NEW GENERATION OF CALCIUM CARBONATE K.K.Mishra 20 Microns Ltd., Mumbai, India GENERAL OUTLOOK Paint, as an aesthetic and protective material, has undergone significant transformation over the years from being just a colour to a performance specific composite material. With this change, the ingredients of paint have evolved into more sophisticated functional raw materials. Extenders once considered as mere fillers are today looked upon as functional input to the paint contributing to rheology, adhesion, gloss control, hiding and PVC optimization. This situation necessitates up gradation of techniques and for the characterization of extenders. MANY paint makers still believe that fillers, (extenders, minerals) are of little importance, low cost and widely available products. But extenders should no longer be viewed in such terms. They have a functional purpose in the paint end product and their properties and qualities will substantially affect this product. Paint makers must expand and modernize their production facilities to cope with increasing technological sophistication. In trying to cut costs, raw materials will be a key consideration. Many paint makers have successfully decreased the use of expensive titanium dioxide by partial replacement of white extenders which are properly ground to the extent of sub-microns to 2microns average particle size. FUNCTIONAL EXTENDERS Extender pigment or simply extenders are also so called because such materials are used to “Extend” the effect of expensive white and coloured pigments, so cheapening the paint formulation. However, it is now recognized that extender pigments contribute much more to paint properties. Careful selection of the type and quantity of extenders can affect such features in paints & coating as: 1. Opacity or hiding. 2. Gloss or sheen. 3. Flow, leveling and smoothness. - 1 -
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NEW GENERATION OF CALCIUM CARBONATE
K.K.Mishra
20 Microns Ltd., Mumbai, India
GENERAL OUTLOOK
Paint, as an aesthetic and protective material, has undergone significant transformation over the years from
being just a colour to a performance specific composite material. With this change, the ingredients of paint
have evolved into more sophisticated functional raw materials. Extenders once considered as mere fillers are
today looked upon as functional input to the paint contributing to rheology, adhesion, gloss control, hiding and
PVC optimization. This situation necessitates up gradation of techniques and for the characterization of
extenders.
MANY paint makers still believe that fillers, (extenders, minerals) are of little importance, low cost and widely
available products. But extenders should no longer be viewed in such terms. They have a functional purpose
in the paint end product and their properties and qualities will substantially affect this product. Paint makers
must expand and modernize their production facilities to cope with increasing technological sophistication. In
trying to cut costs, raw materials will be a key consideration. Many paint makers have successfully decreased
the use of expensive titanium dioxide by partial replacement of white extenders which are properly ground to
the extent of sub-microns to 2microns average particle size.
FUNCTIONAL EXTENDERS
Extender pigment or simply extenders are also so called because such materials are used to “Extend” the
effect of expensive white and coloured pigments, so cheapening the paint formulation. However, it is now
recognized that extender pigments contribute much more to paint properties. Careful selection of the type and
quantity of extenders can affect such features in paints & coating as:
1. Opacity or hiding.
2. Gloss or sheen.
3. Flow, leveling and smoothness.
4. Durability and appearance of the paint film.
5. Pigment settlement on storage.
6. Barriers effect and water permeability etc.
Conventionally, extenders have been characterized employing simple techniques like visual colour
assessment, sieving, specific gravity, oil and water demand, pH and microscopic examination. These tests do
give very useful information to the paint formulator in deciding upon fundamental formulation parameters like
PVC, weight per liter, finish and the like. However, if one desires to establish the closer relationship between
characteristics of the extenders on one hand and various paint making, application and performance
parameters on the other, then the use of modern analytical techniques become unavoidable. These
techniques possess the capability to look at the micro structure of extenders in terms of size, shape, surface
chemistry and crystallography. Correlations established between different extender parameters and a paint
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performance property enables the technologist to diagnose the cause of the quality or performance problem.
More importantly, it provides predictive capability to envisage performance of a paint which incorporates
certain type of extenders.
While examining various modern techniques, it is important to take over view of various particle size analysis
techniques like, electron microscopy forms a very important tool for examination of particle shape which has
significant bearing on RHEOLOGY, GLOSS AND OPACITY AND SURFACE FINISH.
For the sake of simplicity the term “Extenders” will be retained in this article, but it is used in the widest sense.
The main difference between a pigment and an extender is that pigments impart colour and hiding power to
the paint where as extenders have little or no hiding power themselves. The manufacturers of mineral
extenders are generally required to give high technical service back up, and bear above average the R&D
costs. The efficient processing is important, as is the ability to upgrade and modify products term as a “New
Generation Extenders” by using ultrafine grinding technology without any oversized particles (nib
free), calcining or surface modifications.
FUNCTIONAL PERPORTIES OF EXTENDERS
Selection of extenders by the paint maker depends on a number of factors:
GENERAL
The colour should be bright, clear, intense and reproducible. It depends on the mineral, chemical composition,
the brightness, the cleanliness and the intensity on the difference between the refractive indices of pigment
extenders and medium, and on particle size and size distribution, particle shape and crystal habit. The opacity
or hiding power is a function of the difference between refractive indices of the pigment and dispersion
medium. Both pigments and extenders are opaque as dry powders, but when dispersed in media, pigments
are opaque in both organic and aqueous media, whereas the extenders are practically transparent in organic
media but opaque in aqueous media. This is because the refractive indices of extenders are very close to
those of oils and resins.
Extenders have a low refractive index, similar to that of binders and so are effectively transparent. They are
usually white or off-white and contribute either no color or an undesirable one to paint film. How, then, can
extenders increase the efficacy of pigments if they possess neither of the basic properties required. ? There
are five aspects to consider:
1. PARTICLE SIZE DISTRIBUTION.
The particle size is very important and it is one of the properties which can be altered substantially by the
processor. Hiding power and tinting strength are both related to the particle size. The particle size also
influences gross consistency and settlement. Particle sizes have directly co-relation with surface area of
the particle which effects viscosity, flow characteristics, dispersion stability and oil absorption. Particle
shape effects flow characteristics settlement and film durability.
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2. HIGH BRIGHTNESS.
They should be as bright as possible so that no pigment is, as it were, wasted covering the unwanted
colour of the extender. The brightness depends on the chemical composition of the deposit. Sometimes
the colour can be improved by washing or flotation.
3. HINDER RE-AGLOMERATION.
This is done by introducing sufficient physical barriers so that the likelihood of two pigment particles
colliding and re-agglomerating in the liquid paint system is reduced.
4. IMPROVED PIGMENT DISPERSION.
They help to break down the pigment agglomerates. It has been calculated that if all the titanium dioxide
used were perfectly dispersed, the world demand for titanium dioxide would fall to about 14% of the
present usage. It is evident that extender producers can help a lot here.
The extender must itself be easy to disperse. The individual particles collide with pigment agglomerates,
breaking them up. The extender must be fine since if it is too coarse it encourages “crowding” thus
defeating the objective. Ideally, the pigment particles should be half the wave length of light in diameter
and the distance between them should also be half the wave length of visible light. Please note that we no
longer speak of spacing extenders. This theory has been proved wrong by simple experiment. If the
pigment and extender are disperse separately in half of the binder and then subsequently mixed, there is
only a slight increase in opacity and much less than when the extender and pigment are mixed together in
the first place. The slight increase in opacity is caused by hindering re-agglomeration as mentioned
above.
5. DECREASE CRITICAL PVC.
They can decrease the critical PVC to below that of the paint so that there is insufficient binder to
completely coat each organic particle. Tiny pockets of air are trapped on the surface of some of the
particles, increasing the amount of light diffracted and hence the opacity or hiding power of the paint film.
Of course, this also lowers the scrub resistance and increases the tendency of the film to pick up
atmospheric dirt. The extender must have a high absorption. Suitable ones are calcined clay or synthetic
aluminium silicate. This usage is only practical for interior paints and even then it is limited due the poorer
scrub resistance.
A NEW GENERATION CALCIUM CARBONATES – LEADING THE FIELD
In quantity terms calcite, dolomite and whiting are the most widely used carbonate extender minerals in
paints. Calcite is basically used as a pigment extender for the improvement of pigment efficiency because of
the spacing and refractive index. Paint makers may use any grade size from a coarser grade (400 Mesh) to a
micronized grade (20 Microns and 10 Microns). In general, the finer the particle size, the higher the gloss of
the paint.
Calcium carbonate does not contribute significantly to opacity in itself but a new generation calcium
carbonate is said to “bring out” the opacity of prime white pigments by spacing them correctly. High
brightness and proper micronisation is desirable to improve paint colour characteristics. Properly micronized
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carbonates may be used to improve film cohesion, higher gloss and higher loading (pigment volume
concentration).
In paints & coating, the endless opportunity for modifying the optical and mechanical properties with calcium
carbonate, make this mineral particularly popular main extenders which offer functional properties with
regards to high brightness low oil absorption, dispensability, weather resistance, low abrasiveness, low
electrolyte content, pH stabilizing effect, and improved anti-corrosion and rheological properties.
a. Decorative coating
Interior emulsion paint is the most important application of the calcium carbonate of the coating industry,
and calcium carbonate also provide economical advantages and optimize properties performance in
exterior emulsion paint and decorative enamel, where calcium carbonate filler loading is comparatively
lower.
b. Industrial Coating
Industrial coatings are generally formulated with lower filler content, primarily use for protection, where
durability is a main paint film property against environmental condition.
Application Extenders Content
Interior emulsion paints Up to 65%
Exterior emulsion paints Up to 45%
Brushing enamels Up to 10 -15%
Powder coatings Up to 5 -20%
Industrial coatings Up to 5 -20%
Road marking paints Up to 30 -50%
Primer Up to 5 -20%
Inks Up to 15%
To meet the challenging demands of its customers, 20 Microns Limited now produces New Generation
Calcium Carbonates, mainly
1. O Carb
Purest, ultra white and closely controlled superfine narrow particle size calcium carbonate from world best
deposit.
O Carb is white, closely controlled, micronized purest, natural calcium carbonate selected from world best
deposit, specially developed for Paints-Coating, adhesives and sealants industry ‘O’ Carb narrow particle
size distribution optimizes particle packing leaving less void space to be filled by expensive resin, which
leads to enhance opacity with gloss in all type of premium water base formulation.
2. Vaporlite 90T
Sub-micron calcium carbonate produced by new engineered wet – milling techniques, which act as a
spacers between prime pigment and contribute to batter coating opacity and high gloss.
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Vaporlite 90T is an ultra fine sub-micron natural calcium carbonate. The sub-micron particles of
Vaporlite 90T can act as spacers between TiO2 particles leading to increase the efficiency of TiO2 in the
paints and coating application. The size and numbers of Vaporlite 90T particles enable efficient
separation at TiO2 particles and inhibit re-agglomeration after dispersion whereas agglomerates are less
efficient at scattering light when compared to the fine primary particles. As light beams are refracted at the
particle surface it follows that smaller and more numerous fine particles offer more opportunities for
refraction and thus lead to better coating OPACITY and HIGHGLOSS.
Fig 1. SPACING EFFECT OF VAPORLITE 90T WITH PRIME PIGMENT TiO2
Fig-1
3. Vaporcifier
Modified calcium carbonate for partial replacement of Titanium Dioxide (TiO2)
Vaporcifier is a new and innovative product designed especially for emulsion paints. Vaporcifier is a
natural calcium carbonate where particle structures are modified by physical and chemical process which
creates particle with an amorphous structure to offer excellent opacity of the paint and lower overall cost
by extension of TiO2. Vaporcifier display a very amorphous structure which leads to the assumption that
in addition to the external surface an internal surface also exists which significantly increase a specific
area and oil absorption whereas micronized GCC shows a compact surface structure.