The intention of plastic electroplating is to coat the plastic surface with metal, not only to add beauty, but also to compensate for the shortcomings of plastics, to give the properties of metal, and to give full play to the characteristics of plastics and metals. Today, many plastic electroplating products are used in electronics and automobiles. , Household goods and other industries.
Metal processing
Process (1) Cleaning: To remove dirt and fingerprints left during the plastic molding process, it can be washed with an alkaline agent, then neutralized with acid immersion and washed with water.
(2) Solvent treatment: Wetting the surface of the plastic so as to interact with the conditioner effect of the next process. (3) Conditioning: Roughening the plastic surface into internally locked cavities to make the plating layer close and not easy to peel off, also known as chemical roughening.
(4) Sensitization: Adsorb the reducing agent on the surface, commonly used (stannous chloride) or other tin compounds, that is, sn^++ ions adsorbed on the plastic surface have a reductive appearance.
(5) Nucleation: A catalytic substance such as gold is adsorbed on a sensitized (reductive) surface, and after the reduction effect is nucleated into a catalytic metal seed (seed), which can then be used for electroplating metal. The response is as follows: sn+ + pd+ = sn4+ + pdsn+ +2ag+ = sn4+ +2ag
The formula is composed of solvent treatment liquid: including washing: washing without dilute acid or neutral washing and 1-2% interfacial activator. Mix and soak at 40-65°C for 1 to 2 minutes.
Solvent treatment: use acetone, methane diacetate, and other active agents.
Conditioning: chemical roughening and chemical etching. Example 1 Anhydrous chromic acid cro3 20 g/l Sulfuric acid h2so4 Specific gravity 1.84 600cc/l Liquid temperature 60℃ 15-30 minutes Example 2 Anhydrous chromic acid cro3 20 g/l Phosphoric acid h3po3 100 cc/l Sulfuric acid h2so4 500 cc/l 10-20 minutes at a liquid temperature of 69℃
Sensitizing: stannous chloride sncl2 20～40 g/l hydrochloric acid hcl 10～20 cc/l
Nucleation or activating 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
Affecting factors plastic parts selection
There are many types of plastics, but not all plastics can be electroplated. Some plastics and metal coatings have poor bonding strength and have no practical value; some physical properties of some plastics and metal coatings, such as expansion coefficients, are too different, and it is difficult to ensure their function in a high temperature difference environment. ABS is now used more for electroplating, followed by PP. In addition, there are also successful electroplating methods for PSF, PC, PTFE, etc., but it is more difficult.
Plastic part modeling
On the premise of not affecting the appearance and use, the plastic part shape design should try to satisfy the following requirements.
(1) The metallic luster will make the original shrinkage more obvious, so the uneven wall thickness of the product should be avoided to avoid shrinkage, and the wall thickness should be moderate, so as to avoid the wall is too thin (less than 1.5 mm), otherwise It will result in poor rigidity, easy to deform during electroplating, poor adhesion of the coating, and easy to deform during use to cause the coating to fall.
(2) Avoid blind holes, otherwise the treatment liquid remaining in the blind holes will not be easy to clean and clean, which will cause pollution in the next process, which will affect the quality of electroplating.
(3) The electroplating process has the phenomenon of thickening of sharp edges. The sharp edges in electroplating will cause tip discharges and form corner plating bulges. Therefore, rounded corners should be used as far as possible to transition, and the radius of rounded corners should be at least 0.3 mm. Flat-shaped plastic parts are difficult to electroplating. The center part of the plated part has a thin coating. The more the edge is, the thicker the coating. The entire coating is uneven. The flat surface should be changed to a slightly rounded 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 slightly parabolic surface can improve the gloss uniformity of the plating surface.
(4) Minimize grooves and outstanding parts on plastic parts. Because deep concave parts are easy to expose plastic during electroplating, and outstanding 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 a circular arc. When there is a grid, the hole width should be equal to the beam width and less than 1/2 of the thickness.
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(5) The plated parts should be designed with a satisfactory mounting orientation, and the contact surface with the hanging tool should be 2 to 3 times larger than the metal parts.
(6) The design of the plastic parts should make the parts easy to demould when they are sinking, otherwise the surface of the plated parts will be strained or sprained when demolding forcefully, or the internal stress of the plastic parts will be formed, which will affect the bonding force of the coating.
(7) When knurling is required, the knurling direction should be in line with the demolding direction. The distance between the knurling stripe and the stripe should be as large as possible.
(8) Try not to use metal inserts for plastic parts, otherwise the inserts will be easily corroded during pre-plating treatment.
(9) The appearance of plastic parts should ensure a certain degree of surface roughness.
Advantages Compared with metal parts, plastic electroplated products can not only achieve a good metal texture, but also reduce the weight of the product. While effectively improving the appearance and decoration of the plastic, it also improves its electrical, thermal and corrosion resistance. Function to improve the mechanical strength of its appearance. However, the selection of plastic materials for electroplating requires comprehensive consideration of the processing functions, mechanical functions, cost of materials, electroplating costs, ease of electroplating, and dimensional accuracy. Because of its structural advantages, ABS plastic not only has excellent comprehensive functions, is easy to process and shape, and the appearance of materials is easy to corrode to obtain higher plating adhesion, so it is now widely used in electroplating.
With the rapid development of the industry and the increasing use of plastic electroplating, it has become one of the important methods for the appearance of plastic products. Now 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, especially ABS plastic electroplating is widely used, and the electroplating effect is better.
