JPH07278892A - Alkali zinc-silica plating method - Google Patents

Abstract

PURPOSE:To solve problems due to the process in which suspension and gel formation of an alkaline zinc-silica plating bath are occurred and due to physical properties of a plating film. CONSTITUTION:The problem due to the suspension and gel formation of a bath can be solved by using an alkaline zinc plating bath having 6 to 40g/l zinc concn., 120-200g/l caustic soda concn., and 10 to 100g/l silica concn. all dissolved in the bath. By subjecting a metal surface to electroplating and then to chromate treatment, the corrosion resistance is improved and processing of the waste liquid is made easy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high corrosion resistance zinc-containing silica in which silica is dissolved in a plating bath for plating metal parts.
The present invention relates to a silica plating method.

[0002]

2. Description of the Related Art Conventionally, electroplating, which is low in cost and excellent in corrosion resistance, has been widely used as one of the methods for preventing corrosion of steel sheets and molded parts. For the electroplating of steel sheets, an acidic zinc plating bath containing zinc sulfate or zinc chloride as a metal source is used, which allows high current density work for plating in a short time and easy bath management. Further, with respect to surface-treated steel sheets for automobiles and the like, those having high corrosion resistance are required year after year, and acidic zinc alloy plating such as zinc-nickel and zinc-iron for electroplating zinc and other metals has been put into practical use. However, a steel sheet acidic zinc plating bath or an acidic zinc alloy plating bath is generally inferior in roundness and is difficult to use for molded parts. For this reason, alkaline zinc plating baths, which are generally good in molding properties and have low cost, are widely used. In addition, as environmental problems have been highlighted, non-cyan alkaline zincate plating baths have been increasingly used instead of highly toxic cyan plating baths. However, this plating bath also does not fully meet the needs for corrosion resistance, and in response, an alkaline zinc-based alloy plating bath in which a metal other than zinc is dissolved using a chelating agent based on the conventional alkaline zincate plating bath has been developed. It was However, this alkaline zinc alloy plating bath is extremely poor in wastewater treatment due to the influence of the chelating agent as compared with the alkaline zincate plating bath, and it is difficult to remove heavy metals from the plating wastewater.
The spread is hindered because the OD value becomes very high.

In view of the above problems, a zinc-silica composite plating manufacturing method has been developed in which silica is compounded with zinc, which has no problem of treating wastewater in the plating bath, and attempts have been made in recent years to improve conventional problems. It is being appreciated. However, in the alkaline zinc-silica composite plating bath composition described in the literature relating to the conventional zinc-silica composite plating production method (for example, JP-A-61-143597), the plating bath is in a suspended and gel state. The electrolytic treatment must be carried out with stirring. Further, if the plating solution is suspended and gelled, the appearance of the plating film is poor and the uniformity of the plating film is reduced. Further, since the gel-like plating bath component adheres to the surface of the component after the electrolytic treatment, there is a problem that it takes time to wash with water after the electrolytic treatment.

[0004]

[Problems to be Solved by the Invention] As described above,
Conventional alkaline zincate plating baths are low in price and excellent in wastewater treatment, but poor in corrosion resistance.Alkaline zinc alloy plating baths with improved corrosion resistance have a problem in wastewater treatment because they use chelating agents. is there. Although the conventional alkaline zinc-silica composite plating bath has good corrosion resistance and coating physical properties, it has various problems due to the suspension of the plating bath as described above.

[0005]

[Means for Solving the Problems] Here, the present inventors have paid attention to the good wastewater treatability of the alkaline zincate plating bath, and by introducing silica therein, the physical properties of the film are improved without impairing the wastewater treatability. Therefore, we have developed an alkaline zinc-silica plating bath that has improved corrosion resistance and that does not form a suspension or gel in the plating bath. As a result, it was found that the corrosion resistance and the film physical properties superior to those of the plating film obtained by electroplating with an alkaline zincate plating bath were obtained. That is, in the alkaline zinc-silica plating method of the present invention, the plating bath composition contains zinc concentration of 6 to 40 g / l, caustic soda concentration of 120 to 200 g / l, and dissolved silica as silica concentration of 10 to 100 g / l. The method is characterized in that the metal surface is electroplated using an alkaline zinc plating bath. In particular, the corrosion resistance can be easily improved by performing the existing chromate treatment after the electrolytic treatment.

The details of the plating bath of the present invention are as follows. The component of the alkaline zinc plating bath containing silica has a zinc concentration of 6 to 40 g / l (preferably 1
5-25g / l), caustic soda concentration 120-200g /
l (preferably 150 to 170 g / l), silica concentration 1
It is in the range of 0 to 100 g / l (preferably 35 to 55 g / l). Zinc and silica are indispensable as electrodeposition components, and caustic soda is indispensable as a supporting electrolyte while at the same time dissolving silica to make zinc an ionic state capable of electrodeposition.

The reasons for limiting the respective concentrations will be described.
Regarding the zinc concentration, if it is less than 6 g / l, the electrodeposition rate becomes extremely slow, and if it exceeds 40 g / l, the high current density part is burnt and the throwing power of the low current density part is insufficient. Concerning the caustic soda concentration, if it is less than 120 g / l, silica becomes a suspension or gel and does not dissolve, and if it exceeds 200 g / l, burns are likely to occur in the high current density part. When the silica concentration is less than 10 g / l, high corrosion resistance cannot be obtained, and when it exceeds 100 g / l, the current efficiency decreases.

As the silica and its compound used as the bath component, colloidal silica, a powdery one which becomes colloidal silica when dispersed in water, silicon No. 3, etc. can be used.

Like the usual alkaline zincate plating bath, when the electrolytic bath is used for the plating bath used in the present invention as it is, the high current density portion is burnt and the low current density portion is insufficient in throwing power. For this reason, it is essential to use a brightening agent as an additive, but regarding the type and the addition amount, a commercially available additive for a non-cyan alkaline zincate plating bath may be used. As a brightener, a reaction product of various amines (alkylamine, polyalkylene polyamine, etc.) and epihalohydrin or an alkylated compound is mainly used, and one or more aromatic aldehydes such as vanillin, heliotropin and anisaldehyde are used. Included
For example, Nippon Surface Chemical Co., Ltd. # 8200 (dimethylamine, imidazole, the reaction product of diethylenetriamine and epichlorohydrin, and a mixture of aldehydes) etc. are mentioned.

In the present invention, the chromate treatment is essential for obtaining excellent corrosion resistance. As the chromate treatment, it is possible to use glossy chromate, colored chromate, black chromate, and green chromate which are used after usual alkaline zincate plating. For example, Rohmate # 62 (colored chromate) manufactured by Nippon Surface Chemical Co., Ltd. may be used.

[0011]

According to the present invention, by using an alkaline zinc-silica plating bath having a specific composition, the plating bath does not become a suspension and does not become a gel, so that the physical properties of the electroplating film are improved and chromate The treatment further improves the corrosion resistance. Further, since the plating bath used in the present invention does not use a chelating agent, the wastewater treatment property of the alkaline zincate plating bath is not impaired. In the alkaline zinc-silica composite plating bath of the prior art such as JP-A-61-143597, the electroplating treatment must be performed while stirring because the plating bath is in a suspension and gel state. Then alkaline zinc-
This problem was solved by configuring the silica plating bath with a specific composition, and the insufficient corrosion resistance was also sufficiently solved by the chromate treatment.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments. Examples 1-8

[0013]

[Table 1]

A brightening agent (# 8200, Nippon Surface Chemical Co., Ltd.) was added to the aqueous solution having the composition shown in Table 1 as an additive.
4 ml / l was added to prepare an alkaline zinc-silica plating bath. The colloidal silica used here was Cataloid SI-30 manufactured by Catalysts & Chemicals Industry Co., Ltd.

SPCC-SD prepared by using the above composition, using a stainless steel plate for the anode, and alkali degreasing and pickling.
A strip plate (100 mm x 50 mm x 1 mm) is used as a cathode, electrolytic treatment is performed at a plating bath temperature of 22 ° C ± 2 ° C and a current density of 2 A / dm ^{2 so} that the plating film thickness is 5 μm, and the appearance is visually evaluated, followed by chromate treatment. (Romate # 62 manufactured by Nippon Surface Chemical Co., Ltd.) was performed. And this is JIS-Z237
In the salt spray test according to No. 1, the time until the occurrence of white rust and red rust was investigated. The results of the above salt spray test are shown in Table 3.

Example 9 The composition of the plating bath was the same as in Example 1, and a brightening agent (# 8200, manufactured by Nippon Surface Chemical Co., Ltd.) as an additive was added to the composition.
It was adjusted by adding 6, 24 ml / l. Using a stainless steel plate as the anode, alkaline degreasing and pickling SPCC-SD
A strip plate (100 mm × 50 mm × 1 mm) was used as a cathode, and electrolytic treatment was carried out at a plating bath temperature of 18 ° C. ± 2 ° C. and a current density of 2 A / dm ^{2 so} that the plating film thickness was 10 μm. Each test piece was subjected to a film physical property test with the following test items, and the evaluation is shown in Table 4.

Comparative Examples 1 to 4

[0018]

[Table 2]

A brightening agent (# 8200 Nippon Surface Chemical Co., Ltd.) was added to the aqueous solution having the composition shown in Table 2 as an additive.
4 ml / l was added to prepare an alkaline zinc-silica plating bath. In Comparative Examples 1 to 3, electroplating and chromate treatment were performed under the same conditions as in Examples 1 to 8 and in Comparative Example 4 under the same conditions as in Example 9. Table 3 shows the results of Examples 1 to 8 and Comparative Examples 1 to 3.

[0020]

[Table 3]

The results of Example 9 and Comparative Example 4 are shown in Table 4. The test items are as follows. (1) Secondary workability This is a test that is carried out after the primary processed part is plated, because the plating film may peel off when it is processed further. It was tested under an extrusion condition of 5 mm using an Erichsen tester. (2) Heat Adhesion To check the adhesion of the plating film due to heat history, 200
Heat treatment was performed at 4 ° C. for 4 hours. (3) Adhesion with time In order to check the adhesion of the plating film with time, heat treatment was performed at 60 ° C. for 144 hours.

[0022]

[Table 4]

From Tables 3 and 4, the plating film obtained from the alkaline zinc-silica plating bath according to the present invention has excellent corrosion resistance and film without deteriorating the plating appearance as compared with the plating film from the conventional alkaline zincate plating bath. The physical properties were obtained.

[0024]

As described above, according to the present invention, silica can be dissolved in an alkaline zinc plating bath, and plating with the alkaline zinc-silica plating bath has good film properties and excellent corrosion resistance. . Then, by performing the chromate treatment, the corrosion resistance is further improved. In addition, since no chelating agent is used, wastewater treatment is easier than in the conventional alkaline zinc alloy plating bath. The silica preferably used in the present invention is industrially mass-produced and supplied at a low price.

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[Procedure amendment]

[Submission date] May 20, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art Conventionally, electroplating, which is low in cost and excellent in corrosion resistance, has been widely used as one of the methods for preventing corrosion of steel sheets and molded parts. For the electroplating of steel sheets, an acidic zinc plating bath containing zinc sulfate or zinc chloride as a metal source is used, which allows high current density work for plating in a short time and easy bath management. Further, with respect to surface-treated steel sheets for automobiles and the like, those having high corrosion resistance are required year after year, and acidic zinc alloy plating such as zinc-nickel and zinc-iron for electroplating zinc and other metals has been put into practical use. However , acidic zinc plating baths for steel sheets or acidic zinc-based alloy plating baths are generally poor in circumstance and are difficult to use for molded parts. For this reason, alkaline zinc plating baths, which are generally good in molding properties and have low cost, are widely used. In addition, as environmental problems have been highlighted, non-cyan alkaline zincate plating baths have been increasingly used instead of highly toxic cyan plating baths. However, this plating bath also does not fully meet the needs for corrosion resistance, and in response, an alkaline zinc-based alloy plating bath in which a metal other than zinc is dissolved using a chelating agent based on the conventional alkaline zincate plating bath has been developed. It was However, the alkaline zinc-based alloy plating bath, an alkaline zincate baths wastewater treatability is extremely poor due to the influence of the ratio Bekireto agent, it is difficult to heavy metal removal of the plating wastewater, further C
The spread is hindered because the OD value becomes very high.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008] The silica and of base material that is used as a bath component, colloidal silica, when dispersed in water in powder form which becomes colloidal silica, silicate No. 3 saw
Da etc. can be used.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

[0013]

[Table 1]

Claims (2)

[Claims] 1. A zinc concentration of 6 to 40 g / l, a caustic soda concentration of 120 to 200 g / l, and a dissolved silica concentration of 10.
A method for alkaline zinc-silica plating, characterized in that the metal surface is electroplated using an alkaline zinc plating bath having a concentration of -100 g / l and then chromated. 2. The alkaline zinc-silica plating method according to claim 1, wherein a brightener for a non-cyan alkaline zincate plating bath is further used.