User login

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.


click an image below to view slideshow

By Thomas Trimingham

 

The illustration in Figure 1 shows some of the more common on-press registration problems and the likely causes. As always with screen printing, there are exceptions to every variable, but understanding the usual tendencies can save you time on many jobs.

Two registration difficulties that are hard to illustrate are caused by squeegee angle and ink viscosity. Both of these can contribute to the problem of screen stretch, where the printed image will distort and “grow” longer as it is printed. If an ink is too thick, it can necessitate a higher print pressure and more squeegee flex, which will pull the mesh of the screen over the length of the print and cause visible distortion. This is common with an underbase because the white ink tends to be higher in tack and viscosity. Watch the squeegee during the printing process to see if the blade bends a lot. If you suspect this may be causing the misregistration, then back off the squeegee pressure and reduce the viscosity of the ink as recommended to make it more print friendly without damaging opacity.



Most other registration issues can be combated through a combination of proper trapping of separations and careful screenmaking. For many printers, incorporating a pin registration system in their film/CTS process can literally revolutionize their shops. Set-up times and misprint rates will be slashed because the design elements will be in the same position on every screen, pre-registering the job before it gets to the press. 

Dot Gain Compensation
Halftones can let screen printers get more value from their inks by producing more colors with fewer screens. 


Terms:

Did you enjoy this article? Click here to subscribe to the magazine.