ES2534650T3 - Carbon fiber beam that develops excellent mechanical performance - Google Patents

Abstract

A carbon fiber bundle formed of individual carbon fiber: each individual carbon fiber having no non-uniform surface structure having a length of 0.6 μm or more and extending in the longitudinal direction of the individual fiber, having each individual carbon fiber a non-uniform structure in which the difference in height (Rp - v) between a portion that is the highest and a portion that is the lowest of the surface of the individual fiber is 5 to 25 nm, and in the that an average roughness Ra is from 2 to 6 nm, and each of which has a ratio of 1.00 to 1.01 of a major axis with respect to a minor axis (major axis / minor axis) of a cross section of the individual fiber; wherein a mass of the individual fiber per unit length falls within the range of 0.030 to 0.042 mg / m; a measured resistance according to JIS R7601 is 5900 MPa or more; a modulus of elasticity of rope measured by the ASTM method is 250 to 380 GPa; and a knot toughness is 900 N / mm2 or more.

Description

Carbon fiber beam that develops excellent mechanical performance

Technical field

The present invention relates to a bundle of carbon fibers that has excellent mechanical characteristics and is used in particular to obtain a fiber reinforced resin using a high tenacity heat resistant resin as a matrix for use in the construction of planes.

Prior art

Conventionally, in order to improve the mechanical characteristics of resin-molded products, a resin has been commonly used in combination with a fiber that serves as a reinforcing material. In particular, a composite molding material formed of a carbon fiber having excellent specific strength and specific elasticity in combination with a high performance resin develops extremely high mechanical characteristics. Because of this, a molding material of this type has been used willingly as a construction material for airplanes, bodies moving at high speed, etc. In addition, there is a demand to develop a material that is stronger and has a higher stiffness as well as having an excellent specific strength and specific stiffness. Given these circumstances, it is desired to further improve the performance of the carbon fiber, such as an improved strength and modulus of elasticity.

For example, patent literature 1 proposes a method of stretching a coagulated fiber that still contains a solvent in a solvent-based stretching bath, thereby improving uniformity in structure and orientation, in order to obtain a bundle of acrylic fibers that is used as a precursor to a carbon fiber by a dry-wet spinning method. Stretching a coagulated fiber in a bath containing a solvent is a method that is commonly known as a solvent drawing technique that enables a stable stretching process through the use of solvent plasticization. Therefore, this method is considered as an extremely excellent technique to obtain a fiber that has a high uniformity in structure and orientation. However, if a fiber bundle is stretched that is in a swollen state due to the presence of a solvent, the solvent inside a filament is quickly removed from the filament simultaneously after stretching. The resulting filament structure tends to be less dense and, thus, a desired filament having a dense structure cannot be obtained.

In addition, patent literature 2, which pays attention to the fine pores distributed in a coagulated fiber, proposes a technique to obtain a precursor fiber in which excellent resistance is developed by dry densification of a coagulated fiber having a structure high density The distribution of fine pores, which is obtained by a method of introduction under pressure with mercury, reflects the bulk state from the surface layer to the interior of the filament. This is an extremely excellent method to assess the overall density of a fiber structure. From the bundle of precursor fibers having at least a certain level density as a whole, a very resistant carbon fiber can be obtained in which the formation of defect points is suppressed. However, the observation of fractures in the carbon fiber shows that the fractures have originated from near the surface layer at an extremely high ratio. This means that a defective point is present near the surface layer. In other words, this technique is insufficient to manufacture a bundle of precursor fibers having an excellent density near the surface layer.

Patent literature 3 proposes a method for manufacturing a bundle of acrylonitrile-based precursor fibers that not only has a high overall density but also has an extremely high surface density. In addition, patent literature 4 proposes, taking into account that an oil solution enters the surface layer portion of a fiber and inhibits densification, a technique to suppress the permeation of an oil solution by focusing on microscopic gaps of the portion of surface layer. However, both a technique to suppress the entry of an oil solution and a technique to suppress the formation of defective points are difficult to put into practical use, because very complicated stages are required. Therefore, in the techniques that have been analyzed above, the effect of stably suppressing the entry of an oil solution into the surface layer portion is insufficient and the reinforcing effect of a carbon fiber is still Find far enough.

EP 1 837424 A1 refers to a carbon fiber having a narrow individual filament module distribution, a carbon fiber production method capable of producing said carbon fiber and an oily agent for a precursor fiber of carbon fiber that is used in said production method. US 6 641 91581 refers to a bundle of acrylonitrile fibers for a carbon fiber precursor, and a process for producing a bundle of acrylonitrile fibers for a carbon fiber precursor comprising the steps of discharging a solution of Spinning feed of an acrylonitrile polymer to prepare a coagulated fiber, stretch the coagulated fiber and then strain the coagulated fiber.

Appointment List

Patent literature

Patent literature 1: JP05–5224A Patent literature 2: JP04–91230A Patent literature 3: JP06–15722A Patent literature 4: JP11–124744A

Summary of the invention

Technical problem

An object of the present invention is the provision of a bundle of carbon fibers to obtain a fiber reinforced resin having high mechanical characteristics.

Solution to the problem

The object is achieved by the invention set forth below. The present invention is directed to a bundle of carbon fibers formed of individual carbon fibers, each of which has no non-uniform surface structure of any length of 0.6 µm or more that extends in the longitudinal direction of the individual fiber; which has a non-uniform structure that has a difference in height (Rp-v) of 5 to 25 nm between the highest portion and the lowest portion of the surface of the individual fiber and an average roughness Ra of 2 to 6 nm, and having a ratio of the major axis to the minor axis (major axis / minor axis) of a cross section of the individual fiber from 1.00 to 1.01, in which one mass of the individual fiber per unit in length it falls within the range of 0.030 to 0.042 mg / m, a rope resistance measured in accordance with JIS R7601 is 5900 MPa or more, a rope elastic modulus measured by the ASTM method is 250 to 380 GPa and a knot toughness is 900 N / mm2 or more. Note that the knot toughness can be obtained by dividing the tensile stress of a bundle of knotted carbon fibers by the cross-sectional area of the fiber bundle (mass and density per unit length).

Advantageous effects of the invention

According to the carbon fiber beam of the present invention, it is possible to provide a fiber reinforced resin having high mechanical characteristics.

In addition, a bundle of carbon fibers having an even better performance is obtained by acquiring a "surface surface energy formed by fracture" such that it reaches 30 N / m or more.

In addition, a carbon fiber composite material that has an extremely high mechanical performance can be obtained by forming a carbon fiber beam having an ipa value of 0.05 to 0.25 µA / cm2 which is obtained by a electrochemical measurement method (cyclic voltammetry), and in which the amount of an oxygen-containing functional group (O1S / C1S) on a carbon fiber surface, which is obtained by X-ray photoelectronic spectroscopy, is within the range from 0.05 to 0.10.

Description of realizations

The non-uniform surface structure present on the surface of a carbon fiber and extending in the longitudinal direction thereof and a gluing agent bonded on the surface play very important roles in the development of mechanical characteristics of a resin material. Fiber reinforced using carbon fiber as a reinforcing material. This is because the non-uniform surface structure and the bonding agent bonded on the surface are directly involved in the formation of the interface phase between a carbon fiber and a resin as well as characteristics thereof. The mechanical performance of the fiber reinforced resin material is influenced by the performance of each of the three constituent factors, that is, the fiber, the matrix resin and the interface phase. Even if only one of the three factors is unsatisfactory, the fiber reinforced resin material cannot develop excellent mechanical performance.

(Non-uniform surface structure of an individual fiber that extends in the longitudinal direction)

A carbon fiber that is obtained by a general manufacturing method for a bundle of carbon fibers has, in general, a non-uniform surface structure that forms almost parallel to the direction of the fiber axis. The non-uniform structure has an undulation structure that is almost parallel with respect to the fiber axis and which extends in the fiber axis. The depth of the non-uniform structure is generally from about 50 nm to several hundred nm and the length thereof is generally from about 0.6 µm to several µm and, sometimes, several tens of µm. A surface structure does not

Uniform of this type is usually referred to as superficial wrinkle. The carbon fiber beam of the present invention does not have a non-uniform surface structure having a length of 0.6 µm or more and extending in the longitudinal direction of an individual fiber.

In contrast, the carbon fiber beam of the present invention has a non-uniform structure that is more small than the non-uniform structure mentioned above on the surface of a fiber individual. The depth of the non-uniform surface structure present on an individual carbon fiber is defined by the difference in height (Rp - v) between the highest portion and the lowest portion on the surface of a fiber and the average roughness Ra, in an area range surrounded by a length of 1.0 µm in the direction in circumferential direction of fiber and a length of 1.0 µm in the direction of the fiber axis. The (Rp - v) and Ra can Obtained by scanning the surface of an individual fiber by using a force microscope Atomic scanning (AFM). It is desired that the difference in height (Rp - v) be 5 to 25 nm and that the roughness Ra average from 2 to 6 nm. It is more preferable that the difference in height (Rp-v) is 5 to 18 nm and that the Ra be from 2 to 5 nm.

In the present invention, each of the individual fibers constituting a carbon fiber has no structure. non-uniform surface that is 0.6 µm or more in length and extends in the longitudinal direction of the fiber, on the surface of an individual fiber. In the interphase phase of a composite material, the effort It tends to concentrate on such a large non-uniform surface structure. In addition, the tenacity to Carbon fiber tissue fracture around such a non-uniform structure is low. Therefore, in the non-uniform surface structure of this size, an interface failure tends to originate from a point near the non-uniform structure even if the level of effort that is applied to a composite material is not very big. As a result, the mechanical performance of the composite material decreases significantly.

A more specific embodiment of the non-uniform surface structure of each of the individual fibers that constitute a bundle of carbon fibers of the present invention is as follows. Generally, the carbon fiber surface has a non-uniform structure with a length of 0.6 µm or more which is called a wrinkle structure, which has a set of several fibrils as a unit and that extends in the longitudinal direction of the fiber, and a non-uniform microscopic structure that is smaller than the non-uniform structure called a wrinkle structure and that is present in each of the own fibril bodies. On the contrary, on the surface of each of the individual fibers that constitute a bundle of fibers of carbon of the present invention, a non-uniform structure having a length of 0.6 µm or more and extending in the longitudinal direction of a fiber, but only one non-uniform microscopic structure that is smaller than the non-uniform structure and that is present in each of the fibril bodies themselves. In addition, a non-uniform microscopic structure of this type has a length of 300 nm or less. The non-uniform structure is defined by (Rp - v) and Ra as it has been mentioned above. In order to be specific, the non-uniform structure is a structure of undulation having a difference in height (Rp - v) of 5 to 25 nm and an average roughness Ra of 2 to 6 nm, which they are present in an area range surrounded by a length (1.0 µm) in the direction in the direction circumferential fiber of an individual fiber surface and a length (1.0 µm) in the direction of the fiber axis. Preferably, (Rp-v) is 5 to 18 nm and Ra is 2 to 5 nm. The direction of the microscopic structure does not uniform is not particularly limited and can be parallel or perpendicular to the direction of the axis of fiber or may be present at an angle to the direction of the fiber axis.

(Individual fiber cross section)

In addition, the ratio of the major axis and the minor axis (major axis / minor axis) of a fiber cross section Individual is from 1.00 to 1.01. This means that the individual fiber must have a circular cross-section. complete or almost complete circular. This is because if the cross section is a complete circle, the portion near the fiber surface has excellent structural uniformity, with the result that the concentration of effort can be reduced. The ratio is preferably from 1.00 to 1.005. In addition, for the same reason, the mass of the individual fiber per unit length is 0.030 to 0.042 mg / m. If the mass of the individual fiber per unit in length (individual fiber weight per unit area) is low, the fiber diameter is small, and the irregularity Structural along the cross section is small. This means that the mechanical performance in the Perpendicular direction with respect to the fiber axis is high. Therefore, in a composite material, tolerance the effort applied in the perpendicular direction with respect to the fiber axis is improved and the performance Mechanical composite material can be enhanced.

(Beam of carbon fibers)

In the present invention, to obtain a fiber reinforced resin having mechanical characteristics excellent, the strength of a carbon fiber beam out must be 5900 MPa or more, which are about values that are measured in accordance with JIS R7601. The end resistance of a carbon fiber beam is preferably 6000 MPa or more and more preferably 6100 MPa or more. It will be better the higher the rope resistance; however, taking into account the balance between the endurance and the resistance to

Compression of a composite material, 10,000 MPa are sufficient. In addition, in the present invention, to obtain a fiber reinforced resin having excellent mechanical characteristics, the elastic modulus of a carbon fiber bundle must be 250 to 380 GPa, which are measured values. using the ASTM method. If the modulus of elasticity is less than 250 GPa, the modulus of elasticity of a bundle of carbon fibers will be insufficient and sufficient mechanical characteristics cannot be developed. On the contrary, if the modulus of elasticity exceeds 380 GPa, the graphite crystal size of the surface and the inside of a carbon fiber will increase. Accordingly, the resistance along the cross section of the fiber and the compressive strength in the direction of the fiber axis decrease and the performance balance between the tension and compression of a composite material cannot be maintained. As a result, an excellent composite material cannot be obtained. In addition, surface inactivation progresses as the size of the graphite crystal increases, and the adhesiveness with a matrix resin decreases. As a result, the mechanical performance such as the tensile strength of the composite material in the direction of 90 °, the resistance to shear stresses between layers, the resistance to shear stresses in the plane and the compressive strength at 0 ° significantly decrease .

Furthermore, in the present invention, it is important that the knot toughness, which is obtained by dividing the tensile stress at the time of the breakage of a bundle of carbon fibers knotted by the cross-sectional area of the fiber bundle (mass and density per unit length), be 900 N / mm2 or more. More preferably, the knot toughness is 1000 N / mm2 or more and even more preferably, 1100 N / mm2 or more. The knot toughness serves as an index that reflects the mechanical performance of a fiber bundle except in the direction of the fiber axis. In particular, the performance in the perpendicular direction with respect to the fiber axis can be checked simply by the knot toughness. In the composite material, because a material is often formed by pseudo-isotropic lamination, a complicated stress field is formed. At this time, in addition to a tension and compression effort in the direction of the fiber axis, an effort is also generated in the direction of the fiber axis. In addition, if a relatively high velocity deformation is applied, as it is in an impact test, the state of stress generated inside the composite material is considerably complicated and resistance in the direction becomes important. which is different from the resistance in the direction of the fiber axis. Therefore, if the knot toughness is less than 900 N / mm2, it does not develop sufficient mechanical performance in a pseudo-isotropic material. On the other hand, if the knot toughness exceeds 3000 N / mm2, the degree of orientation in the direction of the fiber axis must be reduced. Therefore, the knot strength should be controlled to be 3000 N / mm2 or less.

In addition, in the carbon fiber beam of the present invention, a "surface surface energy formed by fracture" is preferably 30 N / m or more. The surface energy of the surface formed by fracture is obtained by forming a hemispherical defect that has a size previously determined by means of a laser on the surface of an individual fiber, and by breaking the fiber at the hemispherical defective site in a test of traction and by calculating from the resistance to breakage of the fiber and the size of the hemispherical defect according to the following Griffith equation (1).

σ = (2E / πC) 1/2  (surface surface energy formed by fracture) 1/2… (1)

In the present case, "σ" is the breaking strength; "E" is the ultrasonic elastic modulus of a carbon fiber bundle; and "C" is the size of a hemispherical defect. The "surface energy of the surface formed by fracture" is more preferably 31 N / m or more and even more preferably 32 N / m or more.

The surface energy of the surface formed by fracture herein is used as an index of resistance to breakage of a carbon fiber to represent the strength of the substrate. Carbon fiber is a material that shows a fragile fracture and tensile strength is controlled by the defective point. If the carbon fibers have the same defective points, the breaking strength increases as the strength of the substrate increases. In addition, a matrix resin for a high performance composite material often has a high adhesiveness with a carbon fiber, with the result that the critical fiber length decreases, which serves as an index for stress transfer. As a result, the resistance in an even shorter length is reflected in the strength of the composite. Therefore, it can be conceived that the substrate resistance is an important index. On the contrary, if the surface energy produced by breakage exceeds 50 N / m, it is necessary to reduce the degree of orientation in the direction of the fiber axis. Therefore, the surface energy produced by breakage should be 50 N / m or less.

In the present invention, the ipa value that is obtained by an electrochemical measurement method (cyclic voltammetry) is preferably from 0.05 to 0.25 µA / cm2. The value of ipa is influenced by the number of functional groups that contain oxygen from a carbon fiber, the surface roughness involved in the formation of an electric double layer and the microscopic graphite structure of a carbon fiber surface. In particular, a carbon fiber whose surface is subject to chemical attack to a large extent and a carbon fiber having an intercalation compound that is formed by inserting an anion between layers of a graphite crystal have a large ipa value. . In the development of a composite material that has excellent mechanical performance, the interface between a carbon fiber and a resin is important. In particular, it is discovered that a carbon fiber having a surface on which a functional group containing

appropriate oxygen and in which a small electrical double layer is formed, forms the most appropriate interface. If a value of ipa is 0.05 µA / cm2 or more, it indicates that the surface has a sufficient number of oxygen-containing functional groups, and this shows sufficient adhesion to an interface. On the contrary, if a value of ipa is 0.25 µA / cm2 or less, the surface is not subjected to excessive chemical attack and an intercalation compound is not formed. Such a surface can adhere strongly to a matrix resin, with the result that the surface can adhere sufficiently to the interface with a resin. The value of ipa is more preferably from 0.07 to 0.20 µA / cm2 and even more preferably from 0.10 to 0.18 µA / cm2.

Furthermore, in the present invention, it is desired that the amount of an oxygen-containing functional group on a carbon fiber surface (obtained by X-ray photoelectronic spectroscopy) be within the range of 0.05 to 0.15 . This is because it is important to have proper adhesiveness with a matrix resin at the interface.

Furthermore, in the present invention, an amount of Si measured by ICP emission spectrometry is desirably 200 ppm or less. In order to make a high-strength carbon fiber, usually an oil solution containing silicone oil is bonded onto a bundle of precursor fibers. Silicone oil has extremely excellent thermal resistance properties and can impart excellent mold release characteristics. Therefore, silicone oil is considered the most suitable as an oil solution for a bundle of carbon fiber precursors, which is a multi-filament beam that is formed by mounting a large number of filaments that have, each, an extremely small diameter and additionally each subject to a high temperature treatment that is performed at a temperature of 200 ° C or more for several tens of minutes to several hours. However, in the carbonization treatment that is performed after the stabilization treatment, the silicone oil decomposes and disperses for the most part. Consequently, the amount of silicone compound that remains on the surface of a carbon fiber becomes extremely low. In addition, it has been found that the remaining silicone compound, which is present near the surface of a carbon fiber, contributes to the formation of gaps. Therefore, if the amount of such a silicone compound is reduced as much as possible, a carbon fiber can be made that has few gaps. As a result, the resistance of a carbon fiber beam can be increased. The most preferable Si amount is 150 ppm or less and an even more preferable Si amount is 100 ppm or less.

(Precursor fiber bundle and its manufacturing method)

The starting material for obtaining a bundle of carbon fibers of the present invention is not particularly limited; however, the starting material that can be obtained from an acrylonitrile based precursor fiber (referred to hereinafter, appropriately, as "precursor fiber") is preferred from the point of view of the development of mechanical performance. The acrylonitrile-based copolymer constituting the precursor fiber is obtained from acrylonitrile (96% by mass or more) and various types of copolymerizable monomers. More preferably, the acrylonitrile composition ratio is 97% by mass or more. Examples of copolymer components except acrylonitrile that are used appropriately include acrylic acid derivatives such as acrylic acid, methacrylic acid, itaconic acid, methyl acrylate and methyl methacrylate; and acrylamide derivatives such as acrylamide, methacrylamide, N-methiolacrylamide and N, N-dimethyl acrylamide and vinyl acetate. These can be used alone or in combination. A preferable copolymer is an acrylonitrile-based copolymer that is obtained by copolymerizing a monomer having one or more carboxyl groups as an essential component.

As an appropriate method for copolymerizing a mixture of monomers, any polymerization method can be used, including, for example, redox polymerization that is performed in an aqueous solution, suspension polymerization that is performed in an inhomogeneous system and emulsion polymerization using a dispersant The difference between the polymerization methods does not limit the present invention. The precursor fiber is preferably manufactured by dissolving the acrylonitrile-based polymer mentioned above in an organic solvent such as dimethyl acetamide, dimethyl sulfoxide or dimethyl formamide to prepare a spinnable mass. Because these organic solvents do not contain a metal component, the content of a metal component in the resulting carbon fiber bundle can be reduced. The concentration of solid substances of the spinnable mass is preferably 20% by mass or more and more preferably 21% by mass or more.

The spinning method can be either wet spinning or dry spinning - wet spinning. More preferably, a dry-wet spinning is used. In dry spinning - wet spinning, the spinning dough that is prepared is spun, first of all, from a spinning nozzle that has numerous ejection holes disposed therein in the air and then introduced into a coagulated liquid loaded with a solution mixture of an organic solvent and water whose temperature is controlled such that the spinning mass will be coagulated. Coagulated fiber is extracted, washed and stretched. As a washing method, any method can be used as long as the solvent can be removed. Note that, before the coagulated fiber that has been removed is washed, if the stretching is carried out in the pre-stretching tank containing a solvent whose concentration is lower than in a coagulated liquid and whose temperature is higher than the of the liquid

coagulated, a structure of fibrils can be formed. When a coagulated fiber is stretched, the temperature of the stretching tank preferably falls within the range of 40 to 80 ° C. If the temperature is less than 40 ° C, stable stretching cannot be ensured and this results in the stretching being bad, with the result that a uniform fibril structure cannot be formed. On the contrary, if the temperature exceeds 80 ° C, an excessively strong plasticizing action takes place by means of heat, and a solvent is quickly removed from a fiber surface and the result is a non-uniform stretching. Therefore, the quality of the precursor fiber bundle deteriorates. A more preferable temperature is 50 to 75 ° C. In addition, the concentration of the stretching tank is preferably 30 to 60% by mass. This is because if the concentration is less than 30% by mass, a stable stretch cannot be ensured; while, if the concentration is beyond 60% by mass, an excessively large plasticizing effect is obtained and interference with stable stretching occurs. A more preferable concentration is 33 to 55% by mass.

The stretching ratio in the stretching tank is preferably 2 to 4 times. If the stretch ratio is less than twice, the stretch is insufficient and a desired fibril structure cannot be formed. On the contrary, if the stretch ratio is beyond 4 times, a structure of fibrils in itself is broken. The result is a bundle of precursor fibers that has an extremely low density. The stretch ratio is more preferably 2.2 to 3.8 times and even more preferably 2.5 to 3.5 times.

Furthermore, after washing, if a fiber bundle that is processed in a swollen state without solvent is stretched in hot water, the degree of fiber orientation can be further enhanced. If a relaxation stage is performed slightly, the distortion caused by stretching in the previous stage can be eliminated. Preferably, in order to improve the degree of orientation of a fiber by increasing the total stretch ratio, the stretching is performed in hot water at a ratio of 1.1 to 2.0 times.

Next, an oil solution that is composed of a silicone-based compound is bonded in order to apply 0.8 to 1.6% by mass and the resulting fiber is subjected to dry densification. Dry densification is not particularly limited as long as a dry densification is carried out by a known drying method. Preferably, a method of passing a fiber through a plurality of heated cylinders is employed. After the dry densification process has been carried out, the acrylic fiber bundle is stretched, if necessary, in pressurized steam of 130 to 200 ° C, in a dry heat medium of 100 to 200 ° C, between heated cylinders from 150 to 220 ° C or on a heating plate up to 1.8 to 6.0 times. After the degree of orientation is further improved and densification is performed, the fiber bundle is rolled to obtain a bundle of precursor fibers.

In addition, a bundle of carbon fibers of the present invention can be manufactured from the bundle of precursor fibers mentioned above as follows. The precursor fiber bundle is fed to a stabilization furnace which is a type of furnace that causes hot air to circulate at a temperature of 220 to 260 ° C for 30 to 100 minutes to obtain a stabilized fiber having a density of 1,335 to 1,360 g / cm3. At this time, an operation is carried out to extend the fiber by 0 to 10%. The stabilization reaction consists of a cyclization reaction with heat and an oxidation reaction with oxygen. It is important to balance the two reactions. In order to balance the two reactions, the time to perform the stabilization treatment is preferably 30 to 100 minutes. If the reaction time is less than 30 minutes, an individual fiber has a portion in which the oxidation reaction does not advance sufficiently, inside the fiber, with the result that a large structural diversity is generated throughout of the cross section of the individual fiber. As a result, the carbon fiber obtained has a structure that forms unevenly and cannot develop high mechanical performance. On the contrary, if the reaction time exceeds 100 minutes, a larger amount of oxygen will be present near the surface of an individual fiber. After the above, in the next heat treatment performed at a high temperature, a reaction takes place that consumes an excessive amount of oxygen to form a defective point. Because of this, high strength cannot be obtained. A more preferable stabilization treatment time is 40 to 80 minutes.

In the case where the density of a stabilized fiber is less than 1,335 g / cm3, a stabilization treatment is insufficient. In the next heat treatment performed at a high temperature, a decomposition reaction takes place to form a defective point. Because of this, high strength cannot be obtained. If the density of a stabilized fiber exceeds 1,360 g / cm3, the fiber's oxygen content increases. In the next heat treatment performed at a high temperature, a reaction takes place that consumes an excessive amount of oxygen to form a defective point. Because of this, high strength cannot be obtained. A more preferable density range of a stabilized fiber is 1,340 to 1,350 g / cm3.

An appropriate extension of a fiber that is performed in an oven is required for stabilization in order to maintain and improve the degree of orientation of a structure of fibrils that constitute a fiber. If the extension is less than 0%, the degree of orientation of a fibril structure cannot be maintained; the degree of orientation along the fiber axis is not sufficient to form a carbon fiber structure; can not

Develop excellent mechanical performance. On the contrary, if the extension exceeds 10%, the fibril structure itself will break, with the result that the formation of a carbon fiber structure will be affected and the fracture point will change to a defective point. As a result, a carbon fiber that has a high strength cannot be obtained. A more preferable extension rate is 3 to 8%.

Next, a stabilized fiber is passed through a first carbonization furnace of an inert atmosphere such as nitrogen having a temperature gradient of 300 to 800 ° C, while extending it from 2 to 7% . A preferable processing temperature is 300 to 800 ° C and the stabilized fiber is processed under linear temperature gradient conditions. Taking into account the temperature in the stabilization treatment stage, the initiation temperature is preferably 300 ° C or more. If the highest temperature exceeds 800 ° C, the fiber that is processed becomes very fragile and the next stage is difficult to operate. A more preferable temperature range is 300 to 750 ° C. The temperature gradient is not particularly limited; however, a linear gradient is preferably used.

If the extension rate is less than 2%, the orientation of a fibril structure cannot be maintained and the degree of orientation along the fiber axis in the formation of a carbon fiber structure will not be sufficient, with the result that excellent mechanical performance cannot be developed. On the contrary, if the extension rate exceeds 7%, the fibril structure itself is broken, with the result that the formation of a carbon fiber structure will be affected and a fracture point will change to a defective point. As a result, a carbon fiber that has a high strength cannot be obtained. A more preferable extension rate is 3 to 5%.

In the first carbonization furnace, a preferable heat treatment time is 1.0 to 3.0 minutes. If the treatment time is less than 1.0 minute, the temperature will rise steeply, and this will be accompanied by a severe decomposition reaction. As a result, a carbon fiber that has a high strength cannot be obtained. If the treatment time exceeds 3.0 minutes, a plasticizing effect will occur in the previous stage, with the result that the degree of orientation of a crystal will tend to decrease. As a result, the mechanical performance of the resulting carbon fiber will be affected. A more preferable heat treatment time is 1.2 to 2.5 minutes.

In addition, the stabilized fiber is subjected to a second carbonization furnace that has an inert atmosphere such as nitrogen that has a temperature gradient of 1000 to 1600 ° C and is treated under heat under tension to obtain a carbon fiber. In addition, if necessary, the carbon fiber is optionally subjected to a third carbonization furnace that has a desired temperature gradient and is heat treated in an inert atmosphere under tension.

The temperature for the carbonization treatment is determined depending on the desired modulus of elasticity of a carbon fiber. In order to obtain a carbon fiber having a high strength property, the highest temperature of the carbonization treatment is preferably low. In addition, the modulus of elasticity can be increased by increasing the treatment time. As a result, the highest temperature can be reduced. In addition, the temperature gradient can be adjusted so that it changes gradually by increasing the treatment time. This is effective in suppressing the formation of defective points. The temperature of the second carbonization furnace varies depending on the temperature of the first carbonization furnace; however, the temperature is acceptable provided there is a temperature of 1000 ° C or more and preferably 1050 ° C or more. The temperature gradient is not particularly limited; however this is preferably adjusted to change linearly.

In the second carbonization furnace, the heat treatment time is preferably 1.3 to 5.0 minutes and more preferably 2.0 to 4.2 minutes. In heat treatment, the fiber contracts significantly during processing. Therefore, it is important to perform a heat treatment under tension.

An extension rate is preferably from –6.0 to 0.0%. If the extension rate is less than –6.0%, the orientation of a crystal in the direction of the fiber axis is not satisfactory and sufficient performance cannot be obtained. On the contrary, if the extension rate exceeds 0.0%, the structure formed so far is broken and defective points are formed significantly, with the result that the resistance is significantly reduced. More preferably, the extension rate ranges from –5.0% to –1.0%.

Next, the carbon fiber bundle is subjected to a surface oxidation treatment. Examples of the surface treatment method include known methods, that is, oxidation treatments such as electrolytic oxidation, chemical oxidation and air oxidation. Any one of these methods can be used. The electrolytic oxidation treatment widely used at industrial level is preferred because a surface oxidation treatment can be stably performed. Furthermore, to control the value of ipa, which represents a preferable state of surface treatment in the present invention, such that the value of ipa falls within the range mentioned above, the simplest method is to perform the Electrolytic oxidation treatment while varying the electrical quantity. In this case, even if the electrical quantity is the same, the value of ipa varies significantly depending on the electrolyte and its concentration.

be used In the present invention, the electrolytic oxidation treatment can preferably be carried out in an aqueous alkaline solution of pH> 7 with a carbon fiber as an anode while supplying an electrical amount of 10 to 200 coulombs / g. By using an oxidation treatment, the ipa value of 0.05 to 0.25 µA / cm2 can be obtained. Examples of electrolyte that is preferably used include ammonium carbonate, ammonium bicarbonate, calcium hydroxide, sodium hydroxide and potassium hydroxide.

Next, the carbon fiber bundle of the present invention is subjected to a sizing treatment. The sizing agent is dissolved in an organic solvent or dispersed in water with the help of an emulsifier to prepare an emulsion solution. The above preparation is applied to a carbon fiber beam according to a roller immersion method, a roller contact method, etc. Subsequently, the carbon fiber beam is dried. In this way, a gluing treatment can be performed. Note that the amount of the sizing agent bonded to the surface of a carbon fiber can be controlled by controlling the concentration of the sizing agent solution and the amount of pressure application thereof. In addition, drying can be done by using hot air, a hot plate, a heating roller and various infrared heaters.

The most preferred sizing agent composition to be applied to the surface of the carbon fiber of the present invention is a urethane modified epoxy resin, which is a reaction product of (a) an epoxy resin containing a hydroxy group ( referred to hereinafter, appropriately, as a component (a)), (b) a polyhydroxy compound (referred to hereinafter, appropriately, as a component (b)) and (c) a diisocyanate containing an aromatic ring (referred to hereinafter, appropriately, as a component (c)). In addition, a mixture of an epoxy resin modified with urethane is mentioned, which is a reaction product that is obtained by introducing a larger amount of component (a) than is required for a reaction system, and the component (a) left. In addition, a mixture of an epoxy resin modified with urethane is mentioned which is obtained by using an epoxy resin having no hydroxy group (referred to hereinafter, appropriately, as the component (d)) and component (d). Likewise, a mixture of an epoxy resin modified with urethane, component (a) and component (d) is mentioned.

An epoxy group has a very strong interaction with an oxygen-containing functional group present on a carbon fiber surface and, thus, can strongly allow a sizing agent component to adhere to the carbon fiber surface. In addition, because a urethane bonding unit is contained, which is produced from a polyhydroxy compound and a diisocyanate containing an aromatic ring, flexibility and strong interaction with a carbon fiber surface can be imparted due to the polarity of a urethane bond and an aromatic ring. Accordingly, the urethane modified epoxy resin having an epoxy group and the above urethane bonding unit is a compound that is capable of bonding strongly to a carbon fiber surface and that has flexibility. In other words, such a sizing agent composition forms a flexible interface layer that adheres strongly to a carbon fiber surface. Therefore, the mechanical performance of the composite material obtained by impregnating a carbon fiber with a matrix resin and inserting the resin can be improved.

Component (a) is not particularly limited, and the number of hydroxy groups that are contained in component (a) is not limited. For example, glycidol, methyl glycidol, epoxy resin F of bisphenol type, epoxy resin A of bisphenol type and glycidyl ester epoxy resin of oxycarboxylic acid can be used. A particular preferable resin is a bisphenol-type epoxy resin. Because these resins have an aromatic ring, they interact strongly with a carbon fiber surface. Furthermore, in view of thermal resistance and stiffness, an epoxy resin having an aromatic ring is often used as the matrix resin in a composite material. This is because the compatibility with such a matrix resin is excellent. As component (a), two or more types of epoxy resins can be used.

In addition, component (b) is preferably constituted by any one of an addition product of bisphenol A with an alkylene oxide, an aliphatic polyhydroxy compound and a polyhydroximonocarboxy compound

or a mixture of these. This is because these compounds can soften urethane modified epoxy resins that have been mentioned above. Specific examples thereof include an addition product of bisphenol A with 4 to 14 moles of ethylene oxide, an addition product of bisphenol A with 2 to 14 moles of propylene oxide, an addition product of bisphenol A with ethylene oxide block copolymer -

propylene oxide, polyethylene glycol, trimethylolpropane and dimethylolpropionic acid.

In addition, component (c) is not particularly limited and a particular preferable component is toluene diisocyanate or xylene diisocyanate.

In addition, an epoxy resin that serves as component (d) is not particularly limited. Preferably, an epoxy resin having two or more epoxy groups in a molecule is used. This is because the surface of a carbon fiber interacts strongly with an epoxy group and, thus, these compounds adhere strongly to the surface. The type of epoxy group is not particularly limited and can be used

a glycidyl type, an alicyclic epoxy group, etc. Examples of preferable epoxy resin that can be used include an epoxy resin F of the bisphenol type, an epoxy resin A of the bisphenol type, an epoxy resin of the novolak type, an epoxy resin of the dicyclopentadiene type (Epiclon HP-7200 series: manufactured by DIC Corporation ), tris (hydroxyphenyl) methane epoxy resin (Epicoat 1032H60, 1032S50: manufactured by Japan Epoxy Resins Co., Ltd.), DPP Novolak epoxy resin (Epicoat 157S65, 157S70: manufactured by Japan Epoxy Resins Co., Ltd .) and epoxy resin with added alkylene oxide and bisphenol A.

In the manufacture of the mixture containing the component (d), when the component (a), the component (b) and the component (c) are reacted, the component (d) can be added simultaneously with the component (to). Alternatively, after completion of the urethane reaction, component (d) can be added. As a dispersion of water containing these compounds, HYDRAN N320 (manufactured by DIC) is mentioned.

The carbon fiber bundle of the present invention having an elastic modulus of 250 GPa or more is obtained through a carbonization process that is performed at a relatively high temperature. Therefore, it is beneficial that the carbon fiber is obtained from a precursor fiber that contains as few impurities, such as a metal, as possible. The amount of metal content in the resulting carbon fiber bundle is preferably small. In particular, the total amount of metal components including an alkali metal, alkaline earth metal, zinc, iron and aluminum is preferably 50 ppm or less. These metals react with carbon, melt or vaporize at a temperature beyond 1000 ° C, and this is one reason why defective spots are formed. An extremely strong carbon fiber cannot be manufactured.

Examples

In the following, the present invention will be described in detail by way of examples. Note that the performance of a carbon fiber beam in the examples was measured and evaluated according to the following method.

<1. Measurement of non-uniform surface structure of individual fiber>

The non-uniform surface structure can be measured based on the surface shape as follows: Several individual fibers of a bundle of carbon fibers were placed on a sample holder and immobilized at both ends. In addition, Dotite was applied around the fibers to prepare a measurement sample. A 1000 nm range in the circumferential direction of an individual fiber was scanned by an atomic force microscope (SPI3700 / SPA-300 (trade name) manufactured by Seiko Instruments Inc.) using a cantilever beam formed of silicon nitride , in an AFM mode at the same time as it was slowly sliding over a distance of 1000 nm in the direction of the fiber axis. From the resulting measured image, a low frequency component was separated according to a two-dimensional Fourier transform and, after the above, underwent an inverse transformation. From the planar image resulting from a cross-section from which the curvature of the individual fiber was removed, an area range surrounded by a length of 1.0 µm in the circumferential direction of fiber and a length of fiber was selected. 1.0 µm in the direction of the fiber axis and the difference in height between the highest portion and the lowest portion was read, and Ra is obtained by performing a calculation according to the following expression (2) .

Ly LX

Ra = {1 / (Lx  Ly)} · ∫ 0∫ 0 | f (x, y) | dxdy… (2)

"Central surface": A plane that is parallel to the plane that has a minimum deviation from the height from the place to the real surface and that divides the real surface equally in two based on the volume. In other words, the portion that is surrounded by the plane and the actual surface, the volumes V1 and V2 that are correspond to both side portions of the plane are equal to each other. “F (x, y)”: Difference in height between the actual surface and the central surface, "Lx, Ly": Size of the XY plane.

In addition, when an atomic force microscope was used to take measurements, the presence or absence of a non-uniform structure of a length of 0.6 µm or more and the length of a non-structure was measured uniform of a length of 300 nm or less.

<2. Evaluation of an individual fiber cross-sectional shape>

The ratio of the major axis and the minor axis (major axis / minor axis) of the cross section of the individual fibers constituting a bundle of carbon fibers was determined as follows: A beam of carbon fibers for measurement was passed to through a tube formed of a vinyl chloride resin having an inner diameter of 1 mm. The tube was cut in a circle by means of a knife to prepare samples. Subsequently, each sample was allowed to adhere to an SEM sample holder such that the cross section was facing up; Au was deposited at a thickness of approximately 10 nm by atomic bombardment metallization; and a fiber cross section was observed by a

scanning electron microscope (product name: XL20, manufactured by Philips) under the following conditions: an acceleration voltage of 7.00 kV and a migration distance of 31 mm to measure the major axis and minor axis of the cross section of the individual fiber.

<

 3. Evaluation of physical properties of carbon fiber beam rope>

The preparation of a test sample of a carbon fiber bundle impregnated with a resin and the measurement of the resistance of the sample were carried out in accordance with JIS R7601. However, the modulus of elasticity was calculated in the deformation range according to the ASTM standard.

<

 4. Measurement of carbon fiber beam knot toughness>

The knot toughness was measured as follows: At both ends of a bundle of carbon fibers of a length of 150 mm, a grip portion of a length of 25 mm was attached to prepare a test sample. When preparing the test sample, a load of 0.1 × 10–3 N / denier was applied to dispose, unidirectionally, carbon fiber bundles. In the test sample, a single knot formed almost in the center. The tension was performed at a crosshead rate of 100 mm / min. Twelve beams were used for a test. The smallest value and the largest value were eliminated and the average value of 10 beams was obtained and used as a measurement value.

<

 5. Evaluation of “surface energy of the surface formed by fracture” of carbon fiber beam>

An individual carbon fiber was cut into pieces in the length of 20 cm. Each of the individual fiber pieces was allowed to adhere and immobilize on a frame for a tensile test for an individual fiber of a 10 mm sample length shown in JIS R7606. An additional extruded portion was cut and removed from the mount. In this way, samples were prepared.

Next, these samples that were attached to the mount were irradiated with a laser to obtain a hemispherical defect. As a laser interface system, a MicroPoint (300 µJ pulse energy) manufactured by Photonic Instruments Co., Ltd was used. As the optical microscope that is required to make the laser light converge, an ECLIPSE LV100 was used manufactured by Nikon. The opening stop of the optical microscope was set to a minimum and an objective lens was set 100 times. Under the conditions, a laser (an impulse) having a wavelength of 435 nm, the intensity of which was attenuated by 10% by an attenuator, was applied to the center of a sample in the direction of the fiber axis and in the perpendicular direction of the fiber axis to form a hemispherical defect.

To avoid a contraction breakage of a sample carbon fiber, the sample that was attached to a mount was additionally intercalated by films and the space inside the films was loaded with a viscous liquid and then subjected to a tensile test To give a more specific description, a film of a width of approximately 5 mm and a length of approximately 15 mm was prepared and allowed to adhere to the upper portion of both surfaces of the sample frame with an adhesive and intercalated with In order to wrap the sample including the frame. The space inside the film was loaded with a solution of aqueous glycerin (glycerin: water = 1: 2). A tensile test was performed at a tension rate of 0.5 mm / min to measure the breaking load.

Next, a sample of a pair of pieces, which was divided into two pieces in the tensile test, was removed from the mount, carefully washed with water and dried naturally. Subsequently, a sample piece was immobilized on a support of SEM samples with carbon paste so that the fracture was in an upward-facing position to enable the preparation of a sample for SEM observation. The fracture surface of the sample obtained for SEM observation was observed by SEM, that is, a JSM6060 (acceleration voltage: from 10 to 15 kV, increase: from 10,000 to 15,000) manufactured by JEOL Ltd.

The SEM image obtained was imported into a personal computer and analyzed by image analysis software. In this way, the size of a hemispherical defect and the cross-sectional area of a fiber were measured.

Next, the tensile strength (σ) (cross-sectional area of rupture / fiber load) and the size of a hemispherical defect (C) were plotted. The slope of the data was obtained.

σ = (2E / πC) 1/2  (surface surface energy formed by fracture) 1/2… (1)

According to equation (1), the surface energy of the surface formed by fracture was obtained from the slope and the ultrasonic elastic modulus (E) of a carbon fiber beam.

<6. Measurement of carbon fiber beam ipa>

An Ipa value was measured by the following method. An electrolyte is adjusted to pH 3 with a 5% aqueous phosphoric acid solution and bubbled with nitrogen to eliminate the effect of dissolved oxygen. A sample carbon fiber was immersed in the electrolyte as one of the electrodes, while a platinum electrode having a sufficient surface area is used as the other electrode. In this document, as an reference electrode, an Ag / AgCl electrode was used. A sample of a 12000 filament continuous filament tape having a length of 50 mm was formed. The potential to be applied between the carbon fiber electrode and the platinum electrode varies from –0.2 V from + 0.8 V and its scanning speed was adjusted to be 2.0 mV / s . A current-voltage curve was drawn using an X-Y recording device. After the scan was performed three times or more to obtain a stable curve, a current value i was read with a potential of + 0.4 V applied to the Ag / AgCl reference electrode that was used as a reference potential, and a value of ipa was calculated according to the following expression (3).

ipa = 1 (μA) / sample length (cm)  {4π  weight per unit area (g / cm) 

number of filaments / density (g / cm3)} ½… (3)

The apparent surface area was calculated from the sample length, the sample density obtained by the method described in JIS R7601 and the mass per unit area. The current value i was divided by the value obtained to obtain a value of ipa. The measurement was performed using a cyclic voltammetry analyzer Type P – 1100 manufactured by Yanagimoto Mfg. Co., Ltd.

<7. Si quantity measurement of carbon fiber bundles>

A sample of a bundle of carbon fibers was placed in a platinum crucible whose tare was known and calcified in a 600 to 700 ° C muffle furnace. Its mass was measured to obtain the ash content. Subsequently, a previously determined amount of sodium carbonate was added, and the mixture was melted by a burner and dissolved with deionized water in a 50 ml polymetering flask. The sample was measured by ICP emission spectrometry to determine the amount of Si.

(Examples of production 1 to 7 of precursor fiber bundle)

Precursor Fiber (1)

An acrylonitrile-based polymer containing acrylonitrile (98% by mass) and methacrylic acid (2% by mass) was dissolved in dimethylformamide to prepare a 23.5% mass by mass. The spinning mass was ejected from a spinning nozzle having a diameter of 0.15 mm with 2000 ejection holes arranged therein in a dry-wet spinning type. To give a more specific explanation, the spinnable mass was ejected into the air, passed through a space of approximately 5 mm and then solidified in a coagulated liquid charged with an aqueous solution containing 79.0 dimethyl formamide. % by mass and monitored at a temperature of 10 ° C to obtain a coagulated fiber. Subsequently, the coagulated fiber was stretched (1.1 times) in the air and stretched (2.5 times) in a stretching tank loaded with an aqueous solution containing 35% dimethyl formamide by mass and controlled at 60 ° C . After the stretching process, the fiber bundle in which a solvent was present was washed with clean water and then stretched (1.4 times) in hot water at 95 ° C. Sequentially, an oil solution containing an amino modified silicone as a major component was applied to the fiber bundle in order to apply 1.1% by mass, dried and densified. After the drying and densification stage, the fiber bundle was stretched (2.6 times) between heated cylinders to further improve the degree of orientation and densification. After the above, the beam was rolled to obtain a bundle of acrylonitrile-based precursor fibers. The fiber denier was 0.77 dtex.

Precursor Fiber (2)

The precursor fiber bundle (2) was obtained under the same conditions as in the precursor fiber bundle (1) except that the stretch ratio before washing with water was adjusted to be 2.9 times and the Stretch ratio in hot water after washing was adjusted to be 1.2 times.

Precursor Fiber (3)

The precursor fiber bundle (3) was obtained under the same conditions as in the precursor fiber bundle (2) except that the denier of the precursor fiber was adjusted to be 0.67 dtex.

Precursor Fiber (4)

The precursor fiber bundle (4) was obtained under the same conditions as in the precursor fiber bundle (2) except that the denier of the precursor fiber was adjusted to be 0.90 dtex. 5 Precursor fiber (5)

The precursor fiber bundle (5) was obtained under the same conditions as in the precursor fiber bundle (1) except that the stretching ratio before washing with water was adjusted to be 4.1 times, The stretching ratio in hot water after washing was adjusted to be 0.9 times and the stretching that was performed between heated cylinders was adjusted to be 2.4 times.

Precursor Fiber (6)

The precursor fiber bundle (6) was obtained under the same conditions as in the precursor fiber bundle (1) except that the stretch ratio before washing with water was adjusted to be 1.9 times and The stretching ratio in hot water after washing was adjusted to be 2.0 times.

Precursor Fiber (7)

The precursor fiber bundle (7) was obtained under the same conditions as in the precursor fiber bundle (2) except that the denier of the precursor fiber was adjusted to be 1.0 dtex. The manufacturing conditions for the precursor fiber bundles (1) to (7) are shown in Table 1.

(Examples 1 to 7, Comparative Examples 1 to 4)

(Preparation of carbon fiber beam)

A plurality of precursor fiber bundles (1), (2), (3), (4), (5), (6) or (7) were arranged in parallel and placed in a furnace for stabilization. Heated air at 220 to 280 ° C was sprayed into the precursor fiber bundles to perform a stabilization treatment. In this way, stabilized fiber bundles having a density of 1,345 g / cm3 were obtained. The extension rate was adjusted to be 6% and the stabilization treatment time was 70 minutes.

Next, the stabilized fiber bundles were passed through a first carbonization furnace having a temperature gradient of 300 to 700 ° C in nitrogen while the extension rate was increased by 4.5%. The temperature gradient was adjusted in order to change linearly. The treatment time was 2.0 minutes. In addition, a heat treatment was performed using a second carbonization furnace having a nitrogen atmosphere in which the temperature gradient of 1000 to 1600 ° C could be adjusted, to the previously determined temperatures shown in Table 2 or Table 3. Subsequently, a heat treatment was performed using a third carbonization furnace that has a nitrogen atmosphere in which the temperature gradient of 1200 to 2400 ° C could be adjusted, to the previously determined temperatures shown in table 2 or table 3 to obtain beams of carbon fibers. The total extension rate of the fiber bundles through the treatments in the second carbonization furnace and the third carbonization furnace was -4.0%, and the total treatment time was adjusted to be 3 ,5 minutes. Subsequently, the fiber bundles were fed into a 10% mass aqueous ammonium bicarbonate solution. Current was supplied between a bundle of carbon fibers that serves as an anode and a counterpolar in order to obtain an amount of electricity of 40 coulombs per carbon fiber (1 g) to be treated. Next, the fiber bundles were washed with hot water at 90 ° C and dried. Next, Hydran N320 (referred to hereinafter as "sizing agent 1") was attached to the fiber bundles in the amount of 0.5% by mass and rolled up by means of a coil to obtain a beam of carbon fibers.

(Preparation of unidirectional prepreg)

On a mold release paper coated with epoxy resin No. 410 (which can be used at 180 ° C) [manufactured by Mitsubishi Rayon Co., Ltd.] in phase B, 156 bundles of carbon fibers released from one coil and passed through a hot compression roller. In this way, the carbon fiber bundles were impregnated with epoxy resin. A protective film was laminated on the resulting beams to prepare a prepreg arranged unidirectionally (referred to hereinafter as a "prepreg of UD") having a resin content of approximately 33% in mass, a mass of carbon fiber per unit area of 125 g / m2 and a width of 500 mm.

(Molding of a laminate board and evaluation of mechanical performance)

A laminated material board was prepared by using the prepreg of UD and the tensile strength of the laminated material board with an angle of 0 ° was evaluated by the evaluation method in accordance with ASTM D3039. The manufacturing conditions for a carbon fiber beam and the evaluation results are shown in Table 2 and Table 3. Note that it was confirmed that, in any of the examples, an individual fiber does not have a non-uniform surface structure. having a length of 0.6 µm or more and extending in the longitudinal direction of a fiber but having a microscopic non-uniform structure that is 300 nm or less in length.

[Table 2]

(Production example 8 of precursor fiber bundle)

A spinning mass, which was prepared in the same way as in production example 1, was ejected from a spinning nozzle having a diameter of 0.13 mm with 2000 ejection holes arranged therein in a 5 Dry spinning type - wet. To give a more specific explanation, the spinnable mass was ejected into the air, passed through a space of approximately 5 mm and then solidified in a coagulated liquid charged with an aqueous solution containing 77.0 dimethyl formamide. % by mass and monitored at a temperature of 5 ° C to obtain a coagulated fiber. Subsequently, the coagulated fiber was stretched (1.3 times) in the air and stretched (2.0 times) in a stretching tank loaded with a controlled aqueous solution at 60 ° C. After the stretching process, the fiber bundle in which a solvent was present was washed with clean water and then stretched (2.0 times) in hot water at 95 ° C. Sequentially, to the fiber bundle, an oil solution containing an amino-modified silicone as a main component was attached, in order to apply 1.0% by mass, dried and densified. After the drying and densification stage, the fiber bundle was stretched (1.9 times) between heated cylinders to further improve the degree of orientation and

15 densification. After the above, the beam was rolled to obtain the precursor fiber bundle. The fiber denier was 0.77 dtex.

(Example 8)

A carbon fiber bundle was prepared under the same carbonization conditions as in Example 5 except that the third carbonization furnace was not used. In addition, a laminate board was prepared in the same way and the mechanical performance was evaluated to obtain the results shown in Table 2. Note that it was confirmed that the individual fiber has no non-uniform surface structure of any length having a length 0.6 µm or more and that extends in the longitudinal direction of the fiber and has a structure

25 microscopic non-uniform having a length of 300 nm or less.

(Examples 9 to 11, Comparative Examples 6 to 8)

Beams of carbon fibers were obtained in the same manner as in Example 2 except that the

30 carbonization conditions. The results of the evaluation are shown in Table 4. Note that, in any one of the examples, it was confirmed that the individual fiber does not have any non-uniform surface structure that is 0.6 µm or more in length and extends in the longitudinal direction of the fiber and has a non-uniform microscopic structure that is 300 nm or less in length.

35 [Table 4]

(Examples 12 and 13)

Beams of carbon fibers were obtained in the same manner as in Example 5 except that the surface treatment conditions were changed. The results of the evaluation are shown in Table 5. Note that, in any of the examples, it was confirmed that the individual fiber does not have any non-uniform surface structure that is 0.6 µm or more in length and extends in the longitudinal direction of the fiber and has a non-uniform microscopic structure that is 300 nm or less in length.

(Examples 14 to 16)

Beams of carbon fibers were obtained in the same manner as in Example 5 except that the linked types and amounts of sizing agents were changed. The results of the evaluation are shown in Table 5. Note that in any one of the examples, it was confirmed that the individual fiber does not have any non-uniform surface structure that is 0.6 µm or more in length and extends in the longitudinal direction of the fiber and has a non-uniform microscopic structure that is 300 nm or less in length. Note that, the sizing agent 2, the sizing agent 3 and the sizing agent 4 were prepared as follows:

(Sizing agent 2)

“Epicoat 828” (80 parts by mass) manufactured by Japan Epoxy Resins Co., Ltd. was mixed as a main agent and “Pluronic F88” (20 parts by mass) manufactured by ADEKA Corporation as an emulsifier to obtain an aqueous dispersion by phase transfer emulsion.

(Sizing agent 3)

In a flask, polyol (3.2 moles) consisting of 1.8 moles of a bisphenol A addition product with 8 moles of propylene oxide, 0.8 moles of trimethylolpropane and 0.6 moles of dimethylolpropionic acid were placed . In addition, 0.5 g of 2,6-di (t-butyl) 4-methylphenol (BHT) was added as a reaction inhibitor and 0.2 g of dibutyltin dilaurate as a reaction catalyst and stirred until it was obtained a homogeneous mixture. Here, if necessary, methyl ethyl ketone was added as a viscosity moderator. To the homogeneously dissolved mixture, methaxylene diisocyanate (3.4 mol) was added dropwise and polymerization of a urethane prepolymer was carried out while stirring at a reaction temperature of 50 ° C for a reaction time 2 hours Next, Epicoat 834 (manufactured by JER) (0.25 mol) was added and reacted with an isocyanate group at one end of the urethane prepolymer to obtain an epoxy modified urethane resin. The epoxy modified urethane resin (90 parts by mass) and "Pluronic F88" (10 parts by mass) manufactured by ADEKA Corporation were mixed as an emulsifier to prepare an aqueous dispersion.

(Sizing agent 4)

In a flask, polyethylene glycol 400 (2.5 moles) and Epicoat 834 (manufactured by JER) (0.7 moles) were placed and 2,6-di (t-butyl) 4-methylphenol (BHT) (0 , 25 g) as a reaction inhibitor, and dibutyltin dilaurate (0.1 g) as a reaction catalyst. The mixture was stirred until it became homogeneous. Here, if necessary, methyl ethyl ketone was added as a viscosity moderator. To the homogeneously dissolved mixture, a methaxylene diisocyanate (2.7 mol) was added dropwise. The reaction was carried out at a temperature of 40 ° C for 2 hours while stirring to obtain an epoxy modified urethane resin. The epoxy modified urethane resin (80 parts by mass) and Pluronic F88 (20 parts by mass) manufactured by ADEKA Corporation were mixed as an emulsifier to prepare an aqueous dispersion.

[Table 5]

Susceptibility of industrial application

The carbon fiber beam of the present invention can be used as a building material for airplanes and bodies moving at high speed.

Claims (10)

one.

A bundle of carbon fibers formed of individual carbon fiber: each individual carbon fiber not having any non-uniform surface structure having a length of 0.6 µm or more and extending in the longitudinal direction of the individual fiber, having each individual carbon fiber a non-uniform structure in which the difference in height (Rp - v) between a portion that is the highest and a portion that is the lowest of the surface of the individual fiber is 5 to 25 nm, and in the that an average roughness Ra is from 2 to 6 nm, and each of which has a ratio of 1.00 to 1.01 of a major axis with respect to a minor axis (major axis / minor axis) of a cross section of the individual fiber; wherein a mass of the individual fiber per unit length falls within the range of 0.030 to 0.042 mg / m; a measured resistance according to JIS R7601 is 5900 MPa or more; a modulus of elasticity of rope measured by the ASTM method is 250 to 380 GPa; and a knot toughness is 900 N / mm2 or more.

2.

A bundle of carbon fibers according to claim 1, wherein the non-uniform structure is 300 nm or less in length.

3.

The carbon fiber beam according to claim 1 or 2, wherein a hemispherical defect having a size within a previously determined range is formed on a single fiber surface by means of a laser, the fiber is broken at the site hemispherical defect by means of a tensile test, and the “surface energy of the surface formed by fracture” that is obtained from the resistance to breakage of the fiber and the size of the hemispherical defect according to the Griffith equation (1) it is 30 N / m or more, where σ is a breaking strength; E is a module of ultrasonic elasticity of a bundle of carbon fibers; and C is a size of a hemispherical defect.

σ = (2E / πC) 1/2  (surface surface energy formed by fracture) 1/2… (1)

Four.

The carbon fiber beam according to any one of claims 1 to 3, wherein an ipa value that is obtained by an electrochemical measurement method (cyclic voltammetry) is 0.05 to 0.25 µA / cm2, and an amount of an oxygen-containing functional group (O1S / C1S) on a carbon fiber surface that is obtained by X-ray photoelectronic spectroscopy falls within the range of 0.05 to 0.15.

5.

The carbon fiber beam according to any one of claims 1 to 4, wherein an amount of Si measured by ICP emission spectrometry is 200 ppm or less.

6.

The carbon fiber bundle according to any one of claims 1 to 5, glued by a sizing agent composition comprising a urethane modified epoxy resin, which is a reaction product of (a) an epoxy resin having a hydroxy group, (b) a polyhydroxy compound and (c) a diisocyanate containing an aromatic ring, or glued by a sizing agent composition comprising a mixture of the urethane modified epoxy resin and (a) an epoxy resin which it has a hydroxy group and / or (d) an epoxy resin that has no hydroxy group.

7.

The carbon fiber bundle according to claim 6, wherein (a) the epoxy resin having a hydroxy group is a bisphenol-type epoxy resin.

8.

The carbon fiber bundle according to claim 6 or 7, wherein (b) the polyhydroxy compound is any one of an addition product of a bisphenol A with an alkylene oxide, an aliphatic polyhydroxy compound and a monocarboxy polyhydroxy compound or a mixture thereof.

9.

The carbon fiber bundle according to any one of claims 6 to 8, wherein (c) the diisocyanate containing an aromatic ring is toluene diisocyanate or xylene diisocyanate.

10.

The carbon fiber beam according to any one of claims 1 to 9, wherein a total metal content including an alkali metal, an alkaline earth metal, zinc, iron and aluminum is 50 ppm or less.