| 摘要 |
PURPOSE: Provided are water soluble or water dispersible, urethane-modified polyisocyanate mixtures, which have excellent solvent resistance, chemical resistance, impact resistance and elasticity, and thus are suitable to be used in an aqueous stoving lacquer composition. CONSTITUTION: The aqueous stoving lacquer composition comprises (a) a water dispersible or water soluble polyhydroxyl compound and (b) a polyisocyanate mixture having blocked isocyanate groups. The water dispersible or water soluble polyhydroxyl compound (a) comprises a urethane-modified polyester resin which has an acid number of 12 to 30, a hydroxyl number of 30 to 130 and a solvent content below 5.5 wt%, and comprises the reaction product of (a1) a polyester polyol, (a2) a bis(hydroxymethyl) alkane-carboxylic acid, (a3) a low molecular weight diol or triol, and (a4) a polyisocyanate component, at least 60% of which is a linear aliphatic polyisocyanate having a molecular weight of 168 to 1000. The polyisocyanate mixture (b) has urethane groups and blocked isocyanate groups and an average NCO-functionality, based on reversibly blocked isocyanate groups, of 2.0 to 2.6, and comprises the reaction product of (i) at least one organic diisocyanate with (ii) at least one monofunctional blocking agent for isocyanate groups, (iii) at least one monobasic or dibasic hydroxycarboxylic acid, (iv) at least one dihydric to hexahydric alcohol, and (v) at least one diol, wherein the reaction product is converted into a salt form by the at least partial neutralization of the incorporated carboxyl groups.
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