JPH0565600B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a composite plating method in which a plating metal, SiO ₂ and Al ₂ O ₃ are simultaneously electrodeposited. <Conventional technology and its problems> Zn-plated steel sheets have a plating layer made of pure zinc.
Since it is electrochemically less base than the iron in steel sheets, it has a sacrificial corrosion-preventing effect, so it is widely used in applications such as automobiles, building materials, and home appliances. However, since the corrosion rate of the pure zinc layer itself is extremely fast, there is a problem that the period during which sacrificial corrosion protection is effective in a severe corrosive environment is short. Therefore, with the intention of improving the corrosion resistance of the Zn-plated steel sheet by making the corrosion products of the Zn-plated steel sheet have the protective effect of the plating layer, Al ₂ O ₃ and SiO were added to the Zn-plated layer. ₂
Attempts have been made to develop composite plating in which the following elements are dispersed. Conventionally, in composite plating, the following methods have been used to uniformly and widely disperse electrodeposited particles in a plating layer. That is, (1) 0.5 to 5% alumina sol (weight converted to Al ₂ O ₃ ), 0.1 to 10% aluminum powder (weight),
Cationic or nonionic surfactants
Aluminum is electrodeposited on a conductive substrate by electrophoresis using an aqueous solution containing 0.05 to 1% (by weight) (see JP-A-49-21332). (2) Insoluble particles that have been treated with cation adsorption. Composite plating method in which cation adsorption treatment is NH ₄ ⁺ ion adsorption treatment (patent application 1983-
(See No. 31895). Examples include. Other methods include improving the stirring conditions of the plating bath and selecting the particle size of the particles. In such composite plating, Al ₂ O ₃ and
Better corrosion resistance can be expected by simultaneously dispersing and eutectoiding both Al ₂ O ₃ and SiO ₂ than by dispersing SiO ₂ alone. However, by the conventional method described above, Al ₂ O ₃
If you try to deposit SiO 2 and SiO ₂ at the same time, the following problems will occur. (a) When electrodepositing SiO ₂ or Al ₂ O ₃ by adding a surfactant, there is a risk that unnecessary or harmful organic compounds may be mixed into the plated metal matrix. (b) It is difficult to select the particle size of SiO ₂ and Al ₂ O ₃ and improve the stirring method by simply controlling mechanical collisions of SiO ₂ and Al ₂ O ₃ particles, and to obtain sufficient effects. . (c) Merely subjecting SiO ₂ or Al ₂ O ₃ to cation adsorption treatment, especially NH ₄ ⁺ ion adsorption treatment, is not sufficient to increase the amount of electrodeposition. Furthermore, when uniformly dispersing alumina colloid in a plating solution, some alumina colloid products may rapidly increase their viscosity when the pH exceeds 5, or increase the amount of electrodeposition, which may cause problems in the plating layer. If a large amount of alumina colloid is added to the plating solution, the viscosity of the plating solution increases, making plating difficult. In particular, in a high concentration chloride plating bath, if alumina colloid is used alone, the aluminum compound will gel due to the following reaction, resulting in poor dispersibility in the plating bath. AlOOH+HCl→ Al gelation<OH Cl↓+OH ^- <Object of the invention> Therefore, the present invention was made as a result of repeated research to solve such problems, and its purpose is to The object of the present invention is to provide a composite plating method that can increase the amount of SiO ₂ and Al ₂ O ₃ eutectoided therein and uniformly eutectoid. <Structure of the Invention> That is, according to the present invention, positively charged alumina sol and metal cations with a charge of two or more valences are adsorbed on the surface of a negatively charged water-dispersible silica sol, thereby making the surface positively charged as a whole. to be charged. This improves the dispersibility in the plating solution,
Furthermore, since it is positively charged as a whole, it can be electrostatically deposited uniformly and in large quantities by electrostatically adhering to a negatively charged object to be plated. Next, the present invention will be explained in more detail. In the composite plating of the present invention, the metal ions to be adsorbed on the surface of the water-dispersible silica colloid are preferably cations with a charge of two or more valences.
If monovalent cations such as K ⁺ , Na ⁺ , Cs ⁺ , and NH ₄ ⁺ are simply adsorbed, SiO ₂ and Al ₂ O ₃ will not be present in the plating layer.
A sufficient effect cannot be obtained in increasing the amount of eutectoid. Any silica colloid may be used as long as it is water-dispersible. Further, as the alumina colloid to be adsorbed, for example, an amorphous alumina colloid can be used. In order to deposit a large amount of SiO ₂ or Al ₂ O ₃ into the plating layer, it is sufficient to adsorb a large amount of alumina colloid on the surface of silica colloid, but there is a limit. That is, even if a positively charged alumina colloid is adsorbed onto a negatively charged silica colloid, there is a limit and the silica-alumina composite colloid cannot be positively charged. Therefore, in the present invention, in addition to simply adsorbing alumina colloid to silica colloid, we also perform a process to adsorb metal ions with a valence of two or more using electric charge, thereby creating a positively charged sol with good dispersibility. This positively charged silica colloid forms
An alumina colloid/metal ion complex with a valence of 2 or higher is electroplated using an acidic plating bath, and the complex is electrodeposited onto the plated object. This results in
SiO ₂ and Al ₂ O ₃ can now be efficiently electrodeposited in large amounts, and corrosion resistance can be significantly improved. Here, the reason why the charge is defined as two or more is that the charge is a monovalent cation (e.g., K ⁺ , Na ⁺ , Cs ⁺ ,
This is because, if NH ₄ ⁺ ) is adsorbed, a sufficient increase in the amount of electrodeposition cannot be obtained. Further, the amounts of metal cations and alumina colloid to be adsorbed are preferably adjusted to a molar ratio Me ^m+ /Al ₂ O ₃ =0.4 to 1.8 in terms of alumina. The reason is that the above molar ratio is 0.4
This is because if it is less than 1.8, no increase in the amount of electrodeposition is observed, and if it is more than 1.8, adsorption becomes difficult. The following procedure may be used to adsorb alumina colloid or aluminum ions on the surface of silica colloid. That is, the alumina colloid is added to the silica colloid aqueous solution with sufficient stirring. By sufficiently stirring the silica colloid, the alumina colloid directly adsorbs onto the negatively charged hydroxyl groups on the silica colloid surface, surpassing the stabilizer Na ions surrounding the silica colloid surface. Furthermore, metal cations of divalent or higher valence can be further adsorbed onto the silica colloid-alumina colloid aggregate thus obtained as follows. That is, an aqueous solution containing the metal ion, such as an aqueous solution of a salt of the metal, is added to the aqueous solution of the silica colloid-alumina colloid aggregate with sufficient stirring. In this way,
A colloid aggregate is obtained in which divalent or higher metal cations and alumina colloid or aluminum ions are adsorbed on the surface of the silica colloid. <Examples> Next, the present invention will be specifically described in terms of examples and comparative examples. Example 1-A to I Water-dispersible silica colloid aqueous solution (SiO ₂ minutes: 20
%) was added to an aqueous potassium chloride solution (KCl: 7 g/L) adjusted to pH 4 to make a total volume of 1 L.
While stirring this solution, 10 g of an amorphous alumina colloid aqueous solution (Al ₂ O ₃ minutes: 20%) was added to this solution at a rate of 1 g per minute to obtain a silica colloid aqueous solution with adsorbed alumina colloid. Next, while stirring this aqueous solution, CoCl ₂ .6H ₂ O, NiCl ₂ .
6H ₂ O, MgCl ₂ , ZnCl ₂ , CrCl ₃・6H ₂ O, TiCl ₄ ,
Co ₂₊ ^, Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , Cr ³⁺ , Ti ⁴⁺ ,
Zr ⁴⁺ was adsorbed. Next, the treated colloid was added to a chloride Zn plating solution (ZnCl ₂ : 210 g/, KCl: 360 g/). Table 1 shows the physical properties of various colloids. After the thus obtained plating solution was circulated using a pump and sufficiently stirred, composite plating was applied to the Fe plate under the following plating conditions. The results are shown in Table 3. Current density 75A/dm ² PH 4.0 Bath temperature 50℃ Flow rate Approx. 60m/min Plating amount 20g/m ² Figure 1 shows the EPMA (Erectron) composite plated plate obtained in Experimental Example 1-A. Probe Micro
Showing Al spot count by Analyzer)
The photo is 400x magnified. As you will see,
Al ₂ O ₃ was electrodeposited in a dense and uniform state. Conventional Example 1 Composite plating was performed using the amorphous alumina colloid as it was under the same plating conditions as in Experimental Example 1. The results are shown in Table 3. The alumina colloid precipitates in the plating solution, the liquid viscosity increases, and Al
The second photo, which is a 400x photo showing the spot count of
As shown in the figure, only a composite plating in which a small amount of Al ₂ O ₃ was non-uniformly electrodeposited was obtained. Experimental example 2-A to I Water-dispersible silica colloid aqueous solution (SiO ₂ minutes: 20
%) was added to an aqueous potassium chloride solution (KCl: 7 g/L) adjusted to pH 4 to make a total volume of 1 L.
While stirring this solution, 10 g of an amorphous alumina colloid aqueous solution (Al ₂ O ₃ minutes: 20%) was added to this solution at a rate of 1 g per minute to obtain a silica colloid aqueous solution with adsorbed alumina colloid. Next, while stirring this aqueous solution, CoCl ₂ .6H ₂ O, NiCl ₂ .
6H ₂ O, MgCl ₂ , ZnCl ₂ , CrCl ₃・6H ₂ O, TiCl ₄ ,
Co ₂₊ ^, Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , Cr ³⁺ , Ti ⁴⁺ ,
Zr ⁴⁺ was adsorbed. Next, Zn sulfuric acid bath ( _ZnSO4・
7H ₂ O: 440g/, AlCl ₃・6H ₂ O: 20g/,
The treated colloid was added to Na ₂ SO ₄ .10H ₂ O: 80 g/). Table 2 shows the physical properties of various colloids. After the thus obtained plating solution was circulated using a pump and thoroughly stirred, composite plating was applied to the Fe plate under the following plating conditions. The results are shown in Table 3. Current density 40A/dm ² PH 4.0 Bath temperature 50℃ Flow rate Approximately 60m/min Plating amount 20g/ ^m 2Similar to the chloride bath in Experimental Example 1, Al ₂ O ₃ was electrodeposited in a dense and uniform state. did. Comparative Example 2 Plating was performed under the same plating conditions as in Experimental Example 2 using the amorphous alumina colloid as it was. The results are shown in Table 3. Only a small amount of Al ₂ O ₃ was non-uniformly electrodeposited and only a smudge was obtained.

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[Table] ○: Uniformly electrodeposited ×: Heterogeneously electrodeposited <Effects of the invention> As is clear from the above, the present invention is a composite plating method in which SiO ₂ and Al ₂ O ₃ are simultaneously electrodeposited. As a pretreatment, positively charged alumina colloid or aluminum ions and metal ions with a charge of two or more are adsorbed onto the surface of negatively charged silica colloid, without causing colloid denaturation. , evenly and in large quantities
Al ₂ O ₃ and SiO ₂ can be electrodeposited.

[Brief explanation of the drawing]

Figures 1 and 2 are photographs substituted for drawings, and
EPMA (Electron Probe) for showing metallographic structure
This is a 400x photograph showing spot counts of Al using a Micro-Analyzer. FIG. 1 is a photograph of the Al spot count by EPMA of Experimental Example 1 A, and FIG. 2 is a photograph of the Al spot count by EPMA of Conventional Example 1.

Claims (1)

[Claims] 1. On the surface of the negatively charged silica colloid, positively charged alumina colloid and metal cations with a charge value of two or more are present, with a molar ratio of alumina colloid to metal cations calculated as alumina in the range of 1:0.4 to 1.8. A composite method characterized by simultaneously electrodepositing plating metal, alumina, and silica onto a plating body using an acidic plating bath in which alumina and silica are adsorbed and treated to be positively charged as a whole. How to attach.