Electrophoretic display medium and display device

1. An electrophoretic display medium, comprising one or more set of colored particles in a dielectric fluid, wherein at least one of the one or more set of particles comprise colored particles having attached to an external surface thereof additive particles, and

wherein the display medium has an electrical conductivity of about 10 −11 to about 10 −15 S/m.

2. The electrophoretic display medium according to claim 1 , wherein the at least one set of particles is comprised of from about 0.1 to about 20% by weight of the particles of the additive particles.

3. The electrophoretic display medium according to claim 1 , wherein the additive particles comprise at least one of surface treated silicon dioxide, surface treated titanium dioxide, surface treated titanic acid, surface treated cerium oxide, surface treated calcium stearate and surface treated zinc stearate, and have an average size of from about 5 nm to about 250 nm.

4. The electrophoretic display medium according to claim 3 , wherein the additive particles have an average size of from about 30 nm to about 140 nm.

5. The electrophoretic display medium according to claim 1 , wherein the additive particles are selected from the group consisting of silica treated with PDMS, silica treated with HMDS, silica treated with a mixture of HMDS and aminopropyltriethoxysilane, silica treated with a mixture of HMDS and aminopropyltriethoxysilane, silica treated with octylsilane, titania treated with at least one of i-butyltrimethoxysilane, n-propyltrimethoxysilane, n-butyltrimethoxysilane, n-hexyltrimethoxysilane, n-decyltrimethoxysilane and 3,3,3-trifluortrimethoxysilane, and combinations thereof.

6. The electrophoretic display medium according to claim 1 , wherein the at least one set of particles is comprised of emulsion aggregation polymer particles.

7. The electrophoretic display medium according to claim 1 , wherein the at least one set of colored particles has a charge of from about ±0.1 to about ±20 μC/g.

8. The electrophoretic display medium according to claim 1 , wherein the at least one set of colored particles include a colorant selected from the group consisting of pigment, dye, and combinations thereof.

9. The electrophoretic display medium according to claim 1 , wherein the fluid comprises from about 10% to about 95% by weight of the display medium and the at least one set of colored particles comprises from about 5% to about 50% by weight of the display medium.

10. The electrophoretic display medium according to claim 1 , wherein the at least one set of particles has an average particle size of from about 0.5 to about 25 μm, an upper geometric standard deviation (GSD) by volume for (D84/D50) is in the range of from about 1.1 to about 1.25, and an average circularity of about 0.92 to about 0.99.

11. The electrophoretic display medium according to claim 1 , wherein the additive particles are treated with an agent comprised of:

(1) a halogen-containing compound selected from the group consisting of ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), polytetrafluoroethylene fluorinated ethylene propylene (PTFE-FEP), polytetrafluoroethylene perfluoroalkoxy (PTFE-PFA), polyvinylidene fluoride (PVDF) and mixtures thereof,

(2) a silane compound that is an alkylalkoxysilane represented by:

wherein R represents an alkyl group and A, B, and C independently represent alkoxy groups;

(3) a silane compound selected from the group consisting of hexamethyldisilane (HMDS), decyltriethoxysilane (DTES), decyltrimethoxysilane (DTMS), polydimethylsiloxane (PDMS), octyltriethoxysilane (OTES), octyltrimethoxysilane (OTMS), (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FDTES), (tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane, i-butyltrimethoxysilane, n-propyltrimethoxysilane, n-butyltrimethoxysilane, n-hexyltrimethoxysilane, n-decyltrimethoxysilane, 3,3,3-trifluorotrimethoxysilane and mixtures thereof; or

(4) combinations thereof.

12. An electrophoretic display device, comprising a multiplicity of individual reservoirs containing a display medium between conductive substrates, at least one of which is transparent, wherein the display medium comprises one or more set of colored particles in a dielectric fluid, wherein at least one of the one or more set of particles comprise colored particles having attached to an external surface thereof additive particles, and

wherein the display medium has an electrical conductivity of about 10 −11 to about 10 −15 S/m.

13. The electrophoretic display device according to claim 12 , wherein the at least one set of colored particles has a charge of from about 0.1 to about ±20 μC/g.

14. The electrophoretic display device according to claim 12 , wherein the additive particles comprise at least one of surface treated silicon dioxide, surface treated titanium dioxide, surface treated titanic acid, surface treated cerium oxide, surface treated calcium stearate and surface treated zinc stearate, and have an average size of from about 5 nm to about 250 nm.

15. The electrophoretic display device according to claim 12 , wherein the additive particles comprise, or are treated with an agent comprised of, at least one of a halogen-containing compound, a silane compound, and a combination thereof.

16. The electrophoretic display device according to claim 12 , wherein the additive particles are treated with an agent comprised of:

(1) a halogen-containing compound selected from the group consisting of ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), polytetrafluoroethylene fluorinated ethylene propylene (PTFE-FEP), polytetrafluoroethylene perfluoroalkoxy (PTFE-PFA), polyvinylidene fluoride (PVDF) and mixtures thereof,

(2) a silane compound that is an alkylalkoxysilane represented by:

wherein R represents an alkyl group and A, B, and C independently represent alkoxy groups;

(3) a silane compound selected from the group consisting of hexamethyldisilane (HMDS), decyltriethoxysilane (DTES), decyltrimethoxysilane (DTMS), polydimethylsiloxane (PDMS), octyltriethoxysilane (OTES), octyltrimethoxysilane (OTMS), (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FDTES), (tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane, i-butyltrimethoxysilane, n-propyltrimethoxysilane, n-butyltrimethoxysilane, n-hexyltrimethoxysilane, n-decyltrimethoxysilane, 3,3,3-trifluorotrimethoxysilane and mixtures thereof; or

(4) combinations thereof.

17. An electrophoretic display medium, comprising one or more set of colored particles in a dielectric fluid, wherein at least one of the one or more set of particles comprise colored particles having attached to an external surface thereof additive particles,

wherein the additive particles are treated with an agent comprised of:

(1) a halogen-containing compound selected from the group consisting of ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-tetrafluoro ethylene (ETFE), polytetrafluoroethylene (PTFE), polytetrafluoroethylene fluorinated ethylene propylene (PTFE-FEP), polytetrafluoroethylene perfluoroalkoxy (PTFE-PFA), polyvinylidene fluoride (PVDF), and mixtures thereof;

(2) a silane compound that is an alkylalkoxysilane represented by:

wherein R represents an alkyl group and A, B, and C independently represent alkoxy groups;

(3) a silane compound selected from the group consisting of hexamethyldisilane (HMDS), decyltriethoxysilane (DTES), decyltrimethoxysilane (DTMS), polydimethylsiloxane (PDMS), octyltriethoxysilane (OTES), octyltrimethoxysilane (OTMS), (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FDTES), (tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane, i-butyltrimethoxysilane, n-propyltrimethoxysilane, n-butyltrimethoxysilane, n-hexyltrimethoxysilane, n-decyltrimethoxysilane, 3,3,3-trifluorotrimethoxysilane and mixtures thereof; or

(4) combinations thereof.

18. The electrophoretic display medium according to claim 17 , wherein the agent is the halogen-containing compound selected from the group consisting of ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), polytetrafluoroethylene fluorinated ethylene propylene (PTFE-FEP), polytetrafluoroethylene perfluoroalkoxy (PTFE-PFA), polyvinylidene fluoride (PVDF), and mixtures thereof.

19. The electrophoretic display medium according to claim 17 , wherein the agent is the silane compound that is an alkylalkoxysilane represented by:

wherein R represents an alkyl group and A, B, and C independently represent alkoxy groups.

20. The electrophoretic display medium according to claim 17 , wherein the agent is the silane compound selected from the group consisting of hexamethyldisilane (HMDS), decyltriethoxysilane (DTES), decyltrimethoxysilane (DTMS), polydimethylsiloxane (PDMS), octyltriethoxysilane (OTES), octyltrimethoxysilane (OTMS), (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FDTES), (tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane, i-butyltrimethoxysilane, n-propyltrimethoxysilane, n-butyltrimethoxysilane, n-hexyltrimethoxysilane, n-decyltrimethoxysilane, 3,3,3-trifluorotrimethoxysilane and mixtures thereof.