Epoxy resin composition for fiber-reinforced composite material and prepreg using same

Abstract

An epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention comprises: [A] an epoxy resin; [B] dicyandiamide; [C] at least one compound selected from urea and imidazole compounds; and [D] boronic acid. Therefore, the epoxy resin composition has excellent storage stability at room temperature and can be rapidly cured to be suitable for mass production.

Description

Epoxy resin composition for fiber-reinforced composite materials and prepreg using the same

[0001] The present invention relates to an epoxy resin composition for fiber-reinforced composite materials and a prepreg using the same, and more specifically, to an epoxy resin composition having excellent storage stability and suitable for mass production of fiber-reinforced composite materials, and a prepreg using the same.

[0002] In general, fiber-reinforced composite materials have high specific strength and specific modulus, and are widely used in various fields such as sports leisure applications, aviation applications, automobile and railway applications, self-product applications, and general industrial applications.

[0003] The methods for manufacturing such fiber-reinforced composite materials include molding methods such as filament winding, infusion, RTM (Resin Transfer Molding), pultrusion, and press. In particular, prepreg, an intermediate product in which reinforcing fibers are pre-impregnated with matrix resin, is applied to molding methods such as autoclave, vacuum bag, sheet winding, and bladder molding. When prepreg, which is an intermediate substrate, is used, it is easy to increase the fiber content, which greatly affects the mechanical properties of fiber-reinforced composite materials, or to uniformly manage the target fiber content, and it is easy to reduce the occurrence of internal defects such as voids, and to improve physical properties such as heat resistance and impact strength.

[0004] However, conventional prepregs and the autoclave molding method, which is a representative molding method using prepregs, require cutting the prepreg, laminating it on a mold of the desired shape, vacuum bagging, and then heating and curing for several hours, which requires a long process time, making it not only unsuitable for mass production, but also requiring investment in expensive autoclave equipment. In particular, since the molding time must be shortened to less than 10 minutes for mass production, a press molding method that does not require vacuum bagging and can be automated is desirable. This press molding method does not require expensive equipment such as an autoclave, and can utilize commonly used press equipment.

[0005] Meanwhile, prepregs manufactured from general thermosetting epoxy resin compositions require a curing time of approximately 1 to 3 hours at a temperature of 125 to 175°C. At this time, if the amount of the curing agent and curing accelerator in the resin composition is increased in order to shorten the curing time, or a curing accelerator with a fast curing speed is applied, the storage stability of the prepreg is rapidly reduced, and the thermal and mechanical properties of the cured resin composition are deteriorated, resulting in a problem of deterioration in the properties of the final molded fiber-reinforced composite material.

[0006] The present invention has been devised to solve the above problems and to meet the conventional requirements, and the problem to be solved by the present invention is to provide an epoxy resin composition that has excellent storage stability required as a prepreg for fiber-reinforced composite materials and can be cured within a short period of time to enable mass production, and a prepreg using the same.

[0007] In addition, another problem to be solved by the present invention is to provide a layered structure including a fiber-reinforced composite material formed by curing the above-described prepreg and a laminated product in which prepregs are laminated.

[0008] The above and other objects and advantages of the present invention will become apparent from the following description of preferred embodiments.

[0009] The above object is achieved by an epoxy resin composition for a fiber-reinforced composite material comprising an epoxy resin, dicyandiamide, at least one compound selected from urea and imidazole compounds, and boronic acid.

[0010] Preferably, the epoxy resin may be a mixture of a difunctional bisphenol A type epoxy resin and a tetrafunctional glycidyl amine type epoxy resin.

[0011] Preferably, the epoxy resin may have an average epoxy equivalent of 250 g / eq or less.

[0012] Preferably, the epoxy resin composition for fiber-reinforced composite materials may satisfy Equation 1.

[0013] (Formula 1)

[0014] 0.4 ≤ B / (C + D) ≤ 2.8

[0015] Here, B is the content of dicyandiamide, C is the content of at least one compound selected from urea and imidazole compounds, and D is the content of boronic acid.

[0016] Preferably, it may contain 3 to 8 parts by weight of the dicyandiamide per 100 parts by weight of the epoxy resin.

[0017] Preferably, the glass transition temperature of the epoxy resin composition for fiber-reinforced composite materials may be 140°C or higher.

[0018] Preferably, the epoxy resin composition for fiber-reinforced composite materials may be cured at 150°C, and the time until the degree of curing reaches 90% may be within 5 minutes.

[0019] Preferably, the epoxy resin composition for fiber-reinforced composite materials may have a phase angle of 70° to 90° at a temperature of 80°C.

[0020] Preferably, the epoxy resin composition for fiber-reinforced composite materials may have a cured product having a phase angle of 18° or less when cured at 150°C.

[0021] Preferably, the epoxy resin composition for fiber-reinforced composite materials may be one in which the time for doubling the initial viscosity when stored at 30°C is 504 hours or more.

[0022] In addition, the above object is achieved by a prepreg formed by impregnating reinforcing fibers with the epoxy resin composition for fiber-reinforced composite materials described above.

[0023] Preferably, the prepreg has a fiber areal weight (FAW) of 50 to 300 g / m. 2 , and the resin content (RC) may be 25% to 35%.

[0024] Preferably, the prepreg may have a volume ratio of 25 to 50 volume% of the epoxy resin composition for fiber-reinforced composite materials when cured at 150°C for 5 minutes.

[0025] In addition, the above object is achieved by a fiber-reinforced composite material formed by curing the above-described prepreg.

[0026] In addition, the above object is achieved by a layered structure including a laminate in which the above-described prepreg is laminated.

[0027] According to the epoxy resin composition for fiber-reinforced composite materials according to the present invention and the prepreg using the same, by optimizing the components and composition of the epoxy resin, curing agent, curing accelerator, and additives, etc., there are effects such as excellent storage stability at room temperature during prepreg production and rapid curing suitable for mass production.

[0028] In particular, the epoxy resin composition for fiber-reinforced composite materials of the present invention is cured by 90% or more within 5 minutes at a temperature of 150°C, has a glass transition temperature (Tg) of 140°C or more, and has storage stability of at least 504 hours (21 days) or more when stored at 30°C, thereby having effects such as being able to simultaneously satisfy rapid curing characteristics and excellent storage stability.

[0029] However, the effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of a conflict, the present specification, including its definitions, will govern. Furthermore, although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

[0031] In this specification, the terms "~-based resin", "~-based polymer", or / and "~-based copolymer" are broad concepts encompassing all of "~ resin", "~ polymer", "~ copolymer", or / and "derivatives of ~ resin, polymer, or copolymer." In addition, in this specification, the term "polymer or copolymer crosslinked with these resins" means "polymer or copolymer crosslinked with the aforementioned resin."

[0032] In this specification, “compound” is a broad concept that includes “monatomic molecules,” “oligomers,” and “polymer compounds including homopolymers and copolymers.”

[0033] The term "including" in this specification means that other components may be included rather than excluding other components unless specifically stated to the contrary.

[0034] The term "combination of these" in this specification means a mixture or combination of one or more of the described components.

[0035] As used herein, the term "and / or" is meant to include any and all combinations of one or more of the items described herein. As used herein, the term "or" means "and / or." The expressions "at least one" or "one or more" preceding elements herein may supplement the entire list of elements and do not imply that they supplement individual elements described above.

[0036] Unless otherwise stated herein, all percentages, parts, ratios, etc. are by weight. Additionally, whenever an amount, concentration, or other value or parameter is given as a range, a preferred range, or a list of upper preferred values ​​and lower preferred values, this should be understood to specifically disclose all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed.

[0037] When a range of numerical values ​​is mentioned in this specification, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range. The scope of the present invention is not intended to be limited to the specific values ​​mentioned when defining the range.

[0038] In this specification, each component is a concept that includes both singular and plural.

[0039] First, an epoxy resin composition for a fiber-reinforced composite material according to one aspect of the present invention may include an epoxy resin, dicyandiamide, at least one compound selected from urea and imidazole compounds, and boronic acid.

[0040] In the present invention, the epoxy resin imparts reactivity and adhesiveness to the resin composition, and imparts functions such as heat resistance, toughness, and chemical resistance to the resin composition after curing.

[0041] These epoxy resins may include at least one epoxy resin selected from among bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl epoxy resin, novolac type epoxy resin, naphthalene type epoxy resin, glycidyl ester type epoxy resin, glycidyl amine type epoxy resin, dicyclopentadiene type epoxy resin, and alicyclic epoxy resin, or may include modified epoxy resins thereof.

[0042] In an epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention, it is preferable to use a bifunctional bisphenol A type epoxy resin, a trifunctional or higher novolac epoxy resin, and a glycidyl amine type epoxy resin in combination. When only a bifunctional epoxy resin is used as the epoxy resin, the toughness is excellent but the heat resistance is low, and when only a trifunctional or higher epoxy resin is used, the heat resistance is high due to the high crosslinking density, but the toughness is low, and the possibility of deformation occurring due to high shrinkage during curing increases. Therefore, it is preferable to use a bifunctional bisphenol A type epoxy resin in combination with a trifunctional or higher epoxy resin, and as the trifunctional or higher epoxy resin, it is more preferable to use a tetrafunctional glycidyl amine type epoxy resin in consideration of the curing speed, heat resistance, viscosity, etc.

[0043] As an example, it is preferable that the epoxy resin composition for a fiber-reinforced composite material of the present invention includes a mixture of a difunctional bisphenol A type epoxy resin (difunctional BPA type epoxy resin) and a tetrafunctional glycidyl amine type epoxy resin.

[0044] Examples of such tetrafunctional glycidyl amine type epoxy resins include tetraglycidyl diaminodiphenyl methane, tetraglycidyl diaminodiphenyl ether, tetraglycidyl diaminodiphenylamide, tetraglycidyl xylenediamine and halogen-substituted products and hydrogenated products thereof, and more than one of these may be used. Among these, tetraglycidyl diaminodiphenyl methane is preferable in terms of heat resistance and compatibility with difunctional bisphenol A type epoxy resins. For example, commercially available products related to tetraglycidyl diaminodiphenyl methane include ELM434 from Sumitomo Chemical, YH434L from Nippon Steel Chemical Company, JER 604 from Mitsubishi Chemical Corporation, and Araldite MY9655 and MY720 from Huntsman Advanced Materials.

[0045] In addition, it is preferable that the epoxy resin included in the epoxy resin composition for a fiber-reinforced composite material according to the present invention has an average epoxy equivalent of 250 g / eq or less. This is because when the average epoxy equivalent of the epoxy resin exceeds 250 g / eq, the glass transition temperature (Tg) of the molded cured product is lowered, which may cause deformation of the fiber-reinforced composite material during the demolding process during press molding.

[0046] In the present invention, the epoxy resin composition for fiber-reinforced composite materials preferably includes dicyandiamide as a curing agent. When dicyandiamide is used as a curing agent, the epoxy resin composition exhibits excellent storage stability, and the cured product of the epoxy resin composition can exhibit high heat resistance. Furthermore, in the present invention, dicyandiamide may include a dicyandiamide derivative, which is a derivative thereof.

[0047] In addition, it is preferable that the epoxy resin composition for fiber-reinforced composite materials contain 3 to 8 parts by weight of dicyandiamide per 100 parts by weight of epoxy resin. This is to be used so that the active hydrogen equivalent ratio of dicyandiamide is 30 to 80% compared to the average equivalent weight of the mixed epoxy resin components. Here, if the content of dicyandiamide is less than 3 parts by weight or the equivalent ratio is less than 30%, there is a concern that the epoxy resin may not participate in the curing reaction, thereby lowering the heat resistance and mechanical properties of the cured product. In addition, if the content of dicyandiamide exceeds 8 parts by weight or the equivalent ratio exceeds 80%, the brittleness of the cured product becomes excessively high, making it easy to break, and lowering the heat resistance.

[0048] For example, commercially available products related to dicyandiamide include Dicy-7 and Dicy-15 from Mitusbishi Chemical, Dyhard 100S and 100SF from Alzchem, CG1400 from Air products, and DDA5 from CVC Thermoset Specialties.

[0049] An epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention preferably comprises at least one compound selected from urea and an imidazole compound. These components act as a curing accelerator of the curing agent in the epoxy resin composition for a fiber-reinforced composite material. In the present invention, urea may include a urea derivative, which is a derivative thereof.

[0050] Among these curing accelerators, urea (or urea derivatives) preferably include isomers of 2,6 and 2,4 toluene bis dimethyl urea (known as 2,6 and 2,4 TDI urone), and examples of commercially available products of urea (or urea derivatives) include Alzchem's UR500.

[0051] Also imidazole compounds include 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 2-undecyl imidazole, 2-heptadecyl imidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4´,5´-dihydroxymethylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 4-hydroxymethyl-5-methyl-2-phenylimidazole and 2,4-diamino-6-[2'-methylimidazoli-(1')]-ethyl-s-triazine isocyanuric acid adduct dihydrate, 2-phenyl-4,5-dihydroxymethylimidazole, 2, It is preferred to include at least one selected from 4-diamino6-[2'-methylimidazolyl(1')]-ethyl-s-triazine, 2,4-diamino6-[2'-ethyl-4'-methylimidazolyl(1')]-ethyl-s-triazine and 2,4-diamino6-[2'-undecyl imidazolyl-(1')]-ethyl-s-triazine. As an example, an example of a commercially available product as an imidazole compound is 2MA-OK from Shikoku, etc.

[0052] An epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention may include a stabilizer or a modifier, and a boronic acid (or boronic acid compound) containing a boronic acid group (-RB(OH)2, where R represents an alkyl, hydroxyalkyl, or aryl group, etc.) is preferable as the stabilizer. For example, an example of a commercially available product containing boronic acid is Alzchem's DYHARD LA1.

[0053] These boronic acids (or boronic acid compounds) improve the storage stability of the resin at room temperature by combining with the accelerator at room temperature and inhibiting curing by the accelerator, thereby inhibiting curing at room temperature.

[0054] It is preferable that the epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention satisfies the following formula 1.

[0055] (Formula 1)

[0056] 0.4 ≤ B / (C + D) ≤ 2.8

[0057] Here, B is the content of dicyandiamide, C is the content of at least one compound selected from urea and imidazole compounds, and D is the content of boronic acid.

[0058] If the value of the above formula 1 is less than 0.4, the cured product tends to soften or is poorly cured, and storage stability is greatly reduced, making it impossible to use as a resin composition for prepreg. In addition, if the value of the above formula 1 is more than 2.8, it may be difficult to express rapid curing properties or may cause deterioration of physical properties.

[0059] In an epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention, when a curing accelerator which is at least one compound selected from urea and imidazole compounds and a stabilizer boronic acid are mixed and used, the curing reaction is controlled in the process of increasing the temperature to the press molding temperature, and after the press molding temperature is reached, a rapid curing reaction proceeds and is completed by the function of the curing accelerator, thereby making it possible to satisfy both storage stability and rapid curing properties.

[0060] An epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention may additionally include another curable resin in addition to the above-described composition. As such, examples of the curable resin additionally used in the epoxy resin composition include, but are not limited to, unsaturated polyester resins, curable acrylic resins, curable amino resins, curable melamine resins, curable urea resins, curable cyanate ester resins, curable urethane resins, curable oxetane resins, and curable epoxy / oxetane composite resins.

[0061] An epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention may additionally contain a coupling agent, thermosetting resin particles, carbon black, conductive particles such as carbon particles or metal-plated organic particles, or inorganic fillers such as silica gel or clay, within a range that does not interfere with the effects of the present invention. The addition of these has the effect of increasing the viscosity of the epoxy resin composition and adjusting the viscosity to reduce resin flow, improving the elastic modulus and heat resistance of the cured resin, and improving the wear resistance.

[0062] In addition, an epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention is used as a matrix resin for manufacturing a prepreg using a hot melt method without using a solvent, and can be manufactured by the following method.

[0063] A method for producing an epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention comprises placing an epoxy resin (component [A]) into a container such as a glass flask, stirring at a temperature of 80 to 120 to 130°C for 2 hours or more to completely dissolve the base resin, and then cooling the base resin to a temperature of 60 to 90°C. At this time, the epoxy resin (component [A]) may include a solid bisphenol A type epoxy resin and a glycidyl amine type epoxy resin.

[0064] Next, some of the epoxy resin (component [A]), dicyandiamide (component [B]), urea or imidazole (component [C]), and boronic acid (component [D]) are weighed and mixed, and then uniformly dispersed through a 3 Roll Mill to prepare a hardener paste.

[0065] Finally, the manufactured base resin and hardener paste can be mixed at a temperature of 60 to 90°C to manufacture an epoxy resin composition.

[0066] The glass transition temperature of the epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention is preferably 140°C or higher. If the glass transition temperature of the epoxy resin composition is lower than 140°C, deformation of the fiber-reinforced composite material occurs during the demolding process during press molding, and the curing reaction speed becomes slow.

[0067] According to one embodiment of the present invention, the epoxy resin composition for fiber-reinforced composite materials preferably reaches 90% curing degree within 5 minutes when cured at 150°C, more preferably within 4 minutes. If the time until 90% curing degree is reached exceeds 5 minutes, the excessive curing time consumes a lot of time and costs, and is not suitable for mass production.

[0068] Meanwhile, the stiffness of a general viscoelastic prepreg is characterized by a resin exhibiting a high elastic rheological response, and for this purpose, it is desirable for the epoxy resin composition to satisfy the following rheology.

[0069] In addition, the epoxy resin composition for fiber-reinforced composite material according to one embodiment of the present invention has a viscosity of 1 x 10 at a temperature of 80°C. 1 Pa to 5 x 10 1 It has a storage modulus G' of Pa and a strain of 1 x 10 2 Pa to 5 x 10 2It is desirable to have a loss modulus (G") of Pa. If the rheology, such as the storage modulus (G') and loss modulus (G'') described above, is lower than the above range, the flowability of the resin is very high, so that the resin flows excessively during the molding process time (e.g., a molding process time of 150°C and 5 minutes), which may cause voids to be created inside or fiber meandering. If the rheology is higher than the above range, the rigidity of the manufactured prepreg may increase, which may cause a problem of breaking.

[0070] An epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention has a viscosity of 1 x 10 at a temperature of 80°C. 1 Pa.s to 5 x 10 1 It is desirable to have a complex viscosity of Pa.s. The complex viscosity at a temperature of 80℃ is 1 x 10 1 If it is less than Pa.s, the flowability of the resin is very high, and the resin may flow excessively during the molding process, which may cause voids inside or fiber meandering, and 5 x 10 1 If the Pa.s is exceeded, the stiffness of the manufactured prepreg may increase, which may cause it to break.

[0071] In addition, the epoxy resin composition for fiber-reinforced composite materials according to one embodiment of the present invention has a viscosity of 1 x 10 at a temperature of 150°C for 5 minutes. -1 It is desirable to have a complex viscosity of Pa.s or more. The complex viscosity after 5 minutes at a temperature of 150℃ is 1 x 10 -1 If it is less than Pa.s, the fibers of the prepreg being manufactured may become loose and problems such as resin bleeding to the edges may occur.

[0072] In addition, the epoxy resin composition for fiber-reinforced composite material according to one embodiment of the present invention has a viscosity of 1 x 10 at a temperature of 80°C. 1Pa to 5 x 10 1 It has a storage modulus G' of Pa and a strain of 1 x 10 2 Pa to 5 x 10 2 It is desirable to have a loss modulus (G") of Pa. If the rheology, such as the storage modulus (G') and loss modulus (G'') described above, is lower than the above range, the flowability of the resin is very high, so that the resin flows excessively during the molding process time (e.g., a molding process time of 150°C and 5 minutes), which may cause voids to be created inside or fiber meandering. If the rheology is higher than the above range, the rigidity of the manufactured prepreg may increase, which may cause a problem of breaking.

[0073] In addition, it is preferable that the epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention has a phase angle of 70° to 90° at a temperature of 80°C. The phase angle of the epoxy resin composition represents the physical state of the epoxy resin composition. The phase angle is low when the resin does not flow but is solid or semi-solid, and increases as the temperature of the resin increases as the flow ability increases. When the phase angle of the epoxy resin composition is less than 70° at a temperature of 80°C, the flowability is very low during molding of a fiber-reinforced composite material, resulting in a problem of poor impregnation.

[0074] In addition, the epoxy resin composition for fiber-reinforced composite materials according to one embodiment of the present invention preferably has a phase angle of 18° or less when cured at 150°C, and more preferably has a phase angle of 10° or less. Generally, in an epoxy resin composition containing a heat-activated curing agent, the crosslinking action of the epoxy resin caused by the action of the curing agent solidifies the resin and reduces the phase angle when the temperature is increased. Therefore, the phase angle is for determining the temperature when the shape and molding of the resin are sufficiently solid to be easily removed from the mold. In the present invention, since the epoxy resin composition has a phase angle of 18° or less when cured at 150°C, the cured article (cured product) can be separated from the mold without excessive delay. On the other hand, if the epoxy resin composition has a phase angle exceeding 18° when cured at 150°C, the cured article (cured product) has a problem in that it is not easily separated from the mold due to the fluidity of the resin. In this way, the present invention can provide a prepreg including an epoxy resin composition that provides a cured resin having the above-described phase angle and reinforcing fibers (fiber reinforcing material).

[0075] In addition, it is preferable that the epoxy resin composition for fiber-reinforced composite material according to one embodiment of the present invention has a flexural strength of 50 to 200 MPa when cured at 150°C for 30 minutes.

[0076] An epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention preferably has a viscosity of 5,000 to 30,000 cps as measured at 80°C. This viscosity is a viscosity range suitable for manufacturing a hot-melt prepreg.

[0077] In addition, it is preferable that the epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention has a time for doubling of the initial viscosity when stored at 30°C of 504 hours (21 days) or more. In this way, the epoxy resin composition for a fiber-reinforced composite material according to one embodiment of the present invention, when stored for a long period of time under constant temperature conditions of 30°C, maintains the viscosity at less than twice the initial viscosity even after 21 days or more, more preferably 30 days or more, and can exhibit excellent storage stability.

[0078] A prepreg according to another aspect of the present invention may be formed by impregnating reinforcing fibers with the epoxy resin composition for fiber-reinforced composite materials described above.

[0079] In general, a prepreg can be obtained by impregnating reinforcing fibers into a matrix resin such as an epoxy resin composition. At this time, methods for impregnating the reinforcing fibers into the epoxy resin composition may include a dry method (hot melt method) and a wet method (solution method). Here, the wet method is a method of manufacturing a prepreg by immersing reinforcing fibers in an epoxy resin composition solution prepared by dissolving the epoxy resin composition in a solvent such as a ketone or alcohol, and then passing the epoxy resin composition through a drying oven to remove the solvent. In particular, the prepreg according to one embodiment of the present invention is preferably manufactured by applying a hot melt method, which is a dry method, to the epoxy resin composition.

[0080] An example of such a hot melt method is as follows. First, an epoxy resin composition is heated to a temperature of 60 to 100°C to ensure fluidity and reduce viscosity, and then the composition is coated on a release paper to a pre-calculated thickness to produce a resin film. At this time, coating methods for producing the resin film may include comma coating, roll coating, slot die coating, etc. Next, the produced resin film and the reinforcing fibers spread out in a flat shape are combined or laminated using heat and pressure to impregnate the reinforcing fibers with resin, thereby producing a prepreg. The present invention has the advantage of being able to produce a prepreg that does not contain residual solvent through the above-described hot melt method.

[0081] There are no particular limitations on the reinforcing fibers used in the present invention, and continuous fibers such as tows, fabrics, chopped fibers, mats, etc., such as carbon fibers, graphite fibers, glass fibers, and polymer fibers, can be used. In particular, carbon fibers and graphite fibers are preferred because they have excellent specific strength and specific elastic modulus, which can exhibit the lightweight characteristics of fiber-reinforced composite materials.

[0082] When carbon fiber is used in the present invention, the fiber content per unit area (FAW, Fiber Areal Weight) of the prepreg is 50 to 300 g / m 2 It is desirable that FAW is 50 g / m 2 If it is less than 300 g / m, the number of prepreg layers increases to manufacture a molded product of the desired thickness, which increases the working time and cost, and if FAW is less than 300 g / m 2 If it is excessive, the drape property of the prepreg deteriorates, making it unsuitable for manufacturing molded products with complex shapes including curved surfaces, and the thickness of the cross-section of the prepreg increases, making complete impregnation difficult.

[0083] In addition, it is preferable that the resin content (RC) of the prepreg be 25% to 35%. If the RC is less than 25%, the reinforcing fibers are not completely impregnated into the resin during prepreg manufacturing, resulting in voids inside. The reinforcing fibers are exposed on the surface after molding, making it difficult to secure excellent surface quality. In addition, if the RC exceeds 35%, the reinforcing fiber content is relatively low, resulting in a disadvantage of reduced mechanical strength such as specific strength and specific elasticity. In addition, during press molding, the flow of the excessively included resin may increase, disrupting the arrangement of the reinforcing fibers or causing problems such as resin leaking out near the edge of the molded product (bleeding).

[0084] In the present invention, it is preferable that the volume ratio of the epoxy resin composition for fiber-reinforced composite material when the prepreg is cured at 150°C for 5 minutes is 25 to 50 volume% of the prepreg.

[0085] According to another aspect of the present invention, a fiber-reinforced composite material may be formed by curing the prepreg described above. In the present invention, a method for manufacturing a fiber-reinforced composite material using a prepreg can be applied to any type of molding method, such as conventional autoclave, vacuum bag, and press molding, but it is particularly preferable to manufacture a fiber-reinforced composite material with high productivity and excellent surface quality through press molding. In particular, it is preferable to manufacture a prepreg using an epoxy resin composition according to an embodiment of the present invention, and press molding the prepreg in a mold at a temperature of 140 to 160°C for 2 to 10 minutes to manufacture a fiber-reinforced composite material, and at this time, the pressure condition is 5 to 10 kgf / cm 2 It is desirable that.

[0086] In the present invention, it is preferable that the glass transition temperature of the fiber-reinforced composite material be less than 20°C lower than the press molding temperature or the temperature within the mold. If the glass transition temperature of the fiber-reinforced composite material is 20°C or more lower than the press molding temperature or the temperature within the mold, defects such as warping or deformation of the part may occur when the molded fiber-reinforced composite material is removed from the mold. For example, when press molding is performed at 150°C, the glass transition temperature of the fiber-reinforced composite material is preferably 130°C or higher.

[0087] A layered structure according to another aspect of the present invention may include a laminate in which the above-described prepregs are laminated.

[0088] That is, the present invention may include not only the single prepreg configuration described above, but also a layered structure comprising a laminate in which two or more prepregs are laminated. For example, a layered structure in which two or more prepregs are laminated may be formed as needed to achieve the required thickness and mechanical strength.

[0089] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only to illustrate the present invention and the scope of the present invention is not limited to the following examples.

[0090] [Example]

[0091] [Examples 1 to 7]

[0092] Bisphenol A type epoxy resin and glycidyl amine type epoxy resin were weighed as epoxy resin (component [A]), placed in a glass flask, stirred at 150°C for 2 hours to completely dissolve, and then cooled to a temperature of 80°C to prepare a base resin.

[0093] On the one hand, in order to uniformly disperse the hardener, some of the epoxy resin (component [A]), dicyandiamide (component [B]), urea or imidazole (component [C]), and boronic acid (component [D]) were measured and mixed, and then a hardener paste was prepared through a 3 Roll Mill.

[0094] Next, the manufactured base resin and hardener paste were mixed at a temperature of 80°C to prepare an epoxy resin composition.

[0095] At this time, the compounds of each component and their contents are as shown in Table 1, and the contents in Table 1 are parts by weight (phr) based on 100 parts by weight of epoxy resin (total [A] component).

[0096] Type Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 [A] (1) 10101010101010 (2) 30303030303030 (3) ------- (4) 60606060606060 [B] (5) 6666638 [C] (6) --- 42 -- (7) 842-26.52.5 [D] (8) 20.60.20.60.610.46 Formula 10.61.32.71.31.30.42.7 (1) Liquid bisphenol A type epoxy resin: Hexion, EPON 828, EEW 185~192 (2) Solid bisphenol A type epoxy resin: Hexion, EPON 1001, EEW 525~550(3) Solid bisphenol A type epoxy resin: Hexion, EPON 1004, EEW 800~950(4) Glycidyl amine type epoxy resin: Huntsman, MY720, EEW 117~134(5) Dicyandiamide: Air product, CG1400(6) TBDMU: toluene bis dimethyl urea, Alzchem, UR500(7) Imidazole: Shikoku, 2MA-OK(8) Boronic acid: Alzchem, DYHARD LA1

[0097] [Comparative example]

[0098] [Comparative Examples 1 to 8]

[0099] An epoxy resin composition was prepared in the same manner as in Example 1, except that the compounds and contents of each component were as shown in Table 2 below.

[0100] TypeComparison Example 1Comparison Example 2Comparison Example 3Comparison Example 4Comparison Example 5Comparison Example 6Comparison Example 7Comparison Example 8[A](1)1010101010401010(2)303030303030303030(3)-----30--(4)6060606060-6060[B](5)66666629[C](6)151-4--(7)151-0.8-62.5[D](8)55--0.20.60.60.6Mathematical Formula 10.30.36.06.06.01.30.32.9(1) Liquid bisphenol A type epoxy resin: Hexion, EPON 828, EEW 185~192(2) Solid bisphenol A type epoxy resin: Hexion, EPON 1001, EEW 525~550(3) Solid bisphenol A type epoxy resin: Hexion, EPON 1004, EEW 800~950(4) Glycidyl amine type epoxy resin: Huntsman, MY720, EEW 117~134(5) Dicyandiamide: Air product, CG1400(6) TBDMU: toluene bis dimethyl urea, Alzchem, UR500(7) Imidazole: Shikoku, 2MA-OK(8) Boronic acid: Alzchem, DYHARD LA1

[0101] The physical properties of the epoxy resin compositions according to Examples 1 to 7 and Comparative Examples 1 to 8 were measured through the following experimental examples, and the results are shown in Table 3 below.

[0102] [Experimental Example]

[0103] (1) Analysis of epoxy resin composition using differential scanning calorimetry

[0104] The glass transition temperature (Tg) of the epoxy resin composition was measured according to the differential mechanical analysis according to the test method ASTM D7028, and Tg is considered to be the temperature at which the decrease in the storage modulus begins. At this time, a digital scanning calorimeter was used to monitor the time to reach 95%, 90%, and 80% cure, and accordingly, heating was started from 25°C to 250°C at a rate of 10°C / min. Through this, the degree of cure was measured using the digital scanning calorimeter for the epoxy resin composition after 1 hour of curing at a temperature of 150°C.

[0105] (2) Analysis of epoxy resin composition using a rheometer

[0106] The phase angle of the epoxy resin composition was measured using a rheometer equipped with a disposable 25 mm diameter aluminum plate. The phase angle properties were measured through a vibration test under temperature conditions increasing from 40°C to 150°C at a rate of 2°C / mm with a controlled frequency of 1 Hz and a gap of 1,000 micrometers.

[0107] (3) Measurement of viscosity and storage stability of epoxy resin composition

[0108] The viscosity of the epoxy resin composition was measured at 80°C using a Brookfield viscometer (CAP-2000). In addition, the viscosity was measured while the epoxy resin composition was stored in an oven at 30°C, and the time (days) required for the initial viscosity to double was measured, and storage stability was evaluated based on this.

[0109] Tg(℃, DSC)Cure(%)Storage stability(days, at 30℃)Phase angle(°, at 150℃)Example 114096248Example 215095309Example 3156923011Example 4151923110Example 515193309Example 6145952511Example 715592357Comparative Example 112597128Comparative Example 212597138Comparative Example 3156732617Comparative Example 4156683319Comparative Example 5156703418Comparative Example 611994259Comparative Example 7138892030Comparative Example 814888357

[0110] As can be confirmed in Table 3 above, the epoxy resin composition according to Example 1 has a degree of curing of 96% after curing at 150°C for 5 minutes, and achieves a degree of curing of 80% or more before 2 minutes and 30 seconds have passed, which means that it is very suitable for mass production. In other words, when manufacturing a prepreg using an epoxy resin composition, it can be said that demolding from a press mold is possible only when the degree of curing (conversion) is at least 80%, and therefore, it can be seen that the epoxy resin composition according to Example 1 is very suitable for mass production. In addition, it can be confirmed that the epoxy resin compositions according to Examples 2 to 7 also have a degree of curing of 92% or more after curing at 150°C for 5 minutes, and thus have a fast-curing property suitable for mass production.

[0111] In addition, it can be seen that the epoxy resin compositions according to Examples 1 to 7 have a phase angle of 70 to 90° (at 80°C), which is a phase angle range suitable for manufacturing a hot melt type prepreg, and when stored at 30°C, the time for the viscosity increase to double the initial viscosity is 20 days or more, which shows excellent storage stability, and the glass transition temperature after curing is 140°C or more, which shows high heat resistance.

[0112] On the other hand, it can be seen that the epoxy resin compositions according to Comparative Examples 1 and 2 did not satisfy Equation 1 due to the excessive use of the imidazole curing accelerator, resulting in a decrease in the storage stability of the epoxy resin composition and a lower glass transition temperature. In addition, it can be seen that Comparative Example 1, which uses only the curing accelerator, requires a high molding temperature of 150°C or higher, and also has a problem in that it cannot be used as a prepreg due to the decrease in room temperature storage stability.

[0113] In addition, it can be seen that the epoxy resin compositions according to Comparative Examples 3, 4, and 5 have low degrees of curing although they satisfy the glass transition temperature and storage stability by using a small amount of a curing accelerator. In addition, the epoxy resin compositions according to Comparative Examples 3, 4, and 5 have a disadvantage in that they are not suitable for mass production because the rate of increase in the degree of curing is very slow above a certain level even when the molding time is long at a molding temperature of 150°C, making it difficult to meet the desired molding time. In particular, in Comparative Example 5, it was confirmed that poor curing occurred because a small amount of a curing accelerator and a stabilizer were used at the same time.

[0114] In addition, Comparative Example 6 used a solid bisphenol A type epoxy resin instead of a glycidyl amine type epoxy resin, and as a result, it was found to have a low glass transition temperature as a result of not including an epoxy resin having an average epoxy equivalent of 250 g / eq or less and having 4 or more epoxy groups.

[0115] In addition, it can be seen that Comparative Example 7 has an insufficient content of dicyandiamide, urea, and imidazole compounds, and in particular, dicyandiamide is not sufficient compared to the content of epoxy resin, so that curing does not occur properly, storage stability is low, and the phase angle is also high, and Comparative Example 8 has an excessive content of dicyandiamide, while the content of imidazole is low compared to dicyandiamide, so that the curing speed is slow and the curing degree is low.

[0116] As described above, the epoxy composition according to one embodiment of the present invention and the prepreg manufactured using the same not only have the advantage of being easy to apply to mass production by significantly shortening the curing time and molding time, but also have the advantage of being able to realize the quality of a molded product with excellent storage stability and thermal / mechanical properties and excellent surface quality without internal defects, even using a press instead of an expensive autoclave facility without increasing the amount of a curing agent and a curing accelerator.

[0117] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. Epoxy resin; dicyandiamide; At least one compound selected from urea and imidazole compounds; and Boric acid; An epoxy resin composition for a fiber-reinforced composite material, comprising:

2. In paragraph 1, An epoxy resin composition for a fiber-reinforced composite material, wherein the epoxy resin is a mixture comprising a difunctional bisphenol A type epoxy resin and a tetrafunctional glycidyl amine type epoxy resin.

3. In paragraph 1, The above epoxy resin is an epoxy resin composition for fiber-reinforced composite materials, having an average epoxy equivalent of 250 g / eq or less.

4. In paragraph 1, The above epoxy resin composition for fiber-reinforced composite materials satisfies Equation 1: (Formula 1) 0.4 ≤ B / (C + D) ≤ 2.8 Here, B is the content of dicyandiamide, C is the content of at least one compound selected from urea and imidazole compounds, and D is the content of boronic acid.

5. In paragraph 1, An epoxy resin composition for a fiber-reinforced composite material, comprising 3 to 8 parts by weight of the dicyandiamide per 100 parts by weight of the epoxy resin.

6. In paragraph 1, An epoxy resin composition for a fiber-reinforced composite material, wherein the glass transition temperature of the epoxy resin composition for the fiber-reinforced composite material is 140°C or higher.

7. In paragraph 1, The above epoxy resin composition for a fiber-reinforced composite material is an epoxy resin composition for a fiber-reinforced composite material, wherein, when cured at 150°C, the time until the degree of curing reaches 90% is less than 5 minutes.

8. In paragraph 1, The epoxy resin composition for the above fiber-reinforced composite material has a phase angle of 70° to 90° at a temperature of 80°C.

9. In paragraph 1, The above epoxy resin composition for a fiber-reinforced composite material is an epoxy resin composition for a fiber-reinforced composite material, wherein the cured product has a phase angle of 18° or less when cured at 150°C.

10. In paragraph 1, The above epoxy resin composition for a fiber-reinforced composite material is an epoxy resin composition for a fiber-reinforced composite material, wherein the time for doubling the initial viscosity when stored at 30°C is 504 hours or more.

11. As a prepreg, A prepreg formed by impregnating reinforcing fibers with an epoxy resin composition for a fiber-reinforced composite material according to Article 1.

12. In paragraph 11, The above prepreg has a fiber content per unit area (FAW, Fiber Areal Weight) of 50 to 300 g / m 2 A prepreg having a resin content (RC) of 25% to 35%.

13. As a fiber-reinforced composite material, A fiber-reinforced composite material formed by curing a prepreg according to claim 11 or 12.

14. As a layered structure, A layered structure comprising a laminated product in which the prepreg according to claim 11 or 12 is laminated.