Carbon fiber bundle containing sizing agent and manufacturing method thereof

Abstract

To provide a carbon fiber bundle containing sizing agent, which has adequate bundling property and frictional property for handleability and is particularly suitable for being combined with thermoplastic matrix resin because sizing agent having good affinity to water is applied on carbon fibers having a specific cross-sectional shape.SOLUTION: A carbon fiber bundle containing sizing agent contains polyethylene glycol and / or surface active agent and satisfies all the following conditions (i) to (iii). (i) A dry F-F friction coefficient is 0.20 or more and 0.39 or less. (ii) The carbon fiber bundle contains 40% or more of single fiber whose cross section perpendicular to a fiber direction satisfies following formulas (1) and (2) in shape: 1.00≤La / Lb≤1.20 ...(1); 1.00≤Ld / Lc≤1.25 ...(2). (iii) A sizing agent coating weight after washing with water for 50 seconds is 0.12 mass% or less in 100 mass% of the carbon fiber bundle containing sizing agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sizing-agent-containing carbon fiber bundle in which a sizing agent that exhibits sizing ability and frictional properties suitable for the handling of the sizing-agent-containing carbon fiber bundle and that easily enhances resin impregnation due to its good affinity with water in an aqueous process represented by a wet powder impregnation method is applied to carbon fibers containing, as a main component, single fibers having a specific cross-sectional shape, and a method for producing the sizing-agent-containing carbon fiber bundle. [Background technology]

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

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

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

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

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

[0007] Furthermore, it has been disclosed that the cross-sectional shape of carbon fibers or their precursor fibers can be controlled to control the processability of carbon composite materials. For example, Patent Document 8 discloses that high levels of convergence and openability can be achieved by producing an acrylic fiber bundle containing a specific mixture of broad bean-shaped, elliptical, and circular single fibers. However, this requires a complex spinneret with broad bean-shaped, elliptical, and circular holes, and in order to stably produce single fibers with widely differing cross-sectional shapes, it is necessary to set conditions to match the cross-sectional shape with the lowest processability, making it difficult to apply to industrial processes. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 3,957,716 [Patent Document 2] Japanese Patent Application Publication No. 57-171767 [Patent Document 3] International Publication No. 2006 / 019139 Brochure [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-54269 [Patent Document 5] Patent No. 6571892 [Patent Document 6] Japanese Patent Application Publication No. 2017-137603 [Patent Document 7] Japanese Patent Application Publication No. 59-144679 [Patent Document 8] Japanese Patent Application Laid-Open No. 2012-188766 Summary of the Invention [Problem to be solved by the invention]

[0009] On the other hand, when handling and interfacial properties are controlled by applying a sizing agent to carbon fiber bundles as described above, when combined with a thermoplastic matrix resin that requires high molding temperatures, depending on the components of the sizing agent, the heat resistance of the matrix resin or the adhesion between the carbon fiber and the matrix resin may be reduced, which may prevent CFRP from achieving its full performance.

[0010] That is, although studies have been conducted on suppressing the generation of fuzz from carbon fiber bundles by applying a sizing agent and on improving processability in aqueous processes, there has been no idea of ​​removing the sizing agent from the carbon fiber from the perspective of minimizing the risk of the above-mentioned effects on the thermoplastic matrix resin in advanced processing, while applying a sizing agent to achieve both suppression of fuzz generation due to breakage of single fibers in the carbon fiber bundle and good openability in water, with the aim of imparting high mechanical properties, typified by the strand strength, of the carbon fiber bundle to the composite material in carbon fiber processing in an aqueous process.

[0011] Furthermore, the idea of ​​combining the suppression of fuzzing by the sizing agent and the ability to open fibers in water with carbon fibers with controlled cross-sectional shapes to obtain a carbon fiber composite material with excellent mechanical properties was also unheard of.

[0012] The present invention has been made in view of the above, and has an object to provide a sizing-agent-containing carbon fiber bundle that is particularly suitable for combination with a thermoplastic matrix resin, in which a sizing agent that exhibits sizing properties and frictional properties suitable for ease of handling and that easily increases resin impregnation due to its good affinity with water in an aqueous process is applied to carbon fibers containing, as a main component, single fibers having a specific cross-sectional shape, thereby reducing the amount of sizing agent remaining after processing into an intermediate substrate. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, the present invention provides a sizing-agent-containing carbon fiber bundle containing a sizing agent containing polyethylene glycol and / or a surfactant, wherein the sizing-agent-containing carbon fiber bundle satisfies all of the following (i) to (iii): (i) The dry FF friction coefficient is 0.20 or more and 0.39 or less. (ii) The fiber contains 40 or more single fibers whose cross-sectional shape perpendicular to the fiber direction satisfies the following formulas (1) and (2): 1.00 ≦ La / Lb ≦ 1.20 (1) 1.00 ≦ Ld / Lc ≦ 1.25 (2) (Here, the line segment passing through the two most distant points on the circumference of a single fiber cross section is defined as the a-axis, and the line segment passing through the midpoint of the a-axis and two points on the circumference and intersecting at right angles to the a-axis is defined as the b-axis, the length of the a-axis is defined as La, and the length of the b-axis is defined as Lb, with La ≥ Lb. Furthermore, when the a-axis is divided into four equal parts, the lengths of the two line segments passing through a point other than the midpoint of the a-axis and two points on the circumference and intersecting at right angles to the a-axis are defined as Lc and Ld, with Lc ≤ Ld.) (iii) After washing with water for 50 seconds under the following conditions, the amount of sizing agent attached is 0.12 mass % or less based on 100 mass % of the sizing-agent-containing carbon fiber bundle. <Method for washing carbon fiber bundles containing a sizing agent> The sizing-agent-containing carbon fiber bundle is introduced into water via rollers, and the sizing agent is dissolved into the water. The sizing-agent-containing carbon fiber bundle placed in the unwinding process is passed through the water in the water washing tank via free rollers before the water washing tank, free rollers in the water washing tank, and free rollers after the water washing tank during the water washing process. It then passes continuously through a drying process to dry the water and is wound up in the winding process. The water temperature is 25°C, the unwinding tension from the creel is 800 g, the process speed is 2.4 m / min, the diameter of the free roller in the water washing tank is 150 mm, and the contact angle between the sizing-agent-containing carbon fiber bundle and the free roller in the water washing tank is π rad. The liquid level is adjusted so that the time of passage through water is 50 seconds. The drying process is non-contact drying, and the sizing-agent-containing carbon fiber bundle after water washing is dried at a drying temperature of 150°C for 1 minute to obtain a water-washed and dried sizing-agent-containing carbon fiber bundle. The amount of sizing agent attached to the sizing-containing carbon fiber bundle after washing with water and drying is measured to obtain the amount of sizing agent attached.

[0014] Furthermore, the method for producing a sizing-agent-containing carbon fiber bundle of the present invention is the method for producing the above-mentioned sizing-agent-containing carbon fiber bundle, characterized in that it includes a drying step of drying the carbon fiber bundle coated with the sizing agent after a coating step of coating the carbon fiber bundle with a sizing agent containing polyethylene glycol and / or a surfactant. [Effects of the Invention]

[0015] According to the present invention, a sizing agent that exhibits bundling properties and frictional properties suitable for ease of handling and that easily increases resin impregnation due to its good affinity with water in aqueous processes is applied to carbon fibers containing, as a main component, single fibers having a specific cross-sectional shape. This reduces the amount of sizing agent remaining after processing into an intermediate substrate, and makes it possible to obtain a sizing-agent-containing carbon fiber bundle that is particularly suitable for combination with a thermoplastic matrix resin. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing how La·Lb·Lc·Ld are defined in the cross section of a single carbon fiber. [Figure 2] FIG. 2 is a diagram showing the evaluation method for 50-second water washing. [Figure 3] FIG. 3 is a diagram showing the evaluation method for 25-second water washing. [Figure 4] In FIG. 4, (A) and (B) are examples of the die holes that can be suitably used in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described.

[0018] The sizing-agent-containing carbon fiber bundle of the present invention is a sizing-agent-containing carbon fiber bundle that contains a sizing agent containing polyethylene glycol and / or a surfactant, and satisfies all of the following (i) to (iii): (i) The dry FF friction coefficient is 0.20 or more and 0.39 or less. (ii) The cross-sectional shape perpendicular to the fiber direction contains 40% or more of single fibers that satisfy the following formulas (1) and (2): 1.00 ≦ La / Lb ≦ 1.20 (1) 1.00 ≦ Ld / Lc ≦ 1.25 (2) (Here, the line segment passing through the two most distant points on the circumference of a single fiber cross section is defined as the a-axis, and the line segment passing through the midpoint of the a-axis and two points on the circumference and intersecting at right angles to the a-axis is defined as the b-axis, the length of the a-axis is defined as La, and the length of the b-axis is defined as Lb, with La ≥ Lb. Furthermore, when the a-axis is divided into four equal parts, the lengths of the two line segments passing through a point other than the midpoint of the a-axis and two points on the circumference and intersecting at right angles to the a-axis are defined as Lc and Ld, with Lc ≤ Ld.) (iii) After washing with water for 50 seconds under the following conditions, the amount of sizing agent attached is 0.12 mass % or less based on 100 mass % of the sizing-agent-containing carbon fiber bundle. <Method for washing carbon fiber bundles containing a sizing agent> The sizing-agent-containing carbon fiber bundle is introduced into water via rollers, and the sizing agent is dissolved into the water. The sizing-agent-containing carbon fiber bundle placed in the unwinding process is passed through the water in the water washing tank via free rollers before the water washing tank, free rollers in the water washing tank, and free rollers after the water washing tank during the water washing process. It then passes continuously through a drying process to dry the water and is wound up in the winding process. The water temperature is 25°C, the unwinding tension from the creel is 800 g, the process speed is 2.4 m / min, the diameter of the free roller in the water washing tank is 150 mm, and the contact angle between the sizing-agent-containing carbon fiber bundle and the free roller in the water washing tank is π rad. The liquid level is adjusted so that the time of passage through water is 50 seconds. The drying process is non-contact drying, and the sizing-agent-containing carbon fiber bundle after water washing is dried at a drying temperature of 150°C for 1 minute to obtain a water-washed and dried sizing-agent-containing carbon fiber bundle. The amount of sizing agent attached to the sizing-containing carbon fiber bundle after washing with water and drying is measured to obtain the amount of sizing agent attached.

[0019] Through investigations by the present inventors, it was found that when a sizing agent that improves handleability after application to carbon fiber bundles is used, the affinity of the sizing agent with water on the sizing-agent-containing carbon fiber bundles decreases, the sizing agent is likely to remain, and the mechanical properties are likely to decrease during prepreg production. To address this issue, the present inventors have found that even when a compound that is easy to handle is used as the sizing agent, by using a sizing agent containing polyethylene glycol and / or a surfactant to control the coefficient of friction and the amount of sizing agent attached after water washing, and then applying the sizing agent to carbon fibers containing single fibers having a specific cross-sectional shape as the main component, it is possible to achieve both good handleability of the sizing-agent-containing carbon fiber bundles and good elution of the sizing agent in water, while also improving the physical properties of the carbon fiber composite material.

[0020] The sizing agent constituting the present invention must contain polyethylene glycol and / or a surfactant, and the sizing-agent-containing carbon fiber bundle containing the sizing agent must satisfy specific conditions. The surfactant referred to here is an anionic surfactant, a nonionic surfactant, or an amphoteric surfactant.

[0021] The sizing-agent-containing carbon fiber bundle of the present invention must have a dry FF friction coefficient of 0.20 or more and 0.39 or less. At 0.20 or more, force is easily applied between the individual fibers, which tends to improve bundling ability. A coefficient of 0.22 or more is more preferable, and 0.25 or more is even more preferable. At 0.39 or less, the frictional force between the individual fibers in the carbon fiber bundle is reduced, thereby reducing fluff generated by friction when the carbon fiber bundle is unwound from the bobbin and fluff generated by friction within the bundle when it comes into contact with a metal bar. A coefficient of 0.36 or less is more preferable, and 0.30 or less is even more preferable. The dry FF friction coefficient can be controlled by the roughness of the carbon fiber surface, the type and amount of surfactant contained in the sizing agent, or, more simply, the drying temperature after application of the sizing agent. It can also be controlled by the amount of sizing agent attached, etc. The procedure for evaluating the dry FF friction coefficient specified in the present invention will be explained in the examples.

[0022] The sizing-agent-containing carbon fiber bundle of the present invention is a sizing-agent-containing carbon fiber bundle containing 40% or more of single fibers whose cross-sectional shape perpendicular to the fiber direction satisfies the following formulas (1) and (2). 1.00 ≦ La / Lb ≦ 1.20 (1) 1.00 ≦ Ld / Lc ≦ 1.25 (2) where the line segment passing through the two most distant points on the circumference of a single fiber cross section is the a-axis, and the line segment passing through the midpoint of the a-axis and two points on the circumference and intersecting perpendicular to the a-axis is the b-axis, the length of the a-axis is defined as La, the length of the b-axis is defined as Lb, and La ≥ Lb. Furthermore, when the a-axis is divided into four equal parts, the lengths of the two line segments passing through a point other than the midpoint of the a-axis and two points on the circumference and intersecting perpendicular to the a-axis are defined as Lc and Ld, and Lc ≤ Ld.

[0023] In the present invention, the cross section perpendicular to the fiber direction includes not only a cross section cut strictly perpendicular to the length direction of the fiber but also a tensile fracture cross section, because carbon fiber is a brittle material and the tensile fracture cross section tends to be nearly perpendicular to the fiber direction.

[0024] In this invention, the a-axis refers to a line segment passing through the two most distant points on the periphery, and the b-axis refers to a line segment passing through the midpoint of the a-axis and two points on the periphery and perpendicular to the a-axis, with their lengths designated La and Lb, respectively. If the cross-sectional shape is extremely close to a perfect circle and the a-axis cannot be determined, any line segment passing through the center of the circle and two points on the periphery is determined to be the a-axis. Note that if the cross-sectional shape is significantly crushed inward, such as a beta shape or broad bean shape, and the a-axis or b-axis cannot be determined, La, Lb, etc. cannot be defined and are deemed out of range (N / A).

[0025] Furthermore, of the three points required to divide the a-axis into four equal parts, for the two points other than the intersection of the a-axis and the b-axis, two line segments can be drawn that pass through these three points, the a-axis and two other points on the perimeter, and are perpendicular to the a-axis. The lengths of these line segments are defined as Lc and Ld, and Lc ≦ Ld. According to this definition, a circle is a special case where La / Lb = Ld / Lc = 1, and an ellipse is when La / Lb is greater than 1 and Ld / Lc = 1.

[0026] Equation (1) is the ratio of the length of the a-axis La to the length of the b-axis Lb; when La / Lb is 1, the shape is circular, and as it increases, the shape becomes flatter. Equation (2) expresses the deviation from an ellipse; when Ld / Lc is 1, the shape is elliptical, and as it increases, the distance between the intersection of the a-axis and the b-axis and the center of gravity increases, resulting in a highly asymmetric oval shape.

[0027] As La / Lb and Ld / Lc increase above 1.00, the circumferential length per unit area increases. In other words, the surface area of ​​a single fiber of the same weight increases, increasing the contact area between the carbon fiber and the resin and improving adhesion. On the other hand, if La / Lb and Ld / Lc are too large, the tensile strength of the single fiber decreases, tending to result in a decrease in overall strand strength. However, if La / Lb is 1.20 or less and Ld / Lc is 1.25 or less, respectively, there is no or a negligible decrease in strand strength compared to a circular fiber. The cross-sectional shape of the single fiber can be controlled by adjusting the coagulation bath concentration conditions and the spinneret, as described below.

[0028] In the carbon fiber bundle of the present invention, in order to suppress a decrease in strand strength, it is necessary that the proportion of single fibers that simultaneously satisfy the above formulas (1) and (2) is at least a certain value. If this proportion is low, the strand strength may decrease. If the content of single fibers that simultaneously satisfy formulas (1) and (2) is 40% or more on a number basis, the decrease in strand strength can be suppressed. The higher this proportion, the better, with 50% or more being more preferable, 60% or more being even more preferable, 70% or more being particularly preferable, and 100% being the most preferable. This proportion can be controlled by setting the conditions for the coagulation bath concentration and the conditions for the spinneret, which will be described later, or by changing the distance of the space through which the spinning solution passes after being discharged from the spinneret in dry-wet spinning.

[0029] In the present invention, <la lb>and <ld lc>is the average value of La / Lb and Ld / Lc for each single fiber in the carbon fiber bundle. A specific evaluation method will be explained in the Examples. Even if the proportion of single fibers that simultaneously satisfy the above formulas (1) and (2) is 50% or more, if the other single fibers are extremely deviated from a circular or elliptical shape, the carbon fiber bundle obtained by containing these single fibers with reduced tensile strength may have increased fluff and pilling, resulting in a decrease in quality. Therefore, <la lb>is 1.20 or less, <ld lc>It is preferable that the condition of 1.20 or less is satisfied at the same time.

[0030] The cross-sectional shape parameters La, Lb, Lc, and Ld are evaluated by observing the cross section of a single fiber. Tensile fracture surfaces and polished cross sections can be observed and evaluated using optical microscopes, digital microscopes, scanning electron microscopes, transmission electron microscopes, and the like. These parameters require a resolution of 0.2% of the length to be measured, so if the minor axis is 5 μm, evaluation must be performed using an electron microscope. Specific evaluation methods are described in the Examples section. Note that if there are small depressions or chips of 100 nm or more on the periphery of the sampled single fiber as described above, the single fiber should not be used for measurement, and a new single fiber should be randomly sampled and used.

[0031] <How to calculate the amount of sizing agent attached after rinsing with water for 50 seconds> The sizing-agent-containing carbon fiber bundle of the present invention must have a sizing agent adhesion amount of 0.12% by mass or less after washing with water for 50 seconds. If the amount of remaining sizing agent is reduced by extending the water washing time, the contribution of the surface functional groups of the carbon fiber to the physical properties of the matrix resin increases, which is preferable, thereby improving the mechanical properties. At 0.12% by mass or less, the effect of the sizing agent on the matrix resin is reduced, and the contribution of the surface functional groups of the carbon fiber to the physical properties of the matrix resin increases, improving the mechanical properties. A content of 0.10% by mass or less is even more preferable.

[0032] Here, the method of washing a sizing-agent-containing carbon fiber bundle for 50 seconds with water, as specified in the present invention, can be carried out by the following procedure. The sizing-agent-containing carbon fiber bundle is introduced into water via rollers, and the sizing agent is dissolved into the water. This washing procedure is shown in Figure 2. The washing of the sizing-agent-containing carbon fiber bundle can be carried out by the following procedure. The sizing-agent-containing carbon fiber bundle 1a placed in the unwinding process 11 is passed through a pre-water-washing-tank free roller 15, a free roller in the water-washing tank 16, and a free roller after the water-washing tank 17 in the water-washing process 12, and then passed through similar pre-water-washing-tank free rollers 19, a free roller in the water-washing tank 20, and a free roller after the water-washing tank 21, and then passed through water 1e in the water-washing tank 22, and then continuously passed through a drying process 13 to dry the bundle, and then wound up in a winding process 14. The water temperature was 25°C, the unwinding tension from the creel was 800 g, the process speed was 2.4 m / min, the diameter of the free roller in the water washing tank was 150 mm, and the contact angle between the sizing-containing carbon fiber bundle and the free roller in the water washing tank was π rad. The liquid level was adjusted so that the time spent underwater in one water washing tank was 25 seconds, for a total of 50 seconds in the two water washing tanks. The drying process was non-contact drying, and the washed sizing-containing carbon fiber bundle 1b was dried at a drying temperature of 150°C for 1 minute to obtain the washed and dried sizing-containing carbon fiber bundle 1c. The sizing-containing carbon fiber bundle 1c was then measured for its adhesion weight.

[0033] <How to calculate the amount of sizing agent attached after rinsing with water for 25 seconds> The sizing agent-containing carbon fiber bundle of the present invention preferably has a sizing agent adhesion amount of 0.12% by mass or less after 25 seconds of water washing. At 0.12% by mass or less, the effect of the sizing agent on the matrix resin is reduced, and the contribution of the surface functional groups of the carbon fiber to the physical properties of the matrix resin increases, improving the mechanical properties. 0.08% by mass or less is even more preferable.

[0034] The 25-second water washing method for a sizing-agent-containing carbon fiber bundle, as specified in the present invention, can be carried out by the following procedure. The sizing-agent-containing carbon fiber bundle is introduced into water via rollers, and the sizing agent is dissolved into the water. This water washing procedure is shown in Figure 3. The sizing-agent-containing carbon fiber bundle 1a placed in the unwinding process 11 is passed through water 1d in a water washing tank 18 via a pre-water washing tank free roller 15, a water washing tank free roller 16, and a water washing tank free roller 17 in a water washing process 12. The bundle then passes continuously through a drying process 13 to dry the water, and is wound up in a winding process 14. The water temperature is 25°C, the unwinding tension from the creel is 800 g, the process speed is 2.4 m / min, the diameter of the free roller in the water washing tank is 150 mm, and the contact angle between the sizing-agent-containing carbon fiber bundle and the free roller in the water washing tank is π rad. The liquid level is adjusted so that the time of passage through water is 25 seconds. The drying process is a non-contact drying process, in which the washed carbon fiber bundle 1b containing the sizing agent is dried at a drying temperature of 150°C for 1 minute to obtain the washed and dried carbon fiber bundle 1c containing the sizing agent. The amount of sizing agent attached to this washed and dried carbon fiber bundle 1c is measured to obtain the amount of sizing agent attached.

[0035] Furthermore, in the sizing-agent-containing carbon fiber bundle of the present invention, after washing for 50 seconds using the water washing method described above, the average surface area ratio of single fibers measured using an atomic force microscope by the method described below is preferably 1.01 to 1.07, more preferably 1.02 to 1.05, and particularly preferably 1.03 to 1.04. The surface area ratio is expressed as the ratio of the actual surface area to the projected area of ​​the carbon fiber surface, and indicates the degree of surface roughness. The closer the surface area ratio is to 1, the smoother the surface is, which tends to be advantageous for improving the tensile strength of the carbon fiber. Furthermore, the larger the surface area ratio, the greater the surface roughness, which tends to be advantageous for improving resin impregnation by reducing friction of the carbon fiber and for improving adhesion by increasing the contact area with the resin.

[0036] If the surface area ratio is 1.01 or more, the presence of surface irregularities can be expected to improve resin impregnation and adhesion, while if it is 1.07 or less, the decrease in strength due to variations in the surface wrinkle morphology is small, so it is preferable to control it within the range of 1.01 to 1.07. This surface area ratio can be controlled by the precursor spinning method and coagulation method described below. Note that if the amount of sizing agent attached after 50 seconds of water rinsing is large, the surface irregularities may be covered with the sizing agent, resulting in a surface area ratio of 1.00.

[0037] An anionic surfactant is a surfactant with an anionic hydrophilic group. When a carbon fiber bundle coated with an anionic surfactant is placed in water, the elution of the sizing agent is improved. As a result, the amount of sizing agent remaining in the carbon fiber bundle is reduced. Although the mechanism is not clear, it is thought that the anionic surfactant ionizes in water, and the anionic hydrophilic group repels the carbon fiber surface, resulting in excellent elution. In addition, anionic surfactants are easier to reduce in molecular weight than nonionic surfactants and amphoteric surfactants, and therefore are thought to be more likely to exhibit excellent elution when washed with water.

[0038] Examples of the anionic surfactant include carboxylates, sulfonates, carboxylate and sulfonate salts, sulfates, and phosphates.

[0039] Specific examples of carboxylates include soap, polyoxyethylene alkyl ether carboxylates, and alkyl hydroxy ether carboxylates. Specific examples of sulfonates include alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkanoyl methyl taurides, and dialkyl sulfosuccinate salts. Specific examples of carboxylates and sulfonates include alkyl sulfosuccinate di-salts and polyoxyethylene alkyl ether sulfosuccinate di-salts. Specific examples of sulfates include higher alkyl sulfates, polyoxyethylene alkyl ether sulfates, sulfated oils, sulfated fatty acid esters, and sulfated olefins. Specific examples of phosphates include higher alkyl phosphates, polyoxyethylene alkyl ether phosphates, and dithiophosphate salts. The cations constituting the salts include alkali metal cations such as sodium and alkaline earth metal cations such as calcium, with alkali metal cations being preferred for increased water solubility. Furthermore, ammonium salts may be used instead of metal salts.

[0040] When an anionic surfactant is used as the surfactant, the amount of sizing agent attached to the sizing-agent-containing carbon fiber bundle is preferably 0.20% by mass or more and 0.80% by mass or less, based on 100% by mass of the sizing-agent-containing carbon fiber bundle. By setting the amount of sizing agent attached to 0.20% by mass or more, the handleability of the sizing-agent-containing carbon fiber bundle can be improved, fluffing during production and processing can be suppressed, and the quality of the carbon fiber bundle, such as smoothness, can be improved. An attached amount of 0.25% by mass or more is more preferable, and 0.30% by mass or more is particularly preferable. On the other hand, by setting the amount of sizing agent attached to 0.80% by mass or less, it is possible to reduce the remaining amount in a short period of time, thereby reducing the impact on the mechanical properties of the composite material. An attached amount of sizing agent is more preferably 0.60% by mass or less, and particularly preferably 0.45% by mass or less.

[0041] In the sizing agent of the present invention, the ratio of hydrophilic groups in the anions constituting the anionic surfactant is preferably 17% or more.

[0042] By making the hydrophilic group ratio in the anions 17% or more, the elution property of the anion moiety into water is improved, so that the sizing agent is easily eluted during washing with water, and the amount of sizing agent remaining on the carbon fiber bundle can be reduced. A ratio of 20% or more is preferable, and 30% or more is more preferable.

[0043] The hydrophilic group ratio is calculated from the molecular weight of the anionic surfactant. It can be calculated from the ratio of the molecular weight of the hydrophilic group part of the anion of the anionic surfactant to the molecular weight of the anionic surfactant. Here, the hydrophilic group is a sulfate ester group (SO4 - ), sulfonic acid group (SO3 - ), and carboxyl groups (COO - ), phosphate group (HPO3 - ), hydroxyl group (OH - In addition, if unreacted moieties remain during the production of the anionic moiety of the surfactant, the reaction rate is calculated from the total amount of the starting material and the reacted material (anion of the anionic surfactant) and the amount of the reacted material, and the hydrophilic group ratio calculated from the molecular weight of the anionic moiety of the anionic surfactant is multiplied by the reaction rate to obtain the hydrophilicity rate of the anionic moiety of the present invention.

[0044] A nonionic surfactant is a surfactant with a hydrophilic group that does not ionize. When carbon fiber bundles coated with polyethylene glycol and / or a nonionic surfactant are placed in water, the elution of the sizing agent is improved. As a result, the amount of sizing agent remaining in the carbon fiber bundle is reduced. Although the mechanism is unclear, it is thought that the hydrophilic group of polyethylene glycol and / or a nonionic surfactant easily interacts with water, resulting in excellent elution. Furthermore, because polyethylene glycol and / or a nonionic surfactant have a hydrophilic group that does not ionize, the strength of their interaction with the carbon fiber surface is not affected by factors such as the pH of the aqueous solution, and it is thought that they are likely to exhibit stable elution.

[0045] Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene dodecyl ether, polyoxyethylene oleyl ether, and polyoxyethylene stearyl ether; polyoxyethylene polyoxypropylene glycol; polyoxyethylene alkylphenyl ethers; sorbitan fatty acid esters such as sorbitan monooleate, sorbitan monostearate, sorbitan sesquioleate, sorbitan coconut oil fatty acid, sorbitan monopalmitate, sorbitan tristearate, and sorbitan trioleate; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate; polyoxyethylene glycerin fatty acid esters such as polyoxyethylene glyceryl monooleate; polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbit tetraoleate; and polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbitan tetraoleate. Examples include ethylene hydrogenated castor oil; polyethylene glycol fatty acid esters such as polyglycerin fatty acid esters, sucrose fatty acid esters, PEG monocaprylate, PEG monoheptylate, PEG monopelargonate, PEG monocaprate, PEG monolaurate, PEG monomyristate, PEG monopentadecylate, PEG monopalmitate, PEG monolinoleate, PEG dilaurate, PEG monooleate, PEG dioleate, PEG monostearate, PEG distearate, PEG dicaprylate, PEG diheptylate, PEG dipelargonate, PEG dicaprate, PEG dilaurate, PEG dimyristate, PEG dipentadecylate, PEG dipalmitate, and PEG dilinoleate. These nonionic surfactants can be used alone or in combination with PEG. "PEG" stands for "polyethylene glycol."

[0046] When polyethylene glycol and a nonionic surfactant are combined, the mixing ratio of polyethylene glycol to nonionic surfactant is preferably 50 parts by mass or more per 100 parts by mass of the total mixture. By using 50 parts by mass or more of polyethylene glycol, the hydrophilicity of polyethylene glycol improves elution, making it easier for the sizing agent to elute during washing with water, and reducing the amount of sizing agent remaining on the carbon fiber bundle. The mixing ratio of polyethylene glycol is more preferably 70 parts by mass or more per 100 parts by mass.

[0047] When a nonionic surfactant is used as the surfactant, the amount of sizing agent attached to the sizing-agent-containing carbon fiber bundle is preferably 0.15% by mass or more and 0.60% by mass or less, based on 100% by mass of the sizing-agent-containing carbon fiber bundle. By setting the amount of sizing agent attached to 0.15% by mass or more, the handleability of the sizing-agent-containing carbon fiber bundle can be improved, fluffing during production and processing can be suppressed, and the quality of the carbon fiber bundle, such as smoothness, can be improved. An attached amount of 0.20% by mass or more is more preferable, and 0.25% by mass or more is particularly preferable. On the other hand, by setting the amount of sizing agent attached to 0.60% by mass or less, it is possible to reduce the remaining amount in a short period of time, thereby reducing the impact on the mechanical properties of the composite material. An attached amount of sizing agent is more preferably 0.50% by mass or less, and particularly preferably 0.45% by mass or less.

[0048] In the sizing agent of the present invention, the lipophilic-hydrophilic balance (HLB) of the polyethylene glycol and / or nonionic surfactant is preferably 15 to 20, or 12 to less than 15, and the ratio of hydroxyl groups at the molecular chain terminals is preferably 50% or more. The HLB value specified in the present invention is a value calculated from the molecular structure based on Griffin's method described in "New Introduction to Surfactants," p. 128 (1992). By adjusting the HLB value of the nonionic surfactant to 15 to 20, the hydrophilicity is improved, making the sizing agent more easily eluted during water washing, and the amount of sizing agent remaining on the carbon fiber bundle can be reduced. The HLB value is preferably 16 or more. Furthermore, even if the HLB value is 12 to less than 15, by adjusting the ratio of hydroxyl groups at the molecular chain terminals to 50% or more, the hydrophilicity of the terminals improves the elution of the nonionic surfactant into water, making the elution of the sizing agent more easily during water washing, and reducing the amount of sizing agent remaining on the carbon fiber bundle.

[0049] In the sizing agent constituting the present invention, it is preferable that the weight-average molecular weight Mw of the polyethylene glycol and / or nonionic surfactant is 300 or more and 5,000 or less, or that the weight-average molecular weight Mw is 120 or more and less than 300, and the proportion of polyalkylene glycol structures is 60 mass% or more. The weight-average molecular weight Mw is measured by gel permeation chromatography (hereinafter abbreviated as GPC) using polyethylene glycol as a standard substance. When the sizing agent constituting the present invention contains both polyethylene glycol and a nonionic surfactant, the measured value of the mixture thereof is used as the weight-average molecular weight Mw.

[0050] The larger the Mw, the higher the viscosity of the polyethylene glycol and / or nonionic surfactant, and therefore the rate of elution from the carbon fiber surface decreases. By setting the Mw to 5,000 or less, the viscosity, which is an index of the mobility of the polyethylene glycol and / or nonionic surfactant, is reduced, and the amount of entanglement of molecular chains during elution in water is reduced, thereby improving the elution of the polyethylene glycol and / or nonionic surfactant into water. The Mw is preferably 2,000 or less, and more preferably 1,000 or less. On the other hand, from the viewpoint of application, the larger the Mw, the more suppressed volatilization during sizing agent application can be, and the more the amount of sizing agent adhered can be increased, thereby suppressing the generation of fuzz. The lower limit of Mw is preferably 300 or more. Even when the Mw is 120 or more but less than 300, by setting the proportion of polyalkylene glycol structures to 60% by mass or more, the intermolecular interaction can be enhanced, thereby suppressing volatilization during sizing agent application and increasing the amount of sizing agent adhered, thereby suppressing the generation of fuzz. The proportion of the polyalkylene glycol structure is more preferably 70% by mass or more, and even more preferably 80% by mass or more. The molecular weight of the polyethylene glycol and / or nonionic surfactant contained in the sizing-agent-containing carbon fiber bundle can be confirmed by extracting the sizing agent from the sizing-agent-containing carbon fiber bundle with water and evaluating it by GPC.

[0051] An amphoteric surfactant is a surfactant that has both an anionic and a cationic moiety in the same molecule. When carbon fiber bundles coated with an amphoteric surfactant are placed in water, the elution of the sizing agent is improved. As a result, the amount of sizing agent remaining in the carbon fiber bundle is reduced. Although the mechanism is unclear, it is thought that the hydrophilic group portion of the amphoteric surfactant interacts easily with water over a wide pH range, unlike other nonionic, anionic, and cationic surfactants, resulting in excellent elution.

[0052] Examples of amphoteric surfactants include amino acid surfactants, betaine surfactants, sulfobetaine surfactants, and amine oxide surfactants.

[0053] Specific examples of amphoteric surfactants include betaine surfactants such as fatty acid amidopropyl betaine, myristyl amidopropyl betaine, coconut oil fatty acid amidopropyl betaine, lauric acid amidopropyl betaine, cocamidopropyl betaine, fatty acid amidopropyl dimethylaminoacetic acid betaine, coconut fatty acid amidopropyl dimethylaminoacetic acid betaine, lauric acid amidopropyl dimethylaminoacetic acid betaine, stearyl dimethylaminoacetic acid betaine, lauryl dimethylaminoacetic acid betaine, lauryl dihydroxyethyl betaine, and 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine; sulfobetaine surfactants such as alkyl hydroxy sulfobetaine, cocamidopropyl hydroxy sulfobetaine, and lauramidopropyl hydroxy sulfobetaine; fatty acid amidopropyl dimethylaminoacetic acid betaine; and amine oxide surfactants such as lauryl amine oxide, lauric acid amidopropyl dimethylamine oxide, lauryl dimethylamine oxide, coconut oil alkyl dimethylamine oxide, dodecyl dimethylamine oxide, decyl dimethylamine oxide, and tetradecyl dimethylamine oxide; and amino acid surfactants such as N-lauroyl-N'-carboxymethyl-N'-hydroxyethyl ethylenediamine sodium, N-coconut oil fatty acid acyl-N'-carboxyethyl-N'-hydroxyethyl ethylenediamine sodium, sodium β-lauryl aminopropionate, sodium cocaminopropionate, alkyl carboxymethyl hydroxyethyl imidazolium betaine, lauryl dimethyl aminoacetic acid betaine, alkyl diaminoethyl glycine hydrochloride, and sodium lauryl aminodipropionate.

[0054] When an amphoteric surfactant is used as the surfactant, the amount of sizing agent attached to the sizing-agent-containing carbon fiber bundle is preferably 0.15% by mass or more and 0.45% by mass or less, based on 100% by mass of the sizing-agent-containing carbon fiber bundle. By setting the amount of sizing agent attached to 0.15% by mass or more, it is possible to improve the handleability of the sizing-agent-containing carbon fiber bundle, suppress the generation of fluff during production and processing, and improve the quality of the carbon fiber bundle, such as smoothness. An attached amount of 0.20% by mass or more is more preferable, and 0.25% by mass or more is particularly preferable. On the other hand, by setting the amount of sizing agent attached to 0.45% by mass or less, it is possible to reduce the remaining amount in a short period of time, thereby reducing the impact on the mechanical properties of the composite material. An attached amount of sizing agent is more preferably 0.40% by mass or less, and particularly preferably 0.35% by mass or less.

[0055] In the sizing agent of the present invention, the average number of carbon atoms in the alkyl groups constituting the amphoteric surfactant is preferably 17 or less.

[0056] By setting the average carbon number of the alkyl group to 17 or less, the elution property of the amphoteric surfactant into water is improved, making it easier for the sizing agent to be eluted during washing with water, and the amount of sizing agent remaining on the carbon fiber bundle can be reduced. The average carbon number of the alkyl group is more preferably 16.5 or less, and even more preferably 16 or less. Also, 8 or more is preferable. If the average carbon number is less than 8, the surface free energy of the sizing agent increases, resulting in a high dry FF friction coefficient.

[0057] The average carbon number of the alkyl groups that make up the amphoteric surfactant can be evaluated by extracting the sizing agent from a carbon fiber bundle containing the sizing agent with water and evaluating it. One method is to freeze-dry the extracted sizing agent and then evaluate its structure from the IR spectrum obtained by infrared spectroscopy, in combination with proton NMR, carbon NMR, and mass spectrometry analysis of the freeze-dried product.

[0058] <How to determine the absorbance of carbon fiber extract> In the sizing-agent-containing carbon fiber bundle constituting the present invention, when the surfactant is an amphoteric surfactant, the absorbance of the water extract is preferably 0.06 or more. By making the absorbance 0.06 or more, contaminants such as oxides attached to the carbon fiber surface are easily removed, improving adhesion. The absorbance is more preferably 0.08 or more, and even more preferably 0.10 or more.

[0059] The absorbance of the water extract of the carbon fiber extract containing a sizing agent as defined in the present invention can be determined by the following procedure. 3 The carbon fiber bundle was placed in a glass container with a lid and 10.0 g of distilled water at 25°C was added. The shaker was set to an amplitude of 30 mm and a shaking speed of 120 rpm. The glass container was placed in the shaker and shaken for 1 minute. After shaking, the carbon fiber bundle was immediately removed from the solution. The solution extracted from the carbon fiber was placed in a quartz cell with a light path length of 1.0 cm. Using distilled water as a control solution, the absorbance from 200 to 900 nm was measured using a UV-visible spectrophotometer, and the absorbance at 600 nm was recorded. The shaker used was a Shaking Bath SB-13 manufactured by AS ONE Corp. The ultraviolet-visible spectrophotometer used was a V-550 manufactured by JASCO Corporation.

[0060] In the sizing agent constituting the present invention, the total amount of polyethylene glycol and / or surfactant in the total amount of sizing agent (100% by mass) is preferably 70% by mass or more. By making the total amount of polyethylene glycol and / or surfactant 70 parts by mass or more, the hydrophilic groups in the surfactant improve elution, making it easier for the sizing agent to be eluted during washing with water, and reducing the amount of sizing agent remaining on the carbon fiber bundle. 85 parts by mass or more is more preferable, and 95 parts by mass or more is even more preferable.

[0061] In addition to polyethylene glycol and / or a surfactant, other components may be included. Hereinafter, the other components may be referred to as the second component. Examples of the other components include aliphatic or alicyclic compounds and / or aliphatic or alicyclic compounds in which two hydroxyl groups are bonded to two different carbon atoms, polyvinyl alcohol, polyglycidyl ether, and polyethyleneimine. Of these, aliphatic or alicyclic compounds and / or aliphatic or alicyclic compounds in which two hydroxyl groups are bonded to two different carbon atoms are particularly preferred.

[0062] In the sizing agent of the present invention, the applied polyethylene glycol and / or surfactant preferably have a mass residual ratio of 35% or less when the temperature reaches 300°C when heated in air at a rate of 10°C / min. When the sizing agent of the present invention contains both polyethylene glycol and a surfactant, the mass residual ratio is the measured value for the mixture of these. By keeping the mass residual ratio at 35% or less, the low-heat-resistant components of the sizing agent decompose before the matrix resin melts, reducing the amount of sizing agent incorporated into the matrix resin. This reduces the impact on the mechanical properties of the composite material and stabilizes the properties. A mass residual ratio of 20% or less is more preferable, and 5% or less is even more preferable.

[0063] In the sizing agent of the present invention, the applied polyethylene glycol and / or surfactant preferably have a mass residual ratio of 30% or less when the temperature reaches 350°C when heated in air at a rate of 10°C / min. When the sizing agent of the present invention contains both polyethylene glycol and a surfactant, the mass residual ratio is the measured value for the mixture of these components. By keeping the mass residual ratio at 30% or less, the low-heat-resistant components of the sizing agent decompose before the high-heat-resistant matrix resin melts, reducing the amount of sizing agent incorporated into the matrix resin. This reduces the impact on the mechanical properties of the composite material and stabilizes the properties. A mass residual ratio of 25% or less is more preferable, and 5% or less is even more preferable.

[0064] Next, the components constituting the sizing agent-containing carbon fiber bundle used in the present invention will be described.

[0065] The carbon fiber bundle of the present invention preferably has a strand strength of 5.0 GPa or more. If the carbon fiber bundle has a strand strength of 5.0 GPa or more, the strand strength of the carbon fiber bundle after washing off the sizing agent with water is sufficiently high, and the effect of improving the mechanical properties of the composite material is likely to be obtained.

[0066] Although there are no particular limitations on the carbon fiber bundles used in the present invention, polyacrylonitrile-based carbon fibers are preferably used from the viewpoint of mechanical properties. Polyacrylonitrile-based carbon fiber bundles can be obtained by subjecting carbon fiber precursor fibers made of polyacrylonitrile-based polymers to flame retardation treatment in an oxidizing atmosphere at a maximum temperature of 200 to 300°C, followed by preliminary carbonization treatment in an inert atmosphere at a maximum temperature of 500 to 1,200°C, and then carbonization treatment in an inert atmosphere at a maximum temperature of 1,200 to 2,000°C.

[0067] In the production of a carbon fiber precursor fiber bundle, either a dry-wet or wet spinning method may be used as the spinning method, but dry-wet spinning is preferred because it is advantageous in terms of production stability, the mechanical properties of the resulting carbon fiber bundle, and furthermore, advanced processability. The spinning process comprises a spinning step in which the fiber is discharged from a spinneret by a dry-wet spinning method and spun into a fiber, a water-washing step in which the fiber obtained in the spinning step is washed in a water bath, a water-bath drawing step in which the fiber obtained in the water-washing step is drawn in a water bath, and a dry-heat treatment step in which the fiber obtained in the water-bath drawing step is dry-heat treated, and may optionally include a steam drawing step in which the fiber obtained in the dry-heat treatment step is steam-drawn.

[0068] In the production of carbon fiber precursor fiber bundles, the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and sodium thiocyanate (sodium rhodanide) aqueous solution used as the solvent for the spinning solution, as well as a so-called coagulation accelerator. The coagulation accelerator can be one that does not dissolve the polyacrylonitrile polymer and is compatible with the solvent used for the spinning solution. Specifically, it is preferable to use water as the coagulation accelerator.

[0069] Dry-wet spinning tends to produce a smooth surface, but an uneven surface can be obtained by enlarging the fibrils, which are the minute coagulation units, or by bringing them to the surface. For example, a method of increasing the temperature of the coagulation bath can be used to enlarge the fibrils. For example, a method of bringing the fibrils to the surface can be used to thin the skin layer by increasing the solvent concentration in the coagulation bath to slow the coagulation rate, or by increasing the draw ratio in a warm water bath.

[0070] In the present invention, adjusting the shape of the spinneret holes allows for the production of carbon fiber precursor fibers suitable for obtaining carbon fibers having a specific cross-sectional shape. The spinneret holes can be shaped to have the same cross-sectional shape as the desired single fiber. However, when using a dry-wet spinning method as the spinning method, it is also preferable to arrange two or more holes closely together so that the extruded polymers can easily coalesce while passing through the air gap. This is because single fibers with controlled cross-sectional shapes can be obtained simply by combining circular holes, which have relatively low processing costs. The preferred spinneret hole shapes in the present invention can be optimized by those skilled in the art through trial and error, and examples such as (A) and (B) in Figure 4 are preferred. However, the spinneret hole shapes should not be interpreted as being limited to these. Furthermore, in the present invention, when one coagulated single fiber is obtained from two or more closely arranged holes, such two or more holes are collectively counted as one spinneret hole. The cross-sectional area of ​​the spinneret hole is 0.002 to 0.1 mm. 2 It is preferable to set the above value in order to obtain carbon fibers having a small single fiber fineness, which is advantageous for the development of mechanical properties. The hole pitch, the number of holes, and the hole arrangement can be easily optimized by a person skilled in the art.

[0071] In the present invention, the proportion of single fibers that simultaneously satisfy the above formulas (1) and (2) can be controlled to a certain value or more by changing the distance through which the spinning solution passes after being discharged from the spinneret in dry-wet spinning. Specifically, the greater the distance, the higher the proportion of cross-sectional shapes that approach a circle. It is preferable to control this distance to approximately several mm.

[0072] 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.

[0073] 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.

[0074] The carbon fiber bundle in the present invention preferably has a surface oxygen concentration of 0.08 or more and 0.25 or less as measured by X-ray photoelectron spectroscopy.

[0075] The presence of functional groups on the carbon fiber surface creates affinity with the matrix resin, enabling it to exhibit high adhesive strength. If the surface oxygen concentration (O / C) is less than 0.08, the affinity between the carbon fiber surface and the matrix resin decreases, resulting in low adhesive strength. If the O / C exceeds 0.25, the number of functional groups increases, but the surface layer of the carbon fiber becomes more susceptible to peeling, resulting in low adhesive strength.

[0076] Next, the method for producing the sizing agent-containing carbon fiber bundle of the present invention will be described.

[0077] First, the means for applying (applying) the sizing agent to the carbon fiber bundle constituting the present invention will be described.

[0078] 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.

[0079] Examples of application methods include a method of immersing a carbon fiber bundle in a sizing agent solution via a roller, a method of bringing a carbon fiber bundle into contact with a roller to which the sizing agent solution is attached, and a method of spraying a mist of the sizing agent solution onto the carbon fiber bundle. In producing the sizing-agent-containing carbon fiber bundle of the present invention, the method of immersing a carbon fiber bundle in a sizing agent solution via a roller is preferably used. The sizing agent may be applied by either a batch method or a continuous method, but the continuous method is preferred because it has good productivity and small variations. Another preferred embodiment is to ultrasonically vibrate the carbon fiber bundle when applying the sizing agent.

[0080] In the present invention, after applying the sizing agent solution, it is preferable to obtain a sizing-agent-containing carbon fiber bundle by contact drying means, for example, by bringing the carbon fiber bundle into contact with a heated roller. The carbon fiber bundle introduced into the heated roller is pressed against the heated roller by tension and rapidly dried, so the flat shape of the carbon fiber bundle expanded by the heated roller is easily fixed by the sizing agent. The flattened carbon fiber bundle has a smaller contact area between individual fibers, which increases the contact area with water when immersed in water, making it more likely to have high elution properties. In addition, in the present invention, after passing the carbon fiber bundle through a heated roller as a preliminary drying step, a further heat treatment may be performed as a second drying step. For the heat treatment as the second drying step, a non-contact heating method is preferable, which makes it easy to perform heat treatment at a high temperature. By performing the heat treatment, the dilution solvent remaining in the sizing agent can be further removed, and the viscosity of the sizing agent can be stabilized, thereby stably increasing elution properties.

[0081] Furthermore, by carrying out the heat treatment, the surface free energy of the surfactant on the carbon fiber can be controlled and the coefficient of friction can be reduced, thereby improving the handleability of the sizing-agent-containing carbon fiber bundle. The heat treatment temperature is preferably in the range of 120 to 260°C. At 120°C or higher, the ionization of the surfactant can be controlled by removing the dilution solution, suppressing electrical interactions, and thus improving the handleability. 150°C or higher is more preferred, and 180°C or higher is even more preferred. On the other hand, by setting the upper limit of the heat treatment temperature to 260°C or lower, thermal degradation of the surfactant component can be suppressed, making it easier to maintain elution. 240°C or lower is more preferred, and 220°C or lower is even more preferred.

[0082] The heat treatment can also be carried out by microwave irradiation and / or infrared irradiation. [Example]

[0083] Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0084] <Single fiber cross-sectional shape (La / Lb, Ld / Lc)> A single fiber was removed from the sizing-containing carbon fiber bundle and fractured by pulling along the fiber axis. The fracture split the single fiber into two. One fiber was discarded, and the remaining fiber was attached to the SEM sample stage using carbon tape with the fracture surface facing upward. This procedure was repeated 25 times to create an SEM sample stage with 25 fracture surfaces attached. Platinum-palladium was then vacuum-deposited to a thickness of approximately 10 nm, and the specimens were then observed using a Hitachi High-Technologies Corporation S-4800 scanning electron microscope (SEM) at an accelerating voltage of 5.0 kV and a working distance of 8 mm.

[0085] The cross-sectional shapes of the 25 carbon fibers were measured as follows.

[0086] (a) Determining the a-axis The a-axis was determined from the SEM image of the fracture surface. The longest line passing through any two points on the periphery of the fracture surface, such that the areas of the two regions resulting from dividing the fracture surface into two equal parts, was taken as the longest line. Because this evaluation was performed visually, the angle of the long axis determined by the measurer varied slightly depending on the time of evaluation, even for the same measurer. However, the variation due to such factors was small, at a maximum of about ±10 degrees, so the average of the results of two consecutive evaluations by the same measurer was used.

[0087] (b) Measurement of La, Lb, Lc, and Ld The open-source image analysis software "ImageJ ver1.47" was used for the measurements. The length of the a-axis, La, was determined by measuring the length of the a-axis determined in (a) in pixel units and converting it to actual length (units: μm) using the scale bar attached to the SEM observation image. Next, three points were placed to divide the a-axis into four equal parts, and three line segments perpendicular to the a-axis were determined, passing through each of these points and two points on the outer periphery of the fiber. Of these, the one passing through the midpoint of the a-axis was defined as the b-axis, and the length of the b-axis, Lb, was determined in the same way as La. The lengths of the remaining two line segments were determined in the same way as La, with the shorter length being Lc and the longer length being Ld.

[0088] In this way, La / Lb and Ld / Lc were calculated for 25 single fibers. Each single fiber was checked to see if it met formula (1) and formula (2), and the number of single fibers that satisfied both formulas was divided by the number of samples (25) to determine the percentage. 1.00≦La / Lb≦1.20 (1) 1.00≦Ld / Lc≦1.25 (2).

[0089] <Average value of cross-sectional shape ( <la lb> 、 <ld lc>)> The La / Lb and Ld / Lc values ​​for 25 single fibers obtained as above were simply averaged, and <la lb>and <ld lc>was calculated.

[0090] <Surface area ratio of single fiber to carbon fiber bundle> Several single precursor fibers to be evaluated were placed on a sample stage and fixed at both ends with an adhesive (e.g., correction fluid). Using an atomic force microscope (Seiko Instruments, SPI3800N / SPA-400), an image of the three-dimensional surface shape was obtained under the following conditions. Probe: Silicon cantilever (Seiko Instruments, DF-20) Measurement mode: Dynamic Force Mode (DFM) Scanning speed: 1.5Hz Scanning range: 3μm x 3μm Resolution: 256 pixels x 256 pixels.

[0091] The obtained measurement image was fitted using the accompanying software to determine a linear plane from all image data using the least squares method, taking into account the curvature of the fiber cross section, and a linear slope correction was performed to correct the in-plane slope. Subsequently, a quadratic slope correction was similarly performed to correct the quadratic curve. After that, the surface roughness was analyzed using the accompanying software and the surface area ratio was calculated. Three different single fibers were randomly sampled, and the measurement was performed once for each single fiber, a total of three times, and the average value was used as the surface area ratio.

[0092] <Method for measuring the amount of sizing agent attached> 2.0±0.5 g of sizing agent-containing carbon fiber bundle was weighed (W1) (read to four decimal places), and then placed in an electric furnace (capacity 120 cm) set at 450°C in a nitrogen gas flow of 50 ml / min. 3 ) for 15 minutes to completely pyrolyze the sizing agent. The carbon fiber bundle was then transferred to a container in a dry nitrogen gas flow of 20 liters / minute and cooled for 15 minutes. The carbon fiber bundle was then weighed (W2) (read to four decimal places) and the heat loss was calculated by subtracting W1 from W2. This heat loss was converted to parts by mass relative to 100 parts by mass of the sizing-agent-containing carbon fiber bundle (rounded to two decimal places), and this value was taken as the amount of sizing agent (parts by mass). The measurement was performed twice, and the average value was taken as the amount of sizing agent attached.

[0093] <Method for measuring the residual mass rate of polyethylene glycol and / or surfactant> The mass residual ratios of polyethylene glycol and / or surfactant were measured using a thermogravimetric-differential thermal analyzer (TG-DTA). 10 ± 0.5 mg of polyethylene glycol and / or surfactant were weighed into an aluminum pan (W3) (read to four decimal places), placed in a heating device, and heated from 25°C to 450°C at a rate of 10°C / min in an airflow of 100 mL / min to thermally decompose the surfactant. The masses at 300°C (W4) (read to four decimal places) and 350°C (W5) (read to four decimal places) were measured, and the mass residual ratios at 300°C and 350°C were calculated from W4 / W3 × 100 (%) and W5 / W3 × 100 (%).

[0094] In the present invention, the measuring device used was a TG-DTA2000SA manufactured by Bruker.

[0095] <Method for measuring the amount of functional groups on the surface of carbon fiber bundles> In this example, the surface oxygen concentration of the carbon fiber bundle was measured by X-ray photoelectron spectroscopy according to the following procedure: First, the carbon fiber bundle was cut into 20 mm pieces, spread out and arranged on a copper sample support, and then AlKα was used as an X-ray source. 1、2 The sample chamber was filled with 1×10 -8 X-ray photoelectron spectroscopy was performed at a constant pressure of 100 Torr and a photoelectron escape angle of 45°. 1S The binding energy value of the main peak of C was adjusted 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 linear baseline in the binding energy range of 525 to 540 eV. The X-ray photoelectron spectroscopy device used was an ESCA-1600 manufactured by ULVAC-PHI, Inc.

[0096] <CF Fluff Measurement Method> Two metal bars (material: made of stainless steel SUS304) with a diameter of 50 mm and a surface roughness Rmax of 0.3 μm were arranged vertically at an interval of 150 mm, and the carbon fiber bundle passed through while contacting the metal bars at a total angle of 0.785π (rad). Then, the carbon fiber bundle was draped over the metal bars, the unwinding tension from the package was set to 800 g, and the carbon fiber bundle was pulled at a speed of 6 m per minute by the driving roll to pass through the metal bars. After passing through the second metal bar, a laser beam was irradiated perpendicularly from the side to the fiber yarn, and the fluff number was detected and counted for 5 minutes by the fluff detection device, and the number was recorded.

[0097] In the present invention, the preferable range of handleability was evaluated in three levels according to the following criteria, and S and A were regarded as qualified, and B was regarded as unqualified.

[0098] S: Less than 15 fluffs / m A: 15 fluffs / m or more and less than 25 fluffs / m B: 25 fluffs / m or more.

[0099] <Dry F-F Friction Coefficient Measurement Method> On a bobbin fixed so as not to rotate, a sizing agent-containing carbon fiber bundle with a thickness of 5 to 10 mm and a winding density of 0.9 to 1.4 g / cm was wound so as to have a uniform thickness. The same carbon fiber bundle as the wound material was wound around the surface of the sizing agent-containing carbon fiber bundle so that the contact angle was 3π (rad) and it did not overlap itself, typically with a gap of 3 to 5 mm in the width direction. A weight (T1 = 0.25 g / tex) was attached to one end of the wound carbon fiber bundle, and the other end was pulled at a speed of 1 m / min only by a spring. The tension when the wound carbon fiber bundle started to move was taken as T2, and the dry F-F friction coefficient was calculated from the following formula. The measurement was performed twice, and the average value was taken as the dry F-F friction coefficient. The measurement bobbin used was placed in the measurement ambient temperature and humidity conditions (measurement conditions: 23 ± 3°C / 60 ± 5%) more than 2 hours before the measurement. 3

[0100] Dry F-F friction coefficient = ln(T2 / T1) / θ T2: Tension when the carbon fiber bundle starts to move (= spring balance reading) T1: Weight of weight (=0.25g / tex) θ: Total contact angle between the wound object and the wound thread (=3πrad).

[0101] <Strand strength and strand modulus of carbon fiber bundle> The strand strength and strand modulus of a carbon fiber bundle are determined according to the following procedure in accordance with the resin-impregnated strand test method of JIS R7608 (2004). However, if the carbon fiber bundle has twists, they are untwisted by twisting the bundle in the opposite direction the same number of times as the twists. The resin formulation used is "Celloxide (registered trademark)" 2021P (manufactured by Daicel Chemical Industries, Ltd.) / boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / acetone = 100 / 3 / 4 (parts by mass), and the curing conditions are atmospheric pressure, 125°C, and 30 minutes. Ten strands of the carbon fiber bundle are measured, and the average values ​​are used as the strand strength and strand modulus. The strain range for calculating the strand modulus is 0.1 to 0.6%.

[0102] <Method for measuring interfacial shear strength> Single fibers were extracted from the carbon fiber bundle, sandwiched from above and below between laminated resin films to a thickness of 0.4 mm or more, heated and pressurized in a heat press, and then cooled to room temperature while maintaining the pressurized state to obtain a molded plate with the carbon fiber single fibers embedded. Dumbbell-shaped test pieces for IFSS measurement were punched out from this molded plate using an SD-type lever cutter.

[0103] Both ends of the dumbbell-shaped sample were clamped, and a tensile force was applied in the fiber axis direction (longitudinal direction) at a rate of 2.0 mm / min, generating a strain of 12%. A 20 mm section was then cut from the center of the specimen and heated above the melting point of the thermoplastic resin while sandwiched between glass plates on a hot plate. The fragmented fiber length inside the sample, which had been made transparent by heating, was observed under a microscope. Furthermore, the critical fiber length lc was calculated from the average broken fiber length la using the formula lc (μm) = (4 / 3) × la (μm). The strand tensile strength σ and the diameter d of the carbon fiber single yarn were measured, and the interfacial shear strength (IFSS), an index of the adhesive strength at the interface between the carbon fiber and the resin, was calculated using the following formula. In the examples, the test results were the average of five measurements (n = 5).

[0104] IFSS(MPa)=σ(MPa)×d(μm) / (2×lc)(μm).

[0105] In the present invention, the preferable range of IFSS for the following resins was evaluated on a three-point scale based on the following criteria, with A and B being considered acceptable.

[0106] Resin: Polyether ether ketone A: IFSS 35 or higher B: IFSS is 30 or more and less than 35 C: IFSS less than 30 The materials and components used in each example and comparative example are as follows:

[0107] <Spinneret> [A] Spinneret A: Spinneret A was a type of spinneret shown in Figure 2 (B) having 100 pairs of holes, each pair consisting of a circular hole with a diameter (d1) of 0.2 mm and a circular hole with a diameter (d2) of 0.06 mm, with a center-to-center distance (L) of 0.16 mm. [B] Spinneret B: Spinneret B was a type of spinneret shown in Figure 2 (B) having 100 pairs of holes, each pair consisting of a circular hole with a diameter (d1) of 0.3 mm and a circular hole with a diameter (d2) of 0.06 mm, with a center-to-center distance (L) of 0.22 mm. [C] Spinneret C: Spinneret C was a type of spinneret shown in Figure 2 (B) having 100 pairs of holes, each pair consisting of a circular hole with a diameter (d1) of 0.3 mm and a circular hole with a diameter (d2) of 0.04 mm, with a center-to-center distance (L) of 0.20 mm. [D] Spinneret D: A spinneret having 100 circular holes with a diameter of 0.2 mm was used as spinneret D.

[0108] Component (A): Anionic surfactant A-1: Sodium bis(2-ethylhexyl) sulfosuccinate (Tokyo Chemical Industry Co., Ltd.) A-2: Oleic acid butyl ester sulfated oil (Lion Corporation "Rotat (registered trademark)" OH-104K, reaction rate: 79%) A-3: Sodium alkylnaphthalene sulfonate (Tokyo Chemical Industry Co., Ltd.) A-4: Sodium dodecylbenzenesulfonate (Kao Corporation "Neo Operex (registered trademark)" G15) A-5: Sodium lauryl sulfate (Kao Corporation "EMAL (registered trademark)" 10G) A-6: Disodium lauryl sulfosuccinate (Sanyo Chemical Industries, Ltd. "Viewlite (registered trademark)" SSS) A-7: Sodium 2-ethylhexyl sulfate ("Sandet (registered trademark)" ONA manufactured by Sanyo Chemical Industries, Ltd.).

[0109] Component (B): polyethylene glycol and / or nonionic surfactant B-1: PEG distearate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" DS4000, HLB: 16.6) B-2: PEG monostearate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" MS1000, HLB: 15.7) B-3: PEG monooleate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" MO600, HLB: 13.8) B-4: PEG monooleate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" MO400, HLB: 11.7) B-5: PEG dioleate ester ("IONET (registered trademark)" DO1000, HLB: 12.9, manufactured by Sanyo Chemical Industries, Ltd.) B-6: PEG dioleate ester (Sanyo Chemical Industries, Ltd. "IONET (registered trademark)" DO600, HLB: 10.5) B-7: Polyethylene glycol (PEG600, manufactured by Sanyo Chemical Industries, Ltd., HLB: 20, molecular weight: 600) B-8: Polyethylene glycol (PEG4000, manufactured by Sanyo Chemical Industries, Ltd., HLB: 20, molecular weight: 4,000) B-9: Polyethylene glycol (PEG20000 manufactured by Sanyo Chemical Industries, Ltd., HLB: 20, molecular weight: 20,000). B-10: Polyethylene glycol (Triethylene glycol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., HLB: 20, molecular weight: 150) B-11: Polyethylene glycol (PEG200, manufactured by Sanyo Chemical Industries, Ltd., HLB: 20, molecular weight: 200) (C) Component: Amphoteric surfactant C-1: Lauryl dimethylaminoacetic acid betaine (Kao Corporation "Amphitheater (registered trademark) 24B") C-2: N,N-dimethyldecylamine oxide ("Cadenax (registered trademark) DM10D-W" manufactured by Lion Specialty Chemicals Co., Ltd.) C-3: Lauryl dimethylamine oxide ("Cadenax (registered trademark) DM12D-W(C)" manufactured by Lion Specialty Chemicals Co., Ltd.) C-4: N,N-dimethylmyristylamine oxide ("Cadenax (registered trademark) DM14D-N" manufactured by Lion Specialty Chemicals Co., Ltd.)

[0110] (D) Ingredients: Other ingredients D-1: Propylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd.) D-2: 2-propanol (Fujifilm Wako Pure Chemical Industries, Ltd.) D-3: Diglycerol polyglycidyl ether (Nagase ChemteX Corporation "Deconal (registered trademark)" Ex-421) D-4: Polyethyleneimine ("Lupasol (registered trademark)" G20 Waterfree, manufactured by BASF Japan Ltd.).

[0111] (E) Component: Thermoplastic resin E-1: Polyether ether ketone (Victrex (registered trademark) 450G manufactured by Victrex Co., Ltd.).

[0112] Example 1 This example comprises the following first to fifth steps.

[0113] First process: A process for producing carbon fiber bundles as raw materials A polyacrylonitrile copolymer consisting of 99.5 mol% acrylonitrile and 0.5 mol% itaconic acid, with a weight-average molecular weight of 400,000 and an Mz / Mw ratio of 2.1, was produced by radical polymerization. This polyacrylonitrile polymer was neutralized with ammonia in dimethyl sulfoxide to a polymer concentration of 19% by mass, yielding a spinning solution. The resulting spinning solution was extruded into the air at 40°C using spinneret A, passed through a space of approximately 5 mm, and then introduced into a coagulation bath containing a 79% by mass aqueous solution of dimethyl sulfoxide controlled at 5°C using a dry-wet spinning method to produce coagulated yarns. The coagulated yarns were then washed with water, stretched, oiled, and dried and densified using standard methods to obtain a polyacrylonitrile precursor fiber bundle with a single fiber fineness of 1.0 dtex and 500 single fibers.

[0114] Next, after flame-proofing treatment in air at a temperature of 240 to 300°C, a preliminary carbonization treatment was performed in a nitrogen atmosphere at a temperature of 300 to 800°C, and then a carbonization treatment was performed in a nitrogen atmosphere at a maximum temperature of 1,300°C to obtain a carbon fiber bundle. The carbon fiber bundle was then subjected to an electrolytic surface treatment using an aqueous ammonium bicarbonate solution as the electrolyte at an electrical charge of 30 coulombs per gram of carbon fiber bundle. The carbon fiber bundle subjected to this electrolytic surface treatment was then washed with water and dried in heated air to obtain carbon fiber bundle A as the raw material. The strand strength, strand modulus, cross-sectional shape, and surface oxygen concentration of the carbon fiber bundle A obtained in this first step were also measured. The evaluation results are shown in Table 1.

[0115] [Table 1]

[0116] Second step: A step of applying a sizing agent to the carbon fiber bundle Compound (A) (A-1) was used as compound (A) with the composition shown in Table 1, and water was added to uniformly dissolve the compound to obtain an approximately 0.8% by mass aqueous solution. This aqueous solution was used as a sizing agent aqueous solution, and the sizing agent was applied to a surface-treated carbon fiber bundle by immersion. The bundle was then heat-treated with a hot roller at 120°C for 15 seconds as a preliminary drying step, and subsequently heat-treated in heated air at 210°C for 60 seconds as a second drying step to obtain a sizing-agent-containing carbon fiber bundle. The amount of sizing agent attached was adjusted to 0.40% by mass based on 100% by mass of the total amount of the surface-treated sizing-agent-containing carbon fiber bundle. The mass residual ratio of the sizing agent applied in this second step was measured. The mass residual ratio was 25% when the temperature reached 300°C, and 17% when the temperature reached 350°C, demonstrating sufficient thermal decomposition.

[0117] Third step: Evaluation of the handling properties of carbon fiber bundles containing sizing agents Using the sizing-agent-containing carbon fiber bundle obtained in the second step, the handleability was evaluated based on the evaluation method of the friction coefficient and the measurement method of CF abrasion fluff. As a result, it was found that the dry FF friction coefficient was 0.33, and fluffing was unlikely to occur during the processing step, and the handleability was sufficiently good.

[0118] · Fourth step: Evaluation of the amount of sizing agent attached after rinsing The sizing-agent-containing carbon fiber bundle obtained in the previous step was washed with water as described above in the sections <Method for calculating the amount of sizing agent attached after 50 seconds of water washing> and <Method for calculating the amount of sizing agent attached after 25 seconds of water washing>. The sizing-agent-containing carbon fiber bundle was obtained after 50 seconds of water washing and after 25 seconds of water washing. The sizing-agent attachment amounts after 50 seconds of water washing and after 25 seconds of water washing were calculated. As a result, the amount of sizing agent attached after 50 seconds of water washing was 0.03 mass% of 100 mass% of the sizing-agent-containing carbon fiber bundle, and the amount of sizing agent attached after 25 seconds of water washing was 0.06 mass% of 100 mass% of the sizing-agent-containing carbon fiber bundle, indicating that the remaining amount was small and the elution rate was sufficiently high. Furthermore, when the surface area ratio after 50 seconds of water washing was evaluated, the surface area ratio was 1.02, indicating the presence of fine surface irregularities.

[0119] - Fifth step: Preparation and evaluation of test specimens for IFSS measurement Using the sizing agent-containing carbon fiber bundle obtained in the previous step after water washing and (D-1) as the thermoplastic resin (D), a test piece for IFSS measurement was prepared based on the method for measuring interfacial shear strength.

[0120] Next, the IFSS was measured using the obtained test piece for IFSS measurement. As a result, the IFSS was 37 MPa when using the carbon fiber bundle containing a sizing agent after 50 seconds of water washing, and 37 MPa when using the carbon fiber bundle containing a sizing agent after 25 seconds of water washing, indicating sufficiently high adhesiveness. The above results are summarized in Table 2.

[0121] [Table 2]

[0122] Example 2 Carbon fiber bundle B was obtained in the same manner as in Example 1, except that in the first step, spinneret B was used and the space through which the spinning solution passed after being discharged from the spinneret was set to about 3 mm, and various evaluations were carried out in the same manner as in Example 1 for the second to fifth steps. The results are shown in Tables 1 and 2, and it was found that the handleability was good, the elution property was sufficiently high, and the adhesiveness was high.

[0123] (Comparative Example 1) Carbon fiber bundle C was obtained in the same manner as in Example 1, except that in the first step, spinneret C was used and the space through which the spinning solution passed after being discharged from the spinneret was set to about 3 mm, and various evaluations were carried out in the same manner as in Example 1 for the second to fifth steps. The results are shown in Tables 1 and 2, and it was found that the handleability was good and the elution property was sufficiently high, but the strand strength was lower than in Example 1.

[0124] Example 3 Carbon fiber bundle D was obtained in the same manner as in Example 1, except that in the first step, spinneret D was used, the space through which the spinning solution passed after being discharged from the spinneret was set to about 4 mm, and the coagulation bath was a 30 mass % aqueous solution of dimethyl sulfoxide controlled at 15°C, and various evaluations were carried out in the same manner as in Example 1 for the second to fifth steps. The results are shown in Tables 1 and 2, and it was found that the handleability was good and the elution property was also sufficiently high.

[0125] Example 4 In the first step, a carbon fiber bundle E was obtained in the same manner as in Example 3, except that only the allocation of the draw ratio was changed while maintaining the single fiber fineness when obtaining a polyacrylonitrile precursor fiber bundle, and various evaluations were carried out by carrying out the second to fifth steps in the same manner as in Example 1. The results are shown in Tables 1 and 2, and it was found that the handleability was good, the elution property was sufficiently high, and the adhesiveness was also high.

[0126] (Comparative Example 2) A carbon fiber bundle F was obtained in the same manner as in Example 3, except that in the first step, the coagulation bath was a 55% by mass aqueous solution of dimethyl sulfoxide controlled at 30°C, and various evaluations were carried out in the same manner as in Example 1 for the second to fifth steps. The results are shown in Tables 1 and 2, and it was found that the handleability was good and the elution property was sufficiently high, but the strand strength was lower than in Example 1.

[0127] (Comparative Example 3) A carbon fiber bundle G was obtained in the same manner as in Example 3, except that the amount of surface treatment in the first step was changed to 80 coulombs / g and the amount of sizing agent attached in the second step was changed as shown in Table 2, and various evaluations were carried out by carrying out the third to fifth steps in the same manner as in Example 1. The results are shown in Tables 1 and 2. The elution was sufficiently high, but the dry FF friction was high and the handleability was insufficient.

[0128] Comparative Example 4 Carbon fiber bundle H was obtained in the same manner as in Example 3, except that the amount of surface treatment in the first step was set to 0 coulomb / g and the amount of sizing agent attached in the second step was changed as shown in Table 2, and various evaluations were carried out by carrying out the third to fifth steps in the same manner as in Example 1. The results are shown in Tables 1 and 2. The elution property was sufficiently high, but the dry FF friction was low and the handleability was insufficient.

[0129] Example 5 Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Example 1, except that the amount of sizing agent applied in the second step was changed as shown in Table 3. The results are shown in Table 3, and it was found that the handleability was good and the elution property was also sufficiently high.

[0130] [Table 3]

[0131] (Comparative Example 5) Sizing-agent-containing carbon fibers were obtained and evaluated in the same manner as in Comparative Example 3, except that the drying temperature in the second drying step in the second step was changed to 80°C and the amount of sizing agent applied was changed as shown in Table 3. The results are shown in Table 3, and although the elution was sufficiently high, the dry FF friction was high and the handleability was insufficient.

[0132] (Comparative Example 6) Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Example 2, except that the composition and amount of sizing agent applied in the second step were changed as shown in Table 3. The results are shown in Table 3. The handleability was good, but the ratio of anionic hydrophilic groups in the anionic surfactant was low, and the elution was insufficient.

[0133] Examples 6 to 9 Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Example 4, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 3. The results are shown in Table 3, and it was found that the handling properties were good and the elution properties were also sufficiently high.

[0134] Examples 10 to 12 Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Example 4, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 4. The results are shown in Table 4, and it was found that the handling properties were good and the elution properties were also sufficiently high.

[0135] [Table 4]

[0136] (Examples 13 to 16) Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Example 4, except that a second component was added to the sizing agent used in the second step and the composition and amount of the sizing agent were changed as shown in Table 4. The results are shown in Table 4, and it was found that the handling properties were good and the elution properties were also sufficiently high.

[0137] (Examples 17 to 21) Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 5. The results are shown in Table 5, and it was found that the handling properties were good and the elution properties were also sufficiently high.

[0138] [Table 5]

[0139] (Comparative Example 7) Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Comparative Example 3, except that the composition and amount of sizing agent applied in the second step were changed as shown in Table 5. The results are shown in Table 5, and the dry FF friction was high and the handleability was insufficient.

[0140] (Comparative Examples 8 to 10) Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Example 3, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 6. The results are shown in Table 5, and although the handleability was good, the elution property was insufficient due to the low HLB or the low terminal hydroxyl group ratio.

[0141] Examples 22 to 26 Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Example 4, except that the composition and amount of sizing agent applied in the second step were changed as shown in Table 6. The results are shown in Table 6, and it was found that the handling properties were good and the elution properties were also sufficiently high.

[0142] [Table 6]

[0143] (Examples 27 to 28) In the second step, the composition and amount of the sizing agent applied were changed as shown in Table 6, the heating time at 120°C in the pre-drying step was changed to 5 seconds, and the second drying step was omitted. Except for this, sizing-agent-containing carbon fibers were obtained in the same manner as in Example 4, and various evaluations were carried out. The results are shown in Table 6, and it was found that the handling property was good and the elution property was also sufficiently high.

[0144] (Examples 29 to 31) Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Example 1, except that the composition and amount of sizing agent applied in the second step were changed as shown in Table 7. The results are shown in Table 7, and it was found that the handling properties were good and the elution properties were also sufficiently high.

[0145] [Table 7]

[0146] Examples 32 to 34 Sizing-agent-containing carbon fibers were obtained in the same manner as in Example 4, except that the composition and amount of sizing agent applied in the second step were changed as shown in Table 7, and the second drying step was not performed after heat treatment with a hot roller at a temperature of 120°C for 15 seconds as a preliminary drying step, and various evaluations were performed. The results are shown in Table 7, and it was found that the handleability was good and the elution property was also sufficiently high.

[0147] (Comparative Example 11) Sizing-agent-containing carbon fibers were obtained and various evaluations were carried out in the same manner as in Comparative Example 3, except that the composition and amount of sizing agent applied in the second step were changed as shown in Table 7. The results are shown in Table 7, and the dry FF friction was high and the handleability was insufficient. [Industrial Applicability]

[0148] According to the present invention, a sizing agent that exhibits bundling properties and frictional properties suitable for ease of handling and that easily enhances resin impregnation due to its good affinity with water in aqueous processes is applied to carbon fibers containing, as a main component, single fibers having a specific cross-sectional shape, thereby reducing the amount of sizing agent remaining after processing into an intermediate substrate and providing a sizing-agent-containing carbon fiber bundle that is particularly suitable for combination with a thermoplastic matrix resin.The thermoplastic resin composite using the present invention is lightweight yet has excellent strength, and can therefore be suitably used in many fields, such as aircraft components, spacecraft components, automobile components, ship components, civil engineering and construction materials, and sporting goods. [Explanation of symbols]

[0149] 11: Unwinding process 12: Washing process 13:Drying process 14: Winding process 15: Free roller in front of the washing tank 16: Free roller in the washing tank 17: Free roller after washing tank 18:Washing tank 19: Free roller in front of the washing tank 20: Free roller in the washing tank 21: Free roller after washing tank 22:Washing tank 1a: Carbon fiber bundle containing sizing agent 1b: Carbon fiber bundle containing sizing agent after washing with water 1c: Carbon fiber bundle containing sizing agent after washing and drying 1d: Water 1e: Water< / ld> < / la> < / ld> < / la> < / ld> < / la> < / ld> < / la>

Claims

1. A sizing-agent-containing carbon fiber bundle containing a sizing agent containing polyethylene glycol and / or a surfactant, the sizing-agent-containing carbon fiber bundle satisfying all of the following (i) to (iii): (i) The dry FF friction coefficient is 0.20 or more and 0.39 or less. (ii) The fiber contains 40% or more of single fibers whose cross-sectional shape perpendicular to the fiber direction satisfies the following formulas (1) and (2): 1.00≦La / Lb≦1.20...(1) 1.00≦Ld / Lc≦1.25...(2) (Here, the line segment passing through the two most distant points on the circumference of a single fiber cross section is defined as the a-axis, and the line segment passing through the midpoint of the a-axis and two points on the circumference and perpendicular to the a-axis is defined as the b-axis, the length of the a-axis is defined as La, the length of the b-axis is defined as Lb, and La ≧ Lb. In addition, when the a-axis is divided into four equal parts, the lengths of the two line segments that pass through a point other than the midpoint of the a-axis and two points on the circumference and perpendicular to the a-axis are defined as Lc and Ld, and Lc ≦ Ld.) (iii) After washing with water for 50 seconds under the following conditions, the amount of sizing agent attached is 0.12 mass % or less based on 100 mass % of the sizing-agent-containing carbon fiber bundle. <Method of washing carbon fiber bundle containing sizing agent> The sizing agent-containing carbon fiber bundle is introduced into water through a roller, and the sizing agent is dissolved in water. The sizing agent-containing carbon fiber bundle installed in the unwinding process is passed through the water in the water washing tank through a free roller before the water washing tank, a free roller in the water washing tank, and a free roller after the water washing tank in the water washing process, and then passes through a drying process continuously to dry the water and wind it up in the winding process. The water temperature is 25°C, the unwinding tension from the creel is 800g, the process speed is 2.4m / min, the free roller diameter in the water washing tank is 150mm, and the contact angle between the sizing agent-containing carbon fiber bundle and the free roller in the water washing tank is πrad. In addition, the liquid level is adjusted so that the water passing time is 50 seconds. The drying process is a non-contact drying process, and the sizing agent-containing carbon fiber bundle after water washing is dried at a drying temperature of 150°C for 1 minute to obtain a sizing agent-containing carbon fiber bundle after water washing and drying. The amount of sizing agent attached to the sizing-agent-containing carbon fiber bundle after washing with water and drying is measured to obtain the amount of sizing agent attached.

2. 2. The sizing-agent-containing carbon fiber bundle according to claim 1, wherein the average surface area ratio of single carbon fibers after washing with water for 50 seconds by the water washing method for the sizing-agent-containing carbon fiber bundle is 1.01 or more and 1.07 or less.

3. 3. The sizing agent-containing carbon fiber bundle according to claim 1, wherein the sizing agent contains polyethylene glycol and / or a nonionic surfactant, and the amount of the sizing agent attached is 0.15 mass% or more and 0.60 mass% or less in 100 mass% of the sizing-agent-containing carbon fiber bundle.

4. 3. The sizing-agent-containing carbon fiber bundle according to claim 1 or 2, comprising a sizing agent containing the surfactant, the surfactant being an anionic surfactant, and a sizing-agent adhesion amount being 0.20 mass % or more and 0.80 mass % or less in 100 mass % of the sizing-agent-containing carbon fiber bundle.

5. 3. The sizing-agent-containing carbon fiber bundle according to claim 1 or 2, comprising a sizing agent containing the surfactant, the surfactant being an amphoteric surfactant, and a sizing-agent adhesion amount being 0.15 mass % or more and 0.45 mass % or less in 100 mass % of the sizing-agent-containing carbon fiber bundle.

6. The sizing agent-containing carbon fiber bundle according to claim 3, wherein the polyethylene glycol and / or the nonionic surfactant satisfies the following (iv) or (v): (iv) The HLB is 15 or greater and 20 or less. (v) The HLB is 12 or more and less than 15, and the ratio of hydroxyl groups at the molecular terminals is 50% or more.

7. The sizing agent-containing carbon fiber bundle according to claim 3, wherein the polyethylene glycol and / or the nonionic surfactant satisfies the following (vi) or (vii): (vi) The weight average molecular weight Mw is 300 or more and 5,000 or less. (vii) The weight average molecular weight Mw is 120 or more and less than 300, and the proportion of the polyalkylene glycol structure is 60 mass% or more.

8. 5. The sizing-agent-containing carbon fiber bundle according to claim 4, wherein the ratio of hydrophilic groups in the anions constituting the anionic surfactant is 17% or more.

9. The sizing-agent-containing carbon fiber bundle according to claim 5, wherein the average carbon number of the alkyl groups constituting the amphoteric surfactant is 17 or less.

10. 6. The sizing-agent-containing carbon fiber bundle according to claim 5, wherein an extract obtained by extracting the sizing-agent-containing carbon fiber bundle with distilled water for 1 minute has an absorbance at 600 nm of 0.06 or more.

11. 3. The sizing-agent-containing carbon fiber bundle according to claim 1, wherein a total amount of the polyethylene glycol and / or the surfactant is 70% by mass or more based on 100% by mass of the total amount of the sizing agent.

12. 3. The sizing-agent-containing carbon fiber bundle according to claim 1, wherein the amount of sizing agent attached after washing with water for 25 seconds under the following conditions is 0.12 mass% or less based on 100 mass% of the sizing-agent-containing carbon fiber bundle. <Method of washing carbon fiber bundle containing sizing agent> The sizing agent-containing carbon fiber bundle is introduced into water through a roller, and the sizing agent is dissolved in water. The sizing agent-containing carbon fiber bundle installed in the unwinding process is passed through the water in the water washing tank through a free roller before the water washing tank, a free roller in the water washing tank, and a free roller after the water washing tank in the water washing process, and then passes through a drying process continuously to dry the water and wind it up in the winding process. The water temperature is 25°C, the unwinding tension from the creel is 800g, the process speed is 2.4m / min, the free roller diameter in the water washing tank is 150mm, and the contact angle between the sizing agent-containing carbon fiber bundle and the free roller in the water washing tank is πrad. The liquid level is adjusted so that the water passing time is 25 seconds. The drying process is a non-contact drying process, and the sizing agent-containing carbon fiber bundle after water washing is dried at a drying temperature of 150°C for 1 minute to obtain a sizing agent-containing carbon fiber bundle after water washing and drying. The amount of sizing agent attached to the sizing-agent-containing carbon fiber bundle after washing with water and drying is measured to obtain the amount of sizing agent attached.

13. 3. The sizing-agent-containing carbon fiber bundle according to claim 1, wherein the polyethylene glycol and / or the surfactant have a mass residual rate of 35% or less when the temperature reaches 300°C when the temperature is raised at 10°C / min in air.

14. 3. The sizing-agent-containing carbon fiber bundle according to claim 1, wherein the polyethylene glycol and / or the surfactant have a mass residual rate of 30% or less when the temperature reaches 350°C when the temperature is raised in air at 10°C / min.

15. 3. The sizing-agent-containing carbon fiber bundle according to claim 1, wherein the strand strength of the carbon fiber bundle is 5.0 GPa or more.

16. 3. The method for producing a sizing-agent-containing carbon fiber bundle according to claim 1 or 2, comprising a coating step of coating a sizing agent containing polyethylene glycol and / or a surfactant onto a carbon fiber bundle, and then a drying step of drying the carbon fiber bundle coated with the sizing agent.

17. The method for producing a sizing-agent-containing carbon fiber bundle according to claim 16, wherein the carbon fiber bundle coated with the sizing agent is dried at 120 to 260° C. in the drying step of drying the carbon fiber bundle coated with the sizing agent.

Images