and covering layer(s) - Google Patents

Abstract

In a polyester film (I) consisting of at least one base layer and at least one covering layer, the base layer contains (in addition to a thermoplastic polyester) a cycloolefin copolymer (COC) and the film contains at least one UV stabilizer. An Independent claim is included for the preparation of (I), by coextruding the starting materials necessary for the base, covering and optionally intermediate layers using an extruder having a flat die and biaxially orienting, thermo-fixing and optionally further processing the obtained film.

Description

The present invention relates to a white, high-gloss, UV-stabilized, biaxial oriented, coextruded polyester film, which consists of at least one base layer and at least one cover layer, the base layer being a polyester and a Contains cycloolefin copolymer (COC). The invention further relates to a method for Production of the polyester film and its use.

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

DE-A 23 53 347 describes a process for producing a single or multilayer, milky polyester film described, which is characterized is that a mixture of particles of a linear polyester and 3 to 27 wt .-% a homopolymer or copolymer of ethylene or propylene which 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, otherwise the film discolored or turns yellow. The process is therefore uneconomical. Also points the film has high roughness and therefore has a very matt appearance (very low Gloss), which is undesirable for many applications.

EP-A 0 300 060 describes a single-layer polyester film which, apart from Polyethylene terephthalate still 3 to 40 wt .-% of a crystalline propylene polymer and contains 0.001 to 3% by weight of a surfactant. The Surfactant causes the number of vacuoles in the film to increase  while decreasing in size to the extent desired. This will create a achieved higher opacity and a lower density of the film. Another disadvantage is that the regrind produced during the production of the film (essentially a Mixture of polyester raw material and propylene homopolymer) is no longer used can otherwise be discolored yellow. The procedure is however uneconomical. In addition, the film has clearly too high roughness and has hence 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 has a base layer with fine vacuoles, the density of which is between 0.4 and 1.3 kg / dm ³ and at least one cover layer, the density of which is greater than 1. 3 kg / dm ³ . The vacuoles are created 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), increases the surface tension and reduces the roughness of the laminated surface. It is also disadvantageous here 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, since otherwise the film is discolored yellow. The process is therefore uneconomical. In addition, the films listed in the examples 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 has 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 whose density is greater than 1. 3 kg / dm ³ . The vacuoles are created by adding 5 to 45% by weight of a thermoplastic polymer to the polyester raw material of the base layer 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. However, it is also disadvantageous here that the regrind obtained in the production of the film (essentially a mixture of polyester raw material and the additive raw material) can no longer be used, since otherwise the color of the film is changed indefinitely, which is undesirable for many applications . The process is therefore uneconomical. In addition, the films listed in the examples have 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 has 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 created by adding 3 to 40% by weight of a thermoplastic resin to the polyester raw material of the base layer and then biaxially stretching the film. Thermoplastic resins include polypropylene, polyethylene, polymethylpentene, 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 good tear strength and good isotropy properties. The disadvantage remains that the regrind produced in the production of the film can no longer be used, since otherwise the color of the film is changed indefinitely, which is undesirable for many applications. The process is therefore uneconomical. In addition, the films listed in the examples have high roughness and thus have a matt appearance (low gloss), which is undesirable for many applications.

The object of the present invention was therefore a white polyester film To provide, which is particularly characterized by a very high gloss and by a improved manufacturability, d. H. low manufacturing costs, distinguished and the above also has a high UV stability without the above to have negative characteristics. In particular, it should be ensured that the Regenerate accumulating in the manufacturing process in a concentration of preferably 10 to 70 wt .-%, based on the total weight of the film again can be used without affecting the physical properties of the film noticeably affected. In particular, the Regenerate addition no significant discoloration or yellowing of the film occur.

High UV stability means that the films are exposed to sunlight or other UV Radiation not or only extremely little damage, so that the films for Outdoor applications and / or critical indoor applications are suitable. In particular should the films not yellow after several years of outdoor use, none Show embrittlement or cracking of the surface and also no deterioration of mechanical properties. High UV stability therefore means that the film absorbs UV light and only lets light through in the visible range.

A high surface gloss means that the gloss at <100 (DIN 67530, at a Measuring angle of 20 °), preferably <120 and in particular <130.

The task is solved by a white, high-gloss, UV-stabilized, biaxial oriented, coextruded polyester film in the thickness range of preferably 4 to 500 microns consisting of at least one base layer and at least one cover layer,  wherein at least the base layer additionally contains a cycloolefin copolymer (COC). The concentration of the COC is preferably from 2 to 60% by weight, based on the Weight of the base layer. The glass transition temperature of the cycloolefin copolymer (COC) is preferably in the range from 70 to 270 ° C. and at least one The film surface (top layer) has a gloss value (measuring angle 20 °) of greater than 100 on. The film contains at least one UV stabilizer as a light stabilizer.

Under a white polyester film in the sense of the present invention is a film understood that a whiteness of more than 70%, preferably of more than 75% and particularly preferably of more than 80%. Furthermore, the opacity is the film of the invention more than 55%, preferably more than 60% and especially preferably more than 65%.

To achieve the desired degree of whiteness of the film according to the invention, the The proportion of the cycloolefin copolymer (COC) in the base layer may be greater than 2%. On the other hand, if the cycloolefin copolymer (COC) content is greater than 60%, there is the risk that the film can no longer be produced economically, since it is under Circumstances that can no longer be reliably drawn under certain circumstances.

It is further preferred that the glass transition temperature of the used Cycloolefin copolymers (COC) is greater than 70 ° C. Otherwise (with one Glass transition temperature of less than 70 ° C) the raw material mixture is worse processable (more difficult to extrude), the desired degree of whiteness may become no longer reached and the regrind used leads to a film that increases May have yellowing. On the other hand, the glass transition temperature of the selected cycloolefin copolymers (COC) greater than 270 ° C, so the Raw material mixture may no longer be sufficiently homogeneous in the extruder disperse. This would then have a film with inhomogeneous properties Episode.  

In the preferred embodiment of the film according to the invention, the Glass transition temperature of the COCs used 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 Cycloolefin copolymers (COC) in the manner described above a white, opaque, glossy 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. With this measure it is possible to share with others To largely do without common white and opaque additives. Furthermore was it is very surprising that the surface roughness of the film is much less and so that the gloss of the film is much higher than with comparable films after State of the art. Completely surprising was the additional effect that the Regenerate not, like the polymeric additives according to the prior art, for Yellow discoloration tends.

All of the features described were unpredictable. This is all the more because z. B. COCs largely to the preferred polyester polyethylene terephthalate are incompatible, but as is well known, with similar stretching ratios and Stretching temperatures are oriented like polyethylene terephthalate. Under these A person skilled in the art would have expected that the inventive Manufacturing conditions no white, opaque film with high gloss can be produced can.

In particular in the preferred and the particularly preferred embodiments the film according to the invention is characterized by high UV protection, by a high / or through a particularly high degree of whiteness and a high / or. by a  particularly high opacity in combination with a high surface gloss at least one film surface, the color change of the film by the The amount of regeneration remains extremely low.

The film according to the invention contains at least one UV stabilizer as light protective means, preferably directly via the so-called masterbatch technology is metered in during film production, the amount of UV stabilizer being preferred in the range of 0.01 to 5% by weight, preferably 0.3 to 4% by weight, in particular 0.5 to 3 wt .-% based on the weight of the finished layer, where the Base layer and / or the cover layers and any existing Intermediate layers can be equipped with a UV stabilizer. It can too Mixtures of different UV stabilizers can be used.

Light, especially the ultraviolet portion of solar radiation, i.e. H. the Wavelength range from 280 to 400 nm, initiates degradation processes with thermoplastics, as a result not only the visual appearance due to color change or yellowing changes, but also the mechanical-physical properties be adversely affected.

The inhibition of these photooxidative degradation processes is of considerable technical and economic importance, since otherwise the application possibilities of numerous thermoplastics are drastically restricted.

Polyethylene terephthalates, for example, start below 360 nm UV Absorb light, its absorption increases considerably below 320 nm and is very pronounced below 300 nm. The maximum absorption is between 280 and 300 nm.

In the presence of oxygen there are mainly chain cleavages, but none Networking observed. Carbon monoxide, carbon dioxide and carboxylic acids are the  quantitatively predominant photo-oxidation products. In addition to the direct Photolysis of the ester groups still need to consider oxidation reactions which also result in the formation of carbon dioxide via peroxide radicals to have.

The photooxidation of polyethylene terephthalates can also take place Hydrogen elimination in the α-position of the ester groups to form hydroperoxides and their Decomposition products and the associated chain cleavages (H. Day, D. M. Wiles: J. Appl. Polym. Sci 16, 1972, page 203).

UV stabilizers or UV absorbers as light stabilizers are chemical Compounds involved in the physical and chemical processes of light-induced Can intervene. Soot and other pigments can partially Effect sun protection. However, these substances are for transparent films unsuitable as they lead to discoloration or color change. For transparent, matt Films are only suitable for organic and organometallic compounds that do not stabilizing thermoplastics no or only an extremely low color or Apply color change, d. H. which are soluble in the thermoplastic.

UV stabilizers suitable as light stabilizers for the purposes of the present invention are UV stabilizers which are at least 70%, preferably 80%, particularly preferred 90% of the UV light in the wavelength range from 180 nm to 380 nm, preferably Absorb 280 to 350 nm. These are particularly suitable if they are in the Temperature range of 260 to 300 ° C are thermally stable, d. H. don't decompose and do not lead to outgassing. Suitable UV stabilizers are light stabilizers for example 2-hydroxybenzophenones, 2-hydroxybenzotriazoles, organo-nickel Compounds, salicylic acid esters; Cinnamic acid ester derivatives, resorcinol monobenzoates, Oxalic acid anilides, hydroxybenzoic acid esters, sterically hindered amines and triazines, the 2-hydroxybenzotriazoles and the triazines being preferred.  

It was surprising that the use of the combination of COC according to the invention plus UV stabilizers leads to usable films with very good properties. Man would probably have first tried a certain UV stability over one To achieve oxidation stabilization, but should have determined after weathering, that the film quickly turns yellow.

The film according to the invention contains at least one UV stabilizer Light stabilizers, the concentration of the UV stabilizer preferably in Range from 0.01% by weight to 5.0% by weight, in particular in the range from 0.1% by weight to 3 wt .-%, based on the weight of the layer of crystallizable Thermoplastics. The UV stabilizer can expediently on the so-called masterbatch technology can be added directly during film production.

It is completely surprising that the use of the above UV stabilizers in Slides leads to the desired result. When trying to get some UV To achieve stability via an antioxidant, the film quickly becomes weathered yellow.

If commercially available UV stabilizers are used which absorb the UV light and thus generally offer protection, it is found that

• - The UV stabilizer has a lack of thermal stability and is Temperatures decomposed or outgassed between 200 ° C and 240 ° C,
• - Large amounts (approx. 10 to 15% by weight) of UV stabilizer are incorporated so that the UV light is absorbed and the film is not damaged.

At these high concentrations, the film shows up already after production yellow appearance, with yellowness index differences (YID) around 25. Furthermore the mechanical properties are negatively affected. Kick when stretching unusual problems on how -

• - Demolition due to lack of strength, d. H. Modulus too low  
• - Nozzle deposits, which leads to profile fluctuations
• - Roller deposits from the UV stabilizer, which affects the optical properties (poor cloudiness, adhesive defects, inhomogeneous Surface)
• - Deposits in stretching or fixing frames that drip onto the film.

It was therefore more than surprising that excellent UV protection was achieved even with low concentrations of the UV stabilizer. It was very surprising that this excellent UV protection

• - The yellowness index of the film compared to a non-stabilized film in the frame the measuring accuracy does not change;
• - no outgassing, no nozzle deposits, none Frame evaporation set, which gives the film an excellent look and has an excellent profile and flatness;
• - The UV-stabilized film has excellent stretchability distinguished so that they are reliable and stable on high speed film lines up to production reliably at speeds of 420 m / min can.

Furthermore, it was not foreseeable that the regrind can also be used again, without negatively affecting the yellowness index of the film.

In a very particularly preferred embodiment, the film according to the invention contains 0.01% by weight to 5.0% by weight of 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5- ( hexyl) oxy phenol of the formula

or 0.01% to 5.0% by weight of 2,2-methylene-bis (6- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) - phenol of the formula

or 0.01% to 5.0% by weight of 2,2 '- (1,4-phenylene) to [4H-3,1-benzoxazin-4-one]

In a preferred embodiment, mixtures of these UV Stabilizers or mixtures of at least one of these two UV stabilizers can be used with other UV stabilizers, the total concentration Light stabilizers preferably between 0.01% and 5.0% by weight, based on the weight of crystallizable polyethylene terephthalate.

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 and at least one more top layer. In a preferred embodiment, the COC-containing layer, the base layer of the film with at least one, preferably with cover layers on both sides, whereby optionally on one side or on both sides Intermediate layers can be present, all layers with UV stabilizer can be equipped. The layer structure would then be z. B. A-B-C, where B is the Base layer and A and C are the top layers, which are the same or different  can. In a further preferred embodiment, the COC-containing layer forms also an intermediate layer of the multilayer film. Further embodiments with COC containing intermediate layers are built up of five layers and, in addition to the COC base layer containing COC-containing intermediate layers on both sides. In another Embodiment can the COC-containing layer in addition to the base layer, one-sided form a cover layer on the base or intermediate layer. The base layer is in According to the present invention, that layer which preferably 50% to 99.5%, preferably 60 to 95% of the total film thickness. The top layers are the layers that form the outer layers of the film.

The COC-containing base layer of the film according to the invention contains one thermoplastic polyester, preferably a polyester homopolymer, a COC, a UV stabilizer and any additional additives in each case effective amounts. In general, this layer preferably contains 20% by weight to 98% by weight, preferably 40 to 98% by weight, in particular 70 to 98% by weight thermoplastic polyester and 0.1 to 5 wt .-% UV stabilizer, preferably 0.5 up to 3% by weight UV stabilizer, based on the weight of the base layer.

Suitable thermoplastic polyesters for the base layer are preferably polyesters made 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-cyclohexane dimethylene 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 introductions come from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids, such as z. B. in layer A  (A = top layer 1) and / or layer C (C = top layer 2) of a multilayer Foil ABC (B = base layer) can occur.

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 ) ₂ -, -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.

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 (in particular biphenyl-4,4'-dicarboxylic acid), diphenylacetylene-x, x '-dicarboxylic acids (especially diphenylacetylene-4,4'-dicarboxylic acid) or stilbene-x, x'-dicarboxylic acids. Of the cycloaliphatic dicarboxylic acids, cyclohexanedicarboxylic acids (in particular cyclohexane-1,4-dicarboxylic acid) should be mentioned. Of the aliphatic dicarboxylic acids, the (C ₃ -C ₁₉ ) alkanedioic acids are particularly suitable, the alkane fraction being straight-chain or branched.

The preparation of the polyesters to be used according to the invention can, for. B. after Transesterification procedures are carried out. One starts from dicarboxylic acid esters and diols from that with the usual transesterification catalysts, such as zinc, calcium, lithium, Magnesium and manganese salts are implemented. The intermediate products are then in the presence of common polycondensation catalysts, such as Antimony trioxide or titanium salts, polycondensed. The production can be just as good by the direct esterification process in the presence of  Polycondensation catalysts take place. You go straight from the Dicarboxylic acids and the diols.

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

Cycloolefin polymers are generally homopolymers or copolymers which contain polymerized cycloolefin units and optionally acyclic olefins as comonomers. Particularly suitable for the present invention are cycloolefin polymers which contain 0.1 to 100% by weight, preferably 10 to 99% by weight, particularly preferably 50-95% by weight, based in each case on the total mass of the cycloolefin polymer, of polymerized cycloolefin units . 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 of one another, the same or different and denote 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, identical 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 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.

Optionally, the cycloolefin polymers according to the invention can 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 a 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 cycloolefin polymers which are ring-opening Polymerization of at least one of the monomers of the formulas I to VI and subsequent hydrogenation can be obtained.

Cycloolefin homopolymers are composed of a monomer of the formulas I-VI. These cycloolefin polymers are less for the purposes of the present invention suitable. For the purposes of the present invention, in particular Cycloolefin copolymers (COC) suitable, which at least one cycloolefin Contain formulas I to VI and at least one as a comonomer. Preferred Comonomers are the acyclic olefins of formula VIII. In the above as in The following are the cycloolefin copolymers that can be used according to the invention Called COC. Preferred acyclic olefins VIII are those which contain 2 to 20 carbon atoms.  Have atoms, especially unbranched acyclic olefins with 2 to 10 carbon atoms such as 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 cycloolefin copolymer.

Among the cycloolefin copolymers, those are particularly preferred polymerized units of polycyclic olefins with norbornene basic structure, especially preferably contain norbornene, 5-methyl-norbornene, or tetracyclododecene. Suitable monomers are also dimethyl octahydronaphthalone and cyclopentene. Cycloolefin copolymers (COC) which polymerized are also particularly preferred Contain units of acyclic olefins, especially ethylene. Again special preferred are norbornene / ethylene and tetracyclododecene / ethylene copolymers, which Contain 5 to 80 wt .-%, preferably 10 to 60 wt .-%, of acyclic olefin VIII (based on the weight of the copolymer).

The cycloolefin polymers described generally have Glass transition temperatures between -20 ° C and 400 ° C. Are for the invention preferably cycloolefin copolymers (COC) can be used, the one Glass transition temperature of greater than 70 ° C, preferably greater than 90 ° C and have in particular greater than 110 ° C. The viscosity number (decalin, 135 ° C, DIN 53 728) is expediently between 0.1 and 200 ml / g, preferably between 50 and 150 ml / g.

The cycloolefin copolymers (COC) are produced by a heterogeneous process or homogeneous catalysis with organometallic compounds and is in a variety described by documents. Suitable catalyst systems based on Mixed catalysts made of titanium or vanadium compounds in connection with Aluminum organyls are described in DD 109 224, DD 237 070 and EP-A-0 156 464 described. EP-A-0 283 164, EP-A-0 407 870, EP-A-0 485 893 and EP-A-0 503 422  describe the production of cycloolefin copolymers (COC) with catalysts, based on soluble metallocene complexes. To the writings mentioned above Manufacturing process of cycloolefin polymers described is hereby expressly referred.

The cycloolefin copolymers are incorporated into the film either as pure granules or as granulated concentrates (masterbatch) by premixing the polyester granules or powder with the cycloolefin copolymer (COC) or the cycloolefin copolymer (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 cycloolefin copolymer (COC), generally at least 5 ° C., preferably 10 to 180 ° C., in particular 15 to 150 ° C., above the glass transition temperature of the cycloolefin copolymer (COC).

In principle, the same polymers can be used for the intermediate layers and cover layers used as for the base layer. The cover layers and if necessary, the intermediate layers of a mixture of polymers, a copolymer or a homopolymer consisting of ethylene-2,6-naphthalate units and / or contain ethylene terephthalate units. Up to 30 mol% of the polymers can consist of further comonomers (e.g. ethylene isophthalate units).

It is preferred that at least one cover layer is not coated with cycloolefin copolymer (COC) is equipped. This top layer essentially contains the above thermoplastic polyester and is optionally with UV stabilizer, with antiblock and / or Equipped with lubricants.

The base layer and the other layers can additionally conventional additives such as e.g. B. stabilizers and antiblocking agents. You will be expedient to that  Polymer or the polymer mixture added 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, talc, magnesium carbonate, barium carbonate, calcium sulfate, Ba rium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, Lithium fluoride, calcium, barium, zinc or manganese salts of the used Dicarboxylic acids, carbon black, titanium dioxide, kaolin or cross-linked 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 size can be selected. The particles can Polymers of the individual layers of the film in the most advantageous Concentrations, e.g. B. as a glycolic dispersion during polycondensation or via masterbatches during extrusion. As particularly suitable have shown pigment concentrations of 0 to 25 wt .-% (based on the Weight of each layer). A detailed description of suitable ones Antiblocking agents can be found, for example, in EP-A-0 602 964.

Suitable lubricants are e.g. B. polydimethylsiloxane, carboxylic acids, metal salts of Carboxylic acids, carboxylic acid amides, carboxylic acid esters. A detailed description can be found, for example, in Plastic Additives, 2nd Edition, Carl Hanser Verlag, Munich, Vienna, pp. 309 to 347.

To improve the degree of whiteness of the film, the base layer and / or possibly a other additional layer contain another pigmentation. Here it has proven to be particularly favorable as additional barium sulfate additives in one  Grain size of preferably 0.3-0.8 microns, in particular 0.4-0.7 microns or titanium dioxide in a grain size of preferably 0.05-0.3 microns to choose. This gives the film a brilliant, white look. The particle concentration of barium sulfate is preferably 1 to 25% by weight, preferably 1 to 20% by weight, and very preferably at 1 to 15 wt .-%, based on the weight of the layer equipped with it.

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 particularly preferred. The thickness of the, if applicable existing intermediate layer (s) is generally independent in each case 0.5 to 15 µm from one another, with intermediate layer thicknesses of 1 to 10 µm, in particular 1 to 8 μm, are preferred. The values given refer to each on an intermediate layer. The thickness of the cover layers is independent of selected the other layers and is preferably in the range from 0.1 to 10 μm, in particular 0.2 to 5 microns, preferably 0.3 to 2 microns, with applied on both sides Cover layers with respect to thickness and composition may be the same or different can. The thickness of the base layer results from the difference of Total thickness of the film and the thickness of the top and intermediate layers applied and can therefore vary within wide limits analogously to the total thickness.

The invention further relates to a method for producing the invention Polyester film according to the known coextrusion process.

Within the framework of this process, the individual layers are processed the melt corresponding to the film are co-extruded through a flat die, the film thus obtained is pulled off on one or more rollers for consolidation, the film is then biaxially stretched (oriented), the biaxially stretched film heat-set and, if necessary, on the treatment Surface layer is corona or flame treated.  

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. This leads to an orientation of the molecular chains. Stretching in The longitudinal direction is preferably carried out with the help of two in accordance with the desired Stretch ratio of rolls running at different speeds. Used for cross stretching generally a corresponding tenter frame.

A simultaneous, i.e. H. simultaneous stretching of the film according to the invention in both Directions (MD direction and TD direction) with the help of a suitable one Clip frame has not proven to be useful. That is, this stretch can lead to a film that has too little whiteness and too little opacity having.

The temperature at which the drawing is carried out can be in a relative vary widely and depends on the desired properties of the Foil. In general, the longitudinal stretching at 80 to 130 ° C and the transverse stretching carried out at 90 to 150 ° C. The aspect 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.

In the subsequent heat setting, the film is held at about 0.1 to 10 s Temperature kept from about 150 to 250 ° C. Then the film is in the usual Way wrapped up.

The film can be chemically treated to set other desired properties will be corona and flame treated as well. The intensity of treatment should be be chosen so that the surface tension of the film is generally about 45 mN / m.  

The film can also be coated to set further properties. Typical coatings are adhesion-promoting, antistatic, slip-improving or layers with an adhesive effect. It makes sense to add these additional layers over in-line coating by means of aqueous dispersions before transverse stretching on the film to apply.

The particular advantage of the film according to the invention is expressed by a high level Whiteness, due to a high opacity in combination with at least one high-gloss surface and high UV stability. The 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%. The gloss of the invention The film is at least on one side more than 100, preferably more than 120 and particularly preferably more than 130 at a measuring angle of 20 ° (DIN 67 530).

Another advantage of the invention is that this is in the manufacture of the film Regenerate accumulating in a concentration of 10 to 70 wt .-%, based on the total weight of the film, can be used again without the physical properties of the film are significantly affected. In particular, by the regenerate (essentially from polyester raw material and Cycloolefin copolymers (COC), the film is not undefined in color changed what is the case with the films according to the prior art. It is preferred that the high-gloss top layer remains regenerate-free.

In addition, another advantage of the invention is that the Manufacturing costs of the film according to the invention are comparable to conventional ones transparent films according to the state of the art. The other processing and Properties relevant to the use of the film according to the invention remain in the essentially unchanged or even improved.  

In addition to an application for. The film is suitable, for example, in trade fair construction and for trade fair articles excellent for packaging light and / or air sensitive food and Luxury goods. It is also excellent for industrial use Area, e.g. B. in the manufacture of stamping foils or as a label film, suitable. In addition, the film is of course particularly suitable for imaging papers, Print sheets, magnetic recording cards and for applications in Outside, to name just a few possible applications.

The processing and winding behavior of the film, especially on high-speed machines (winders, metallizers, printing and laminating machines) very good. The coefficient of friction is a measure of the processing behavior the film that is less than 0.6. The winding behavior is next to a good one Thickness profile, excellent flatness and low coefficient of friction decisively influenced by the roughness of the film. It has been found that the winding of the film according to the invention is particularly good when under Retaining the other properties mean roughness in a range from 50 to 250 nm. The roughness can a. by varying the COC concentration of the Cover layer thickness, possibly the cover layer formulation, and the process parameters for Manufacturing process vary in the specified range.

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

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

SV value (standard viscosity)

The standard viscosity SV (DCE) is based on DIN 53 728 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

The friction was determined in accordance with 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 according to 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 filters. A barium sulfate compact (DIN  5033, part 9) is used. A detailed description is e.g. B. in Hansl Loos "Color measurement", Verlag Beruf und Schule, Itzehoe (1989).

Translucency

The light transmittance is measured in accordance with ASTM-D 1033-77.

shine

The gloss was determined in accordance with DIN 67 530 at a measuring angle of 20 °. Measured was the reflector value as an optical parameter for the surface of a film. A 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

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). The device DSC 1090 from DuPont was used. The heating rate was 20 K / min and the initial weight was about 12 mg. The glass transition T _{g 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 step was observed in the thermogram when it was first heated.

Weathering (both sides), UV stability

The UV stability is tested according to the test specification ISO 4892 as follows:
Test device: Atlas Ci 65 Weather Ometer
Test conditions: ISO 4892, ie artificial weathering
Irradiation time: 1000 hours (per side)
Irradiation: 0.5 W / m ² , 340 nm
Temperature: 63 ° C
Relative humidity: 50%
Xenon lamp: inner and outer filter made of borosilicate
Irradiation cycles: 102 minutes of UV light, then 18 minutes of UV light with water spraying the samples, then again 102 minutes of UV light, etc.

The following examples serve to explain the invention in more detail: are co-extruded, multilayer films.

example 1

According to the coextrusion technology, a 23 µm thick multilayer film with the layer sequence ABA is produced, where B is the base layer and A the cover layers. The base layer B is 21 µm thick and the two cover layers which cover the base layer are each 1 µm thick. Polyethylene terephthalate chips (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, Germany ®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 170 ° C also fed to the extruder for the base layer B. The proportion of the cycloolefin copolymer (COC) in the base layer was 10% by weight. In addition, 1.0% by weight of the UV stabilizer 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5- (hexyl) oxyphenol (®Tinuvin 1577 from Ciba-Geigy , Basel, Switzerland) via masterbatch technology (Masterbatch 2) added. Tinuvin 1577 has a melting point of 149 ° C and is thermally stable up to approx. 330 ° C.

The 1 µm thick cover layers contain 88% polyester (RT49, Kosa, Germany), 7% of a masterbatch 1, which in addition to polyester 10,000 ppm Contains silicon dioxide (®Sylobloc, Grace., Germany) and 5% of a masterbatch 2, which contains 20% by weight of ®Tinuvin 1577 (Ciba Geigy, Switzerland) in addition to polyester.

A white, opaque, UV-stabilized three-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:
85.0% by weight of polyethylene terephthalate homopolymer (RT49, Kosa, Germany)
10.0% by weight of cycloolefin copolymers (COC) from Ticona, ®Topas 6015
5.0% by weight of masterbatch 2 which, in addition to RT49 (Kosa, Germany), contains 20% by weight of ®Tinuvin 1577 (Ciba Geigy, Switzerland).

The manufacturing conditions in the individual process steps were:

Extrusion

Base and top layer temperatures 280 ° C Pull roller temperature 30 ° C

Longitudinal extension

temperature 80-125 ° C Longitudinal stretch ratio 4.2

Transverse stretching

temperature 80-135 ° C Cross stretch ratio 4.0

Fixation

temperature 230 ° C Duration 3 s

The film had the required good properties and shows the desired handling and the desired processing behavior. The properties achieved in this way Films produced are summarized in Table 2.

Example 2

In comparison to Example 1, 50% by weight of regenerate was now added to the base layer. The concentration of the cycloolefin copolymer (COC) in the film thus produced was again 10% by weight. The concentration of the UV stabilizer was not changed compared to Example 1. The process parameters were not changed compared to Example 1. The yellowing of the film was observed visually. Table 2 shows that hardly any yellow discoloration of the film has become visible.
Base layer B, mixture of:
40.0% by weight of polyethylene terephthalate homopolymer (RT49, Kosa, Germany)
50.0% by weight of regrind (90% by weight of polyester + 10% by weight of Topas 6015)
5.0% by weight of cycloolefin copolymers (COC) from Ticona, ®Topas 6015
5.0% by weight of masterbatch 2 which, in addition to RT49 (Kosa, Germany), contains 20% by weight of ®Tinuvin 1577 (Ciba Geigy, Switzerland).
Cover layers: As in example 1.

Example 3

In comparison to Example 1, an ABA film with a thickness of 96 μm was now produced, the 92 μm thick base layer being covered by the 2 μm thick cover layers. The concentration of the cycloolefin copolymer (COC) in the base layer was 8% by weight and the concentration of the UV stabilizer was 0.4% by weight. The process parameters were not changed compared to Example 1. The yellowing of the film was observed visually. Table 2 shows that no yellowing of the film has become visible.
Base layer B (92 µm), mixture of:
90.0% by weight of polyethylene terephthalate homopolymer (RT49, Kosa, Germany)
8.0% by weight of cycloolefin copolymers (COC) from Ticona, ®Topas 6015
2.0% by weight of masterbatch 2 which, in addition to RT49 (Kosa, Germany), contains 20% by weight of ®Tinuvin 1577 (Ciba Geigy, Switzerland).
Cover layers: As in Example 1. However, the thickness of the cover layers is 2 µm.

Example 4

In comparison to Example 3, 50% by weight of regenerate was now added to the base layer. The concentration of the cycloolefin copolymer (COC) in the base layer was again 8% by weight and that of the UV stabilizer was 0.4% by weight. The process parameters were not changed compared to Example 1. The yellowing of the film was observed visually. Table 2 shows that hardly any yellow discoloration of the film has become visible.
Base layer B, mixture of:
45.0% by weight of polyethylene terephthalate homopolymer (RT49, Kosa, Germany)
50.0% by weight of self-regenerated material (90% by weight of polyester + 10% by weight of Topas 6015)
3.0% by weight of cycloolefin copolymers (COC) from Ticona, ®Topas 6015
2.0% by weight of masterbatch 2 which, in addition to RT49 (Kosa, Germany), contains 20% by weight of ®Tinuvin 1577 (Ciba Geigy, Switzerland).
Cover layers: As in example 3.

Comparative Example 1

Example 1 from DE-A 23 53 347 was reworked. In a modification of the example, an additional 50% by weight of regrind was processed. Table 2 shows that a clear yellowing of the film has become visible. In addition, the roughness of the film is too high for many applications and the gloss is too low for many applications.
Base layer B, mixture of:
47.5% by weight of polyethylene terephthalate homopolymer (RT49, Kosa, Germany)
50.0% by weight of regenerated material (95% by weight of polyester + 5% by weight of polypropylene)
2.5% by weight polypropylene.

Comparative Example 2

Example 1 from EP-A 0 300 060 was reworked. In a modification of the example, an additional 50% by weight of regrind was processed. Table 2 shows that a clear yellowing of the film has become visible. In addition, the roughness of the film is too high for many applications and the gloss is too low for many applications.
Base layer B, mixture of:
45.0% by weight of polyethylene terephthalate homopolymer (RT49, Kosa, Germany)
50.0% by weight of regenerated material (95% by weight of polyester + 5% by weight of polypropylene)
5.0 wt% polypropylene.

Comparative Example 3

Example 1 from EP-A 0 360 201 was reworked. In a modification of the example, an additional 50% by weight of regrind was processed. Table 2 shows that a clear yellowing of the film has become visible. In addition, the roughness of the film is too high for many applications and the gloss is too low for many applications.
Base layer B, mixture of:
40.0% by weight of polyethylene terephthalate homopolymer (RT49, Kosa, Germany)
50.0% by weight of regenerated material (95% by weight of polyester + 5% by weight of polypropylene)
10.0% by weight of polypropylene.

Comparative Example 4

Example 1 from DE-A 195 40 277 was reworked. In a modification of the example, an additional 50% by weight of regrind was processed. Table 2 shows that a clear yellowing of the film has become visible. In addition, the roughness of the film is too high for many applications and the gloss is too low for many applications. Base layer B, mixture of:
43.5% by weight of polyethylene terephthalate homopolymer (RT49, Kosa, Germany)
50.0% by weight of self-regenerated material (95% by weight of polyester + 5% by weight of polystyrene)
6.5% by weight of polystyrene.

All prepared according to Examples 1 to 4 and Comparative Examples 1 to 4 Sheets were weathered 1000 hours per side with Atlas Ci 65 Weather Ometer exposed.

The films produced according to Examples 1 to 4 according to the invention show Weathering hardly made any difference to unweathered foils. The mechanical Properties are unchanged compared to unweathered films.

In contrast, the films of Comparative Examples 1 to 4 showed after 1000 hours Weathering with Atlas Ci 65 Weather Ometer on the cracks and surfaces Signs of embrittlement. A precise property profile - especially that mechanical properties - could therefore no longer be measured on these films will. In addition, these films show a visually clearly visible yellowing.

Claims (21)

1. polyester film which has at least one base layer (B) and at least one cover layer, characterized in that at least the base layer contains a thermoplastic polyester, a cycloolefin copolymer (COC) and the film contains at least one UV stabilizer. 2. Polyester film according to claim 1, characterized in that it has a Layer structure A-B-C has, with the outer layers A and C the same or ver are different and at least one of the outer layers does not contain COC. 3. Polyester film according to claim 1 or 2, characterized in that it is white tere top and / or intermediate layers. 4. Polyester film according to one or more of claims 1 to 3, characterized characterized in that the thermoplastic polyester ethylene glycol and Terephthalic acid units or ethylene glycol and naphthalene-2,6-dicarbon contains acid units. 5. Polyester film according to one or more of claims 1 to 4, characterized characterized in that the thermoplastic polyester is poly ethylene terephthalate. 6. Polyester film according to one or more of claims 1 to 5, characterized characterized that the layers equipped with the COC the COC of 2 to 60% by weight, preferably 4 to 50% by weight, in particular 6 to 40% by weight,  each based on the weight of the layers equipped with it, contain. 7. polyester film according to one or more of claims 1 to 6, characterized characterized in that the COC polynorbornene, polytetracyclododecene, poly dimethyloctahydronaphthalene, polycyclopentene or poly (5-methyl) norbornene contains. 8. Polyester film according to one or more of claims 1 to 7, characterized characterized in that the COC as a copolymer ethylene, propylene and / or Contains butylene, preferably ethylene. 9. Polyester film according to one or more of claims 1 to 8, characterized characterized in that the COC is a norbornene / ethylene or a tetracyclo dodecene / ethylene copolymer. 10. Polyester film according to one or more of claims 1 to 9, characterized characterized that the COC has a glass transition temperature of 70 to 270 ° C, preferably 90 to 250 ° C, in particular from 110 to 220 ° C. 11. Polyester film according to one or more of claims 1 to 10, characterized characterized in that the film preferably has a degree of whiteness of greater than 70% greater than 75%, in particular greater than 80%. 12. Polyester film according to one or more of claims 1 to 11, characterized characterized in that the film has an opacity of greater than 55%, preferably greater 60%, in particular greater than 65%.   13. Polyester film according to one or more of claims 1 to 12, characterized characterized in that the film has a surface gloss of at least one side greater than 100, preferably greater than 120, in particular greater than 130. 14. Polyester film according to one or more of claims 1 to 13, characterized characterized in that as UV stabilizers 2-hydroxbenzotriazoles, Benzoxazi none or triazines or mixtures of these UV stabilizers or mixtures these UV stabilizers can be used with others. 15. Polyester film according to one or more of claims 1 to 14, characterized characterized in that 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5- as UV stabilizers (hexyl) oxyphenol or 2,2'-methylene-bis-6- (2H-benzotriazol-2-yl) -4- (1,1,3,3- tetramethylbutyl) phenol or 2,2 '- (1,4-phenylene) bis [4H-3,1-benzoxazin-4-one] or mixtures of these UV stabilizers or mixtures of these UV Stabilizers can be used with others. 16. Polyester film according to one or more of claims 1 to 15, characterized characterized in that the film contains the UV stabilizer from 0.01 to 5% by weight, based on the weight of the layers equipped with it. 17. Polyester film according to one or more of claims 1 to 16, characterized characterized in that the film also contains conventional additives such as antiblocking agents, Contains pigments, stabilizers or lubricants. 18. A method for producing a polyester film according to one or more of the Claims 1 to 17, characterized in that one for the manufacture the base and top layers and, if necessary, intermediate layers raw materials coextruded through extruders through a flat die and the The film obtained is biaxially stretched and heat-set and optionally further acts.   19. The method according to claim 18, characterized in that the UV Stabilizer is added using masterbatch technology. 20. Use of a polyester film according to one or more of the claims 1 to 18 for the production of moldings. 21. Shaped body produced using a polyester film according to a or more of claims 1 to 18.