JP2632955B2 - Manufacturing method of porous carbon plate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon plate used for an electrode, a fuel cell, a heat insulator and the like of a fuel cell.

2. Description of the Related Art As a porous carbon plate used for an electrode or the like of a fuel cell, a method of forming a sheet by maintaining a short pitch, making it infusible and carbonized (JP-A-50-121505), using a mixture of organic fibers and pulp There is a method of making a sheet, impregnating it with a polymer, and carbonizing (US Pat. No. 4,697,696).

In addition, filaments of polyacrylonitrile (PAN) based fibers are infusibilized and then cut to form a sheet with the short fibers, which is carbonized. At that time, a bonding agent is added to the sheet (US Patent No. 406427). There is a materialless method (US Pat. No. 4,080,413).

Problems to be Solved by the Invention The method of carbonizing a sheet of pitch staple fibers is weaker than pitch-based carbon fibers compared to PAN-based carbon fibers, and because it is a sheet of short fibers, tension cannot be applied in the infusibilizing step, so Even high strength carbon fiber is not obtained. Further, an additive such as glycol is used for the sheet, but since the pitch and the thermosetting resin are not added, the bending strength of the carbon material is low.

In the above method of the mixed sheet of the organic fiber and the pulp, the strength of the fiber after carbonization is weak because there is no tension in the infusibilizing step.

The PAN fiber filament is infusibilized and cut,
In the method of forming a sheet using the short fibers, it is possible to apply tension in the infusibilizing step, but since the filaments are infusibilized without fusing each other, the fusion bonding at the contact point of the filaments is not performed. Therefore, the reinforcing effect of the fibers on the carbon plate is not sufficient.

An object of the present invention is to improve the strength and electric conductivity of a porous carbon plate by increasing the fiber strength and improving the wettability between the fiber and the binder in a fiber-reinforced porous carbon plate. .

Means for Solving the Problems If the woven or non-woven fabric of the PAN fiber is subjected to infusibility treatment under tension, not only the strength of the obtained carbon fiber is increased, but also at the point where the filaments intersect, fusion occurs in the infusibilization step. Get up,
Join. Therefore, the bonding in a state where the fibers are entangled is improved. Further, since the infusibilized fiber has good wettability with an organic binder such as pitch, the binderability between the fiber after carbonization and the carbide of the binder is good.

The present invention has been made based on these findings. The gist of the present invention is to infiltrate a woven or non-woven fabric of PAN-based fiber under tension, impregnate it with an organic binder such as pitch, and prepare a non-oxidizing atmosphere. This is a method for producing a porous carbon plate comprising carbonizing underneath.

As the PAN-based fiber, PAN or a copolymer of PAN and another organic compound which is usually used for producing carbon fiber can be used.
The weaving method of the woven fabric is not particularly limited, and any known ones such as plain weave can be used. In the present invention, a non-woven fabric can be used in addition to the woven fabric, but since tension is applied in the infusibilization step, the fibers used must be longer than a certain length.

If the thickness of the woven or non-woven fabric is too high, it is difficult to infusibilize the inside of the woven fabric or the non-woven fabric, and it also hinders the uniform impregnation of the organic binder, so make it about 1 mm or less in thickness and laminate it.
Alternatively, it is preferable to laminate after impregnation of the organic binder.

Infusibilization is performed by heating in an oxidizing atmosphere such as air.
The conditions are the same as those for infusibilizing carbon fibers from PAN filaments, for example, about 180 to 250 ° C.
It is also known to apply tension at this time. When tension is applied to the woven or nonwoven fabric, it is desirable to apply the tension in two orthogonal directions. However, when infusible in a continuous process, the two-direction tension is difficult. Direction. The magnitude of the tension may correspond to the tension in infusibilizing a known filament.

The infusibilized woven or nonwoven fabric is then impregnated with an organic binder. At this time, impregnation may be performed after laminating according to the desired thickness of the carbon plate. Even if the layers are laminated, the impregnation of the organic binder is not particularly hindered. Also, a woven or nonwoven fabric after impregnation can be laminated.

For the impregnation of the organic binder, it is desirable to first place the infusibilized woven or nonwoven fabric in a container under vacuum, pour the liquefied organic binder into it, and then apply pressure.

As the type of the organic binder, pitch, thermosetting resin, thermoplastic resin and the like can be used. Examples of the thermosetting resin include a phenol resin and a furan resin, and examples of the thermoplastic resin include tar, pitch, and petroleum resin.

These binders are selected depending on the intended porous carbon plate. For example, the electrodes of a fuel cell are required to have high electric conductivity, and therefore, the pitch is preferable to the resin type. In order to obtain a carbon plate having a high porosity, a thermoplastic resin having a low carbonization ratio may be used. However, a pitch or a thermosetting resin may be reduced and used.

The amount of the organic binder varies depending on the target carbon plate and the porosity thereof, but the pitch of the fuel cell electrode is preferably 20 to 40% (% by weight, hereinafter the same) in the total amount after impregnation. In general, however, organic binders can range from a minimum of around 10% to a maximum that almost fills the pores of the woven or nonwoven fabric. This amount is about 100% for a conventional PAN infusible woven or nonwoven fabric.

The content of the organic binder can also be adjusted by squeezing the woven or nonwoven fabric after impregnation and discharging excess binder.

After the impregnation, in the case of a thermosetting resin, it is preferable to heat the resin to about 200 ° C. to cure the resin, and then to carbonize the resin.

Carbonization is generally performed in a non-oxidizing atmosphere at 1000 ° C. or higher. If necessary, it can be graphitized at 2500 ° C. or higher. In order to prevent the carbon plate from warping, the baking is performed, for example, by sandwiching the carbon plate between graphite plates. At this time, if the pressure is applied, it tends to be dense, so that the pressure is preferably applied as little as possible.

Function and Effect In the present invention, since the PAN woven fabric or the nonwoven fabric is made infusible, the fibers are fused and bonded at the crossing points. Therefore, the reinforcing effect of the carbonized carbon plate by the carbon fibers increases. In addition, since PAN is used to make it infusible under tension, the strength of the carbon fibers in the carbon plate is greater than that of other fibers. The infusibilized fiber has good wettability with the binder and good bondability between the fiber and the carbide of the binder. Further, the infusibilized fiber emits volatile components in the subsequent carbonization step, and becomes carbon fiber while shrinking. This shrinkage also contributes to the strengthening action of the carbon plate.

Since PAN fibers are generally thicker than cellulosic fibers, the pores of a porous carbon plate using the fibers are large. As the pores of the electrodes of the fuel cell, those using a PAN-based resin are suitable.

The carbon plate of the present invention has high strength for the porous material and good electric conductivity. The pore size and porosity of this carbon plate are as follows:
Although it varies depending on the manufacturing conditions, in a general range, the pore diameter is 5 to 100 μm, the porosity is 40 to 80%, the bending strength is 100 to 300 kg / cm ² , and the electric resistance is 0.001 to 0.03 Ωcm. When the tension in the infusibilizing step is one direction, the strength in the direction of tension and electrical conductivity are high, but in many cases, a woven or non-woven fabric is laminated, so that the directions of tension are alternately laminated at that time. Thereby, a carbon plate having almost no anisotropy is obtained. The above characteristic values indicate those in this case.

Example A PAN fiber (diameter: about 10 μm) woven cloth (thickness: 0.5 mm) was infusibilized in air at 220 ° C. for 20 minutes. Woven cloth is 40cm wide and 4 long
It was made infusible by applying a tension of 0.5 kg in the length direction at 0 cm.

A 300 mm square was cut out from the infusibilized woven fabric, and fifteen of them were alternately laminated so that the direction of tension was at a right angle. This laminate was sandwiched between two stainless steel plates with almost no pressure applied, and the four corners of the stainless steel plate were fixed with bolts.
This was preheated with hot air at 200 ° C., put into a pitch filling phase, the inside of the tank was degassed under vacuum, then a liquid pitch at 200 ° C. was poured, and N ₂ gas was introduced and pressurized at 5 kg / cm ² . The softening point of this pitch is 90 ° C. The impregnated nonwoven fabric was carbonized by being heated to 600 ° C. for 72 hours in a N ₂ gas atmosphere while being sandwiched between stainless steel plates. The carbide was removed from the stainless steel plate and heated to 2500 ° C. in a graphitization furnace for 72 hours to graphitize. The obtained porous graphite plate was 250 mm square and 3 mm thick.

Comparative Example A part of the data shown in Table 4 of JP-A-50-121505 and a part of the data shown in Table 2 of U.S. Pat. No. 4,697,966 are shown in Table 1 as Comparative Example 1 and Comparative Example 2, respectively.

Claims (2)

(57) [Claims] 1. A method for producing a porous carbon plate, comprising infusing a woven or nonwoven fabric of polyacrylonitrile fiber under tension, impregnating it with an organic binder, and carbonizing in a non-oxidizing atmosphere. Law. 2. A method for producing a porous carbon plate, comprising: impregnating the organic binder of claim 1; laminating; and carbonizing in a non-oxidizing atmosphere.