Process for preparing granules of pigments by means of double extrusion

Abstract

A process for the production of a particle composition containing, at least one resin and at least one pigment is described, said process comprising the following steps: *extrusion of a mixture containing said at least one resin and said at least one pigment without induced heating; *subsequent extrusion, with induced heating, of the mixture obtained from the preceding extrusion; *granulation of the mixture thus obtained. With the abovementioned process it is possible to obtain a composition having granules with an average diameter less than 2 microns and a greater homogeneity than the known processes.

The invention claimed is: 
     
       1. A process for the production of a particle composition containing at least one of aldehyde, ketone and acrylic resin, and at least one pigment, comprising the following steps:
 (a) extrusion, in a co-rotating twin-screw extruder, of a mixture containing said at least resin and said at least one pigment without induced heating, using only the heat developed naturally by the cutting and friction forces inside the extruder, wherein the temperature inside the extruder according to step (a) varies from 5 to 50° Celsius, and the screws of the extruder according to step (a) have a length 20-40 25-48 times the diameter, and wherein an extrudate leaves the co-rotating twin-screw extruder after step (a) and comprises a non-granulated homogenous mixture of the at least one resin and the at least one pigment; 
 (b) subsequent extrusion, with induced heating, of the mixture obtained from the extrusion according to step (a), wherein the temperature inside the extruder according to step (b) varies from 80 to 130° Celsius, and the screws of the extruder according to step (b) have a length 30-60 times the diameter; and 
 (c) granulation of the mixture thus obtained, wherein the extrusion of step (a) comprises a plurality of zones that are temperature controlled such that a temperature of at least one zone is set to a temperature within a range of from 10 to 15° C. and wherein the temperature of one or more zones of the first extrusion step is controlled with at least a cooling set, and 
 wherein the extrusion of step (b) comprises a plurality of zones that are temperature controlled such that a temperature of at least one zone increases from a temperature in a previous zone. 
 
     
     
       2. The process according to  claim 1 , wherein step (b) is performed in a co-rotating twin-screw extruder. 
     
     
       3. The process according to  claim 2 , wherein the screws of the extruder according to step (a) have a diameter of 27-110 mm. 
     
     
       4. The process according to  claim 3 , wherein the screws of the extruder according to step (a) have a diameter of 30-87 mm. 
     
     
       5. The process according to  claim 3 , wherein said screws of the extruder according to step (a) have a length 25-40 times the diameter. 
     
     
       6. The process according to  claim 5 , wherein said screws of the extruder to step (a) have a length 32-40 times the diameter. 
     
     
       7. The process according to  claim 1 , wherein the temperature inside one or more zones of the extruder according to step (a) varies from 5 to 35° C. 
     
     
       8. The process according to  claim 1 , wherein the flowrate of the extrusion according to step (a) is 5-20 kg/h. 
     
     
       9. The process according to  claim 1 , wherein the flowrate of the extrusion according to step (a) is 10-15 kg/h. 
     
     
       10. The process according to  claim 2 , wherein the screws of the extruder according to step (b) have a diameter of 27-110 mm. 
     
     
       11. The process according to  claim 10 , wherein the screws of the extruder according to step (b) have a diameter of 30-87 mm. 
     
     
       12. The process according to  claim 1 , wherein said screws of the extruder to step (b) have a length 48-60 times the diameter. 
     
     
       13. The process according to  claim 1 , wherein the temperature inside the extruder according to step (b) varies from 80 to 110° C. 
     
     
       14. The process according to  claim 1 , wherein the flowrate of the extrusion according to step (b) is 15-35 kg/h. 
     
     
       15. The process according to  claim 14 , wherein the flowrate of the extrusion according to step (b) is 20-30 kg/h. 
     
     
       16. The process according to  claim 1 , wherein the granulation is performed by means of cutting with a water jet. 
     
     
       17. The process according to  claim 1 , wherein the granulation is performed by means of cutting with a water jet. 
     
     
       18. The process according to  claim 1 , wherein said at least one pigment is organic and/or inorganic. 
     
     
       19. The process according to  claim 18 , wherein said further comprising a mineral filler and wherein the mineral filler is a barium sulphate. 
     
     
       20. The process according to  claim 1 , wherein the mixture further contains at least one dispersant. 
     
     
       21. The process according to  claim 20 , wherein said dispersant is non-ionic. 
     
     
       22. The process according to  claim 20 , wherein said dispersant is selected from the group consisting of epoxidized sorbitan and soy bean oil esters. 
     
     
       23. The process according to  claim 22 , wherein said dispersant is the epoxidized sorbitan ester. 
     
     
       24. The process according to  claim 1 , wherein said mixture further contains water.