Serigrafia-Halftones

July 2010

MURAKAMI

Technical Newsletter
MURAKAMI SCREEN U.S.A., INC. 745 Monterey Pass Rd. Monterey Park, CA 91754 Tel 323.980.0662
How to prevent Moire from appearing in your print especially your textile base plates. 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. Generallymoire is controlled by placing halftones on a speci c angle when creating lm via a RIP program and having four or more mesh open areas per half tone dot.

Moire

Moire Controlled
Using the 4.5 x Halftone Count Math

Moire Example

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 lm with the halftone on a speci c 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 ne for graphics where printing with high mesh counts is the norm, but what about printinghalftone 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 incrediblybright 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!

In this extreme example 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 wouldrequire 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.

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July 2010

MURAKAMI

Technical Newsletter
MURAKAMI SCREEN U.S.A., INC. 745 MontereyPass Rd. Monterey Park, CA 91754 Tel 323.980.0662

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 ne mesh due to the mathdescribed 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. Without a bright base plate the image is muted, or needs to have overlay colors be as opaque as possible to keep color intensity in the design. However many subtlecolor transitions are lost as either opacity of overlay colors blocks the color transitions, or the thinned base plate lowers the color quality of the transparent overlay colors.

The Solution?
S-thread or the new LX Mesh from Smartmesh sold by Murakami is the answer in achieving brighter base plates. Both have a higher percentage of open area than typical mesh and allow the printer to lay downan opaque base plate with unmodi ed inks right out of the container. No need to lower the opacity of your white base plate ink, just switch to a better mesh. S mesh and LX Mesh sold by Murakami USA allows the ink to be printed on the surface of the shirt. The squeegee needs less pressure to print the thick base plate ink. This results in less dot gain and more opacity in the base plate and...