WO2023007917A1

WO2023007917A1 - Optical sheet laminate, backlight unit, liquid crystal display device, and information apparatus

Info

Publication number: WO2023007917A1
Application number: PCT/JP2022/020854
Authority: WO
Inventors: 博暉植野; 承亨蔡
Original assignee: 恵和株式会社
Priority date: 2021-07-26
Filing date: 2022-05-19
Publication date: 2023-02-02
Also published as: JP2023017428A; TW202307532A

Abstract

An optical sheet laminate 100 that is to be interposed between a light source 42 and a prism sheet 44 of a backlight unit 40. The optical sheet laminate 100 comprises a plurality of light diffusion sheets 43 that have a plurality of substantially inverted-rectangular-pyramid-shaped recesses 22 at one surface. The recesses 22 of a first light diffusion sheet 43A that is closest to the prism sheet 44 are at a light emission surface 21a. The recesses 22 of at least one second light diffusion sheet 43B of the light diffusion sheets 43 that are not the first light diffusion sheet 43A are at a light incidence surface 21b. The first light diffusion sheet 43A contains 0–2 mass% of a diffusion agent.

Description

Optical sheet laminate, backlight unit, liquid crystal display device, and information equipment

The present disclosure relates to optical sheet laminates, backlight units, liquid crystal display devices, and information equipment.

In recent years, liquid crystal display devices (hereinafter also referred to as liquid crystal displays) have been widely used as display devices for various information devices such as smartphones and tablet terminals. As a backlight for a liquid crystal display, a direct type in which a light source is arranged on the back surface of a liquid crystal panel or an edge light type in which a light source is arranged in the vicinity of a side surface of the liquid crystal panel is mainly used.

When using a direct type backlight, light diffusion sheets, prism sheets, etc. are required to diffuse the light from light sources such as LEDs (Light Emitting Diodes) and improve the uniformity of brightness and chromaticity over the entire screen. An optical sheet is used (see, for example, Patent Document 1).

In the direct type backlight unit of thin displays such as laptops and tablets, the brightness uniformity is improved by stacking multiple light diffusion sheets.

JP 2011-129277 A

Portable information terminals such as laptops and tablets are required to have even lower power consumption. Along with this, the optical sheet incorporated in the backlight unit is also required to realize a high-brightness screen with low power consumption.

However, in a backlight configuration that generally improves brightness, brightness uniformity tends to decrease. In other words, there is a trade-off between luminance and luminance uniformity.

An object of the present disclosure is to realize a high-brightness screen even with low power while maintaining brightness uniformity in a backlight unit.

In order to achieve the above object, an optical sheet laminate according to the present disclosure is provided between a plurality of light sources and a prism sheet in a liquid crystal display device in which a plurality of light sources are dispersed on the back side of a display screen. incorporated. An optical sheet laminate according to the present disclosure includes a plurality of light diffusion sheets each having a plurality of substantially inverted quadrangular pyramid-shaped concave portions provided on one surface thereof. In the first light diffusion sheet closest to the prism sheet among the plurality of light diffusion sheets, the plurality of concave portions are arranged on the light exit surface. In at least one second light diffusion sheet among the plurality of light diffusion sheets other than the first light diffusion sheet, the plurality of concave portions are arranged on the light incident surface. The content of the diffusing agent in the first light diffusion sheet is 0% by mass or more and 2% by mass or less.

According to the optical sheet laminate according to the present disclosure, by using a plurality of light diffusion sheets (hereinafter sometimes referred to as pyramid sheets) having a plurality of substantially inverted quadrangular pyramid-shaped concave portions on one surface, the brightness is uniform. can improve sexuality. In addition, in the first light diffusion sheet closest to the prism sheet, the substantially inverted quadrangular pyramid-shaped concave portion is arranged on the light exit surface. It becomes easier to converge in the direction of . Furthermore, by suppressing the content of the diffusing agent in the first light diffusion sheet to 2% by mass or less, the convergence of the emitted light from the first light diffusion sheet is improved, so that the brightness can be increased even with low power. .

Therefore, by using the optical sheet laminate according to the present disclosure in a backlight unit, it is possible to realize a high-brightness screen even with low power while maintaining brightness uniformity.

In the optical sheet laminate according to the present disclosure, when the second light diffusion sheet is thicker than the first light diffusion sheet, the following effects are obtained. That is, if the thickness of the second light diffusion sheet in which the substantially inverted quadrangular pyramid-shaped recesses are arranged on the light incident surface is increased, the light is diffused by the recesses on the light incident surface and travels in the second light diffusion sheet in an oblique direction. becomes longer. Therefore, the diffusion distance of light in the direction parallel to the light incident surface is increased, so that the light diffusibility is increased and the brightness uniformity is further improved. Further, by making the first light diffusion sheet thinner than the second light diffusion sheet, the thickness of the entire optical sheet laminate can be suppressed, and the thickness of the backlight unit, that is, the liquid crystal display device can be reduced.

A backlight unit according to the present disclosure is a backlight unit that is incorporated in the liquid crystal display device and guides light emitted from the plurality of light sources to the display screen side, wherein the plurality of light sources and the prism sheet The optical sheet laminate according to the present disclosure described above is provided therebetween.

According to the backlight unit according to the present disclosure, since it includes the optical sheet laminate according to the present disclosure described above, it is possible to realize a high-brightness screen even with low power while maintaining brightness uniformity.

In the backlight unit according to the present disclosure, the plurality of light sources may be arranged on a reflective sheet provided on the opposite side of the prism sheet when viewed from the optical sheet laminate. With this arrangement, the light is further diffused by multiple reflections between the light diffusion sheet and the reflection sheet that constitute the optical sheet laminate, so that the luminance uniformity is further improved.

In the backlight unit according to the present disclosure, the distance between the plurality of light sources and the optical sheet laminate may be 2 mm or less. By doing so, the thickness of the backlight unit can be reduced.

A liquid crystal display device according to the present disclosure includes the aforementioned backlight unit according to the present disclosure and a liquid crystal display panel.

According to the liquid crystal display device according to the present disclosure, since the backlight unit according to the present disclosure described above is provided, it is possible to realize a high-brightness screen even with low power while maintaining brightness uniformity.

The information equipment according to the present disclosure includes the above-described liquid crystal display device according to the present disclosure.

According to the information equipment according to the present disclosure, since the liquid crystal display device according to the present disclosure is provided, it is possible to realize a high-brightness screen even with low power while maintaining brightness uniformity.

According to the present disclosure, it is possible to realize a high-brightness screen even with low power while maintaining brightness uniformity in the backlight unit.

1 is a cross-sectional view of a liquid crystal display device including a backlight unit according to an embodiment; FIG. FIG. 4 is a cross-sectional view of a backlight unit incorporating the optical sheet laminate according to the embodiment; 4 is a cross-sectional view of a light diffusion sheet included in the optical sheet laminate according to the embodiment; FIG. 1 is a perspective view of a light diffusion sheet included in an optical sheet laminate according to an embodiment; FIG. 5 is a cross-sectional view of a backlight unit incorporating an optical sheet laminate according to Comparative Example 1. FIG. FIG. 10 is a cross-sectional view of a backlight unit incorporating an optical sheet laminate according to Comparative Example 2; FIG. 5 is a diagram showing the results of examining the relationship between luminance and luminance uniformity in optical sheet laminates according to Examples and Comparative Examples.

(embodiment)
An optical sheet laminate, a backlight unit, a liquid crystal display device, and an information device according to embodiments will be described below with reference to the drawings. Note that the scope of the present disclosure is not limited to the following embodiments, and can be arbitrarily changed within the scope of the technical ideas of the present disclosure.

<Structure of liquid crystal display device>
As shown in FIG. 1, the liquid crystal display device 50 includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the lower surface of the liquid crystal display panel 5, and a second polarizing plate attached to the upper surface of the liquid crystal display panel 5. 7 and a backlight unit 40 provided on the back side of the liquid crystal display panel 5 with the first polarizing plate 6 interposed therebetween.

The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 facing each other, a liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2, and the TFT substrate 1 and the CF substrate 2. A frame-shaped sealing material (not shown) is provided to seal the liquid crystal layer 3 between them.

The shape of the display screen 50a of the liquid crystal display device 50 viewed from the front (upper side in FIG. 1) is, in principle, rectangular or square, but is not limited thereto, and may be a rectangular shape with rounded corners, an elliptical shape, a circular shape, or the like. Any shape such as a trapezoid or an automobile instrument panel (instrument panel) may be used.

In the liquid crystal display device 50 , in each sub-pixel corresponding to each pixel electrode, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 to change the alignment state of the liquid crystal layer 3 . Thereby, the transmittance of the light incident from the backlight unit 40 through the first polarizing plate 6 is adjusted. The light whose transmittance has been adjusted is emitted through the second polarizing plate 7 to display an image.

The liquid crystal display device 50 of the present embodiment can be used for various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, portable information terminals such as notebook computers and tablets, portable game machines, copiers, ticket vending machines, It is used as a display device incorporated in an automatic teller machine, etc.).

The TFT substrate 1 includes, for example, a plurality of TFTs provided in a matrix on a glass substrate, an interlayer insulating film provided so as to cover each TFT, and a plurality of TFTs provided in a matrix on the interlayer insulating film. and an alignment film provided to cover each pixel electrode. The CF substrate 2 includes, for example, a black matrix provided in a grid pattern on a glass substrate, a color filter including a red layer, a green layer, and a blue layer provided between the grids of the black matrix, and a black matrix and a color filter. A common electrode is provided to cover the filter, and an alignment film is provided to cover the common electrode. The liquid crystal layer 3 is made of a nematic liquid crystal material or the like containing liquid crystal molecules having electro-optical properties. The first polarizing plate 6 and the second polarizing plate 7 each include, for example, a polarizer layer having a unidirectional polarization axis and a pair of protective layers provided to sandwich the polarizer layer.

<Structure of Backlight Unit and Optical Sheet Laminate>
As shown in FIG. 2, the backlight unit 40 includes a reflective sheet 41, a plurality of light sources 42 two-dimensionally arranged on the reflective sheet 41, and an optical sheet laminate provided above the plurality of light sources 42. 100 and a pair of

prism sheets

44 and 45 provided on the upper side of the optical sheet laminate 100 .

For example, a blue light source may be used as the light source 42 in this embodiment. In this case, as shown in FIG. 2, a color conversion sheet 46 may be provided between the optical sheet laminate 100 and the

prism sheets

44 and 45 . Alternatively, for example, a white light source may be used as the light source 42 . In this case, the color conversion sheet 46 may not be provided. The optical sheet laminate 100 may be configured by laminating, for example, three light diffusion sheets 43 each having a plurality of recesses 22 each having a substantially inverted quadrangular pyramid shape. Alternatively, the optical sheet laminate 100 may be configured by laminating two or four or more light diffusion sheets 43 . The pair of

prism sheets

44 and 45 may be a lower prism sheet 44 and an upper prism sheet 45 whose prism stretching directions (directions in which prism ridgelines extend) are orthogonal to each other. Each of the light diffusion sheets 43, the

prism sheets

44 and 45, and the like that constitute the optical sheet laminate 100 may be film-like or plate-like. These optical sheets may be laminated within the frame (not shown) of the backlight unit 40 by their own weight without using an adhesive.

The reflective sheet 41 is composed of, for example, a white film made of polyethylene terephthalate resin, a silver-deposited film, or the like.

Although the type of the light source 42 is not particularly limited, it may be, for example, an LED element, a laser element, or the like, and an LED element may be used from the viewpoint of cost, productivity, and the like. The light source 42 may have a rectangular shape when viewed from above, in which case the length of one side is 10 μm or more (preferably 50 μm or more) and 20 mm or less (preferably 10 mm or less, more preferably 5 mm or less). There may be. When LED elements are used as the light source 42, a plurality of LED chips of several millimeters square may be arranged on the reflective sheet 41 at regular intervals. A lens may be attached to the LED element in order to adjust the light emission angle characteristics of the LED element serving as the light source 42 . The number of light sources 42 to be arranged is not particularly limited, but when a plurality of light sources 42 are arranged in a distributed manner, it is preferable to arrange them regularly on the reflection sheet 41 . Arranging regularly means arranging with a certain rule, and for example, the case where the light sources 42 are arranged at regular intervals corresponds to this. When the light sources 42 are arranged at regular intervals, the center-to-center distance between two adjacent light sources 42 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less. When a blue light source is used as the light source 42, the blue light source may emit light with x<0.24 and y<0.18 in the CIE1931 chromaticity coordinates, for example. When a white light source is used as the light source 42, the white light source includes an LED element whose peak wavelength is in the blue region, an LED element whose peak wavelength is in the green region, and an LED element whose peak wavelength is in the red region. and 0.24<x<0.42 and 0.18<y<0.48 in chromaticity coordinates.

Of the plurality of light diffusion sheets 43 forming the optical sheet laminate 100, in the first light diffusion sheet 43A closest to the lower prism sheet 44, the plurality of concave portions 22 are arranged on the light output surface 21a. Among the plurality of light diffusion sheets 43 other than the first light diffusion sheet 43A, in at least one second light diffusion sheet 43B, the plurality of recesses 22 are arranged on the light incident surface 21b. In this embodiment, the two light diffusion sheets 43 other than the first light diffusion sheet 43A are both the second light diffusion sheets 43B in which the concave portions 22 are arranged on the light entrance surface 21b. However, instead of this, only one of the light diffusion sheets 43 of the first layer or the second layer from the light source 42 side is the second light diffusion sheet 43B, and the other is provided with the recessed portion 22 on the light exit surface 21a. It is good also as the 1st light-diffusion sheet 43A.

The

light diffusion sheets

43A and 43B each have a base material layer 21 as shown in FIGS. 3(a) and 3(b).

Light diffusion sheets

43A and 43B have a light exit surface 21a and a light entrance surface 21b. That is, the

light diffusion sheets

43A and 43B are arranged with the light incident surface 21b facing the light source 42 . The base material layer 21 is not particularly limited as long as it is made of a resin material that allows light to pass through. It may be cellulose acetate, polyimide, or the like. The base material layer 21 may contain a diffusing agent and other additives, or may contain substantially no additives. When a diffusing agent is added to the base material layer 21 of the first light diffusion sheet 43A, the content of the diffusing agent may be 0% by mass or more and 2% by mass or less. Additives that can be contained in the base material layer 21 are not particularly limited. It may be organic particles such as polystyrene, polyamide, and the like.

The thickness of the

light diffusion sheets

43A and 43B is not particularly limited, but may be, for example, 3 mm or less (preferably 2 mm or less, more preferably 1.5 mm or less, still more preferably 1 mm or less) and 0.1 mm or more. . When the thickness of the

light diffusion sheets

43A and 43B is 3 mm or less, the thickness of the liquid crystal display can be reduced. When the thickness of the

light diffusion sheets

43A and 43B is 0.1 mm or more, the brightness uniformity is improved.

As shown in FIG. 4, a plurality of concave portions 22 having a substantially inverted quadrangular pyramid shape (inverted pyramid shape) are formed on the light exit surface 21a of the first light diffusion sheet 43A and the light entrance surface 21b of the second light diffusion sheet 43B. Arranged in a dimensional matrix. In other words, the plurality of recesses 22 are arranged along two directions orthogonal to each other. Adjacent recesses 22 are separated by ridgelines 111 . The ridgeline 111 extends along two directions in which the recesses 22 are arranged. The center 112 of the recess 22 (the apex of the inverted pyramid) is the deepest part of the recess 22 . For simplicity, FIG. 4 illustrates a state in which the recesses 22 are arranged in a matrix of 5×5, but the actual number of recesses 22 is much larger. In the two-dimensional arrangement of the plurality of recesses 22, the recesses 22 may be provided without gaps, or may be provided at predetermined intervals. Moreover, some recesses 22 may be arranged randomly to the extent that the light diffusion effect is not impaired.

The apex angle θ of the recesses 22 may be, for example, 90°, the arrangement pitch p of the recesses 22 may be, for example, 100 μm, and the depth of the recesses 22 may be, for example, 50 μm. The apex angle θ of the concave portion 22 is a plane (longitudinal section) perpendicular to the surface on which the light diffusion sheet 43 is arranged, and is a pair of angles that pass through the center of the concave portion 22 (apex 112 of the inverted pyramid) and face each other across the center. The angle formed by the cross-sectional lines of the slope in the cross section that appears when the slope is cut perpendicularly across it. The arrangement pitch p of the recesses 22 is the distance between the centers (the apexes 112 of the inverted pyramids) of the adjacent recesses 22 (the distance along the direction parallel to the arrangement surface of the light diffusion sheet 43). .

The light entrance surface 21b of the first light diffusion sheet 43A and the light exit surface 21a of the second light diffusion sheet 43B may be matte surfaces, flat surfaces (mirror surfaces), or embossed surfaces, for example. Further, the light exit surface 21a of the second light diffusing sheet 43B may be provided with a plurality of concave portions having, for example, a substantially inverted quadrangular pyramid shape (inverted pyramid shape). The

light diffusion sheets

43A and 43B may be configured with a single-layer structure of the base material layer 21 having an uneven shape (recesses 22) on one surface. The

light diffusing sheets

43A and 43B may have a two-layer structure of a substrate layer having flat surfaces on both sides and a layer having unevenness on one surface. The

light diffusion sheets

43A and 43B may have a structure of three or more layers including a layer having unevenness on one surface. A method for manufacturing the

light diffusion sheets

43A and 43B is not particularly limited, but for example, an extrusion molding method, an injection molding method, or the like may be used.

The procedure for manufacturing a single-layer light diffusion sheet having an uneven surface using an extrusion molding method is as follows. First, pellet-shaped plastic particles to which a diffusing agent has been added (along with pellet-shaped plastic particles to which no diffusing agent has been added may be mixed) are put into a single-screw extruder, heated and melted, knead. After that, the molten resin extruded by the T-die is sandwiched between two metal rolls, cooled, transported using guide rolls, and cut into flat plates by a sheet cutter to produce a light diffusion sheet. . Here, by sandwiching the molten resin using metal rolls having a surface that is the reverse of the desired uneven shape, the reverse shape of the roll surface is transferred to the resin. can be shaped into In addition, since the shape transferred to the resin does not always correspond to the shape of the roll surface that is 100% transferred, the shape of the roll surface may be designed by calculating backward from the degree of transfer.

When manufacturing a light diffusion sheet with a two-layer structure having an uneven surface using an extrusion molding method, for example, pellet-shaped plastic particles necessary for forming each layer are supplied to each of two single-screw extruders. After charging, the same procedure as described above is performed for each layer, and each sheet thus produced may be laminated.

Alternatively, a light diffusion sheet with a two-layer structure having an uneven surface may be produced as follows. First, pellet-like plastic particles necessary for forming each layer are put into each of two single-screw extruders, melted and kneaded while being heated. After that, the molten resin for each layer is put into one T-die, laminated in the T-die, and the laminated molten resin extruded by the T-die is sandwiched between two metal rolls and cooled. After that, the laminated molten resin may be conveyed using guide rolls and cut into flat plates with a sheet cutter to produce a light diffusion sheet having a two-layer structure having an uneven surface.

Alternatively, the light diffusion sheet may be manufactured as follows by shape transfer using UV (ultraviolet). First, a roll having an inverted shape of the uneven shape to be transferred is filled with an uncured UV curable resin, and the substrate is pressed against the resin. Next, in a state in which the roll filled with the ultraviolet curable resin and the substrate are integrated, the resin is cured by irradiating ultraviolet rays. Next, the sheet on which the concavo-convex shape has been shape-transferred by the resin is separated from the roll. Finally, the sheet is irradiated with ultraviolet light again to completely harden the resin, thereby producing a light diffusion sheet having an uneven surface.

In the present disclosure, in consideration of the fact that it is difficult to form a geometrically strict inverted quadrangular pyramid recess by a normal shape transfer technique, the notation “substantially inverted quadrangular pyramid” is used, but “substantially "Inverted square pyramid" shall include shapes that can be considered true or substantially inverted square pyramids. Further, the term "substantially" means that it can be approximated, and the term "substantially inverted quadrangular pyramid" means a shape that can be approximated to an inverted quadrangular pyramid. For example, an "inverted quadrangular truncated pyramid" with a flat top is also included in the "substantially inverted quadrangular pyramid" if the top area is small enough to maintain the effects of the present invention. Further, a shape that is deformed from the "inverted square pyramid" within the range of unavoidable variations in shape due to processing accuracy in industrial production is also included in the "substantially inverted square pyramid".

The

prism sheets

44 and 45 are made mainly of a transparent (for example, colorless and transparent) synthetic resin because they need to transmit light. The

prism sheets

44 and 45 may be integrally formed. The lower prism sheet 44 has a substrate layer 44a and a row of projections composed of a plurality of ridge prism portions 44b laminated on the surface of the substrate layer 44a. Similarly, the upper prism sheet 45 has a substrate layer 45a and a row of projections composed of a plurality of ridge prism portions 45b laminated on the surface of the substrate layer 45a. The

ridge prism portions

44b and 45b are laminated in stripes on the surfaces of the substrate layers 44a and 45a, respectively. The

ridge prism portions

44b and 45b are triangular prisms whose back surfaces are in contact with the surfaces of the substrate layers 44a and 45a, respectively. The extension direction of the ridge prism portion 44b and the extension direction of the ridge prism portion 45b are orthogonal to each other. As a result, the light rays incident from the first light diffusion sheet 43A are refracted by the lower prism sheet 44 in the normal direction, and the light rays emitted from the lower prism sheet 44 are directed to the display screen 50a by the upper prism sheet 45. It can be refracted so as to proceed substantially perpendicular to it.

The lower limit of the thickness of the prism sheets 44 and 45 (the height from the back surface of the base material layers 44a and 45a to the vertices of the

ridge prism portions

44b and 45b) is, for example, about 50 μm, more preferably about 100 μm. good. The upper limit of the thickness of the

prism sheets

44 and 45 may be approximately 200 μm, more preferably approximately 180 μm. The lower limit of the pitch of the

ridge prism portions

44b and 45b on the

prism sheets

44 and 45 may be, for example, about 20 μm, more preferably about 25 μm. The upper limit of the pitch of the

prismatic protrusions

44b and 45b on the

prism sheets

44 and 45 may be, for example, approximately 100 μm, more preferably approximately 60 μm. The apex angles of the

ridge prism portions

44b and 45b may be, for example, 85° or more and 95° or less. The lower limit of the refractive index of the

ridge prism portions

44b and 45b may be, for example, 1.5, more preferably 1.55. The upper limit of the refractive index of the

ridge prism portions

44b and 45b may be, for example, 1.7.

Prism sheets

44 and 45 are formed by providing

ridge prism portions

44b and 45b, which are shape-transferred using a UV curable acrylic resin, on

substrate layers

44a and 45a made of, for example, PET (polyethylene terephthalate) film. Alternatively, the

ridge prism portions

44b and 45b may be formed integrally with the base layers 44a and 45a.

The color conversion sheet 46 is a wavelength conversion sheet that converts light from the light source 42, which is, for example, a blue light source, into light having a peak wavelength of an arbitrary color (for example, green or red). The color conversion sheet 46 converts, for example, blue light with a wavelength of 450 nm into green light with a wavelength of 540 nm and red light with a wavelength of 650 nm. In this case, if the light source 42 that emits blue light with a wavelength of 450 nm is used, the blue light is partially converted into green light and red light by the color conversion sheet 46, so that the light transmitted through the color conversion sheet 46 becomes white light. Become. As the color conversion sheet 46, for example, a QD (quantum dot) sheet, a fluorescent sheet, or the like may be used.

Although not shown, an upper light diffusion sheet may be further provided above the prism sheets 44 and 45 (on the display screen 50a side). The upper light diffusion sheet somewhat diffuses the light rays incident from the upper prism sheet 45 side, and suppresses luminance unevenness caused by the shape of the ridged

prism portions

44b and 45b of the

prism sheets

44 and 45 and the like. The upper light diffusion sheet may be laminated directly on the surface of the upper prism sheet 45 . The thickness of the top light diffusion sheet is not particularly limited, but may be, for example, 50 μm or more and 3 mm or less. When the thickness of the top light diffusion sheet exceeds 3 mm, it becomes difficult to achieve thinning of the liquid crystal display. Become. The top light diffusion sheet may be film-like or plate-like. As the light diffusing sheet for top use, for example, a PET film on at least one surface of which a UV-curing acrylic resin is used to provide an uneven shape may be used.

Although not shown, a polarizing sheet may be provided above the prism sheets 44 and 45 (on the display screen 50a side). The polarizing sheet prevents the light emitted from the backlight unit 40 from being absorbed by the first polarizing plate 6 of the liquid crystal display device 50, thereby improving the brightness of the display screen 50a.

<Features of Embodiment>
The optical sheet laminate 100 of the present embodiment is provided between the light source 42 and the

prism sheets

44 and 45 in the backlight unit 40 of the liquid crystal display device 50 in which a plurality of light sources 42 are dispersed on the back side of the display screen 50a. incorporated into. The optical sheet laminate 100 of this embodiment includes a plurality of light diffusion sheets 43 each having a plurality of substantially inverted quadrangular pyramid-shaped concave portions 22 provided on one surface thereof. In the first light diffusion sheet 43A that is closest to the

prism sheets

44 and 45 among the plurality of light diffusion sheets 43, the plurality of concave portions 22 are arranged on the light exit surface 21a. In at least one second light diffusion sheet 43B among the plurality of light diffusion sheets 43 other than the first light diffusion sheet 43A, the plurality of recesses 22 are arranged on the light incident surface 21b. The content of the diffusing agent in the first light diffusion sheet 43A is 0% by mass or more and 2% by mass or less.

According to the optical sheet laminate 100 of the present embodiment, by using a plurality of light diffusion sheets (hereinafter also referred to as pyramid sheets) 43 each having a plurality of recesses 22 in the shape of a substantially inverted square pyramid on one surface, the , the luminance uniformity can be improved. In addition, in the first light diffusion sheet 43A closest to the

prism sheets

44 and 45, the substantially inverted quadrangular pyramid-shaped concave portion 22 is arranged on the light exit surface 21a. In comparison, it becomes easier to converge the emitted light toward the

prism sheets

44 and 45 . Furthermore, by suppressing the content of the diffusing agent in the first light diffusion sheet 43A to 2% by mass or less, the convergence of the emitted light of the first light diffusion sheet 43A is improved, so that the brightness can be increased even at low power. can be done.

Therefore, by using the optical sheet laminate 100 of the present embodiment in the backlight unit 40, it is possible to realize a high-brightness screen even with low power while maintaining brightness uniformity.

In the optical sheet laminate 100 of this embodiment, when the second light diffusion sheet 43B is thicker than the first light diffusion sheet 43A, the following effects are obtained. That is, if the thickness of the second light diffusion sheet 43B, in which the concave portions 22 of approximately inverted quadrangular pyramid shape are arranged on the light incident surface 21b, is increased, the light will be diffused by the concave portions 22 of the light incident surface 21 and will be inside the second light diffusion sheet 43B. The optical path of light traveling obliquely becomes longer. Therefore, the diffusion distance of light in the direction parallel to the light entrance surface 21b is increased, so that the light diffusion property is increased and the brightness uniformity is further improved. In addition, by making the first light diffusion sheet 43A thinner than the second light diffusion sheet 43B, the thickness of the optical sheet laminate 100 as a whole is suppressed, and the thickness of the backlight unit 40, that is, the liquid crystal display device 50 is reduced. You can also plan.

The backlight unit 40 of this embodiment is incorporated in the liquid crystal display device 50, and guides the light emitted from the light source 42 to the display screen 50a side. The backlight unit 40 of this embodiment includes the optical sheet laminate 100 of this embodiment between the light source 42 and the

prism sheets

44 and 45 .

According to the backlight unit 40 of the present embodiment, since the optical sheet laminate 100 of the present embodiment is provided, it is possible to realize a high-brightness screen even with low power while maintaining brightness uniformity.

In the backlight unit 40 of this embodiment, the light source 42 may be arranged on the reflection sheet 41 provided on the opposite side of the

prism sheets

44 and 45 when viewed from the optical sheet laminate 100 . In this way, the light is further diffused by multiple reflections between the light diffusion sheet 43 and the reflection sheet 41 that constitute the optical sheet laminate 100, thereby improving luminance uniformity.

In the backlight unit 40 of this embodiment, if the distance between the light source 42 and the optical sheet laminate 100 is 2 mm or less, the backlight unit 40 can be miniaturized. Further, in anticipation of future thinning of small- and medium-sized liquid crystal displays, the distance between the light source 42 and the optical sheet laminate 100 may be more preferably 1 mm or less, and ultimately 0 mm.

The liquid crystal display device 50 of this embodiment includes the backlight unit 40 of this embodiment and the liquid crystal display panel 5 . Therefore, with the backlight unit 40 of the present embodiment, it is possible to realize a high-brightness screen even with low power while maintaining brightness uniformity. A similar effect can be obtained with an information device (for example, a portable information terminal such as a notebook computer or a tablet) in which the liquid crystal display device 50 is incorporated.

(Example)
Examples are described below.

The optical sheet laminate 100 of the example was constructed by stacking three light diffusion sheets (pyramid sheets) 43 each having a plurality of recesses 22 each having a substantially inverted quadrangular pyramid shape. Specifically, as shown in Table 1 below, the upper layer (the layer closest to the lower prism sheet 44) has a surface (pyramidal surface) on which the concave portions 22 are provided, and a 160-μm-thick third layer which is the light exit surface 21a. 1 light diffusion sheet 43A is arranged, and two second light diffusion sheets 43B having a thickness of 220 μm whose pyramid surface is the light entrance surface 21b are arranged in the lower layer and the middle layer to form the optical sheet laminate 100 of the example. Configured. The arrangement pitch and apex angle of the recesses (inverted pyramids) 22 in the first light diffusion sheet 43A are 100 μm and 90°, respectively, and the arrangement pitch and apex angle of the recesses (inverted pyramids) 22 in the second light diffusion sheet 43B are 180 μm and 180 μm, respectively. 80°. Further, as the optical sheet laminate 100 of the example, the content of the diffusing agent in the first light diffusion sheet 43A was changed stepwise from 0% by mass to 8% by mass (specifically, 0% by mass, 0.0% by mass, 0.00% by mass, and 0.00% by mass). 2% by mass, 0.4% by mass, 0.8% by mass, 2% by mass, 4% by mass, and 8% by mass) were prepared. Here, the content of the diffusing agent is the ratio of the weight of the diffusing agent to the total weight of the first light diffusion sheet 43A. No diffusing agent was added to the two second light diffusion sheets 43B.

In the example, each of the

light diffusion sheets

43A and 43B was formed with a single layer structure in which the inverted pyramid-shaped concave portions 22 were two-dimensionally arranged by extruding the polycarbonate that serves as the base material layer 21 . In addition, the light entrance surface 21b of the first light diffusion sheet 43A and the light exit surface 21a of the second light diffusion sheet 43B are processed into matte surfaces. Silicone beads having an average particle diameter of 2 μm were used as the diffusion agent added to the first light diffusion sheet 43A.

The optical sheet laminate 100 of the example described above was incorporated into the backlight unit 40 shown in FIG. 2, and luminance was measured using a 2D spectroradiometer SR-5000HS manufactured by Topcon Technohouse. As the plurality of light sources 42, blue LEDs arranged in an array with a pitch of 2.8 mm were used. In the luminance measurement, a two-dimensional luminance distribution in a range of 40 mm square is obtained with a luminance unevenness measuring instrument, and after correcting the overall luminance balance, the luminance average value and standard deviation are calculated, and "luminance = average value” and “luminance uniformity=mean value/standard deviation”, and the luminance and luminance uniformity were calculated.

Also, the optical sheet laminates 100 of Comparative Examples 1 and 2 shown in Table 1 were respectively incorporated into the backlight units 40 shown in FIGS. Specifically, a third light diffusion sheet 43C having a thickness of 220 μm whose pyramid surface is the light incident surface 21b is arranged as the upper layer, and two light diffusion sheets 43C having a thickness of 190 μm whose pyramid surface is the light incident surface 21b are arranged as the lower and middle layers. An optical sheet laminate 100 of Comparative Example 1 was constructed by arranging two second light diffusion sheets 43B. In addition, a fourth light diffusion sheet 43D having a thickness of 160 μm whose pyramid surface is the light entrance surface 21b is arranged as the upper layer, and two 210 μm thick light diffusion sheets 43D whose pyramid surface is the light entrance surface 21b are arranged as the lower and middle layers. An optical sheet laminate 100 of Comparative Example 2 was constructed by arranging two light diffusion sheets 43B.

The arrangement pitch and apex angle of the concave portions (inverted pyramids) 22 in each of the third light diffusion sheet 43C (Comparative Example 1) and the fourth light diffusion sheet 43D (Comparative Example 2) were set to 100 μm and 90°, respectively. In Comparative Example 1, the content of the diffusing agent in the third light diffusion sheet 43C was set to 0.8% by mass, while in Comparative Example 2, the content of the diffusing agent in the fourth light diffusion sheet 43D was set to 0% by mass. to 8% by mass (specifically, 0% by mass, 0.2% by mass, 0.4% by mass, 0.8% by mass, 2% by mass, 4% by mass, 8% by mass (set) were prepared.

Further, in Comparative Examples 1 and 2, the third light diffusion sheet 43C and the fourth light diffusion sheet 43D are each processed by extrusion molding the polycarbonate that serves as the base material layer 21, and the inverted pyramid-shaped concave portions 22 are arranged two-dimensionally. It was formed with a single layer structure. Further, the light incident surfaces 21b of the third light diffusion sheet 43C and the fourth light diffusion sheet 43D are processed into matte surfaces. Silicone beads having an average particle diameter of 2 μm were used as the diffusion agent added to the third light diffusion sheet 43C and the fourth light diffusion sheet 43D.

FIG. 7 is a diagram showing the results of examining the relationship between luminance and luminance uniformity in the optical sheet laminates 100 according to Example and Comparative Examples 1 and 2 described above. The numerical values shown in the figure represent the content of the diffusing agent in the sheet when the weight of the light diffusion sheet in the upper layer is set to 1. Further, the luminance is represented by relative luminance when the luminance of Comparative Example 1 is set to 1.

As shown in FIG. 7, in the optical sheet laminate 100 of the example, the content of the diffusing agent in the first light diffusion sheet 43A arranged in the upper layer with the light exit surface 21a as the pyramid surface is 0% by mass (0) or more. In the range of mass % (0.02) or less, compared with Comparative Example 1, the luminance could be increased by 3% or more while maintaining the luminance uniformity to the same extent.

On the other hand, in the optical sheet laminate 100 of Comparative Example 2, the content of the diffusing agent in the fourth light diffusion sheet 43D arranged in the upper layer with the light incident surface 21b as the pyramid surface is 0% by mass (0) or more and 2% by mass ( 0.02), compared to Comparative Example 1, the brightness uniformity could be maintained at the same level, but the increase in brightness was less than 3%.

(Other embodiments)
In the above-described embodiments (including examples; the same shall apply hereinafter), the shape of the concave portion 22 provided on one surface of the

light diffusion sheets

43A and 43B included in the optical sheet laminate 100 is an inverted quadrangular pyramid. Other inverted polygonal pyramid shapes that can be arranged two-dimensionally, such as inverted triangular pyramids and inverted hexagonal pyramids, may also be used. Also, instead of the concave portions 22 that can be arranged two-dimensionally, a row of protrusions such as a prism portion may be provided.

Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the disclosure. That is, the foregoing description of the embodiments is merely illustrative in nature and is not intended to limit the present disclosure, its applications or uses.

1 TFT substrate 2 CF substrate 3 liquid crystal layer 5 liquid crystal display panel 6 first polarizing plate 7 second polarizing plate 21 base material layer 21a light exit surface 21b light entrance surface 22 concave portion 40 backlight unit 41 reflective sheet 42 light source 43 (43A, 43B ) Light diffusion sheet 44 Lower prism sheet 44a Base material layer 44b Ridge prism part 45 Upper prism sheet 45a Base material layer 45b Ridge prism part 46 Color conversion sheet 50 Liquid crystal display device 50a Display screen 100 Optical sheet laminate 111 Ridge line 112 Recess center (inverted pyramid apex)

Claims

An optical sheet laminate to be incorporated between the plurality of light sources and a prism sheet in a liquid crystal display device in which a plurality of light sources are dispersed on the back side of the display screen,
Equipped with a plurality of light diffusion sheets having a plurality of substantially inverted square pyramid-shaped recesses on one surface,
In the first light diffusion sheet closest to the prism sheet among the plurality of light diffusion sheets, the plurality of concave portions are arranged on a light exit surface,
In at least one second light diffusion sheet among the plurality of light diffusion sheets excluding the first light diffusion sheet, the plurality of recesses are arranged on a light incident surface,
The optical sheet laminate, wherein the content of the diffusing agent in the first light diffusion sheet is 0% by mass or more and 2% by mass or less.
The optical sheet laminate according to claim 1, wherein the second light diffusion sheet is thicker than the first light diffusion sheet.
A backlight unit incorporated in the liquid crystal display device and guiding light emitted from the plurality of light sources toward the display screen,
A backlight unit comprising the optical sheet laminate according to claim 1 or 2 between the plurality of light sources and the prism sheet.
4. The backlight unit according to claim 3, wherein the plurality of light sources are arranged on a reflective sheet provided on the opposite side of the prism sheet when viewed from the optical sheet laminate.
4. The backlight unit according to claim 3, wherein the distance between the plurality of light sources and the optical sheet laminate is 2 mm or less.
a backlight unit according to any one of claims 3 to 5;
A liquid crystal display device comprising a liquid crystal display panel.
An information device comprising the liquid crystal display device according to claim 6.