TWI762661B - Nickel electroplating bath for depositing a decorative nickel coating on a substrate - Google Patents

Abstract

The present invention is related to a nickel electroplating bath for depositing a decorative nickel coating on a substrate to be treated characterized in that the electroplating bath comprises at least a nickel ion source, at least one amino acid and/or at least one carboxylic acid, which is not an amino acid; wherein the total concentration of the amino acid(s) is ranging from 1 to 10 g/l, wherein the total concentration of carboxylic acid(s), which is/are not an amino acid, is ranging from 10 to 40 g/l; wherein the electroplating bath is free of boric acid; wherein the total concentration of the nickel ions is ranging from 55 to 80 g/l; and wherein the nickel electroplating bath has a chloride content ranging from 7.5 to 40 g/l. The present invention is also related to a method for depositing a nickel coating on a substrate to be treated; and the use of such an inventive nickel electroplating bath for depositing a bright, semi-bright, satin, matte or non-conductive particle containing nickel coating by conducting such a method.

Description

Nickel electroplating bath for depositing decorative nickel coatings on substrates

The present invention relates to a nickel electroplating bath for depositing decorative nickel coatings on substrates to be treated. The present invention also relates to a method of depositing a decorative nickel coating on a substrate to be treated. Furthermore, the present invention relates to the use of this inventive nickel electroplating bath for depositing bright, semi-bright, satin, matt or non-conductive particle-containing nickel coatings by implementing such a method.

In nickel electroplating baths it is often extremely important to maintain pH within defined ranges.

Therefore, buffer systems have been applied to nickel baths in the past to meet this goal.

The most conventional systems are based on the so-called "Watts electrolytic bath", which has the following general composition: 240-550 _g /l nickel _sulfate ( _NiSO4.7H2O or _NiSO4.6H2O ), 30-150 g/l nickel chloride (NiCl ₂ · 6 H ₂ O), and 30-55 g/l boric acid (H ₃ BO ₃ ).

A large amount of nickel sulfate provides the necessary concentration of nickel ions, while nickel chloride improves anode corrosion and increases conductivity. Boric acid acts as a weak buffer to maintain pH.

Additionally, to achieve the bright and glossy appearance of nickel electroplated coatings, organic and inorganic agents (brighteners) are often added to the electrolyte. The type of brightener added and its concentration determine the appearance of the nickel coating, ie, shiny, bright, semi-gloss, satin, matte, etc.

However, boric acid is also classified as a toxic substance and is considered banned from the world market. Therefore, there is a strong demand in the industry to replace boric acid with other non-toxic substances.

OBJECTS OF THE INVENTION In view of the prior art, it is therefore an object of the present invention to provide nickel electroplating baths that will be free of boric acid.

Furthermore, the object of the present invention is in particular to provide nickel electroplating baths which will be suitable as a basis for depositing various types of different nickel coatings with respect to their optical appearance and their chemical properties, such as bright nickel coatings, semi-bright nickel coatings , satin nickel coating, matt nickel coating or nickel coating with non-conductive particles.

Furthermore, the object of the present invention is to provide the deposition of various types of different nickel coatings (eg bright nickel coatings, semi-bright nickel coatings, satin nickel coatings, matte nickel coatings or Nickel Coatings Containing Non-Conductive Particles).

These objectives and others not explicitly stated but immediately derivable or identifiable by means of the introduction of the relationships discussed herein are achieved by a nickel electroplating bath having all the characteristics of Option 1. Appropriate modifications to the baths of the invention are protected in sub-claims 2 to 8. In addition, technical solution 9 relates to a method for depositing a decorative nickel coating on a substrate to be processed, while technical solutions 10 to 14 focus on appropriate modifications of this solution. The technical solution 15 relates to the use of such a nickel electroplating bath for depositing bright, semi-bright, satin, matt or non-conductive particle-containing nickel coatings by implementing such a method.

Accordingly, the present invention provides a nickel electroplating bath for depositing a decorative nickel coating on a substrate to be treated, characterized in that the electroplating bath comprises at least one source of nickel ions, at least one amino acid and/or at least one non-amine group Carboxylic acids of acids; wherein the total concentration of amino acid(s) is in the range from 1 to 10 g/l, and wherein the total concentration of carboxylic acids other than amino acids is in the range of 10 to 40 g/l wherein the electroplating bath is free of boric acid; wherein the total concentration of the nickel ions is in the range of 55 to 80 g/l; and wherein the nickel electroplating bath has a chlorine content in the range of 7.5 to 40 g/l .

Herein, at least one amino acid and/or at least one carboxylic acid represent complexing agents for complexing nickel ions in the respective nickel electroplating baths. In this context, the "classical" complexing agent of the prior art (ie, boronic acid) should and has been avoided. Therefore, the nickel electroplating bath of the present invention is boric acid free.

It is thus possible to provide nickel electroplating baths in an unforeseen manner, which are free of boric acid and have less impact on the environment.

In addition, it has been successfully achieved to provide nickel electroplating baths which are suitable as a basis for depositing various types of different nickel coatings with respect to their optical appearance and their chemical properties, such as bright nickel coatings, semi-bright nickel coatings, satin Nickel coating, matt nickel coating or nickel coating with non-conductive particles. The nickel electroplating bath also showed good levelling properties and produced well leveled coatings.

Brief Description of Tables The objects, features and advantages of the present invention will also become apparent upon reading the following description in conjunction with the Tables: Table 1 presents inventive tests for bright nickel coatings according to examples of the invention. Table 2 presents comparative tests of bright nickel coatings of comparative examples outside the scope of the present invention. Table 3 presents inventive tests of bright nickel coatings according to other embodiments of the present invention.

In a preferred embodiment of the present invention, the nickel electroplating bath has a chlorine content in the range of 10 to 30 g/l.

The expression "chlorine content" in the context of the present invention means a source of chloride ions.

Nickel chloride can be partially replaced by sodium chloride.

In addition, the chloride in the electrolyte can be partially replaced by an equivalent amount of bromide.

In the context of the present invention, the source of nickel ions may be any type of nickel salt or nickel complex suitable for providing free nickel ions in the respective nickel electrodeposition bath, such as nickel chloride and/or nickel sulfate.

The nickel electroplating bath of the present invention can be used to deposit a decorative nickel coating on a plurality of die castings based on metals and/or metal alloys, in particular steel, copper, brass, aluminum, bronze, magnesium and/or zinc to be treated on different types of substrates; or on "POP" substrates. "POP" in the sense of the present invention means "electroplating on plastic". Thus, the POP substrate comprises a synthetic substrate, preferably based on at least one polymeric compound, more preferably on acrylonitrile-butadiene-styrene (ABS), polyamide, polypropylene or ABS/PC (polycarbonate).

In a preferred embodiment of the present invention, the nickel electroplating bath is substantially free, preferably completely free, of any other metal ions (other than those always provided in the electroplating baths of the present invention) that can be electrolytically deposited as a nickel alloy layer with a source of nickel ions other than the nickel ion source).

Specifically, the nickel electroplating bath is preferably substantially free, preferably completely free of iron, gold, copper, bismuth, tin, zinc, silver, lead, and aluminum ion sources.

The expression "substantially free" in the context of the present invention means that the concentration of the respective source of metal ions is less than 1 g/l, preferably less than 0.1 g/l and more preferably less than 0.01 g/l.

In one embodiment, the at least one amino acid is selected from the group consisting of beta alanine, glycine, glutamic acid, DL-aspartic acid, threonine, valine, glutamic acid or L-serine.

In one embodiment, the at least one carboxylic acid that is not an amino acid is selected from the group consisting of: a monocarboxylic acid, a dicarboxylic acid, or a tricarboxylic acid.

In its preferred embodiment, the at least one carboxylic acid that is not an amino acid is selected from the group consisting of: tartaric acid, glycolic acid, malic acid, acetic acid, lactic acid, citric acid, succinic acid, propionic acid, formic acid or glutaric acid.

In one embodiment, the electroplating bath comprises at least two different carboxylic acids, neither of which are amino acids; wherein the total concentration of the two different carboxylic acids is in the range of 10 to 40 g/l.

In one embodiment, the electroplating bath comprises at least one amino acid and one carboxylic acid other than an amino acid; wherein the total concentration of the amino acids is in the range of 1 to 10 g/l, wherein the amino acids are not The total concentration of the carboxylic acid of the acid is in the range of 10 to 40 g/l.

In a preferred embodiment, the total concentration of the nickel ions is in the range of 60 to 75 g/l and preferably 62 to 72 g/l.

In one embodiment, the pH of the electroplating bath is in the range of 2 to 6, preferably 3 to 5, more preferably 3.5 to 4.7.

Additionally, the nickel electroplating baths may in certain embodiments of the present invention include at least one wetting agent, such as 2-ethylhexyl sulfate, di-alkylsulfosuccinate, polymeric naphthalene sulfonate, lauryl sulfate salt or lauryl ether sulfate, wherein the concentration of this wetting agent (when used) is in the range of 5 to 500 mg/l, preferably in the range of 10 to 350 mg/l and more preferably in the range of 20 to 250 within the range of mg/l.

The electroplating bath may further comprise benzoic acid or an alkali metal benzoate in a concentration in the range of 0.005 to 5 g/l, preferably 0.02 to 2 g/l, more preferably 0.05 to 0.5 g/l. These additive compounds help reduce internal stress in the deposited coating.

The electroplating bath may also further comprise salicylic acid in a concentration in the range of 0.1 to 10 g/l, preferably 0.3 to 6 g/l, more preferably 0.5 to 3.5 g/l. This additive positively affects the hardness, durability and optical properties of the resulting coating.

The electroplating bath may further comprise selected from brighteners, levelers, internal stressors, specifically in the range of 0.005 to 5 g/l, preferably 0.02 to 2 g/l, more preferably 0.05 to 0.5 g/l Additional compounds for reducing and wetting agents.

Exemplarily, primary brighteners such as unsaturated, in most cases aromatic sulfonic acids, sulfonamides, sulfoimidides, N - Sulfonylcarboxamides, sulfinates, diarylidene or salts thereof, in particular sodium or potassium salts.

The most familiar compounds are, for example, isophthalic acid, sulfonimide benzoate (saccharin), trisodium 1,3,6-naphthalenetrisulfonate, sodium benzenemonosulfonate, dibenzenesulfonimide, benzene Sodium monosulfinate, vinyl sulfonic acid, allyl sulfonic acid, sodium salt of allyl sulfonic acid, p-toluenesulfonic acid, p-toluenesulfonic acid amide, sodium propargyl sulfonate, benzoic acid sulfonic acid imines, 1,3,6-naphthalenetrisulfonic acid and benzylbenzenesulfonamides.

Furthermore, this primary brightener may comprise propargyl alcohol and/or its derivatives (ethoxylated or propoxylated).

The primary brightener may be added to the electrolyte bath at a concentration in the range of 0.001 to 8 g/l, preferably 0.01 to 2 g/l, more preferably 0.02 to 1 g/l. Several primary brighteners can also be used at the same time.

Furthermore, the object of the present invention is also solved by a method for depositing a decorative nickel coating on a substrate to be treated, the method comprising the following method steps: i) bringing the substrate to be treated into contact with the nickel electroplating bath of the present invention; ii ) contacting at least one anode with a nickel electroplating bath; iii) applying a voltage to the substrate to be treated and the at least one anode; and iv) electrodepositing a decorative nickel coating on the substrate to be treated.

In one embodiment, the deposition method is performed in an operating temperature range of 30°C to 70°C, preferably 40°C to 65°C, and more preferably 50°C to 60°C.

In one embodiment, the deposition method is performed in an operating current density range of 1 to 7 amps/dm ² (ASD), preferably 1.5 to 6 ASD, and more preferably 2 to 5 ASD.

In one embodiment, the deposition method is in the range of 5 to 50 minutes, preferably 6 to 35 minutes and more preferably 8 to 25 minutes for applying a voltage and then electrodepositing a decorative nickel coating (method step iii) and iv)) during the working hours.

In one embodiment, the electroplating bath further comprises at least one saccharin and/or saccharin derivative in the form of a saccharin salt, preferably a sodium salt of saccharin, in a concentration of 1 to 10 g/l, preferably 1.5 to 7 g/l l, preferably in the range of 2 to 6 g/l; and at least one sulfonic acid and/or a sulfonic acid derivative in the form of a sulfonate salt, preferably selected from the group consisting of: allylsulfonic acid, vinylsulfonic acid Sulfonic acid, sodium salt of allylsulfonic acid, sodium salt of vinylsulfonic acid or mixtures thereof, in a total concentration of 0.1 to 5 g/l, preferably 0.25 to 3.5 g/l, more preferably 0.5 to 2.0 g/l within the range of l. Thereby, a bright nickel coating is deposited. The selective choice of additives described above shows the unique application of the nickel electroplating baths of the present invention for the purpose of depositing decorative nickel coatings of varying optical appearance and chemical properties.

In another alternative to the foregoing embodiment, the electroplating bath further comprises at least one diol, preferably selected from the group consisting of 2,5 hexynediol and 1,4 butynediol, at a concentration of 10 to 300 mg/l, preferably 50 to 250 mg/l, more preferably 100 to 220 mg/l; or at least one selected from the group consisting of pyridinium propylsulfobetaine (PPS) or derivatives thereof (eg PPS-OH ) with a total concentration in the range of 5 to 350 mg/l, preferably 10 to 200 mg/l, more preferably 50 to 150 mg/l.

Thereby, a semi-bright nickel coating is deposited. The selective selection of the above-mentioned additives, again as in the above-mentioned alternative examples, demonstrates the unique application of the nickel electroplating baths of the present invention for the purpose of depositing decorative nickel coatings of different optical appearances and chemistries.

In addition, the object of the present invention is also solved by utilizing such a nickel electroplating bath by implementing such a method for depositing bright, semi-bright, satin, matt or non-conductive particle-containing nickel coatings.

Accordingly, the present invention addresses the provision of boric acid-free nickel electroplating baths for depositing decorative nickel coatings of varying optical appearance and chemistries (e.g. bright nickel coatings, semi-bright nickel coatings, satin nickel coatings, matte nickel coatings coatings or nickel coatings containing non-conductive particles).

The following non-limiting examples are provided to illustrate embodiments of the invention and to facilitate an understanding of the invention, but are not intended to limit the scope of the invention, which is defined by the scope of the claims appended hereto.

General Notes: Substrates are always pretreated before they are used for nickel deposition: i) degreased by hot dip cleaner ii) electrolytic degreased iii) rinsed, iv) acid leached with 10 vol% sulfuric acid

The sample substrate has been scratched for subjective optical judgment of leveling. The sparkle of the resulting nickel coating on the substrate was also judged optically. The size of the sample substrate is typically 7 cm x 10 cm (width x length), which makes the surface to be treated 70 cm ² on one side (Tables 1, 2 and 3).

All concentrations given in Tables 1, 2 and 3 for the complexing agent in acid form are listed in g/l unless otherwise stated.

The tests given in Tables 1, 2 and 3 are numbered sequentially.

Turning now to the Table, Table 1 shows the tests performed for bright nickel coatings according to embodiments of the present invention.

For all tests listed in Table 1, nickel deposition was performed in a Hull cell with 2.5 amps (A) applied for 10 minutes at a temperature of 55°C +/- 3°C. In addition, 3 liters/min of compressed air was introduced during nickel deposition.

For all tests listed in Table 1, the nickel concentration was 67 g/l.

It is clearly seen that all of the inventive tests listed in Table 1 produced uniformly bright and leveled nickel coatings. These boric acid-free baths consistently gave good significant results even when scrutinizing several different acids as complexing agents for nickel ions. All acids are used in the specific respective concentration ranges claimed in solution 1, which depend on the chemical nature of the acid of the amino acid or the carboxylic acid which is not an amino acid.

The respective rows show the test number, the acid used as complexing agent, the concentration of acid used as complexing agent, the pH of the nickel bath, and the nickel coating achieved in the range from the highest current density to the lowest current density on the Hall cell panel. Layer results (total length considered 10 cm) (rows of Table 1 have been described from left to right). Table 1 : Testing of Bright Nickel Coatings

Table 2 presents comparative tests of bright nickel coatings of comparative examples outside the scope of the present invention.

For all tests listed in Table 2, nickel deposition was carried out as for the tests listed in Table 1 in a Hall cell at a temperature of 55°C +/- 3°C. In addition, 3 liters/min of compressed air was introduced during nickel deposition. Each row shows the test number, acid used as complexing agent, concentration of acid used as complexing agent, pH of nickel bath, applied current (expressed in amperes (A)), nickel ion concentration (in g/l ), the time of application of the current (in minutes), and the nickel coating results achieved (the rows of Table 2 have been described from left to right). Table 2 : Comparative Test of Bright Nickel Coatings

Experiments 30 to 35 show comparative experiments using the same acids as some of the experiments in Table 1 but with different concentrations of the respective acids as complexing agents. All runs 30 to 35 had complexing agent concentrations for nickel ions that were too low or too high compared to the claimed concentration range.

Experiments 36 to 38 show comparative experiments. Here, the acid system was used at the claimed concentration range, but with altered operating parameters, namely current (run 36), application time (run 37), and nickel ion concentration (run 38). Individual values have been highlighted and underlined in Table 2 for illustrative purposes.

It is clear that all the comparative tests listed in Table 2 resulted in poorer results than the Table 1 tests. Obviously, the selection of appropriate different parameters to deposit a uniform bright nickel coating is unpredictable. Thus, the claimed bath and method are inventive as selection inventions based on the inventive selection of the required parameters, where it is clearly seen that changing even only one parameter results in a poor nickel coating rather than a bright and uniform nickel coating.

Comparative Runs 30 to 38 were also boric acid-free.

Experiments 39 to 41 show comparative experiments based on boric acid which has hitherto been commonly used as a complexing agent for nickel ions. Therefore, this represents common prior art.

Table 3 presents inventive tests of bright nickel coatings according to other embodiments of the present invention.

The tests listed in Table 3 have been carried out in the same manner as those listed in Table 1. Here, runs 42 to 46 show a combination of two carboxylic acids, neither of which are amino acids (runs 42 and 43); and a combination of an amino acid and a carboxylic acid that is not an amino acid ( Trials 44 to 46). All results of these inventive examples in Table 3 have the same good results as in Table 1 . All result in a uniform bright nickel coating. The row (concentration) has the concentrations of the two acids. Table 3 : Other Tests for Bright Nickel Coatings

While the principles of the invention have been illustrated with respect to certain specific embodiments and provided for illustrative purposes, it should be understood that various modifications to the invention will become apparent to those skilled in the art upon reading this specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims. The scope of the present invention is limited only by the scope of the appended claims.

Claims (14)

A nickel electroplating bath for depositing a decorative nickel coating on a substrate to be treated, the electroplating bath comprising at least one source of nickel ions, at least one amino acid and/or at least one carboxylic acid other than amino acid; wherein the The total concentration of (etc.) amino acids is in the range of 1 to 10 g/l, wherein the total concentration of the (etc.) carboxylic acids that are not amino acids is in the range of 10 to 40 g/l; wherein the electroplating The bath is free of boric acid; wherein the total concentration of the nickel ions is in the range of 55 to 80 g/l; and wherein the nickel electroplating bath has a chlorine content in the range of 7.5 to 40 g/l, characterized in that the nickel electroplating The bath further comprises: - saccharin and/or saccharin derivatives in the form of saccharin salts in a concentration in the range from 1.5 to 10 g/l, and - at least one sulfonic acid and/or sulfonic acid derivatives in the form of sulfonate salts, Its total concentration is in the range of 0.1 to 5 g/l. The nickel electroplating bath of claim 1, wherein the at least one amino acid is selected from the group consisting of beta alanine, glycine, glutamic acid, DL-aspartic acid, threonine, valine , glutamic acid or L-serine. The nickel electroplating bath of claim 1 or 2, wherein the at least one carboxylic acid that is not an amino acid is selected from the group consisting of: a monocarboxylic acid, a dicarboxylic acid, or a tricarboxylic acid. The nickel electroplating bath of claim 3, wherein the at least one carboxylic acid that is not an amino acid is selected from the group consisting of: tartaric acid, glycolic acid, malic acid, acetic acid, lactic acid, citric acid, succinic acid acid, propionic acid, formic acid or glutaric acid. The nickel electroplating bath of claim 1 or 2, wherein the electroplating bath comprises at least two different carboxylic acids, neither of which are amino acids; wherein the total concentration of the two different carboxylic acids is between 10 and 40 g/l within the range. The nickel electroplating bath of claim 1 or 2, wherein the electroplating bath comprises at least one amino acid and a carboxylic acid other than an amino acid; wherein the total concentration of the amino acids is in the range of 1 to 10 g/l , wherein the total concentration of the carboxylic acids other than amino acids is in the range of 10 to 40 g/l. The nickel electroplating bath of claim 1 or 2, wherein the total concentration of the nickel ions is in the range of 60 to 75 g/l. The nickel electroplating bath of claim 1 or 2, wherein the pH of the electroplating bath is in the range of 2 to 6. A method for depositing a decorative nickel coating on a substrate to be treated, comprising the method steps of: i) bringing the substrate to be treated in contact with a nickel electroplating bath as claimed in any one of claims 1 to 8; ii) bringing At least one anode is in contact with the nickel electroplating bath; iii) a voltage is applied to the substrate to be treated and the at least one anode; and iv) a decorative nickel coating is electrodeposited on the substrate to be treated. The method for depositing a decorative nickel coating as claimed in claim 9, wherein the deposition method is performed in an operating temperature range of 30°C to 70°C. A method for depositing a decorative nickel coating as claimed in claim 9 or 10, wherein the deposition method is performed in an operating current density range of 1 to 7 ampere/dm2 (ASD). A method for depositing a decorative nickel coating as claimed in claim 9 or 10, wherein the deposition method is in the range of 5 to 50 minutes for applying the voltage and subsequently electrodepositing the decorative nickel coating (method steps iii) and iv)) during working hours. The method for depositing a decorative nickel coating as claimed in claim 9 or 10, wherein the concentration of the saccharin and/or saccharin derivatives in the form of saccharin salts is in the range of 1.5 to 7 g/l; and the at least one sulfonic acid The total concentration of acid and/or sulfonic acid derivatives in the form of sulfonates is in the range of 0.25 to 3.5 g/l. Use of a nickel electroplating bath according to any of the preceding claims 1 to 8 for depositing a bright nickel coating by carrying out the method according to any of the claims 9 to 13.