Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1996-08-13
2001-01-23
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S402000, C523S408000, C523S409000, C523S412000, C523S414000, C524S108000, C524S109000, C524S114000, C524S510000, C524S531000
Reexamination Certificate
active
06177488
ABSTRACT:
The present invention relate to a novel aqueous colored base coating composition which is capable of forming a coating film excellent in chipping resistance, water resistance and the like, and a novel method for forming a multi-layer topcoat comprising a colored base coat and a clear coat, the topcoat being excellent in chipping resistance, intercoat adhesion, water resistance, acid resistance, weatherability and the like.
Substrates such as automotive exterior panels are usually finished by successively forming an undercoat such as a cationic electrodeposition coat or the like, an intercoat and a topcoat. The topcoat is formed generally by a 2-coat system using a solid- or metallic-colored base coating composition and a clear coating composition.
Conventionally, for forming the topcoat, an aqueous coating composition mainly comprising a hydroxyl- and carboxyl-containing acrylic resin, a melamine resin, a neutralizing agent and a coloring pigment, and a coating composition mainly comprising a hydroxyl-containing resin and a melamine resin are chiefly used as the colored base coating composition and the clear coating composition, respectively.
However, said aqueous colored base coating composition has the drawbacks of giving a coating film which is unsatisfactory in strength and poor in chipping resistance, water resistance and the like. Further, the topcoat formed from said base coating composition and the clear coating composition mentioned above is unsatisfactory in chipping resistance, intercoat adhesion between the colored base coat and the clear coat (hereinafter referred to simply as “intercoat adhesion”), water resistance, weatherability and the like. On the other hand, it has been proposed to improve the acid resistance of the topcoat by using a clear coating composition which does not contain a melamine resin and is cured by the crosslinking reaction between a carboxyl group and an epoxy group. However, the resulting topcoat is also unsatisfactory in chipping resistance, intercoat adhesion, water resistance, weatherability and the like.
An object of the present invention is to provide a novel aqueous coating composition which is capable of forming a coating film excellent in chipping resistance, water resistance and the like.
Another object of the present invention is to provide a method for forming a multi-layer topcoat which is good in acid resistance, chipping resistance, intercoat adhesion, water resistance, weatherability and the like.
These and other objects of the invention will become apparent from the following description.
The present invention provides an aqueous colored base coating composition (A) comprising a hydroxyl- and carboxyl-containing acrylic resin (A-1), a melamine resin (A-2), an alicyclic epoxy-containing compound (A-3), a neutralizing agent (A-4) and a coloring pigment (A-5).
The present invention also provides a method for forming a topcoat which comprises applying the aqueous colored base coating composition (A) to a substrate and applying to the base coat an organic solvent type clear coating composition (B) to be cured by the crosslinking reaction between a carboxyl group and an epoxy group.
The present inventors conducted extensive research and found that a coating film excellent in chipping resistance, water resistance and the like can be formed when using, as an aqueous colored base coating composition, a composition which comprises a hydroxyl- and carboxyl-containing acrylic resin, a melamine resin, a neutralizing agent and a coloring pigment and further contains an alicyclic epoxy-containing compound. The present inventors also found that a multi-layer topcoat which is good in acid resistance, chipping resistance, intercoat adhesion, water resistance, weatherability and the like can be formed when using said colored base coating composition and an organic solvent type coating composition to be cured by the crosslinking reaction between a carboxyl group and an epoxy group. The present invention has been accomplished based on these novel findings.
The aqueous colored base coating composition (A) of the present invention is described below in detail.
The aqueous colored base coating composition (A) mainly comprises a hydroxyl- and carboxyl-containing acrylic resin (A-1), a melamine resin (A-2), an alicyclic epoxy-containing compound (A-3), a neutralizing agent (A-4) and a coloring pigment (A-5). Water is chiefly used as the solvent or disperse medium for the coating composition (A).
The component (A-1) is an acrylic resin having at least one hydroxyl group and at least one carboxyl group in one molecule.
Said acrylic resin is obtained by copolymerizing a hydroxyl-containing monomer, a carboxyl-containing monomer and an acrylic monomer as the essential components, together with other monomers when necessary.
The hydroxyl-containing monomer is a compound having at least one hydroxyl group and at least one polymerizable unsaturated bond in one molecule. Examples of said monomer include monoesterified products of acrylic or methacrylic acid and a C
2-10
glycol having two hydroxyl groups, such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate and the like.
The carboxyl-containing monomer is a compound having at least one carboxyl group and at least one polymerizable unsaturated bond in one molecule. Examples of said monomer are acrylic acid, methacrylic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, and anhydrides and half-esterified products of these acids.
The acrylic monomer is a monoesterified product of acrylic or methacrylic acid and a C
1-20
monohydric alcohol having one hydroxyl group. Useful acrylic monomers are, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate and the like.
Said other monomers are monomers other than those mentioned above, and include, for example, styrene, vinyltoluene, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, glycidyl acrylate, glycidyl methacrylate and the like. Said other polymerizable monomers are used in an amount equivalent to or less than the amount of the acrylic monomer.
The component (A-1) is obtained by polymerizing the above monomers by a known method such as solution polymerization, emulsion polymerization or the like, and preferably has a number average molecular weight of about 3,000 to about 100,000, especially about 5,000 to about 50,000, a hydroxyl value of about 20 to about 150 mg KOH/g, especially about 30 to about 100 mg KOH/g and an acid value of about 5 to about 100 mg KOH/g, especially about 10 to about 70 mg KOH/g.
The acrylic resin (A-1) is used in the form of an aqueous solution or dispersion wherein the carboxyl groups in the resin are neutralized with the component (A-4) described below.
The component (A-2) is a melamine resin which acts as the crosslinking agent for the acrylic resin (A-1). Usable as the component (A-2) are methylolated melamine, alkyletherified melamine obtained by etherifying some or all of the methylol groups with a C
1-10
monohydric alcohol, and the like. The component (A-2) preferably has a number average molecular weight of about 400 to about 3,000, especially about 500 to about 1,200, and may be either hydrophobic or hydrophilic.
The component (A-3) is an alicyclic epoxy-containing compound having at least one alicyclic epoxy group in one molecule. The alicyclic epoxy group in said compound is a functional group wherein the epoxy group consists of two adjacent carbon atoms which form an alicyclic hydrocarbon skeleton ring, and one oxygen atom. Said alicyclic hydrocarbon skeleton may be a 4- to 10-membered, preferably 5- or 6-membered saturated hydrocarbon ring, or a condensed hydrocarbon ring consisting of at least two hydrocarbon rings. Further, these hydrocarbon rings may be bonded to each other by a bridge such as an alkylene group or the like, to form bridged hydrocarbon rings.
Specific examples of the alicyclic epoxy compounds
Kajima Junichi
Kasari Akira
Oda Hiroaki
Shimakawa Mikio
Armstrong, Westerman Hattori, McLeland & Naughton
Kansai Paint Company Limited
Reddick Judy M.
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