Pigment printing - Textile Printing

Pigment
printing

TEXTILE
PRINTING:

It can be described as a localized form of
dyeing, applying colorant to selected areas of
the fabric to build up the design.

Textile printing, like textile dyeing, is a process
for applying color to a substrate.

However, instead of coloring the
wholesubstrate (cloth, carpet or yarn) as in
dyeing, print color is applied only to defined
areas to obtain the desired pattern.

Dyeing can hold single color where as printing
can handle 12 to 20 colors in single go.
Pigment printing:
“A fabric that has been printed with a paste
made of an insoluble pigment mixed with a
binder and a thickener.”

In pigment printing, insoluble pigments, which have
no affinity for the fiber, are fixed on to the textile
with binding agents in the pattern required.

Pigment printing is most economical printing
process and allows maximum output of goods

because of the elimination of washing off, quick
sampling and high printing speeds.

It is not possible to apply it directly on the fabric.
Binder must be used to apply the pigment dye on the
fabric.
Printing can simply be classified according to
technique, fiber type and dye class:


As, Chart Describes major portion of textile printing
is covered by Pigment Printing so it becomes an
important topic to discuss.

To print on different substrates different chemistry
is required for example printing on natural
cellulose is majorly done with reactive dyes.

Polyester is printed with disperse dyes.

Cotton is printed with sulfur dyes.

But, Pigment printing can be applied to various type
of fibers like Cotton, Polyester, Blend PC, Polyamide
and many more.
Pigment Printing process

Pigment printing has gained much importance today
and for some fibers (e.g. cellulose fibers) is by far the
most commonly applied technique. Pigments can be used

on almost all types of textile substrates and, thanks to
increased performance of modern auxiliaries, it is now
possible to obtain high-quality printing using this
technique.

Pigment printing pastes contain a thickening agent, a
binder and, if necessary, other auxiliaries such as
fixing agents, plasticizers, defoamers, etc.
Pigment Printing
process

White spirit-based emulsions, used in the past as thickening
systems, are used only occasionally today (mainly half-
emulsion thickeners).

After applying the printing paste, the fabric is dried and
then the pigment is normally fixed with hot air (depending
on the type of binder in the formulation, fixation can also
be achieved by storage at 20°C for a few days).

The advantage of pigment printing is that the process can be
done without subsequent washing (which, in turn, is needed
for most of the other printing techniques).
Pigment Printing
Process:
Pre-treatment
↓
Printing (with binder and fixer)
(roller/rotary printing)
↓

Drying ( Drying the printed fabric)
(90-100%/110-120°C)
(dryer)
↓
Curing (Fixation of the printed dye or pigment)
(cotton 140-160°C/110-120°C 3-5 min)
(polyester 160-220°C , 30-60s)
(stenter)
Steps of printing
process:
A Typical Printing Process Involves the
Following Steps:

Color paste preparation
when printing textiles, the dye or pigment is
not in an aqueous liquor, instead, it is
usually finely dispersed in a printing paste,
in high concentration.

Textile Printing
The dye or pigment paste is applied to the
substrate using different techniques, which
are discussed below.
Steps of printing
process:

Fixation
Immediately after printing, the fabric is
dried and then the prints are fixed
mainly with steam or hot air (for

pigments). (Conversion of binder monomer
into polymer).

After-treatment
this final operation consists in washing
and drying the fabric (it is not necessary
when printing with pigments or with
other particular techniques such as
transfer printing).
Classification of
pigments:

According to origin

Natural/Mineral: Iron ores, clays, chalk etc

Synthetic/chemical: white lead, ZnO, TiO2 and large number of inorganic and organic
color

According to Reactivity

Reactive pigment: some pigments on account of the chemical character react with oil,
fatty acids and soaps. These are called reactive pigments e.g. ZnO, red lead

Inert pigment: TiO2

According to Chemical Nature

Organic pigment:


Azo pigment

Diarylide orange and yellows

Phthalocyanine

Hasna yellow

Inorganic pigment
Printing process:

Printing process may be further
divided into two steps:
1. Preparation of the print paste.
2. Printing the fabric.
Typical Recipe for
Pigment Printing:
Soft Water          700
g/Kg
Anti Foamer              1g/Kg
Binder
   200g/Kg
Fixative
  10g/Kg
Softener
 10g/Kg
Urea 

  50g/Kg
Thickener          

15g/Kg
Total
    1 Kg
Components of pigment
printing:
A pigment printing system consists of three essential components:

Pigment dispersion: Specific pigments are treated in a grinding mill in
the presence of suitable non-ionic surfactants. A particle size of 0.1-3 m is μ
typical. Generally, the pigment pastes are aqueous based and contain the
dispersing agent, humectants (to prevent evaporation and drying out).

Binders and cross-linking agents (polymers): The binders used in
pigment printing systems are film-forming substances made up of long-
chain macro molecules which, when heated with a suitable acid-donating
catalyst, form a three-dimensional structure in the pigment.

Thickeners and auxiliary agents: These give the required print
thickening power (rheology).
Binders:

Binders plays key role in pigment printing. Binder
are monomers which on heating get converted into
polymers. Just by simple heating, no pressure , no
steaming , no electricity.
Binders{Monomer} Heat > Plasticizer/Plastic{Polymer}

Binders form plastic but, its too soft and
transparent that its difficult to see it but we can
feel its harshness on the fabric. That s why pigment ’

printed fabric have more harshness when compared
to other printing techniques.
Binders:

Binder actually hold the pigment color and
sandwich it between fabric surface and
plastic coating and this coating help color to
stick there and stand with high and severe
conditions.

In addition to binder an other component is
also added to the textile pigment printing
paste and that is called fixer. Fixers are
mostly formaldehyde based, which helps in
strengthening of binder to hold on pigment.

The working of binder that how
binder sandwiches pigment in
between itself and substrate. As,
nearly 90 to 95% of pigment is
successfully entrapped in between
so no need of washing as it was
required in case of reactive
printing to wash off unfixed dye.
This is big advantage of pigment
over other techniques which make
it economical.
Printing methods:
A decorative pattern or design is
usually applied to constructed

fabric by:
1. Screen printing method
a. Rotary screen methods
b. Flat screen methods
2. Roller printing method
Screen printing
method:

Screen printing is by far the most popular technology in use
today.

Screen printing consists of three elements:

The screen which is the image carrier;

The squeegee;

Ink.

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.

A stencil is produced on the screen either manually or
photochemically.

The stencil defines the image to be printed in other printing

technologies this would be referred to as the image plate.
flat bed screen printing:

For each color in the print design, a separate screen must be
constructed or engraved.

The modern flat-bed screen-printing machine consists of an
in-feed device, a glue trough, a rotating continuous flat
rubber blanket, flat-bed print table harnesses to lift and
lower the flat screens, and a double-blade squeegee trough.

The in-feed device allows for precise straight feeding of the
textile fabric onto the rubber blanket.

As the cloth is fed to the machine, it is lightly glued to the
blanket to prevent any shifting of fabric or distortion
during the printing process.
flat bed screen printing:

The blanket carries the fabric under the screens, which are in
the raised position. Once under the screens, the fabric stops,
the screens are lowered, and an automatic squeegee trough
moves across each screen, pushing print paste through the
design or open areas of the screens.

Remember, there is one screen for each color in the pattern.

The screens are raised, the blanket precisely moves the fabric to
the next color, and the process is repeated.


Once each color has been applied, the fabric is removed from the
blanket and then processed through the required fixation process.
flat bed screen printing:

The rubber blanket is continuously washed, dried, and
rotated back to the fabric in-feed area.

The flat-bed screen process is a semi-continuous, start-
stop operation. Flat screen machines are used today
mostly in printing terry towels.

Can produce as many as 25,000 impressions without
significant degradation of the image.

The process is slow with production speeds in the range
of 15-25 yards per minute.

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 between
the screen and a steel or rubber impression roller immediately
below the screen. (The impression roller serves the same function as

the press bed on a flatbed press.)

As the fabric passes through the rotary unit, the screen spins at a
rate that identically matches the speed of substrate movement.
rotary screen printing:

The squeegee on a rotary press is in a fixed position with its edge making
contact with the inside surface of the screen precisely at the point where
the screen, substrate, and impression roller come together .

Ink is automatically fed into the center of the screen and collects in a
wedge-shaped well formed by the leading side of the squeegee and the “ ”
screen s interior surface. ’

The motion of the screen causes this bead of ink to roll, which forces ink
into stencil openings, essentially flooding the screen without requiring a
floodbar.

The squeegee then shears the ink as the stencil and substrate come into
contact, allowing the ink to transfer cleanly to the material.

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