JPH05239187A - Method for curing epoxy resin - Google Patents

Abstract

PURPOSE:To carry out the curing of an epoxy resin having a short curing time within a medium-temperature region, excellent in preservation stability and compatibility and useful as coatings, etc., by using an alkyldihydroxymethylimidazole compound as a curing agent, etc. CONSTITUTION:The curing of an epoxy resin is carried out by using a 2- alkyl-4,5-dihydroxymethylimidazole compound such as 2-methyl-4,5- dihydroxymethylimidazole of the formula (R is H or 1-17C alkyl) as a curing agent or a curing accelerator. Furthermore, this compound is used in an amount of preferably 0.05-5 pts.wt. based on 100 pts.wt. epoxy resin. The compound is preferably used with an organic acid anhydride such as hexahydrophthalic anhydride or dicyandiamide in combination.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for curing an epoxy resin, and more specifically, an epoxy resin formulation having a sufficiently long pot life in a system in which an epoxy resin and a curing agent are premixed prior to use thereof. The present invention relates to so-called one-component epoxy resin formulations.

[0002]

2. Description of the Related Art Today, various imidazole compounds have been proposed and used as curing agents and curing accelerators for epoxy resins.

Generally, an epoxy resin curing agent is a room temperature curing agent capable of curing an epoxy resin at its curing temperature, for example, 15 to 35 ° C., a medium temperature curing agent curing at 60 to 100 ° C., a high temperature curing at a temperature of 100 ° C. or higher. The curing agent is classified into a curing agent and the like, and the imidazole curing agent is classified into a medium temperature curing agent and a high temperature curing agent.

Therefore, when a conventional imidazole compound is used as a curing agent, the imidazole compound which can be cured even if the composition has a short curing time in the medium temperature range, or a one-part liquid with good workability at the sacrifice of the above-mentioned characteristics One of the imidazole compounds that can be used as a formulation must be selected, and an epoxy resin formulation that cures even in a short curing time in the medium temperature range and has good storage stability when made into a one-part formulation is obtained. It was impossible.

2-Methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-phenylimidazole and the like are used because of the characteristics that a cured product having a medium temperature curability and a high heat distortion temperature can be obtained. It is used a lot. However, the pot life of the formulations using them is extremely short at 1 day at room temperature, and even with the most curable 2-methylimidazole, it is only a few hours.

Under these circumstances, various attempts have been made in recent years to develop a curing agent that can be used as a one-part compounding agent by taking advantage of the medium-temperature curing properties of these imidazole compounds and achieving a long pot life. For example, a method in which an adduct (adduct compound) of 2-methylimidazole and an epoxy resin such as bisphenol A diglycidyl ether is made into a fine powder, and the surface thereof is coated with a polyisocyanate compound to form a kind of microencapsulating curing agent ( JP-A-58-13623 and 61-192722), or a method of curing a salt of the above-mentioned adduct and a polyhydric phenol compound (JP-A-59-53526) is proposed. ..

The epoxy resin formulation using the imidazole / epoxy resin adduct compound as a curing agent has a long pot life of 6 months or more and can be practically used as a one-liquid type, and has a temperature of 80 ° C. in the middle temperature range. At 3
It can be thermoset in 0 to 60 minutes and in a high temperature range of 150 ° C. in 0.5 to 2 minutes, and the heat distortion temperature of the resin after curing is as high as 150 ° C. Therefore, it is an excellent curing agent as long as it cures even in a medium temperature range even if the curing time is short, and the storage stability is compatible.

Imidazole compounds are used as curing accelerators for other curing agents such as organic acid anhydride compounds, dicyandiamide, cyanamide, guanamines, biguanides, aromatic polyamines, alicyclic amines, hydrazine derivatives and organic acid hydrazides. Also in this case, the storage stability of the preparation is almost the same as when the above-mentioned imidazole compound is used as a curing agent, unless the curing agent, the imidazole compound and the epoxy resin form a liquid compatibility at room temperature. there were.

However, the above-mentioned imidazole / epoxy resin adduct curing agent has poor compatibility with the epoxy resin even when heated and is recognized as forming a thixotropic structure upon curing, and has the following drawbacks. It was That is, when used as a curing agent for epoxy resin coatings, the surface of the coating film becomes matte and matte, and when used as a casting material, the surface of the cured product becomes matte and inside the cured resin. Easy to nest. Especially when the filler is highly filled, such a heavy defect is likely to be caused, and even when the filling amount is relatively small, the mechanical strength of the cured resin is lowered and the water absorption rate is increased. It was also a hardener with restrictions.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can be cured even in a medium temperature range with a short curing time, and has good workability (pot life or one-liquid stability). It is an object of the present invention to provide a curing agent or curing accelerator for an epoxy resin that is not subject to formulation restrictions or application restrictions.

[0011]

Means for Solving the Problems The present inventors have conducted various tests and studies on the curing reaction between a 2-alkyl-4,5-disubstituted imidazole compound and an epoxy resin, and as a result, 2
The 2-alkyl-4,5-dihydroxymethylimidazole compound represented by Chemical formula 2 obtained by the reaction of an -alkylimidazole compound and formaldehyde is found to be excellent as a curing agent or a curing accelerator, and the object of the present invention is achieved. I was able to do it.

[0012]

[Chemical 2]

2-Alkyl-Suitable for Practicing the Method of the Invention
Examples of the 4,5-dihydroxymethylimidazole compound include 2-methyl-4,5-dihydroxymethylimidazole, 2-ethyl-4,5-dihydroxymethylimidazole, 2-isopropyl-4,5-dihydroxymethylimidazole and 2-undecyl. -4,5-Dihydroxymethylimidazole and 2-heptadecyl-4,5-
These include dihydroxymethylimidazole and the like, and each of these may be used alone, or any number of them may be used in combination.

The epoxy resin used in the method of the present invention is a known epoxy resin, and there is no particular limitation in use. Typical examples thereof are polyglycidyl ether compounds obtained from polyphenols such as bisphenol A, bisphenol F, bisphenol AD or novolac resins, and polyglycidyl ester compounds obtained from polycarboxylic acids such as phthalic acid and adipic acid. , Polyglycidyl ether compounds obtained from polyhydric alcohols such as polyethylene glycol, polypropylene glycol or glycerin, alicyclic epoxy resins, trisglycidyl isocyanurate and epoxidized polyolefins, and these may be used alone. You may mix and use 2 or more types. Further, if necessary, a low-viscosity monoepoxy compound or the like can be added as a reactive diluent. Further, flame retardation may be achieved by appropriately using a halogenated epoxy resin.

In carrying out the method of the present invention, when a 2-alkyl-4,5-dihydroxymethylimidazole compound is used as a curing agent, the compounding ratio to the epoxy resin is 3 to 20 parts by weight based on 100 parts by weight of the epoxy resin. Especially, when the toughness and high strength adhesiveness of the cured resin are required, good results can be obtained by increasing the amount of addition and adding a slight amount. However, even in this case, if the blending ratio exceeds 20 parts by weight, the moisture resistance of the cured resin will decrease, and if it is 3 parts by weight or less, the curing rate will be inferior. is there.

In the practice of the method of the present invention, the compounds used in the method of the present invention are used in applications such as improving the medium-temperature curability of the preparation and utilizing the rapid curing property at high temperature, such as liquid epoxy resin injection molding. Microencapsulation may be carried out by a conventional method such as coating the surface, and the method of the present invention also includes such surface treatment.

In the practice of the method of the present invention, when the 2-alkyl-4,5-dihydroxymethylimidazole compound is used as a curing accelerator for other curing agents, other curing agents include organic polybasic acid anhydrides and polyhydric acids. Examples thereof include phenol compounds, dicyandiamide, cyanamide, guanamines, biguanides, aromatic polyamines, alicyclic amines, hydrazine derivatives and organic acid hydrazides. Examples of these compounds include hexahydrophthalic anhydride,
Methylhexahydrophthalic anhydride (substitution position of methyl group is arbitrary), succinic anhydride, polyadipic anhydride, organic polybasic anhydride such as trimellitic anhydride, novolac resin, cresol novolac resin Phenol compounds, benzoguanamine, orthotoluyl biguanide, monoepoxide adduct, cyanoethylated product, dicyandiamide, monoepoxide adduct, metaphenylenediamine, monoepoxide adduct, cyanoethylated product, diaminodiphenylmethane, monoepoxide adduct , Isophthalic acid dihydrazide, 2,4-dihydrazino-6-methylamino-s-triazine and the same monoepoxide adduct.

In carrying out the method of the present invention, when a 2-alkyl-4,5-dihydroxymethylimidazole compound is used as a curing accelerator, the proper mixing ratio with respect to the epoxy resin is 0.0 based on 100 parts by weight of the epoxy resin.
5 to 5 parts by weight. When the amount of the accelerator added is large, the rapid curing property is excellent, and when the amount of the accelerator is small, a formulation having excellent storage stability is obtained.

In the practice of the present invention, a coloring agent such as a dye or a coloring pigment for coloring, an extender pigment for reinforcing a cured product, a reinforcing material such as a fibrous reinforcing material or whiskers, and a light scattering material. A light scattering agent (finely divided pigment) or the like can be added. Furthermore, a release agent, an internal release agent,
Additives such as lubricants, defoaming agents, leveling agents or penetrants for improving workability may be used as long as the effects of the method of the present invention are not adversely affected.

[0020]

In carrying out the method of the present invention, 2-alkyl-
The epoxy resin dispersion containing the 4,5-dihydroxymethylimidazole compound is an emulsion liquid at a storage temperature of room temperature or lower, but is rapidly dissolved in the epoxy resin at a curing temperature of 90 ° C. or higher and uniformly. Since it becomes a transparent liquid, the problem that the surface of the cured product becomes matte does not occur. Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

[0021]

【Example】

(Examples 1 and 2 and Comparative Examples 1 to 3) Epoxy resin (Epoxy resin manufactured by Asahi Kasei KK, trade name: AER-331,
Bisphenol A diglycidyl ether) 100 parts by weight, and the 2-alkyl-4,5- listed in Table 1 as a curing agent.
Predetermined parts by weight of dihydroxymethylimidazole compound,
Silica airgel as an anti-settling agent (Japan Aerosil K
2 parts by weight manufactured by K, trade name: EROSIL 300) were added, and the mixture was stirred and mixed, and then a mixture was obtained by passing through a three-roll machine.
Also, a similar formulation was obtained using the conventional imidazole compounds listed in Table 1 in place of the 2-alkyl-4,5-dihydroxymethylimidazole compound.

The resulting formulations were heat curable at temperatures above 60 ° C. and rapidly curable at temperatures above 90 ° C. When the epoxy resin curability (gel time) at 150 ° C. and the storage stability (pot life) at room temperature of each formulation were examined, the results are shown in Table 1. The pot life was defined as the end point when the formulation was stored at room temperature and the viscosity thereof exceeded twice the initial value.

[0023]

[Table 1]

Examples 3 to 4 100 parts by weight of an epoxy resin (epoxy resin manufactured by Asahi Kasei KK, trade name: AER-331, bisphenol A diglycidyl ether) and 4-methylhexahydrophthalic anhydride as a curing agent. (Shin-Nippon Rika KK acid anhydride, trade name: RIKACID MH-70
0) A mixture of 90 parts by weight and 2 as a curing accelerator
-Isopropyl-4,5-dihydroxymethylimidazole compound (1 part by weight) was added, and the mixture was stirred and mixed to obtain a formulation of Example 3. A formulation of Example 4 was obtained by the same method, using 2-undecyl-4,5-dihydroxymethylimidazole instead of 2-isopropyl-4,5-dihydroxymethylimidazole of Example 3.

The resulting formulations are each 3 mm thick x 100 mm
Pour into a mold of × 150 mm, heat cure at 100 ° C. for 2 hours, and heat cure at 150 ° C. for 4 hours.
Table 2 shows the results of performance evaluation by cutting out to a predetermined size. The evaluation test in each example is
Each cured product obtained by painting or casting was cut into a predetermined size to prepare a test piece, and the test piece was subjected to the following test standards and conditions.

Bending strength: JIS K-7203 25 ° C. Bending elastic modulus: JIS K-7203 25 ° C. Heat distortion temperature: JIS K-7207 2 ° C./min Volume resistivity: JIS K-6911 25 ° C. Volume resistivity after boiling : JIS K-6911 After boiling for 1 hour, 25 ° C Dielectric constant: JIS K-6911 25 ° C, 6
0 Hz dielectric loss tangent: JIS K-6911 25 ° C, 6
0Hz Boiling water absorption rate: JIS K-7209 After boiling for 1 hour Dielectric breakdown voltage: JIS K-6911 Test variation thickness: 1.5mm, 20 ° C

[0027]

[Table 2]

(Examples 5 to 6) 6 parts by weight of dicyandiamide (manufactured by Nippon Carbide KK) as a curing agent and 100 parts by weight of Epicoat 828 (made by Yuka Shell Epoxy KK, bisphenol A diglycidyl ether type epoxy resin) Silica airgel as a tropic property-imparting agent (manufactured by Nippon Aerosil KK, trade name: Erosil 300)
Example 5: 2 parts by weight and 0.5 parts by weight of 2-isopropyl-4,5-dihydroxymethylimidazole were weighed and mixed, and kneaded and mixed using a three-roll machine so that the maximum particle diameter was 15 μm or less. A formulation of Example 5
The preparation of Example 6 was obtained in the same manner as in Example 5 except that 2-undecyl-4,5-dihydroxymethylimidazole was used in place of the 2-isopropyl-4,5-dihydroxymethylimidazole used in. The performance of the cured products obtained by thermosetting these formulations at a temperature of 120 ° C. for 30 minutes was as shown in Table 3.

[0029]

[Table 3]

[0030]

The epoxy resin curing method using a 2-alkyl-4,5-dihydroxymethylimidazole compound as a curing agent or a curing accelerator is capable of curing even in a medium temperature range even if the curing time is short and has good storage stability. Since it has good compatibility with the epoxy resin even when heated, it is suitable for applications such as paints, electrical insulation casting materials, adhesives, etc., and has a great practical effect.

Claims (4)

[Claims] 1. 2-Alkyl-4,5-represented by Chemical formula 1
A method for curing an epoxy resin, which comprises using a dihydroxymethylimidazole compound as a curing agent or a curing accelerator. [Chemical 1] 2. The 2-alkyl-4,5-dihydroxymethylimidazole compound of claim 1 is 2-methyl-
4,5-dihydroxymethylimidazole, 2-ethyl-4,5-dihydroxymethylimidazole, 2-isopropyl-4,5-dihydroxymethylimidazole,
An epoxy resin curing method, which is one or more selected from 2-undecyl-4,5-dihydroxymethylimidazole and 2-heptadecyl-4,5-dihydroxymethylimidazole. 3. A method for curing an epoxy resin, which comprises using a 2-alkyl-4,5-dihydroxymethylimidazole compound and an organic acid anhydride together. 4. A method for curing an epoxy resin, which comprises using a 2-alkyl-4,5-dihydroxymethylimidazole compound and dicyandiamide together.