JP2023010616A - Carbon fiber bundle containing sizing agent and manufacturing method thereof - Google Patents

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

The present invention exhibits bundling properties and friction properties suitable for handleability of sizing agent-containing carbon fiber bundles, and enhances resin impregnation properties due to good affinity with water in water-based processes typified by wet powder impregnation methods. The present invention relates to a sizing agent-containing carbon fiber bundle in which a sizing agent is applied to carbon fibers mainly composed of single fibers having a specific cross-sectional shape, and a method for producing the sizing agent-containing carbon fiber bundle.

Carbon fiber is light in weight and has excellent strength and elastic modulus. Therefore, it is used as a composite material in combination with various matrix resins for aircraft parts, spacecraft parts, automobile parts, ship parts, civil engineering and construction materials, sporting goods, and the like. used in the field of A representative form of a composite material using carbon fibers is a molded article obtained by press-molding a preform obtained by laminating prepregs (a molding method in which defoaming is performed under pressure and shaping is performed). This prepreg is generally produced by impregnating a carbon fiber substrate in which continuous carbon fiber bundles are arranged in one direction with a resin. Composite materials using discontinuous carbon fibers (chopped, web, etc.) have been proposed, which have excellent conformability to complex shapes and can be molded in a short time. In terms of stability, prepreg is superior in practical performance as a structural material.

In recent years, carbon fiber composite materials are required to have molding materials with excellent moldability, handleability, and mechanical properties of the resulting molded products. ing. As one of the answers to this demand, the development of prepregs using a thermoplastic resin as the matrix resin is underway. As an example of the manufacturing method, a thermoplastic resin slurry in which a powdery thermoplastic matrix resin is dispersed with a surfactant is passed through to prepare a carbon fiber tape in which the powdery thermoplastic matrix resin is gripped. A method of impregnating the inside of the carbon fiber tape with a thermoplastic resin is mentioned.

In order to take advantage of the excellent properties of carbon fibers after composite processing, it is important to have excellent handleability during carbon fiber processing, and to reduce fuzz wrapping and breakage due to wrapping. Carbon fiber bundles to which no sizing agent is applied lack bundling properties and generate a large amount of fluff. Therefore, in order to improve the handleability of the carbon fiber bundle, a method of applying a sizing agent to the carbon fiber bundle and imparting a scratch-resistant coating film on the surface of the carbon fiber is usually performed (Patent Document 1). and 2).

For the carbon fiber bundle, a method has also been proposed in which continuous fibers are cut, dispersed into single fibers, and used for papermaking. The process of making paper from carbon fiber bundles is often a water-based process. It is important to achieve both bundling ability and excellent opening ability to quickly disperse into single fibers when put into an aqueous medium in the papermaking process and suppress reaggregation. A sizing agent that achieves both is applied. In general, epoxy resin or the like is often attached as a sizing agent to improve the handling of carbon fiber bundles. Too high action tends to result in poor openability in water when applied to aqueous processes. Therefore, for example, in Patent Documents 3 to 5, by using a surfactant or a water-soluble polymer as a sizing agent in the carbon fiber bundle, the handling property when cutting into chopped carbon fibers is improved, and the opening property in water is improved. have been proposed to improve

The excellent properties of carbon composite materials are greatly influenced by the properties of the interface between carbon fibers and 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 of obtaining a carbon fiber composite material having excellent mechanical performance by uniformly applying a sizing agent by applying a sizing agent after applying a surfactant to a carbon fiber bundle. there is Further, Patent Document 7 proposes a method of applying a surfactant to spun yarn of flame-resistant fibers to increase affinity with a powdery matrix resin and improve impregnability during assembly production.

It also discloses controlling the cross-sectional shape of carbon fibers or precursor fibers thereof for processability control of carbon composite materials. For example, Patent Document 8 discloses that by forming an acrylic fiber bundle in which broad bean-shaped, elliptical, and circular single fibers are mixed at a specific ratio, both convergence and opening properties can be achieved at a high level. However, complex spinnerets with broad bean, elliptical, and circular holes are essential, and in order to stably produce single fibers with greatly different cross-sectional shapes, the conditions are set according to the cross-sectional shape with the lowest processability. It is difficult to apply to industrial processes, such as the need for

U.S. Pat. No. 3,957,716 JP-A-57-171767 International Publication No. 2006/019139 Pamphlet JP-A-2000-54269 Japanese Patent No. 6571892 JP 2017-137603 A JP-A-59-144679 JP 2012-188766 A

On the other hand, when the handleability and interfacial properties are controlled by applying a sizing agent to the carbon fiber bundle as described above, when combined with a thermoplastic matrix resin that requires a high molding temperature, the sizing agent component lowers the heat resistance of the matrix resin or lowers the adhesiveness between the carbon fibers and the matrix resin. Therefore, CFRP may not exhibit sufficient performance.

In other words, studies have been conducted to suppress fluff generation from carbon fiber bundles by applying a sizing agent and to improve workability in water-based processes. With the aim of imparting high mechanical properties, such as strand strength, to the composite material, we applied a sizing agent to suppress the generation of fluff due to single fiber breakage in the carbon fiber bundle, and to achieve both the ability to open the fibers in water. However, there was no idea of removing the sizing agent from the carbon fiber from the viewpoint of minimizing the risk of the above influence on the thermoplastic matrix resin in advanced processing.

In addition, after realizing both the suppression of fluff generation by the above-mentioned sizing agent and the openability in water, by combining it with carbon fibers whose cross-sectional shape is controlled, a carbon fiber composite material with excellent mechanical properties can be obtained. I had no idea.

The present invention has been made in view of the above, and provides a sizing agent that exhibits bundling properties and frictional properties suitable for handling, and that easily enhances resin impregnation due to good affinity with water in aqueous processes. , By being applied to carbon fibers containing monofilaments having a specific cross-sectional shape as a main component, the amount of sizing agent remaining after processing to the intermediate base material is reduced, and it is particularly suitable for combination with thermoplastic matrix resins. An object of the present invention is to provide a suitable sizing agent-containing carbon fiber bundle.

The present invention for solving the above-mentioned problems is a sizing agent-containing carbon fiber bundle containing a sizing agent containing polyethylene glycol and/or a surfactant, the sizing agent satisfying all of the following (i) to (iii): Agent-containing carbon fiber bundles.
(i) The dry FF friction coefficient is 0.20 or more and 0.39 or less.
(ii) 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)
(However, the line segment passing through the two furthest points on the outer circumference of the 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 outer circumference and perpendicular to the a-axis is the b-axis. Define the length as La and the length of the b-axis as Lb, where La≧Lb.In addition, when the a-axis is divided into four equal parts, , the lengths of two line segments perpendicular to the a-axis are defined as Lc and Ld, and Lc≦Ld.)
(iii) The sizing agent adhesion amount after washing with water for 50 seconds under the following conditions is 0.12% by mass or less based on 100% by mass of the sizing agent-containing carbon fiber bundle.
<Method of Washing Carbon Fiber Bundles Containing Sizing Agent>
The sizing agent-containing carbon fiber bundle is introduced into water through a roller to dissolve the sizing agent into the water. The sizing agent-containing carbon fiber bundle installed in the unwinding process is passed through the water in the washing tank through the free roller before the washing tank, the free roller in the washing tank, and the free roller after the washing tank in the washing process, and then continuously. It passes through a drying process, dries the water, and is wound up in a winding process. 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 washing tank was 150 mm, and the contact between the sizing agent-containing carbon fiber bundle and the free roller in the washing tank. Let the angle be π rad. In addition, the liquid surface is adjusted so that the underwater passage time is 50 seconds. The drying step is non-contact drying, and the sizing agent-containing carbon fiber bundle after washing with water is dried at a drying temperature of 150° C. for 1 minute to obtain a sizing agent-containing carbon fiber bundle after washing with water and drying. The sizing agent adhesion amount is obtained by measuring the sizing agent adhesion amount of the sizing agent-containing carbon fiber bundle after washing with water and drying.

Further, the method for producing a sizing agent-containing carbon fiber bundle of the present invention is the above-described method for producing a sizing agent-containing carbon fiber bundle, wherein a sizing agent containing polyethylene glycol and/or a surfactant is applied to the carbon fiber bundle. It is characterized by having a drying step of drying the carbon fiber bundles coated with the sizing agent after the coating step.

According to the present invention, a sizing agent that exhibits bundling properties and frictional properties suitable for handleability and that easily enhances resin impregnation due to good affinity with water in an aqueous process is a single unit having a specific cross-sectional shape. The sizing agent-containing carbon fiber bundle is particularly suitable for combination with a thermoplastic matrix resin because it is applied to carbon fibers containing fiber as a main component, reducing the amount of sizing agent remaining after processing to an intermediate base material. can be obtained.

FIG. 1 is a diagram showing a method of defining La, Lb, Lc, and Ld in a single fiber cross section of carbon fibers. FIG. 2 is a diagram showing a 50-second washing evaluation method. FIG. 3 is a diagram showing a 25-second washing evaluation method. (A) and (B) in FIG. 4 are examples of mouthpiece holes that can be preferably used in the present invention.

EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated.

The sizing agent-containing carbon fiber bundle of the present invention is a sizing agent-containing carbon fiber bundle containing a sizing agent containing polyethylene glycol and/or a surfactant, the sizing agent satisfying all of the following (i) to (iii): containing carbon fiber bundles.
(i) The dry FF friction coefficient is 0.20 or more and 0.39 or less.
(ii) Contain 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)
(However, the line segment passing through the two furthest points on the outer circumference of the 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 outer circumference and perpendicular to the a-axis is the b-axis. Define the length as La and the length of the b-axis as Lb, where La≧Lb.In addition, when the a-axis is divided into four equal parts, , the lengths of two line segments perpendicular to the a-axis are defined as Lc and Ld, and Lc≦Ld.)
(iii) The sizing agent adhesion amount after washing with water for 50 seconds under the following conditions is 0.12% by mass or less based on 100% by mass of the sizing agent-containing carbon fiber bundle.
<Method of Washing Carbon Fiber Bundles Containing Sizing Agent>
The sizing agent-containing carbon fiber bundle is introduced into water through a roller to dissolve the sizing agent into the water. The sizing agent-containing carbon fiber bundle installed in the unwinding process is passed through the water in the washing tank through the free roller before the washing tank, the free roller in the washing tank, and the free roller after the washing tank in the washing process, and then continuously. It passes through a drying process, dries the water, and is wound up in a winding process. 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 washing tank was 150 mm, and the contact between the sizing agent-containing carbon fiber bundle and the free roller in the washing tank. Let the angle be π rad. In addition, the liquid surface is adjusted so that the underwater passage time is 50 seconds. The drying step is non-contact drying, and the sizing agent-containing carbon fiber bundle after washing with water is dried at a drying temperature of 150° C. for 1 minute to obtain a sizing agent-containing carbon fiber bundle after washing with water and drying. The sizing agent adhesion amount is obtained by measuring the sizing agent adhesion amount of the sizing agent-containing carbon fiber bundle after washing with water and drying.

According to studies by the present inventors, when a sizing agent that improves handling properties after being applied to the carbon fiber bundle is used, the sizing agent on the sizing agent-containing carbon fiber bundle has a low affinity for water, and the sizing agent remains. It was found that there was a problem that the mechanical properties tended to deteriorate during prepreg production. To solve this problem, even when a compound that is easy to handle is used as a sizing agent, a sizing agent containing polyethylene glycol and/or a surfactant is used to control the coefficient of friction and prevent adhesion of the sizing agent after washing with water. By controlling the amount and applying it to carbon fibers containing single fibers having a specific cross-sectional shape as the main component, it is possible to achieve high handling properties of the sizing agent-containing carbon fiber bundles and good dissolution of the sizing agent into water. It was found that the physical properties of the carbon fiber composite material can be improved while achieving both.

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 term "surfactant" as used herein means an anionic surfactant, a nonionic surfactant, or an amphoteric surfactant.

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. If it is 0.20 or more, force is likely to be applied between the single fibers, and bundling properties are likely to be improved. 0.22 or more is more preferable, and 0.25 or more is even more preferable. If it is 0.39 or less, the frictional force between the single yarns in the carbon fiber bundle is reduced, so it is caused by fluff caused by friction when the carbon fiber bundle is pulled out from the bobbin and friction within the bundle when it comes into contact with the metal bar. Feather is reduced. 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, and more simply by the drying temperature after applying the sizing agent. In addition, it can be controlled by the amount of the sizing agent adhered. The procedure for evaluating the dry FF friction coefficient specified in the present invention will be described in Examples.

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)
However, the line segment passing through the two most distant points on the outer circumference of the single fiber cross section is the a-axis, the line segment passing through the midpoint of the a-axis and two points on the outer circumference and perpendicular to the a-axis is the b-axis, and the length of the a-axis is The length is defined as La, the length of the b axis is defined as Lb, and La≧Lb. Also, when the a-axis is divided into quarters, the lengths of two line segments that pass through a point other than the midpoint of the a-axis and two points on the outer circumference and are orthogonal to the a-axis are defined as Lc and Ld, Let Lc≦Ld.

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 surface. This is because carbon fiber, which is a brittle material, tends to have a tensile fracture surface almost perpendicular to the fiber direction.

In the present invention, the a-axis refers to a line segment passing through the two furthest points on the outer circumference, and the b-axis refers to a line segment perpendicular to the a-axis passing through the midpoint of the a-axis and two points on the outer circumference. and their lengths are La and Lb, respectively. If the cross-sectional shape is very close to a perfect circle and the a-axis cannot be determined, an arbitrary line segment passing through the center of the circle and two points on the outer circumference is determined as the a-axis. In addition, if the cross-sectional shape is a shape that is greatly crushed toward the inside, such as a β shape or a fava bean shape, and the a-axis and b-axis cannot be determined, La and Lb, etc. cannot be defined and are out of the range (N / A). and

In addition, among the three points necessary to divide the a-axis into four equal parts, two points other than the intersection of the a-axis and the b-axis pass through the respective points and the two points on the outer circumference, and You can draw two line segments perpendicular to the a-axis. The lengths of this line segment are defined as Lc and Ld, and Lc≦Ld. According to this definition, a circle can be expressed as a special case of La/Lb=Ld/Lc=1, and an ellipse when La/Lb is greater than 1 and Ld/Lc=1.

Formula (1) relates to the length ratio between the a-axis La and the b-axis Lb. When La/Lb is 1, the shape is circular, and the larger the ratio, the flatter the shape. Equation (2) expresses the deviation from the elliptical shape. When Ld/Lc is 1, the shape is elliptical. It becomes an oval shape with a high

As La/Lb and Ld/Lc are larger than 1.00, the perimeter of the same area becomes longer. increase and improve adhesion. On the other hand, when La/Lb and Ld/Lc are too large, the tensile strength of the single fiber decreases, and the strand strength tends to decrease as a whole. is 1.25 or less, there is no reduction in strand strength compared to the circular case, or it is negligible. The shape of the single fiber cross section can be controlled by setting conditions for the concentration of the coagulation bath, which will be described later, and by devising the spinneret.

In the carbon fiber bundle of the present invention, in order to suppress the decrease in strand strength, it is necessary that the proportion of single fibers that satisfy the above formulas (1) and (2) at the same time is greater than or equal to a certain value. Such low percentages may reduce strand strength. If the content of single fibers that simultaneously satisfy the formulas (1) and (2) is 40% or more based on the number of fibers, a decrease in strand strength can be suppressed. The higher the ratio, the better, more preferably 50% or more, even more preferably 60% or more, particularly preferably 70% or more, and most preferably 100%. Such a ratio can be controlled by setting conditions for the concentration of the coagulation bath, setting conditions for the spinneret described later, and changing the distance of the space through which the spinning solution is passed after being discharged from the spinneret in dry-wet spinning.

In the present invention, <La/Lb> and <Ld/Lc> are average values of La/Lb and Ld/Lc in each single fiber in the carbon fiber bundle. A specific evaluation method will be described in Examples. Even if the percentage of single fibers that satisfy the above formulas (1) and (2) at the same time is 50% or more, if the other single fibers are extremely deviated from a circular or elliptical shape, their tensile strength will decrease. When the carbon fiber bundle contains such single fibers, the resulting carbon fiber bundle may have increased fluff and fluff, resulting in a decrease in quality. Therefore, <La/Lb> preferably satisfies 1.20 or less and <Ld/Lc> satisfies 1.20 or less at the same time.

The cross-sectional shape parameters La, Lb, Lc, and Ld are evaluated by observing the cross section of the single fiber. A tensile fracture surface, a polished surface, or the like can be observed and evaluated with an optical microscope, a digital microscope, a scanning electron microscope, a transmission electron microscope, or the like. These parameters require a resolution of 0.2% of the length to be measured, so if the minor axis is 5 μm, it is necessary to evaluate using an electron microscope. A specific evaluation method will be described in Examples. As described above, if there is a small dent or chip of 100 nm or more on the outer periphery of the sampled single fiber, the single fiber should not be measured and a new single fiber should be sampled at random and used. do.

<Method for calculating the amount of sizing agent adhered after washing 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 remaining sizing agent is reduced by lengthening the water washing time, the contribution of the surface functional groups of the carbon fibers to the physical properties of the matrix resin is increased, which is preferable because the mechanical properties are improved. At 0.12% by mass or less, the influence of the sizing agent on the matrix resin is reduced, and the surface functional groups of the carbon fibers contribute more to the physical properties of the matrix resin, improving the mechanical properties. 0.10% by mass or less is more preferable.

Here, the method of washing the sizing agent-containing carbon fiber bundle for 50 seconds specified in the present invention can be carried out according to the following procedure. The sizing agent-containing carbon fiber bundle is introduced into water through a roller to elute the sizing agent into the water. This washing procedure is shown in FIG. The sizing agent-containing carbon fiber bundle can be washed with water according to the following procedure. The sizing agent-containing carbon fiber bundle 1a installed in the unwinding process 11 is fed into the water 1d in the water washing tank 18 through the pre-water washing tank free roller 15, the water washing tank free roller 16, and the water washing tank free roller 17 in the water washing process 12. After that, the water 1e in the water washing tank 22 is passed through the free roller 19 before the water washing tank, the free roller 20 in the water washing tank, and the free roller 21 after the water washing tank. Then, the water is dried and wound in a winding step 14.例文帳に追加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 washing tank was 150 mm, and the contact between the sizing agent-containing carbon fiber bundle and the free roller in the washing tank. Let the angle be π rad. In addition, the liquid surface is adjusted so that the underwater transit time in one washing tank is 25 seconds, and the total time in two washing tanks is 50 seconds. The drying step is non-contact drying, and the washed and dried sizing agent-containing carbon fiber bundles 1b are dried at a drying temperature of 150° C. for 1 minute to obtain the washed and dried sizing agent-containing carbon fiber bundles 1c. The sizing agent adhesion amount is obtained by measuring the sizing agent adhesion amount of the sizing agent-containing carbon fiber bundle 1c after washing and drying.

<Method for calculating the amount of sizing agent adhered after washing 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 washing with water for 25 seconds. At 0.12% by mass or less, the influence of the sizing agent on the matrix resin is reduced, and the surface functional groups of the carbon fibers contribute more to the physical properties of the matrix resin, improving the mechanical properties. 0.08% by mass or less is more preferable.

Here, the method of washing the sizing agent-containing carbon fiber bundles specified in the present invention for 25 seconds can be carried out according to the following procedures. The sizing agent-containing carbon fiber bundle is introduced into water through a roller to elute the sizing agent into the water. This washing procedure is shown in FIG. The sizing agent-containing carbon fiber bundle 1a installed in the unwinding process 11 is fed into the water 1d in the water washing tank 18 through the pre-water washing tank free roller 15, the water washing tank free roller 16, and the water washing tank free roller 17 in the water washing process 12. It is then passed through a drying step 13 to dry the water and wound up in a winding step 14.例文帳に追加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 washing tank was 150 mm, and the contact between the sizing agent-containing carbon fiber bundle and the free roller in the washing tank. Let the angle be π rad. In addition, the liquid level is adjusted so that the underwater passage time is 25 seconds. The drying step is non-contact drying, and the washed and dried sizing agent-containing carbon fiber bundles 1b are dried at a drying temperature of 150° C. for 1 minute to obtain the washed and dried sizing agent-containing carbon fiber bundles 1c. The sizing agent adhesion amount is obtained by measuring the sizing agent adhesion amount of the sizing agent-containing carbon fiber bundle 1c after washing and drying.

In addition, in the sizing agent-containing carbon fiber bundle of the present invention, the average value of the surface area ratio of the single fibers measured by the method described later using an atomic force microscope after washing with water for 50 seconds by the above washing method is 1.01. Above, it is preferably 1.07 or less, more preferably 1.02 or more and 1.05 or less, and particularly preferably 1.03 or more and 1.04 or less. The surface area ratio is expressed by the ratio between the actual surface area and 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 carbon fiber, which tends to be advantageous for improving the tensile strength of the carbon fiber. Also, the larger the surface area ratio, the larger the unevenness of the surface, which tends to be advantageous for improving the impregnating property of the resin by reducing the friction of the carbon fiber and improving the adhesiveness by increasing the contact area with the resin.

If the surface area ratio is 1.01 or more, improvement in resin impregnation and adhesion can be expected due to the presence of surface irregularities. It is preferable to control in the range of ~1.07. Such a surface area ratio can be controlled by the spinning method and coagulation method of the precursor, which will be described later. In addition, when the sizing agent adhesion amount after washing with water for 50 seconds is large, the surface unevenness may be covered with the sizing agent, resulting in a surface area ratio of 1.00.

An anionic surfactant is a surfactant having an anionic hydrophilic group. A carbon fiber bundle coated with an anionic surfactant improves the dissolution of the sizing agent when placed in water. As a result, the sizing agent remaining in the carbon fiber bundle is reduced. Although the mechanism is not clear, it is thought that the anionic surfactant is ionized in water, and the anionic hydrophilic group repels the surface of the carbon fiber, thereby exhibiting excellent dissolution properties. In addition, anionic surfactants are more likely to have a smaller molecular weight than nonionic surfactants and amphoteric surfactants, so it is believed that they tend to exhibit excellent dissolution properties during water washing.

Examples of anionic surfactants include carboxylates, sulfonates, carboxylates and sulfonates, sulfate ester salts, and phosphate ester salts.

Specific examples of carboxylates include soaps, polyoxyethylene alkyl ether carboxylates, alkyl hydroxy ether carboxylates, and the like. Specific examples of sulfonates include alkylbenzenesulfonates, alkylnaphthalenesulfonates, alkanoylmethyl taurides, and dialkylsulfosuccinic acid ester salts. Specific examples of carboxylates and sulfonates include alkyl sulfosuccinate disalts and polyoxyethylene alkyl ether sulfosuccinate disalts. Specific examples of sulfates include higher alkyl sulfates, polyoxyethylene alkyl ether sulfates, sulfated oils, sulfated fatty acid esters, and sulfated olefins. Specific examples of the phosphate include higher alkyl phosphate, polyoxyethylene alkyl ether phosphate, and dithiophosphate. The cations constituting the salt include cations of alkali metals such as sodium and cations of alkaline earth metals such as calcium, and the cations of alkali metals are preferred in order to improve water solubility. Also, instead of the metal salt, an ammonium salt may be used.

When an anionic surfactant is used as the surfactant, the sizing agent adhesion amount of the sizing agent-containing carbon fiber bundle is 0.20% by mass or more and 0.80% by mass or less in 100% by mass of the sizing agent-containing carbon fiber bundle. is preferred. By setting the amount of the sizing agent attached to 0.20% by mass or more, the handling of the sizing agent-containing carbon fiber bundle is improved, the generation of fluff during manufacturing and processing is suppressed, and the smoothness of the carbon fiber bundle is improved. Quality can be improved. The adhesion amount is more preferably 0.25% by mass or more, and particularly preferably 0.30% by mass or more. On the other hand, by setting the amount of the 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. The sizing agent adhesion amount is more preferably 0.60% by mass or less, and particularly preferably 0.45% by mass or less.

In the sizing agent constituting the present invention, it is preferable that the hydrophilic group ratio in the anions constituting the anionic surfactant is 17% or more.

By setting the hydrophilic group ratio in the anion to 17% or more, the elution of the anion site into water is improved, so the sizing agent is easily eluted during washing with water, and the residual amount of the sizing agent on the carbon fiber bundle. can be reduced. 20% or more is preferable, and 30% or more is more preferable.

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 portion of the anionic surfactant to the molecular weight of the anionic surfactant. The hydrophilic group here means a sulfate group (SO ₄ ⁻ ), a sulfonic acid group (SO ₃ ⁻ ), a carboxyl group (COO ⁻ ), a phosphate group (HPO ₃ ⁻ ), a hydroxyl group (OH ⁻ ), and the like. Sites with negative charges correspond. In addition, if an unreacted portion remains during the production of the anionic portion of the surfactant, the reaction rate is calculated from the sum of the starting material and the post-reaction substance (anion of the anionic surfactant) and the amount of the post-reaction substance, The hydrophilicity of the anionic moiety of the present invention is calculated by multiplying the hydrophilic group ratio calculated from the molecular weight of the anionic moiety of the anionic surfactant by the reaction rate.

A nonionic surfactant is a surfactant having a hydrophilic group that is not ionized. A carbon fiber bundle coated with polyethylene glycol and/or a nonionic surfactant improves the dissolution of the sizing agent when immersed in water. As a result, the sizing agent remaining in the carbon fiber bundle is reduced. Although the mechanism is not clear, polyethylene glycol and/or nonionic surfactants are considered to exhibit excellent dissolution properties because the hydrophilic group portion easily interacts with water. In addition, since polyethylene glycol and/or nonionic surfactants have hydrophilic groups that do not ionize, the strength of interaction with the carbon fiber surface is not affected by the pH of the aqueous solution, etc., and stable dissolution is likely to occur. Conceivable.

Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene dodecyl ether, polyoxyethylene oleyl ether, and polyoxyethylene stearyl ether, polyoxyethylene polyoxypropylene glycol, polyoxyethylene alkylphenyl ether, and monoolein. Sorbitan fatty acid esters such as sorbitan acid, sorbitan monostearate, sorbitan sesquioleate, sorbitan coconut oil fatty acid, sorbitan monopalmitate, sorbitan tristearate, sorbitan trioleate, polyoxyethylene sorbitan monooleate, poly trioleate Polyoxyethylene sorbitan fatty acid esters such as oxyethylene sorbitan, polyoxyethylene glycerin fatty acid esters such as polyoxyethylene glyceryl monooleate, polyoxyethylene sorbitol fatty acid esters such as polyoxyethylene sorbitol tetraoleate, polyoxyethylene hydrogenated castor oil ; Polyglycerin fatty acid ester, sucrose fatty acid ester, PEG monocaprylate, PEG monoheptylate, PEG monopelargonate, PEG monocaprate, PEG monolaurate, PEG monomyristate, PEG monopentadecyl acid Ester, 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, PEG dilinoleate, and other polyethylene glycol fatty acid esters. These nonionic surfactants can be used singly or in combination of two or more, or in combination with PEG. "PEG" is an abbreviation for "polyethylene glycol".

When polyethylene glycol and nonionic surfactant are combined, the mixing ratio of polyethylene glycol and nonionic is preferably 50 parts by mass or more of polyethylene glycol per 100 parts by mass of the total mixed amount. When the content of polyethylene glycol is 50 parts by mass or more, the elution property is improved due to the hydrophilicity of polyethylene glycol. Therefore, the sizing agent is easily eluted during washing with water, and the residual amount of the sizing agent on the carbon fiber bundle can be reduced. . More preferably, the mixing ratio of polyethylene glycol is 70 parts by mass or more in 100 parts by mass.

When a nonionic surfactant is used as the surfactant, the sizing agent adhesion amount of the sizing agent-containing carbon fiber bundle is 0.15% by mass or more and 0.60% by mass or less in 100% by mass of the sizing agent-containing carbon fiber bundle. is preferred. By setting the amount of the sizing agent attached to 0.15% by mass or more, the handling of the sizing agent-containing carbon fiber bundle is improved, the generation of fluff during manufacturing and processing is suppressed, and the smoothness of the carbon fiber bundle is improved. Quality can be improved. The adhesion amount is more preferably 0.20% by mass or more, and particularly preferably 0.25% by mass or more. On the other hand, by setting the amount of the sizing agent attached to 0.60% by mass or less, it is possible to reduce the residual amount in a short period of time, thereby reducing the impact on the mechanical properties of the composite material. The sizing agent adhesion amount is more preferably 0.50% by mass or less, and particularly preferably 0.45% by mass or less.

In the sizing agent constituting the present invention, the polyethylene glycol and/or the nonionic surfactant have a lipophilic/hydrophilic balance (HLB) of 15 or more and 20 or less, or an HLB of 12 or more and less than 15, and a hydroxyl group ratio at the molecular chain end of 50. % or more. The HLB defined in the present invention is a value calculated from the molecular structure based on Griffin's method described in "New Introduction to Surfactants", page 128, (1992). By setting the HLB of the nonionic surfactant to 15 or more and 20 or less, the hydrophilicity is improved, so that the sizing agent is easily eluted during washing with water, and the residual amount of the sizing agent on the carbon fiber bundle can be reduced. HLB is preferably 16 or more. In addition, even if the HLB is 12 or more and less than 15, by setting the hydroxyl group ratio at the end of the molecular chain to 50% or more, the hydrophilicity of the end improves the dissolution of the nonionic surfactant in water, so it can be washed with water. Sometimes the sizing agent is easily eluted, and the residual amount of the sizing agent on the carbon fiber bundle can be reduced.

In the sizing agent constituting the present invention, the weight average molecular weight Mw of the polyethylene glycol and/or the nonionic surfactant is 300 or more and 5,000 or less, or the weight average molecular weight Mw is 120 or more and less than 300, and the proportion of the polyalkylene glycol structure is It is preferably 60% by mass or more. The weight average molecular weight Mw is measured by a gel permeation chromatography (hereinafter abbreviated as GPC) method, and is obtained using polyethylene glycol as a standard substance. When the sizing agent constituting the present invention contains both polyethylene glycol and nonionic surfactant, the measured value of the mixture is taken as the weight average molecular weight Mw.

As the Mw increases, the viscosity of the polyethylene glycol and/or the nonionic surfactant increases, so the rate of elution from the surface of the carbon fiber decreases. By setting Mw to 5,000 or less, the viscosity, which is an index of the ease of movement of polyethylene glycol and/or nonionic surfactants, is reduced, and the amount of molecular chain entanglement during elution in water is reduced. Dissolution of polyethylene glycol and/or nonionic surfactants into water is improved. Mw is preferably 2,000 or less, more preferably 1,000 or less. On the other hand, in terms of application, the larger Mw is, the more the sizing agent is applied, the more it is possible to suppress the volatilization of the sizing agent, and the more the sizing agent is applied, the more it is possible to suppress the generation of fluff. The lower limit of Mw is preferably 300 or more. In addition, even when Mw is 120 or more and less than 300, by making the ratio of the polyalkylene glycol structure 60% by mass or more, the intermolecular interaction can be enhanced, so volatilization during application of the sizing agent is suppressed. The amount of the sizing agent adhered can be improved, so the generation of fluff can be suppressed. 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 water extraction of the sizing agent from the sizing agent-containing carbon fiber bundle and GPC evaluation.

An amphoteric surfactant is a surfactant having an anionic site and a cationic site in the same molecule. A carbon fiber bundle coated with an amphoteric surfactant improves the dissolution of the sizing agent when placed in water. As a result, the sizing agent remaining in the carbon fiber bundle is reduced. The mechanism is not clear, but unlike other nonionic, anionic, and cationic surfactants, the hydrophilic group in the amphoteric surfactant easily interacts with water over a wide pH range, resulting in excellent elution. It is thought that it expresses sexuality.

Types of amphoteric surfactants include amino acid-type surfactants, betaine-type surfactants, sulfobetaine-type surfactants, amine oxide-type surfactants, and the like.

Specific examples of amphoteric surfactants include fatty acid amidopropyl betaine, myrityl amidopropyl betaine, coconut oil fatty acid amidopropyl betaine, lauramidopropyl betaine, cocamidopropyl betaine, fatty acid amidopropyl dimethylaminoacetate betaine, coconut Fatty acid amidopropyldimethylaminoacetate betaine, lauramidopropyldimethylaminoacetate betaine, stearyldimethylaminoacetate betaine, lauryldimethylaminoacetate betaine, lauryldihydroxyethyl betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium Betaine-type surfactants such as betaine, sulfobetaine-type surfactants such as alkyl hydroxysulfobetaine, cocamidopropyl hydroxysulfobetaine, lauramidopropyl hydroxysulfobetaine, fatty acid amidopropyl dimethylamine oxide, lauramidopropyl dimethylamine oxide , lauryldimethylamine oxide, coconut oil alkyldimethylamine oxide, dodecyldimethylamine oxide, decyldimethylamine oxide, amine oxide surfactants such as tetradecyldimethylamine oxide, N-lauroyl-N'-carboxymethyl-N'- Hydroxyethylethylenediamine sodium, N-coconut fatty acid acyl-N'-carboxyethyl-N'-hydroxyethylethylenediamine sodium, β-laurylaminopropionate sodium, cocaminopropionate sodium, alkylcarboxymethylhydroxyethylimidazolium betaine, lauryl Amino acid-type surfactants such as betaine dimethylaminoacetate, alkyldiaminoethylglycine hydrochloride, sodium laurylaminodipropionate, and the like are included.

When an amphoteric surfactant is used as the surfactant, the sizing agent adhesion amount of the sizing agent-containing carbon fiber bundle is 0.15% by mass or more and 0.45% by mass or less in 100% by mass of the sizing agent-containing carbon fiber bundle. is preferred. By setting the amount of the sizing agent attached to 0.15% by mass or more, the handling of the sizing agent-containing carbon fiber bundle is improved, the generation of fluff during manufacturing and processing is suppressed, and the smoothness of the carbon fiber bundle is improved. Quality can be improved. The adhesion amount is more preferably 0.20% by mass or more, and particularly preferably 0.25% by mass or more. On the other hand, by setting the amount of the 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. The sizing agent adhesion amount is more preferably 0.40% by mass or less, particularly preferably 0.35% by mass or less.

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

By setting the average carbon number of the alkyl group to 17 or less, the elution of the amphoteric surfactant in water is improved, so the sizing agent is easily eluted during washing with water, and the amount of sizing agent remaining on the carbon fiber bundle is reduced. can be made The average carbon number of the alkyl group is more preferably 16.5 or less, more preferably 16 or less. Moreover, 8 or more are preferable. When the average number of carbon atoms is less than 8, the surface free energy of the sizing agent increases, resulting in a high dry FF friction coefficient.

The average carbon number of the alkyl groups constituting the amphoteric surfactant can be evaluated by extracting the sizing agent from the sizing agent-containing carbon fiber bundle with water and evaluating the result. There is a method of combining structure evaluation from IR spectrum obtained by infrared spectroscopy after lyophilization of the water-extracted sizing agent, proton NMR, carbon NMR and mass spectral analysis evaluation of the lyophilized product.

<Method for determining 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. When the absorbance is 0.06 or more, contaminants such as oxides adhering to the surface of the carbon fiber are easily removed, and the adhesion is improved. The absorbance is more preferably 0.08 or more, more preferably 0.10 or more.

Here, the absorbance of the water extract of the sizing agent-containing carbon fiber extract specified in the present invention can be obtained by the following procedure. 1.0 g of carbon fiber bundle is cut out, placed in a glass container with a lid and having a volume of 20 cm ³ , and 10.0 g of distilled water at 25° C. is added. The shaker was set at an amplitude of 30 mm and a shaking speed of 120 rpm, and the glass container was placed on the shaker and shaken for 1 minute. Immediately after shaking, the carbon fiber bundle is taken out from the solution. The solution extracted from the carbon fiber was placed in a quartz cell with an optical path length of 1.0 cm, the absorbance at 200 to 900 nm was measured using a UV-visible spectrophotometer, and the absorbance at 600 nm was recorded using distilled water as a control solution.
As a shaker, Shaking Bath SB-13 manufactured by AS ONE Co., Ltd. was used. The ultraviolet-visible spectrophotometer used was V-550 manufactured by JASCO Corporation.

In the sizing agent constituting the present invention, the total amount of polyethylene glycol and/or surfactant is preferably 70% by mass or more in 100% by mass of the total amount of the sizing agent. When the total amount of polyethylene glycol and/or surfactant is 70 parts by mass or more, the hydrophilic group in the surfactant improves the elution property, so that the sizing agent is easily eluted during washing with water, and the carbon fiber bundle The amount of residual sizing agent can be reduced. 85 parts by mass or more is more preferable, and 95 parts by mass or more is even more preferable.

In addition to polyethylene glycol and/or surfactants, other ingredients may also be included. Below, another component may be called a 2nd component. Other components include aliphatic or alicyclic compounds and/or aliphatic or alicyclic compounds in which two hydroxyl groups are attached to two different carbons, polyvinyl alcohol, polyglycidyl ether, polyethyleneimine, etc. Aliphatic or cycloaliphatic compounds and/or aliphatic or cycloaliphatic compounds in which two hydroxyl groups are attached to two different carbons are particularly preferred.

In the sizing agent constituting the present invention, the polyethylene glycol and/or surfactant to be applied has a mass residual rate of 35% or less when the temperature reaches 300° C. when heated at 10° C./min in air. preferable. In addition, when the sizing agent constituting the present invention contains both polyethylene glycol and surfactant, the measured value of the mixture thereof is defined as the mass residual ratio. By setting the mass residual ratio to 35% or less, the low heat-resistant component of the sizing agent is decomposed before the matrix resin melts, and the amount of the sizing agent incorporated into the matrix resin is reduced. The effect is reduced and the physical properties are stabilized. 20% or less is more preferable, and 5% or less is even more preferable.

In the sizing agent constituting the present invention, the polyethylene glycol and/or surfactant to be applied has a mass residual rate of 30% or less when it reaches 350 ° C. when heated at 10 ° C./min in air. preferable. In addition, when the sizing agent constituting the present invention contains both polyethylene glycol and surfactant, the measured value of the mixture thereof is defined as the mass residual ratio. By setting the mass residual ratio to 30% or less, the low heat-resistant component of the sizing agent is decomposed before the high heat-resistant matrix resin melts, and the amount of the sizing agent incorporated into the matrix resin is reduced. The effect on physical properties is reduced and the physical properties are stabilized. 25% or less is more preferable, and 5% or less is even more preferable.

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

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

Although the carbon fiber bundle used in the present invention is not particularly limited, polyacrylonitrile-based carbon fibers are preferably used from the viewpoint of mechanical properties. Polyacrylonitrile-based carbon fiber bundles are obtained by subjecting carbon fiber precursor fibers made of polyacrylonitrile-based polymer to flame resistance treatment at a maximum temperature of 200 to 300 ° C. in an oxidizing atmosphere, and then heating them to a maximum temperature of 500 to 500 in an inert atmosphere. It is obtained by pre-carbonizing at 1,200° C. and then carbonizing at a maximum temperature of 1,200 to 2,000° C. in an inert atmosphere.

In the production of the carbon fiber precursor fiber bundle, either a dry-wet spinning method or a wet spinning method may be used. preferably by The spinning process includes a spinning process in which the fibers are discharged from a spinneret by a dry-wet spinning method and spun, a washing process in which the fibers obtained in the spinning process are washed in a water bath, and the fibers obtained in the washing process are washed in a water bath. It consists of a water bath drawing step for drawing and a dry heat treatment step for drying and heat treating the fibers obtained in the water bath drawing step, and optionally includes a steam drawing step for steam drawing the fibers obtained in the dry heat treatment step. good.

In the production of carbon fiber precursor fiber bundles, the coagulation bath contains a solvent such as dimethylsulfoxide, dimethylformamide, dimethylacetamide, and an aqueous solution of sodium thiocyanate (rhodan soda) used as a solvent for the spinning dope, and a so-called coagulation accelerating component. It is preferable to As the coagulation promoting component, a component that does not dissolve the polyacrylonitrile-based polymer and is compatible with the solvent used for the spinning solution can be used. Specifically, it is preferable to use water as the coagulation promoting component.

Dry-wet spinning tends to provide a smooth surface, but the surface can be made uneven by enlarging fibrils, which are fine coagulation units, or exposing them to the surface. As a method for enlarging fibrils, for example, there is a method of increasing the temperature of the coagulation bath. In addition, as a method of exposing the fibrils to the surface, for example, a method of setting the solvent concentration of the coagulation bath at a high level to slow down the coagulation rate to make the skin layer thinner, or a method of increasing the draw ratio in a hot water bath. There is

In the present invention, a carbon fiber precursor fiber suitable for obtaining carbon fibers having a specific cross-sectional shape can be obtained by adjusting the shape of the spinneret hole. The spinneret hole may have the same shape as the cross-sectional shape of the desired single fiber. Arranging two or more holes close to each other is also preferable in that a monofilament having a controlled cross-sectional shape can be obtained simply by combining circular holes whose processing cost is relatively low. A preferable shape of the mouthpiece hole in the present invention can be optimized by a person skilled in the art through trial and error, and for example, (A) and (B) in FIG. 4 are preferable. However, the shape of the base hole should not be construed as being limited to these. Further, in the present invention, when one coagulated yarn single fiber is obtained from two or more holes arranged close to each other, such two or more holes are collectively counted as one spinneret hole. The spinneret hole preferably has a cross-sectional area of 0.002 to 0.1 mm ² in order to obtain a carbon fiber with a small single fiber fineness, which is advantageous in developing mechanical properties. A person skilled in the art can easily optimize the hole pitch, the number of holes, and the hole arrangement.

In the present invention, in order to control the ratio of single fibers satisfying the above formulas (1) and (2) at the same time to a certain value or more, the distance of the space through which the spinning solution is passed after being discharged from the spinneret in dry-wet spinning is changed. can be controlled by Specifically, the greater the distance, the higher the proportion of the cross-sectional shape approaching a circular shape. It is preferable to control such a distance to approximately several millimeters.

In the present invention, in order to improve the adhesiveness between the carbon fiber bundle and the matrix resin, it is preferable to introduce oxygen-containing functional groups to the surface by subjecting the carbon fiber bundle to an oxidation treatment. Gas-phase oxidation, liquid-phase oxidation, and liquid-phase electrolytic oxidation are used as the oxidation treatment method. Liquid-phase electrolytic oxidation is preferably used from the viewpoint of high productivity and uniform treatment.

In the present invention, the electrolytic solution used in the liquid-phase electrolytic oxidation includes an acidic electrolytic solution and an alkaline electrolytic solution. 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; or ammonium sulfate and ammonium hydrogen sulfate. and the like. Among them, sulfuric acid and nitric acid, which are strongly acidic, are preferably used. Specific examples of alkaline electrolytes include aqueous solutions of hydroxides such as sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide and barium hydroxide, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, Aqueous solutions of carbonates such as barium carbonate and ammonium carbonate, aqueous solutions of carbonates such as sodium hydrogencarbonate, potassium hydrogencarbonate, magnesium hydrogencarbonate, calcium hydrogencarbonate, barium hydrogencarbonate and ammonium hydrogencarbonate, ammonia, tetraalkylammonium hydroxide and an aqueous solution of hydrazine.

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.

By having a functional group on the surface of the carbon fiber, affinity with the matrix resin is generated, and high adhesive strength can be exhibited. When the surface oxygen concentration (O/C) is less than 0.08, the affinity between the carbon fiber surface and the matrix resin is low, resulting in low adhesive strength. When O/C exceeds 0.25, the surface layer of the carbon fiber tends to peel off although the number of functional groups increases, resulting in a decrease in adhesive strength.

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

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

In the present invention, the sizing agent is preferably diluted with a solvent and used as a uniform solution. Examples of such solvents include water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, dimethylformamide, and dimethylacetamide. Therefore, water is preferably used.

Examples of application means include a method of immersing the carbon fiber bundle in the sizing agent solution through a roller, a method of contacting the carbon fiber bundle with a roller to which the sizing agent solution is attached, and a method of atomizing the sizing agent solution and applying it to the carbon fiber bundle. Although there is a method of spraying, a method of immersing the carbon fiber bundle in the sizing agent solution via a roller is preferably used in producing the sizing agent-containing carbon fiber bundle of the present invention. The sizing agent may be applied by either a batch method or a continuous method, but the continuous method is preferably used because of its high productivity and small variation. It is also a preferred embodiment to vibrate the carbon fiber bundle with ultrasonic waves when applying the sizing agent.

In the present invention, after applying the sizing agent solution, it is preferable to obtain a sizing agent-containing carbon fiber bundle by contacting the carbon fiber bundle with a heated roller, for example, by contact drying means. The carbon fiber bundle introduced into the heated roller is pressed against the heated roller by tension and dried rapidly, so that the flat shape of the carbon fiber bundle widened by the heated roller is easily fixed by the sizing agent. A carbon fiber bundle in a flat form has a small contact area between single fibers, so when immersed in water, the contact area with water increases and the elution tends to be high. Moreover, in the present invention, after passing through a heated roller as a preliminary drying step, heat treatment may be further added as a second drying step. For the heat treatment as the second drying step, a non-contact heating method that facilitates heat treatment at a high temperature is preferred. By performing the heat treatment, the diluent solvent remaining in the sizing agent can be further removed and the viscosity of the sizing agent can be stabilized, so that the dissolution property can be stably enhanced.

Moreover, by performing the heat treatment, the surface free energy of the surfactant on the carbon fibers can be controlled and the coefficient of friction can be reduced, so that the handleability of the sizing agent-containing carbon fiber bundle can be improved. The heat treatment temperature is preferably in the temperature range of 120 to 260.degree. When the temperature is 120° C. or higher, the removal of the dilute solution controls the ionization of the surfactant and suppresses the electrical interaction, so that the handleability can be easily improved. 150° C. or higher is more preferable, and 180° C. or higher is even more preferable. On the other hand, by setting the upper limit of the heat treatment temperature to 260° C. or less, the thermal deterioration of the surfactant component can be suppressed, and the dissolution property can be easily maintained. 240° C. or lower is more preferable, and 220° C. or lower is even more preferable.

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

EXAMPLES Next, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

<Cross-sectional shape of single fiber (La/Lb, Ld/Lc)>
A single fiber was taken out from the sizing agent-containing carbon fiber bundle and was broken by pulling in the fiber axis direction. Although one fiber becomes two by breaking, one fiber was discarded, and only the remaining fiber was attached to the SEM sample stage using a carbon tape so that the fractured surface faced upward. This operation was repeated 25 times to prepare an SEM sample stage on which 25 fractured surfaces were attached. After that, platinum-palladium was vacuum-deposited to a thickness of about 10 nm, and observed with an S-4800 scanning electron microscope (SEM) manufactured by Hitachi High-Technologies Corporation under conditions of an acceleration voltage of 5.0 kV and a working distance of 8 mm.

The cross-sectional shape of the above 25 carbon fibers was measured as follows.

(a) Determination of a-axis The a-axis was determined from the SEM observation image of the fracture surface. At that time, the longest straight line that passes through any two points on the outer periphery of the fractured surface and that divides the fractured surface into two by the straight line so that the areas of the two regions are approximately equal to each other. is the long axis. Since such evaluation is performed visually, the angle of the major axis determined slightly differs depending on the measurer, and even for the same measurer, depending on the time of evaluation. Therefore, the average of the results of two consecutive evaluations by the same person was adopted.

(b) Measurement of La, Lb, Lc, and Ld An open-source image analysis software “ImageJ ver1.47” was used for measurement. For the a-axis length La, the length of the a-axis determined in (a) was measured in units of pixels and converted to actual length (unit: μm) using the scale bar attached to the SEM observation image. Next, three points were set so as to divide the a-axis into four equal parts, and three line segments perpendicular to the a-axis passing through each point and two points on the outer periphery of the fiber were obtained. Of these, the one passing through the midpoint of the a-axis was defined as the b-axis, and the length Lb of the b-axis was determined in the same manner as La. The lengths of the remaining two line segments were determined in the same manner as La, with the length of the short one being Lc and the length of the long one being Ld.

La/Lb and Ld/Lc for 25 single fibers were calculated as described above. For each single fiber, it was confirmed whether the formulas (1) and (2) were satisfied, and the ratio was obtained by dividing the number of single fibers satisfying both formulas by the number of samples, 25 (fibers).
1.00≤La/Lb≤1.20 (1)
1.00≦Ld/Lc≦1.25 (2).

<Average value of cross-sectional shape (<La/Lb>, <Ld/Lc>)>
<La/Lb> and <Ld/Lc> were calculated by simple averaging La/Lb and Ld/Lc for 25 single fibers obtained as described above.

<Surface ratio of single fibers of carbon fiber bundle>
Several precursor fiber single fibers to be evaluated were placed on a sample stage, and both ends were fixed with an adhesive liquid (for example, correction liquid for stationery) as a sample, and an atomic force microscope (manufactured by Seiko Instruments, SPI3800N / SPA-400 ) was used to obtain a three-dimensional surface profile image under the following conditions.
・Probe: Silicon cantilever (manufactured by Seiko Instruments, DF-20)
・Measurement mode: Dynamic force mode (DFM)
・Scanning speed: 1.5Hz
・Scanning range: 3 μm × 3 μm
• Resolution: 256 pixels x 256 pixels.

The obtained measurement image is fitted with a primary plane using the least squares method from all the image data, taking into consideration the curvature of the fiber cross section, and the primary tilt correction is performed to correct the in-plane tilt. After that, the surface roughness was analyzed by the attached 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 taken as the value of the surface area ratio.

<Method for measuring the amount of sizing agent adhered>
After weighing (W ₁ ) (reading to the fourth decimal place) of 2.0 ± 0.5 g of the sizing agent-containing carbon fiber bundle, an electric furnace ( A volume of 120 cm ³ ) was left for 15 minutes to completely thermally decompose the sizing agent. Then, the carbon fiber bundle was transferred to a container in a dry nitrogen stream at 20 liters/minute, cooled for 15 minutes, and then weighed (W ₂ ) (read to the fourth decimal place), and the weight loss due to heating was determined by W ₁ −W ₂ . asked for A value (rounded to the third decimal place) obtained by converting this heating weight loss to 100 parts by mass of the sizing agent-containing carbon fiber bundle was defined as the adhesion amount (parts by mass) of the adhering sizing agent. The measurement was performed twice, and the average value was taken as the adhesion amount of the sizing agent.

<Method for measuring mass residual rate of polyethylene glycol and/or surfactant>
The mass residual rate of polyethylene glycol and/or surfactant was measured using a thermogravimetric/differential thermal analyzer (TG-DTA). 10 ± 0.5 mg of polyethylene glycol and / or surfactant was weighed (W ₃ ) (read to the fourth decimal place) in an aluminum pan, placed inside the heating device, and heated in an air stream of 100 ml / min for 25 minutes. C. to 450.degree. C. at a rate of 10.degree. C./min to thermally decompose the surfactant. Read the mass (W ₄ ) (read to the fourth decimal place) when reaching 300 ° C. and the mass (W ₅ ) (read to the fourth decimal place) when reaching 350 ° C., W ₄ /W ₃ × 100 (%) , and W ₅ /W ₃ ×100 (%) were calculated to obtain the mass retention rate (%) when reaching 300°C and the mass retention rate (%) when reaching 350°C.

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

<Method for measuring the amount of functional groups on the surface of the carbon fiber bundle>
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, after cutting the carbon fiber bundle into 20 mm and arranging it on a copper sample support, using AlKα ₁ , 2 as an X-ray source, the inside of the sample chamber was maintained at 1×10 ⁻⁸ Torr, and the photoelectrons escaped. X-ray photoelectron spectroscopy was performed at an angle of 45°. The binding energy value of the main peak of C _1S was adjusted to 285 eV as a correction value for the peak associated with electrification during measurement. The C _1S peak area was determined by drawing a linear baseline over the range of 275 to 290 eV as binding energy values. The O _1s peak area was determined by drawing a linear baseline over the range of 525 to 540 eV as binding energy. ESCA-1600 manufactured by ULVAC-Phi, Inc. was used as an X-ray photoelectron spectrometer.

<Method for measuring CF rubbed fluff>
Two metal bars (material: stainless steel SUS304) having a diameter of 50 mm and a surface roughness Rmax of 0.3 μm were placed at an interval of 150 mm, and the carbon fiber bundle was attached to the metal bar at an angle of 0.785 π (rad) in total. They were arranged in the vertical direction so that they could pass through while being in contact with each other. Then, the carbon fiber bundle is stretched over the metal bar, the unwinding tension from the package is set to 800 g, the carbon fiber bundle is pulled by the drive roll at a speed of 6 m per minute, and passed through the metal bar. After passing through the metal bar, the fiber thread was irradiated with a laser beam perpendicularly from the side surface, and the number of fluffs was detected and counted by a fluff detector for 5 minutes, and the number of fluffs was recorded.

In the present invention, the preferable range of handleability was evaluated in three stages according to the following criteria, and S and A were regarded as acceptable, and B was regarded as unacceptable.

S: Less than 15 fluff/m A: More than 15 fluff/m and less than 25 fluff/m B: More than 25 fluff/m.

<Method for measuring dry FF friction coefficient>
On the surface of the sizing agent-containing carbon fiber bundle wound on a bobbin fixed so as not to rotate so that the thickness is uniform, the thickness is 5 to 10 mm, and the winding density is in the range of 0.9 to 1.4 g / cm ³ . The same carbon fiber bundle as the object was wound so as not to overlap with itself so as to have a contact angle of 3π (rad), typically with an interval of 3 to 5 mm in the width direction. A weight (T1 = 0.25 g/tex) is attached to one end of the wound carbon fiber bundle, and the opposite end is pulled with a spring scale at a speed of 1 m / min, and the tension when the wound carbon fiber bundle starts to move is measured. As T2, the dry FF friction coefficient was calculated from the following formula. The measurement was performed twice, and the average value was taken as the dry FF friction coefficient. The measurement bobbins used were placed in the measurement atmosphere temperature and humidity conditions (measurement conditions: 23±3° C./60±5%) two hours or more before the measurement.

Dry FF friction coefficient = ln (T2/T1)/θ
T2: Tension when the carbon fiber bundle begins to move (=indicated value of the spring balance)
T1: weight weight (= 0.25 g/tex)
θ: the total contact angle between the scroll and the wound thread (=3πrad).

<Strand Strength and Strand Elastic Modulus of Carbon Fiber Bundle>
The strand strength and strand elastic modulus of the carbon fiber bundle are obtained according to the resin-impregnated strand test method of JIS R7608 (2004) according to the following procedures. However, when the carbon fiber bundle has a twist, it is untwisted by imparting the same number of reverse rotation twists as the number of twists, and then evaluated. As the resin formulation, "Celoxide (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) was used. The curing conditions are normal pressure, temperature of 125° C., and time of 30 minutes. Ten strands of the carbon fiber bundle are measured, and the average value is taken as the strand strength and strand elastic modulus. The strain range for calculating the strand elastic modulus is 0.1 to 0.6%.

<Method for measuring interfacial shear strength>
A single yarn is extracted from the carbon fiber bundle, sandwiched from the top and bottom with resin films laminated to a thickness of 0.4 mm or more, heated and pressurized with a hot press, and then cooled to room temperature while maintaining the pressurized state. After cooling, a molded plate in which the carbon fiber single yarn was embedded was obtained. A dumbbell-shaped test piece for IFSS measurement was punched out from this molded plate using an SD-type lever cutting machine.

A dumbbell-shaped sample was sandwiched at both ends, a tensile force was applied in the direction of the fiber axis (longitudinal direction), and a strain of 12% was produced at a speed of 2.0 mm/min. After that, a 20 mm central portion of the test piece was cut off, sandwiched between glass plates on a hot plate, and heated to the melting point of the thermoplastic resin or higher. Fragmented fiber lengths inside the sample that had been made transparent by heating were observed under a microscope. Further, the critical fiber length lc was calculated from the average broken fiber length la by 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), which is an index of the adhesive strength between the carbon fiber and the resin interface, was calculated by the following formula. In the examples, the average of the number of measurements n=5 was used as the test result.

IFSS (MPa) = σ (MPa) x d (μm)/(2 x lc) (μm).

In the present invention, the preferred range of IFSS for the following resins was evaluated in three stages according to the following criteria, and A and B were regarded as acceptable.

Resin: Polyetheretherketone A: IFSS of 35 or more B: IFSS of 30 or more and less than 35 C: IFSS of less than 30 Materials and components used in each example and each comparative example are as follows.

<Spinneret>
[ _A ] Spinneret _A : The type of (B) in FIG. A spinneret having 100 sets of holes drilled at 0.16 mm was designated spinneret A.
[B] Spinneret B: The type of (B) in FIG. 2, in which a circular hole with a diameter (d1) of 0.3 mm and a circular hole with a diameter (d2) of 0.06 mm have a center-to-center distance (L) of 0.22 mm. Spinneret B was a spinneret having 100 sets of holes drilled in .
[C] Spinneret C: The type of (B) in FIG. 2, in which a circular hole with a diameter (d1) of 0.3 mm and a circular hole with a diameter (d2) of 0.04 mm have a center-to-center distance (L) of 0.20 mm. Spinneret C was a spinneret having 100 sets of holes drilled in .
[D] Spinneret D: Spinneret D was a spinneret having 100 circular holes with a diameter of 0.2 mm.

(A) component: anionic surfactant A-1: sodium bis(2-ethylhexyl) sulfosuccinate (manufactured by Tokyo Chemical Industry Co., Ltd.)
A-2: Oleic acid butyl ester sulfated oil (“Rotat (registered trademark)” OH-104K manufactured by Lion Corporation, reaction rate: 79%)
A-3: Sodium alkylnaphthalene sulfonate (manufactured by Tokyo Chemical Industry Co., Ltd.)
A-4: Sodium dodecylbenzenesulfonate ("Neooperex (registered trademark)" G15 manufactured by Kao Corporation)
A-5: Sodium lauryl sulfate ("Emar (registered trademark)" 10G manufactured by Kao Corporation)
A-6: disodium lauryl sulfosuccinate ("Beaulite (registered trademark)" SSS manufactured by Sanyo Chemical Industries, Ltd.)
A-7: Sodium 2-ethylhexyl sulfate (“Sandet (registered trademark)” ONA manufactured by Sanyo Chemical Industries, Ltd.).

(B) Component: Polyethylene glycol and/or nonionic surfactant B-1: PEG distearate (“Ionet (registered trademark)” DS4000 manufactured by Sanyo Chemical Industries, Ltd., HLB: 16.6)
B-2: PEG monostearate (“Ionet (registered trademark)” MS1000 manufactured by Sanyo Chemical Industries, Ltd., HLB: 15.7)
B-3: PEG monooleate (manufactured by Sanyo Chemical Industries, Ltd. “Ionet (registered trademark)” MO600, HLB: 13.8)
B-4: PEG monooleate (manufactured by Sanyo Chemical Industries, Ltd. “Ionet (registered trademark)” MO400, HLB: 11.7)
B-5: PEG dioleate ("Ionet (registered trademark)" DO1000 manufactured by Sanyo Chemical Industries, Ltd., HLB: 12.9)
B-6: PEG dioleate (manufactured by Sanyo Chemical Industries, Ltd. “Ionet (registered trademark)” DO600, HLB: 10.5)
B-7: polyethylene glycol (manufactured by Sanyo Chemical Industries, Ltd. PEG600, 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: betaine lauryldimethylaminoacetate ("Amphitol (registered trademark) 24B" manufactured by Kao Corporation)
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.).

(D) Component: Other components D-1: Propylene glycol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.)
D-2: 2-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
D-3: diglycerol polyglycidyl ether (manufactured by Nagase ChemteX Co., Ltd. "Decanal (registered trademark)" Ex-421)
D-4: Polyethylenimine (“Lupasol (registered trademark)” G20 Waterfree, manufactured by BASF Japan Ltd.).

(E) Component: Thermoplastic resin E-1: Polyetheretherketone (“Victrex (registered trademark)” 450G manufactured by Victrex Co., Ltd.).

(Example 1)
This embodiment consists of the following 1st to 5th steps.

・First step: A step of producing a carbon fiber bundle as a raw material Polyacrylonitrile-based copolymer consisting of 99.5 mol% acrylonitrile and 0.5 mol% itaconic acid, with a weight average molecular weight of 400,000 and Mz/Mw of 2.1 The coalescence was prepared by radical polymerization. This polyacrylonitrile-based polymer was neutralized with ammonia in dimethylsulfoxide to prepare a spinning solution having a polymer concentration of 19% by mass. The obtained spinning solution was once discharged into the air using a spinneret A at 40°C, passed through a space of about 5 mm, and then coagulated in a coagulation bath consisting of an aqueous solution of 79 mass% dimethyl sulfoxide controlled at 5°C. It was made into a coagulated yarn by a dry-wet spinning method introduced into the. The coagulated filaments were washed with water, drawn, oiled, dried and densified by a conventional method to obtain a polyacrylonitrile-based precursor fiber bundle having a single fiber fineness of 1.0 dtex and 500 single fibers.

Next, after flameproofing treatment in air at a temperature of 240 to 300°C, preliminary carbonization treatment is performed in a nitrogen atmosphere at a temperature of 300 to 800°C, and then carbonization treatment is performed in a nitrogen atmosphere at a maximum temperature of 1,300°C. was performed to obtain a carbon fiber bundle. Then, the carbon fiber bundle was subjected to an electrolytic surface treatment using an ammonium hydrogen carbonate aqueous solution as an electrolytic solution with an amount of electricity of 30 coulombs per 1 g of the carbon fiber bundle. The carbon fiber bundle subjected to the electrolytic surface treatment was subsequently washed with water and dried in hot air to obtain a carbon fiber bundle A as a raw material. In addition, the strand strength, strand elastic modulus, cross-sectional shape, and surface oxygen concentration of the carbon fiber bundle A obtained in the first step were measured. Table 1 shows the evaluation results.

・Second step: A step of attaching a sizing agent to the carbon fiber bundle As the compound (A), (A-1) has the composition shown in Table 1, and water is added to uniformly dissolve about 0.8% by mass of an aqueous solution. Obtained. Using this aqueous solution as a sizing agent aqueous solution, the sizing agent is applied to the surface-treated carbon fiber bundle by an immersion method, and then heat treated with a hot roller at a temperature of 120 ° C. for 15 seconds as a preliminary drying step. As a drying step, heat treatment was performed in heated air at a temperature of 210° C. for 60 seconds to obtain a sizing agent-containing carbon fiber bundle. The adhesion amount of the sizing agent was adjusted so as to be 0.40% by mass in 100% by mass of the total surface-treated carbon fiber bundle containing the sizing agent. Also, the mass residual ratio of the sizing agent applied in the second step was measured. It was found that the mass residual rate was 25% when reaching 300°C and the mass residual rate was 17% when reaching 350°C, indicating sufficient thermal decomposition.

・Third step: Evaluation of handleability of sizing agent-containing carbon fiber bundle Using the sizing agent-containing carbon fiber bundle obtained in the second step, handle based on the friction coefficient evaluation method and the CF rubbing fluff measurement method. evaluated the sex. As a result, the dry FF coefficient of friction was found to be 0.33.

Fourth step: Evaluation of sizing agent adhesion amount after washing with water For the sizing agent-containing carbon fiber bundle obtained in the previous step, the above <Method for calculating the sizing agent adhesion amount after washing with water for 50 seconds> and <25 seconds Calculation method of sizing agent adhesion amount after washing with water>, the sizing agent-containing carbon fiber bundle was washed with water, and after washing with water for 50 seconds, after obtaining the sizing agent-containing carbon fiber bundle after 25 seconds, 50 The sizing agent adhesion amount after washing with water for 2 seconds and the sizing agent adhesion amount after washing with water for 25 seconds were calculated. As a result, the sizing agent adhesion amount after washing with water for 50 seconds was 0.03% by mass in 100% by mass of the sizing agent-containing carbon fiber bundle, and the sizing agent adhesion amount after washing with water for 25 seconds was in 100% by mass of the sizing agent-containing carbon fiber bundle. 0.06% by mass of the residual amount, and it was found that the dissolution property was sufficiently high. Moreover, when the surface area ratio after washing with water for 50 seconds was evaluated, the surface area ratio was 1.02, indicating the presence of fine surface irregularities.

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

Subsequently, IFSS was measured using the obtained test piece for IFSS measurement. As a result, the IFSS when using the carbon fiber bundle containing the sizing agent after washing with water for 50 seconds was 37 MPa, and the IFSS when using the carbon fiber bundle containing the sizing agent after washing with water for 25 seconds was 37 MPa, indicating sufficiently high adhesion. I found out. The above results are summarized in Table 2.

(Example 2)
In the first step, a carbon fiber bundle B was obtained in the same manner as in Example 1, except that the spinneret B was used and the space through which the spinning solution was passed after being discharged from the spinneret was set to about 3 mm. Various evaluations were performed in the same manner as in Example 1. The results are shown in Tables 1 and 2, indicating good handleability, sufficiently high dissolution properties, and high adhesiveness.

(Comparative example 1)
In the first step, a carbon fiber bundle C was obtained in the same manner as in Example 1 except that the spinneret C was used and the space through which the spinning solution was discharged from the spinneret and passed through was set to about 3 mm. Various evaluations were performed in the same manner as in Example 1. The results are shown in Tables 1 and 2, and it was found that the strand strength was lower than in Example 1, although the handleability was good and the dissolution property was sufficiently high.

(Example 3)
Example 1 except that, in the first step, the spinneret D was used, the space through which the spinning solution was discharged from the spinneret was about 4 mm, and the coagulation bath was an aqueous solution of 30% by mass of dimethyl sulfoxide controlled at 15°C. A carbon fiber bundle D was obtained in the same manner as in Example 1, and various evaluations were performed in the same manner as in Example 1 for the second to fifth steps. The results are shown in Tables 1 and 2, indicating good handleability and sufficiently high dissolution.

(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 the polyacrylonitrile-based precursor fiber bundle. Various evaluations were performed in the same manner as in Example 1 for the second to fifth steps. The results are shown in Tables 1 and 2, indicating good handleability, sufficiently high dissolution properties, and high adhesiveness.

(Comparative example 2)
Carbon fiber bundles F were obtained in the same manner as in Example 3 except that in the first step, the coagulation bath was controlled to 30° C. and an aqueous solution of 55% by mass of dimethyl sulfoxide was used. Various evaluations were performed in the same manner as in 1. The results are shown in Tables 1 and 2, and it was found that the strand strength was lower than in Example 1, although the handleability was good and the dissolution property was sufficiently high.

(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 80 coulombs/g, and the amount of sizing agent adhered in the second step was changed as shown in Table 2. Then, various evaluations were performed in the same manner as in Example 1 for the third to fifth steps. The results are shown in Tables 1 and 2. Although the dissolution was sufficiently high, the dry FF friction was high and the handleability was insufficient.

(Comparative Example 4)
A carbon fiber bundle H was obtained in the same manner as in Example 3 except that the surface treatment amount in the first step was 0 coulomb/g and the amount of sizing agent adhered in the second step was changed as shown in Table 2. Then, various evaluations were performed in the same manner as in Example 1 for the third to fifth steps. The results are shown in Tables 1 and 2. Although the dissolution was sufficiently high, the dry FF friction was low and the handleability was insufficient.

(Example 5)
A sizing agent-containing carbon fiber was obtained in the same manner as in Example 1, except that the sizing agent adhesion amount in the second step was changed as shown in Table 3, and various evaluations were performed. The results are as shown in Table 3, and it was found that the handleability was good and the dissolution was sufficiently high.

(Comparative Example 5)
A sizing agent-containing carbon fiber was obtained 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 adhered was changed as shown in Table 3. , various evaluations were performed. The results are shown in Table 3. Although the dissolution was sufficiently high, the dry FF friction was high and the handleability was insufficient.

(Comparative Example 6)
A sizing agent-containing carbon fiber was obtained in the same manner as in Example 2, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 3, and various evaluations were performed. The results are as shown in Table 3. Although the handling property was good, the ratio of hydrophilic groups of anions in the anionic surfactant was low, and the dissolution property was insufficient.

(Examples 6-9)
A sizing agent-containing carbon fiber was obtained 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, and various evaluations were performed. The results are as shown in Table 3, and it was found that the handleability was good and the dissolution was sufficiently high.

(Examples 10-12)
A sizing agent-containing carbon fiber was obtained 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, and various evaluations were performed. The results are shown in Table 4, and it was found that the handleability was good and the dissolution was sufficiently high.

(Examples 13-16)
A sizing agent-containing carbon fiber was obtained in the same manner as in Example 4 except that the second component was added to the sizing agent used in the second step, and the composition and amount of adhesion were changed as shown in Table 4, and various evaluations were performed. went. The results are shown in Table 4, and it was found that the handleability was good and the dissolution was sufficiently high.

(Examples 17-21)
A sizing agent-containing carbon fiber was obtained 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, and various evaluations were performed. The results are as shown in Table 5, and it was found that the handleability was good and the dissolution was sufficiently high.

(Comparative Example 7)
A sizing agent-containing carbon fiber was obtained in the same manner as in Comparative Example 3, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 5, and various evaluations were performed. The results are as shown in Table 5. Dry FF friction was high and handleability was insufficient.

(Comparative Examples 8-10)
A sizing agent-containing carbon fiber was obtained 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, and various evaluations were performed. The results are as shown in Table 5, and the handleability was good, but the elution was insufficient due to the low HLB or the low terminal hydroxyl group ratio.

(Examples 22-26)
A sizing agent-containing carbon fiber was obtained 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 6, and various evaluations were performed. The results are as shown in Table 6, and it was found that the handleability was good and the dissolution was sufficiently high.

(Examples 27-28)
Example 4 except that in the second step, the composition and amount of the sizing agent were changed as shown in Table 6, the heating time at 120°C in the preliminary drying step was set to 5 seconds, and the second drying step was omitted. A sizing agent-containing carbon fiber was obtained in the same manner as above, and various evaluations were performed. The results are as shown in Table 6, and it was found that the handleability was good and the dissolution was sufficiently high.

(Examples 29-31)
A sizing agent-containing carbon fiber was obtained 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 7, and various evaluations were performed. The results are as shown in Table 7, and it was found that the handleability was good and the dissolution was sufficiently high.

(Examples 32-34)
The composition and amount of the sizing agent in the second step were changed as shown in Table 7, and after heat treatment with a hot roller at a temperature of 120 ° C. for 15 seconds as a preliminary drying step, the second drying step was not used. obtained a sizing agent-containing carbon fiber in the same manner as in Example 4, and performed various evaluations. The results are as shown in Table 7, and it was found that the handleability was good and the dissolution was sufficiently high.

(Comparative Example 11)
A sizing agent-containing carbon fiber was obtained in the same manner as in Comparative Example 3, except that the composition and amount of the sizing agent applied in the second step were changed as shown in Table 7, and various evaluations were performed. The results are shown in Table 7. The dry FF friction was high and the handleability was insufficient.

According to the present invention, a sizing agent that exhibits bundling properties and frictional properties suitable for handleability and that easily enhances resin impregnation due to good affinity with water in an aqueous process is a single unit having a specific cross-sectional shape. The sizing agent-containing carbon fiber bundle is particularly suitable for combination with a thermoplastic matrix resin because it is applied to carbon fibers containing fiber as a main component, reducing the amount of sizing agent remaining after processing to an intermediate base material. can be provided. The thermoplastic resin composite using the present invention is lightweight and has excellent strength, so it is suitably used in many fields such as aircraft members, spacecraft members, automobile members, ship members, civil engineering and construction materials, and sporting goods. be able to.

11: Unwinding process 12: Washing process 13: Drying process 14: Winding process 15: Free roller before washing tank 16: Free roller in washing tank 17: Free roller after washing tank 18: Washing tank 19: Free roller before washing tank 20: Free roller in 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 1c: Carbon fiber bundle containing sizing agent after washing and drying 1d: water 1e: water

Claims (17)

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) Contain 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)
(However, the line segment passing through the two furthest points on the outer circumference of the 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 outer circumference and perpendicular to the a-axis is the b-axis. Define the length as La and the length of the b-axis as Lb, where La≧Lb.In addition, when the a-axis is divided into four equal parts, , the lengths of two line segments perpendicular to the a-axis are defined as Lc and Ld, and Lc≦Ld.)
(iii) The sizing agent adhesion amount after washing with water for 50 seconds under the following conditions is 0.12% by mass or less based on 100% by mass of the sizing agent-containing carbon fiber bundle.
<Method of Washing Carbon Fiber Bundles Containing Sizing Agent>
The sizing agent-containing carbon fiber bundle is introduced into water through a roller to dissolve the sizing agent into the water. The sizing agent-containing carbon fiber bundle installed in the unwinding process is passed through the water in the washing tank through the free roller before the washing tank, the free roller in the washing tank, and the free roller after the washing tank in the washing process, and then continuously. It passes through a drying process, dries the water, and is wound up in a winding process. 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 washing tank was 150 mm, and the contact between the sizing agent-containing carbon fiber bundle and the free roller in the washing tank. Let the angle be π rad. In addition, the liquid surface is adjusted so that the underwater passage time is 50 seconds. The drying step is non-contact drying, and the sizing agent-containing carbon fiber bundle after washing with water is dried at a drying temperature of 150° C. for 1 minute to obtain a sizing agent-containing carbon fiber bundle after washing with water and drying. The sizing agent adhesion amount is obtained by measuring the sizing agent adhesion amount of the sizing agent-containing carbon fiber bundle after washing with water and drying. The sizing agent-containing carbon according to claim 1, wherein the average value of the surface area ratio of the carbon fiber single fibers after washing with water for 50 seconds by the method for washing the sizing agent-containing carbon fiber bundle is 1.01 or more and 1.07 or less. fiber bundle. The sizing agent contains polyethylene glycol and/or a nonionic surfactant, and the sizing agent adhesion amount is 0.15% by mass or more and 0.60% by mass or less in 100% by mass of the sizing agent-containing carbon fiber bundle. The sizing agent-containing carbon fiber bundle according to claim 1 or 2. It contains a sizing agent containing the surfactant, the surfactant is an anionic surfactant, and the sizing agent adhesion amount is 0.20% by mass or more and 0.80% by mass in 100% by mass of the sizing agent-containing carbon fiber bundle. The sizing agent-containing carbon fiber bundle according to claim 1 or 2, wherein the sizing agent-containing carbon fiber bundle is mass% or less. It contains a sizing agent containing the surfactant, the surfactant is an amphoteric surfactant, and the sizing agent adhesion amount is 0.15% by mass or more and 0.45% by mass in 100% by mass of the sizing agent-containing carbon fiber bundle. The sizing agent-containing carbon fiber bundle according to claim 1 or 2, wherein the sizing agent-containing carbon fiber bundle is mass% or less. The sizing agent-containing carbon fiber bundle according to claim 3, wherein the polyethylene glycol and/or the nonionic surfactant satisfy the following (iv) or (v).
(iv) HLB is 15 or more and 20 or less.
(v) HLB is 12 or more and less than 15, and the ratio of hydroxyl groups at molecular terminals is 50% or more. 7. The sizing agent-containing carbon fiber bundle according to claim 3, wherein said polyethylene glycol and/or nonionic surfactant satisfies (vi) or (vii) below.
(vi) 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 polyalkylene glycol structure is 60% by mass or more. 5. The sizing agent-containing carbon fiber bundle according to claim 4, wherein the proportion of hydrophilic groups in the anions constituting the anionic surfactant is 17% or more. The sizing agent-containing carbon fiber bundle according to claim 5, wherein the average number of carbon atoms of the alkyl groups constituting the amphoteric surfactant is 17 or less. The sizing agent-containing carbon fiber bundle according to claim 5 or 9, 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. The sizing agent-containing carbon fiber bundle according to any one of claims 1 to 10, wherein the total amount of polyethylene glycol and/or surfactant is 70% by mass or more in 100% by mass of the total amount of the sizing agent. The sizing agent-containing carbon fiber according to any one of claims 1 to 11, wherein the sizing agent adhesion amount after washing with water for 25 seconds under the following conditions is 0.12% by mass or less in 100% by mass of the sizing agent-containing carbon fiber bundle. bundle.
<Method of Washing Carbon Fiber Bundles Containing Sizing Agent>
The sizing agent-containing carbon fiber bundle is introduced into water through a roller to dissolve the sizing agent into the water. The sizing agent-containing carbon fiber bundle installed in the unwinding process is passed through the water in the washing tank through the free roller before the washing tank, the free roller in the washing tank, and the free roller after the washing tank in the washing process, and then continuously. It passes through a drying process, dries the water, and is wound up in a winding process. 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 washing tank was 150 mm, and the contact between the sizing agent-containing carbon fiber bundle and the free roller in the washing tank. Let the angle be π rad. In addition, the liquid level is adjusted so that the underwater passage time is 25 seconds. The drying step is non-contact drying, and the sizing agent-containing carbon fiber bundle after washing with water is dried at a drying temperature of 150° C. for 1 minute to obtain a sizing agent-containing carbon fiber bundle after washing with water and drying. The sizing agent adhesion amount is obtained by measuring the sizing agent adhesion amount of the sizing agent-containing carbon fiber bundle after washing with water and drying. The sizing agent according to any one of claims 1 to 12, wherein the polyethylene glycol and/or surfactant have a mass residual rate of 35% or less when the temperature reaches 300°C when heated at 10°C/min in air. Containing carbon fiber bundles. The sizing agent according to any one of claims 1 to 13, wherein the polyethylene glycol and/or surfactant have a mass residual rate of 30% or less when the temperature reaches 350°C when the temperature is raised at 10°C/min in air. Containing carbon fiber bundles. The sizing agent-containing carbon fiber bundle according to any one of claims 1 to 14, wherein the carbon fiber bundle has a strand strength of 5.0 GPa or more. 16. The method for producing a sizing agent-containing carbon fiber bundle according to any one of claims 1 to 15, wherein the sizing agent is applied to the carbon fiber bundle after the step of applying the sizing agent containing polyethylene glycol and/or a surfactant to the carbon fiber bundle. A method for producing a sizing agent-containing carbon fiber bundle, comprising a drying step of drying the carbon fiber bundle to which the agent is applied. The method for producing a sizing agent-containing carbon fiber bundle according to claim 16, wherein in the drying step of drying the carbon fiber bundle coated with the sizing agent, the carbon fiber bundle coated with the sizing agent is dried at 120 to 260°C.

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