The purpose of plastic electroplating is to coat the surface of plastic with metal, which not only enhances its appearance but also compensates for the shortcomings of plastic and endows it with the properties of metal, fully integrating the characteristics of both plastic and metal. Today, a large number of plastic electroplated products are applied in industries such as electronics, automobiles, and household goods.

Process (1) Cleaning: Remove dirt and fingerprints left during the plastic molding process. This can be done by washing with an alkaline agent, followed by neutralization in an acid bath and thorough rinsing with water.

2) Solvent treatment: This process makes the plastic surface wettable to facilitate the subsequent interaction with the conditioner in the next step. (3) Conditioning: This step roughens the plastic surface into interlocking pits to ensure that the coating adheres firmly and is less likely to peel off. It is also known as chemical roughening.

(4) Sensitization: Adsorb a reducing agent on the surface, commonly stannous chloride or other tin compounds, which means adsorbing Sn^++ ions on the plastic surface to form a reducing surface.

(5) Nucleation: Catalytic substances such as gold are adsorbed onto a sensitized (reductive) surface. Through reduction, catalytic metal seeds are formed and can then be used for electroplating metals. The reactions are as follows: Sn2+ + Pd2+ = Sn4+ + Pd Sn2+ + 2Ag+ = Sn4+ + 2Ag

The composition of the formula: Solvent treatment solution: including cleaning: cleaning without dilute acid or neutral cleaning and 1-2% interface activator. Mix and impregnate at 40-65℃ for 1-2 minutes. Solvent treatment: use acetone, dichloromethane, etc. as active agents.

Conditioning: This refers to chemical roughening and chemical etching. Example 1: Anhydrous chromic acid (CrO3) 20 g/L, sulfuric acid (H2SO4) with a specific gravity of 1.84 600 cc/L, liquid temperature 60°C, 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°C, time 10 to 20 minutes.

Sensitizing: Tin(II) chloride (SnCl2) 20 - 40 g/L, Hydrochloric acid (HCl) 10 - 20 cc/L.

Nucleation or activation examples:

Example 1: Palladium chloride (PdCl2) 0.1 - 0.3 g/L, Hydrochloric acid (HCl) 3 - 5 cc/L

Example 2: Silver nitrate (AgNO3) 0.5 - 5 g/L, Ammonia water in appropriate amount

Example 3: Gold chloride (AuCl3) 0.5 - 1 g/L, Hydrochloric acid (HCl) 1 - 4 cc/L

Influencing factors: Material selection for plastic parts

There are many types of plastics, but not all of them can be electroplated. Some plastics have very poor adhesion with metal layers and thus have no practical value. Some plastics have significant differences in certain physical properties such as expansion coefficients from metal coatings, making it difficult to ensure their performance in environments with large temperature differences. Currently, the most commonly electroplated plastic is ABS, followed by PP. Additionally, successful electroplating methods for PSF, PC, and PTFE have been developed, but the process is more challenging.

Plastic part modeling

When designing the shape of plastic parts, the following requirements should be met as much as possible without affecting the appearance and usability.

Metallic luster will make the existing shrinkage and depression more obvious. Therefore, it is necessary to avoid uneven wall thickness of the product to prevent shrinkage and depression. Moreover, the wall thickness should be moderate to avoid being too thin (less than 1.5 mm), otherwise it will result in poor rigidity, easy deformation during electroplating, poor adhesion of the coating, and easy deformation during use, causing the coating to fall off.

(2) Avoid blind holes, otherwise the treatment liquid remaining in the blind holes is difficult to clean thoroughly, which may cause contamination in the subsequent process and thus affect the electroplating quality.

(3) There is a phenomenon of edge thickening in the electroplating process. Sharp edges in electroplating can cause discharge, resulting in raised corners and edges of the coating. Therefore, it is advisable to use rounded corners with a radius of at least 0.3 mm. Flat-shaped plastic parts are difficult to electroplate, with the coating being thinner in the center and thicker towards the edges, presenting an uneven coating. The flat shape should be modified to a slightly curved surface or an orange peel texture to create a matte surface. The larger the surface area to be electroplated, the greater the difference in gloss between the center and the edges. A slightly parabolic surface can improve the uniformity of the coating's gloss.

(4) Minimize the grooves and protrusions on the plastic parts. During electroplating, deep concave areas are prone to exposing the plastic, while protruding areas are likely to get scorched. The depth of the grooves should not exceed one-third of the width, and the bottom should be rounded. When there are grilles, the hole width should be equal to the beam width and less than half of the thickness.

(5) Sufficient 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 part should facilitate easy demolding when the part sinks; otherwise, forcibly demolding may scratch or twist the surface of the plated part, or cause internal stress in the plastic part, which would affect the adhesion of the plating layer.

When knurling is required, the knurling direction should be consistent with the demolding direction and in a straight line. The distance between the knurling stripes should be as large as possible.

(8) Metal inserts should be avoided in plastic parts as much as possible; otherwise, the inserts are prone to corrosion during pre-treatment before plating.

The surface of the plastic part should be ensured to have a certain surface roughness.

Compared with metal parts, plastic electroplated products can not only achieve a good metallic feel, but also reduce the weight of the products. While effectively improving the appearance and decorative properties of plastics, it also enhances their performance in terms of electricity, heat and corrosion resistance, and improves the surface mechanical strength. However, the selection of plastic materials for electroplating needs to comprehensively consider factors such as processing performance, mechanical properties, material cost, electroplating cost, the difficulty of electroplating and dimensional accuracy. And ABS plastic, due to its structural advantages, not only has excellent comprehensive performance and is easy to process and form, but also its surface is easy to erode to obtain a higher coating adhesion, so it is currently widely used in electroplating.

With the rapid development of industry and the increasingly widespread application of plastic electroplating, it has become one of the important means of surface decoration for plastic products. Currently, electroplating has been widely carried out on the surfaces of various plastics such as ABS, polypropylene, polysulfone, polycarbonate, nylon, phenolic glass fiber reinforced plastic, and polystyrene both at home and abroad. Among them, ABS plastic electroplating is the most widely used and has the best electroplating effect.