Chemically produced toner and process therefor
View Patent ↗A toner for developing an electrostatic image comprising toner particles which include a binder resin, a wax and a colorant, wherein the wax has a melting point of between 50 and 150° C., the wax exists in the toner particles in domains of 2 μm or less mean particle size and (a) the mean circularity of the toner particles as measured by a Flow Particle Image Analyser is at least 0.90; and (b) the shape factor, SF1, of the toner particles is at most 165. A process for the manufacture of said toner which comprises the following steps: providing a latex dispersion; providing a wax dispersion; providing a colorant dispersion; mixing the latex dispersion, wax dispersion and colorant dispersion; and causing the mixture to flocculate.
1. A toner for developing an electrostatic image comprising toner particles which include a binder resin, a wax and a colorant, wherein the wax has a melting point of between 50 and 150° C., and the wax exists in the toner particles in domains of 2 μm or less mean particle size and wherein
(a) the mean circularity of the toner particles as measured by a Flow Particle Image Analyser is at least 0.90; and
(b) the shape factor, SF1, of the toner particles is in the range from 130 to 150; and wherein the binder resin is prepared from at least one latex containing a resin having a monomodal molecular weight distribution and at least one latex containing a resin having a bimodal molecular weight distribution, and
(c) the ratio SF1/SF2 of the shape factor, SF1, to the shape factor, SF2, is from 1.07 to 1.13.
2. A toner according to claim 1 wherein the mean circularity of the toner particles is in the range from 0.93 to 0.99.
3. A toner according to claim 2 wherein the mean circularity of the toner particles is in the range from 0.94 to 0.96.
4. A toner according to claim 2 wherein SF2 of the toner particles is in the range from 125 to 135.
5. A toner according to claim 1 wherein SF1 of the toner particles is at most 145.
6. A toner according to claim 5 wherein SF1 of the toner particles is in the range from 135 to 145.
7. A toner according to claim 1 wherein SF2 of the toner particles is in the range from 120 to 140.
8. A toner according to claim 1 wherein the BET surface area of the particles is 0.7-1.1 m 2 /g.
9. A toner according to claim 1 wherein the wax exists in the toner in domains of mean diameter 1.5 μm or less.
10. A toner according to claim 1 wherein the monomodal molecular weight resin is a low molecular weight resin and has a number average molecular weight of from 3000 to 10000.
11. A toner according to claim 1 wherein the bimodal resin has a weight average molecular weight of from 100,000 to 500,000.
12. A toner according to claim 1 wherein the resin comprises a copolymer of (i) a styrene or substituted styrene, (ii) at least one alkyl acrylate or methacrylate and (iii) an hydroxy-functional acrylate or methacrylate.
13. A toner according to claim 1 wherein the amount of wax is from 3 to 20 wt %.
14. A toner according to claim 1 which further comprises a charge control agent.
15. A process for forming an image, the process comprising developing an electrostatic image using a toner according to claim 1 , wherein the haze at a print density of 1.0 mg/cm 2 is below 40, and the ratio of the values at fusion temperatures of 130 and 160° C. is at most 1.5.
16. A toner for developing an electrostatic image comprising toner particles which include a binder resin, a wax and a colorant, wherein the wax has a melting point of between 50 and 150° C., and the wax exists in the toner particles in domains of 2 μm or less mean particle size and wherein
(a) the mean circularity of the toner particles as measured by a Flow Particle Image Analyser is in the range from 0.94 to 0.96;
(b) the shape factor, SF1, of the toner particles is in the range from 135 to 145; and wherein the binder resin is prepared from at least one latex containing a resin having a monomodal molecular weight distribution and at least one latex containing a resin having a bimodal molecular weight distribution, and
(c) SF1>SF2.
17. A process for the manufacture of a toner for developing an electrostatic image comprising toner particles which include a binder resin, a wax and a colorant, wherein the wax has a melting point of between 50 to 150° C.; and the wax exists in the toner particles in domains of 2 μm or less mean particle size and wherein
(a) the mean circularity of the toner particles as measured by a Flow Particle Image Analyser is at least 0.90; and
(b) the shape factor, SF1, of the toner particles is at most 165, which process comprises the following steps:
I. providing a latex dispersion which has at least one latex with a monomodal molecular weight distribution and has at least one latex with a bimodal molecular weight distribution;
II. providing a wax dispersion;
III. providing a colorant dispersion;
IV. mixing the latex dispersion, wax dispersion and colorant dispersion; and
V. causing the mixture to flocculate to produce said toner.
18. A process according to claim 17 wherein the monomodal molecular weight latex has a number average molecular weight of from 3000 to 10000.
19. A process according to claim 18 wherein the monomodal molecular weight latex has a number average molecular weight of from 3000 to 6000.
20. A process according to claim 17 wherein the bimodal latex has a weight average molecular weight of from 100,000 to 500,000.
21. A toner according to claim 20 wherein the bimodal latex has a weight average molecular weight of from 200,000 to 400,000.
22. A process according to claim 17 further comprising heating the flocculated mixture obtained after step (v) to form loose aggregates of particle size from 3 to 20 μm.
23. A process according to claim 22 further comprising heating the aggregates to a temperature above the T g of the latex to induce coalescence to form toner particles.
24. A process according to claim 17 wherein the latex dispersion comprises an ionic surfactant.
25. A process according to claim 17 wherein the latex containing a resin having a bimodal molecular weight distribution is prepared by a process comprising the successive steps of forming a polymer of high molecular weight distribution followed by forming a polymer of low molecular weight distribution such that the resulting latex comprises composite particles comprising both said low molecular weight polymer and said high molecular weight polymer.
26. A process according to claim 17 which, prior to step iv, further comprises the step of providing a charge control agent dispersion, which dispersion is then incorporated in step iv by mixing.
27. A process according to claim 26 wherein the charge control agent is milled with the colorant.
28. A process according to claim 17 wherein the preparation of the wax dispersion comprises the mixing together of the wax with an ionic surfactant.
29. A process according to claim 17 wherein the preparation of the colorant dispersion comprises the milling together of the colorant with an ionic surfactant.
30. A process according to claim 17 wherein the dispersions of latex, colorant, wax, and charge control agent where present, have the same sign charge on the surfactant.
31. A process according to claim 30 wherein the surfactant present in the dispersions contains a group which can be converted from an ionic to a non-ionic form and vice versa by adjustment of pH.
32. A toner for developing an electrostatic image which has been obtained by the process of claim 17 .