CA2364748A1

CA2364748A1 - Acrylic resin-impregnated bodies formed of expanded graphite

Info

Publication number: CA2364748A1
Application number: CA 2364748
Authority: CA
Inventors: Oswin Oettinger; Juergen Bacher
Original assignee: SGL Carbon SE
Current assignee: SGL Carbon SE
Priority date: 2000-12-07
Filing date: 2001-12-06
Publication date: 2002-06-07
Also published as: US20020127390A1; DK1221432T3; JP4425510B2; EP1221432B1; EP1221432A2; JP2002256083A; DE50113627D1; EP1221432A3; PT1221432E; ATE386709T1; DE10060838A1; ES2300303T3

Abstract

Bodies made of expanded graphite are impregnated with low-viscosity, solvent-free, storage-stable, polymerising acrylic resins. Bodies are made of a primary product made of expanded graphite with an open pore system, with a particularly preferred range of bulk densities from about 0.5 to about 1.3 g/cm3 and with an ash value of not more than about 4% by weight. Such bodies can also contain a proportion of additives. The impregnated, shaped and rapidly curable graphite bodies are employed as sealing elements, as components in fuel cells or as heat-conducting elements.

Description

ACRYLIC RESIN-IMPREGNATED BODIES FORMED OF EXPANDED GRAPHITE
Description The invention relates to a body made of expanded or at least partially recompressed expanded graphite impregnated with a synthetic resin and to a process for producing such a body.
Material composites of graphite and plastics are widely used in many technical applications. For example, particles of electrographite are processed with fluoroplastics into highly corrosion-resistant components for the construction of chemical apparatus, but these are comparatively expensive owing to the costs of the fluoroplastics and the processing technique required. A
subject which in terms of content is even closer to the application concerned here is set out in US Patent No.
4,265,952 which describes that expanded graphite is mixed with, for example, fine PTFE powder and subsequently compressed. To this extent, the production technique differs from the impregnating technique described in the present application.
Another example of a material composite of graphite and plastic is a superficially resin-impregnated foil made of natural graphite, which is predominantly employed in the form of flat seals against particularly aggressive media. Many references to this second example are found in technical literatures. Today, thousands of tons of foils made of natural graphite are produced worldwide every year.
Processes used therefor are described in Patent Publications EP 0 087 489 US Patent No. 3,404,061 and US Patent No.
3,494,382.

The teaching of these references can be summarized as follows: an intercalating agent, such as, for example, concentrated sulfuric acid, acts on natural graphite, preferably platelike or flaky natural graphite, in the presence of an oxidising agent, such as, for example, concentrated nitric acid or hydrogen peroxide. This results in graphite intercalation compounds in the shape of flakes or platelets. By brief heating, for example by introduction into the flame of a gas burner, the flakes are thermally decomposed and, as a result of the gas pressure arising in their interior during this decomposition process, puff up to form loose graphite particles of wormlike shape. This product is also referred to as "expanded" graphite or as graphite expandate.
Expanded graphite is extremely plastic and can be readily shaped without the aid of a special binder while being compressed to a greater or lesser degree. Economically the most important product thus produced is a flexible graphite foil, which can be produced efficiently on calender belts. Such products have typical bulk densities between 0.7 and 1.3 g/cm3. However, other bodies of different geometry, for instance individual sealing bodies which, on average, are compressed to a greater degree and have bulk densities of 1.0 to 1.8 g/cm3, are also possible. There are also sponge-like bodies of, on average, low bulk density, having values of 0.1 to 1.0 g/cm3. All of these bodies of different shapes and different bulk densities have an open pore system. They are referred to hereinbelow as "primary product".
Material composites formed of such a primary product and of synthetic resins or plastics materials perform a variety of tasks. Synthetic resins or plastics materials lower the permeability, improve the surface properties, for example the scratch resistance, increase the strength to a , 25861-32 ' small extent, lower the thermal stability of a material composite containing expanded graphite, and can reduce the electrical conductivity or modify the resistance to media. An expedient technique for the production of the material composites is impregnation.
According to German Patent Publication DE 32 44 595, the sticking action of graphite foils to metal surfaces can be reduced by impregnating the primary product with furan resin in regions close to the surface.
According to the prior art, the substantial impregnation of shaped bodies made of expanded and partially recompressed graphite is difficult. To overcome the difficulties, WO 99/16141 (US Patent No. 6,037,074) teaches that such a body can be satisfactorily impregnated when it is interspersed with mineral fibres, which also pass through the surface of the particular bodies. In this way, small channels are formed along these mineral fibres, in which the resin can flow into the interior of the bodies during the impregnation.
In this specification, a phenolic resin dissolved in acetone - i.e. a solvent-containing thermosetting resin with condensation reactions during the curing - is cited as the impregnating agent.
Another method for achieving good impregnation of bodies made of expanded graphite consists in converting the desired resins by means of solvents into low-viscosity liquids, whereby the impregnation becomes more complete. In Japanese Patent Publication JP 1987-257526, the thermosetting resins cited are based on phenols, epoxides, polyimides, melamines, polyesters and furans, which are used in a mixture solution with polyvinylbutyral.
Japanese Patent Publication JP 1-308,872 A2 describes a solution to another problem. A material composite formed of a glass fibre nonwoven fabric and an expanded graphite foil is produced in order to strengthen the latter and obtain a liquid-tight material. This is achieved by impregnating the nonwoven fabric with epoxy resin, the resin penetrating the nonwoven fabric, with the composite material being formed during the subsequent curing. At the same time the resin also penetrates into the surface, i.e. partially into the foil, and seals the surface.
The impregnation of expanded graphite foil with phenolic resin or epoxy resin, set out in Japanese Patent Publication JP 60-242,041 A2 (DE 35 12 867 C2), serves similar purposes, namely to improve strength and gas-tightness. The special feature here lies in a degassing process for the liquid resins and the foil present therein which is repeated a number of times, presumably with the aim of improving the quality of the impregnation.
German Patent Publication DE 43 32 346 A1 describes the impregnation of the expanded graphite foils for the purpose of improving adhesion to elastomer layers lying thereon. The viscosity of the epoxy resins used in this case is 2100 to 2400 mPa~s.
Japanese Patent Publication JP 11-354,136 A2 entitled "Fuel Cell, Separator for Fuel Cell, and Manufacture Therefor" describes the production of expanded graphite in sheet-like form. This partially recompressed expanded graphite is subsequently comminuted (pulverised) and then mixed selectively with resins, solvent-free epoxy resin, solid epoxy resin, melamine resin, acrylic resin, phenolic resin, polyamide resin, and the like. This mixture is subsequently shaped. As will be shown later, this technique differs from the bodies according to the invention which are , 25861-32 of an entirely different structure in that the resins are mixed into an expanded graphite granulate.
Patent Publication WO 98/09926 describes a graphite foil which is coated with a plastic on at least one side.

5 This is done by first applying an aqueous solution of an acrylic resin to the surface, which resin remains there, but also penetrates into regions of the foil close to the surface, and then drying the resin in.
The prior art set out above discloses various synthetic resin-containing bodies produced using expanded graphite and processes for their production. It would be easily understood that it is difficult to produce high-quality, synthetic resin-containing graphite bodies from recompressed, expanded graphite. All the processes described have disadvantages. Some of these disadvantages are serious.
For instance if resins diluted by solvents and thus of lower viscosity are used during the impregnation, it is true that the impregnation is easier, although the vapours, in most cases, from the readily volatile solvents cause serious problems during the impregnation itself, especially during subsequent process steps. In particular, as a result of the fact that the vapours escape during the curing of the resins, the vapours leave behind fine channels, raising the permeability of the bodies produced. If an increased permeability is neither tolerated or desired, a further general problem exists. Namely if the curing is not performed very slowly, a time-consuming process, blisters and cracks are formed in the bodies, which lower their quality considerably. The same disadvantages apply to resin systems which release gases from condensation reactions during the curing.

As a result of the fact that solvents or other gases and vapours escape, a residual porosity arises in the bodies. Attempts are now frequently made to eliminate the residual porosity by one or more additional impregnating operations. The attendant increase in expenditure is obvious and the success is really limited. Also, solvent-containing resins always require, above all, measures to allow their safe handling and the harmless removal or recovery of the solvents, which increases the expenditure even further. The addition of fibres penetrating the surfaces of the body may improve the impregnating properties of the body, but this solution does not eliminate the problems outlined for the use of solvent-containing resins releasing vapours or gases. In addition, one always has a product containing certain fibres, which is more expensive to produce.
The problems with solvents present in the resin systems which have been discussed also apply to aqueous resins. For example, according to Patent Publication WO/09926 a graphite foil is provided with an aqueous resin system which results in the formation of a coat of plastics material at the surface of the foil for the purpose of reinforcement. During the application of this resin, it also penetrates into regions of the foil close to the surface.
The plastics material coat has on the one hand the effect that a second coating with improved adhesion can be applied and on the other hand the effect of electrical insulation.
Both aspects, i.e. the resin system dissolved in water and the electrical insulation at the surface of the body, are regarded as disadvantageous for the use of the bodies according to the present application.
An object of the invention is to provide a body made of expanded or at least partially recompressed expanded graphite, having a liquid-accessible pore system completely or partially filled with an uncured or partially or completely cured synthetic resin. This body should not contain such defects as blisters or cracks that may be caused by reactions of the synthetic resin during the curing, that is, curing the resin system to polymerise the resin does not generate a low molecular weight cleavage product. The body should be producible with comparatively little expenditure.
It should be corrosion-resistant, electrically and thermally conductive and, depending on the degree of compression, be liquid-permeable or gas-tight.
Hence, the present invention provides bodies made of expanded or partially recompressed expanded graphite impregnated with at least one solvent-free, low-viscosity and storage-stable acrylic resin systems or cured acrylic resin systems. The resin systems are introduced into the body by impregnating the primary product with solvent-free, low-viscosity, storage-stable and polymerisable acrylic resin systems.
A preferred embodiment of the solvent-free, low-viscosity, storage-stable acrylic resin systems or cured acrylic resin systems of the present invention includes the following acrylic resin systems: acrylic acids, esters thereof, methacrylic acids, esters thereof, acrylonitriles and acrylamides.
Preferentially, the acrylic resin system comprises a methacrylic acid ester as the main component.
Polymerisation of the methacrylic acid ester resin system, is preferentially achieved by using a thermal initiator such as an azo initiator. Preferred azo initiators comprise azo substituted dinitriles.

The polymer that is the result of the curing comprises at least two to four monomer units.
The acrylic resin system preferentially comprises 99.0-99.5 by weight of the main component with 0.5-1.0$ by weight of the initiator.
The acrylic resin system generally has a viscosity of less than 100 mPa~s at room temperature, preferably of less than 50 mPa~s and particularly preferably of less than 20 mPa~s.
In order to eliminate the aforementioned disadvantages of solvent-containing resin systems and to achieve the advantages of resin systems of low viscosity and storage stability, the following~special solvent-free resin system is an example of a particularly preferred acrylic resin system employed according to the invention presented herewith:
The main component is triethyleneglycol dimethacrylate and the initiator systems come from the azo initiators group. Examples are 2,2'-dimethyl-2,2'-azodipropiononitrile and/or 1,1'-azobis(1-cyclohexanecarbonitrile) and/or azoisobutyric acid dinitrile.
A possible selection of the proportions of the individual components in the overall mixture is mentioned in the examples.
The low viscosities at processing temperature of the resin systems ensure good and efficient impregnation of the primary product and the polyadditions which take place during the curing do not generate any low-molecular-weight cleavage products, which could cause blistering or even cracks in the body. The testing of the resin systems is described in more detail in the examples.

At room temperature, the specified mixture has a viscosity of between 10 and 20 mPa~s which is markedly below that of solvent-free, low-viscosity, storage-stable and polymerisable resin systems based on isocyanates and their co-reactants or epoxides. At room temperature the acrylic resin systems have a storage-stability of more than two days and preferably of more than two weeks. The main component of the acrylic resin system can be characterised from the development of the viscosities over time in the unit [mPa~s]
at room temperature: fresh mixture approx. 13, after eight days approx. 13, and after 48 days approx. 14.
The small rate of change, which is demonstrated by means of these viscosity measurements, of the resin at room temperature and over a period of several weeks will be referred to hereinafter by the term "high storage stability".
The expanded graphite used to produce the primary product consists of fanned-out, wormlike structures, in which very fine graphite platelets are joined together in the form of a defective concertina bellows. During the compression of the primary product, these platelets slide in and over one another. They become interlocked and thus come into contact again so as no longer to be able to be released without destruction. This gives rise in the primary product to a porous graphite framework or network which has good electrical and also good thermal conductivity owing to the good contacts between the graphite platelets. Since these properties are based on the framework function of the graphite in the primary product, they are not adversely affected by the impregnation with synthetic resin. They can even be further improved during a subsequent compression of the primary product impregnated with resin.

The primary product is permeated throughout by open pores which are interconnected in a variety of ways. As a result of this network of interconnected pores, the synthetic resin penetrates into the primary-product body during the 5 impregnation and may even completely fill it under suitable conditions. The network of pores then becomes a network of synthetic resin. Both networks, the graphite network and the pore/synthetic resin network, in combination result in the outstanding properties of the end products thus produced. By 10 adjusting them in a specific manner, it is also possible to control the level of properties of the end products. For example, a primary-product body which has undergone little precompression and is thus highly porous has a lower electrical and thermal conductivity and a lower degree of anisotropy than a more highly compressed primary-product body. On the other hand, it can take up more synthetic resin and has modified strength properties. This situation is reversed with greatly compressed primary-product bodies.
After the impregnation and curing of the synthetic resin, they give products with improved electrical and thermal conductivity, as well as good mechanical strengths. All the bodies according to the invention which are described here are highly impermeable to liquids and gases when their pore network has been completely filled with synthetic resin.
Known methods, such as, for example, those described in Patent Publication DE 35 12 867, can be used for the impregnation of the primary-product bodies. It is preferable however to use immersion methods, in particular immersion methods with prior evacuation of the vessel containing the primary-product body and flooding of the evacuated vessel with the synthetic resin. Where appropriate, the vessel is also subjected to a gas pressure after it has been flooded with the synthetic resin. If the primary-product body is to be merely impregnated close to the surface or is to be partially impregnated, the impregnating period is shortened or the surfaces from which the impregnation is to start are suitably coated or sprayed with synthetic resin or the body is only partially immersed. Following this treatment, the excess resin is removed from the surface.
An aspect of this invention is efficient and damage-free impregnation and curing. Rapid blister- and crack-free curing possible by virtue of the polyaddition reactions has been discussed above. Efficient impregnation depends on the viscosity of the resin system. The present acrylic resin system has a very low viscosity at less than mPa~s, which is why the impregnating success is very high.
The primary product can be impregnated with an 15 amount of up to 100$ of its own weight of resin, depending on the degree of compression of the primary product and the open pore volume conditional thereon. If, however, a high electrical conductivity is desired of the end product, it is expedient to start with a primary-product body which has 20 undergone greater precompression and has a lower open pore volume and can then take up, for example, only 20~ by weight of resin based on its own weight. After the curing of the resin, such a body can be highly impermeable to liquids and gases, see Table 2, and has good strength properties.
The kinetics of the curing reaction are extremely temperature-dependent with the acrylic resin systems used.
For instance, at room temperature virtually no curing reaction takes place, whereas at higher temperatures, and when the preferred azo initiators become effective, it starts suddenly and can be completed in less than one hour at temperatures in excess of 60°C. In general, virtually no viscous transition state of the resin systems is observed.

The curing times of the acrylic resin systems fall in proportion to the rise in the temperature. Examples are:
Temperature 60C 80C 100C 150C

Curing time days 35 10 1 minute minutes minutes If large series of components or bodies are to be produced using the techniques described above, it is desirable to efficiently combine a number of process steps.
This is possible particularly with the shaping of impregnated primary-product bodies with simultaneous curing. In a preferred embodiment, the impregnated primary product -generally in the form of a semifinished product or blank - is put into a mould which is already hot and the mould is closed. The semifinished product thereby takes on the desired geometry, is simultaneously thoroughly heated and cures completely.
A relatively wide variety of graphites based on synthetic production and natural occurrence exist, both types being mentioned in the US Patent No. 3,404,061. Only natural graphite will be discussed hereinbelow, the graphite being present as raw material in the bodies described herein.
Natural graphite is obtained by mining and is separated from the gangue rock with considerable effort.
Nevertheless, very small amounts of rock also remain, attached to the natural graphite flakes or having intergrown into the flakes. These "foreign constituents" are characteristic of every source of natural graphite and can also be specified as an ash value. A method for determining such ash values is described in DIN 51 903 under the title "Testing of carbon materials - determination of the ash value".
In view of the end uses of the synthetic resin-containing graphite bodies according to the invention, the ash values and ash composition of the graphite present are quite important. If such bodies are employed, for example, as inherently corrosion-resistant seals in installations subjected to corrosive media, certain ash constituents together with the corrosive medium may result in pitting in the corrosion-resistant seals adjoining the flanges or bushes, of stuffing-box packings and eventually to the failure of the sealed joint.
Another example of a possible adverse effect of too high an ash value or an unfavourable ash composition of the graphite in a synthetic resin-containing body according to the invention is found in fuel cell technology. Thus, for example, bipolar plates of proton exchange membrane fuel cells can be produced from the material according to the invention. If such a plate now has too high an ash content, some of the harmful ash constituents may be released from the plate during the operation of the fuel cell and poison the sensitive catalysts located close to the surfaces of the bipolar plate, resulting in a premature loss of power of the cell.
Owing to the potential adverse effects of an excessively high ash content, the ash content of the graphite used to produce the bodies according to the invention is 4 percent by weight and less, preferably less than 2 percent by weight and in special cases no more than 0.15 percent by weight.
It may be convenient to strengthen the body according to the invention with fillers, the selection of the fillers having to be matched to the application (e. g. fuel cell). Fillers may be electrically conductive materials closely related to expanded natural graphite, such as, for example, materials from the group consisting of naturally occurring flake graphites, synthetically produced electrographites, carbon blacks or carbons, and graphite or carbon fibres. Furthermore, use may be made of silicon carbide in granular or fibrous form or else electrically conductive or electrically non-conductive ceramic or mineral fillers in granular, platelike or fibrous form, such as silicates, carbonates, sulfates, oxides, glasses or selected mixtures thereof.
The present invention also relates to a process for producing the above-mentioned body. In one embodiment, the process comprises the following process steps:
(a) providing a primary product that is a body made of expanded or at least partially recompressed expanded graphite;
(b) impregnating the primary product with at least one solvent-free, low-viscosity, storage-stable, polymerisable acrylic resin systems and (c) curing the impregnated primary product.
Prior to step (b), the primary product can first be mixed with ceramic or mineral electrically non-conductive or electrically conductive fillers and then processed to form a filler-containing primary product.
Step (b) is preferably an immersion method.
Prior to step (c), the uncured product can be processed to form a shape. This process may be performed using a mould. Further, this processing to form a shape may be conducted simultaneously with the curing step (c).
The curing step (c) may be conducted at temperatures between about 60°C to about 200°C, with curing 5 times ranging from days to less than one minute.
The bodies according to the invention can be used wherever electrically and thermally conductive components of low weight together with good corrosion resistance are required. Further properties which are essential for various 10 applications are low ash values and relatively high impermeability. The bodies according to the invention are used in particular for components of fuel cells, for seals and for heat-conducting elements, for example for conducting away the excess heat from integrated circuits.

15 The invention is explained in more detail hereinbelow with the aid of examples. For the purpose of the examples, the following are methods for obtaining the data on the electrical properties and gas-tightness.
To determine the gas-tightness, the resin-impregnated graphite body was pressed as a separating plate (test specimen) between two chambers of a testing apparatus.
A constantly maintained helium gas pressure of 2 bar absolute prevailed in the first chamber. In the second chamber there was a metal grid which mechanically supported the test specimen. In addition, this chamber was connected at ambient pressure to a liquid-filled burette, as used, for example, in the leakage measurement of flat seals according to DIN 3535.
The helium gas emerging from the first chamber and diffusing through the test specimen was collected in the second chamber and measured by displacement of the liquid in the burette. It was thus possible to determine the volume of the helium gas which diffused through the sample per unit of time. Taking account of the helium density and the testing area, a leakage rate was ascertained which is specified by the unit mg/ (m2 ~ s ) .
The material composite of partially recompressed expanded graphite and synthetic resin has anisotropic properties, i.e. the individual graphite platelets of the expanded graphite have a preferred orientation due to the production technique. For example, the electrical resistance parallel to this preferred orientation is low and perpendicularly thereto it is higher. In the present case, the cured shaped bodies according to the invention were characterised comparatively by measuring the electrical resistance perpendicularly to the preferred orientation of the graphite layers. For this purpose, the body was clamped between two gold-plated electrodes with a diameter of 50 mm, with defined and in each case identical surface pressure. The electrical resistances R established with the aid of a (Resistomat 2318)* device from Burster (Gernsbach, Germany) are specified by the magnitude [m~] hereinbelow.
* Trade-mark Example 1 The following primary-product plates were impregnated at room temperature by immersion:
Type of Thickness Bulk Ash primary- [mm] density value[~

product [g/cm3] by plate weight]

Example F0251OC 0.25 1.0 < 2.0 la Example L10010C 1.0 1.0 < 2.0 1b Example L40005Z 4.0 0.5 < 0.15 lc Table 1:
Primary-product plates made of partially recompressed expanded graphite used for the impregnation with an acrylic resin system.
The resin system used had the following composition:
99.2 of triethyleneglycol dimethacrylate (methacrylic acid ester) 0.3$ of 2,2'-dimethyl-2,2'-azodipropiononitrile 0.5~ of l,1'-azobis(1-cyclohexanecarbonitrile) The methacrylic acid ester came from Rohm GmbH
(Darmstadt, Germany) and had the trade name PLEX 6918-0*.
*Trade-mark The two other components of the resin system had the function of an initiator. 2,2'-Dimethyl-2,2'-azodipropiononitrile came from Pergan GmbH (Bocholt, Germany) and had the trade name Peroxan AZDN*. 1,1'-Azobis(1-cyclohexanecarbonitrile) came from Wako Chemicals GmbH (Neuss, Germany) and bore the designation V40*. The viscosity of the resin system was in the range from 10 - 15 mPa~s at room temperature.
The primary-product plates were completely immersed in the resin bath and after one, five and nine hours they were removed from the immersion bath and the resin adhering to the surface was wiped off. The plates were subsequently put into a circulating-air oven at 100°C and cured for 30 min. On visual inspection, the impregnated primary-product plates showed no blisters or cracks at all despite this shock curing. The values of the resin content, volume resistance R
and helium permeability A determined on the plates were summarised in Table 2 and compared with the values for non-impregnated plates.
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H f=, ,-a~.7 H Gu a .a N O U ,~ rti ~ f1 H U r~ .N a As is evident from Table 2, the resin content of the composite materials is greatly dependent on the bulk density of the primary product, its geometry (plate thickness) and the impregnating time. The volume resistance 5 of the impregnated plates rises comparatively little with increasing resin content, since the electron conduction is borne by the existing graphite network. The helium permeability of the plates is drastically reduced by the impregnating treatment. Depending on the resin content of the 10 plate, the permeability falls by more than 2 powers of ten compared with corresponding primary-product plates without impregnation.
Example 2 The resin system used was the same as the resin 15 system in Example 1. The primary product had a thickness of 2.7 mm and a density of 0.65 g/cm3, the ash value of the graphite was less than 0.15. After an impregnating period of one hour at room temperature, the now impregnated plate was taken out of the resin bath and, weighed after the resin 20 adhering to the surface had been wiped off. The proportion of resin determined was 20$ by weight. The impregnated plate was placed in a pressing die preheated to 150°C. The die, which was furnished with an anti-stick coating, was closed and the impregnated graphite pressed into the mould, in the course of which a further compression of the composite material took place. After five minutes under the effect of pressing force and temperature, the die was opened and the cured shaped body removed. On visual inspection, the shaped body was free from cracks and blisters and the surface showed no resin film visible to the eye.

Besides these above-mentioned examples, a multiplicity of further bodies and procedures can be realised according to the teaching of this invention. Accordingly, the invention is not restricted to the embodiments illustrated in the examples. Variants which are not shown but which a person skilled in the art could produce owing to the information offered by this disclosure are therefore also to be included in this patent application.

Claims

1. A body made of expanded or at least partially recompressed expanded graphite impregnated with at least one solvent-free, low-viscosity, storage-stable, polymerisable acrylic resin system or polymers obtained by curing at least one such resin system, wherein the resin system undergoes a polymerisation reaction during curing without generating a low molecular weight cleavage product.

2. The body according to claim 1, wherein the acrylic resin system has a viscosity at room temperature of less than about 100 mPa~s.

3. The body according to any one of claims 1 or 2, wherein the expanded or at least partially recompressed expanded graphite has an ash value of not more than about 4%.

4. The body according to any one of claims 1, 2 or 3, wherein the expanded or at least partially recompressed expanded graphite has a bulk density of about 0.1 to about 1.8 g/cm3.

5. The body according to any one of claims 1 to 4, wherein the acrylic resin system has a storage stability at room temperature of more than two weeks.

6. The body according to any one of claims 1 to 5, wherein the acrylic resin system comprises a methacrylic acid ester.

7. The body according to claim 6, wherein the methacrylic acid ester is triethyleneglycol dimethacrylate.

8. The body according to claim 7, wherein the acrylic resin system contains about 99.0% to about 99.5% by weight of the methacrylic acid ester.

9. The body according to claim 8, wherein the acrylic resin system contains about 99.3% by weight of the triethyleneglycol dimethacrylate.

10. The body according to any one of claims 6, 7, 8 or 9, wherein the acrylic resin system further comprises at least one thermal initiator.

11. The body according to claim 10, wherein the thermal initiator comprises at least one azo initiator.

12. The body according to claim 11, wherein the azo initiator is 2,2'-dimethyl-2,2'-azodipropiononitrile.

13. The body according to claim 11, wherein the azo initiator is 1,1'-azobis(1-cyclohexanecarbonitrile).

14. The body according to claim 11, wherein the azo initiator is azoisobutyric acid dinitrile.

15. The body according to claim 11, wherein the azo initiator is 2,2'-dimethyl-2,2'-azodipropiononitrile and 1,1'-azobis(1-cyclohexanecarbonitrile).

16. The body according to any one of claims 11 to 15, wherein the acrylic resin system contains about 0.5% to about 1.0% by weight of the azo initiator.

17. The body according to claim 15, wherein the acrylic resin system contains about 0.3% by weight of 2,2'-dimethyl-2,2'-azodipropiononitrile and about 0.5% by weight of 1,1'-azobis(1-cyclohexanecarbonitrile).

18. The body according to any one of claims 1 to 14, wherein the impregnated graphite body contains up to 100% by weight of the acrylic resin.

19. The body according to claim 17, wherein the impregnated body contains about 5% to about 25% by weight of the resin.

20. The body according to any one or more of claims 1 to 16, wherein the expanded or at least partially recompressed expanded graphite contains a ceramic or mineral electrically non-conductive or electrically conductive filler.

21. The body according to any one of claims 1 to 19, wherein the body comprises at least two networks each held together independently, one of which consists of a connected framework made of expanded or of expanded and thereafter at least partially recompressed graphite of good electrical conductivity and thermal conductivity, and the other of which consists of a connected network made of synthetic resin which has penetrated into pores in the graphite.

22. The body according to any one of claims 1 to 20, wherein the body contains the acrylic resin system only in a region close to the surface or in part of the body.

23. The body according to claim 21, which does not comprise a continuous resin film at its surface and is electrically conductively contactable.

24. A process for producing a body according to any one of claims 1 to 19, which comprises

25 (a) providing a primary product that is a body made of the expanded or at least partially recompressed expanded graphite (b) impregnating the primary product with the solvent-free, low-viscosity, storage-stable, polymerisable acrylic resin system; and (c) curing the impregnated primary product.

25. The process according to claim 24, in which step (b) is an immersion method.

26. The process according to any one of claims 24 or 25, in which before step (c), the uncured product is processed to form a shape.

27. The process according to claim 26, in which the processing step to form a shape and step (c) are conducted simultaneously.

28. The process according to any one of claims 24 to 27, wherein step (c) is thermal curing.

29. The process according to claim 28, wherein the thermal curing is conducted at temperatures between about 60°C to 200°C.

30. The process according to any one of claims 24 to 29, in which before step (b), the primary product is first mixed with ceramic or mineral electrically non-conductive or electrically conductive fillers and then processed to form a filler-containing primary product.

31. Use of one or more of the body according to any one of claims 1 to 23, as a sealing element, as a component in a fuel cell, or as a heat-conducting element.