WO2020120388A1 - Zinc electrolyte devoid of boric acid and ammonia for the deposition of electroplated zinc coatings - Google Patents

Abstract

The invention relates to an aqueous electrolyte devoid of boric acid and ammonia for the deposition of electroplated zinc coatings and to a method for producing such electrolyte. The electrolyte comprises (a) Zn2+ in a concentration of 15 to 70 g/L; (b) Cl- in a concentration of 100 to 200 g/L; (c) K+ and/or Na+ overall in a concentration of 0,75 to 6,0 mol/L; (d) acetate in a concentration of 5,0 to 45 g/L; (e) glycine and/or alanine overall in a concentration of 0,5 to 30 g/L; and (f) water. The electrolyte has a pH of 4.5 to 6.5. In a preferred variant, the electrolyte (g) contains nicotinic acid and/or (h) ethoxylated thiodiglycol. The invention further relates to a method for producing such a component having a zinc coating, which uses the electrolyte.

Description

Boric acid and ammonium free zinc electrolyte for the galvanic deposition of zinc coatings

description

Technical field

The invention relates to a boric acid and ammonium-free aqueous electrolyte for the electrodeposition of zinc coatings, a method for producing the electrolyte and a method for producing a component with zinc coating by electrodeposition from the electrolyte.

Technical background

Zinc coatings are used in many technical areas

used because they can provide a very good cathodic protection against corrosion of components, in particular

Iron materials. The zinc coatings can be formed by galvanic (electrochemical) deposition from a zinc electrolyte on the metallic component. The deposition is preferably carried out from weak acid

Electrolytes, because these generally allow much higher deposition rates than alkaline electrolytes. A good deposition speed is important for an economical coating of components, for example accessories for automobile production.

In general there is a good visual impression, i.e. a homogeneous and shiny surface of the zinc coating

wanted. Furthermore, it is technical for many

Applications are also common to temper the zinc coatings. The annealing becomes that in the electro-technical

Coating process expelled hydrogen expelled to counteract the risk of subsequent embrittlement of the component. In the case of high-strength steel components in particular, there is an increased risk of a material hydrogen-induced brittle fracture present. When annealing it is desirable to have bubbles and other defects

are avoided as far as possible and a good visual impression is retained.

So far, it is state of the art for the deposition of zinc coatings a weakly acidic zinc electrolyte

use that contains boric acid as a buffer. Boric acid is considered necessary to be able to work at high current densities (eg 6 to 8 A / dm ² ), which is high

Separation speed is desirable. Boric acid

prevents disorderly and dendritic growth of the zinc layer at high current densities, which for the

Temperability and optical properties of the zinc coating is important. If boric acid is omitted, usually disordered, powdery, black zinc layers are deposited.

Boric acid also prevents the reduction of protons

Hydrogen (2 H ⁺ + 2e -> f), which can occur on the cathode in addition to the reduction of zinc ions to zinc (Zn ²⁺ + 2e -> Zn). The reduction of protons increases the pH in the vicinity of the cathode, since an excess of negatively charged hydroxide ions is generated. This means that zinc hydroxide precipitates directly on the cathode surface and can lead to coating errors.

Boric acid is also characterized by a low price, electrochemical stability, process compatibility and unproblematic wastewater treatment.

However, boric acid and related boron-containing ones apply

Connections, e.g. Disodium tetraborate, diboron trioxide and tetraborine sodium heptaoxide, as toxic for reproduction

(teratogenic) category 1B and were included in the candidate list for the REACh regulation on June 18, 2010. The European Chemicals Agency (ECHA) spoke up

01.07.2015 after thorough examination and consideration of all Known data and facts for the inclusion of boric acid in Annex XIV of the REACh regulation on substances subject to authorization and submitted a corresponding recommendation to the EU Commission. Although boric acid and the other boron compounds mentioned above meet the criteria for inclusion in Annex XIV of the REACh regulation, the EU Commission decided not to use these compounds initially

Classification subject to approval (Regulation (EU) 2017/999, on June 13, 2017 in the Official Journal of the European Union

released) .

Even if boric acid is not (yet) in the EU

is subject to approval, it would be for reasons of

Sustainability and occupational safety are desirable to reduce or avoid the use of boric acid.

Occasionally, boric acid-free electrolytes containing zinc have been described in the literature:

In a publication by J. Heber (Galvanotechnik, 2014, Vol. 105, 2150-2156) it was proposed to replace boric acid with acetic acid. In this publication it was noted that by using acetic acid the

Application at high current densities is limited. Furthermore, the exchange of boric acid with acetic acid worsens the metal distribution on the substrate and the cloud point (temperature at which the organic additives fail) is reduced. Furthermore, a lower one

Current efficiency as observed with boric acid.

EP 2 706 132 A1 describes the use of a boric acid-free, weakly acidic zinc-nickel electrolyte, which in particular uses a mixture of adipic acid, succinic acid, glutaric acid, sulfosuccinic acid and propionic acid to replace boric acid. In addition to these organic acids used as buffer substances, a zinc-nickel electrolyte also requires stronger complexing agents (e.g. DETA or EDA) for the nickel, so that sufficient nickel (typically 12 to 15% by weight) can be incorporated into the zinc-nickel layer. These complexing agents in turn require complex wastewater treatment.

DE 2 251 103 Al describes an acidic zinc electrolyte which is free of boric acid. In addition to zinc sulfate and zinc chloride, the electrolyte contains sodium succinate, nicotinamide and large amounts of ammonium chloride. The use of

However, ammonium chloride and other ammonium salts are environmentally problematic, because ammonium or ammonia should not get into the wastewater. One reason for this is that ammonia is a very good ligand for various heavy metals and increases their mobility. The use of

Ammonium compounds is problematic because of that

Waste water treatment not desirable.

US 4,877,497 describes an acidic zinc electrolyte which contains no boric acid. The electrolyte contains

essential zinc chloride, ammonium chloride or potassium chloride. Succinic acid, acetic acid, lactic acid, malonic acid, adipic acid, tartaric acid and citric acid or their salts can also be present. The pH is preferably between 3 and 4. Ammonium chloride requires complex process wastewater treatment, as already described above. The low pH values in these electrolytes lead to a high solubility of the zinc anodes (anode solubility). The high anode solubility means that

When the electrolyte is not operating, a steady increase in the zinc concentration in the electrolyte is observed.

As described above, it is desirable, above all for health reasons and in terms of occupational safety, to reduce the use of boric acid in zinc electrolytes and, in particular, to avoid it altogether. Likewise, other CMR substances, i.e. substances that are carcinogenic, mutagenic or

reproductive are avoided. Ammonium chloride should be for ecological reasons due to the

Waste water problems can be avoided. There is therefore a need for a zinc electrolyte that does not require boric acid or ammonium chloride and yet can be operated economically and is largely harmless from a health and ecological point of view. The electrolyte should be the

Allow deposition of shiny zinc layers even at high current densities.

Summary of the invention

The invention has for its object to provide a zinc electrolyte for the galvanic deposition of zinc coatings, which does not contain boric acid and

Ammonium compounds needed. The zinc electrolyte is said to be able to be operated in particular at high current densities and to use buffer substances which are ecological and

are largely harmless to health. The electrolyte is intended in particular to deposit shiny zinc coatings with an advantageous visual impression

enable. Furthermore, the electrolyte should preferably also enable the galvanic deposition of temperable zinc coatings, which also have good mechanical properties after the tempering

Have properties and give a good visual impression. Other tasks are to develop a process for

Production of the zinc electrolyte and a method for

Production of a component with a zinc coating, which

To provide electrolyte used for galvanic deposition of zinc.

These tasks are accomplished through the zinc electrolyte, the

Process for its preparation and the process for

Production of a component with zinc coating according to the

independent claims solved. The present invention relates in particular to the following:

(1) Boric acid and ammonium free aqueous electrolyte for electrodeposition of zinc coatings, comprising:

(a) Zn ²⁺ in a concentration of 15 to 70 g / L;

(b) CI in a concentration of 100 to 200 g / L;

(c) Total K ⁺ and / or Na ⁺ in a concentration of

0.75 to 6.0 mo1 / L;

(d) acetate at a concentration of 5.0 to 45 g / L;

(e) total glycine and / or alanine in a concentration of 0.5 to 30 g / L; and

(f) water;

wherein the electrolyte has a pH of 4.5 to 6.5.

(2) Electrolyte according to (1), the concentration of Zn ²⁺

Is 20 to 60 g / L.

(3) Electrolyte according to (1) or (2), the concentration of Zn ^{2+ being} 25 to 50 g / L, preferably 35 g / L.

(4) electrolyte according to any one of (1) to (3), wherein the

Concentration of CI is 120 to 190 g / L.

(5) electrolyte according to any one of (1) to (4), wherein the

Concentration from CI 130 to 180 g / L, preferably 160 g / L.

(6) electrolyte according to any one of (1) to (5), wherein the

Concentration of K ⁺ 0.75 to 6.0 mol / L is.

(7) electrolyte according to any one of (1) to (6), wherein the

Concentration of K ⁺ 2.7 to 4.8 mol / L is.

(8) electrolyte according to any one of (1) to (7), wherein the

Concentration of K ⁺ 3.3 to 4.1 mol / L is.

(9) Electrolyte according to one of (1) to (8), optionally containing Na ⁺ at 0 to 0.5 mol / L, preferably 0 to 0.2 mol / L.

(10) Electrolyte according to one of (1) to (9), wherein Zn ²⁺ , K ⁺ and Na ⁺ at least 95% by weight, preferably at least 98% by weight, most preferably at least 99% by weight or Make up 100% by weight of all cations in the electrolyte.

(11) Electrolyte according to one of (1) to (10), wherein Zn ²⁺ and K ⁺ at least 90% by weight, preferably at least 95% by weight, most preferably at least 99% by weight or 100%. - Make up% of all cations in the electrolyte. (12) Electrolyte according to any one of (1) to (11), wherein the

Concentration of acetate is 7.5 to 30 g / L.

(13) electrolyte according to any one of (1) to (12), wherein the

Concentration of acetate is 10 to 20 g / L, preferably 12 g / L.

(14) Electrolyte according to any one of (1) to (13), wherein the

The total concentration of glycine and / or alanine is in the range from 0.5 to 20 g / L.

(15) electrolyte according to any one of (1) to (14), wherein the

The total concentration of glycine and / or alanine is in the range from 1.0 to 10 g / L.

(16) Electrolyte according to any one of (1) to (15), wherein the

The total concentration of glycine and / or alanine is in the range from 1.5 to 5 g / L, preferably 2.5 g / L.

(17) Electrolyte according to one of (1) to (16) containing glycine and optionally 0 to 1.5 g / L, preferably 0 to 0.5 g / L, alanine.

(18) electrolyte according to any one of (1) to (17) containing (g)

Nicotinic acid in a concentration of 0.01 to 2.0 g / L.

(19) electrolyte according to any one of (1) to (18) containing (g)

Nicotinic acid in a concentration of 0.5 to 1.0 g / L.

(20) Electrolyte according to one of (1) to (19), containing (g)

Nicotinic acid in a concentration of 0.08 to 0.5 g / L, preferably 0.1 g / L.

(21) Electrolyte according to one of (1) to (20) containing (h) ethoxylated thiodiglycol with an average of at least 20 structural units derived from ethylene oxide in a concentration of 0.3 to 10 g / L.

(22) Electrolyte according to one of (1) to (21) containing (h) ethoxylated thiodiglycol with an average of at least 20 structural units derived from ethylene oxide in a concentration of 0.5 to 5 g / L.

(23) Electrolyte according to one of (1) to (22), containing (h) ethoxylated thiodiglycol with an average of at least 20 structural units derived from ethylene oxide in one

Concentration from 1.0 to 3.5 g / L, preferably 2.1 g / L. (24) Electrolyte according to any one of (1) to (23), wherein the pH is 4.5 to 6.0, preferably 4.8 to 5.3.

(25) A method for producing an electrolyte according to any one of (1) to (24), comprising the steps:

A) creating an aqueous solution of

(a ') zinc chloride and / or zinc acetate;

(b ') potassium chloride and / or sodium chloride;

(c ') at least one of potassium acetate, sodium acetate and

Acetic acid;

(d ') at least one of the group consisting of glycine, a salt thereof, alanine and a salt thereof; and (e ') optionally nicotinic acid or a salt thereof; and

(f ') optionally ethoxylated thiodiglycol with an average of at least 20 structural units derived from ethylene oxide; and

B) optionally adjusting the pH to 4.5 to 6.5 by adding hydrochloric acid or by adding

Potassium hydroxide and / or sodium hydroxide, which can be added as a solid or in the form of an aqueous solution.

(26) A method of manufacturing a zinc-coated component, comprising electrodepositing zinc on a metallic component from an electrolyte according to any one of (1) to (24).

(27) Method according to (26), wherein the metallic component comprises or consists of iron or an iron alloy.

(28) Method according to (26) or (27), wherein at one

Temperature of 20 to 50 ° C is deposited.

(29) Method according to one of (26) to (28), wherein the deposition is carried out at a temperature of 25 to 40 ° C.

(30) The method according to any one of (26) to (29), wherein the

Current density when depositing from 0.2 to 10 A / dm ² .

(31) The method according to any one of (26) to (30), wherein the

Current density when depositing 0.5 to 8.0 A / dm ² , preferably 1.0 to 8.0 A / dm ² .

(32) The method according to any one of (26) to (31), wherein the

Current density when depositing 0.5 to 6 A / dm ² , preferably 2.0 to 6 A / dm ² . (33) Method according to one of (26) to (32), wherein the zinc-coated component is subjected to a passivation treatment after the electrodeposition.

(34) Method according to one of (26) to (32), wherein the component with a zinc coating is annealed after the electrodeposition, optionally before or after a passivation treatment.

(35) Process according to (34), wherein the temperature during annealing is 180 to 230 ° C, preferably 200 to 230 ° C.

(36) Method according to (34) or (36), wherein the annealing is carried out for 2 to 24 h.

Detailed description

(1) It becomes a boric acid and ammonium free aqueous

Electrolyte for the galvanic deposition of zinc coatings (also referred to herein as "electrolyte" or "zinc electrolyte"). The electrolyte includes:

(a) Zn ²⁺ in a concentration of 15 to 70 g / L;

(b) CI in a concentration of 100 to 200 g / L;

(c) Total K ⁺ and / or Na ⁺ in a concentration of

0.75 to 6.0 mo1 / L;

(d) acetate at a concentration of 5.0 to 45 g / L;

(e) total glycine and / or alanine in a concentration of 0.5 to 30 g / L; and

(f) water.

The electrolyte has a pH of 4.5 to 6.5.

At this pH, acetate can be in protonated and / or deprotonated form. Glycine or

Alanine is also present in protonated and / or deprotonated form.

Surprisingly, it was found that with the special

Combination of acetate with glycine and / or alanine in the concentrations given above does not require the addition of boric acid or the addition of ammonium to provide versatile zinc electrolyte for the galvanic deposition of zinc coatings. Acetate and glycine or alanine serve, among other things, as buffer substances in order to keep the pH in the electrolyte constant. Acetate and the amino acids glycine and alanine are, of course, completely harmless from both a health and ecological point of view and can be disposed of via waste water without any problems. Furthermore, acetate, glycine and alanine are inexpensive and available almost indefinitely and therefore represent a particularly advantageous substitute for the use of boric acid or related boron compounds as well as ammonium compounds such as ammonium chloride.

With the electrolyte according to the invention, zinc coatings can be deposited over a practical current density range such as 0.2 to 8 A / dm ² . Especially at high

Current densities, i.e. in the range of 6 to 8 A / dm ² , can significantly improve the quality of the

deposited zinc coatings in the form of the optical impression, that is to say a homogeneous gloss and reduction in burns compared to zinc electrolytes without these substances. "Burn-ons" are generally understood to mean mis-colored, dark, amorphous or coarsely crystalline, mostly powdery areas, as a result of which the zinc coating can become unusable for many applications.

The electrolyte is suitable for metallic components

(Substrates) with dense, homogeneous zinc coatings

coat that provide good, adherent corrosion protection, for example on iron or iron alloys.

It was also possible to produce temperable zinc coatings with the zinc electrolyte. With the buffer substances acetate, glycine or alanine, the evolution of hydrogen,

in particular at high current densities, are reduced during the electrodeposition, as a result of which pH changes in the electrolyte and the precipitation of zinc hydroxide on the cathode are reduced or avoided. Another advantage that results from the combination of acetate and glycine is that it is versatile

Process control in the electrodeposition is made possible. For example, zinc salts and conductive salts

(Potassium chloride or sodium chloride) in broad

Concentration ranges are used and the temperature can be varied over a wide range such as 15 to 50 ° C. The electrolyte is also suitable for common ones

Separation devices, for example drum or

Molding devices.

Another advantage of these buffer compounds is that they bind only weakly to most foreign metals such as iron. Iron can therefore be readily present in the presence of this

Buffer compounds in the form of iron (III) hydroxide (Fe (OH) _{3) are} precipitated and removed. Furthermore, the

Buffer compounds do not increase anode solubility (usually zinc anodes) when the electrolyte is not in use. This is beneficial because the concentrations are not

operated electrolyte remain largely constant.

(2) The zinc salts naturally serve to provide the metal to be deposited zinc. Because the zinc salts in the

Once the electrolyte is dissolved, it is often no longer possible to determine which counterion was present in the zinc salt. For this reason, the essential Zn ²⁺ concentration in the electrolyte is given here. Basically everyone can

water-soluble zinc salts such as Zinc sulfate,

Zinc methanesulfonate, zinc acetate and zinc chloride are used. It goes without saying that all types of salts, for example anhydrous salts or salts with

Crystal water, can be used. Zinc acetate and / or zinc chloride are preferably used because the anions are acetate and chloride for the buffering action or

Improving the conductivity of the electrolyte are advantageous and the galvanic zinc deposition is not disadvantageous affect. Zinc chloride is particularly preferred

due to the better conductivity, its good solubility and for reasons of economy.

As mentioned above, the zinc concentration can vary over a wide range and so can the electrolyte

specifically adapted to different needs. The concentration of Zn ²⁺ in the electrolyte is 15 to 70 g / L. The concentration of Zn ²⁺ is in particular 20 to 60 g / L, preferably 25 to 50 g / L, more preferably 30 to 40 g / L and most preferably 35 g / L. If the zinc concentration is too low, it increases

Separation speed. If the zinc concentration is too high, solubility problems can occur. With the zinc concentrations according to the invention, both the deposition rate, the stability of the zinc electrolyte and the quality of the zinc coatings are particularly good.

(3) In addition to zinc, which is of course required for the formation of the zinc coating, the electrolyte also contains one or more conductive salts. Conductive salts increase the conductivity of the electrolyte, which is important in order to be able to coat with zinc at high current densities and with a good deposition rate. Potassium chloride and / or sodium chloride are used in particular as conductive salts. Is preferred

Potassium chloride because it has a higher conductivity than

Sodium chloride.

The conductive salt is naturally dissolved in the electrolyte, which is why the concentrations of the respective ions are given here. The concentration of CI in the electrolyte is 100 to 200 g / L. The concentration of CI can in particular be 120 to 190 g / L, preferably 130 to 180 g / L and more preferably 160 g / L. At these chloride or the corresponding conductive salt concentrations, the

Electrolyte are operated well. (4) The cations K ⁺ and / or Na ⁺ can get into the electrolyte from different reagents. On the one hand, K ⁺ and / or Na ⁺ come from the conductive salt described above. Furthermore, these ions can also be introduced into the electrolyte as a component of other salts. For example, acetate, glycine or alanine and other weak acids can also be in the form of the corresponding potassium salt and / or

Sodium salt can be used for the formation of the electrolyte.

Potassium and sodium are naturally harmless from a health and ecological point of view and do not interfere with

Handling the electrolyte. The electrolyte can, but does not have to, contain other cations in addition to Zn ²⁺ and K ⁺ and / or Na ⁺ . Zn ²⁺ , K ⁺ and Na ⁺ preferably make up at least 95% by weight, more preferably at least 98% by weight, most preferably at least 99% by weight or 100% by weight of all cations in the electrolyte. Because of the advantages of potassium chloride described above, the electrolyte preferably contains Zn ²⁺ and K ⁺ . Zn ²⁺ and K ⁺ can make up at least 90% by weight, more preferably at least 95% by weight, most preferably at least 99% by weight or 100% by weight of all cations in the electrolyte.

The total concentration of K ⁺ and / or Na ⁺ in the

Electrolyte is in the range of 0.75 to 6.0 mol / L. Because of the different masses of K ⁺ and Na ⁺ , the

Mol concentration stated. The electrolyte preferably contains K ⁺ and optionally Na ⁺ , the concentration of K ^{+ being} 0.75 to 6.0 mol / L, in particular 2.7 to 4.8 mol / L, preferably 3.3 to 4.1 mol / L, is. The concentration of Na ⁺ is preferred

0.5 mol / L or less, and more preferably 0.2 mol / L or less, which includes 0 mol / L (i.e. 0 to 0.5 mol / L or 0 to 0.2 mol / L).

(5) As already mentioned above, the electrolyte contains acetate as a buffer substance. With the pH prevailing in the electrolyte A value of 4.5 to 6.5, the acetate (AcCr) is naturally in equilibrium with the conjugate acid (AcOH = acetic acid). AcCr and AcOH form a conjugated acid-base pair, or the deprotonated and protonated form of the acetate. At low pH values, the proportion of the conjugate acid

(protonated form) higher than at higher pH values. As

Acetate reagent, ie as a source for the acetate in the electrolyte, at least one of potassium acetate, sodium acetate and acetic acid, preferably potassium acetate, can be used.

The statement of the concentration of the acetate relates to the mass of the acetate ion (AcO), that is to say the mass of the

deprotonated form, regardless of how large the

Equilibrium proportion of the conjugate acid (AcOH), i.e. the protonated form. It can be calculated from the amount of acetate reagent added. The concentration of acetate in the electrolyte is 5.0 to 45 g / L. she can

in particular 7.5 to 30 g / L, preferably 10 to 20 g / L, most preferably 12 g / L.

On the one hand, the acetate serves as a buffer substance to keep the pH of the electrolyte constant. Furthermore, the acetate helps to produce shiny and tempered zinc coatings. In particular at high current densities, acetate turned out to be essential for the operation of the electrolyte. If the acetate concentration (which includes the conjugate acid as described above) is too low, the desired effects are insufficiently obtained. Solubility problems may occur at higher concentrations. The economics of the electrolyte and the quality of the zinc coatings are best in the preferred areas.

(6) As already stated above, the electrolyte also contains glycine and / or alanine in addition to acetate, which also serve as buffer substances. Glycine and / or a water-soluble salt thereof can be used as the source of the glycine. Alanine and / or a can be used as the source of the alanine water-soluble salt thereof can be used. At least one of glycine, potassium salt of glycine is preferred

(Potassium glycinate), sodium salt of glycine (sodium glycinate), alanine, potassium salt of alanine (potassium alaninate) and

Sodium salt of alanine (sodium alaninate) used.

Glycine and / or alanine are particularly preferably used. Glycine is most preferably used.

Glycine has two _pK values, so may be a function of the pH from 4.5 to 6.5, glycine in equilibrium in several species in the electrolyte. Glycine can

basically completely protonated (H ₃ N-CH2-C02H ⁺ ,

protonated form), externally neutral (H2N-CH2-CO2H or H ₃ N ⁺ -CH2-C02) and completely deprotonated (H2N-CH2-CO2A deprotonated form) are present in the electrolyte. The species form conjugated acid-base pairs. The same applies to alanine, which also completely protonates

(H ₃ N-CHCH ₃ -C0 ₂ H ⁺ , protonated form), externally neutral (H ₂ N-CHCH ₃ -C0 ₂ H or H ₃ N ⁺ -CHCH ₃ -C0 ₂ ) and complete

deprotonated (H ₂ N-CHCH ₃ -C0 ₂ , deprotonated form) in

Electrolyte can be present.

The statement that acetate, glycine or alanine also in

protonated and / or deprotonated form can express that acetate, glycine or alanine in all protonated, deprotonated or externally neutral species occurring at pH values from 4.5 to 6.5

may occur. The species automatically form in equilibrium in the electrolyte at the corresponding pH, as is typical for weak acids and is known to the person skilled in the art.

The concentration of glycine or alanine is

regardless of which of the species is in equilibrium or is in equilibrium, with respect to the mass of glycine (H ₂ N-CH ₂ -C0 ₂ H) or alanine (H ₂ N-CHCH ₃ - CO2H) as such calculated. This is in the electrolyte Concentration of glycine and / or alanine total 0.5 to 30 g / L. The concentration of glycine and / or alanine can in particular be 0.5 to 20 g / L, preferably 1.0 to 10 g / L, more preferably 1.5 to 5 g / L and most preferably 2.5 g / L, be. If the electrolyte contains too little glycine or alanine, the desired effects are only insufficiently obtained. Solubility problems may occur if the amounts are too large.

The electrolyte preferably contains glycine and optionally alanine. In this embodiment, the electrolyte preferably contains glycine in a concentration of 0.5 to 20 g / L, more preferably 1.0 to 10 g / L, even more preferably 1.5 to 5 g / L and most preferably 2.5 g / L, and alanine in a concentration of less than 1.5 g / L and more preferably 0.5 g / L or less, which includes 0 g / L (i.e. 0 to 1.5 g / L or 0 to 0.5 g / L).

As stated above, the pH of the

Electrolytes 4.5 to 6.5. It can preferably be 4.5 to 6.0 and more preferably 4.8 to 5.3. At these pH values, good separation rates and low

Anode solubility observed. The pH of the electrolyte can only result from the composition of the components. It is also possible to adjust the pH as described below.

According to a further embodiment, the electrolyte also contains one or more further buffer substances. The further buffer substance is in particular at least one

Buffer substance selected from the group consisting of succinic acid, adipic acid, malic acid, 2- (N-morpholino) ethanesulfonic acid, tris (hydroxymethyl) aminomethane, triethanolamine, taurine, b-alanine, glutamic acid,

Glycylglycine, threonine, bicine, tricine, ascorbic acid,

Citric acid and salts thereof. The salts are especially potassium and / or sodium salts. The additional buffer substance is therefore optional and can be used in a concentration of 0.1 to 40 g / L.

(7) It goes without saying that the various embodiments are those present in the electrolyte

Components can be combined with one another as desired. According to a preferred variant, the electrolyte contains:

(a) Zn ²⁺ in a concentration of 20 to 60 g / L;

(b) CI at a concentration of 120 to 190 g / L;

(c) K ⁺ in a concentration of 2.7 to 4.8 mol / L and 0 to 0.5 mol / L Na ⁺ ;

(d) acetate at a concentration of 7.5 to 30 g / L; and

(e) Total glycine and / or alanine in a concentration of 0.5 to 20 g / L.

According to a preferred development of this variant, the electrolyte contains:

(a) Zn ²⁺ in a concentration of 20 to 60 g / L;

(b) CI at a concentration of 120 to 190 g / L;

(c) K ⁺ in a concentration of 2.7 to 4.8 mol / L and 0 to 0.5 mol / L Na ⁺ ;

(d) acetate at a concentration of 10 to 20 g / L; and

(e) Glycine and / or alanine in a concentration of 1.0 to 10 g / L.

According to a further preferred development of this variant, the electrolyte contains:

(a) Zn ²⁺ in a concentration of 20 to 60 g / L;

(b) CI at a concentration of 120 to 190 g / L;

(c) K ⁺ in a concentration of 2.7 to 4.8 mol / L and 0 to 0.2 mol / L Na ⁺ ;

(d) acetate at a concentration of 10 to 20 g / L; and

(e) Glycine in a concentration of 1.5 to 5 g / L and 0 to 0.5 g / L alanine.

(8) According to a further embodiment, the

Electrolyte additionally (g) nicotinic acid and / or (h) ethoxylated thiodiglycol. The electrolyte particularly preferably contains nicotinic acid and ethoxylated thiodiglycol.

Nicotinic acid as such or water-soluble salts thereof, in particular the potassium and / or sodium salt thereof, can be used as the source of nicotinic acid. Simply nicotinic acid is preferably used.

Because nicotinic acid is a weak acid, it can balance the protonated and deprotonated form at pH 4.5 to 6.5 in the electrolyte

conjugated acid-base pair. Nicotinic acid can therefore be present in the form of the conjugate base and / or the conjugate acid analogously to the acetate and glycine or alanine.

The concentration is calculated in relation to the mass of nicotinic acid (C ₆ H ₅ NO ₂₎ as such. The concentration of

Nicotinic acid in the electrolyte is in particular 0.01 to 2.0 g / L, preferably 0.05 to 1.0 g / L, more preferably 0.08 to 0.5 g / L, most preferably 0.1 g / L L.

It was found completely surprisingly that the addition of small amounts of nicotinic acid significantly improves the quality of the zinc coatings even at high current densities such as 6 to 8 A / dm ² . In addition to the visual impression

(Gloss) of the deposited zinc coatings, in particular their tempering ability is further improved. Even at high current densities, temperable zinc coatings can be produced which, after tempering, have little or no defects such as bubbles and have a very advantageous optical impression, that is to say a homogeneous gloss without clouding or fog. The concentration is on

If nicotinic acid is too high, the formation of fog or clouding in the zinc coating can increase again.

(9) Ethoxylated thiodiglycol is an oligomeric or polymeric compound that results from the addition reaction of Thiodiglycol (HO-CH2-CH2-S-CH2-CH2-OH) with ethylene oxide

(Oxirane, C2H4O) is obtained. A suitable ethoxylated thiodiglycol has an average of at least 20

Structural units derived from ethylene oxide.

It preferably has an average of 20 to 100

Structural units derived from ethylene oxide. With fewer structural units derived from ethylene oxide, the beneficial effects could not be observed to the same extent.

Ethoxylated thiodiglycol can be in the form of an aqueous

Solution are added to the electrolyte. Is on sale

ethoxylated thiodiglycol, for example as 70%

aqueous solution available, such as CHE ED 7127 70% (from Erbslöh) or Aduxol TDG-027 70% (from Schärer & Schläpfer).

The concentration of the ethoxylated thiodiglycol with

an average of at least 20 structural units derived from ethylene oxide in the electrolyte can be 0.3 to 10 g / L, preferably 0.5 to 5 g / L, more preferably 1.0 to 3.5 g / L and most preferably 2 , 1 g / L.

Completely surprisingly, it was also found for the ethoxylated thiodiglycol described above that the quality of the zinc coatings is significantly improved even at high current densities such as 6 to 8 A / dm ² . In addition to the visual impression (gloss) of the deposited zinc coatings, their tempering ability in particular is further improved. Even at high current densities, temperable zinc coatings can be produced that have little or no defects such as bubbles after annealing and one

have a favorable visual impression. With too high

Concentrations, the visual impression of the zinc coatings deteriorates again.

(10) According to a further variant of the electrolyte, it contains (g) Nicotinic acid in a concentration of 0.05 to 1.0 g / L, and / or

(h) Average ethoxylated thiodiglycol

at least 20 structural units derived from ethylene oxide in a concentration of 0.5 to 5 g / L.

The advantageous effects of nicotinic acid and ethoxylated thiodiglycol are, as stated above, quite similar, although the substances are structured quite differently.

It was also surprisingly found that the advantageous properties of the zinc coatings can be improved once again by using a combination of nicotinic acid and ethoxylated thiodiglycol. The electrolyte therefore preferably contains nicotinic acid and ethoxylated thiodiglycol, in particular those specified above

Concentrations.

In addition to the components described above, the electrolyte can also contain one or more conventional additives for zinc electrolytes in suitable amounts, as is known per se to the person skilled in the art. The electrolyte can, for example, at least one additive from the group consisting of

Wetting agents (e.g. alkoxylated ß-naphthol), base gloss (e.g. sodium benzoate), solubilizers or hydrotropes (e.g. sodium cumene sulfonate) and brighteners (e.g.

Benzalacetone and / or o-chlorobenzaldehyde).

Wetting agents serve to lower the surface tension of the electrolyte and ensure good wetting of the surface to be coated. Solubilizers or hydrotropes ensure a sufficiently good solubility for

organic substances. In combination, basic glossers and brighteners serve to further control the degree of gloss and

Brilliance of the zinc coating.

Suitable additives are commercially available. For example, at Schlotter SLOTANIT BSF 1668 (an additive for zinc electrolytes, which wetting agents and Contains basic gloss) and SLOTANIT BSF 1662 (an additive for zinc electrolytes, which contains solubilizers and brighteners). These additives can be used in customary amounts according to the corresponding use and

Work instructions from the manufacturer are used.

(11) As a further aspect of the invention there is provided a method for producing the electrolyte according to one of the above

described embodiments provided. The process includes the steps:

A) creating an aqueous solution of

(a ') zinc chloride and / or zinc acetate;

(b ') potassium chloride and / or sodium chloride;

(c ') at least one of potassium acetate, sodium acetate and acetic acid;

(d ') at least one of the group consisting of glycine, a salt thereof, alanine and a salt thereof; and

(e ') optionally nicotinic acid or a salt thereof; and (f ') optionally ethoxylated thiodiglycol with

an average of at least 20 structural units derived from ethylene oxide; and

B) optionally adjusting the pH to 4.5 to 6.5

by adding hydrochloric acid or by adding

Potassium hydroxide and / or sodium hydroxide, which as

Solid or in the form of an aqueous solution can be added.

In step A), an aqueous solution of the components is generated. The components can be added in the order given or in any other order. Further buffer substances and additives as described above can also be contained in the aqueous solution. In particular (g ') customary wetting agents, base glosses, solubilizers and brighteners can be added to the aqueous solution, for example the additives SLOTANIT BSF 1668 and SLOTANIT BSF 1662 from Schlotter. Regarding of the components and the respective embodiments of the electrolyte is made to the above statements.

To step A), in particular (a ') to (c')

accelerate, the mixture can be mixed, in particular stirred. Furthermore, it can also be heated for acceleration, for example to 60 ° C. After formation of the aqueous solution can then again to a lower

Temperature can be cooled.

The pH of the electrolyte from 4.5 to 6.5 can result solely from the composition of the components. It is also possible to adjust the pH in an optional step B)

adjust. This can be done by adding hydrochloric acid to lower the pH. For example, the hydrochloric acid can be diluted (1N) or more concentrated. Concentrated hydrochloric acid (approx. 12 N) can also be used. 5 or 6 N (semi-concentrated) hydrochloric acid is particularly suitable because it can be handled quite safely and does not lead to any significant thinning of the electrolyte.

The pH can be lowered by adding potassium hydroxide and / or sodium hydroxide. These bases can be used as

Solid or in the form of an aqueous solution. For example, 50% potassium hydroxide solution (KOH) can be used.

Hydrochloric acid, potassium hydroxide and sodium hydroxide are particularly suitable because they do not introduce any additional ions into the electrolyte.

(12) As a further aspect of the invention, a method for producing a component with a zinc coating is provided. The method comprises the galvanic deposition of zinc on a metallic component from an electrolyte according to one of the embodiments described above. (13) Basically any metallic substrate can be used that is suitable for the galvanic deposition of zinc. The component preferably comprises iron or an iron alloy or consists entirely of it. For example, accessories for the automotive industry can be coated with zinc. The process can also be used, for example, for the galvanic deposition of zinc coatings on components made of cast materials such as

Use forged cast iron or gray cast iron.

As a rule, the component is pretreated before galvanic deposition in order to clean it, in particular to degrease it. Suitable measures are known to the person skilled in the art and suitable reagents are commercially available.

For example, the component, e.g. a steel sheet, first 1) degreased in a hot cleaning solution, 2) pickled in acid (e.g. semi-concentrated hydrochloric acid), 3) electrolytically degreased and then 4) picked up with dilute hydrochloric acid. After steps 1) to 4), rinsing with water is carried out.

(14) Usual for galvanic deposition

Conditions are used. As stated above, it is possible with the electrolyte according to the invention to vary the temperature over a wide range. The temperature for the electrodeposition can in particular be 20 to 50 ° C., preferably 25 to 40 ° C.

Practical current densities, for example 0.2 to 10 A / dm ² , in particular 0.5 to 8.0 A / dm ² , preferably 1.0 to 8.0 A / dm ² or 0.5 to 6 A / dm ² , more preferably 2.0 to 6 A / dm ² , are applied. As a result, the process can be operated with good economy.

If desired or necessary, the pH can be adjusted during the process. The procedure can be analogous to step B) described above. Iron can optionally precipitated as iron (III) hydroxide and removed.

All common devices are suitable for the method, for example drum or rack devices. Multiple cathodes or anodes can be used. The electrolyte is usually mixed during electrodeposition. For example, one or more of

Stirring devices, circulation pumps (also in combination with Venturi nozzles) or air injections can be used.

For the galvanic deposition of zinc, the metallic component is switched as a cathode and divalent zinc ions are reduced to metallic zinc on its surface, as a result of which the zinc coating is formed. Zinc is usually used as the anode.

(15) According to a further embodiment of the method, the component with a zinc coating is subjected to a passivation treatment after the electrodeposition. For this, the component with a zinc coating is coated with a suitable one

Passivation agents treated as is known per se to the person skilled in the art. For this purpose, the coated components can, for example, be coated with a thin layer or

Thick film passivation are treated. Such

Passivations typically contain chromium (III) - and

Cobalt ions as corrosion inhibitors, and others

layer-forming substances (e.g. fluorides, sulfates, nitrates). A commercially available passivation solution for zinc coatings is thin film passivation, for example

SLOTOPAS Z 20 Blue or the passivation concentrate SLOTOPAS Z 21 Blue, which are available from Schlotter. It can be carried out according to the manufacturer's instructions for use.

The passivation treatment takes place after the galvanic deposition. The components are usually coated with zinc First rinse the coating with water. If the components are annealed with zinc coating, the passivation treatment can always be carried out before or after

Annealing done.

(16) According to a further embodiment of the method, the component with a zinc coating is annealed after the electrodeposition. Annealing expels the hydrogen absorbed during the electroplating process in order to counteract the risk of subsequent embrittlement of the component by the hydrogen. Particularly with high-strength steel components, there is an increased risk of hydrogen-induced brittle fracture due to the material.

For tempering, the temperature is usually heated to 180 to 230 ° C., preferably 200 to 230 ° C. Heat is usually applied over a longer period of time, for example 2 to 24 hours.

Before annealing, the component is usually rinsed with water and dried.

The annealing is basically optional and can be carried out regardless of whether a passivation treatment is carried out. If a passivation treatment is carried out, this can take place both before and after the tempering.

To clarify the invention, reference is made to the figures and the examples below.

Brief description of the figures

Fig. 1 shows a schematic experimental setup for the galvanic deposition of zinc on an angled

Sheet steel. Fig. 2 shows a schematic experimental setup for the galvanic deposition of zinc on a straight line

Sheet steel.

At games

Production of the electrolytes El to E6

Method :

The electrolytes were prepared at room temperature by adding and stirring the other components to deionized water. The dissolution of the solids was accelerated by heating to 60 ° C. After the solution was formed, it was cooled to 25 ° C.

If necessary, the pH was brought to 5.2 by adding 5 N hydrochloric acid or 50% potassium hydroxide solution (756 g / L KOH)

set.

Reagents used:

Potassium chloride was used in technical quality.

Zinc chloride HP from Schlotter was used as zinc chloride.

The additives SLOTANIT BSF 1668 (basic additive) and SLOTANIT BSF 1662 (brightener additive), all of which are available from Schlotter, were used.

Potassium acetate was used in "pure" quality.

Glycine was used in "pure" quality.

Nicotinic acid was used in technical quality.

A 70% solution, namely CHE ED 7127 70%, available from Erbslöh, or Aduxol TDG-027 70%, available from Schärer & Schläpfer, was used as the ethoxylated thiodiglycol. Components for electrolyte El (basic electrolyte):

73 g / L ZnCl ₂ (corresponds to 35 g / L Zn ²⁺ and 38 g / L CI) 260 g / L KCl (corresponds to 136 g / LK ⁺ and 124 g / L CI)

35.0 ml / L SLOTANIT BSF 1668

0.3 ml / L SLOTANIT BSF 1662

Components for electrolyte E2:

73 g / L ZnCl ₂

260 g / L KCl

35.0 ml / L SLOTANIT BSF 1668

0.3 ml / L SLOTANIT BSF 1662

20 g / L potassium acetate (corresponds to 8 g / LK ⁺ and 12 g / L AcO)

Components for electrolyte E3:

73 g / L ZnCl ₂

260 g / L KCl

35.0 ml / L SLOTANIT BSF 1668

0.3 ml / L SLOTANIT BSF 1662

20 g / L potassium acetate

2.5 g / L glycine

Components for electrolyte E4:

73 g / L ZnCl ₂

260 g / L KCl

35.0 ml / L SLOTANIT BSF 1668

0.3 ml / L SLOTANIT BSF 1662

20 g / L potassium acetate

2.5 g / L glycine

2.11 g / L CHE ED 7127 70% or Aduxol TDG-027 70%

Components for electrolyte E5:

73 g / L ZnCl ₂

260 g / L KCl

35.0 ml / L SLOTANIT BSF 1668

0.3 ml / L SLOTANIT BSF 1662

20 g / L potassium acetate

2.5 g / L glycine 0.113 g / L nicotinic acid

Components for electrolyte E6:

73 g / L ZnCl ₂

260 g / L KCl

35.0 ml / L SLOTANIT BSF 1668

0.3 ml / L SLOTANIT BSF 1662

20 g / L potassium acetate

2.5 g / L glycine

2.11 g / L CHE ED 7127 70% or Aduxol TDG-027 70%

0.113 g / L nicotinic acid

Pretreatment of the steel sheets

1) Boiling degreasing with SLOTOCLEAN 160 (from Schlotter) for 15 min at 65 ° C and subsequent rinsing with water.

2) Hydrochloric acid pickle with 19% hydrochloric acid and 40 mL / L

Pickling degreaser SLOTOCLEAN BEF 30 (Schlotter) for 7 min at 25 ° C and then rinsing with water.

3) Electrolytic degreasing using anodic degreasing with SLOTOCLEAN DCG (from Schlotter) at one

cathodic current density of 3 to 6 A / dm ² for 2 min at 25 ° C and subsequent rinsing with water.

4) Pickling with dilute hydrochloric acid (1:10 dilution of concentrated hydrochloric acid) for 1 min at 25 ° C and

then rinsing with water.

Electroplating

Deposition parameters in the galvanic zinc electrolyte:

Electrolyte volume: 3.0 L.

pH of the electrolyte: 5.2.

Electrolyte temperature: 25 ° C.

Set stirring speed on the magnetic stirrer: 300 rpm. General procedure:

The experimental setup for the galvanic deposition with an angle sheet made of steel is illustrated in FIG. 1. Of the

Experimental setup for the galvanic deposition with a straight sheet of steel is illustrated in Fig. 2.

The electrolyte (1) is in a beaker (10) and was by means of a magnetic stirrer (15) and a magnetic one

Mixing stick (length: 40 mm, diameter: 8 mm) (16)

kept in constant motion. A Schott Duran beaker (3.0 L, low shape) was used as the beaker. The temperature was controlled and kept constant via a contact thermometer (17) which is connected to the heating relay of the magnetic stirrer. It was in the examples

Magnetic stirrer with heatable plate of the type IKA RET basic from the FA. IKA used. A served as a power source

Constant (rectifier) (20) from Gossen Metrawatt type SLP 240-40. A current of 3.0 A and a voltage of 2.5 V are illustrated by way of example.

There were two anodes (2, 2 ') for galvanic

Deposition used. Fine zinc anodes (99.99% Zn) according to DIN EN 1179 were used as anode material (length: 10 cm, width: 5 cm, thickness: 1 cm). The anodes were immersed 9 cm deep in the electrolyte.

Before the cathode sheets were introduced, they were subjected to the pretreatment described for steel sheets.

The cathode sheet (3) was placed in the center of the two anodes in the beaker. The distance from the anodes to the front and back of the cathode sheet is 6 cm. The cathode sheet is so deep in the electrolyte

immersed so that the total immersed area (front and back) is one square decimeter. If necessary, the pH was brought to 5.2 by adding 5 N hydrochloric acid or 50% potassium hydroxide solution (756 g / L KOH)

Start of deposition stopped.

It was given in each case in the examples

Current density from the respective electrolyte galvanically

deposited.

Passivation:

The coated sheets were galvanized

Deposition of zinc immediately rinsed with water and

then lightened in dilute hydrochloric acid (15 mL 25% HCl in 1 L water). After rinsing again with water, SLOTOPAS Z

20 blue (prepared with the passivation concentrate SLOTOPAS Z

21 BLUE from Schlotter, 35 mL / L) passivated at 25 ° C, pH = 1.9 and 60 s immersion time. The coated sheets were then rinsed with water and dried at 80 ° C for 15 minutes in a forced air oven. Before the assessment or the further treatment of the sheets was on

Cooled to room temperature.

Test A): Burns on the angle plate

Examples 1 to 4, Comparative Examples 1 and 2:

Angle plates with the geometry of type 2 according to DIN 50957-2 were used. The material of the angle plates was

Cold strip steel according to DIN EN 10139/10140 (quality DC03 LC MA RL). The angle sheets were pretreated according to the procedure described above and then coated. For Comparative Examples 1 and 2 (VB1 and VB2) and for Examples 1 to 4, the electrolytes E1 to E6 were used as in

Table 1 used. The current density was

varied and was 0.25, 1.0, 2.0, 4.0, 6.0 and 8.0 A / dm ² . The deposited layer thicknesses were 10 gm. The sheets were then passivated as described above.

The optics of the deposited zinc coating in the edge area of the angle plates and the number of

Burns (mis-colored, dark, amorphous or

coarse crystalline, mostly powdery areas in the

Coating) caused by increased local current densities

can arise from being judged by eye inspection.

It means:

D no burns

o slight burns

• moderate burns

▲ severe burns

The results are summarized in Table 1.

Table 1 - Burnings on the angle plate

At low and medium current densities up to 2 A / dm ² , a usable zinc layer could be deposited from all electrolytes El to E6. At high current densities of 4 or 8 A / dm ² , there were considerable differences in the individual electrolytes.

In Comparative Example 1 (VB1) the boric acid and

ammonium-free electrolyte El without the buffer substances acetate and glycine unsuitable zinc coatings, which on the Edge areas had massive burns. The addition of acetate then made the first improvements in Comparative Example 2 (VB2) with electrolyte E2, but at 8 A / dm ^{2 there} were still too many burns

observed.

In contrast to this, in example 1 high-quality zinc coatings were obtained with the electrolyte E3 even at high current densities, which showed only slight burns even at 8 A / dm ² . The electrolyte E3 according to the invention therefore represents a verifiable boric acid and ammonium-free substitute for conventional electrolytes containing boric acid.

In Examples 2 to 4, the additives ethoxylated thiodiglycol or nicotinic acid could again be used to achieve a significant improvement.

Experiment B): tempering ability

Examples 5 to 8, Comparative Examples 3 and 4:

Straight steel sheets measuring 0.3 mm thick, 50 mm wide and 130 mm long were used. The material of the straight steel sheets was cold-rolled steel according to DIN EN

10139/10140 (quality DC03 LC MA RL). The steel sheets were pretreated according to the procedure described above and then coated. There were for the comparative examples 3 and 4 (VB3 and VB4) and for examples 5 to 8

Electrolytes El to E6 are used (see Table 2 and Table 3). The current density was varied and was 0.25, 1.0, 2.0, 4.0, 6.0 and 8.0 A / dm ² . The deposited layer thicknesses were 10 pm.

After the galvanic zinc deposition, the sheets were then passivated as described above for 48 hours

Stored at room temperature and then annealed at 210 ° C for 24 h. The blistering caused by the tempering was then assessed at room temperature.

It means:

D no blistering

o slight blistering

• moderate blistering

▲ severe blistering

The results are summarized in Table 2.

Table 2 - Bubble formation after annealing

In example 5, the electrolyte E3, which contains potassium acetate and glycine, could be used for zinc coatings of very good temperature at common current densities between 0.25 and 2 A / dm ²

are produced in which no blistering

was observed.

A further improvement of the tempering ability of the zinc coatings deposited at higher current densities was for the

Electrolytes E4 and E5 found in Examples 6 and 7, which contained ethoxylated thiodiglycol (E4) and nicotinic acid (E5), respectively. By combining both additives in the electrolyte E6, a completely bubble-free tempered zinc coating could still be obtained even at a current density of 8 A / dm ² (see Example 8). Furthermore, the visual impression (gloss) was assessed at room temperature.

It means:

D no milky look

o slightly milky look

• moderate milky appearance

▲ very milky look

The results are summarized in Table 3.

Table 3 - Gloss after tempering

In comparative examples 3 and 4, the electrolytes 1 and 2 free of boric acid and ammonium gave a very milky appearance with numerous streaks. With the acetate and glycine

containing electrolyte E3, the gloss was improved and the milky appearance was somewhat reduced.

The addition of ethoxylated thiodiglycol in the electrolyte E4 and in particular the addition of nicotinic acid in the electrolytes 5 and 6 then further improved the gloss of the annealed zinc coatings (see Examples 6 to 8). Regardless of the current density used, the zinc coatings showed only a slight or no milky cloudy appearance or streaks. Experiment C): thermal shock test

Examples 9 to 12, Comparative Examples 5 and 6:

Straight steel sheets measuring 0.3 mm thick, 50 mm wide and 130 mm long were used. The material of the straight steel sheets was cold-rolled steel according to DIN EN

10139/10140 (quality DC03 LC MA RL). According to the above

The procedure described was pretreated and then coated at a current density of 3.0 A / dm ² . The electrolytes E1 to E6 were used for comparative examples 5 and 6 (VB5 and VB6) and for examples 9 to 12 (see table 4). The secluded

Layer thicknesses were 10 pm.

After the galvanic zinc deposition, the sheets, as described above, were passivated, stored for 48 hours at room temperature and then stored at 220 ° C. for 30 minutes and immediately added to filtered tap water heated to 20 ° C.

First, the tap water was on any

Glitter formation examined and evaluated.

Following the thermal shock test, the sheets were dried for 15 min at 80 ° C. in a forced air oven and, after cooling to room temperature, the adhesive strength was checked again visually

examined. For this purpose, 4 cm long, 19 mm wide

Adhesive strips (tesa ^® film crystal clear from Tesa SE) are glued to the metal sheets and removed after 60 s. The zinc coatings were checked for damage.

Both liability tests are passed if none

Glitter or other particles, flaking, bubbles or

Damage was observed.

It means:

D passed (no tinsel and good adhesion) The results are summarized in Table 4.

Table 4 - Adhesion after thermal shock test

No tinsel formation was found for all electrolytes, and the zinc coating adhered well to the steel sheet. Consequently, with the boric acid and

ammonium-free electrolyte adhesive-resistant zinc coatings can be produced.

Claims

Claims 1. A boric acid and ammonium-free aqueous electrolyte for the galvanic deposition of zinc coatings, comprising: (a) Zn ²⁺ in a concentration of 15 to 70 g / L; (b) Ci in a concentration of 100 to 200 g / L; (c) Total K ⁺ and / or Na ⁺ in a concentration of 0.75 to 6.0 mo1 / L; (d) acetate at a concentration of 5.0 to 45 g / L; (e) total glycine and / or alanine in a concentration of 0.5 to 30 g / L; and (f) water; wherein the electrolyte has a pH of 4.5 to 6.5. 2. Electrolyte according to claim 1, wherein the concentration of Zn ²⁺ in the electrolyte is 20 to 60 g / L, preferably 25 to 50 g / L, more preferably 30 to 40 g / L and most preferably 35 g / L . 3. Electrolyte according to claim 1 or 2, wherein the Concentration of Ci in the electrolyte is 120 to 190 g / L, preferably 130 to 180 g / L and more preferably 160 g / L. 4. Electrolyte according to one of claims 1 to 3, wherein the electrolyte contains K ⁺ and the concentration of K ⁺ 0.75 to 6.0 mol / L, preferably 2.7 to 4.8 mol / L and more preferably 3, Is 3 to 4.1 mol / L. 5. Electrolyte according to one of claims 1 to 4, wherein the concentration of acetate in the electrolyte is 7.5 to 30 g / L, preferably 10 to 20 g / L, most preferably 12 g / L. 6. Electrolyte according to one of claims 1 to 5, wherein the concentration of glycine and / or alanine in total in the electrolyte in the range of 0.5 to 20 g / L, preferably 1.0 to 10 g / L, more preferably 1.5 to 5 g / L and most preferably 2.5 g / L. 7. Electrolyte according to one of claims 1 to 6, wherein the electrolyte (a) Zn ²⁺ in a concentration of 20 to 60 g / L; (b) CI at a concentration of 120 to 190 g / L; (c) K ⁺ in a concentration of 2.7 to 4.8 mol / L and 0 to 0.5 mol / L Na ⁺ ; (d) acetate at a concentration of 7.5 to 30 g / L; and (e) Total glycine and / or alanine in a concentration of 0.5 to 20 g / L contains. 8. Electrolyte according to one of claims 1 to 7, wherein the electrolyte additionally (g) nicotinic acid in a concentration of 0.01 to 2.0 g / L, preferably 0.05 to 1.0 g / L, more preferably 0, 08 to 0.5 g / L, most preferably 0.1 g / L. 9. Electrolyte according to one of claims 1 to 8, wherein the electrolyte additionally (h) ethoxylated thiodiglycol with an average of at least 20 structural units derived from ethylene oxide in a concentration of 0.3 to 10 g / L, preferably 0.5 to 5 g / L, more preferably 1.0 to 3.5 g / 1, and most preferably 2.1 g / L. 10. Electrolyte according to one of claims 1 to 9, wherein the electrolyte (g) Nicotinic acid in a concentration of 0.05 to 1.0 g / L, and / or (h) Average ethoxylated thiodiglycol contains at least 20 structural units derived from ethylene oxide in a concentration of 0.5 to 5 g / L. 11. A method for producing an aqueous electrolyte according to any one of claims 1 to 10, comprising the steps: A) creating an aqueous solution of (a ') zinc chloride and / or zinc acetate; (b ') potassium chloride and / or sodium chloride; (c ') at least one of potassium acetate, sodium acetate and acetic acid; (d ') at least one of the group consisting of glycine, a salt thereof, alanine and a salt thereof; and (e ') optionally nicotinic acid or a salt thereof; and (f ') optionally ethoxylated thiodiglycol with an average of at least 20 structural units derived from ethylene oxide; and B) optionally adjusting the pH to 4.5 to 6.5 by adding hydrochloric acid or by adding Potassium hydroxide and / or sodium hydroxide, which as Solid or in the form of an aqueous solution can be added. 12. A method for producing a component with a zinc coating, comprising the galvanic deposition of zinc on a metallic component from an electrolyte according to one of claims 1 to 10. 13. The method according to claim 12, wherein the metallic component comprises or consists of iron or an iron alloy. 14. The method according to claim 12 or 13, wherein at a temperature of 20 to 50 ° C, preferably 25 to 40 ° C, is deposited, and a current density of 0.2 to 10 A / dm ² , preferably 0.5 to 6 A / dm ² , is used for the deposition. 15. The method according to any one of claims 12 to 14, wherein the zinc-coated component is subjected to a passivation treatment after the electrodeposition. 16. The method according to any one of claims 12 to 15, wherein the Component with zinc coating after the galvanic deposition, optionally before or after a passivation treatment.