Biaxially oriented, single- or multi-layer polyester film with an adhesion-promoting coating based on a co-polyester and an anchoring component

Description

Field of the invention

[0001] The invention relates to a single- or multi-layer, biaxially oriented polyester film which has an inline adhesion-promoting coating applied to at least one side, which is formed from at least one copolyester and at least one anchoring component. The film according to the invention is ideally suited for printing with various printing inks, in particular UV printing inks. background

[0002] Polyester films are used in a wide variety of applications. Their surfaces are often coated with other materials. For this coating to be successful, the surface must be wettable with the coating material, and the coating material must then adhere well to the polyester substrate. This can sometimes be achieved directly on the surface of the polyester film or by pretreating the surface with corona or plasma treatment. The surface properties of polyester films can be modified more specifically through chemical pretreatment using a coating that is applied during the manufacturing process of the polyester film itself. This coating then acts as an adhesion-promoting layer between the actual polyester film and the actual coating material, such as the decorative print. State of the art

[0003] Polyester films coated with an adhesion promoter are sufficiently described, see for example DE 10035327 A1 and EP 0322529 A1.

[0004] Copolyester coatings are also described as adhesion-promoting layers, see, for example, EP-A 0 144 878. However, the copolyester layers described in EP-A 0 144 878 are sensitive to moisture and very easily washed off. Especially when the subsequent process steps involve aqueous media (e.g., printing inks or coating dispersions), the adhesion is often poor. The moisture sensitivity of these layers is also known, see, for example, https: / / www.eastman.com / Literature Center / P / POLEUCOAT002.pdf.

[0005] A well-known method for improving the adhesion of coatings to the substrate and simultaneously increasing their solvent resistance is the introduction of a crosslinker that reacts with both the substrate (here, the polyester film) and the crosslinking medium. Epoxies react well with polyesters, and the crosslinking of sulfo-copolyesters with epoxides is described, for example, in US Pat. No. 5,350,601. The disadvantage of such epoxy compounds, however, is that they are suspected of being genotoxic, and their production is therefore associated with risks. Furthermore, the use of coatings containing such components is prohibited in food contact applications.

[0006] In addition to avoiding health risks during production, the direct reusability of unsaleable film residues generated during production is crucial for the economic viability of the film. These are collected, chopped, and reintroduced into the process either as chopped material or, after prior extrusion and granulation, as regenerated material. This must not lead to gelling or discoloration of the film.

[0007] Furthermore, it is of great importance for the applications mentioned that the coating is largely free of defects, i.e. free of streaks and larger inclusions, as these would disrupt the printed image or, for example, would immediately be perceived as visually disturbing in a metal layer. Task

[0008] The polyester films according to the prior art are disadvantageous because they either do not have sufficient adhesion of the copolyester adhesion-promoting coating to the polyester and / or to the target coating medium, and / or contain components that make use, for example, in food contact applications impossible, or reduce economic manufacturability by requiring special protective measures during production. Accordingly, the object of the present invention was to provide a polyester film having a copolyester-containing coating that adheres well to printing inks, particularly UV printing inks, and that also endures under humid conditions. The polyester film should also be economical to produce. In particular, the film should be free of components with an epoxy function that would prevent use in food contact applications. Solution to the task

[0009] The problem is solved by a multilayer polyester film according to claim 1. Detailed description

[0010] The total film thickness is at least 4 µm and a maximum of 500 µm. The preferred film thickness is at least 10 µm and a maximum of 250 µm, and ideally at least 11.5 µm and a maximum of 125 µm. If the film thickness is below 4 µm, the mechanical strength of the film is no longer sufficient for good-quality printing. Above 500 µm, the film becomes too stiff to be coated inline with good quality. Even above 250 µm, the coating quality visibly decreases due to the high film stiffness, which manifests itself, for example, in the form of uncoated areas that are visually recognizable as spots.

[0011] The film has a base layer B. Single-layer films consist only of this base layer B. In a multi-layer embodiment, the film consists of the (i.e. one) base layer B and at least one further layer, which, depending on its position in the film, is referred to as an intermediate layer (at least one further layer is then located on each of the two surfaces) or cover layer (the layer forms an outer layer of the film). In the multi-layer embodiment, the thickness of the base layer B is at least as great as the sum of the other layer thicknesses. Preferably, the thickness of the base layer in multi-layer embodiments is at least 55% of the total film thickness and ideally at least 63% of the total film thickness. If the cover layers become too thick, the economic efficiency decreases because the maximum proportion of reclaimed material that can be used also decreases.To ensure properties are maintained, reclaimed material (recycled film residues from film production) should only be added to the base layer. If the base layer thickness is too thin compared to the total thickness, an excessive percentage of reclaimed material would have to be added to this base layer to close the reclaimed material cycle. This can then negatively impact properties such as color and transparency of the film via the base layer. In addition, top layers usually contain particles to improve slip properties (improvement in windability). In thick top layers, these particles lead to a loss of transparency and to haze due to backscattering. However, in graphic applications in particular - such as the present application - films with low haze and high transparency are preferred, which are negatively impacted by too many particles.

[0012] The base layer B consists of at least 70 wt.% of a thermoplastic polyester, the remaining components being formed by additives such as UV stabilizers, particles, flame retardants, polyolefins, cycloolefin copolymers (COCs) and other additives and / or polyester-compatible polymers, such as polyamides. According to the invention, the other additives and / or polyester-compatible polymers (such as polyamides) are present in the base layer B at ≤ 20 wt.%, preferably at ≤ 2 wt.% and particularly preferably not at all. The use of other additives and / or polymers can lead to an undesirable yellowing of the film when the regrind is recycled in the film production process, which means that the proportion of regrind has to be reduced and thus the economic efficiency of the process is reduced. Furthermore, the use of other additives can lead to a deterioration in the mechanical properties of the film.

[0013] Suitable thermoplastic polyesters have proven to be polyesters made from ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), from ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene-2,6-naphthalate, PEN), 2,5-furandicarboxylic acid and ethylene glycol, as well as from any mixtures of the aforementioned carboxylic acids and diols. Polyesters consisting of at least 75 mol%, preferably at least 90 mol%, and particularly preferably at least 92 mol% ethylene glycol and terephthalic acid units are preferred. The use of naphthalene-2,6-dicarboxylic acid offers no advantages over terephthalic acid, so that, due to its higher price, it is usually avoided. 2,5-furandicarboxylic acid is also generally not used due to its higher price. The remaining monomer units originate from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids.

[0014] 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 preferably less than 10, cyclohexanedimethanol, butanediol, propanediol, etc. Suitable other dicarboxylic acids are, for example, isophthalic acid, adipic acid, etc.

[0015] A polyester according to this above description represents the main component, ie at least 70% by weight, of the base layer B and also the main component, ie at least 70% by weight, of the other layers of the film.

[0016] The film according to the invention has an SV value of >600, preferably >650, and particularly preferably >700. The SV value of the film is <950 and preferably <850. If the SV value is below 600, the film becomes so brittle during production that it frequently breaks. Furthermore, in the end applications, a more rapid further loss of viscosity occurs, resulting in a loss of flexibility of the film and subsequent breakage. Furthermore, the mechanical strengths mentioned below can no longer be reliably achieved at a lower SV value.

[0017] If the film is to have a SV higher than 950, then the polymers used for film production would have to have an SV value of at least 950. However, these polymers would then remain so viscous in the melt in the extruder that excessively high currents would occur during operation of the extruder's electric motors and pressure fluctuations would occur in the extrusion, leading to poor productivity.

[0018] The SV value of the film depends on the SV value of the raw materials used, as well as the selected process conditions. For example, the extrusion of the raw materials causes a reduction in the SV value due to mechanical stress (through shear) and temperature. To adjust the SV value of the film, the extrusion-induced SV degradation must be compensated for by using raw materials with a correspondingly higher SV value. The extent of extrusion-induced SV degradation is a machine-specific variable that must be determined separately for each film production line.

[0019] If several raw materials with different SV values ​​are used, an average SV value can be assumed for the raw material mixture. The average SV value is the sum of the SV values ​​of the raw material components (SV i ), weighted according to their mass fraction (wi ): SV = ∑ i SV i ⋅ w i

[0020] White-colouring polymers which are incompatible with the main component polyester, such as polypropylene, cycloolefin copolymers (COCs), polyethylene, uncrosslinked polystyrene, etc., are contained in the invention at less than 0.1 wt.% (based on the weight of the film) and ideally not at all (at 0 wt.%), since they greatly reduce transparency, negatively influence fire behaviour and tend to yellow heavily under regeneration conditions (production and recycling of the reclaimed material), which significantly reduces economic efficiency.

[0021] The base and cover layer(s) may contain particles to improve windability. Such inorganic or organic particles include, for example, calcium carbonate, apatite, silicon dioxide, aluminum oxide, cross-linked polystyrene, cross-linked polymethyl methacrylate (PMMA), zeolites and other silicates such as aluminum silicates, or even white pigments such as TiO 2 or BaSO 4 . These particles are preferably added to the cover layers to improve the windability of the film. In a preferred transparent embodiment, the use of silicon dioxide-based particles is preferred, as they have little transparency-reducing effect. In a preferred transparent embodiment, the proportion of these or other particles in any layer does not exceed 3 wt.% and is preferably less than 1 wt.% and particularly preferably less than 0.2 wt.% in each layer (in each case based on the total weight of the respective layer).In the case of a multilayer embodiment, these particles are preferably added to only one or both outer layers, and thus only a small proportion of them pass into the base layer via the reclaimed material. This achieves a minimal reduction in transparency due to the particles required for the winding. Preferably, at least one outer layer contains at least 0.07 wt.% of these particles.

[0022] In further preferred embodiments, the film is white. In these embodiments, the film contains at least one white pigment, preferably titanium dioxide or barium sulfate. The white pigment content, based on the total weight of the film, is at least 1 wt.%, preferably at least 3 wt.%, and particularly preferably at least 5 wt.%. The proportion of white pigment is < 38 wt.%, preferably < 20 wt.%, and ideally < 15 wt.%. The higher the proportion of white pigment, the more opaquely white the film is, but the lower the productivity because this leads to increased film tears during the production process.

[0023] In a further preferred embodiment, the film is matte on at least one side. In these cases, the film contains an inorganic and / or organic particle system. Examples of this, without being limited to this, can be found in EP-A 1 197 327. The use of mutually incompatible polymers to produce matte surfaces is also possible. Coating

[0024] The film according to the invention contains an adhesion-promoting coating on at least one side. This coating is preferably applied inline. Inline means that the coating is applied during the manufacturing process of the polyester film before the first roll-up. The coating can also be applied offline, but since this requires an additional unwinding and rewinding step, this is generally not economically viable.

[0025] The coating of the ready-to-use film has a thickness of 5–170 nm. The thickness is preferably 10–130 nm and ideally 20–110 nm. The thicker the coating in this inventive range up to approximately 50 nm, the better the adhesion-promoting effect is generally. Layer thicknesses greater than 50 nm are possible, but are no longer accompanied by the same degree of increased adhesion and therefore offer little advantage over 50 nm. The thicker the coating, the more pronounced coating irregularities become. From 170 nm, defect-free inline application is no longer possible.

[0026] The coating essentially consists of a copolyester component and a silane component. It is assumed that the copolyester component is primarily responsible for the adhesion, while the silane compound causes crosslinking of the copolyester to the polyester substrate.

[0027] The epoxysilanes described in US-A 5,350,601 (e.g., (3-glycidyloxypropyl)-trimethoxysilane), which enable good anchoring of the coating to the film surface, are ruled out due to toxicity. Other silanes with non-epoxy functionalization, however, were found in US-A 5,350,601 to have only insufficient anchoring effect. The publication "Geniosil - Organofunctional Silanes from Wacker" (accessed in 2018 at https: / / www.wacker.com / cms / media / publications / downloads / 6085_DE.pdf) also does not provide an obvious solution for crosslinking polyester when epoxysilanes are not an option.

[0028] Contrary to expectations, it was surprisingly found that a narrower selection of silanes with vinyl group functionalization, or less preferably methacrylic group functionalization, still enables a very good anchoring effect of the copolyester-containing coating component towards the polyester film substrate.

[0029] It is assumed that the alkoxy groups, or less preferably the acetoxy groups, undergo a condensation reaction with terminal hydroxyl groups of the copolyester or polyester film substrate after hydrolysis in the aqueous dispersion medium. Apparently, the vinyl group function promotes further crosslinking of the silanes to a similar extent as epoxy functions.

[0030] In particular, ethoxysilanes with short-chain vinyl functionalization appear to be particularly suitable with regard to gel formation behavior in the aqueous coating dispersion and anchoring function on the film substrate. Copolyester of the coating

[0031] The copolyester component in the coating is the product of a polycondensation of dicarboxylic acid and diol units, whereby various monomers are possible, particularly for the dicarboxylic acid component, such as terephthalic acid and isophthalic acid.

[0032] A (homo)polyester is composed of a dicarboxylic acid unit and a diol unit. A copolyester is composed of at least two different dicarboxylic acid units and / or at least two different diol units. The copolyester in the coating contains, in addition to non-sulfonate-group-bearing monomers, at least one sulfonate-group-bearing monomer in the dicarboxylic acid moiety. Suitable sulfonate-group-bearing monomers are described in EP-A 0 144 878. However, salts of 5-sulfoisophthalic acid are preferred. The counterion is of minor importance but is usually sodium or hydrogen. 5-sulfoisophthalic acid (counterion = H +< ) can be used with the best yields in the polymerization and leads to thermally stable polymers that do not lead to thermal decomposition during the film production process. Further suitable dicarboxylic acids without sulfonate groups can also be found in EP-A 0 144 878, but preference is given to, among others:for the reasons already mentioned for 5-sulfoisophthalic acid (5-SIPA), terephthalic acid and isophthalic acid are preferred. Isophthalic acid is particularly preferred because the use of isophthalic acid leads to particularly good water solubility of the resulting polymers, which is advantageous for the production of coating dispersions. The proportion of isophthalic acid in the monomer units not bearing sulfonate groups in the dicarboxylic acid moiety is therefore preferably greater than 50 mol%, particularly preferably greater than 75 mol%, and ideally greater than 85 mol%. The proportion of monomers bearing sulfonate groups in the dicarboxylic acid moiety is between 2 and 50 mol%, preferably between 6 and 30 mol%, and ideally between 8 and 15 mol%. Below 2 mol%, polymers are no longer sufficiently water-soluble, and below 6 mol% they are only poorly water-soluble (the dispersions would have to be heated).Above 15 mol%, the moisture sensitivity of the coating increases significantly. Above 30 mol%, the polymers can only be produced with low yields.

[0033] Suitable diols can also be found in EP-A 0 144 878. Ethylene glycol, diethylene glycol (DEG), polyethylene glycol (PEG), propanediol, or 1,4-cyclohexanedimethanol (CHDM) are preferred. Ethylene glycol (EG) is particularly preferred because it produces a particularly thermally stable polymer and, due to its widespread use in industry, is the most cost-effective.

[0034] Such polymers or their dispersions are commercially available, for example, under the brand name Eastek ®< from Eastman Chemical (USA).

[0035] It has also proven advantageous if the glass transition temperature of the copolyesters used is significantly above room temperature, since the adhesion of layers applied to them is then not subject to changes if temperatures above room temperature are briefly experienced during further processing or storage. In a preferred embodiment, the glass transition temperature of the copolyesters used is therefore > 35 °C, preferably > 50 °C and ideally > 65 °C. Higher glass transition temperatures can be achieved if other dicarboxylic acids are used in addition to 5-SIPA, isophthalic acid and terephthalic acid. However, aliphatic dicarboxylic acids, such as maleic acid, lead to a reduction in the glass transition temperature. Diols other than ethylene glycol should be avoided, especially CHDM. Silane the coating

[0036] In addition to the copolyester, the coating dispersion contains at least one silane bearing vinyl (or methacrylic) groups. This silane follows the general formula: where X, Y, Z are independently identical or different and are CH 3 -CO 2 - or (CH 3 -(CH 2 ) n ) m -CH p -O-, with n = 0 − 4 , preferably 0, m = 3 − p , p = 0 − 2 , preferably 2, or less preferably Z = (CH 3 -(CH 2 ) f ) g -CH h with f = 0 − 4 g = 3 − h h = 0 − 2 and V is a radical carrying at least one vinyl group, preferably V = -(CH 2 ) e -CH=CH 2 , with e = 0 − 4 and preferably = 0, less preferably V = -(CH 2 ) d -O-CO-C(CH 3 )=CH 2 , with d = 1 − 4

[0037] Particularly preferred is X = Y = Z and particularly preferably corresponds to CH 3 CH 2 -O-, since ethanol is then released during the hydrolysis reaction in the aqueous coating dispersion, which is easier to handle in production than, for example, methanol or other alcohols. Of course, from a purely functional point of view, p can also be 3.

[0038] In a less preferred embodiment, one or more of the radicals X, Y, and Z can also be an acetoxy radical -(CO 2 -CH 3 ). The remaining non-acetoxy radicals then correspond to the formulas for X - Z given above. However, acetoxy radicals lead to gel formation in the coating dispersion, particularly at higher silane concentrations, which leads to a significant deterioration in the coating quality after just a short time (< 6 h).

[0039] Vinylsilanes, in which the vinyl group is directly bonded to the silicon, have proven particularly effective. If CH2 groups are present between the silicon and the vinyl function, or if methacrylsilanes (less preferred variants of V) are used, gel formation occurs in the coating dispersion, especially at higher silane concentrations, which leads to a significant deterioration in the coating quality after just a short time (< 6 h). Coating dispersion

[0040] In a preferred embodiment, the coating dispersion contains water as a dispersant, as well as the copolyester and the silane in the following amounts: The coating dispersion contains at least 0.3 wt.%, preferably at least 1 wt.%, and particularly preferably at least 2 wt.% of the copolyesters according to the invention. The copolyester content is a maximum of 9 wt.%, preferably a maximum of 6 wt.%, and ideally a maximum of 3.5 wt.%.

[0041] The coating dispersion contains at least 0.3 wt.%, preferably at least 0.6 wt.%, and particularly preferably at least 1 wt.% of the silanes according to the invention. The silane content is a maximum of 3 wt.%, preferably a maximum of 2.3 wt.%, and ideally a maximum of 1.8 wt.%.

[0042] If the silane or copolyester content is too low, ideal film formation will not occur, as too much water must be evaporated. If the silane or copolyester content is too high, gel formation occurs more quickly and the coating quality deteriorates. The best results are achieved within the above limits.

[0043] The silane content in wt.% is preferably lower than that of the copolyester in wt.% and is particularly preferably ≤ 75% of the copolyester content in wt.%. This leads to a reduced crosslinking tendency within the coating dispersion and thus to better coating quality, even over longer production periods.

[0044] The coating dispersion may contain additional components such as surfactants to improve wetting, defoamers, or particles to improve slip properties.

[0045] The coating dispersion does not contain any epoxy-functional components, as these could enter the room air during production, or residues of the same could later migrate from the coating, thus making it impossible to use in contact with food or skin (e.g. medical applications). Method for applying the coating

[0046] According to the preferred embodiment, the adhesion-promoting coating is applied in-line during the manufacturing process of the biaxially oriented polyester film. The coating (on one side) or the coatings (on both sides) are applied after longitudinal and before transverse stretching (or, less preferably, in a simultaneous stretching system, before longitudinal and transverse stretching). To achieve good wetting of the polyester film with the water-based coating, the film surfaces are preferably first corona-treated. The coating(s) can be applied using a conventional suitable method such as a slot coater or a spraying process. Particularly preferred is the application of the coating(s) using the reverse gravure-roll coating process, which allows for extremely homogeneous application of the coating(s).Application by the Meyer Rod process is also preferred, allowing for greater coating thicknesses. The coating components can react with each other during drying and stretching of the polyester film, and especially during the subsequent heat treatment, which can reach temperatures of up to 240 °C. The in-line process is more economically attractive, as one or both coatings can be applied simultaneously with the film manufacturing process, thus eliminating a process step (see below: off-line process).

[0047] In an alternative, less preferred process, one or both coatings are applied using off-line technology. The coating according to the present invention is applied to the corresponding surface(s) of the polyester film using off-line technology in an additional process step downstream of the film production, using, for example, a gravure roll (forward gravure). The maximum coating thickness limits are determined by the process conditions and the viscosity of the coating dispersion, and are limited by the processability of the coating dispersion. Film production process

[0048] The polyester polymers of the individual layers are produced by polycondensation, either starting from dicarboxylic acids and diol or from the esters of the dicarboxylic acids, preferably the dimethyl esters, and diol.

[0049] Polyesters suitable for film production can have SV values ​​in a range of preferably 500 to 1300. The decisive factor for subsequent film production is not the SV value of a single raw material component, but rather the SV value averaged across all raw material components of the mixture intended for extrusion. According to the invention, this average SV value is greater than 700, and preferably greater than 750.

[0050] The particles, if present, can be added during polyester production. For this purpose, the particles are dispersed in the diol, optionally ground, decanted, and / or filtered, and added to the reactor either during the (trans)esterification or polycondensation step. A concentrated particle-containing or additive-containing polyester masterbatch can preferably be produced using a twin-screw extruder and diluted with particle-free polyester during film extrusion. It has proven advantageous not to use masterbatches containing less than 30% by weight of polyester. In particular, a masterbatch containing SiO2 particles should not contain more than 20% by weight of SiO2 (due to the risk of gel formation). Another option is to add particles and additives directly during film extrusion in a twin-screw extruder.

[0051] When using single-screw extruders, it has proven advantageous to dry the polyesters beforehand. When using a twin-screw extruder with a venting zone, the drying step can be omitted.

[0052] First, the polyester or polyester blend of the layer, or in the case of multilayer films, the individual layers, is compressed and liquefied in extruders. The melt(s) is then formed into a flat melt film in a single- or multi-layer die, pressed through a slot die, and drawn off onto a chill roll and one or more take-off rolls, where the melt film cools and solidifies.

[0053] The film according to the invention is biaxially oriented, i.e., biaxially stretched. Biaxial stretching of the film is most commonly performed sequentially. Stretching is preferably carried out first in the longitudinal direction (i.e., in the machine direction, = MD direction) and then in the transverse direction (i.e., perpendicular to the machine direction, = TD direction). Stretching in the longitudinal direction can be performed using two rolls rotating at different speeds, depending on the desired stretch ratio. A suitable tenter frame is generally used for transverse stretching.

[0054] The temperature at which stretching is carried out can vary within a relatively wide range and depends on the desired properties of the film. In general, stretching is carried out in the longitudinal direction in a temperature range of 80 to 130 °C (heating temperatures 80 to 130 °C) and in the transverse direction in a temperature range of 90 °C (start of stretching) to 140 °C (end of stretching). The longitudinal stretching ratio is in the range of 2.5:1 to 4.5:1, preferably 2.8:1 to 3.4:1. A stretching ratio above 4.5 leads to significantly impaired manufacturability (tears). The transverse stretching ratio is generally in the range of 2.5:1 to 5.0:1, preferably 3.2:1 to 4:1. A transverse stretching ratio higher than 5 leads to significantly impaired manufacturability (tears) and should therefore preferably be avoided.To achieve the desired film properties, it has proven advantageous if the stretching temperature (in MD and TD) is below 125 °C and preferably below 118 °C. Before transverse stretching, one or both surfaces of the film are preferably coated in-line using methods known per se. During the subsequent heat setting, the film is held under mechanical tension at a temperature of 150 to 250 °C for a period of approximately 0.1 to 10 s and, to achieve the preferred shrinkage values ​​(see below), is relaxed by at least 1%, preferably by at least 3%, and particularly preferably by at least 4% in the transverse direction. This relaxation preferably takes place in a temperature range of 150 to 190 °C. To reduce the transparency bow, the temperature in the first fixing field is preferably below 220 °C and particularly preferably below 190 °C.For the same reason, at least 1%, preferably at least 2%, of the total transverse stretch ratio should be in the first fixation zone, where no further stretching typically occurs. The film is then wound up in the usual way.

[0055] In a particularly economical production method for polyester film, the waste material (regrind) can be returned to the extrusion process in an amount of up to 60% by weight, based on the total weight of the film, without the physical properties of the film being significantly negatively affected. Film properties

[0056] The film according to the invention produced by the process described above preferably has a shrinkage in the longitudinal and transverse directions of less than 5%, preferably less than 2%, and particularly preferably less than 1.5% at 150°C. This film also has an expansion of less than 3%, preferably less than 1%, and particularly preferably less than 0.3% at 100°C. This dimensional stability can be achieved, for example, by suitable relaxation of the film before winding (see process description). This dimensional stability is important in order to avoid deterioration of the printed image or coating quality during subsequent printing, coating, or metallization of the film, where temperatures of > 100°C can occur, which can occur if the film shrinks or expands. Application

[0057] The films according to the invention are outstandingly suitable for printing with aqueous and solvent-based ink systems, particularly for printing with UV inks. The latter exhibit particularly good adhesion to the base film on the coating according to the invention. Furthermore, the films according to the invention are very easy to metallize and exhibit very good metal adhesion. Another characteristic is that the adhesion remains very good even after contact with water. Analytics

[0058] The following measurement methods were used to characterize the raw materials and the films: SV value (standard viscosity)

[0059] The standard viscosity in dilute solution (SV) was measured in an Ubbelohde viscometer at (25 ± 0.05)°C, based on DIN 53 728 Part 3. Dichloroacetic acid (DCE) was used as the solvent. The concentration of the dissolved polymer was 1 g polymer / 100 ml pure solvent. The polymer was dissolved for 1 hour at 60°C.

[0060] The dimensionless SV value is determined from the relative viscosity (η rel = η / η s ) as follows: SV = η rel − 1 × 1000

[0061] The method is equally suitable for determining polyester raw material and polyester film. The measurement procedure, including sample preparation, is independent of the sample shape. However, the SV value of film and the SV value of raw material represent different properties that are not equivalent to each other and must be considered separately. shrink

[0062] Thermal shrinkage was determined on square film samples with an edge length of 10 cm. The samples were cut so that one edge was parallel to the machine direction and one edge was perpendicular to the machine direction. The samples were precisely measured (the edge length L 0 was determined for each machine direction TD and MD, L 0 TD and L 0 MD ) and annealed for 15 minutes at the specified shrinkage temperature (here 150 °C) in a forced-air drying cabinet. The samples were removed and precisely measured at room temperature (edge ​​length L TD and L MD ). The shrinkage is calculated from the equation: Schrumpf % MD = 100 · L 0 MD − L MD / L 0 MD , bzw . Schrumpf % TD = 100 · L 0 TD − L TD / L 0 TD expansion

[0063] Thermal expansion was determined on square foil samples with an edge length of 10 cm. The samples were precisely measured (edge ​​length L 0 ), annealed for 15 minutes at 100 °C in a forced-air drying cabinet, and then precisely measured at room temperature (edge ​​length L). The expansion is calculated from the equation: Ausdehnung % = 100 * L − L 0 / L 0 and was determined separately in each film direction. Assessment of coating quality

[0064] The film is visually inspected across the production width and a length of at least 5 meters. For this purpose, the film is illuminated from different directions with a strong light source and assessed by two people viewing the film from different angles. The coating quality is assessed with the following grades: 1. No visible defects (inclusions, streaks, uncoated areas) 2. Smaller inclusions (gels etc.) just visible 3. Single larger, easily recognizable inclusions and / or streaks shorter than 1 cm 4. Many larger, easily recognizable inclusions and / or streaks longer than 1 cm 5. Larger inclusions and / or streaks longer than 1 cm and / or uncoated areas > 1 cm 2< almost across the entire film width

[0065] From grade 4 onwards, the coating is no longer commercially usable.

[0066] The coating quality is assessed initially, i.e., at the start of production, and after 3 hours of production. After 3 hours of production, information is obtained about the stability of the coating dispersion and its tendency to form gels. Measurement of adhesive strength

[0067] The adhesion to the film is tested for printing inks and metallization using the cross-cut method based on EN ISO 2409. A grid of 8 x 8 lines, spaced 2 mm apart, is cut into the coated surface. The cut is made deep enough to cut into the polyester film surface without severing the film. An adhesive tape (tesafilm®< 4129 from Tesa SE Germany) is then applied over the cut surface and removed manually with a sharp jerk.

[0068] The evaluation follows the following scheme: Parameter 0: Completely smooth cut edges. No chipped squares in the cross-cut. Parameter 1: Small chippings at the intersections of the grid lines. However, no more than 5% of the grid's inner surface. Parameter 2: Chipping along the grid lines and at the intersection points of the grid lines. However, not more than 15% of the grid's inner surfaces. Parameter 3: Partial or extensive chipping along the grid lines and chipping of some squares. However, not more than 35% of the grid's interior surfaces. Parameter 4: Wide chipping along the grid lines and chipping of some squares. However, no more than 65% of the grid's interior surfaces. Parameter 5: Chipping of more than 65% of the inner surfaces of the grille.

[0069] Values ​​above 2 are unsuitable for most applications. Measurement of adhesion strength after moisture exposure

[0070] For this purpose, the cross-cut is performed as described in "Measuring Adhesion Strength." The cut film is then stored in 25°C warm water for 24 hours, then removed and carefully dried with a dry paper towel. The next step is to proceed and evaluate the film as described in "Measuring Adhesion Strength." Measurement of adhesive strength after exposure to moisture and heat

[0071] For this purpose, the cross-cut is performed as described in "Measuring Adhesion Strength." The cut film is then stored in 60°C warm water for 24 hours, then removed and carefully dried with a dry paper towel. The next steps and evaluation are as described in "Measuring Adhesion Strength." Oppression

[0072] The film is offset printed using UV inks from the NewV poly series from hubergroup Deutschland GmbH and cured using a standard mercury UV lamp. 3 mm wide lines of yellow, cyan, magenta, and black were printed side by side. Metallization

[0073] The film is coated with aluminum in a vacuum, whereby the optical density of the film is then 2. Film production of the examples

[0074] For all examples listed, the film was produced as follows. The following raw materials were melted in one extruder per layer at 292°C and extruded through a three-layer slot die after electrostatic application to a take-off roll heated to 50°C. The resulting amorphous pre-film was then first stretched longitudinally. The longitudinally stretched film was corona-treated in a corona unit and then coated inline with one of the following dispersions by reverse gravure coating. The film was then transversely stretched, fixed, and rolled up. The conditions in the individual process steps were: Longitudinal stretching Heating temperature 75-115 °C Stretching temperature 115 °C Longitudinal stretch ratio 3,8 Transverse extension Heating temperature 100 °C Stretching temperature 112 °C Transverse stretch ratio (including stretching 1st fixation) 3,9 Fixation temperature 237 - 150 °C Length of time 3 s Relaxation in TD at 200 - 150 °C 5 % Fixation Temperature 1. Fixing field 170 °C

[0075] The following starting materials were used to produce the film in the examples: PET1 = Polyethylene terephthalate raw material made from ethylene glycol and terephthalic acid with an SV value of 820. PET2 = Polyethylene terephthalate raw material with an SV value of 700 and 15 wt.% amorphous SiO 2 , type Sylobloc 46 (manufacturer: Grace, Germany); average particle diameter d 50 according to the data sheet: 3.6 - 4.2 µm. The SiO 2 was incorporated into the polyethylene terephthalate in a twin-screw extruder.

[0076] A three-layer film with a thickness of 36 µm was produced. The thickness of outer layers A and C was 1.5 µm each. The polymer blend for outer layers A and C was 99% PET1 and 1% PET2. Base B consisted of 50% PET1 and 50% reclaimed material.

[0077] The shrinkage of the film at 150 °C was 1.2% in the longitudinal direction and 0.1% in the transverse direction. Composition of the coating dispersion Coating 1:

[0078] The following composition of the coating solution was used 90.0 wt% deionized water 10.0 wt% Eastek™< 1400

[0079] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use.

[0080] Eastek 1400 is a commercially available polymer dispersion from Eastman USA with a 30% polymer content. The polyester consists of sulfoisophthalic acid (5-SIPA) in the dicarboxylic acid fraction. The polymer has a glass transition temperature of 29 °C. Coating 2:

[0081] The following composition of the coating solution was used 90.9 wt% deionized water 9.1 wt% Eastek ™< 1100

[0082] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use.

[0083] Eastek 1100 is a commercially available polymer dispersion with a 33% polymer content. The polyester consists of sulfoisophthalic acid (5-SIPA) and isophthalic acid in the dicarboxylic acid fraction, with the isophthalic acid content being higher than that of 5-SIPA. The polymer's glass transition temperature is 55 °C. Coating 3:

[0084] The following composition of the coating solution was used 90.0 wt% deionized water 10.0 wt% Eastek™< 1200

[0085] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use.

[0086] Eastek 1200 is a commercially available polymer dispersion with a 30% polymer content. The polyester consists of sulfoisophthalic acid (5-SIPA) and isophthalic acid in the dicarboxylic acid fraction, with the isophthalic acid content being significantly higher than that of 5-SIPA.

[0087] Glass transition temperature of polymer 63 °C. Coating 4:

[0088] The following composition of the coating solution was used 97 wt.% deionized water 3.0 wt.% polyester from Example 1 of EP-A 0 144 878

[0089] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use.

[0090] The polyester consists in the dicarboxylic acid fraction of 10 mol% sulfoisophthalic acid and 90 mol% isophthalic acid, the diol fraction consists of ethylene glycol, glass transition temperature polymer 69 °C. Coating 5:

[0091] The following composition of the coating solution was used 97 wt.% deionized water 3.0 wt.% polyester from Example 4 of EP-A 0 144 878

[0092] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use.

[0093] The polyester's dicarboxylic acid fraction consists of 10 mol% sulfoisophthalic acid, 70 mol% isophthalic acid, and 20 mol% malonic acid. The diol fraction consists of ethylene glycol. A broad glass transition temperature is observed at 20 °C. Coating 6:

[0094] The following composition of the coating solution was used 88.5 wt% deionized water 10.0 wt% Eastek™< 1400 1.5 wt% Geniosil™< GF56 from Wacker Chemie AG (vinyltriethoxysilane)

[0095] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use. Coating 7:

[0096] The following composition of the coating solution was used 89.4 wt% deionized water 9.1 wt% Eastek™< 1100 1.5 wt% Geniosil™< GF56 (vinyltriethoxysilane)

[0097] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use. Coating 8:

[0098] The following composition of the coating solution was used 88.5 wt% deionized water 10.0 wt% Eastek™< 1200 1.5 wt% Geniosil™< GF56 (vinyltriethoxysilane)

[0099] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use. Coating 9:

[0100] The following composition of the coating solution was used 95.5 wt% deionized water 3.0 wt% polyester from Example 1 of EP-A 0 144 878 1.5 wt% Geniosil ™< GF56 (vinyltriethoxysilane)

[0101] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use. Coating 10:

[0102] The following composition of the coating solution was used 95.5 wt% deionized water 3.0 wt% polyester from Example 4 of EP-A 0 144 878 1.5 wt% Geniosil ™< GF56 (vinyltriethoxysilane)

[0103] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use. Coating 11:

[0104] The following composition of the coating solution was used 95.35 wt% deionized water 3.0 wt% polyester from Example 1 of EP-A 0 144 878 1.65 wt% Geniosil ™< GF62 (vinyltriacetoxysilane)

[0105] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use. Coating 12:

[0106] The following composition of the coating solution was used 95.45 wt% deionized water 3.0 wt% polyester from Example 1 of EP-A 0 144 878 1.55 wt% Geniosil ™< XL 32 ((Methacryloxymethyl)-methyldimethoxysilane)

[0107] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use. Coating 13:

[0108] The following composition of the coating solution was used 95.35 wt.% deionized water 3.0 wt.% polyester from Example 1 from EP-A 0 144 878 1.65 wt.% Z6040 from Dow Corning Corporation ((3-Glycidyloxypropyl)-trimethoxysilane))

[0109] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use.

[0110] Coating dispersion 13 contains a glycidyl component and must therefore be handled with particular care to avoid endangering employees. The production effort is therefore significantly higher and the cost-effectiveness is therefore far lower. Use in food contact applications or medical products that come into contact with the skin is excluded. This dispersion is therefore not within the scope of the invention and is for comparison purposes only. Coating 14:

[0111] The following composition of the coating solution was used 93.0 wt% deionized water 3.0 wt% polyester from Example 1 of EP-A 0 144 878 4.0 wt% Geniosil ™< GF56 (vinyltriethoxysilane)

[0112] The individual components were slowly added to deionized water while stirring and stirred for at least 30 min before use.

[0113] Unless otherwise stated, the coating is applied in-line using the reverse gravure process. Table 1 below summarizes the formulations, manufacturing conditions, and resulting film properties: Table 1: Properties of the slides of the examples Example VB1 VB2 VB3 VB4 VB5 VB6 V87 VB8 VB9 B1 B2 B3 B4 B5 B6 B7 B8 Coating dispersion no 1 2 3 4 5 9 13 14 6 7 8 9 10 9 11 12 Coating thickness 0nm 35 35 35 35 35 200 35 35 35 35 35 35 35 12 35 35 Initial coating quality - 2 1 1 1 1 3 1 2 2 1 1 1 1 1 1 1 Coating quality after 3 hours - 3 1 1 1 1 4 2 4 3 1 1 1 1 1 1 3 - UV printing adhesion 3 3 2 2 2 2 0 0 1 1 0 0 0 0 0 0 0 Adhesion strength of UV printing after exposure to moisture 4 4 3 3 3 3 0 1 2 1 0 0 0 1 1 0 0 Adhesion strength of UV printing after heat / moisture exposure 5 5 5 4 3 5 1 2 2 2 2 1 0 2 1 0 1 Adhesion strength metallization 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Adhesion strength of metallization after exposure to moisture 3 3 3 2 2 3 1 1 1 1 1 1 1 1 1 1 1 Adhesion strength of metallization after heat / moisture exposure 3 4 3 3 2 4 2 2 1 2 2 1 1 2 2 1 1

Claims

1. Polyester film provided with a coating at least on one side, wherein the coating is the drying product of an aqueous dispersion, the composition of which comprises not only water but also at least one copolyester component and one silane component, where • the copolyester component is formed to an extent of 3 to 35 mol% of a monomer unit bearing sulfonate groups, and is present in the dried coating in a proportion of 40-85% by weight, and characterized in that • the silane component bears vinyl groups or methacryloyl groups, and also alkoxy groups, and is present in the dried coating to an extent of 15-60% by weight; and • the coating has a thickness of 5-170 nm; and • the dispersion of the coating contains 0.3 - 3% by weight of the silane component.

2. Polyester film according to Claim 1, wherein the film is a multilayer film.

3. Polyester film according to either of Claims 1 and 2, wherein the aqueous dispersion does not contain any components bearing epoxy functions.

4. Polyester film according to any of Claims 1 to 3, wherein the copolyester in the coating contains units derived from 5-sulfoisophthalic acid in the dicarboxylic acid moiety.

5. Polyester film according to any of Claims 1 to 4, wherein the copolyester in the coating contains units derived from terephthalic acid and / or isophthalic acid in the dicarboxylic acid moiety.

6. Polyester film according to any of Claims 1 to 5, wherein the glass transition temperature of the copolyester in the coating is > 35°C.

7. Polyester film according to any of Claims 1 to 6, wherein the silane bearing vinyl groups or methacryloyl groups has the general formula: where X, Y, Z are independently the same or different and are CH3-CO2- or (CH3-(CH2)n)m-CHp-O-, with n = 0 − 4 , m = 3 − p , p = 0 − 2 and V is a radical bearing at least one vinyl group.

8. Polyester film according to any of Claims 1 to 6, wherein the silane bearing vinyl groups or methacryloyl groups has the general formula: where X, Y, Z are independently the same or different and are CH3-CO2- or (CH3-(CH2)n)m-CHp-O-, with n = 0 − 4 , m = 3 − p , p = 0 − 3 and V is a radical bearing at least one vinyl group.

9. Polyester film according to any of Claims 1 to 8, wherein the aqueous dispersion contains at least 0.3% by weight of silane component and / or 0.3% by weight of copolyester component,10. Polyester film according to any of Claims 1 to 9, wherein the content in % by weight of silane component is smaller than that of the copolyester component.

11. Process for producing a polyester film according to Claim 1, wherein the polyester or polyester mixture of the layer, or of the individual layers in the case of multilayer films, is compressed and liquefied in (an) extruder(s), the resultant melt(s) is / are formed in a single- or multilayer nozzle to a flat melt film, pushed through a slot die and drawn off on a chill roll and one or more draw rolls, and the cooled and consolidated melt film is biaxially oriented and, before, during or after the biaxial orientation, coated inline with an aqueous dispersion, wherein the dispersion comprises not only water but also at least one copolyester component and one silane component, where • the copolyester component is formed to an extent of 3 to 35 mol% of a monomer unit bearing sulfonate groups, and is present in the dried coating in a proportion of 40-85% by weight, characterized in that • the silane component bears vinyl groups or methacryloyl groups, and also alkoxy groups, and is present in the dried coating to an extent of 15-60% by weight, and then the coated film is heat-set, relaxed and rolled up, and • the coating has a thickness of 5-170 nm; and • the dispersion of the coating contains 0.3 - 3% by weight of the silane component.

12. Use of a film according to Claim 1 for printing from aqueous and solventborne ink systems.

13. Use according to Claim 12 for printing with UV printing inks.

14. Use of a film according to Claim 1 for production of metallized films.