DE1935821C - - Google Patents

Description

3. The method according to claim 1, characterized in that it involves an unusually high amount of work indicates that, as salts of the metals, those of the bath management and of the pre- and post-treatment subgroups V and VI of the periodic table, which corresponds to that of the high-performance nickel baths; Vanadates and / or molybdates can be used. 35 and makes the work process considerably more expensive.

Thus, known (German excerpts)

legend 1 150 255) cyanide-free. alkaline zinc

baths in addition to well-known brighteners such as gelatine

The invention relates to a method for and aldehydes (benzaldehyde, vanillin, heliotropin. Production of a gloss additive for aqueous alkaline, 40 anisaldehyde), compounds of the metals, which the Vl. cyanide-free zinc baths for galvanic deposition and VI. Subgroup of the periodic table of the FI Zinc coatings. to belong to. Both according to the doctrine of the

In operational practice, bright zinc - previously published patents - are added to the baths of the most varied kind of application, the adding gelatine as well as some of the as Badje Aldehydes recommended according to their composition in the following 45 additives are in strongly alka groups can be classified as: lisrhemum medium not very resistant. These types of baths

a) strongly alkaline, cyanidic, ko:.

b) strongly alkaline, free of cyanide, set.

c) weakly alkaline, contains pyrophosphate, _o ^ ^{m the} ^ separation of the known

d) ^{To improve slightly acidic 5} ° Batler, one made additional use

e) strongly acidic 'complexing substances, such as

Triethanolamine, polyethyleneimine, ethylenediamine

Of these, the strongly alkaline cyanide tctraacetate, triisopropanolamine, and dimethylamine played as well containing and the strongly acidic bath types up to polyamines (e.g. diethylenetriamine, triethyleneshortcm because of their stability and easy hand- 55 tramin, p-cntaethylene hexamine or hexahabui j a dominant role. Both baths have methylene tetramine). On the one hand, can be through Verjcdoch several, especially in industrial use, of such additives are more important for the electrolyte Disadvantages on, one of which to achieve stability, will be the same / hasty, however, the Abcyanidischen Pictures, including the following, make water treatment much more difficult because the above denomination cn are: 60 named polyamines both zinc and others

Strong toxicity metals even at pH values that would otherwise lead to precipitation

expensive wastewater treatment. ^dcr β «« «1« η metal compounds are sufficient, in com

Keep plexer bond in solution.

Gliinz / .iisiilze for such baths are for example in the combined use of ketones

of the German Auslegeschrift i 133 '.' 58 described. 65 and polyamines as gloss hikers is already before-Im If the strongly acidic zinc hides yell, the Uli have been beaten. The common use

Sufficient syrup and the lack of gloss of these substances for alkaline zinc baths are both

: ils disadvantageous, for example in British patents I 091 171,

1091172 included. The ones in these prior publications Brighteners recommended as bath additives should also work well in the area of higher current densities shiny zinc precipitates result, but the stability of these ketones is even lower than that of the Aldehydes already mentioned, which after a short period of operation of the baths lead to a sharp drop in gloss and leads to a substantial reduction in the applicable current density. For all of the above Bath types and gloss-balancer compositions, however, are the same as compared to the cyanidic zinc baths strongly decreasing current yield curve with decreasing current density characteristic.

In recognition of the identified shortcomings of known alkaline zinc baths, the inventors have the The task is to provide a method for producing a brightener for alkaline cyanide-free zinc baths to develop, cas does not have the deficiencies inherent in the previously known baths.

The object thus posed is achieved according to the invention through the use of a method for the development a gloss additive for alkaline zinc baths, the zinc salts. Alkali hydroxides and other known ones Contain gloss-forming additives, dissolved, in the course of which a mixture consisting of one or more Polyamines, one or more salts of subgroups V and VI of the periodic table and one or more sulfur-containing aliphatic, aromatic or aromatic-heterocyclic compounds, which easily split off sulfur, is caused to react at about 2 ° C. in water resulting reaction product is subjected to a post-reaction at about 70 C in water and finally the reaction with gradual cooling to about 20 ° C with the addition of formaldehyde and Caustic soda is terminated.

The following substances, for example, can be used as sulfur-releasing compounds Find:

Mercapto-thiazoline,

Mercapto pyridine,

Thiourea and its derivatives,

Di-thiocarhamic acid and its derivatives.

Thioacetamide,

Thiocarbanilide.

found that due to the reduced content of complexing agents in the zinc bath according to the specification also the complex-bound zinc in one Dilution of over 1: 100 precipitates and a residual content of dissolved zinc of less than 3 mg / l can be achieved.

Another advantage of the gloss additives: according to the invention results from the compared to the known State of the art, for example

ίο through the examples of the German explanatory document 1 150 255 is described, significantly reduced proportion . of heavy metal salts in the zinc bath, which significantly increases the corrosion resistance of the deposited Zinc coatings result.

The structural design of this reaction product is not yet known in detail, but it would proved by comparative tests that the addition of the individual components to the Zinc baths do not produce the desired results in terms of gloss formation and gloss depth scattering revealed. The results obtained allow the conclusion that the aforementioned reaction product is a metal sulfide amino complex, which is only formed when the reaction conditions already described are observed. Even minor deviations in the reaction temperature or the concentration of the individual components have changes in the course of the reaction result in particular the resistance of the end product in strong have an unfavorable effect on alkaline, cyanide-free zinc baths. The examples below for cyanide-free alkaline zinc baths explain the composition and practical use of the reaction product according to the invention:

35

example 1

50.0 g'l zinc chloride, 230.0 g'I sodium hydroxide, 1.0 g 1 vanillin, 20 ml / 1 reaction product, made from:

2.0 g tetraethylene pentamine, 0.1 g ammonium molybdate, 0.1 g sodium dimethyl dithiocarbamate, 0.5 g formaldehyde 40 ".

0.5 g sodium hydroxide,

Rest water.

40

45

According to the invention, the salts of the metals belonging to subgroups V and VI of the periodic table are found preferably use of vanadates and molybdates. To the improving effect of the bath additive Achieving this in an alkaline, cyanide-free zinc bath is, however, compliance with the following manufacturing conditions described are required. The stated components of the reaction mixture the proportions of which are contained in the examples listed below are in water added and after thorough mixing by adding about 80 ° C hot water a post-reaction subjected to gradual cooling by adding formaldehyde and if necessary Sodium hydroxide is controlled so that a water soluble end product looks.

Al ", the reduced one proves to be particularly advantageous Content of complexing agents in an according to the invention set bright zinc bath compared to the ones made known by the previous publications State of the art.

So was in the context of screening

Example 2

3O ₁ OgZl zinc oxide, 200.0 g / l sodium hydroxide, 1.0 g 1 vanillin, 20 ml / 1 reaction product, made from:

4.0 g pentaethylene hexamine, 0.2 g thiourea,

1.0 g mercapto-thiazoline,

0.1 g of sodium diethyl dithiocarbamate.

0.2 g ammonium molybdate, 0.4 g formaldehyde 35 "/ <. Ig, 0.5 g sodium hydroxide,

Rest water.

Example 3

130.0 g / l zinc sulfate, crystallized, 250.0 g / l sodium hydroxide, 0.4 g / l piperonal, 0.4 g / l vanillin. 20 ml / 1 reaction product, made from:

2.0 B telraethylene pentamine. 1.0 g thiourea,
1.5 g of triethylamine.
1.0 g thioacctnmide,

5 '6

04 g ammonium vanadate, O. ^ g morpholinodithiocarbamic acid

0.5 g formaldehyde 35%, sodium,

0.5 g sodium hydroxide,. 0.15 g ammonium molybdate,

Rest water. 0.2 g formaldehyde 35%,

Example 4 ⁵ 0.4 g thiourea,

^v rest water.

30.0 g / l zinc oxide, 180.0 g / l sodium hydroxide, 0.5 g / l
Vanillin, 20 ml / 1 reaction product, made from: Respective working conditions:

Temperature 10 to 30 ° C

2.0 g of triethylenetetramine, ₁₀ current density 0.5 ibs 4 A / dm ²

0.2 g ammonium molybdal, exposure time 10 to 20 minutes

0.5 g of 4-mercapiopyridine,

0.5 g formaldehyde 35%, "The amounts given in the examples of each

0.5 g sodium hydroxide, because taking into account the specified quantities

Rest water. ₁₅ ratios produced reaction products

Example 5 the zinc baths which are those mentioned in the examples

Menpen contain zinc compounds and caustic soda,

1 g zinc sulfate, 230 g / l sodium hydroxide, 0.5 φ added. Among the same fr '·; specified working heliotropin, 20 ml / 1 reaction product, prepared conditions were obtained with a current yield largely identical to that of cyanide zinc from: 20 baths, 2.0 g of tetraethylene pentamine, and metal distribution brilliantly shiny zinc low-0.6 g of thiazoline thiol.

Claims (2)

In the course of the further development of the patent claims: Relevant industry strongly alkaline, cyanide-free and weakly alkaline, pyrophosphate-containing as well 1. Process for the production of a gloss - weakly acidic high-performance electrolyte offered. So Addition for known alkaline zinc baths, the 5 describes the German Auslegeschrift 1 150 255 a Zinc ointment, alkali hydroxides and the well-known glossy cyanide-free, alkaline glossy zinc bath that is next to Formative additives contain, thereby gelatine, piperonal, vanillin and triethanolamine indicates that a mixture consisting of hexamethylenetetramine contains. The German interpretation one or more polyamines, a script 232 800 describes a cyanide-free, alkali or more salts of the subgroups V io lisches zinc bath to which the polymerization products and VI of the periodic table and one or more of the unsaturated aliphatic carbons Sulfur-containing aliphatic, aromatic hydrogens are added. or aromatic-heterocyclic compounds, by the German Auslegeschrift 1 253 003 are which easily split off sulfur, at about 20 ° C in thio-water in addition to the already mentioned bath additive, the reaction product, which consists of de-urea and vanillin as an effective brightener, has become known at about 70 ° C. Further describes the German AusWasser is subjected to a post-reaction and Legeschrift 1 243 4S8 - which in the additional ratio / v. Finally, the reaction with a gradual removal of the German design table already mentioned: cool to about 20 ° C with the addition of form-1,232,800-triazole derivatives and aromatist. Icaldehyde and caustic soda are terminated. 20 Aldehydes as effective gloss-forming substances. 2. The method according to claim 1, characterized by said and in the publications indicates that bath types easily described as reactive could, however, only the Sulfur-releasing compounds are strongly alkaline, cyanide-free and weakly acidic Mercapto-thiazoline, zinc baths prevail, as those containing pryophosphate Mercapto-Pvridin ^{a5 z} ' ^nk ° veins are complicated to handle and a. Thiourea and its derivatives. make wastewater treatment difficult Dithio-carbamic acid and its derivatives, _A weakly acidic zinc baths, are for example in the Thioacetamide German patent specification 1269 855 and in the German Thiocarbanilid ^'s Ausegeschrift 1 253 986 described ^ 30 The well-known weakly acidic zinc bailci can be used individually or in combination. work partially satisfactorily, but conditionally