Carbon fiber bundle containing sizing agent and method for producing same

Abstract

Provided is a carbon fiber bundle containing a sizing agent, the carbon fiber bundle showing bundling performance appropriate for easy handling as a result of including a sizing agent that tends to thermally decompose at a low temperature under which the surface properties of the carbon fibers can be retained. The carbon fiber bundle thus provided contains a reduced amount of the sizing agent that remains after intermediate substrate processing, where the sizing agent is particularly suitable for combination with a thermoplastic resin, allowing the surface properties of the carbon fibers to be exhibited.

Description

Carbon fiber bundle containing sizing agent and method for producing same

[0001] The present invention relates to a carbon fiber bundle containing a sizing agent and a method for producing a carbon fiber bundle containing a sizing agent.

[0002] Carbon fiber, being lightweight yet possessing excellent strength and elastic modulus, is used in a wide range of applications, including aircraft, spacecraft, automobile, marine, civil engineering, and sporting goods, 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 composites 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 stability of properties.

[0003] In recent years, carbon fiber reinforced 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 through a thermoplastic resin slurry in which powdered thermoplastic resin is dispersed with a surfactant to produce a powdered thermoplastic resin-containing carbon fiber tape, which is then impregnated 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 fibers, a method is usually used in which a sizing agent is applied to the carbon fiber bundles and an abrasion-resistant coating film is applied to the carbon fiber surface (see Patent Documents 1 and 2).

[0005] If the sizing agent applied to the carbon fibers can be easily thermally decomposed, the sizing agent heated to high temperatures will decompose or volatilize when molded into a carbon fiber reinforced composite material using a prepreg impregnated with a matrix resin such as a super engineering plastic that has a high molding temperature, thereby reducing the amount of gas in the matrix resin and suppressing voids inside the molded product (see Patent Document 3).

[0006] Furthermore, before impregnating the carbon fiber with the matrix resin, in order to improve the adhesion between the carbon fiber and the matrix resin, the carbon fiber surface is usually subjected to an oxidation treatment such as gas phase oxidation or liquid phase oxidation, thereby introducing oxygen-containing functional groups such as carboxyl groups and aldehyde groups onto the carbon fiber surface (see Patent Document 4).

[0007] US Patent No. 3,957,716 JP 57-171767 A International Publication No. 2020 / 0138139 JP 04-361619 A

[0008] On the other hand, when the sizing agent is removed from the carbon fiber surface by heat treatment as described above, a high temperature is required for thermal decomposition depending on the type of sizing agent, and the oxygen-containing functional groups on the carbon fiber surface necessary for imparting physical properties to the matrix resin are also decomposed, resulting in a difference from the original carbon fiber surface in some cases.

[0009] That is, studies have been conducted on suppressing the generation of fluff from carbon fibers by applying a sizing agent, and on sizing agents that are easily thermally decomposed. However, in processing carbon fibers that contain a sizing agent that is easily thermally decomposed, there has been no idea of ​​applying a sizing agent to suppress the generation of fluff due to breakage of single fibers in carbon fiber bundles, 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 added, thereby maintaining many of the surface functional groups of the carbon fibers, and thus reflecting this state in a carbon fiber reinforced composite material.

[0010] The present invention has been made in view of the above, and has an object to provide a carbon fiber bundle containing a sizing agent, and a method for producing the same, which are suitable for producing a prepreg from which a carbon fiber reinforced composite material having extremely few voids and reflecting the surface properties of the carbon fiber, which has a highly heat-resistant thermoplastic resin as a matrix resin, can be obtained, by which the sizing agent on the carbon fiber bundle exhibits good thermal decomposition properties and the amount of sizing agent can be reduced while maintaining the surface functional groups of the carbon fiber, even when the carbon fiber bundle containing a sizing agent is easy to handle, and which has an extremely low void content and reflects the surface properties of the carbon fiber.

[0011] The present invention, which solves the above-mentioned problems, provides a carbon fiber bundle containing carbon fibers and a sizing agent that satisfies all of the following (i) to (iv): (i) Satisfies either (a) or (b) below: (a) The proportion of polyalkylene glycol structures in the total mass of the sizing agent is 60 mass% or more; (b) The sizing agent contains an acetylene structure, and the proportion of polyalkylene glycol structures in the total mass of the sizing agent is 20 mass% or more; (ii) The thermal weight loss rate A obtained under the following measurement conditions is 5.0% or less; (iii) The thermal weight loss rate B obtained under the following measurement conditions is 11.0% or more; (iv) The thermal weight loss rate C obtained under the following measurement conditions is 90.0% or more. <Thermal weight loss rate A> The sizing agent is weighed in the range of 10±2 mg, and this weighed mass is expressed as W Ａ０ The temperature was increased from 30°C at a rate of 10°C / min in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min using a thermogravimetric analyzer, and the mass of the sizing agent was measured when it reached 140°C. Ａ１(mg), and calculate the thermal weight loss rate A using the following formula (A): Thermal weight loss rate A (%) = {(W Ａ０ -W Ａ１ ) / W Ａ０}×100 (A) <Thermal Weight Loss Rate B> The sizing agent was weighed in the range of 10±2 mg (this weighed mass was Ｂ０ The temperature was increased from 30°C at a rate of 10°C / min in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min using a thermogravimetric analyzer, and the mass of the sizing agent was measured when it reached 250°C. Ｂ１ (mg), and calculate the thermal weight loss rate B using the following formula (B): Thermal weight loss rate B (%) = {(W Ｂ０ -W Ｂ１ ) / W Ｂ０}×100 (B) <Thermal Weight Loss Rate C> The sizing agent was weighed in the range of 10±2 mg (this weighed mass was Ｃ０ The temperature was increased from 30°C at a rate of 10°C / min in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min using a thermogravimetric analyzer, and the mass of the sizing agent was measured when it reached 350°C. Ｃ１ (mg), and calculate the thermal weight loss rate C using the following formula (C): Thermal weight loss rate C (%) = {(W Ｃ０ -W Ｃ１ ) / W Ｃ０}×100...(C).

[0012] The method for producing a carbon fiber bundle containing a sizing agent of the present invention is characterized by having a drying step of drying the carbon fiber bundle containing the sizing agent after the step of impregnating the carbon fiber with the sizing agent.

[0013] According to the present invention, even when the carbon fiber bundle containing a sizing agent is easy to handle, since the carbon fiber contains a sizing agent that has good thermal decomposition properties and is easily thermally decomposed at low temperatures, it is possible to obtain a carbon fiber reinforced composite material with extremely few voids that reflects the surface characteristics of the carbon fiber, and it is possible to obtain a carbon fiber bundle containing a sizing agent that is particularly suitable for combination with a thermoplastic resin.

[0014] Hereinafter, embodiments for carrying out the present invention will be described. The carbon fiber bundle containing a sizing agent of the present invention is a carbon fiber bundle containing carbon fibers and a sizing agent that satisfies all of the following (i) to (iv). (i) Satisfies either (a) or (b) below. (a) The proportion of polyalkylene glycol structures in the total mass of the sizing agent is 60 mass% or more. (b) The sizing agent contains an acetylene structure, and the proportion of polyalkylene glycol structures in the total mass of the sizing agent is 20 mass% or more. (ii) The thermal weight loss rate A obtained under the following measurement conditions is 5.0% or less. (iii) The thermal weight loss rate B obtained under the following measurement conditions is 11.0% or more. (iv) The thermal weight loss rate C obtained under the following measurement conditions is 90.0% or more. <Thermal weight loss rate A> The sizing agent is weighed in the range of 10±2 mg (this weighed mass is expressed as W Ａ０ The mass of the sizing agent was measured using a thermogravimetric analyzer in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min at a rate of 10°C / min from 30°C, and the mass of the sizing agent was measured when the temperature reached 140°C (this measured mass was referred to as W Ａ１ (mg), and the thermal weight loss rate A is calculated using the following formula (A): Thermal weight loss rate A (%) = {(W Ａ０ -W Ａ１ ) / W Ａ０}×100 (A) <Thermal Weight Loss Rate B> The sizing agent was weighed in the range of 10±2 mg (this weighed mass was Ｂ０ The mass of the sizing agent was measured using a thermogravimetric analyzer in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min at a rate of 10°C / min from 30°C, and the mass of the sizing agent was measured when the temperature reached 250°C (this measured mass was referred to as W Ｂ１ (mg), and the thermal weight loss rate B is calculated using the following formula (B): Thermal weight loss rate B (%) = {(W Ｂ０ -W Ｂ１ ) / W Ｂ０}×100 (B) <Thermal Weight Loss Rate C> The sizing agent was weighed in the range of 10±2 mg (this weighed mass was Ｃ０The mass of the sizing agent was measured using a thermogravimetric analyzer in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min at a rate of 10°C / min from 30°C, and the mass of the sizing agent was measured when the temperature reached 350°C (this measured mass was referred to as W Ｃ１ (mg), and the thermal weight loss rate C is calculated using the following formula (C): Thermal weight loss rate C (%) = {(W Ｃ０ -W Ｃ１ ) / W Ｃ０}×100...(C).

[0015]

[0003] Through investigations by the present inventors, it has been found that when a sizing agent that improves handleability after incorporation into carbon fibers is used, the thermal decomposition of the sizing agent on the carbon fiber bundle containing the sizing agent is reduced, making the sizing agent more likely to remain, and voids are more likely to occur during prepreg production. Furthermore, when heated at high temperatures to further enhance thermal decomposition, the surface properties of the original carbon fiber cannot be reflected. To address these issues, the present inventors have found that, even when a sizing agent with high handleability is used, it is possible to achieve both high handleability of the carbon fiber bundle containing the sizing agent and good thermal decomposition at low temperatures of the sizing agent by controlling the thermal decomposition by controlling the proportion of alkylene glycol structures contained in the entire sizing agent, or by controlling the proportion of alkylene glycol structures containing an acetylene structure.

[0016] The sizing agent of the present invention must satisfy either (a) or (b) below: (a) The proportion of polyalkylene glycol structures in the total mass of the sizing agent is 60 mass% or more, or (b) the sizing agent contains an acetylene structure, and the proportion of polyalkylene glycol structures in the total mass of the sizing agent is 20 mass% or more.

[0017] The polyalkylene glycol structure is a structure of the following general formula (1).

[0018]

[0019] In general formula (1), R is a hydrogen atom or a methyl group, and n is an integer of 2 to 20.

[0020] A carbon fiber bundle containing a sizing agent with a controlled proportion of polyalkylene glycol structures undergoes good thermal decomposition without reacting with the surface of the carbon fiber. As a result, the amount of sizing agent remaining in the carbon fiber bundle is reduced, making it easier to maintain the original surface state of the carbon fiber. In formula (1), R is a hydrogen atom or a methyl group, and a hydrogen atom is preferred from the viewpoint of water solubility. n is an integer from 2 to 20, and a smaller value is preferred from the viewpoint of reducing the molecular weight and improving thermal decomposition properties, 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 thermal decomposition properties decrease.

[0021] Examples of sizing agents containing a structure represented by general formula (1) include polyethylene glycol, acetylene glycol, polyoxyethylene alkyl ethers such as polyoxyethylene dodecyl ether, polyoxyethylene oleyl ether, and polyoxyethylene stearyl ether, propylene glycol, polyoxyethylene polyoxypropylene glycol, and polyoxyethylene alkyl phenyl ethers. Each of these can be used alone or in combination of two or more.

[0022] An acetylene structure is a structure with a triple bond between carbon and carbon. Examples of sizing agents containing an acetylene structure include acetylene alcohol and acetylene glycol.

[0023] The sizing agent may be one kind or a mixture of two or more kinds.

[0024] Regarding requirement (a), the proportion of the polyalkylene glycol structure in the total mass of the sizing agent is preferably 80 mass% or more, and a larger proportion of the polyalkylene glycol structure is more preferable, and 85 mass% is more preferable. If the proportion of the polyalkylene glycol structure is less than 60 mass% of the total amount of the sizing agent, the contact probability of the sizing agent, which is less reactive with the surface functional groups of the carbon fiber, decreases, increasing heat resistance and making it less susceptible to thermal decomposition.

[0025] Just to be clear, the sizing agent is diethylene glycol (HO(CH ２ CH２ O) ２ The proportion of polyalkylene glycol structures in the case of only triethylene glycol (HO(CH)) is approximately 83 mass % ((106-18) / 106 x 100 (note: decimals of atomic weights are omitted)). ２ CH ２ O) ３ When only H) is present, the proportion of the polyalkylene glycol structure is approximately 88 mass % ((150-18) / 150×100 (note: decimals of atomic weights are omitted)).

[0026] Regarding requirement (b), when the sizing agent contains an acetylene structure, the proportion of polyalkylene glycol structures in the total mass of the sizing agent must be 20% by mass or more. When an acetylene structure is contained, the acetylene structure has a triple bond within the structure, which makes the compound more linear and reduces interactions due to entanglement. Therefore, when the proportion of polyalkylene glycol structures is 20% by mass or more, good thermal decomposition properties are exhibited. When the proportion of acetylene structures is less than 20% by mass, the increased proportion of acetylene structures increases heat resistance and makes thermal decomposition more difficult. When an acetylene structure is contained, the proportion of polyalkylene glycol structures in the total mass of the sizing agent is more preferably 50% by mass or more.

[0027] Just to be clear, the sizing agent is bis(1-hydroxyethyl)acetylene (CH ３ CH(OH)CCCH(OH)CH ３ ) alone, the proportion of the acetylene structure is about 21 mass % (24 / 114 × 100 (note: decimals of atomic weight are omitted)).

[0028] The proportions of polyalkylene glycol structures and acetylene structures in the total sizing agent contained in carbon fiber can be calculated from the structural formula of the sizing agent, if the structural formula is known. If it is unknown, the sizing agent is extracted from a carbon fiber bundle containing the sizing agent, and the structure is identified by a known method such as proton NMR, carbon NMR, mass spectrometry, or TOF-SIMS, and the proportions can be calculated. If there are multiple components, they are separated using a column and evaluated. An example of extraction conditions is shown below.

[0029] <Extraction Conditions> A weighed carbon fiber bundle containing 1 g of sizing agent is added to a 100 mL solution of a 1:1 mixture of chloroform and methanol, followed by 30 minutes of ultrasonic irradiation and overnight standing. The resulting extract is recovered and evaporated to dryness. The mass % of the extract relative to the carbon fiber bundle containing the sizing agent is calculated, and it is confirmed that this agrees with the measurement result of the sizing agent content in the carbon fiber bundle within an error range of 10%. If the results do not agree even after repeated measurements several times, the sample is outside the scope of the present invention.

[0030] If the sizing agent contained in the carbon fiber bundle contains an epoxy group, an amino group, or an oxazoline group as a structure other than a polyalkylene glycol structure, it reacts with the surface functional groups of the carbon fiber, improving the heat resistance and making it less susceptible to thermal decomposition. Therefore, the sizing agent containing an epoxy group, an amino group, or an oxazoline group preferably accounts for 30 mass% or less of the total mass of the sizing agent, and is preferably not substantially contained. "Substantially not contained" means less than 1 mass% of 100 mass% of the sizing agent.

[0031] Whether or not the sizing agent on the carbon fiber bundle contains a sizing agent containing an epoxy group, an amino group, or an oxazoline group can be calculated from the structural formula, if the structural formula of the sizing agent is known. If it is unknown, the sizing agent can be extracted from the carbon fiber bundle containing the sizing agent, and the structure can be identified and the proportion calculated using a known method such as proton NMR, carbon NMR, mass spectrometry, or TOF-SIMS. If there are multiple components, the structure can be identified and the proportion calculated by evaluating the components by adding an operation of separating them using a column.

[0032] The sizing agent constituting the present invention must have a thermal weight loss rate A of 5.0% or less as determined under the following measurement conditions.

[0033] <Measurement conditions for thermal weight loss rate A> The sizing agent was weighed in the range of 10±2 mg (this weighed mass was Ａ０ The mass of the sizing agent was measured using a thermogravimetric analyzer in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min at a rate of 10°C / min from 30°C, and the mass of the sizing agent was measured when the temperature reached 140°C (this measured mass was referred to as W Ａ１(mg), and the thermal weight loss rate A is calculated using the following formula (A): Thermal weight loss rate A (%) = {(W Ａ０ -W Ａ１ ) / W Ａ０}×100...(A).

[0034] If the thermal loss rate A is 5.0% or less, the sizing agent can be prevented from thermal decomposition or volatilization when the sizing agent is applied to untreated carbon fibers, and therefore, a carbon fiber bundle containing a sizing agent that is less prone to fluffing due to mechanical friction such as fiber opening and has excellent handleability can be obtained.

[0035] If the thermal weight loss rate A exceeds 5.0%, the sizing agent contains a large amount of components that increase the thermal weight loss rate A. Such components that increase the thermal weight loss rate A have a small molecular weight and have a reduced adhesive force to the carbon fibers, and therefore, the larger the thermal weight loss rate A, the less the sizing agent can adhere to the carbon fibers, resulting in a carbon fiber bundle containing a sizing agent that is poor in handleability.

[0036] The thermal weight loss rate A is preferably 3.0% or less, and more preferably 1.0% or less. The smaller the value of the thermal weight loss rate A, the more preferable, and 0% is particularly preferable. In other words, the lower limit of the thermal weight loss rate A is preferably 0%.

[0037] The sizing agent constituting the present invention must have a thermal weight loss rate B of 11.0% or more as determined under the following measurement conditions.

[0038] <Thermal Weight Loss Rate B> A sizing agent was weighed in the range of 10±2 mg (this weighed mass was expressed as W Ｂ０ The mass of the sizing agent was measured using a thermogravimetric analyzer in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min at a rate of 10°C / min from 30°C, and the mass of the sizing agent was measured when the temperature reached 250°C (this measured mass was referred to as W Ｂ１ (mg), and the thermal weight loss rate B is calculated using the following formula (B): Thermal weight loss rate B (%) = {(W Ｂ０ -W Ｂ１ ) / W Ｂ０}×100...(B).

[0039] If the thermal loss rate B is 11.0% or more, in the stage of heating the carbon fiber bundle containing a sizing agent at a low temperature, most of the gas generated by the thermal decomposition or volatilization of the sizing agent is completed and removed from the carbon fiber reinforced composite material, and therefore voids are less likely to remain, and a good-quality molded product (carbon fiber reinforced composite material) that is able to exhibit the surface characteristics of the original carbon fiber can be obtained.

[0040] If the thermal weight loss rate B is less than 11.0%, the sizing agent contains a large amount of a component that reduces the thermal weight loss rate B. Such a component that reduces the thermal weight loss rate B has a large molecular weight and is likely to coat the surface of the carbon fiber, and therefore, the smaller the thermal weight loss rate B, the more likely the surface of the carbon fiber bundle after heat treatment will be different from the surface of the original carbon fiber, in a carbon fiber bundle containing a sizing agent.

[0041] The thermal weight loss rate B is preferably 30.0% or more, more preferably 60.0% or more, and even more preferably 90.0% or more. The larger the value of the thermal weight loss rate B, the better, and 100.0% is particularly preferable. In other words, the upper limit of the thermal weight loss rate B is preferably 100.0%.

[0042] The sizing agent constituting the present invention must have a thermal weight loss rate C of 90.0% or more as determined under the following measurement conditions.

[0043] <Thermal Weight Loss Rate C> The sizing agent was weighed in the range of 10±2 mg (this weighed mass was expressed as W Ｃ０ The mass of the sizing agent was measured using a thermogravimetric analyzer in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min at a rate of 10°C / min from 30°C, and the mass of the sizing agent was measured when the temperature reached 350°C (this measured mass was referred to as W Ｃ１ (mg), and the thermal weight loss rate C is calculated using the following formula (C): Thermal weight loss rate C (%) = {(W Ｃ０ -W Ｃ１ ) / W Ｃ０}×100...(C).

[0044] If the thermal loss rate C is 90.0% or more, at the stage when the heating of the carbon fiber bundle containing the sizing agent is completed, most of the gas generated by the decomposition or volatilization of the sizing agent is completed and removed from the carbon fiber reinforced composite material, so that voids are less likely to remain, and a carbon fiber reinforced composite material of good quality can be obtained.

[0045] If the thermal weight loss rate C is less than 90.0%, the sizing agent contains a large amount of components that reduce the thermal weight loss rate C. Such components that reduce the thermal weight loss rate C have high heat resistance in air and are likely to remain as residues on the carbon fiber surfaces, and therefore, the smaller the thermal weight loss rate C, the more likely the carbon fiber bundle surface after heat treatment is to contain a sizing agent that is likely to differ from the surface of the original carbon fibers.

[0046] The thermal weight loss rate C is 90.0% or more, more preferably 95.0% or more, and even more preferably 99.0% or more. The larger the value of the thermal weight loss rate C, the more preferable it is, and 100.0% is particularly preferable. In other words, the upper limit of the thermal weight loss rate C is preferably 100.0%.

[0047] The thermal weight loss rates A, B, and C can be controlled by changing the elements and partial structures contained in the sizing agent, and the number average molecular weight Mn, which will be described later.

[0048] Regarding the thermal weight loss rate A, the thermal weight loss rate B, and the thermal weight loss rate C, no difference was observed between the values ​​obtained by evaluating the sizing agent and the values ​​obtained by evaluating the sizing agent extracted under the following extraction conditions from the carbon fiber bundle containing the sizing agent.

[0049] <Extraction Conditions> A weighed carbon fiber bundle containing 1 g of sizing agent is added to a 100 mL solution of a 1:1 mixture of chloroform and methanol, followed by 30 minutes of ultrasonic irradiation and then leaving to stand overnight. The resulting extract is recovered and evaporated to dryness. The mass % of the extract relative to the carbon fiber bundle containing the sizing agent is calculated, and it is confirmed that this agrees with the measurement result of the sizing agent content in the carbon fiber bundle within a 10% error range.

[0050] 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 number average molecular weight Mn is measured by gel permeation chromatography (hereinafter abbreviated as GPC) and is obtained using polystyrene as a standard substance. By setting Mn to less than 300, the molecular chain becomes shorter and thermal decomposition improves, making it possible to thermally decompose at a lower temperature in a shorter time. 250 or less is more preferable, and 200 or less is even more preferable. On the other hand, in terms of application, by setting it to 120 or more, volatilization or thermal decomposition of the sizing agent can be suppressed when it is incorporated into untreated carbon fibers. 135 or more is more preferable.

[0051] 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 by the above-mentioned extraction method and evaluating it by GPC.

[0052] <Method for measuring number average molecular weight Mn> The number average molecular weight of a sizing agent can be measured by a known method using GPC with polystyrene as a standard substance. The following conditions are used for GPC measurement in the present invention. Measuring device: Shimadzu Corporation Column used: TSKgel HXL-L + TSKgel α-3000 manufactured by TOSOH BIOSCIENCE Eluent: Dimethylformamide 0.01 mol / L lithium bromide solution Standard substance: Polystyrene (manufactured by Tosoh Corporation) Detector: Differential refractometer (manufactured by Shimadzu Corporation).

[0053] When the sizing agent of the present invention contains a plurality of components, the measured value for the mixture of these components is taken as the number average molecular weight Mn.

[0054] The sizing agent used in the present invention preferably contains substantially no aromatic rings. Structures containing aromatic rings, such as bisphenol A and benzene, have high heat resistance, so their inclusion in the sizing agent reduces thermal decomposition. "Substantially no aromatic rings" means that the content is less than 1% by mass relative to 100% by mass of the sizing agent.

[0055] The proportion of aromatic rings contained in the sizing agent on the carbon fiber bundle containing the sizing agent can be confirmed from the structural formula if the structural formula is known. If it is unknown, the sizing agent can be extracted from the carbon fiber bundle containing the sizing agent, and the structure can be identified and the proportion calculated by a known method such as proton NMR, carbon NMR, mass spectrometry, or TOF-SIMS. If there are multiple components, the structure can be identified and the proportion calculated by evaluating the components by adding an operation of separating them using a column.

[0056] The sizing agent content of the carbon fiber bundle containing the sizing agent constituting the present invention is preferably 0.3 mass % or more and 1.2 mass % or less, based on 100 mass % of the carbon fiber bundle containing the sizing agent. 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.

[0057] By setting the sizing agent content to 0.3% by mass or more, the handleability of the carbon fiber bundle containing the sizing agent can be improved, fluffing during production and processing can be suppressed, and the quality of the carbon fiber sheet, such as smoothness, 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, it is possible to reduce the residual amount at low temperatures in a short time, thereby 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.

[0058] The sizing agent-containing carbon fiber bundle constituting the present invention is a carbon fiber bundle that has been heated at 250°C for 20 seconds in an oxidizing atmosphere, and the carbon content of the fiber surface is measured by X-ray photoelectron spectroscopy using AlKα as an X-ray source at a photoelectron escape angle of 45°. １Ｓ It is preferable that the ratio (photoelectron intensity (b) / photoelectron intensity (a)) of the photoelectron intensity (b) (cps) detected at an energy of 286.1 eV (C-O) in the core spectrum to the photoelectron intensity (a) (cps) detected at a binding energy of 284.6 eV (C-C) is 0.2 or more and 0.8 or less.

[0059] In the following, the C on the fiber surface measured by X-ray photoelectron spectroscopy using AlKα as the X-ray source at a photoelectron escape angle of 45° is １Ｓ The ratio of the photoelectron intensity (b) (cps) detected at an energy of 286.1 eV (C-O) in the core spectrum to the photoelectron intensity (a) (cps) detected at a binding energy of 284.6 eV (C-C) is sometimes referred to as the "photoelectron intensity ratio (b) / (a)" or simply as the "photoelectron intensity ratio."

[0060] On the surface of carbon fiber, there are multiple carbon atoms with different types of adjacent atoms and different bonding states. Therefore, the C on the surface of carbon fiber measured by X-ray photoelectron spectroscopy １Ｓ The core spectrum is obtained as a composite peak consisting of multiple sub-peaks with different binding energies. １Ｓ The binding energy of 284.6 eV in the core spectrum is the central position of the subpeaks attributed to the bonding states C—H, C—C, and C═C. １Ｓ The binding energy of 286.1 eV in the inner-shell spectrum is the binding energy at the center of the subpeak whose binding state is attributed to C—O. Therefore, the photoelectron intensity ratio (b) / (a) between the photoelectron intensity (a) (cps) detected at a binding energy of 284.6 eV and the photoelectron intensity (b) (cps) detected at a binding energy of 286.1 eV represents the proportion of carbon atoms having C—O bonds on the carbon fiber surface, and the smaller the photoelectron intensity ratio (b) / (a), the fewer carbon atoms having C—O bonds there are.

[0061] In the present invention, when the photoelectron intensity ratio (b) / (a) on the carbon fiber surface is 0.8 or less, the amount of sizing agent having a C—O bond remaining on the carbon fiber surface is extremely small, which is a preferred range. The smaller the ratio, the closer the carbon fiber surface after heat treatment becomes to the surface of the carbon fiber before the sizing agent is incorporated. Therefore, the surface properties of the original carbon fiber can be reflected in the matrix resin. In particular, a range of 0.5 or less is more preferred. When the ratio is 0.2 or more, the surface functional groups of the original carbon fiber remain, allowing the surface properties to be reflected in the matrix resin. In particular, a range of 0.3 or more is more preferred.

[0062] In heating, an oxidizing atmosphere is an atmosphere containing a large amount of oxidizing gas (oxygen, ozone, etc.), and air is preferable from the viewpoint of ease of handling.

[0063] Heating of a carbon fiber bundle containing a sizing agent at 250°C for 20 seconds can be performed using the following procedure. The carbon fiber bundle containing the sizing agent is introduced into a heated air atmosphere via a roller, and the sizing agent is thermally decomposed. The carbon fiber bundle containing the sizing agent, which is installed in the unwinding process, is passed through a heating furnace via a pre-furnace free roller and a post-furnace free roller, and then wound up in the winding process. The unwinding tension from the creel was 800 g, the process speed was 6 m / min, and the section in the heating furnace where the temperature reached 250°C was adjusted to 2 m, resulting in a heating time of 20 seconds. XPS measurement of the carbon fiber bundle containing the sizing agent after this heat treatment was performed to determine the photoelectron intensity ratio (b) / (a) of the carbon fiber surface, and the sizing agent content in the carbon fiber bundle, thereby obtaining the content after heat treatment.

[0064] The carbon fiber bundle containing the sizing agent of the present invention can have a sizing agent content of 0.02 mass % or more and 0.1 mass % or less after heat treatment at 250° C. for 20 seconds in an oxidizing atmosphere. 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.

[0065] If the sizing agent content is 0.1% by mass or less after heat treatment at 250°C for 20 seconds in an oxidizing atmosphere, most of the gas generated by thermal decomposition or volatilization of the sizing agent is completed and removed from the carbon fiber reinforced composite material. As a result, voids are less likely to remain, and a high-quality molded product (carbon fiber reinforced composite material) that reflects the surface characteristics of the original carbon fiber can be obtained. In particular, the sizing agent content is more preferably less than 0.08% by mass, even more preferably less than 0.06% by mass, and particularly preferably 0.04% by mass or less.

[0066] A sizing agent content of 0.02 mass % or more after heat treatment at 250° C. for 20 seconds in an oxidizing atmosphere is a preferred range because the original surface functional groups of the carbon fibers are maintained.

[0067] In the present invention, the amount of oxygen atoms present on the surface of the carbon fiber before the application of the sizing agent is not particularly limited, but from the viewpoint of the mechanical properties of the resulting carbon fiber reinforced composite material, the surface oxygen concentration of the carbon fiber (amount of functional groups, O / C) measured by X-ray electron spectroscopy of the carbon fiber is preferably 0.11 or more and 0.25 or less, and more preferably 0.15 or more and 0.20 or less. If the amount of functional groups on the surface of the carbon fiber is too small, the adhesion between the carbon fiber and the matrix resin tends to be low. On the other hand, if the amount of functional groups is too large, the functional groups are easily decomposed during processing of the carbon fiber reinforced composite material, which involves heating, so that the difference in the amount of functional groups before and after processing is large, making it difficult to reflect the properties of the original carbon fiber.

[0068] The carbon fibers used in the present invention before application of the sizing agent preferably have a fiber-to-fiber friction coefficient of 0.25 or more and 0.43 or less. When the coefficient is 0.25 or more, force is easily applied between the individual fibers, and the bundling ability is easily improved. When the coefficient is 0.25 or more, the coefficient is more preferably 0.28 or more, and even more preferably 0.30 or more. When the coefficient is 0.43 or less, the frictional force between the individual yarns in the carbon fiber bundle is reduced, thereby reducing the amount of fluff generated by friction when the carbon fiber bundle is unwound from the bobbin. When the coefficient is 0.39 or less, and even more preferably 0.35 or less, the fiber-to-fiber friction coefficient can be controlled by the roughness of the carbon fiber surface, the type and amount of surface treatment, etc.

[0069] Next, the components constituting the carbon fiber bundle containing the sizing agent used in the present invention will be described.

[0070] Although there are no particular limitations on the carbon fiber used in the present invention, polyacrylonitrile-based carbon fibers are preferably used from the viewpoint of mechanical properties. The polyacrylonitrile-based carbon fiber bundle used in the present invention can be obtained by subjecting a carbon fiber precursor fiber made of a polyacrylonitrile-based polymer to a flame retardation treatment in an oxidizing atmosphere at a maximum temperature of 200 to 300°C, followed by a preliminary carbonization treatment in an inert atmosphere at a maximum temperature of 500 to 1200°C, and then a carbonization treatment in an inert atmosphere at a maximum temperature of 1200 to 2000°C.

[0071] 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.

[0072] 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, 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.

[0073] Next, a method for producing a carbon fiber bundle containing a sizing agent according to the present invention will be described.

[0074] First, the means for incorporating (applying) the sizing agent into (to) the carbon fibers constituting the present invention will be described.

[0075] 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.

[0076] Examples of methods for applying a sizing agent 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 a carbon fiber bundle containing the sizing agent of the present invention, the method of immersing a carbon fiber 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 a continuous method is preferably used because it has good productivity and small variation. Another preferred embodiment is to ultrasonically vibrate the carbon fiber when applying the sizing agent.

[0077] In the present invention, after applying the sizing agent solution, a drying step is preferably performed by contact drying means, for example, by contacting the carbon fiber bundle 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 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 reduces the contact area between the individual fibers, which increases the contact area with gas during thermal decomposition of the sizing agent, making it more likely to achieve high decomposition efficiency. Furthermore, in the present invention, after passing the carbon fiber bundle through a heated roller as a preliminary drying step, a second drying step may be performed in which a heat treatment is further performed. A non-contact heating method, which facilitates high-temperature heat treatment, is preferred for the heat treatment in the second drying step. By performing this heat treatment, the dilution solvent remaining in the sizing agent can be further removed, stabilizing the viscosity of the sizing agent and thereby stably enhancing its elution. The drying temperature is preferably in the range of 110 to 140°C. If the drying temperature is 110°C or higher, the moisture content of the sizing agent can be reduced, making it easier to increase thermal decomposition. 120°C or higher is more preferable. On the other hand, by setting the upper limit of the drying temperature to 140°C or lower, partial volatilization of the sizing agent can be suppressed, making it easier to maintain handleability. 135°C or lower is more preferable.

[0078] The heat treatment can also be carried out by microwave irradiation and / or infrared irradiation.

[0079] EXAMPLES Next, the present invention will be specifically explained by way of examples, but the present invention is not limited to the descriptions of these examples, and should not be interpreted as being limited thereto.

[0080] <Method for measuring the content of sizing agent in carbon fiber bundle and the amount of thermal decomposition of carbon fiber> A carbon fiber bundle containing 2.0±0.5 g of sizing agent was weighed (W １ (g)) (read to four decimal places), and then place in an electric furnace (capacity 120 cm) set to a temperature of 450°C in a nitrogen gas flow of 50 ml / min. ３ ) for 15 minutes to completely decompose the sizing agent. Then, the carbon fiber bundle was transferred to a container in a dry nitrogen gas flow of 20 liters / minute, and cooled for 15 minutes, after which the carbon fiber bundle was weighed (W ２ (g)) (read to four decimal places) and W １ -W ２ The mass of the sizing agent was determined by the above formula. The mass of this sizing agent was converted into mass % relative to 100 mass % of the carbon fiber bundle containing the sizing agent (rounded to two decimal places), and this value was taken as the sizing agent content (mass %). The measurement was performed twice, and the average value was taken as the sizing agent content. When no sizing agent was added to the carbon fiber, the value obtained by this measurement was taken as the amount of thermal decomposition of the carbon fiber.

[0081] In the present invention, the preferable range of the sizing agent content in the carbon fiber bundle after heat treatment at 250°C for 20 seconds in an oxidizing atmosphere was evaluated on a four-point scale based on the following criteria: A: The sizing agent content was 0.02% by mass or more and less than 0.06% by mass B: The sizing agent content was 0.06% by mass or more and less than 0.08% by mass C: The sizing agent content was 0.08% by mass or more and 0.10% by mass D: The sizing agent content was less than 0.02% by mass or more than 0.10% by mass.

[0082] <Surface oxygen concentration (O / C) of carbon fiber> The surface oxygen concentration (O / C) of carbon fiber was measured by X-ray photoelectron spectroscopy according to the following procedure: First, carbon fibers were cut into 20 mm pieces and spread out on a copper sample support.１、２ The sample chamber was filled with 1 × 10 －８ Torr, and the photoelectron escape angle was set to 45°. １Ｓ The binding energy value of the main peak of C was set to 285 eV. １Ｓ The peak area was determined by drawing a linear baseline in the range of 275 to 290 eV as the binding energy value. １ｓ The peak area was determined by drawing a straight baseline in the binding energy range of 525 to 540 eV. The X-ray photoelectron spectroscopy apparatus used was an ESCA-1600 manufactured by ULVAC-PHI, Inc.

[0083] <Photoelectron intensity ratio (b) / (a) on the surface of carbon fiber> The photoelectron intensity ratio (b) / (a) on the surface of carbon fiber is the C obtained according to the above procedure. １Ｓ It was determined from the core spectrum according to the following procedure. １Ｓ The linear baseline from 282 to 292 eV from which the peak area was determined was defined as the origin of the photoelectron intensity, and the photoelectron intensity (a) (cps: photoelectron intensity per unit time) detected at a binding energy of 284.6 eV and the photoelectron intensity (b) (cps) detected at a binding energy of 286.1 eV were determined, and (b) / (a) was calculated.

[0084] In the present invention, the preferable range of the equivalence to the original carbon fiber surface state was evaluated in four stages based on the following criteria: A: Photoelectron intensity ratio (b) / (a) is 0.3 or more and 0.5 or less; B: Photoelectron intensity ratio (b) / (a) is more than 0.5 and 0.6 or less; C: Photoelectron intensity ratio (b) / (a) is 0.2 or more and less than 0.3, or more than 0.6 and 0.8 or less; D: Photoelectron intensity ratio (b) / (a) is less than 0.2, or more than 0.8.

[0085] <Method for measuring the coefficient of friction between fibers> The coefficient of friction between fibers was determined by the following procedure. A fiber was wound on a bobbin fixed so as not to rotate, with a thickness of 5 to 10 mm and a winding density of 0.9 to 1.4 g / cm. ３A carbon fiber bundle identical to the wound object was wrapped around the surface of a carbon fiber bundle containing a sizing agent, which had been wound within a range of 100°C (0.15°F) and had a contact angle of 3π (rad), without overlapping on the circumference. A weight (T1 = 0.25 g / tex) was attached to one end of the wound carbon fiber bundle, and the other 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 (g / tex), and the fiber-to-fiber friction coefficient was calculated from the following formula. Measurements were performed twice, and the average value was taken as the fiber-to-fiber friction coefficient. The measurement bobbin used had been placed under ambient temperature and humidity conditions (measurement conditions: 23±3°C / 60±5%) for at least two hours before the measurement.

[0086] Fiber-to-fiber friction coefficient=ln(T2 / T1) / θ T2: tension when the carbon fiber bundle starts to move T1: weight mass (=0.25 g / tex) θ: total contact angle between the wound object and the wound yarn (=3πrad).

[0087] <Method for measuring CF abrasion fluff> Four metal bars (material: stainless steel SUS304) having a diameter of 20 mm and a surface roughness Rmax (JIS B 0601 (1982)) of 0.3 μm were arranged at 150 mm intervals in the vertical direction so that the carbon fiber bundle passed while contacting the metal bars at a total angle of 1.57π (rad). Then, the carbon fiber bundle was hung on the metal bars, the unwinding tension from the package was set to 500 g, and the carbon fiber bundle was pulled by a drive roll at a speed of 6 m per minute to pass the metal bars. A laser beam was irradiated perpendicularly from the side to the fiber yarn after passing the fourth metal bar, and the number of fluffs was detected and counted for 1 minute using a fluff detector, and the number was recorded. In the present invention, the preferable range of handleability was evaluated on a three-point scale based on the following criteria, with A and B being considered acceptable and C being considered unacceptable. A: Less than 4 fluffs / m B: 4 fluffs / m or more and less than 8 fluffs / m C: 8 fluffs / m or more The materials and components used in each example and comparative example are as follows.

[0088] Component (A): A-1: ​​Triethylene glycol (molecular weight: 150, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) A-2: Polyethylene glycol (molecular weight: 200, manufactured by Sanyo Chemical Industries, Ltd. PEG200) A-3: Acetylene glycol surfactant (molecular weight: 290, manufactured by Nissin Chemical Industry Co., Ltd. "Surfynol (registered trademark)" 440) A-4: Polyethylene glycol (molecular weight: 300, manufactured by Sanyo Chemical Industries, Ltd. PEG300) A-5: Polypropylene glycol (molecular weight: 400, manufactured by Sanyo Chemical Industries, Ltd. Newpol GP400) A-6: Diethylene glycol (molecular weight: 106, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) A-7: Polyethylene glycol (molecular weight: 600, manufactured by Sanyo Chemical Industries, Ltd. PEG600) A-8: Polypropylene glycol (molecular weight: 600, manufactured by Sanyo Chemical Industries, Ltd. PPG600) A-9: Acetylene glycol surfactant (molecular weight: 466, manufactured by Nissin Chemical Industry Co., Ltd., "Surfynol (registered trademark)" 465) A-10: Bisphenol A ethylene oxide adduct (molecular weight: 490, manufactured by Sanyo Chemical Industries, Ltd., Newpol BPE60) A-11: Glycerol polyglycidyl ether (molecular weight: 400, manufactured by Nagase ChemteX Corporation, "Denacol (registered trademark)" Ex-313) A-12: 4-tert-butylphenyl glycidyl ether (molecular weight: 206, manufactured by Tokyo Chemical Industry Co., Ltd.) A-13: Polyethyleneimine (molecular weight: 800, manufactured by BASF Japan Ltd., "Lupasol (registered trademark)" FG)

[0089] First, a reference example will be described, which comprises the following two steps.

[0090] Reference Example 1 - Step of Producing Carbon Fiber as Raw Material An acrylonitrile copolymer was spun and calcined to obtain a carbon fiber having a total filament count of 12,000, a total fineness of 800 tex, a strand tensile strength of 5.1 GPa, and a strand tensile modulus of 240 GPa. Next, the carbon fiber bundle was 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. The carbon fiber subjected to this electrolytic surface treatment was then washed with water and dried in heated air at 150°C to remove water, thereby obtaining a carbon fiber as a raw material. The amount of thermal decomposition of the carbon fiber obtained in this first step, the surface oxygen concentration, the photoelectron intensity ratio of the carbon fiber bundle surface, and the fiber-to-fiber friction coefficient were measured. As a result, the amount of thermal decomposition of the carbon fiber bundle was 0.05% by mass, the surface oxygen concentration of the carbon fiber was 0.18, the photoelectron intensity ratio of the carbon fiber bundle surface was 0.4, and the fiber-to-fiber friction coefficient was 0.42.

[0091] Evaluation of sizing agent content in carbon fiber bundle after heat treatment and surface state of carbon fiber The carbon fiber obtained in the previous step was heat treated at 250°C for 20 seconds by the method described above, and then the amount of pyrolysis and the photoelectron intensity ratio of the carbon fiber bundle surface were measured.

[0092] As a result, the amount of thermal decomposition of the carbon fiber was 0.04 mass %, and the photoelectron intensity ratio was 0.4, which were found to be very close to the values ​​before and after the heat treatment. The results are summarized in Table 1.

[0093]

[0094] (Reference Example 2) In the evaluation of the sizing agent content in the carbon fiber bundle after the heat treatment and the surface state of the carbon fiber, heat-treated carbon fibers were obtained and various evaluations were carried out in the same manner as in Reference Example 1, except that the heat treatment temperature was changed to 400° C. The results are shown in Table 1, and the photoelectron intensity ratio on the surface of the carbon fiber bundle decreased.

[0095] (Reference Example 3) Carbon fibers were obtained in the same manner as in Reference Example 1, except that in the process of producing the carbon fibers used as the raw material, the amount of electricity was changed to 10 coulombs per 1 g of carbon fiber for the electrolytic surface treatment, and various evaluations were carried out. The results are shown in Table 1, and it was found that the values ​​after the heat treatment were very close to those before the treatment, but the amount of functional groups in the original carbon fibers was small.

[0096] (Reference Example 4) In the process of producing the carbon fibers used as the raw material, the amount of electricity was changed to 10 coulombs per 1 g of carbon fiber for electrolytic surface treatment, and in the evaluation of the sizing agent content in the carbon fiber bundle after heat treatment and the surface state of the carbon fiber, the heat treatment temperature was changed to 400° C. Carbon fibers were obtained in the same manner as in Reference Example 1, and various evaluations were carried out. The results are shown in Table 1, and it was found that the values ​​after heat treatment were very close to those before treatment, but the amount of functional groups in the original carbon fibers was small.

[0097] Next, a description will be given of Example 1. Example 1 comprises the following first to fourth steps.

[0098] Example 1 - First step: step of producing carbon fiber as raw material An acrylonitrile copolymer was spun and calcined to obtain a carbon fiber having a total filament count of 12,000, a total fineness of 800 tex, a strand tensile strength of 5.1 GPa, and a strand tensile modulus of 240 GPa. Next, the carbon fiber bundle was 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. The carbon fiber subjected to this electrolytic surface treatment was then washed with water and dried in heated air at 150°C to remove water, thereby obtaining a carbon fiber as raw material. The surface oxygen concentration of the carbon fiber obtained in this first step, the photoelectron intensity ratio of the carbon fiber bundle surface, and the fiber-to-fiber friction coefficient were measured.

[0099] Second step: Step of incorporating a sizing agent into carbon fibers. As a sizing agent, (A-1) was used in the composition shown in Table 2, and water was added to dissolve the sizing agent to obtain an approximately 1.5% by mass aqueous solution. This aqueous solution was used as a sizing agent solution, and the sizing agent was incorporated into a surface-treated carbon fiber bundle by immersion. The resulting bundle was then heat-treated with a hot roller at 120°C for 5 seconds as a drying step, yielding a carbon fiber bundle containing the sizing agent. The sizing agent content was adjusted to 0.7% by mass, based on 100% by mass of the total amount of the surface-treated carbon fiber bundle containing the sizing agent. Furthermore, the thermal weight loss of the sizing agent was evaluated using the following method. The thermal weight loss A was 4.8%, the thermal weight loss B was 99.5%, and the thermal weight loss C was 99.8%.

[0100] <Thermal Weight Loss Rate A> The sizing agent was weighed in the range of 10±2 mg (this measured mass was expressed as W Ａ１ The mass of the sizing agent was measured using a thermogravimetric analyzer in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min at a rate of 10°C / min from 30°C, and the mass of the sizing agent was measured when the temperature reached 140°C (this measured mass was referred to as W Ａ１ (mg), and the thermal weight loss rate A is calculated using the following formula (A): Thermal weight loss rate A (%) = {(W Ａ０ -W Ａ１ ) / W Ａ０}×100 (A) <Thermal Weight Loss Rate B> The sizing agent was weighed in the range of 10±2 mg (this weighed mass was Ｂ０ The mass of the sizing agent was measured using a thermogravimetric analyzer in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min at a rate of 10°C / min from 30°C, and the mass of the sizing agent was measured when the temperature reached 250°C (this measured mass was referred to as W Ｂ１ (mg), and the thermal weight loss rate B is calculated using the following formula (B): Thermal weight loss rate B (%) = {(W Ｂ０ -W Ｂ１ ) / W Ｂ０}×100 (B) <Thermal Weight Loss Rate C> The sizing agent was weighed in the range of 10±2 mg (this weighed mass was Ｃ０The mass of the sizing agent was measured using a thermogravimetric analyzer in a nitrogen gas flow of 200 ml (volume at 1 atmosphere and 25°C) / min at a rate of 10°C / min from 30°C, and the mass of the sizing agent was measured when the temperature reached 350°C (this measured mass was referred to as W Ｃ１ (mg), and the thermal weight loss rate C is calculated using the following formula (C): Thermal weight loss rate C (%) = {(W Ｃ０ -W Ｃ１ ) / W Ｃ０}×100...(C).

[0101] -Third step: Evaluation of handleability of carbon fiber bundle containing sizing agent Using the carbon fiber bundle obtained in the second step, handleability was evaluated based on the measurement method for CF abrasion fluff. As a result, it was found that fluff was unlikely to occur in the processing step and that the handleability was very good.

[0102] - Fourth step: Evaluation of sizing agent content and carbon fiber surface state after heat treatment The carbon fiber bundle containing the sizing agent obtained in the previous step was pyrolyzed by the burn-off method described above, and a carbon fiber bundle containing the sizing agent after burn-off at 250°C for 20 seconds was obtained.

[0103] Subsequently, the sizing agent content was measured, and the photoelectron intensity ratio of the carbon fiber bundle surface was measured. As a result, it was found that the sizing agent content after the heat treatment was 0.04 mass%, which was a small amount of residual sizing agent, 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.

[0104] The above results are summarized in Table 2.

[0105]

[0106] (Example 2) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that in the second step, the sizing agent was mixed at a ratio of 90 mass % (A-1) and 10 mass % (A-11), and various evaluations were performed. The results are shown in Table 2, and it was found that the handleability was very good, the thermal decomposition of the sizing agent was very high, and the carbon fiber surface was sufficiently close to the original value shown in Reference Example 1.

[0107] (Example 3) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that in the second step, the sizing agents were mixed at a ratio of 80 mass % of (A-1) and 20 mass % of (A-12), and various evaluations were performed. The results are shown in Table 2, and it was found that the handleability was very good, the thermal decomposition of the sizing agent was very high, and the carbon fiber surface was sufficiently close to the original value shown in Reference Example 1.

[0108] (Example 4) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-2) in the second step, and various evaluations were performed. The results are shown in Table 2, and it was found that the handleability was very good, 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.

[0109] (Example 5) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-3) in the second step, and various evaluations were performed. The results are shown in Table 2, and it was found that the handleability was very good, 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.

[0110] (Example 6) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-4) in the second step, and various evaluations were performed. The results are shown in Table 2, and it was found that the handleability was very 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.

[0111] (Example 7) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-5) in the second step, and various evaluations were performed. The results are shown in Table 2, and it was found that the handleability was very 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.

[0112] (Example 8) Except for changing the sizing agent content to 0.4 mass% in the second step, a carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 3, and it was found that the handleability was very good, 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.

[0113]

[0114] Examples 9 to 11 Carbon fiber bundles containing a sizing agent were obtained and subjected to various evaluations in the same manner as in Example 1, except that in the second step, the sizing agent and the content of the sizing agent before the heat treatment were changed as shown in Table 2. The results are shown in Table 3, and it was found that the handleability was sufficiently good, the thermal decomposition of the sizing agent was very high, and the carbon fiber surfaces were very close to the original values ​​shown in Reference Example 1.

[0115] Examples 12 and 13 Carbon fiber bundles containing a sizing agent were obtained and subjected to various evaluations in the same manner as in Example 1, except that in the second step, the sizing agent and the content of the sizing agent before the heat treatment were changed as shown in Table 2. The results are shown in Table 3, and it was found that the handleability was sufficiently good, the thermal decomposition property of the sizing agent was sufficiently high, and the carbon fiber surface was sufficiently close to the original value shown in Reference Example 1.

[0116] (Example 14) Carbon fibers were obtained in the same manner as in Example 1, except that in the first step, the amount of electricity was changed to 10 coulombs per 1 g of carbon fiber for electrolytic surface treatment, and various evaluations were performed. The results are shown in Table 3. The handleability was sufficiently good, the thermal decomposition of the sizing agent was very high, and the photoelectron intensity ratio (b) / (a) of the carbon fiber surface after heat treatment was low, but it was found that the carbon fiber surface was very close to the original value shown in Reference Example 3.

[0117] (Example 15) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that in the second step, the sizing agent was mixed in a ratio of 90 mass% of (A-1) as the first component and 10 mass% of (A-10) as the second component, and various evaluations were performed. The results are shown in Table 3, and it was found that the handleability was very 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.

[0118] (Comparative Example 1) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-6) in the second step, and various evaluations were performed. The results are shown in Table 4. The thermal weight loss rate A was significantly volatilized, and the sizing agent could not be attached to the carbon fiber, resulting in poor handleability.

[0119]

[0120] (Comparative Example 2) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-7) in the second step, and various evaluations were performed. The results are shown in Table 4. The handleability was very good, but the thermal weight loss rate B was small and the thermal decomposition of the sizing agent was poor, and a very large amount of the sizing agent remained on the carbon fiber surface even after the heat treatment, making it impossible to perform carbon fiber surface analysis.

[0121] (Comparative Example 3) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-8) in the second step, and various evaluations were performed. The results are shown in Table 4. The handleability was very good, but the thermal weight 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 even after the heat treatment.

[0122] (Comparative Example 4) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-9) in the second step, and various evaluations were performed. The results are shown in Table 4. The handleability was very good, but the thermal weight loss rates B and C were small, the thermal decomposition of the sizing agent was poor, and a very large amount of the sizing agent remained on the carbon fiber surface even after the heat treatment, making it impossible to perform carbon fiber surface analysis.

[0123] (Comparative Example 5) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-10) in the second step, and various evaluations were performed. The results are shown in Table 4. The handleability was very good, but the thermal weight loss rates B and C were small, the thermal decomposition of the sizing agent was poor, and a very large amount of the sizing agent remained on the carbon fiber surface even after the heat treatment, making it impossible to perform carbon fiber surface analysis.

[0124] (Comparative Example 6) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-11) in the second step, and various evaluations were performed. The results are shown in Table 4. The handleability was very good, but the proportion of the component satisfying formula (1) was less than 50% by mass, and the thermal weight loss rate C was small, so the thermal decomposition of the sizing agent was poor, and the sizing agent remained on the carbon fiber surface even after heat treatment.

[0125] (Comparative Example 7) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-13) in the second step, and various evaluations were performed. The results are shown in Table 4. The handleability was very good, but the proportion of the component satisfying formula (1) was less than 50% by mass, and the thermal weight loss rate C was small, so the thermal decomposition of the sizing agent was poor, and the sizing agent remained on the carbon fiber surface even after heat treatment.

[0126] (Comparative Example 8) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that the sizing agent was changed to (A-7) in the second step and the heating temperature was changed to 400°C in the fourth step, and various evaluations were performed. The results are shown in Table 4. The handleability was very good and no sizing agent remained, but the photoelectron intensity ratio (b) / (a) on the surface of the carbon fiber after heating was low, and even the surface of the original carbon fiber was decomposed.

[0127] (Comparative Example 9) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that (A-1) and (A-11) were mixed and contained in a ratio of 30 mass % and 70 mass % in the second step, and various evaluations were performed. The results are shown in Table 4. The handleability was very good, but the thermal loss rate C was small, so the thermal decomposition of the sizing agent was poor, and the sizing agent remained on the surface of the carbon fiber even after the heat treatment.

[0128] (Comparative Example 10) A carbon fiber bundle containing a sizing agent was obtained in the same manner as in Example 1, except that (A-1) and (A-12) were mixed and contained in a ratio of 30 mass% and 70 mass% in the second step, and various evaluations were performed. The results are shown in Table 4. The handleability was very good, and no sizing agent remained. However, since the proportion of the component satisfying formula (1) was less than 50 mass%, the photoelectron intensity ratio (b) / (a) on the carbon fiber surface after heating was high, and the sizing agent remained on the carbon fiber surface even after heat treatment.

[0129] According to the present invention, it is possible to provide a carbon fiber bundle containing a sizing agent that exhibits good handleability, while the sizing agent on the carbon fiber bundle exhibits thermal decomposition at a low temperature that suppresses thermal decomposition of the oxygen-containing functional groups on the carbon fiber surface, thereby reducing voids in the carbon fiber reinforced composite material and allowing the surface properties of the original carbon fiber to be reflected in the matrix resin.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.

Claims

1. A carbon fiber bundle comprising carbon fibers and a sizing agent that satisfies all of the following (i) to (iv). (i) Satisfies either of the following (a) or (b). (a) The proportion of the polyalkylene glycol structure in the total mass of the sizing agent is 80% by mass or more, and the number average molecular weight of the sizing agent is 120 or more 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 20% by mass or more (ii) The thermal weight loss rate A determined under the following measurement conditions is 5.0% or less. (iii) The thermal weight loss rate B determined under the following measurement conditions is 11.0% or more. (iv) The thermal weight loss rate C determined under the following measurement conditions is 90.0% or more. <Thermal weight loss rate A> Weigh the sizing agent in the range of 10 ± 2 mg (let this weighed mass be W Ａ０ (mg)), and using a thermogravimetric analyzer, heat it up at a rate of 10 °C / min from 30 °C in a nitrogen gas stream of 200 milliliters (volume at 1 atm and 25 °C) / min, and measure the mass of the sizing agent when it reaches 140 °C (let this measured mass be W Ａ１ (mg)), and calculate the thermal weight loss rate A from the following formula (A). Heat reduction rate A (%) = { (W Ａ０ - W Ａ１ ) / W Ａ０} × 100... (A) <Thermal weight loss rate B> Weigh the sizing agent in the range of 10 ± 2 mg (let this weighed mass be W Ｂ０ (mg)), and using a thermogravimetric analyzer, heat it at a rate of 10 °C / min from 30 °C in a nitrogen gas stream of 200 milliliters (volume at 1 atm and 25 °C) / min until it reaches 250 °C, and measure the mass of the sizing agent at this time (let this measured mass be W Ｂ１ (mg)), and calculate the thermal weight loss rate B from the following formula (B). Heat reduction rate B (%) = { (W Ｂ０ - W Ｂ１ ) / W Ｂ０} × 100... (B) <Thermal weight loss rate C> Weigh the sizing agent in the range of 10 ± 2 mg (let this weighed mass be W Ｃ０ (mg)), and using a thermogravimetric analyzer, increase the temperature at a rate of 10 °C / min from 30 °C in a nitrogen gas stream of 200 milliliters (volume at 1 atm and 25 °C) / min, and measure the mass of the sizing agent when reaching 350 °C (let this measured mass be W Ｃ１ (mg)), and calculate the thermal weight loss rate C from the following formula (C). Heat reduction rate C (%) = { (W Ｃ０ - W Ｃ１ ) / W Ｃ０} × 100... (C)

2. The carbon fiber bundle according to Claim 1, wherein in the case of (i)(b) above, 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 substantially contain an aromatic ring.

4. The carbon fiber bundle according to Claim 1 or 2, wherein the sizing agent content is 0.3% by mass or more and 1.2% by mass or less.

5. The carbon fiber bundle according to Claim 1 or 2, wherein the fiber-fiber interfacial friction coefficient of the carbon fiber before application of the sizing agent is 0.25 or more and 0.43 or less.

6. The carbon fiber bundle according to Claim 1 or 2, wherein the surface oxygen concentration of the carbon fiber measured by X-ray photoelectron spectroscopy of the carbon fiber before application of the sizing agent is 0.11 or more and 0.25 or less.

7. A manufacturing method for manufacturing the carbon fiber bundle according to Claim 1 or 2, comprising a step of applying the sizing agent to the carbon fiber, and a drying step of drying the carbon fiber bundle to which the sizing agent has been applied after the application step.

8. The manufacturing method of the carbon fiber bundle according to Claim 7, wherein the drying step is a drying step of drying the carbon fiber bundle at 110 to 140 °C.

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