JPH081040B2 - Method for manufacturing porous carbon plate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel method for producing a porous carbon plate.
More specifically, a sheet obtained from a specific raw material by a papermaking method is impregnated with a resin and then fired to obtain a bulky, thick porous carbon excellent in chemical resistance, electrical conductivity, gas permeability, and strength. It relates to a method of manufacturing a plate.

[Conventional technology]

Conventionally, as a method for obtaining a carbon fiber sheet, a carbon fiber-mixed paper is known in which carbon fiber that has been fired in advance is made with cellulose pulp and a binder. However, such a mixed paper has a relatively high electric resistance value, lacks chemical resistance, and is unsuitable for applications such as an electrode base material for fuel cells. As a method of improving these performances, a method is known in which the carbon fiber-mixed paper is impregnated with a solution of a thermosetting resin and heated and carbonized again in an inert atmosphere. In this method, since an organic substance such as cellulose pulp is carbonized by heat treatment, a fiber paper having a low electric resistance value and improved chemical resistance can be obtained. However, since the carbon fibers themselves have a high elastic modulus, the contact portions of the fibers are not sufficiently bonded, and thus it is difficult to sufficiently lower the electric resistance value.

Further, since carbon fiber has a high specific gravity, it is difficult to obtain a bulky porous plate, and it is difficult to control the bulk density and the pore diameter suitable for various applications.

Moreover, since a firing process is required at each stage of fiberizing and sheeting, there is a disadvantage that the obtained carbon plate becomes very expensive, and therefore development of an inexpensive manufacturing method is required. Was wanted. Further, in the above conventional method, it is difficult to make a thick sheet having a uniform thickness, and the carbon fiber is not hydrophilic and has high elasticity, so that the adhesion with the cellulose pulp is poor and the sheet strength is weak. Therefore, it was necessary to mix binder fibers other than pulp (Japanese Patent Publication No. 53-18603). The present inventors have previously
Proposal of carbon fiber sheet manufacturing method by wet papermaking
59-144625), but since the binder fiber is used as in the above method, there is a drawback that it is difficult to obtain a porous sheet. Further, this method has a drawback in that binder fibers and the like adhere to a dryer or a canvas during paper making, which makes steady operation difficult.

Further, even in a wet papermaking method using no binder fiber, in the case of ordinary wet papermaking, it is necessary to mix cellulose pulp, and as the amount of pulp mixed increases, the tightness of the papermaking sheet is It became difficult to make a large and bulky sheet, and it was not possible to make a carbon plate with high porosity.

[Problems to be solved by the invention]

The present invention improves the above-mentioned drawbacks by forming a sheet without using cellulose pulp, and a porous carbon plate having any average pore diameter and any porosity, using a commonly used paper machine, An object is to provide a method of manufacturing at low cost.

[Means for solving problems]

The method for producing a porous carbon plate of the present invention comprises 50 to 90% by weight of organic fibers for producing carbon fibers, has a Canadian freeness of 500 ml or less, and is a fibrillated polyacrylic fiber, polyethylene fiber, polypropylene fiber, and Organic synthetic fiber selected from para-aramid fiber 10-50% by weight
A sheet is prepared from a raw material containing and by a wet papermaking method, the sheet is dried, the dried sheet is impregnated with an organic polymer substance, and dried, and then this is heated in an inert gas atmosphere at a temperature of 800 ° C. or higher. It is characterized in that it is carbonized by heating.

The method for producing the porous carbon plate of the present invention will be described in detail below.

The organic fiber for carbon fiber used in the present invention may be an ordinary rayon or other regenerated cellulose fiber, pitch fiber, lignin fiber, phenol resin fiber, acrylic fiber, or any other organic fiber commonly used as a raw material for producing carbon fiber. Any of them can be used. As the fiber, 0.5 to 15 denier, 2 mm to 50 mm in length, preferably 1.5 to 10 denier and 5 to 20 mm in length from the viewpoint of easy sheet formation and easy preparation of pore size after firing. It is selected according to the purpose and used alone or in combination of two or more.

Since the organic fibers for carbon fibers have weak hydrophilicity, it is difficult to make paper by themselves. Wood pulp is generally used as a connecting fiber in order to improve the papermaking property.
When wood pulp is used, it is difficult to obtain a bulky sheet. In the present invention, a bulky sheet can be obtained by using, as the connecting fiber, a fibrillated organic synthetic fiber having a Canadian freeness of 500 ml or less.
Here, the "fibrillated organic synthetic fiber" is a fibrillated organic synthetic fiber fibrillated by beating or other mechanical means, as well as by a method of polymerizing while applying a shearing force, etc. It includes fibrillated organic synthetic fibers (generally also called "synthetic pulp") produced in fibrillated form. Examples of the fibrillated synthetic fibers by beating include beaten polyacrylic fibers, and as the organic synthetic fibers obtained in a fibrillated form, fibrillated polyethylene fibers, fibrillated polyacrylonitrile fibers, fibrillated polypropylene fibers, fibrils. Para-aramid fiber and the like. The fibrillated organic synthetic fibers may be used alone or in combination of two or more. The fibrillated organic synthetic fiber used for papermaking in the method of the present invention has a Canadian freeness of 500 ml or less, preferably 300 ml or less.

The mixing ratio of the organic fiber for producing carbon fiber and the fibrillated organic synthetic fiber is 50 to 90% by weight of the former, preferably 75 to 90% by weight, and 10 to 50% by weight of the latter, preferably 10 to
25% by weight. When the organic fiber for carbon fiber production is less than 50% by weight, it becomes difficult to control the pore diameter, the porosity, etc. On the other hand, when the organic fiber exceeds 90% by weight, it is difficult to form a good sheet during papermaking. .

Preparation of a sheet by wet papermaking from the above raw material fibers for papermaking and drying of the sheet can be carried out by a conventional method.

The papermaking sheet is impregnated with an organic polymer and then dried. Examples of the organic polymer substance used for impregnating the papermaking sheet include phenol resin, epoxy resin, unsaturated polyester resin, furan resin, thermosetting resin such as polydivinylbenzene, vinyl chloride resin, vinylidene chloride resin, and fluorinated resin. Thermoplastic resins such as vinyl resin, vinylidene fluoride resin, acrylic resin and the like, as well as those such as lignin, pitch or tar are also used. These polymer compounds are either soluble in some solvent or melted at a high temperature during heat treatment, and have a carbon content of 30% by weight or more, and after carbonization, bond carbon fibers as a carbonaceous binder. Those that are useful for are preferred. Among the above organic polymer substances, thermosetting resins are particularly preferable.

When the solution of the organic polymer substance is impregnated into a sheet, if the amount of the solution adhered to the sheet by impregnation is too small, the strength of the carbon plate is reduced and the carbonization yield during carbonization is poor. On the other hand, when the amount of adhesion is excessive, it causes clogging, which makes it difficult to adjust the porosity and becomes brittle. The preferable impregnated amount is 20 to 160% by weight, and preferably 60 to 120% by weight, based on the solid content of the papermaking sheet.

When regenerated cellulose, such as rayon, is used as the organic fiber for carbon fiber production, the combined use of the organic polymer and the impregnation of the heat resistance improve the carbonization yield and strength. And bring a good effect. As the heat resistance improver, any of those generally used in producing rayon carbon fibers can be used. For example, as the metal phosphate, monobasic magnesium phosphate,
Monobasic calcium phosphate, monobasic sodium phosphate, monobasic potassium phosphate, and the like, as ammonium salts of various acids, ammonium chloride, ammonium sulfate, ammonium hydrogen sulfate, ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, Ammonium salts of polyphosphoric acid, ammonium borate and the like are preferably used.

The impregnated sheet may be directly subjected to heat carbonization treatment after being dried, or may be subjected to press treatment before heat carbonization if necessary. The impregnated sheet may be pre-cured by heating before the press treatment. Pre-curing makes it difficult for the organic polymer substance in the sheet to flow, so that a uniform press treatment can be performed. As a pre-curing treatment condition, a condition that does not completely cure, specifically, 105 ° C to 180 ° C, 1 minute to 30 minutes is suitable. The pressing process has the required thickness for the final carbon plate,
It is given to give shape, porosity, and pore diameter, at that time,
It is preferable to cure the resin in the impregnated sheet by using heat treatment together. This curing process makes it possible to maintain a constant sheet thickness and at the same time obtain a flat sheet. Further, the thickness, the porosity, and the pore system of the carbon plate can be arbitrarily changed by adjusting the pressing pressure or the thickness of the spacer.

At the time of the above press treatment, the required number of thin impregnated sheets,
A thick carbon plate can be easily obtained by preferably stacking three or more sheets and applying a pressing treatment in the same manner as described above. When superposing the impregnated sheets, if the sheets are alternately laminated in the longitudinal direction and the transverse direction, the orientation of the sheets is lost and a carbon plate having a uniform thickness without cracks can be obtained. The heating conditions for the heating effect in the press treatment are 150 to 220 ° C., 1
~ 60 minutes is suitable.

The impregnated sheet or the sheet subjected to the above press treatment is further subjected to a stabilization treatment by heating in air, if necessary, and then fired to obtain a target porous carbon plate.
The stabilization treatment is performed to improve the carbonization yield and the graphitization rate of the organic fiber after the heating and carbonization step. When the organic fiber for producing carbon fiber is acrylic fiber or pitch fiber, the stabilizing treatment is particularly effective. The stabilizing treatment conditions are not particularly limited, and the treatment is preferably performed in air at 150 to 350 ° C. for several tens of minutes to several tens of hours. The preferred conditions vary somewhat depending on the type of organic fiber used. The above stabilized sheet,
Next, the target porous carbon plate is obtained by heating and firing at a temperature of 800 ° C. or higher in an inert gas atmosphere.
The carbonization step can be performed by a conventional method.

[Invention and Effect of Invention]

The first feature of the method of the present invention is that a papermaking sheet is prepared from a precursor fiber raw material without using wood pulp, so that a sheet having a low sheet density can be obtained, and since carbon fiber is not used, 800 ° C or higher. In the heating and calcination, about half of the raw material disappears as a gas, whereby a porous carbon plate having a very high porosity can be easily obtained. For example,
In the conventional carbon plate obtained from the paper sheet of carbon fiber, the porosity was 70% as the upper limit value, but in the method of the present invention,
A carbon plate having a porosity of 80% can be easily obtained. Such a carbon plate has excellent gas permeability and liquid permeability.

The second feature of the method of the present invention is that the raw material sheet can be produced by a normal wet paper machine, so that the productivity is improved and an inexpensive raw material sheet can be used.

A third feature of the method of the present invention is that a uniform and flat sheet having less basis weight unevenness can be easily obtained as compared with the conventional carbon fiber papermaking method. Since the carbon plate obtained by the method of the present invention has uniform gas permeability and liquid permeability, it is useful as an electrode convenient for fuel cells, secondary batteries and the like.

A fourth aspect of the method of the present invention is according to a preferred embodiment,
By stacking thin sheets and performing press processing,
The point is that it is possible to manufacture a porous carbon plate having an arbitrary thickness. Further, in the method of the present invention, by selecting the thickness of the raw material fibers, adjusting the blending, and adjusting the press treatment, the pore diameter and porosity of the plate which become particularly problematic when used as an electrode base material for a fuel cell or a secondary battery. Can be controlled freely and easily.

〔Example〕

In order to make the present invention easier to understand, the examples will be specifically described below, but the following examples do not limit the present invention. In the examples, "parts" and "%" are "parts by weight" and "% by weight", respectively.

Example 1 A beatable polyacrylic fiber having a thickness of 3 denier and a length of 2 mm (A104, Asahi Kasei Kogyo Co., Ltd.) beaten to a Canadian freeness of 250 ml, 20 parts by weight, unbeaten thickness 7
50 parts by weight of denier, 3 mm long polyacrylic fiber, and 30 parts by weight of unbeaten 3 denier, 3 mm long polyacrylic fiber were mixed with water to prepare a slurry, which was then used in a round net paper machine. A sheet having a basis weight of 150 g / m ^{2 was} produced by the method.
This sheet was impregnated with a 23% methanol solution containing 70% polymer material (phenolic resin, Gunei Kagaku PL-2215) based on the weight of the sheet and dried at a temperature of 105 ° C. This is laminated as a single sheet as it is without pressing
It was sandwiched between 5 mm graphite plates and heat-stabilized in air at 220 ° C. for 4 hours, and then the graphite plates were heated and carbonized in a nitrogen gas atmosphere at 1000 ° C. for 1 hour.

Example 2 A beatable polyacrylic fiber having a thickness of 3 denier and a length of 2 mm (A104, Asahi Kasei Kogyo Co., Ltd.) beaten to a Canadian freeness of 250 ml, 20 parts by weight, unbeaten thickness 7
50 parts by weight of denier, 3 mm long polyacrylic fiber, and 30 parts by weight of unbeaten 3 denier, 3 mm long polyacrylic fiber were mixed with water to prepare a slurry, which was then used in a round net paper machine. The sheet was made into a sheet having a basis weight of 150 g / m ² by the method.
This sheet was impregnated with a 23% methanol solution containing 70% polymer material (phenolic resin, Gunei Kagaku PL-2215) based on the weight of the sheet and dried at a temperature of 105 ° C. Then, the sheets were pressed without being laminated, and pressed so that the thickness became 0.6 mm, and simultaneously heat-treated at 180 ° C. for 15 minutes. Then, after heat-stabilizing treatment in air at 220 ° C. for 4 hours, heating and carbonization was performed for 1 hour in a nitrogen gas atmosphere at 1000 ° C. between graphite plates.

Example 3 A beatable polyacrylic fiber having a thickness of 3 denier and a length of 2 mm (A104, Asahi Kasei Kogyo Co., Ltd.) beaten to a Canadian freeness of 250 ml 20 parts by weight, unbeaten thickness 7
50 parts by weight of denier, 3 mm long polyacrylic fiber, and 30 parts by weight of unbeaten 3 denier, 3 mm long polyacrylic fiber were mixed with water to prepare a slurry, which was then used in a round net paper machine. The sheet was made into a sheet having a basis weight of 150 g / m ² by the method.
This sheet was impregnated with a 25 methanol solution containing 87% of a polymer substance (phenolic resin, Gunei Kagaku PL-2215) based on the weight of the sheet, and dried at a temperature of 105 ° C. Then, five sheets were laminated and pressed by a press to a thickness of 2.92 mm, and simultaneously heat-treated at 180 ° C. for 15 minutes.
Then, after heat-stabilizing treatment in air at 220 ° C. for 4 hours, heating and carbonization was performed for 1 hour in a nitrogen gas atmosphere at 1000 ° C. between graphite plates.

Example 4 20 ml of fibrillated and 200 ml Canadian freeness paraamide fiber (Dupont Kepler), 7 denier unrefined thickness, 50 parts by weight of polyacrylic fiber 3 mm long, and 3 denier unrefined thickness , Length 3m
Water was added to 30 parts by weight of m-polyacrylic fiber to prepare a slurry, and the slurry was made into a sheet having a basis weight of 150 g / m ² by a conventional method using a round net paper machine. On this sheet, based on the sheet weight
95% polymer (phenolic resin, Gunei Chemical PL-221
It was impregnated with a 25 methanol solution containing 5) and dried at a temperature of 105 ° C. Next, five of the sheets were laminated and pressed with a press to a thickness of 2.91 mm, and simultaneously heat-treated at 180 ° C. for 15 minutes. Next, after heat-stabilizing in air at 220 ° C for 4 hours, sandwich between the graphite plates for 1000
Carbonization was carried out by heating in a nitrogen gas atmosphere at 0 ° C for 1 hour.

Comparative Example 1 20 parts by weight of NBKP beaten to a Canadian freeness of 250 ml, 50 parts by weight of an unbeaten thickness of 7 denier and a length of 3 mm of polyacrylic fiber, and an unbeaten thickness of 3 denier and a length of 3 mm of poly Water was added to 30 parts by weight of acrylic fiber to prepare a slurry, which was then weighed by a conventional method on a cylinder paper machine.
Paper was made into a sheet of 150 g / m ² . This sheet was impregnated with 25% methanol solution containing 95% polymer material (phenolic resin, Gunei Kagaku PL-2215) based on the weight of the sheet, and the temperature was 105 ° C.
Dried at a temperature of. Next, 5 sheets are laminated and pressed by a press to a thickness of 2.72 mm, and at the same time, 180 ° C., 15
Heat treatment was performed for minutes. Then, after performing heat stabilization treatment in air at 220 ° C. for 4 hours, heating carbonization was performed for 1 hour in a nitrogen gas atmosphere at 1000 ° C. with sandwiching between graphite plates.

Table 1 shows the characteristics of the porous carbon plates obtained in Examples 1 to 4 and Comparative Example 1.

As is clear from Table 1, all the carbon plates produced by the method of the present invention had high porosity and excellent gas permeability. The carbon plate of Comparative Example 1 was unsatisfactory in gas permeability.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display area D21H 15/02 D21J 1/16 // H01M 4/80

Claims (1)

[Claims] 1. 50 to 90% by weight of organic fiber for producing carbon fiber,
Polyacrylic fiber, polyethylene fiber, which has a Canadian freeness of 500 ml or less and is fibrillated,
A sheet is prepared by a wet papermaking method from a raw material containing 10 to 50% by weight of an organic synthetic fiber selected from polypropylene fiber and para-aramid fiber, and the sheet is dried, and the dried sheet is impregnated with an organic polymer substance. To dry
Next, a method for producing a porous carbon plate, which comprises heating and carbonizing this at a temperature of 800 ° C. or higher in an inert gas atmosphere.