Nickel plating process in the gravure printing industry
Release Time:
Aug 29,2015
The nickel plating of gravure printing plates mainly ensures that the copper layer can bond firmly with the roller core. This is an important step that needs to be taken seriously.
[One]
The installation of the roller must be stable, with good conductivity and proper sealing at the shaft end to prevent liquid leakage.
[Two]
Before electroplating, the roller must first be cleaned. If there is oil on the surface of the roller, the quality of the nickel plating cannot be guaranteed, leading to defects such as poor adhesion and thin plating. The steps are as follows:
(1) Rinse the plate roller and protective cover with clean water, then activate the surface with a 3% to 5% dilute sulfuric acid (H2SO4).
(2) Use a specialhigh-efficiency degreaserto remove debris (for example, the high-efficiency degreaser from Dongguan Changjin Company:Good degreasing effect, no residue left on the surface;Low dosage, fast degreasing speed;Non-corrosive and rust-proof to the workpiece;No heating required, can be operated at room temperature, saving energy;Pleasant fragrance, free of ether and other organic components, harmless to the human body;Economical and environmentally friendly.) When using, prepare the cleaning agent into a 2% to 5% aqueous solution, soak and scrub at room temperature, and heating will yield better results. Generally, use 600# water sandpaper or scouring pads with the cleaning agent to evenly and forcefully polish the roller.
(3) Rinse the plate roller and protective cover thoroughly with distilled water. The standard for cleanliness is that no water droplets hang on the plate surface and it is completely wet. Inadequate cleaning can cause bubbling and peeling of the nickel layer. After cleaning, it can be placed in the nickel plating tank for electroplating.
[Three]
Nickel is one of the iron group metals, and its plating solution has significant cathodic and anodic polarization effects during the electroplating process. Without adding complexing agents, a fine and dense nickel layer can be obtained. The main purpose of nickel plating is to prevent iron from displacing copper (the solution is nickel sulfate), allowing the copper layer to bond firmly with the iron rod.
1. Main components of the nickel plating solution
(1) Nickel sulfate (NiSO4·7H2O), the content in the plating solution is specified by some companies as 200~250g/L. If the nickel sulfate content is high, the plating layer will have a uniform color and allow for higher current density, resulting in a faster deposition rate.
(2) Nickel chloride (NiCl2·6H2O) content in the plating solution is specified by some companies as 30~50g/L, some as 55~60g/L, and others as 40~50g/L. Nickel chloride acts as an anode activator; on one hand, chloride ions can activate the anode, and on the other hand, nickel ions can replenish the concentration of nickel ions in the solution. Both are effective components. The content of nickel chloride is influenced by the electroplating process and product structure. If the area of the anode nickel block is sufficient, the product diameter is small, and the pH of the plating solution is low, the lower limit should be chosen; otherwise, excessive anode sludge will be produced, and the utilization efficiency of the nickel block will be low. If the process conditions are reversed, the upper limit should be chosen; otherwise, oxygen absorption will occur at the edges of the anode nickel block, leading to instability in the pH of the plating solution, which will gradually decrease, making later adjustments more troublesome.
(3) Boric acid (H3BO3) is a buffer that can release hydrogen ions (H+) and borate ions (H2BO32-). Its content in the plating solution is specified as 40~45g/L. Boric acid plays a role in stabilizing the pH value in the nickel plating solution. During the nickel plating process, the pH of the plating solution must be maintained within a certain range, generally specified as 4.0~4.6, often set at 4.2. If the pH is too low, H+ is easily discharged, reducing the current efficiency of nickel plating, and the plating layer is prone to pinholes; if the pH is too high, the plating solution becomes turbid, and metal ions around the cathode can be incorporated into the plating layer in the form of metal hydroxides, degrading the mechanical properties and roughening the appearance of the plating layer. Therefore, strict control of the pH value is essential in production. In addition to stabilizing the pH value, boric acid also helps the plating layer crystallize finely and prevents burning. When using high current density, a higher boric acid content (45g/L) should be used in the plating solution.
2. Preparation method of the plating solution
First, measure the volume of the plating tank, clean it, and calculate the usage of the main components. Then, inject 70% pure water into the tank and heat it to 40 degrees. Add the materials to the tank, turn on the plating solution circulation, and wait for all materials to dissolve. After that, supplement with pure water to the standard liquid level, continue filtering for more than 2 hours, replace the filter element when the plating solution is clear, sample and analyze the composition of the plating solution, and further adjust to the standard content. Perform low current electrolysis (1V) for 2 hours. Then, you can test the formal plating.
3. Process conditions
(1) Temperature of the nickel plating solution. The temperature of the nickel plating solution is generally controlled at 40℃±1℃. Increasing the temperature of the plating solution can enhance the solubility and conductivity of salts in the solution, accelerate the diffusion rate of nickel ions to the cathode, reduce concentration polarization, and decrease internal stress in the plating layer, making it flexible and ductile. It can also speed up deposition and increase the current efficiency of both the anode and cathode with higher cathodic current density. However, increasing the temperature also increases the evaporation of the plating solution, and nickel salts are prone to hydrolysis, generating nickel hydroxide precipitate. Especially when iron impurities in the plating solution hydrolyze, iron hydroxide precipitate will form, leading to more pinholes and burrs in the plating layer. Therefore, when using high temperature and high current density plating solutions, the amount of boric acid should be increased.
(2) Cathodic current density. In the nickel plating process, the cathodic current density is closely related to temperature, nickel ion concentration, pH value, and stirring degree. Generally, when the concentration of the plating solution is high, the pH value is low, and accompanied by heating and stirring, a higher cathodic current density is allowed. However, when both the temperature and concentration of the plating solution are low, only a smaller cathodic current density can be used. In actual production, the plating current density is 3~4A/dm2.
(3) The Bome degree (Be°) is standardized by some companies as 17-20, and by others as 20-22. Note that a high Bome degree can easily lead to the formation of pits, so it must be strictly controlled within the optimal range during actual production.
(4) The plating time is generally 5-6 minutes.
(5) The anode in the nickel plating tank is an electrolytic nickel plate.
4. Process Maintenance
(1) Ensure that the solution ratio is accurate and make appropriate adjustments based on different equipment. If the effective component content of the solution is low, the current will be too low. Therefore, the pH value and Be° value should be checked daily, and any deficiencies should be supplemented. Records should be made during shift changes, the liquid level should be sufficient, and the pH value should meet the standard (not less than 3.8). The nickel plating solution should be tested twice a week.
(2) A filtration pump should be added to the nickel tank to filter the nickel solution to ensure it is clean.
(3) Some companies have a higher ratio of nickel sulfate and other components, which can easily cause the plating layer to blister when the new solution is prepared, so the solution should be slightly diluted. After nickel plating, it should be polished with 1000# fine sandpaper or a scouring pad, and fingerprints must not be allowed.
(4) After nickel plating, it must be rinsed thoroughly with pure water. If rinsed with tap water, poor water quality can affect the adhesion between nickel and copper.
(5) Zinc and iron are the biggest hazards to nickel plating, so copper solution must never enter the nickel plating tank during hoisting.
(6) After nickel plating, if long-term storage is required, the plated rollers should not be rinsed; the components of the plating solution will form crystals on the surface of the rollers, protecting the nickel layer from being passivated by air. When rinsing the plate surface again before entering the copper tank, the large amount of chloride ions within the crystals will further activate the nickel layer, ensuring that the subsequent copper layer adheres well to the nickel layer.
(7) If many pinholes are found in the nickel layer, a pinhole prevention agent, hydrogen peroxide, can be used. Dilute 30% hydrogen peroxide to 1-3 ml/L, slowly pour it into the plating solution while stirring continuously to remove impurities from the solution. The plating solution should then be filtered.
5. Quality Standards for Nickel Plating Layer
(1) The thickness of the nickel layer on one side is 1-1.5 μm.
(2) The nickel layer is a slightly yellow, fully covered plating layer, and defects such as burrs are not allowed.
(3) If there are a large number of copper and iron examples in the nickel plating tank, it is recommended to configure the nickel electrolytic tank from Changjin Company.Nickel Electrolytic Tank, or a nickel plating solution impurity remover, which has good effects and strong practical applicability.
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