3. Photo emulsion is what makes the
modern day screen printing process
possible. The emulsion is a
substance that reacts to ultraviolet
light. Once it has been exposed to
the correct ultraviolet
wavelength, the emulsion hardens
and becomes impermeable. There
are many different types of emulsion
in the market, as well as many
different methods of application. In a
later post, I’ll dive into the two most
popular methods for coating the
screen mesh with emulsion.
4. A squeegee is a flat, rubber or
urethane blade set into a handle.
Some people may argue that this
is not necessary and that
brushes or sponges can be used
to push the ink through the
screen. They are correct and it
can be done, but the results and
time consumption can lead to
very mixed results. Almost all
professional screen printers use
squeegees to produce
consistent, high quality results.
5. This is a tool that is used to
coat the screen with a
thin, uniform layer of liquid
photo emulsion. Without
the scoop coater it is
possible to use a squeegee
to spread the photo
emulsion but this can
sometimes lead to uneven
thickness and poor
exposure results.
6. The film positive refers to the artwork
which is typically printed or drawn onto
on a transparent medium. The artwork
must be opaque in order to produce
proper results when exposing the screen.
One of the cheapest ways to create the
film positive is to print directly onto
transparency film from your laser or ink
jet printer. Be sure to have the printer
settings set to produce the darkest black
possible for your artwork. As an
alternative, vellum can also be used as a
film positive. If you are using vellum add
approximately 20% to the exposure time
due to the reduced transparency of the
vellum.
7. In order to properly expose
the emulsion and “burn” the
screen, a light source is
required that contains
Ultraviolet Radiation in the
350-420 Nanometer
spectrum. Fluorescent
unfiltered tubes, metal
halide lamps and even the
sun can be used to expose
a screen.
8. These are essential if you
plan on screen printing
paper goods or other flat
objects. The hinge clamps
you to keep your screen in
the same position, allowing
for easy registration and
consistent prints.
9. There are kinds of tape that I use
on a regular basis. The first is
painter’s tape which use for easy
registration of
screens, positioning acetate, etc.
The second type of tape that I
use is a tape made for screen
printing which is water and
solvent resistant. This one is
used for taping my screens. I
have also used plastic packing
tape with great results.
10. During the coating and exposure
process it is important to create
light safe conditions. Premature
exposure to UV light
(sunlight, regular household
lights, etc) can pre-expose the
coated screens resulting in poor
results. Yellow bulbs filter out the
spectrum of light that can expose
the emulsion, making it “safe” to
work under those conditions.
12. There are two main types of inks that are
used for screen printing, each with their
own advantages and disadvantages.
Water-based inks utilize either dyes or
pigments in a suspension with water as the
solvent. The evaporation of the water is
necessary to set or cure the ink.
Plastisol is a thermoplastic ink. It is
composed of PVC (polyvinyl chloride)
particles suspended in a plasticizer. High
temperatures are required to cause the
molecules of PVC resin and plasticizer to
cross-link and fully cure.
13. Water-based inks tend to be a little more
environmentally friendly and give printed
fabrics a soft “hand”. A soft hand means that
your hand cannot easily feel the ink when it
passes across the surface of the fabric. Water
based inks printed on fabric can also be
ironed (Plastisol will melt and smear if heated
up to it’s curing temperature). For paper
screen printing applications water-based inks
are ideal as they will air dry as the water
content in the ink evaporates. Clean up is
easy and can be done without much impact to
the environment.
14. Water-based ink is much more difficult to cure than
plastisol for fabric applications. With water-based
ink, the curing temperature must be reached and
then held until all of the solvent (water) is removed.
If you don’t fully cure the ink (for example on a T-
shirt), the ink will fade with repeated washings. If
water-based ink is left in open mesh for even a
short period of time, it can clog the mesh and ruin
the screen. You don’t really have to worry with
regards to paper applications however. The other
thing is that water-based inks will break down
regular emulsion very quickly and even break
down water resistant emulsions over time leading
to screen breakdown for longer print runs.
15. Plastisolinks are not water-soluble and the
ink will not dry if left in the screen for
extended periods of time. It can be left in
the screen for extended periods of time
without worrying about clogging the mesh.
Platisol will not break down the screen
emulsion like water-based inks. They also
happen to be very opaque and great for
applications on colored fabric
16. Plastisol inks will not air dry and need to be cured
(heated) as a result. Curing the inks can be done with
a flash dryer, or more inexpensively, any home oven.
Be careful not to burn your house down! Most
plastisols need to reach a temperature of about 350
Fahrenheit before being fully cured.
Plastisol tends to sit on top of the threads instead of
soaking into them, which typically results in a
raised, plasticized texture. There
are, however, plastisol additives that can give the ink a
softer “hand”. If the ink is under-cured, the print will
crack and peel over time.
Plastisol inks are generally considered harsher on the
environment. Fortunately, there are a number of
plastisol inks on the market that contain less
toxins, and there are also eco-friendly solvents that are
available for clean up.
19. The screen frame is a structure
that the woven mesh is stretched
upon and adhered to. Screen
frames come in a variety of
shapes and sizes, depending on
the size of the art work and
printing surface. The mesh is
either stapled or glued to the
frame with sufficient tension to
provide a flat printing surface that
20. Typically, frames are made out of
wood or aluminum. Personally I
recommend aluminum frames
over wood because they are
easily cleaned and can be reused
indefinitely without losing their
shape.
21. Wood screens will be fine for a
while but repeated water
exposure tends to warp the frame
over time. Over time, with
extended use, both wood and
aluminum screen meshes will lose
some tension which may result in
poorer quality printing results. If
you start to notice this occurring
it’s best to have the screens re-
22. Always choose a screen frame
that is larger than the area you
are attempting to print by at least
2 inches on every side. This will
make your life easier when
applying emulsion, exposing
artwork and printing.
25. Woven mesh is the “silk” in silkscreen. Typically this
mesh is made out of mono-filament polyester fabric
which is stretched taut over a screen frame. The
spaces between the mesh make the fabric porous
which allows ink to pass through.
Screen fabric come in a wide variety of mesh counts.
Lower mesh counts means that the fibers of the mesh
are spaced farther apart, allowing more ink to pass
through. Higher mesh counts deposit smaller amounts
of ink and are generally better for fine details and line
work. A general rule of thumb is 110 – 160 mesh count
for fabrics and 230+ if you are printing on paper. If you
are on a budget and only want one screen, 150 should
do the trick for both fabric and paper.
Screen mesh is available in either white or dyed mesh
(typically yellow). Dyed mesh cuts down the amount of
light diffusion during the exposure process which leads
to a sharper print. For lower mesh counts around 110 it
doesn’t really make a difference if the color is white or
dyed.
