Light pipe and method for producing the same

• US 6,659,615 B2
• Filed: 01/16/2001
• Issued: 12/09/2003
• Est. Priority Date: 01/13/2000
• Status: Expired due to Fees

• Current Assignee: Nitto Denko Corporation
• Original Assignee: Nitto Denko Corporation
• Inventors: Umemoto, Seiji
• Primary Examiner(s): O'Shea, Sandra
• Assistant Examiner(s): TRUONG, BAO Q
• Application Number:
  US09/759,238
• Publication Number:
  US 20010010630A1
• Time in Patent Office: 1,057 Days
• Field of Search: 362/26, 362/29, 362/31, 362/32, 362/302, 362/309, 362/331, 385/901, 359/580, 359/831, 359/599
• US Class Current: 362/600
• 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 6/005 provided by one optical element, or plurality thereof, placed on the light output side of the light guide
• CPC Class Codes: Y10S 385/901 Illuminating or display apparatus

Abstract

A light pipe has a transparent resin plate having an average in-plane retardation of not larger than 20 nm, a transparent film having an average in-plane retardation of not larger than 20 nm, and an adhesive layer having a refractive index different by 0.1 or less from that of the transparent film. The transparent film is bonded to the transparent resin plate through the adhesive layer and wherein in the transparent film includes a repetitive prismatic structure constituted by optical path control slopes which are disposed on an outer surface of the transparent film and which are aligned in a substantially predetermined direction so that each of the optical path control slopes is inclined at an inclination angle in a range of from 35 to 48 degrees with respect to a film plane.

Claims

1. A light pipe comprising:

a transparent resin plate having an average in-plane retardation of not larger than 20 nm;

a transparent film having an average in-plane retardation of not larger than 20 nm; and

an adhesive layer having a refractive index different by 0.1 or less from that of said transparent film,

wherein said transparent film is bonded to said transparent resin plate through said adhesive layer, and

wherein said transparent film includes a repetitive prismatic structure constituted by optical path control slopes which are disposed on an outer surface of said transparent film and which are aligned in a substantially predetermined direction so that each of said optical path control slopes is inclined at an inclination angle in a range of from 35 to 48 degrees with respect to a film plane,

wherein a projected area, onto said film plane, of flat surfaces each having an inclination angle of not larger than 5 degrees with respect to said film plane is not smaller than 10 times as large as a projected area, onto said film plane, of slopes each having an inclination angle of not smaller than 35 degrees with respect to said film plane.

2. A light pipe according to claim 1, wherein

said optical path control slopes aligned in a substantially predetermined direction contain at least two kinds of surfaces, one kind of surfaces being a reference, the other kind of surfaces being made to face a direction opposite to said reference, and

a refractive index difference between said transparent resin plate and said adhesive layer is not larger than 0.1.

3. A light pipe according to claim 1, wherein said inclination angle of each of said optical path control slopes with respect to said film plane is in a range of from 38 to 45 degrees.

4. A light pipe according to claim 1, wherein said optical path control slopes are formed based on a structure of grooves each substantially shaped like an isosceles triangle or any other triangle in section.

5. A light pipe according to claim 1, wherein said optical path control slopes are formed based on a structure of grooves or protrusions each substantially shaped like a tetragon or a pentagon in section.

6. A light pipe according to claim 1,

wherein said prismatic structure is constituted by said optical path control slopes each inclined at said inclination angle in a range of from 38 to 45 degrees with respect to said film plane, and said flat surfaces each inclined at said inclination angle of not larger than 5 degrees with respect to said film plane, said flat surfaces having a width of not smaller than 10 times as large as that of said optical path control slopes, and

wherein said prismatic structure is formed by continuous grooves from one end to the other end of said transparent film, each groove substantially being shaped like a triangle in section.

7. A light pipe according to claim 1, wherein said prismatic structure constituted by said optical path control slopes is formed by discontinuous grooves each substantially shaped like a polygon such as a triangle, a tetragon or a pentagon in section,

wherein a length of each of said discontinuous grooves is not smaller than 5 times as large as a depth of said groove;

wherein said optical path control slopes are formed in a direction of the length of said grooves and inclined at said inclination angle in a range of from 38 to 45 degrees with respect to said film plane, and

wherein a projected area, onto said film plane, of said discontinuous grooves is not larger than 10 % of said film plane.

8. A light pipe according to claim 1, further comprising a reflection layer disposed closely on a surface of said transparent film on which said prismatic structure having said optical path control slopes is formed.

9. A light pipe according to claim 1, wherein ridgelines of said optical path control slopes are disposed in parallel to one side of said transparent film or with an inclination angle range of ±

30 degrees with respect to said one side.

10. A light pipe according to claim 1, wherein said adhesive layer is of a light diffuse type.

11. A light pipe according to claim 1, wherein said transparent resin plate is molded from a plate by a casting system.

12. A method for producing a light pipe, comprising steps of:

forming a repetitive prismatic structure on one surface of a transparent film through a mold having a predetermined prismatic structure so that said repetitive prismatic structure has optical path control slopes which are aligned in a substantially predetermined direction and each of which is inclined at an inclination angle in a range of from 35 to 48 degrees with respect to a film plane;

providing an adhesive layer on a surface of said transparent film on which said repetitive prismatic structure is not formed;

molding said transparent film and a transparent resin plate into predetermined shapes respectively; and

bonding said transparent film to said transparent resin plate through said adhesive layer provided on said transparent film,

wherein a projected area, onto said film plane, of flat surfaces each having an inclination angle of not larger than 5 degrees with respect to said film plane is not smaller than 10 times as large as a projected area, onto said film plane, of slopes each having an inclination angle of not smaller than 35 degrees with respect to said film plane.

13. A method for producing a light pipe according to claim 12, wherein the step of forming said repetitive prismatic structure having said optical path control slopes includes steps of:

applying an ultraviolet-curable resin on one surface of said transparent film to thereby form a coating layer of said ultraviolet-curable resin;

curing said coating layer of said ultraviolet-curable resin by irradiation with ultraviolet rays while bringing said coating layer into close contact with a surface of said mold on which a predetermined prismatic structure is formed; and

stripping said transparent film off from said mold to collect said transparent film.

14. A method for producing a light pipe according to claim 12, wherein the step of molding said transparent resin plate into said predetermined shape includes the step of cutting a resin plate formed by a casting system into a predetermined shape.

15. A method for producing a light pipe according to claim 12, wherein the step of bonding said transparent film to said transparent resin plate through said adhesive layer provided on said transparent film includes steps of:

bonding said transparent film to said transparent resin plate through said adhesive layer; and

fixing said transparent film to said transparent resin plate by heat and under pressure.

16. A light pipe comprising:

a transparent resin plate having an average in-plane retardation of not larger than 20 nm;

a transparent film having an average in-plane retardation of not larger than 20 nm; and

an adhesive layer having a refractive index different by 0.1 or less from that of said transparent film,

wherein said transparent film is bonded to a first surface of said transparent resin plate through said adhesive layer, and

wherein said transparent film includes a repetitive prismatic structure constituted by optical path control slopes which are disposed on an outer surface of said transparent film and which are aligned in a substantially predetermined direction so that each of said optical path control slopes is inclined at an inclination angle in a range of from 35 to 48 degrees with respect to a film plane, and wherein said optical path control slopes face an incidence side surface of the light pipe, and wherein a second surface of said transparent resin plate, that is opposite to said first surface and not bonded to said transparent film, is formed as a flat surface and functions as a light emitting surface.

17. A method for producing a light pipe having a transparent resin plate having an average in-plane retardation of not larger than 20 nm, said transparent resin plate having a first and second surface;

a transparent film having an average in-plane retardation of not larger than 20 nm; and

an adhesive layer having a refractive index different by 0.1 or less from that of said transparent film, and wherein said second surface of said transparent resin plate, that is opposite to said first surface, has a flat surface

comprising steps of;

forming a repetitive prismatic structure on one surface of the transparent film through a mold having a predetermined prismatic structure so that said repetitive prismatic structure has optical path control slopes which are aligned in a substantially predetermined direction and each of which is inclined at an inclination angle in a range of from 35 to 48 degrees with respect to a film plane;

providing the adhesive layer on a surface of said transparent film on which said repetitive prismatic structure is not formed;

molding said transparent film and said transparent resin plate into predetermined shapes respectively; and

bonding said transparent film to first surface of said transparent resin plate through said adhesive layer provided on said transparent film,

wherein a projected area, onto said film plane, of flat surfaces each having an inclination angle of not larger than 5 degrees with respect to said film plane is not smaller than 10 times as large as a projected area, onto said film plane, of slopes each having an inclination angle of not smaller than 35 degrees with respect to said film plane.