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Catching the On-Press Culprit

(February/March 2019) posted on Mon Mar 04, 2019

Whether it was the art, screen, ink, or a combination that caused your job to go south on press, here are four steps you can take to identify the snag – and prevent it from happening again.

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By Thomas Trimingham

Before You Begin to Troubleshoot
In order to diagnose a printing issue, you must have the proper tools to measure different variables. The three most important: a loupe so you can view your films or CTS output under magnification, a Newton meter to measure screen tension, and a level to check your press alignment.

If you have an automatic press and you are noticing problems on press that are consistent from job to job, it’s worth the small investment to get a tune-up and have a technician check the machine’s surfaces and printing functions. Everything should be level and even from one platen to another. The pressure, speed, and printing motion at each station should be consistent and smooth.

Then check your screens and make sure they are properly tensioned for the mesh being used, or at least consistent from screen to screen. If you reclaim your screens, check your inventory for screens with insufficient tension. Either retension them or put controls in place to be sure they aren’t used on multicolor jobs.

Next, take a close look at your film positives or the output from your CTS machine using your loupe. Check the edge quality of lines and halftone dots. If they look fragmented or pixelated, then you may need to adjust your settings, get your device recalibrated, or even consider upgrading or replacing your unit. A fundamental truth of screen printing is that your prints will never be better than the quality of your stencil. There is no shortcut to compensate for poor quality positive films or images. 

Finally, look at your exposed and washed out screens under magnification, paying attention to fine details like halftones. Make sure the edges of the stencil look as clean and sharp as on the positive. If you see a lot of ripped edges, it can indicate the screen was over- or underexposed. 

Once you are confident that things are under control with your press and screen making, you can look at specific on-press issues with more clarity.

Registration Issues
Getting colors to line up with one another is one of the most common challenges printers face. Start by looking closely at where the print is out of register from one part of the design to another. Assuming the press and screens are in good shape (as outlined above), then you can guess what might be causing the registration issue.


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