JP2003055881A - Precursor for carbon fiber, method for producing the same and method for producing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precursor for carbon fibers capable of suppressing factors in deteriorating the operating efficiency of a silicone finish oil essential for improving performances of the carbon fibers in a baking step and making the improvement of the performances in physical properties of the carbon fibers compatible with an improvement of the operating efficiency. SOLUTION: This precursor for the carbon fibers comprises the finish oil composed of the following two components and applied in an amount of 0.1-3 wt.% based on the fiber weight. Component A: a silicone finish oil having an oscillation period difference T of a pendulum measured by a damped oscillation method with a rigid body pendulum and satisfying the following formulae 0.03<=T<=0.4 and T=T30-T180 [wherein, T30 is the oscillation period (s) at 30 deg.C; and T180 is the oscillation period (s) after heat treatment at 180 deg.C for 10 min] and component B: a resin component having >=80% residual ratio r1 after heat treatment under conditions of 250 deg.C and 1 h and <=10% residual ratio r2 after heat treatment under conditions of 500 deg.C for 5 min or >=70% residual ratio r3 after keeping the finish oil at 240 deg.C for 2 h and <=10% residual ratio r4 after keeping the finish oil at 470 deg.C for 1 h.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a precursor for a carbon fiber for efficiently obtaining a carbon fiber having excellent tensile strength, a method for producing the same, and a method for producing the carbon fiber.

[0002]

2. Description of the Related Art Carbon fibers have excellent specific strength and specific elastic modulus as compared with other fibers, and therefore, due to their excellent mechanical properties, they are industrially widely used as reinforcing fibers for composite materials with resins. It's being used. In recent years, carbon fiber composite materials have become more and more superior, especially in sports and aerospace applications.

In order to produce such a high performance carbon fiber, it is necessary to suppress the generation of defects which are particularly the starting points of fracture. In particular, since most of the carbon fiber fractures start from the surface and the contribution of surface defects is large, various oil agent technologies have been conventionally proposed. Japanese Patent Publication 51-
Japanese Patent No. 12739 discloses a technique of applying silicone to prevent fusion and damage of fibers during firing, and Japanese Patent Publication No. 53-10175 discloses operation by adding amino-modified silicone. There is disclosed a technique in which the carbon properties are remarkably improved, the firing time is shortened, and a carbon fiber having good compatibility with a resin is obtained. Further, in JP-B-4-33892 and JP-B-4-40152, by adding a combination of silicone oil agents having different modifying groups such as amino-modified, epoxy-modified, and alkylene oxide-modified, the oil agent is resinified. Promote
A technique for suppressing the adhesion between single yarns during heat treatment is disclosed.

However, the silicone oil agent is liable to easily generate silicon carbide and silicon nitride in the firing step, and these scales produced in the heat treatment furnace also have the disadvantage of degrading the process stability. Is proposed. For example, Japanese Unexamined Patent Publication No. 2000-136485 discloses a method of solving a decrease in yarn focusing property when the amount of silicone is reduced by adding a silicone-based straight oil agent as a finishing oil agent. Although the total amount of silicone can be reduced by this technology, there is a limit to the reduction because the silicone-based oil agent is added.
Further, Japanese Patent Laid-Open No. 2000-199183 discloses a technique for reducing the amount of silicone by combining with a non-silicone oil agent having high heat resistance, but it is not possible to obtain carbon fiber having high physical properties and high quality. Had the problem.

[0005]

In view of such background of the prior art, the present invention suppresses the factor of deterioration of operability in the firing step of the silicone oil agent which is essential for improving the performance of carbon fiber, and the carbon fiber. It is intended to provide a precursor for a carbon fiber, a method for producing the same, and a method for producing the carbon fiber, which can achieve both high performance of physical properties and improvement of operability.

[0006]

The present invention employs the following means in order to solve the above problems. That is, the precursor for carbon fiber of the present invention is characterized in that the oil agent containing the following two components is attached in an amount of 0.1 to 3% by weight based on the weight of the fiber.

A component: Silicone oil agent whose vibration period difference T measured by the free damping vibration method of a rigid pendulum satisfies the following formula: 0.03≤T≤0.4 T = T30-T180 T30: 30 ° C Vibration cycle (second) T180: Vibration cycle (second) after heat treatment at 180 ° C. for 10 minutes B component: Heat treatment condition 250 ° C. × 1 hour residual rate r1 of 80% or more and 500 ° C. × 5 minutes After survival rate r
2 is a resin component whose content is 10% or less, or 2 at 240 ° C
Resin component having a residual rate r3 after holding for 70 hours or more and a residual rate r4 after holding for 1 hour at 470 ° C. of 10% or less. Further, the method for producing a precursor for carbon fiber of the present invention is
The oil emulsion containing the A component and the B component is applied to the fiber and dried to densify it, or the emulsion containing the A component is applied to the fiber and dried and densified, and then the B component is applied. It is what

Further, the method for producing carbon fiber of the present invention is characterized in that the precursor for carbon fiber is fired substantially without twisting.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention aims to prevent the above-mentioned problems, namely, to suppress the deterioration factor of the operability of the silicone oil agent in the firing step, which is essential for improving the performance of carbon fiber, and to improve the performance of carbon fiber physical properties. A carbon fiber precursor capable of achieving both improved operability has been earnestly studied, and when a carbon fiber precursor was used in combination with a specific silicone oil agent and a heat-resistant non-silicone oil agent, surprisingly,
It has been clarified that these problems can be solved at once.

According to the prior art, by using a silicone oil agent and a heat-resistant non-silicone oil agent together, the amount of silicone used can be reduced, and the production of scales such as silicon carbide and silicon nitride in the heat treatment furnace can be reduced. In the worst case, yarn breakage and fluffing occur locally.
There is a problem in that the yarn may be cut and the operability is deteriorated.

When a silicone oil agent and a non-silicone oil agent are used in combination, the affinity between them is low, and therefore they often exist separately on the fiber. First, a silicone oil agent centered on amino-modified silicone, which has a high affinity for polyacrylonitrile, is located around the single fiber, and a non-silicone oil agent is separately present on the outside thereof.

As a result of examining the causes of the local yarn breakage and the occurrence of fluff as described above, the present inventors have found that the non-silicone oil agent located outside the silicone oil agent causes oxygen into the yarn thread necessary in the flameproofing process. It was found that the part where the permeation was suppressed and the flameproofing reaction was insufficient caused local yarn breakage and fuzzing.

Furthermore, it has been found that by specifying the properties of the silicone used in combination, local yarn breakage and fluff generation can be suppressed. That is, the present invention is one in which an oil agent containing the specific silicone oil agent of the following component A and the specific non-silicone oil agent of the component B is attached to the carbon fiber precursor in an amount of 0.1 to 3% by weight based on the weight of the fiber. .

Component A: Silicone oil agent in which the vibration period difference T of the pendulum measured by the free damping vibration method of a rigid pendulum satisfies the following formula: 0.03≤T≤0.4 T = T30-T180 T30: 30 ° C Vibration cycle (second) T180: Vibration cycle (second) after heat treatment at 180 ° C. for 10 minutes B component: Heat treatment condition 250 ° C. × 1 hour residual rate r1 of 80% or more and 500 ° C. × 5 minutes After survival rate r
2 is a resin component whose content is 10% or less, or 2 at 240 ° C
The residual rate r3 after holding for 70 hours or more, and 4
Resin component having a residual ratio r4 of 10% or more after being kept at 70 ° C. for 1 hour The carbon fiber of the present invention may be any of acrylic, pitch, rayon, etc., but acrylic precursor is particularly preferable.

The precursor for acrylic carbon fiber will be described in detail.

The polyacrylonitrile which constitutes the precursor of the 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 their salts or alkyl esters can be used.

It is also preferable to copolymerize a polymerizable unsaturated monomer which accelerates the flameproofing reaction such as unsaturated carboxylic acid. The copolymerization amount of the polymerizable unsaturated monomer is preferably 0.1 to 10% by weight, more preferably 0.3 to 5% by weight, and particularly preferably 0.5 to 3% by weight. Specific examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid and the like. Further, in order to obtain a high-strength carbon fiber, it is preferable to copolymerize at least one selected from the alkyl ester of unsaturated carboxylic acid and vinyl acetate. The copolymerization amount is preferably 0.
It is 1 to 10% by weight, more preferably 0.3 to 5% by weight, and particularly 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 is used. Acids, propyl, butyl, isobutyl and secondary butyl esters of methacrylic acid are preferably used.

As a method for polymerizing polyacrylonitrile which constitutes the precursor of such an acrylic carbon fiber,
Conventionally known methods such as suspension polymerization, solution polymerization and emulsion polymerization can be adopted. As the degree of polymerization, the intrinsic viscosity ([η]) is preferably 1.0 or more, more preferably 1.25 or more, and particularly preferably 1.5 or more. From the viewpoint of spinning stability, [η] is preferably 5.0 or less.

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

The polymer can be made into a precursor by a known method. The spinning may be carried out by a wet spinning method in which it is directly spun into a coagulation bath, a dry-wet spinning method in which it is once spun into air and then coagulated in the bath, or a dry spinning method or melt spinning, but high strength carbon fiber Dry-wet spinning is preferred to obtain

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 drawing conditions in the bath are usually about 2 to 6 times in a drawing bath at 50 to 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 may be stretched at a higher temperature (for example, in pressure steam), whereby a precursor having a predetermined fineness and orientation can be obtained.

A feature of the present invention is that, in such a precursor, an oil agent in which a specific silicone oil agent and a specific heat-resistant non-silicone oil agent are combined is applied prior to dry densification, or prior to dry densification. A specific silicone oil agent is applied, and after drying and densification, a specific heat-resistant non-silicone oil agent is applied.

When a specific heat-resistant non-silicone oil agent is applied after such dry densification, the heat-resistant non-silicone may be applied as an emulsion or solution, or may be a pure product which is not diluted with a solvent or the like. Drying may or may not be added after the heat-resistant non-silicone is applied, but no drying is preferable for simplifying the process. Furthermore, in the case of no drying, it is preferable that the heat resistant non-silicone is not diluted with a volatile solvent such as water or an organic solvent, so that a pure product is imparted or isopropyl palmitate, isopropyl myristate, ethylhexyl laurate is added. It is preferable to apply it after diluting it with a non-volatile solvent.

The silicone oil for carbon fibers of the present invention is characterized in that the vibration period difference T of the pendulum measured by the free damping vibration method of the rigid pendulum satisfies the following formula.

0.03 ≦ T ≦ 0.4 T = T30−T180 T30: Vibration cycle at 30 ° C. (second) T180: Vibration cycle after heat treatment at 180 ° C. for 10 minutes (second) The present inventors made flame resistant. The inventors have found that there is a correlation between the firing unevenness in the above step and the curing behavior of the silicone oil agent applied in the yarn making step during the heat treatment, and arrived at the present invention. That is, the vibration period difference T of the pendulum measured by the method described below (hereinafter,
It is possible to effectively suppress firing unevenness due to flame resistance by using a silicone oil agent in which the vibration period difference T is simply controlled to a specific range.

In the present invention, the silicone means a diorganopolysiloxane having a siloxane bond (-SiO-) in the basic skeleton, and the group bonded to the silicon atom is a hydrogen atom and / or an alkyl group or a phenyl group. Is mentioned. Of these, dimethylsiloxane is particularly preferable as the basic skeleton.

Further, as the silicone, a modified silicone such as amino-modified, epoxy-modified, or alkylene-oxide-modified which is modified at the molecular side chain and / or at the molecular end with an amino group, an epoxy group, an alkylene oxide or the like is preferably used.

As the silicone oil agent, it is preferable to include an alkylene oxide-modified silicone in the silicone oil agent from the viewpoint of enhancing the emulsion stability of the silicone oil agent. The alkylene oxide-modified silicone is preferably one modified with ethylene oxide, modified with propylene oxide, or modified with both. By modifying with a alkylene oxide, appropriate hydrophilicity is imparted to the silicone oil agent, the self-emulsifying property is improved, and the silicone oil agent can have a function similar to that of the surfactant. By doing so, desirable properties such as stability in water and uniform adherence to the yarn surface can be imparted to the silicone oil agent. Further, the compatibility with the heat resistant non-silicone used in combination is also improved.

The amount of modification of silicone with an alkylene oxide structure is preferably 10 to 80% by weight, and more preferably 20 to 70% by weight. If it is less than 10% by weight, the self-emulsifying property may be insufficient, and if it exceeds 80% by weight, the heat resistance may be lowered.

The number of alkylene oxide units (= repeating units) is preferably 25 or less from the viewpoint of ensuring the heat resistance of the silicone oil agent. Further, since the higher the molecular weight of silicone, that is, the higher the kinematic viscosity, the higher the heat resistance, the kinematic viscosity at 25 ° C. is preferably 100 cSt or more, more preferably 200 cSt or more, and more preferably 300 cSt or more. Is good. If the kinematic viscosity exceeds 10,000 cSt, it may be difficult to disperse it in water.

Further, in addition to the alkylene oxide-modified silicone, an amino-modified silicone and / or an epoxy-modified silicone can be combined.

The amino-modified silicone is not particularly limited and may be monoamine type or polyamine type. Here, the amino group may be introduced into the side chain or may be introduced into the molecular chain terminal, but in the case of modification of only the molecular chain terminal, the modification amount may be small. Furthermore, it may be introduced into both the side chain and the end of the molecular chain. The higher the molecular weight of the amino-modified silicone, that is, the higher the kinematic viscosity, the more the heat resistance is improved. Therefore, the kinematic viscosity at 25 ° C. is preferably 1000 cSt or more, and more preferably 20
00 cSt or more, and more preferably 3000 cSt or more. Further, modification amount of the terminal amino group was converted with -NH ₂ of modifying groups may have from 0.05 to 10 wt%, preferably from 0.1 to 5 wt%, more preferably from 0.2 to 3 wt% . If it is less than 0.05% by weight, the affinity with the yarn may be insufficient, and if it exceeds 10% by weight, the heat resistance may decrease.

The epoxy-modified silicone is not particularly limited, and may be a glycidyl group or an alicyclic epoxy group, but from the viewpoint of ensuring affinity with the yarn, 1,2-epoxycyclohexyl group or 1,2-epoxy group. Alicyclic epoxy modifications such as cyclopentyl groups are preferred. Here, the epoxy group may be introduced into the side chain or may be introduced into the end of the molecular chain. Further, it may be introduced into both the side chain and the end of the molecular chain, but those introduced into both ends of the molecular chain are preferable from the viewpoint of the reactivity of the epoxy group. The higher the molecular weight of the epoxy-modified silicone, that is, the higher the kinematic viscosity, the more the heat resistance is improved. Therefore, the kinematic viscosity at 25 ° C. is preferably 100 cSt or more, more preferably 500 cSt or more, and more preferably 1000 cSt or more. Things are good. Modified weight converted as -CHCH ₂ O terminal epoxy group of the epoxy-modified silicone has good 0.05 to 10 wt%, preferably 0.1 to
It is preferably 5% by weight, more preferably 0.2 to 3% by weight.
If it is less than 0.05% by weight, the affinity with the yarn may be insufficient, and if it exceeds 10% by weight, the heat resistance may decrease.

When the amino-modified silicone and the epoxy-modified silicone are combined, the optimum ratio of their mixing ratios varies depending on the respective modification amounts, but it is preferable that the number of moles of the amino group and the epoxy group is close to the equivalent. Here, it is preferable that the ratio of the amino-modified silicone is higher than that of the epoxy-modified silicone, from the viewpoint of enhancing the affinity with the yarn and the heat resistance of the silicone oil agent. Therefore, the weight ratio of amino-modified silicone to epoxy-modified silicone is preferably 1:10 to 100: 1, and preferably 1: 3-3.
The ratio is 0: 1, more preferably 1: 2 to 10: 1, further preferably 1: 1 to 3: 1.

The higher the heat resistance of the silicone oil agent applied to the yarn, the better. Therefore, the heating residual rate r of the silicone oil agent is preferably 20% by weight or more, and preferably 30%.
As described above, more preferably 40% or more. At present, it is difficult to set the heating residual rate r to 90% or more.

The heating residual ratio r was measured by the following method.

The oil sample to be measured is about 1 g and the diameter is about 60.
The sample is placed in an aluminum container having a size of 20 mm and a height of about 20 mm, and dried in an oven at 105 ° C. for 5 hours. The obtained substance was measured by a thermobalance (TG) under the following conditions for 120 minutes in air at 240 ° C. for 120 minutes and subsequently in nitrogen at 450 ° C. for 30 minutes, and the total weight retention rate on the thermobalance was defined as the heating residual rate r. To do.

Sample pan: made of aluminum, diameter 5 m
m, height 5 mm-Sample amount: 15 to 20 mg-Heat treatment in air (procedure 1) Air flow rate: 30 ml / min Temperature rising rate: 10 ° C / min (room temperature to 240 ° C) Heat treatment time (240 ° C): 120 minutes Atmosphere change (procedure 2) Change from air to nitrogen at 240 ° C and hold for 5 minutes ・ Heat treatment in nitrogen (procedure 3) Nitrogen flow rate: 30 ml / min Temperature rising rate: 10 ° C / min (240 to 450 ° C) Heat treatment time (450 ° C.): 30 minutes It is preferable to add 0.01 to 2% by weight of such silicone. If it is less than 0.01% by weight, the effect of suppressing the adhesion between single yarns may be reduced, and if it exceeds 2% by weight, the processability may be deteriorated due to dropping into the process. More preferably 0.02-1.5% by weight
And more preferably 0.03 to 1% by weight,
It is particularly preferably 0.05 to 0.7% by weight.

Generally, as the molecular weight of silicone increases, the contact angle to polyacrylonitrile increases,
Since the silicone is less likely to spread on the surface of the yarn and uneven adhesion may occur, the contact angle of the silicone base oil to the polyacrylonitrile film is preferably 40 ° or less, more preferably 30 ° or less, It is more preferably 20 ° or less.
Generally, it is currently difficult to make the contact angle 3 ° or less.

The contact angle is measured by the following method. A solution of homopolymer of acrylonitrile in dimethylsulfoxide was prepared, spread thinly on a glass plate, and the solution was mixed at 120 ° C for 6 minutes.
Dry for an hour to form a polyacrylonitrile film. About 2 microliters of silicone oil base oil is placed thereon, and the contact angle is measured at 25 ° C. If the measurement is difficult, set the amount of base oil used for measurement to 1 to
It can be appropriately changed within the range of 10 microliters.

In the present invention, it is preferable to add an emulsifier in order to facilitate the production of the emulsion and keep it stable. An emulsifier has surface activity and is generally composed of a hydrophilic group and a hydrophobic group. The ratio R1 of the emulsifier is preferably 40% or less of the non-volatile component, more preferably 30% or less, and 20
% Or less is more preferable. As an emulsifier,
Any of nonionic, cationic, and anionic surfactants can be used. Among them, nonionic surfactants are preferable, and alkyl ether of polyethylene glycol, alkyl phenyl ether, and alkyl amine ether are particularly preferable.

Further, by flameproofing the acrylic precursor for producing carbon fibers having the silicone oil agent of the present invention on its surface, flameproofed fibers with less uneven firing can be obtained, and yarn breakage and fluff generation in the subsequent carbonization step can be suppressed. Is possible,
As a result, it has been clarified that it is possible to obtain a carbon fiber having higher yarn density, higher tension, higher speed, and excellent cost performance without lowering productivity as compared with the conventional firing technique.

The silicone fluid of the present invention has a vibration period difference T
Is preferably 0.03 to 0.4, 0.05 to 0.3
It is more preferably 5, and even more preferably 0.10 to 0.30. If it deviates from the above range, the effect of the present invention becomes difficult to obtain. That is, they have the following relationship.

0.03 ≦ T ≦ 0.4 T = T30-T180 T30: Vibration cycle at 30 ° C. (seconds) T180: Vibration cycle after heat treatment at 180 ° C. for 10 minutes (seconds) Free damping vibration method of rigid pendulum The principle is, for example, coloring material,
51 (1978), 403p, etc.,
Unlike general rheometers, viscoelastic behavior can be measured in the open system and thin film state. The vibration period measured by the measuring method corresponds to the degree of crosslinking of the silicone oil agent, and the smaller the period, the higher the degree of crosslinking. Therefore, the vibration cycle difference T
(= T30-T180) corresponds to the curing behavior at the time of heating, and the larger the value, the easier the curing is, that is, the easier the crosslinking is. Although the mechanism is not clear, it is possible to suppress firing unevenness due to flame resistance by applying a silicone oil agent whose vibration cycle is controlled within the above range.

The vibration period of the silicone fluid by the free damping vibration method of the rigid pendulum was determined as follows.

Based on the free damping vibration method of a rigid pendulum, a rigid pendulum type physical property tester RPT- manufactured by A & D Co., Ltd.
The vibration period is measured using 3000. Length 5cm, width 2c
m, a thickness of 0.5 mm, on a zinc-coated steel coated substrate (STP-012 manufactured by A & D Co., Ltd.), the silicone oil to be used for the measurement should have a substrate width of 20 to 30 μm in terms of pure content. Apply over the entire surface. Immediately after application, set the tester and start measurement. After adjusting the temperature to 30 ℃ in advance and setting the coating plate and pendulum, 50
The temperature is raised to 180 ° C. at a rate of ° C./min and held at 180 ° C. for 10 minutes. Meanwhile, the period is continuously measured at 7 second intervals. The following pendulum is used.

Edge used: Knife-shaped edge (RBE-160 manufactured by A & D Co., Ltd.) Pendulum weight / inertia ratio: 15 g / 640 gcm (FRB-100 manufactured by A & D Co., Ltd.) Also, in combination with silicone. The heat-resistant non-silicone oil agent used is a resin component having a residual rate r1 after heat treatment of 250 ° C. × 1 hour of 80% or more and a residual rate r2 of 500 ° C. × 5 minutes of 10% or less, or , 240
The residual rate r3 after being kept at ℃ for 2 hours is 70% or more, and 47
It is a resin component having a residual rate r4 of 10% or less after holding at 0 ° C. for 1 hour.

The residual ratios r1 and r2 were measured by the following method.

An oil sample to be measured is about 1 g and has a diameter of about 60.
The sample is placed in an aluminum container having a size of 20 mm and a height of about 20 mm, and dried in an oven at 105 ° C. for 5 hours. The material obtained is heated in air at 250 ° C. for 1 hour and subsequently in nitrogen at 500 ° C. for 5 hours.
Min., Measured by a thermobalance (TG) under the following conditions, the total weight retention rate on the thermobalance is taken as the heating residual rate, the residual rate after 1 hour treatment at 250 ° C in air is r1, and at 500 ° C in nitrogen. The residual rate after 5 minutes of treatment is r2.

Sample pan: made of aluminum, diameter 5 m
m, height 5 mm-Sample amount: 15 to 20 mg-Heat treatment in air (procedure 1) Air flow rate: 30 ml / min Temperature rising rate: 10 ° C / min (room temperature to 250 ° C) Heat treatment time (250 ° C): 60 minutes Atmosphere change (procedure 2) Change from air to nitrogen at 250 ° C and hold for 5 minutes ・ Heat treatment in nitrogen (procedure 3) Nitrogen flow rate: 30 ml / min Temperature rising rate: 10 ° C / min (240-500 ° C) Heat treatment time (500 ° C.): 5 minutes Further, r3 and r4 were measured by the following method.

Except for the temperature profile, the same procedure as in the measurement of r1 and r2 was carried out. The substance obtained by drying in an oven at 105 ° C. for 5 hours was heated in air at 240 ° C. for 2 hours, and subsequently in nitrogen at 470 ° C. for 1 hour. Measured with a balance (TG), the total weight retention rate on the thermobalance was taken as the heating residual rate, and the residual rate after 2 hours treatment at 240 ° C in air was r3, and the residual rate after 1 hour treatment at 470 ° C in nitrogen. Let the rate be r4.
The temperature rising rate was 10 ° C./min.

The heat-resistant non-silicone is not particularly limited as long as it satisfies the above-mentioned residual rate. For example, a reaction product of a saturated aliphatic dicarboxylic acid with a monoalkyl ester of an ethylene oxide and / or a propylene oxide adduct of bisphenol A and the like can be used. Can be mentioned.

The ratio of heat resistant non-silicone is preferably 0.1 to 10 with respect to silicone, more preferably 0.2 to 7, and even more preferably 0.5 to 5. If the ratio of the heat-resistant non-silicone is too high, flame resistance unevenness may occur. On the other hand, if the ratio is too low, the effect of the present invention of reducing the amount of silicone may not be sufficiently obtained.

As the method for applying the oil agent, a method of applying the thread to a driven or non-driving roller in a process oil bath or a fixed or non-fixed guide bar to apply the thread to the thread, or in a process oil solution blown upward There are various methods such as a method of running and applying a yarn on the yarn, a method of dropping an oil solution onto the running yarn from above, a method of running the thread in a space sprayed with the oil solution, and the like can be appropriately selected. it can. Further, silicone may be further added after the drying and densification. In this case as well, the above-mentioned applying method can be adopted, but it is common to apply straight oil that does not need to be dried. In order to apply the oil agent uniformly, it is effective to arrange a plurality of free rollers in succession after applying the oil agent and pass the precursor fiber in a zigzag manner so that the total contact angle is 8π or more. The larger the contact angle, the more preferable, but 16π or less is practical in view of cost or space.

In order to obtain a carbon fiber having a high strength, a precursor having a high density is effective. As for precision,
A dense precursor having a lightness difference ΔL as measured by the iodine adsorption method is preferably 45 or less, more preferably 30 or less, and further preferably 15 or less. As means for obtaining a dense precursor having a ΔL of 45 or less, dry-wet spinning, high concentration of spinning dope, swelling degree of coagulated yarn due to low temperature of spinning dope and coagulation bath solution and low tension during coagulation It is effective to keep the swelling degree of the bath-drawn yarn low by optimizing the number of drawing steps, the draw ratio and the drawing temperature during bath drawing. That is, the degree of yarn swelling when applying an oil agent is preferably 150% or less, and 1
It is more preferably 20% or less, still more preferably 90% or less.

In a drawing bath having a high temperature, since the thermocompression bonding by the entrance side roller tends to cause the adhesion between the single fibers,
It is effective to put the roller out of the hot bath. Further, in order to remove the pseudo adhesion, it is also effective to provide a vibration guide in the bath to vibrate the yarn bundle. The frequency at that time is preferably 5 to 100 Hz, and the amplitude is 0.1
10 mm is preferable. By combining these techniques, bath drawing at a high temperature of 60 to 100 ° C. becomes easy even in the dry-wet spinning method.

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,
Hunter color difference meter [CM-25 manufactured by Color Machine Co., Ltd.
Type] to measure the lightness (L value) (L1).

On the other hand, the corresponding sample not subjected to the adsorption treatment of iodine was opened, the lightness (L0) was measured by the Hunter color difference meter in the same manner, and the lightness difference ΔL was obtained from L0-L1.

The degree of swelling is determined by the following method. Adhesive water was removed from the swelled yarn using a drawing dehydrator (300
(0 rpm, 15 minutes) and the weight w0 after drying this with a hot air dryer at 110 ° C. for 2 hours,
Calculate by the following formula.

Swelling degree (%) = (w−w0) × 100 / w0 The single fiber fineness of the precursor is preferably thin so that firing unevenness does not occur in the subsequent flameproofing step from the viewpoint of improving strength, and preferably It is 1.5 d or less, more preferably 1.0 d or less, and further preferably 0.8 d or less.

By firing such a precursor
Therefore, high-performance carbon fiber can be obtained. Flameproof condition
As the above, a conventionally known method can be adopted as the oxidation.
Tension, or in the range of 200 to 300 ° C in a sexual atmosphere
Stretching conditions are preferably used and a density of 1.
25 g / cm³Or more, more preferably 1.30 g / cm
³Heat treatment is performed until the above is reached. This density is 1.
60 g / cm³It is common to keep
If it is above, the physical properties may deteriorate. General atmosphere
Regarding air, known air, oxygen, nitrogen dioxide, chloride water
It is possible to use an oxidizing atmosphere such as oxygen, but from the economical point of view
Air is preferred.

The yarn which has been subjected to flame resistance is carbonized in an inert atmosphere by a conventionally known method. The carbonization temperature in such carbonization treatment is preferably 1000 ° C. or higher in view of the physical properties of the resulting carbon fiber, and may be 20 if necessary.
It can be graphitized at a temperature of 00 ° C or higher. Also, 3
The rate of temperature increase at 50 to 500 ° C and 1000 to 1200 ° C is preferably 500 ° C / min or less, more preferably 300 ° C / min or less, still more preferably 150 ° C / min.
It is less than a minute. This makes it possible to obtain a dense carbon fiber having few internal defects such as voids. If the rate of temperature increase is 10 ° C./minute or less, the productivity will be too low. Further, at 350 to 500 ° C. or 2300 ° C. or higher, it is important to perform stretching of preferably 1% or more, more preferably 5% or more, still more preferably 10% or more in order to improve the denseness. Stretching of more than 40% is not preferable because fuzzing is likely to occur.

From the viewpoint of improving the spreadability of the obtained carbon fiber, it is preferable to fire the carbon fiber substantially without twisting.
"Untwisted" means that the twist of the yarn in the process is -1.0.
~ + 1.0 turns / m. The finally obtained carbon fiber has a twist number of -0.5 to +.
0.5 turn / m, preferably -0.2 to +0.2 turn / m, more preferably -0.1 to +0.1 turn / m
Is good.

The number of twists is evaluated as follows. About the fiber to be measured, a space of 4 m was provided, and both ends of the fiber were firmly fixed by clips so that the fiber did not move. Insert a 1mmφ metal rod into the innermost part of one clip,
The metal rod was slid to the other end, the number of twists between them was measured 5 times, and the arithmetic average A was taken. Further, the number of twists was calculated by the following formula.

Number of twists (turns / m) = A / 4 By firing without twisting, it is expected that the quality of the resulting carbon fiber will be improved, such as the spreadability of the resulting carbon fibers, and the subsequent untwisting work is unnecessary. It also has the merit of cost reduction.

The carbon fiber thus obtained is subjected to electrolytic oxidation treatment in an electrolytic cell made of an aqueous acid or alkali solution, or to gas 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. As an electrolytic solution for electrolytic treatment, either acidic or alkaline can be adopted. As the acidic electrolyte, specifically, sulfuric acid,
Inorganic acids such as nitric acid, hydrochloric acid, phosphoric acid, boric acid, carbonic acid, acetic acid,
Examples thereof include organic acids such as butyric acid, oxalic acid, acrylic acid and maleic acid, and salts such as ammonium sulfate and ammonium hydrogensulfate. Sulfuric acid and nitric acid which show strong acidity are preferable. Specific examples of the alkaline electrolyte include hydroxides such as sodium hydroxide, potassium hydroxide and barium hydroxide, inorganic salts such as ammonia, sodium carbonate and sodium hydrogen carbonate, organic salts such as sodium acetate and sodium benzoate. Further, these potassium salts, barium salts or other metal salts, and ammonium salts, tetraethylammonium hydroxide or an organic compound such as hydrazine, but preferably ammonium carbonate containing no alkali metal which causes curing failure of the resin, Ammonium hydrogen carbonate, tetraalkylammonium hydroxides and the like are preferable.

The amount of electricity is preferably optimized according to the carbonization degree of the carbon fiber to be treated. From the viewpoint of controlling the deterioration of the crystallinity of the surface layer within an appropriate range, the total amount of electricity during the energization treatment is 5 to 1
000 coulomb / g, further 10-500 coulomb / g
It is preferably in the range of g.

After performing 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 existing on the re-surface of the carbon fiber are likely to disappear by thermal decomposition. Therefore, it is desirable to dry at a temperature as low as possible. Specifically, the drying temperature is 250.
It is preferable to dry at a temperature of not higher than 0 ° C, more preferably not higher than 210 ° C.

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

The mechanical strength of the carbon fiber produced from the precursor for producing carbon fiber according to the present invention as described above is such that the resin-impregnated strand has a tensile strength of 3000 MPa or more. Preferably 4000
MPa or more, more preferably 5000 MPa or more, still more preferably 6000 MPa or more. The tensile modulus of the carbon fiber is 200 GPa or more, preferably 220
GPa or more, more preferably 240 GPa or more, and further preferably 280 GPa or more. When the above-mentioned strand strength or elastic modulus is less than 3000 MPa or less than 200 GPa, respectively, the desired properties as a structural material may not be obtained when it is made into a composite.

The carbon fiber thus obtained can be made into a carbon fiber composite material by a known method. The resin that serves as a matrix when used as a prepreg or a composite material is not particularly limited, epoxy resin, phenol resin, polyester resin, vinyl ester resin, bismaleimide resin, polyimide resin, polycarbonate resin,
Conventionally used materials such as polyamide resin, polypropylene resin and ABS resin are used. Moreover, not only resin but also cement, metal, ceramics, etc. can be used for the matrix.

Next, an example of the method for producing the carbon fiber composite material of the present invention will be described. There is also a method of forming a resin-impregnated sheet in which carbon fibers are aligned in one direction, that is, a unidirectional prepreg, or a woven prepreg in which carbon fibers are previously woven and then impregnated with resin. Composite material
It can be obtained by laminating and curing these prepregs in any direction, and a filament winding method or the like in which the resin is directly impregnated and wound without passing through the prepreg can also be applied. In addition, there is also a method of cutting into chopped fibers in advance and extruding while kneading with the resin, or withdrawing long fibers together with the resin, and a composite material is manufactured using these methods.

In addition to prepreg, the carbon fiber of the present invention is once processed into sheet molding compound (SMC), chopped fiber, etc., and then hand layup method, press molding method, autoclave method, pultrusion method, etc. It can also be used as a composite material when used in the molding method.

The above-described carbon fiber or carbon fiber composite material of the present invention is used for primary and secondary structural materials of aircraft, sports equipment such as golf shafts, fishing rods, tennis rackets, snowboards, ski poles, masts for yachts, and boats. Used for marine products such as hulls, flywheels, CNG tanks, hydrogen gas tanks, oil risers, wind turbines, turbine blades and other energy and general industrial applications, road and bridge pier repair and reinforcement equipment, and curtain wall construction equipment. In particular, it can be suitably used for a flywheel for energy use, a CNG tank, a hydrogen gas tank, and the like.

[0076]

EXAMPLES The present invention will be described in more detail below with reference to examples.

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

"Bakelite" ERL-4221 (registered trademark, manufactured by Union Carbide Co., Ltd.) / Boron trifluoride monoethylamine (BF ₃ .MEA) / acetone = 1
Carbon fiber was impregnated with 00/3/4 parts, and the obtained resin-impregnated strand was heated at 130 ° C. for 30 minutes to be cured, and J
It was measured according to the resin-impregnated strand test method defined in IS-R-7601.

As the amino-modified silicone, dimethylsiloxane having a basic skeleton represented by the following structural formula (1), a modification amount of 1% by weight and a kinematic viscosity of 2000 cSt was used. As the epoxy-modified silicone, dimethylsiloxane having a basic skeleton represented by the following structural formula (2), a modification amount of 1% by weight, and a kinematic viscosity of 10,000 cSt was used. As the alkylene oxide-modified silicone, ethylene oxide modification including a basic skeleton represented by the following structural formula (3), modification amount 50% by weight, kinematic viscosity 300 cS
t dimethyl siloxane was used. As the component B, aromatic polyesters A and B having the following structural formulas (4) and (5) were used. The heat resistance r1 and r2 of the aromatic polyester A are 85% and 5%, respectively, and the heat resistance r3 of the aromatic polyester B is r3 and
r4 was 75% and 5%, respectively.

[0080]

[Chemical 1]

[0081]

[Chemical 2]

[0082]

[Chemical 3]

[0083]

[Chemical 4]

[0084]

[Chemical 5]

Examples 1 to 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. After the polymerization, ammonia gas was blown in until the pH reached 8.5 to neutralize itaconic acid and introduce an ammonium group into the polymer to improve the hydrophilicity of the spinning dope. The obtained spinning solution was set to 40 ° C., once it was discharged into the air through a spinneret for 3000 filaments to run in a space portion of about 3 mm, and then 10 ° C.
Was coagulated in a 30% by weight aqueous solution of dimethyl sulfoxide, and the coagulated yarn was washed with water and drawn by bath up to 3 times. Furthermore, it is stretched up to 4 times in pressurized steam and single yarn fineness 1d, total fineness 3
I got a precursor of 000D. The amount of oil agent adhered is as shown in Table 1.

The precursor thus obtained was substantially twist-free to 2
A flame-resistant yarn having a density of 1.32 g / cm ³ was obtained by heating at a draw ratio of 0.90 in air of 40 to 280 ° C. Then, it was fired up to 1400 ° C. in a nitrogen atmosphere.

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 was dried in heated air at 150 ° C. Table 1 shows the physical properties of the carbon fiber thus obtained.

Comparative Examples 1 and 2 Carbon fibers were obtained in the same manner as in Example 1 except that the oil agents shown in Table 1 were added. The physical properties are shown in Table 1.

Examples 5 to 8 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. After the polymerization, ammonia gas was blown in until the pH reached 8.5 to neutralize itaconic acid and introduce an ammonium group into the polymer to improve the hydrophilicity of the spinning dope. The obtained spinning solution was set to 40 ° C., once it was discharged into the air through a spinneret for 3000 filaments to run in a space portion of about 3 mm, and then 10 ° C.
Was coagulated in a 30% by weight aqueous solution of dimethylsulfoxide, and the coagulated yarn was washed with water and drawn by bath up to 3 times, and an oil agent having the composition shown in Table 2 was applied to dry and densify. Further, it was stretched up to 4 times in pressurized steam, and the amount of the aromatic polyester A attached in Table 2 was applied to obtain a single yarn fineness 1d and a total fineness 3000.
I got the D precursor. The amount of oil agent adhered is as shown in Table 2.

Carbon fibers were obtained from the obtained precursor in the same manner as in Example 1. Table 2 shows the physical properties of the obtained carbon fibers.
Shown in.

[0091]

[Table 1]

[0092]

[Table 2]

As is clear from Tables 1 and 2, Examples 1 to 1
In the case of No. 8 as compared with those in Comparative Examples 1 and 2, no yarn breakage occurred in the process, and no process trouble due to generation of silica occurred.

Examples 9 to 12 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. After the polymerization, ammonia gas was blown in until the pH reached 8.5 to neutralize itaconic acid and introduce an ammonium group into the polymer to improve the hydrophilicity of the spinning dope. The obtained spinning dope was set at 30 ° C., was once discharged into the air through a spinneret for 3000 filaments, and was run in a space of about 3 mm, then at 10 ° C.
Was solidified in a 30% by weight aqueous solution of dimethylsulfoxide, and four coagulated yarns were combined into 12K, and after washing with water,
Bath drawing is performed up to 3 times, and an oil agent having the composition shown in Table 3 is applied,
It was dried and densified at 180 ° C. Further, it was drawn up to 4 times in pressurized steam to obtain a precursor having a single yarn fineness of 1d and a total fineness of 12000D. Table 3 shows the amount of applied oil.

The obtained precursor was used in a substantially twist-free 2
A flame-resistant yarn having a density of 1.32 g / cm ³ was obtained by heating at a draw ratio of 0.88 in air of 40 to 280 ° C. Then, it was fired up to 1400 ° C. in a nitrogen atmosphere.

Subsequently, using a sulfuric acid aqueous solution having a concentration of 0.1 mol / l as an electrolytic solution, electrolytic treatment was performed at 10 coulomb / g, and washing with water was performed.
It was dried in heated air at 150 ° C. Table 3 shows the physical properties of the carbon fiber thus obtained. The carbon fiber has a basis weight of 0.80 g / m and a specific gravity of 1.80.

Comparative Examples 3 and 4 Carbon fibers were obtained in the same manner as in Example 9 except that the oil agents shown in Table 3 were added. The physical properties are shown in Table 3.

Examples 13 to 16 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. After the polymerization, ammonia gas was blown in until the pH reached 8.5 to neutralize itaconic acid and introduce an ammonium group into the polymer to improve the hydrophilicity of the spinning dope. The obtained spinning dope was set at 30 ° C., was once discharged into the air through a spinneret for 3000 filaments, and was run in a space of about 3 mm, then at 10 ° C.
Was solidified in a 30% by weight aqueous solution of dimethylsulfoxide, and four coagulated yarns were combined into 12K, and after washing with water,
Bath drawing up to 3 times and applying an oil agent having the composition shown in Table 4,
Dried and densified. Further, it was stretched up to 4 times in pressurized steam, and after the aromatic polyester B having the adhesion amount shown in Table 4 was applied, two plied yarns were combined, and a single yarn fineness 1d and a total fineness 24000D were obtained.
Got the precursor of. Table 4 shows the amount of attached oil agent.

The precursor thus obtained was treated with 2
A flame-resistant yarn having a density of 1.32 g / cm ³ was obtained by heating at a draw ratio of 0.88 in air of 40 to 280 ° C. Then, it was fired up to 1300 ° C. in a nitrogen atmosphere.

Then, using a sulfuric acid aqueous solution having a concentration of 0.1 mol / l as an electrolytic solution, electrolytic treatment was performed at 10 coulomb / g and washing with water was performed.
It was dried in heated air at 150 ° C. Table 4 shows the physical properties of the carbon fiber thus obtained. The carbon fiber has a basis weight of 1.65 g / m and a specific gravity of 1.80.

Comparative Examples 5 and 6 Carbon fibers were obtained in the same manner as in Example 13 except that the oil agents shown in Table 4 were added. The physical properties are shown in Table 4.

[0102]

[Table 3]

[0103]

[Table 4]

As is clear from Tables 3 and 4, Examples 9 to
In No. 16, as compared with Comparative Examples 3 to 6, no yarn breakage occurred in the process, and no process trouble due to the generation of silica occurred.

[0105]

Industrial Applicability According to the present invention, a carbon fiber precursor for easily obtaining a high-strength carbon fiber can be obtained.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yama ▲ Saki ▼ Katsumi             1515 Tsutsui, Oita, Matsumae-cho, Iyo-gun, Ehime             Les Ehime Factory F-term (reference) 4L033 AA09 AB02 AC09 CA59                 4L037 CS03 FA01 PA55 PA65 PC11                       PF29 PF45 PS02 PS12 PS18                       UA09

Claims (11)

[Claims] 1. A precursor for carbon fiber, wherein an oil agent containing the following two components is attached in an amount of 0.1 to 3% by weight based on the weight of fiber. Component A: Vibration period difference T of the pendulum measured by the free damping vibration method of a rigid pendulum satisfies the following formula: Silicone oil agent 0.03 ≦ T ≦ 0.4 T = T30−T180 T30: Vibration period at 30 ° C. (Second) T180: Vibration cycle after heat treatment at 180 ° C. for 10 minutes (second) B component: Residual rate r1 after heat treatment condition 250 ° C. × 1 hour is 80% or more, and remaining after 500 ° C. × 5 minutes Rate r
2 is a resin component in which 10% or less, or the residual rate r3 after holding at 240 ° C. for 2 hours is 70% or more, and 4
Resin component having a residual rate r4 of 10% or less after holding at 70 ° C. for 1 hour 2. Amino-modified silicone, alkylene oxide-modified silicone and component B (heat treatment condition 250 ° C. ×
The residual rate r1 after 1 hour is 80% or more, and 50
Resin component whose residual rate r2 after 0 ° C. × 5 minutes is 10% or less, or residual rate r3 after 2 hours holding at 240 ° C. is 7
0.1% to 3% by weight per fiber weight of an oil agent containing 3 components, which is 0% or more and a resin component whose residual ratio r4 after holding at 470 ° C. for 1 hour is 10% or less). Precursor for carbon fiber characterized in that 3. The precursor for carbon fiber according to claim 1, wherein the component B is liquid at 250 ° C. after a heat treatment condition of 250 ° C. for 1 hour and is liquid at 250 ° C. 4. The precursor for carbon fibers according to claim 1, wherein the oil agent contains an epoxy-modified silicone. 5. The amount of the amino-modified silicone attached is 0.0.
It is 5 to 1% by weight, and the precursor for carbon fiber according to any one of claims 1 to 4. 6. The viscosity of the amino-modified silicone at 25 ° C. is 100 cSt or more, and the amount of modification with an amino group is 0.05 to 10% by weight.
6. The precursor for carbon fiber according to any one of to 5. 7. The alkylene oxide-modified silicone has a viscosity at 25 ° C. of 10 cSt or more and a modification amount with an alkylene oxide structure of 10 to 80% by weight, according to any one of claims 1 to 6. Precursor for carbon fiber. 8. The method according to claim 4, wherein the epoxy-modified silicone has a viscosity at 25 ° C. of 1000 cSt or more and a modification amount with an epoxy group of 0.05 to 10% by weight. Precursor for carbon fiber. 9. A method for producing a precursor for carbon fiber, which comprises applying an oil emulsion containing the following components A and B to fibers, and drying the mixture to densify it. Component A: Vibration period difference T of the pendulum measured by the free damping vibration method of a rigid pendulum satisfies the following formula: Silicone oil agent 0.03 ≦ T ≦ 0.4 T = T30−T180 T30: Vibration period at 30 ° C. (Second) T180: Vibration cycle after heat treatment at 180 ° C. for 10 minutes (second) B component: Residual rate r1 after heat treatment condition 250 ° C. × 1 hour is 80% or more, and remaining after 500 ° C. × 5 minutes Rate r
2 is a resin component whose content is 10% or less, or 2 at 240 ° C
A resin component having a residual rate r3 of 70% or more after holding for 1 hour and a residual rate r4 of 10% or less after holding for 1 hour at 470 ° C. 10. A method for producing a precursor for carbon fiber, which comprises applying the emulsion containing the component A to fibers, drying and densifying the fibers, and then adding the component B. 11. A method for producing carbon fibers, which comprises firing the precursor for carbon fibers according to claim 9 or 10 substantially without twisting.