TW201518557A - Trivalent chromium plating bath - Google Patents

Abstract

The present invention provides a trivalent chromium plating bath which comprises an aqueous solution containing a trivalent chromium compound, a complexing agent, a fluoride, aluminum sulfate and a boric acid compound. According to the present invention, a novel trivalent chromium plating bath can be produced, which has a high coating film deposition rate, is suitable for thick plating, and has improved deposition performance in a low current density range and an improved deposition rate.

Description

Trivalent chrome plating bath Field of invention

The present invention relates to a trivalent chromium plating bath which can be thickened.

Background of the invention

Chrome plating having high hardness, excellent corrosion resistance, and abrasion resistance is widely used in automobile parts, molding dies, press rolls, printing rolls, and the like. In particular, in applications such as molding dies and rollers, chrome plating of a so-called hard chrome-plated thick coating is performed.

Heretofore, a chrome plating bath mainly used for such a purpose is a hexavalent chromium plating bath containing hexavalent chromium as a chromium component. In particular, in the case of hard chrome plating which requires a thick plating layer, a sufficient deposition rate is necessary, and thus a hexavalent chromium plating bath is widely used.

However, in recent years, environmental concerns and effects on the human body caused by the use of a harmful hexavalent chromium plating bath have been questioned, and an alternative technology that can be used to replace the hexavalent chromium plating bath has become a top priority.

Therefore, a plating bath containing trivalent chromium which is less toxic than hexavalent chromium has been developed, but a trivalent chromium plating bath which can be used for thickening plating has not yet progressed to practical use. Degree. For example, Patent Document 1 listed below discloses a trivalent chromium plating bath containing potassium chromium sulfate, oxalate, aluminum sulfate, and sodium fluoride as a trivalent value for a chromium plating layer having a thickness of about 100 μm or more. Chrome plating bath. However, the chrome-plated film formed by this plating bath has a relatively good plating film at a high current density portion, but the deposition property in a low current portion is poor, and the adhesion uniformity is inferior, and it cannot be applied to an article having a complicated shape. In addition, there is still room for further improvement regarding the rate of chrome plating.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2008-506035

Summary of invention

The present invention has been made in view of the above-mentioned state of the art, and its main object is to provide a trivalent chromium plating bath which is excellent in deposition rate of a plating film, suitable for thick plating, and in the field of low current density. A novel trivalent chromium plating bath which has improved precipitation and improved in precipitation speed.

Inventors of this case have devoted themselves to research in order to achieve the above objectives. As a result, it has been found that by adding a fluoride, an aluminum sulfate, and a boric acid compound simultaneously in a plating bath containing a trivalent chromium compound and a complexing agent, the precipitation in the field of low current density can be improved, and Make the adhesion uniformity better. And by further plating here The addition of conductive salts to the bath improves adhesion uniformity and greatly increases the rate of precipitation. The present invention has been completed based on the findings of this review and further intensive review.

That is, the present invention is to provide the following trivalent chromium plating bath.

Item 1. A trivalent chromium plating bath comprising an aqueous solution containing a trivalent chromium compound, a complexing agent, a fluoride, an aluminum sulfate, and a boric acid compound.

Item 2. The trivalent chromium plating bath according to the above item 1, which further contains a conductive salt.

Item 3. The trivalent chromium plating bath according to the above item 1, wherein the coupling agent is at least one compound selected from the group consisting of aqueous aliphatic carboxylic acids and salts thereof.

Item 4. The trivalent chromium plating bath according to any one of the items 1 to 3 above, wherein the conductive salt is a sulfate.

The trivalent chromium plating bath according to any one of the items 1 to 4 above, wherein the complexing agent is contained in an amount of 0.1 to 0.3 mol per 1 mol of the trivalent chromium ion.

The trivalent chromium plating bath according to any one of the items 1 to 5, wherein the trivalent chromium compound and the complexing agent are blended in a solution of a trivalent chromium complex. The chrome complex solution is obtained by keeping an aqueous solution containing a trivalent chromium compound and a complexing agent under heating.

Item 7. The trivalent chromium plating bath according to any one of the above items 1 to 6, which has a pH of from 1 to 2.5.

Item 8. A trivalent chromium plating method, wherein the plated material is used as a cathode in the trivalent chromium plating bath according to any one of items 1 to 7 above. Line power up.

Hereinafter, the trivalent chromium plating bath of the present invention will be specifically described.

The trivalent chromium plating bath of the present invention contains a trivalent chromium compound, a complexing agent, a fluoride, aluminum sulfate, and boric acid as essential components. By using such a component, it is possible to improve the precipitation property in the field of low current density and form a chromium plating film having good adhesion uniformity.

Further, in the above-described chrome plating bath, by adding a conductive salt as needed, it is possible to improve the precipitation property in the field of low current density and to greatly increase the deposition rate of the plating layer.

Hereinafter, each component contained in the trivalent chromium plating bath of the present invention will be specifically described.

(1) Trivalent chromium compounds

The trivalent chromium compound may be a water-soluble trivalent chromium compound, and for example, chromium sulfate, basic chromium sulfate, or the like can be used. The trivalent chromium compound may be used alone or in combination of two or more.

The concentration of the trivalent chromium compound is not particularly limited, but it is preferably set to, for example, a chromium metal concentration of about 20 to 40 g/L, and preferably about 25 to 35 g/L.

(2) wrong agent

The compound to be used is a compound which has a mismatching ability to trivalent chromium, and is not particularly limited. In particular, at least one compound selected from the group consisting of aqueous aliphatic carboxylic acids and salts thereof (hereinafter sometimes referred to as "carboxylic acid compound") is preferably used.

There is no particular limitation on the type of the aqueous aliphatic carboxylic acid. Any carboxylic acid which can be formulated into an aqueous solution of a predetermined concentration can be used. For example, an aliphatic monocarboxylic acid such as formic acid or acetic acid; an aliphatic dicarboxylic acid such as oxalic acid, malonic acid or succinic acid (succinic acid); an aliphatic hydroxymonocarboxylic acid such as gluconic acid: malic acid can be used. An aliphatic hydroxy dicarboxylic acid such as hydroxysuccinic acid; an aliphatic hydroxy tricarboxylic acid such as citric acid or the like.

The salt of the water-soluble aliphatic carboxylic acid may be a water-soluble salt of the above various carboxylic acids, and an alkaline earth metal such as an alkali metal salt such as a sodium salt or a potassium salt, a calcium salt or a magnesium salt may be used. Salt, ammonium salt, etc.

The amount of the miscible agent used is preferably about 0.1 to 0.8 mol with respect to 1 mol of the trivalent chromium ion contained in the plating bath. In particular, it is possible to form a deposition rate of the chrome-plated film by forming 0.1 to 0.3 mole with respect to 1 mol of the trivalent chromium ion.

(3) Fluoride

In the trivalent chromium plating bath of the present invention, fluoride must be blended, whereby current efficiency can be improved.

Specific examples of the fluoride include sodium fluoride, ammonium fluoride, potassium fluoride, boron fluoride, and calcium fluoride. These fluorides may be used alone or in combination of two or more.

The concentration of the fluoride should be set to about 10 to 50 g/L, preferably about 25 to 35 g/L.

(4) Aluminum sulfate and boric acid compounds

In the trivalent chromium plating bath of the present invention, aluminum sulfate and a boric acid compound must be simultaneously blended. By using these components at the same time, the precipitation property in the field of low current density can be improved, and the adhesion uniformity can be improved.

The concentration of aluminum sulfate should be set at about 50 to 150 g/L, preferably about 80 to 120 g/L.

In addition to boric acid, a borate such as sodium borate or potassium borate may be used, and these components may be used singly or in combination of two or more. The concentration of the boric acid compound should be set to about 20 to 80 g/L, preferably about 30 to 60 g/L.

(5) Conductive salts

In the trivalent chromium plating bath of the present invention, a conductive salt may be added as needed. By blending the conductive salt with the above-mentioned essential components, the adhesion uniformity and the deposition rate of the chrome-plated film can be greatly improved.

As the conductive salt, for example, a sulfate such as potassium sulfate, sodium sulfate or ammonium sulfate, an alkali metal chloride such as potassium chloride or sodium chloride, or the like can be used. These conductive salts may be used alone or in combination of two or more.

Among these conductive salts, it is particularly preferable to use a sulfate such as potassium sulfate, sodium sulfate or ammonium sulfate.

The concentration of the conductive salt is not particularly limited. However, in order to sufficiently exhibit the above effects, it is preferably set to about 50 to 200 g/L, preferably about 100 to 180 g/L.

Trivalent chrome plating bath

The trivalent chromium plating bath of the present invention is prepared by dissolving the above-mentioned trivalent chromium compound, a complexing agent, a fluoride, an aluminum sulfate, a boric acid compound, and a conductive salt which is further required in water, and each of them is prepared. The order of dissolution of the ingredients is not limited.

The pH of the trivalent chromium plating bath of the present invention is usually set at 1 to 3.0. The range around. In particular, when it is set in the range of about 1.8 to 2.5, the precipitation property in the field of low current density can be improved and the adhesion uniformity can be improved.

Complex solution containing trivalent chromium compound

In the trivalent chromium plating bath of the present invention, although the trivalent chromium compound and the complexing agent can be dissolved in water to directly prepare the plating bath, it is particularly preferable to mix the trivalent chromium compound with the complexing agent in advance. , fully matured under heating to prepare a stable solution of a complex solution containing a trivalent chromium compound, and prepared into a trivalent chromium plating by dissolving the obtained complex solution together with other components in water. bath. By using the trivalent chromium complex solution obtained as described above, a good chrome plating film can be formed even when the chrome plating bath is just completed, and a long-time electrolytic treatment is not required, so that Improve work efficiency. Moreover, the formed chrome-plated film can be made to have a good appearance, and in particular, the appearance of the low current density portion can be improved.

The complex solution containing a trivalent chromium compound can be obtained by maintaining an aqueous solution containing a trivalent chromium compound and a complexing agent under heating. Usually, it can be obtained by adding a trivalent chromium compound to an aqueous solution in which a complexing agent is dissolved, and maintaining it under heating for a certain period of time.

The order of dissolving the trivalent chromium compound and the complexing agent is not limited, and the method is applicable, and the method of adding a trivalent chromium compound after dissolving the dissolving agent in water, and dissolving the trivalent chromium compound in water, and then adding a wrong agent, is wrong. Any of various methods such as a method in which a mixture is dissolved in water at the same time as a trivalent chromium compound. At this time, the liquid temperature is preferably about 40 to 100 ° C, preferably about 50 to 90 ° C.

A complex solution containing a trivalent chromium compound is usually used by diluting it while making a bath for a trivalent chromium plating bath. Therefore, although for the complex The concentration of the trivalent chromium compound in the solution is not particularly limited. However, for example, the concentration of the chromium compound is preferably set to about 30 to 150 g/L, preferably about 50 to 100 g/L.

The amount of the dopant to be added is preferably set to about 0.1 to 0.8 mol, preferably about 0.1 to 0.3 mol, as described above, with respect to 1 mol of the trivalent chromium ion.

Further, the concentration of the complexing agent in the solution containing trivalent chromium is not particularly limited, but is preferably set to, for example, about 10 to 200 g/L, preferably about 20 to 100 g/L.

Next, the solution containing the trivalent chromium compound can be obtained by maintaining the aqueous solution containing the complexing agent and the trivalent chromium compound at a temperature of about 40 to 100 ° C, more preferably about 50 to 90 ° C. . The time to maintain the temperature range is usually set to about 30 minutes or more, preferably about 1 hour or more, and more preferably about 2 hours or more. Specifically, the lower the heating temperature, the more preferable it is to maintain it for a long period of time. For example, it is preferably maintained at a heating temperature of about 40 ° C for about 5 hours or more, and preferably at a heating temperature of about 80 ° C for more than 3 hours. . Thereby, a solution of a complex solution containing divalent chromium is obtained.

Chrome plating method

The plating method using the trivalent chromium plating bath of the present invention is not particularly limited, and may be carried out in the same manner as the plating method using a general trivalent chromium plating bath.

The anode used for the plating is not particularly limited, and a known insoluble anode such as a Ti-Pt electrode can be usually used. Especially for use In the case of the Ti electrode coated with the Ir-Ta composite oxide film, it is advantageous in that the formation of hexavalent chromium can be suppressed.

In the bath temperature of the trivalent chromium plating bath, when the bath temperature during the plating operation is low, the adhesion uniformity is improved, whereas when the bath temperature is high, the adhesion uniformity to the low current density is lowered. tendency. Moreover, when the bath temperature is too low, there is a fear that the components will crystallize. Considering this point, the bath temperature should be set at about 25~50 °C, preferably around 30~40 °C.

The range of the current density at the time of using the trivalent chromium plating bath of the present invention is not particularly limited, but the trivalent chromium plating bath of the present invention can be formed in a low current density field with good precipitation property, and A chrome-plated film with a good appearance in a wide range of current densities. For example, a chrome-plated film having a good appearance can be formed in a cathode current density range of about 10 to 40 A/dm ² .

Regarding the plating time, the film thickness of the target chrome-plated film can be appropriately determined. In particular, according to the trivalent chromium plating bath of the present invention, even if plating is performed for a long period of time, the plating film does not stop growing, and the thickness of the plating film can be increased in accordance with the plating time. Therefore, for example, thick chrome plating having a thickness exceeding 50 μm can be performed.

Article with chrome film

The trivalent chromium plating bath of the present invention can be used in various applications such as industrial chrome plating and decorative chrome plating. In particular, according to the trivalent chromium plating bath of the present invention, it is possible to form a good plating film which is excellent in corrosion resistance and has a sufficient film thickness in a wide current density range. Therefore, the trivalent chromium plating bath of the present invention is particularly suitable for use in industrial chrome plating. Use the above.

Industrial chrome plating can be used in various industrial fields due to its high hardness, wear resistance, corrosion resistance, adhesion, and mold release properties, and can be used, for example, in molds, rolling rolls, and printing cylinders. Waiting for the production. In the industrial chrome plating, as the material to be plated, for example, metal materials such as steel, stainless steel, brass, and zinc die-casting are mainly used. In industrial chrome plating applications, thick plating of about 50 μm or more is usually performed.

Further, chrome plating for decoration is used as a protective layer of a nickel plating layer, and the hardness of the chrome plating film and the characteristic color tone are utilized. Decorative chrome is widely used in, for example, automotive-related industries. In addition to the above-mentioned metal materials, various functional plastic materials such as ABS, PC/ABS, PC, and nylon can be used.

When a chrome-plated film is formed on each of these materials, a chrome-plated film can be directly formed on the metal material using the trivalent chromium plating bath of the present invention. Further, in the case of improvement in appearance, corrosion resistance, and the like, there is a case where chrome plating is performed after copper plating, nickel plating, or the like.

In order to form a chrome-plated film on a plastic material, it is possible to form a conductive plating film by electroless nickel plating, electroless copper plating, or the like after etching (etching), giving a catalyst, etc., according to a conventional method. The general practice of electroplating copper, electroplating nickel, etc., and then forming a chrome-plated film, but is not limited to this step. In the case where a chrome-plated film is formed for the purpose of decoration, a chrome-plated film having a thin film thickness of about 0.1 to 0.5 μm is usually formed.

According to the trivalent chromium plating bath of the present invention, the following remarkable effects can be achieved.

(1) Good adhesion uniformity in the field of low current density, and a good chrome plating film can be formed in a wide current density range.

(2) Since the coating can be grown in response to the plating time, it can be thickened to more than 50 μm.

(3) The deposition rate of the coating film is fast, and the thick coating film can be formed in a short time. Therefore, it is a plating bath with high work efficiency.

(4) The chrome-plated film formed has a high plating hardness and is excellent in corrosion resistance.

(5) A chrome-plated film having good corrosion resistance can be formed even without chromic acid immersion treatment.

Form for implementing the invention

Hereinafter, the present invention will be described in more detail by way of examples.

Manufacturing example 1

Add oxalic acid 2 hydrate 48g / L (0.38mol / L) to 200mL of pure water, increase the bath temperature to 60 ° C, and add 40% chromium sulfate aqueous solution 610mL / L (Cr = 100g / L, 1.9mol / L After that, stir it to dissolve completely.

Thereafter, heating was continued for 8 hours while maintaining the bath temperature at 60 °C. After 8 hours, the heating was stopped and cooled to room temperature to obtain trivalent chromium. A solution of the complex. A 250 mL/L (Cr = 25 g/L) solution of this complex was used. This was taken as a trivalent chromium complex solution A.

Manufacturing Example 2

Add oxalic acid 2 hydrate 72g / L (0.57mol / L) in 400mL of pure water, increase the bath temperature to 60 ° C, and add 40% chromium sulfate aqueous solution 610mL / L (Cr = 100g / L, 1.9mol / L After that, stir it to dissolve completely.

Thereafter, heating was continued for 8 hours while maintaining the bath temperature at 60 °C. Heating was stopped after 8 hours and cooled to room temperature to obtain a solution containing a trivalent chromium complex. A 250 mL/L (Cr = 25 g/L) solution of this complex was used. This was taken as a trivalent chromium complex solution B.

Manufacturing Example 3

Add oxalic acid 2 hydrate 96g / L (0.76mol / L) in 200mL of pure water, increase the bath temperature to 60 ° C, and add 40% chromium sulfate aqueous solution 610mL / L (Cr = 100g / L, 1.9mol / L After that, stir it to dissolve completely.

Thereafter, heating was continued for 8 hours while maintaining the bath temperature at 60 °C. Heating was stopped after 8 hours and cooled to room temperature to obtain a solution containing a trivalent chromium complex. A 310 mL/L (Cr = 31 g/L) solution of this complex was used. This was taken as a trivalent chromium complex solution C.

Manufacturing Example 4

Add oxalic acid 2 hydrate 96g / L (0.76mol / L) in 200mL of pure water, increase the bath temperature to 60 ° C, and add 40% chromium sulfate aqueous solution 610mL / L (Cr = 100g / L, 1.9mol / L After that, stir it to dissolve completely.

Thereafter, heating was continued for 8 hours while maintaining the bath temperature at 60 °C. After 8 hours, the heating was stopped and cooled to room temperature to obtain trivalent chromium. A solution of the complex. A 250 mL/L (Cr = 25 g/L) solution of this complex was used. This was taken as a trivalent chromium complex solution D.

Manufacturing Example 5

Add 192 g/L (1.52 mol/L) of oxalic acid 2 hydrate to 400 mL of pure water, raise the bath temperature to 60 ° C, and add 40% aqueous solution of chromium sulfate to 610 mL/L (Cr=100 g/L, 1.9 mol/L). After that, stir it to dissolve completely.

Thereafter, heating was continued for 8 hours while maintaining the bath temperature at 60 °C. Heating was stopped after 8 hours and cooled to room temperature to obtain a solution containing a trivalent chromium complex. A 250 mL/L (Cr = 25 g/L) solution of this complex was used. This was taken as a trivalent chromium complex solution E.

Examples 1 to 9 and Comparative Examples 1 to 2

Each component shown in the following Table 1 and Table 2 was dissolved in water to prepare a trivalent chromium plating bath. As the trivalent chromium compound and the complexing agent, in the comparative example 1, the comparative example 2, and the ninth embodiment, the trivalent chromium compound and the complexing agent were used, and the above-mentioned manufacturing was used in Example 1. In the third embodiment, the trivalent chromium complex solution C prepared in Example 3 was used. In Example 2, the trivalent chromium complex solution D prepared in the above Production Example 4 was used, and in Example 3, the above-mentioned Production Example 5 was used. In the third embodiment, the trivalent chromium complex solution E was used in Example 4, and the trivalent chromium complex solution B prepared in the above Production Example 2 was used. In Examples 5 to 8, the above-mentioned Production Example 1 was used. Valence Chromium Complex Solution A.

The plating test was carried out by the following method using each of the above-mentioned trivalent chromium plating baths, and the adhesion uniformity and the deposition rate were evaluated.

First of all, in terms of being plated, the light is used on a brass plate. A sample (having a size of 10 cm × 6 cm) made of a film of about 3 μm was plated with Ni, and a Hull cell test was performed using each of the trivalent chromium plating baths. The Hull cell test conditions were set to a cell current of 5 A and a plating time of 5 minutes, and as the anode, a Ti electrode coated with an Ir-Ta composite oxide film was used.

In the evaluation of the adhesion uniformity, it is possible to visually confirm that a range of a good plating film is formed for each of the plated objects (the Hull channel plate) after chrome plating, and to form a length of a good plating portion from a high current portion. It is expressed by the ratio of the length (10 cm) of the entire Hull groove plate. The larger the ratio, the better the chrome-plated film can be formed even with the low current portion, and the adhesion uniformity is better.

In terms of the deposition rate of chrome plating, a current density distribution meter is used, and a portion corresponding to 10, 15, 20, ²⁵ , 30, and 40 A/dm ² in the primary current density is determined on the Hull plate. The film thickness of each current density portion of the chrome-plated Hull channel plate was measured using an electrolytic film thickness meter to calculate the deposition rate per 5 minutes. The results are shown in Tables 3 and 4 below.

From the above results, the following points can be clearly understood.

(1) The plating bath of Comparative Example 1 has the same composition as the plating bath described in Example 2 of [0041] of Patent Document 1, but the evaluation result of adhesion uniformity is 17%, which is low. The precipitation of the current portion is poor. Further, in the plating bath of Comparative Example 2 in which ammonium sulfate was added to the plating bath of Comparative Example 1, the adhesion uniformity tends to be lowered.

On the other hand, in the plating bath of Example 1 in which boric acid was added to the plating bath of Comparative Example 1, the adhesion uniformity was 35%, and the precipitation property of the low current density portion was also improved.

(2) The plating baths of Examples 2 to 9 all contain aluminum sulfate and boric acid in addition to chromium sulfate, oxalic acid dihydrate, and potassium fluoride, and even ammonium sulfate as a conductive salt. In the case of using these plating baths, the formed chromium plating film is excellent in both adhesion uniformity and deposition rate.

(3) In particular, the plating baths of Examples 2 to 4 and 6 to 9 having a pH of 2 have good adhesion uniformity.

(4) In the case where boric acid and ammonium sulfate were simultaneously contained, and the molar ratio of oxalic acid to Cr was 0.2 to 0.3, a good deposition rate was exhibited (Examples 4 to 9).

(5) As is clear from the comparison between Example 6 and Example 8, when the bath temperature of the plating bath was set to 35 ° C, the deposition rate was improved and the adhesion uniformity was also improved.

(6) The plating bath of Example 9 which is used in such a manner that the trivalent chromium compound and the complexing agent are not previously mixed, is excellent in adhesion uniformity and deposition rate, but forms a strip in a low current portion. The coating is not good. On the other hand, in the plating bath of Example 8 which has the same composition as that of Example 9, and a complex solution in which a trivalent chromium compound and a complexing agent are previously mixed, the low current portion can be used. A coating that forms a good appearance.

Claims (8)

A trivalent chromium plating bath is composed of an aqueous solution containing a trivalent chromium compound, a complexing agent, a fluoride, an aluminum sulfate, and a boric acid compound. The trivalent chromium plating bath according to claim 1, which further contains a conductive salt. The trivalent chromium plating bath according to claim 1 or 2, wherein the complexing agent is at least one compound selected from the group consisting of aqueous aliphatic carboxylic acids and salts thereof. The trivalent chromium plating bath according to any one of claims 1 to 3, wherein the conductive salt is a sulfate. The trivalent chromium plating bath according to any one of claims 1 to 4, wherein the complexing agent is contained in an amount of 0.1 to 0.3 mol with respect to 1 mol of the trivalent chromium ion. The trivalent chromium plating bath according to any one of claims 1 to 5, wherein the trivalent chromium compound and the complexing agent are blended with a trivalent chromium complex solution, and the trivalent chromium is mismatched. The solution is obtained by maintaining an aqueous solution containing a trivalent chromium compound and a complexing agent under heating. The trivalent chromium plating bath according to any one of claims 1 to 6, which has a pH of from 1 to 2.5. A trivalent chromium plating method according to any one of claims 1 to 7, wherein the material to be plated is used as a cathode to conduct electricity.