Impresssions - March 2017 - 38

The No. 1 cause of poor screen exposure is exposing
the screen before the emulsion is completely dry.

After the screen is exposed, wet both sides
immediately and wait for a few minutes to
allow the emulsion to soften in the areas
that need to be washed out. Next, use a
power washer to spray out the image area.
After the washout stage, the screen must
be completely dry before taping and setting
up on the press.

Quality Control

The No. 1 cause of poor screen exposure is
exposing the screen before the emulsion is
completely dry. To remedy this problem, dry
screens in a commercial screen dryer. Printing with underexposed screens can allow ink
components to get absorbed by the stencil
during the printing process, making it difficult to reclaim the screen later.
Using harsh solvents to clean the screen
after printing also can cause a problem when
reclaiming the stencil. It's best to use a milder
solvent with a higher flash point.
It's also recommended to hang a hygrometer in your screen room to indicate
humidity level. Ideally, it should be 30% or
less, as trying to dry screens in a room with
humidity in the upper range of 60%-90% is
difficult. Screen emulsions will never dry properly in humid conditions, even when using a
commercial screen dryer, since recirculating
moisture-laden air will not thoroughly evaporate the water from the stencil.
Note: Screen-printing shops located in
high-humidity regions may need to add a
dehumidifier in the screen room to lower
the humidity level.
A moisture meter also can be used to determine the moisture content in the coated
screen prior to exposure. This tool features a
probe that is put in direct contact with the
emulsion surface and displays a readout of
the moisture content.
A stencil-thickness gauge can be used to
measure the EOM on the screen. This tool
works by placing a contact probe on the screen's
squeegee side and a metal plate on the opposite side to measure the stencil thickness in
microns. Many larger shops that specialize
in special-effects (SFX) printing have this

P.38

important tool.
Finally, an Rz meter is used for determining the flatness of the stencil's contact side. It
is an important tool for CD and electronic
circuit printers who need a good seal (gasket)
against the substrate when printing UV inks
and conductive materials.
Screen preparation is an easy process, but
it's important to choose the correct screen
emulsion and tools for your application to
be successful. Quality screen making only
happens after much study and practice.

Following the aforementioned guidelines will
help you take your shop to the next level. 
James Ortolani currently is a sales account manager for PolyOne/ Wilflex Inks. He has more than
30 years of experience in the decorated apparel
industry. He is a member of the Specialty Graphic
Imaging Association (SGIA) Educational Committee and the Academy of Screen and Digital
Print Technologies (ASDPT). For more information or to comment on this article, email James at
james.ortolani@polyone.com.

Here is a magnified look at a stencil made
with pure photo polymer direct emulsion.
Photo courtesy of KIWO Inc.

Faster Exposure
New advancements in UV LED exposure units have proven to be a
real game changer in terms of speeding up screen-exposure times.
Previously in the two- to three-minute range with traditional
UV bulbs or fluorescent units, these times have been reduced
to two or three seconds with LED exposure units.

I M P R E S S I O N S M A G . C O M MARCH 2017

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2/16/17 12:53 PM

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