Pop quiz: During the print stroke, what is the ideal pressure on the platen which leads to optimized loading on the superstructure? In case you don’t know, we will get to the answer shortly.
Before we answer that question, a far more critical feature (the benefit and incentive to buy) on a screen-printing press is how it applies force to the blade and pressure to the screen.
The universal goals for top-quality imaging are as follows:
- Minimum force on the blade to overcome off-contact gap
- Minimum blade angle
- Blade dynamic interface fitted to mesh
- Minimum blade deflection during the stroke
- Maximum stroke speed
- Zero net pressure on the platen
As an experiment to answer this question, we used a press with two cylinders on the squeegee and two cylinders on the flood and maximized the travel on both. We had a high-fill/low-capacity 150/45 mesh at 25N/cm², an 85A double bevel at a zero angle, 0.160" gap, and a highly shear-thinning/low tack level (less than 25 percent tack) white plastisol.
We ran a stroke speed of 40 inches per second (as fast as the press would go) and the squeegee pressure was 18 PSI. Case in point: we had near zero pressure on the platen while cleaning the non-image areas and completely clearing the mesh openings. At the settings listed herein, we easily achieved the maximum print quality, productivity, and screen/stencil life. For additional PSI suggestions, refer to the diagram above.