Universal aqueous coating compositions for pretreating metal surfaces

Abstract

A universal aqueous composition and a process for using such a composition for pretreating metal substrates is provided. The aqueous composition includes a hydroxy functional cyclic compound, such as a tannin, in an amount of at least about 500 ppm, phosphate ions, an oxidizer-accelerator, and at least one Group IVB metal compound capable of converting to a metal oxide upon application to the metal substrate, such as a fluorozirconate or fluorotitanate. The composition may further contain fluoride ions and/or iron The composition is particularly useful for corrosion resistance with a variety of metals such as iron, steel; zinc-coated surfaces, aluminum, and alloys thereof. A disaccharide may further be provided to prolong the useful life of the composition, particularly when used in spray applications.

1 . An aqueous composition for pretreating metal substrates comprising: 
 a) at least one hydroxy functional cyclic compound present in an amount of at least about 500 ppm, said hydroxy functional cyclic compound selected from the group consisting of polyhydroxy phenolic compounds and heterocyclic nitrogen-containing compounds having hydroxy functionality;    b) phosphate ions;    c) at least one oxidizer-accelerator selected from alkali metal chlorate, alkali metal bromate, alkali metal perchlorate, alkali metal chlorite, alkali metal nitrite, alkali metal perborate, ammonium chlorate, ammonium bromate, ammonium perchlorate, ammonium chlorite, ammonium nitrite, ammonium perborate, hydrogen peroxide, nitroguanidine, halo- or nitro-substituted benzene sulfonic acids, alkali metal salts of halo- or nitro-substituted benzene sulfonic acids, ammonium salts of halo- or nitro-substituted benzene sulfonic acids, and mixtures thereof;    d) at least one Group IVB metal compound capable of converting to a metal oxide upon application to the metal substrate; and    e) water.    
     
     
         2 . The composition of  claim 1  wherein the hydroxy functional cyclic compound is selected from the group consisting of catechol, methylene-bridged poly(alkylphenols), coumaryl alcohol, coniferyl alcohol, hydroxyalkyl celluloses, lignin, tannin, sinapyl alcohol, and mixtures thereof.  
     
     
         3 . The composition of  claim 1  wherein the hydroxy functional cyclic compound is at least one tannin material.  
     
     
         4 . The composition of  claim 3  wherein the tannin material is selected from the group consisting of vegetable tannin, hydrolyzable tannin, condensable tannin, tannic acid, and mixtures thereof.  
     
     
         5 . The composition of  claim 4  wherein the tannin material is at least one of quebracho and mimosa tannins.  
     
     
         6 . The composition of  claim 1  wherein said hydroxy functional cyclic compound is present in an amount of about 500 ppm to about 2,500 ppm.  
     
     
         7 . The composition of  claim 1  wherein said phosphate ions are present in an amount of about 125 to about 300 ppm.  
     
     
         8 . The composition of  claim 1  wherein said oxidizer accelerator is present in an amount of about 10 to about 10,000 ppm.  
     
     
         9 . The composition of  claim 1  wherein said Group IVB metal compound is present in an amount of about 60 to about 600 ppm.  
     
     
         10 . The composition of  claim 1 , having a pH within the range of about 3.5 to about 5.  
     
     
         11 . The composition of  claim 1  wherein said Group IVB metal compound is selected from the group consisting of hexafluorozirconic acid and hexafluorotitanic acid and their soluble salts.  
     
     
         12 - 13 . (cancelled)  
     
     
         14 . The composition of  claim 1 , wherein said oxidizer-accelerator comprises a mixture of an alkali metal salt of meta-nitrobenzene sulfonic acid and at least one alkali metal chlorate.  
     
     
         15 . The composition of  claim 1 , further comprising at least one disaccharide.  
     
     
         16 . The composition of  claim 15 , wherein the disaccharide is selected from the group consisting of lactose and sucrose.  
     
     
         17 . The composition of  claim 11  wherein the disaccharide is present in an amount of 500 to 10,000 ppm.  
     
     
         18 . A process for pretreating a metal substrate comprising contacting the substrate with an aqueous composition which comprises: 
 a) at least one hydroxy functional cyclic compound present in an amount of at least about 500 ppm, said hydroxy functional cyclic compound selected from the group consisting of hydroxy phenolic compounds and heterocyclic nitrogen-containing compounds having hydroxy functionality;    b) phosphate ions;    c) at least one oxidizer-accelerator selected from alkali metal chlorate, alkali metal bromate, alkali metal perchlorate, alkali metal chlorite, alkali metal nitrite, alkali metal perborate, ammonium chlorate, ammonium bromate, ammonium perchlorate, ammonium chlorite, ammonium nitrite, ammonium perborate, hydrogen peroxide, nitroguanidine, halo- or nitro-substituted benzene sulfonic acids, alkali metal salts of halo- or nitro-substituted benzene sulfonic acids, ammonium salts of halo- or nitro-substituted benzene sulfonic acids, and mixtures thereof;    d) at least one Group IVB metal compound capable of converting to a metal oxide upon application to the metal substrate; and    e) water.    
     
     
         19 . The process of  claim 18  wherein the metal substrate is selected from the group consisting of cold rolled steel, steel surface-treated with any of zinc metal, zinc compounds and zinc alloys; aluminum; aluminum alloys; zinc-aluminum alloys; aluminum plated steel; and aluminum alloy plated steel.  
     
     
         20 . The process of  claim 18  wherein the metal substrate is a combination of two or more metal substrates assembled together.  
     
     
         21 . The process of  claim 18  wherein the metal substrate is contacted with the aqueous composition by immersion.  
     
     
         22 . The process of  claim 18  wherein the metal substrate is contacted with the aqueous composition by spray application.  
     
     
         23 . The process of  claim 18  wherein the aqueous composition further comprises at least one disaccharide selected from the group consisting of lactose and sucrose.  
     
     
         24 . The process of  claim 18  wherein the aqueous composition is at ambient temperature.  
     
     
         25 . The process of  claim 18  further comprising the step of rinsing the metal substrate with an aqueous solution containing silane after contact with the aqueous composition.