Polymer-dispersed liquid crystal material with in-situ polymerized liquid crystal polymer grains dispersed in a layer of liquid crystal material sealed between substrates and field electrodes

• US 5,305,126 A
• Filed: 11/26/1991
• Issued: 04/19/1994
• Est. Priority Date: 11/26/1990
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Kobayashi, Hidekazu, Samizu, Kiyohiro, Wu, Jin-Jei
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MAI, HUY KIM
• Application Number:
  US07/798,478
• Time in Patent Office: 875 Days
• Field of Search: 359/51, 359/52, 359/73, 359/70, 359/96, 359/101, 359/93, 359/94, 359/103
• US Class Current: 349/94
• CPC Class Codes: C09K 19/3852 Poly(meth)acrylate derivatives
• CPC Class Codes: C09K 19/542 Macromolecular compounds
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/13345 Network or three-dimensional gels
• CPC Class Codes: G02F 1/13347 working in reverse mode, i.e. clear in the off-state and scattering in the on-state
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G02F 1/1347 Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
• CPC Class Codes: G02F 1/13725 based on guest-host interaction G02F1/13762, G02F1/13737, take precedence
• CPC Class Codes: G02F 2203/02 reflective

Abstract

A polymer dispersed liquid crystal material (PDLC) device is fabricated by sealing a composite layer mixture of components comprising a polymer and liquid crystal material while both are in their liquid phase in a gap portion formed between two substrates of the device. A predetermined directional alignment is transmitted to the polymer via the liquid crystal material by means, for example, of formed directional alignment on surfaces in contact with the composite layer, such as, by deposited alignment films on a surface of at least one of the substrates. The predetermined directional alignment of the polymer is thereafter fixed by means of a polymer hardening method, such as, for example, by polymerization of a polymer precursor, so that the predetermined directional alignment of the polymer is permanently retain within the liquid crystal material, i.e., the polymer is in a solid phase and the liquid crystal material remains in its liquid phase. For better results, a chiral component and/or a light absorbing component may be added to the liquid crystal material.

Claims

1. A method of fabricating a polymer dispersed liquid crystal display having a polymer dispersed liquid crystal medium formed in a gap portion in said display comprising the steps of:

forming a mixture of liquid crystal material and thermoplastic polymer to cause said liquid crystal material and polymer to be soluble in one other;

injecting said soluble mixture in the gap portion,

aligning the liquid crystal material and polymer in a predetermined direction while said mixture remains in its soluble state; and

causing said mixture to bring about a phase separation between the liquid crystal material and the polymer forming polymer grains dispersed throughout the liquid crystal material retaining their original alignment in said predetermined direction.

2. The method of fabricating of claim 1, further comprising, before the step of injecting, the step of preparing at least one inner surface of said gap portion with a means for aligning liquid crystal material and polymer in a direction substantially parallel with or perpendicular to the plane of a substrate proximate to said gap.

3. A method of fabricating a polymer dispersed liquid crystal display comprising the steps of:

forming a mixture of liquid crystal material and polymer precursor to cause said liquid crystal material and polymer precursor to be soluble in one other in their liquid phases,

aligning said liquid crystal material and polymer precursor in a predetermined direction while in their liquid phases; and

polymerizing said polymer precursor in-situ to form a plurality of solid polymer grains dispersed throughout said liquid crystal material with a phase separation occurring between the liquid crystal material and the polymer grains wherein the polymer grains maintain said predetermined directional alignment.

4. The method of fabricating of claim 3, further comprising the steps, before polymerizing, of:

sealing said mixture between two substrates and

aligning said liquid crystal material and said polymer precursor in said predetermined direction by means of an orientation process provided on at least one of said substrates.

5. The method of fabricating of claim 3, further comprising the step of controlling the rate of polymerization to adjust the rate of phase separation to yield polymer grain sizes in the range of about 0.1 μ

m-10.0 μ

m.

6. The method of claim 3 wherein said polymer precursor comprises a liquid crystal phase.

7. A method of fabricating a polymer dispersed liquid crystal display comprising the steps of:

processing at least one inner surface of a pair of planar substrates having inner electrodes to align a liquid crystal material and a polymer precursor in contact therewith in a direction substantially parallel with or perpendicular to the plane of said substrates;

forming a mixture of the liquid crystal material and polymer precursor into each other;

sealing said mixture between said substrates; and

polymerizing said polymer precursor in-situ to yield a polymer, such that a phase separation is exhibited between the liquid crystal material and polymer with the polymer retaining said alignment.

8. A method of fabricating a polymer dispersed liquid crystal display comprising the steps of:

processing a surface of a first substrate to enable a liquid crystal material and a polymer precursor to align in a common direction substantially parallel with or perpendicular to the plane of said substrate;

forming a mixture of the liquid crystal material and the polymer precursor into each other to form a soluble liquid phase and coating said mixture onto said substrate;

aligning the liquid crystal material and said polymer precursor in said common direction while in said soluble liquid phase; and

polymerizing said polymer precursor to yield a polymer, so as to have a phase separation between the liquid crystal material and polymer which retains said common direction alignment.

9. The method of fabricating of claim 8 wherein said polymer precursor comprises a derivative form of at least one of biphenyl methacrylate, biphenyl acrylate, naphthyl methacrylate and naphthyl acrylate.

10. The method of fabricating of claim 8 wherein said polymer precursor comprises a mixture of an ester and at least one of a derivative of biphenylmethyl methacrylate and a derivative of biphenylmethyl acrylate.

11. A liquid crystal device made according to the process of:

sealing in said device a mixture of a liquid crystal material and a polymer precursor while both are in their liquid phase;

transmitting a predetermined direction of alignment to said polymer precursor through said liquid crystal material utilizing an alignment means; and

solidifying the polymer precursor into a hardened polymer while causing the precipitation of said polymer from said mixture into a plurality of solid grains dispersed throughout said liquid crystal material such that said predetermined direction of alignment is permanently retained by said polymer grains.

12. The liquid crystal device of claim 11 wherein the step of transmitting said predetermined direction of alignment is derived from rubbing the inside of at least one substrate in contact with said mixture.

13. The liquid crystal device of claim 11 wherein the step of transmitting said predetermined direction of alignment is derived from forming an aligning layer on an inside surface of at least one substrate in contact with said mixture.

14. A polymer dispersed liquid crystal device comprising a mixture of in-situ fixation of pre-aligned polymer grains dispersed in a layer of liquid crystal medium sealed by at least one substrate in contact with said mixture.

15. The polymer dispersed liquid crystal device of claim 14 wherein the amount of liquid crystal material in said mixture exceeds the amount of polymer grains and is in the range between 50% and 97% of the mixture with said polymer.

16. The polymer dispersed liquid crystal device of claim 14 further comprising means for establishing an aligning direction for said polymer grains before and during fixing of the orientation of said polymer grains in said mixture, said liquid crystal material transmitting said aligning direction for said polymer grains before and during said orientation fixing.

17. The device of claim 16 wherein said fixing is accomplished by polymerization.

18. The polymer dispersed liquid crystal device of claim 16 wherein said alignment means comprises an alignment treatment applied to a surface of said one at least substrate in contact with said mixture.

19. The polymer dispersed liquid crystal device of claim 14 wherein said mixture includes a component for orienting said polymer grains and said liquid crystal medium in an elongated helical twist.

20. The polymer dispersed liquid crystal device of claim 19 wherein said component comprises a chiral component.

21. An improved polymer dispersed liquid crystal device having a drive voltage requirement under five volts, the improvement comprising:

a polymer precursor comprising a monomethacrylate and not a diacrylate; and

a liquid crystal layer comprising a liquid crystal material having a cholesteric pitch in the range of about 30 μ

m to about 0.60 μ

m.

22. The polymer dispersed liquid crystal device of claim 21 wherein the polymer precursor and liquid crystal material are mixed together in a solution with the polymer precursor being in the range between 3% and 50%.

23. The polymer dispersed liquid crystal device of claim 21 wherein the polymer precursor has been polymerized into grains that are not necessarily spherical.

24. The polymer dispersed liquid crystal device of claim 21 wherein the polymer precursor and liquid crystal material subsequent to polymerization are such that light dispersion in one of the field-ON and field-OFF conditions is caused by a substantial difference that exists in the respective refractive indices of the polymer and the liquid crystal material and not by a phase transition that occurs between the cholesteric phase and the nematic phase.

25. A polymer dispersed liquid crystal device having a spatial gap portion formed between spaced electrodes formed on respective substrates, comprising:

a liquid crystal phase in said gap portion,

a polymer phase comprising a plurality of polymeric grains dispersed in said liquid crystal phase,

said liquid crystal phase having positive or negative dielectric anisotropy,

alignment means provided relative to at least one of said substrates for orienting optical axes of both said liquid crystal phase and said polymer phase in a predetermined direction relative to a surface of said electrodes,

means to fix the orientation of said polymer phase in said predetermined direction, and

means to apply a field between said electrodes to switch between two conditions comprising matching and mismatching of the optical axes of said liquid crystal phase relative to said fixed polymer phase so that in one condition a light transparent state is created and in another condition a light dispersion state is created.

26. The polymer dispersed liquid crystal device of claim 25 wherein the total amount of said polymer phase within said liquid crystal phase is less than the total amount of liquid crystal phase present in said gap portion.

27. The polymer dispersed liquid crystal device of claim 26 wherein the total amount of said liquid crystal phase relative to said polymer phase is in the range between 50% and 97%.

28. The polymer dispersed liquid crystal device of claim 25 wherein said direction of orientation of the optical axis of said polymer phase is oriented and fixed in said liquid crystal phase in a direction substantially parallel to the surface of said electrodes.

29. The polymer dispersed liquid crystal device of claim 25 wherein said direction of orientation of the optical axis of said polymer phase is oriented and fixed in said liquid crystal phase in a direction substantially perpendicular to the surface of said electrodes.

30. The polymer dispersed liquid crystal device of claim 25 wherein said liquid crystal phase comprises a nematic liquid crystal containing a chiral component.

31. The polymer dispersed liquid crystal device of claim 25 wherein said liquid crystal phase includes a dichroic dye material.

32. The polymer dispersed liquid crystal device of claim 25 wherein one of said electrodes has a light reflecting surface.

33. The polymer dispersed liquid crystal device of claim 25 wherein said polymer phase comprises a polymer precursor hardened by ultraviolet light or heat comprising said fixing means.

34. The polymer dispersed liquid crystal device of claim 25 wherein said polymer phase comprises a thermoplastic polymer, a liquid crystal polymer or a polymer having a cosolvent with a liquid crystal.

35. The polymer dispersed liquid crystal device of claim 25 wherein said fixing means for said polymer phase is obtained from polymerization of one or more polymer precursors containing molecules having one or more polymerizable portions and one or more aromatic ring portions.

36. The polymer dispersed liquid crystal device of claim 35 wherein said ring portions comprise phenyl or biphenyl or naphthyl or derivatives thereof.

37. The polymer dispersed liquid crystal device of claim 25 further comprising a phase-shift plate positioned between said gap portion and one of said substrates, and a reflection layer formed on said one substrate.

38. The polymer dispersed liquid crystal device of claim 25 further comprising a polarizing plate and a reflector plate formed on a back surface of one of said substrates.

39. The polymer dispersed liquid crystal device of claim 25 further comprising a phase correcting plate, a light attenuating plate, and a reflector plate formed on a back surface of one of said substrates.

40. The polymer dispersed liquid crystal device of claim 25 wherein said polymer phase comprises a polymer having no liquid crystal characteristics.

41. The polymer dispersed liquid crystal device of claim 25 wherein said alignment means is applied to said substrates, alignment relative to a surface of one of said substrates being such that molecules in the liquid crystal phase and polymer grains in the polymer phase approximate to the one substrate surface align parallel with the one substrate surface, and alignment relative to a surface of the other of said substrates being such that molecules in the liquid crystal phase and polymer grains in the polymer phase approximate to the other substrate surface align perpendicular to the other substrate surface.

42. A polymer dispersed liquid crystal device having a spatial gap portion formed between spaced electrodes formed on respective substrates, comprising:

a liquid crystal phase in said gap portion,

a polymer phase comprising solid polymeric grains dispersed in said liquid crystal phase,

optical axes of said liquid crystal phase and said polymer phase alignable in a common direction substantially parallel with a surface of said electrodes,

means provided in said liquid crystal phase to provide a helical twist to said polymer phase extending through said gap portion in a direction transverse to said electrode surface, and

means to apply a field between said electrodes to switch between two conditions comprising matching and mismatching of the optical axes of said liquid crystal phase relative to said polymer so that in one condition a light transparent state is created and in another condition a light dispersion state is created.

43. The polymer dispersed liquid crystal device of claim 42 wherein said provided means comprises a chiral element is added to said liquid crystal phase to bring about said helical twist.

44. The polymer dispersed liquid crystal device of claim 43 wherein said optical axes of said polymer phase and said liquid crystal phase are gradually twisted about an axis perpendicular to said planar electrode surface.

45. The polymer dispersed liquid crystal device of claim 42 wherein one of said electrodes has a light reflecting surface.

46. The polymer dispersed liquid crystal device of claim 42 wherein said liquid crystal phase comprises a nematic liquid crystal containing a chiral component whereby said polymer phase and said liquid crystal phase are oriented between said electrodes in an elongated helical structure having an axial orientation substantially perpendicular to a planar extent of said electrodes.

47. The polymer dispersed liquid crystal device of claim 42 wherein the helical twist provided to said liquid crystal phase includes a dichroic dye material.

48. The polymer dispersed liquid crystal device of claim 42 wherein said polymer phase is fixed in its orientation by inclusion of a polymer precursor hardened by ultraviolet light or heat.

49. The polymer dispersed liquid crystal device of claim 42 wherein said polymer phase comprises a thermoplastic polymer, a liquid crystal polymer or a polymer having a cosolvent with a liquid crystal.

50. The polymer dispersed liquid crystal device of claim 42 wherein said polymer is obtained from polymerization of one or more polymer precursors containing molecules having one or more polymerizable portions and one or more aromatic ring portions.

51. The polymer dispersed liquid crystal device of claim 50 wherein said ring portions comprise phenyl or biphenyl or naphthyl or derivatives thereof.

52. The polymer dispersed liquid crystal device of claim 42 wherein said polymer phase comprises a polymer having no liquid crystal characteristics.

53. A polymer dispersed liquid crystal device having a light modulating material formed between spatially disposed electrodes, comprising:

said light modulating material comprising a polymer phase and a liquid crystal phase,

said polymer phase and a liquid crystal phase having optical axes alignable together in a predetermined direction,

light absorption additive included in said liquid crystal phase to provide for light absorption when said optical axes are aligned in said predetermined direction,

means to apply a field between said electrodes to switch between two conditions comprising alignment and misalignment of the optical axes of said liquid crystal phase relative to said polymer phase so that in one condition a light absorption state is created in said material and in another condition a light dispersion state is created in said material.

54. The polymer dispersed liquid crystal device of claim 53 wherein said light absorption state occurs when the optical axes of said polymer phase and a liquid crystal phase are aligned in said predetermined direction, and said light dispersion state occurs when said optical axes are misaligned.

55. The polymer dispersed liquid crystal device of claim 54 wherein said misalignment is the case wherein the optical axes of said liquid crystal phase is substantially orthogonal to said predetermined direction.

56. The polymer dispersed liquid crystal device of claim 53 wherein said predetermined direction is substantially parallel to said electrodes.

57. The polymer dispersed liquid crystal device of claim 53 wherein said liquid crystal phase has positive dielectric anisotropy and optical axes of said polymer phase and said liquid crystal phase are aligned to be substantially parallel to a surface of said electrodes.

58. The polymer dispersed liquid crystal device of claim 57 wherein said light absorption additive comprises a dichroic dye material.

59. The polymer dispersed liquid crystal device of claim 53 wherein said light absorption state occurs when said applied field is OFF and said light dispersion state occurs when said field is ON.

60. The polymer dispersed liquid crystal device of claim 53 wherein one of said electrodes has a light reflecting surface.

61. The polymer dispersed liquid crystal device of claim 53 wherein said liquid crystal phase comprises a nematic liquid crystal containing a chiral component.

62. The polymer dispersed liquid crystal device of claim 53 wherein said polymer phase comprises a precursor hardened by ultraviolet light or heat.

63. The polymer dispersed liquid crystal device of claim 53 wherein said polymer phase comprises a thermoplastic polymer, a liquid crystal polymer or a polymer which has a cosolvent with a liquid crystal.

64. The polymer dispersed liquid crystal device of claim 53 wherein said polymer phase comprises a polymer having no liquid crystal characteristics.

65. The polymer dispersed liquid crystal device of claim 53 wherein said polymer phase is obtained from polymerization of one or more polymer precursors containing molecules having one or more polymerizable portions and one or more aromatic ring portions.

66. The polymer dispersed liquid crystal device of claim 65 wherein said ring portions comprise phenyl or biphenyl or naphthyl or derivatives thereof.

67. The polymer dispersed liquid crystal device of claim 53 further comprising a substrate for supporting each of said electrodes, a phase-shift plate positioned between said material and one of said substrates, and a reflection layer formed on said one substrate.

68. The polymer dispersed liquid crystal device of claim 53 further comprising a substrate for supporting each of said electrodes, and alignment means provided relative to at least one of said substrates for orienting optical axes of both said liquid crystal phase and said polymer phase in said predetermined direction relative to a surface of said planar electrodes.

69. A polymer dispersed liquid crystal device having a light modulating material formed between spatially disposed electrodes, comprising:

said light modulating material comprising a polymer phase dispersed in a liquid crystal phase,

said polymer phase and a liquid crystal phase having optical axes alignable together in a predetermined direction,

means to apply a field between said electrodes to switch between two conditions comprising matching and mismatching of the optical axes of said liquid crystal phase relative to said polymer phase wherein in a field-OFF condition, incident light on said device is transparent in said material and wherein in a field-ON state, incident light on said device is absorbed and dispersed.

70. The polymer dispersed liquid crystal device of claim 69 wherein said liquid crystal phase has negative dielectric anisotropy, said aligned optical axes of said polymer phase and said liquid crystal phase substantially perpendicular to a surface of said electrodes during the occurrence of said field-OFF state.

71. The polymer dispersed liquid crystal device of claim 69 wherein said liquid crystal phase includes a dichroic dye material.

72. The polymer dispersed liquid crystal device of claim 69 wherein said polymer phase comprises a precursor hardened by ultraviolet light or heat.

73. The polymer dispersed liquid crystal device of claim 69 wherein said polymer phase comprises a thermoplastic polymer, a liquid crystal polymer or a polymer which has a cosolvent with a liquid crystal.

74. The polymer dispersed liquid crystal device of claim 69 wherein said polymer phase comprises a polymer having no liquid crystal characteristics.

75. The polymer dispersed liquid crystal device of claim 69 wherein said polymer phase is obtained from polymerization of one or more polymer precursors containing molecules having one or more polymerizable portions and one or more aromatic ring portions.

76. The polymer dispersed liquid crystal device of claim 75 wherein said ring portions comprise phenyl or biphenyl or naphthyl or derivative thereof.

77. A polymer dispersed liquid crystal device having a light modulating material formed between spatially disposed electrodes, comprising:

said light modulating material comprising a polymer phase and a liquid crystal phase,

said polymer phase and a liquid crystal phase having optical axes alignable together in a direction substantially perpendicular to a planar extent of said electrodes,

light absorption additive included in said liquid crystal phase to provide for light absorption and scattering when said optical axes are nonaligned in said direction,

means to apply a field between said electrodes to switch between two conditions comprising matching and mismatching of the optical axes of said liquid crystal phase relative to said polymer phase wherein in a field-OFF condition, said polymer phase and a liquid crystal phase optical axes are aligned and incident light on said device is transparent in said material and wherein in a field-ON state, said polymer phase and a liquid crystal phase optical axes are misaligned and incident light on said device is absorbed and scattered.

78. The polymer dispersed liquid crystal device of claim 77 wherein said polymer phase is dispersed in a liquid crystal phase.

79. The polymer dispersed liquid crystal device of claim 77 wherein said light absorption additive comprises a dichroic dye material.

80. The polymer dispersed liquid crystal device of claim 77 wherein said polymer phase comprises a precursor hardened by ultraviolet light or heat.

81. The polymer dispersed liquid crystal device of claim 77 wherein said polymer phase comprises a thermoplastic polymer, a liquid crystal polymer or a polymer which has a cosolvent with a liquid crystal.

82. The polymer dispersed liquid crystal device of claim 77 wherein said polymer phase comprises a polymer having no liquid crystal characteristics.

83. The polymer dispersed liquid crystal device of claim 77 wherein said polymer phase is obtained from polymerization of one or more polymer precursors containing molecules having one or more polymerizable portions and one or more aromatic ring portions.

84. The polymer dispersed liquid crystal device of claim 83 wherein said ring portions comprise phenyl or biphenyl or naphthyl or derivatives thereof.

85. A light modulating liquid crystal layer comprising

a birefringent, polymer, solid phase having no liquid crystal characteristics dispersed in a birefringent, liquid crystal phase,

optical axes of said phases aligned relative to at least one surface of two surfaces between which the layer is maintained, ordinary and extraordinary indices of refraction of said phases being matched whereby the layer is transparent when the respective optical axes of said phases are in an aligned state, and the layer is opaque when the respective optical axes of said phases are in an unaligned state wherein said respective optical axes are substantially in orthogonal relation,

said unaligned state occurring when an electric field is applied across said liquid crystal layer and said aligned state occurring in the absence said electric field across said liquid crystal layer.

86. The light modulating liquid crystal material of claim 85 wherein said relative alignment is either substantially perpendicular to or parallel with said material surface.

87. The light modulating liquid crystal material of claim of 85 wherein a chiral component is added to said liquid crystal phase.

88. The light modulating liquid crystal material of claim 85 wherein said birefringent, polymer, solid phase comprises a plurality of polymeric solid grains dispersed throughout said liquid crystal phase comprising a liquid crystal medium.

89. The light modulating liquid crystal material of claim of 88 wherein said polymeric solid grains are formed from a methacrylate having no liquid crystal side chains.

90. The light modulating liquid crystal material of claim of 89 wherein said methacrylate comprises naphthyl methacrylate, biphenyl methacrylate or biphenylmethyl methacrylate.

91. A light modulating liquid crystal layer comprising

a birefringent, liquid crystal or solid polymer dispersed in a birefringent, liquid crystal phase wherein said solid polymer,

the ratio of said liquid crystal phase to said polymer being greater than 1:

1,

a chiral type component additive included in said liquid crystal phase to provide a helical twist orientation to both said polymer and liquid crystal phase,

means to fix the helical twist orientation of said polymer in said liquid crystal phase,

optical axes of said liquid crystal phase and said polymer aligned relative to at least one surface of two surfaces between which the layer is maintained,

ordinary and extraordinary indices of refraction of said liquid crystal phase and said polymer being matched whereby the layer is transparent when the optical axes of said liquid crystal phase and polymer are in an aligned state, and the layer is opaque when the optical axes of said liquid crystal phase and polymer are in unaligned state.

92. The light modulating liquid crystal material of claim 91 wherein said liquid crystal phase is between 50% and 97% of said material.

93. The light modulating liquid crystal material of claim 91 wherein said material is transparent in a field-OFF state and is opaque in a field-ON state.

94. A light modulating liquid crystal material comprising:

a birefringent, polymer, solid phase having no liquid crystal characteristics dispersed in a birefringent, liquid crystal phase,

light absorption additive included in said liquid crystal phase,

the effective indices of refraction of the polymer solid phase and the liquid crystal phase being matched for all directions of incident light so that the material is transparent in a field-OFF state, and the effective indices of refraction are mismatched in directions of incident light so that the material is light absorbing and scattering in a field-ON state.

95. An improved polymer dispersed liquid crystal device having a drive voltage requirement under five volts, the improvement comprising:

a polymer precursor comprising a monomethacrylate and not a diacrylate; and

a liquid crystal layer comprising a liquid crystal material having a chiral component in the range of 0.1% to 5%.