JP5489831B2 - Carbon fiber sheet, heat-treated flame-resistant fiber sheet, and method for producing them - Google Patents

Description

  The present invention relates to a carbon fiber sheet, a heat-treated flame-resistant fiber sheet-like processed product (hereinafter also referred to as “heat-treated flame-resistant fiber sheet”), and a method for producing them. More specifically, the present invention relates to a carbon fiber sheet having excellent surface smoothness and high sheet thickness uniformity, a heat-treated flame resistant fiber sheet that becomes the carbon fiber sheet by firing, and a method for producing the same.

  Carbon fiber sheets such as carbon fiber cloth, carbon fiber felt, and carbon fiber paper are lightweight and have excellent mechanical properties and electrical conductivity. Therefore, they are used as fuel cell electrode materials and reinforcing fiber sheets that are combined with resin. Widely used industrially.

  The carbon fiber sheet is manufactured by processing a carbon fiber such as a filament yarn or a stable yarn by weaving or paper making. In this manufacturing method, since a highly rigid carbon fiber is processed into a sheet, the sheet processing is difficult. Therefore, it is difficult to produce a thin carbon fiber sheet.

  In order to solve this problem, a method has been proposed in which a flame resistant fiber, which is a carbon fiber precursor fiber, is processed into a sheet in advance, and the sheet is fired to produce a carbon fiber sheet. Since the flame resistant fiber has low rigidity, sheet processing is easy.

  In Patent Document 1, a flame resistant fiber sheet, which is a carbon fiber precursor fiber, is made together with a binder material to prepare a flame resistant fiber sheet, and then fired while applying a press pressure, whereby a thin carbon fiber sheet is obtained. A method of manufacturing is disclosed. However, in this production method, since the flame-resistant fiber contracts during firing, wrinkles and undulation are generated in the obtained carbon fiber sheet. Therefore, a carbon fiber sheet with high surface smoothness cannot be obtained.

  Patent Document 2 discloses a method for producing a carbon fiber sheet by weaving a flame resistant fiber sheet, which is a carbon fiber precursor fiber, and then firing the flame resistant fiber sheet. However, in this carbon fiber sheet, since the flame-resistant fiber contracts during firing, the thickness of the central portion of the sheet surface is greater than the thickness of the outer edge portion of the sheet surface. Therefore, even in this method, a carbon fiber sheet having high thickness uniformity cannot be obtained.

  As described above, a thin carbon fiber sheet having high surface smoothness and thickness uniformity and a thickness of 500 μm or less has not been obtained.

JP 2004-27435 A JP 2003-268651 A

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a thin carbon fiber sheet having a high surface smoothness and a uniform thickness and having a thickness of 500 μm or less, and a method for producing the same.

  The inventors of the present invention have found that the heat shrinkage rate (described later) of the flame resistant fiber is decreased by preliminarily heat-treating the flame resistant fiber, which is a carbon fiber precursor fiber, under predetermined conditions (hereinafter referred to as heat treatment). The applied flame resistant fiber is also referred to as “heat treated flame resistant fiber”). Further, it has been found that by performing heat treatment so that the fiber specific gravity falls within a predetermined range, the heat treated flame resistant fiber maintains flexibility and sheet processing can be easily performed. And when this heat-treated flame resistant fiber was processed and fired, it was found that even if the sheet thickness was thin, a carbon fiber sheet having high surface smoothness and high uniformity of thickness was obtained, and the present invention was completed. .

  The present invention for solving the above problems is as follows.

[1]
The carbon fiber sheet has an average thickness of 50 to 500 μm, and the difference between the maximum value and the minimum value of the thickness of the carbon fiber sheet is less than 10% of the average thickness of the carbon fiber sheet. Carbon fiber sheet characterized by

[2]
(A) A flame resistant fiber, which is a precursor fiber of carbon fiber, is heat-treated at 500 to 900 ° C. for 0.1 to 60 minutes in an inert atmosphere, and has a fiber specific gravity of 1.35 to 1.75 and heat. Obtaining a heat treated flame resistant fiber having a shrinkage of 2.0-15%;
(B) a step of processing the heat-treated flame resistant fiber to obtain a heat treated flame resistant fiber sheet;
(C) firing the heat-treated flame resistant fiber sheet in an inert atmosphere to obtain a carbon fiber sheet;
[1] The method for producing a carbon fiber sheet according to [1].

[3]
The heat-treated flame-resistant fiber sheet for producing a carbon fiber sheet according to [1], comprising a heat-treated flame-resistant fiber having a fiber specific gravity by an Archimedes method of 1.35 to 1.75 and a heat shrinkage rate of 2.0 to 15%.

[4]
(A) A flame resistant fiber, which is a precursor fiber of carbon fiber, is heat-treated at 500 to 900 ° C. for 0.1 to 60 minutes in an inert atmosphere, and has a fiber specific gravity of 1.35 to 1.75 and heat. Obtaining a heat treated flame resistant fiber having a shrinkage of 2.0-15%;
(B) a step of processing the heat-treated flame resistant fiber to obtain a heat treated flame resistant fiber sheet;
[3] The method for producing a heat-resistant flame-resistant fiber sheet according to [3].

  The carbon fiber sheet of the present invention is obtained by baking a heat-treated flame resistant fiber after sheet processing. The heat-treated flame resistant fiber is flexible because the fiber specific gravity is adjusted within a predetermined range, and can be easily processed into a thin sheet. Moreover, since this heat-resistant flame resistant fiber has a small thermal shrinkage rate, the surface smoothness and thickness uniformity of the carbon fiber sheet obtained after firing are high.

(Carbon fiber sheet)
In the present invention, the carbon fiber sheet refers to a sheet-like material such as carbon fiber cloth, carbon fiber felt, or carbon fiber paper.

  The carbon fiber sheet of the present invention (hereinafter abbreviated as “the present carbon fiber sheet”) has a thickness average value of 50 to 500 μm, preferably 100 to 400 μm. When the thickness average value is less than 50 μm, the strength of the carbon fiber sheet is lowered, and the handleability is lowered. When the average thickness exceeds 500 μm, the uniformity of the thickness along the surface direction of the sheet is deteriorated. The average thickness value can be controlled by adjusting the basis weight and the temperature and pressure during thermal compression.

  The difference between the maximum value and the minimum value of the thickness of the carbon fiber sheet is less than 10% of the average thickness of the carbon fiber sheet. In the case of 10% or more, the thickness uniformity of the carbon fiber sheet is low, and the use of the carbon fiber sheet is limited.

  In the present invention, the “thickness” of the carbon fiber sheet represents the thickness of the sheet when a 1.2 N load (61.9 kPa) is applied in the sheet thickness direction using a circular pressure plate having a diameter of 5 mm. "Thickness average value" is a 10 cm square sheet surface divided into 9 faces in a grid pattern (ie, approximately 3.33 cm square and divided into 9 faces), and the thickness at the center of each of the divided faces And the average value of these nine thickness measurements. Further, the “maximum value” and “minimum value” of the thickness mean the maximum value and the minimum value in the measured values of the thickness at the nine points.

  The fiber diameter of the present carbon fiber sheet is preferably 5 to 20 μm, and more preferably 6 to 13 μm. In the case of carbon fibers having a flat cross section, the average of the major axis and the minor axis is defined as the fiber diameter. When the fiber diameter is less than 5 μm, the sheet strength is insufficient because the single fiber diameter is too thin and the fiber strength is low. In addition, the carbon fibers dropped from the carbon fiber sheet may adversely affect the human body. When the fiber diameter exceeds 20 μm, the shape of the outer periphery of the carbon single fiber constituting the sheet rises on the sheet surface, and irregularities are formed on the sheet surface. As a result, the surface smoothness is deteriorated. Moreover, since the contact electrical resistance of the carbon fiber sheet is increased due to the irregularities formed on the sheet surface, it is not preferable for applications such as electrode materials that require a low electrical resistance. Furthermore, the fiber strength is reduced during firing, and a large amount of fine carbon fiber powder is generated.

Basis weight of the carbon fiber sheet is preferably ^{30~200g / m 2, 50~150g / m} 2 is more preferable. When the basis weight is less than 30 g / m ² , the sheet strength is lowered, and the handleability is lowered. When the basis weight exceeds 200 g / m ² , it becomes difficult to obtain a carbon fiber sheet having a desired thickness.

The bulk density of the present carbon fiber sheet is preferably 0.2 to 0.7 g / cm ³ . When the bulk density is less than 0.2 g / cm ³ , the sheet strength is lowered, and the handleability of the sheet is lowered. When the bulk density exceeds 0.7 g / cm ³ , the uniformity of thickness in the surface direction of the sheet is deteriorated.

  As long as the physical properties of the present carbon fiber sheet are within the above range, the production method is not particularly limited. For example, the carbon fiber sheet can be produced by the following method.

(Method for producing the carbon fiber sheet)
This carbon fiber sheet is manufactured by sheet-treating a heat-treated flame-resistant fiber obtained by heat-treating a flame-resistant fiber that is a precursor fiber of carbon fiber to obtain a heat-treated flame-resistant fiber sheet, and firing the heat-treated flame-resistant fiber sheet. .

  Flame resistant fibers are produced by heating carbon fiber precursor fibers in air at 200-400 ° C. for 2-5 hours. This manufacturing method is a known method. The fiber raw material constituting the precursor fiber may be any fiber such as polyacrylonitrile (PAN) fiber, pitch fiber, rayon fiber, etc., but PAN fiber having relatively high strength and elongation is preferred. .

  The PAN-based fiber can be obtained by a known wet or dry spinning of a PAN-based polymer. Examples of the PAN polymer include those obtained by homopolymerizing an acrylonitrile monomer and those obtained by copolymerizing an acrylonitrile monomer and another vinyl monomer. As other vinyl monomers, known vinyl monomers such as acrylic acid, itaconic acid, esters thereof, salts, acrylamide and the like are used. The copolymerization ratio of other vinyl monomers is preferably within 12% by mass, and particularly preferably within 8% by mass.

  The flame resistant fiber obtained as described above is subjected to heat treatment by heating to 500 to 900 ° C. in an inert gas. When the heating temperature is less than 500 ° C., the heat shrinkage rate of the heat-treated flame resistant fiber is not sufficiently lowered. For this reason, the carbon fiber sheet produced using this heat-treated flame resistant fiber has many wrinkles and undulations on the surface of the sheet, resulting in poor surface smoothness and thickness uniformity. When heating temperature exceeds 900 degreeC, the rigidity of a heat-resistant flame resistant fiber becomes high and it becomes difficult to process it into a sheet form.

  The heating time is 0.1 to 60 minutes, preferably 0.2 to 30 minutes, and more preferably 1 to 10 minutes. When the heating time is less than 0.1 minutes, the heat shrinkage rate of the heat-treated flame resistant fiber is not sufficiently lowered. When the heating time exceeds 60 minutes, the rigidity of the heat-treated flame resistant fiber becomes high and it becomes difficult to process it into a sheet shape.

  Examples of the inert gas include nitrogen, argon, helium and the like.

  The heat treatment is preferably performed while freely shrinking the flame resistant fiber in order to reduce the heat shrinkage rate of the heat treated flame resistant fiber.

  The fiber specific gravity by the Archimedes method of the heat-resistant flame-resistant fiber obtained by the said heat processing is 1.35-1.75, 1.39-1.70 are preferable and 1.42-1.68 are more preferable. When the fiber specific gravity is less than 1.35, the heat shrinkage of the fiber during firing becomes large, and undulation and wrinkles are generated on the surface of the obtained carbon fiber sheet, so that the surface smoothness is deteriorated. When the fiber specific gravity exceeds 1.75, the rigidity of the fiber becomes high, and the fiber breaks when the sheet is produced, and the sheet becomes fluffy.

  Moreover, the heat shrinkage rate of the heat-resistant flame resistant fiber obtained by the said heat processing is 2.0 to 15%, 2.5 to 12% is preferable and 3.0 to 10% is more preferable. When the thermal shrinkage rate exceeds 15%, fiber shrinkage during firing is large, undulation and wrinkles are generated on the surface of the carbon fiber sheet, and surface smoothness is lowered. Moreover, it becomes easy to produce a difference in the thickness of the center part along the sheet | seat surface of a carbon fiber sheet, and an outer edge part, and the uniformity of thickness falls. When the heat shrinkage rate is less than 2.0%, the fiber has high rigidity and sheet processing becomes difficult.

  In the present invention, the heat shrinkage rate refers to the shrinkage rate of the fiber when fired at 1000 ° C. for 10 minutes under non-tension, and is a value calculated by the following formula (1).

  The heat treated flame resistant fiber is processed into a sheet by a known method such as weaving or paper making to produce a heat treated flame resistant fiber sheet. Examples of the heat treated flame resistant fiber sheet include heat treated flame resistant fiber cloth, heat treated flame resistant fiber felt, heat treated flame resistant fiber paper and the like.

  The heat treated flame resistant fiber cloth is a heat treated fiber having a fiber length of 30 to 75 mm and a fineness of 0.5 to 3.4 dtex, a dry strength of 16 mN / dtex or more, and a twist coefficient of 150 to 900 times / m. It is obtained by producing a flame resistant fiber spun yarn and weaving it. The weaving structure may be any of plain weaving, twill weaving, satin weaving and the like.

  The heat treated flame resistant fiber felt is obtained by forming a heat treated flame resistant fiber having a fiber length of 20 to 75 mm and a fineness of 0.5 to 3.4 dtex by using a needle punch, a water jet, an air jet or the like.

  The heat treated flame resistant fiber paper is obtained by mixing or impregnating a heat treated flame resistant fiber having a fiber length of 1 to 30 mm and a fineness of 0.5 to 3.4 dtex and a binder. As the binder, a binder having a residual carbon ratio of 0.5 to 50% by mass during the post-baking process is used. Specifically, an aramid resin, a phenol resin, a water-soluble thermoplastic resin, a thermoplastic organic fiber, or the like can be given. Examples of the thermoplastic organic fiber include polyester fiber, polyolefin fiber, and vinylon fiber. Examples of the polyester fiber include polyethylene terephthalate (PET) fiber, polybutyl terephthalate (PBT) fiber, polyarylate (PAT) fiber, and composite fiber including copolymer fibers belonging to these fibers. Examples of the polyolefin fibers include polypropylene (PP) fibers and composite fibers including a copolymer belonging to the fibers. Examples of vinylon fibers include polyvinyl alcohol (PVA) fibers and composite fibers containing copolymers belonging to them.

  The heat-resistant flame-resistant fiber sheet obtained as described above is fired in an inert gas without applying a surface pressure or while applying a surface pressure of 1.0 kPa or less, preferably 0.1 to 0.5 kPa. By doing this, it becomes this carbon fiber sheet. The application of the surface pressure is preferably performed through firing, using contact pressure application by contact with a batch press, intermittent press, calendar press, belt press, roller, or the like. The firing temperature is preferably 1000 to 2500 ° C, more preferably 1300 to 2300 ° C. When the firing temperature is less than 1000 ° C., the strength and electrical conductivity as carbon fiber are insufficient, which is not preferable. When the firing temperature exceeds 2500 ° C., the carbon fiber sheet becomes rigid and the strength tends to decrease. Furthermore, problems such as generation of carbon fine powder are likely to occur.

  The firing time of the heat-treated flame resistant fiber sheet is 10 to 60 minutes.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

  Each physical property was measured and evaluated by the following methods.

[Unit weight]
The 10 cm square sheet was calculated from the mass value after drying at 120 ° C. for 1 hr.

[Thickness average value]
The sheet surface of 10 cm square is divided into 9 planes in a grid pattern (that is, divided into 9 planes of about 3.33 cm square), and the thickness of the sheet at the center of each of the divided surfaces is measured. The average value of the point thickness measurements was used. The thickness was measured when a load of 1.2 N (61.9 kPa) was applied in the thickness direction of the sheet with a circular pressure plate having a diameter of 5 mm.

[Thick spots]
The difference between the maximum value and the minimum value of the nine measured thickness values was defined as thickness spots. Moreover, the ratio with respect to the average thickness value of the thickness spots was expressed as a percentage (%). Practically, when the thickness unevenness is 40 μm or less, it can be used for various purposes without problems.

[specific gravity]
It was measured by the Archimedes method (solvent acetone).

[Heat shrinkage]
A heat-treated flame resistant fiber having a length of 1 m was baked in a batch furnace (under no tension) in a nitrogen atmosphere at 1000 ° C. for 10 minutes, and then the length of the baked fiber was measured and calculated by the following formula (2).

[Surface smoothness]
Visually evaluated. In the case where wrinkles and fluff were not observed on the surface of the sheet and no undulation was observed in the surface direction of the sheet, the evaluation was ○.

[Examples 1-4, Comparative Examples 1-4]
The precursor fiber used as a raw material was manufactured by heating a polyacrylonitrile (PAN) fiber in air at 250 ° C. for 2 hours for flame resistance treatment.

  This flame resistant fiber was heated under the conditions described in Table 1 or 2 for heat treatment. Thereafter, the heat-treated flame resistant fiber sheet was processed according to the conditions described in Table 1 or 2 to prepare a heat treated flame resistant fiber sheet. The obtained heat-treated flame resistant fiber sheet was fired under the conditions described in Table 1 or 2 to obtain a carbon fiber sheet. The evaluation results of the obtained carbon fiber sheet are shown in Table 1 or 2.

  As shown in Table 1, in Examples 1 to 4, carbon fiber sheets with good surface smoothness were obtained. In the carbon fiber sheet of Comparative Example 1, since the specific gravity of the flame resistant fiber was small, wrinkles were generated in the carbon fiber sheet, and good surface smoothness was not obtained. In the carbon fiber sheet of Comparative Example 2, since the specific gravity of the flame resistant fiber was large, the carbon fiber of the sheet was broken and fluff was generated on the surface. Since the carbon fiber sheet of Comparative Example 3 had a large shrinkage ratio of the flame resistant fiber, the thickness unevenness of the carbon fiber sheet was 60 μm, and the thickness uniformity was low. In Comparative Example 4, since the specific gravity of the carbon fiber was large, the fiber was rigid and could not be woven as a woven fabric.

Claims (4)

The thickness average value a carbon fiber paper 50 to 500 [mu] m, the difference between the maximum value and the minimum value of the thickness of the carbon fiber paper, Ri less than 10% der thickness average value of the carbon fiber paper Carbon fiber paper characterized by having no fluff on the surface of the carbon fiber paper . (A) A flame resistant fiber, which is a carbon fiber precursor fiber, is heat-treated at 700 to 900 ° C. for 0.1 to 60 minutes in an inert atmosphere, and has a fiber specific gravity of 1.35 to 1.75 and heat. Obtaining a heat-treated flame-resistant fiber having a shrinkage ratio of 2.0 to 7.0 %;
(B) a step of blending or impregnating the heat treated flame resistant fiber with a binder to obtain a heat treated flame resistant fiber paper ;
(C) firing the heat-treated flame resistant fiber paper in an inert atmosphere to obtain carbon fiber paper ;
The manufacturing method of the carbon fiber paper of Claim 1 which has these. The heat-treated flame-resistant fiber for producing carbon fiber paper according to claim 1, comprising a heat-treated flame-resistant fiber having a fiber specific gravity of 1.35 to 1.75 and a heat shrinkage rate of 2.0 to 7.0 % by Archimedes method. Paper . (A) A flame resistant fiber, which is a carbon fiber precursor fiber, is heat-treated at 700 to 900 ° C. for 0.1 to 60 minutes in an inert atmosphere, and has a fiber specific gravity of 1.35 to 1.75 and heat. Obtaining a heat-treated flame-resistant fiber having a shrinkage ratio of 2.0 to 7.0 %;
(B) a step of blending or impregnating the heat treated flame resistant fiber with a binder to obtain a heat treated flame resistant fiber paper ;
The manufacturing method of the heat-resistant flame-resistant fiber paper of Claim 3 which has these.