Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
  • C25D3/06—Electroplating: Baths therefor from solutions of chromium from solutions of trivalent chromium
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
  • C25D17/10—Electrodes, e.g. composition, counter electrode
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
  • C25D3/10—Electroplating: Baths therefor from solutions of chromium characterised by the organic bath constituents used
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/627—Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D9/00—Electrolytic coating other than with metals
  • C25D9/04—Electrolytic coating other than with metals with inorganic materials
  • C25D9/08—Electrolytic coating other than with metals with inorganic materials by cathodic processes

Definitions

• the present invention refers to an electroplating bath for electroplating a chro- mium or chromium alloy layer, the bath comprising trivalent chromium ions, organic carboxylic acid, sulfate ions, sodium conductive ions, and additives in the form of inorganic sulfur compound and boric acid as well as a process using such an electroplating bath.
• Chrome deposits from trivalent chrome electrolytes are widely used in the in- dustry due to their unique properties they allow substrates to work longer and under tougher conditions that they would normally survive in.
• Decorative chrome plating is designed to be aesthetically pleasing and durable. Thicknesses range from 0.05 to 0.5 ⁇ m, however they are usually between 0.13 and 0.25 ⁇ m. Decorative chrome plating is also very corrosion resistant and is often used on car parts, tools and kitchen utensils.
• hexavalent chrome deposits were featuring a blue-white appearance that is distinguishing from the trivalent chrome deposits. This colour is still very appreciated by customers that are used to hexavalent chrome products.
• JP2009035806 describes a trivalent chromium plating bath and a method for producing a chromium plating.
• This plating bath contains (1) complex solution of trivalent chromium obtained by maintaining under heating at least 1 type of component chosen from group which consists of aqueous solution aliphatic car- boxylic acid and its salt, and aqueous solution containing trivalent chrome com- pound, (2) conductive salt (3) buffer for pH, and (4) at least 1 type of sulfur- containing compound chosen from the group having an S02 group.
• the draw- back of such a plating solution is the use of a sulfur-containing organic com- pound instead of inorganic one and they do not use iron in the plating bath.
• JP2010189673 describes novel trivalent chromium plating bath capable of forming a trivalent chromium plating film having better corrosion resistance as compared with the prior art.
• a trivalent chromium plating bath comprising an aqueous solution containing a water-soluble trivalent chromium compound, a conductive salt, a pH buffer, a sulfur-containing compound and an aminocar- boxylic acid.
• the drawback of such a plating bath is the lack of sodium and iron ions in the plating bath which will not get the desired color.
• WO2019117178 describes a trivalent chromium plating solution containing: a trivalent chromium compound; a complexing agent; potassium sulfate and am- monium sulfate as conductive salts; a pH buffer; and a sulfur-containing organic compound.
• the trivalent chromium plating solution is practical and has a high plating deposition rate.
• the drawback of such a plating solution is the use of a sulfur-containing organic compound instead of inorganic one and they do not use iron in the plating bath.
• EP2411567 describes a chromium electroplating solution comprising a chro- mium electroplating solution comprising: (1) a water soluble trivalent chro- mium salt; (2) at least one complexant for trivalent chromium ions; (3) a source of hydrogen ions sufficient to create a pH of from 2.8-4.2; (4) a pH buffering compound; and (5) a sulfur-containing organic compound.
• the chromium elec- troplating solution is usable in a method for producing an adherent metallic coating on a decorative article, such coating having enhanced resistance to cor- rosion in environments containing calcium chloride.
• the drawback of such a solution is the use of a sulfur-containing organic compound instead of inorganic one and the absence of iron ions in the solution.
• an electroplating bath for depositing a chromium or chromium alloy layer which comprises a) at least one source of trivalent chromium ions, b) at least one source of sulfate ions, 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.
• the sulfate based trivalent chromium ions bath allows to obtain a whiter colour of the plating opposed to chloride based bath that get a darker plating with a higher carbon percentage.
• the choice of the sodium is preferred to increase the whiteness of the plat- ing.
• the use of ferric or ferrous ions also increase the corrosion resistance per- mitting to pass the PV1073 A test.
• the combination of ferric, sodium and sulfate ions permit to obtain a blue and white colour close to those from hexavalent chrome deposits.
• an inorganic sulfur such as an oxyacid anion containing sulfur having the valence lower than 6 is preferred.
• the at least one organic acid is 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.
• malic acid preferably selected from the group consisting of malic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, and mixtures thereof.
• succinic acid preferably selected from the group consisting of malic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, and mixtures thereof.
• succinic acid preferably selected from the group consisting of malic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, and mixtures thereof.
• adipic acid preferably selected from the group consisting of malic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, and mixtures thereof.
• malic acid
• the concentration of the at least one organic acid is from 5 to 40 g/L, preferably from 10 to 30 g/L, more preferably from 15 to 25 g/L.
• the concentration of the at least one trivalent chro- mium ion is from 5 to 25 g/L, preferably from 8 to 20 g/L.
• the concentration of the sulfate ions from at least one source of sulfate ions is from 150 to 300 g/L, preferably from 180 to 280 g/L, more preferably from 200 to 250 g/L.
• the source of trivalent chromium ions is chro- mium(lll) sulphate in acidic or basic form.
• the at least one inorganic sulfur compound is selected from the group of oxyacid anions comprising sulfur having a valence lower than 6, preferably selected from the group consisting of:
• the concentration of the at least one inorganic sul- fur compound is from 5 to 500 mg/L, preferably from 10 to 200 mg/L.
• the electroplating bath can comprise at least one source of ferric or ferrous ions.
• concentration of the ferric or ferrous ions from 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, and even more preferably from 40 to 100 mg/L.
• the concentration of the at least one pH buffer is in a range from 50 to 120 g/L, preferably from 60 to 110 g/L, more preferably from 80 to 100 g/L.
• a pH buffer it is preferred to use at least one of the group boric acid, citric acid, succinic acid, lactic acid, tartaric acid, and mixtures thereof. Particular pre- ferred is the use of boric acid as pH buffer.
• the pH of the bath is preferably in the range from 1 to 5, more preferably from 2 to 4, and even more preferably from 3.1 to 3.9.
• the concentration of the sodium vinyl sulfonate is preferably from 0.1 to 5 g/L, more preferably from 0.2 to 3 g/L.
• the bath is (substantially) free of at least one of chloride ions, ammonium ions, amino carboxylic acid ions and hexavalent chromium ions. In particular, it is preferred that some or all of these ions are absent.
• the concentration of sodium saccharin is from 0.1 to 10 g/L, and more preferably from 1 to 5 g/L.
• the at least one polyalkylene glycol has a molecular weight of lower than 2000 g/mol and is preferably selected from the group consisting of:
• the advantage of having at least one polyalkylene glycol, especially at least one polyalkylene glycol with a molecular weight of lower than 2000 g/mol, in the bath is that thicknesses of the deposits which are obtainable with the bath are higher than with baths that do not contain said polyalkylene glycol.
• the concentration of the at least one polyalkylene glycol is from 1 to 15 g/L, preferably from 5 to 10 g/L.
• a preferred embodiment of the electroplating bath for depositing a chromium or chromium alloy layer comprises: a) 5 to 25 g/L of trivalent chromium ions from at least one source of chro- mium ions, b) 150 to 300 g/L of sulfate ions from at least one source of sulfate ions, c) 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) 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) 50 to 120 g/L of at least one pH buffer, and, optionally, i) 20 to 200 mg/L of ferric or ferrous ions from at least one source of fer- ric or ferrous ions.
• a method for preparing an electroplated product by electroplating a substrate comprising the following steps:
• A) providing an electroplating bath comprising : a) at least one source of trivalent chromium ions, b) at least one source of sulfate ions, 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;
• the cathode current density is in a range from B to 14 A/dm 2 , preferably from 5 to 10, and/or the anode current density is in a range from 4 to 12 A/dm 2 , preferably from 5 to 10 A/dm 2 .
• the anodes consist of a mixed metal oxide, preferably a mixed metal oxide selected from the group consisting of mixed metal oxides of at least two of platinum, ruthenium, iridium and tantalum, more preferably mixed metal oxides of iridium and tantalum.
• the deposition rate during step C) is from 0.01 to 0.5 ⁇ m/min, preferably from 0.02 to 0.3 ⁇ m/min, and more preferably from 0.03 to 0.2 ⁇ m/min.
• step C) is conducted at a temperature from 35 to 60°C, pref- erably from 40 to 58°C, more preferably from 45 to 55°C.
• the alloy obtainable from this method com- prises or consists of carbon, sulphur, oxygen, chrome and, optionally, iron.
• the alloy has a colour measured by L, a, b values from 80 to 86, -0.8 to 0, -1.5 to 1.0.
• the L, a, b values are from 80 to 86, -0.8 to 0, -0.8 to 1.
• the L, a, b values are from 83 to 85, -0.7 to -0.4, -0.5 to 0.2.
• the percentage of carbon in the alloy is preferably from 1 to 5 atomic % (at%), more preferably from 2 to 4 at%.
• the alloy preferably comprises from 0,5 to 4 at%, more preferably from 1 to 3 at% sulfur.
• the alloy preferably comprises from 1 to 5 at%, preferably from 2 to 4 at% of oxygen.
• the alloy preferably comprises from 0 to 12 at% of iron.
• the percentage of iron in the alloy is from 3 to 12 at%, preferably from 5 to 10 at%.
• the alloy preferably com- prises from 74 to 94.5 at%, more preferably from 79 to 90 at%, chrome.
• the atomic % (at%) of the alloy can be determined by optical emission spectroscopy (OES).
• Fig.l shows the chromium coverage on a Hull cell panel with the three points (HCD, MCD, LCD) used for the examples.
• the panels were evaluated: the thickness of Chromium using the X-Ray method EN ISO 3497 in three points 1cm from the left edge define as HCD (High Current Density), 5 cm from the left edge define as MCD (Medium Current Density), 7 cm from the left edge defined as LCD (Low Current Density).
• the colour at the point defined as MCD was measured by a Colorimeter KONICA MINOLTA CM2600 defining the colour as CIELAB (L, a, b).
• Chromium deposit coverage measuring the mm from the left edge to the maximum coverage of the deposit to the right.
• Chromium deposit was tested to the PV1073 A that is an auto- motive standard used to evaluate the corrosion performance of Chromium de- posit to the Calcium Chloride.
• the present invention refers to the alloy carried out with the example n°6 char- acterized in that the alloy composition contains 5-10 at % of Fe, 1-3 at % of S, 2-4 at % of C, 2-4 at % of O, remaining at % Cr (up to 100 at %) and reaching a comparable color to the reference example and a good deposition rate, with the features of claim 1 and the method for preparing an electroplated product by using the electroplating bath with the features of claim 10.
• the bath did not contain Methyl Polyethylen Glycol (Mw 500).
• Mw 500 Methyl Polyethylen Glycol
• the disadvantage of omitting said compound in the bath is that the ob- tained thickness at HCD is much lower than with the bath according to the in- vention (bath n°6).
• the oxyacid sul- phuranion anion of sodium dithionite
• alone is not able to increase the com- pliance regarding the color, the coverage and the PV 1073A.
• the bath did not contain an oxyacid sulphur anion, i.e. did not contain sodium dithionite in the present case.
• the disadvantage of omitting said compound in the bath is that the thicknesses at HCD, MCD and LCD are much lower than with the bath according to the invention (bath n°6). Color, coverage and PV 1073A are complying.
• the example n°6b shows a similar results to the n°6 but with the better colour performance. In particular the b value reaches a very close value to the refer- ence CrVI, wherein the efficiency is just a little bit, i.e. not significantly, reduced.

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• 2020
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