How To Prevent Moire

Moire

How to prevent Moire from appearing in your print especially your textile base plates.

(informational as data is subjective given environment)

Moire is the interference of halftones and mesh. This interference is the result of mesh or mesh knuckles blocking some or part of the halftones in an image. Generally moire is controlled by placing halftones on a specific angle when creating film via a RIP program and having four or more mesh open areas per half tone dot.

In this extreme example (see PDF for better viewing) both the mesh (shown in red for visual purposes) and the halftone were set to 55 lines per inch. Normally in screen printing we would multiply the halftone count by 4 or 4.5 to know what mesh count to use. this would require a 240 thread per inch mesh to prevent moire from appearing. Example 2 shows no moire, however this is one tonal value, a gradation halftone from 0-100% can still exhibit spot moire in certain tonal areas. Smartmesh has very precise square openings when stretched to prevent spot moire issues.

This example shows no moire since the mesh (shown in red) has at least 4 threads or mesh open areas per halftone dot resulting in no blockage of the halftone print. This formula of multiplying halftone line count by 4 or 4.5 yields good results providing we output the film with the halftone on a specific angle. Not all angles work at preventing moire. We have included charts in this article to show what angle works for various Smartmesh thread counts.

The math above works fine for graphics where printing with high mesh counts is the norm, but what about printing halftone base plates for textile? White textile base plate ink on 250 to 300 mesh simply won’t print well. So how can you print bright white base plates with good halftones and no moire? S-thread mesh answers this question and also prints base plates much better than conventional T thread mesh.

S-thread mesh with it’s larger open area can use 45 and 55 line count halftones and produce incredibly bright halftone base plates using mesh counts lower than the mesh count achieved by multiplying by 4 or 4.5. These combinations of mesh and angle work!

Bright Halftone Base Plates

Notice the use of the word ‘bright’. Too often printers settle for a halftone base plate for simulated process or index printing that is anything but bright. We thin the white base plate ink with viscosity reducers, halftone base, softeners, all in an attempt to get it to print well through a fine mesh due to the math described on the previous page. A bright white base plate simply allows the printer to massage the overlying colors by increasing transparency to obtain secondary and tertiary colors that develop as the overlay colors mix during print.