Reference Book
Screen Printing Process
First, porous fabric is stretched across the frame. Next, a stencil is adhered to
the fabric, blocking out certain portions of the fabric and leaving open the
desired image areas. Ink is poured on to the fabric and forced through the
image areas using a rubber or plastic blade called a squeegee. The ink is
deposited on a substrate below, producing an image of the cut stencil. Additional
prints are made by repeating the squeegee action on new substrates.
Squeegees:- A handheld squeegee has a smooth wooden or aluminium handle
and a rubber or polyurethane blade. Squeegee blades are rated by hardness, as
determined by a shore durometer.
Different substrates require different blade edges. There
are six squeegee blade shapes. The square-edge blade
is used for flat surfaces and general-purpose printing.
The squared-edge with rounded corners provide extra
heavy ink deposits on flat substrates and is used when
a light colour will be printed on a dark substrate.
A rounded-edge blade is used primarily in textile
printing where an extra-heavy ink film is required.
Single beveled edge blades are used for printing on
glass. The double beveled edge with flat point is used
for printing on ceramics and the double beveled edged
is used for printing on cylindrical objects such as bottles and containers.
Screen printing inks:- The type of ink depends upon the type of stencil being
used, the substrate, and the intended product. The ink pigment and ink vehicle
in screen printing must freely pass through screen fabric and create an image
of acceptable density on the receiving surface. Screen inks are thinner than
letterpress or lithographic inks but thicker than inks used in gravure.
Solvents:- Screen printing solvents are classified as thinners, retarders and
washup solvents. Thinners are solvents added to inks to change the viscosity
(thickness) of the ink. Retarders are solvents added to inks to thin the viscosity
and slow the drying time. Washup solvents are used to remove ink from the
screen.
Drying system:-Oven drying systems are used now instead of drying racks for
faster drying times and an efficient use of floor space.Screen frames and Fabrics
The screen frame serves several important functions. A frame:
Provides a means of attaching fabric at the proper tension
Provides rigidity and dimensional stability
Resists mechanical stress and warpage