DE102005058915A1 - Biaxially oriented polyester film useful for food-or-drink containers e.g. yoghurt pot comprises base layer of whitening pigment and outer layer of whitening pigment and antiblocking agent with specific median particle diameter - Google Patents

Abstract

A white, biaxially oriented polyester film comprises a base layer (B1) and at least one outer layer (A). The base layer (B1) comprises 3 - 15 wt.% of a whitening pigment, and the outer layer (A) comprises 2 - 15 wt.% of a whitening pigment and also 0.01 - 2 wt.% of an antiblocking agent whose median particle diameter (d50) is 2 - 8 mu m. An independent claim is included for production of the polyester film involving producing a multilayer film via co-extrusion; optionally, functionally coating or treating at least one surface of the film; biaxially stretching the film and heat-setting the stretched film.

Description

The The invention relates to a multilayer, white, biaxially oriented polyester film comprising a base layer (B) which is a thermoplastic Polyester and a white pigment contains and at least one outer layer (A). The cover layer (A) contains beside a white pigment additionally an anti-blocking agent. The film according to the invention has at least a functionalized surface, the z. B. good adhesion to other polymer or metal layers or printing inks. For this purpose, this surface is with an adhesion-promoting layer coated in-line. The invention further relates to a process for the production of the film and their use.

White, biaxial oriented polyester films, in particular for the cover application in yogurt cups, are known in the art.

EP-A-0 605 130 describes a multilayer, coextruded composite film having a thickness in the range of 30 to 400 μm. The film comprises a cloudy crystalline first polyester layer which is substantially impervious to visible light, has a density greater than or equal to 1.30 g / cm ³ , a thickness greater than or equal to 25 μm, and a deformation index greater than or equal to 2.5 % having. The deformation index is measured at a temperature of 200 ° C and under a pressure of 2 MPa. In addition, the film comprises a transparent crystalline second polyester layer which is substantially permeable to visible light and has a transmission optical density (TOD) of 0.005 to 0.2. Furthermore, in the context of the invention, a transparency of this layer is still present if less than 2% particles are present in it, which have a particle size of 0.1 to 10 microns. Preferably, the base layer of this film may be provided with an adhesion-promoting layer for printing inks and paints based on an acrylic resin. The film is characterized by a good opacity, but it has deficiencies in their production (no optimal role presentation), in their processing to cover and in particular in the optical properties.

The EP 1 176 004 A1 describes a white biaxially oriented, usually monolayer polyester film with a base layer (B), which is due to their special mechanical properties very well as a lidding film, in particular as a lidding film for yogurt cups, is suitable. The film is characterized in that the R value is less than or equal to 45 daN / mm ² and the e _max ratio is less than or equal to 2.5. By complying with these values, the film is less susceptible to delamination and exhibits good peel performance from the cup. The film is still characterized by good opacity, but it still has deficiencies in their production (no optimal role presentation) and in the optical properties.

task The present invention was therefore a white, biaxial oriented polyester film, especially for the yoghurt lid application, to provide, facing each other the polyester films known in the art by improved Properties, in particular by improved manufacturability (Especially by an improved winding), an improved Processing behavior, improved optical properties (gloss, Appearance) and good adhesion to colors, Adhesives, primers, metallic and ceramic layers.

• a) die Basisschicht (B) ein weißfärbendes Pigment in einer Konzentration von 3 bis 15 Gew.-% enthält (bezogen auf das Gewicht der Basisschicht (B)),
• b) die Deckschicht (A) ein weißfärbendes Pigment in einer Konzentration von 2 bis 15 Gew.-% enthält und zusätzlich 0,01 bis 2 Gew.-% eines Antiblockmittels mit einem mittleren Durchmesser (d₅₀-Wert) im Bereich von bevorzugt 2 bis 8 μm enthält (Gew.-% Angaben bezogen auf das Gewicht der Deckschicht (A)) und
• c) zumindest eine der beiden Folienoberflächen eine funktionsvermittelnde Schicht trägt oder funktionsvermittelnd behandelt ist.

The object is achieved by providing a white, coextruded, biaxially oriented polyester film with a base layer (B) and at least one cover layer (A), wherein

• a) the base layer (B) contains a white-coloring pigment in a concentration of 3 to 15% by weight (based on the weight of the base layer (B)),
• b) the top layer (A) contains a white-coloring pigment in a concentration of 2 to 15 wt .-% and additionally 0.01 to 2 wt .-% of an antiblocking agent having an average diameter (d ₅₀ value) in the range of preferably 2 contains up to 8 microns (wt .-% information based on the weight of the outer layer (A)) and
• c) at least one of the two film surfaces carries a function-promoting layer or is treated function-mediating.

These Layer is preferred as aqueous Dispersion applied to the film.

Under a whitewashing Pigment are also mixtures of various white-coloring pigments or mixtures from whitewashing Pigments of the same composition but different particle size understood.

The white, biaxially oriented film according to the present invention has at least two layers. It then consists of the base layer (B) and the cover layer (A) applied thereto by coextrusion, both layers containing at least one white pigment and the cover layer (A) having an additional layer Royal, for the production of the film (winding) conducive antiblocking agent contains. In addition, the film according to the invention has on at least one film surface a preferably adhesion-promoting layer, which is preferably applied to the film as an aqueous dispersion.

In the preferred embodiment is the slide three - or more than three layers, for example four or five layers, built up.

in the Case of the preferred three-layer embodiment, the film is made from the base layer (B), the cover layer (A) and one of the cover layer (A) opposite Cover layer (C) - layer structure ABC. Particularly preferred here is the symmetrical three-layered Construction (ABA), in which the layers (A) and (C) in the context of production-related Fluctuations are to be regarded as equal. This film structure brings in terms of proper processing of the film the best Conditions with it. For example, have unbalanced Foil structures, such as (ABC) or in particular the aforementioned (AB) structure (see EP-A-0 605 130) a specific Curling, which is undesirable. The curl becomes main only visible at the lid punched out of the film web. Of the Lid is no longer flat on a flat surface in this case on, but arches depending on the edges on top or he will be bulbous. In this case he can, for example during further transport or during feeding into the sealing tool hang stay, causing an increase the reject rate leads.

It has been found that with the preferred use of substantially TiO ₂ as a coloring pigment (white pigment), the film becomes less susceptible to tearing and delamination. The addition of the TiO ₂ preferably via the masterbatch technology has the advantage that color differences, for. B. by non-constant regenerative properties, can be easily corrected. When using TiO ₂ as the sole white pigment, the film is particularly smooth and thus shinier, but tends to block.

preferred Polymers for the base layer (B) and for the cover layers.

Base layer (B)

The base layer (B) of the film is preferably at least 80 wt .-%, in particular at least 85 wt .-% and particularly preferably at least 90 wt .-% of a thermoplastic polyester. Suitable for this are z. Example, polyester from ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), from ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene-2,6-naphthalate, PEN), from 1,4-bis-hydroxymethyl-cyclohexane and terephthalic acid = Poly (1,4-cyclohexanedimethylene terephthalate, PCDT)] and ethylene glycol, naphthalene-2,6-dicarboxylic acid and biphenyl-4,4'-dicarboxylic acid (= polyethylene-2,6-naphthalate bibenzoate, PENBB). Particular preference is given to polyesters which consist of at least 90 mol%, in particular at least 95 mol%, of ethylene glycol and terephthalic acid units or of ethylene glycol and naphthalene-2,6-dicarboxylic acid units. The remaining monomer units are then derived from other aliphatic, cycloaliphatic or aromatic diols or other dicarboxylic acids. The base layer preferably consists of PET. Suitable other aliphatic diols are, for example, diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO- (CH ₂ ) _n -OH, where n is 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 having up to 6 carbon atoms. Of the cycloaliphatic diols, mention may be made of cyclohexanediols (in particular cyclohexane-1,4-diol). 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 benzene dicarboxylic 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, mention may be made of cyclohexanedicarboxylic acids (in particular cyclohexane-1,4-dicarboxylic acid). 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 preparation of the polyester can z. B. carried out according to the known transesterification. It is based on dicarboxylic acid esters and diols, which are reacted with the usual transesterification catalysts, such as zinc, calcium, lithium, magnesium and manganese salts. The intermediates are then in the presence of commonly used polycondensation catalysts, such as antimony trioxide or titanium salts, poly condensed. The preparation can also be carried out by the direct esterification process in the presence of polycondensation catalysts. It starts directly from the dicarboxylic acids and diols.

Cover layer (A)

For the top layer (A), for any additional cover layer (C) and for any existing further intermediate layers (D) and (E) are preferred used the same polymers as previously given for the base layer (B) were. In particular, the base layer and the further layers contain identical polymers (polyesters).

white pigment

To achieve the abovementioned properties, in particular the desired whiteness of the film, the necessary white pigments are incorporated in the base layer (B) and at least in a cover layer (A), but possibly also in other existing layers. In question are titanium dioxide, barium sulfate, zinc sulfide or zinc oxide. Preferably, TiO _{2 is used} as the sole coloring pigment. It is added in the preferred embodiment as Extrusionsmasterbatch the original raw material. Typical ranges for the TiO ₂ concentration in the extrusion masterbatch are 20 to 70% by weight. The titanium dioxide may be of the rutile type as well as the anatase type or a mixture of rutile and anatase type. Preferably, rutile type titanium dioxide is used. The particle size of the titanium dioxide is generally between 0.05 and 0.5 .mu.m, preferably between 0.1 and 0.3 .mu.m. The film gets a brilliant white appearance through the incorporated pigments in the intended concentrations.

Around to the desired whiteness (> 60) and to the desired low transparency (<60 %) of the film, the base layer (B) should be highly filled. The amount of white pigment to achieve the desired low transparency is between 3 and 15 wt .-%, preferably between 3.5 and 14 wt .-% and particularly preferably between 4 and 13 wt .-%, based on the total weight of the layer containing them.

To further increase the whiteness, suitable optical brighteners can be added to the base layer and / or the other layers. Suitable optical brighteners are, for example Hostalux KS ^® from Clariant ^® or Eastobrite OB-1 from Eastman.

According to the invention, the cover layer contains (A), optionally also the further outer layer (C) and optionally further intermediate layers (D) and (E) at least one white-dyeing Pigment in a concentration of 2 to 15 wt .-%. The concentration is thereby preferably chosen that whiteness (according to Berger) the film is larger than 60 is. In the other case, the film is for the preferred application (eg sealed lidding foil on yogurt cup) from the optical Properties less suitable because they are too translucent can.

Contains the topcoat (A) a whitewashing Pigment system in which the concentration of the whitening pigment is less than or equal to is less than 2%, the brilliant white character of the film is lost and the subsequently applied print appears on this page the viewer faulty. contains the outer layer (A), however, a whitening pigment system, at the concentration of whitening Pigment is larger than 15%, so the danger is great that the white pigment chalking.

It has been found that the windability of the film and the roll presentation can be significantly improved if the cover layer (A) and optionally also the further cover layer (C) contains an antiblocking agent. It was found that, in particular, the average particle diameter d ₅₀ and the concentration of the antiblocking agent in the cover layer (A) are important for good windability and good processability of the film.

To improve the winding and processability of the film, at least the outer layer (A) contains an antiblocking agent in which the average diameter (d ₅₀ value) is in the range of preferably 2 to 8 μm.

In the preferred embodiment contains the cover layer (A) an antiblocking agent, wherein the average diameter in the range of 2.1 to 7 μm, and in the most preferred embodiment, the cover layer (A) an antiblocking agent in which the mean diameter is in the range from 2.2 to 6 μm lies.

On the other hand, if the outer layer (A) contains an antiblocking agent with an average outside diameter of the preferred range, this has a negative effect on the winding, the processability and on the optical properties of the film.

Contains the topcoat (A) an antiblocking agent in which the mean diameter is greater than 8 μm, so the optical properties and the winding of the film deteriorate. contains the outer layer (A) of the film, however, a pigment system in which the average diameter is smaller than 2 μm, the winding becomes the film and thus the roll dressing worse.

The Cover layer (A) and optionally also the further cover layer (C) are used to improve the winding behavior and processability comparatively high filled with the other pigments. The antiblocking agent can the polymers of the outer layers) in the respectively advantageous Concentrations z. B. as a glycolic dispersion during the Polycondensation or over Masterbatches in the extrusion, to be added. The concentration the antiblocking agent in the outer layer (A) and optionally also in the further outer layer (C) lies in the preferred embodiment between 0.05 and 1.8% by weight and in the most preferred embodiment between 0, 1 and 1.6 wt .-% and depends essentially on the to be achieved optical properties and the windability to be achieved the foil.

typical Antiblocking agents are inorganic and / or organic particles, for example, calcium carbonate, amorphous silica, talc, magnesium carbonate, Barium carbonate, calcium sulfate, lithium phosphate, calcium phosphate, Magnesium phosphate, alumina, LiF, calcium, barium, zinc or manganese salts of the dicarboxylic acids used, kaolin or crosslinked Polystyrene or acrylate particles.

When Antiblocking agents (further pigment) can also be mixtures of two or more different antiblocking agents or mixtures of antiblocking agents same composition, but different particle size can be selected. The particles can the individual layers in the respectively advantageous concentrations, z. B. as a glycolic dispersion during the polycondensation or over Masterbatches in the extrusion, to be added.

The Addition of antiblocking agent in the concentration of the invention in the topcoat (A) has the desired positive effect on the roughness and the friction coefficient the cover layer (A). To continue the processing behavior of the film to improve, should be in a favorable Case the concentration of the antiblocking agent is chosen so that for the roughness and for the coefficient of friction can be achieved.

Of the Coefficient of friction (COF) of the side (A) against itself should preferably less than or equal to 0.4. Otherwise, the winding behavior and the further processing of the film unsatisfactory.

The roughness of the cover layer (A), expressed as its R _a , should preferably be greater than or equal to 40 nm and less than or equal to 150 nm. Lower R _a values than 40 nm have negative effects on the winding and processing behavior of the film, and R _a values greater than 150 nm impair the optical properties (gloss) of the film. The coefficients of friction and roughness of the outer layer (A) refer to the untreated / uncoated top layer (A).

Especially Preferably, the base layer and the outer layers contain A and C in each case a white coloring Pigment, in particular titanium dioxide. As anti-blocking agent in the outer layers is preferably in each case an identical pigment, in particular silica, used.

at the film is the thickness of the cover layer (A) and / or (C) in general greater than 0.4 μm and is preferably in the range of 0.5 to 5 microns and more preferably in Range of 0.6 to 4 microns.

The Base layer (B) and the other layers z. B. (A) and (C) can in addition usual additives such as B. stabilizers included. They usually become the polymer or added to the polymer mixture before melting. As stabilizers For example, phosphorus compounds such as phosphoric acid or organophosphate used.

The Thickness of the polyester film according to the present invention can be within continue to vary borders. It is preferably 5 to 500 microns, in particular 8 to 400 μm and more preferably 10 to 300 microns, wherein the base layer has a Has a proportion of preferably 50 to 95% of the total thickness.

According to the invention, at least one film surface is functionally coated and / or be is. The contact angle of this surface to water is ≦ 64 °, preferably ≦ 62 ° and particularly preferably ≦ 60 °. In particular, this surface has an increased adhesion to other materials.

This is achieved by a corona or flame treatment, which usually follows the thermosetting of the film. Likewise, the treatment at other locations in the film production process, for example, after the longitudinal stretching, take place. As an alternative or in addition to the surface treatment described above, the film can be coated on one (or both) surface (s) with a functional coating, such that the coating on the finished film has a thickness of preferably 5 to 2000 nm, in particular 20 to 500 nm and particularly preferably 30 to 200 nm. The coating is preferably applied in-line, ie during the film production process, expediently before the transverse extension. The application by means of the "reverse gravure-roll coating" process, in which the coating can be applied extremely homogeneously in layer thicknesses of up to 200 nm, is also particularly preferred The application is likewise preferred by the Meyer-Rod method, which allows larger coating thicknesses The coatings are preferably applied as solutions, suspensions or dispersions, particularly preferably as aqueous solution, suspension or dispersion, The coatings mentioned give the film surface an additional function, for example, the film becomes sealable, printable, metallizable, sterilizable, antistatic or for example, they enhance the aroma barrier or allow adhesion to materials that would otherwise not adhere to the film surface Examples of fabrics / compositions that impart additional functionality are: acrylates, such as described in WO94 / 13476, Et hylvinylalkohole, PVDC, waterglass (Na ₂ SiO _4), hydrophilic polyesters (5-Na-sulfoisophthalsäurehaltiger PET / IPA polyesters as are described for example in EP-A-0144878, US-A-4252885 or EP-A-0296620) , Polyvinylacetate, as described for example in WO94 / 13481, polyurethanes, alkali metal or alkaline earth metal salts of C ₁₀ -C ₁₈ fatty acids, butadiene copolymers with acrylonitrile or methyl methacrylate, mathacrylic acid or esters thereof.

The mentioned substances / compositions are as dilute solution, emulsion or dispersion, preferably as aqueous solution, emulsion or dispersion on one or both surfaces of the film applied and then becomes the solvent volatilized. If the coatings are applied in-line before the transverse stretching, usually enough the temperature treatment in the transverse extension and subsequent heat fixation off to the solvent to evaporate and to dry the coating.

In a preferred embodiment of the invention, a copolyester coating is used to achieve better adhesion. The preferred coating copolyesters are prepared by polycondensation of (α) isophthalic acid, (β) an aliphatic dicarboxylic acid having the formula HOOC (CH ₂ ) _n COOH, wherein n is in the range of 1 to 11, (γ) a sulfomonomer containing an alkali metal sulfonate group on the aromatic part of an aromatic dicarboxylic acid and (δ) at least one aliphatic or cycloaliphatic alkylene glycol of about 2 to 11, preferably 2 to 8, more preferably 2 to 6 carbon atoms produced. The total acid equivalents present should correspond, on a molar basis, essentially to the total glycol equivalents present.

It has been shown that the proportionate shares the components (α), (β), (γ) and (δ) for the production the preferred Copolyesterbeschichtungen be used, crucial for the Achieve a coated film with satisfactory adhesion are. So should preferably z. B. isophthalic acid (component α) to at least about 65 mole percent as the acid component to be present. Preferably, the component (α) is pure isophthalic acid, which in an amount of about 70 to 95 mol% is present. For component (β), it holds that every acid with the formula mentioned brings satisfactory results, wherein Adipic acid, azelaic acid, sebacic acid, malonic acid, succinic acid, glutaric acid and Mixtures of these acids to be favoured. The target amount within the specified Range is preferably 1 to 20 mol%, based on the acid components of the copolyester, if the component (β) contained in the composition. The component (γ) of the preferred Copolyester coating forming monomers should preferably be in one Amount of at least 5 mol% may be included in this system the primer is dispersible with water. Especially preferred the amount of monomer of component (γ) is about 6.5 to 12 mol%. The glycol component (δ) is about stoichiometric Crowd present.

In a further preferred embodiment of the invention, an acrylate coating is used to achieve better adhesion. The acrylic copolymers preferably used consist in wesentli at least 50 wt .-% of one or more polymerized acrylic and / or methacrylic monomers and 1 to 15 wt .-% of a copolymerizable comonomer in the copolymerized state under the action of elevated temperature, optionally without the addition of a separate resinous Venetzungsmittels to training is capable of intermolecular crosslinks.

The acrylic component of the primer copolymers is preferred in an amount of 50 to 99 wt .-% present and is preferred from an ester of methacrylic acid, especially an alkyl ester whose alkyl group has up to ten carbon atoms Contains atoms, such as As the methyl, ethyl, n-propyl, isopropyl, n-butyl, Isobutyl, tertiary Butyl, hexyl, 2-ethylhexyl, heptyl and n-octyl groups. acrylic copolymers derived from a lower alkyl acrylate (C1 to C4), especially ethyl acrylate, together with a lower alkyl methacrylate a particularly good adhesion between the polyester roll and on it applied reprographic coatings and matt coatings. Adhesion promoter copolymers are very particularly preferred Alkyl acrylate, e.g. B.

ethyl acrylate or butyl acrylate, together with an alkyl methacrylate, e.g. Methyl methacrylate, in particular in equal molar proportions and in a total amount from 70 to 95 wt .-%, used. The acrylate comonomer such Acrylic / methacrylic combinations are preferably in one portion from 15 to 65 mole%, and preferably the methacrylate comonomer in a proportion which is generally greater by 5 to 20 mol% as the proportion of the acrylate comonomer. The methacrylate is preferred in a proportion of 35 to 85 mol% in the combination.

to increase the solvent resistance can optionally suitable for the formation of crosslinks comonomers be used, such. N-methylolacrylamide, N-methylolmethacrylamide and the corresponding ethers; Epoxy materials such. Glycidyl acrylate, Glycidyl methacrylate and allyl glycidyl ether; Containing carboxyl groups Monomers such. Crotonic acid, itaconic or acrylic acid; Anhydrides such. For example, maleic anhydride or itaconic anhydride; Hydroxyl-containing monomers such. B. allyl alcohol and Hydroxyethyl or hydroxypropyl acrylate or methacrylate; amides such as As acrylamide, methacrylamide or maleic acid amide and isocyanates such z. For example, vinyl isocyanate or allyl isocyanate. From the above crosslinking comonomers are N-methylolacrylamide and N-methylolmethacrylamide preferred, primarily because copolymer chains, containing one of these monomers, under the action of elevated temperatures for condensation with each other and thus for the formation of the desired intermolecular crosslinks are capable. The optionally desired Solvent resistance but the preferred acrylate coating can also by the presence a foreign crosslinking agent such. B. a melamine or urea-formaldehyde condensation product be achieved. Will not solvent resistance needed so can be dispensed with crosslinking agent.

The preferred acrylate coating can be applied to the film on one or both sides. However, it is also possible to provide only one side of the film with the coating according to the invention and to apply another coating to the opposite side. The coating formulation may contain known additives such as. As antistatic agents, wetting agents, surfactants, pH regulators, antioxidants, dyes, pigments, anti-blocking agents such. Colloidal SiO ₂ , etc. Normally, it is convenient to incorporate a surfactant to increase the ability of the aqueous coating to wet the polyester support sheet.

• 1. Eine Mischung aus einem aromatischen Copolyester (I-1) mit einer in Wasser dispergierbaren funktionellen Gruppe und einem Polyvinylalkohol (II-1),
• 2. Eine Mischung aus einem aromatischen Copolyester (I-2) mit einer in Wasser dispergierbaren funktionellen Gruppe und einem Polyglycerolpolyglycidylether (II-2), oder
• 3. Eine Mischung aus einem wässrigen Polyurethan (I-3) und einem Polyvinylalkohol (II-3).

In a further preferred embodiment of the invention, a water-soluble or hydrophilic coating is used to achieve better adhesion with hydrophilic layers or printing inks. The preferred hydrophilic coating can be achieved in three ways:

• 1. A mixture of an aromatic copolyester (I-1) having a water-dispersible functional group and a polyvinyl alcohol (II-1),
• 2. A mixture of an aromatic copolyester (I-2) having a water-dispersible functional group and a polyglycerol polyglycidyl ether (II-2), or
• 3. A mixture of an aqueous polyurethane (I-3) and a polyvinyl alcohol (II-3).

The aromatic copolyesters (I-1 and I-2) are selected from aromatic dicarboxylic acids such as terephthalic acid, 2,6-naphthalene dicarboxylic acid or isophthalic acid, optionally branched or fused aliphatic diols such as. Example, ethylene glycol, diethylene glycol, 2-methylpropanol or 2,2-dimethylpropanol and an ester-forming compound which carries a water-dispersible functional group. Examples of the functional groups are: hydroxyl, carboxyl, sulfonic acid or phosphoric acid groups or salts thereof. Preference is given to sulfonic acid and carboxylic acid salts. As the polyvinyl alcohol component (II-1 and II-3), any polyvinyl alcohol which is water-soluble and can be produced by normal polymerization techniques can be used. Generally, such polyvinyl alcohols are produced by the Versei made of polyvinyl acetates. The saponification degree should preferably be at least 70%, but better still 80-99.9%. As polyglycerol polyglycidyl ether (II-2) reaction products of glycerol and epichlorohydrin having molecular weights between about 250 and 1200 g / mol are used. The aqueous polyurethane (I-3) is made of a polyol such as glycol-terminated polyester, polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol or acrylic polyls, and a diisocyanate such as xylene diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, toluidine diisocyanate , Phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate and 1,5-naphthalene diisocyanate.

In a further preferred embodiment According to the invention, the adhesion-promoting layer consists of an amino-functional one Silane, which the film in addition steam-sterilized (a laminate of, for example, film, coating, Glue or coated metallic and ceramic layers does not delaminate) and above out for the direct extrusion coating with polymers receptive power.

As a general rule the aminofunctional silane is hydrolyzed in water and placed on a or more surfaces of the oriented polyester by conventional methods such as spraying or Roll coating applied. If the silane coating once is dried, the thus primed polyester is steam sterilizable and receptive for the direct extrusion with other polymers. The extrusion coating can be done with a conventional process.

In its broadest sense, the present invention is directed in this regard to an oriented polyester film having an adhesion-promoting layer that enables the film to be steam-sterilized and receptive to direct extrusion coating. The adhesion-promoting layer is described in its unhydrolyzed state by the following general formula:
The invention also encompasses a steam-sterilisable laminate consisting of an oriented polyester film, an adhesion-promoting layer and a polymer extruded directly thereon.

silanes are water-soluble after hydrolysis or can be dispersed in water, with amino-functional silanes especially good water-soluble are. It has been found that aminosilanes have good adhesion to paints, Adhesives, primers and metallic and ceramic coatings too have after steam sterilization and also good adhesion from extrusion coated polymers to polyester films without one additional impart adhesion-promoting layer or corona treatment. Of the Blend of polyester film with aminosilane coating can be regenerated become.

Aminofunctional silanes that can be used for the purpose of this invention are described in their unhydrolyzed form by the following formula: (R ¹ ) _a Si (R ² ) _b (R ³ ) _c , wherein R ^{1 contains} at least one amino group; R ² is a hydrolyzable group selected from short chain alkoxy groups of 1-8 carbon atoms, an acetoxy group or halides; and R ³ is an unreactive, nonhydrolyzable group, either a short chain alkyl group of 1-8 carbon atoms or a phenyl group; with (a) greater than or equal to 1; (b) greater than or equal to 1; (c) greater than or equal to 0 and a + b + c = 4.

Examples of aminosilanes conforming to this formula are N-2- (aminoethyl) -3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyltriethoxysilane, 4-aminobutyldimethylmethoxysilane, and p-aminophenyltrimethoxysilane. The preferred silane is N-2- (aminoethyl) -3-aminopropyltrimethoxysilane having the following formula: H ₂ N (CH ₂ ) ₂ NH (CH ₂ ) ₃ Si (OCH ₃ ) ₃ ,

The hydrolyzed aminosilane can in principle to every possible Time in the production of the film are applied, i. before or during of the stretching process, it can also be applied to the finished foil (eg) before be applied to the reel.

The adhesion promoting layer is prepared by mixing aminosilane with water, preferably in a range of 0.2-6% by weight. Optionally, a weak acid, such as. As acetic acid, are added to promote the hydrolysis. At least one of the hydrolyzable groups of the silane is hydrolyzed to a silanol group (SiOH). It is believed that the hydrolysis product of the aminosilane has a partially hydrolyzed cyclic structure wherein the amino group is likely to have ionic bonds to the Silicon part of the molecule forms. Thus, the term hydrolyzed used herein also refers to these partially hydrolyzed structures.

The coating according to the invention described above is described in detail in EP 0 359 017 B1 (Pages 3 to 5), to which reference is expressly made at this point. This document also provides information about other specific combinations of such hydrolyzable aminosilanes.

The preferred copolyester, acrylate, silane and hydrophilic coatings may further contain other known additives such as e.g. As antistatic agents, wetting agents, surfactants, pH regulators, antioxidants, dyes, pigments, antiblocking agents such. B. colloidal SiO _2, etc.

production method

• a) das Herstellen einer mehrschichtigen Folie aus einer Basisschicht (B) und Deckschichten) A (und C) durch Coextrusion und Ausformen der Schmelzen zu flachen Schmelzefilmen,
• b) Beschichten der Folie mit der funktionsvermittelnden Schicht (vorzugsweise zwischen dem ersten und dem zweiten Streckschritt) und/oder funktionsvermittelnde Behandlung der Folie und
• c) biaxiales Strecken der Folie und Thermofixieren der gestreckten Folie.

The present invention also provides a process for producing the films according to the invention. It includes

• a) the production of a multilayer film from a base layer (B) and cover layers) A (and C) by coextrusion and shaping of the melts into flat melt films,
• b) coating the film with the function-promoting layer (preferably between the first and the second stretching step) and / or function-promoting treatment of the film and
• c) biaxially stretching the film and thermosetting the stretched film.

First, will the polymer or the polymer mixture of the individual layers in each compressed an extruder and liquefied. The smelting will be simultaneously on top of each other through a slot die pressed, and the extruded multilayer film is on a or several take-off rolls, whereby it cools down and solidifies.

The Biaxial stretching is generally performed sequentially. there is preferably only in the longitudinal direction (i.e., in the machine direction, = MD direction) and then in Transverse direction (i.e., perpendicular to machine direction, = TD direction) stretched. The stretching in the longitudinal direction let yourself with the help of two different according to the desired stretch ratio fast running rollers. For cross-stretching you generally use a corresponding clip frame.

The temperature at which the biaxial orientation, in particular of PET, can generally be carried out may vary within a relatively wide range and depends on the desired properties of the film. The longitudinal stretching is generally carried out at about 80 to 140 ° C and the transverse extension at about 80 to 150 ° C. The longitudinal stretching ratio λ _MD is preferably in the range from 2.0: 1 to 5: 1. The transverse stretch ratio λ _TD is generally in the range of 2.5: 1 to 5.0: 1. Preferably, before the transverse stretching one or both surfaces of the film according to the invention according to the known methods coated in-line. The in-line coating can be used, for example, for improved adhesion of a metal layer or any later to be applied ink, but also for improving the antistatic behavior or the processing behavior.

at the subsequent heat-setting, the film is about 0.1 to 10 s long at a temperature of about 150 to 250 ° C. Subsequently, will the foil in usual Wrapped up way.

The inventive film shows a very good handling, very good winding properties and a very good processing behavior. It is characterized by a Excellent peeling behavior from the cup. The film of the invention is suitable as packaging material for food and beverages, especially as a cover sheet for Food containers such as B. yogurt cups. The film is also ideal for Packaging of moisture and / or air sensitive food and stimulants which are also contained in such cups can.

The Besides, film according to the present invention has excellent properties optical properties, showing excellent processing properties and an excellent role featuring. The film is suitable due to their very good handling and their very good processing properties especially for Processing on high-speed machines. Also owns the film has an excellent whiteness, which in addition to the film very attractive, promotional look.

In the production of the film is ensured that the regenerated z. B. obtained as a blend in the film production, in a concentration of about 20 to 60 wt .-%, based on the total weight the film, the extrusion can be fed again, without affecting the physical properties of the film significantly negatively affected.

The The table below (Table 1) summarizes the most important film properties together again.

To characterize the raw materials and the films, the following measuring methods were used:
DIN = German Institute for Standardization
ASTM = American Society for Testing and Materials

transparency

The Transparency is measured according to ASTM-D 1003-00.

roughness

The arithmetic mean roughness R _a was determined according to DIN 4762.

whiteness

The degree of whiteness is determined by Berger, with more than 20 layers of film usually being stacked on top of each other. The whiteness is determined with the aid of the ELREPHO electric remission photometer from Zeiss, Oberkochem (DE), standard illuminant C, 2 ° normal observer. The whiteness WG is called WG = RY + 3RZ - 3RX where RX, RY, RZ are respective reflection factors when using an X, Y, Z color measurement filter. As white standard, a compact of barium sulfate (DIN 5033, Part 9) is used. A detailed description is z. B. in Hans Loos, color measurement, publishing profession and school, Itzehoe (1989) described.

SV value (standard viscosity)

The standard viscosity SV (DCE) is measured, based on DIN 53726, at 25 ° C. in dichloroacetic acid. The intrinsic viscosity (IV) is calculated from the standard viscosity as follows IV [η] = 6.907 x 10 -4 SV (DCE) + 0.063096 [dl / g]

friction

The Friction was determined according to DIN 53 375. The sliding friction coefficient was Measured 14 days after production.

shine

Of the Gloss was determined according to DIN 67 530. The reflector value was measured as an optical parameter for the surface of a Foil. Based on standards ASTM-D 523-78 and ISO 2813 the angle of incidence is set at 20 °. A light beam hits below the set angle of incidence the flat test surface and is reflected or scattered by this. The on the photoelectronic receiver striking light rays are called proportional electric Size displayed. The measured value is dimensionless.

Measurement of the mean diameter d ₅₀

The determination of the mean diameter d ₅₀ was carried out by laser on a Malvern Master Sizer according to the standard method (other measuring devices are for example Horiba LA 500 or Sympathec Helos, which use the same measuring principle). The samples were placed in a cuvette with water and then placed in the meter. The measuring process is automatic and includes the mathematical determination of the d ₅₀ value.

By definition, the d ₅₀ value is determined from the (relative) cumulative curve of the particle size distribution: the point of intersection of the 50% ordinate value with the cumulative curve immediately gives the desired d ₅₀ value on the abscissa axis. How to understand this will be in 1 clarified in more detail.

Winding behavior of the film

+:

Die Maschinenrolle ist einwandfrei gewickelt. Es wurden keine Falten, kein Verschießen der Folienbahn und keine Blockpickel infolge von Verblockung von Folienlagen festgestellt.

-:

Die Maschinenrolle ist fehlerbehaftet gewickelt. Es wurde mindestens einer der folgenden Fehler beobachtet: Falten, Verschießen der Folienbahn, Blockpickel infolge von Verblockung von Folienlagen.

The winding behavior of the film was assessed visually when winding the machine roll directly after the biaxial orientation.

+:

The machine roll is wound properly. There were no wrinkles, no film sheet slippage and no block picks due to blocking of film layers.

-:

The machine roll is wound with an error. At least one of the following defects has been observed: wrinkles, film sheet slippage, block picks due to blocking of film layers.

roll formation

+:

Die Kundenrolle ist einwandfrei gewickelt. Es wurden keine Falten, keine Rillen in der Folienbahn und keine Blockpickel infolge von Verblockung von Folienlagen festgestellt.

-:

Die Kundenrolle ist fehlerbehaftet gewickelt. Es wurde mindestens einer der folgenden Fehler beobachtet: Falten, Rillen in der Folienbahn, Blockpickel infolge von Verblockung von Folienlagen.

The role presentation was judged visually after packaging the machine roll to narrower customer roles.

+:

The customer role is perfectly wound. No wrinkles, no grooves in the film web and no block picks due to blocking of film layers were found.

-:

The customer role is wrapped with errors. At least one of the following defects was observed: wrinkles, grooves in the film web, block picks due to blocking of film layers.

processing behavior the foil

+:

Das Verarbeitungsverhalten der Folie ist einwandfrei. Es wurde z. B. kein Curling, kein hängen bleiben des Deckels im Siegelwerkzeug, etc. festgestellt.

-:

Das Verarbeitungsverhalten der Folie ist fehlerbehaftet. Es wurde mindestens einer der folgenden Fehler beobachtet: Curling, hängen bleiben des Deckels im Siegelwerkzeug.

The processing behavior of the film was visually evaluated in the manufacture of lids.

+:

The processing behavior of the film is flawless. It was z. B. no curling, no hanging of the lid in the sealing tool, etc. found.

-:

The processing behavior of the film is faulty. At least one of the following defects was observed: curling, hanging the lid in the sealing tool.

Contact angle with water

The polarity the surface was determined by a peripheral angle measurement of distilled water. The measurement took place at 23 ° C. and 50% r. F. held. By means of a Dosing syringe becomes a 1-2 mm wide drop of distilled water applied to the film surface. Because the measurement is due to heat the lighting (evaporation), charging or spreading behavior is time-dependent, the needle remains in the drop, so that the drop during the Measurement carefully enlarged and then immediately read the contact angle by means of a goniometer eyepiece becomes. (Measurement of the progression angle). From 5 measurements becomes the Mean value formed.

example 1

polyethylene terephthalate, Polyethylene terephthalate containing titanium dioxide as white pigment were dried and fed to the base layer extruder (B). Also were polyethylene terephthalate containing polyethylene terephthalate Titanium dioxide as white pigment and polyethylene terephthalate containing an antiblocking agent and the extruder for the two (same) outer layers (A) supplied.

Then, by coextrusion and subsequent stepwise orientation in the longitudinal and transverse directions, fixation and subsequent corona treatment (2 kW / m ² ) of one of the two outer layers a white, three-layer film with ABA structure and a total thickness of 60 microns was prepared. The thickness of the two cover layers was 2 μm in each case.

Base layer (B): 86% by weight Polyethylene terephthalate with an SV value of 800 14% by weight Masterbatch from Sukano (Schindellegi, CH) with 50 wt .-% rutile titanium dioxide (average particle diameter titanium dioxide about 0.3 microns) and 50 wt .-% polyethylene terephthalate with an SV value of 800

Covering layer (A), mixture of: 70% by weight Polyethylene terephthalate with an SV value of 800 14% by weight Masterbatch from Sukano (Schindellegi, CH) with 50 wt .-% rutile titanium dioxide (average particle diameter titanium dioxide about 0.3 microns) and 50 wt .-% polyethylene terephthalate with an SV value of 800 16% by weight Masterbatch of 97.5 wt .-% polyethylene terephthalate (SV value of 800) and 2.5 wt .-% Sylobloc ^® 44 H (synthetic SiO ₂ from Grace, diameter = 2.5 microns)

The production conditions in the individual process steps were:

It was a film with a very good look, with very good winding behavior, a very good winding quality and a very good processing behavior. The foil had the desired improved adhesion, the contact angle to water was 63.7 °. The foil continued to show the desired Behavior when removing the film from the cup.

Example 2

The film was made as in Example 1, but without corona treatment after biaxial stretching. A 4.5% solids by weight solids consisting of a copolymer of 60% by weight of methyl methacrylate, 35% by weight of ethyl acrylate, and 5% by weight of N-methylolacrylamide and a surfactant was used as a primer coating according to the following procedure applied to the C layer of the polyester film: The elongated film was corona treated (8 kW / m ² ) and then coated by reversographic gravure coating on the A layer with the above-described latex.

The biaxially stretched film was heat-set at 230 ° C. The dry weight of the coating was about 0.035 g / m ² at a coating thickness of about 40 nm.

The desirable and properties of the invention of the film are as in Example 1. The contact angle to water was 63.8 °. The Film was tested for its reprographic adhesion and gave good adhesion.

Example 3

The film was prepared as in Example 2. An aqueous dispersion having 6% by weight of copolyester consisting of 95% by mole of isophthalate, 5% by mole of Na-5 sulfoisophthalate and 100% by mole of ethylene glycol, and 0.56% by weight of colloidal SiO ₂ became as follows Method applied as a coating on the polyester film: The elongated film was coated by reversographic gravure coating on the A layer with the copolyester dispersion described above.

The biaxially stretched film was heat-set at 230 ° C. The dry weight of the coating was about 0.030 g / m ² at a coating thickness of about 35 nm.

The Seal and peel properties of the film were as in Example 1. The contact angle to water was 57 °.

Two Samples of the one-side coated film thus prepared were placed in a vacuum lab coater, in such a way that at one coated and the other uncoated Side was metallized. The vacuum chamber was down to under 10 Torr evacuated, and from a tungsten filament were about 500 AC Aluminum on both the uncoated side and the coated one Sample vapor-deposited.

Within every 30 seconds after removal from the vacuum chamber, each sample was tested for "metal abrasion". To this The purpose was on each sample tested with a cotton fleece with the same number of strokes and about the same pressure slightly over the metal surface rubbed. The "abrasion behavior" of the coated Side of the film was rated as good.

Example 4

The film was made as in Example 1, but without corona treatment after biaxial stretching. An aqueous dispersion with 7 wt .-% solids, consisting of 50 wt .-% of the aromatic copolyester Al (copolyester containing 90 mol% terephthalate, 10 mol% 5-Natriumsulfoisophtalat, 80 mol% of ethylene glycol and 20 mol% diethylene glycol ), 45 wt .-% of the water-dispersible polymer B2 (polyvinyl alcohol having a saponification degree of 88 mol% and a polymerization degree of 1700) and 5 wt .-% of inert particles D1 (colloidal SiO ₂ having a particle diameter of 0.05 microns) was coated on a polyester film according to the following procedure:
The elongated film was coated by reverse gravure coating with the copolyester dispersion described above. The dry weight of the coating was about 0.040 g / m ² at a coating thickness of about 0.05 μm.

The Seal and peel properties of the film were as in Example 1. The contact angle to water was 50.0 °.

to Evaluation of the adhesion promoter effect of the coating became a aqueous Polyvinyl acetal solution (S-Lec KX-1, manufactured by Sekisui Chemical Co., Ltd .; as KX-1) applied to the coated film and dried. The coating solution had a concentration of 8% by weight and was applied with an applicator of Baker type applied with a layer thickness of 127 microns. The coated one Foil became instantaneous for drying at 100 ° C for Put in an oven for 4 minutes. A black square (area: 12 × 12 cm) was dried on the surface of an ink-jet printer (BJC-600J, Canon Inc.) KX-1 coating printed and for 12 hours at 23 ° C and 50% relative humidity below Air dried. An adhesive tape (cello-tape, Nichiban Inc.) 18 mm) was glued to the printed surface and peeled off quickly. The degree of the printed surface separated with the adhesive tape became visual certainly. The coated film showed good adhesion properties.

Comparative Example 1

A Film as in Example 1 was produced, but without corona treatment. The contact angle to water was 65.5 °, and the adhesion to metal was noticeably worse.

The Results are summarized in Table 2.

Claims (22)

White, biaxially oriented polyester film comprising a base layer (B) and at least one cover layer (A), wherein a) the base layer (B) contains a white-coloring pigment in a concentration of 3 to 15 wt .-%, b) the top layer (A) a white-coloring pigment in a concentration of 2 to 15 wt .-% and additionally 0.01 to 2 wt .-% of an antiblocking agent having a mean particle diameter (d ₅₀ ) of 2 to 8 microns and c) at least one film surface carries a function-promoting layer or is function-mediated treatment. Polyester film according to claim 1, characterized that the whitening pigment Titanium dioxide is. Polyester film according to claim 1 or 2, characterized that the whitening pigment in the base layer (B) and in the cover layer (A) is titanium dioxide. Polyester film according to claim 2 or 3, characterized the titanium dioxide in the base layer is of the anatase type. Polyester film according to claim 2, 3 or 4, characterized characterized in that the titanium dioxide in the rutile-type topcoat is. Polyester film according to one or more of claims 1 to 5, characterized in that the additional pigment (antiblocking agent) in the topcoat (A) is silica. Polyester film according to one or more of claims 1 to 6, characterized in that the base layer (B) to at least 80 wt .-% consists of a thermoplastic polyester. Polyester film according to one or more of claims 1 to 7, characterized in that the thermoplastic polyester of Base Layer (B) Units of ethylene glycol and terephthalic acid and / or units of ethylene glycol and naphthalene-2,6-dicarboxylic acid. Polyester film according to one or more of claims 1 to 8, characterized in that the thermoplastic polyester of Base layer (B) is polyethylene terephthalate. Polyester film according to one or more of claims 1 to 9, characterized in that the thermoplastic polyester of Base layer (B) and the thermoplastic polyester of the cover layer (A) are identical. Polyester film according to one or more of claims 1 to 10, characterized in that the polyester film has an ABC layer structure has, wherein the outer layers (A) and (C) are the same or different. Polyester film according to one or more of claims 1 to 11, characterized in that the polyester film has an ABA layer structure Has. Polyester film according to one or more of claims 1 to 12, characterized in that the whiteness of the film Berger greater than 60 is. Polyester film according to one or more of claims 1 to 13, characterized in that at least one foil surface corona treated is. Polyesterfolic according to one or more of claims 1 to 14, characterized in that the function-promoting layer an adhesion-promoting layer. Polyester film according to one or more of claims 1 to 15, characterized in that the adhesion-promoting layer a Contains copolyester. Polyester film according to one or more of claims 1 to 16, characterized in that the adhesion-promoting layer is a Acrylate layer is. Polyester film according to one or more of claims 1 to 17, characterized in that the adhesion-promoting layer is a hydrophilic layer. Polyester film according to one or more of claims 1 to 18, characterized in that the adhesion-promoting layer a Contact angle to water of less than or equal to 64 °. Process for producing a polyester film according to one or more of the claims 1 to 19 comprising the steps a) producing a multilayered Film by coextrusion, b) function-promoting coating or treating a film surface, c) baxial stretching the foil and d) thermosetting the stretched film. Use of a polyester film after one or several of the claims 1 to 19 as packaging material for food and beverages. Use of a polyester film according to claim 21 as a cover foil for Food containers, in particular yogurt cups.