Water-dispersible polyisocyanate

Charge the OH functional urethane water dispersion prepared in Example 8 (200 g, 0.1603 eq. OH) to a suitable container. Vigorously stir the dispersion with a mechanical stirrer and slowly add the 18.8% NCO water-dispersible polyisocyanate described above (40.0 g, 0.1791 eq.). This will give an NCO-OH equivalent ratio (index) of 1.12. To this mixture, add Silwet L-77 (a flow aid from OSi Specialties) and thoroughly mix. Use a draw-down bar to make 6-mil (0.006-in.) wet-thickness films on glass plates and 5-mil (0.005-in.) films on Bonderite-treated steel panels (Bonderite is from Henkel). Condition the resultant films at 72°F and 50% RH for 2-3 weeks before evaluating. For the finished... 

Water-dispersible polyisocyanate compositions containing polyethylene oxide were previously prepared by the authors (2) and used as aqueous resin adhesives. 

Hydroxy alkyl acrylate and water-dispersible polyisocyanates... 

Two-component waterborne urethane dispersions are similar to the one-component PUD s in that a polyurethane dispersion comprises one of the two components. The second component is usually a crosslinker from the following classes of materials (a) polyisocyanates, (b) aziridines, (c) polycarbodiimides, and (d) epoxies. Many of the crosslinkers are not inherently water-soluble or water-dispersible. Therefore, they must be modified with surface active agents themselves, so as to become emulsifiable in water. 

In contrast to solvent-based systems, the PUR dispersions (Section 5.4) are characterized by their incombustibility and thus by considerably smoother processing. They are high molecular weight hydroxyl polyurethanes disperged in water. Apart from the physically setting one-component systems, two-component systems are also applied, with component B containing special polyisocyanates that react with the -O-H-groups of the hydroxyl polyurethane in aqueous solution. 

Aqueous two-pack polyurethane paints are obtained by combining, for example, hydroxyl-containing polyacrylate dispersions with water-emulsifiable, low-reactive aliphatic polyisocyanates. 

Mixing conventional polyisocyanates into the polyol after reduction with water can result in problems resulting from nonuniform stoichiometry. Hydrophih-cally modified polyisocyanates made by reacting a fraction of the —NCO groups on a polyisocyanate (such as HDI or IPDI isocyanurate) with a polyglycolmonoether are more easily mixed. The modified polyisocyanate is stirred into an aqueous dispersion of a coreactant to form a heterogeneous dispersion in which the polyisocyanate and coreactant are in separate dispersed particles (39-41). 

Efforts are underway to improve superabsorbent polymers used for coolants and water-absorption sheet materials. A water-absorption sheet material made of a polyurethane connected-pore foam from a special polyol and polyisocyanate can be used to disperse superabsorbent polymer powder. This water-absorption sheet has a high rate of water absorption, no volumetric changes, and excellent water-holding ability. Thus, it is ideal for the application of the aforementioned immersing self-absorbing coolant. In the presence of a superabsorbent polymer, urethane reaction takes place to form a polyurethane foam that includes the superabsorbent polymer powder [6]. 

One-component water-borne polyurethane systems can be derived from polyurethane dispersions or blocked polyisocyanates (refer to Section 3.2.1). Blocked isocyanates are added to the co-reactant resins providing one-component systems with excellent shelf life. This type of adhesives is principally used for non-porous materials and the bonding of unlike metals such as aluminium to steel, and stainless steel to mild steel. They are also usefiil in bonding some of the high pressure laminates such as those based on phenoUcs and melamine [39]. Systems based on water-borne blocked polyisocyanate crosslinkers and suitable waterborne polymers approach the performance levels previously obtained only by solvent-borne systems [16]. 

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