Evaluating squeegee materials for quality and performance on press is one of the keys to successful screen printing. This article describes material formulations, essential vocabulary, and criteria for making effective comparisons.
By James Elliot
The fact that screen printers are without a set of standardized tests for modulus does not diminish its importance in our industry. For years we have specified durometer and talked about the importance of soft and hard squeegees. Instead, hardness should be considered an index of compressibility.
Printers sometimes interchangeably think of durometer as an indicator of both hardness and modulus. But developments over time give evidence that even though we did not know the appropriate vocabulary, we did, at some level, understand some distinction between the two properties. Almost every twist on standard squeegee configuration has been an attempt to modify the squeegee to achieve a different balance of compression and flex.
Consider the following: Angled squeegees are created to change angle to the screen but, without printers realizing it, are sometimes used to achieve variance in flex and compression. Backing plates are inserted in the holder behind squeegees to stiffen a softer material. Urethane-tipped fiberglass—one of the most extreme examples—involves compressible urethane edge bonded to a dissimilar high-modulus material. Finally, dual/ triple-durometer blades use available urethane technology to couple a compressible outer skin to a stiff, high-durometer, high-modulus support layer.
You could even suppose that an angle adjustment on press can, in part, serve as compensation for a less than satisfactory modulus. The blade bends too much, so the angle is changed to compensate. Either that or put in a harder (stiffer) squeegee. Keep in mind that modulus is a measurement of force related to the cross-section of the material. By changing angle, you change the vector of force, thereby (slightly) changing the shear stress applied to the squeegee. Considering force to cross-section means that in a multi-durometer construction, the modulus will not default to the highest modulus material included. Higher and lower modulus materials can be played off against each other such that two different constructions could have different durometers but the same modulus; likewise, it is possible to use the same durometers, but change the amounts of each material to vary the modulus.
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