Now we are in the age of printing, textile printing becomes popular day by day. Screen printing has been taken large place in textile printing sector. Trying to give a short description on it.

1. Screen printing in
textile sector
Hasibul Haque
Chowdhury
B.Sc. in Textile Engineering

2. Printing
Textile printing is the process of applying colour to fabric
in definite patterns or designs. In properly printed fabrics the
colour is bonded with the fiber, so as to resist washing and
friction. In printing one or more colours are applied to it in
certain parts only, and in sharply defined patter.
In short, Printing Applying coloured patterns and designs
to decorate a finished fabric is called ‘Printing’.

3. Screen Printing
Screen printing is a printing technique whereby a mesh is
used to transfer ink onto a substrate, except in areas made
impermeable to the ink by a blocking stencil. Screen printing is
also a stencil method of print making in which a design is
imposed on a screen of polyester or other fine mesh. As the
screen rebounds away from the substrate the ink remains on the
substrate.
One color is printed at a time, so several screens can be used
to produce a multicoloured image or design.

4. Why Called ?
Traditionally the process was called screen
printing or silkscreen printing because silk was used in the
process prior to the invention of polyester mesh.
Currently, synthetic threads are commonly used in the screen
printing process. The most popular mesh in general use is made
of polyester. There are special-use mesh materials of nylon and
stainless steel available to the screen printer.

5. Mesh
The screen printing process uses a porous mesh stretched tightly
over a frame made of wood or metal. Proper tension is essential for
accurate color registration. The mesh is made of porous fabric or
stainless steel.
Screen mesh refers to the number of threads per inch of fabric.
The more numerous the threads per inch the finer the screen.Finer
mesh fabric should be 200-260 threads per inch. These are generally
used in graphic and industrial printing.Course mesh fabric will be
160-180 threads per inch.
Mesh = Thread/Inch
Courser Mesh use to apply more color but not very good printing.
Finer Mesh use to apply less color and for very good printing.

6. Mesh Fabric Image

7. Chemicals
The Dyes used for printing mostly include vat, reactive, naphthol
and disperse colours which have good fastness properties.
The pigments, which are not truly dyes, are also used extensively
for printing. These colours are fixed to the fiber through resins that
are very resistant to laundering or drycleaning. Pigments are among
the fastest known colours and are effective for light to medium
shades.
For cotton printing vat and reactive dyes are generally used. Silk
is usually printed with acid colours. Wool is printed with acid or
chrome dyes but before printing it is treated with chlorine to make it
more receptive to colours. Manmade fibers are generally printed with
disperse and cationic dyes.

8. Types
Screen printing is by far the most common technology today.
Based on the type of the screen used.
Two types exist: 1) Rotary screen printing
2) Flat (bed) screen printing.
A blade (squeegee) squeezes the printing paste
through openings in the screen onto the fabric. This causes the
ink to wet the substrate and be pulled out of the mesh apertures as
the screen springs back after the blade has passed.

9. Flat Screen Printing
In flat bed screen printing, this process is an automated
version of the older hand operated silk screen printing. For each
color in the print design, a separate screen must be constructed or
engraved.
If the design has four colors, then four separate screens must
be engraved. The flat-bed screen process is a semi-continuous,
start-stop operation. Flat screen machines are used today mostly
in printing terry towels.
Currently, approximately 15-18% of printed fabric production
worldwide is done on flat-bed screen machines.

10. Figure

11. Rotary Screen Printing
Rotary screen printing is so named because it uses a
cylindrical screen that rotates in a fixed position rather than a flat
screen that is raised and lowered over the same print location.
Rotary presses place the squeegee within the screen. These
machines are designed for roll-to-roll printing on fabric ranging
from narrow to wide-format textiles. In rotary printing, the
fabric travels at a consistent speed.
By converting the screen-printing process from semi-
continuous to continuous, higher production speeds are obtained
than in flat bed printing. Typical speeds are from 50-120 yards
per minute for rotary screen printing depending upon design
complexity and fabric construction.

12. Figure

13. Thanks