Optical sheet and display device having the optical sheet

• US 6,822,707 B2
• Filed: 10/08/2002
• Issued: 11/23/2004
• Est. Priority Date: 10/11/2001
• Status: Expired due to Fees

• Current Assignee: Nitto Denko Corporation
• Original Assignee: Nitto Denko Corporation
• Inventors: Adachi, Masaya, Tsumura, Makoto, Ariyoshi, Toshihiko
• Primary Examiner(s): TON, MINH TOAN T
• Application Number:
  US10/265,769
• Publication Number:
  US 20030072080A1
• Time in Patent Office: 777 Days
• Field of Search: 349/64, 349/112, 349/95, 359/619, 359/599, 359/707
• US Class Current: 349/112
• CPC Class Codes: G02B 3/0031 Replication or moulding, e.g. hot embossing, UV-casting, injection moulding
• CPC Class Codes: G02B 3/005 arranged along a single direction only, e.g. lenticular sheets G02B3/0043 takes precedence
• CPC Class Codes: G02B 3/0056 arranged along two different directions in a plane, e.g. honeycomb arrangement of lenses G02B3/0043 takes precedence; miniaturised objectives for electronic devices employing wafer level optics G02B13/0085
• CPC Class Codes: G02B 5/0242 by means of dispersed particles
• CPC Class Codes: G02B 5/0278 used in transmission
• CPC Class Codes: G02F 1/133504 Diffusing, scattering, diffracting elements associated to illuminating devices G02F1/133606
• CPC Class Codes: G02F 1/133526 Lenses, e.g. microlenses or Fresnel lenses
• CPC Class Codes: G03B 21/56 Projection screens

Abstract

An optical sheet has a transparent base material; a fine lens array constituted by a plurality of fine unit lenses formed on a front surface of the transparent base material; a diffusing layer formed on a rear surface of the transparent base material opposite to the surface on which the fine lens array is formed; and a light absorbing layer formed on the diffusing layer and including fine opening portions substantially located at focal points of the unit lenses; wherein: the diffusing layer is made of a transparent medium containing transparent fine particles different in refractive index from the transparent medium; and the transparent fine particles have a mean particle size in a particle size range for maximizing a value of Q/R at each of wavelengths in a visible region when Q is a scattering sectional area per transparent fine particle, and R is a radius of each of the transparent fine particles.

Claims

1. An optical sheet comprising:

a transparent base material;

a fine lens array constituted by a plurality of fine unit lenses formed on a front surface of said transparent base material;

a diffusing layer formed on a rear surface of said transparent base material opposite to said surface on which said fine lens array is formed; and

a light absorbing layer formed on said diffusing layer and including fine opening portions substantially located at focal points of said unit lenses;

wherein said diffusing layer is made of a transparent medium containing transparent fine particles different in refractive index from said transparent medium, and

said transparent fine particles have a mean particle size in a particle size range for maximizing a value of Q/R at each of wavelengths in a visible region when Q is a scattering sectional area per transparent fine particle, and R is a radius of each of said transparent fine particles.

2. An optical sheet according to claim 1, wherein said transparent fine particles have a mean particle size in a particle size range for maximizing a value of Q/R in a wavelength range of from 525 to 575 nm.

3. An optical sheet according to claim 1, wherein said unit lenses constituting said fine lens array are arranged at intervals of a pitch of not larger than 10 μ

m, Δ

n is in a range of from 0.03 to 0.2 when Δ

n is the refractive index difference between said transparent medium and said transparent fine particles, and said diffusing layer has a thickness smaller than 20 μ

m.

4. An optical sheet comprising:

a transparent base material;

a fine lens array constituted by a plurality of fine unit lenses formed on a front surface of said transparent base material;

a diffusing layer formed on a rear surface of said transparent base material opposite to said surface on which said fine lens array is formed; and

a light absorbing layer formed on said diffusing layer and including fine opening portions substantially located at focal points of said unit lenses;

wherein said diffusing layer is made of a transparent medium containing transparent fine particles different in refractive index from said transparent medium, and

said transparent fine particles have a mean particle size in one range selected from a particle size range for maximizing a value of Q/R at each of wavelengths in a visible region and a range which is near said particle size range and in which variation in the value of Q/R due to the wavelengths in the visible region is reduced, when Q is a scattering sectional area per transparent fine particle, and R is a radius of each of said transparent fine particles.

5. A back projection type display device comprising:

a projector including a light source, a two-dimensional optical switching element for modulating light emitted from said light source in accordance with image information to form an optical image, and a projection lens for projecting said optical image while magnifying said optical image; and

a transmission type screen having a back surface for receiving light projected from said projector, and a front surface for displaying said light, said transmission type screen including an optical sheet, and a Fresnel lens sheet provided on a projection light incidence side of said optical sheet, said optical sheet having a transparent base material, a fine lens array constituted by a plurality of fine unit lenses formed on a front surface of said transparent base material, a diffusing layer formed on a rear surface of said transparent base material opposite to said surface on which said fine lens array is formed, and a light absorbing layer formed on said diffusing layer and having fine opening portions substantially located at focal points of said unit lenses;

wherein said diffusing layer of said optical sheet is made of a transparent medium containing transparent fine particles different in refractive index from said transparent medium, and said transparent fine particles have a mean particle size in one range selected from a particle size range for maximizing a value of Q/R at each of wavelengths in a visible region and a range which is near said particle size range and in which variation in the value of Q/R due to the wavelengths in the visible region is reduced, when Q is a scattering sectional area per transparent fine particle, and R is a radius of each of said transparent fine particles.

6. A liquid-crystal display device comprising:

a pair of transparent substrates each of which is constituted by a laminate of a transparent electrode and an oriented film and which are bonded to each other through a predetermined gap so that surfaces on which said oriented films are formed are opposite to each other;

a liquid-crystal layer held between said pair of transparent substrates;

a unit for applying a voltage corresponding to an image signal between said transparent electrodes; and

polarizers arranged on a light incidence surface side and a light emitting surface side of said pair of transparent substrates respectively;

wherein said liquid-crystal display device further comprises a backlight unit disposed on a back surface side of said pair of transparent substrates for outputting substantially parallel light rays, and an optical sheet disposed on a light emitting surface side of said pair of transparent substrates, said optical sheet including a transparent base material, a fine lens array constituted by a plurality of fine unit lenses formed on a front surface of said transparent base material, a diffusing layer formed on a rear surface of said transparent base material opposite to said surface on which said fine lens array is formed, and a light absorbing layer formed on said diffusing layer and having fine opening portions substantially located at focal points of said unit lenses;

said diffusing layer of said optical sheet is made of a transparent medium containing transparent fine particles different in refractive index from said transparent medium; and

said transparent fine particles have a mean particle size in one range selected from a particle size range for maximizing a value of Q/R at each of wavelengths in a visible region and a range which is near said particle size range and in which variation in the value of Q/R due to the wavelengths in the visible region is reduced, when Q is a scattering sectional area per transparent fine particle, and R is a radius of each of said transparent fine particles.