JP7356769B1 - Post-processing technology for trivalent chromium plating film - Google Patents

Abstract

An object of the present invention is to provide a technology for further improving corrosion resistance of a trivalent chromium plating film while further suppressing color change. [Solution] An aqueous solution containing hydrogen peroxide and a phosphorus compound and used for cathodic electrolytic treatment of a trivalent chromium plating film. [Selection diagram] None

Description

The present invention relates to post-treatment technology for trivalent chromium plating films.

Chrome plating is used as a final surface treatment for interior and exterior parts of automobiles, faucet metal parts, etc. to give them excellent appearance and corrosion resistance. Conventional chromium plating has generally used hexavalent chromium, but in recent years the use of hexavalent chromium has begun to be restricted due to its toxicity and adverse effects on the working environment.

Therefore, trivalent chromium plating has been developed as an alternative to hexavalent chromium plating. Depending on the bath composition, it is possible to obtain a film with a dark tone (L* value in the L*a*b* color system is 70 or less) that cannot be obtained with hexavalent chromium plating. Trivalent chromium plating is becoming widespread. However, the trivalent chromium plating film has inferior corrosion resistance compared to the hexavalent chromium plating film.

Therefore, in order to meet strict standards for corrosion resistance, it is now common practice to perform electrolytic chromate using hexavalent chromium in the post-treatment of trivalent chromium plating films. Therefore, in reality, there is no process that does not use hexavalent chromium, and research is being conducted on post-treatment agents that do not use hexavalent chromium.

Japanese Patent Application Publication No. 2005-097701

Recently, there has been an increase in reports on various types of hexavalent chromium-free post-treatments, and product development is also underway. However, its actual corrosion resistance is not as good as that of hexavalent chromium electrolytic chromate, and its effect on corrosion resistance is particularly weak on dark-colored trivalent chromium plating films. Another problem is that the color tone changes due to post-treatment regardless of the presence or absence of hexavalent chromium (particularly an increase in the b* value in the L*a*b* color system).

Patent Document 1 discloses a rust preventive agent containing a phosphate, an oxidizing agent, and a nonionic surfactant, with the remainder being water. However, this rust preventive agent has insufficient effect on improving corrosion resistance.

An object of the present invention is to provide a technique for further improving the corrosion resistance of a trivalent chromium plating film while further suppressing color change.

As a result of intensive research in view of the above problems, the present inventor found that the above problems could be solved by an aqueous solution containing hydrogen peroxide and a phosphorus compound and used for cathodic electrolytic treatment of trivalent chromium plating films. Ta. The present inventor conducted further research based on this knowledge and completed the present invention. That is, the present invention includes the following aspects.

Item 1. An aqueous solution containing hydrogen peroxide and a phosphorus compound for use in cathodic electrolytic treatment of trivalent chromium plating films.

Item 2. Item 1. The aqueous solution according to item 1, which has a pH of 1.5 to 5.5.

Item 3. Item 2. The aqueous solution according to Item 1, wherein the hydrogen peroxide content is 1 g/L or more.

Item 4. Item 2. The aqueous solution according to Item 1, wherein the content of the phosphorus compound is 1 g/L or more.

Item 5. Item 2. The aqueous solution according to Item 1, wherein the hydrogen peroxide content is 1 to 500 g/L, and the phosphorus compound content is 1 to 200 g/L.

Item 6. The phosphorus compound is phosphoric acid, dipotassium hydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, pyrophosphoric acid and its salts, tripolyphosphoric acid and its salts, etidronic acid and its salts, and Item 2. The aqueous solution according to Item 1, which is at least one selected from the group consisting of aminotrimethylenephosphonic acid and salts thereof.

Section 7. Item 7. A method for producing a corrosion-resistant trivalent chromium plating film, the method comprising cathodic electrolyzing the trivalent chromium plating film in the aqueous solution according to any one of Items 1 to 6.

Section 8. Item 8. The manufacturing method according to item 7, wherein the cathode current density is 0.01 to 3 A/dm ² .

Item 9. Item 7. The manufacturing method according to Item 7, wherein the energization time is 30 to 1000 seconds.

Item 10. Item 7. The manufacturing method according to Item 7, wherein the bath temperature during cathode electrolysis is 10 to 50°C.

Item 11. Item 7. A method for post-treatment of a trivalent chromium plating film, which comprises cathodically electrolyzing the trivalent chromium plating film in the aqueous solution according to any one of Items 1 to 6.

Item 12. Item 7. A corrosion-resistant trivalent chromium plating film obtained by the manufacturing method according to item 7.

Item 13. Item 13. An article comprising the corrosion-resistant chromium plating film according to Item 12.

According to the present invention, it is possible to provide a technique for further improving corrosion resistance of a trivalent chromium plating film while further suppressing color change. More specifically, the present invention provides an aqueous solution for use in cathodic electrolytic treatment of a trivalent chromium plating film, a method for producing a corrosion-resistant trivalent chromium plating film, a post-treatment method for a trivalent chromium plating film, and a corrosion-resistant trivalent chromium plating film. It is possible to provide articles containing a chromium plating film, a corrosion-resistant trivalent chromium plating film, and the like.

In this specification, the expressions "contain" and "including" include the concepts of "containing", "comprising", "consisting essentially" and "consisting only".

1. Aqueous solution In one aspect, the present invention provides an aqueous solution containing hydrogen peroxide and a phosphorus compound for use in cathodic electrolytic treatment of a trivalent chromium plating film (herein also referred to as "aqueous solution of the present invention"). ).

Hydrogen peroxide acts as an oxidizing agent in the aqueous solution of the present invention. Hydrogen peroxide can form a phosphoric acid film together with an oxide film and/or phosphorus on the trivalent chromium plating film. Further, depending on the anode material, hydrogen peroxide can also suppress dissolution of the anode.

The content of hydrogen peroxide is not particularly limited, but from the viewpoint of improving corrosion resistance, suppressing dissolution of the anode, etc., it is preferably 1 g/L or more, more preferably 2 g/L or more, even more preferably 5 g/L or more, and more. More preferably, it is 7 g/L or more, particularly preferably 10 g/L or more. The upper limit of the content of hydrogen peroxide is not particularly limited, and is, for example, 500 g/L. From the viewpoint of cost, the upper limit is preferably 300 g/L, more preferably 200 g/L, still more preferably 150 g/L, and even more preferably 120 g/L. The range of the content of hydrogen peroxide can be any combination of the above lower limit and the above upper limit, for example, 1 to 500 g/L, preferably 2 to 300 g/L, more preferably 5 to 200 g/L, More preferably, it is 5 to 150 g/L.

The phosphorus compound allows a phosphoric acid film to be formed on the outermost layer of the film formed on the trivalent chromium plating film. Further, the phosphorus compound can also suppress the decomposition of hydrogen peroxide.

The phosphorus compound is not particularly limited as long as it is a phosphorus-containing compound, and both inorganic and organic compounds that can be added to post-plating treatment can be used. Inorganic phosphorus compounds are preferably phosphoric acid, dipotassium hydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, pyrophosphoric acid and its salts (e.g., potassium pyrophosphate, sodium pyrophosphate). etc.), tripolyphosphoric acid and its salts (eg, potassium tripolyphosphate, sodium tripolyphosphate, etc.). Preferable examples of the organic phosphorus compound include etidronic acid and its salts, aminotrimethylenephosphonic acid and its salts, and the like.

The phosphorus compounds can be used alone or in combination of two or more.

The content of the phosphorus compound is not particularly limited, but from the viewpoint of improving corrosion resistance, suppressing consumption of hydrogen peroxide, etc., it is preferably 1 g/L or more, more preferably 2 g/L or more, even more preferably 3 g/L or more, It is even more preferably 5 g/L or more, particularly preferably 7 g/L or more, particularly preferably 10 g/L or more. The upper limit of the content of the phosphorus compound is not particularly limited, and is, for example, 200 g/L. The upper limit is preferably 150 g/L, more preferably 100 g/L, still more preferably 80 g/L, and even more preferably 60 g/L from the viewpoint of suppressing attack on the anode and facilitating waste liquid treatment. The range of the content of the phosphorus compound can be any combination of the above lower limit and the above upper limit, for example, 1 to 200 g/L, preferably 2 to 150 g/L, more preferably 3 to 100 g/L, and Preferably it is 5 to 80 g/L.

Due to the combination of hydrogen peroxide and a phosphorus compound, by subjecting the aqueous solution of the present invention to the cathodic electrolytic treatment described below, it is possible to further improve the corrosion resistance of trivalent chromium plating films while further suppressing color changes. can be done.

The pH of the aqueous solution of the present invention is preferably 1.5 or higher from the viewpoint of corrosion resistance. Further, the pH is preferably 5.5 or less from the viewpoint of suppressing decomposition of hydrogen peroxide. From the above two viewpoints, the pH is preferably 1.5 to 5.5, more preferably 2.0 to 5.0.

The aqueous solution of the present invention can contain, for example, an organic acid for the purpose of functioning as a buffer. Preferred organic acids include citric acid, succinic acid, acetic acid, formic acid, and oxalic acid.

The organic acids can be used alone or in combination of two or more.

The content of organic acid is, for example, 0 to 100 g/L, preferably 0 to 30 g/L.

The aqueous solution of the present invention can improve corrosion resistance without relying on metals. From this point of view, the metal ion content of the aqueous solution of the present invention is, for example, 0 to 0.5 g/L, preferably 0 to 0.2 g/L, more preferably 0 to 0.1 g/L, and even more preferably 0. ~0.01 g/L, more preferably 0 ~ 0.001 g/L, particularly preferably 0 g/L.

The aqueous solution of the present invention can improve corrosion resistance without relying on hexavalent chromium. From this point of view, the content of hexavalent chromium ions in the aqueous solution of the present invention is, for example, 0 to 0.1 g/L, preferably 0 to 0.05 g/L, more preferably 0 to 0.02 g/L, and even more preferably is 0 to 0.01 g/L, even more preferably 0 to 0.001 g/L, particularly preferably 0 g/L.

The aqueous solution of the present invention is used for cathodic electrolytic treatment of trivalent chromium plating films. Based on the new finding that when the aqueous solution of the present invention is used for cathodic electrolytic treatment of a trivalent chromium plating film, it is possible to further improve the corrosion resistance while further suppressing color change of the trivalent chromium plating film. It has been found that the aqueous solution of the present invention is suitable for the above uses.

Therefore, in one aspect, the present invention provides a method for producing a corrosion-resistant trivalent chromium plating film, which comprises cathodically electrolyzing a trivalent chromium plating film in the aqueous solution of the present invention, and The present invention relates to a method for post-processing a trivalent chromium plating film, which includes cathodic electrolysis of the chromium plating film. These two methods may be collectively referred to as the "method of the present invention."

The trivalent chromium plating film is a plating film obtained using a plating solution containing trivalent chromium ions, and is not particularly limited as long as it is a plating film that mainly contains chromium as a metal, and includes so-called trivalent chromium alloy plating. do. In one aspect of the present invention, the chromium content in the trivalent chromium plating film is, for example, 1 at% or more, 2 at% or more, 5 at% or more, 10 at% or more, 20 at% or more with respect to 100 at% (atomic percent) of the metal. , 30 at% or more, 40 at% or more, or 45 at% or more, and can be 100 at% or less, 90 at% or less, 80 at% or less, 70 at% or less, 60 at% or less, or 50 at% or less. The above upper and lower limits can be arbitrarily combined. The content can be measured by energy dispersive X-ray analysis (EDX). Examples of metals other than chromium in the trivalent chromium plating film include Co, Fe, Mn, Ni, and Zn.

The plating solution for forming the trivalent chromium plating film preferably has a lower content of hexavalent chromium ions, and the content is, for example, 0 to 0.1 g/L, preferably 0 to 0.05 g/L. L, more preferably 0 to 0.02 g/L, even more preferably 0 to 0.01 g/L, even more preferably 0 to 0.001 g/L, particularly preferably 0 g/L.

Trivalent chromium plating film can be either white (L* value in L*a*b* color system is 70 or more) or black (L* value in L*a*b* color system is 70 or less). It can also be. According to the method of the present invention, even for black trivalent chromium plating films for which the corrosion resistance improvement effect of conventional hexavalent chromium-free post-treatments is limited, it is possible to exhibit better effects on corrosion resistance.

The target articles on which the trivalent chromium plating film is formed are not particularly limited, and include, for example, automobile parts; molding molds; easily worn parts of various machinery; tools; printing, paper making, rolling, film processing, Examples include rolls used in iron manufacturing, faucet fittings, bicycle parts, fishing gear, mobile phones, cameras, ornaments, and miscellaneous goods.

The trivalent chromium plating film can be formed according to or in a similar manner to a known method.

Cathode electrolysis of the trivalent chromium plating film is carried out by immersing the trivalent chromium plating film as a cathode and the anode in the aqueous solution of the present invention, and performing electrolysis.

The anode is not particularly limited, and various insoluble anodes or soluble anodes can be used.

Examples of insoluble anodes include carbon, Ti/Pt (Ti coated with platinum), Ti/Ir oxide (Ti coated with Ir oxide), Ti/Ru oxide (Ti coated with Ir oxide), and Ti/Ru oxide (Ti coated with Ir oxide). (Ru oxide coating), Ti/Ir oxide-Ru oxide (Ti coated with a mixture of Ir oxide and Ru oxide), Ti/Ir oxide-Ta oxide ( Ti/Pt/Ir oxide-Ru oxide (Ti/Pt coated with a mixture of Ir oxide and Ru oxide) Ti/Pt/Ir oxide-Ta oxide (Ti/Pt coated with a mixture of Ir oxide and Ta oxide), stainless steel, aluminum, lead alloy (Pb-Sn alloy, Pb-Ag alloy, Pb-Sb alloy), lead oxide (lead monoxide, lead dioxide, lead trioxide, trilead tetroxide), lead, tin oxide, carbon, diamond electrode (diamond containing nitrogen or boron) Examples include those coated on a substrate such as silicon or niobium), ITO electrodes (indium tin electrodes), and the like.

Examples of the soluble anode include nickel, tin, cobalt, iron, and the like.

As the anode, nickel or stainless steel is preferably used.

The bath temperature in cathode electrolysis is not particularly limited, but from the viewpoint of suppressing decomposition of hydrogen peroxide, etc., it is preferably 10 to 50°C, more preferably 15 to 35°C.

The cathode current density is not particularly limited, but from the viewpoint of improving corrosion resistance, anodic dissolution, etc., it is preferably 0.01 to 3 A/dm ² , more preferably 0.1 to 1.5 A/dm ² .

The current application time is not particularly limited, but from the viewpoint of improving corrosion resistance, cost, etc., it is preferably 30 to 1000 seconds, more preferably 60 to 600 seconds.

By the method of the present invention, a corrosion-resistant trivalent chromium plating film and an article containing the corrosion-resistant trivalent chromium plating film can be obtained.

The present invention will be described in detail below based on Examples, but the present invention is not limited to these Examples.

Test Example 1. Post-treatment test of trivalent chromium plating film <Test Example 1-1. Formation of trivalent chromium plating film>
Plating films were formed on a 5 cm x 10 cm resin plate in the following order: a copper plating film with a thickness of 20 μm, a semi-bright Ni plating film with a thickness of 8 μm, a bright Ni plating film with a thickness of 6 μm, and a microporous Ni plating film with a thickness of 2 μm. Furthermore, a white trivalent chromium plating film or a black trivalent chromium plating film was formed on the outermost microporous Ni plating film. The white trivalent chromium plating film was formed using Top Fine Chrome (manufactured by Okuno Pharmaceutical Industries) as a plating solution, and the black trivalent chromium plating film was formed using Topfalbe BLB Plus (manufactured by Okuno Pharmaceutical Industries) as a plating solution. was formed using.

<Test Example 1-2. Post-treatment of trivalent chromium plating film>
(Comparative example 1)
No post-treatment was performed on the trivalent chromium plating film obtained in Test Example 1-1.

(Comparative example 2)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (ECB-Y, manufactured by Okuno Pharmaceutical Co., Ltd., pH 3.5), and subjected to hexavalent chromium electrolytic chromate treatment (conditions: cathode current density 0.5 A). /dm ² , current application time 1 minute, bath temperature 25° C.).

(Comparative example 3)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (Elup CCS, manufactured by Okuno Pharmaceutical Co., Ltd., pH 3.5), and subjected to trivalent chromium electrolytic chromate treatment (conditions: cathode current density 0.5 A/ dm ² , current application time 1 minute, bath temperature 25° C.).

(Comparative example 4)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (aqueous solution containing 20 g/L of hydrogen peroxide and 40 g/L of disodium hydrogen phosphate, pH 4.0) without electrolytic treatment. It was left standing for 5 minutes (bath temperature 25°C).

(Comparative example 5)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (aqueous solution containing 60 g/L of dipotassium hydrogen phosphate without hydrogen peroxide, pH 4.0), and the plating film was A cathodic electrolytic treatment (conditions: cathode current density 0.5 A/dm ² , current application time 3 minutes, bath temperature 25° C.) was performed.

(Comparative example 6)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (an aqueous solution containing 20 g/L of hydrogen peroxide and no phosphorus compound, pH 4.0), and the plating film was subjected to cathodic electrolysis treatment. (Conditions: cathode current density 0.5 A/dm ² , current application time 3 minutes, bath temperature 25° C.).

(Example 1)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (aqueous solution containing 10 g/L of hydrogen peroxide and 30 g/L of sodium pyrophosphate, pH 4.0), and the plating film was subjected to cathodic electrolysis. Treatment (conditions: cathode current density 0.5 A/dm ² , current application time 3 minutes, bath temperature 25° C.) was performed.

(Example 2)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (aqueous solution containing 30 g/L of hydrogen peroxide and 50 g/L of potassium dihydrogen phosphate, pH 3.5). Cathode electrolysis treatment (conditions: cathode current density 0.2 A/dm ² , current application time 5 minutes, bath temperature 30° C.) was performed.

(Example 3)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (aqueous solution containing 100 g/L of hydrogen peroxide and 10 g/L of etidronic acid, pH 4.5), and the plating film was subjected to cathodic electrolysis treatment. (Conditions: cathode current density 1 A/dm ² , current application time 2 minutes, bath temperature 20° C.).

(Example 4)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (aqueous solution containing 80 g/L of hydrogen peroxide and 20 g/L of sodium tripolyphosphate, pH 3.0), and the plating film was subjected to cathodic electrolysis. Treatment (conditions: cathode current density 0.3 A/dm ² , current application time 10 minutes, bath temperature 35° C.) was performed.

(Example 5)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (aqueous solution containing 50 g/L of hydrogen peroxide and 35 g/L of disodium hydrogen phosphate, pH 2.0). Cathode electrolytic treatment (conditions: cathode current density 0.1 A/dm ² , current application time 8 minutes, bath temperature 40° C.) was performed.

(Example 6)
The trivalent chromium plating film obtained in Test Example 1-1 was immersed in a treatment solution (aqueous solution containing 150 g/L of hydrogen peroxide and 55 g/L of sodium dihydrogen phosphate, pH 5.0). Cathode electrolytic treatment (conditions: cathode current density 1.5 A/dm ² , current application time 4 minutes, bath temperature 15° C.) was performed.

<Test Example 1-3. Corrosion resistance evaluation>
The corrosion resistance of the post-treated plating film (test piece) obtained in Test Example 1-2 was evaluated by a CASS test. Specifically, a test piece was placed in a test tank at 50 ° C., and a solution containing 50 g/L of sodium chloride and 0.205 g/L of copper chloride and adjusted to pH 3.0 with acetic acid was sprayed. The degree of corrosion was checked at regular intervals. Evaluation was made according to the following evaluation criteria.
○: The corrosion area of the test piece 48 hours after the start of the test is less than 1%.
Δ: The corrosion area of the test piece 48 hours after the start of the test is 1% or more and less than 10%.
×: The corrosion area of the test piece 48 hours after the start of the test is 10% or more.

<Test Example 1-4. Evaluation of color tone change>
The color of the surface of the trivalent chromium plating film obtained in Test Example 1-1 and the surface of the post-treated plating film obtained in Test Example 1-2 was measured using a color difference meter (product name: CM-3700A, Konica Manufactured by Minolta, measurement conditions: SCI). Change value of b* value before and after post-treatment in L*a*b* color system (=b* value of plating film after post-treatment obtained in Test Example 1-2 - b* value obtained in Test Example 1-1 b* value) of the trivalent chromium plating film was calculated and evaluated according to the following evaluation criteria. Note that the L* value of the surface of the trivalent chromium plating film obtained in Test Example 1-1 was 83.5 for white and 58.4 for black.
Good: The change in b* value before and after post-processing is less than 0.1.
Δ: Change value of b* value before and after post-processing is 0.1 or more and less than 0.3.
×: The change value of b* value before and after post-processing is 0.3 or more.

<Results>
The results are shown in Tables 1 and 2.

It has been found that when a trivalent chromium plating film is subjected to cathodic electrolysis treatment with an aqueous solution containing hydrogen peroxide and a phosphorus compound, corrosion resistance can be further improved while further suppressing color change.

Claims (11)

Contains hydrogen peroxide and phosphorus compounds,
The hydrogen peroxide content is 1 to 500 g/L, and the phosphorus compound content is 1 to 200 g/L,
pH is 1.5 to 5.5, and
The content of metal ions or chromium ions is 0 to 0.01 g/L,
Aqueous solution for use in cathodic electrolytic treatment of trivalent chromium plating films. The aqueous solution according to claim 1, having a pH of 2.0 to 5.0 . The aqueous solution according to claim 1, wherein the hydrogen peroxide content is 2 to 300 g/ L . The aqueous solution according to claim 1, wherein the content of the phosphorus compound is 2 to 150 g/ L . The aqueous solution according to claim 1, wherein the hydrogen peroxide content is 2 to 300 g/L, and the phosphorus compound content is 2 to 150 g/L. The phosphorus compound is phosphoric acid, dipotassium hydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, pyrophosphoric acid and its salts, tripolyphosphoric acid and its salts, etidronic acid and its salts, and The aqueous solution according to claim 1, which is at least one selected from the group consisting of aminotrimethylenephosphonic acid and salts thereof. A method for producing a corrosion-resistant trivalent chromium plating film, the method comprising cathodic electrolyzing the trivalent chromium plating film in the aqueous solution according to any one of claims 1 to 6. The manufacturing method according to claim 7, wherein the cathode current density is 0.01 to 3 A/dm ² . The manufacturing method according to claim 7, wherein the energization time is 30 to 1000 seconds. The manufacturing method according to claim 7, wherein the bath temperature during cathode electrolysis is 10 to 50°C. A method for post-treatment of a trivalent chromium plating film, comprising cathodic electrolyzing the trivalent chromium plating film in an aqueous solution according to any one of claims 1 to 6.