Carbon fiber bundles containing sizing agent and their manufacturing method

Abstract

The present invention provides a carbon fiber bundle containing a sizing agent, which exhibits bundle properties suitable for handling and reduces the amount of sizing agent remaining after processing into an intermediate substrate by imparting a sizing agent that is easily thermally decomposed at low temperatures that can maintain the surface properties of the carbon fiber. It is particularly suitable for combination with thermoplastic resins that can reflect the surface properties of the carbon fiber.

Description

Technical Field

[0001] This invention relates to carbon fiber bundles containing a sizing agent and a method for manufacturing carbon fiber bundles containing a sizing agent. Background Technology

[0002] Carbon fiber is not only lightweight but also boasts excellent strength and modulus of elasticity. Therefore, it is used as a composite material combined with various matrix resins in many fields, including aircraft components, spacecraft components, automotive components, ship components, civil engineering materials, and sporting goods. A representative form of carbon fiber composite material is the molded product formed by press molding (a molding method involving degassing and shaping under pressure) of a preform obtained by laminating prepregs. This prepreg is typically manufactured by impregnating a carbon fiber matrix with continuous carbon fiber bundles arranged unidirectionally using resin. Composite materials using discontinuous carbon fibers (chopped fibers, meshes, etc.) with excellent shape-following capabilities for complex shapes and the ability to be molded in a short time have also been proposed. However, in terms of specific strength, specific stiffness, and other mechanical properties, as well as property stability, prepregs offer superior practical performance as structural materials.

[0003] In recent years, there has been a growing demand for carbon fiber reinforced composites, requiring molding materials with excellent formability, workability, and mechanical properties of the resulting molded products. Industrial applications also require higher economic efficiency and productivity. In response to these demands, the development of prepregs using thermoplastic resins as the matrix resin is underway. An example of a manufacturing method is as follows: A carbon fiber ribbon containing the powdered thermoplastic resin is formed by passing a thermoplastic resin slurry obtained by dispersing powdered thermoplastic resin using a surfactant; the carbon fiber ribbon is then impregnated with the thermoplastic resin using heat and pressure.

[0004] To fully utilize the superior properties of carbon fibers after composite processing, excellent workability during carbon fiber processing and minimizing fuzz entanglement or breakage caused by entanglement are crucial. Uncoated carbon fiber bundles lack cohesion, generating a large amount of fuzz. This fuzz accumulates during the prepreg manufacturing process, leading to a deterioration in prepreg quality. Therefore, to improve the workability of carbon fibers, a method is typically employed that coats the carbon fiber bundles with a sizing agent, imparting a friction-resistant coating to the carbon fiber surface (see Patent Documents 1 and 2).

[0005] If the sizing agent coated on the carbon fiber is prone to thermal decomposition, when the carbon fiber reinforced composite material is molded using a prepreg obtained by impregnating a matrix resin with a high molding temperature such as a super engineering plastic, the sizing agent heated to a high temperature decomposes or volatilizes, which can reduce the amount of gas in the matrix resin and thus suppress the internal voids of the molded article (see Patent Document 3).

[0006] In addition, before impregnating the matrix resin, in order to improve the adhesion between the carbon fiber and the matrix resin on the carbon fiber surface, oxidation treatments such as gas phase oxidation and liquid phase oxidation are usually performed on the carbon fiber to introduce oxygen-containing functional groups such as carboxyl groups and aldehyde groups on the carbon fiber surface (see Patent Document 4).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: U.S. Patent No. 3,957,716

[0010] Patent Document 2: Japanese Patent Application Publication No. 57-171767

[0011] Patent Document 3: International Publication No. 2020 / 0138139

[0012] Patent Document 4: Japanese Patent Application Publication No. 04-361619 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] On the other hand, when the sizing agent is removed from the carbon fiber surface by heat treatment as described above, depending on the type of sizing agent, there are cases where a high temperature is required for its thermal decomposition, the oxygen-containing functional groups on the carbon fiber surface that are required for the matrix resin to react with the physical properties also decompose, and the carbon fiber surface is different from the original carbon fiber surface.

[0015] That is, research is underway on suppressing the formation of fluff from carbon fibers by applying sizing agents, and research on sizing agents that are easily thermally decomposed. However, there is no concept of using sizing agents to suppress the formation of fluff caused by the breakage of single fibers in carbon fiber bundles during the processing of carbon fibers containing sizing agents that are easily thermally decomposed, and of decomposing the sizing agent at a temperature that can maintain the same surface state of the carbon fibers as before the sizing agent was applied, so that the state of the surface functional groups of the carbon fibers is more reflected in the carbon fiber reinforced composite material.

[0016] The present invention was made in view of the above circumstances, and its object is to provide a carbon fiber bundle containing a sizing agent and a method for manufacturing the same. In this method, even when the carbon fiber bundle containing the sizing agent has excellent operability, by making the sizing agent on the carbon fiber bundle exhibit good thermal decomposition properties and reducing the amount of sizing agent while maintaining the surface functional groups of the carbon fiber, the carbon fiber bundle containing the sizing agent is also suitable for manufacturing a prepreg blank of a carbon fiber reinforced composite material with a high heat-resistant thermoplastic resin as the matrix resin, minimal porosity, and reflecting the surface properties of the carbon fiber.

[0017] Methods for solving problems

[0018] The present invention for solving the above-mentioned problems is a carbon fiber bundle comprising carbon fiber and a sizing agent satisfying all of (i) to (iv) below.

[0019] (i) Satisfies either (a) or (b) below.

[0020] (a) The proportion of polyalkylene glycol structure in the total mass of the sizing agent is more than 60% by mass.

[0021] (b) The sizing agent contains an acetylene structure, and the proportion of the polyalkylene glycol structure in the total mass of the sizing agent is more than 20% by mass.

[0022] (ii) The heat loss rate A obtained under the following test conditions is less than 5.0%.

[0023] (iii) The heat loss rate B obtained under the following test conditions is 11.0% or more.

[0024] (iv) The heat loss rate C obtained under the following test conditions is 90.0% or higher.

[0025] <Calibration of heat A>

[0026] Weigh the sizing agent in the range of 10 ± 2 mg and denote the mass of this weighing as W. A0 (mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 140°C was determined and set as W. A1 (mg), calculate the rate of heat loss A according to the following formula (A).

[0027] Heat loss rate A (%) = {(W)} A0 -W A1 ) / W A0}×100···(A)

[0028] <Calibration of Heat B>

[0029] Weigh the sizing agent in the range of 10 ± 2 mg (let the mass of this weighing be W). B0 (mg)), the mass of the sizing agent at 250°C was determined using a thermogravimetric analyzer by heating it from 30°C to 250°C at a rate of 10°C / min in a nitrogen stream of 200 ml (1 atm, 25°C) / min. This mass was set as W. B1 (mg), calculate the rate of heat loss B according to the following formula (B).

[0030] Heat loss rate B (%) = {(W)} B0 -W B1 ) / W B0}×100···(B)

[0031] <Calibration of heat C>

[0032] Weigh the sizing agent in the range of 10 ± 2 mg (let the mass of this weighing be W). C0 (mg)), the mass of the sizing agent at 350°C was determined using a thermogravimetric analyzer by heating it from 30°C to 350°C at a rate of 10°C / min in a nitrogen stream of 200 ml (1 atm, 25°C) / min. This mass was set as W. C1 (mg), calculate the loss on heat C according to the following formula (C).

[0033] Heat loss rate C (%) = {(W)} C0 -W C1 ) / W C0}×100···(C).

[0034] Furthermore, the method for manufacturing carbon fiber bundles containing sizing agent according to the present invention is characterized by a drying step of drying the carbon fiber bundles containing sizing agent after the step of containing sizing agent in the carbon fiber bundles.

[0035] The effects of the invention

[0036] According to the present invention, even when the carbon fiber bundle containing the sizing agent has excellent workability, by containing a sizing agent in the carbon fiber that is easily thermally decomposed at low temperatures due to its good thermal decomposition properties, it is possible to obtain a carbon fiber bundle containing the sizing agent that yields a carbon fiber reinforced composite material with very few voids and reflects the surface properties of the carbon fiber, which is particularly suitable for combination with thermoplastic resins. Detailed Implementation

[0037] The following describes the method for carrying out the present invention. The carbon fiber bundle containing sizing agent of the present invention is a carbon fiber bundle comprising carbon fibers and a sizing agent satisfying all of (i) to (iv) below.

[0038] (i) Satisfies either (a) or (b) below.

[0039] (a) The proportion of polyalkylene glycol structure in the total mass of the sizing agent is more than 60% by mass.

[0040] (b) The sizing agent contains an acetylene structure, and the proportion of the polyalkylene glycol structure in the total mass of the sizing agent is more than 20% by mass.

[0041] (ii) The heat loss rate A obtained under the following test conditions is less than 5.0%.

[0042] (iii) The heat loss rate B obtained under the following test conditions is 11.0% or more.

[0043] (iv) The heat loss rate C obtained under the following test conditions is 90.0% or higher.

[0044] <Calibration of heat A>

[0045] Weigh the sizing agent in the range of 10 ± 2 mg (let the mass of this weighing be W). A0 (mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (volume at 1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 140°C was determined (this measured mass is denoted as W). A1 (mg)), calculate the rate of heat loss A according to the following formula (A).

[0046] Heat loss rate A (%) = {(W)} A0 -W A1 ) / W A0}×100···(A)

[0047] <Calibration of Heat B>

[0048] Weigh the sizing agent in the range of 10 ± 2 mg (let the mass of this weighing be W). B0 (mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (volume at 1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 250°C was determined (this measured mass is denoted as W). B1 (mg)), calculate the loss on heat B according to the following formula (B).

[0049] Heat loss rate B (%) = {(W)} B0 -W B1 ) / W B0}×100···(B)

[0050] <Calibration of heat C>

[0051] Weigh the sizing agent in the range of 10 ± 2 mg (let the mass of this weighing be W). C0 (mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (volume at 1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 350°C was determined (this measured mass is denoted as W). C1 (mg)), calculate the loss on heat C according to the following formula (C).

[0052] Heat loss rate C (%) = {(W)} C0 -W C1 ) / WC0}×100···(C).

[0053] According to the inventors' research, when using sizing agents that improve workability in carbon fibers, there are issues such as decreased thermal decomposability of the sizing agent on the carbon fiber bundles containing the sizing agent, leading to sizing agent residue and void formation during prepreg fabrication; furthermore, heating at high temperatures to further thermally decompose the sizing agent fails to reflect the original surface properties of the carbon fibers. To address these issues, it has been discovered that even when using sizing agents with high workability, thermal decomposability can be controlled by adjusting the proportion of alkylene glycol structures in the total sizing agent, or by including acetylene structures and controlling the proportion of alkylene glycol structures. This allows for a balance between high workability of the sizing agent-containing carbon fiber bundles and good low-temperature thermal decomposability of the sizing agent.

[0054] The sizing agent constituting the present invention needs to satisfy either (a) or (b) below.

[0055] (a) The proportion of polyalkylene glycol structure in the total mass of the sizing agent is more than 60% by mass.

[0056] (b) The sizing agent contains an acetylene structure, and the proportion of the polyalkylene glycol structure in the total mass of the sizing agent is more than 20% by mass.

[0057] The structure of polyalkylene glycol is the following general formula (1).

[0058] [Chemical Formula 1]

[0059] -[CH2-CH(R)-O] n General formula (1)

[0060] In general formula (1), R is a hydrogen atom or a methyl group.

[0061] n is an integer from 2 to 20.

[0062] Carbon fiber bundles containing a sizing agent with a controlled proportion of polyalkylene glycol structure decompose well during thermal decomposition without reacting with the carbon fiber surface. As a result, the amount of sizing agent remaining in the carbon fiber bundle is reduced, and the original carbon fiber surface state is easily maintained. In formula (1), R is a hydrogen atom or a methyl group, and from the viewpoint of water solubility, a hydrogen atom is preferred. n is an integer from 2 to 20, and from the viewpoint of reducing molecular weight and improving thermal decomposability, it is preferred to be smaller, more preferably 5 or less, and even more preferably 3 or less. When n is an integer of 21 or more, the molecular weight increases, and the thermal decomposability decreases.

[0063] Examples of sizing agents comprising the structure represented by general formula (1) include polyethylene glycol, acetylene glycol, polyoxyethylene dodecyl ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene alkyl ether, propylene glycol, polyoxyethylene polyoxypropylene glycol, and polyoxyethylene alkylphenyl ether. Each can be used alone or in combination of two or more.

[0064] Acetylene has a structure with triple bonds between carbon atoms. Examples of sizing agents containing acetylene structures include acetylenol and acetylenediol.

[0065] It should be noted that the above-mentioned sizing agent can be one type or a mixture of two or more sizing agents.

[0066] Regarding requirement (a), the proportion of polyalkylene glycol structure in the total mass of the sizing agent is preferably 80% by mass or more, and the higher the proportion of polyalkylene glycol structure, the more preferred, and even more preferably 85% by mass. When the proportion of polyalkylene glycol structure is less than 60% by mass in the total mass of the sizing agent, the contact probability of the sizing agent that is difficult to react with the surface functional groups of carbon fiber becomes smaller, the heat resistance increases and it becomes less prone to thermal decomposition.

[0067] For reference, the proportion of polyalkylene glycol structure when the sizing agent is only diethylene glycol (HO(CH2CH2O)2H) is approximately 83% by mass ((106-18) / 106×100 (Note: atomic weights are omitted below the decimal point), and the proportion of polyalkylene glycol structure when the sizing agent is only triethylene glycol (HO(CH2CH2O)3H) is approximately 88% by mass ((150-18) / 150×100 (Note: atomic weights are omitted below the decimal point).

[0068] Regarding requirement (b), if the sizing agent contains an acetylene structure, the proportion of the polyalkylene glycol structure in the total mass of the sizing agent must be 20% by mass or more. When the acetylene structure is included, it has a triple bond, thus the compound is more linear, and the interleaved interactions are reduced. Therefore, if the proportion of the polyalkylene glycol structure is 20% by mass or more, it exhibits good thermal decomposition properties. If it is less than 20% by mass, the proportion of the acetylene structure increases, thereby increasing heat resistance and making it less prone to thermal decomposition. In the case of containing an acetylene structure, the proportion of the polyalkylene glycol structure in the total mass of the sizing agent is more preferably 50% by mass or more.

[0069] For reference, the proportion of acetylene structure in the case where the sizing agent is only bis(1-hydroxyethyl)acetylene (CH3CH(OH)CCCH(OH)CH3) is approximately 21% by mass (24 / 114×100 (Note: atomic weights are omitted below the decimal point)).

[0070] Regarding the proportions of polyalkylene glycol structures and acetylene structures in the total sizing agent contained in carbon fibers, if the structural formula of the sizing agent is known, it can be calculated from the structural formula. If the structural formula is unknown, the sizing agent can be extracted from the carbon fiber bundle containing the sizing agent, and its structure can be identified and the proportions calculated using known methods such as proton NMR, carbon NMR, mass spectrometry, and TOF-SIMS. If multiple components are present, chromatographic column separation and evaluation are used. An example of extraction conditions is shown below.

[0071] <Extraction criteria>

[0072] Add 1 g of sizing agent to 100 mL of a solution prepared by mixing chloroform and methanol in a 1:1 ratio, then irradiate with ultrasound for 30 minutes and let stand overnight. Recover the resulting extract and evaporate to dryness. Calculate the mass percentage of the extract relative to the carbon fiber bundle containing the sizing agent, and confirm that it is consistent with the determination of the sizing agent content in the carbon fiber bundle within an error range of 10%. If inconsistencies persist even after multiple repetitions, the extract is excluded from the scope of this invention.

[0073] When a sizing agent contained in carbon fiber bundles contains epoxy, amino, or oxazoline groups (other than the polyalkylene glycol structure), these groups react with the surface functional groups of the carbon fibers, increasing their heat resistance and making them less prone to thermal decomposition. Therefore, sizing agents containing epoxy, amino, or oxazoline groups are preferably 30% by mass or less of the total sizing agent, and preferably substantially free of them. "Substantially free of" means less than 1% by mass of the sizing agent out of 100% by mass.

[0074] Whether the sizing agent on the carbon fiber bundle contains epoxy, amino, or oxazoline groups can be determined by calculating the sizing agent's structure if the structure is known. If the structure is unknown, the sizing agent can be extracted from the carbon fiber bundle containing it, and its structure and proportion can be determined using known methods such as proton NMR, carbon NMR, mass spectrometry, and TOF-SIMS. If multiple components are present, a column chromatography step-by-step separation and evaluation can be performed to identify the structure and calculate the proportion.

[0075] The heat loss rate A of the sizing agent constituting the present invention, as determined under the following testing conditions, must be less than 5.0%.

[0076] <Determination conditions for heat loss rate A>

[0077] Weigh the sizing agent in the range of 10±2 mg (let the mass of this weighing be W). A0 (mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (volume at 1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 140°C was determined (this measured mass is denoted as W). A1(mg)), calculate the rate of heat loss A according to the following formula (A).

[0078] Heat loss rate A (%) = {(W)} A0 -W A1 ) / W A0}×100···(A)

[0079] If the heat loss rate A is below 5.0%, then when the sizing agent is applied to the untreated carbon fiber, the thermal decomposition and volatilization of the sizing agent can be suppressed. Therefore, carbon fiber bundles containing sizing agent can be obtained with less fuzzing caused by mechanical friction such as fiber opening and excellent handling properties.

[0080] If the heat loss rate A exceeds 5.0%, the sizing agent contains a large amount of components that increase the heat loss rate A. These components that increase the heat loss rate A have small molecular weights. The force adhering to the carbon fibers decreases; therefore, the larger the heat loss rate A, the less likely the sizing agent can adhere to the carbon fibers, resulting in carbon fiber bundles with poor workability containing the sizing agent.

[0081] The rate of heat loss A is preferably 3.0% or less, more preferably 1.0% or less. A smaller value for the rate of heat loss A is preferred, and particularly preferably 0%. That is, the lower limit of the rate of heat loss A is preferably 0%.

[0082] The heat loss rate B of the sizing agent constituting the present invention, as determined under the following testing conditions, must be 11.0% or more.

[0083] <Calibration of Heat B>

[0084] Weigh the sizing agent in the range of 10±2 mg (let the mass of this weighing be W). B0 (mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (volume at 1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 250°C was determined (this measured mass is denoted as W). B1 (mg)), calculate the loss on heat B according to the following formula (B).

[0085] Heat loss rate B (%) = {(W)} B0 -W B1 ) / W B0}×100···(B)

[0086] If the heat loss rate B is 11.0% or higher, then during the stage of heating the carbon fiber bundles containing the sizing agent at low temperature, the generation of gases caused by the thermal decomposition or volatilization of the sizing agent almost ends and is removed from the carbon fiber reinforced composite material. Therefore, it is less likely to leave voids, and a high-quality molded article (carbon fiber reinforced composite material) that can exhibit the surface characteristics of the original carbon fiber can be obtained.

[0087] If the heat loss rate B is less than 11.0%, the sizing agent contains a large amount of components that reduce the heat loss rate B. These components that reduce the heat loss rate B have large molecular weights and are easily coated on the carbon fiber surface. Therefore, the smaller the heat loss rate B, the more likely the surface of the heat-treated carbon fiber bundle will be different from that of the original carbon fiber, resulting in a carbon fiber bundle containing the sizing agent.

[0088] The rate of heat loss B is preferably 30.0% or more, more preferably 60.0% or more, and even more preferably 90.0% or more. A higher value for the rate of heat loss B is preferred, and particularly preferably 100.0%. That is, the upper limit of the rate of heat loss B is preferably 100.0%.

[0089] The heat loss rate C of the sizing agent constituting the present invention must be 90.0% or more under the following test conditions.

[0090] <Calibration of heat C>

[0091] Weigh the sizing agent in the range of 10 ± 2 mg (let the mass of this weighing be W). C0 (mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (volume at 1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 350°C was determined (this measured mass is denoted as W). C1 (mg)), calculate the loss on heat C according to the following formula (C).

[0092] Heat loss rate C (%) = {(W)} C0 -W C1 ) / W C0}×100···(C).

[0093] If the heat loss rate C is above 90.0%, then at the end of the heating stage of the carbon fiber bundle containing the sizing agent, the generation of gas caused by the decomposition or volatilization of the sizing agent almost ends and is removed from the carbon fiber reinforced composite material. Therefore, it is not easy to leave voids, and high-quality carbon fiber reinforced composite materials can be obtained.

[0094] If the heat loss rate C is less than 90.0%, the sizing agent contains a large amount of components that reduce the heat loss rate C. These components that reduce the heat loss rate C have high heat resistance in air and easily become residues on the carbon fiber surface. Therefore, the smaller the heat loss rate C, the more likely the surface of the heat-treated carbon fiber bundle will be different from that of the original carbon fiber, resulting in a carbon fiber bundle containing the sizing agent.

[0095] The rate of heat loss C is 90.0% or more, more preferably 95.0% or more, and even more preferably 99.0% or more. A higher value for the rate of heat loss C is preferred, and particularly preferably 100.0%. That is, the upper limit of the rate of heat loss C is preferably 100.0%.

[0096] The heat loss rate A, heat loss rate B, and heat loss rate C can be controlled by changing the elements contained in the sizing agent, the types of some structures, and the number-average molecular weight Mn (described later).

[0097] It should be noted that no difference was found in the values ​​for heat loss rate A, heat loss rate B, and heat loss rate C when evaluating the sizing agent and when evaluating the sizing agent extracted from carbon fiber bundles containing the sizing agent under the following extraction conditions.

[0098] <Extraction criteria>

[0099] Add 1 g of sizing agent to 100 mL of a solution prepared by mixing chloroform and methanol in a 1:1 ratio, then irradiate with ultrasound for 30 minutes and let stand overnight. Recover the resulting extract and evaporate to dryness. Calculate the percentage of the extract relative to the sizing agent content in the carbon fiber bundle, confirming consistency with the determination of the sizing agent content in the carbon fiber bundle within an error range of 10%.

[0100] The number-average molecular weight (Mn) of the sizing agent constituting the present invention is preferably 120 or more and less than 300. The above-mentioned number-average molecular weight (Mn) is determined by gel permeation chromatography (hereinafter referred to as GPC), using polystyrene as a standard. By making Mn less than 300, the molecular chain is shortened and the thermal decomposability is improved, thus enabling thermal decomposition at a lower temperature and in a shorter time. More preferably, it is 250 or less, and even more preferably 200 or less. On the other hand, from the perspective of imparting properties, by having Mn of 120 or more, when it is present in untreated carbon fibers, the volatilization and thermal decomposition of the sizing agent can be suppressed. More preferably, it is 135 or more.

[0101] The number-average molecular weight Mn of the sizing agent on the carbon fiber bundle containing the sizing agent can be confirmed by extracting the sizing agent from the carbon fiber bundle containing the sizing agent using the extraction method described above and then performing GPC evaluation.

[0102] <Method for determining number-average molecular weight Mn>

[0103] The number-average molecular weight of the sizing agent can be determined by a known method using GPC with polystyrene as a standard. In this invention, the following conditions are used as the determination conditions for GPC.

[0104] Measuring device: Shimadzu Corporation

[0105] Chromatographic column used: TOSOH BIOSCIENCE TSKgel HXL-L + TSKgel α-3000

[0106] Eluent: 0.01 mol / L lithium bromide solution with dimethylformamide

[0107] Standard material: Polystyrene (manufactured by Tosoh Corporation)

[0108] Detector: Differential refractometer (manufactured by Shimadzu Corporation).

[0109] It should be noted that when there are multiple components constituting the sizing agent of the present invention, the measured value of their mixture is taken as the number-average molecular weight Mn.

[0110] The sizing agent used in this invention is preferably substantially free of aromatic rings. Structures containing aromatic rings such as bisphenol A and benzene have high heat resistance, and therefore, if contained in the sizing agent, their thermal decomposition properties decrease. "Substantially free of" means less than 1% by mass in 100% by mass of the sizing agent.

[0111] Regarding the proportion of aromatic rings in the sizing agent on carbon fiber bundles containing sizing agent, if the structural formula of the sizing agent is known, it can be determined based on the structural formula. If the formula is unknown, the sizing agent can be extracted from the carbon fiber bundle containing the sizing agent, and its structure can be identified using known methods such as proton NMR, carbon NMR, mass spectrometry, and TOF-SIMS to calculate the proportion. If there are multiple components, a column chromatography step-by-step separation operation can be used for evaluation to identify the structure and calculate the proportion.

[0112] The sizing agent content in the carbon fiber bundle containing the sizing agent constituting the present invention is preferably 0.3% to 1.2% by mass out of 100% by mass of the carbon fiber bundle containing the sizing agent. It should be noted that when the carbon fiber bundle contains multiple sizing agents, the total amount of the multiple sizing agents is taken as the sizing agent content of the carbon fiber bundle.

[0113] By setting the sizing agent content to 0.3% by mass or more, the workability of the carbon fiber bundles containing the sizing agent can be improved, the generation of fuzz during manufacturing and processing can be suppressed, and the smoothness and other qualities of the carbon fiber sheets can be improved. The adhesion amount is more preferably 0.4% by mass or more, and even more preferably 0.5% by mass or more. On the other hand, by setting the sizing agent content to 1.2% by mass or less, the residual amount can be reduced at low temperature and for a short time, thus reducing the impact on the matrix resin. The sizing agent content is more preferably 1.0% by mass or less, and even more preferably 0.8% by mass or less.

[0114] Regarding the carbon fiber bundle containing the sizing agent constituting the present invention, using AlKα as the X-ray source, the carbon fiber surface C was measured by X-ray photoelectron spectroscopy at a photoelectron emission angle of 45° at a carbon fiber surface heated at 250° for 20 seconds in an oxidizing atmosphere. 1s The ratio of the photoelectron intensity (b) (cps) detected at the bond energy of 286.1 eV (CO) to the photoelectron intensity (a) (cps) detected at the bond energy of 284.6 eV (CC) (photoelectron intensity (b) / photoelectron intensity (a)) is preferably 0.2 or more and 0.8 or less.

[0115] It should be noted that, in the following, AlKα will sometimes be used as the X-ray source, and the carbon content of the fiber surface will be measured by X-ray photoelectron spectroscopy at a photoelectron emission angle of 45°. 1s The ratio of the photoelectron intensity (b) (cps) detected at the bond energy of 286.1 eV (CO) to the photoelectron intensity (a) (cps) detected at the bond energy of 284.6 eV (CC) is denoted as "photoelectron intensity ratio (b) / (a)" or simply "photoelectron intensity ratio".

[0116] The surface of carbon fiber contains multiple carbon atoms of different types and bonding states among its neighboring atoms. Therefore, the carbon content of the carbon fiber surface measured by X-ray photoelectron spectroscopy... 1s The core level energy spectrum is obtained as a composite peak of multiple sub-peaks with different bond energies. C 1s The bond energy of 284.6 eV in the core level spectrum is the bond energy at the center of the sub-peaks belonging to the bonding states CH, CC, and C=C. On the other hand, C... 1s The bond energy of 286.1 eV in the core level spectrum is the central position of the sub-peak that corresponds to the bonded state belonging to CO. Therefore, the photoelectron intensity ratio (b) / (a) of the photoelectron intensity detected at bond energy 284.6 eV (a)(cps) to that detected at bond energy 286.1 eV (b)(cps) represents the proportion of carbon atoms with CO bonds on the carbon fiber surface. The smaller the photoelectron intensity ratio (b) / (a), the fewer carbon atoms with CO bonds there are.

[0117] In this invention, when the photoelectron intensity ratio (b) / (a) of the carbon fiber surface is 0.8 or less, the amount of sizing agent with CO bonds remaining on the carbon fiber surface is very small, which is a preferred range. The smaller the value, the closer the surface of the carbon fiber after heat treatment is to the surface of the carbon fiber before containing the sizing agent. Therefore, the surface properties of the original carbon fiber can be reflected in the matrix resin. In particular, 0.5 or less is a further preferred range. When it is 0.2 or more, the surface functional groups of the original carbon fiber remain, and the surface properties can be reflected in the matrix resin. In particular, 0.3 or more is a more preferred range.

[0118] In heating, an oxidizing atmosphere refers to an atmosphere containing a large amount of oxidizing gases (oxygen, ozone, etc.), and from an operational point of view, air is preferred.

[0119] Heating carbon fiber bundles containing sizing agent at 250°C for 20 seconds can be performed using the following steps: The carbon fiber bundles containing sizing agent are introduced into a heated air atmosphere via rollers to thermally decompose the sizing agent. The carbon fiber bundles containing sizing agent, which are part of the winding process, are passed through the heating furnace via free rollers before and after the furnace, thereby being wound in the winding process. The unwinding tension from the spool holder is set to 800g, the process speed is set to 6m / min, the 250°C range in the heating furnace is adjusted to 2m, and the heating time is set to 20 seconds. The content of the sizing agent after heat treatment is obtained by measuring the photoelectron intensity ratio (b) / (a) of the carbon fiber surface and the sizing agent content in the carbon fiber bundle using XPS.

[0120] The sizing agent content of the carbon fiber bundle containing the sizing agent of the present invention, after being heat-treated at 250°C for 20 seconds in an oxidizing atmosphere, can be 0.02% by mass or more and 0.1% by mass or less. It should be noted that when the carbon fiber bundle contains multiple sizing agents, the total amount of the multiple sizing agents is taken as the sizing agent content of the carbon fiber bundle.

[0121] If the sizing agent content after heat treatment at 250°C for 20 seconds in an oxidizing atmosphere is less than 0.1% by mass, the generation of gases caused by the thermal decomposition or volatilization of the sizing agent is almost completely stopped and removed from the carbon fiber reinforced composite material. Therefore, it is less likely to leave voids, and a high-quality molded article (carbon fiber reinforced composite material) that reflects the surface properties of the original carbon fibers can be obtained. In particular, the sizing agent content is more preferably less than 0.08% by mass, more preferably less than 0.06% by mass, and 0.04% by mass or less is a particularly preferred range.

[0122] When the content of the sizing agent after heat treatment at 250°C for 20 seconds in an oxidizing atmosphere is 0.02% by mass or more, the surface functional groups of the original carbon fiber are maintained, which is therefore a preferred range.

[0123] In this invention, the amount of oxygen atoms present on the surface of the carbon fiber before applying the sizing agent is not particularly limited. From the viewpoint of the mechanical properties of the obtained carbon fiber reinforced composite material, it is preferable that the surface oxygen concentration (functional group content, O / C) of the carbon fiber, as measured by X-ray photoelectron spectroscopy, is 0.11 or more and 0.25 or less, more preferably 0.15 or more and 0.20 or less. When the surface functional group content of the carbon fiber is too low, the adhesion between the carbon fiber and the matrix resin tends to decrease; on the other hand, when the functional group content is too high, the functional groups are prone to decomposition during the processing of the carbon fiber reinforced composite material accompanied by heating. Therefore, the difference in the functional group content before and after processing is large, and it tends to be difficult to reflect the original characteristics of the carbon fiber.

[0124] The carbon fibers used in this invention, before being coated with the sizing agent, preferably have a fiber-to-fiber friction coefficient of 0.25 or higher and 0.43 or lower. When the coefficient is 0.25 or higher, it is easier to apply force between individual fibers, thus improving the bundle cohesion. More preferably, it is 0.28 or higher, and even more preferably, it is 0.30 or higher. When the coefficient is 0.43 or lower, the friction between the individual filaments within the carbon fiber bundle decreases, thereby reducing the fuzz generated by friction when the carbon fiber bundle is pulled from the bobbin. More preferably, it is 0.39 or lower, and even more preferably, it is 0.35 or lower. The fiber-to-fiber friction coefficient can be controlled by the surface roughness of the carbon fiber, the type and amount of surface treatment, etc.

[0125] The components constituting the carbon fiber bundle containing the sizing agent used in this invention will now be described.

[0126] There are no particular limitations on the carbon fiber used in this invention, but from the viewpoint of mechanical properties, polyacrylonitrile-based carbon fibers are preferred. The polyacrylonitrile-based carbon fibers used in this invention can be obtained by: subjecting a carbon fiber precursor fiber containing a polyacrylonitrile polymer to a flame-retardant treatment at a maximum temperature of 200–300°C in an oxidizing atmosphere, then performing a pre-carbonization treatment at a maximum temperature of 500–1200°C in an inactive atmosphere, followed by a carbonization treatment at a maximum temperature of 1200–2000°C in an inactive atmosphere.

[0127] In this invention, to improve the adhesion between the carbon fiber bundle and the matrix resin, it is preferable to introduce oxygen-containing functional groups into the surface by performing an oxidation treatment on the carbon fiber bundle. As an oxidation treatment method, gas-phase oxidation, liquid-phase oxidation, and liquid-phase electrolytic oxidation can be used, but from the viewpoint of high productivity and uniform processing, liquid-phase electrolytic oxidation is preferred.

[0128] In this invention, acidic and alkaline electrolytes can be used as electrolytes in liquid-phase electrolytic oxidation. 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 bisulfate. Sulfuric acid and nitric acid, which exhibit strong acidity, are preferred. Examples of alkaline electrolytes include aqueous solutions of hydroxides such as sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, and barium hydroxide; aqueous solutions of carbonates such as sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, and ammonium carbonate; aqueous solutions of bicarbonates such as sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, calcium bicarbonate, barium bicarbonate, and ammonium bicarbonate; and aqueous solutions of ammonia, tetraalkylammonium hydroxide, and hydrazine.

[0129] The method for manufacturing carbon fiber bundles containing a sizing agent as described in this invention will now be explained.

[0130] First, the means by which the sizing agent constituting the present invention is contained (imparted) in carbon fiber will be described.

[0131] In this invention, the sizing agent is preferably diluted with a solvent to form a homogeneous solution. Examples of such solvents include water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, dimethylformamide, and dimethylacetamide. Water is preferred because it is advantageous from the viewpoints of ease of operation and safety.

[0132] As a means of applying sizing agent, there are methods such as immersing carbon fiber bundles in a sizing agent solution via rollers, contacting carbon fiber bundles with rollers coated with a sizing agent solution, and spraying the sizing agent solution into a mist and onto the carbon fiber bundles. When manufacturing the carbon fiber bundles containing sizing agent according to the present invention, it is preferable to use the method of immersing carbon fibers in a sizing agent solution via rollers. Furthermore, the means of applying the sizing agent can be either batch or continuous, with a continuous method preferred due to its high productivity and ability to reduce deviations. Additionally, applying ultrasonic vibration to the carbon fibers during sizing is also a preferred method.

[0133] In this invention, it is preferable to apply a sizing agent solution and then, as a drying step, use a contact drying method, such as drying the carbon fiber bundle by contacting it with a heated roller, to obtain a carbon fiber bundle containing the sizing agent. The carbon fiber bundle introduced into the heated roller is pressed against the heated roller due to tension and is dried rapidly. Therefore, the flattened shape of the carbon fiber bundle, broadened by the heated roller, is easily fixed by the sizing agent. The contact area between the individual fibers of the flattened carbon fiber bundle is reduced, thus increasing the contact area with the gas during the heating and decomposition of the sizing agent, and making the decomposition efficiency easier to increase. Furthermore, in this invention, after passing through the heated roller as a pre-drying step, a heat treatment can be further applied as a second drying step. In this second drying step, a non-contact heating method that allows for easy implementation of high-temperature heat treatment is preferred. By performing this heat treatment, residual diluent in the sizing agent can be further removed, stabilizing the viscosity of the sizing agent, and thus steadily improving the solubility. The preferred drying temperature is in the range of 110–140°C. At temperatures above 110°C, the moisture content of the sizing agent can be reduced, thus easily improving thermal decomposition resistance. More preferably, the temperature is above 120°C. On the other hand, by setting the upper limit of the drying temperature to 140°C or below, partial volatilization of the sizing agent can be suppressed, making it easier to maintain workability. More preferably, the temperature is below 135°C.

[0134] In addition, the heat treatment can also be performed by microwave irradiation and / or infrared irradiation.

[0135] Example

[0136] The present invention will now be specifically described through embodiments, but the present invention is neither limited to nor construed as such in these embodiments.

[0137] <Methods for determining the sizing agent content and thermal decomposition of carbon fibers in carbon fiber bundles>

[0138] After weighing carbon fiber bundles (W1(g)) containing 2.0±0.5g of sizing agent (read to 4 decimal places), they were placed in an electric furnace (capacity 120cm³) at a temperature set to 450°C in a nitrogen flow of 50 mL / min. 3 The carbon fiber bundle was placed in a container for 15 minutes to allow complete thermal decomposition of the sizing agent. Then, it was transferred to a container in a dry nitrogen stream of 20 L / min, and the carbon fiber bundle was weighed after 15 minutes of cooling (W2(g)) (read to 4 decimal places). The mass of the sizing agent was calculated from W1-W2. This mass of the sizing agent was converted to a mass percentage relative to 100% of the mass of the carbon fiber bundle containing the sizing agent, and the resulting value (rounded to the 3rd decimal place) was taken as the sizing agent content (mass%). Two measurements were performed, and the average value was taken as the sizing agent content. In the case where the carbon fiber did not contain sizing agent, the value obtained in this measurement was the amount of thermal decomposition of the carbon fiber.

[0139] In this invention, the preferred range of sizing agent content in carbon fiber bundles after heat treatment at 250°C for 20 seconds under an oxidizing atmosphere is evaluated in four grades according to the following criteria.

[0140] A: The sizing agent content is 0.02% by mass or more but less than 0.06% by mass.

[0141] B: The sizing agent content is ≥0.06% by mass and <0.08% by mass.

[0142] C: The content of sizing agent is between 0.08% and 0.10% by mass.

[0143] D: The sizing agent content is less than 0.02% by mass or greater than 0.10% by mass.

[0144] <Surface oxygen concentration (O / C) of carbon fiber>

[0145] The surface oxygen concentration (O / C) of carbon fibers was determined by X-ray photoelectron spectroscopy according to the following steps. 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 The sample chamber was kept at a temperature of 1×10. -8 Torr, with the photoelectron emission angle set to 45°, performed X-ray photoelectron spectroscopy measurements. It should be noted that C was used as a correction value for the peak associated with charging during the measurement. 1S The bond energy of the main peak was adjusted to 285 eV. C was determined by plotting a linear baseline in the range of 275 to 290 eV. 1S Peak area is used as the bond energy value. O is determined by plotting a linear baseline in the range of 525 to 540 eV. 1s Peak area is used as bond energy. The X-ray photoelectron spectroscopy apparatus used is the ULVAC-PHI ESCA-1600.

[0146] <Photoelectron intensity ratio of carbon fiber surface (b) / (a)>

[0147] The photoelectron intensity ratio (b) / (a) of the carbon fiber surface is based on the C obtained according to the steps described above. 1s The core level energy spectrum is obtained by following these steps. The C0 value will then be calculated. 1S The linear baseline of the peak area of ​​282–292 eV is defined as the origin of the photoelectron intensity. The photoelectron intensity (a) detected at the bond energy of 284.6 eV (cps) and the photoelectron intensity (b) detected at the bond energy of 286.1 eV (cps) are calculated, and (b) / (a) is calculated.

[0148] In the present invention, the preferred range of equivalence with the surface state of the original carbon fiber is evaluated in four grades according to the following criteria.

[0149] A: The photoelectron intensity ratio (b) / (a) is 0.3 or more and 0.5 or less.

[0150] B: The photoelectron intensity ratio (b) / (a) is greater than 0.5 and 0.6 or less.

[0151] C: The photoelectron intensity ratio (b) / (a) is 0.2 or more and less than 0.3, or greater than 0.6 and 0.8 or less.

[0152] D: The photoelectron intensity ratio (b) / (a) is less than 0.2, or greater than 0.8.

[0153] <Method for Measuring Fiber-Fiber Friction Coefficient>

[0154] The fiber-fiber friction coefficient is obtained according to the following steps. On a bobbin fixed in a non-rotating manner, on the surface of a carbon fiber bundle containing a sizing agent wound in a range of thickness of 5 to 10 mm and winding density of 0.9 to 1.4 g / cm 3 so that the thickness becomes uniform, a carbon fiber bundle identical to the wound object is wound so that the contact angle becomes 3π (rad) and there is no overlap on the circumference. A weight (T1 = 0.25 g / tex) is applied to one end of the wound carbon fiber bundle, and the opposite end is stretched with a spring scale at a speed of 1 m / min. The tension when the wound carbon fiber bundle starts to move is set as T2 (g / tex), and the fiber-fiber friction coefficient is calculated according to the following formula. Two measurements are performed, and the average value is taken as the fiber-fiber friction coefficient. It should be noted that the measuring bobbin is the one placed under the measuring atmosphere temperature and humidity conditions (measurement conditions: 23 ± 3°C / 60 ± 5%) for more than 2 hours before measurement.

[0155] Fiber-fiber friction coefficient = ln(T2 / T1) / θ

[0156] T2: Tension when the carbon fiber bundle moves

[0157] T1: Mass of the weight (= 0.25 g / tex)

[0158] θ: Total contact angle of the wound object and the wound wire (= 3π rad) <舍入误差的测定方法>

[0159] <Method for Measuring CF Friction Fluff>

[0160] Four metal rods (made of SUS304 stainless steel), each 20 mm in diameter and with a surface roughness Rmax (JIS B 0601 (1982)) of 0.3 μm, are arranged vertically at 150 mm intervals. The carbon fiber bundles contact and pass through the metal rods at an angle totaling 1.57π (rad). The carbon fiber bundles are then placed on the metal rods, and the unwinding tension from the package is set to 500 g. A drive roller pulls the carbon fiber bundles through the metal rods at a speed of 6 m / min. After passing through the fourth metal rod, the fiber yarn is illuminated from the side at a right angle, and the number of fibers is counted and recorded using a fiber detection device for one minute. In this invention, the preferred range of operability is evaluated on a three-level scale according to the following criteria: A and B are acceptable, and C is unacceptable.

[0161] A: Fewer than 4 fibers / m

[0162] B: The number of fibers is 4 or more per meter but less than 8 per meter.

[0163] C: The number of fibers per meter is 8 or more.

[0164] The materials and components used in each embodiment and comparative example are shown below.

[0165] (A) Ingredients:

[0166] A-1: Triethylene glycol

[0167] (Molecular weight: 150, manufactured by Fujifilm and Kohden Chemical Co., Ltd.)

[0168] A-2: Polyethylene glycol

[0169] (Molecular weight: 200, PEG200 manufactured by Sanyo Chemical Industries, Ltd.)

[0170] A-3: Ethynylene glycol surfactant

[0171] (Molecular weight: 290, manufactured by Nissin Chemical Industry Co., Ltd., "Surfynol (registered trademark)" 440)

[0172] A-4: Polyethylene glycol

[0173] (Molecular weight: 300, PEG300 manufactured by Sanyo Chemical Industries, Ltd.)

[0174] A-5: Polypropylene glycol

[0175] (Molecular weight: 400, Newpol GP400 manufactured by Sanyo Chemical Industries, Ltd.)

[0176] A-6: Diethylene glycol

[0177] (Molecular weight: 106, manufactured by Fujifilm and Kohden Chemical Co., Ltd.)

[0178] A-7: Polyethylene glycol

[0179] (Molecular weight: 600, PEG600 manufactured by Sanyo Chemical Industries, Ltd.)

[0180] A-8: Polypropylene glycol

[0181] (Molecular weight: 600, PPG600 manufactured by Sanyo Chemical Industries, Ltd.)

[0182] A-9: Ethylene glycol surfactant

[0183] (Molecular weight: 466, manufactured by Nissin Chemical Industry Co., Ltd., "Surfynol (registered trademark)" 465)

[0184] A-10: Bisphenol A ethylene oxide adduct

[0185] (Molecular weight: 490, Newpol BPE60 manufactured by Sanyo Chemical Industry Co., Ltd.)

[0186] A-11: Glyceryl polyglycidyl ether

[0187] (Molecular weight: 400, manufactured by Nagase ChemteX Co., Ltd., "Denacol (registered trademark)" Ex-313)

[0188] A-12: 4-tert-butylphenyl glycidyl ether

[0189] (Molecular weight: 206, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0190] A-13: Polyethyleneimine

[0191] (Molecular weight: 800, manufactured by BASF Japan Co., Ltd., "Lupasol (registered trademark)" FG).

[0192] First, let's explain the reference example. The reference example includes the following two steps.

[0193] (Refer to Example 1)

[0194] • The process of manufacturing carbon fiber as a raw material

[0195] Acrylonitrile copolymer was spun and sintered to obtain carbon fibers with a total filament count of 12,000, a total fineness of 800 tex, a tensile strength of 5.1 GPa, and a tensile modulus of elasticity of 240 GPa. Next, the carbon fiber bundle was subjected to electrolytic surface treatment using ammonium bicarbonate aqueous solution as the electrolyte and a charge of 80 coulombs per gram of carbon fiber. The treated carbon fibers were then washed with water and dried in heated air at 150°C to remove water, yielding the raw carbon fiber. The thermal decomposition amount, surface oxygen concentration, photoelectron intensity ratio of the carbon fiber bundle surface, and fiber-fiber friction coefficient of the carbon fiber obtained in the first step were measured. The results showed that the thermal decomposition amount of the carbon fiber bundle was 0.05% by mass, the surface oxygen concentration was 0.18, the photoelectron intensity ratio of the carbon fiber bundle surface was 0.4, and the fiber-fiber friction coefficient was 0.42.

[0196] Evaluation of sizing agent content and carbon fiber surface condition in heat-treated carbon fiber bundles

[0197] After heating the carbon fibers obtained in the previous process at 250°C for 20 seconds using the method described herein, the amount of thermal decomposition and the photoelectron intensity ratio of the carbon fiber bundle surface were then measured.

[0198] The results showed that the thermal decomposition rate of carbon fiber was 0.04% by mass and the photoelectron intensity ratio was 0.4, indicating that the values ​​after heat treatment were very close to those before treatment. The results are summarized in Table 1.

[0199] [Table 1]

[0200] Table 1

[0201]

[0202] (See Example 2 for reference)

[0203] In the evaluation of the sizing agent content and carbon fiber surface condition in the carbon fiber bundles after the above heat treatment, the heat treatment temperature was changed to 400°C. Otherwise, the heat-treated carbon fibers were obtained in the same manner as in Reference Example 1, and various evaluations were performed. The results are shown in Table 1. The photoelectron intensity ratio on the surface of the carbon fiber bundle decreased.

[0204] (Refer to Example 3)

[0205] In the aforementioned process of manufacturing carbon fibers as raw materials, the electrolytic surface treatment was changed to use 10 coulombs of charge per 1g of carbon fiber. Otherwise, carbon fibers were obtained in the same manner as in Reference Example 1, and various evaluations were performed. The results are shown in Table 1. It can be seen that the values ​​after heat treatment are very close to those before treatment, but the amount of functional groups in the original carbon fibers is low.

[0206] (Refer to Example 4)

[0207] In the aforementioned process of manufacturing carbon fibers as raw materials, the electrolytic surface treatment was changed to use 10 coulombs of charge per 1g of carbon fiber. In evaluating the sizing agent content and surface condition of the carbon fiber bundles after heat treatment, the heat treatment temperature was changed to 400°C. Otherwise, carbon fibers were obtained in the same manner as in Reference Example 1, and various evaluations were performed. The results are shown in Table 1. It can be seen that the values ​​after heat treatment are very close to those before treatment, but the amount of functional groups in the original carbon fibers is lower.

[0208] The following is a description of Embodiment 1. Embodiment 1 includes the following steps 1 to 4.

[0209] (Example 1)

[0210] • Step 1: The process of manufacturing carbon fiber as a raw material

[0211] Acrylonitrile copolymer was spun and sintered to obtain carbon fibers with a total filament count of 12,000, a total fineness of 800 tex, a bundle tensile strength of 5.1 GPa, and a bundle tensile modulus of elasticity of 240 GPa. Next, the carbon fiber bundle was subjected to electrolytic surface treatment using ammonium bicarbonate aqueous solution as the electrolyte and an electrolytic charge of 80 coulombs per gram of carbon fiber. The treated carbon fibers were then washed with water and dried in heated air at 150°C to remove water, yielding the raw carbon fibers. The surface oxygen concentration of the carbon fibers obtained in this first step, the ratio of photoelectron intensity on the surface of the carbon fiber bundle, and the fiber-to-fiber friction coefficient were measured.

[0212] • Step 2: The process of applying a sizing agent to the carbon fiber

[0213] As a sizing agent, (A-1) was dissolved in water according to the composition in Table 2 to obtain an aqueous solution of approximately 1.5% by mass. Using this aqueous solution as the sizing agent, the surface-treated carbon fiber bundles were impregnated with the sizing agent, followed by a drying process involving heat treatment at 120°C for 5 seconds using heated rollers to obtain carbon fiber bundles containing the sizing agent. The sizing agent content was adjusted to 0.7% by mass out of 100% of the total surface-treated carbon fiber bundles containing the sizing agent. Furthermore, the results of evaluating the heat loss rate of the sizing agent using the following methods were obtained: heat loss rate A was 4.8%, heat loss rate B was 99.5%, and heat loss rate C was 99.8%.

[0214] <Calibration of heat A>

[0215] Weigh the sizing agent in the range of 10 ± 2 mg (let the mass of this weighing be W). A0(mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (volume at 1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 140°C was determined (this measured mass is denoted as W). A1 (mg)), calculate the rate of heat loss A according to the following formula (A),

[0216] Heat loss rate A (%) = {(W)} A0 -W A1 ) / W A0}×100···(A)

[0217] <Calibration of Heat B>

[0218] Weigh the sizing agent in the range of 10 ± 2 mg (let the mass of this weighing be W). B0 (mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (volume at 1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 250°C was determined (this measured mass is denoted as W). B1 (mg)), calculate the rate of heat loss B according to the following formula (B),

[0219] Heat loss rate B (%) = {(W)} B0 -W B1 ) / W B0}×100···(B)

[0220] <Calibration of heat C>

[0221] Weigh the sizing agent in the range of 10 ± 2 mg (let the mass of this weighing be W). C0 (mg) was measured using a thermogravimetric analyzer in a nitrogen stream of 200 ml (volume at 1 atm, 25°C) / min from 30°C at a rate of 10°C / min, and the mass of the sizing agent at 350°C was determined (this measured mass is denoted as W). C1 (mg)), calculate the rate of heat loss C according to the following formula (C),

[0222] Heat loss rate C (%) = {(W)} C0 -W C1 ) / W C0}×100···(C).

[0223] • Step 3: Operational evaluation of carbon fiber bundles containing sizing agent

[0224] The operability was evaluated using the carbon fiber bundles obtained in the second step based on the CF friction lint measurement method. The results showed that lint was not easily generated during the processing, and the operability was excellent.

[0225] • Step 4: Evaluation of sizing agent content and carbon fiber surface condition after heat treatment

[0226] The carbon fiber bundles containing sizing agent obtained in the previous process were thermally decomposed using the incineration method described above, resulting in carbon fiber bundles containing sizing agent after incineration at 250°C for 20 seconds.

[0227] Next, the sizing agent content and the photoelectron intensity ratio of the carbon fiber bundle surface were measured. The results showed that the sizing agent content after heat treatment was 0.04% by mass, with a small residual amount, and the photoelectron intensity ratio was 0.4. The thermal decomposition of the sizing agent was very high, and the carbon fiber surface was very close to the original value shown in Reference Example 1.

[0228] The results are summarized in Table 2. [Table 2]

[0229] Table 2

[0230]

[0231] (Example 2)

[0232] In the second step, a sizing agent was mixed at a ratio of 90% by mass for (A-1) and 10% by mass for (A-11). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2. It can be seen that the workability is very good, the thermal decomposition of the sizing agent is very high, and the carbon fiber surface is very close to the original value shown in Reference Example 1.

[0233] (Example 3)

[0234] In the second step, a sizing agent was mixed at a ratio of 80% by mass for (A-1) and 20% by mass for (A-12). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2. It can be seen that the workability is very good, the thermal decomposition of the sizing agent is very high, and the carbon fiber surface is very close to the original value shown in Reference Example 1.

[0235] (Example 4)

[0236] In the second step, the sizing agent was changed to (A-2). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2. It can be seen that the operability is very good, the thermal decomposition of the sizing agent is very high, and the carbon fiber surface is very close to the original value shown in Reference Example 1.

[0237] (Example 5)

[0238] In the second step, the sizing agent was changed to (A-3). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2. It can be seen that the operability is very good, the thermal decomposition of the sizing agent is very high, and the carbon fiber surface is very close to the original value shown in Reference Example 1.

[0239] (Example 6)

[0240] In the second step, the sizing agent was changed to (A-4). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2. It can be seen that the operability is very good, the thermal decomposition of the sizing agent is sufficiently high, and the carbon fiber surface is very close to the original value shown in Reference Example 1.

[0241] (Example 7)

[0242] In the second step, the sizing agent was changed to (A-5). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2. It can be seen that the operability is very good, the thermal decomposition of the sizing agent is sufficiently high, and the carbon fiber surface is very close to the original value shown in Reference Example 1.

[0243] (Example 8)

[0244] In the second step, the sizing agent content was changed to 0.4% by mass. Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 3. It can be seen that the operability is very good, the thermal decomposition of the sizing agent is very high, and the carbon fiber surface is very close to the original value shown in Reference Example 1.

[0245] [Table 3]

[0246] Table 3

[0247]

[0248] (Examples 9-11)

[0249] In the second step, the content of the sizing agent and the sizing agent before heat treatment were changed as shown in Table 2. Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 3. It can be seen that the workability is excellent, the thermal decomposition of the sizing agent is very high, and the carbon fiber surface is very close to the original value shown in Reference Example 1.

[0250] (Examples 12 and 13)

[0251] In the second step, the content of the sizing agent and the sizing agent before heat treatment were changed as shown in Table 2. Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 3, indicating that the workability was sufficiently good, the thermal decomposition of the sizing agent was sufficiently high, and the carbon fiber surface was sufficiently close to the original value shown in Reference Example 1.

[0252] (Example 14)

[0253] In step 1, the electrolytic surface treatment was changed to 10 coulombs of charge per 1g of carbon fiber. Otherwise, carbon fibers were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 3. It can be seen that the workability is quite good, the thermal decomposition of the sizing agent is very high, and the photoelectron intensity ratio (b) / (a) of the carbon fiber surface after heat treatment is low, but the carbon fiber surface is very close to the original value shown in Reference Example 3.

[0254] (Example 15)

[0255] In the second step, a sizing agent was mixed with (A-1) as the first component at a ratio of 90% by mass and (A-10) as the second component at a ratio of 10% by mass. Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 3. It can be seen that the workability is very good, the thermal decomposition of the sizing agent is sufficiently high, and the carbon fiber surface is very close to the original value shown in Reference Example 1.

[0256] (Comparative Example 1)

[0257] In the second step, the sizing agent was changed to (A-6). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The heat loss rate A volatilized significantly, making it impossible for the sizing agent to adhere to the carbon fiber, resulting in poor operability.

[0258] [Table 4]

[0259] Table 4

[0260]

[0261] (Comparative Example 2)

[0262] In the second step, the sizing agent was changed to (A-7). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The operability was very good, but the heat loss rate B was small and the thermal decomposition of the sizing agent was poor. After heat treatment, a lot of sizing agent remained on the carbon fiber surface, making it impossible to perform carbon fiber surface analysis.

[0263] (Comparative Example 3)

[0264] In the second step, the sizing agent was changed to (A-8). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The operability was very good, but the heat loss rate B was small, the thermal decomposition of the sizing agent was poor, and the sizing agent remained on the surface of the carbon fiber after heat treatment.

[0265] (Comparative Example 4)

[0266] In the second step, the sizing agent was changed to (A-9). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The operability was very good, but the heat loss rates B and C were small, the thermal decomposition of the sizing agent was poor, and a lot of the sizing agent remained on the carbon fiber surface after heat treatment, making it impossible to perform carbon fiber surface analysis.

[0267] (Comparative Example 5)

[0268] In the second step, the sizing agent was changed to (A-10). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The operability was very good, but the heat loss rates B and C were small, the thermal decomposition of the sizing agent was poor, and a lot of the sizing agent remained on the carbon fiber surface after heat treatment, making it impossible to perform carbon fiber surface analysis.

[0269] (Comparative Example 6)

[0270] In the second step, the sizing agent was changed to (A-11). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The operability was very good, but the proportion of the component that satisfies formula (1) was less than 50% by mass, and the heat loss rate C was small. Therefore, the thermal decomposition of the sizing agent was poor, and the sizing agent remained on the surface of the carbon fiber after heat treatment.

[0271] (Comparative Example 7)

[0272] In the second step, the sizing agent was changed to (A-13). Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The operability was very good, but the proportion of the component that satisfies formula (1) was less than 50% by mass, and the heat loss rate C was small. Therefore, the thermal decomposition of the sizing agent was poor, and the sizing agent remained on the surface of the carbon fiber after heat treatment.

[0273] (Comparative Example 8)

[0274] In step 2, the sizing agent was changed to (A-7), and in step 4, the heating temperature was changed to 400°C. Otherwise, carbon fiber bundles containing the sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The operability was very good, and there was no residual sizing agent. However, the photoelectron intensity ratio (b) / (a) of the heated carbon fiber surface was low, indicating that the original carbon fiber surface decomposed.

[0275] (Comparative Example 9)

[0276] In the second step, carbon fiber bundles containing sizing agent were mixed at a ratio of 30% by mass for (A-1) and 70% by mass for (A-11). Otherwise, carbon fiber bundles containing sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The workability was very good, but the heat loss rate C was small, indicating poor thermal decomposition of the sizing agent. The sizing agent also remained on the surface of the carbon fiber after heat treatment.

[0277] (Comparative Example 10)

[0278] In the second step, carbon fiber bundles containing sizing agent were mixed at a ratio of 30% by mass for (A-1) and 70% by mass for (A-12). Otherwise, carbon fiber bundles containing sizing agent were obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 4. The workability was very good and there was no residual sizing agent. However, the proportion of the components that satisfy formula (1) was less than 50% by mass. Therefore, the photoelectron intensity ratio (b) / (a) of the carbon fiber surface after heating was high, and the sizing agent remained on the carbon fiber surface after heat treatment.

[0279] Industrial availability

[0280] According to the present invention, a carbon fiber bundle containing a sizing agent can be provided, wherein the carbon fiber bundle containing the sizing agent exhibits good workability, and the sizing agent on the carbon fiber bundle exhibits thermal decomposability at low temperatures that can suppress the thermal decomposition of oxygen-containing functional groups on the carbon fiber surface, thereby reducing porosity in the carbon fiber reinforced composite material and reflecting the surface properties of the original carbon fiber in the matrix resin. The thermoplastic resin composite using the present invention is lightweight and has excellent strength, making it suitable for many applications such as aircraft components, spacecraft components, automotive components, ship components, civil engineering materials, and sporting goods.

Claims

1. A carbon fiber bundle comprising carbon fibers and a sizing agent satisfying all of the following (i) to (v), (i) Satisfies either (a) or (b) below: (a) The proportion of polyalkylene glycol structure in the total mass of the sizing agent is more than 80% by mass, and the number average molecular weight of the sizing agent is more than 120 and less than 300. (b) The sizing agent contains an acetylene structure, and the proportion of the polyalkylene glycol structure in the total mass of the sizing agent is more than 20% by mass; (ii) The rate of heat loss A, determined under the following test conditions, is 5.0% or less; (iii) The heat loss rate B, determined under the following test conditions, is 11.0% or more; (iv) The heat loss rate C obtained under the following test conditions is 90.0% or higher; (v) The surface oxygen concentration of the carbon fibers before applying the sizing agent, as determined by X-ray photoelectron spectroscopy, is ≥0.11 and ≤0.

25. Heat loss rate A: Weigh the sizing agent in the range of 10 ± 2 mg, and denote the mass of this weighed amount as W. A0 (mg), the mass of the sizing agent was determined using a thermogravimetric analyzer in a nitrogen stream of 200 ml / min at 1 atm and 25°C, from 30°C to 140°C, with the temperature increased at a rate of 10°C / min. This determined mass is denoted as W. A1 (mg), calculate the rate of heat loss A according to the following formula (A), Heat loss rate A (%) = {(W)} A0 -W A1 ) / W A0 }×100···(A) Heat loss rate B: Weigh the sizing agent in the range of 10 ± 2 mg, and denote the mass of this weighed amount as W. B0 (mg), the mass of the sizing agent was determined using a thermogravimetric analyzer in a nitrogen stream of 200 ml / min at 1 atm and 25°C, from 30°C to 250°C at a rate of 10°C / min, and the determined mass was set as W. B1 (mg), calculate the rate of heat loss B according to the following formula (B), Heat loss rate B (%) = {(W)} B0 -W B1 ) / W B0 }×100···(B) Heat loss rate C: Weigh the sizing agent in the range of 10 ± 2 mg, and denote the mass of this weighed amount as W. C0 (mg), the mass of the sizing agent was determined using a thermogravimetric analyzer in a nitrogen stream of 200 ml / min at 1 atm and 25°C, from 30°C to 350°C at a rate of 10°C / min, and the determined mass was set as W. C1 (mg), calculate the rate of heat loss C according to the following formula (C), Heat loss rate C (%) = {(W)} C0 -W C1 ) / W C0 }×100···(C).

2. The carbon fiber bundle according to claim 1, wherein, In case (b), the number-average molecular weight of the sizing agent is 120 or more and less than 300.

3. The carbon fiber bundle according to claim 1 or 2, wherein, The sizing agent does not actually contain aromatic rings.

4. The carbon fiber bundle according to claim 1 or 2, wherein, The content of the sizing agent is above 0.3% by mass and below 1.2% by mass.

5. The carbon fiber bundle according to claim 1 or 2, wherein, The fiber-to-fiber friction coefficient of the carbon fiber before being coated with the sizing agent is 0.25 or higher and 0.43 or lower.

6. A method for manufacturing carbon fiber bundles, comprising the method for manufacturing carbon fiber bundles according to any one of claims 1 to 5, wherein, The manufacturing method includes: a step of applying the sizing agent to the carbon fibers; and a drying step of drying the carbon fiber bundles that have been applied the sizing agent after the application step.

7. The method for manufacturing carbon fiber bundles according to claim 6, wherein, The drying process is a process of drying the carbon fiber bundles at 110-140°C.

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