JPH09176923A - Precursor for carbon fiber, its production and production of carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a carbon fiber having high tensile strength and useful as a reinforcing fiber for composite material in high productivity by baking a carbon fiber precursor produced by forming an organic polymer coating layer on the surface of a precursor fiber. SOLUTION: The fiber surface of a carbon fiber precursor is coated with an organic polymer such as an acryl-silicone copolymer and the coated precursor fiber is baked to suppress the damage on the fiber surface and the welding of fibers in baking. The coating layer keeps its shape at the flameproofing treatment temperature and preferably has a carbonization residue of <=50%.

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 capable of obtaining carbon fiber having excellent tensile strength, a method for producing the same, and a method for producing carbon fiber using the precursor.

[0002]

2. Description of the Related Art Since carbon fibers have excellent specific strength and specific elastic modulus as compared with other fibers, they are industrially widely used as reinforcing fibers for composite materials with resins by utilizing their excellent mechanical properties. It's being used. In recent years, the superiority of the carbon fiber composite material has been further increased, and particularly in sports and aerospace applications, there is a strong demand for high performance of the carbon fiber composite material. The properties of the composite material largely depend on the properties of the carbon fiber itself, and this demand is, of course, a demand for higher performance of the carbon fiber itself.

[0003] In order to produce such high-performance carbon fibers, it is necessary to suppress the generation of defects which may be the starting point of breakage. In particular, it can be seen that the breaking of the carbon fiber mostly started from the surface, and the contribution of surface defects was large. On the other hand, conventionally, there has been proposed a technique of removing surface defects by etching the surface layer by subjecting carbon fiber to various post-treatments such as vapor-phase treatment, liquid-phase treatment, and electrolytic treatment (for example, Japanese Patent Laid-Open No. 2000-242242). JP-A-58-214527 and JP-A-61-225330). However, although the strength is improved by the above technique, the operation and the process become very complicated, and it is difficult to adopt as an actual production technique,
In addition, there is a problem that productivity is poor because the manufacturing cost is significantly increased. The demand for higher performance of carbon fiber is strong, but at the same time, there is a strong sense of cost, and it is the current situation that only carbon fiber with high cost performance can be accepted in the market.

Further, for the purpose of improving the process passability during the production of the precursor or during firing and improving the tensile strength of the resulting carbon fiber, an organosilicon compound, for example, may be added to the precursor as an oil agent. However, in such a technique, the precursor is often contacted with, for example, a roller in the process, so that a scratch is often generated on the precursor, and the carbon fiber having a desired tensile strength cannot be obtained with high efficiency. Is the actual situation.

In view of the above problems of the prior art, the inventors of the present invention have arrived at the present invention as a result of earnest studies on obtaining high-strength carbon fibers with high productivity and efficiency.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a precursor for producing carbon fiber, which is capable of producing a carbon fiber having high tensile strength with high productivity and efficiency, and a production method suitable for obtaining such a carbon fiber. To provide.

[0007]

The precursor of the present invention has the following constitution in order to achieve the above object. That is, the precursor for carbon fiber has a coating layer made of an organic polymer on the fiber surface.

In order to achieve the above object, the method for producing a precursor for producing carbon fiber of the present invention has the following constitution. That is, it is a method for producing a precursor for carbon fiber, which comprises forming a coating layer made of an organic polymer on the surface of the fiber.

Further, the method for producing carbon fiber of the present invention is
In order to achieve the above object, the following configuration is provided. That is, the present invention provides a method for producing carbon fibers, which comprises firing the precursor for carbon fibers.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

Since a simple method such as dipping can be adopted as the method of providing the coating layer, the strength can be improved without a large increase in cost, and the carbon fiber having high cost performance, and thus the composite having high cost performance, can be obtained. The material can be obtained.

The carbon fiber precursor of the present invention has a coating layer on the fiber surface. As a result, direct contact between the fibers or direct contact between the fibers and the roller is suppressed, so that scratches are unlikely to be generated on the fiber itself, and fusion between the single fibers due to heating during firing occurs. It gets harder. Therefore, high-strength carbon fibers can be obtained by firing such a precursor for carbon fibers.

In the present invention, the coating layer means a layer at least partially coating the fiber surface, and the fiber surface coverage is preferably 50% or more, more preferably 90%.
% Or more, and more preferably 99% or more. If the coverage is too low, the action and effect of the present invention of suppressing the generation of scratches on the fiber itself will not be exhibited. Most preferably, the coverage is 100%, and each single fiber independently has a coating layer. If there are too many locations where the coating layers of a plurality of monofilaments are integrated, there may be cases where desired quality and physical properties may not be obtained in the resulting carbon fibers due to firing spots in the subsequent firing step. Means that it has carbon in the main chain and has a structure with a degree of polymerization of about 100 or more, and does not include a compound consisting only of a silicone skeleton, that is, a so-called silicone compound. Conventionally, a silicone compound may be applied as an oil agent to a precursor for carbon fiber, but in this case, the precursor is often contacted with a roller or the like in the process, for example, a scratch is often generated on the precursor, which is desired. In reality, it was not possible to obtain carbon fibers having tensile strength with high efficiency. However, for example, in the case of a comb-type graft polymer (acrylic-silicone copolymer) in which the trunk portion is an acrylic polymer skeleton and the branch portion is a silicone skeleton, or the trunk portion is a silicone skeleton and the branch portion is an acrylic polymer skeleton. As described above, if a part of the acrylic part satisfies the above-mentioned requirements, it may be used as the organic polymer in the present invention. In this case, the part other than the silicone skeleton is 1
It is preferable that the amount is 0% by weight or more, preferably 20% by weight or more, more preferably 30% by weight or more, and further preferably 40% by weight or more. Specific examples of the organic polymer include acrylic copolymer, polyamide resin, polyetherimide resin, polyetheretherketone, polyethylene, polystyrene, polycarbonate, polysulfone, ABS resin, ketone resin, vinyl chloride resin, fluorine-based aqueous resin. ,
Phenolic resin, melamine resin, urea resin, guanamine resin, diallyl phthalate resin, vinyl ester resin,
Examples thereof include epoxy resin, acrylic-silicone copolymer, polystyrene, polyethylene, unsaturated polyester resin, polyimide resin, bismaleimide resin, furan resin, urethane resin, polyester-modified silicone resin and the like. Acrylic-silicone copolymer is preferable as the organic polymer because it is easy to form a uniform coating layer when used in combination with a high-performance silicone oil agent as a process oil agent, particularly an amino-modified silicone oil agent,
A cationic acrylic-silicone copolymer is more preferable from the viewpoint of stability with an amino-modified silicone.

In the present invention, the coating layer is a thermosetting resin or a thermoplastic resin having a melting temperature of 300 ° C. or higher from the viewpoint of maintaining its shape at the flameproofing temperature and suppressing fusion between the single fibers. It is preferably composed of a polymer. As such an organic polymer, specifically, a self-crosslinking acrylic copolymer, a fluorine-based aqueous resin, a phenol resin, a vinyl ester resin, a melamine resin, a urea resin, a guanamine resin, a diallyl phthalate resin, an epoxy resin, an acrylic-silicone. Examples thereof include copolymers, unsaturated polyester resins, polyimide resins, bismaleimide resins, furan resins, urethane resins, polyether ether ketones, and the like.

Further, it is preferable that the organic polymer forming the coating layer is crosslinked. Cross-linking means that the polymer forms a three-dimensional network structure, and the cross-linked polymer has high heat resistance and high hardness, which is preferable for increasing the strength of the carbon fiber. Examples of organic polymers capable of introducing such a structure include self-crosslinking acrylic copolymers, phenol resins, vinyl ester resins, melamine resins, urea resins, guanamine resins, diallyl phthalate resins, epoxy resins, unsaturated polyester resins. , Bismaleimide resin, furan resin and the like.

The heat resistance of the organic compound in the present invention is 5
% Or more, preferably 10% or more, more preferably 20%
The above is more preferred. The heat resistance of the organic compound is measured and defined as follows. Using a high-temperature differential TG-DTA, once the vacuum is drawn and the pressure is restored with nitrogen, the carbonization loss is measured up to 800 ° C. at a temperature rising rate of 500 ° C./min under a nitrogen stream of 30 ml / min. At this time, the sample weight W at room temperature
_The heat resistance is defined as follows from the ratio of ₁ to the sample weight W _{2 at} 500 ° C.

Heat resistance (%) = 100 × (W ₂ / W ₁ ) If the carbonization residual rate of the organic polymer in the coating layer is too high, single yarn-to-yarn adhesion or the like tends to occur during firing.
The carbonization residual rate of the coating layer in the present invention is preferably 50% or less, more preferably 20% or less, further preferably 10% or less, and most preferably substantially 0%. It should be noted that it is difficult to actually obtain an organic polymer having a carbonization residual rate of less than 1%, or the degree of improvement in tensile strength of the obtained carbon fiber tends to be saturated.

The carbonization residual rate of the organic polymer can be measured as follows. Using a high-temperature differential TG-DTA, once the vacuum is drawn and the pressure is restored with nitrogen, the carbonization loss is measured up to 800 ° C. at a temperature rising rate of 500 ° C./min under a nitrogen stream of 30 ml / min. At this time, the sample weight W at room temperature
_The carbonization residual rate is defined as follows from the ratio of ₃ to the sample weight W _{4 at} 700 ° C.

Residual carbonization rate (%) = 100 × (W ₄ / W ₃ ) In the examples described later, the TAS-300 high temperature differential TG-DT manufactured by Rigaku Denki Co., Ltd. was used as the high temperature differential TG-DTA.
A was used.

In the present invention, the coating layer preferably contains substantially no metal or metal compound. If they are substantially contained, they may react with the precursor during carbonization to form a carbide, which may reduce the strength. The term "substantially free of metal or metal compound" means that the total content of metal components is preferably 1000 ppm or less, more preferably 100 ppm or less, and further preferably 10 p.
It means that it is pm or less. Ideally, it is most preferable not to contain it, but the total content of metal components is 0.01 pp
When it is less than m, it may be difficult to actually obtain it due to mixing of impurities, and the improvement width of the tensile strength of the obtained carbon fiber tends to be saturated.

If the coating amount of the coating layer is too small, it is difficult to evenly apply the coating layer, and the effect tends to be small. If the coating amount is too large, yarn breakage at the time of carbonization, which is considered to be due to poor flame resistance, occurs, or the yarn making process. As a result, the organic polymer forming the coating layer may adhere to the drying drum or the like and the process passability may be reduced. From this point of view, the amount of coating layer adhered in the present invention is
0.001 to less than 5% by weight based on the weight of the fiber is preferable,
0.005 to 3% by weight is more preferable, and 0.01 to 1% by weight is further preferable.

Further, from the viewpoint of suppressing scratches generated on the precursor by the coating layer according to the present invention, the coating layer is preferably hard, and the pencil hardness is preferably B or more,
HB or higher is more preferable, and H or higher is further preferable. The hardness of the coating layer is measured after drying the precursor and before firing.

In the present invention, when measuring the characteristics of the coating layer, it is preferable to measure the coating layer separated from the precursor as follows.

When the organic polymer forming the coating layer is not dissolved in a good solvent for the precursor, the following method can be adopted.

About 5 g of the precursor having a coating layer was dipped in 200 cc of a good solvent for the precursor and kept at 120 ° C. for 2 hours.
Heat for a period of time to dissolve the precursor. Then, it is filtered with a glass fiber filter, further washed with a good solvent for a precursor of 100 cc or more and pure water of 100 cc or more in order, and dried at 120 ° C. for 2 hours to separate the organic polymer, which is then used for weighing, thermal analysis and the like. . For example, when the precursor is acrylic, dimethyl sulfoxide can be used as a good solvent.

When the organic polymer forming the coating layer is dissolved in a good solvent for the precursor, it is difficult to separate it. Therefore, the organic polymer before application can be directly analyzed. If it is a powder, it can be analyzed as it is, or in the case of a water emulsion or an organic solvent solution,
It can be analyzed after sufficient removal of water and organic solvent. In this case, the adhered amount is obtained by the following formula from the dry weight w ₁ of the yarn 10m when the coating layer is applied and the dry weight w ₀ when the coating layer is not applied. The drying conditions can be appropriately determined depending on the type of solvent, but in the case of water, the drying conditions are 120
℃ × 2 hours.

Coating layer adhesion rate (%) = 100 × (w ₁ −w ₀ ) / w _{0 In the} present invention, the precursor may be any of acrylic fibers, pitch fibers, rayon fibers, etc.
An example of a method for manufacturing an acrylic precursor will be described.

The polyacrylonitrile constituting the precursor of acrylic carbon fiber is preferably a polymer containing 85% by weight or more of acrylonitrile and 15% by weight or less of a polymerizable unsaturated monomer copolymerizable with acrylonitrile. Examples of the polymerizable unsaturated monomer include acrylic acid, methacrylic acid, itaconic acid and their alkali metal salts, ammonium salts and alkyl esters, acrylamide, methacrylamide and their derivatives, allylsulfonic acid, methallylsulfonic acid and Examples thereof include salts or alkyl esters thereof. In addition, it is preferable to copolymerize a polymerizable unsaturated monomer such as an unsaturated carboxylic acid which promotes a flame-resistant reaction. The copolymerization amount is preferably 0.1 to 10% by weight, more preferably 0.3 to 5% by weight, and 0.1 to 10% by weight.
More preferably, it is 5 to 3% by weight. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid,
Examples thereof include itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid and the like.
In order to obtain high-strength carbon fibers, it is preferable to copolymerize at least one selected from alkyl esters of unsaturated carboxylic acids and vinyl acetate. The copolymerization amount is 0.
It is preferably 1 to 10% by weight, more preferably 0.3 to 5% by weight, and further preferably 0.5 to 3% by weight. Specific examples of the alkyl ester of unsaturated carboxylic acid include methyl acrylate, methyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, and secondary butyl methacrylate. Among them, acrylic acid, Methacrylic acid propyl, butyl, isobutyl,
Secondary butyl ester is preferred.

As the polymerization method, suspension polymerization, solution polymerization,
A conventionally known method such as emulsion polymerization can be employed.
As the degree of polymerization, the intrinsic viscosity ([η]) is preferably 1.
It is 0 or more, more preferably 1.25 or more, and further preferably 1.5 or more. [Η] is preferably 5.0 or less from the viewpoint of spinning stability.

As the solvent in the case of solution spinning, known organic and inorganic solvents can be used. Specifically, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, aqueous solution of rhodanese and aqueous solution of zinc chloride are used as the solvent. The polymer solution to be used is the spinning dope.

The polymer can be made into a precursor by a known method. The spinning may be performed by a wet spinning method of directly spinning into a coagulation bath, a dry-wet spinning method of once spinning into air and then coagulating in a bath, or a dry spinning method or a melt spinning, but a high-strength carbon fiber Dry-wet spinning is preferred in order to obtain the desired properties.

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 drawn in the bath after washing with water to remove the solvent and the plasticizer.
The condition of stretching in a bath is usually about 2 to 6 times stretching in a stretching bath at 50 to 98 ° C. The dried and densified yarn is dried by a hot drum or the like after drawing in a bath to achieve dry densification.
The drying temperature, time and the like can be appropriately selected. If necessary, the dried and densified yarn may be drawn at a higher temperature (for example, in pressurized steam), whereby a precursor having a predetermined fineness and orientation can be obtained. Also, prior to drying and densification,
It is preferable to add a silicone oil agent for the purpose of imparting heat resistance. Above all, it is more preferable to use an amino-modified silicone or an epoxy-modified silicone, and it is further preferable to use a combination of an amino-modified silicone and an epoxy-modified silicone.

In the present invention, the organic polymer can be added to the fiber in any of the above-mentioned yarn making steps to form a coating layer on the surface of the fiber. The organic polymer can be applied to the fiber by immersing the fiber in a liquid in which the organic polymer is dispersed or dissolved and then drying the fiber to remove the solvent. In particular, from the viewpoint of work environment and disaster prevention, it is preferable to use water as the liquid and disperse the organic polymer. Further, in general, it is difficult to sufficiently disperse a solid organic polymer in a dry state in water, and therefore it is preferable to use an aqueous dispersion originally prepared by a method such as emulsion polymerization or emulsion polymerization in water. When an organic solvent is used as the liquid, if a common solvent with the precursor polymer is used, adhesion between single fibers may occur, so it is preferable to use an organic solvent that is not the common solvent with the precursor polymer.

The organic polymer is uniformly applied into the fiber bundle,
In order to form the coating layer on the surface of the fiber, it is preferable to add an organic polymer in the region where the yarn width is widened, and the organic polymer dispersed in water in a washing bath, a drawing bath, a process oil bath, etc. It is more preferable to add a molecule. It can also be applied by immersing it in a process oil bath containing a mixed liquid in which the process oil and the organic polymer are both dispersed. The concentration of the organic polymer at that time is preferably 0.001 to 100% by weight, more preferably 0.005 to 10% by weight, as a dry weight, in a weight ratio with respect to the process oil agent and the entire organic polymer, and 0.01
-1% by weight is more preferred. It is also possible to add the organic polymer before or after the application of the step oil agent, and to insert a drying step in between.

There is no drying step between the steps of applying the process oil agent and the organic polymer, and particularly when the process oil agent and the organic polymer are applied as a mixed liquid in which both are dispersed, the process oil agent and the organic polymer are applied. The ionicity of is important. For example, if the process oil agent is cationic and the organic polymer is anionic, agglomeration will start when both are mixed, the stability of the mixed solution will decrease, and the transfer amount to the heat roller will increase in the subsequent drying process. However, not only the processability may deteriorate, but it may be difficult to form a uniform coating layer on the fiber surface, and the purpose of obtaining the high-strength carbon fiber of the present invention may not be achieved. Therefore, it is preferable that the organic polymer is nonionic or has the same ionicity as the process oil. Specifically, when the process oil is anionic, the organic polymer is preferably anionic or nonionic, and when the process oil is cationic, the organic polymer is preferably cationic or nonionic. When the process oil is nonionic, the ionicity of the organic polymer is not particularly limited.

Regardless of whether the coating amount of the coating layer is large or small, an uncoated portion or a portion in which the coating layers for coating a plurality of single fibers are integrated with each other to cause apparent single-fiber adhesion. It is preferable to reduce the number of such defects and the number of adhesion spots. For that purpose, it is preferable that the wettability of the dispersion liquid of the organic polymer and the fiber of the solution is high. Specifically, the contact angle between the organic polymer dispersion or solution and the fiber base material is preferably 40 degrees or less, more preferably 30 degrees or less, and further preferably 20 degrees or less. Further, in order to improve such wettability, it is possible to add a surfactant to a dispersion or solution of an organic polymer or to provide another layer on the fiber in advance. The contact angle can be measured on a film made of a polymer forming fibers.

As a method for applying the oil agent and the coating layer, a method of applying a thread to a driven roller in an oil agent bath, a non-driving roller, or a fixed or non-fixed guide bar to apply the thread to the thread, or a method in which liquid is blown upward Various methods can be considered, such as a method of running and applying the yarn to the yarn, a method of dropping the liquid onto the running yarn from above, a method of causing the yarn to run in the space where the liquid is sprayed, and can be appropriately selected. When the organic polymer is applied to the fiber, the yarn width of the fiber is preferably 3 mm or more, more preferably 10 mm or more, and further preferably 20 mm to 50 mm per 3000 filaments.

From the viewpoint of forming a uniform coating layer, it is preferable to add the organic polymer to the fiber in the spinning process, but after the spinning process, the organic polymer is applied to the fiber before the subsequent firing process. You can also

In order to obtain a carbon fiber having a high strength, a precursor having a high density is effective. As for elaboration,
The value of the lightness difference ΔL by the iodine adsorption method is preferably 45
Or less, more preferably 30 or less, further preferably 5 to
15 precise precursors are good. Means for obtaining a dense precursor having a ΔL of 45 or less include dry-wet spinning, increasing the concentration of the spinning dope, lowering the temperature of the spinning dope and the coagulating bath solution, and lowering the tension during coagulation. It is effective to keep the swelling degree of the bath drawn yarn low by optimizing the number of drawing steps, drawing ratio and drawing temperature during bath drawing.

ΔL is a value obtained by the following method. About 0.5 g of a dried sample having a fiber length of 5 to 7 cm was precisely weighed and placed in a 200 ml Erlenmeyer flask with a ground stopper, and an iodine solution (I ₂ : 51 g, 2,4-dichlorophenol 10 g, acetic acid 90 g and iodinated was added thereto. 100 g of potassium is precisely weighed, transferred to a 1-liter volumetric flask and dissolved in water to a constant volume) 100 ml is added, and adsorption treatment is performed at 60 ° C. for 50 minutes while shaking. The sample that adsorbed iodine was washed with running water for 30 minutes and then centrifugally dehydrated (2000 rpm x
1 minute) and air dry quickly. After opening this sample,
The lightness (L value) is measured with a Hunter type color difference meter (L ₁ ).
On the other hand, the corresponding sample not subjected to the adsorption treatment of iodine is opened, the lightness (L ₀ ) is measured by the Hunter type color difference meter in the same manner, and the lightness difference ΔL is obtained from L ₀ -L ₁ . In the examples described below, CM-25 type manufactured by Color Machine Co., Ltd. was used as the Hunter color difference meter.

In the present invention, the single fiber fineness of the precursor is preferably thin so as not to cause firing unevenness in the subsequent flameproofing step from the viewpoint of improving the strength, preferably 1.5d or less, more preferably 1.0d. Hereafter, it is more preferably 0.1 to 0.8 d.

By firing such a precursor, a high performance carbon fiber can be obtained. As the oxidizing condition, a conventionally known method can be adopted. Tension or stretching conditions are preferably used in an oxidizing atmosphere at a temperature of 200 to 300 ° C., and the density is preferably 1.25.
Heat treatment is performed until the amount reaches at least g / cm ³ , more preferably at least 1.30 g / cm ³ . This density is 1.60g
/ Cm ³ or less is generally maintained, and if it exceeds this, the physical properties may deteriorate.

As the atmosphere, generally known oxidizing atmospheres such as air, oxygen, nitrogen dioxide and hydrogen chloride can be used, but air is preferable from the economical point of view.

The yarn that has been made flame resistant is carbonized in an inert atmosphere by a conventionally known method. The carbonization temperature is preferably 1000 ° C. or higher in view of the physical properties of the obtained carbon fiber, and can be graphitized at a temperature of 2000 ° C. or higher if necessary. Also, 350 to 500 ° C and 1
The heating rate at 000 to 1200 ° C. is preferably 50
0 ° C./min or less, more preferably 300 ° C./min or less, further preferably 150 ° C./min or less. Thereby, a dense carbon fiber having few internal defects such as voids can be obtained. If the heating rate is 10 ° C./min or less, the productivity is too low. 350-500 ° C
Alternatively, it is preferably 1% or more at 2300 ° C. or more,
It is more important to stretch 5% or more, more preferably 10% or more, from the viewpoint of improving the denseness.
Stretching exceeding 40% is not preferred because fluff is likely to occur.

The carbon fiber thus obtained is subjected to electrolytic oxidation treatment in an electrolytic bath made of an acid or alkali aqueous solution, or to vapor phase or liquid phase oxidation treatment to obtain a composite material. It is preferable to improve the affinity and adhesiveness between the carbon fiber and the matrix resin.

In particular, electrolytic oxidation is preferable because it can be oxidized in a short time and the degree of oxidation can be easily controlled. Both acidic and alkaline electrolytes can be used as the electrolytic solution for the electrolytic treatment. Any acidic electrolyte may be used as long as it exhibits acidity in an aqueous solution, and specific examples thereof include inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, carbonic acid, acetic acid, butyric acid, oxalic acid, acrylic acid, and maleic acid. And organic acids such as ammonium sulfate, ammonium hydrogensulfate, and the like. Sulfuric acid and nitric acid which show strong acidity are preferred. Any alkaline electrolyte may be used as long as it shows alkalinity in an aqueous solution. Specifically, sodium hydroxide, potassium hydroxide,
Hydroxides such as barium hydroxide, inorganic salts such as ammonia, sodium carbonate and sodium hydrogen carbonate, organic salts such as sodium acetate and sodium benzoate, and potassium salts, barium salts or other metal salts thereof, and ammonium salts And organic compounds such as tetraethylammonium hydroxide and hydrazine. Preferred are ammonium carbonate, ammonium hydrogencarbonate, and tetraalkylammonium hydroxide which do not contain an alkali metal which causes a curing failure of the resin.

The amount of electricity is preferably optimized in accordance with the degree of carbonization of the carbon fiber to be treated, and a high elastic modulus yarn requires a larger amount of electricity. From the viewpoint of improving the productivity while improving the crystallinity of the surface layer and preventing the strength of the carbon fiber substrate from decreasing, it is preferable to repeat the electrolytic treatment a plurality of times with a small amount of electricity. Specifically, the amount of electricity supplied to one electrolytic cell is preferably 5 coulombs / g · tank (1 g of carbon fiber, the amount of electricity per cell) to 100 coulombs / g · tank, and more preferably 10 coulombs / g. / G · tank or more, 80
Coulomb / g · tank or less, more preferably 20 coulomb / g · tank or more and 60 coulomb / g · tank or less. In addition, from the viewpoint of reducing the crystallinity of the surface layer to an appropriate range, the total amount of electricity in the energization treatment is preferably in the range of 5 to 1000 coulombs / g, and more preferably in the range of 10 to 500 coulombs / g.

After electrolytic treatment or cleaning treatment,
It is preferable to wash with water and dry. In this case, if the drying temperature is too high, the functional groups present on the resurface of the carbon fiber are easily lost by thermal decomposition, so it is desirable to dry at the lowest possible temperature, but if it is too low, it takes too much time to dry. Or the length of the dryer becomes too large. From this viewpoint, specifically, the drying temperature is preferably from 80 to 250 ° C, more preferably from 100 to 210 ° C.
C., and more preferably 120 to 210.degree. C. for drying.

Furthermore, sizing can be performed by a conventionally known technique, if necessary.

By using the present invention as described above,
Mechanical property, for example, tensile strength of resin-impregnated strand is 3000 MPa or more, preferably 4000 M
Pa or more, more preferably 5000 MPa or more, further preferably 6000 to 10000 MPa, and the tensile elastic modulus is 200 GPa or more, preferably 220 GP.
It is possible to obtain a carbon fiber having a or more, more preferably 240 GPa or more, and further preferably 280 to 1040 GPa.

[0051]

The present invention will be described more specifically with reference to the following examples.

The tensile strength and elastic modulus in the present invention were obtained by the resin-impregnated strand method.

Tensile strength, elastic modulus "Bakelite" ERL-4221 (registered trademark, manufactured by Union Carbide Co., Ltd.) / Boron trifluoride monoethylamine (BF ₃ .MEA) / acetone = 100/3/4
Part was impregnated with carbon fiber, and the obtained resin-impregnated strand was heated at 130 ° C. for 30 minutes to be cured, and then JIS-R-7
It was measured according to the resin-impregnated strand test method defined in 601.

Example 1 By a solution polymerization method using dimethyl sulfoxide as a solvent,
A spinning dope was obtained which was composed of 99% by weight of acrylonitrile and 1% by weight of itaconic acid and had [η] of 1.70 and a polymer concentration of 20% by weight. This was once discharged into the air through a 3000 filament spinner and allowed to run in a space of about 3 mm, then coagulated in a 30 wt% aqueous solution of dimethyl sulfoxide at 10 ° C., and the coagulated yarn was washed with water up to 4 times. After drawing in a bath and applying a water emulsion of 2% by weight of a self-crosslinking acrylic copolymer, 2% by weight of an amino-modified silicone oil agent
A process oil consisting of was added to make it dry and densified. further,
Stretching up to 2.5 times in pressurized steam, single yarn fineness 0.8
d, a precursor having a total fineness of 2400D was obtained. The coating amount of the coating layer was 0.5% by weight. The carbonization residual rate of this coating layer was 5%. The heat resistance of this coating layer is 25%
Met.

The obtained precursor is 240 to 280 ° C.
In the air at a draw ratio of 1.05 and a density of 1.37 g
/ Cm ³ was obtained. Then, in a nitrogen atmosphere 35
The rate of temperature increase in the temperature range of 0 to 500 ° C. was set to 200 ° C./min, and the film was stretched at 2% and then fired to 1400 ° C.

Subsequently, an aqueous solution of sulfuric acid having a concentration of 0.1 mol / l was used as an electrolytic solution, electrolytic treatment was performed at 10 coulomb / g, and washing was performed with water.
It dried in 150 degreeC heating air. Table 1 shows the physical properties of the carbon fibers thus obtained.

Comparative Example 1 A carbon fiber was obtained in the same manner as in Example 1 except that the coating layer was not applied. Table 1 shows the physical properties.

Example 2 A carbon fiber was obtained in the same manner as in Example 1 except that a fluorine-based aqueous resin was applied as the coating layer. Table 1 shows the physical properties. The amount of the coating layer deposited was 0.4% by weight, and the carbonization residual rate was 0.1%. The heat resistance of this coating layer is 30%.
Met.

Example 3 A carbon fiber was obtained in the same manner as in Example 1 except that the phenol resin was applied as a methanol solution as a coating layer. Table 1 shows the physical properties. The amount of the coating layer deposited was 1% by weight, and the carbonization residual rate was 40%. The heat resistance of this coating layer was 50%.

Example 4 By a solution polymerization method using dimethyl sulfoxide as a solvent,
A spinning dope was obtained which was composed of 99% by weight of acrylonitrile and 1% by weight of itaconic acid and had [η] of 1.70 and a polymer concentration of 20% by weight. This was once discharged into the air through a 3000 filament spinner and allowed to run in a space of about 3 mm, then coagulated in a 30 wt% aqueous solution of dimethyl sulfoxide at 10 ° C., and the coagulated yarn was washed with water up to 4 times. The solution was stretched in a bath, and a process oil solution containing 2% by weight of an amino-modified silicone oil agent was applied. Further, a water-based emulsion of 2% by weight of a cationic acrylic-silicone copolymer, which is a comb-shaped graft polymer having a backbone of an acrylic skeleton copolymerized with diethylaminoethyl methacrylate and methyl methacrylate and a branch of a silicone skeleton, is used per dry weight of the yarn. 30% by weight
After application, the copolymer was migrated into the yarn by squeezing it with 10 free rollers having a diameter of 20 mm arranged in a zigzag, and then dried and densified. Further, it was drawn up to 2.5 times in pressurized steam to obtain a precursor having a single yarn fineness of 0.8 d and a total fineness of 2400D. The coating amount of the coating layer was 0.5% by weight. The carbonization residual rate of this coating layer was 1%. The heat resistance of this coating layer was 20%.

The obtained precursor is 240 to 280 ° C.
In the air at a draw ratio of 1.05 and a density of 1.37 g
/ Cm ³ was obtained. Then, in a nitrogen atmosphere 35
The rate of temperature increase in the temperature range of 0 to 500 ° C. was set to 200 ° C./min, and the film was stretched at 2% and then fired to 1400 ° C.

Subsequently, an aqueous solution of sulfuric acid having a concentration of 0.1 mol / l was used as an electrolytic solution, electrolytic treatment was performed at 10 coulomb / g, and washing was performed with water.
It dried in 150 degreeC heating air. Table 1 shows the physical properties of the carbon fibers thus obtained.

Comparative Example 2 After application of a process oil agent consisting of 2% by weight of amino-modified silicone oil agent, 30% by weight of water was applied per dry weight of the yarn, and 10 free rollers having a diameter of 20 mm arranged in a zigzag pattern were used. A carbon fiber was obtained in the same manner as in Example 4 except that the carbon fiber was dried and densified after being hot. Table 1 shows the physical properties.

Example 5 A spinning stock solution having a copolymer composition of 98% by weight of acrylonitrile, 1% by weight of itaconic acid and 1% by weight of isobutyl methacrylate, [η] of 1.50 and a polymer concentration of 25% by weight was used. A carbon fiber was obtained in the same manner as in Example 4 except for the above. Table 1 shows the physical properties.

Comparative Example 3 A carbon fiber was obtained in the same manner as in Example 5 except that the coating layer was not applied. Table 1 shows the physical properties.

Example 6 Example 1 except that the coating layer is a water soluble melamine resin.
A carbon fiber was obtained in the same manner as in. The coating amount of this coating layer is 1
The weight percentage and the residual carbonization rate were 10%. The heat resistance of this coating layer was 25%. Table 1 shows the physical properties.

Example 7 A carbon fiber was obtained in the same manner as in Example 1 except that the coating layer was a water-soluble urea resin. The coating amount of this coating layer is 0.8
The weight% and the residual carbonization rate were 5%. The heat resistance of this coating layer was 15%. Table 1 shows the physical properties.

Example 8 A carbon fiber was obtained in the same manner as in Example 1 except that an epoxy solution was applied as an acetone solution as a coating layer. The coating amount of the coating layer was 0.6% by weight, and the residual carbonization rate was 10%.
Met. The heat resistance of this coating layer was 25%. Table 1 shows the physical properties.

Example 9 The water emulsion concentration of the self-crosslinking acrylic copolymer was 2
A precursor was obtained in the same manner as in Example 1 except that the content was 0% by weight. The coating amount of the coating layer was 6% by weight,
Since the coating layer was too thick, there were some areas where flame resistance was poor even when flame resistant for a long period of time, and there were many fluffs and the quality was degraded.

Example 10 The spinning dope was discharged directly from the spinneret into a coagulation bath, 4% by weight of stearyl alcohol ethylene oxide adduct,
A carbon fiber was obtained in the same manner as in Example 4 except that a process oil agent containing 1% by weight of amino-modified silicone was used. The coating amount of this coating layer was 1% by weight. Table 1 shows the physical properties.

Comparative Example 4 A carbon fiber was obtained in the same manner as in Example 10 except that the coating layer was not added. Table 1 shows the physical properties.

Example 11 Instead of the cationic acrylic-silicone copolymer, an anionic acrylic-silicone copolymer whose backbone is an acrylic skeleton in which acrylic acid and methyl methacrylate are copolymerized and whose branches are silicone skeletons A carbon fiber was obtained in the same manner as in Example 5 except that the polymer was used.
Table 1 shows the physical properties. When sampling the raw yarn, the transfer amount of the oil agent and the organic polymer onto the heat roller for dry densification was larger than that in Example 5. It is considered that the combination of the amino-modified silicone, which is a cationic process oil, and the anionic organic polymer resulted in aggregation and increased the transfer amount. The coating amount of the coating layer was 0.5% by weight. The carbonization residual rate and heat resistance of this coating layer were 1% and 20%, respectively.

Example 12 A carbon fiber was obtained in the same manner as in Example 5 except that a water-soluble polyester-modified silicone resin was used instead of the cationic acrylic-silicone copolymer. Table 1 shows the physical properties. The coverage of the coating layer was 0.3% by weight. Also,
The carbonization residual rate and heat resistance of this coating layer were 1% and 20%, respectively.
%Met.

[0074]

[Table 1]

[0075]

According to the present invention, carbon fibers having high tensile strength can be efficiently obtained with good productivity.

Claims (9)

[Claims] 1. A precursor for carbon fiber, which has a coating layer made of an organic polymer on the surface of the fiber. 2. The precursor for carbon fiber according to claim 1, wherein the carbonization residual rate of the organic polymer is 50% or less. 3. The precursor for carbon fiber according to claim 1, wherein the coating layer has an adhesion amount of less than 5% by weight. 4. The organic polymer is an acrylic copolymer,
4. At least one selected from the group consisting of a fluorine-based aqueous resin, a phenol resin, a melamine resin, a urea resin, an epoxy resin, and an acryl-silicone copolymer, according to any one of claims 1 to 3. Precursor for carbon fiber. 5. The precursor for carbon fiber according to claim 1, wherein the organic polymer is an acrylic-silicone copolymer. 6. The precursor for carbon fiber according to claim 1, wherein the organic polymer is crosslinked. 7. A method for producing a precursor for carbon fiber, which comprises forming a coating layer made of an organic polymer on the surface of the fiber. 8. The method for producing a precursor for carbon fiber according to claim 7, wherein the carbonization residual rate of the organic polymer is 50% or less. 9. A method for producing carbon fiber, which comprises firing the precursor for carbon fiber according to claim 1 to obtain carbon fiber.