DE1521029C3 - Acid galvanic bright zinc bath - Google Patents

Description

a) an aromatic carboxylic acid, an aromatic aldehyde, an aromatic ketone or an aromatic carboxylic acid ester,

b) a nonionic, surface-active polyoxyethylene compound, in which at least 6 ethylene oxide molecules are condensed with long-chain fatty acids or alkylphenols and

c) ammonium chloride or another ammonium salt with a sufficient amount of one other chlorides,

■ · 2. zinc bath according to claim 1, characterized in that the content of component a) of 0.1 up to 20 g per liter of bath.

3. zinc bath according to claim 1, characterized in that the content of component b) of 0.5 up to 20 g per liter of bath.

4. zinc bath according to claim 1, characterized in that the content of ammonium chloride as Component c) is 5 to 60 g per liter of bath.

Technically usable zinc electrolytes for the metal goods industry must be deposited bare to allow shiny zinc layers within a large current density range. You must also have a have good covering power in order to achieve sufficient zinc deposition even on deeper parts of the surface to ensure. Cyanide or cyanide-free alkaline zinc baths meet these requirements usually. However, there are considerable disadvantages associated with the operation of such baths. Because those of the Authorities have long required the decontamination of wastewater in the interests of environmental protection a great technical effort. This also applies to cyanide-free alkaline zinc baths, because these complexing agents included so that they can meet the technical requirements mentioned above. With the cyanidic Baths have a further disadvantage that when they are operated, the risk of poisoning cannot be ruled out can be.

The difficulties outlined occur with acidic zinc baths which are operated in the pH range from 2 to 6 will not be on. The rinsing water that occurs in acidic zinc baths can be easily neutralized in this way are dealt with so that they comply with the relevant regulations. In spite of this, however, it has lasted for decades Efforts have not succeeded in producing technically satisfactory results with acidic zinc baths, which is gloss and Concerning opacity to get. In particular, it is not possible in the known acidic zinc baths completely to deposit similar-looking, shiny zinc precipitates over a large current density range. It is only possible to obtain bare to shiny deposits in narrowly limited areas of the current density. In addition, the hiding power of such baths is not properly referred to as bright zinc baths in the true sense of the word Electrolytes are practically just as low as the acidic matt zinc baths that have been known for a long time.

The invention remedies the disadvantages mentioned. Their task is therefore to create an acidic zinc bath by creating bright to shiny zinc deposits within a large current density range good coverage. For a better understanding of the technical difficulties that have so far been satisfactory Solution of the said problem

! 0 den, it should be noted that in general electroplating Most objects that are electroplated with metal layers, one have more or less complicated surface structure. As a result, corners, edges, Peak very high current densities occur. In depressions and parts of the surface facing away from the anode on the other hand, the current densities are considerably lower than the mean current density, which can be obtained from the total current which is picked up by the object and can calculate the total surface of the object (Average current density = absorbed current: total surface of the object).

So it is not uncommon for technical objects to be electroplated to the various Current densities occurring on the surface of these objects behave as 20: 1. An electrolyte for the deposition of., shiny zinc layers, which should be useful in general electroplating, must be deposited in a further current density range completely similar looking shiny metal layers allow. If it does not have this property, the surface may be shiny and matt deposits side by side.

A galvanic zinc bath that meets the stated requirements of electroplating is characterized according to the invention by a content of

a) an aromatic carboxylic acid, an aromatic aldehyde, an aromatic ketone or a aromatic carboxylic acid ester,

b) a nonionic, surface-active polyoxyethylene compound, with at least 6 ethylene oxide molecules with long-chain fatty alcohols, long-chain Fatty acids or alkylphenols are condensed and

c) ammonium chloride or another ammonium salt with a sufficient amount of another Chlorides.

Add non-ionic surface-active substances to acidic zinc baths in order to improve the hiding power, is known from GB-PS 6 02 591. This publication deals with the special task of and to improve the throwing power of electroplating baths.

In DE-PS 7 31 835 the teaching is contained, the gloss formation of electrolytic zinc deposits thereby to improve that colloids and aldehydes are added to acidic baths at the same time. To note is that in said document for the invention described there a prior art is considered is drawn, after which it was already known, for the production of shiny zinc coatings by electroplating baths Add magnesium sulfate and aluminum sulfate.

It had also been tried at the time, by adding of colloids alone, e.g. B. of dextrin, and by the simultaneous addition of colloids and metal salts, like magnesium sulfate, the luster of the electrolytic

To improve zinc precipitation.

With the bath according to DE-PS 7 31 835, shiny deposits are obtained only in the area of high current densities. The shine should be »deepest and most beautiful at current densities as close as possible before burning the zinc precipitates lie «. Such a bath is at best suitable for bright galvanizing objects with a simple interface, d. H. of objects that have a largely over their entire surface same current density occurs as it is, for. B. is the case with ribbons and wires. With profiled objects such a bath fails.

The person skilled in the art receives from the described prior art, regardless of whether one has the considered Publications taken individually or in their entirety, no suggestion as to how he did the task could solve to create a bath that within a large current density range bright to shiny zinc deposits allowed to produce. In no case does DE-PS 7 31 835 teach to improve shiny zinc deposits only add aldehydes to acidic baths. Because attempts made using the HuIl cell have been carried out have shown that when using aldehydes alone without the addition of a Colloid, partly black or dark gray, deep matt zinc deposits form. This is also consistent with DE-PS 7 41 668 (p. 2, line 15 ff.), according to which in an acidic zinc bath by adding furfural, So an aldehyde, a pronounced gloss effect does not occur. Through this reference the Discouraged by those skilled in the art from using aldehydes in acidic zinc baths in the expectation that it would Shine improved.

Tests with a bath according to Example 5 of GB-PS 6 02 591 with a content of a non-ionic, Surface-active polyoxyethylene compounds have shown on the basis of Hull cell sheets that the said additive improves the hiding power compared to an acidic zinc bath without the additive only has a very low hiding power. The precipitation in question lacks any shine.

Finally, experiments have been carried out in which an electrolyte according to DE-PS 7 31 835 a nonionic surface-active polyoxyethylene compound was added. There were black ones Deposits on the Hull cell sheet, however. no shiny precipitate.

According to the discussed state of the art and the results of the experiments, it is completely surprising that you get an acidic bright zinc bath for the first time through the composition of the bath according to the invention that meets all the requirements of electroplating.

The bath according to the invention is operated at pH values of 2.5 to 5.5. At pH values higher than 5.5 as a rule, basic zinc salts precipitate. If the pH value is too low, the zinc anodes will also dissolve without it Current impact on; the zinc concentration in the bath increases, which is undesirable.

Suitable aromatic carboxylic acids, aromatic aldehydes, aromatic ketones or aromatic carboxylic acid esters, The following are examples of aromatic carbonyl compounds:

Benzoic acid, cinnamic acid, salicylic acid, phenylpropiolic acid, benzoylacetic acid, o-coumaric acid, cinnamaldehyde, m-oxybenzaldehyde, acetophenone, benzophenone, benzoyl acetic acid ethyl ester, Benzalacetone.

These compounds are effective in the range between 0.1 and 20 g per liter of electrolyte, with the dosage can fluctuate within 25% without harming the effect. ■;

Carbonyl compounds that have a solubility less than 0.1 g / l bath are generally not more sufficiently effective.

The non-ionic, surface-active polyoxyethylene compound, with at least 6 ethylene oxide molecules with long-chain fatty alcohols, long-chain fatty acids or alkylphenols are condensed (component b)) preferably contains 10 or more oxyethylene groups in the molecule because it improves the water solubility. Component b) is expedient added in an amount of 0.5 to 20 g per liter of bath.

The ammonium salt (component c)) is preferably in the form of ammonium chloride in an amount used from 5 to 60 g per liter. Instead of ammonium chloride you can also use another ammonium salt, like ammonium sulfate or ammonium acetate, if you use a sufficient amount at the same time of another chloride such as zinc chloride or sodium chloride.

The following examples explain the invention:

The baths deliver current densities between 1 and 5 amps / qdm and bath temperatures between 15 and 30 ° C bright to shiny zinc layers with good coverage. With strong movement of goods or electrolytes considerably higher current densities can be used.

example 1
J '- ■ ) -

300 g / l zinc sulphate,
25 g / l ammonium chloride,
0.6 g / l cinnamic acid,

3.0 g / l surface-active compound made from isononyl alcohol and about 15 (C2H,) O) groups in the Molecule,

pH = 4.5.

B is ρ ie 1 2 ^{! L}

225 g / l zinc sulfate,

30 g / l zinc chloride,

25 g / l ammonium chloride,

6 g / l benzoic acid,

5 g / l surface-active compound made of nonyl

phenol and about 30 (C2H4O) groups in the Molecule,

pH = 5.0.
B is ρ ie 1 3

70 g / l zinc chloride,
165 g / l ammonium chloride,

17 g / l surface-active compound of tributylphenol and approx. 13 (C2H ₄ O) groups in the molecule,
5 g / l phenylpropiolic acid,

pH = 5.0.

Example 4

250 g / l zinc sulfate,
35 g / l ammonium chloride,

5 6

0.25 g / l benzalacetone, B e i s ρ i e 1 9

4.5 g / l surface-active compound from tributyl

phenol and about 50 (C ₂ H4O) groups in the 85 g / l zinc chloride,

Molecule, 50 g / l ammonium chloride,

5 8 g / l surface-active compound of nonyl

pH = 3.0. phenol and approx. 20 (C ₂ H ₄ O) groups in the

liiil

Example5 _ .. £ ^u :. ..

7 g / l salicylic acid.

g / l zinc sulfate,

35 g / l ammonium chloride, io example 10

15 g / l surface-active compound from isononyl

alcohol and approx. 15 (C ₂ H ₄ O) groups per month - 75 g / l zinc chloride,

lekül, 155 g / l ammonium chloride,

1.6 g / l benzophenone. 16 g / I surface-active compound of nonyl

^{T he 1615} phenol and approx. 14 (C ₂ H ₄ O) groups in the

cool,

g / l zinc sulfate, 2.8 g / l benzoylacetic acid.

25 g / l ammonium chloride,

0.25 g / l m-oxybenzaldehyde, 'Example 11

3 g / l surface-active treatment from Hexanol 20

and about 15 (C ₂ H ₄ O) groups in the molecule, 90 g / l zinc chloride,

70 g / l ammonium chloride,

pH = 3.7. : 10 g / l surface-active compound made of octylphe-

nol and approx. 14 (C ₂ H ₄ O) groups in the molecule,

Example? 25 4 g / l O-coumaric acid.

175g / l zinc sulfate,. Example 12

30 g / l zinc chloride,

30 g / l ammonium chloride, 150 g / l zinc sulfate,

0.4 g / l benzoylacetic acid ethyl ester, 30 35 g / l ammonium chloride,

10 g / l surface-active compound from isononyl- 15 g / l surface-active compound from isononyl alcohol and about 15 (C ₂ H ₄ O) groups in the alcohol and about 15 (C ₂ H ₄ O) groups in the Mo molecule, lekül , ^J 'ν

0.7 g / l cinnamaldehyde. pH = 4.5. 35

Example 13 Example 8

80 g / l zinc chloride,

g / l zinc chloride, 70 g / l ammonium chloride,

25 g / l ammonium chloride, 40 9 g / l surface-active compound from linear

0.5 g / l benzalacetone, C, ₂ / Ci ₅ alcohol and approx. 11 (C ₂ H ₄ O) groups

10 g / l isononyl surface-active compound in the molecule,

alcohol and ethylene oxide with about 15 1.4 g / l acetophenone.

(C ₂ H ₄ O) groups in the molecule.

Claims (1)

Patent claims: 1. Acid galvanic zinc bath with a pH value of 2.5 to 5.5 for the deposition of well-covering, bright to shiny zinc deposits in a large current density range, marked by a content of