JPS59137511A - Preparation of graphite yarn - Google Patents

Abstract

PURPOSE:To obtain graphite yarn having improved strength, graphitizing an organic yarn precursor to which a specific amount of a carbonizable high polymer is attached. CONSTITUTION:0.1-5wt%, preferably 0.5-2wt% carbonizable organic high polymer (preferably high polymer of vinyl alcohol, high polymer of acrylonitrile) is used with warm water, DMF, etc. and attached to the surface of an organic yarn precursor (obtained by carbonizing preferably polyacrylonitrile yarn at 800-1,500 deg.C). The yarn is then heat-treated preferably at 150-400 deg.C, and graphitized at >=2,000 deg.C, to give the desired graphite yarn.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing graphite fibers, in which an organic fiber precursor, such as a polyacrylonitrile fiber precursor, is subjected to flame-retardant treatment at 200C to aooC in air, and then treated in an inert atmosphere. It is already known that graphite fibers with high elasticity can be produced by carbonizing at 800-1500 C in an inert atmosphere and graphitizing at 2000-1500 C in an inert atmosphere.

Graphite fibers are increasingly used in structural materials due to their high elasticity, but their strength has traditionally been unsatisfactory.

- When the organic fiber precursor is carbonized in an inert atmosphere after flame-retardant treatment, the best strength is obtained at 1200 to 140 (I'), but as the subsequent treatment temperature increases, This is attributable to the general property that the strength decreases especially when graphitized at a temperature exceeding 2000 Ct.

The present inventors conducted intensive studies on improving graphite fibers having such drawbacks, and arrived at the present invention.

That is, the gist of the present invention is a method for producing graphite fiber, which is characterized in that graphite fibers are attached from an organic fiber precursor and then graphitized, thereby making it possible to produce graphite fibers with excellent strength. .

The term "carbonizable" as used herein means that after performing an infusible treatment such as thermal oxidation, if necessary, at least 1% of the original weight at graphitization temperature in a non-oxidizing atmosphere such as nitrogen or argon.
This means that % can be maintained.

Normally, when producing graphite fibers, organic fiber precursors such as polyacrylonitrile fibers, pitch fibers, regenerated cellulose fibers, lignin/poval fibers, polyvinyl alcohol fibers, etc. are processed by thermal oxidation, etc., if necessary. After the infusibility treatment, carbonization is carried out at 800 to 15001:l', and then graphitization treatment is performed. desirable.

Examples of carbonizable organic polymers that can be used include vinyl alcohol, polyacrylonitrile, pitch, lignin/poval, polyamide, polyimide, phenol, and furan polymers. Among these, vinyl alcohol-based and polyacrylonitrile-based polymers are particularly preferred. Vinyl alcohol polymers include vinyl alcohol, esterified products, acetalized products, and ketalized products. Examples of vinyl alcohol esterified products include thioglycolic acid, adipic acid, and acetal of vinyl alcohol. Examples of such compounds include those based on acetaldehyde, formaldehyde, glyoxal, and benzaldehyde. The polyacrylonitrile polymer contains an acrylonitrile homopolymer or copolymer, and examples of copolymerizable monomers include esters such as methyl acrylate, ethyl acrylate, methyl methacrylate 1, and ethyl methacrylate. Amidomethylol compounds such as vinyl acetate, vinyl chloride, vinylidene chloride, methacrylonitrile, α-chloroacrylonitrile, styrene, methylstyrene, acrylamide, diacetone acrylamide, N-methylol acrylamide, etc., other divinyl compounds, methacrylic acid, Carboxylic acids such as acrylic acid and alcohols such as allyl alcohol are used. One or more of these compounds can be used.

The amount of carbonizable organic polymer attached to the fiber is α
The amount is 1 to 5% by weight. If the amount of adhesion is less than 0.1% by weight, the carbonaceous substance formed on the surface of the graphite fiber is too small to achieve the effect of the present invention.If the amount of adhesion exceeds 5% by weight, it will be difficult to obtain the effect of the present invention when making the graphite fiber into a composite material. The dispersibility of the graphite fibers and the adhesion with the matrix resin are reduced, resulting in a significant deterioration in performance when used as a composite material.

Therefore, the amount of carbonizable organic polymer attached to the fiber is 0.1 to 5% by weight, preferably α5 to 2.
Weight%.

Although there are no particular restrictions on the method of attaching the carbonizable polymer to the fibers, it is preferable to dissolve the above-mentioned polymer in a solvent and attach it as uniformly as possible to the fiber surface. Examples of the solvent include warm water when the polymer is polyvinyl alcohol, and dimethyl sulfoxide, dimethyl formamide, and dimethyl formamide when the polymer is polyacrylonitrile.
Alternatively, an aqueous solution of Rodan salt, zinc chloride, etc. can be used. When using these solvents, it is desirable to dry the fibers sufficiently and then graphitize them.

After the carbonizable polymer is thus attached to the fibers, graphitization is carried out according to a conventional method. Graphitization treatment is carried out in a substantially non-oxidizing atmosphere, but in reality it is impossible to achieve a completely non-oxidizing atmosphere, and the graphitization process contains at least several ppm of oxygen. Graphitization treatment is 200
Since the process is carried out at a high temperature that exceeds the QC, even if a trace amount of oxygen of several ppm is present, the surface of the graphite fiber will be damaged by oxidation, and this will inevitably lead to a decrease in performance, especially in strength. Accordingly, when graphitizing fibers to which a carbonizable polymer is attached, the fiber surface is protected by forming a thin carbon film on the surface of the graphite fiber, so the oxidation damage is minimized. As a result, it became possible to obtain graphite fibers with excellent strength.

In the case of vinyl alcohol polymers or acrylonitrile polymers, which are preferably used as carbonizable polymers, after adhering to fibers and before graphitization treatment, they are heated at 150C to 400C in an oxidizing atmosphere, for example in air. Heat treatment is preferred. By this infusibility treatment, a carbonaceous film made of the above-mentioned polymer is firmly formed on the surface of the graphite fiber, thereby obtaining a graphite fiber with particularly excellent strength.

Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited thereto.

Example 1 Polyacrylonitrile fiber (6000 filaments)
, single yarn denier 1.5) after flame-retardant treatment 1200t:l
1.2% by weight of polyvinyl alcohol dissolved in warm water was adhered thereto, dried at 120C, and graphitized at 2700C. 1200 above for comparison
After applying only warm water containing no polyvinyl alcohol to the carbonized fibers at C, the fibers were dried at 120C and graphitized at 2700C in the same manner as described above. Graphite fibers obtained by each method were impregnated with epoxy resin and after curing, tensile strength and elastic modulus were measured using a sample length of 200 μL, and the following results were obtained.

Example 2 After attaching 0.996% of polyacrylonitrile (a copolymer consisting of 987% acrylonitrile and 2% methyl acrylate) dissolved in dimethylformamide to carbon fibers prepared in the same manner as in Example 1, the carbon fibers were heated at 180C. It was dried and graphitized at 2650 t:'. For comparison, the carbonized fibers were coated with only dimethylacetamide containing no polyacrylonitrile, dried at 180C in exactly the same manner as the above method, and graphitized at 265CI'. The tensile strength and elastic modulus of the graphite fibers were measured in the same manner as in Example 1,
The following results were obtained.

Example 3 Carbon fibers coated with polyvinyl alcohol obtained in the same manner as in Example 1 were heat treated in air at 250C for 1 hour and then graphitized at 2700C. The tensile strength and elastic modulus of the obtained graphite fiber were measured in the same manner as in Example 1, and the tensile strength was 298 kg/, j, and the tensile modulus was 4 &
The strength was further improved compared to Example 1, which was 2t/-.

Patent Applicant: Mitsubishi Rayon Co., Ltd. Procedural Amendment Writing Method) % Formula % 1. Indication of the case, Showa 5S Patent Application No. 5940, 2. Name of the invention, Method for manufacturing graphite fiber 3. Related: Patent applicant Osamu Kanazawa 34, President and CEO of Mitsubishi Rayon Co., Ltd., 3-19 Kyobashi 2-chome, Chuo-ku, Tokyo (603), Agent No. 8-1 Toranomon 2-chome, Minato-ku, Tokyo, April 26, 1982 Shipping 6, Specification to be amended (frame line of table) After dressing, it was dried at 120°C in exactly the same manner as above, and graphitized at 2700°C. Graphite fibers obtained by each method were impregnated with epoxy resin and after curing, sample length 2
The tensile strength and elastic modulus were measured at 0wn, and the following results were obtained.

Example 2 After attaching 0.9 g of polyacrylonitrile (a copolymer of 987 mol of acrylonitrile and 2 mol of methyl acrylate) dissolved in trimethylformamide to carbon fibers prepared in the same manner as in Example 1. , dried at 180°C and graphitized at 2650°C. For comparison, only dimethylacetamide containing no polyacrylonitrile was attached to the carbonized fibers, and then dried at 180°C in the same manner as above and graphitized at 2650°C.
Example 3 The tensile strength and elastic modulus of the graphite fibers obtained by each method were the same as in Example 1. Carbon fibers coated with polyvinyl alcohol obtained in the same manner as in Example 1 were heated in air at 250°C for 1 hour. After heat treatment for a period of time, graphitization was performed at 270°C. The tensile strength and elastic modulus of the graphite fibers obtained were measured in the same manner as in Example 1, and the tensile strength was 298 kg/2 and the tensile modulus was 43.
The strength was further improved compared to Example 1, which was 2 t/ltrm2.

Patent applicant: Mitsubishi Rayon Co., Ltd. Agent Patent Attorney 1) Taketoshi Mura

Claims (2)

[Claims] (1) A method for producing graphite fibers, which comprises graphitizing an organic fiber precursor to which α1 to 5% by weight of a carbonizable organic polymer is attached. (2) Method 6 for producing graphite fiber according to claim 1, using a vinyl alcohol polymer or an acrylonitrile polymer as the carbonizable organic polymer. % attached organic fiber precursor in an oxidizing atmosphere at 150C to 4%.
1. A method for producing graphite fibers, which comprises heat treatment at 00C and then graphitization treatment.