What is the difference of Aluminum Frames and Roller Screen Printing Frames?
Everybody knows that tight screens print faster, thus better.
Higher tension means the mesh pulls itself out of the ink film.
Higher tension means you can print with lower off-contact, thus less distortion of the image as you bring the stencil in-contact with the squeegee blade.
Static or rigid frames can't retension mesh so your fresh, new, unstable mesh is continuously changing which may or may not frustrate your printing registration. Your critical first step in the judgement process is to buy a tension meter so you can learn how much your mesh is elongating from beginning to end of run.
Prepare for the shock as you find out hardly any static frame you use has more than 10 newtons of tension and know that snobs like me don't want to waste time fiddling with anything fewer than 25-35 newtons. Ask a friend or salesman to bring a tension meter to your shop so you can try, before you buy.
Roller frames do require more maintenance to keep the mesh "in tune" but that's the reason you would buy them. Increased production, easier printing and better registration will pay for the extra effort. If you don't want that, you've made your decision.
If you're having printing problems, there are lots of time consuming tricks you can use to avoid stabilizing or increasing mesh tension which won't fix or cure your problem, just prolong it like filling your car tire every morning before work rather than fixing the leak once and forever.
If you're a manual printer, buy aluminium frames because they weigh a pound less than well built wooden frames - so you have less weight to spin around, and stop as you print, each, color.
If you have an automatic press, weight doesn't matter - so you'll find wooden frames just as stable as aluminium. They both support mesh as well as the other - it's the mesh that betrays you as it elongates with every stroke of your viscous squeegee blade.
Stop now if you don't want to spoil your read with details.
FATIGUE AND COLD FLOW
Even if stretched properly, polyester will gradually lose tension. This is due to 'cold flow' characteristics of synthetics which causes them to adjust to the stress, (tension) applied to them.
Tension loss after initial tension is always critical. If you stretch and glue, you'll see a drop in tension as you cut the mesh from the stretcher and transfer the force to the frame. On retensionable frames, the number of Newtons/cm lost and how long it took will determine how quickly you can re-tension and how much higher you can go above initial tension, into the stratosphere of high tension.
When a polyester filament relaxes, it gets longer, and it takes the stencil image right along with it. Too much tension, correct tension, and low tension all cause different problems, solutions, and results, but they all have one trait: the filaments will elongate during printing.
If the filaments get longer, they loose tension. If the screen loses tension, the stencil changes size by getting bigger. When the stencil gets bigger, the image won't match the positive and you are out of register. There is very little you can do to fix this at the press because the image no longer matches the positive.
TENSION LOSS OR ELONGATION FROM BEGINNING TO END OF RUN
When you push on unstabilized mesh with the squeegee (you brute) you stretch the filaments. As you print, the change is gradual from beginning to end of run. If you were printing a single, first color on paper, each image would be unique and different -microscopically larger every time.
This is why graphic printers might print the first sheet again at the end of the run to see how much the stencil changed. This is also why graphic printers will re-stack the job so they can print the second color, on the first sheet, hoping they will both grow at the same pace. This can work - IF both screens start at the same tension and elongate at the same rate.
Textile printers don't have this same problem because we print one shirt completely as we progress through the job.
TENSION METER TO CHECK LOSS DURING RUN
You should monitor this change with a tension meter or (the hard way) compare the positive to the screen after the run. If there is a substantial drop in tension there has been a substantial change in image size.
If you lost tension, the positive won't fit the image anymore and you might as well reclaim the mesh. You can re-imaged that same screen with the same positive and the stencil will match the positive again, but alas the screen will have lost tension and ink won't transfer as well.
Chart the life of your test mesh as you retention it by recording the number of prints and the tension loss in Newtons/cc. If you still use stretch and glue frames, write the date, tension and number of prints progressively on the mesh with a permanent marker every time you re-coat the mesh. Everybody knows that a tight screen prints better.
Low Tension Problems Like Blurs
Low tension prints worse. The lazy mesh doesn't want to pull itself out of the ink film and the force of the squeegee, will roll the mesh in front of the blade lip. The rolling action smears the print and changes the size of the image making it hard to achieve good registration.
Experienced printers know how to combat this problem. THEY SLOW DOWN THE PRESS, and stop to wipe the blurry screens more often. Ask yourself, why do I have to clean the bottom of even a one color print?
Slowing the press reduces image distortion and the slower press speed lowers production. (Take your time - we've got all night). This one of the greatest causes of waste in the screen printing business.