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
1998-09-11
2001-02-20
Yoon, Tae (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...
C524S544000, C524S547000, C524S556000, C526S310000
Reexamination Certificate
active
06191211
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a water-dispersible polymeric composition that can be used to prepare quick-set films or coatings.
Coatings provide protective barriers for a variety of things including floors, automobiles, exteriors and interiors of houses, and human skin. Protective coatings for floors, for example, have been known since the mid 1950s. Many of the early coating materials were applied using petroleum- or naphthene-based solvents and as such were undesirable due to the toxicity and flammability of these solvents.
Water-based synthetic emulsion compositions, such as styrene resin emulsions, styreneacrylate copolymer resin emulsions, and acrylate emulsions, developed in the early 1960s, gradually replaced organic solvent-based compositions. Although these water-based compositions are less toxic and more environmentally friendly than organic solvent-based compositions, the water-based compositions tend to be slow to set and difficult to remove in an application where removability is desired. Removal of coatings may be desirable because even the most durable coatings tend to deteriorate due to soiling or wear and tear. In other applications, such as protective care products for the skin, the advantages of water-based removable coatings are obvious.
Removable, water-based coatings are known. For example, polymers that contain ammonium carboxylate functionality are water compatible, but become incompatible through the loss of solvent and ammonia.
Coatings made by the above-illustrated process can be subsequently removed by contact with an aqueous alkaline liquid, which converts the acid back into the compatible salt.
For example, in U.S. Pat. No. 4,622,360, Gomi et al. discloses a removable water-borne polyurethane resin containing carboxyl groups. Coating compositions can be prepared by adding a polyvalent complex-forming metal to the water-borne resin. The polyvalent metal forms a stable water-dispersible complex with an amine or ammonia in the aqueous solution. When the dispersion is applied to a floor surface, noxious volatile materials evaporate to allow the polyvalent metal ions to initiate a crosslinking of two or more carboxyl groups, thereby forming a hardened, water-incompatible coating. This hardened coating can be removed, but only with a harsh alkaline solution containing ligands such as ethylene diamine tetraacetic acid.
The ammonium carboxylate coating suffers from several disadvantages: 1) the formulations are malodorous and irritating to the eyes and skin; 2) long set times are required to attain acceptable physical properties of the coating; and 3) the removal or stripping process requires the use of hazardous alkaline liquids.
In view of the deficiencies of the known art, it would be desirable to have a composition that provides a quick-set film or coating that can be removed without the use of harsh chemicals in applications where such removal is desirable. It would further be desirable to render such a coating resistant to common organic solvents in applications where general solvent resistance is desired.
It would further be useful to have a hypoallergenic, non-toxic, water-based composition that provides a coating that gives long-lasting protection to the skin against sun, dryness, and harsh chemicals.
SUMMARY OF THE INVENTION
The present invention is a composition comprising an aqueous-based sol of a polymer having a backbone that contains pendant cationic groups and pendant acid groups, which sol is prepared by the steps of:
a) forming a solution of a polymer that contains pendant cationic groups and pendant acid groups in an aqueous-based solvent for the polymer, which solvent contains a first organic solvent; and
b) removing a sufficient amount of the first organic solvent from the solution to form a composition characterized by being reversibly dissolvable and reconstitutable by addition and removal of a second organic solvent.
In a second aspect, the present invention is a method of coating a substrate comprising the step of applying to a surface of the substrate a composition containing a water-compatible coalescing agent and an aqueous-based sol of a polymer having a backbone that contains pendant cationic groups and pendant acid groups, wherein the sol is prepared by the steps that comprise:
a) forming an aqueous-based solution of the polymer, which solution contains an organic solvent;
b) removing a sufficient amount of the organic solvent from the solution to form a composition having a minimum solids content such that the viscosity of the sol is less than half the viscosity of the solution having the same solids content;
wherein the coalescing agent is an organic liquid having a boiling point greater than 100° C.
In a third aspect the present invention is a composition comprising an aqueous-based sol of a polymer having a backbone that contains pendant cationic groups and pendant acid groups wherein the sol is further characterized by being reversibly dissolvable and reconstitutable by addition and removal of an organic solvent for the sol.
The composition of the present invention provides quick-set films that can be prepared in the absence of additional surface active agents and with a substantial absence of organic solvents. The sol affords a higher concentration of solids at considerably lower viscosities than a corresponding solution.
DETAILED DESCRIPTION OF THE INVENTION
The composition of the present invention comprises an aqueous-based sol of a polymer having a backbone that contains pendant cationic groups and pendant acid groups.
As used herein, the terms “aqueous-based sol” or “sol” refer to a suspension of the polymer in a water-containing medium. The medium must include water, and may include a suitable organic solvent. The sol is characterized by being reversibly dissolvable and reconstitutable (that is, returned to the sol state) by addition and subsequent removal of a suitable organic solvent, which may be the same as or different from the organic solvent that may be present in the sol. It is also possible to remove all of the aqueous-based solvent from the sol to form a solid, and then reconstitute the sol by dissolving the solid in a suitable aqueous-based solvent, then removing a sufficient amount of the organic solvent (and optionally adding sufficient water) to reconstitute the sol. The suspended particles preferably have an average particle size (as measured by a Coulter Model N4MD Sub-Micron Particle Analyzer) of not less than 10 nm, and more preferably not less than about 20 nm, and preferably not more than about 500 nm, more preferably not more than about 300 nm, and most preferably not more than 200 nm.
The dissolved polymer is differentiated from the sol by the differences in the viscosities of the two compositions at a given minimum polymer concentration and the amount of organic solvent needed to form a solution. Specifically, the viscosity of the sol is preferably less than half, more preferably less than one-third, and most preferably less than one-tenth the viscosity of the dissolved polymer at a polymer concentration of not less than about 5 weight, more preferably not less than about 10 percent, based on the weight of the solution or sol. Furthermore, the minimum amount of organic solvent required to form a solution is greater than the maximum amount of organic solvent required by a sol. Specifically, the minimum amount of organic solvent required to form a solution is typically greater than 20 weight percent based on the weight of the polymer and the aqueous-based solvent. On the other hand, the maximum amount of the organic solvent required by a sol is typically less than 20, more preferably less than 10, and most preferably less than 6 weight based on the weight of the polymer and the sol.
The polymer is characterized by containing pendant cationic groups and pendant acid groups. Generally, these pendant groups can be formed from the polymerization of a polymerizable cationic monomer, preferably a strong cationic monomer, and a polymerizable acid monomer, which may b
Mussell Robert D.
Rose Gene D.
Schmidt Donald L.
The Dow Chemical Company
Willis Reid S.
Yoon Tae
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