Plastic plating is currently undergoing unprecedented changes.
The traditional decorative plastic plating substrates have been ABS and ABS/PC, but recently a new type of decorative and functional plastic plating substrates are entering the market. Previously, ABS and ABS/PC accounted for 95% of the plastic plating market: today, their use has dropped to 85%. Driven by weight reduction and energy savings as key factors in the automotive and other sectors, the use of polymers is expanding in search of new materials with specific properties. With the development of new materials, plastics suppliers and platers must work together to develop two new systems and methods to ensure that new substrates are plated with the same quality as ABS substrates. This paper focuses on the nylon (PA) substrate plating pre-treatment process in order to obtain high-quality nylon plating quality.
In recent years, nylon has been widely used as a plastic substrate in industry. As a thermoplastic, nylon can be easily processed in the liquid state and has good stability in the temperature range of -30~110 0C. In addition, it has excellent heat resistance, high impact strength, low elastic deformation, friction resistance and vibration damping, while its low melt viscosity makes it easy to process and mold. All in all, nylon is not only light weight and has low manufacturing cost but also has excellent physical properties.
Various nylon plastics such as PA6, PA11, PA12 and PA66 can be identified by the number of polar amino groups.
This property is the basis for distinguishing nylon plastics from ABS and ABS/PC plastics. Pre-treatment of nylon plastics with chromic acid roughening can have some effect on the amino groups and do not give the expected good decorative effect. Therefore, before nylon plating. Two important influencing factors need to be considered: First, when injection molding different characteristics of nylon plastic, different fillers (such as mineral fiber, glass fiber, etc.) will be added to enhance the mechanical strength, hardness and other properties of plastic: Second, different injection molding conditions. Both of these factors have a significant impact on the success of nylon plastic plating or not.
Based on the above description of nylon plastics, it is clear that there cannot be one universal pretreatment process for every type of nylon plastic. Therefore, it is important to match the pretreatment process to the type of nylon plastic. The pretreatment process described in this paper is suitable for nylon plastics such as Toyob0 777-02, Durethan BM 240 and Minlon 73M40. For other types of nylon plastics, further adjustments must be made. Here, we will not discuss in detail. For a clearer understanding of this process, Figure 1 shows the specific process of nylon plastic plating. The roughening and swelling process is a key factor in the appearance and bonding of the plating. This process step ensures that the surface of the nylon plastic is roughened uniformly and prepares a functional surface for the subsequent process.
Figure l Process flows for polyamide electroplating The conventional ABS plastic plating process uses chromic acid to roughen and remove butadiene from the plastic to provide a good bond for the subsequent metal plating. In nylon plating, the chromic acid roughening process is replaced by a swelling system due to a change in the base material. The organic components contained in the swelling system and the other chemicals added remove some of the fillers from the nylon plastic. Since not all fillers can be removed, this causes some nylon plastics to be more difficult or impossible to plating.
Figure 2 shows that the surface morphology of polyamide plastic after inflating clearly shows a uniform roughening effect on the surface of the workpiece, which provides a solid foundation for subsequent decorative plating with good adhesion.
In the standard ABS plating process, there is a reduction process after chromic acid roughening to reduce the residual hexavalent chromium to ensure that the subsequent activation solution is not oxidized. In the nylon plastic pretreatment process, this step is replaced by an acidic fluoride tuning process. The purpose of the tuning is to prevent excess organic solvents from being carried into the subsequent activation solution and to adjust the surface of the nylon plastic so that it can better adsorb vantage ions. Figure 3 shows an AFM diagram of the various stages of the nylon pretreatment process, including the untreated, swelling, and then tuning steps.
After the tuning process, the workpiece enters the activation process. In this process, the vantage ions are adsorbed on the surface of the workpiece, and then in the reduction process, the vantage ions are reduced to active vantage metals. The relationship between the adsorbed vantage ions on the nylon workpiece and the concentration of vantage ions in the activation solution is shown in Figure 4.
Figure 4 Relationship between Pd2+adsorption amount on the surface ofpolyamide and Pd2+content in the activation bathFigure 4 4 shows that the content of active metal on the surface of the workpiece depends on the concentration of ions in the activation bath. And the amount of active silver metal obtained after reduction is almost linearly related to the concentration of silver ions in the activation bath.
The significant difference of nylon pretreatment compared to conventional ABS plastic pretreatment is that this process requires only a relatively small amount to catalyze the subsequent chemical nickel reaction.
Another particularly important advantage is that the hangers are rarely plated during the chemical nickel deposition process.
The nylon electroless nickel solution is an ammonia-free nickel-phosphorus alloy solution developed especially for nylon plating.
In addition to offering a wide operating range for high volume production, it can also be operated at low temperatures. To ensure a good filler effect, the electroless nickel must be followed by a preplated nickel layer of 2 to 5um and an acid copper layer of about 20m. In order to improve corrosion resistance and to achieve the decorative requirements of high gloss, the thickness of bright nickel is about 12 m. The final surface finishing plating is bright chrome with a thickness of about 0.3 um.
After the aforementioned pre-treatment process, the nylon plastic can be coated with good adhesion and decorative properties. By changing the components or parameters of the pretreatment process, different types of nylon plastics can be plated.
By replacing the conventional chromic acid/sulfuric acid roughening process with the above process, not only can we obtain a better plating layer, but also avoid the environmental hazards of hexavalent chromium. This process is not much different from the traditional process, only the existing plating equipment needs to be changed slightly, and the hangers are rarely plated according to this process.