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
2001-04-13
2003-09-23
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...
C525S100000, C525S101000, C525S119000, C525S393000, C525S403000
Reexamination Certificate
active
06624260
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a rubber-modified epoxy resin composition which can be easily handled before curing due to the low viscosity thereof and has an elevated peel strength without worsening the shear strength of the epoxy resin. This composition is sufficiently curable even at a relatively low temperature and achieves an excellent shear strength and peel strength.
DESCRIPTION OF THE RELATED ART
Owing to the excellent mechanical characteristics, electrical characteristics, heat resistance and adhesiveness, epoxy resins have been widely employed in, for example, casting compounds, laminates, sealing compounds, adhesives, coatings, maintenances for concrete and various composite materials. However, cured matters thus obtained are hard and brittle and thus suffer from a problem that only a poor peel strength can be achieved when employed as an adhesive.
To overcome the problem of the brittleness of cured epoxy resins, attempts have been made to modify these resins with the use of liquid carboxyl-terminal acrylonitrile-butadiene copolymers (CTBN) and thus an improvement in the peel strength is successfully achieved while sustaining a high shear strength. In the CTBN-modification method, however, phase separation is performed in the step of curing. Therefore, the dispersion state and the acrylonitrile-butadiene copolymer (NBR) phase size are frequently changed depending on the curing agent and curing conditions employed, which makes it difficult to achieve stable physical properties.
JP-A-6-107908 proposes a method wherein crosslinked NBR has been preliminarily dispersed in an uncured epoxy resin so as to prevent changes in the physical properties depending on the curing conditions (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). Although the scattering of the physical properties can be overcome by this method, there still remains a problem that the epoxy resin has a high viscosity before curing and thus the working properties are seriously damaged.
SUMMARY OF THE INVENTION
An object of the invention is to improve the working properties of such a rubber-modified epoxy resin to thereby give stable adhesion properties (for example, improved peel strength) without worsening the shear strength.
To solve these problems, the inventors have conducted intensive studies. As a result, they have developed a curable composition based on an epoxy resin comprising a reactive silicon group-containing polyoxyalkylene polymer, optionally together with a copolymer having a molecular chain comprising (preferably substantially consisting of) one or more alkyl acrylate monomer units and/or alkyl methacrylate monomer units, and a specific curing agent for epoxy resins at a specific ratio, thereby completing the invention.
According to the first aspect, the invention relates to a curable composition comprising, per 100 parts by weight of an epoxy resin which is the component (A), from 1 to 50 parts by weight of a reactive silicon group-containing polyoxyalkylene polymer which is a component (B), and from 1 to 90 parts by weight of a curing agent for epoxy resins, which is a component (C), capable of compatibilizing the mixture of the component (A) and the component (B) at room temperature.
Note that throughout this specification, components D and Da are referred to as copolymers; however, it should be understood that components D and Da may be either a homopolymer or a copolymer.
In a preferable embodiment, the invention relates to a curable composition comprising, per 100 parts by weight of an epoxy resin which is the component (A)a, from 1 to 50 parts by weight of a reactive silicon group-containing polyoxyalkylene polymer which is a component (B), from 1 to 50 parts by weight of a copolymer, which is a component (D), having a molecular chain comprising (preferably substantially consisting of) one or more alkyl acrylate monomer units and/or alkyl methacrylate monomer units, and from 1 to 90 parts by weight of a curing agent for epoxy resins, which is a component (C), capable of compatibilizing the mixture of the component (A), the component (B) and the component (D) at room temperature.
In a still preferable embodiment, the invention relates to a curable composition as described above, wherein the reactive silicon group in the polyoxyalkylene polymer serving as the component (B) is represented by the following general formula (1):
—[Si(R
1
2−b
)(X
b
)O]
m
Si(R
2
3−a
)X
a
(1)
wherein R
1
and R
2
are the same or different and each represents an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, or a triorganosiloxy group represented by (R′)
3
SiO—, provided that when there are two or more R
1
s or R
2
s, they may be either the same or different (wherein R′ represents a monovalent hydrocarbyl group having 1 to 20 carbon atoms and three R′s may be either the same or different); X represents a hydroxyl group or a hydrolyzable group, and when there are two or more Xs, they may be either the same or different; a is 0, 1, 2 or 3 and b is 0, 1 or 2, provided that the requirement a+&Sgr;b≧2 is satisfied and b′s in m —Si(R
1
2−b
)(X
b
)—O— groups may be either the same or different; and m is an integer of 0 to 19.
In a still preferable embodiment, the invention relates to a curable composition as described above wherein the main chain skeleton of the polyoxyalkylene polymer serving as the component (B) comprises polyoxypropylene.
In a still preferable embodiment, the invention relates to a curable composition as described above wherein the component (D) is a copolymer having a molecular chain comprising (preferably substantially consisting of) (a) an alkyl acrylate monomer unit and/or an alkyl methacrylate monomer unit carrying an alkyl group having 1 to 8 carbon atoms, and (b) an alkyl acrylate monomer unit and/or an alkyl methacrylate monomer unit carrying an alkyl group having 10 or more carbon atoms.
In a still preferable embodiment, the invention relates to a curable composition as described above wherein the component (D) is a copolymer having a silicon-containing group which can be crosslinked by forming a siloxane bond.
In a still preferable embodiment, the invention relates to a curable composition as described above wherein the curing agent for epoxy resins serving as the component (C) is an alicyclic amine, a polyoxyalkylene amine or an epoxy-modified product of the same.
In a still preferable embodiment, the invention relates to a curable composition as described above wherein the curing agent for epoxy resins serving as the component (C) is an epoxy-modified product of isophoronediamine.
DETAILED DESCRIPTION OF THE INVENTION
Now, the invention will be described in greater detail.
As the epoxy resin which is to be used as the component (A) in the invention, use can be broadly made of publicly known ones. Examples thereof include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AD type epoxy resins, bisphenol S type epoxy resins and epoxy resins prepared by hydrogenating the same, glycidyl ester type epoxy resins, glycidylamine type epoxy resins, alicyclic epoxy resins, novolak type epoxy resins, urethane-modified epoxy resins having urethane bond, fluorinated epoxy resins, rubber-modified epoxy resins containing polybutadiene or NBR and flame-retardant epoxy resins such as glycidyl ether of tetrabromobisphenol A. Either one of these epoxy resins or a combination of two or more thereof may be used. It is particularly preferable to use a bisphenol A type resin from the viewpoints of working properties, curability, adhesive strength and the balance of the availability for adherends.
The reactive silicon group in the component (B) to be used in the invention is not particularly restricted. As typical examples thereof, groups represented by the following general formula (1) may be cited.
—[Si(R
1
2−b
)(X
b
)O]
m
Si(R
2
3−a
)X
a
Ando Katsuhiro
Kawakubo Fumio
Takase Junji
Armstrong Westerman & Hattori, LLP
Dawson Robert
Kaneka Corporation
Zimmer Marc S
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