JPH05295616A - Precursor for production of carbon fiber and its production - Google Patents

Abstract

PURPOSE:To provide a precursor capable of producing a carbon fiber exhibiting a high strength, a high elasticity and a high compression strength. CONSTITUTION:This invented precursor for producing a carbon fiber is composed of a mixture of one or two or more kinds of substances selected from a polyimide, a polyamide-imide, a polybenzobisoxazole, a polybenzoxazole, a polyoxadiazole, a polybenzobisthiazole, a polybenzothiazole, a polybenzobisimidazole, a polybenzoimidazole, a polyphenylene vinylene and their precursors with a polyacrylonitrile-based polymer. The method for producing the recursor is another invention in this patent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precursor for producing carbon fiber and a method for producing the same.

[0002]

2. Description of the Related Art Carbon fiber has excellent mechanical properties, particularly high specific strength and high specific elastic modulus.
It has come to be widely used for aerospace applications, leisure applications, and general industrial applications. However, the performance is not sufficient for some applications, and the demand for the development of high-performance carbon fibers having higher strength and elastic modulus is increasing day by day. Further, not only tensile properties but also compressive strength are being strongly demanded.

Therefore, a technique for mixing fine particles with carbon fibers for the purpose of imparting functionality (Japanese Patent Publication No. 61-58404, Japanese Patent Application Laid-Open No. 2-251615, Japanese Patent Application No. 3-346).
No. 64) has been proposed.

[0004]

However, in the above-mentioned carbon fiber containing fine particles, the fine particles act as foreign matter, which not only causes difficulty in the yarn making process but also causes deterioration of mechanical properties such as tensile strength. ..

That is, an object of the present invention is to provide a precursor for producing carbon fiber and a method for producing the same, which can modify the fine structure of carbon fiber without using fine particles.

[0006]

In order to solve the above-mentioned problems, the precursor for producing carbon fiber of the present invention has the following constitution. That is, from the group consisting of polyimide, polyamideimide, polybenzobisoxazole, polybenzoxazole, polyoxadiazole, polybenzobisthiazole, polybenzothiazole, polybenzobisimidazole, polybenzimidazole, polyphenylenevinylene and precursors thereof. A precursor for carbon fiber production, comprising a mixture of one or more selected types and a polyacrylonitrile polymer.

The method for producing a precursor for producing carbon fiber has the following constitution in order to solve the above problems. That is, from the group consisting of polyimide, polyamideimide, polybenzobisoxazole, polybenzoxazole, polyoxadiazole, polybenzobisthiazole, polybenzothiazole, polybenzobisimidazole, polybenzimidazole, polyphenylenevinylene and precursors thereof. A method for producing a precursor for producing carbon fiber, which comprises mixing one or more selected types and a polyacrylonitrile polymer and spinning the mixture.

That is, the precursor for producing carbon fibers of the present invention is a polyimide, polyamideimide, polybenzobisoxazole, polybenzoxazole, polyoxadiazole, polybenzobisthiazole, polybenzothiazole, polybenzobisimidazole, polybenzo Since it is a mixture of one or more kinds selected from the group consisting of imidazole, polyphenylene vinylene and precursors thereof and a polyacrylonitrile polymer, the carbon fiber finally obtained can be obtained without mixing fine particles. The fine structure can be controlled.

In the present invention, the polyacrylonitrile polymer is 85% or more of acrylonitrile and 15% or less of a polymerizable unsaturated monomer copolymerizable with acrylonitrile, from the viewpoint of improving the physical properties and yield of the obtained carbon fiber. It is preferably a polymer containing. As the polymerizable unsaturated monomer, unsaturated carboxylic acids or their alkali metal salts, ammonium salts, alkyl esters, acrylamide, methacrylamide or their derivatives or allylsulfonic acid, methallylsulfonic acid or their salts, Examples thereof include alkyl esters.

Of these, unsaturated carboxylic acids are preferred because they promote the flameproofing reaction. Specific examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid and mesaconic acid.

As a method for polymerizing the polyacrylonitrile polymer, conventionally known methods such as suspension polymerization, solution polymerization and emulsion polymerization can be adopted.

The polymer or polymer precursor to be mixed with the polyacrylonitrile polymer is polyimide, polyamideimide, polybenzobisoxazole, polybenzoxazole, polyoxadiazole, polybenzobisthiazole, polybenzothiazole. At least one selected from the group consisting of polybenzobisimidazole, polybenzimidazole, polyphenylenevinylene and precursors thereof is used. Of these, graphitizable polymers such as polyimide, polybenzobisoxazole, polyoxadiazole, polybenzobisthiazole, polybenzobisimidazole, and polyphenylenevinylene are preferable.

Specific examples of the graphitizable polymer include poly (4,4'-diphenyletherpyromellitimide) and poly (paraphenylenebenzobisoxazole).
Etc. can be mentioned.

However, if the yield of the polymer or precursor mixed with the polyacrylonitrile-based polymer is low after firing, not only the effect of modifying the resulting carbon fiber is small, but also many voids are generated and carbon fiber has low physical properties. The yield of the polymer or precursor mixed with the polyacrylonitrile-based polymer at 600 ° C. is preferably 5% or more, more preferably 10% or more, still more preferably 20% or more, because the yield may not be obtained. Here, the yield at 600 ° C. means
After treating the polymer or precursor in air at 240 ° C. for 2 hours, using a differential thermal balance (TG-DTA) standard type CN8078B1 manufactured by Rigaku Denki Co., at a temperature rising rate of 20 ° C./min and a nitrogen flow rate of 30 ml / min. When measured, it refers to the weight retention ratio with respect to the sample weight before measurement when reaching 600 ° C.

If the ratio of the polymer or precursor to be mixed with the polyacrylonitrile polymer in the precursor (hereinafter referred to as the mixing ratio) is less than 1%, the resulting modifying effect is small, and therefore the mixing ratio is 1%. 5% or more is preferable
The above is more preferable, and 10% or more is further preferable.

In the present invention, the polyacrylonitrile-based polymer is mixed with the above-mentioned other polymer or precursor, and the mixing method is to prepare a spinning dope by premixing with a homomixer or the like. Alternatively, each polymer or precursor or a solution thereof may be mixed by a static mixer or the like immediately before spinning. Further, the mixed polymers may be completely compatible with each other, or may be present in a state of being dispersed in an incompatible state.

It is also possible to arrange them in a core-sheath shape, a bimetal shape, or a sea-island shape by composite spinning of the mixed polymer as described above and a polyacrylonitrile-based polymer. You can place it.

The polymer mixture obtained as described above can be used as a precursor by a known method. The spinning method may be a wet spinning method of spinning directly into a coagulation bath, a dry-wet spinning method or a dry spinning method of once spinning into air and then solidifying in a bath, or melt spinning. In the case of the spinning method using a solvent and a plasticizer, the spun yarn may be drawn directly in the bath, or may be washed in water to remove the solvent and the plasticizer and then drawn in the bath. The stretching condition in the bath is usually 50.
It is stretched about 2 to 6 times in a stretching bath at -98 ° C. Dry densification is achieved by drying the yarn after drawing in the bath with a hot drum or the like. The drying temperature, time, etc. can be appropriately selected. If necessary, the dried and densified yarn is also stretched at a higher temperature (for example, in pressure steam), whereby a precursor having a predetermined fineness and orientation can be obtained.

As the solvent in the solution spinning, known organic and inorganic solvents can be used. It is desirable that the solvent of the polyacrylonitrile-based polymer and the other polymer are the same, but the solvent is not limited thereto, and a plurality of solvents may be finally mixed and used. Also,
In the case of a polymer such as polyimide or polybenzobisthiazole, which is difficult to be dissolved in an ordinary solvent and is difficult to be melted, it is also possible to convert the polymer into a desired polymer after fibrating it with a precursor thereof.

When a spinning solution containing a polyamic acid, which is a precursor of polyimide, is spun into a spinning solvent / water-based coagulation bath, the coagulated yarn is devitrified and voids are formed to give a precursor having low compactness. Therefore, it is preferable that the polyamic acid is partially imide-cyclized beforehand. For partial ring closure, a chemical means such as acetic anhydride or a heating means is used. Further, the proportion of imide ring closure is preferably 1 to 90%, more preferably 5 to 50% from the viewpoint of sufficient devitrification prevention effect while preventing a decrease in solubility.

The carbon fiber-producing precursor thus obtained is composed of a mixture of a polymer other than the polyacrylonitrile-based polymer in a state of being uniformly mixed or non-uniformly finely dispersed with the polyacrylonitrile-based polymer. From the viewpoint of the uniformity of the precursor, it is preferable that the mixed state is uniform or the period in which the same phase in the finely dispersed state appears is smaller than the single fiber diameter, and the compatibility with the polyacrylonitrile-based polymer is controlled. Therefore, the polymer or precursor to be mixed with the above polyacrylonitrile-based polymer, it is also possible to previously modified by a method such as copolymerization, chemical modification, etc., also, a polymer other than the polyacrylonitrile-based polymer It is also possible to further mix a compatibilizer composed of a block copolymer or a graft copolymer of the constituent monomers and an acrylonitrile monomer. Insufficient uniformity of the precursor may cause uneven firing behavior, which may cause fluffing.

By firing such a precursor, a high performance carbon fiber can be obtained. As the flameproofing condition, a conventionally known method can be adopted, and tension or stretching conditions are preferably used in the range of 200 to 300 ° C. in an oxidizing atmosphere. In addition, depending on the type of polymer to be mixed, chemical treatment may be performed in a liquid phase or a gas phase to make the polymer infusible or improve the carbonization yield.

The precursor obtained in the present invention is
A carbon fiber can be obtained by performing a carbonization treatment in an inert atmosphere by a conventionally known method through a flameproofing step or an infusibilizing step. The carbonization temperature at that time is 100 from the viewpoint of making the physical properties of the obtained carbon fiber excellent.
It is preferably 0 ° C. or higher, and particularly preferably graphitized at 2000 ° C. or higher. In addition, depending on the type of polymer or precursor mixed with the polyacrylonitrile-based polymer, a slow heating rate may be preferable from the viewpoint of yield and denseness of the finally obtained carbon fiber, and thus 300 to
The rate of temperature increase at 1200 ° C. is preferably 500 ° C./min or less, more preferably 100 ° C./min or less, still more preferably 50 ° C./min or less. Then, if necessary, surface treatment, sizing, and the like can be further performed by a conventionally known technique.

[0024]

The present invention will be described in more detail with reference to the following examples. In the present invention, the tensile strength and the single fiber compressive strength were obtained by the resin-impregnated strand method and the loop method, respectively.

[Tensile Strength] "Bakelite" ERL-4
221 (registered trademark, Union Carbide Co., Ltd.) /
Boron trifluoride monoethylamine (BF ₃ · MEA) /
The carbon fiber was impregnated with acetone = 100/3/4 parts, and the obtained resin-impregnated strand was heated at 130 ° C. for 30 minutes to be cured, and measured according to the resin-impregnated strand test method defined in JIS R7601.

[Single Fiber Compressive Strength] A single fiber of 10 cm is placed on a slide glass, 1 to 2 drops of glycerin is dropped in the central portion to form a loop while twisting the single fiber, and a cover glass is placed thereon. Tensile strain is applied at a constant speed while pressing both ends of the loop with fingers, and the minor axis D and major axis Φ of the loop until it breaks are measured. From single fiber diameter d and D, ε = 1.0
The strain ε obtained by 7 × (d / D) is calculated and plotted on a graph with ε as the horizontal axis and the ratio Φ / D of the major axis and the minor axis as the vertical axis.

The value of strain ε at which Φ / D started to increase suddenly from a constant value (about 1.3) was measured as the compressive yield strain for 10 single fibers, and the average value was obtained. The obtained average value was multiplied by the tensile modulus obtained in the above-mentioned strand tensile test to obtain the single fiber compressive strength.

[Crystal Size (Lc)] As an X-ray source, N
Using the Kα line of Cu monochromated by the i filter, 2θ
The half width of the peak of the surface index (002) observed in the vicinity of = 26.0 ° was scanned from the peak obtained by scanning in the equatorial direction, and calculated by Lc = λ / (β ₀ cos θ). Here, β ₀ is the true half width obtained from β ₀ ² = β _e ² −β _l ² , λ is the wavelength of the X-ray [1.5418 Å], θ is the diffraction angle, and β _e is the apparent half. Price range, β
_l is a device constant (1.05 × 1 in the case of the device used in the present invention [4036A2 type X-ray generator manufactured by Rigaku Denki Co., Ltd.]
0 ^-2 rad).

Example 1 Pyromellitic dianhydride and 4,
Polyamic acid, which is a polyimide precursor obtained by condensation with 4'-diaminodiphenyl ether, was dissolved in dimethyl sulfoxide to prepare a 10 wt% solution. In addition, 1 mol% of methacrylic acid was also used in dimethyl sulfoxide.
Polymerization of copolymerized polyacrylonitrile polymer 2
It was a 0 wt% solution. These two kinds of solutions were mixed using a homomixer so that the polyamic acid was 10 wt% with respect to the whole polymer, and defoamed under reduced pressure for 3 hours.

The resulting polymer solution was once discharged into the air through a spinneret having a hole diameter of 0.10 mm and a number of holes of 3000, and was run in a space of about 5 mm, then at a temperature of 10 ° C. and a concentration of 35.
% Aqueous dimethylsulfoxide solution. After washing the coagulated yarn with water and stretching it 3.0 times in a three-stage drawing bath to apply a silicon-based oil agent, it is brought into contact with the roller surface heated to 130 to 170 ° C. to densify it, and further 4. It was stretched 4.0 times with a pressure steam of 0 kgf / cm ² to obtain a fiber bundle having a single fiber fineness of 1.0 d and a total fineness of 3000 D.

The obtained precursor is 240 to 280 ° C.
Was heated in the air at a draw ratio of 1.05 to obtain a flame-resistant yarn having a density of 1.39. Then, carbonization was performed in a nitrogen atmosphere having a maximum temperature of 1700 ° C. to obtain carbon fibers. Further, the obtained carbon fiber was fired at a draw ratio of 1.05 in a nitrogen atmosphere at 2600 ° C. to obtain a graphitized fiber.

The strand characteristics of the obtained graphitized fiber are
The tensile elastic modulus was 63 × 10 ³ kgf / mm ^2, which was a high elastic modulus, and the tensile strength was 500 kgf / mm ² , which was a high strength and a high elastic modulus.
The single fiber compressive strength was 390 kgf / mm ² . The crystal size Lc was 55 Å.

(Comparative Example 1) Spinning and firing were carried out in the same manner as in Example 1 except that a polymer solution consisting only of a polyacrylonitrile polymer obtained by copolymerizing 1 mol% of methacrylic acid was used in Example 1. The tensile strength of the obtained graphitized fiber was as high as 500 kgf / mm ² , but the tensile modulus was 54 × 10 ³ kgf / mm ² . The single fiber compressive strength was 400 kgf / mm ² . The crystal size Lc was 50 Å.

(Example 2) 2,5-diamino-1,4-
A polybenzobisthiazole precursor obtained by condensing bisisopropylthiobenzene and terephthalic acid dichloride in polyphosphoric acid was dissolved in N-methylpyrrolidone to obtain 10 wt%.
It was a solution. Similarly, a polyacrylonitrile polymer obtained by copolymerizing 1 mol% of itaconic acid in N-methylpyrrolidone was polymerized to obtain a 20 wt% solution. The two kinds of solutions were mixed using a homomixer so that the polybenzobisthiazole precursor was 20 wt% with respect to the whole polymer,
Degassed under reduced pressure for 3 hours.

The polymer solution thus obtained was once discharged into the air through a spinneret having a hole diameter of 0.10 mm and a number of holes of 3000, and was run in a space of about 5 mm, then at a temperature of 10 ° C. and a concentration of 35.
% N-methylpyrrolidone aqueous solution. After washing the coagulated yarn with water and stretching it 3.0 times in a three-stage stretching bath to apply a silicon-based oil agent, it is brought into contact with the roller surface heated to 130 to 170 ° C. to be dried and densified, and further 4.
It was stretched 4.0 times with a pressure steam of 0 kgf / cm ² to obtain a fiber bundle having a single fiber fineness of 1.0 d and a total fineness of 3000 D.

The obtained precursor is 240 to 280 ° C.
In air, it was heated at a draw ratio of 1.05 to obtain a flame-resistant yarn having a density of 1.37. Then, carbonization was performed in a nitrogen atmosphere having a maximum temperature of 1700 ° C. to obtain carbon fibers. Further, the obtained carbon fiber was fired at a draw ratio of 1.05 in a nitrogen atmosphere at 2600 ° C. to obtain a graphitized fiber.

The strand characteristics of the graphitized fiber obtained are
Tensile elastic modulus 65 × 10 ³ kgf / mm ² , tensile strength 500k
The gf / mm ² and single fiber compressive strength were 420 kgf / mm ² .
The crystal size Lc was 60 Å.

(Comparative Example 2) A yarn was prepared and fired in the same manner as in Example 2 except that a polymer solution consisting only of a polyacrylonitrile polymer obtained by copolymerizing 1 mol% of itaconic acid was used. , Tensile strength is 500kgf / mm
^2, tensile modulus is ^{56 × 10 3 kgf / mm 2} , single fiber compressive strength of 430kgf / mm ^2. The crystal size Lc was 49 Å.

Example 3 Pyromellitic dianhydride and 4,
To a polyamic acid obtained by condensation with 4'-diaminodiphenyl ether, a pyridine solution containing 0.25 equivalent of acetic anhydride as an amic acid unit was added dropwise, and the mixture was stirred at room temperature for 4 hours.
After stirring for a period of time, the imide ring was partially closed. The ratio of partial ring closure was 23%.

This partially ring-closed polyamic acid was isolated and dissolved in dimethyl sulfoxide to prepare a 10 wt% solution.

Separately, a polyacrylonitrile polymer obtained by copolymerizing 1 mol% of methacrylic acid in dimethyl sulfoxide was polymerized to prepare a 20 wt% solution.

These two kinds of solutions were mixed using a homomixer so that the polyamic acid partially imide ring-closed was 10 wt% with respect to the whole polymer, and defoamed under reduced pressure for 3 hours.

When the obtained polymer solution was spun and fired in the same manner as in Example 1, the strand characteristics of the graphitized fiber obtained were as follows: high tensile elasticity of 65 × 10 ³ kgf / mm ^2. The tensile strength was as high as 530 kgf / mm ² . The crystal size Lc was 55 Å.

[0044]

By using the precursor obtained according to the present invention, the fine structure of the carbon fiber can be controlled without impairing the strength, and the carbon fiber having high strength, high elastic modulus and high compressive strength can be produced. You can

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Claims (4)

[Claims] 1. From polyimide, polyamideimide, polybenzobisoxazole, polybenzoxazole, polyoxadiazole, polybenzobisthiazole, polybenzothiazole, polybenzobisimidazole, polybenzimidazole, polyphenylenevinylene and their precursors. A precursor for carbon fiber production, comprising a mixture of one or more selected from the group consisting of a polyacrylonitrile polymer. 2. The precursor for producing carbon fiber according to claim 1, wherein the polyimide precursor is a polyamic acid in which imide is partially ring-closed. 3. Polyimide, polyamideimide, polybenzobisoxazole, polybenzoxazole, polyoxadiazole, polybenzobisthiazole, polybenzothiazole, polybenzobisimidazole, polybenzimidazole, polyphenylenevinylene and precursors thereof. A method for producing a precursor for producing carbon fiber, which comprises mixing one or more selected from the group consisting of a polyacrylonitrile polymer and spinning the mixture. 4. The method for producing a precursor for producing carbon fiber according to claim 3, wherein the polyimide precursor is a polyamic acid in which an imide ring is partially closed.