JP2869085B2 - Precursor for carbon fiber production - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a precursor for producing carbon fiber, particularly carbon having high quality and high performance even when shortening the oxidization resistance time or increasing the single fiber fineness. The present invention relates to a precursor for producing carbon fibers from which fibers can be obtained.

[Prior art] A method for producing carbon fiber from an acrylic fiber is widely known. First, in an air or other oxidizing gas atmosphere, there is provided a flame-resistant fiber which has been flame-resistant at 200 to 300 ° C. Next, this is treated in an atmosphere of an inert gas such as nitrogen, argon, etc.
Manufactured by carbonization at 0-2000 ° C. Also 2000 ° C
Graphitization is carried out in the above inert gas atmosphere to produce graphite fibers having an even higher elastic modulus.

The above-mentioned flame-proofing step involves heat generation by oxidation and cyclization,
It is necessary to carry out the reaction while controlling the reaction sufficiently. In addition, in order to obtain carbon fibers having high physical properties, it is necessary to sufficiently diffuse oxygen necessary for the oxidation reaction into the inside of the single yarn, but this takes a long time. Its share in manufacturing costs is high.

Therefore, in order to shorten the flame resistance time, hot air is sprayed on the precursor fiber, and for example, Japanese Patent Publication No. 53-21396 discloses a method of intermittently contacting the surface of a heated solid. No. -190301 discloses a method of achieving flame resistance in a fluidized heating heat medium. Each of these methods is a technique of efficiently removing heat of oxidation reaction and performing high-temperature treatment while suppressing runaway reaction.

[Problems to be Solved by the Present Invention] However, according to the above method, although the oxidization time is simply shortened, the physical properties of the obtained carbon fiber are significantly reduced. For example, in order to obtain a certain elastic modulus, it was necessary to increase the carbonization temperature. Then, the present inventors examined the oxygen concentration distribution in the cross-sectional direction of the oxidized single yarn, and as a result of firing the oxidized yarn having a more uniform oxygen concentration distribution, it was possible to obtain carbon fibers having extremely high physical properties. The present inventors have also found that a decrease in the physical properties can be extremely reduced by maintaining this uniformity even when the flame resistance time is shortened or the single fiber fineness is increased, and the present invention has been accomplished.

In addition, the present inventors have studied the hydrogen concentration distribution in the cross-sectional direction of the oxidized yarn single yarn, the oxidized yarn having a low hydrogen concentration inside the single yarn has a small difference in inner and outer structures, and when the oxidized yarn is fired, It has been found that carbon fibers having extremely high physical properties can be obtained, and furthermore, the reduction in the physical properties can be extremely reduced if this condition is satisfied even when the flame resistance time is shortened or when the single fiber fineness is increased. It is a thing.

That is, an object of the present invention is to efficiently produce high-quality, high-performance carbon fibers.

[Means for Solving the Problems] The object of the present invention is to provide at least 85% of acrylonitrile, normal propyl ester, normal butyl ester, isobutyl ester, secondary butyl ester of acrylic acid or methacrylic acid, and alkyl having 5 or more carbon atoms. At least one polymerizable unsaturated carboxylic acid acrylic ester selected from the group consisting of
And a copolymer consisting of at least one polymerizable unsaturated carboxylic acid selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid in an amount of 0.25 to 5%, and
The oxygen concentration ratio of the inner and outer layer of the single yarn obtained by secondary ion mass spectrometry (SIMS) after oxidizing at 260 ° C for 5 minutes and at 280 ° C for 5 minutes in air at normal pressure is 6 or less And a precursor for producing carbon fiber.

Here, "in air" means that the atmosphere used for the flame resistance reaction is air, and includes a method of heating in a fluidized heating heat medium.

That is, in the precursor for carbon fiber production of the present invention (hereinafter simply referred to as “precursor”), the single yarn determined by SIMS after flame resistance at 260 ° C. for 5 minutes and further at 280 ° C. for 5 minutes in air at normal pressure. The inner / outer layer oxygen concentration ratio is determined by the following equation using O / C by SIMS which is obtained by arranging single yarns of the obtained oxidized yarn.

(O / C) o: ¹⁶ O ⁻ / at a depth 2.5% of the single yarn diameter from the surface
¹² O ^- (intensity ratio) (O / C) i: 16 in 40% deep of single fiber diameters from the surface O ^- /
¹² O ^- (intensity ratio) is a single yarn diameter referred to herein means the maximum inscribed circle diameter of the single yarn cross-section.

To achieve the object of the present invention, at 260 ° C. for 5 minutes,
Further, the oxygen concentration ratio of the single yarn inner and outer layers determined by SIMS after oxidizing at 280 ° C. for 5 minutes in air at normal pressure is 6 or less, preferably 5.5 or less, more preferably 5 or less. If it exceeds 6, only carbon fibers having low strength and low elastic modulus can be obtained.

The object of the present invention is selected from the group consisting of 85% or more of acrylonitrile, normal propyl ester, normal butyl ester, isobutyl ester, secondary butyl ester of acrylic acid or methacrylic acid, and esters of alkyl having 5 or more carbon atoms. At least one polymerizable unsaturated carboxylic acid alkyl ester
10%, and a copolymer consisting of 0.25 to 5% of at least one polymerizable unsaturated carboxylic acid selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid;
And at 260 ° C for 5 minutes, and at 280 ° C for 5 minutes, in air,
H / C of inner layer obtained by SIMS after flame resistance at normal pressure
Is 0.03 or less. That is, in the precursor of the present invention, at 260 ° C. for 5 minutes,
H / C determined by SIMS after flame resistance in air at normal pressure for 5 minutes at 80 ° C. is ¹ H ⁻ / ¹² C ⁻ of the inner layer at a depth of 40% of the single yarn diameter from the surface (strength ratio Say). The single yarn diameter referred to herein means the maximum inscribed circle diameter of the single yarn cross section.

To achieve the object of the present invention, at 260 ° C. for 5 minutes,
Further, the H / C of the inner layer determined by SIMS after flame resistance at 280 ° C. for 5 minutes in air at normal pressure is 0.03 or less, preferably 0.025 or less, and more preferably 0.02 or less. 0.03
If it exceeds, only carbon fibers having low strength and low elastic modulus can be obtained.

The used SIMS device name and measurement conditions are as follows.

· Atomika Co. A-DIDA3000 · Primary ion species: Cs ^+, Primary ion acceleration voltage: 12 kV · Primary ion current: 200 nA · Raster area: 300 [mu] m × 300 [mu] m - analysis region: Gate 20% Measuring Vacuum degree: 7 × 10 ^{- 9} Torr ・ E-GUN: 0.3kV-3.0A (Focus: 0) ・ HQH: # 12 Also, as a simple method for detecting the difference between the inner and outer layer structure of the single-layered flame-resistant yarn, a room temperature curing type There is a method of observing the polished cross-section embedded in epoxy resin and polished by a reflection microscope, but with the precursor of the present invention, it is flame-resistant at 260 ° C. for 5 minutes, further at 280 ° C. for 5 minutes in air at normal pressure. The oxidized yarn does not show a substantial two-layer structure in the above-mentioned reflection microscopic image.

Further, the precursor of the present invention is acrylonitrile 85
% Or more, at least one polymerizable unsaturated carboxylic acid selected from the group consisting of normal propyl ester, normal butyl ester, isobutyl ester, secondary butyl ester and alkyl ester having 5 or more carbon atoms of acrylic acid or methacrylic acid The copolymer is composed of 1 to 10% of an alkyl ester and 0.25 to 5% of at least one polymerizable unsaturated carboxylic acid selected from the group consisting of acrylic acid, methacrylic acid and itaconic acid.

The copolymer composition is expressed by weight unless otherwise specified.

If the copolymerization amount of the polymerizable unsaturated carboxylic acid alkyl ester is small, the obtained effect is small, while if it is too large, the physical properties and carbonization yield of the obtained carbon fiber are reduced. Therefore, it is more preferably 2 to 9%, and still more preferably 3 to 8%.

The polymerizable unsaturated carboxylic acid alkyl ester, acrylic acid, methacrylic acid ester from the viewpoint of versatility and effect, specifically, normal propyl acrylate, normal butyl methacrylate, isobutyl methacrylate,
Examples thereof include cyclohexyl acrylate and stearyl methacrylate. Among them, normal propyl ester, normal butyl ester, and isobutyl ester of acrylic acid or methacrylic acid are particularly preferable.

These copolymer components do not themselves promote the oxidization reaction, but improve the oxygen permeability. The present inventors have studied the oxygen concentration distribution in the cross section direction of the oxidized yarn single yarn, when firing the oxidized yarn having a more uniform oxygen concentration distribution, it is possible to obtain carbon fibers with extremely high physical properties, It has been found that even when the flame resistance time is shortened or when the single fiber fineness is increased, if the uniformity is maintained, the decrease in physical properties can be extremely reduced.

In addition, as a result of the improved oxygen permeability, the unsaturation of the main chain has progressed further, and when the oxidized yarn having a low hydrogen concentration inside the single yarn is fired, carbon fibers having extremely high physical properties can be obtained. It was also found that even when the flame-proofing time was shortened or when the single fiber fineness was increased, if the uniformity was maintained, the decrease in physical properties could be extremely reduced.

In addition, in the precursor of the present invention, the polymerizable unsaturated carboxylic acid alkyl ester does not promote the flame-proofing reaction, and therefore, in order to further shorten the flame-proofing time, the polymerizable unsaturated carboxylic acid that promotes the flame-proofing reaction is used. Is preferably copolymerized at 0.25 to 5%. And when the copolymerization amount is small, the effect of promoting the oxidization resistance reaction is small and the physical properties of the obtained carbon fiber are low, and also, the physical properties of the obtained carbon fiber are reduced even if it is too large, so that the copolymerization amount is 0.5 to 4.5% is more preferable, and 0.75 to 4% is still more preferable. As the unsaturated carboxylic acid, acrylic acid, methacrylic acid, or itaconic acid is used.

It is also possible to copolymerize with other polymerizable unsaturated monomers copolymerizable with acrylonitrile.

The polymerization method may be any of known methods such as solution polymerization, suspension polymerization, and emulsion polymerization.

As a solvent used for spinning, a known organic or inorganic solvent can be used. In the present invention, the acrylic polymer solution is spun, stretched in a bath, and dried and densified according to a known method. Spinning may be spun directly into the coagulation bath,
Once spun into air, it may be coagulated in a bath. Stretching in the bath may be carried out directly on the spun yarn, or may be carried out after once washing with water to remove the solvent. Stretching in a bath is usually performed in a stretching bath at 50 to 98 ° C. by about 2 to 6 times, but the present invention is not limited to this. Drying and densification are performed by drying the drawn yarn in a bath with a hot drum or the like, and the drying temperature, time, and the like can be appropriately selected. Further, if necessary, the dried and densified yarn is subjected to pressure steam stretching. Further, the precursor fiber may be treated with a silicone oil agent in order to impart heat resistance capable of shortening the flame-proofing time by treating at a high temperature. As a method of giving, a usual method such as dip giving can be used.

In addition, the precursor of the present invention can be made into a flame-resistant yarn by any known flame-proofing method, but in order to exhibit its characteristics, a method of flame-resistance in a fluidized heating heat medium, It is preferable to perform flame resistance in a place where the flame resistance time can be shortened, such as a method of intermittently contacting the heated solid surface.

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples.

Example 1 By a solution polymerization method using dimethyl sulfoxide as a solvent, a spinning solution having a polymer concentration of 20% was obtained, spun into a dimethyl sulfoxide aqueous solution using a 3,000-hole die, and then stretched in boiling water. After washing with water while drying and densifying, the fibers were further stretched in pressurized steam to obtain single yarn denier 1.0d, 3,000 filaments, and fibers A to E having the copolymer compositions shown in Table 1. This fiber was oxidized in a graphite powder heat medium fluidized with heated air at 260 to 280 ° C. for 10 minutes, and heat-treated to 1300 ° C. in a nitrogen stream to obtain a carbon fiber. The results are shown in Table 2. The results of measuring the distribution of ¹⁶ O ⁻ / ¹² C ⁻ and ¹ H ⁻ / ¹² C ^{− in} the cross section direction of the single yarn of the flame resistant yarn by SIMS are shown in FIGS. 1 and 2 for the fiber C, respectively. Show.

Comparative Example 1 Fibers F to H having the copolymer compositions shown in Table 1 were obtained in the same manner as in Example 1. This fiber was fired in the same manner as in Example 1 to obtain a carbon fiber. The results are shown in Table 2.

Example 2 In the same manner as in Example 1, single-filament denier 1.0d, 3,000 filament fibers I to I of the copolymer composition shown in Table 3
M was obtained. This fiber was fired in the same manner as in Example 1 to obtain a carbon fiber. The results are shown in Table 4.

Comparative Example 2 Fibers N to P having the copolymer compositions shown in Table 3 were obtained in the same manner as in Example 1. This fiber was fired in the same manner as in Example 1 to obtain a carbon fiber. The results are shown in Table 4.

Example 3 Acrylonitrile was prepared by a suspension polymerization method using water as a solvent.
A copolymer consisting of 92.5%, itaconic acid 1.5%, and normal butyl methacrylate 6% was obtained, and the polymer concentration was 25%.
Of dimethylformamide and spun into an aqueous solution of dimethylformamide, and spun in the same manner as in Example 1 to obtain 3,000 filaments and fibers Q and R having a single fiber fineness shown in Table 5. The fiber was made flame-resistant at 240 to 260 ° C. for 30 minutes in the air and heat-treated to 1300 ° C. in a nitrogen stream to obtain a carbon fiber. The results are shown in Table 6.

[Effect of the Invention] The precursor of the present invention is composed of a copolymer having the above-mentioned specific copolymer composition, and is oxidized at 260 ° C. for 5 minutes and 280 ° C. for 5 minutes in air at normal pressure. By maintaining the oxygen concentration ratio of the inner and outer layers of the single yarn obtained by SIMS at 6 or less, or by maintaining the H / C of the inner layer obtained by SIMS at 0.03 or less; Improvement • Shortening of flame resistance time without lowering physical properties. • Larger single-fiber fineness is possible without lowering physical properties, which has the effect of reducing carbon fiber costs.

[Brief description of the drawings]

FIG. 1 shows the results obtained by SIMS after oxidizing the precursor according to the present invention (Example 1, Fiber C) at 260 ° C. for 5 minutes and further at 280 ° C. for 5 minutes in air at normal pressure. ¹⁶ of the single yarn cross-sectional direction O ^- / ¹² C ^- is a distribution diagram. Since the diameter of the single yarn of this flame-resistant yarn is 10 μm, the oxygen concentration ratio between the inner and outer layers of the single yarn is calculated from ¹⁶ O ⁻ / ¹² C ^{− at} 250 nm and 4000 nm from the surface. FIG. 2 is a ¹ H ⁻ / ¹² C ⁻ distribution diagram in the single yarn cross-sectional direction obtained by SIMS for the same flame-resistant yarn. H / C is 40% of the single yarn diameter from the surface and ¹ H ⁻ / ¹² C ⁻ at 4000 nm.

────────────────────────────────────────────────── (5) Continuation of the front page (51) Int.Cl. ⁶ Identification code FI C08F 220: 18) (56) References JP-A-63-59409 (JP, A) JP-A-58-200143 (JP, A) JP-A-61-74950 (JP, A)

Claims (4)

(57) [Claims] At least one selected from the group consisting of 85% or more of acrylonitrile, normal propyl ester, normal butyl ester, isobutyl ester, secondary butyl ester of acrylic acid or methacrylic acid, and alkyl ester having 5 or more carbon atoms. From 1 to 10% of a polymerizable unsaturated carboxylic acid alkyl ester, and 0.25 to 5% of at least one polymerizable unsaturated carboxylic acid selected from acrylic acid, methacrylic acid and itaconic acid, And after oxidizing at 260 ° C for 5 minutes and further at 280 ° C for 5 minutes in air at normal pressure,
A precursor for producing carbon fiber, wherein the oxygen concentration ratio of the inner and outer layers of the single yarn determined by secondary ion mass spectrometry (SIMS) is 6 or less. 2. At least one selected from the group consisting of acrylonitrile 85% or more, normal propyl ester, normal butyl ester, isobutyl ester, secondary butyl ester of acrylic acid or methacrylic acid, and alkyl ester having 5 or more carbon atoms. From 1 to 10% of a polymerizable unsaturated carboxylic acid alkyl ester, and 0.25 to 5% of at least one polymerizable unsaturated carboxylic acid selected from acrylic acid, methacrylic acid and itaconic acid, And after oxidizing at 260 ° C for 5 minutes and further at 280 ° C for 5 minutes in air at normal pressure,
H / C of inner layer determined by secondary ion mass spectrometry (SIMS)
A precursor for producing carbon fiber, which is not more than 0.03. 3. At least one selected from the group consisting of acrylonitrile 85% or more, normal propyl ester, normal butyl ester, isobutyl ester, secondary butyl ester of acrylic acid or methacrylic acid, and alkyl ester having 5 or more carbon atoms. From 1 to 10% of a polymerizable unsaturated carboxylic acid alkyl ester, and 0.25 to 5% of at least one polymerizable unsaturated carboxylic acid selected from acrylic acid, methacrylic acid and itaconic acid, And after oxidizing at 260 ° C for 5 minutes and further at 280 ° C for 5 minutes in air at normal pressure,
A precursor for carbon fiber production, wherein the oxygen concentration ratio of the inner and outer layers of the single yarn determined by secondary ion mass spectrometry (SIMS) is 6 or less, and the H / C of the inner layer is 0.03 or less. 4. The method according to claim 1, wherein said polymerizable unsaturated carboxylic acid alkyl ester is at least one selected from the group consisting of normal propyl ester, normal butyl ester and isobutyl ester of acrylic acid or methacrylic acid. The precursor for producing carbon fiber according to any one of the above items (1) to (3).