5 октября, 2015 
Malyar Solventless, multifunctional isocyanates are available based on aromatic diphenyl methene-4-4’-di-isocyanate (MDI) or aliphatic hexamethylene di-isocyanate (HMDI), although due to toxicity reasons, HMDI itself would not be used, but lower volatility adducts may be an alternative. In dried coatings, the water dispersible isocyanates undergo the usual reaction with active hydrogen groups. See Figure 7-18. (Also see isocyanate Chapter for more details on isocyanate reactions ).
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Figure 7-18: Reaction of Polyisocyanate with Active Hydrogen |
The competing reaction with water limits the pot life of the formulation to a few hours. Aqueous formulations do not exhibit an increase in viscosity unlike their solvent based counterparts as the end of the pot life is approached, they simply fail to improve coating system properties. This can be a problem for any continuous production process.
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