Fig. 4
Surface smoothness can affect your
substrate to stencil gasket. The lower
Rz numbers will be produced only by
machine coating or film products.
Direct/indirect and capillary films will
produce the lowest Rz numbers
possible for screen stencils. High solids
content emulsions and face coating
(second or more coats of emulsion over
dry first coatings) can also lower your
Rz measurements. (Fig. 4) Exact EOM
and Rz numbers can only be measured
by special testing equipment.
Indirect film products are
presensitized emulsions on film. They
are produced to expose and develop
before they are attached to the screen
mesh. Indirect film has fallen out of
general use as products that are easier
to use and have superior reproduction
properties are now available.
Fig. 5
Capillary films are a photosensitive
emulsion layered onto a film backing.
(Fig. 5) The name is indicative of the
action that causes the adhesion,
capillary action. With wet screen fabric
the film will draw into the mesh when
placed in contact with the face of the
screen.
Capillary films suffer from past bad
reputation for delamination (Fig. 6) the
current products available are capable
of long runs and excellent detail.
Capillary films produce the lowest Rz
numbers possible and can save large
amounts of screen room production
time.
Fig. 6
Capillary films are best applied with the
(emulsion up) on a hard flat surface.
(Fig. 7)
Fig. 7
Place a screen (squeegee side up)
onto the film, lightly mist the mesh with
a spray gun until the screen starts to
draw up the capillary film into the fabric.
(Fig. 8)
Fig. 8
Direct/indirect film products
(combination stencils) are two-part film
and emulsion combinations. Films
assure low Rz numbers and high detail
print quality. Direct emulsions produce
high stencil durability. Direct/indirect film
systems combine the best features of
direct emulsion and film products,
creating a strong, high definition stencil
that will make longer runs possible with
direct emulsion.
Direct/indirect film products require a
coating of direct emulsion. Then the film
can be adhered to the face (substrate
side) of the screen. One method is to
coat the screen (one stroke on each
side of the screen) then place the
screen (squeegee side up) on the film
(emulsion side up) and stroke the
squeegee side of the screen with a low
pressure stroke with a soft squeegee.
(Fig. 9) The use of newsprint on your
work surface will help with clean up.
Fig. 9
Stay consistent and you will be able to
predict your results with greater
accuracy. Your goal should be
consistency, predictability, and
repeatability.
Graphics and text copyright 2002
Douglas Grigar [email protected]
Pg. 14
