Functions of dispersing additives in ink

Functions of Dispersing
Additives in Ink
By :
Adesh Katariya
Manager- R&D, Tirupati Inks Ltd
plast.adesh@gmail.com

Pigment
 A pigment is a coloring particle which is insoluble in the
application media.
 Particle size and crystal structure of pigments determine
the application properties like gloss, tinting strength etc
2
Primary particles are single
crystallites or sub crystallites which
are strongly connected by their
surface areas. They can not be
destroyed during normal grinding
processes.

Pigments in Comparison
Property
Organic
Pigment
Inorganic
Pigment
Particle size (µm) Small Large
Surface area (m2/g) Large Small
Polarity Non-polar Polar
4

Objective of Pigment Dispersion
 To separate the pigment agglomerates which are formed
(by hydrophilic aggregation) during the drying processes in
pigment manufacture.
5
As particle size is reduced, the
surface area so created
increases, leading to an
improvement in optical
properties, such as tinctorial
strength, gloss, brightness,
opacity or transparency.

Improved Dispersion and Dispersing Additive
 The improved dispersion means a smaller average particle
size with a narrower particle size distribution.
 Small particles are generally more prone to re-
agglomeration or flocculation.
7
With dispersing additives reducing
inter-particle attraction, dispersions
are significantly more stable to
flocculation and agglomeration
than those produced by
conventional means.

De-flocculation -Flocculation
8

Wetting and Dispersing Process
High brilliance and color strength are characterized by a perfect pigment
dispersion, optimal pigment particle size, and long-term stabilization of
the dispersed particle in the formulation.
9

Pigment wetting:
All of the air and moisture is displaced from the surface
and between the particles of the pigment aggregates and
agglomerates (clusters) and is replaced by the resin
solution.
10
The solid/gaseous interface (
pigment/air) is transformed into a
solid/liquid interface (pigment/resin
solution).

Wetting and Surface tension
The efficiency of the wetting depends primarily on the
comparative surface tension properties of the pigment and
the vehicle, as well as the viscosity of the resultant mix. The
adsorption mechanism depends on the chemical nature of
the pigment and the types of dispersing agents used.
12

Grinding stage:
Through mechanical energy (impact and shear forces), the
pigment agglomerates are broken up and disrupted into
smaller units and dispersed (uniformly distributed).
Ideally, a fully deflocculated state will arise, in which all
pigment particle agglomerates have been broken up into
their primary particles.
13

Stabilization of pigment suspension :
The pigment dispersion is stabilized by the adsorption of
binder species or molecules at the pigment surface
14

Pigment Stabilization Mechanism
System Stabilization Mechanism
Solvent-based Steric stabilization
Water Based Electrostatic / Steric stabilization
Emulsion Electrostatic stabilization
Polymerics (UV) Steric stabilization
16

WHY Dispersant Required ?
Dispersing Additives have two fundamental roles in surface
coatings;
o they produce improved pigment dispersion
o they reduce inter-particulate attraction within that
dispersion.
17

Dispersing Agent and Rheology
The greater steric repulsion generated by the addition of polymeric
dispersants moves the minimum in the Potential Energy Curve, and thus
reduces the overall viscosity.
18

Dispersants families
In term of chemical structure one can divide dispersing
agents into the two following classes:
1. Polymeric dispersants -Sterical stabilization
2. Surfactants-Electrostatic stabilization
The main differences of those two types of dispersants
being the molecular weight, the stabilization mechanism
and the resulting let down stability.
19

Electrostatic stabilization
A charge is generated on the pigment surface, and a more
diffuse cloud of oppositely charged ions develops around it.
20
As two particles approach each other the
charge effectively provides a barrier to
closer particle interactions.

Sterical stabilization
 Steric Stabilization occurs
by the adsorption of a
layer of resin or polymer
chains on the surface of
the pigment.
 Effective in media of low
dielectric constant.
21

Mechanism of Steric Stabilization
22

23
.

24

25

26

Polymeric dispersants
Polymeric dispersants stabilize ink systems via a steric
stabilization mechanism previously described. They have a
two-component structure which combines the following two
very different requirements:
o It must be capable of being strongly adsorbed into the
particle surface and thereby possess specific anchoring
groups .
o The molecule must contain polymeric chains that give
steric stabilization in the required solvent or resin solution
system.
35

Structure of Wetting and Dispersing
Additives
36

Dispersing Additives :Advantages
38
 Higher gloss
 Lower haze
 Higher color strength
 Improved hiding power
 Better transparency
 Low viscosity / Newtonian Flow
 No flooding & floating

Co-polymer/functional polymer
configurations
39

Dispersing Additives : How to stabilize
the pigments
40

Dispersing Additives : How to stabilize
the pigments
41

Adsorption/Anchoring of Dispersing agent
on Pigment Surface
42

Anchoring Mechanisms
As the nature of the surface of pigments differ, according to their
chemical type, many different chemical groups can be found as anchor
groups for polymeric dispersants.
This wide range of anchoring possibility enables polymeric dispersants
to disperse inorganic pigments as well as pigments with polar surfaces.
The actual anchoring can then take place through a variety of
mechanisms;.
1. Through Ionic or Acidic/Basic Groups.
2. Through Hydrogen-Bonding Groups
3. Through Polarizing Groups
4. Through Solvent-Insoluble Polymer Blocks
43

Anchoring Through Ionic or Acidic/Basic
Groups
When a pigment particle has a relatively reactive surface
(eg: inorganic pigments) it is possible to form an ion-pair
bond between a charged site on the particle surface and
an oppositely charged atom or functional group on the
dispersant.
44

Anchoring Through Hydrogen-Bonding
Groups
A strong interaction may
be developed between the
pigment particle and a
polymeric dispersant
containing many
hydrogen-bond donors
and acceptors in its
anchor chain
45

Anchoring Through Polarizing Groups
An interaction can also take place
between polarized or polarizable
groups on an organic pigment
particle surface, and similarly
polarized or polarizable groups on
the anchoring function of the
polymeric dispersant. Again, these
interactions will often be relatively
weak, but strong interaction may be
developed with a polymeric
dispersant possessing an anchor
chain composed of several of these
groups.
46

Anchoring Through Solvent-Insoluble
Polymer Blocks
It is possible to anchor a
polymeric dispersant onto a
pigment particle surface
simply via van der Waals
interactions and without
recourse to ionic, hydrogen-
bonding, or polarizing effects.
The polymeric block within
the dispersant must simply be
insoluble in the medium
47

Groups on Carbon black Surfaces
50

Interaction W/D Additives with other
Pigments
51

Wetting and Dispersing Additives: Class
52

Low molecular weight dispersants
 Found in anionic, cationic,
electro-neutral or non-ionic Stage
 The molecular weight of these
products is low, usually between
300 and 2,000 g/mol.
 Example : mono functional oleo-
alkylene oxide block copolymers.
53

Oligomeric dispersants
 Based upon fatty acid
chemistry, having polar
heads based on tertiary
amines.
 Typically, these
molecules are oligo-
functional, meaning that
more than two amino
anchoring groups are
present.
 The molecular weight
ranges from 1,000 to
3,000 g/mol.
54

High molecular wt dispersants
 High molecular weight dispersing agents can be linear or branched
molecules with molecular weights between 5,000 and 20,000
g/mol.
 Excellent stabilization, due to a high number of anchoring groups
along the polymer backbone which bind to numerous sites on the
pigment surface.
55

Polyurethanes
Best suited dispersants for viscosity depression ,higher
pigment loads, more economical mill base formulations
and lower VOCs.
56
PU dispersants usually have a
branched backbone with a three
dimensional network structure.
Different anchoring groups are
introduced at various points on this
network structure.

Star-shaped dispersing polymers
 Having core-shell morphology.
 During the dispersing step the
polymer segments in the core
adsorb on the pigment surface.
 The very high density of
pigment affinic groups results in
a very strong adhesion on the
pigment surface.
 The polymer chains in the shell
orient into the solvent and
stabilize the pigment very
effectively.
57

Block copolymers Dispersant
 Based on Controlled free Radical Polymerization (CFRP) technology
, enables the precise design of polymer structures.
 With the CFRP technology, well-defined block copolymers can be
prepared that are designed to optimally fit pigment and resin
chemistry.
 Typically, a longer stabilizer block is synthesized first, which has to
be compatible with the relevant ink systems. The anchoring block
contains functional groups which interact strongly with the pigment
surface to allow for efficient and stable adsorption. For demanding
applications like organic pigments, the anchoring block typically
contains aminic groups, which can optionally be modified further.
58

CFRP Technology based Dispersant's
structure
59

Polyacrylates
Polyacrylic dispersing agents have linear structures with a
C-C backbone that bears various functional side groups
and short side chains.
The main difference to polyurethane-based dispersants is
their higher molecular weight.
60

Co-polymer dispersants :
Anionic dispersing agents based on poly-carboxylic co-polymers .
Their narrow molecular
weight distributions provide
optimum dispersion
efficiency, translating into
maximum performance at
the lowest possible
formulation cost.
Anionic dispersants are
especially effective in
stabilizing inorganic
pigments and fillers
61

Comparison in Poly Acrylic and
Polycorboxylic co-polymer base D.A.
62

Surfactants
Surfactant molecules are able to modify the
properties and, in particular, they lower the
interfacial tension between the pigment and
the resin solution.
This surface activity arises because the
surfactants' structure consists of two groups
of contrasting solubility or polarity.
In aqueous systems, the polar group is
known as a hydrophilic group and the non-
polar group as hydrophobic or lipophilic.
In non-aqueous systems, the polar group is
known as the oleophobic group and the non-
polar group as oleophilic.
63

Surfactants
Surfactants are classified according to their chemical structure and, more
specifically, their polar group: anionic, cationic, electroneutral and non-ionic .
64

Surfactants : Points
 Surfactant’s effectiveness is determined by:
o The absorption of the polar group onto the pigment
surface. The anchoring groups can be amino,
carboxylic, sulfonic, phosphoric acids or their salts.
o The behavior of the nonpolar chain in the medium
surrounding the particle. This part of the molecule
(aliphatic or aliphatic-aromatic segments) must be
highly compatible with the binder system.
 The stabilization mechanism is electrostatic.
 Due to the Brownian movement the pigment particles
frequently encounter each other in the liquid medium
thus having a strong tendency to re-flocculate on the let
down stage
65

Types of Surfactants
o Fatty acid derivatives
o Phosphate esters
o Sodium polyacrylates / polyacrylic acid
o Acetylene diols
o Soya lecithin
66

Fatty Acid Derivatives
 Nonionic fatty acid derivatives such as the alkyl phenol ethoxylates
(APEs) and fatty alcohol ethoxylates (FAEs)
67

Polyacrylic acid/ Sodium polyacrylate
Polyacrylic acid (PAC) and salts of polyacrylates are
anionic surfactants.
Polyacrylic Acid structure and conversion to sodium
polyacrylate
69

Acetylene Diols
To reduce the side effects of standard surfactant types of dispersing
agent such as foaming, oligomeric acetylenic ethoxylate glycols have
been developed with multi-functional properties and especially
defoaming property .
Ethoxylated acetylene diols
70

Functions of dispersing additives in ink

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