Impressions - April 2015 - 64

Screen Printing Technique

A backlit washout tank allows for
quality inspection during processing throughout
the reclaim and degreasing process.

You want the stencil thickness to be on the print side of the screen
when properly coating the stencil. This dictates that whatever coating
combination you use, you will coat the ink side of the screen last.

highest tension achievable for the frame
with which you are working. Although
reaching and maintaining the manufacturer's recommended tension level is
easy with retensionable frames, printers
using static frames will need to monitor
the screen's tension over time.

SCREEN PREPARATION
Degreasing and emulsion-removal techniques play a critical role in making a
quality screen. The screen requires a
complete degreasing prior to the ﬁrst
coating. This is a repetitive process, where
attention to detail can be lost in a short
period of time. This (as well as every
aspect of the screen-making process)
requires written procedures that must be
adhered to from screen to screen. Shortcuts are not acceptable.
The ﬁrst tool required for this process
is a good pressure washer - an industrialstrength unit with a 2,000-2,500 psi capacity. Smaller units will require more
time to properly process a screen and
could slow productivity.
When degreasing or reclaiming a
screen, always work from top to bottom
with the pressure washer. The objective is
to thoroughly clean and remove all residue from the screen mesh's surface. Since
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Impressions | April/May 2015

the majority of the stencil resides on the
print side of the screen, follow these steps:
* Process the initial reclaim procedure
from the ink side of the screen ﬁrst.
* Repeat the process on the print side.
* Starting at the top, thoroughly rinse
the frame on both the print and ink
sides of the screen.
* Rinse both sides from top to bottom
to ensure there is no residual emulsion left.
* Inspect.
Use a backlit washout tank during the
reclaiming and degreasing process. This
allows for section-by-section inspection
and eliminates the need for a separate examination at the end of the process.
Once properly degreased, place the
screens on a drying rack prior to coating.
This rack should have its own area that is
located away from the contaminated production area, but also not near the freshly
coated screens. Once dried, they are ready
for the coating procedure.

COATING TECHNIQUES
Coating procedures vary from facility
to facility since there is no hard, fast rule
regarding a correct or incorrect method.
The objective of the coating procedure
is to properly encapsulate the mesh in an

emulsion coating with the stencil thickness on the print side of the screen.
You want the stencil thickness to be on
the print side of the screen. This dictates
that regardless of the coating combination you use, you will coat the ink side of
the screen last. This process will push the
emulsion coating to the print side. Otherwise, your stencil thickness will reside on
the ink side, which will result in numerous
printing issues, starting with the ink not
properly releasing from the screen. You
should maintain a thin emulsion coating
when printing on ﬁner mesh counts. This
will allow for high resolution and faster
exposure times.

Coating Variations
First Side

Last Side

Print Side

Ink Side

The chart above shows the variations in
coating procedures used in different facilities. These vary based on the desired end
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Impressions - April 2015

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