EP3781848A1

EP3781848A1 - Layer composite for a seal

Info

Publication number: EP3781848A1
Application number: EP19728691.7A
Authority: EP
Inventors: Thomas Kirschbaum; Lea Schumann; Rainer Zeuss; Martin Reinthaler
Original assignee: SGL Carbon SE
Current assignee: SGL Carbon SE
Priority date: 2018-06-06
Filing date: 2019-06-05
Publication date: 2021-02-24
Also published as: CN112219048A; CN112219048B; WO2019234128A1; JP7235774B2; DE102018208967A1; JP2021527185A; US20210088139A1

Abstract

The present invention relates to a layer composite for a seal, comprising a planar substrate layer, e.g. a graphite foil layer, and a two-dimensionally contiguous polytetrafluoroethylene cover layer which adheres to a surface of the substrate layer, characterized in that the polytetrafluoroethylene cover layer contains less than 200 g/m² polytetrafluoroethylene.

Description

COATING CONNECTION FOR ONE SEAL Description

The present invention relates to a composite layer for a seal, preferably for a flat gasket, which is particularly suitable for sealing flanges in the chemical industry, the petrochemical industry, in power plants and in the automotive industry, e.g. in industrial pipelines, in particular in chemical, oil and gas applications, as well as in thermal energy systems, e.g. in an exhaust gas treatment system of a power plant or a motor vehicle.

The use of particulate polytetrafluoroethylene (PTFE) in conjunction with graphite is known.

For example, the utility model RU 41 430 U1 describes a cylinder head gasket comprising a layer of thermally expanded graphite, wherein a PTFE coating is applied to at least one of the surfaces. The coating can be applied from a suspension, for example by spraying. The optimum thickness should be 5-20 microns. The PTFE coating proposed here is thus a layer of mutually arranged PTFE particles which are so small that they can be brought into suspension. A flat gasket composed of one or more graphite foils, in which at least one film surface is coated in one part with a substance in the form of particles which reduces the static friction and sliding friction, is known from German Offenlegungsschrift No. 2,441,602 to Sigri Elektrographit GmbFI known. Suitable coating materials are compounds having a layered lattice structure, such as molybdenum disulfide, boron nitride and graphite fluoride, temperature-resistant, anti-adhesive polymers such as PTFE and polyimide and metal soaps and phthalocyanines or mixtures of these substances. The thickness of the layer consisting of said lubricants should preferably be 5 to 200 μm. In addition, it is described that the friction-reducing substances are applied as a dispersion. The friction-reducing substances are preferably rolled into the film. For example, in the film surfaces, firmly anchored PTFE particles are obtained which form island-like complexes.

Also composites comprising sheet-like graphite foil layers and adhering, flat-connected plastic-containing layers are known

For example, DE 691 17 992 T2 describes a flexible graphite laminate which is to be suitable as a sealing element in which a polymer resin, e.g. PTFE-coated material is introduced and bonded between two sheets of flexible graphite material. In the flexible graphite laminate described here, the PTFE thus lies inside, between graphite layers.

DE 10 2012 202 748 A1 describes a method for Fierstellung a graphite foil with a particularly low basis weight. In this process, in an expansion step, graphite salt particles are expanded on a base to give graphite expandate. The graphite pandate remains on the substrate and it is compressed in a compression step on the substrate to the graphite foil. It is described that the graphite foil can form a laminate with at least one plastic film. The plastic film may consist of at least one of the plastics from the group comprising polyethylene terephthalate (PET), polyolefins such as polyethylene (PE) and polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyester, polyimide (PI), fluoroplastics, such as PVDF and PTFE, polycarbonate and biopolymers such as polylactide (PLA), cellulose acetate (CA) and starch blends. In addition, it is described that graphite foil and plastic film can be bonded together without adhesive. The plastic film may be perforated, with a hole diameter between 0.25 and 2 mm is described. An application in sealing technology is also proposed. KR 0158051 B1 relates to gaskets containing expanded graphite. It is proposed to impregnate with a sealing material such as PTFE, in particular PTFE particles are mentioned. Also, a PTFE film is called, without specifying a thickness.

PTFE films and films are formed from PTFE blocks by removing a layer from the surface of the PTFE block with a flat cutting tool.

It turned out that the layer has to comply with a certain minimum thickness, otherwise film production is not possible. The use of PTFE plastic films therefore inevitably leads to specific, high PTFE basis weights.

The utility model G 92 08 943.7 U1 describes a gland packing with a plurality of graphite sealing rings which are laid on top of each other to form a gland packing. At least one of the graphite gaskets has a graphite core and a PTFE sheath. The casing may be formed from a PTFE film or PTFE sheet or sintered onto the graphite core in a diffusion-tight manner. The envelope of PTFE can be designed as a closed envelope or as a channel-shaped enclosure. A strength of the PTFE cladding is not mentioned. The figures show very thick PTFE sheathings. Both in the case of the closed envelope, as well as in the case of the channel-shaped enclosure, two circumferential edges of the graphite core are covered with PTFE.

The utility model DE 21 2008 000 051 U1 relates to a gasket for sealing a flange connection. Described is a core ring made of expanded graphite, which is coated with a coating layer of porous polytetrafluoroethylene. The coating layer is formed by spirally winding a coating tape around the surface of the core ring. The utility model also teaches that the turns of the coating tape should be overlapping. Thus, the coating tape covers not only the two surfaces of the core ring completely, but also the inner one and outer edge of the core ring. The coating tape may have a thickness of 0.045 to 0.25 mm, depending on the diameter of the core ring. It will be described that the porosity of the coating tape can be, for example, 30 to 40% or 50 to 60%. The seals described in DE 21 2008 000 051 U1 have the disadvantage that the thickness of the coating is always inconsistent, since areas with multiple overlapping and areas with only a simple overlap always form during winding. In addition, the winding is associated with a lot of effort and difficult to automate. The present invention has for its object to provide a universally applicable sealing material, which can be produced in a particularly simple manner and environmentally friendly and can easily be detached from the surfaces with the sealing material even after prolonged use at high pressure and high temperatures stay in contact.

This object is achieved by a layer composite for a seal, in particular for a flat gasket, comprising a flat substrate layer, eg a graphite foil layer, a polytetrafluoroethylene cover layer adhering to a surface of the substrate layer, wherein the polytetrafluoroethylene cover layer is less than 200 g / m ² polytetrafluoroethylene Contains (PTFE). The cover layer thus contains less than 200 g PTFE per square meter of cover layer, generally at most 190 g / m ² PTFE, in particular at most 175 g / m ² PTFE, preferably at most 160 g / m ² PTFE, further preferably at most 150 g / m ² PTFE, more preferably at most 130 g / m ² PTFE, most preferably at most 1 10 g / m ² PTFE, most preferably at most 100 g / m ² PTFE, for example at most 80 g / m ² PTFE.

The polytetrafluoroethylene cover layer is areal coherent. A layer-connected layer is understood to be a layer which can be closed in a planar manner (eg closed in a gas-tight manner), can be porous or has a net-like structure may have. By contrast, a layer consisting of adjacent particles is not a surface-coherent layer.

The feature "areal coherent" refers to the polytetrafluoroethylene. Thus, the areal coherent polytetrafluoroethylene cover layer is not a layer of polytetrafluoroethylene particles which are converted into other substances, e.g. embedded in other polymers or incorporated into the surface of the substrate layer, e.g. the graphite foil layer, are pressed. Surprisingly, it has been found that layer composites according to the invention can be obtained in a particularly simple manner by the method according to the invention described below using microporous polytetrafluoroethylene layers which are e.g. in US Pat. No. 3,962,153 and will be discussed in more detail below in connection with the inventive method. For example, stretched polytetrafluoroethylene layers can be used which are known from completely different fields of technology, for example as so-called GORE-TEX® membranes from the clothing industry. However, seals are not formed there with the aid of these materials, but instead layers of clothing which are permeable to water vapor and specifically promote the removal of water vapor from the body, that is to say quasi "imperfections". The proposed use is so far in contrast to the hitherto known main application of microporous PTFE layers.

The layer composites according to the invention and the process according to the invention are environmentally compatible since only a very thin polytetrafluoroethylene cover layer with a very low basis weight of less than 200 g PTFE per square meter cover layer is formed. Although PTFE-containing coatings have been proposed in the aforementioned prior art. However, these are formed by means of suspensions or dispersions of PTFE particles. So they are not flat connected, but essentially formed of adjacent PTFE particles. in the Compared with the use of microporous, areally connected polytetrafluoroethylene cover layers proposed according to the invention, suspensions and dispersions containing PTFE particles entail a much higher risk of polluting PTFE releases, in particular during spraying. Since the PTFE particles are not connected to one another, they are practically indistinguishable from the remaining sealing material, which makes disposal more difficult. On the other hand, surface-coherent PTFE can be detached at least in large part from the sheet-like substrate layer. Compared with the PTFE films mentioned in the prior art, there is the advantage of a lower basis weight; It is therefore less total PTFE needed, which increases the environmental impact.

The layer composite according to the invention is universally applicable, for example in a very wide range up to particularly high pressures and temperatures. If one uses PTFE layers with a higher basis weight at particularly high pressures and temperatures in flat gaskets in flanges, the contact pressure of the flange drops significantly over the service life, since substantial amounts of PTFE "creep" out of the gasket. It was found that the contact pressure of the flange remains permanently high when flat gaskets are used with the layer composite according to the invention. On the one hand, the particularly thin polytetrafluoroethylene backings seem to reduce the creep of PTFE as a whole. On the other hand, the thickness of the flat gasket decreases only minimally when the PTFE creeps, because there is anyway only very little PTFE because of the small basis weight according to the invention. It can therefore, if at all, only very little PTFE "creep out" of the seal. Consequently, the thickness of the gasket only decreases very slightly when "creeping out" of PTFE and the contact pressure remains correspondingly high. As a result, the maintenance effort suffers because screws on flanges do not have to be retightened or less often to maintain the desired contact pressure. It was found that flat gaskets according to the invention can be detached from the flange by hand even after 24 hours at 300 ° C. and 30 MPa with little effort and without visible residues. The layer composite comprises a flat substrate layer. The flat substrate layer has two surfaces, which merge into one another in a peripheral edge region. The peripheral edge region defines the outline of the substrate layer.

The polytetrafluoroethylene backsheet adheres to one surface of the substrate layer. The polytetrafluoroethylene liner layer may extend into an area outside the outline of the substrate layer. Typically, the polytetrafluoroethylene cover layer does not extend beyond this contour or extends beyond this contour only in one or more sections of the peripheral edge region. The total length of the partial section or of the sections in which the polytetrafluoroethylene cover layer extends beyond the outline is at most 99.9%, generally at most 90%, in particular at most 80%, preferably at most 70%, particularly preferably at most 60%, most preferably at most 50%, for example at most 35% of the length of the peripheral edge region. According to the invention, it is possible for the polytetrafluoroethylene cover layer also to extend around partial sections of the peripheral edge region of the substrate layer. Then, areas of the polytetrafluoroethylene cover layer covering the edge region also contribute to the total area of the polytetrafluoroethylene cover layer. According to the invention, however, it is preferred if more than 80%, generally more than 85%, preferably more than 95%, particularly preferably more than 98%, of the total area of the polytetrafluoroethylene cover layer lies within the outline of the substrate layer. This is preferred because it further reduces the total amount of PTFE required, which further improves the environmental compatibility of the layer composite according to the invention. As a flat substrate layer, it is possible to use any sheet material on the surface of which a microporous polytetrafluoroethylene layer can be applied by the method according to the invention. The suitability of a substrate layer can easily be tested by a person skilled in the art. The planar substrate layer can be, for example, a graphite foil layer or a metal foil layer, wherein the metal is preferably selected from stainless steel, nickel, nickel alloys, steel and copper, for example under stainless steel and nickel alloys.

The flat substrate layer is preferably a graphite foil layer. The graphite foil layer is, for example, a graphite foil layer produced from expanded graphite. As is known, graphite foils can be produced by treating graphite with certain acids to form a graphite salt with acid anions interposed between graphene layers. The graphite salt is then expanded by exposure to high temperatures of, for example, 800 ° C. The graphite expan- date obtained during the expansion is then pressed into the graphite foil. A process for the production of graphite foils is described, for example, in EP 1 120 378 B1. The DE 10 2012 202 748 A1 mentioned in the introduction also describes a method for producing a graphite foil. In the composite layer, the density of the graphite foil layer is generally from 0.7 to 1.3 g / cm ³ , preferably from 1.0 to 1.2 g / cm ³ , particularly preferably from 0.1 to 1.1 g / cm ³ .

According to the invention, the polytetrafluoroethylene cover layer lies outside in the layer composite. This is expressed by the syllable "deck". On the side of the polytetrafluoroethylene cover layer facing away from the flat substrate layer, therefore, no further surface-related material layer is applied. In the case of the microparticulate coating which, according to certain embodiments of the invention, is connected to the substrate layer via the polytetrafluoroethylene cover layer, this is not a further, spatially coherent material layer. The polytetrafluoroethylene liner adheres to the surface of the substrate sheet. By this is meant that the polytetrafluoroethylene cover layer is bonded so firmly to the surface of the substrate layer that the layer composite can be cut by water jet cutting or by punching without the layer composite dissolving. In general, the tensile strength of the compound of both layers is higher than 1 N / mm ² , preferably higher than 2 N / mm ² . Surprisingly, it has been found that microporous polytetrafluoroethylene layers can be attached very firmly to flat substrate layers and in particular to graphite foil layers solely by pressing on and / or increasing the temperature. It is assumed that microscopic unevenness of the substrate layer interlocks with the micropores of the polytetrafluoroethylene layer during pressing on and / or with an increase in temperature and this ensures an unexpectedly high adhesive strength to the substrate layer which goes far beyond the technical requirements.

According to the invention, the polytetrafluoroethylene cover layer adheres to a surface of the flat substrate layer. In general, one of the two surfaces of the polytetrafluoroethylene cover layer is (almost) completely in contact with the surface of the substrate layer, eg at least 90% of one of the two surfaces of the polytetrafluoroethylene cover layer is in contact with the surface of the substrate layer. In certain layer composites, for example corrugated gaskets, the substrate layer is corrugated. Wavy means that the substrate layer has wave extrema, ie maxima and minima. One of the two surfaces of the polytetrafluoroethylene backsheet may be almost completely in contact with one of the surfaces of the substrate layer. It then rests on the surface of the substrate layer both in the region of the maxima and in the region of the minima and in the regions lying between the minima and maxima. Preferably, partial areas of one of the two surfaces of the polytetrafluoroethylene cover layer are in contact with partial areas of one of the two surfaces of the corrugated substrate layer. For example, the contact between substrate layer and polytetrafluoroethylene cover layer is only in the region of the maxima. Polytetrafluoroethylene is a highly fluorinated polyethene which is usually at least 85% by weight, preferably at least 90% by weight, particularly preferably at least 95% by weight, for example at least 98% by weight, of -CF ₂ -CF ₂ - Subunits exists. In polytetrafluoroethylene, the molar ratio of F atoms to F atoms is preferably more than 10, in particular more than 20, preferably more than 30.

The average thickness of the polytetrafluoroethylene cover layer is preferably in the range from 10 to 50 .mu.m, in particular in the range from 10 to 40 .mu.m, preferably in the range from 10 to 30, mhh. In general, the cover layer contains 1 to 190 g / m ² PTFE, in particular 2.5 to 175 g / m ² PTFE, preferably 4 to 160 g / m ² PTFE, further preferably 5 to 150 g / m ² PTFE, particularly preferably 7 up to 130 g / m ^{2 of} PTFE, very particularly preferably 9 to 1 10 g / m ^{2 of} PTFE, very preferably 10 to 100 g / m ^{2 of} PTFE, eg 12 to 80 g / m ^{2 of} PTFE. The layer composite according to the invention is preferably 0.5 to 4.0 mm thick, particularly preferably 1.5 to 3.0 mm thick.

In one embodiment of the layer composite according to the invention, the polytetrafluoroethylene cover layer is uncoated on the surface facing away from the flat substrate layer. It has been observed that the polytetrafluoroethylene - after prolonged use at high pressure and at high temperature - still relatively strongly adheres to the flange and the composite of polytetrafluoroethylene and substrate layer dissolves when Fleraus- take the flat gasket. However, after the removal of the remaining flat gasket, the polytetrafluoroethylene can be easily removed completely from the flange without any tools and essentially in one piece.

In another embodiment of the layer composite according to the invention, the polytetrafluoroethylene cover layer is coated on the surface facing away from the flat substrate layer. Any non-stick coating which has been described in the prior art is conceivable, in particular in connection with seals for flanges. The layer composite according to the invention preferably has a microparticulate coating which is bonded to the substrate layer via the polytetrafluoroethylene cover layer.

The coating may completely or partially cover a surface of the polytetrafluoroethylene cover layer facing away from the substrate layer, e.g. from 5 to 99%, in particular from 10 to 98.5%, preferably from 20 to 98%, particularly preferably from 25 to 97%, very particularly preferably from 30 to 95%.

The coating may comprise particles, for example graphite particles having an average particle size (d50) in the range from 1 to 50 μm, in particular in the range from 1 to 25 μm, for example in the range from 1 to 10 μm. The mean particle size d50 describes a value determinable by laser granulometry according to ISO 13320-2009, in which the distribution sum curve Q ₃ (X) of the particle size distribution is 50%.

Embodiments of the invention having a microparticulate coating have the advantage of further reducing the adhesion of the polytetrafluoroethylene cover layer to the flange. This means that flat gaskets with a microparticulate coating can reliably be removed from the flange in one piece, even after prolonged use at high pressure and at high temperatures. Subsequent detachment of delaminated PTFE from the flange is then not required. This offers the additional decisive advantage that safe operation of the process can be ensured even after the replacement of a seal. This is because, in particular, hard-to-reach flanges tend to overlook PTFE or PTFE-based residues of old gaskets. Under newly introduced flat gaskets PTFE residues lead to uneven contact pressure, which in the worst case can lead to uncontrolled discharges of hot fluids. After all, with microparticulate coating, we therefore achieve a particularly reliable process operation after gas exchange even at high pressure and at high temperatures with even greater safety than when using layer composites without microparticulate coating. In principle, the microparticulate coating can comprise the most varied of particles, for example quartz flour, silicates, for example phyllosilicates, mica, pigments, iron oxides, talc, metal oxide particles, for example Al ₂ O ₃ , SiO ₂ , and / or TiO ₂ .

Preferably, however, the microparticulate coating is a microparticulate solid lubricant coating.

The solid lubricant coating may e.g. Graphite particles, molybdenum disulfide particles and / or soft metal particles, e.g. Include aluminum, copper or lead particles. Particularly preferred solid lubricant coatings include graphite particles and / or molybdenum disulfide particles. A most preferred solid lubricant coating comprises graphite particles.

Solid lubricant coatings have the advantage that, in their application, the porosity or residual porosity of the polytetrafluoroethylene cover layer generally does not increase. Solid lubricant particles are soft and therefore their application causes no appreciable violation of the Polytetrafluorethylendecklage. The application of the solid lubricant coating thus generally does not result in an undesirable degree of fluid permeability. The layer composite is preferably fluid-tight, i. Essentially impermeable to gases and liquids. This can be e.g. according to DIN EN 13555.

The layer composite according to the invention preferably contains substances which, when heated, reach a temperature in the range from 100.degree. C. to 400.degree. C. and subsequent deposition. Cooling to room temperature Adhesive residues do not form or only between fluid-tight layers. This causes adhesive residues not in contact with the

Flange, so that a made of the layer composite gasket can be easily solved at any time by the flange.

In addition to the two layers mentioned in claim 1, the layer composite may have other layers, for example metal layers, preferably one or more steel sheet layers or stainless steel sheet layers and / or further substrate layers, for example further graphite foil layers. The sheet layers may be e.g. to trade smooth sheet layers or spike sheet layers.

The layer composite according to the invention preferably comprises a second areal-connected polytetrafluoroethylene cover layer. A polytetrafluoroethylene cover layer then covers the layer composite on the front side and the second polytetrafluoroethylene cover layer then covers the layer composite on the back side.

For the second polytetrafluoroethylene cover sheet coextensive, the above statements on the coherent polytetrafluoroethylene cover sheet apply correspondingly.

A second areal coherent Polytetrafluorethylendecklage is particularly desirable if the layer composite, a flat gasket for a

Flange connection of pipe sections of a pipeline is made. In flanged joints of pipe sections, both sides of the gasket are exposed to the fluid passing through the pipeline as well as flashing and pressure to a similar extent, so that the problem of disengaging the gasket from the flanges of both pipe sections is often the same. Even after 24 hours at 300 ° C. and 30 MPa, composite layers according to the invention which are covered on both sides with polytetrafluoroethylene cover can be easily detached from both flanges. The second, cohesively connected polytetrafluoroethylene cover layer may also have a microparticulate coating. This is called a second microparticulate coating. For the second microparticulate coating, the above statements on the microparticulate coating apply accordingly.

The two polytetrafluoroethylene covers can be e.g. each adhere to one of the two surfaces of a flat substrate layer. For example, the two polytetrafluorethylene cover layers adhere to the two surfaces of the graphite foil layer. In this embodiment, the layer composite comprises a graphite foil layer and two polytetrafluoroethylene cover layers adhering to one another on the two surfaces of the graphite foil layer.

In a particularly preferred layer composite according to the invention, the one polytetrafluoroethylene cover layer adheres to the surface of a flat substrate layer, e.g. the graphite foil layer and the second polytetrafluoroethylene liner layer on the surface of a second sheet substrate layer, e.g. a second graphite foil layer. The two flat substrate layers can, for example, be provided with the surfaces of the flat substrate layers facing away from the polytetrafluoroethylene covers on the two surfaces of a thin, e.g. 25 to 250 μm thick, flat metal layer, in particular stainless steel sheet layer, e.g. Glattblechlage or pike plate layer adhere.

An inventive layer composite accordingly has the following layer structure:

- Polytetrafluorethylenendecklage

- flat substrate layer, e.g. Graphite foil,

- flat metal layer,

- flat substrate layer, e.g. Graphite foil,

- Polytetrafluorethylenendecklage. Alternatively, the one substrate layer with the surface of the substrate layer facing away from the polytetrafluoroethylene cover layer adheres to a thin, eg 25 to 250 μm thick metal layer, in particular stainless steel sheet layer, eg smooth sheet layer and the second substrate layer with the surface facing away from the second polytetrafluoroethylene cover layer second substrate layer on another thin, eg 25 to 250 pm thick metal layer, in particular stainless steel sheet, eg smooth sheet layer. Then, the two metal layers adhere to the surfaces of the two metal layers facing away from the polytetrafluoroethylene cover layers on the opposing surfaces of a third planar substrate layer

An inventive layer composite accordingly has the following layer structure:

- Polytetrafluorethylenendecklage

- flat substrate layer, e.g. Graphite foil,

- flat metal layer,

- flat substrate layer, e.g. Graphite foil,

- flat metal layer,

- flat substrate layer, e.g. Graphite foil,

- Polytetrafluorethylenendecklage.

The layer composite according to the invention may contain further, planar layers.

Another layer composite according to the invention has the following layer structure: polytetrafluoroethylene cover layer

- flat substrate layer, e.g. Graphite foil,

- flat metal layer,

- flat substrate layer, e.g. Graphite foil,

- flat metal layer,

- flat substrate layer, eg graphite foil layer, - flat metal layer,

- flat substrate layer, e.g. Graphite foil,

- Polytetrafluorethylenendecklage. Under the brand name Sigraflex®, the applicant offers a wide variety of layer composites with graphite foil layers, e.g. also multi-layer composites with several layers of stainless steel foil and graphite foil. It is understood that laminated layers according to the invention comprise all those layer composites which have hitherto been obtainable under the trademark Sigraflex®, wherein a polytetrafluoroethylene cover layer according to the invention has been applied to at least one of the graphite foil surfaces or metal surfaces of these layer composites.

An object of the present invention is a seal, in particular a flat gasket, comprising a layer composite according to the invention. However, the seal can also be a corrugated gasket, comb profile gasket or spiral gasket comprising the layer composite according to the invention.

In particular, it is particularly advantageous for flat gaskets when the layered composite according to the invention has a certain flexural strength. It turned out that the composite can then be processed universally into large and small flat gaskets which can easily be inserted between flanges overhead, without the sealing material bending or even buckling.

Particularly preferred layer composites according to the invention have a flexural strength (FS 3P) of at least 4.0 MPa, in particular at least 5.0 MPa, for example at least 5.5 MPa. Flexural strength is determined according to ISO 178 as described below. Very particularly preferred layer composites according to the invention have a bending strength of at least 6.0 MPa, for example more than 6.5 MPa. Then the layer composites for flat gaskets are predestined and can be particularly well over head between see flanges. On the other hand, they are then not suitable for the production of Stuffing box seals, since they can no longer be processed into a sealing thread required for this purpose, at least no longer by processing the layer composite into strips, twisting the strips and then braiding the twisted strips into a sealing yarn.

The flat gasket according to the invention can be cut out of the composite according to the invention, e.g. by punching or by water jet cutting.

The invention also relates to a process for the preparation of a laminated joint according to the invention, wherein

a) a surface of a sheet substrate layer, e.g. a graphite sheet layer is contacted with a microporous polytetrafluoroethylene layer, and

b) the polytetrafluoroethylene layer is pressed onto the surface of the substrate layer so strongly and / or the temperature is increased until the polytetrafluoroethylene layer adheres to the substrate layer and a polytetrafluoroethylene cover layer adhering to the substrate layer is obtained.

The microporous polytetrafluoroethylene layer is a conventional porous and gas-permeable polytetrafluoroethylene membrane obtainable by stretching polytetrafluoroethylene and used in garment materials for purposely removing water vapor from the body. The preparation of such porous membranes is described, for example, in US Pat. No. 3,962,153. The mean pore size of the microporous polytetrafluoroethylene layer can vary within a wide range, preferably in the range from 0.1 μm to 500 μm. The average pore size of the polytetrafluoroethylene microporous layer may be e.g. in the range of 0.1 to 10 pm.

It was found that the resulting polytetrafluoroethylene backsheet still has a significant residual porosity. This is lower than the porosity of the microporous po- lytetrafluorethylenschicht. Surprisingly, the flat gaskets produced from the layer composite according to the invention nevertheless have a very high sealing capacity. The inventors assume that convex regions of the substrate layer protrude into the pores remaining in the polytetrafluoroethylene cover layer and this ultimately contributes decisively to the unexpectedly high sealing capacity.

The pressure in step b) can be varied within wide limits. For example, the polytetrafluoroethylene layer is pressed at a pressure in the range from 0.2 to 10 N / mm ² , preferably at a pressure in the range from 0.4 to 5 N / mm ² . This offers the advantage that the pressure can be adjusted so that the substrate layer, eg the graphite foil layer, is compressed to a desired extent, ie to a desired density.

The temperature in step b) can be varied within wide ranges. For example, the temperature is increased in a range of 320 to 440 ° C. The person skilled in the art selects a higher temperature of up to 440 ° C when there is little time to treat the substrate layer in contact with the microporous polytetrafluoroethylene layer. For example, in a continuous process step b), if only a very short fleece zone is available and if the substrate layer in contact with the microporous polytetrafluoroethylene layer is to be passed through the fleece zone very rapidly. The skilled artisan will choose a lower temperature at or just above 320 ° C if there is plenty of time to treat the substrate layer in contact with the microporous polytetrafluoroethylene layer. For example, in a continuous process step b) if a very long heating zone is available and / or if the substrate layer in contact with the microporous polytetrafluoroethylene layer is to be passed slowly through the fleece zone. In a further method step c), a microparticulate coating can be applied to the surface of the polytetrafluoroethylene cover layer facing away from the substrate layer, which is bonded to the substrate layer via the polytetrafluoroethylene cover layer. Preferably, the bond between microparticles and polytetrafluoroethylene backsheet is made by sintering at 330 to 400 ° C. Preferably, the sintering is carried out at a temperature in the range of 350 to 410 ° C, for example 365 to 395 ° C. Pores optionally remaining in the polytetrafluoroethylene backsheet partially or completely close during sintering in the presence of the microparticles. The invention also relates to the use of a microporous polytetrafluoroethylene layer for reducing the gas permeability of flat substrate layers.

The invention also relates to the use of a microporous polytetrafluoroethylene layer for forming a polytetrafluoroethylene cover layer which adheres to a surface of a graphite foil layer or metal foil layer.

The invention also relates to the use of a microporous polytetrafluoroethylene layer as a carrier of a microparticulate coating, e.g. a microparticulate solid lubricant coating. Microparticulate solid lubricant coatings have been discussed in detail above.

In the context of this invention, the preferred values for the basis weight of the microporous polytetrafluoroethylene layer are the preferences given above for the polytetrafluoroethylene cover layer. Because of steps a) and b), the PTFE surface virtually does not change, so that the initial basis weight of the microporous layer corresponds to the surface weight of the cover layer. The polytetrafluoroethylene layer thus contains less than 200 g of PTFE per square meter of polytetrafluoroethylene layer. In general, the polytetrafluoroethylene layer contains 1 to 190 g / m ^{2 of} PTFE, in particular 2.5 to 175 g / m ^{2 of} PTFE, preferably 4 to 160 g / m ^{2 of} PTFE, further preferably 5 to 150 g / m ² PTFE, particularly preferably 7 to 130 g / m ^{2 of} PTFE, very particularly preferably 9 to 1 10 g / m ^{2 of} PTFE, most preferably 10 to 100 g / m ^{2 of} PTFE, for example 12 to 80 g / m ^{2 of} PTFE.

Microporous polytetrafluoroethylene layers with very different thicknesses can be used. For example, very porous polytetrafluoroethylene layers are thicker at a given basis weight than less porous polytetrafluoroethylene layers. Typically, the thickness of the microporous polytetrafluoroethylene layer ranges from 25 to 400 microns. The roughness of the surface of the sheet substrate layer is preferably Rz 1, 5pm to Rz 30pm, e.g. Rp 3pm to Rz 15pm. It is assumed that convex areas of the surface of the substrate layer interlock with pores of the microporous polytetrafluoroethylene layer and the application of pressure and / or the increase in temperature in step b) reinforces the toothing and this enhances the strength of the polytetrafluoroethylene layer increased at the surface. The expert can control the roughness of a

Substrate layer, e.g. For example, adjust a graphite foil layer by treating the graphite foil with a textured roller.

The planar substrate layer is preferably compressible. The compressibility of the sheet substrate layer is preferably 5 to 80%, e.g. 20 to 60%. If the substrate layer yields under the application of pressure in step b), the toothing seems to solidify, so that especially in the case of compressible, flat substrate layers alone the application of pressure in step b) leads to a strong adhesion of the polytetrafluoroethylene cover layer leads to the flat substrate layer.

Other features and advantages of the invention will become apparent from the following embodiment. example

Graphite foil was coated by means of a calender at room temperature with an ePTFE membrane (thickness about 100 pm). The ePTFE membrane used was a conventional, porous and gas permeable, white polytetrafluoroethylene membrane obtainable by stretching polytetrafluoroethylene. Thereafter, the mixture was subjected to a temperature treatment at 380 ° C., forming a colorless, glassy polytetrafluoroethylene cover layer (thickness: about 20 μm) on the graphite foil, which adhered firmly to the graphite foil.

In an experiment, the layer composite obtained from the calender was coated with graphite powder (particle size 2-1 Opm) before the temperature treatment. The graphite particles partly penetrate into open pores of the ePTFE membrane. In the subsequent temperature treatment, the graphite particles were melted into the surrounding polytetrafluoroethylene and thus very firmly immobilized. This produced a non-stick coating.

Flexural strength: The flexural strength (FS 3p) was determined with a 3-point bending test, the test specimen being positioned on two supports in accordance with ISO 178 and loaded with a test stamp in the middle.

Tested for bending strength layers and layer composites:

L1: graphite foil with 1, 3mm thickness at density 0.7g / cm ³

L2: Graphite foil L1, coated on one side with an ePTFE cover layer

L3: ePTFE overlay graphite foil L1 sprocket with 80pm thick graphite foil

L1 -ePTFE liner. The two in the composite layer outside In addition, ePTFE cover layers were superficially coated with microparticulate graphite powder

L4: graphite foil L1 spiked plate with 100 pm thickness graphite foil L1 4 or 5 material samples of each layer or each layer composite were tested for flexural strength. The results are shown in the following table:

Claims

claims

1. Layer composite for a seal, comprising

a flat substrate layer,

a polytetrafluoroethylene backsheet adhering to a surface of the substrate layer,

characterized in that

the polytetrafluoroethylene backsheet contains less than 200 g / m ² polytetrafluoroethylene

2. layer composite according to claim 1, characterized in that the average thickness of the polytetrafluoroethylene cover layer is in the range of 10 to 50 pm.

3. Layer composite according to claim 1, characterized by a microparticulate coating which is connected via the polytetrafluoroethylene cover layer to the substrate layer, wherein the coating at least partially covers a surface of the polytetrafluoroethylene cover layer facing away from the substrate layer.

4. layer composite according to claim 3, characterized in that the coating comprises particles having an average particle size in the range of 1 to 50 pm.

5. Layer composite according to claim 3, characterized in that the microparticulate coating is a microparticulate solid lubricant coating.

6. Layer composite according to claim 1, characterized in that it does not contain substances which on heating to a temperature in the range of 100 ° C to 400 ° C and subsequent cooling to room temperature adhesive residues or contains only between fluid-tight layers ,

7. Layer composite according to claim 1, characterized in that the flat substrate layer is a graphite foil layer.

8. seal, characterized in that it comprises a layer composite according to claim 1.

9. A method for producing a composite layer according to claim 1, characterized in that

a) a surface of a flat substrate layer is brought into contact with a microporous polytetrafluoroethylene layer, and

10. The method according to claim 9, characterized in that in step b) the polytetrafluoroethylene layer is pressed with a pressure in the range of 0.2 to 10 N / mm ² and / or the temperature in a range of 320 to 440th ° C is increased.

1 1 .Method according to claim 9, characterized in that

c) a microparticulate coating is applied to the surface facing away from the substrate layer of the polytetrafluoroethylene end layer, which is connected to the substrate layer via the polytetrafluoroethylene cover layer.

12. The method according to claim 11, characterized in that the connection between microparticles and Polytetrafluorethylendecklage is prepared by sintering at 330 to 400 ° C.

13. Use of a microporous polytetrafluoroethylene layer containing less than 200 g / m ² polytetrafluoroethylene, to reduce the gas permeability of a flat substrate layer.

14. Use of a microporous polytetrafluoroethylene layer containing less than 200 g / m ² polytetrafluoroethylene, to form a Polytetrafluorethylendeck- layer which adheres to a surface of a Graphitfolienlage or metal foil layer.

15. Use of a microporous polytetrafluoroethylene layer containing less than 200 g / m ² polytetrafluoroethylene, as a carrier of a microparticulate coating, such as a microparticulate solid lubricant coating.