Too much or too little resistance of the coating will affect the operation of the electrostatic spray equipment . If the resistance of the coating is too large , the charging rate is low during the spraying process, and the conductivity is good. After the coating with small resistance is charged, the electric charge disappears too fast, and the static voltage does not go up, which also affects the spraying effect.
When the conductivity of the coating is too strong, the current intensity of the system is large, and the electrostatic spray coating effect is poor, and the paint mist particles cannot fall on the surface of the coated workpiece to affect the coating effect. Studies have shown that some coatings are easy to charge, and some are not easy to be charged. This has a lot to do with the nature of the resin in the coating. For example, melamine resin has good conductivity, alkyd resin has certain conductivity, and epoxy resin. Poor conductivity. The color and solvent properties of the coating also have a large effect on the conductivity of the coating. The conductivity of a pigment is related to its particle shape in addition to its nature. Generally, the finer the particle, the better the conductivity, so the pigment of the diamond particle and the spherical particle is finely ground. Coatings generally do not produce coatings that are used directly for electrostatic spraying, but can provide solvents that are added to the coating during electrostatic spraying. Adding these solvents to ordinary coatings can turn them into coatings for electrostatic spraying. Electrostatic spraying should use easy-to-charge coatings. Generally, the resistivity is 5~50MΩ·cm. For coatings with poor electrical conductivity above 100MΩ, a polar solvent (such as diacetone alcohol) should be added to improve the coating. Conductivity, but should pay attention to the amount of addition should be appropriate, more will affect the coating’s hiding and durability. Coatings with too low resistivity such as water-based paints and metallic flash paints require a non-polar solvent to increase their electrical resistance.
Metal powder has strong electrical conductivity. By adding a non-polar solvent to surround the metal powder particles, it can reduce its conductivity, but this segmentation is closely related to the shape of the metal particles, and there is no sharp corner. The round particles are more easily surrounded by the segmentation. After the application of high voltage, the metal powders are not connected to form a conductive path, but if the metal particles have sharp corners and are used in a non-circulating electrostatic spraying system, It is easy to break through the separation of the solvent to form a conductive path, and the more sharp the corners, the easier it is to form a conductive path. Therefore, when the metal paint is electrostatically sprayed, not only a non-polar solvent but also a circulation system should be used. At the same time of coating the impedance, it is also necessary to balance the leveling property of the coating, that is, with a high boiling point solvent, to control the proper evaporation rate of the solvent, to achieve a better leveling, and to improve the decorativeness of the coating.
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