CLIAMS:We Claim:

1. A process for de-agglomeration of pigments comprising:
providing a pre-mix of pigment powders and medium in a premix vessel to provide a homogenized pigment mix involving controlling the viscosity of the said homogenized pigment mix in the range of 400 -1000 gms (Stormer viscosity); followed by
pumping of the thus obtained viscosity controlled homogenized pigment mix under pressure involving passing through a static mixer free of any moving parts to effect de-agglomeration of pigments.

2. A process for de-agglomeration of pigments as claimed in claim 1 wherein said static mixer free of any moving parts comprises of SMX geometry.

3. A process for de-agglomeration of pigments as claimed in anyone of claims 1 or 2 wherein said pumping of the thus obtained viscosity controlled homogenized pigment mix under pressure through a static mixer is done in the pressure range of 70-200 PSI.

4. A process for de-agglomeration of pigments as claimed in anyone of claims 1 to 3 wherein said viscosity of the said homogenized pigment mix in maintained preferably in the range of 500 to 900 g and more preferably in the range of 600 to 700 g and said pumping pressure is maintained preferably in the range of 90 to 160 PSI more preferably in the range of 120 to 150 PSI.

5. A process for de-agglomeration of pigments as claimed in anyone of claims 2 to 4 wherein said SMX geometry based static mixer comprise of 3 to 12, preferably 9 elements and said elements having aspect ratio of 0.8 to 1.2 preferably of 1.0.

6. A process for de-agglomeration of pigments as claimed in anyone of claims 1 to 5 wherein the passing of said viscosity controlled homogenized pigment mix under pressure through said static mixer is carried out in two passes.

7. A process for de-agglomeration of pigments as claimed in claim 6
wherein output from the static mixer is increased under same operating pressure by involving elements of higher diameter to obtain de-agglomerated pigments as pigment dispersion with full TS (Tinting Strength) values ranging from 97-103% against their respective references after only upto two passes.

8. A process for de-agglomeration of pigments as claimed in anyone of claims 1 to 7 comprising the steps of
(i) providing said static mixer;
(ii) pumping and passing said premix of pigment powders and medium as homogenized material with Stormer viscosity in the range of 400 to 1000 g through said static mixer under a pressure drop of 70-200 PSI and corresponding flow rates of 3-10 L/min;
(iii) allowing plurality of passes through the static mixer; and
(iv) obtaining therefrom de-agglomerated pigments as pigment dispersion.

9. A process for de-agglomeration of pigments as claimed in anyone of claims 1 to 8 wherein said step of providing homogenized premix pigment powders and medium involve gentle stirring in a paddle type mixer.

10. A process for de-agglomeration of pigments as claimed in anyone of claims 1 to 9optionally involving the step of sand milling for attaining said full TS (Tinting Strength) values at par with the reference standard.

11. A process for de-agglomeration of pigments as claimed in anyone of claims 1 to 10 involving de-agglomeration of pigments including Iron Oxides, Titanium Dioxide, Carbon Black, Quinacridone, Phthalocyanine, DPP, Azocondensation mono arilide, Isoindolinone, Quinophthalone, Dioxazine.

12. A process for de-agglomeration of pigments as claimed in anyone of claims 1 to 11 wherein said medium for providing the premix of pigments is selected from water, glycols, surfactants and/ or mixtures thereof.

Dated this the 29th day of April, 2015 Anjan Sen
Of Anjan Sen and Associates
(Applicants Agent)

,TagSPECI:FIELD OF INVENTION
The present invention particularly provides a process for de-agglomeration of pigments comprising providing a premix feed having controlled Stormer viscosity in the range of 400-1000 gms and passing it through static mixer under pressure of SMX geometry free of any moving parts and obtaining therefrom said de-agglomerated pigments as pigment dispersion. More particularly, the present invention provides for said process wherein output from the static mixer increasesunder same operating pressure by involving elements of higher diameter to obtain de-agglomerated pigments as pigment dispersion with full TS (Tinting Strength) values ranging from 97-103% against their respective references after only two passes.
Advantageously, thus the process of the present invention facilitates pigment de-agglomeration with higher levels of productivityin involving facile operation thus less time consuming and in being free ofmoving parts also requires less energy and saves energy substantially.

BACKGROUND ART
The manufacturing processes for preparing pigment dispersions vary widely depending upon the pigment and the specific application but typically they involve usage of high energy rotary devices such as saw tooth impeller, Rotor-stator,ball mills, sand mills etc.
Saw tooth Impellers consist of flat disk-shaped blades with serrations of unique design notched about its rim driven at a high speed on a vertical shaft. A rolling doughnut type circulation is induced by the rotation of impeller blade. The de-agglomeration is due to shearing and smashing, but the shearing action dominates.
Rotor stator consists of a rotor at the center and stator outside. Owing to the high rotor speed the mill base is drawn in to the dispersing head and is then thrown radially through the slots of the stator. The passage of material through the small gap between the rotor and the stator imparts high shear. Additionally the lamellar movement of the mill base causes shearing of pigment agglomerates. The decisive factor for the efficiency of dispersion is the result of shearing gradient and dwell time of the particle in the shearing field.
In sand mills a homogeneous mixture of pigment and vehicle is pumped through cylindrical bank of sand which is subjected to intense agitation. During passage through the agitated sand zone the mill base is caught and ground between the sand particles; astrong shearing action which effects the dispersion of the pigment in the vehicle. On emerging from the active sand zone, the dispersed mill base overflows through an exit often sized to permit free flowof the pigment dispersion but holding back the sand particles.
It is also not uncommon to use combination of devices, for e.g., a rotor-stator followed by sand milling.
While these devices are effective in breaking down pigment agglomerates to primary particles, they are energy intensive and since they contain moving parts operating at high rpm, require frequent maintenance. In case of Rotor-Stator, the clearance between the rotor and the stator is typically as low as 0.2 mm. When such devices operate at high rpm, there is considerable engineering effort required to ensure the alignment between the parts.
An alternative device for achieving breaking down of pigment agglomerates is a static mixer. As the name suggests, there are no moving parts here.
Static Mixers consist of a series of identical, motionless inserts (elements) that redistribute the fluid in radial and tangential directions. This is done using only the energy of the flowing liquid. Since there are no moving parts, these mixers are also called as motion-less mixers. Some of the known advantages of static mixers are lower energy consumption and less maintenance.
Many types of static mixers are known in literature and they are described by their geometry. For example, Kenics KM, HEV(High Efficiency Vortex), SMX, SMV etc., to name a few.
Kenics KM mixer consists of helical mixing elements which direct the material radially to the pipe walls and back to the centre. Additional velocity reversal and flow division result from combining alternating right- and left-hand elements, increasing mixing efficiency. The alternating helical elements of the KM Static Mixer continually divide, stretch and reorient the flow stream to produce complete mixing with minimum pressure drop.
In the HEV Static Mixer, the tab geometry maximizes the conversion of turbulent energy into efficient mixing. The HEV produces complete stream uniformity through controlled vortex structures generated by the mixing elements. Each tab of the HEV Static Mixer generates a pair of stream wise counter-rotating vortices that produce vigorous cross-stream mixing and rapid uniformity.
The SMX is composed oftwo elements, periodically repeated in an axial directionand placed in a circular tube. The second element is anidentical copy of the first element with 90° rotationin tangential direction. Each static element consists ofmultiple X-shaped cross-bars and the angle between these opposite cross-bars is 90 °. SMX mixer splits the material into individual streams that meet other streams as they flow transversely through the element.

In SMV mixer several stacked sheets of corrugated metal run at 30 or 45 ° to the pipeaxis. Adjacent elements are rotated 900 relative to each other. The mixer is predominantly used in the turbulent flow regime for mixing of fluids.

Use of static mixers is well known(R K Thakur et al, Trans IChemE, Vol 81, Part A, August 2003) for a long time but they came to be used more and more in the process industries since the 70’s. Heat transfer, mixing of liquids, liquid-liquid and gas-liquid dispersions are some of the applications in which static mixers have been used. Static mixer based processes are known to be energy efficient and also maintenance costs are low because of absence of moving parts. However, their use in solid-liquid systems are limited.

Reference is drawn to Japanese Patent JPS63268734 thatdescribes a process of using static mixer for preparing a dispersion of white pigment in a molten polymer. White pigment is first kneaded into part of the molten polymer where a concentrated mass is formed. This mass is subsequently dispersed in the virgin polymer using a static mixer so that a uniform dispersion of white pigment in the molten polymer is achieved. Although static mixer is used for preparing the final dispersion here, break up of pigment agglomerates could not be achieved using the static mixer.

German Patents DE 202005015303 and 102004059897 describe use of static mixer for dispersing pigment particles but here again the device is used to achieve uniform mixing of pigment particles in a carrier liquid and not for the purpose of breaking down pigment agglomerates.

US Patent 8252393 describes use of static mixer with pigment dispersions but use of static mixer for preparing the dispersions as such has not been taught. This patent teaches mixing of the dispersion already formed with polymeric coating materials using static mixer.

WO 2005030826 discloses use of static mixer for effective mixing of additives and pigments to polyurethane components.

Romanian Patent RO 96954 A2 19890530 describes use of static mixer turbulent flows to achieve uniform coloration of polymer suspensions with dyes and pigments. The focus of the invention is about ease of achieving uniform coloration at low energy consumption using the turbulent flows of static mixer. The de-agglomeration of pigment agglomerates using static mixer has not been taught in this prior art.

US Patent 6949138 describes preparation of pigment dispersions having narrow size distribution primarily for use in printing inks. The pigment particle formation is achieved under stirring by addition of pigment solution and a pigment insoluble medium. The invention here is formation of pigment particles of small size while mixing under agitation in dynamic or static mixers. In other words, use of static mixer is primarily for achieving rapid mixing of the two components so that pigment particles precipitate out. Break up of pigment agglomerates with use of static mixers is not taught in this prior art.

Russian publication authored by Nedialkov et al inLakokrasochnyeMaterialy I IkhPrimenenie (1990), (4), 74-6 Language Russian disclosed preparation of pigment slurries in a static mixer in the form of a tube and a nozzle consisting of three types of alternating elements wherein the three elements form a block. The first two elements are helical type; the helix of one rotating in the opposite direction of the previous and the third element has the shape of a star. Several such units consisting of blocks of three elements are present. As the linear velocity changed from 0.3 m/s to 1.5 m/s, the effectiveness of disaggregation improved. It is also described that at a particular velocity of 1.3 m/s when the slurry was circulated in a closed loop through the static mixer system consisting of 8 blocks, the authors did not find any further improvement in extent of disaggregation with time.

Therefore in the backdrop of the prevalent state of the art it is thus a longfelt need to provide for a facile and simple process for de-agglomeration of pigments involving static mixer with high levels of productivity based on the simplicity of operations whereby the productivity can be increased by simple maneuvering of the process parameters, which process in completely eliminating moving parts is energy saving as well as time saving.

OBJECTS OF THE INVENTION
It is thus the primary object of the present invention to provide for a process for the de-agglomeration of pigments involving static mixer which process based on the controlled viscosity of the homogenized premix of pigment powder and medium would be effectively de-agglomerated when passed through the static mixer under pressure.
It is another object of the present invention to provide for said process involving static mixer which static mixer in being selectively configured and in the absence of any moving parts would enable the de-agglomeration of pigments based on the controlled viscosity of the premix when passed under pressure.
It is yet another object of the present invention to provide for said process which in involving static mixer and in being free of any moving parts is energy saving process.
It is another object of the present invention to provide for said process with high levels of productivity based on the simplicity of operations and is thus also time saving whereby the productivity would increase by simple maneuvering of the process parameters.
It is another object of the present invention to provide for said process that would be industrially facile in involving simple operations and would involve lesser number of process steps to achieve de-agglomeration of pigments in only two passes.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention a process for de-agglomeration of pigments is provided comprising:
providing a pre-mix of pigment powders and medium in a premix vessel to provide a homogenized pigment mix involving controlling the viscosity of the said homogenized pigment mix in the range of 400 -1000gms (Stormer viscosity); followed by
pumping of the thus obtained viscosity controlled homogenized pigment mix under pressure involving passing through a static mixer free of any moving parts to effect de-agglomeration of pigments.

It is thus surprisingly found by way of the present invention that a process for de-agglomeration of pigments could be achieved based on the controlled viscosity of the pre-mix of pigment powder and medium which when passed through a configurationally simple static mixer free of any moving parts under pressure,effected de-agglomeration of pigments inadvantageously only two passes such as to obtain de-agglomerated pigments as pigment dispersion with full TS (Tinting Strength) values ranging from 97-103% against their respective references.
Significantly the process economizes on time and energywherein output from the static mixer and hence productivity could be advantageously increased to obtain the same effective de-agglomeration of pigments under same operating pressure by simply involving elements of higher diameter in said static mixer, and further said static mixer in being free of any moving parts is energy efficient.
According to a preferred aspect of the present invention said process for de-agglomeration of pigments is provided wherein said static mixer free of any moving parts comprises of SMX geometry.
Preferably in said process for de-agglomeration of pigments said pumping of the thus obtained viscosity controlled homogenized pigment mix under pressure through a static mixer is done in the pressure range of 70-200 PSI.
According to another preferred aspect of the present invention in said process for de-agglomeration of pigments said viscosity of the said homogenized pigment mix is maintained preferably in the range of 500 to 900 g and more preferably in the range of 600 to 700 g and said pumping pressure is maintained preferably in the range of 90 to 160 PSI more preferably in the range of 120 to 150 PSI.

According to a yet another preferred aspect of the present invention in said process for de-agglomeration of pigments said SMX geometry based static mixer comprise of 3 to 12, preferably 9 elements and said elements having aspect ratio of 0.8 to 1.2 preferably of 1.0.
Advantageously, in said process for de-agglomeration of pigments wherein the passing of said viscosity controlled homogenized pigment mix under pressure through said static mixer is carried out in two passes.
According to another preferred aspect of the present invention a process for de-agglomeration of pigments is provided wherein output from the static mixer is increased under same operating pressure by involving elements of higher diameter to obtain de-agglomerated pigments as pigment dispersion with full TS (Tinting Strength) values ranging from 97-103% against their respective references after only upto two passes.
According to a yet another preferred aspect of the present invention said process for de-agglomeration of pigments is provided comprising the steps of
(i) providing said static mixer;
(ii) pumping and passing said premix of pigment powders and medium as homogenized material with Stormer viscosity in the range of 400 to 1000 g through said static mixer under a pressure drop of 70-200 PSI and corresponding flow rates of 3-10 L/min;
(iii) allowing plurality of passes through the static mixer; and
(iv) obtaining therefrom de-agglomerated pigments as pigment dispersion.
Preferably, in said process for de-agglomeration of pigments said step of providing homogenized premix pigment powders and medium involve gentle stirring in a paddle type mixer.
According to yet another preferred aspect of the present invention said process for de-agglomeration of pigments optionally involve the step of sand milling for attaining said full TS (Tinting Strength) values at par with the reference standard.
According to another preferred aspect of said process for de-agglomeration of pigments wherein the pigments including Iron Oxides, Titanium Dioxide, Carbon Black, Quinacridone, Phthalocyanine, DPP, Azocondensation mono arilide, Isoindolinone, Quinophthalone, Dioxazine are deagglomerated.
Preferably, in said process for de-agglomeration of pigments said medium for providing the premix of pigments is selected from water, glycols, surfactants and/ or mixtures thereof.
The present invention is described hereunder in greater details in relation to the non-limiting exemplary illustrations and figure.
BRIEF DESCRIPTION OF ACCOMPANYING FIGURE
Fig. 1: illustrates the experimental setup of the process for de-agglomeration of pigments.
DETAILED DESCRIPTION OF THE INVENTION
As discussed hereinbefore, the present invention provides a process for de-agglomeration of pigments comprising providing a premix feed having selective Stormer viscosity in the range of 400-1000 gms and passing said premix feed under pressure in a static mixer free of any moving parts to obtaintherefrom the de-agglomerated pigments as pigment dispersion. Stormer viscometer operates on stroboscope principle, operating at 200 rpm. The measurements are done at 30±1 °C. More particularly, said static mixer comprises of SMX geometry and is selectively predisposed with plurality of elements and provides for said process wherein output from the static mixer increasesunder same operating pressure by involving elements of higher diameter to obtain de-agglomerated pigments as pigment dispersion with full TS (Tinting Strength) values ranging from 97-103% against their respective references after only two passes.
Advantageously, thus the process of the present invention facilitates pigment de-agglomeration with higher levels of productivity in involving facile operation and in being free of moving parts also requires less energy and saves energy substantially.
In an embodiment of the present invention a static mixer was used for preparing the pigment dispersion. The experimental set up which is the schematic of static mixer as shown in Fig 1 consists of 1. Vessel for preparation of premix 2. Pump 3. Static Mixer containing 9 elements 4. Material Receiving Tank.
The static mixer elements employedwere of SMX geometry, 12 mm length and aspect ratio of 1.0.The pre-mixing of pigment powders and medium was done with gentle stirring in a simple paddle type stirrer in a cylindrical vessel, the premix vessel (1). The homogenized material, hereinafter referred to as pre-mix, having controlled viscosity between 400 to 1000 g was then passed through the static mixer (3) via a pump (2). Viscosity of the premix was controlled and measured on a Stormer Viscometer where the viscosity units are expressed in grams. Pressure drop was maintained between 70 and 200 PSI. The corresponding flow rates were between 3 - 10 L /min and de-agglomerated pigments were received in the receiving vessel (4). Pigment dispersions were thus successfully prepared in the above set up for a number of pigments. The pigments dispersed were across wide range of chemistry such as Iron Oxides, Titanium Dioxide, Carbon Black, Quinacridone, Phthalocyanine, DPP, Azocondensation mono arilide, Isoindolinone, Quinophthalone, Dioxazine and others.
The dispersions thus prepared were characterized by determining the particle size on a Malvern Mastersizer operating on dynamic light scattering principle. The D50 value of the homogenized blend prior to passing through the static mixer was 0.86 ? which came down to 0.69 ? after one pass and down to 0.58 ? after second pass. Further passes did not bring any improvement. The largest size particle came down from 5.87 ? to 4.47 ? after first pass and remained same thereafter. These were the values obtained for Iron oxide Yellow pigment PY 42. Similar experiments run with PY 110 pigment had a starting D50 value of 0.60 ? which came down to 0.34 ? after two passes.
One of the performance tests for the dispersions is determination of tinting strength. Those skilled in the art regard this as directly proportional to the extent of de-agglomeration of pigment particles in the dispersion. This is determined by mixing 5ml of the prepared pigment dispersion into a white paint.The color strength, also known to those skilled in the art as Tinting Strength (TS), obtained is measured on aX Rite spectrophotometer (Model CE 7000A) equipped with Propalette software. The reflectance valueobtained is compared against that of a reference made with standard pigment dispersion. The reflectance value of the reference is taken as 100 and the tinting strength of the sample is expressed in percentage terms. If the value comes lower than 100 it means the degree of dispersion is lower than the reference. When the value obtained is 100 +/- 3 those skilled in the art consider that the two dispersions are equal.
Both the dispersions prepared above showed TS values in the range of 97 – 103 % against their respective reference. The starting material had aTS in the range of 80 – 85 for these.
Similar results were obtained with many pigments described earlier. There were also some pigments for which full tinting strength could not be attained through static mixer although there was much improvement. Optionally subjecting to sand milling enabled attainment of the tinting strength on par with reference standard.
With Phthalocyanine Blue, PB 15:1, the TS value at the start was 84% which went up to 89 after 2 passes and did not improve thereafter. This dispersion when subjected to sand milling gave afinal TS of 98%.
Similar results were obtained when static mixer elements having 40 mm diameter were used. Higher output rates were obtained here for the same operating pressure. The extent of pigment de-agglomeration as determined by tinting strength was identical. Those skilled in the art would recognize this as the process being scalable.
Effect of premix viscosity: It was surprisingly found that viscosity of the pre-mix influenced de-agglomeration. As can be seen in Table I, when the premix viscosity was 525 g, the TS value after 3 passes through static mixer went up to only 96 from starting value of 94. When the premix viscosity was raised to 675 g, the TS value after 3 passes through static mixer was 100. Variation in premix viscosity was brought about by withholding some water.
Pre Mix Viscosity TS Pre Mix TS Static Mixer Pass III
525 g 94 96
675 g 93 100

Table I : Effect of lowering of Viscosity on TS (PR 101)
While de-agglomeration is facilitated with increase in premix viscosity above, on the other hand it was found that very high viscosity of the premix above Stormer viscosity 1080 g does not lead to any increase of de-agglomeration for a given pressure applied. At the other end when viscosity is too low the energy may not be getting effectively transferred to the agglomerates. In other words, no additional de-agglomeration was found when the viscosity was higher at 1080 g in comparison to viscosity of 810 g. The data are presented in Table II.

Pre Mix Viscosity TS Pre Mix TS Static Mixer Pass III
810 gms 96 99
1080 gms 93 100

Table II: Effect of high viscosity on TS (PR 122)

When the premix viscosity was 265 g, no de-agglomeration was seen even after 3 passes through static mixer. The relevant data are presented in Table – III. This data is generated on Pigment Blue 15: 3.
Pre Mix Viscosity TS Pre Mix TS after
I Pass TS after
II Pass TS Static
after III Pass
265 g 79 79 78 80

Table – III : Effect of Low viscosity on TS (PB15:3)
The savings in time and power as compared to the standard process is given in Tables IV and V.These were computed for a production quantity of 2500 Litres.

Serial No Process Operation Standard Process
(minutes) Static Mixer Based process (minutes) Power Saving
(KWH)
1 Addition of Liquid ingredients 15 15 0
2 Addition of Pigments 45 45 0
3 Premix preparation 20 20 0
4 Deagglomeration in Rotor-Stator 180 0 317
5 Deagglomeration in Static Mixer 0 40 -8
Total 260 120 309

Table IV: Power and Time Saving in Pigment Concentrate based on PW 6
Thus there is time saving of 140 minutes and power saving of 309 KWH for a batch of 2500 Litres dispersion in the case of PW6.
As can be seen from Table-V below for the case of PY 110, there is time saving of 430 minutes and power saving of 418 KWH for a batch of 2500 Litres dispersion.

Serial No Process Operation Standard Process
(minutes) Static Mixer Based process (minutes) Power Saving
(KWH)
1 Addition of Liquid ingredients 15 15 0
2 Addition of Pigments 45 45 0
3 Premix preparation 20 20 0
4 Deagglomeration in Rotor-Stator 180 0 317
5 Overhead Mixer Discharge 5 0 1
6 Deagglomeration in Static Mixer 0 30 -6
7 Sandmill Pass 275 0 106
Total 540 110 418

Table V: Power and Time Saving in Pigment Concentrates based on PY 110.

It is thus possible by way of the present invention to provide a process for de-agglomeration of pigments involving static mixer free of moving parts and controlled viscosity of the premix employed to pass through said static mixer under pressure to obtain therefrom de-agglomerated pigments as pigment dispersion with full TS (Tinting Strength) values ranging from 97-103% against their respective references after only two passes. Advantageously, a process is provided wherein output from the static mixer significantly increased without changing the pressure by choosing elements of higher diameter, whereby the elimination of moving parts in the static mixer while saved energy substantially further in involving simple configuration and simplicity of operations is also economical with respect to time.