Brushstrokes - October 2011 - Surface Coatings Association of New ...

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Table 1 – interior wall paint formulation techniques to achieve the optimum particle size distribution without affecting the unique morphology. The deposit is fine and white with a high carbonate content and an iron content of only 0.03%. Details of the morphology and physical properties can be seen in figure 1 and table 1. It occurs naturally as an aggregate of platy crystals with sides of ≈ 0.5 – 1.0µm and an aspect ratio of 10:1. The defining properties are the high brightness, low particle size and the high oil absorption/ surface area. The advantages of these properties will be shown in the following work. The properties of the other test fillers (as measured by SSME) are summarised in table 3. Where quoted, the manufacturers D50 particle size is also given. Measurements were made using the Sedigraph technique which is useful for platy materials such as hydrous kaolin, but can give discrepancies for round or needle shaped particles such as PCC. A lower value would be expected for the calcined kaolin suggesting this sample was highly agglomerated. Methods 7% TiO2 7% TiO2 + 20% Binder 3.5% TiO2 Dispersion - All coatings were produced using a high speed disperser with a toothed blade. The water, dispersants, calcium scavenger, biocide, antifoam and thickener were dispersed at 6 SURFACE COATINGS ASSOCIATION OF NEW ZEALAND 3.5% TiO2 + 10% Binder Water 270 270 270 270 Dispersant A 4 4 4 4 Na HMP 1 1 1 1 Dispersant B 1 1 1 1 Biocide 3 3 3 3 Antifoam 2 2 2 2 Cellulose thickener 3 3 3 3 TiO2 80 80 40 40 5µm GCC 290 290 290 290 Test extender 100 100 140 140 Talc 80 80 80 80 Styrene Acrylic binder 160 192 160 176 Thickener 3 3 3 3 TiO2 PVC 7 6.7 3.5 3.4 Total PVC 72.2 68.4 72.7 70.8 Figure 3 Ankerpoort mine in Greece Figure 4 (left) - Morphology of complex carbonate extender Table 2 - Physical properties of complex carbonate extender Density 2.7g/cm3 Mohs Hardness 2 - 3 Refractive index 1.61 – 1.64 D50 (Sedigraph) 0.56µm Oil Absn 55-60g/100g BET 18m2/g Brightness (Ry) 95 Brightness (ISO) 92.3 pH 10 Table 3 – physical properties of competitive test extenders Fine GCC PCC low speed until fully dissolved. The pigment, fillers and extender were added and dispersed at high speed for 30 minutes until a grind of 5 or better was achieved. Following this the binder and thickener were added and dispersed at low speed for a further 30 minutes until a uniform dispersion was achieved. Brightness and contrast ratio - The coatings were drawn down onto a Leneta No. 2 opacity chart using a bird type applicator to give a 150µm wet film thickness and allowed to dry for 7 days. Brightness was measured as L* using a spectrophotometer. Contrast ratio was measured as the ratio of reflected light from the coating over the black and white portions of the card (RB/RW) expressed as a percentage. Viscosity measurement - Viscosity was measured using a Brookfield viscometer fitted with spindle 5. High and low shear measurements were made at 100rpm and 10rpm. Results and discussion Hydrous Kaolin Calcined Kaolin Density 2.7 2.6 2.6 2.6 D50 (Sedigraph) 1.1 1.38 0.62 6.6 D50 (TDS) 0.2 - 0.3 0.7 Oil Absn 30.5 37.5 42.0 74.5 Brightness (ISO) 91.0 95.5 85.5 90.9 The results for all test measurements are shown in table 4a and 4b. There was no significant difference in the brightness measured for all formulations, being in the range 95.0 ± 0.6 although it should be mentioned that the highest brightness for each series
Table 4a – test results for 7% TiO2 formulation 7% Titan 7% Titan + 20% Binder was given by the complex carbonate extender. As may be expected the brightness of the coatings containing 7% TiO2 was higher than those containing 3.5% TiO2, although in reality the difference was on average only half a point. Gloss measurements were also very similar for all samples ranging from 2.4 to 3.8. All coating would be suitable for low sheen applications. The variation in contrast ratio was far greater, ranging from a low of 90.1 to a high of 96.2. Once again the complex carbonate formulations had the highest value in all test series, in some cases by a significant margin, being at least two points above the average value for each series of tests. The results for the fine GCC and the PCC were very similar and it would be difficult to place one above the other in terms of contrast ratio. The lowest contrast ratio was given by the hydrous and calcined kaolins which were also very similar. In terms of particle size and shape the hydrous kaolin was closest in morphology to the complex carbonate, however the results show it is not as effective as the complex carbonate as a TiO2 extender. There was some variation between the contrast ratio of the higher and lower TiO2 contents. Increasing the level of extender and reducing the level of TiO2 gave a higher contrast ratio for the complex carbonate, fine GCC and hydrous kaolin while a lower value for PCC and calcined kaolin. The area which showed the greatest difference between the complex carbonate and the other extenders was viscosity. The GCC, PCC and hydrous kaolin give reasonably similar viscosities, however the complex carbonate gives a noticeably higher viscosity and the calcined kaolin a noticeably lower viscosity. The highly thixotropic nature of dispersions containing the complex carbonate can be an advantage in that settling is less pronounced and thickener levels can reduced. If lower viscosities are required then subsequent work has shown that alternative combinations of dispersant and thickener are Portafill H5 Fine GCC PCC Hydrous Kaolin Calcined Kaolin Brightness L* 95.8 95.0 95.4 94.9 95.4 CR/% 96.4 92.4 92.5 92.4 90.1 Gloss 85° 2.8 2.4 3.2 2.5 2.6 Viscosity100rpm/cP 2640 1880 2040 1680 1240 Viscosity10rpm/cP 14000 7200 7600 7200 4400 Brightness L* 95.8 95.3 CR/% 95.9 94.9 Gloss 85° 2.6 2.7 Table 4b – test results for 3.5% TiO2 formulation 3.5% Titan 3.5% Titan + 10% Binder Portafill H5 Fine GCC PCC Hydrous Kaolin Calcined Kaolin Brightness L* 95.6 94.5 95.1 94.4 94.8 CR/% 95.2 94.3 91.1 92.2 92.0 Gloss 85° 3.6 3.4 3.8 2.9 2.9 Viscosity100rpm/cP 3600 1880 1680 1920 1160 Viscosity10rpm/cP 21200 7600 5600 9200 2000 Brightness L* 93.2 94.4 94.4 94.1 CR/% 94.5 92.0 90.3 91.5 Gloss 85° 3.2 3.1 2.8 3.1 effective in controlling the rheological behaviour. The relatively low viscosity of the mixes containing the calcined kaolin, despite the highest oil absorption, may be further evidence of the difficulty in deagglomerating the material and achieving a fine dispersion. This in turn would account for the poor performance in terms of contrast ratio. Conclusions SSME’s complex carbonate extender is an ultrafine, platy extender and has been compared in this series of tests against ultrafine carbonate extenders and ultrafine platy extenders. Overall the results show that it works well as a TiO2 extender, brightness in the test formulations was slightly better than the competitive materials however the most important result was contrast ratio. In formulations above critical PVC it is relatively easy to achieve a good brightness using white fillers but dry hiding power can be difficult to maintain as TiO2 levels are reduced. This work shows that increasing the level of the complex carbonate extender in a formulation allows the TiO2 level to be reduced while actually increasing the dry hiding power to a level not achieved by other fillers. This has advantages both in terms of cost reduction and quality improvement. In addition the rheological behaviour makes this extender highly suitable for viscous materials such as sealants, underbody coatings and putties. References 1. Titanium dioxide price pressure, Industrial Minerals, March 2009 2. Titanium dioxide market most “buoyant” for a decade, Industrial Minerals, Jan 2011 3. The Effect of Fine Particle Size Extenders and Entrapped Air on TiO2 in Emulsion Paints, Paul F. Dietz, PCI Magazine, September 2003. Contact details Simon Bussell, Sibelco Europe, Brookside Hall, Sandbach, Cheshire, UK. Contact: Simon.bussell@sibelco.com, Ph: +44 1270 752914, +44 7889 057206 SURFACE COATINGS ASSOCIATION OF NEW ZEALAND 7
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