The rigid particles that can form a porous cake layer make the filter cake have good permeability and low fluid resistance. It has chemical stability. Incompressibility within the operating pressure range. In the paper industry, filter aids are chemicals added to improve the water repellency and dehydration rate of wet paper from the papermaking web. Generally, it is a cationic polymer polyelectrolyte, such as polyethylene imide, cationic starch, polyamide, polyacrylamide, etc.

The use method of filter aid: one is to mix the filter aid with the suspension to be filtered in a certain proportion, and then filter together; The other is to prepare a suspension containing only filter aid, filter it first, form a pre coating on the filter medium, and then filter the filter slurry. The pre coating of the filter aid can withstand a certain pressure without deformation, and can prevent the filter cloth from increasing resistance due to clogging.