Method of continuously forming an aqueous colorant dispersion using a screw extruder
View Patent ↗A continuous process for making a pigment dispersion includes continuously feeding a pigment into a feed section of a screw extruder at a controlled rate, continuously feeding a surfactant into the feed section of the screw extruder at a controlled rate, continuously feeding water downstream of the feed section to emulsify the pigment and the surfactant, forming a water-in-pigment dispersion, continuously feeding additional water downstream of the previously fed water to cause a phase inversion of the water-in-pigment dispersion, forming a pigment-in-water dispersion, continuously homogenizing the pigment-in-water dispersion in the screw extruder to create a homogenous aqueous pigment dispersion and collecting the homogenous aqueous pigment dispersion from an exit section of the screw extruder.
1. A continuous process for making a pigment dispersion, the continuous process comprising:
continuously feeding a pigment into a feed section of a screw extruder at a controlled rate in the absence of a solvent;
continuously feeding a surfactant in solid form into the feed section of the screw extruder at a controlled rate in the absence of a solvent;
continuously feeding water downstream of the feed section at a rate of 40 g/min to 65 g/min to emulsify the pigment and the surfactant, forming a water-in-pigment dispersion;
continuously feeding additional water downstream of the previously fed water at a rate of 65 g/min to 90 g/min to cause a phase inversion of the water-in-pigment dispersion, forming a pigment-in-water dispersion having a solid content that is less than a solid content of the water-in-pigment dispersion;
continuously homogenizing the pigment-in-water dispersion in the screw extruder to create a homogenous aqueous pigment dispersion; and
collecting the homogenous aqueous pigment dispersion from an exit section of the screw extruder.
2. The process of claim 1 , wherein the feed section includes a first feed line for the pigment and a second feed line for the surfactant.
3. The process of claim 1 , wherein the water and the additional water fed into the screw extruder is de-ionized water.
4. The process of claim 1 , wherein the screw extruder includes a screen and an automatic screen changer, wherein the homogenous aqueous pigment dispersion passes through the screen as it exits the screw extruder.
5. The process of claim 1 , wherein the pigment and surfactant are each in a solid form when fed into the feed section.
6. The process of claim 5 , wherein the surfactant is in a powder form.
7. The process of claim 1 , wherein the screw extruder is segmented.
8. The process of claim 7 , wherein each segment is independently heated to a temperature of from about 25° C. to about 110° C.
9. The process of claim 7 , wherein the extruder includes 13 segments.
10. The process of claim 1 , wherein the feeding of additional water is separated into two separate feedings, one feeding is downstream of the other, wherein the downstream second feeding of water creates the pigment-in-water dispersion.
11. A method comprising,
continuously feeding a colorant into a feed section of a screw extruder at a controlled rate in the absence of a solvent;
continuously feeding a surfactant in solid form into the feed section of the screw extruder at a controlled rate to form a pre-dispersion in the absence of a solvent;
emulsifying an aqueous solution into the pre-dispersion in the screw extruder to create a water-in-colorant dispersion;
phase inverting the water-in-colorant dispersion to create a colorant-in-water dispersion in the screw extruder such that the colorant-in-water dispersion has a solid content that is less than a solid content of the water-in-colorant dispersion;
homogenizing the colorant-in-water dispersion to create a homogeneous colorant dispersion in the screw extruder; and
collecting the homogenous aqueous colorant dispersion through an exit portion of the screw extruder.
12. The method of claim 11 , wherein the homogeneous colorant dispersion is filtered as it exits the screw extruder.
13. The method of claim 11 , wherein the surfactant and the colorant are each in a solid phase when fed into the feed section.
14. The method of claim 13 , wherein the solid phase of the surfactant is a powder form.
15. The method of claim 13 , wherein the feed section includes a first feed line for the colorant and a second feed line for the surfactant.
16. The method of claim 11 , wherein the screw extruder is segmented, and each segment is independently heated or cooled to a temperature of from about 25° C. to about 110° C.
17. The method of claim 11 , wherein the screw extruder is a multi-screw extruder.
18. The method of claim 11 , wherein the aqueous solution is water.
19. The method of claim 11 , wherein the feeding of additional water is separated into two separate feedings, one feeding is downstream of the other, wherein the downstream second feeding of water creates the colorant-in-water dispersion.
20. An aqueous pigment dispersion, formed by the continuous process of claim 1 , wherein an average particle size of a pigment in the aqueous pigment dispersion is about 138 nm.