EP3712302B1 - Electrolytic nickel plating composition and electrolytic nickel plating method using the same composition - Google Patents

Description

The invention relates to a composition according to the preamble of claim 1 and a method for electrolytic nickel plating according to the preamble of claim 5.

Classic nickel baths consist of a mixture of nickel sulfate, nickel chloride, sodium saccharin or allyl sulfonate (so-called primary brighteners), secondary brighteners, which generally have an alkyne group as functionality, and boric acid as a so-called conductive salt or buffer substance. The area of application for such nickel baths is in a pH range of 3.5 to 4.8.

Due to recurring concerns about the mutagenic properties of boric acid at correspondingly high levels of exposure and the strong restrictions imposed by legislation (cf. CLP Regulation 1272/2008/EC; SVHC candidate list according to Articles 57 and 59 REACh Regulation), boric acid-free compositions are increasingly being used offered and used for electrolytic nickel plating. However, these compositions generally have the disadvantage that the nickel layers deposited from them are less shiny and, in particular, less leveled.

GB 244,167 A discloses the use of a small amount of hydroquinone as a reducing agent of iron, which is present as a contaminant in the anodes and leads to the formation of pores in the nickel layer.

DE 865 695 B discloses the use of phenolic compounds as brighteners in nickel baths with high fluoride concentrations.

From the EP 3 431 634 A1 a composition is known which comprises 2-phenyl-5-benzimidazole sulfonic acid, salts thereof or mixtures thereof as a buffer substance.

The invention is based on the object of providing a composition for electrolytic nickel plating which has the properties of the The nickel layer produced on the substrate is equal to or better than that which can be achieved with a boric acid-containing composition. In addition, the invention is based on the object of providing a corresponding process for electrolytic nickel plating using such a composition.

This object is achieved by a composition with the features of claim 1 and a process for electrolytic nickel plating with the features of claim 5. Advantageous embodiments of the invention are specified in dependent claims 2 to 4.

According to the invention, an improved composition for electrolytic nickel plating is provided by comprising one or more nickel ion sources and a mono- or di-hydroxybenzene compound, preferably a hydroquinone compound, or salts thereof or mixtures thereof.

This results in very good nickel layers with comparable leveling, comparable level of gloss and comparable freedom from pores without boric acid.

An electrolytic nickel plating composition in the context of this invention means a nickel bath used for electrodeposition of a nickel layer on a substrate, the nickel ion source being nickel sulfate, nickel chloride and/or nickel sulfamate.

The mono- or di-hydroxybenzene compound preferably has a pK _s value between 6.5 and 12.5.

According to the invention, a mono-hydroxybenzene compound is 4-phenolsulfonic acid, a di-hydroxybenzene compound is catechol, resorcinol or hydroquinone.

From the series of di-hydroxybenzene compounds, hydroquinone (I) or its salts are particularly preferred.

According to the invention it is provided that the composition comprises an additional source of sulfoxylation ions and an additional source of carboxylation ions.

The additional sulfoxylation source or the additional carboxylation source is used as a weak complexing agent and, together with the mono- or di-hydroxybenzene compound, serves as a buffer substance. The sulfoxylation source or the carboxylation source also has a pKa value in the range from 6.5 to 12.5 and/or <3.

This allows a pH value of the composition of 3 to 9 to be achieved. If sulfoxylate or carboxylate ion sources are used that have pK _s values between 3 and 6.5, they must not exceed a concentration of more than 1 g/l.

The composition according to the invention, in conjunction with Ni ²⁺ ions, enables the formation of a new buffer region, which is between the working range of the composition and the region in which nickel hydrolysis begins, i.e. predominantly in a pH range between 3 and 7, preferably 5 to 7, lies.

It is assumed that - analogous to boric acid - the Ni ²⁺ ions are not coordinately saturated and therefore remain accessible to the acetylene-like shine carriers. This accessibility is a prerequisite for the shine carriers, as electron-deficient compounds, to be able to develop their π-backbonding properties and thus to stabilize transition states of deep oxidation states of nickel, which leads to the inhibition of electrocrystallization and the associated leveling.

The leveling performance of the composition is comparable to that of Boric acid. In addition, the degree of gloss of the nickel layer that can be achieved is comparable to that of boric acid.

The composition according to the invention also makes the nickel layers produced largely free of pores. So-called burning in the high current density range due to the formation of hydrogen and nickel hydroxide is avoided.

According to the invention, the additional sulfoxylation and carboxylation source is 5-sulfosalicylic acid (formula II).

It is assumed that at pH values of 3 to 5 there is no or only a very slight reaction between 5-sulfosalicylic acid (pKi 2.75, pK ₂ 12.38) and Ni ²⁺ ions. After deprotonation, 5-sulfosalicylic acid prefers the formation of an intramolecular hydrogen bond, which is so strong that complex formation with divalent nickel only becomes significant above a pH of 5.5. This behavior is practically identical to that between Ni ²⁺ ions and boric acid or borate.

A composition which comprises hydroquinone and 5-sulfosalicylic acid is particularly advantageous.

Advantageously, the mono- or di-hydroxybenzene compound, preferably the hydroquinone, or their salts or mixtures thereof, is present in amounts of 5-30 g/l, preferably 10-20 g/l, preferably 15 g/l.

The 5-sulfosalicylic acid is advantageously present in amounts of 5-40 g/l, preferably 5-25 g/l, preferably 10 g/l.

• das Bereitstellen des Substrats;
• das Kontaktieren des Substrats mit einer der vorgenannten Zusammensetzungen; und
• das Anlegen eines elektrischen Stroms an die Zusammensetzung und das Substrat.

According to the invention, the method for electrolytic nickel plating on a substrate comprises:

• providing the substrate;
• contacting the substrate with one of the aforementioned compositions; and
• applying an electrical current to the composition and substrate.

This causes a nickel layer to be deposited on the substrate, which has the properties described above.

For this purpose, the applied electrical current preferably has a strength of 0.5 to 4 A, preferably 1.5 to 3.5 A, preferably 3 A.

The following examples serve to explain the invention.

In order to assess the leveling performance, commercially available brass sheets (Hullzellbleche, Ossian) are coated using electrolytic nickel plating and then etched on the lower edge for 10 minutes with a 40 ° C warm aqueous solution containing sodium peroxodisulfate in an amount of 200 g / l .

To prepare the composition, 1000 ml of demineralized water are placed in a 2 l beaker (from VWR) and heated to 55 °C. While stirring, add the following compounds:
Basic substances: Nickel sulfate hexahydrate 200g/l Nickel chloride hexahydrate 60g/l Sodium saccharinate dihydrate 3.2 g/l Sodium allyl sulfonate 2.8g/l 1-(3-Sulfopropyl)-pyridinum betaine 35% 100ppm Propargyl alcohol 4 ppm Sodium lauryl sulfate 1g/l

Additions according to the invention: example 1

Hydroquinone 15g/l 5-Sulfosalicylic acid 10g/l

The solution is made up to 1500 ml with deionized water.

The pH value is determined electrochemically using a pH measuring chain on a pH meter (Metrohm 744 pH meter). The device is calibrated with appropriate commercial solutions (CertiPUR Buffer Solution for pH values 1, 4 and 7 from Merck) before the measurement. A calibrated Fluke 175 True RMS multimeter is used to measure current. The measured pH value is 5.

Solid anodes made of solid nickel material (1 cm thick) are used as anodes Wrappings used.

Commercially available brass sheets (Hullzellbleche, Ossian) are coated with 3 A for 780 min at 55 °C after the usual pretreatment (degreasing, rinsing, activation, rinsing). A magnetic stirring core with 100 revolutions per minute is used to move the electrolyte.

After coating, the pH of the electrolyte is also measured using the method described above. The measured pH value is 5.1.

As part of the investigation of the leveling performance, a homogeneous, high-gloss layer was found from 0.05 A/dm ² to the upper edge of the Hull cell sheet, with leveling at least as good as that in the comparative example with boric acid (45 g/l instead of hydroquinone and 5 -Sulfosalicylic acid) is the case.

The combination of hydroquinone and 5-sulfosalicylic acid has a strong inhibiting effect on layer growth in the high current density range, with an extremely homogeneous layer thickness distribution being achieved without any visible hydrogen evolution.

Example 2

4-phenolsulfonic acid, Na salt 40g/l 5-Sulfosalicylic acid 5g/l

Example 3 (not according to the invention)

4-phenolsulfonic acid, Na salt 40g/l Hydroquinone 10g/l

Example 4 (not according to the invention)

4-phenolsulfonic acid, Na salt 40g/l Hydroquinone sulfonic acid, K-salt 10g/l

Examples 2 to 4 are carried out and evaluated analogously to Example 1. What all examples have in common is that they produce high-gloss, high-leveling and ductile layers.

Furthermore, when using 4-phenolsulfonic acid alone, a corresponding layer can be produced that meets all the requirements of a layer of a bright nickel bath with the exception of a slight burning in the high current density range, which is usually not relevant in practice. This limitation at high current densities can be corrected very efficiently by adding the second substances specified in the examples, which makes the applicable current density range significantly larger than with corresponding boric acid processes while maintaining all other aspects of a bright nickel layer.

It is assumed that this expansion of the current density range is largely due to the complexing properties of the additionally introduced phenolic compounds, which are effective precisely in the pH range of nickel hydroxide formation.

Claims (5)

1. A composition for electrolytic nickel plating comprising one or more sources of nickel ions in the form of nickel sulfate, nickel chloride and/or nickel sulfamate, a mono- or dihydroxybenzene compound or the salts or mixtures thereof as a complexing agent in a quantity greater than 5 g/L and 5 sulfosalicylic acid as an additional source of sulfoxylate and carboxylate ions, wherein the composition contains 4 phenolsulfonic acid or hydroquinone, pyrocatechol or resorcinol as the mono- or dihydroxybenzene compound.
2. The composition according to Claim 1, characterised in that the mono- or dihydroxybenzene compound, preferably the hydroquinone, or the salts or mixtures thereof, is present in quantities of 5-30 g/l, preferably 10-20 g/l, preferably 15 g/l.
3. The composition according to any one of the preceding claims, characterised in that the 5-sulfosalicylic acid is present in quantities of 2-40 g/l, preferably 5-25 g/l, preferably 10 g/l.
4. The composition according to any one of the preceding claims, characterised in that it has a pH of 3 to 7.
5. A method for electrolytic nickel plating on a substrate, characterised in that it comprises:

   - providing the substrate;

   - contacting the substrate with a composition for electrolytic nickel plating according to any one of Claims 1 to 4; and

   - applying an electrical current to the composition for electrolytic nickel plating and the substrate.