Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
2001-09-28
2003-09-30
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C106S018330, C514S188000, C514S937000, C516S031000, C523S122000
Reexamination Certificate
active
06627665
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to copper pyrithione compositions, and more particularly to a non-dusting copper pyrithione dispersion of solid copper pyrithione particles dispersed in water or an organic dispersant. The dispersion additionally contains a dust-inhibiting agent selected from the group consisting of surfactants, polymer resins, binders, and combinations thereof.
2. Description of the Related Art
Pyrithione salts are well known compounds useful in a wide variety of applications including biocides such as fungicides and bactericides. Heavy metal salts of pyrithione, including zinc, tin, cadmium and zirconium, as well as the magnesium and aluminum salts, in the form of flat platelets suitable for use in shampoo, are disclosed in U.S. Pat. Nos. 4,345,080 and 4,323,683. For example, paints containing a pyrithione salt (e.g. zinc or sodium pyrithione) plus a copper salt (e.g. cuprous oxide or cuprous thiocyanate) are known in the art, as disclosed, for example, in U.S. Pat. No. 5,057,153.
U.S. Pat. No. 5,185,033 describes a process for making a paint or paint base containing copper pyrithione or pyrithione disulfide plus cuprous oxide, wherein the paint exhibits stability against gelation during storage.
U.S. Pat. No. 5,246,489 discloses a process for providing in situ generation of copper pyrithione in a paint or paint base which comprises incorporating a metal salt of pyrithione, cuprous oxide and a controlled amount of water into the paint either during or after the formation of the paint.
In many applications, copper pyrithione offers several advantages over other forms of pyrithione such as zinc pyrithione. For example, copper pyrithione is more stable than zinc pyrithione when added to paint products and therefore is less likely to cause gelation during storage.
Commercially available copper pyrithione is typically sold as a dry powder, which easily generates dust. Copper pyrithione powder was shown to be more toxic than zinc pyrithione powder when tested for acute inhalation toxicity in rats. The copper pyrithione dust can pose an inhalation hazard when handling powder in poorly ventilated areas. The advantage of a non-dusting copper pyrithione product over the powder product is the significant reduction of the inhalation hazard to the customers and/or the employees working with the non-dusting product, as compared to the powder.
Certain non-dusting forms of copper pyrithione have been previously disclosed. More specifically, PCT publication WO00/54589 discloses coated copper pyrithione particles having a coating selected from among glycerol, dialkyl phthalates, lubricating oils, acrylic resins, rosins, fatty acid amides, dialkylpolysulfides, polybutene, paraffins, and vaseline. Unfortunately, the process of producing these coated particles typically necessitates the cumbersome steps of mixing/kneading or distillation of solvent under reduced pressure, as described on the page preceding the working examples of the WO00/54589 publication. Accordingly, what is now needed is simpler methodology for providing non-dusting copper pyrithione. The liquid/solid dispersions of the present invention provide one answer to that need.
SUMMARY OF THE INVENTION
In one aspect, the present invention is directed to a non-dusting copper pyrithione dispersion of solid copper pyrithione in a liquid dispersant. More specifically, the dispersion comprises (a) from about 20% to about 99% (preferably from about 20% to about 70%) by weight of solid copper pyrithione particles dispersed in (b) from about 0.05% to about 80% by weight of a liquid dispersant selected from the group consisting of water, organic solvents, and combinations thereof. The dispersion additionally comprises (c) from about 0.05% to about 30% of a dust-inhibiting agent selected from the group consisting of surfactants, polymer resins, binders, and combinations thereof. All of these weight percents are based on the total weight of the dispersion.
In another aspect, the present invention is directed to a method of making a non-dusting copper pyrithione dispersion by dispersing component (a) in component (b), either prior to, simultaneously, or after, combining dust inhibiting additive (c) with component (b) in order to prepare the desired dispersion comprising (a) plus (b) plus (c).
A dispersion of solid non-dusting copper pyrithione particles in a liquid dispersant, said copper pyrithione particles being coated with a coating compound selected from the group consisting of hydrocarbon resin monomer produced from co-polymerization of vinyltoluene and alpha-methylstyrene, rosins, polystyrene, cellulose, shellac, acrylic polymers, poly-D,L-lactic acid, poly-D,L-lactic-co-glycolic acid, zein, polymer esters of dicarboxylic acids, polyvinylacetate phthalate, polyvinyl alcohol, polyacrylic acid, ethyleneglycol, polyvinyl pyrrolidone, sodium lignosulfonate, chitosan, guar gums, polysaccharides, and combinations thereof.
These, and other aspects of the present invention, will become apparent upon reading the following detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an improved solution to the dusting problem typically associated with dry powders of copper pyrithione. The present inventors have solved this problem combining copper pyrithione with one or more dust-inhibiting agents in a solvent to provide a substantially non-dusting or dust-free copper pyrithione composition. The non-dusting or dust-free copper pyrithione composition of the present invention takes the form of a solid/liquid dispersion. This solid/liquid dispersion is easy to handle, minimizing solids handling problems, and reducing or eliminating the risk of inhalation exposure of airborne levels of copper pyrithione. Moreover, the inclusion of a dust-inhibiting component in the dispersion of the present invention contributes both to the inhibition of dust formation from the dispersion, and to the inhibition of the formation of gels or thick thixotropic precipitates, thus contributing to an enhanced shelf life for these dispersions.
As used herein, the term “dispersion” is intended to encompass both low viscosity solid/liquid admixtures, and higher viscosity solid/liquid compositions, such as pastes. Generally, the viscosity of the dispersion is in the range of from about 1,000 cps to about 100,000 cps at room temperature, preferably between about 5,000 cps and 70,000 cps at room temperature, wherein “cps” denotes Centipoise.
As used herein, the terms “non-dusting” and “dust-free” refer to a composition that is substantially free, advantageously greater than least 99% by weight free, of airborne copper pyrithione particles. The term “dust-inhibiting agent” refers to compounds that prevent or inhibit the formation of dust, as compared to a composition that does not include those compounds. “Airborne particles” are described in detail under the “Sampling Criteria for Airborne Particulate Matter” found in the “1999 Threshold Limit Values and Biological Exposure Indices” published by the American Conference of Governmental Industrial Hygienists. More specifically, that publication states that, for chemical substances present in inhaled air as suspensions of solid particles or droplets, the potential hazard associated with airborne particles depends on particle size as well as mass concentration.
As indicated above, the present invention is a non-dusting copper pyrithione dispersion comprising copper pyrithione, a dispersant, and a dust-inhibiting compound selected from the group consisting of surfactants, polymer resins, binders, and combinations thereof. Each of these components is discussed in more detail below.
Copper pyrithione is available commercially (from Arch Chemicals, Inc., Norwalk, Conn.) in the form of a dry powder. This form of copper pyrithione may be used directly in the dispersion of the invention, or copper pyrithione may be made my conventional methods known in the art, as disclosed in U.S. Pat. Nos. 5,650,095; 5,540,860; 5,238
Hobbs Patrick
Waldron Craig
Arch Chemicals Inc.
Carlson Dale Lynn
Lovering Richard D.
Wiggin & Dana LLP
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