DE2737748A1 - GALVANIC CHROME BATH - Google Patents

Description

Godfather> clay walls
Dipl. Inf. ». Hums Iiirtron Garbage? · Dr. r »i. n: t Thonms IJcrfndt Dr. - Inf. Hans J.cyh

Lucile Orohn-Straß «36Ud ΜυηΑεη BO

PS 586

Munich, August 22, 1977 sch

Albright and Wilson Limited

Oldbury . Warley, West Midlands, England

Galvanic chrome bath

8 C-309/0853

The invention relates to chrome plating from baths of trivalent chrome.

Applicant's GB patent application No. 57872/73 describes a galvanic chromium bath, consisting of an aqueous solution containing trivalent chromium, formate or Acetate, bromide and ammonia together and preferably additions of borates and conductive salts, e.g. B. Alkali metal chlorides or contains sulfates. A problem that occurs every now and then with such baths is that the chrome tends to fail.

It has been found that an electroplating bath with very high stability is obtained by using formate and acetate can be added in certain amounts as an admixture.

The galvanic aqueous chromium bath according to the invention contains 0.1-1.2 mol / 1 trivalent chromium, 0.5-3 mol per formate mol of trivalent chromium, 0.1-0.5 mol of acetate per mol of formate, at least 0.01 mol / l bromide and at least 0.05 mol / l Ammonia.

The chromium bath preferably contains at least 0.1 mol / 1 borate and also preferably at least 0.5 mol / 1 alkali metal,

z. B. sodium or potassium. The bath preferably also contains 0.5-5 mol of sulfate and / or 0.5-5 mol of chloride. Furthermore can the bath contains fluoride and preferably a wetting agent.

The invention thus relates to electroplating baths which contain trivalent chromium and which act as complexing agents a carboxylic acid, a bromide and ammonia are included;

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such baths have greater stability, the carboxylic acid being a mixture of formate and up to one third of the weight is the carboxylic acid of an acetate.

The bath components are as follows: A) Trivalent chrome

This is an essential part of the bath according to the invention. Proportions less than 0.1 mol / 1 or more than 1.2 mol / l trivalent chromium results in a significant loss in hiding power and concentration should therefore be kept within these limit values, preferably from Ο.2-0.6 mol / l. Is preferred the bath is essentially free of hexavalent chromium, and also preferably the chromium in the bath is essentially substantially free present entirely as trivalent chromium prior to deposition.

B) bromide

This is also an essential part. The bromide concentration should be kept above 0.01 mol / l to prevent the formation of hexavalent chromium and a decrease in the electroplating rate. the Although the maximum concentration is not critical, it is typically less than 4 mol / l and preferably less than 1 mol / 1. Iodide has a similar effect to bromide, but has the disadvantage that free iodide, which is

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would be hitting formed only up to 0.03 wt -.% water soluble while Eromid up to 4% is soluble. As a result, attempting to use iodide in place of eromide results in unacceptable precipitation of iodide. Iodide is also too expensive to be used economically in place of bromide. However, it is in principle possible to replace a small portion of the eromide with iodide, and subsequent references to bromide do not rule out eromide, which contains traces of iodide.

C) formate

Formate is an essential part of the bathroom. Typically the ratio of formate to chromium should not exceed 3: 1 and is preferably not more than 2.5: 1 on an ilol basis, so that an unacceptably high level of precipitation of the corresponding chromium salt is avoided. If the ratio is less than 0.5: 1, the hiding power is undesirably greatly reduced. The total molar ratio of formate and acetate to chromium is preferably 3: 1 to 1: 1, particularly preferably between 2.5: 1 and 1: 1, e.g. B. approx. 2: 1.

D) acetate

Acetate is also an essential bath ingredient. The presence of acetate in addition to formate increases the stability of the bath. Less than about 0.1 mol of acetate per mol of formate results in an undesirably high risk of

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Precipitation of chrome from the bathroom. Lu a lot of acetate has a Reduction in the rate of precipitation as a result. The proportion of acetate must not exceed 0.5 mol per mol of formate. Purely satisfactory economic galvanization rates the acetate content is preferably in the range of 0.2-0.4 mol per mol of lithium ormate, particularly preferably in the range of 0.2-0.3 e.g. B. 0.25 moles per mole of formate.

E) ammonium

The presence of ammonium is an essential feature of the invention. Ormally when the ammonium concentration is less than 0.1 mol / l, there is a loss of hiding power at high current density. the The upper limit is not critical and ammonium can be used in amounts up to saturation, i.e. H. up to about 4 mol / l, present be. The ammonium is preferably present in a concentration in the range from 1-3 mol / l. Ammonium is as NH. even present. Substituted is preferred Ammonium, e.g. B. hydroxylammonium, hydrazonium, alkylammonium. Acrylammonium or heterocyclic ions such as pyridine, not present, as this causes precipitation is adversely affected by chromium.

P) borate

It is possible to deposit chromium from baths according to the invention which do not contain borate by electroplating;

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however, it does not produce absolutely satisfactory results suitable for retail trade. Borate concentrations below 0.1 mol / l result in a undesirably low opacity. While the upper limit is not critical, it is usually preferred between 0.5 and 1 mol / l borate is used. The function of the lorate is unknown; its beneficial effects can partly be attributed to its buffering effect. Other buffer salts, e.g. B. phosphates and citrates, however, are relatively ineffective.

G) hydrogen ion

The best results are obtained when the bath is low in acid. At low pH values (below 2) occurs a certain loss of hiding power below pH 1 becomes unacceptably large. If the pH is higher than 4, the plating rate tends to be undesirable becomes slow. The optimal pH is between 2 and 3.5.

H) chloride and / or fluorld

This ingredient is optional but is preferred in the case of chloride. The length varies from zero to to the highest proportion that is possible based on solubility considerations. Chloride is commonly called Anion of the conductive salt (e.g. sodium chloride) introduced into the bath as ammonium chloride; this is a simple one

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Method of introducing the required amount of ammonia into the bath, in the form of chromium chloride, the is optionally used to provide at least part of the chromium required and / or as hydrochloric acid, which is then used in a simple manner to adjust the pH of the ead, preferably is Chloride content at least 0.5 mol / 1, preferably at least 1 mol / l, e.g. E. 1.5-5 mol / 1. A particularly suitable range is between 2 and 3 »5 mol / l.

I) sulfate

Sulphate is an optional but preferred component of the chrome bath. The amount of sulfate can be like that of the Chloride fluctuate between coolant and the maximum value that is compatible with the bath. Especially for one preferred type of pad, the amount of sulfate is less than the total content of halide, preferably less than the total chloride content. In another type of bath, however, the sulfate content is greater than the halide content and can be the predominant anion in the bath. Just like that Chloride can be the sulfate in the bath as the anion of the conductive salt or the ammonium or chromium salt or as Sulfuric acid are introduced. Typical sulfate concentrations are in the range of 0.5 mol / l, preferably from 0.5-4 mol / l, e.g. B, 0.6-3 mol / l, most preferably im Range of 0.6-1.2 mol / l. Preferably the combined chloride and sulfate concentrations are at least 1 mol / l, e.g. B. at least 2 mol / l, preferably from 2.5-3.5 mol / l :.

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J) trace metals

Iron and / or liickel are preferred in the baths after of the invention are present in proportions between a total of 30 and 150 ppm, so that optimum hiding power is obtained will. The iron content can exceed this value if chromium-iron alloys are to be metallized. The nickel content however, it should not exceed 150 ppm by itself or 100 ppm in the presence of substantial amounts of iron. Higher amounts of nickel cause discoloration of the precipitate. Most other trace metals including Cobalt, copper, lead and zinc are highly undesirable if any of them are in excess of 30 ppm is available. The total concentration of such trace metals should preferably be less than 30 ppm, ideally be less than 20 ppm.

K) alkali metals and / or alkaline earths

These are zv / ar optional, but preferably present in the case of the alkali metals. You can use sodium, potassium or lithium, less preferably alkaline earth metals v / ie calcium or magnesium or other metal ions, the not be precipitated with the chromium from the solution. The quantity of such metals is not critical, provided that that they do not fail in the presence of the other components. Your presence is useful to the electrical Increase the conductivity of the bath. They are preferably used in an amount of at least 0.1 mol / l There is saturation in the solution.

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L) Surfactants

These are optional, but preferably present in effective and tolerable amounts. Wetting agents and defoamers are used throughout the electroplating art and many suitable examples are known to those skilled in the art. Any of the wetting agents commonly used in electroplating in a hexavalent chrome bath can be used be used with the bath according to the invention. However, since the baths according to the invention oxidize far less than hexavalent chromium baths, it is also possible and even preferred to use the cheaper wetting agents that usually used in the less aggressive electroplating baths. The biggest limitation in terms of The effectiveness of the wetting agents arises from the presence of free bromine in the bath. Surface-active Substances that brominate easily are therefore not recommended, e.g. B. most non-ionic surfactants Fabrics. The surfactants used in the invention are typically cationic or preferred anionic, e.g. B. sulfosuccinates, alkylbenzenesulfonates with 8-20 aliphatic carbon atoms such as sodium dodecylbenzenesulfonate, alkyl sulfates with 8-20 Carbon atoms such as sodium lauryl sulfate and alkyl ether sulfates such as sodium lauryl polyethoxysulfate. If the bath shows undesirable foaming tendencies, it is also possible Optionally compatible defoamers, e.g. B. fatty alcohols such as octyl alcohol to be added. The choice of surfactants Substances for the bathroom of the invention is a routine matter well within the knowledge of those skilled in the art is in this area. The amount of wetting agent used corresponds to normal practice, e.g. B. 0.1-10 Thousandths.

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The baths according to the invention should preferably consist essentially of the components mentioned above. They 'are compatible with the bathrooms and the galvanizing' presence of small amounts of other substances »· not elerungselgenschaften adversely affect, however, is not excluded · Not normally 1st the · nitration Essentially present, as it tends to inhibit the chromium deposit . The sulfite ion, which was previously recommended as an additive to electroplating chromium baths, also has a disadvantageous effect if it is present in quantities of more than approx. 0.01 mol / l, but other organic or inorganic substances that cause electroplating of the Chrome, or not noticeably affecting opacity, or causing unacceptable toxicity problems, may optionally be present. Whether any particular substance in the solution can be tolerated can be routinely determined by simple experiments.

The bath is advantageously prepared in that water-soluble salts of the required kind are dissolved in sufficient quantity to obtain the desired concentration. Typical salts that are used for this are chromium chloride, chromium sulfate, potassium bromide, Sodium bromide, ammonium bromide, potassium formate, sodium borate, ammonium chloride, ammonium sulfate and sodium chloride.

If desired, the cationic species can be completely or partly as bases, e.g. B. ammonia, added

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will. A particularly suitable form of chromium is basic chromium sulfate, which is commercially available in chrome tanning liquids. For example, 3396 is basic Chromium sulfate obtained by reducing sodium dichromate with sulfur dioxide is an item of commerce, and an advantage of the invention is that it it is possible to use such relatively inexpensive and readily available sources of chromium. The usage However, salts such as chromium formate or acetate are not excluded.

The anionic species can be added at least partially in the form of acids, e.g. B. as hydrochloric acid, Sulfuric acid, boric acid, formic acid or acetic acid. Preference is given to the dissolution of the essential substances the pH adjusted by adding z. B. ammonium, sodium or potassium hydroxide. Preferred is the pH first in the upper part of the preferred range, e.g. B. with 2.5-4, set. In operation, the pH value to drop and should be kept in the range of 2.5-3.5 through occasional readjustments.

The chrome bath can be prepared at room temperature. Alternatively, it can be used at higher temperatures, e.g. B.

70 ⁰ C, after which it is allowed to cool.

Typically the bath is allowed to cool for a period of 10-24 hours. Unlike known, on For formate-based baths, it is not necessary to have an initial one immediately after preparing the bath

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electrodeposition process or excessive amounts during bath preparation Add formate.

The solution is preferably used at temperatures between 15 and 30 ^° C., e.g. B. 20-25 ⁰ C, used. Current densities between 5 and 1000 A / 0.3 πΓ ² (ζ. Β. Approx. 100 A / 0.3 m ~) can be used.

The system is for electroplating plastic and ferrous substrates as well as conventional ones Iron or nickel substrates suitable. Galvanic hitting of plastic (usually acrylonitrile butadiene styrene) usually takes place from hexavalent chromium baths. The procedures are general known and z. B. in "Electroplating of Plastics" by William Goldie and in an article by the Society of Automotive Engineers, "Electroplating of Plastics" by Sauvestre, Jan. 1965. To be favoured in the baths according to the invention, the same processes are used as previously used for electroplating of hexavalent chromium have been applied to plastic, but instead of those previously used hexavalent chromium baths, the baths according to the invention can be used.

Inert anodes, e.g. B. carbon anodes, used. Other inert anodes such as platinum titanium or platinum anodes can be used, however, they are more expensive. For galvanic low

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suggest on alloys, however, it is possible, e.g. B. to use iron or chromium-iron anodes.

The following examples serve to illustrate the invention.

example 1

A bath was prepared by dissolving the following ingredients in water at laboratory temperature (20-25 ⁰ C) and diluting to 1. 1

The chrome tanning liquid used was a 33 % basic liquid. It is a commercially available article for tanning leather and is obtained by reducing sodium dichromate with sulfur dioxide. The reaction product has a basicity of 33 % _t , the "basicity" being a measure of the substitution of sulfate by hydroxyl to obtain products of different compositions. The liquid contained 130 g / l Cr.

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150 ml approx. mol / 1 Chrome tan liquid 1 ml 0.4 i etsmittel 90 g Aluminum chloride 75 g 1.7 Potassium chloride 10 g 1.0 Ammonium bromide 50 g 0.1 r-orsäuro 15 g 0.8 i atriumac e did 55 g 0.2 Ammon iumf ο rmi a t 2 ml 0.87 Sulfuric acid SC 1.84

During preparation, the pH was 3.4, and the electrodeposition with a carbon anode began within 30 minutes at a volume flow density of 0.5 A / l. After one hour galvanic hiederschlagens, ie after 0.5 Ah / 1, a sample was taken for evaluation in a] Iull-'ielle with circulation cooling, was maintained in a temperature in the range of 20-25 ⁰ C.

A current of 10 A was passed for 3 minutes using a carbon anode, and the following distribution the board was recorded by standard coulometric thickness measurements.

Current density (mA / cm).
Thickness in / um

432
0.30

216 0.20

108 0.15

54 0.20

27 0.10

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BATH ORIGINAL

The plating range was 1080-8.64 mA / cm (1000-8 ASF) estimated at a working pIi-Y / ert of 3.0.

example

A comparison test was carried out as follows:

Baths A and B were made by dissolving the ingredients in cold water and electrolytic charge cleaning was performed using a carbon anode for 10 Ah / 1 at a volume current density of 0.5 A / l.

Bad A Bathroom Β Potassium chloride 150 g 150 g Ammonium chloride 40 g 40 g Boric acid 50 g 50 g Sodium bromide 10 g 10 g Sodium acetate - 15 g Ammonium formate 55 g 55 g Chrome tanning liquid 130 ml 130 ml (150 g / l Cr) Wetting agents 1 ml 1 ml PH value 2.9 3.3

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The pH value of both baths was set in the specified manner set, and the bath B 5 g / l ammonium formate added. The combination of a high pH value and a high addition of formate is known to support precipitation of chromium formate.

The baths were kept in polyethylene for two weeks, after which bath A showed precipitation, while the I? Ad B was clear.

After eight weeks, severe precipitation had occurred in bath A, whereas in bath B no precipitation occurred.

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ORIGINAL

Claims (8)

Patents claims 1y Aqueous galvanic chromium bath containing 0.1-1.2 mol / l trivalent chromium, at least 0.01 mol / l bromide, at least 0.05 mol / l ammonia and a carboxylic acid complexing agent for trivalent chrome, characterized, that the carboxylic acid complexing agent is a mixture of pormate and acetate, consisting of 0.5-3 mol of pormate per mol of trivalent Chromium and 0.1-0.5 moles of acetate per mole of formate. 2. Chrome bath according to claim 1, characterized in that the acetate content is in the range of 0.2-0.4 mol per mol of Pormiat lies. 3. Chrome bath according to claim 1 or 2, characterized in that the total proportion of formate and acetate between 2.5 and 1 mol per mol of trivalent chromium is 4. Chrome bath according to one of the preceding claims, characterized in that it contains at least 0.1 mol of borate. 5. Chrome bath according to one of the preceding claims, characterized in that there is at least 0.5 mol of chloride and / or Contains sulphate. 6. Chrome bath according to one of the preceding claims, characterized in that there is a total of between 30 and 150 ppm of iron and / or contains nickel. 809809/0 853 7. Chrome bath according to one of the preceding claims, characterized in that it is at least 0.1 mol / l sodium and / or contains potassium. 8.9809 / 0853