Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
  • C04B41/46—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with organic materials
  • C04B41/48—Macromolecular compounds
  • C04B41/483—Polyacrylates
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
  • C04B41/81—Coating or impregnation
  • C04B41/82—Coating or impregnation with organic materials
  • C04B41/83—Macromolecular compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/08—Ingredients agglomerated by treatment with a binding agent
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/02—Constructions of heat-exchange apparatus characterised by the selection of particular materials of carbon, e.g. graphite
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
  • C04B2111/00853—Uses not provided for elsewhere in C04B2111/00 in electrochemical cells or batteries, e.g. fuel cells
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/10—Compositions or ingredients thereof characterised by the absence or the very low content of a specific material
  • C04B2111/1006—Absence of well-defined organic compounds
  • C04B2111/1012—Organic solvents
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249924—Noninterengaged fiber-containing paper-free web or sheet which is not of specified porosity
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/25—Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles

Definitions

• the invention relates to a synthetic resin-impregnated body made of expanded or at least partially recompressed expanded graphite, a process for producing such a body and sealing elements, fuel cell components and heat-conducting elements formed of the bodies.
• synthetic resin-impregnated body is understood to mean a body made of expanded graphite which is impregnated by synthetic resin.
• 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 oxidizing agent such as concentrated nitric acid or hydrogen peroxide, for example. That results in graphite intercalation compounds in the graphite flakes or graphite platelets.
• the flakes are thermally decomposed by brief heating, for example by introduction into the flame of a gas burner and, as a result of the gas pressure arising in their interior during that decomposition process, puff up to form loose graphite particles with a wormlike shape.
• That 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 of between 0.7 and 1.3 g/cm 3 . However, other parts having 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/cm 3 , are also possible. There are also sponge-like parts on average having low bulk density, with values of 0.1 to 1.0 g/cm 3 . All of those bodies with different shapes and different bulk densities have an open pore system. They are referred to hereinbelow as a “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 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.
• thermosetting resins cited are based on phenols, epoxides, polyimides, melamines, polyesters and furans, which are used in a mixture solution with polyvinylbutyral.
• a material composite formed of a glass fiber nonwoven fabric and an expanded graphite foil is produced in order to thus strengthen the latter and overall obtain a liquid-tight material. That is achieved by impregnating with epoxy resin. The resin penetrates the nonwoven fabric and at the same time also penetrates into the surface, i.e. partially into the foil. During subsequent curing, the supporting part of the composite material is formed from the impregnated nonwoven fabric and is then also sealed at the surface.
• German Published, Non-Prosecuted Patent Application 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 that case is 2100 to 2400 mPa ⁇ s.
• a synthetic resin-impregnated body comprising expanded or at least partially recompressed expanded graphite.
• the graphite contains either at least one solvent-free, low-viscosity, storage-stable, polymerizable acrylic resin system or polymers obtained by curing the at least one resin system.
• the object of the present invention is achieved with a body of the type mentioned at the outset by subjecting the primary product or the body obtained from the impregnated primary product to at least partial compression containing either solvent-free, low-viscosity, storage-stable acrylic resin systems or cured acrylic resin systems.
• the resin systems enter into the body by impregnating the primary product with solvent-free, low-viscosity, storage-stable and polymerizable acrylic resin systems.
• 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 give rise to 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.
• 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 polymerizable resin systems from the group of isocyanates and their co-reactants and/or epoxides.
• the main component of the acrylic resin system can be characterized from the development of the viscosities over time in a unit [mPa ⁇ s] at room temperature, as follows: fresh mixture ⁇ 13, after eight days ⁇ 13 and after 48 days ⁇ 14.
• the expanded graphite used to produce the primary product is formed of fanned-out, wormlike structures, in which very fine graphite platelets are joined together in the form of a defective accordion bellows.
• these platelets slide in and over one another. They become interlocked and thus come into contact again so as to no longer be able to be released without destruction.
• the primary product is permeated throughout by open pores which are interconnected in a variety of ways.
• the synthetic resin penetrates into the primary-product body during the 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 adjusting them in a specific manner, it is also possible to control the level of properties of the end products.
• 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.
• 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 yield products with improved electrical and thermal conductivity, as well as good mechanical strengths. All of the bodies according to the invention which are described herein are highly impermeable to liquids and gases when their pore network has been completely filled with synthetic resin.
• All of the known methods 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 essential aspect of the present invention is efficient and damage-free impregnation and curing.
• the rapid blister-free and crack-free curing which is possible by virtue of the polyaddition reactions has been discussed above.
• Efficient impregnation depends essentially on the viscosity of the resin system.
• the present acrylic resin system has a very low viscosity at less than 20 mPa ⁇ s, which is why the impregnating success is very high.
• the primary product can take-up an 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 of the end product is desired, it is expedient to start with a primary-product body which has undergone greater precompression, 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, as is seen in Table 2, and has good strength properties.
• the impregnated primary product which is generally in the form of a semifinished product or blank, is expediently put into a mold which is already hot and the mold is closed.
• the semifinished product thereby takes on the desired geometry, is simultaneously thoroughly heated and cures completely.
• 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. Those “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 (German Industrial Standard) 51 903 under the title “Testing of Carbon Materials-Determination of the Ash Value”.
• the ash values and ash composition of the graphite that is 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 flanges or bushes of stuffing-box packings and eventually lead to the failure of the sealed joint.
• bipolar plates of proton exchange membrane fuel cells can be produced from the material according to the invention. If such a plate 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.
• 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.
• 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 fibers. Furthermore, use may be made of silicon carbide in granular or fibrous form or else 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 bodies according to the invention can be used wherever electrically and thermally conductive components having low weight together with good corrosion resistance are required. Further properties which are essential for various 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 excess heat from integrated circuits.
• a 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 a first chamber.
• a metal grid which mechanically supported the test specimen was disposed in a second chamber.
• this chamber was connected at ambient pressure to a liquid-filled burette such as is used, for example, in the leakage measurement of flat seals according to DIN 3535.
• 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.
• the electrical resistance parallel to this preferred orientation is low and perpendicularly thereto it is higher.
• the cured shaped bodies according to the invention were characterized comparatively by measuring the electrical resistance perpendicularly to the preferred orientation of the graphite layers.
• the body was clamped between two gold-plated electrodes having a diameter of 50 mm, with defined and in each case identical surface pressure.
• the electrical resistances R established with the aid of a device (Resistomat 2318) from the firm Burster (Gernsbach, Germany) are specified by the magnitude [m ⁇ ] hereinbelow.
• the resin system which was used had the following composition:
• the methacrylic acid ester came from the firm Röhm GmbH (Darmstadt, Germany) and had the trade name PLEX 6918-O.
• the two other components of the resin system had the function of an initiator.
• 2,2′-Dimethyl-2,2′-azodipropiononitrile came from the firm Pergan GmbH (Bocholt, Germany) and had the trade name Peroxan AZDN.
• 1,1′-Azobis(1-cyclohexanecarbonitrile) came from the firm 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. 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 ⁇ determined on the plates are summarized in Table 2 and compared with the values for non-impregnated plates. TABLE 2 Comparison of primary-product plates (varying thickness and bulk density) impregnated with an acrylic resin system with non-impregnated primary-product plates (of likewise varying thickness and bulk density).
• 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 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.
• the permeability falls by more than 2 powers of ten as compared with corresponding primary-product plates without impregnation.
• the resin system that was used was the same as the resin system in Example 1.
• the primary product had a thickness of 2.7 mm and a density of 0.65 g/cm 3 and the ash value of the graphite was less than 0.15% by weight.
• the now impregnated plate was taken out of the resin bath and weighed after the resin adhering to the surface had been wiped off. The proportion of resin which was determined was 20% by weight.
• the impregnated plate was placed in a pressing die preheated to 1500° C.
• the die which was furnished with an anti-stick coating, was closed and the impregnated graphite was pressed into the mold, in the course of which a further compression of the composite material took place.
• the die was opened and the cured shaped body was removed. The shaped body was free from cracks and blisters and the surface showed no resin film visible to the eye.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Physics & Mathematics (AREA)
• General Engineering & Computer Science (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Health & Medical Sciences (AREA)
• Thermal Sciences (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Fuel Cell (AREA)
• Carbon And Carbon Compounds (AREA)
• Gasket Seals (AREA)
• Reinforced Plastic Materials (AREA)
• Sealing Material Composition (AREA)

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Citations (9)

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• 2000
  • 2000-12-07 DE DE10060838A patent/DE10060838A1/de not_active Withdrawn
• 2001
  • 2001-11-29 PT PT01128296T patent/PT1221432E/pt unknown
  • 2001-11-29 EP EP20010128296 patent/EP1221432B1/de not_active Expired - Lifetime
  • 2001-11-29 ES ES01128296T patent/ES2300303T3/es not_active Expired - Lifetime
  • 2001-11-29 DK DK01128296T patent/DK1221432T3/da active
  • 2001-11-29 AT AT01128296T patent/ATE386709T1/de active
  • 2001-11-29 DE DE50113627T patent/DE50113627D1/de not_active Expired - Lifetime
  • 2001-12-04 JP JP2001369801A patent/JP4425510B2/ja not_active Expired - Fee Related
  • 2001-12-06 CA CA 2364748 patent/CA2364748A1/en not_active Abandoned
  • 2001-12-07 US US10/006,419 patent/US20020127390A1/en not_active Abandoned

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