Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/82—After-treatment
  • C23C22/83—Chemical after-treatment

Definitions

• a process for treating a phosphate coated ferrous metal surface which comprises rinsing the phosphate coating with a dilute aqueous solution of a primary phosphate selected from primary phosphate of ammonia, amines and mixtures thereof.
• the preferred phosphates are ammonium dihydrogen phosphate and triethanolamine dihydrogenphosphate, which phosphates are desirably present in the aqueous solution in an amount from about 0.1 to about grams per liter.
• This invention relates to an improved method for treating metal surfaces and more particularly it relates to an improved rinse solution for application to metal surfaces which have been treated to provide a protective and/or paint-base coating.
• a phosphate-containing solution such as a zinc phosphate or iron phosphate solution
• a phosphate coating acts as a corrosion preventive or paint-base coating.
• the coated surface is rinsed in hot or cold water and, thereafter, given a final rinse in dilute phosphoric acid and/or chromic acid.
• chromate rinses i.e., rinses of chromic acid or of various salts thereof the rinsed surface may be discolored or stained and this may be objectionable in some cases, particularly where the rinsed surface is left unpainted or where a transparent or light colored protective coating is applied.
• phosphoric acid rinses it has been found that their use may result in undue corrosion of equipment, particularly heating coils and portions of the circulating system in the treating vessels or tanks used. Notwithstanding these difficulties, however, rinses of this type are widely used since failure to use such rinses has often resulted in an appreciable decrease in the corrosion resistance of the coated metal surfaces.
• an object of the present invention to provide an improved method for treating ferrous metal surfaces to provide a protective and/ or paint-base coating on the metal surface.
• a further object of the present invention is to provide an improved rinse treatment for phosphate coated ferrous metal surfaces, which rinse treatment is not subject to the disadvantages which have heretofore been encountered when using chromic acid and/or phosphoric acid rinses.
• the present invention includes a process for treating a phosphate coated metal surface which comprises rinsing the phosphate coated surface with a dilute aqueous solution containing at least one water dispersible primary phosphate selected from the group consisting of primary phosphates of ammonia, primary hosphates of amines and mixtures thereof.
• the thus-treated surfaces have been found to be very effective in resisting stain or discoloration, particularly when the primary phosphate rinse solution is used after an unaccelerated phosphate coating solution, and are further found to improve the corrosion resistance of the phosphate coatmg.
• a metal surface having thereon a phosphate coating
• a dilute aqueous solution of a water dispersible primary or dihydrogen phosphate of ammonia and/or an amine is maintained in contact with the phosphated surface for a period of time sufficient to effect the desired rinsing of the phosphate surface.
• Various means for effecting contact between the rinse solution and the phosphate surface may be utilized, as for example immersion, spraying, flowing, flooding and the like. In general, satisfactory results have been obtained by spraying the rinse solution on the phosphate surface and this contacting technique is preferred.
• Contact times which are suitable to effect the desired rinsing of the phosphate'surface may be from several seconds, e.g., 10, up to l to 2 minutes, with contact times within the range of about 30 seconds to 60 seconds being typical. It is to be appreciated, however, that contact times in excess of two minutes, e.g., 5 minutes or more, may be used without deleterious results.
• the rinse solutions used in the present method are dilute aqueous solutions of a primary phosphate of ammonia and/ or an amine.
• the primary phosphates used in formulating these rinse solutions may be characterized generally by the following structural formula:
• R R and R are each selected from the group consisting of hydrogen, alkyl groups containing from about 1 to 8 carbon atoms, alkanol groups containing from about 1 to 8 carbon atoms and phenyl groups. These compounds may be classified generally as ammonium, mono-, di-, and trialkyl, alkanol and aryl dihydrogen or primary phosphates.
• Exemplary of specific compounds falling within this group which may be used in formulating the rinse solutions of the present invention are ammonium dihydrogen phosphate, methylamine dihydrogen phosphate, diethylamine dihydrogen phosphate, tributylamine dihydrogen phosphate, octylamine dihydrogen phosphate, dipropanol amine dihydrogen phosphate, triethanolamine dihydrogen phosphate, diheptanolamine dihydrogen phosphate, phenylamine dihydrogen phosphate, pentanolamine dihydrogen phosphate, trihexylamine dihydrogen phosphate, trimethanolamine dihydrogen phosphate, diphenylamine dihydrogen phosphate, as well as other similar monodi-, and tri-, alkyl, alkanol and phenyl. amine derivatives of the above.
• these compounds are water dispersible and contain from about 1 to 8 carbon atoms in each alkyl or alkanol group. Additionally, it is to be appreciated that mixtures of two or more of the primary or dihydrogen phosphate salts may also be used.
• the preferred phosphates are ammonium dihydrogen phosphate and triethanolamine dihydrogen phosphate, as well as mixtures of ammonium dihydrogen phosphate with triethanolamine dihydrogen phosphate.
• the rinse solutions of the present invention are formulated as dilute aqueous solutions of the primary phosphate, typical examples of which have been set forth hereinabove. Desirably, these dilute solutions will contain the primary phosphate in an amount within the range of about 0.1 to 10 grams per liter, with amounts within the range of about 0.1 to 5 grams per liter being preferred. It is to be appreciated, however, that in some instances both greater and lesser concentrations may also be useful, e.g. 0.01 to 40 grams per liter. In general, concentrations of about 1 gram per liter have been found to be very suitable. Desirably, these dilute aqueous solutions are used at a temperature above about 15 degrees centigrade and are preferably used at temperatures within the range of about 60 to 75 degrees centigrade.
• the present invention includes not only the treatment of a phosphate coated metal surface with the aqueous rinse solutions which have heretofore been described but, additionally, includes the overall process wherein a metal surface is treated with a phosphate containing coating solution to form a phosphate coating on the surface and the thus-phosphate coated surface is thereafter rinsed with the aqueous primary phosphate rinse solutions. Accordingly, in the practice of this overall process, a metal surface and preferably a ferrous metal surface, is contacted with a phosphate containing coating solution so as to form a phosphate coating on the metal surface.
• the phosphate coating solutions which may be used are conventional and well known in the art and include acidic ferrous phosphate coating solutions, acidic zinc phosphate coating solutions, and alkali metal phosphate coating solutions, as well as other similar phosphate coating solutions which will produce either a zinc or iron phosphate coating on the ferrous metal surface treated.
• the ferrous metal surfaces are first subjected to standard cleaning operations, utilizing alkaline cleaning solutions, and/or acidic pickling solutions, where these are necessary to effect derusting of the surface.
• each of these cleaning operations will be followed by a water or neutralizing rinse to remove the residue of the various alkaline and acidic cleaning solutions from the metal surface and prevent contamination of the next processing solution.
• the phosphate coating is desirably rinsed with water and is, thereafter, rinsed with the aqueous dihydrogen phosphate rinsing solutions as have been described hereinabove.
• Ferrous metal surfaces which have been treated in accordance with the above procedure have been found to exhibit good corrosion resistance and, further, have been found to be substantially free of stains or discoloration.
• a second portion of the phosphate coated steel surfaces was similarly rinsed with a hot aqueous solution containing 1 gram per liter of ammonium dihydrogen phosphate. Thereafter, both portions of the rinsed steel workpieces were dried in an oven and were compared to similar phosphate coated steel workpieces which had been given no dihydrogen phosphate rinse, but had been dried in the oven immediately following the water rinse. It was found that the workpieces which had been given only the water rinse before drying were badly stained while those pieces which had been rinsed in the ammonium dihydrogen phosphate solution were found to be substantially free of stain.
• EXAMPLE 2 Slightly rusted, oiled steel was cleaned in a phosphoric acid-solvent cleaning solution, rinsed in cold water and then given a phosphate coating by immersion in a conventional zinc dihydrogen phosphate coating solution. The phosphate coated surface was rinsed in cold water and then given a final rinse by spraying for about 60 seconds with an aqueous solution containing 0.25 gram per liter of ammonium dihydrogen phosphate, which solution was at a temperature of about 70 degrees centigrade. The thus-rinsed steel was then dried in an oven.
• Example 3 The procedure of Example 2 was repeated with the exception that the dihydrogen phosphate rinse used contained 0.25 gram per liter of triethanolamine dihydrogen phosphate instead of the ammonium dihydrogen phosphate. After drying, the treated steel surfaces showed no evidence of staining or discoloration.
• Example 4 The procedure of Example 1 was repeated with the exception that the dihydrogen phosphate rinse solution used contained 1 gram per liter of ammonium dihydrogen phosphate and 1 gram per liter of triethanolamine dihydrogen phosphate. Comparable results were obtained.
• a method for treating a ferrous metal surface having thereon a phosphate coating produced by coating said ferrous metal surface with a phosphate coating composition selected from the group consisting of acidic ferrous phosphate coating solutions, acidic zinc phosphate coating solutions and alkali metal phosphate coating solutions which comprises contacting said surface with a dilute aqueous solution consisting essentially of from about 0.1 to about grams per liter of at least one primary phosphate selected from the group consisting of primary phosphate of ammonia, primary phosphates of amines, each carbon chain of which contains from about 1 to 8 carbon atoms, and maintaining the phosphate coated surface in contact with the said aqueous solution for a period of time sufficient to effect rinsing of the phosphate coated surface.
• a phosphate coating composition selected from the group consisting of acidic ferrous phosphate coating solutions, acidic zinc phosphate coating solutions and alkali metal phosphate coating solutions, which comprises contacting said surface with a dilute aqueous solution consisting
• the primary phosphate in the dilute aqueous rinse solution has the formula wherein R R and R are each selected from the group consisting of hydrogen, alkyl groups having from 1 to 8 carbon atoms, alkanol groups having from one to eight carbon atoms, and phenyl groups.
• a method for treating a ferrous metal surface to provide a protective coating thereon which comprises contacting said ferrous metal surface with a phosphate solution selected from the group consisting of acidic ferrous phosphate, acidic zinc phosphate and alkali metal phosphate coating solutions so as to form a protective phosphate coating on the surface and thereafter rinsing the thus-formed phosphate coating with a dilute aqueous solution consisting essentially of from about 0.1 to about 10 grams per liter of at least one primary phosphate selected from the group consisting of primary phosphates of ammonia and primary phosphates of amines, each carbon chain of which contains from about 1 to 8 carbon atoms.
• a phosphate solution selected from the group consisting of acidic ferrous phosphate, acidic zinc phosphate and alkali metal phosphate coating solutions so as to form a protective phosphate coating on the surface and thereafter rinsing the thus-formed phosphate coating with a dilute aqueous solution consisting essentially of
• R R and R are each selected from the group consisting of hydrogen, alkyl groups containing 1 to 8 carbon atoms, alkanol groups containing from 1 to 8 carbon atoms and phenyl groups.

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

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Cited By (10)

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• 0
  • GB GB1050860D patent/GB1050860A/en active Active
• 1965
  • 1965-08-14 DE DE19651521864 patent/DE1521864A1/de active Pending
  • 1965-08-19 BE BE668526D patent/BE668526A/xx unknown
  • 1965-08-25 US US482606A patent/US3493440A/en not_active Expired - Lifetime
  • 1965-09-03 ES ES0317084A patent/ES317084A1/es not_active Expired

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