Reference Book
edges of the image smooth and sharp. As the mesh count increase, fabric
strength and durability decrease.
Fabric strength:- It is directly related to the thread diameter. As the mesh
count increase, thread diameter must decrease or no porous areas will exist.
Types of fabrics:-Three types of fabrics are used as screens- natural, synthetic,
and metal mesh. Natural fabrics are always multi-filament. Synthetic fabrics
may be either multi-filament or monofilament. Metal mesh is a monofilament.
Typically it is stainless steel, but it can also be bronze, copper or brass. It is
used for printing with heated inks on plastics.Stencil preparation
Stencils can be classified into three groups: Hand cut, Tusche and glue and
photographic stencils.
Hand cut stencils
Hand cut stencils are prepared by removing the printing image areas manually
from some form of base or support material.
Tusche and glue stencils
It is an art process which involves drawing directly on the screen fabric with
lithographic tusche (an oil based pigment) and then blocking out non-image
areas with waterbased glue material.
Photographic stencils
They are generally produced by a thick, light sensitive, gelatin based emulsion
that is exposed and developed either on supporting film or directly on the
screen itself. Only hand cut and photographic stencils are used in commercial
printing.
The primary advantage of photographic stencil is the possibility for complex
and high quality line details. This method allowed the screen printers to enter
the field of packaged product illustration. A colour image can be screen printed
with nearly any ink on nearly any surface shape (flat, cylinder or irregular)
with this process
All photographic stencil process are divided into 3 types:
Indirect, direct and direct-indirect
Indirect:-The indirect process uses a dry emulsion on a plastic support sheet.
The stencil emulsion is sensitised by the manufacturer and is purchased by the
printer in rolls. The stencil film is exposed through a transparent, right reading
positive and is then treated with developer solution. The area that the light
reaches (non-image area) harden during exposure. The remaining areas are
washed away with a warm water spray to form the image area. The stencil is
adhered to a clean screen while it is wet from the spray and support sheet
removed after the stencil dries.