WO2005088589A1

WO2005088589A1 - Reflective display

Info

Publication number: WO2005088589A1
Application number: PCT/SE2005/000377
Authority: WO
Inventors: Kent Skarp; Gustav Franklin; Christian ADÅS
Original assignee: Swedish Lcd Center Ab
Priority date: 2004-03-18
Filing date: 2005-03-16
Publication date: 2005-09-22
Also published as: SE0400715D0

Abstract

The present invention relates to an LCD (1) adapted to work in reflective mode, comprising a front and a back substrate (11, 12), a front and a back electrode (13, 14), and a front and a back polarizer (15, 16). The present invention specifically teaches that the back electrode is reflective (14), that the back polarizer (16) is made out of a thin film polarizer, and that a transparent layer (17) is positioned between the reflective back electrode (14) and the back polarizer (16).

Description

REFLECTIVE DISPLAY

Field of invention The present invention relates to a liquid crystal display (LCD) adapted to work in reflective mode, comprising a front and a back substrate, a front and a back electrode, and a front and a back polarizer.

Description of the background art Various kinds of LCD's are known to the art. Certain applications where LCD's are used require a thin and sometimes flexible display, which enables displays in new portable products such as smart cards, toys and mobile phones etc that have an increasing demand for thinner and more flexible products. It is known that different components on a smart card share a mutual printed circuit board as a base that the card is built upon. It would be possible to build an LCD directly on such a smart card, using the printed circuit board as a substrate for the LCD. These applications require thin LCD's with high reflectance and high contrast and it is a problem to manufacture LCD's according to these requirements.

Summary of the present invention From the standpoint of the field of invention, as described above, the present invention relates to an LCD with a reflective back electrode, thus minimising the thickness of the combination of the electrode and the reflective layer. The present invention also teaches that the back polarizer is made out of a thin film polarizer, again in order to minimise the thickness of the LCD. With the purpose of increasing the amount of light that is reflected from the reflector the present invention teaches that a transparent layer is positioned between the reflective back electrode and the back polarizer. With the purpose of minimising the reflection of light in the transition be- tween the transparent layer and the back thin film polarizer it is proposed that the transparent layer has a refractive index that is close to the refractive index of the back thin film polarizer. With the purpose of providing the highest possible transmission of light through the transparent layer it is proposed that the transparent layer has a trans- mission of light that is at least more than 85%, and preferably more than 95%, in the visible light range. The transparent layer may be made out of a light or thermal curable material. With the purpose of preventing short circuits between the front and back electrode it is proposed that the transparent layer is made out of an electrically insulating material. The transparent layer can also act as a diffusion barrier for material that is degrading the LC-fluid, and it can act as a mechanical protection layer for the elec- trode and reflector in the LCD. An inventive LCD may be built on different kinds of back substrates. One embodiment teaches that the back substrate is a flexible back substrate. An example of a flexible back substrate is a paper-based substrate. With the purpose of overcoming the problems of diffusion through a paper based sub- strate the present invention teaches that the surface of such back substrate is preferably coated with a polymeric coating providing a required surface roughness. It is also possible to form an inventive LCD on a glass back substrate. Due to the possibility to form very thin LCD's through the present invention it is proposed that an inventive LCD is formed on a back substrate that is a part of an integrated printed circuit board for a product, where other components belonging to the product and the LCD are interconnected through the circuit board. Such product may for instance be a smart card or any kind of disposal casing such as a carton or other wrapping material. The back LC-alignment layer of an inventive LCD can be realised in vari- ous ways. One possible embodiment teaches that the LCD comprises a separate back LC-alignment layer in combination with said back thin film polarizer. This separate back LC-alignment layer may for instance be made out of a light curable or thermal curable polymer Another possible embodiment teaches that the LCD comprises a back LC- alignment layer that is made out of the back thin film polarizer. In order to overcome the problem of contamination of the LC from a thin film polarizer used as a back LC-alignment layer, the present invention teaches that a thin polymeric protective layer is positioned between the back thin film polarizer and the liquid crystal. The front substrate may be made out of a polymer foil or glass. If a polymer foil is used for front or back substrate then this foil may be made out of PET, PES, PEN, PC, polycyclic olefin, polyimide, poly arylate or other polymeric material. The front polarizer may also be realised in different ways. It may for instance be made out of an external polarizer, which may be made out of a thin film polarizer or out of a conventional plastic foil polarizer. The front polarizer may also be made out of an internal polarizer, which may be made out of a thin film polarizer. In this case the LCD may comprise a separate front LC-alignment layer in combination with the internal front thin film polarizer, in which case the front LC- alignment layer may be made out of a light curable or thermal curable polymer. It is also possible to make the front LC-alignment layer out of the internal front thin film polarizer. If the latter embodiment is used, then the present invention teaches that a thin polymeric protective layer is positioned between the internal front thin film polarizer and the liquid crystal of the LCD in order to overcome the problem of contamination of the LC from the thin film polarizer used as an LC-alignment layer.

Advantages The advantages of the present invention are that it allows the manufacturing of displays with a thin design, with high brightness and good contrast even at high multiplexing levels. An inventive LCD can also be integrated into a product where the back substrate act as a printed circuit board with several mounted electrical components which enables more efficient production of the product.

Brief description of drawings An LCD according to the present invention will now be described in more detail with reference to accompanying drawings, in which: Figure 1 is a schematic and simplified cross sectional view of a first embodiment of an inventive LCD, Figure 2 is a simplified view of a smart card with an inventive LCD, Figure 3 is a simplified view of a carton with an inventive LCD, Figure 4 is a schematic and simplified cross sectional view of a second embodiment of an inventive LCD, and Figure 5 is a schematic and simplified cross sectional view of a third embodiment of an inventive LCD.

Detailed description of embodiments as presently preferred Figure 1 is a schematic view of a liquid crystal display (LCD) 1 adapted to work in reflective mode, comprising a front and a back substrate 11 , 12, a front and a back electrode 13, 14, and a front and a back polarizer 15, 16. The present invention specifically teaches that the back electrode 14 is reflective, that the back polarizer 16 is made out of a thin film polarizer, and that a transparent layer 17 is positioned between the reflective back electrode 14 and the back polarizer 16. The transparent layer 17 has certain purposes and properties in order to achieve these purposes. One property is that the transparent layer 17 has a refractive index that is close to the refractive index of the back polarizer 16 in order to eliminate or minimise any reflection of light in the transition between the back polarizer 16 and the transparent layer 17. It is also proposed that the transparent layer 17 has a transmission of light that is more than 85%, or preferably more then 95%, in the visible light range. The transparent layer 17 may be made out of a light or thermal curable material and it is preferably made by an electrically insulating material. A transparent layer 17 with the above described properties will increase the light reflected from the reflector, and thus the overall performance of the LCD. It can also prevent short circuits between the front and back electrode13, 14, it can act as a diffusion barrier for material that is degrading the LC-fluid, and it can act as a mechanical protection layer for the electrode/reflector 14 in the LCD. The present invention teaches that the back substrate 12 may be a flexible back substrate. Thus, the back substrate may be paper based, in which case the surface of said back substrate is coated with a polymeric coating providing a required surface roughness. The back substrate 12 may also be made out of a polymer foil. The present invention may also be implemented on a back substrate 12 made out of glass. Since the present invention makes it possibility to manufacture thin LCD's, an inventive LCD is suitable to form on a back substrate that is a part of an integrated printed circuit board for a product where other components belonging to the product and the LCD are interconnected through the circuit board. Figure 2 shows that such a product is a smart card A with an LCD 1 and thereto belonging driver electronics and other electrical circuits 1a such as a computer unit, formed on a mutual substrate where in this case the card A itself forms the substrate. Figure 3 shows that the product B is a carton with an LCD 1 and thereto belonging driver electronics and other electrical circuits 1a, formed on a mutual substrate where in this case the carton B itself, or part of the carton, forms the substrate. It is obvious that the product may be any of wrapping or any other kind of disposal casing. An inventive LCD can be formed in different ways. Figure 1 shows that the LCD comprises a separate back LC-alignment layer 18 in combination with the back thin film polarizer 16. The figure also shows a separate front LC alignment layer 20. The LC-alignment layers 18, 20 may for instance be made out of a light curable or thermal curable polymer or a photo alignment material. Figure 4 shows that the LCD comprises a back LC-alignment layer 18' made out of the back thin film polarizer 16. A thin polymeric protective layer 19 is positioned between the back thin film polarizer 16 and the liquid crystal 2 belonging to the LCD 1. The front substrate 11 may, just as the back substrate, be made out of a polymer foil, such as a polymer foil made out of PET, PES, PEN, PC, polycyclic olefin, polyimide, poly arylate or other polymeric material. The front substrate 11 may also be made out of glass. Figure 1 shows a front polarizer 15 made out of an external polarizer, which may be made out of a thin film polarizer or a conventional plastic foil polarizer. Figure 4 shows that the front polarizer 15' is made out of an internal polarizer, which may be made out of a thin film polarizer. The figure shows that the LCD comprises a separate front LC-alignment layer 20 in combination with the internal front thin film polarizer 15'. This front LC- alignment layer 20 may for instance be made out of a light curable or thermal curable polymer or a photo alignment material. Figure 5 shows an alternative embodiment where the LCD comprises a front LC-alignment 20' layer made out of the internal front thin film polarizer 15'. The figure also shows that a thin polymeric protective layer 21 is positioned between the internal front thin film polarizer 15' and the liquid crystal 2 belonging to the LCD. It is obvious that the above described different embodiments of a back polarizer 16 and a front polarizer 15, 15', with respective LC alignment layer 18, 18', 20, 20' and protective layer 19, 21 , may be combined in any way. It will be understood that the invention is not restricted to the aforede- scribed and illustrated exemplifying embodiment thereof and that modifications can be made within the scope of the inventive concept as illustrated in the accompanying Claims.

Claims

1. A liquid crystal display adapted to work in reflective mode, comprising a front and a back substrate, a front and a back electrode, and a front and a back polarizer, characterised in, that said back electrode is reflective, that said back polarizer is made out of a thin film polarizer, and that a transparent layer is positioned between said reflective back electrode and said back polarizer.

2. An LCD according to Claim 1 , characterised in, that said transparent layer has a refractive index that is close to the refractive index of said back polarizer.

3. An LCD according to Claim 2, characterised in, that said transparent layer has a transmission of light that is more than 85% in the visible light range.

4. An LCD according to Claim 3, characterised in, that said transparent layer is made by a light or thermal curable material.

5. An LCD according to Claim 4, characterised in, that said transparent layer is made out of an electrically insulating material.

6. An LCD according to Claim 4 or 5, characterised in, that said transparent layer is made out of material that will act as a diffusion barrier for material that is degrading the LC-fluid and as a mechanical protection layer for the electrode and reflector in the LCD.

7. An LCD according to any preceding Claim, characterised in, that said back substrate is a flexible back substrate.

8. An LCD according to Claim 7, characterised in, that said back substrate is paper based, and that the surface of said back substrate is coated with a polymeric coating providing a required surface roughness.

9. An LCD according to Claim 7, characterised in, that said back substrate is made out of a polymer foil.

10. An LCD according to any one of Claims 1 to 6, characterised in, that said back substrate is a glass substrate.

11. An LCD according to any preceding Claim, characterised in, that said back substrate is a part of an integrated printed circuit board for a product, and that other components belonging to said product and said LCD are interconnected through said circuit board.

12. An LCD according to Claim 11 , characterised in, that said product is a smart card.

13. An LCD according to Claim 11 , characterised in, that said product is a carton, wrapping or any other kind of disposal casing.

14. An LCD according to any preceding Claim, characterised in, that said LCD comprises a separate back LC-alignment layer in combination with said back thin film polarizer.

15. An LCD according to Claim 13, characterised in, that said back LC-alignment layer is made out of a light curable or thermal curable polymer.

16. An LCD according to Claim 15, characterised in, that said back LC-alignment layer is made out of a photo alignment material.

17. An LCD according to any one of Claims 1 to 13, characterised in, that said LCD comprises a back LC-alignment layer, and that said back LC-alignment layer is made out of said back thin film polarizer.

18. An LCD according to Claim 17, characterised in, that a thin polymeric protective layer is positioned between said back thin film polarizer and the liquid crystal belonging to said LCD.

19. An LCD according to any preceding Claim, characterised in, that said front substrate is made out of a polymer foil.

20. An LCD according to Claim 9 or 19, characterised in, that said polymer foil is made out of PET, PES, PEN, PC, polycyclic olefin, polyimide, poly arylate or other polymeric material.

21. An LCD according to any one of Claims 1 to 18, characterised in, that said front substrate is made out of glass.

22. An LCD according to any preceding Claim, characterised in, that said front polarizer is made out of an external polarizer.

23. An LCD according to Claim 22, characterised in, that said external polarizer is made out of a thin film polarizer.

24. An LCD according to Claim 22, characterised in, that said external polarizer is made out of a conventional plastic foil polarizer.

25. An LCD according to any one of Claims 1 to 21 , characterised in, that said front polarizer is made out of an internal polarizer.

26. An LCD according to Claim 25, characterised in, that said front polarizer is made out of a thin film polarizer.

27. An LCD according to Claim 26, characterised in, that said LCD comprises a separate front LC-alignment layer in combination with said internal front thin film polarizer.

28. An LCD according to Claim 27, characterised in, that said front LC-alignment layer is made out of a light curable or thermal curable polymer.

29. An LCD according to Claim 27, characterised in, that said front LC-alignment layer is made out of a photo alignment material.

30. An LCD according to Claim 26, characterised in, that said LCD comprises a front LC-alignment layer, and that said front LC-alignment layer is made out of said internal front thin film polarizer.

31. An LCD according to Claim 30, characterised in, that a thin polymeric protective layer is positioned between said internal front thin film polarizer and the liquid crystal belonging to said LCD.