DE film coating machine in common phenomenon of shrinkage cavity

When the surface tension of high coating coated on the surface free energy of the lower substrate, coating and the substrate surface tension is the surface tension is too big, easy to cause the coating to the substrate of poor wettability, contact Angle, make the coating has a tendency to keep dropwise and revealed the coated surface, especially the varnish and paint coat less paint, is easier to appear this kind of defect, and it is not easy to repair. Shrinkage cavity is made up of low surface tension of small particles or droplets of sundry, they may exist in plastic substrate, coating or fall after coating with good wet membrane. Some low surface tension substances dissolved in the wet film from a local surface tension difference, Marangoni effect will be the lower part of the wet film surface tension from the particles away and tried to cover around the high surface tension of the wet film. Along with the flow, solvent volatilization, difference of surface tension increases, flow continued, evaporation of the solvent increases the viscosity, obstruct the flow and eventually form a concave shrinkage cavity. Common solution using additive to reduce surface tension increased to reduce shrinkage cavity flow. Surface tension can be reduced to the most of it will cause shrinkage below the surface tension of the clutter.