Polyurethane films and dispersions for the preparation thereof

A polyurethane film is disclosed, wherein the film is prepared from a polyurethane dispersion, the dispersion being prepared from a non-ionic polyurethane prepolymer, and the prepolymer being prepared from a polyurethane prepolymer formulation including a diisocyanate and an active hydrogen containing material. The dispersion is formed in a two or more step process wherein, in a first step the prepolymer is formed and, in a subsequent step, an aqueous dispersion of the prepolymer is formed, in the presence of an anionic surfactant, both steps occurring in the substantial absence of an organic solvent. A process for preparing the film and a dispersion useful in making the film are also disclosed. The present invention substantially avoids many of the handling concerns with the dispersions and films of the prior art. Moreover, the present invention is suitable for use in applications such as, for example, medical applications, including gloves, condoms, medical bags, and catheters.

The following examples are for illustrative purposes only and are not intended to limit the scope of the claimed invention. Percentages are in weight percents unless otherwise stated. 
 EXAMPLES The following materials are used in the examples below: Polyether Polyol is a 2000 molecular weight polyoxypropylene diol having 12.5 percent ethylene oxide end capping. Low Molecular Weight Diol is a 425 molecular weight all polyoxypropylene diol. Polyisocyanate A is MDI having a 4, 4′ isomer content of 98 percent and an isocyanate equivalent weight of 125. Polyisocyanate B is MDI having a 4, 4′ isomer content of 50 percent and an isocyanate equivalent weight of 125. Surfactant is 22 percent solution of sodium dodecyl benzene sulfonate in water. Diamine is a 230 molecular weight polyoxypropylene diamine. 
 Example 1 A polyurethane prepolymer is prepared by admixing 52.0 parts of Polyether Polyol and 14.7 parts of Low Molecular Weight Diol and then heating the admixture to 50° C. This material is then admixed with 33.3 parts of Polyisocyanate A which has also been warmed to 50° C. A small amount of benzoyl chloride is added to neutralize residual base in the polyols. The admixture is then heated at 70° C. for 4 hours and then tested to determine NCO content. The NCO content is 5.75 percent. A polyurethane dispersion is prepared by admixing 200 g of the prepolymer admixed with 13 g water and 38 g surfactant using a high shear mixer running at about 2500 rpm. Additional water is slowly added until a phase inversion is observed. Additional water is added until the solids content is 40 percent. A film is then prepared by a coagulation process by heating a steel plate in and oven until it reached a temperature of from 100 to 120° F. (38-49° C.). The plate is then dipped into a 20 percent solution of calcium nitrate in 1:1 by weight of water and methanol which also included about 1 wt % of a ethoxylated octylphenol surfactant. The plate is then placed into an oven at 230° F. (110° C.) for approximately 15 minutes to form a very thin film of calcium nitate on the plate. The plate is allowed to cool to 105° F. (40° C.) and then dipped into the polyurethane dispersion diluted to 23% solids with deionized water and removed (total dwell time is approximately 20 sec). The plate is held for 5 minutes at room temperature to allow the film to generate enough gel strength, followed by leaching in a water bath at 115° F. (46° C.) for 10 minutes. Both sides of the plate is then sprayed with water at 115° F. (40° C.) for two additional minutes. The plate is then heated to 230° F. (110° C.) for 30 minutes and then cooled to ambient temperature. A polyurethane film is peeled from the substrate and tested using ASTM Designation D 412-98 a (Die C; overall length&equals;4.5″, width of narrow section&equals;0.25″, and gauge length&equals;1.31″) Testing results are presented in the table. It is tactilely soft and yet has good physical properties. 
 Example 2 A polyurethane dispersion is prepared by dispersing the prepolymer of Example 1 as in Example 1 except that the water added to the dispersion after the phase inversion includes Diamine at a concentration of 0.25 equivalent stoichiometry based on available isocyanate content). The polyurethane dispersion was then diluted to 23% solids and coagulated according to the procedure described in the Example 1. 
 Examples 3 and 4 These polyurethane prepolymers are prepared substantially similarly to the procedure in Example 1 except that the prepolymer compositions are changed as indicated in the table, and the prepolymers are reacted with water and surfactant as described in the Example 1. The polyurethane dispersions are then diluted to 23% solids and coagulated according to the procedure described in the Example 1. 
 Example 5 A polyurethane prepolymer and dispersion are prepared substantially similarly to Example 4 except that the water added to the dispersion after the phase inversion includes Diamine at a concentration of 0.25 NCO stoichiometry. The polyurethane dispersion was then diluted to 23% solids and coagulated according to the procedure described in the Example 1. 1 TABLE EXAMPLE 1 2 3 4 5 POLYETHER 52 52 53 52 52 POLYOL (parts by wt) LOW MWT DIOL 14.7 14.7 15 14.7 14.7 (parts by wt) POLY- 33.3 33.3 17 29.1 29.1 ISOCYANATE A (parts by wt) POLY- — — 15 4.2 4.2 ISOCYANATE B (parts by wt) % NCO 5.75 5.75 5.40 5.80 5.80 Chain extension Water Diamine Water Water Diamine (0.25 (0.25 stoichiome stoichiome try) try) TENSILE (PSI) 5830 4342 2604 4976 3020 ELONGATION AT 644 747 995 672 783 BREAK (%) STRESS AT 100% 421 247 173 398 192 ELONGATION (PSI)