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
2001-02-21
2003-11-11
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S221000, C526S318500, C524S430000, C524S522000, C524S523000
Reexamination Certificate
active
06646058
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to coatings and in particular to water-borne paint compositions having improved hiding.
Generally, a water-borne paint composition is composed of four basic components: binder, aqueous carrier, pigment(s) and additive(s). The binder is a nonvolatile resinous material that is dispersed in the aqueous carrier to form a latex. When the aqueous carrier evaporates, the binder forms a paint film that binds together the pigment particles and other non-volatile components of the water-borne paint composition.
The pigment(s) used in a water-borne paint composition typically include an opacifying pigment, which imparts opacity or hiding to the paint film. One of the most effective and, hence, one of the most widely used opacifying pigments is titanium dioxide. Although very effective, titanium dioxide is expensive, typically being the most expensive component of a water-borne paint composition. Accordingly, it is desirable to achieve the desired degree of hiding in a paint film using the least amount of titanium dioxide possible. Various paint compositions have been proposed for utilizing titanium dioxide more efficiently; however, most of these paint compositions have reduced scrub resistance.
Based on the foregoing, there is a need in the art for a water-borne paint composition having improved hiding and good scrub resistance. The present invention is directed to such a water-borne paint composition.
SUMMARY OF THE INVENTION
In accordance with the present invention, a water-borne paint composition is provided that includes an opacifying pigment and a core-shell polymer with acid functionality. The core-shell polymer includes a shell and a core. The weight of the shell is less than 10% of the weight of the core. The water-borne paint composition also includes a polymer polymerized from a group of monomers including an unsaturated carboxylic acid monomer, a monoethically unsaturated monomer different from the carboxylic acid monomer, and a macromonomer including a hydrophobic portion and an alkoxylated portion that is polymerizable with the carboxylic acid monomer and the monoethylenically unsaturated monomer.
Also provided in accordance with the present invention is a water-borne paint composition that includes an opacifying pigment, a binder latex having a core-shell polymer with acid functionality, and a dispersant polymer polymerized from a group of monomers including a macromonomer having a hydrophobic portion and an alkoxylated portion. The core-shell polymer has a core and a shell respectively polymerized from first and second sets of monomers, each of which includes at least 48 weight percent of one or more vinyl monomers. The weight of the shell is less than 10% of the weight of the core.
DETAILED DESCRIPTION OF THE INVENTION
Parts are parts by weight and percents are weight percents unless otherwise indicated or apparent.
As used herein with regard to a paint composition, the term “pigment volume concentration” (hereinafter referred to as “PVC”) means the ratio (expressed as a percentage) of the volume of inorganic particles (i.e., opacifying pigment and extender particles) to the volume of total non-volatile material (i.e., inorganic particles and polymeric particles) present in the paint composition.
As used herein with regard to a paint composition, the term “total solids by volume” means the ratio (expressed as a percentage) of the volume of total non-volatile material (i.e., inorganic particles and polymeric particles) present in the paint composition to the total volume of the paint composition.
As used herein, “(meth)acrylate” denotes both “acrylate” and “methacrylate”, and “(meth)acrylic” denotes both “methacrylic” and “acrylic.”
As used herein, the term “vinyl monomer” means any monomer having vinyl functionality, i.e., ethylenic unsaturation, exclusive of monomers having acrylic functionality.
The water-borne paint composition of the present invention includes a binder latex comprising a core-shell polymer, a dispersant latex formed from a monomer mixture comprising a macromonomer, and an opacifying pigment. The water-borne paint composition also preferably includes an extender and a thickener.
The binder latex comprises a core-shell polymer dispersed in an aqueous medium. The core-shell polymer comprises a core polymer having an outer surface and a shell polymer in physical contact with and covering at least a part of the outer surface of the core polymer. The core-shell polymer is formed using a two-stage free radical emulsion polymerization technique. In a first stage, the core polymer is polymerized from a first set of monomers in an emulsion. In a second stage, a second set of monomers is added to the emulsion and polymerized to form the shell polymer. The core-shell polymer does not have cross-linking functionality.
Suitable monomers for producing the core and shell polymers include copolymerizable monoethylenically unsaturated monomers, such as vinyl monomers and acrylic monomers. None of the monomers used to produce the core and shell polymers have “latent cross-linking capability”, which, as used herein, means the ability to further react some time after initial polymer formation.
Preferred vinyl monomers are selected from the group consisting of vinyl esters, vinyl aromatic hydrocarbons, vinyl aliphatic hydrocarbons, vinyl alkyl ethers and mixtures thereof. Examples of vinyl esters that may be used include vinyl acetate, vinyl propionate, vinyl laurate, vinyl pivalate, vinyl nonanoate, vinyl decanoate, vinyl neodecanoate, vinyl butyrates, vinyl benzoates, and vinyl isopropyl acetates. Examples of vinyl aromatic hydrocarbons that may be used include styrene, methyl styrenes and other lower alkyl styrenes, chlorostyrene, vinyl toluene, vinyl naphthalene and divinyl benzene. Examples of vinyl aliphatic hydrocarbons that may be used include vinyl chloride and vinylidene chloride as well as alpha olefins such as ethylene, propylene, isobutylene, as well as conjugated dienes such as 1,3 butadiene, methyl-2-butadiene, 1,3-piperylene, 2,3-dimethyl butadiene, isoprene, cyclohexene, cyclopentadiene, and dicyclopentadiene. Examples of vinyl alkyl ethers that may be used include methyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether.
Acrylic monomers suitable for use in the present invention include any compounds having acrylic functionality. Preferred acrylic monomers are selected from the group consisting of alkyl (meth)acrylates, acrylic acids, as well as aromatic derivatives of (meth)acrylic acid, acrylamides and acrylonitrile. Typically, the alkyl (meth)acrylate monomers (also referred to herein as “alkyl esters of (meth)acrylic acid”) will have an alkyl ester portion containing from 1 to 12, preferably about 1 to 5, carbon atoms per molecule.
Suitable acrylic monomers include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, propyl (meth)acrylate, 2-ethyl hexyl (meth)acrylate, cyclohexyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, benzyl (meth)acrylate, isobomyl (meth)acrylate, neopentyl (meth)acrylate, 1-adamatyl methacrylate and various reaction products such as butyl, phenyl, and cresyl glycidyl ethers reacted with (meth)acrylic acid, hydroxyl alkyl (meth)acrylates, such as hydroxyethyl and hydroxypropyl (meth)acrylates, amino (meth)acrylates, as well as acrylic acids such as (meth)acrylic acid, ethacrylic acid, alpha-chloroacrylic acid, alpha-cycanoacrylic acid, crotonic acid, beta-acryloxy propionic acid, and beta-styryl acrylic acid.
Preferably, the first and second sets of monomers each include a vinyl monomer and an acrylic monomer. The first and second sets of monomers each preferably comprise at least 48 weight percent, more preferably from about 48 to about 90 weight percent, more preferably from about 58 to about 88 weight percent, more preferably from about 65 to about 85 weight percent of one or more vinyl monomers.
Importantly, the second set of monomers includes an acid functional monomer. Suitable acid functional
Hu Henry S.
Katterle Paul R.
McDonald Robert E.
The Sherwin-Williams Company
Tsang Vivien Y.
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