JP2013124265A - Curing agent for epoxy resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a curing agent for an epoxy resin with a difference in ability to cure the epoxy resin at around 80°C and around 150°C, which can selectively perform a curing reaction of the epoxy resin at around 150°C.SOLUTION: The curing agent for an epoxy resin comprises an imidazole-based compound represented by general formula (1), wherein R1 to R3 are each independently H, 1-10C alkyl or phenyl; R is 1-10C alkyl or phenyl; n is an integer of 1-5; m is an integer of 1-4; and k is an integer of 0-4, provided that the sum of m and k is an integer of 1-5.

Description

  The present invention relates to a curing agent for epoxy resins using an imidazole compound.

  Conventionally, epoxy resins have excellent performance in mechanical properties, electrical properties, thermal properties, chemical resistance, etc., so that they can be used in a wide range of applications such as paints, insulating materials for electrical and electronic products, and adhesives. Various curing agents such as imidazoles, amines, dicyandiamide, acid anhydrides, phenols, hydrazines, and guanidines have been widely used as epoxy resin curing agents.

  Among these, imidazole-based epoxy resin curing agents are used for a wide range of applications. For example, Patent Document 1 discloses 1 as an epoxy resin curing agent (curing accelerator) used for sealing electronic circuit components of semiconductor devices. Various imidazole compounds such as-(2-hydroxyethyl) imidazole are used, and Patent Document 2 discloses a so-called prepreg obtained by impregnating an epoxy resin composition into a reinforcing fiber material in a fiber-reinforced composite material application. An imidazole compound such as 2-methylimidazole is used in the formation.

  As for the curing conditions for epoxy resins, the thermal environment varies greatly depending on the resin composition and the application used. Therefore, epoxy resin curing agents used for curing epoxy resins have also been used under various temperature conditions in recent years. There is a demand for stable and efficient epoxy resin curing performance, and it is important to select and develop an epoxy resin curing agent suitable for each application.

  For example, in an electronic circuit component sealing application as in Patent Document 1, a curing agent having a curing performance in a high temperature region of about 150 to 170 ° C. is used, and a fiber-reinforced composite material as in Patent Document 2 is used. In use, a curing agent is used that does not exhibit curing performance at room temperature, and exhibits primary curing performance in a temperature range of 80 ° C. or lower and secondary curing performance in a temperature range of 130 ° C. or higher.

JP 2000-68418 A JP 2003-73456 A

  However, in recent years, the usage of epoxy resin has been diversified, and even when the epoxy resin is cured in a high temperature region around 130 to 170 ° C. as in the above Patent Document 1 and Patent Document 2, Applications that require selective curability, such as non-curability being required in a low temperature region around 60 to 100 ° C., have also arisen. In applications requiring such selective curability, imidazole curing agents such as 1- (2-hydroxyethyl) imidazole and 2-methylimidazole described in Patent Document 1 and Patent Document 2 are used. It was something that could not be done.

  Therefore, in the present invention, in such a background, there is a difference in the curing performance of the epoxy resin between about 80 ° C. and about 150 ° C., and the epoxy resin can selectively cure the epoxy resin near 150 ° C. It is an object of the present invention to provide a curing agent.

  However, as a result of intensive studies in view of such circumstances, the present inventors have used an imidazole compound represented by the following general formula (1) as a curing agent for an epoxy resin, so that the curing performance for an epoxy resin is around 80 ° C. However, it has been found that the epoxy resin can be cured in a short time at around 150 ° C., but the present invention has been completed.

（Ｒ１〜Ｒ３はそれぞれ独立して水素原子、炭素数１〜１０のアルキル基、またはフェニル基であり、Ｒは炭素数１〜１０のアルキル基、またはフェニル基である。ｎは１〜５の整数であり、ｍは１〜４の整数であり、ｋは０〜４の整数である。ただし、ｍとｋの和は１〜５の整数である。） That is, the gist of the present invention is an epoxy resin curing agent comprising an imidazole compound represented by the following general formula (1).

(R1 to R3 are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a phenyl group, and R is an alkyl group having 1 to 10 carbon atoms or a phenyl group. N is 1 to 5) (M is an integer of 1 to 4, and k is an integer of 0 to 4. However, the sum of m and k is an integer of 1 to 5.)

  According to the present invention, the curing performance of the epoxy resin is not exhibited at around 80 ° C., or the curing speed is so slow as to be impractical, but the epoxy resin can be selectively cured at around 150 ° C. Become.

  The present invention is described in detail below. In the present invention, the epoxy resin curing agent includes not only one that functions as a curing agent but also one that functions as a curing accelerator (curing aid).

  First, an imidazole compound represented by the following general formula (1) (hereinafter sometimes simply referred to as “imidazole compound”) will be described.

  R1 to R3 in the general formula (1) are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a phenyl group. The alkyl group preferably has 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, and specific examples thereof include a methyl group, an ethyl group, an isopropyl group, a butyl group, and an isobutyl group. In particular, all of R1 to R3 are hydrogen atoms, or that R1 is a hydrogen atom, a methyl group, or an ethyl group, and that R2 and R3 are a hydrogen atom or a methyl group, the curing performance according to the present invention is easily exhibited. Is preferable.

  The alkyl group and the phenyl group may have a substituent, and examples of the substituent include a halogen atom, a hydroxyl group, an alkoxy group, an amino group, a sulfanyl group, an aryl group, a heteroaryl group, and the like. Of these, a hydroxyl group and an aryl group are preferable.

  In the general formula (1), n is an integer of 1 to 5, preferably 1 to 3, particularly preferably 2.

  M in the general formula (1) is an integer of 1 to 4, preferably 1. That is, the hydroxyl group in the aromatic ring in the general formula (1) may be one or plural. The hydroxyl group may be one in which any of the ortho-position, meta-position or para-position hydrogen atom on the aromatic ring is substituted, but is preferably one in which at least the para-position hydrogen atom is substituted, and particularly preferably the para-position. In which only the hydrogen atom is replaced.

  K in the said General formula (1) shows the number of the substituents R on an aromatic ring, is an integer of 0-4, and satisfy | fills the conditions from which the sum with said m becomes an integer of 1-5. That is, the general formula (1) may be one in which a hydrogen atom on an aromatic ring not substituted with a hydroxyl group is substituted with R. R is a C1-C10 alkyl group or a phenyl group, and the same substituent as the C1-C10 alkyl group and phenyl group demonstrated by said R1-R3 is mentioned. When a plurality of R are present on the aromatic ring, each R may be the same or different.

  Examples of the imidazole compound represented by the general formula (1) include 1- (p-hydroxybenzyl) imidazole, 1- (p-hydroxybenzyl) -2-methylimidazole, 1- (p-hydroxyphenethyl) imidazole, 1- (p-hydroxyphenethyl) -2-methylimidazole, 1- [3- (p-hydroxyphenyl) propyl] imidazole, 1- [3- (p-hydroxyphenyl) propyl] -2-methylimidazole, 1- [ 4- (p-hydroxyphenyl) butyl] imidazole, 1- [4- (p-hydroxyphenyl) butyl] -2-methylimidazole, 1- [5- (p-hydroxyphenyl) pentyl] imidazole, 1- [5 -(P-hydroxyphenyl) pentyl] -2-methylimidazole and the like. Among these, 1-(p-hydroxybenzyl) imidazole, 1-(p-hydroxybenzyl) -2-methylimidazole is preferred.

The imidazole compound represented by the general formula (1) is a known compound, and can be produced, for example, by performing an N-alkylation reaction between (halogenated) methoxybenzene and imidazole, followed by a phenolization reaction. (See Special Table 2007-526274).
In particular, when n = 1 in the general formula (1), it is preferably produced by a condensation reaction of hydroxymethylphenol and 1-unsubstituted imidazole (see Bioorganic & Medicinal Chemistry Letters, 19, 2009, 4698). ).

  The epoxy resin targeted by the curing agent of the present invention has, on average, two or more epoxy groups in one molecule. Typical epoxy resins include bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethyl bisphenol A, tetramethyl bisphenol F, tetramethyl bisphenol AD, tetramethyl bisphenol S, and tetrabromobisphenol A. Bisphenol type epoxy resin, biphenol, dihydroxynaphthalene, epoxy resin obtained by glycidylation of other dihydric phenols such as 9,9-bis (4-hydroxyphenyl) fluorene, 1,1,1-tris (4-hydroxy Phenyl) methane, glycidylation of trisphenols such as 4,4- (1- (4- (1- (4-hydroxyphenyl) -1-methylethyl) phenyl) ethylidene) bisphenol Epoxy resin, epoxy resin obtained by glycidylation of tetrakisphenols such as 1,1,2,2-tetrakis (4-hydroxyphenyl) ethane, phenol novolak, cresol novolak, bisphenol A novolak, brominated phenol novolak, brominated bisphenol A Glycidylation of novolak epoxy resins obtained by glycidylating novolaks, aliphatic ether type epoxy resins obtained by glycidylating polyhydric alcohols such as glycerin and polyethylene glycol, and hydroxycarboxylic acids such as p-oxybenzoic acid and β-oxynaphthoic acid Ether ester type epoxy resin, ester type epoxy resin obtained by glycidylation of polycarboxylic acid such as phthalic acid and terephthalic acid, 4,4-diaminodiphenylmethane, m-aminophenol, etc. Amine-type epoxy resins such as glycidylated amine compounds and triglycidyl isocyanurate, and alicyclic epoxides such as 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate, etc. A mixture of two or more types is used.

  Various additives such as a diluent, a flexibility imparting agent, a silane coupling agent, an antifoaming agent, a leveling agent, a filler, a pigment, and a dye can be added to the epoxy resin as necessary.

  When the imidazole compound is used as a curing agent for the epoxy resin, the amount of the imidazole compound used is usually 0.1 to 30 parts by weight, preferably 0.2 to 25 parts by weight with respect to 100 parts by weight of the epoxy resin. Particularly preferred is 0.3 to 20 parts by weight. If the amount used is too large, the physical properties of the cured product tend to be reduced, and if it is too small, the curing reaction tends not to proceed.

  The imidazole compound in the present invention can be used alone as a curing agent, and is generally used as amines, polyamines, hydrazines, acid anhydrides, dicyandiamide, onium salts, polythiols, phenols, ketimines, etc. It can also be used in combination with a curing agent. Moreover, it is also possible to use a known general epoxy resin curing accelerator (curing aid) in combination.

  In addition, the curing agent for epoxy resin comprising the imidazole compound in the present invention can be used in combination with the above-mentioned general curing agent to promote the curing performance catalytically.

  As a method for mixing the imidazole compound with the epoxy resin, for example, an epoxy resin mixture containing a predetermined amount of the imidazole compound and the epoxy resin is kneaded using a roll kneader, a kneader, an extruder, or the like. Subsequently, the epoxy resin cured product can be obtained by heating the kneaded epoxy resin mixture. As heating conditions, the heating temperature and the heating time can be appropriately selected in consideration of the type of epoxy resin, the type of curing agent, the type of additive, and the blending amount of each component.

  Thus, in the present invention, a cured epoxy resin can be obtained by using the imidazole compound represented by the general formula (1) as a curing agent.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In the examples, “parts” and “%” mean weight basis unless otherwise specified.

Example 1
“Synthesis of 1- (p-hydroxybenzyl) imidazole”
To a 50 ml reactor, 54.8 g (0.81 mol) of imidazole and 20.0 g (0.16 mol) of p-hydroxybenzyl alcohol were added. Next, the reaction solution was heated to 130 ° C. and reacted at 130 ° C. for 30 minutes. After completion of the reaction, the reaction solution was charged into 200 ml of 50 ° C. warm water to precipitate crystals. The precipitated crystals were collected by filtration, and the crystals were washed with 50 ml of warm water at 50 ° C. The obtained crystal was dried at 50 ° C. under reduced pressure to obtain 27.2 g of 1- (p-hydroxybenzyl) imidazole as a curing agent. The yield was 97%.

Example 2
“Synthesis of 1- (p-hydroxybenzyl) -2-methylimidazole”
To a 50 ml reactor, 82.7 g (1.01 mol) of 2-methylimidazole and 25.0 g (0.20 mol) of p-hydroxybenzyl alcohol were added. Next, the reaction solution was heated to 130 ° C. and reacted at 130 ° C. for 30 minutes. After completion of the reaction, the reaction solution was charged into 200 ml of 50 ° C. warm water to precipitate crystals. The precipitated crystals were collected by filtration, and the crystals were washed with 50 ml of warm water at 50 ° C. The obtained crystal was dried at 50 ° C. under reduced pressure to obtain 37.3 g of 1- (p-hydroxybenzyl) imidazole as a curing agent. The yield was 98%.

[Curing property test]
A curability test was conducted using the curing agents obtained in Examples 1 and 2 and 1-benzyl-2-methylimidazole described in JP-A-1-316365 as the curing agent of Comparative Example 1. An epoxy resin composition was prepared by adding and mixing 5 parts by weight of each curing agent with respect to 100 parts by weight of a bisphenol A type epoxy resin (trade name: jER828, manufactured by Japan Epoxy Resin Co., Ltd.). Gelation time at 80 ° C. and 150 ° C. using a gel time tester (manufactured by Yasuda Seiki Seisakusho) using 2 g of the obtained mixed composition (curing time: time required for the rotor torque to reach about 3.3 Kg · cm) Was measured.

  From the above test results, the curing agents described in Examples 1 and 2 do not exhibit curing performance with respect to the epoxy resin at 80 ° C., but have curing performance as good as Comparative Example 1 at 150 ° C. It became clear. That is, it can be seen that the curing agents described in Examples 1 and 2 have specific curing performance for curing the epoxy resin only at around 150 ° C.

  On the other hand, 1-benzyl-2-methylimidazole used in Comparative Example 1 has good curing performance at 150 ° C., but exhibits curability in less than 20 minutes at 80 ° C., and at 150 ° C. in curing performance. The selectivity was inferior to those of Examples 1 and 2.

  The curing agent for epoxy resin of the present invention has a difference in curing performance of the epoxy resin at around 80 ° C. and around 150 ° C., and can selectively cure the epoxy resin at around 150 ° C. Therefore, temperature-selective curability is required in a wide range of applications such as prepregs (particularly prepregs used for matrix resins of fiber reinforced composite materials, epoxy resin laminates such as printed circuit boards and copper clad laminates). When used, the curing agent for epoxy resins of the present invention is useful.

Claims (1)

The hardening | curing agent for epoxy resins which consists of an imidazole type compound shown by following General formula (1).

(R1 to R3 are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a phenyl group, and R is an alkyl group having 1 to 10 carbon atoms or a phenyl group. N is 1 to 5) (M is an integer of 1 to 4, and k is an integer of 0 to 4. However, the sum of m and k is an integer of 1 to 5.)