Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-10-17
2002-04-09
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S340000, C524S549000, C524S556000, C524S559000, C524S592000, C524S593000, C524S612000, C525S09200D, C525S398000, C525S471000, C528S501000, C536S043000, C536S044000
Reexamination Certificate
active
06369132
ABSTRACT:
BACKGROUND OF THE INVETION
1. Field of Invention
The present invention relates to low bulk density thermoplastic polymers and more particularly it relates to fine particle size water-soluble synthetic or semisynthetic associative thickeners having low bulk density.
2. Description of the Prior Art
In general, the bulk density of polymer particles is lowered for ease of processing, handling and flow. In many situations, it is desirable to temporarily suspend polymer particles in a liquid medium for ease of handling and transportation. One of the ways to achieve this goal is to lower the bulk density of the polymer particles. In addition, by lowering bulk density, dissolution of polymer particles in an appropriate solvent can be accelarated. Low bulk density polymer particles are of special interest for fabricating light-weight products and separating solvents.
Various water-soluble polymers are used to thicken and control rheology of waterborne industrial systems, such as latex paints and personal care products. These include natural and chemically modified polysaccharides, proteins and synthetic water-soluble polymers. Examples include hydroxyethylcellulose (HEC), hydrophobically modified hydroxyethylcellulose (HM-HEC), ethylhydroxyethylcellulose, hydrophobically modified ethylhydroxyethylcellulose, methylhydroxypropylcellulose, carboxymethylcellulose, guar and guar derivatives, starch and starch derivatives, casein, polyacrylates, polyacrylamides, and polyalkylene oxides.
In the last fifteen years, a new class of hydrophobically modified synthetic water-soluble polymers (HM-WSPs) have gained extensive commercial importance for formulating waterborne coatings and suspensions to achieve desired paint properties, such as flow, leveling, film build and gloss. These HM-WSPs are composed of water-soluble and water-insoluble components. They are dubbed “associative thickeners” as they thicken aqueous systems by intermolecular hydrophobic associations and/or hydrophobic associations between their hydrophobic moieties and other hydrophobic entities present in the system. Various types of synthetic associative thickeners (SATs) include, but are not limited to, hydrophobically modified polyether-polyurethanes (U.S. Pat. Nos. 4,079,028, 4,155,892, 4,496,708, 4,426,485, 4,499,233, 5,023,309 and 5,281,654), hydrophobically modified polyether-polyurethanes bearing terminal hydrophilic groups (PCT International WO 96/40820), hydrophobically modified polyether-polyols (U.S. Pat. Nos. 4,288,639, 4,354,956, 4,904,466), copolymers of ethylene oxide and long chain epoxyalkane (U.S. Pat. No. 4,304,902), hydrophobically modified polyacetal-polyethers (U.S. Pat. No. 5,574,127 ), hydrophobically modified alkali-soluble emulsions (U.S. Pat. Nos. 4,514,552, 4,421,902, 4,423,199, 4,429,097, 4,663,385, 4,008,202, 4,384,096, 5,342,883). For other references on hydrophobically modified alkali-soluble emulsions see, “E. J. Schaller and P. R. Perry, in “Handbook of Coatings Additives”, Ed., L. J. Calbo, Marcel Dekker, Inc., New York, Vol. 2, 1992, Chapter 4, p. 114 and G. D. Shay in “Polymers in Aqueous Media”, Ed. J. E. Glass, Advances in Chemistry Series, Vol. 223, Chapter 25, p. 480, 1989; American Chemical Society, Washington, D.C.), hydrophobically modified polyacrylamide (U.S. Pat. Nos.4,425,469, 4,432,881, 4,463,151, 4,463,152, 4,722,962), hydrophobically modified aminoplast-polyethers (PCT International WO 96/40625 and WO 96/40185).
To thicken aqueous systems, water-soluble polymers are commonly used in dry powder form. However, there are several problems associated with the use of dry powder polymers. These include, dusting during transfer, poor dispersibility (lump formation), unusually long dissolution time, and poor handling. Particularly, complete dissolution of solid water-soluble polymers is a formidable task when they are directly added to highly filled systems, such as latex paints, containing limited amount of free water.
To eliminate these problems, manufacturers of SATs have searched for means to deliver these polymers as high solids pourable/pumpable aqueous emulsions or solutions.
One class of SATs comprised of hydrophobically modified alkali-soluble polyacrylates and hydrophobically modified polyacrylamides are made by free radical emulsion polymerization processses in water and the polymers formed remained as stable colloidal dispersions. Hence, they are currently sold as 20-50% solids dispersions. At the point of applications, these dispersions are directly added to the aqueous system to be thickened and the polymer dissolved in water by exposing them to an alkali or a base. Alternatively, they can be first dissolved in water by adding an alkali or a base and the resulting polymer solution can be added to the aqueous system to be thickened.
Another class of important SATs is based on copolymers of polyalkylene oxides and other appropriate functional reagents. These polyalkylene oxide based SATs are made by step growth copolymerization processes and are widely used in a multitude of industrial applications. Examples of such commercial SATs include hydrophobically modified polyether-polyurethanes (sold under the trademark Acrysol® RM-825 and RM-1020 by Rohm and Haas Company and Rheolate 244, 255 and 278 by Rheox, Inc.) and hydrophobically modified polyether-polyols (sold under the trademark RHEOLATE® 300 by Rheox, Inc.). Currently these SATs are sold as 20-30% solids solution in a mixture of water and a water miscible organic solvent, such as diethylene glycol monobutyl ether (also known as Butyl carbitol™) or ethylene glycol or propylene glycol. The organic cosolvents are used to suppress the solution viscosity of SATs so that they can be delivered as high solids pourable/pumpable solutions.
While these organic solvents do provide the intended function, they eventually get released to the atmosphere and contribute to environmental pollution. Due to recent changes in environmental regulations in the United States, Western Europe and other parts of the world, there is a mounting pressure to formulate waterborne systems, such as latex paints, free of volatile organic compounds (VOCs). Since the above-mentioned polyalkylene oxide based SATs are dissolved in a mixture of water and an organic cosolvent, they are not the systems of choice for formulating VOC free waterborne coatings. Hence, manufacturers of SATs have been actively seeking for ways to deliver SATs in aqueous systems free of VOCs.
U.S. Pat. Nos. 5,137,571 and 5,376,709 describe the use of cyclodextrins to suppress the solution viscosity of SATs. It has been proposed that cyclodextrins, which are cyclic oligosaccharides composed of 6, 7 or 8 &agr;-D-anhydroglucose units, reversibly complex with the hydrophobic moieties of SATs and occasion breakdown of hydrophobic association and attendant viscosity loss.
A recent patent (U.S. Pat. No. 5,425,806), issued to Rheox, Inc., describes the use of an anionic or a nonionic surfactant to lower the solution viscosity of SATs and reduce the VOC of the thickening composition.
Although cyclodextrins and surfactants can suppress the aqueous solution viscosity of SATs, they can severely restrict the coating formulator's ability to formulate paints. This restriction could arise due to the fact that the ingredients (latex binders, pigments, extenders, surfactants, and dispersants) of VOC free waterborne coatings can interact with cyclodextrins and surfactants to occasion instability to the paint and detract from achieving the target paint properties. For example, the presence of additional surfactants or cyclodextrins arising from the thickener solution can negatively impact the viscosifying ability of the SAT and can cause excessive foaming during the manufacture of the coating. Certain latex film properties, such as early blister resistance, block resistance, water resistance, and scrub resistance could also be adversely affected by incorporation of an excess of cyclodextrins or surfactants. In addition, cyclodextrins are fairly expensive and not cost effective based on their recommended
Edwards David
Hercules Incorporated
Szanto Ivan G.
Szekely Peter
LandOfFree
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