JP2024064038A - CURABLE EPOXY RESIN COMPOSITION AND FIBER-REINFORCED COMPOSITE MATERIAL USING SAME - Google Patents

Abstract

【assignment】
The present invention provides a resin composition which has low viscosity, excellent fast curing properties, and high toughness in molded products obtained upon curing, and is therefore suitable for use as a matrix resin for fiber-reinforced composite materials which are excellent in productivity and strength.
SOLUTION
A resin composition for fiber-reinforced composite materials, comprising as essential components a non-urethane-modified epoxy resin (A), a urethane-modified epoxy resin (B), an acid anhydride-based curing agent (C), and a curing accelerator (D), characterized in that the viscosity at 25°C measured with an E-type viscometer is in the range of 50 to 800 mPa·s, the weight average molecular weight Mw of the urethane-modified epoxy resin (B) is 5,000 to 50,000 measured with gel permeation chromatography, and the proportion of structures derived from polyether polyol in the urethane-modified epoxy resin (B) is 20 to 50% by weight.
[Selection diagram] None

Description

The present invention relates to a resin composition for fiber-reinforced composite materials and a fiber-reinforced composite material using the same.

Fiber-reinforced composite materials are composed of reinforcing fibers such as glass fibers, aramid fibers, and carbon fibers, and thermosetting matrix resins such as unsaturated polyester resins, vinyl ester resins, epoxy resins, phenolic resins, benzoxazine resins, cyanate resins, and bismaleimide resins. They are lightweight and have excellent mechanical properties such as strength, corrosion resistance, and fatigue resistance, and are therefore widely used as structural materials for aircraft, automobiles, civil engineering and construction, sporting goods, and other applications.

Manufacturing methods for fiber-reinforced composite materials include autoclave molding and press molding, which use prepregs in which the reinforcing fibers have already been impregnated with a thermosetting matrix resin, and wet layup molding, pultrusion molding, filament winding molding, and RTM methods, which include a process of impregnating the reinforcing fibers with liquid matrix resin and a molding process by thermosetting. Among these, the wet layup molding, pultrusion molding, filament winding molding, and RTM methods use low-viscosity matrix resins in order to quickly impregnate the reinforcing fibers with the resin.

Conventionally, thermosetting resins such as unsaturated polyester resin, vinyl ester resin, and epoxy resin have been used in the wet lay-up molding method, pultrusion molding method, and filament winding molding method. Unsaturated polyester resin and vinyl ester resin, which have radical polymerization properties, have low viscosity and excellent fast curing properties, but have the problem that they have a large cure shrinkage rate during molding and the mechanical properties of the molded product, such as tensile elongation and toughness, are relatively low. On the other hand, epoxy resin can produce molded products with high heat resistance and strength, but has the problem that the resin viscosity is relatively high.

The tensile breaking elongation of the reinforcing fibers used in fiber-reinforced composite materials generally ranges from 3.0 to 6.0% for glass fibers, 2.0 to 5.0% for aramid fibers, and 1.5 to 2.0% for carbon fibers. Therefore, in order to obtain a fiber-reinforced composite material with excellent strength, it is desirable to use a matrix resin with a higher tensile breaking elongation than the reinforcing fibers.

Patent Documents 1 and 2 propose examples of applications in which a resin composition consisting of an epoxy resin and an acid anhydride curing agent is used as the matrix resin for the pultrusion molding method. The use of a low-viscosity epoxy resin improves impregnation of reinforcing fibers, and the addition of an internal mold release agent improves pultrusion moldability. By curing a resin composition consisting of an epoxy resin and an acid anhydride, a cured product with high strength and excellent heat resistance can be obtained, but there is an issue of low toughness and brittleness.

Patent documents 3 and 4 describe the addition of core-shell rubber to a resin composition consisting of an epoxy resin and an acid anhydride curing agent as a method for imparting toughness to the cured product. Although the addition of core-shell rubber particles imparts toughness without reducing heat resistance, the elastic modulus of the molded product decreases due to the flexible chemical structure of the rubber particles. The decrease in elastic modulus is undesirable because it leads to a decrease in strength as a fiber-reinforced composite material.

Attempts have been made to impart toughness by adding a urethane-modified epoxy resin to a resin composition consisting of an epoxy resin and an acid anhydride curing agent (Patent Documents 5 to 7). In all cases, the urethane-modified epoxy resin is synthesized using polyol, polyisocyanate, and epoxy resin as raw materials. To be suitably used as a resin composition for pultrusion molding, it is required that the resin composition has a low viscosity and a fast curing speed before curing to ensure productivity, and that the molded fiber-reinforced composite material has excellent strength due to a high elastic modulus and toughness after curing. Therefore, in order to satisfy the above-mentioned physical properties, it is necessary to pay attention to the composition ratio of each raw material when making a urethane-modified epoxy resin.

Urethane-modified epoxy resins have urethane bonds in their structure, and the urethane bonds aggregate together through hydrogen bonds to form hard segments, while soft segments can be formed by incorporating compounds that exhibit rubber elasticity, such as polyols, into the structure. Furthermore, a crosslinked structure is formed by reacting the urethane-modified epoxy resin with a curing agent, resulting in a cured product that contains hard and soft segments. In order to achieve both a high elastic modulus and toughness in the cured product, it is necessary to pay attention to the ratio of hard and soft segments, that is, the type and composition, and molecular weight of the epoxy resin, polyisocyanate, polyol, etc. used as raw materials for the urethane-modified epoxy resin.

Patent No. 5028903 Japanese Patent No. 5263120 JP 2018-35210 A Japanese Patent No. 5403184 Patent No. 6593573 Patent No. 6739921 Patent No. 6958751

When manufacturing fiber-reinforced composite materials industrially, particularly in the pultrusion molding method, it is common to continuously mold the material at high temperatures in order to increase productivity. For this reason, it is desirable to use a resin composition with a fast curing rate as the matrix resin used. In addition, the cured molded product is required to have excellent fracture toughness, so that cracks do not occur due to curing strain of the resin even when cured for a short time at high temperatures.

The present invention aims to provide a resin composition that has low viscosity, excellent fast curing properties, and high toughness in the molded products obtained upon curing, and is therefore suitable for use as a matrix resin for fiber-reinforced composite materials that are excellent in productivity and strength.

As a result of investigations to solve the above-mentioned problems, the inventors focused on the ratio and molecular weight of the constituent components of the urethane-modified epoxy resin, and discovered that the resin composition maintains a low viscosity while producing a molded product that has a high elastic modulus and toughness upon curing, thereby solving the above-mentioned problems, leading to the completion of the present invention.

That is, the present invention is a resin composition for fiber-reinforced composite materials, which contains non-urethane-modified epoxy resin (A), urethane-modified epoxy resin (B), acid anhydride-based curing agent (C), and curing accelerator (D) as essential components, has a viscosity at 25°C measured with an E-type viscometer in the range of 200 to 20,000 mPa·s, the weight-average molecular weight Mw of the urethane-modified epoxy resin (B) measured by gel permeation chromatography is 5,000 to 50,000, and the ratio of structures derived from polyether polyol in the urethane-modified epoxy resin (B) is 20 to 50% by weight.

In the resin composition of the present invention, it is preferable that bisphenol F type epoxy resin is contained in an amount of 40 parts by weight or more out of 100 parts by weight of the non-urethane modified epoxy resin (A).

In the resin composition of the present invention, the amount of urethane-modified epoxy resin (B) is preferably 8 to 32 parts by weight per 100 parts by weight of the total amount of components (A), (B), (C), and (D).

It is preferable that the weight ratio of urethane bonds in the urethane-modified epoxy resin (B) is 3.0 to 10.0% by weight.

The epoxy equivalent of the urethane-modified epoxy resin (B) is preferably 300 to 500 g/eq.

In the resin composition of the present invention, it is preferable that the curing accelerator (D) is an imidazole that is liquid at 25°C, and that the amount of component (D) is 0.5 to 3.0 parts by weight per 100 parts by weight of the total amount of components (A), (B), (C), and (D).

The preferred volume content of reinforcing fibers in the fiber-reinforced composite material of the present invention is 55 to 75 volume percent.

A fiber-reinforced composite material can be suitably obtained by continuously impregnating reinforcing fibers with the resin composition for a fiber-reinforced composite material of the present invention and molding the same by a pultrusion molding method in which the composition is cured by heating.

The resin composition for fiber-reinforced composite materials of the present invention is a resin composition that has excellent impregnation into reinforcing fibers due to its low viscosity, and cures quickly to produce molded products with high strength and toughness. The resin composition for fiber-reinforced composite materials of the present invention is particularly suitable for pultrusion molding, and fiber-reinforced composite materials can be suitably produced by carrying out the pultrusion molding method.

1 shows a GPC chart of the urethane-modified epoxy resin of Synthesis Example 1.

Hereinafter, an embodiment of the present invention will be described in detail.
The resin composition for fiber-reinforced composite materials of the present invention contains as essential components a non-urethane-modified epoxy resin (A), a urethane-modified epoxy resin (B), an acid anhydride-based curing agent (C), and a curing accelerator (D). Hereinafter, the non-urethane-modified epoxy resin (A), the urethane-modified epoxy resin (B), the acid anhydride-based curing agent (C), and the curing accelerator (D) will also be referred to as component (A), component (B), component (C), and component (D), respectively.

As the non-urethane-modified epoxy resin (A) used in the present invention, an epoxy compound having two or more epoxy groups in one molecule and not modified with urethane can be used. For example, bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, bisphenol E-type epoxy resin, bisphenol S-type epoxy resin, bisphenol Z-type epoxy resin, and isophorone bisphenol-type epoxy resin, or halogenated, alkyl-substituted, hydrogenated, or monomeric, high molecular weight compounds having multiple repeating units, glycidyl ethers of alkylene oxide adducts of these bisphenols, novolac-type epoxy resins such as phenol novolac-type epoxy resin, cresol novolac-type epoxy resin, and bisphenol A novolac-type epoxy resin,

Alicyclic epoxy resins such as 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and 1-epoxyethyl-3,4-epoxycyclohexane, aliphatic epoxy resins such as trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, and polyoxyalkylene diglycidyl ether, glycidyl esters such as phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, and dimer acid glycidyl ester, and glycidyl amines such as tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenylsulfone, triglycidylaminophenol, triglycidylaminocresol, and tetraglycidylxylylenediamine can be used. Among these epoxy resins, from the viewpoint of low viscosity, epoxy resins that are liquid at 25°C are preferred, and epoxy resins that are semi-solid or solid at 25°C are not preferred. These may be used alone or in combination of two or more.

A preferred embodiment for achieving the effects of the present invention is to contain 40 parts by weight or more, preferably 45 to 85 parts by weight, and more preferably 50 to 70 parts by weight, of 100 parts by weight of non-urethane modified epoxy resin (A). By containing 40 parts by weight or more of bisphenol F type epoxy resin, the viscosity of the resin composition can be reduced and the impregnation of reinforcing fibers can be improved.

The amount of non-urethane modified epoxy resin (A) used in the resin composition for fiber reinforced composite materials of the present invention is preferably 25 to 50 parts by weight, more preferably 30 to 50 parts by weight, per 100 parts by weight of the total amount of components (A), (B), (C), and (D).

The urethane-modified epoxy resin (B) used in the present invention has a weight-average molecular weight Mw measured by gel permeation chromatography (GPC) of 5,000 to 50,000, preferably 8,000 to 40,000, and more preferably 12,000 to 30,000. If the Mw is less than 5,000, the toughness of the resin composition cannot be increased when cured, and if the Mw exceeds 50,000, the viscosity of component (B) becomes significantly high, impairing the ability to impregnate fibers.

In addition, the ratio of structures derived from polyether polyol (polyether polyol structure ratio) in the urethane-modified epoxy resin (B) used in the present invention is 20 to 50% by weight, preferably 25 to 45% by weight, and more preferably 27 to 40% by weight. By having the ratio of structures derived from polyether polyol in component (B) within this range, it is possible to achieve both high elastic modulus and toughness when the resin composition is cured while maintaining the low viscosity of component (B).

The proportion of urethane bonds in the urethane-modified epoxy resin (B) used in the resin composition for fiber-reinforced composite materials of the present invention is preferably 3.0 to 10.0% by weight, and more preferably 4.0 to 7.0% by weight. If it is less than 3.0% by weight, the elastic modulus and toughness of the resin composition when cured will be insufficient, and if it exceeds 10.0% by weight, aggregation due to hydrogen bonds caused by the urethane bonds will cause the resin composition to become highly viscous, which may impair its ability to impregnate reinforcing fibers.

Here, the ratio (% by weight) of the urethane bonds in the urethane-modified epoxy resin (B) used in the resin composition for a fiber-reinforced composite material can be calculated by the following formula.
Proportion of urethane bonds=100×(weight of polyisocyanate used in synthesis of urethane-modified epoxy resin×(47/isocyanate equivalent of polyisocyanate used in synthesis of urethane-modified epoxy resin))/total weight of raw materials used in synthesis of urethane-modified epoxy resin

The epoxy equivalent of the urethane-modified epoxy resin (B) used in the present invention is preferably 300 to 500 g/eq, more preferably 300 to 400 g/eq. Within this range, the elastic modulus and toughness of the resulting cured product can be increased. That is, if the epoxy equivalent is less than 300 g/eq, the crosslink density increases during curing, resulting in reduced toughness, and if it exceeds 500 g/eq, high toughness is exhibited but the elastic modulus decreases.

The urethane-modified epoxy resin (B) is obtained by reacting an epoxy resin having a hydroxyl group in the molecule with a polyol compound such as polyether polyol, and a polyisocyanate compound under heat. The urethane-modified epoxy resin may contain unmodified epoxy resin that is not bonded to polyurethane.

As the epoxy resin having a hydroxyl group in the molecule (hereinafter also referred to as raw epoxy resin) which is the raw material of the urethane-modified epoxy resin (B), a bisphenol-type epoxy resin having a hydroxyl group in the molecule is preferred. By using this, the toughness of the cured product can be increased without decreasing the heat resistance. The hydroxyl equivalent of the raw epoxy resin is preferably 500 to 10,000 g/eq, more preferably 1,000 to 5,000 g/eq. If the hydroxyl equivalent is less than 500 g/eq, the viscosity of the urethane-modified epoxy resin (B) will increase, and if it is more than 10,000 g/eq, the toughness of the cured product will decrease. The epoxy equivalent of the raw epoxy resin is preferably 100 to 300 g/eq, more preferably 160 to 260 g/eq.

The polyol compound and polyisocyanate compound (hereinafter also referred to as raw polyol compound and raw polyisocyanate compound, respectively) that are the raw materials of the urethane-modified epoxy resin (B) are not particularly limited and various types can be used as long as the desired urethane-modified epoxy resin (B) can be obtained.

As the raw polyol compound, preferably, one or more polyol compounds selected from the group consisting of medium molecular weight polyols with a hydroxyl group equivalent of 240 to 2000 g/eq, such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyester polyol, polycarbonate polyol, etc., and low molecular weight polyols with a hydroxyl group equivalent of 30 to 120 g/eq, such as ethylene glycol, propanediol, butanediol, hexanediol, glycerin, etc., can be used. In addition, it is desirable to use a combination of a medium molecular weight polyol and a low molecular weight polyol as the raw polyol compound, since it is possible to form soft segments and hard segments in the urethane-modified epoxy resin, thereby increasing the elastic modulus and toughness of the cured product.

As the raw material polyisocyanate compound, one or more polyisocyanate compounds selected from the group consisting of tolylene diisocyanate and diphenylmethane diisocyanate can be used.

The amount of the urethane-modified epoxy resin (B) used in the resin composition for fiber-reinforced composite materials of the present invention is desirably 8 to 32 parts by weight per 100 parts by weight of the total amount of components (A), (B), (C), and (D). If it is less than 8 parts by weight, the toughness of the resin composition when cured will be insufficient, and if it exceeds 32 parts by weight, the resin composition will become highly viscous and will be unable to impregnate the reinforcing fibers. In addition, the elastic modulus of the cured product will be low when the resin composition is cured.

The resin composition for fiber-reinforced composite materials of the present invention contains an acid anhydride-based curing agent (C). A carboxylic acid anhydride can be used as the acid anhydride-based curing agent (C). The amount of the acid anhydride-based curing agent (C) is preferably 0.8 equivalents or more and 1.2 equivalents or less per equivalent of the total epoxy group of the non-urethane-modified epoxy resin (A) and the urethane-modified epoxy resin (B). If the ratio of the acid anhydride-based curing agent (C) is less than 0.8 equivalents, poor curing is likely to occur, and if the acid anhydride is more than 1.2 equivalents, poor curing is likely to occur and the acid anhydride remains after curing, which may cause effects such as hydrolysis. However, this is not the case when there is a risk of the acid anhydride or epoxy resin volatilizing during the curing process, and it may be used in an amount of 0.5 equivalents or more and 1.5 equivalents or less.

The resin composition for fiber-reinforced composite materials of the present invention contains a curing accelerator (D). The curing accelerator is preferably an imidazole compound or a phosphorus-based compound.

The content of the imidazole curing accelerator (D) contained in the resin composition for fiber-reinforced composite materials of the present invention is preferably 0.1 to 10 parts by weight, preferably 0.5 to 5.0 parts by weight, and particularly preferably 0.8 to 2.4 parts by weight, per 100 parts by weight of the acid anhydride curing agent (C). When the imidazole curing accelerator is contained within this range, a molded product that has excellent short-term curing properties and high heat resistance when heated and cured can be obtained.

As the imidazole-based curing accelerator (D), in order to more satisfactorily achieve the fast curing property during heat curing and the heat resistance during curing in the present invention, it is preferable to use one or more imidazole compounds selected from the group consisting of 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-6-4',5'-dihydroxymethylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole. As the curing accelerator (D), imidazole compounds that are liquid at 25°C are particularly preferable.

The content of the phosphorus-based curing accelerator (D) contained in the resin composition for fiber-reinforced composite materials of the present invention is preferably 0.2 to 12 parts by weight, preferably 0.4 to 4.0 parts by weight, and particularly preferably 0.6 to 2.0 parts by weight, per 100 parts by weight of the acid anhydride-based curing agent (C). When the phosphorus-based curing accelerator is contained within this range, a molded product is obtained that has excellent curing properties in a short time and has high elasticity and heat resistance when cured by heating.

In order to more satisfactorily achieve the rapid curing property during heat curing and the heat resistance during curing in the present invention as the phosphorus-based curing accelerator (D), the curing accelerator may be selected from the group consisting of tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tetrabutylphosphonium acetate, methyltriphenylphosphonium bromide, ethyltriphenylphosphonium bromide, propyltriphenylphosphonium bromide, butyltriphenylphosphonium bromide, benzyltriphenylphosphonium chloride, tetraphenylphosphonium bromide, tetraphenylphosphonium tetraphenylborate, and tetraphenylphosphonium tetra-p-tolylborate. ester, triphenylethylphosphonium tetraphenylborate, tris(3-methylphenyl)ethylphosphonium tetraphenylborate, tris(2-methoxyphenyl)ethylphosphonium tetraphenylborate, (4-methylphenyl)triphenylphosphonium thiocyanate, triphenylphosphine, tributylphosphine, tri-tert-butylphosphine, trioctylphosphine, di-tert-butyl(3-methyl-2-butenyl)phosphine, dibutylphenylphosphine, di-tert-butylphenylphosphine, methyldiphenylphosphine, ethyldiphenylphosphine, butyldiphenylphosphine,

Diphenylcyclohexylphosphine, triphenylphosphine, tri-o-tolylphosphine, tri-m-tolylphosphine, tri-p-tolylphosphine, tris(4-ethylphenyl)phosphine, tris(4-propylphenyl)phosphine, tris(4-isopropylphenyl)phosphine, tris(4-butylphenyl)phosphine, tris(4-tert-butylphenyl)phosphine, tris(2,4-dimethylphenyl)phosphine, tris(2,5-dimethylphenyl)phosphine, tris(2,6-dimethylphenyl)phosphine, tris(3,5-dimethylphenyl)phosphine, tris(2,4,6- It is preferable to use one or more phosphorus compounds selected from the group consisting of 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane, and 2,2'-bis(diphenylphosphino)diphenyl ether.

The resin composition for fiber-reinforced composite materials of the present invention can also be blended with other curable resins. Such curable resins 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.

The resin composition for fiber-reinforced composite materials of the present invention is produced by uniformly mixing at least the above-mentioned components (A), (B), (C) and (D).
The resin composition for fiber reinforced composite materials of the present invention has a viscosity in the range of 200 to 20,000 mPa·s, preferably 1,000 to 17,000 mPa·s, and more preferably 2,000 to 15,000 mPa·s, as measured using a cone-plate type E-type viscometer at 25° C. When the viscosity is within this range, the resin composition has good impregnation properties into reinforcing fibers, and the resin is less likely to drip from the fibers during the impregnation process.

Methods for producing fiber-reinforced composite materials from the resin composition for fiber-reinforced composite materials of the present invention include the wet lay-up method, in which a fabric of reinforcing fibers is arranged and laminated in a mold, coated with a resin composition, and then heated and molded to obtain a cured molded body; the pultrusion method, in which reinforcing fibers are continuously passed through an impregnation layer filled with a curable resin composition, then heated and passed through a mold to continuously obtain a rod-shaped molded body; the filament winding method, in which reinforcing fibers are continuously passed through an impregnation layer filled with a curable resin composition, then wound around a mandrel and heated and molded to obtain a molded body with a circular cross section; and the transfer molding method, in which the fibers are placed in a transfer molding machine and heated and molded. These methods allow the molding of fiber-reinforced composite materials with few voids and high strength.

The resin composition for fiber-reinforced composite materials of the present invention can be used to obtain fiber-reinforced composite materials by wet layup molding, pultrusion molding, filament winding molding, or transfer molding. Pultrusion molding is particularly preferred. The pultrusion molding method is also called the pull-com or continuous pultrusion molding method, and is a method for producing fiber-reinforced composite materials by applying the resin composition for fiber-reinforced composite materials to reinforcing fibers and continuously heating and curing the applied materials.

Specifically, a strip of reinforcing fiber is fed through a resin tank filled with the resin composition for fiber-reinforced composite materials of the present invention, the excess resin is wiped off, the fiber is degassed, and the fiber is introduced into one end of a mold equipped with a heating device and heated. After heating for a predetermined time in the mold, the reinforcing fiber is pulled out from the other end of the mold. This operation is carried out continuously to obtain a strip of fiber-reinforced composite material. The pulled-out strip of fiber-reinforced composite material is cut into the desired size and shape. This pultrusion molding method allows for highly productive production of molded bodies of fiber-reinforced composite material.

The reinforcing fibers used in the fiber-reinforced composite material of the present invention are selected from glass fibers, aramid fibers, carbon fibers, boron fibers, etc., but in order to obtain a fiber-reinforced composite material with excellent strength, it is particularly preferable to use carbon fibers.

In a fiber-reinforced composite material composed of the resin composition for fiber-reinforced composite materials of the present invention and reinforcing fibers, the volume content of the reinforcing fibers is preferably in the range of 55 to 75%, and more preferably in the range of 60 to 70%. When the volume content of the reinforcing fibers is in this range, a molded product with few voids and a high volume content of the reinforcing fibers can be obtained, resulting in a fiber-reinforced composite material molded product with excellent strength.

The resin composition for fiber-reinforced composite materials of the present invention has low viscosity, and therefore has excellent impregnation properties into reinforcing fibers, and also has rapid curing properties when heated, as well as high elastic modulus and toughness of molded products, and is therefore particularly suitable for use in pultrusion molding. In other words, a preferred embodiment of the present invention is a method for producing a fiber-reinforced composite material in which reinforcing fibers are continuously impregnated with the resin composition for fiber-reinforced composite materials of the present invention and cured by heating.

Next, the present invention will be specifically described based on examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. Parts indicating the blend amount are parts by weight unless otherwise specified. The unit of epoxy equivalent is g/eq.

The abbreviations for each component used in the examples are as follows.
YD-128: Bisphenol A type epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd., epoxy equivalent 187 g/q)
YDF-170: Bisphenol F type epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd., epoxy equivalent 168 g/q)
PG30: Polypropylene glycol having an average molecular weight of 3000 and a hydroxyl equivalent of 1509 g/eq
TMG30: Polytetramethylene glycol having an average molecular weight of 3000 and a hydroxyl equivalent of 1497 g/eq
BD: 1,4-butanediol, hydroxyl equivalent 45 g/eq
TDI: toluene diisocyanate MDI: diphenylmethane diisocyanate MTH: methyltetrahydrophthalic anhydride (acid anhydride equivalent: 166, viscosity: 53 mPa·s at 25° C.)
MHH: Methylhexahydrophthalic anhydride (acid anhydride equivalent: 168, viscosity at 25°C: 61 mPa·s)
DMZ: 1,2-dimethylimidazole TBBr: Tributylmethylammonium bromide

Synthesis Example 1
A glass separable flask equipped with a stirrer, a thermometer, a reflux tube, a nitrogen gas inlet, was charged with 120 parts of YD-128 and 70.9 parts of PG30, and the temperature was raised to 110 ° C. while stirring. Next, 23.1 parts of TDI were added from the inlet, and after 1 hour, 6.2 parts of BD were added, and the reaction temperature was kept at 130 ° C. and reacted for 2 hours, to obtain 209 parts of a urethane-modified epoxy resin having a weight average molecular weight Mw of 18,400, a polyether polyol structure ratio of 32 wt%, a urethane bond weight ratio of 5.7 wt%, and an epoxy equivalent of 339. This urethane-modified epoxy resin is referred to as EPU1.

Synthesis Example 2
In a similar apparatus to that of Synthesis Example 1, 120 parts of YD-128 and 87.2 parts of PG30 were charged, and the temperature was raised to 110°C while stirring. Next, 23.1 parts of MDI were charged from the charging port, and after 1 hour had elapsed, 5.3 parts of BD were charged, and the reaction temperature was further maintained at 130°C and reacted for 2 hours, obtaining 228 parts of a urethane-modified epoxy resin having a weight average molecular weight Mw of 23,700, a polyether polyol structure ratio of 37% by weight, a urethane bond weight ratio of 4.9% by weight, and an epoxy equivalent of 350. This urethane-modified epoxy resin is referred to as EPU2.

Synthesis Example 3
Into an apparatus similar to that of Synthesis Example 1, 117 parts of YD-128 and 55.0 parts of TMG30 were charged, and the temperature was raised to 110°C while stirring. Next, 23.1 parts of MDI were charged from the charging port, and after 1 hour had elapsed, 5.3 parts of BD were charged, and the reaction temperature was further maintained at 130°C and reacted for 2 hours, obtaining 190 parts of a urethane-modified epoxy resin having a weight average molecular weight Mw of 15,700, a polyether polyol structure ratio of 37% by weight, a urethane bond weight ratio of 5.7% by weight, and an epoxy equivalent of 319. This urethane-modified epoxy resin is referred to as EPU3.

Synthesis Example 4
Into an apparatus similar to that of Synthesis Example 1, 133 parts of YD-128 and 24.1 parts of PG30 were charged, and the temperature was raised to 110°C while stirring. Next, 9.1 parts of TDI were charged from the charging port, and after 1 hour had elapsed, 2.3 parts of BD were charged, and the reaction temperature was further maintained at 130°C and reacted for 2 hours, obtaining 163 parts of a urethane-modified epoxy resin having a weight average molecular weight Mw of 5,900, a polyether polyol structure ratio of 14% by weight, a urethane bond weight ratio of 2.9% by weight, and an epoxy equivalent of 235. This urethane-modified epoxy resin is referred to as EPU4.

Synthesis Example 5
In an apparatus similar to that of Synthesis Example 1, 88 parts of YD-128 and 132 parts of PG30 were charged, and the temperature was raised to 110°C while stirring. Next, 18.0 parts of MDI were charged from the charging port, and after 1 hour had passed, 1.6 parts of BD were charged, and the reaction temperature was further maintained at 130°C and the reaction was carried out for 2 hours, obtaining 232 parts of a urethane-modified epoxy resin having a weight average molecular weight Mw of 32,300, a polyether polyol structure ratio of 55% by weight, a urethane bond weight ratio of 2.8% by weight, and an epoxy equivalent of 511. This urethane-modified epoxy resin is referred to as EPU5.

(Measurement of weight average molecular weight Mw)
The weight average molecular weight Mw of the urethane modified epoxy (B) was measured using a gel permeation chromatography HLC-8420GPC manufactured by Tosoh Corporation, equipped with columns TSKgel G4000HXL, TSKgel G3000HXL, and TSKgel G2000HXL manufactured by Tosoh Corporation in series. Gel permeation chromatography was performed at a column temperature of 40°C, tetrahydrofuran was used as the eluent, the flow rate was 1 ml/min, and an RI (differential refractometer) detector was used as the detector. Only the peak of the n=0 body of the epoxy resin used as the raw material was excluded, and the weight average molecular weight Mw was calculated based on polystyrene standards by adding up all other peaks.

Example 1
(Production of resin composition for fiber reinforced composite material)
39 parts of YD-128 as the component (A), 21 parts of EPU1 obtained in Synthesis Example 1 as the component (B), 39 parts of MTH as the component (C), and 1.2 parts of DMZ as the component (D) were placed in a 150 mL plastic container and mixed with stirring at room temperature for 5 minutes using a vacuum mixer “Awatori Rentaro” (product name; manufactured by Thinky Corporation) to obtain a resin composition for fiber-reinforced composite materials.

(Viscosity Measurement)
The viscosity value at 25° C. was measured using a cone-plate type E-type viscometer. The resin composition for fiber-reinforced composite materials was prepared, and 0.8 mL of it was immediately subjected to measurement. The measurement value 60 seconds after preparation was regarded as the viscosity value of the resin composition for fiber-reinforced composite materials.

(Gel Time Measurement)
The curable resin composition was added onto the plate of a gelation tester (manufactured by Nisshin Scientific Co., Ltd.) that had been heated to 150°C, and the mixture was stirred at a speed of two rotations per second using a fluororesin rod. The time required for the curing of the curable resin composition to progress and lose its plasticity was recorded as the gelation time.

(Measurement of bending modulus and bending strength)
The resin composition for fiber-reinforced composite materials was poured into a mold having a length of 60 mm and a width of 240 mm and having a 4 mm-thick spacer cut into a flat plate shape, and cured at 140°C for 4 hours to prepare a molded plate for measurement, which was used to measure the flexural modulus and flexural strength.
The obtained molded plate was cut into a size of 80 mm × 10 mm using a benchtop band saw, and a bending test was performed on the bending test piece using a universal material testing machine (Autograph AGS-H manufactured by Shimadzu Corporation) at a temperature condition of 23 ° C. in accordance with a method conforming to JIS 7171, and the bending modulus and bending strength were calculated.

(Measurement of fracture toughness)
The resin composition for fiber-reinforced composite materials was poured into a mold measuring 60 mm in length and 240 mm in width and equipped with a 2 mm-thick spacer cut into a flat plate shape, and cured at 140°C for 4 hours to prepare a measurement molded plate, which was used for measuring fracture toughness.
The obtained molded plate was cut into a size of 50 mm x 10 mm using a bench band saw, and a crack was made in accordance with ASTM E399 to measure the fracture toughness at a temperature of 23°C using a universal material testing machine (Autograph AGS-H manufactured by Shimadzu Corporation).

(Preparation of test pieces for measuring glass transition temperature)
The resin composition for fiber-reinforced composite materials was poured into a mold having a length of 80 mm and a width of 80 mm and having a 4 mm-thick spacer cut into a flat plate shape, and cured at 140°C for 4 hours. The obtained molded plate was then cut into a size of 50 mm x 10 mm using a bench band saw, and used for measuring the glass transition temperature described below.

(Measurement of Glass Transition Temperature)
The molded plate was cut to a size of 2.5 mm x 2.5 mm using a benchtop band saw, and further polished to a thickness of approximately 0.8 mm using a belt disk sander. Measurement was performed using a differential scanning calorimeter (DSC7000X, Hitachi High-Tech Science Co., Ltd.) under a nitrogen atmosphere at a temperature rise rate of 10°C/min, and the intersection point between the tangent at the inflection point of the DSC curve and the temperature at which the inflection begins, i.e., the tangent in the temperature range 15 to 30°C lower than the inflection point, was determined, and this temperature was taken as the glass transition temperature Tg.

(Preparation of pultrusion plate)
The obtained resin composition for fiber reinforced composite materials was poured into a resin bath and kept at 40 ° C. 37 carbon fibers (Toray Industries, Inc., Torayca T700SC-24K) were bundled from a creel stand and introduced into the resin bath, and while pulling out at 0.2 m / min using a pulling device, the resin composition for fiber reinforced composite materials was impregnated, and then the excess resin composition was squeezed out by passing through a slit, and the obtained band-shaped carbon fiber impregnated with the resin composition was passed through a mold heated to 140 ° C. with a cross-sectional dimension of 50 mm × 1.0 mm and a length of 400 mm, and further passed through a mold heated to 160 ° C. with a cross-sectional dimension of 50 mm × 1.0 mm and a length of 400 mm, to obtain a plate of carbon fiber reinforced composite material with a length of 2 m, a width of 50 mm, and a thickness of 1.0 mm by drawing. The plate produced was a fiber reinforced composite material containing carbon fibers with a volume content of 66% and aligned in one direction.

(Appearance evaluation of pultrusion molded plates)
The carbon fiber reinforced composite plate produced by the above-mentioned pultrusion molding process was visually inspected to evaluate whether there was any fraying of the carbon fiber on the surface. The area where the carbon fiber was peeled off from the surface of the molded plate by a length of 20 mm or more was counted as fraying. If the total number of fraying was 4 or less, the plate was evaluated as ◯, and if the total number of fraying was more than 4, the plate was evaluated as ×.

(Measurement of 0° bending strength and 90° bending strength)
The plate of the carbon fiber reinforced composite material obtained by the molding process was cut using a milling machine to a size of 60 mm in the fiber parallel direction and 15 mm in the fiber perpendicular direction, and used for measuring the 0° bending strength. Similarly, the plate of the carbon fiber reinforced composite material was cut to a size of 15 mm in the fiber parallel direction and 50 mm in the fiber perpendicular direction, and used for measuring the 90° bending strength. A three-point bending test was performed at a temperature of 23°C and a support distance of 40 mm according to a method in accordance with JIS K7074, and the 0° bending strength and the 90° bending strength were measured.

Examples 2 to 12, Comparative Examples 1 to 4
A resin composition for a fiber-reinforced composite material was prepared under the same mixing conditions as in Example 1, except that the raw materials were used in the compositions shown in Tables 1 and 2 as components (A) to (D), and viscosity measurement, gel time measurement, bending test, fracture toughness test, and glass transition temperature measurement were carried out in the same manner as in Example 1. In addition, preparation of a pultrusion molded plate, evaluation of appearance, and evaluation of 0° and 90° bending strength were carried out in the same manner as in Example 1.

The test results for Examples 1 to 12 and Comparative Examples 1 to 4 are shown in Tables 1 and 2, respectively.

The fiber-reinforced composite material molded using the resin composition for fiber-reinforced composite materials of the present invention can be suitably used as a structural material for aircraft, spacecraft, ships, automobiles, civil engineering and construction, sporting goods, etc.

Claims (9)

The epoxy resin composition comprises, as essential components, a non-urethane-modified epoxy resin (A), a urethane-modified epoxy resin (B), an acid anhydride-based curing agent (C), and a curing accelerator (D), and has a viscosity at 25°C measured by an E-type viscometer in the range of 200 to 20,000 mPa s,
and wherein the urethane-modified epoxy resin (B) has a weight average molecular weight Mw of 5,000 to 50,000 as measured by gel permeation chromatography, and the ratio of structures derived from polyether polyol in the urethane-modified epoxy resin (B) is 20 to 50% by weight. The resin composition for fiber-reinforced composite materials according to claim 1, characterized in that, out of 100 parts by weight of the non-urethane modified epoxy resin (A), 40 parts by weight or more of bisphenol F type epoxy resin is contained. The resin composition for fiber-reinforced composite materials according to claim 1, characterized in that the amount of urethane-modified epoxy resin (B) is 8 to 32 parts by weight per 100 parts by weight of the total amount of components (A), (B), (C), and (D). The resin composition for fiber-reinforced composite materials according to claim 1, characterized in that the weight ratio of urethane bonds to 100 parts by weight of the urethane-modified epoxy resin (B) is 3.0 to 10.0 parts by weight. The resin composition for fiber-reinforced composite materials according to claim 1, characterized in that the epoxy equivalent of the urethane-modified epoxy resin (B) is 300 to 500 g/eq. The resin composition for fiber-reinforced composite materials according to claim 1, characterized in that the curing accelerator (D) is an imidazole compound that is liquid at 25°C, and the amount of component (D) is 0.5 to 3.0 parts by weight per 100 parts by weight of the total amount of components (A), (B), (C), and (D). A fiber-reinforced composite material obtained by blending reinforcing fibers with the resin composition for fiber-reinforced composite materials according to any one of claims 1 to 6 and curing the blend. The fiber-reinforced composite material according to claim 7, in which the volume content of the reinforcing fibers is 55 to 75 volume %. A method for producing a fiber-reinforced composite material, comprising continuously impregnating reinforcing fibers with the resin composition for fiber-reinforced composite materials described in any one of claims 1 to 6 and then heat-curing the material.

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