White, vapour sterilisable, extrusion coatable polyester film

The invention relates to the use of a single-layer or multilayer, white, biaxially oriented polyester film containing a thermoplastic polyester, which is coated on at least one side with a water-soluble adhesion-promoting layer made of a hydrolyzed amino-functional silane, as a steam-sterilizable film.

A known application of white colored, biaxially oriented polyester films are e.g. B. Lid for yogurt cups. They are used there as an alternative to aluminum foils. Such lids are printed and embossed on the outside and provided on the inside with a varnish or hot melt with which the lids are glued to the cups. To improve the shelf life of the yogurt, both the cup and the lid must ensure sufficient light protection. This is usually done by coloring the lid with suitable pigments. In addition, it is desirable for special applications if the complete lid or the complete system can be sterilized, or at least steam-sterilized. Another requirement for the lidding film is that when it is pulled off the cup, it neither delaminates nor tears in and out. The film obtains the properties required for this from the biaxial stretching and from a correspondingly large thickness. The mechanical properties of the lid (rigidity, puncture resistance, tear resistance) improve disproportionately with the thickness of the film. Polyester films with a thickness of 30 to 90 µm have proven their worth for lidding on yoghurt. The thickness of the film cannot be arbitrarily large, since with the thickness the material costs increase and the sealing cycle times decrease, which is undesirable from an economic point of view. There is a trend towards lower thicknesses.

Lids made from polyester films generally have a number of advantages:<ul id="ul0001" list-style="bullet" compact="compact"><li>The lid has a smooth, high-gloss surface, which guarantees excellent color rendering and thus looks very appealing.</li><li>The film has up to 700% higher puncture resistance than conventional material, which results in significantly higher product protection.</li><li>The lid is easy to open without fragments of the lid getting stuck on the cup, as is the case with conventional materials, e.g. B. aluminum foils is observed. This property is particularly appreciated by the consumer.</li><li>The complete separation of the cup and lid is of great advantage for the recyclability of the two materials. The lidding film is made of thermoplastic polyester, which is excellently recyclable. The product is therefore environmentally friendly.</li><li>Furthermore, the polyester film for the lid application is extremely easy to process due to its high rigidity and good sliding properties.</li><li>The lid is also completely metal-free. This guarantees a very high level of security in metal detection, which is increasingly used in the production of food. With this method, the proportion of metallic components that may be contained in the filling material can be determined with high accuracy.</li></ul>

Attempts to provide a conventional transparent film with the desired combination of properties by adding pigment failed. The film delaminated when pulled off the yogurt cup.

Processors use certain criteria for the behavior of the films when they are processed into yoghurt cups. The test variables commonly used in the production of lidding films are the R value and the e_Max-Relationship. The R value can be given as a measure of the orientation and is measured directly after the film has been produced in the middle of the film web. The e_Max-Ration describes the orientation distribution over the web width (the so-called bow) and is also measured during the production of the film, but at discrete intervals over the entire width of the film web (see measurement methods). In the case of transparent films (not the present white films), the values ​​for the R value are in a range from 45 to 48 and for the e_Max- Ratio in a range from 2.6 to 2.8.

Studies have shown that these values ​​cannot be transferred from transparent films to the existing white films. If the stated values ​​for white film are observed, this generally leads to delamination of the film. The film delaminates itself, it tears in the direction of the thickness, the tear destroys the film and the film continues to tear.

The properties mentioned above are not achieved in their entirety by the films known from the prior art.

For example, the <patcit id="pcit0001" dnum="EP0605130A"><text>EP-A-0 605 130</text></patcit> a multilayer film for lid use, which has at least one opaque layer and at least one transparent layer of crystalline polyester. Furthermore, the film is described by a deformation index that should be greater than or equal to 2.5%. In addition, the film can be coated with certain substances, which improves the adhesion to printing inks and / or inks. About the R values ​​and the e_Max- The ratio of the film does not provide any information. One after the<patcit id="pcit0002" dnum="EP0605130A"><text>EP-A-0 605 130</text></patcit> (Example 1, longitudinal stretching temperature approx. 80 ° C., stretching ratio in the longitudinal stretching 3.3) delaminated re-film, it also showed poor processing behavior, since the film curled out to the lids after punching.

From an economic point of view, it is necessary to permanently reduce the costs for the production of the cover film. An important lever for this is the thickness of the film. A lower thickness of the lid goes hand in hand with a reduction in material costs and leads to higher filling speeds due to the lower sealing cycle times. However, the thickness of the lid cannot be reduced arbitrarily, since this leads to processing and handling problems. Lids made of polyester film that are too thin tend to tear and delaminate. Product safety and the advantage of 100% separation of the lid and cup are no longer guaranteed. The risk of tearing and delamination of the lid increases, the more pigments and the larger pigments are incorporated into the polyester film. Pigments, especially coarser ones, form weak points in the film where the film begins to be destroyed when it is pulled off the cup.

The <patcit id="pcit0003" dnum="EP1176004A"><text>EP-A-1 176 004</text></patcit> describes polyester films with R values ​​less than 43 N / mm² and a_Max- have a ratio of less than 2.5. The films can also be coated. However, a coating with a steam sterilization-resistant layer made of a hydrolyzed amino-functional silane is not described.

The object of the invention is therefore to provide a white, biaxially oriented polyester film, in particular for lid use, which is distinguished from the polyester films established on the market by improved properties and does not have the disadvantages of the prior art.

The object is achieved by using a single-layer or multilayer, at least one base layer B, white, biaxially oriented polyester film containing a thermoplastic polyester which is coated on at least one side with an adhesion-promoting hydrolyzed amino-functional silane and whose R value is less than 43 N / mm² is and their e_MaxRatio is less than 2.5, as a steam sterilizable film.

Surprisingly, it has been shown that the desired combination of good adhesion to paints, primers, adhesives, metallic and ceramic layers and sterilizability is achieved by using an adhesion-promoting layer of a hydrolyzed amino-functional silane which is applied to the film as an aqueous dispersion .

The film has the following combination of properties:<ul id="ul0002" list-style="bullet" compact="compact"><li>economic producibility, good windability, good processability;</li><li>good adhesion of at least one side of the film to paints, adhesives, sealing waxes;</li><li>steam sterilizable, ie it has good adhesion to paints, adhesives, primers, metallic and ceramic layers even after steam sterilization;</li><li>very good peeling behavior from the cup, no delamination, no tearing and tearing;</li><li>good optical properties, especially when adding self-regenerated material in film production, and good light protection properties.</li></ul>

By applying metallic or ceramic layers to the film, for example, the barrier effect of the lid against the permeability of oxygen, aroma or water vapor can be significantly improved.

A method is also described for improving the adhesion of the film to paints, adhesives, primers and to metallic and ceramic layers after steam sterilization. Furthermore, a method is described with which the film is made ready for absorption by the adhesion-promoting coating for a subsequent extrusion coating with other polymers. However, it does not lose its other advantageous properties, for example good optics. This is an important point, especially for a possible use of self-regenerated material in the production of the film, which necessarily contains the coating material.

The film is usually constructed in one layer and then consists of the base layer B and the adhesion-promoting layer, which is applied to the film as a solution or as an aqueous dispersion. In addition, it can also be constructed in multiple layers. In this case, it has proven to be advantageous to make the layer structure of the film symmetrical. Advantageous embodiments of multilayer films are, for example, ABA or ACBCA, A being the outer cover layers, C the intermediate layers and B the base layer. In the case of multilayer films, the adhesion-promoting layer is always on the outside of the film.

The base layer B of the film consists of at least 80% by weight, preferably at least 85% by weight and in particular at least 90% by weight, of a thermoplastic polyester. Polyesters of ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), of ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene-2,6-naphthalate, PEN), of 1,4-bis-hydroxymethyl-cyclohexane and terephthalic acid are suitable for this [= Poly (1,4-cyclohexanedimethylene terephthalate, PCDT) and from ethylene glycol, naphthalene-2,6-dicarboxylic acid and biphenyl-4,4'-dicarboxylic acid (= polyethylene-2,6-naphthalate bibenzoate, PENBB). Particularly preferred are polyesters which consist of at least 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 come 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- (CH₂)_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) can be mentioned. Suitable other aromatic diols correspond, for example, to the formula HO-C₆H₄-XC₆H₄-OH. where X for -CH₂-, -C (CH₃)₂-, -C (CF₃)₂-, -O-, -S- or -SO₂- stands. In addition, bisphenols of the formula HO-C are also₆H₄-C₆H₄-OH well suited.

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 (C₃-C₁₉) Alkanedioic acids are particularly suitable, the alkane fraction being straight-chain or branched.

In addition to polyesters, the base layer B can contain other thermoplastic polymers, additives and pigments. Suitable polymers are, for example, aliphatic and aromatic polyamides, polyolefins and cyclic olefin copolymers (COC). Suitable additives and pigments are described below.

The polyester can be produced, for example, by the known transesterification process. The starting point is dicarboxylic acid esters and diols, which are reacted with the usual transesterification catalysts, such as zinc, calcium, lithium, magnesium and manganese salts. The intermediates are then polycondensed in the presence of generally customary polycondensation catalysts, such as antimony trioxide or titanium salts. The preparation can also be carried out by the direct esterification process in the presence of polycondensation catalysts. Here one starts directly from the dicarboxylic acids and the diols.

In principle, the same polymers as described above for the base layer B can be used for any cover layers A or for any intermediate layers C that are present.

The R-value of the film is determined directly after its production, the required samples being taken from the middle of the film web. The e_MaxRatio is also determined directly after the production of the film, but the test specimens are separated from the total width of the film web at defined intervals.

The film is characterized by a low R value. The R value is a measure of the orientation of the film and in the present case replaces the otherwise usual orientation dimensions Δn or Δp. These can only be measured with a transparent film, but not with the present white film.

The R-value of the film is measured in the middle of the film web at an angle of 45 ° to the machine direction (MD direction), one time to the right to the MD direction and the other time to the left to the MD direction (see measurement methods). This regulation takes into account the fact that with yoghurt lids the film is usually pulled off the cup at an angle of 45 ° to the machine direction.

The roll is used to manufacture the cover (printing, stamping). The roll direction (= web direction) of the film corresponds to the MD direction. The film web is printed in such a way that the covers to be punched out are either exactly in the MD direction or exactly in the TD direction (TD = 90 ° to MD). It follows that the pulling direction of the cover always coincides with the 45 ° angle to the MD direction. For this reason, it is necessary to determine the R value at 45 ° to the MD direction.

It was found that the smaller the R value of the film, the more favorable or less the tear and tear behavior of the lid. The tendency of the film to delaminate is then very slight. The R-value of the film is less than 43 N / mm², preferably less than 42 N / mm² and especially less than 40 N / mm². In contrast, in the other case (R value is greater than 43 N / mm²) the film is more susceptible to tearing and delamination. This disadvantage must then be compensated for by a considerably greater thickness of the film.

The film is next to it with a low e_Max- Ratio marked. The e_Max- Ratio is measured at defined intervals across the entire web width of the machine roll. This is done at an angle of 45 ° to the MD direction, one time to the right to the MD direction and the other time to the left to the MD direction (see measurement method). In the middle of the film sheeting is e_MaxRatio almost one and usually increases the closer you get to the edges of the film. The e_MaxRatio describes the properties of the film over the width of the roll, in particular the change in properties compared to the center of the film web. The lower the e., The better the application requirements_Max-Ration is, ie the more uniform the film properties across the width.

The e_MaxRatio of the film is less than 2.5, preferably less than 2.2 and particularly preferably less than 2.0. In the other case (e_MaxRatio is greater than 2.5) the film is more susceptible to tearing and delamination. This disadvantage must then also be made up for by a greater thickness of the film, which is uneconomical.

To achieve the aforementioned properties, in particular the desired degree of whiteness of the film, the necessary pigments are incorporated into the base layer B, but possibly also instead or in addition to existing other layers. For example, titanium dioxide, calcium carbonate, barium sulfate, zinc sulfide or zinc oxide are suitable. TiO is preferred₂ used as the sole coloring pigment. It is preferably added to the original raw material as an extrusion masterbatch (the titanium dioxide concentration here is significantly higher than in the biaxially oriented film). Typical values ​​for the TiO₂Concentration in the extrusion masterbatch is 50% by weight titanium dioxide. The titanium dioxide can be of the rutile type as well as the anatase type. Rutile-type titanium dioxide is preferably used. The grain size of the titanium dioxide is generally between 0.05 and 0.5 μm, preferably between 0.1 and 0.3 μm. The incorporated pigments give the film a brilliant white appearance. In order to achieve the desired whiteness (&gt; 60) and the desired low transparency (&lt;60%), the base layer should be filled up. The particle concentration to achieve the desired low transparency is above 3% by weight, but below 20% by weight, preferably above 4% by weight, but below 18% by weight and very particularly preferably above 5% by weight. %, but below 16% by weight, based on the total weight of the layer containing it.

It has been found that with the preferred use of essentially TiO₂. As a coloring pigment, the film becomes less susceptible to tearing and delamination. The addition of the TiO₂ preferably over the masterbatch technology has the advantage that color differences z. B. can be corrected relatively easily by non-constant regenerate properties. When using TiO₂ as the sole pigment, the film becomes particularly smooth and therefore more shiny, but may tend to block.

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 or ^®Eastobrite OB-1.

The base layer as well as existing further layers can additionally contain conventional additives such. B. contain stabilizers. They are usually added to the polymer or the polymer mixture before melting. For example, phosphorus compounds such as phosphoric acid or phosphoric acid esters are used as stabilizers.

The thickness of the polyester film can vary within wide limits. It is generally 10 to 120 μm, preferably 15 to 105 μm, in particular 20 to 80 μm, the base layer having a share of preferably 50 to 100% of the total thickness.

At least one side of the film is coated with an aqueous adhesion-promoting dispersion. The coating on the finished film has a thickness of 5 to 2000 nm, preferably 10 to 1000 nm, in particular 20 to 500 nm. The coating is applied in-line, ie during the film production process, advantageously before the transverse stretching. It is particularly preferred to apply the coating by means of the "reverse gravure-roll coating" method, in which the coatings can be applied extremely homogeneously. It is also preferred to apply the coating by means of the Meyer Rod process, with which greater coating thicknesses can be achieved.

This adhesion-promoting layer consists of an amino-functional silane, which makes the film steam-sterilisable (the laminate, e.g. made of film, coating, adhesive or applied metallic and ceramic layers, does not delaminate) and also makes it ready for direct extrusion coating with polymers.

The invention therefore also represents a steam-sterilizable laminate consisting of an oriented polyester film, an adhesion-promoting layer and a directly extruded polymer.

The adhesion-promoting layer, ie the silane used for this, has the following general formula in the unhydrolyzed state:         (R¹)_aSi (R²)_b(R³)_c, where R¹ is a functional group with at least one primary amino group. R² is a hydrolyzable group, for example a short-chain alkoxy group with 1-8 carbon atoms, an acetoxy group or a halide. R³ is an unreactive, non-hydrolyzable group, either a short chain alkyl group with 1-8 carbon atoms or a phenyl group; in the formula, (a) is greater than or equal to 1; (b) greater than or equal to 1; (c) greater than or equal to 0; where a + b + c = 4.

After hydrolysis, silanes are water-soluble or can be dispersed in water, with amino-functional silanes being particularly readily water-soluble. It has been found that aminosilanes have good adhesion to paints, adhesives, primers and metallic and ceramic layers even after steam sterilization and also have good adhesion of extrusion-coated polymers to polyester films without an additional adhesion-promoting layer or corona treatment.

For example, the amino-functional silane is hydrolyzed in water and applied to one or more surfaces of the oriented polyester using conventional methods such as spray or roller coating. Once the silane coating has dried, the polyester primed in this way can be steam sterilized and absorbed for direct extrusion with other polymers. The extrusion coating can be carried out using a conventional process. The waste of polyester film with aminosilane coating can be regenerated.

Examples of aminosilanes which correspond to the formula mentioned are N-2- (aminoethyl) -3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyltriethoxysilane, 4-aminobutyldimethylmethoxysilane, and p-aminophenyltrimethoxysilane. Preferred is N-2- (aminoethyl) -3-aminopropyltrimethoxysilane with the following formula:         H₂N (CH₂)₂NH (CH₂)₃Si (OCH₃)₃.

In principle, the hydrolyzed aminosilane can be applied at any possible time during the production of the film, ie before or during the stretching process, it can also be applied to the finished film (for example) before rolling up.

The hydrolyzed aminosilane to form the adhesion-promoting layer, based on the unhydrolysed aminosilane, is applied to the film as an aqueous solution in a concentration of 0.2 to 6.0% by weight. A weak acid such as acetic acid, phosphoric acid or the like is then added in amounts of up to 0.2% by weight to facilitate hydrolysis. At least one of the hydrolyzable groups of the silane is hydrolyzed to a silanol group (SiOH). The preferred concentration of the hydrolyzed aminosilane is 0.25 to 3.5 percent by weight. The preferred concentration is such that the final goal is a dry application weight of the adhesion-promoting layer of 0.5 mg / m² is present.

The coating described above is detailed in the <patcit id="pcit0004" dnum="EP0359017A"><text>EP-A-0 359 017</text></patcit> to which reference is made at this point. This document also provides information about other specific combinations of such hydrolyzable aminosilanes, the reproduction of which is not given here.

The coating can be applied to one or both outer sides of the polyester film; however, it can also be applied to only one side and the back can be provided with a further, differently structured coating. This can then e.g. B. be a thermosetting acrylate or methacrylate coating as in<patcit id="pcit0005" dnum="US4214035A"><text>US Patent No. 4,214,035</text></patcit> described.

The coating formulation may also contain other ingredients as long as these other ingredients do not reduce the adhesion-promoting properties of the hydrolyzed aminosilane. This includes smaller amounts of colloidal silica, dyes, pH regulators, wetting aids or the like.

A waste coated with the adhesion-promoting layer that arises during the film production can be chopped, mixed with fresh polymer, melted again and extruded to produce oriented films. With a regrind coated in this way with significant amounts in a proportion of up to approx. 60 % By weight, preferably 10 to 50% by weight, based in each case on the total weight of the film produced, the physical properties of the film are not appreciably negatively influenced. Consequently, the film coated with the adhesion-promoting layer offers commercial advantages for the film manufacturer compared to other coated films. For example, films that are coated with polymers containing vinylidene chloride (cf.<patcit id="pcit0006" dnum="US2627088A"><text>US 2,627,088</text></patcit> and <patcit id="pcit0007" dnum="US2698240A"><text>US 2,698,240</text></patcit>) to degrade and discolor when regenerated in the manner described.

A particular advantage of the invention is that the production costs of the film are only slightly above those of a film made from standard polyester raw materials. The processing and use-relevant properties of the film are significantly improved compared to films according to the prior art.

A method for producing the films is described below. It includes<ul id="ul0003" list-style="bullet" compact="compact"><li>the production of a single-layer or multilayer film from a base layer B and optionally top layer (s) A (and C) by coextrusion and shaping the melts into flat melt films,</li><li>Coating the film with the water-soluble, adhesion-promoting and steam-sterilizable layer (preferably between the first and the second stretching step),</li><li>biaxial stretching of the film and heat setting of the stretched film,</li></ul>the coating being carried out before, during or after the biaxial orientation.

First, the polymer or the polymer mixture for the individual layers is compressed and liquefied in an extruder. The melt (s) is (are simultaneously) pressed through a slot die, and the pressed (multilayer) film is drawn off on one or more take-off rolls, where it cools and solidifies.

Biaxial stretching is generally carried out sequentially. It is preferably stretched first in the longitudinal direction (ie in the machine direction, = MD direction) and then in the transverse direction (ie perpendicular to the machine direction, = TD direction). The stretching in the longitudinal direction can be carried out with the aid of two rolls running at different speeds in accordance with the desired stretching ratio. A corresponding tenter frame is generally used for transverse stretching.

The temperature at which the biaxial stretching of PET can generally be carried out can vary within a relatively wide range and depends on the desired properties of the film. The longitudinal stretching is generally carried out at approximately 80 to 140 ° C. and the transverse stretching at approximately 80 to 150 ° C. The longitudinal stretching ratio λ_MD lies in the range from 2.0: 1 to 5: 1. The transverse stretching 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 are preferably coated with the water-soluble adhesion-promoting and steam-sterilizable layer by the known methods.

For the production of a film with very good peeling and delamination behavior (the film must not delaminate when being peeled off), it has proven to be advantageous if the R value of the film is less than 43 N / mm² and the e_MaxRatio is less than 2.5. In this case, the strength of the film in the thickness direction is so great that when the cover is pulled off the cup, the film definitely does not delaminate, does not tear or tear further.

The main factors influencing the R value and the e_Max The ratio of the film is the process parameters in longitudinal and transverse stretching as well as the SV value of the raw materials used. The process parameters include in particular the stretching ratios in the longitudinal and transverse directions (λ_MD and λ_TD), the stretching temperatures in the longitudinal and transverse directions (T_MD and T_TD) and the film web speed.

For example, you get R values ​​and e on a film line_Max-Relationships that are above the above-mentioned values, suitable films can nevertheless be produced by increasing the temperatures in the longitudinal stretching and in the transverse stretching and / or reducing the stretching ratios in the longitudinal stretching and in the transverse stretching. Usual values ​​for the parameters mentioned are for films that are not used for yoghurt cup lids<tables id="tabl0001" num="0001"><table frame="none"><tgroup cols="3" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="33mm" /><colspec colnum="2" colname="col2" colwidth="28mm" /><colspec colnum="3" colname="col3" colwidth="26mm" /><thead><row><entry valign="top" /><entry valign="top">Longitudinal extension</entry><entry valign="top">Transverse stretching</entry></row></thead><tbody><row><entry>Stretching temperatures</entry><entry>80 up to 118 ° C</entry><entry>90 up to 120 ° C</entry></row><row><entry>Stretching ratios</entry><entry>4.2 to 4.8</entry><entry>4.1 to 4.4</entry></row></tbody></tgroup></table></tables>

In contrast, the temperatures and stretching ratios for the suitable films are within the ranges as shown in the table below.<tables id="tabl0002" num="0002"><table frame="none"><tgroup cols="3" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="33mm" /><colspec colnum="2" colname="col2" colwidth="28mm" /><colspec colnum="3" colname="col3" colwidth="26mm" /><thead><row><entry valign="top" /><entry valign="top">Longitudinal extension</entry><entry valign="top">Transverse stretching</entry></row></thead><tbody><row><entry>Stretching temperatures</entry><entry>80 up to 130 ° C</entry><entry>80 up to 135 ° C</entry></row><row><entry>Stretching ratios</entry><entry>2.5 to 4.0</entry><entry>3.5 to 4.0</entry></row></tbody></tgroup></table></tables>

A further lowering of the stretching ratios is not advantageous, since otherwise undesirable defects can appear in the film. If, for example, the longitudinal stretching ratio is lowered below a value of 2.5, cross-shots can be obtained in the film, which can be clearly seen.

If, for example, you get an R-value of 50 N / mm with a machine for film production² with the parameter set λ_MD = 4.8 and λ_TD= 4.0, the stretching temperatures in the longitudinal and transverse directions T_MD = 115 ° C and T_TD = 90 - 125 ° C, this is obtained by increasing the longitudinal stretching temperature to T._MD = 125 ° C or by increasing the transverse stretching temperature to T_TD = 90 - 135 ° C or by lowering the longitudinal stretching ratio to λ_MD = 4.0 or by lowering the transverse stretching ratio to λ_TD = 3.6 an R-value of 38. It has surprisingly been found that these measures also e_Max- Ratio reaches the desired range. The web speed of the finished film was 140 m / min and the SV value of the film was 730. The temperatures relate to the roll temperatures in the longitudinal stretching and to the film temperature in the transverse stretching, which were measured by means of IR (infrared).

In the subsequent heat setting, the film is held at a temperature of approximately 150 to 250 ° C. for approximately 0.1 to 10 seconds. The film is then wound up in the usual way.

The hydrolyzed aminasilane layer in the form of an aqueous coating can be applied in-line in one of three steps during film production:<ul id="ul0004" list-style="bullet" compact="compact"><li>in the <i>In front</i>Stretching phase at the point between the take-off roller and the first stretching step as in <patcit id="pcit0008" dnum="GB1411564A"><text>British Patent No. 1,411,564</text></patcit> described;</li><li>in the <i>Between</i>Phase at the point between the stretching operations after the first but before the second stretching as in <patcit id="pcit0009" dnum="US4214035A"><text>U.S. Patent No. 4,214,035</text></patcit> described; or</li><li>in the <i>To</i>Stretching phase after the biaxial stretching, but before the film is wound up.</li></ul>

Usually the heat used to stretch or fix the film is sufficient to evaporate the water or other volatile substances and to dry the adhesion-promoting layer; an additional drying step is necessary if the coating is applied after the heating steps described.

In the preferred embodiment, the film is first stretched in the longitudinal direction before coating. In this preferred embodiment, the film is coated in any shape according to the prior art after the longitudinal stretching. This can be, for example, by roller coating, spray coating or by nozzle coating (= "slot coating").

In a further preferred embodiment, the polyester film is coated by an engraving roller. The monoaxially oriented film can also be subjected to a prior art corona discharge prior to coating. The corona treatment weakens the hydrophobic character of the polyester film surface, which allows the water-based adhesion-promoting layer to better wet the surface and consequently improves the adhesion of the adhesion-promoting layer to the film surface.

In addition, steam-sterilizable laminates can be produced by the known process of extrusion coating, the molten polymer layer being applied continuously to the primed surface of the running film web. Laminates of polyester with polyethylene, ethylene-vinyl acetate or ethylene-methacrylic acid copolymers, polyvinyl alcohol, polyvinyl acetate and other polymers can easily be produced by extrusion coating.

As a general instruction to achieve the desired R-value and the desired e_MaxRatio can be expediently such that - starting from a parameter set in which the film with unsuitable R values ​​and e_Max- Ratios will be obtained either:<ul id="ul0005" list-style="bullet" compact="compact"><li>the stretching temperature in the MD direction is increased by ΔT = 3 to 15 K, preferably by ΔT = 5 to 12 K and particularly preferably by ΔT = 7 to 10 K</li><li>the stretching ratio in the MD direction is reduced by Δλ = 0.3 to 0.8, preferably by Δλ = 0.35 to 0.7 and particularly preferably by Δλ = 0.4 to 0.6</li><li>the stretching temperature in the TD direction is increased by ΔT = 4 to 15 K, preferably by ΔT = 5 to 12 K and particularly preferably by ΔT = 7 to 10 K</li><li>the stretching ratio in the TD direction is reduced by Δλ = 0.3 to 0.8, preferably by Δλ = 0.35 to 0.7 and particularly preferably by Δλ = 0.4 to 0.6.</li></ul>

If appropriate, one or more of the above measures can also be combined. It has proven to be particularly advantageous to combine the first two measures with one another.

After the biaxial stretching, one or both surfaces of the film are preferably additionally corona or flame treated by one of the known methods. The treatment intensity is generally over 50 mN / m.

The film shows very good handling, very good winding properties and very good processing behavior. It is also characterized by excellent pull-off behavior from the cup. In particular, the tendency towards tearing and tearing and delamination is extremely low. The film is therefore suitable as packaging material for food and beverages, in particular as a lid film for food containers such as yoghurt pots. The film is also ideal for packaging moisture and / or air sensitive food and beverages, which are also contained in such cups.

The film also has excellent optical properties, shows excellent processing properties and an excellent roll presentation. Due to its very good handling and its very good processing properties, the film is particularly suitable for processing on high-speed machines. In addition, the film impresses with an excellent degree of whiteness, which also gives the film a very attractive, effective advertising appearance.

The table below (Table 1) summarizes the most important film properties.<tables id="tabl0003" num="0003"><table frame="all"><title><b>Table 1</b></title><tgroup cols="7"><colspec colnum="1" colname="col1" colwidth="10mm" /><colspec colnum="2" colname="col2" colwidth="36mm" /><colspec colnum="3" colname="col3" colwidth="27mm" /><colspec colnum="4" colname="col4" colwidth="21mm" /><colspec colnum="5" colname="col5" colwidth="28mm" /><colspec colnum="6" colname="col6" colwidth="18mm" /><colspec colnum="7" colname="col7" colwidth="29mm" /><thead><row><entry namest="col1" nameend="col2" align="center" valign="top" /><entry align="center" valign="top"><b>expedient area</b></entry><entry align="center" valign="top"><b>prefers</b></entry><entry align="center" valign="top"><b>particularly preferred</b></entry><entry align="center" valign="top"><b>unit</b></entry><entry align="center" valign="top"><b>Measurement method</b></entry></row></thead><tbody><row><entry>1</entry><entry>R value</entry><entry align="center">&lt;43</entry><entry align="center">&lt;42</entry><entry align="center">&lt;40</entry><entry align="center">N / mm²</entry><entry align="center">as described</entry></row><row><entry>2</entry><entry>e_Max-Relationship</entry><entry align="center">&lt;2.5</entry><entry align="center">&lt;2.2</entry><entry align="center">&lt;2.0</entry><entry align="center">-</entry><entry align="center">as described</entry></row><row><entry>3</entry><entry>transparency</entry><entry align="center">&lt;60</entry><entry align="center">&lt;55</entry><entry align="center">&lt;50</entry><entry align="center">%</entry><entry align="center">ASTM-D 1033-77</entry></row><row><entry>4</entry><entry>Whiteness</entry><entry align="center">&gt;60</entry><entry align="center">&gt;65</entry><entry align="center">&gt;70</entry><entry align="center">-</entry><entry align="center">according to Berger</entry></row><row><entry>5</entry><entry>thickness</entry><entry align="center">10-120</entry><entry align="center">15-105</entry><entry align="center">20-80</entry><entry align="center">µm</entry><entry align="center" /></row><row><entry>6</entry><entry>Coated side friction against itself (COF)</entry><entry align="center">&lt;0,6</entry><entry align="center">&lt;0.55</entry><entry align="center">&lt;0,5</entry><entry align="center">-</entry><entry align="center">DIN 53 375</entry></row><row><entry>7</entry><entry>Medium roughness on the coated side</entry><entry align="center">&lt;50</entry><entry align="center">&lt;45</entry><entry align="center">&lt;40</entry><entry align="center">nm</entry><entry align="center">DIN 4768, cut-off of 0.25 mm</entry></row><row><entry>8</entry><entry>Gloss (20 ° measuring angle)</entry><entry align="center">&gt;50</entry><entry align="center">&gt;55</entry><entry align="center">&gt;60</entry><entry align="center">-</entry><entry align="center">DIN 67 530</entry></row><row><entry>9</entry><entry>Yellow number</entry><entry align="center">&lt;50</entry><entry align="center">&lt;45</entry><entry align="center">&lt;40</entry><entry align="center">-</entry><entry align="center">ASTM-D 1925-70</entry></row><row><entry>10</entry><entry>Filler concentration of the base layer (white pigment)</entry><entry align="center">&gt; 3 and &lt;20</entry><entry align="center">&gt; 4 and &lt;18</entry><entry align="center">&gt; 5 and &lt;16</entry><entry align="center">% By weight</entry><entry align="center" /></row><row><entry>11</entry><entry>Metal adhesion, adhesion to adhesives or to polymers applied by direct extrusion before sterilization (medium peeling force)</entry><entry align="center">&gt;2,5</entry><entry align="center">&gt;3,0</entry><entry align="center">&gt;3,5</entry><entry align="center">N / 25 mm</entry><entry align="center">as described</entry></row><row><entry>12</entry><entry>Metal adhesion, adhesion to adhesives or to polymers applied by direct extrusion after sterilization (medium peeling force)</entry><entry align="center">&gt;2,0</entry><entry align="center">&gt;2,5</entry><entry align="center">&gt;3,0</entry><entry align="center">N / 25 mm</entry><entry align="center">as described</entry></row></tbody></tgroup><tgroup cols="7" rowsep="0"><colspec colnum="1" colname="col1" colwidth="10mm" /><colspec colnum="2" colname="col2" colwidth="36mm" /><colspec colnum="3" colname="col3" colwidth="27mm" /><colspec colnum="4" colname="col4" colwidth="21mm" /><colspec colnum="5" colname="col5" colwidth="28mm" /><colspec colnum="6" colname="col6" colwidth="18mm" /><colspec colnum="7" colname="col7" colwidth="29mm" /><tbody><row><entry namest="col1" nameend="col7" align="justify">The following measurement methods were used to characterize the raw materials and the foils: DIN = German Institute for Standardization ASTM = American Society for Testing and Materials</entry></row></tbody></tgroup></table></tables>

transparency

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

Yellow number

The yellow number of the film is determined in accordance with ASTM-D 1925-70 using a spectrophotometer type Lamda 12 from Perkin Elmer (USA), standard illuminant D65, 10 ° normal observer. The yellowness index YI is calculated from the measured standard color values ​​X, Y, Z in accordance with the equation<maths id="math0001" num=""><math display="block"><mi>YI</mi><mo mathvariant="normal">=</mo><mfenced open="[" close="]" separators=""><mn mathvariant="normal">100</mn><mo mathvariant="normal">×</mo><mn mathvariant="normal">1</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">28</mn><mo mathvariant="normal">×</mo><mi mathvariant="normal">X</mi><mo mathvariant="normal">-</mo><mn mathvariant="normal">1</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">06</mn><mo mathvariant="normal">×</mo><mi mathvariant="normal">Z.</mi></mfenced><mo mathvariant="normal">/</mo><mi mathvariant="normal">Y</mi></math><img file="EP1591237B1_D0001.tif" /></maths>

Whiteness

The degree of whiteness is determined according to Berger, whereby more than 20 layers of film are usually placed on top of each other. The degree of whiteness is determined with the aid of the electric reflectance photometer ELREPHO from Zeiss, Oberkochen (DE), standard illuminant C, 2 ° normal observer. The whiteness WG is called<maths id="math0002" num=""><math display="block"><mi>Flat share</mi><mo>=</mo><mi>RY</mi><mo>+</mo><mn>3</mn><mo>⁢</mo><mi>RZ</mi><mo>-</mo><mn>3</mn><mo>⁢</mo><mi>RX</mi></math><img file="EP1591237B1_D0002.tif" /></maths> defined, where RX, RY, RZ are corresponding reflection factors when using an X, Y, Z color measurement filter. A compact made of barium sulfate (see DIN 5033, part 9) is used as the white standard. A detailed description is e.g. B. in Hansl Loos, color measurement, Verlag Beruf und Schule, Itzehoe (1989).

SV value (standard viscosity)

The standard viscosity SV (DCE) is measured based on DIN 53726 in dichloroacetic acid. The intrinsic viscosity (IV) is calculated from the standard viscosity as follows<maths id="math0003" num=""><math display="block"><mi>IV</mi><mo mathvariant="normal">=</mo><mfenced open="[" close="]"><mi mathvariant="normal">η</mi></mfenced><mo mathvariant="normal">=</mo><mn mathvariant="normal">6</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">907</mn><mo mathvariant="normal">⋅</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">4</mn></msup><mspace width="1em" /><mi>SV</mi><mrow><mspace width="1em" /><mo mathvariant="normal">(</mo><mi>DCE</mi><mo mathvariant="normal">)</mo></mrow><mo mathvariant="normal">+</mo><mn mathvariant="normal">0</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">063096</mn><mrow><mspace width="1em" /><mo mathvariant="normal">[</mo><mi>dl</mi><mo mathvariant="normal">/</mo><mi mathvariant="normal">G</mi><mo mathvariant="normal">]</mo></mrow></math><img file="EP1591237B1_D0003.tif" /></maths>

friction

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

Roughness

The roughness is determined according to DIN 4768.

shine

The gloss is determined in accordance with DIN 67 530. The reflector value is measured as an optical parameter for the surface of a film. Based on the standards ASTM-D 523-78 and ISO 2813, the angle of incidence is set at 20 °. A light beam hits the flat test surface at the set angle of incidence and is reflected or scattered by it. The light rays striking the photoelectronic receiver are displayed as a proportional electrical quantity. The measured value is dimensionless and must be specified with the angle of incidence.

Determination of the R value

The R-value of the film is measured in the middle of the film web.<img file="EP1591237B1_D0004.tif" />

As the schematic diagram shows, 2 film strips of 15 mm width and 200 mm length (film strips right and left = Fr and FI) are cut out from the center of the film at an angle of 45 ° to the MD direction. Strain gauge (Zwick, type 010, Ulm, DE) clamped and stretched. The respective R-value is calculated using the following equation:<maths id="math0004" num=""><math display="block"><mi mathvariant="normal">R</mi><mo mathvariant="normal">-</mo><msub><mi>value</mi><mfenced><mi>Fl</mi></mfenced></msub><mo mathvariant="normal">:</mo><mo mathvariant="normal">≈</mo><mn mathvariant="normal">1</mn><mo mathvariant="normal">/</mo><mn mathvariant="normal">3</mn><mo mathvariant="normal">×</mo><mfenced separators=""><msub><mi mathvariant="normal">σ</mi><mrow><mn mathvariant="normal">30</mn><mo mathvariant="normal">%</mo><mrow><mspace width="1em" /><mo mathvariant="normal">(</mo><mi>Fl</mi><mo mathvariant="normal">)</mo></mrow></mrow></msub><mo mathvariant="normal">-</mo><msub><mi mathvariant="normal">σ</mi><mrow><mn mathvariant="normal">0</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">2</mn><mo mathvariant="normal">%</mo><mrow><mspace width="1em" /><mo mathvariant="normal">(</mo><mi>Fl</mi><mo mathvariant="normal">)</mo></mrow></mrow></msub></mfenced><mo>⁢</mo><mi mathvariant="normal">N</mi><mo mathvariant="normal">/</mo><msup><mi>mm</mi><mn mathvariant="normal">2</mn></msup></math><img file="EP1591237B1_D0005.tif" /></maths><maths id="math0005" num=""><math display="block"><mi mathvariant="normal">R</mi><mo mathvariant="normal">-</mo><msub><mi>value</mi><mfenced><mi>Fr</mi></mfenced></msub><mo mathvariant="normal">:</mo><mo>=</mo><mn mathvariant="normal">1</mn><mo mathvariant="normal">/</mo><mn mathvariant="normal">3</mn><mo mathvariant="normal">×</mo><mfenced separators=""><msub><mi mathvariant="normal">σ</mi><mrow><mn mathvariant="normal">30</mn><mo mathvariant="normal">%</mo><mrow><mspace width="1em" /><mo mathvariant="normal">(</mo><mi>Fr</mi><mo mathvariant="normal">)</mo></mrow></mrow></msub><mo mathvariant="normal">-</mo><msub><mi mathvariant="normal">σ</mi><mrow><mn mathvariant="normal">0</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">2</mn><mo mathvariant="normal">%</mo><mspace width="1em" /><mfenced><mi>Fr</mi></mfenced></mrow></msub></mfenced><mo>⁢</mo><mi mathvariant="normal">N</mi><mo mathvariant="normal">/</mo><msup><mi>mm</mi><mn mathvariant="normal">2</mn></msup></math><img file="EP1591237B1_D0006.tif" /></maths>

In this equation, the measurands have σ_30% and σ_0.2% the following meaning:<dl id="dl0001" compact="compact"><dt>σ_30% =</dt><dd>Tensile stress in the film at 30% elongation, measured at 45 ° to the MD direction of both samples,</dd><dt>σ_{0,2 %} =</dt><dd>Tensile stress in the film at 0.2% elongation, measured at 45 ° to the MD direction, of both samples.</dd></dl>

In the case of the film, the R value of the film is smaller for both the film strip on the right and the film strip on the left than: <maths id="math0006" num=""><math display="block"><mi mathvariant="normal">R</mi><mo mathvariant="normal">-</mo><mi>value</mi><mo mathvariant="normal">&lt;</mo><mn mathvariant="normal">43</mn><mspace width="1em" /><mi mathvariant="normal">N</mi><mo mathvariant="normal">/</mo><msup><mi>mm</mi><mn mathvariant="normal">2</mn></msup></math><img file="EP1591237B1_D0007.tif" /></maths>

Determination of the e

<u style="single">Max</u>

Ratio

The e_Max-Ration is determined over the entire width of the film web (d, h, over the width of the machine roll). The distance between two measuring points (in the TD direction, = width direction of the film web) is usually 50 cm. As with the determination of the R value, 2 film strips of 15 mm width and 200 mm length (film strips right and left = Fr and Fl) are cut out of the film web at an angle of 45 ° to the MD direction for each measuring point, the center of the strips determining the respective distance from the edge of the film web.

The scheme of sampling for the determination of the e_Max-Relationship is again illustrated by the sketch below:<img file="EP1591237B1_D0008.tif" />

The e_MaxThe ratio at the respective point on the film web is measured at an angle of 45 ° to the MD direction using the two samples. In the middle of the film sheeting is e_MaxRatio almost one and increases the further one gets from the center of the film to the edges of the film.

The samples are then stretched in a tensile strain gauge, as described above when determining the R value. The e_Max-Ratio at the respective position of the film web is calculated using the following equation: <maths id="math0007" num=""><math display="block"><msub><mi mathvariant="normal">e</mi><mi>Max</mi></msub><mo>-</mo><mi>Relationship</mi><mo>:</mo><mo>=</mo><msub><mi mathvariant="normal">ϵ</mi><mi>Fl</mi></msub><mo>/</mo><msub><mi mathvariant="normal">ϵ</mi><mi>Fr</mi></msub><mspace width="1em" /><mi>or</mi><mspace width="1em" /><msub><mi mathvariant="normal">ϵ</mi><mi>Fr</mi></msub><mo>/</mo><msub><mi mathvariant="normal">ϵ</mi><mi>Fl</mi></msub></math><img file="EP1591237B1_D0009.tif" /></maths>ε_Fl is the elongation at break of the film at 45 ° to the MD direction, left ε_Fr, the elongation at break of the film is below 45 ° to the MD direction, on the right.

By definition, this is e_MaxRatio always greater than 1. When measuring across the width of the film web, it follows that the first relation ε for approximately the first half of the web_Fl/ ε_Fr applies and ε applies to the second half of the path_Fl. It has been shown that the film has the e_Max-Ration at any point across the width of the film is less than 2.5: <maths id="math0008" num=""><math display="block"><msub><mi mathvariant="normal">θ</mi><mi>Max</mi></msub><mo mathvariant="normal">-</mo><mi mathvariant="normal">relationship</mi><mo mathvariant="normal">&lt;</mo><mn mathvariant="normal">2</mn><mo mathvariant="normal">,</mo><mn mathvariant="normal">5.</mn></math><img file="EP1591237B1_D0010.tif" /></maths>

Assessment of the peeling behavior of the film from a yoghurt cup

The peel behavior of the film from the cup is assessed visually. In this test method, the film (the lid) is glued to the cup (sealing wax is e.g.^®Novacote) and after a storage time (hardening time) of 48 hours. The peeling behavior is with<ul id="ul0006" list-style="none" compact="compact"><li>++ (= good) rated if the film neither tears nor delaminates;</li><li>- (= bad) rated if the film tears and / or delaminates.</li></ul>

Adhesion to adhesives, metallic and ceramic layers and adhesion to polymers that have been applied to the coated side by direct extrusion

are

Only the measurement of the adhesive force to adhesives is described below. The corresponding other measurements are to be carried out analogously.

The film sample (300 mm lengthways. 180 mm across) is placed on a smooth cardboard (200 mm lengthways. 180 mm across; weight approx. 400 g / m) before gluing², bleached, outer layers coated), the two protruding film ends (each 50 mm) must be turned over on the back and fixed with adhesive tape.

The film is glued with a standard polyester film with a thickness of 12 µm (e.g. ^®Melinex 800) is carried out using a doctor blade and doctor rod No. 3 from Erichsen, first using about 1.5 ml of adhesive (Novacote NC 275 + CA 12; mixing ratio: 4/1 + 7 parts of ethyl acetate) on the surface of the above mentioned film pattern is applied. After the solvent has been vented, the standard polyester film of the appropriate size is laminated onto the surface of the film sample provided with adhesive using a metal roller (width 200 mm, diameter 90 mm, mass 10 kg, in accordance with DIN EN 20 535), with the standard polyester film at least at the ends Protrudes 50 mm. The parameters of the lamination are:<tables id="tabl0004" num="0004"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="53mm" /><colspec colnum="2" colname="col2" colwidth="51mm" /><tbody><row><entry>Amount of adhesive:</entry><entry>5 (+/- 1) g / m²</entry></row><row><entry>Ventilate after applying the adhesive:</entry><entry>4th min (+/- 15 s)</entry></row><row><entry>Squeegee strength (Erichsen):</entry><entry>3</entry></row><row><entry>Squeegee speed level:</entry><entry>approx. 133 mm / s</entry></row><row><entry>Hardening time of the bond:</entry><entry>2nd h at 70 ° C in a forced air oven</entry></row></tbody></tgroup></table></tables>

Using a strip cutter with a width of 25 (+/- 1) mm, approx. 100 mm long samples are taken from the described assembly (laminated test sample), which consist of approx. 50 mm assembly and 50 mm unsealed individual layers. The latter are necessary to fix / clamp the test specimen. The test specimens are to be affixed to the back of the film (base layer B or cover layer C) over the entire surface of a carrier sheet using double-sided adhesive tape. The plate with the bonded composite is to be clamped in the lower jaw of the tensile testing machine. The clamping distance is 100 mm. The non-laminated end of the standard polyester film, that is 50 mm, is to be clamped in the upper jaw of the tensile testing machine (e.g. Instron, Zwick) so that a peeling angle of 180 ° results. The average peeling force is given in N / 25 mm (see Table 1, No. 11 and 12), rounded to one decimal place.<tables id="tabl0005" num="0005"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="55mm" /><colspec colnum="2" colname="col2" colwidth="22mm" /><tbody><row><entry>Sample width:</entry><entry>25th mm</entry></row><row><entry>Preload:</entry><entry>0.1 N</entry></row><row><entry>Measuring length:</entry><entry>25th mm</entry></row><row><entry>Withdrawal speed up to preload:</entry><entry>25th mm / min</entry></row><row><entry>First of all:</entry><entry>5 mm</entry></row><row><entry>Test route:</entry><entry>40 mm</entry></row><row><entry>Sensitivity:</entry><entry>0.01 N</entry></row><row><entry>Take-off speed:</entry><entry>100 mm / min</entry></row></tbody></tgroup></table></tables>

The measurement result for the peeling force is to be equated with the minimum adhesive force between the layers, since the adhesive force between the adhesive and the standard film is significantly greater.

Sterilizability

To determine the sterilizability, the film is exposed to a steam jet at a temperature of approx. 100 ° C for 10 seconds. The liability is then determined as described above (see Table 1, No. 12).

Examples

example 1

N-2- (Aminoethyl) -3-aminopropyltrimethoxysilane (AE-APTMS) (offered by Dow Corning as Z-6020 and by Union Carbide as A-1120) was in conventional tap water at a concentration of 2.0 wt. % dispersed. To this end, 5% acetic acid was added in a concentration of 0.2% by weight in order to facilitate the hydrolysis.

Chips of polyethylene terephthalate were dried at 160 ° C. to a residual moisture content of less than 50 ppm and fed to the extruder for the base layer B. A uniaxially oriented film was obtained by extrusion and subsequent stepwise orientation in the longitudinal direction.

The elongated film was corona-treated with a corona discharge device and then coated with the hydrolyzed aminosilane solution, which was prepared as described above, using the reverse engraving technique.

The corona treated, elongated, coated film was dried at a temperature of about 110 ° C. Thereafter, the film was stretched in the transverse direction with an aspect ratio of 3.8 x 1 to produce a biaxially oriented film. The thickness of the stretched film was 55 µm. The biaxially oriented film was then heat-set at a temperature of 230 ° C. The dry application weight of the coating was about 2.5 mg / m².

Base layer B:

<tables id="tabl0006" num="0006"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="21mm" /><colspec colnum="2" colname="col2" colwidth="145mm" /><tbody><row><entry>85 % By weight</entry><entry>Polyethylene terephthalate with an SV value of 800</entry></row><row><entry>15 % By weight</entry><entry>PET masterbatch from Sukano (Schindellegi, CH), polyethylene terephthalate SV value of 800, with 50% by weight titanium dioxide (average particle diameter titanium dioxide approx. 0.3 µm).</entry></row></tbody></tgroup></table></tables>

The manufacturing conditions in the individual process steps were:<tables id="tabl0007" num="0007"><table frame="none"><tgroup cols="3" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="28mm" /><colspec colnum="2" colname="col2" colwidth="37mm" /><colspec colnum="3" colname="col3" colwidth="14mm" /><tbody><row><entry>Longitudinal extension</entry><entry>Stretching temperature:</entry><entry>100 ° C</entry></row><row>&lt;entry /&gt;<entry>Longitudinal stretch ratio:</entry><entry>3,4</entry></row><row><entry>Transverse stretching</entry><entry>Stretching temperature:</entry><entry>115 ° C</entry></row><row>&lt;entry /&gt;<entry>Lateral stretch ratio:</entry><entry>3,8</entry></row><row><entry>Fixation</entry><entry>Temperature:</entry><entry>230 ° C</entry></row><row>&lt;entry /&gt;<entry>Duration:</entry><entry>3s</entry></row></tbody></tgroup></table></tables>

A single-layer film with very good optics, a low coefficient of friction, very good processing behavior and very good winding quality was obtained. The film showed the desired behavior when removing the film from the cup. The film does not tear and shows no tendency to delaminate (Table 2).

Example 2

Example 1 was repeated, but the process parameters were changed:<tables id="tabl0008" num="0008"><table frame="none"><tgroup cols="3" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="28mm" /><colspec colnum="2" colname="col2" colwidth="37mm" /><colspec colnum="3" colname="col3" colwidth="14mm" /><tbody><row><entry>Longitudinal extension</entry><entry>Stretching temperature:</entry><entry>120 ° C</entry></row><row>&lt;entry /&gt;<entry>Longitudinal stretch ratio:</entry><entry>4,0</entry></row><row><entry>Transverse stretching</entry><entry>Stretching temperature:</entry><entry>110 ° C</entry></row><row>&lt;entry /&gt;<entry>Lateral stretch ratio:</entry><entry>3,4</entry></row><row><entry>Fixation</entry><entry>Temperature:</entry><entry>230 ° C</entry></row><row>&lt;entry /&gt;<entry>Duration:</entry><entry>3rd s</entry></row></tbody></tgroup></table></tables>

Even under these conditions, a film with a very good appearance, a low coefficient of friction, a very good processing behavior and a very good winding quality was obtained. The film also showed the desired behavior when removing the film from the cup. The film does not tear and shows no tendency to delaminate.

Example 3

Example 1 was repeated, but the thickness of the film was reduced from 55 μm to 36 μm. This comparatively thin film is also characterized by good processing behavior, very good winding quality and the desired peeling behavior of the film from the cup.

Comparative Example 1

Example 1 was repeated, but the process conditions were changed:<tables id="tabl0009" num="0009"><table frame="none"><tgroup cols="3" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="28mm" /><colspec colnum="2" colname="col2" colwidth="37mm" /><colspec colnum="3" colname="col3" colwidth="14mm" /><tbody><row><entry>Longitudinal extension</entry><entry>Stretching temperature:</entry><entry>118 ° C</entry></row><row>&lt;entry /&gt;<entry>Longitudinal stretch ratio:</entry><entry>4,3</entry></row><row><entry>Transverse stretching</entry><entry>Stretching temperature:</entry><entry>110 ° C</entry></row><row>&lt;entry /&gt;<entry>Lateral stretch ratio:</entry><entry>4,2</entry></row><row><entry>Fixation</entry><entry>Temperature:</entry><entry>230 ° C</entry></row><row>&lt;entry /&gt;<entry>Duration:</entry><entry>3rd s</entry></row></tbody></tgroup></table></tables>

The film did not show the desired processing behavior and in particular did not show the desired behavior when the film was removed from the cup. The film tears and showed a high tendency to delaminate.

Comparative Example 2

Example 1 was repeated, but the film was not coated. The film did not show the desired processing behavior, it showed insufficient adhesion to adhesives, the desired steam sterilizability and did not have the required high winding quality.

The results of the examples / comparative examples are summarized in Table 2.<tables id="tabl0010" num="0010"><img file="EP1591237B1_D0011.tif" /></tables>