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EP-4462013-B1 - OPTICAL SHEET LAMINATE, BACKLIGHT UNIT, LIQUID CRYSTAL DISPLAY DEVICE, INFORMATION EQUIPMENT, AND PRODUCTION METHOD FOR BACKLIGHT UNIT

EP4462013B1EP 4462013 B1EP4462013 B1EP 4462013B1EP-4462013-B1

Inventors

  • UENO HIROAKI
  • TSAI CHENGHENG

Dates

Publication Date
20260513
Application Date
20221115

Claims (12)

  1. An optical sheet laminate (100) suitable to be built 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; and a pair of prism sheets (44, 45) layered above the plurality of diffusion sheets (43A, 43B) and having prism extending directions perpendicular to each other, 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 optical sheet laminate (100) of claim 1, wherein the apex angle is 110° or less.
  3. The optical 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 optical 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 optical 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 optical 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 device and such that the optical 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.
  12. A production method for a backlight unit (40) built in a liquid crystal display device (50) and leading light emitted from a plurality of point light sources (42) toward a display screen (50a), the method comprising: arranging and layering a plurality of diffusion sheets (43A, 43B) between the plurality of point light sources (42) and the display screen (50a), where the plurality of diffusion sheets (43A, 43B) each have surfaces, at least one of the surfaces has a plurality of recesses (22) having a substantially inverted quadrangular pyramid shape; and arranging a pair of prism sheets (44, 45) between the plurality of diffusion sheets (43A, 43B) and the display screen (50a), where the pair of prism sheets (44, 45) have prism extending directions perpendicular to each other, 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 the plurality of diffusion sheets (43A, 43B) and the pair of prism sheets (44, 45) are arranged so that 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.

Description

TECHNICAL FIELD The present disclosure relates to an optical sheet laminate, a backlight unit, a liquid crystal display device, an information equipment, and a production method for the backlight unit. 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, Japanese Unexamined Patent Publication No. JP 2011-129277 A). 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. WO 2010/010840 A1 shows a photodiffusion plate comprising a light incident surface, on which a light is incident, and a light-emitting surface formed on the surface opposite to the light incident surface for diffusing and emitting the light incident on the light incident surface, wherein at least one of the light incident surface and the light-emitting surface includes recess-projection regions having a plurality of repetition units, wherein each of the repetition units includes at least one recess-projection structure having at least two surfaces, wherein at least two of the surfaces in the repetition units are rough, wherein the ratio of the rough surfaces to the surface of the entire region having the repetition units in each of the recess-projection regions is 50 % or less, and wherein at least one of the surfaces facing a rough surface in the repetition units is also rough. The recessed structures may have a substantially inverted quadrangular pyramid shape with an apex angle of 160°. Further, the concavo-convex structure and the edge (212) of the light diffusing plate may have an angle within the range of 5° and 40°. Further prior art is known from JP 2021 162840 A and WO 2005/083475 A1. 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, an optical sheet laminate of the present disclosure built in a backlight unit includes: a plurality of diffusion sheets each having surfaces, at least one of the surfaces having a plurality of recesses having a substantially inverted quadrangular pyramid shape; and 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 120° or less, preferably 110° 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 optical sheet laminate structure, the optical 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 thin