JP5322083B2 - Trivalent chromium plating bath and manufacturing method thereof - Google Patents

Description

  The present invention relates to a plating bath containing a trivalent chromium compound and a method for producing the same.

  Chrome plating is used in various fields for decoration and industrial use. However, conventionally used chromium plating baths contain a large amount of harmful hexavalent chromium as a chromium component, and development of a plating solution with low toxicity is strongly desired.

  As a plating bath containing trivalent chromium, which is less toxic than hexavalent chromium, a part of the decorative bath having a thin plating thickness has been put into practical use. For example, trade name: Alekla 3000 (Albright and Wilson Co. ), Trade name: Envirochrome (Canning), trade name: Trichlorite (Eugelite), trade name: Trichrome Plus (Atotech Japan), etc. are commercially available.

However, the conventional trivalent chromium plating bath has various problems shown below (see Non-Patent Documents 1 and 2 below).
1) A smooth surface cannot be obtained with a chromium plating film thickness of 1 μm or more.
2) Since the corrosion resistance is low, an immersion treatment in a hexavalent chromic acid solution is necessary after plating.
3) Since the film hardness is low, sufficient wear resistance cannot be obtained.
4) Immediately after the bathing, complex formation between the complexing agent and the chromium salt is not sufficient, so that it is necessary to carry out a weak electrolytic treatment for a long time in order to obtain sufficient throwing power, and productivity is lowered.
Surface Technology Vol.47, No.3, 245p (1996) Kinki Aluminum Surface Treatment Study Group Autumn 2006 Special Lecture Lecture Collection

  The present invention has been made in view of the above-described problems of the prior art, and its main purpose is to eliminate the above-described problems of the conventional trivalent chromium plating bath and to be effectively used for industrial use. It is to provide a novel trivalent chromium plating bath.

  The present inventor has intensively studied to achieve the above-described object. As a result, after mixing the trivalent chromium compound and the water-soluble aliphatic carboxylic acid or salt thereof, the mixture is sufficiently aged under heating to form a stable chromium complex solution, and then this solution is made into other components such as conductive salts. The trivalent chromium plating bath obtained by mixing with can form a good chromium plating film immediately after the building bath, and the formed chromium plating film has good corrosion resistance and can be thickened. The present inventors have found that a high-hardness chromium plating film is formed, and have completed the present invention.

That is, this invention provides the following trivalent chromium plating bath and its manufacturing method.
1. A trivalent chromium plating bath containing the following components (1) to (4):
(1) A trivalent chromium complex solution obtained by holding an aqueous solution containing at least one component selected from the group consisting of an aliphatic carboxylic acid and a salt thereof and a trivalent chromium compound under heating,
(2) Conductive salt (3) pH buffer and (4) at least one sulfur-containing compound selected from the group consisting of a compound having an SO ₂ group and a compound having an SO ₃ group.
2. The complex solution of trivalent chromium holds an aqueous solution containing at least one component selected from the group consisting of an aqueous aliphatic carboxylic acid and a salt thereof and a trivalent chromium compound at a liquid temperature of 40 to 100 ° C. for 30 minutes or more. Item 3. The trivalent chromium plating bath according to Item 1, which is obtained in the above manner.
3. A trivalent chromium complex solution is obtained by adding 0.1 to 2 mol of at least one component selected from the group consisting of an aqueous aliphatic carboxylic acid and a salt thereof to 1 mol of a trivalent chromium compound. Item 3. The trivalent chromium plating bath according to Item 1 or 2, wherein
4). An aqueous solution containing at least one component selected from the group consisting of an aliphatic carboxylic acid and a salt thereof and a trivalent chromium compound is maintained under heating to form a complex solution of trivalent chromium, and then the complex solution, conductivity A method for preparing a trivalent chromium plating bath, comprising dissolving at least one sulfur-containing compound selected from the group consisting of a salt, a pH buffer, a compound having an SO ₂ group and a compound having an SO ₃ group in water .
5. An article having a chromium plating film formed using the trivalent chromium plating bath according to any one of Items 1 to 3.

  The following trivalent chromium plating bath of the present invention will be described in detail.

Trivalent Chromium Complex Solution In the present invention, first, a stable complex solution containing a trivalent chromium compound is prepared, and a plating bath is constructed using this.

  The complex solution containing a trivalent chromium compound comprises an aqueous solution containing at least one component selected from the group consisting of an aqueous aliphatic carboxylic acid and a salt thereof (hereinafter sometimes referred to as “carboxylic acids”) and a trivalent chromium compound. It can be obtained by holding under heating. Usually, it can be obtained by adding a trivalent chromium compound to an aqueous solution in which carboxylic acids are dissolved and holding the mixture for a certain period of time under heating.

  The type of the aqueous aliphatic carboxylic acid is not particularly limited as long as it is a carboxylic acid that can be an aqueous solution having a predetermined concentration. For example, aliphatic monocarboxylic acids such as formic acid and acetic acid; aliphatic dicarboxylic acids such as oxalic acid, malonic acid and succinic acid; aliphatic hydroxymonocarboxylic acids such as gluconic acid: aliphatic hydroxydicarboxylic acids such as malic acid; Aliphatic hydroxytricarboxylic acids such as citric acid can be used.

  The salt of the water-soluble aliphatic carboxylic acid may be any of the above-described water-soluble salts of various carboxylic acids. For example, alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt and magnesium salt An ammonium salt or the like can be used.

  The above carboxylic acids can be used singly or in combination of two or more.

  As the trivalent chromium compound, any water-soluble trivalent chromium compound may be used. For example, chromium sulfate, basic chromium sulfate and the like can be used. A trivalent chromium compound can also be used individually by 1 type or in mixture of 2 or more types.

  The order in which the trivalent chromium compound and the carboxylic acid are dissolved is arbitrary. A method of adding the trivalent chromium compound after dissolving the carboxylic acid in water, and then dissolving the trivalent chromium compound in water, Arbitrary methods, such as the method of adding and the method of dissolving carboxylic acid and a trivalent chromium compound in water simultaneously, are applicable. At this time, the liquid temperature is preferably about 40 to 100 ° C, and more preferably about 50 to 90 ° C.

  The complex solution containing a trivalent chromium compound is usually used after being diluted when a trivalent chromium plating bath is constructed. For this reason, the concentration of the trivalent chromium compound in the complex solution is not particularly limited. For example, the chromium concentration is preferably about 30 to 150 g / L, and preferably about 50 to 100 g / L. Is more preferable.

  The amount of the carboxylic acid added may be an amount that can form a stable complex when added to the aqueous solution containing the trivalent chromium compound. For example, 0.1 mol of the carboxylic acid is added to 1 mol of the trivalent chromium compound. It is preferable to use about ˜2 mol, and more preferably about 0.3 to 1 mol.

  The concentration of the carboxylic acids in the complex solution containing trivalent chromium is not particularly limited, but is preferably about 10 to 200 g / L, and more preferably about 20 to 100 g / L. preferable.

  Next, a complex solution containing a trivalent chromium compound can be obtained by maintaining an aqueous solution containing a carboxylic acid and a trivalent chromium compound in a temperature range of about 40 to 100 ° C., preferably about 50 to 90 ° C. The time maintained in this temperature range is usually preferably about 30 minutes or more, more preferably about 1 hour or more, and further preferably about 2 hours or more. Specifically, it is preferable to hold for a longer time as the heating temperature is lower, for example, to hold for about 5 hours or more at a heating temperature of about 40 ° C., and to hold for 3 hours or more at a heating temperature of about 80 ° C. Is preferred. Thereby, a stable complex solution containing trivalent chromium can be obtained.

Trivalent chromium plating bath The trivalent chromium plating bath of the present invention has a complex solution containing trivalent chromium, a conductive salt, a pH buffer, a compound having an SO ₂ group, and an SO ₃ group prepared by the method described above. It consists of an aqueous solution containing at least one sulfur-containing compound selected from the group consisting of compounds.

  Among the above-described components, as the conductive salt, for example, sulfates such as potassium sulfate, sodium sulfate, and ammonium sulfate, alkali metal chlorides such as potassium chloride, and sodium chloride can be used. These conductive salts can be used singly or in combination of two or more.

  The concentration of the conductive salt is not particularly limited, but when the concentration is low, the bath voltage rises and the bath temperature rises during electrolysis, so that it is necessary to cool the electrolytic cell in order to maintain a constant temperature. In addition, when the conductive salt concentration is high, the bath voltage decreases, but it is difficult to dissolve at the time of bathing, and when the plating operation is stopped and the temperature of the plating bath decreases, precipitation or the like may occur. Will be generated. From these points, the concentration of the conductive salt is preferably about 50 to 200 g / L, and more preferably about 100 to 150 g / L.

  As the pH buffering agent, boric acid, sodium borate and the like can be used. When the pH buffer concentration is low, the pH rises at the cathode reaction interface, and chromium hydroxide and the like are produced, so that a good chromium plating film cannot be obtained. From this, in order to obtain a good chromium plating film, the concentration of the pH buffering agent is preferably about 70 to 120 g / L, and more preferably about 80 to 100 g / L.

At least one sulfur-containing compound selected from the group consisting of a compound having an SO ₂ group and a compound having an SO ₃ group is an effective component for making the formed chromium film dense and good in appearance.

Of these, examples of the compound having an SO ₂ group include saccharin and sodium saccharin, and examples of the compound having an SO ₃ group include sulfobenzaldehyde, benzenesulfonic acid, toluenesulfonic acid, and salts thereof. These sulfur-containing compounds can be used singly or in combination of two or more.

  Although it does not specifically limit about the density | concentration of a sulfur-containing compound, Usually, it is preferable to set it as about 1-10 g / L, and it is more preferable to set it as about 2-7 g / L.

  The trivalent chromium plating bath of the present invention is obtained by dissolving the above-described complex solution containing a trivalent chromium compound, a conductive salt, a pH buffering agent, and a sulfur-containing compound in water, and the order of dissolving each component is arbitrary. It is.

  The chromium concentration in the trivalent chromium plating bath of the present invention is not particularly limited, but when the chromium concentration is low, the throwing power to the low current density region is good, but the film forming speed is low, Conversely, when the chromium concentration is high, the throwing power decreases but the film forming speed increases. In consideration of this point, the chromium concentration may be determined. Usually, in order to achieve both appropriate throwing power and film forming speed and be suitable for industrial use, the chromium concentration is 3 to 3. About 30 g / L is preferable, and about 5 to 15 g / L is more preferable.

  The pH of the trivalent chromium plating solution bathed using the above-described components varies somewhat depending on the type of complexing agent used, but is usually preferably within the range of about pH 2-4.

  According to the trivalent chromium plating solution of the present invention, when the bath temperature at the time of plating is low, the throwing power is improved, but the film-forming speed tends to decrease, and conversely, when the bath temperature is high, Although the film forming speed is improved, the throwing power to the low current density region tends to be lowered. An appropriate bath temperature may be determined in consideration of this point, but generally, a temperature range of about 30 to 60 ° C. is preferable as a bath temperature for industrial use.

  The anode used at the time of plating is not particularly limited, and usually a known insoluble anode such as a Ti—Pt electrode can be used. In particular, when a Ti electrode covered with an Ir—Ta composite oxide thin film is used, it is advantageous in that generation of hexavalent chromium can be suppressed.

According to the trivalent chromium plating bath of the present invention, a chromium plating film having a good appearance in a wide current density range can be obtained, for example, a good appearance in a cathode current density range of about 1 to 20 A / dm ^2. The chrome plating film can be formed.

Articles having a chromium plating film The trivalent chromium plating bath of the present invention can be used for various applications such as industrial chromium plating and decorative chromium plating.

  Industrial chrome plating is used in various industrial fields by utilizing the high hardness, wear resistance, corrosion resistance, adhesion, releasability, etc. of the chrome plating film. For example, for the production of molds, etc. It is used. In industrial chrome plating, for example, a metal material such as steel, stainless steel, brass, or zinc die casting is mainly used as an object to be plated.

  In addition, decorative chromium plating is mainly used as a protective layer for nickel plating, and the hardness and specific color tone of the chromium plating film are utilized. Decorative chrome plating is widely used for automobiles, for example, and various functional plastic materials such as ABS, PC / ABS, PC, and nylon are used in addition to the metal materials described above. It has been.

  When forming a chromium plating film on these various materials, it is possible to directly form a chromium plating film on a metal material using the trivalent chromium plating bath of the present invention. Further, for the purpose of improving the appearance and corrosion resistance, chromium plating may be performed after copper plating, nickel plating, or the like.

  In order to form a chromium plating film on a plastic material, after conducting steps such as etching and catalyst application according to a conventional method, a conductive film is formed by electroless nickel plating, electroless copper plating, etc. It is common to perform electrolytic copper plating, electrolytic nickel plating, etc., and then form a chromium plating film, but this step is not limited. When a chrome plating film is formed for the purpose of decoration, a chrome plating film having a relatively thin film thickness of about 0.1 to 0.5 μm is usually formed in many cases.

According to the trivalent chromium plating bath of the present invention, the following remarkable effects are exhibited.
(1) A good chromium plating film can be formed immediately after the bath. This eliminates the need for long-term electrolytic treatment and greatly improves work efficiency.
(2) It has excellent throwing power in a low current density region and can form a good chromium plating film in a wide current density range.
(3) Since the plating film grows according to the plating time, it is possible to apply a thickness exceeding 1 μm.
(4) A chromium plating film having a high film hardness can be obtained.
(5) Even when chromic acid immersion treatment is not performed, a chromium plating film having good corrosion resistance can be formed.

  Hereinafter, the present invention will be described in more detail with reference to production examples and examples.

Production Example 1
After adding 38 g / L (0.2 mol / L) of citric acid to 400 ml of pure water and sufficiently dissolving it, the bath temperature is raised to 60 ° C., and a 40% chromium sulfate aqueous solution 500 ml / L (Cr = 52 g / L, 1.0 mol / L) was added and stirred until completely dissolved.

  Thereafter, heating was continued for 8 hours while maintaining the bath temperature at 60 ° C. Heating was stopped after 8 hours, and the solution was cooled to room temperature to obtain a solution containing a trivalent chromium complex. This is designated as chromium complex liquid A.

Production Example 2
After adding acetic acid (60 g / L (1.0 mol / L)) to 400 ml of pure water and dissolving it sufficiently, the bath temperature is raised to 80 ° C., and 40% chromium sulfate aqueous solution is added to 500 ml / L (Cr = 52 g / L). , 1.0 mol / L) was added and stirred until completely dissolved.

  Thereafter, heating was continued for 5 hours while maintaining the bath temperature at 80 ° C. After 5 hours, heating was stopped and the mixture was cooled to room temperature to obtain a solution containing a trivalent chromium complex. This is designated as chromium complex solution B.

Production Example 3
After adding 90 g / L (0.65 mol / L) of malic acid to 500 ml of pure water and sufficiently dissolving it, the bath temperature was raised to 80 ° C., and 400 g / L of basic chromium sulfate (Cr = 64 g / L, 1 .23 mol / L) was added and dissolved.

  Thereafter, heating was continued for 7 hours while maintaining the bath temperature at 80 ° C. Thereafter, the heating was stopped and the mixture was cooled to room temperature to obtain a solution containing a trivalent chromium complex. This is designated as chromium complex solution C.

Production Example 4
After adding 90 g / L (1.0 mol / L) of oxalic acid to 500 ml of pure water and sufficiently dissolving it, the bath temperature was raised to 80 ° C. and then 400 g / L of basic chromium sulfate (Cr = 64 g / L). L, 1.23 mol / L) was added and dissolved.

  Thereafter, heating was continued for 5 hours while maintaining the bath temperature at 80 ° C. Thereafter, heating was stopped and the solution was cooled to room temperature to obtain a solution containing a trivalent chromium complex. This is designated as chromium complex solution D.

Examples 1-4 and Comparative Examples 1-2
Using the chromium complex solutions A to D prepared by the above-described method, each component shown in Table 1 below is dissolved in water to prepare a trivalent chromium plating bath, and a plating test is performed at the pH value and bath temperature shown in the table. Went.

A plating test was performed by the following method using each of the above trivalent chromium plating baths. The results are shown in Table 2 below.
(Plating test method)
1) Hull cell test Using each trivalent chromium plating bath immediately after the building bath, a Hull cell test was performed using a product obtained by forming a bright Ni plating on a brass plate with a thickness of about 3 μm. The Hull cell test conditions were a cell current of 5 A and a plating time of 5 minutes, and a Ti electrode coated with an Ir—Ta composite oxide thin film was used as the anode.

About the to-be-plated object (Hull cell board) after chromium plating, it was judged to which part the plating corresponding to the current density was deposited on the basis of the current density distribution scale, and the throwing power was evaluated. Then, the film thickness in each current density of a hull cell board was measured using the electrolytic film thickness meter. Table 2 below shows the film thickness of the portion corresponding to 10 A / dm ² in terms of primary current density.

2) Relationship between film formation time and film thickness Using each trivalent chromium plating bath, changing the plating time to a Ni-plated brass plate under a current density of 7.5 A / dm ² , depositing a chromium plating film, and forming the film The relationship between the film thickness and the film thickness was investigated. The film thickness was calculated from the precipitation weight and area.

3) Vickers hardness measurement Vickers hardness was measured about the to-be-plated object which was able to be thickened by the said test.

4) Evaluation of corrosion resistance Using each trivalent chromium plating bath, a trivalent chromium plating film of about 0.1 μm was formed on a brass plate plated with bright Ni. After washing with water, a salt spray test (JIS 2371) was conducted without chromic acid immersion treatment. After 72 hours, the product was taken out from the apparatus, and after rinsing with water, the progress of corrosion was evaluated by the ratio of the area where white rust was generated to the entire plated product.

From the above results, the following is clear.
(1) Each of the trivalent chromium plating baths of Examples 1 to 4 shows good throwing power in the Hull cell test immediately after the building bath, and a good chromium plating film up to a low current density range of about 1 A / dm ^2. I was able to form. On the other hand, in the plating baths of Comparative Examples 1 and 2 obtained by directly dissolving the trivalent chromium compound and the carboxylic acid in water, the throwing power to the low current density region is not sufficient immediately after the building bath, In the Hull cell test, plating was deposited only up to a portion corresponding to 4 A / dm ² .

  (2) In each of the trivalent chromium plating baths of Examples 1 to 4, the film thickness increased with the film forming time, and the film forming time and the film thickness showed a substantially linear relationship even when 5 hours had elapsed. It was possible to increase the film thickness by extending the length. The thick chromium plating film showed a high Vickers hardness of about 1000 HV.

  On the other hand, in the trivalent chromium plating baths of Comparative Examples 1 and 2, the film forming speed is greatly reduced after about 60 minutes have elapsed, and the chromium plating film is about 3 μm even if the film forming time is increased. It was not possible to increase the film thickness.

  (3) The chromium plating film formed from each trivalent chromium plating bath of Examples 1 to 4 exhibited good corrosion resistance even when the chromic acid immersion treatment was not performed.

Claims (4)

A trivalent chromium plating bath containing the following components (1) to (4):
(1) An aqueous solution in which at least one component selected from the group consisting of a water-soluble aliphatic carboxylic acid and a salt thereof and a component composed of a trivalent chromium compound is dissolved in water at a temperature of 40 to 100 ° C. for 30 minutes or more A complex solution of trivalent chromium obtained by holding,
(2) conductive salt,
(3) a pH buffer, and (4) at least one sulfur-containing compound selected from the group consisting of a compound having an SO ₂ group and a compound having an SO ₃ group. A trivalent chromium complex solution is obtained by adding 0.1 to 2 mol of at least one component selected from the group consisting of a water-soluble aliphatic carboxylic acid and a salt thereof to 1 mol of a trivalent chromium compound. The trivalent chromium plating bath according to claim 1, wherein An aqueous solution in which at least one component selected from the group consisting of water-soluble aliphatic carboxylic acids and salts thereof and a component composed of a trivalent chromium compound is dissolved in water is maintained at a temperature of 40 to 100 ° C. for 30 minutes or more. After forming a complex solution of valent chromium, at least one sulfur-containing compound selected from the group consisting of the complex solution, a conductive salt, a pH buffer, a compound having an SO ₂ group and a compound having an SO ₃ group is added to water. A method for preparing a trivalent chromium plating bath, which comprises melting. An article having a chromium plating film formed using the trivalent chromium plating bath according to claim 1.