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
2000-07-24
2002-05-21
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S222000, C525S225000, C525S227000, C525S232000, C525S240000, C525S241000, C427S407100
Reexamination Certificate
active
06391973
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns curable coating compositions, especially compositions for high-gloss topcoats, particularly for clearcoats of color-plus-clear composite coatings.
BACKGROUND OF THE INVENTION
Curable, or thermosettable, coating compositions are widely used in the coatings art, particularly for topcoats in the automotive and industrial coatings industry. Basecoat-clearcoat composite coatings are particularly useful as topcoats for which exceptional gloss, depth of color, distinctness of image, or special metallic effects are desired. The automotive industry has made extensive use of these coatings for automotive body panels.
Aqueous coating compositions and powder coating compositions have been increasingly used to meet legal restrictions on organic solvent emissions. In recent years, waterborne basecoat compositions, in particular, have gained prominence. Waterborne basecoat compositions have been prepared by different methods. One method to prepare the basecoat is by emulsion polymerizing an acrylic polymer and combining the emulsion polymer with other materials, such as pigments and a crosslinker. while emulsion polymerization provides advantages, the basecoats have been found to have viscosity instability. Metallic basecoat colors in particular depend highly on maintaining a stable viscosity over the life of the product to achieve the control of the metal flake pigment and/or pearlescent flake pigment need to achieve the desired lustrous color effect.
The basecoat, as integral layer of a composite coating on a substrate, must also aid in providing the excellent resistance to chipping required of automotive coatings. Further, the basecoat must have excellent adhesion to the any underlying primer layer, as well as to the clearcoat applied over the basecoat, so that the composite coating is strong. Likewise, the applied basecoat compositions must not cause pinholing or popping of the topcoat because such defects cause poor coating performance as well as resulting in poor appearance. Recent interest in aqueous powder slurry clearcoats has introduced a new compatibility requirement for basecoat compositions. Known basecoat compositions have produced a “mudcracking” appearance when used with powder slurry waterborne clearcoats.
An improved aqueous coating composition was thus needed to addresses these various problems of basecoat compositions.
SUMMARY OF THE INVENTION
The coating composition of the invention includes an aqueous two-stage polymer emulsion. The two-stage emulsion polymer contains composite polymeric particles of a first stage polymer and a second stage polymer. The composite polymeric particles have a theoretical glass transition temperature of not more than about 30° C. and from about 0.8% to about 2% by weight, based on the total weight of monomers polymerized in the first stage and second stages, of at least one monomer having carboxylic acid functionality.
The first stage polymer has an acid content of no more than about 0.5% by weight, based on total weight of monomers polymerized in the first stage, of a carboxylic acid functional monomer. Preferably, the first stage polymer is prepared by polymerizing a combination of addition monomers that does not include a carboxylic acid-functional monomer, by which it is meant that no carboxylic acid-functional monomer is intentionally added, although some carboxylic-acid functional monomer may be present as an impurity in one or more of the monomers of the combination. The combination of addition monomers includes from about 0.25% to about 5% by weight, based on the total weight of monomers polymerized in the first stage, of at least one monomer having at least two polymerizable ethylenically unsaturated groups and from about 2.5% to about 10% by weight, based on the total weight of monomers polymerized in the first stage, of at least one monomer having hydroxyl functionality. The first stage combination of addition monomers preferably also includes at least about 50% by weight, based on the total weight of monomers polymerized in the first stage that have no functional group other than the polymerizable ethylenically unsaturated group, of at least one hydrophobic monomer. “Hydrophobic monomer,” in connection with the present invention, refers to a monomer that is either an aromatic vinyl monomer or is a monomer having the structure
in which R is H or a methyl group and R′ is an alkyl group (including cycloalkyl group) having at least four carbons.
The second stage polymer has a theoretical glass transition temperature of at least about 50° C. and is prepared by polymerizing, in the presence of the first stage polymer emulsion, a combination of addition monomers that is preferably substantially free of monomers having more than one polymerizable ethylenically unsaturated group. The combination of addition monomers of the second stage polymer includes from about 25% to about 50% by weight of at least one hydroxyl-functional monomer and from about 3% to about 9% by weight of at least one carboxylic acid-functional monomer, each percentage being based on the total weight of monomers polymerized in the second stage. The combination of addition monomers of the second stage preferably also includes at least about 25% by weight of at least one hydrophobic monomer having no functional group other than the polymerizable ethylenically unsaturated group, based on the total weight of monomers polymerized in the second stage.
The invention further provides an article having a surface coated with a coating derived from the coating composition of the invention, particularly a composite coating having a basecoat layer and a clearcoat layer, and a method of producing such a coating on a substrate, particularly as a basecoat/clearcoat composite coating, with the coating composition of the invention being at least the basecoat of the composite coating. The method of the invention particularly provides preparing a basecoat layer from the coating composition of the invention and a clearcoat layer from an aqueous powder slurry coating composition and the composite coating produced by the method.
The coating composition of the invention provides improved viscosity stability. In particular, the present coating composition provides more stable metal control characteristics in a metallic basecoat coating composition compared to previous coating compositions based on two-stage emulsion polymers. Further, the particular combination of monomers used to prepare the two-stage emulsion polymer provides excellent chip and adhesion results while avoiding pinholing and popping problems in a basecoat/clearcoat composite coating. It has also been discovered that, while previous basecoat compositions produced a “mudcracking” appearance when used with aqueous powder slurry clearcoat compositions, the basecoat of the present invention avoids the problem of mudcracking and provides a composite coating with an excellent appearance.
DETAILED DESCRIPTION OF THE INVENTION
The two-stage emulsion polymer of the coating composition contains composite polymeric particles produced by emulsion polymerization of a first stage polymer followed by emulsion polymerization of a second stage polymer in the presence of the first stage polymer. A two-stage emulsion polymer produced in this way has properties that are different from either a blend of separate emulsion of the first stage and second stage polymers or a two-stage emulsion polymer in which the order of polymerization of the first stage and second stage polymers is reversed.
The composite polymeric particles of the emulsion polymer have a theoretical glass transition temperature of not more than about 30° C., and preferably no more than about 25° C. In a more preferred embodiment, the composite polymeric particles of the emulsion polymer have a theoretical glass transition temperature of not more than about 0° C. The composite coating in which the basecoat is derived from the coating composition of the invention has excellent result in chip testing, such as automotive coating gr
Balatan Sergio E.
Law David
Ohrbom Walter H
Scott S. Kendall
St. Henry Thomas E.
BASF Corporation
Budde Anne M.
Nutter Nathan M.
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