The purpose of plastic electroplating is to coat the plastic surface with metal, which not only increases the aesthetics, but also compensates for the shortcomings of plastics, endows metal with properties, and gives full play to the characteristics of plastic and metal. Today, a large number of plastic electroplating products are used in electronics and automobiles. , household goods and other industries.
- Cleaning: Remove the dirt and fingerprints left in the plastic molding process, wash with alkaline agent, neutralize with acid immersion and wash with water.
- Solvent treatment: the plastic surface can be wetted so as to act with the conditioner of the next step.
- Conditioning: Roughening the surface of the plastic into inner-locked concavities so that the coating is not easily peeled off, also known as chemical roughening.
- Sensitization: The reducing agent is adsorbed on the surface, commonly used (stannous chloride) or other tin compounds, that is, the adsorption of sn^++ ions on the plastic surface has a reducing surface.
- Nucleation: A catalytic substance, such as gold, is adsorbed on a sensitized (reductive) surface, and then nucleated into a catalytic metal seed (seed) by reduction, which can then be used for metal plating. The response is as follows: sn+ + pd+ = sn4+ + pdsn+ +2ag+ = sn4+ +2ag
Formula composition Solvent treatment solution: Including cleaning: cleaning without dilute acid or neutral cleaning and 1-2% surface activator. Mixing and soaking at 40-65 ℃ for 1-2 minutes.
Solvent treatment: with acetone, diacetate methane, and other active agents.
Conditioning: chemical roughening, chemical etching. Example 1 Anhydrous chromic acid cro3 20 g/l sulfuric acid h2so4 Specific gravity 1.84 600cc/l liquid temperature 60 ℃ time 15 to 30 minutes Example 2 Anhydrous chromic acid cro3 20 g/l phosphoric acid h3po3 100 cc/l sulfuric acid h2so4 500 cc/l Liquid temperature 69 ℃ time 10 to 20 minutes
Sensitizing: stannous chloride sncl2 20～40 g/l hydrochloric acid hcl 10～20 cc/l
Nucleation or activation Example 1 Palladium chloride pdcl2 0.1～0.3g/l Hydrochloric acid hcl 3～5 cc/l Example 2 Silver nitrate agno3 0.5～5 g/l Ammonia appropriate amount Example 3 Gold chloride aucl3 0.5～ 1 g/l hydrochloric acid HCl 1～4 cc/l
Influencing factors plastic parts selection
There are many types of plastics, but not all plastics can be electroplated. Some plastics and metal layers have poor bonding force and have no practical value; some physical properties such as expansion coefficients of some plastics and metal coatings are too different to ensure their performance in high temperature environments. At present, the most used for electroplating is ABS, followed by PP. In addition, PSF, PC, PTFE, etc. also have successful electroplating methods, but they are more difficult.
Under the premise of not affecting the appearance and use, the plastic parts should be designed to meet the following requirements as far as possible.
- The metallic luster will make the original shrinkage more obvious, so it is necessary to avoid uneven wall thickness of the product to avoid shrinkage, and the wall thickness should be moderate to avoid the wall being too thin (less than 1.5 mm), otherwise It will cause poor rigidity, easy deformation during electroplating, poor bonding force of the coating, and easy deformation during use, causing the coating to fall off.
- Avoid blind holes, otherwise the treatment solution remaining in the blind holes will not be easy to clean, which will cause contamination in the next process, thereby affecting the quality of electroplating.
- The electroplating process has the phenomenon of sharp edge thickening. Sharp edges in electroplating can cause tip discharge, which can cause edge plating to bulge. Therefore, the transition of rounded corners should be adopted as far as possible, and the radius of the rounded corners should be at least 0.3 mm. Flat-shaped plastic parts are difficult to be electroplated. The center part of the plated parts is thin, and the coating is thicker toward the edge. The whole coating is in an uneven state. The flat shape should be changed to a slightly arc surface or a matte surface with orange peel . The larger the surface area of electroplating, the greater the difference in gloss between the center and the edge. A slight paraboloid can improve the uniformity of the gloss of the plating surface.
- Minimize grooves and protrusions on plastic parts. Because the deep concave parts are easy to be exposed during electroplating, and the protruding parts are easy to be scorched. The depth of the groove should not exceed 1/3 of the groove width, and the bottom should be arc. When there is a grid, the hole width should be equal to the beam width and less than 1/2 of the thickness.
- Sufficient installation and hanging positions should be designed on the plated parts, and the contact surface with the hanging tool should be 2 to 3 times larger than that of the metal parts.
- The design of the plastic parts should make the parts easy to demould when they sink. Otherwise, the surface of the plated parts will be stretched or sprained during forced demoulding, or the internal stress of the plastic parts will affect the bonding force of the coating.
- When knurling is required, the knurling direction should be consistent with the demolding direction and in a straight line. The distance between the knurling stripe and the stripe should be as large as possible.
- Try not to use metal inserts for plastic parts, otherwise the inserts will be easily corroded during pre-plating treatment.
- The surface of the plastic parts should be guaranteed to have a certain surface roughness.
Advantages Compared with metal parts, plastic electroplating products can not only achieve good metal texture, but also reduce the weight of products. While effectively improving the appearance and decoration of plastics, it also improves its electrical, thermal and corrosion resistance. performance and improve the mechanical strength of its surface. However, the selection of plastic materials for electroplating should comprehensively consider factors such as material processing performance, mechanical properties, material cost, electroplating cost, difficulty of electroplating, and dimensional accuracy. Because of its structural advantages, ABS plastic not only has excellent comprehensive properties, is easy to process and shape, but also has a high coating adhesion due to the easy erosion of the material surface. Therefore, it is currently widely used in electroplating.
With the rapid development of the industry, the application of plastic electroplating is becoming more and more extensive, and it has become one of the important means of surface decoration in plastic products. At present, it has been widely used in ABS, polypropylene, polysulfone, polycarbonate, nylon, phenolic glass fiber reinforced at home and abroad. Electroplating is carried out on the surface of plastics, polystyrene and other plastics, among which ABS plastic electroplating is the most widely used, and the electroplating effect is the best.