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
2000-12-22
2004-03-02
Seidleck, James J. (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...
C525S330500, C525S191000, C525S193000, C525S194000, C525S095000, C525S098000, C524S598000, C526S301000
Reexamination Certificate
active
06699943
ABSTRACT:
RELATED APPLICATIONS
This patent application claims priority to and all advantages of German Application No. 10029803.6, entitled “Clearcoat Material And Its Use To Produce Clearcoats And Multicoat Color And/Or Effect Coating Systems,” which was filed on Jun. 16, 2000.
FIELD OF THE INVENTION
The subject invention generally relates to a curable, water-based coating composition utilized primarily in waterborne coating systems, such as waterborne basecoat (WBBC) systems, waterborne clearcoat (WBCC) systems, and waterborne primer systems. More specifically, the coating composition includes a water-based copolymer, having a carbamate functional group, and a cross-linking agent that is reactive with the carbamate functional group and dispersible in water. The subject invention also relates to a method of preparing the coating composition as well as a method of preparing a cured film of the coating composition.
BACKGROUND OF THE INVENTION
Water-based coating compositions include water-based copolymers and cross-linking agents as components. The water-based copolymers are desirable for use in coating systems in the automotive and industrial coatings industries because these copolymers enable formulation of waterborne coating systems, such as WBBC, WBCC, and waterborne primer systems. It is known in the art that waterborne coating systems are ideal as compared to solventbome coating systems because waterbome coating systems have lower content of volatile organic compounds (VOCs).
The water-based copolymers of the prior art have proven to be inadequate for use as a component in water-based coating compositions. The water-based copolymers of the prior art are ineffective because these copolymers are highly viscous, as secondary dispersions, and generally have poorly defined film forming characteristics, as primary dispersions. Furthermore, the cross-linking between these copolymers and select conventional cross-linking agents are often particularly susceptible to environmental acid etch.
The water-based copolymers of the prior art are also deficient because these copolymers often incorporate additional components such as co-solvents and increased amounts of surfactants which are both undesirable components in waterborne coating systems. For instance, conventional water-based copolymers typically incorporate a co-solvent to promote dispersibility of the copolymer in water, and these co-solvents contribute to increased VOCs. Conventional water-based copolymers also typically incorporate increased amounts of surfactants directly into the copolymer to achieve and maintain miscibility and incorporation of the copolymer in water, and as understood by those skilled in the art, use of increased amounts of surfactants in the coating composition frequently contributes to water sensitivity, humidity, and ‘cratering’ as well as other coating defects detrimental to the appearance of the waterbome coating system.
The free-radical polymerization methods of preparing the water-based copolymers of the prior art are also deficient. These conventional methods are typically highly exothermic and are therefore difficult to predict and control. The unpredictability of these methods leads to uncontrollable and inconsistent physical properties of the water-based copolymer and ultimately of the water-based coating composition which includes the copolymer as a component. More specifically, the unpredictability of these methods frequently leads to inconsistent molecular weight distribution of the copolymer, and to incomplete conversion of monomer components into the copolymer. Furthermore, in the preparation of conventional water-based copolymers, distribution of the monomer components is random and does not produce a ‘tailored’ polymeric architecture that is able to meet particular needs depending on whether the copolymer is utilized in a WBBC, WBCC, or waterborne primer system. It is understood in the art that inconsistent molecular weights, incomplete conversion of monomer components, and even random distribution of the monomer components affects, among other things, the stability of the viscosity of the copolymer and can even result in ‘gelling’ of the copolymer and of the water-based coating composition. Additionally, poor appearance characteristics of the WBBC, WBCC, or waterbome primer system, such as gloss and distinctness of image (DOI), can result from poor rheology, i.e., flow, of the coating composition upon application that is due to the inconsistencies in the water-based copolymer.
In sum, the prior art water-based copolymers which are components of the water-based coating composition, as detailed above, are characterized by one or more inadequacies. Due to the inadequacies identified in the prior art, it is desirable to provide a novel water-based copolymer and coating composition to be utilized in WBBC, WBCC, and waterborne primer systems as well as a novel method of preparing the coating composition and a cured film.
SUMMARY OF THE INVENTION
A curable, water-based coating composition is disclosed. The water-based coating composition of the subject invention is the reaction product of a water-based copolymer (A) and at least one water-dispersible cross-linking agent (B). The water-based copolymer (A) is prepared by free-radical polymerization and includes a first block polymer, or first block, (A)(I) and a second block (A)(II). The first block (A)(I) is preferably a hydrophilic block, and the second block (A)(II) is preferably a hydrophobic block. More specifically, the first block (A)(I) of the copolymer (A) is the reaction product of at least one ethylenically unsaturated monomer (A)(I)(a), and at least one vinylaromatic hydrocarbon monomer (A)(I)(b). The second block (A)(II) of the copolymer (A) is the reaction product of a plurality of ethylenically unsaturated monomers (A)(II)(a) different than the ethylenically unsaturated monomer (A)(I)(a), wherein at least one of the plurality includes at least one carbonate functional group for modification into a carbamate functional group. The cross-linking agent (B) is reactive with the carbamate functional group and is dispersible in water.
In the preferred water-based coating composition of the subject invention, the at least one ethylenically unsaturated monomer (A)(I)(a) of the first block (A)(I) is further defined as a first and second ethylenically unsaturated monomer where the first ethylenically unsaturated monomer is preferably acrylic acid, and the second ethylenically unsaturated monomer is preferably methyl methacrylate. Furthermore, the at least one vinylaromatic hydrocarbon monomer (A)(I)(b) of the first block (A)(I) is preferably diphenylethylene. Also in the preferred embodiment, the plurality of ethylenically unsaturated monomers (A)(II)(a) of the second block (A)(II) that are different than the at least one ethylenically unsaturated monomer (A)(I)(a) are styrene, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and carbonate-modified glycidyl methacrylate having the carbonate functional group. In the preferred embodiment, the carbonate functional group of the carbonate-modified glycidyl methacrylate is modified by an ammonia-containing compound, preferably ammonium hydroxide, into the carbamate functional group. Finally, the preferred water-dispersible cross-linking agent (B) that is reactive with the carbamate functional group is hexamethoxymethyl melamine.
A method of preparing the water-based coating composition is also disclosed. According to this method, the first block (A)(I) is first formed. Next, the second block (A)(II), having the at least one carbonate functional group, is polymerized with the first block (A)(I) to establish the water-based copolymer (A). The at least one carbonate functional group is then converted into at least one carbamate functional group. The copolymer (A) is then combined with the water-dispersible cross-linking agent (B) such that the cross-linking agent (B) reacts with the carbamate functional group to form the water-based coating composition of the subject invention.
The general object of the s
Bremser Wolfgang
Lessek Paul
Ramesh Swaminathan
Asinovsky Olga
BASF Corporation
Seidleck James J.
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