JPH05195324A - Precursor for carbon fiber production and method for producing the precursor - Google Patents

Abstract

PURPOSE:To obtain the subject precursor capable of modifying the fine structure of carbon fiber without using any fine particles by spinning a mixture of cellulose (derivative), polyvinyl alcohol, ABS resin, etc., with polyacrylonitrile-based polymer. CONSTITUTION:The objective precursor can be obtained by spinning a mixture of (A) cellulose (derivative), polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl chloride, polyvinylidene chloride, polybutadiene, ABS resin, AS resin, AB resin, phenol resin and/or furan resin with (B) a polyacrylonitrile-based polymer.

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.
Widely used in aerospace applications, leisure applications, general industrial applications, etc. However, the performance is not sufficient for some applications, and the demand for the development of high-performance carbon fibers having high mechanical properties such as strength and elastic modulus is increasing day by day. Furthermore, not only tensile properties but also compressive strength are being strongly demanded.

Therefore, a technique of mixing different kinds of compounds in the form of fine particles into the carbon fiber for the purpose of imparting functionality (Japanese Patent Publication No. 61-58404, JP-A-2-2516).
No. 15, gazette and Japanese Patent Application No. 3-34664) have been proposed.

[0004]

However, in the above-described carbon fibers containing fine particles, the fine particles act as foreign matters, which not only makes the yarn-making process difficult but also causes a decrease in mechanical properties such as tensile strength. .. Further, as one means for improving the compressive strength, it is known that it is effective to reduce the size of the graphite crystals constituting the carbon fiber to increase the shear strength between the graphite crystals or the transverse strength. However, when fine particles containing a metal element are mixed, there is a case where the crystal grows conversely due to the catalytic graphitization action, which is disadvantageous to the compressive strength.

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

[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, one or more selected from the group consisting of cellulose or a derivative thereof, polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl chloride, polyvinylidene chloride, polybutadiene, ABS resin, AS resin, AB resin, phenol resin, furan resin, or A precursor for carbon fiber production, which comprises a mixture of two or more kinds and a polyacrylonitrile polymer.

The method for producing a precursor for producing carbon fiber of the present invention has the following constitution in order to solve the above problems. That is, one or more selected from the group consisting of cellulose or a derivative thereof, polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl chloride, polyvinylidene chloride, polybutadiene, ABS resin, AS resin, AB resin, phenol resin, furan resin, or A method for producing a precursor for producing carbon fiber, which comprises mixing two or more kinds and a polyacrylonitrile-based polymer and spinning the mixture.

That is, the precursor for producing carbon fiber of the present invention comprises cellulose or its derivative, polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl chloride, polyvinylidene chloride, polybutadiene, ABS resin, AS resin, AB resin, phenol resin, Since it is composed of a mixture of one or more selected from the group consisting of furan resin and a polyacrylonitrile polymer, it is possible to control the fine structure of the finally obtained carbon fiber without mixing fine particles. ..

In other words, in the case of mixing fine particles, there are cases where the strength is decreased due to the mixing and the fine structure of carbon fiber cannot be controlled at the molecular level, but by mixing the above-mentioned polymer, such a problem occurs. Not only that, but the above-mentioned polymer is a so-called non-graphitizable polymer than a polyacrylonitrile-based polymer, therefore, by firing the growth of graphite crystals than when using a precursor consisting of a polyacrylonitrile-based polymer alone It became clear that it could be suppressed.

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.

Examples of the polymerizable unsaturated monomer include unsaturated carboxylic acids or their alkali metal salts, ammonium salts, alkyl esters, acrylamide, methacrylamide or their derivatives, or allylsulfonic acid, methallylsulfonic acid or Examples thereof include salts and alkyl esters.

Of these, unsaturated carboxylic acids are preferred because they promote the flameproofing reaction. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid,
Examples thereof include 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.

As the polymer to be mixed with the polyacrylonitrile polymer, cellulose or its derivative, polyvinyl alcohol, polyvinyl acetate,
Polyvinyl acetal, polyvinyl chloride, polyvinylidene chloride, polybutadiene, ABS resin, AS resin, AB
One or more selected from the group consisting of resin, phenol resin and furan resin are used.

Examples of cellulose or its derivative include cellulose acetate, nitrocellulose, carboxymethyl cellulose and the like. Examples of polyvinyl acetal include polyvinyl butyral and polyvinyl formal. Examples of the phenol resin include novolac type phenol resin. However, when the yield of the polymer to be mixed with the polyacrylonitrile-based polymer is low at the time of firing, not only the effect of modifying the carbon fiber obtained is small, but also the occurrence of voids increases and only carbon fiber with low physical properties is obtained. 60% of the polymer that should be mixed with the polyacrylonitrile-based polymer
The yield at 0 ° C is preferably 5% or more, more preferably 10% or more, still more preferably 20% or more. here,
The yield at 600 ° C. reached 600 ° C. when measured with a differential thermobalance (TG-DTA) standard type CN8078B1 manufactured by Rigaku Denki Co., Ltd. at a temperature rising rate of 20 ° C./min and a nitrogen flow rate of 30 ml / min. The weight retention ratio with respect to the sample weight before measurement.

If the ratio of the polymer to be mixed with the polyacrylonitrile-based polymer in the precursor (hereinafter, mixing ratio) is less than 1%, the effect of modifying the obtained carbon fiber is small, and the mixing ratio is 99%. If it exceeds, the characteristics of the polyacrylonitrile polymer will be lost, so the mixing ratio is preferably 1 to 99%, more preferably 5 to 95%, and further preferably 10 to 90%.

In the present invention, the polyacrylonitrile polymer and the above-mentioned other polymers are mixed, but the mixing method may be pre-mixing with a homomixer or the like to prepare the spinning dope. The respective polymers or their solutions may be mixed with 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 non-compatible state in a continuous phase or in a dispersed state in the form of discontinuous particles.

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 polymer. You can place it.

The polymer mixture obtained as described above can be used as a precursor for carbon fiber production by a known method. The spinning method is a wet spinning method of spinning directly into a coagulating bath, a dry-wet spinning method of spinning into air and then solidifying in a bath, a dry spinning method, or a melt spinning method. In the case of wet or dry-wet spinning, it is preferable to carry out bath drawing, but in the bath drawing, the spun yarn may be directly subjected to bath drawing, or may be subjected to bath drawing after washing with water to remove the solvent and the plasticizer. Good.
The conditions for bath stretching are usually about 2 in a stretching bath at 50 to 98 ° C.
~ 6 times stretched. The yarn after bath drawing is dried and densified by drying with a hot drum or the like. The drying temperature, time, etc. can be appropriately selected. Also,
If necessary, the dried and densified yarn is also subjected to pressure steam drawing, 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. The solvent of the polymer to be mixed with the solvent of the polyacrylonitrile polymer is preferably the same, but the solvent is not limited thereto, and it is possible to use a plurality of solvents.

The precursor for producing carbon fibers thus obtained is composed of a mixture of a polyacrylonitrile polymer and other polymers in a state of being uniformly mixed or non-uniformly finely dispersed. From the viewpoint of the uniformity of the precursor, it is preferable that the mixed state is uniform or that the period in which the same phase in the finely dispersed state appears is smaller than the single fiber diameter. In order to enhance compatibility with polyacrylonitrile-based polymer and to mix them at the molecular level to form fibers, the polymer to be mixed with polyacrylonitrile-based polymer must be modified beforehand by a method such as copolymerization or chemical modification. It is also possible to further mix a compatibilizer composed of a block copolymer or a graft copolymer of a monomer constituting the polymer other than the polyacrylonitrile-based polymer and an acrylonitrile monomer. Insufficient uniformity of the precursor may cause uneven firing behavior, which may cause fluffing.

By further firing such a precursor, a high performance carbon fiber can be obtained. As a flameproofing condition, a conventionally known method can be adopted, and it is preferably used to perform heat treatment under tension or stretching conditions in an oxidizing atmosphere at 200 to 300 ° C. Further, depending on the kind of the polymer to be mixed, it is also possible to separately carry out an oxidation treatment in a liquid phase or a gas phase suitable for the polymer to make the polymer infusible or to 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 gas atmosphere by a conventionally known method through a flameproofing step or an infusibilizing step. The carbonization temperature at that time is 10 from the viewpoint of making the physical properties of the obtained carbon fiber excellent.
It is preferably 00 ° C or higher. Further, depending on the type of polymer to be mixed, lowering the temperature raising rate may improve yield and denseness. Therefore, the temperature raising rate at 300 to 1200 ° C. is preferably 500 ° C./min or less, The temperature is preferably 100 ° C./min or less, more preferably 50 ° C./min or less. Further, if necessary, a graphitization treatment, a surface treatment, a sizing, etc. can be 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 R 7601.

[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) Polyvinyl butyral having a degree of butylation of 55% was treated with dimethyl sulfoxide (hereinafter referred to as D).
MSO) to give a 20 wt% solution. Also, DMS
A polyacrylonitrile polymer obtained by copolymerizing 1 mol% of methacrylic acid in O was dissolved to prepare a 20 wt% solution. These two kinds of solutions were mixed using a homomixer so that polyvinyl butyral would be 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.
% DMSO in water. 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. 0 kgf / cm
Stretched 4.0 times with pressurized steam of ² to obtain single fiber fineness of 1.
A fiber bundle having 0d and a total fineness of 3000D was obtained.

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 1.35. 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
Tensile elastic modulus is 54 × 10 ³ kgf / mm ² , tensile strength is 500
It had a high strength and a high elastic modulus of kgf / mm ² . The single fiber compressive strength was 480 kgf / mm ² and the crystal size Lc was 45 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. However, the tensile modulus is 54 ×
10 ³ kgf / mm ^2, the tensile strength was the 500 kgf / mm ^2, single fiber compressive strength as low as 400 kgf / mm ^2, the crystal size Lc is crystalline than graphitized fibers were mixed 50 Angstroms and polyvinyl butyral It was a little advanced.

Example 2 Cellulose acetate having a degree of acetylation of 53% was dissolved in DMSO to prepare a 20 wt% solution. Further, a polyacrylonitrile polymer obtained by copolymerizing 1 mol% of itaconic acid was dissolved in DMSO to prepare a 20 wt% solution. The two types of solutions were mixed using a homomixer so that cellulose acetate was 20 wt% with respect to the entire polymer, and defoamed under reduced pressure for 3 hours.

The resulting polymer solution was spun into fibers in the same manner as in Example 1 to obtain a fiber bundle having a single fiber fineness of 1.0 d and a total fineness of 3000 D. This precursor was heated in air at 240 to 280 ° C. at a draw ratio of 1.05 to convert it into a flame resistant yarn having a density of 1.37, and then carbonized in a nitrogen atmosphere at 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 have a tensile modulus of 55 × 10 ³ kgf / mm ² and a tensile strength of 500 kg.
It had a high strength and a high elastic modulus of f / mm ² and a single fiber compressive strength of 550 kgf / mm ² . The crystal size Lc was 43 Å.

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

[0038]

By using the precursor obtained according to the present invention, the fine structure of carbon fiber can be controlled without impairing the strength, and especially the growth of graphite crystals can be suppressed, so that high compressive strength and high strength and high elasticity can be obtained. Of high performance carbon fiber can be produced.

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Claims (2)

[Claims] 1. A material selected from the group consisting of cellulose or its derivatives, polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl chloride, polyvinylidene chloride, polybutadiene, ABS resin, AS resin, AB resin, phenol resin, and furan resin. A precursor for carbon fiber production, which comprises a mixture of one or more kinds and a polyacrylonitrile polymer. 2. A material selected from the group consisting of cellulose or its derivatives, polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl chloride, polyvinylidene chloride, polybutadiene, ABS resin, AS resin, AB resin, phenol resin and furan resin. A method for producing a precursor for producing carbon fiber, which comprises mixing one or more kinds and a polyacrylonitrile polymer and spinning the mixture.