JPH0848577A - Production of impermeable carbonaceous formed body - Google Patents

Abstract

PURPOSE:To produce an impermeable carbonaceous formed body having stable quality. CONSTITUTION:A mixed paper making sheet made of a blend of 40-60wt.% pulp with 5-25wt.% carbonaceous powder and 30-50wt.% thermoplastic resin having >=30% rate of residual carbon is heated to a temp. above the m.p. of the resin and press-formed or such sheets are laminated, heated and press- formed. The resultant green formed body is carbonized by firing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an impervious carbonaceous molding used for a separator plate of a phosphoric acid fuel cell.

[0002]

2. Description of the Related Art Conventionally, a separator plate used in a phosphoric acid fuel cell or the like has a carbon fiber or a cellulosic fiber such as pulp made into paper, and then impregnated with a thermosetting resin, followed by lamination, heating and pressurizing steps. Made by carbonization through
114, JP-A-62-70215).

[0003]

However, although the above paper-making process can mass-produce homogeneous products, the adhesiveness and uniformity between the sheets are not improved during the resin impregnation process, lamination, heating, and pressurization process. Problems are likely to occur, and warpage and surface patterns are likely to occur even in the carbonization process, and various measures have to be taken to avoid this.

Generally, a sheet for making an impervious carbonaceous molded article needs to have a high tenacity as in the case of kraft paper or linter paper, and this sheet is impregnated with a thermosetting resin such as phenol resin. After stacking, heating and pressure molding to obtain a desired green molded body, the following points must be noted.

In order to maintain the adhesiveness between the sheets during lamination, heating, and pressing, the degree of resin curing by preheating after impregnation with the thermosetting resin must be suppressed.

A sheet impregnated with a thermosetting resin (hereinafter referred to as a prepreg sheet) as described above does not undergo hardening of the resin, and since the sheet is tight, the amount of resin permeation tends to be non-uniform during impregnation. Therefore, in order to eliminate this, devise a method of diluting the impregnating liquid with a solvent to an appropriate viscosity, leaving the prepreg sheet for several days after impregnation and aging, and scraping off the excess resin at the time of impregnation with a scraping rod. It is necessary to ensure the homogeneity of the equal impregnation resin.

[0007] When the prepreg sheet is left for a long time, volatile components are dissipated and the adhesiveness is deteriorated, which affects the next lamination, heating and pressing steps. In order to avoid this, it is necessary to store the prepreg sheet in a cool and dark place. When the prepreg sheet is carbonized and fired, voids are likely to be formed due to decomposition and volatilization of the thermosetting resin, and warping and surface patterns are likely to occur unless the uniformity of the impregnated resin is ensured. In order to avoid this, it was necessary to devise such as raising the temperature over a considerably long time, and the yield was also poor.
It is an object of the present invention to provide a method for efficiently producing an impervious carbonaceous molded article of stable quality at low cost.

[0008]

In view of the above circumstances, the inventors of the present invention have earnestly studied in order to obtain an impermeable carbonaceous molding having stable product properties, and as a result, pulp / carbonaceous powder / thermoplastic resin was selected. The inventors have invented that the above-mentioned problems are solved by using a mixed papermaking sheet that has been blended and omitting the step of impregnating a thermosetting resin.

That is, the method for producing an impervious carbonaceous molded article according to the present invention is as follows: 40-60 wt% pulp, 5-25
% Carbonaceous powder, 30-50% by weight residual carbon rate 30%
A mixed papermaking sheet containing the above thermoplastic resin is heated to a temperature not lower than the melting point of the thermoplastic resin, pressure-molded, or the sheets are laminated and heated, pressure-molded to form a green molded body, and fired. Carbonization is a feature of the structure.

Hereinafter, the present invention will be described in detail. Pulp is a solid-phase carbonized fiber that is a factor that governs the physical properties of products such as the mechanical strength of impermeable carbonaceous compacts and ensures papermaking properties. That is, when carbonized, the fibers of the pulp follow solid-phase carbonization, so that the shape of the green molded body is maintained as it is until the product. Fibers that follow solid-phase carbonization include not only pulp but also other cellulosic fibers such as rayon fiber and cotton yarn, but pulp that is easily available and inexpensive is suitable for the purpose of the present invention.

The carbonaceous powder is a factor that governs the physical properties of the impervious carbonaceous compact such as electrical conductivity and thermal conductivity, and the grain size of the range which does not cause a problem in the papermaking property is used.
The particle size of this carbonaceous powder is in the range of 50 μm or less, preferably 1 μm to 30 μm, and graphitized to improve electric conductivity and thermal conductivity, for example, carbon fiber powder, natural graphite powder, artificial graphite powder. Etc. are desirable.

The thermoplastic resin is a factor which controls the impermeability and mechanical strength of the impervious carbonaceous molded article, and the residual carbon rate is 3
It is preferably 0% or more. That is, the thermoplastic resin melts during lamination, heating, and pressure molding, can exhibit the binder function between the pulp and the carbonaceous powder, and fills the voids in the mixed papermaking sheet to contribute to impermeability. The product retains its properties up to the product through the firing and carbonization process.

As the thermoplastic resin, vinyl chloride resin,
Chlorinated vinyl chloride resin, polyacrylonitrile resin,
There are polyvinyl alcohol, polyphenylene ether, polyamide imide, polydivinyl benzene and the like, and polyacrylonitrile resin, polyvinyl alcohol and polyamide imide are particularly preferable.

The shape of the resin is not particularly limited, but a fiber form is preferable from the viewpoint of paper making property, and a fiber diameter of 4 denier or less and a length of 1 to 10 mm are preferable. That is, if the fiber diameter is too large, it is difficult to obtain uniform adhesiveness during the lamination, heating, and pressing steps, and if the fiber length is long, it becomes difficult to make paper.

The mixed papermaking sheet is blended in such a manner that the weight ratio of pulp, carbonaceous powder and thermoplastic resin is 40 to 60% by weight, 5 to 5% by weight.
25 wt% and 30 to 50 wt% are preferable. If it deviates from this weight ratio, defects in the green molded product due to deterioration of paper-making property, deterioration of interlayer adhesiveness, defects during firing and carbonization such as warpage and cracking, and deterioration of product properties occur.

The mixed papermaking sheet thus adjusted and blended is heated, pressure-molded or laminated, heated and pressure-molded to obtain a desired green molded body by controlling the molding temperature and molding pressure. As a matter of course, the higher the molding temperature and the higher the molding pressure, the higher the bulk density of the green molded body.

The molding is performed by pressing the above-mentioned sheet or the laminated papermaking sheet having a predetermined shape. The pressure molding method is not particularly limited and is generally performed by a press, a roll or the like. Further, for example, in the case of producing a cylindrical complicated shape, a mold having a predetermined shape is prepared in advance, and a mixed papermaking sheet having a predetermined shape is installed,
It can be manufactured by pressurizing and molding a mold heated by a press or the like. The molding pressure is 5 kg / cm ² or more, especially 10 kg / cm ² in order to maintain the in-plane uniformity and impermeability.
It is desirable to set the above.

The heating temperature is such that the thermoplastic resin exhibits sufficient fluidity. The setting of the heating temperature differs depending on the type of thermoplastic resin, but the melting point and fluidity of the thermoplastic resin are considered.
Generally, the heating temperature is 10 to 10 above the melting point of the selected thermoplastic resin.
In the temperature range of 100 ° C., preferably in the range of 20-80 ° C.

For firing and carbonization, a large number of green compacts are laminated, sandwiched between graphite plates, and subjected to a load, and then fired at 800 to 3000 ° C. in a non-oxidizing atmosphere by a conventional method. Load a few g / cm ² ~ Number 10 g / cm ² or so, preferably from 5g / cm ² ~50g / cm ² approximately. When the load is small, the object to be fired is likely to be warped. On the other hand, the number 10
If a load of 0 g / cm ² or more is applied, a graphite plate with a weight of several tons is required due to the shape of the impervious carbonaceous compact, and handling during firing becomes complicated, which is not realistic.

[0020]

According to the present invention, a mixed papermaking sheet of pulp, carbonaceous powder and thermoplastic resin is heated and pressure-molded, or laminated, heated and pressure-molded to obtain a thermoplastic resin uniformly dispersed in the sheet. The resin melts and penetrates between pulp fibers to improve the adhesion with the carbonaceous powder. Even at the time of firing and carbonization, the thermoplastic resin is evenly permeated into the sheet, so that carbonization proceeds uniformly and warpage and surface pattern are reduced.
Further, the green molded body can be manufactured only by heating, pressure molding, or laminating, heating, and pressure molding, so that the process is simplified and the cost can be reduced.

[0021]

【Example】

Examples 1 to 5 The present invention will be described below with examples. Pulp (wood pulp beaten to 650 ml Canadian Freeness),
Artificial graphite powder (Showa Denko KK UFG-30, 10
μm), acrylonitrile fiber (Toho Rayon Co., Ltd. Superior, 3 denier, 5 mm) were prepared according to the prescribed composition shown in Table 1 to prepare a mixed slurry aqueous solution, and then a round net paper machine (Toyo Seiki Seisakusho KK) , TSS type sheet machine) was used to prepare a mixed papermaking sheet.

This mixed papermaking sheet was cut into 150 mm square pieces, 6 sheets were laminated and set in a flat plate-shaped mold. This mold is heated to 200 ° C. and 240 ° C. and heated to 10 kg / cm ² , 20
A green molded body was produced by molding with a pressure of kg / cm ² and 30 kg / cm ² .

These green compacts were sandwiched between graphite plates according to a conventional method to obtain 5 g / cm ² , 10 g / cm ² and 30 g / cm ² .
A load of cm ² was applied, and firing was performed at 1000 ° C. or higher for 10 days in a N ₂ atmosphere to produce an impermeable carbonaceous molded body.

[0024]

【Example】

Examples 6 to 10 Pulp (wood pulp beaten to 650 ml Canadian Freeness), carbon fiber powder (Kureha Chemical Industry Co., Ltd.)
Middle fiber (10 μm) and vinyl alcohol fiber (Kuraray Co., Ltd., vinylon, 2 denier, 4 mm) were adjusted according to the prescribed composition shown in Table 2 to prepare a mixed slurry aqueous solution, and then a round net paper machine (Toyo Corporation) Made by Seiki Seisakusho,
A mixed papermaking sheet was prepared using a TSS type sheet machine.

This mixed papermaking sheet was cut into 150 mm square pieces, 6 sheets were laminated and set in a flat plate-shaped mold. This mold is heated to 200 ° C, 210 ° C, 220 ° C and 10 kg / c
It was molded under a pressure of m ² of 30 kg / cm ² to prepare a green molded body.

The sandwiching these green compact graphite plate according to a conventional method under a load of ^{10g / cm 2, 20g / cm} 2 and, N ₂ atmosphere, firing the impermeable carbonaceous molding 10 days at 1000 ° C. The body was made.

The manufacturing conditions of each example are shown in Tables 1 and 2. The characteristic values are shown in Table 3. Each characteristic was evaluated by the following measurements. Bending strength: Three-point bending method (JIS K6911) Electrical resistivity: In-plane four-terminal method (JIS R7202) Thermal conductivity: Laser flash method 200 ° C, Thickness direction Air permeability: N ₂ gas Room temperature, differential pressure 1 Barometric pressure

The carbonaceous molded body obtained in the present invention is
Bending strength, electrical resistivity, thermal conductivity are good, and air permeability is 10
^-5 cc · cm / cm ² sec or less has good impermeability.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

As described above, according to the present invention, the step of impregnating the thermosetting resin can be omitted, and the preheating for determining the degree of resin curing, the uneven distribution of the resin due to gravity, and the non-uniformity of the impregnated resin. The conditions that affect the physical properties of the product are reduced. Therefore, the obtained carbonaceous molded article has stable physical properties, good productivity, and a low-cost impervious carbonaceous molded article can be produced. In particular, a separator used for a phosphoric acid fuel cell or the like can be provided at low cost.

Claims (2)

[Claims] 1. A mixed papermaking sheet containing 40-60% by weight of pulp, 5-25% by weight of carbonaceous powder, and 30-50% by weight of a thermoplastic resin having a residual carbon content of 30% or more is used as the thermoplastic resin. A method for producing an impervious carbonaceous molded article, which comprises heating to a temperature equal to or higher than the melting point of a resin, press-molding or laminating the above-mentioned sheets, heating and press-molding to form a green molded article, and calcining and carbonizing. 2. The method for producing an impervious carbonaceous molded article according to claim 1, wherein heating is performed at 20 to 80 ° C. or higher on the melting point of the thermoplastic resin having a residual carbon rate of 30% or higher.