JPH11264073A - Electroless tin-zinc alloy plating liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely suppress elution of a copper ion even if a plating film is thin after executing a plating treatment on the surface of the copper or a copper alloy compared with a conventional electroless Sn plating liq. SOLUTION: 0.01 0.25 mol/l bivalent Sn ion, 0.03-0.5 mol/l bivalent Zn ion, 0.3-2.0 mol/l more than one kind of thiourea and its deriv., 0.3-2.0 mol/l more than one kind free acid selected among an inorg. acid of hydrochloric acid, sulfuric acid, phosphoric acid, borofluoric acid and an org. acid of alkanesulfonic acid, alkanol sulfonic acid and arom. sulfonic acid are incorporated as plating liq. components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing Sn-Zn on a copper or copper alloy surface, particularly on the inner surface of a copper pipe through which tap water or hot water flows.
The present invention relates to an electroless Sn—Zn alloy plating solution for forming an alloy film.

[0002]

2. Description of the Related Art A copper pipe as a pipe material for tap water or hot water can be wound up and transported in a coil shape even if it is long, and the workability of construction is good, and the tap water and hot water Widely used because of its high corrosion resistance to water. However, copper ions are eluted from the inner surface of the copper tube under the condition of relatively low pH water, and thus a copper tube with an inner surface plated with Sn has been proposed (Japanese Patent Laid-Open No. 4-45282).
The copper tube coated with Sn on its inner surface is practical because the Sn plating film does not peel off even in various processes during construction, and the elution of copper ions is suppressed if the Sn plating film is relatively thick, Corrosion resistance can be prevented. In addition, since the coating method is performed by flowing an electroless Sn plating solution through the inner surface of the copper tube, it can be applied to a long copper tube.

[0003]

However, the above-mentioned Japanese Patent Application Laid-Open No.
In the electroless Sn plating solution disclosed in JP-A-45282, the plated copper material is immersed in tap water for 24 hours, and the amount of copper ions eluted into tap water is examined. The thickness of the Sn plating film is 0.4 μm or less. 0.03 ppm
The above-mentioned elution of copper ions is observed, and there is still a point to be improved. An object of the present invention is to provide an electroless Sn-Zn alloy plating solution that can reliably suppress elution of copper ions even when a plating film is thin, after performing plating treatment on a copper or copper alloy surface. It is in.

[0004]

According to the present invention, 0.01 to 0.25 mol / l of divalent Sn ion is contained as a plating solution component.
And 0.03 to 0.5 mol / l of divalent Zn ions;
One or more of thiourea and its derivatives are contained in 0.3 to 2.
0 mol / l and 0.3 or more free acids selected from the group consisting of inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid and borofluoric acid, and organic acids such as alkanesulfonic acid, alkanolsulfonic acid and aromatic sulfonic acid. Electroless Sn-Zn containing up to 2.0 mol / l
Alloy plating solution. In the conventional method, electroless Sn plating reverses the standard potentials of Cu and Sn by adding thiourea and its derivatives to the plating solution, and when copper is immersed in the plating solution, Cu ions elute and Sn ions are reduced at the same time. To be plated on the copper surface. On the contrary,
In the present invention, it is the same as inverting the standard potential of Cu and Sn by adding thiourea and its derivative to the plating solution, but Zn has a lower standard potential than Cu because the standard potential is lower than Sn. No reversal occurs and therefore Cu and Z
Although the substitution reaction of n does not take place, when the Sn ion is reduced, nearby Zn ions are also induced and reduced, and Sn-Z
An n-alloy plating film is formed on the copper surface.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The copper or copper alloy to be plated according to the present invention is a copper product in which the leaching of copper is severely suppressed when used. For example, a phosphorous deoxidized copper pipe (JIS H3300 C1220) generally used as a pipe material for water supply and hot water supply is suitable as a product to be plated. Further, the present invention is also applied to a deoxidized copper tube using B, Mg, Si or the like as a deoxidizing agent. Further, when the copper content is 96% by weight or more, the present invention is also applied to a copper alloy tube to which a small amount of Sn, Al, Zn, Mn, Mg or the like is added in order to improve corrosion resistance. The plating solution of the present invention is preferably used at a temperature of 30 ° C. or higher to increase the plating deposition rate, and the solution temperature is preferably 90 ° C. or lower to prevent precipitation of stannic oxide and self-decomposition of the plating solution. preferable. Further, it is preferable to stir the solution during the plating process in order to form a uniform plating film. This stirring is performed by a stirrer or mechanical rocking, and air blowing is avoided. This is for preventing oxidation of Sn ions and Zn ions in the liquid. When plating is applied to the inner surface of the copper tube, a plating film can be formed uniformly by flowing a plating solution through the tube.

Next, the components of the plating solution will be described in detail. (a) Divalent Sn ions The concentration of divalent Sn ions in the plating solution is 0.1 mol / l.
If it is less than 10, the precipitation of Sn becomes insufficient, and a sufficient plating film thickness cannot be obtained even if the plating time is lengthened, or pinholes increase in the plating film. Further, the upper limit of 0.25 mol / l is determined depending on the solubility. As a source of divalent Sn ions, stannous oxide, stannous chloride, stannous sulfate, tin methanesulfonate, or the like can be used. (b) Divalent Zn ions The concentration of divalent Zn ions in the plating solution was 0.03 mol /
When it is less than 1, the precipitation of Zn becomes insufficient, a Sn plating film containing no Zn is formed, and the effect of suppressing the dissolution of copper is reduced. Also, the upper limit of 0.5 in relation to solubility.
Mol / l is determined. As a source of divalent Zn ions, zinc oxide, zinc chloride, zinc sulfate, or the like can be used.

(C) Thiourea, etc. In the present invention, one or more of thiourea and its derivatives are used as a complexing agent for copper ions. The complexing agent is Cu
In order to carry out substitutional precipitation of Sn by strongly complexing with ions and remarkably reducing the activity of copper ions in the plating solution, inverting the standard potential of Cu in the plating solution to the standard potential of Sn to make it base. In addition to Even in the plating solution containing this complexing agent, the standard potential of Zn is lower than that of Sn, and therefore, the reversal of the standard potential with Cu does not occur. Therefore, the substitution reaction between Cu and Zn does not occur, but the Sn ions are reduced. In the process, nearby Zn ions are also induced and reduced, and Sn-
A Zn alloy plating film is formed on a copper surface.
The concentration of one or more of thiourea and its derivatives is 0.3
When the molar ratio is less than 1 mol / l, the above substitution does not occur and S
It becomes difficult for n and Zn to precipitate. Further, the upper limit of 2.0 mol / l is determined depending on the solubility. As thiourea derivatives, N-methylthiourea, N, N'-dimethylthiourea and the like can be used.

(D) Free acid The free acid lowers the pH of the plating solution, promotes the elution of copper, and facilitates the substitution reaction.
It is added to stably dissolve ions in a divalent state. When the concentration of the free acid is less than 0.3 mol / l, the elution of copper is insufficient, so that the substitution reaction hardly occurs and a uniform plating film cannot be obtained. On the other hand, if it exceeds 2.0 mol / l, re-dissolution of precipitated Zn tends to occur, which is not preferable. As the free acid, one or more acids selected from inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, and borofluoric acid, and organic acids such as alkanesulfonic acid, alkanolsulfonic acid, and aromatic sulfonic acid are used.

(E) Other components Other components include organic carboxylic acids and surfactants. The organic carboxylic acid forms a weak complex with Sn ions and Zn ions in the plating solution and has an action of controlling a deposition rate and a deposition composition by controlling a deposition state. Organic carboxylic acids include citric acid, tartaric acid, malic acid, gluconic acid, succinic acid, ethylenediaminetetraacetic acid (EDT
A) can be used. A surfactant may be added to obtain a uniform and smooth plating film. Examples of the surfactant include sodium lauryl sulfate, lauryl pyridium chloride, polyethylene glycol mono-4-octylphenyl ether (trade name: Triton X-100), and the like.

[0010]

Embodiments of the present invention will be described below. <Examples 1 to 24> The surface area was 1 dm ² (50 mm × 10
24 sheets of deoxidized copper (0 mm, 0.5 mm thick) were prepared. These plates were subjected to alkaline degreasing (C-4000, manufactured by Uemura Kogyo Co., Ltd.) for 10 minutes at 60 ° C., followed by washing with water and
After soft etching at 25 ° C. for 2 minutes with sodium persulfate at 25 ° C., it was further washed with water and pickled with 10% sulfuric acid at 25 ° C. for 30 seconds. Next, the above-mentioned plate material was immersed in the plating solution with a magnetic stirrer at a plating solution temperature and a plating time shown in Table 3 using six types of 1 liter plating solutions A to F shown in Tables 1 and 2. And electroless plating. After plating, it was washed with water and dried. Twenty-four types of test pieces electrolessly plated by the above treatment were obtained.

[0011]

[Table 1]

[0012]

[Table 2]

<Comparative Examples 1 to 16> Sixteen sheets of deoxidized copper having the same shape, the same size and the same quality as in Example 1 were prepared. These plates were subjected to electroless plating in the same process as in Example 1. Here, zinc sulfate or zinc chloride in the plating solutions A to D was excluded. Otherwise, the components were the same as in Examples 1 to 16. These were designated as plating solutions G to J. Sixteen test pieces of the comparative example electrolessly plated by the above treatment were obtained.

<Comparative Test and Evaluation> Obtained Examples 1 and 2
4 and the test pieces of Comparative Examples 1 to 16, the thickness of the plating film and the elution amount of copper ions were measured. Examples 1 to
For No. 24, the Zn content in the plating film was measured.
The test piece was cut into two pieces having a size of 50 mm x 50 mm, immersed in 50 ml of 5% nitric acid to dissolve the plating film. This solution was quantified by the emission spectrometry, the percentage of Zn in the deposited film was determined in percentage, and the thickness of the plated film was determined by calculation. The amount of copper ion eluted was measured by applying a masking tape to prevent the elution from the cross section of each of the other two test pieces. Then, the test pieces were immersed in 500 ml of an aqueous HCl solution diluted to 100 ppm for 5 hours at 50 ° C.
Was measured by emission spectrometry.

Table 3 shows the results of Examples 1 to 24, and Table 4 shows the results of Comparative Examples 1 to 16.

[0016]

[Table 3]

[0017]

[Table 4]

As is clear from Tables 3 and 4, in Comparative Examples 1 to 16, when the thickness of the Sn-containing plating film containing Zn was 0.4 μm or less, the elution amount of copper ions was 0.01 ppm. ~ 0.05 ppm,
In Examples 1 to 24, even when the thickness of the plating film was 0.4 μm or less, the elution amount of copper ions was less than 0.01 ppm, and it was confirmed that copper elution was surely prevented.

[0019]

As described above, the electroless Sn of the present invention is used.
-According to the Zn alloy plating solution, after performing the plating treatment on the copper or copper alloy surface, the elution of copper ions is surely suppressed even when the plating film is thin as compared with the conventional electroless Sn plating solution. It has excellent effects.

Claims (1)

[Claims] 1. A divalent Sn ion of 0.01 to 0.25 mol / l, a divalent Zn ion of 0.03 to 0.5 mol / l, thiourea and derivatives thereof as plating solution components One or more of which are selected from 0.3 to 2.0 mol / l of hydrochloric acid, sulfuric acid, phosphoric acid, inorganic acids of borofluoric acid, organic acids of alkanesulfonic acid, alkanolsulfonic acid and aromatic sulfonic acid. 0.3 to 2.0 of one or more free acids
Electroless Sn-Zn alloy plating solution containing mol / l.