How to Make a
Screen Using Vellum
Most experienced screen printers will likely
find this page of our vellum resource guide to be a bit too elementary,
however, we have frequently fielded questions from individuals -
particularly those considering entering the screen printing business - as to
how screens are made. For the benefit of those individuals, or as an
educational tool for your customers, here is an overview of the screen
making process.
| A screen starts
as a frame and a piece of special fabric. Frames can be made of wood or
metal. Historically, frames have been made of a number of other
materials, even porcelain, but modern frames usually fall into one of
these two categories. The frame in this picture is a special high-tech
frame which provides it's own stretching mechanism. Fabric for screen
printing is rarely made from silk these days, even though a few people
still use the term "silk-screen." Most screen printing fabrics are made
from precision crafted monofilament polyester, meaning that the strands
of thread in the fabric are a single filament - like fishing line. These
threads are manufactured to exacting standards where every thread is
exactly the same diameter throughout the weave and the distance between
threads in the weave is exactly controlled. |
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| Fabric is
attached to the frame and then stretched across the frame in both the height
and width dimensions. Stretching a frame forces the screen maker
to walk something of a tightrope. Since the piece of fabric used on a
single garment-size frame may cost more than $20, it is important that
care is exercised not to tear the fabric when stretching. On the other
hand, if the fabric is not extremely tight, the screen will produce
poor-quality prints. A special device for measuring tension is a very
wise investment to help you bring screens to optimal tension without
costly breakage. Modern screen
fabrics can withstand tremendous tensions, and the fabric on a properly
stretched 110 mesh frame feels much like placing your hand on a solid
wall. |
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| Once stretched,
the screen undergoes an initial washing / preparation for it's first
use. Special chemicals will be employed at this stage to degrease the
screen and slightly abrade the smooth surface of it's fibers so that
emulsion can firmly attach itself to the fabric. |
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| After the
screen dries, it is coated with a special photo-sensitive emulsion. The
emulsion may be a liquid (direct) emulsion, or a film on a carrier
sheet. (Indirect) Special techniques are employed in coating the screen
so that no air bubbles form in the emulsion, and so that the emulsion
coating is smooth and uniform. The
emulsion-coated screen is now light-sensitive, and must be placed in a
special drying cabinet which allows air to pass over the screen to dry
the emulsion, while keeping light out. |
|
| When the screen
is dry, it is ready for a design is to be exposed or "burned" into it.
To accomplish this, the design is printed onto a piece of SMR Premium
Vellum, and the vellum is placed on the light-sensitized screen, with
the design in contact with the emulsion. The exposure unit uses a vacuum
or some sort of compression mechanism to ensure positive contact between
the vellum and the screen to make sure that the design cannot move, and
air space between the screen and vellum cannot create distortion. The
exposure unit emits light with a high UV content toward the screen.
Areas of the emulsion which receive this light harden, while areas where the
printed design hold back light stay "soft."
See Also:
Determining Correct Exposure for Vellum |
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| Once the screen
has been exposed, it is removed from the exposure unit and washed.
"Soft" areas of the screen - the areas that did not receive light
because light was blocked by the print on the vellum - wash away leaving
the open mesh of the screen exposed. In the areas that received a proper
amount of UV light, the molecules in the emulsion have "Linked" and
hardened. These areas are very difficult to wash away, and form the
stencil for the design you wish to print. |
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| Once the screen
has been dried, it is placed in a press for printing. Ink is passed over
the screen, and the ink is pushed through the holes in the open mesh.
But ink cannot flow through the areas where emulsion still coats the
screen. When the screen is lifted from the garment, ink has formed a
copy of the image that is on the screen. Once the ink has been cured or
dried, the shirt is ready. |
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