Curable resin composition

Details Curable resin composition Curable resin composition

2001-11-20

2004-05-18

Robertson, Jeffrey B. (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...

C528S015000, C528S025000, C528S027000, C528S029000, C528S031000

Reexamination Certificate

active

06737482

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a curable resin composition which can be used broadly in various applications such as adhesives and coatings, has toughness and high bond strength, and shows good adhesion to various adherends.
BACKGROUND ART
Epoxy resin has been used in a broad spectrum of applications such as various molding materials, adhesives, coatings, plywood, laminates and so on but, because of its cured brittleness, has the drawback of low peel strength when used in adhesives and the like.
To overcome the above-mentioned drawback, it was proposed to achieve improvements in cured brittleness and peel strength by using a composition comprising a blend of such an epoxy resin with a reactive silicon group-containing polyoxyalkylene polymer which would give a rubber-like elastomer on curing at atmospheric temperature (e.g. Japanese Kokai Publication Sho-61-268720).
However, such a composition is inferior to a composition comprised of an epoxy resin alone in cured tensile strength and tensile shear bond strength so that it has not been used successfully in applications calling for high strength.
Japanese Kokoku Publication Hei-7-2828 proposes to facilitate handling before curing and, at the same time, improve the tensile characteristics, chemical resistance and water resistance by narrowing the molecular weight distribution of the reactive silicon group-containing polyoxyalkylene polymer in such a composition.
However, neither of the above publications refers to the relationship of the silicon group introduction rate of a reactive silicon group-containing polyoxyalkylene polymer to bond strength and adhesion.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a curable resin composition reflecting improvements in cured tensile strength and tensile shear bond strength and in adhesion to various substrates while the toughness and high peel strength of a reactive silicon group-containing polyoxyalkylene polymer-epoxy resin blend are fully sustained.
The present invention, therefore, is directed to a curable resin composition comprising
(I) a reactive silicon group-containing polyoxyalkylene polymer wherein the introduction rate of a reactive silicon group into a molecular chain terminus is not less than 85% as analyzed by
1
H-NMR spectrometry and
(II) an epoxy resin.
DETAILED DESCRIPTION OF THE INVENTION
The above object of the invention is accomplished by insuring that, in a curable resin composition comprising a reactive silicon group-containing polyoxyalkylene polymer and an epoxy resin, the introduction rate of the reactive silicon group into the molecular chain terminus of the former will be not less than 85% as analyzed by
1
H-NMR spectrometry.
The term “reactive silicon group” in the context of the present invention means any group capable of forming a siloxane bond upon intergroup condensation and, as such, is not particularly restricted. However, the group represented by the following general formula (4) can be mentioned as a typical example.
—(Si(R
3
2-b
)(X
b
)O)
m
Si(R
4
3-a
)X
a
  (4)
(wherein R
3
and R
4
each represents an represents an alkyl group containing 1 to 20 carbon atoms, an aryl group containing 6 to 20 carbon atoms, an aralkyl group containing 7 to 20 carbon atoms or a triorganosiloxy group of the formula (R′)
3
SiO—; when two or more R
3
and R
4
groups are present, they may be the same or different; R′ represents a univalent hydrocarbon group containing 1 to 20 carbon atoms and the three R′ groups may be the same or different; X represents a hydroxyl group or a hydrolyzable group and when two or more X groups are present, they may be the same or different; a represents 0, 1, 2 or 3 and b represents 0, 1 or 2; as regards b in —Si(R
3
2-b
)(X
b
)—O— which occurs in m repeats, the value of b may be different over the repeats; m represents an integer of 0 to 19; provided, however, that the relation of a+&Sgr;b≧1 is satisfied).
The hydrolyzable group mentioned above for X is not particularly restricted but can be a known hydrolyzable group. Thus, for example, hydrogen, halogen, alkoxy, acyloxy, ketoximato, amino, amido, acid amido, aminoxy, mercapto and alkenyloxy can be mentioned. Among these groups, in view of mild hydrolyzability and ease of handling, alkoxy groups such as methoxy, ethoxy, propoxy and isopropoxy are preferred.
The hydroxyl group and/or hydrolyzable group may be attached, in a varying number of 1 to 3, to one silicon atom but the (a+&Sgr;b) value is preferably in the range of 1 to 5. When two or more hydroxyl and/or hydrolyzable groups exist in the reactive silicon group, they may be the same or different.
The number of silicon atoms in the reactive silicon group may be one or more than one but, in the case of the reactive silicon group in which silicon atoms are linked by siloxane bonding or the like, may be about 20.
The reactive silicon group of the following general formula (5) is preferred from availability points of view.
—Si(R
4
3-a
)X
a
  (5)
(wherein R
4
, X and a are as defined above)
Referring to the above general formulas (4) and (5), R
3
and R
4
each may be an alkyl group such as methyl or ethyl; a cycloalkyl group such as cyclohexyl; an aryl group such as phenyl; an aralkyl group such as benzyl; or a triorganosiloxy group represented by the formula (R′)
3
SiO— in which R′ stands for methyl or phenyl, for instance. Particularly preferred for R
3
, R
4
and R′ are methyl.
Referring to the polyoxyalkylene polymer (I), the introduction rate of the reactive silicon group of formula (4) or (5) into the molecular chain terminus is not less than 85% as analyzed by
1
H-NMR spectrometry. By insuring that the introduction rate of the reactive silicon group is not less than 85%, tensile strength and tensile shear bond strength of the cured products as well as adhesion to various substrates thereof can be improved while the toughness and high peel strength can be sustained. If the above-mentioned introduction rate is less than 85%, tensile strength and tensile shear bond strength as well as adhesion to various substrates will not be sufficient so that the object of the invention will not be accomplished. The introduction rate of the reactive silicon group is preferably not less than 90% for expression of more satisfactory characteristics of the cured products, more preferably not less than 95% for expression of still better characteristics of the cured products. Still more preferred introduction rate is not less than 98%.
The introduction rate of such a reactive silicon group may be determined by various techniques but, as used in this specification, the term means the value found by
1
H-NMR analysis of the reactive silicon group-containing polyoxyalkylene polymer (I). The introduction rate of the reactive silicon group can be defined as the value found by comparing, from
1
H-NMR data, the integral value of the molecular chain termini into which the reactive silicon group has been introduced, with the integral value of the molecular chain termini into which the reactive silicon group has not been introduced and calculating the percentage of the termini into which the reactive silicon group has been introduced based on the total number of molecular termini.
The number of units of said reactive silicon group per molecule need be at least one but is preferably an average of 1.5 to 4 for insuring sufficient curability.
The main chain structure of the polyoxyalkylene polymer for use as the (I) component in the present invention need only to be a polymer exclusively composed of repeating units of —R—O— in which R may be a bivalent organic group containing 1 to 20 carbon atoms. Moreover, the polymer may be a homopolymer in which all repeating units are the same or a copolymer comprising 2 or more kinds of repeating units. Its main chain structure may even have a branched structure.
R specifically includes —CH
2
CH
2
—, —CH(CH
3
)CH
2
—, —CH(C
2
H
5
)CH
2
—, —C(CH
3
)
2
CH
2
— and —CH
2
CH
2
CH
2
CH
2
—, among others. The par

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