White trivalent chromium plating bath and method for plating white trivalent chromium onto substrates using the same

Abstract

To provide plating technology in which the deposition rate of plating in a trivalent chromium plating bath is fast and an appearance suitable for decorative use can be obtained.SOLUTION: A white trivalent chromium plating bath contains one or two or more types of sulfur-containing organic compounds represented by trivalent chromium compound, complexing agent, sulfate as conductive salt, pH buffer and a general formula (I), where, R represents -H, -NH2, -OH, -CH3, -(CH2)n-CH3 or -(CH2)n-COOH, the n represents an integer ranging 1 to 4, and each of X and Y independently represents CH2, C=O or C=S. There is also provided a white trivalent chromium plating method using them.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a white trivalent chromium plating bath and a method for plating an object with white trivalent chromium using the same. [Background technology]

[0002] Chrome plating has a silvery white appearance and is used as a decorative coating film. Hexavalent chromium was used for this chrome plating, but in recent years, its use has been restricted due to the environmental impact of hexavalent chromium, and there has been a shift to technology using trivalent chromium.

[0003] Many techniques using trivalent chromium have been reported, and for example, a chromium electroplating solution containing a water-soluble trivalent chromium salt, a complexing agent for trivalent chromium ions such as malic acid, a pH buffer compound, a sulfur-containing organic compound such as thiourea, and a water-soluble compound such as saccharin, and having a pH of 2.8 to 4.2, is known (Patent Document 1).

[0004] However, this trivalent chromium plating bath had a slow plating deposition rate and was not practical. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5696134 [Patent Document 2] International publication brochure WO2019 / 117178 Summary of the Invention [Problem to be solved by the invention]

[0006] The applicant has developed a practical trivalent chromium plating bath with a fast plating deposition rate (Patent Document 2: A trivalent chromium plating bath containing a trivalent chromium compound, a complexing agent, potassium sulfate and ammonium sulfate as conductive salts, a pH buffer, and a sulfur-containing organic compound, characterized in that the complexing agent is a carboxylic acid having two or more hydroxy groups and two or more carboxy groups or a salt thereof, and the sulfur-containing organic compound is a combination of saccharin or a salt thereof and a sulfur-containing organic compound having an allyl group), but the applicant set out to develop a plating technology with a simpler composition that can produce an appearance suitable for decorative purposes. [Means for solving the problem]

[0007] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by adding a sulfur-containing organic compound having a specific structure to a white trivalent chromium plating bath, and have thus completed the present invention.

[0008] That is, the present invention provides a compound comprising a trivalent chromium compound, a complexing agent, a sulfate as a conductive salt, a pH buffer, and a compound represented by the following general formula (I): [ka] (In formula (I), R is —H, —NH2, —OH, —CH3, —(CH2) n -CH3 or -(CH2) n -COOH, wherein n is an integer of 1 to 4, and X and Y each independently represent CH2, C=O, or C=S. The white trivalent chromium plating bath is characterized by containing one or more sulfur-containing organic compounds represented by the following formula:

[0009] The present invention also provides a method for white trivalent chromium plating an object to be plated, comprising electroplating the object to be plated with the above-mentioned white trivalent chromium plating bath.

[0010] Furthermore, the present invention relates to a method for improving the deposition rate of white trivalent chromium plating, characterized by adding the sulfur-containing organic compound represented by the above general formula (I) to a white trivalent chromium plating bath containing a trivalent chromium compound, a complexing agent, a sulfate as a conductive salt, and a pH buffer. [Effects of the Invention]

[0011] By using the white trivalent chromium plating bath of the present invention, it is possible to produce white trivalent chromium plating that has a color tone and deposition rate equivalent to those of hexavalent chromium plating. DETAILED DESCRIPTION OF THE INVENTION

[0012] The white trivalent chromium plating bath of the present invention (hereinafter referred to as "the plating bath of the present invention") contains a trivalent chromium compound, a complexing agent, a sulfate as a conductive salt, a pH buffer, and a sulfur-containing organic compound.

[0013] The sulfur-containing organic compound is represented by the following general formula (I): [ka] (In formula (I), R is —H, —NH2, —OH, —CH3, —(CH2) n -CH3 or -(CH2) n -COOH, n is an integer of 1 to 4, and X and Y each independently represent CH2, C=O or C=S).

[0014] Preferred examples of the sulfur-containing organic compounds represented by the general formula (I) include those represented by the following general formula (II): [ka] (In formula (II), R represents -H, -NH2, -OH, -CH3, -(CH2)n-CH3 or -(CH2)n-COOH, more preferably -H or -NH2, n represents an integer of 1 to 4, more preferably 1 to 2, and X1 and Y1 each independently represent C=O or C=S).

[0015] More preferred examples of the sulfur-containing organic compound represented by general formula (I) include thiazolidine, rhodanine, thiazolidin-2-one, 3-methylthiazolidine-2-thione, 4-thioxo-1,3-thiazolidin-2-one, 2-mercaptothiazoline (also known as 2-thiazoline-2-thiol), 2,4-thiazolidinedione, 3-methyl-1,3-thiazolan-2,4-dione, 3-aminorhodanine, 3-methylrhodanine, 3-ethylrhodanine, rhodanine-3-acetic acid, and rhodanine-3-propionic acid, among which rhodanine, 2,4-thiazolidinedione, 3-aminorhodanine, and 3-ethylrhodanine are preferred. These sulfur-containing organic compounds can be used alone or in combination of two or more.

[0016] The content of the sulfur-containing organic compound represented by general formula (I) etc. in the plating bath of the present invention is not particularly limited, but is, for example, 1 to 500 mg / L, preferably 5 to 100 mg / L.

[0017] The trivalent chromium compound used in the plating bath of the present invention is not particularly limited, but examples thereof include basic chromium sulfate, chromium sulfate, chromium chloride, chromium sulfamate, and chromium acetate, with basic chromium sulfate and chromium sulfate being preferred. These trivalent chromium compounds can be used alone or in combination of two or more. The content of the trivalent chromium compound in the plating bath of the present invention is not particularly limited, but is, for example, 1 to 25 g / L, preferably 1 to 15 g / L, of metallic chromium.

[0018] The complexing agent used in the plating bath of the present invention is not particularly limited, but examples thereof include dicarboxylic acids such as malic acid and tartaric acid, and salts of dicarboxylic acids such as sodium malate, sodium tartrate, and diammonium tartrate, with malic acid or diammonium tartrate being preferred. These complexing agents can be used alone or in combination of two or more. The content of the complexing agent in the plating bath of the present invention is not particularly limited, but is, for example, 1 to 90 g / L, preferably 2 to 50 g / L.

[0019] The conductive salt used in the plating bath of the present invention is a sulfate such as potassium sulfate, ammonium sulfate, or sodium sulfate. Of these sulfates, potassium sulfate is preferred. These sulfates can be used alone or in combination of two or more. The content of the sulfate in the plating bath of the present invention is not particularly limited, but is, for example, 100 to 300 g / L, and preferably 120 to 240 g / L.

[0020] The pH buffer used in the plating bath of the present invention is not particularly limited, but examples thereof include boric acid, sodium borate, potassium borate, phosphoric acid, and dipotassium hydrogen phosphate, with boric acid and sodium borate being preferred. These pH buffers can be used alone or in combination of two or more. The content of the pH buffer in the plating bath of the present invention is not particularly limited, but is, for example, 30 to 150 g / L, and preferably 50 to 110 g / L.

[0021] The plating bath of the present invention preferably further contains saccharin or a salt thereof to stabilize chromium deposition. Examples of saccharin or a salt thereof include saccharin and sodium saccharinate. These saccharins or salts may be used alone or in combination of two or more. The content of saccharin or a salt thereof in the plating bath of the present invention is not particularly limited, but is, for example, 0.5 to 10 g / L, preferably 2 to 8 g / L. It should be noted that the content of saccharin in the plating bath of the present invention is not included in the content of the sulfur-containing organic compound represented by the general formula (I) or the like.

[0022] A preferred embodiment of the plating bath of the present invention may contain, for example, the above-mentioned components, but it goes without saying that it may also contain only the above-mentioned components (consisting of the above-mentioned components).

[0023] The plating bath of the present invention may further contain polymeric compounds such as polyethylene glycol, ascorbic acid, sodium ascorbate, hydrogen peroxide, surfactants, chloral hydrate, iminodiacetic acid, and the like, within limits that do not impair the effects of the present invention.

[0024] The pH of the plating bath of the present invention is not particularly limited as long as it is acidic, and is preferably, for example, 2 to 4.5, more preferably 3 to 4.5.

[0025] The method for preparing the plating bath of the present invention is not particularly limited. For example, the plating bath can be prepared by adding and mixing a trivalent chromium compound, a complexing agent, a sulfate as a conductive salt, a pH buffer, and a sulfur-containing organic compound (saccharin or a salt thereof, if necessary) to water at 50 to 60°C, and finally adjusting the pH with sulfuric acid, aqueous ammonia, or the like, if necessary.

[0026] The plating bath of the present invention, like conventional chromium plating baths, can provide white trivalent chromium plating to an object to be plated by electroplating the object with the plating bath of the present invention.

[0027] The electroplating conditions are not particularly limited, but for example, the bath temperature is 30 to 60°C, the anode is carbon or iridium oxide, and the cathode current density is 2 to 20 A / dm 2 Electroplating can be performed for 1 to 15 minutes.

[0028] Examples of substrates that can be electroplated include metals such as iron, stainless steel, and brass, and resins such as ABS and PC / ABS. The substrates may be pre-plated with copper or nickel before being plated with the plating bath of the present invention.

[0029] When white trivalent chromium plating is performed using the plating bath of the present invention, the deposition rate is 0.03 to 0.17 μm / min, preferably 0.04 to 0.13 μm / min, which is equal to or higher than that of conventional hexavalent chromium plating.

[0030] Therefore, the deposition rate of white trivalent chromium plating can be improved by adding the sulfur-containing organic compound represented by the above-mentioned general formula (I) or the like to a white trivalent chromium plating bath containing a trivalent chromium compound, a complexing agent, a sulfate as a conductive salt, and a pH buffer.

[0031] The chrome plated product thus obtained is white and has a color difference of L measured using a colorimeter. * The value is 80 or more, preferably 82 or more, more preferably 83 or more, and particularly preferably 83 to 84, and the color tone is equivalent to that of hexavalent chromium plating.

[0032] This white chrome plated product can be used for the same purposes as conventional hexavalent chrome plated products, but is particularly suitable for decorative applications such as on cars, motorcycles, and metal fittings. [Example]

[0033] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0034] Example 1 White chrome plating: A trivalent chromium plating bath was prepared by dissolving the components listed in Table 1 in water and adjusting the pH with aqueous ammonia. A hull cell test was conducted on this trivalent chromium plating bath using a nickel-plated brass plate. The hull cell test conditions were a current of 5 A and a plating time of 3 minutes. After plating, the brass plate was exposed to a current density of 10 A / dm 2 The thickness of the film at the corresponding points was measured by fluorescent X-rays, and the deposition rate was calculated. Furthermore, the appearance after plating was measured using a color difference meter (Konica Minolta) * value, a * value, b * The results are also shown in Table 1.

[0035] [Table 1]

[0036] From these results, it can be seen that the plating bath of the present invention, by using the compound of general formula (I) as the sulfur-containing organic compound, has a high plating deposition rate and a white appearance. * It was found that the value was 80 or more. In particular, by using the compound of general formula (II) as the sulfur-containing organic compound, the plating deposition rate was fast, the appearance was white, and the L * It was found that the value was 83 or more. It was also found that the deposition of chromium was stabilized by further adding saccharin or a salt thereof to the plating bath of the present invention. [Industrial Applicability]

[0037] The plating bath of the present invention can be used for various purposes in the same manner as white plating using hexavalent chromium.

Claims

1. The present invention comprises a trivalent chromium compound, a complexing agent, a sulfate as a conductive salt, and a pH buffer, and the compound is represented by the following general formula (I): 【Chemistry 1】 (In formula (I), R is —H, —NH ２ , —OH, —CH ３ , -(CH ２ ) ｎ -CH ３ or -(CH ２ ) ｎ -COOH, n is an integer of 1 to 4, and X and Y are each independently CH ２ , C=O or C=S) and the resulting white trivalent chromium plating has an L* value of 80 or more as measured using a color difference meter.

2. A white trivalent chromium plating bath containing 5 to 100 mg / L of a trivalent chromium compound, a complexing agent, a sulfate as a conductive salt, a pH buffer, and one or more sulfur-containing organic compounds selected from the group consisting of thiazolidine, thiazolidin-2-one, 3-methylthiazolidine-2-thione, 4-thioxo-1,3-thiazolidin-2-one, 2,4-thiazolidinedione, 3-methyl-1,3-thiazolan-2,4-dione, 3-aminorhodanine, 3-methylrhodanine, 3-ethylrhodanine, rhodanine-3-acetic acid, and rhodanine-3-propionic acid, wherein the resulting white trivalent chromium plating has an L* value of 80 or more as measured using a color difference meter.

3. 3. The white trivalent chromium plating bath according to claim 1, wherein the complexing agent is a dicarboxylic acid or a salt thereof.

4. 4. The white trivalent chromium plating bath according to claim 3, wherein the dicarboxylic acid is malic acid and / or tartaric acid.

5. The white trivalent chromium plating bath according to any one of claims 1 to 4, further comprising saccharin or a salt thereof.

6. A method for white trivalent chromium plating an object to be plated, comprising electroplating the object to be plated with the white trivalent chromium plating bath according to any one of claims 1 to 5.

7. The following general formula (I) 【Chemistry 2】 (In formula (I), R is —H, —NH ２ , —OH, —CH ３ , -(CH ２ ) ｎ -CH ３ or -(CH ２ ) ｎ -COOH, n is an integer of 1 to 4, and X and Y are each independently CH ２ , C=O or C=S) A method for improving the deposition rate of white trivalent chromium plating having an L* value of 80 or more as measured using a color difference meter, comprising adding 5 to 100 mg / L of a sulfur-containing organic compound represented by the formula (excluding compounds corresponding to rhodanine and 2-mercaptothiazoline) to a white trivalent chromium plating bath containing a trivalent chromium compound, a complexing agent, a sulfate as a conductive salt, and a pH buffer.

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