Process and solution for providing a thin corrosion inhibiting coating on a metallic surface

Abstract

The invention relates to a process for coating metallic surfaces with a phosphating coating by contacting metallic surfaces at a temperature not above 45° C. and at a pH value less than 3.5 with an aqueous acidic alkali metal phosphating solution or dispersion containing: At least one compound of at least one phosphorus containing acid and/or at least one of their derivates like esters and salts in a total content of all kinds of acids and all their derivates like esters and salts together of less than 20 g/L calculated on mole base as orthophosphate, whereby the content of such phosphorus containing compounds/ions is at least 50% by weight in comparison to all such compounds/ions and at least one ion selected from the group consisting of at least one alkali metal ion and ammonium ion, whereby the phosphating coating has a coating composition with a phosphorus content of not more than 8 atomic % as measured by Secondary Neutral Mass Spectroscopy (SNMS) and whereby the phosphating coating has a coating weight in the range from 0.01 to 0.5 g/m 2 .

1 . Process for coating metallic surfaces with a phosphating coating by contacting metallic surfaces at a temperature not above 45° C. and at a pH value less than 3.5 with an aqueous acidic alkali metal phosphating solution or dispersion containing: 
 At least one compound of at least one phosphorus containing acid and/or at least one of their derivates like esters and salts in a total content of all kinds of acids and all their derivates like esters and salts together of less than 20 g/L calculated on mole base as orthophosphate, whereby the content of such phosphorus containing compounds/ions is at least 50% by weight in comparison to all such compounds/ions and  
 at least one ion selected from the group consisting of at least one alkali metal ion and ammonium ion,  
 whereby the phosphating coating has a coating composition with a phosphorus content of not more than 8 atomic % as measured by Secondary Neutral Mass Spectroscopy (SNMS) and  
 whereby the phosphating coating has a coating weight in the range from 0.01 to 0.5 g/m 2 .  
 
     
     
         2 . Process according to  claim 1 , whereby the phosphating solution or dispersion contains at least one accelerator like such on the base of chlorate, guanidine, of an organic compound with at least one nitro group like nitroguanidine and/or nitrobenzenesulfonic acid and its derivatives, of hydrogen peroxide, hydroxylamine, nitrate, and/or of other nitrogen containing accelerators.  
     
     
         3 . Process according to  claim 1 , whereby the phosphating solution or dispersion contains an amount of PO 4  ions in the range from 0.1 to 10 g/L.  
     
     
         4 . Process according to  claim 1 , whereby the phosphating solution or dispersion contains an amount of SO 4  ions in the range from 0.1 to 10 g/L.  
     
     
         5 . Process according to  claim 1 , whereby the phosphating solution or dispersion contains an amount of NO 3  ions in the range from 0.1 to 10 g/L.  
     
     
         6 . Process according to any of the preceding claims, whereby an amount of Fe 2+  ions is added to the phosphating solution or dispersion, preferably in the range from 0.01 to 1 g/L.  
     
     
         7 . Process according to  claim 1 , whereby the phosphating solution or dispersion contains free fluoride, preferably in the range from 0.01 to 1 g/L, and/or complex fluoride, especially of aluminum, boron, silicon, titanium and/or zirconium, preferably in the range from 0.01 to 1 g/L.  
     
     
         8 . Process according to  claim 1 , whereby to the phosphating solution or dispersion contains an amount of nitroguanidine and/or other accelerators on the base of guanidine in the total range from 0.01 to 5 g/L.  
     
     
         9 . Process according to  claim 1 , whereby the phosphating solution or dispersion contains at least one surfactant, especially when cleaning and phosphating is carried out with the same solution or dispersion, preferably with an amount of all surfactants together in the range from 0.01 to 10 g/L.  
     
     
         10 . Process according to  claim 1 , whereby the phosphating solution or dispersion contains at least one solvent like a propylene glycol and/or a glycol ether, at least one biocide, at least one stabilizing agent for a surfactant like a condensed sulfonic salt, at least one stabilizing agent for the accelerator like a fine-particular silicate-, clay- or clay-like material and/or at least one stabilizing agent for the solution or dispersion itself like a biopolymer.  
     
     
         11 . Process according to  claim 1 , whereby a phosphating coating is generated showing a colourless, faint colouring, silvery, yellowish, golden, yellowish-brownish, yellowish-reddish and/or bluish colour.  
     
     
         12 . Process according to  claim 1 , whereby a clean, a cleaned and/or a pickled metallic surface is contacted with the solution resp. dispersion.  
     
     
         13 . Process according to  claim 1 , whereby the metallic surface is contacted with the solution resp. dispersion by immersing, spraying, steam-phosphating, roll-coating and/or squeegeeing.  
     
     
         14 . Process according-to  claim 1 , whereby the coated metallic surface is dried after contacting with the solution resp. dispersion or after at least one thereon succeeding rinsing step by air-drying, oven-drying and/or infrared-drying, especially at temperatures in the range from 20 to 250° C.  
     
     
         15 . Process according to  claim 1 , whereby there are applied at least two coatings one after the other on the metallic surface whereby at least one of them is applied with a phosphating solution resp. dispersion and whereby at least one other coating may optionally be applied with a conversion coating solution like a zinc- and/or manganese-rich phosphating.  
     
     
         16 . Process according to  claim 1 , whereby first a alkali metal phosphating coating is generated on a metallic surface and then a coating selected from the group consisting of a conversion coating like a zinc-and/or manganese-rich phosphate coating, a stearate coating and an organic polymer coating is applied thereon, especially for coldforming.  
     
     
         17 . Process according to  claim 1 , whereby a metallic surface consisting essentially of metallic materials of aluminum, chromium, titanium and/or zinc as well as at least one alloy containing aluminum, chromium, copper, iron, magnesium, tin, titanium and/or zinc alloys is covered with a coating of a phosphating solution or dispersion.  
     
     
         18 . Method of use of the coating prepared with a process according to one of the  claims 1  to  17  for the short-term passivation, for the pretreatment prior to at least one succeeding paint layer, layer of any other organic coating and/or adhesive coating, as a lubricant carrier or as one of the lubricating coatings e.g. prior to coldforming.  
     
     
         19 . Phosphating coating on a metallic surface prepared by contacting metallic surfaces with an aqueous acidic alkali metal phosphating solution or dispersion having a coating thickness of not more than 0.15 μm and having a good corrosion protection for the protected metallic material.  
     
     
         20 . Method of use of the coating prepared with a process according to one of the  claims 1  to  18  for the corrosion inhibition and/or the lubrication of metallic surfaces, especially for use in aerospace industry, automobile industry, rail transportation, shipbuilding, metal forming, metal working (machining, grinding), metallic container and especially can production, coil industry, for metal sheet applications, wire production, appliances, housings, machines and construction of buildings.