JPH03817A - Carbon fiber and production thereof - Google Patents

Abstract

PURPOSE:To simply and inexpensively obtain the title fiber useful to filler for plastics, etc., having excellent mechanical performances, chemical resistance and a smaller size than existing fiber by carbonizing a specific (meth) acrylonitrile-based polymer in a short-fiber form. CONSTITUTION:A monomer comprising (meth)acrylonitrile-based polymer as an essential component and containing an oil-soluble polymerization initiator [0.01-20wt.% based on polymerizable monomer] such as benzoyl peroxide is dispersed into very small liquid drops in a water medium such as water by stirring, polymerized in this state, optionally cleaned and dried to give a (meth) acrylonitrile-based polymer in a short-fiber form having 0.1-50mum diameter minor axis and 1-500mum diameter of major axis and 5-100 aspect ratio, the polymer is heated in a nonoxidizing atmosphere and carbonized to give the aimed short fibers. When the polymerizable monomer is dispersed, a dispersant may be added to the water medium to make the liquid drops stably exist in the water medium.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to filtering materials for acids, alkalis, high-temperature gases, etc., plastic fillers, infrared radiators, conductivity imparting agents, electrical ribbons, and various other uses. [Conventional technology] Regarding carbon fibers used in There is something.

In the case of carbon products whose main raw materials are coke, natural graphite, etc.
Manufacture carbon products in the form of fibers, strings, thin films, etc., including graphite molded products using tar, etc. as a binder, carbon black glue graphite, activated carbon, and other ultrafine or powdered products. difficult to do.

In the case of carbon products whose main raw material is an acrylonitrile polymer, the carbon product is obtained by carbonizing short fibers or thin films of the acrylonitrile polymer through heat treatment or the like. The short fibers of the acrylonitrile polymer have conventionally been produced in the following manner. First, a monomer component consisting of acrylonitrile alone or a small amount of a copolymerizable monomer mixed with acrylonitrile is polymerized to obtain polymer particles, and the polymer particles are melted or dissolved in a solvent. The spinning solution is made into a viscous spinning solution, which is extruded through pores and formed into fibers to produce long fibers, which are then cut into short lengths to obtain short fibers of arbitrary length.

(Meth)acrylonitrile polymer particles have conventionally been produced by suspension polymerization or solution polymerization. For example, JP-A-63-105034 describes polymer particles obtained by a suspension polymerization method using a polymerizable monomer containing acrylonitrile as a main component. Special Public Service 1977
Publication No. 34596 describes a method of polymerizing (meth)acrylonitrile in a solvent such as triol or quijirole;
Alternatively, a solution polymerization method is described in which this method is carried out in the presence of an oil-soluble polymer dispersant.

Polymer particles obtained by suspension polymerization are spherical particles, and polymer particles obtained by solution polymerization exist in a solution. Therefore, in order to obtain short fibers of (meth)acrylonitrile polymers, the polymer is first processed into long fibers as described above, and then cut into short fibers of arbitrary length. be.

[Problem to be solved by the invention]

Cutting long fibers into short lengths to produce short fibers requires a special cutting machine, which poses a problem of low productivity.

For this reason, the short fibrous polymer thus obtained is very expensive, and the carbon fiber obtained by oxidizing it is inevitably expensive.

Moreover, the short fibrous polymer used as a raw material has a short axis diameter of 5
n or more, a major axis diameter of 1oan or more, and an aspect ratio of about 10. Short fibers smaller than this cannot be obtained by cutting long fibers as described above.

Therefore, the first object of this invention is to provide carbon fibers that have excellent mechanical performance, chemical resistance, heat resistance, and electrical conductivity, are smaller than conventional carbon fibers, and can be used for various purposes. do. Furthermore, a second object of the present invention is to provide a manufacturing method that can easily obtain such carbon fibers with high productivity and at low cost.

[Means to solve the problem]

In order to solve the first problem, the carbon fiber according to the invention according to claim 1 is a short fiber having a short axis diameter of 0.1 to 50 μm, a long axis diameter of 1 to 5QQn, and an aspect ratio of 5 to 100. It is said to be obtained by carbonizing a (meth)acrylonitrile-based polymer.

In order to solve the above second problem, the method for producing carbon fiber according to the invention according to claim 2 provides a carbon fiber manufacturing method in which the (meth)acrylonitrile polymer is carbonized to obtain carbon fibers. As a union, (meta)
A short fibrous polymer is produced by polymerizing a polymerizable monomer containing acrylonitrile as an essential component and an oil-soluble polymerization initiator in the form of minute droplets in an aqueous medium. shall be.

The short fibrous (meth)acrylonitrile polymer used in this invention has a short axis diameter of 0.1 to 50n and a long axis diameter of 1 to 500μ.
m, and the aspect ratio is 5 to 100, so by carbonizing this, it becomes a carbon fiber smaller than conventional ones. Such carbon fibers can be used, for example, as a coloring agent and as an agent for imparting conductivity to non-conductive materials such as plastics.

When the minor axis diameter is below the above range, the strength may be reduced, and when it exceeds the above range, the effects brought about by the fiber form may be reduced. When the major axis diameter is below the above range, the effect brought about by the fiber form may be reduced, and when it exceeds the above range, the strength may be reduced. Furthermore, if the aspect ratio is below the above range, the amount of carbon fiber added may be significantly increased when the obtained carbon fiber is used to obtain conductivity, and if it exceeds the above range, the fiber strength will decrease. There is a risk.

In this invention, short fiber-like refers not only to short fibers in the usual sense, but also includes short fibers with a small aspect ratio, that is, thick and short rod-like fibers.

The polymerizable monomer used in this invention is a polymerizable monomer containing (meth)acrylonitrile (that is, one or both of acrylonitrile and methacrylonitrile) as an essential component, and is a polymerizable monomer that contains (meth)acrylonitrile alone. Alternatively, (meth)acrylonitrile and other polymerizable monomers may be used together.

As the polymerizable monomer other than (meth)acrylonitrile, for example, a monomer having a vinyl group (hereinafter referred to as "vinyl monomer") is used. Examples of vinyl monomers include styrene, 〇-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene,
Styrenic monomers such as p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, O-chlorostyrene, m-chlorostyrene, p-chlorostyrene; acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, stearyl acrylate, acrylic acid 2
- Acrylics such as ethylhexyl, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-butyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, etc. Acid or methacrylic acid monomers include ethylene, propylene, butylene, vinyl chloride, vinyl acetate, acrylamide, methacrylamide, N-vinylpyrrolidone, etc., and one or more of these may be used.

The ratio of (meth)acrylonitrile to the polymerizable monomers is not particularly limited as long as the produced polymer does not dissolve in the monomer and precipitates in the form of short fibers. For example, when (meth)acrylonitrile and other vinyl monomers are used together, a polymerizable monomer containing (meth)acrylonitrile of 70% by weight or more is preferably used.

If the proportion of (meth)acrylonitrile is less than 70% by weight, the produced polymer will dissolve in the monomer and may not be precipitated into short fibers. 100% of the polymerizable monomer is (
It may also be meth)acrylonitrile, in which case a homopolymer of (meth)acrylonitrile is produced.

The polymerization initiator used in this invention must be oil-soluble, and there are particular restrictions if the polymerization initiator is oil-soluble, that is, it can be dissolved in a polymerizable monomer containing (meth)acrylonitrile as an essential component. For example, (meta)
Those commonly used in the polymerization of acrylonitrile are used,
In particular, oil-soluble peroxide-based polymerization initiators or azo-based polymerization initiators are preferable.Because the polymerization initiator is oil-soluble, the polymerization initiator dissolves in the polymerizable monomer, and the same polymerizable monomer Polymerization takes place in the body's droplets.

Examples of oil-soluble peroxide-based polymerization initiators include benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, methyl ethyl ketone peroxide,
Examples include diisopropyl peroxydicarbonate, cumene hydroperoxide, cyclohexanone peroxide, -butyl hydroperoxide, diisopropylbenzene hydroperoxide, and the like. In addition, as an oil-soluble azo polymerization initiator, for example, 2
．． 2'-azobisisobutyronitrile, 2.2'-azobis-(2,4-dimethylvaleronitrile), 2.2'
-azobis-2,3-dimethylbutyronitrile, 2.2
'-Azobis(2-methylbutyronitrile), 2.2'
-azobis-2,33-trimethylbutyronitrile, 2
．． 2'-azobis-2-isopropylbutyronitrile,
1.1'-azobis-(cyclohexane-1-carbonitrile), 2.2'-azobis=(4-methoxy-2,
4-dimethylvaleronitrile), 4,4-azobis-4
-cyanovaleric acid, 2-(carbamoylazo)isobutyronitrile, dimethyl-2,2'-azobisisobutyrate, and the like.

The polymerization initiator is preferably used in a proportion of 0.01 to 20% by weight, with a proportion of 0.1 to 10% by weight based on the polymerizable monomer containing (meth)acrylonitrile as an essential component. If the proportion of the polymerization initiator used is less than the above range, the polymerization reaction may not be completed, and if it is greater than the above range, the polymerization reaction may be completed in a short time. In this invention, a polymerizable monomer containing (meth)acrylonitrile as an essential component and an oil-soluble polymerization initiator is dispersed in an aqueous medium to form micro droplets. Polymerization is carried out in this state. To disperse the droplets in an aqueous medium, for example,
Conventional methods such as stirring can be employed. Unlike the usual suspension polymerization of (meth)acrylonitrile, in this invention an aqueous medium is used as the dispersion medium. This allows the droplets to become minute and dispersed in the medium.

The aqueous medium refers to water or an aqueous solution. A dispersant may be added to the aqueous medium in order to make the droplets stably exist in the aqueous medium. Dispersants include water-soluble polymers such as polyvinyl alcohol, starch, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, sodium polyacrylate, and sodium polymethacrylate; anionic surfactants, cationic surfactants, and zwitterionic surfactants. In addition, barium sulfate, calcium sulfate, barium carbonate, magnesium carbonate, calcium phosphate, talc, clay, diatomaceous earth, metal oxide powder, etc. are used. Each may be used alone or two or more may be used in combination.

Examples of the anionic surfactants include fatty acid salts such as sodium oleate and potassium castor oil; alkyl sulfate ester salts such as sodium lauryl sulfate and ammonium lauryl sulfate; alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate; alkylnaphthalenesulfonic acids. Salts; dialkyl sulfosuccinates; alkyl phosphate ester salts; naphthalene sulfonic acid formalin condensates; polyoxyethylene alkyl sulfate ester salts.

Examples of the cationic surfactants include alkylamine salts such as laurylamine acetate and stearylamine acetate; and quaternary ammonium salts such as lauryltrimethylammonium chloride and stearyltrimethylammonium chloride.

Examples of the zwitterionic surfactant include lauryltrimethylammonium chloride.

Examples of the nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, polyoxyethylene fatty acid ester,
Examples include sorbitan fatty acid ester, polyoxysorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin, fatty acid ester, and oxyethylene-oxybrobylene block polymer.

It is preferable to adjust the composition and amount of the dispersant as appropriate so that the aspect ratio of the obtained short fibrous polymer is within the range of 5 to 100. For example, as a dispersant, a water-soluble When using a polymer, the proportion is preferably 0.01 to 20% by weight, more preferably 0.1 to 10% by weight based on the polymerizable monomer. If the proportion of the water-soluble polymer is less than 0601% by weight, there is a risk that a stable dispersion state of the polymerizable monomer cannot be maintained, and if it exceeds 20% by weight, emulsion polymers will form as the polymerization reaction progresses. There is a risk that When using a surfactant as a dispersant, for the same reason, the proportion is preferably 0.01 to 10% by weight, and preferably 0.1 to 5% by weight, based on the polymerizable monomer. More preferred.

As shown in FIG. 1(a), the polymerizable monomer is dispersed in an aqueous medium 1 to form minute droplets 2, and is heated to a radical generation temperature of an oil-soluble polymerization initiator. By setting the temperature above, polymerization begins due to the action of radicals generated. The generated polymer is insoluble in the polymerizable monomer and the aqueous medium, and as shown in FIG. 1(b), short fibers are present in the droplets 2 of the polymerizable monomer. Polymer 3...
is precipitated. As the polymerization reaction progresses, the short fibrous polymers 3... elongate as shown in FIG. 1(C), and the polymerization reaction is completed. The short fibrous polymer 3 may partially protrude from the droplet 2 into the aqueous medium 1 and extend, but the overall length of the short fibrous polymer 3 is limited by the size of the droplet. be done.

In the conventional suspension polymerization method and emulsion polymerization method, when polymerization starts in droplets of polymerizable S-mer dispersed in a medium,
Since the generated polymer is dissolved in the monomer droplets, the viscosity of the droplets only increases as the polymerization progresses, and the polymer does not precipitate, and when the polymerization reaction is completed, the polymer particles are formed. . In contrast, in the present invention, a short fibrous (meth)acrylonitrile polymer is produced simultaneously with polymerization. Although the details are unknown, this is due to the fact that an aqueous medium is used as a dispersion medium, and preferably a dispersion stabilizer is used in addition to this, and as a result, the polymerizable monomer becomes minute droplets. Easily dispersed in the medium, the generated polymer precipitates without being dissolved in the polymerizable monomer and the aqueous medium, the size of the polymer is limited by the size of the microdroplets, etc. This is thought to be due to

After polymerization, the short fibrous (meth)acrylonitrile polymer can be taken out through a washing step and a drying step, if necessary. The short fibrous polymer thus obtained may be short or short depending on the type and amount of dispersant used, monomer composition, and stirring conditions. The ratio of the average major axis diameter to the average minor axis diameter (aspect ratio) of the a-fibers is within the range of, the minor axis diameter is 0.1 to 50 μm, and
The major axis diameter is 1 to 500n. However, the size and shape of the short fibrous (meth)acrylonitrile polymer used in the production method according to the present invention are not limited to those shown here.

In this invention, carbonization is performed, for example, as follows. When the resulting short fibrous (meth)acrylonitrile polymer is heated in a non-oxidizing atmosphere, at a temperature around 300°C, a thermal decomposition reaction generates hydrogen and other decomposition gases, resulting in a black body. . In addition to carbon atoms, such a low-temperature heat-denatured organic material still contains relatively large amounts of hydrogen, nitrogen, and other foreign atoms contained in the raw material organic material. When the heat treatment temperature is gradually increased, the foreign atoms are gradually released and their content decreases, reaching a carbon content of nearly 90% by weight at a temperature of around 800°C, and a carbon content of around 1200°C. shows a carbon content of nearly 95% by weight. In this way, fibers containing carbon or graphite as an essential component, ie, carbon fibers, are obtained.

In addition, by providing a gradual temperature rise rate and providing an oxidizing atmosphere at a low temperature during carbonization, charcoal s#a fibers that retain the shape of the starting short fibrous (meth)acrylonitrile polymer, for example, Minor axis diameter is 0.0
8-40. w, short fiber-like carbon fibers having a major axis diameter of 0.8 to 400n and an aspect ratio of 5 to 100 can be obtained.

In this invention, there are no particular restrictions on the conditions for carbonization, and for example, carbonization can be performed as described above. The carbon content of the carbon fiber of this invention and the carbon fiber obtained by the manufacturing method of this invention is not particularly determined.

The carbon fibers of the present invention and the carbon fibers obtained by the production method of the present invention retain the shape of the short fibrous (meth)acrylonitrile polymer that is the starting material, have a unique shape, and are excellent. It has properties such as mechanical performance, chemical resistance, heat resistance, and electrical conductivity. For this reason, various uses,
In particular, in a non-oxidizing atmosphere, it can be used as a filtering material for acids, alkalis, high-temperature gases, etc., plastic fillers, infrared ray emitters, conductivity imparting agents, electrical ribbons, and various other uses.

[For production]

A short fibrous (meth)acrylonitrile polymer having a minor axis diameter of 0.1 to 50n, a major axis diameter of 1 to 500x, and an aspect ratio of 5 to 100 has not been previously available. By carbonizing a short fibrous (meth)acrylonitrile polymer exhibiting such a size and shape, carbon fibers with a size and shape not previously seen can be obtained. Such carbon fibers can be used not only as coloring agents but also as conductivity imparting agents for plastics and the like.

When a polymerizable monomer containing (meth)acrylonitrile as an essential component and an oil-soluble polymerization initiator is dispersed in an aqueous medium to form minute droplets, the resulting polymer is Since it is difficult to dissolve in aqueous monomers and in an aqueous medium, it begins to precipitate in minute droplets, but because it is limited in size by the minute droplets, it becomes short fibrous. By carbonizing such a short fibrous polymer, short fibrous carbon fibers can be obtained.

〔Example〕

Specific examples and comparative examples of the present invention are shown below, but the present invention is not limited to the following examples. In addition, in the following, all "parts" are based on weight.

Example 1 - A solution prepared by dissolving 3 parts of polyvinyl alcohol (PVA-205, manufactured by Kuraray ■) in 897 parts of deionized water was charged into a flask equipped with a stirrer, an inert gas introduction tube, a reflux condenser, and a thermometer. is. A mixture of 1 part of lauroyl peroxide and a polymerizable monomer of 100 parts of acrylonitrile prepared in advance was charged into this mixture, and a mixture of 1 part of lauroyl peroxide and 1 part of a polymerizable monomer of acrylonitrile prepared in advance was charged, and 8
The mixture was stirred at 000 rpm for 5 minutes to form a homogeneous suspension. Then, while blowing nitrogen gas, it was heated to 70°C, stirred at this temperature for 6 hours, further heated to 80°C, and stirred at this temperature for 2 hours to perform a polymerization reaction, and then cooled and polymerized. A combined suspension was obtained.

After filtering and washing this polymer suspension, it is dried to produce a polymer suspension having a short axis diameter of 0.2 to 1jr@, a long axis diameter of 1 to 20n, and an aspect ratio of 5 to 20. Fibrous polyacrylonitrile was obtained.

FIG. 2 shows an electron micrograph (magnification: 10,000 times) of this short fibrous polyacrylonitrile.

In the photograph of FIG. 2, the white or gray elongated objects are short fibrous polyacrylonitrile.

10 g of this short fibrous polyacrylonitrile was
11. It was filled into an alumina porcelain boat with a total length of 15C11, and the boat was placed in a tubular silicon carbide furnace. Nitrogen gas passed through scorching copper powder for oxygen removal was fed into one end of the furnace, and exhausted from the other end, and the inside of the furnace was filled. The air was replaced with nitrogen. Thereafter, in a nitrogen stream, the temperature was increased to 600°C at a rate of 50°C per hour, and from 600°C to 80°C at a rate of increase of 100°C per hour.
It was heated to temperatures of 0°C and 1200°C and allowed to cool in a nitrogen stream to obtain short fibrous (non-spherical granular) carbon.

Table 1 shows the results of elemental analysis of the obtained carbon fibers. Third
The figure shows this carbon fiber scanning electron W! Microscopic photograph (magnification 10)
000 times). As shown in Figure 3, the carbon fibers (fibrous material in the photo) had the same shape as the short fibrous polymer before firing in Table 1. Example 2. Example 1. 10 g of short fibrous polyacrylonitrile obtained in the same manner as in Example 1 except that the carbonization of the short fibrous polyacrylonitrile was carried out as follows was carried out in the same manner as in Example 1. After filling a porcelain boat and leaving it at 200℃ for 10 hours, it was placed in a tubular silicon carbide furnace, and nitrogen gas passed through scorching copper powder for oxygen removal was fed into one end of the furnace, and exhausted from the other end. The air in the furnace was replaced with nitrogen. Thereafter, in a nitrogen stream, the temperature was increased to 500°C at a rate of 50°C per hour, and from 500°C to 80°C at a rate of increase of 100°C per hour.
It was heated to temperatures of 0°C and 1200°C and allowed to cool in a nitrogen stream to obtain short fibrous (non-spherical granular) carbon.

Table 2 shows the results of elemental analysis of the obtained carbon fibers. Fourth
The figure shows a scanning electron micrograph (magnification: 100) of this carbon fiber.
00 times). As shown in Figure 4, this carbon fiber (
The carbon fibers of this invention have a unique shape, especially small fibers, as seen in the results in Table 2 and above. It has excellent mechanical performance, chemical resistance,
It has poor heat resistance and electrical conductivity.

Furthermore, the carbon fiber manufacturing method of the present invention uses short fibrous polymers directly obtained by polymerization, so it is superior in terms of productivity and cost compared to conventional manufacturing methods.

〔Effect of the invention〕

Since the carbon fiber according to the invention of claim 1 is as described above, it retains the unique shape of the starting polymer, is smaller than conventional carbon fibers, and has mechanical strength. Excellent performance, chemical resistance, heat resistance and electrical conductivity. Therefore, the carbon fibers can be used for various purposes.

Since the method for producing carbon fiber according to the invention of claim 2 is as described above, the polymer used as a raw material can be obtained in the form of short fibers at the same time as polymerization, resulting in high productivity and low cost. . The resulting carbon fibers can be smaller than conventional ones.

[Brief explanation of drawings]

FIGS. 1(a) to (C1 are explanatory diagrams schematically showing the manufacturing process of a short fibrous (meth)acrylonitrile polymer;
The figure is a scanning electron micrograph (magnification: 1o) showing the shape of the fibers.
ooo times), and the fibrous material in the same photograph is an example of a short fibrous (meth)acrylonitrile polymer used in the production method according to the present invention, and FIG. 3 is a scan showing the shape of the fiber. This is an electron micrograph (magnification: 10,000 times), and the fibrous material in the photograph is an example of carbon fiber obtained by the manufacturing method according to the present invention. Figure 4 is a scan showing the shape of the fiber. Electronic W4 mirror photograph (10,000x magnification)
The fibrous material in the same photograph is another example of carbon fiber obtained by the manufacturing method according to the present invention. 1...Aqueous medium 2...Minute droplets 3...Short fibrous polymer Figure 1 Agent Patent attorney Takehiko Matsumoto Figure 4

Claims (1)

[Claims] 1. Short axis diameter 0.1 to 50 μm, long axis diameter 1 to 500 μm,
and short fibrous (meta) with an aspect ratio of 5 to 100.
Carbon fiber obtained by carbonizing acrylonitrile polymer. 2. In carbonizing a (meth)acrylonitrile polymer to obtain carbon fibers, as the (meth)acrylonitrile polymer, a polymerizable monomer containing (meth)acrylonitrile as an essential component and an oil-soluble polymerization initiator, A method for producing carbon fibers, which comprises using a short fibrous polymer that is polymerized in a dispersed state to form minute droplets in an aqueous medium.