EP2451997B1 - Nickel electrolyte - Google Patents

Abstract

A nickel electrolyte comprising: nickel salts, organic acid or salts thereof, from 0.05 to 1 g/l of inorganic solid with a grain size (d50) of from 0.1 to 3 μm.

Description

The present invention relates to a nickel electrolyte and its use.

Galvanic nickel electrolytes are known to those skilled in various designs. For example, for surface refinement, components are provided with copper layers, which are typically provided with two or three nickel layers and a chromium layer or other alloys. While the outer layers serve the visual appearance of the component, the lower layers essentially serve to protect against corrosion.

Typical applications are, for example, panels, strips, radiator grille on automobiles.

• NiSO₄•7H₂O    240 bis 310 g/l
• NiCl₂•6H₂O    45 bis 50 g/l
• H₃BO₃    30 bis 40 g/l.

The most commonly used nickel electrolytes are based on the so-called Watts electrolyte, which typically has the following composition:

• NiSO ₄ • 7H ₂ O 240 to 310 g / l
• NiCl ₂ • 6H ₂ O 45 to 50 g / l
• H ₃ BO ₃ 30 to 40 g / l.

For corrosion protection, microcracked and microporous layers are used in the case of nickel layers. For microcracked layers, the deposition of nickel by the use of organic acids creates stresses. A microscope image of such a layer is in FIG. 3 shown. The cracks in the nickel layer continue in the chromium deposited thereon. Corrosive attacks are thereby passed on from the outer chromium layer on the inner nickel layer and do not affect the surface.

Microporous layers have displaced the microcracked layers in many areas. In microporous layers in addition to sulfur compounds and solids are used, but no organic acids.

FIG. 4 shows a picture of a microporous layer.

Although numerous variants of nickel electrolytes are known, there is still a need for improved nickel electrolytes that result in coatings that have altered or improved corrosion properties.

US 3,471,271 describes a process in which cracks are generated in the nickel layer by adding large amounts of solids.

The object of the present invention was to provide nickel electrolytes with which coatings with other, preferably improved, corrosion properties can be obtained.

• Nickelsalze
• 5 bis 150 g/l organische Säure, oder deren Salze
• 0,05 bis 1 g/l anorganischen Feststoff mit einer Korngröße (d50) von 0,1 bis 3 µm
• < 10 g/l Borsäure;

wobei der Nickelelektrolyt kein EDTA enthält.The problem is solved by a nickel electrolyte containing:

• nickel salts
• 5 to 150 g / l of organic acid, or salts thereof
• 0.05 to 1 g / l of inorganic solid with a particle size (d50) of 0.1 to 3 microns
• <10 g / l boric acid;

wherein the nickel electrolyte does not contain EDTA.

Suitable nickel compounds are various nickel salts, in particular nickel chloride, nickel acetate, nickel sulfate and mixtures thereof.

The amount of nickel in the nickel electrolyte is preferably 5 to 300 g / L, with an amount of 200 to 280 g / L, each calculated to NiCl, being preferred.

In particular, low molecular weight organic acids such as formic acid, acetic acid, propionic acid, butyric acid and mixtures thereof are suitable as the organic acid. Suitable amounts of the acid are 5 to 150 g / l, preferably 10 to 30 g / l or 40 to 70 g / l.

Furthermore, the nickel electrolyte according to the invention contains an inorganic solid, for example aluminum oxide, silicon dioxide, silicates such as, for example, talc, silicon carbide or mixtures thereof. Preferred contents of the inorganic solid are in the range of 0.1 to 0.8 g / l, with an amount of 0.1 to 0.3 g / l being preferred.

The nickel electrolyte preferably contains more than 0.1 g / l of solids, for example 0.15 g / l or 0.2 g / l. Preferably, the nickel electrolyte contains less than 0.8 g / L or less than 0.7 g / L, more preferably less than 0.5 g / L, and more preferably less than 0.4 g / L or less than 0.3 g / l.

In some embodiments, the amount of inorganic solids may also be 0.05 g / L to 100 g / L or 0.1 to 60 g / L. As average particle size of the inorganic solid (d50), preference is given to using particle sizes of from 0.1 to 3 μm, more preferably from 0.8 to 3 μm, even more preferably from 1 to 2.2 μm. In other embodiments, the mean grain size may be in the range of 200 nm to 5 μm or 0.8 to 3 μm.

According to the invention, it is achieved by the electrolyte that inorganic particles are incorporated in the layer. The result is a microcracked layer containing embedded inorganic particles. The corresponding layers obtained have hitherto not been known to the person skilled in the art.

The nickel electrolyte may contain conventional further ingredients of electrolytes, in particular wetting agents, buffer substances and / or brighteners.

In one embodiment, the nickel electrolyte additionally contains ammonia.

The content of boric acid is lead <10 g / l.

In one embodiment of the invention, the nickel electrolyte according to the invention contains no boric acid. It is preferred that the content of boric acid is <5 g / l, more preferably <1 g / l.

Preferably, the nickel electrolyte according to the invention contains no reducing agent such as hypophosphite, as it is used for electroless deposition. Preferably, the content of Reduktionsmütel <10 g / l, more preferably <5 g / l, even more preferably <1 g / l.

Reduction agent is an agent that can reduce to Ni from the Ni ²⁺ electrolyte.

The nickel electrolyte of the invention is preferably adjusted to an acidic pH between pH 1.5 and 6.5, more preferably 2 to 5, and even more preferably 3 to 4.5. This can be done in the usual way by adding acids or alkalis.

The invention also provides a process for electroplating a component comprising the step of contacting the component with the nickel electrolyte according to the invention and applying a current density of 2 to 15, preferably 5 to 10 A / dm ² at a temperature of 20 to 55, preferably 25 to 35 ° C.

According to the invention, a nickel electrolyte is used which already leads to a microcracked structure without the addition of solid, regardless of how the further treatment of the electrolyte is carried out, for example whether the further treatment of the layer involves hot or cold rinsing. For the purposes of this application, a nickel electrolyte (without the addition of a solid) is considered to be a microcracked nickel electrolyte if, on application of a current density of 5 A / dm ² and a temperature of 25 ° C. at a layer thickness of 2 μm, followed by cold rinsing, a cracked surface appears.

It has been found that for a particularly good incorporation of a larger number of solid particles, it is important that the nickel layer produced is thicker than the d50 value of the particles used. The thicker the layers, the deeper and stronger the solid appears to have been incorporated. Layer thicknesses of more than 2 μm up to 5 μm are particularly preferred. The chrome layer thickness shows less influence. Chromium layer thicknesses in the range of about 0.375 to 2 microns are suitable.

In the process implementation shows an influence of the movement of the bath. A slight movement of the bath appears to be required to keep the inorganic solids dispersed in nickel electrolytes. Too much movement on the other hand seems to be detrimental, as it is believed that particles are ripped out of the cracks before they are sufficiently tightly bound.

Electroplating with nickel electrolytes is known in principle to the person skilled in the art and customary process measures for plating with nickel electrolytes are also applicable to the novel electrolyte according to the invention.

By using the new electrolyte, a special structure is obtained which has defined pores and cracks. Surprisingly, this leads to a significant change in the corrosion properties.

Typically, the component being electroplated is plastic or metal. In a conventional method, one or more copper layers are applied, which are then coated by one or more nickel layers and finally by decorative layers, for example chrome layers. At least one of the nickel layers is a nickel layer according to the invention.

The nickel electrolyte according to the invention can advantageously be applied with conventional galvanic equipment, so that no structural measures are required.

The invention furthermore relates to a component which has one or more layers obtainable by the process according to the invention.

• Figur 1 zeigt die Ergebnisse eines CASS-Tests mit Bauteilen, die gemäß Vergleichsbeispiel 1 (hinten) bzw. Vergleichsbeispiel 2 (vorne) beschichtet wurden.
• Figur 2 zeigt Ergebnisses eines Tests gegen Calciumchloridsalze auf Basis von Kaolinpasten. Verglichen wurde ein Bauteil mit einer Beschichtung gemäß Beispiel 2 (oben) mit einer Beschichtung gemäß dem Vergleichsbeispiel 1 (unten).
• Figur 3 zeigt eine Aufnahme einer mikrorissigen Schicht des Standes der Technik.
• Figur 4 zeigt eine mikroporige Schicht gemäß dem Stand der Technik.
• Figur 5 zeigt eine Struktur, die mit dem erfindungsgemäßen Nickelelektrolyten erhalten wurde.
• Figur 6 zeigt eine Oberflächenaufnahme, die mit dem des erfindungsgemäßen Elektrolyten erhalten wurde, aber ohne Zusatz eines anorganischen Feststoffes.
• Figur 7 zeigt eine rasterelektronenmikroskopische Aufnahme ohne Feststoff der Oberfläche gemäß Figur 6.
• Figur 8 eine rasterelektronenmikroskopische Aufnahme der erfindungsgemäßen Schichten mit einem eingebauten Feststoff.
• Figur 9 zeigt eine Beschichtung wie sie mit einem Elektrolyten der US 3,471,271 Beispiel 1 erhalten wurde (ohne Zusatz von Feststoff).
• Figur 10 zeigt unter identischen Bedingungen die Abscheidung eines erfindungsgemäßen Elektrolyten gemäß Beispiel 2 (ohne Zusatz von Feststoff).

Another object of the invention is the use of the nickel electrolyte according to the invention for coating components.

• FIG. 1 shows the results of a CASS test with components coated according to Comparative Example 1 (back) and Comparative Example 2 (front).
• FIG. 2 shows results of a test against calcium chloride salts based on kaolin pastes. A component with a coating according to Example 2 (top) with a coating according to Comparative Example 1 (bottom) was compared.
• FIG. 3 shows a photograph of a microrissigen layer of the prior art.
• FIG. 4 shows a microporous layer according to the prior art.
• FIG. 5 shows a structure obtained with the nickel electrolyte of the present invention.
• FIG. 6 shows a surface image obtained with that of the electrolyte according to the invention, but without the addition of an inorganic solid.
• FIG. 7 shows a scanning electron micrograph with no solid surface according to FIG. 6 ,
• FIG. 8 a scanning electron micrograph of the layers of the invention with a built-solid.
• FIG. 9 shows a coating as with an electrolyte of US 3,471,271 Example 1 was obtained (without addition of solid).
• FIG. 10 shows under identical conditions, the deposition of an inventive electrolyte according to Example 2 (without the addition of solid).

Surprisingly, it has been found that the layers according to the invention show improved corrosion resistance, in particular in the corrosion of calcium chloride as road salt. Calcium chloride has a lower dew point than other salts and is extremely active due to its strong hyposcopic behavior. The widespread microporous chromium coatings are often attacked clearly visible already after a winter.

The invention is explained in more detail by the following examples.

Example 1 (comparative example)

nickel sulfate 240 g / l Nickel chloride: 45 g / l boric acid: 30 g / l Alumina, d50 = 2.5 μm 0.3 g / l Glossy carrier: 20 ml / l Wetting agent: 10 ml / l Brightener: 0.5 ml / l Temperature: 55 ° C current density 4 A / dm ² PH value: 3.8 Exposure time: 3 min

Movement by air injection

The coating produced shows a solids-dependent microporous surface with at least 8,000 pores / cm ² .

Example 2

Nickel chloride: 250 g / l ammonium acetate: 30 g / l Ammonium chloride: 20 g / l Acetic acid: 15 ml / l Brightener: 1 ml / l Alumina, d50 = 2μm: 0.5 g / l Temperature: 27 ° C Current density: 5 A / dm ² PH value: 3.5 Exposure time: 3 min

Movement by air injection

After the hot flushing process, the coating shows a defined, coherent structure combination with increased surface area and micropores.

Example 3

Nickel chloride: 180 g / l ammonium acetate: 30 g / l Sodium chloride: 50 g / l Acetic acid: 8 ml / l propionic acid: 5 ml / l Brightener: 0.5 ml / l Talc + alumina, d50 = 3 μm: 0.7 g / l Temperature: 30 ° C Current density: 6 A / dm ² PH value: 3.2 Exposure time: 3 min

Movement by air injection

After the hot flushing process, the coating shows a defined, coherent structure combination with increased surface area and micropores.

Example 4

Nickel chloride: 210 g / l Nickel sulfate: 44 g / l ammonium acetate: 20 g / l ammonium: 10 g / l Acetic acid: 10 ml / l Brightener: 1.0 ml / l Talc + silica, d50 = 1.5 μm 0.6 g / l Temperature: 29 ° C Current density: 5.5 A / dm ² PH value: 3.5 Exposure time: 3 min

Movement by air injection

After the hot flushing process, the coating shows a defined, coherent structure combination with increased surface area and micropores.

Example 5 - CASS test

• 50 g/l Natriumchlorid
• 0,26 g/l Kupfer-(II)-Chlorid • 2 H₂O
• Essigsäure zur pH-Einstellung auf 3,1 bis 3,3

The CASS test (copper accelerated acidic salt spray test) is described in DIN 50021. In a chamber, test pieces are sprayed with a saline solution of the following composition:

• 50 g / l sodium chloride
• 0.26 g / l copper (II) chloride • 2 H ₂ O
• Acetic acid for pH adjustment to 3.1 to 3.3

After 24, 48 or 96 hours, the part is removed from the mist, rinsed thoroughly and dried. The dissolved copper salt causes a dissolution of the most precious metal in the layer system.

The CASS test shows the corrosion path in the layer system.

Example 6 - Results of the CASS Tests

FIG. 1 shows the results of the CASS test after 96 h. In the case of the rear component, coated according to Comparative Example 1, corrosion phenomena can be seen, while the component with a coating according to Example 2 (front) shows no signs of corrosion.

Example 7 - Calcium chloride kaolin test

A paste is prepared from 5 ml of saturated calcium chloride solution and 3 g of kaolin and a pH of 6.5 to 7.5. It is a mushy substance. A defined amount is applied to a sample body in a suitable diameter and stored at 60 ° C for 48 h. This is an accelerated test for assessing resistance to calcium chloride-containing road salt.

Example 8 - Results of the Calcium Chloride Kaolin Assay

FIG. 2 shows that the coated according to Comparative Example 1 component (front) shows significant signs of corrosion, while the inventively coated part (rear) shows no signs of corrosion.

Example 9

A nickel electrolyte, as used in Example 1 of the US 3, 471, 271 was described without the addition of a solid at a current strength of 6 A / dm ² coated. FIG. 9 shows that the structure has no cracks without addition of solid.

Under identical coating conditions, the electrolyte was coated according to Example 2. FIG. 10 shows that this electrolyte gives already cracked structures without the addition of solids.

Claims (15)

1. A nickel electrolyte containing:

   - nickel salts

   - from 5 to 150 g/I of organic acid or salts thereof

   - from 0.05 to 1 g/I of inorganic solid with a grain size (d50) of from 0.1 to 3 µm;

   - < 10 g/I of boric acid;

   wherein said electrolyte does not contain EDTA.
2. The nickel electrolyte according to claim 1, characterized in that the content of nickel is from 5 to 300 g/I, preferably from 200 to 280 g/I, based on NiCl.
3. The nickel electrolyte according to claim 1 or 2, characterized in that said organic acid is selected from formic acid, acetic acid, propionic acid, butyric acid, and salts thereof and mixtures thereof, and/or that said organic acid is contained in an amount of from 10 to 30 g/l, or from 40 to 70 g/l.
4. The nickel electrolyte according to claim 1 to 3, characterized in that said nickel electrolyte forms layers that contain microcracks.
5. The nickel electrolyte according to at least one of claims 1 to 4, characterized in that said inorganic solid is selected from aluminum oxide, silicon dioxide, silicates, such as talcum, silicon carbide, and mixtures thereof.
6. The nickel electrolyte according to at least one of claims 1 to 5, characterized in that its content of inorganic solid is from 0.1 g/l to 0.3 g/l.
7. The nickel electrolyte according to at least one of claims 1 to 6, characterized in that the average grain size of the inorganic solid (d50) is from 0.8 to 3 µm, preferably from 1 µm to 2.2 µm.
8. The nickel electrolyte according to at least one of claims 1 to 7, characterized in that one or more of the ingredients wetting agents, buffer substances, brighteners, ammonia, alkali compound, alkaline earth compound, ammonium compounds are contained therein.
9. The nickel electrolyte according to at least one of claims 1 to 8, characterized in that said nickel is introduced therein in the form of nickel chloride, nickel sulfate, nickel acetate, or mixtures thereof.
10. The nickel electrolyte according to at least one of claims 1 to 9, characterized in that its pH is from 1.5 to 6.5, preferably from 3 to 4.5.
11. The nickel electrolyte according to at least one of claims 1 to 10, characterized in that no reducing agent and/or no boric acid are contained therein.
12. A process for electroplating a component, comprising the step of contacting the component with a nickel electrolyte according to any of claims 1 to 11, and applying a current density of 2 to 15 A/dm², preferably from 5 to 10 A/dm², at a temperature of from 20 to 55 °C, preferably from 25 to 35 °C.
13. The process according to claim 12, characterized in that one or more copper layers and optionally further nickel layers are applied to the component, and finally one or more cover layers, chromium layers are applied, and optionally a hot rinsing process is performed at least at 50 °C.
14. A component comprising one or more layers, wherein at least one layer is obtainable by the process according to claim 12 and contains inorganic solids.
15. Use of a nickel electrolyte according to any of claims 1 to 11 for the coating of components.

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