Resin composition, preparation method thereof, and carbon fiber prepreg

Abstract

The present invention discloses a resin composition, a preparation method thereof, and a carbon fiber prepreg, relating to the technical field of composite materials. The resin composition comprises an epoxy resin component, a thermoplastic resin, and an aromatic curing agent with flexible side chains. The thermoplastic resin is added in an amount of 3% to 28% of the epoxy resin component, and the molar ratio of active hydrogen in the aromatic curing agent to the number of epoxy groups in the epoxy resin component is 0.7 to 1.3. The epoxy resin component comprises, by mass percentage, 5% to 50% of a first epoxy resin having a cyclohexane structure and 50% to 95% of a second epoxy resin having a benzene ring structure. The resin composition provided herein has good flexibility and heat resistance. The flexible chain segments of the first epoxy resin and the curing agent can eliminate large deformation caused by tensile stress in the composite material, delay the breakage of the resin chain segments, and achieve a high strength conversion rate for the carbon fibers.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to a resin composition, a preparation method thereof, and a carbon fiber prepreg. Background Art

[0002] Thermosetting carbon fiber composites are high-performance structural materials made from thermosetting resins and carbon fibers. After curing, they have specific strength and specific stiffness far exceeding those of traditional metal materials such as steel. Therefore, they are widely used in aerospace, rail transportation, shipbuilding, sports and leisure, and other fields. In particular, with the policy trends of countries around the world in recent years on energy, the demand for pressure vessels, wind power, and other fields has increased dramatically. Prepregs have been a more mainstream composite molding material due to their good product quality control level and process operability. All advanced carbon fiber products are first used in prepreg products. However, researchers usually find that the tensile strength of advanced carbon fibers themselves is very high, but the tensile strength of the composite laminates finally produced is relatively low. For applications such as wings, wind turbine blades, and gas cylinders, this "shortcoming" directly restricts the further application of composite materials.

[0003] As an important component of the composite material structure, the interface has an important influence on the mechanical properties and destructive behavior of the composite material. A good interface can increase the integrity of the composite material structure, so that the load is effectively transferred to the fiber through the matrix resin, and the tensile strength and other mechanical properties of the composite material are significantly improved. In order to improve the weak bonding between carbon fiber and matrix resin, scholars usually improve the weak interface problem from three aspects: 1) through sizing agent modification research to prevent the formation of a weak interface layer; 2) etching the carbon fiber surface to produce a rough surface, thereby producing an anchoring effect, so as to achieve the purpose of improving the interfacial bonding performance; 3) improving the affinity between the resin matrix and the carbon fiber parts, thereby improving the bonding between the two parts. So for the resin matrix, if you want to improve the tensile strength of the composite material, on the one hand, you need to increase the bonding force of the structural groups of the resin itself, and on the other hand, you can also improve the deformation ability of the composite material under load by reducing the crosslinking density or improving the chain segment movement, thereby delaying the generation of interface cracks. However, it is certain that the decrease in the cross-linking density of thermosetting resins will inevitably affect their heat resistance to a certain extent, and they cannot be used in certain extreme working conditions. Therefore, how to simultaneously take into account the tensile strength and heat resistance of composite materials through the resin matrix is ​​a more difficult issue.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The object of the present invention is to provide a resin composition which has both flexibility and heat resistance and is beneficial to improving the tensile strength of carbon fiber.

[0006] The object of the present invention is to provide a method for preparing a resin composition, which is simple and easy to operate.

[0007] The object of the present invention is to provide a carbon fiber prepreg having good process operability and viscosity.

[0008] The present invention is achieved in that:

[0009] In a first aspect, the present invention provides a resin composition comprising an epoxy resin component, a thermoplastic resin, and an aromatic curing agent having flexible side chains;

[0010] The amount of the thermoplastic resin added is 3% to 28% of the epoxy resin component, and the molar ratio of the active hydrogen of the aromatic curing agent to the number of epoxy groups in the epoxy resin component is 0.7 to 1.3;

[0011] The epoxy resin component comprises 5% to 50% of a first epoxy resin having a cyclohexane structure and 50% to 95% of a second epoxy resin having a benzene ring structure in terms of mass percentage; the aromatic curing agent has the structural formula: wherein R1 and R6 are each independently a primary amino group, R3, R4, R8, and R9 are each independently selected from a hydrogen atom or a halogen atom, and R2, R5, R7, and R 10 Each is independently selected from an aliphatic hydrocarbon group having 2 to 5 carbon atoms.

[0012] In a second aspect, the present invention provides a method for preparing the resin composition as described in any one of the aforementioned embodiments, wherein the components are mixed uniformly.

[0013] In a third aspect, the present invention provides a carbon fiber prepreg comprising, by mass percentage, 40% to 85% of carbon fiber and 25% to 60% of the resin composition according to any one of the aforementioned embodiments.

[0014] The present invention has the following beneficial effects:

[0015] The resin composition provided by the present application is compounded by the first epoxy resin with cyclohexane structure and the second epoxy resin with benzene ring structure, wherein the second epoxy resin with benzene ring structure can provide good rigidity and heat resistance for the resin composition. The first epoxy resin with cyclohexane structure can provide bending motion characteristics for the resin composition, thereby maintaining good flexibility, the flexible segment of the first epoxy resin with cyclohexane structure and the curing agent eliminates the large deformation of the composite material tensile stress, delays the fracture of the resin segment, ensures the good combination of the resin and fiber interface, is conducive to stress transfer, and realizes the high strength conversion rate of carbon fiber; by the second epoxy resin with benzene ring structure and the curing agent benzene ring structure, ensures the cross-linking density and rigidity of the resin, avoids the decline of the heat resistance of the composite material due to the introduction of the flexible structure, realizes the compatibility of the two, and is conducive to improving the tensile strength of carbon fiber.

[0016] The prepreg prepared by using the resin composition has good process operability and viscosity, and has excellent Tg value, tensile strength and post-impact compressive strength. DETAILED DESCRIPTION

[0017] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0018] The invention provides a resin composition, the components of which include epoxy resin component, thermoplastic resin and aromatic curing agent with flexible side chains.

[0019] The epoxy resin component includes 5% to 50% of a first epoxy resin having a cyclohexane structure and 50% to 95% of a second epoxy resin having a benzene ring structure by mass percentage; preferably, the epoxy resin component includes 10% to 40% of the first epoxy resin and 60% to 90% of the second epoxy resin by mass percentage.

[0020] In this application, a first epoxy resin having a cyclohexane structure and a second epoxy resin having a benzene ring structure are compounded. The benzene ring, as a closed conjugated system, has six carbon atoms with identical π electron cloud distributions. Typically, the carbon atoms are coplanar, maintaining excellent rigidity, and are therefore widely used in the manufacture of high-heat-resistant, high-strength structural parts. In contrast, the carbon atoms of cyclohexane (also known as a six-membered ring) are not coplanar, but generally exhibit a chair-like shape, exhibiting certain bending motion characteristics, thereby maintaining good flexibility.

[0021] In this application, by compounding the first and second epoxy resins, the epoxy resin component contains a certain amount of cyclohexane structure. When the multifunctional epoxy resin has a cyclohexane structure, its good flexibility prevents the resin segments from prematurely breaking under tensile stress after curing, leading to premature damage to the resin-carbon fiber interface layer, thereby affecting the tensile strength of the carbon fiber. Furthermore, the multifunctional structure of the first and second epoxy resins in this application ensures the crosslinking density of the resin curing, which has little effect on the heat resistance of the final composite material structure.

[0022] In addition, when the hydrogen on the benzene ring is replaced, the originally stable electron cloud distribution will be destroyed, resulting in an increase in polarity. At the same time, the hydrocarbon substituent group will also give the structure a certain flexibility. This structure has a certain improvement effect on the resin / carbon fiber interface and the flexibility of the resin itself, further improving the tensile strength of the composite material.

[0023] Among them, the first epoxy resin is an ester ring multifunctional epoxy resin; preferably, the first epoxy resin includes a combination of one or more of tetraglycidyl-1,3-bisaminomethylcyclohexane (AG-602, commercially available at Wuhan Kemik Biotechnology Co., Ltd.), 4,4'-diaminodicyclohexylmethane glycidylamine (Tailuk-AG-80H, commercially available at Tohto Kasei Co., Ltd., Japan) and a six-membered ring multifunctional epoxy resin. The six-membered ring multifunctional epoxy resin can be independently prepared by conventional methods. For example, in an autoclave and a trickle bed reactor, aromatic glycidylamine-based multifunctional epoxy resins and their derivatives are hydrogenated under the action of a supported catalyst such as ruthenium, palladium, rhodium, platinum, or nickel to obtain the six-membered ring multifunctional epoxy resin. Alternatively, the six-membered ring multifunctional epoxy resin can be obtained by condensing a hydrogenated aromatic polyamine with epichlorohydrin and removing hydrogen chloride. Examples of the hydrogenated aromatic polyamine include bis(4-amino-3-methylcyclohexyl)methane (C260, BASF, Germany), 4,4'-diaminodicyclohexylmethane (PACM, Jiangsu Qingquan Chemical Co., Ltd.), and the like.

[0024] The second epoxy resin has an epoxy functionality of 3 or more; the second epoxy resin includes a combination of one or more of tetraglycidyldiaminodiphenylmethane (TTA520, commercially available from Jiangsu Taitel New Materials Technology Co., Ltd.), triglycidylaminophenol (AFG-90M, commercially available from Wuhan Kemik Biopharmaceutical Technology Co., Ltd.), tetraglycidyldiaminodiphenylsulfone, and a naphthyl multifunctional epoxy resin (EBA-65, commercially available from Shanghai Huayi Resin Co., Ltd.). The second epoxy resin can be obtained by conventional glycidyl synthesis using diaminodiphenylmethane, diaminodiphenyl ether, xylenediamine, diaminodiphenylsulfone, and aminophenol, and their structural isomers.

[0025] In the present application, by matching epoxy resin component and thermoplastic resin, it is dissolved and can obtain the required prepreg viscosity state and impact toughness. In the present application, in order to ensure good heat resistance, thermoplastic resin includes but is not limited to one or more combinations of powder particles of PES, PEI, PPO, PEK, PEEK, etc. with high Tg, such as taking full account of comprehensive mechanical properties, optional high modulus PES (E2010G3, commercially available in Suzhou Di Plastic Engineering Plastics Co., Ltd.), PEK (2287A, commercially available in RTP Company of the United States), PEEK (450G, commercially available in VICTREX Company of the United Kingdom), etc. Relative to the gross mass of epoxy resin, the addition amount of thermoplastic resin is 3% to 28% of the epoxy resin component, preferably 10% to 20%. By regulating and controlling the proportion of this component, the good process operability and viscosity of the final prepreg product are achieved.

[0026] Aromatic curing agents have flexible side chains. To ensure good heat resistance, amine curing agents with 1 to 6 benzene ring structures can be selected. At the same time, considering the influence of the rigidity of the benzene ring structure on the tensile strength of carbon fiber, Friedel-Crafts reaction can be performed to replace the hydrogen at the 2 and 6 substitution positions on the benzene ring with alkyl groups to form a structural formula of The curing agent, the long chain alkyl structure can give the resin a certain flexibility. In the above general formula, R1 and R6 are independently primary amino groups, R3, R4, R8, and R9 are independently selected from hydrogen atoms and halogen atoms, R2, R5, R7, and R 10 Each of the aromatic curing agents is independently selected from an aliphatic hydrocarbon group having 2 to 5 carbon atoms. Preferably, the aromatic curing agent includes but is not limited to 4,4'-methylene-bis(2,6-diethylaniline) and 4,4-methylene-bis-(2-methyl-6-diethylaniline). In the present application, the molar ratio of the active hydrogen of the aromatic curing agent to the number of epoxy groups in the epoxy resin component is 0.7 to 1.3; while ensuring sufficient curing, reducing the amount of curing agent can increase the flexibility of the resin. Therefore, the aromatic curing agent is added with a molar ratio of the active hydrogen of the aromatic curing agent to the number of epoxy groups in the epoxy resin component preferably meeting 0.8 to 1.1.

[0027] In this application, the first epoxy resin with a cyclohexane structure and the flexible chain segment of the curing agent are used to eliminate the large deformation of the composite material caused by tensile stress, delay the breakage of the resin chain segment, ensure good bonding between the resin and the fiber interface, facilitate stress transfer, and achieve a high strength conversion rate of the carbon fiber; the second epoxy resin with a benzene ring structure and the benzene ring structure of the curing agent are used to ensure the cross-linking density and rigidity of the resin, avoid the decrease in heat resistance of the composite material due to the introduction of the flexible structure, and achieve compatibility between the two.

[0028] Furthermore, the present invention provides a method for preparing a resin composition, comprising uniformly mixing the components. Specifically, uniformly mixing the components comprises: first dispersing and dissolving the epoxy resin component and the aromatic curing agent at 90-110°C until they become transparent, cooling the temperature to 70-80°C, and then adding and dissolving the thermoplastic resin. To ensure sufficient dissolution and dispersion of the resin, a planetary agitator is preferably used for heating and dispersion until the viscosity reaches 10,000 cP to 1,000,000 cP as measured by a lamina viscometer at 70-80°C, thereby ensuring that the resin can effectively impregnate the carbon fiber.

[0029] In addition, the present invention also provides a carbon fiber prepreg, which comprises 40% to 85% of carbon fiber and 25% to 60% of the above resin composition in terms of mass percentage, and the resin composition is melt-compounded on the surface of the carbon fiber.

[0030] In this application, the carbon fiber is any type of commercially available carbon fiber, preferably a high-performance carbon fiber with a low carbon fiber strength conversion rate, for example, at least one of T700, T800, T1100 and M40X; the carbon fiber is a unidirectional fabric, a warp knitted fabric or a three-dimensional woven fabric; the surface density of the carbon fiber is 50 to 1000 g / m 2 .

[0031] The epoxy resin composition of the present invention and carbon fiber are heated and melt-compounded using a prepreg device using a single-film process, a two-film process, or a multi-film process to form a prepreg. The prepreg of the present invention can be prepared as needed to meet the specifications of prepregs in forms such as hand placement, fiber placement, tape placement, and winding, and can be used in molding processes such as autoclaves and Out-of-Line (OoA). Different curing temperatures and times can be selected based on the type and quality of the curing agent in the resin composition. Preferably, curing is performed at 120°C to 210°C for 0.5h to 8h.

[0032] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0033] The components used in the subsequent examples or comparative examples are listed below:

[0034] (1) First epoxy resin:

[0035] Tailuk-AG-80H, epoxy value 0.9 mol / 100g;

[0036] AG-602, epoxy value is 0.96mol / 100g;

[0037] JER806, a bisphenol F-type difunctional epoxy resin, does not have a cyclohexane structure, is produced by Shanghai Zhongsi Industrial Co., Ltd., and has an epoxy value of 0.63 mol / 100 g;

[0038] The C260 compound has an epoxy value of 0.93 mol / 100g. The preparation method for the C260 compound is as follows: 15g of C260 and 0.13g of tetramethylammonium chloride catalyst are added dropwise to a four-necked reaction flask equipped with a stirrer, thermometer, and oil-water separator, followed by the dropwise addition of 15g of epichlorohydrin for an addition reaction; 0.13g of tetramethylammonium chloride catalyst and 30g of 50% sodium hydroxide solution are then gradually added dropwise for a cyclization reaction, followed by water fractionation by vacuum distillation at 65°C. After cooling, methanol is added for recrystallization, yielding a six-membered multifunctional epoxy compound with an epoxy value of 0.93 mol / 100g as the C260 compound.

[0039] (2) Second epoxy resin:

[0040] TTA520, epoxy value is 0.9 mol / 100g;

[0041] EBA-65, epoxy value is 0.71 mol / 100g.

[0042] (3) Thermoplastic resin:

[0043] 2287A, through grinding and screening, the D90 particle size is controlled below 120 microns;

[0044] E2010G3, through grinding and screening, the D90 particle size is controlled below 100 microns.

[0045] (4) Aromatic curing agent:

[0046] MMEA, active hydrogen equivalent is 70.5;

[0047] MDEA, active hydrogen equivalent is 77.5;

[0048] 3,3'-DDS, Zhangjiagang Yarui Chemical Co., Ltd., active hydrogen equivalent is 62.

[0049] Example 1

[0050] This embodiment provides a resin composition comprising an epoxy resin component, a thermoplastic resin, and an aromatic curing agent. The epoxy resin component comprises, by mass, 15% Tailuk-AG-80H and 85% TTA520. The thermoplastic resin is 2287A, added in an amount that is 10% of the total mass of the epoxy resin component. The aromatic curing agent is MMEA, added in an amount such that the molar ratio of active hydrogen of the aromatic curing agent to the number of epoxy groups in the epoxy resin component is 0.8.

[0051] The preparation method includes: dispersing and dissolving the epoxy resin component and the aromatic curing agent in a planetary mixer at 100°C until they are transparent, cooling to 75°C, adding a thermoplastic resin and gradually dissolving them, and obtaining the desired resin state by controlling the dispersion time.

[0052] Examples 2-10 and Comparative Examples 1-5

[0053] The preparation methods of Examples 2-10 and Comparative Examples 1-5 are the same as those of Example 1, with the main difference being the selection and dosage of the epoxy resin component, thermoplastic resin, and aromatic curing agent. Specifically, the composition ratios of each Example and Comparative Example are shown in Table 1, where the aromatic curing agent ratio is the molar ratio of active hydrogen in the curing agent to the number of epoxy groups in the epoxy resin.

[0054] Table 1. Composition ratio of different examples

[0055]

[0056] Experimental example

[0057] (1) Prepreg preparation

[0058] Jiangsu Hengshen HF40 carbon fiber (T800 grade) and HF30 carbon fiber (T700 grade) were used as reinforcing materials. The resin compositions prepared in Examples 1-15 and Comparative Examples 1-7 were heated and pressurized on an impregnation device by melt impregnation, and then compounded with the reinforcing materials to form a unidirectional prepreg. The prepared fiber surface density was 194 g / m 2 , the resin content is 34%.

[0059] Curing was carried out at 180°C for 2 hours, and samples were prepared according to the dimensions required by the test standards ASTM D3418, ASTM D3039, ASTM D7136 & ASTM D7137. The DMATg, 0° tensile strength, and post-impact compressive strength of the cured prepreg were tested.

[0060] Among them, the test method for DMATg of prepreg is ASTM D3418;

[0061] The test method for 0° tensile strength is ASTM D3039;

[0062] The test method for compressive strength after impact is ASTM D7136 & ASTM D7137.

[0063] Please see Table 2 for the test results.

[0064] Table 2. Statistics of performance test results for different examples

[0065]

[0066] As can be seen from Table 1 and Table 2;

[0067] 1) Examples 1-15: Prepregs produced using components and ratios within the requirements of this invention maintain heat resistance above 185°C and fully utilize fiber strength. The composites, determined by fiber strength, exhibit high 0° tensile strength. Increasing the toughening agent content achieves the desired high damage tolerance without compromising the desired performance.

[0068] 2) Comparison of Examples 1 to 15 with Comparative Examples 1 and 5 shows that the curing agent used in Comparative Examples 1 and 5 is 3,3'-DDS, which has no branched structure on the benzene ring, resulting in poor tensile strength of the composite materials in Comparative Examples 1 and 5. This indicates that the use of a curing agent with a hydrocarbon side chain can improve the flexibility of the resin and achieve an improvement in the conversion rate of tensile strength of the carbon fiber;

[0069] 3) Examples 2, 3, and Comparative Example 2: Good performance was achieved when the curing agent ratio was within a reasonable range. When the molar ratio was too high, the resin structure would be over-crosslinked, affecting the overall flexibility and heat resistance.

[0070] 4) Comparison of Examples 6, 7, and 9 with Comparative Examples 3 and 4 shows that Comparative Example 3 only contains a conventional benzene ring structure multifunctional second epoxy resin, while Comparative Example 4 uses JER806 as the first epoxy resin, which does not have a cyclohexane structure and is a bisphenol F-type difunctional epoxy resin. Therefore, both Comparative Examples 3 and 4 cannot achieve both heat resistance and fiber strength conversion rate.

[0071] 5) Comparison between Example 2 and Comparative Example 6 shows that although too many ester ring structures can show a high fiber strength conversion rate, it will lead to a significant decrease in heat resistance.

[0072] In summary, the resin composition provided by the present application is compounded by compounding the first epoxy resin with a cyclohexane structure and the second epoxy resin with a benzene ring structure, wherein the second epoxy resin with a benzene ring structure can provide good rigidity and heat resistance for the resin composition. The first epoxy resin with a cyclohexane structure can provide bending motion characteristics for the resin composition, thereby maintaining good flexibility, the flexible chain segment of the first epoxy resin with a cyclohexane structure and the curing agent eliminates the large deformation caused by the tensile stress of the composite material, delays the breakage of the resin chain segment, ensures good bonding between the resin and the fiber interface, is conducive to stress transfer, and achieves a high strength conversion rate of carbon fiber; by the second epoxy resin with a benzene ring structure and the curing agent benzene ring structure, the crosslinking density and rigidity of the resin are ensured, the decline in the heat resistance of the composite material due to the introduction of the flexible structure is avoided, and the compatibility of the two is achieved, which is conducive to improving the tensile strength of carbon fiber.

[0073] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A resin composition, characterized in that Its components include epoxy resin component, thermoplastic resin and aromatic curing agent with flexible branched chain; The amount of the thermoplastic resin added is 3% to 28% of the epoxy resin component, and the molar ratio of the active hydrogen of the aromatic curing agent to the number of epoxy groups in the epoxy resin component is 0.7 to 1.3; The epoxy resin component comprises, by mass percentage, 5% to 50% of a first epoxy resin having a cyclohexane structure and 50% to 95% of a second epoxy resin having a benzene ring structure; the first epoxy resin comprises a combination of one or more of tetraglycidyl-1,3-bisaminomethylcyclohexane, 4,4'-diaminodicyclohexylmethane glycidylamine, and a six-membered ring multifunctional epoxy resin; The structural formula of the aromatic curing agent is wherein R1 and R6 are each independently a primary amino group, R3, R4, R8, and R9 are each independently selected from a hydrogen atom or a halogen atom, and R2, R5, R7, and R 10 They are independently selected from aliphatic hydrocarbon groups with 2 to 5 carbon atoms, and the aromatic curing agent includes at least one of 4,4'-methylene-bis(2,6-diethylaniline) and 4,4-methylene-bis-(2-methyl-6-diethylaniline).

2. The resin composition according to claim 1, wherein The epoxy resin component includes 10% to 40% of a first epoxy resin and 60% to 90% of a second epoxy resin in terms of mass percentage; the added amount of the thermoplastic resin is 10% to 20% of the epoxy resin component; and the molar ratio of the active hydrogen of the aromatic curing agent to the number of epoxy groups in the epoxy resin component is 0.8 to 1.

1.

3. The resin composition according to claim 1, wherein The second epoxy resin includes one or more of tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, tetraglycidyldiaminodiphenylsulfone and naphthyl multifunctional epoxy resin.

4. The resin composition according to claim 1, characterized in that The thermoplastic resin includes one or more of PES, PEI, PPO, PEK and PEEK.

5. A method for preparing the resin composition according to any one of claims 1 to 4, characterized in that: Mix the components thoroughly.

6. The method for preparing the resin composition according to claim 5, wherein Mixing the components uniformly includes: first dispersing and dissolving the epoxy resin component and the aromatic curing agent at 90-110° C. until they are transparent, cooling to 70-80° C., and adding the thermoplastic resin to dissolve them.

7. A carbon fiber prepreg, characterized in that: The carbon fiber comprises 40% to 85% of carbon fiber and 25% to 60% of the resin composition according to any one of claims 1 to 4 in terms of mass percentage.

8. The carbon fiber prepreg according to claim 7, characterized in that The carbon fiber includes at least one of the features (1)-(3): Feature (1): The carbon fiber is selected from at least one of T700, T800, T1100 and M40X; Feature (2): The carbon fiber is a unidirectional fabric, a warp knitted fabric or a three-dimensional woven fabric; Feature (3): The surface density of the carbon fiber is 50 to 1000 g / m 2 .

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