Prepreg and method for manufacturing the same

Abstract

To provide a prepreg which achieves both drape stability that is a retention rate to change of drape property with time and quick curability, and is excellent in resin impregnation property at the time of manufacture, and a method for manufacturing the prepreg.SOLUTION: A prepreg is obtained by impregnating a carbon fiber as a component [A] with an epoxy resin composition having an epoxy resin containing a component [B], an epoxy resin curing agent containing [C] and [D], wherein in the epoxy resin composition, the component [C] accounts for 85 mass% or more of the epoxy resin curing agent, a ratio (H / E) of a mol number (H) of active hydrogen contained in the epoxy resin curing agent to a mol number (E) of an epoxy group of the epoxy resin is 1.1 or more and 1.6 or less, and a mass ratio d dissolved in the epoxy resin composition in the component [C], which is determined by differential scanning calorimeter, is 0.6 or more and 0.9 or less. [A] A carbon fiber, [B] a liquid epoxy resin, [C] diaminodiphenyl sulfone, and [D] a thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to prepregs and methods for producing the same.

Background Art

[0002] Prepregs obtained by impregnating reinforcing fibers such as carbon fibers with a thermosetting resin composition such as an epoxy resin are used in a wide range of fields, such as the sports field of golf clubs and tennis rackets, and structural materials for aircraft and automobiles. In recent years, for the purpose of improving the production efficiency of molded products, there has been a demand for the development of a fast-curing prepreg that can be cured in a short time while having a retention rate against the change over time of drapability (hereinafter, draping stability) comparable to that of the prior art. Generally, the curing speed and draping stability are in a trade-off relationship. In order to achieve both of these, the use of a latent curing agent that starts the curing reaction only when heated above a certain temperature and the improvement of the function for increasing the curing speed of the prepreg by such a curing agent are effective. For example, in Patent Document 1, an aromatic amine compound and an organic acid hydrazide compound are used in combination as curing agents to increase the curing speed while suppressing the change over time of the properties of the prepreg and maintaining it stably. The organic acid hydrazide compound has high reactivity with the epoxy resin when dissolved in the epoxy resin composition, but exists as a powder without being dissolved in the epoxy resin composition at room temperature, so the change over time of the properties of the prepreg is small. Generally, the curing reaction of the organic acid hydrazide compound starts at a lower temperature than that of the aromatic amine compound. That is, when the organic acid hydrazide compound is used, the curing reaction starts at an early stage of temperature rise, so the curing speed of the prepreg increases. Further, in Patent Document 2, a mode is described in which the curing agent is localized only in the surface layer of the prepreg and the inner layer that affects the draping stability of the prepreg does not contain the curing agent, thereby improving the draping stability.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the case of a molding method that cures isothermally without including a heating process like the press molding method, the means described in Patent Document 1 cannot initiate the curing reaction during the heating process, so the effect of rapid curing was not observed. Further, although the prepreg described in Patent Document 2 has excellent drape stability, in the case where a relatively large amount of curing agent is present in the surface layer of the prepreg, there are problems such as a decrease in the tack stability of the prepreg and variations in mechanical properties due to localization of the curing agent in the entire prepreg and resulting curing defects. Furthermore, while the curing rate of the prepreg surface layer with a large amount of curing agent increases, there was concern that the curing rate of the prepreg inner layer without the presence of the curing agent would decrease.

[0005] An object of the present invention is to provide a prepreg that is excellent in both drape stability, which is the retention rate of drapeability over time, and rapid curability, and also excellent in the impregnability of the resin during production, and a method for producing the prepreg.

Means for Solving the Problems

[0006] To solve the above problems, the present invention provides a prepreg and a method for producing the same as shown below. 1. A prepreg in which a carbon fiber as component [A] is impregnated with an epoxy resin containing component [B], an epoxy resin curing agent containing component [C], and an epoxy resin composition having component [D], In the epoxy resin composition, component [C] occupies 85% by mass or more of the epoxy resin curing agent, and the ratio (H / E) of the number of moles (H) of active hydrogen contained in the epoxy resin curing agent to the number of moles (E) of epoxy groups of the epoxy resin is 1.1 or more and 1.6 or less, Moreover, a prepreg in which the mass ratio d of component [C] dissolved in the epoxy resin composition, as determined by differential scanning calorimetry, is 0.6 or more and 0.9 or less. [A] Carbon fiber [B] Liquid epoxy resin [C] Diaminodiphenylsulfone [D] Thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition 2. The prepreg according to 1 above, wherein the water absorption rate of the prepreg calculated by the water absorption test is 5% or less. 3. The prepreg according to 1 or 2 above, wherein among 100 parts by mass of the total amount of the epoxy resin contained in the epoxy resin composition, the bifunctional epoxy resin is 30 parts by mass or more and 70 parts by mass or less, and the trifunctional or higher epoxy resin is 30 parts by mass or more and 70 parts by mass or less. 4. The prepreg according to any one of 1 to 3 above, wherein the amount of the reaction product of the epoxy resin and component [C] is less than 5% by mass based on the amount of the epoxy resin composition. 5. A prepreg in which the carbon fiber as component [A] is impregnated with an epoxy resin composition having an epoxy resin containing component [B], an epoxy resin curing agent containing component [C], and component [D], in the epoxy resin composition, component [C] occupies 85% by mass or more of the epoxy resin curing agents, and the ratio (H / E) of the number of moles of active hydrogen (H) contained in the epoxy resin curing agent to the number of moles of epoxy groups (E) of the epoxy resin is 1.1 or more and 1.6 or less. When the enthalpy change per unit mass of the endothermic peak observed in the range of 70°C or more and 90°C or less, obtained from the temperature increase process at 5°C / min in differential scanning calorimetry, is ΔH1, ΔH1 is 0.08 J / g or more and 0.4 J / g or less. Moreover, when the enthalpy change per unit mass of the exothermic peak observed in the range of 100°C or more and 300°C or less is ΔH3, the ratio ΔH1 / ΔH3 of ΔH1 to ΔH3 is 5×10 -4 or more and 4×10 -3 or less. [A] Carbon fiber [B] Liquid epoxy resin [C] Diaminodiphenylsulfone [D] A thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition 6. A method for producing a prepreg obtained by impregnating component [A] with an epoxy resin composition in which an epoxy resin containing component [B], an epoxy resin curing agent containing component [C], and component [D] are mixed, A method for producing a prepreg, comprising performing steps 1, 2, and 3 in this order. Step 1: Charge component [C] in an amount of 60% by mass or more and less than 90% by mass based on the total amount of component [C] charged in steps 1 and 2, and dissolve it in the epoxy resin composition containing components [B] and [D]. Step 2: Charge component [C] in an amount of 10% by mass or more and less than 40% by mass based on the total amount of component [C] charged in steps 1 and 2 into the epoxy resin composition prepared in step 1, and disperse it in the epoxy resin composition. Step 3: Impregnate component [A] with the epoxy resin composition prepared in step 2. [A] Carbon fiber [B] Liquid epoxy resin [C] Diaminodiphenylsulfone [D] A thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition 7. Two types of diaminodiphenylsulfone with different particle size distributions are used as component [C], The method for producing a prepreg according to 6 above, wherein the D50 of component [C] charged in step 1 is less than 10 μm, and the D50 of component [C] charged in step 2 is 10 μm or more. 8. A method for producing a prepreg obtained by impregnating component [A] with an epoxy resin composition in which an epoxy resin containing component [B], an epoxy resin curing agent containing component [C], and component [D] are mixed, Two types of diaminodiphenylsulfone with different particle size distributions are used as component [C], and steps 4 and 5 are performed in this order. A method for producing a prepreg. Step 4: The two types of component [C] are simultaneously put into an epoxy resin composition containing components [B] and [D], and only some of component [C] is dissolved in the epoxy resin composition by heat treatment. Step 5: Impregnate component [A] with the epoxy resin composition prepared in Step 4. [A] Carbon fiber [B] Liquid epoxy resin [C] Diaminodiphenyl sulfone [D] Thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition 9. The method for producing a prepreg according to item 8 above, wherein the two types of component [C] with different particle size distributions have a difference in D50 in the particle size distribution of 5 μm or more. 10. Among the two types of component [C] with different particle size distributions, the smaller D50 is 5 μm or less, and the larger D50 is 10 μm or more and 30 μm or less, and the D90 of the particle size distribution of the component [C] with the smaller D50 is smaller than the D10 of the particle size distribution of the component [C] with the larger D50. The method for producing a prepreg according to item 8 or 9 above. [Advantages of the Invention]

[0007] According to the present invention, a prepreg excellent in drape stability, rapid curability, and resin impregnability during production can be obtained. [Embodiments for Carrying Out the Invention]

[0008] Hereinafter, the prepreg and the method for producing the prepreg of the present invention will be described in detail.

[0009] The prepreg of the present invention is obtained by impregnating carbon fiber as component [A] with an epoxy resin composition having an epoxy resin containing component [B], an epoxy resin curing agent containing component [C] (hereinafter sometimes simply referred to as a curing agent), and component [D]. [A] Carbon fiber [B] Liquid epoxy resin [C] Diaminodiphenyl sulfone [D]A thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition Here, when referring to an "epoxy resin composition", unless otherwise specified or explained, it is an epoxy resin composition having components [B], [C], and [D]. However, any composition formed by the epoxy resin and other components in the epoxy resin composition can be referred to as an "epoxy resin composition". For example, a composition consisting of components [B] and [D] without component [C], or a composition containing components [B] and [D] and a part of component [C] may also be referred to as an "epoxy resin composition".

[0010] Examples of the carbon fiber, which is component [A] in the present invention, include carbon fibers such as acrylic-based and pitch-based carbon fibers. Particularly for applications such as aircraft and automobiles, acrylic-based carbon fibers with high tensile strength are preferably used. Commercially available products of acrylic-based carbon fibers include "Torayca (registered trademark)" T1100G-24K, "Torayca (registered trademark)" T800G-24K, "Torayca (registered trademark)" T800S-24K, "Torayca (registered trademark)" T700G-12K, and "Torayca (registered trademark)" T700S-12K (all manufactured by Toray Industries, Inc.).

[0011] The carbon fiber, which is component [A], preferably has a number of filaments in one fiber bundle in the range of 2500 to 50000. If the number of filaments is less than 2500, the fiber arrangement is likely to meander and cause a decrease in strength. Also, if the number of filaments exceeds 50000, it may be difficult to impregnate the resin during prepreg production or molding. The number of filaments is more preferably in the range of 2800 to 40000.

[0012] Regarding the form and arrangement of the carbon fiber, it can be appropriately selected from unidirectionally aligned long fibers (fiber bundles), fabrics, etc. However, in order to obtain a carbon fiber reinforced composite material (hereinafter referred to as a composite material) that is lightweight and has a higher level of durability, the form of the carbon fiber is preferably continuous fibers such as unidirectionally aligned long fibers or fabrics.

[0013] The liquid epoxy resin, which is Component [B], is necessary for dissolving the solid epoxy resin and the powder components when Components [C] and [D] are powder components. At 40°C, when an iron metal piece is placed on the measured epoxy resin and the metal piece is instantaneously buried by gravity, it can be said that the epoxy resin is in a liquid state. From the viewpoints of the drape stability and rapid curability of the prepreg, it is preferable that the prepreg of the present invention contains 50 parts by mass or more of Component [B] with respect to 100 parts by mass of the total amount of the blended epoxy resin, and more preferably 70 parts by mass or more.

[0014] In particular, it is preferable that the epoxy resin composition contained in the prepreg of the present invention contains both a bifunctional epoxy resin and a trifunctional or higher-functional epoxy resin. Part or all of Component [B] may or may not be a bifunctional epoxy resin. Here, the bifunctional epoxy resin refers to an epoxy resin having two epoxy groups in one molecule, and the trifunctional or higher-functional epoxy resin refers to an epoxy resin having three or more epoxy groups in one molecule. When 30 parts by mass or more and 70 parts by mass or less of the bifunctional epoxy resin and 30 parts by mass or more and 70 parts by mass or less of the trifunctional or higher-functional epoxy resin are contained with respect to 100 parts by mass of the total amount of the epoxy resin, the prepreg has particularly excellent drape stability and rapid curability. Generally, a trifunctional or higher-functional epoxy resin easily deteriorates the drape stability of the prepreg because the reaction with a curing agent containing Component [C] gradually proceeds even at room temperature, but the drape stability is excellent in the above mixing ratio.

[0015] Also, from the perspective of rapid curing, when the glass transition temperature of the cured product of the epoxy resin composition (hereinafter sometimes simply referred to as "resin cured product") exceeds the molding temperature, the difference is preferably less than 30 °C, more preferably less than 20 °C. If the glass transition temperature of the resin cured product becomes too high compared to the molding temperature, the curing rate decreases during molding and the degree of cure does not increase sufficiently. However, from the perspective of heat resistance when used as an aircraft structural material, the glass transition temperature of the resin cured product is preferably 180 °C or higher. Therefore, considering that the general molding temperature for aircraft structural materials and the like is 180 °C to 190 °C, the glass transition temperature of the resin cured product is preferably 180 °C or higher and less than 220 °C, more preferably 190 °C or higher and less than 210 °C.

[0016] Among bifunctional epoxy resins, bifunctional epoxy resins with a molecular weight of 400 or less do not have a sharp increase in molecular weight before and after reaction even when reacting with a curing agent. Therefore, the viscoelastic change of the epoxy resin composition at room temperature is small, and the drape stability of the prepreg is better. Specific examples of such bifunctional epoxy resins include bisphenol A type epoxy resins with an epoxy equivalent of 400 or less, bisphenol F type epoxy resins with an epoxy equivalent of 400 or less, and diglycidyl-p-phenoxy aniline, but are not limited thereto. In particular, diglycidyl aniline type epoxy resins having a substituent on the benzene ring, such as diglycidyl-p-phenoxy aniline, have a slow curing reaction and are more excellent in drape stability at room temperature. Furthermore, it is preferable because it is easy to obtain a resin cured product having a high elastic modulus and a low rubbery state elastic modulus, and it is preferably contained in an amount of 10 parts by mass or more and 40 parts by mass or less based on 100 parts by mass of the total amount of the epoxy resin.

[0017] Commercially available products of bisphenol A type epoxy resins with an epoxy equivalent of 400 or less include "jER (registered trademark)" 825, "jER (registered trademark)" 828 (both manufactured by Mitsubishi Chemical Corporation), and the like.

[0018] Examples of commercially available bisphenol F type epoxy resins having an epoxy equivalent of 400 or less include "EPICLON (registered trademark)" 830 (manufactured by DIC Corporation).

[0019] Examples of commercially available diglycidyl-p-phenoxyaniline include "TOREP (registered trademark)" A-204E (manufactured by Toray Fine Chemical Co., Ltd.).

[0020] Specific examples of trifunctional or higher epoxy resins include, but are not limited to, triglycidyl-m-aminophenol, triglycidyl-p-aminophenol, and tetraglycidyl-4,4'-diaminodiphenylmethane. In particular, from the viewpoints of rapid curability and drape stability by optimal design of the glass transition temperature of the above-described resin cured product, tetraglycidyl-4,4'-diaminodiphenylmethane is preferably contained in an amount of 40 parts by mass or more and 65 parts by mass or less, more preferably 45 parts by mass or more and 60 parts by mass or less, based on 100 parts by mass of the total amount of the epoxy resin.

[0021] Examples of commercially available triglycidyl-m-aminophenol include "Araldite (registered trademark)" MY0600 (manufactured by Huntsman Japan K.K.).

[0022] Examples of commercially available triglycidyl-p-aminophenol include "Araldite (registered trademark)" MY0500 (manufactured by Huntsman Japan K.K.).

[0023] Examples of commercially available tetraglycidyl-4,4'-diaminodiphenylmethane include "Araldite (registered trademark)" MY721 (manufactured by Huntsman Japan K.K.), ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), and the like.

[0024] The diaminodiphenylsulfone of component [C] is a curing agent for epoxy resins. Since its curing rate is slower than that of other curing agents, the prepreg has very good drape stability at room temperature. Also, a resin cured product with excellent heat resistance can be obtained. As the diaminodiphenylsulfone, various isomers such as 3,3'-diaminodiphenylsulfone and 4,4'-diaminodiphenylsulfone can be used. From the viewpoint of the drape stability of the prepreg, among the epoxy resin curing agents contained in the epoxy resin composition, 85% by mass or more is component [C]. As component [C], 4,4'-diaminodiphenylsulfone, which has particularly low solubility in the epoxy resin composition, is preferred.

[0025] Commercially available products of diaminodiphenylsulfone include "Seika Cure (registered trademark)"-S (manufactured by Wakayama Seika Kogyo Co., Ltd.), 3,3'-DAS (manufactured by Konishi Chemical Industry Co., Ltd.), and the like.

[0026] Reasons for the slow curing rate of diaminodiphenylsulfone include its low solubility in the epoxy resin composition and the low nucleophilicity of the amino groups contained in diaminodiphenylsulfone. Usually, at room temperature, diaminodiphenylsulfone does not dissolve in the epoxy resin composition and exists as a powder dispersed therein. Therefore, the curing reaction hardly proceeds, and the prepreg has excellent drape stability. Note that the dispersion referred to in the present invention refers to a state in which an enthalpy change due to endotherm is observed in differential scanning calorimetry (DSC), and the dissolution referred to in the present invention refers to a state in which the above enthalpy change is not observed.

[0027] Even if part of the diaminodiphenylsulfone is dissolved as in the present invention, due to its low nucleophilicity, the drape stability at room temperature can be maintained for the prepreg using it. Also, when the step of dissolving part of the diaminodiphenylsulfone is carried out before the step of impregnating the epoxy resin composition into component [A] to obtain a prepreg, preferably at the initial stage of forming the epoxy resin composition, the diaminodiphenylsulfone can be dissolved in the epoxy resin composition at a temperature lower than the temperature in the step of obtaining the prepreg, and since the time for diffusion without the curing reaction progressing can be shortened, the curing rate when heated increases. In particular, under the conditions of heat molding with isothermal holding such as the press molding method, a remarkable difference in the curing rate is observed compared to the case where diaminodiphenylsulfone is not dissolved without adopting the above method. However, if the diaminodiphenylsulfone is completely dissolved, the curing reaction partially progresses even without heating to obtain a resin cured product, and the drape stability of the prepreg deteriorates. Therefore, it is preferable to dissolve it to such an extent that the curing reaction does not progress. In order to achieve both the drape stability and fast curing property of the prepreg at room temperature, the mass ratio (d) of the diaminodiphenylsulfone dissolved in the epoxy resin composition is 0.6 or more and 0.9 or less. Preferably, such a mass ratio d is 0.7 or more and 0.8 or less. When the amount of the powder component contained in the epoxy resin composition is large, it becomes difficult to impregnate the carbon fiber, but by adjusting the amount of the diaminodiphenylsulfone to be dissolved within the above range, the amount of the powder component can be reduced, and it becomes easier to impregnate.

[0028] In addition, the ratio (H / E) of the number of moles of active hydrogen (H) contained in the entire epoxy resin curing agent including the component [C] to the number of moles of epoxy groups (E) contained in the epoxy resin composition is 1.1 or more and 1.6 or less, preferably 1.2 or more and 1.4 or less, and more preferably 1.2 or more and 1.3 or less. 85% by mass or more of the component [C] occupying the epoxy resin curing agent has two primary amines in the molecule, and when the primary amine reacts with the epoxy resin, it becomes a secondary amine. This secondary amine can further react with the epoxy resin, but generally, it is known that the reaction rate of the primary amine is higher. Therefore, the higher the value of H / E, the more the amount of the primary amine with a high reaction rate increases, and the curing rate increases. Although the mechanical properties slightly decrease due to the decrease in the crosslinking density of the resin cured product as H / E increases, if it is 1.6 or less, the influence is small, and the effect of increasing the curing rate is greater.

[0029] As a method for dissolving diaminodiphenylsulfone in the epoxy resin composition, diaminodiphenylsulfone may be dissolved in an appropriate solvent and mixed with an epoxy resin or the like, or the epoxy resin composition may be heat-treated and dissolved without using a solvent.

[0030] The mass ratio d in the component [C] is calculated by measurement using DSC. Prepare a prepreg and a powdery component [C] having the same chemical structure as that contained in the prepreg, and perform a temperature increase measurement at 5 ° C. / min by DSC for each as a sample, and obtain the enthalpy change of the endothermic peak of the component [C] observed at 70 ° C. or higher and 90 ° C. or lower, respectively, and calculate according to the following formula. ΔH1 (J / g): Enthalpy change per unit mass observed at 70 ° C. or higher and 90 ° C. or lower for the prepreg (measurement of the endothermic peak for the component [C] contained in the prepreg) ΔH2 (J / g): Enthalpy change per unit mass observed at 70 ° C. or higher and 90 ° C. or lower for the powdery component [C] having the same chemical structure as that contained in the prepreg α: Mass ratio of the component [C] contained in the epoxy resin composition when the mass of the entire epoxy resin composition is taken as 1 β: The mass ratio of the epoxy resin composition when the mass of the prepreg is set to 1 Mass ratio d = 1 - ΔH1 / (ΔH2 × α × β) This endothermic peak is derived from the transition of the crystal structure of diaminodiphenylsulfone and is not observed in the diaminodiphenylsulfone dissolved in the epoxy resin composition. ΔH1 is an index representing the mass of diaminodiphenylsulfone contained in the prepreg that is not dissolved in the epoxy resin composition, and is 0.08 J / g or more and 0.4 J / g or less, preferably 0.13 J / g or more and 0.35 J / g or less. Note that α and β can be determined by the following procedure. First, the prepreg is immersed in chloroform to extract the epoxy resin composition. The insoluble matter is dissolved in an organic solvent such as methanol or dichloromethane until only the carbon fiber can be separated, and β is calculated from the mass ratio of the carbon fiber contained in the prepreg. The soluble matter obtained in each of these processes is fractionated by gel permeation chromatography (GPC), and the mass of each fraction is measured. Further, the area ratio of the peaks in the nuclear magnetic resonance (NMR) measurement of these fractions is calculated to calculate α. ΔH2 is, as described above, a component [C] having the same chemical structure as the component [C] contained in the prepreg, and is measured by DSC in the same manner, but a powdery component [C] collected from the prepreg may be used. When the prepreg contains two or more types of components [C] having different chemical structures, a sample in which they are mixed is measured for ΔH2 by DSC. Here, the value of ΔH2 is determined by the chemical structure and purity of the component [C]. For example, the ΔH2 of 4,4'-diaminodiphenylsulfone is about 8 J / g, and the ΔH2 of 3,3'-diaminodiphenylsulfone is about 12 J / g. When the prepreg contains both 3,3'-diaminodiphenylsulfone and 4,4'-diaminodiphenylsulfone, a sample for measuring ΔH2 is prepared by mixing them according to the mass ratio.

[0031] In order to obtain a prepreg having excellent drape stability, it is preferable that the reaction between the epoxy resin containing component [B] and component [C] has not proceeded, and the amount of these reaction products is preferably less than 5% by mass based on the epoxy resin composition. The amount of the reaction products can be calculated by using NMR of the epoxy resin composition, high performance liquid chromatography (HPLC) measurement, or the like.

[0032] In the present invention, the dissolution / dispersion degree of diaminodiphenyl sulfone can also be determined from the exothermic behavior of the prepreg measured by DSC. When the prepreg is heated at a rate of 5 °C / min by DSC, in addition to the endothermic peak derived from component [C] observed at 70 °C or higher and 90 °C or lower, an exothermic peak derived from the curing reaction is observed at 100 °C or higher and 300 °C or lower. Here, since the enthalpy change per unit mass of the prepreg at 100 °C or higher and 300 °C or lower mainly originates from the heat of reaction between the epoxy resin and the curing agent, when defined as ΔH3 as described below, ΔH1 / ΔH3, which is the ratio of the enthalpy change per unit mass of ΔH1 and ΔH3, serves as an index of the amount of diaminodiphenyl sulfone not dissolved in the epoxy resin composition in the prepreg. ΔH3 (J / g): The enthalpy change per unit mass observed at 100 °C or higher and 300 °C or lower for the prepreg (measuring the exothermic peak for the curing reaction of the epoxy resin containing component [B] and the epoxy resin curing agent containing component [C] contained in the prepreg) ΔH1 / ΔH3 is 5 × 10 -4 or more and 4 × 10 -3 or less is preferable, and more preferably 1 × 10 -3 or more and 3 × 10 -3 or less. This ratio is calculated by the following formula. Ratio of enthalpy change per unit mass = ΔH1 / ΔH3 Component [D] is a thermoplastic resin soluble in any of the epoxy resins contained in the epoxy resin composition used for the prepreg of the present invention, and is effective for adjusting the viscoelasticity of the epoxy resin composition and improving the toughness of the resin cured product. In the prepreg, usually, component [D] is present dissolved in the epoxy resin composition.

[0033] In particular, among these, thermoplastic resins containing functional groups having reactivity with epoxy resins are preferable from the viewpoints of improving the toughness of the resin cured product and high compatibility with epoxy resins. Specific examples include, but are not limited to, polyethersulfone, polysulfone, polyetherimide, and polycarbonate. From the viewpoints of the tack of the prepreg near room temperature, the handleability of the resin film of the epoxy resin composition, and the suppression of resin flow during the molding of the prepreg laminate, component [D] is preferably contained in an amount of 5% by mass or more and 20% by mass or less based on the total amount of the epoxy resin composition.

[0034] Commercially available polyethersulfones include "Sumikaexcel (registered trademark)" PES3600P, "Sumikaexcel (registered trademark)" PES5003P, "Sumikaexcel (registered trademark)" PES5200P, "Sumikaexcel (registered trademark)" PES7600P (all manufactured by Sumitomo Chemical Co., Ltd.), "Ultrason (registered trademark)" E2020P SR, "Ultrason (registered trademark)" E2021SR (both manufactured by BASF), "Virantage (registered trademark)" VW-10700RFP (manufactured by Solvay Advanced Polymers), and the like.

[0035] Commercially available polyetherimides include "Ultem (registered trademark)" 1000, "Ultem (registered trademark)" 1010, "Ultem (registered trademark)" 1040 (all manufactured by SABIC Petrochemicals Japan Co., Ltd.), and the like.

[0036] In addition to the above components, epoxy resins other than component [B], epoxy resin curing agents other than component [C], organic particles, inorganic particles, etc. may be contained within a range that does not impair the effects of the present invention.

[0037] The prepreg of the present invention can be manufactured by a known method using carbon fiber as component [A] and the above epoxy resin composition. For example, it can be manufactured by a wet method in which the epoxy resin composition is dissolved in a solvent to reduce the viscosity and impregnated, or a hot melt method in which the viscosity is reduced by heating and impregnated. However, the hot melt method is preferred because it is easier to control the mass ratio of the components existing in a dissolved state in component [C].

[0038] In the prepreg of the present invention, there is no limitation on the basis weight of the carbon fiber, but the larger the basis weight, the more remarkable the effect of improving the impregnation property of the epoxy resin composition due to partial dissolution of component [C]. However, when the basis weight exceeds 1000 g / m 2 the drapeability of the prepreg tends to deteriorate. Therefore, the basis weight of the carbon fiber is preferably 100 g / m 2 or more and 1000 g / m 2 or less.

[0039] The mass content of the carbon fiber in the prepreg of the present invention is preferably 40% by mass or more and 90% by mass or less, more preferably 50% by mass or more and 80% by mass or less. That is, when the prepreg is composed of carbon fiber and an epoxy resin composition, the mass content of the epoxy resin composition is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less. If the mass content of the carbon fiber is less than 40% by mass, the ratio of the epoxy resin composition is large, and the excellent mechanical properties of the carbon fiber cannot be utilized, and the amount of heat generated during curing of the carbon fiber reinforced composite material may become too high. Further, when the mass content of the carbon fiber exceeds 90% by mass, poor impregnation of the epoxy resin composition may occur, so voids are likely to occur in the carbon fiber reinforced composite material.

[0040] The prepreg of the present invention preferably has the epoxy resin composition sufficiently impregnated in the carbon fibers. The degree of impregnation of the resin into the carbon fibers in the prepreg is preferably such that the water absorption rate (WPU) of the prepreg calculated by the water absorption test is 5% or less, more preferably 3% or less. If the WPU is too high, it may cause the prepreg to crack in the out-of-plane direction when laminating the prepreg, and there is also a risk that voids will remain in the carbon fiber reinforced composite material after molding.

[0041] The WPU of the prepreg in the present invention is measured as follows. First, prepare a 100 mm × 100 mm square prepreg with carbon fibers arranged in one direction and measure its mass. Let the mass at this time be W1. Grip the prepared prepreg from both sides with thin aluminum plates so that the prepreg protrudes 5 mm. At this time, the protruding prepreg has a fiber direction of 5 mm and a surface orthogonal to the fibers of 100 mm. Grip the aluminum plates with a clamp. Immerse the 5 mm protruding part in water at a temperature of 23°C for 5 minutes. After immersion, take out the prepreg, remove all the water on the surface layer of the prepreg, and measure the mass of the water-absorbed prepreg. Let the mass at this time be W2. At this time, WPU is WPU (%) = (W2 - W1) / W1 × 100 calculated by

[0042] The prepreg of the present invention can be applied to prepregs in all forms such as unidirectional prepregs in which the reinforcing fibers are arranged in one direction and woven prepregs in which the reinforcing fibers have a woven form. However, for applications that require high specific strength and specific modulus, unidirectional prepregs in which carbon fiber bundles are aligned in a single direction are most preferred.

[0043] As a method of laminating the prepreg of the present invention in a predetermined form and then heating and pressurizing to cure the epoxy resin composition for molding, known methods such as autoclave molding method, press molding method, bagging molding method, wrapping tape method, and internal pressure molding method can be used.

[0044] Hereinafter, the manufacturing method of the first prepreg of the present invention will be described. In such a manufacturing method, as a method of impregnating the component [A] with an epoxy resin composition in which the components [B], [C] and [D] are mixed, the following steps 1, 2 and 3 are carried out in this order. Step 1: Component [C] is added in an amount of 60% by mass or more and less than 90% by mass based on the total amount of component [C] added in Steps 1 and 2, and dissolved in the epoxy resin composition containing components [B] and [D]. Step 2: Component [C] is added to the epoxy resin composition prepared in Step 1 in an amount of 10% by mass or more and less than 40% by mass based on the total amount of component [C] added in Steps 1 and 2, and dispersed in the epoxy resin composition. Step 3: The epoxy resin composition prepared in Step 2 is impregnated into component [A].

[0045] Regarding the preferable temperature control in the steps from the preparation of the epoxy resin composition to the preparation of the prepreg in the method for producing the first prepreg of the present invention, it is as follows. First, in Step 1, except for the component [A] and the epoxy resin curing agent containing the component [C], the raw materials of the epoxy resin composition containing the components [B] and [D] are uniformly mixed at a high temperature of 140°C or higher. Then, 60% by mass or more and less than 90% by mass of the component [C] is added, and usually heated at 80°C or higher and 120°C or lower for a short time, so that the component [C] can be dissolved in the epoxy resin composition. At this time, it is preferable to sufficiently stir the epoxy resin composition into which the component [C] has been added. However, in order to sufficiently dissolve the component [C] without proceeding the reaction between the epoxy resin and the component [C], the stirring time is preferably less than 30 minutes. Then, the temperature is quickly lowered to 75°C or lower, and subsequently, in Step 2, the remaining component [C] and the epoxy resin curing agent other than the component [C] are added and uniformly dispersed in the epoxy resin composition in a short time. Finally, the epoxy resin composition obtained in Step 2 is impregnated into the component [A] in Step 3 to obtain a prepreg. Although the impregnation method is not limited, in order to easily control the mass ratio of the components existing in a dissolved state by the component [C], it is preferable to adopt a method in which the temperature during handling of the epoxy resin composition is low and the handling time at 100°C or higher is short. As an example, the epoxy resin composition obtained in Step 2 is applied onto a release sheet at 75°C or lower to prepare a resin film, and then the resin film is heated and pressed in a state where it is disposed on one or both sides of the component [A] for impregnation to obtain a prepreg. It is also possible to further dispose a resin film on one or both sides of this prepreg and heat and press it. In the step of impregnating the resin film, it is necessary to adjust the impregnation temperature and the conveyance speed (line speed) of the resin film so that the dissolution and curing reaction of the component [C] do not proceed. Specifically, the impregnation temperature is preferably 100°C or higher and 160°C or lower, and the line speed is preferably 1 m / min or higher.

[0046] When the component [C] input in Step 1 and the component [C] input in Step 2 are both powders, one type with the same particle size distribution may be used. Or, two types with different particle size distributions but the same D50 may be used, with different types of powders input in each of Step 1 and Step 2. However, two types of particles with different particle size distributions and different D50s can also be used. In that case, for the component [C] input in Step 1, it is better if its D50 is smaller for easier dissolution. Specifically, it is preferably that the D50 of the particles input in Step 1 is less than 10 μm, and more preferably less than 8 μm. On the other hand, when the component [C] input in Step 2 is a powder, it is better if its D50 is larger so that it is difficult to dissolve in the prepreg manufacturing process. However, if the D50 is too large, there is a possibility that a resin film with a uniform thickness cannot be obtained in the resin film manufacturing process, or the component [C] may not be uniformly present in the resin film. Therefore, when the component [C] input in Step 2 is a powder, the D50 is preferably 10 μm or more and 30 μm or less. Note that in the method for manufacturing the first prepreg, it is not prohibited to use three or more types of particles with different particle size distributions.

[0047] Here, D50 can be measured by the following method. Using a particle size distribution analyzer, in a dry unit, measure the D50 of the particles dispersed in air three times according to JIS Z8825-1(2001), and obtain the average value. As the particle size distribution analyzer, for example, a particle size distribution measuring device LA-950 (manufactured by HORIBA, Ltd.) can be used.

[0048] Hereinafter, the method for manufacturing the second prepreg of the present invention will be described. In such a manufacturing method, in a method for manufacturing a prepreg in which a component [A] is impregnated with an epoxy resin composition in which components [B], [C], and [D] are mixed, it is premised that two types of diaminodiphenylsulfone having different particle size distributions are used as component [C], and the following steps 4 and 5 are performed in this order. The two types of diaminodiphenylsulfone having different particle size distributions referred to here specifically refer to those having different D50 values. Note that steps 4 and 5 are not steps performed subsequent to the above-described steps 1 to 3. Also, in the method for manufacturing the second prepreg, it is not prohibited to use three or more types of particles having different particle size distributions. Step 4: Two types of component [C] having different particle size distributions are simultaneously introduced into an epoxy resin composition containing components [B] and [D], and only a part of component [C] is dissolved in the epoxy resin composition by heat treatment. Step 5: The epoxy resin composition prepared in step 4 is impregnated into component [A].

[0049] In the method for manufacturing the second prepreg, at least two types of diaminodiphenyl sulfone, namely component [C] with a large D50 and component [C] with a small D50, are introduced to adjust the ease of dissolution of component [C] in component [B], and the mass ratio of dissolved component [C] can be controlled. Also, since the two types of diaminodiphenyl sulfone are introduced simultaneously, a prepreg made of an epoxy resin composition in which a part of component [C] is dissolved can be produced in a shorter time and more easily than in the method for manufacturing the first prepreg. Regarding the preferable temperature control in the steps from the production of the epoxy resin composition to the production of the prepreg in the method for manufacturing the second prepreg of the present invention, it is as follows. First, in step 4, except for component [A] and the epoxy resin curing agent containing component [C], the raw materials of the epoxy resin composition containing components [B] and [D] are uniformly mixed at a high temperature of 140°C or higher. Then, component [C] and the epoxy resin curing agent other than component [C] are introduced and heated at 80°C or higher and 120°C or lower for a short time. Among component [C], those with a smaller particle diameter tend to dissolve in other components faster, so the component [C] with a small D50 can be preferentially dissolved in the epoxy resin composition. The stirring time when stirring the epoxy resin composition into which component [C] has been introduced is preferably less than 30 minutes, similar to step 1. Then, the temperature is quickly lowered to 75°C or lower to obtain an epoxy resin composition. Subsequently, the epoxy resin composition obtained in step 4 can be impregnated into component [A] in step 5 to obtain a prepreg. The impregnation method is the same as that in the method for manufacturing the first prepreg. To make it easier to control the mass ratio of dissolved component [C], it is better that the difference in D50 between the component [C] with a smaller D50, which is preferentially soluble in step 4, and the component [C] with a larger D50, which is expected to be dispersed without dissolving, is larger. Specifically, it is preferable that the difference in D50 between the two is 5 μm or more. Among them, it is more preferable that the smaller D50 of component [C] is 5 μm or less, and the larger D50 of component [C] is 10 μm or more and 30 μm or less.Furthermore, it is more preferable that D90 of the particle size distribution of the component [C] with the smaller D50 is smaller than D10 of the particle size distribution of the component [C] with the larger D50. This also applies to the case of using two types of components [C] with different particle size distributions in the method for producing the first prepreg. When using three or more types of particles with different particle size distributions, for any combination of two of them, it is sufficient if the particle size distributions are in the above relationship. If D50 of the particles with the smaller D50 is too large, there is a possibility that a resin film with a uniform thickness cannot be obtained in the resin film production process, or that the component [C] may not be uniformly present in the resin film.

[0050] In addition, the upper and lower limits of the numerical ranges described above can be arbitrarily combined.

Examples

[0051] Hereinafter, the effects of the present invention will be more specifically described with reference to examples. Note that the present invention is not limited to the following examples.

[0052] The raw materials used in the present examples and comparative examples are as follows.

[0053] <Component [A]> · "Torayca (registered trademark)" T700GC-12K-31E (number of filaments: 12,000 filaments / bundle, manufactured by Toray Industries, Inc.).

[0054] <Component [B]> · ELM434 (tetraglycidyl-4,4'-diaminodiphenylmethane, tetrafunctional epoxy resin, molecular weight: 488 g / mol, epoxy equivalent: 122 g / mol, manufactured by Sumitomo Chemical Co., Ltd.). · "TOREP (registered trademark)" A-204E (diglycidyl-p-phenoxyaniline, bifunctional epoxy resin, molecular weight: 324 g / mol, epoxy equivalent: 162 g / mol, manufactured by Toray Fine Chemical Co., Ltd.). · "EPICLON (Registered Trademark)" 830 (Bisphenol F type epoxy resin, bifunctional epoxy resin, molecular weight: 340 g / mol, epoxy equivalent: 170 g / mol, manufactured by DIC Corporation).

[0055] <Component [C]> · 4,4'-DDS (4,4'-Diaminodiphenyl sulfone, active hydrogen equivalent: 62 g / mol, manufactured by Wakayama Seika Kogyo Co., Ltd.) Five types of 4,4'-DDS (4,4'-DDS1 to 5) with different particle size distributions obtained by crushing and classifying commercially available products were used. As a result of measuring the particle size distributions of these 4,4'-DDS using the above-mentioned particle size distribution measuring device, only one maximum value of the peak was observed in each case. Also, the respective D10, D50, and D90 were as follows. 4,4'-DDS1 (D50: 4 μm, D90: 9 μm) 4,4'-DDS2 (D10: 3 μm, D50: 7 μm, D90: 15 μm) 4,4'-DDS3 (D10: 4 μm, D50: 9 μm, D90: 18 μm) 4,4'-DDS4 (D10: 7 μm, D50: 15 μm) 4,4'-DDS5 (D10: 10 μm, D50: 20 μm) <Component [D]> · "SUMIKA Excel (Registered Trademark)" PES5003P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd.).

[0056] <Epoxy resin curing agent other than Component [C]> · CAF (9,9-Bis(3-chloro-4-aminophenyl)fluorene, active hydrogen equivalent: 104 g / mol, manufactured by Lonza Ltd.). CAF1 with D50 of 7 μm and CAF2 with D50 of 20 μm obtained by crushing and classifying the above-mentioned commercially available products were used. · "jER Cure (Registered Trademark)" WA (diethyltoluenediamine, active hydrogen equivalent: 45 g / mol, manufactured by Mitsubishi Chemical Corporation).

[0057] <Preparation method 1 of epoxy resin composition> Components [B] and [D] were added in predetermined amounts, heated to 140 to 160 °C, stirred for 1 hour to obtain a transparent viscous liquid. In each example and comparative example, two types of particles with different particle size distributions were used as the epoxy resin curing agent. While stirring was continued, the temperature was lowered to 80 to 120 °C, and a predetermined amount of the particle with a smaller D50 among the above two types of particles was added and stirred for 15 minutes (Step 1 in the method for producing the first prepreg). Then, the temperature was lowered to 75 °C or lower, a predetermined amount of the particle with a larger D50 was added, and stirring was continued for another 30 minutes to obtain an epoxy resin composition (Step 2 in the method for producing the first prepreg). The component compounding ratios of each example and comparative example are as shown in Table 1. The numerical values for the curing agent in Table 1 are displayed with the unit of equivalent, which indicates the H / E of each curing agent with respect to the epoxy resin, and the same applies hereinafter.

[0058] <Method for Preparing Epoxy Resin Composition 2> Components [B] and [D] were added in predetermined amounts, heated to 140 to 160 °C, stirred for 1 hour to obtain a transparent viscous liquid. While stirring was continued, the temperature was lowered to 80 to 120 °C, the entire amount of Component [C] was added, and stirring was carried out for 15 minutes. Then, the temperature was lowered to 75 °C or lower and stirring was continued for another 30 minutes to obtain an epoxy resin composition. The component compounding ratios of each example and comparative example are as shown in Table 1.

[0059] <Method for Preparing Epoxy Resin Composition 3> Components [B] and [D] were added in predetermined amounts, heated to 140 to 160 °C, stirred for 1 hour to obtain a transparent viscous liquid. While stirring was continued, the temperature was lowered to 75 °C or lower, the entire amount of Component [C] was added, and stirring was carried out for 30 minutes to obtain an epoxy resin composition. The component compounding ratios of the comparative examples are as shown in Table 1.

[0060] <Method for Producing Prepreg 1> The epoxy resin composition prepared by <Method for Preparing Epoxy Resin Composition 1> was applied onto a release sheet so that the mass of the epoxy resin composition was 70 g / m 2A resin film was produced. Then, the resin side of the resin film was placed on both sides of component [A] and heated and pressed, and impregnated with an epoxy resin composition at a line speed of 2 m / min to obtain a prepreg (carbon fiber mass: 270 g / m 2 , epoxy resin composition content: 34% by mass).

[0061] <Production method 2 of prepreg> Using the epoxy resin composition prepared by <Preparation method 2 of epoxy resin composition>, a prepreg was produced in the same procedure as in Production method 1 of prepreg.

[0062] <Production method 3 of prepreg> Using the epoxy resin composition prepared by <Preparation method 3 of epoxy resin composition>, a prepreg was produced in the same procedure as in Production method 1 of prepreg.

[0063] In the "Production method of prepreg" in the table, for each example and comparative example, which of the above Production methods 1 to 3 of prepreg was used is indicated by a numerical value.

[0064] <Molding method of prepreg laminate> The produced prepreg was cut into a square with a side length of 250 mm, and 8 sheets were laminated in one direction to obtain a prepreg laminate. The laminate placed in a mold was sandwiched between upper and lower press plates preheated to 190 °C, pressed at a surface pressure of 0.6 MPa, and heated for a certain period of time to obtain a composite material.

[0065] <Calculation method of mass ratio of component [C] dissolved and present in prepreg> For the produced prepreg, it was determined according to the calculation method of the mass ratio (d) of the above component [C] dissolved and present in the epoxy resin composition.

[0066] <Calculation method of ratio of enthalpy change per unit mass of endothermic peak and exothermic peak observed in DSC measurement of prepreg> For the prepared prepreg, ΔH1 and ΔH3 were determined respectively, and calculated according to the calculation method of the ratio of enthalpy change per unit mass (ΔH1 / ΔH3) described above.

[0067] <Method for Evaluating Impregnability of Prepreg> The water absorption rate (WPU) of the prepreg prepared by the above water absorption test was measured to evaluate the impregnability of the prepreg. WPU of 3% or less was designated as A, 5% or less as B, 8% or less as C, and more than 8% as D. A, B, and C are in order of preference, and A, B, and C are qualified, while D is unqualified.

[0068] <Method for Evaluating Drape Stability of Prepreg> The glass transition temperature (Tg) of the prepreg left standing at 23°C for 30 days and the Tg of the prepreg immediately after production were measured by DSC, and the difference ΔTg (°C) between the two was used as an index of drape stability. 10 - 15 mg of the prepreg was packed in a sealed sample container, and in the DSC curve detected in the range of -50°C to 50°C when the temperature was raised at 5°C / min, the temperature at the intersection of the curve of the stepped change part in the glass transition state and the straight line equidistant in the vertical axis direction from the two straight lines obtained by extending the respective baseline before and after the glass transition was defined as Tg. ΔTg of 5°C or less was designated as A, 7°C or less as B, 10°C or less as C, and more than 10°C as D. A, B, and C are in order of preference, and A, B, and C are qualified, while D is unqualified.

[0069] <Method for Evaluating Quick Curing Property of Prepreg> The prepared prepreg was cured by <Method for Molding Laminate of Prepreg>, and the heating time required for the degree of cure to reach 95% was used as an index of quick curing property. The degree of cure was calculated by the following method. 10 - 15 mg of the prepared prepreg or the composite material cured therefrom was packed in a sealed sample container, and the enthalpy change of the exothermic peak observed at 100°C or higher and 300°C or lower when the temperature was raised at 5°C / min by DSC was determined respectively, and calculated by the following formula. ΔH3 (J / g): Enthalpy change per unit mass for the prepreg ΔH4 (J / g): Enthalpy change per unit mass for the composite material Degree of hardening (%) = (1 - ΔH4 / ΔH3) × 100 The time to reach 95% degree of hardening was designated as A if it was 35 minutes or less, B if it was 40 minutes or less, C if it was 60 minutes or less, and D if it exceeded 60 minutes. In the order of A, B, C, D, they are preferably in this order. A, B, and C are qualified, and D is unqualified.

[0070] <Method for evaluating heat resistance of composite material> The Tg of the composite material obtained by curing the laminate of the produced prepreg was used as an index of heat resistance. Tg was measured and determined using a dynamic viscoelasticity measuring device (DMA) for a test piece with a length of 35 mm, a width of 10 mm, and a thickness of 2 mm made using the composite material. In the storage elastic modulus G' curve, the intersection temperature value between the tangent line in the region indicating that the target composite material is in a glass state and the tangent line in the region indicating that it is in a transition state was defined as Tg (°C). Here, the measurement was performed at a heating rate of 5 °C / min and a frequency of 1 Hz. The Tg of the composite material was designated as A if it was 180 °C or more and less than 210 °C, B if it was 210 °C or more and less than 220 °C, C if it was 220 °C or more, and D if it was less than 180 °C. In the order of A, B, C, D, they are preferably in this order. A, B, and C are qualified, and D is unqualified.

[0071] <Examples 1 to 9> According to <Manufacturing method 1 of prepreg>, prepregs of Examples 2, 7, and 8 were produced with the component compounding ratios shown in Table 1, and according to <Manufacturing method 2 of prepreg>, prepregs of Examples 1, 3 to 6, and 9 were produced. When it contains components [A], [B], [C], and [D], component [C] occupies 85% by mass or more of the epoxy resin curing agent, H / E is 1.1 or more and 1.6 or less, and the mass ratio d of component [C] dissolved in the epoxy resin composition is 0.6 or more and 0.9 or less, a prepreg excellent in drape stability, rapid curability, and impregnation property was obtained, and the heat resistance of the composite material was also within a preferable range. Examples 2 and 3 were excellent in the impregnation property of the prepreg and were particularly excellent from the viewpoint of achieving both drape stability and rapid curability.

[0072] <Comparative Example 1> According to <Production Method 3 of Prepreg>, a prepreg was produced with the component compounding ratios shown in Table 1. When the step of dissolving component [C] was not included in the preparation stage of the epoxy resin composition, dissolution did not progress significantly even in the prepreg production step. As a result, the amount of powder contained in the epoxy resin composition was large and the impregnability was not favorable. Also, although rapid curability was observed due to the value of H / E being greater than 1, since the dissolved amount of component [C] in the produced prepreg was small, the further effect of improving the curing rate by pre-dissolving component [C] could not be obtained.

[0073] <Comparative Example 2> According to <Production Method 1 of Prepreg>, a prepreg was produced using CAF instead of component [C] as per the component compounding ratios shown in Table 1. When CAF was used as the epoxy resin curing agent, the time to reach 95% cure degree was slower compared to the case of 4,4’-DDS. Also, since the active hydrogen equivalent of CAF was large, the powder ratio in the entire epoxy resin composition was high and the impregnability was not favorable.

[0074] <Comparative Example 3> According to <Production Method 1 of Prepreg>, a prepreg was produced using 4,4’-DDS3 as the component [C] with the smaller D50 and jER Cure WA instead of the component [C] with the larger D50 as per the component compounding ratios shown in Table 1. When a part of 4,4’-DDS was replaced with jER Cure WA, which is a liquid epoxy resin curing agent, the reaction rate between the epoxy resin and jER Cure WA was high, resulting in a large ΔTg of the prepreg and deterioration of the drape stability.

[0075] <Comparative Examples 4 - 7> According to <Production Method 2 of Prepreg>, a prepreg was produced with the component compounding ratios shown in Table 1. As shown in Comparative Example 4 of Table 1, when H / E was less than 1.1, the rapid curability deteriorated. As shown in Comparative Example 7, when it exceeded 1.6, deterioration of the drape stability and deterioration of the heat resistance of the composite material were observed. Also, as shown in Comparative Example 5, when the mass ratio d was less than 60%, the rapid curability and impregnability decreased. As shown in Comparative Example 6, when the mass ratio d exceeded 90%, deterioration of the drape stability was observed.

[0076]

Table 1

Industrial Applicability

[0077] According to the present invention, a prepreg excellent in drape stability, rapid curability, and impregnation property can be obtained. Further, a composite material obtained by laminating and molding such a prepreg is particularly suitably used as a structural material. For example, in aerospace applications, it is suitably used for primary aircraft structural materials such as wings and fuselages, secondary structural materials such as tail fins, floor beams, flaps, ailerons, cowls, fairings, and interior materials, rocket motor cases, and satellite structural materials. Also, in general industrial applications, it is suitably used for structural materials such as automobiles.

Claims

1. A prepreg obtained by impregnating carbon fiber as component [A] with an epoxy resin containing component [B], an epoxy resin curing agent containing component [C], and an epoxy resin composition having component [D], in the epoxy resin composition, component [C] occupies 85% by mass or more of the epoxy resin curing agent, and the ratio (H / E) of the number of moles of active hydrogen (H) contained in the epoxy resin curing agent to the number of moles of epoxy groups (E) of the epoxy resin is 1.1 or more and 1.6 or less, and a prepreg in which the mass ratio d of component [C] dissolved in the epoxy resin composition, determined from the temperature increase process at 5 °C / min in differential scanning calorimetry, is 0.6 or more and 0.9 or less. [A]Carbon fiber [B]Liquid epoxy resin [C]Diaminodiphenyl sulfone [D]A thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition

2. The prepreg according to claim 1, wherein the water absorption rate of the prepreg calculated by a water absorption test is 5% or less.

3. The prepreg according to claim 1, wherein among 100 parts by mass of the total amount of the epoxy resin contained in the epoxy resin composition, the bifunctional epoxy resin is 30 parts by mass or more and 70 parts by mass or less, and the trifunctional or higher epoxy resin is 30 parts by mass or more and 70 parts by mass or less.

4. The prepreg according to claim 1, wherein the amount of the reaction product of the epoxy resin and component [C] is less than 5% by mass based on the amount of the epoxy resin composition.

5. A prepreg obtained by impregnating carbon fiber as component [A] with an epoxy resin containing component [B], an epoxy resin curing agent containing component [C], and an epoxy resin composition having component [D], in the epoxy resin composition, component [C] occupies 85% by mass or more of the epoxy resin curing agent, and the ratio (H / E) of the number of moles of active hydrogen (H) contained in the epoxy resin curing agent to the number of moles of epoxy groups (E) of the epoxy resin is 1.1 or more and 1.6 or less, assuming that the enthalpy change per unit mass of the endothermic peak observed in the range of 70 °C or more and 90 °C or less obtained from the temperature increase process at 5 °C / min in differential scanning calorimetry is ΔH1, ΔH1 is 0.08 J / g or more and 0.4 J / g or less, Moreover, when the enthalpy change per unit mass of the exothermic peak observed in the range of 100°C or higher and 300°C or lower is defined as ΔH3, the ratio of ΔH1 to ΔH3, ΔH1 / ΔH3, is 5×10 －４ or more and 4×10 －３ or less prepreg. [A]Carbon fiber [B]Liquid epoxy resin [C]Diaminodiphenyl sulfone [D]A thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition

6. A method for producing a prepreg obtained by impregnating a component [A] with an epoxy resin composition containing a component [B], an epoxy resin curing agent containing a component [C], and a component [D]. A method for producing a prepreg, comprising performing steps 1, 2, and 3 in this order. Step 1: 60% by mass or more and less than 90% by mass of the component [C] is added based on the total amount of the component [C] added in steps 1 and 2, and dissolved in the epoxy resin composition containing the components [B] and [D]. Step 2: 10% by mass or more and less than 40% by mass of the component [C] is added based on the total amount of the component [C] added in steps 1 and 2 to the epoxy resin composition prepared in step 1, and dispersed in the epoxy resin composition. Step 3: The epoxy resin composition prepared in step 2 is impregnated into the component [A]. [A] Carbon fiber [B] Liquid epoxy resin [C] Diaminodiphenyl sulfone [D] A thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition

7. Two types of diaminodiphenyl sulfone with different particle size distributions are used as the component [C]. The method for producing a prepreg according to claim 6, wherein the D50 of the component [C] added in step 1 is less than 10 μm, and the D50 of the component [C] added in step 2 is 10 μm or more.

8. A method for producing a prepreg obtained by impregnating a component [A] with an epoxy resin composition containing a component [B], an epoxy resin curing agent containing [C], and [D], Two types of diaminodiphenyl sulfone with different particle size distributions are used as the component [C], and steps 4 and 5 are performed in this order. The method for producing a prepreg. Step 4: The two types of component [C] are simultaneously added to the epoxy resin composition containing the components [B] and [D], and only a part of the component [C] is dissolved in the epoxy resin composition by heat treatment. Step 5: The epoxy resin composition prepared in step 4 is impregnated into the component [A]. [A] Carbon fiber [B] Liquid epoxy resin [C] Diaminodiphenyl sulfone [D] A thermoplastic resin soluble in the epoxy resin contained in the epoxy resin composition

9. The method for producing a prepreg according to claim 8, wherein the difference in D50 in the particle size distribution between the two types of component [C] is 5 μm or more.

10. Among two types of components [C] having different particle size distributions, the smaller D50 is 5 μm or less, and the larger D50 is 10 μm or more and 30 μm or less, and the D90 of the particle size distribution of the component [C] with the smaller D50 is smaller than the D10 of the particle size distribution of the component [C] with the larger D50. The method for manufacturing a prepreg according to claim 8.

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