JPH0152410B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid curing agent for epoxy resins. More specifically, the present invention relates to a solid curing agent for epoxy resins that is easy to handle industrially and is made of an adduct of an imidazole compound having a secondary amino group on the imidazole ring and an epoxy resin that is liquid at room temperature.

Imidazole compounds as curing agents for epoxy resins can be used in a small amount to obtain a cured product with high heat resistance under relatively low temperature and short curing conditions, and because they also have a tertiary amino group, It has the characteristic that it can also be used as a curing accelerator for other types of curing agents such as dicyandiamide and dicyandiamide.

However, imidazole compounds alone have shortcomings such as short storage stability in coexistence with epoxy resins, volatility and hygroscopicity, and as a countermeasure, imidazole compounds are used as adducts with epoxy compounds. It is being used.

Conventionally, an adduct of an imidazole compound and an epoxy compound has been made by using an epoxy resin that is liquid at room temperature and reacting the epoxy group with the secondary amino group of the imidazole compound at a ratio of 1:1. Using an epoxy resin that is liquid at room temperature is easy to react because it is liquid, and liquid resin has a smaller molecular weight than solid resin, so the amine content of the adduct is higher, and the amount added as a curing agent is smaller. It depends on the reason.

However, adducts produced under these conditions have a softening temperature of about 80°C even when using 2-methylimidazole, which has a high melting point, and it is difficult to powderize them when industrially producing them in large quantities. Due to the heat generated during the crushing process, it fuses to the wall of the crusher, which has the drawback of significantly hindering productivity.

As a result of research to eliminate these drawbacks, the present inventors have found that if the adduct is manufactured under certain conditions, it is possible to obtain an adduct with a softening temperature of 100°C or higher, thereby eliminating the drawbacks of the conventional adducts described above. This led to the completion of the present invention.

The present invention provides an adduct containing 5 to 20% by weight of inorganic powder based on the total weight of the adduct and having a softening temperature of 100°C or higher.
The present invention relates to a solid curing agent composition for epoxy resin, which contains 0.5 to 50 parts by weight of an inorganic fine powder as an anti-agglomeration agent, based on 100 parts by weight of an adduct of an imidazole compound and an epoxy resin that is liquid at room temperature.

The softening temperature referred to herein refers to the softening temperature measured by the Durand mercury method after removing the solvent used in the reaction. The Duran mercury method is described, for example, in "Plastic Materials Course 1, Epoxy Resins" by Kunihiko Hashimoto (published by Nikkan Kogyo Shimbun), pages 48-49.

Imidazole compounds have the general formula (X ₁ , X ₂ , and X ₃ represent hydrogen, halogen, or hydrocarbon residues). Such imidazole compounds include imidazole, 2-
Methylimidazole, 2-ethylimidazole,
Examples include 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-dodecylimidazole, and the like. Typical imidazole compounds are 2-
It is methylimidazole.

The epoxy resin used in the present invention may contain two or more epoxy groups in one molecule and be liquid at room temperature.

Preferred epoxy resins are, for example, diglycidyl ethers of diphenylalkanes such as 2,2-bis(4-hydroxyphenyl)propane and bis(4-hydroxyphenyl)methane.
A typical example is diglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane (commonly known as bisphenol A).

In addition, polyglycidyl ethers of aliphatic polyhydroxy compounds, polyglycidyl esters of polyhydric carboxylic acids, polyglycidyl esters of polymers of unsaturated fatty acids, etc. can also be used.

Examples of the inorganic powder used in the present invention include silicic anhydride, kaolin, silica sand, diatomaceous earth, talc, and bentonite, and finely powdered silicic anhydride is preferable. The addition of these inorganic powders to the adduct is
This may be done at the time of adduct production, or it may be kneaded using a heating roll or an extruder after adduct production. The purpose of increasing the softening temperature can be achieved by adding 5 to 20% by weight of the inorganic powder to the adduct.

The reaction may be carried out without a solvent, but it is customary to dissolve the imidazole compound in a suitable solvent and drop the epoxy resin, and either may be used. The solvent is preferably an aromatic or ketone solvent that is inert to the epoxy resin, such as toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, and the like.

Since the adduct of the present invention is solid, it is used in powder form, but it has a strong tendency to agglomerate under pressure during storage. For this purpose, it is desirable to add inorganic fine powder as an anti-agglomeration agent. As the inorganic fine powder, those mentioned above for the inorganic powder added to the adduct can be used, but fine powder of silicic anhydride is particularly preferred. The purpose can be achieved by adding 0.5 to 10% by weight of the inorganic fine powder to 100 parts by weight of the adduct powder.

This composition can be used alone as a curing agent for epoxy resins, but it can also be used in combination with curing agents for epoxy resins such as amines, polycarboxylic acid anhydrides, phenolic resins, melamine resins, and urea resins. Suitable amines include ethylenediamine,
Aliphatic polyamines such as diethylenetriamine, dicyandiamide, guanidine, cycloaliphatic diamines such as di(4-aminocyclohexyl)methane, isophoronediamine, m-phenylenediamine, p,p'-bis(aminophenyl)methane, etc. Examples include aromatic amines. Examples of the polycarboxylic anhydride include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylated hexahydrophthalic anhydride, trimellitic anhydride, and the like.

The compositions according to the invention retain the characteristics of the previously known adducts, namely long-term storage stability and rapid curing under heat.

Curing of the epoxy resin is achieved by mixing the epoxy resin, the present composition, and optionally other curing agents, and heating the mixture. At that time, the epoxy resin or this composition may contain diluents, pigments, fillers, plasticizers,
Additives such as coal tar may also be added.

Since the composition according to the invention is solid, it is particularly suitable for powder coatings, but it is also possible to use it dispersed in liquid epoxy resins.

Hereinafter, the present invention will be explained in more detail by giving examples, but the scope of the present invention is not limited by these examples. In the examples, parts represent parts by weight.

Comparative Example 1 3 with stirrer, dropping device, and condenser
2-methylimidazole in a glass flask
300 g of xylene and 900 g of xylene were charged and heated to 110 to 120°C in an oil bath while stirring to dissolve them.
AER330 (trade name of diglycidyl ether of bisphenol A manufactured by Asahi Kasei Corporation) at 120℃.
680 g of epoxy equivalent (185) was added dropwise over one and a half hours to cause a reaction. The ratio of epoxy group to secondary amino group is 1:1. In order to suppress heat generation during the reaction, the temperature of the oil bath was lowered to lower the reaction temperature.
The temperature was controlled at 120°C. The produced adduct was separated from the system because it was insoluble in xylene.

Stirring was stopped, the upper layer of xylene was decanted and separated, and the remaining xylene was distilled off at 140°C under a reduced pressure of 10 mmHg. The molten state was poured out of the flask into a flat shallow dish, and further dried at 180°C for 1 hour, and then dried in the dark. A reddish-brown adduct was obtained.

When the softening temperature of this adduct was measured using the Durand mercury method, it was 80°C.

30kg of adduct was manufactured using the method of
After coarsely pulverizing it to a mesh size, I tried to use a fine grinder (turbo mill) to grind it into 80 mesh passes, but it fused to the machine wall, and I had to stop twice to disassemble the grinder and remove it.

5 parts of adduct, 0.075 parts of Aerosil 200 (1.5 parts per 100 parts of adduct) crushed into 80 mesh passes, 100 parts of AER664P, 40 parts of rutile titanium oxide pigment, 0.4 parts of fluidity modifier (Modaflow manufactured by Mitsubishi Monsanto) and mixed respectively,
The mixture was melted and mixed in a Busu co-kneader and pulverized to form a powder coating. When this powder coating was left in an atmosphere at 50° C. for one month under a pressure of 50 g/cm ² , some aggregation was observed. This was applied to a mild steel plate using an electrostatic coating method and baked at 180°C for 15 minutes. The physical properties of the coating film (thickness 70μ) were: Erichsen value (m/m) 7.1 Dupont impact value 1/8φ500g 50 passes Goblin test passed Gloss (reflectance) (%) 90.

Example 1 A reaction was carried out in accordance with Comparative Example 1. However, in advance
100 g of Aerosil 200 (product name of Nippon Aerosil Co., Ltd., a finely powdered silicic anhydride) was added to AER330, and a dropwise reaction was carried out in a dispersed state. The softening temperature of the adduct obtained by separating and drying xylene in the same manner as in Comparative Example 1 was 115°C by the Durand mercury method.

30kg of adduct was manufactured using the method of
After coarsely pulverizing it to mesh size, I tried to grind it to 80 mesh passes using a fine grinder (turbo mill). The adduct could be crushed without any problems, and it did not adhere to the machine wall.

AER664P (trade name of bisphenol A type solid epoxy resin for powder coatings, manufactured by Asahi Kasei Industries, Ltd., epoxy equivalent: 910) was used to crush into 80 mesh passes. 1 g of a composition containing 100 g of that, 0.5 g of Adduct, 0.05 g of Aerosil 200, and 4.5 g of didiandiamide was placed on a hot plate at 160°C, and pulled up while stirring with a wooden stick.
The gel time was measured by measuring the time until thread breakage occurred as the curing progressed. gel time is
It took 380 seconds.

The gel time of a composition in which only 5.0 g of dicyandiamide was added to 100 g of the same AER664P 80 mesh powder was about 1 hour.

Comparison of the above results shows the promoting effect of this adduct.

5 parts of this adduct, 0.075 parts of Aerosil 200 (1.5 parts per 100 parts of adduct) were ground into 80 mesh passes, 100 parts of AER664P, 40 parts of rutile-type titanium oxide pigment, and 0.4 parts of fluidity modifier (Modaflow manufactured by Mitsubishi Monsanto). and mixed respectively,
The mixture was melted and mixed in a Busu co-kneader and pulverized to form a powder coating. When this powder coating was left in an atmosphere at 50° C. under a pressure of 50 g/cm ² for one month, no agglomeration occurred. This was applied to a mild steel plate using an electrostatic coating method and baked at 180°C for 15 minutes. The physical properties of the coating film (thickness 70μ) were excellent: Erichsen value (m/m) 7.1 Dupont impact value 1/8φ500g 50 passes Goblin test passed Gloss (reflectance) (%) 87.

According to Examples and Comparative Examples, the adduct of the present invention:
It can be seen that it does not adhere to the wall of the pulverizer during pulverization, and the operation is extremely easy and efficient, which is very advantageous from an industrial perspective.

Claims (1)

[Claims] 1. Inorganic powder as an anti-agglomeration agent is added to 100 parts by weight of an adduct of an imidazole compound and an epoxy resin which is liquid at room temperature and has a softening temperature of 100°C or higher and contains 5 to 20% by weight of inorganic powder based on the total weight of the adduct. A solid curing agent composition for epoxy resin containing 0.5 to 50 parts by weight of fine powder.