Claims:
1. A process to increase the durability of titanium dioxide particles by coating it with nano silica and nano alumina, said process characterized by:
• heating TiO2 slurry of particle size 300nm to 700C;
• adding nano silica as seeding agent to sodium silicate solution, and mixing thoroughly;
• treating TiO2 slurry with said mixture to provide a coating of nano silica on titanium dioxide particles, wherein up to 6% silica is coated on titanium dioxide slurry based on the weight of titanium dioxide nano particles;
• digesting the slurry for 30 minutes, whereupon the pH of slurry is adjusted to 5.5 with H2SO4;
• adding 0.3% citric acid and 0.1% isopropyl alcohol to the slurry;
• adding nano alumina as seeding agent to sodium aluminate solution and mixing thoroughly;
• treating the slurry with said mixture to provide a coating of nano alumina on nano silica coated titanium dioxide particles, wherein up to 4% alumina is coated on titanium dioxide slurry based on the weight of titanium dioxide nano particles;
• digesting the slurry for 20 minutes, wherein the final pH is adjusted to 5.2-5.5 with H2SO4; and
• filtering the slurry followed by micronising the dried cake with organic coating.

2. The process as claimed in claim 1, wherein nano-silica seeded sodium silicate solution is added slowly to the TiO2 slurry over a duration of 15-20 minutes under constant stirring.

3. The process as claimed in claim 1, wherein nano alumina seeded sodium aluminate solution is added slowly to the TiO2 slurry over a duration of 15-20 minutes under constant stirring, wherein H2SO4 is simultaneously added to maintain the pH less than 8.

4. A process to coat titanium dioxide particles with nano alumina, said process characterized by:
• heating TiO2 slurry of particle size 300nm to 700C;
• adding 0.3% citric acid and 0.1% isopropyl alcohol to the TiO2 slurry, wherein it is homogenously mixed;
• adding nano alumina as seeding agent to sodium aluminate solution, and mixing thoroughly;
• treating the slurry with said mixture to provide a coating of nano alumina on titanium dioxide particles, wherein up to 4% alumina is coated on titanium dioxide slurry based on the weight of titanium dioxide nano particles;
• digesting the slurry for 20 minutes, wherein the final pH is adjusted to 5.2-5.5 with H2SO4; and
• filtering the slurry followed by micronising the dried cake.

5. The process as claimed in claim 4, wherein nano alumina seeded sodium aluminate solution is added slowly to the TiO2 slurry over a duration of 15-20 minutes under constant stirring, wherein H2SO4 is simultaneously added to maintain the pH below 8.

6.The process as claimed in claims 1 or 4, wherein the initial pH of TiO2 slurry is 9.5 – 10.
, Description:[0014] The preferred embodiments of the present invention will now be explained in detail. It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description is not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail.

[0015] The preferred embodiment of the present invention teaches a process for making high durable titanium dioxide pigment, without compromising its dispersion ability. To improve the pigmentary properties such as brightness, gloss, and dispersion, as well as durability, titanium dioxide particles are coated with silica and the alumina. Silica coating provides durability, whereas alumina deposits improve the dispersibility and enhances the gloss and opacity of the pigment.

[0016] As per the preferred embodiment, TiO2 slurry is initially heated to a temperature of 700C. For said process, approximately 650ml of TiO2 slurry of particle size 250nm –300nm is taken, wherein the gpl (grams/litre) of TiO2 content in said slurry is 300gm. The initial pH is 9.5-10.

[0017] 0.15 gm nanosilica (silicon dioxide) is seeded to 29 ml sodium silicate solution and is properly mixed. The resultant mixture is then slowly added to the TiO2 slurry over a duration of 20 minutes under constant stirring. The nano-seeded sodium silicate is added in order to make the coating of silica on TiO2to form at nano size. Said formation of nano silica causes to enhance the durability of TiO2. The slurry is then digested for thirty minutes (30 minutes) and the final pH of the slurry is made to 5.5 with H2SO4.

[0018] Further, to the above-said slurry is added a thoroughly mixed solution containing 0.3% citric acid and 0.1% isopropyl alcohol. Then, 0.15gm nano-alumina (aluminium oxide nanoparticles) is seeded to sodium aluminate solution and homogeneously mixed, wherein said mixture is slowly added to the silica coated TiO2 slurry. Sulphuric acid is also simultaneously added to the slurry in order to keep the pH < 8. The slurry is then digested for 20 minutes and the final pH is made to 5.5 with H2SO4. The nano-alumina seeding is done to obtain a coating of nano-alumina on TiO2.

[0019] The pigments prepared as a result of this coating has a level of durability that is equivalent to most of the high durable pigments that are currently available in the market. Even 1% nano silica and 1% nano alumina coating is found to give high durable pigment. Even in samples with 1% alumina showed good durability values. The nano-alumina and nano-silica coating was found to enhance the durability of TiO2, without affecting its dispersibility and other optical properties.

Durability

[0020] The durability of TiO2 pigments is assessed by ultraviolet light irradiation based TiO2 catalysed reduction of lead carbonate to lead. Specifically, the pigments are mixed with basic lead carbonate, glycerol, and fumed silica paste, wherein said mixture is taken in two glass microscopic slides and irradiated with ultraviolet (UV) light for 7 hours. The initial and final brightness values were measured in Hunter lab (colorflex EZ model) colour difference metre. If the pigment sample is of high durable grade, then it will retain the whiteness. Otherwise, it changes to grey and subsequently to black. The samples prepared were also compared with high durable grade available in the market and were found to be comparable.

Dispersibility Testing

[0021] Dispersibility Testing is performed by dispersing the pigment in linseed oil in a mixer. The resulting mixture is then drawn on a Hegman gauge. The number of undispersed particles has to be minimum to qualify as good dispersion. Standards and samples were compared and were found to be comparable.

Acid solubility test

[0022] For this testing 25 ml con H2SO4 was taken in 50 ml Nessler’s cylinder and heated at 1750 C for 20 minutes. To this was added 0.5gmTiO2 pigment. The mixture was digested for 60 minutes at 1750 C with intermittent shaking for every 15 minutes. Cool to room temperature and transfer to 100 ml volumetric flask, wash and make up to 100 ml. Filter the contents to a round bottom flask and titrate with ferric alum to find out the percentage of TiO2 in the solution. Lower the TiO2 content in solution better the coating. The particle size of residue, mainly undissolved silica, was measured and was found to be in range of 7 to 8 nm.

Example 1

[0023] 650 ml of TiO2 slurry of particle size 300 nm, havingTiO2 content of 300 gm, was heated to 700C. The initial pH of slurry was 9.5-10. 0.15 gm nano silica (silicon dioxide) was seeded to 29 ml (265 gm SiO2 per litre) sodium silicate solution - equivalent to make 2.5 % coating of nano silica on TiO2 - and was homogenously mixed. The resultant mixture was then slowly added to the TiO2 slurry over a duration of 15-20 minutes under constant stirring. The nano-seeded sodium silicate was added in order to make the coating of silica on TiO2to form at nano size. Said formation of nano silica causes to enhance the durability of TiO2. The slurry was then digested for thirty minutes (30 minutes) and the final pH of the slurry was made to 5.5 with H2SO4.

[0024] Further, to the above-said slurry was added a thoroughly mixed solution containing 0.3% citric acid and 0.1% isopropyl alcohol. Then, 0.15gm nano-alumina (Aeroxide AluC) was seeded to 24 ml (322 gm Al2O3 per litre) of sodium aluminate solution, equivalent to make 2.5% coating of nano alumina, and was homogeneously mixed. The nano-alumina seeding was done to obtain a coating of nano-alumina on TiO2. The resultant mixture was slowly added to the TiO2 slurry, wherein sulphuric acid was also simultaneously added to said slurry in order to keep the pH < 8. The slurry was then digested for 20 minutes and the final pH is made to 5.2 to 5.5 with H2SO4. The resultant cake was washed and micronized with organic coating. The durability index was found to be greater than 10 and dispersion was found to be greater than 7 in Hegman gauge.

Example 2

[0025] 650 ml of TiO2 slurry of particle size 300 nm, with TiO2 content of 300 gm was heated to 700C. The initial pH of the slurry was 9.5-10. Now, 0.15 gm of nano silica (fumed silica or silicon dioxide nano particles) was seeded to 8 ml (265 gm SiO2 per litre) sodium silicate solution, equivalent to make 1 % coating of nano silica on TiO2, and was homogenously mixed. The resultant mixture was then slowly added to the TiO2 slurry over a duration of 15-20 minutes under constant stirring. The nano-seeded sodium silicate was added in order to make the coating of silica on TiO2 to form at nano size. The slurry was then digested for thirty minutes (30 minutes) and the final pH of the slurry was adjusted to 5.5 with H2SO4.

[0026] Further, to the above-said slurry was added 0.3% citric acid and 0.1% isopropyl alcohol and was thoroughly mixed. Then, 0.15gm of nano alumina (Aeroxide AluC) was seeded to 7 ml (322 gm Al2O3 per litre) sodium aluminate solution, equivalent to make 1% coating of nano alumina, wherein the resultant mixture was then slowly added to the TiO2 slurry, wherein sulphuric acid was also simultaneously added to said slurry in order to keep the pH < 8. The resultant slurry was digested for 20 minutes wherein its final pH was made to 5.2 to 5.5 with H2SO4. The cake obtained is washed and micronized with organic coating. The Durability index was found to be > 10 and dispersion was > 7 in Hegman gauge. This pigment was suitable to be used as a coating grade.

Example 3

[0027] 650 ml of TiO2 slurry of particle size 300 nm, having TiO2 content of 300 gm, was heated to 70oC. The initial pH of the slurry was 9.5 - 10. Now, 0.15 gm of nano silica (fumed silica or silicon dioxide nano particles) was seeded to 50 ml (265 gm SiO2 per litre) sodium silicate solution, equivalent to make 5.5 % coating of nano silica on TiO2, and was homogenously mixed. The resultant mixture was then slowly added to the TiO2 slurry over a duration of 15-20 minutes under constant stirring. The slurry was then digested for thirty minutes (30 minutes) and the final pH of the slurry was made to 5.5 with H2SO4.

[0028] Further, to the above-said slurry was added 0.3% citric acid and 0.1% isopropyl alcohol mixture and was thoroughly mixed. Then, 0.15 gm of nano alumina (Aeroxide AluC) was seeded to 26 ml (322 gm Al2O3 per litre) sodium aluminate solution, equivalent to make 3.5% coating of nano alumina, wherein the resultant mixture was then slowly added to the TiO2 slurry, wherein sulphuric acid was also simultaneously added to said slurry in order to keep the pH less than 8.The resultant slurry was digested for 20 minutes and the final pH was made to 5.2 to 5.5 with H2SO4. Finally, the cake was washed and micronized. Durability index was found to be > 10 and dispersion was> 7 in Hegman gauge. This can be used as an exterior coating grade.

Example 4

[0029] 650 ml of TiO2 slurry of particle size 300 nm and having TiO2 content of 300 gm was heated to 70oC. The initial pH of the slurry was 9.5- 10. Now, 0.15 gm of nano silica (fumed silica or silicon dioxide nano particles) was seeded to 53 ml (265 gm SiO2 per litre) sodium silicate solution, equivalent to make 6.5 % coating of nano silica on TiO2, and was homogenously mixed. The resultant mixture was then slowly added to the TiO2 slurry over a duration of 15-20 minutes under constant stirring. The slurry was then digested for thirty minutes (30 minutes) and the final pH of the slurry was made to 5.5 with H2SO4.

[0030] Further, to the above-said slurry was added 0.3% citric acid and 0.1% isopropyl alcohol mixture and was thoroughly mixed. Then, 0.15 gm of nano alumina (Aeroxide AluC) was seeded to 20 ml (322 gm Al2O3 per litre) sodium aluminate solution, equivalent to make 3% coating of nano alumina, wherein the resultant mixture was then slowly added to the TiO2 slurry, wherein sulphuric acid was also simultaneously added to said slurry in order to keep the pH below 8.The resultant slurry was digested for 20 minutes and the final pH was made to 5.2 to 5.5 with H2SO4. Finally, the cake was washed and micronized. Durability index was found to be > 10 and dispersion was> 7 in Hegman gauge. This can be used as an exterior plastic grade.

Example 5

[0031] 650 ml of TiO2 slurry of particle size 300 nm and with TiO2 content of 300 gm was heated to 70oC. The initial pH was 9.5- 10. In this case, there was no silicate coating provided. 0.3% citric acid and 0.1% isopropyl alcohol mixture was added to the slurry and homogenously mixed. 0.15 gm of nano alumina (Aeroxide Aluc) was seeded into 7 ml (322 gm Al2O3 per litre) of sodium aluminate equivalent to make 1% coating of nano alumina on TiO2, wherein the resultant mixture was then slowly added to the TiO2 slurry, wherein sulphuric acid was also simultaneously added to said slurry in order to keep the pH < 8. The resultant slurry was digested for 30 minutes and then final pH was made to 5.2 to 5.5 with H2SO4. The cake was washed and micronized with organic coating. Durability index was >10 and dispersion was >7 in Hegman gauge. This can be used as a plastic grade.

Example 6

[0032] 650 ml of TiO2 slurry of particle size 300 nm and with TiO2 content of 300 gm was heated to 70oC. The initial pH was 9.5-10. In this case, there was no silicate coating. 0.3% citric acid and 0.1% isopropyl alcohol mixture was added to the slurry and homogenously mixed. 0.15 gm of nano alumina (Aeroxide Aluc) was seeded into 26 ml (322 gm Al2O3 per litre) of sodium aluminate equivalent to make 3% coating of nano alumina on TiO2, wherein the resultant mixture was then slowly added to the TiO2 slurry, wherein sulphuric acid was also simultaneously added to said slurry in order to keep the pH < 8. The resultant slurry was digested for 30 minutes and then final pH was made to 5.5 with H2SO4. The cake was washed and micronized with organic coating. Durability index was found to be >10 and dispersion was> 7 in Hegman gauge. This can be used as an ink grade.

[0033] Although the present invention has been described in connection with the preferred embodiments thereof, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention unless they depart there from.