This work is related to partially replacement of TiO2 pigment with Calcium Aluminum Silicate and Magnesium Aluminum Silicate in Non Aqueous and Aqueous paints respectively with negligible effect on the quality of paint. The cent percent replacement of TiO2 is impossible and an attempt is made to replace it partially with cost benefit without affecting whiteness, brightness and opacity of paint. Both the extender pigments showed potential of replacing TiO2 in different type of coatings ranging from 5% to 18% by weight depending on the desired end properties.

1. INTRODUCTION:

1.1 HIDING BY SPACING OF TiO2 PIGMENT PARTICLES:

The concept of spacing is basically rather easy: If it happens, that two or more titanium dioxide pigment particles are not completely dispersed but still have contacts with each other, it can be calculated that the theoretical maximum of white pigment efficiency is not reached. As the scattering volumes are larger than the particles themselves the volumes will overlap, influence each other and are all together decreased therefore.

If it is possible to place an inert filler particle just between these agglomerated titanium dioxide particles, the pigments are pushed apart so that the scattering volumes are free again. Scattering power recovers to 100% of the theoretical maximum value. Due to the increased efficiency of the pigment the titanium dioxide loading can be reduced respectively. 2

Calcium Aluminum Silicate (CaAl2Si2O8) and Magnesium Aluminum Silicate (MgAl2Si2O8) have potential to replace Rutile or Anatase TiO2 partially for solvent based and Water based paints respectively. It has been reported that Calcium Aluminum Silicate liberate Calcium ions in water based coatings resulting in gradual increase in viscosity of the paint hence it is used only for solvent based paints. 3 & 4 Both the extenders are synthesized from naturally occurring mineral “Actinolite”.

PRESENT WORK:

In the present work Enamels, Primers were prepared using Calcium Aluminum Silicate with different percent replacement (5% to 25%) of Titanium Dioxide. These two coatings of low and high PVC respectively enabled the study of different PVC on performance properties of Coatings. Similarly Magnesium Aluminum Silicate was used in Water based coating systems namely Premium interior emulsion paint and Acrylic washable distemper. The effect on properties of water-based paint was studied by replacement ranging from 1% to 18% of Rutile TiO2 with Magnesium Aluminum Silicate. The coatings prepared were studied with coating based entirely on Titanium Dioxide and their properties evaluated.

EXPERIMENTAL:

MATERIALS:

Both Calcium Aluminum Silicate and Magnesium Aluminum Silicate provide better whiteness, opacity and coverage with significant cost reduction. As compared to other functional fillers both Calcium and Magnesium Aluminum Silicate have better wet hiding properties. There use does not reduce any gloss in the final products due to its lower Oil Absorption Values. These are the prime reasons why it is considered as a better additive to Titanium Dioxide. The detailed properties of both these fillers are shown in the Table: 1.

Table: 1: Physical Properties of Calcium Aluminum Silicate and Magnesium Aluminum Silicate

Their properties were compared with convential fillers and extenders like Calcined Clay, Calcium Carbonate, Kaolin, Talcum, Barytes and Zeolite and are shown in Table: 2.

Table: 2: Comparative Physical properties of the Functional Fillers.5

The shape of the functional fillers is plate like needle structure. It is used for giving “Spacing Effect” between two TiO2 particles. The particle size of TiO2 pigment is 0.2 microns. Thus spacing effect enables to form aggregates between the two TiO2 particles.6
Figure 1 and Figure 2 show particle shape of Calcium Aluminum Silicate and Magnesium Aluminum Silicate functional fillers.

The enamels and Primers were prepared in laboratory Bead mill and High Speed Disk Disperser. The mill base was ascertained by Daniel flow point7 technique and pigment was grinded for enamel and primer to a Hegman scale of 7+ and 5+ respectively. The white synthetic enamel is prepared by using the formula as shown in Table: 3 with different % replacement of TiO2 Rutile RC – 822 ranging from 1% to 10% by Calcium Aluminum Silicate.

The Interior Emulsion Paints and Acrylic Washable Distempers were prepared in High Speed Disk Disperser. The pigment was grinded to a Hegman scale of 5+. The Magnesium Aluminum Silicate is suitable for the Water based system. The Premium gloss interior emulsion paint is made using different replacement with Magnesium Aluminum Silicate ranging from 1% to 15% of TiO2 Rutile RC – 822, and 5% to 25% of TiO2 Anatase for Acrylic Distemper. Table 4 & 5 shows the different formulations with Magnesium Aluminum Silicate for Interior Plastic Paint and Distemper respectively.

Various Physical, Optical and Mechanical properties like Contrast Ratio, Gloss, Tinting Strength, Viscosity, Adhesion, Hardness, Impact Resistance, Flexibility, % Solids etc. of both Water Based and Solvent Based paints has been evaluated by Standard methods (BIS and ASTM)8 The results are given in Table 6, 7 & 8 for Synthetic Enamel, Interior Plastic Paint and Acrylic Distemper respectively.

The effect of replacement in the optical properties viz Opacity (Contrast Ratio), Whiteness Index and Gloss are shown in Figure 3 to Figure 8.

Table: 3: COMPOSITION OF SYNTHETIC ENAMEL WITH VARIOUS REPLACEMENT OF CALCIUM ALUMINUM SILICATE:

The results of the performance properties shown in the Table 6 and Table 7 for the Solvent Based and Water based coatings reveal the followings.

% Non Volatile Matter:
The Non volatile content in Enamel, Primer, Interior Emulsion paint and Acrylic Washable Distemper was in perfect agreement with theoretical values.

Viscosity:
The viscosity was not affected in the Non-aqueous paint based on Calcium Aluminum Silicate and Aqueous coatings based in Magnesium Aluminum Silicate. The viscosity was almost stable in the accelerated storage test. There was however a 15% increase in viscosity in enamel having 10% replacement with Calcium Aluminum Silicate.

Finish & Grinding:
The comparatively large particle size of Calcium Aluminum Silicate and Magnesium Aluminum Silicate did not affect the degree of grinding of pigment in any of the coatings prepared based in them.

Mechanical Properties:
The mechanical properties of coatings viz Adhesion, Flexibility, Hardness and Impact resistance are affected as PVC in increased.9 Abnormality in these properties is seen at PVC = CPVC. With the use of these functional fillers no such abnormality in these mechanical properties is seen as PVC is increased.

Opacity:
The optical property of vital importance is Opacity. This was studied by evaluating Contrast Ratio (K/S Values)10. In Calcium Aluminum Silicate based Synthetic Enamels it was noticed that it increase with percent replacement at a certain point then slightly decreases at certain range of PVC value before finally increasing. This slight increase in Contrast Ratio at 3-5% is attributed to the Spacing effect of the TiO2 pigment particles spaced by Calcium Aluminum Silicate extender particle. Thus we find that 8% to 9% replacement of TiO2 with Calcium Aluminum Silicate is possible without disturbing the Contrast Ratio of the Paint entirely based on TiO2.

In Aqueous paint there is no effect of 10% replacement with Magnesium Aluminum Silicate of TiO2 on the Contrast ratio of paint.

Whiteness Index:
As revealed by Whiteness Index both CAS and MAS do not deter whiteness of the paint system when used as replacement of TiO2 mentioned above.

Gloss:
Gloss is not much affected in both Aqueous and Non Aqueous paint when either of these functional fillers are used as 8% replacement of TiO2 for Water based paints and 5% replacement of TiO2 for Solvent based paints.

Tinting Strength:
Tinting Strength of the paint system shows that as the % replacement increases the shade will become darker and brighter. So there is a chance of Colour Pigment saving in the coloured paint in both the system.

CONCLUSION:

The results reveals that Calcium Aluminum Silicate and Magnesium Aluminum Silicate can be successfully used in the Non Aqueous and Aqueous systems respectively upto a level of 8% replacement of TiO2 without affecting the quality of final paint products. On the cost factor aspect it is found that there is approximate cost saving of Rs 1.5 to Rs. 4.0 per liter by having 8% replacement of TiO2 by either Calcium Aluminum Silicate or Magnesium Aluminum Silicate.

ACKNOWLEDGEMENT:

The authors wish to express their gratitude to the Executive Director, Sophisticated Instrumentation Center for Applied Research and Testing (SICART), Vallabh Vidyanagar, Director, Institute of Science and Technology for Advanced Studies and Research (ISTAR), Vallabh Vidyanagar and Executive Director, Aromax Corporation, Ahmedabad for providing necessary facilities.

REFERENCES:

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14. http://www.mineral.galleries.com/minerals/silicate/grossula/grossula.htm
15. http://www.mineral.galleries.com/minerals/silicate/pyrope/pyrope.htm
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