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The Subtle Relation Between Printing Pressure & Film Thickness

It is said that higher printing pressure (the pressure exerted upon the squeegee) makes the film-thickness (the thickness of the printed ink) thinner.
It is most likely because the squeegee pressure scrapes off the ink squeezed out of the screen.
We also got such results from our experiments with the squeegee hardness of 80 degrees.
Film thickness change (hardness 80 degrees) by the seal pressure
However, the results are not always so.
For example, from experiments with the squeegee hardness of 60 degrees, we got results shown in the chart below.
Film thickness change (hardness 60 degrees) by the seal pressure
Unlike the upper chart, the film-thickness does not linearly become thinner; on the contrary, it turns to be thicker at 0.25mpa.
This is not only because the increased printing pressure lets the pressure leak out of the flexure of the squeegee, caused by the printing pressure itself; the flexure of the squeegee decreases the actual angle of the squeegee, and more ink is squeezed out.
Bend of the squeegee
The higher the hardness of the squeegee is, the more the squeegee tends to bend and, the lower the hardness is, the less the squeegee tends to bend.
However, note that if the hardness is extremely high, it makes it harder to squeeze ink out, with the other bad effects.
 
Also, the hardness of squeegees slightly differs according to the maker or material, with errors of plus and minus 5.
The printing pressure that an actuator generates also often differs according to the actuator.
How can we get a fixed film-thickness under such unsettled conditions, then?
Let us superimpose the upper chart on the lower one.
Film thickness change by the squeegee hardness and the seal pressure
From this chart, 7.5um can be thought to be the standard film-thickness, and that the printing pressure between 0.15 and 0.25mpa brings out the steadiest quality under the condition of the machine with the combination of ink and gauze used in this series of experiments.
 

The experiments here are carried out by NEWLONG, and the results may be different according to the ink, screen, squeegee speed, push quantity, clearance and so on. 
Try measuring variation in film-thickness on the printed surface, and you will get interesting data!smiley
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