Stock material or miscellaneous articles – Composite
Reexamination Certificate
2001-08-09
2003-06-24
Niland, Patrick D. (Department: 1714)
Stock material or miscellaneous articles
Composite
C428S423100, C428S500000
Reexamination Certificate
active
06582822
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to aqueous coating compositions and, more particularly, to their use in multi-component composite coating compositions as primers, pigmented or colored basecoats and/or transparent topcoats which provide good smoothness and appearance in automotive coating applications.
BACKGROUND OF THE INVENTION
Over the past decade, there has been a concerted effort to reduce atmospheric pollution caused by volatile solvents which are emitted during the painting process. However, it is often difficult to achieve high quality, smooth coating finishes, such as are required in the automotive industry, without using organic solvents which contribute greatly to flow and leveling of a coating.
One of the major goals of the coatings industry is to minimize the use of organic solvents by formulating waterborne coating compositions which provide a smooth, high gloss appearance, as well as good physical properties including resistance to acid rain. Unfortunately, many waterborne coating compositions, particularly those containing metallic flake pigments, do not provide acceptable appearance because they deposit as a rough film under conditions of low humidity. Although smooth films can be obtained if the humidity is controlled within narrow limits, this often is not possible in industrial applications without incurring considerable expense.
Therefore, it would be desirable to provide a waterborne coating composition which is useful as an original finish for automobiles and which can be applied as a smooth film under a variety of humidity conditions.
SUMMARY OF THE INVENTION
The present invention provides an aqueous coating composition comprising: (a) at least one crosslinkable film-forming resin; and (b) at least one amphiphilic adjuvant comprising: a water-soluble polar end comprising at least one terminal hydroxyl group; and a water-insoluble hydrocarbon end comprising at least seven contiguous carbon atoms, the adjuvant having an acid value of less than 30 and being present in an amount ranging from about 0.01 to about 25 weight percent on a basis of total resin solids of the aqueous coating composition, the film-forming resin and adjuvant being present in an aqueous medium.
Another aspect of the present invention is a multi-component composite coating composition comprising a basecoat deposited from an aqueous basecoat coating composition and a transparent topcoat applied over the basecoat in which the transparent topcoat is deposited from a topcoat coating composition, the basecoat coating composition comprising: (a) at least one crosslinkable film-forming resin; and (b) at least one amphiphilic adjuvant comprising: a water-soluble polar end comprising at least one terminal hydroxyl group; and a water-insoluble hydrocarbon end comprising at least seven contiguous carbon atoms, the adjuvant being present in an amount ranging from about 0.01 to about 25 weight percent on a basis of total resin solids of the basecoat coating composition. A substrate having a surface coating of the above multi-component composite coating composition is also provided.
Another aspect of the present invention is a method for increasing the surface tension of a basecoat in a multi-component composite coating composition comprising the steps of depositing an aqueous basecoat coating composition comprising at least one crosslinkable film-forming resin to form a crosslinked basecoat and applying a topcoat coating composition over the basecoat to form a transparent topcoat thereon, wherein the improvement comprises: the basecoat coating composition further comprising at least one amphiphilic adjuvant comprising: a water-soluble polar end comprising at least one terminal hydroxyl group; and a water-insoluble hydrocarbon end comprising at least seven contiguous carbon atoms, the adjuvant being present in an amount ranging from about 0.01 to about 25 weight percent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The aqueous film-forming coating composition of the present invention can be used as any of the waterborne compositions useful in coatings applications, particularly automotive applications. The aqueous coating composition of the present invention can be used as a monocoat, but preferably is used as a primer, colored base coat layer or transparent topcoat layer in a “color-plus-clear” coating system.
The aqueous coating composition of the present invention comprises one or more crosslinkable film-forming resins and one or more amphiphilic adjuvants, which will be discussed in detail below.
Useful crosslinkable film-forming resins include acrylic polymers, polyesters, including alkyds, polyurethanes, polyamides, polyethers and copolymers and mixtures thereof. These resins can be self-crosslinking or crosslinked by reaction with suitable crosslinking materials included in the coating composition.
Suitable acrylic polymers include copolymers of one or more alkyl esters of acrylic acid or methacrylic acid, optionally together with one or more other polymerizable ethylenically unsaturated monomers. Useful alkyl esters of acrylic acid or methacrylic acid include aliphatic alkyl esters containing from 1 to 30, and preferably 4 to 18 carbon atoms in the alkyl group. Non-limiting examples include methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, and 2-ethyl hexyl acrylate. Suitable other copolymerizable ethylenically unsaturated monomers include vinyl aromatic compounds such as styrene and vinyl toluene; nitriles such as acrylonitrile and methacrylonitrile; vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride; and vinyl esters such as vinyl acetate.
The acrylic copolymer can include hydroxyl functional groups which are often incorporated into the polymer by including one or more hydroxyl functional monomers in the reactants used to produce the copolymer. Useful hydroxyl functional monomers include hydroxyalkyl acrylates and methacrylates, preferably having 2 to 4 carbon atoms in the hydroxyalkyl group, such as hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, hydroxy functional adducts of caprolactone and hydroxyalkyl acrylates, and corresponding methacrylates. The acrylic polymer can be prepared with N-(alkoxymethyl)acrylamides and N-(alkoxymethyl) methacrylamides which result in self-crosslinking acrylic polymers.
Acrylic polymers can be prepared via aqueous emulsion polymerization techniques and used directly in the preparation of the aqueous coating composition, or via organic solution polymerization techniques with groups capable of salt formation such as acid or amine groups. Upon neutralization of these groups with a base or acid, the polymers can be dispersed into aqueous medium.
As discussed above, the crosslinkable film-forming resin can be an alkyd resin or a polyester. Such polymers can be prepared in a known manner by condensation of polyhydric alcohols and polycarboxylic acids. Suitable polyhydric alcohols include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, diethylene glycol, glycerol, trimethylol propane and pentaerythritol. Suitable polycarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid and trimellitic acid. Besides the polycarboxylic acids mentioned above, functional equivalents of the acids such as anhydrides where they exist or lower alkyl esters of the acids such as methyl esters can be used. Where it is desired to produce air-drying alkyd resins, suitable drying oil fatty acids can be used and include those derived from linseed oil, soya bean oil, tall oil, dehydrated castor oil, or tung oil. The polyesters and alkyd resins contain a portion of free hydroxyl and/or carboxyl groups which are available for further crosslinking reactions.
Polyurethanes can also be used as the crosslinkable film-forming resin of the coating composition. Useful polyurethanes include polymeric polyols which are prepared by
Faler Dennis L.
Glas Djurdjica
Hille Hans-Dieter
Jäger Michael
Metzger Walter
Miles Jacques B.
Niland Patrick D.
PPG Industries Ohio Inc.
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