Images Magazine December 2016

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COMPUTER-TO-SCREEN & PRE-PRESS KB
Direct thermal imaging
Direct thermal imaging systems, such as the Riso Goccopro, use a
special silicon-coated screen mesh. The stencil is then imaged by a
thermal print head, which melts the silicon coating and opens up the
mesh to allow the ink to pass through. This eliminates the need for a
darkroom as well as the exposure and washout processes, and makes
the need for screen reclaim completely redundant. It is a simple, fast
and clean process.
It does, however, mean that screens cannot be re-used – instead the
mesh needs to be re-stretched for each print job.
Direct thermal imaging is sometimes called ‘digital screen making’ as
it removes some of the ‘analogue’ screen making processes, namely
screen exposure and washout. But it would be more accurate to de-
scribe all CTS technology as a ‘digital’ process as the image is digitally
transposed directly onto the screen and image positioning is digitally
performed by computer technology.
CTS versus film
All CTS methods offer significant advantages compared with using
film positives.
Labour and consumable cost-savings are often cited as the main
reasons for making the jump to CTS. The image is digitally placed
on the screen and multicolour job registration from screen to screen
is performed automatically. The ink consumables used by the inkjet
systems are generally much cheaper than the cost of polyester film,
and direct exposure systems eliminate the consumable element com-
pletely. Only the direct thermal imaging system is more expensive than
using conventional film, but this approach has other savings as screen
reclaim is no longer required.
Cost savings aside, the biggest reason to make the change to CTS
is improved print quality. No matter how good a film positive, it will
never produce the highlight dot quality that can be achieved by a
good CTS stencil. What few screen printers appreciate is how much
fine detail is being lost during the exposure process when using a film
positive. Under-cutting, whereby the UV light ‘creeps’ around small
highlight dots, thereby exposing the emulsion underneath, is virtually
eliminated with a good CTS stencil.
Do I need it?
For small print shops and hobbyists, CTS is probably overkill. Textile
screen printers have been using film positives and other more basic
stencil solutions for years, and for many smaller customers CTS may
not be worth the investment outlay.
However, for medium size and larger screen shops, the convenience
of CTS and the way in which it simplifies the workflow will be of
great importance. These labour and time savings costs combined with
cheaper screen production consumables can add up to considerable
savings. Also, for screen printers doing complicated halftone work,
the print quality improvements are immediate and difficult to ignore.
The M&R i-Image and Exile/MHM Spyder II inkjet systems require
a minimum screen production of 40-50 screens per day to be able
to make a sensible return on investment. These systems will be the
‘heavy lifters’ for larger customers with two or more fully automatic
presses for whom productivity and production cost per screen are the
key issues.
The more affordable Goccopro and FreeStyler systems are aimed at
screen printers who may only be making 10, 20 or 30 screens per day.
Implementing a computer to screen system is a big decision, but
one that has significant cost and quality benefits. The combination of
fast high end systems such as the i-Image and Spyder II for the bigger
textile screen shops combined with the introduction of more afford-
able alternatives such as the Goccopro and FreeStyler means that CTS
has finally arrived in the mainstream and is now worthy of serious
consideration.
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It is a simple, fast and clean process ”
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