Coating process is a process based on the study of the physical properties of fluids, in which one or more layers of liquid are coated on a substrate, usually a flexible film or lining paper, and then the coated liquid coating is dried or cured in an oven to form a film layer with special functions. At present, the most important coating methods for lithium ion battery are comma-roller transfer coating and slit extrusion coating.

The properties of coating solution itself have a great influence on coating results.The shear rate-viscosity data of the coating solution is an important consideration before you apply the coating.When the coating solution has a very strong viscoelasticity, usually about the coating process, will bring greater difficulty.

Viscoelasticity is the reaction of viscosity and elasticity after fluid deformation. Some fluids have only viscosity change under shear force, while more complex fluids have strong elastic energy after shear deformation.How do you determine the viscoelastic energy of a fluid?It can be judged by the curve of shear force and viscosity.

After the pressure release, this change in the fluid will greatly affect the effect of coating.

What effect does that have?

In the slit coating, if the solution with a greater shear force from the coating head lip extrusion, or with a faster speed coating, because the solution in the coating after completion, in the case of pressure release, there will be shrinkage, resulting in the formation of similar vertical stripes.Even in severe cases, retraction of the solution can result in electrode creases and crimping.

So how do you prevent these defects?

In the slit coating process, we have to be very careful to control the flow of fluid in the coating head, so that the solution is very uniform flow out of the lip, and the solution of the shear force as much as possible to control to the minimum.

Generally speaking, the general coating solution has the ability of self-leveling, and viscoelastic body is not easy to flow, so the formation of the film will be a little lower.

When you want to coat a viscoelastic body, you must first fully understand the reaction of the polymer with a higher molecular weight under stress, so as to better offset the resulting defects in the coating process through control of the process.

In general, making this kind of fluid coating under low shear force is the best way to reduce the probability of defects!