JP2021123812A - Method for producing carbon fiber bundle - Google Patents

Abstract

To provide a method for producing a carbon fiber bundle enabling the reduction of contamination in a furnace in a flame-proofing process, satisfactory in quality because of an excellent process passability and having high strand tensile strength.SOLUTION: In a method for producing a carbon fiber bundle where a silicone based oil agent is applied to a fiber bundle, thereafter drying is performed to obtain a polyacrylonitrile based precursor fiber bundle having a density of 1.15 to 1.18 g/cm3, the same is subjected to a flame-proofing process of being heat-treated at 200 to 300°C in an oxidizing atmosphere till its density reaches 1.28 to 1.48 g/cm3 to obtain a fire-proofing fiber bundle, and thereafter, the same is subjected to a carbonization process of being heat-treated at 1,200 to 3,000°C in an inert atmosphere to obtain a carbon fiber bundle, the deposition rate of the silicon element in the fiber bundle directly after the application of the silicone based agent is defied as A (mass%), the deposition rate of the silicon element in the fiber bundle having a density of 1.15 to 1.18 g/cm3 upon the start of the flame-resistant process is defined as B (mass%), and the deposition rate of the silicon element in the fiber bundle in which density is increased by 0.06 g/cm3 from the start of the flame resistant process by the heat treatment of the flame-resistant process is defined as C (mass%), inequalities (1) to (3) are satisfied: 1.0≤(A-B)/A×100≤20.0(1), (B-C)/B×100≤5.0(2) and C≥0.150(3).SELECTED DRAWING: None

Description

The present invention relates to a method for producing a carbon fiber bundle having high quality and high resin-impregnated strand tensile strength because it enables reduction of contamination in a furnace in a flame resistance process and is excellent in process passability.

Composite materials using carbon fiber bundles are used not only for aeronautical and space applications but also for sports applications such as bicycles and golf clubs, and have recently been expanded to industrial applications such as automobile parts and pressure vessels. There is. In industrial applications, it is required to improve the productivity of carbon fiber bundles in order to reduce the cost of expensive carbon fiber bundles. In order to improve the productivity of carbon fiber bundles, it is necessary to improve continuous productivity by preventing contamination of the furnace and to prevent process troubles such as fluff.

The carbon fiber bundle is generally produced by heating a polyacrylonitrile-based precursor fiber bundle in a flame-resistant furnace at 200 to 300 ° C. in an oxidizing gas atmosphere to obtain a flame-resistant fiber bundle, and then under an inert gas atmosphere. It is obtained by heating at 1200 ° C. or higher. The polyacrylonitrile-based precursor fiber bundle usually consists of 1,000 to 80,000 single fibers, but in order to prevent fusion of the single fibers in the flame resistance process, a silicone-containing oil agent is added to the polyacrylonitrile-based precursor fiber bundle. The method of granting is widely known.

Further, the silicone-containing oil agent applied to the polyacrylonitrile-based precursor fiber bundle is a carbon fiber bundle manufacturing process for heat-treating the polyacrylonitrile-based precursor fiber bundle, a so-called firing step (hereinafter, may be abbreviated as a subsequent step). It was easy to produce silicon compounds such as silicon oxide, silicon carbide, and silicon nitride. It is known that the formation of silicon compounds leads to deterioration of industrial productivity and product quality. On the other hand, in order to reduce the amount of silicon compounds in the subsequent process, it is possible to reduce the adhesion rate of silicon elements in the polyacrylonitrile-based precursor fiber bundle by lowering the silicone ratio in the oil agent or reducing the amount of the oil agent attached. There is a problem that the fusion between the fibers is large and the tensile strength of the resin-impregnated strand (hereinafter, may be abbreviated as the tensile strength of the strand) is remarkably lowered.

In order to avoid these problems, the silicone content can be reduced by using an oil agent that suppresses the volatilization of compounds containing silicon elements and organic compounds (non-silicone compounds) that can replace silicone without changing the amount of adhesion. Reduced oils and the like have been proposed. Patent Document 1 proposes that by using a silicone from which a low boiling point component has been removed, the amount of a low molecular weight silicon compound produced in a subsequent process can be suppressed, and stable operability can be obtained. Patent Document 2 proposes that silicon dioxide powder generated during heating can be suppressed by reducing the oligomer component in the silicone component. Patent Document 3 proposes that the production process of a polyacrylonitrile-based precursor fiber bundle can be stabilized by using silicone in which molecules having a molecular weight of 1000 or more account for 92 to 100% by weight. Patent Document 4 proposes that the use of silicone having a high kinematic viscosity improves the heat resistance of the silicone and improves the strand tensile strength of the carbon fiber bundle. In Patent Documents 5 and 6, by using a compound having a bisphenol-type skeleton with high heat resistance in combination with silicone, a carbon fiber bundle having excellent mechanical properties while suppressing a decrease in operability even if the adhesion rate of silicon elements is low can be obtained. It is proposed to get. Patent Document 7 proposes that a high-quality carbon fiber bundle with less fluff can be obtained by using an oil agent having a residual ratio of 95% or more at 250 ° C. measured by a thermogravimetric analyzer.

Japanese Unexamined Patent Publication No. 2003-201346 Japanese Unexamined Patent Publication No. 4-178829 Japanese Unexamined Patent Publication No. 2004-244771 Japanese Unexamined Patent Publication No. 11-36143 International Publication No. 2016/0244551 International Publication No. 2012/117514 JP-A-2018-145562

However, the background technology has the following problems.

In Patent Documents 1 and 2, although the low boiling point component that easily volatilizes is removed, the silicone that decomposes at the temperature after the flame resistance step cannot be removed, and the generation of silicon compounds after the flame resistance step is not sufficiently suppressed. rice field. In Patent Document 3, the low molecular weight component was removed to stabilize the post-stretching of the polyacrylonitrile-based precursor fiber bundle under pressure steam, but the reduced malleability caused adhesion spots of the oil agent. , There was a problem that the strand tensile strength of the carbon fiber bundle was lowered. In Patent Document 4, although the strand tensile strength of the carbon fiber bundle was improved by increasing the heat resistance by increasing the molecular weight of silicone, the low molecular weight component that easily volatilizes in the flame resistance step could not be completely removed. Therefore, the suppression of the generation of silicon compounds after the flame resistance step was not sufficient. In Patent Documents 5 and 6, since the adhesion rate of the silicon element is low, the strand tensile strength of the carbon fiber bundle decreases, and when the adhesion rate of the silicon element is increased, the tar generated by volatilizing components other than silicone is the fiber. It has been a problem that the quality of the fiber bundle is deteriorated by adhering to the bundle. In Patent Document 7, since the evaluation was made based on the residual ratio measured by a thermogravimetric analyzer, the evaluation focused on the generation of silicon compounds in addition to the fact that it is less likely to volatilize than the evaluation on a fiber bundle having a large specific surface area. Furthermore, since it was not a method and the low molecular weight components that were easily volatilized in the flame resistance step could not be completely removed, the generation of silicon compounds after the flame resistance step could not be suppressed.

As described above, a method of removing a low boiling point component that easily volatilizes and a method of improving the heat resistance of silicone have been proposed in order to suppress the generation of silicon compounds after the flame resistance step, but at the initial stage of the flame resistance step. In addition to the fact that the molecular weight of silicone, which is easily volatilized, could not be clarified, the adhesion spots of the oil agent caused by the decrease in spreadability could not be reduced. It was not possible to achieve both the strand tensile strength of the carbon fiber bundle. Further, although the method of removing the low boiling point oligomer component is described as described above, the flame resistance step while ensuring the malleability at the time of applying the oil agent by positively adding the low boiling point oligomer component. It was not easy to come up with the idea of volatilizing the oligomeric component before.

An object of the present invention is to provide a method for producing a carbon fiber bundle having high quality and high strand tensile strength because it enables reduction of contamination in a furnace in a flame resistance process and is excellent in process passability.

In order to achieve such an object, the present invention has the following configuration.

That is, in the method for producing a carbon fiber bundle of the present invention, a polyacrylonitrile-based precursor fiber bundle having a ^{density of 1.15 to 1.18 g / cm 3 obtained by applying a silicone-based oil to the fiber bundle and then drying it is used.} Heat treatment is performed in an oxidizing atmosphere at 200 to 300 ° C. until the density reaches 1.28 to 1.48 g / cm ^3. After obtaining flame-resistant fiber bundles by a flame-resistant step, heat treatment is performed at 1200 to 3000 ° C. in an inert atmosphere. In the method for producing a carbon fiber bundle to obtain a carbon fiber bundle by the carbonization step, the adhesion rate of the silicon element of the fiber bundle immediately after applying the silicone-based oil is A (mass%), and the density at the start of the flame resistance step is 1. The adhesion rate of the silicon element of the fiber bundle of 15 to 1.18 g / cm ³ was B (mass%), and the density was increased by ^{0.06 g / cm 3} from the start of the flame resistance process by the heat treatment of the flame resistance process. This is a method for producing a carbon fiber bundle satisfying the formulas (1) to (3), where C (mass%) is the adhesion rate of the element.

1.0 ≦ (AB) / A × 100 ≦ 20.0 ・ ・ ・ (1)
(BC) / B × 100 ≦ 5.0 ・ ・ ・ (2)
C ≧ 0.150 ・ ・ ・ (3)

According to the present invention, it is possible to reduce the contamination in the furnace in the flame resistance process, and it is possible to produce a carbon fiber bundle having good quality and high strand tensile strength because of its excellent process passability.

The present inventors have made it possible to reduce the contamination in the furnace in the flameproofing process, and regarding the conditions for producing a carbon fiber bundle having high quality and high strand tensile strength due to excellent process passability, before the flameproofing process. By increasing the volatilization rate of the silicon element in the above, suppressing the volatilization of the silicon element in the initial stage of the flame resistance process, and further increasing the residual rate of the silicon element in the initial stage of the flame resistance process, silicone is added to the polyacrylonitrile-based precursor fiber bundle. It was found that the kinematic viscosity is lowered when the kinematic viscosity is applied, so that the silicone can be uniformly applied by improving the spreadability, and further, the volatilization of the compound containing the silicon element in the flame resistance step is remarkably reduced. The present invention has been reached.

First, an oil agent applied to the polyacrylonitrile-based precursor fiber bundle of the present invention (hereinafter, may also be referred to as “polyacrylonitrile-based precursor fiber bundle oil agent”) will be described.

The oil for polyacrylonitrile-based precursor fiber bundle of the present invention contains silicone (the oil for polyacrylonitrile-based precursor fiber bundle containing silicone may be hereinafter referred to as "silicone-based oil"). The silicone used in the oil for polyacrylonitrile-based precursor fiber bundle of the present invention has a basic structure of polydimethylsiloxane. Various modified products such as amino-modified, epoxy-modified, and polyether-modified are known as some of the side chains and terminal methyl groups, and some of the above compounds of the present invention preferably contain at least amino-modified silicone. It has been. The amino group as the modifying group may be a monoamine type or a polyamine type, but from the viewpoint of promoting cross-linking, the polyamine type is preferable, and the diamine type is more preferably used. Only one kind of these silicones may be used, or two or more kinds of silicones may be used. In this case, the modifying group and the modification position of the silicone used for mixing and the molecular weight distribution described later are not particularly specified, and the same one may be used or different ones may be used.

The silicone in the oil for polyacrylonitrile-based precursor fiber bundle of the present invention preferably has a molecular weight of 100 g / mol or more and less than 1000 g / mol, preferably 1.0 to 10.0% by mass and a molecular weight of 1000 g / mol or more and 10000 g. The content of molecules of / mol or less is preferably 1.0 to 19.0% by mass, more preferably 2.0 to 7.0% by mass and 1.0 to 19.0% by mass, respectively. It is preferably 2.5 to 5.0% by mass and 2.0 to 15.0% by mass, respectively. When two or more types of silicones are mixed and used, it is preferable that each silicone satisfies the above range. Generally, commercially available silicone has a molecular weight of 1000 g / mol or more and 10000 g / mol or less and a molecular content of 20.0% by mass or more, and has a molecular weight of 1000 g / mol or more and 10000 g / mol or less due to the influence of the polymerization raw material and the polymerization method. It was difficult to control the molecular content of the above to such a range. Therefore, in order to control the content of molecules having a molecular weight of 1000 g / mol or more and 10000 g / mol or less within such a range, it is not necessary to control the molecular weight distribution at the time of polymerization or purify with a column, instead of using commercially available silicone. There is a need to do. If the content of molecules having a molecular weight of 100 g / mol or more and less than 1000 g / mol is 1.0% by mass or more and the content of molecules having a molecular weight of 1000 g / mol or more and 10,000 g / mol or less is 1.0% by mass or more, the polyacrylonitrile-based precursor When silicone is applied to the body fiber bundle, the spreadability is improved and the silicone is uniformly applied, which is preferable because a carbon fiber bundle having good quality and high strand tensile strength can be obtained. If the content of molecules having a molecular weight of 100 g / mol or more and less than 1000 g / mol is 10.0% by mass or less and the content of molecules having a molecular weight of 1000 g / mol or more and 10,000 g / mol or less is 15.0% by mass or less, the flame resistance step. It is preferable because it is sufficient to reduce the contamination in the furnace and the carbon fiber bundle having good quality can be obtained because of its excellent process passability. The mass fraction of a molecule having a molecular weight of 100 g / mol or more and less than 1000 g / mol and the mass fraction of a molecule having a molecular weight of 1000 g / mol or more and 10000 g / mol or less can be calculated from the peak area obtained by gel permeation chromatography and the mass of the molecule. The mass fraction of molecules having a molecular weight of 100 g / mol or more and less than 1000 g / mol can be adjusted by adjusting the polymerization rate when polymerizing silicone, atmospheric distillation of the remaining polymerization raw material oligomer, cyclic siloxane 4 to 6-mer or linear. This can be achieved by adding a 4 to 6-mer siloxane, or adding a required amount of siloxane having a molecular weight of 100 g / mol or more and less than 1000 g / mol to the polymerized silicone. The mass fraction of a molecule having a molecular weight of 1000 g / mol or more and 10000 g / mol or less can be achieved by controlling the molecular weight distribution at the time of polymerization or purifying with a column.

The silicone in the oil for polyacrylonitrile-based precursor fiber bundle of the present invention has a weight average molecular weight of preferably 20000 to 100,000 g / mol, more preferably 30,000 to 80,000 g / mol, and further preferably 40,000 to 60,000 g / mol. Is. When the weight average molecular weight is 20000 g / mol or more, the silicone easily adheres uniformly to the polyacrylonitrile-based precursor fiber bundle, and thus a carbon fiber bundle having good quality and high strand tensile strength can be obtained, which is preferable. When the weight average molecular weight is 100,000 g / mol or less, it is possible to prevent a decrease in malleability when silicone is applied to the polyacrylonitrile-based precursor fiber bundle, and the silicone is uniformly applied, resulting in good quality and strand tensile strength. Is preferable because a high carbon fiber bundle can be obtained. The weight average molecular weight of silicone can be measured by gel permeation chromatography. The weight average molecular weight of silicone can be controlled by the molecular weight distribution of silicone and additives.

_{The amino equivalent, which is an index of the amount of amino group (NH 2} ) in the amino-modified silicone, is preferably 1000 to 14000 g / mol, more preferably 1500 to 6000 g / mol, and further preferably 2000 to 4000 g / mol. .. When two or more types of silicones are mixed and used, it is preferable that each silicone satisfies the above range. When the amino equivalent is 1000 g / mol or more, adhesion spots due to excessive progress of cross-linking can be suppressed, and the generation of fluff during the process can be suppressed, which is preferable. When the amino equivalent is 6000 g / mol or less, the silicone can be sufficiently crosslinked and high strand tensile strength can be exhibited, which is preferable. The amino equivalent can be measured by a known method such as neutralization titration. The amino equivalent can be controlled by the amount of amine added when polymerizing the amino-modified silicone.

The oil for polyacrylonitrile-based precursor fiber bundle of the present invention contains a nonionic surfactant in the oil, preferably 5 to 70% by mass, more preferably 15 to 60% by mass, and further preferably 20 to 50% by mass. Here, when an oil agent is emulsified and dispersed in a volatile component such as a solvent to give it to a fiber bundle, and then the volatile component is volatilized to obtain a polyacrylonitrile-based precursor fiber bundle, the polyacrylonitrile-based precursor fiber bundle is used. The oil agent refers only to the non-volatile component which is a residue excluding the volatile component in the air at 120 ° C. for 2 hours. Nonionic surfactants are used as emulsifiers, antistatic agents and the like. Nonionic surfactants refer to surfactants having hydrophilic groups in their molecules, such as hydroxyl groups, ether bonds, acid amides, and esters, which do not generate ions even when dissolved in water. The nonionic surfactant is not particularly limited, and known ones can be appropriately selected and used. The nonionic surfactant may be used alone or in combination of two or more. If the amount of the nonionic surfactant is 5% by mass or more, since the emulsification is sufficient, the silicone easily adheres uniformly to the polyacrylonitrile-based precursor fiber bundle, so that the carbon fiber has good quality and high strand tensile strength. It is preferable because a bundle can be obtained. When the nonionic surfactant is 70% by mass or less, the ratio of silicone can be increased, and a carbon fiber bundle having good quality and high strand tensile strength can be obtained, which is preferable. The ratio of the nonionic surfactant can be easily achieved by changing the mass ratio at the time of preparing the oil agent.

Examples of the nonionic surfactant include polyoxyalkylene linear alkyl ethers such as polyoxyethylene hexyl ether, polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, and polyoxyethylene cetyl ether, and poly. Polyoxyalkylene branched primary alkyl ethers such as oxyethylene 2-ethylhexyl ether, polyoxyethylene isocetyl ether, polyoxyethylene isostearyl ether, polyoxyethylene 1-hexylhexyl ether, polyoxyethylene 1-octylhexyl ether, Polyoxyalkylene branched secondary alkyl ethers such as polyoxyethylene 1-hexyl octyl ether, polyoxyethylene 1-pentyl heptyl ether, polyoxyethylene 1-heptyl pentyl ether, and polyoxyalkylene such as polyoxyethylene oleyl ether. Polyoxyalkylene alkyl phenyl ethers such as alkenyl ethers, polyoxyethylene octyl phenyl ethers, polyoxyethylene nonyl phenyl ethers, polyoxyethylene dodecyl phenyl ethers, polyoxyethylene tristyryl phenyl ethers, polyoxyethylene distyryl phenyl ethers, polyoxy Polyoxyalkylene alkylarylphenyl ethers such as ethylenestyrylphenyl ethers, polyoxyethylene tribenzylphenyl ethers, polyoxyethylene dibenzylphenyl ethers, polyoxyethylene benzylphenyl ethers, polyoxyethylene monolaurates, polyoxyethylene monooleates, Polyoxyalkylene fatty acid esters such as polyoxyethylene monostearate, polyoxyethylene monomyristylate, polyoxyethylene dilaurate, polyoxyethylene diolate, polyoxyethylene dimyristylate, and polyoxyethylene distearate, sorbitan mono Sorbitane esters such as palmitate and sorbitan monooleate, polyoxyalkylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, glycerin monostearate, glycerin monolaurate, glycerin monopalmitate, etc. Glycerin fatty acid ester, polyoxyalkylene sorbitol fatty acid Polyoxyalkylene hydrogenated oil ethers such as esters, sucrose fatty acid esters, polyoxyethylene hydrogenated oil ethers, polyoxyalkylene hydrogenated castor oil ethers such as polyoxyethylene hydrogenated castor oil ethers, polyoxyethylene laurylamino ethers, polyoxyethylene stearylamino ethers, etc. Polyoxyalkylene alkyl amino ether, oxyethylene-oxypropylene block or random copolymer, oxyethylene-oxypropylene block or random copolymer terminal alkyl ether, oxyethylene-oxypropylene block or random copolymer terminal sho Sugar ethers, polyoxyalkylene alkylamides such as polyoxyethylene laurylamide and polyoxyethylene stearylamide, polyoxyethylene bisphenol A ethers such as 2,2-bis (4-polyoxyethylene-oxyphenyl) propane, polyoxy Aromatic esters such as ethylene bisphenol A lauric acid ester and triisodecyl trimellitic acid, aliphatic esters such as polyethylene glycol diacrylate and pentaerythritol tetrastearate, ethylene oxide (EO), propylene oxide (PO), butylene oxide (BO) Examples thereof include polyalkylene glycol obtained by addition-polymerizing alkylene oxide (AO) such as. Further, as the acetylene-based surfactant, acetylene alcohol, acetylene diol, a compound in which alkylene oxide is added to acetylene alcohol, a compound in which alkylene oxide is added to acetylene diol, and the like can also be used.

The oil for polyacrylonitrile-based precursor fiber bundle of the present invention contains a surfactant other than the nonionic surfactant such as an anionic surfactant and a cationic surfactant as long as the effect of the present invention is not impaired. You may.

Further, the oil for polyacrylonitrile-based precursor fiber bundle of the present invention may contain components other than the above-mentioned components as long as the effects of the present invention are not impaired. Other components include acidic phosphoric acid esters, phenol-based, amine-based, sulfur-based, phosphorus-based, quinone-based antioxidants, acetic acid, benzoic acid, blended acid compounds such as arginine and phosphoric acid, and higher alcohols. Antistatic agents such as sulfate ester salts of higher alcohol ethers, sulfonates, phosphoric acid ester salts of higher alcohol / higher alcohol ethers, quaternary ammonium salt type cationic surfactants, amine salt type cationic surfactants, etc. Examples thereof include alkyl esters of higher alcohols, higher alcohol ethers, smoothing agents such as waxes, antibacterial agents, preservatives, rust preventives and hygroscopic agents.

Regarding the oil for polyacrylonitrile-based precursor fiber bundle of the present invention, the ratio of silicone in the oil is preferably 30 to 95% by mass, more preferably 40 to 85% by mass, and further preferably 50 to 80% by mass. Is. Here, when an oil agent is emulsified and dispersed in a volatile component such as a solvent to give it to a fiber bundle, and then the volatile component is volatilized to obtain a polyacrylonitrile-based precursor fiber bundle, the polyacrylonitrile-based precursor fiber bundle is used. The oil agent refers only to the non-volatile component which is a residue excluding the volatile component in the air at 120 ° C. for 2 hours. The ratio of the amino-modified silicone in the oil agent is the ratio of the amino-modified silicone to all the components including the nonionic surfactant and other components other than the amino-modified silicone. When the ratio of the amino-modified silicone in the oil is 30% by mass or more, the amino-modified silicone can be sufficiently adhered to the polyacrylonitrile-based precursor fiber bundle, so that a carbon fiber bundle having good quality and high strand tensile strength can be obtained. It is preferable because it can be obtained. When the ratio of the amino-modified silicone in the oil is 95% by mass or less, the silicone is easily adhered uniformly to the polyacrylonitrile-based precursor fiber bundle because the emulsification is sufficient, so that the quality is good and the strand tensile strength is high. It is preferable because a high carbon fiber bundle can be obtained. The ratio of amino-modified silicone can be easily achieved by changing the mass ratio at the time of preparing the oil preparation.

The oil for polyacrylonitrile-based precursor fiber bundle in the present invention refers to only a non-volatile component, but may also contain a volatile component such as water or alcohol. As the volatile component, water is preferable from the viewpoint of uniform adhesion of the oil agent to the polyacrylonitrile-based precursor fiber bundle.

The oil for polyacrylonitrile-based precursor fiber bundle of the present invention can be produced by mixing the components described above. The method for emulsifying and dispersing the components described above is not particularly limited, and a known method can be adopted. Examples of such a method include a method in which each component constituting the polyacrylonitrile-based precursor fiber bundle oil is added to warm water under stirring to emulsify and disperse, or a polyacrylonitrile-based precursor fiber bundle oil is used. Examples thereof include a method in which each of the constituent components is mixed and water is gradually added to emulsify the phase while applying a mechanical shearing force using a homogenizer, a homomixer, a ball mill or the like. When a self-emulsifying nonionic surfactant is used, it can be dissolved in water and mixed with other components, or a method of emulsifying at the same time as other components such as amino-modified silicone can be adopted. .. When an ester compound that is difficult to emulsify is used, only the ester compound can be emulsified and mixed with other emulsions, or a method of emulsifying at the same time as other components such as amino-modified silicone can be adopted. ..

Next, a method for producing the polyacrylonitrile-based precursor fiber bundle of the present invention will be described.

The polyacrylonitrile-based precursor fiber bundle used as a raw material in the present invention preferably uses a polyacrylonitrile-based polymer. In the present invention, the polyacrylonitrile-based polymer means that at least acrylonitrile is the main constituent component of the polymer skeleton, and the main constituent component usually occupies 90 to 100% by mass of the polymer skeleton. It refers to a component. In the production of the polyacrylonitrile-based precursor fiber bundle, the method for producing the polyacrylonitrile-based polymer can be selected from known polymerization methods.

The polyacrylonitrile-based precursor fiber bundle used in the present invention needs to be dried after applying the above-mentioned silicone-based oil agent to the water-swelled yarn obtained by wet spinning or dry-wet spinning and then washing with water. be. The drying method is preferably heat treatment. The heat treatment is preferable because the fiber bundles are densified and the density is increased. As an application method, it may be appropriately selected and used in consideration of the fact that it can be applied uniformly to the inside of the thread. Specifically, an oil agent is prepared as an aqueous dispersion using an appropriate emulsifier, and the application method is used. A means of applying the water dispersion to the water-swelling fibers by a dipping method, a spraying method, a touch roll method, a guide lubrication method, or the like is adopted. As a method of drying, a method of air-drying with wind, a method of using an oven, a method of using a roller, or a heat treatment method is adopted.

The adhesion ratio A (mass%) of the silicon element of the fiber bundle immediately after applying the silicone-based oil agent in the present invention is preferably 0.150 to 0.280% by mass, and more preferably 0.170 to 0.250. It is by mass, more preferably 0.180 to 0.230% by mass. The fiber bundle immediately after the silicone-based oil is applied is a fiber bundle in which excess silicone-based oil is removed by niping or gas spraying immediately after the silicone-based oil is applied, and refers to a fiber bundle before drying. When the adhesion ratio A is 0.150% by mass or more, fusion between single fibers can be sufficiently suppressed, and the strand tensile strength of the carbon fiber bundle is improved, which is preferable. When the adhesion ratio A is 0.280% by mass or less, fusion between the single fibers via silicone does not occur, and the strand tensile strength of the carbon fiber bundle is improved, which is preferable. The adhesion rate A of the silicon element of the fiber bundle immediately after the silicone-based oil is applied can be measured by fluorescent X-rays described later. The adhesion rate A can be controlled by, for example, adjusting the concentration of the oil agent or controlling the adhesion amount of the silicone-based oil agent by niping or the like.

The density of the polyacrylonitrile-based precursor fiber bundle of the present invention obtained by applying a silicone-based oil to the fiber bundle and then drying it is 1.15 to 1.18 g / cm ³ , preferably 1.16. It is ~ 1.18 g / cm ³ , and more preferably 1.17 to 1.18 g / cm ³ . The density of the polyacrylonitrile-based precursor fiber bundle means the density of the polyacrylonitrile-based precursor fiber bundle including silicone. The density of the polyacrylonitrile-based precursor fiber bundle is generally used as an index showing the density. When the density is 1.15 g / cm ³ or more, the strand tensile strength of the obtained carbon fiber bundle can be improved. Further, when it is 1.18 g / cm ³ or less, the wrapping when winding the polyacrylonitrile-based precursor fiber bundle and when supplying the polyacrylonitrile-based precursor fiber bundle in the subsequent flame resistance step is reduced, and the quality is improved. Can be made to. The density of the polyacrylonitrile-based precursor fiber bundle can be measured by the method described later. The density of the polyacrylonitrile-based precursor fiber bundle can be achieved by controlling the heat treatment temperature and time, or by adopting a known void control method.

It is preferable that the dried yarn is further post-stretched in pressurized steam or under dry heat from the viewpoint of compactness and productivity of the obtained polyacrylonitrile-based precursor fiber bundle. The steam pressure or temperature at the time of post-stretching and the post-stretching ratio should be appropriately selected and used within a range in which yarn breakage and fluffing do not occur. The adhesion rate B (mass%) of the silicon element of the fiber bundle ^{having a density of 1.15 to 1.18 g / cm 3} at the start of the flame resistance step in the present invention is preferably 0.150 to 0.250% by mass. It is more preferably 0.170 to 0.230% by mass, and even more preferably 0.180 to 0.210% by mass. When the adhesion ratio B is 0.150% by mass or more, fusion between single fibers can be sufficiently suppressed and the strand tensile strength of the carbon fiber bundle is improved, which is preferable. When the adhesion ratio B is 0.250% by mass or less, fusion between the single fibers via silicone does not occur, and the strand tensile strength of the carbon fiber bundle is improved, which is preferable. The adhesion rate B of the silicon element of the fiber bundle having a density of 1.15 to 1.18 g / cm ^{3 at the start of the flame resistance step can be measured by fluorescent X-rays described later.} The adhesion rate B can be controlled by, for example, adjusting the concentration of the oil agent, controlling the adhesion amount of the silicone-based oil agent by nip or the like, or adjusting the drying conditions.

The polyacrylonitrile-based precursor fiber bundle in the present invention has an adhesion rate of silicon element of A (mass%) in the fiber bundle immediately after the silicone-based oil is applied, and a density of 1.15 to 1.18 g / at the start of the flame resistance process. When ^{the adhesion rate of the silicon element in the fiber bundle of cm 3} is B (mass%), the formula (1) is satisfied.

1.0 ≦ (AB) / A × 100 ≦ 20.0 ・ ・ ・ (1)
At this time, the left side and the right side are preferably 1.5 and 13.0, respectively, more preferably 2.0 and 10.0, respectively, and further preferably 2.5 and 8.0, respectively. The formula (1) is the ratio of the silicon element adhesion rate of the fiber bundle having a density of 1.15 to 1.18 g / cm ^{3 at the start of the flame resistance process to the silicon element adhesion rate of the fiber bundle immediately after applying the silicone-based oil agent.} This means the volatility of the compound containing a silicon element in the drying step after the addition of the silicone-based oil agent. When the left side of the formula (1) is 1.0 or more, the spreadability is improved when silicone is applied to the polyacrylonitrile-based precursor fiber bundle, and the silicone is uniformly applied, so that the quality is good and the strand tension is good. A carbon fiber bundle having high strength can be obtained. When the left side of the formula (1) is 20.0 or less, it is sufficient to reduce the contamination in the furnace in the flame resistance step, and the carbon fiber bundle having good quality can be obtained because the step passability is excellent. The adhesion rate of the silicon element in the fiber bundle can be measured by fluorescent X-rays described later. In order to control the formula (1) within such a range, it is achieved by adjusting the polymerization rate when polymerizing the silicone, atmospheric distillation, adding a required amount of a low molecular weight siloxane oligomer to the polymerized silicone, and the like. can.

Next, a method for producing the carbon fiber bundle used in the present invention will be described.

It can be obtained by subjecting the polyacrylonitrile-based precursor fiber bundle to flame resistance treatment and then carbonization treatment in order.

The flame-resistant treatment of the polyacrylonitrile-based precursor fiber bundle is carried out in an oxidizing atmosphere until the ^{density becomes 1.28 to 1.48 g / cm 3.} The density is preferably 1.30 to 1.45 g / cm ³ , and more preferably 1.32 to 1.42 g / cm ³ . The density of the obtained flame-resistant fiber bundle is generally used as an index showing the degree of progress of the flame-resistant reaction. When the density is 1.28 g / cm ³ or more, the structure has high heat resistance, so that it is difficult to decompose when heat-treated at a high temperature, and the process passability such as suppression of fluff is improved. Is improved. Further, when the amount is 1.48 g / cm ³ or less, it is not necessary to perform more heat treatment than necessary for passing through the subsequent carbonization treatment step, so that fluff and the like are suppressed and the quality is improved. Here, the oxidizing atmosphere is an atmosphere containing 10% by mass or more of known oxidizing substances such as oxygen and nitrogen dioxide, and an air atmosphere is preferable from the viewpoint of simplicity. Such a density can be measured by a method described later, and the density can be adjusted by the heat treatment temperature and the heat treatment time.

The heat treatment temperature for the flameproofing treatment of the polyacrylonitrile-based precursor fiber bundle is 200 to 300 ° C., preferably 210 to 290 ° C., more preferably 220 to 280 ° C., and further preferably 230 to 270 ° C. be. If the heat treatment temperature of the flame-resistant treatment is 200 ° C. or higher, the structure has high heat resistance, so that it is difficult to decompose during heat treatment at a high temperature, and fluff is suppressed, which improves process passability. Is improved. When the heat treatment temperature of the flame-resistant treatment is 300 ° C. or lower, the heat storage in the flame-resistant process can be controlled, and the process passability such as suppression of fluff is improved, so that the quality is improved. The heat treatment temperature can be obtained by measuring the atmospheric gas temperature with a thermocouple or the like. The heat treatment temperature of the flameproofing treatment can be easily controlled by changing the set temperature of the heat treatment apparatus such as an oven.

The polyacrylonitrile-based precursor fiber bundle and the fiber bundle in the flameproofing step in the present invention have a density of 1.15 to 1.18 g / cm ³ at the start of the flameproofing step, and the adhesion rate of the silicon element of the fiber bundle is B (mass). %), The formula (2) is satisfied when the adhesion rate of the silicon element of the fiber bundle whose ^{density is increased by 0.06 g / cm 3} from the start of the flame resistance step by the heat treatment in the flame resistance step is C (mass%).

(BC) / B × 100 ≦ 5.0 ・ ・ ・ (2)
At this time, the right side is preferably 4.5, and more preferably 4.0. In the formula (2), the density increased by ^{0.06 g / cm 3} from the start of the flame resistance step by the heat treatment of the flame resistance step with respect to the adhesion rate of the silicon element of the fiber bundle having ^{a density of 1.18 g / cm 3 at the start of the flame resistance step.} It is the ratio of the adhesion rate of silicon element in the fiber bundle, and means the volatilization rate of the compound containing silicon element up to the fiber bundle ^{whose density has increased by 0.06 g / cm 3 from the start of the flame resistance step. Here, the fiber bundle whose density has increased by 0.06 g / cm 3} from the start of the flame resistance step by the heat treatment in the flame resistance step is a fiber bundle in the middle of flame resistance. Therefore, the formula (2) means the degree of contamination at the initial stage of the flame resistance step because it is the volatility of the compound containing the silicon element at the initial stage of the flame resistance step. Within the range where the formula (2) is applied, the volatilization of the compound containing silicon element at the initial stage of the flame resistance process can be suppressed, so that the contamination at the initial stage of the flame resistance process can be reduced, and the quality is good because the process passability is excellent. A carbon fiber bundle is obtained. In order to confirm whether the density is such that the fiber bundle is applied, the fiber bundle in the middle of the flame resistance step is sampled and the density is measured by the method described later. The adhesion rate of the silicon element in the fiber bundle can be measured by fluorescent X-rays described later. In order to control the formula (2) within such a range, it can be controlled by using a silicone from which a specific molecular weight silicone obtained by controlling the molecular weight distribution at the time of polymerization or purification by a column has been removed.

^{In the fiber bundle in the flame resistance step in the present invention, the density of the fiber bundle increased by 0.06 g / cm 3} from the start of the flame resistance step by the heat treatment in the flame resistance step, and the adhesion rate of the silicon element of the fiber bundle was set to C (mass%). Then, the equation (3) is satisfied.

C ≧ 0.150 ・ ・ ・ (3)
At this time, the right side is preferably 0.160, and more preferably 0.170. ^{Equation (3) is the adhesion rate of silicon element in the fiber bundle whose density has increased by 0.06 g / cm 3} from the start of the flame resistance process, and the adhesion rate of silicon element in the initial stage of the flame resistance process, that is, the silicon remaining in the fiber bundle. It means the adhesion rate of elements. Within the range in which the formula (3) is applied, it is possible to prevent the single fibers from being fused to each other at the initial stage of the flame resistance process, so that a carbon fiber bundle having excellent quality can be obtained because the process passability is excellent. In order to confirm whether the density is such that the fiber bundle is applied, the fiber bundle in the middle of the flame resistance process is sampled, or the polyacrylonitrile-based precursor fiber bundle is heat-treated in a batch oven and the density is measured by the method described later. do. The adhesion rate of the silicon element in the fiber bundle can be measured by fluorescent X-rays described later. In order to control the formula (3) within such a range, it can be controlled by controlling the ratio and concentration of silicone in the oil for polyacrylonitrile-based precursor fiber bundle.

The flame-resistant fiber bundle produced by the above-mentioned method for producing a flame-resistant fiber bundle is preferably precarbonized. In the pre-carbonization step, it is preferable to heat-treat the obtained flame-resistant fiber bundle in an inert atmosphere at a maximum temperature of 500 to 1200 ° C. ^{until the density reaches 1.50 to 1.80 g / cm 3.}

Following the preliminary carbonization, carbonization is performed. In the present invention, in the carbonization step, the obtained preliminary carbonized fiber bundle is heat-treated in an inert atmosphere at a maximum temperature of 1200 to 3000 ° C., preferably 1200 to 1800 ° C., more preferably 1200 to 1600 ° C. If the maximum temperature is 1200 ° C. or higher, the nitrogen content in the carbon fiber bundle is reduced, and a carbon fiber bundle with less fluff and good process passability and good quality can be produced. When the maximum temperature is 3000 ° C. or lower, a carbon fiber bundle having less fluff and good quality can be obtained because scratching is reduced. Examples of the gas used in the inert atmosphere include nitrogen, argon and xenon, and nitrogen is preferably used from an economical point of view.

The carbon fiber bundle obtained as described above is preferably subjected to an oxidation treatment, and an oxygen-containing functional group is introduced. For the electrolytic surface treatment of the present invention, vapor phase oxidation, liquid phase oxidation and liquid phase electrolytic oxidation are used, but liquid phase electrolytic oxidation is preferably used from the viewpoint of good quality and uniform treatment. In the present invention, the method of liquid phase electrolytic oxidation is not particularly limited, and a known method may be used.

After such an electrolytic treatment, a sizing treatment can be performed in order to impart a focusing property to the obtained carbon fiber bundle. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected according to the type of the matrix resin used for the composite material.

The methods for measuring various physical property values described in the present specification are as follows.

<Mass fraction of amino-modified silicone>
Amino-modified silicone is stirred at room temperature by adding tetrahydrofuran added with ethanolamine, filtered using a filter, and the filtrate is measured by gel permeation chromatography. As the column, TSKgel GMH _HR- N (φ7.8 mm × 30 cm, manufactured by Tosoh) is used. A calibration curve is prepared from monodisperse polystyrene to obtain a polystyrene-equivalent molecular weight distribution. The mass fraction is calculated from the ratio of the peak area of a specific molecular weight to the peak area of all molecular weight ranges.

<Density of polyacrylonitrile-based precursor fiber bundles and flame-resistant fiber bundles>
Collect 1 to 3 g of a polyacrylonitrile-based precursor fiber bundle, a fiber bundle in the process of being flame-resistant, or a flame-resistant fiber bundle, and dry at 120 ° C. for 2 hours. Next, the absolute dry mass D (g) is measured, then impregnated with ethanol to sufficiently defoam, and then the mass E (g) of the fiber bundle in the ethanol solvent bath is measured, and the density = (D × ρ). The density is calculated by / (DE). ρ is the ethanol density at the measured temperature.

<Adhesion rate of silicon element>
A fiber bundle immediately after applying a silicone-based oil agent, a polyacrylonitrile-based precursor fiber bundle, and a fiber bundle in the process of being made flame-resistant 0.5 to 0.7 g are wound around a 2 cm-thick "Teflon (registered trademark)" plate and fluorescent X-ray. Therefore, the silicon content (mass%) of each fiber bundle is defined as the adhesion rate of the silicon element of the fiber bundle. Instead of using the measured value of fluorescent X-ray as it is, a calibration curve is prepared from a polyacrylonitrile-based precursor fiber bundle having a known amount of Si, and the measured value of fluorescent X-ray is converted into the amount of Si and calculated by the above formula. do.

<Pollution in heat treatment furnace>
Although it is difficult to quantitatively measure the degree of contamination in the heat treatment furnace, it is possible to easily evaluate the degree of contamination in the heat treatment furnace by the amount of fine particles generated as a model. After drying, the polyacrylonitrile-based precursor fiber bundle is cut to about 1 cm, 1000 mg is placed in an aluminum dish with a diameter of 4 cm, covered with an aluminum dish, placed in a hot air oven in an air atmosphere, and treated at 250 ° C. for 2 hours. do. The inside of the lid of the treated aluminum dish is weighed, and the mass difference before the treatment is calculated to obtain the amount of fine particles produced. If the amount of fine particles produced is 1.5 mg or more, it is considered as “presence”, and if it is less than 1.5 mg, it is considered as “absent”.

<Quality of fiber bundle in flame resistance process>
The number of single fiber breaks (hereinafter referred to as fluff) and aggregates of single fiber breaks (hereinafter referred to as pills) in the fiber bundle while running the flameproof fiber bundle of 6000 filaments at a speed of 1 m / min. The total was counted and evaluated on a three-point scale. The evaluation criteria are as follows. When the flame-resistant fiber bundle is 3000 filaments, the number of fluffs and pills is increased by 1.4 times, and when the carbon fiber bundle is 12000 filaments, the number of fluffs and pills is increased by 0.7 times. Evaluation criteria can be matched. The numerical value is rounded off to the nearest whole number.
・ ◎: 1 or less in 600 m of fiber bundle ・ ○: 2 to 4 in 600 m of fiber bundle ・ Δ: 5 to 30 in 600 m of fiber bundle.

<Strand tensile strength of carbon fiber bundle>
The strand tensile strength of the carbon fiber bundle is determined according to the resin impregnated strand test method of JIS R7608 (2004) according to the following procedure. As the resin formulation, "Ceroxide (registered trademark)" 2021P (manufactured by Daicel Chemical Industry Co., Ltd.) / Boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / Acetone = 100/3/4 (part by mass) is used. As the curing conditions, normal pressure, temperature 125 ° C., and time 30 minutes are used. Ten strands of the carbon fiber bundle are measured, and the average value thereof is taken as the strand tensile strength.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited thereto. Each measurement method in this embodiment is as described above.

(Example 1)
A copolymer composed of acrylonitrile and itaconic acid was polymerized by a solution polymerization method using dimethylsulfoxide as a solvent to produce a polyacrylonitrile-based copolymer to obtain a spinning solution. The obtained spinning solution was once discharged into the air from the spinneret and introduced into a coagulation bath consisting of an aqueous solution of 35% dimethyl sulfoxide controlled at 3 ° C. to obtain a fiber bundle coagulated by a dry-wet spinning method. This fiber bundle was washed with water at 30 to 98 ° C. by a conventional method and stretched at that time. Subsequently, with respect to the fiber bundle after stretching in the water bath, 12.2% by mass is 100 g / mol or more and less than 1000 g / mol, 18.0% by mass is 1000 g / mol or more and 10000 g / mol or less, and the weight average molecular weight is 28000 g / mol. A silicone-based oil prepared by emulsifying mol of amino-modified silicone with a nonionic emulsifier was applied, and the fiber bundle was sampled to measure the adhesion rate of the silicon element to give A (mass%). At this time, the concentration of the oil agent was adjusted and applied so that the adhesion rate of the silicon element was 0.189% by mass. After that, a drying and densifying treatment was performed using a heating roller at 160 ° C. to obtain 12,000 single fibers, and then the fibers were stretched 3.7 times in pressurized steam under pressure steam to increase the total yarn-making draw ratio to 13. As a doubling, a polyacrylonitrile-based precursor fiber bundle having 12,000 single fibers was obtained. The density of the obtained fiber bundle was 1.17 g / cm ³ . When the adhesion rate of the silicon element of the polyacrylonitrile-based precursor fiber bundle was measured and set to B (mass%), (AB) / A × 100 was 10.6.

The obtained polyacrylonitrile-based precursor fiber bundle was heat-treated in an oven at an air atmosphere of 230 to 280 ° C. with a draw ratio of 1, and converted into a flame-resistant fiber bundle having ^{a density of 1.38 g / cm 3.} At this time, the fiber bundle in the middle of flame resistance was sampled, and the adhesion rate of the silicon element of the fiber bundle (density 1.23 g / cm ^{3 ) whose density increased by 0.06 g / cm 3 from the start of the flame resistance process was measured.} When C (mass%) was used, (BC) / B × 100 was 4.7 and C was 0.161% by mass. The obtained flame-resistant fiber bundle was subjected to pre-carbonization treatment in a nitrogen atmosphere at a maximum temperature of 800 ° C. to obtain a pre-carbonized fiber bundle. The obtained preliminary carbonized fiber bundle was carbonized in a nitrogen atmosphere at a maximum temperature of 1500 ° C. The obtained carbon fiber bundle was surface-treated and sizing agent-coated. The quality of the fiber bundle in the flame resistance process was good, and no contamination in the heat treatment furnace was observed. The strand tensile strength of the carbon fiber bundle was as high as 5.4 GPa. The evaluation results are shown in Table 1.

(Example 2)
The mass fraction of 100 g / mol or more and less than 1000 g / mol of the amino-modified silicone is 7.5 mass%, the mass fraction of 1000 g / mol or more and 10000 g / mol or less of the amino-modified silicone is 16.0 mass%, and the weight average of the silicone. When the same as in Example 1 except that the molecular weight was set to 42000 g / mol, (AB) / A × 100 was 10.6 and (BC) / B × 100 was 4.7, which was a flame resistance step. The quality of the fiber bundle was good, and no contamination was observed in the heat treatment furnace. Further, the strand tensile strength of the carbon fiber bundle was as high as 5.4 GPa. The evaluation results are shown in Table 1.

(Example 3)
The mass fraction of 100 g / mol or more and less than 1000 g / mol of the amino-modified silicone is 11.0 mass%, the mass fraction of 1000 g / mol or more and 10000 g / mol or less of the amino-modified silicone is 13.2 mass%, and the weight average of the silicone. When the same as in Example 1 except that the molecular weight was set to 27,000 g / mol, (AB) / A × 100 was 12.7 and (BC) / B × 100 was 1.8, which was a flame resistance step. The quality of the fiber bundle was good, and no contamination was observed in the heat treatment furnace. Further, the strand tensile strength of the carbon fiber bundle was as high as 5.3 GPa. The evaluation results are shown in Table 1.

(Example 4)
According to JP-A-2004-244771, the mass fraction of 100 g / mol or more and less than 1000 g / mol of amino-modified silicone is 0.5% by mass, and the mass fraction of 1000 g / mol or more and 10,000 g / mol or less of amino-modified silicone. 14.4, and the weight average molecular weight of the silicone was 32000 g / mol, but the same procedure as in Example 1 was carried out. Was 4.4, and the quality of the fiber bundle in the flame resistance process was good, and no contamination in the heat treatment furnace was observed. Further, the strand tensile strength of the carbon fiber bundle was as high as 5.5 GPa. The evaluation results are shown in Table 1.

(Example 5)
The mass fraction of 100 g / mol or more and less than 1000 g / mol of the amino-modified silicone is 0.3% by mass, the mass fraction of 1000 g / mol or more and 10000 g / mol or less of the amino-modified silicone is 7.0 mass%, and the weight average of the silicone. When the same procedure as in Example 1 was carried out except that the molecular weight was set to 50,000 g / mol, (AB) / A × 100 was 0.5 and (BC) / B × 100 was 4.3. The quality of the fiber bundle was good, and no contamination was observed in the heat treatment furnace. Further, the strand tensile strength of the carbon fiber bundle was as high as 5.4 GPa. The evaluation results are shown in Table 1.

(Example 6)
A mass fraction of 100 g / mol or more and less than 1000 g / mol of amino-modified silicone is 0.5 mass%, a mass fraction of 1000 g / mol or more and 10000 g / mol or less of amino-modified silicone is 5.0 mass%, and the weight average of silicone. When the same procedure as in Example 1 was carried out except that the molecular weight was set to 62000 g / mol, (AB) / A × 100 was 1.1 and (BC) / B × 100 was 4.8. The quality of the fiber bundle was good, and no contamination was observed in the heat treatment furnace. Further, the strand tensile strength of the carbon fiber bundle was as high as 5.3 GPa. The evaluation results are shown in Table 1.

(Comparative Example 1)
The mass fraction of 100 g / mol or more and less than 1000 g / mol of the amino-modified silicone is 7.2 mass%, the mass fraction of 1000 g / mol or more and 10000 g / mol or less of the amino-modified silicone is 38.0 mass%, and the weight average of the silicone. When the same procedure as in Example 1 was carried out except that the molecular weight was set to 26000 g / mol, (AB) / A × 100 was 7.4 and (BC) / B × 100 was 9.1. The quality of the fiber bundle in the above was slightly deteriorated, and contamination in the heat treatment furnace was observed. The strand tensile strength of the carbon fiber bundle was 5.4 GPa. The evaluation results are shown in Table 1.

(Comparative Example 2)
The mass fraction of 100 g / mol or more and less than 1000 g / mol of amino-modified silicone is 8.6 mass%, the mass fraction of 1000 g / mol or more and 10000 g / mol or less of amino-modified silicone is 52.0 mass%, and the weight average of silicone. When the same as in Example 1 except that the molecular weight was set to 18000 g / mol, (AB) / A × 100 was 9.0 and (BC) / B × 100 was 11.6, which was a flame resistance step. The quality of the fiber bundle in the above was slightly deteriorated, and contamination in the heat treatment furnace was observed. The strand tensile strength of the carbon fiber bundle was 5.0 GPa. The evaluation results are shown in Table 1.

(Comparative Example 3)
The mass fraction of 100 g / mol or more and less than 1000 g / mol of the amino-modified silicone is 0.3% by mass, the mass fraction of 1000 g / mol or more and 10000 g / mol or less of the amino-modified silicone is 2.0% by mass, and the weight average of the silicone. When the same procedure as in Example 1 was carried out except that the molecular weight was set to 31200 g / mol, (AB) / A × 100 was 0 and (BC) / B × 100 was 1.7, and the fibers in the flame resistance step were used. The quality of the bundle was slightly deteriorated, and no contamination was observed in the heat treatment furnace, but the strand tensile strength of the carbon fiber bundle was reduced to 4.8 GPa. The evaluation results are shown in Table 1.

(Comparative Example 4)
The mass fraction of 100 g / mol or more and less than 1000 g / mol of amino-modified silicone is 7.5 mass%, the mass fraction of 1000 g / mol or more and 10000 g / mol or less of amino-modified silicone is 20.0 mass%, and the weight average of silicone. The same as in Example 1 except that the molecular weight was 42000 g / mol and the adhesion rate A of the silicon element of the fiber bundle immediately after the addition of the silicone-based oil agent was 0.142% by mass, (AB) / A × 100 was 4.2, (BC) / B × 100 was 2.9, and C was 0.132% by mass, and no contamination was observed in the heat treatment furnace, but the quality of the fiber bundle in the flame resistance process was high. It got worse. Further, the strand tensile strength of the carbon fiber bundle decreased to 4.9 GPa. The evaluation results are shown in Table 1.

(Comparative Example 5)
When the same procedure as in Example 1 was carried out except that the adhesion rate A of the silicon element of the fiber bundle immediately after the addition of the silicone-based oil was set to 0.079% by mass, (AB) / A × 100 was 4.7. (BC) / B × 100 was 3.7 and C was 0.079% by mass, and no contamination was observed in the heat treatment furnace, but the quality of the fiber bundle in the flame resistance step was deteriorated. Further, the strand tensile strength of the carbon fiber bundle was significantly reduced to 4.5 GPa. The evaluation results are shown in Table 1.

(Reference Examples 1 to 9)
In order to evaluate the difference between the weight average molecular weight and the volatile amount in the evaluation method, a thermogravimetric analyzer (Burker AX) using a monodisperse polydimethylsiloxane reagent (manufactured by Alfa Aesar) having a weight average molecular weight of 1250 to 63000 g / mol was used. The volatilization amount was evaluated for each of TG-DTA2000SA) and fiber bundles manufactured by the company. In the thermogravimetric analyzer, 10 mg of each of the polydimethylsiloxane reagents was weighed in a sample pan, the temperature was raised from room temperature to 250 ° C. at 10 ° C./min, and the volatilization rate was determined from the weight loss rate after holding for 60 minutes. The evaluation of the fiber bundle was carried out by obtaining a polyacrylonitrile-based precursor fiber bundle in the same manner as in Example 1 except that an oil agent emulsified with a nonionic emulsifier was added to each polydimethylsiloxane reagent, and the obtained polyacrylonitrile-based precursor was obtained. The fiber bundle was wrapped around a metal frame and heat-treated in a convection oven at 250 ° C. for 60 minutes in an air atmosphere. The adhesion rate of silicon element in the fiber bundle before and after firing was measured using fluorescent X-rays according to the above-mentioned method for measuring the adhesion rate of silicon element. The adhesion rate of the silicon element before firing was a mass%, the adhesion rate of the silicon element after firing was b mass%, and the volatilization rate of the fiber bundle at 250 ° C. was determined by (ab) / a × 100. Table 2 shows the results of each evaluation. The volatility evaluated by the fiber bundle was significantly larger than the volatility evaluated by thermogravimetric analysis. In particular, as the molecular weight increased to 2000 g / mol or more, the difference between the respective evaluation methods increased. The above results indicate that the thermogravimetric analysis could not correctly evaluate the behavior of the volatility in the fiber bundle.

Claims (4)

After applying a silicone-based oil agent to the fiber bundle, a polyacrylonitrile-based precursor fiber bundle density 1.15~1.18g / cm ³ obtained by drying, a density 1.28~1.48g / cm ³ After obtaining a flame-resistant fiber bundle by a flame-resistant step of heat-treating in an oxidizing atmosphere of 200 to 300 ° C., a carbon fiber bundle is obtained by a carbonization step of heat-treating at 1200 to 3000 ° C. in an inert atmosphere. In the production method of, the adhesion rate of the silicon element of the fiber bundle immediately after applying the silicone-based oil is A (mass%), and the silicon of the fiber bundle ^{having a density of 1.15 to 1.18 g / cm 3 at the start of the flame resistance process.} When the adhesion rate of the element is B (mass%) and the adhesion rate of the silicon element of the fiber bundle whose ^{density is increased by 0.06 g / cm 3} from the start of the flame resistance step by the heat treatment of the flame resistance step is C (mass%). , A method for producing a carbon fiber bundle satisfying the formulas (1) to (3).
1.0 ≦ (AB) / A × 100 ≦ 20.0 ・ ・ ・ (1)
(BC) / B × 100 ≦ 5.0 ・ ・ ・ (2)
C ≧ 0.150 ・ ・ ・ (3) 1.0 to 10.0% by mass of molecules in the silicone-based oil having a molecular weight of 100 g / mol or more and less than 1000 g / mol and 1.0 to 19.0% by mass of molecules having a molecular weight of 1000 g / mol or more and 10000 g / mol or less. The method for producing a carbon fiber bundle according to claim 1, which comprises. The method for producing a carbon fiber bundle according to claim 1 or 2, wherein the weight average molecular weight of the silicone in the silicone-based oil is 20000 to 100,000 g / mol. The method for producing a carbon fiber bundle according to any one of claims 1 to 3, wherein the silicone in the silicone-based oil contains an amino-modified silicone.