JP2002266217A - Carbon fiber nonwoven fabric and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carbon fiber nonwoven fabric having excellent electroconductivity, thermal conductivity, heat resistance and corrosion resistance, controlling surface roughness and falling off of fibers and to provide a method for producing the same. SOLUTION: This carbon fiber nonwoven fabric is characterized in that the nonwoven fabric comprises >=70 mass % of polyacrylonitrile-based short carbon fibers and the short carbon fibers are mutually interlaced by a water current. In this method for carbon fiber nonwoven fabric comprising at least carbon fibers, a slurry containing at least polyacrylonitrile-based short carbon fibers is prepared so that the content of the short carbon fibers in the nonwoven fabric is >=70 mass %, the slurry is made into paper by a continuous papermaking method to give a web, to which a columnar high-pressure water current is applied and the short carbon fibers are interlaced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention can be used for various purposes such as heating equipment as a wiping of dust and dirt accumulated on equipment and devices used at high temperature and as a heat conductive mat, and furthermore, gas permeation of fuel cells and the like. Carbon fiber non-woven fabric with excellent electrical conductivity, thermal conductivity, heat resistance, and corrosion resistance, which is also suitable as a material for an electrode substrate where the property is required, and a carbon fiber non-woven fabric capable of fully exhibiting the properties of carbon fiber It relates to a manufacturing method.

[0002]

2. Description of the Related Art Carbon fibers are more dispersible than other fibers.
The entanglement between the fibers is weak, and it is difficult to maintain the shape as a nonwoven fabric unless a large amount of binder is used. Therefore, the original function of the carbon fiber cannot be sufficiently exhibited. It is considered that the reason is that the carbon fiber has high strength and high elasticity as compared with other fibers and the yarn is hard and hard to bend, and the surface friction force of the yarn surface is small. In addition, it is considered that the decrease in the number of binding points of the fibers due to the poor dispersibility is one of the causes of the difficulty in maintaining the shape.

[0003] On the other hand, a method in which fibers are entangled with each other by striking a high-pressure columnar water stream is generally used. However, when this method is applied to carbon fibers, carbon fibers have higher strength than other fibers. -Due to the high elasticity and the hardness of the yarn, there is a problem in that when the fibers are entangled, the surface of the base material becomes rough, and the fibers fall off from that part. Therefore, relatively soft,
The mainstream method is to entangle in the state of oxidized short fibers and then to carbonize them.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, reduces the amount of binder used, and improves the properties of carbon fibers such as conductivity, heat conductivity, heat resistance and corrosion resistance. It is an object of the present invention to provide a carbon fiber nonwoven fabric which is excellent and in which surface roughness and fiber dropout are suppressed, and a method for producing the same.

[0005]

In order to solve the above-mentioned problems, the present invention provides a polyacrylonitrile-based carbon short fiber of 70%.
It is a carbon fiber nonwoven fabric containing not less than 10% by mass and wherein the carbon fibers are hydroentangled with each other. The nonwoven fabric of the present invention has a strong binding force to each other even if the amount of the binder is small, and can maintain the shape.

Further, the present invention provides a method for producing a carbon fiber nonwoven fabric containing at least carbon fibers, wherein a slurry containing at least polyacrylonitrile-based carbon short fibers has a content of the carbon short fibers in the nonwoven fabric of 70% by mass or more. A method for producing a carbon fiber nonwoven fabric, characterized in that the carbon short fibers are entangled by applying a columnar high-pressure water stream to a web obtained by making the slurry by a continuous papermaking method.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the present invention, the polyacrylonitrile-based short carbon fiber is contained in the nonwoven fabric in an amount of 70% by mass or more, and the carbon fibers are hydroentangled with each other so that even if the amount of the binder is small, the binding force between them is strong, and Is obtained. The carbon fiber nonwoven fabric here is all that is formed into a sheet by being entangled with short carbon fibers or with other fibers, and includes those subjected to post-formation treatment.

[0009] Polyacrylonitrile (PA) is used as carbon fiber.
There are also pitch-based, phenol-based, and graphite-based types besides N) -based ones, but since these have a larger fiber diameter than polyacrylonitrile-based ones, a higher water pressure is required for hydroentanglement. come. In addition, since polyacrylonitrile-based fibers are the strongest and are less likely to be damaged by water pressure, among carbon fibers, polyacrylonitrile-based carbon fibers are suitable for hydroentanglement.

It is essential that the ratio of the polyacrylonitrile-based carbon fiber is 70% by mass or more, and preferably 9% by mass.
0% or more, more preferably 95% or more is required. When the polyacrylonitrile-based carbon fiber is less than 70% by mass,
The electric conductivity, heat conductivity, heat resistance and corrosion resistance peculiar to carbon fiber cannot be utilized.

[0011] As a component other than the polyacrylonitrile-based carbon fiber, the nonwoven fabric of the present invention may include any component that can be mixed with the polyacrylonitrile-based carbon fiber and hydroentangled. Compounds that can be mixed and hydro-entangled include, for example, those that act as a binder, such as fibrous, powder-like, and pulp-like organic polymers necessary to increase the binding force between fibers, and hydro-entanglement. Organic fibers having high flexibility for activating the polymer, and other conductive materials, heat-resistant materials, and corrosion-resistant materials.

In the nonwoven fabric of the present invention, as shown in FIG. 1, the carbon fibers are strongly bound to each other by hydroentanglement. The web in which the carbon fibers are strongly bound to each other by the hydroentanglement is dried by a press, a drier, or the like, and is completed as a nonwoven fabric. Alternatively, a mixed material such as a binder in the non-woven fabric is reduced or removed by a baking treatment or the like, or a non-woven fabric to which a binder or the like is further adhered is also a non-woven fabric and is included in the present invention. In the present specification, the latter nonwoven fabric is referred to as “post-treated nonwoven fabric”, and simply referred to as “nonwoven fabric” refers to the former.

The conventional carbon fiber paper not subjected to the hydroentanglement treatment is not preferable because it has a low wet strength and requires a large amount of a binder. It is not preferable because it becomes something.

In the nonwoven fabric of the present invention, the total content of the polyacrylonitrile-based carbon short fibers and the polyacrylonitrile-based flame-retardant staple fibers is preferably 90% by mass or more. It is more preferable to use only one. Since the polyacrylonitrile-based flame-resistant fiber is more flexible than the carbon fiber, it is suitable for hydroentanglement, and a nonwoven fabric obtained by hydroentanglement of the polyacrylonitrile-based flameproof staple fiber is generally used. When polyacrylonitrile-based flame-retardant short fibers are mixed with polyacrylonitrile-based short carbon fibers, strong entanglement can be achieved even when the water pressure is low, and the wet strength is increased. For this reason, the papermaking speed can be increased, which leads to an improvement in productivity. Also,
Even when fired at a temperature of 1000 ° C. or more, the flame-resistant fiber is good in that it remains much more excellent in conductivity, heat conductivity, heat resistance, and corrosion resistance than a general binder. .

The fiber length of the oxidized fiber used in the present invention is preferably longer than that of carbon fiber from the viewpoint of maintaining strength such as bending strength and tensile strength. Specifically, the average fiber length of the oxidized fiber is preferably 1 to 15 mm longer than the average fiber length of the carbon fiber, and more preferably 3 to 10 mm.

The polyacrylonitrile-based short carbon fiber preferably contains a polyacrylonitrile-based short carbon fiber having a fiber diameter of 5 μm or less and a fiber length of 15 mm or less, more preferably 6 mm or less.
It is more preferable to include the above. Large fiber diameter,
On the other hand, if the length is long, relatively high pressure is required for the hydroentanglement treatment, which is disadvantageous in that the possibility that the fiber is projected increases. In particular, those having a long fiber length are disadvantageous from the viewpoint that the dispersibility is reduced. The total length of the polyacrylonitrile-based carbon short fibers is preferably 8 μm or less and 15 mm or less.

The lower limit of the fiber diameter and the fiber length of the polyacrylonitrile-based carbon short fiber is not particularly limited, but it is disadvantageous in that the short fiber which is missing increases the possibility of causing damage to the human body. This is disadvantageous in that the degree of reinforcement by water confounding is reduced. From such a viewpoint, a preferable lower limit is a fiber diameter of 3 μm and a fiber length of 2 mm.
It is.

In the nonwoven fabric of the present invention, the ratio of the organic polymer compound used as a binder, that is, a binder, is preferably 5% by mass or less (including 0% by mass) from the viewpoint of maintaining good conductivity of the nonwoven fabric. Is preferred. Here, the ratio of the organic polymer compound is a mass ratio in the nonwoven fabric, and is not a ratio mixed as a raw material when manufacturing the nonwoven fabric. For example, as a general binder, polyvinyl alcohol (PV
When papermaking is performed using 10% of A) in the raw material, the ratio of the binder in the obtained nonwoven fabric is about 7 to 8 wt% in consideration of the fact that PVA dissolves in water and is lost. The conductivity of the non-woven fabric is 10
Since it is less than one-tenth, the function is reduced. This is because there is almost no substance having higher conductivity than carbon fiber as a binder that can be used in papermaking, such as when used as an electrode substrate.

Examples of the organic polymer compound usable as the binder include polyvinyl alcohol (PVA), polyvinyl acetate, polyacrylonitrile, polyethylene, polyurethane, cellulose pulp and the like. Even if a binder having better conductivity, heat conductivity, heat resistance and corrosion resistance than carbon fiber is present, it is expensive and cannot be generally used. When the hydroentanglement process is not performed, it is difficult to maintain the shape if the amount of the binder is small. However, the hydroentanglement process can obtain a sufficiently strong nonwoven fabric even when the binder is 5% by mass or less.

In the present invention, it is preferable from the viewpoint of the strength of the nonwoven fabric that pores having an average pore diameter of 50 to 500 μm are formed by hydroentanglement. Basically, larger pores tend to be entangled more strongly, and when the average pore diameter is 50 μm or less, it is disadvantageous in that the effect of hydroentanglement is reduced. On the other hand, if the average pore diameter exceeds 500 μm, the sheet is reticulated, which is disadvantageous in that the binding force between the fibers becomes weaker. The opening not only improves the gas permeability, but also increases the strength in the longitudinal direction as compared with the case of ordinary papermaking. In addition, since the basis weight of carbon fiber paper does not change even by water jet, it does not lead to a decrease in the conductivity of the nonwoven fabric.

The average pore diameter of the pores formed by the hydroentanglement is determined as follows. That is, about 0.2 g of the carbon fiber nonwoven fabric is precisely weighed and put into a dilatometer. Next, the inside of the container is evacuated (7 Pa or less) using a mercury injection device, and then filled with mercury. Then, the measurement is performed using a porosimeter. The pore volume is determined from the mercury intrusion amount. continue,
The pore radius at each pressure is determined from the following formula, and then only the pores formed by the hydroentanglement are selected, and the pore volume and the pore diameter distribution of the pore radius at each pressure are determined, indicating a pore volume of 50%. The radius at this time is defined as the average radius of the holes formed by the hydroentanglement. Since mere papermaking does not form pores of 50 to 500 μm, all pores of 50 to 500 μm can be determined to be pores formed by hydroentanglement.

[0022]

(Equation 1)

Σ: surface tension of mercury (0.48 N / m) θ: contact angle p: pressure The mercury porosimeter is Quantachrome.
Company, PoleMaster-60 was used.

The method for producing a carbon fiber nonwoven fabric according to the present invention is the method for producing a carbon fiber nonwoven fabric containing at least carbon fibers, wherein the slurry containing at least the polyacrylonitrile-based carbon short fibers is mixed with the carbon short fibers in the nonwoven fabric. 7
0 mass% or more, and a method for producing a carbon fiber nonwoven fabric, comprising tangling the carbon short fibers by applying a columnar high-pressure water stream to a web obtained by making the slurry by a continuous papermaking method. is there. The content of the short carbon fiber is not the content in the slurry nor the content in the web, but the content in the obtained nonwoven fabric.

The medium used for preparing the slurry is not particularly limited, but water is preferable from the viewpoint of availability. Slurry can be obtained by dispersing polyacrylonitrile-based carbon short fibers and other components in a medium.

As the continuous papermaking method, any method can be used as long as it is a method of continuously producing fibers, and examples thereof include a circular net type, a long net type, a short net type, and an inclined wire net type. Type and inclined wire mesh type are preferred. This is due to the weak binding force between carbon fibers, but when continuous papermaking is performed using the long net or short net type, or the inclined wire netting type, the amount of binder can be suppressed as compared with the case of the circular net type. It is. Further, handmade papermaking can suppress anisotropy as compared with continuous papermaking, but is not preferred because of its low mechanical strength and difficulty in hydroentanglement.

The water entanglement can be performed by applying a columnar high-pressure water stream to the web, and the columnar high-pressure water stream can be formed by jetting water from a nozzle in a columnar manner. If the water pressure of the columnar high-pressure water flow is less than 0.5 MPa, it is disadvantageous in that it tends to be difficult to entangle the water flow. Conversely, if the water pressure is higher than 10 MPa, the web is damaged,
It is disadvantageous in that it tends to be cut, so 0.5 to
It is preferably 10 MPa.

When the hole diameter of the nozzle for generating the columnar high-pressure water flow is less than 0.05 mm, it is disadvantageous in that the water entanglement tends not to be recognized.
If it is larger than 0.05 mm, it is disadvantageous in that the web tends to be damaged and cut.
15 mm is preferable, and when the span of the nozzle is also wider than 3 mm, it is disadvantageous in that the hydroentanglement tends to be not recognized. Conversely, when the hole diameter is smaller than 0.3,
It is preferably 0.3 to 3 mm because it is disadvantageous in that the web tends to be damaged and cut.

If the number of nozzles for generating the columnar high-pressure water flow is too large, it is disadvantageous in that the water content of the web increases and the mechanical strength becomes weak.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments, but the present invention is not limited to the embodiments of the present invention. In addition, the component ratio in Examples and Comparative Examples,
The tensile strength, elongation at break, gas permeability coefficient, and sheet resistance in the thickness direction were determined by the following test methods.

1) Component Ratio The obtained carbon fiber nonwoven fabric was fired at 1200 ° C. in a nitrogen atmosphere, and the weight loss was calculated as the PVA component weight.

The component ratio referred to here is a mass ratio of each component in the nonwoven fabric or the post-treated nonwoven fabric.

2) Tensile strength According to JIS-P8113, a carbon fiber nonwoven fabric was cut into a width of 15 mm and a length of 25 cm in the longitudinal and transverse directions, and the load at break was measured using a tensilon measuring device. And In order to prevent the sample from being damaged by the chuck, a thick paper was stuck on both sides 2.5 cm above and below the sample and chucked.

3) Elongation at break In accordance with JIS-P8132, the maximum tensile strain rate shown before the fracture was measured using a Tensilon measuring device in the same manner as described above, and was defined as the elongation at break.

4) Gas Permeability Coefficient According to JIS-P8117, the time required for a 200 cm ³ gas to pass was measured and calculated using a Gurley-type densometer.

5) Measurement of Area Resistance in Thickness Direction The "specific resistance in the thickness direction" of the electrode substrate is obtained by inserting a sample between copper plates, applying a pressure of 1 MPa from above and below the copper plate, and applying 10 mA / cm.
The resistance value when a current was passed at a current density of ² was measured, and the resistance was determined by the following equation.

[0037]

(Equation 2)

The compositions and performances of the nonwoven fabrics in Examples and Comparative Examples are summarized in Tables 1 and 2.

Example 1 A fiber bundle of polyacrylonitrile (PAN) -based carbon fibers having an average fiber diameter of 4 μm was cut to obtain short fibers having an average fiber length of 3 mm. This carbon short fiber and polyvinyl alcohol (PVA) short fiber as a binder (average fiber length = 3 m) are added to a pulper of a continuous papermaking apparatus.
m) was added so that the mass ratio of short carbon fibers / PVA was 85/15, and the mixture was defibrated in water and mixed well to prepare a slurry. The slurry is sent out of the tank and paper is formed to form a web.
Use a nozzle of 00 μm, span 1 mm, 1.0MP
A high-pressure water stream was jetted at a water pressure of a to form an entangled web having holes and dried by a dryer to obtain a carbon fiber nonwoven fabric. In addition, the mass per unit area of the obtained carbon fiber paper was adjusted to 30 g / m ² .

At this time, when the tensile strength, elongation at break, gas permeability coefficient, area resistance and thermal conductivity of the obtained nonwoven fabric were measured, good values were obtained.

Example 2 Short Carbon Fiber / P in Slurry
A carbon fiber nonwoven fabric was continuously produced in the same manner as in Example 1 except that PVA was added so that the VA mass ratio became 95/5. Compared with Example 1, even when the PVA was reduced, a large decrease in tensile strength and lack of fibers were not observed, and the sheet resistance was significantly reduced.

Example 3 The water pressure of the water entanglement treatment was 3.0.
A carbon fiber nonwoven fabric was continuously produced in the same manner as in Example 2 except that the measurement was performed at MPa. Although the surface was rougher than in Example 2, the gas permeability and strength were improved.

Example 4 The nonwoven fabric obtained in Example 3 was heated in a baking oven at 2000 ° C. for 10 minutes in a nitrogen gas atmosphere to remove PVA, thereby obtaining a post-treated carbon fiber nonwoven fabric. A carbon fiber nonwoven fabric having excellent conductivity and heat conductivity was obtained because it had sufficient strength to hold the shape sufficiently and had no binder.

Example 5 Half of the carbon fiber having an average fiber diameter of 4 μm was changed to an average fiber diameter of 7 μm and a fiber length of 6 mm. That is, a carbon fiber nonwoven fabric was continuously produced in the same manner as in Example 3, except that the mass ratio of 4 μm carbon fiber / 7 μm carbon fiber was 50/50. Compared with Example 3, it is considered that the hydroentanglement effect is weak because the fiber diameter is large, but the strength was not so small because the fiber length was long.

[Comparative Example 1] A slurry was prepared in the same manner as in Example 1, and then JIS was performed using a standard square sheet machine.
Papermaking was performed by a batch papermaking method in accordance with the P-8209 method to obtain a carbon fiber nonwoven fabric. In addition, it adjusted so that the mass per unit area of the obtained carbon fiber nonwoven fabric might be set to 30 g / m < ² >. In this case, many fibers were missing and it was difficult to maintain the shape.

Comparative Example 2 Short carbon fiber / P in slurry
Except that the VA mass ratio was adjusted to be 65/35,
A carbon fiber nonwoven fabric was obtained in the same manner as in Comparative Example 1. In this case, there was almost no loss of the fiber, but the conductivity was very small, and the properties of the carbon fiber were lost.

Comparative Example 3 The nonwoven fabric obtained in Comparative Example 2 was heated in a baking furnace at 2000 ° C. for 10 minutes in a nitrogen gas atmosphere to remove PVA, thereby obtaining a post-treated carbon fiber nonwoven fabric. The conductivity was very high, but the shape could hardly be maintained.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

According to the present invention, there is provided a carbon fiber non-woven fabric capable of maintaining a shape even when the amount of a binder is small, and a shape of the carbon fiber non-woven fabric can be maintained. Thus, it has become possible to provide a high-performance nonwoven fabric utilizing the properties of carbon fibers such as thermal conductivity, heat resistance, and corrosion resistance.

[Brief description of the drawings]

FIG. 1 is an electron micrograph of a carbon fiber nonwoven fabric according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Mitsuo Hamada 20-1 Miyukicho, Otake City, Hiroshima Prefecture Inside the Central Technology Research Laboratory, Mitsubishi Rayon Co., Ltd. No. 10-18, Awa Paper Co., Ltd. BA23 DA01 FA18 FA22 FA25 FA37 4L047 AA03 AA16 AA28 AB02 BA04 BA21 CB05 CB10 CC14

Claims (9)

[Claims] 1. A polyacrylonitrile-based carbon short fiber comprising:
A carbon fiber nonwoven fabric containing 0% by mass or more, wherein the carbon fibers are hydroentangled with each other. 2. A combination of the polyacrylonitrile-based short carbon fibers and the polyacrylonitrile-based flame-retardant short fibers in total of 90.
The carbon fiber nonwoven fabric according to claim 1, wherein the carbon fiber nonwoven fabric is contained in an amount of not less than mass%. 3. The carbon fiber nonwoven fabric according to claim 1, wherein a part or all of the polyacrylonitrile-based carbon short fibers have a fiber diameter of 5 μm or less and a fiber length of 15 mm or less. 4. The method according to claim 1, wherein the organic polymer compound used as a binder is not contained or contained in an amount of 5% by mass or less.
The carbon fiber nonwoven fabric according to any one of the preceding claims. 5. The carbon fiber nonwoven fabric according to claim 1, wherein pores having an average pore diameter of 50 to 500 μm are formed by hydroentanglement. 6. A method for producing a carbon fiber nonwoven fabric containing at least carbon fibers, wherein a slurry containing at least polyacrylonitrile-based carbon short fibers is prepared such that the content of the carbon short fibers in the nonwoven fabric is 70% by mass or more. A method for producing a carbon fiber nonwoven fabric, comprising applying a columnar high-pressure water stream to a web obtained by making the slurry by a continuous papermaking method to entangle the carbon short fibers. 7. The water pressure of the columnar high-pressure water stream is 0.5 to 10M.
The method for producing a carbon fiber nonwoven fabric according to claim 6, which is Pa. 8. The carbon fiber according to claim 6, wherein a hole diameter of the nozzle for generating the columnar high-pressure water flow is 0.05 to 0.15 mm, and a span of an adjacent hole of the nozzle is 0.3 to 3 mm. Manufacturing method of nonwoven fabric. 9. The method for producing a carbon fiber nonwoven fabric according to any one of claims 6 to 8, wherein the number of nozzles for generating the columnar high-pressure water flow is one to three.