DE2251103A1 - ACID BATH FOR ZINC ELECTROPLATING - Google Patents

Description

Nippon Kokan Kabushiki Kaisha, Tokyo / Japan Acid bath for zinc electroplating

The present invention relates to an acidic bath for zinc electroplating which is used for producing shinier Zinc coatings with dense crystal structures under high current densities is suitable.

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It is known to use acidic zinc plating baths containing zinc sulfate, zinc chloride or zinc fluoroborate or the like as a source of Zn ²⁺ ions. To increase the conductivity of the bath, sulfate or chloride is often added to the bath. With such plating baths, it is possible to produce plating of considerably high densities when the plating bath is agitated during the plating operation. At high current densities, however, the surface of the coatings is coarse and not shiny. In addition, large crystals are formed. In order to avoid these difficulties, it has been proposed to add small amounts of organic matter such as liquorice, glue, rubber arabic, dextrose, β naphthol or the like to the bath. Incorporation of such organic substances enables high quality plating to be produced within a certain range of current density, although the practical range of current density is relatively limited and it has been impossible to produce beautiful coatings at high currents.

p ρ

density, in particular in a range from 50 A / dm to 100 A / dm to obtain.

The invention has set itself the task of providing an improved bath for zinc electroplating, which the production thick and shiny claddings in a wide range

ρ ρ allows current densities of 10 A / dm to 100 A / dm.

According to the invention, an acidic bath is used for zinc electroplating made available, which is made from a mixture of an aqueous solution, from 200 to 650 g / l zinc sulfate, 50 - 200 g / l zinc chloride, 10-70 g / l ammonium chloride, 5-30 g / l sodium succinate and at least one compound below 0.1 to 10 g / l nicotinic acid amide and 0.01 to 0.1 g / l ethoxylated c <-naphtholsulfonic acid is selected.

2+

Zinc sulfate and zinc chloride are used as the source of Zn ions, and their concentrations are based on the following certainly. Especially with a zinc sulfate concentration of

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less than 200 g / l it is impossible to avert high current densities, as the surface of the plating is burned while at. a concentration above 650 g / l the tendency to generate of precipitation occurs. These precipitates represent zinc ammonium sulfate, which is the conductor roller for the delivery , electric current or deposit on the surface of the plating film and deteriorate the plating film.

If the concentration of zinc chloride is less than 50 g / l, the conductivity is too low to generate high current densities, while at a concentration of more than 200 g / l, the appearance of the plating deteriorates if it is with treated with a phosphate or chromic acid.

The purpose of adding ammonium chloride is to improve the conductivity. If the concentration is less than 10 g / l, this goal of ammonium chloride cannot be achieved become, while at a concentration above 70 g / l a There is a tendency to deposit deposits. In the electrolysis using the electrolysis bath according to FIG According to the invention, the favorable pH value of the electrolysis bath is between 3.5 and 4.5 and preferably 4.0. A pH of the electrolytic bath above 4.5, iron and zinc compounds would be deposited. A pH of the electrolytic bath below 3 5 would lead to the evolution of hydrogen in the bath, which would be absorbed by the plating film and cause pinholes in the plating film.

The main task of the sodium succinate is to stabilize it the pH of the plating bath. At a sodium succinate concentration of less than 5 g / l its effect for buffering the pH is not sufficient, while - with a Concentration above 50 g / l the preference of sodium succinate is not increased.

Nicotinic acid amide and ethoxylated naphtholsulfonic acid are

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added to by dense and shiny flatting surfaces to obtain. They can be used individually or in coordination will. The incorporation creates fine crystals, resulting in smooth, shiny and beautifully plated surfaces.

A quantity of 0.1 to 10 g / l nicotinic acid amide is suitable. A concentration lower than 0.1 g / l is not effective, while a concentration higher than 10 g / l is the desired one Advantage not increased. A suitable concentration of ethoxyllerter-o < -naphtholsulfonic acid is in the range from 0.01 g / l to 0.1 g / l. While a concentration of less than 0.01 g / l is not effective, a concentration greater than 0.1 g / l will result in the formation of pinholes in the plated surfaces and cloudy clad surfaces with an unfavorable appearance.

"Will- a plating bath of a composition within the Using the range of limits described above and stirring this bath vigorously during the plating operation, it is possible, plated surfaces with diohter crystal structure

ρ ρ

obtainable at high current densities of 10 A / dm to 100 A / dm.

For a better understanding of the invention, the following examples, which represent preferred embodiments, are given: although these are not to be regarded as a restriction.

example 1

A cold-rolled steel plate was produced under the following conditions plated.

Composition of the bath:

Zinc sulfate (ZnSO _if. 7H ₂ O) 450 g / l

Zinc chloride (ZnCl ₂ ) 150 g / l

Sodium succinate ((CH ₂ COONa) ₂ .6H ₃ O) 15 g / l

Ammonium chloride (NHj ₊ Cl) 40 g / l

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2251103 Nicotinic acid amide (C ₆ H ₆ N ₂ O ₂ ) 3 g / l Ethoxylated-ot -naphtholsulfonic acid 0.02 g / l (C ₁₂ H ₁₂ O ₅ S) Current density 100 A / dm ² Plating time 5 sec. Example 2

Composition of the bath:

Zinc sulfate zinc chloride (ZnCl ₂ ) ammonium chloride sodium suocinate (nicotinic acid amide

300 g / l 80 g / l 20th g / l 10 g / l 5 g / l 60 A / dm ²

Current density

Plating tent. 8 sec.

Example 3
Composition of the bath;

Zinc sulfate (ZnSO ₂₁ -TH ₂ O) 350 g / l

Zinc chloride (ZnCl ₂ ) '200 g / l ammonium chloride (NHhCl). '. 50 g / l sodium succinate ((CH ₂ COONa) _{2 .6H 3} O) 20 g / l

Ethoxylated -cC-naphthol sulfonic acid O0O5 g / l

Current density 80 A / dm

Plating time 4 sec "

The plating produced in accordance with the corresponding cases coatings v / iron sen. dense crystal structures with a good appearance, and are smooth and shiny,

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As a control or reference test, the electroplating operation was carried out with the compositions of Examples 1 to J5 but without a content of nicotinic acid amide and / or ethoxylated naphthol sulfonic acid and it was found that the films formed were coarse and the surface of the plating was not
becomes smooth and shiny.

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Claims (1)

JP a t e jti; t a η s ρ r u ο h 1. Acid bath for zinc electroplating with a Content of zinc ions and an additive to increase the conductivity of the bath, characterized in that that the bath is an aqueous solution of 200 to 650 g / l zinc sulfate, 50 to 200 g / l zinc chloride, 10 to 70 g / l ammonium chloride, 5 to 30 g / l sodium suocinate and 0.1 to 10 g / l nicotinic acid amide and / or 0.01 to 0.1 g / l ethoxylated-o (-naphtholsulfonic acid contains. 3098 21/1003