Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-04-08
2001-07-24
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S118000, C525S533000
Reexamination Certificate
active
06265470
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a curable composition for top coating, and to articles coated with it. Precisely, it relates to a curable composition for top coating favorable for cars, industrial machines, steel furniture, interior and exterior decorations for constructions, household electric appliances, plastic goods, etc., and to articles coated with the composition. More precisely, the invention relates to a curable composition for top coating, which forms coating films having high acid resistance and scratch resistance, good outward appearance, high waterproofness and weather resistance, and high hardness, and which has good storage stability, and to articles coated with it. The composition is especially favorable for top coating cars.
BACKGROUND ART
For coating cars, industrial machines, steel furniture, interior and exterior decorations for constructions, household electric appliances, plastics and others, coating compositions consisting essentially of melamine resins such as alkydmelamines, acrylic melamines and the like have heretofore been used.
However, the conventional coating compositions consisting essentially of such melamine resins are problematic in that they generate a large amount of harmful formalin when cured, and that the cured films have poor acid resistance and are therefore often corroded by acid rain. In particular, the problem with acid rain caused by recent air pollution has become more serious, and the conventional coating films are often etched, whitened or stained by acid rain.
In order to solve this problem, a coating composition has been proposed in Japanese Patent Application Laid-Open (JP-A) Hei-2-45577 and Hei-3-28650, in which are formed ester bonds that act as crosslinking points, through reaction of an acid with an epoxy group.
The coating film of the proposed composition has good acid resistance, but is still defective in that it is whitened in an accelerated weather resistance test. In addition, the low-temperature curability of the composition is poor, the coating film of the composition formed around car bodies is often scratched with brushes when the car bodies are washed with a car washer, and the storage stability of the composition is poor.
For finishing car bodies by top coating, generally employed is any of two types of metallic color finishing and solid color finishing.
For the metallic color finishing of those two, generally employed is a 2-coat 1-bake method of heating and curing coating composition, which comprises coating a substrate with a metallic base coat followed by overcoating it with a clear coat of an acrylic melamine resin composition in an wet-on-wet system.
For the other solid color finishing, generally employed is a 1-coat 1-bake method of using an alkydmelamine resin composition, in which the composition is heated and cured to form top coating. For recent severe requirements for the properties of coating films, including, for example, finish appearance, weather resistance, acid resistance, scratch resistance and stain resistance thereof, a method of overcoating a solid color-finished substrate with a clear coat of an acrylic melamine resin composition or the like has been proposed. However, even in the proposed method of overcoating the solid color finish with such a clear coat, coated articles having the properties of good acid resistance, good scratch resistance and good weather resistance could not as yet be obtained.
The present invention has been made in consideration of the current situation noted above, and its object is to provide a curable composition for top coating, which has good thermal curability to form good coating films having good acid resistance, weather resistance, waterproofness, scratch resistance and outward appearance, and which additionally has good storage stability. In particular, the composition forms excellent clear coats when used in forming car bodies. The invention further provides articles as coated with the composition.
DISCLOSURE OF THE INVENTION
The curable composition for top coating of the invention comprises (A) 100 parts by weight of a resin having at least 2 epoxy groups in one molecule and having an epoxy equivalent of from 200 to 2,000 g/mol, and (B) from 0.001 to 100 parts by weight of a compound having at least 2 carboxyl groups in one molecule, in a molar ratio of the epoxy group to the carboxyl group of from 0.2/1 to 5.0/1, and contains (C) at least one organic solvent selected from glycol monoalkyl ethers, vinyl ethers and cyclic ethers, and at least one selected from monoalkyl alcohol compounds and compounds capable of giving alcohols through hydrolysis, each in an amount of from 1.0 to 30 parts by weight relative to 100 parts by weight of the total solid resin content of the composition.
In the curable composition for coating noted above, the resin of the component (A) may have alcoholic hydroxyl groups in a ratio of not smaller than 400 g/mol in terms of the hydroxyl equivalent, and have hydrolyzable silyl groups in a ratio of not smaller than 500 g/mol in terms of the hydrolyzable silyl equivalent; and the component (B) may be an oligomer compound as obtained through half-esterification of a polyol compound with an acid anhydride to have at least 2 carboxyl groups in one molecule and have a molecular weight of not larger than 2,000.
The curable composition for coating of the invention may contain (D) a curing catalyst in an amount of from 0.001 to 10 parts by weight relative to 100 parts by weight of the total solid content of the components (A) and (B).
The curable composition for coating of the invention may contain (E) a hydroxyl group-having resin in an amount of from 0 to 80 parts by weight relative to 100 parts by weight of the total solid content of the components (A) and (B).
The hydroxyl group-having resin of the component (E) may be composed of from 5 to 30 parts by weight of at least one, hydroxyl group-having vinylic monomer and from 70 to 95 parts by weight of at least one vinylic monomer having no hydroxyl group. The resin may be a non-aqueous dispersed polymer to be prepared through dispersion polymerization of at least one, hydroxyl group-having vinylic monomer and at least one vinylic monomer having no hydroxyl group in an organic solution that contains an organic solvent-soluble polymer having a number-average molecular weight of from 1,000 to 25,000, and the non-aqueous dispersed polymer thus prepared is insoluble in the organic solution.
The curable composition of the invention may further contain (F) an amino resin in an amount of not larger than 30 parts by weight relative to 100 parts by weight of the total solid content of the components (A) and (B).
The coated article of the invention has a clear top coat as formed over the surface of the substrate previously coated with a coating composition that contains metallic powder and/or color pigment, in which the clear top coat consists essentially of the composition of the invention noted above.
The terminology “vinylic” as referred to herein is meant to indicate the group derived from a compound having polymerizable C═C bonding, such as vinyl group, vinylidene group, etc.
BEST MODES OF CARRYING OUT THE INVENTION
The constituent components (A) to (F) and others that may constitute the curable composition for top coating of the invention are described below in order.
Component (A)
The component (A) of the basic, epoxy group-having resin for use in the invention includes, for example, the following four types of resins [1], [2], [3], [4]:
[1] Epoxy group-having resin (hereinafter referred to as “resin [1]”).
[2] Resin having both epoxy and hydroxyl groups (hereinafter referred to as “resin [2]”).
[3] Resin having both epoxy and hydrolyzable silyl groups (hereinafter referred to as “resin [3]”).
[4] Resin having all epoxy, hydrolyzable silyl and hydroxyl groups (hereinafter referred to as “resin [4]”).
These resins [1] to [4] are des
Inoue Masaharu
Nakamura Seigo
Nanbu Toshirou
Aylward D.
Dawson Robert
Jordan and Hamburg LLP
Kaneka Corporation
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