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EP-4741887-A2 - OPTICAL SHEET LAMINATE, BACKLIGHT UNIT, LIQUID CRYSTAL DISPLAY DEVICE, INFORMATION EQUIPMENT, AND PRODUCTION METHOD FOR BACKLIGHT UNIT

EP4741887A2EP 4741887 A2EP4741887 A2EP 4741887A2EP-4741887-A2

Abstract

An diffusion sheet laminate 100 is built in a backlight unit 40. The diffusion sheet laminate 100 includes a plurality of diffusion sheets 43 each having a first surface 21a having a plurality of recesses 22 having a substantially inverted quadrangular pyramid shape, suitable to be built under a pair of prism sheets 44 and 45 having prism extending directions perpendicular to each other. The recesses 22 have an apex angle of 95° or more. The recesses 22 are arrayed in a two-dimensional matrix. The prism extending direction of a lower prism sheet 44 and the arrangement direction of the recesses 22 on an upper diffusion sheet 43A intersect with each other at an angular difference of 30° or less.

Inventors

  • UENO, HIROAKI
  • TSAI, CHENGHENG

Assignees

  • KEIWA Incorporated

Dates

Publication Date
20260513
Application Date
20221115

Claims (11)

  1. A diffusion sheet laminate (100) suitable to be built under a pair of prism sheets having prism extending directions perpendicular to each other in a backlight unit (40), comprising: a plurality of diffusion sheets (43A, 43B) each having surfaces, at least one of the surfaces having a plurality of recesses (22) having a substantially inverted quadrangular pyramid shape, wherein the plurality of recesses (22) have an apex angle of 95° or more, and of 120° or less, the plurality of recesses (22) are arrayed in a two-dimensional matrix, and a prism extending direction of a lower prism sheet (44) which is one of the pair of prism sheets (44, 45) and is closer to the plurality of diffusion sheets (43A, 43B) and an arrangement direction of the plurality of recesses (22) on an upper diffusion sheet (43A) which is one of the plurality of diffusion sheets (43A, 43B) and is closest to the lower prism sheet (44) intersect with each other at an angular difference of 30° or less.
  2. The diffusion sheet laminate (100) of claim 1, wherein the apex angle is 110° or less.
  3. The diffusion sheet laminate (100) of any one of claims 1 to 2, wherein another optical sheet is not interposed between the upper diffusion sheet (43A) and the lower prism sheet (43B).
  4. The diffusion sheet laminate (100) of any one of claims 1 to 3, wherein the plurality of recesses (22) are provided on a light emission surface (21a) of the upper diffusion sheet (43A) which faces the lower prism sheet (44).
  5. The diffusion sheet laminate (100) of any one of claims 1 to 4, wherein the plurality of diffusion sheets (43A, 43B) include a lower diffusion sheet (43B) on which an arrangement direction of the plurality of recesses (22) is different from the arrangement direction of the plurality of recesses (22) on the upper diffusion sheet (43A).
  6. A backlight unit (40) comprising: a plurality of point light sources (42), and the diffusion sheet laminate (100) of any one of claims 1 to 5, wherein the plurality of diffusion sheets (43A, 43B) are arranged between the plurality of point light sources (42) and the pair of prism sheets (44, 45) and wherein the backlight unit (40) is suitable to be built in a liquid crystal display device (50) such that the backlight unit (40) is suitable to lead light emitted from the plurality of point light sources (42) toward a display screen (50a) of the liquid crystal display device (50) and such that the diffusion sheet laminate (100) is between the display screen (50a) and the plurality of point light sources (42).
  7. The backlight unit (40) of claim 6, wherein the plurality of point light sources (42) are white light sources.
  8. The backlight unit (40) of claim 6 or 7, wherein the plurality of point light sources (42) are arranged on a reflection sheet (41) provided opposite to the display screen (50a) when viewed from the plurality of diffusion sheets (43A, 43B).
  9. The backlight unit (40) of any one of claims 6 to 8, wherein a distance between the plurality of point light sources (42) and the plurality of diffusion sheets (43A, 43B) is 5 mm or less.
  10. A liquid crystal display device (50), comprising: the backlight unit (40) of any one of claims 6 to 9; and a liquid crystal display panel (5).
  11. An information equipment, comprising: the liquid crystal display device (50) of claim 10.

Description

TECHNICAL FIELD The present disclosure relates to a diffusion sheet laminate, a backlight unit, a liquid crystal display device, and an information equipment. BACKGROUND ART Liquid crystal display devices (hereinafter referred to as liquid crystal displays in some cases) have been widely used as display devices for various information equipment such as smartphones and tablet terminals. A major type of a backlight of a liquid crystal display is a direct type in which light sources are arranged on the back surface of the liquid crystal panel. When the direct type backlight is adopted, an optical sheet such as a diffusion sheet or a prism sheet is used to diffuse light emitted from a light source such as a light emitting diode (LED) to the improve uniformity of luminance and chromaticity over the entire screen (see, e.g., Patent Document 1). In general, in a direct type backlight unit, two prism sheets whose respective prism ridges perpendicularly cross each other are arranged above a diffusion sheet (i.e., closer to a display screen). Further, to improve the uniformity of luminance in a display screen (in-plane luminance uniformity), a plurality of diffusion sheets may be layered and used. CITATION LIST PATENT DOCUMENT Patent Document 1: Japanese Unexamined Patent Publication No. 2011-129277 SUMMARY OF THE INVENTION TECHNICAL PROBLEM As a backlight unit is required to be made thinner, the thickness of a diffusion sheet and the number of layered diffusion sheets are required to be reduced. Further, since the direct type backlight unit has light sources arranged directly below the display screen, the distance between the light sources and the diffusion sheet is also required to be reduced. However, the reduction in thickness by the thickness of a diffusion sheet or the number of layered diffusion sheets being reduced, the distance between the light sources and the diffusion sheet being reduced, or the like leads to decrease in the in-plane luminance uniformity. It is an object of the present disclosure to achieve less reduction in the in-plane luminance uniformity even when the backlight unit is made thinner. SOLUTION TO THE PROBLEM To achieve the object, a diffusion sheet laminate of the present disclosure built in a backlight unit includes: a plurality of diffusion sheets each having surfaces, at least one of which has a plurality of recesses having a substantially inverted quadrangular pyramid shape, suitable to be built under a pair of prism sheets layered above the plurality of diffusion sheets and having prism extending directions perpendicular to each other, wherein the plurality of recesses have an apex angle of 95° or more and of 120° or less, the plurality of recesses are arrayed in a two-dimensional matrix, and a prism extending direction of a lower prism sheet which is one of the pair of prism sheets and is closer to the plurality of diffusion sheets and an arrangement direction of the plurality of recesses on an upper diffusion sheet which is one of the plurality of diffusion sheets and is closest to the lower prism sheet intersect with each other at an angular difference of 30° or less. With the same light sources and the same diffusion sheet laminate structure, the diffusion sheet laminate of the present disclosure can provide more significantly increased in-plane luminance uniformity than when the recesses having a substantially inverted quadrangular pyramid shape in each diffusion sheet have an apex angle of less than 95° or when the angular difference between the recess arrangement direction of the upper diffusion sheet and the prism extending direction of the lower prism sheet is more than 30°. This enables less reduction in the in-plane luminance uniformity even when the backlight unit is made thinner by the thickness of the diffusion sheet or the number of layered diffusion sheets being reduced or the like. In the diffusion sheet laminate of the present disclosure, when the apex angle is 120° or less, preferably 110° or less, the light diffusing effect by the plurality of recesses can be less reduced. In the diffusion sheet laminate of the present disclosure, when another optical sheet is not interposed between the upper diffusion sheet and the lower prism sheet, this enables less degradation in optical characteristics such as the in-plane luminance uniformity and the like attributed to the above other optical sheet. In the diffusion sheet laminate of the present disclosure, when the plurality of recesses are provided on the light emission surface, which faces the lower prism sheet, of the upper diffusion sheet, the in-plane luminance uniformity can be more increased than when the recesses are provided on the light incident surface. In the diffusion sheet laminate of the present disclosure, when the plurality of diffusion sheets include a lower diffusion sheet on which an arrangement direction of the plurality of recesses is different from the arrangement direction of the plurality of reces