CN101091010B - Oil agent for carbon fiber precursor fiber, carbon fiber and method for producing carbon fiber - Google Patents

Abstract

By using an oil agent for precursor fiber of carbon fiber containing a base compound and a liquid fine particle, and said liquid fine particle contains a liquid of which kinematic viscosity at 150 DEG C is 15000 cSt or more, it is possible to suppress an uneven stabilization in stabilizing process, and it becomes possible to provide a carbon fiber of high performance and uniform quality.

Description

Oil agent for carbon fiber precursor fiber, carbon fiber and preparation method of carbon fiber

technical field

The present invention relates to carbon fibers having a small single-fiber elastic modulus distribution, a carbon fiber production method capable of producing the carbon fibers with high operability, and an oil agent for carbon fiber precursor fibers used in the production method. the

Background technique

Compared with other fibers, carbon fiber has higher specific strength and specific elastic modulus. Therefore, as a reinforcing fiber for composite materials, it is not only used in sports, aviation and space, but also in automobiles, civil engineering, construction, pressure vessels, Widely used in general industrial applications such as windmill blades. Especially in sports and aerospace applications, there is an increasing demand for higher strength and higher elastic modulus of carbon fibers. Furthermore, while the above-mentioned high performance is required, it is also required to improve the material allowable value by improving the reliability of carbon fibers. the

The most widely used polyacrylonitrile carbon fibers in carbon fibers can be prepared in the industry through the following procedures: wet spinning or dry-wet spinning of polyacrylonitrile polymers as precursors to obtain carbon fiber precursor fibers (hereinafter referred to as Precursor fiber) spinning process; heating the precursor fiber in an oxidative atmosphere at a temperature of 200 to 400 ° C to convert it into a refractory fiber; and heating and carbonizing the precursor fiber in an inert atmosphere at a temperature of at least 1000 ° C Refractory fibers are converted into carbon fibers in the carbonization process. the

In order to obtain high-performance carbon fibers, the tension is increased or the draw ratio is set to be high in each of the above-mentioned production steps. However, at this time, since thermal bonding occurs between single fibers, the grade and quality tend to be lowered. Therefore, in order to carry out stable production, there is a problem that the draw ratio has to be compromised. the

In view of the above problems, a number of technical solutions for imparting a high heat-resistant silicone oil agent to polyacrylonitrile precursor fibers have been proposed, and are widely used in industry. For example, it is disclosed that when an oil agent mixed with specific amino-modified siloxane, epoxy-modified siloxane, or alkylene oxide-modified siloxane (alkylene oxide-modified silicone) is heated in air and nitrogen, The content that the weight loss is small and the thermal adhesion prevention effect is high (for example, patent document 1). However, the silicone oil agent used here intervenes between single fibers in the flame-resistant process, preventing the supply of oxygen necessary for the flame-resistant reaction, resulting in uneven progress of the flame-resistant reaction (so-called uneven firing). In addition, problems such as yarn breakage and fluffing are likely to occur in the subsequent carbonization process, which often hinders the improvement of productivity. In response to this problem, techniques for improving the curing properties of a specific silicone oil agent have been disclosed (for example, Patent Document 2), but the extent to which carbon fibers can be further enhanced in performance is limited. the

Patent Document 1: Patent Publication No. 3-40152 (full text)

Patent Document 2: JP-A-2001-172880 Gazette (full text)

Contents of the invention

The present invention provides an oil agent for carbon fiber precursor fibers for producing high-quality and homogeneous carbon fibers capable of solving the above-mentioned problems, a method for producing carbon fibers using the oil agent, and high-quality and homogeneous carbon fibers. the

The inventors of the present invention conducted intensive studies on the effects of oil agents and found the following solutions. the

That is, the present invention relates to an oil agent for carbon fiber precursors, which contains a main ingredient and liquid fine particles, and the liquid fine particles contain a liquid having a kinematic viscosity of 15000 cSt or more at 150°C. the

The present invention also relates to an oil agent for carbon fiber precursor fibers containing a main ingredient and a thermosensitive polymer. the

The present invention also relates to an oil agent for carbon fiber precursor fibers, which contains a silicone compound having an average kinematic viscosity of 10 to 1500 cSt at 25°C, and the silicone compound freely attenuates vibration using a rigid pendulum The difference between the vibration period of the pendulum at 30°C and 180°C measured by the method is 0.03-0.4 seconds. The present invention also relates to a method for preparing carbon fibers, which at least includes the following steps: spinning polyacrylonitrile polymers to obtain carbon fiber precursor fibers; A refractory process of converting the refractory fibers into refractory fibers by heating in an oxygen atmosphere; and a carbonization process of heating the refractory fibers in an inert atmosphere with a temperature of at least 1000°C to convert them into carbon fibers, wherein, in the silk making process In the method, an oil agent for carbon fiber precursor fibers satisfying at least one of the above conditions is applied to the precursor fibers. the

In addition, the present invention also relates to a carbon fiber having a coefficient of variation of a single fiber elastic modulus determined by a single fiber tensile test of 10% or less. the

The oil agent for carbon fiber precursors of the present invention (hereinafter simply referred to as oil agent) contains, in addition to the main agent, liquid fine particles whose kinematic viscosity at 150° C. is 15000 cSt or more as an essential component, thereby being able to be used in carbon fiber precursor fibers ( Hereinafter abbreviated as precursor fibers) thermal bonding between single fibers can be suppressed in the spinning process, and at the same time, bonding between single fibers can be suppressed without damaging the precursor fibers in the subsequent refractory process. the

Another aspect of the oil agent of the present invention is to contain a thermosensitive polymer in addition to the main agent, so that the effect of the oil agent can be equalized in the whole fiber bundle. the

In addition, another aspect of the oil agent of the present invention is that by reducing the average kinematic viscosity of the oil agent at 25° C. while maintaining the curability, an oil agent film with a smooth surface and no deformation can be formed on the precursor fiber. the

Therefore, by applying an oil agent that satisfies at least one of the above-mentioned conditions in the spinning step of the precursor fiber, oxygen can be uniformly supplied to the individual fibers of the precursor fiber bundle in the subsequent flame-resistant step, thereby Suppress uneven firing. Therefore, even under higher filament density, high tension, and high-speed firing conditions than before, carbon fibers can be produced with stable quality without fuzzing and yarn breakage, so high-quality fibers with narrow distribution of elastic modulus can be obtained. homogeneous carbon fiber. As long as the carbon fibers are used, a high-performance and highly reliable composite material can be formed. the

Detailed ways

One aspect of the oil agent of the present invention contains a main ingredient and liquid fine particles, and the liquid fine particles contain a liquid having a kinematic viscosity of 15000 cSt or higher at 150° C. as an essential component. the

By using the above-mentioned liquid fine particles for the precursor fiber, firing unevenness can be suppressed in the refractorizing step. Although the reason for this is unclear, it is considered for the following reasons. That is, the firing unevenness in the flame-proofing step is due to the occurrence of insufficient supply of oxygen due to the obstruction of the penetration of oxygen into the tow. Direct thermal bonding between the single fibers of the precursor fiber, or the oil agent used to suppress the thermal bonding is conversely bound between the single fibers, and this is a factor that hinders oxygen permeation. In the latter case, the oil agent enters between the single fibers and acts as a binder to bind between the single fibers. When oxygen penetrates into the tow, if there are thermally bonded single fibers or oil solidified between the single fibers, the oxygen passes through and diffuses. The amount of permeation decreases, and uneven firing occurs due to uneven supply of oxygen. Usually, the oil agent is applied immediately before the drying step in the silk-making step, and then heat-drying treatment is performed. When performing this heating and drying treatment, if a droplet of the oil agent exists between the single fibers, spreads to the single fibers on both sides, and is directly solidified, the possibility of the oil agent acting as a binder is high, and as a result, firing failure occurs. all. In addition, even if the liquid droplets of the oil agent present on the single fiber are integrated with the liquid droplets on the adjacent single fiber before curing, they also function as a binder. However, in this solution, due to the existence of specific liquid particles, in the silk making process, the liquid particles with high kinematic viscosity act as spacers, and by creating gaps between single fibers, the adhesion between single fibers is suppressed. combine. In addition, in the flameproofing process, since the oxygen supply path is ensured, oxygen can be uniformly supplied into the tow, so that uniform firing can be achieved. Although the same effect can be expected using solid fine particles as spacers, there are inconveniences in that the solid fine particles damage the precursor fibers or contaminate the production process with the solid fine particles detached from the single fibers. However, the liquid microparticles in this embodiment are liquids unlike solid ones, and therefore have the advantage of not damaging the precursor fibers and rarely falling off from rolls or the like into the production process due to their own deformation. However, if the viscosity of the liquid microparticles is too low, the liquid microparticles are deformed during the spinning process, resulting in a decrease in the gap between single fibers. Therefore, the higher the kinematic viscosity of the liquid contained in the liquid fine particles is, the more preferable it is. For this reason, the kinematic viscosity at 150° C. close to the temperature of the spinning and drying process is 15000 cSt or more, preferably 80000 cSt or more, more preferably 150000 cSt or more. The upper limit of the kinematic viscosity is not particularly limited. Since micronization is difficult when the kinematic viscosity is too high, the kinematic viscosity is preferably 15000000 cSt or less for micronization, but when micronization can be performed by emulsion polymerization or the like, even a higher viscosity than this kinematic viscosity is acceptable. However, it is preferable that the liquid is deformable at 150° C. in order to exhibit the properties of the liquid particles. Here, the term "deformable at 150°C" means that a liquid is applied to a hot plate maintained at 150°C, the hot plate is placed vertically, and the shape changes when observed 1 hour later. In addition, when measuring the liquid in an oil agent, it can measure after separating a liquid using centrifugation etc. as follows. the

The kinematic viscosity of a liquid can be calculated as follows. 10 mL of liquid maintained at a predetermined temperature is placed in an Ostwald type viscometer (capillary viscometer), and the time t (sec) required for the upper surface of the measurement liquid to pass through a certain distance is measured. The kinematic viscosity was calculated according to the following formula by setting the viscosity of the reference liquid as η ₀ (cP), the density as ρ ₀ (g/cm ³ ), and the falling time as t ₀ (sec).

Kinematic viscosity (cSt) = (η ₀ /ρ ₀ )×(t/t ₀ )

When measuring the kinematic viscosity of the liquid in the oil agent, the liquid particles are obtained by centrifugal separation, the emulsifier is separated from the separated liquid particles by adjusting the pH, and the kinematic viscosity is measured after the liquid is extracted. the

The liquid used in this aspect is not particularly limited as long as it satisfies the above-mentioned range, and oils such as mineral oil, synthetic oil, and silicone oil are preferably used. Among them, silicone oil is particularly preferably used because it has a small temperature coefficient of viscosity and high mold releasability. the

As the silicone oil, a silicone oil having a linear siloxane skeleton is basically preferable. It may have some branched or cross-linked structures, but the entire molecule is preferably constituted by a linear structure. Examples of organic groups bonded to silicon atoms in the molecule include alkyl groups such as methyl, ethyl, propyl, butyl, and hexyl; cycloalkyl groups such as cyclohexyl; and alkenyl groups such as vinyl and allyl. ; Aryl groups such as phenyl and tolyl groups; Glycidyl groups, alicyclic epoxy groups, amino groups, etc. When the above-mentioned organic group is reactive, a cross-linking reaction can be caused before the flame-proofing step, and the liquid particles become solid spacers. Therefore, it is preferable that the organic group is non-reactive. The organic group is particularly preferably a methyl group or an alicyclic epoxy group, most preferably a methyl group. When a part of the organic group contains a reactive group, the equivalent weight of the reactive group is preferably 4,000 g/mol or more, more preferably 10,000 g/mol or more, and even more preferably 50,000 g/mol from the viewpoint of inhibiting gelation. above. As another group bonded to a silicon atom, an alkoxy group, a hydroxyl group, a hydrogen atom, or the like may be partially contained. Examples of the terminal group of the molecular chain include a triorganosilyl group or a group in which a part of the organic group is substituted with a hydroxyl group. A trimethylsilyl group having low reactivity is particularly preferable. The above-mentioned silicone oils may be used alone or in combination of two or more. the

The kinematic viscosity of the silicone oil at 150°C can also be calculated by using the kinematic viscosity at 25°C, where T is 150°C in the following formula. However, when the calculated value is different from the above-mentioned actual measurement value, the actual measurement value is used. the

logη ^T ={763.1/(273+T)}-2.559+logη ²⁵

T: 150 (°C), logη ^T : kinematic viscosity (cSt) at T°C, logη ²⁵ : kinematic viscosity (cSt) at 25°C.

As the preparation method of the liquid microparticles used in the oil agent of this embodiment, for example, a method of emulsifying a liquid with a high kinematic viscosity such as the above-mentioned silicone oil using a dispersant, a method of obtaining liquid microparticles by emulsion polymerization of silicone oil, etc., etc. An organic solvent may be used as the dispersant, but water is preferably used from the viewpoint of imparting uniformity to the precursor fibers and ease of imparting. the

When using water as a dispersant, it is preferable to use a surfactant in combination. The type of surfactant is not particularly limited, and any of anionic, cationic, nonionic, and amphoteric surfactants can be used. In addition to combinations of anionic surfactants and cationic surfactants, the above-mentioned substances can also be used in combination. Among them, cationic surfactants are preferable, weak cationic surfactants containing amino groups and the like are also preferable, and nonionic surfactants are particularly preferably used. Examples of nonionic surfactants include polyethylene glycol alkyl ethers, alkylphenyl ethers, and alkylamine ethers. The hydrodynamic average particle size of the liquid fine particles obtained by emulsification and dispersion is preferably 0.05 to 5 μm, more preferably 0.1 to 1 μm, and even more preferably 0.2 to 0.7 μm. If the hydrodynamic average particle size of the liquid fine particles is too small, emulsification and dispersion tend to be difficult although the effect tends to be saturated. If the hydrodynamic average particle size of the liquid particles is too large, the particles may not reach near the center of the fiber bundle, causing uneven adhesion. The above-mentioned hydrodynamic average particle diameter can be measured by the Cumulant method using a particle size distribution meter based on the principle of light scattering or the like. In the case of using a surfactant, from aspects such as emulsifying performance and storage stability, the addition amount of the surfactant is preferably 5 to 30 parts by weight relative to 100 parts by weight of the high-kinematic viscosity liquid contained in the above-mentioned liquid particles. Preferably it is 10-20 weight part. When using multiple types of surfactants, it is a preferable method because emulsification and dispersion can be performed stably. the

The liquid microparticles of the present invention have an effect of suppressing thermal bonding between single fibers, but on the other hand, if the liquid microparticles are solidified and the single fibers are bonded to each other, the above-mentioned effect is reduced. Therefore, it is preferable to prevent the solidification of the liquid fine particles as much as possible during the spinning process. From this point of view, it is preferable that the difference in pendulum vibration period between 30° C. and 200° C. of the liquid fine particles measured by the rigid pendulum free damping vibration method is 0.1 second or less. The vibration cycle difference is more preferably 0.05 seconds or less, and more preferably less than 0.03 seconds. The measurement by the rigid pendulum free damping vibration method will be described later in detail. The measurement by the rigid pendulum free damping vibration method is different from the measurement using a general rheometer (rheometer), and can measure the viscoelastic properties in an open system and in a thin film state. The vibration period measured according to the above measurement method corresponds to the degree of crosslinking of the liquid particles, and the smaller the vibration period, the higher the degree of crosslinking. Therefore, the difference between the pendulum vibration period at 30°C and 200°C corresponds to the curing characteristics during heating, and the larger the vibration period difference, the easier it is to cure by heating, that is, the easier crosslinking occurs. On the contrary, the smaller the difference between the vibration period of the pendulum at 30°C and 200°C, the harder it is to cure by heating, that is, the harder it is to crosslink. Since the degree of solidification of the liquid fine particles during heating is lower, it is more preferable. Therefore, it is more preferable that the pendulum vibration period difference between 30° C. and 200° C. is smaller. By using liquid particles whose pendulum vibration period difference between 30°C and 200°C is within the above range, the degree of solidification of the liquid particles in the silk-making process can be suppressed to a low level, so it is rarely used as a bond between single fibers. The role of the adhesive. In order that the liquid particles do not cause bonding between single fibers in the subsequent refractorization process, the difference in vibration period of the pendulum at 30°C and 300°C is preferably 0.1 seconds or less, more preferably 0.05 seconds or less. liquid particles.

The so-called main ingredient in the present invention refers to the component with the largest weight content in the oil agent except liquid fine particles, thermosensitive polymer and liquid medium. However, as will be described later, for example, when a plurality of siloxane compounds are mixed and used as the main ingredient, the entire mixture of the plurality of siloxane compounds becomes the main ingredient. The main ingredient is not particularly limited as long as it is confirmed that it has the effect of preventing thermal adhesion between single fibers or the effect of bundling single fibers. However, as described in the background art, silicone compounds generally have a high It is preferable to use because of its thermal adhesion prevention effect. Silicone compounds can also be used for the above-mentioned liquid fine particles. However, in order to make the above-mentioned silicone compounds exhibit the spacer effect, a silicone compound with a high kinematic viscosity is selected, and it is difficult to completely coat the fibers, and the effect of preventing thermal adhesion is insufficient. Therefore, the main ingredient cannot contain liquid particles. When the kinematic viscosity of the siloxane compound used as the main ingredient is low, it forms a uniform film due to its excellent spreadability and suppresses thermal adhesion between single fibers, which is preferable. In order to quickly form a uniform film with a smooth surface, the kinematic viscosity of the siloxane compound at 25° C. is preferably 10 to 10,000 cSt, more preferably 100 to 2,000 cSt, and even more preferably 300 to 1,000 cSt. the

As the siloxane compound, polydiorganosiloxanes such as polydimethylsiloxane, or amino-modified siloxanes based on them, alicyclic epoxy-modified siloxanes, or epoxy compounds are known. Various modified products such as alkane-modified siloxane (also called polyether-modified siloxane) can be used in the present invention. Amino-modified silicone has a high affinity with fibers. Alkylene oxide-modified siloxane is excellent in emulsion stability. Alicyclic epoxy-modified siloxane is excellent in heat resistance. It is preferred that the main agent contains at least amino-modified siloxane, more preferably amino-modified siloxane and alkylene oxide-modified siloxane, particularly preferably amino-modified siloxane and alicyclic epoxy-modified silicone. Alkane and alkylene oxide modified silicones. The content of the amino-modified siloxane in the main agent is preferably 20 to 100% by weight, more preferably 30 to 90% by weight, and even more preferably 40 to 80% by weight. the

In addition, the main ingredient of the oil agent of the present invention is not particularly limited as long as it is a main ingredient that can be dissolved in a liquid medium, or a main ingredient that can self-emulsify, but if it is insoluble or does not self-emulsify, In order to emulsify and disperse, it is preferable to use surfactants, such as an emulsifier and a dispersant, together. The type of surfactant used in the oil agent of the present invention is not particularly limited, and any of anionic, cationic, nonionic, and amphoteric surfactants can be used. In addition to combinations of anionic surfactants and cationic surfactants, the above surfactants may also be used in combination. Among them, cationic surfactants are preferable, weak cationic surfactants containing amino groups and the like are more preferable, and nonionic surfactants are particularly preferably used. Examples of nonionic surfactants include polyethylene glycol alkyl ethers, alkylphenyl ethers, and alkylamine ethers. The hydrodynamic average particle diameter of the main ingredient obtained by emulsification and dispersion is preferably 0.001-1 μm, more preferably 0.01-0.5 μm, particularly preferably 0.05-0.2 μm. When the hydrodynamic average particle diameter of the main ingredient is less than 0.001 μm, although the effect tends to be saturated, emulsification and dispersion tend to be difficult. When the hydrodynamic average particle size of the main agent is greater than 0.5 μm, the particles sometimes cannot reach near the center of the fiber bundle, causing uneven adhesion. The above-mentioned hydrodynamic average particle diameter can be obtained by the Cumulant method using a particle size distribution meter based on the principle of light scattering or the like. The amount of surfactant added relative to the main agent is determined by the combination of surfactant, main agent and liquid medium, and cannot be generalized. However, it is preferable to have the above-mentioned average particle diameter, and to be 0 to 60 parts by weight, preferably 0 to 35 parts by weight, of the surfactant based on 100 parts by weight of the main ingredient. When using multiple types of surfactants, it is a preferable method because emulsification and dispersion can be performed stably. the

The concentration of the main agent is also closely related to how many fiber bundles the oil is given, and since the effect of the main agent also varies depending on the type, it cannot be generalized, but it is preferably about 0.1 to 10% by weight relative to the total amount of the oil. %. More importantly, as mentioned above, it is preferred that the viscosity of the oil does not exceed 50 cP. the

The weight ratio of the above-mentioned liquid particles to the main agent varies according to the type of the main agent, etc., and cannot be generalized. The preferred liquid particles are 0.1 to 50 parts by weight relative to 100 parts by weight of the main agent, more preferably 1 to 50 parts by weight, and further Preferably it is 5-15 weight part. the

Another embodiment of the oil agent of the present invention is an oil agent containing a main ingredient and a thermosensitive polymer. the

The so-called temperature-sensitive polymer in this scheme refers to a polymer with the following properties, that is, in a mixture of polymer and liquid medium, it is substantially dissolved at a temperature lower than a certain temperature, and at a temperature higher than The property that at least a part of the polymer is precipitated from the liquid medium at a certain temperature. This specific temperature is called the cloud point or the lower critical eutectic temperature. the

As a thermosensitive polymer, for example, a molecule having a weight-average molecular weight of 2000 or more formed of an oxirane chain and a hydrophobic part, such as an alkyl group or an alkylene oxide chain having 3 or more carbon atoms, is more preferably heavy. A molecule with an average molecular weight of 5,000 or more, more preferably a molecule with a weight average molecular weight of 10,000 or more, or a homopolymer of N-alkyl (meth)acrylamide or a copolymer of the above-mentioned monomers and (meth)acrylic acid; A copolymer of polyfunctional monomers such as methylaminoethyl (meth)acrylate and ethylene glycol dimethacrylate; or a mixture of the above substances. Among them, it is preferable to use either one of N-isopropylacrylamide or dimethylaminoethyl methacrylate, or a polymer containing both as monomer components. In the case of N-isopropylacrylamide, the lower critical solution temperature of its homopolymer in water is about 32°C, but the cloud point or lower critical solution temperature can be controlled by copolymerization. Basically, when anionic monomers, cationic monomers, nonionic hydrophilic monomers, etc. are copolymerized, the lower critical solution temperature increases. Examples of the anionic monomer include (meth)acrylic acid and a monomer having a sulfonic acid group, more specifically, styrenesulfonic acid, and the like. Examples of cationic monomers include nitrogen-containing monomers such as N,N-dimethylacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylacrylamide, and the like. Examples of nonionic hydrophilic monomers include vinyl compounds or (meth)acrylates having hydrophilic groups, more specifically N-vinyl-2-pyrrolidone; or hydroxyalkyl As (meth)acrylate etc., more specifically, 2-hydroxyethyl (meth)acrylate etc. are mentioned. Not limited to the above-mentioned monomers, various monomers may be used. the

For example, when an ionic substance is contained in the oil agent, in order not to cause adverse effects on the function or state of the oil agent due to aggregation or the like, it is preferable that the thermosensitive polymer is at least not an ion having a sign different from that of the ionic substance. type. Specifically, when the emulsifier is cationic or the main ingredient contains an amino group, the thermosensitive polymer is preferably cationic or nonionic. the

In order to express the hot spot or the lower critical solution temperature of the thermosensitive polymer, the liquid medium is preferably a hydrophilic medium, especially water. the

The current oil agent consists of a main agent and a liquid medium, but by using a temperature-sensitive polymer in combination, the adhesion prevention effect or thermal adhesion prevention effect between the single fibers of the carbon fiber precursor fiber bundle can be further improved. Although the mechanism thereof is not clear, it is presumed as follows. That is, in the spinning process, after applying an oil agent composed of a main ingredient and a liquid medium to the precursor fiber bundle, heat drying treatment is performed. At this time, the liquid medium volatilizes from the surface of the precursor fiber bundle into the environment, and the liquid medium in the fiber bundle moves to the surface of the fiber bundle. The main agent dissolved, emulsified or dispersed in the liquid medium also moves, resulting in insufficient main agent inside the fiber bundle, which weakens the effect of the oil agent. However, in the presence of a thermosensitive polymer, if the oil is heated to a temperature exceeding the hot spot of the thermosensitive polymer or the lower critical eutectic temperature, the thermosensitive polymer is precipitated and the oil as a whole becomes a gel shape. This can suppress the movement of the main agent when the liquid medium volatilizes, and eliminate the shortage of the main agent in the fiber bundle, so that the effect of the oil agent can be substantially uniform throughout the fiber bundle. In addition, the oil agent present between the single fibers is extruded due to the movement of the single fibers during the heating process, and the single fibers may be thermally bonded or bonded to each other, but the oil agent gels under the action of the temperature-sensitive polymer. It is difficult to be extruded and can suppress thermal bonding or adhesion between single fibers. This effect is due to the temperature-sensitive polymer having a hot spot or the lower critical eutectic temperature, but there is no such effect when using a non-temperature-sensitive polymer. For example, when the liquid medium is water, even if common water-soluble polymers such as polyvinyl alcohol or various water-soluble rubbers are used, since the above-mentioned polymers are concentrated at the place where water volatilizes, that is, on the surface of the fiber bundle, and exceed the saturation solubility, Therefore, it cannot inhibit the movement of the main agent from the inside of the fiber bundle to the surface, and has no effect on the extrusion of the oil agent from between the single fibers. the

Based on the above presumed mechanism, it is preferable that the hot spot or lower critical solution temperature of the thermosensitive polymer is higher than the temperature of the oil when the oil is applied to the carbon fiber precursor fiber bundle, and preferably lower than the boiling point of the liquid medium. Specifically, the preferred cloud point or lower critical eutectic temperature is 20-98°C, more preferably 30-80°C, even more preferably 35-70°C. Even if the cloud point or the lower critical eutectic temperature is lower than 20°C, as long as the oil can be applied to the fiber bundle at a temperature lower than this temperature, it is not particularly limited. However, if the usual room temperature is considered, especially in summer Since it is necessary to cool the oil agent or equip the preparation space with air-conditioning equipment, it is not preferable in terms of production cost or operability. On the other hand, when the cloudy point or the lower critical eutectic temperature is higher than 98°C, the temperature difference between room temperature and the cloudy point or the lower critical eutectic temperature is large. eutectic temperature, but the surface of the fiber bundle reaches the boiling point of the liquid medium, and the possibility that the liquid medium, main agent or thermosensitive polymer begins to move from the inside of the fiber bundle to the surface increases, so it is not preferred. Therefore, it is practical and can exert the greatest effect to use a thermosensitive polymer whose hot spot or lower critical eutectic temperature is set to be the highest during one year at the production site. The lowest possible temperature in the temperature range where the oil temperature is also high. the

The preferred value of the concentration of the thermosensitive polymer varies depending on the combination of the thermosensitive polymer and the type of liquid medium used, so it cannot be generalized, but it is preferably about 0.0001 to 10% by weight based on the total amount of the oil agent. More importantly, the viscosity of the oil is preferably 1 to 50 cP, more preferably 1 to 20 cP, and particularly preferably 2 to 10 cP at the temperature at which the oil is applied to the carbon fiber precursor fiber bundle. When the viscosity exceeds 50 cP, it becomes difficult to apply the oil agent uniformly inside the fiber bundle. The lower limit of the viscosity is not particularly limited, and the lower the viscosity, the better from the viewpoint of uniform adhesion. However, for example, if water with a viscosity of about 1 cP is selected as the liquid medium at around room temperature, when a thermosensitive polymer or main ingredient is added, the viscosity of the oil agent will be as high as 2 cP or more. In addition, the viscosity of an oil agent can be measured using the commercially available rotational viscometer. In this case, the measurement temperature is the temperature of the oil agent when the oil agent is applied to the precursor fiber bundle. When the oil agent has properties such as thixotropy that changes in viscosity according to shear force, the viscosity when the shear force changes gradually is taken as the viscosity described in the present invention. When it is difficult to predict the asymptotic viscosity with a rotational viscometer, twice the viscosity measured when the highest shear force is applied to the rotational viscometer is defined as the viscosity described in the present invention. As an example of a preferable rotary viscometer which can be used, R-type viscometer (model number: RE115L) by Toki Sangyo Co., Ltd. is mentioned. the

The mixing ratio of the temperature-sensitive polymer and the main ingredient varies with the type, etc., and cannot be generalized. The temperature-sensitive polymer is preferably 0.001 to 50 parts by weight, more preferably 0.01 to 20 parts by weight, based on 100 parts by weight of the main ingredient. , particularly preferably 0.1 to 10 parts by weight. the

In addition, it is preferable to combine the above-mentioned liquid microparticles in addition to the thermosensitive polymer and the main agent and use it as an oil agent because synergistic effects can be exhibited as described below. That is, the effect of the thermosensitive polymer suppresses the movement of the oil agent from the interior of the fiber bundle to the surface and suppresses the extrusion of the oil agent from between the single fibers during heat drying treatment. By the effect of liquid particles, voids can be created between single fibers, preventing the solidification of the cured film formed by the thermosensitive polymer and the main ingredient. the

The weight ratio of liquid particles, temperature-sensitive polymers and the main agent varies according to the type of the main agent, etc., and cannot be generalized. It is preferably about 0.1 to 50/0.001 to 50/50 to 99.899, more preferably 1 to 50/0.01 to 20/50 to 98.99, more preferably 5 to 15/0.1 to 10/75 to 94.9. the

Another solution of the oil agent of the present invention is to contain a siloxane compound with an average kinematic viscosity of 10 to 1500 cSt at 25°C, and the pendulum vibration of the siloxane compound at 30°C and 180°C measured by the rigid pendulum free attenuation vibration method The cycle difference is 0.03 to 0.4 seconds. the

Here, the average kinematic viscosity is a value obtained by weight-averaging the kinematic viscosities of the respective silicone compounds based on the mixing ratio of the silicone compounds contained in the oil agent. Except for silicone compounds contained in liquid particles. That is, the average kinematic viscosity is the weight average of the kinematic viscosities of the silicone compound contained as the main ingredient in the oil agent. If one type of siloxane compound is contained in the oil agent, its kinematic viscosity is the average kinematic viscosity. The kinematic viscosity was measured at 25°C using an Ostwald type viscometer. the

The average kinematic viscosity of the siloxane compound in this solution is 10-1500cSt at 25°C. The average kinematic viscosity is preferably 50 to 1000 cSt, more preferably 100 to 500 cSt. the

Conventional oils tend to use silicone compounds with high kinematic viscosity in view of heat resistance, but the silicone compound in this embodiment has a lower kinematic viscosity than conventional silicone compounds. When the above-mentioned low kinematic viscosity siloxane compound is used as the main ingredient, firing unevenness can be suppressed in the flame-proofing step. When the kinematic viscosity of the siloxane compound exceeds 1500 cSt, the effect of suppressing uneven firing is insufficient. On the other hand, when the kinematic viscosity of the siloxane compound is lower than 10 cSt, the viscosity of the oil agent is insufficient, and when the oil agent is throttled by pliers or the like in the spinning process, the oil agent is difficult to be held between the single fibers, and the oil agent is difficult to hold in the drying process, etc. The effect of preventing thermal bonding between single fibers cannot be sufficiently obtained. the

Here, the pendulum vibration cycle difference T at 30°C and 180°C measured by the rigid pendulum free damping vibration method refers to the silicon contained in the oil agent as the main ingredient by the rigid pendulum free damping vibration method described in detail later. The difference between the vibration period (seconds) at 30°C when the oxane compound was measured and the vibration period (seconds) obtained by similarly measuring the siloxane compound after heat treatment at 180°C for 20 minutes. That is, as shown in the following formula, the vibration period difference T is 0.03 to 0.4 seconds. the

0.03≤T≤0.4

T＝T30-T180

T30: Vibration period at 30°C (seconds)

T180: Vibration period after heat treatment at 180°C for 20 minutes (seconds)

The vibration period difference T of the low kinematic viscosity siloxane compound in this solution is 0.03-0.4 seconds, preferably 0.05-0.35 seconds, more preferably 0.10-0.30 seconds. If a siloxane compound having the above-mentioned vibration period difference T is used, firing unevenness can be suppressed in the flame-proofing step. the

The reason why firing unevenness can be suppressed by using a siloxane compound having the above characteristics is not clear, but it is estimated as follows. In other words, the firing unevenness in the flameproofing step is due to the occurrence of insufficient supply of oxygen due to the obstruction of penetration of oxygen into the tow. That is, the silicone oil agent enters between the single fibers and functions as a sealant. Usually, the silicone oil agent is applied immediately before the drying step in the silk-making process, and then heat-drying treatment is performed. Existing oils contain a silicone compound having a high kinematic viscosity as a main ingredient. Therefore, the spreading speed of the oil droplet of the oil agent on the precursor fiber is slow, and the oil agent often solidifies before forming a smooth film, so surface irregularities corresponding to the shape of the oil droplet remain on the precursor fiber. The above-mentioned protrusions on the surface of the precursor fiber inhibit the supply of oxygen into the tow in the flameproofing step, resulting in uneven firing. The oil agent of this aspect can form a smooth film without surface irregularities by containing a low-kinematic-viscosity siloxane compound as a main ingredient, so that firing unevenness can be suppressed. the

In addition, the inventors of the present invention found that only the siloxane compound has a kinematic viscosity within the above-mentioned range, and the effect of suppressing uneven firing is insufficient. When the siloxane compound has a low kinematic viscosity, the oil agent forms a smooth film, but the oil agent flows and accumulates between the single fibers in large quantities, and as a result, the supply of oxygen into the tow is hindered. When the pendulum vibration cycle difference T between 30° C. and 180° C. of the siloxane compound of this embodiment falls within the above-mentioned range, it is possible to prevent the above-mentioned oil agent from flowing. The pendulum vibration cycle difference T at 30°C and 180°C corresponds to the curing characteristics during heating, and the larger the vibration cycle difference is, the easier it is to cure by heating, that is, the easier crosslinking occurs. On the contrary, the smaller the difference in the vibration period of the pendulum at 30°C and 180°C, the harder it is to cure by heating, that is, the harder it is for crosslinking to occur. The siloxane compound of this solution is easier to solidify than the siloxane compound used in the existing oil agent, can suppress the flow of the above-mentioned oil agent, prevent the oil agent from accumulating in large quantities between single fibers, and suppress firing unevenness. However, when the curing of the siloxane compound is significant, the bond between the single fibers may be strengthened instead, and as a result, firing unevenness may occur. Therefore, it is preferable that the vibration period difference T is within an appropriate range. the

That is, since the oil agent of the present aspect forms a smooth coating without deformation of the coating, firing unevenness can be suppressed. the

The low-kinematic-viscosity silicone compound is not particularly limited as long as it satisfies the above characteristics, but the following compounds are preferably used. the

As the siloxane compound, a siloxane compound having a polydimethylsiloxane as a basic structure and having a part of methyl group modified is preferably used. An amino group, an alicyclic epoxy group, an epoxyalkyl group, etc. are preferable as a modifying group, and it is more preferable to use a modifying group which undergoes a crosslinking reaction by heating. It is also possible to use a siloxane compound having a plurality of modifying groups, or to use a mixture of siloxane compounds having different modifying groups. the

From the viewpoint of imparting uniformity to the precursor fiber, it is preferable to use an amino-modified silicone compound. The modifying group may be a monoamine type or a polyamine type, and it is particularly preferable to use a modifying group represented by the following general formula. That is, in the general formula -Q-(NH-Q') _P -NH ₂ , Q and Q' represent the same or different divalent hydrocarbon groups having 1 to 10 carbon atoms, and P represents an integer of 0 to 5. Considering that the amino group becomes the starting point of the cross-linking reaction, the higher the modification amount, the more the cross-linking reaction is promoted, but since the silicone oil agent falls off on the drying roll and winds up on the roll, the so-called sticking roll (gum up) increases, Therefore, when the amount of terminal amino groups is converted into the weight of -NH2, the modification amount is preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight. In addition, the lower the kinematic viscosity of the amino-modified siloxane at 25° C., the more smooth the surface of the oil film can be formed. Specifically, it is preferably 10 to 10,000 cSt, more preferably 100 to 2,000 cSt, and even more preferably 300 to 1,000 cSt.

Conventional alkylene oxide-modified siloxanes have a low heating residual rate and have not been actively used. However, the amount of silicon remaining in the alkylene oxide-modified siloxane was high until the pre-carbonization step when viewed from the amount of remaining silicon, not the overall remaining rate. On the other hand, it is important to have a high residual silicon content from the viewpoint of preventing thermal bonding between single fibers, so it is preferable to use alkylene oxide-modified siloxane. The lower the kinematic viscosity of the alkylene oxide-modified siloxane at 25° C., the smoother the oil film can be formed. Specifically, it is preferably 10 to 1000 cSt, more preferably 50 to 800 cSt, and even more preferably 100 to 500 cSt. The content of the alkylene oxide-modified siloxane is preferably 15 to 900 parts by weight relative to 100 parts by weight of the amino-modified siloxane. The lower limit of the content of the alkylene oxide-modified siloxane is more preferably 25 parts by weight or more, more preferably 30 parts by weight or more, based on 100 parts by weight of the amino-modified siloxane. The upper limit of the content of the alkylene oxide-modified siloxane is more preferably 200 parts by weight or less, further preferably 100 parts by weight or less, particularly preferably 40 parts by weight or less, based on 100 parts by weight of the amino-modified siloxane. The content range of the alkylene oxide-modified siloxane is more preferably 25-200 parts by weight, more preferably 30-100 parts by weight, and particularly preferably 30-40 parts by weight relative to 100 parts by weight of the amino-modified siloxane. When the content exceeds 900 parts by weight, the crosslinking reaction of other siloxanes may be delayed, and it may be difficult to obtain the effect of the present invention. When the content is less than 15 parts by weight, the effect of improving the heat-resistant residual property of silicon cannot be significantly obtained. the

As the alkylene oxide used in the alkylene oxide-modified siloxane, it is preferable to use a polymer of ethylene oxide (hereinafter referred to as EO), a polymer of propylene oxide, or a block copolymer of both. EO is particularly preferred. the

From the viewpoint of bundling properties, it is preferable to use alicyclic epoxy-modified siloxane. The amount of modification is preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight. In addition, considering the bundling properties, the higher the kinematic viscosity of the alicyclic epoxy-modified siloxane at 25° C., the better, preferably 100 to 10,000 cSt, more preferably 500 to 6,000 cSt, and even more preferably 1,000 to 4,000 cSt. If the ratio of the alicyclic epoxy-modified siloxane is 0 to 20 parts by weight with respect to 100 parts by weight of all the siloxane compounds, a sufficient effect is often obtained, which is preferable. The lower limit of the content of the alicyclic epoxy-modified siloxane is preferably 3 parts by weight or more, more preferably 6 parts by weight or more, based on 100 parts by weight of all the siloxane compounds. The upper limit of the content of the alicyclic epoxy-modified siloxane is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, based on 100 parts by weight of all the siloxane compounds. The content range of alicyclic epoxy-modified siloxane is more preferably 3 to 20 parts by weight, more preferably 3 to 15 parts by weight, particularly preferably 6 to 10 parts by weight, based on 100 parts by weight of all siloxane compounds. 10 parts by weight. When the content of the alicyclic epoxy-modified siloxane exceeds 20 parts by weight, the crosslinking reaction of other siloxanes will be delayed, making it difficult to obtain the effects of the present invention. the

As the alicyclic epoxy group used in the alicyclic epoxy-modified siloxane, a compound in which an alicyclic group such as cyclohexenyloxy group is epoxidized is preferably used. the

In order to further enhance the effect of inhibiting the thermal bonding of single fibers, it is preferable to use the low kinematic viscosity silicone compound of this embodiment as the main ingredient, and use the above-mentioned liquid fine particles or the above-mentioned thermosensitive polymer in combination. It is preferable to use the low kinematic viscosity siloxane compound of this embodiment, the above-mentioned liquid fine particles, and the above-mentioned thermosensitive polymer in combination because the effect is the best. the

In addition to the above-mentioned components, the oil agent of the present invention may also contain a smoothing agent, a hygroscopic agent, a viscosity modifier, a release agent, a spreading agent, an antioxidant, an antibacterial agent, a preservative, an antiseptic Rust agent and pH adjuster and other ingredients. the

The preparation method of the above-mentioned oil agent is not particularly limited, and a known mixing method of chemicals or an emulsification method can be used. For example, as a preparation apparatus, a propeller stirrer, a homomixer, a homogenizer, etc. can be used. In addition, if emulsification is required during operation, the emulsification method with forced stirring or the phase inversion emulsification method that is easy to generate uniform and fine particle sizes can be used. It is roughly divided into oil agent component 1 composed of main agent and liquid medium, oil agent component 2 composed of thermosensitive polymer and liquid medium, and oil agent component 3 composed of liquid particles and liquid medium. Apparatus and operation After preparing separately, oil component 1 and oil component 2, oil component 1 and oil component 3, or oil components 1 to 3 are mixed. Alternatively, after preparing the above-mentioned oil component 1, the thermosensitive polymer, or the oil component 3, or the thermosensitive polymer and the oil component 3 may be mixed in the oil component 1 by appropriately selecting and using the above-mentioned apparatus and operation. , to prepare the oil agent. Alternatively, the main ingredient, the thermosensitive polymer, and the liquid medium can also be initially charged, mixed and emulsified using the above-mentioned equipment and operation, and then the separately prepared oil component 3 can be appropriately mixed to prepare the oil. However, when the step involving the thermosensitive polymer is performed below the hot spot of the thermosensitive polymer or the lower critical eutectic temperature, it is preferable to form a uniform oil agent for the thermosensitive polymer. the

Next, a method of producing carbon fibers will be described. the

The oil agent of the present invention can be applied at any stage of the fiber spinning process of the precursor fiber, but in order to effectively prevent the adhesion or thermal bonding between the single fibers, it is preferable to apply the oil agent without the oil agent between the single fibers of the precursor fiber. Oil is applied before the process where thermal bonding is generated. As the precursors of carbon fibers, polyacrylonitrile fibers, pitch fibers, cellulose fibers, etc. are known. invented oil. A more preferable embodiment will be described below, particularly taking the case of use in polyacrylonitrile-based fibers, which are often used as high-performance carbon fiber precursor fibers, as an example. the

After spinning the spinning stock solution containing polyacrylonitrile-based polymers by a prescribed spinning method, the above-mentioned oil agent is applied to the water-swelled filaments obtained after washing with water, and then heated at 130-200°C Drying treatment to prepare precursor fibers. the

As a component of the polyacrylonitrile polymer, at least 95 mol% or more, more preferably 98 mol% or more of acrylonitrile and 5 mol% or less, more preferably 2 mol% or less of acrylonitrile can be suitably used to promote flame resistance and have the ability to copolymerize with acrylonitrile. A polymer obtained from a permanent fire resistance promoting component. It is preferable to use a vinyl group-containing compound as the above-mentioned flame resistance promoting component. Specific examples of vinyl group-containing compounds include acrylic acid, methacrylic acid, and itaconic acid, but are not limited thereto. In addition, it is more preferable to use an ammonium salt of acrylic acid, methacrylic acid, or itaconic acid partially or completely neutralized with ammonia water as the flame resistance promoting component. the

The spinning dope can be obtained by solution polymerization, suspension polymerization, emulsion polymerization and the like. As the solvent used in the spinning dope, organic or inorganic solvents can be used, and organic solvents are particularly preferably used. As the organic solvent, specifically, dimethylsulfoxide, dimethylformamide, dimethylacetamide, etc. can be used, and dimethylsulfoxide is particularly preferably used. the

The spinning method is preferably a dry-wet spinning method or a wet spinning method. Among them, it is more preferable to use a dry-wet spinning method from the viewpoint of producing precursor fibers with a smoother surface with good productivity. the

The spinning dope is directly or indirectly sprayed from the nozzle into the coagulation bath to obtain coagulated filaments. From the viewpoint of simplicity, it is preferable that the coagulation bath liquid is composed of a solvent and a coagulation accelerator component used in the spinning dope. As a coagulation accelerator component, water is preferably used. The ratio of the spinning solvent to the coagulation-accelerating component and the temperature of the coagulation bath in the coagulation bath can be appropriately selected and used according to the compactness, surface smoothness and spinnability of the obtained coagulated yarn. the

The obtained coagulated silk can be washed and stretched in one or more water baths whose temperature is controlled at 20-98°C. The draw ratio can be appropriately set within a range in which filament breakage and adhesion between single fibers do not occur, but in order to obtain a precursor fiber with a smoother surface, the draw ratio is preferably 5 times or less, more preferably 4 times or less, and further Preferably it is 3 times or less. In addition, the maximum temperature of the drawing bath is preferably 50°C or higher, more preferably 70°C or higher, in consideration of improving the compactness of the obtained precursor fiber. the

The above-mentioned oil agent is applied to the water-swelled yarn after washing and stretching. As the application method, a method that can be uniformly applied to the interior of the thread can be appropriately selected and used. However, as described above, depending on the action of the thermosensitive polymer, it is preferable to set the temperature of the oil agent at 35°C or lower from a practical point of view. bestow. The lower limit temperature reaches approximately the freezing point of the liquid medium. As a specific imparting method, the following method can be adopted: use a dispersant such as water, prepare the concentration of the oil component to be 0.01 to 10% by weight, and apply by dipping, spraying, touch roll, or guide. The oil method etc. apply an oil agent to the water-swollen thread. When the concentration of the oil component is too low, the effect of suppressing the thermal bonding between single fibers of the precursor fibers decreases. When the concentration of the oil component is too high, the oil becomes too viscous and fluidity deteriorates, making it difficult to uniformly process the oil into the fiber bundle of the precursor fiber. the

The amount of oil attached is adjusted so that the ratio of the oil component excluding the liquid medium is preferably 0.1 to 5% by weight, more preferably 0.3 to 3% by weight, and even more preferably 0.5 to 2% by weight relative to the dry weight of the precursor fiber. %. When the amount of the oil agent adhered is too small, thermal bonding between single fibers occurs, and the tensile strength of the obtained carbon fibers decreases. If the amount of oil attached is too large, the oil will cover between the single fibers, which may result in poor oxygen permeation in the fireproofing process. the

The thread to which the oil agent has been applied can be dried quickly. The drying method is not particularly limited, but it is preferable to use a method of directly contacting a plurality of heated rolls. From the viewpoint of productivity, the higher the drying temperature, the more preferable, so the drying temperature can be set to a higher temperature within the range where thermal bonding between single fibers does not occur. Specifically, the drying temperature is preferably 120 to 220°C, more preferably 140 to 210°C, and even more preferably 160 to 200°C. When the drying temperature exceeds 220°C, bonding between single fibers is likely to occur. When the drying temperature is lower than 120° C., drying may take time, resulting in reduced efficiency. The heating time is preferably 5 to 120 seconds, more preferably 10 to 90 seconds, and still more preferably 15 to 60 seconds. When the heating time is less than 5 seconds, the effect of drying and densification decreases. Even if the heating time exceeds 120 seconds, the effect of drying and densification is usually saturated. The heating time can be appropriately determined according to the heating temperature or heating method (for example, contact heating or non-contact heating, etc.). As the heating method, a tenter (Tenter) in which air heated by an electric heater or steam or the like is passed through the precursor fiber bundle, non-contact heating such as an infrared heating device, a plate heater, a drum heater, or the like can be used. Any one of the similar contact heating methods, the contact heating method is more preferable from the viewpoint of heat conduction efficiency. the

In view of improving the compactness and productivity of the obtained precursor fibers, it is preferable to further post-draw the dried filaments in pressurized steam or under dry heat. The steam pressure, temperature, and post-stretching ratio during post-stretching can be appropriately selected and used within a range in which yarn breakage and fluff do not occur. the

The single fiber fineness of the precursor fiber is preferably 0.1 to 2.0 dTex, more preferably 0.3 to 1.5 dTex, even more preferably 0.5 to 1.2 dTex. From the viewpoint of improving the tensile strength or elastic modulus of the obtained carbon fibers, the smaller the single fiber fineness is, the more advantageous it is, but this usually results in a decrease in productivity. Therefore, the single fiber fineness of the precursor fibers can be selected according to the balance of performance and cost. the

The number of single fibers constituting the filaments of the precursor fiber is preferably 1,000 to 96,000, more preferably 12,000 to 48,000, and still more preferably 24,000 to 48,000. Here, the number of single fibers constituting the filaments of the precursor fibers refers to the number of single fibers immediately before the refractory treatment. When the number of single fibers is too small, productivity generally deteriorates. When the number of single fibers is too large, firing unevenness tends to easily occur in the refractory step. the

The above-mentioned method is used to carry out refractory treatment on the prepared precursor fibers to convert them into refractory fibers. the

The refractory treatment is usually carried out in an oxygen-containing gas atmosphere, preferably in an air atmosphere, at a temperature of 200 to 400°C, preferably 200 to 300°C. Refractorizing at a temperature 10 to 20° C. lower than the temperature at which filament breakage occurs due to heat storage of reaction heat is preferable because cost can be reduced and performance of the obtained carbon fiber can be improved. From the viewpoint of improving productivity and performance of the obtained carbon fibers, the time for the refractory treatment is preferably 10 to 100 minutes, more preferably 30 to 60 minutes. The time for this refractory treatment is the entire time that the filament stays in the refractory furnace. If the treatment time is too short, the difference in structure between the oxidized outer peripheral portion and the insufficiently oxidized inner portion of each single fiber becomes significant as a whole, and it may be difficult to obtain the effect of the present invention. The filament draw ratio in the fire-resistant treatment step is preferably 0.85-1.10, more preferably 0.88-1.06, and still more preferably 0.92-1.02. By increasing the draw ratio, the modulus of elasticity of the carbon fiber can be increased with the same amount of heat treatment. the

Following the refractorization step, a carbonization step of carbonizing the obtained refractory wire to convert it into carbon fibers is performed. It is preferable to provide a pre-carbonization step of treating the refractory wire in an inert atmosphere at 300 to 800° C., preferably in a nitrogen or argon atmosphere, before the carbonization step. From the viewpoint of improving the properties of the obtained carbon fibers, the draw ratio in the pre-carbonization step can be preferably set to 0.90-1.25, more preferably 1.00-1.20, and even more preferably 1.05-1.15. the

The carbonization treatment is usually carried out in an inert atmosphere at a temperature of 1000°C or higher, preferably at a temperature of 1000 to 2000°C. The highest temperature of the carbonization treatment is appropriately selected according to the required properties of the carbon fibers, but if the treatment temperature is too low, the tensile strength and modulus of elasticity of the obtained carbon fibers may decrease. From the viewpoint of improving the properties of the obtained carbon fibers, the draw ratio in the carbonization treatment step is preferably 0.95-1.05, more preferably 0.97-1.02, and even more preferably 0.98-1.01. the

The carbon fiber of the present invention obtained through the above operation has a coefficient of variation of the single fiber elastic modulus distribution measured by the method described later to be 10% or less. The elastic modulus of carbon fiber is mainly controlled by the internal structure of the material. Since the internal structure of single fibers is different, the orientation of the graphite structure is uneven. It is estimated that the above orientation is affected by the fiber tension in the refractory step and the carbonization step. Oxidation reaction in the refractorization step or uneven intermolecular crosslinking may occur between the single fibers, causing uneven tension of each single fiber in the refractorization step and the carbonization step, resulting in uneven orientation. Compared with the conventional carbon fiber, the carbon fiber of the present invention has less thermal bonding and adhesion between single fibers in the precursor fiber, so the above-mentioned uneven orientation can be suppressed, and the distribution of the elastic modulus of the single fiber can be narrowed. When the coefficient of variation of the single fiber modulus of elasticity of the carbon fibers exceeds 10%, the reliability of the carbon fiber reinforced composite material obtained using the carbon fibers decreases. The coefficient of variation of the single fiber elastic modulus is preferably 8% or less, more preferably 6% or less. From the viewpoint of the reliability of carbon fiber reinforced composite materials, the lower the coefficient of variation of the elastic modulus of the single fiber is, the better it is, and it is most preferably 0%. However, when it is less than 0.1%, the effect is almost saturated in most cases, so the actual value 0.1% or more. The coefficient of variation of the elastic modulus of the single fiber is more preferably 4% or more. the

The average value of the single fiber modulus of elasticity of carbon fibers is preferably 400 GPa or less. In order to obtain carbon fibers with a high average elastic modulus, a method of firing at a high temperature in the carbonization process, a method of firing while stretching, etc. can be used. In the case of carbonization with a maximum temperature of 2000°C or higher, The compressive strength is significantly reduced. The average value of the single fiber modulus of elasticity of carbon fibers is more preferably 360 GPa or less, further preferably 320 GPa or less. When the carbonization treatment is performed so that the single fiber modulus of elasticity of the carbon fibers falls within the above-mentioned range, the decrease in the compressive strength of the obtained carbon fibers and the unevenness of the single fiber modulus of elasticity can be effectively suppressed at the same time. the

When it is desired to obtain carbon fibers with a higher elastic modulus, graphitization treatment may be performed after carbonization treatment. The graphitization treatment is usually carried out in an inert atmosphere at a temperature of 2000 to 3000°C. According to the required characteristics of carbon fiber, its maximum temperature is appropriately selected. The draw ratio in the graphitization treatment step can be appropriately selected within a range in which quality deterioration such as fuzzing does not occur according to the properties required of the carbon fiber. the

By surface-treating the obtained carbon fibers, it is possible to further increase the bonding strength with the matrix when it is made into a composite material. As the surface treatment method, gas-phase or liquid-phase treatment can be used, and liquid-phase treatment is preferably used in consideration of productivity and quality unevenness, and electrolytic treatment (anodizing treatment) is particularly preferably used. the

As the electrolytic solution used in the electrolytic treatment, an aqueous solution containing an acid such as sulfuric acid, nitric acid, or hydrochloric acid, an alkali such as sodium hydroxide, potassium hydroxide, or tetraethylammonium hydroxide, or a salt thereof can be used. Among these, it is particularly preferable to use an aqueous solution containing ammonium ions. Specifically, for example, ammonium nitrate, ammonium sulfate, ammonium persulfate, ammonium chloride, ammonium bromide, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium bicarbonate, ammonium carbonate, or a mixture of these compounds can be preferably used. aqueous solution. the

The amount of electricity applied to carbon fibers in electrolytic treatment varies depending on the carbon fibers used. For example, the higher the degree of carbonization of carbon fibers, the higher the amount of electricity required. Generally, from the viewpoint of improving the adhesion properties, it is preferable to set the electric quantity so that the surface oxygen concentration O/C and the surface nitrogen concentration N/C of the carbon fiber measured by X-ray photoelectron spectroscopy (ESCA) are 0.05 to 0.40, respectively. The power within the range of 0.02 to 0.30. By satisfying the above conditions, it is possible to make the bonding of the carbon fiber and the matrix at an appropriate level when making a composite material. Therefore, the following defects can be prevented, thereby exhibiting longitudinal and non-longitudinal balanced composite material properties. The defect is that the bonding between carbon fiber and matrix is too strong, and brittle failure is prone to occur, resulting in a decrease in the longitudinal tensile strength of the composite material. Defects, or although the longitudinal tensile strength of the composite material is strong, the adhesion between the carbon fiber and the matrix is too low, resulting in the defect that the composite material does not have non-longitudinal mechanical properties. the

If necessary, the obtained carbon fibers can also be subjected to sizing treatment. The sizing agent is preferably a sizing agent with good compatibility with the substrate, and is selected and used together with the substrate. the

The carbon fiber obtained through the above operations can be made into a prepreg and then formed into a composite material, or it can be made into a preform such as a fabric by hand lay up (hand lay up) method, drawing molding method and resin transfer molding. Formed into composite materials by plastic method. In addition, it can also be formed into a composite material by winding method, or by injection molding after performing chopped fiber or milled fiber. the

The composite material using the carbon fiber obtained by the present invention can be applied to sports applications such as golf clubs and fishing rods, aerospace applications, automotive structural parts such as hoods and drive shafts, and energy-related applications such as flywheels and CNG containers. the

Example

The present invention will be further specifically described below using examples. the

In addition, in this Example, each characteristic was measured by the following method. In addition, the kinematic viscosity of a silicone compound uses the catalog value provided by the silicone compound manufacturer. the

<Measurement of vibration period difference of liquid particles by rigid pendulum free attenuation vibration method>

Based on the rigid pendulum free attenuation vibration method, the vibration period was measured using a rigid pendulum type physical property testing machine RPT-3000 manufactured by A&D Corporation. The liquid particles used for the measurement can be used directly if they are not mixed with the dispersion medium. In the case of mixing with the dispersion medium to make an emulsion, put about 1g of the emulsion into an aluminum alloy with a diameter of about 60mm and a height of about 20mm. In the container, dry at 40°C for 10 hours. Next, on a 5 cm long, 2 cm wide, and 0.5 mm thick galvanized steel coated substrate (STP-012 manufactured by A&D Co., Ltd.), liquid particles are coated on the entire lateral surface of the substrate to a thickness of 20 to 30 μm. Coated board. Immediately after coating, the coated panel was placed on the testing machine, and the measurement was started. The temperature of the testing machine was adjusted to 30°C in advance, and after the coated plate and the pendulum were placed, the temperature was raised to 300°C at a rate of 10°C/min. During the measurement, the cycle was continuously measured at intervals of 7 seconds, and the difference in the vibration cycle at 30°C and 200°C or the difference in the vibration cycle at 30°C and 300°C was calculated from the cycle values at 30°C, 200°C, and 300°C, respectively. Each measurement was performed 7 times, and the maximum value and the minimum value of the vibration period difference were removed, and the average value of the 5 times was taken as the value of the vibration period difference. In addition, the measurement was performed using the following pendulum. the

Blade used: Knife-like blade (RBE-160 manufactured by A&D Co., Ltd.)

Pendulum weight/moment of inertia: 15 g/640 g·cm (FRB-100 manufactured by A&D Co., Ltd.). the

<Measurement of vibration period difference T of siloxane compound by rigid pendulum free damping vibration method>

Based on the rigid pendulum free attenuation vibration method, the vibration period was measured using a rigid pendulum type physical property testing machine RPT-3000 manufactured by A&D Corporation. The siloxane compound used for the measurement can be used directly if it is not mixed with the liquid medium. In the case of mixing with the liquid medium to make a solution or emulsion, put about 1g of the solution or emulsion into a diameter of about 60mm, Dry at 40° C. for 10 hours in an aluminum container with a height of about 20 mm. Next, on the same coated substrate as above, the dry sample was coated on the entire lateral surface of the substrate to a thickness of 20 to 30 μm to produce a coated plate. Immediately after coating, the coated panel was placed on the testing machine, and the measurement was started. Adjust the temperature of the testing machine to 30°C in advance, place the coated plate and the pendulum, raise the temperature to 180°C at a rate of 50°C/min, and keep at 180°C for 20 minutes. During the measurement, the period was continuously measured at intervals of 7 seconds, and the difference T between the vibration periods at 30°C and 180°C was calculated from the period value at 30°C and the period value after holding at 180°C for 20 minutes. The measurement was carried out 7 times, the maximum value and the minimum value were removed, and the average value of the 5 times was used as the value of the vibration cycle difference T. In addition, the measurement was performed using the same pendulum as above. the

The vibration period difference T is calculated according to the following formula. the

T＝T30-T180

T30: Vibration period at 30°C (seconds)

T180: Vibration period after heat treatment at 180°C for 20 minutes (seconds)

<Determination of the hydrodynamic average particle size of liquid particles or main ingredients>

The average particle diameter was measured using FPAR-1000 manufactured by Otsuka Electronics Co., Ltd. based on the dynamic light scattering method. The measurement temperature was set at 25° C., and the probe used was a probe for a micro volume. The sample was diluted with the same dispersion medium as that of the sample to make the liquid fine particles or main ingredient 0.01% by weight, and then used for measurement. Analysis was performed by the Cumulant method, and the Cumulant average particle diameter was used as the value of the hydrodynamic average particle diameter. the

<Measurement of variation coefficient of single fiber elastic modulus of carbon fiber>

Based on JIS R7601 (1986), the single fiber modulus of elasticity of carbon fibers was obtained as follows. That is, first, a carbon fiber bundle with a length of about 20 cm was roughly divided into four equal parts, and 50 monofilaments were sequentially taken out from the four fiber bundles as samples. In this case, the sample is sampled as uniformly as possible from the entire fiber bundle. The monofilament as a sample was fixed on a perforated mount using an adhesive. The backing paper on which the monofilament was fixed was mounted on a tensile testing machine, and a tensile test was performed under the conditions of a sample length of 25 mm, an inclination speed of 1 mm/min, and a number of 50 monofilament samples. The modulus of elasticity is defined by the following formula. the

Elastic modulus = (obtained strength)/(cross-sectional area of single fiber × obtained elongation) 

For the measured fiber bundle, the cross-sectional area of a single fiber is calculated as follows: the weight per unit length (g/m) is divided by the density (g/m ³ ), and the obtained value is divided by the number of filaments to obtain the single fiber. wire cross-sectional area. Density was measured using the Archimedes method with o-dichloroethylene as the specific gravity solution. For the 50-point elastic modulus values measured as described above, the coefficient of variation was calculated according to the following formula.

Coefficient of variation (%) = (standard deviation of elastic modulus) / (average value of elastic modulus) × 100

The tow tensile strength and tensile elastic modulus of carbon fibers were measured as follows. Carbon fiber bundles were impregnated with an epoxy resin composition having the following composition, and cured at a temperature of 130° C. for 35 minutes to form filament bundles. Based on JIS R7601 (1986), tensile tests were carried out on six tows, and the strength and elastic modulus obtained in each test were averaged to obtain the tensile strength and tensile elastic modulus of carbon fibers. the

*Resin composition

3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate (ERL-4221, manufactured by Union Carbide) 100 parts by weight

3-boron fluoride monoethylamine (manufactured by STELLACHEMIFA Co., Ltd.) 3 parts by weight

・Acetone (manufactured by Wako Pure Chemical Industries, Ltd.) 4 parts by weight

[Example 1]

Prepare the carbon fiber precursor oil of the following formulation. the

Amino-modified siloxane 66 parts by weight

Alicyclic epoxy modified siloxane 28 parts by weight

Alkylene oxide modified siloxane 5 parts by weight

Nonionic surfactant 30 parts by weight

Water 4000 parts by weight

As the amino-modified siloxane, a siloxane compound obtained by substituting a part of the side chain of dimethylsiloxane with an amino group represented by the following chemical formula 1 was used. The amino equivalent of the amino-modified siloxane is 2000 mol/g, and the kinematic viscosity at 25° C. is 1000 cSt. As the alicyclic epoxy-modified siloxane, a siloxane compound obtained by substituting a part of the dimethylsiloxane side chain with an alicyclic epoxy group represented by the following chemical formula 2 was used. The epoxy equivalent of the alicyclic epoxy-modified siloxane is 6000 mol/g, and the kinematic viscosity at 25° C. is 6000 cSt. As the alkylene oxide-modified siloxane, a siloxane compound obtained by substituting a part of the side chain of dimethylsiloxane with a polyethylene oxide group represented by the following chemical formula 3 was used. As the alkylene oxide-modified siloxane, an alkylene oxide-modified siloxane whose kinematic viscosity at 25° C. is 300 cSt has an alkylene oxide moiety in an amount of 50% by weight of the total weight was used. As the nonionic surfactant, polyoxyethylene alkylphenyl ether was used. the

Add the above three siloxane compounds, surfactants and water, and use a homomixer or homogenizer to prepare an emulsion. Add the emulsion KM902 (Shin-Etsu Chemical Industry (Shin-Etsu Chemical Industry ( Co., Ltd.), stirred to obtain an oil agent. The hydrodynamic average particle size of KM902 measured by a particle size distribution meter is 0.6 μm. The difference between the pendulum vibration period at 30°C and 200°C measured by the rigid pendulum free damping vibration method is 0.02, and the difference between the pendulum vibration period at 30°C and 300°C is 0.02. the

A copolymer formed of 99.5 mol% acrylonitrile and 0.5 mol% itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent to obtain a spinning dope with a concentration of 22% by weight. After polymerization, ammonia gas is introduced to pH 8.5 to neutralize itaconic acid, and the hydrophilicity of the spinning dope can be improved by introducing ammonium groups into the polymer components. At a temperature of 40°C, the spinning dope obtained is sprayed into the air at one time from a spinning nozzle with a diameter of 0.15 mm and a number of holes of 4000, and then introduced into the temperature controlled at 3°C after passing through a space of about 4 mm. A coagulation bath composed of an aqueous solution of methyl sulfoxide is used for coagulation by this dry-wet spinning. The obtained coagulated silk was washed with water, stretched 3 times in warm water at 70°C, passed through an oil bath composed of the oil prepared above, and the oil was attached by dipping-kneading. Then, drying treatment was carried out with a heating roller at 180° C., and the contact time was 40 seconds. The obtained dried yarn was stretched in a pressurized steam of 0.4 MPa, so that the total draw ratio of the yarn was 14 times, and a precursor fiber with a monofilament fineness of 0.7 dTex and a single fiber number of 4000 was obtained. It should be noted that the amount of oil attached to the obtained precursor fibers was 1.0% by weight in terms of pure components. the

Six obtained precursor fibers were collected so that the number of single fibers became 24,000, and then heated in air at 240 to 280° C. to convert them into refractory fibers. The fire-resistant treatment time was 40 minutes, and the stretch ratio in the fire-resistant treatment step was 1.00. the

Next, the refractory fiber is heated in a nitrogen atmosphere at 300-800°C for pre-carbonization, and then heated in a nitrogen atmosphere with a maximum temperature of 1500°C for carbonization. The draw ratio in the preliminary carbonization treatment step was 1.10, and the draw ratio in the carbonization treatment step was 0.97. Then, the fibers obtained by the carbonization treatment were anodized in an aqueous sulfuric acid solution with an electric charge of 10 coulombs/g-CF to obtain carbon fibers. During this period, no significant fluffing or cutting occurred on the carbon fibers that would affect the workability. The obtained carbon fibers were of good quality, with a tensile strength of 6.7GPa and a tensile modulus of elasticity of 320GPa. the

[Comparative example 1]

Carbon fibers were obtained in the same manner as in Example 1 except that KM902 used in Example 1 was not used. As a result, a large amount of fluff occurs in the preliminary carbonization process. The tensile strength of the obtained carbon fiber was 6.1 GPa, and the tensile modulus of elasticity was 320 GPa. the

[Example 2]

Carbon fibers were obtained in the same manner as in Example 1 except that the oil of the following formulation was used instead of the oil for carbon fiber precursors used in Example 1. the

Amino-modified siloxane 100 parts by weight

Nonionic surfactant 30 parts by weight

Water 4000 parts by weight

As the amino-modified siloxane, a siloxane compound obtained by substituting a part of the side chain of dimethylsiloxane with an amino group represented by the following chemical formula 1 was used. The amino equivalent of the amino-modified siloxane is 2000mol/g, and the kinematic viscosity at 25°C is 3500cSt. Add the above-mentioned siloxane, surfactant and water, and use a homomixer and a homogenizer to prepare an emulsion. KM902 (manufactured by Shin-Etsu Chemical Co., Ltd.) was added to this emulsion, and stirred to obtain an oil preparation. the

During the production of the carbon fibers, significant fuzzing and cutting which would affect the workability did not occur. The obtained carbon fibers were of good quality, with a tensile strength of 6.4GPa and a tensile modulus of elasticity of 320GPa. the

[Comparative example 2]

Carbon fibers were obtained in the same manner as in Example 2 except that KM902 used in Example 2 was not used. As a result, a large amount of fluff occurs in the preliminary carbonization process. Carbon fiber of good quality could not be obtained. the

[Example 3]

An oil agent for carbon fiber precursor fibers with the following formulation was prepared. the

main agent

Amino-modified siloxane 50 parts by weight

Alicyclic epoxy modified siloxane 25 parts by weight

Alkylene oxide modified siloxane 25 parts by weight

Nonionic surfactant 30 parts by weight

thermosensitive polymer

N-isopropylacrylamide copolymer 0.5 parts by weight

Water 4000 parts by weight

As the amino-modified siloxane, a siloxane compound obtained by substituting a part of the side chain of dimethylsiloxane with an amino group represented by the following chemical formula 1 was used. The amino equivalent of the amino-modified siloxane is 2000mol/g, and the kinematic viscosity at 25°C is 1000cSt. As the alicyclic epoxy-modified siloxane, a siloxane compound obtained by substituting a part of the side chain of dimethylsiloxane with an alicyclic epoxy group represented by the following chemical formula 2 is used. The epoxy equivalent of alicyclic epoxy-modified siloxane is 6000mol/g, and the kinematic viscosity at 25°C is 6000cSt. As the alkylene oxide-modified siloxane, a siloxane compound obtained by substituting a part of the side chain of dimethylsiloxane with a polyethylene oxide group represented by the following chemical formula 3 was used. As the alkylene oxide-modified siloxane, an alkylene oxide-modified siloxane whose kinematic viscosity at 25° C. is 300 cSt has an alkylene oxide moiety in an amount of 50% by weight of the total weight was used. As the nonionic surfactant, ethylene oxide (hereinafter abbreviated as EO) adducts of nonylphenol (equal weight mixtures of adducts with 10, 8, and 6 moles added) was used. As the N-isopropylacrylamide-based copolymer, a copolymer obtained by copolymerizing 97 mol% of N-isopropylacrylamide and 3 mol% of N,N-dimethylaminopropylacrylamide was used. the

The above-mentioned three kinds of siloxane compounds and the surfactant were stirred with a propeller at 25°C, and 3500 parts by weight of water at 25°C were slowly added. On the other hand, N-isopropylacrylamide-based copolymer was added to 500 parts by weight of water at 25°C at 25°C, stirred until dissolved, and added to the above-mentioned mixture consisting of silicone compound, surfactant, and water. in the emulsion. the

The average particle diameter of the obtained oil agent was measured with a particle size distribution meter and found to be 0.2 μm. the

The oil agent was adhered to polyacrylonitrile fibers (0.7 dtex, 3000 filaments) by dipping-kneading method at 25°C, and then dried at 170°C for 30 seconds. Then, the carbon fiber precursor fiber bundle was obtained by steam stretching at a draw ratio of 5. the

After gathering 8 precursor fiber bundles for carbon fibers as described above so that the number of single fibers becomes 24,000, the refractorization step at 250°C with a draw ratio of 1.00, the pre-carbonization step at 650°C with a draw ratio of 1.10, and the 1450°C A carbonization step with a draw ratio of 1.00 was used to obtain carbon fibers. During this process, significant fuzzing and cutting did not occur in the carbon fiber, which would affect the workability. The obtained carbon fibers are of good quality, with a tensile strength of 7.1 GPa and a tensile modulus of elasticity of 350 GPa. the

[Comparative example 3]

Except that the thermosensitive polymer used in Example 3 was not used, other operations were the same as in Example 3. As a result, a large amount of fluff occurred in the preliminary carbonization step, and carbon fibers of good quality could not be obtained. the

[Examples 4-9, Comparative Examples 4-8]

Silicone oil agents having the composition ratios shown in Table 1 were prepared, and the vibration period difference T was measured. As the siloxane compound used in the preparation of the oil agent, an amino group represented by the following chemical formula 1 and an alicyclic epoxy group represented by the following chemical formula 2 were used for a part of the side chains of dimethyl siloxane having a methyl group at the end. , and three types of siloxane compounds obtained by substituting polyethylene oxide groups represented by the following chemical formula 3. The modification amount of the amino-modified siloxane was 1.0% by weight. The modification amount of the epoxy-modified siloxane was 1.0% by weight. The modification amount of the alkylene oxide-modified siloxane was 50% by weight. With respect to the total amount of 100 parts by weight of the above-mentioned 3 kinds of siloxane compounds, add 30 parts by weight of nonionic surfactant and water, and use a homomixer or homogenizer to make a silicone oil agent with a pure component of 30% by weight , for the above determination. the

chemical formula 1

chemical formula 2

chemical formula 3

A copolymer composed of 99.5 mol% acrylonitrile and 0.5 mol% itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent to obtain a spinning dope with a concentration of 22% by weight. After polymerization, ammonia gas is blown in until the pH is 8.5 to neutralize itaconic acid, and the hydrophilicity of the spinning dope can be improved by introducing ammonium groups into the polymer components. At a temperature of 40°C, the spinning dope is sprayed into the air at one time from a spinning nozzle with a diameter of 0.15 mm and a number of holes of 4000. After passing through a space with a distance of about 4 mm, it is introduced into a 35-weight % dimethyl sulfoxide aqueous solution, it was coagulated by the above-mentioned dry-wet spinning. After the obtained coagulated silk was washed with water, it was stretched three times in warm water at 70° C., and passed through an oil bath composed of the oil prepared above to adhere the oil. The concentration in the oil bath was adjusted by diluting with water so that the pure component was 2.0% by weight. Then, drying treatment was carried out with a heating roller at 180° C., and the contact time was 40 seconds. The obtained dried filaments were stretched in a pressurized steam of 0.4 MPa-G, so that the total draw ratio of the filaments was 14 times, and a precursor fiber with a single filament fineness of 0.7 dTex and a single fiber number of 24,000 was obtained. It should be noted that the amount of silicone oil agent attached to the obtained precursor fibers was 1.0% by weight in terms of pure components. the

The resulting precursor fibers are heated in air at 240-280°C to transform into refractory fibers. The fire-resistant treatment time was 40 minutes, and the stretch ratio in the fire-resistant treatment process was 0.90 and 1.00. the

Next, after pre-carbonizing the refractory fiber in an inert atmosphere at 300-800°C, carbonization is carried out in an inert atmosphere at a maximum temperature of 1500°C. When the stretching ratio in the flame-proofing step is 0.90, the stretching ratio in the pre-carbonization step is 1.00, and when the stretching ratio in the flame-proofing step is 1.00, the stretching ratio in the pre-carbonization step is 1.10. When the stretching ratio in the flameproofing step is 0.90, the stretching ratio in the carbonization treatment step is 0.97, and when the stretching ratio in the flameproofing step is 1.00, the stretching ratio in the carbonization treatment step is 1.00. Then, the obtained carbon fibers were anodized at 10 coulomb/g-CF in an aqueous sulfuric acid solution. The strength and single-fiber elastic modulus of the obtained carbon fibers were measured, and the average value and variation coefficient of the single-fiber elastic modulus were obtained. The results are shown in Table 2. the

However, the refractory wires of Comparative Examples 5 to 8 treated with a flame-resistant draw ratio of 1.00 were broken at a pre-carbonized draw ratio of 1.10, and could not be handled, so the measurement was terminated. In addition, many carbon fibers of the comparative example were fluffed. the

[Example 10]

An oil agent was prepared in the same manner as in Example 7 except that a thermosensitive polymer was further added. Add 0.5 parts by weight of the thermosensitive polymer N-isopropylacrylamide copolymer used in Example 3 to 500 parts by weight of water at 25°C, stir until dissolved at 25°C, then add to 400 parts by weight and implement The pure components of the same oil composition in Example 7 are in a 30% by weight emulsion. The obtained oil preparation was diluted with water so that the pure component was 2.0% by weight and used. Except changing the oil agent, it carried out similarly to Example 7, and obtained the carbon fiber. The conditions used were: the stretching ratio in the refractory step was 1.00, the stretching ratio in the pre-carbonization step was 1.10, and the stretching ratio in the carbonization step was 1.00. As a result, as shown in Table 2, the carbon fiber strength was 7.2 GPa, and the single fiber elastic modulus variation coefficient was 7%, which were good results. the

[Example 11]

An oil agent was prepared in the same manner as in Example 7 except that liquid fine particles were further added. Add 10 parts by weight of dimethylsiloxane (150 DEG C kinematic viscosity is 180000cSt), 2.3 parts by weight of nonionic An emulsion SM8701EX (manufactured by TORAY Dow Corning Co., Ltd.) consisting of a surfactant and 26 parts by weight of water was stirred to obtain an oil. The hydrodynamic average particle size of SM8701EX was measured with a particle size distribution meter, and the result was 0.2 μm. In addition, the difference between the vibration period of the pendulum at 30°C and 200°C measured by the rigid pendulum free damping vibration method is 0.02, and the difference between the vibration period of the pendulum at 30°C and 300°C measured by the same method is 0.04. The obtained oil preparation was diluted with water so that the pure component was 2.0% by weight and used. Except changing the oil agent, it carried out similarly to Example 10, and obtained the carbon fiber. As a result, as shown in Table 2, the carbon fiber strength was 7.2 GPa, and the single fiber elastic modulus variation coefficient was 7%, which were good results. the

[Example 12]

An oil agent was prepared in the same manner as in Example 7 except that a thermosensitive polymer and liquid fine particles were further added. Add 0.5 parts by weight of the thermosensitive polymer N-isopropylacrylamide copolymer used in Example 3 to 500 parts by weight of water at 25°C, stir until dissolved at 25°C, then add to 400 parts by weight and implement The pure component of the same oil composition in Example 7 is in a 30% by weight emulsion. Then add emulsion SM8701EX (manufactured by TORAY Dow Corning Co., Ltd.) consisting of 10 parts by weight of dimethylsiloxane (kinematic viscosity at 150°C: 180,000 cSt), 2.3 parts by weight of nonionic surfactant, and 26 parts by weight of water. , stir to obtain the oil. The obtained oil preparation was diluted with water so that the pure component was 2.0% by weight and used. Except changing the oil agent, it carried out similarly to Example 10, and obtained the carbon fiber. As a result, as shown in Table 2, the carbon fiber strength was 7.3 GPa, and the coefficient of variation of elastic modulus of single fiber was 6%, which were good results. the

Table 1

Table 2

Industrial availability

Use of the oil agent for carbon fiber precursors of the present invention can suppress firing unevenness in the flame-proofing step. Even under higher filament density, high tension, and high-speed firing conditions than before, carbon fibers can be produced with stable quality without fuzzing or broken filaments, so high-quality and homogeneous carbon fibers can be obtained. Using the above-mentioned carbon fiber, it is possible to form a composite material with high performance and high reliability. The composite material obtained by using the carbon fiber of the present invention can be applied to sports applications such as golf clubs and fishing rods, aerospace applications, automotive structural parts such as hoods and drive shafts, and energy-related applications such as flywheels and CNG containers. the

Claims (6)

1. An oil agent for carbon fiber precursor fibers, which contains a main agent and liquid particles, the main agent contains a siloxane compound with a kinematic viscosity of 10 to 10000 cSt at 25°C, and the liquid particles contain For silicone oil with a viscosity of 15000 cSt or more, the liquid particles have a hydrodynamic average particle size of 0.05-5 μm, and the weight ratio of the liquid particles to the main agent is 0.1-50 parts by weight relative to 100 parts by weight of the main agent. 2 . The oil agent for carbon fiber precursor fibers according to claim 1 , wherein the pendulum vibration period difference between 30° C. and 200° C. measured by the rigid pendulum free damping vibration method of the liquid particles is 0.1 second or less. 3. The oil agent for carbon fiber precursor fibers according to claim 1, wherein the main ingredient contains a siloxane compound having an average kinematic viscosity of 10 to 1500 cSt at 25° C., and the siloxane compound is The difference between the pendulum vibration periods at 30°C and 180°C measured by the free damping vibration method is 0.03-0.4 seconds. 4. The carbon fiber precursor fiber oil agent as claimed in claim 3, wherein containing amino-modified siloxane, alicyclic epoxy-modified siloxane and alkylene oxide modified siloxane, and relative to 100 The proportion of amino-modified siloxane and alkylene oxide-modified siloxane is 15-900 parts by weight, relative to 100 parts by weight of all siloxane compounds, the proportion of alicyclic epoxy-modified siloxane is 0 to 20 parts by weight. 5. The carbon fiber precursor fiber oil agent as claimed in claim 1, wherein, also contain thermosensitive macromolecule, described thermosensitive macromolecule is to contain and be selected from N-isopropylacrylamide and methacrylic acid two At least one monomer in the methyl amino ethyl ester is used as a polymer of the monomer component, and the mixing ratio of the temperature-sensitive polymer and the main agent is that the temperature-sensitive polymer is 0.001 to 100 parts by weight of the main agent. 50 parts by weight. 6. A method for preparing carbon fibers, said preparation method at least comprising the following steps: A process of spinning polyacrylonitrile polymers to obtain carbon fiber precursor fibers; The refractory process of heating the precursor fiber in an oxygen-containing gas atmosphere at a temperature of 200-400°C to transform it into a refractory fiber; The refractory fiber is heated in an inert atmosphere with a temperature of at least 1000°C, carbonized, and converted into carbon fiber. Here, in the spinning step, the oil agent for carbon fiber precursor fibers according to claim 1 is applied to the precursor fibers.