IL30660A - Method and compositions for producing a uniform phosphate coating on metals - Google Patents

Description

Method and compositions for producing uniform phosphate coating on metals AK IENGESELLSCHAFT 28895 Ion for coating metal surfaces and more particularly it relates to a composition and process for producing a zinc phosphate coating on a metal The use of phosphate and particularly aqueous acidic zinc phosphate to form coatings on metal surfaces has long been in the it is the practice to various accelerating such as ni trate nitrite chlorate ferrous iron and the the aqueous acidic zinc phosphate coating Depend ng upon the particular accelerating components the characteristics the coat i ng produced on the metal surfaces treated as well as the process operating conditions which may be for phosphate coating solution is used containing chlorate ion the temperatures at the coating process is carried out may generally be then those can be used when other accelerating components are Although the phosphate coatings produced with such chlorate accelerated phosphating solutions are general te satisfactory when solutions are applied by spray the application of such solutions by immersion techniques often result In coatings which undes rably thin or light weight and which sometimes become dusty after While these difficulties encountered when using chlorate phosphating an immersion process can be overcome when a accelerator is such solutions must be operated at an appreciably higher temperature than the chlorate accelerated in order to obtain optimum coating up to the present it has not generally been possible to obtain phosphate coatings of the type produced by nitrite acce i in an immersion when an object of present invention to provide an improved chlorate ng j Λ further object of present invention is to chlorate accelerated di c zinc phosphate coating which solution produce uniform coatings in an immersion ί which coatings are icantly heavier in weight than those normally produced by chlorate accelerated j A further object of the present invention to provide an Improved method for coat c which method uti lizes chlorate aqueous acidic zinc phosphate coating These and other become apparent to those ski lled in the art from the description of the invention which fol i Pursuant to the above the present invention includes a composition suitable coating metal which composi tion an aqueous acidic zinc phosphate substantially free of ferrous iron which solution contains chlorate ions and a coating weight accelerating amount of a polybasic organic It has been found that when the acidic zinc phosphate containing chlorate ions as the accelerator are the polybasic organic acid in the solution acts as a coating weight accelerator so that there is produced on the metal surface treated a heavy zjnc phosphate This Is in contrast to results obtained when lar zinc phosphate solutions are used but which contain nitrite ions as the In these latter the polybasic organic acid acts as a coating weight producing an appreciably thinner phosphate coating then is normal ly obtained with such More f i in the practice of the method of the present the coating composition an aqueous chlorate and a polybasic organic arc present in the treating solution in the following by h Zinc to to i 0 to 10 to Polybasic organic acid to i i The polybasic organic acid used in the present composition desirably a aliphatic polycarboxy i acid having 2 to 6 carbon atoms and may have the carbon atom adjacent to at least one of the carboxy groups subs ti tuted th a hydroxy Exemplary of such are citric tartaric the Of in many the preferred polybasic 5 organic acid use in the present composition has been found to citric acid hereinafter primary reference will be made a coating weight accelerating amount of the organic acid is that amount which is effective in producing the increase in the coating weight of the phosphate coatings 0 produced on the metal it has been found that such accelerating amounts is at about by of the phosphating It is to be that in addition to the above the metal treating solutions of the present invention 5 also contain additional including metal such as and in a preferred the solutions of the present invention may include the components in the amounts The coatings of the present invention may be to a metal preferably a ferrous metal surface such as or the by immersing the surface in or flooding the surface with a coating Although other coating such as and the also be the advantages obtained by of the present in terms of heavier uni coat ng weights are most pronounced when or flow coating techniques are primary reference be made to such application i the coating solution is applied at an elevated temperature within the range of about 50 to 100 degrees with temperatures within the range of about to 75 degrees centigrade being It is to be that temperatures which are either higher or lower than the preferred ranges have been indicated may also be used in many using lower the contact times between the coating solution and surface are necessary to produce the desired coating may have to be Typical contact times utilized to the coatings at temperatures the preferred ranges which have been are from about to minutes contact times the range of about 2 to 10 minutes being The coatings formed on the metal when using the coating solutions of the present invention typically have a coating weight the range of about to300 per square foot and are preferably within the range of about 175 to 225 milligrams per square The phosphate coatings of the present invention may be convenient is to those in the the phosphate coatings produced in accordance h the present Invention may serve as a protec ive such it may be desirable to treat the phosphate coating 5 with an aqueous chroraic acid containing rinse solution the application of phosphate coating The chromic acid solutions used may be any of the commercially avai lable chromic acid solutions which typically about to about and may be admixture of other such as phosphoric the 10 In many it is also desirable to rinse the phosphate coated metal surface with before any subsequent treatment and after the final the surface is preferably either in a drying or the coated metal surface of the present invention 15 to subjected to a forming it is found that the phosphate coating produced thereon is an excellent base for the applied lubricant Simi where the phosphate coating is to serve as a protective paint base it found that either with or without the application 20 of an additional protective such as a paint or the the phosphate coat good resistance to In order that those skilled in the art may better understand the invention and the manner in which it may be the following specific examples are In these 25 unless otherwise temperatures are in degrees centigrade and parts and percents are by It is to that these examples are intended merely to be illustrative of the present invention and are not to be taken as a limitation EXAMPLE A zinc phosphate i ng solution was prepared containing x inch clean steel panels were coated by immersing the panels above treating solution being at a temperature of about 7Q degrees the panels were removed from the coating rinsed in cold water and then air The coating weight produced on the panels using this procedure were as Immersion Time Coating weight square foot 5 EXAMPLE The procedure of Example 1 repeated with the exception that prior to immersing the steel panels in the coating the solution was aged with scrap to simulate an actual operating coating the steel panels were by immersion in this aged solution for varying periods as in Example the following coating weights were Immersion Time Coating n er sq f t 93 The procedure of Example 1 was repeated the exception that addi tional by weight of citric acid was added to the coating to give a total citric acid of by The resulting bath was then aged with scrap steel as in Example and upon coating the steel panels by immersion in this solution for varying periods of the following results were Coating time Coating weight minutes Z 202 202 212 EXAM By way of rocedure of Example 2 was repeated with the exception that the coating solution used did not contain any citric When the steel panels were immersed in this solution for varying of using rocedure of Example the coating weights were Coating time Coating weight minutes in m9 ft 92 From a comparison of the results obtained in Example with those obtained in Examples 1 through can be seen that the chlorate accelerated phosphate coating solutions contain citric the coating weight of t phosphate coating are at produced in Exam 2 were with a standard elcctrocoat primer paint and subjected to the standard salt spray After hours there was found to be less than inch creepage from the scribe on the While there have been described various of the the compositions and methods described are not intended to be understood as limiting the scope of the invention as it is realized that therewi thin are possible and it is each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing the same results in the or equivalent it being intended to cover the invention broadly in whatever form its principle may be insufficientOCRQuality

Claims (1)

1. V/ΙΙΛΤ IS CLAIMED IS : - . .; ~ ; " " ' . ' ' ■' ■ ' . .' - l - · ■ '· . ' ■■ · ■■■ " - .·. . · ; ' A composition suitable for coating metal surfaces which comprises an aqueous acidic zinc, phosphate solution, substantially free of ferrous iron ions which solution contains chlorate iohs and a coating weight accelerating amount of a polybasic organic acid. The composition as claimed In Claim 1 wherein the weight ratio of the organic acid to the phosphate in the coating solution is within the range of about 0.15 to about 2.5. ·'* The composition as claimed in Claim 2 wherein there is contained the following components in the amounts indicated: ■ ' · Components % by wei ht • Zinc · . 0.05 to 5.0 ' ' - · POi, ■■' · ' ":V; ■ · '... 0.2 to 10.0 ..' CIO^ * * ' * * · . '' ·."·' ."' 0.05 to 5.0 ■'. '. . · N03 '·:,'.··· ' ■··■· 0 ;to 10.0 : _ Polybasic organic acid * '. . 0.1 to 5.0 The composition as claimed in Claim 3 wherein the polybasic organic acid is citric acid. : . .. _'· · - 5 - . ■ > ■■ ··· .' . · · * . The composition as claimed Pn Claim h wherein there is also present nickel ions in an amount within the range of about 0.0012 to about 0.005¾ by weight of the coating solution. - 6 - A method for coating metal surfaces to provide a uniform' phosphate coatiny thereon, v/h i ch~ compr i scs contacting the surface to be coated with a coating composition as claimed in. Claim 1 and maintaining the composition in contact with the m t l surface for The method os .claimed in Claim 6 wherein, in the coating composition used, the ratio of organic acid to pliosphate is within the range of about 0.15 t 2.5. - 8 - ' ■ . · ' ■ '■ • The method as claimed in Claim 7 wherein the coating composition used contains the following components in amounts wi-thin range of about 0.0012 to about 0.005% by weight of the coating composition.. ' · . . .. 1 :' ' . · . " .' .' . · - Ί1.- · ' '■ ■ ' ·. The method as claimed in Claim 10 wherein the coating composition is at a temperature v/ithin the range of about 50 to 100 degrees centigrade and the metal surface is contacted wi th the . composition by immersing if th