JP5960402B2 - Carbon fiber bundle and method for producing carbon fiber bundle - Google Patents

Description

  The present invention relates to a carbon fiber bundle suitable for use as a composite material and a method for producing the carbon fiber bundle.

  Carbon fiber has excellent specific strength and specific elastic modulus, and is excellent in lightness. Therefore, as a reinforcing fiber for thermosetting and thermoplastic resin, not only conventional sports and general industrial applications, but also aerospace applications, Widely used for automotive applications. And with such expansion of applications, carbon fiber composite materials are required to have higher performance.

  The performance of carbon fiber composite materials is greatly influenced not only by the difference in the mechanical properties of the carbon fiber and matrix resin used, but also by the characteristics of the interface between the carbon fiber and the resin, particularly the difference in adhesion between the fiber and the resin. The In order to control the adhesion between the carbon fiber and the resin, the carbon fiber bundle is generally subjected to a surface oxidation treatment and a sizing agent application treatment (sizing treatment) in the carbon fiber production process. The sizing agent suppresses the fluffing of the fiber bundle and provides convergence, and at the same time, when used as a composite material, it serves to connect the fibers and the matrix resin to enhance the adhesiveness. Conventionally, in the sizing treatment, after a sizing agent solution is applied to a carbon fiber bundle, the sizing agent is attached to the carbon fiber bundle by heating and drying with a hot air drying method or a heating roller method.

  By the way, in the composite material, it is desirable that the adhesion between the fiber and the resin is uniform over the entire member. When there is a variation in the adhesion between the fiber and the resin, when stress or impact is applied to the composite material, the fiber-resin is peeled off at the weakly bonded part, and the cracks that are generated are stretched. It is because it will lead to the fracture | rupture of. In order to make the adhesion between the fiber and the resin uniform, various improvement measures have been studied so that the sizing agent is uniformly attached to the fiber surface without unevenness.

  For example, Patent Document 1 proposes a method of uniformly attaching a sizing agent by performing sizing treatment a plurality of times using a low concentration sizing agent solution. However, in Patent Document 1, after applying the sizing agent solution, drying is performed by a hot air circulation method, and thus temperature unevenness occurs inside and outside the fiber bundle. Therefore, drying of the outer surface of the fiber bundle precedes, and the sizing agent solution remaining inside the fiber bundle diffuses outward. As a result, there is a problem that the amount of adhesion on the inside tends to be low, and the amount of adhesion inside and outside the fiber bundle is uneven.

As a sizing agent drying method for the carbon fiber bundle, a heating roller method is generally used in addition to the hot air circulation method. (For example, patent document 2) However, in a heating roller system, there exists a problem that the adhesion amount of the fiber bundle outer surface tends to fall. When the heating roller method is used for drying the sizing agent, since it is a contact method, the sizing agent resin on the outer surface of the fiber bundle adheres on the roller, and the attached amount of the outer surface of the fiber bundle tends to decrease. For this reason, the amount of adhesion inside and outside the fiber bundle tends to be uneven. Also, the sizing agent adheres to the heating roller, the frictional force between the roller and the fiber changes, and the process tension is not constant, so that the sizing agent solution exudation from the fiber bundle during drying is not constant, Unevenness is likely to occur in the amount of adhesion.
As described above, it is difficult to uniformly attach the sizing agent to the carbon fiber bundle, and particularly to make the adhesion uniform between the outer surface and the inner side of the fiber bundle, and further improvement is required.

JP 2009-242964 A Japanese Patent Laid-Open No. 1-292038

  An object of the present invention is to provide a carbon fiber bundle having uniform interface adhesion and high resistance to stress and impact, and a method for producing a carbon fiber bundle for obtaining such a carbon fiber bundle when a composite material is used. There is to do.

The carbon fiber bundle of the present invention is a carbon fiber bundle in which a sizing agent is uniformly attached inside and outside the fiber bundle. Specifically, it is a carbon fiber bundle composed of carbon fibers, and the ratio of the sizing agent adhesion amount on the surface of the fiber bundle to the sizing agent adhesion amount inside the fiber bundle is 0.5 to 1.1. It is a bunch.

Moreover, the method for producing a carbon fiber bundle of the present invention, after adding a sizing agent solution, which is an emulsion aqueous solution in which a sizing agent resin is emulsified by adding a surfactant to a carbon fiber bundle composed of carbon fibers, Carbon to be heat-dried in a multi-stage treatment in which an electromagnetic wave having a wavelength of 3 μm or more is heated at least in a temperature range of 80 to 120 ° C. for 1 to 10 minutes and further heated in a temperature range of 150 to 250 ° C. for 1 to 10 minutes. It is a manufacturing method of a fiber bundle. Among electromagnetic waves, it is preferable to use infrared rays having a wavelength of 3 to 30 μm, which is the absorption wavelength of the sizing agent resin. The sizing agent solution used in the present invention is preferably an aqueous emulsion solution obtained by emulsifying a sizing agent resin with 5 to 20% by mass of a nonionic surfactant based on the mass of the sizing agent resin.

In the carbon fiber bundle of the present invention, since the sizing agent is uniformly attached inside and outside the fiber bundle, the adhesive property between the fiber and the resin is uniform when a composite material is used. For this reason, the composite material composed of the carbon fiber bundle and the matrix resin of the present invention is less likely to cause stress concentration and interfacial peeling between the fiber and the resin, and the physical properties of the carbon fiber composite material are improved.
According to the method for producing a carbon fiber bundle of the present invention, uneven adhesion of the sizing agent can be suppressed, and the carbon fiber bundle of the present invention in which the sizing agent is uniformly adhered inside and outside the fiber bundle can be obtained.

The carbon fiber bundle of the present invention is a carbon fiber bundle in which the ratio of the sizing agent adhesion amount on the surface of the fiber bundle to the sizing agent adhesion amount inside the fiber bundle is 0.5 to 1.1 .
In the carbon fiber bundle of the present invention, the sizing agent is uniformly attached inside and outside the fiber bundle. Therefore, when a composite material is used, the adhesiveness between the fibers and the resin is uniform, and the carbon fiber single fibers are easily dispersed in the matrix resin. For this reason, even when a load is applied to the composite material composed of the carbon fiber bundle and the matrix resin of the present invention, stress concentration hardly occurs and interface separation between the fiber and the resin hardly occurs. As a result, physical properties as a carbon fiber composite material are improved, and variations in physical properties are also reduced.

  The amount of the sizing agent adhering to the carbon fiber can be measured as the light emission amount of the fluorescent substance contained in the sizing agent using a fluorescent electron microscope. Therefore, the amount of luminescence of the carbon fiber located on the outer surface of the carbon fiber bundle and the carbon fiber inside the fiber bundle which is exposed by dividing the fiber bundle at the center, the sizing agent adhesion amount on the surface of the fiber bundle, By determining the ratio of the amount of light emitted from the outer surface of the carbon fiber bundle to the amount of light emitted from the inner surface of the carbon fiber bundle (the amount of light emitted from the outer surface of the carbon fiber bundle / the amount of light emitted from the inner surface of the carbon fiber bundle). The uneven adhesion of the sizing agent inside and outside the bundle can be evaluated.

As the ratio of the sizing agent adhesion amount on the surface of the fiber bundle to the sizing agent adhesion amount inside the fiber bundle is closer to 1, the adhesion unevenness of the size agent is smaller.
If the ratio of the adhesion amount is in the range of 0.5 to 2.0, the sizing agent is uniformly adhered inside and outside the fiber bundle, so that when the composite material is used, stress concentration and interfacial peeling are less likely to occur. The physical properties as a carbon fiber composite material are improved. Furthermore, variation in physical properties is also reduced. However, if the ratio of the amount of adhesion exceeds 2.0, the amount of adhesion of the sizing agent inside the carbon fiber is small, so that the adhesion between the fiber and the resin is lowered, and the physical properties of the composite material are lowered. On the other hand, when the ratio of the adhesion amount is less than 0.5, the adhesion amount of the sizing agent on the surface of the carbon fiber bundle is too small, so that the physical properties of the composite material are lowered and the abrasion resistance of the fiber bundle is also lowered.

  The amount of sizing agent attached to the carbon fiber bundle can be changed in a timely manner. However, if the amount attached exceeds 3.0% by mass, the openability of the carbon fiber bundle is reduced, and the matrix resin is poorly impregnated inside the fiber bundle. Tend to cause. If the amount of the sizing agent attached is small, the fiber convergence and scratch resistance tend to be lowered, so 0.05% by mass or more is preferably attached. From this, the adhesion amount is preferably 0.05 to 3.0% by mass, and more preferably 0.1 to 1.5% by mass.

The carbon fiber constituting the carbon fiber bundle of the present invention is not particularly limited, and any carbon fiber such as pitch, rayon, or polyacrylonitrile (PAN) can be used, but operability, process passability, mechanical strength, and the like. In view of the above, the PAN system is preferable. There are no particular restrictions on the fineness and strength of the carbon fiber, and any known carbon fiber can be used without restriction.
The fineness of the carbon fiber bundle used in the present invention is not particularly limited, but the single fiber fineness is preferably 0.5 to 1.0 dtex, and the total fineness of the carbon fiber bundle is 50 to 5000 tex. Is preferred.

  The number of filaments of the carbon fiber bundle used in the present invention is preferably 1000 to 100,000, more preferably 3000 to 50000. Moreover, 12000 or more are more preferable from the surface of manufacturing efficiency, and 24000 or more are further more preferable. The number of filaments per unit width is preferably 5000 / mm or less, more preferably 3000 / mm or less. If it exceeds 5000 / mm, the variation in sizing agent tends to increase.

The strength of the carbon fiber bundle used in the present invention is preferably 1000 to 10000 MPa, more preferably 2000 to 7000 MPa, and the elastic modulus is preferably 100 to 1000 GPa, more preferably 200 to 600 GPa.
The carbon fiber referred to in the present invention includes carbonized fiber and graphitized fiber, and the carbon content obtained by elemental analysis is preferably 95% by mass or more, and more preferably 97% by mass or more.
The PAN-based carbon fiber can be produced, for example, by the following method.

<Precursor fiber>
A polyacrylonitrile fiber obtained by spinning a spinning solution obtained by polymerizing a monomer containing 95% by mass or more of acrylonitrile in a coagulation liquid, followed by washing, drying and stretching is used as a precursor fiber. The number of filaments of the precursor fiber is preferably 1000 or more, more preferably 12000 or more, and further preferably 24000 or more in terms of production efficiency.

<Flame resistance treatment>
The obtained precursor fiber is infusibilized in heated air at 200 to 300 ° C. for 10 to 100 minutes. In the infusibilization treatment, it is preferable to subject the precursor fiber to a drawing treatment within a range of a draw ratio of 0.90 to 1.20.

<Carbonization treatment>
Carbon fiber is obtained by carbonizing the infusible precursor fiber at 300 to 2000 ° C. In order to obtain a carbon fiber bundle having a dense internal structure with higher tensile strength, after low-temperature carbonization at 300 ° C. to 1000 ° C., through a two-stage carbonization step of high-temperature carbonization at 1000 to 2000 ° C., It is preferable to perform carbonization treatment. When a higher elastic modulus is required, the graphitization treatment may be further performed at a high temperature of 2000 to 3000 ° C.

<Surface treatment>
The carbon fiber bundle is subjected to a surface treatment in order to improve wettability with a sizing agent and a resin as a matrix. The surface treatment can be performed by any conventionally known method, but since the apparatus is simple and management in the process is easy, it is common to use electrolytic oxidation industrially.
The carbon fiber bundle of the present invention can be produced, for example, by subjecting the carbon fiber bundle thus obtained to sizing treatment using the method for producing a carbon fiber bundle described below.

  Another method of producing a carbon fiber bundle according to the present invention is to apply a sizing agent solution to a carbon fiber bundle composed of carbon fibers, and then heat-dry the solvent from the sizing agent solution, thereby sizing agent resin on the fiber surface. Is a method for producing a carbon fiber bundle, in which heat treatment is performed using an electromagnetic wave having a wavelength of 3 μm or more when fixing is carried out.

  As a result of intensive studies, the present inventor can reduce the adhesion unevenness inside and outside the fiber bundle by drying the sizing agent solution using electromagnetic waves, particularly infrared rays, and in particular, the adhesion unevenness of the sizing agent inside and outside the fiber bundle. It has been found that the sizing agent can be uniformly attached even when the number of filaments of the carbon fiber bundle that tends to be large is large.

  The heating method using electromagnetic waves is different from the hot air circulation method using a heating medium because it is direct heating, so it is uniform regardless of conditions such as the number of filaments of the fiber to be treated, the packing density of the running strand, and the process tension. The fiber can be heated. For this reason, drying can be performed at a uniform temperature between the outer surface and the inside of the fiber bundle, and a difference in drying speed between the inside and outside of the fiber bundle is unlikely to occur. As a result, uneven adhesion of the sizing agent due to diffusion of the emulsion solution during drying can be suppressed, and a difference in the amount of adhesion between inside and outside the fiber bundle can be suppressed.

  Also, drying by electromagnetic waves not only directly heats the sizing agent resin to be heated to a high temperature, but also heats the treated fiber itself and heats the inside of the fiber, so the temperature inside and outside the fiber bundle Unevenness is unlikely to occur. In particular, carbon fibers having a carbon content of 95% by mass or more have a high heat generation efficiency due to electromagnetic waves, and thus can provide a great effect.

  Furthermore, since it is a non-contact type drying method, unlike the contact type heating roller method, fluctuations in drying conditions due to stickiness of the resin adhering to the roller, process tension, and the like can be suppressed. Moreover, since the electromagnetic wave is immediately converted into thermal energy when absorbed by the substance, heating starts simultaneously with the irradiation of the electromagnetic wave, and the heating efficiency is high. For this reason, it is difficult to cause uneven adhesion due to bleeding of the emulsion from the fiber bundle during drying, and the sizing agent can be uniformly attached.

  On the other hand, when heated by the hot air circulation method and the heating roller method, which are conventional methods, the propagation of heat from the fiber bundle surface to the inside depends on the heat transfer. It will be heated. As a result, rapid drying occurs on the fiber bundle surface, and the sizing agent resin cannot sufficiently coat the fiber surface.

  The electromagnetic wave used in the present invention is an electromagnetic wave having a wavelength of 3 μm or more that can heat the sizing agent resin, and among them, infrared rays having a wavelength of 3 to 30 μm are preferable because the effect of heating the sizing agent resin is high.

  The sizing agent resin used in the sizing agent solution used in the present invention is not particularly limited. For example, epoxy resin, urethane resin, polyester resin, vinyl ester resin, polyamide resin, polyether resin, acrylic resin, polyolefin resin, polyimide resin And a modified product thereof, and a suitable sizing agent can be appropriately selected according to the matrix resin of the composite material. Moreover, this sizing agent resin can also be used in combination of 2 or more types. In addition, auxiliary components such as a dispersant and a surfactant may be added to the sizing agent in order to improve the handleability, scratch resistance, fluff resistance, and impregnation of the carbon fiber.

  As a solvent for the sizing agent used in the present invention, an ordinary solvent in which the sizing agent resin is soluble, for example, water, ethanol, acetone, methyl ethyl ketone, N, N-dimethylformamide, N, N-dimethylacetamide, N- Examples include methyl pyrrolidone, toluene and styrene. These solvents can be used alone or in combination of two or more. In particular, an aqueous solvent is preferable from the viewpoints of handleability and safety, and a sizing agent that is hardly soluble in the aqueous solvent is preferably added as an emulsion aqueous solution by appropriately adding a surfactant or the like. What is necessary is just to change suitably the sizing agent resin density | concentration of a sizing agent solution according to the adhesion amount of the target sizing agent, and 1.0-10 mass% is preferable.

  In the production method of the present invention, in order to further improve the adhesion uniformity, the sizing agent solution emulsifies the sizing agent resin by using 5 to 20% by mass of a nonionic surfactant based on the mass of the sizing agent resin. It is preferable to prepare an aqueous emulsion solution and impart it to the fiber bundle. Nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene styrenated phenyl ethers, polyethylene glycol aliphatic esters and the like, and anionic surfactants include alkylbenzenesulfonic acid ammonium salts, Examples thereof include polyoxyethylene styrenated phenyl ether sulfate ammonium salt.

  In the production method of the present invention, the method for applying the sizing agent solution to the carbon fiber is not particularly limited, and a roller sizing method, a roller dipping method, a spray method, and other known methods can be used. Among these, a roller dipping method that easily imparts a sizing agent solution uniformly is also preferably used for carbon fiber bundles having a large number of single fibers per bundle. The liquid temperature of the sizing agent solution is preferably in the range of 10 to 50 ° C. in order to suppress fluctuations in the sizing agent concentration due to solvent evaporation. Moreover, the adhesion amount of a sizing agent can also be adjusted by adjusting the amount of squeezing out the excess sizing agent after applying the sizing agent solution.

  The drying of the sizing agent solution can be performed at any temperature sufficient for the evaporation of the solvent. However, particularly when the sizing agent is used as an emulsion aqueous solution, it is a multi-stage treatment in which heat drying is performed in a temperature range of two or more stages. It is preferable.

  When heat drying is performed with the temperature range set in multiple stages, it is preferably heated at 80 to 120 ° C. for 1 to 10 minutes and then heated at 150 to 250 ° C. for 1 to 10 minutes. The temperature range of 80 to 120 ° C. is a cloud point temperature of a general surfactant. When the sizing agent is used as an aqueous emulsion, phase separation of water and resin occurs in the temperature range of 80 to 120 ° C. At this time, since the surfactant tries to form a network and diffuses the resin on the fiber surface, the sizing agent resin can be uniformly adhered to the fiber surface. On the other hand, the temperature range of 150 to 250 ° C. is a temperature at which the sizing agent resin is softened. By heating at the softening point of the sizing agent resin, the sizing agent resin is further diffused on the fiber to form a uniform resin film. Therefore, after heating at 80 to 120 ° C. for a certain period of time, further heating at 150 to 250 ° C. allows the sizing agent resin to adhere more uniformly to the fiber surface. In order to adhere more uniformly to the fiber surface, the process tension when performing heat drying is preferably 1 to 10 g per 1 tex of the fiber to be treated.

  From the viewpoint of production efficiency, the number of filaments of the carbon fiber bundle preferably used in the production method of the present invention is more preferably 12,000 or more, and further preferably 24,000 or more. The number of filaments per unit width is preferably 5000 / mm or less, more preferably 3000 / mm or less. If it exceeds 5000 / mm, the variation in sizing agent tends to increase.

In this way, the carbon fiber bundle of the present invention can be produced. Using the carbon fiber bundle of the present invention, a composite material can be obtained by a known means / method such as autoclave molding, press molding, resin transfer molding, filament winding molding, etc., in combination with a matrix resin.
Carbon fiber is usually used as a sheet-like reinforcing fiber material. Examples of the sheet-like material include those obtained by arranging fiber materials in a sheet shape in one direction, those obtained by forming a fiber material into a fabric such as a woven or knitted fabric and a nonwoven fabric, and multiaxial woven fabrics.

  As the matrix resin, a thermosetting resin or a thermoplastic resin is used. Specific examples of thermosetting matrix resins include epoxy resins, unsaturated polyester resins, phenol resins, vinyl ester resins, cyanate ester resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins and cyanate ester resins. And a prepolymerized resin, bismaleimide resin, polyimide resin and polyisoimide resin having acetylene terminal, and polyimide resin having nadic acid terminal. These can also be used as one type or a mixture of two or more types. Of these, epoxy resins and vinyl ester resins excellent in heat resistance, elastic modulus, and chemical resistance are particularly preferable. These thermosetting resins may contain commonly used colorants and various additives in addition to the curing agent and the curing accelerator.

  Examples of the thermoplastic resin include polypropylene, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, aromatic polyamide, aromatic polyester, aromatic polycarbonate, polyetherimide, polyarylene oxide, thermoplastic polyimide, polyamide , Polyamideimide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyacrylonitrile, polyaramid, polybenzimidazole and the like.

The content of the resin composition in the composite material is 10 to 90% by mass, preferably 20 to 60% by mass, and more preferably 25 to 45% by mass.
Such a carbon fiber composite material has excellent mechanical properties and small variations, and thus can be widely used for sports applications, leisure applications, general industrial applications, aerospace applications, automobile applications, and the like.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The physical properties of the fibers and composite materials in each of the examples and comparative examples were evaluated by the following methods.

<Strand tensile strength, elastic modulus>
The tensile strength and tensile modulus of the epoxy resin impregnated strand were measured according to JIS R-7608.

<Sizing agent adhesion amount>
The carbon fiber bundle 10g was taken out, acetone was used as a solvent, and the adhesion amount of the sizing agent was determined based on JIS R7604 A method (solvent extraction method).

<Evaluation of uniformity of sizing agent adhesion inside and outside the fiber bundle>
The carbon fiber was fixed on a carbon tape, and the light emission amount of the fluorescent material derived from the sizing agent was measured using an analytical color fluorescent electron microscope CLEM (manufactured by Topcon). The measurement was performed at 5 locations per sample in a 12 μm × 9 μm visual field, and the average value of the luminescent area measured by the image was used as the amount of sizing agent attached. The amount of sizing agent attached to the surface of the fiber bundle is the carbon fiber located on the outer surface of the carbon fiber bundle, and the amount of sizing agent attached to the inside of the fiber bundle is the carbon fiber inside the fiber bundle that is exposed by dividing the fiber bundle at the center. Each was used as a sample. A value obtained by dividing the adhesion amount of the sizing agent on the surface of the fiber bundle by the adhesion amount of the sizing agent inside the fiber bundle was used as an index indicating the adhesion uniformity of the sizing agent.

<Carbon content>
Using an elemental analyzer manufactured by FISONS Instruments, elemental analysis was performed at a combustion tube of 1000 ° C. and a reduction tube of 650 ° C., and the carbon content was calculated.

<Preparation method of prepreg>
The obtained carbon fiber bundles were aligned and aligned in one direction to obtain a carbon fiber sheet (weight per unit area 190 g / m ² ). Liquid bisphenol-type epoxy resin “jER 828” (manufactured by Mitsubishi Chemical Corporation), multifunctional epoxy resin “jER 604” (manufactured by Mitsubishi Chemical Corporation), and 4,4′-diaminodiphenyl sulfone which is an aromatic amine curing agent (Wakayama) Seiko Co., Ltd.) was kneaded to prepare an epoxy resin composition for prepreg. The obtained epoxy resin composition was apply | coated on the release paper using the knife coater, and the resin film was created. Next, two resin films are stacked on the carbon fiber sheet from both sides of the carbon fiber, and the resin composition is impregnated by heating and pressing at 90 degrees to prepare a unidirectional prepreg (curing temperature 180 ° C., resin content 33%). did.

<0 ° tensile test>
The produced unidirectional prepreg was laminated so that the thickness after molding was 1 mm, and then cured at 180 ° C. to obtain a composite having a carbon fiber volume content of 60%. This was subjected to a tensile test in the direction of 0 ° with respect to the fiber at room temperature in accordance with ASTM D 303, and 0 ° tensile strength (0TS) and 0 ° tensile elastic modulus (0TM) were measured.

<In-plane shear stress (IPSS)>
After laminating eight produced unidirectional prepregs so that the fiber direction is [+ 45 ° / −45 ° / −45 ° / + 45 ° / + 45 ° / −45 ° / −45 ° / + 45 °] The composite was cured at 180 ° C. to obtain a carbon fiber volume content of 60%. This was measured for in-plane shear stress (IPSS) according to a ± 45 ° direction tensile method described in JIS K 7079.

[Example 1]
PAN fiber (single fiber fineness 0.7 dtex, filament number 24000), which is a precursor fiber, is flame-resistant at 250 ° C. in air until the fiber has a specific gravity of 1.35, and then a maximum temperature of 650 in a nitrogen gas atmosphere. Low temperature carbonization was performed at ° C. Thereafter, carbon fibers produced by high-temperature carbonization at 1500 ° C. in a nitrogen atmosphere are subjected to surface treatment by electrolytic oxidation at an electrolytic solution temperature of 40 ° C. and an electric quantity of 20 C / g using an aqueous solution of 10.0% by mass ammonium sulfate. An unsized carbon fiber bundle (tensile strength 5880 MPa, tensile elastic modulus 310 MPa, carbon content 98 mass%, filament number 24000, total fineness 800 tex, fiber bundle width 8 mm) was obtained.
The obtained unsized carbon fiber bundle is dipped in a sizing agent solution having a sizing agent resin concentration of 4% by mass, and then dried with a far-infrared heater with a reflector having a maximum energy intensity at a wavelength of 4 μm as a heating device using electromagnetic waves. Using two machines, while applying a tension of 2.5 g / tex to the fiber to be treated, heating was performed at a drying temperature of 100 ° C. for 5 minutes as the first drying, followed by a drying temperature of 200 ° C. as the second drying. Heat drying for 5 minutes and sizing treatment was performed. As the sizing agent solution, an aqueous emulsion solution in which the sizing agent resin was emulsified using 10% by mass of a nonionic surfactant based on the mass of the sizing agent resin was used. A bisphenol A epoxy resin was used as the sizing agent resin, and polyoxyethylene alkyl ether was used as the nonionic surfactant.
The carbon fiber bundle thus obtained has a sizing agent adhesion amount of 1.0% by mass, a ratio of the sizing agent adhesion amount on the outer surface of the carbon fiber bundle to the adhesion amount inside the carbon fiber bundle (surface adhesion amount / internal The carbon fiber bundle had a high adhesion uniformity of the sizing agent having an adhesion amount of 1.0. Table 1 shows the physical properties of this carbon fiber bundle and the composite material produced using this carbon fiber bundle.
By the method for producing a carbon fiber bundle of the present invention, the carbon fiber of the present invention having high adhesion uniformity inside and outside the fiber bundle has been obtained. The carbon fiber bundle of the present invention exhibited excellent composite material properties.

[Examples 2 and 3]
A carbon fiber bundle was obtained as a sizing solution in the same manner as in Example 1 except that the concentration of the sizing agent solution was changed and the adhesion amount of the sizing agent was changed. Table 1 shows the physical properties of this carbon fiber bundle and the composite material produced using this carbon fiber bundle.
By using the method of the present invention, the carbon fiber of the present invention having high adhesion uniformity inside and outside the fiber bundle can be obtained regardless of the amount of sizing agent deposited. Further, the physical properties of the composite material produced using this carbon fiber bundle were all excellent.

[Comparative Example 1]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the drying method of the sizing agent was changed from heating using electromagnetic waves to a hot air circulating furnace at 150 ° C. Table 1 shows the physical properties of this carbon fiber bundle and the composite material produced using this carbon fiber bundle.
The amount of sizing applied was the same as in Example 1, but it was dried by the hot air circulation method, which is a normal drying method. The adhesion uniformity of the sizing agent was 2.2, which was high on the outer surface of the fiber bundle. . Also, sufficient composite material properties could not be obtained.

[Comparative Example 2]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the drying method of the sizing agent was changed from heating using electromagnetic waves to a heating roller of 150 ° C. Table 1 shows the physical properties of this carbon fiber bundle and the composite material produced using this carbon fiber bundle.
In the comparative example 2, it dried with the heating roller which is a normal drying method, the adhesion uniformity of the sizing agent was 0.4, and the adhesion amount of the fiber bundle outer surface was low compared with the inside of a fiber. Also, sufficient composite material properties could not be obtained.

[ Comparative Examples 3 to 5 ]
A carbon fiber bundle was obtained in the same manner as in Example 1 except that the drying temperature of the sizing agent was changed to the temperature shown in Table 1. Table 1 shows the physical properties of this carbon fiber bundle and the composite material produced using this carbon fiber bundle.
In Comparative Example 3 , the first drying temperature was 70 ° C., which was lower than that in Example 1. Although the adhesion uniformity was slightly reduced as compared with Example 1, sufficient composite material properties were obtained.
In Comparative Example 4 , the second drying temperature was 100 ° C., which was lower than that in Example 1. Although the adhesion uniformity was slightly reduced as compared with Example 1, sufficient composite material properties were obtained.
In Comparative Example 5 , both the first drying temperature and the second drying temperature were 150 ° C., which was the same as Comparative Example 1. Since drying was performed by the far-infrared method, compared with Comparative Example 1, the adhesion uniformity was as good as 1.2, and sufficient composite material properties were obtained.

[Examples 4 and 5 ]
A sizing treatment was performed in the same manner as in Example 1 except that the number of filaments in the fiber bundle was changed from 24,000 in Example 1 to the number shown in Table 2 to obtain a carbon fiber bundle. Table 2 shows the physical properties of these carbon fiber bundles and composite materials produced using the carbon fiber bundles.
Example 4 produced a carbon fiber bundle by reducing the number of filaments of the fiber to be treated as compared with Example 1. Adhesion uniformity comparable to that of Example 1 was obtained, and the physical properties of the composite material were sufficient.
Example 5 produced a carbon fiber bundle by increasing the number of filaments of the fiber to be treated as compared with Example 1. When the method for producing a carbon fiber bundle of the present invention was used, carbon fibers excellent in adhesion uniformity were obtained even when the number of filaments was increased. The properties of the composite material of the obtained carbon fiber were sufficient.

[Comparative Examples 6 and 7 ]
A sizing treatment was performed in the same manner as in Comparative Example 1 except that the number of filaments in the fiber bundle was changed from 24000 to the number shown in Table 2 to obtain a carbon fiber bundle. Table 2 shows the physical properties of these carbon fiber bundles and composite materials produced using the carbon fiber bundles.
Comparative Example 6 produced a carbon fiber bundle by reducing the number of filaments of the fiber to be treated as compared with Comparative Example 1. Although the adhesion uniformity was slightly improved as compared with Comparative Example 1, it was insufficient as compared with Examples, and sufficient physical properties of composite materials could not be obtained.
Comparative Example 7 produced a carbon fiber bundle by increasing the number of filaments of the fiber to be treated as compared with Comparative Example 1. Since the number of filaments increased, the adhesion uniformity further decreased as compared with Comparative Example 1.

[Comparative Example 8 ]
A sizing treatment was performed in the same manner as in Comparative Example 2 except that the number of filaments in the fiber bundle was changed from 24000 to 48000 to obtain a carbon fiber bundle. Table 2 shows the physical properties of these carbon fiber bundles and composite materials produced using the carbon fiber bundles.
Comparative Example 8 produced a carbon fiber bundle by increasing the number of filaments of the fiber to be treated as compared with Comparative Example 2. Since the number of filaments increased, the adhesion uniformity was further reduced as compared with Comparative Example 2.

Claims (6)

  A carbon fiber bundle composed of carbon fibers, wherein the ratio of the sizing agent adhesion amount on the surface of the fiber bundle to the sizing agent adhesion amount inside the fiber bundle is 0.5 to 1.1. bundle. After applying a sizing agent solution, which is an emulsion aqueous solution in which a sizing agent resin is emulsified by adding a surfactant to a carbon fiber bundle composed of carbon fibers, at least using electromagnetic waves having a wavelength of 3 μm or more, A method for producing a carbon fiber bundle, characterized by heating and drying in a multi-stage treatment in which heating is performed at a temperature range of 80 to 120 ° C for 1 to 10 minutes and further heating at a temperature range of 150 to 250 ° C for 1 to 10 minutes .   The method for producing a carbon fiber bundle according to claim 2, wherein the electromagnetic wave is an infrared ray having a wavelength of 3 to 30 µm.   The method for producing a carbon fiber bundle according to claim 2 or 3, wherein the sizing agent solution is an emulsion aqueous solution containing 5 to 20% by mass of a nonionic surfactant with respect to the mass of the sizing agent resin.   The method for producing a carbon fiber bundle according to any one of claims 2 to 4, wherein the process tension during the heat drying is 1 to 10 g per 1 tex of the fiber to be treated.   The method for producing a carbon fiber bundle according to any one of claims 2 to 5, wherein the number of filaments per unit width of the carbon fiber bundle is 5000 or less.