Process for producing a thin carbonaceous plate

Abstract: A thin carbonaceous plate useful, for example, as a sepa­ rator in a fuel cell is prepared by a process wherein a carbona­ ceous raw material which is carbonized and solidifies after be­ ing softened by heating is press-molded by a heating press, the thus press-molded carbonaceous raw material is heated under pressure thereby to carbonize the said material and the thus carbonized material is calcined in a vacuum or in an inert gas to obtain the said thin carbonaceous plate, characterized in that a said carbonaceous raw material is sandwiched in the said heating press between layers of a paper-like substance capable of being carbonized without melting, the said layers of the said paper-like substance being in contact with the pressing sur­ faces of the heating press.

Description: The present invention relates to a process for producing a carbonaceous thin plate, and in more detail, relates to a process for producing a carbonaceous thin plate of a large size without the occurrence of crevices and cracks therein. Since carbonaceous materials are excellent in heat-resistance, corrosion-resistance and electric conductivity, the application of a carbonaceous material of a thin plate type, which is dense and small in permeability to gases, and liquids to separators of phosphoric acid type fuel cells or electrodes for zinc-halogen accumulators has been tried, and the establishment of an industrial process for producing a carbonaceous thin plate of a large type has been desired. The carbonaceous thin plate according to the present invention may be used for the above-mentioned purposes and for other purposes, for instance, electrodes for electrolysis, diaphragms for heat-resistant and corrosion-resistant heat exchangers. Hitherto, as a graphite thin plate and a process for producing the same, a graphite thin plate prepared by adding a liquid thermosetting resin to micronized graphite preliminary treated at a temperature of not less than 2700°C and of not more than 100 micrometers in particle size; kneading the thus obtained mixture, thereby obtaining a paste; molding the thus obtained paste into the shape of a thin plate by a roll-molding machine; hardening the thus molded thin plate by heating or hardening the thus molded thin plate while contacting heated plates with both sides of the thin plate under pressure; and subjecting the hardened material to the conventional heating and carbonizing treatment and a process of production thereof have been disclosed in JP-A-59-26907 (1984). However, in such a graphite thin plate, the adherence of the micronized graphite powders to the thermosetting resin is poor, and voids are apt to be formed in the interface therebetween at the time of subjecting the paste to carbonizing treatment. It has been regarded difficult to make the gas-permeability of the product less than 1 × 10⁻⁵ cm²/s. Namely, such a graphite thin plate has a defect that the thickness of the plate must be large enough in the case where a high impermeability to gases is required. In JP-A-59-21512 (1984), disclosed is a process for producing a glass-like carbon thin plate, comprising mixing a chlorinated vinyl chloride resin and/or a vinyl chloride resin with a furan resin; kneading the mixture; molding the thus obtained blend into a film or a sheet-like material; subjecting the thus obtained molded body to a heat-treatment thereby obtaining a carbon-precursor; and calcining the thus formed carbon-precursor in an inert atmosphere. Although the gas-permeability of the thus obtained thin plate is as small as 10⁻¹¹ to 10⁻¹⁰ cm²/s (He, ΔP=1 atm), since the yield of carbonization of the resin in the steps of calcination and carbonization is small and the contraction rate of the material is large, it is extremely difficult to produce a thin plate of large in the size without the occurrence of crevices and cracks and with accurate dimensions. In addition, since the resin as the raw material contains chlorine atoms, the chlorine atoms separate therefrom as strongly corrosive gaseous chlorine or hydrogen chloride. Accordingly, special consideration for the construction and material of the apparatus is necessary in the case of carrying out the process actually. In JP-A-58-150275 (1983), a cell separator of fuel cells comprising a glass-like carbon produced by molding and carbonizing a liquid furan resin, a liquid phenol resin or a mixture thereof is disclosed. Although the gas-permeability of glass-like carbon is extremely small, it takes a long period of time to produce the glass-like carbon and its producibility is poor resulting in a high cost of production. Although the production of the carbonaceous thin plate has been tried by each of the above-mentioned processes, there is another process wherein a carbonaceous thin plate is produced by carbonizing a carbonaceous raw material, which is carbonized and solidifies after being softened by heating, while applying a pressure thereto by a heating press. Namely, a carbonaceous thin plate is produced by uniformly filling a carbonaceous raw material such as a pitch, etc. into a metal mold of a heating press; heating the carbonaceous raw material; and after pressing at a temperature at which the carbonaceous raw material is softened, calcining and carbonizing the carbonaceous raw material at the temperature up to about 600°C under the pressure, further calcining or graphitizing the thus carbonized material at a predetermined temperature in a vacuum or in an inert gas. In the above-mentioned process, the decomposition gas of the carbonaceous raw material generated at the time of carbonization under a pressure by the heating press is scattered and lost to the outside through the thin plate or to the outside through the interface between the thin plate and the pressing surface, or remains as bubbles within the thin plate. Accordingly, with the increase of the dimensions of the thin plate, it becomes difficult for the decomposition gas of the carbonaceous raw material to scatter to the outside. As a result, the decomposition gas remains as bubbles within the thin plate and it becomes impossible to obtain a dense carbonaceous thin plate. In addition, since the volume of the carbonaceous raw material such as a pitch, etc. is reduced by calcination and carbonization, the thin plate apts to contract also in the direction of its surface. With the increase of the dimensions of the thin plate, the friction between the thin plate and the pressing surface of the heating press is increased resulting in impossibility of contraction and finally in occurrence of crevices and cracks in the thin plate. The above-mentioned phenomena are remarkable in the case where a carbonaceous raw material is used which has a small carbonization yield but which contracts a large amount during carbonization. Accordingly, hitherto a method has been adopted wherein the carbonization under pressure is slowly carried out for a long time. Alternatively a method has been taken wherein the carbonaceous raw material is preliminarily subjected to thermal treatment thereby improving the yield of carbonization and reducing the amount of the decomposition gas at the time of carbonization. However, the above-mentioned processes are insufficient for the purpose. US-A-4359438 discloses a process for making bipolar fuel cell collecting plates comprising the steps of: (a) (i) blending 25 parts of a phenol formaldehyde resin having a mole ratio of 1.0 mole phenol to 0.60 to 0.90 mole formaldehyde, a curing amount to reduce weight loss on exposure to high temperature acidic conditions, of hexamethylene tetramine, 75 parts of graphite filler and an effective amount of furfural wetting agent in 100 grams of resin graphite blend; or (ii) blending 25 parts of a styrenated phenol formaldehyde resin having a mole ratio of 4 moles phenol to 0.1 to 4.0 moles styrene to 3.2 moles formaldehyde, a curing amount of hexamethylene tetramine, 75 parts of graphite filler and an effective amount, to reduce weight loss on exposure to high temperature acidic conditions of furfural wetting agent in 100 grams of resin graphite blend; (b) charging the blend into a heated mold; (c) heating the charged mold under pressure; (d) releasing the pressure allowing the escape of gaseous products; (e) further heating the charged mold under pressure; (f) cooling the mold; (g) removing the formed plate; and (h) postcuring the formed plate. EP-A-0118232 discloses a process of manufacturing a "green" carbon product comprising the steps of filling a mould cavity with fine particulate bituminous coal having a percentage of impurities acceptable for the final use to which the carbon product is to be put, keeping the particles within the mould in an oxygen free atmosphere at a controlled temperature at or adjacent the maximum contraction of incipient carbonisation to allow compaction of the particles to a density level acceptable for further processing to produce high quality forms of carbon. EP-A-0127887 discloses a process for producing a carbon product of controlled porosity having a thickness in the range of about 0.25 to 5 mm characterized by (a) impregnating porous cellulose material of desired size and shape with an impregnant selected from the group consisting of coal tar, solvent-cut coal tar pitch, slurry oil and creosote oil and mixtures thereof; (b) curing the impregnated material; (c) baking the cured material to carbonize the impregnant; and (d) repeating steps (a), (b) and (c) if required until the desired porosity is achieved. As a result of the present inventors' studies for solving the problems of the above-mentioned conventional processes, it has been found by the present inventors that in the production of a carbonaceous thin plate by carbonizing a carbonaceous raw material while applying pressure thereto by a heating press, the scattering of the decomposition gas to the outside is facilitated by interposing a paper-like substance which is carbonized without melting between the carbonaceous raw material and the pressing surface of the heating press. The paper-like substance prevents the adhesion of the carbonaceous raw material to the pressing surface of the heating press. As a result the carbonaceous thin plate slides easily on the pressing surface thereof, and the occurrence of crevices and cracks due to contraction during carbonization is prevented. Namely, the first object of the present invention is to provide a process for easily producing industrially a dense carbonaceous thin plate of low permeability to gases or liquids and of a large size, for instance about one meter each in length and width, without occurrence of crevices and cracks. The second object of the present invention is to provide a carbonaceous thin plate of a large size not having crevices nor cracks. According to the present invention there is provided a process for producing a thin carbonaceous plate, which process comprises; (i) sandwiching a carbonaceous raw material which is carbonized and solidifies after being softened by heating in a heating press between layers of a paper-like substance capable of being carbonized without melting, the said layers of the said paper-like substance being in contact with the pressing surfaces of the heating press; (ii) press-molding the resulting sandwich at a temperature of from 150 to 450°C and a presence of not more than 9901 kPa (110 kg/cm²G) for from 10 to 120 minutes; (iii) heating the press-molded sandwich continuously to a temperature of from 600 to 650°C under a pressure of from 111 to 9901 kPa (0.1 to 100 kg/cm²G) thereby to carbonize the sandwich; and (iv) calcining the carbonized sandwich in a vacuum or in an inert gas; thereby to obtain a said thin carbonaceous plate having a thickness of from 0.2 to 5 mm. In the present invention, a carbonaceous raw material which is carbonized after being softened by heating is used as the carbonaceous raw material. This is due to the necessity of once softening of the raw material for molding and sintering the molded material by heating and pressing thereof in the carbonization step. Pitches or mixtures of a pitch and a pulverized carbonaceous material may be mentioned as the carbonaceous raw material. As the pitch, a petroleum pitch, a coal pitch, a material produced by subjecting a petroleum pitch or a coal pitch to oxidative treatment, a material produced by pitchifying the product obtained by subjecting a coal tar, an asphalt, etc. to oxidative treatment, etc. may be used. As the pulverized carbonaceous material, carbon black, pulverized coke, pulverized graphite, etc. may be mentioned. In addition, as the carbonaceous raw material, those having a high carbonization yield are favorable for producing a dense carbonaceous thin plate because of the small amount of the decomposition gas generated at the time of carbonization which is insufficient for forming bubbles in the product, and because generally of their small contraction on carbonization. Those having a small contraction on carbonization hardly show any occurrence of crevices and cracks. However, since a carbonaceous raw material having a high carbonization yield shows a high softening point and is difficult to deform plastically, such a material is generally poor in terms of its shaping property and sintering property. Consequently, it is preferable to carry out the selection of the carbonaceous raw materials while at least considering the above-mentioned situations. Although it is difficult to establish clear standards, those exhibiting a carbonization yield of 40 to 95% at the temperature up to 900°C are preferable. Accordingly, the above-mentioned pitches are preferably used. Pulverized carbonaceous materials such as carbon black may be added thereto for improving the carbonization yield and for reducing the contraction of the material on carbonization. However, since the addition of a large amount of such a material reduces the density, increases the permeability to gases and liquids and reduces the strength of the thus obtained thin plate, the amount of pulverized carbonaceous material added is preferably less than half of the total amount of the raw material although it depends on the object of use of the product. The process of the present invention is typically put into practice by the steps of (1) inserting a paper-like substance which is carbonized in a solid state without melting between the carbonaceous raw material such as a pitch, etc. and the pressing surface of a heating press and (2) carbonizing the carbonaceous raw material and the paper-like substance by raising the temperature of the heating press slowly while applying pressure. A decomposition gas is generated from the carbonaceous raw material such as pitch, etc. in the step of carbonization (the step of raising the temperature). The thus generated decomposition gas is released easily outside the system through the layer of the paper-like substance inserted between the carbonaceous raw material and the pressing surface of the heating press. Accordingly, the decomposition gas does not remain as bubbles within the thin plate, and it is possible to produce a dense carbonaceous thin plate. The paper-like substance herein mentioned typically indicates the substance prepared by twisting vegetable fibers and other fibers and agglutinating thereof. Since the paper-like substance is constituted by the twisting of the fibers, there are voids therein and the paper-like substance is permeable to gases. In order that the paper-like substance exhibits permeability to gases during the step of carbonization under pressure, it is necessary that the paper-like substance is carbonized in a solid state without melting, thereby retaining its permeability to gases. In the conventional process of not inserting the paper-like substance, since the carbonaceous raw material is directly contacted with the pressing surface of the heating press and is softened without giving any passage of the decomposition gas to the outside, it is difficult to release the decomposition gas to the outside and the decomposition gas is apt to remain as bubbles within the thin plate resulting in the difficulty of producing the dense carbonaceous thin plate. According to the process of the present invention, the direct contact of the carbonaceous raw material with the pressing surface of the heating press is prevented by the paper-like substance, and the paper-like substance is carbonized without melting. Consequently, the thin plate may easily slide on the pressing surface of the heating press without adhering thereto. Accordingly it is possible to prevent the occurrence of crevices and cracks in the carbonaceous thin plate. As the paper-like substance satisfying the above-mentioned objectives, a sheet of paper manufactured from vegetable fibers by a known method is adequate for the objectives. Generally the paper-like substance employed in the present invention consists of or mainly consists of vegetable fibers. In addition, a sheet of paper manufactured mainly from vegetable fibers with a small amount of synthetic fibers may be used as far as the permeability of the sheet of paper to gases is not remarkably deteriorated by the melting of the synthetic fibers in the step of carbonization under pressure. As the synthetic fibers used in a small amount, those of polyethylene, polypropylene, rayon, acetate, vinylon, nylon, acrylate, polyester, etc. may be mentioned. The amount of addition thereof is preferably not more than 30% by weight of the raw material for the sheet of paper. The paper-like substance used according to the present invention remains as a carbonized material in the outer layer part of the carbonaceous thin plate while constituting a part of the carbonaceous thin plate. Consequently, the density of the outer layer part of the carbonaceous thin plate is different from the density of the inner part thereof. The thickness of the outer layer part depends to the thickness of the paper-like substance used. Although the thickness of the paper-like substance is decided in consideration of the use of the product, namely the carbonaceous thin plate, the effect in the steps of production and the economicity in production, it is preferable that the thickness of the paper-like substance is not more than 100 micrometers. In most of the papers produced at present, an inorganic substance such as a filler of terra alba, titanium oxide, etc. and pigments is added for the purpose of densifying, opaquing and coloring of the paper. For the purpose of the present invention, a sheet of paper containing such an inorganic substance is suitably used. However, there are cases where the presence of inorganic impurities is not favorable according to the use of the product, namely the carbonaceous thin plate. Accordingly, paper which has manufactured without addition of inorganic substances such as fillers, pigments, etc. and has not been subjected to after-processing such as coating is large in permeability to gases and prevents the adhesion of the carbonaceous raw material to the metal mold. Such a paper is particularly favorable for use in the present invention. As the method of inserting the paper-like substance which is carbonized without melting between the carbonaceous raw material and the pressing surface of the heating press, either of the following two methods is adopted. Namely in the first method, a paper-like substance is disposed on the bottom of the metal mold of the press and after filling a pulverized carbonaceous raw material uniformly in the upper space thereon, another paper-like substance and the upper metal mold of the press are disposed in that order. In the second method, the carbonaceous raw material is converted into a slurry or a solution by a solvent, a carbonizable supporting body is coated or impregnated with the slurry or solution, a sheet-like carbonaceous raw material is produced by evaporating the solvent from the supporting body, a necessary number of such a sheet-like carbonaceous raw material are laminated, paper-like substances are disposed above and below the thus laminated sheet-like carbonaceous raw materials, and the thus combined material is filled in the metal mold of the heating press. As the carbonizable supporting body used for processing the carbonaceous raw material into a sheet form, those which come to be one-body with the carbonaceous raw material after being carbonized, thereby constituting a carbonaceous thin plate, are favorable. The paper-like material manufactured from organic fibers, carbon fibers or a mixture thereof is suitable for the purpose. According to the present invention, the carbonaceous thin plate is produced by inserting a paper-like substance which is carbonized without melting between the carbonaceous raw material and the pressing surface of the heating press, raising the temperature of the heating press, press-molding the carbonaceous raw material and the paper-like substance and continuing the heating under a pressure, thereby carbonizing the press-molded material. As the conditions of press-molding, a pressure of not more than 9901 kPa (100 kg/cm²G) at the temperature of 150 to 450°C at which the carbonaceous raw material softens and a pressure-retaining time of 10 to 120 min are used. The carbonization is carried out under a pressure of 111 to 9901 kPa (0.1 to 100 kg/cm²G) while heating the material to a temperature of about 600 to 650°C. Since the carbonization under pressure is carried out for preventing bubbling due to the generation of the decomposition gas from the carbonaceous raw material which is still in the softened state and also for preventing the bending of the thus produced carbonaceous thin plate, it is sufficient to carry out the carbonization by heating the heating press to a temperature of about 600 to 650°C at which the carbonaceous raw material solidifies. The thin plate which has been heated to the temperature of about 600 to 650°C under a pressure, thereby having been carbonized as taken out from the press after cooling. After being interposed between the two flat and smooth graphite plates, the carbonized thin plate is further calcined or graphitized under a reduced pressure or in an inert gas to obtain the carbonaceous thin plate. The carbonaceous thin plate has a thickness of from 0.2 to 5 mm, for example from 0.2 to 1.5 mm. According to a process of the present invention comprising disposing a composite material comprising a carbonaceous raw material which is carbonized and solidifies after being softened by heating and paper-like substances which are carbonized without melting between the pressing-surfaces of a heating press, so as to sandwich said carbonaceous raw material between said paper-like substances and to contact said paper-like substances with each of the pressing-surfaces of said heating press, press-molding said composite material by raising a temperature of said heating press continuously heating the thus press-molded composite material under a pressure, thereby carbonizing the thus press-molding composite material, and calcining the thus carbonized material under a reduced-pressure or in an inert gas, that is, in the production of a carbonaceous thin plate by carbonizing a carbonaceous raw material such as a pitch, etc. while pressing the carbonaceous raw material by a heating press, (1) inserting a paper-like substance, for instance, a sheet of vegetable fibers paper which is carbonized in a solid state without melting between the above-mentioned carbonaceous raw material and the pressing surface of the heating press, thereby (2) releasing the decomposition gas generated at the time of carbonization of the carbonaceous raw material to outside of the system and (3) letting the decomposition gas not to remain as bubbles within the carbonaceous thin plate, a dense carbonaceous thin plate of a large size is easily produced. Also, according to a process of the present invention comprising disposing the paper-like substance on the both sides of the carbonaceous raw material, thereby avoiding the direct contact of the carbonaceous raw material with the pressing surface of the heating press, preventing the adherence of the carbonaceous raw material to the pressing surface of the heating press, facilitating the sliding of the carbonaceous thin plate along the pressing surface of the heating press, facilitating the easily shrinking of the carbonaceous thin plate with the progress of the carbonization and preventing the occurrence of crevices and cracks in the product, a carbonaceous thin plate of a large size is easily produced. The present invention will be explained more in detail while referring to the non-limitative Examples and Comparative Example as follows: In this connection, the softening point of the material and the permeation coefficient of the material to a gas are determined by the following methods, respectively. Determination of the softening point of a material While using a KOKA-type flowtester (made by SHIMAZU Works Co., Ltd.), one gram of a specimen pulverized to a size of not more than 250 micrometers is filled up in a cylinder which is 1 cm² in cross-sectional area and has a nozzle of 1 mm in diameter at the bottom thereof and the specimen is heated at a temperature raising rate of 6°C/min while applying a pressure of 1081 kPa (10 kg/cm²G.) on the specimen. With the raising of the temperature, although the packing rate of the specimen in the cylinder is improved by the softening of the specimen, the reduction of the volume of the specimen stops over the certain temperature. With the further continued raising of the temperature, the specimen melts and flows to outside from the nozzle at the bottom of the cylinder. The temperature at which the reduction of the volume of the powdery specimen stops is defined as the softening point of the specimen. In addition, there may be cases where such a flowing of the molten specimen from the nozzle does not occur when the softening point of the specimen is high enough. Determination of the gas permeability of the specimen The gas permeability of a specimen is determined in conformity to "Method for determination of the mobility of oxygen gas through a plastic film and sheet" of, ASTM D-3985-81. Namely, while flowing gaseous nitrogen along one side of the specimen (a thin plate) to intercept a oxygen gas permeation from an atmosphere thereinto and introducing oxygen gas of 100% in purity into the other side of the specimen, the amount of the oxygen gas which permeates and passes through the thickness of the specimen into the nitrogen gas side is determined by an electrically quantifiable method while using an oxygen sensor. Accordingly, the value of the gas permeation coefficient (the unit: cm²/s) according to the present invention is the determined value in the case and the total pressure is due to gaseous oxygen under a pressure of 1 atm (the partial pressure of gaseous oxygen, namely ΔP, is 1 atm) at a determination temperature of 20°C, and the determined value is represented by the value calculated as the gas volume under standard state. In addition, on the assumption that the specimen of the carbonaceous thin plate of the present invention has a uniform quality all over, the rate of gas-permeability [cm³ (S.T.P.)/cm² · s] is multiplied by the thickness of the specimen (the unit: cm) to obtain the gas permeation coefficient (cm²/s; O₂, ΔP=1 atm). Example 1 An ethylene bottom oil was pitchfied by subjecting the oil to thermal treatment for 3 hours at 370°C, thereby promoting the heavification thereof, and at the same time, removing the low-boiling components therefrom, and the thus produced pitch was pulverized into particles of not more than 100 micrometers in size and was heated to 190°C at a rate of 10°C/hour in air to obtain the pitch (A) which showed a softening point of 285°C and a carbonization yield of 72% by weight under the calcination at 900°C. The pitch (B) was produced by thermally treating the pitch (A) for 2 hours in gaseous nitrogen atmosphere at 400°C and showed a softening point of 314°C and a carbonization yield of 82% by weight under the calcination at 900°C. On the bottom of a metal mold (600 mm × 600 mm) of a heating press, a sheet of paper of 35 micrometers in thickness which was manufactured by only using pulp without the addition of any inorganic substances was disposed. A carbonaceous raw material prepared by uniformly mixing the pitch (A) and the pitch (B) in a weight ratio of 1:1 in a Henschel mixer was filled in the upper space on the sheet of paper without unevenness. After covering the thus combined material with a sheet of the same paper as above, the upper metal mold of the heating press descended. The heating press was heated to 380°C at a rate of 100°C/hour. After pressing the material for 30 min under a pressure of 1571 kPa (15 kg/cm²G.) the pressure was reduced to 297 kPa (2 kg/cm²G) The heating press was heated to 600°C at a rate of 50°C/hour. The heating press was cooled to obtain a thin plate. The thus obtained thin plate was interposed between the two flat and smooth graphite plates and then was calcined in a vacuum oven at 2000°C. Thereby, it was possible to produce a dense carbonaceous thin plate without any occurrence of crevices and cracks therein. The specific properties of the thus obtained carbonaceous thin plate are shown in Table 1. Thickness (mm) Apparent density (g/cm³) Gas permeation coefficient (cm²/s) Specific resistance (Ohm cm) Bending strength (kg/cm²) 1.1 2.05 3.04 × 10⁻⁸ 2.33 × 10⁻³ 1980 Comparative example In the same manner as in Example 1 except for not inserting the sheet of paper between the carbonaceous raw material and the pressing surface of the heating press, a carbonaceous thin plate was produced by cooling the heating press after heating to 600°C. It was found that the thus produced thin plate was split into a mosaic-like state in the metal mold. A number of bubbles were observed in the thus split thin plate. Example 2 The pitch (C) of a softening point of 224°C and of a yield of carbonization of 69% by weight under calcination at 900°C was produced by thermally treating an ethylene bottom oil for 5 hours at 400°C under a reduced pressure of 2.67 kPa (20 mmHg) abs. By uniformly mixing 70% by weight of the pitch (C) pulverized to not more than 10 micrometers in size and 30% by weight of a powdery graphite of not more than 10 micrometers in size in a Henschel mixer, a carbonaceous raw material was prepared. The thus prepared carbonaceous raw material and a sheet of paper manufactured from a mixture of a pulp and 20% by weight of Vinylon® fibers (made by KURARE Co., Ltd. under the registered trade name of KURAREVINYLON VPB 105-2 × 3 mm) were disposed in a heating press in the same manner as in Example 1. The heating press was heated to 350°C at a rate of 100°C/hour. After pressing for 30 min under a pressure of 5001 kPa (50 kg/cm²G), the pressure was reduced to 591 kPa (5 kg/cm²G.) and the heating press was heated to 500°C at a rate of 30°C/hour. Thereafter, the pressure was released and the heating press was heated to 600°C at a rate of 50°C/hour. Then the thus heated carbonaceous raw material was calcined at 2000°C to obtain a carbonaceous thin plate 1.3 mm in thickness. The specific properties of the thus obtained carbonaceous thin plate are shown in Table 2. Thickness (mm) Apparent density (g/cm³) Gas permeation coefficient (cm²/s) Specific resistance (Ohm cm) Bending strength (kg/cm²) 1.3 1.95 2.24 × 10⁻⁸ 2.33 × 10⁻³ 1580 Example 3 A slurry was prepared by pulverizing and mixing 6 parts by weight of the pitch (A) used in Example 1, 14 parts by weight of the pitch (B) also used in Example 1, 0.5 part by weight of methylcellulose (made by SHINETSU Chem. Co., Ltd. under the registered trade name of METLOSE 90SH-4000) and 80 parts by weight of water for 24 hours in a ball mill. On the other hand, by using fibers prepared by subjecting pitch fibers to oxidative infusibilization and further calcining the thus infusibilized pitch fibers at 600°C in gaseous nitrogen, a paper-like supporting body of an aeral weight of 30 g/m² was prepared. After impregnating the thus prepared paper-like supporting body uniformly with the above-mentioned slurry, the wet supporting body was dried to obtain a sheet-like carbonaceous raw material of an aeral weight of 210 g/m². The material prepared by laminating 4 pieces of the thus obtained sheet-like carbonaceous raw material was named as X₁, the sheet of paper used in Example 1 was named as Y₁ and a stainless-steel plate of 0.4 mm in thickness having two flat and smooth surfaces was named as Z₁. A metal mold (of a dimension of 600 mm × 600 mm) of the heating press was filled with the above three kinds of material in the order of Z₁ Y₁ X₁ Y₁ Z₁ Y₁ X₁ Y₁ Z₁.........Z₁ Y₁ X₁ Y₁ Z₁ from the bottom of the metal mold, so as to fill 30 pieces of X₁ in total therein. The upper metal mold descended. The heating press was heated to 390°C at a rate of 100°C/hour. After pressing the thus combined materials for 30 min under a pressure of 2061 kPa (20 kg/cm²G), the pressure was reduced to 395 kPa (3 kg/cm²G) and the heating press was heated to 600°C at a rate of 30°C/hour and then cooled to room temperature to obtain a thin plate. The thus obtained thin plate was interposed between the two graphite plates having flat and smooth surfaces and then was calcined in a vacuum oven at 2000°C. Thereby, 30 pieces of the dense carbonaceous thin plate could be produced. The specific properties of the thus obtained carbonaceous thin plate are shown in Table 3. Thickness (mm) Apparent density (g/cm³) Gas permeation coefficient (cm²/s) Specific resistance (Ohm cm) Bending strength (kg/cm²) 0.47 1.98 2.78 × 10⁻⁸ 2.26 × 10⁻³ 2030 Example 4 The pitch (D) showing a softening point of 330°C and a yield of carbonization of 85% by weight under calcination at 900°C was prepared by subjecting a coal tar to thermal treatment for 3 hours at 300°C while blowing air thereinto, pulverizing the thus treated coal tar to not more than 100 micrometers in size and heating the thus pulverized material to 225°C at a rate of 10°C/hour in air. A slurry was prepared by pulverizing and mixing 12 parts by weight of the pitch (A) prepared in Example 1, 18 parts by weight of the thus obtained pitch (D), 65 parts by weight of water, 5 parts by weight of methanol and 0.4 part by weight of the methylcellulose (refer to Example 3) for 24 hours in a ball mill. After applying the thus prepared slurry onto a paper-like supporting body of an aeral weight of 25 g/m² manufactured from flame-proof fibers of polyacrylonitrile series (made by TOHO Rayon Co., Ltd. under the registered trade name of PYROMEX), the thus treated supporting body was dried to obtain a sheet-like carbonaceous raw material of an aeral weight of 190 g/m². After laminating two pieces of the thus obtained sheet-like carbonaceous raw material and interposing the laminate between two sheets of the same paper as in Example 1, the thus combined materials were filled in the metal mold of a heating press. The heating press was heated to 430°C at a rate of 50°C/hour. After pressing the combined materials for one hour under a pressure of 6961 kPa (70 kg/cm²G), the pressure was reduced to 591 kPa (5 kg/cm²G) Then the heating press was heated to 650°C at a rate of 15°C/hour. Thereafter, the heating press was cooled to obtain a thin plate. The thus obtained thin plate was interposed between two graphite plates having flat and smooth surfaces and was calcined at 2000°C to produce the carbonaceous thin plate. The specific properties of the thus produced carbonaceous thin plate are shown in Table 4. Thickness (mm) Apparent density (g/cm³) Gas permeation coefficient (cm²/s) Specific resistance (Ohm cm) Bending strength (kg/cm²) 0.23 1.76 3.51 × 10⁻⁸ 2.9 × 10⁻³ 1820

Claims: A process for producing a thin carbonaceous plate, which process comprises; (i) sandwiching a carbonaceous raw material which is carbonized and solidifies after being softened by heating in a heating press between layers of a paper-like substance capable of being carbonized without melting, the said layers of the said paper-like substance being in contact with the pressing surfaces of the heating press; (ii) press-molding the resulting sandwich at a temperature of from 150 to 450°C and a presence of not more than 9901 kPa (110 kg/cm²G) for from 10 to 120 minutes; (iii) heating the press-molded sandwich continuously to a temperature of from 600 to 650°C under a pressure of from 111 to 9901 kPa (0.1 to 100 kg/cm²G) thereby to carbonize the sandwich; and (iv) calcining the carbonized sandwich in a vacuum or in an inert gas; thereby to obtain a said thin carbonaceous plate having a thickness of from 0.2 to 5 mm. A process according to claim 1, wherein the paper-like substance consists of or mainly consists of vegetable fibers. A process according to claim 1 or 2, wherein the thickness of the paper-like substance is not more than 100 micrometers. A process according to any one of the preceding claims wherein the thickness is from 0.2 to 1.5 mm.

Inventors: AJIMA SHIGETOSHI, HIRUTA MASARU, SAITO HATSUO, YOSHIDA AKIO, AJIMA, SHIGETOSHI, HIRUTA, MASARU, SAITO, HATSUO, YOSHIDA, AKIO
Applicants: KUREHA CHEMICAL IND CO LTD, KUREHA KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1986
Main classification: C04B35
IPC codes: H01M4, D01F9, C04B35, C01B31, C25B11