Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-04-16
2003-06-24
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S402000, C106S413000, C106S447000, C106S460000, C106S465000, C106S471000, C106S476000, C106S487000, C106S491000, C106S493000, C106S494000, C106S495000, C106S496000, C106S497000, C106S498000, C523S161000
Reexamination Certificate
active
06582510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the use of comb-branched copolymers as pigment dispersants, and more specifically to pigment dispersions containing pigment, a carrier medium, and a comb-branched copolymer pigment dispersant, and a method for making the pigment dispersions.
2. Background Art
Pigmented coating compositions are used in a wide variety of applications including paints, inks, and varnishes. The preparation of pigmented coating compositions generally involves mixing binder resin(s), crosslinker(s), additives, e.g., flow additives, and solvents with a compatible pigment dispersion. Pigment dispersions are typically prepared by mixing dry pigment (inorganic or organic) with a pigment dispersant in the presence of a carrier medium, e.g., an aqueous carrier such as water, or solvent based carriers.
Dry pigments are available commercially in the form of agglomerated pigment particles. Pigment agglomerates are more likely to settle out of pigment dispersions and/or pigmented coating compositions and are accordingly undesirable. To break the pigment agglomerates down into smaller agglomerates and/or individual particles generally requires a use of energy intensive mixing means (commonly referred to as grinding), e.g., sand mills and ball mills. During the grinding process, the pigment agglomerates are broken down into small agglomerates and/or individual particles the surfaces of which are wetted by the pigment dispersant. Pigment dispersants are provided in the pigment dispersion to suspend or disperse the pigment particles in the carrier medium and prevent their re-agglomeration on storage. It is desirable that the pigment dispersant function to effectively wet, disperse and stabilize both inorganic and organic pigments in either aqueous or non-aqueous solvents.
Some commercially available dispersants may act operatively for the above stated purposes, but disadvantageously create a relatively high amount of foam. In this context, foam is described as a frothy mass of fine bubbles formed in or on the surface of a liquid. A stabilized foam is usually the result of air entrainment in the liquid due to mechanical mixing. The problems of high levels of foam during the dispersion phase can be encountered in both the pre-mix and milling chambers of traditional dispersing equipment. The presence of foam slows down the dispersion process. Foam can also adversely affect film properties of derived coatings such as moisture resistance. In addition to being operable without generating high amounts of foam, suitable dispersants should be capable of forming stable pigment dispersions that have relatively high pigment loading capabilities.
Accordingly, it would be desirable to provide a pigment dispersant that forms the above needed functions of a pigment dispersant and foams less than other prior art dispersants.
SUMMARY OF THE INVENTION
It has now been surprisingly discovered that the above and other objectives can be met by providing a dispersant comprising an acrylic/polyether comb-branched copolymer.
It has been further surprisingly discovered that very stable dispersions having a dispersant comprising an acrylic/polyether comb-branched copolymer have relatively low foaming.
Accordingly, the present invention comprises a stable, low foaming dispersion comprising: a) pigment; b) carrier; and c) an acrylic/polyether comb-branched copolymer dispersant wherein the polyether portion of the copolymer is free of any acidic groups.
Moreover, the present invention comprises a method of making a dispersion suitable for use in pigmented coating compositions. The method includes mixing together, in any combination: a) pigment; b) carrier; and c) an acrylic/polyether comb-branched copolymer dispersant wherein the polyether portion of the copolymer is free of any acidic groups.
Furthermore, the present invention comprises a pigment coating composition comprising the dispersion described above.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Dispersions made in accordance with the present invention comprise, at a minimum pigment, carrier, and a dispersant comprising an acrylic/polyether comb-branched copolymer.
The acrylic/polyether comb-branched copolymer preferably has a molecular weight of 400 grams per mole to about 1,000,000 grams per mole, more preferably between about 600 grams per mole to about 800,000 grams per mole, and most preferably between about 1,000 grams per mole to about 600,000 grams per mole. The copolymer preferably has a mole ratio of acrylic monomer units to polyether units of about 1/99 to about 99/1, more preferably from about 1/1 to about 20/1, and most preferably from about 2/1 to about 20/1. The pendant polyether chain of the copolymer is free of any acidic groups, preferably free of any ionic groups, and more preferably free of any phosphate groups.
The comb-branched copolymer can be made by any suitable process for copolymerizing acrylic units with polyether units. In one preferred method, the copolymer is formed by reacting a polyether polymer or macromonomer with a polyacrylic acid polymer or acrylic monomer. The process may be continuous, batch, or semi-batch. Following the copolymerization process, any relatively volatile unreacted monomers are generally stripped from the product.
More preferably, the comb-branched copolymer is made according to one of the three following processes. The first process (i) comprises copolymerizing an unsaturated polyether macromonomer with at least one ethylenically unsaturated comonomer selected from the group consisting of carboxylic acids, carboxylic acid salts, hydroxyalkyl esters of carboxylic acids, and carboxylic acid anhydrides. The second process (ii) comprises reacting a carboxylic acid polymer and (a) a polyether prepared by polymerizing a C
2
-C
4
epoxide or (b) a polyether mixture comprising (1) a monofunctional polyether prepared by polymerizing a first epoxide selected from the group consisting of C
2
-C
4
epoxides and mixtures thereof onto a monofunctional initiator and (2) a difunctional polyether prepared by polymerizing a second epoxide selected from the group consisting of C
2
-C
4
epoxides and mixtures thereof, which may be the same as or different from the first epoxide, onto a difunctional initiator wherein the carboxylic acid polymer and the polyethers are reacted under conditions effective to achieve partial cleavage of the polyether and esterification of the polyether and cleavage products thereof by the carboxylic acid polymer. The third process (iii) comprises polymerizing a polymerizable acid monomer containing at least one ethylenically unsaturated group in conjugation with a carboxyl group selected from the group consisting of carboxylic acid, carboxylic anhydride and carboxylic ester groups in a reaction medium comprising a polyether, wherein the polyether is prepared by polymerizing a C
2
-C
4
epoxide, to form a carboxylic acid polymer; and reacting the carboxylic acid polymer and the polyether under conditions effective to achieve esterification of the polyether by the carboxylic acid polymer to form the comb-branched copolymer.
The preferred polyether macromonomer preferably comprises ethylene oxide and propylene oxide and has a molecular weight of about 300 grams per mole to about 100,000 grams per mole, more preferably between about 500 grams per mole to about 75,000 grams per mole, and most preferably between about 1,000 grams per mole to about 10,000 grams per mole. All molecular weights are number average molecular weights unless stated otherwise. Preferably, the ratio of propylene oxide (PO) to ethylene oxide (EO) of the polyether polymer or polyether macromonomer is between about 99/1 to about 1/99, more preferably between about 95/5 to about 1/99, and even more preferably between about 80/20 to about 1/99 by weight, and most preferably between about 50/50 to about 30/70.
A preferred process for making the copolymer comprises: (a) forming a monomer stream, an initiator stream, and an optional chain transfer agent stream; (b) pol
ARCO Chemical Technology L.P.
Brooks & Kushman P.C.
Green Anthony J.
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