JPS5827355B2 - Sanseiden Kimetsuki Enyoku - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an acidic zinc bath for the electrolytic deposition of bright zinc deposits.

Unlike the highly toxic alkaline cyanide electrolyte, the acidic bright zinc bath is used to detoxify wastewater to avoid environmental pollution.
Since this problem does not exist, it is extremely important in practice.

However, a prerequisite for this is that the acidic electrolyte does not contain complexing agents that prevent or make zinc precipitation difficult.

In this case, in the absence of a complexing agent, simple neutralization is sufficient to precipitate the metallic zinc quantitatively as a hydroxide.

However, such electrolytes usually require the addition of ammonium salts in order to obtain a brightness formation and adhesive strength of the zinc deposits that meet the practical requirements to some extent.

So, German Patent Publication No. 1,263,445,
The acidic zinc baths proposed in German Patent No. 1,269,855, German Patent No. 1,521,029 and German Patent No. 1,904,319 each contain a large amount of ammonium salts. Ru.

However, this ammonium salt content is such that, on the one hand, ammonium ions can only be removed quantitatively at great expense, and on the other hand, a small amount of it is already sufficient to have a toxic effect on fish. This makes purification of wastewater extremely difficult.

It was therefore an object of the present invention to provide an acidic zinc bath which allows the electrolytic deposition of bright zinc precipitates while avoiding the disadvantages of the known baths and at the same time ensures that the wastewater is free from toxic substances. be.

This problem is solved according to the invention by the use of substituted heterocyclic compounds having one nitrogen atom or their salts for the electrolytic deposition of bright zinc precipitates while at the same time rendering the waste water free of toxic substances. In an acidic aqueous bath containing ammonium salts and which can be worked with relatively low zinc concentrations and high current densities, the general formula: [where N is pyridine, one or several represents pyridine, pyridone, pyrrole, piperidine, pyrrolidine or pyrrolidinone with the same or different substituted external alkyl, alkenyl, alkoxy or hydroxyl groups, R is a saturated or unsaturated fatty acid having 1 to 3 carbon atoms; represents a group hydrocarbon chain, X represents a -5O3H group or a -COOH group, or a salt thereof with an inorganic or organic base, n represents O or an integer from 1 to 3, and m represents 1
or 2] or its salt from 0.01 to
:ro, 0.9/A' in an acidic electroplating zinc bath.

In the general formula, the radical R representing a saturated or unsaturated hydrocarbon chain represents, for example, methylene, ethylene, propylene, vinylene and vinylidene and others.

Alkyl, alkenyl and alkoxy derivatives of pyridine include, for example, methyl, ethyl, methoxy-
and vinylpyridine.

For salt formation, suitable inorganic and organic bases include, for example, alkali- and alkaline-earth metal hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, zinc hydroxide and N-containing primary, secondary and tertiary bases.

Compounds of the type described are, for example, pyridine-3-acetic acid, pyridine-3-sulfonic acid, pyridine-3-carboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-3° 4-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-4-carboxylic acid,
Pyridine-3-propionic acid, pyridine-2,3-dicarboxylic acid.

4-pyridone-2,6-dicarboxylic acid, 2-methyl-pyridine-5-carboxylic acid, 4-methyl-pyridine-3-
carboxylic acid, 4-ethyl-pyridine-3-carboxylic acid,
2,4-dimethyl-nicotinic acid, 2,6-dimethyl-nicotinic acid, 2,3,4-trimethylpyridine-5-carboxylic acid, 2-vinyl-nicotinic acid, 3-(3-pyridyl)-acrylic acid, 2β-pyridyl-benzoic acid, β-pyridyl-acetic acid, α-[6-methyl-pyridyl-(3)]
Acrylic acid, 6-hydroxynicotinic acid, 4-oxy-2,6-dimethyl-nicotinic acid, 4-oxy-pyridine-3-carboxylic acid, 6-methoxy-pyridine-3-carboxylic acid, β-Cr-piperidylcoic acid -carboxylic acid, L-
Pyrrolidinone-2-carboxylic acid, L-pyrrolidine-2-
It is a carboxylic acid.

These compounds are known per se or can be produced by methods known per se.

The amount of the characterized compound that can be added to the zinc electrolyte is 0.01 to 10.0.9 #1, especially 0.1 to L
O9/l! It is.

As the electrolytic solution, a zinc chloride aqueous solution having a concentration of generally 4 or less is used, that is, 30 to 150 g/l of zinc chloride.

Other zinc salts such as zinc sulfate, zinc acetate and zinc fluoroborate can also be used in place of zinc chloride.

Conductive salts include the additives customary for electrolytes, such as sodium chloride, potassium chloride,
Sodium sulfate and others are added.

The concentration used is about 50-250 i/ill.

Additionally, the electrolyte may contain small amounts of boric acid or aliphatic and/or aromatic carboxylic acids and salts thereof, such as acetic acid, benzoic acid, or salicylic acid.

Although not absolutely necessary, the electrolyte can further contain customary brightening agents, among which are acetophenone, benzylideneacetone, benzoylacetone, 3-acetylcoumarin, 3-acetylpyridine and m - Carbonyl compounds such as oxybenzaldehyde, which are homogeneous (Ein
ebnung), clearly improving the flatness and giving rise to high gloss.

The additives proposed by the present invention and the above-mentioned carbonyl compounds have a synergistic effect in the bath, which far exceeds the expected additive effect, e.g. in improving the behavior during deposition in the high current density range. It seems that it will work.

This carbonyl compound is about 0.01 to 2.0 fl/11
, in particular a mixing ratio of 1 part by weight of the carbonyl compound to 1 to 10 parts by weight of the compound to be characterized should be maintained.

Further additives include other customary gloss-forming agents, such as thio compounds, polymeric compounds and/or aromatic aldehydes, as well as non-foaming wetting agents, in particular anionic alkylol sulfates and ethoxylated amphoteric Compounds can be used, the latter having a range of 0.1 to 309/1. , especially G can be used at a concentration of 1.0 to 10.1/l.

The working conditions of the zinc bath according to the invention are as follows: pH value: 3. O~7.01 Especially 4.5~5.5 Permanence: 15~30'C1 Especially 20~30'C Current density:
0.1 to 2 OA/dm" baths (preferably working in the pH range of 4.5 to 5.5, however this does not significantly reduce the performance) G also works in the neutral range You can also do that.

The bath according to the invention not only has advantages with respect to the treatment of waste water, but also, by the addition of the characterized compounds, the quality of the deposited coating is significantly improved with respect to the gloss effect, with relatively low zinc concentrations and high current densities. can work with.

The bath according to the invention is suitable for the bright galvanizing of materials to be galvanized, including cast iron in frames, drums or bell-shaped devices.

The invention will now be explained with reference to examples.

From this electrolyte, at room temperature, 0.
A current density range of 0.04 - IOA/dm2 has a uniform and good gloss when kneaded, is ductile and strong (it can deposit a zinc coating of any thickness).

This electrolyte produces a somewhat glossy zinc coating of 0 to 3
It can be deposited in a narrow range of A/d m2 (
Not too harsh.

In comparison, this electrolyte has a current density range of 0 to 8 A/d m"4 at room temperature with the addition of pyridine-3-carboxylic acid 0.19/1.
A good shiny zinc coating is deposited throughout.

High gloss zinc coating is lower than this electrolyte by at least 15A//Ct
It is possible to deposit any layer thickness up to a current density of .

This electrolyte produces a bright zinc coating at only about 5A/di.
” can only be deposited up to a maximum current density of .

When 0.49/IJ of pyridine-3-carboxylic acid is added to this electrolyte, a particularly good density distribution (Tiefen-8tre
The current density range for high-gloss zinc deposits with high-gloss zinc deposits extends to at least 15 A/dm''.

This electrolyte deposits a bright zinc coating in the current density range of 0 to about 5 A/d m''.

Above about 5.5 Aid m'', zinc is slightly insufficient.
It simply precipitates as a sticky gray-black powder.

In comparison, this electrolyte contained 0.49/l of pyridine-3-sulfonic acid! A high gloss zinc coating with good adhesion when added with a minimum of 15A/
Deposition can be carried out at current densities of up to 4 .mu.m", which results in deposition rates of about 4 .mu.m/.mu.m".

Next, embodiments of the present invention (related matters) will be listed.

(1) Additionally, carbonyl compounds, especially acetophenone, benzylideneacetone, benzoylacetone,
Zinc bath according to the claims, characterized in that it contains 3-acetyl-coumarin, 3-acetylpyridine or m-oxybenzaldehyde.

(2. A method for electrolytically depositing bright zinc precipitates using the acidic zinc bath described in the claims and item 1 above.

Claims (1)

[Claims] 1. Containing a substituted heterocyclic compound having one nitrogen atom or a salt thereof for electrolytic deposition of a bright zinc precipitate while at the same time making the waste water free from toxic substances. , in an acidic aqueous bath without ammonium salts, which can be worked with relatively low zinc concentrations and high current densities, in the general formula [where N is pyridine, one or several of the same or pyridine, pyridone, pyrrole, piperidine, pyrrolidine or pyrrolidinone with different substituents alkyl, alkenyl, alkoxy or hydroxyl; R is a saturated or unsaturated aliphatic hydrocarbon having 1 to 3 carbon atoms; chain, X represents a -8O3H group or a -COOH group or a salt thereof with an inorganic or organic base, n represents O or an integer from 1 to 3, and m represents
or 2] or its salt from 0.01 to
An acidic electroplating zinc bath characterized in that the bath contains zinc at a concentration of 10.09/l.