Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-09-27
2004-01-06
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S402200, C525S243000, C525S094000, C521S056000, C521S059000, C521S060000, C521S065000
Reexamination Certificate
active
06673451
ABSTRACT:
This invention relates to a process for forming an aqueous polymeric dispersion, an aqueous polymeric dispersion formed by the process, and a coating composition such as, for example, a waterborne paper or paperboard coating composition or a paint composition comprising the aqueous polymeric dispersion. More specifically, this invention relates to an aqueous multimodal polymeric dispersion including at least two emulsion polymers of differing particle diameter, at least one of which emulsion polymers includes a core and at least two shells, the first shell having a glass transition temperature (“Tg”) greater than 50° C. and the outermost shell having a Tg from 10° C. to −50° C. and contains at least one void.
Coated paper and paperboard is usually printed and the coating must exhibit a useful level of smoothness and opacity as well as sufficient strength to withstand the printing operation. Coating opacity and strength are primarily effected by the selection of and amounts of polymeric binder and pigments to be used in the coating with some contribution from the coating application, drying, and finishing methods used. Aqueous polymeric dispersions having a multimodal particle size distribution offer the potential of higher solids emulsion polymer products and higher solids paper and paperboard coatings compositions which properties are beneficial for improving sheet gloss, particularly in formulations containing as pigment predominant amounts of calcium carbonate. Aqueous polymeric dispersions having a bimodal particle size distribution also offer the potential of higher solids paint compositions such as, for example, interior and exterior paints for architectural substrates which properties are beneficial for lessening thickener demand and providing greater formulation latitude.
U.S. Pat. No. 4,567,099 discloses bimodal latexes having two separate and distinct particle size distributions. The latexes are employed in coating paper in conjunction with a mineral filler. The larger size particles contain both relatively harder cores and relatively softer shell domains. The smaller size particles are either separately formed and subsequently blended together or prepared by adding a seed latex simultaneously to or after the shell domain of the large size particle is formed. However, void-containing particles and higher levels of solids than can be achieved with these coatings is desirable.
JP 5-170802 discloses emulsion particles including a group of hollow particles in which voids are present inside the particles during drying and, additionally, a group of smaller particles for use in paper coatings.
EP 959176 discloses hollow sphere organic pigment for use in paper or paper coatings, the hollow sphere organic pigment being formed by a multistage emulsion polymerization, the emulsion particles having at least one core and two shells.
The problem faced by the inventors is the provision of a process for forming aqueous polymeric dispersion suitable for forming coating compositions such as aqueous coating compositions for coating paper and paperboard and aqueous paint compositions. Although emulsion polymer particles containing a void have been disclosed for use in aqueous coatings, such particles contain a void filled with water, or, on drying, a void filled with air. The larger the void, the lower the effective density of the particle and the lower the solids of the emulsion polymer and, all else being equal, the lower the maximum solids content of the coating composition at a useable viscosity. We have now found that aqueous polymeric dispersion of this invention afforded by a bimodal emulsion polymer particle size distribution with at least one of the particle populations containing voids permits higher solids paper and paperboard coating compositions than could otherwise have been formed resulting in higher sheet gloss, particularly in certain calcium carbonate-containing formulations, and lowered drying energy requirements. We have also found that the aqueous polymeric dispersion of this invention is suitable for forming paint compositions.
STATEMENT OF THE INVENTION
According to a first aspect of the present invention there is provided a process for forming an aqueous polymeric dispersion including (1) forming emulsion-polymerized multistaged first polymer particles having (a) a hydrophilic core polymer formed from 5% to 100% by weight, based on the total weight of the core polymer, of a hydrophilic monoethylenically unsaturated monomer and from 0% to 95% by weight, based on the total weight of the core polymer, of at least one nonionic monoethylenically unsaturated monomer; (b) a first shell polymer formed from 90% to 99.9% by weight, based on the total weight of the first shell polymer, of at least one nonionic monoethylenically unsaturated monomer and from 0.1% to 10% by weight, based on the total weight of the first shell polymer, of an acid functional monoethylenically unsaturated monomer, wherein the first shell polymer fully encapsulates the core polymer, wherein the ratio of the weight of the core polymer to the weight of the first shell polymer is from 1:2 to 1:100, and wherein the first shell polymer has a glass transition temperature greater than 50° C. and (c) a second shell polymer formed from 93% to 99.9% by weight, based on the total weight of the second shell polymer, of at least one nonionic monoethylenically unsaturated monomer and from 0.1% to 7% by weight, based on the total weight of the second shell polymer, of an acid functional monoethylenically unsaturated monomer, wherein the second shell polymer is formed in the presence of the first shell polymer, and wherein the second shell polymer has a glass transition temperature from 10° C. to −50° C., and wherein the second shell polymer is at least 10% by weight of the total weight of the first shell polymer and the second shell polymer; (2) forming a second emulsion polymer in the presence of the first emulsion polymer by (a) adding, after the core polymer has been formed, an amount of surfactant sufficient to generate new particles or an emulsion-polymerized seed latex having a particle diameter less than 200 nanometers to the polymerization; (b) then adding any remainder of the first shell polymer monomer mixture and then any remainder of the second shell polymer monomer mixture and from 0 to 90% by weight, based on the weight of the solids of the aqueous polymeric dispersion, of at least one ethylenically unsaturated monomer; (3) effecting polymerization of at least 95% of all added monomer by weight based on the weight of the solids of the aqueous polymeric dispersion; and (4) neutralizing the aqueous dispersion formed with a base so as to swell the core and form particles which, when dry, contain a void.
According to a second aspect of the present invention there is provided a process for forming an aqueous polymeric dispersion including (1) forming a first emulsion polymer having particles formed from at least one ethylenically unsaturated monomer; (2) forming a second emulsion polymer including (a) a hydrophilic core polymer formed from 5% to 100% by weight, based on the total weight of the core polymer, of a hydrophilic monoethylenically unsaturated monomer and from 0% to 95% by weight, based on the total weight of the core polymer, of at least one nonionic monoethylenically unsaturated monomer; (b) a first shell polymer formed from 90% to 99.9% by weight, based on the total weight of the first shell polymer, of at least one nonionic monoethylenically unsaturated monomer and from 0.1% to 10% by weight, based on the total weight of the first shell polymer, of an acid functional monoethylenically unsaturated monomer, wherein the first shell polymer fully encapsulates the core polymer, wherein the ratio of the weight of the core polymer to the weight of the first shell polymer is from 1:2 to 1:100, and wherein the first shell polymer has a glass transition temperature greater than 50° C.; and c) a second shell polymer formed from 93% to 99.9% by weight, based on the total weight of the sec
Bardman James Keith
Blankenship Robert Mitchell
Finch William Christopher
Bakule Ronald D.
Rohn and Haas Company
Tarazano D. Lawrence
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