JP2002069758A - Method for manufacturing graphite fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a graphite fiber having excellent adhesivity to a matrix resin and excellent in a compression strength at 0 deg.C, a polyacrylonitrile fiber suitably used as the raw material and a method for manufacturing the polyacrylonitrile fiber. SOLUTION: The method for manufacturing a polyacrylonitrile fiber comprises subjecting a polyacrylonitrile-based copolymer to wet spinning or dry-wet spinning, washing the resultant fiber with water, subsequently applying a phenolic resin on the fiber, and further making the treated fiber compact by drying.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a graphite fiber for a fiber-reinforced composite material and a polyacrylonitrile fiber used as a raw material thereof.

[0002]

2. Description of the Related Art Carbon fibers have a high specific strength and a high specific elastic modulus, and are utilized in various applications by utilizing their characteristics.

In particular, polyacrylonitrile (hereinafter referred to as PAN)
) -Based fibers are widely used because of their excellent workability.

[0004] When a carbon fiber is used as a matrix resin of a thermosetting resin or a thermoplastic resin to form a fiber-reinforced composite material, the carbon fiber is required to effectively exhibit its excellent specific strength and specific elastic modulus.
It is known that the adhesion between the carbon fiber and the matrix resin (hereinafter simply referred to as adhesion) is good. For this reason, it is common practice to apply a functional group such as -COOH to the surface layer of the carbon fiber by subjecting it to electrolytic oxidation treatment or the like in an aqueous acid or alkali solution.

However, in such a method, in order to increase the elastic modulus of the carbon fiber, the adhesiveness tends to decrease as the carbonization temperature is increased. As a cause of this, as the temperature of carbonization is increased, the crystallization of the carbon fiber is promoted, that is, the surface layer of the fiber is hardly oxidized due to the development of the crystal structure of the graphite structure,
This is presumed to be due to a decrease in the amount of generated functional groups.

[0006] On the other hand, even if the oxidation treatment is increased, the degree of improvement in the adhesiveness is limited, and there has been a problem that the bending strength, which affects the 0 ° compression strength, decreases as the carbonization temperature increases.

In general, the degree of crystallinity of the carbon fiber is higher in the surface layer than in the inner layer because oxygen which promotes crystallization during flame resistance diffuses from the surface layer of the fiber to the inner layer. Because of the non-uniform structure, the strength tends to decrease due to minute defects in the surface layer of the fiber.

[0008] To solve the above problems, Japanese Patent Laid-Open No. 10-884
No. 3 localizes a flame retardant element such as boron in the surface layer of the PAN-based fiber, suppresses the crystallization of the surface layer of the fiber, increases the adhesiveness, and prevents diffusion of oxygen from inside the fiber.
A technique for increasing the strength is disclosed.

However, in such a method, 2000
If the graphitization treatment is performed at a temperature of not less than ° C., boron acts as a catalyst for the carbonization treatment, and there is a disadvantage that the crystallinity of the surface layer of the fiber becomes excessive.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a graphite fiber having good adhesiveness with a matrix resin and excellent 0 ° compression strength.
And a polyacrylonitrile fiber suitably used as a raw material thereof and a method for producing the same.

[0011]

The present invention has the following arrangement to solve the above-mentioned problems. That is, it is a polyacrylonitrile fiber in which a phenol resin is attached to the surface layer.

Further, the present invention has the following configuration in order to solve the above problems. That is, this is a method for producing a polyacrylonitrile-based fiber in which a fiber obtained by spinning a polyacrylonitrile-based copolymer by a wet or dry-wet spinning method is washed with water, a phenol resin is applied to the fiber, and the fiber is further dried and densified.

Further, the present invention has the following configuration in order to solve the above problems. That is, this is a method for producing graphite fibers in which the polyacrylonitrile-based carbon fiber obtained by the above-mentioned production method is subjected to flame resistance and carbonization treatment, and then graphitized at 2000 ° C. or higher.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies,
Attach phenolic resin to the surface layer of PAN fiber,
When this was carbonized and then graphitized at a temperature of 2000 ° C. or higher, it was surprisingly found that a graphite fiber which could solve the above-mentioned problems at once was obtained.

The PAN fiber of the present invention is obtained by attaching a phenol resin to the surface layer of the fiber.

Examples of the phenol resin include resins obtained from phenols (phenol, cresol, xylenol, resorcin, etc.) and aldehydes (formaldehyde, acetaldehyde, furfural, etc.), and modified resins thereof. Among them, a phenol resin composed of phenol and formaldehyde is suitably used in the present invention.

The amount of the phenol resin adhered was a fiber weight of 10
The amount is 0.5 to 10% by weight, preferably 0.5 to 5% by weight, based on 0% by weight. When the content is less than 0.5% by weight, the effect of suppressing crystallization of the surface layer portion of the fiber decreases,
If it exceeds 10% by weight, crystallization of the whole fiber is suppressed, and the elastic modulus of the carbon fiber may be greatly reduced.

The PAN fiber of the present invention is, for example, PAN
The fiber can be produced by spinning a copolymer by a wet or dry-wet spinning method, washing the fiber with water, applying a phenol resin to the fiber, and further drying and densifying the fiber.

First, either a wet spinning method in which a PAN copolymer is directly discharged from a spinneret into a coagulation bath, or a dry-wet spinning method in which a PAN copolymer is once passed through an air path and discharged into a coagulation bath through a spinneret. Form fibers.

Here, the PAN copolymer preferably contains acrylonitrile in an amount of 90% by weight or more, preferably 95% by weight or more. As the solvent used for preparing the spinning dope, inorganic solvents such as zinc chloride and sodium thiocyanate, and organic solvents such as dimethylsulfoxide, dimethylformamide, dimethylacetamide and N-methylpyrrolidone can be used.

Next, in order to wash the solvent remaining in the fiber, the fiber is washed with warm water, and the phenol resin is further washed with 0.3%.
It is passed through an aqueous solution dissolved at a concentration of １．５1.5% by weight, preferably 0.5-1.0% by weight. If the concentration is out of the range, the adhesion efficiency of the phenol resin may decrease. As described above, the phenol resin is usually preferably provided in the form of an aqueous solution, and thus, the above-mentioned water-soluble phenol resin is preferably used. Therefore, as the phenol resin, a resol-based resin reacted with an alkali is preferably used rather than a novolak-based resin reacted with an acid.

The phenol resin preferably does not contain a metal element. When a metal element is contained, the oxidation resistance of graphite fibers or the like obtained by carbonizing or graphitizing the fibers may decrease.

In order to effectively adhere the phenol resin to the surface layer of the fiber, the fiber has a swelling degree of 50 to 300.
%, Preferably 100 to 250%, so-called water-swellable fibers. When the degree of swelling is less than 50%,
The phenolic resin may be difficult to penetrate from the fiber surface, and if it exceeds 300%, it penetrates to the inner layer of the fiber, the crystallinity of the whole fiber is reduced, and the elastic modulus of the obtained carbon fiber is greatly increased. May drop.

The degree of swelling is determined based on the hydrophilicity of the PAN copolymer, the concentration of the spinning solution, the type of solvent used, the concentration of the solvent in the coagulation bath,
Since these factors depend on the coagulation bath temperature, bath stretching temperature, bath stretching ratio, and the like, it is preferable to appropriately adjust these factors so that the degree of swelling of the fiber falls within the above-mentioned range.

Immediately after the phenolic resin is adhered, a silicone oil such as amino denaturation may be applied to the fiber in order to prevent single yarn adhesion.

Next, it is dried and densified at a temperature of 130 to 200 ° C. If the drying temperature is lower than 130 ° C., the evaporation of water is slow, the phenol resin penetrates into the inner layer of the fiber, and the elastic modulus of the fiber as a whole may decrease. Adhesion between fibers may be promoted.

After the drying and densification, if necessary, the film is drawn in a heat medium such as pressurized steam to adjust the fiber orientation, and further subjected to a heat treatment at 130 to 200 ° C. if necessary. Can be obtained.

The carbon fiber according to the present invention is obtained by converting the PAN fiber obtained by the above-described method to 200 to 300.
C., preferably from 0.95 to 1.05 times in an oxidizing atmosphere such as air at 230 to 270 ° C., and then at a maximum temperature of 600 to 900 ° C., preferably 700 to 800 ° C. Stretched 1.0 to 1.1 times in an inert atmosphere, and then stretched 0.95 to 1.0 times in an inert atmosphere such as nitrogen at a maximum temperature of 1600 to 1800 ° C. it can.

The graphite fiber according to the present invention is obtained by subjecting the above carbon fiber to an inert atmosphere such as nitrogen at a maximum temperature of 2000 to 3000 ° C., preferably 2000 to 2800 ° C.
It can be obtained by stretching 01 to 1.2 times. In the present invention, after the carbonization treatment or the graphitization treatment, the fiber surface may be subjected to an electrolytic treatment at 10 to 200 coulomb / g in an acid or alkali aqueous solution to generate a functional group which enhances the adhesiveness on the fiber surface. it can.

[0030]

EXAMPLES The present invention will be described more specifically with reference to the following examples. In the examples, the measurement of each physical property value was performed by the following method. <Strand strength, modulus of elasticity> A carbon fiber bundle to be measured is impregnated with a resin having the following composition, cured at 130 ° C for 35 minutes, and then subjected to a tensile test according to JIS R7601. 100 parts of epoxy resin ERL-4221 (manufactured by Union Carbide Co.) 3 parts of boron trifluoride monoethylamine (BF3 / MEA) 4 parts of acetone <Interlayer shear strength (ILSS), bending strength> It is wound around a metal frame, and the volume content of carbon fiber (V
f) is set to 60% in a concave mold having a groove width of 6 mm, a resin having the following composition (1) is poured into the mold, and then heated and vacuum degassed. After that, it is set on a press machine and thickness 2.5
A spacer having a width of 2 mm is sandwiched, the irregularities of the mold are engaged with each other, and the resin is cured by applying pressure and heating under the following conditions to prepare a test piece having a width of 6 mm and a thickness of 2.5 mm.

The measurement was performed using an Instron tester, and the obtained results were converted to Vf of 60%. (1) Resin composition Ep828 (manufactured by Petrochemicals Co., Ltd.) 100 parts Boron trifluoride monoethylamine 3 parts (2) Molding conditions-Defoaming: 80 ° C x 4 hours under vacuum (≤ 10 mmHg)-Molding: Press pressure 4.9 MPa, 170 ° C. × 1 hour ・ After cure: After removing the test piece from the mold, 1
70 ° C. × 2 hours (3) Measurement: ILSS: Cut the length of the test piece to 18 mm, use a three-point bending jig, make the support span 4 times the thickness of the test piece, and measure n = 6, average Find the value. (4) Flexural strength: Cut the length of the test piece to 90 mm,
Using a three-point bending jig, the support span is set to 24 times the test piece, and n = 5 is measured, and the average value is determined. Example 1 20% by weight of a PAN copolymer having a composition of 99% by weight of acrylonitrile and 1% by weight of itaconic acid and an intrinsic viscosity of 1.7% dimethyl sulfoxide (hereinafter referred to as DMS)
O) solution, ammonia gas was blown into the solution to obtain a pH of 8.
A spinning solution of 0 was prepared.

The undiluted spinning solution was introduced into a coagulation bath filled with an aqueous solution having a concentration of DMSO of 60% by weight and a temperature of 60 ° C. through a spinneret having 3,000 holes, and was taken out at a speed of 10 m / min.

Next, the film was washed with water while maintaining a total draw ratio of 1.15 times in a water bath containing 6 stages of warm water at 55 to 75 ° C., and then stretched 3.9 times in a hot water bath. Swelling degree 200
% Water-swelled fiber.

Next, this water-swelled fiber was converted to a resin composed of a water-soluble phenol resin, phenol and formaldehyde (Shownol BRL-2854, manufactured by Showa Polymer Co., Ltd.).
[Trademark, model number]) dissolved at 0.7% by weight at a temperature of 20
After passing through an aqueous solution at ℃ and removing excess solution adhered to the fiber surface with a nip roll, an aqueous treatment liquid in which amino-modified silicone having a viscosity of 3000 cSt was dispersed was passed. Next, the excess solution was removed again by a nip roll, and then dried and densified by a heating roller having a surface temperature of 150 ° C.

Further, in a steam pressurized at 145 ° C.
After drawing 89 times, it was dried with a heating roller having a surface temperature of 170 ° C. to obtain a PAN-based fiber having a single fiber fineness of 0.8 dtex.

The obtained fiber is heated at 245 ° C. and then at 255 ° C.
Was passed through a 1.0-fold non-stretching and non-shrinking state of the heated air, and heated to a specific gravity of 1.34 to obtain an oxidized fiber.

Next, the steel sheet was passed through a pre-carbonization furnace in a nitrogen atmosphere having a maximum temperature of 750 ° C. while being stretched 1.05 times while being stretched to 0.97 times in a carbonization furnace in a nitrogen atmosphere having a maximum temperature of 1700 ° C. While passing through a graphitization furnace in a nitrogen atmosphere having a maximum temperature of 2300 ° C. while being stretched 1.03 times to obtain graphite fibers.

The obtained graphite fiber is subjected to electrolytic treatment using dilute sulfuric acid as an electrolytic solution at an electric quantity of 40 coulombs / g, followed by washing with water.
Dried and rolled up.

The graphite fiber was measured for the resin-impregnated strand strength and elastic modulus.
a, 406 GPa, and as a result of measuring ILSS and bending strength, 72.5 MPa and 1395 MPa, respectively,
Each showed good physical property values. Comparative Example 1 A graphite fiber was obtained in the same manner as in Example 1 except that the phenol resin was not passed through an aqueous solution in which the phenol resin was dissolved, and the phenol resin was not attached to the surface layer of the fiber. As a result of evaluating the resin-impregnated strand strength and elastic modulus,
They are 4.50 GPa and 415 GPa, respectively, and ILS
As a result of measuring S and bending strength, each was 65.2MP.
a, a lower physical property value of 1253 MPa.

[0040]

According to the present invention, there are provided a graphite fiber having good adhesion to a matrix resin and excellent in 0 ° compressive strength, a polyacrylonitrile fiber suitably used as a raw material thereof, and a method for producing the same. Can be provided.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4L033 AA05 AB01 CA34 CA70 4L037 AT02 CS03 CS04 FA03 PA55 PA65 PC10 PC11 PC13 PF29 PF41 PF45 PG07 PS00 PS02 PS10 PS19 UA12

Claims (4)

[Claims] 1. A polyacrylonitrile fiber in which a phenol resin is adhered to a surface layer. 2. A method for producing a polyacrylonitrile-based fiber, comprising spinning a polyacrylonitrile-based copolymer by a wet or dry-wet spinning method, washing the fiber with water, applying a phenol resin to the fiber, and further drying and densifying the fiber. 3. The method for producing a polyacrylonitrile fiber according to claim 2, wherein said phenol resin is a water-soluble phenol resin. 4. A method for producing graphite fiber, comprising subjecting the polyacrylonitrile-based carbon fiber obtained by the production method according to claim 2 to oxidization-resistant and carbonizing treatment and then graphitizing it at 2,000 ° C. or higher.