DE1294134B - Galvanic bath and process to produce shiny zinc coatings - Google Patents

Description

1 2

The invention is concerned with particularly good zinc coatings containing additives.

Pyrophosphate zinc baths. Twist of a bath obtained, its zinc content

As a replacement for the cyanide bath for galvanic 10 to 60 g per liter, so that a pyro-

Bright galvanizing, alkaline solutions are known, phosphate-zinc weight ratio between 6.5: 1 and the complex compounds of zinc and alkali 5 gives 8.0: 1 and its pH in the range between 10.5

Pyrophosphates contain to keep this way under and 12 is kept.

The combination of brighteners after the Erfin detoxification of the wastewater, which is necessary when using manure with an aldehyde, especially with furfural, and cyanidic baths, has to be avoided. Bis-sulfonaphthyl-methane provides excellent results. The galvanic deposition of zinc from pyrophos- io nisse, which reduces the roughness, increases phatbaths, but with low current densities of the gloss and increase of the coverage shows poor coverage with low, practically no gloss and current densities concerns, with which at the same time a host gives only an uneven coating. Attempts to work ethically is possible. Even with this lack of the bath by adding small, preferred combination of furfural bis-sulfonaphthyl amounts of comparatively expensive additives, such as methane, it has proven to be particularly expedient to add 0-hydroxy-m-methoxybenzaldehyde, vanillin and, if the bis- Sulphonaphthyl methane in a concentration of phenolsulphonate condensation product, removing about 0.9 to 1.6 g per liter of solution and helping, were only partially successful, so that zinc baths the concentration of the aldehyde between about 0.05 pyrophosphate baths containing these aldehydes and is 0.1 g per liter of solution,
have not found any technical application. Ahn- 20 For the addition of the brightener, there are no particular working instructions that apply to some other carbonyls as well. The addition of aldehyde or compounds of the aldehyde and ketone type is most conveniently carried out in the form of a dilute ketone which, although from a certain favorable host, is aqueous solution. In the case of higher concentrations, the pyrophosphate bath is kung, but these additives also contain basic aqueous solutions which do not contain completely flawless, glossy and even alkali metal hydroxide. The moderately smooth electrolytic zinc precipitate and the low resistance of such solutions make good coverage at low current necessary at the same time, so that they can be freshly prepared when required. will be presented. Are solutions required that

It has now been found, completely surprising, that they are more permanent and at least for a certain period of time Defects can be eliminated and stored at a lower temperature than 30, so one dissolves the aldehyde or

Current density from alkaline, aldehydes or ketones ketone in aqueous alcohol.

Zinc pyrophosphate solutions containing zinc never- As a brightener, the following connectors of great uniformity and considerable fertilization have proven to be particularly suitable:
better shine can be obtained if the

According to the invention, solutions as gloss carriers are one of 35 _a) bis-sulfonaphthyl-methane;
following connections

b) naphthalene derivatives:

Bis-sulfonaphthyl-methane, 2,6-naphthalene-disulfonic acid,

a naphthalene derivative, the sulfonic acid or 8-amino-l-naphthalene sulfonic acid,

Alkali sulfonate groups, hydroxyl, amino or 6,6-Immo-bi & -l-naphthol-3-sulfonic acid,

Has imino groups, 2-naphthol-6,8-disulfonic acid,

a benzene derivative, the sulfonic acid or alkali 2,3-dihydroxy-6-naphthalene sulfonic acid,

or ammonium sulfonate groups or alkyl sodium salt,

or has imino groups, or 1,5-dihydroxynaphthalene,

Allylsulfonic acid or one of its alkali salts 45 1,4-dihydroxynaphthalm;

c) Benzene derivatives:

in an amount of about 0.5 to 5.0 g per liter of solution benzene sulfonic acid, sodium salt,

contain. Benzenesulfonic acid amide,

When producing shiny precipitates under toluenesulfonic acid, sodium salt,

Use of the bath according to the invention has 50 o-sulfobenzoic acid imide;

Proven to be advantageous at a bath temperature. _A11 . «.. _XT . ,

to work between about 40 and 50 ° C. ^d > Allylsulfonic acid, sodium salt.

The aldehyde or ketone content of the bath can

about 0.05 to 0.2 g per liter of solution. As aldehydes and ketones can compounds

The brighteners 55 used according to the invention with the structural formulas
can be done in any concentration within the

specified area can be used successfully, "",

however, they are generally preferred in concentrations _χ X _n

trations between about 0.9 and about 1.6 g, C = O and, C = O

used per liter. Aldehyde or ketone are used 60 jj / ^ j> /
preferably at a concentration of about 0.05
applied to about 0.1 g per liter.

It has been shown that the highest gloss of the low- are used, where R is hydrogen, alkyl, aryl

shock can not be achieved if the concentration or heterocyclic radicals with oxygen or

tration of these carbonyl compounds is too low. 65 sulfur atoms and R 'and R "are an alkyl or

A high concentration of these carbonyl compounds means aryl radical. Both the alkyl and the aryl

leads on the other hand to a poorer coverage in groups of R, R 'and R "can substituents such as

low current densities. have about alkoxyl or hydroxyl groups.

From the group of aldehydes, the following compounds are preferred:

m-hydroxybenzaldehyde,

p-hydroxybenzaldehyde,

Piperonal,

o-hydroxybenzaldehyde,

Veratraldehyde,

Benzaldehyde,

/ 3-methoxypropionaldehyde,

Furfural,

Glyceraldehyde,

Anisaldehyde,

Salicylaldehyde propylsultone,

Ethyl vanillin,

Thiophene-2-aldehyde.

Among the ketones, acetophenone, acetylacetone, isophorone and dihydroxyacetone have proven to be special proven expedient.

In the production of shiny zinc coatings using the bath according to the invention can the optimal working conditions, such as pH, temperature and current density, depending on according to the bath composition and the object to be coated within certain limits vary. In general, good shiny zinc deposits can only be found within a specific one Range of working conditions can be achieved. If z. B. the pH significantly above the desired If the pH is too low, the zinc precipitate loses its shine

ίο lies, then the current yield drops. Likewise an increase in temperature leads to a reduction in the gloss of the zinc precipitate, but will this also increases the maximum current density that can be applied without causing the precipitates get rough. An increase in temperature also leads to a decrease in the current yield at the Cathode. Table I summarizes the ranges of bath composition and working conditions, with which coatings with the desired properties can be obtained. The preferred compositions and conditions are also given.

Table I.

area More preferred until area 10 up to 60 20th L to 30th 6.5: 1 to 8.0: 1 7.0: 1 11.0 8.0: 1 10.5 to 12.0 until 40 to 55 45 until 47 0.22 to 4.31 0.43 until 2.15 0.5 to 5.0 0.9 until 1.6 0.05 up to 0.2 0.05 0.1

Zinc concentration, g / l

P ₂ O, / Zn weight ratio

PH value

Temperature, ⁰ C

Current density, A / dm ²

Brightener, g / l

Aldehyde or ketone, g / l

During the separation, the bath should be stirred vigorously but evenly; this can be either be achieved mechanically or with the aid of an air stirrer. When stirred, you can higher current densities are used.

It is of particular importance that any contamination of the bath with foreign metals is avoided to ensure the achievement of a shiny metallic deposit. The strongest disturbances are caused by contamination by the following foreign metals: cadmium, copper and lead. The usual cleaning methods can be used to remove such metallic impurities can be applied. Contamination by organic substances should also be removed. B. by pumping the pyrophosphate solution through an activated carbon filter or through filters from other exchange or absorption media can happen.

The following examples are intended to explain the invention in more detail and the synergistic one To show the effect of the brighteners with the aldehyde or ketone. For each of these examples, a typical pyrophosphate bath with the following basic composition is used:

Zn as Zn ₃ P ₂ O ₇ · xH ₂ O (31% Zn) .. 81 g / l

K ₄ P ₂ O ₇ 290 g / l

Total P ₂ O ₇ 188 g / L

PaO ^ Zn weight ratio 7.5: 1

The pH of the baths was approximately 11 in all cases; its temperature was maintained at about 45 ⁰ C. In each example, the deposition was carried out in a HULL test cell with air circulation, so that the effect of the additives could be observed over a wide current density range. In all examples, the zinc precipitate was applied to a HULL plate with dimensions of 6.35 · 9.84 cm with a current of 1 A per plate for a period of 10 minutes.

To carry out the experiments described in the examples, a HULL plate was first used in each case coated in the basic solution, which did not contain any additives, whereupon for each combination of additives, as listed in the examples, two plates have been provided with a zinc coating by one of which was treated in a bath containing only one additive, while the second was completely was plated according to the method of the invention. The coatings obtained were through visual assessment compared, both in the areas of high current densities and in the areas with low current densities. Also the cover on the back of the panels, which the Identifying scatter was checked visually. The results are shown in Table II. she clearly reveal the synergistic effect of different carbonyl compounds of the nature of the Recognize aldehydes and ketones in connection with bisulfonaphthyl methane as brighteners.

Table II

additive Brightener Area higher
Current density Visual assessment Coverage of
back at
game Aldehyde or
Ketone _ rough roughness: Area lower
Current density low precipitation, 1 _ fine grain and half coarse-grained and matt: the greater part of the shiny, color of even down The back remained without Precipitation: dark blow Precipitation - Roughness less; incomplete coverage 2 m-hydroxy Precipitation shiny fine grain and half benzaldehyde and metallic glittering; Color of Precipitation: dark Bis-sulfo- Roughness less; speckled excellent coverage 0.75 g / l naphthyl Precipitation shiny smoother and shinier methane and metallic Precipitation 1.2 g / l - Roughness less; low precipitation, 3 p-hydroxy Precipitation shiny Precipitation matt and the greater part of the benzaldehyde with veil, unequal unevenly The back remained without moderate Precipitation Bis-sulfo- Precipitation shiny excellent coverage 0.25 g / l naphthyl and metallic Precipitation shiny methane and fine-grained; 1.2 g / l uniformity - Precipitation rough, improved Incomplete coverage 4th Piperonal shiny with veil fine-grained, semi-glossy Bis-sulfo- Precipitation shiny zend, uneven Excellent coverage 0.25 φ naphthyl and metallic Precipitation shiny methane and metallic, the same 1.2 g / l moderate - reduced roughness, low coverage 5 o-hydroxy Precipitation shiny coarse-grained, matte benzaldehyde with veil, unequal
TVIQ RiOr Precipitation, Bis-sulfo- reduced roughness, unevenly excellent coverage 0.05 g / l naphthyl Precipitation shiny better shine and methane with veil, larger ones larger evenly 1.2 g / l uniformity speed - rougher, shinier incomplete coverage 6th Veratraldehyde Precipitation with Precipitation shiny veil and metallic; Bis-sulfo- Precipitation shiny patchy and blotchy excellent coverage 0, IgA naphthyl and metallic Precipitation shiny methane and metallic 1.2 g / l - rougher, shinier incomplete coverage 7th Benzaldehyde Precipitation with fine grain, half Veil, unequal shiny down moderate beat, unevenly iis-sulfo- besides, shinier excellent coverage , 4 g / l naphthyl Precipitation with better shinier methane veil Precipitation 1.2 g / l —— besides, shinier incomplete coverage 8th -Methoxy- Precipitation with coarse-grained, matte propionic Veil, unequal Precipitation, aldehyde moderate unevenly 3is-sulfo- tepid, shinier excellent coverage , 6 g / l naphthyl Precipitation with better shine and methane Veil, unequal larger evenly 1.2 g / l moderate speed

Table II (continued)

additive Brightener Area higher
Current density Visual assessment frosted Coverage of
back at
game Aldehyde or
Ketone somewhat less rough Area lower
Current density low coverage 9 Furfural speed, finer-grained. semi-glossy Precipitation fine grain, half ßis-sulfo- fine grain, half shiny down excellent coverage 0.1 g / l naphthyl shiny down blow methane blow 1.2 g / l fine grain, half - rougher, shinier and shiny down incomplete coverage 10 Glycerinalde- metallic down blow hyd blow, sketchy, unevenly fine grain, half Bis-sulfo- rougher, shinier and shiny down excellent coverage 0.1 g / l naphthyl metallic down blow methane blow, sketchy, 1.2 g / l unevenly shiny down - rougher, shinier blow your veil, low coverage 11 Anisaldehyde Precipitation with uneven, veil sketchy Precipitation shiny Bis-sulfo- rougher, shinier and and metallic incomplete coverage 0.6 g / l naphthyl metallic down methane blow 1.2 g / l fine grain, half - ■ reduced roughness, shiny down incomplete coverage 12th Salicylalaldehyde Precipitation shiny blow, sketchy, hyd-propyl- and metallic unevenly sulton Precipitation stronger Bis-sulfo- reduced roughness, shiny, even excellent coverage 0.05 g / l naphthyl Precipitation shiny methane and metallic 1.2 g / l fine grain, half - rougher, shinier shiny down incomplete coverage 13th Ethyl vanillin Precipitation with beat, unevenly veil stronger shinier Bis-sulfo- rougher, shinier Precipitation excellent coverage 0.4 g / l naphthyl Precipitation with methane veil 1.2 g / l frosted - rougher, shinier incomplete coverage 14th Thiophene Precipitation with 2-aldehyde veil shiny precipitate 3is-sulfo- rougher, shinier with veil excellent coverage 0.2 g / l naphthyl Precipitation with methane veil 1.2 g / l fine grain, half - reduced roughness, shiny down incomplete coverage 15th Acetylacetone shiny down blow from darker blow with veil colour shiny, metallic 3is-sulfo- reduced roughness, looking down excellent coverage naphthyl shiny down blow methane blow with veil 1.2 g / l

The other brighteners in the context of the present invention can be used in a similar manner Achieving a synergistic effect with one

Aldehyde or ketone combine to increase electrolytic zinc precipitation Shine, a greater evenness and a

909518/492

to bring about better coverage in the range of low current densities. The following further examples is the effect of these brighteners on the zinc deposit when used alone and with Use in combination with an aldehyde or ketone. The ones used in these examples Basic solutions and working conditions were the same as in the previous examples.

Example 16

2 g / l 8-amino-1-naphthalene sulfonic acid were dissolved in the pyrophosphate base solution. From this Solution was deposited on a HULL zinc plate. Then the solution that the Containing brightener, 0.1 g / l furfural was added. A second HULL plate was then placed in this solution galvanized. The two plates thus obtained were visually compared with each other. It was clear it can be seen that the coating of the plate treated by the method according to the invention is shinier and was more even and that there was better coverage on the back.

B is ρ ie 1 17 to 22 ^a 5

According to the procedure used in Example 16, the effect of the following brighteners was investigated: 6,6 '- imino - to -1 - naphthol - 3 - sulfonic acid; 2 - naphthol - 6,8 - disulfonic acid; 2,6 - naphthalenedisulfonic acid; 2,3 - dihydroxy - 6 - naphthalenesulfonic acid, sodium salt; 1,5-dihydroxynaphthalene; 1,4-dihydroxynaphthalene, which were used individually in different examples. With the visual Comparison of those obtained in the various examples Plate pairs was the one that had been treated by the method of the invention, either more glossy or more uniform, or showed better coverage of the reverse side.

Example 23 to 26

After the procedure as it was followed in the examples described above, the The effect of benzenesulfonate (sodium salt) as a brightener was investigated and in a concentration of 0.4 g / l applied. The two plates were again compared visually with one another. It turned out that the plate treated by the method according to the invention was superior to that in the solution was coated, which only contained the brightener.

Claims (2)

Patent claims: 1. Galvanic bath for producing shiny zinc coatings, consisting of at least one Zinc salt, an aqueous alkaline pyrophosphate solution containing an aldehyde or ketone, characterized in that as a brightener Bis-sulfonaphthyl-methane, a naphthalene derivative that contains sulfonic acid or alkali sulfonate groups, Has hydroxyl, amino or imino groups, a benzene derivative, the sulfonic acid or Has alkali or ammonium sulfonate groups or alkyl or imino groups, or allylsulfonic acid or one of its alkali salts in an amount of about 0.5 to 5.0 g per liter of solution. 2. A method for producing shiny zinc coatings using a bath according to claim 1, characterized in that the bath temperature is kept ^{between about 40 and 50 0 C during the electrolysis.}