TW202415814A - Trivalent chromium plating method - Google Patents

Abstract

A trivalent chromium plating method is provided, including following steps of: degreasing: removing grease from a surface of a workpiece; plating semi-bright nickel layer: immersing the workpiece in a semi-bright nickel plating solution and applying a current thereto so as to deposit a semi-bright nickel layer on the surface of the workpiece; plating bright nickel layer: immersing the workpiece in a bright nickel plating solution and applying a current thereto so as to deposit a bright nickel layer on the semi-bright nickel layer; plating chromium layer: immersing the workpiece in a trivalent chromium plating solution and applying a current thereto so as to deposit a chromium layer on the bright nickel layer; wherein the trivalent chromium plating solution includes a conductive agent, a trivalent chromium agent, a trivalent chromium auxiliary, a regulator and a modifier; and passivation: immersing the workpiece in a passivating agent to form a passivating layer on the chromium layer.

Description

Trivalent chromium electroplating method

The present invention relates to electroplating technology, and in particular to a trivalent chromium electroplating method.

Chromium metal has the characteristics of high hardness and wear resistance. Generally, hexavalent chromium can be reduced to chromium metal through electroplating technology and deposited on the surface of a workpiece, thereby giving the workpiece a black or silver appearance, which is aesthetically pleasing and durable.

However, in the process of chromium electroplating, chromic acid that provides hexavalent chromium is a highly corrosive and volatile substance. In addition to easily causing problems such as volatility of the electroplating solution and damage to production equipment, hexavalent chromium will also cause health hazards to the operator's skin, respiratory tract, eyes, etc., and even has a carcinogenic risk, which poses occupational safety concerns. In addition, in order to comply with environmental regulations, hexavalent chromium electroplating technology requires a complicated wastewater treatment process, which leads to increased production costs.

Therefore, it is necessary to provide a novel and advanced trivalent chromium electroplating method to solve the above problems.

The main purpose of the present invention is to provide a trivalent chromium electroplating method which is simple and safe to operate and easy to treat wastewater.

To achieve the above-mentioned object, the present invention provides a trivalent chromium electroplating method, comprising the following steps: degreasing: removing grease from the surface of a workpiece; electroplating a semi-gloss nickel layer: immersing the workpiece in a semi-gloss nickel electroplating solution and applying a current to deposit a semi-gloss nickel layer on the surface of the workpiece; electroplating a full-gloss nickel: immersing the workpiece in a full-gloss nickel electroplating solution and applying a current to deposit a full-gloss nickel layer on the semi-gloss nickel layer; electroplating a chromium layer: immersing the workpiece in a trivalent chromium electroplating solution and applying a current to deposit a full-gloss nickel layer on the semi-gloss nickel layer. Applying a current to deposit a chromium layer on the all-gloss nickel layer, the trivalent chromium plating solution includes a conductive agent, a trivalent chromium agent, a trivalent chromium auxiliary agent, an adjusting agent and a correcting agent, wherein the conductive agent includes at least one ammonium salt, the trivalent chromium agent and the trivalent chromium auxiliary agent each include at least one trivalent chromium salt, the adjusting agent includes polyoxyethylene alkyl sodium sulfate, and the correcting agent includes ferric chloride; and passivation: immersing the workpiece in a passivating agent to form a passivation film on the chromium layer.

The following examples are merely used to illustrate possible implementations of the present invention, but are not intended to limit the scope of protection of the present invention, so it should be noted in advance.

Please refer to FIG. 1 , which shows a preferred embodiment of the present invention. The trivalent chromium electroplating method of the present invention includes the following steps.

Degreasing S1: Remove grease from the surface of a workpiece to prevent impurities from affecting subsequent coating. In this embodiment, the workpiece has a metal surface; the degreasing step S1 includes a thermal degreasing step S1-1, an electrolytic degreasing step S1-2, an acid degreasing step S1-3, and a terminal electrolytic degreasing step S1-4, which are performed in sequence to ensure that the grease on the surface of the workpiece is removed. The thermal degreasing step S1-1 is to immerse the workpiece in a thermal degreasing solution containing 60 grams per liter (g/L) to 100 g/L of a thermal degreasing agent, and control the temperature of the thermal degreasing solution to 65°C (±5°C), the specific gravity to be between 4 and 6, the degreasing speed is fast, and it is resistant to hard water. The electrolytic degreasing step S1-2 is to immerse the workpiece in an electrolytic degreasing solution containing 60 g/L to 100 g/L of electrolytic degreasing agent, and the temperature of the electrolytic degreasing solution is controlled to be 60°C (±5°C) and the specific gravity is between 5 and 7. The acid degreasing step S1-3 is to immerse the workpiece in a room temperature sulfuric acid solution containing 60 g/L to 120 g/L, and the specific gravity of the sulfuric acid solution is between 4 and 6. It is low in cost and can remove the metal oxide layer on the surface of the workpiece. The terminal electrolytic degreasing step S1-4 is to immerse the workpiece in a terminal electrolytic degreasing solution containing 40 g/L to 80 g/L of terminal electrolytic degreasing agent, and control the temperature of the terminal electrolytic degreasing solution to be 50°C (±5°C) and the specific gravity to be between 3 and 5, so that the effect is good and it is easy to wash with water. Preferably, after the degreasing step S1, a neutralization step S6 is further included, in which the workpiece is immersed in a neutralizing solution to neutralize the residues on the surface of the workpiece generated in the degreasing step S1. The neutralizing solution is, for example, a 10% hydrochloric acid solution, and other reagents can also be selected as required. In other embodiments, the workpiece may also have a plastic surface; the degreasing step may also select some sub-steps depending on the surface characteristics of the workpiece.

Electroplating semi-gloss nickel layer S2: Immerse the workpiece in a semi-gloss nickel electroplating solution and apply current to deposit a semi-gloss nickel layer on the surface of the workpiece, which has a good anti-corrosion effect and can effectively fill the surface of the workpiece. The semi-gloss nickel electroplating solution includes nickel sulfate, nickel chloride and boric acid; the content of nickel sulfate is 70 grams per liter (g/L) to 90 g/L, the content of nickel chloride is 90 g/L to 110 g/L, the content of boric acid is 35 g/L to 55 g/L, and the specific gravity of the semi-gloss nickel electroplating solution is between 11 and 14.

Electroplating full-gloss nickel S3: Immerse the workpiece in a full-gloss nickel electroplating solution and apply current to deposit a full-gloss nickel layer on the semi-gloss nickel layer to increase corrosion resistance and provide a bright appearance. The full-gloss nickel electroplating solution includes nickel sulfate, nickel chloride and boric acid; the content of nickel sulfate is 70 g/L to 90 g/L, the content of nickel chloride is 80 g/L to 110 g/L, the content of boric acid is 35 g/L to 55 g/L, and the specific gravity of the full-gloss nickel electroplating solution is between 11 and 15. In this embodiment, the reaction temperature of the electroplating step S2 of the semi-gloss nickel layer and the electroplating step S3 of the full-gloss nickel layer is 58°C to 60°C, and the deposition effect is good.

Electroplating chromium layer S4: The workpiece is immersed in a trivalent chromium electroplating solution and a current is applied to deposit a chromium layer on the full-gloss nickel layer. The trivalent chromium electroplating solution includes a conductive agent, a trivalent chromium preparation, a trivalent chromium auxiliary agent, a regulator and a corrector, wherein the conductive agent includes at least one ammonium salt, the trivalent chromium preparation and the trivalent chromium auxiliary agent each include at least one trivalent chromium salt, the regulator includes polyoxyethylene alkyl sodium sulfate, and the corrector includes ferric chloride, so as to provide a stable electroplating solution, so that chromium metal can be deposited on the outer surface of the workpiece, thereby having a gun-colored appearance and good wear resistance.

Specifically, the content of the conductive agent is 375 g/L to 450 g/L. The conductive agent includes ammonium chloride with a weight percentage concentration not exceeding 50%, which provides a conductive component. If the concentration of the conductive agent is too high, it is easy to cause crystallization of the trivalent chromium plating solution, and if the concentration is too low, it will cause poor conductivity. It should be adjusted accurately. The content of the trivalent chromium preparation is between 70 g/L and 90 g/L; the weight percentage concentration of the at least one trivalent chromium salt in the trivalent chromium preparation is between 30% and 50%; the trivalent chromium preparation further includes at least one halide with a weight percentage concentration between 30% and 50% and at least one ammonium salt with a weight percentage concentration between 25% and 40%, so that metallic chromium can be plated out stably. The trivalent chromium preparation is consumed during the electroplating process, and therefore needs to be replenished at a rate of 1600 ml per kiloampere hour. In the trivalent chromium additive, the weight percentage concentration of the at least one trivalent chromium salt is between 80% and 90%; the trivalent chromium additive further includes at least one halide with a weight percentage concentration between 5% and 10% and at least one ammonium salt with a weight percentage concentration between 5% and 10% to replenish the chromium and conductive components lost due to the trivalent chromium electroplating solution. In this embodiment, for every 1 kg of the conductive agent added, 40 ml to 45 ml of the trivalent chromium additive is added as a supplement for the loss of the carryover.

In this embodiment, the weight percentage concentration of polyoxyethylene alkyl sodium sulfate in the modifier can be, for example, 10%; the content of the modifier is 6 mL/L to 20 mL/L, which can remove the black streaks on the chromium layer and make it bright; when the content of the modifier is too low, the deposition rate of the medium current plating area decreases, and the chromium layer will have black streaks, which should be carefully controlled. The content of the corrector is 1 mL/L to 2 mL/L, and the weight percentage concentration of ferric chloride in the corrector is between 1% and 5%. In this embodiment, each 1 mL/L of the corrector can increase the iron content by 33 ppm. It is used to improve the deep plating ability of the trivalent chromium plating solution when the tank is opened, and can be added selectively. The correcting agent preferably further includes a stabilizer, the weight percentage concentration of the stabilizer is between 10% and 20%, so that each component can be stably dispersed. Preferably, the trivalent chromium electroplating solution can further include a blackening agent, the content of the blackening agent is 50 mL/L to 100 mL/L, and the blackening agent includes ammonium chloride with a weight percentage concentration of at least 8% (10% in this embodiment) to adjust the color of the chromium layer to meet different appearance requirements.

In the electroplating chromium layer step S4, an electrode is provided as an anode and the workpiece is provided as a cathode. The area ratio of the electrode to the workpiece is controlled to be between 1.5 and 2.0:1, and a good deposition effect is achieved. In this embodiment, the electrode is a graphite anode and is fixed with an anode hook made of titanium-containing material, which has a good conductive effect; the electroplating conditions are controlled as follows: the cathode current density is 800~160 amperes/square meter, and the anode current density is 325~550 amperes/square meter, so as to have a better deposition distribution; the pH value of the trivalent chromium plating solution is 2.7 to 3.5, preferably between 3.0 and 3.2, the temperature is 30°C to 40°C, the voltage is between 9~12 volts and the ripple rate is less than 10%. When the pH value of the trivalent chromium plating solution is low, the deposition rate of the chromium layer is fast and the coverage rate of the low current area is poor; when the pH value of the trivalent chromium plating solution is high, the deposition rate of the chromium layer is slow and the coverage rate of the low current area is good, which can be adjusted with concentrated hydrochloric acid or ammonia water. In addition, when the temperature of the trivalent chromium electroplating solution is lower than 30°C, the deposited chromium layer is darker, the deposition rate is slower and precipitates are precipitated; when the temperature of the trivalent chromium electroplating solution is higher than 40°C, the deposited chromium layer is lighter in color, the deposition rate is faster and the expected appearance cannot be achieved, so the temperature needs to be carefully controlled. Preferably, the deposition rate of the chromium layer is controlled to be 0.05 micrometers/minute (μ/min) to 0.1μ/min, which has a faster deposition rate than hexavalent chromium electroplating and better production efficiency.

Preferably, in the electroplating chromium layer step S4, a plating tank for accommodating the trivalent chromium plating solution is provided, and the inner wall of the plating tank is made of polyvinyl chloride (PVC), ABS resin or polyethylene material to avoid affecting the plating effect; the plating tank is also equipped with an air agitator and an ion exchanger, the air agitator is used to stir the trivalent chromium plating solution to make the components evenly mixed and distributed, and the ion exchanger is used to remove metal impurities in the trivalent chromium plating solution to avoid the metal impurity content in the trivalent chromium plating solution being too high, resulting in the color of the workpiece being uniform, black shadows or black lines, etc.

The following is a specific example to illustrate the bath preparation process of the trivalent chromium electroplating solution. First, the electrode is installed on one side of the plating tank, pure water is injected, the air agitator is started and the temperature is heated to 60-65°C; the conductive agent is slowly and in small amounts, and pure water is injected to 85% of the required total volume, and stirred at 60-65°C for at least 16 hours to ensure that the conductive agent is completely dissolved; after cooling to 45°C, the trivalent chromium preparation is slowly and in small amounts, and stirred at 45°C for at least 4 hours; after cooling to 45°C, the adjusting agent, the correcting agent and the trivalent chromium auxiliary agent are added and dissolved in sequence; pure water is injected to the required total volume and stirred for at least 2 hours. After cooling to 32°C, the pH value of the trivalent chromium plating solution is tested and adjusted as needed to meet the plating conditions; finally, the trivalent chromium plating solution is electrolyzed at a current density of 10.8 amperes per square meter for 2 hours under the plating conditions (e.g., 32°C) before trial plating.

Passivation S5: The workpiece is immersed in a passivating agent to form a passivation film on the chromium layer. The reaction temperature in the passivation step S5 is preferably 58°C to 60°C, which can enhance the passivation effect of the chromium layer and increase the adhesion, and reduce the water stain residue on the workpiece after air drying.

It should be noted that between the aforementioned steps, water washing, ultrasonic vibration, activation, wind shearing, solution recovery and color fixation steps may be included according to the process requirements, as shown in FIG1 , which will not be described in detail here. Through the above steps, the trivalent chromium electroplating method of the present invention does not contain chromic acid and does not require the use of a reducing agent, which can effectively reduce the volatility of harmful gases. Compared with the hexavalent chromium electroplating process, it has the advantages of simple operation, safety, and simple wastewater treatment. In addition, through the composition of the trivalent chromium electroplating solution, the deposition rate of the chromium layer is fast and the coverage rate is good, which can effectively improve production capacity and reduce production costs.

S1~S6,S1-1~S1-4: Steps

FIG1 is a block flow chart of a preferred embodiment of the present invention.

S1~S6,S1-1~S1-4: Steps

Claims (10)

A trivalent chromium electroplating method comprises the following steps: Degreasing: removing grease from the surface of a workpiece; Electroplating a semi-gloss nickel layer: immersing the workpiece in a semi-gloss nickel electroplating solution and applying a current to deposit a semi-gloss nickel layer on the surface of the workpiece; Electroplating a full-gloss nickel: immersing the workpiece in a full-gloss nickel electroplating solution and applying a current to deposit a full-gloss nickel layer on the semi-gloss nickel layer; Electroplating chromium layer: immersing the workpiece in a trivalent chromium electroplating solution and applying a current to deposit a chromium layer on the full-gloss nickel layer, the trivalent chromium electroplating solution includes a conductive agent, a trivalent chromium preparation, a trivalent chromium auxiliary, an adjusting agent and a correcting agent, wherein the conductive agent includes at least one ammonium salt, the trivalent chromium preparation and the trivalent chromium auxiliary each include at least one trivalent chromium salt, the adjusting agent includes polyoxyethylene alkyl sodium sulfate, and the correcting agent includes ferric chloride; and Passivation: immersing the workpiece in a passivating agent to form a passivation film on the chromium layer. The trivalent chromium electroplating method as described in claim 1, wherein the content of the conductive agent is 375 grams per liter (g/L) to 450 g/L, and the conductive agent includes ammonium chloride with a weight percentage concentration not exceeding 50%. The trivalent chromium electroplating method as described in claim 1, wherein the semi-gloss nickel electroplating solution comprises nickel sulfate, nickel chloride and boric acid; the content of nickel sulfate is 70 g/L to 90 g/L, the content of nickel chloride is 90 g/L to 110 g/L, and the content of boric acid is 35 g/L to 55 g/L. The trivalent chromium electroplating method as described in claim 1, wherein the all-bright nickel electroplating solution comprises nickel sulfate, nickel chloride and boric acid; the content of nickel sulfate is 70 g/L to 90 g/L, the content of nickel chloride is 80 g/L to 110 g/L, and the content of boric acid is 35 g/L to 55 g/L. The trivalent chromium electroplating method as described in claim 1, wherein for every 1 kg of the conductive agent added, 40 ml to 45 ml of the trivalent chromium additive is added; in the trivalent chromium additive, the weight percentage concentration of the at least one trivalent chromium salt is between 80% and 90%. The trivalent chromium electroplating method as described in claim 1, wherein the content of the trivalent chromium preparation is between 70 g/L and 90 g/L; in the trivalent chromium preparation, the weight percentage concentration of the at least one trivalent chromium salt is between 30% and 50%. A trivalent chromium electroplating method as described in claim 1, wherein the trivalent chromium electroplating solution further includes a blackening agent, the blackening agent includes ammonium chloride with a weight percentage concentration of at least 8%, and the content of the blackening agent is 50 milliliters per liter (mL/L) to 100 mL/L. A trivalent chromium electroplating method as described in any one of claims 1 to 7, wherein in the electroplating chromium layer step, an electrode is provided as an anode and the workpiece is provided as a cathode, and the area ratio of the electrode to the workpiece is controlled to be between 1.5 and 2.0:1. A trivalent chromium electroplating method as described in any one of claims 1 to 7, wherein in the chromium layer electroplating step, an electrode is provided as an anode, the workpiece is used as a cathode, and the electroplating conditions are controlled as follows: the cathode current density is 800~160 amperes per square meter, the anode current density is 325~550 amperes per square meter, the pH value of the trivalent chromium electroplating solution is 2.7 to 3.5, and the temperature is 30°C to 40°C. The trivalent chromium electroplating method as described in claim 6, wherein the degreasing step comprises a thermal degreasing step, an electrolytic degreasing step, an acid degreasing step and a terminal electrolytic degreasing step performed in sequence; after the degreasing step, a neutralization step is further included, wherein the workpiece is immersed in a neutralizing solution to neutralize the residues on the surface of the workpiece generated in the degreasing step; the semi-gloss nickel electroplating solution comprises nickel sulfate, nickel chloride and boric acid; the content of nickel sulfate is 70 g/L to 90 g/L, the content of nickel chloride is 90 g/L to 110 g/L, and the content of boric acid is 35 g/L to 55g/L, the specific gravity of the semi-gloss nickel electroplating solution is between 11 and 14; the reaction temperature of the electroplating semi-gloss nickel layer step and the electroplating full-gloss nickel layer step is 58°C to 60°C; the full-gloss nickel electroplating solution includes nickel sulfate, nickel chloride and boric acid; the content of nickel sulfate is 70 g/L to 90 g/L, the content of nickel chloride is 80 g/L to 110 g/L, the content of boric acid is 35 g/L to 55g/L, the specific gravity of the full-gloss nickel electroplating solution is between 11 and 15; the content of the conductive agent is 375 g/L to 450 g/L g/L, the conductive agent includes ammonium chloride with a weight percentage concentration of not more than 50%; for every 1 kg of the conductive agent, 40 ml to 45 ml of the trivalent chromium additive is added; in the trivalent chromium additive, the weight percentage concentration of the at least one trivalent chromium salt is between 80% and 90%; the trivalent chromium additive further includes at least one halide with a weight percentage concentration between 5% and 10% and at least one ammonium salt with a weight percentage concentration between 5% and 10%; the trivalent chromium electroplating solution further includes a blackening agent, the blackening agent includes ammonium chloride with a weight percentage concentration of at least 8%, and the content of the blackening agent is 50 ml/L (mL/L) to 100 ml/L (mL/L). mL/L; the content of the adjusting agent is 6 mL/L to 20 mL/L; the content of the correcting agent is 1 mL/L to 2 mL/L; in the correcting agent, the weight percentage concentration of ferric chloride is between 1% and 5%; the correcting agent further includes a stabilizer, and the weight percentage concentration of the stabilizer is between 10% and 20%; in the electroplating chromium layer step, an electrode is provided as an anode, and the workpiece is used as a cathode, and the area ratio of the electrode to the workpiece is controlled to be between 1.5 and 2.0:1, and the electroplating conditions are controlled to be: the cathode current density is 800 to 160 amperes per square meter, and the anode current density is 325-550 amperes per square meter, voltage between 9-12 volts and ripple rate less than 10%, pH value of the trivalent chromium plating solution between 2.7 and 3.5, temperature between 30°C and 40°C; control the deposition rate of the chromium layer to be between 0.05 micrometers per minute (μ/min) and 0.1 μ/min; the electrode is a graphite anode and is fixed with an anode hook made of a titanium-containing material; and the reaction temperature in the passivation step is between 58°C and 60°C.