printing is one of the leading printing processes. In this process, which was
previously known as silk screen printing, an image is produced on a flat screen
by blocking the pores in the nonprinting areas. This can be done manually by
cutting out templates and mounting them on the screen or it can be done
photomechanically by coating the screen with a photosensitive material, exposing
a positive and developing out the image
areas. Previously, flat
screens were made essentially using bichromated compositions. Environmental
concerns led to development and use of diazo as well as photopolymer systems.
screens are made of polyester, nylon or stainless steel filaments. Silk fabric
is hardly used. The mesh count usually ranges from 17 to about 500 per
inch. The actual printing operation
involves placing the surface to be decorated
under a stencil and drawing a mass of ink across the stencil surface by a rubber
squeegee. The ink is forced through the open areas of the stencil and deposited
on the surface to be printed. Automated multi-color presses are available.
stencil systems fall into two broad categories : 1) Indirect, wherein the image
and nonimage areas are fully formed on the stencil material before it is adhered
to the screen mesh and 2) direct, in which the image and nonimage areas are
formed after the stencil material is on or in the mesh. Indirect materials are
usually in film form and the direct systems may be either liquid or film type.
The liquid systems are generally referred to as emulsions.
are either gelatin- or polyvinyl alcohol based films sensitized with inorganic
or diazo compounds. Direct emulsions are supplied in either unsensitized or
presensitized forms. Conventional emulsions are mixtures of polyvinyl alcohol
(solvent-resistant but water-sensitive) and polyvinyl acetate (water-resistant
but solvent-sensitive) resins. The "dual-cure emulsions" incorporate diazo as
well as photopolymer technologies. These usually consist of polyvinyl alcohol/diazo
sensitizer/acrylic monomer/photoinitiator compositions. The diazo sensitizer is
usually added to the emulsion just prior to the screen preparations.
stencil systems are referred to as PVA/SBQ. The abbreviation SBQ stands for
stilbazole quaternary. The system is based on photodimerizable resin, which is
produced by reacting a styrylpyridine salt possessing a formal or an acetal
group with polyvinyl alcohol. These polymers are water-soluble in
generally offer higher solids content, faster photospeed, better resolution and
increased shelf life compared with diazo systems. Applications of screen
printing range from T-shirts to electronic circuits to CD/DVD disc printing.
Newer processes such as pad printing and inkjet digital printing now compete
with screen printing.
Chromaline Screen Print Products (Ikonics)
© 2007-2008 Savla Associates