Method for coating zinc-plated steel strips with aqueous formulations of acidic polymers

Abstract

Continuous method of passivating galvanized steel strips with acidic aqueous formulations which comprise at least one water-soluble polymer comprising acidic groups.

1 . A method of continuously passivating a galvanized steel strip with an acidic aqueous formulation comprising at least one water-soluble polymer X comprising acidic groups,
 the polymer X having at least 0.6 mol of acid groups/100 g of polymer,   the pH of the formulation being not more than 5, and   the amount of all the polymers X together being 10% to 30% by weight, based on the amount of all the components of the formulation,   
     and the galvanized steel strip being moved in its longitudinal direction through an adjustable gap between two opposing rolls, which rotate in the direction of travel of the steel strip, and wherein
 the acidic aqueous formulation is applied to at least one of the two rolls using an applicator means, and between the applicator means and the gap in the direction of rotation of the roll there is at least one doctor means with which, by removal of excess formulation, it is possible to set the amount of the aqueous formulation per unit area of the roll, 
 the film located on the roll, on contact with the galvanized surface of the steel strip, is transferred wholly or partly to the galvanized surface, and 
 the wet film is dried in a drying means disposed downstream of the pair of rolls in the direction of travel of the strip. 
 
   
   
       2 . The method according to  claim 1 , wherein the doctor means comprises a means comprising at least one rotating doctor rod. 
   
   
       3 . The method according to  claim 2 , wherein the rotating doctor rod has grooves in the surface. 
   
   
       4 . The method according to  claim 1 , wherein the doctor means comprises a means comprising at least one doctor knife. 
   
   
       5 . The method according to  claim 1 , wherein formulation removed by the doctor means is returned to the coating operation. 
   
   
       6 . The method according to  claim 1 , wherein the amount of the aqueous formulation per unit area of the roll is set such that no build-up is formed ahead of the gap. 
   
   
       7 . The method according to  claim 1 , wherein the thickness of the dried passivation coat formed is less than 1 μm. 
   
   
       8 . The method according to  claim 1 , wherein the acidic groups of the polymer X are groups selected from the group consisting of carboxyl groups, sulfonic acid groups, phosphoric acid groups, and phosphonic acid groups. 
   
   
       9 . The method according to  claim 1 , wherein the acidic groups of the polymer X are groups selected from the group consisting of carboxyl groups, phosphoric acid groups, and phosphonic acid groups. 
   
   
       10 . The method according  claim 1 , wherein the acidic, water-soluble polymer X is a homopolymer or copolymer comprising (meth)acrylic acid units. 
   
   
       11 . The method according to  claim 1 , wherein the acidic, water-soluble polymer X is a copolymer X1 which is composed of the following monomeric units—based in each case on the amount of all the monomers copolymerized into the copolymer:
 (A) 30% to 90% by weight of (meth)acrylic acid,   (B) 10% to 70% by weight of at least one further monoethylenically unsaturated monomer, different from (A), which has one or more acidic groups, and also   (C) optionally 0% to 40% by weight of at least one (meth)acrylic ester having OH groups,   (D) optionally 0% to 30% by weight of at least one further ethylenically unsaturated monomer, different from (A), (B) or (C).   
   
   
       12 . The method according to  claim 11 , wherein the monomers (B) are monomers selected from the group consisting of
 (B1) monoethylenically unsaturated dicarboxylic acids having 20 to 23 carbon atoms, and/or   (B2) monoethylenically unsaturated phosphoric and/or phosphonic acids.   
   
   
       13 . The method according to  claim 1 , wherein the amount of monomer (C) is 1% to 30% by weight. 
   
   
       14 . The method according to  claim 1 , wherein not more than 25 mol % of the acid groups of the polymer X are neutralized. 
   
   
       15 . The method according to  claim 1 , wherein the amount of acids in the formulation does not exceed 20% by weight relative to the amount of all the polymers X together. 
   
   
       16 . (canceled) 
   
   
       17 . The method according to  claim 2 , wherein formulation removed by the doctor means is returned to the coating operation. 
   
   
       18 . The method according to  claim 3 , wherein formulation removed by the doctor means is returned to the coating operation. 
   
   
       19 . The method according to  claim 4 , wherein formulation removed by the doctor means is returned to the coating operation. 
   
   
       20 . The method according to  claim 2 , wherein the amount of the aqueous formulation per unit area of the roll is set such that no build-up is formed ahead of the gap. 
   
   
       21 . The method according to  claim 3 , wherein the amount of the aqueous formulation per unit area of the roll is set such that no build-up is formed ahead of the gap.