KR20220119012A - Sulfate-based ammonium-free trivalent chromium decorative plating process - Google Patents

Abstract

The present invention relates to an electroplating bath for electroplating a layer of chromium or a chromium alloy comprising an additive in the form of trivalent chromium ions, organic carboxylic acids, sulfate ions, sodium conductive ions, and inorganic sulfur compounds and boric acid. , as well as to processes using such electroplating baths.

Description

Sulfate-based ammonium-free trivalent chromium decorative plating process

The present invention relates to an electroplating bath for electroplating a chromium or chromium alloy layer, comprising an additive in the form of trivalent chromium ions, organic carboxylic acids, sulfate ions, sodium conducting ions, and inorganic sulfur compounds and boric acid. Electroplating baths, as well as processes using such electroplating baths.

Chromium deposits from trivalent chromium electrolytes are widely used in industry because of their unique properties that allow substrates to function longer in the harsher conditions they would normally withstand.

In recent decades, deposition methods relying on trivalent chromium have become more common for health and environmental purposes. Indeed, hexavalent chromium substances are under regulatory pressure due to their toxic properties. They have been classified as CMRs and the European Union has decided to give up their use for certain approvals under REACH regulations.

Decorative chrome plating is designed to be aesthetically pleasing and durable. The thickness ranges from 0.05 to 0.5 μm, but is generally from 0.13 to 0.25 μm. Decorative chrome plating is also very corrosion resistant and is often used in automotive parts, tools and kitchen utensils.

However, the hexavalent chromium deposit was characterized by a blue-white appearance that was distinct from the trivalent chromium deposit. The color is still highly appreciated by customers accustomed to hexavalent chromium products.

JP2009035806 describes a trivalent chromium plating bath and a method for producing chromium plating. This plating bath comprises (1) a complex solution of trivalent chromium obtained by holding under heating an aqueous solution of at least one type of component selected from the group consisting of an aqueous solution containing an aliphatic carboxylic acid and salts thereof, and an aqueous solution containing a trivalent chromium compound, (2 ) conductive salts, (3) a buffer for pH, and (4) at least one type of sulfur-containing compound selected from the group having an SO2 group. A disadvantage of this plating solution is that it uses a sulfur-containing organic compound instead of an inorganic one, and does not use iron in the plating bath.

JP2010189673 describes a novel trivalent chromium plating bath capable of forming a trivalent chromium plating film having better corrosion resistance compared to the prior art. The trivalent chromium plating bath comprises an aqueous solution containing a water-soluble trivalent chromium compound, a conductive salt, a pH buffer, a sulfur-containing compound and an aminocarboxylic acid. A disadvantage of these plating baths is that the plating bath lacks sodium and iron ions and the desired color is not obtained.

WO2019117178 discloses a trivalent chromium compound; complexing agent; potassium sulfate and ammonium sulfate as conductive salts; pH buffer; and a trivalent chromium plating solution containing a sulfur-containing organic compound. The trivalent chromium plating solution is practical and has a high plating deposition rate. A disadvantage of this plating solution is that it uses a sulfur-containing organic compound instead of an inorganic one, and does not use iron in the plating bath.

EP2411567 discloses (1) water-soluble trivalent chromium salts; (2) at least one complex to a trivalent chromium ion; (3) a source of hydrogen ions sufficient to produce a pH of 2.8 to 4.2; (4) pH buffering compounds; and (5) a chromium electroplating solution comprising a chromium electroplating solution containing a sulfur-containing organic compound. The chromium electroplating solution can be used in a method for producing an adherent metallic coating on a decorative article, such a coating having improved resistance to corrosion in environments containing calcium chloride. A disadvantage of these solutions is the use of sulfur-containing organic compounds instead of inorganic ones and the absence of iron ions in the solution.

None of these prior art documents focus on obtaining L, a, b values close to hexavalent chromium deposits for trivalent chromium decorative applications with good corrosion resistance and high deposition rates averaging 0.4 μm in 5 min. is not aligning

Accordingly, starting from this prior art, it is an object of the present invention to have good corrosion resistance with L, a, b values (consisting of 80 to 85, -0.8 to 0, -0.5 to 1.0) approximate to hexavalent chromium deposits. (Can pass Volkswagen test PV1073 A) to give a chrome plated product obtained with good deposition rate.

This problem is solved by an electroplating bath having the features of claim 1, and is solved by a method for manufacturing an electroplated product using the electroplating bath having the features of claim 10. Further dependent claims describe preferred embodiments.

According to the present invention, there is provided an electroplating bath for depositing a layer of chromium or a chromium alloy, comprising:

a) a source of at least one trivalent chromium ion;

b) a source of at least one sulfate ion;

c) at least one organic acid as a complexing agent;

d) sodium saccharin,

e) at least one polyalkylene glycol,

f) sodium vinyl sulfonate,

g) at least one inorganic sulfur compound,

h) at least one pH buffer, and optionally,

i) an electroplating bath comprising at least one source of ferric or ferrous ions.

Surprisingly, it has been found that the sulfate-based trivalent chromium ion bath allows to obtain a whiter color plating as opposed to the chloride-based bath which provides a darker plating with a higher carbon percentage. As the conductive ion, the choice of sodium is desirable to increase the whiteness of the plating. The use of ferric or ferrous ions also increases the corrosion resistance to pass the PV1073 A test. The combination of ferric, sodium and sulfate ions makes it possible to obtain a bluish-white color close to that of hexavalent chromium deposits.

It has also been found that the use of inorganic sulfur, such as a sulfur containing oxyacid anion having a valence of less than 6, is preferred. In practice, most decomposition products of organosulfur compounds cause chromium ability problems. The advantage of the use of sulfur-containing oxyacid anions is that they do not affect the plating bath because they already contain sulfate ions, as they will produce sulfate as a decomposition product. A further advantage of having a sulfur-containing oxyacid anion having a valence of less than 6 in the bath is that the thickness of the deposit obtainable by said bath is higher than with a bath not containing a sulfur-containing oxyacid anion having a valence of less than 6.

The at least one organic acid is preferably selected from the group of dicarboxylic acids, preferably selected from the group consisting of malic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, and mixtures thereof. Particular preference is given to the use of malic acid as organic acid.

It is preferred that the concentration of the at least one organic acid is between 5 and 40 g/L, preferably between 10 and 30 g/L, more preferably between 15 and 25 g/L.

In a preferred embodiment, the concentration of the at least one trivalent chromium ion is between 5 and 25 g/L, preferably between 8 and 20 g/L.

In a preferred embodiment, the concentration of sulfate ions from the at least one source of sulfate ions is between 150 and 300 g/L, preferably between 180 and 280 g/L, more preferably between 200 and 250 g/L.

In a preferred embodiment, the source of trivalent chromium ions is chromium(III) sulfate in acidic or basic form.

The at least one inorganic sulfur compound is preferably selected from the group of oxyacid anions comprising sulfur having a valence of less than 6, selected from the group consisting of:

중아황산염 또는 메타중아황산염,

bisulfite or metabisulfite;

디티온산염 또는 하이드로설파이트,

dithionate or hydrosulfite;

티오설페이트,

thiosulfate,

테트라티오네이트,

tetrathionate,

설파이트 및

sulfites and

이들의 혼합물.

mixtures thereof.

In a preferred embodiment, the concentration of the at least one inorganic sulfur compound is from 5 to 500 mg/L, preferably from 10 to 200 mg/L.

The electroplating bath may include at least one source of ferric or ferrous ions. The concentration of ferric or ferrous ions from the at least one source of ferric or ferrous ions is preferably from 20 to 200 mg/L, more preferably from 30 to 150 mg/L, even more preferably preferably 40 to 100 mg/L.

It is preferred that the concentration of the at least one pH buffer is in the range of 50 to 120 g/L, preferably 60 to 110 g/L, more preferably 80 to 100 g/L.

As the pH buffer, it is preferable to use at least one of boric acid, citric acid, succinic acid, lactic acid, tartaric acid, and mixtures thereof. Particular preference is given to the use of boric acid as pH buffer. The pH of the bath preferably ranges from 1 to 5, more preferably from 2 to 4, and even more preferably from 3.1 to 3.9.

The concentration of sodium vinyl sulfonate is preferably 0.1 to 5 g/L, more preferably 0.2 to 3 g/L.

Preferably, the bath is (substantially) free of at least one of chloride ions, ammonium ions, amino carboxylate ions and hexavalent chromium ions. In particular, it is preferred that some or all of these ions are absent.

According to a preferred embodiment, the concentration of sodium saccharin is from 0.1 to 10 g/L, more preferably from 1 to 5 g/L.

In certain embodiments, the at least one polyalkylene glycol has a molecular weight of less than 2000 g/mol, and is preferably selected from the group consisting of:

폴리에틸렌 글리콜 모노메틸 에테르,

polyethylene glycol monomethyl ether,

에틸렌옥사이드/프로필렌옥사이드 공중합체,

Ethylene oxide / propylene oxide copolymer,

폴리에틸렌 글리콜 및

polyethylene glycol and

이들의 혼합물.

mixtures thereof.

The advantage of having at least one polyalkylene glycol in the bath, in particular at least one polyalkylene glycol having a molecular weight of less than 2000 g/mol, is that the thickness of the deposit obtainable by the bath does not contain the polyalkylene glycol. It is higher than by Joe who does not.

In a preferred embodiment, the concentration of the at least one polyalkylene glycol is between 1 and 15 g/L, preferably between 5 and 10 g/L.

Preferred embodiments of electroplating baths for depositing chromium or chromium alloy layers include:

a) trivalent chromium ions from a source of 5 to 25 g/L of at least one chromium ion,

b) 150 to 300 g/L of sulfate ions from a source of at least one sulfate ion,

c) from 5 to 40 g/L of at least one organic acid as a complexing agent,

d) 0.1 to 10 g/L of sodium saccharin,

e) from 1 to 15 g/L of at least one polyalkylene glycol,

f) 0.1 to 5 g/L of sodium vinyl sulfonate,

g) 5 to 500 mg/L of at least one inorganic sulfur compound,

h) from 50 to 120 g/L of at least one pH buffer, and optionally,

i) ferric or ferrous ions from a source of 20 to 200 mg/L of at least one ferric or ferrous ions.

According to the present invention, there is also provided a method for producing an electroplated article by electroplating a substrate comprising the steps of:

A) providing an electroplating bath comprising:

a) a source of at least one trivalent chromium ion;

b) a source of at least one sulfate ion;

c) at least one organic acid as a complexing agent;

d) sodium saccharin,

e) at least one polyalkylene glycol,

f) sodium vinyl sulfonate,

g) at least one inorganic sulfur compound,

h) at least one pH buffer, and optionally,

i) at least one source of ferric or ferrous ions;

B) immersing the substrate in the electroplating bath; and

C) applying an electric current between the anode and the substrate as a cathode to deposit the chromium or chromium alloy layer on the substrate.

In a preferred embodiment, the cathode current density is in the range of 3 to 14 A/dm, preferably 5 to 10 A/dm, and/or the anode current density is 4 to 12 A/dm, preferably 5 to It is in the range of 10 A/dm2.

The anode preferably consists of a mixed metal oxide, preferably a mixed metal oxide selected from the group consisting of a mixed metal oxide of at least two of platinum, ruthenium, iridium and tantalum, more preferably a mixed metal oxide of iridium and tantalum.

In a preferred embodiment, the deposition rate during step C) is from 0.01 to 0.5 μm/min, preferably from 0.02 to 0.3 μm/min, more preferably from 0.03 to 0.2 μm/min.

Step C) is preferably carried out at a temperature of 35 to 60°C, preferably 40 to 58°C, more preferably 45 to 55°C.

According to the invention, the alloy obtainable from this process comprises or consists of carbon, sulfur, oxygen, chromium and optionally iron. The alloy has a color with L, a, and b values ranging from 80 to 86, -0.8 to 0, and -1.5 to 1.0. In a preferred embodiment, the L, a, b values are from 80 to 86, from -0.8 to 0, from -0.8 to 1. In a more preferred embodiment, the L, a, b values are 83 to 85, -0.7 to -0.4, -0.5 to 0.2.

The percentage of carbon in the alloy is preferably 1 to 5 atomic % (at %), more preferably 2 to 4 at %. The alloy preferably comprises 0.5 to 4 at% sulfur, more preferably 1 to 3 at% sulfur. The alloy preferably comprises 1 to 5 at% oxygen, preferably 2 to 4 at% oxygen. The alloy preferably contains 0 to 12 at% iron. Optionally, the percentage of iron in the alloy is between 3 and 12 at%, preferably between 5 and 10 at%. The alloy preferably comprises 74 to 94.5 at%, more preferably 79 to 90 at% chromium. The atomic % (at %) of the alloy can be determined by optical emission spectroscopy (OES).

With reference to the following drawings and examples, the subject matter according to the present invention is to be described in more detail, and is not intended to limit the subject matter to the specific embodiments shown herein.

1 shows the chrome coverage on a Hull cell panel with three points (HCD, MCD, LCD) used in the example.

Example

All examples were performed in a Hull cell (250 mL) using a nickel plated brass panel using an MMO anode (titanium mesh cover with mixed metal oxide Ir/Ta) at 55° C. for 5 minutes with 5 A application.

The panels were evaluated: using the X-ray method EN ISO 3497 the chromium thickness was defined as 3 points from the left edge, i.e. 1 cm as HCD (high current density) and 5 cm from the left edge as MCD (medium current density). ), and 7 cm from the left edge is defined as LCD (low current density). The color at the points defined by the MCD was measured by the Colorimeter KONICA MINOLTA CM2600, which defines the color as CIELAB (L, a, b).

Chrome deposit coverage was assessed by measuring the same panel in mm from the left edge to the maximum coverage of the deposit. In addition, chromium deposits were tested with PV1073 A, an automotive standard used to evaluate the corrosion performance of chromium deposits on calcium chloride.

Example 1

Example 2

Example 3

Example 4

Example 5

Example 5b

Example 5c

Example 6

Example 6b

Example 7 Reference Test

The results of the examples are shown in the table below. The table shows how each component has different effects in terms of thickness, coverage, color and performance for the PV 1073 A corrosion test.

In particular, it shows that Reference Example 7, in which deposition is performed from a hexavalent chromium electrolyte, exhibits a very blue color due to very negative values of a and b, but does not pass the PV1073 A test.

The present invention relates to an alloy composition comprising 5 to 10 at% Fe, 1 to 3 at% S, 2 to 4 at% C, 2 to 4 at% O, and the remainder at% Cr (up to 100 at%). Electroplating using an electroplating bath having the characteristics of claim 10, and an alloy having the characteristics of claim 1, which is carried out according to Example 6, characterized in that it contains a color and good deposition rate comparable to that of the reference example. It relates to a method of manufacturing a product.

In Example 5b, the bath contained no methyl polyethylene glycol (Mw 500). A disadvantage of omitting this compound in the bath is that the thickness obtained in the HCD is much lower than with the bath according to the invention (bath example 6). Moreover, in the absence of this compound, the sulfur oxyacid anion (an anion of sodium dithionate) (alone) cannot be high in color, coverage and conformance to PV 1073 A.

In Example 5c, the bath contained no oxyacid sulfur anions, ie no sodium dithionate in this case. A disadvantage of omitting this compound in the bath is that the thicknesses in HCD, MCD and LCD are much lower than with the bath according to the invention (bath example 6). Color, coverage and PV 1073 A conform.

Example 6b shows similar results to Example 6, but with better color performance. In particular, the value of b approaches a value very close to the reference CrVI, where the efficiency is only marginal, ie, does not decrease significantly.

Table showing the results:

Claims (15)

An electroplating bath for depositing a chromium or chromium alloy layer comprising:
a) a source of at least one trivalent chromium ion;
b) a source of at least one sulfate ion;
c) at least one organic acid as a complexing agent;
d) sodium saccharin,
e) at least one polyalkylene glycol,
f) sodium vinyl sulfonate,
g) at least one inorganic sulfur compound,
h) at least one pH buffer, and optionally,
i) an electroplating bath comprising at least one source of ferric or ferrous ions. The method according to claim 1, wherein the concentration of ferric or ferrous ions is preferably from 20 to 200 mg/L, more preferably from 30 to 150 mg/L, even more preferably from 40 to 100 mg/L. characterized in that, Joe. 3. A compound according to claim 1 or 2, characterized in that said at least one inorganic sulfur compound is selected from the group of oxyacid anions comprising sulfur having a valence of less than 6, preferably selected from the group consisting of By, Joe:

bisulfite or metabisulfite;

dithionate or hydrosulfite;

thiosulfate,

tetrathionate,

sulfites and

mixtures thereof. Crude according to any one of the preceding claims, characterized in that the concentration of the at least one inorganic sulfur compound is from 5 to 500 mg/L, preferably from 10 to 200 mg/L. The crude according to any one of the preceding claims, characterized in that the at least one polyalkylene glycol has a molecular weight of less than 2000 g/mol and is preferably selected from the group consisting of:

polyethylene glycol monomethyl ether,

Ethylene oxide / propylene oxide copolymer,

polyethylene glycol and

mixtures thereof. The crude according to any one of the preceding claims, characterized in that the concentration of the at least one polyalkylene glycol is between 1 and 15 g/L, preferably between 5 and 10 g/L. 7. The method of any one of claims 1 to 6, wherein the at least one organic acid comprises:
i) selected from the group consisting of dicarboxylic acids, preferably selected from the group consisting of malic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, and mixtures thereof, preferably malic acid, wherein said at least one organic acid is particularly preferably malic acid;
ii) crude, characterized in that it is contained in a concentration of 5 to 40 g/L, preferably 10 to 30 g/L, more preferably 15 to 25 g/L. 8. The pH buffer according to any one of the preceding claims, characterized in that the at least one pH buffer is selected from the group consisting of boric acid, the pH of the bath being preferably from 1 to 5, more preferably from 2 to 4, and even more preferably 3.1 to 3.9. 9. The method of any one of claims 1 to 8, wherein the bath is substantially free of at least one ion selected from the group consisting of chloride ions, ammonium ions, amino carboxylate ions, hexavalent chromium ions, and combinations thereof. Joe, characterized in that, preferably absent. A method for producing an electroplated article by electroplating a substrate comprising the steps of:
A) providing an electroplating bath comprising:
a) a source of at least one trivalent chromium ion;
b) a source of at least one sulfate ion;
c) at least one organic acid as a complexing agent;
d) sodium saccharin,
e) at least one polyalkylene glycol,
f) sodium vinyl sulfonate,
g) at least one inorganic sulfur compound,
h) at least one pH buffer, and optionally,
i) at least one source of ferric or ferrous ions;
B) immersing the substrate in the electroplating bath; and
C) applying an electric current between the substrate as a cathode and an anode to deposit the chromium or chromium alloy layer on the substrate. 11 . The anode current density according to claim 10 , wherein the cathode current density is in the range of 3 to 14 A/dm, preferably 5 to 10 A/dm, and/or the anode current density is 4 to 12 A/dm, preferably is in the range of 5 to 10 A/dm 2 . 12. The at least one anode according to claim 10 or 11, wherein said at least one anode is made of a mixed metal oxide, preferably a mixed metal oxide of at least two of platinum, ruthenium, iridium and tantalum, more preferably a mixed metal oxide of iridium and tantalum. A method, characterized in that it consists of a mixed metal oxide selected from the group consisting of. 13. The method according to any one of claims 10 to 12, wherein the deposition rate during step b is from 0.01 to 0.5 μm/min, preferably from 0.02 to 0.3 μm/min, more preferably from 0.03 to 0.2 μm/min. A method, characterized in that the range of. 14. The method according to any one of claims 10 to 13, characterized in that step C) is carried out at a temperature of 35 to 60 °C, preferably 40 to 58 °C, more preferably 45 to 55 °C. Way. 15. An alloy obtainable by the process according to any one of claims 10 to 14, wherein 1 to 5 at% carbon, 0.5 to 4 at% sulfur, 1 to 5 at% oxygen, 0 to 12 at% carbon. of iron and/or 74 to 94.5 at% chromium.

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