JPH01266223A - Production of anisotropic porous carbon formed product - Google Patents

Abstract

PURPOSE:To obtain the title formed product of high chemical resistance, by making a slurry of organic fibers for producing carbon fibers and pulp into paper sheets, impregnating them with an organic polymer, further making a specific formed precursor, then calcining the precursor. CONSTITUTION:A mixture of 65-90wt.% of organic fibers for producing carbon fibers such as acrylic fibers and 10-35wt.% of pulp is combined with water to prepare a slurry, and the slurry is made into paper sheets by the wet method, to give paper sheets of more than 2.0 ratio of the lengthwise strength to crosswise strength. Then, one or more paper sheets are impregnated with an organic polymer, the fibers and pulp are oriented almost in the same direction and the polymer is cured to form a formed precursor. Finally the formed precursors are calcined in an inert atmosphere at temperature over 800 deg.C to give the subject formed product of high quality inexpensively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an anisotropic porous carbon molded body. More specifically, the present invention relates to a method for producing a porous carbon molded body that exhibits anisotropy in terms of mechanical strength and electrical conductivity, and is useful as an electrode for fuel cells.

[Conventional technology]

Conventionally, a known method for obtaining carbon fiber sheets is to cut pre-fired carbon fibers into short pieces, mold them into a sheet, and then fire this sheet. It has been difficult to impart anisotropy to carbon fiber sheets produced by carbon fibers. The inventors
A carbon fiber sheet with isotropy is manufactured by alternately stacking a large number of carbon fiber sheets manufactured by a papermaking method in the longitudinal direction (papermaking direction; hereinafter referred to as MD) and the transverse direction (papermaking direction; hereinafter referred to as CD). proposed a method to do so.

However, carbon fiber sheet laminates can be used for fuel cells or
When used in applications such as secondary batteries, it is required to have excellent strength in a specific direction and electrical conductivity.

For example, in the case of fuel cell electrodes, grooves are formed on the negative side of the electrode to allow gas or oxygen-containing gas to pass through, but the bending strength in the direction perpendicular to the grooves within this groove formation surface becomes extremely weak. There is a problem. In addition, in the case of chlorine-zinc type secondary battery electrodes, a current collector plate is attached to one side of the electrode, so the electrical conductivity is higher in the direction perpendicular to the current collector plate than in the case of isotropic electrical conductivity. Something better is desired.

Carbon fiber boards with excellent mechanical strength and electrical conductivity in specific directions are desirable for the above-mentioned applications, but a method for manufacturing carbon fiber molded bodies with such anisotropy has not yet been known. It is.

[Problem to be solved by the invention]

The present invention solves the above problems and provides a method for producing a porous carbon molded body that has excellent chemical resistance, is inexpensive, and has high quality, and exhibits anisotropy in electrical conductivity and strength. The challenge is to do so.

[Means to solve the problem]

The method for producing an anisotropic porous carbon molded body of the present invention that solves the above problems is to produce a wet-type porous carbon body from a slurry containing a mixture of 65 to 90% by weight of organic fibers for forming carbon fibers and 10 to 35% by weight of pulp. a step of producing a paper sheet having a ratio of longitudinal tensile strength to lateral tensile strength of 2.0 or more by a papermaking method; a step of impregnating at least one of the paper sheets with an organic polymeric substance; The carbon fiber-forming organic fibers and the pulp are oriented in substantially the same direction from one organic polymer material-impregnated sheet, the organic polymer material is hardened, and the material has a predetermined shape and size. a step of forming a precursor molded body having
The precursor molded body is heated at 800° C. in at least an inert atmosphere.
The method is characterized in that it includes a step of performing a firing treatment at a temperature above.

In the method of the present invention, a paper sheet is produced by a wet papermaking method from a slurry containing a mixture of 65 to 95% by weight of organic fibers for forming carbon fibers and 10 to 35% by weight of pulp.

Organic fibers for forming carbon fibers The organic fibers for forming carbon fibers used in the method of the present invention include:
Pitch fiber, acrylic fiber, rayon fiber, phenol fiber, polyvinyl chloride fiber, aramid fiber, etc. are used. As such organic fibers, those having a length of 0.5 to 15 denier and a length of 1 to 15 ml11 are used, but from the viewpoint of paper-making properties, preferably 0.5 to 8 denier fibers with a length of 1.5 ml are used. -10 mm is selected depending on the purpose and used alone or in combination of two or more of these.

This organic fiber is converted into carbon fiber in the firing step of the method of the present invention.

Pulp The above-mentioned organic fibers for forming carbon fibers generally have low hydrophilicity;
Therefore, paper cannot be made using organic fibers alone.

Therefore, in the present invention, pulp is blended as a reinforcing fiber to improve papermaking properties.

As the pulp used for this purpose, in addition to cellulose pulp, various synthetic pulps made of hydrophilic synthetic resins can be used.

Mixing ratio of organic fiber and pulp The mixing ratio of organic fiber and pulp is 65 to 90% organic fiber.
It is necessary that the pulp content be 10 to 35% by weight (as solid content).

When the blending ratio of organic fibers is lower than 65% by weight, it becomes difficult to control the pore diameter and porosity of the resulting carbon fiber board, while when the blending ratio of organic fibers is higher than 90% by weight, it becomes difficult to control the pore size and porosity of the obtained carbon fiber board. It becomes difficult to form a good sheet. Furthermore, if the pulp content ratio is lower than 10% by weight, papermaking properties will deteriorate and sheet formation will become difficult, and if the pulp content ratio is higher than 35% by weight, a sufficiently bulky sheet will not be obtained. Generally, it is preferable that the blending ratio is within the range of 75 to 90% by weight of organic fiber and 10 to 25% by weight of pulp.

Paper making method In order to obtain a sheet with high fiber orientation, it is preferable to use a circular mesh paper machine.Increasing the paper making speed can further increase the orientation of the fibers within the paper sheet, resulting in less tension in the MD force direction. The intensity is higher than that in the CD direction. For example, in one embodiment of the method of the present invention, 17 m/
When paper is made at a speed of 30 m/min, the tensile strength ratio (MD/CD) of the paper sheet obtained is 2.1, whereas when paper is made at a speed of 30 m/min, the tensile strength of the paper sheet obtained is 2.1. The ratio (MD/CD) is 2.8
becomes. In a Fourdrinier paper machine, the degree of orientation of fibers within a paper sheet can be easily increased by changing the ratio of the raw material outflow speed from the inlet to the paper wire speed (jet wire ratio; J/W). . Normally, when making high-quality paper using a Fourdrinier paper machine, the J/W ratio is set from 0.9 to 1.2.
When paper is made as follows, the tensile strength ratio (M
D/CD) is 2.0 or less, but when paper is made with a J/W ratio of 1.5 or more, the tensile strength ratio of the resulting paper is <
MD/CD) is 2.0 or more, and therefore a sheet with high fiber orientation, that is, high anisotropy in various properties such as mechanical strength and electrical conductivity, can be obtained.

In the method of the present invention, a paper-like paper sheet is produced from an aqueous dispersion containing the organic fiber-pulp mixture by a wet paper-making method, and the longitudinal direction (
In other words, the ratio of the tensile strength in the paper making direction to the tensile strength in the horizontal direction is controlled to be 2.0 or more. This intensity ratio is 2.
More preferably, it is 2 or more. When this strength ratio is lower than 2.0, the resulting porous carbon plate has an unsatisfactory anisotropy in electrical conductivity and mechanical strength.

In the method of the present invention, a papermaking sheet is impregnated with an organic polymeric substance. This organic polymer substance has solidification or hardening properties.

Organic polymer substances used for impregnating paper sheets include, for example, phenolic resins, epoxy resins, unsaturated polyester resins, thermosetting resins such as polydivinylbenzene, and polyvinyl chloride resins. Thermoplastic resins such as polyvinylidene chloride resin, polyvinylidene fluoride resin, polyvinylidene fluoride resin, and polyacrylic resin are used, and other materials such as lignin, pitch, or tar can also be used. Preferable properties that these polymer compounds should have include being soluble in some kind of solution or melting at high temperatures during heat treatment, and having a carbon content of 30% by weight or more and forming a carbonaceous binder after being fired. For example, it can help bond carbon fibers together. As the polymer compound having such properties, it is preferable to use a thermosetting resin.

The organic polymer material is impregnated in an amount of 20 to 160% by weight, preferably 60 to 100% by weight based on the weight of the sheet.

The organic polymeric substance to be impregnated into the papermaking sheet may be mixed with carbonaceous powder. The mixing ratio at this time is preferably 5% to 40% of the carbonaceous powder to 20% to 160% (solid weight) of the organic polymer material. By using such carbonaceous powder, a carbon molded body with excellent electrical conductivity can be obtained.

Regenerated cellulose fiber as organic fiber for forming heat resistance improver carbon fiber,
For example, when using rayon, in addition to the above-mentioned mixed impregnation treatment with carbonaceous powder and organic polymer, impregnation treatment with a heat resistance improver can be used to obtain good results in terms of carbonization yield, strength, etc. can get. As the heat resistance improver, any of those commonly used in producing rayon carbon fibers can be used. Such heat resistance improvers include, for example,
Phosphate metal salts include monobasic magnesium phosphate, monobasic calcium phosphate, monobasic sodium phosphate, monobasic potassium phosphate, etc.Ammonium salts of various acids include ammonium chloride, ammonium sulfate, ammonium hydrogen sulfate, and ammonium phosphate. , ammonium hydrogen phosphate,
Ammonium dihydrogen phosphate, ammonium salt of polyphosphoric acid, ammonium borate, etc. can be suitably used.

In the method of the present invention, the polymeric substance to be impregnated into the paper sheet is dissolved, emulsified, or dispersed in a suitable solvent such as water, methanol, or toluene, and the sheet is impregnated with this treatment liquid by a conventional impregnation method. This is dried or precured to produce an organic polymer material-impregnated sheet.

In the method of the present invention, a preformed body having a desired shape and dimensions is formed from at least one sheet impregnated with an organic polymeric substance. In this molded body, the organic fibers for forming carbon fibers and the pulp fibers therein are oriented in the same direction, and the impregnated organic polymer substance is hardened.

That is, the precursor molded body may be formed from a single impregnated sheet, or may be formed by stacking two or more resin-impregnated sheets so that their papermaking directions coincide. This precursor molded body is preferably pressed.

When producing a preformed body from the organic polymer substance-impregnated sheet as described above, impregnation is performed as necessary to give the desired product the thickness, shape, porosity, and pore size required for the porous carbon plate. The sheet may be subjected to lamination treatment, press treatment, and/or preliminary curing treatment.

Pre-curing treatment When the impregnated sheet is pre-cured, the organic polymeric substance within the sheet no longer flows, making it easier to perform uniform molding treatments such as pressing. The pre-curing treatment conditions include conditions in which the organic polymer substance is not completely cured, for example, from 105°C to
180°C and about 1 minute to 30 minutes are suitable. The precursor molded body may be hot press-molded after the precuring treatment or at the same time. This press forming is effective for imparting the required thickness, shape, porosity, and pore size to the final product, the porous carbon plate. At that time, the organic polymer substance in the impregnated sheet may be cured by using heat treatment in combination.

In the method of the present invention, the precursor molded body (including a precured one) may be hot press molded.

Heat press molding and hardening treatment When an impregnated sheet or a laminate thereof is subjected to a press treatment to form a precursor molded body, anisotropy in the orientation direction of the fibers can be improved. The press heating conditions are 15
A temperature of 0 to 220°C for 1 to 60 minutes is appropriate. This pressing process made it possible to maintain the thickness of the molded body constant and to obtain a flat molded body. In addition, by adjusting the press pressure, the porosity and pore diameter of the target carbon plate can be arbitrarily controlled. When stacking two or more impregnated sheets, if the sheets are stacked alternately in the MD direction and the CD direction, the resulting sheet will have no directionality, and a desirable sheet with anisotropy will not be obtained. The precursor molded body is preferably then subjected to a stabilization treatment.

Stabilization Treatment In the method of the present invention, the precursor molded body subjected to the hot press treatment is preferably subjected to a stabilization treatment prior to firing. The stabilization treatment is performed to improve chemical resistance and carbonization yield of the organic fiber after the heating carbonization step. This is particularly effective when the organic fiber is acrylic fiber or pitch fiber. The stabilization treatment conditions vary depending on the type of organic fiber used, but are preferably in the range of 150 to 350°C and several hours to several hundred hours, and more preferably in the range of 180 to 350°C.
The treatment is carried out at 250° C. for 6 to 200 hours in an oxygen-containing atmosphere.

The stabilized precursor molded body is then subjected to a firing treatment.

Firing Treatment The stabilized precursor molded body is heated and fired at a temperature of 800° C. or higher in an inert gas atmosphere, thereby converting it into the porous carbon plate of the present invention.

If the firing temperature is lower than 800° C., the transformation into a porous carbon plate will be insufficient or will take an excessively long time.

〔Example〕

The present invention will be further illustrated by the following examples, but these examples are not intended to limit the invention. In addition, in the example,
Parts and percentages are by weight, respectively.

Example 1 and Comparative Examples 55 parts and 25 parts of a polyacrylic fiber (Asahi Kasei A10) with a thickness of 7 denier and a length of 3 mm (Asahi Kasei A10) and a polyacrylic fiber (Asahi Kasei Al0L) with a thickness of 3 denier and a length of 3, respectively, Canadian Freeness 400- Pulp (
A slurry was prepared by adding water to a mixture with 20 parts of NBKP), and a paper sheet having a basis weight of 180 g/m'' was made from this slurry by a conventional method using a circular paper machine.Tensioning the above sheet in the vertical direction The ratio of tensile strength in the horizontal direction was as shown in Table 1. This paper sheet was immersed in a solution consisting of a polymeric substance and methanol. -2215), and after the impregnation with the phenolic resin solution, which was impregnated at a ratio of 80% of the weight of the paper, was completed, it was dried in a drying chamber at 105°C.Then, this sheet was kept constant in the papermaking direction. Laminate six sheets aligned in the direction of , press the laminate to a thickness of 3.0 mm,
At the same time, heat treatment was performed at a temperature of 180° C. for 15 minutes to produce a cured laminate. Next, this cured laminate was heat-stabilized at 220°C for 5 hours in an enzyme-containing atmosphere, and then sandwiched between graphite plates and fired for 1 hour in a nitrogen gas atmosphere at 2000°C. Ta.

Table 1 shows the carbonization yield, bending strength, and volume resistivity of the obtained carbon molded body.

In the comparative example, the same operation as in Example 1 was performed. However, when stacking six impregnated sheets, adjacent sheets were alternately stacked so that their papermaking directions were at 90 degrees to each other. Table 1 shows the performance of the comparative carbon molded body obtained.

Example 2 Polyacrylic fibers (Asahi Kasei A10) with a thickness of 7 denier and a length of 3 mm, 55 parts and 25 parts of acrylic fibers (Asahi Kasei Al0L) with a thickness of 3 denier and a length of 3 IIl, respectively, and Canadian Freeness 40 A slurry was prepared by adding water to 20 parts of 〇- pulp (NBKP). From this slurry, a paper machine with a basis weight of 1
A paper sheet of 80 g/m' was produced. The ratio of the tensile strength in the longitudinal direction to the tensile strength in the transverse direction of the above sheet was as shown in Table 1. This paper sheet was immersed in a solution consisting of a polymeric substance and methanol. This polymer substance is a phenol resin (PL-22i) manufactured by Gunei Chemical.
5) and was impregnated at a ratio of 80% (solid content) based on the weight of the paper. After the impregnation with the phenolic resin solution was completed, it was dried in a drying chamber at 105°C. Next, the above-mentioned sheets were pressed one by one without being laminated to a thickness of 0.5 mm, and at the same time, they were heat-treated at 180° C. for 15 minutes. Then 22
After performing heat stabilization treatment in an oxygen-containing gas at 0°C for 48 hours, this was sandwiched between graphite plates and fired in a nitrogen gas atmosphere at 2000°C for 1 hour. Table 1 shows the performance of the obtained carbon plate.

Example 3 A polyacrylic fiber having a thickness of 7 denier and a length of 3 stripes (10 to Asahi Kasei) and a polyacrylic fiber having a thickness of 3 denier and a length of 3 mm (Asahi Kasei Al0L) were mixed with 55 parts and 25 parts, respectively, of Canadian Pulp with a freeness of 400-
NBKP) 20 parts and water are added to make a slurry, and from this thriller, the JZW ratio is set to 2.0 using a Fourdrinier paper machine.
A sheet was made to have a basis weight of 180 g/m'.

The above sheet was immersed in a solution consisting of a polymeric substance and methanol. The polymer material in the solution was a phenolic resin PL-2215 manufactured by Gunei Kagaku ■, and 80% of the weight (solid content) of the paper was impregnated therein. After the impregnation with the polymeric substance solution was completed, it was dried in a drying chamber at 105°C. Next, the sheet was heat-stabilized at 220°C for 48 hours in an oxygen-containing gas without being laminated or pressed, and then sandwiched between graphite plates.
Firing was performed for 1 hour in a nitrogen gas atmosphere at 000°C. Table 1 shows the performance of the obtained carbon plate.

〔Effect of the invention〕

By the method of the present invention, a porous carbon plate having anisotropy in strength can be produced. When a current collector plate is placed at one end to support the electrode, such as in the case of a chlorine-zinc type secondary battery electrode, placing the current collector plate in the direction where the strength of the carbon plate is strong will prevent the battery from being used before it is used. Also, it is less likely to be damaged during use, which is very convenient.

Alternatively, when using grooves such as fuel cell electrodes, cutting the grooves in such a way that the direction of the grooves crosses the fiber orientation direction reduces the decrease in strength due to cutting the grooves and improves the strength. A relatively high electrode plate is obtained, and a preferable electrode is obtained with less damage during handling.

Further, by the method of the present invention, a porous carbon plate having anisotropy in electrical resistance can be produced. If the carbon plate is oriented in such a way that when the current collector plate is at one end and collects current, as in the case of secondary battery electrodes, the electrical conductivity will improve in that direction, there will be no electricity loss due to Joule heat generation, and power generation will be possible. It is possible to manufacture an excellent current collector plate that can increase efficiency.

By the method of the present invention, since the raw material sheet is made from organic fibers and pulp, a porous carbon plate with a low sheet density can be obtained.Also, since no carbon fiber is used, the precursor molded body is Since about half of the amount is gasified and lost, a porous carbon plate with extremely high porosity can be easily obtained.

In the method of the present invention, the raw material sheet can be made into paper using a normal wet paper machine, so productivity is improved and the raw material sheet can be obtained at low cost. In addition, the raw material blend slurry of the present invention has better paper-making properties than slurry containing only carbon fibers, so it has the advantage that uniform and flat sheets can be easily obtained, and the basis weight of the sheet can also be adjusted as desired. be.

Furthermore, by laminating thin sheets in the direction of the present invention,
By applying a press treatment to this, it became possible to manufacture an anisotropic porous carbon plate of any thickness. In addition, by selecting the thickness of the raw material fibers, adjusting the blending and press processing, we can reduce the pore size and porosity of the plate, which is a particular problem when the obtained carbon plate is used as an electrode base material for fuel cells and secondary batteries. It is now possible to control freely and easily.

Claims (1)

[Claims] 1. 65 to 90% by weight of organic fibers for forming carbon fibers;
A step of producing a paper sheet having a ratio of longitudinal tensile strength to transverse tensile strength of 2.0 or more from a slurry containing a mixture with 0 to 35% by weight of pulp by a wet papermaking method; a step of impregnating a papermaking sheet with an organic polymeric substance; and a step of impregnating a papermaking sheet with an organic polymeric substance; A step of forming a precursor molded body in which a polymeric substance is hardened and has a predetermined shape and dimensions, and a firing treatment of the precursor molded body at a temperature of 800°C or higher in at least an inert atmosphere. A method for producing an anisotropic porous carbon molded body, the method comprising: