Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-06-18
2003-01-07
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C528S090000
Reexamination Certificate
active
06503967
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a curing agent for epoxy resin and epoxy resin composition.
BACKGROUND ART
Epoxy resin is widely used as sealing material, coating composition, adhesive, casting material, 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. However, in case of mixing a filler to the epoxy resin, the mixture sometimes has a high viscosity which causes a problem depending on use. In these cases, an organic solvent is usually added to the mixture to reduce the viscosity.
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, 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.
Meanwhile, 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 resin 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 the curing reaction by heating.
Such characteristic of epoxy resin adhesive 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 resin have problems that curing ability decreases with 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.
As means for overcoming such problems, the present inventors proposed compounds represented by the formula (1), typically 1-aminopyrrolidine, as a curing agent for epoxy resins which agent can quickly cure an epoxy resin even at room temperature or at a low temperature without lowering the curability in the presence of water (Japanese Patent Application Nos. 137743/1998 and 285932/1998).
These compounds are excellent in curability in a low temperature range compared with conventional curing agents for epoxy resins. However, the cured epoxy resin is insufficient in water resistance immediately after curing, and takes a long time (aging for about 48 hours) until the cured product becomes satisfactory in water resistance. Consequently, there is a need for further reducing such aging period in order to shorten the term of construction works.
In recent years, a demand exists for materials which are safe and outstanding in resource-saving capability and in environmental conservation. There is a growing interest in using aqueous solvents in place of organic solvents for diluting purposes in view of control of volatile organic compounds (VOC) concerning the discharge of solvents. Especially the concern for this matter is positive in the fields of coating compositions and adhesive agents. In such applications, the curing agents are mostly used in situations where people are living. Accordingly, it is important that the curing agents scarcely smell, assure safety against a fire, explosion and the like and take only a short period until completion of operation. In this background, epoxy resin emulsions are increasingly used as a substitute, since the emulsions contain little or no volatile organic solvent, prevent environmental pollution, and are excellent in safety and hygiene and in preventive effect against fire hazards.
In preparing an epoxy resin emulsion, generally an epoxy resin is made hydrophilic with an emulsifier and is dispersed in an aqueous solvent. The epoxy resin emulsion, when used, is cured with a curing agent. Mostly conventional per se known curing agents for epoxy resin emulsions are made hydrophilic with an emulsifier and dispersed in an aqueous solvent. For this reason, the curing agent poses problems of reducing the curability, requiring a prolonged period of time in curing, and seriously degrading the properties of cured product.
Known as commercial aqueous products of epoxy resins are, for example, epoxy resin emulsions available under the trade name EPI-REZ series manufactured by Yuka Shell Epoxy Co., Ltd. Known curing agents include, for example, those available under the trade name Epicure series (polyamideamine adduct or the like) manufactured by Yuka Shell Epoxy Co., Ltd. However, the above- mentioned curing agents retard curing at room temperature and take a long period of time in curing.
An object of the present invention is to provide a curing agent for epoxy resins which can quickly cure the epoxy resin in a low temperature range and which imparts water resistance to a cured product in a short time, and an epoxy resin composition containing the curing agent.
Another object of the invention is to provide a curable epoxy resin emulsion composition which is quickly curable at room temperature.
DISCLOSURE OF THE INVENTION
The present invention provides a curing agent for epoxy resins, the curing agent containing as an active ingredient a compound represented by the formula (1) or a salt thereof and an amine compound or a salt thereof, the curing agent being characterized in that at least one of the compound represented by the formula (1) and the amine compound is a salt of thiocyanic acid:
NH
2
N(R
1
)(R
2
) (1)
wherein R
1
and R
2
are the same or different and each represents alkyl having 1 to 8 carbon atoms, aryl, a nitrogen-containing heterocyclic group or when taken together, represents alkylene having 2 to 11 carbon atoms or a group represented by —R
3
—R
4
—R
5
— wherein R
3
and R
5
are the same or different and each represents alkylene having 1 to 8 carbon atoms, and R
4
is an oxygen atom, a sulfur atom or a group ═NR
6
or ═NNH
2
, wherein R
6
is a hydrogen atom or alkyl having 1 to 8 carbon atoms.
The present invention also provides an epoxy resin composition which comprises an epoxy resin and the curing agent for epoxy resins as defined in claim 1.
The present invention further provides an epoxy resin emulsion composition which comprises an epoxy resin emulsion and a compound represented by the formula (1) or a salt thereof.
The curing agent for epoxy resins according to the invention can quickly cure the epoxy resin at room temperature or in a lower temperature range, or even at a temperature as low as −20° C. although depending on the case. Consequently, for example, even if an epoxy resin adhesive agent for outdoor use is used in a construction work, the adhesive agent can be cured without heating by use of the curing agent for epoxy resins according to the invention, whereby great benefit is brought to the construction works. Further, construction work using an epoxy resin in cold climate can be easily and quickly performed by using the curing agent of the invention.
The curing agent for epoxy resins according to the present invention contains as an active ingredient a compound re
Kitajima Takashi
Nabeshima Akihiro
Aylward D.
Dawson Robert
Kubovcik & Kubovcik
Otsuka Nagaku Kabushiki Kaisha
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