JP5582268B1 - Carbon fiber coated with sizing agent - Google Patents

Abstract

A sizing agent-coated carbon fiber for producing a carbon fiber composite material exhibiting excellent tensile elastic modulus and perforated plate tensile strength and a method for producing the same are provided.
SOLUTION: When the single fiber apparent stress is 15.3 GPa by the fragmentation method of the single fiber composite of carbon fiber, the number of fiber breaks is 2.0 pieces / mm or more, and the single fiber apparent stress is 12.2 GPa. Carbon fiber having a fiber breakage number of 1.3 pieces / mm or less. Also preferably, the sizing agent-coated carbon fiber obtained by applying a sizing agent containing an epoxy compound to the carbon fiber. When the single fiber diameter of the carbon fiber is 4.5 μm or less and the single fiber apparent stress is 10.0 GPa, the number of fiber breaks is 0.8 pieces / mm or less, the average tearable distance is 300 mm to 710 mm, Carbon fiber with sizing agent applied, which is virtually untwisted.
[Selection figure] None

Description

  The present invention relates to carbon fibers and sizing agent-coated carbon fibers that are suitably used for aircraft members, spacecraft members, automobile members, ship members, sports applications such as golf shafts and fishing rods, and other general industrial applications. . More specifically, the present invention relates to a sizing agent-coated carbon fiber having a specific single fiber strength distribution and excellent adhesion to a matrix resin, and a prepreg using the carbon fiber has good physical properties, particularly a high perforated plate. A carbon fiber reinforced composite material having tensile strength (hereinafter sometimes abbreviated as OHT) is obtained.

  Carbon fiber has contributed to weight reduction of aircraft by being used for aircraft applications as a reinforcing fiber of fiber reinforced composite material due to its high specific strength and specific modulus. The flow of is being accelerated. For reducing the weight of aircraft, it is most effective to improve the tensile modulus of carbon fiber that governs the rigidity of the carbon fiber reinforced composite material. Therefore, it is required to have a wide balance of physical properties such as further improvement of mechanical properties of carbon fiber, and further improvement of tensile / compressive strength and perforated plate tensile / compressive strength as a carbon fiber reinforced composite material. In particular, when carbon fiber reinforced composite materials are used for aircraft applications, it is often the case that perforated plates are used rather than the tensile strength of unidirectional carbon fiber reinforced composite materials because they are often used with fasteners by drilling pseudo isotropic materials. Tensile strength is important. Since many factors affect the perforated plate tensile strength, the mechanism of its strength development is often unclear, and the influence of carbon fiber on the perforated plate tensile strength is generally It was known to be proportional to strength.

Strand strength is used as a simple method for examining the strength potential of carbon fiber, which is a reinforcing fiber. Tensile strength of a simple unidirectional carbon fiber reinforced composite material obtained by impregnating a specific epoxy resin. (Hereinafter referred to as unidirectional composite material strength). The unidirectional composite material strength is generally strongly related to the single fiber strength distribution, and the predicted value σ _c ^* of the unidirectional composite material strength generally agrees with the actually measured value when predicted by the following formula shown in Non-Patent Document 1. It has been known.

Here, σ ₀ , m, L ₀ , and τ represent the Weibull shape factor, Weibull scale factor, test length, and interfacial shear strength in the single fiber strength test, respectively, and the strand strength that is a kind of unidirectional carbon fiber reinforced composite material In the case of the test, the interfacial shear strength is 7 MPa.

  The single fiber strength test is widely studied as a method for examining fiber strength more precisely than the strand strength test (Non-patent Documents 2 and 3, Patent Documents 1 and 2). As shown in these documents, the behavior of the apparent strength distribution changes by shortening the sample length (specifically, the Weibull shape factor of the single fiber strength distribution increases as the sample length decreases). Has disclosed various behaviors, and there was no unified view of these behaviors. In order to cope with such a problem, there is a method of evaluating the single fiber strength distribution from a fragmentation test of a single fiber composite in which the stress distribution in the longitudinal direction of the single fiber is interpreted in detail (Non-Patent Documents 4 and 5). ). However, compared with the generally used single fiber strength test, the fragmentation test of the single fiber composite is immature as an evaluation method of the single fiber strength distribution, and there are not many examination examples. For this reason, there has been no discussion of precise intensity distribution in the short sample length region.

  There are examples of investigating the characteristics of carbon fibers for the purpose of improving the tensile strength of the perforated plate of carbon fiber reinforced composite materials (Patent Documents 3 and 4). In Patent Document 3, it is an attempt to improve the perforated plate tensile strength of the carbon fiber reinforced composite material by changing the surface morphology of the carbon fiber and the surface treatment conditions for the carbon fiber. It was not something to control. Patent Document 4 discloses a concept of increasing the perforated plate tensile strength of the carbon fiber reinforced composite material by controlling the spreadability of the carbon fiber and the wettability of the surface thereof. It was a low level.

  In recent years, in order to improve the tensile elastic modulus of carbon fibers irrespective of the control of the maximum temperature of the carbonization process, several techniques for stably performing firing at a high stretching tension have been proposed (Patent Document 5, 6 and 7). In Patent Document 5, although having a specific molecular weight distribution, the strand strength / elastic modulus level is high in a normal condition range, but the single fiber strength distribution in the short test length region of the carbon fiber is not controlled. Patent Documents 6 and 7 focus on the tensile modulus of carbon fiber, and the single fiber strength of the carbon fiber cannot be controlled.

  Moreover, in order to improve the single fiber strength of carbon fiber, the technique which controls the single fiber diameter of carbon fiber small and reduces the existence probability of a surface defect is proposed (patent document 8). According to such a technique, although the strand strength / elastic modulus level is high, the stretching tension in the firing step is increased without controlling the entanglement of the pre-carbonized fiber bundle used for the production of the carbon fiber bundle to a specific state, In the carbonization process, the stress of the single fiber that breaks with a certain probability will be borne by other single fibers that are not broken, in order to induce structural variation between single fibers and accompanying single fiber strength variation, The single fiber strength distribution in the short test length region of carbon fiber was not controlled. Moreover, generation | occurrence | production of the fluff and thread breakage was induced in the carbonization process, and the fall of operativity and the fall of the quality of the carbon fiber bundle obtained were not avoided.

JP 2010-013772 A JP 2009-256833 A JP 2010-047865 A JP 2010-111957 A JP 2008-248219 A JP 2008-308776 A JP 2008-308777 A Japanese Patent Laid-Open No. 11-241230

“Journal of American Ceramics Society” (USA), 1991, 74, 11, p. 2837-2845. “Composites: Part A” (Netherlands), 1999, 30, p. 1017-1021. “Journal of Materials Science” (Switzerland) 26 (1985), p. 3260-3270. “Composites: Part A” (Netherlands), 2002, 33, p. 1327-1335. “Composites Science and Technology” (Netherlands), 1995, 55, p. 33-39.

  In combination with a specific matrix resin that expresses extremely high perforated plate tensile strength in carbon fibers having an excellent tensile modulus, the present inventors have developed a carbon fiber reinforced composite material even if the strand strength of the carbon fibers is increased. The perforated plate tensile strength is not improved, so that the perforated plate tensile strength is not satisfactory (in other words, the order of the carbon fiber strand strength and the order of the perforated plate tensile strength of the carbon fiber reinforced composite material are The effect of carbon fiber reinforced composite materials on the perforated plate tensile strength due to changes in the surface condition of carbon fibers is small, and therefore the single fiber strength distribution in the short test length region of carbon fibers I came to pay attention. Then, this invention aims at providing the carbon fiber thru | or sizing agent application | coating carbon fiber used in order to produce the carbon fiber reinforced composite material which expresses the outstanding tensile elasticity modulus and perforated board tensile strength.

  As a result of various studies such as matrix resin, interface, and fiber morphology of the composite material, the present inventors have controlled the single fiber strength distribution in the short test length region of carbon fiber that could not be clearly measured conventionally. It has been found that the perforated plate tensile strength can be improved.

The present invention for achieving the above object has the following configuration. That is,
A sizing agent-coated carbon fiber in which a sizing agent is applied to carbon fiber, and the number of fiber breaks is 2.0 pieces / mm or more when the single fiber apparent stress is 15.3 GPa by the fragmentation method of the single fiber composite of carbon fiber A sizing agent-coated carbon fiber having a fiber breakage number of 1.3 pieces / mm or less when the single fiber apparent stress is 12.2 GPa. Further preferably, the sizing agent is an epoxy compound containing Musa customizing agent coating the carbon fibers.

  The carbon fiber and sizing agent-coated carbon fiber of the present invention can achieve excellent perforated plate tensile strength by controlling the single fiber strength distribution in the short test length region of the carbon fiber.

FIG. 1 is a diagram illustrating a method of measuring a tearable distance.

  In the present invention, the carbon fiber has a fiber breakage number of 1.3 pieces / mm or less when the single fiber apparent stress by a fragmentation method of a single fiber composite (specific method will be described later) is 12.2 GPa. Preferably it is 1.1 piece / mm or less, More preferably, it is 0.8 piece / mm or less. Fragmentation method of single fiber composite is to count the number of fiber breaks at each strain while giving strain stepwise to a composite in which carbon fiber single fiber is embedded in resin (single fiber composite). The intensity distribution can be examined. In order to convert the single fiber composite strain when the fiber is broken into the single fiber strength, it is necessary to consider the difference between the single fiber composite strain and the fiber strain and the elastic modulus at each fiber strain. In addition, the description regarding the single fiber strength will be described later. Here, the single fiber apparent stress indicates a product of single fiber composite strain and single fiber elastic modulus of carbon fiber. When fiber breakage occurs, there is a difference between single fiber composite strain and fiber strain to show the behavior that fiber stress recovers as the distance from the fiber breakage portion increases. Considering the behavior, the maximum fiber stress may hardly increase even if the single fiber composite strain is increased. However, the difference between the single fiber apparent stress and the maximum fiber stress is often very small up to 1.0 fiber breaks / mm, and the difference increases as the number of fiber breaks further increases. Since there is a correlation between the apparent stress and the maximum fiber stress, it is easy to use the single fiber apparent stress. It should be noted here that the elastic modulus of the carbon fiber has an elastic modulus nonlinearity that increases as the strain increases, and that the correct fiber stress cannot be obtained by a simple calculation. When the number of such fiber breaks exceeds 1.3 pieces / mm, the OHT decreases due to insufficient single fiber strength of the carbon fiber, and the smaller the number of such fiber breaks, the higher the single fiber strength. The number is preferably 1.3 pieces / mm or less. Normally, the strength of a unidirectional carbon fiber reinforced composite material is 6 or 7 GPa or less even when divided by the fiber cross-sectional area under the assumption that the load applied to the entire composite material is borne by the fiber alone. However, the relationship between the carbon fiber rupture probability exceeding the strength and the strength of the carbon fiber reinforced composite material has not been discussed in the past. It was clarified that the carbon fiber breakage probability in the high-strength region has a strong influence on the OHT.

  The single fiber strength test is generally used as a method for evaluating the single fiber strength distribution of carbon fibers. In the single fiber strength test, the chuck is embedded with a single fiber using a cyanate or epoxy adhesive in the chuck. As a result, stress is applied to the fibers in the adhesive and the fibers may break in the adhesive. That is, the present inventors pay attention to the fact that the single fiber strength test is a single fiber pull-out test from the adhesive, and in the single fiber strength test, stress is applied to several mm of fibers in the resin. It was revealed that it was loaded. In other words, the inventors of the present invention have a longer substantial test length even when the distance between chucks is less than 5 mm. In particular, the shorter the distance between chucks, the greater the difference between the actual test length and the distance between chucks. This revealed that the single fiber strength distribution in the long region could not be evaluated. In order to deal with such a problem, the present inventors decided to evaluate the single fiber strength distribution from the fragmentation test of the single fiber composite. And since the results of the single fiber strength distribution calculated from the fragmentation test of the single fiber composite and the single fiber strength test with a test length of 25 mm are in good agreement, the fragmentation test is the single fiber strength distribution. It was revealed that this is an excellent evaluation method. Furthermore, if the matrix resin used for the single fiber composite is appropriately selected and the bond strength at the single fiber-matrix resin interface is set to a certain level, the strength distribution can be evaluated with high accuracy up to a short test length of about 1 mm. Became clear. Heretofore, there has been no example in which precise intensity distribution in such a high strength (short sample length) region has been discussed.

  In the present invention, the carbon fiber has a fiber breakage number of 2.0 pieces / mm or more, preferably 2.5 pieces / mm or more when the single fiber apparent stress by the fragmentation method of the single fiber composite is 15.3 GPa. Yes, more preferably 3.0 / mm or more. When the number of fiber breaks is less than 2.0 pieces / mm, when the number of fiber breaks increases due to a decrease in the interfacial adhesion between the carbon fiber and the matrix resin, the fibers cannot bear stress and the OHT is lowered. Stress is transmitted to the fiber between the break points from the break point where the stress load is 0 by interfacial shear with the resin. Especially when the number of breaks increases in this way, the fiber stress is difficult to increase, so the number of fiber breaks Becomes saturated. Therefore, it should be mentioned here that the actual fiber stress is smaller than the single fiber apparent stress. If the single fiber elastic modulus of the carbon fiber is low, the single fiber composite may break before loading the single fiber apparent stress to 15.3 GPa, but if the fiber breakage is saturated, that breakage is substituted. can do. Here, saturation means that the number of fiber breaks is Δ0.2 / mm when the change in strain of the single fiber composite is Δ1%.

  Further, in the present invention, the carbon fiber preferably has a fiber breakage number of 0.8 pieces / mm or less when the single fiber apparent stress by the fragmentation method of the single fiber composite is 10.0 GPa, more preferably 0.8. 7 pieces / mm or less, more preferably 0.5 pieces / mm or less. When the number of fiber breaks exceeds 0.8 / mm, OHT is lowered due to insufficient single fiber strength of the carbon fiber. When the number of fiber breaks is 0.8 pieces / mm or less, since the single fiber strength of the carbon fiber is high, fiber breakage can be suppressed in a wide range around the carbon fiber composite material circular hole at the time of the OHT test, OHT increases.

  In the present invention, the strand strength of the carbon fiber is preferably 7.0 GPa or more, more preferably 7.2 GPa or more, and further preferably 7.5 GPa or more. Moreover, it is preferable that the strand elastic modulus of carbon fiber is 320 GPa or more, More preferably, it is 340 GPa or more, More preferably, it is 350 GPa or more. When the carbon fiber strain in the fragmentation method is converted into fiber stress, the strand elastic modulus is necessary. Essentially, it is important that the fiber breakage is small even at high fiber stress. Therefore, when the strand elastic modulus is less than 320 GPa OHT may decrease. In the present invention, the strand tensile strength and elastic modulus of carbon fibers can be determined according to the following procedure in accordance with the resin impregnated strand test method of JIS-R-7608 (2004). That is, as a resin prescription, “Celoxide (registered trademark)” 2021P (manufactured by Daicel Chemical Industries) / 3 boron fluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / Acetone = 100/3/4 (parts by mass) As a curing condition, normal pressure, 130 ° C., and 30 minutes are used. Ten strands of the carbon fiber bundle are measured, and the average value is defined as the strand tensile strength and the strand elastic modulus. The strain range when measuring the strand elastic modulus is 0.45 to 0.85%.

  In this invention, it is preferable that the single fiber elastic modulus of carbon fiber is 320 GPa, More preferably, it is 340 GPa or more, More preferably, it is 350 GPa or more. In the fragmentation method, in order to evaluate the single fiber strength, it is essential that the fiber breakage is small even at a high fiber stress rather than the fiber breakage is small at a high single fiber composite strain. Convert to fiber stress. In order to convert the carbon fiber strain into the fiber stress in the fragmentation method, the strand elastic modulus or single fiber elastic modulus of the carbon fiber is necessary. Here, the single fiber elastic modulus is used. The higher the single fiber elastic modulus, the higher the fiber stress is applied even if the composite fiber single fiber composite strain is low, and the OHT decreases when the single fiber elastic modulus is less than 320 GPa due to the relationship with the matrix resin properties. Sometimes. In this invention, the single fiber elastic modulus of carbon fiber can be calculated | required based on JIS-R-7606 (2000). That is, in the single fiber tensile test, the slip occurs between the carbon fiber and the adhesive of the chuck part in the chuck, so it is not possible to accurately measure the single fiber elastic modulus. However, the longer the gauge length, the smaller the error. Therefore, the gauge length is 50 mm. The strain range when measuring the single fiber modulus is the entire range from 0% strain to breakage.

  In the present invention, the total fineness of the carbon fibers is preferably 400 to 3000 tex. The number of filaments of carbon fiber is preferably 10,000 to 30,000.

  The manufacturing method of the sizing agent application | coating carbon fiber of this invention is demonstrated.

  In the present invention, the polyacrylonitrile-based polymer used for producing the polyacrylonitrile-based precursor fiber preferably has an intrinsic viscosity of 2.5 to 4.0, and more preferably 3.0 to 4.0. In the case of a low molecular weight polyacrylonitrile-based polymer whose intrinsic viscosity is less than 2.5, the molecular arrangement of the polyacrylonitrile-based precursor fiber is lowered, and the strength characteristics of the resulting carbon fiber may be reduced. If it exceeds 4.0, the alignment state of the molecules may be deteriorated due to a decrease in drawability of the yarn, and the structural characteristics of the precursor fiber may increase, resulting in a decrease in strength characteristics of the carbon fiber obtained. The intrinsic viscosity of the polyacrylonitrile-based polymer can be controlled by changing the amounts of monomers, initiators, chain transfer agents and the like during polymerization. Specifically, the intrinsic viscosity can be increased by increasing the monomer concentration at the start of polymerization, decreasing the initiator concentration, and decreasing the chain transfer agent concentration. In the present invention, the polyacrylonitrile-based polymer means that at least acrylonitrile is the main constituent of the polymer skeleton, and the main constituent usually occupies 85 to 100 mol% of the polymer skeleton. Say.

  In the present invention, the polyacrylonitrile-based polymer suitably used in the production of the sizing agent-coated carbon fiber contains a copolymer component from the viewpoint of improving the yarn production and efficiently performing the flameproofing treatment. Generally, when the amount of the copolymer component is small, the flameproofing reaction becomes non-uniform, and when the amount of the copolymer component is large, the site itself may be thermally decomposed and recognized as a carbon fiber defect. A preferable amount of the copolymer component is 0.1 to 0.8% by mass. Preferred examples of the copolymer component include those having one or more carboxyl groups or amide groups from the above viewpoint. In order to prevent a decrease in heat resistance, it is preferable to use a small amount of a monomer having a high flame resistance promoting effect, and it is preferable to use a copolymer component having a carboxyl group rather than an amide group. Further, the number of amide groups and carboxyl groups contained is more preferably two or more than one, and from this viewpoint, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid Maleic acid and mesaconic acid are preferred, itaconic acid, maleic acid and mesaconic acid are more preferred, and itaconic acid is most preferred.

  As a polymerization method for producing the polyacrylonitrile polymer suitably used in the present invention, a known polymerization method can be selected. The spinning solution suitably used in the production of the sizing agent-coated carbon fiber of the present invention is obtained by dissolving the polyacrylonitrile polymer in a solvent in which a polyacrylonitrile polymer such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide is soluble. It is a thing. The polyacrylonitrile polymer used in the present invention is preferably a spinning solution having a concentration of 10 to 18% by mass. If the concentration of the spinning solution is less than 10% by mass, voids are formed in the carbon fiber and the strength tends to decrease in a high strength region. If the concentration of the spinning solution exceeds 18% by mass, spinning is performed. The weight average molecular weight of the polymer may have to be lowered due to its properties.

  The method for producing a polyacrylonitrile-based precursor fiber suitably used in the production of the sizing agent-coated carbon fiber of the present invention includes a spinning process in which spinning is performed by discharging from a spinneret by a dry and wet spinning method, and the fiber obtained in the spinning process. A water-washing process for washing in a water bath, a water-bath drawing process for drawing the fibers obtained in the water-washing process in a water bath, and a drying heat-treatment process for drying and heat-treating the fibers obtained in the water-bath drawing process. Accordingly, the process includes a steam stretching step of steam stretching the fiber obtained in the drying heat treatment step.

  In the present invention, the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide used as a solvent for the spinning solution and a so-called coagulation promoting component. As the coagulation accelerating component, a component that does not dissolve the polyacrylonitrile polymer and is compatible with the solvent used in the spinning solution can be used. Specifically, it is preferable to use water as a coagulation promoting component.

  The water bath temperature in the water washing step is preferably 20 ° C. to 100 ° C. using a water bath having a plurality of stages. Moreover, it is preferable that the draw ratio in a water bath extending process is 1-5 times, More preferably, it is 2-4 times. After the water bath stretching step, it is preferable to apply an oil agent made of silicone or the like to the yarn for the purpose of preventing adhesion between single fibers. As such a silicone oil agent, it is preferable to use a modified silicone, and it is preferable to use one containing an amino-modified silicone having high heat resistance.

  After the water washing step, the water bath stretching step, the oil agent applying step, and the drying heat treatment step performed by a known method, by performing steam stretching as necessary, the poly used suitably in the production of sizing agent-coated carbon fibers. Acrylonitrile-based precursor fibers are obtained. In the present invention, the steam stretching is preferably performed at least three times or more in the pressurized steam.

  In the present invention, the polyacrylonitrile-based precursor fiber is preferably adjusted to have a fineness of 0.60 dtex or less, more preferably 0.41 dex or less, and still more preferably 0.26 dtex or less. Such fineness can be controlled by adjusting the discharge amount of the spinning solution and the spinning speed.

  In the method for suitably producing the sizing agent-coated carbon fiber of the present invention, the above-mentioned polyacrylonitrile-based precursor fiber is flame-resistant, pre-carbonized, and carbonized to obtain a carbon fiber.

  In the present invention, the flame resistance of the polyacrylonitrile-based precursor fiber is preferably performed at as high a temperature as possible without causing a runaway reaction. Specifically, it is preferably performed in air at 200 to 300 ° C. In the present invention, the flameproofing treatment time can be suitably selected within a range of 10 to 100 minutes, but for the purpose of improving the mechanical properties of the obtained carbon fiber, the specific gravity of the obtained flameproof fiber. Is preferably set in a range of 1.3 to 1.4.

Subsequent to the flame resistance, preliminary carbonization is performed. In the preliminary carbonization step, it is preferable that the obtained flame-resistant fiber is heat-treated in an inert atmosphere at a maximum temperature of 500 to 1200 ° C. until the specific gravity is 1.5 to 1.8 g / cm ³ .

Subsequent to the preliminary carbonization, carbonization is performed. In the present invention, in the carbonization step, the pre-carbonized fiber bundle obtained is carbonized in an inert atmosphere at a maximum temperature of 1200 to 2000 ° C. so that the carbonization tension satisfies the formula (1). And it is preferable that it is a manufacturing method of the carbon fiber whose average tearable distance of a pre-carbonized fiber bundle is 450-750 mm.
4.9 ≦ carbonization tension (mN / dtex) ≦ −0.0225 × (average tearable distance of pre-carbonized fiber bundle (mm)) + 23.5 (1).

  The temperature of the carbonization step is preferably higher from the viewpoint of increasing the strand elastic modulus of the carbon fiber to be obtained, but if it is too high, the strength of the high strength region may decrease, and it is set in consideration of both. Is good. A more preferable temperature range is 1200 to 1800 ° C, and a more preferable temperature range is 1200 to 1600 ° C.

  The tension (carbonization tension) in the carbonization step is represented by a value obtained by dividing the tension (mN) measured on the outlet side of the carbonization furnace by the fineness (dtex) of the polyacrylonitrile-based precursor fiber when it is completely dried. When the tension is lower than 4.9 mN / dtex, the crystallite orientation of the carbon fiber cannot be increased, and a high strand elastic modulus is not exhibited. The tension is preferably higher from the viewpoint of increasing the strand elastic modulus of the carbon fiber to be obtained, but if it is too high, the process passability and the quality may be lowered, and the range satisfying the formula (1) is satisfied. It is preferable to set. The meaning of the first-order coefficient −0.0225 on the right-hand side of equation (1) is the tension gradient that can be set as the average tearable distance increases, and the constant term 23.5 represents the average tearable distance to the limit. This tension can be set when the length is shortened.

  The tearable distance of the pre-carbonized fiber bundle in the carbonization step is an index that represents the entangled state of the fiber bundle, and is determined as follows. First, the fiber bundle is cut to a length of 1160 mm, and one end thereof is fixed on a horizontal base so as not to move with an adhesive tape (this point is referred to as a fixing point A). One end of the fiber bundle that is not fixed is divided into two with fingers, and one of the ends is tensioned and fixed on the table so as not to move with an adhesive tape (this point is referred to as a fixing point B). Move the other of the two halves along the table so that the fixed point A becomes a fulcrum and does not come loose, rest at a position where the linear distance from the fixed point B is 500 mm, and fix it on the table so that it does not move with adhesive tape. (This point is called a fixed point C). The area surrounded by the fixed points A, B, and C is visually observed, the entanglement point farthest from the fixed point A is found, and the distance projected on the straight line connecting the fixed point A and the fixed point B is 1 mm at the minimum scale. Read with the ruler of, and make the tearable distance. The arithmetic average value of 30 measurements of the above operation is defined as the average tearable distance. A method of measuring the tearable distance is shown in FIG. In this measurement method, the entanglement point farthest from the fixed point A is the point where the linear distance from the fixed point A is the longest and three or more single fibers having no slack are entangled.

  Conventionally, the hook drop method has been generally used as a method for evaluating the entangled state. As defined in JIS L1013 (2010), the degree of entanglement of the fiber bundle by the hook drop method is fixed to the upper part of the drooping device, the weight is suspended at the lower end of the fiber bundle, and the sample is placed vertically. After that, a hook with a weight of 10 g with a smooth surface of 0.6 mm in diameter is inserted so as to divide the fiber bundle into two parts 1 cm below the upper fixed end of the sample, and the descent distance is measured. .

  In the present invention, as the degree of entanglement of the pre-carbonized fiber bundle in the carbonization process, not by the conventional hook drop method, but by making the average tearable distance within a specific range, while avoiding the strength reduction of the carbon fiber high strength region High stretch tension in the carbonization process can be expressed. In order to apply a high drawing tension in the carbonization process, it is necessary to create a fiber bundle state in which the stress transmission ability between single fibers is high. For that purpose, it is important to form a fine entanglement network between single fibers. The conventional hook drop method is an evaluation at a “point” using a hook, whereas the tearable distance is an evaluation at a “surface” that looks at the entire bundle. Due to this difference, in the carbonization process, It is considered that a state for expressing a high stretching tension can be appropriately defined.

  In the present invention, the shorter the tearable distance of the pre-carbonized fiber bundle in the carbonization process, the higher the degree of entanglement, the higher the stress transmission ability between single fibers, and the higher the stretching tension in the carbonization process. When the distance is less than 450 mm, the strength of the carbon fiber high-strength region is lowered and OHT tends to be lowered. If the entanglement treatment with a tearable distance exceeding 750 mm is not performed or weak, the other single fiber not ruptured bears the stress of the single fiber that breaks with a certain probability that is a carbonization process, The structural variation between the single fibers and the accompanying strength variation are induced, and the single fiber strength distribution in the short length region of the carbon fiber cannot be controlled, resulting in a reduction in OHT.

  As the means for achieving the average tearable distance of the preliminary carbonized fiber, any method can be adopted as long as the numerical range described above can be achieved. In the present invention, as a method for controlling the average tearable distance, The entanglement process by the fluid to the fiber bundle is preferably used. Among them, it is preferable to perform the fluid entanglement process in any of the manufacturing process and the flameproofing process of the polyacrylonitrile-based precursor fiber, that is, in a place where a fiber bundle having a fiber elongation of 5% or more is processed. In other steps, OHT may be lowered.

  As the fluid used for the fluid entanglement treatment, both gas and liquid can be used, but air or nitrogen is preferable because it is inexpensive. In the fluid entanglement process, the fluid is preferably sprayed onto the fiber bundle using a nozzle, and the shape of the nozzle that sprays the fluid is not particularly limited, but it is preferable to use one having 2 to 8 ejection holes. The arrangement of the ejection ports is not particularly limited, but an even number of ejection holes are arranged so as to surround the fiber bundle so that the angle formed by the fiber bundle longitudinal direction and the fluid blowing direction is in the range of 88 ° to 90 °. It is preferable to arrange the jet holes at positions facing each other so as to form a pair of two holes. Other conditions such as fiber bundle tension and fluid discharge pressure during the fluid entanglement process may be examined so as to adjust the tearable distance appropriately.

  The carbon fiber of the present invention is a fiber bundle in which single fibers are bundled, and the number of single fibers is preferably 3000 to 48000, more preferably 10,000 to 20000. In the present invention, the carbon fiber is preferably substantially untwisted. As used herein, “substantially untwisted” means that there is no turn or no more than 0.5 turns per m of carbon fiber even if there is a twist. When the carbon fiber is untwisted, when used as a reinforcing fiber for a carbon fiber reinforced composite material, the carbon fiber is easily spread and the physical properties of the carbon fiber reinforced composite material are often excellent.

  The carbon fiber of the present invention preferably has an average tearable distance of 300 to 710 mm. When the distance is less than 300 mm, the matrix resin is less likely to be impregnated between the single fibers, and may reduce OHT. When the distance is 710 mm or more, thread cracking during widening is induced in prepreg processing, It may not be suitable for producing a thin prepreg with a low basis weight. Furthermore, when a carbon fiber reinforced composite material is used, stress transmission in the carbon fiber reinforced composite material also becomes non-uniform, which may reduce OHT. The average tearable distance of the carbon fiber is more preferably 300 to 650 mm.

  The single fiber diameter of the carbon fiber bundle is preferably 4.5 μm or less, more preferably 3.0 μm or less. When the single fiber diameter is 4.5 μm or less, the probability of existence of surface defects can be reduced, so that the single fiber strength is increased, and the adhesion with the matrix resin is improved by increasing the surface area ratio of the carbon fibers, The stress transmission in the carbon fiber reinforced composite material is also uniform, resulting in a higher OHT. However, the larger the single fiber diameter, the more easily the matrix resin is impregnated between the single fibers, and as a result, the OHT can be increased. Therefore, the single fiber diameter is preferably 2.0 μm or more. As the means for achieving the single fiber diameter of the carbon fiber bundle, any method can be adopted as long as the above numerical range can be achieved. In the present invention, the single fiber diameter of the carbon fiber bundle is as described above. It can be controlled by adjusting the fineness of the polyacrylonitrile precursor fiber.

  The obtained carbon fiber is usually subjected to an oxidation treatment to introduce an oxygen-containing functional group in order to improve adhesion with the matrix resin. As the oxidation treatment method, vapor phase oxidation, liquid phase oxidation, and liquid phase electrolytic oxidation are used. From the viewpoint of high productivity and uniform treatment, liquid phase electrolytic oxidation is preferably used.

  In the present invention, examples of the electrolytic solution used in the liquid phase electrolytic oxidation include an acidic electrolytic solution and an alkaline electrolytic solution. From the viewpoint of adhesion, a liquid phase electrolytic oxidation is performed in an alkaline electrolytic solution, and then a sizing agent is applied. Is more preferable.

  Examples of the acidic electrolyte 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. Of these, sulfuric acid and nitric acid exhibiting strong acidity are preferably used.

  Specific examples of the alkaline electrolyte 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 bicarbonates such as sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, calcium bicarbonate, barium bicarbonate and ammonium bicarbonate, ammonia, tetraalkylammonium hydroxide And an aqueous solution of hydrazine. Among these, from the viewpoint of not containing an alkali metal that causes curing inhibition of the matrix resin, an aqueous solution of ammonium carbonate and ammonium hydrogen carbonate or an aqueous solution of tetraalkylammonium hydroxide exhibiting strong alkalinity is preferably used.

  The concentration of the electrolytic solution used in the present invention is preferably in the range of 0.01 to 5 mol / liter, more preferably in the range of 0.1 to 1 mol / liter. When the concentration of the electrolytic solution is 0.01 mol / liter or more, the electrolytic treatment voltage is lowered, which is advantageous for the operating cost. On the other hand, when the concentration of the electrolytic solution is 5 mol / liter or less, it is advantageous from the viewpoint of safety.

  The temperature of the electrolytic solution used in the present invention is preferably in the range of 10 to 100 ° C, more preferably in the range of 10 to 40 ° C. When the temperature of the electrolytic solution is 10 ° C. or higher, the efficiency of the electrolytic treatment is improved, which is advantageous for the operating cost. On the other hand, when the temperature of the electrolytic solution is 100 ° C. or lower, it is advantageous from the viewpoint of safety.

  In the present invention, the amount of electricity in the liquid phase electrolytic oxidation is preferably optimized in accordance with the carbonization degree of the carbon fiber, and a larger amount of electricity is required when processing the carbon fiber having a high elastic modulus.

In the present invention, the current density in the liquid phase electrolytic oxidation is preferably in the range of 1.5 to 1000 amperes / m ² per 1 m ² of the surface area of the carbon fiber in the electrolytic treatment solution, more preferably 3 to 500 amperes. / M ^{2 in} the range. When the current density is 1.5 amperes / m ² or more, the efficiency of the electrolytic treatment is improved, which is advantageous for the operating cost. On the other hand, when the current density is 1000 amperes / m ² or less, it is advantageous from the viewpoint of safety.

  In the present invention, it is preferable to wash and dry the carbon fiber after the electrolytic treatment. As a cleaning method, for example, a dip method and a spray method can be used. Especially, it is preferable to use a dip method from a viewpoint that washing | cleaning is easy, Furthermore, it is a preferable aspect to use a dip method, vibrating a carbon fiber with an ultrasonic wave. Also, if the drying temperature is too high, the functional groups present on the outermost surface of the carbon fiber are likely to disappear due to thermal decomposition, so it is desirable to dry at the lowest possible temperature. Specifically, the drying temperature is preferably 250 ° C. or lower. More preferably, drying is performed at 210 ° C. or lower.

In the present invention, by applying the electrolytic treatment or a known sizing agent, the number of fiber breaks may be controlled when the single fiber apparent stress is 15.3 GPa by the fragmentation method of the single fiber composite. Since an epoxy resin is often used, a sizing agent-coated carbon fiber obtained by applying a sizing agent containing an epoxy compound to the carbon fiber of the present invention is preferable. More preferably, the sizing agent-coated carbon fiber is a sizing agent-coated carbon fiber that is a carbon fiber coated with a sizing agent containing at least the aliphatic epoxy compound (A) and the aromatic epoxy compound (B). More preferably, the sizing agent surface has a C _1s inner-shell spectrum (a) CHx, C—C, and C = C binding energy attributed to C = C (measured by X-ray photoelectron spectroscopy at a photoelectron escape angle of 15 °). The ratio (a) / (b) between the height (cps) of the component of 284.6 eV) and the height (cps) of the component (286.1 eV) attributed to C—O is 0. A sizing agent-coated carbon fiber characterized in that it is 50 to 0.90.

  In this invention, it is preferable to use together an aliphatic epoxy compound (A) and an aromatic epoxy compound (B).

  According to the knowledge of the present inventors, such a range is excellent in the interfacial adhesion between the carbon fiber and the matrix resin, and also when the sizing agent-coated carbon fiber is used for the prepreg when the prepreg is stored for a long period of time. The change over time is small, and it is suitable for sizing agent-coated carbon fibers for carbon fiber reinforced composite materials.

  Carbon fiber consisting of only aromatic epoxy compound (B) and coated with sizing agent that does not contain aliphatic epoxy compound (A) as epoxy compound has low reactivity between sizing agent and matrix resin, and preserves prepreg for a long time There is an advantage that the change in physical properties is small. There is also an advantage that a rigid interface layer can be formed. However, it has been confirmed that the aromatic epoxy compound (B) is slightly inferior in adhesion between the carbon fiber and the matrix resin as compared with the aliphatic epoxy compound (A) due to the rigidity of the compound. .

  In addition, it has been confirmed that carbon fibers coated with a sizing agent composed only of an aliphatic epoxy compound (A) as an epoxy compound have high adhesiveness with a matrix resin. Although the mechanism is not certain, the aliphatic epoxy compound (A) is derived from a flexible skeleton and a structure having a high degree of freedom, and the functional group of the carboxyl group and hydroxyl group on the surface of the carbon fiber and the aliphatic epoxy compound are strongly interacting with each other. It is considered possible to form an action. However, the aliphatic epoxy compound (A) exhibits high adhesiveness due to the interaction with the carbon fiber surface, while having high reactivity with the compound having a functional group represented by the curing agent in the matrix resin, When stored for a long time in this state, it has been confirmed that the structure of the interface layer changes due to the interaction between the matrix resin and the sizing agent, and the physical properties of the carbon fiber reinforced composite material obtained from the prepreg deteriorate.

  In the present invention, when the aliphatic epoxy compound (A) and the aromatic epoxy compound (B) are mixed, the aliphatic epoxy compound (A) having a higher polarity is unevenly distributed on the carbon fiber side, and is opposite to the carbon fiber. There is a phenomenon that the aromatic epoxy compound (B) having a low polarity tends to be unevenly distributed in the outermost layer of the sizing layer. As a result of the gradient structure of the sizing layer, the aliphatic epoxy compound (A) has a strong interaction with the carbon fiber in the vicinity of the carbon fiber, thereby enhancing the adhesion between the carbon fiber and the matrix resin. In addition, the aromatic epoxy compound (B) present in a large amount in the outer layer plays a role of blocking the aliphatic epoxy compound (A) from the matrix resin when the sizing agent-coated carbon fiber is used as a prepreg. As a result, the reaction between the aliphatic epoxy compound (A) and the highly reactive component in the matrix resin is suppressed, so that stability during long-term storage is exhibited. When the aliphatic epoxy compound (A) is almost completely covered with the aromatic epoxy compound (B), the interaction between the sizing agent and the matrix resin is reduced and the adhesiveness is lowered. The ratio of the aliphatic epoxy compound (A) to the aromatic epoxy compound (B) is important.

  In this invention, it is preferable that the epoxy equivalent of the sizing agent apply | coated to carbon fiber is 350-550 g / mol. It is preferable for it to be 550 g / mol or less because the adhesion between the carbon fiber coated with the sizing agent and the matrix resin is improved. Moreover, since it is 350 g / mol or more, when this sizing agent application | coating carbon fiber is used for a prepreg, since the reaction with the resin component and sizing agent which are used for a prepreg can be suppressed, prepreg is stored for a long time This is also preferable because the physical properties of the obtained carbon fiber reinforced composite material are improved. The epoxy equivalent of the carbon fiber coated with the sizing agent in the present invention is that the sizing agent-coated fiber is immersed in a solvent typified by N, N-dimethylformamide, and is eluted from the fiber by ultrasonic cleaning. It can be obtained by acid-base titration by opening the epoxy group with hydrochloric acid. Epoxy equivalent is preferably 360 g / mol or more, and more preferably 380 g / mol or more. Moreover, 530 g / mol or less is preferable and 500 g / mol or less is more preferable. In addition, the epoxy equivalent of the sizing agent applied to the carbon fiber can be controlled by the epoxy equivalent of the sizing agent used for application and the heat history in drying after application.

  In this invention, it is preferable that the aliphatic epoxy compound (A) eluted from a sizing agent application | coating fiber is 0.3 mass part or less with respect to 100 mass parts of sizing agent application | coating carbon fibers. By setting the elution amount to 0.3 parts by mass or less, when the sizing agent-coated carbon fiber of the present invention is used as a prepreg together with a thermosetting resin, the reaction between the resin component of the thermosetting resin and the sizing agent is performed. Since it can suppress, the physical property of the carbon fiber reinforced composite material obtained also when the prepreg is stored for a long period of time is preferable. 0.1 mass part or less is more preferable, and 0.05 mass part or less is still more preferable. In the present invention, the elution amount of the aliphatic epoxy compound (A) eluted from the sizing agent-coated fiber is determined by the following procedure.

  After immersing 0.1g of carbon fiber coated with sizing agent in 10ml of a mixture of acetonitrile and chloroform at a volume ratio of 9: 1, ultrasonic cleaning is performed for 20 minutes to elute the sizing agent from the fiber, and then 5ml of the sample solution. The sample is collected, the solvent is distilled off in nitrogen, and the above-mentioned mixed solution of acetonitrile and chloroform is added to a constant volume until the volume becomes 0.2 ml, and a 25-fold concentrated solution is prepared. The solution is separated from the other peaks of the aliphatic epoxy compound (A) by liquid chromatography using a mixture of water and acetonitrile as a mobile phase and detected by an evaporative light scattering detector (ELSD). . Then, by creating a calibration curve using the peak area of the solution of the aliphatic epoxy compound (A) whose concentration is known in advance, and quantifying the concentration of the aliphatic epoxy compound (A) based on that, The elution amount of the aliphatic epoxy compound (A) with respect to 100 parts by mass of the sizing agent-coated carbon fiber is determined.

The present invention relates to (a) CHx, C-C, C = C binding energy (284.C) of the C _1s core spectrum measured on the sizing agent surface by X-ray photoelectron spectroscopy at a photoelectron escape angle of 15 °. The ratio (a) / (b) between the height (cps) of the component of 6 eV) and the height (cps) of the component of (b) binding energy (286.1 eV) attributed to C—O is 0.50 0.90. Preferably, it is 0.55 or more, more preferably 0.57 or more. Moreover, Preferably it is 0.80 or less, More preferably, it is 0.74 or less. That (a) / (b) is large indicates that there are many compounds derived from aromatics on the surface and few compounds derived from aliphatic esters. The present invention has been made by finding that when this (a) / (b) falls within a specific range, it has excellent adhesion to the matrix resin and has little deterioration in physical properties when stored for a long time in the state of a prepreg. It is a thing.

  X-ray photoelectron spectroscopy measurement method is an analysis method that irradiates a sample carbon fiber with X-rays in an ultra-high vacuum and measures the kinetic energy of photoelectrons emitted from the surface of the carbon fiber with an apparatus called an energy analyzer. That is. By examining the kinetic energy of the photoelectrons emitted from the carbon fiber surface of the sample, the binding energy converted from the energy value of the X-rays incident on the carbon fiber of the sample is uniquely determined. From the binding energy and the photoelectron intensity The type and concentration of elements present on the outermost surface (˜nm) of the sample and the chemical state thereof can be analyzed.

In the present invention, the peak ratio of (a) and (b) on the sizing agent surface of the sizing agent-coated fiber is determined by X-ray photoelectron spectroscopy according to the following procedure. Cut the sizing agent-coated carbon fiber to 20 mm, spread and arrange it on a copper sample support, and then use AlKα _1,2 as the X-ray source and keep the sample chamber at 1 × 10 ⁻⁸ Torr for measurement. Is called. As correction of the peak accompanying charging during measurement, first, the binding energy value of the main peak of C _1s is adjusted to 286.1 eV. At this time, the peak area of C _1s is obtained by drawing a straight baseline in the range of 282 to 296 eV. Further, a linear base line of 282 to 296 eV obtained by calculating the area at the C _1s peak is defined as the origin (zero point) of the photoelectron intensity, and (b) the peak of the binding energy 286.1 eV attributed to the CO component is obtained. The height (cps: photoelectron intensity per unit time) and the height (cps) of the component having a binding energy of 284.6 eV attributed to (a) CHx, C—C, C = C are obtained, and (a) / ( b) is calculated.

(A) Component of binding energy (284.6 eV) belonging to (a) CHx, C—C, C = C of the C _1s inner-shell spectrum measured by X-ray photoelectron spectroscopy with a photoelectron escape angle of 15 ° in the inner layer of sizing The ratio (a) / (b) of the height (cps) of the component (b) and the height (cps) of the component of the binding energy (286.1 eV) attributed to C—O is 0.45 to 1.0. Preferably there is. The inner layer of the sizing agent was obtained by ultrasonically washing the sizing-coated carbon fiber with an acetone solvent for 1 to 10 minutes and then washing away with distilled water, and the remaining sizing agent adhering to the carbon fiber was 0.10 ± 0.05% by mass After controlling to a range, a measurement is performed by the method mentioned above.

  In the present invention, the sizing agent contains at least an aliphatic epoxy compound (A) and an aromatic epoxy compound (B). It is preferable that 35-65 mass% of aliphatic epoxy compounds (A) are contained with respect to the applied sizing agent. Adhesiveness improves by being applied 35 mass% or more. Moreover, by being 65 mass% or less, components other than aliphatic epoxy can be used as the sizing agent, and the prepreg produced using the obtained sizing agent-coated fiber is also obtained when stored for a long time. The physical properties of the fiber reinforced composite material are improved. 38 mass% or more is more preferable, and 40 mass% or more is further more preferable. Moreover, 60 mass% or less is more preferable, and 55 mass% or more is further more preferable.

  It is preferable that 35-60 mass% of aromatic epoxy compounds (B) are contained. By containing 35% by mass or more of the aromatic epoxy compound (B), the composition of the aromatic compound in the outer layer of the sizing agent can be maintained high, so that the aliphatic epoxy compound and matrix that are highly reactive during long-term storage of the prepreg Reduction in physical properties due to reaction with the reactive compound in the resin is suppressed. The amount of 60% by mass or less is preferable because the above-described inclined structure in the sizing agent can be expressed and the adhesiveness can be maintained. 37 mass% or more is more preferable, and 39 mass% or more is further more preferable. Moreover, 55 mass% or less is more preferable, and 45 mass% or more is further more preferable.

  As an epoxy component in the sizing agent in the present invention, an aliphatic epoxy compound (A) and an aromatic epoxy compound (B) are included. The mass ratio (A) / (B) of the aliphatic epoxy compound (A) and the aromatic epoxy compound (B) is preferably 52/48 to 80/20. When (A) / (B) is 52/48 or more, the ratio of the aliphatic epoxy compound (A) present on the carbon fiber surface is increased, and the adhesion between the carbon fiber and the matrix resin is improved. As a result, the composite properties such as tensile strength of the obtained carbon fiber reinforced resin are preferably increased. Moreover, 80/20 or less is preferable because the amount of the highly reactive aliphatic epoxy compound present on the surface of the carbon fiber is reduced and the reactivity with the matrix resin can be suppressed. The mass ratio of (A) / (B) is more preferably 55/45 or more, and further preferably 60/40 or more. Moreover, 75/35 or less is more preferable, and 73/37 or less is further more preferable.

  In this invention, it is preferable that the adhesion amount of a sizing agent is the range of 0.1-3.0 mass parts with respect to 100 mass parts of carbon fibers, More preferably, it is 0.2-3.0 mass parts. It is a range. When the amount of the sizing agent is within such a range, high OHT can be expressed.

  The method for measuring the amount of sizing agent attached is that 2 ± 0.5g of sizing coated carbon fiber is sampled and the amount of mass change before and after the heat treatment when heat treatment is performed at 450 ° C. for 15 minutes in a nitrogen atmosphere. It is the mass% of the value divided by the previous mass.

  In this invention, it is preferable that the adhesion amount of an aliphatic epoxy compound (A) is the range of 0.05-2.0 mass parts with respect to 100 mass parts of carbon fibers, More preferably, it is 0.2-2. The range is 0.0 parts by mass. More preferably, it is 0.3-1.0 mass part. It is preferable that the adhesion amount of the aliphatic epoxy compound (A) is 0.05 parts by mass or more because the adhesion between the sizing agent-coated carbon fiber and the matrix resin is improved by the aliphatic epoxy compound (A) on the carbon fiber surface.

  The aliphatic epoxy compound (A) in the present invention is an epoxy compound containing no aromatic ring. Since it has a flexible skeleton with a high degree of freedom, it can have a strong interaction with carbon fibers. As a result, the adhesiveness of the sizing agent-coated carbon fiber is improved, which is preferable.

  In the present invention, the aliphatic epoxy compound (A) has one or more epoxy groups in the molecule. As a result, a strong bond between the carbon fiber and the epoxy group in the sizing agent can be formed. The number of epoxy groups in the molecule is preferably 2 or more, and more preferably 3 or more. In the case of an epoxy compound having two or more epoxy groups in the molecule, even if one epoxy group forms a covalent bond with the oxygen-containing functional group on the surface of the carbon fiber, the remaining epoxy group is covalently bonded to the matrix resin. Alternatively, it is preferable because a hydrogen bond can be formed and adhesion can be further improved. There is no particular upper limit on the number of epoxy groups, but 10 is sufficient from the viewpoint of adhesion.

  In the present invention, the aliphatic epoxy compound (A) is preferably an epoxy compound having 3 or more of 2 or more types of functional groups, and more preferably an epoxy compound having 4 or more of 2 or more types of functional groups. . The functional group possessed by the epoxy compound is preferably selected from a hydroxyl group, an amide group, an imide group, a urethane group, a urea group, a sulfonyl group, or a sulfo group in addition to the epoxy group. In the case of an epoxy compound having three or more epoxy groups or other functional groups in the molecule, even if one epoxy group forms a covalent bond with an oxygen-containing functional group on the carbon fiber surface, the remaining two or more The epoxy group or other functional group can form a covalent bond or a hydrogen bond with the matrix resin, and the adhesion is further improved. There is no particular upper limit on the number of functional groups containing an epoxy group, but 10 is sufficient from the viewpoint of adhesiveness.

  In this invention, it is preferable that the epoxy equivalent of an aliphatic epoxy compound (A) is less than 360 g / mol, More preferably, it is less than 270 g / mol, More preferably, it is less than 180 g / mol. When the epoxy equivalent is less than 360 g / mol, an interaction with the carbon fiber is formed at a high density, and the adhesion between the carbon fiber and the matrix resin is further improved. There is no particular lower limit of the epoxy equivalent, but 90 g / mol or more is sufficient from the viewpoint of adhesiveness.

  In the present invention, specific examples of the aliphatic epoxy compound (A) include, for example, a glycidyl ether type epoxy compound derived from a polyol, a glycidyl amine type epoxy compound derived from an amine having a plurality of active hydrogens, and a polycarboxylic acid. Examples thereof include an induced glycidyl ester type epoxy compound and an epoxy compound obtained by oxidizing a compound having a plurality of double bonds in the molecule.

  Examples of the glycidyl ether type epoxy compound include a glycidyl ether type epoxy compound obtained by a reaction with epichlorohydrin. Further, as glycidyl ether type epoxy compounds, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, trimethylene glycol, 1,2 -Butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, polybutylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,4 -Cyclohexanedimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, glycerol, diglycerol, polyglycerol, trimethylolpropane, pen Erythritol, sorbitol, and the arabitol, glycidyl ether type epoxy compound obtained by reaction of epichlorohydrin are also exemplified. Examples of the glycidyl ether type epoxy compound include a glycidyl ether type epoxy compound having a dicyclopentadiene skeleton.

  Examples of the glycidylamine type epoxy compound include 1,3-bis (aminomethyl) cyclohexane.

  Examples of the glycidyl ester type epoxy compound include a glycidyl ester type epoxy compound obtained by reacting dimer acid with epichlorohydrin.

  Examples of the epoxy compound obtained by oxidizing a compound having a plurality of double bonds in the molecule include an epoxy compound having an epoxycyclohexane ring in the molecule. Furthermore, the epoxy compound includes epoxidized soybean oil.

  Examples of the aliphatic epoxy compound (A) used in the present invention include epoxy compounds such as triglycidyl isocyanurate in addition to these epoxy compounds.

  In the present invention, the aliphatic epoxy compound (A) is at least one selected from one or more epoxy groups and a hydroxyl group, amide group, imide group, urethane group, urea group, sulfonyl group, carboxyl group, ester group and sulfo group. It is preferable to have one or more functional groups. Specific examples of the epoxy compound include, for example, a compound having an epoxy group and a hydroxyl group, a compound having an epoxy group and an amide group, a compound having an epoxy group and an imide group, a compound having an epoxy group and a urethane group, and an epoxy group and a urea group. Compounds having an epoxy group and a sulfonyl group, and compounds having an epoxy group and a sulfo group.

  Examples of the compound having a hydroxyl group in addition to the epoxy group include sorbitol-type polyglycidyl ether and glycerol-type polyglycidyl ether. Specifically, “Denacol (registered trademark)” EX-611, EX-612, EX -614, EX-614B, EX-622, EX-512, EX-521, EX-421, EX-313, EX-314, and EX-321 (manufactured by Nagase ChemteX Corporation).

  Examples of the compound having an amide group in addition to the epoxy group include an amide-modified epoxy compound. The amide-modified epoxy can be obtained by reacting an epoxy group of an epoxy compound having two or more epoxy groups with a carboxyl group of an aliphatic dicarboxylic acid amide.

  Examples of the compound having a urethane group in addition to the epoxy group include a urethane-modified epoxy compound. Specifically, “Adeka Resin (registered trademark)” EPU-78-13S, EPU-6, EPU-11, EPU- 15, EPU-16A, EPU-16N, EPU-17T-6, EPU-1348, EPU-1395 (manufactured by ADEKA Corporation) and the like. Alternatively, by reacting the terminal hydroxyl group of the polyethylene oxide monoalkyl ether with a polyvalent isocyanate equivalent to the amount of the hydroxyl group, and then reacting the isocyanate residue of the obtained reaction product with the hydroxyl group in the polyvalent epoxy compound. Can be obtained. Here, examples of the polyvalent isocyanate used include hexamethylene diisocyanate, isophorone diisocyanate, and norbornane diisocyanate.

  Examples of the compound having a urea group in addition to the epoxy group include a urea-modified epoxy compound. A urea-modified epoxy can be obtained by reacting an epoxy group of an epoxy compound having two or more epoxy groups with a carboxyl group of an aliphatic dicarboxylic acid urea.

  The aliphatic epoxy compound (A) used in the present invention is ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetra from the viewpoint of high adhesiveness. Propylene glycol, polypropylene glycol, trimethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, polybutylene glycol, 1,5-pentanediol, neo Pentyl glycol, 1,6-hexanediol, glycerol, diglycerol, polyglycerol, trimethylolpropane, pentaerythritol, sorbitol, and arabitol , Glycidyl ether type epoxy compound obtained by reaction of epichlorohydrin is more preferable.

  Among the above, the aliphatic epoxy compound (A) in the present invention is preferably a polyether type polyepoxy compound and / or a polyol type polyepoxy compound having two or more epoxy groups in the molecule from the viewpoint of high adhesiveness.

  In addition, the aliphatic epoxy compound (A) is ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, trimethylene glycol, 1, 2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, polybutylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1, 4-cyclohexanedimethanol, glycerol, diglycerol, polyglycerol, trimethylolpropane, pentaerythritol, sorbitol, and arabitol, and epi More preferably glycidyl ether type epoxy compound obtained by reaction with Rorohidorin.

  In the present invention, the aliphatic epoxy compound is more preferably polyglycerol polyglycidyl ether.

  In the present invention, the aromatic epoxy compound (B) has one or more aromatic rings in the molecule. The aromatic ring may be an aromatic ring hydrocarbon composed only of carbon, or a heteroaromatic ring such as furan, thiophene, pyrrole or imidazole containing a heteroatom such as nitrogen or oxygen. The aromatic ring may be a polycyclic aromatic ring such as naphthalene or anthracene. In a fiber-reinforced composite material composed of sizing agent-coated carbon fibers and a matrix resin, a so-called interface layer in the vicinity of the carbon fibers may be affected by the carbon fibers or the sizing agent and have different characteristics from the matrix resin. When the epoxy compound has one or more aromatic rings, a rigid interface layer is formed, the stress transmission ability between the carbon fiber and the matrix resin is improved, and the mechanical properties such as 0 ° tensile strength of the fiber reinforced composite material are improved. improves. Further, the hydrophobicity is improved by the aromatic ring, so that the interaction with the carbon fiber is weaker than that of the aliphatic epoxy compound, and the aliphatic epoxy compound can be covered and exist in the outer layer of the sizing layer. Thus, when the sizing agent-coated carbon fiber is used for a prepreg, it is preferable because a change with time when stored for a long period of time can be suppressed. Having two or more aromatic rings is preferable because long-term stability due to the aromatic rings is improved. There is no particular upper limit on the number of aromatic rings, but 10 is sufficient from the viewpoint of suppressing the reaction with the mechanical properties and the matrix resin.

  In the present invention, the aromatic epoxy compound (B) has at least one kind in the molecule having one or more epoxy groups and one or more aromatic rings in the molecule. The functional group other than the epoxy group is preferably selected from a hydroxyl group, an amide group, an imide group, a urethane group, a urea group, a sulfonyl group, a carboxyl group, an ester group or a sulfo group, and two or more types are included in one molecule. Also good. In addition to the aromatic epoxy compound (B), an aromatic ester compound and an aromatic urethane compound are preferably used in order to improve the stability and high-order processability of the compound.

  In the present invention, the number of epoxy groups of the aromatic epoxy compound (B) is preferably 2 or more, and more preferably 3 or more. Moreover, it is preferable that it is 10 or less.

  In the present invention, the aromatic epoxy compound (B) is preferably an epoxy compound having 3 or more functional groups of 2 or more, more preferably an epoxy compound having 4 or more of 2 or more functional groups. . The functional group possessed by the epoxy compound is preferably selected from a hydroxyl group, an amide group, an imide group, a urethane group, a urea group, a sulfonyl group, or a sulfo group in addition to the epoxy group. In the case of an epoxy compound having three or more epoxy groups or other functional groups in the molecule, even if one epoxy group forms a covalent bond with an oxygen-containing functional group on the carbon fiber surface, the remaining two or more The epoxy group or other functional group can form a covalent bond or a hydrogen bond with the matrix resin, and the adhesion is further improved. There is no particular upper limit on the number of functional groups containing an epoxy group, but 10 is sufficient from the viewpoint of adhesiveness.

  In this invention, it is preferable that the epoxy equivalent of an aromatic epoxy compound (B) is less than 360 g / mol, More preferably, it is less than 270 g / mol, More preferably, it is less than 180 g / mol. When the epoxy equivalent is less than 360 g / mol, covalent bonds are formed at a high density, and the adhesion between the carbon fiber and the matrix resin is further improved. There is no particular lower limit of the epoxy equivalent, but 90 g / mol or more is sufficient from the viewpoint of adhesiveness.

  In the present invention, specific examples of the aromatic epoxy compound (B) include, for example, a glycidyl ether type epoxy compound derived from a polyol, a glycidyl amine type epoxy compound derived from an amine having multiple active hydrogens, and a polycarboxylic acid. Examples thereof include an induced glycidyl ester type epoxy compound and an epoxy compound obtained by oxidizing a compound having a plurality of double bonds in the molecule.

  Examples of the glycidyl ether type epoxy compound include bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetrabromobisphenol A, phenol novolac, cresol novolac, hydroquinone, resorcinol, 4,4′-dihydroxy-3,3 ′, 5. , 5′-tetramethylbiphenyl, 1,6-dihydroxynaphthalene, 9,9-bis (4-hydroxyphenyl) fluorene, tris (p-hydroxyphenyl) methane, and tetrakis (p-hydroxyphenyl) ethane. Examples of the glycidyl ether type epoxy include a compound and a glycidyl ether type epoxy compound having a biphenyl aralkyl skeleton.

  Examples of the glycidylamine type epoxy compound include N, N-diglycidylaniline, N, N-diglycidyl-o-toluidine, m-xylylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylmethane and 9,9. -Bis (4-aminophenyl) fluorene.

  Further, for example, as a glycidylamine type epoxy compound, both the hydroxyl group and amino group of aminophenols of m-aminophenol, p-aminophenol, and 4-amino-3-methylphenol are reacted with epichlorohydrin. And an epoxy compound obtained.

  Examples of the glycidyl ester type epoxy compound include glycidyl ester type epoxy compounds obtained by reacting phthalic acid, terephthalic acid, and hexahydrophthalic acid with epichlorohydrin.

  As the aromatic epoxy compound (B) used in the present invention, besides these epoxy compounds, epoxy compounds synthesized from the above-mentioned epoxy compounds, for example, oxazolidone from bisphenol A diglycidyl ether and tolylene diisocyanate An epoxy compound synthesized by a ring formation reaction is exemplified.

  In the present invention, in addition to one or more epoxy groups, at least one functional group selected from a hydroxyl group, an amide group, an imide group, a urethane group, a urea group, a sulfonyl group, a carboxyl group, an ester group, and a sulfo group. Preferably used. For example, compounds having epoxy group and hydroxyl group, compounds having epoxy group and amide group, compounds having epoxy group and imide group, compounds having epoxy group and urethane group, compounds having epoxy group and urea group, epoxy group and sulfonyl Examples thereof include compounds having a group and compounds having an epoxy group and a sulfo group.

  Examples of the compound having an amide group in addition to the epoxy group include glycidyl benzamide and an amide-modified epoxy compound. The amide-modified epoxy can be obtained by reacting an epoxy group of an epoxy compound having two or more epoxy groups with a carboxyl group of a dicarboxylic acid amide containing an aromatic ring.

  Examples of the compound having an imide group in addition to the epoxy group include glycidyl phthalimide. Specific examples include “Denacol (registered trademark)” EX-731 (manufactured by Nagase ChemteX Corporation).

  As a compound having a urethane group in addition to an epoxy group, the terminal hydroxyl group of polyethylene oxide monoalkyl ether is reacted with a polyvalent isocyanate containing an aromatic ring having a reaction equivalent to the amount of the hydroxyl group, and then the reaction product obtained It can be obtained by reacting an isocyanate residue with a hydroxyl group in a polyvalent epoxy compound. Here, examples of the polyvalent isocyanate used include 2,4-tolylene diisocyanate, metaphenylene diisocyanate, paraphenylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, and biphenyl-2,4,4′-triisocyanate. It is done.

  Examples of the compound having a urea group in addition to the epoxy group include a urea-modified epoxy compound. The urea-modified epoxy can be obtained by reacting the epoxy group of an epoxy compound containing an aromatic ring having two or more epoxy groups with the carboxyl group of the dicarboxylic acid urea.

  Examples of the compound having a sulfonyl group in addition to the epoxy group include bisphenol S-type epoxy.

  Examples of the compound having a sulfo group in addition to the epoxy group include glycidyl p-toluenesulfonate and glycidyl 3-nitrobenzenesulfonate.

  In the present invention, the aromatic epoxy compound (B) is preferably either a phenol novolac epoxy compound, a cresol novolac epoxy compound, or tetraglycidyl diaminodiphenylmethane. These epoxy compounds have a large number of epoxy groups, a small epoxy equivalent, and have two or more aromatic rings. In addition to improving the adhesion between carbon fiber and matrix resin, fiber reinforced composite materials Improve mechanical properties such as 0 ° tensile strength. More preferred are phenol novolac epoxy compounds and cresol novolac epoxy compounds.

  In the present invention, when the prepreg is stored for a long time, the aromatic epoxy compound (B) is a phenol novolak type epoxy compound, a cresol novolak type epoxy compound, a tetraglycidyl diaminodiphenylmethane, a bisphenol A type epoxy compound or a bisphenol F type epoxy compound. From the viewpoint of stability and adhesiveness, it is preferably a bisphenol A type epoxy compound or a bisphenol F type epoxy compound.

  Furthermore, the sizing agent used in the present invention may contain one or more components other than the aliphatic epoxy compound (A) and the aromatic epoxy compound (B). Accelerator that enhances adhesion between carbon fiber and sizing agent. Convergence or flexibility is imparted to carbon fiber coated with sizing agent to improve handling, scratch resistance and fluff resistance, and improve matrix resin impregnation. In order to improve the long-term stability of the prepreg in the present invention, compounds other than (A) and (B) can be contained. For the purpose of stabilizing the sizing agent, auxiliary components such as a dispersant and a surfactant may be added.

  In the present invention, the carbon fiber has a surface oxygen concentration (O / C), which is a ratio of the number of atoms of oxygen (O) and carbon (C) on the fiber surface measured by X-ray photoelectron spectroscopy. The thing within the range of 05-0.50 is preferable, More preferably, it is a thing within the range of 0.06-0.30, More preferably, it is a thing within the range of 0.07-0.25. When the surface oxygen concentration (O / C) is 0.05 or more, an oxygen-containing functional group on the surface of the carbon fiber can be secured and strong adhesion with the matrix resin can be obtained. In addition, since the surface oxygen concentration (O / C) is 0.50 or less, the decrease in the single fiber strength of the carbon fiber itself due to oxidation is suppressed, that is, the single fiber apparent stress by the fragmentation method of the single fiber composite is reduced. The number of fiber breaks at 10.0 GPa can be controlled to 0.8 pieces / mm or less, and the number of fiber breaks at 12.2 GPa can be controlled to 1.3 pieces / mm or less.

The surface oxygen concentration of the carbon fiber is determined by X-ray photoelectron spectroscopy according to the following procedure. First, carbon fibers from which dirt and the like adhering to the carbon fiber surface were removed with a solvent were cut into 20 mm, spread and arranged on a copper sample support base, and then AlKα ₁ and ₂ were used as X-ray sources. The inside of the chamber was measured at 1 × 10 ⁻⁸ Torr. As a correction value for the peak accompanying charging during measurement, the binding energy value of the C _1s main peak (peak top) is adjusted to 284.6 eV. The C _1s peak area is obtained by drawing a straight base line in the range of 282 to 296 eV, and the O _1s peak area is obtained by drawing a straight base line in the range of 528 to 540 eV. The surface oxygen concentration O / C is represented by an atomic ratio calculated by dividing the ratio of the O _1s peak area by the sensitivity correction value unique to the apparatus. When ESCA-1600 manufactured by ULVAC-PHI Co., Ltd. is used as the X-ray photoelectron spectroscopy apparatus, the sensitivity correction value unique to the apparatus is 2.33.

  The sizing agent-coated carbon fiber of the present invention is obtained by trial and error by paying attention to the points of the above preferred production method and according to the conventional means of those skilled in the art so that the fragmentation fracture behavior matches the scope of the present invention. be able to.

  The measuring method of various physical property values described in this specification is as follows.

<Fragmentation method>
Measurement of the number of fiber breaks by the fragmentation method is performed according to the following procedures (a) to (e).

(A) Preparation of resin 190 parts by mass of bisphenol A type epoxy resin compound “Epototo YD-128” (manufactured by Nippon Steel Chemical Co., Ltd.) and 20.7 parts by mass of diethylenetriamine (manufactured by Wako Pure Chemical Industries, Ltd.) Stir with a spatula and defoam using an automatic vacuum defoamer.

(B) Sampling of carbon fiber single fiber and fixing to mold A carbon fiber bundle having a length of about 20 cm was divided into approximately four equal parts, and single fibers were sampled in order from the four bundles. At this time, the entire bundle is sampled as evenly as possible. Next, a double-sided tape is applied to both ends of the perforated mount, and the single fibers are fixed to the perforated mount in a state where a constant tension is applied to the sampled single fibers. Next, a glass plate on which a polyester film “Lumirror (registered trademark)” (manufactured by Toray Industries, Inc.) is attached is prepared, and a 2 mm-thick spacer for adjusting the thickness of the test piece is fixed on the film. . A perforated mount with monofilaments fixed thereon is placed on the spacer, and a glass plate on which a film is similarly attached is set on the spacer with the surface on which the film is attached facing downward. At this time, in order to control the fiber embedding depth, a tape having a thickness of about 70 μm is attached to both ends of the film.

(C) From resin casting to curing The resin adjusted in the procedure (a) is poured into the mold (the space surrounded by the spacer and the film) in the procedure (b). The mold into which the resin has been poured is heated for 5 hours using an oven that has been heated to 50 ° C. in advance, and then the temperature is lowered to a temperature of 30 ° C. at a temperature lowering rate of 2.5 ° C./min. Thereafter, the mold is removed and cut to obtain a test piece of 2 cm × 7.5 cm × 0.2 cm. At this time, the test piece is cut so that the single fiber is located within the center 0.5 cm width of the test piece width.

(D) Fiber Embedding Depth Measurement Fiber embedding depth for the test piece obtained by the procedure (c) above using a laser Raman spectrophotometer (JASCO NRS-3000) laser and a 532 nm notch filter. Measure. First, a laser is applied to the surface of the single fiber, the stage height is adjusted so that the beam diameter of the laser becomes the smallest, and the height at that time is defined as A (μm). Next, a laser is applied to the surface of the test piece, the stage height is adjusted so that the beam diameter of the laser becomes the smallest, and the height at that time is defined as B (μm). The fiber embedding depth d (μm) is calculated by the following formula using the refractive index of the resin 1.732 measured using the laser.

(E) Four-point bending test Tensile strain is applied to the test piece obtained in the procedure (c) by four-point bending using a jig having an outer indenter interval of 50 mm and an inner indenter interval of 20 mm. Stepwise is strained every 0.1%, the specimen is observed with a polarizing microscope, and the number of breaks at the center 10 mm in the longitudinal direction of the specimen is measured. A value obtained by dividing the measured number of breaks by 10 is defined as the number of fiber breaks (pieces / mm). Further, the strain ε (%) was measured using a strain gauge attached at a position about 5 mm away from the center of the test piece in the width direction. The strain ε _c of the final single fiber composite is as follows in consideration of the gauge factor κ of the strain gauge, the fiber embedding depth d (μm) measured by the above procedure (d), and the residual strain of 0.14 (%). Calculate with the following formula.

The n number of the test is 25.

<Strand tensile strength and strand elastic modulus of carbon fiber>
The strand tensile strength and strand elastic modulus of the carbon fiber bundle are determined according to the following procedure in accordance with the resin impregnated strand test method of JIS-R-7608 (2004). As the resin formulation, “Celoxide (registered trademark)” 2021P (manufactured by Daicel Chemical Industries) / 3 boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / Acetone = 100/3/4 (part by mass) is used. As curing conditions, normal pressure, temperature of 125 ° C., and time of 30 minutes are used. Ten strands of the carbon fiber bundle are measured, and the average value is defined as the strand tensile strength and the strand elastic modulus.

<Single fiber elastic modulus of carbon fiber>
The single fiber elastic modulus of the carbon fiber is determined as follows based on JIS R7606 (2000). That is, first, a bundle of carbon fibers of about 20 cm is divided into approximately four equal parts, and single yarns are sampled in order from the four bundles, and the whole bundle is sampled as evenly as possible. The sampled single yarn is fixed to the perforated mount using an adhesive. A base sheet on which a single yarn is fixed is attached to a tensile tester, and a tensile test is performed with a gauge length of 50 mm, a strain rate of 2 mm / min, and 20 samples. The elastic modulus is defined by the following formula.
Elastic modulus = (obtained strength) / (cross-sectional area of single fiber × obtained elongation)
The obtained strength is the cross-sectional area of the single fiber, and the cross-sectional area of the single fiber is determined by dividing the mass per unit length (g / m) by the density (g / m ³ ) for the fiber bundle to be measured, and further filament Divide by the number to obtain the single fiber cross-sectional area. The density is measured by Archimedes method using a specific gravity liquid as o-dichloroethylene.

<Single fiber diameter of carbon fiber>
For the carbon fiber bundle to be measured, the cross-sectional shape is true from the single fiber cross-sectional area obtained by dividing the mass per unit length (g / m) by the density (g / m ³ ) and further dividing by the number of filaments. Calculated assuming a yen.

<Tearable distance>
The fiber bundle is cut to a length of 1160 mm, and one end thereof is fixed on a horizontal base so as not to move with an adhesive tape (this point is referred to as a fixing point A). One end of the fiber bundle that is not fixed is divided into two with fingers, and one of the ends is tensioned and fixed on the table so as not to move with an adhesive tape (this point is referred to as a fixing point B). Move the other of the two halves along the table so that the fixed point A becomes a fulcrum and does not come loose, rest at a position where the linear distance from the fixed point B is 500 mm, and fix it on the table so that it does not move with adhesive tape. (This point is called a fixed point C). The area surrounded by the fixed points A, B, and C is visually observed, the entanglement point farthest from the fixed point A is found, and the distance projected on the straight line connecting the fixed point A and the fixed point B is 1 mm at the minimum scale. Read with the ruler of, and make the tearable distance. The arithmetic average value of 30 measurements of the above operation is defined as the average tearable distance. A method of measuring the tearable distance is shown in FIG. In this measurement method, the entanglement point farthest from the fixed point A is the point where the linear distance from the fixed point A is the longest and three or more single fibers having no slack are entangled.

<X-ray photoelectron spectroscopy on the surface of the sizing agent-coated carbon fiber>
In the present invention, the peak ratio of (a) and (b) on the sizing agent surface of the sizing agent-coated fiber is determined by X-ray photoelectron spectroscopy according to the following procedure. Sizing agent-coated carbon fibers are cut to 20 mm, spread and arranged on a copper sample support, and AlKα ₁ and ₂ are used as an X-ray source, and the sample chamber is kept at 1 × 10 ⁻⁸ Torr for measurement. . As correction of the peak accompanying charging during measurement, first, the binding energy value of the main peak of C _1s is adjusted to 286.1 eV. At this time, the peak area of C _1s is obtained by drawing a straight baseline in the range of 282 to 296 eV. Further, a linear base line of 282 to 296 eV obtained by calculating the area at the C _1s peak is defined as the origin (zero point) of the photoelectron intensity, and (b) the peak of the binding energy 286.1 eV attributed to the CO component is obtained. The height (cps: photoelectron intensity per unit time) and the height (cps) of the component having a binding energy of 284.6 eV attributed to (a) CHx, C—C, C = C are obtained, and (a) / ( b) is calculated.

Incidentally, when the peak of from (a) is large _(b), when combined binding energy of the main peak of _{C 1s} to _286.1, the peak of _{C 1s} does not fall within the scope of 282～296EV. In that case, after adjusting the binding energy value of the C _1s main peak to 284.6 eV, (a) / (b) is calculated by the above method.

<Perforated plate tensile strength>
Performed in accordance with ASTM D5766 (Open-hole Tensile Strength of Polymer Matrix Composite Laminates).
a. Test condition and room temperature (RTD): 69 ° F (20.6 ° C) ± 5 ° F
Low temperature condition (LTD): -75 ° F (-59.4 ° C) ± 5 ° F
b. Laminated structure 16ply (45/90 / -45 / 0) _2s
c. After cutting the molding condition prepreg to a predetermined size and laminating it so as to have the configuration of b described above, a vacuum bag is formed, and the temperature is raised to 180 ° C. at a heating rate of 1.5 ° C./min using an autoclave. And cured at a pressure of 6 atm for 2 hours to obtain a pseudo isotropic reinforcing material (carbon fiber composite material).
d. Sample size Dimensions: length 308 mm × width 38.1 mm × thickness 4.5 mm.

The materials and components used in each example and each comparative example are as follows.
-(A) component: A-1 to A-3
A-1: “Sumiepoxy (registered trademark)” ELM434 (manufactured by Sumitomo Chemical Co., Ltd.)
Tetraglycidyldiaminodiphenylmethane Epoxy equivalent: 120 g / mol
A-2: “jER (registered trademark)” 828 (manufactured by Mitsubishi Chemical Corporation)
Diglycidyl ether of bisphenol A Epoxy equivalent: 189 g / mol
A-3: GAN (manufactured by Nippon Kayaku Co., Ltd.)
N-diglycidylaniline (B) component:
“Seika Cure (registered trademark)” S (4,4′-diaminodiphenyl sulfone, manufactured by Wakayama Seika Co., Ltd.)
・ Thermoplastic resin "Sumika Excel (registered trademark)" 5003P (manufactured by Sumitomo Chemical Co., Ltd.)
Polyethersulfone.

  In a kneading apparatus, as component (A), 35 parts by mass of (A-1), 35 parts by mass of (A-2), 30 parts by mass of (A-3), and 16 parts by mass of Sumika Excel 5003P were blended. Then, 40 parts by mass of 4,4′-diaminodiphenylsulfone as component (B) was kneaded to prepare an epoxy resin composition for a carbon fiber reinforced composite material.

The obtained epoxy resin composition was coated on a release paper with a resin basis weight of 52 g / m ² using a knife coater to prepare a resin film. This resin film is superposed on both sides of a sizing agent-coated carbon fiber (weight per unit area 190 g / m ² ) aligned in one direction, and a heat roll is used to heat and press at 100 ° C. and 1 atm. Was impregnated into a sizing agent-coated carbon fiber to obtain a prepreg, a carbon fiber reinforced composite material was molded, and an OHT test was performed.

[Example 1]
A copolymer composed of 99.4 mol% of acrylonitrile and 0.6 mol% of itaconic acid is polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent and 2,2′-azobisisobutyronitrile as an initiator, and polyacrylonitrile series A copolymer was produced. Ammonia gas is blown into the produced polyacrylonitrile polymer until the pH reaches 9.0, and while itaconic acid is neutralized, an ammonium group is introduced into the polyacrylonitrile copolymer, and the intrinsic viscosity is 3.4. A spinning solution was obtained. The obtained spinning solution was discharged at 30 ° C. using a spinneret having a diameter of 0.10 mm and a number of holes of 6,000, once passed through the space of about 4 mm, and then controlled at 0 ° C. 35 A coagulated yarn was obtained by a dry and wet spinning method introduced into a coagulation bath comprising an aqueous solution of% dimethyl sulfoxide. The coagulated yarn was washed with water by a conventional method, and then the temperature of the fourth bath was set to 95 ° C. by raising the temperature from the first bath by 10 ° C. in 4 warm water baths. At this time, the total draw ratio was 2.5 times. Subsequently, an amino-modified silicone-based silicone oil agent is applied to the fiber bundle after stretching in the water bath, a drying densification treatment is performed using a heating roller at 160 ° C., two yarns are combined, and a single fiber After the number of yarns is 12,000, the yarn is stretched 3.7 times in pressurized steam to increase the total draw ratio of yarn production to 13 times, and then entangled to give a single fiber fineness of 0.41 dtex and a single fiber of 12,000 polyacrylonitrile. A system precursor fiber was obtained. Here, the entanglement treatment means that the angle formed by the fiber bundle longitudinal direction and the fluid blowing direction is 90 °, and eight ejection holes are arranged so as to surround the fiber bundle, and each ejection hole is composed of two holes. Using fluid spray nozzles arranged at opposing positions so as to form a set, the tension of the fiber bundle was adjusted to 3 mN / dtex, and the fluid discharge pressure was set to 0.35 MPa. Next, flameproofing treatment was performed while stretching at a stretch ratio of 1.00 in air at a temperature of 250 to 280 ° C. to obtain a flameproof fiber bundle having a specific gravity of 1.36 g / cm ³ . The obtained flame-resistant fiber bundle was subjected to a preliminary carbonization treatment while being stretched at a stretch ratio of 1.10 in a nitrogen atmosphere at a temperature of 300 to 800 ° C. to obtain a preliminary carbonized fiber bundle. The obtained pre-carbonized fiber bundle was carbonized at a maximum temperature of 1500 ° C. and a tension of 9.8 mN / dtex in a nitrogen atmosphere. The obtained carbon fiber was subjected to electrolytic surface treatment with an aqueous solution of ammonium hydrogen carbonate having a concentration of 0.1 mol / liter as an electrolytic solution at an electric quantity of 80 coulomb per gram of carbon fiber. The carbon fiber subjected to the electrolytic surface treatment was subsequently washed with water and dried in heated air at a temperature of 150 ° C. to obtain a carbon fiber as a raw material. Subsequently, 10 parts by mass of “jER (registered trademark)” 828 (manufactured by Mitsubishi Chemical Corporation), 10 parts by mass of “jER (registered trademark)” 1001 (manufactured by Mitsubishi Chemical Corporation), 2 mol of EO of bisphenol A 20 parts by weight of a condensate of 2 moles of adduct, 1.5 moles of maleic acid and 0.5 moles of sebacic acid, and 10 parts by weight of polyoxyethylene (70 moles) styrenated (5 moles) cumylphenol as an emulsifier After preparing the water-dispersed emulsion, 50 parts by weight of “Denacol (registered trademark)” EX-521 (manufactured by Nagase ChemteX Corporation) was mixed to prepare a sizing solution. After this sizing agent was applied to the carbon fiber surface-treated by the dipping method, heat treatment was performed at a temperature of 210 ° C. for 75 seconds to obtain a sizing agent-coated carbon fiber bundle. The adhesion amount of the sizing agent was adjusted to be 1.0 part by mass with respect to 100 parts by mass of the surface-treated carbon fiber. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Example 2]
A sizing agent-coated carbon fiber bundle was obtained in the same manner as in Example 1 except that the discharge amount of the spinning solution was adjusted so that the single fiber fineness of the polyacrylonitrile-based precursor fiber was 0.26 dtex. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Example 3]
A sizing agent-coated carbon fiber bundle was obtained in the same manner as in Example 1 except that the discharge amount of the spinning solution was adjusted so that the single fiber fineness of the polyacrylonitrile-based precursor fiber was 0.14 dtex. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Example 4]
A sizing agent-coated carbon fiber bundle was obtained in the same manner as in Example 1 except that the discharge amount of the spinning solution was adjusted so that the single fiber fineness of the polyacrylonitrile-based precursor fiber was 0.60 dtex. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Comparative Example 1]
A copolymer composed of 99.5 mol% of acrylonitrile and 0.5 mol% of itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent and 2,2′-azobisisobutyronitrile as an initiator, and a weight average molecular weight was obtained. A polyacrylonitrile copolymer having 700,000 and Mz / Mw of 1.8 was produced. Ammonia gas was blown into the manufactured polyacrylonitrile-based polymer until the pH reached 8.5, and the polymer concentration was adjusted to 15% by mass to obtain a spinning solution. The obtained spinning solution was discharged into the air once at 40 ° C. using a spinneret having a diameter of 0.15 mm and a hole number of 6,000, passed through a space of about 4 mm, and then controlled at 3 ° C. 35 A coagulated yarn was obtained by a dry and wet spinning method introduced into a coagulation bath comprising an aqueous solution of% dimethyl sulfoxide. The coagulated yarn was washed with water by a conventional method, and then stretched 3.5 times in two warm water baths. Subsequently, an amino-modified silicone-based silicone oil agent is applied to the fiber bundle after stretching in the water bath, a drying densification treatment is performed using a heating roller at 160 ° C., two yarns are combined, and a single fiber After the number of yarns is 12,000, the yarn is stretched 3.7 times in pressurized steam, the yarn drawing total draw ratio is 13 times, and then the entanglement treatment is performed to obtain a single fiber fineness of 0.70 dtex and a single fiber number of 12,000 polyacrylonitrile. A system precursor fiber was obtained. Here, the entanglement treatment means that the angle formed by the fiber bundle longitudinal direction and the fluid blowing direction is 90 °, and eight ejection holes are arranged so as to surround the fiber bundle, and each ejection hole is composed of two holes. Using fluid spray nozzles arranged at opposing positions so as to form a set, the tension of the fiber bundle was adjusted to 3 mN / dtex, and the fluid discharge pressure was set to 0.35 MPa. Next, in the air of 240-260 degreeC, it flame-proofed, extending | stretching by the draw ratio 1, and obtained the flame-resistant fiber bundle of specific gravity 1.35-1.36. The obtained flame-resistant fiber bundle was subjected to a preliminary carbonization treatment while being stretched at a stretch ratio of 1.15 in a nitrogen atmosphere at a temperature of 300 to 800 ° C. to obtain a preliminary carbonized fiber bundle. The obtained pre-carbonized fiber bundle was carbonized at a maximum temperature of 1500 ° C. and a tension of 5.5 mN / dtex in a nitrogen atmosphere. The obtained carbon fiber was subjected to electrolytic surface treatment with an aqueous solution of ammonium hydrogen carbonate having a concentration of 0.1 mol / liter as an electrolytic solution at an electric quantity of 80 coulomb per gram of carbon fiber. The carbon fiber subjected to the electrolytic surface treatment was subsequently washed with water and dried in heated air at a temperature of 150 ° C. to obtain a carbon fiber as a raw material. Subsequently, 20 parts by mass of component (A), 2 mol of an EO2 mol adduct of bisphenol A, 1.5 mol of maleic acid, and 20 mol parts of a condensate of 0.5 mol of sebacic acid and polyoxyethylene (70 After preparing an aqueous dispersion emulsion comprising 10 parts by mass of (mol) styrenated (5 mol) cumylphenol, 50 parts by mass of component (B) was mixed to prepare a sizing solution. After this sizing agent was applied to the carbon fiber surface-treated by the dipping method, heat treatment was performed at a temperature of 210 ° C. for 75 seconds to obtain a sizing agent-coated carbon fiber bundle. The adhesion amount of the sizing agent was adjusted to be 1.0 part by mass with respect to 100 parts by mass of the surface-treated carbon fiber. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Comparative Example 2]
A sizing agent-coated carbon fiber bundle was obtained in the same manner as in Comparative Example 1 except that the amount of spinning solution discharged was adjusted so that the single fiber fineness of the polyacrylonitrile-based precursor fiber was 0.62 dtex. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Comparative Example 3]
Regarding the sizing agent, “jER (registered trademark)” 828 (manufactured by Mitsubishi Chemical Corporation), “jER (registered trademark)” 1001 (manufactured by Mitsubishi Chemical Corporation), 2 mol of EO2 mol adduct of bisphenol A and maleic acid Condensate of 1.5 mol and 0.5 mol of sebacic acid, “Denacol (registered trademark)” EX-521 (manufactured by Nagase ChemteX Corp.) from 10: 10: 20: 50 to 22.5: 22.5 : A sizing agent-coated carbon fiber bundle was obtained in the same manner as in Example 1 except that the ratio was changed to 45: 0. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Comparative Example 4]
A sizing agent-coated carbon fiber bundle was obtained in the same manner as in Comparative Example 3, except that the amount of spinning solution discharged was adjusted so that the single fiber fineness of the polyacrylonitrile-based precursor fiber was 0.14 dtex. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Comparative Example 5]
In the manufacturing process of the polyacrylonitrile-based precursor fiber, a sizing agent-coated carbon fiber bundle was obtained in the same manner as in Example 1 except that the entanglement treatment was not performed. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Comparative Example 6]
In the production process of the polyacrylonitrile-based precursor fiber, a sizing agent-coated carbon fiber bundle was obtained in the same manner as in Example 3 except that the entanglement treatment was not performed. Table 1 summarizes the characteristics of the obtained sizing agent-coated carbon fiber bundle and the OHT test results.

[Comparative Example 7]
Analysis was performed using a commercially available “Torayca (registered trademark)” T800S (manufactured by Toray Industries, Inc.). The characteristics of the carbon fiber bundle are summarized in Table 1.

[Comparative Example 8]
Analysis was performed using a commercially available “TENAX (registered trademark)” IM600 (manufactured by Toho Tenax Co., Ltd.). The characteristics of the carbon fiber bundle are summarized in Table 1.

  Judging from Table 1, the higher the strand strength, the smaller the number of fiber breaks when the single fiber apparent stress is 10.0 GPa, and the lower the number of fiber breaks when the single fiber apparent stress is 12.2 GPa, The OHT tends to be high. Among the commercially available prepregs, even “Hexply (registered trademark)” IM-10 / M91 having the largest catalog value of OHT (room temperature conditions) was about 600 MPa (= 88 ksi).

1: Fiber bundle 2: Fixed point A
3: Fixed point B
4: Fixed point C
5: Entanglement point 6: Tearable distance

  The carbon fiber composite material using the sizing agent-coated carbon fiber of the present invention has high physical properties such as tensile elastic modulus and perforated plate tensile strength. Therefore, it can greatly contribute to the weight reduction of the aircraft and improve the fuel consumption rate of the aircraft.

Claims (7)

A sizing agent-coated carbon fiber in which a sizing agent is applied to carbon fiber, and the number of fiber breaks is 2.0 pieces / mm or more when the single fiber apparent stress is 15.3 GPa by the fragmentation method of the single fiber composite of carbon fiber A sizing agent-coated carbon fiber having a fiber breakage number of 1.3 pieces / mm or less when the single fiber apparent stress is 12.2 GPa. The sizing agent-coated carbon fiber according to claim 1, wherein the number of fiber breaks is 0.8 pieces / mm or less when a single fiber apparent stress is 10.0 GPa by a fragmentation method of a single fiber composite. Sizing agent application | coating carbon fiber of Claim 1 or 2 whose single fiber diameter of a carbon fiber is 4.5 micrometers or less. Sizing agent comprises an epoxy compound, sizing agent applying carbon fiber according to any one of claims 1 to 3. Sizing agent application | coating carbon fiber of Claim 4 in which an epoxy compound contains an aliphatic epoxy compound. The sizing agent-coated carbon fiber according to claim 5, wherein the epoxy compound further contains an aromatic epoxy compound. Sizing agent application | coating carbon fiber in any one of Claims 4-6 which is 300 mm-710 mm in average tearable distance, and is substantially untwisted.

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