METHOD OF HARDENING EPOXY RESINS

Abstract: A curing agent for epoxy resin which comprises at least one selected from the compound of the formula (1) and its salt, as an effective component wherein X is -(CH 2 )n- or -(CH 2 )1-Y-(CH 2 )m- , Y is -N(R 1 )-, -O- or -S- , R 1 is alkyl having 1 to 8 carbon atoms or amino. n is a number of 2, 3, 5 to 11, 1 and m are each a number of 1 to 8.

Description: TECHNICAL FIELD The present invention relates to a method of hardening an epoxy resin composition. BACKGROUND ART Epoxy resin is widely used as sealing material, coating composition, adhesive, etc, in a variety of fields such as electricity, electronics, and civil engineering and construction, because a cured product of epoxy resin has excellent electrical insulating properties, moisture proof, heat resistance, soldering resistance, chemical resistance, durability, adhesive property, and mechanical strength. Conventionally, the curing of epoxy resin is carried out by adding a curing agent to epoxy resin, followed by heating. As typical representative examples of curing agent, there are, for example, diethylenetriamine, triethylenetetramine, isophoronediamine, diaminodiphenylmethane, diaminodiphenylsulfone, polyamides, dicyandiamide, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methyl nadic anhydride, novolac type phenol resin, tertiary amines, imidazoles, and amine complex of boron trifluoride. Of these curing agents, ones which can cure epoxy resin at room temperature are amine curing agents such as diethylenetriamine, triethylenetetramine, polyamides, and tertiary amines. However, these curing agents require a long time of four to seven days for curing. It is difficult for other curing agents to be cured at room temperature, and they generally require a curing temperature of 80 to 200 °C, and a curing time of 0.5 to 6 hours. An epoxy resin adhesive for outdoor construction is generally used in the field of civil engineering and construction. With a conventional curing agent, however, it is very difficult to cure epoxy resins without heating, as previously described. Even with one capable of curing, it takes an extremely long period of time, namely, four to seven days. Especially, for winter-season execution of works in which the outdoor temperature is often 10 °C and below, it is essential to initiate or promote the curing reaction by heating. Such characteristic of epoxy resin adhesives prolongs the period of execution of works in civil engineering and construction, which is also one of the causes of interfering with labor saving. Further, most of conventional curing agents for epoxy resins have problems that curing ability decreases in the presence of water, a long time is required for curing, characteristics of cured product are greatly impaired, or cured product is not obtained. Therefore, in fact, use of curing agent is greatly limited in outdoor under rain or in shore-protection works. An object of the present invention is to provide a method of hardening an epoxy resin composition which can rapidly cure the epoxy resin at ordinary temperatures around 20°C or at low temperatures in the range near 0°C. Furthermore, the curing ability should not be disturbed, and the curing velocity even be enhanced in the presence of water. DISCLOSURE OF THE INVENTION The present invention provides a method of hardening an epoxy resin composition comprising an epoxy resin selected from glycidyl ether epoxy resins and glycidylamine epoxy resins, which method comprises curing the epoxy resin composition in the presence of water with at least one curing agent for the epoxy resin selected from compounds of formula (1) and salts thereof: wherein X is - (CH 2 ) n - or - (CH 2 ) l -Y-(CH 2 ) m -, Y is -N(R 1 )- , -O- or -S-, R 1 is alkyl having 1 to 8 carbon atoms or amino, n is a number of 2, 3or 5 to 11, 1 and m are each a number of 1 to 8. The curing agent used in accordance with the present invention is capable of curing epoxy resins at low temperatures of ordinary temperature or below and, in some instances, at extremely low temperatures in the range of near - 20 °C. Thus, when an epoxy resin adhesive for outdoor is used, for example, in civil engineering and construction, the adhesive can be cured without applying heat, by using a curing agent for epoxy resin of the invention. This is of great benefit for the working process. The present curing agent for epoxy resin has unexpected properties in that it is not impaired in curing ability even in the presence of water, but is enhanced in curing velocity with addition of a suitable amount of water. Thus, the present curing agent can preferably be used in outdoor or under water circumstances. Further, the present curing agent can be provided in the form of an aqueous solution or aqueous composition. The amount of water is usually up to 3, preferably 0.8 to 2 in terms of molar ratio of water/curing agent. In R 1 of the formula (1), examples of alkyl having 1 to 8 carbon atoms are methyl, ethyl, propyl, butyl, hexyl and octyl. Examples of amino are NH 2 or those wherein one or two hydrogens of NH 2 are replaced by alkyl having 1 to 4 carbon atoms. Examples of alkyl having 1 to 4 carbon atoms are the same as above. Examples of compounds of the formula (1) are 1-aminopiperidine, 1-aminohomopiperidine (AHP), 1-aminopiperazine, 1-amino-N'-methylpiperazine (AMPI), N,N'-diaminopiperazine, N-aminomorpholine (AMP), N-aminoaziridine (AAD), N-aminoazacycloundecene (AACU), N-aminothiomorpholine (ATMP) and 1-amino-4-octylpiperazine (AOPI). Among these compounds particularly preferable are 1-aminohomopiperidine (AHP), 1-amino-N'-methylpiperazine (AMPI), N-aminomorpholine (AMP) and N-aminothiomorpholine (ATMP). Examples of salts of these compounds are hydrochloride, phosphate and sulfate. Although the compound of the above formula (1) can be added directly, in the form of powder or liquid, to epoxy resin as a curing agent for epoxy resin. Alternatively, these are used in the form of an aqueous solution, organic solvent solution, or dispersion. Examples of organic solvent are lower alcohols such as methanol, ethanol and isopropanol; aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane; ethers; polar solvent; and halogenated hydrocarbons. In addition, a solution of water and a suitable organic solvent or dispersion may be used. Of these various forms, an aqueous solution is particularly preferred. The amount of curing agent for epoxy resin to be used to epoxy resin is not specifically limited. It may be suitably selected from a wide range, depending on various conditions such as the kind of epoxy resin, the kind and amount of other additives, the use of a cured product of epoxy resin to be obtained, and the curing conditions (the designed curing time and temperature, curing location, etc.). It is usually about 0.5 to 2 equivalents, preferably about 0.7 to 1.2 equivalents of epoxy group of the epoxy resin per equivalent of amine group of the effective compound. Conventional curing agent and curing accelerator can be added, as required, to a curing agent for epoxy resin of the invention insofar as its preferred characteristic is not impaired. As a curing agent, the same various ones as mentioned in prior art are usable, and it is also possible to use melamine, methylolmelamine, resol type compound, etc. As a curing accelerator are used, for example, tertiary amines such as tri-n-butylamine, benzylmethylamine and 2,4,6-tris-(dimethylaminomethyl)phenol; and imidazoles such as 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole and 2-phenylimidazole. These curing agents and curing accelerators can be used singly or in a combination of at least two of them. Epoxy resin which can be cured with the curing agent of the invention is not specifically limited, and various epoxy resins are usable. Examples thereof are glycidyl ether type epoxy resin, glycidyl ester resin and glycidylamine type epoxy resin. Examples of glycidyl ether type epoxy resin are bisphenol A type, bisphenol F type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol S type, bisphenol AF type, biphenyl type, naphthalene type, fluorene type, phenol novolac type, cresol novolac type, DPP novolac type, trifunctional type, tris(hydroxyphenyl)methane type, and tetraphenylolethane type epoxy resins. Examples of glycidyl ester type epoxy resin are hexahydrophthalate type and phthalate type epoxy resins. Examples of glycidylamine type epoxy resin are tetraglycidyldiaminodiphenylmethane, triglycidyl isocyanurate, hydantoin type, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, aminophenol type, aniline type, and toluidine type epoxy resins. To epoxy resin can be added, as required, a filler and reinforcing agent, which have conventionally been added to epoxy resin. Examples of fillers are silica, fused quartz, calcium carbonate, barium carbonate, barium sulfate, alumina hydrate, alumina, magnesia hydrate, zircon, cordierite, silicon nitride, boron nitride, and aluminum nitride. Examples of reinforcing agents are talc, mica, glass fiber, potassium titanate fiber, titanium dioxide fiber, wallastonite, xonotlite, zinc silicate fiber, aramide fiber, carbon fiber and boron fiber. It is possible to suitably change the kind, amount or the like of a filler and reinforcing agent in order to obtain desired properties of a cured epoxy resin product. Usually, it is suitable to add about 20 to 160 parts by weight of a filler and reinforcing agent, preferably about 50 to 120 parts by weight, based on 100 parts by weight of epoxy resin. Filler and reinforcing agent may be used singly or in a combination of at least two of them. Further, various additives may be added as required to the above epoxy resin composition. Examples of such additives are inorganic pigment (particulate titanium dioxide, carbon black, red iron oxide, yellow iron oxide, etc.), organic pigment, viscosity adjusting agent, leveling agent, antifoamer, coupling agent, plasticizer, diluent, flame retardant (magnesium hydroxide, aluminum hydroxide, antimony oxide, alkyl phosphates or phosphazenes), and organic solvent. The above epoxy resin composition is applicable to coat, bond, or repair materials such as metal, synthetic resin, cement, ceramics, knitting or fabric of inorganic or organic fiber (glass cross, etc.) and papers, or to prepare a shaped product using the composition. Specifically, an article of various shape may be dipped in the epoxy resin composition, alternatively, the epoxy resin composition is applied or coated to the article surface, or poured into the article or filled into opening between articles, and then allowed to stand as it is, for curing. When curing, heating is not required particularly, but it is possible to heat to about 40 to 120 °C as required depending on the composition. Also, the above epoxy resin composition can be formed into a shaped product of a desired shape, in accordance with the usual molding method, e.g., casting molding and injection molding. The present invention will be described in more detail with reference to the following examples to which, however, the invention is not limited. Example 1 An epoxy resin composition was obtained by mixing equivalent amounts of a compound listed in Table 1 and an epoxy resin (Epikote® 828, epoxy equivalent: 190). About 3 g of the obtained epoxy resin composition was weighed out with an aluminum cup. This was then allowed to stand at room temperature to observe the cured state every prescribed hour. Table 1 gives the results. Example 2 An epoxy resin composition was obtained by mixing equivalent amounts of a compound listed in Table 1 having an equivalent amount of water added therein, and an epoxy resin (Epikote® 828, epoxy equivalent: 190). About 3 g of the obtained epoxy resin composition was weighed out with an aluminum cup. This was then allowed to stand at room temperature to observe the cured state every prescribed hour. Table 1 gives the results. Example 3 An epoxy resin composition was obtained by mixing equivalent amounts of a compound listed in Table 2 and an epoxy resin (Epikote® 828, epoxy equivalent: 190). About 3 g of the obtained epoxy resin composition was weighed out with an aluminum cup. This was then allowed to stand at 0 °C to observe the cured state every prescribed hour. Table 2 gives the results. Example 4 An epoxy resin composition was obtained by mixing equivalent amounts of a compound listed in Table 2 having an equivalent amount of water added therein, and an epoxy resin (Epikote® 828, epoxy equivalent: 190). About 3 g of the obtained epoxy resin composition was weighed out with an aluminum cup. This was then allowed to stand at 0 °C to observe the cured state every prescribed hour. Table 2 gives the results. compound water (hour) 4 11 18 AHP added Δ ○ none Δ ○ Examples 5 to 8 An epoxy resin composition was obtained by mixing equivalent amounts of a compound listed below and an epoxy resin (Epikote® 828, epoxy equivalent: 190). About 3 g of the obtained epoxy resin composition was weighed out with an aluminum cup. This was then allowed to stand at room temperature to observe the cured state. Table 3 gives the results. Further, an epoxy resin composition was cured at room temperature in the same manner as above except of using the compound having an equivalent amount of water added therein. Table 3 also gives the results. N-Aminoaziridine (AAD) N-Aminoazacycloundecene (AACU) N-Aminothiomorpholine (ATMP) 1-Amino-4-octylpiperazine (AOPI) compound water gel time curing time AAD added 20 min. 40 min. none 40 min. 90 min. AACU added 3 hour 5 hour none 8 hour 14 hour ATMP added 30 min. 1 hour none 4 hour 11 hour AOPI added 3 hour 6 hour none 10 hour 40 hour INDUSTRIAL APPLICABILITY In accordance with the present invention, a curing agent for epoxy resin is used which can rapidly cure epoxy resins at ordinary temperature around 20 °C or a low temperatures in the range of near 0 °C. In addition, the curing agent for epoxy resin has an excellent effect that the curing ability is not disturbed and the curing velocity is even enhanced in the presence of water.

Claims: A method of hardening an epoxy resin composition comprising an epoxy resin selected from glycidyl ether epoxy resins and glycidylamine epoxy resins, which method comprises curing the epoxy resin composition in the presence of water with at least one curing agent for the epoxy resin selected from compounds of formula (1) and salts thereof: wherein X is - (CH 2 ) n - or -(CH 2 ) l -Y-(CH 2 ) m -, Y is -N(R 1 )-, -O- or -S-, R 1 is alkyl having 1 to 8 carbon atoms or amino, n is a number of 2, 3 or 5 to 11, 1 and m are each a number of 1 to 8. A method according to claim 1 wherein the compound of formula (1) is 1-aminohomopiperidine, 1-amino-N'-methylpiperazine, N-aminomorpholine or N-aminothiomorpholine.

Inventors: FURUICHI TOMOHIRO, ISHIKAWA KEIICHIRO, KITAJIMA TAKASHI, NABESHIMA AKIHIRO, TOMOTAKI YOSHIHISA, FURUICHI, TOMOHIRO, ISHIKAWA, KEIICHIRO, KITAJIMA, TAKASHI, NABESHIMA, AKIHIRO, TOMOTAKI, YOSHIHISA, FURUICHI, Tomohiro Otsuka Kagaku KK, ISHIKAWA, Keiichiro Otsuka Kagaku KK, KITAJIMA, Takashi Otsuka Kagaku KK, NABESHIMA, Akihiro Otsuka Kagaku KK, TOMOTAKI, Yoshihisa Otsuka Kagaku KK
Applicants: OTSUKA KAGAKU KK, OTSUKA KAGAKU KABUSHIKI KAISHA
Application year: 1999
Main classification: C08G59
IPC codes: C08K3, C08K13, C08K5, C08G59, C08L63