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
Specifications are the values or nomenclature about physical properties of an item used to accurately communicate material selection or requirements. The information generally used to specify a squeegee for ordering purposes covers only a small portion of the material properties. Information typically used includes:
• Profile, the cross-sectional shape (rectangular, single-bevel, etc.)
• Hardness, expressed in Shore A durometer (i.e., 75 durometer or 75A)
• Color, usually not an option, but included for accuracy of description
• Size, the overall dimensions of the cross-section (i.e., 0.375 x 2.0 in. or 9.5 x 50 mm) and the length of roll or precut piece.
You will note that hardness is the only true specification of a physical performance parameter. The physical performance criteria that have bearing on performance—and when comparing materials—are:
• Chemical resistance, no standardized test methodology for our industry
• Abrasion resistance, no standardized test methodology for our industry
• Hardness, the one value for which there is an applicable measurement
• Modulus, the great unknown—again, no standardized test methodology for our industry
Test procedures may prove a specific property related to some of the above, but the tests are structured for laboratory evaluation as opposed to being designed to provide usable comparative values for screen-printing production. The questions then become, how do we work around the lack of information, and what is this thing called modulus?
Everything in modulation
Let’s tackle the topic of modulus first. The term is short for flexible modulus, sometimes called Young’s modulus, which is an expression of the relationship between applied shear stress and resultant shear strain for a given material. Simply put, it is a means of gauging flexibility. Stiff is high modulus; a squeegee that folds over is low modulus. Again, our industry lacks a standardized test method for this.
A materials-science lab would design fixtures and methods for different material requirements and perform the measurements using recognized industrial testing tools. The lab then plugs the values obtained into a series of formulas to arrive at a specific value fo that specific situation. If we were to add in the factor of the dynamic force applied to the material during printing—compression, squeegee movement, friction—the mathematics would become truly daunting. I can honestly say that my memory of calculus is not sufficient.
Did you enjoy this article? Click here to subscribe to the magazine.