The electroplating intermediate is a material used in the electroplating process to adjust characteristics such as grain size, gloss, thickness and plating speed. Most of them are configured as electroplating additives. Then, it is added to the electroplating production process for additional use. According to different types of plating, it can be divided into nickel plating intermediate, copper plating intermediate, tin plating intermediate, gold plating intermediate, silver plating intermediate, etc. According to different functions, it can be divided into surfactant, brightener, wetting agent, softener, anti-fogging agent, etc.
The multilayer nickel plating system is usually composed of semi-bright nickel, high-sulfur nickel and bright nickel, and is widely used for items requiring high corrosion resistance, such as motorcycles, home appliances, plumbing equipment, etc. The quality of multilayer nickel is determined by the performance of the additives used in each process, and the quality and appropriate combination of electroplating intermediates determines the performance of the additives. The following discusses the application of electroplating intermediates in multilayer nickel plating systems in terms of multilayer nickel corrosion resistance mechanism, multilayer nickel additives and multilayer nickel process management.
Corrosion Resistance Mechanism in Multilayer Nickel System
Multilayer nickel usually consists of double-layer nickel and three-layer nickel. The reason why multilayer nickel has excellent corrosion resistance is that its main mechanism of action is electrochemical protection. The Cu-Ni-Cr system is a cathodic coating relative to the steel substrate, which acts as a mechanical protection for the substrate. Once corrosion cracks appear in the coating, the corrosion on the steel substrate will accelerate.
To improve corrosion resistance, the coating can only be thickened to reduce porosity. The multi-layer nickel system is different, such as the double-layer nickel system, which is composed of semi-bright nickel and bright coating. The former has a low sulfur content (usually 0.003%~0.005%), and the latter has a high sulfur content (usually 0.04%.) ~0.08).
Multilayer nickel additive
Multilayer nickel can improve the corrosion resistance of the coating. The credit goes to the multilayer nickel additive. Therefore, it is very important to choose high quality additives, and the quality of additives is determined by the quality of intermediates.
(1) Semi-bright nickel additive
The semi-bright nickel additive is characterized by low or no sulfur content, good flexibility and ductility, thus ensuring the bonding force with the bright nickel layer. The main raw materials that can be used as semi-bright nickel additives are BMP (butynediol propoxylate), BEO (butynediol ethoxylate), HD (2,5-hexynediol), etc. It plays a brightening and leveling role in semi-bright nickel additives.
(2) High Sulfur Nickel Additive
The high-sulfur nickel additive has a high sulfur content (generally 0.1%~0.3%), and it can provide a suitable sulfur content to the coating during the electroplating process. The main raw materials that can be used as high-sulfur nickel additives are BBI (diphenylsulfonylpropylamine), ATPN (hydroxyethylthiourea-betaine), and sodium benzenesulfinate and saccharin. They provide a source of sulfur in high-sulfur nickel additives and deliver the correct amount of sulfur to the deposit in a controlled and uniform manner during the plating process.
(3) Bright Nickel Additive
The sulfur content of bright nickel additives is moderate, and the main raw materials used as bright nickel additives are: BMP (butynediol propoxylate), BEO (butynediol ethoxylate), which are long acting brighteners in the plating solution. PA (propynyl alcohol), PAP (propynyl alcohol propoxylate), PME (propynyl alcohol ethoxylate), and DEP (diethylamino propargyl) are used as levelers and brighteners in the plating solution. PS (sodium propyne sulfonate) is used as a positioning and contamination control agent. BBI (diphenyl sulfonate propylamine) is used as a softener and anti-impurities agent. ALS (sodium allyl sulfonate) serves as a softening agent and whitening agent. ATPN (hydroxyethylthiourea betaine) is used as a displacement agent and as an anti-purity agent. VS (sodium vinyl sulfonate) acts as dislocation agent and plasticizer. PPS (pyridine propoxy base sulfide) and PPS-OH (pyridine propoxy betaine) serve as leveling agents, while EHS (sodium ethylhexyl sulfate) serves as wetting agent.