Sizing agent-coated carbon fiber bundle and method for producing the same

Abstract

[Problem] To provide a sizing-agent-coated carbon fiber bundle in which, even when the sizing-agent-coated carbon fiber bundle has superior handling properties, the sizing agent on the sizing-agent-coated carbon fiber bundle exhibits excellent solubility in water and the adhesion amount of remaining sizing agent is reduced. [Solution] A sizing-agent-coated carbon fiber bundle obtained by applying polyethylene glycol and / or a surfactant to a carbon fiber bundle as a sizing agent, wherein all of the following conditions (i)-(iii) are satisfied. (i) The adhesion amount of the sizing agent is 0.15-0.80 parts by mass (inclusive) per 100 mass parts of the sizing-agent-coated carbon fiber bundle 100. (ii) The dry F-F friction coefficient is 0.39 or less. (iii) The adhesion amount of the sizing agent after washing for 50 seconds under the conditions disclosed in the specification is 0.12 parts by mass or less per 100 parts by mass of the sizing-agent-coated carbon fiber bundle 100.

Description

[Technical Field]

[0001] The present invention relates to a sizing-agent-coated carbon fiber bundle coated with a sizing agent that exhibits bundling properties and frictional properties suitable for the handling of the sizing-agent-coated carbon fiber bundle and exhibits good elution into water in an aqueous process represented by a wet powder impregnation method, and to a method for producing the sizing-agent-coated carbon fiber bundle. [Background technology]

[0002] Carbon fiber, being lightweight yet possessing excellent strength and elastic modulus, is used in a wide range of applications, including aircraft, spacecraft, automobile, ship, civil engineering, and sports equipment, as composite materials in combination with various matrix resins. A typical example of a carbon fiber composite is a molded product obtained by press-molding (a molding method in which preforms obtained by laminating prepregs are degassed and shaped under pressure). Prepregs are typically produced by impregnating a carbon fiber substrate, consisting of continuous carbon fiber bundles aligned in one direction, with resin. While composite materials using discontinuous carbon fibers (chopped, web, etc.) have been proposed, which offer excellent conformability to complex shapes and allow for rapid molding, prepregs offer superior practical performance as structural materials in terms of mechanical properties such as specific strength and specific rigidity, as well as the stability of their properties.

[0003] In recent years, carbon fiber composite materials have come to require molding materials with excellent moldability, ease of handling, and mechanical properties of the resulting molded products. This has led to the need for higher economic efficiency and productivity in the industrial sector. One answer to this demand is the development of prepregs using thermoplastic resins as the matrix resin. One example of a manufacturing method involves passing a carbon fiber tape containing powdered thermoplastic matrix resin through a thermoplastic resin slurry in which the powdered thermoplastic matrix resin is dispersed with a surfactant, and then impregnating the carbon fiber tape with the thermoplastic resin using heat and pressure.

[0004] To make the most of the excellent properties of carbon fibers after composite processing, it is important to ensure excellent handleability during carbon fiber processing and reduce winding of fuzz and breakage due to winding. Carbon fiber bundles that are not coated with a sizing agent lack bundling ability and generate a large amount of fuzz, which can accumulate during the prepreg production process and deteriorate the prepreg quality. Therefore, to improve the handleability of carbon fiber bundles, a method is usually used in which a sizing agent is applied to the carbon fiber bundle and an abrasion-resistant coating film is applied to the carbon fiber surface (see Patent Documents 1 and 2).

[0005] A method has also been proposed in which continuous fibers of carbon fiber bundles are cut and dispersed into single fibers for use in papermaking. The process of making paper from carbon fiber bundles is often an aqueous process. To utilize the excellent properties of carbon fiber bundles, it is important to achieve both bundling properties to maintain the shape of the carbon fiber bundles when handling them in the chopping process prior to the papermaking process, and excellent openability to quickly disperse them into single fibers when introduced into an aqueous medium in the papermaking process and suppress re-agglomeration. Therefore, a sizing agent that combines bundling properties and water dispersibility is applied. Generally, to improve the handleability of carbon fiber bundles, epoxy resins or the like are often attached as sizing agents (sizing agents). However, the sizing agents themselves have strong interactions or too strong interactions with the carbon fiber surfaces, which tend to result in poor openability in water when applied to aqueous processes. For this reason, for example, Patent Documents 3 to 5 propose methods of using surfactants or water-soluble polymers as sizing agents for carbon fiber bundles to improve handleability when cut into chopped carbon fibers and improve openability in water.

[0006] The excellent properties of carbon composite materials are significantly influenced by the properties of the interface between the carbon fiber and the resin. Therefore, the properties of the sizing agent present at the interface between the carbon fiber and the resin are important. For example, Patent Document 6 proposes a method in which a surfactant is applied to a carbon fiber bundle and then a sizing agent is applied, thereby uniformly applying the sizing agent and obtaining a carbon fiber composite material with excellent mechanical properties. Patent Document 7 also proposes a method in which a surfactant is applied to a spun yarn of flame-resistant fiber to increase its affinity with the powdered matrix resin and improve impregnation during assembly production. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 3,957,716 [Patent Document 2] Japanese Patent Application Publication No. 57-171767 [Patent Document 3] International Publication No. WO2006 / 019139 Pamphlet [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-54269 [Patent Document 5] Patent No. 6571892 [Patent Document 6] Japanese Patent Application Publication No. 2017-137603 [Patent Document 7] Japanese Patent Application Publication No. 59-144679 Summary of the Invention [Problem to be solved by the invention]

[0008] On the other hand, when handling and interfacial properties are controlled by applying a sizing agent to carbon fiber bundles as described above, when combined with a thermoplastic matrix resin that requires high molding temperatures, depending on the components of the sizing agent, the heat resistance of the matrix resin or the adhesion between the carbon fiber and the matrix resin may be reduced, which may prevent CFRP from achieving its full performance.

[0009] That is, although studies have been conducted on suppressing the generation of fuzz from carbon fiber bundles by applying a sizing agent and on improving processability in aqueous processes, there has been no idea of ​​removing the sizing agent from the carbon fiber from the perspective of minimizing the risk of the above-mentioned effects on the thermoplastic matrix resin in advanced processing, while applying a sizing agent to achieve both suppression of fuzz generation due to breakage of single fibers in the carbon fiber bundle and good openability in water, with the aim of imparting high mechanical properties, typified by the strand strength, of the carbon fiber bundle to the composite material in carbon fiber processing in an aqueous process.

[0010] The present invention has been made in view of the above, and has an object to provide a sizing-agent-coated carbon fiber bundle that is particularly suitable for combination with a thermoplastic matrix resin, even when the sizing-agent-coated carbon fiber bundle is easy to handle, because the sizing agent on the sizing-agent-coated carbon fiber bundle exhibits good solubility in water and the amount of remaining sizing agent attached is reduced. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the present invention provides a sizing-agent-coated carbon fiber bundle in which polyethylene glycol and / or a surfactant is applied to a carbon fiber bundle as a sizing agent, and the sizing-agent-coated carbon fiber bundle satisfies all of the following (i) to (iii): (i) The amount of the sizing agent attached is 0.15 to 0.80 parts by mass relative to 100 parts by mass of the sizing-agent-coated carbon fiber bundle. (ii) The dry FF friction coefficient is 0.39 or less. (iii) The amount of sizing agent attached after washing with water for 50 seconds under the conditions described in the specification is 0.12 parts by mass or less.

[0012] Furthermore, the method for producing a sizing-agent-coated carbon fiber bundle of the present invention is the method for producing the above-mentioned sizing-agent-coated carbon fiber bundle, characterized in that it includes a drying step of drying the sizing-agent-coated carbon fiber bundle at 120 to 260°C after a step of applying a sizing agent containing polyethylene glycol and / or a surfactant to the carbon fiber bundle. [Effects of the Invention]

[0013] According to the present invention, even when the sizing-agent-coated carbon fiber bundle is easy to handle, the sizing agent on the sizing-agent-coated carbon fiber bundle exhibits good solubility in water, and the amount of sizing agent remaining after processing is reduced, so that a sizing-agent-coated carbon fiber bundle that is particularly suitable for combination with a thermoplastic matrix resin can be obtained. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing the evaluation method for 50-second water washing. [Figure 2] FIG. 2 is a diagram showing the evaluation method for 25-second water washing. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described.

[0016] The sizing-agent-coated carbon fiber bundle of the present invention is a sizing-agent-coated carbon fiber bundle obtained by coating a carbon fiber bundle with polyethylene glycol and / or a surfactant as a sizing agent, and is a sizing-agent-coated carbon fiber bundle that satisfies all of the following (i) to (iii): (i) The amount of the sizing agent attached is 0.15 parts by mass or more and 0.80 parts by mass or less with respect to 100 parts by mass of the sizing-agent-coated carbon fiber bundle. (ii) The dry FF friction coefficient is 0.39 or less. (iii) After washing with water for 50 seconds under the conditions described in the specification, the amount of sizing agent attached is 0.12 parts by mass or less per 100 parts by mass of the sizing-agent-coated carbon fiber bundle.

[0017] Through investigations by the present inventors, it was found that when a sizing agent that improves handleability after application to a carbon fiber bundle is used, the solubility of the sizing agent in water on the sizing-agent-coated carbon fiber bundle decreases, the sizing agent is likely to remain, and the mechanical properties are likely to decrease during prepreg production. To address this issue, the present inventors have found that even when a compound that is easy to handle is used as the sizing agent, it is possible to achieve both good handleability of the sizing-agent-coated carbon fiber bundle and good solubility of the sizing agent in water by using a sizing agent containing polyethylene glycol and / or a surfactant to control the sizing agent adhesion amount and friction coefficient and thereby control the sizing agent adhesion amount after water washing.

[0018] The sizing agent constituting the present invention must contain polyethylene glycol and / or a surfactant, and the sizing agent formed by applying the sizing agent to a carbon fiber bundle must satisfy specific conditions. The surfactant referred to here is an anionic surfactant, a nonionic surfactant, or an amphoteric surfactant.

[0019] Anionic surfactants are surfactants with anionic hydrophilic groups. When carbon fiber bundles coated with anionic surfactants are placed in water, the elution of the sizing agent is improved. As a result, the amount of sizing agent remaining in the carbon fiber bundles is reduced. Although the mechanism is unclear, it is thought that anionic surfactants ionize in water, and the anionic hydrophilic groups repel the carbon fiber surface, resulting in excellent elution.

[0020] Examples of the anionic surfactant include carboxylates, sulfonates, carboxylate and sulfonate salts, sulfates, and phosphates.

[0021] Specific examples of carboxylates include soap, polyoxyethylene alkyl ether carboxylates, and alkyl hydroxy ether carboxylates. Specific examples of sulfonates include alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkanoyl methyl taurides, and dialkyl sulfosuccinate salts. Specific examples of carboxylates and sulfonates include alkyl sulfosuccinate di-salts and polyoxyethylene alkyl ether sulfosuccinate di-salts. Specific examples of sulfates include higher alkyl sulfates, polyoxyethylene alkyl ether sulfates, sulfated oils, sulfated fatty acid esters, and sulfated olefins. Specific examples of phosphates include higher alkyl phosphates, polyoxyethylene alkyl ether phosphates, and dithiophosphate salts. The cations constituting the salts include alkali metal cations such as sodium and alkaline earth metal cations such as calcium, with alkali metal cations being preferred for increased water solubility. Furthermore, ammonium salts may be used instead of metal salts.

[0022] A nonionic surfactant is a surfactant with a hydrophilic group that does not ionize. Carbon fiber bundles coated with polyethylene glycol and / or a nonionic surfactant exhibit improved elution of the sizing agent when placed in water. As a result, the amount of sizing agent remaining in the carbon fiber bundle is reduced. Although the mechanism is unclear, it is thought that the hydrophilic group of polyethylene glycol and / or a nonionic surfactant easily interacts with water, resulting in excellent elution.

[0023] Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene dodecyl ether, polyoxyethylene oleyl ether, and polyoxyethylene stearyl ether; polyoxyethylene polyoxypropylene glycol; polyoxyethylene alkylphenyl ether; sorbitan fatty acid esters such as sorbitan monooleate, sorbitan monostearate, and sorbitan trioleate; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; and polyoxyethylene glyceryl monooleate. Examples include ethylene glycerin fatty acid esters, polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbitol tetraoleate, and polyethylene glycol fatty acid esters such as PEG monocaprylate, PEG monoheptylate, PEG monopelargonate, PEG monopentadecylate, PEG monopalmitate, PEG monolinoleate, PEG dilaurate, PEG monooleate, PEG dioleate, PEG monostearate, PEG distearate, PEG dilaurate, and PEG dilinoleate. These nonionic surfactants can be used alone or in combination with PEG. Note that "PEG" is an abbreviation for "polyethylene glycol."

[0024] When polyethylene glycol and a nonionic surfactant are combined, the mixing ratio of polyethylene glycol to nonionic surfactant is preferably 50 parts by mass or more per 100 parts by mass of the total mixture. By using 50 parts by mass or more of polyethylene glycol, the hydrophilicity of polyethylene glycol improves elution, making it easier for the sizing agent to elute during washing with water, and reducing the amount of sizing agent remaining on the carbon fiber bundle. The mixing ratio of polyethylene glycol is more preferably 70 parts by mass or more per 100 parts by mass.

[0025] An amphoteric surfactant is a surfactant that has both an anionic and a cationic moiety in the same molecule. When carbon fiber bundles coated with an amphoteric surfactant are placed in water, the elution of the sizing agent is improved. As a result, the amount of sizing agent remaining in the carbon fiber bundle is reduced. Although the mechanism is unclear, it is thought that the hydrophilic group portion of the amphoteric surfactant interacts easily with water over a wide pH range, unlike other nonionic, anionic, and cationic surfactants, resulting in excellent elution.

[0026] Examples of amphoteric surfactants include amino acid surfactants, betaine surfactants, sulfobetaine surfactants, and amine oxide surfactants.

[0027] Specific examples of amphoteric surfactants include betaine surfactants such as fatty acid amidopropyl betaine, myristyl amidopropyl betaine, lauric acid amidopropyl betaine, cocamidopropyl betaine, fatty acid amidopropyl dimethylaminoacetic acid betaine, lauric acid amidopropyl dimethylaminoacetic acid betaine, stearyl dimethylaminoacetic acid betaine, lauryl dimethylaminoacetic acid betaine, lauryl dihydroxyethyl betaine, and 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine; alkyl hydroxy sulfobetaine, cocamidopropyl hydroxy sulfobetaine, and lauric acid amidopropyl betaine; sulfobetaine surfactants such as propyl hydroxysulfobetaine; amine oxide surfactants such as fatty acid amidopropyl dimethylamine oxide, lauric acid amidopropyl dimethylamine oxide, lauryl dimethylamine oxide, coconut oil alkyl dimethylamine oxide, dodecyl dimethylamine oxide, decyl dimethylamine oxide, and tetradecyl dimethylamine oxide; and amino acid surfactants such as alkyl carboxymethyl hydroxyethyl imidazolium betaine, lauryl dimethyl aminoacetic acid betaine, alkyl diaminoethyl glycine hydrochloride, and sodium lauryl aminodipropionate.

[0028] Whether a sizing-coated carbon fiber bundle contains polyethylene glycol and / or surfactants can be determined by extracting the sizing agent from the sizing-coated carbon fiber bundle with water and evaluating it. One method combines structural evaluation from the IR spectrum obtained by infrared spectroscopy after freeze-drying the water-extracted sizing agent with proton NMR and mass spectrometry analysis of the freeze-dried product.

[0029] The amount of sizing agent attached to the sizing-agent-coated carbon fiber bundle constituting the present invention must be 0.15 to 0.80 parts by mass relative to 100 parts by mass of the sizing-agent-coated carbon fiber bundle.

[0030] By setting the amount of sizing agent to 0.15 parts by mass or more, the handleability of the sizing-coated carbon fiber bundle can be improved, the generation of fluff during production and processing can be suppressed, and the quality of the carbon fiber bundle, such as smoothness, can be improved. The amount of sizing agent is preferably 0.25 parts by mass or more, and more preferably 0.30 parts by mass or more. On the other hand, by setting the amount of sizing agent to 0.80 parts by mass or less, it is possible to reduce the remaining amount in a short period of time, thereby reducing the impact on the mechanical properties of the composite material. The amount of sizing agent is preferably 0.60 parts by mass or less, and more preferably 0.45 parts by mass or less.

[0031] The sizing-agent-coated carbon fiber bundle of the present invention must have a dry FF friction coefficient of 0.39 or less. If the coefficient is 0.39 or less, the frictional force between the single fibers in the carbon fiber bundle is reduced, thereby reducing the amount of fluff generated by friction when the carbon fiber bundle is unwound from a bobbin and the amount of fluff generated by friction within the bundle when it comes into contact with a metal bar. A coefficient of 0.36 or less is more preferable, and 0.30 or less is even more preferable. Furthermore, a coefficient of 0.15 or more is preferable. If the coefficient is less than 0.15, force is not easily applied between the single fibers, and the bundling ability tends to decrease. The dry FF friction coefficient can be controlled by the roughness of the carbon fiber surface, the type and amount of anionic surfactant contained in the sizing agent, or more simply, the drying temperature after application of the sizing agent. It can also be controlled by the amount of sizing agent attached, etc. The procedure for evaluating the dry FF friction coefficient specified in the present invention will be explained in the examples.

[0032] <How to calculate the amount of sizing agent attached after rinsing with water for 50 seconds> The sizing-coated carbon fiber bundle of the present invention must have a sizing agent adhesion amount of 0.12 parts by mass or less after being washed with water for 50 seconds. If the amount of remaining sizing agent is reduced by extending the water washing time, the contribution of the surface functional groups of the carbon fiber to the physical properties of the matrix resin increases, which is preferable, thereby improving the mechanical properties. At 0.12 parts by mass or less, the effect of the sizing agent on the matrix resin is reduced, and the contribution of the surface functional groups of the carbon fiber to the physical properties of the matrix resin increases, improving the mechanical properties. 0.08 parts by mass or less is preferred, and 0.06 parts by mass or less is even more preferred.

[0033] Here, the method of rinsing a sizing-agent-coated carbon fiber bundle for 50 seconds as specified in the present invention can be carried out by the following procedure. The sizing-agent-coated carbon fiber bundle is introduced into water via a roller, and the sizing agent is dissolved into the water. This rinsing procedure is shown in Figure 1. The sizing-agent-coated carbon fiber bundle can be washed by the following procedure. The sizing-agent-coated carbon fiber bundle 1a placed in the unwinding process 11 is passed through a pre-rinsing tank free roller 15, a pre-rinsing tank free roller 16, and a post-rinsing tank free roller 17 in the water rinsing process 12, and then passed through water 1d in the water rinsing tank 18 via a pre-rinsing tank free roller 19, a pre-rinsing tank free roller 20, and a post-rinsing tank free roller 21, and then passed through water 1e in the water rinsing tank 22, and then continuously passed through a drying process 13 to dry the carbon fiber bundle, and then wound up in a winding process 14. The water temperature was 25°C, the unwinding tension from the creel was 800 g, the process speed was 2.4 m / min, the diameter of the free roller in the water washing tank was 150 mm, and the contact angle between the sizing-coated carbon fiber bundle and the free roller in the water washing tank was π rad. The liquid level was adjusted so that the time spent underwater in one water washing tank was 25 seconds, for a total of 50 seconds in the two water washing tanks. The drying process was non-contact, and the washed, sizing-coated carbon fiber bundle 1b was dried at a drying temperature of 150°C for 1 minute to obtain the washed and dried sizing-coated carbon fiber bundle 1c. The sizing-coated carbon fiber bundle 1c was then measured for adhesion weight to determine the adhesion weight.

[0034] <How to calculate the amount of sizing agent attached after rinsing with water for 25 seconds> The sizing agent-coated carbon fiber bundle of the present invention preferably has a sizing agent adhesion amount of 0.12 parts by mass or less after rinsing with water for 25 seconds. At 0.12 parts by mass or less, the effect of the sizing agent on the matrix resin is reduced, and the contribution of the surface functional groups of the carbon fiber to the physical properties of the matrix resin increases, improving the mechanical properties. 0.08% by mass or less is even more preferable.

[0035] The 25-second water washing method for a sizing-coated carbon fiber bundle, as specified in the present invention, can be carried out by the following procedure. The sizing-coated carbon fiber bundle is introduced into water via rollers, and the sizing agent is dissolved into the water. This water washing procedure is shown in Figure 2. The sizing-coated carbon fiber bundle 1a placed in the unwinding process 11 is passed through water 1d in the water washing tank 18 via free rollers 15 before the water washing tank, free rollers 16 in the water washing tank, and free rollers 17 after the water washing tank in the water washing process 12. It then passes continuously through the drying process 13 to dry the water and is wound up in the winding process 14. The water temperature is 25°C, the unwinding tension from the creel is 800 g, the process speed is 2.4 m / min, the diameter of the free roller in the water washing tank is 150 mm, and the contact angle between the sizing-coated carbon fiber bundle and the free roller in the water washing tank is π rad. The liquid level is adjusted so that the time of passage through water is 25 seconds. The drying process is a non-contact drying process, in which the sizing agent-coated carbon fiber bundle 1b after washing with water is dried at a drying temperature of 150°C for 1 minute to obtain the sizing agent-coated carbon fiber bundle 1c after washing with water and drying. The amount of sizing agent attached to this sizing agent-coated carbon fiber bundle 1c after washing with water and drying is measured to obtain the amount of sizing agent attached.

[0036] The sizing-coated carbon fiber bundle constituting the present invention preferably has a wet FM friction coefficient of 0.28 or less. In the aqueous thermoplastic matrix resin impregnation process in which a sizing-coated carbon fiber bundle is impregnated with a thermoplastic matrix resin in an aqueous solvent, there is considerable friction with guide bars and rollers not only in the air but also in the water, which can cause fuzzing. A coefficient of 0.28 or less is preferable because it reduces the frictional force generated between the stainless steel SUS304 and the fiber, thereby reducing fuzzing due to friction. A coefficient of 0.27 or less is preferred, and 0.25 or less is even more preferred. In the present invention, stainless steel SUS304 with a surface roughness of 0.8 to 1 S is used to evaluate the friction coefficient. The friction coefficient between the fiber and stainless steel SUS304 can be controlled by the roughness of the carbon fiber surface, the type and amount of anionic surfactant contained in the sizing agent, or, more simply, the drying temperature after application of the sizing agent. It can also be controlled by other factors such as the amount of sizing agent applied. The procedure for evaluating the friction coefficient between the fiber and stainless steel SUS304 specified in the present invention will be explained in the Examples.

[0037] In the sizing agent constituting the present invention, the weight-average molecular weight Mw of each of the anionic surfactant, polyethylene glycol, nonionic surfactant, and amphoteric surfactant is preferably 150 or more and 5000 or less. The weight-average molecular weight Mw is measured by gel permeation chromatography (hereinafter abbreviated as GPC) using polyethylene glycol as a standard substance. The larger the Mw, the higher the viscosity, and therefore the slower the rate of elution from the carbon fiber surface.

[0038] Setting the Mw to 5,000 or less reduces the viscosity, which is an index of the mobility of the anionic surfactant, polyethylene glycol, nonionic surfactant, or amphoteric surfactant, and reduces the amount of entanglement of molecular chains when the surfactant dissolves in water, thereby improving the dissolution of the anionic surfactant, polyethylene glycol, nonionic surfactant, or amphoteric surfactant into water. The Mw is more preferably 600 or less, and even more preferably 500 or less. On the other hand, from the viewpoint of application, a higher Mw can suppress volatilization during application of the sizing agent. The lower limit of Mw is preferably 150 or more, and even more preferably 200 or more. The weight-average molecular weight Mw of the anionic surfactant, polyethylene glycol, nonionic surfactant, or amphoteric surfactant applied to a sizing-agent-coated carbon fiber bundle can be confirmed by extracting the sizing agent from the sizing-agent-coated carbon fiber bundle with water, evaluating it with GPC, and identifying the metal elements using elemental analysis such as XPS.

[0039] In the sizing agent constituting the present invention, it is preferred that the total amount of surfactants is 70 parts by mass or more relative to 100 parts by mass of the total amount of the sizing agent, and that the amount of anionic surfactants, polyethylene glycol, nonionic surfactants and / or amphoteric surfactants is 50 parts by mass or more relative to the total amount of surfactants.

[0040] By making the total amount of surfactants 70 parts by mass or more, the hydrophilic groups in the surfactants improve elution, making it easier for the sizing agent to elute during water washing, and the amount of sizing agent remaining on the carbon fiber bundle can be reduced. 85 parts by mass or more is preferred, and 95 parts by mass or more is even more preferred. Furthermore, by making the amount of polyethylene glycol and / or nonionic surfactant 50 parts by mass or more of the total amount of surfactants, the hydrophilic group portions of the polyethylene glycol and / or nonionic surfactant easily interact with water, making it easier for the sizing agent to elute during water washing, and the amount of sizing agent remaining on the carbon fiber bundle can be reduced. In the sizing agent of the present invention, the lipophilic-hydrophilic balance (HLB) of the nonionic surfactant is preferably 15 to 20, or 12 to less than 15, and the ratio of hydroxyl groups at the molecular chain terminals is preferably 50% or more. The HLB specified in the present invention is a value calculated from the molecular structure based on Griffin's method described in "New Introduction to Surfactants," p. 128 (1992). By adjusting the HLB of the nonionic surfactant to 15 to 20, the hydrophilicity of the nonionic surfactant is improved, making the sizing agent more easily eluted during water washing, and reducing the amount of sizing agent remaining on the carbon fiber bundle. The HLB is preferably 16 or more. Furthermore, even if the HLB is 12 to less than 15, by adjusting the ratio of hydroxyl groups at the molecular chain terminals to 50% or more, the hydrophilicity of the terminals improves the elution of the nonionic surfactant into water, making the elution of the sizing agent more easily during water washing, and reducing the amount of sizing agent remaining on the carbon fiber bundle.

[0041] In the sizing agent constituting the present invention, the weight-average molecular weight Mw of the polyethylene glycol and / or nonionic surfactant is preferably 300 or more and 5000 or less. The weight-average molecular weight Mw is measured by gel permeation chromatography (hereinafter abbreviated as GPC) using polyethylene glycol as a standard substance. The larger the Mw, the higher the viscosity of the polyethylene glycol and / or nonionic surfactant, resulting in a slower rate of elution from the carbon fiber surface. Setting the Mw to 5000 or less reduces the viscosity, which is an indicator of the ease of movement of the polyethylene glycol and / or nonionic surfactant, and reduces the amount of entanglement of molecular chains during elution into water, thereby improving the elution of the polyethylene glycol and / or nonionic surfactant into water. The Mw is preferably 2000 or less, and more preferably 1000 or less. On the other hand, from the viewpoint of application, the higher the Mw, the more effectively the volatilization during application of the sizing agent can be suppressed. The lower limit of Mw is preferably 300 or more. The molecular weight of the polyethylene glycol and / or nonionic surfactant applied to the sizing-coated carbon fiber bundle can be confirmed by extracting the sizing agent from the sizing-coated carbon fiber bundle with water and performing GPC analysis.

[0042] Furthermore, by making the amount of the anionic surfactant 50 parts by mass or more of the total amount of surfactants, the hydrophilic group in the anion of the anionic surfactant repels the carbon fiber surface, improving elution, so that the sizing agent is more likely to be eluted during washing with water, and the amount of sizing agent remaining on the carbon fiber bundle can be reduced.

[0043] Furthermore, in addition to polyethylene glycol and / or a surfactant, other components may be contained. Hereinafter, the other components may be referred to as the second component. Examples of the other components include aliphatic or alicyclic compounds and / or aliphatic or alicyclic compounds in which two hydroxyl groups are bonded to two different carbon atoms, polyvinyl alcohol, polyglycidyl ether, polyethyleneimine, etc., and aliphatic or alicyclic compounds and / or aliphatic or alicyclic compounds in which two hydroxyl groups are bonded to two different carbon atoms are particularly preferred.

[0044] Here, in addition to polyethylene glycol and / or a surfactant, it is preferable to contain 0.1 to 30 parts by mass of an aliphatic or alicyclic compound in which one hydroxyl group is bonded to a carbon and / or an aliphatic or alicyclic compound in which two hydroxyl groups are bonded to two different carbons (alcohol, diol) relative to 100 parts by mass of the total amount of the sizing agent. By setting it to 0.1 part by mass or more, lipophilic groups on the carbon fiber surface can be exposed to the air interface, which is preferable, and friction can be reduced, and by setting it to 20 parts by mass or more, it is even more preferable, as the effect can be more uniformly exerted.

[0045] Specific examples of aliphatic or alicyclic compounds having one and / or two hydroxyl groups bonded to a carbon include aliphatic alcohols such as methyl alcohol, 2-propanol, n-butyl alcohol, isobutyl alcohol, n-decyl alcohol, myristyl alcohol, ethylene glycol, and propylene glycol; alicyclic alcohols such as cyclohexanol; ethylene glycol; propylene glycol; 1,3-propanediol; 1,2-butanediol; 1,4-butanediol; 2-methyl-1,2-propanediol; aliphatic diols such as hexanediol, 1,5-pentanediol, 1,6-hexanediol, 2,3-dimethyl-2,3-butanediol, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and 2,4,7,9-tetramethyldecane-4,7-diol; and alicyclic diols such as hexanediol, cyclohexanediol, and 1,4-cyclohexanedimethanol.

[0046] In the sizing agent of the present invention, the ratio of hydrophilic groups in the anions constituting the anionic surfactant is preferably 17% or more.

[0047] By making the hydrophilic group ratio in the anions 17% or more, the elution property of the anion moiety into water is improved, so that the sizing agent is easily eluted during washing with water, and the amount of sizing agent remaining on the carbon fiber bundle can be reduced. A ratio of 20% or more is preferable, and 30% or more is more preferable.

[0048] The hydrophilic group ratio is calculated from the molecular weight of the anionic surfactant. It can be calculated from the ratio of the molecular weight of the hydrophilic group part of the anion of the anionic surfactant to the molecular weight of the anionic surfactant. Here, the hydrophilic group is a sulfate ester group (SO4 - ), sulfonic acid group (SO3 - ), and carboxyl groups (COO - ), phosphate group (HPO3 - ), hydroxyl group (OH - In addition, if unreacted moieties remain during the production of the anionic moiety of the surfactant, the reaction rate is calculated from the total amount of the starting material and the reacted material (anion of the anionic surfactant) and the amount of the reacted material, and the hydrophilic group ratio calculated from the molecular weight of the anionic moiety of the anionic surfactant is multiplied by the reaction rate to obtain the hydrophilicity rate of the anionic moiety of the present invention.

[0049] In the sizing agent constituting the present invention, the weight-average molecular weight Mw of the anionic surfactant is preferably 150 or more and 600 or less. The larger the Mw, the higher the proportion of hydrophobic groups in the anionic surfactant, and therefore the rate of elution from the carbon fiber surface decreases. By setting the Mw to 600 or less, the hydrophilic group ratio, which is an index of the elution property of the anionic surfactant, is increased, thereby improving the elution property of the anionic surfactant in water. The Mw is preferably 500 or less. On the other hand, in terms of processability, the larger the Mw, the stronger the sizing agent film becomes, and the lower the friction can be reduced. The lower limit of Mw is more preferably 250 or more. The weight-average molecular weight Mw of the anionic surfactant applied to the sizing-agent-coated carbon fiber bundle can be confirmed by extracting the sizing agent from the sizing-agent-coated carbon fiber bundle with water, evaluating the sizing agent, and identifying the metal elements by elemental analysis such as XPS in combination.

[0050] Furthermore, by using an amphoteric surfactant in an amount of 50 parts by mass or more of the total amount of surfactants, the hydrophilic group portion of the amphoteric surfactant interacts with water, improving elution, and therefore the sizing agent becomes more easily eluted during washing with water, making it possible to reduce the amount of sizing agent remaining on the carbon fiber bundles. In the sizing agent of the present invention, the average number of carbon atoms in the alkyl groups constituting the amphoteric surfactant is preferably 17 or less.

[0051] By setting the average carbon number of the alkyl group to 17 or less, the elution property of the amphoteric surfactant into water is improved, making it easier for the sizing agent to be eluted during washing with water, and the amount of sizing agent remaining on the carbon fiber bundle can be reduced. The average carbon number of the alkyl group is more preferably 16.5 or less, and even more preferably 16 or less. Also, 8 or more is preferable. If the average carbon number is less than 8, the surface free energy of the sizing agent increases, resulting in a high dry FF friction coefficient.

[0052] The average carbon number of the alkyl groups that make up the amphoteric surfactant can be evaluated by extracting the sizing agent from a coated carbon fiber bundle with water and evaluating it. One method is to freeze-dry the extracted sizing agent and then evaluate its structure from the IR spectrum obtained by infrared spectroscopy, in combination with proton NMR, carbon NMR, and mass spectrometry analysis of the freeze-dried product.

[0053] <How to determine the absorbance of carbon fiber extract> The sizing-agent-coated carbon fiber bundle constituting the present invention preferably has an absorbance of 0.06 or more for the water extract. By making the absorbance 0.06 or more, contaminants such as oxides adhering to the carbon fiber surface are easily removed, improving adhesion. The absorbance is preferably 0.08 or more, and more preferably 0.10 or more.

[0054] The absorbance of the water extract of the sizing agent-coated carbon fiber extract defined in the present invention can be determined by the following procedure: 1.0 g of a carbon fiber bundle is cut out and placed in a container with a volume of 20 cm 3The carbon fiber bundle was placed in a glass container with a lid and 10.0 g of distilled water at 25°C was added. The shaker was set to an amplitude of 30 mm and a shaking speed of 120 rpm. The glass container was placed in the shaker and shaken for 1 minute. After shaking, the carbon fiber bundle was immediately removed from the solution. The solution extracted from the carbon fiber was placed in a quartz cell with a light path length of 1.0 cm. Using distilled water as a control solution, the absorbance from 200 to 900 nm was measured using a UV-visible spectrophotometer, and the absorbance at 600 nm was recorded. The shaker used was a Shaking Bath SB-13 manufactured by AS ONE Corp. The ultraviolet-visible spectrophotometer used was a V-550 manufactured by JASCO Corporation.

[0055] In the sizing agent constituting the present invention, the weight-average molecular weight Mw of the amphoteric surfactant is preferably 150 or more and 600 or less. The larger the Mw, the higher the viscosity of the amphoteric surfactant, and therefore the rate of elution from the carbon fiber surface decreases. By setting the Mw to 600 or less, the viscosity, which is an index of the elution property of an anionic surfactant, can be reduced, and the elution property of the amphoteric surfactant in water improves. The Mw is more preferably 250 or less. On the other hand, from the viewpoint of application, the larger the Mw, the more the volatilization during application of the sizing agent can be suppressed. The lower limit of Mw is preferably 150 or more. The weight-average molecular weight Mw of the amphoteric surfactant applied to the sizing-agent-coated carbon fiber bundle can be confirmed by extracting the sizing agent from the sizing-agent-coated carbon fiber bundle with water, followed by GPC evaluation, in combination with identifying metal elements by elemental analysis such as XPS.

[0056] In the sizing agent of the present invention, the applied polyethylene glycol and / or surfactant preferably have a mass residual ratio of 35% or less when the temperature reaches 300°C when heated in air at a rate of 10°C / min. By keeping the mass residual ratio at 35% or less, the low-heat-resistant components of the sizing agent decompose before the matrix resin melts, reducing the amount of sizing agent incorporated into the matrix resin, thereby reducing the impact on the mechanical properties of the composite material and stabilizing the properties. A mass residual ratio of 20% or less is preferred, and 5% or less is even more preferred.

[0057] In the sizing agent constituting the present invention, the applied polyethylene glycol and / or surfactant preferably have a mass residual ratio of 35% or less when the temperature reaches 350°C when heated in air at a rate of 10°C / min. By keeping the mass residual ratio at 30% or less, the low-heat-resistant components of the sizing agent decompose before the high-heat-resistant matrix resin melts, reducing the amount of sizing agent incorporated into the matrix resin. This reduces the impact on the mechanical properties of the composite material and stabilizes the properties. A mass residual ratio of 25% or less is preferred, and 5% or less is even more preferred.

[0058] Next, the components constituting the sizing agent-coated carbon fiber bundle used in the present invention will be described.

[0059] Although there are no particular limitations on the carbon fiber bundle used in the present invention, polyacrylonitrile-based carbon fibers are preferably used from the viewpoint of mechanical properties. The polyacrylonitrile-based carbon fiber bundle can be obtained by subjecting a carbon fiber precursor fiber made of a polyacrylonitrile-based polymer to flame retardation treatment in an oxidizing atmosphere at a maximum temperature of 200 to 300°C, followed by preliminary carbonization treatment in an inert atmosphere at a maximum temperature of 500 to 1200°C, and then carbonization treatment in an inert atmosphere at a maximum temperature of 1200 to 2000°C.

[0060] The carbon fiber bundle of the present invention preferably has a strand strength of 4.0 GPa, more preferably 4.9 GPa or more. If the carbon fiber bundle has a strand strength of 4.0 GPa or more, the strand strength of the carbon fiber bundle after washing off the sizing agent with water is sufficiently high, and the effect of improving the mechanical properties of the composite material is likely to be obtained.

[0061] In the present invention, in order to improve the adhesion between the carbon fiber bundles and the matrix resin, it is preferable to introduce oxygen-containing functional groups onto the surfaces of the carbon fiber bundles by subjecting the carbon fiber bundles to an oxidation treatment. As the oxidation treatment method, gas phase oxidation, liquid phase oxidation, and liquid phase electrolytic oxidation are used, but liquid phase electrolytic oxidation is preferably used from the viewpoints of high productivity and enabling uniform treatment.

[0062] In the present invention, the electrolyte used in the liquid-phase electrolytic oxidation may be an acidic electrolyte or an alkaline electrolyte. Examples of acidic electrolytes include inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, and carbonic acid; organic acids such as acetic acid, butyric acid, oxalic acid, acrylic acid, and maleic acid; and salts such as ammonium sulfate and ammonium hydrogen sulfate. Among these, sulfuric acid and nitric acid, which exhibit strong acidity, are preferred. Examples of alkaline electrolytes include aqueous solutions of hydroxides such as sodium hydroxide, calcium hydroxide, and barium hydroxide; aqueous solutions of carbonates such as sodium carbonate, calcium carbonate, barium carbonate, and ammonium carbonate; aqueous solutions of bicarbonates such as sodium bicarbonate, calcium bicarbonate, barium bicarbonate, and ammonium bicarbonate; and aqueous solutions of ammonia, tetraalkylammonium hydroxide, and hydrazine.

[0063] The carbon fiber bundle in the present invention preferably has a surface oxygen concentration of 0.08 or more and 0.25 or less as measured by X-ray photoelectron spectroscopy.

[0064] The presence of functional groups on the carbon fiber surface creates affinity with the matrix resin, enabling high adhesive strength to be achieved. If the surface oxygen concentration (O / C) is less than 0.08, the affinity between the carbon fiber surface and the matrix resin decreases, resulting in low adhesive strength. The surface oxygen concentration is preferably 0.15 or higher. A concentration of 0.15 or higher is preferred because it increases the affinity between the carbon fiber surface and the matrix resin. Furthermore, an O / C of 0.25 or lower is more preferred. If the O / C exceeds 0.25, the number of functional groups increases, but the surface layer of the carbon fiber becomes more susceptible to peeling, resulting in lower adhesive strength.

[0065] Next, the method for producing the sizing agent-coated carbon fiber bundle of the present invention will be described.

[0066] First, the means for applying (applying) the sizing agent to the carbon fiber bundle constituting the present invention will be described.

[0067] In the present invention, the sizing agent is preferably diluted with a solvent and used as a homogeneous solution. Examples of such solvents include water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, dimethylformamide, and dimethylacetamide. Among these, water is preferred because it is easy to handle and has safety advantages.

[0068] Examples of application methods include a method of immersing a carbon fiber bundle in a sizing agent solution via a roller, a method of bringing a carbon fiber bundle into contact with a roller to which the sizing agent solution is attached, and a method of spraying a mist of the sizing agent solution onto the carbon fiber bundle. In producing the sizing-agent-coated carbon fiber bundle of the present invention, the method of immersing a carbon fiber bundle in a sizing agent solution via a roller is preferably used. The sizing agent may be applied by either a batch method or a continuous method, but the continuous method is preferred because it has good productivity and small variations. Another preferred embodiment is to ultrasonically vibrate the carbon fiber bundle when applying the sizing agent.

[0069] In the present invention, after applying the sizing agent solution, it is preferable to obtain a sizing-coated carbon fiber bundle by contact drying means, for example, by bringing the carbon fiber bundle into contact with a heated roller. The carbon fiber bundle introduced into the heated roller is pressed against the heated roller by tension and rapidly dried, so the flat shape of the carbon fiber bundle expanded by the heated roller is easily fixed by the sizing agent. The flattened carbon fiber bundle has a smaller contact area between individual fibers, which increases the contact area with water when immersed in water, making it more likely to be eluted. The temperature of the contact drying means is preferably 120°C or higher. At 120°C or higher, the carbon fiber bundle is easily fixed in a flat shape. 130°C or higher is more preferable. In the present invention, after passing the carbon fiber bundle through heated rollers as a preliminary drying step, a further heat treatment may be performed as a second drying step. A non-contact heating method, which makes it easy to perform heat treatment at high temperatures, is preferable for the heat treatment as the second drying step. By carrying out the heat treatment, the dilution solvent remaining in the sizing agent can be further removed and the viscosity of the sizing agent can be stabilized, thereby stably increasing the elution property.

[0070] Furthermore, by performing this heat treatment, the surface free energy of the polyethylene glycol and / or surfactant on the carbon fiber can be controlled, reducing the coefficient of friction and improving the handleability of the sizing-agent-coated carbon fiber bundle. The heat treatment temperature is preferably in the range of 120 to 260°C. At 120°C or higher, the ionization of the anionic surfactant or amphoteric surfactant can be controlled by removing the dilution solution, suppressing electrical interactions and making the handleability easier. Furthermore, the viscosity due to the interaction of the polyethylene glycol and / or nonionic surfactant with water is reduced, making the handleability easier to improve. 150°C or higher is preferred, and 180°C or higher is more preferred. On the other hand, by setting the upper limit of the heat treatment temperature to 260°C or lower, thermal degradation of the polyethylene glycol and / or surfactant components can be suppressed, making it easier to maintain elution. 240°C or lower is preferred, and 220°C or lower is more preferred.

[0071] The heat treatment can also be carried out by microwave irradiation and / or infrared irradiation. [Example]

[0072] Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0073] <Method for measuring sizing adhesion amount> 2.0±0.5 g of sizing-coated carbon fiber bundle was weighed (W1) (read to four decimal places) and then placed in an electric furnace (capacity 120 cm) set at 450°C in a nitrogen gas flow of 50 ml / min. 3 ) for 15 minutes to completely pyrolyze the sizing agent. The carbon fiber bundle was then transferred to a container in a dry nitrogen gas flow of 20 liters / minute and cooled for 15 minutes. The carbon fiber bundle was then weighed (W2) (read to four decimal places) and the heat loss was calculated by subtracting W1 from W2. This heat loss was converted to parts by mass relative to 100 parts by mass of the sizing-coated carbon fiber bundle (rounded to two decimal places), and this value was taken as the amount of sizing agent (parts by mass). The measurement was performed twice, and the average value was taken as the amount of sizing agent attached.

[0074] <Method for measuring the residual mass rate of polyethylene glycol and / or surfactant> The mass retention of sizing agents, such as polyethylene glycol and / or surfactants, was measured using a thermogravimetric-differential thermal analyzer (TG-DTA). 10 ± 0.5 mg of surfactant was weighed into an aluminum pan (W3) (read to four decimal places) and placed in a heating device. The temperature was increased from 25 °C to 450 °C at 10 °C / min in an airflow of 100 mL / min to thermally decompose the surfactant. The mass at 300 °C (W4) (read to four decimal places) and the mass at 350 °C (W5) (read to four decimal places) were measured, and the mass retention rates at 300 °C and 350 °C (%) were calculated using the formulas W4 / W3 × 100 (%) and W5 / W3 × 100 (%).

[0075] In this invention, TG-DTA2000SA manufactured by Bruker was used as the measuring device.

[0076] <Method for Measuring the Amount of Functional Groups on the Surface of Carbon Fiber Bundles> In this embodiment, the surface oxygen concentration of the carbon fiber bundle was measured by X-ray photoelectron spectroscopy according to the following procedure. First, the carbon fiber bundle was cut into 20 mm pieces, spread out and arranged on a copper sample support stage, and then AlKα was used as the X-ray source. 1、2 was used, the inside of the sample chamber was maintained at 1×10 -8 Torr, and X-ray photoelectron spectroscopy measurement was performed with the photoelectron escape angle set at 45°. In addition, as the correction value for the peak associated with charging during measurement, the binding energy value of the main peak of C 1S was adjusted to 285 eV. The C 1S peak area was determined by drawing a straight baseline in the range of binding energy values from 275 to 290 eV. The O 1s peak area was determined by drawing a straight baseline in the range of binding energy from 525 to 540 eV. As the X-ray photoelectron spectroscopy apparatus, ESCA-1600 manufactured by ULVAC-PHI Co., Ltd. was used.

[0077] <Method for Measuring CF Abraded Fuzz> Two metal bars with a diameter of 50 mm and a surface roughness Rmax of 0.3 μm (material: made of stainless steel SUS304) were arranged vertically at an interval of 150 mm such that the carbon fiber bundle passed while contacting the metal bars at a total angle of 0.785π (rad). Then, the carbon fiber bundle was draped over the metal bars, the unwinding tension from the package was set to 800 g, the carbon fiber bundle was pulled at a speed of 6 m per minute by a driving roll to pass through the metal bars, a laser beam was irradiated perpendicularly from the side to the fiber yarn after passing through the second metal bar, and the number of fuzz was detected and counted for 5 minutes by a fuzz detection device, and the number was recorded.

[0078] In this invention, the preferable range of handleability was evaluated in three levels according to the following criteria, with S and A being considered qualified and B being considered unqualified.

[0079] S: Less than 15 fuzz per meter A: Fluff: 15 or more / m and less than 25 / m B: More than 25 fluffs / m.

[0080] <Method for measuring the coefficient of friction of dry FF> The bobbin is fixed to prevent rotation and is wound to a uniform thickness of 5 to 10 mm with a winding density of 0.9 to 1.4 g / cm. 3 The same carbon fiber bundle as the wound object was wound around the surface of the sizing-coated carbon fiber bundle wound within a range of 100°C (0.15 sq. m). The same carbon fiber bundle was wound around the surface of the wound object, typically with a 3-5 mm gap in the width direction, so as not to overlap with itself and to provide a contact angle of 3π (rad). A weight (T1 = 0.25 g / tex) was attached to one end of the wound carbon fiber bundle, and the opposite end was pulled with a spring balance at a speed of 1 m / min. The tension at which the wound carbon fiber bundle began to move was defined as T2, and the dry FF friction coefficient was calculated using the following formula. Measurements were performed twice, and the average value was used as the dry FF friction coefficient. The measurement bobbin was placed under ambient temperature and humidity conditions (measurement conditions: 23±3°C / 60±5%) for at least two hours before the measurement.

[0081] Dry FF friction coefficient = ln(T2 / T1) / θ T2: Tension when the carbon fiber bundle starts to move (= spring balance reading) T1: Weight of weight (=0.25g / tex) θ: Total contact angle between the wound object and the wound thread (=3πrad).

[0082] <Wet FM friction coefficient measurement method> A 50 mm stainless steel SUS304 bar was fixed parallel to the ground and prevented from rotating. A sizing-coated carbon fiber bundle was cut from a bobbin and immersed in pure water for 1 second. It was then wrapped around the fixed bar with a uniform thickness of 1–3 mm and a contact angle of 3π (rad), typically with 3–5 mm spacing in the width direction, without overlapping itself. A weight (T3 = 0.25 g / tex) was attached to one end of the wrapped carbon fiber bundle, and the opposite end was pulled by a spring balance at a speed of 1 m / min. The tension at which the wrapped carbon fiber bundle began to move was defined as T4. The wet friction coefficient between the fiber and the stainless steel SUS304 was calculated using the following formula. Measurements were performed twice, and the average was used as the wet FM friction coefficient.

[0083] Wet FM friction coefficient = ln(T4 / T3) / θ T4: Tension when the carbon fiber bundle starts to move (= spring balance reading) T3: Weight of weight (=0.25g / tex) θ: Total contact angle between the wound object and the wound thread (=3πrad).

[0084] <Strand strength and strand modulus of carbon fiber bundle> The strand strength and strand modulus of a carbon fiber bundle are determined according to the following procedure, in accordance with the resin-impregnated strand test method of JIS R7608 (2004). However, if the carbon fiber bundle has twists, they are untwisted by twisting the bundle in the opposite direction the same number of times as the twists. The resin formulation used is "Celloxide (registered trademark)" 2021P (manufactured by Daicel Chemical Industries, Ltd.) / boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / acetone = 100 / 3 / 4 (parts by mass), and the curing conditions are atmospheric pressure, 125°C, and 30 minutes. Ten strands of the carbon fiber bundle are measured, and the average values ​​are used as the strand strength and strand modulus. The strain range for calculating the strand modulus is 0.1 to 0.6%.

[0085] <Method for measuring interfacial shear strength> Single fibers were extracted from the carbon fiber bundle, sandwiched from above and below between laminated resin films to a thickness of 0.4 mm or more, heated and pressurized in a heat press, and then cooled to room temperature while maintaining the pressurized state to obtain a molded plate with the carbon fiber single fibers embedded. Dumbbell-shaped test pieces for IFSS measurement were punched out from this molded plate using an SD-type lever cutter.

[0086] Both ends of the dumbbell-shaped sample were clamped, and a tensile force was applied in the fiber axis direction (longitudinal direction) at a rate of 2.0 mm / min, generating a strain of 12%. A 20 mm section was then cut from the center of the specimen and heated above the melting point of the thermoplastic resin while sandwiched between glass plates on a hot plate. The fragmented fiber length inside the sample, which had been made transparent by heating, was observed under a microscope. Furthermore, the critical fiber length lc was calculated from the average broken fiber length la using the formula lc (μm) = (4 / 3) × la (μm). The strand tensile strength σ and the diameter d of the carbon fiber single yarn were measured, and the interfacial shear strength (IFSS), an index of the adhesive strength at the interface between the carbon fiber and the resin, was calculated using the following formula. In the examples, the test results were the average of five measurements (n = 5).

[0087] IFSS(MPa)=σ(MPa)×d(μm) / (2×lc)(μm).

[0088] In the present invention, the preferable range of IFSS was evaluated in three stages according to different criteria for each of the following resins, with A being considered acceptable.

[0089] Resin: Polyether ether ketone A: IFSS 38 or higher B: IFSS is 35 or more and less than 38 C: IFSS less than 35.

[0090] The materials and components used in each example and comparative example are as follows:

[0091] Component (A): polyethylene glycol and / or nonionic surfactant A-1: PEG distearate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" DS4000, HLB: 16.6) A-2: PEG monostearate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" MS1000, HLB: 15.7) A-3: PEG monooleate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" MO600, HLB: 13.8) A-4: PEG monooleate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" MO400, HLB: 11.7) A-5: PEG dioleate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" DO1000, HLB: 12.9) A-6: PEG dioleate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" DO600, HLB: 10.5) A-7: Polyethylene glycol (PEG600, manufactured by Sanyo Chemical Industries, Ltd., HLB: 20, molecular weight: 600) A-8: Polyethylene glycol (PEG4000, manufactured by Sanyo Chemical Industries, Ltd., HLB: 20, molecular weight: 4000) A-9: Polyethylene glycol (PEG20000, manufactured by Sanyo Chemical Industries, Ltd., HLB: 20, molecular weight: 20000) (B) Component: Anionic surfactant B-1: Sodium bis(2-ethylhexyl) sulfosuccinate (Tokyo Chemical Industry Co., Ltd.) B-2: Oleic acid butyl ester sulfated oil (Lion Corporation's "Rotat (registered trademark)" OH-104K, reaction rate: 79%) B-3: Sodium alkylnaphthalene sulfonate (Tokyo Chemical Industry Co., Ltd.) B-4: Sodium dodecylbenzenesulfonate (Kao Corporation "Neo Operex (registered trademark)" G15) B-5: Sodium lauryl sulfate (Kao Corporation "Emar (registered trademark)" 10G) B-6: Disodium lauryl sulfosuccinate (Sanyo Chemical Industries, Ltd. "Viewlite (registered trademark)" SSS) B-7: Sodium 2-ethylhexyl sulfate (Sandet (registered trademark) ONA manufactured by Sanyo Chemical Industries, Ltd.).

[0092] (C) Component: Amphoteric surfactant C-1: Lauryl dimethylaminoacetic acid betaine (Kao Corporation's "Amphitol (registered trademark) 24B") C-2: 2-Alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine (Kao Corporation's "Amphitol (registered trademark) 20Y-B") C-3: N,N-dimethyldecylamine oxide ("Cadenax (registered trademark) DM10D-W" manufactured by Lion Specialty Chemicals Co., Ltd.) C-4: Lauryl dimethylamine oxide ("Cadenax (registered trademark) DM12D-W(C)" manufactured by Lion Specialty Chemicals Co., Ltd.) C-5: N,N-dimethylmyristylamine oxide ("Kadenax (registered trademark) DM14D-N" manufactured by Lion Specialty Chemicals Co., Ltd.) C-6: Stearyl dimethylaminoacetic acid betaine (Kao Corporation "Amphithor (registered trademark) 86B") (D) Alcohol and diol components D-1: Propylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd.) D-2: 2-propanol (Fujifilm Wako Pure Chemical Industries, Ltd.) (E) Ingredients: Other ingredients E-1: Polyvinyl alcohol (PVA (degree of polymerization approximately 500) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). E-2: Diglycerol polyglycidyl ether (Nagase ChemteX Corporation "Denacol (registered trademark)" Ex-421) E-3: Polyethyleneimine ("Lupasol (registered trademark)" G20 Waterfree, manufactured by BASF Japan Ltd.).

[0093] (F) Component: Thermoplastic resin F-1: Polyether ether ketone (Victrex (registered trademark) 450G manufactured by Victrex Co., Ltd.).

[0094] This example comprises the following first to fifth steps.

[0095] First process: A process for producing carbon fiber bundles as raw materials An acrylonitrile copolymer was spun and calcined to obtain a carbon fiber bundle with a total filament count of 12,000 and a total fineness of 800 tex. The strand strength and strand modulus of this carbon fiber bundle were evaluated and found to be 5.1 GPa and 240 GPa, respectively. The carbon fiber bundle was then subjected to an electrolytic surface treatment using an aqueous ammonium bicarbonate solution as the electrolyte at an electrical charge of 80 coulombs per gram of carbon fiber bundle. The carbon fiber bundle subjected to this electrolytic surface treatment was then washed with water and dried in heated air to obtain the carbon fiber bundle that would serve as the raw material. The surface oxygen concentration of the carbon fiber bundle obtained in this first step was measured.

[0096] Second step: A step of applying a sizing agent to the carbon fiber bundle Compound (A) (A-1) was used as compound (A) with the composition shown in Table 1, and water was added to uniformly dissolve the compound (A) in an approximately 0.8% by mass aqueous solution. This aqueous solution was used as a sizing agent aqueous solution, and the sizing agent was applied to a surface-treated carbon fiber bundle by immersion. The bundle was then heat-treated with a hot roller at 120°C for 15 seconds as a preliminary drying step, and subsequently heat-treated in heated air at 210°C for 60 seconds as a second drying step to obtain a sizing-agent-coated carbon fiber bundle. The amount of sizing agent attached was adjusted to 0.25 parts by mass per 100 parts by mass of the total amount of the surface-treated, sizing-agent-coated carbon fiber bundle. The mass residual ratio of the sizing agent applied in this second step was also measured. The mass residual ratio was 3% when the temperature reached 300°C, and 1% when the temperature reached 350°C, demonstrating sufficient thermal decomposition.

[0097] Third step: Evaluating the handling properties of the sizing-coated carbon fiber bundles Using the sizing-coated carbon fiber bundle obtained in the second step, the handleability was evaluated based on the evaluation method for the friction coefficient and the measurement method for CF abrasion fluff. As a result, the dry FF friction coefficient was 0.22, and the wet FM friction coefficient was 0.22, indicating that fluffing was unlikely to occur during the processing step in which the bar was present in air and water, and that the handleability was sufficiently good.

[0098] · Fourth step: Evaluation of the amount of sizing agent attached after rinsing The sizing-agent-coated carbon fiber bundle obtained in the previous step was washed with water as described above in the sections <Method for calculating the amount of sizing agent attached after 50-second water washing> and <Method for calculating the amount of sizing agent attached after 25-second water washing>. After obtaining sizing-agent-coated carbon fiber bundles after 50-second water washing and 25-second water washing, the amounts of sizing agent attached after 50-second water washing and 25-second water washing were calculated. As a result, the amount of sizing agent attached after 50-second water washing was 0.10 parts by mass relative to 100 parts by mass of the sizing-agent-coated carbon fiber bundle, and the amount of sizing agent attached after 25-second water washing was 0.11 parts by mass relative to 100 parts by mass of the sizing-agent-coated carbon fiber bundle, indicating that the remaining amount was small in both cases and that the elution property was sufficiently high.

[0099] - Fifth step: Preparation and evaluation of test specimens for IFSS measurement Using the sizing-coated carbon fiber bundles obtained in the previous step after washing with water and (F-1) as the thermoplastic resin (F), a test piece for IFSS measurement was prepared based on the method for measuring interfacial shear strength.

[0100] Next, the IFSS was measured using the obtained IFSS measurement specimen. The results showed that the IFSS was 38 MPa when using a carbon fiber bundle coated with a sizing agent after 50 seconds of water washing, and 38 MPa when using a carbon fiber bundle coated with a sizing agent after 25 seconds of water washing. In either case, the adhesion was found to be sufficiently high. The results are summarized in Table 1.

[0101] [Table 1]

[0102] Example 2 A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent in the second step was changed as shown in Table 1. The results are shown in Table 1, and it was found that the handleability was good and the elution property was also sufficiently high.

[0103] Examples 3 to 5 A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent and the amount of sizing agent applied in the second step were changed as shown in Table 1. The results are shown in Table 1, and it was found that the handleability was good and the elution property was also sufficiently high.

[0104] (Comparative Example 1) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent and the amount of sizing agent attached in the second step were changed as shown in Table 1. The results are shown in Table 1. The handleability was good, but the amount of sizing agent attached was high and the elution was insufficient.

[0105] (Comparative Example 2) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent and the amount of sizing agent applied in the second step were changed as shown in Table 1. The results are shown in Table 1, and the dry FF friction coefficient was high and the handleability was insufficient.

[0106] (Comparative Examples 3 to 5) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent in the second step was changed as shown in Table 1. The results are shown in Table 1. The handleability was good, but the HLB was low, the terminal hydroxyl group ratio was low, and the elution property was insufficient.

[0107] Example 6 A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent in the second step was changed as shown in Table 2. The results are shown in Table 2, and it was found that the handleability was good and the elution property was also sufficiently high.

[0108] [Table 2]

[0109] Example 7 A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the amount of surface treatment in the first step was changed to 40 coulombs / g and the composition of the sizing agent in the second step was changed as shown in Table 1. The results are summarized in Table 2, and it was found that the handleability was good and the elution property was also sufficiently high.

[0110] (Examples 8 and 9) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent and the amount of sizing agent applied in the second step were changed as shown in Table 2. The results are shown in Table 2, and it was found that the handleability was good and the elution property was also sufficiently high.

[0111] (Comparative Example 6) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent and the amount of sizing agent applied in the second step were changed as shown in Table 2. The results are shown in Table 2, and the dry FF friction coefficient was high and the handleability was insufficient.

[0112] (Examples 10 and 11) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent in the second step was changed as shown in Table 2. The results are shown in Table 2, and it was found that the handleability was good and the elution property was also sufficiently high.

[0113] (Comparative Example 7) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent and the amount of sizing agent applied in the second step were changed as shown in Table 2. The results are shown in Table 2, and although the handleability was good, the hydrophilicity was insufficient and the elution property was insufficient.

[0114] Example 12 Sizing-agent-coated carbon fiber bundles were obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition of the sizing agent and the amount of sizing agent applied in the second step were changed as shown in Table 3. The results are summarized in Table 3, and it was found that the handleability was good and the elution property was also sufficiently high.

[0115] [Table 3]

[0116] Example 13 A sizing-agent-coated carbon fiber bundle was obtained in the same manner as in Example 12, except that the drying temperature in the second drying step in the second step was changed to 150° C., and various evaluations were performed. The results are shown in Table 3, and it was found that the handleability was good and the elution property was also sufficiently high.

[0117] (Comparative Example 8) A sizing-agent-coated carbon fiber bundle was obtained in the same manner as in Example 12, except that the drying temperature in the second drying step in the second step was changed to 80° C., and various evaluations were performed. The results are shown in Table 3. Although the elution was sufficiently high, the dry FF friction coefficient was high and the handleability was insufficient.

[0118] Comparative Example 9 A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 12, except that the amount of sizing agent applied in the second step was changed as shown in Table 3. The results are shown in Table 3. Although the elution property was sufficiently high, the dry FF friction coefficient was high and the handleability was insufficient.

[0119] Example 14 Sizing-agent-coated carbon fiber bundles were obtained and various evaluations were carried out in the same manner as in Example 12, except that the amount of sizing agent applied in the second step was changed as shown in Table 3. The results are summarized in Table 3, and it was found that the handleability was good and the elution property was also sufficiently high.

[0120] Example 15 A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 12, except that the amount of surface treatment in the first step was changed to 40 coulombs / g and the amount of sizing agent applied in the second step was changed as shown in Table 3. The results are summarized in Table 3, and it was found that the handleability was good and the elution property was also sufficiently high.

[0121] (Comparative Example 10) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 12, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 3. The results are summarized in Table 1, and although the handleability was good, the ratio of anionic hydrophilic groups in the anionic surfactant was low, and the elution was insufficient.

[0122] (Examples 16 to 18) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 12, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 3. The results are summarized in Table 3, and it was found that the handleability was good and the elution property was also sufficiently high.

[0123] Examples 19 to 22 A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 12, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 3. The results are summarized in Table 4, and it was found that the handleability was good and the elution property was also sufficiently high.

[0124] [Table 4]

[0125] Example 23 Sizing-agent-coated carbon fiber bundles were obtained and various evaluations were carried out in the same manner as in Example 12, except that the amount of sizing agent applied in the second step was changed as shown in Table 4 and (D-1) was added as the second component in the proportion relative to the total amount of sizing shown in Table 4. The results are summarized in Table 4, and it was found that the handleability was good and the elution property was also sufficiently high.

[0126] Example 24 Sizing-agent-coated carbon fiber bundles were obtained and various evaluations were carried out in the same manner as in Example 12, except that the amount of sizing agent applied in the second step was changed as shown in Table 4 and (D-2) was added as the second component in the proportion relative to the total amount of sizing shown in Table 4. The results are summarized in Table 4, and it was found that the handleability was good and the elution property was also sufficiently high.

[0127] Example 25 Sizing-agent-coated carbon fiber bundles were obtained and various evaluations were carried out in the same manner as in Example 12, except that the amount of sizing agent applied in the second step was changed as shown in Table 4 and (E-2) was added as the second component in the proportion relative to the total amount of sizing shown in Table 4. The results are summarized in Table 4, and it was found that the handleability was good and the elution property was also sufficiently high.

[0128] Example 26 Sizing-agent-coated carbon fiber bundles were obtained and various evaluations were carried out in the same manner as in Example 12, except that the amount of adhesion in the second step was changed as shown in Table 4 and (E-3) was added as the second component in the proportion relative to the total amount of sizing shown in Table 4. The results are summarized in Table 4, and it was found that the handleability was good and the elution property was also sufficiently high.

[0129] Example 27 Sizing-agent-coated carbon fiber bundles were obtained and various evaluations were carried out in the same manner as in Example 1, except that the amount of sizing agent applied in the second step was changed as shown in Table 5. The results are shown in Table 5, and it was found that the handleability was good and the elution property was also sufficiently high.

[0130] [Table 5]

[0131] (Examples 28 and 29) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 27, except that the amount of sizing agent applied in the second step was changed as shown in Table 5. The results are shown in Table 5, and it was found that the handleability was good and the elution property was also sufficiently high.

[0132] (Examples 30 and 31) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 27, except that (C-2) was used as compound (C) in the second step and the amount of sizing agent applied was changed as shown in Table 5. The results are shown in Table 5, and it was found that the handleability was good and the elution property was also sufficiently high.

[0133] Example 32 A sizing-agent-coated carbon fiber bundle was obtained in the same manner as in Example 27, except that in the second step, (C-3) was used as compound (C), the amount of sizing agent applied was changed as shown in Table 5, and the second drying step was not performed after heat treatment with a hot roller at a temperature of 120°C for 15 seconds as a pre-drying step, and various evaluations were performed. The results are shown in Table 5, and it was found that the handleability was good and the elution property was also sufficiently high.

[0134] Example 33 A sizing-coated carbon fiber bundle was obtained in the same manner as in Example 27, except that in the second step, (C-4) was used as compound (C), the amount of sizing agent applied was changed as shown in Table 5, and the second drying step was not performed after heat treatment with a hot roller at a temperature of 120°C for 15 seconds as a pre-drying step, and various evaluations were performed. The results are shown in Table 5, and it was found that the handleability was good and the elution property was also sufficiently high.

[0135] Example 34 A sizing-coated carbon fiber bundle was obtained in the same manner as in Example 27, except that in the second step, (C-5) was used as compound (C), the amount of sizing agent applied was changed as shown in Table 5, and the second drying step was not performed after heat treatment with a hot roller at a temperature of 120°C for 15 seconds as a pre-drying step, and various evaluations were performed. The results are shown in Table 5, and it was found that the handleability was good and the elution property was also sufficiently high.

[0136] (Comparative Example 11) A sizing-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 25, except that the amount of sizing agent applied in the second step was changed as shown in Table 5. The results are shown in Table 1, and the dry FF friction coefficient was high and the handleability was insufficient.

[0137] (Comparative Example 12) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 25, except that the amount of sizing agent attached in the second step was changed as shown in Table 5. The results are shown in Table 1, and although the handleability was good, the amount of attachment was high and the elution was insufficient.

[0138] (Comparative Example 13) A sizing-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 25, except that (C-2) was used as compound (C) in the second step and the amount of sizing agent applied was changed as shown in Table 5. The results are shown in Table 5, and the dry FF friction coefficient was high and the handleability was insufficient.

[0139] (Comparative Example 14) A sizing-agent-coated carbon fiber bundle was obtained and various evaluations were carried out in the same manner as in Example 25, except that (C-6) was used as compound (C) in the second step and the amount of sizing agent applied was changed as shown in Table 5. The results are shown in Table 5, and the number of carbon atoms in the alkyl group was large, and the elution property was insufficient. [Industrial Applicability]

[0140] According to the present invention, it is possible to provide a sizing-agent-coated carbon fiber bundle that exhibits good handleability while the sizing agent on the carbon fiber bundle exhibits good elution into water in a water-washing step, thereby reducing contamination of the sizing agent into the matrix resin and stabilizing physical properties.The thermoplastic resin composite using the present invention is lightweight yet has excellent strength, and is therefore suitable for use in many fields, such as aircraft components, spacecraft components, automobile components, ship components, civil engineering and construction materials, and sporting goods. [Explanation of symbols]

[0141] 11: Unwinding process 12: Washing process 13:Drying process 14: Winding process 15: Free roller in front of the washing tank 16: Free roller in the washing tank 17: Free roller after washing tank 18:Washing tank 19: Free roller in front of the washing tank 20: Free roller in the washing tank 21: Free roller after washing tank 22:Washing tank 1a: Sizing agent-coated carbon fiber bundle 1b: Carbon fiber bundle coated with sizing agent after washing with water 1c: Carbon fiber bundle coated with sizing agent after washing and drying 1d: Water 1e: Water

Claims

1. A sizing-agent-coated carbon fiber bundle obtained by coating a carbon fiber bundle with a sizing agent containing a surfactant, wherein the total amount of the surfactant is 70 parts by mass or more relative to 100 parts by mass of the total amount of the sizing agent, and the sizing-agent-coated carbon fiber bundle satisfies all of the following (i) to (iii): The surfactant comprises a nonionic surfactant, and the nonionic surfactant satisfies any one of the following (vi) to (v): (i) The amount of the sizing agent attached is 0.15 parts by mass or more and 0.80 parts by mass or less per 100 parts by mass of the sizing-agent-coated carbon fiber bundle. (ii) The dry FF friction coefficient is 0.39 or less. (iii) The amount of sizing agent adhered after washing with water for 50 seconds is 0.12 parts by mass or less based on 100 parts by mass of the sizing-agent-coated carbon fiber bundle. (vi) HLB is 15 or more and 20 or less. (v) The HLB is 12 or more and less than 15, and the ratio of hydroxyl groups at molecular terminals is 50% or more. The amount of sizing agent attached after the 50-second water wash is measured as follows. The sizing-agent-coated carbon fiber bundle is passed through the water in the water washing tank via a free roller before the water washing tank, a free roller in the water washing tank, and a free roller after the water washing tank, and then passed through the water in the water washing tank via the same free roller before the water washing tank, a free roller in the water washing tank, and a free roller after the water washing tank, and then continuously passed through a drying process to dry the water and then wound up in a winding process. The water temperature is 25°C, the unwinding tension from the creel is 800 g, the process speed is 2.4 m / min, the diameter of the free roller in the water washing tank is 150 mm, and the contact angle between the sizing-agent-coated carbon fiber bundle and the free roller in the water washing tank is π rad. The liquid level is adjusted so that the underwater passage time in one water washing tank is 25 seconds, and the total time in the two water washing tanks is 50 seconds. The sizing-agent-coated carbon fiber bundle 1b after water washing is dried for 1 minute using non-contact drying at a drying temperature of 150°C to obtain a sizing-agent-coated carbon fiber bundle after water washing and drying. The amount of sizing agent attached to the sizing-coated carbon fiber bundle after washing and drying is measured to obtain the amount of sizing agent attached.

2. A sizing-agent-coated carbon fiber bundle obtained by coating a carbon fiber bundle with a sizing agent containing polyethylene glycol and a surfactant or containing a surfactant, wherein the sizing-agent-coated carbon fiber bundle satisfies all of the following (i) to (iii): The sizing agent-coated carbon fiber bundle, wherein the surfactant contains an anionic surfactant, and the ratio of hydrophilic groups in the anions constituting the anionic surfactant is 17% or more. Here, the hydrophilic group is a sulfate ester group (SO ４ -), sulfonic acid group (SO ３ -), carboxyl group (COO-), phosphate group (HPO ３ This applies to negatively charged sites such as hydroxyl groups (OH-), but does not include the hydrophilic backbone attached to them. (i) The amount of the sizing agent attached is 0.15 parts by mass or more and 0.80 parts by mass or less per 100 parts by mass of the sizing-agent-coated carbon fiber bundle. (ii) The dry FF friction coefficient is 0.39 or less. (iii) The amount of sizing agent adhered after washing with water for 50 seconds is 0.12 parts by mass or less based on 100 parts by mass of the sizing-agent-coated carbon fiber bundle. The amount of sizing agent attached after the 50-second water wash is measured as follows. The sizing-agent-coated carbon fiber bundle is passed through the water in the water washing tank via a free roller before the water washing tank, a free roller in the water washing tank, and a free roller after the water washing tank, and then passed through the water in the water washing tank via the same free roller before the water washing tank, a free roller in the water washing tank, and a free roller after the water washing tank, and then continuously passed through a drying process to dry the water and then wound up in a winding process. The water temperature is 25°C, the unwinding tension from the creel is 800 g, the process speed is 2.4 m / min, the diameter of the free roller in the water washing tank is 150 mm, and the contact angle between the sizing-agent-coated carbon fiber bundle and the free roller in the water washing tank is π rad. The liquid level is adjusted so that the underwater passage time in one water washing tank is 25 seconds, and the total time in the two water washing tanks is 50 seconds. The sizing-agent-coated carbon fiber bundle 1b after water washing is dried for 1 minute using non-contact drying at a drying temperature of 150°C to obtain a sizing-agent-coated carbon fiber bundle after water washing and drying. The amount of sizing agent attached to the sizing-coated carbon fiber bundle after washing and drying is measured to obtain the amount of sizing agent attached.

3. A sizing-agent-coated carbon fiber bundle obtained by coating a carbon fiber bundle with a sizing agent containing polyethylene glycol and a surfactant or containing a surfactant, wherein the sizing-agent-coated carbon fiber bundle satisfies all of the following (i) to (iii): A sizing-agent-coated carbon fiber bundle, wherein the total amount of surfactants is 70 parts by mass or more relative to 100 parts by mass of the total amount of organic components in the sizing agent, and the amount of amphoteric surfactants is 50 parts by mass or more of the total amount of surfactants. (i) The amount of the sizing agent attached is 0.15 parts by mass or more and 0.80 parts by mass or less per 100 parts by mass of the sizing-agent-coated carbon fiber bundle. (ii) The dry FF friction coefficient is 0.39 or less. (iii) The amount of sizing agent adhered after washing with water for 50 seconds is 0.12 parts by mass or less based on 100 parts by mass of the sizing-agent-coated carbon fiber bundle. The amount of sizing agent attached after the 50-second water wash is measured as follows. The sizing-agent-coated carbon fiber bundle is passed through the water in the water washing tank via a free roller before the water washing tank, a free roller in the water washing tank, and a free roller after the water washing tank, and then passed through the water in the water washing tank via the same free roller before the water washing tank, a free roller in the water washing tank, and a free roller after the water washing tank, and then continuously passed through a drying process to dry the water and then wound up in a winding process. The water temperature is 25°C, the unwinding tension from the creel is 800 g, the process speed is 2.4 m / min, the diameter of the free roller in the water washing tank is 150 mm, and the contact angle between the sizing-agent-coated carbon fiber bundle and the free roller in the water washing tank is π rad. The liquid level is adjusted so that the underwater passage time in one water washing tank is 25 seconds, and the total time in the two water washing tanks is 50 seconds. The sizing-agent-coated carbon fiber bundle 1b after water washing is dried for 1 minute using non-contact drying at a drying temperature of 150°C to obtain a sizing-agent-coated carbon fiber bundle after water washing and drying. The amount of sizing agent attached to the sizing-coated carbon fiber bundle after washing and drying is measured to obtain the amount of sizing agent attached.

4. The sizing-agent-coated carbon fiber bundle according to any one of claims 1 to 3, wherein the wet FM friction coefficient is 0.28 or less.

5. The sizing-agent-coated carbon fiber bundle according to any one of claims 1 to 3, wherein the amount of sizing agent attached after washing with water for 25 seconds is 0.12 parts by mass or less per 100 parts by mass of the sizing-agent-coated carbon fiber bundle. The amount of sizing agent attached after the 25-second water wash is measured as follows. The sizing-agent-coated carbon fiber bundle is passed through the water in the washing tank via a free roller before the washing tank, a free roller in the washing tank, and a free roller after the washing tank, and then continuously passes through a drying process to dry the water and then is wound up in a winding process. The water temperature is 25°C, the unwinding tension from the creel is 800 g, the process speed is 2.4 m / min, the diameter of the free roller in the washing tank is 150 mm, and the contact angle between the sizing-agent-coated carbon fiber bundle and the free roller in the washing tank is π rad. The liquid level is also adjusted so that the water passage time is 25 seconds. The sizing-agent-coated carbon fiber bundle 1b after washing is dried for 1 minute using non-contact drying at a drying temperature of 150°C to obtain a washed and dried sizing-agent-coated carbon fiber bundle. The sizing agent adhesion amount of this washed and dried sizing-agent-coated carbon fiber bundle is measured to obtain the sizing agent adhesion amount.

6. The sizing-agent-coated carbon fiber bundle according to claim 2, wherein the total amount of the surfactants is 70 parts by mass or more relative to 100 parts by mass of the total amount of the sizing agent.

7. 2. The sizing-agent-coated carbon fiber bundle according to claim 1, wherein the total amount of the surfactants is 70 parts by mass or more and the nonionic surfactant is 50 parts by mass or more relative to 100 parts by mass of the total amount of the sizing agents.

8. 4. The sizing-agent-coated carbon fiber bundle according to claim 1, wherein the surfactant has a weight average molecular weight Mw of 150 or more and 5,000 or less.

9. 3. The sizing-agent-coated carbon fiber bundle according to claim 2, wherein the total amount of the surfactants is 70 parts by mass or more and the anionic surfactant is 50 parts by mass or more of the total amount of the surfactants relative to 100 parts by mass of the total amount of the sizing agents.

10. 4. The sizing-agent-coated carbon fiber bundle according to any one of claims 1 to 3, further comprising, in addition to the polyethylene glycol and / or surfactant, 0.1 parts by mass or more and 30 parts by mass or less of an aliphatic or alicyclic compound in which one hydroxyl group is bonded to a carbon and / or an aliphatic or alicyclic compound in which two hydroxyl groups are bonded to two different carbons, relative to 100 parts by mass of the total amount of the sizing agent.

11. The sizing-agent-coated carbon fiber bundle according to any one of claims 1 to 3, wherein the amount of sizing agent attached after the 50-second water washing is 0.08 parts by mass or less relative to 100 parts by mass of the sizing-agent-coated carbon fiber bundle.

12. The sizing-agent-coated carbon fiber bundle according to any one of claims 1 to 3, wherein the amount of the sizing agent attached is 0.25 to 0.45 parts by mass per 100 parts by mass of the sizing-agent-coated carbon fiber bundle.

13. 4. The sizing agent-coated carbon fiber bundle according to claim 3, wherein the average number of carbon atoms in the alkyl groups constituting the amphoteric surfactant is 17 or less.

14. 4. The sizing-agent-coated carbon fiber bundle according to claim 1, wherein the absorbance at 600 nm of an extract obtained by extracting the carbon fiber bundle with distilled water for 1 minute is 0.06 or more.

15. 4. The sizing-agent-coated carbon fiber bundle according to claim 1, wherein the mass residual rate at 300°C when the polyethylene glycol and / or surfactant is heated in air at a rate of 10°C / min is 35% or less.

16. 4. The sizing-agent-coated carbon fiber bundle according to claim 1, wherein the mass residual rate at 350°C when the polyethylene glycol and / or surfactant is heated in air at a rate of 10°C / min is 30% or less.

17. The sizing-agent-coated carbon fiber bundle according to any one of claims 1 to 3, wherein the strand strength of the carbon fiber bundle is 4.0 GPa or more.

18. The method for producing a sizing-agent-coated carbon fiber bundle according to any one of claims 1 to 3, comprising a drying step of drying the sizing-agent-coated carbon fiber bundle at 120 to 260°C after a step of applying a sizing agent containing polyethylene glycol and / or a surfactant to the carbon fiber bundle.

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