DE102005058917A1 - 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 (whitening Pigment) in addition Anti-blocking agents. The invention further relates to a method for the Production of the film and its use.

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

The EP 0 605 130 B1 describes a multilayer, coextruded composite film having a thickness in the range of 30 to 400 microns. The film comprises a cloudy crystalline first polyester layer substantially impermeable to visible light, a density greater than 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%. 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. 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 and improved optical properties (gloss, Appearance), distinguished.

• a) die Basisschicht (B) ein weißfärbendes Pigment in einer Konzentration von 3 bis 15 Gew.-% enthält (bezogen auf das Gewicht der Basisschicht (B)) und
• 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 2 bis 8 µm enthält (Gew.-% Angaben bezogen auf das Gewicht der Deckschicht (A)).

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 wt .-% (based on the weight of the base layer (B)) and
• b) the cover 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 2 to 8 microns contains (wt .-% information based on the weight of the outer layer (A)).

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

The white, biaxially oriented film according to the present invention Invention is constructed at least two layers. It then exists from the base layer (B) and coated on this by coextrusion Cover layer (A), wherein both layers at least one white pigment and the cover layer (A) an additional, for the production of the film (Winding) beneficial Antiblock contains.

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 consists of the base layer (B), the cover layer (A) and a cover layer (C) opposite the cover layer (A) - layer structure ABC. Particularly preferred here is the symmetrical three-layer structure (ABA), in which the layers (A) and (C) are to be regarded as equal within the framework of production-related fluctuations. This film structure brings with regard to proper processing of the film the best conditions. Thus, for example, unsymmetrical film constructions such as (ABC) or in particular the abovementioned (AB) structure (cf. EP 0 605 130 B1 ) a certain curling, which is undesirable. The tendency to curl is mainly visible only when the lid punched out of the film web. The lid is in this case no longer flat on a flat surface, but bulges depending on the edges up or he is bulbous. In this case, for example, it may become stuck during further transport or during feeding into the sealing tool, which leads to an increase in the reject rate.

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 pigment, the film becomes particularly smooth and therefore more shiny, 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 polyesters may e.g. according to the known transesterification process respectively. It is based on dicarboxylic acid esters and diols, the with the usual Transesterification catalysts, such as zinc, calcium, lithium, magnesium and manganese salts, to be implemented. The intermediates will be then generally more common in the presence Polycondensation catalysts, such as antimony trioxide or titanium salts, polycondensed. The production can be just as good after the direct esterification process in the presence of polycondensation catalysts. there starting directly from the dicarboxylic acids and diols.

Cover layer (A)

For the cover layer (A), for a possible further cover layer (C) and for any further intermediate layers (D) and (E) present, preference is given to using the same polymers as previously indicated for the base layer (B). In particular, the base layer and the others contain Layers of identical polymers (polyester).

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, anatase-type titanium dioxide is used in the base layer and rutile-type titanium dioxide is used in the cover layer. 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 (preferably> 60) and to the desired low transparency (preferably <60 %) of the film, the base layer (B) should be highly filled. The particle concentration to achieve the desired low transparency is between 3 and 15% by weight, preferably between 3.5 and 14% by weight and particularly preferably between 4.0 and 13 wt .-%, based on the total weight of the layer containing it.

In a particular embodiment, suitable optical brighteners may be added to the base layer and / or the other layers to further increase the whiteness. 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-coloring 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 (e.g., sealed lidding film 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% by weight, 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 additionally used 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, wherein the average diameter (d ₅₀ value) in the range of preferably 2 to 8 microns.

In the preferred embodiment contains the cover layer (A) an antiblocking agent, wherein the average diameter in the range of 2.1 to 7μm 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.

Contains the topcoat (A) on the other hand, an antiblocking agent in which the mean diameter outside the preferred range, so this has a negative effect on the Winding, the processability and on the optical properties the slide off.

Contains the topcoat (A) an antiblocking agent in which the mean diameter is greater than 8μm is, so the optical properties and the winding of the film deteriorate. contains the outer layer (A) of the film, however, an antiblocking agent 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 equipped with the antiblocking agent. The concentration of antiblocking agents in the topcoat (A) and optionally also in the further outer layer (C) lies in the preferred embodiment between 0.05 and 1.8 wt .-% and in the particularly preferred embodiment between 0.1 and 1.6 wt .-% and depends essentially on the achieving 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 organic particles such as polystyrene or acrylate particles.

When Antiblocking agents can also mixtures of two or more different antiblocking agents or mixtures of antiblocking agents of the same composition, but different particle size can be selected if for the mixtures the conditions given above in terms of total amount and average particle diameter are satisfied. The antiblocking agents can the polyester of the cover layer in the respective advantageous concentrations, e.g. as a glycolic dispersion during 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 value, 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.

Especially Preferably, the base layer and the outer layers contain A and C in each case a white coloring Pigment, in particular titanium dioxide, identical in all layers is. As antiblocking agent in the outer layers is also preferred 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 in the range of 0.4 μm to 6 μm, preferably in the range of 0.5 to 5 microns and more preferably in the 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 proportion of preferably 50 to 95% of the total thickness.

production method

object The present invention is also a process for the preparation of the films according to the invention. It involves making a multilayer film from one Base layer (B) and top layer (s) (A) (and C) by coextrusion and shaping the melts into a flat melt film and biaxially stretching the film and thermosetting the stretched film.

First, the polymer or the polymer mixture of the individual layers is compressed in each case in an extruder and liquefied. The melts are simultaneously pressed over each other through a slot die, and the extruded multilayer film is peeled off on one or more take-off rolls while cooling and solidifying.

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. Before the transverse stretching, one or both surfaces of the film can be coated according to the known methods 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.

Preferably, after biaxial stretching, one or both surfaces of the film are additionally corona or flame treated by one of the known methods. The treatment intensity is generally above 50 mN / m ^2.

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 excellent for packaging 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.

at the production of the film is ensured that the regenerated material, the Z. B. is obtained as a blend in the film production, in a concentration of about 20 to 60 wt .-%, based on the total weight of Foil, re-extrusion can be fed without The physical properties of the film are appreciably negative to be influenced.

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

DIN

= Deutsches Institut für Normung

ASTM

= American Society for Testing and Materials

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 a 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 properly wound. There were no wrinkles, no slipping of the film web and no block pick as a result of blocking of film layers found.
• -: The machine roll is wound with errors. 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. For example, no curling, no sticking of the lid in the sealing tool, etc. was 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.

example 1

crisps of polyethylene terephthalate and polyethylene terephthalate containing Titanium dioxide as white pigment were dried and fed to the base layer extruder (B). Also were chips of polyethylene terephthalate, polyethylene terephthalate containing 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 direction, a white, three-layer film with ABA structure and a total thickness of 60 microns was prepared. The thickness of the two outer 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 showed the desired Behavior when removing the film from the cup.

Example 2

Compared to Example 1, only the composition of the outer layers (A) has been changed. All other parameters were retained. Covering layer (A), mixture of: 82.6% by weight Polyethylene terephthalate with an SV value of 800 5.4% 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 having an SV value of 12% 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) 800

Example 3

Compared to Example 1, the base layer (B) was changed. All other parameters were retained. Base layer (B): 35% by weight Polycondensation of the company Invista (DE) with 20 wt .-% anatase titanium dioxide (average particle diameter titanium dioxide about 0.32 microns) and 80 wt .-% polyethylene terephthalate with an SV value of 800 65% by weight Polyethylene terephthalate with an SV value of 800

Comparative Example 1

Compared to Example 2, only the composition of the outer layers (A) has been changed. The PET-MB with the antiblock agent in the cover layers was omitted. All other parameters were retained. Covering layer (A), mixture of: 94.6% by weight Polyethylene terephthalate with an SV value of 800 5.4% 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

Comparative Example 2

It was the example 1 of EP 0 605 130 B1 reworked. The film shows due to their layer structure a pronounced curl, which is very disadvantageous. In addition, the film has drawbacks in role presentation and processing performance.

Comparative Example 3

It Example 1 of EP-A-1 176 004 was followed. The foil has disadvantages in winding behavior, in role presentation and in processing behavior.

The Results of Examples / Comparative Examples are summarized in Table 2.

Claims (18)

A white, biaxially oriented polyester film which has 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 and 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 particle diameter (d ₅₀ ) of 2 to 8 microns. 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 antiblocking agent in the cover layer (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 cover layer (A) of the film a average roughness of 40 to 150 nm. Polyester film according to one or more of claims 1 to 13, characterized in that the friction value of the cover layer (A) is less than or equal to 0.4 to the cover layer (A). Polyester film according to one or more of claims 1 to 14, characterized in that the degree of whiteness of the film Berger greater than 60 is. Process for producing a polyester film according to one or more of the claims 1 to 15 comprising the steps a) producing a multilayered Film by coextrusion, b) biaxial stretching of the film and c) Thermofixing the stretched film. Use of a polyester film after one or several of the claims 1 to 15 as packaging material for food and beverages. Use of a polyester film according to claim 17 as a cover foil for Food containers, in particular yogurt cups.