polymeric pigments / core shell emulsions

Polymeric Pigments and Paint Formulation

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OBJECTIVE AND SCOPE OF INVESTIGATION

The main objectives of the entire work is to synthesize a polymeric pigment (also called Core

Shell emulsion polymer ) and use it in paint to partially replace white pigment Titanium dioxide.

In this work , about 15 % of Titanium dioxide will be tried to replace.

The general method of approach will be :

1. Preparation of a soft core (copolymer) by emulsion polymerization using Butyl acrylate,

Methyl methacrylate and Methacrylic acid as monomers.

2. Using the above formed core as seed , formation of a hard polymer shell by emulsion

polymerization over it. Monomers used are Styrene and Acrylonitrile.

3. Characterization of Polymeric pigment synthesized.

4. Formulating a white decorative emulsion paint using TiO2 in one batch

5. Formulating a white decorative emulsion paint using 85% TiO2 and 15% synthesized

Polymeric pigment.

5. Comparing the properties of two paints.


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POLYMERIC PIGMENTS

1. Introduction :

Titanium dioxide is the most widely used white pigment because of its brightness and very

high refractive index. It provides excellent whiteness and opacity to the paint coatings.

However due to it‟s very high cost, several alternatives have been developed which can

replace some part of TiO2 thus reducing cost of paint without affecting its properties.

Polymeric Pigments are one of the novel developments.

Polymeric pigments are the dried form of core-shell emulsion which provides opacity/hiding

power to the paint formulation to which they are added. They behave as if they are pigments

once the water gets evaporated. Their concentration in formulation is higher than that of

additives and lesser than pigments. They serve as a partial replacement for TiO2 pigments

which are very costly and thus reduce the cost per liter of a formulation.

2. Polymeric pigments

These belong to a class of pigments that use the difference in the refractive index of two

polymers that are polymerized as layered spherical particles. They are core – shell type of

polymers that is they comprise a softer core made of one polymer and harder shell made of

the other one. They are synthesized by continuous emulsion polymerization. The polymeric

pigment particles suspended in emulsion have a core which is initially filled with water.

When the emulsion is allowed to dry , the water from the core diffuses through the shell and


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gets evaporated. Thus the particle gets an encapsulated air void which is mainly responsible

for scattering. They use the principle of continuous reflection of light before it is thrown back

into atmosphere.

The general structure and mechanism of formation can be shown as:

3. Advantages of Polymeric Pigments

Polymeric pigments have an encapsulated air void which is responsible for scattering of light.

This gives us the freedom of formulating a low PVC composition with all the resistance

properties kept at its best and still achieving the desired opacity.

As compared to other organic pigments and inorganic extenders present in the system, these

have low binder demand. That is they have low oil absorption value when measured on (v/v)

basis. [Generally oil absorption value is measured as wt. of oil required to wet 100 gms of a

given pigment. In (v/v) basis, we measure it as volume of oil required to wet give volume of

pigment]. So it saves our cost on resin part.

One of the reasons for the less binder demand is the uniform spherical shape of these

particles. In case of spherical systems, surface area to volume ratio is lower as compared with

other geometries. The diameter of inorganic extenders is high than polymeric pigments, but


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being non- spherical in nature, extenders have same oil absorption (v/v) as compared to their

polymer counterparts.

In case of core shell polymer , because of low binder demand, CPVC is high i.e. the region in

which we can adjust PVC is broad as compared to others and this allows us in formulating

paints with high PVC values, but still get good resistance. [As contrast to others, at high

PVC, the resistance of film is poor].

They have low density as compared to organic pigments and extenders.

They have small particle size than the general film thickness, uniform particle size

distribution, thus have very high gloss.

They serve as a replacement for TiO2 in formulation which is very costly. Thus it helps in

reducing the overall cost of the formulation.

As it partially replaces non-durable extender, durability of paint is increased.

Without polymeric pigment paints lighten over a period because of chalking , so by using

them this problem can be solved

TiO2 and others exhibit the phenomenon of crowding whereas these pigments do not. Here

with increasing PVC, scattering efficiency increases too.

Here the source of scattering is encapsulated air voids, which scatter light to equal extent

irrespective of void conc. So in this formulation scattering is independent of inter particle

distance. So no need of going for above CPVC formulation. If we go, we will have more

hiding.


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4. Synthesis techniques

The synthesis of polymeric pigment requires two step emulsion polymerization. Thus the

pigment particles obtained are in dispersed form in water. To know how synthesis of core

shell emulsion takes place , first we briefly discuss about emulsion polymerization.

4.1 Emulsion Polymerization

Emulsion polymerization is a type of radical polymerization that usually starts with an

emulsion incorporating water, monomer, and surfactant. The most common type of emulsion

polymerization is an oil-in-water emulsion, in which droplets of monomer (the oil) are

emulsified (with surfactants) in a continuous phase of water. The name "emulsion

polymerization" is a misnomer that arises from a historical misconception. Rather than

occurring in emulsion droplets, polymerization takes place in the latex particles that form

spontaneously in the first few minutes of the process. These latex particles are typically 100

nm in size, and comprise many individual polymer chains. The particles are stopped from

coagulating with each other because each particle is surrounded by the surfactant; the charge

on the surfactant repels other particles electro statically. Emulsion polymerization is used to

manufacture several commercially important polymers. Many of these polymers are used as

solid materials and must be isolated from the aqueous dispersion after polymerization. In

other cases the dispersion itself is the end product. A dispersion resulting from emulsion

polymerization is often called latex. They are finding increasing acceptance and are preferred

over solvent-based products in these applications as a result of their eco-friendly

characteristics due to the absence of VOCs (Volatile Organic Compounds) in them.


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Advantages of emulsion polymerization include:

• High molecular weight polymers can be made at fast polymerization rates. By contrast, in

bulk and solution free radical polymerization, there is a tradeoff between molecular weight

and polymerization rate.

• The continuous water phase is an excellent conductor of heat and allows the heat to be

removed from the system, allowing many reaction methods to increase their rate.

• Since polymer molecules are contained within the particles, viscosity remains close to

that of water and is not dependent on molecular weight.

• The final product can be used as is and does not generally need to be altered or processed.

4.2 Polymeric Pigment Synthesis

The synthesis of polymeric pigments is usually done by two step emulsion polymerization

technique. The second stage monomers are polymerized in the presence of seed latex

particles. The resulting latexes are thus known as “core-shell” latex, implying a particle

structure with the initially polymerized polymer located at the centre of the particle, and the

later formed polymers becoming incorporated into the outer shell layer. The core may be

solid polymer particle or hydrogel and shell is made of hard polymer. Osmotic Swelling is a

basic synthesis technique for polymeric pigments. Some alternate methods are also discussed

below.

4.2.1 Osmotic Swelling

The development of hollow particles by osmotic swelling typically requires the synthesis of a

structured particle, such as a core-shell latex, by sequential emulsion polymerization. The


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core or a component of the core is designed to be ionizable based on different chemical

approaches, e.g. pH change, hydrolysis. A subsequent swelling process imbibes water into

the center of the particle. This water leaves a void upon evaporation, as, for example, during

the drying of a coating formulation.

Structural factors such as composition, core - shell ratio, and network structure are critical to

obtaining a stable hollow morphology. The basic principle involves making a structured

particle with a carboxylated core polymer and one or more outer shells. The ionization of the

carboxylated core with a base under the appropriate temperature conditions expands the core

by osmotic swelling to produce hollow particles with water and polyelectrolyte in the

interior.

The polymerization should be such that the hydrophobic shell completely encapsulates the

hydrophilic core. Such core-shell emulsion is then heated in the presence of a base such as

sodium hydroxide or ammonia to a temperature above the softening point of the shell

polymer. However a volatile base is preferred in order that coatings formulated with these

particles are not damaged by the presence of permanent base. The base neutralizes the core

polymer forming a polyelectrolyte within the particle. The subsequent imbibing of water into

the interior due to osmotic pressure leads to expansion and void formation. Once expanded,

the structure must be stable to any temperature changes.


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Typically, the shells of these particles are high glass transition temperature (Tg)

thermoplastics like styrene or acrylonitrile. The art involved in developing a thermally stable

shell that both transports water and base is considerable.

Although, in principle, formation of such a particle is straightforward, surface energies would

favor the formation of a polar surface dispersed in a polar medium such as water: the

opposite morphology to that suggested above. Thermodynamic equilibrium would favor

particles with a hydrophobic core encapsulated with hydrophilic alkali-swellable shells. Such

equilibrium conditions, however, are hard to achieve in an emulsion polymerization, as has

been mentioned.


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Other molecular and processing characteristics can overcome this thermodynamic tendency,

namely molecular structure (i.e. cross-link density), conversion kinetics, and additives such

as surfactants, and monomer feed profile.

Some of the essential requirements inherent to hollow latexes made by osmotic swelling for

commercial applications are:

1. The swellable core of the particles should be of sufficient volume relative to the volume of

the particle to form a micro void inside the particle sufficient to scatter light efficiently. This

efficiency is defined by the diameter of the void relative to the wavelength of visible light

and the thickness of the shell. The void volume fractions of commercial hollow products are

typically from 30 to 50%.

2. The shell should have the appropriate transport properties as adjusted by the composition

and network structure to facilitate the transport of water into the interior of the particle.

3. The shell must have thermoplastic flow properties at the expansion temperature and be

sufficiently cohesive and uniform to maintain the integrity of the particle. Yet it must be

strong enough to avoid collapse during further processing or application conditions, e.g. the

compressive forces experienced during drying and film formation in a coating.


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4.2.2 Alternate Methods

The incorporation of high levels of carboxylic acid into an emulsion copolymer has several

disadvantages. Copolymers of polar materials do not absorb surfactants well, leading to

instability and coagulation. Further, polarizable monomer can partition significantly into the

water phase of the emulsion, leading to the formation of oligomeric species which can

behave as dispersants or flocculants depending on their molecular weight. With structured

particles having the core made from a carboxylic acid copolymer, full encapsulation of the

core polymers is problematic. The core tends to remain at the polymer–water interface.

As an alternative approach, Rohm & Haas developed technology which did not depend on

osmotic swelling based on copolymerized ionic monomers. In this case, they imbibe low

molecular weight organic acids such as benzoic acid or acid anhydrides into the cores for

later encapsulation followed by ionization with a base. Avoiding copolymerization of an

ionic comonomer into a core seed was also possible with the use of vinyl acetate monomer.

Instead of an acrylic ester composition leading to ionic groups along the main chain of the

copolymer, a polyvinyl acetate containing core is initially polymerized. After hydrolysis, this

comonomer produces hydroxyl groups along the chain as well as acetic acid. With this

technology, either acid or basic conditions may be used to accomplish the hydrolysis and

osmotic swelling.


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5. Application

5.1 Architectural coatings:

Pigments are a critical ingredient in architectural coatings serving to provide color, to hide

the substrate, and to modify the performance of a coating, e.g. functional pigments can

enhance corrosion resistance. Hiding is a critical coating property, and a large fraction of all

paint formulations contains white pigment. Typically these are small fine particle size

dispersions. Titanium dioxide is the major white opacifying pigment used in the coating

industry, added because of its high refractive index compared to the coating binder polymers.

However , as the level of TiO2 in paint film increases, its light scattering efficiency decreases

due to the close packing or crowding of TiO2 particles. The light scattering properties of

hollow latex particles make them an effective hiding additive for water-borne latex paints.

The coatings industry has long recognized the utility of air as a hiding ingredient for paint.

Hollow latex particles are a convenient and cost-effective way to introduce air voids into the

paint film without increasing the porosity of the film. Even though the hollow particle shell,

the air it contains, and the surrounding film forming paint binder are all transparent to light,

there are significant differences in refractive index (air – 1.0 and polymeric pigment – 1.58).

When light passes through one transparent material into another of different refractive index,

it is scattered. Thus, light moving through a hollow particle will be scattered when it hits the

air at the center of the particle. The light is refracted a second time when it encounters the

shell on the other side of the void. The cumulative effects of multiple scattering events as the

light beam travels through the film increases the hiding of the paint film. Thus, the use of

hollow latex particles allows the paint manufacture to reduce some of the main hiding


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pigment in the paint, which is typically the titanium dioxide, without losing the hiding

properties. The hollow latex particles also have a lower binder demand then that of the

pigments they replace thus overall binder may be reduced in the formulation without

adversely affecting paint performance. The optimum particle size of the hollow latex particle

was determined empirically to be having a diameter of 0.5–0.6 mm with a void diameter of

0.25–0.3 mm. A number of models have been published on how to convert paint

formulations to the use of hollow pigments. The commercial products sold into the coating

market are uniform in particle size, typically between 0.4 and 0.5 mm, and have a void

volume fraction of 25–40%.They are typically supplied at approximately 40% weight solids.

The addition of the hollow latex lowered the cost due to the need to use less TiO2. Porosity,

gloss and paint viscosity was not affected by the formulation change but hiding, brightness

and wet scrub resistance was increased.

5.2 Paper coatings:

In coated paper, solid polystyrene latex particles have been used for some time to enhance

the sheet gloss and print gloss of coated paper. The solid polystyrene latex particles also

reduce the density of the coating formulation because they are of lower density than the

mineral pigments present. With hollow latex particles, both the particle size and the void

volume have an impact on paper properties. The presence of a void within the particles

significantly reduces the density of the plastic pigment and at the same time contributing to

opacity. The presence of the void also has an impact on the response the paper properties

have to the finishing process. Since the shell polymer is thermoplastic it will deform under


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stress that is applied during the calendaring process. This ability to deform leads to an

improvement in the micro-smoothness of the sheet. The greater response of the hollow latex

particles to calendaring is due to the voids making the particle more easily deformed by the

calendar. The large hollow particle samples have a lower uncalendered gloss but a higher

finished gloss. Less severe calendaring conditions may possibly be used if hollow latex

particles are utilized in the coated paper formulation. The brightness and opacity of papers

coating formulations containing hollow latex particles increase due to the light scattering

capability of these particles described above. Since both brightness and opacity increase with

the use of hollow latex particles, only a few of the hollow particles at the surface must

deform during the calendering process. Obviously the ultimate impact of hollow latex

particles on finished coated paper properties is dependent on several factors such as overall

formulation composition, calendaring conditions, and base stock properties.

An important note to make about the use of hollow latex particles in paper coatings is the fact

that the optimum particle is a large diameter particle with a void in the range of 50–55%.

Since a large portion of the water is contained inside the particle these latex samples are

supplied at relatively low weight solids. The rheology characteristics of these latex samples

will be typical of samples with a solids content of double the actual weight solids. The

material supplier often will quote effective solids on these products. The effective solids

determine the rheology and runability characteristics of the formulations containing the

hollow latex particles.


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6. Experimental work

6.1 Synthesis of Carboxylated latex particles (CORE)

The Core shell emulsion was synthesized in a 500 ml four necked flask. Heating mantle and

temperature controller were used to maintain proper thermodynamic conditions. The Teflon

stirrer was attached to a motor whose R.P.M. could be controlled digitally. Two dropping

funnels were used for continuous addition. In the first step of emulsion polymerization, Core

was synthesized. The following monomers used for Core synthesis are:

a) Methyl methacrylate (MMA)

1. Molecular formula : C5H8O2

2. Molecular mass : 100.12 gm/mole

3. Density : 0.94 g/cm3 @ 25 °C, liquid

4. Tg of homopolymer : 106°C

5. Melting point : -48 °C

6. Boiling point : 101 °C

b) Butyl acrylate (BA)




4. Tg of homopolymer: - 49°C

5. Melting point : - 64 °C


http://en.wikipedia.org/wiki/Chemical_formula

http://en.wikipedia.org/wiki/Molar_mass

http://en.wikipedia.org/wiki/Density

http://en.wikipedia.org/wiki/Melting_point

http://en.wikipedia.org/wiki/Boiling_point







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c) Methacrylic acid (MAA)





5. Melting point : 14 °C


All the monomers were washed by 5% sodium hydroxide solution followed by washing with

distilled water to remove the inhibitors. The initiators Sodium persulfate (SPS), Ammonium

persulfate (APS), Sodium meta bisulfite (SMBS) and surfactant Sodium lauryl sulphate

(SLS) were used without purification. Deionized water was used in the synthesis of the

latexes.

Preparation Of Core:

a) Mixture of monomers, MMA 23.37 g, MAA 1 g, BA 26.00 g were emulsified in a

separate vessel using 0.7 g surfactant (SLS) and water 26 g. The pre-emulsion was made

using a high speed disperser such that a homogenous solution was obtained.

b) The reactor was charged with 120 g water and to it catalyst solution (APS 0.2 g with

water 5 g) and SMBS 0.6 g was added directly with stirring at 200 r.p.m. The reaction

temperature was raised to 55 oC and pre-emulsified monomer 4 g was added at a time.

c) After 15 minutes, the rest of pre emulsion was added continuously at a speed of 10 ml/15

min. Simultaneously SMBS solution (.07 g in 20ml water) was added continuously such

that it's addition rate was same as pre emulsion's addition.







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d) After the addition of pre-emulsion the reaction was hold for 1.5 hours at temperature of

60 ◦C. After 1.5 hours, the heating was stopped and post addition was done.

e) In post addition , redox catalysts Sodium Formaldehyde Sulphoxylate (SFS) .03 g and

tert-Butyl hydroperoxide (t-BHP) .04 g were added.

f) To maintain pH, buffer solution i.e. 0.6g of Ammonia solution (33%) was added. The

mixture was stirred for another half hour and then emulsion was allowed to cool at room

temperature.

INGREDIENTS QUANTITY (g.)

Reactor charge :

1. Deionized water

2. SLS

3. APS

4. SMBS

125

0.6

0.2

0.6

Monomer Pre-Emulsion :

1. Deionized water

2. BA

3. MMA

4. MAA

5. SLS

16

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23.37

1

0.7

Continuous feed ( Reducing agent) :

1. Deionized water

2. SMBS

20

0.07


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Redox Catalyst and post addition

1. t-BHP

2. SFS

3. Ammonia (33%)

0.04

0.03

0.6

6.2 Synthesis of Core-Shell Latex particle (Polymeric Pigment)

The synthesized core was analyzed for it‟s properties. The properties were fairly agreeable

and then it was used as seed for Core-Shell polymer. Like core, it is also synthesized by

emulsion polymerization. The shell is made of hard monomers so as to give good pigmentary

properties. The monomers used for Shell formation are:

a) Styrene

7. Molecular formula : C8H8












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b) Acrylonitrile

1. Molecular formula : C3H3N


3. Density : 0. 81 g/cm3 @ 25 °C, liquid




All the monomers were washed by 5% sodium hydroxide solution followed by washing with

distilled water to remove the inhibitors. The initiator potassium persulfate (PPS) was used

without purification. Deionized water was used in the synthesis of the latexes.

Preparation of Core-Shell:

a) The reactor was charged with 90 g of water and temperature was increased to 85 oC.

b) 25 g of core latex prepared in stage 1 was added to the reactor slowly along with catalyst

i.e. PPS solution (0.04 g in 10.00 g water).

c) Then the monomer mixture styrene 55 g and Acrylonitrile 36 g was added slowly within 3

hours . Simultaneously catalyst solution PPS (0.53 g in 20 g water) was added slowly for

3 hours.

d) After completion of feeding, the reaction was hold for 1 hour for complete conversion.

e) Then ammonia solution (7.5 g in 15 g) water was added to the reaction mixture. The

heating was stopped and emulsion was stirred for another 2 hours.







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INGREDIENTS QUANTITY (g.)

Reactor Charge:

1. Deionized water

2. CORE LATEX

3. PPS

100

25

0.04

Monomer Mixture:

1. Styrene

2. Acrylonitrile

55

36

Continuous feed ( Catalyst ):

1. Deionized water

2. PPS

20

0.53

Post Addition:

1. Deionized water

2. Ammonia solution (33%)

15

7.5


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7. Characterization of Core and Polymeric pigment

The synthesized emulsions were characterized for:

a) Non Volatile Matter content

b) pH

c) Viscosity

d) UV-Visible Absorption Spectroscopy (UV-Vis)

e) Fourier transform infrared spectroscopy (FTIR)

f) Differential Scanning Calorimetry (DSC)

a) Total Solids Content or Non Volatile Matter content (NVM):

A known weight of the paint sample was taken in a Petridis and allowed to be in oven at

1200c for about an hour. It was weighed and then kept back in oven. The heating was

continued till constant weight was obtained. The difference between the two weights gives

the amount of volatile material lost and hence the % NVM can be found out

b) pH

The pH of an emulsion is important for its stability. It is adjusted by adding liq. NH3

It was measured by using pH paper and comparing with pH scale.

c) Viscosity

Viscosity was determined by using Brookfield Viscometer according to ASTM D2196-05

of appropriate spindle. It was reported in centipoises.


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d) UV-Visible Absorption Spectroscopy (UV-Vis)

Ultraviolet-visible spectroscopy refers to absorption spectroscopy in the UV-visible

spectral region. This means it uses light in the visible and adjacent (near-UV and near-

infrared (NIR)) ranges. The absorption in the visible range directly affects the perceived

color of the chemicals involved. In this region of the electromagnetic spectrum,

molecules undergo electronic transitions. When the light is absorbed, transitions takes

place from the ground state to the excited state. Thus the absorption spectra is recorded

for a particular compound. The instrument used in ultraviolet-visible spectroscopy is

called a UV/Vis. spectrophotometer. It measures the intensity of light passing through a

sample (I), and compares it to the intensity of light before it passes through the sample

(Io). The ratio I / Io is called the transmittance, and is usually expressed as a percentage

(%T). The absorbance, A, is based on the transmittance:

A = − log (%T / 100%)

e) Fourier transform infrared spectroscopy (FTIR)

FTIR is the subset of spectroscopy that deals with the infrared region of the

electromagnetic spectrum. It covers a range of techniques, the most common being a

form of absorption spectroscopy. As with all spectroscopic techniques, it can be used to

identify compounds and investigate sample composition. The infrared portion of the

electromagnetic spectrum is usually divided into three regions; the near-, mid- and far-

infrared, named for their relation to the visible spectrum. The far-infrared, approximately

400–10 cm−1 (1000–30 μm), lying adjacent to the microwave region, has low energy and

may be used for rotational spectroscopy. The mid-infrared, approximately 4000–400


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cm−1 (30–2.5 μm) may be used to study the fundamental vibrations and associated

rotational-vibrational structure. The higher energy near-IR, approximately 14000–4000

cm−1 (2.5–0.8 μm) can excite overtone or harmonic vibrations.

Infrared spectroscopy exploits the fact that molecules absorb specific frequencies that are

characteristic of their structure. These absorptions are resonant frequencies, i.e. the

frequency of the absorbed radiation matches the frequency of the bond or group that

vibrates. The energies are determined by the shape of the molecular potential energy

surfaces, the masses of the atoms, and the associated vibronic coupling.

f) Differential Scanning Calorimetry (DSC)

Differential scanning calorimetry or DSC is a thermoanalytical technique in which the

difference in the amount of heat required to increase the temperature of a sample and

reference are measured as a function of temperature. Both the sample and reference are

maintained at nearly the same temperature throughout the experiment. Generally, the

temperature program for a DSC analysis is designed such that the sample holder

temperature increases linearly as a function of time. The reference sample should have a

well-defined heat capacity over the range of temperatures to be scanned.

The main application of DSC is in studying phase transitions, such as melting, glass

transitions, or exothermic decompositions. These transitions involve energy changes or

heat capacity changes that can be detected by DSC with great sensitivity.

Glass transitions may occur as the temperature of an amorphous solid is increased. These

transitions appear as a step in the baseline of the recorded DSC signal. This is due to the

sample undergoing a change in heat capacity; no formal phase change occurs.


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PAINT FORMULATION

1. Emulsion Paints

The introduction of synthetic emulsion polymers in emulsion form presented a stunning

start towards the development of paints. They are not only comparable to conventional

solvent based coatings but also far superior in some instances. Moreover since the sole

solvent is water only, emulsion paints are free from VOCs, this advantage has put emulsion

paints a step ahead of others for decorative paints. Today, where we concerned with the

environmental effects of the paint industry, the diversion towards the water based products

is definitely desired.

2. Paint Ingredients

Emulsion based paint mainly consist of emulsion as pigments, binders and additives such

as wetting and dispersing agent, thickener, defoamer, buffer etc.

a) Pigments

Pigments are used to provide a visual effect, mainly colour and opacity. Having achieved

the required colour and opacity, it is also important to ensure the pigment will remain

essentially insoluble in the system in which it is used and will give the required physical

properties, such as light fastness, weatherability, and resistance to chemicals


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Hiding power is the ability of a pigmented coating to obliterate the surface. It is dependent

on the ability of the film to absorb and scatter light. Naturally, the thickness of the film and

the concentration of the pigment play a fundamental role.

A key factor in the opacity of a pigment is its refractive index (RI), which measures the

ability of a substance to bend light. The opacifying effect is proportional to the difference

between the refractive index of the pigment and that of the medium in which it is dispersed.

This is one of the main reasons why titanium dioxide is now almost universally used as the

white pigment in paint. Titanium dioxide absorbs almost no light, yet its ability to scatter

light due to high refractive index ensures that at a high enough concentration it will cover

all the substrate being coated.

There is a new class of pigments called Polymeric Pigments. They use the difference in the

refractive index of two polymers that are polymerized as layered spherical particles. They

are core – shell type of polymers that is they comprise a softer core made of one polymer

and harder shell made of the other one. They are synthesized by continuous emulsion

polymerization. The polymeric pigment particles suspended in emulsion have a core which

is initially filled with water. When the emulsion is allowed to dry, the water from the core

diffuses through the shell and gets evaporated. Thus the particle gets an encapsulated air

void which is mainly responsible for scattering. They can partially replace inorganic

pigment like TiO2 without changing the opacity or major properties of paint. The

advantages of polymeric pigments have been discussed in previous section.

There are other types of pigment that are used for specific purposes, such as „extenders‟.

Extenders do not usually affect the colour or opacity of a paint film, but may play an


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important role in the film properties such as reinforcement, gloss (usually to make the film

less glossy), hardness, etc. They can also affect the properties of the paint itself, such as its

rheological properties, settling characteristics, or simply its cost.

b) Binders

Formulation of most coatings usually starts with the selection of the main film former or

„binder‟ even though most of the properties are extensively modified by pigmentation.

Mainly two types of binders are used „Emulsion polymers‟ and „Alkyds‟. The former are

polymeric dispersions carried in water, while the later are solutions of oil-modified

polyesters carried in hydrocarbon solvents. Emulsion polymerization is very well

established as the route to dispersion binders with diverse properties. Characteristically free

radical initiators are used to polymerize monomers of low water solubility to produce an

insoluble polymer. Paint properties will be influenced by the choice of monomers, particle

size, and stabilizer system.

The effect of monomer type on mechanically related properties can be interpreted through

the Tg. Hard monomers included methyl methacrylate, vinyl acetate, styrene etc. while the

soft monomers are n-alkyl acrylates, alkyl maleates etc. Most latexes used in the decorative

market are copolymers or terpolymers with the ratios chosen to suit specific sectors. In very

general terms softer polymers will favour extensibility, exterior durability, and film

integration, while hard polymers give lower dirt retention, gloss retention, and scrub

resistance.


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c) Surfactants

Surfactants help to reduce surface tension and improve wetting and spreading (wetting

agents); aid in dispersion of pigments. They comprise very minor portion of paint. Anionic

surfactants are major type used to improve wetting and dispersion of pigments. Both

anionic dispersant and non-ionic wetting agents contribute to overcome pigment floating

and settling. Each pigment particle requires a particular amount to disperse and stabilize it.

Excessive amounts of surfactants should not be used because this can lead to colour and

other appearance changes

Non-ionic surfactant: Stearic hindrance takes place when the hydrophobic portion of a non-

ionic surfactant is absorbed onto the surface of pigment particles. The long hydrophilic

chain in the liquid medium and it acts as a bumper that prevents the stabilized pigment

particles from too closely approaching each other. This is mechanism by which non-ionic

surfactant functions.

Ionic surfactant: When the hydrophilic portion of the surfactant is adsorbed on the pigment

particles, the ionic portion of the molecule or hydrophile will be found in liquid phase. This

charged portion of the molecule will repel particles that contain like electrostatic charges

on other particles with the result, a stabilized system.

d) Thickeners

Paint requires a thickener to yield the viscosity that will hold the paint ingredients in a

homogeneous state and also contribute to its rheological properties. For water borne

coatings most commonly used thickeners are cellulose thickeners. Hydroxy ethyl cellulose,

carboxymethyl cellulose are most commonly used. These thickeners are non-ionic water


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soluble polymers in powder form. These powders dissolve in either hot or cold water and

may be surface treated to prevent agglomeration.

e) Defoamers

Although foam may occur as an interfering factor during paint production, most problem

arises when it cause surface defects during the application process. Defoaming agents are

additional adjuncts in the latex paints. They are required to suppress or eliminate any foam

that tends to develop during manufacture or in container filling operations. In an aqueous

formulation, it is almost impossible to totally eliminate all foams. The correct foam control

agent will help to prevent foam, but of most importance, will allow the dried film to be free

of foam and any resultant film defects that might result from an air void in the film.

f) pH Stabilizers

Styrene acrylics, acrylics latexes achieve their maximum stability in alkaline systems.

Consequently, the systems are usually adjusted to pH of 9.0 to 9.5. Aqueous ammonia was

used earlier days, but now days AMP-95 (2-amino-2-methyl-1-propanol) is most

commonly used as pH stabilizer.

3. Formulation Of Paint

Ball Mill and a Dispersing Equipment – “High Speed Disperser” were used to prepare

paint. The equipment consisted of a pitch blade turbine type impeller which rotates at

high speed. Following sequence is to be followed for paint manufacturing:


28

GRIND STAGE

Ingredients Nature Batch „A‟

100% TiO2

(g.)

Batch „B‟

85% TiO2

(g.)

Water _ 10 10

TAMOL 731 from BASF Ltd. Anionic Surfactant 0.3 0.3

TRITON (Dow-Rohm& Haas) Non ionic Surfactant 0.2 0.2

Di Ethylene Glycol Wet edge Additive 1.2 1.2

Natrosol Plus(Dow-Rohm & Haas) Thickener 0.25 0.25

Pidicryl 8261 (Pidilite Ltd.) 50% pure Acrylic Binder 5 5

TiO2 (Tronex , Australia) Pigment 18 15.3

China Clay

Talc

CaCO3

Extenders

5

9

5

5

9

5


29

LET DOWN STAGE

Ingredients Nature Batch „A‟

100% TiO2

(g.)

Batch „B‟

85% TiO2

(g.)

Water _ 20 20

TAMOL 731 from BASF Ltd. Anionic Surfactant 0.4 0.4

TRITON (Dow-Rohm& Haas) Non ionic Surfactant 0.2 0.2

Di Ethylene Glycol Wet edge Additive 1 1

Natrosol Plus(Dow-Rohm & Haas) Thickener 0.25 0.25

Pidicryl 8261 (Pidilite Ltd.) 50% pure Acrylic Binder 30 30

SYNTHESIZED POLYMERIC

PIGMENT

Pigment 0 7.68

Liquor Ammonia (33%) pH stabilizer 0.15 0.15

BYK 022 ( Dow-Rohm & Haas ) Defoamer 0.2 0.2

Sodium hexametaphosphate Buffer 0.2 0.2


30

M

I

L

L

B

A

S

E

Procedure to be followed

Water

Surfactant

Mix well and then add

Thickener

Form a uniform jelly

Wet Edge additive

Emulsion


TiO2

China Clay

Talc

CaCO3

Grind the mix for about 1.5 – 2 hours

L

E

T

D

O

W

N

Water

Surfactants

Emulsion

Mill Base


Thickener

Wet Edge additive

Agitate well

Ammonia

Defoamer

Buffer

Agitate well

In second batch, Synthesized Core-Shell Emulsion was added in Let Down Stage.


31

4. Analysis of Paint

The Paint formulated was analyzed for :

a) Non Volatile Matter Content

b) Viscosity

c) Weight per liter

d) Finish of dispersion

e) Gloss at 20o and 60

o

f) Computer Colour Matching ( CCM )

1) Total Solids Content or Non Volatile Matter content (NVM):

A known weight of the paint sample was taken in a Petridis and allowed to be in oven at

1200c for about an hour. It was weighed and then kept back in oven. The heating was

continued till constant weight was obtained. The difference between the two weights gives

the amount of volatile material lost and hence the % NVM can be found out

2) Viscosity

Viscosity was determined by using Brookfield Viscometer according to ASTM D2196-05

of appropriate spindle. It was reported in centipoises.

3) Weight per liter

Weight per liter was calculated according to IS: 1964. Initially the dry, empty weight per

liter cup was weighed. It was then filled with the emulsion sample so that it overflows the

vent cap. The cup was weighed again after cleaning the excess paint. The difference


32

between the two weights gives the weight of the paint sample held in the volume of

100ml of cup from which the weight per litre of paint was found out.

4) Finish of dispersion

The fineness of grind or dispersion was found according to ASTM D 1210-05, according

to which the finish was checked with the help of Hegmen gauge. The paint was taken at

the 0 end of the Hegmen gauge kept in horizontal position. It was then drawn with the

help of the applicator along with grooves. The gauge was viewed immediately to the

paint surface was designated as the finish of the paint.

5) Gloss at 20o and 60

o

The gloss of the paint was found using Gloss meter at 20o and 60

o. For each panel five

readings were taken at different positions and the average was calculated.

6) Computer Colour Matching

In this analysis , it matches if two shades of colour are equal and upto what extent. CCM

measures the % reflectance of colour and also Lab Colour Space values ( L* ,a* ,b*).

Lab color space is a color-opponent space with dimension L for lightness and a and b for

the color-opponent dimensions, based on nonlinearly-compressed CIE XYZ color space

coordinates. It is designed to approximate human vision. It aspires to perceptual

uniformity, and its L component closely matches human perception of lightness. It can

thus be used to compare shades and make accurate color balance corrections by

modifying output curves in the a and b components, or to adjust the lightness contrast

using the L component.

C value is also calculated by CCM which gives chroma or intensity of colour.


33

RESULTS AND DISCUSSION

a) Core and Polymeric pigment ( Core-Shell ):

ANALYSIS CORE CORE-SHELL

Composition BA , MMA , MAA CORE , Styrene , ACN

i) N.V.M. 19.02 % 35.15%

ii) pH 4 9

iii) Viscosity (cPs) 30 70

i) N.V.M.

The NVM of Core and Core-Shell is nearly same as the theoretical calculation. It means

the extent of conversion is fairly decent.

ii) pH

The Core shows acidic nature which is because of the presence of carboxylic acid due to

Methacrylic acid. Though the emulsion is stable at room temperature. The Core-Shell

pigment is basic in nature due to addition of ammonia. Ammonia neutralizes acidic group

of core to form amide and water.

iii) Viscosity

The viscosity here is dependent on % solids. In Core, it is less as NVM is less as

compared to Polymeric pigment. However both are emulsions so their viscosity is not

high.


34

iv) UV- Visible Absorption Spectroscopy (UV-Vis)

The UV-Vis is done only on Core-Shell to find its absorption peak and compare it with

that of TiO2. Below are the Absorption graphs of TiO2 and synthesized Core-Shell.

Absorption graph of TiO2

Absorption graph of Polymeric Pigment


35

The Maximum absorbance of TiO2 is at 210 nm while for Polymeric pigment it is 222 nm

(shown by arrow 2 in figure). Both absorb mainly in Ultraviolet region. Thus Core-Shell

show nearly similar absorbance properties to TiO2.

v) Fourier transform infrared spectroscopy (FTIR)

The Core and Core-Shell were analyzed for the function groups present using FTIR. Below are

the FTIR graphs.

FTIR for CORE

The peaks at various positions identifies the functional group present in Core thus telling us

about the presence of reactants.


36

For Ester group conformation: 1654.3 cm-1

For Aliphatic group conformation: 2954 , 2874 cm-1

For carboxylic group ( COOH ) : 1731.8 cm-1

FTIR for CORE-SHELL

For Ester group conformation: 1877 cm-1

For Aliphatic group conformation: 2946.6 cm-1

For carboxylic group ( COOH ) : 1730 cm-1

For aromatic group conformation : 1423 , 1453 cm-1

7501000125015001750200022502500275030003250350037504000

1/cm

80

82.5

85

87.5

90

92.5

95

97.5

100

102.5

% T3

02

5.1

4

29

45

.10

22

37

.27

19

47

.97

18

77

.57

17

30

.03

14

93

.77

14

53

.26

75

9.9

0

69

9.1

5

Core Shell Latest


37

For ammonia conformation : 3028 cm-1

For nitrile group conformation : 2237 cm-1

Thus the FTIR graph shows that all the raw materials have reacted and are present in our

compound.

vi) Differential Scanning Calorimetry (DSC)

The glass transition temperature of both Core and Core-Shell are found using Tg. Since

core is a simple copolymer it should show only 1 Tg value. Core-Shell should show three

Tg values i.e. 3 shifts in baseline. It shows Tg of Core, Interface and Shell. Below are the

DSC curves:

DSC Curve of CORE


38

Only one Tg is shown in Core at 6.2 oC. It matches roughly with the theoretical calculated

value of 8.3 oC. It may be concluded that reactants have reacted stoichiometrically.

DSC Curve of CORE-SHELL

The DSC curve here shows 2 Tg only. At Interface Tg is 34.93 oC and for shell it is 111.48

oC.

The Tg for Core could not be shown as the amount of Core present in Core-Shell is very small

and after drying, the volume of polyelectrolyte in core decreases significantly. Thus it‟s presence

was not detected easily.


39

b) Paint: Batch A and Batch B

Batch A: 100 % TiO2

Batch B: 85% TiO2 and 15% Dried Polymeric Pigment (w/w%)

ANALYSIS BATCH ‘A’ BATCH ‘B’

i) N.V.M. 48.27% 46.20%

ii) Viscosity

iii) WPL 1.36 1.35

iv) Fineness of grind 5+ 5+

v) Gloss

@ 20o

@ 60o

2.5

6.1

2.62

7.8

i) N.V.M.

The NVM of both the paints were found to be nearly same to their theoretical value.

However paint A has more TiO2 pigment having high density thus its NVM is greater

than paint B

ii) Viscosity

The Viscosity of paint A is slightly greater than paint B due to more amount of TiO2.


40

iii) WPL

The weight per liter of Paint A is slightly grater than paint B due to high density of TiO2

pigment as compared to polymeric pigment.

iv) Fineness of grind

Both the paints show same fineness of grind or dispersion. This means core-shell pigment

is easily dispersible in Emulsion paints.

v) Gloss

As the amount of pigment and extender is high in both paints and due to nature of binder,

sufficient gloss was not obtained. However the gloss of paint B is slightly greater than

paint A. Thus addition of polymeric pigment helps in increasing gloss.

vi) Computer Colour Matching

Glass panels were coated with Paint A and B. After drying they were analyzed for

optical properties using CCM Spectraflash SF300. Following are the results :

ANALYSIS STANDARD

WHITE TILE

PAINT „A‟ PAINT „B‟

% Reflectance 83.34 68.54 59.17

L* 94.10 89.61 86.02

a* -0.62 -1.82 -2.09

b* -0.27 -1.39 -3.56

c 0.67 2.29 4.12

h 203.74 217.28 239.60


41

The L* a* b* values of both the paints are comparable. Thus addition of polymeric

pigment has no effect in change of colour. Infact after looking at the value of c

(chroma), Paint B shows more brightness as compared to paint A. Thus by CCM testing

we can say that the optical properties of paint have not been tampered by addition of

polymeric pigment in its formulation.


42

CONCLUSIONS

The synthesis of Polymeric Pigment by emulsion polymerization is an eco-friendly way of

producing pigment which can partially replace TiO2 concentrations in paints. Though cost is the

major factor for TiO2 replacement, Polymeric pigments can also show some better properties

when incorporated. They increase the gloss and brightness of paint without compromising on

other properties. They have less binder demand as compared to inorganic pigments due to their

uniform spherical shape. Thus high CPVC paints can be formulated with Polymeric pigments.

They also eliminate the problem of crowding experienced by TiO2 pigments.

Thus we can conclude that incorporation of polymeric pigments in paints helps in increasing the

property of paint with cutting of raw material cost.


43

REFERENCES

1. A.K. Khana, B.C. Raya, S.K. Dolui ; “Preparation of core-shell emulsion polymer and

optimization of shell composition with respect to opacity of paint film” ; Progress in Organic

Coatings 62 (2008) 65–70

2. McDonald, C.J.; Devon, M.J. “Hollow latex particles: synthesis and applications”

Advances in Colloid and Interface Science (2002), 99, p.181–213.

3. ROPAQUE™ ULTRA E Opaque Polymer, Product Description, Rohm and Hass

Pvt. Ltd.

4. Fasano, D.M.; Williams E. JR. “Opaque Polymers” Handbook of Coating

Additives Vol. 2, Marcel Dekker Inc., 1992.

5. Nobuyuki, I; Tooru, M.; Ichirou O.; Masayuki H.; Kiyoshi K. “Cross-linked hollow

polymer particles by emulsion polymerization” Colloids and Surfaces A:

Physiochemical and Engineering Aspects (1999), 153, p.311-316.

6. Malshe V.C.; Sikchi M. , Basics of Paint Technology – I, Color Publications Ltd., 2004

polymeric pigments / core shell emulsions

Documents

differential scanning calorimetry

volatile matter content

total solids content

volatile material lost

aliphatic group conformation

ester group conformation

layered spherical particles

hollow latex particles