US-12625401-B2 - Light diffusion sheet, back-light unit, liquid crystal display device, information apparatus, and method for manufacturing back-light unit

US12625401B2US 12625401 B2US12625401 B2US 12625401B2US-12625401-B2

Abstract

A light diffusion sheet is incorporated in a backlight unit using a plurality of light sources arranged in a two-dimensional matrix. The light diffusion sheet has surfaces, on at least one of which a plurality of recesses having a substantially inverted quadrangular pyramid shape are arranged in a two-dimensional matrix. An intersecting angle between an arrangement direction of the plurality of recesses and an arrangement direction of the plurality of light sources is 30° or more and 60° or less.

Inventors

Chengheng TSAI

Assignees

KEIWA INCORPORATED

Dates

Publication Date: 20260512
Application Date: 20250425
Priority Date: 20220309

Claims (11)

1 . A light diffusion sheet capable of being incorporated into a backlight unit using a plurality of light sources arranged in a two-dimensional matrix, the light diffusion sheet comprising: surfaces on at least one of which a plurality of recesses having a substantially inverted quadrangular pyramid shape are arranged in a two-dimensional matrix, wherein an intersecting angle between an arrangement direction of the plurality of recesses and an arrangement direction of the plurality of light sources is 30° or more and 60° or less; wherein the light diffusion sheet has a luminance uniformity of 150 or more, the luminance uniformity determined based on an average value of luminance divided by a standard deviation of luminance.
2 . The light diffusion sheet of claim 1 , wherein the intersecting angle is 35° or more and 55° or less.
3 . The light diffusion sheet of claim 1 , wherein the plurality of recesses are provided on a light emitting surface.
4 . A backlight unit incorporated in a liquid crystal display device and leading light emitted from a plurality of light sources arranged in a two-dimensional matrix to a display screen, comprising: the light diffusion sheet of claim 1 provided between the display screen and the plurality of light sources.
5 . The backlight unit of claim 4 , wherein the light diffusion sheet includes a plurality of the light diffusion sheets.
6 . The backlight unit of claim 4 , comprising: a color conversion sheet provided between the display screen and the plurality of light sources and configured to convert a wavelength of light emitted from the plurality of light sources.
7 . The backlight unit of claim 4 , comprising: a luminance enhancing sheet provided between the light diffusion sheet and the display screen and configured to enhance luminance of light emitted from the plurality of light sources.
8 . The backlight unit of claim 4 , wherein the plurality of light sources are arranged on a reflection sheet provided opposite to the display screen when viewed from the light diffusion sheet.
9 . A liquid crystal display device, comprising: the backlight unit of claim 4 ; and a liquid crystal display panel.
10 . An information apparatus comprising the liquid crystal display device of claim 9 .
11 . A method for manufacturing a backlight unit incorporated in a liquid crystal display device and leading light emitted from a plurality of light sources arranged in a two-dimensional matrix to a display screen, comprising: arranging the plurality of light sources; and arranging a light diffusion sheet having surfaces, on at least one of which a plurality of recesses having a substantially inverted quadrangular pyramid shape are arranged in a two-dimensional matrix, wherein the plurality of light sources and the light diffusion sheet are arranged so that an intersecting angle between an arrangement direction of the plurality of recesses and an arrangement direction of the plurality of light sources is 30° or more and 60° or less, wherein the light diffusion sheet has a luminance uniformity of 150 or more, the luminance uniformity determined based on an average value of luminance divided by a standard deviation of luminance.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. application Ser. No. 18/825,724, filed Sep. 5, 2024, which is a continuation of International Application No. PCT/JP2022/041405, filed Nov. 7, 2022, which claims priority to and the benefit of Japanese Application No. 2022-035936, filed Mar. 9, 2022; the contents of all of which are hereby incorporated by reference in their entirety. BACKGROUND The present disclosure relates to a light diffusion sheet, a backlight unit, a liquid crystal display device, an information apparatus, and a method for manufacturing the backlight unit. Liquid crystal display devices (hereinafter referred to as liquid crystal displays in some cases) have been widely used as display devices for various information apparatuses such as smartphones and tablet terminals. A major type of a backlight of a liquid crystal display is an edge light type in which light sources are arranged near a side surface of a liquid crystal panel. When the direct-type backlight is adopted, a light diffusion sheet is used to diffuse light emitted from a light source such as a light emitting diode (LED) to improve uniformity of luminance and chromaticity over the entire screen (e.g., see Japanese Unexamined Patent Publication No. 2011-129277). A direct-type backlight unit for a thin display such as a laptop computer or a tablet computer is used with, e.g., a light diffusion sheet having two-dimensionally arranged recesses having an inverted pyramid shape. BRIEF SUMMARY However, traditional light diffusion sheets have not yet yielded sufficient luminance uniformity. It is an object of the present disclosure to provide a light diffusion sheet that enables improvement in the luminance uniformity. To achieve the above object, the light diffusion sheet of the present disclosure is a light diffusion sheet incorporated in a backlight unit using a plurality of light sources arranged in a two-dimensional matrix, wherein the light diffusion sheet has surfaces, on at least one of which a plurality of recesses having a substantially inverted quadrangular pyramid shape are arranged in a two-dimensional matrix, and an intersecting angle between an arrangement direction of the plurality of recesses and an arrangement direction of the plurality of light sources is 30° or more and 60° or less. According to the light diffusion sheet of the present disclosure, the intersecting angle between the arrangement direction of the recesses and the arrangement direction of the light sources is set to 30° or more and 60° or less. Thus, the intensity of light emitted from the light diffusion sheet can be increased in the diagonal direction of the light source arrangement where the distance between the light sources is long and the luminance is likely to decrease (the direction inclined by 45° with respect to the arrangement direction of the light source). Therefore, the luminance uniformity can be improved. In the present disclosure, the expression “the plurality of light sources are arranged in a two-dimensional matrix” encompasses “light source groups each consisting of several small light sources are arranged in a two-dimensional matrix,” and in this case, the small light sources themselves constituting each light source group may not be arranged in a two-dimensional matrix. In the light diffusion sheet of the present disclosure, if the intersecting angle is 35° or more and 55° or less, and more preferably 40° or more and 50° or less, the luminance uniformity can be further improved. In the light diffusion sheet of the present disclosure, if the recesses are provided on the light emitting surface, the intensity of light emitted from the light diffusion sheet can be easily increased in the diagonal direction of the light source arrangement. A backlight unit of the present disclosure is a backlight unit incorporated in a liquid crystal display device and leading light emitted from a plurality of light sources arranged in a two-dimensional matrix to a display screen. The backlight unit includes the light diffusion sheet of the present disclosure provided between the display screen and the plurality of light sources. The backlight unit of the present disclosure includes the light diffusion sheet of the present disclosure, and thus the luminance uniformity can be improved. If, in the backlight unit of the present disclosure, the light diffusion sheet includes a plurality of the light diffusion sheets, the plurality of the light diffusion sheets diffuse light repeatedly, and thus the luminance uniformity can be further improved. The backlight unit of the present disclosure may further include a color conversion sheet provided between the display screen and the plurality of light sources and configured to convert a wavelength of light emitted from the plurality of light sources. Accordingly, even when the light sources are light sources other than white light sources, the backlight unit can be configured. The