DE1521025B2 - GALVANIC CYANIDIC SHINY SILVER BATH - Google Patents

Description

The invention relates to a galvanic cyanidic bright silver bath containing organic glossy images containing nitrogen and sulfur.

The shiny silver baths in use today do not satisfy the demands of the in every respect Technology. There are known baths that generate silver precipitates over a large current density range, the gloss of which shows a slight blue haze, but the following one, for hollow ware almost always the usual paintwork to get their light color and for moderate demands on the appearance the silver plating are usable. Other baths probably bring veil-free silver layers in one big one Current density range, but show a slight clouding after painting when the silver deposit is not lightly polished before painting. Bring other types of bath only in too limited a current density range ■ clear silver precipitates, which also after lacquering stay clear.

From the German patent specification 959 775 cyanidic shiny silver baths are known, which ring-shaped Contains condensation products of dithiocarbazates with carbon disulfide. These connections however, there are no silver baths that meet the greatly increased demands on technically usable Bright silver baths are sufficient.

Bright silver baths that deliver clear, glossy coatings over a large current density range, their Brilliance persists even after painting, have therefore not yet become known.

A completely satisfactory glossy silver bath must also have soft soldering points glossy and without blistering silvering and when silvering »repair goods«, d. H. of used goods, which after When the polishing is silvered again, the boundaries between the polished ones are allowed after the silvering Do not mark places or the remaining silver deposit.

The invention is therefore based on the object of providing a cyanide glossy silver bath of the type mentioned at the beginning Kind to make available that meets the above requirements and that in particular is able to do this, over a large current density range, coatings which have a clear gloss with a brilliant Deliver appearance.

This object is achieved according to the invention in that the bright silver bath is used as a brightener with alkali metal salts of the thiosemicarbazide of dithiocarbonic acid with the formula

H ₂ N - C - NH - NH - C - SMe

The brighteners are expediently contained in the bath in amounts of from 0.005 to 5 g / l, preferably from 0.05 to 0.5 g / l. With current densities of 1 to 2 A / dm ² , the addition of the abovementioned brighteners produces extremely shiny silver precipitates.

With the gloss silver bath according to the invention, all requirements with regard to gloss, gloss scattering range, Surprising behavior when painting and silvering soldering points and repairs well satisfied.

By forced relative movement between the

Electrolytes and the goods to be silvered can be the technically usable current density range, as in general known to be expanded according to higher values.

The following examples provide information on the applicability of the brighteners according to the invention.

example 1

Silver bath with 30 g / l silver, bound in shape

of silver cyanide
125 g / l free potassium cyanide

0.1 g / l alkali salt of the T-iriosemicarbazide of dithiocarbonic acid
Bath temperature: 25 ⁰ C

Such a bath gives clear silver precipitates in the range between 0.8 and 1.6 A / dm ^2. Higher current densities result in a slight blue haze. In the range of lower current densities, the gloss decreases.

contains, in which Me means an alkali metal.

The shiny silver bath according to the invention can expediently also contain a condensation product of naphthalenesulfonic acid with formaldehyde. Sulphonated fatty oils are also used as additives saponified form, such as saponified Turkish red oil.

The addition of these compounds, which when used alone in silver baths do not develop a gloss-forming effect, has the advantage that a slight blue haze can be removed, which sometimes occurs when current densities outside the range of 1 to 2 A / dm ² is working.

Example 2

Silver bath with 25 g / l silver, bound in shape

of silver cyanide
90 g / l free sodium cyanide
0.06 g / l alkali salt of the thiosemicarbazide of dithiocarbonic acid
Bath temperature: 22 ⁰ C ^: ·

This bath behaves very similarly to that of the first example, although the current density range is approximately between 0.6 and 1.2 A / dm ² .

Example 3

Silver bath with 30 g / l silver, bound in shape

of silver cyanide
140 g / l free potassium cyanide
0.15 g / l alkali salt of the thiosemicarbazide of the dithiocarbon

acid

Bath temperature:

0.8 g / l condensation product of naphthalene sulfonic acids and formaldehyde
22 to 25 ⁰ C

^{This bath gives a} haze-free high gloss in the range from 0.1 to 4 A / dm a. In the case of current densities above 1.5 A / dm ² , a movement of goods or a relative movement between goods and bath is appropriate. The precipitates have a clear shine even with silvering times of 10 to 20 seconds. They also don't lose any of their brilliance when they are varnished and stoved.

Example4

Silver bath with 40 g / l silver, bound in shape

of silver cyanide
100 g / l free sodium cyanide
0.075 g / l alkali salt of the thiosemicarbazide of dithiocarbonic acid

3.0 g / l condensation product of naphthalene sulfonic acids and formaldehyde
Bath temperature: 25 to 28 ⁰ C

With such a bath, a haze-free high gloss in the range from 0.1 to 3 A / dm ^{2 is obtained} . In the case of current densities above 1.4 A / dm ² , a relative movement between the goods and the bathroom is advisable. The precipitate remains clear even after painting and baking.

Example 5

Silver bath with

30 g / l silver, bound in shape

of silver cyanide
160 g / l free potassium cyanide
0.3 g / l alkali salt of the thiosemicarbazide of dithiocarbonic acid

2 g / l saponified Turkish red oil
Bath temperature: 22 to 25 ° C

a) According to German patent specification 959 775:

Potassium silver cyanide 55 g / l

Potassium cyanide 65 g / l

Potassium salt of Dimerkapto-Thiodi-

azoles lg / 1

b) According to the invention:

Potassium silver cyanide 55 g / l

Potassium cyanide 140 g / l

Potassium salt of the thiosemicarbazide of dithiocarbonic acid 0.15 g / l

The polished copper sheets were each after a customary pre-silvering (10 seconds at about volts in a bath with about 1.5 g / l Ag and 100 g / l ίο NaCn) at 20 to 22 ° C and at a cathodic current density of 1 A / dm ² silver-plated. The exposure time was 10 minutes in each case. Examination of the samples shows that a considerably better and more uniform appearance of the deposited precipitate is achieved with the bath according to the invention.

The bath temperature can also be chosen to be lower than indicated in the examples. In order to The maximum permissible current densities decrease, but the gloss scatter range does not decrease touches, since the lower current density limit also decreases.

Claims (5)

Patent claims: 1. Galvanic cyanidic shiny silver bath ~ with a content of organic, nitrogen and Sulfur-containing brighteners, thereby characterized in that it is alkali metal salts of the thiosemicarbazide of dithiocarbonic acid as brighteners with the formula With this bath, clear, glossy, excellent paintable silver layers are available, provided the current density is between 1.5 and 2.0 A / dm ² and the goods are moved across from the bath. Examples This example shows the progressiveness of the invention Bright silver baths compared to the bright silver baths known from German patent specification 959 775. The following baths were worked on: H ₂ N - C - NH - NH - C SMe contains, in which Me means an alkali metal. 2. Silver bath according to claim 1, characterized in that there is also a condensation product of naphthalenesulfonic acids with formaldehyde. 3. Silver bath according to claim 1, characterized in that there is also a sulfonated fatty oil contains in saponified form. 4. silver bath according to claim 3, characterized in that it is a sulfonated, saponified fatty oil Contains saponified Turkish red oil. 5. Silver bath according to claim! to 4, characterized in that it contains the brighteners in quantities contains from 0.005 to 5 g / l.