The chemical composition of electrophoretic coating is the fundamental factor determining its film-forming performance, stability, and coating effect.It uses resin as a framework, supplemented by pigments, additives, and water to form a composite system capable of electro-controlled deposition. Understanding the characteristics and synergistic effects of these components helps to grasp the rules in the formulation design and application of electrophoretic coatings, and also provides a scientific basis for quality control and process optimization.
Resin is the core film-forming substance of electrophoretic coatings, commonly using epoxy resin, acrylic resin, polyurethane resin, or their modified varieties. They determine the mechanical strength, corrosion resistance, adhesion, and weather resistance of the coating film. In water-based electrophoretic coatings, the resin is mostly a polymer containing carboxyl or amine groups, which is converted into water-soluble or water-dispersible salts by a neutralizing agent, thereby forming charged particles under the action of an electric field and migrating to the workpiece surface for deposition. The molecular weight and functional group distribution of the resin affect the flexibility, cross-linking density, and corrosion resistance of the coating film. Combinations of different types of resins can balance hardness and toughness, adapting to various working conditions.
Pigments play a crucial role in electrophoretic coatings, providing color, opacity, and functional enhancement. Inorganic pigments, such as titanium dioxide, offer high hiding power and weather resistance, while phosphate pigments also provide corrosion protection. Organic pigments offer a rich variety of colors but require high dispersion and stability. Pigment particles must be uniformly dispersed in the coating solution; otherwise, they will form color spots or uneven deposition during electrophoresis. To improve dispersion stability, pigments are often used in conjunction with dispersants, and grinding processes are employed to control the particle size within a suitable range (example data: D50 for most systems is between submicron and several micrometers), ensuring smooth particle migration during electrophoresis.
Additives are key to the fine-tuning of electrophoretic coating performance; they are diverse and complementary in function. Neutralizing agents convert the acid or alkalinity of the resin into an ionic form that can exist stably in water, directly affecting the pH and conductivity of the emulsion. Surfactants reduce interfacial tension, improving the compatibility and dispersion of the resin and pigments. Defoamers suppress bubbles generated during production and application, preventing pinholes in the film. Leveling agents help smooth the paint film surface and reduce defects such as orange peel. Conductive agents, corrosion inhibitors, and thickeners optimize electric field response, enhance corrosion resistance, and adjust viscosity, respectively. The type and amount of additives must be precisely matched to the resin system and application conditions; otherwise, it can easily cause emulsion instability or a decline in paint film performance.
Water is the continuous phase in waterborne electrophoretic paint systems, responsible for dissolving and neutralizing products, transferring ions, and adjusting viscosity. Strict water quality requirements are necessary; the water must have low conductivity and be free of harmful metal ions or organic matter to avoid interfering with electrophoretic behavior and paint film quality. Some systems may also add a small amount of co-solvent to adjust the evaporation rate and film-forming environment adaptability, but the amount must be controlled to maintain environmental friendliness and low VOC characteristics.
In two-component or self-crosslinking electrophoretic paints, crosslinking agents or curing catalysts are added. After electrophoretic deposition, these react with heat or at room temperature to form a stable network between resin molecular chains, improving the film's hardness, chemical resistance, and durability. The reactivity of these components must be matched with the baking process; otherwise, insufficient crosslinking or excessive embrittlement may occur.
The chemical composition of electrophoretic paint consists of film-forming resin, functional pigments, various additives, and an aqueous phase medium. Under the influence of an electric field, these components work synergistically to complete the dispersion, migration, and film formation processes. The resin provides the structural and performance basis, the pigments impart color and protection, the additives finely control the process window and finished product quality, and the aqueous phase ensures environmental friendliness and workability. Only when the proportions of each component are appropriate and their compatibility is good can a stable and reliable electrophoretic paint be produced, providing high-quality raw materials for efficient and uniform coating.
