Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-09-12
2002-08-27
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S025000, C528S106000, C528S403000, C528S408000, C528S029000, 82, 82, 82
Reexamination Certificate
active
06441106
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a curing agent for epoxy resin, an epoxy resin composition and a method for preparing a siloxane-modified phenol resin.
BACKGROUND ART
Epoxy resins have been used usually in combination with curing agents. Particularly, phenol novolac resins have been suitably used as curing agents for epoxy resin in the field of electric and electronic materials because of their excellent heat resistance, chemical resistance, electrical characteristic, etc. However, the recent development in the electric and electronic material field has been requiring high-performance epoxy resin compositions. Therefore, the epoxy resin compositions containing the phenol novolac resins as curing agents do not have sufficient heat resistance.
In order to improve the heat resistance of the epoxy resin compositions, glass fibers, glass particles, mica and like fillers are added to epoxy resins in addition to phenol novolac resins used as curing agents. However, these methods using fillers can not impart sufficient heat resistance to the resin compositions. By these methods, the transparency of the cured epoxy resin composition is deteriorated and the interfacial adhesion between the fillers and resins is lowered. Thus, the cured epoxy resin compositions are given insufficient mechanical properties such as elongation rate.
Japanese Unexamined Patent Publication No. 1997-216938 proposes a method for improving the heat resistance of cured epoxy resin composition. In this method, the complex of a phenol novolac resin and silica prepared by hydrolysis and condensation of alkoxysilane in the presence of a phenol novolac resin is used as a curing agent for epoxy resin. The heat resistance of the cured epoxy resin composition comprising such complex as a curing agent is improved to some extent. However, water contained in the curing agent or water and alcohols such as methanol produced during curing cause voids (air bubbles) inside the cured product. Further, increasing the amount of alkoxysilane to further improve the heat resistance of the cured product results in impaired transparency and whitening of the product due to silica aggregation. In addition, solation of a large amount of the alkoxysilane necessitates a large amount of water, which leads to the bends and cracks in the cured product.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a novel phenol resin-based curing agent for epoxy resin which is free from the aforementioned problems of the prior art.
Another object of the present invention is to provide a novel epoxy resin composition which is capable of providing cured products having high heat resistance and no voids (air bubbles) or cracks using a specific phenol resin-based curing agent for epoxy resin.
Another object of the present invention is to provide a novel method for preparing a siloxane-modified phenol resin which is useful as a phenol resin-based curing agent for epoxy resin.
Other objects and features of the present invention will be apparent from the following description.
The present invention provides a curing agent for epoxy resin, the curing agent containing a siloxane-modified phenol resin (
3
) obtained by dealcoholization condensation reaction between a phenol resin (
1
) and hydrolyzable alkoxysilane (
2
).
The present invention also provides an epoxy resin composition comprising an epoxy resin and the above curing agent for epoxy resin.
Further, the present invention provides a method for preparing a siloxane-modified phenol resin (
3
) characterized by subjecting a phenol resin (
1
) and hydrolyzable alkoxysilane (
2
) to dealcoholization condensation reaction.
The inventors of the present invention conducted extensive research to solve the above-mentioned problems of the prior art. Consequently, the inventors found the following: by using the epoxy resin composition comprising a siloxane-modified phenol resin obtained by dealcoholization condensation reaction of a phenol resin and hydrolyzable alkoxysilane as a curing agent for epoxy resin, a cured product having high heat resistance and no voids (air bubbles) and cracks can be obtained. The present invention was accomplished based on this novel finding.
In the present invention, the phenol resins (
1
) forming the siloxane-modified phenol resin (
3
) may be any of novolac phenol resins and resol phenol resins. The former can be prepared by reacting a phenol compound and an aldehyde compound in the presence of an acid catalyst, and the latter by reacting a phenol compound and an aldehyde compound in the presence of an alkaline catalyst. The resol phenol resins usually contain condensation water, which may cause hydrolysis of the hydrolyzable alkoxysilane (
2
). Therefore, the novolac phenol resins are preferably used in the present invention. The phenol resins (
1
) preferably have an average phenolic unit number of about 3 to about 8.
Examples of useful phenol compounds mentioned in the above include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, p-ethylphenol, p-isopropylphenol, p-tertiary butyl phenol, p-chlorophenol and p-bromophenol. Examples of useful formaldehyde compounds include formalin and formaldehyde-generating compounds such as paraformaldehyde, trioxane and tetraoxane. As the acid catalyst or alkaline catalyst, any of those conventionally known is useful.
An example of the hydrolyzable alkoxysilane (
2
) forming the siloxane-modified phenol resin (
3
) in the present invention is a compound represented by the following formula or the partial condensate thereof:
R
1
n
Si(OR
2)
4−n
(wherein n is an integer of 0 to 2; R
1
represents a lower alkyl group which may have a functional group directly bonded to a carbon atom, an aryl group or an unsaturated aliphatic hydrocarbon group; when n is 2, the two R
1
's may be the same or different; R
2
represents a hydrogen atom or a lower alkyl group and may be the same or different, with the proviso that at least one R
2
group is a lower alkyl group.). Examples of the above functional group include a vinyl group, a mercapto group, an epoxy group and a glycidoxy group. The term lower alkyl group indicates a straight-chain or branched-chain alkyl group having 6 carbon atoms or less.
The hydrolyzable alkoxysilane (
2
) may be suitably selected from the compounds represented by the above formula or their partial condensates, and may be used singly or at least two of them in mixture. However, the hydrolyzable alkoxysilane (
2
) is preferably a partial condensate whose average number of Si per molecule is about 2 to about 100. The hydrolyzable alkoxysilane whose average number of Si is less than 2 suffers an increase in the amount of unreacted alkoxysilane discharged together with the alcohol from the reaction system during the dealcoholization condensation reaction with the phenol resin (
1
). When the average number of Si is 100 or greater, the reactivity of the alkoxysilane with the phenol resin (
1
) is decreased and thus the desired substance is hard to obtain. Because of the availability of commercial products, the average number of Si per molecule may be about 3 to about 20.
Examples of the hydrolyzable alkoxysilane (
2
) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, tetrabutoxysilane and like tetraalkoxysilanes; methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 3,4-epoxycyclohexylethyltrimetboxysilane, and like trialkoxysilanes; dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane and like dialkoxysilanes; and the partial cond
Goda Hideki
Takeda Shoji
Arakawa Chemical Industries Ltd.
Baker & Botts LLP
Dawson Robert
Robertson Jeffrey B.
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