Method for producing polymer coated pigment particles by precipitation
Described is a process for preparing polymer-enrobed pigment particles, which comprises mixing in the presence of finely dispersed pigment particles a solution of a polymer in a first solvent with a second solvent in which the polymer is substantially insoluble. The pigment particle can be specifically modified by judicious selection of the polymer.
1. A process for preparing polymer-enrobed pigment particles, which comprises
dissolving a polymer in a first solvent
mixing the solution of said polymer in said first solvent with a second solvent which contains finely dispersed pigment particles and in which said polymer is substantially insoluble,
said second solvent being miscible with the first solvent, whereby said polymer is precipitated from the mixture of solvents onto said finely dispensed pigment particles
wherein the first solvent is selected from organic water-miscible solvents.
2. A process as claimed in claim 1 , wherein the second solvent is water.
3. A process as claimed in claim 1 , wherein the polymer comprises a polyester, a polyvinyl acetal, polyacetal, polyurethane and/or a polyurea.
4. A process as claimed in claim 3 , wherein said polymer comprises a polycarbonate.
5. A process as claimed in claim 1 , wherein the polymer comprises a polymer polymerized from 10-100% by weight of one or more water-insoluble ethylenically unsaturated monomers, 0-90% by weight of one or more water-soluble lethylenically unsaturated monomers and 0-30% by weight of one or more crosslinking monomers.
6. A process as claimed in claim 1 , wherein the first solvent and/or the second solvent contain(s) an emulsifier and/or a protective colloid in solution.
7. A process as claimed in claim 1 , wherein the polymer has a glass transition temperature of from −100 to +250° C.
8. Pigmentary composition, suitable for use in an ink jet printing formulation, comprising composite particles of pigment from 10 nm to 500 nm in size and a polymer robe surrounding the pigment particle, said polymer enrobed pigment particles being made by the process of claim 1 .
9. A pigmentary composition of claim 8 , wherein said polymer comprises a polyester, a polyvinyl acetal, polyacetal, polyurethane and/or a polyurea.
10. A pigmentary composition of claim 8 , wherein said polymer is comprised of from 10-100% by weight of one or more water-insoluble ethylenically unsaturated monomers, 0-90% by weight of one or more water-soluble ethylenically unsaturated monomers and 0-30% by weight of one or more crosslinking monomers.
11. A pigmentary composition of claim 8 , wherein said polymer comprises a polycarbonate.
12. A pigmentary composition of claim 8 , wherein said polymer comprises a mixture of polycarbonate and a copolymer of polyethylene and acrylic acid.
13. A pigmentary composition as set forth in claim 8 wherein said polymer comprises a terpolymer of styrene, acrylic acid and 4-vinylpyridine.
14. A method of printing sheetlike substrates comprising ink jet printing said substrates with an ink jet ink comprising the pigmentary composition of claim 13 .
15. A method of printing sheetlike substrates comprising ink jet printing said substrate with an ink jet ink comprising the pigmentary composition of claim 8 .
16. A process as claimed in claim 1 wherein the solubility of said polymer in the second solvent is less than 1 g/l.
17. A process as claimed in claim 1 , wherein said polymer comprises a mixture of polycarbonate and a copolymer of polyethylene and acrylic acid.
18. A process as claimed in claim 1 , wherein said second solvent is water and said second solvent contains a protective colloid.
19. A process as claimed in claim 1 , where the polymer enrobed particles produced have an average particle size in the range of from 10 nm to 5 μm and a particle size distribution width (variance) of ≦60%.