Process for production of a metal substrate containing a protective coating

Abstract

The present invention relates to a process for the production of metal substrates containing a protective coating, especially substrates based on iron, like steel, galvanized steel, or electrogalvanized steel, generally used in construction and in the automotive industry.

1 . A process for the production of a metal substrate, containing a protective coating, said substrate being based on iron, like steel, galvanized steel or electrogalvanized steel, or based on aluminum or its alloys, said process comprising the following steps: 
 (a) degreasing of the substrate with an alkaline solution, this step being optional when treatment is carried out directly on a continuous galvanizing or electrogalvanizing line;    (b) rinsing with water, preferably demineralized;    (c) activation of the metal substrate with an activation composition based on at least one metal fluoroacid;    (d) drying of the metal substrate;    (e) application of an aqueous primer composition capable of being polymerized by irradiation with UV radiation or by electron bombardment, to form film of aqueous primer composition at least on 1 μm thick, preferably 3 to 5 μm thick, said primer composition containing: 
 a polymer binder, containing:  
 40 to 85 % by weight, relative to the total weight of said primer composition, of at least one unsaturated polymer resin, containing at least one acrylate group and capable of being polymerized by irradiation with UV radiation or by electron bombardment;  
 5 to 50 % by weight, relative to the total weight of said primer composition, of at least one saturated polymer resin not containing an acrylate group; and  
 in the case, where polymerization is performed by irradiation with UV radiation, 1 to 10 % by weight, relative to the weight of the said primer composition, of at least one photoinitiator;  
 a pigment paste, containing:  
 a grinding resin;  
 1 to 20 % by weight, relative to the total weight of said primer composition, of at least one corrosion inhibitor pigment; and  
 optionally, at least one filler; and  
 water, preferably demineralized, as dispersion medium of said primer composition,  
   (f) heat treatment to eliminate the residual water of the film of aqueous primer composition, and    (g) crosslinking of the film of aqueous primer composition to obtain a primer film, having a thickness of at least 1 μm, and preferably 3 to 5 pm, after crosslinking.    
   
   
       2 . The process according to  claim 1 , characterized by the fact that degreasing step (a) of the substrate is carried out with an alkaline solution with a pH equal to or greater than 12, preferably about 13.  
   
   
       3 . The process according to  claim 1  or  2 , characterized by the fact that the alkaline solution used in degreasing step (a) of the substrate is a solution based on potassium hydroxide or sodium hydroxide.  
   
   
       4 . The process according to any of the  claims 1  to  3 , characterized by the fact that the degreasing step (a) of the substrate is carried out by immersion in a bath of said alkaline solution, whose temperature ranges from55 to 60° C.  
   
   
       5 . The process according to any of the preceding claims, characterized by.the fact that the metal fluoroacid of the activation composition of step (c) is chosen from fluorozirconic acid, fluorotitanic acid and fluorosilicic acid.  
   
   
       6 . The process according to  claim 5 , characterized by the fact that the fluoroacid is fluorozirconic acid.  
   
   
       7 . The process according to  claim 6 , characterized by the fact that the fluorozirconic acid is present in an amount of 0.1 g/L to 20 g/L, relative to the weight of the activation composition.  
   
   
       8 . The process according to  claim 6  or  7 , characterized by the fact that the fluorozirconic acid is associated with a resin having an epoxide structure, preferably a resin derived from polyepoxides, especially bisphenol A.  
   
   
       9 . The process according to any of the preceding claims, characterized by the fact that the unsaturated polymer resin, containing at least one acrylate group of the primer composition of step e), is a resin, chosen from epoxy-acrylates, urethane-acrylates, polyester-acrylates, polyester-urethane-acrylates, ether acrylates, amine acrylates or their mixtures.  
   
   
       10 . The process according to  claim 9 , characterized by the fact that the unsaturated polymer resin, containing at least one acrylate group, is a urethane-acrylate resin.  
   
   
       11 . The process according to one of the preceding claims, characterized by the fact that the saturated polymer resin not containing an acrylate group of the primer composition of step e) is chosen among dispersions or emulsions of acrylic, acrylic-styrene, acrylic-urethane and polyester resin.  
   
   
       12 . The process according to any of the preceding claims, characterized by the fact that the photoinitiator of the primer composition of step e) is chosen among benzyl ketones, dialkylacetylphenones, alpha-hydroxyalkylphenones, acylphosphine oxides and benzophenone.  
   
   
       13 . The process according to any of the preceding claims, characterized by the fact that the grinding resin of the primer composition of step e) consists of a saturated polymer resin not containing an acrylate group of said primer composition.  
   
   
       14 . The process according to any of the preceding claims, characterized by the fact that the inhibitor pigment or pigments of the pigment paste of the primer composition is (or are) chosen among calcium chromates, phosphates, borate, molybdates and silicates.  
   
   
       15 . The process according to one of the preceding claims, characterized by the fact that the primer composition has a pigment concentration in CPV volume of inhibitor pigments ranging from 0.1 to 0.25, preferably 0.1 to 0.15.  
   
   
       16 . The process according to one of the. preceding claims, characterized by the fact that the inhibitor pigment or pigments of the pigment paste of the primer composition is (or are) associated with one or more corrosion inhibitor(s) in liquid form.  
   
   
       17 . The process according to  claim 16 , characterized by the fact that the corrosion inhibitor or inhibitors in liquid form is (or are) chosen among aqueous solutions of 1-(benzo-thiazol-2-ylthio)succinic acid and aqueous solutions of ethylene methacrylate phosphate.  
   
   
       18 . The process according to any of the preceding claims, characterized by the fact that the crosslinking of step g) is carried out under a UV lamp under nitrogen with an oxygen level lower than 200 ppm.  
   
   
       19 . The process according to any of the preceding claims, characterized by the fact that it comprises, after the crosslinking step g) of the aqueous primer composition film, a finishing step h), comprising: 
 application of finishing composition on the primer film, followed by    crosslinking of said finishing composition to obtain a finishing coat.    
   
   
       20 . The process according to  claim 19 , characterized by the fact that the finishing step h) is a finishing [process-translator], comprising: 
 application of a finishing composition based on polyester melamine or polyester urethane or polyvinyl difluoride, followed by    crosslinking of said finishing composition by heating in a drying cabinet with a temperature in the range from 240-250° C., to obtain a crosslinked finishing coat.    
   
   
       21 . The process according to  claim 19 , characterized by the fact that finishing of step h) is cold finishing, comprising: 
 application of a finishing composition based on urethane-acrylate, followed by    crosslinking of said finishing composition by electron bombardment, to obtain a finishing coat.