TE-424 Textile Printing

Lecture 2 :Printing inks

TE-424 Textile Printing 1

 In this lecture….

About printing inks

• Printing ink ingredients

• Characteristics of different ingredients
• Working mechanism of different ingredients

Dr. Muhammad Ali

TE-424 Textile Printing 2
Associate Professor, TXD, NEDUET
 Broad classification

Printing inks

Pigment printing Dyestuff printing

Ink formulation is
Ink can be applied to according to the
all types of substrates substrate to be
printed

Dr. Muhammad Ali

TE-424 Textile Printing 3
Associate Professor, TXD, NEDUET
 Basic formulation
Pigment printing ink: Dyestuff printing ink:
Can be applied on all types of Formulation is specific to the type of
substrates substrate being printed
• Vehicle/Solvent/Carrier medium, e.g., • Vehicle/Solvent/Carrier medium, e.g.,
Water Water
• Thickener • Thickener
• Binder • Binder
• Colorant (Pigment) • Colorant (Dyestuff)
• Auxiliary chemicals • Auxiliary chemicals

Dr. Muhammad Ali

TE-424 Textile Printing 4
Associate Professor, TXD, NEDUET
 Vehicle/Solvent/Carrier medium
• The base material in which the print paste is prepared.
• By weight, solvent is usually the largest component of an ink
• About 70 wt% or more is the solvent in any given amount of ink.
• Solvent determines the type of ink
• Water-based ink – Solvent is water
• Solvent-based ink – Solvent is an organic solvent
• Usually a co-solvent is also used to improve the ‘performance’ of the ink. For
example, in water-based inks, ethylene/propylene glycol could be added in water
to reduce the drying rate of ink

Dr. Muhammad Ali

TE-424 Textile Printing 5
Associate Professor, TXD, NEDUET
 Thickener

Dr. Muhammad Ali

TE-424 Textile Printing 6
Associate Professor, TXD, NEDUET
 Thickener
• Screen printing inks are required to have viscosity high enough for proper printing.
• The ink applied on to the fabric should ‘stay’ within ‘specified’ boundaries
• Usually the viscosity of inks is in the range of 12000 – 20000 cps (Centi-Poise)
• Viscosity is measured using a viscometer/rheometer (Practical No: 1)
• The required viscosity is built up by using the appropriate amount of a ‘thickener’ in ink
formulation

Dr. Muhammad Ali

TE-424 Textile Printing 7
Associate Professor, TXD, NEDUET
 Thickener – working mechanism

• Think about Sugar syrup

• Presence of sugar molecules in water create hindrance
in the flow of water molecules
• As the number of sugar molecules in a given amount
of water increases, the viscosity of the sugar syrup
increases.

Dr. Muhammad Ali

TE-424 Textile Printing 8
Associate Professor, TXD, NEDUET
 Thickener – working mechanism
• Thickeners for textile printing are large organic molecules
with numerous functional groups (e.g., carboxylic groups).
• The large molecules are in a “coiled” form.
• Under the right conditions (pH), the functional groups
acquire a charge and the collapsed molecular chain expands
due to electrostatic forces.
• As the molecule expands, it begins to interact with a large
number of water molecules and hinders their flow.

Dr. Muhammad Ali

TE-424 Textile Printing 9
Associate Professor, TXD, NEDUET
 Thickener types – according to the source

Thickeners

Man-
Natural
made

Fully
Modified
synthetic

Dr. Muhammad Ali

TE-424 Textile Printing 10
Associate Professor, TXD, NEDUET
 Thickener types – on the basis of molecular
weight

Thickeners

High molecular Low molecular

weight weight

Dr. Muhammad Ali

TE-424 Textile Printing 11
Associate Professor, TXD, NEDUET
 Thickener types – on the basis of molecular
weight
High molecular weight (HMW) thickener Low molecular weight (LMW) thickener
- Longer polymeric chains - Shorter polymeric chains
Which one will create more hindrance in the flow of water molecules?

Dr. Muhammad Ali

TE-424 Textile Printing 12
Associate Professor, TXD, NEDUET
 Thickener – Key considerations:
Cost and Quantity used
High molecular weight thickener Low molecular weight thickener

• More costly compared to LMW thickeners • Less costly compared to LMW thickeners
• Used in smaller amount to achieve a • Used in larger amount to achieve a
certain viscosity (see slide No 12) certain viscosity

• Amounts ~ 1.5 wt% - 3 wt% • Amounts ~ 8 wt% - 10 wt%

Example calculation: Example calculation:

If 2 wt% of a HMW thickener has to be used in a If 10 wt% of a LMW thickener has to be used in a
total of 100 gm print paste then; total of 100 gm print paste then;
• Amount of thickener = 2 g • Amount of thickener = 10 g
• Rest of the ingredients = 98 g • Rest of the ingredients = 90 g

Dr. Muhammad Ali

TE-424 Textile Printing 13
Associate Professor, TXD, NEDUET
 Thickener – Key considerations
Flow behavior Viscosity increases -
Shear thickening fluids

• Fluids behave differently when subjected to

shear force (e.g., high speed mixing)

Viscosity
No change in viscosity
Newtonian fluids

Viscosity decreases -
Shear thinning fluids

Shear rate

Dr. Muhammad Ali

TE-424 Textile Printing 14
Associate Professor, TXD, NEDUET
 Thickener – Key considerations
Flow behavior
• In a typical printing processes, we want the print
paste to;
• Start flowing relatively easily when we apply a force on it.
• Stop flowing when we remove the force on it.
• Otherwise?

• So what should be the flow behavior of printing inks?

• Newtonian
• Shear thinning
• Shear thickening

Dr. Muhammad Ali

TE-424 Textile Printing 15
Associate Professor, TXD, NEDUET
 Thickener – Key considerations:
Flow behaviour

• Sudden and sharp decrease in viscosity • Gradual and lesser decrease in viscosity
• HMW thickeners usually provide a ‘short flow’ • LMW thickeners usually provide a ‘long flow’

Dr. Muhammad Ali

TE-424 Textile Printing 16
Associate Professor, TXD, NEDUET
 Thickener – Key considerations
Stability
• The viscosity that is built up should be retained for a certain duration.
• A printing ink is gradually consumed during printing
• Thus, we do not want a printing ink for which the viscosity changes significantly from the
time of preparation till the time of application.
• What happens to a corn flour thickening as its temperature drops?
• The thickener should be able to maintain the desired viscosity if there are slight fluctuations in
the conditions, e.g., pH

Dr. Muhammad Ali

TE-424 Textile Printing 17
Associate Professor, TXD, NEDUET
 Thickener – Key considerations
Impact on hue/saturation

• If the thickener film itself has a particular color/tint, then it will affect the hue/saturation
of the printing ink on the substrate.
• Ideally, we want a thickener which produces a colorless film.

Thickener
layer

Colourant

Dr. Muhammad Ali

TE-424 Textile Printing 18
Associate Professor, TXD, NEDUET
 Thickener – Key considerations
• Cost
• Quantity to build up a desired viscosity
• Compatibility with the colorant and other ingredients of the printing ink
• Should have no affinity towards the colorant (particular consideration in dyestuff printing).
• Viscosity stability
• Flow behavior (shear thinning)
• Impact on the hue/saturation of the actual color of an ink
• Free from impurities (to avoid screen choking)
• Good film-forming (ink layer should not flake-off after drying)
• Post-printing behavior – stiffness, washability, etc

Dr. Muhammad Ali

TE-424 Textile Printing 19
Associate Professor, TXD, NEDUET
 Binder

Dr. Muhammad Ali

TE-424 Textile Printing 20
Associate Professor, TXD, NEDUET
 Binder
• Pigments have no chemical interaction with the substrate and hence do not bond with
the substrate on their own
• Thus, a ‘binder’ is always used in pigment printing
• Binder is like a ‘glue’.
• A crosslinking polymer which entraps the pigment particles on the substrate.

Dr. Muhammad Ali

TE-424 Textile Printing 21
Associate Professor, TXD, NEDUET
 Binder – working mechanism

HEAT

Binder forms a 3D web in which the

pigment particles are physically entrapped

Dr. Muhammad Ali

TE-424 Textile Printing 22
Associate Professor, TXD, NEDUET
 Binder - calculations

• The amount of binder is directly proportional

to the amount of pigment in an ink.
• Binder supplier also provides guideline
calculations.
• Technical datasheet of the product being used
should always be referred to.

Reference: Archroma Binder 77N datasheet

Dr. Muhammad Ali

TE-424 Textile Printing 23
Associate Professor, TXD, NEDUET
 Example calculations - Overall
• Pigment = 4 wt%
• Thickener = 2 wt%
• Binder = 1.75 x Pigment = 1.75 x 4 = 7 wt%
• Total paste required = 100 g

• Pigment = 4 g
• Thickener = 2 g
• Binder = 7 g
• Water = 100-(4+2+7) = 87 g

• Repeat the calculations for 500 g paste.

Dr. Muhammad Ali

TE-424 Textile Printing 24
Associate Professor, TXD, NEDUET
 Binder – Key considerations
• Soft hand feel
• Excellent film forming property
• Clear, translucent film
• Mechanical characteristics of the film
• Elasticity
• Strength
• Good adhesion but no tack
• Resistance to ageing (brittleness of film)
• Non-yellowing

Dr. Muhammad Ali

TE-424 Textile Printing 25
Associate Professor, TXD, NEDUET
 Binder – Key considerations

Hand feel
• The hand-feel of a pigment printed article depends on the ‘glass-transition temperature
(Tg)’ of the polymer.
• Binder polymer could be based on following monomers (and their combinations)
• Ethylene, butadiene, butyl acrylate, ethyl acrylate, vinyl chloride, styrene, methyl
methacrylate, etc

Dr. Muhammad Ali

TE-424 Textile Printing 26
Associate Professor, TXD, NEDUET
 Binder – Key considerations
Hand feel
The lower the Tg, the softer is the hand feel

Monomer Tg (ºC)
Ethylene -125
Butadiene -78
Butyl acrylate -52
Ethyl acrylate -22
Vinyl chloride +80
Styrene +105

Dr. Muhammad Ali

TE-424 Textile Printing 27
Associate Professor, TXD, NEDUET
 Binder – Recent developments

• Increasingly soft hand feel of the printed article

• Binders resulting in hand feel almost as good as dyestuff printed articles are available
• Improved fastness properties
• Pigment printing was known for inferior fastness properties
• Reduction on residual free-monomer content
• Free monomers - the monomers that do not become a part of the binder polymer chain
during the synthesis (polymerization) process.
• Health concerns.
• Formaldehyde-free pigment printing systems

Dr. Muhammad Ali

TE-424 Textile Printing 28
Associate Professor, TXD, NEDUET
 Auxiliary chemicals
• In addition to the basic ingredients, a number of other auxiliary chemicals are added into
the ink.
• The purpose is to meet specific requirements of a printing process and to improve the
overall ‘performance’ of the printing ink.
• Some of the more commonly used auxiliary chemicals are;
• Alkali
• Urea
• Biocides
• Defoaming agents
• Mild oxidizing agent
• Emulsifiers
• Others….

Dr. Muhammad Ali

TE-424 Textile Printing 29
Associate Professor, TXD, NEDUET
 Auxiliary chemicals for Pigment Printing
The more important auxiliary chemicals used in pigment printing are;

a. Defoamer
• When binder is added and stirred, it can create foam.
• Defoamer is added to prevent foaming

b. Softener
• To improve print softness
• To improve dry rubbing fastness

c. Fixative (Fixing agent)

• To improve wet rubbing fastness
• Softener and fixing agents are usually provided by binder supplier.

d. Dispersing agents
• To prevent aggregation of pigment particles in the print paste

Dr. Muhammad Ali

TE-424 Textile Printing 30
Associate Professor, TXD, NEDUET
 Auxiliary chemicals for Reactive Printing
The more important auxiliary chemicals used in reactive printing are;

a. Alkali
• Soda Ash (sodium carbonate)
• Helps the reactive dye react with the fiber

b. Wetting agent
• Used in small amounts (< 1wt%)
• Improve print paste penetration and dye uptake

c. Urea
• As Humectant – fiber swelling
• Improved dye solubilization
• As Levelling agent – even distribution of dye molecules on substrate

d. Other auxiliaries
• Sequestering agents (to deal with water hardness), defoamers, etc

Dr. Muhammad Ali

TE-424 Textile Printing 31
Associate Professor, TXD, NEDUET
 Thank you

Dr. Muhammad Ali

TE-424 Textile Printing 32
Associate Professor, TXD, NEDUET