Polymer additives used in color electrophoretic display medium
An electrophoretic medium may be incorporated into an electrophoretic display that includes a dispersion containing a non-polar fluid, a plurality of first charged colored particles, polyisobutylene, and an additive selected from co-polymers of vinyl aromatics and at least one hydrocarbon having 2 to 5 carbons and at least one double bond. The co-polymer and the ratio of the co-polymer to polyisobutylene is selected, such that bistability performance is maintained while improving the color state performance of the display.
1. An electrophoretic medium comprises:
(a) a non-polar fluid;
(b) a plurality of first charged particles;
(c) polyisobutylene; and
a co-polymer comprising ethylene, propylene, and a vinyl aromatic.
2. The electrophoretic medium of claim 1 , wherein the vinyl aromatic is selected from the group consisting of styrene, alpha-methyl styrene, 2-methyl styrene, 3-methyl styrene, 4-methyl styrene, 44-butyl styrene, 4-cyclohexyl styrene, 4-dodecyl styrene, 2,4-diisopropyl styrene, 2,4,6-trimethyl styrene, 2-ethyl-4-benzyl styrene, 4-(phenyl butyl)styrene, 1-vinyl naphthalene, 2-vinyl naphthalene, vinyl anthracene, 4-methoxy styrene, monochlorostyrene, dichlorostyrene, divinyl benzene, indene, methyl indene, and combinations thereof.
3. The electrophoretic medium of claim 1 , wherein the vinyl aromatic comprises styrene.
4. The electrophoretic medium of claim 1 , wherein the weight percent of the vinyl aromatic in the copolymer is 20% to 40%.
5. The electrophoretic medium of claim 1 , wherein the weight ratio of polyisobutylene to co-polymer in the dispersion is 1:5 to 5:1.
6. The electrophoretic medium of claim 1 , wherein the first charged particles are red, green, blue, cyan, yellow, or magenta.
7. The electrophoretic medium of claim 6 further comprising a plurality of second charged particles dispersed in the non-polar fluid.
8. The electrophoretic medium of claim 7 , wherein the second charged particles are white or black.
9. The electrophoretic medium of claim 8 , wherein the second charged particles are white and the first and second charged particles have opposite charge polarities.
10. The electrophoretic medium of claim 9 , wherein the second charged particles comprise titania.
11. The electrophoretic medium of claim 9 further comprising a plurality of third charged particles dispersed in the non-polar fluid.
12. The electrophoretic medium of claim 11 , wherein the third charged particles are black and the first and third charged particles have the same charge polarity.
13. The electrophoretic medium of claim 12 , wherein the third charged particles comprise, carbon black or copper chromite.
14. The electrophoretic medium of claim 1 , further comprising an ionic surfactant.
15. An electrophoretic medium comprising:
(a) a non-polar fluid;
(b) a plurality of first charged particles;
(c) polyisobutylene; and
(d) an additive selected from co-polymers of a vinyl aromatic and at least one substituted or unsubstituted hydrocarbon having 2 to 5 carbons and at least one double bond,
wherein the combined weight percent of polyisobutylene and additive is 0.1 to 2.5% based on the total weight of the dispersion.
16. The electrophoretic medium of claim 15 , wherein the combined weight percent of polyisobutylene and additive is 0.5 to 1% based on the total weight of the dispersion.
17. The electrophoretic medium of claim 1 , further comprising a plurality of second charged particles and a plurality of third charged particles dispersed in the non-polar fluid, wherein the first, second, or third charged particles are red, green, blue, cyan, yellow, magenta, white, or black.
18. The electrophoretic medium of claim 1 , wherein the non-polar fluid comprises C6-C18 branched alkanes.