JP2008201005A - Carbon fiber sheet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber sheet having a flat and smooth surface and showing a good handling (high tensile strength and a high flexion amount of a bend) and flexibility. <P>SOLUTION: Carbon fiber paper 6 is laminated on one surface or each of both surfaces of a carbon fiber woven fabric or a carbon fiber felt 4 to be integrated into the carbon fiber sheet 2. Preferably, the carbon fiber sheet is 150 to 600 μm thick, and has a unit weight of 40 to 200 g/m<SP>2</SP>, a tensile strength of 0.5 N/cm or more, a tensile elongation of 1% or more, a bending strength of 1 to 50 MPa and a deflection in bending of 1 to 5 mm, and the surface smoothness Ra of the lamination surface of the paper is not more than 15 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a carbon fiber sheet applied to an electrode material such as a gas diffusion electrode for a fuel cell, a heat insulating material, a heat-resistant material, and the like, and a method for producing the same.

  Carbon fiber sheets applied to electrode materials such as gas diffusion electrodes for fuel cells, heat insulating materials, heat-resistant materials, etc. include paper types (for example, see Patent Document 1), fabric types (for example, see Patent Document 2), felts, etc. A type (for example, refer to Patent Document 3) is used.

  A paper type thing is obtained by resin-molding carbon fiber paper or oxidation fiber paper, and carbonizing. This paper type is excellent in planar smoothness, but is not flexible and rigid, so it is brittle and has poor handleability.

  The woven fabric type is excellent in strength / flexibility, but has poor flatness due to irregularities based on the woven structure of the surface.

  The felt type is excellent in flexibility, but tends to cause fluff and has poor surface smoothness.

As described above, each carbon fiber sheet has a problem depending on its type.
JP 2006-89331 A (Claims) JP 2003-288906 A (Claims) JP 2003-239163 A (Claims)

  The present inventor has been diligently examining the above problems, and by laminating carbon fiber paper on one or both sides of the carbon fiber woven fabric or carbon fiber felt, the carbon fiber woven fabric or the carbon fiber felt plain carbon fiber sheet. It has been found that a carbon fiber sheet to which no planar smoothness is imparted can be obtained.

  Since this carbon fiber sheet has a carbon fiber fabric or carbon fiber felt, the carbon fiber paper has a handleability (high tensile strength, high bending deflection) and flexibility that are not found in the carbon fiber sheet of plain carbon fiber paper. The present inventors have found that a sheet can be obtained and the process stability during processing can be improved, and the present invention has been completed.

  Accordingly, an object of the present invention is to provide a carbon fiber sheet and a method for producing the same, which have solved the above problems.

  The present invention for achieving the above object is as follows.

  [1] A carbon fiber sheet formed by laminating and integrating carbon fiber papers on one side or both sides of a carbon fiber fabric and a carbon fiber felt.

[2] Thickness is 150 to 600 μm, basis weight is 60 to 200 g / m ² , tensile strength is 0.5 N / cm or more, tensile elongation is 1% or more, bending strength is 1 to 50 MPa, bending deflection is 1 to The carbon fiber sheet according to [1], which is 5 mm.

  [3] The carbon fiber sheet according to [1], wherein the planar smoothness of the laminated paper surface is Ra = 15 μm or less.

  [4] A gas diffusion layer for a polymer electrolyte fuel cell formed of the carbon fiber sheet according to [1].

  [5] Carbon fiber paper or oxidized fiber paper is laminated on one or both sides of carbon fiber fabric, oxidized fiber spun yarn fabric and oxidized fiber felt, and after thermocompression treatment, 1300 to 1300 in an inert gas atmosphere. A method for producing a carbon fiber sheet, comprising firing at 2800 ° C.

  [6] The method for producing a carbon fiber sheet according to [5], wherein the binder used when laminating the carbon fiber paper or the oxidized fiber paper is a resin or fiber having a residual carbon ratio of 0.5% by mass or more.

  Since the carbon fiber sheet of the present invention is formed by laminating and integrating the carbon fiber paper on one side or both sides of the carbon fiber fabric and the carbon fiber felt, the carbon fiber fabric or the carbon fiber felt is a simple carbon fiber sheet. It is a carbon fiber sheet to which no flatness is imparted. Also, the carbon fiber sheet of the present invention, the other side or the intermediate layer of the carbon fiber sheet is composed of carbon fiber woven fabric or carbon fiber felt, so that the carbon fiber paper plain carbon fiber sheet is not easy to handle ( A carbon fiber sheet with high tensile strength, high bending deflection) and flexibility, and when used after processing such as bending, it is easy to handle and there is little damage to the sheet. From this, the carbon fiber sheet of this invention is suitable for manufacture of electrode materials, such as a gas diffusion electrode, a heat insulating material, and a heat resistant material.

  Hereinafter, the present invention will be described in detail.

  The carbon fiber sheet of the present invention is formed by laminating and integrating carbon fiber paper on one or both sides of either a carbon fiber fabric or a carbon fiber felt. FIG. 1 shows a schematic side sectional view of an example of a carbon fiber sheet 2 in which carbon fiber paper 6 is laminated and integrated on one surface of a carbon fiber fabric or carbon fiber felt 4. FIG. 2 shows a schematic side cross-sectional view of a carbon fiber sheet 12 in which carbon fiber papers 16a and 16b are laminated and integrated on both surfaces of a carbon fiber fabric or carbon fiber felt 14 as another example.

  FIG. 3 shows an example of the carbon fiber sheet 22 in which the carbon fiber paper 26 is laminated and integrated on one surface or both surfaces of the carbon fiber fabric 24 in the example of FIG. 1 or FIG. 2 is a schematic plan sectional view of the vicinity of an interface with paper 26. FIG.

  In FIG. 3, there are carbon fiber spun yarn or strand portions 28 and gap portions 30 on the carbon fiber fabric 24 side of the interface between the carbon fiber fabric 24 and the carbon fiber paper 26. Since the carbon fiber paper 26 having a smooth surface is laminated also on the gap portion 30 of the carbon fiber woven fabric 24, the carbon fiber sheet 22 has a planar smoothness as compared with the carbon fiber woven plain carbon fiber sheet. improves. Similarly, when the carbon fiber sheet of the present invention is formed by laminating carbon fiber paper on carbon fiber felt instead of carbon fiber fabric, planar smoothness is improved by laminating carbon fiber paper having a smooth surface.

Mesuki portion is preferably 0.01 mm ² ~ 1 mm ^2. If the gap portion is smaller than 0.01 mm ² , the air permeability and water permeability are too low, which causes flooding and the like in which water accumulates in the base material. If the gap portion is larger than 1 mm ² , the water permeability becomes too high, which causes the membrane to dry out.

The carbon fiber sheet has a basis weight of 60 to 200 g / m ² and more preferably 70 to 150 g / m ² . If the basis weight is less than 60 g / m ² , the tensile strength is low, and cutting or the like may occur in the post-processing step. When the basis weight exceeds 200 g / m ² , it is difficult to produce a sheet having an intended thickness.

  The carbon fiber sheet has a thickness of 150 to 600 μm, and more preferably 150 to 290 μm. When the thickness is less than 150 μm, the strength is low. When the thickness exceeds 600 μm, the conductivity in the thickness direction decreases.

  The carbon fiber sheet has a tensile strength of 0.5 N / cm or more, more preferably 0.7 to 100 N / cm, and particularly preferably 1 to 50 N / cm. When the tensile strength is less than 0.1 N / cm, the handleability decreases. The tensile strength can be adjusted, for example, by adjusting denier (fiber diameter), basis weight, bulk density, binder amount, and binder type of oxidized fiber or carbon fiber.

  The carbon fiber sheet has an elongation of 1% or more, and more preferably 2 to 50%. When the elongation is less than 1%, the handleability is lowered, which is not preferable. In order to make the elongation within this range, for example, the denier, basis weight, bulk density, binder amount, and binder type of the oxidized fiber or carbon fiber can be adjusted.

  The carbon fiber sheet has a bending strength of 1 to 50 MPa, and more preferably 1 to 20 MPa. When the bending strength is less than 1 MPa, the strength during processing is low and the handleability is poor. When the bending strength exceeds 50 MPa, it is too stiff and brittle, so that inconveniences such as being unable to form a roll wound around a paper tube having an outer diameter of 50 cm or less occur. In order to make the bending strength within this range, for example, the denier, basis weight, bulk density, binder amount, and binder type of oxidized fiber or carbon fiber can be adjusted.

  The carbon fiber sheet has a bending deflection of 1 to 5 mm, and more preferably 1 to 4 mm. When the amount of bending deflection is less than 1 mm, the handleability is lowered because it is hard. When the amount of bending deflection exceeds 5 mm, it is not preferable because the handling property is poor and the inconvenience of falling into the groove of the separator occurs. In order to make the bending deflection amount within this range, for example, it is possible to adjust the denier, basis weight, thickness, binder amount, and binder type of oxidized fiber or carbon fiber.

The carbon fiber sheet preferably has an electric resistance value of 200 mΩ · cm ² or less. When the electrical resistance value exceeds 200 mΩ · cm ² , the electrical conductivity is poor and application as an electrode material is difficult.

  The carbon fiber sheet preferably has a surface smoothness of 15 μm or less. If the surface smoothness exceeds 15 μm, the contact resistance when the cells are assembled is poor, resulting in problems such as a reduction in battery performance. The surface smoothness of the carbon fiber sheet can be adjusted by selecting the surface smoothness of the carbon fiber paper or the oxidized fiber paper of the raw material sheet.

The carbon fiber sheet preferably has a gas permeability of 10,000 to 40,000 ml / min · cm ² and 14,000 to 25,000 ml / min · cm ² . When the gas permeability is less than 10,000 ml / min · cm ² , the diffusibility of the fuel gas or the like is lowered and the battery characteristics are lowered, which is not preferable. When the gas permeability exceeds 40,000 ml / min · cm ² , the gas diffusibility is good, but the generated water is greatly discharged, and the polymer film is dried, so that the battery characteristics are deteriorated.

The carbon fiber sheet preferably has a battery characteristic of 0.6 V or more (at 0.6 mA / cm ² ). A battery characteristic of less than 0.6 V is not preferable because good power generation performance cannot be obtained.

  The gas permeability is adjusted by adjusting the carbon fiber paper or the oxidized fiber paper denier, carbon fiber denier, basis weight, binder amount, binder type, carbon fiber felt or oxidized fiber felt punch density, basis weight, In the case of carbon fiber spun yarn fabric and oxidized fiber spun yarn fabric, the bulk density can be adjusted by adjusting the woven density, the spun yarn thickness, and the bulk density.

[Method for producing carbon fiber sheet]
As long as the physical properties of the carbon fiber sheet of the present invention are within the above range, the production method is not particularly limited. For example, carbon fiber paper or oxidized fiber paper is used as a carbon fiber fabric or oxidized fiber. A raw material sheet before firing (carbonization) is obtained by laminating on one side or both sides of a spun yarn fabric, carbon fiber felt, and oxidized fiber felt, and performing thermocompression treatment. Subsequently, this raw material sheet is pre-baked while being held at a temperature of 500 to 1000 ° C. for 0.5 to 10 minutes in an inert atmosphere. Furthermore, if necessary, it can be produced by holding at a temperature of 1300 to 2300 ° C. for 0.5 to 10 minutes and post-baking in an inert atmosphere.

[Textile raw materials]
Oxidized fiber spun yarn fabrics, carbon fiber fabrics, oxidized fiber felts, carbon fiber felts, oxidized fiber papers, fiber raw materials that make up carbon fiber papers are polyacrylonitrile (PAN) -based oxidized fibers, PAN-based carbon fibers, pitch-based oxidized fibers Any conventionally known oxidized fiber such as pitch-based carbon fiber or carbon fiber can be used. The oxidized fiber used in this example is a fiber obtained by subjecting precursor fibers such as PAN and pitch fiber to flame resistance treatment.

  Among the above oxidized fibers and carbon fibers, PAN-based oxidized fibers and PAN-based carbon fibers having relatively high strength and elongation are most suitable for performing the thermocompression treatment and the carbonization treatment.

  For example, in order to obtain a PAN-based oxidized fiber, a PAN-based fiber composed of a copolymer containing an acrylonitrile structural unit as a main component and containing vinyl monomer units such as itaconic acid, acrylic acid, and acrylic ester within 10 mol% is used. Treat in air at high temperature (flame resistant).

  By this flameproofing treatment, a cyclization reaction of the PAN-based fiber is caused, and the amount of oxygen bonds is increased to make it infusible and flame-retardant to obtain a PAN-based oxidized fiber. The PAN-based carbon fiber can be obtained by treating the PAN-based oxidized fiber at a higher temperature in an inert atmosphere.

[Oxidized fiber spun yarn (OPF spun yarn)]
A spun yarn obtained by spinning an oxidized fiber, the fineness of the oxidized fiber being 0.5 to 3.4 dtex, the dry strength of the spun yarn being 16 mN / dtex or more, and the number of twists of the spun yarn being 150 to 900 times / The oxidized fiber spun yarn is preferably m.

[Oxidized fiber spun yarn fabric (OPF spun yarn fabric)]
It is a woven fabric obtained by weaving oxidized fiber spun yarn.

[Carbon fiber fabric (CF fabric)]
A fabric obtained by weaving carbon fiber bundles (carbon fiber strands), or a fabric obtained by carbonizing the oxidized fiber spun yarn fabric. There are plain weaving, twill weaving, satin weaving, cedar twill weaving, etc., but plain weaving is preferable from the viewpoint of shaping.

[Oxidized fiber felt (OPF felt)]
A felt obtained by felting oxidized fiber with a needle punch, water jet or the like.

[Carbon fiber felt (CF felt)]
A felt obtained by carbonizing an oxidized fiber felt.

[Oxidized fiber paper (OPF paper)]
It is a paper obtained by making an oxidized fiber having a fiber length of 1 to 30 mm, and the thickness is preferably 0.05 to 0.5 mm.

[Carbon fiber paper (CF paper)]
It is a paper obtained by papermaking carbon fiber having a fiber length of 1 to 30 mm, and the thickness is preferably 0.05 to 0.5 mm.

[Lamination]
When laminating, a raw material sheet (oxidized fiber spun yarn fabric, carbon fiber fabric, oxidized fiber felt, oxidized fiber paper, carbon fiber paper) before carbonization treatment is impregnated with an adhesive binder component, and thermocompression treatment There is a method of laminating by a method, a method of inserting a resin sheet having adhesiveness between sheets at the time of adhesion, and a method of adhering the sheets.

  As a method of impregnating the raw material sheet with an adhesive binder component, a method of mixing the binder fiber and / or resin at the time of raw material sheet preparation (mixing at the time of preparation) and a method of impregnating the resin after preparation of the raw material sheet (impregnation after preparation) ) The binder component is preferably a carbonizable resin or fiber having a residual carbon ratio of 5% by mass or more, particularly 5 to 50% by mass.

[Resin impregnation and attachment to raw material sheet before lamination]
The resin is adhered to the raw material sheet by immersing the raw material sheet in a resin bath having a predetermined concentration and spraying the resin by spraying.

[Resin type]
Water-soluble resins having good handleability such as polyethylene terephthalate (PET), polyacrylic acid ester, carboxymethyl cellulose and polyvinyl alcohol (PVA) are preferred.

[Resin amount]
A resin amount of 1 to 10% by mass is preferable with respect to the raw material sheet. When the amount of resin is less than 1% by mass, the adhesiveness is not sufficient, and thus is not appropriate. When the amount of resin exceeds 10% by mass, the carbon fiber sheet after carbonization treatment becomes stiff and brittle. Therefore, when fired in a roll shape, process stability such as cutting and poor appearance of wrinkles / swells Is not appropriate.

[Mixing of fiber and / or resin to raw material sheet before lamination]
It is mixed at the time of making the oxidized fiber paper to be laminated. The mixing amount is the same as the amount described in the above [Resin amount] column.

[Type of fiber and / or resin]
Shapes such as powders, pellets, short fibers, and pulps of organic polymers such as aromatic polyamide (aramid), PET, phenol resin, polyimide, PAN, and phenol quinol can be used. Among these shapes, pulp-like and fibrid-like materials are preferable in consideration of dispersibility during sheet production, thickness variation, distortion, strength, etc. of the carbon fiber sheet after firing.

  By laminating carbon fiber paper or oxidized fiber paper on one or both sides of carbon fiber fabric, oxidized fiber spun yarn fabric and oxidized fiber felt, and thermocompression-bonding, both are integrated via the binder component. A precursor sheet is produced.

  The thermocompression treatment temperature is preferably 120 to 500 ° C., and the treatment pressure is preferably 5 to 30 MPa. When the thermocompression treatment temperature is less than 120 ° C., the strength of the precursor sheet and the strength of the carbon fiber sheet after carbonization are not preferable. When the thermocompression treatment temperature exceeds 500 ° C., unevenness occurs in the thickness of the obtained carbon fiber sheet. Furthermore, the strength of the precursor fiber sheet and the strength of the carbon fiber sheet after carbonization are reduced. A treatment pressure of less than 5 MPa is not preferable because the strength of the precursor sheet and the strength of the carbon fiber sheet after carbonization are lowered. When the treatment pressure exceeds 30 MPa, the thickness of the carbon fiber sheet is uneven. Furthermore, the strength of the precursor fiber sheet and the strength of the carbon fiber sheet after carbonization are reduced.

  The lamination method may be performed using either a hot press or a heat roller.

[Carbonization]
It is baked at a temperature of 1300 ° C. to 2800 ° C. in an inert gas atmosphere in a batch or continuously and carbonized. Nitrogen, argon, helium or the like is used as the inert gas. When the firing temperature is less than 1300 ° C., the electrical conductivity of the obtained sheet is lowered, which is not preferable. When it exceeds 2800 ° C., the carbon fiber sheet becomes rigid and the strength decreases. Furthermore, it is not preferable because problems such as generation of carbon fine powder occur.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, evaluation of operation conditions and measurement of each physical property were based on the following methods.

[Cavity]
A photograph was taken with a microscope, and the vertical and horizontal lengths of the void portions without the spun yarn were measured, and the average value of N = 50 was calculated.

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

[thickness]
The thickness when a load of 1.2 N (61.9 kPa) was applied in the thickness direction with a circular pressure plate having a diameter of 5 mmφ was measured.

[Tensile strength]
A sample having a width of 50 mm and a length of 120 mm or more was fixed on a jig having a distance between chucks of 100 mm, and the breaking strength when pulled at a speed of 30 mm / min was obtained from a value converted into a numerical value per 10 mm width.

[Tensile elongation]
It calculated | required as elongation at the time of the fracture | rupture at the time of intensity | strength measurement.

[Bending strength: Conducted by 3-point bending test method]
Based on JIS K 6911, the test piece size was determined from values measured at a width of 10 mm × 50 mm, a test speed of 1 mm / min, an indenter radius of 3.2 mm, a fulcrum radius of 3.2 mm, and a distance between fulcrums of 16 mm.

[Bending deflection]
It calculated | required as bending amount at the time of a fracture | rupture at the time of a bending strength measurement.

[Electric resistance value]
Two 50mm square (thickness 10mm) gold-plated electrodes sandwich a carbon fiber sheet sample so that the electrodes are in full contact with each other, and a load of 10kPa is applied in the thickness direction of the sheet. Was calculated by the following calculation formula: electric resistance value = (electric resistance value in the thickness direction) × sample area.

[Battery characteristics]
The carbon fiber sheet was cut into a 50 cm square, and 0.2 mg / cm ² of catalyst (Pt-Rt) was supported on the carbon fiber sheet. A cell was constructed by bonding carbon fiber sheets carrying the catalyst on both sides of a polymer electrolyte membrane (Nafion 117). The cell voltage was measured at a temperature of 80 ° C. and a current density of 0.6 / cm ² to obtain performance (battery characteristics).

[Flatness: Evaluation by non-contact with confocal microscope (surface roughness measurement)]
Based on JIS B 060 to 1982, the cut-off values were calculated from the average value of the values measured at n = 10 for Ra of 5 mm length with λc = 0.8 and λS = 0.025.

[Gas permeability measurement method]
Measured according to ISO 2965-1997.

[Remaining charcoal rate]
From the mass before and after heat treatment, the following formula residual carbon ratio (mass%) = B / A x 100
A is the mass of the raw material dried at 120 ° C. for 1 hr (mass before heat treatment)
B is the mass of heat-treated at 900 ° C. for 30 minutes in a nitrogen atmosphere (mass after heat treatment)
Calculated by

[Examples 1-4, Comparative Examples 1-3, Examination Examples 1-3]
Carbon fiber sheets were produced under the conditions shown in Tables 1 to 3, and the above physical properties were measured. The results are shown in Tables 1-3.

  When impregnating the binder, aramid fiber was used as binder A, and PET fiber was used as binder B, and a ratio of 4/3 in the A / B mass ratio was impregnated at the time of papermaking.

  As shown in Tables 1 to 3, carbon fiber sheets with good physical properties were obtained in Examples 1 to 4. However, in the comparative example 1, since the carbon fiber paper was not laminated | stacked, the plane smoothness was bad, it was weak with respect to a bending, and the carbon fiber sheet of favorable physical property was not obtained. Also in the comparative example 2, since the carbon fiber paper was not laminated | stacked, the plane smoothness was bad, it was weak with respect to a bending, the battery characteristic was low, and the carbon fiber sheet of a favorable physical property was not obtained. Since the carbon fiber paper was simple in Comparative Example 3, the amount of bending deflection and the tensile elongation were insufficient, the electric resistance value was poor, the battery characteristics were low, and a carbon fiber sheet with good physical properties could not be obtained.

  In Study Example 1, since the firing temperature was low, the electrical resistance value was high, and a carbon fiber sheet showing good battery characteristics was not obtained. In Study Example 2, since the basis weight and thickness were small, the tensile strength at break and bending strength were small, and a carbon fiber sheet having good physical properties could not be obtained. In Study Example 3, a carbon fiber sheet having a large basis weight, large thickness, high electric resistance, and good battery performance could not be obtained.

  In Tables 1 to 3, the location indicated by x deviates from the configuration of the present invention or the preferred configuration.

It is a schematic sectional side view showing an example of a carbon fiber felt of the present invention (an example of a carbon fiber sheet formed by laminating and integrating carbon fiber paper on one surface of a carbon fiber fabric or carbon fiber felt). It is a schematic sectional side view showing another example of the carbon fiber felt of the present invention (an example of a carbon fiber sheet formed by laminating and integrating carbon fiber papers on both sides of a carbon fiber fabric or carbon fiber felt). In the example of FIG. 1 or FIG. 2 of the carbon fiber felt of the present invention, in the example of the carbon fiber sheet formed by laminating and integrating the carbon fiber paper on one side or both sides of the carbon fiber fabric, the carbon fiber fabric and the carbon fiber paper It is a schematic plane sectional view which shows the interface vicinity with.

Explanation of symbols

2, 12, 22 Carbon fiber sheet 4, 14 Carbon fiber fabric or carbon fiber felt 6, 16a, 16b, 26 Carbon fiber paper 24 Carbon fiber fabric 28 Carbon fiber spun yarn or strand part of carbon fiber fabric 30 of carbon fiber fabric Gap part

Claims (6)

A carbon fiber sheet formed by laminating and integrating carbon fiber paper on one or both surfaces of a carbon fiber fabric and a carbon fiber felt. The thickness is 150 to 600 μm, the basis weight is 60 to 200 g / m ² , the tensile strength is 0.5 N / cm or more, the tensile elongation is 1% or more, the bending strength is 1 to 50 MPa, and the bending deflection amount is 1 to 5 mm. The carbon fiber sheet according to claim 1. The carbon fiber sheet according to claim 1, wherein the planar smoothness of the laminated paper surface is Ra = 15 μm or less. A gas diffusion layer for a polymer electrolyte fuel cell formed of the carbon fiber sheet according to claim 1. Carbon fiber paper or oxidized fiber paper is laminated on one side or both sides of carbon fiber fabric, oxidized fiber spun yarn fabric and oxidized fiber felt, and after thermocompression treatment, in an inert gas atmosphere at 1300-2800 ° C. A method for producing a carbon fiber sheet, characterized by firing. The method for producing a carbon fiber sheet according to claim 5, wherein the binder used when laminating the carbon fiber paper or the oxidized fiber paper is a resin or fiber having a residual carbon ratio of 0.5% by mass or more.

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