Laminating Stencils

screen printing screen

All shops can expand their screen printing opportunities with simple stencil
making procedures that are sure to surprise even the veteran screen printer
with the graphic results.

For those shops using liquid emulsion, each mesh count produces a different coating thickness,
and therefore dimension to the ink deposit.  A 305 monofilament is typically
35 microns thick.  110 mesh is 80 microns, and 60 is 125 microns.  Emulsion
fills the mesh creating a depth to the ink well.

The exposure time for liquid emulsion and capillary film varies with thickness, chemistry
(such as, diazo, dual cure and photopolymer), and manufacturer.  With
liquid emulsion the coating thickness is also affected by the angle of the
scoop coater, pressure and speed of application, quality of coating instrument,
and screen tension.  On soft screens the liquid emulsion can be thicker
and darker in the center compared to the outside edges where there is better
support for the mesh.  Those are a lot of variables affecting exposure
time and ink deposit.

Capillary film is a coating of liquid emulsion on a plastic sheet at a precise thickness
as marked on the packaging by the manufacturer.  Thicknesses from 10 to
1000 microns are available.  All the uncertainties of liquid emulsion
have been replaced by an exposure time and ink dimension that is exactly predictable.  Welcome
to quality control!

For those shops that had to expose a second screen when the first screen was unacceptable,
you can now eliminate that extra work.  An investment of about $35 in
an exposure calculator allows measuring the exact exposure time required for
each thickness, chemistry and manufacturer of capillary film.  Under exposed
screens with scum in the image, blisters and ragged edges, and over exposed
screens that are hard to wash out are replaced with “goof-proof” screens.  Precise
light exposure is particularly important when using gray images on inexpensive
vellum rather than dense black images.

The impact on the printed image can be truly astounding.  Here are some samples.  An
image created with 305 or higher mesh and 20 or thinner capillary film can
be printed so that the image can be seen, but not felt.  If colors are
overlapped to make registration easier, using a slightly thicker stencil for
the color on top adds opacity to reduce the risk of the first color bleeding
through the second color.  Image edges created with hard edge capillary
film have better resolution than ink deposits influenced or blocked by mesh
in the image rather than above the image.

Some of the most exciting graphics, however, are on textured garments and with textured
images.  Ink printed through a screen coated with liquid emulsion follows
the texture like pique resulting in ragged edges.  The same images exposed
in a film coated under the mesh produces hard, straight edges when using ink
with three dimensional properties.  A 100 micron capillary film will bury
the texture of pique golf shirts and 600 denier tote bags so that the texture
and color of the substrate does not show through the ink film.

Textured images have more than a width and length.  They stand off the garment.  The
amount of that third dimension is determined by the stencil thickness.  So
realistic bumps can be laid on a basketball surface that is printed on corduroy
(see the February 2003 Printwear cover).  A mascot like a tiger can be
printed with deep socket eyes by printing with thicker stencils around the
eyes.  Corporate logos can be photographic copies of corporate advertising,
signs, packaging and stationary.

Stencils of various thicknesses can be created with almost any exposure unit.  One
piece of capillary film is exposed, washed out, and then covered with a second
piece of capillary film to build the stencil thickness, and therefore ink deposit.  The
key to success is locating the positive exactly in the same spot for each exposure.  For
those who don’t have pin registration systems, a screen registration
guide is the equivalent. 

A screen registration guide is simply a flat board  larger than the screen and
with a 2” x 2” board affixed to one edge.  A screen is butted
against the 2x2, and the frame is used to locate a second 2x2 at the edge of
the frame and perpendicular to the first 2x2.  Every time a screen is
pushed against these two 2x2’s, the screen will be exactly in the same
spot.  Now draw the vertical and horizontal center lines on a screen and
on a piece of graph paper.  Lay the screen against the 2x2’s and
locate the graph paper under the screen with the center lines of the graph
paper matching the center lines of the screen.  Tape the graph paper
in place, cover with a sheet of clear plastic, such as from capillary film,
and tape the plastic to the board.  Done!

Now, make two copies of the positive and tape one where the image is to be exposed in
the screen.  Tape the second positive over the first in precise registration
and secure in place with one piece of adhesive tape.  Add 1” strips
of tape that is adhesive on both sides in each of the four corners of the top
positive.  Butt a coated screen against both 2x2’s, and then down
on the double stick tape.  Pick the screen up, and the top positive is
sticking to the bottom, or print side, of the screen.  After exposure,
the second positive can again be located exactly in the same spot using the
first positive for registration.  The process can be repeated as many
times as desired to create a stencil of any thickness.  This is simple,
and free!

Here are some tips.  When building thick stencils, the first piece of film should
be 50 or 100 microns thick.  Thinner film like 50 microns exposes and
washes out easier.  Selecting a film with double the thickness more than
doubles the exposure time.  After this first piece of stencil has been
washed out, and while it is still wet (“the wetter, the better”),
lay a second piece of capillary film over the image like covering a hamburger
with a slice of cheese.  The water will bond the two slices like superglue.  After
the second layer of capillary film has dried, the plastic sheet has been removed,
and the image exposed again, both sides of the image should have water run
over the image, but not sprayed with  pressure.  Water will absorb
into the stencil from both sides to speed the washout process.

If a thick stencil is the objective, that first, thinner stencil, holds subsequent thicker
pieces off of the mesh like a gasket to facilitate washout.  Also, thinner
films dry quicker, because the moisture evaporates out of only the emulsion
side of the capillary film.  A 400 micron film, for example, can take
a long time to dry.  Washing out thinner films is easier and more like
the experience of washing out liquid emulsion.  Drying can be expedited
with a heater fan.

Washout out can also be accelerated by laying a screen in a horizontal position, laying
a paper towel over the image, and spraying with water.  The wet paper
holds the moisture on the image so water will be absorbed into the stencil.  The
paper towel should be removed within 1-2 minutes, or the water could get between
the stencil and mesh causing blisters or images to lift up.  If that happens,
dry the mesh from the ink side of the screen with a towel and then store the
screen to dry completely.  The film will re-adhere to the mesh.  Then
wet the screen and continue the wash out process until the image is clean.

Never squeegee capillary film into mesh, because that pushes soft emulsion into the screen
and the ink deposit will be less than as marked on the stencil packaging.  However,
if removing the plastic liner to capillary film is difficult, either moisture
is still in the stencil or the stencil should have been squeegeed into the
mesh around the edge of the film, and beyond the image, to create a mechanical
bond between the capillary film and mesh without adversely affecting the thickness
of the ink deposit.

Laminated films add a new dimension to your work, fun and profit potential.  Your
customers will be impressed.