Aqueous polyurethane dispersion for use as binder in quick-drying paint for cars, is based on high- and low-molecular weight diol compounds with polyhydroxy component, polyisocyanate and hydroxy- or amino-acid

摘要

Aqueous polyurethane dispersion from high- and low-mol. wt. diols, polyisocyanates and compounds with an acid group and 1 or 2 hydroxyl or amino groups, in which all the neutralizing agent is added before chain extension, the degree of neutralization is 40-105%, one of the diols contains at least 1 wt% tri- or higher-functional component and the urea group content is 1-4 wt%. An aqueous polyurethane (PUR) dispersion contains the reaction product of: (A) difunctional polyol(s) with a mol. wt. of 500-6000; (B) at least difunctional low-mol. wt. alcohol(s); (C) di- and/or tri-functional isocyanate(s); and (D) compound(s) with an acid group and one or two hydroxyl and/or prim. or sec. amino groups in an amount such that the product shows an acid number of less than 25 mg KOH/g solid. In this system: (i) all the neutralizing agent is added before the chain extension reaction; (ii) the degree of neutralization is in the range 40-105% based on acid groups; (iii) the starting materials for polyol(s) (A) or the low-mol. wt. component (B) contain(s) at least 1 wt% tri- or higher-functional components, based on total solid in (A-D); and (iv) the content of isolated urea groups, i.e. groups -(NH-CO-NH)- in the formula (I) is 1-4 wt%. (PUR-DIR)-(NH-CO-NH)-(DIR-PUR) (I) DIR = a di-isocyanate residue. Independent claims are also included for: (a) a process for the production of aqueous PUR dispersions by making an NCO- and acid-functional prepolymer from components (A-D) in organic solution, adding neutralizing agent (NA) equivalent to 40-105% of the acid groups, dispersing the prepolymer in or with water, possibly adding more NA up to the maximum (equivalent to 105%), stirring at 25-75 deg C to complete the chain extension with the NCO/water reaction and removing solvent (to a content of less than 5%) during or after dispersion or during or after chain extension; and (b) paint for barrier layers, containing 30-90 wt% PUR dispersion as described, 0-20 wt% crosslinker, 5-70 wt% pigments and/or fillers and 0-65 wt% other binders, plus the usual additives etc. for vehicle paint and possibly water to adjust the spray viscosity.