Impressions - March 2014 - 69

And are you willing to make the necessary
workﬂow changes to take full advantage of
LED technology?
You have to weigh the beneﬁt of increased exposure speed against the changes
you must make to accommodate it. Again,
we're still talking about exposing screens,
and the same variables factor in: screen
mesh, mesh count, emulsion, how you coat
the mesh, human resources and more.
Having presented seminars on efﬁcient screen making and cleaning at trade
shows, as well as doing time studies in my
own shop for improvement purposes, I
have identiﬁed the steps in what I call "the
screen loop." Using the ﬁlm technique, I
have identiﬁed 27 steps in the process. Using the CTS method, those 27 steps are
reduced to about 20 steps.
For shops using ﬁlms, no matter which
bulb (LED or conventional) is used, there
remain the steps involved in creating the
ﬁlms (vellum or waterproof) on an inkjet printer or imagesetter. The outputting
process has to be monitored, the ﬁlms
inspected and a preregistration system
should be used to position ﬁlms on the
glass for exposing.
The LED bulbs dramatically speed up
the process in exposure time. LED bulbs
come in a range of types that vary in exposure speeds. If you choose the fastest
LED bulb to replace a ﬂuorescent bulb in

a traditional exposure unit, exposure times
will be reduced from 20 minutes to 20 seconds. If a shop has an exposure unit with
low-wattage metal halide bulbs, the exposure time using a fast LED bulb potentially
drops from about six minutes to 20 seconds.
Manufacturers offering the LED technology in conventional screen exposure
units using "slow" LED bulbs are dropping
the typical exposure time from 20 minutes per screen to potentially four to six
minutes when compared to a bank of ﬂuorescent bulbs. So it is, by rough estimate,
tripling the output from three screens per
hour to 10 screens per hour.
However, the speed is relative and the
amount of time saved depends on where
you're starting. It may take 20 minutes
to expose one screen on a unit that uses
a bank of ﬂuorescent tubes, compared to
only three to six minutes on a unit that
uses the same workﬂow, but with LED as
the light source.
But the savings likely will not be nearly as
dramatic if that LED unit's exposure time is
compared with that of a current-generation,
single-point metal-halide light source, where
30-second to two-minute exposures are not
uncommon with the right emulsion.
Granted, shaving a 30-second exposure
to 12 seconds would be a signiﬁcant decrease
in exposure time, but would your throughput or workﬂow increase correspondingly?

Depending on how you are handling other
aspects of screen making and exposure, the
decrease in exposure time may not effectively yield any additional screens per hour.

NEW CONSIDERATIONS
You must consider whether you're using CTS - jetting a liquid or wax directly
onto the screen - or using ﬁlm, a vacuum
unit and glass, in which case you have to
factor in all the ﬁlm prep time, vacuum
draw-down and release time.
The draw-down time of a vacuum may
now be considerably longer than the exposure time (the opposite used to be the
rule), and faster exposure times may indicate the need for a larger vacuum pump,
with multiple ports to keep up. Remember, you never really get rid of bottlenecks,
you just move them around.
With either type of exposure unit, you
move the bottleneck down the line to the
screen washout process. If screens are being exposed every 20 seconds, you will
quickly have a big pile of screens waiting
to undergo this step.
With a CTS system, all the steps relating to creating the ﬁlms and outputting
them are eliminated. If you are already
outputting 20-30 screens an hour, now
you can do 60. So if you add this technology, you now have new options to consider
and questions to ask. Do you buy a second

Lightspeed Equipment's LED
UV exposure units feature patent-pending
multispectrum technology. They work as well
with polymers as they do with dual cure and
diazo emulsions.

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March 2014 | Impressions

69
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Impressions - March 2014

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