Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1999-02-23
2001-05-15
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S090000, C528S094000
Reexamination Certificate
active
06232426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a one-part polythiol-type epoxy resin composition having an excellent low-temperature quick curability (i.e., being excellent in quick and low-temperature curability) and a good storage stability or shelf stability (i.e., being good in storage stability).
2. Discussion of the Background
An epoxy resin composition prepared by using a polythiol as a curing agent and a tertiary amine as a curing accelerator has been used as a low-temperature quick-curable epoxy resin composition which can be cured even at such a low temperature of from 0° C. to −20° C., and has been used as an adhesive, a sealer or a casting mold.
However, such an epoxy resin composition has usually quite a short pot life of from several seconds to several minutes after the mixing of the starting ingredients, involving such defect that the mixing of the starting ingredients, and the defoaming and coating of the resulting mixture cannot be conducted for a satisfactorily long period of time. Further, it is poor in workability since a worker has to prepare an epoxy resin composition whenever it is used. Furthermore, the leftover from such a composition cannot be stored, and therefore, has to be discarded, which, in turn, is undesirous from the view point of an energy saving and an environmental problem.
For example, the use of a thiol compound obtained by an esterification reaction of a polyol with a mercapto organic acid as a curing agent for an epoxy resin composition is described in JP-B-41-7236, JP-B-42-26535, JP-B-47-32319, JP-A-46-732 and JP-B-60-21648. However, curing accelerators used in such epoxy resin compositions are liquid amines. Such compositions obtained by using liquid amines as a curing accelerator are very short in their pot life, from several minutes to several tens of minutes, and such very short pot life is quite problematic in the working operation. Under these circumstances, the development of a polythiol-type epoxy resin composition which has a satisfactorily long pot life or which is rendered one-part type to improve a workability has been in high demand.
In order to solve this problem, a method in which an acid anhydride or a mercapto organic acid is added as a curing retarder to prolong a pot life was studied (JP-A-61-159417), but it was not said to be well satisfactory.
JP-A-06-211969 and JP-A-06-211970 describe an example of a polythiol-type epoxy resin composition obtained by using a solid dispersion-type amine adduct latent curing accelerator or a reaction product of a compound having an isocyanate group with a compound having at least one primary or secondary amino group in one molecule as a curing accelerator to improve a pot life. However, the composition is not yet satisfactory in shelf stability, and a low-temperature quick curability as a merit of a thiol-type epoxy resin composition is not brought out sufficiently.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide a polythiol-type one-part epoxy resin composition which exhibits a low-temperature quick curability being by far better than that of the conventional epoxy resin composition and which has a good shelf stability.
The present inventors have assiduously conducted investigations to solve the problems, and have consequently found that a one-part polythiol-type epoxy resin composition having a good shelf stability can be obtained by adding a composition composed of three components, (1) an epoxy resin, (2) a polythiol compound having two or more thiol groups in one molecule as a curing agent and (3) a solid dispersion-type latent curing accelerator as a curing accelerator, further with (4) a borate ester compound. They have further found that, when the mixing ratio of such epoxy resin to such thiol compound is set at from 0.5 to 1.2 in terms of the ratio of the SH gram equivalent number of the thiol compound to the epoxy gram equivalent number of the epoxy resin, and the amounts of such solid dispersion-type latent curing accelerator and such borate ester compound are set at from 1 to 60 parts by weight and from 0.1 to 30 parts by weight, per 100 parts by weight of the epoxy resin, respectively, then such a low-temperature quick curability which has not been so far provided is exhibited while maintaining a good shelf stability. These findings have led to the completion of the present invention.
Accordingly, the present invention relates to an epoxy resin composition comprising, as essential ingredients, (1) an epoxy resin having two or more epoxy groups in one molecule, (2) a thiol compound having two or more thiol groups in one molecule, (3) a solid dispersion-type latent curing accelerator and (4) a borate ester compound. And, it also relates to such epoxy resin composition, wherein the epoxy resin and the thiol compound are comprised in a ratio of from 0.5 to 1.2 in terms of the ratio of the SH gram equivalent number of the thiol compound to the epoxy gram equivalent number of the epoxy resin, and the solid dispersion-type latent curing accelerator is comprised in an amount of between 1 to 60 parts by weight and the borate ester compound is comprised in an amount of between 0.1 and 30 parts by weight, respectively, per 100 parts by weight of the epoxy resin.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
In accordance with the present invention, any epoxy resin can be used insofar as it has two or more epoxy groups per one molecule on the average. Examples thereof include a polyglycidyl ether obtainable by reacting a polyhydric phenol such as bisphenol A, bisphenol F, bisphenol AD, catechol or resorcinol or a polyhydric alcohol such as glycerol or polyethylene glycol with epichlorohydrin; a glycidyl ether ester obtainable by reacting a hydroxycarboxylic acid such as p-hydroxybenzoic acid or &bgr;-hydroxynaphthoic acid with epichlorohydrin; a polyglycidyl ester obtainable by reacting a polycarboxylic acid such as phthalic acid or terephthalic acid with epichlorohydrin; an epoxydized phenolic novolak resin; an epoxydized cresol novolak resin; an epoxydized polyolefin; an alicyclic epoxy resin; and a urethane-modified epoxy resin. However, these are not critical.
The polythiol compound (a thiol compound having two or more thiol groups in one molecule) usable in accordance with the present invention is preferably a thiol compound in which basic impurities are contained in amounts as small as possible from the standpoint of the good shelf stability. Examples thereof include thiol compounds having two or more thiol groups per one molecule, which compounds can be produced through an esterification reaction of a polyol and a mercapto organic acid without the need of a basic substance as the reaction catalyst, such as trimethylolpropane tris(thioglycolate), pentaerythritol tetrakis(thioglycolate), ethylene glycol dithioglycolate, trimethylolpropane tris(&bgr;-thiopropionate), pentaerythritol tetrakis(&bgr;-thiopropionate) and dipentaerythritol poly(&bgr;-thiopropionate).
Likewise, a thiol compound having two or more thiol groups in one molecule which has been produced in the presence of a basic substance as the reaction catalyst and in which the alkali metal ion concentration has been reduced to 50 ppm or less through dealkalization, can also be used. Examples thereof include an alkyl polythiol compound such as 1,4-butanedithiol, 1,6-hexanedithiol or 1,10-decanedithiol; a terminal thiol group-containing polyether; a terminal thiol group-containing polythiol ether; a thiol compound obtainable by the reaction of an epoxy compound with hydrogen sulfide; and a terminal thiol group-containing thiol compound obtainable by the reaction of a polythiol compound with an epoxy compound.
Examples of the method of dealkalization of a polythiol compound product produced in the presence of a basic substance as the reaction catalyst include a method in which a polythiol compound product to be dealkalized is dissolved in an organic solvent such as acetone or methanol, and the res
Hirai Kiyomiki
Orikabe Hiroshi
Ajinomoto Co. Inc.
Aylward D.
Dawson Robert
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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