JP2022104130A - Curable resin composition and prepreg using the same - Google Patents

Abstract

To provide a curable resin composition which has excellent viscosity stability during long-term storage, shows a high cure rate when thermally cured, and a cured article thereof, even after short-time curing, shows high heat resistance.SOLUTION: Provided is a curable resin composition, comprising an epoxy resin (A), dicyandiamide or a derivative thereof (B), a solid aromatic urea compound (C), and a curing accelerator (D) as essential components. The curing accelerator (D) is at least one selected from an organic amine salt, a quaternary ammonium salt, an organic phosphorus compound, and an organic phosphonium salt. An addition amount of the curing accelerator (D) is 0.05 to 3.0 pts.mass relative to a total of 100 pts.mass of the (A) component, (B) component, (C) component, and (D) component.SELECTED DRAWING: None

Description

The present invention relates to an epoxy resin composition that can obtain high heat resistance at the time of curing, and a prepreg using the same.

The fiber-reinforced composite material includes reinforcing fibers such as glass fiber, aramid fiber and carbon fiber, and a thermosetting matrix such as unsaturated polyester resin, vinyl ester resin, epoxy resin, phenol resin, benzoxazine resin, cyanate resin and bismaleimide resin. Since it is made of resin and is lightweight and has excellent mechanical properties such as strength, corrosion resistance and fatigue resistance, it is widely applied as a structural material for aircraft, automobiles, civil engineering and construction and sporting goods.

The method for producing the fiber-reinforced composite material includes an autoclave molding method using a prepreg in which a thermosetting matrix resin is pre-impregnated in the reinforcing fiber, a press molding method, a step of impregnating the reinforcing fiber with a liquid matrix resin, and thermosetting. There are methods such as a wet lay-up molding method, a pultrusion molding method, a filament winding molding method, and an RTM method, which include a molding step according to the above method.

Various efforts have been made in order to increase productivity in the method for producing a fiber-reinforced composite material, and one of them is studying to increase the curing rate of a matrix resin. On the other hand, the prepreg is required to have long-term viscosity stability during storage, that is, the curing reaction of the matrix resin does not proceed at the storage temperature.

As a method for maintaining the storage stability of the matrix resin, dicyandiamide, a hydrazide compound, an imidazole compound, a diaminodiphenyl sulfone, or the like, which are solid curing agents, are used as the curing agent for the epoxy resin. Since these solid curing agents have extremely low solubility in epoxy resin near room temperature, the curing reaction does not proceed. On the other hand, the curing agent can be dissolved by heating, or the curing agent can be dissolved in the epoxy resin by thermal decomposition to promote the curing reaction (Patent Documents 1 and 2).

As a method for increasing the curing rate of the matrix resin, Patent Documents 3 and 4 study adding an imidazole compound or a urea compound in addition to the epoxy resin and dicyandiamide which is a solid curing agent.

As a method for improving the storage stability of the matrix resin, Patent Document 5 studies using a reaction product of an epoxy resin and an amine compound as a curing agent. Although the rate of increase in viscosity of the matrix resin can be suppressed by this method, a hard and brittle molded product tends to be obtained.

As a method to improve the storage stability of matrix resin. In Patent Document 6, it is studied to suppress the viscosity increase rate of the matrix resin by adding a boric acid ester compound in addition to the epoxy resin and the solid curing agent, but the curing rate is lowered by this method.

Efforts are being made to add phosphorus compounds as a method for imparting functions to the matrix resin. In Patent Documents 7 and 8, flame retardancy is imparted by using a specific phosphorus compound.

As a method for adjusting the curability of the matrix resin, Patent Document 9 makes an effort to add a specific phosphorus-based compound or organic base compound. In this method, a matrix resin having a high curing temperature of 180 ° C. and exhibiting high curability at a lower temperature is required.

Japanese Unexamined Patent Publication No. 2010-265371 International Publication No. 2018/2146 International Publication No. 2019/98028 Japanese Unexamined Patent Publication No. 2016-522278 Japanese Unexamined Patent Publication No. 2019-189833 Japanese Unexamined Patent Publication No. 9-157498 International Publication No. 2016/198957 Japanese Patent No. 5648685 Japanese Unexamined Patent Publication No. 2019-65282

The present invention has excellent viscosity stability during long-term storage and a high curing rate during thermosetting. Therefore, an object of the present invention is to provide a resin composition used as a matrix resin for a fiber-reinforced composite material that is molded in a short time. do.

As a result of studies to solve the above-mentioned problems, the present inventors have obtained a resin composition having viscosity stability during long-term storage and a high curing rate during curing by using a solid curing agent and a specific compound. It was found that it could be obtained, and the present invention was completed.

（式（１）中、Ｒは水素原子、炭素原子数１～２０の１価の有機残基であり、Ｘ^－は有機アニオン、ハロゲン化物イオンであり、ｍは０～４の整数である。）

（式（２）中、Ｒ^１はそれぞれ独立に炭素原子数１～１０の１価の有機残基であり、Ｙ^－は有機アニオン、ハロゲン化物イオンを表す。）

（式（３）中、Ｒ^２はそれぞれ独立に炭素原子数１～１０の１価の有機残基を表す。）

（式（４）中、Ｒ^３はそれぞれ独立に炭素原子数１～１０の１価の有機残基であり、Ｚ^－は有機アニオン、ハロゲン化物イオンを表す。） That is, the present invention is a curable resin composition containing an epoxy resin (A), a dicyandiamide or a derivative thereof (B), a solid aromatic urea compound (C), and a curing accelerator (D) as essential components. The curing accelerator (D) is an organic amine salt represented by the following general formula (1), a quaternary ammonium salt represented by the following general formula (2), and an organic phosphorus represented by the following general formula (3). The compound is a compound selected from at least one of the organic phosphonium salts represented by the following general formula (4), and the blending amount of the curing accelerator (D) is the component (A), the component (B), and the component (C). , (D) is a curable resin composition characterized in that it is 0.05 to 3.0 parts by mass with respect to 100 parts by mass in total.

(In the formula (1), R is a hydrogen atom and a monovalent organic residue having 1 to 20 carbon atoms, X ⁻ is an organic anion and a halide ion, and m is an integer of 0 to 4. )

(In the formula (2), R ¹ is an independently monovalent organic residue having 1 to 10 carbon atoms, and Y ⁻ represents an organic anion and a halide ion.)

(In formula (3), R ² independently represents a monovalent organic residue having 1 to 10 carbon atoms.)

(In the formula (4), R ³ is an independently monovalent organic residue having 1 to 10 carbon atoms, and Z ⁻ represents an organic anion and a halide ion.)

In the curable resin composition of the present invention, the viscosity at 25 ° C. measured by an E-type viscometer is V, the viscosity after 168 hours at 25 ° C. is W, and the viscosity increase rate W / V is less than 1.25. It is preferable to have.

Another aspect of the present invention is a prepreg characterized in that the curable resin composition is blended with reinforcing fibers so that the volume content is 45 to 70%, and the prepreg is heat-molded. It is a molded product obtained.

The curable resin composition of the present invention is excellent in viscosity stability during storage and a high curing rate during curing, and improves the productivity of the molded product due to the long-term storage property and high curing rate of the prepreg using the same. , Suitable for fiber reinforced composite materials.

Hereinafter, embodiments of the present invention will be described in detail.
The curable resin composition of the present invention contains an epoxy resin (A), a dicyandiamide or a derivative thereof (B), a solid aromatic urea compound (C), and a curing accelerator (D) as essential components. Hereinafter, the epoxy resin (A), the dicyandiamide or its derivative (B), the solid aromatic urea compound (C), and the curing accelerator (D) are added to the components (A), (B), and (C), respectively. And (D) component.

The epoxy resin (A) is an epoxy resin having two or more epoxy groups on average in one molecule, and is, for example, a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a bisphenol E type epoxy resin, or a bisphenol S. Bisphenol type epoxy resins such as type epoxy resins, bisphenol Z type epoxy resins, and isophorone bisphenol type epoxy resins, and halogens, alkyl substituents, hydrogenated products, and monomers of these bisphenol type epoxy resins are not limited to multiple repeating units. Novolak type epoxy resin such as high molecular weight body, glycidyl ether of alkylene oxide adduct, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolak type epoxy resin, 3,4-epoxy-6-methylcyclohexyl Alicyclic type such as methyl-3,4-epoxy-6-methylcyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 1-epoxyethyl-3,4-epoxycyclohexane Epoxy resins, aliphatic epoxy resins such as trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, polyoxyalkylene diglycidyl ether, phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, and dimer acid glycidyl ester. Etc., and glycidyl amines such as tetraglycidyl diaminodiphenylmethane, tetraglycidyl diaminodiphenyl sulfone, triglycidyl aminophenol, triglycidyl aminocresol, and tetraglycidyl xylylene diamine can be used. These may be used alone or in combination of two or more. The epoxy resin (A) used in the present invention is preferably 80 to 96 parts by mass, preferably 84 to 94 parts by mass, out of a total of 100 parts by mass of the components (A) to (D).

The curable resin composition of the present invention uses dicyandiamide or a derivative thereof (B) as a curing agent. Diciandiamide is a curing agent that is solid at room temperature and hardly dissolves in epoxy resin at room temperature, but dissolves when heated to 180 ° C or higher and has the property of reacting with epoxy groups. It has excellent storage stability potential at room temperature. It is a curing agent. As the derivative, an N-substituted dicyandiamide derivative such as N-hexyldicyandiamide can be used. The amount to be used is preferably 0.2 to 0.8 equivalents (calculated with 1 mol of dicyandiamide as 4 equivalents) with respect to 1 equivalent of the epoxy group of the epoxy resin (A). More preferably, it is 0.35 to 0.65 equivalent. If it is less than 0.2 equivalents with respect to the epoxy equivalent, the crosslink density of the cured product becomes low and the fracture toughness tends to be low. There is a tendency. From another viewpoint, the range of 0.01 to 7 parts by weight is preferable with respect to 100 parts by weight of the curable resin composition.

The solid aromatic urea compound (C) preferably acts as a curing aid for dicyandiamide and more satisfies the heat resistance at the time of curing in addition to the impregnation property into the reinforcing fibers at the time of mixing. It is essential that it is solid, and its melting point is preferably 100 ° C. or higher, more preferably 150 ° C. or higher.

Examples of the solid aromatic urea compound include 3- (3,4-dichlorophenyl) -1,1-dimethylurea, 3- (3,4-dichlorophenyl) -1,1-dimethylurea and N-phenyl-N'. , N'-dimethylurea, N- (4-chlorophenyl) -N', N'-dimethylurea, N- (3,4-dichlorophenyl) -N', N'-dimethylurea, N- (3-chloro- 4-Methylphenyl) -N', N'-dimethylurea, N- (3-chloro-4-ethylphenyl) -N', N'-dimethylurea, N- (3-chloro-4-methoxyphenyl)- N', N'-dimethylurea, N- (4-methyl-3-nitrophenyl) -N', N'-dimethylurea, 2,4-bis (N', N'-dimethylureide) toluene, methylene- Bis (p-N', N'-dimethylureidophenyl) and the like can be mentioned, among which 3- (3,4-dichlorophenyl) -1,1-dimethylurea, 3- (3,4-dichlorophenyl)-. Examples include 1,1-dimethylurea. These may be used alone or in combination of two or more, and are not limited to the above as long as they are chemically stable and do not dissolve in the epoxy resin at room temperature.

The amount of the solid aromatic urea compound (C) used is preferably 0.5 to 8 parts by mass, more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the total of the components (A) to (D). .. If it exceeds 8 parts by mass, the viscosity during storage will increase. If it is less than 0.5 parts by mass, the curability is insufficient.

式（１）中、Ｒは水素原子、炭素原子数１～２０の１価の有機残基であり、Ｘ^－は有機アニオン、ハロゲン化物イオンであり、ｍは０～４の整数である。Ｒは、好ましくは水素原子、アルキル基、アラルキル基、アリール基又はヘテロアリール基であり、より好ましくは水素原子、又は炭素原子数１～６のアルキル基である。特に好ましくは水素原子である。Ｘ^－は、好ましくはフェニル構造を含むアニオンである。ｍは、好ましくは０～２である。

式（２）中、Ｒ^１はそれぞれ独立に炭素原子数１～１０の１価の有機残基であり、Ｙ^－は有機アニオン、ハロゲン化物イオンである。Ｒ^１は、好ましくはアルキル基、アラルキル基、アリール基又はヘテロアリール基であり、より好ましくは炭素原子数１～６のアルキル基、炭素原子数６～１０のアラルキル基又はアリール基である。特に好ましくは炭素原子数３～６のアルキル基である。Ｙ^－は、好ましくはハロゲン化物イオン、又は水酸化物イオンである。

式（３）中、Ｒ^２はそれぞれ独立に炭素原子数１～１０の１価の有機残基である。Ｒ^２は、好ましくはアルキル基、アラルキル基、アリール基又はヘテロアリール基であり、より好ましくは炭素原子数１～６のアルキル基、炭素原子数６～１０のアラルキル基又はアリール基である。特に好ましくは炭素数６～１０のアリール基であり、炭素数１～３のアルキル基やアルコキシ基の置換基を有してもよい。

式（４）中、Ｒ^３はそれぞれ独立に炭素原子数１～１０の１価の有機残基であり、Ｚ^－は有機アニオン、ハロゲン化物イオンである。Ｒ^３は、好ましくはアルキル基、アラルキル基、アリール基又はヘテロアリール基であり、より好ましくは炭素原子数１～６のアルキル基、炭素原子数６～１０のアラルキル基又はアリール基である。Ｚ^－は、好ましくはハロゲン化物イオン、又は水酸化物イオンである。 The component (D) is a salt represented by the following general formula (1), a quaternary ammonium salt represented by the following general formula (2), an organic phosphorus compound represented by the following general formula (3), and the following general. It is a compound selected from at least one of the organic phosphonium salts represented by the formula (4), and the blending amount of the component (D) is the component (A), the component (B), the component (C), and (D). ) The total amount of the components is 0.05 to 3.0 parts by mass with respect to 100 parts by mass. By using these compounds, a high curing rate is exhibited at the time of heat curing without causing an increase in viscosity during long-term storage. If the amount of the component (D) added is less than 0.05 parts by mass, the curing rate does not improve, and if it exceeds 3.0 parts by mass, the viscosity during storage increases and the heat resistance of the molded product decreases. It is preferably 0.10 to 2.0 parts by mass, and more preferably 0.50 to 1.0 parts by mass.

In the formula (1), R is a hydrogen atom and a monovalent organic residue having 1 to 20 carbon atoms, X ⁻ is an organic anion and a halide ion, and m is an integer of 0 to 4. R is preferably a hydrogen atom, an alkyl group, an aralkyl group, an aryl group or a heteroaryl group, and more preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A hydrogen atom is particularly preferable. X ⁻ is preferably an anion containing a phenyl structure. m is preferably 0 to 2.

In formula (2), R ¹ is an independently monovalent organic residue having 1 to 10 carbon atoms, and Y ⁻ is an organic anion and a halide ion. R ¹ is preferably an alkyl group, an aralkyl group, an aryl group or a heteroaryl group, and more preferably an alkyl group having 1 to 6 carbon atoms and an aralkyl group or an aryl group having 6 to 10 carbon atoms. Particularly preferably, it is an alkyl group having 3 to 6 carbon atoms. Y ⁻ is preferably a halide ion or a hydroxide ion.

In formula (3), R ² is a monovalent organic residue having 1 to 10 carbon atoms independently. ^R2 is preferably an alkyl group, an aralkyl group, an aryl group or a heteroaryl group, and more preferably an alkyl group having 1 to 6 carbon atoms and an aralkyl group or an aryl group having 6 to 10 carbon atoms. Particularly preferably, it is an aryl group having 6 to 10 carbon atoms, and may have an alkyl group having 1 to 3 carbon atoms or a substituent of an alkoxy group.

In formula (4), R ³ is an independently monovalent organic residue having 1 to 10 carbon atoms, and Z ⁻ is an organic anion and a halide ion. R3 is preferably an alkyl group ^, an aralkyl group, an aryl group or a heteroaryl group, and more preferably an alkyl group having 1 to 6 carbon atoms and an aralkyl group or an aryl group having 6 to 10 carbon atoms. Z ⁻ is preferably a halide ion or a hydroxide ion.

Among the components (D), examples of the salt of the cyclic amine compound such as diazabicycloundecene represented by the formula (1) include a phenol salt of diazabicycloundecene and a phenol salt of diazabicyclononene. ..
Examples of the quaternary ammonium salt represented by the formula (2) include tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium hydroxide, triethylmethylammonium chloride, tetraethylammonium chloride, tetraethylammonium bromide, and tetraethylammonium iodide. Tetrapropylammonium bromide, tetrapropylammonium hydroxide, tetrabutylammonium chloride, tetrabutylammonium bromide, decyltrimethylammonium bromide, tetrabutylammonium iodide, benzyltrimethylammonium chloride, benzyltrimethylammonium bromide, benzyltrimethylammonium hydroxide, benzyltributyl Examples thereof include ammonium chloride and phenyltrimethylammonium chloride.
Examples of the organic phosphorus compound represented by the formula (3) include triphenylphosphine, tri-n-propylphosphine, tri-n-butylphosphine, triphenylphosphine, tris (methoxyphenyl) phosphine, tris (dimethoxyphenyl) phosphine and the like. Can be mentioned.
Examples of the quaternary phosphonium compound represented by the formula (4) include tetramethylphosphonium bromide, tetramethylphosphonium iodide, tetramethylphosphonium hydroxide, trimethylcyclohexylphosphonium chloride, trimethylcyclohexylphosphonium bromide, trimethylbenzylphosphonium chloride, and trimethylbenzyl. Phosphonium bromide, tetraphenylphosphonium bromide, triphenylmethylphosphonium bromide, triphenylbutylphosphonium bromide, triphenylmethylphosphonium iodide, triphenylethylphosphonium chloride, triphenylethylphosphonium bromide, triphenylethylphosphonium iodide, triphenylbenzylphosphonium Examples thereof include chloride and triphenylbenzylphosphonium bromide.
These may be used alone or in combination of two or more, and are not limited to the above.

Among these, salts of cyclic amine compounds such as diazabicycloundecene include phenol salts of diazabicycloundecene, and quaternary ammonium salts include tetrabutylammonium bromide, decyltrimethylammonium bromide, and organophosphorus compounds. It is desirable to use tris (methoxyphenyl) phosphin, tris (dimethoxyphenyl) phosphin, and as the quaternary phosphonium compound, triphenylbutylphosphonium bromide and triphenylethylphosphonium iodide.

The component (D) is preferably solid or semi-solid, like the component (B) and the component (C).

The curable resin composition of the present invention has a viscosity increase rate W / V of 1.25 when the viscosity at 25 ° C. measured by an E-type viscometer is V and the viscosity after 168 hours at 25 ° C. is W. If this is the case, it is preferable that the product can be handled for a long period of time without any difference from that immediately after production. The viscosity increase rate W / V is more preferably 1.10 or less.

Further, another curable resin can be further added to the curable resin composition of the present invention. Examples of such curable resins include unsaturated polyester resins, curable acrylic resins, curable amino resins, curable melamine resins, curable urea resins, curable cyanate ester resins, curable urethane resins, and curable oxetane resins. Examples thereof include, but are not limited to, a curable epoxy / oxetane composite resin.

The curable resin composition of the present invention includes a coupling agent, conductive particles such as carbon particles and metal-plated organic particles, thermosetting resin particles, inorganic fillers such as silica gel, nanosilica, alumina fiber and clay, and the like. A conductive filler can be blended. The conductivity of the cured resin product or the fiber-reinforced composite material obtained by using the conductive particles or the conductive filler can be improved.

Examples of the conductive filler include carbon black, carbon nanotubes, fullerenes, metal nanoparticles and the like, and they may be used alone or in combination. Among these, it is widely known that the compounding of carbon nanotubes not only improves the conductivity but also enhances the impact strength of the fiber-reinforced composite material even if the compounding amount is less than 1 wt% with respect to the fiber-reinforced composite material. , Can be suitably used.

The curable resin composition of the present invention is impregnated into reinforcing fibers or bundles to form a prepreg. The method of making a prepreg may be a known method. The prepreg thus obtained is suitably used for a fiber-reinforced composite material obtained by an autoclave molding method, a press molding method, or a filament winding molding method.

The reinforcing fiber used in the prepreg of the present invention is selected from glass fiber, aramid fiber, carbon fiber, boron fiber and the like, but it is preferable to use carbon fiber in order to obtain a fiber-reinforced composite material having excellent strength. ..

In the prepreg composed of the curable resin composition of the present invention and the reinforcing fibers, the volume content of the reinforcing fibers is preferably 45 to 70%, more preferably 50 to 66%, and there are few voids. Moreover, since a molded body having a high volume content of the reinforcing fibers can be obtained, a molding material having excellent strength can be obtained.

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 the gist of the present invention is not exceeded. The portion indicating the blending amount is a mass portion unless otherwise specified. The unit of epoxy equivalent is g / eq.

The abbreviations of each component used in the examples are as follows.
(A) Ingredient YD-128: Bisphenol A type epoxy resin, epoxy equivalent 187 (manufactured by Nittetsu Chemical & Materials Co., Ltd.)
(B) Component DICY: dicyandiamide (C) component DCMU: 3- (3,4-dichlorophenyl) -1,1-dimethylurea, solid (melting point 155 to 160 ° C.)
TDU: 1,1'-(4-methyl-1,3-phenylene) bis (3,3-dimethylurea), solid (melting point 180-195 ° C)
(D) Ingredient SA851: Phenolic novolak resin salt of diazabicycloundecene (manufactured by San-Apro), Semi-solid 5002: Tetraphenylborate salt of diazabicycloundecene derivative (manufactured by San-Apro), Solid TBAB: Tetrabutylammonium bromide , Solid (melting point 102-106 ° C)
TDMPP: Tris (dimethoxyphenyl) phosphine, solid (melting point 145-147 ° C)
ETPPI: Triphenylethylphosphonium iodide, solid (melting point 164 to 168 ° C)
Component (D') (curing accelerator other than formulas (1) to (4))
DBU: diazabicycloundecene, liquid TBB: tributylborate, liquid

Example 1
93 parts of YD-128 as the component (A), 0.7 part of TDMPP as the component (D), put in a 150 mL plastic container, and stir at 70 ° C.-1.5 h on a hot stirrer to make the component (D). Add 4.0 parts of DICY as the component (B) and 3.0 parts DCMU as the component (C) to the plastic container, and use a vacuum mixer (Awatori Rentaro, manufactured by Shinky). Then, the mixture was mixed at 25 mmHg at room temperature with stirring under reduced pressure for 5 minutes to obtain a curable resin composition.

(Measurement of initial viscosity, viscosity after 168 hours, viscosity increase rate)
The viscosity value at 25 ° C. was measured using an E-type viscometer cone plate type. The curable resin composition was adjusted, 1.1 mL of which was used for measurement, and the value 60 seconds after the start of measurement was defined as the value of initial viscosity V. Further, the adjusted curable resin composition was allowed to stand in a constant temperature water bath set at 25 ° C. for 168 hours, and then the viscosity was measured in the same manner using an E-type viscometer cone plate type, and 60 seconds from the start of the measurement. The value after the lapse was defined as the viscosity value W after the lapse of 168 hours. Further, the viscosity increase rate was calculated using the formula of W / V (viscosity after 168 hours / initial viscosity).

(Measurement of gel time)
The curable resin composition is added onto a plate of a gelling tester (manufactured by Nissin Kagaku) that has been heated to 150 ° C., and the mixture is stirred with a fluororesin rod at a rate of 2 rotations per second to cure. The time required for the resin composition to proceed with curing and lose its plasticity was defined as the gelation time.

(Manufacturing of molded plate for measuring glass transition temperature)
A mold is made by sandwiching a 2 mm thick U-shaped spacer between two steel plates of length 80 mm x width 80 mm x thickness 8 mm, and it is heated to 150 ° C by standing in a hot air circulation oven for 1 hour. After that, the curable resin composition was poured into a mold and cured by allowing it to stand in an oven at 150 ° C. for 0.5 h to obtain a molded product having a thickness of 60 mm × 60 mm × thickness 2 mm, and the glass transition temperature described later. Was used for the measurement of.

(Measurement of glass transition temperature)
The obtained molded plate was cut into a size of 3 mm × 3 mm with a tabletop band saw, and further polished to a thickness of about 0.8 mm using a belt disc sander. Using a differential scanning calorimeter, the measurement was performed under the condition of a temperature rise rate of 10 ° C./min under a nitrogen atmosphere, and the temperature at the inflection point of the DSC curve was defined as the glass transition temperature Tg.

Examples 2 to 8, Comparative Examples 1 to 4
A curable resin composition was prepared in the same manner as in Example 1 except that the components (A) to (D) and the components (D') were used in the compositions shown in Tables 1 and 2. Using this curable resin composition, the initial viscosity, the viscosity after 168 hours, the viscosity increase rate, the gel time, and the glass transition temperature were measured in the same manner as in Example 1.

The test results are shown in Tables 1 and 2, respectively.

Claims (4)

A curable resin composition containing an epoxy resin (A), a dicyandiamide or a derivative thereof (B), a solid aromatic urea compound (C), and a curing accelerator (D) as essential components, wherein the curing accelerator (D) is used. Is an organic amine salt represented by the following general formula (1), a quaternary ammonium salt represented by the following general formula (2), an organic phosphorus compound represented by the following general formula (3), and the following general formula. It is a compound selected from at least one of the organic phosphonium salts represented by (4), and the blending amount of the curing accelerator (D) is the component (A), the component (B), the component (C), ( D) A curable resin composition characterized by having a total of 0.05 to 3.0 parts by mass with respect to 100 parts by mass of the components.

(In the formula (1), R is a hydrogen atom and a monovalent organic residue having 1 to 20 carbon atoms, X ⁻ is an organic anion and a halide ion, and m is an integer of 0 to 4. )

(In the formula (2), R ¹ is an independently monovalent organic residue having 1 to 10 carbon atoms, and Y ⁻ represents an organic anion and a halide ion.)

(In formula (3), R ² independently represents a monovalent organic residue having 1 to 10 carbon atoms.)

(In formula (4), R ³ is an independently monovalent organic residue having 1 to 10 carbon atoms, and Z ⁻ represents an organic anion and a halide ion.) The first aspect of claim 1 is that the viscosity at 25 ° C. measured by an E-type viscometer is V, the viscosity after 168 hours at 25 ° C. is W, and the viscosity increase rate W / V is less than 1.25. The curable resin composition according to the above. A prepreg according to claim 1 or 2, wherein the curable resin composition is blended with reinforcing fibers so that the volume content is 45 to 70%. A molded product obtained by heat-molding the prepreg according to claim 3.