JP2023043149A - Carbon fiber composite material - Google Patents

Abstract

To provide a carbon fiber composite material that can improve impact resistance.SOLUTION: A carbon fiber composite material includes: a carbon fiber having the strand strength of 7.5 to 8.5 GPa, the elongation of 2.65 to 3.20%, and the single fiber diameter of 4.0 to 6.0 μm; and an epoxy resin composition having amine type epoxy resin [A], thermoplastic resin [B] which dissolves into epoxy resin, and epoxy resin curing agent [C], where the degree of cure of the epoxy resin composition is 90% or more, and the storage elastic modulus of a cured product of the epoxy resin at 275°C when the cured product is heated at the speed of 5°C/min. by using a dynamic viscoelasticity measuring apparatus according to SACMA SRM 18R-94, and measured at the torsional mode of 1.0 Hz is 1 to 10 MPa. The carbon fiber composite material can improve impact resistance.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a high elongation carbon fiber composite material obtained by combining high elongation carbon fiber excellent in energy absorption and an epoxy resin composition that maximizes its performance.

Polyacrylonitrile-based carbon fiber is a lightweight material with high strength and high elastic modulus, and is an indispensable material for weight reduction of members. Also, the deformation of the carbon fiber is characterized by elastic deformation without plastic deformation. Therefore, carbon fibers have the advantage of having a wider usable elongation range than metals with large plastic deformation.

In recent years, carbon fiber composite materials are sometimes required to have both lightness and impact resistance. In order to meet this demand, compositional design of the resin used for the matrix and sizing agents for changing the interfacial properties between the carbon fiber and the matrix resin are being studied.

Attempts have been made to improve the strand strength or strand elongation of carbon fibers. In Patent Document 1, a carbon fiber having a maximum strand strength of 9.0 GPa (Example 8) is obtained by reducing defects by reducing the fineness of the precursor fiber. Similarly, in Patent Document 2, carbon fibers with a maximum strand strength of 8.0 GPa (Example 14) and an elongation of 2.60% (Comparative Examples 4 and 5) were obtained by reducing the fineness of precursor fibers and then drawing them. ing. In Patent Document 3, a carbon fiber having a maximum strand strength of 8.4 GPa (Example 3) is obtained by increasing the fracture toughness value of the carbon fiber. In Patent Document 4, a carbon fiber having a maximum elongation of 2.68% (Example 15) is obtained by using a technique in which the strand strength does not easily decrease even if the single fiber diameter of the carbon fiber is increased. In Patent Document 5, high elongation is aimed at by adjusting production conditions such as polymer, spinning, and flame resistance, and a carbon fiber with a maximum elongation of 2.36% (Example 1) is obtained. In Patent Document 6, with the aim of maximizing the elongation of the carbon fiber, the maximum temperature of the carbonization process is lowered to obtain carbon fibers with a maximum elongation of 2.60% (Example 4). there is Although Patent Document 7 describes obtaining carbon fibers with high strength and high elongation by adjusting the surface properties of the carbon fibers, the elongation of the carbon fibers is about 2.1%, and the high strength It was the general technical level of carbon fiber. In Patent Document 8, a carbon fiber (Example 4) having a maximum elongation of 2.71% is obtained by adding boron to the polymer.

Further, as a study to improve the impact resistance of a carbon fiber composite material, in Patent Document 9, a modifier is added to a thermoplastic resin that is a matrix.

In Patent Document 10, the impact resistance, tensile strength, and compressive strength of the carbon fiber composite material are enhanced by adjusting the rigidity of the rubber-like flat portion above the glass transition point. In Patent Document 11, the interlayer toughness and compressive strength in a high-temperature environment of the carbon fiber composite material are increased by adjusting the rigidity of the rubber-like flat portion above the glass transition point. In Patent Document 12, the compressive strength of the carbon fiber composite material is increased by adjusting the compressive yield stress of the cured resin. In Patent Document 13, carbon fiber having a specific single fiber strength and an epoxy resin composition having a specific composition are combined to increase the perforated plate tensile strength of a carbon fiber composite material.

JP-A-11-241230 WO2008/40963 JP 2017-137614 A WO 97/45576 JP 2008-163537 A JP-A-2005-256211 JP-A-2002-69754 JP-A-11-152626 JP 2018-59087 A Japanese Patent Application Laid-Open No. 2001-323046 WO2016/67736 Japanese Patent Application Laid-Open No. 2003-277471 WO2014/115762

However, the conventional techniques have the following problems.

In the technique of Patent Document 1, the single fiber diameter of the carbon fiber is small, the strain energy per single fiber is small, and the strand elastic modulus is high and the elongation is low. could not be ensured.

In the technique of Patent Document 2, the single fiber diameter of the carbon fiber is small, the strain energy per single fiber is small, and in addition, there is a problem that a satisfactory elongation is not obtained.

In the technique of Patent Document 3, there is a problem that a satisfactory elongation is not obtained, and since the strand elastic modulus is high, sufficient impact resistance cannot be ensured in a bending stress field.

With the technique of Patent Document 4, the level of strand strength and elongation is insufficient, and sufficient impact resistance cannot be ensured. Moreover, it was not assumed that both strand strength and elongation are achieved.

The technique of Patent Document 5 cannot ensure sufficient impact resistance.

In the technique of Patent Document 6, the strand elastic modulus level was too low and sufficient impact resistance could not be ensured.

In the technique of Patent Document 7, the elongation level was too low and sufficient impact resistance could not be ensured.

In the technique of Patent Document 8, although the elongation of the carbon fiber is increased, the strand strength is low for those with high elongation, and since there was no concept of strain energy density, it was assumed that the strand strength and elongation would be compatible. was not

Thus, there has been no carbon fiber that satisfies all of single fiber diameter, strand strength and elongation.

Further, in Patent Document 9, although the composition of the thermoplastic resin is designed for the impact resistance of the carbon fiber composite material, there is no mention of the mechanical properties of the carbon fiber itself.

In Patent Documents 10 to 12, although the mechanical properties of the cured epoxy resin are designed to maximize the mechanical properties of the existing carbon fiber, they do not focus on the elongation of the carbon fiber composite material. The elongation level was also not at a satisfactory level.

In Patent Document 13, although the perforated plate tensile strength of the carbon fiber composite material is improved not only by the single fiber strength of the carbon fiber but also by combining with a specific epoxy resin composition, the elongation of the carbon fiber composite material is not satisfactory. I wasn't at the level to do it.

An object of the present invention is to provide a carbon fiber composite material with improved impact resistance.

In order to achieve the above objects, the carbon fiber composite material of the present invention has a strand strength of 7.5 to 8.5 GPa, an elongation of 2.65 to 3.20%, and a single fiber diameter of 4.0 to 6.0%. 0 μm carbon fiber, an epoxy resin composition having an amine type epoxy resin [A], a thermoplastic resin soluble in the epoxy resin [B], and an epoxy resin curing agent [C], and The degree of cure is 90% or more, and the cured product of the epoxy resin was heated at a rate of 5° C./min using a dynamic viscoelasticity measuring device according to SACMA SRM 18R-94, and measured in a torsion mode of 1.0 Hz. The storage modulus at 275°C is 1-10 MPa.

By using the carbon fiber composite material of the present invention, the impact resistance represented by the strain energy density of the carbon fiber composite material can be improved.

In order to improve the impact resistance of carbon fiber composite materials, the inventors focused on the strain energy density of carbon fibers. The strain energy density is the area of a stress-strain curve obtained from a tensile property test of a resin-impregnated strand (hereinafter sometimes abbreviated as strand). However, since ^it is difficult to accurately calculate the nonlinearity, in the present invention, an approximate is the strain energy density. That is, the strand strength and elongation of carbon fibers are important. Since the strain energy density of the carbon fiber is large, it can be expected that the impact resistance of the resulting carbon fiber composite material will be improved.

The carbon fiber of the present invention has a strand strength of 7.5 to 8.5 GPa, preferably 7.8 to 8.5 GPa, more preferably 8.0 to 8.5 GPa. Strand strength is an index showing how difficult it is to break when a load is applied to carbon fibers. The strand strength of carbon fibers can be evaluated according to a tensile test of resin-impregnated strands described in JIS R7608:2004. If the strand strength is 7.5 GPa or more, it is easy to increase the strain energy density. There is no upper limit to the strand strength, but if it is 8.5 GPa, the strain energy density tends to be at a satisfactory level. Strand strength can be controlled by manufacturing according to the carbon fiber manufacturing method described later, such as defect suppression and fracture toughness improvement.

The carbon fiber of the present invention has an elongation of 2.65% or more, preferably 2.75% or more, more preferably 2.85% or more, and still more preferably 2.95% or more. The elongation of carbon fibers can be evaluated according to the tensile test of resin-impregnated strands described in JIS R7608:2004. It is difficult to measure the elongation of carbon fibers because the stress-strain curve exhibits nonlinearity, but in this tensile test, the elongation is calculated by dividing the above-mentioned strand strength by the strand elastic modulus. If the elongation is 2.65% or more, it is easy to increase the strain energy density. There is no upper limit to elongation, but as little as 3.20% is often sufficient to increase strain energy density. The elongation of the carbon fiber can be adjusted by controlling the manufacturing conditions of the carbon fiber so as to balance the strand strength and the strand elastic modulus.

The carbon fiber of the present invention has a single fiber diameter of 4.0 to 6.0 μm, preferably 4.5 μm or more, more preferably 5.0 μm or more, still more preferably 5.3 μm or more. Since the breaking load per single fiber is determined by the strand strength and single fiber cross-sectional area, the single fiber diameter affects the breaking load per single fiber. In addition, the larger the single fiber diameter, the higher the single fiber compressive strength of the carbon fiber, which tends to increase the energy absorption. Therefore, if the single fiber diameter is 4.0 μm or more, energy absorption tends to increase. If the upper limit of the single fiber diameter is 6.0 μm, sufficient impact resistance can be ensured in many cases. The single fiber diameter of carbon fibers can be calculated from the total fineness, density and number of filaments of carbon fibers. In addition, if the number of filaments is unknown, the carbon fiber is embedded in resin and the cross section is observed with an optical microscope. Fiber diameter can be evaluated. If the two measurement methods do not match, the former value is adopted. Single fiber diameter can be controlled by the diameter of the precursor fiber and the draw ratio in subsequent steps.

The carbon fiber of the present invention preferably has a strain energy density of 95 J/mm ³ or higher, more preferably 100 J/mm ³ or higher, and even more preferably 105 J/mm ³ or higher. If the strain energy density is 95 J/mm ³ or ^more , energy absorption is often sufficient, and there is no upper limit. sometimes The strain energy density can be adjusted by controlling the carbon fiber production conditions so as to achieve both strand strength and elongation.

The carbon fiber of the present invention preferably has a strand elastic modulus of 240 to 300 GPa, more preferably 250 to 290 GPa, still more preferably 250 to 280 GPa. The strand elastic modulus is an index that indicates the resistance to deformation of carbon fibers when a load is applied. The strand elastic modulus of carbon fibers can be evaluated according to the tensile test of resin-impregnated strands described in JIS R7608:2004. Although the stress-strain curve of carbon fiber exhibits downwardly convex nonlinearity, the strand elastic modulus in the strain range of 0.1 to 0.6% is used in the present invention. If the strand elastic modulus is 240 GPa or more, it is easy to increase the strain energy density. If the strand elastic modulus is 300 GPa or less, the carbon fiber has high compressive strength and high energy absorption. The strand elastic modulus can be controlled by the maximum temperature in the carbonization process, the heat treatment time at the maximum temperature, the heating rate, the stretching ratio, and the like.

The carbon fiber of the present invention preferably has a total fineness of 0.8 g/m or more, more preferably 0.9 g/m or more. The total fineness is the mass per 1m of carbon fiber bundle, and is related to the single fiber diameter and the number of filaments of the carbon fiber. The higher the total fineness, the easier it is to increase the productivity of the carbon fiber composite material. Therefore, if the total fineness is 0.8 g/m or more, a carbon fiber composite material with excellent impact resistance can be obtained with good productivity. A total fineness of 2.0 g/m or less is preferable because a carbon fiber composite material having an appropriate thickness can be obtained, and as a result, the impact resistance can be enhanced. The total fineness can be controlled by adjusting the single fiber diameter or the number of filaments, but if the number of filaments is too large, uniform production becomes difficult and the strand strength tends to decrease.

The carbon fibers of the present invention preferably have a density of 1.75-1.85 g/cm ³ . The higher the density of the carbon fibers, the finer the fine structure, and the higher the strand strength. Therefore, if the density is 1.75 g/cm ³ or more, energy absorption tends to be at a satisfactory level, and if it is 1.85 g/cm ³ or less, elongation is high and energy absorption is easily maintained at a high level. The lower limit of density is more preferably 1.78 g/cm ³ . The upper limit of density is more preferably 1.83 g/cm ³ . The density of the carbon fibers can be controlled by the drawing ratio and heating rate in the carbonization process.

Next, a carbon fiber production method suitable for obtaining the carbon fiber of the present invention will be described.

As an industrial production method for carbon fibers, polyacrylonitrile-based carbon fiber precursor fibers (hereinafter sometimes abbreviated as precursor fibers) are converted into flame-resistant fibers in an oxidizing atmosphere at 200 to 310°C. a carbonization step, a preliminary carbonization step of pre-carbonizing under an inert atmosphere of 500-1,200° C., and a carbonization step of carbonizing under an inert atmosphere of 1,000-1,500° C. are known. ing.

A polyacrylonitrile-based polymer is preferably used as the raw material for the production of the precursor fiber. In the present invention, the polyacrylonitrile-based polymer is a polymer in which at least acrylonitrile accounts for 90 to 100 mol % of the polymer. In the production of the precursor fiber, the polyacrylonitrile-based polymer preferably contains a copolymer component from the viewpoint of improving strand strength. As a monomer that can be used as a copolymerization component, a monomer containing one or more carboxylic acid groups or amide groups is preferably used from the viewpoint of promoting flame resistance.

In producing the precursor fiber, either a dry-wet spinning method or a wet-spinning method may be used, but it is preferable to use the dry-wet spinning method, which is advantageous for the strand strength of the obtained carbon fiber. The spinning process includes a spinning process in which a spinning solution is discharged from a spinneret into a coagulating bath by a dry-wet spinning method and spun, a water washing process in which the fibers obtained in the spinning process are drawn while washing them in a water bath, and the water washing. It comprises a dry heat treatment step of dry heat-treating the fibers obtained in the step, and if necessary, preferably includes a steam drawing step of steam-drawing the fibers obtained in the dry heat treatment step. In addition, it is also possible to change the order of each step as appropriate. The spinning solution is obtained by dissolving the polyacrylonitrile-based polymer described above in a solvent in which polyacrylonitrile is soluble, such as dimethylsulfoxide, dimethylformamide and dimethylacetamide.

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

As the water washing bath in the water washing step, it is preferable to use a water washing bath having a temperature of 30 to 98° C. and comprising a plurality of stages. Further, the draw ratio in the washing step is preferably 2 to 6 times. After that, for the purpose of improving the strand strength, the fibers are preferably provided with an oil such as silicone. Such silicone oils preferably contain amino-modified silicones.

A known method can be used for the dry heat treatment step. For example, the drying temperature is 100-200°C.

Precursor fibers suitable for obtaining the carbon fibers of the present invention can be obtained by performing steam drawing, if necessary, after the water washing step and the drying heat treatment step. Steam drawing is preferably performed at a draw ratio of 2 to 6 times in pressurized steam.

In order to increase the strand strength of the carbon fiber, in the flameproofing process, the resulting flameproofed fiber should have a ratio of peak intensity at 1,453 cm ^-1 to peak intensity at 1,370 cm ^-1 in the infrared spectrum of 0.5. 70 to 0.75, and the ratio of the peak intensity at 1,254 cm ^-1 to the peak intensity at 1,370 cm ^-1 in the infrared spectrum is controlled to be in the range of 0.50 to 0.65. is preferred. The peak at 1,453 cm ⁻¹ in the infrared spectrum is derived from alkene, and decreases as flame resistance progresses. A peak at 1,370 cm ⁻¹ and a peak at 1,254 cm ⁻¹ are peaks derived from the flameproof structure, and increase as the flameproofing progresses. Note that the standard flame-resistant fiber with a specific gravity of 1.35 has a ratio of peak intensity at 1,453 cm ^-1 to peak intensity at 1,370 cm ^-1 of about 0.63 to 0.69. shows that, in the flameproofing step, it is preferred that the resulting flameproofed fiber retains more of the alkene-derived structure than usual. The ratio of the peak intensity at 1,254 cm ^-1 to the peak intensity at 1,370 cm ^-1 decreases as the flame resistance progresses. The peak intensity ratio may not be 0.65 or less.

In order to make these two peak intensity ratios compatible within the target range, basically, the amount of the copolymer component contained in the polyacrylonitrile-based polymer constituting the precursor fiber is small, and the amount of the precursor fiber Conditions may be set mainly by paying attention to a high degree of crystal orientation, a small single fiber fineness of the precursor fiber, and a high flameproofing temperature in the latter half. Specifically, the flameproofing step is performed for 8 to 25 minutes until the ratio of the peak intensity at 1,453 cm ^-1 to the peak intensity at 1,370 cm ^-1 in the infrared spectrum is in the range of 0.98 to 1.10. a first flameproofing step, preferably for 8 to 15 minutes, and the fiber obtained by the first flameproofing step is subjected to a peak intensity of 1,370 cm ⁻¹ in the infrared spectrum at a peak of 1,453 cm ⁻¹ The intensity ratio is in the range of 0.70 to 0.75, and the ratio of the 1,254 cm ^-1 peak intensity to the 1,370 cm ^-1 peak intensity in the infrared spectrum is in the range of 0.50 to 0.65. 5 to 14 minutes, preferably 5 to 10 minutes, is preferably carried out in two stages of the second flameproofing step.

The flameproofing temperature in the first flameproofing step is preferably 200 to 250°C, more preferably 230 to 250°C, in order to control the infrared spectrum within the range described above.

The flameproofing temperature in the second flameproofing step is higher than that in the first flameproofing step. In order to shorten the flameproofing time in the second flameproofing step, the flameproofing temperature should be adjusted to a high value, but the appropriate flameproofing temperature depends on the properties of the precursor fiber. The flameproofing temperature is preferably 280 to 310°C, more preferably 280 to 300°C, and even more preferably 285 to 295°C, in order to control the infrared spectrum within the range described above. The flameproofing temperature need not be constant, and may be set in multiple stages. In order to increase the strand strength of the obtained carbon fiber, it is preferable that the flameproofing temperature is high and the flameproofing time is short.

In the present invention, flameproofing means heat-treating the precursor fiber at 200 to 310° C. in an oxygen-containing atmosphere.

The flameproofing time mentioned here means the time the fiber stays in the flameproofing furnace. A flameproof fiber means a fiber after the flameproofing step and before the preliminary carbonization step. In addition, the peak intensity described here is the absorbance at each wavelength after baseline correction of the spectrum obtained by measuring the infrared spectrum of a small amount of the flame-resistant fiber sampled. Not performed. Further, the concentration of the sample when measuring the infrared spectrum is diluted with KBr so as to be 0.67% by mass. In this way, the infrared spectrum may be measured each time the setting of the flameproofing conditions is changed, and the conditions should be examined according to the preferred manufacturing method described later. By appropriately controlling the infrared spectrum peak intensity ratio of the flameproof fiber, the strand strength of the resulting carbon fiber can be controlled.

The total treatment time of the flameproofing step can be appropriately selected, preferably within the range of 13 to 20 minutes. For the purpose of improving the strand strength of the obtained carbon fiber, the specific gravity of the obtained flame-resistant fiber is preferably in the range of 1.28 to 1.32, more preferably 1.30 to 1.32. set the processing time for the conversion. A more preferable treatment time for the flameproofing step depends on the flameproofing temperature. Unless the specific gravity of the flameproof fiber is 1.28 or more, the strand strength of the carbon fiber may be lowered. If the specific gravity of the flameproof fiber is 1.32 or less, the strand strength can be increased. The specific gravity of the flameproof fiber is controlled by the treatment time of the flameproofing process and the flameproofing temperature. Moreover, the timing of switching from the first flameproofing step to the second flameproofing step is preferably set so that the specific gravity of the fiber is in the range of 1.21 to 1.23. Also in this case, the conditions of the flameproofing step are controlled with priority given to satisfying the range of the infrared spectrum intensity ratio. The preferred range of the treatment time for flameproofing and the flameproofing temperature varies depending on the properties of the precursor fiber and the copolymer composition of the polyacrylonitrile polymer.

In the pre-carbonization step of pre-carbonizing the fiber bundle obtained in the flame-proofing step, the resulting flame-proofed fiber is treated in an inert atmosphere at a maximum temperature of 500 to 1,200° C. to a specific gravity of preferably 1.5. It is heat-treated until it becomes 5-1.8. The draw ratio in the preliminary carbonization step is preferably 1.16-1.25. If the draw ratio in the preliminary carbonization step is 1.16 or more, the strand elastic modulus tends to increase, and the strand strength tends to increase. When the draw ratio in the preliminary carbonization step is 1.25 or less, the strand elastic modulus is easily suppressed to 300 GPa or less.

The pre-carbonized fiber is heated in an inert atmosphere preferably at a maximum temperature of 1,000 to 1,500°C, more preferably at a maximum temperature of 1,100 to 1,300°C, more preferably at a maximum temperature of 1,150 to 1,150°C. Carbonize at 250°C. From the viewpoint of increasing the elongation of the resulting carbon fiber, the maximum temperature in the carbonization step is preferably as low as possible.

Also, the treatment time X at the highest temperature in the carbonization step is preferably 20 to 60 seconds, more preferably 20 to 38 seconds. The treatment time X at the highest temperature of the carbonization process is the time required for the fiber to pass through the highest temperature compartment in the carbonization furnace. Carbonization furnaces often have multiple compartments that are controlled in stepwise temperature increases with heater blocks. Each section is assumed to be a constant temperature for calculation. The shorter the treatment time at the maximum temperature, the lower the strand elastic modulus can be controlled, so the treatment time X is preferably 60 seconds or less. If the treatment time X is 20 seconds or more, a stable strand elastic modulus can be easily obtained.

The temperature increase rate Y in the carbonization step is preferably 0.40 to 1.1° C./second, more preferably 0.40 to 1.0° C./second, still more preferably 0.40 to 0.40° C./second. 60° C./sec. The rate of temperature rise in the carbonization step affects the desorption rate of cracked gas, and therefore affects the strand strength. In the present invention, the rate of temperature increase refers to the region where the temperature of the compartment exceeds 1,000 ° C. when the fiber passes through a plurality of compartments in which the temperature is controlled to rise in stages in the carbonization furnace. is defined as the average rate at which the fiber passes in degrees Celsius per second. Specifically, for example, if the fiber passes from entering the compartment with a temperature of 1,000 ° C. in the carbonization furnace to reaching the next compartment with a temperature of 1,100 ° C. in 100 seconds, The heating rate is 1.0° C./sec. In another example, if a fiber enters a section of the carbonization furnace at a temperature of 950° C. and passes through the next section at a temperature of 1,150° C. in 200 seconds, the heating rate is 1.0°C/sec. Also, when setting the maximum temperature of the carbonization process to less than 1,100° C., the heating rate up to the maximum temperature is utilized. That is, when the maximum temperature is 1,050 ° C., it takes 50 seconds for the fiber to pass from entering the compartment with a temperature of 1,000 ° C. in the carbonization furnace until reaching the next compartment with a temperature of 1,050 ° C. Then, the temperature rise rate becomes 1.0° C./sec. The temperature of the first compartment in the carbonization furnace is preferably 1,000°C or less. If the heating rate is 0.40° C./second or more, a stable strand elastic modulus can be easily obtained. If the heating rate is within 1.1° C./second, it is easy to suppress the decrease in strand strength.

The maximum temperature treatment time X and temperature increase rate Y in the carbonization step are preferably in the range of 0.015X≤Y≤0.015X+0.6. This formula is derived from the inventor's study results for increasing the elongation of carbon fibers. By adjusting the treatment time X and the temperature increase rate Y so as to satisfy such a relationship, the elongation of the carbon fibers can be easily increased.

The carbon fibers obtained as described above are preferably further subjected to electrolytic surface treatment to introduce oxygen-containing functional groups. As for the electrolytic surface treatment, gas phase oxidation, liquid phase oxidation and liquid phase electrolytic oxidation are all used, but from the viewpoint of high productivity and uniform treatment, liquid phase electrolytic oxidation is preferably used. In the present invention, the liquid-phase electrolytic oxidation method is not particularly limited, and a known method may be used.

After such an electrolytic surface treatment, a sizing treatment may be applied to impart bundling properties to the obtained carbon fibers. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected according to the type of the matrix resin used in the carbon fiber composite material.

Next, the carbon fiber composite material of the present invention will be described. The carbon fiber composite material of the present invention is an epoxy resin composition comprising the carbon fiber of the present invention described above and a matrix resin, an amine-type epoxy resin [A], a thermoplastic resin soluble in epoxy resin [B], and an epoxy resin curing agent. Including the thing [C].

Examples of the amine-type epoxy resin [A] used in the present invention include tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenylsulfone, tetraglycidylxylylenediamine, triglycidylaminophenol, triglycidylaminocresol, diglycidylaniline, and diglycidyl. Toluidine, or halogen-substituted, alkyl-substituted or hydrogenated products thereof may be mentioned. Among them, tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, or halogen-substituted, alkyl-substituted, or hydrogenated products thereof are preferable because they can impart elastic modulus and heat resistance.

Commercially available products of tetraglycidyldiaminodiphenylmethane include "Sumiepoxy" (registered trademark) ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), YH434L (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), and "jER" (registered trademark) 604 ( Mitsubishi Chemical Corporation), "Araldide" (registered trademark) MY720, "Araldide" (registered trademark) MY721, "Araldide" (registered trademark) MY9512, "Araldide" (registered trademark) MY9663 (the above, Huntsman Advanced Materials Co., Ltd.) and the like.

Commercially available products of tetraglycidyldiaminodiphenylsulfone include TG3DAS (manufactured by Mitsui Chemicals Fine, Inc.).

Commercially available products of tetraglycidylxylylenediamine and hydrogenated products thereof include "TETRAD" (registered trademark)-X and "TETRAD" (registered trademark)-C (manufactured by Mitsubishi Gas Chemical Company, Inc.). .

Commercial products of triglycidylaminophenol or triglycidylaminocresol include "Sumiepoxy" (registered trademark) ELM100, "Sumiepoxy" (registered trademark) ELM120 (manufactured by Sumitomo Chemical Co., Ltd.), and "Araldide" (registered trademark). ) MY0500, “Araldide” (registered trademark) MY0510, “Araldide” (registered trademark) MY0600 (manufactured by Huntsman Advanced Materials), “jER” (registered trademark) 630 (manufactured by Mitsubishi Chemical Corporation), etc. is mentioned.

Commercially available diglycidylanilines include GAN (manufactured by Nippon Kayaku Co., Ltd.) and TOREP-E204 (manufactured by Toray Fine Chemicals Co., Ltd.).

Commercial products of diglycidyl toluidine include GOT (manufactured by Nippon Kayaku Co., Ltd.).

In the present invention, the amine-type epoxy resin [A] is preferably contained in 50 to 100 parts by mass, more preferably in the range of 70 to 100 parts by mass, in 100 parts by mass of the total epoxy resin. If the amount of the amine-type epoxy resin is less than 50 parts by mass with respect to 100 parts by mass of the total amount of the epoxy resin blended, the resulting epoxy resin composition may lack heat resistance and elastic modulus. Furthermore, the compressive strength may decrease when made into a carbon fiber composite material.

In the epoxy resin composition of the present invention, the amine-type epoxy resin [A] preferably contains a bifunctional amine-type epoxy resin and a tri- or more functional amine-type epoxy resin. Including a bifunctional amine type epoxy resin extends the distance between cross-linking points, reduces the storage elastic modulus at 275° C., and improves the elongation of the cured epoxy resin. Furthermore, by blending a trifunctional or higher amine-type epoxy resin, the heat resistance and elastic modulus are improved, resulting in a well-balanced resin composition.

In addition to the amine-type epoxy resin [A], other epoxy resin components may be included as the epoxy resin within a range that does not impair the effects of the present invention. These may be added singly or in combination. By blending an epoxy resin having a weight-average molecular weight of 400 or more, the distance between cross-linking points can be extended, and the storage elastic modulus at 275° C. can be reduced, so that it is preferably used. Specifically, phenol novolak-type epoxy resins, cresol novolac-type epoxy resins, resorcinol-type epoxy resins, dicyclopentadiene-type epoxy resins, urethane- and isocyanate-modified epoxy resins, epoxy resins having a biphenyl skeleton, epoxy resins having a fluorene skeleton, As the bisphenol type epoxy resin, bisphenol A type, bisphenol F type, bisphenol S type, bisphenol AD type, or halogen-, alkyl-substituted or hydrogenated bisphenols are used. Specific examples of such epoxy resins include the following.

Commercially available phenolic novolac epoxy resins include "jER" (registered trademark) 152, "jER" (registered trademark) 154 (manufactured by Mitsubishi Chemical Corporation), "Epiclon" (registered trademark) N-740, "Epiclon" (registered trademark) N-770, "Epiclon" (registered trademark) N-775 (manufactured by DIC Corporation) and the like.

Commercial products of cresol novolak type epoxy resins include "Epiclon" (registered trademark) N-660, "Epiclon" (registered trademark) N-665, "Epiclon" (registered trademark) N-670, and "Epiclon" (registered trademark). ) N-673, “Epiclon” (registered trademark) N-695 (manufactured by DIC Corporation), EOCN-1020, EOCN-102S, EOCN-104S (manufactured by Nippon Kayaku Co., Ltd.), etc. be done.

Specific examples of resorcinol-type epoxy resins include “Denacol” (registered trademark) EX-201 (manufactured by Nagase ChemteX Corporation).

Commercially available dicyclopentadiene type epoxy resins include "Epiclon" (registered trademark) HP7200, "Epiclon" (registered trademark) HP7200L, "Epiclon" (registered trademark) HP7200H (manufactured by DIC Corporation), and Tactix558 (manufactured by DIC Corporation). Huntsman Advanced Materials Co., Ltd.), XD-1000-1L, XD-1000-2L (manufactured by Nippon Kayaku Co., Ltd.) and the like.

Commercial products of urethane- and isocyanate-modified epoxy resins include AER4152 (manufactured by Asahi Kasei E-Materials Co., Ltd.) and ACR1348 (manufactured by Asahi Denka Co., Ltd.) having an oxazolidone ring.

Commercially available epoxy resins having a biphenyl skeleton include "jER" (registered trademark) YX4000H, "jER" (registered trademark) YX4000, "jER" (registered trademark) YL6616 (manufactured by Mitsubishi Chemical Corporation), NC -3000 (manufactured by Nippon Kayaku Co., Ltd.) and the like.

Commercially available epoxy resins having a fluorene skeleton include ESF300 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), “Oncoat” (registered trademark) EX-1010, “Oncoat” (registered trademark) EX-1011, “ On Coat” (registered trademark) EX-1012, “On Coat” (registered trademark) EX-1020, “On Coat” (registered trademark) EX-1030, “On Coat” (registered trademark) EX-1040, “On Coat ” (registered trademark) EX-1050, “On Coat” (registered trademark) EX-1051 (manufactured by Nagase ChemteX Corporation) and the like.

Commercially available bisphenol A epoxy resins include "Epototh" (registered trademark) YD128 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), "jER" (registered trademark) 825, "jER" (registered trademark) 828, “jER” (registered trademark) 834, “jER” (registered trademark) 1001, “jER” (registered trademark) 1004, “jER” (registered trademark) 1007, “jER” (registered trademark) 1009, “jER” (registered trademark) Trademark) 1010 (manufactured by Mitsubishi Chemical Corporation) and the like.

Commercially available bisphenol F type epoxy resins include "Epiclon" (registered trademark) 830, "Epiclon" (registered trademark) 835 (manufactured by DIC Corporation), "jER (registered trademark) 806," jER" ( Registered trademark) 807, “jER” (registered trademark) 4004P, “jER” (registered trademark) 4007P, “jER” (registered trademark) 4009P, “jER” (registered trademark) 4010P (manufactured by Mitsubishi Chemical Corporation) , “Epotoot (registered trademark) YDF170” and “Epotoot” (registered trademark) YDF2001 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.).

Examples of bisphenol S-type epoxy resins include "Epiclon" (registered trademark) EXA-1514 (manufactured by DIC Corporation).

Examples of bisphenol AD type epoxy resins include "EPOMIK" (registered trademark) R710 and "EPOMIK" (registered trademark) R1710 (manufactured by Printec Co., Ltd.).

The epoxy resin composition of the present invention is used by mixing or dissolving the thermoplastic resin [B].

In the present invention, by combining the amine-type epoxy resin [A] with the thermoplastic resin [B], it is possible to obtain high toughness while avoiding a decrease in heat resistance. degree is greatly improved.

The thermoplastic resin [B] in the present invention is in a crystalline or glassy state at room temperature and has thermoplasticity.

Such a thermoplastic resin [B] generally has a carbon-carbon bond, an amide bond, an imide bond, an ester bond, an ether bond, a carbonate bond, a urethane bond, a thioether bond, a sulfone bond and a carbonyl bond in the main chain. It is preferably a thermoplastic resin having a bond selected from Further, this thermoplastic resin [B] may have a partially crosslinked structure, and may be crystalline or amorphous. In particular, polyamides, polycarbonates, polyacetals, polyphenylene oxides, polyphenylene sulfides, polyarylates, polyesters, polyamideimides, polyimides, polyetherimides, polyimides having a phenyltrimethylindane structure, polysulfones, polyethersulfones, polyetherketones, polyetherethers At least one resin selected from the group consisting of ketone, polyaramid, polyethernitrile and polybenzimidazole is preferably dissolved in any one of the epoxy resins contained in the epoxy resin composition.

In the present invention, the thermoplastic resin [B] is contained in the epoxy resin composition in an amount of 8 to 40% by mass, preferably 8 to 35% by mass, more preferably 12 to 35% by mass, still more preferably 16 to 35% by mass. , and most preferably 20 to 30% by weight. When the content of the thermoplastic resin [B] is less than 8% by mass, the toughness of the cured resin is lowered, and the interlaminar toughness of the resulting fiber-reinforced composite material is insufficient. On the other hand, if it exceeds 40% by mass, the viscosity of the thermosetting resin composition increases, and the thermosetting resin composition and the prepreg have insufficient production processability and handleability.

Further, the weight average molecular weight of the thermoplastic resin [B] is preferably in the range of 4,000 to 40,000 g/mol, more preferably 10,000 to 40,000 g/mol, still more preferably 15,000 g/mol. 000 to 30,000 g/mol. If the weight average molecular weight is less than 4,000 g/mol, the elongation and toughness of the cured epoxy resin may be insufficient. On the other hand, if it is higher than 40,000 g/mol, when the thermoplastic resin is dissolved in the epoxy resin composition, the viscosity of the epoxy resin becomes high, making kneading difficult and prepreg-forming may be difficult.

Furthermore, the glass transition temperature of the thermoplastic resin [B] in the present invention is preferably 150°C or higher, more preferably 200°C or higher, still more preferably 220°C or higher. If the glass transition temperature of the thermoplastic resin [B] is less than 150°C, the carbon fiber composite material may be easily deformed by heat.

Examples of the thermoplastic resin [B] include polycarbonate (glass transition temperature (also referred to as Tg): 150°C), polysulfone (Tg: 190°C), polyetherimide (Tg: 215°C), polyethersulfone (Tg: 225°C °C) and the like. The glass transition temperature of the thermoplastic resin [B] was measured by DSC (differential scanning calorimetry) from 30° C. to a temperature 30° C. higher than the predicted glass transition temperature at a heating rate of 20° C./min. and held for 1 minute, then once cooled to 0 ° C. under a temperature drop condition of 20 ° C./min, held for 1 minute, and then measured again under a temperature rise condition of 20 ° C./min. It is the observed glass transition temperature.

Commercially available polycarbonate products include "Panlite" (registered trademark) K1300Y (manufactured by Teijin Limited). Commercially available polysulfone products include "Udel" (registered trademark) P-1700, "Udel" (registered trademark) P-3500LCD, "Virantage" (registered trademark) DAMS VW-30500RP (manufactured by Solvay Specialty Polymers), and the like. is mentioned. Commercially available products of polyetherimide include "Ultem" (registered trademark) 1000 and "Ultem" (registered trademark) 1010 (manufactured by SABIC). Commercially available products of polyethersulfone include "Sumika Excel" (registered trademark) PES3600P, "Sumika Excel" (registered trademark) PES5003P, "Sumika Excel" (registered trademark) PES5200P, "Sumika Excel" (registered trademark) PES7600P (the above , Sumitomo Chemical Co., Ltd.), "Ultrason" (registered trademark) E2020P SR, (manufactured by BASF), "Virantage" (registered trademark) VW-10200RP, "Virantage" (registered trademark) VW-10700RP (above, manufactured by Solvay Specialty Polymers) and the like.

Further, as terminal functional groups of the thermoplastic resin [B], hydroxyl groups, carboxyl groups, amino groups, thiol groups, acid anhydrides and the like are preferably used. Examples of thermoplastic resins having hydroxyl groups include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, and phenoxy resins. Moreover, polyether sulfone can be mentioned as a thermoplastic resin having a sulfonyl group.

Specifically, commercially available phenoxy resins include "Phenotote" (registered trademark) YP-50, "Phenotote" (registered trademark) YP-50S (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) and the like. .

In the present invention, the epoxy resin curing agent [C] is a curing agent for the epoxy resin contained in the epoxy resin composition of the present invention, and is a compound having active hydrogen capable of reacting with an epoxy group. group amines, acid anhydrides and phenols. Specific examples of aromatic amines include diaminodiphenyl sulfone, diaminodiphenylmethane, diaminodiphenyl ether, diaminobenzanilide, toluenediamine, and diethyltoluenediamine. Among them, diaminodiphenylsulfone or its isomers are preferably used. Diaminodiphenyl sulfone or its isomers are preferably used because they give a cured epoxy resin with good heat resistance. Isomers of diaminodiphenyl sulfone include 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone.

Liquid diethyltoluenediamine is preferably used in resin transfer molding (RTM), pultrusion molding, and the like.

Aliphatic amine curing agents include isophoronediamine, m-xylenediamine, mensendiamine, diaminodicyclohexylmethane, and the like. Acid anhydrides include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, and succinic anhydride.

Phenols include phenol novolak, cresol novolak, phenol aralkyls, bisphenols such as bisphenol A and bisphenol S, resorcinol, naphthalene diol, hydroquinone, and the like.

The total amount of epoxy resin curing agent [C] is such that the number of moles of active hydrogen contained in [C] is 0.6 to 2.0 times the number of moles of epoxy groups contained in the entire epoxy resin composition. It should be blended as much as possible, preferably in the range of 0.6 to 1.0 times for improving the compressive yield stress, and preferably 1.1 times for reducing the storage modulus at 275 ° C. It is desired to be blended so as to have a ratio of up to 1.8 times, more preferably 1.2 to 1.5 times. When the number of moles of such active hydrogen is 1.0 times or less the number of moles of epoxy groups contained in the entire epoxy resin composition, the crosslink density is increased, so that a high compressive yield stress is easily obtained, and the number of moles is 1.1 times or more. In the case of , the resin elongation is improved because the crosslink density is low. On the other hand, when it exceeds 2.0 times, the heat resistance is remarkably lowered and the viscosity of the epoxy resin composition is increased, which may make it difficult to produce the prepreg.

Commercially available aromatic amines include Seikacure S (manufactured by Wakayama Seika Kogyo Co., Ltd.), MDA-220 (manufactured by Mitsui Chemicals, Inc.), “jER Cure” (registered trademark) W (manufactured by Mitsubishi Chemical Corporation). ), and 3,3′-DAS (manufactured by Mitsui Chemicals Fine Co., Ltd.), “Lonzacure” (registered trademark) M-DEA, “Lonzacure” (registered trademark) M-DIPA, “Lonzacure” (registered trademark) M- Examples include MIPA and "Lonzacure" (registered trademark) DETDA80 (manufactured by Lonza).

These epoxy resin curing agents [C] may be used alone or in combination. In addition, an epoxy resin and an epoxy resin curing agent [C], or a pre-reacted product of some of them, can be blended into the composition. This method may be effective in adjusting viscosity and improving storage stability.

In the present invention, the epoxy resin cured product can be obtained by heating and curing the epoxy resin composition of the present invention under temperature conditions such that the degree of cure obtained by DSC is 90% or more. Such temperature conditions can be appropriately set according to the type and amount of the curing agent and accelerator. For example, when diaminodiphenylsulfone is used as the curing agent, a temperature condition of 180° C. for 2 hours can be suitably used. . The degree of cure is calculated by the following formula from the total calorific value QT of the epoxy resin composition and the residual calorific value QR of the cured product obtained by DSC (differential scanning calorimetry).
Degree of cure (%) = (QT-QR)/QT x 100.

In the present invention, the epoxy resin cured product was heated at a rate of 5°C/min using a dynamic viscoelasticity measuring device in accordance with SACMA SRM 18R-94, and the storage modulus at 275°C was measured in a 1.0 Hz torsional mode. is 1 to 10 MPa, preferably 5 to 9 MPa, and 6 to 8 MPa. Such a storage modulus is related to the property of suppressing stress concentration when tensile stress is applied to the carbon fiber composite material and breakage at the single fiber level begins. If the storage elastic modulus is 1 MPa or more, the epoxy resin cured product has sufficient heat resistance, and if it is 10 MPa or less, chain breakage of single fibers due to stress concentration is suppressed and the elongation of the carbon fiber composite material is increased. be able to.

In the present invention, the cured product of the epoxy resin composition preferably has a compression yield strain of 10 to 15%, more preferably 11 to 15%. The compression yield strain is a parameter related to the degree of cross-linking of the cured epoxy resin, and the lower the degree of cross-linking, the more the strand strength of the carbon fiber can contribute to the 0° tensile strength of the carbon fiber composite material. If the strain is 10% or more, the 0° tensile strength of the carbon fiber composite material is often satisfied, and if the strain is 15% or less, the relationship with the elastic modulus of the epoxy resin cured product is often satisfied. . Details of such compression measurements will be described later. Since this strain can be controlled mainly by the degree of cross-linking and the distance between cross-linking points, it can be adjusted by the type of epoxy curing agent, the ratio with the epoxy resin, the number of epoxy groups of the epoxy resin, and the like.

In the present invention, the cured product of the epoxy resin composition preferably has a compressive yield stress of 90 to 140 MPa, more preferably 95 to 120 MPa, still more preferably 100 to 110 MPa. Such compressive yield stress is related to interfacial adhesion between carbon fiber and cured epoxy resin. It often has an excellent balance with the strain.

In the present invention, the prepreg is obtained by impregnating the above reinforcing fiber with the above epoxy resin composition. The fiber mass fraction of the prepreg is preferably 40-90% by mass, more preferably 50-80% by mass. If the fiber mass fraction is too low, the resulting composite material will have an excessive mass, and the advantage of the carbon fiber composite material having an excellent specific elastic modulus may be impaired. Poor impregnation of the composition may occur, and the obtained carbon fiber composite material tends to have many voids, and its mechanical properties may be significantly deteriorated.

The form of the carbon fibers is not particularly limited, and for example, continuous fiber sheets or tows aligned in one direction, woven fabrics, mats, and the like are used.

In the present invention, the epoxy resin composition is dissolved in a solvent such as methyl ethyl ketone or methanol to reduce the viscosity, and impregnated into carbon fibers (wet method). It can be produced by a hot melt method (dry method) or the like.

After laminating the obtained prepregs, the carbon fiber composite material of the present invention is produced by a method of heating and curing the epoxy resin composition while applying pressure to the laminate. Here, as a method for applying heat and pressure, a press molding method, an autoclave molding method, a bagging molding method, a wrapping tape method, an internal pressure molding method, or the like is employed.

The carbon fiber composite material of the present invention is produced by impregnating carbon fibers directly with an epoxy resin composition without passing through a prepreg, and then heating and curing such as a hand layup method, a filament winding method, a pultrusion method, and a resin injection method. It can be produced by a molding method such as a molding method and a resin transfer molding method. In these methods, it is preferable to prepare the epoxy resin composition by mixing the two liquids of the epoxy resin main agent and the epoxy resin curing agent immediately before use.

The carbon fiber composite material of the present invention preferably has a 0° tensile strength of 4.0 GPa or more, more preferably 4.1 GPa or more, and still more preferably 4.2 to 4.5 GPa. 0° tensile strength is an impact factor for carbon fiber composites. The 0° tensile strength can be evaluated according to JIS K7165 (2008). If the 0° tensile strength is 4.0 GPa or more, it is easy to increase the strain energy density of the carbon fiber composite material. There is no upper limit to the 0° tensile strength, but as long as it is 4.5 GPa, the strain energy density of the carbon fiber composite material tends to reach a satisfactory level. The 0° tensile strength can be controlled by the strand strength of the carbon fiber, the storage elastic modulus of the cured epoxy resin, and the like.

The carbon fiber composite material of the present invention preferably has an elongation of 2.5% or more, more preferably 2.6 to 2.8%. Such elongation can be evaluated with a strain gauge according to JIS K7165 (2008). If the elongation of the carbon fiber composite material is 2.5% or more, it is easy to increase the strain energy density of the carbon fiber composite material. There is no upper limit to the elongation, but as little as 2.8% is often sufficient to increase the strain energy density of carbon fiber composites. The elongation of the carbon fiber composite material can be adjusted by the 0° tensile strength and strand elastic modulus of the carbon fiber composite material.

Methods for measuring various physical property values used in the present invention are as follows.

<Total fineness>
For the carbon fiber to be measured, a sample of 10 m in length is sampled, dried at 120° C. for 2 hours, and the measured mass is divided by 10 to obtain the total fineness, which is the mass per 1 m.

<Density>
The carbon fiber to be measured is dried at 120° C. for 2 hours and then measured. A dry automatic densitometer is used to measure the density, nitrogen is used as the measuring medium, a 10 cc type sample container is used, and the volume of the sample is adjusted to 3 to 6 cc. Measurement is performed 3 times and the average value is used. In addition, in this measurement, an Accupic 1330 type dry automatic density meter manufactured by Shimadzu Corporation was used.

<Single fiber diameter>
It is calculated from the obtained total fineness and density and the number of filaments of the carbon fiber used for the measurement.

<Strand strength, strand elastic modulus, elongation>
The strand strength, strand elastic modulus and elongation of the carbon fiber are obtained according to the resin-impregnated strand test method of JIS R7608:2004, according to the following procedure. As the resin formulation, "Celoxide" (registered trademark) 2021P (manufactured by Daicel Chemical Industries, Ltd.) / boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / acetone = 100/3/4 (parts by mass) was used. The curing conditions are normal pressure, temperature of 125° C., and time of 30 minutes. The strand strength, strand elastic modulus and elongation of 10 carbon fiber strands are measured, and the average value is used. The strain range for calculating the strand elastic modulus is 0.1 to 0.6%.

<Strain energy density of carbon fiber>
Strain energy density is calculated by the following formula.
Strain energy density (J/mm ³ )=strand strength (GPa)×1,000×elongation (%)/100/2.

<Production of carbon fiber composite material>
(1) Preparation of epoxy resin composition A predetermined amount of the amine type epoxy resin [A] or an epoxy resin other than [A] and the thermoplastic resin [B] are added to a kneader and kneaded at a temperature of 150°C or higher to dissolve. to give a clear viscous liquid. After lowering the temperature to 60° C. or lower while kneading, the epoxy resin curing agent [C] and other components are added in predetermined amounts and further kneaded to obtain an epoxy resin composition.

In compositions 5 and 6 described later, a liquid obtained by mixing an amine type epoxy resin [A] or an epoxy resin other than [A] at a temperature of 60 ° C. or higher and component [C] are mixed at a temperature of 60 ° C. or higher to obtain a solid component. The two dissolved liquids are mixed at a temperature of 60° C. or less and degassed under vacuum for 1 hour to obtain an epoxy resin composition.

(2) Production of prepreg In Compositions 1 to 4 described below, epoxy resin compositions are applied onto release paper using a knife coater to produce resin films. Next, two resin films are superimposed on the carbon fibers arranged in one direction in a sheet form from both sides of the carbon fibers, and the resin is impregnated into the carbon fibers by heating and pressurizing, so that the basis weight of the carbon fibers is 190 g/m ² . A unidirectional prepreg having an epoxy resin composition mass fraction of 35.5% is obtained.

(3) Production of RTM Laminate In Compositions 5 and 6, which will be described later, carbon fiber composite materials were produced by the following RTM molding method.

A plurality of sheet-shaped fiber base materials with carbon fibers arranged in one direction are laminated so as to have a predetermined fiber basis weight, placed on the surface of a flat aluminum mold, and peeled ply on top of it for release treatment. A polyester cloth to which the heat treatment was applied and a polypropylene knit as a resin diffusion medium were arranged in this order, and a bag material and a sealant were used to form a cavity by sealing the above with a resin injection port and a vacuum suction port. Then, the inside of the cavity was sucked from the vacuum suction port by a vacuum pump, and the degree of vacuum was adjusted to -90 kPa or less. A hot air dryer was used for temperature adjustment. The resin composition is preheated at 70° C. for 30 minutes, the preheated liquid resin composition is set in the resin inlet of the mold, and the pressure inside the cavity and the atmospheric pressure are added to the evacuated cavity. The thermosetting resin composition was injected by utilizing a differential pressure of 100.degree. C. to impregnate the arrayed fiber substrate. When the resin composition reached the vacuum suction port, the resin injection port was closed, and the vacuum suction port was closed after holding for one hour while continuing the suction from the vacuum suction port.

Then, the temperature was raised from 70° C. to 140° C. at a rate of 1.5° C./min, precured at 140° C. for 2 hours, and then cooled to room temperature. After removing the pre-cured product from the mold and removing each secondary material such as peel ply, the temperature is raised to 180°C at 1.5°C/min in a hot air dryer, and then cured at 180°C for 2 hours to reinforce the fiber. A composite material (laminate) was obtained.

<Measurement of DSC Curing Degree of Resin Cured Material>
5 mg of the epoxy resin composition prepared in (1) above was taken, and the temperature was raised from 30° C. to 350° C. at a rate of 10° C./min using DSC, and an exothermic curve was obtained. is integrated to calculate the total calorific value QT of the epoxy resin composition. Also, the epoxy resin composition prepared in (1) above was defoamed in vacuum and cured at a temperature of 180° C. for 2 hours to obtain a cured epoxy resin. 5 mg of the obtained resin cured product is sampled, and the temperature is measured from 30° C. to 350° C. at a rate of temperature increase of 10° C./min using DSC to obtain an exothermic curve. If there is a residual exothermic peak, the residual exothermic value QR is calculated by integrating the exothermic peak. If there is no residual exothermic peak, QR=0.

<Glass transition temperature of cured resin and storage modulus at 275°C measured in torsion mode at 1.0 Hz>
A test piece with a width of 10 mm and a length of 40 mm was cut out from a plate of the epoxy resin cured product obtained in the same manner as the DSC curing measurement of the cured resin product, and a dynamic viscoelasticity measuring device (ARES: manufactured by TA Instruments) ), set the test piece on a solid torsion jig, and measure the temperature range from 30 to 300° C. at a temperature increase rate of 5° C./min, a frequency of 1 Hz, and a strain amount of 0.1%. At this time, the glass transition temperature is the temperature at the intersection of the tangent line drawn to the glass region and the tangent line drawn to the glass transition region in the obtained graph of storage modulus and temperature. The storage modulus at 275°C measured in the torsional mode at 1.0 Hz is taken as the storage modulus at 275°C in the resulting graph of storage modulus versus temperature. When multiple glass transition temperatures occur, the lowest value is adopted as the glass transition temperature.

<Compressive Yield Stress of Cured Epoxy Resin and Strain at Compressive Yield>
A plate of cured epoxy resin having a thickness of 6 mm is prepared, and a cubic specimen having a side length of 6 mm is cut out from the plate. The compressive yield stress and strain at compressive yield are measured at a test speed of 1±0.2 mm/min and other conditions conforming to JIS K7181 (2011).

<0° tensile strength of carbon fiber composite material>
Using the unidirectional prepreg produced by the above method, 6 plies are laminated with the fiber direction aligned, and molded in an autoclave at 180 ° C. for 2 hours, under a pressure of 0.59 MPa, at a temperature increase rate of 1.5 ° C./min. to produce a laminate. Also, the RTM was adjusted by the method described above so as to have the same fiber amount as the 6-ply prepreg to obtain a laminate. The 0° tensile strength (GPa) of this laminate is determined according to JIS K7165 (2008). The 0° tensile strength is indicated by converting the measured value to a carbon fiber volume fraction of 60%. Strain is measured using a strain gauge.

<Strain energy density of carbon fiber composite material>
Strain energy density is calculated by the following formula.
Strain energy density (J/mm ³ )=0° tensile strength (GPa) of carbon fiber composite material×1,000×strain (%) of carbon fiber composite material/100/2.

EXAMPLES The present invention will be described in detail below based on examples, but the present invention is not limited to these.

[Resin raw material]
<Amine type epoxy resin [A]>
・ “Sumiepoxy” (registered trademark) ELM434 (tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd.)
- GAN (N,N-diglycidylaniline, manufactured by Nippon Kayaku Co., Ltd.).

<Epoxy resin other than [A]>
・ “Epotato” (registered trademark) jER825 (bisphenol A type epoxy resin, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.)
・ “Epiclon” (registered trademark) HP7200L (dicyclopentadiene type epoxy resin, manufactured by DIC Corporation)
- "Araldite" AER4152 (an epoxy resin having an oxazolidone ring, manufactured by Asahi Kasei E-Materials Co., Ltd.).

<Thermoplastic resin [B]>
- "Sumika Excel" (registered trademark) PES5003P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd., weight average molecular weight: 47,000).

<Epoxy resin curing agent [C]>
• Seikacure S (manufactured by Wakayama Seika Kogyo Co., Ltd.).
・ “jER Cure” (registered trademark) W (manufactured by Mitsubishi Chemical Corporation)
- 3,3'-DAS (Mitsui Chemicals Fine Co., Ltd.;

[Epoxy resin composition]
The resin raw materials were kneaded according to the composition shown in Table 1, and the characteristic values are shown (in Table 1, the numbers represent parts by mass). Furthermore, prepregs were produced for compositions 1 to 4.

[Carbon fiber 1]
A spinning solution containing a polyacrylonitrile-based copolymer and dimethyl sulfoxide as a solvent was once extruded into the air from a spinneret and introduced into a coagulation bath consisting of an aqueous solution of dimethyl sulfoxide to obtain a coagulated filament by a dry-wet spinning method.

After the coagulated yarn was washed with water by a conventional method, it was drawn 3.5 times in two hot water baths. Subsequently, an amino-modified silicone-based silicone oil agent was applied to the fiber bundle after the water-bath drawing, and a drying and densification treatment was performed using a heating roller at 160°C. 12,000 single fibers are drawn 3.7 times in pressurized steam to increase the total draw ratio to 13 times, and then entangled to obtain a degree of crystal orientation of 93% and 12 single fibers. ,000 carbon fiber precursor fiber bundles were obtained. The single fiber fineness of the carbon fiber precursor fiber bundle was 0.7 dtex.

Next, the conditions for the first flameproofing step are a flameproofing temperature of 250°C and a flameproofing time of 11 minutes, and the second flameproofing step is carried out under the conditions of a flameproofing temperature of 280°C and a flameproofing time of 6 minutes. The carbon fiber precursor fiber bundle was subjected to a flameproofing treatment while being drawn at a draw ratio of 1 in an atmospheric oven to obtain a flameproofed fiber.

The ratio of peak intensity at 1,453 cm ⁻¹ to peak intensity at 1,370 cm ⁻¹ in the infrared spectrum of the fiber after the first flameproofing step was 1.04. The ratio of the peak intensity at 1,453 cm ⁻¹ to the peak intensity at 1,370 cm ⁻¹ in the infrared spectrum of the fiber after the second flameproofing step is 0.70, the peak intensity at 1,254 cm ⁻¹ to the peak intensity at 1,370 cm ^{−1 .} The ratio of peak intensities of ¹ was 0.61.

The resulting flameproof fiber was subjected to preliminary carbonization treatment at a draw ratio of 1.22 in a nitrogen atmosphere at a maximum temperature of 800° C. to obtain a preliminary carbonized fiber. The obtained pre-carbonized fiber was carbonized in a nitrogen atmosphere at a maximum temperature of 1,200° C. and a draw ratio of 0.950. At this time, the rate of temperature increase in the carbonization step was 0.45° C./sec. Table 2 shows the physical properties of the final carbon fiber 1 obtained by subjecting the obtained carbon fiber to surface treatment and application of a sizing agent.

[Carbon fibers 2 to 9]
A carbon fiber was obtained in the same manner as in Example 1, except that the draw ratio in the preliminary carbonization step, the draw ratio in the carbonization step, the maximum temperature, the treatment time at the maximum temperature, and the heating rate were changed to those shown in Table 2. . Table 2 shows the physical properties obtained.

[Carbon Fibers 10 and 11]
Carbon fibers were obtained in the same manner as in Example 1, except that the single fiber fineness of the carbon fiber precursor fiber bundle was changed to 0.5 dtex or 0.8 dtex. Table 2 shows the physical properties obtained.

[Reference Examples 1 to 3]
Example 1 except that the conditions of the first flameproofing step were a flameproofing temperature of 240°C and a flameproofing time of 82 minutes, and the conditions of the second flameproofing step were a flameproofing temperature of 250°C and a flameproofing time of 85 minutes. A flame-resistant fiber was obtained in the same manner as above.

The ratio of peak intensity at 1,453 cm ⁻¹ to peak intensity at 1,370 cm ⁻¹ in the infrared spectrum of the fiber after the first flameproofing step was 0.68. The ratio of the peak intensity at 1,453 cm ^-1 to the peak intensity at 1,370 cm ^-1 in the infrared spectrum of the fiber after the second flameproofing step is 0.50, and the peak intensity at 1,254 cm ^-1 to the peak intensity at 1,370 cm ^-1 The ratio of peak intensities of ¹ was 0.56.

The resulting flameproof fiber was subjected to preliminary carbonization treatment at a draw ratio of 1.17 in a nitrogen atmosphere at a maximum temperature of 800° C. to obtain a preliminary carbonized fiber. The obtained pre-carbonized fiber was carbonized in a nitrogen atmosphere at the maximum temperature and time shown in Table 2 at a draw ratio of 0.980. At this time, the rate of temperature increase in the carbonization step was 0.35° C./sec. Table 2 shows the physical properties of the final carbon fiber obtained by subjecting the obtained carbon fiber to surface treatment and application of a sizing agent. Simply changing the maximum temperature in the carbonization process, which is generally used to adjust the strand elastic modulus, does not significantly change the strand strength, and when the strand strength level is at a high level, the It was found that it is necessary to finely adjust the conditions of the preliminary carbonization step and the carbonization step.

[Examples 1 to 7, Comparative Examples 1 to 15]
The obtained carbon fibers 1 to 9 and resin compositions 1 to 6 were combined as shown in Table 3 to prepare carbon fiber composite materials, and the mechanical properties were measured. Table 3 shows the results. Although there is a tendency that the higher the strand strength of the carbon fiber, the higher the 0° tensile strength as a carbon fiber composite material, it was found that the strength varies greatly depending on the combination with the epoxy resin composition. In addition, the elongation as a carbon fiber composite material exceeded 2.3%, and the product of 0° tensile strength and elongation increased to an unprecedented level.

The carbon fiber composite material of the present invention has high impact resistance, high energy absorption, and can reduce the weight of members that require high impact resistance.

Claims (5)

A carbon fiber having a strand strength of 7.5 to 8.5 GPa, an elongation of 2.65 to 3.20%, and a single fiber diameter of 4.0 to 6.0 μm, an amine type epoxy resin [A], and an epoxy resin It contains an epoxy resin composition having a soluble thermoplastic resin [B] and an epoxy resin curing agent [C], and the degree of curing of the epoxy resin composition is 90% or more, and the cured product of the epoxy resin is subjected to SACMA SRM A carbon fiber composite material having a storage modulus of 1 to 10 MPa at 275° C. measured in torsion mode at 1.0 Hz using a dynamic viscoelasticity measuring device heated at a rate of 5° C./min according to 18R-94. The carbon fiber composite material according to claim 1, wherein the carbon fibers have a strand elastic modulus of 240 to 300 GPa and a strain energy density of 95 J/mm ³ or more. 3. The carbon fiber composite material according to claim 1, wherein the cured epoxy resin composition has a compression yield stress of 90 to 140 MPa and a compression yield strain of 10 to 15%. The carbon fiber composite material according to any one of claims 1 to 3, which has a 0° tensile strength of 4.0 GPa or more and an elongation of 2.5% or more. The carbon fiber composite material according to any one of claims 1 to 4, wherein the epoxy resin curing agent [C] is an aromatic amine.