Patent EP-0839885-A1 (EP)
Inventor: WANDELMAIER KLAUS DR
IPC: C09D175/04
Filed: 1997-10-28
Abstract: An aqueous binder dispersion for coating materials which are dried physically contains a mixture comprising (A) 20-80 wt.% of at least one polyurethane containing carbonate groups and having a number average molar weight (Mn) of 70000-500000, present as an aqueous dispersion; and (B) 20-80 wt.% of at least one polyurethane resin containing ionic groups but no carbonate groups and preferably no urea groups, having an Mn of 10000-300000 and an acid value of 5-50, obtained by processing a polyurethane pre-polymer containing hydroxyl groups (OH value = 5-75) and having an Mn of 5000-50000. (A) is prepared by reacting the following components: (a) 10-40 wt.% of one or more organic polyisocyanate containing no groups which are hydrophilic or can be converted into hydrophilic groups; (b) 40-80 wt.% of one or more high molecular weight organic polyhydroxy compounds containing no groups which are hydrophilic or can be converted into hydrophilic groups, comprising at least 50 wt.% of at least one polyhydroxypolycarbonate; (c) 0.2-18 wt.% of one or more low molecular weight compounds containing at least two groups that can react with isocyanate groups, but containing no groups which are hydrophilic or can be converted into hydrophilic groups; (d) 1-12 wt.% of one or more compounds containing at least one anionic group or at least one group that can be converted into an anionic group, in addition to at least one hydrogen atom that can react with an isocyanate group; and (e) 0-8 wt.% of one or more nonionic hydrophilic compounds containing at least one isocyanate group or at least one group that can react with an isocyanate group. (B) is prepared by reacting the following components in an organic medium: (f) at least one compound that can react with an isocyanate and has an acid value of 0-10, in the form of (f1) 70-100 wt.% of one or more (preferably carboxyl group free) polyester polyols and/or polyether polyols with a molecular weight of 500-6000; (g) at least one compound with two or more groups that can react with an isocyanate and with one or more anionic groups or groups capable of being converted into anionic groups ; and (h) at least one polyisocyanate with two or more free isocyanate groups per molecule, added in an amount to give a molar ratio of hydroxyl groups in (f) to the isocyanate groups in (g) and (h) is 1.01-3:1. Components (g) can be added separately or as a reaction product (g1) of (g) and one or more organic diisocyanates (g2), the molar ratio of reactive groups in (g) to the number of isocyanate groups in (g2) being 1:1.5-2.5. The reaction product (g1) can be prepared in the presence of (f) and (g) or (g1) are added to give the desired acid value in the resulting polyurethane resin pre-polymer. Before or after at least partial neutralisation of groups in the pre-polymer that can be converted into ionic groups, the pre-polymer is subjected to a chain extending reaction in the organic medium or following transfer into the aqueous phase, by reacting it with a component (i) comprising at least one polyfunctional isocyanate with a free isocyanate group functionality of at least 1.8, in an amount chosen to give the desired Mn for the polyurethane resin end product.