Aqueous uretdione group-containing compositions and method for producing same

Abstract

The invention relates to aqueous uretdione group-containing compositions comprising or consisting of (A) at least one uretdione group-containing curing agent based on aliphatic, cycloaliphatic, araliphatic, and/or aromatic polyisocyanates which do not contain chemically bonded hydrophilating groups; (B) at least one hydroxy group-containing polyol which contains at least one chemically bonded carboxylic acid group; (C) optionally solvents; and (D) optionally auxiliary agents and additives; wherein the quantity ratio of the components (A) and (B) is measured such that the molar ratio of the NCO groups of the curing agent (A), said groups being provided in the form of uretdione, to the NCO reactive groups of the polyol (B) equals 3.0:0.5 to 0.5:3.0, and A and B are provided as a physical mixture. The invention additionally relates to a method for producing a polyurethane layer using the aqueous uretdione group-containing composition according to the invention, to the polyurethane layer obtained therefrom, and to a substrate which is coated with or adhered to the polyurethane layer.

1 . An aqueous uretdione group-containing compositions comprising;
 (A) at least one uretdione group-containing curing agent based on aliphatic, cycloaliphatic, araliphatic or aromatic polyisocyanates that contains no chemically-bonded hydrophilizing groups;   (B) at least one hydroxyl-containing polyol that contains at least one chemically-bonded carboxylic acid group;   (C) optionally, solvents; and   (D) optionally, auxiliaries and additives;   wherein the quantitative ratio of components (A) and (B) is such that the molar ratio of the NCO groups of the curing agent (A) present as uretdione to NCO-reactive groups of the polyol (B) is 3.0:0.5 to 0.5:3.0 and wherein A and B are present as a mixture.   
     
     
         2 . The composition as claimed in  claim 1 , wherein the at least one uretdione group-containing curing agent (A) is obtained by reacting monomeric isocyanates comprising at least one monomeric isocyanate selected from the group consisting of tetramethylene diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate-, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, dicyclohexylmethane-2,4′-diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, tetramethylxylylene diisocyanate, triisocyanatononane, tolylene diisocyanate, diphenylmethane-2,4′-diisocyanate, diphenylmethane-4,4′-diisocyanate, triphenylmethane-4,4′-diisocyanate, naphthylene-1,5-diisocyanate, and mixtures thereof. 
     
     
         3 . The composition as claimed in  claim 1 , wherein hydroxyl-containing monomers or polymers are used as starting materials for the at least one uretdione group-containing curing agent (A). 
     
     
         4 . The composition as claimed in  claim 1 , wherein the at least one uretdione group-containing curing agent (A) has a free NCO content of less than 5% by weight and a content of uretdione groups of 1% to 18% by weight (calculated as C 2 N 2 O 2 , molecular weight 84 g/mol). 
     
     
         5 . The composition as claimed in  claim 1 , wherein the aqueous composition has an acid value of 1 to 100 mg KOH/g. 
     
     
         6 . The composition as claimed in  claim 1 , wherein the at least one hydroxyl-containing polyol (B) is obtained by reacting hydroxy- or aminocarboxylic acids comprising at least one carboxylic acid selected from the group consisting of 2,2-dimethylolacetic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, α,Ω-diaminovaleric acid, and mixtures thereof. 
     
     
         7 . The composition as claimed in  claim 1 , wherein the polyol (B) containing at least one hydroxyl group has an OH content greater than 1% by weight, calculated as OH groups based on the solids content, a molecular weight of 17 g/mol, and a number-average molecular weight Mn of 500 to 20 000 g/mol. 
     
     
         8 . The composition as claimed in  claim 1 , wherein the solvent is selected from the group consisting of acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, solvent naphtha, propylene glycol mono-n-butyl ether, dipropylene glycol dimethyl ether, methoxypropyl acetate, dibasic esters, and mixtures thereof. 
     
     
         9 . The composition as claimed in  claim 1 , wherein the auxiliaries and additives are selected from the group consisting of leveling agents, light stabilizers, catalysts, fillers, and pigments, and mixtures thereof. 
     
     
         10 . The composition as claimed in  claim 1 , wherein the sum of the proportions by weight of (A), (B), and (D) is 30% to 60% by weight based on the solids content of the total aqueous composition. 
     
     
         11 . A process for producing a polyurethane layer comprising the steps of
 i) providing an aqueous uretdione group-containing composition as claimed in  claim 1 ;   ii) applying to a substrate the composition obtained in i) to produce a mixture;   iii) drying the mixture from step ii), and   iv) curing the mixture from step iii) by heating to from 40° C. to 180° C. for up to 180 minutes.   
     
     
         12 . The process as claimed in  claim 11 , wherein the aqueous uretdione group-containing composition is obtained by mixing the uretdione group-containing curing agent (A) with the polyol (B) containing at least one hydroxyl group in the absence of water to obtain a mixture, and subsequently dispersing the mixture with water. 
     
     
         13 . A polyurethane layer obtained by the process as claimed in  claim 11 . 
     
     
         14 . A substrate coated or bonded with the polyurethane layer as claimed in  claim 13 .