JPH02199010A - Production of thin sheetlike carbon material - Google Patents

Abstract

PURPOSE:To obtain a thin sheetlike carbon material excellent in bending strength, electrical characteristics and gas-impermeability by impregnating a substrate in the form of a fiber aggregate or film with an electrically conductive varnish prepared by mixing and kneading a liquid resin with a filler, carrying out lamination molding of the resultant sheets of prepreg and calcining the laminated sheets. CONSTITUTION:Carbon black especially 10-100nm average particle diameter is mixed with scaly graphite powder having <=100mum average particle diameter preferably at 50-90wt.%:10-50wt.% ratio to prepare a filler. The above-mentioned filler in an amount of 2-50wt.% based on a liquid resin, such as phenolic resin, is then added and mixed therewith to provide an electrically conductive varnish. A substrate consisting of cellulosic paper or film is then impregnated with the above-mentioned electrically conductive varnish. The resultant plural sheets of prepreg are subsequently dried at 100-150 deg.C, then laminated and thermally compression molded at 100-150 deg.C under 50-150kg/cm<2> to afford an electrically conductive laminated sheet. The obtained laminated sheet is then normally calcined at 900-1500 deg.C maximum temperature to provide the objective thin sheetlike carbon material.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a thin plate-like carbon material, and particularly to a method for producing a carbon material for a phosphoric acid fuel cell separator.

<Prior Art> In general, a phosphoric acid fuel cell includes an electrolyte layer holding, for example, phosphoric acid, a porous electrode substrate disposed on both sides of the electrolyte layer and supporting a platinum catalyst, and an electrolyte layer formed on each outer surface of the electrode substrate. A separator is provided to cover a flow groove, and unit cells are stacked with the separator interposed therebetween.

Since fuel gas and oxygen gas flow through the upper and lower surfaces of such a separator, the separator needs to function as a boundary for separating fuel gas and oxygen gas and as a connector between unit cells. Therefore, the material is required to have excellent properties such as gas impermeability, electrical conductivity, mechanical strength, and resistance to phosphoric acid at operating temperatures, and carbon materials are usually used.

Further, as a method for manufacturing the carbon material, a method of laminating and pressing cellulose paper impregnated with a thermosetting resin and containing graphite powder or carbon fiber, hardening and firing is disclosed, for example, in JP-A No. 60-161144. Disclosed in the official gazette.

<Problems to be Solved by the Invention> In the method disclosed in JP-A-60-161144, carbon fillers such as carbon fibers and graphite powder adhere to the surface of the base material without being completely impregnated, and the inside of the base material The final result is a carbon material in which glassy carbon-rich layers made of thermosetting resin and cellulose paper and carbon filler-rich layers alternate in the thickness direction. There is a problem that the conductivity in the direction decreases.

An object of the present invention is to solve the above-mentioned problems and provide a method for producing a thin plate-like carbon material having excellent bending strength, electrical properties, and gas impermeability.

<Means for Solving the Problems> In order to achieve the above object, the present invention uses graphite powder exhibiting a scale shape and carbon black as fillers, and uses a conductive varnish in which the fillers are mixed and kneaded with a thermosetting resin, and is applied to cellulose. Provided is a method for producing a thin plate-like carbon material obtained by subjecting a prepreg obtained by impregnating a base material made of quality paper or cellulose film to lamination molding and firing treatment.

In addition, the mixing ratio of the graphite powder and carbon black is
Graphite powder 1 to 50 to 90 wt% carbon black
It is preferably 0 to 50 wt%.

Further, it is preferable that a mixing ratio of the filler to the thermosetting resin is 2 to 50 wt% with respect to the thermosetting resin.

The invention will now be described in more detail.

In the present invention, first, a fiber aggregate or a film-like base material,
It is impregnated with conductive varnish made by mixing and kneading liquid resin and filler to make conductive prepreg. In particular, in the present invention, the filler includes graphite powder and carbon black that exhibit a scale-like shape.

The carbon black is preferably one that has excellent dispersibility when made into a varnish, can completely and uniformly penetrate into the fiber aggregate or film-like substance that is the base material, and has electrical conductivity. In particular, the average particle diameter is 10 to 1100n, and the specific resistance is 0.1 to 0.1 by JIS-1469 specific resistance measurement method.
Carbon black, which has a resistance of 1.0Ω・cm, has extremely small particles even when impregnated into a base material.
It is preferable because it is uniformly distributed inside the base material and becomes a carbon material with excellent conductivity in both directions and the thickness direction.

Furthermore, it is preferable to use carbon black graphitized at 2500° C. or higher because the conductivity of the final carbon material is further improved.

In addition, the scaly highly crystalline graphite powder used in combination with carbon black includes refined and crushed quiche graphite obtained in the steelmaking process at a steel mill, as well as naturally occurring scaly graphite powder that is refined and crushed. Artificial and natural materials such as pulverized materials with an average particle size of 100 μm or less are preferable.

By using graphite powder exhibiting this scale-like shape, even after being made into a carbon material, it functions to prevent gas from permeating, resulting in a carbon material with excellent gas impermeability.

When blending graphite powder with an average particle size of over 100 μm,
This is undesirable because the surface precision of the resulting carbon material deteriorates, and the fibers that are the base material cannot evenly penetrate into the interior of the pores.

The mixing ratio of carbon black and graphite powder is 10 to 50w of graphite powder to 50 to 90wt% of carbon black.
t% is preferred.

When carbon black exceeds 90 wt%, the effect of flaky graphite powder on gas impermeability is insufficient, and when carbon black is less than 50 wt%, when impregnating a base material, carbon black This is not preferable because the influence on the electrical properties in the thickness direction becomes insufficient.

The method of mixing carbon black and graphite powder to form a filler is carried out using a general mixing device such as a method using a Henschel mixer.

Thereafter, the filler is mixed and kneaded with a thermosetting resin to produce a conductive varnish.

As the thermosetting resin used as the matrix, liquid resins such as phenol resins, furan resins, polyimide resins, and epoxy resins are used.

Examples of the method for mixing and kneading the thermosetting resin and filler include general kneading equipment such as an oven roll kneader, intensive mixer, ball mill, and three-roll kneader.

Further, the mixing ratio of the liquid resin and the filler is preferably 2 to 50 wt% of the filler to the resin. If the filler mixing ratio is less than 2wt%, there is a problem that the conductivity is low.On the other hand, if it is more than 50wt%, the conductivity improves, but when used as a varnish, the viscosity increases and the base material Problems arise in the impregnability of the material.

Furthermore, the base material is impregnated with the varnish.

Fiber aggregates and films used as base materials include:
800℃ like cellulose paper and cellulose film
In the above firing process, the substance remaining in the base material in a carbonized form is used.

As the cellulose paper, general papers such as industrial filter paper and kraft paper can be used, and papers with excellent impregnation properties, such as those used for phenol laminates, are more preferable.

In addition, the cellulose film is preferably a porous film with a pore size of 30 to 100 μm obtained by hydrolyzing acetylcellulose.Furthermore, in order to improve impregnability, a porous material such as polyvinyl alcohol is mixed in advance with the acetylcellulose. However, it is more preferable to use a porous cellulose film whose pore diameter is adjusted to 100 to 500 μm by dissolving the porous material after film forming.

The thickness of the base material is preferably 10 to 1000 μm.
If it is less than 10 μm, the strength as a base material cannot be maintained, and if it exceeds 1000 μm, impregnation, lamination molding,
A problem arises in that the thickness of the carbon material obtained by firing becomes non-uniform.

Methods for impregnating the base material with conductive varnish include dipping the base material in varnish in a vat-shaped container, dipping it into the base material,
A general impregnation method of applying varnish by spraying or the like, a method using an impregnation device having a roll, etc. are used.

By this impregnation treatment, a conductive prepreg having a uniform composition from the surface of the base material to the inside thereof can be obtained.

After drying the obtained prepreg at 100-150℃, several sheets were laminated and heated at 100-150℃ for 50-150k.
g/cm" to form a conductive laminate. The number of prepreg layers to be laminated is adjusted depending on the final thickness of the carbon material. Also, the method used for molding For this purpose, general molding methods such as hot press molding and hot roll molding are used.

Next, the obtained conductive laminate is set in a firing furnace, and fired and carbonized to obtain the desired thin plate-like carbon material. As the furnace used for firing, commercially available Matsufuru furnaces, tunnel furnaces, etc. that can create a non-oxidizing atmosphere inside the furnace can be used.
Firing while passing an inert gas such as N2 or Ar,
It is preferable to fire the sample while filling the periphery with coke fine powder. There are no particular restrictions on the firing temperature, but the maximum temperature is usually 900 to 1500°C.

<Example> EXAMPLES The present invention will be specifically described below with reference to Examples.

(Example 1) Highly conductive carbon black (Toka Black manufactured by Tokai Carbon ■) with a high conductivity of 0.2 Ω・cm was measured using a flaky graphite powder (Kish graphite) with an average particle size of 30 μm and an electrical resistivity measurement method (JIS-1489). , average particle size 50 nm),
30 wt% to 70 wt% were mixed in a Henschel mixer.

This mixed filler was added to a commercially available phenol resin solution (Regitop PL-2211 manufactured by Gunsung Chemical ■, non-volatile content 56 wt%).
was added in an amount of 20 wt% and mixed and kneaded in a ball mill to obtain a conductive varnish.

This varnish was transferred to a stainless steel vat, and a commercially available cellulose paper for laminates (manufactured by Daicel Chemical Co., Ltd.) was passed through the vat for impregnation treatment.

The resulting prepreg was heated in an oven for 10 hours at room temperature.
After drying at 00° C. for 30 minutes, it was cut into a size of 200×200 mm. 15 prepregs of the specified dimensions were laminated, set in a hot press, and then molded at a molding temperature of 150°C and a molding pressure of 150 kg/cm2 to a thickness of 2.5 kg/cm2.
A conductive laminate with a thickness of 0 mm was used.

Next, this molded body was set in a stainless steel firing box, the top and bottom were held with graphite plates, the surrounding area was backed with fine coke powder, and the molded body was heated in a commercially available Matsufuru furnace under an N2 atmosphere.
Carbonization was performed by firing at a heating rate of 10'e/hr and a maximum temperature of 1000°C to obtain a thin plate-like carbon material. The properties of this carbon material are shown in Table 1.

(Example 2) The same flaky graphite powder and highly conductive carbon black as in Example 1 were mixed in a Henschel mixer, added to the same phenol resin as in Example 1, and mixed and kneaded in a ball mill to create a conductive varnish. And so.

This varnish was poured into a stainless steel vat, and a cellulose film obtained by hydrolyzing acetyl cellulose was passed through the vat to perform an impregnation treatment.

The resulting prepreg was heated in an oven for 10 hours at room temperature.
After drying at 00° C. for 30 minutes, it was cut into a size of 200×200 mm. 15 sheets of prepreg having the specified dimensions were laminated, set in a hot press, and then molded at a molding temperature of 150°C and a molding pressure of 100 kg/cm2 to a thickness of 2.
It was made into a 5 mm conductive laminate.

Next, this molded body was set in a stainless steel firing box, the top and bottom were held with graphite plates, the surrounding area was backed with fine coke powder, and the molded body was heated in a commercially available Matsufuru furnace under an N2 atmosphere.
Carbonization was performed by firing at a heating rate of 10 t/hr and a maximum temperature of 1000°C to obtain a thin plate-like carbon material. The properties of this carbon material are shown in Table 1.

(Comparative Example 1) 20 wt % of commercially available artificial graphite powder (average particle size 30 μm) and 80 wt % of the same phenolic resin as in Example 1 were mixed and kneaded in a ball mill to obtain a conductive varnish. This varnish was poured into a stainless steel vat, and a commercially available cellulose paper for laminates (manufactured by Daicel Chemical Co., Ltd.) was passed through the vat for impregnation.

The resulting prepreg was heated in an oven for 10 hours at room temperature.
After drying at 00° C. for 30 minutes, it was cut into a size of 200×200 mm. 15 sheets of prepreg having the specified dimensions were laminated, set in a hot press, and then molded at a molding temperature of 150°C and a molding pressure of 150 kg/cm2 to a thickness of 2.
A conductive laminate with a thickness of 0 mm was used.

Next, this molded body was set in a stainless steel firing box, the top and bottom were held with graphite plates, the surrounding area was backed with fine coke powder, and the molded body was heated in a commercially available Matsufuru furnace under an N2 atmosphere.
Carbonization was performed by firing at a temperature increase rate of 10 t/hr% and a maximum temperature of 1000°C to obtain a thin plate-like carbon material. The properties of this carbon material are shown in Table 1.

<Effects of the Invention> According to the method for producing a carbon material of the present invention, by using scaly graphite powder and highly conductive carbon black in combination,
A prepreg uniformly impregnated with conductive varnish can be obtained. As a result, a carbon material with excellent bending strength, electrical properties, and gas impermeability can be obtained.

Claims (3)

[Claims] (1) A prepreg obtained by impregnating a base material of cellulose paper or cellulose film with a conductive varnish made by mixing and kneading graphite powder and carbon black in a thermosetting resin as fillers, A method for producing a thin plate-like carbon material obtained by lamination molding and firing treatment. (2) The mixing ratio of the graphite powder and carbon black is:
Graphite powder 1 to 50 to 90 wt% carbon black
The method for producing a thin plate-like carbon material according to claim 1, wherein the content is 0 to 50 wt%. (3) The method for manufacturing a thin plate-like carbon material according to claim 1 or 2, wherein a mixing ratio of the filler to the thermosetting resin is 2 to 50 wt% with respect to the thermosetting resin.