Polymer dispersed liquid crystal (PDLC) display element for use in an electronic apparatus

• US 5,993,689 A
• Filed: 02/12/1997
• Issued: 11/30/1999
• Est. Priority Date: 03/29/1993
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Kobayashi, Hidekazu, Iisaka, Hidehito, Chino, Eiji, Yazaki, Masayuki
• Primary Examiner(s): WU, SHEAN CHIU
• Application Number:
  US08/799,487
• Time in Patent Office: 1,021 Days
• Field of Search: 252/299.01, 252/299.5, 349/182, 349/183, 349/184, 349/186, 349/88, 349/89, 349/10, 349/11, 428/1, 359/630, 345/87, 345/92
• US Class Current: 252/299.01
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: C09K 2323/00 Functional layers of liquid crystal optical display excluding electroactive liquid crystal layer characterised by chemical composition
• CPC Class Codes: C09K 2323/04 Charge transferring layer characterised by chemical composition, i.e. conductive
• CPC Class Codes: C09K 2323/05 Bonding or intermediate layer characterised by chemical composition, e.g. sealant or spacer
• CPC Class Codes: G02F 1/13324 Circuits comprising solar cells
• 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

Abstract

A polymer dispersed liquid crystal (PDLC) display element for use in an electronic apparatus wherein the display element operates in a PDLC mode or reverse PDLC mode providing for reduction of visual display haze, improved display contrast. The particular medium includes a liquid crystal portion and a polymer portion and may include a chiral component. In cases where visual display haze and contract is a particular problem in the utility of the reverse PDLC display element, such as in the case where the display element is combined with a solar battery, a sufficient amount of dichroic dye is added to the liquid crystal portion of the medium, and, further, a compound showing no fluorescence emission with respect to a liquid crystal portion, or a polymer or a chiral polymer precursor portion of the medium, is employed. The resulting electronic apparatus can, therefore, incorporate a reverse PDLC type display element in combination with a solar battery or other component that affects display quality in such elements to improve the overall visual quality and contrast in the display rendering the display more useful in more miniaturized applications.

Claims

1. An electronic apparatus comprising:

a display apparatus displaying a first information and

a separate display element displaying a second information,

said display element comprising a liquid crystal and polymer medium formed between a pair of spatially supported substrates, said substrates each having an electrode on one surface thereof, and means for applying an electric field across said medium via said electrodes wherein said medium is placed in a light transmissive state in the absence of the applied electric field and is placed in a light scattering state in the presence of the applied electric field,

said electronic apparatus displaying a superimposed information of both the second information of said display element by light scattering and the first information of said display apparatus,

wherein said liquid crystal portion includes a chiral component and thereby exhibits a variation of chiral pitch not exceeding 20% of an operating range of temperature for the display element.

2. The electronic apparatus according to claim 1 wherein a pitch of said chiral component in said medium is substantially the same as the pitch in liquid crystal portion of said liquid crystal and polymer medium.

3. The electronic apparatus according to claim 1 wherein said chiral component comprises a low molecular weight chiral component and a chiral polymer precursor, said chiral polymer precursor is incorporated into the polymer portion of said liquid crystal-polymer medium and said low molecular weight chiral component is incorporated into the liquid crystal portion of said liquid crystal-polymer medium.

4. The electronic apparatus according to claim 1 wherein said chiral component comprises at least two chiral components exhibiting an opposite temperature dependency in chiral pitch relative to each other.

5. The electronic apparatus according to claim 1 wherein said liquid crystal and polymer medium includes a compound exhibiting a fluorescence quantum yield in the visible region of not more than 0.3 and is provided in said medium in an amount of not less than 60 wt %.

6. The electronic apparatus according to claim 5 wherein said liquid crystal portion includes said compound comprising a biphenyl or tolane skeleton in its molecular composition.

7. The electronic apparatus according to claim 6 wherein said compound has a terphenyl skeleton in its molecular composition in the liquid crystal portion in an amount not exceeding about 10%.

8. The electronic apparatus according to claim 5 wherein said polymer portion includes said compound comprising a biphenyl or tolane skeleton in its molecular composition.

9. The electronic apparatus according to claim 8 wherein said compound has a terphenyl skeleton in its molecular composition in the polymer portion in an amount not exceeding about 10%.

10. The electronic apparatus according to claim 1 wherein the liquid crystal portion includes a dichroic dye.

11. The electronic apparatus according to claim 1 wherein said polymer is in a form selected from the group consisting of independent particles, chain connected particles, coupled particles, and particle aggregates.

12. The electronic apparatus according to claim 1 wherein said polymer is a gel network.

13. The electronic apparatus according to claim 1 wherein said polymer dispersed in the liquid crystal portion in the form of droplets.

14. The electronic apparatus according to claim 1 wherein a non-glare, anti-reflecting surface is provided on one surface of said display element.

15. The electronic apparatus according to claim 1 wherein a color filter is employed on a surface of one of said substrates in contact with liquid crystal and polymer medium.

16. The electronic apparatus according to claim 1 wherein said display element further comprises a plurality of active elements formed on a surface of one of said substrates in contact with said liquid crystal and polymer medium.

17. The electronic apparatus according to claim 1 wherein said polymer portion contains at least one of the following compounds:

##STR20## wherein n is an integer;

R represents an alkyl, alkoxy, cycloalkyl, or cycloalkoxy group;

R₁ and R₂ independently represent an alkyl, cycloalkyl, alkoxy or cycloalkoxy group or H or F; and

X represents H, F, Cl or CN.

18. The electronic apparatus according to claim 1 wherein said polymer portion contains at least one of the following compounds:

##STR21## wherein R and R'"'"' are respectively either H or CH₃ ;

B, B'"'"' and B" are respectively any one of OCO, COO, OCONH, NHCOO, CONH, NHCO, --C.tbd.C--, an alkyl group, O, N or S; and

A₁ and A₂ are respectively a group containing an aromatic ring comprising phenyl, biphenyl, terphenyl, quaterphenyl, naphthalene and anthracene with substitution thereof selected from the group consisting of a halogen, alkyl group and cyano group.

19. The electronic apparatus according to claim 1 wherein one of said substrates includes a reflective surface.

20. The electronic apparatus according to claim 1 further comprising a light absorbing reflective plate positioned on a back surface of said display element.

21. The electronic apparatus according to claim 20 wherein said light absorbing reflective plate comprises a solar battery.

24. The electronic apparatus according to claim 1 wherein said liquid crystal and polymer medium includes a dichroic dye.

25. The electronic apparatus of claim 16, wherein said active elements are selected from the group consisting of TFT, MIM, transistor and ferroelectric elements.

26. The electronic apparatus according to claim 1, wherein said display element is selected from the group consisting of a watch, an automobile meter display panel, an electronic memorandum book, and a display of a domestic electric product.

22. An electronic apparatus comprising:

a display apparatus displaying a first information and

a separate display element displaying a second information,

said display element comprising a liquid crystal and polymer medium formed between a pair of spatially supported substrates, said substrates each having an electrode on one surface thereof, and means for applying an electric field across said medium via said electrodes wherein said medium is placed in a light transmissive state in the absence of the applied electric field and is placed in a light scattering state in the presence of the applied electric field,

said electronic apparatus displaying a superimposed information of both the second information of said display element by light scattering and the first information of said display apparatus,

said electronic apparatus further comprising a refractive layer positioned between said display element and said display apparatus,

wherein said liquid crystal portion includes a chiral component and thereby exhibits a variation of chiral pitch not exceeding 20% of an operating range of temperature for the display element.

23. The electronic apparatus according to claim 22 wherein said refractive layer is transparent.