Description

Screen printing has been used for hundreds of years & although there's

been lots of improvements with the expertise, the system still

consists of forcing ink through a stencil covered fabric or wire mesh

which has been mounted in a sturdy frame. The ink goes through only

the open areas of the stencil & is deposited onto a printing surface

positioned below the frame. Screen printing is versatile & it is often

the only printing system able to handling positive applications.
The equipment costs for screen printing are lower than other printing

processes, but the rate of production is usually slower. Manual screen

printing can be accomplished with only a few simple items: a sturdy

frame, screen fabric, stencils, squeegees, & ink. Automatic press

equipment is obtainable which greatly speeds up the system, but it is

no match for the output delivered by press equipment used for other

print processes.

Applications
Screen printing can be performed on  any type of material including

paper, glass, fabric, plastic, wood, & metal. Products as varied as

signs, posters, circuit boards, mugs, clothing, & soft drink bottles

can be printed using the system. Screen printing is useful when an

picture needs to be wrapped around an object or when images need to be

printed onto oddly formed manufactured objects.

Screen Fabrics

Fabrics for screen printing are selected because of several

properties. type of fabric may be suitable for application & not

another. Fabrics are classified according to the following properties:
Silk was the most common fabric because of its durability, but it is

not used as much today because other fabrics, synthetics, have proven

to be as nice or better & are less expensive.
Organdy is cheap & is nice for short & medium runs.
Nylon is the most long lasting fabric (synthetic or natural). It is a

nice choice for print applications involving convex or concave

surfaces
Polyester is widely used for its durability & flexibility.
Metal Mesh is made of stainless steel, copper, bronze, or brass & is

used when plastic substrates are printed with heated inks.
Stencil Types
Filament refers to the type of thread that makes up the fabric. The

thread can be multifilament or monofilament of which monofilament

provides the best quality. The multifilament threads produce images

with more jagged edges than the monofilament thread, but they are not

as expensive as monofilament.
Mesh Count is the number of threads per linear inch. A higher mesh

count produces finer details & higher quality in the product.
Strength is determined by the diameter of the thread. A bigger thread

diameter will provide greater strength to the fabrics, but the print

quality will decrease.
Weave Patterns for screen printing fabrics are based on types: plain,

which can be used for most applications, gauze, which is selected for

long runs because of its strength, & twill, which is selected for its

low cost & when quality is not an issue.
Most fabrics used for screens are made from of the following

materials:
Knife cut stencils are created with manual cutting & can be paper,

water soluble, or lacquer soluble.
Paper: Stencils cut from paper are used for basic designs & short

runs.
Water Soluble: Water soluble gelatin is cut away from the plastic base

of the stencil. The cut away portions of the gelatin represent the

picture areas. The plastic base & remaining gelatin are placed on the

screen material & water is used to adhere the gelatin layer to the

screen. The plastic base can then be peeled off from the gelatin layer

which remains adhered to the screen fabric.
Lacquer Soluble: A lacquer soluble stencil is used much the same way

as the water soluble stencil except that the stencil is adhered to the

screen material with lacquer solvents.
Photographic stencils are made of photosensitive materials & require

the use of film positives for exposure. There's types of photographic

stencils: indirect, direct, & direct/indirect.
Indirect: An indirect stencil is a photographic stencil which is

produced independent of the screen fabric & is applied to the screen

after exposure.
Direct: A direct stencil is in which the photosensitive material is

applied to the screening fabric so that after exposure, the stencil

becomes part of the fabric. It is long lasting & is useful for long

runs.
Direct/Indirect: A direct/indirect stencil is a mix of the stencil

types. It lasts longer than an indirect stencil, but it cannot match

its quality.

Ink

There is a wide range of inks available for use with screen printing.

The ink for some applications may need to be resistant to ultra-violet

light or they may need to be scratch, fade, or chemical resistant for

other applications. Most of the inks for screen printing are applied

with a heavy coverage so the ink layer takes a long time to dry. The

printed products can be air dried on racks if the number of printed

pieces is small, but most often a heat source is used to speed up the

drying, if the screen printing is performed with higher speed,

automatic equipment.

Most large volume screen printing is performed on automatic printing

equipment which makes the technique much more efficient and cost

effective. Manual screen printing is still used for plenty of of the

smaller runs or for specialized applications. The basic press types

are listed below:

Press Types

Flatbed: A flatbed press is used for printing on flat substrates.
Flatbed Cylinder: A flatbed cylinder press is much like a letterpress

flatbed cylinder press and is used for longer runs of flat

applications.
Cylinder: A cylinder press is used for printing on round or oval

objects.
Textile: T-shirts and other clothing items are printed on a textile

press.
Precision Flatbed: of the major makes use of for the precision flatbed

press is circuit board printing.
Rotary: Higher production rates are a benefit of the rotary presses.

The ink is pumped in to the printing cylinder and a squeegee on the

inside of the cylinder controls the flow of the ink.

(Gold Printing Group)