Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2001-01-12
2003-02-25
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S027000, C528S081000, C528S112000, C528S121000, C528S123000
Reexamination Certificate
active
06525160
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an epoxy resin composition and a method for preparing a silane-modified epoxy resin.
BACKGROUND ART
Epoxy resins have been used usually in combination with curing agents in the field of electric and electronic materials. The recent development in the electric and electronic material field has been requiring high-performance cured products of epoxy resin compositions. In particular, improved heat resistance is desired.
In order to improve the heat resistance of the cured products of the epoxy resin compositions, the compositions containing glass fibers, glass particles, mica and like fillers in addition to epoxy resins and curing agents are used. However, these methods using fillers can not impart sufficient heat resistance to the resin compositions. By these methods, the transparency of the resulting cured products is deteriorated and the interfacial adhesion between the fillers and epoxy resins is lowered. Thus, the cured products are given insufficient mechanical properties such as elongation rate.
Japanese Unexamined Patent Publication No. 1996-100107 proposes a method for improving the heat resistance of cured products of epoxy resin compositions by using the complex of an epoxy resin and silica. The complex of an epoxy resin and silica is prepared by adding hydrolyzable alkoxysilane to a solution of a partially cured epoxy resin to further cure the partially cured product; hydrolyzing the alkoxysilane to cause solation; and polycondensing the sol to cause gelation. The heat resistance of the cured product prepared from such complex is improved to some extent compared to the cured product of the epoxy resin by itself. However, water contained in the complex or water and alcohols 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 the aggregation of silica produced by sol-gel curing reaction. 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.
Also proposed are a composition which is produced by combining a silane-modified epoxy resin prepared by reacting the epoxy resin with a silicone compound, and a phenol novolac resin as a curing agent (Japanese Unexamined Patent Publication No. 1991-201466); and a composition prepared by combining a silane-modified epoxy resin produced by reacting bisphenol A epoxy resin, tetrabromobisphenol A and a methoxy-containing silicone intermediate, and a phenol novolac resin as a curing agent (Japanese Unexamined Patent Publications No. 1986-272243, No. 1986-272244). However, the cured products of these epoxy resin compositions do not have sufficient heat resistance since the main structural unit of the silicone compound and methoxy-containing silicone intermediate is a diorganopolysiloxane unit which can not produce silica.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a novel epoxy resin composition and a method for preparing a silane-modified 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 or cracks using a specific silane-modified epoxy resin, and a method for preparing said silane-modified epoxy resin.
Other objects and features of the present invention will be apparent from the following description.
The present invention provides an epoxy resin composition comprising an alkoxy-containing silane-modified epoxy resin (A) which is obtainable by dealcoholization condensation reaction between a bisphenol epoxy resin (
1
) and hydrolyzable alkoxysilane (
2
); and a curing agent (B) for epoxy resin.
Further, the present invention provides a method for preparing an alkoxy-containing silane-modified epoxy resin, the method comprising dealcoholization condensation reaction between the bisphenol epoxy resin (
1
) and the hydrolyzable alkoxysilane (
2
).
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 specific silane-modified epoxy resin (A) obtained by dealcoholization condensation reaction of a bisphenol epoxy resin (
1
) and hydrolyzable alkoxysilane (
2
), and a curing agent (B) for epoxy resin, an epoxy resin-silica hybrid having high heat resistance and no voids or cracks can be obtained as a cured product. The present invention was accomplished based on this novel finding.
The raw material of the alkoxy-containing silane-modified epoxy resin (A) of the present invention, namely bisphenol epoxy resin (
1
), can be obtained by the reaction between bisphenols and epichlorohydrin or &bgr;-methylepichlorohydrin and like haloepoxides. Examples of the bisphenols include those obtained by the reaction between phenol or 2,6-dihalophenol and formaldehyde, acetaldehyde, acetone, acetophenone, cyclohexanone, benzophenone and like aldehydes or ketones; those obtained by oxidation of dihydroxyphenylsulfide with a peracid; and those obtained by etherification reaction of one or more hydroquinones.
In addition, the bisphenol epoxy resin (
1
) has a hydroxyl group which can form silicic acid ester by dealcoholization condensation reaction with the hydrolyzable alkoxysilane (
2
). Not all the molecules which constitute the bisphenol epoxy resin (
1
) need to have the hydroxyl group, but the bisphenol epoxy resin (
1
) itself needs to have the hydroxyl group.
The epoxy equivalent of the bisphenol epoxy resin (
1
) differs depending on the structure of the bisphenol epoxy resin (
1
). Therefore, the bisphenol epoxy resin (
1
) having an epoxy equivalent suitable for its application may be selected. Usually, the epoxy equivalent is preferably about 180 to about 5,000 g/eq. The epoxy equivalent lower than 180 g/eq decreases the amount of alcoholic hydroxyl groups which react with the hydrolyzable alkoxysilane (
2
) in the epoxy resin molecule. This leads to the reduced formation of the bonds between the epoxy resin (
1
) and alkoxysilane (
2
) caused by dealcoholization reaction. As a result, in the epoxy resin-silica hybrids produced when the alkoxy-containing silane-modified epoxy resin (A) is cured with the curing agent (B), insufficient bonding between the silica and epoxy resin occurs. This prevents silica from being uniformly dispersed in the resin. Thus, the cured product is likely to be unfavorably whitened because of the phase separation of the silica and epoxy resin in the product. The epoxy equivalent higher than 5,000 g/eq increases the number of hydroxyl groups in the epoxy resin molecule. Thus, the epoxy resin is likely to disadvantageously undergo gelation during the dealcoholization condensation reaction with multifunctional hydrolyzable alkoxysilane (
2
). The above-specified epoxy equivalent of 180 to 5,000 g/eq corresponds to a number average molecular weight of 360 to 10,000.
As the bisphenol epoxy resin (
1
), bisphenol A epoxy resin obtained by using bisphenol A is particularly preferable because of its wide applicability and inexpensiveness.
The above bisphenol A epoxy resin is a compound represented by the formula
wherein the average of m is 0.07 to 16.4. The epoxy resin of the formula (I) may contain molecules for which m is 0 provided that it also contains molecules for which m is 1 or greater.
An epoxy compound having reactivity with the hydrolyzable alkoxysilane (
2
) may be used in combination with the bisphenol epoxy resin (
1
). Examples of the epoxy compound include glycidyl ester epoxy resins obtained by reacting phthalic acid, dimer acid and like polybasic acids with epichlorohydrin, and glycidol and the like. The amount of the epoxy compound to be used in combination is usually about 3
Goda Hideki
Higashino Tetsuji
Arakawa Chemical Industries Ltd.
Baker & Botts LLP
Dawson Robert
Zimmer Marc S
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