JPH05279456A - Curing method for epoxy resin - Google Patents

Abstract

PURPOSE:To carry out curing an epoxy resin high in heat distortion temperature, excellent in long-term preservability and curability, useful for a molding using, as curing agent or curing promoter, a specific polyimidazole compound. CONSTITUTION:An epoxy resin such as a bisphenol A-type epoxy resin is cured using, as curing agent or curing promoter, a polyimidazole compound of the formula (R is methyl, ethyl, isopropyl or phenyl; n is 1 or 2) produced by reaction of (A) a 2-alkylimidazole compound bearing no substituents at its 4- and 5-sites, or 2-phenylimidazole with formaldehyde or paraformaldehyde. When this polyimidazole compound is to be used as curing agent, it is preferable that its amount to be used be 5-15 pts.wt. based on 100 pts.wt. of the epoxy resin.

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 particularly to a method for producing a one-pack type epoxy resin composition having both good thermosetting property and long-term storage stability. is there.

[0002]

2. Description of the Related Art There are various characteristics required for a curing agent for an epoxy resin, and among them, even if a curing agent is preliminarily compounded with the epoxy resin, a curing agent for one-liquefaction or a composition that can be stored for a long period of time and is stable Development of a hardening accelerator is desired. As a method for preparing the one-pack type epoxy resin, JP-A-58-131953 discloses a method using hydrazides, and JP-A-58-131953 discloses a method using cyanoguanidines. But
Although these are excellent in storage stability, they require heating at a high temperature of 150 ° C. or higher for a long time for curing.

It is widely known to use an imidazole compound as a curing agent for an epoxy resin, and as an example of a method of using a curing agent that can cope with such one-liquefaction,
Japanese Patent Publication No. 2-310074 proposes a method using a diamide compound obtained by heating and reacting 1-β-aminoethyl-2-methylimidazole with dodecanoic acid or eicosane diacid. However, according to this method, although the curability of the resin is satisfactory, the storage stability thereof is poor, and therefore there has been a demand for the development of a curing agent having longer-term storage stability.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a cured product having a curability in the medium temperature range and a high heat distortion temperature,
Another object of the present invention is to provide an epoxy resin composition which can be stored for a long period of time in a state where an epoxy resin and a curing agent are mixed.

[0005]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors in view of such circumstances, 2-alkylimidazole compound or 2-phenylimidazole and 1 to 2 moles of formaldehyde relative thereto Alternatively, a polyimidazole compound can be obtained by reacting with paraformaldehyde, and when this compound is used as a curing agent or curing accelerator for epoxy resin, a cured product having a curability in the medium temperature range and a high heat distortion temperature is obtained. It was found that the compound can be stored for a long period of time in a state of being blended with an epoxy resin, and the method of the present invention has been completed.

The polyimidazole compound used in carrying out the method of the present invention is obtained by the following synthetic method. That is, using a soda lime filling tube, in a container that has blocked the ingress of carbon dioxide from the outside air, put a solvent containing a hydroxide of an alkali metal, and a predetermined amount of 2-alkylimidazole compound or 2-phenylimidazole Formaldehyde or paraformaldehyde was added, and the mixture was heated and stirred under normal pressure for several hours, and after the reaction product was crystallized, the heating reaction was continued for an appropriate time to complete the reaction, and the reaction mixture was filtered while warm to obtain It is prepared by washing the obtained crystals with hot water to remove alkali metal hydroxides and hot water-soluble substances.

The 2-alkylimidazole compound used in the above synthetic method has 1 to 1 carbon atoms at the 2-position.
It is a compound having an alkyl group of 7, and its representative compounds are 2-methylimidazole, 2-ethylimidazole and 2-isopropylimidazole.
Further, as the formaldehyde to be reacted with the imidazole compound, any of commercially available 37% formalin aqueous solution or paraformaldehyde may be used, and the amount thereof is 1 to 2 times mol, preferably 1 to 1.3 times the imidazole compound. It is in the range of double mole, and the reaction temperature is preferably 80 to 130 ° C., though it varies depending on the kind of the solvent used.

As the solvent used for carrying out the above synthetic reaction, water is most suitable, but methanol,
A mixed solvent of water such as ethanol, n-butanol or methyl cellosolve may be used, and in order to accelerate the reaction, 0.4 to 3 times mol relative to the imidazole compound,
Preferably, hydroxides of alkali metals such as potassium hydroxide, sodium hydroxide, lithium hydroxide and magnesium hydroxide in a molar ratio of 1 to 2.5 are used together.

After the reaction was completed, the crystals collected by filtration were once made into an acidic aqueous solution and filtered again, the filtrate was neutralized with an aqueous alkaline solution, aqueous ammonia or aqueous alkaline carbonate solution, and the precipitated crystals were collected by filtration, If the obtained reaction product is further purified, the cyclic imidazole compound represented by the general formula of Chemical formula 2 is obtained, and the reaction formula is considered to be as shown in Chemical formula 3.

[0010]

[Chemical 2]

[0011]

[Chemical 3]

Further, it is assumed from the results of the analysis that the polyimidazole compound represented by Chemical formula 4 is mixed in the reaction product.

[0013]

[Chemical 4]

Typical cyclic imidazole compounds used in the practice of the method of the present invention include 2-methylimidazole tetramer, 2-ethylimidazole trimer,
2-isopropylimidazole trimer, 2-isopropylimidazole tetramer and 2-phenylimidazole trimer.

The epoxy resin used in the method of the present invention is a known resin, and there is no particular limitation in its use. Typical examples thereof include polyglycidyl ether compounds obtained from polyphenols such as bisphenol A, bisphenol F, bisphenol AD, and novolak resins, and polyglycidyl esters obtained from polycarboxylic acids such as phthalic acid and adipic acid. Compound,
Examples thereof include polyglycidyl ether compounds obtained from polyhydric alcohols such as polyethylene glycol, polypropylene glycol or glycerin, alicyclic epoxy resins, triglycidyl isocyanurate and epoxidized polyolefins, which may be used alone or 2
You may mix and use 1 or more types.

When the polyimidazole compound is used as a curing agent in carrying out the method of the present invention, the compounding ratio with respect to the epoxy resin is 3 to 20 parts by weight, and the curing rate is 3 parts by weight or less. If the amount exceeds 20 parts by weight, the moisture resistance of the cured resin decreases, so the amount should preferably be 5 to 15 parts by weight.

When a polyimidazole compound is used as a curing accelerator in the method of the present invention, other curing agents include organic polybasic acid anhydrides, polyhydric phenol compounds,
Examples thereof include dicyandiamide, cyanamide, guanamines, biguanides, aromatic polyamines, alicyclic amines, hydrazine derivatives and organic acid hydrazides. Examples of these compounds include hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, succinic anhydride, polyadipic anhydride, organic polybasic acid anhydrides such as trimellitic anhydride, novolac resins, cresol novolac resins, etc. Polyphenol compound, benzoguanamine, orthotoluyl biguanide, monoepoxide adduct, cyanoethylated product, dicyandiamide, monoepoxide adduct, metaphenylenediamine, monoepoxide adduct, cyanoethylated product, diaminodiphenylmethane, monoepoxide Examples include adducts, isophthalic acid dihydrazide, 2,4-dihydrazino-6-methylamino-s-triazine, and monoepoxide adducts.

When the polyimidazole compound is used as a curing accelerator in carrying out the method of the present invention, the proper mixing ratio with respect to the epoxy resin is 0.05 to 5 parts by weight with respect to 100 parts by weight of the epoxy resin. If the addition amount of the curing accelerator exceeds this range, the curing property will be high, but the storage stability will be deteriorated. If the addition amount is small, the storage stability will be excellent but the desired curability will not be obtained.

In the practice of the present invention, a coloring agent such as a dye or a coloring pigment, an extender pigment, a reinforcing material such as a fibrous reinforcing material or whiskers, and a light scattering agent may be added. Further, even if an additive such as a release agent, an internal release agent, a lubricant, an antifoaming agent, a leveling agent or a penetrating agent for improving workability is used within a range that does not adversely affect the effect of the method of the present invention. It doesn't matter.

[0020]

【Example】

Example 1 In a reaction vessel equipped with a magnetic stirrer, a reflux condenser and a thermometer, 19.2 g (0.2%) of 2-ethylimidazole was added.
Mol), commercially available 37% formalin 19.6 g (0.2 mol), potassium hydroxide 16.8 g (0.3 mol) and water 18
Add 0 ml of 4 parts, and stir under nitrogen replacement, 2.
The reaction was continued by heating under reflux for 5 hours. Precipitated crystals were collected by filtration while hot, washed with hot water until ash was removed, extracted with methanol, and the extract was concentrated. The obtained concentrate was recrystallized to obtain 6.5 g of 2-ethylimidazole trimer (converted yield: 30 mol%).

Next, polyepoxy resin [AER-33
1. Asahi Kasei Kogyo Co., Ltd.] 100 parts by weight, 5 parts by weight of the 2-ethylimidazole trimer and 2 parts by weight of Aerosil are mixed, and this mixture is homogenized using a three-roll machine. It was a blend. The gelation time (curability), storage stability, and glass transition temperature of the cured product of this compound on a hot plate kept at a temperature of 150 ° C. or 180 ° C. were measured. The results are shown in Table 1. Met.

Example 2 As in Example 1, 2-ethylimidazole 19.2 g (0.2 mol), commercially available 37% formalin 19.6 g (0.2 mol), potassium hydroxide 16.8.
g (0.3 mol) and 180 ml of water were treated in the same manner as in Example 1 to react with each other, and the precipitated crystals were collected by filtration while hot, and washed with hot water until the ash content disappeared. It was dried to obtain 13.5 g (converted yield: 62.5 mol%) of a polyimidazole compound of 2-ethylimidazole.

Next, polyepoxy resin [AER-33
1, manufactured by Asahi Kasei Kogyo Co., Ltd.], 100 parts by weight, 10 parts by weight of the polyimidazole compound of 2-ethylimidazole and 2 parts by weight of Aerosil are mixed, and this mixture is homogenized using a three-roll machine. It was a blend. When the gelation time, the storage stability and the glass transition temperature of the cured product were measured using this formulation in the same manner as in Example 1,
The results are shown in Table 1.

(Example 3) 2-methylimidazole 2
0.8 g (0.26 mol), paraformaldehyde 11.4
g (0.38 mol), potassium hydroxide 28.4 g (0.50 mol) and water (160 ml) were heated and refluxed for 2 hours to react them in the same manner as in Example 1, and the precipitated crystals were heated until no ash was contained. The extract was washed with water, washed with methanol to remove soluble impurities, and dried to obtain 12.0 g (converted yield: 50 mol%) of a polyimidazole compound of 2-methylimidazole.

Next, polyepoxy resin [AER-33
1, manufactured by Asahi Chemical Industry Co., Ltd.] 100 parts by weight, 1 part by weight of the polyimidazole compound of 2-methylimidazole described above,
Dicyandiamide 8 parts by weight and Aerosil 2 parts by weight 4
The ingredients were mixed and a uniform blend was prepared in the same manner as in Example 1. The gelation time, the storage stability and the glass transition temperature of the cured product were measured using this formulation in the same manner as in Example 1. The results are shown in Table 1.

Example 4 22.16 g (0.20 mol) of 2-isopropylimidazole, 20.2 g (0.24 mol) of 37% aqueous formalin solution, 11.2 g of potassium hydroxide.
(0.20 mol) and 160 ml of water were reacted in exactly the same manner as in Example 1, and the precipitated crystals were collected by filtration while hot, and 1N hydrochloric acid aqueous solution was added to the crystals to acidify them, and the crystals were dissolved. Potassium carbonate was added to the product to neutralize it, and the precipitated crystals were collected by filtration. The crystals were washed with hot water until the ash content disappeared, and dried to obtain 14.0 g of polyisopropylimidazole compound of 2-isopropylimidazole (converted yield: 56 mol%).

Next, polyepoxy resin [AER-33
1, Asahi Kasei Kogyo Co., Ltd.] 100 parts by weight, 5 parts by weight of the polyimidazole compound of 2-isopropylimidazole and 2 parts by weight of Aerosil were mixed, and Example 1 was mixed.
A uniform blend was prepared by the same method as described above. The gelation time, the storage stability and the glass transition temperature of the cured product were measured using this formulation in the same manner as in Example 1. The results are shown in Table 1.

Example 5 2-Phenylimidazole 1
8.16 g (0.13 mol), 37% formalin aqueous solution 1
2.4 g (0.15 mol), potassium hydroxide 8.6 g (0.15 mol)
Mol), 80 ml of ethanol and 72 ml of water were reacted in exactly the same manner as in Example 1, the precipitated crystals were collected by filtration while hot, and the crystals were washed with hot water until the ash content disappeared and then dried. 11.4 g (converted yield: 55 mol%) of a polyimidazole compound of 2-phenylimidazole was obtained.

Next, polyepoxy resin [AER-33
1, Asahi Kasei Kogyo Co., Ltd.] 100 parts by weight, 7 parts by weight of the above-mentioned polyimidazole compound of 2-phenylimidazole and 2 parts by weight of Aerosil were mixed, and a uniform mixture was prepared in the same manner as in Example 1. And The gelation time, the storage stability and the glass transition temperature of the cured product were measured using this formulation in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1) Polyepoxy resin [AER-
331, manufactured by Asahi Kasei Kogyo Co., Ltd.] 100 parts by weight, 2-ethylimidazole 2 parts by weight and Aerosil 2 parts by weight were mixed, and a uniform mixture was prepared by the same method as in Example 1. The gelation time, the storage stability and the glass transition temperature of the cured product were measured using this formulation in the same manner as in Example 1. The results are shown in Table 1.

[0031]

[Table 1]

Claims (2)

[Claims] 1. A curing agent or a curing accelerator, 4,
A method for curing an epoxy resin, which comprises using a 2-alkylimidazole compound having no substituent at the 5-position or a polyimidazole compound obtained by reacting 2-phenylimidazole with formaldehyde or paraformaldehyde. 2. A method for curing an epoxy resin, which comprises using a polyimidazole compound represented by the general formula of Chemical formula 1 as an active ingredient of a curing agent or a curing accelerator. [Chemical 1]