JPH0598454A - Electroless nickel plating method for zinc-aluminum alloy, composition for catalyzing treatment, composition for activation and composition electroless nickel striking - Google Patents

Abstract

PURPOSE:To provide an electroless nickel plating method for a Zn-Al alloy capable of giving a perfect plating film having excellent adhesion, corrosion resistance and appearance. CONSTITUTION:When a Zn-Al alloy is subjected to electroless nickel plating, it is pretreated by surface conditioning and degreasing and a palladium-amine complex is stuck to the relevant alloy to carry out catalyzing treatment. Metallic palladium is then deposited by reduction to activate the alloy and electroless nickel striking is carried out prior to electroless nickel plating.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for electroless nickel plating on a zinc-aluminum alloy, a composition for catalytic treatment, a composition for activation treatment and a composition for electroless nickel strike plating.

[0002]

2. Description of the Related Art Die casting alloys, superplastic zinc alloys, etc. are known as zinc-aluminum alloys which are generally regarded as one of the difficult-to-plate metal materials. In the plating treatment of these alloys, the above-mentioned die-cast alloys are put into practical use by performing copper cyanide strike plating by energization. However, in recent years, advanced plating technology has been required due to the complicated shapes of materials to be plated such as thin and complex connector housings, car carburetors, the back surface of fuel pumps, and inside processed holes. As a result, electroplating such as the above-mentioned strike plating cannot meet such requirements. On the other hand, in the case of superplastic zinc alloy, unlike relatively simple materials such as steel, it is difficult to apply electroplating such as copper cyanide strike plating because of the polarization phenomenon between zinc and aluminum. It is said that. Therefore, from the above viewpoint, it is desired to apply electroless plating in place of electroplating in zinc-aluminum alloy plating.

However, zinc-aluminum alloys such as die-cast alloys and superplastic zinc alloys are generally inferior in chemical resistance and have a property of being easily corroded by various treatment liquids. Difficult or impossible. Further, even if the plating treatment is performed, the obtained plating film has extremely low adhesion to the raw material and is poor in practicality.

[0004]

The present invention provides a method for electroless nickel plating on a zinc-aluminum alloy which can provide a coating having excellent adhesion, corrosion resistance and appearance by performing a complete coating of the coating. The main purpose is to provide.

That is, according to the present invention, when electroless nickel plating is applied to a zinc-aluminum alloy, a pretreatment including a surface conditioning and degreasing step is performed, and then the alloy is palladium-catalyzed prior to electroless nickel plating. The present invention relates to a method for electroless nickel plating on a zinc-aluminum alloy, which comprises depositing an amine complex, then reducing and depositing metallic palladium as an activation treatment, and then performing electroless nickel strike plating.

The inventors of the present invention have made diligent studies on the above-mentioned problems, in particular, the problems such as uneven deposition and adhesion in electroless nickel plating on zinc-aluminum alloy, and as a result, specific catalytic conversion was performed prior to electroless nickel plating. It was found that the above object can be achieved when the treatment and the activation treatment are performed and then the electroless nickel strike plating is performed, and the present invention has been completed.

The present invention will be described in detail below.

The zinc-aluminum alloy to be used in the method of the present invention may be any known zinc-aluminum alloy such as zinc die-cast alloy and superplastic zinc alloy. However, in the case of an alloy containing 60% or more of aluminum among the above alloys, the zincate treatment facilitates the plating treatment.

In the electroless nickel plating method of the present invention, first, the surface treatment and degreasing pretreatment of the above alloy are carried out according to a conventional method. The surface may be polished by using a commonly used polishing paper or the like. Further, degreasing can be performed by a known method such as dipping with a commercially available degreasing agent after surface preparation. The surface adjustment may be omitted depending on the degree of contamination of the alloy surface used.

Then, the pretreated zinc-aluminum alloy is subjected to a catalytic treatment. As the composition for catalytic treatment used at this time, an alkali ion type catalyst-providing agent containing a palladium-amine complex may be used, and in particular, a palladium-amine obtained by reacting a palladium salt with ammonia or an amine compound. It is preferable to use an aqueous solution containing the complex and having a pH of 8 to 10.5, preferably 9 to 10.

As the palladium salt, various palladium salts can be used, but it is particularly preferable to use one or two of palladium sulfate and palladium chloride. On the other hand, examples of the above-mentioned amine compound include pyricin and 2-
Examples include various linear amine compounds and cyclic amine compounds such as aminopyridine, 3-aminopyridine, 4-aminopyridine, ethylenediamine, methylamine, ethanolamine, triethanolamine, and ethylenediaminetetraacetic acid, and one of these or Use two or more.
In order to react both of these with each other to obtain the palladium-amine complex, the palladium salt may be reacted with ammonia or an amine compound in a molar ratio of usually 1: 1 to 3. The concentration of the palladium-amine complex formed by reacting the palladium salt with ammonia or an amine compound is 0.005 to 2 g as metallic palladium.
/ L is preferable. This concentration is 0.005g / l
If it is less than the above range, the amount of the above-mentioned complex deposited on the zinc-aluminum alloy is small, the palladium serving as the nucleus of the plating deposition is insufficient, and the state becomes unplated or non-uniform plating deposition is not preferable. On the other hand, the above concentration is 2g
If it exceeds 1 / l, palladium is liberated in the aqueous solution of the composition for catalytic treatment to form a precipitate, which causes the occurrence of roughness of the plating film, and is also unfavorable because of high cost. The pH of the aqueous solution containing the palladium-amine complex may be adjusted by using an alkali hydroxide such as sodium hydroxide or potassium hydroxide.

As a method of catalyzing treatment, a zinc-aluminum alloy may be immersed in the above-mentioned treating composition at about 40 ° C. for usually 4 to 6 minutes. This allows palladium-
The amine complex adheres to the zinc-aluminum alloy.

Next, metal palladium is reduced and precipitated by activation on the catalyzed zinc-aluminum alloy. As the treatment liquid in this case, a neutral aqueous solution containing a reducing agent can be used, and is particularly selected from sodium hypophosphite, potassium hypophosphite, a hydrazine compound, sodium borohydride and dimethylaminoborane. And at least one 0.5-5 g / l aqueous solution, for example hydrochloric acid,
It is preferable to use an aqueous solution (composition for activation treatment) adjusted to pH 5 to 8, preferably 6 to 7 with an inorganic acid such as sulfuric acid or boric acid, to which the alloy is added at room temperature for 4 to 6
If it is immersed for about a minute, it can be suitably activated. still,
The hydrazine compound is not particularly limited as long as it can be used as a reducing agent, and examples thereof include hydrazine hydrate or hydrazine sulfate and hydrazine hydrochloride obtained by neutralizing the hydrazine hydrate with a mineral acid.

Next, electroless nickel strike plating treatment is performed. The electroless nickel strike plating composition used in this case may be a generally used electroless nickel strike plating solution, but particularly preferably 1) nickel sulfate 20 to 35 g / l, 2) citric acid, lactic acid, One or two of succinic acid, malic acid and tartaric acid and their ammonium, sodium and potassium salts.
At least 1 selected from the group consisting of 20 to 80 g / l, and 3) sodium hypophosphite, potassium hypophosphite, dimethylaminoborane and sodium borohydride.
It is preferable to use a plating solution containing 10 to 40 g / l of each seed and adjusted to a pH range of 8 to 9 with aqueous ammonia or the like. The plating conditions are such that the liquid temperature is about 40 ° C. and the immersion is usually for about 15 minutes.

After the above electroless nickel strike plating treatment, known thick electroless nickel plating is performed in accordance with a conventional method in order to improve adhesion, corrosion resistance and the like. A known plating solution can be used as the thickening plating solution, for example, nickel sulfate 20 to 35 g / l, sodium hypophosphite 1
Ammonia water or the like is added to an acidic electroless nickel plating solution having a composition of 0 to 40 g / l, malic acid 10 to 25 g / l, and succinic acid 20 to 30 g / l to adjust the pH to a range of 6 to 8, etc. Can be used, and when the zinc-aluminum alloy is continuously immersed until the plating film at a liquid temperature of about 85 ° C. has a desired thickness, a plating film excellent in adhesion and the like which is the object of the present invention is finally obtained. Obtainable.

After the above electroless nickel plating, usual electroplating such as nickel plating and chrome plating can be further carried out if necessary, and in this case as well, a plating film having high adhesion can be obtained.

[0017]

According to the electroless nickel plating method of the present invention, it is possible to coat a zinc-aluminum alloy, which has been difficult or impossible until now, with a complete plating film without unevenness. It is possible to obtain a plating film having excellent adhesion, corrosion resistance, and a beautiful appearance. Further, since complicated processing steps are not required, process control can be controlled relatively easily, which is advantageous in terms of cost.

[0018]

EXAMPLES Examples will be shown below to further clarify the characteristics of the present invention.

Example 1 A superplastic zinc alloy having a thickness of 1 mm and a size of 5 cm × 10 cm was first pretreated by polishing with # 1000 and # 1500 abrasive paper (manufactured by Nihon Kenshi Co., Ltd.) to adjust the surface. Then, immersion degreasing was performed for 2 to 4 minutes at 50 to 60 ° C. with a 3% solution of an alkaline degreasing agent “A-screen” (manufactured by Okuno Chemical Industries Co., Ltd.).

Next, as a catalytic treatment, palladium-containing 1 mol of palladium sulfate and 2 mol of ethylenediamine were reacted.
The treated alloy was immersed in an aqueous solution in which 2 g / l of amine complex (converted to metallic palladium) was adjusted to pH 9 to 10 with sodium hydroxide at 40 ° C. for 5 minutes to apply the palladium-amine complex to the alloy. Then, hydrazine sulfate 5
Palladium metal was deposited by immersing in an aqueous solution whose pH was adjusted to 6 g / l at room temperature for 5 minutes.

Thereafter, nickel sulfate 20 g / l, sodium hypophosphite 25 g / l, ammonium chloride 30 g / l
1 and citric acid 50 g / l, pH with ammonia water
Electroless nickel strike plating was performed at 40 ° C with an aqueous solution adjusted to 9 and immediately followed by nickel sulfate 2
5 g / l, malic acid 24 g / l, sodium succinate 1
85 ° C in an aqueous solution containing 6 g / l and 25 g / l of sodium hypophosphite and adjusted to pH 6.5 with aqueous ammonia.
Electroless nickel plating was performed for 30 minutes to obtain a plating film having a thickness of 8 μm.

Example 2 A superplastic zinc alloy having a thickness of 1 mm and a size of 5 cm × 10 cm was pretreated in the same manner as in Example 1, and as a catalytic treatment, 1 mol of palladium sulfate and 2 mol of aminopyridine were reacted with palladium. -Amine complex 2 g / l (metal palladium equivalent)
Of the treated alloy is immersed in an aqueous solution whose pH is adjusted to 10 with sodium hydroxide at 40 ° C. for 5 minutes, and palladium-
The amine complex was applied to the alloy. Subsequently, palladium metal was deposited by immersing 5 g / l of dimethylaminoborane in an aqueous solution adjusted to pH 6 for 5 minutes at room temperature. Then, the same electroless nickel plating as in Example 1 was performed to obtain a plated film having a thickness of 8 μm.

Example 3 A zinc die-cast alloy having a thickness of 1 mm and a size of 5 cm × 10 cm was pretreated in the same manner as in Example 1, and as a catalytic treatment, 1 mol of palladium sulfate and 2 mol of aminopyridine were reacted with palladium. The treated alloy was immersed for 5 minutes at 40 ° C. in an aqueous solution in which 2 g / l of amine complex (converted to metallic palladium) was adjusted to pH 9 to 10 with sodium hydroxide, and the palladium-amine complex was applied to the alloy. Subsequently, palladium metal was deposited by immersing 5 g / l of hydrazine sulfate in pH 6 with boric acid at room temperature for 5 minutes.

Thereafter, an aqueous solution containing 20 g / l of nickel sulfate, 25 g / l of sodium hypophosphite, 30 g / l of tartaric acid and 20 g / l of lactic acid and adjusted to pH 9 with aqueous ammonia at 40 ° C. for electroless nickel Strike plating is carried out, and immediately thereafter, nickel sulfate 25 g / l, malic acid 24 g / l, sodium succinate 16 g / l, sodium hypophosphite 25 g / l are added, and ammonia water is added.
Electroless nickel plating was performed at 85 ° C. for 30 minutes with an aqueous solution adjusted to H6.5 to obtain a plating film having a thickness of 6 μm.

Comparative Example 1 A superplastic zinc alloy having a thickness of 1 mm and a size of 5 cm × 10 cm was subjected to solvent degreasing with trichlene, and potassium pyrophosphate 7 was added.
Alkaline etching was performed at 55 ° C. for 1 minute with an aqueous solution of 5 g / l adjusted to pH 12 to 13 with potassium hydroxide. Next, acid activation was carried out in an aqueous solution containing 8 g / l of tartaric acid and 5 g / l of sulfamic acid.

Next, sodium hypophosphite 25 g / l
And an aqueous solution containing 100 g / l of sodium citrate were adjusted to pH 10 with aqueous ammonia, and this aqueous solution was used at room temperature for 2
Activated for minutes. Immediately afterwards, nickel acetate 20g /
1, an aqueous solution consisting of 50 g / l of sodium citrate and 25 g / l of sodium hypophosphite with ammonia water
Nickel plating was performed for 15 minutes at a temperature of 55 ° C. with an alkaline electroless nickel plating solution adjusted to 9.6. Immediately followed by nickel sulfate 25g / l, malic acid 24
g / l, sodium succinate 16g / l and sodium hypophosphite 25g / l, and electroless nickel plating was performed at 85 ° C for 20 minutes with a plating solution adjusted to pH 6.5 by adding aqueous ammonia. A plating film having a thickness of 6 μm was obtained.

Test Example 1 The adhesion test, 90-degree bending test and corrosion resistance test of the plated products obtained in the above Examples and Comparative Examples were carried out as follows.

A. Adhesion test: A cross cut of 2 mm was performed on the plated product, a cross-cut test was performed by peeling the cellophane tape, and the number of peeled plating films at that time was measured, and the ratio was calculated. The test results are shown in Table 1.

B. 90 degree bending test ... 9 plated products
After bending at 0 degree, the peelability of the plating film at the bent portion and the presence or absence of cracks were observed. The test results are shown in Table 1.

[0030]

[Table 1]

C. Corrosion resistance test ... Salt spray test JIS Z
2371-1976. Table 2 shows the results of measurement of the number of cycles until the rust generation of the superplastic zinc alloy material and the plated product according to the example. Incidentally, one cycle was a continuous spray for 24 hours.

[0032]

[Table 2]

From the above results, it can be seen that the electroless nickel plating method of the present invention exerts excellent effects on the adhesion, corrosion resistance and the like of the plating film.

Claims (4)

[Claims] 1. When a zinc-aluminum alloy is subjected to electroless nickel plating, a pretreatment including a surface conditioning and degreasing step is performed, and then a palladium-amine complex is added to the alloy as a catalytic treatment prior to the electroless nickel plating. A method for electroless nickel plating on a zinc-aluminum alloy, which comprises depositing and then reducing and precipitating metallic palladium as an activation treatment, and then performing electroless nickel strike plating. 2. A palladium-amine complex obtained by reacting a palladium salt with ammonia or an amine compound is contained as metal palladium in an amount of 0.005 to 2 g / l, and pH.
The composition for catalytic treatment is characterized in that it is 8 to 10.5. 3. At least one selected from sodium hypophosphite, potassium hypophosphite, a hydrazine compound, sodium borohydride and dimethylaminoborane is contained at 0.5 to 5 g / l and has a pH of 5. The composition for activation treatment is characterized in that 4. Nickel sulfate 20-35 g / l, 2)
20-80 g / l of at least one selected from citric acid, lactic acid, succinic acid, malic acid and tartaric acid, and their ammonium salts, sodium salts and potassium salts, and 3) sodium hypophosphite, hypophosphite A composition for electroless nickel strike plating, comprising 10 to 40 g / l of at least one selected from potassium acid, dimethylaminoborane and sodium borohydride, and having a pH of 8 to 9.