printing is a printing technique that uses a woven
mesh to support an ink blocking stencil. The attached
stencil forms open areas of mesh that transfer ink
as a sharp-edged image onto a substrate.
A squeegee is moved across the screen stencil forcing
or pumping ink past the threads of the woven mesh
in the open areas.
screen is made of porous, finely woven fabric called
mesh stretched over a frame of aluminum or wood. Originally
human hair then silk was woven into screen mesh, currently
most mesh is made of man made materials such as steel,
nylon, and polyester. Areas of the screen are blocked
off with a non-permeable material to form a stencil,
which is a negative of the image to be printed; that
is, the open spaces are where the ink will appear.
screen is placed atop a substrate such as polystyrene,
paper or fabric. Ink is placed on top of the screen,
and a floodbar (also known as a fill bar) is used
to fill the mesh openings with ink. The operator begins
with the floodbar at the rear of the screen and behind
a reservoir of ink. The operator lifts the screen
to prevent contact with the substrate and then using
a slight amount of downward force pulls the floodbar
to the front of the screen. This effectively fills
the mesh openings with ink and moves the ink reservoir
to the front of the screen. The operator then uses
a squeegee (rubber blade) to move the mesh down to
the substrate and pushes the squeegee to the rear
of the screen. The ink that is in the mesh opening
is pumped or squeezed by capillary action to the substrate
in a controlled and prescribed amount, i.e. the wet
ink deposit is equal to the thickness of the mesh
and or stencil. As the squeegee moves toward the rear
of the screen the tension of the mesh pull the mesh
up away from the substrate (called snap-off) leaving
the ink upon the substrate surface.
Screen Printing Process
are three types of screenprinting presses. The 'flat-bed'
(probably the most widely used), 'cylinder', and 'rotary'.
items are printed in multi-color designs using a wet
on wet technique, while graphic items are allowed
to dry between colors that are then printed with another
screen and often in a different color.
Reclaiming A Screen
screen can be re-used after cleaning. However if the
design is no longer needed, then the screen can be
"reclaimed", that is cleared of all emulsion
and used again. The reclaiming process involves removing
the ink from the screen then spraying on stencil remover
to remove all emulsion. Stencil removers come in the
form of liquids, gels, or powders. The powdered types
have to be mixed with water before use, and so can
be considered to belong to the liquid category. After
applying the stencil remover the emulsion must be
washed out using a pressure washer.
screens are ready for recoating at this stage, but
sometimes screens will have to undergo a further step
in the reclaiming process called dehazing. This additional
step removes haze or "ghost images" left
behind in the screen once the emulsion has been removed.
Ghost images tend to faintly outline the open areas
of previous stencils, hence the name. They are the
result of ink residue trapped in the mesh, often in
the knuckles of the mesh, those points where threads
the public thinks of garments in conjunction with
screenprinting, the technique is used on tens of thousands
of items, decals, clock and watch faces, and many
more products. The technique has even been adapted
for more advanced uses, such as laying down conductors
and resistors in multi-layer circuits using thin ceramic
layers as the substrate.
is more versatile than most other traditional printing
techniques. The surface does not have to be printed
under pressure, unlike etching or lithography, and
it does not have to be planar. Screenprinting inks
can be used to work with a variety of materials, such
as textiles, ceramics, wood, paper, glass, metal,
and plastic. As a result, screenprinting is used in
many different industries, from clothing to product
labels to circuit board printing.
The above text was borrowed from Wikipedia.com.