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

• An increasingly used commercial process for the application of siccative coatings to metal surfaces is the process of electrocoating, especially cationic electrocoating.
• Various pretreating processes are known, including the application of a phosphate coating to the metal surface followed by treatment of the phosphated surface with a solution which does not contain chromium, and which accordingly is pollution-free, to improve the corrosion resistance of the metal surface.
• Japanese Patent Publication No. 5622/1978 uses an aqueous solution of phytic acid to treat the phosphated surface
• Japanese Patent Publication No. 21971/1977 uses an aqueous solution of zirconium compound for this purpose. Both techniques have disadvantages.
• the technique proposes the use of complexing agents such as gluconic acid and citric acid.
• complexing agents such as gluconic acid and citric acid.
• gluconic acid and citric acid there is a tendency for corrosive substances to remain on the treated metal surface, so that excessive water washing is required in the following final water washing step.
• zinc-based surfaces so treated are inferior to iron-based surfaces so treated in adhesion and corrosion resistance of the coating film.
• the present invention relates to an improved process for treating a metal surface, especially for subsequent cationic electrocoating.
• the process results in improved adhesion and corrosion resistance of the coating film deposited by cationic electrocoating.
• the invention provides a process for treating a metal surface having a phosphate conversion coating, which process comprises treating said coated surface with an aqueous solution containing:
• the invention also provides a composition for treating a metal surface having a phosphate conversion coating, which composition is this aqueous solution.
• the phosphate conversion coating is one suitable as a conversion coating for this purpose, and can be applied by an acidic aqueous phosphating solution which is already known in the art for this purpose.
• acidic aqueous phosphating solution which is already known in the art for this purpose.
• Such solutions include, for example, a solution containing from 0.4 to 1.5 g/1 of zinc ion, from 5 to 40 g/1 of phosphate ion, and a conversion coating accelerator. Examples of such known phosphating solutions are given in Japanese Patent Publications(unexamined) No. 107784/1980, 145180/1980 and 131177/1980.
• phosphate conversion coating by dipping the metal surface into an acidic aqueous phosphating solution containing from 0.5 to 1.5 g/1, preferably from 0.7 to 1.2 g/l, of zinc ion, from 5 to 30 g/1, preferably from 10 to 20 g/1, of phosphate ion, and a conversion coating accelerator.
• the accelerator can be at least one of the following: 0.01 to 0.2 g/l, preferably 0.04 to 0.15 g/1, of nitrite ion, 0.05 to 2 g/l, preferably 0.1 to 1.5 g/1, of m-nitrobenzene sulphonate ion, and 0.5 to 5 g/1, preferably lto 4 g/l, of hydrogen peroxide (as 100% H 2 0 2 ).
• the phosphating solution may optionally also contain 1 to 10 g/l, preferably 2 to 8 g/l, of nitrate ion, and/or 0.05 to 2 g/l, preferably 0.2 to 1.5 g/1, of chlorate ion.
• the phosphating solution discussed above also contain 0.6 to 3 g/1, preferably 0.8 to 2 g/l, of manganese ion, or 1 to 4, preferably 2 to 2.5 g/1, of nickel ion. It is even more preferred to include both manganese and nickel ions, and when both are included, the manganese ion is preferably employed in the range given above and the nickel ion is employed in the range of 0.1 to 4 g/l, preferably 0.3 to 2 g/l.
• a spray process can be utilized to apply the phosphate coating to the metal surface.
• the following solution is preferred: an acidic aqueous phosphating solution containing from 0.4 to 1 g/l, preferably 0.5 to 0.9 g/1, of zinc ion, 5 to 40 g/l, preferably 10 to 20 g/l, of phosphate ion, 2 to 5 g/1, preferably 2.5 to 4 g/1, of chlorate ion, and 0.01 to 0.2 g/1, preferably 0.04 to 0.15 g/1, of nitrite ion.
• sources of the ions used in the acidic phosphating solutions discussed above commonly known sources can be utilized, for example zinc oxide, zinc carbonate or zinc nitrate for zinc ions; phosphoric acid, sodium phosphate or zinc phosphate for phosphate ions; sodium nitrite or ammonium nitrite for nitrite ions; sodium m-nitrobenzene sulphonate for m-nitrobenzene sulphonate ions; hydrogen peroxide for hydrogen peroxide; chloric acid, sodium chlorate or ammonium chlorate for chlorate ions; manganese carbonate, manganese citrate, manganese chloride or manganese phosphate for manganese ions; and nickel carbonate, nickel nitrate, nickel chloride or nickel phosphate for nickel ions.
• Phosphating of the metal surfaces with the acidic aqueous solutions for phosphating discussed above can be carried out in accordance with conventional procedures.
• the metal surfaces, which have been subjected, as needed, to degreasing and then to a known surface pretreatment (generally employed prior to a dipping treatment), where the dipping treatment is used for phosphating can be treated at 40 0 to 70°C, preferably at 45° to 60°C, for 15 seconds or more (preferably for 30 to 120 seconds), and thus a desired phosphate f coating film of low film amount (1.5 to 3 g/m 2 ) is produced on iron-based surfaces. Also, a uniform phosphate film is formed thereby on zinc-based surfaces.
• the metal so treated may be washed with water according to conventional methods, followed by an after-treatment in accordance with the present invention as described below.
• the after-treatment involves treating the phosphated metal surface with an aqueous solution having a pH of 3 to 7, preferably 4 to 6, and containing:
• a compound is fluorozirconic acid or a salt thereof with a volatile base such as ammonia, a lower alkylamine or a hydroxy lower alkylamine (e.g. monoethanolamine, diethanolamine, triethanolamine, methylamine, ethylamine or dimethylamine).
• a volatile base such as ammonia, a lower alkylamine or a hydroxy lower alkylamine (e.g. monoethanolamine, diethanolamine, triethanolamine, methylamine, ethylamine or dimethylamine).
• Alkali metal salts and alkaline earth metal salts of fluorozirconic acid exhibit a tendency to leave corrosive substances on the surface of the metal after the above-mentioned treatment step, and they are therefore not preferred.
• zirconium carboxylates nor zirconium hydrocarboxyl- ates exhibit as beneficial an effect of the present invention as do fluorozirconic acid and its salts with volatile bases.
• the myo-inositol phosphates and water-soluble salts thereof used in the above-mentioned aqueous solution are esters of myo-inositol having 1 to 6 phosphate groups.
• Phytic acid is a commercially available product that can be employed herein.
• Other useful phosphates can be obtained by hydrolysis of phytic acid.
• salts of volatile bases are preferred, such as ammonia, a lower alkylamine, or a hydroxy-lower alkylamine (examples of these bases being specified above).
• the pH of the above-mentioned solution is in the range 3 to 7.
• the pH of the solution is strongly affected by its concentration.
• the pH of a 0.1, 0.01, 0.001, and 0.0001, mole/l aqueous solution of phytic acid is respectively 0.9, 1.7, 2.68, and 3.61.
• the pH of the present solution is lower than about 3, the phosphate film on the metal surface dissolves excessively and the benefits of the invention cannot be fully realized.
• a zirconium salt of for example phytic acid is not
• the pH must be adjusted, as necessary, to obtain a pH within the required range.
• volatile bases such as ammonia, a lower alkylamine or a hydroxy-lower alkylamine may be employed (and examples of these bases are specified above). Accordingly, a portion of the volatile base needed for pH control can be present as a salt of fluorozirconic acid and/or as a salt of the myo-inositol phosphate. In general, at least about 4 moles of volatile base is required per mole of myo-inositol phosphate.
• phosphoric acid may be employed as a pH lowering agent.
• the aqueous solution used to after-treat a phosphated metal surface preferably contains substantially no substance which will form a x corrosive residue on the metal surface.
• the aqueous solution preferably contains substantially no-alkali metal ions, alkaline earth metal ions; or any organic acid that will form a water-soluble chelate compound.
• the treatment of the phosphated metal surface with the above-mentioned solution can be effected by any conventional contacting method such as by dipping or spraying.
• the treating temperature is preferably in the range of from room temperature to 90°C.
• the treatment time is at least long enough to wet the metal surface sufficiently with the solution, and is usually in the range of from 5 seconds to 5 minutes.
• a cathodic electrolysis treatment may be utilized therefor.
• the metal surfaces so-treated may be dried without first washing with water.
• the metal surface is to be dipped into an electrocoating bath for cationic electrocoating, it is desirable first to rinse the metal surface with pure water (which does not in any way diminish the beneficial effects produced by the present process).
• the treating techniques used which are referred to in Table 1, are given in detail below.
• the aqueous phosphating compositions of each Example are set forth in Table 1, together with the treating solutions used thereafter on the phosphated surfaces, referred to in Table 1 as "After Treatment”.
• the metal surfaces treated and the test results obtained at different stages of coating the metal surfaces are given in Table 2.
• degreasing - washing with water - surface conditioning used only where a dipping process is used for applying a conversion-coating
• conversion coating - washing with water - after-treatment - washing with pure water - drying - coating

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• Chemical Treatment Of Metals (AREA)

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• 1981
  • 1981-03-26 JP JP56044820A patent/JPS6017827B2/ja not_active Expired
• 1982
  • 1982-03-26 GB GB8208993A patent/GB2097429A/en not_active Withdrawn
  • 1982-03-26 IT IT20440/82A patent/IT1151530B/it active
  • 1982-03-26 EP EP82301602A patent/EP0061911A1/en not_active Withdrawn
  • 1982-03-26 FR FR8205238A patent/FR2502645A1/fr not_active Withdrawn
  • 1982-03-26 NL NL8201265A patent/NL8201265A/nl not_active Application Discontinuation

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