DE2210091A1 - Electrolyte for galvanic nickel coatings - Google Patents

Description

DR. K. POSCHENRIEDJiK

DR. E. BOETTNER
DIPL-ING. H.-J. MÜLLER ^ .. "

MÖNCHEN 80 * '

Lucüe-Gralin-Strasse 38 "Dr.B / U

Telephone 475155

Albright & Wilson Ltd., Oldbur.y near Birmingham, Warwickshire (England)

Electrolyte for galvanic hot-tee coatings

The invention relates to improvements in the electrodeposition of nickel.

Nickel is electrodeposited from an aqueous electrolyte bath containing the nickel-II salt. Different Additives are used to improve uniformity, the ductility and gloss of the electroplated coating applied, but this does not affect the corrosion resistance the coatings are intended to affect. In practice, a full shine is only achieved through use of a primary brightening additive, e.g. an acetylene compound in combination with an organic Sulfur-oxygen compound, such as a sulfonic acid, may represent a sulfonamide or sulfimide. the However, the presence of the sulfur compound results in the simultaneous deposition of sulfur in the galvanic Coating, which greatly reduces the corrosion resistance of the nickel. This disadvantage becomes after a procedure overcome that under the designation "duplex" nickel plating is known, with a semi-gloss, 3-sulfur-free galvanic coating applied first

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ORIGINAL INSPECTED

which has good corrosion resistance, and then a fully glossy nickel look over it is applied using an acetylenic compound and a sulfur-oxygen compound, to achieve the desired gloss level. Corrosion of the "duplex" nickel coating3 occurs in the upper layer and does not expose the steel or the other metallic substrate. The ones below The sulfur-free layer lying flat should be even if a satisfactory gloss is achieved afterwards shall be. It should also have a high ductility in order to avoid slight deformation or to be able to withstand another slight damage without tearing. This has often been the case up to now achieved by using coumarin as a smoothing agent, which gives rise to the formation of a ductile galvanic coating gave. The use of coumarin, however, has certain disadvantages. The connection ;; is used during application decomposed to moliotic acid (2-hydroxyphenylpropionic acid), which damages the galvanic coating and must therefore be removed from the electrolyte. This can't go through the usual method of a continuous Filtrierimg of the electrolyte through activated carbon is done, as this is expensive Coumarin itself is removed by such a filtration will. Thus, the bath must be removed periodically and an expensive treatment for regeneration of the electrolyte.

Another system for producing semi-glossy sulfur-free galvanic nickel coatings that some technical Has achieved success is described in British Patent Specification 871,276. Here the gloss additive is the

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Coordination of a carboxylic acid in which the pKa value is between 3.0 and 5.0 and the garbon ylb in the formation of the carboxyl group is not conjugated, together with a further additive, which is preferably a water-soluble acetylene compound. A great number of different suitable acetylene compounds are described in this patent, including cC -Alle oils and reaction products of an alkynol with an epccdd or alene oxide. In practice, the system used was the combination avj ron 2-Bntin-1,4-diol (hereinafter referred to as BYD) and acetic acid. This addition gave coatings with good ductility and useful smoothness, although the latter is often not as good as when using coumarin. It is expedient that the coating is uniformly smooth and ductile and preferably semi-glossy over the widest possible range of current density without sharp edges between smooth and semi-glossy areas. Smoothing with BYD and acetic acid can only be increased at the expense of ductility (e.g. by increasing the concentration of B1 ⁷ D or by decreasing the concentration of acetic acid). Accordingly, the electrolytes of this type, which have been used technically,

a compromise on achieving both the desired Degrees of smoothness as well as the desired dulctility of the coating. Nonetheless, there are some downsides here does not stop using coumarin, as the acetylene compounds are not removed from the electrolyte, if this is filtered through activated charcoal.

It has now been found that a modification of the Method according to British patent specification 871 276

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such that in the electrolyte both an oC - alkynol and an alkylene oxide condensation product of an OC alkynol in a weight ratio of 4: 1 to 1: 4 and the non-conjugated carboxylic acid with the pKa value is between 3.0 and 5.0, the resulting electroplated nickel plating with a superior combination of smoothness and ductility compared to using QC alkyne oils alone in the combination of the British patent specification of optimally obtainable coating. In addition, a satisfactory coverage over a wide range achieved by current densities. This is surprising, since the alkoxylated butynols are often unsatisfactory when used as sole acetylenic additives because of a tendency to deposit nickel to inhibit at low current densities, which gives rise to not can give plated spots on recessed areas of heavily contoured workpieces.

Accordingly, according to one embodiment of the invention, an aqueous electrolyte for electrodeposition of nickel is provided created that (a) at least 30 g per liter of a Nicke1-II salt, (b) 0.1-250 mmol per liter of one Mixture of water soluble acetylenic compounds including both an oC alkynol and a Condensation product of a ° C alkynol with a Alkylene oxide irr. Weight ratio of cC-Alklnol to condensation product from 4: 1 to 1: 4 and (c) 0.1 to 45 g, per liter of a non-conjugated carboxylic acid with contains a pKa value between 3.0 and 5.0.

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The invention is applicable to electrolytes for nickel plating, the at least 30 g per liter of a nickel II salt, for example in the presence of one or more Anions contain chloride, sulfate, sulfamate and borate. Such an electrolyte may, for example, be of the electrolyte type /, att be that of 225 to 350 g / liter of nickel-II-sulfate, 30 to 50 g / liter Nicke 1-II-ciilorid and 20 contains up to 45 g / liter boric acid. Another

known nickel electrolyte is of the type of the high chloride nickel electrolyte and contains 150 up to 350 g / liter Nicke1-II-chloride. The latter A typical embodiment contains electrolyte Nickel-II-sulfate (50-225 g / l), Nickel-II-ehirid (150-200 g / l) and boric acid (30-50 g / l), but alternatively Nicke1-II-ctalorid (150-350 g / l) can be used as contains only nickel salt. The invention is also applicable to electrolytes containing other nickel salts, like Nicke1-II-sUlfamat.

The α-alkinols used are water-soluble compounds with a hydroxyl group in the Ca position to an acetylenic bond. Such compounds preferably have the general formula R ₁ . CHOH.C ^ CR ₂ , in which R ₁ and R _? are each hydrogen atoms or an alkyl, alkenyl or alkynyl group having 1 to 4 carbon atoms, which may optionally contain an amino or hydroxyl group as a substituent. Representative & C - alkynols are included in the following list:

2-butyne-1,4-diol;

1-butyn-3-ol;

Propargyl alcohol (2-propyn-1-ol);

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1-penty-3-ol;
4-methoxy, y-2-butyn-1-ol; 3-hexin-2,5-dol;
4-dietbylamin-2-butyn-1-ol; and 2,4-hexadiyne-1,6-diol.

The first three compounds on this list are special useful.

The alkylene oxide condensation products of r / i -alone oils for the use according to the invention can be all those which are formed when an oC-alkyne oil is reacted with 1 to 20 mol, preferably 1 to 4 mol, of an alkylene oxide. The preferred alkylene oxide is ethylene oxide, but propylene oxide, epichlorohydrin, or epibromohydrin can also be used. Mixtures of such alkylene oxides can also be used, either simultaneously or sequentially in the condensation with the cC-Alid.nol. The oC-alkyne oil can be a compound of the formula R ₁ . Be CIIOHCPcR ₂ as defined above and is preferably a compound from the above combination. The condensation product can be prepared by any of the methods commonly used to prepare polyoxyalkylene ethers by the condensation of an alcohol with an alkylene oxide. The preferred condensation products are formed from 2-butyn-1,4-diol, 1-butyn-3-ol or propargyl alcohol with about 2 moles of ethylene oxide.

The electrolytes according to the invention contain a total of 0.1 to 250, preferably 0.1 to 100 mmol, per liter of the water-soluble acetylenic compounds. That

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Weight ratio of oC-alkynol to condensation product is 1: 4 to 4: 1. This ratio is preferably from 1: 1 to 1: 2, in particular about 1: 1.5.

The electrolytes according to the invention also contain 0.1 to 45 g per liter, preferably less than 10 g / l, e.g. 0.1 to 5 g per liter of a carboxylic acid in which the Carbonyl bond of the carboxyl group is not conjugated (hereinafter referred to as non-conjugated carboxylic acid) and whose pEa value is between 3.0 and 5 * 0. One A list of such acids is given in British Patent No. 871,276. It includes formic acid, acetic acid, Propionic acid, glycolic acid, Y / one acid, lactic acid, succinic acid and phenoxyacetic acid. The preferred acid for use in the present invention is acetic acid, which for example in a concentration of 0.1 to 5 g per liter, preferably 0.5 to 2 g per liter. Here it should be noted that these acids can be added to the electrolyte in the form of derivatives, e.g. in the form of their salts with alkali metals, ammonium, magnesium or nickel or in the form of lactones, Esters, acid chlorides or anhydrides of acids.

The working conditions for the electrolytes according to the invention are generally those which are usually used for electrolytes based on the aforementioned nickel salts. In general, the pH of the electrolyte should be between 2.5 and 5.5, with a pH of 3.5 to 5.0 being preferred, and the temperature should be 40 to 70 ° C., with a Working temperature of 50 to 60 ⁰ C is preferred. The electrolyte can be used in a wide range of currents-

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ρ can be operated densely, for example from 2 to 100 A / 0.093 m and the work piece as cathode can be stirred in the electrolyte during operation or the electrolyte can be stirred, for example by blowing air through it.

The galvanic nickel coatings obtained with the inventive Electrolyte has been produced. use as semi-gloss coatings as such, or they / nechanically be polished to full glossy coatings. They become more common, but as a basic layer of "duplex" nickel plating used, on which a fully polished galvanic nickel coating is then applied is made using a water-soluble acetylenic compound and a sulfur-oxygen compound as an additional combination in the electrolyte. This "duplex" coating, which has an improved corrosion resistance, can in turn with a galvanic chrome coating be coated for maximum gloss in the finished item.

The invention is further illustrated by the following examples explained:

Examples 1 - 7

The thus examples were prepared having the following composition in a Hull cell at 5O ⁰ C with stirring by blowing air using an aqueous electrolyte:

Nickel sulfate 250 g / l nickel chloride 43 g / l boric acid 41 g / l
pH 4.3.

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The remaining additives are in the following table
compiled. EOBTD here means ethoxylated 2-butyne-1,4-diol, which contains about 2 moles of ethylene oxide per mole of ΒΥΏ.

Examples 1-3 are comparative examples.

TABEL

Example Concentration of Additions Description

EOBID BYD carboxylic acid of the coating

1.226 g / l 0.030 g / l none glossy,

(0.35 mM) semi-gloss

over 38 A / s.f. Gloss -4 to 38 A / s.f. No separation below 4 A / s.f.

2. 0.128 g / l 0.088 g / l none glossy, (0.25 mM) (1.01 mM) semi-gloss

over 60 A / s.f. Gloss below 60 A / s.f. "

3. 0.043 g / l 0.148 g / l none glossy, (0.25 mM) (1.72 mM) semi-gloss

over 38 A / s.f. Gloss below 38 A / s.f.

4. like 2 like 2 0.4 ml / l semi-gloss

Acetic acid above 26 A / s.f. (6.96mM) gloss below 26 A / s.f.

5. 0.190 g / l 0.132 g / l 0.4 ml / l glossy, (1.10 mM) (1.53 mM) acetic acid semi-gloss

(6.96 mM) over 60 A / s f. GIaTE under 60 A / s.f.

6. like 2 like 2 0.4 g / l semi-gloss

Glycolic acid above 60 A / s.f.

(5.5 mM) Gloss 2.5-60 A / s.f. None Separation below 2.5 A / s.f.

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Concentration of additives Description

Example EOBTD ΒΥΌ carboxylic acid of the coating

7. like 2 like 2 0.8 g / l semi-gloss

Glycolic Acid Over 40 A / s.f. (11.0 mM) gloss 5-4-0 A / s.f. Koine Separation below 5 A / s.f.

In the following two examples, smoothness tests were carried out on test pieces measuring 0.025 mm (0.001 ") nickel from an electrolyte of the same composition and the same working conditions as indicated with respect to Examples 1-7. Example 8 is a comparative example.

Example 8

Additions: 0.145 g / l BYD (1.78 mM) plus 1.6 g / l acetic acid (28 mM)

initial surface finish 30 microinch OLA final surface finish 20 microinch CLA Smoothness - 33 #.

Example 9

Additions:

0.128 g / L EOBTD (0.7 mM)
0.088 g / l BTD (1.01 mM)

0.4 g / L acetic acid (6.96 mM) initial surface finish 30 microinches CM final surface treatment 10 microinch CLA smoothness

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The comparative examples 1-3 explain the effect at. the change in the quantity ratio EO33YD: BYD with regard to the acetylenic additive, "/ if this If the quantity ratio is too high, no deposition occurs at low current densities. These comparative examples also have an effect if the carboxylic acid is omitted. The precipitate is then shiny and therefore brittle. The examples according to the invention all form ductile, semi-gloss coatings a wide range of current density. Example 9 '.v was chosen to give the optimal combination of good smoothness, ductility over a wide range and no sharp gloss change at low current density to show, compared to Example 3, which explains a similarly optimized bath according to the prior art, that has been used technically up to now.

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Claims (13)

Claims y Aqueous electrolyte for galvanic oil plating, characterized in that he / (a) at least 30 g per liter of a Nicke1-II salt, (b) 0.1 to 250 mmol per liter of a mixture including water-soluble acetylenic compounds an oC-Alkynol and a condensation product of an alkinol with an alkylene oxide in the weight ratio of cC-alkynol: condensation product from 4: 1 to 1: 4 and (c) 0.1 to 45 g per liter of a non-conjugated carboxylic acid is composed with a pKa value between 3.0 and 5.0. 2. Electrolyte according to claim 1, characterized in that the cC -alkinol corresponds to the formula R ₁ -CHOHC ^ CR ₂ , in the R-. and Rp are each hydrogen atoms or an alkyl, alkenyl or alkynyl group having 1 to 4 carbon atoms or such a group having an amino or hydroxyl group as a substituent. 3. Electrolyte according to claim 2, characterized in that that the ° C alkyne oil is 2-butyne-1,4-diol. 4. Electrolyte according to one of claims 1-3, characterized in that the condensation product is a Condensation product from an eC-Alkynol according to Claim 2 is with 1-20 moles of an alkylene oxide. - 13 - 209838/1095 5. Electrolyte after. Claim 4, characterized in that that the condensation product 1-4 moles of ethylene oxide • contains. 6. Electrolyte according to claim 5, characterized in that the condensation product is a condensation product of 2-butyne-1,4-diol. 7. Electrolyte according to one of claims 1-6, characterized in that the carboxylic acid is acetic acid. 8. Electrolyte according to one of claims 1 - 7, characterized in that das.TTickelsalz Ricke 1-II-tihlor id and / or sulfate. 9. electrolyte according to claim 8, characterized in that that it also contains boric acid. 10. Electrolyte according to claim 8-9, characterized in that it is 225 to 35o g / l Mckel-II sulfate, 30 to 50 g / l Uickel-II-öhlorid and 20 to 45 g / l boric acid. 11. Electrolyte according to claim 8-9, characterized in that that it is 50 to 225 g / l Mckel II sulfate, 150 to 200 g / l Contains nickel-II-chloride and 30 Hs, 50 g / l boric acid. 12. A method for coating metal objects with Nicke! Coatings, characterized in that the Articles immersed in an electrolyte according to any one of claims 1-11 and from the electrolyte thereon electrodeposits nickel. 13. Metal objects which have been coated according to claim 12. 209838/1095