Screen Printing - August/September 2017 - 29
n garment printing, the term "special effects" covers a lot
of inks and processes, some of which I've never considered
to be part of this category. Puff, for example, isn't a specialeffect ink to me, even though some consider it to be one.
Other inks are clearly designed for special-effect printing and
can create remarkable results when used correctly. I want to
focus on some of my favorites in this article: high-density
(HD) inks, gels, and bases.
If you aren't familiar with HD inks, they can produce dramatic three-dimensional images. They are designed to print
through very thick stencils and have a high viscosity with
reduced tack and increased flow characteristics compared to
standard plastisol inks. As you'll see, they can achieve thick
ink deposits with extremely sharp edges. Used correctly and
creatively, HD inks allow you to produce truly unique effects.
HD inks lost some popularity for a number of years
because of concerns and regulations over the use of orthophthalates. Once many of the ink companies reformulated
the products, HD inks came back again. Still, few printers use
them because many don't know how. The ultimate goal with
HD inks is to produce a print that has dimension to it after
printing and that stays that way once it's through the curing
unit. I'll discuss the production steps that are unique to HD
printing below and show how the technology was used to
create several award-winning shirts.
One of the most common problems I see in shops that aren't
accustomed to HD printing is screenmaking, especially
selecting the right mesh and creating stencils of sufficient
thickness to achieve the desired effect. You need a thin mesh
that has a good percentage of open area to allow the ink to
pass through the stencil easily without too much squeegee
pressure. The most popular mesh counts for HD printing are
around 80 to 83 threads per inch with a 70 to 71-micron "S"
thread. These meshes have an open area of about 60 percent.
You can make stencils for HD printing with certain types of
direct emulsions or with thick capillary films. I've worked with
both, and my opinion is that capillary films definitely make
more sense for this application. The issues I have with direct
emulsions are the time it takes to apply them, the number of
coats it takes to get the needed thickness, and the difficulty of
duplicating the results across multiple screens, which takes a
high-quality coating machine to do predictably. Capillary films
are easier to apply and you can get them in thicknesses
ranging from 100 to 1000 microns. The most popular films for
HD printing fall between 200 and 400 microns. Thicker films
might require you to use wire meshes with 80-micron threads
and will require very long exposure times. It's also very
difficult to get good, clean prints from such thick ink deposits.
Applying the capillary film to the mesh is where many printers run into problems. Because the films are fairly expensive,
I cut them down to size when I can, leaving a 1-inch border on
all sides of the image area. I find it's easiest to use a "build up"
board that is slightly bigger than the film but smaller than the
inside dimension of the frame, and then laying some newsprint
on the board before placing the capillary film on it (emulsion
side up). Then when I have the screen in the exact position I
want it, I lower it (print side down) onto the emulsion.
Many printers use water to apply the mesh as they do
when making screens for their regular work, but it's not the
right choice for HD printing. For one, the water will reduce
the thickness of the stencil and therefore the ink deposit.
Also, because the capillary films used for HD printing are so
thick, water doesn't always adhere them to the mesh very
well and they can delaminate from it during the printing
process. For this application, use direct emulsion instead
of water to apply the capillary film. I prefer using SBQsensitized pure-photopolymer films and emulsions for HD
screens because they are the fastest to expose.
To get the best results, I apply the emulsion twice. I use
a squeegee for the first coat to attach the film, and then I
A silver HD gel
as it appears in
A close-up of
an HD gel print
with black added
to it. Notice the