Impressions - September 2017 - 32

screen
making

Diazo-photopolymer
optimally cured with
multipoint LED on
yellow 156 mesh.

in a new era
Learn the options available
for today's advanced
digital technologies.

Diazo-photopolymer
optimally cured with
single-point metal halide
on yellow 156 mesh.

By Dave Dennings,
Contributing Writer
igital computer-to-screen (CTS) imaging and LED-exposure
technologies have brought much advancement to the
screen-printing industry and, with it, confusion about screenimaging and exposing choices.
With new CTS systems and the surge in LED-exposure equipment, printers have many exciting screen-making options for imaging
and exposing screens. The following is a clarification of the variety of
equipment available, as well as the emulsions best suited for them.
CTS imaging includes all technologies that image a screen directly
from a digital file without film positives. Two technologies currently
are used: inkjet masking and digital direct exposure. CTS systems save
time and money that once were spent outputting, cutting, tagging,
transporting, repairing and storing film positives by reproducing art
directly onto coated screens.
Exposure glass and vacuum frames are no longer needed. Therefore, time isn't spent cleaning film positives and vacuum-frame glass,
or waiting for the vacuum to draw down. As a result, pinholes are
greatly diminished. Even exposure times are shortened by as much
as 40% because the combination of exposure glass and film positive
blocks about 40% of the ultraviolet (UV) light.
CTS imaging systems can be grouped into two categories - masked
(inkjet) and maskless (direct-light exposure) - and then subdivided by their basic structures. Masked systems use inkjet technology
to apply ink onto a coated screen, forming the UV mask traditionally created by opaque film positives, and are equipped with either
water- or wax-based heads. Maskless systems do not use a mask, but
instead image and expose in one step. A digital light processor (DLP)
traverses a coated screen's surface, exposing only the negative image.
This allows the positive image to washout in developing.
Maskless systems are available with either conventional UV,
LED or laser light sources. The two primary systems in North
America are conventional UV and LED exposure lamps. These
systems are predominately used by graphic printers, but smaller
units are beginning to make some inroads into the transfer- and
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I M P R E S S I O N S M A G . C O M SEPTEMBER 2017

garment-printing markets in Mexico and Central America.

Exposure System Choices
Exposure systems also can be divided into two categories - static
and dynamic - and further subdivided into single-point and multipoint systems.
Static: In static (stationary) exposure systems, the light source and
screen remain stationary as the entire screen or multiple screens are
exposed. These systems allow for the widest variety of emulsion choices
and are available in single-point or multipoint configurations.
Dynamic: With dynamic (moving) exposure systems, either the light
source moves across a stationary screen or the screen moves underneath
a stationary light source. Each part of the screen is momentarily exposed
to light. They rely on their close proximity to the screen to cure the
emulsion and are limited to fast-exposing SBQ emulsions. Dynamic
systems also are available in single-point or multipoint configurations.
Single-Point: Single-point light sources use a single bulb or light
column. Static single-point systems require sufficient distance from
the screen to achieve uniform coverage. Some UV energy reduction
at the perimeter of the exposure area occurs, as light must travel farther to reach these outer areas. UV falloff is minimized through the
use of reflectors that redirect stray light toward the perimeter areas,
and by establishing the correct distance between the light and screen.
Single-point lights are available as static (conventional metal-halide

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Impressions - September 2017

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