Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-11-30
2001-07-10
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S522000
Reexamination Certificate
active
06258887
ABSTRACT:
This invention relates to a multi-stage aqueous emulsion polymer. This invention also relates to a method for providing a dirt pickup resistant coating containing the multi-stage aqueous emulsion polymer. More particularly, this invention relates to a multi-stage emulsion polymer including a first polymer containing a copolymerized ionic monomer and a crosslinked second polymer of different composition. The present invention serves to provide a multi-stage emulsion polymer binder suitable for use in decorative and/or protective coatings for various substrates which coatings maintain a desirable balance of coatings properties, particularly including good film formation and dirt pickup resistance. It has long been known that a high level dirt pickup resistance can be achieved by use of a hard polymer but not without jeopardizing film formation, as may be related to scrub resistance, for example, or requiring environmentally undesirable high levels of coalescing solvents.
U.S. Pat. No. 5,306,743 discloses an aqueous resin dispersions having a core-shell structure. The core-shell emulsion particles contain a core polymer, optionally containing copolymerizable monomers having at least two ethylenically unsaturated groups such as allyl, acryl, or methacryl groups and having a dynamic glass transition temperature above 60° C. and a shell polymer with a dynamic glass transition temperature of below 80° C. and also at least 20° K below the glass transition temperature of the core material. However, the use of such dispersions leads to coatings having inadequate dirt pick-up resistance.
The problem faced by the inventors is the provision of a multi-stage emulsion polymer suitable for use in dirt pickup resistant coatings which provide dried coatings having unexpected levels of dirt pickup resistance without jeopardizing film formation.
In a first aspect of the present invention there is provided a multi-stage aqueous emulsion-polymer suitable for use in dirt pickup resistant coatings including (i) a first polymer including at least one nonionic copolymerized monoethylenically unsaturated monomer, from 0.5% to 7% of a copolymerized monoethylenically unsaturated ionic monomer, based on the weight of the first polymer, and from 0% to 1.0%, based on the weight of the first polymer, of a copolymerized multi-ethylenically unsaturated monomer, the first polymer having a Tg of 15° C. to 105° C.; and (ii) a second polymer comprising at least one nonionic copolymerized monoethylenically unsaturated monomer, from 0% to 2% of a copolymerized monoethylenically unsaturated ionic monomer, and from 0.25% to 6%, based on the weight of the second polymer, copolymerized multi-ethylenically unsaturated monomer, the second polymer having a Tg of −55° C. to 30° C., the second polymer having a different composition than the first copolymer, and the second polymer being from 25% to 75% of the total weight of the first polymer and the second polymer, based on dry polymer weights.
In a second aspect of the present invention there is provided a method for providing a dirt pickup resistant coating including (a) forming an aqueous coating composition including a multi-stage aqueous emulsion-polymer including (i) a first polymer including at least one nonionic copolymerized monoethylenically unsaturated monomer, from 0.5% to 7% of a copolymerized monoethylenically unsaturated ionic monomer, based on the weight of the first polymer, and from 0% to 1.0%, based on the weight of the first polymer, of a copolymerized multi-ethylenically unsaturated monomer, the first polymer having a Tg of 15° C. to 105° C.; and (ii) a second polymer including at least one nonionic copolymerized monoethylenically unsaturated monomer, from 0% to 2% of a copolymerized monoethylenically unsaturated ionic monomer, and from 0.25% to 6%, based on the weight of the second polymer, copolymerized multi-ethylenically unsaturated monomer, the second polymer having a Tg of −55° C. to 30° C., the second polymer having a different composition than the first copolymer, and the second polymer being from 25% to 75% of the total weight of the first polymer and the second polymer, based on dry polymer weights, b) applying the aqueous coating composition to a substrate, and c) drying, or allowing to dry, the applied aqueous coating composition.
The multi-stage aqueous emulsion polymer contains a first polymer including at least one nonionic copolymerized ethylenically unsaturated monomer and from 0.5% to 7% of a copolymerized monoethylenically unsaturated ionic monomer, based on the weight of the first polymer, and from 0% to 1.0%, based on the weight of the first polymer, of a copolymerized multi-ethylenically unsaturated monomer. The multi-stage aqueous emulsion polymer also contains a second polymer including at least one nonionic copolymerized monoethylenically unsaturated monomer, from 0% to 2% of a copolymerized monoethylenically unsaturated ionic monomer, and from 0.25% to 6%, based on the weight of the second polymer, copolymerized multi-ethylenically unsaturated monomer. By “multi-stage aqueous emulsion polymer” herein is meant an emulsion polymer prepared by the sequential addition of two or more different monomer compositions. By “first polymer” and “second polymer” herein are meant two polymers having different compositions regardless of the order in which they were prepared in a multi-stage emulsion polymerization process. By “first stage polymer” herein is meant the emulsion polymer which is formed first; by “second stage polymer” herein is meant a polymer which is formed in the presence of the first polymer. However, the first stage polymer may be formed in the presence of a previously formed dispersed polymer in an amount of 0-10%, by weight based on the weight of the first stage polymer, sometimes known as a seed polymer, of a composition the same as or different from the first stage polymer. One or more additional stages may be formed before or after the first or second stage polymer but they shall not constitute in totality more than 25% by weight of the total weight of the first and second stages. Neither the weight or composition of any seed polymer or any additional stage(s) shall be included in the weight or composition of the first and second stage polymer.
The first polymer and the second polymer each contain at least one nonionic copolymerized ethylenically unsaturated monomer such as, for example, a (meth)acrylic ester monomer including methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, ureido-functional (meth)acrylates and acetoacetates, acetamides or cyanoacetates of (meth)acrylic acid; styrene or substituted styrenes; vinyl toluene; butadiene; monoethylenically unsaturated acetophenone or benzophenone derivatives such as, for example are taught in U.S. Pat. No. 5,162,415; vinyl acetate or other vinyl esters; vinyl monomers such as vinyl chloride, vinylidene chloride, and N-vinyl pyrollidone; (meth)acrylonitrile; N-alkylol (meth)acrylamide. The use of the term “(meth)” followed by another term such as (meth)acrylate or (meth)acrylamide, as used throughout the disclosure, refers to both acrylates or acrylamides and methacrylates and methacrylamides, respectively.
The first polymer contains from 0.5% to 7%, preferably from 1% to 5%, of a copolymerized monoethylenically-unsaturated ionic monomer, based on the weight of the first polymer. The second polymer contains from 0% to 2%, of a copolymerized monoethylenically-unsaturated ionic monomer, based on the weight of the second polymer. By “ionic monomer” herein is meant a monomer unit which, when copolymerized, is at least partially positively or negatively charged at a pH of 2-11. Ionic monomers include acid group-containing monomers such as carboxylic acid monomers including, for example, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, and ma
Bardman James Keith
Even Ralph Craig
Frazza Mark Stephen
Guo Yili
Krasnansky Robert
Michl Paul R.
Rohm and Haas Company
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