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Processing solution for forming hexavalent chromium free, black conversion film on zinc or zinc alloy plating layers, and method for forming hexavalent chromium free, black conversion film on zinc or zinc alloy plating layers

Inactive Publication Date: 2005-05-26
DISPOL CHEMICALS CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0013] The present invention has been completed on the basis of such finding that the foregoing problems associated with the conventional techniques can effectively be solved by depositing a zinc or zinc alloy plating layer(s) on a substrate and then subjecting the plating layer to a trivalent chromate treatment using a processing solution having a specific composition, i.e. containing a low concentration of nitrate ions, cobalt ions and nickel ions.
[0039] In addition, further improvement of the corrosion resistance of the film can be achieved by subjecting the trivalent chromate treated film to aging treatment (heat treatment). In cases where it is applied to zinc-nickel alloy plating layers, particularly good effects are obtained. The aging treatment is conducted at 100 to 250° C. for 10 to 300 minutes, preferably at 150 to 200° C. for 10 to 300 minutes, and more preferably at 200° C. for 4 hours.

Problems solved by technology

However, it is not possible to ensure sufficient corrosion resistance of the metal by such plating alone.
However, a fluoride is used in this plating bath and therefore, a problem of environmental pollution would arise.
However, this method makes use of an oxidizing agent and cerium and therefore, the trivalent chromium may possibly be oxidized into hexavalent chromium, during the processing and / or the storage of the bath.
However, as a result of our experiments to confirm the effects produced by the method, acceptable corrosion resistance could not be obtained.
However, the method suffers from a problem in that it is difficult to stably form a dense film and that the method cannot ensure the stable corrosion resistance of the resulting film.
This makes the post-treatment of the waste water difficult and results in the formation of a vast quantity of sludge after the processing.
Although one can recognize that it is advantageous to use a processing solution free of any hexavalent chromium for ensuring the environmental protection, the method suffers from a serious problem in that it may give a new burden to the environment such that the method generates a vast quantity of waste.
However, in many cases, a Ni eutectoid rate in zinc-nickel alloy plating layers actually produced is less than 8%, and thus it is difficult to obtain a black feature from a practical standpoint.
Furthermore, the black conversion film on zinc-iron alloy plating layers does not have enough corrosion resistivity.
However, these methods never ensure sufficient corrosion resistance of the resulting film as compared with the conventional hexavalent chromate treatment.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

examples 1 to 6

[0052] A steel plate, which had been plated with zincates using a NZ-98 solution available from Dipsol Chemicals Co., Ltd. to form a Zn plating layer having a thickness of 8 μm, was immersed in a trivalent chromate-containing processing solution having a composition as shown in the following Table 1.

TABLE 1Ex. No.123456Cr3+ (g / L)4.54.54.54.54.52NO3− (g / L)0.20.40.10.40.60.4Mole ratio of0.04 / 10.07 / 10.02 / 10.07 / 10.11 / 10.17 / 1NO3− / Cr3+PO43− (g / L)12120151212SO42− (g / L)1500202Cl− (g / L)1010100150Oxalic acid15157000(g / L)Malonic acid007151212(g / L)Succinic acid01020000(g / L)Adipic acid0002000(g / L)Molar ratio of 2.0 / 1 3.0 / 1 3.7 / 1 3.4 / 1 1.4 / 1 1.4 / 1the chelatingagent / Cr3+Co (g / L)11.50.5111Ni (g / L)0.101.000.30.5Other metalSiSiTiSiSiSisaltpH of2.32.32.32.42.62.5ProcessingSoln.Processing505060504030Temp. (° C.)Processing time3060120606060(sec.)

[0053] In Table 1, Cr3+ sources used were CrCl3 (in Examples 1, 2, 3 and 5), CrPO4 (in Examples 4 and 6) and Cr(NO3)3 (in Example 5). The concentrations of NO...

examples 7 to 10

[0054] A steel plate, which had been plated with alkaline zinc-nickel alloy (Ni %: 5 to 15%) or zinc-iron alloy (Fe %: 0.3 to 2.0%) in a thickness of 8 μm, was immersed in a trivalent chromate-containing processing solution having a composition as shown in the following Table 2.

TABLE 2Ex. No.78910Cr3+ (g / L)4.54.54.54.5NO3− (g / L)0.60.40.20.4Mole ratio of NO3− / Cr3+0.11 / 10.07 / 10.04 / 10.07 / 1PO43− (g / L)12121215SO42− (g / L)100152Cl− (g / L)01000Oxalic acid (g / L)1571515Malonic acid (g / L)0700Succinic acid (g / L)10000Adipic acid (g / L)00020Molar ratio of the 3.0 / 1 1.7 / 1 2.0 / 1 3.7 / 1chelating agent / Cr3+Co (g / L)1111Ni (g / L)0.300.10Other metal saltSiSiSiSipH of Processing Soln.2.62.02.32.5Processing Temp. (° C.)35505040Processing time (sec.)60606060Plating Eutectoid rate (%)Zn—NiZn—NiZn—FeZn—Fe6.5150.52.0

[0055] In Table 2, the Cr3+ sources used were CrCl3 (in Example 8) and CrPO4 (in Examples 7, 9 and 10).

[0056] The concentrations of NO3− were adjusted by adding HNO3 (in Example 8) or_NaNO3 (in Exa...

examples 11 to 14

[0057] After the trivalent chromate treatment in Examples 1, 8 and 9, the steel plate was subjected to a topcoating treatment. The conditions for the topcoating treatment used herein are summarized in the following Table 3.

TABLE 3Ex. No.11121314TrivalentExample 1Example 8Example 9Example 9chromatetreatmentKind ofSilicate typeSilicate typePolyurethaneMethacrylicTopcoatinorganic filminorganic filmtype organicresin typefilmorganic filmConcn. Of200 mL / L200 mL / L100 mL / LStock solutionProcessingwas used asSoln.suchProcessing45° C. - 45 sec45° C. - 45 sec25° C. - 60 sec25° C. - 60 secConditionsName andCC-445CC-445SUPERFLEXDIPCOAT WOrigin ofavailable fromavailable fromR3000available fromReagentDipsolDipsolavailable fromDipsolChemicalsChemicalsDai-ichiChemicalsCo., Ltd.Co., Ltd.KogyoCo., Ltd.Seiyaku Co.,Ltd.

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Abstract

It is an object of the present invention to provide a processing solution used for forming a hexavalent chromium free, black conversion film, which is applied onto the surface of zinc or zinc alloy plating layers, and which has corrosion resistance identical to or higher than that achieved by the conventional hexavalent chromium-containing conversion film. According to an aspect of the present invention, there is provided a processing solution for forming a hexavalent chromium free, black conversion film on zinc or zinc alloy plating layers, the processing solution comprising: nitrate ions and trivalent chromium in a mole ratio (NO3− / Cr3+) of less than 0.5 / 1, wherein the trivalent chromium is present in the form of a water-soluble complex with a chelating agent; and cobalt ions and / or nickel ions, wherein the cobalt ions and / or nickel ions are stably present in the processing solution without causing any precipitation by forming a hardly soluble metal salt with the chelating agent; wherein the solution reacts with zinc when it is brought into contact with the zinc or zinc alloy plating to form a hexavalent chromium free, black conversion film containing zinc, chromium, cobalt and / or nickel, and the chelating agent on the plating.

Description

FIELD OF TECHNOLOGY [0002] The present invention relates to a processing solution for forming a hexavalent chromium free, black conversion film on zinc or zinc alloy plating layers, and a method for forming the hexavalent chromium free, black conversion film on zinc or zinc alloy plating layers. TECHNICAL BACKGROUND [0003] As methods for rust preventing the surface of a metal, there has been known a zinc or zinc alloy-plating method. However, it is not possible to ensure sufficient corrosion resistance of the metal by such plating alone. For this reason, there has widely been adopted, in this industrial field, the treatment with chromic acid containing hexavalent chromium or the so-called chromate treatment after the plating. Nevertheless, it has recently been pointed out that the hexavalent chromium may adversely affect the human body and the environment and there has correspondingly been such a strong and active trend that the use of hexavalent chromium should be controlled. [0004...

Claims

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Application Information

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IPC IPC(8): C23C22/17C23C22/47C23C22/53
CPCC23C22/17C23C2222/10C23C22/53C23C22/47
Inventor INOUE, MANABUNAKAJIMA, RYOWATANABE, KAZUHIROWATANABE, TOYOJIWATANABE, FUMIEWATANABE, YUTAKAWATANABE, TAKESHIWATANABE, KIMITAKA
Owner DISPOL CHEMICALS CO LTD
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