MXPA01010637A - Biaxially oriented film for producing ceramic capacitors - Google Patents

Abstract

The invention relates to the use of a multilayered film as a support film for producing a ceramic capacitor. Said multilayered film consists of a base layer and at least one cover layer (A), this cover layer (A) containing a propylene polymer and at least one incompatible polyolefin. Said incompatible polyolefin is an LDPE, HDPE, MDPE, ethylene-propylene-copolymer, cycloolefin polymer or syndiotactic polymer. The surface of the cover layer (A) is rougher than the surface of the film facing it and the film is provided with a ceramic coating on its smoother surface. This coating is dried and then separated from the support film.

Description

BIAX1ALLY ORIENTED FILM FOR THE PRODUCTION OF CERAMIC CAPACITORS DESCRIPTIVE MEMORY The invention relates to a biaxially oriented multilayer polyolefin film which is used as a support film for ceramic layers. The invention also relates to a process for the production of ceramic capacitors. Ceramic capacitors are capacitors in which the dielectric consists of ceramic layers. In order to produce these capacitors, a ceramic starting material, generally a ceramic powder, is first converted into a highly viscous composition using suitable binders and solvents. In subsequent process steps, this composition is further converted into thin layers, which are subsequently provided with a metallic layer (capacitor electrodes). These ceramic layers covered in this way are formatted, stacked, pressed and finally fired at high temperatures in order to concretize the ceramic. The usable capacitor is produced from these preforms by subsequent provision of the electrodes with electrical contacts and encapsulation in a synthetic resin coating (Spektrum der Wissenschaft September 1988, page 88 ff.).

The ceramic layers may consist of different materials.

Suitable ceramic materials are known in the art, such as for example metal oxides and / or titanates, for example barium titanate, magnesium silicate, titanium dioxide, bismuth oxide and mixtures thereof. These ceramics are distinguished by high dielectric constants. Various methods are known to produce the ceramic layers which are subsequently converted into the capacitor. For example, the highly viscous ceramic coating composition is first applied to a suitable flexible substrate and dried. This substrate has to be removed again in subsequent processing steps, during which the resulting ceramic layer or film should not be damaged during peeling. It is known in the prior art to use paper, polyester film or polypropylene film for this purpose. JP 06305041 A describes a multi-layered oriented film having a base layer of polypropylene and upper layers of ethylene-propylene copolymer, whose surface roughness Ra is said to be in the range of 0.08 to 0.5 μm. The roughness values of the two surfaces must differ by no more than 0.1 μm. The ceramic layers generated in this film can only be dried at low temperatures, because otherwise, the adhesion of the ceramic layer to the film would be very large and defects in the ceramic film are generated in the release of the film. support film. JP 01196111 A describes a single-layer oriented polypropylene film, which comprises polydimethylsiloxane as the release agent with respect to the ceramic layer. However, the polydimethylsiloxane can be partially transferred to the surface of the ceramic layer, where it damages the adhesion of the metal coatings to this surface. JP 60206620 H describes a film made from a mixture comprising polypropylene, polymethylpentene and HDPE. It is said that the film has good release properties and surface roughness due to HDPE. The object of the present invention is to provide a film which is suitable as a support film for ceramic layers. On the one hand, there must be adequate adhesion between the film and the ceramic layer in order that the ceramic material can be well applied and the coated film can be rolled up. At the same time, it should be possible to detach the ceramic layer from the film after drying without damaging the ceramic layer, in particular its surface. With respect to the ceramic layer, it is required that it should have the smoothest surface possible after the film has been peeled off. This object is achieved according to the invention, by using a polyolefin oriented multi-layered film as a support film in the production of a ceramic capacitor, wherein: the multi-layer film consists of a base layer and at least one top layer A, where the layer A comprises a polymer of propylene and at least one incompatible polyolefin, and the incompatible polyolefin is a copolymer of LDPE, HDPE, MDPE, ethylene-propylene or [acuna], and the surface of the upper layer A has greater roughness than the other surface of the film, and the film is provided with a ceramic coating on the smoother surface of the film, and this coating is dried and subsequently separated from the support film. The base layer of the multilayer film according to the invention consists essentially of a polyolefin, preferably a propylene polymer, and optionally additives added in effective amounts in each case. The base layer generally comprises at least 90% by weight, preferably from 95 to <; 100% by weight, of polyolefin. The polypropylene polymer comprises mainly (at least 90%) propylene and has a melting point of 140 ° C or more, preferably 150 to 170 ° C. Isotactic polypropylene having a soluble n-heptane content of 6% by weight or less, ethylene and propylene copolymers having an ethylene content of 5% by weight or less, and copolymers of propylene with α-olefins of C- C8 having a content of α-olefins of 5% by weight or less, represent preferred propylene polymers for the base layer, with particular preference being given to isotactic polypropylene. The propylene polymer of the base layer generally has a melt flow index of 0.5 g / 10 min at 15 g / 10 min, preferably 3 g / 10 min at 8 g / 10 min, at 230 ° C and a force of 21.6 N (DIN 53 735). The percentages by weight indicated are based on the respective copolymer.

The upper layer A disposed on the surface of the base layer comprises a propylene polymer and at least one incompatible polyolefin. The incompatible polyolefin is generally present in the upper layer in an amount of 0.5 to 30% by weight, preferably 1 to 25% by weight, in particular 3 to 15% by weight. The propylene polymer is present in an amount of from 70 to 99.5% by weight, preferably from 75 to 99% by weight, in particular from 85 to 97% by weight. If desired, the top layer can additionally comprise additives in effective amounts in each case. The polypropylene polymer of the upper layer A comprises mainly (at least 90%) propylene and has a melting point of 120 ° C or more, preferably 140 to 170 ° C. Isotactic polypropylene having a soluble n-heptane content of 6% by weight or less, ethylene-propylene copolymers having an ethylene content of 10% by weight or less, and copolymers of propylene with C4-α-olefins C8 having a content of α-olefins of 5% by weight or less, represent preferred propylene polymers for the base layer, with particular preference given to isotactic propylene homopolymer. The propylene polymer of the top layer generally has a melt flow index of 0.5 g / 10 min at 15 g / 10 min, preferably 3 g / 10 min at 10 g / 10 min, at 230 ° C and a force of 21.6 N (DIN 53 735). The percentages by weight indicated are based on the respective copolymer. The MFI of the top layer polymer must be at least as large, generally larger (about 25 to 100%) than the MFI of the base layer.

The incompatible polyolefins are those which are not completely miscible with the propylene of the upper layer A and form a separate phase. This incompatibility causes a certain roughness of the surface, which is desired for the present invention. Suitable incompatible polyolefins are HDPE, MDPE, LDPE or syndiotactic polypropylenes or cycloolefin polymers. For the invention, preference is given to high density polyethylenes (HDPE) which have an MFI melt flow index, measured in accordance with ISO 1133 A 21.6 N / 190 ° C, in the range from 0.1 to 2.0 g / 10 min, preferably from 0.5 to 1.5 g / 10 min, and a density, measured at 23 ° C in accordance with DIN 53 479, Method A, or ISO 1183, on the scale from 0.935 to 0.97 g / cm3, preferably from 0.94 to 0.96 g / cm3, and a melting point, measured by DSC (maximum melting curve, heating rate 20 ° C / min), between 120 and 150 ° C, preferably between 125 and 135 ° C . For the invention, preference is given to medium density polyethylenes (MDPE) which have an MFI melt flow index measured in accordance with ISO 1133 to 21.6 N / 190 ° C, in the range of 0.1 to 3.0 g / 10 min. , preferably from 0.6 to 1.5 g / 10 min, and a density, measured at 23 ° C in accordance with DIN 53 479, Method A, or ISO 1183, on the scale from 0.925 to 0.94 g / cm3, preferably 0.925 at 0.935 g / cm3, and a melting point, measured by DSC (maximum melting curve, heating rate 20 ° C / min), between 115 and 145 °, preferably between 115 and 130 ° C.

For the invention, preference is given to low density polyethylenes (LDPE) which have an MFI melt flow index, measured in accordance with ISO 1133 to 21.6 N / 190 ° C, in the range of 0.1 to 3.5 g / 10. min, preferably from 0.5 to 2.0 g / 10 min, and a density, measured at 23 ° C in accordance with DIN 53 479, Method A, or ISO 1183, on the scale of 0.91 to 0.925 g / cm3, preferably 0.915 at 0.925 g / cm3, and a melting point, measured by DSC (maximum melting curve, heating rate 20 ° C / min), between 110 and 135 ° C, preferably between 110 and 125 ° C. Cycloolefinic polymers (COP) are homopolymers formed only of one type of cycloolefin or formed copolymers of cycloolefins and comonomers (COC), wherein the comonomer content is at most 50% by weight, based on the weight of the cycloolefin polymer. Cycloolefins are monocyclic or polyunsaturated polycyclic ring systems, such as cycloalkenes, bicycloalkenes, tricycloalkenes or tetracycloalkenes. The ring systems can be mono- or polysubstituted. Of the POPs described above, preference is given to those which are comprised of monoalkylated or unsubstituted cycloolefins. Particularly preferred cycloolefin homopolymers are polynorbornene, polydimethyloctahydronaphthalene, polycyclopentene and poly (5-methyl) norbomene. The cycloolefin polymers can also be branched. Products of this type can have comb or star structures. If desired, the cycloolefins described above can also be copolymerized with comonomers. These cycloolefin copolymers (COC) contain up to 50% by weight, preferably 1-35% by weight, in particular from 5 to 25% by weight, based on the weight of the COC, of comonomer. Preferred comonomers are olefins having from 2 to 6 carbon atoms, in particular ethylene and butylene. The cycloolefin polymers can be prepared with the aid of transition metal catalysts. Preparation methods are described, for example, in DD-A-109 225, EP-A-0 407 870 and EP-A-0 485 893, which are expressly incorporated herein by reference. The syndiotactic polypropylenes are homopolymers or copolymers having a propylene content of at least 70% by weight, preferably greater than 80%, in particular in the range of 95 to 100% by weight, based on the total weight of the polymer . The propylene content of the polymer has an isotacticity of 15% by weight, in particular <; 6% The average sequence length of the syndiotactic sequences is > 20%, preferably > 25% Suitable comonomers of the copolymer are olefins having from 2 to 8 carbon atoms, of which ethylene and / or butylene are preferred. The polypropylene and the incompatible polyolefin are used as a mixture or as a combination. For the purposes of the present invention, the blends refer to mechanical blends prepared from the individual components. For this purpose, the individual constituents are generally poured together as pressed molds of small size, for example lenticular or spherical granules, and mechanically mixed using a suitable agitation device.

For the purposes of the present invention, a combination is an alloy-like compound of the individual components, which can no longer be divided into the original constituents. A combination has properties as a homogeneous material and can be characterized accordingly, by means of suitable parameters. According to the invention, the surface of the upper layer A is rougher than the opposite film surface. It has been found that a rougher surface is essential for the processing compartment of the film in use according to the invention. Due to the smooth opposite surface C, the film tends to lock. In addition, the winding behavior is extremely problematic in the case of a smooth surface. According to the prior art, anti-blocking agents are incorporated in one of the upper layers in order to overcome said problems. It has been found that the incorporation of anti-blocking agents in the upper layer A is not advantageous for the use according to the invention. It has been observed that embodiments comprising antiblocking agents in the upper layer A, lead to damaged ceramic layers, because the antiblocking agents in the upper layer A leave impressions in the ceramic layer when winding the coated film or can be transferred to the ceramic layer. the same. The ceramic layers damaged in this way can no longer be used for the production of capacitors.

In order to facilitate the processing of the film without antiblocking agents and to avoid damage to the ceramic layer, a surface roughness of the upper layer A according to the invention is generated by means of a mixture of polypropylene and incompatible polyolefins. . Surprisingly, the surface structure generated in this way is sufficiently rough to process the film despite a smooth opposing surface. The film can be rolled and unrolled without any problem without the incompatible polymer incorporated in the upper layer matrix that is being mechanically removed. In contrast to the inorganic pigments normally used to achieve a certain roughness of surface, the structure of the rough surface of the film according to the invention does not result (in particular due to the low hardness of the incompatible polymer) any damage or deformations of surface in the ceramic layer during winding and unwinding. The use according to the invention thus allows the production of thin ceramic layers which have a desirable smooth surface and have no defects or other damages. The thickness of the upper layer A is greater than 0.3 μm and is preferably in the range of 0.4 to 3 μm, preferably 0.6 to 1.5 μm. According to the invention, the opposite surface of the film is smoother than the surface of the upper layer A. This smooth surface can be the surface of the base layer. In a preferred embodiment, the film has a second top layer C, by means of which the smoother surface is formed. The upper layer C consists essentially of a polyolefin, preferably a propylene polymer and, if desired, additives added in effective amounts in each case. The upper layer C generally comprises at least 90% by weight, preferably from 95 to < 100% by weight of the polyolefin. Examples of olefinic polymers of this type are: propylene homopolymer or a copolymer of ethylene and propylene or ethylene and 1-butylene or propylene and 1-butylene or a terpolymer of ethylene and propylene and 1-butylene or particular preference is given to random copolymers ethylene-propylene having an ethylene content of 1 to 10% by weight, preferably 2.5 to 8% by weight, or random copolymers of propylene-1-butylene having a content of butylene of 2 to 25% by weight , preferably from 4 to 20% by weight, in each case based on the total weight of the copolymer, or random ethylene-propylene-1-butylene terpolymers having an ethylene content of 1 to 10% by weight, preferably 2 to 6% by weight, and a content of 1-butylene of 2 to 20% by weight , preferably from 4 to 20% by weight, in each case based on the total weight of the terpolymer. Suitable propylene homopolymers comprise mainly (at least 90%) propylene and have a melting point of 140 ° C or more, preferably 150 to 170 ° C, preference is given to isotactic homopolypropylene having a content of -soluble heptane of 6% by weight or less, based on isotactic homopolypropylene. Generally, the homopolymer has a melt flow index of 0.5 g / 10 min at 15 g / 10 min, preferably 1.5 g / 10 min at 10 g / 10 min, at 230 ° C and a force of 21.6 N ( DIN 53 735).

The copolymers and / or terpolymers described above employed in the upper layer C, generally have a melt flow index of 1.5 to 30 g / 10 min, preferably 3 to 15 g / 10 min. The melting point is on the scale of 120 to 140 ° C. All the melt flow rates given above are measured at 230 ° C and a force of 21.6 N (DIN 53 735). As part of the use according to the invention, the smoother surface of the upper layer C is provided with a ceramic coating. It has been found that the polyolefin surface has adequate adhesion in order to apply a thin layer of ceramic material thereto. However, at the same time, the adhesion between the surface of the film and the ceramic layer is sufficiently low, after the corresponding steps of drying and / or processing, so that the support film is separated from the ceramic layer without damage the ceramic layer produced in this way. The embodiments having a top layer of homopolymer have proven to be particularly advantageous because they have higher heat resistance than the layers of copolymers or terpolymer and thus allow higher temperatures of drying and / or processing in the production of the layer of ceramic In addition, it has been found that the ceramic layer can be separated from the support layer having an upper layer of homopolymer with fewer problems. The upper layer C may comprise conventional neutralizers, stabilizers, if desired anti-static and lubricants. It is essential for use according to the invention, that the top layer C does not comprise any anti-blocking agent that increases the surface roughness. The increased surface roughness would transfer to the surface of the ceramic layer during coating. However, the ceramic layers must have the smoothest surface possible for use as a dielectric in order to avoid defects and air bubbles. In addition, it has been found that the particles of antiblocking agents remain stuck in the ceramic layer during detachment of the support film. This is extremely inconvenient because the antiblocking particles in the ceramic layer result in electrical defects and air bubbles. The thickness of the upper layer C is greater than 0.3 μm and is preferably in the range of 0.4 to 3 μm, preferably 0.6 to 15 μm. The total thickness of the multilayer polyolefin film according to the invention can vary within wide limits and depends on the intended use. This is from 6 to 70 μm, preferably from 10 to 50 μm, with the base layer forming approximately 50 to 98% of the total film thickness. In order to improve certain properties of the polyolefin film, both the base layer and the top layer may comprise additives in an effective amount in each case, preferably antistats and / or lubricants and / or stabilizers and / or neutralizers. All the data of quantities in the following list are in percentages by weight (% by weight), in each case based on the layer or layers to which the additive can be added. Preferred antistats are alkali metal alkane sulphonates, modified with polyether, ie, ethoxylated and / or propoxylated polydiorganosiloxanes (polydialkylsiloxanes, polyalkylphenylsiloxanes and the like) and / or essentially straight chain saturated aliphatic tertiary amines, containing an aliphatic radical having an aliphatic radical. to 20 carbon atoms, which are substituted by α-hydroxyalkyl groups (C -? - C), where N, N-bis (2-hydroxyethyl) alkylamines having from 10 to 20 carbon atoms are particularly suitable , preferably from 12 to 18 carbon atoms, in the alkyl radical. The effective amount of antistatic is on the scale of about 0.05 to 0.3% by weight. Lubricants are higher aliphatic acid amides, higher aliphatic acid esters, waxes and soaps containing metal, as well as polydimethylsiloxanes. The effective amount of lubricant is in the range of 0.1 to 3% by weight. Particularly suitable is the addition of higher aliphatic acid amides in the range of 0.15 to 0.25% by weight in the base layer and / or top layers. A particularly suitable aliphatic acid amide is erucamide. The addition of polydimethylsiloxanes on a scale from 0.3 to 2.0% by weight is preferred, in particular polydimethylsiloxanes having a viscosity of 10,000 to 1,000,000 mm 2 / s. The stabilizers that may be employed are the conventional compounds which have a stabilizing action for polymers of ethylene, propylene and other α-olefins. Its added amount is between 0.05 and 2% by weight. Particularly suitable are phenolic stabilizers, alkali metal or alkali metal stearates and / or alkali metal or alkali metal carbonates. Phenolic stabilizers are preferred in an amount of 0.1 to 0.6% by weight, in particular 0.15 to 0.3% by weight, and having a molecular weight greater than about 500 g / mol. Particularly advantageous are pentaerythrityl tetrakis-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate or 1, 3, 5-trimethyl-2,4,6-tris (3,5-di-terbutyl) benzene. 4-hydroxybenzyl). Also preferred are alkaline earth metal carbonates and / or stearates in an added amount of 0.01 to 0.05% by weight, in particular calcium stearate and / or calcium carbonate having an average particle size of less than 0.1 mm, preferably from 0.03 to 0.07 mm, an absolute particle size of less than 5 μm and a specific surface area of at least 40 m2 / g. As part of the investigations with respect to the present invention, it has been found that the film can also be employed in the application of photoprotections. The photoprotection layers are usually applied to a suitable film material and wound with this support. In some cases, the adhesion between the support film and the applied photoprotection layer is too great, and problems may arise consequently during unwinding and subsequent processing. It has been found that the film described above can be advantageously inserted into the reel as a separation film in order to avoid adhesion between the support film and the photoprotection layer. In order to produce the multilayer film by the coextrusion process, which is known per se, the mergers corresponding to the individual layers of the film are co-extruded through a die of flat film, the resulting film is captured on one or more rollers for solidification, the film is subsequently ially stretched (oriented), the ially stretched (oriented) film is heat set and rolled. The ial stretch (orientation) can be carried out simultaneously or consecutively, with the consecutive ial stretching being preferred, in which the stretching is first performed longitudinally (in the machine direction) and then transversally (perpendicular to the machine direction). First, as is conventional in the coextrusion process, the polymer or polymer mixture or the combination of the individual layers is compressed and liquefied in an extruder, it being possible for any additive to have already been added to the polymer. Then, the fusions are forced simultaneously through a die of flat film (given grooving), and the extruded multi-layer film is captured in one or more pick-up rollers, during which it cools and solidifies. The film obtained in this way is then stretched longitudinally and transversely towards the extrusion direction, which results in alignment of the molecular chains. Stretching in the longitudinal direction is preferably done in a ratio of 4: 1 to 7: 1 and stretching in the transverse direction, preferably it is carried out in a ratio of 8: 1 to 10: 1. Longitudinal stretching is conveniently carried out with the help of two rollers running at different speeds corresponding to the target stretching ratio, and the transverse stretching is conveniently carried out with the aid of a suitable tension frame. The biaxial stretch of the film is followed by heat setting (heat treatment) thereof, in which the film is maintained at a temperature of 150 to 160 ° C for about 0.5 to 10 seconds.

Subsequently, the film is rolled in a conventional manner by means of a winding unit. It has been found to be particularly favorable to maintain the pick-up roller or rollers by means of which the clogged film is cooled and solidified, at an elevated temperature compared to the prior art of 10 to 60 ° C by means of a heating circuit and cooling. In addition, the biaxial stretching is also advantageously carried out at a high film temperature, the longitudinal stretch preferably from 90 to 140 ° C and the transverse stretch preferably from 150 to 190 ° C. The invention also relates to a process for the production of ceramic capacitors in which the film described above is used according to the invention. For this purpose, a ceramic starting material, generally a ceramic powder, is first converted into a highly viscous composition using suitable solvents and binders. Suitable ceramic materials are for example oxides and / or metal titanate, for example barium titanate, magnesium silicate, titanium dioxide, bismuth oxide and mixtures thereof. These ceramics are distinguished by high dielectric constants. The highly viscous ceramic coating composition is applied to the smooth surface C of the film and dried. The film coated in this way is subsequently rolled up. If desired, the ceramic surface can be metallized in a subsequent processing step. The film is finally separated from the ceramic layer. The ceramic layers produced in this way are then subsequently converted into ceramic capacitors in a manner known per se. The invention is now explained in more detail with reference to working examples.

EXAMPLE 1 A three-layer film having an ABC layer structure is extruded by the co-extrusion method from a slotted die at an extrusion temperature of 250 ° C. The base layer consists essentially of a propylene homopolymer having a soluble n-heptane content of 4.5% by weight and a melting point of 163 ° C. The melt flow index of the propylene homopolymer is 3.3. g / 10 min at 230 ° C and a load of 21.6 N (DIN 53 753, ISO 1133). The base layer comprises 0.13% by weight of pentaerythrityl tetrakis-4- (3,5-di-tert-butyl-4-hydroxyphenyl) (lrganox 1010) propionate for stabilization and 0.06% by weight of calcium stearate as a neutralizer. In addition, the base layer comprises 0.14% by weight of N, N-bis (2-hydroxyethyl) (C? O-C2o) alkylamine (®Armostat 300) as antistatic and an erucamide (Armoslip) in an amount of 0.2% by weight as a lubricant. The upper layers A consist essentially of a mixture of 93% by weight of propylene homopolymer and 7% by weight of LDPE. The propylene homopolymer had a soluble n-heptane content of 5% by weight and a melting point of 164 ° C and a melt flow index of 8.0 g / 10 min at 230 ° C and a load of 21.6 N ( DIN 53 735, ISO 1133). The propylene homopolymer comprised 0.05% by weight of Irgafos 168 (tris (2,4-di-tert-butylphenyl) phosphite) and 0.07% by weight of Irganox 1010 for stabilization and 0.06% by weight of calcium stearate as a neutralizer. The LDPE had a melting point of 113 ° C (DSC) and a melt flow index of 0.85 g / 10 min at 190 ° C and a load of 21.6 N (DIN 53 735, ISO 1133) and a density of 0.923. g / cm3 The upper layer C consists essentially (ie, approximately 100% by weight) of a propylene homopolymer. The propylene homopolymer had a soluble N-heptane content of 5% by weight and a melting point of 164 ° C and a melt flow index of 8.0 g / 10 min at 230 ° C and a load of 21.6 N ( DIN 53 735, ISO 1133). The propylene homopolymer comprised 0.05 wt.% Of Irgafos 168 (tris (2) phosphite, 4-di-tert-butyl phenyl) and 0.07% by weight of Irganox 1010 for stabilization and 0.06% by weight of calcium stearate as neutralizer. After co-extrusion, the exempted three-layer film is captured on a first pick-up roller and a subsequent pick-up roller and cooled, then pre-heated, stretched longitudinally, stretched transversely, adjusted and rolled up during the steps of corresponding procedure, selecting the following conditions: Extrusion: Extrusion temperature 250 ° C Temperature of the first pick-up roller 35 ° C Pick-up roller temperature 29 ° C Longitudinal stretching: Pre-heating zone T = 145 ° CT roll Stretching = 145 ° C Longitudinal stretch by factor 4.6 Transverse stretch: T of heating fields = 182 ° CT of stretch fields = 162 ° C Transverse stretch by factor 9.2 Adjustment: Temperature T = 120 ° C The film has a thickness of approximately 45 μm, with the base layer having a thickness of 43 μm and each top layer having a thickness of 1.0 μm.

Comparative Example 1 Example 1 is repeated. Compared to Example 1, only the composition of the upper layer A was changed. The upper layer A essentially consisted of the upper layer homopolymer described in example 1. In addition, the upper layer comprised 0.38% by weight of an anti-blocking agent comprising SiO2 having an average particle diameter of 4.8 μm (Sylobloc 45). The process conditions were essentially unchanged. The film according to the example according to the invention is highly suitable as a support film for ceramic coating. The film can be coated well. The ceramic layer can be peeled off very well after drying and has a smooth surface without defects. Electron photomicrographs show that the surface of the upper layer A has uniform roughness, while the surface A of the film according to the comparative example has dispersed particles (antiblocking agent) which project out of the upper layer. The elevations are pressed in an undesired manner on the opposite side and on the surface of the ceramic coating. In this case, unfavorable defects are formed in the ceramic layer. The following table shows the other properties of the polyolefin films of the example and comparative example.

TABLE 1 The following measurement methods were used to characterize raw materials and films: Melt flow index DIN 53 735 at a load of 21.6 N and 230 ° C.

Melting point DSC measurement, maximum melting curve, heating rate 20 ° C / min.

Roughness Roughness was determined in accordance with DIN 4768 as Rz value and Rmax with a 2.5 mm cut.

Friction Sliding friction was determined in accordance with DIN 53 375 at 23 ° C.

Modulus of elasticity The modulus of elasticity is determined in the first 10 days after production according to EN ISO 521-1 in a sample that has a size of 15 * 100 mm2.

Resistance to tearing, prolongation at rupture The resistance to tearing and extension at rupture are determined in accordance with EN ISO 521-1 at a sample size of 15 * 100 mm2.

Shrinkage: The values of longitudinal and transverse shrinkage refer to the respective length extension of the film (longitudinally Lo and transversely To) before the shrinking process. The longitudinal direction is the machine direction, and the transverse direction is defined in consequence, as the direction transverse to the machine direction. The 10 * 10 cm2 model is shrunk in a fan assisted oven at the respective temperature (100 to 140 ° C) for a period of 15 minutes. The remaining length extensions of the model are subsequently determined longitudinally and transversally (Li and T-i). The shrinkage in percentage is then cited as the difference in the measured length extensions divided by the original length L0 and To by 100.

L -L Longitudinal shrinkage L [%] = * 100 [%] L 0 Transverse shrinkage T [%] = ° "1 * 100 [%] § Tn This method of determination for longitudinal and transverse shrinkage corresponds to DIN 40634.

Density The density is determined in accordance with DIN 53479, Method A.

Claims (8)

NOVELTY OF THE INVENTION CLAIMS

1. - The use of a multi-layer, oriented, polyolefin film as a support film in the production of a ceramic capacitor, wherein the multi-layer film consists of a base layer and at least one top layer A, wherein the layer Upper A comprises a propylene polymer and at least one incompatible polyolefin, and because the incompatible polyolefin is a copolymer of LDPE, HDPE, MDPE, ethylene-propylene or a cycloolefin polymer or a syndiotactic polymer, and the surface of the top layer A has greater roughness than the opposite surface of the film, and the film is provided with a ceramic coating on the smoother surface of the film, and this coating is dried and subsequently separated from the support film.

2. The use as claimed in claim 1, wherein the upper layer A does not contain any anti-blocking agent of particulate material.

3. The use as claimed in claim 1 and / or 2, wherein the film has a second upper layer C, and the surface of this upper layer C forms the smoothest film surface.

4. - The use as claimed in one or more of claims 1 to 3, wherein the upper layer C essentially consists of a propylene homopolymer and does not contain any antiblocking agent.

5. The use as claimed in one or more of claims 1 to 4, wherein the upper layer A comprises the propylene polymer in an amount of 70 to 99.5% by weight and the incompatible polyolefin in an amount of 0.5 to 30% by weight.

6. The use as claimed in one or more of claims 1 to 5, wherein the film coated with a ceramic layer is provided with a metal layer on the surface of the ceramic layer.

7. A ceramic capacitor produced by means of a use as claimed in one or more of claims 1 to 5. 8.- The use of a multilayer oriented film, polyolefin as a support film in the production of photoprotective layers, wherein the multilayer film consists of a base layer and at least one top layer A, wherein the top layer A comprises a propylene polymer and at least one incompatible polyolefin, and because the polyolefin incompatible is a copolymer of LDPE, HDPE, MDPE, ethylene-propylene or a cycloolefin polymer or a syndiotactic polymer, and the surface of the top layer A has greater roughness than the opposite surface of the film, and the film, as a separation film , is put in contact with the photoprotection layer with its smoothest surface