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
2000-07-27
2003-08-12
Sergent, Rabon (Department: 1711)
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...
C128S849000, C128S850000, C424S078020, C424S078030, C424S078370, C427S002100, C524S839000, C524S840000, C528S071000
Reexamination Certificate
active
06605666
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to a composition in the form of a stable hydroalcoholic polyurethane dispersion containing polymers. The composition exhibits film-forming properties and can be formulated to have anti-microbial activity.
BACKGROUND
Polyurethane is a generic term used to describe polymers prepared by the reaction of a polyfunctional isocyanate with a polyfunctional alcohol to form urethane linkages. The term “polyurethane” has also been used more generically to refer to the reaction products of polyisocyanates with any polyactive hydrogen compound including polyfunctional alcohols, amines, and mercaptans. Polyurethanes are used in a variety of applications including as elastomers, adhesives, coatings, and impregnating agents.
For coating applications, polyurethane polymers can be dispersed in water by incorporating stabilizing groups into their backbone. Anionic, cationic and non-ionic dispersion stabilizing groups have been used. Various aqueous polyurethane dispersions have been prepared by those skilled in the art. For example, U.S. Pat. No. 3,479,310 (Dieterich et al.) discloses water-dispersed polyurethane polymers suitable for uses as waterproof coatings. The polymer is prepared from polyhydroxy compounds, polyisocyanates, optional chain lengthening agents, and a sufficient amount of a component having an ionic salt-type group. U.S. Pat. No. 4,307,219 (Larson) discloses dispersible polyurethane resin prepared by reaction of hydrophilic diols, hydrophobic diols, diisocyanates, and, optionally, chain extenders. Such a urethane resin can be used as protective coatings, primers, and binders.
Although aqueous dispersions of polyurethanes have been widely disclosed, the inventors are not aware of any references to stable polyurethane dispersions in alcohol-water solvent systems, particularly when prepared from very hydrophobic polyols. Polyurethane dispersions in hydro-alcohol (i.e., alcohol-water) systems are especially difficult for at least two reasons.
First, the addition of lower alcohols (e.g., C
1
to C
4
) to water decreases the surface tension of the solvent system. For example, a 40 weight percent (wt %) ethanol in water system has a surface tension of about 31 dyne/cm compared to a pure water system, which has a surface tension of about 72 dyne/cm at about 20° C. A 60 wt % ethanol in water system has a surface tension of 27 dyne/cm at about 20° C. The reduction in surface tension can affect the ability to self assemble hydrophilic and hydrophobic domains during the dispersion preparation. Second, many of the polyurethane components (i.e., the starting reactants) are soluble in hydro-alcohol solvent systems, which result in solutions and not dispersions. Polymer solutions have substantially higher viscosity than polymer dispersions, making them harder to process in certain operations, such as coating and spraying operations. Polymer solutions also tend to achieve lower percent solids when compared to polymer dispersions, making the former less attractive during coating operations and during shipping. Lower solids solutions also require longer drying times than dispersions to form a film because of the greater amount of solvent present the higher affinity of the polymer for that solvent, and the immediate formation of a “skin” on the surface of the film as it begins to dry. Furthermore, the molecular weight of soluble polymers is often much lower than that of dispersions.
U.S. Pat. No. 4,507,430 (Shimada et al.) discloses a water-based polyurethane emulsion that comprises a hydrogenated polyalkadiene polyol component and a polyisocyanate component. Shimada discloses that the materials are useful as an adhesive or coating material for a polyolefin resin, and can be applied wet and dried or bonded by dry lamination requiring heat and pressure. While the hydrogenated polyalkadiene polyol component of Shimada is alcohol-water insoluble, there was no disclosure of polyurethane dispersions in hydro-alcohol solvent system.
U.S. Pat. No. 5,672,653 (Frisch et al.) discloses an anionic waterborne polyurethane dispersion prepared by (a) forming a prepolymer from hydroxy terminated polybutadiene resin, an aliphatic isocyanate, and a diol containing acid groups; (b) neutralizing the acid; dispersing it in water; and (c) chain extending the prepolymer with a diamine.
U.S. Pat. No. 4,542,012 (Dell) discloses a dermatologically acceptable film-forming composition. The composition comprises (a) a film-forming polymer that is a reaction product of (i) a prepolymer having a plurality of isocyanate functionalities, (ii) a polyvinyl pyrrolidone polymer; and (iii) a chain extender for the prepolymer and the polyvinyl pyrrolidone polymer; and (b) as an anti-microbial agent, iodine, which forms a complex with the film-forming polymer. The polymer so formed is soluble in the hydroalcoholic solvent. The composition, when applied to skin from a fugitive solvent, is capable of forming a substantially water insoluble, tack-free, flexible film that adheres to skin, releases the anti-microbial agent when the film contacts skin. The film exhibits an elongation of at least about 150% and less than about 1000%.
A need exists in the art for polyurethane dispersions that exhibit anti-microbial activity and are stable in alcohol-water solvent systems, where the dispersion has one or more of the following properties: capable of forming stable dispersions in hydro-alcohol systems, capable of rapidly forming films on skin by simple ambient evaporation, and are compatible with antimicrobial agents. Furthermore, films formed by drying down the dispersions exhibit one or more of the following properties: high self adhesion and yet low tack, low humidity sensitivity, high tensile strength, good elongation, transparent, and capable of releasing added antimicrobial agents.
SUMMARY
The present invention provides a novel polyurethane-urea dispersion that can be prepared in the presence of and is dispersed in a hydro-alcohol system. As used herein, the term “hydro-alcohol” refers to solvents based on C
1
to C
4
lower alcohols mixed with water, where the weight ratio of lower alcohol to water is at least 20:80, preferably at least 40:60, more preferably at least 50:50 and most preferably at least 60:40 by weight. It has been found that rapidly drying dispersions can be formed in hydro-alcohol solvent systems where the ratio of lower alcohol to water is at least 70:30, more preferably at least 80:20 and most preferably at least 85:15 by weight. The preferred lower alcohols include ethanol, 2-propanol, and n-propanol. The term “hydro-alcohol” is synonymous with the term “alcohol-water.”
The polyurethane polymer exists as a dispersion in alcohol-water solvent system. As used herein, a “dispersion” means generally a two phase system where one phase contains discrete particles distributed throughout a bulk substance, the particles being the disperse or internal phase, and the bulk substance the continuous or external phase. In this invention, the continuous phase is the alcohol-water mixture and at least a portion of the polyurethane exists as the discrete particle. By “dispersion,” it is also meant that not necessarily the entire polyurethane polymer needs to be alcohol-water insoluble; at least some of the polymer can be soluble in the alcohol-water mixture. In preferred rapid drying applications, most or all of the polymer is in the dispersed phase. Dispersions are possible through the use of certain components that are insoluble in the alcohol-water solvent system. It is desirable that the dispersion remain stable under ambient conditions. Preferred dispersions are stable at room temperature for more than 30 days, preferably more than 90 days, more preferably for more than 180 days, and most preferably for more than 360 days.
In brief summary, in one aspect, the invention provides a polyurethane dispersion stable in a lower alcohol-water mixture. The dispersion is a reaction product of (a) an isocyanate functional prepolymer comprising the reaction product of: (i) at least one polyacti
Brown Christopher J.
Comstock Kristen L.
Kantner Steven S.
Scholz Matthew T.
Lambert Nancy M.
Sergent Rabon
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