In the present scenario high performance coatings are most widely used to preserve industrial equipment, pipelines, plant and buildings from deterioration by exposure to water, chemicals or weather which find application in automotive, industries and industrial structures, iron, steel and concrete structure, ships and marine structures, reactors, pipelines, machinery components etc.

The present work emphasis on the partial replacement of TiO₂ pigment with Calcium Aluminum Silicate (CAS) and Magnesium Aluminum Silicate (MAS) in high performance coating application without affecting the quality of coating. Different performance coatings were prepared with partial replacement of TiO₂ with CAS & MAS and analyzed for important optical properties like opacity, whiteness, Gloss and brightness. The mechanical properties were also evaluated for these coatings. The CAS & MAS fillers showed potential of replacing 5 – 30% by weight of TiO₂ in different types of performance coatings.

1. INTRODUCTION:

Titanium Dioxide is a multifaceted material in coating applications. It efficiently scatters visible light thereby imparting whiteness, brightness and opacity to paint and coating material. The scattering of light is affected by various factors like refractive index of pigment, pigment volume concentration (PVC) in the coating, degree of dispersion and the distance between pigment particles. The hiding will be the maximum when the pigment particles are separated by distance of one diameter of the pigment.

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. 3 & 4

TiO₂ is often poorly dispersed and crowded by the extender and resin particle. Indeed the higher the pigment and extender volume concentration the worse the crowding can become. It is well understood that by reducing the size of extender particles used, the spacing of TiO₂ can be significantly improved. Replacing 6um extender/ filler with a 2 um would, lead to improve TiO₂ spacing, better opacity and to the possibility of reducing TiO₂ levels. However, to further improve the spacing to levels leading to significant improvements in scattering and opacity would ideally require the extender particle size to be an order of magnitude smaller at least. 5 Figure 01 shows the effect on spacing of TiO₂ particle with decreasing particle size of extender.

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Fig. 01: Effect of decreasing extender particle size on spacing of TiO₂ pigment
The particle size and particle shape of Calcium Aluminum Silicate (CaAl2Si2O8) and Magnesium Aluminum Silicate (MgAl2Si2O8) will claim to replace Rutile or Anatase TiO₂ partially in high performance coating formulations. 6

This extender is synthesized from naturally occurring mineral “Actinolite”. Actinolite is a Calcium Magnesium Iron Silicate Hydroxide. As compared to other functional fillers Calcium Aluminum Silicate and Magnesium Aluminum Silicate has better wet hiding properties due to its higher refractive index compare to other extenders. 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 properties of CAS filler are shown in the Table: 1

2. EXPERIMENTAL:

2.1 MATERIALS:

Calcium Aluminum Silicate and Magnesium Aluminum Silicate was procured from M/s. Aromax Corporation, Ahmedabad and was used without any further modification.

The comparative evaluation of properties of CAS and other conventional fillers & extenders are given in Table: 2. The particle shape in SEM analysis and particle size in Marlvan analysis of Calcium Aluminum Silicate fillers are shown in Figure 2 and Figure 3 respectively.

The hydroxy functional acrylic resin Synocure 862 used for this study was crosslink at room temperature with polyisocyanates and was procured from M/s. Cray Valley India P. Ltd., Mumbai. The technical specifications of Synocure 862 are shown in table 03.

The various extenders such as Talcum, Barytes, china clay, calcite etc. used for the study was procured from M/s. Gayatri Fillers Pvt. Ltd., Ahmedabad.

2.2 METHODS FOR PREPARING DIFFERENT PAINT COMPOSITIONS:

The various protective coating were prepared in laboratory Bead mill and High Speed Disk Disperser. The mill base was ascertained by Daniel flow point8 technique and pigment was grinded for to a Hegman scale of 7+ to 5+. The different coatings were prepared by replacing 5 – 50% of TiO2 Rutile or Anatase with the help of Calcium Aluminum Silicate.

The Polyurethane primer cum surfacer for metal was prepared by using different % replacement with Calcium Aluminum Silicate ranging from 5 – 40% of TiO2 Anatase. Table 07 shows the composition of PU primer cum surfacer.

The epoxy based floor coating was prepared by using different % replacement with Calcium Aluminum Silicate ranging from 5 – 30% of TiO2 Rutile. Table 08 shows the composition of Floor coatings.

The high elastic roof coating was prepared by using different % replacement with Magnesium Aluminum Silicate ranging from 5 – 40% of TiO2 Rutile. Table 09 shows the composition of roof coating.

2.4 CHARACTERISTATION OF DIFFERENT COATING:

Various Optical and Mechanical properties like Contrast Ratio, Gloss, Colour, Adhesion, Hardness, Impact Resistance, Flexibility, Reactivity, Density, Storage Stability, Salt Spray etc. has been evaluated by Standard methods (BIS and ASTM) 9. The results are given in Table 10, 11 and 12 for PU primer cur surfacer, Epoxy floor coating and Roof coating respectively.

The effect of replacement in the Optical properties viz Opacity (Contrast Ratio), Whiteness Index and Gloss are shown in Table 10, 11 & 12 and Figure 4, 5 & 6 for the Polyurethane Primer cum surfacer, Epoxy Floor Coating and Roof Coating respectively.

3.1 Particle Size & Shape of CAS:
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.10 The average particle size of Calcium Aluminum Silicate is about 1.5 um and about 97% particles are about 10 um which does not affect the particle size of the final end product. Lower particle size also makes the smoother finish and easy dispersibility. Also the surface smoothness of the applied films indicates that there is no any detrimental effect of replacing small particle of TiO2 with somewhat higher particles than it. Also the plate like structure for the fillers improves the corrosion resistance in the Floor coating and PU primer.

3.2 Contrast Ratio:
The optical property of vital importance is Opacity. This was studied by evaluating Contrast Ratio (K/S Values)11. In Calcium Aluminum Silicate and Magnesium Aluminum Silicate based Performance Coatings 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 5 - 7% is attributed to the Spacing effect of the TiO2 pigment particles spaced by Calcium Aluminum Silicate and Magnesium Aluminum Silicate extender particle. Thus we find that 15% to 25% replacement of TiO2 with Calcium Aluminum Silicate and Magnesium Aluminum Silicate is possible without disturbing the Contrast Ratio of the Paint entirely based on TiO2 as an opacifying pigment.

3.3 Gloss:
Gloss is not much affected in floor coatings as well as in roof coating by replacing TiO2 with Calcium Aluminum Silicate and Magnesium Aluminum Silicate due to its lower Oil Absorption Value. We can easily replace the 15% of TiO2 without decreasing the gloss of end product.

3.4 Whiteness Index:
As revealed by Whiteness Index of Calcium Aluminum Silicate and Magnesium Aluminum Silicate it does not deter whiteness of the paint system when used as replacement of TiO2 because the CAS and MAS powder it self has a whiteness about 96% to 99% against Mgo Standard respectively.

3.5 Mechanical Properties:
The replacement of true pigment i.e. TiO¬2 with other functional fillers, should not affect the important mechanical properties & corrosion resistance of the coatings in achieving the optical properties. The mechanical properties of coatings viz Adhesion, Flexibility, Hardness and Impact resistance are affected as PVC in increased.12 Abnormality in these properties is seen at PVC = CPVC. With the use of these functional fillers no such abnormality in these mechanical properties, by replacing TiO2 with CAS & MAS, is seen as PVC is increased.

3.6 Corrosion Protection:
As revealed by the result shown from the salt spray resistance test all the panels passes the 1000 hrs but in the case of replacement more than 15% of TiO2 it will shows good result compared to standard. This is attributed due to the plate like structure of the CAS and MAS fillers which contribute the corrosion protection due to the Barrier effect.

3.7 Finish & Grinding:
The comparatively large particle size of CAS and MAS did not affect the degree of grinding of pigment in any of the coatings prepared based in them.

3.8 Viscosity:
The viscosity was not affected in the any of the coating based on Calcium Aluminum Silicate Magnesium Aluminum Silicate. The viscosity was almost stable in the accelerated storage test. This is due to the lower and comparable oil absorption value of CAS and MAS filler.

4. CONCLUSION:

The results reveals that Calcium Aluminum Silicate and Magnesium Aluminum Silicate can be successfully used in the High Performance Coating systems upto a level of 20 - 25% replacement of TiO2 in PU primer cum surfacer, 15 % in floor coating and 20% in roof coating without affecting the quality of final paint products. On the cost factor aspect it is found that there is approximate cost saving of Rs 2.0 to Rs. 4.50 per liter in any of the these system based on CAS & MAS. Similarly these both fillers can be also used in any other solvent based or water based high performance coating system and decorative coating with a replacement of 10 – 30% of TiO2 Rutile or Anatase depending on the quality of product.

ACKNOWLEDGEMENT:

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

REFERENCES:

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