Functions of Squeegee

a) To make ink go through the mesh screen.
b) To keep stencil and substrate proper contact.
c) To make stencil go well with the surface of the substrate.
d) Blade off the residual ink on the stencil during the printing process.
Pressure is problematic. It is very easy to tell when the pressure is too low because there is no print, but when the pressure is too high it is difficult to see all the negative influences that are created. The main problems will be excessive wear of squeegee and stencil, too heavy an ink deposit and the screen itself may loose some dimensional stability because of the high friction between the squeegee and screen.
What is the pressure difference between printing dot 35 microns thick verses 40 microns thick, and what is the impact on the dot diameter or dot grain?
Minimum printing force should be used. The principle force should draw the Squeegee across the screen and not force it down on to the substrate. Stencil breakdown, register and substrate release problems will occur if too much printing pressure is used. Control the squeegee pressure, and keep it absolutely constant and never more than required to deposit the ink on the substrate.
High squeegee pressure causes image distortion and high wear on mesh. Uncontrolled pressure drives the squeegee into the substrate causing the image to deflect, the dots of the ink flatten, and loss of color intensity and other related problems.
Generally any mechanical printing machine will allow the operator to use too much squeegee pressure. Some printing machines will have squeegee pressure equalizing systems to boost print quality. With these systems minimum squeegee pressure can be applied to reduce the wear on the stencil and squeegee. There are two primary versions (1) Pressure cylinders either side of the squeegee holder close to the normal squeegee height adjusters. (2) Sideways moveable single pressure cylinder, this guarantees the same squeegee pressure without further adjustment even if the squeegee is exchanged for a new one.
Correct peel off and squeegee pressure is one ultimately determined by the combined mechanics of the printing ink, opposed to those associated with the screen and substrate. Interface behavior of the ink known as rheology means the squeegee pressure set and the amount of peel off used is based on the rheology influence on the job.
If ink viscosity changes during production then the peel off and squeegee pressure need modification to complete the final ink transfer process in one fashion or another. Changing either function during the run will always alter registration. Solvent evaporation will also cause distortion due to increase in screen drag, which reduces the effectiveness of the peel off function and interferes with off contact. Control ink viscosity decreases excessive squeegee pressure because of changing rheology.

The squeegee functions mentioned above may be affected by many factors. These factors include: the shore hardness of squeegee, the width of squeegee, the angle of squeegee, the printing angle, the length of squeegee, the speed of printing, the direction of force, pressure and the sharp degree of the squeegee, etc.