Study of the moisture evaporation process
Theoretically, it is an evaporation process of water-based coatings from surface to interior in line with vertical drying theory. In the first stage, the resin particles undergo irregular Brownian motion, and the evaporation rate of water at the water-air interface is the same as in pure water; after entering the second stage, the suspension medium of resin particles is reduced, which makes resin particles close to each other, aggregation and coalescence, resulting in the contraction of the water-air interface, reducing the total area of the water-air interface and rapidly reducing the evaporation rate of water; in the final stage, the evaporation rate of water keeps decreases, the remaining water diffuses to the surface of the film air through the capillary in the film.
The whole process develops from the surface layer of resin particles to the inside, and the water evaporation rate decreases with the water content, and the water content changes from the interstitial transfer between particles to the polymer transfer.
Other conductive agents include inorganic and organic electrolyte materials and conductive functional polymer materials that are currently vigorously developed.
Application of conductive agent
When preparing conductive coatings, different conductive agents should be selected according to different coating purposes. For example, when modulating magnetic shielding coatings, the shielding effect of conductive coatings should be fully considered, that is, the specific conductivity and specific permeability of the conductive agent should be considered. At this time, choose iron oxide with lower permeability and high conductivity metal powder to use, or use high conductivity graphite powder to compound with it. At the same time, the magnetic shield coating also requires the film layer to be dense and flame retardant. In this coating, aluminum powder with flame retardant properties can be compounded.
After selecting the type of conductive agent, the shape and size of the conductive agent must also be considered. Because conductive agents of different shapes and sizes have different conductivity properties, this has been mentioned above. Finally, choose the filling amount of the conductive agent. The filling amount of the conductive agent affects the overall performance of the coating such as static electricity and anti-corrosion. The mixing ratio of the conductive agent and the base material is very important. If the amount of base material far exceeds the conductive filler, after the paint film is cured, the conductive filler cannot wax emulsion sds be connected into a chain arrangement, even if it is somewhat conductive, it is unstable. On the contrary, when the amount of conductive filler added exceeds the critical volume concentration, a coating with good conductivity cannot be obtained. For example, when silver powder is used as a conductive agent, when the silver content is 70%~90% (volume ratio 20%~50%), it is suitable. When the silver content is less than 70%, the resistivity change is unstable. When the silver content is greater than 90% When the resistance value increases instead.
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