Claims:
1. A hydrophilic titanium dioxide pigment comprising
a coating of 0.1% to 0.5% of a citrate tungstate complex and 0.75% to 1.05% of alumina on the surface of titanium dioxide pigment.

2. The hydrophilic titanium dioxide pigment as claimed in claim 1, wherein the coating comprises 0.1% to 0.5% of a citrate tungstate complex and 0.25% to 0.35% boehmite alumina on the surface of titanium dioxide pigment.

3. The hydrophilic titanium dioxide pigment as claimed in claim 1 or 2, further comprises a coating of 0.25% to 0.35% amorphous alumina on said boehmite alumina coating.

4. The hydrophilic titanium dioxide pigment as claimed in claim 3, wherein further comprises a coating of 0.25% to 0.35% boehmite alumina on said amorphous alumina coating.

5. The hydrophilic titanium dioxide pigment as claimed in claims 1 to 4 has a particle size of 0.29 to 0.31 micron.

6. The hydrophilic titanium dioxide pigment as claimed in claims 1 to 5 has a moisture of less than 0.5%.

7. A process of coating a hydrophilic titanium oxide pigment comprising:
adding 0.1% to 0.5% of citrate tungstate complex to a slurry of titanium dioxide; adding 0.75% to 1.05% of alumina to said slurry; and forming a coating of citrate tungstate complex and alumina on said titanium dioxide surface.

8. The process as claimed in claim 7, wherein comprises adding 0.1% to 0.3% of citrate tungstate complex to a slurry of titanium dioxide; adding 0.75% to 1.05% of alumina to said slurry; and forming a coating of citrate tungstate complex and alumina on said titanium dioxide surface.

9. The process as claimed in claim 7 or 8, wherein adding alumina to said slurry comprises adding 0.25% to 0.35% boehmite alumina at an acidic pH.

10. The process as claimed in claim 9, wherein further comprises:
a. adding 0.25% to 0.35% of an amorphous alumina after adding said boehmite alumina at an acidic pH; and
b. adding 0.25% to 0.35% of a boehmite alumina after adding said amorphous alumina layer at a neutral pH.

11. The process as claimed in claim 7, wherein process for preparing the citrate tungstate complex comprising:
a. adding 10% citric acid and 10% sodium tungstate in a ratio of 1:1; and
b. adjusting the pH to 1.8 to 2.0.
, Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]

A HYDROPHILIC TITANIUM DIOXIDE PIGMENT FOR PLASTIC AND PROCESS OF PREPARING THEREOF

THE KERALA MINERALS AND METALS LIMITED HAVING ADDRESS AT SANKARAMANGALAM, CHAVARA, KOLLAM, KERALA 691583, INDIA.

THE FOLLOWING SPECIFICATION DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of the Invention
The present invention relates to a hydrophilic, non agglomerated, easy dispersible and medium durable alumina coated titanium dioxide (TiO2) pigment for heavily TiO2 loaded plastic masterbatch applications and an improved process for preparing thereof.
Background of the Invention
Hydrophobic TiO2 pigments are known to be used for making heavily TiO2 (60-70%) loaded plastic master batches due to easy dispersion and low filter Pressure value FPV) in plastic medium. Hydrophilic TiO2 pigment finds its application only in lower TiO2 (40-50 %) loaded plastic master batches as hydrophilic TiO2 pigment are not suitable for heavily TiO2 (60-70%) loaded plastic master batch applications due to the low dispersion, high Filter Pressure Value (FPV) values and lacing problem of hydrophilic TiO2 in plastic medium. Moreover, the blending of hydrophilic TiO2 with polymer requires more consumption of energy compared to hydrophobic TiO2 due to very low dispersion of hydrophilic TiO2 with polymer.
However, producing hydrophobic TiO2 pigment is complex, time consuming and expensive compared to the producing of hydrophilic TiO2 pigment. Separate production streams were required in TiO2 production plant for producing hydrophilic TiO2 and hydrophobic TiO2 pigment, since contamination of one pigment with another create problems in end use applications.
It is known that TiO2 particles with surface modifications improve bulk powder flow and dispersion. However, TiO2 pigment coated with metal oxide have more moisture content and cause dispersion and lacing problems in plastics. The moisture content of the multi oxide coated TiO2 pigment was more compared to single oxide coated pigment. Moreover, in single oxide coated pigment, the concentration of the oxide should be minimum to avoid dispersion problem in plastic. Even though, alumina was also a metal oxide, a threshold concentration of alumina coating on TiO2 surface was required for getting the pigmentary properties and also to improve the flowability of pigment during its manufacturing.
US 3,523,810 discloses boehmite alumina coating on titanium dioxide pigment with varied concentration of alumina coating from 0.5 to 10% at alkaline pH and temperature range of 70-100°C. Since, the amorphous phase alumina makes the pigment durable, the above type of pigment may not have good durability even though they exhibit good dispersion and pigmentary properties.
US 4,022,636 discloses an improved process for coating titanium dioxide with precipitated alumina in two phases for use as a pigment in plastics. First coating of amorphous alumina precipitated on titanium dioxide surface followed by second coating of boehmite alumina. The structure of alumina coating on titanium dioxide pigment varies with the pH range in which the alumina precipitated in an acidic range was amorphous and alumina precipitated on basic pH was boehmite phase. The boehmite phase of alumina improves the pigmentry properties of titanium dioxide where as amorphous for of alumina coating improves the handling characteristics associated with the manufacturing process. The above patent discloses that the titanium dioxide coated with about 1% of alumina possesses superior handling properties when half of the alumina coating was precipitated from acidic medium and remaining portion of the alumina coating was precipitated in basic range. However, anchoring of amorphous alumina over TiO2 surface is difficult compared to boehmite phase and there may be chances for conversion of amorphous phase to boehmite at alkaline pH.
US 5,700.318 discloses improved alumina coated titanium dioxide pigment having a first coating of boehmite alumina, a second coating of amorphous alumina and third coating of boehmite alumina were reported in. The pigment developed in above method reported to having good durability, dispersibility and optical properties in plastic conditions. The first boehmite coating was conducted at pH vale of 1.5, second amorphous phase at pH range of 3-5 and third bonhomie coating at pH range of 7-9. The amorphous alumina coating was stable under acidic pH. However, shifting of pH towards the alkaline region in the third phase coating the part of the amorphous phase may change to pseudoboehmite/ boehmite phase.
US 3,825,438 discloses a process to coating titanium dioxide pigment with hydrous oxides in the presence of polyhydric alcohol and/or carboxylic acid. The carboxylic acid used contained at least two carboxyl group and examples of such type acids were reported as oxalic acid, citric acid, tartaric acid etc. the alcohol and /or acid had high solubility in water to enable the intimate contact achieved between TiO2 and alcohol/acid. The process was reported in which alcohol and/or acid can be added to the titanium dioxide pigment at any convenient stage but prior to the completion of the deposition of the coating. The invention also reveals that alcohol or acid can be added prior to the addition of any coating reagent but it was usually added after the addition of coating reagents prior to the completion of acidic or alkaline reacting material.

Accordingly, there exists a need to develop a non agglomerated, hydrophilic, easy dispersible, medium durable and alumina coated Titanium dioxide (TiO2) pigment suitable for heavily TiO2 loaded plastic master batch applications with easy dispersion in plastic medium thereby having improved dispersion value, reducing the energy consumption, low filter pressure value (FPV) and solving the lacing problem in plastic medium.
Summary of the Invention
In one aspect, the present invention relates to a hydrophilic titanium dioxide (TiO2) pigment. The hydrophilic titanium dioxide pigment comprises coating of 0.1% to 0.5% of a citrate tungstate complex (CTC); and 0.75% to 1.05% of alumina on surface of the titanium dioxide pigment. The hydrophilic titanium dioxide pigment preferably comprises 0.1% to 0.3% of a CTC coating and 0.75% to 1.05% of alumina coating on said coated surface of the titanium dioxide pigment.
In an aspect the alumina coating comprises a coating of 0.25% to 0.35% boehmite alumina on the surface of the titanium dioxide; a coating of 0.25% to 0.35% amorphous alumina on said boehmite alumina coating; and a coating of 0.25% to 0.35% boehmite alumina on said amorphous alumina coating.
The alumina coating can also comprise a coating of 0.25% to 0.35% boehmite alumina. The hydrophilic titanium dioxide pigment can have a particle size of about 0.29 to 0.31 micron. The hydrophilic titanium dioxide pigment can have a moisture of less than 0.5%.
In another aspect, the process of preparing a hydrophilic titanium oxide pigment comprises adding 0.1% to 0.5% of citrate tungstate complex to a slurry of titanium dioxide; adding 0.75% to 1.05% of alumina to said slurry; and forming a coating of citrate tungstate complex and alumina on said titanium dioxide surface. The citrate tungstate complex preferably is in a range of 0.1% to 0.3%. The process for preparing the citrate tungstate complex comprises adding 10% citric acid and 10% sodium tungstate in a ratio of 1:1; and adjusting the pH to about 1.8 to about 2.0.
In another aspect, the adding alumina on said surface to said slurry comprising citrate tungstate complex and titanium dioxide comprises adding 0.25% to 0.35% boehmite alumina at an acidic pH. The process further comprises adding 0.25% to 0.35% of an amorphous alumina after adding said boehmite alumina at an acidic pH; and adding 0.25% to 0.35% of a boehmite alumina layer on said amorphous alumina layer at a neutral pH.
Brief Description of Drawings
Figure 1 shows Transmission electron microscopy (TEM) images of the TiO2 pigment according to a preferred embodiment of the present invention;
Figure 2 shows a graph of resistivity of TiO2 cake during washing with water VS quantity of water in comparison to the existing grade; and
Figure 3 shows extrusion pressure developed in 70% TiO2 pigment loaded Linear Low Density Polyethane (LLDP) master batches according to the present invention.

Detailed Description of Invention
The present invention relates to an improved process for preparing hydrophilic titatnium dioxide pigment. The present invention relates a TiO2 pigment coated with citric acid tungstate complex (CTC) and alumina. The addition of CTC improves the non agglomeration of TiO2 particle, stabilize the amorphous phase of alumina coating and minimize the shifting of amorphous phase of alumina to other phase while changing the pH. The citric acid tungstate complex (CTC) is added before alumina coatings for improved dispersion properties of TiO2 as well to improve the coating properties of alumina. The surface modified TiO2 pigment exhibit good optical and rheological properties, low oil absorption values, medium durability and easy dispersion especially in plastic medium.
In an embodiment, the present invention provides a hydrophilic titanium dioxide pigment. The hydrophilic titanium dioxide (TiO2) pigment comprises coating 0.1% to 0.5% of a citrate tungstate complex (CTC) and 0.75% to 1.05% of alumina on the surface of the TiO2 pigment.
The citric acid tungstate complex (CTC) can be in a range from about 0.10% to about 0.5% by weight, most preferably in a range from about 0.1% to about 0.3%, based on the weight of said pigment material. The optimum concentration range of CTC is preferably in the range of 0.1% to 0.3% of TiO2 pigment, above which affects the handling of pigment during the processing.
The hydrophilic titanium dioxide pigment can have particle size of about 0.29 to 0.31 micron.
The alumina coating can be a multi-layer coating. The multi-layer coating can be of different phase of alumina TiO2 pigment. The multi layer coating can be a single-phase alumina coating, two-phase alumina coating or a three-phase alumina coating. The alumina coating agent can be selected from sodium aluminate.
In an embodiment, the present invention provides titanium dioxide pigment having 0.1% to 0.5% of CTC coating and a single-phase alumina coating on said surface of the TiO2 pigment. The single-phase alumina coating of the present invention comprises a coating of 0.75% to 1.05% boehmite alumina on the surface of the TiO2 pigment comprising CTC.
In another embodiment, the present invention provides titanium dioxide pigment having 0.1% to 0.5% of CTC coating and a two-phase alumina coating comprising 0.35% to 0.525% boehmite alumina on said TiO2 pigment surface comprising CTC and 0.35% to 0.525% amorphous alumina over said boehmite alumina coating.
In a preferred embodiment, the present invention provides titanium dioxide pigment having 0.1% to 0.5% of CTC coating and a three-phase alumina coating on said surface of the titanium dioxide pigment comprising CTC. The three-phase alumina coating has a first coating of 0.25% to 0.35% boehmite alumina on the TiO2 pigment surface comprising CTC; a second coating of 0.25% to 0.35% amorphous alumina over said boehmite alumina coating; and a third coating of 0.25% to 0.35 % boehmite alumina over said amorphous alumina coating. Figure 1 shows transmission electron microscopy (TEM) images of the TiO2 pigment according to the preferred embodiment of the present invention. The TEM image of the Figure 1 clearly shows that the coating of citrate tungstate complex (CTC) and alumina on the surface of the titanium dioxide pigment is very uniform and thin layer in nature. This thin layer and uniform coating of CTC and alumina improve the properties of modified TiO2 pigment.
It has been found that the coating of different phase of alumina coating agent with citric acid tungstate complex (CTC) improves the optical and rheological properties of TiO2 and also to improve the pigmentary properties of TiO2. Durability of the TiO2 pigment grade showed an improved to a value of 6.0 compared to 5.0 for existing grade. Thus, the present invention provides an improved, non agglomerated, hydrophilic, easy dispersible and medium durable TiO2 pigment that is suitable for use in for heavily loaded plastic master batches application.
In an embodiment, the present invention provides a process for preparing a hydrophilic titanium oxide pigment. 0.1% to 0.5% of citrate tungstate complex (CTC), preferably 0.1% to 0.3% of CTC can be added to a slurry of titanium dioxide; adding 0.75 % to 1.05% of an alumina to said slurry where CTC and alumina forms a coating on the TiO2 pigment.
Raw titanium dioxide pigment is slurried with water before subjecting for surface coating procedures. The raw titanium dioxide slurry can be subjected to fine milling using bead mill for deagglomeration of particles known in the art. The slurry is heated to about 68°C to 72°C. pH of the treatment slurry can be adjusted to about 6.0 by using mineral acid such as sulphuric acid. 0.1% to 0.5% of citric acid tungstate complex (CTC) can be added to slurry.
The citrate tungstate complex of the present invention can be prepared by adding 10 % citric acid in water and 10 % sodium tungstate in water in a 1:1 ratio. pH of said mixture is adjusted to about 1.8 to about 2.0. The concentration of citric acid tungstate complex (CTC) to titanium dioxide pigment can be in a range of about 0.1% to 0.5% and preferably 0.1% to 0.3%. The citric acid tungstate complex can be added to the treatment tank comprising the TiO2 slurry before alumina coating to improve the performance of modified pigment in plastic applications. Citric acid tungstate complex (CTC) is added to titanium dioxide oxide pigment material slurry followed by adjusting pH of the slurry comprising the CTC and TiO2 slurry in a range of about 1.8 to 2.0, most preferably 2.0.
The process includes adding of layers of alumina coating on said surface of the TiO2 pigment comprising CTC. The coating can be a single-phase coating or a multi-layer coating such as, two-phase coating or three-phase coating.
In an embodiment, the present invention provides a process of preparing titanium dioxide pigment having single phase coating of alumina. The process comprises adding 0.1% to 0.5% of citric acid tungstate complex and 0.75% to 1.05% of alumina to TiO2 treatment slurry at an acidic pH of about 2.0 and forming a coating of CTC and alumina on titanium dioxide pigment. The pH can be adjusted up to 3.0. Alumina can be added to the titanium dioxide treatment slurry comprising the citric acid tungstate complex by adding as sodium aluminate in water solution to a volume equivalent of 0.75% to 1.05% of alumina, preferably 0.9% of alumina to TiO2. The slurry is then digested to coat boehmite alumina phase on TiO2.
In another embodiment, the present invention provides a process of preparing titanium dioxide pigment having a two-phase coating of alumina on said surface of the TiO2 pigment. The process comprises adding 0.1% to 0.5% of citric acid tungstate complex and adding 0.35% to 0.525% of alumina to TiO2, treatment slurry at an acidic pH of about 2.0. The pH can be adjusted up to 3.0. Alumina can be added to the titanium dioxide treatment slurry comprising the citric acid tungstate complex by adding sodium aluminate in water solution to a volume equivalent of 0.35% to 0.525% of alumina, preferably 0.45% of alumina to TiO2. The slurry is then digested to coat boehmite alumina phase on TiO2 with CTC. To the boehmite coated titanium oxide with CTC, a second coating of amorphous alumina is added at an acidic pH of about 3. The amorphous alumina can be coated by adding sodium aluminate in water solution to a volume equivalent of 0.35% to 0.525%, preferably 0.45% of alumina to TiO2 slurry at pH 3.0. The pH is adjusted to pH 4.0. The slurry is then digested to coat amorphous alumina phase over the boehmite coat.
In a two-phase coating, the top amorphous alumina coating changes to boehmite phase during the down stream process like superheated micronization and the total alumina coated in two-phase behaves as a single-phase alumina coated pigment and properties of two-phase alumina coated has the same as that of single-phase alumina coating. The HSD values for both single phase and two phase TiO2 pigment is of 6.5. This value of 6.5 was less as compared to the three phase TiO2 pigment having preferred value of >6.75. The oil absorption (OA) value of TiO2 pigments coated with CTC and single or two phase alumina were 19 and 18.5 respectively. These values are slightly improved as compared to the existing grade pigment having the OA value of 20.
In a preferred embodiment, the present invention provides a process of preparing titanium dioxide pigment having a coating of 0.1% to 0.5% of citric acid tungstate complex (CTC) and a three-phase coating of an alumina on said surface of the TiO2 pigment. The process comprises adding 0.1% to 0.5% of citric acid tungstate complex and adding 0.25% to 0.35 % of alumina to TiO2 treatment slurry at an acidic pH of about 2.0. The pH can be adjusted up to 3.0. Alumina can be added to the titanium dioxide treatment slurry by adding sodium aluminate in water solution to a volume equivalent of 0.25% to 0.35% of alumina, preferably 0.3% of alumina to TiO2. The slurry is then digested to coat boehmite alumina phase on surface of TiO2 pigment with CTC. To the boehmite coated titanium oxide with CTC, a second coating of amorphous alumina is added at an acidic pH of about 3. The amorphous alumina can be coated by adding sodium aluminate in water solution to a volume equivalent of 0.25% to 0.35%, preferably 0.3% of alumina to TiO2 slurry at pH 3.0. The pH is adjusted to 4.0. The slurry is then digested to coat amorphous alumina phase over the boehmite coat. To the amorphous alumina coated pigment, coating 0.25% to 0.35% boehmite alumina layer on the amorphous alumina layer at a neutral pH is provided. The third coating can be achieved by addition of sodium aluminate in water solution to a volume equivalent of 0.25% to 0.35%, preferably 0.30% of alumina to TiO2 was added to the TiO2 slurry at pH 4.0. pH is then adjusted to 6.0 and digested for final coating of boehmite alumina phase on top layer of surface of TiO2 pigment with CTC.
The titanium dioxide pigment of the present invention is easily dispersible in polymer matrix at 70% load and shows improved dispersion value of the TiO2 pigment. Figure 3 shows extrusion pressure developed in 70% TiO2 pigment loaded LLDP master batches according to the present invention. The low extrusion pressure of the polymer melt containing the developed TiO2 pigment indicates the easy dispersion of developed pigment in polymer matrix. Thus, the coated titanium dioxide pigment of the present invention solves the problem of generating more torque in the blending machine during blending process of TiO2 pigment with polymer and thereby reduces the energy consumption. The TiO2 pigment also showed improved performance of low filter pressure values, low torque values while blending with plastic medium. Further, the water required by pigment of present invention under laboratory condition to achieve resistivity over 10000 ohm was significantly lower than the regular pigment to achieve the same resistance value. Thus, the pigment and the process of the present invention also provides water saving of about 1.2L per 1.0 KG of TiO2 pigment produced.
The process of making the modified pigment was convenient as making of the conventional plastic grade TiO2 pigment manufacturing. The TiO2 pigment of the present invention showed comparatively high optical properties such as high brightness, gloss, colour values etc. as well as good dispersion properties such as low oil absorption values, high HSD values etc. compared to the existing grade. Moreover, the production of new TiO2 pigment grade was very convenient and consumes less water consumption compared to the existing known grade. The conventional plastic grade TiO2 pigment coated with metal oxide have more moisture content and caused dispersion and lacing problems which is reduced by the TiO2 pigment of the present invention which was having low hydroxyl content on the surface. By minimizing the hydroxyl group on the surface of the hydrophilic TiO2 pigment of the present invention solved the lacing problem in plastic medium. The process of the present invention is very convenient and consumes less water consumption compared to the existing plastic grade. An energy savings of 23% is noticed in the present invention hydrophilic TiO2 pigment compared to a hydrophobic grade TiO2 during 60% plastic master batch production. The amorphous alumina improves the durability of pigment. The amorphous alumina coating on TiO2 is to be carried out under very precise condition, otherwise, amorphous phase changed to pseudoboehmite or boehmite. The sandwich of amorphous alumina phase between boehmite alumina phase gives additional stability to amorphous phase. CTC has good interaction with TiO2 pigment and leading non agglomeration of particle. The CTC also interacts with alumina especially in amorphous phase leading to close packing of amorphous phase alumina and is responsible for transferring the pigment of the present invention from low durable grade to medium durable grade. The TiO2 pigment of the present invention showed improved durability value of 6.0 compared to our existing grade having a durability value of 5.0. The filtration time required by the present invention is lower than the time required for regular plastic grade pigment and hence the lower filtration time increases the production capacity in production plant.
Examples
Examples are set forth herein below and are illustrative of different amounts and types of reactants and reaction conditions that can be utilized in practicing the disclosure. It will be apparent, however, that the disclosure can be practiced with other amounts and types of reactants and reaction conditions than those used in the examples, and the resulting devices various different properties and uses in accordance with the disclosure above and as pointed out hereinafter.
The properties of the newly developed pigment were compared with the existing hydrophilic grade pigment and also with a TiO2 pigment of hydrophobic nature.
TiO2 pigment under chloride process was produced by the vapor phase oxidation of titanium tetrachloride with oxygen under 1000°C. The aluminium chloride was added with titanium tetrachloride as a nuclei for crystal growth of titanium dioxide before oxidation. The TiO2 particle was built up over the oxidized aluminium chloride (alumina) particle. The raw Titanium dioxide thus produced contains a core alumina over the TiO2 particles. The percentage of alumina inside TiO2 particle was around 1%. The raw pigment produced in the oxidation process was modified for different end use application by subjecting to surface coating with other organic and inorganic substances usually under wet process. The raw TiO2 pigment was slurried with water before subjected for surface coating procedures. The raw TiO2 slurry was subjected for fine milling using bead mill for deagglomeration of particles. The bead mill outlet TiO2 slurry contained 90% particle having particle size less than 0.63 micron and HSD value around 5.5 (Hegman guage). The bead mill outlet titanium dioxide slurry with specific gravity 1.36 g/cc and containing TiO2 content of 400gpl were taken for surface treatment studies. The process sequence of new surface treatment process for developing new TiO2 pigment grade is given below:
Example 1 – Three-phase coating process
1. Pumping of titanium dioxide slurry to the treatment tank (slurry contain approximately 400 gpl of TiO2 pigment and pH of 9.0, specific gravity 1.36g/cc).
2. Heating the slurry at 68°C to 72°C.
3. pH of the treatment slurry was adjusted to 5.8-6.2, preferably 6.0 by using sulphuric acid.
4. 10% citric acid in water medium and 10% of sodium tungstate in water medium were prepared and 1: 1 ratio of mixing of above solutions. The pH of the mixed solution were adjusted to 1.8-2.0 by addition sulphuric acid and stirred at 30 minutes for the formation of citric acid tungstate complex (CTC). The CTC addition to the treatment slurry in required quantity (0.10% of CTC equivalent to TiO2 pigment in slurry) (addition either by bulk addition to the treatment slurry taken in the treatment tank or staggered addition along with taking of treatment slurry in treatment tank as in step 1).
5. Adjusting the pH 1.8-2.0 by using sulphuric acid.
6. Addition of Sodium aluminate in water solution to a volume equivalent of 0.25%-0.35%, preferably 0.3% of alumina to TiO2 to the treatment slurry at pH 2.0 and adjust the pH to 2.8-3.2, preferably 3.0. Digest the slurry for 10 minutes to coat boehmite alumina phase on TiO2.
7. Addition of Sodium aluminate in water solution to a volume equivalent of 0.25%-0.35%, preferably 0.3% of alumina to TiO2 to the TiO2 slurry at pH 3.8-4.2, preferably 4.0 and adjust the pH at 4.0 and digest the slurry for 10 minutes to coat amorphous alumina phase.
8. Addition of Sodium aluminate in water solution to a volume equivalent of 0.25%-0.35%, preferably 0.3% of alumina to TiO2 to the TiO2 slurry at pH 4.0 and adjust the pH to 5.8-6.2, preferably 6.0. Digest the slurry for 10 minutes for final coating of boehmite alumna phase on top layer of TiO2 pigment.
9. Filter the slurry and wash the slurry with DM water to achieve the resistivity over 10000 ohm.
10. Drying the filtered cake at 175 -185°C, preferably 180oC for 5 hours.
11. Adding the dried cake with 0.2% of Trimethlolethane and subjecting to steam micronization.
12. The micronized pigment having an average particle size of 0.29 - 0.31 micron.
13. The moisture content of the pigment is less than 0.5%.
The process described above is a batch process. The concentration of CTC to TiO2 pigment varied from 0.1 to 0.5%. The addition of CTC was carried out either along with step1 or step 4.
The typical batch treatment procedure under laboratory condition was given in table 1.
Table 1: Newly Developed TiO2 pigment Grade
Steps Producing New TiO2 Grade
1 Volume of slurry 10 L
2 Initial pH of slurry 8.5-9.5
3 pH of slurry by adding sulphuric acid 5.8-6.2 ( preferably 6.0)
4 CTC addition to treatment slurry in treatment tank 0.10 % TiO2
5 Slurry Temperature 70 +/- 2oC
6 Silica addition Nil
7 Sulphuric acid addition pH = 1.8 - 2.0
8 Addition of sodium aluminate (flow rate of 25 Litre per minute) and
(Sulphuric acid to maintain pH between 2.8-3.2) 0.25-0.35%, (preferably 0.3 % ) of TiO2
9 Digestion time 10 Min
10 Addition of sodium aluminate (flow rate of 25 Litre per minute) and
(Sulphuric acid to maintain pH between 3.8-4.2) 0.25-0.35%, (preferably 0.3 % ) of TiO2
11 Digestion time 10 Min
12 Addition of sodium aluminate (flow rate of 25 Litre per minute) and
(Sulphuric acid to maintain pH between 5.8-6.2) 0.25-0.35%, (preferably 0.3 %) of TiO2
13 Digestion time 10 Min
14 Final pH 5.8 -6.2
15 Filtration Vacuum filter
16 Filter cake resistivity 10000 ohm (min)
17 Drying Electric oven
18 Micronization Super heated steam micronization

Example 2 – The process is same as example 1. Only the quantity of CTC was enhanced to 0.15% of TiO2 content in slurry in step 3.
Example 3 - The process is same as example 1. Only the quantity of CTC was enhanced to 0.30% of TiO2 content in slurry in step 3.
Example 4 - The process is same as example 1. Only the quantity of CTC was enhanced to 0.40% of TiO2 content in slurry in step 3.
Example 5 - The process is same as example 1. 0.15% of CTC was added along with taking treatment slurry in staggered manner in step 2 before adjusting the slurry pH to 5.8 - 6.0.
Example 6 - The process is same as example 1. Only 0.15% of Citric acid was added instead of CTC in step 3.
Example 7 - The process is same as example 1. Only 0.15% sodium tungstate was added instead of CTC in step 3.
Example 8 – Single-phase coating process:
1. Titanium dioxide slurry was used for oxide coating containing 400 gpl of TiO2 pigment (specific gravity 1.36 g/cc) pH: 9.0, particle size: 90% of particle below 0.5 micron, HSD: 5.5, OA: 20.
2. The slurry was heated at 70°C and maintained at 70 +/- 2°C and pH of slurry was adjusted to 5.8 – 6.0 by adding sulphuric acid.
3. The slurry of Citric acid tungstate complex (CTC) was prepared in water and 0.15% of CTC equivalent to TiO2 pigment was added in the slurry.
4. The pH was adjusted to 1.8-2.2 (preferably 2.0) by using sulphuric acid.
5. Addition of required volume of sodium aluminate in water solution equivalent of 0.75-1.05% (preferably 0.9%) of alumina to TiO2 pigment was done to the TiO2 slurry. The pH was adjusted to a range of 2.8-3.2 (preferably pH-3.0) and digesting the slurry for 10 minutes to coat 0.9% of boehmite alumina phase on TiO2.
6. pH of the slurry was adjusted to a range of 5.8-6.2, preferably 6.0.
7. The slurry was filtered and washed with DM water to achieve the resistivity over 10000 ohm followed by drying the cake at 175-180°C for 5 hours.
8. To the dried cake was added 0.2% of Trimethlolethane and subjected to steam micronization.
Example 9: Two-phase coating process:
1. Titanium dioxide slurry used for oxide coating containing 400 gpl of TiO2 pigment (specific gravity 1.36 g/cc) pH: 9.0, particle size: 90% of particle below 0.5 micron, HSD: 5.5, OA: 20.
2. Heating the slurry at 70°C and maintained at 70 +/- 2°C and pH of slurry was adjusted to 6.0 -5.8 by adding sulphuric acid.
3. Prepare CTC in water and add 0.15% of CTC equivalent to TiO2 pigment in slurry.
4. Adjusting the pH 1.8-2.2 (preferably 2.0) by using sulphuric acid.
5. First addition of required volume of sodium aluminate in water solution equivalent of 0.35%-0.525% (preferably 0.45%) of alumina to TiO2 pigment to the TiO2 slurry The pH was adjusted to a range of 2.8-3.2 ( preferably pH-3.0) and digest the slurry for 10 minutes to coat 0.45% of boehmite alumina phase on TiO2.
6. Second addition of required volume of sodium aluminate in water solution equivalent of 0.35-0.525% (preferably 0.45%) of alumina to TiO2 pigment was added to the TiO2 slurry. The pH was adjusted to a between 3.8-4.2 (preferably pH-4.0) and digest the slurry for 10 minutes to coat 0.45% of amorphous alumina phase on TiO2.
7. The pH of the slurry was adjusted to pH 5.8- 6.2, preferably 6.0 by adding sulphuric acid.
8. Filter the slurry and wash the slurry with DM water to achieve the resistivity over 10000 ohm followed by drying the cake at 175- 180°C for 5 hours.
9. The dried cake where added with 0.2% of Trimethlolethane and steam micronization.
Example 10- Surface morphology of pigment
The surface morphology of pigment produced under example 2 was shown in the TEM images as illustrated by Figure 1. The TEM image of the Figure 1 clearly shows that the coating of CTC and alumina on the TiO2 surface was very uniform and thin layer in nature. This thin layer and uniform coating of CTC and alumina improves the properties of modified TiO2 pigment.
Example 11- Resistivity of TiO2 cake v/s quantity of water
The treated slurry was filtered and washed with DM water to achieve resistivity over 10000 ohm before subjected to micronization. The quantity of DM water required for washing 250 gram of modified pigment produced in example 2 to achieve the resistivity above 10000 ohm during filtration processes was given in Figure 2. The quantity of water required under the same condition of existing grade was also given in same figure for comparison. From the Figure 2 it is illustrated that 1.2L of water was required by 250 gram of pigment of present invention under laboratory condition to achieve resistivity over 10000 ohm. Under the same condition, the regular pigment consumed 1.5 L of water to achieve the same resistance value. There was water saving of 1.2L per 1.0 KG of TiO2 pigment produced by the present invention. The filtration time required for 250 gram of pigment produced by the present invention was found to be 8 minute compared to 9 minute for regular plastic grade pigment. The lower filtration time increase the production capacity in production plant.
Example 12- Testing of properties of TiO2 pigments prepared in accordance with Examples 1-8:
The properties of the TiO2 pigment developed from examples 1 to 8 of the present invention were given in Table 2. For comparison purpose, the existing known plastic grade pigment was also given in the same table.
Table 2: Properties of TiO2 pigment
Example s 1 2 3 4 5 6 7 8 9 Existing grade
Brightness (L value) 98.1 98.5 98.3 98.1 98.5 98.0 98.0 98.0 98.0 98.0
Color (b value 1.5 1.42 1.45 1.43 1.44 1.45 1.42 1.43 1.43 1.40
OA (%) 15.8 15.2 15.5 15.5 15.2 16.2 16.5 19 18.5 20
HSD 6.75 7.0 7.0 7.0 7.0 6.75 6.75 6.5 6.5 6.5
Resistivity (ohm) 12987 13210 13212 12297 10828 10880 10912 8000 8500 6000
pH 6.0 6.2 5.8 6.0 6.1 6.0 6.1 6.0 6.0 5.8
Moisture (%) 0.40 0.40 0.44 0.45 0.40 0.50 0.50 0.5 0.5 0.5
Al2O3 (%) 1.8 1.9 2.0 2.1 2.0 2.0 2.0 2.0 2.1 2.5
TiO2 (%) 95.3 95.3 95.3 95.2 95.3 95.3 95.3 95.1 95.1 95.0
Organics, (%) 0.35 0.40 0.40 0.47 0.48 0.40 0.38 0.42 0.42 0.35
Rutile (%) 99 99 99 99 99 99 99 99 99 99
All the experiment produced pigment showed superior properties especially for brightness, OA (lower values preferred), and HSD. The 0.15% of CTC was found to be the optimum concentration and above which the pigment properties remain unaltered. Moreover, the CTC above 0.3% was adversely affecting the handling of pigment during manufacturing process. The lower OA values of 15.2 were achieved for 0.15% CTC coated pigment. All the pigments produced with CTC and three phase alumina coating were having HSD above 6.75. The alumina present on the surface of the pigment is responsible for the moisture content and all the pigment produced where having moisture content less than 0.5%. Even though, all the pigment produced in examples 1 to 7 showed improved performance compared to existing grade, very good performance was noticed for example 2 produced pigment and it was tested in plastic formulation.
Example 13: Performance of newly developed TiO2 pigment in 70% TiO2 loaded plastic master batch production using twin screw extruder
The twin screw extrusion tests were conducted with 70% TiO2 pigment loaded linear low-density polyethylene (LLDP) master batch. Zinc stearate at 0.5% by weight ratio of TiO2 was used in this formulation. The raw-meal preparation for producing 70% TiO2 loaded plastic master batches were given in table 3.
Table 3: 70% Master batch
Sl. No. Ingredient Quantity (g)
1 LLDP (Linear Low Density Polyethane) 428
2 TiO2 pigment 1000
3 Zinc Stearate 5
Total 1433

The experiments were conducted with twin screw extruder machine having five heating zones, with temperature ranging from 175 to 350oC. The screen pack used where having mesh size of 150 and 200 US mesh.
Example 14 - Extrusion pressure developed in 70% TiO2 pigment loaded LLDP master batches
The pressure developed during extrusion was given in the Figure 3. The extrusion pressure of the polymer melt loaded with 70% of newly developed TiO2 pigment was lower compared to the polymer melt loaded with existing grade TiO2 pigment. The low extrusion pressure of the polymer melt containing the developed TiO2 pigment indicates the easy dispersion of developed pigment in polymer matrix. The low extrusion pressure also decreases the power consumption; increase the service life of equipment, longer the master batch production without changing the screen pack.
Example 15 - Testing of TiO2 pigment developed according to present invention on 60% LLDP plastic master batch
The new TiO2 pigment developed was again tested on 60% LLDP plastic master batch in a production plant and compared with another hydrophobic grade TiO2 pigment. The raw material for production of 60% plastic master batch for each experiment contains 80 kg of LLDP, 135 kg of TiO2 and 10.0 kg of zinc stearate. Total production time for each experiment is about 30 minutes. Screen packs in the machine consist of four screens with mesh size of 60/80/100/150. There were 10 temperature zones with temperature varying from 92 to 182oC in increasing order. Test results of are summarized in Table-4.
Table 4 : 60% Master batch: Test results
Description Newly developed hydrophilic TiO2 grade (Present invention) Hydrophobic TiO2 grade pigment
Sr. No. Parameter Results
1 Motor roll power, Torque, N.m Ave.131
(112-150) Ave. 170
(150-190)
2 Back Pressure MP-1 ( Pa) Ave.30.75
(30.30-31.20) Ave.30.80
(30.30-31.30)
3 Post screen Pressure MP- 2 (Pa) Ave. 30.2
(29.00-31.40) Ave.30.7
(30.10-31.40)
4 Production (kg/ minute) 7.7 7.7
5 Duration of test, min. 30 30

The TiO2 pigment of the present invention showed improved performance in power consumption compared to hydrophobic pigment in 60% LLDP plastic master batch manufacturing. The motor roll power (torque) generated during blending of polymer with the developed TiO2 pigment varied from 112- 150 N.m with an average value of 131 N.m whereas for the hydrophobic pigment the values varied from 150-180 N. m with an average value of 170 N.m. An energy saving of 23% can be achieved in the case of the using the newly developed TiO2 pigment. The lesser value of motor power resulted from easy dispersion and lower melt flow Index of the developed TiO2 pigment in polymer melt. The lower value of motor roll will lead for easy production of heavily loaded master batch and also decrease the power consumption of the extruder. Moreover, the lower value improves the life of equipment especially the life of gear box. During the master batch extrusion process, the melt pressure before and after the screen pack are measured. The back pressure before screen pack was denoted by MP (1) and post screen pressure was denoted by MP (2). The breakeven point for the MP (1) pressure for the master batch production is 32.50 Pa maximum. The longer the processing duration to reach this pressure is an indication of easy dispersion and lack of un-dispersed aggregates and grits in the pigment. MP(2) was an indication of low melt flow viscosity which controls the melt flow pumping rate for consistent production rate and quality of strands. The average MP (1) readings of developed TiO2 pigment and other hydrophobic pigment tested respectively were 30.75 and 30.80 and corresponding MP (2) readings were 30.2 and 30.7 both of which were comparable. A little bit elastic behaviour of filter cake as well as the partial flotation in water of new developed TiO2 pigment produced was responsible for the low pressure values obtained during extrusion process. The lower pressure value supports continuous and longer run of the unit without intermittent changing the filter pad. The master batch production yields with both the pigment were same.
Example-16: Filter pressure Test value (FPV).
The filter pressure test was conducted in Marshal Filter test machine. The test was conducted as per DIN EN ISO 23900-5 : 2019 -01. Screen pack 1 and Mixture 2 preparation of the standard were followed during the extrusion process. The FPV value of the developed TiO2 pigment was found to be 0.03 bar/g. The low value of FPV indicates the easy dispersion of newly developed TiO2 Pigment in polymer matrix.
The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.
It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.