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Squeegee Is What Squeegee Does

(May 2003) posted on Wed Jun 18, 2003

Tamas S. Frecska counters Professor Steven Abbott's "Confessions of a Squeegee Heretic" with his own perspectives on the role of the squeegee in screen printing.


By Tamas S. Frecska

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Dynamic characteristics Physical characteristics Speed Pressure Angle Durometer Durometer affects printing speed: The harder the durometer the greater the speed. Pressure and durometer modify printing angle. Durometer controls the printing angle relative to speed and pressure. Length Length and speed are inversely proportional in terms of printing controls: The longer the squeegee, the slower the speed for the same level of control. The greater the length, the less uniform the pressure along the entire length. The greater the length, the less uniform the printing angle along the entire length. Thickness Thickness moderates the effects of durometer (see durometer above). Thickness moderates the effects of durometer (see durometer above). Thickness moderates the effects of durometer (see durometer above). Free height Free height and speed are inversely proportional for any given durometer, pressure, and angle: The larger the free-height, the slower the speed. Free-height and pressure are inversely proportional for any given durometer, speed, and angle: The greater the free-height, the smaller the pressure. Free-height and angle are inversely proportional for any given durometer, speed and pressure: The greater the free height, the smaller the angle. Profile Thinner profile reduces the effective durometer near the printing edge (see durometer above). Thinner profile reduces the effective durometer near the printing edge (see durometer above). Thinner profile reduces the effective durometer near the printing edge (see durometer above). Printing edge Printing edge sharpness and speed are directly proportional if all other parameters are the same: The sharper the edge, the greater the allowable speed. Printing edge sharpness and pressure are indirectly proportional if all other parameters are the same: The sharper the edge, the smaller the required pressure. If all other parameters are the same, edge sharpness and angle do not affect one another. Chemical resistance Chemical resistance and speed, in conjunction with ink, determine how long the printing edge lasts. Chemical resistance and pressure, in conjunction with ink, determine the extent of permanent deformation of the blade under pressure. Chemical resistance and angle do not affect one another. Abrasion resistance Abrasion resistance and speed, in conjunction with ink, determine how long the printing edge lasts. Abrasion resistance and pressure do not affect one another. Abrasion resistance and angle do not affect one another. The physical and dynamic squeegee characteristics affect image quality and production yield. Since experience has shown us that it is possible to achieve a perfect print with a squeegee, let's make a generalized statement: For any given screen tension, off-contact distance, and ink rheology, there is only one set of perfectly adjusted squeegee parameters that will give perfect results. For the purposes of this experiment, it is not important how we achieve this perfect squeegee setup. What we are looking for is what happens if we deviate from this perfectly adjusted setup. What happens if we change one or both the physical and dynamic characteristics of the squeegee? If the squeegee is unimportant, we will find a number ways to print without affecting the quality and production yield of the process. If, on the other hand, the squeegee is an important part of the process, then any change in setup will affect quality and/or production yield. Given what we know about the interaction of squeegee screen and ink, some of these effects are listed in Table 2. Note that Table 2 is significantly abbreviated for the sake of clarity and simplicity. Only six of the most important physical and dynamic characteristics from Table 1 are listed (durometer, free height, printing edge, speed, pressure, and angle), and only one third of the possible permutations of these characteristics are given. (For example, under durometer and speed, only the increase or decrease of both are listed. There are four more possibilities where one is increased and the other is decreased or left unchanged. If you are interested, you can work out the rest for yourself, but I guarantee that it will make no difference for this thought experiment.) The most striking observation you can make about Table 2 is that, as far as the squeegee is concerned, screen printing is not as forgiving as most people maintain. First of all, deviating from the "perfect" squeegee setup guarantees that you will reduce your production yield 83% of the time, and for the remaining 17%, you might increase the yield at a significant risk to quality. In terms of overall quality (correct ink deposit, resolution, and acutance), changing the perfect squeegee setup results in reduced quality about 80% of the time. If this is not a vindication of the importance of the squeegee in the process of screen printing, then I don't know what is.

Table 2 Relationship between squeegee characteristics, image quality, and production

Effects on Image Quality and Production Changing squeegee characteristics Ink-thickness requirement Image resolution and acutance Production yield Change durometer and increase speed Less ink Missing elements or no effect Higher but risky decrease speed No effect Smearing Lower increase pressure More ink Smearing or no effect Lower or no effect decrease pressure More ink or no print Smearing Lower increase angle Less ink No effect Lower or no effect decrease angle More ink Smearing Lower Change free height and increase speed More ink Possible smearing Higher but risky decrease speed Less ink or no effect No effect Lower increase pressure More ink Smearing Lower decrease pressure More ink or no effect Smearing or no effect Lower or no effect increase angle More ink or no effect Smearing or no effect Lower or no effect decrease angle More ink Smearing or no effect Lower or no effect Change printing edge and increase speed Less ink Missing elements or no effect Higher but risky decrease speed More ink Smearing or no effect Lower or no effect increase pressure Less ink or no effect No effect Lower or no effect decrease pressure More ink or no print Smearing Lower increase angle Less ink Missing elements or no effect Lower or no effect decrease angle More ink Smearing Lower Whether or not you like using a squeegee, you are stuck with it. It is the single most important processing parameter beside the screen/stencil system. Because, at the present, squeegeeless printing is not an option, at least in the "universal applicability" sense, the best we can do is find ways to use the squeegee better and strive for that elusive "perfect squeegee setup." Perhaps the time has also arrived to seriously contemplate developing product-specific squeegeeless screen-printing systems where or whenever such systems are appropriate. In any case, just complaining about the squeegee is an exercise in futility. Screen-printing companies must make a choice. They can ignore the squeegee and suffer the consequences, or they can learn as much as possible about the purpose and use of the squeegee, then profit from their knowledge.


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