Process and composition for forming an adherent paint or vitreous enamel coating on steel

Abstract

Excellent adhesion of vitreous enamel to steel can be achieved via an intermediate layer formed on the steel by bringing it into contact with a liquid composition that contains water and a component of solute selected from the group consisting of dissolved silicates and dissolved borates and, optionally, surfactant. The modification of the steel surface achieved by treating it with silicates and/or borates is also effective for improving the adhesion of steel to other protective type coatings such as paint.

The invention claimed is:  
     
       1. A process for providing a steel substrate with an adherent solid protective coating, said process comprising operations of: 
       (I) bringing a clean steel substrate surface into contact with a liquid treating composition that comprises a component of solute selected from the group consisting of silicate anions and borate anions and maintaining said substrate surface in contact with said liquid treating composition for a liquid treating interval of time;  
       (II) separating said substrate surface as treated during operation (I) from the bulk of said liquid treating composition with which it was maintained in contact during operation (I) and heating said substrate surface, together with any amount of said liquid treating composition that remains adhered to its surface, to a minimum heat treating temperature and maintaining said substrate at or above said minimum heat treating temperature for a heat treating interval of time that is sufficient to dry said substrate; and  
       (III) bonding a protective coating to the surface of the dried substrate from operation (II).  
     
     
       2. A process according to  claim 1 , wherein said liquid treating composition comprises: 
       (A) a concentration of silicate anions that is stoichiometrically equivalent, the stoichiometry being based on equal numbers of silicon atoms, to a concentration of sodium silicate pentahydrate that is from about 11 to about 100 g/l; and  
       (B) at least one of:  
       a concentration of anionic surfactant that is at least about 0.008 g/l; and  
       a concentration of nonionic surfactant that is at least about 0.04 g/l.  
     
     
       3. A process according to  claim 2 , wherein said liquid treating composition comprises: 
       (A) a concentration of silicate anions that is stoichiometrically equivalent, the stoichiometry being based on equal numbers of silicon atoms, to a concentration of sodium silicate pentahydrate that is from about 13 to about 50 g/l; and  
       (B) at least one of:  
       a concentration of anionic surfactant that is at least about 0.030 g/l, said anionic surfactant being constituted of molecules that are partial esters of at least one inorganic acid; and  
       a concentration of ethoxylated alcohol nonionic surfactant that is at least about 0.15g/l.  
     
     
       4. A process according to  claim 3 , wherein said liquid treating composition comprises: 
       (A) a concentration of sodium silicate pentahydrate that is from about 15 to about 30 g/l; and  
       (B) at least one of:  
       a concentration of partial esters of phosphoric acid surfactant that is at least about 0.060 g/l; and  
       a concentration of ethoxylated alcohol nonionic surfactant that is at least about 0.30 g/l.  
     
     
       5. A process according to  claim 1 , wherein said liquid treating composition has been made by mixing with a first mass of water at least the following additional masses: 
       (A) a second mass of silicate anions that is stoichiometrically equivalent, the stoichiometry being based on equal numbers of silicon atoms, to a mass of sodium silicate pentahydrate that constitutes from about 11 to about 100 g/l of said liquid treating composition; and  
       (B) at least one of:  
       a third mass of anionic surfactant that constitutes at least about 0.008 g/l of said liquid treating composition; and  
       a fourth mass of nonionic surfactant that constitutes at least about 0.04 g/l of said liquid treating composition.  
     
     
       6. A process according to  claim 5 , wherein said liquid treating composition has been made by mixing with a first mass of water at least the following additional masses: 
       (A) a second mass of water soluble sodium silicate that is stoichiometrically equivalent, the stoichiometry being based on equal numbers of silicon atoms, to a mass of sodium silicate pentahydrate that constitutes from about 13 to about 50 g/l of said liquid treating composition; and  
       (B) at least one of:  
       a third mass of anionic surfactant, the molecules of which are partial esters of inorganic acids, that constitutes at least about 0.030 g/l of said liquid treating composition; and  
       a fourth mass of ethoxylated alcohol nonionic surfactant that constitutes at least about 0.15 g/l of said liquid treating composition.  
     
     
       7. A process according to  claim 6 , wherein: 
       said second mass comprises an amount of sodium silicate pentahydrate that constitutes from about 15 to about 30 g/l of said liquid treating composition; and  
       either:  
       said third mass is present in the liquid treating composition and comprises surfactant molecules that are partial esters of phosphoric acid in an amount that constitutes at least about 0.060 g/l of said liquid treating composition; or  
       said fourth mass is present in the liquid treating composition and comprises ethoxylated alcohol nonionic surfactant molecules that constitute at least about 0.30 g/l of said liquid treating composition.  
     
     
       8. A process according to  claim 7 , wherein: 
       the steel substrate in operation (I) has been cleaned with an alkaline cleaner before being brought into contact with the liquid treatment composition;  
       the substrate remains in contact with the liquid treating composition for at least 20 seconds during operation (I);  
       at the beginning of operation (II), the liquid treating composition is allowed to drain under the influence of natural gravity for from 5 to 15 seconds before the substrate is heated;  
       said minimum heat treating temperature in operation (II) is from about 180 to about 235° C.; and  
       said heat treating interval of time is from about 11 to about 25 minutes.  
     
     
       9. A process according to  claim 6 , wherein: 
       the substrate remains in contact with the liquid treating composition for at least 15 seconds during operation (I);  
       at the beginning of operation (II), the liquid treating composition is allowed to drain under the influence of natural gravity for from 2 to 45 seconds before the substrate is heated;  
       said minimum heat treating temperature in operation (II) is from about 170 to about 245° C.; and  
       said heat treating interval of time is from about 7 to about 30 minutes.  
     
     
       10. A process according to  claim 5 , wherein: 
       the substrate remains in contact with the liquid treating composition for at least 8 seconds during operation (I);  
       at the beginning of operation (II), the liquid treating composition is allowed to drain under the influence of natural gravity for from 2 to 45 seconds before the substrate is heated;  
       said minimum heat treating temperature in operation (II) is from about 150 to about 245° C.; and  
       said heat treating interval of time is at least about 5 minutes.  
     
     
       11. A process according to  claim 4 , wherein: 
       the steel substrate in operation (I) has been cleaned with an alkaline cleaner before being brought into contact with the liquid treatment composition;  
       the substrate remains in contact with the liquid treating composition for at least 20 seconds during operation (I);  
       at the beginning of operation (II), the liquid treating composition is allowed to drain under the influence of natural gravity for from 5 to 15 seconds before the substrate is heated;  
       said minimum heat treating temperature in operation (II) is from about 180 to about 235° C.; and  
       said heat treating interval of time is from about 11 to about 25 minutes.  
     
     
       12. A process according to  claim 3 , wherein: 
       the substrate remains in contact with the liquid treating composition for at least 15 seconds during operation (I);  
       at the beginning of operation (II), the liquid treating composition is allowed to drain under the influence of natural gravity for from 2 to 45 seconds before the substrate is heated;  
       said minimum heat treating temperature in operation (II) is from about 170 to about 245° C.; and  
       said heat treating interval of time is from about 7 to about 30 minutes.  
     
     
       13. A process according to  claim 2 , wherein: 
       the substrate remains in contact with the liquid treating composition for at least 8 seconds during operation (I);  
       at the beginning of operation (II), the liquid treating composition is allowed to drain under the influence of natural gravity for from 2 to 45 seconds before the substrate is heated;  
       said minimum heat treating temperature in operation (II) is from about 150 to about 245° C.; and  
       said heat treating interval of time is at least about 5 minutes.  
     
     
       14. A process according to  claim 1 , wherein: 
       the substrate remains in contact with the liquid treating composition for at least 8 seconds during operation (I);  
       at the beginning of operation (II), the liquid treating composition is allowed to drain under the influence of natural gravity for from 2 to 45 seconds before the substrate is heated;  
       said minimum heat treating temperature in operation (II) is from about 150 to about 245° C.; and  
       said heat treating interval of time is at least about 5 minutes.  
     
     
       15. A concentrate useful for preparing a working liquid treatment composition for use in operation (I) of a process according to  claim 1 , said concentrate comprising the following components: 
       (A) a component selected from the group consisting of alkali metal silicates, this component being soluble in or dissolved in water; and  
       (B) at least one of:  
       a mass of salts of partial esters of phosphoric acid that has a ratio to the mass of the component described in part (A) hereof, measured as its stoichiometric equivalent as sodium metasilicate pentahydrate, that is from about 0.004:1.0 to about 0.016:1.00; and  
       a mass of ethoxylated fatty alcohols, said mass of ethoxylated fatty alcohols having a ratio to the mass, measured as its stoichiometric equivalent as sodium metasilicate pentahydrate, of the component described in part (A) hereof in the same concentrate that is from about 0.01:1.00 to about 0.04:1.00.  
     
     
       16. A concentrate according to  claim 15  that is a solid concentrate and comprises at least 0.9% of ethoxylated fatty alcohol molecules as its surfactant component. 
     
     
       17. A concentrate according to  claim 16  that consists essentially of at least about 1.7% of ethoxylated fatty alcohols and a balance of sodium metasilicate pentahydrate. 
     
     
       18. A concentrate according to  claim 15  that is a liquid concentrate and comprises water and: 
       at least about 12 percent of dissolved alkali metal silicate; and  
       at least about 0.5 percent of alkali metal salts of partial esters of phosphoric acid with fatty alcohols.  
     
     
       19. A concentrate according to  claim 18  that comprises at least about 20% of dissolved alkali metal silicate and at least about 0.07 percent of alkali metal salts of partial esters of phosphoric acid with fatty alcohols. 
     
     
       20. A concentrate according to  claim 19 , wherein the dissolved alkali metal silicate before it was dissolved was sodium metasilicate pentahydrate.