Light pipe, plate light source unit and reflection type liquid-crystal display device

• US 6,742,921 B2
• Filed: 06/26/2001
• Issued: 06/01/2004
• Est. Priority Date: 06/26/2000
• Status: Expired due to Fees

• Current Assignee: Nitto Denko Corporation
• Original Assignee: Nitto Denko Corporation
• Inventors: Umemoto, Seiji, Suzuki, Takao, Yano, Shuuji, Ariyoshi, Toshihiko
• Primary Examiner(s): CARIASO, ALAN B
• Application Number:
  US09/888,530
• Publication Number:
  US 20020015314A1
• Time in Patent Office: 1,071 Days
• Field of Search: 349/61-65, 349/67, 362/19, 362/31, 362/330, 362/339, 362/558, 362/561
• US Class Current: 362/561
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02F 1/133616 Front illuminating devices

Abstract

A light pipe includes a plate-like member having light output means formed in its upper surface so that light incident on an incidence side surface of the plate-like member is exited from the lower surface of the plate-like member through the light output means, an adhesive layer having a refractive index lower than that of the plate-like member, and (i) an anti-reflection layer made of a circularly polarizer and bonded to a lower surface of the plate-like member through the adhesive layer or (ii) a light-diffusing layer having a surface of fine prismatic structures and bonded to a lower surface of the plate-like member through the adhesive layer. A plane light source unit includes at least one light source disposed on one side surface of the light pipe. A reflection type liquid-crystal display device includes the plane light source unit and a liquid-crystal cell including a reflection layer disposed on the light output side of the plane light source unit.

Claims

1. A light pipe comprising:

a plate-like member including light output means formed in an upper surface of said plate-like member so that light incident on an incidence side surface of said plate-like member is exited from a lower surface of said plate-like member through said light output means;

an adhesive layer having a refractive index lower than that of said plate-like member; and

an anti-reflection layer made of a circular polarizer and bonded to a lower surface of said plate-like member through said adhesive layer,

wherein said light output means formed in said upper surface of said plate-like member is formed by a repetitive structure of prismatic structures each having an optical path changing face and a lone side face and arranged at intervals of a pitch of from 50 μ

m to 1.5 mm;

each of said optical path changing faces is formed of a slope inclined downward from said incidence side surface to a counter end surface opposite thereto at an inclination angle in a range of from 35 to 48 degrees with respect to a reference plane of said lower surface of said plate-like member;

each of said long side faces is made of a slope inclined at an angle in a range of from 0 to 10 degrees with respect to said reference plane;

a difference between inclination angles of any two lone side faces is not larger than 5 degrees over a surface of said plate-like member;

a difference between said inclination angles of adjacent ones of said long side faces is not larger than 1 degree; and

a projected area of said lone side faces on said reference plane is not smaller than 5 times as large as that of said optical path changing faces on said reference plane.

2. A light pipe according to claim 1, wherein said anti-reflection layer made of a circular polarizer includes a quarter-wave plate, and a linear polarizer.

3. A light pipe according to claim 2, wherein said anti-reflection layer made of a circular polarizer further includes a half-wave plate.

4. A light pipe according to claim 3, wherein a maximum intensity of light exited from said lower surface of said plate-like member in a plane perpendicular to reference planes of both said lower surface and said incidence side surface of said plate-like member is inclined at an angle of not larger than 30 degrees with respect to a normal to said reference plane of said lower surface of said plate-like member.

5. A light pipe according to claim 1, wherein ridgelines defining edges of said optical path changing faces are inclined within a range of ±

30 degrees with respect to a reference plane of said incidence side surface.

6. A light pipe according to claim 1, wherein said refractive index of said adhesive layer for bonding said anti-reflection layer to said lower surface of said plate-like member is lower than that of said plate-like member by 0.01 or more.

7. A light pipe according to claim 1, wherein said refractive index of said adhesive layer for bonding said anti-reflection layer to said lower surface of said plate-like member is not higher than 1.47.

8. A light pipe according to claim 1, wherein said adhesive layer for bonding said anti-reflection layer to said lower surface of said plate-like member is constituted by a tacky layer.

9. A plane light source unit wherein at least one light source is disposed on one side surface of a light pipe defined in claim 1.

10. A reflection type light-crystal display device wherein a liquid-crystal cell including a reflection layer is disposed on a light exit side of a plane light source unit defined in claim 9.

11. A light pipe comprising:

a plate-like member including light output means formed in an upper surface of said plate-like member so that light incident on an incidence side surface of said plate-like member is exited from a lower surface of said plate-like member through said light output means;

an adhesive layer having a refractive index lower than that of said plate-like member; and

a light-diffusing layer including fine prismatic structures formed in a surface thereof and bonded to said lower surface of said plate-like member through said adhesive layer,

wherein said light output means formed in said upper surface of said plate-like member is formed by a repetitive structure of prismatic structures arranged at intervals of a pitch of from 50 μ

m to 1.5 mm and each having an optical path changing face and a long side face;

each of said optical path changing faces is constituted by a slope inclined downward from said incidence side surface side to a counter end side at an inclination angle in a range of from 35 to 48 degrees with respect to a reference plane of said lower surface so that a projected width of each of said slopes on said reference plane is not larger than 40 μ

m; and

each of said long side faces is constituted by a slope inclined at an inclination angle in a range of from 0 to 10 degrees with respect to said reference plane so that an angle difference between any two long side faces over a surface of said plate-like member is not larger than 5 degrees, so that a difference between inclination angles of adjacent ones of said long side faces is not larger than 1 degree and so that a projected area of said long side faces on said reference plane is not smaller than 5 times as large as a projected area of said optical path changing faces on said reference plane.

12. A light pipe according to claim 11, wherein said light-diffusing layer is constituted by a fine prismatic-structure layer provided on a transparent film.

13. A light pipe according to claim 11, wherein said light-diffusing layer further includes an anti-reflection layer provided on said fine prismatic-structure layer.

14. A light pipe according to claim 11, wherein a direction of maximum intensity of light exited from said lower surface in a plane perpendicular both to a reference plane of said lower surface of said plate-like member and to a reference plane of said incidence side surface of said plate-like member is within 30 degrees with respect to a normal to said reference pane of said lower surface.

15. A light pipe according to claim 11, wherein ridgelines defining edges of said optical path changing faces are in a range of ±

30 degrees with respect to a reference plane of said incidence side surface.

16. A light pipe according to claim 11, wherein the refractive index of said adhesive layer for bonding said light-diffusing layer to said lower surface of said plate-like member is lower by a value of from 0.01 to 0.2 than that of said plate-like member;

and a refractive index of aid light-diffusing layer is higher than that of said adhesive layer.

17. A light pipe according to claim 11, wherein the refractive index of said adhesive layer for bonding said light-diffusing layer to said lower surface of said plate-like member is not higher than 1.47.

18. A light pipe according to claim 11, wherein said adhesive layer for bonding said light-diffusing layer to said lower surface of said plate-like member is constituted by a tacky layer.

19. A plane light source unit wherein at least one light source is disposed on one side surface of a light pipe defined in claim 11.

20. A reflection type liquid-crystal display device wherein a liquid-crystal cell including a reflection layer is disposed on a light exit side of a plane light source unit defined in claim 19.