How to Achieve Uniform Coating Adhesion on Non-Conductive Substrates Using Plastic Spraying Electrophoresis?
Publish Time: 2026-01-15
In industrial practice, "plastic spraying electrophoresis" does not usually refer to a true electrophoresis process, but rather a general term for "applying a spray coating combined with an electrophoretic effect or composite pretreatment to the surface of plastic parts," or it refers to a modified electrophoresis applied to plastic surfaces that have undergone special conductive treatment.
I. Core Challenges: The Insulation and Low Surface Energy of Plastics
Untreated plastic surfaces have high resistivity, making it impossible to form an effective electric field, resulting in the inability of electrophoretic coating particles to deposit directionally. Simultaneously, most plastics have low surface energy and lack active groups, making coating wetting difficult and adhesion poor. Forced spraying can easily lead to problems such as orange peel, pinholes, exposed substrate edges, or coating peeling.
II. Key Path to Achieving Uniform Adhesion: Conductive Pretreatment
To achieve a near-electrophoretic uniform coating on plastics, the surface must first be made conductive. Mainstream methods include:
1. Chemically Plated Conductive Layer: A continuous metal film is formed on the plastic surface through sensitization, activation, and chemical copper/nickel plating. This method is costly and complex, and is mostly used for electromagnetic shielding or highly decorative parts, but it can support subsequent electrophoresis.
2. Conductive Primer Spraying: A more economical and practical method is to first spray a layer of primer containing conductive fillers. After the primer dries, it forms a conductive network, giving the plastic part a "metal-like" surface, thus allowing for electrostatic spraying—this is the mainstream process described in the question.
3. Plasma or Flame Treatment: Through high-energy surface modification, polar groups such as -OH and -COOH are introduced to increase surface energy. Although it cannot conduct electricity, it significantly improves the wetting and adhesion of ordinary spraying.
III. Actual Mainstream Process: Electrostatic Spraying Replaces "Electrophoresis" Function
According to the question's description of "thermoplastic or thermosetting powder coatings being adsorbed by an electrostatic spray gun…", it can be inferred that the widely used method on plastic products such as shelves and appliance casings is actually electrostatic powder spraying, not true electrophoresis. Its "uniform adhesion" mechanism is as follows:
The plastic part is grounded after being treated with a conductive primer, becoming the "cathode";
Negatively charged powder particles are adsorbed onto the workpiece surface in the electrostatic field, forming an initial uniform coverage;
During high-temperature curing, the powder melts and flows, filling microscopic unevenness and forming a continuous film thickness.
Although it cannot achieve the advantages of "strong penetration and uniform internal cavity" of metal electrophoresis, electrostatic spraying can provide a sufficiently uniform and colorful protective layer for simple structures and low-precision external surfaces.
IV. Limitations and Applicable Boundaries
Because it relies on a surface conductive layer and electrostatic adsorption, this process still suffers from insufficient coverage in complex internal cavities and deep recesses; and the coating thickness fluctuates significantly, making it difficult to meet precision fitting requirements—this explains why it is mainly used in "occurrences with low precision requirements." Furthermore, color changes require thorough cleaning of the spray gun and powder supply system, resulting in a long cycle and making it unsuitable for small-batch, multi-color production.
Plastic spraying electrophoresis essentially simulates the uniform coverage effect of electrophoresis through conductive pretreatment + electrostatic powder spraying. Its core technology lies in breaking down the insulation barrier of plastics by constructing temporary conductive paths through physical or chemical means, thereby achieving uniform coating adhesion through electrostatic adsorption. Although it has limitations in terms of precision and adaptability to complex structures, it has become a pragmatic choice for plastic surface coating in high-volume, low-precision scenarios such as shelves and appliance casings due to its comprehensive advantages of controllable cost, diverse colors, and moderate corrosion resistance.
