Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1993-03-16
1995-05-23
Zitomer, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
523427, 5253273, 5253288, 5253292, 525523, 525533, C08G 5942
Patent
active
054182972
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to novel crosslinking agents and novel curable compositions having the agent incorporated therein.
BACKGROUND ART
Powder coating compositions are already known which are curable on crosslinking and which comprise an epoxy-containing resin and a compound or resin having a cyclic acid anhydride group and a free carboxyl group. These compositions have actually useful properties. However, when the powder composition is made into a coating composition of the organic solvent type, the resulting composition is low in storage stability and further has the drawback that it is difficult for the liquid composition to have a high solids content. Also known are coating compositions of the organic solvent type which comprise a resin containing both epoxy and hydroxyl, and a cyclic acid anhydride, such as succinic anhydride or methylhexahydrophthalic anhydride, for curing the resin by crosslinking, whereas the acid anhydride has the drawback of being susceptible to hydrolysis, for example, owing to the presence of water in the pigment, diluting solvent, air, etc. and therefore impairing the storage stability and curability of the composition.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a novel crosslinking agent which is useful for curing epoxy-containing resins, epoxy- and hydroxyl-containing resins and like resins by crosslinking.
Another object of the invention is to provide a novel curable composition having the crosslinking agent incorporated therein and free of the foregoing drawbacks of the prior art.
These and other objects of the present invention will become apparent from the following description.
The present invention provides a crosslinking agent which comprises a compound having at least two noncyclic acid anhydride groups and represented by the following formula ##STR2## wherein R is a monovalent hydrocarbon group having 2 to 50 carbon atoms, R' is a bivalent hydrocarbon group having 2 to 50 carbon atoms, the hydrocarbon groups R and R' containing or not containing an ether linkage, urethane linkage or ester linkage, and n is an integer of 1 to 500.
The present invention further provides a curable composition comprising: having at least one epoxy group and at least one hydroxyl group in the molecule, (ii) a resin mixture of a resin having at least two epoxy groups in the molecule and a resin having at least two hydroxyl groups in the molecule, and (iii) a resin having at least two epoxy groups in the molecule, and
We have Conducted intensive research to overcome the foregoing drawbacks of the prior art and found the following facts.
(1) The compound represented by the formula (I) is suitable as a crosslinking agent for curing epoxy-containing resins and epoxy- and hydroxyl-containing resins by crosslinking.
(2) When the crosslinking agent of the formula (I) is admixed with an epoxy-containing resin or epoxy- and hydroxyl-containing resin, a composition is obtained which is curable by crosslinking through an addition reaction between the epoxy group and the noncyclic acid anhydride group in the compound, or through an addition reaction between the hydroxyl group and the noncyclic acid anhydride group and an addition reaction between a carboxyl group produced by the cleavage of the acid anhydride group and the epoxy group.
(3) Since the crosslinking agent does not contain any free carboxyl group which is a polar group, the above composition is low in viscosity. Coating compositions of high solids content are therefore available with ease.
(4) The crosslinking agent, which is not a cyclic acid anhydride but a noncyclic acid anhydride, is less likely to hydrolyze. Accordingly, the agent is not susceptible to hydrolysis even if water is present in solvents, pigments, etc. which will be used conjointly with the agent. Thus, the agent is unlikely to impair the storage stability or crosslinking curability.
(5) The crosslinking agent permits the composition to form cured coatings of improved scratch resistance.
(6) High storage st
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patent: 5179189 (1993-01-01), Domb et al.
Lee et al. "Handbook Of Epoxy Resins", 12-2-12-4, (1967) McGraw-Hill (New York).
Kansai Paint Company Limited
Zitomer Fred
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