JP7161687B2 - Optical structure and display device - Google Patents

Description

The present invention relates to an optical structure that exerts an optical effect on light emitted from a display surface of a display device. The present invention also relates to a display device including the optical structure.

Liquid crystal display devices, which are one example of display devices, are used in various fields. Liquid crystal panels of liquid crystal display devices are roughly classified into a TN (Twisted Nematic) system, a VA (Vertical Alignment) system, and an IPS (In-Plane Switching) system.

A liquid crystal display device expresses colors by mixing a plurality of lights with different wavelengths, but depending on the angle of the light when it passes through the liquid crystal, there may be a large difference in the intensity of the lights with different wavelengths. Specifically, for example, the difference between the intensity of light of one wavelength and the intensity of light of the other wavelength among the lights of mutually different wavelengths may vary greatly on the high angle side compared to when viewed from the front. be. In a liquid crystal panel having such characteristics, the color tone when viewed from an oblique angle can change greatly from the color tone when viewed from the front.

For example, in a VA liquid crystal panel, black is displayed when the voltage applied to the liquid crystal molecules is turned off, and this black becomes very close to actual black when viewed from the front, thereby greatly increasing the contrast ratio when viewed from the front. can be done. On the other hand, when viewed from a direction tilted with respect to the normal direction of the display surface, a relatively large amount of light leaks from the black pixels when viewed from the front. As a result, the contrast ratio and color may vary greatly within the viewing angle. For example, when displaying blue by weakening or blocking the intensity of red and green light among red, green, and blue, the red and green light leaks obliquely, making it look different when viewed from the front and obliquely. A situation is likely to occur in which the color is greatly changed from when viewed from above.

In addition, in the VA liquid crystal panel, the change in the shape of the emission spectrum with respect to the viewing angle of blue display is strong (compared to red display and green display). Due to a change that increases with respect to the "intensity of the wavelength component corresponding to blue," the display color when viewed obliquely tends to turn yellowish when viewed from the front.
It should be noted that the problem of tint that may occur in the VA mode liquid crystal panel described above may also occur in the TN mode.

In view of the problems of variations in contrast ratio and color change as described above, in a VA liquid crystal panel, cells may be formed in a plurality of patterns in a color filter. In this method, for example, by differentiating the light distribution characteristics of light transmitted through cells having different patterns, it is possible to suppress the difference between the color tone when viewed from an oblique direction and the color tone when viewed from the front.

However, in recent years, liquid crystal display devices have been rapidly becoming higher in definition, and when it is attempted to form a plurality of types of cells as described above on a color filter in response to the desired high resolution, the processing is very troublesome. In some cases, processing may be impossible depending on the desired resolution. In particular, in the VA system, it is generally necessary to divide cells more finely than in other systems such as the IPS system. can be difficult. On the other hand, conventionally, proposals have been made to suppress the color change by using an optical sheet provided on the display surface of the liquid crystal panel instead of suppressing the color change on the liquid crystal panel side. Optical sheets of this type are disclosed in Patent Documents 1 to 6, for example.

JP-A-7-43704 Patent No. 3272833 Patent No. 3621959 JP 2016-126350 A JP 2012-145944 A JP 2011-118393 A

The above optical sheet basically expands the viewing angle and improves the display quality within the viewing angle by adjusting the shape of the boundary portion between the low refractive index layer and the high refractive index layer and the refractive index difference. Plan. However, in conventional optical sheets, the shape of the boundary between the low refractive index layer and the high refractive index layer is monotonous. There were cases where the visibility was impaired without

The present invention has been made in consideration of the above-mentioned actual situation, and while expanding the viewing angle, the brightness change and color change within the viewing angle are uniformly changed toward the high angle side, so that good visibility is achieved. An object of the present invention is to provide an optical structure which can ensure the property and a display device having the same.

An optical structure according to the present invention is an optical structure arranged on a display surface of a display device, comprising: a high refractive index layer; and a low refractive index layer lower than the low refractive index layer, wherein the high refractive index layer is arranged in a first direction parallel to the main surfaces of the sheet-like high refractive index layer and the low refractive index layer, and the low refractive index layer The low refractive index layer is laminated on the high refractive index layer so as to enter between the plurality of protrusions, and the protrusions are the first protrusions. and a second convex portion, the side surface of the first convex portion facing the one side in the first direction forms a curved surface or a bent surface, and the side surface of the first convex portion facing the other side in the first direction has a shape different from the side surface of the first convex portion facing one side in the first direction, the side surface of the second convex portion facing the other side in the first direction has a curved surface or a bent surface, The side surface of the second convex portion facing one side in the first direction has a shape different from the side surface of the second convex portion facing the other side in the first direction, and the first direction and the high refractive index layer and the normal direction of the low refractive index layer, the first convex portion and the second convex portion are aligned with the normal direction of the high refractive index layer and the low refractive index layer The optical structure is linearly symmetrical with a parallel axis as an axis of symmetry, and is arranged such that the high refractive index layer faces the display surface side of the display device.

In the optical structure according to the present invention, the side surface of the first convex portion facing the other side in the first direction and the side surface of the second convex portion facing the one side in the first direction form a plane. good too.

In the optical structure according to the present invention, the side surface of the first convex portion facing the other side in the first direction and the side surface of the second convex portion facing the one side in the first direction are curved surfaces or bent surfaces. and the difference between the maximum angle and the minimum angle formed by the side surface of the first convex portion facing one side in the first direction and the normal direction of the high refractive index layer and the low refractive index layer is the first The side surface of the first convex portion facing the other side of the direction is larger than the difference between the maximum angle and the minimum angle formed by the normal directions of the high refractive index layer and the low refractive index layer, and is located on the other side of the first direction. The difference between the maximum angle and the minimum angle formed by the side surface of the second convex portion facing the direction of the normal to the high refractive index layer and the low refractive index layer is the second convex portion facing the one side of the first direction A side surface of the portion may be larger than a difference between a maximum angle and a minimum angle between normal directions of the high refractive index layer and the low refractive index layer.

In the optical structure according to the present invention, a straight line connecting both end points of a side surface of the first convex portion facing one side in the first direction and a side surface of the second convex portion facing the other side in the first direction A straight line connecting the two end points of each of the side surfaces formed by the normal direction of the high refractive index layer and the low refractive index layer has an average slope angle of 20 degrees or more and 30 degrees or less, and the other side of the first direction and a straight line connecting both end points of the side surface of the first convex portion facing one side in the first direction, the high refractive index layer and the low The average slope angle of each side surface to the normal direction of the refractive index layer may be 5 degrees or more and 15 degrees or less.

In the optical structure according to the present invention, the maximum angle and the minimum angle formed by the side surface of the first convex portion facing one side in the first direction and the normal directions of the high refractive index layer and the low refractive index layer are may be 15 degrees or more and 35 degrees or less.

In the optical structure according to the present invention, the side surface of the first convex portion facing one side in the first direction and the side surface of the second convex portion facing the other side in the first direction have the low refractive index. A curved surface or a bent surface that is convex toward the layer side may be formed.

In the optical structure according to the present invention, tips of the first convex portion and the second convex portion may form a plane parallel to the first direction.

In the optical structure according to the present invention, the tip of the low refractive index layer that enters between the adjacent protrusions may form a plane parallel to the first direction.

In the optical structure according to the present invention, the first convex portions and the second convex portions may be arranged alternately.

Further, a display device according to the present invention is a display device in which the optical structure is arranged on a display surface.

The display device includes a liquid crystal panel having the display surface and a rear surface arranged to face the display surface, and a surface light source device arranged to face the rear surface of the liquid crystal panel. good too.

According to the present invention, while widening the viewing angle of the display device, it is possible to ensure good visibility by uniformly changing the luminance change and the color change within the viewing angle toward the high angle side.

1 is a schematic cross-sectional view of a display device having an optical structure according to an embodiment of the invention; FIG. FIG. 2 is a schematic cross-sectional view of the display device for explaining the behavior of light in the display device shown in FIG. 1; 2 is an enlarged cross-sectional view of an optical structure provided in the display device shown in FIG. 1; FIG. 2 is an enlarged view of an interface between a high refractive index layer and a low refractive index layer of the optical structure shown in FIG. 1; FIG. 2A and 2B are diagrams for explaining an optical action of an optical structure provided in the display device shown in FIG. 1; FIG. 3A and 3B are diagrams showing simulation results of a luminance distribution of an image displayed by a display device including the optical structure shown in FIG. 1 and a luminance distribution of an image displayed by a display device according to a comparative example; FIG. FIG. 7 is a schematic cross-sectional view of an optical sheet provided in a display device according to a comparative example in which simulation results of luminance distribution are shown in FIG. 6;

An embodiment of the present invention will be described below with reference to the drawings.

In this specification, terms such as "sheet", "film", "plate", and "layer" are not to be distinguished from each other based only on the difference of names. Therefore, for example, "sheet" is a concept that includes members that can be called films, plates, and layers. In this specification, the term "sheet surface (plate surface, film surface)" refers to the planar direction (surface direction) of the target sheet-shaped member when the target sheet-shaped member is viewed as a whole and broadly. ). Note that the "sheet surface (plate surface, film surface)" may also be referred to as a main surface. Furthermore, in this specification, the normal direction of the sheet-shaped member refers to the normal direction to the sheet surface of the target sheet-shaped member.

First, a basic configuration of a display device 10 including an optical structure 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. FIG. 1 is a schematic cross-sectional view of a display device 10 having an optical structure 100, and FIG. 2 is a schematic cross-sectional view of the display device 10 for explaining the behavior of light in the display device 10. FIG. FIG. 3 is an enlarged cross-sectional view of optical structure 100 and FIG. 4 is an enlarged view of the interface between the high and low refractive index layers of optical structure 100 . For convenience of explanation, hatching may be omitted in each of the above cross-sectional views. 1 to 4 show the _first direction d1 parallel to each sheet surface of the liquid crystal panel 15 and the sheet-like optical structure 100 in the display device 10, and the liquid crystal panel 15 and the sheet-like optical structure in the display device 10. The cross-sectional view in a plane including the normal direction of the structure 100 is shown. In the present embodiment, the _first direction d1 is parallel to the direction in which the light source 24 of the surface light source device 20 of the edge light type emits light to the light guide plate 30 as will be described later. It is the direction in which convex portions 120 formed on the optical structure 100, which will be described later, are arranged.

(Display device)
First, the overall configuration of the display device 10 will be described. As shown in FIG. 1, the display device 10 according to the present embodiment includes a liquid crystal panel 15 and a surface light source that is arranged to face the rear surface 15B of the liquid crystal panel 15 and illuminates the liquid crystal panel 15 from the rear surface 15B side in a plane. A device 20 and a sheet-like optical structure 100 arranged on a display surface 15A of a liquid crystal panel 15 are provided. The liquid crystal panel 15 has a display surface 15A that displays a still image or a moving image, and a back surface 15B arranged to face the display surface 15A. In the display device 10, the liquid crystal panel 15 functions as a shutter that controls transmission or blocking of light from the surface light source device 20 for each region (sub-pixel) forming a pixel. image is displayed.

The illustrated liquid crystal panel 15 includes an upper polarizing plate 13 arranged on the light exit side, a lower polarizing plate 14 arranged on the light entering side, and a liquid crystal panel arranged between the upper polarizing plate 13 and the lower polarizing plate 14 . a layer 12; The polarizing plates 14 and 13 decompose the incident light into two orthogonal polarized components (for example, P wave and S wave), and produce linearly polarized components (for example, P wave) vibrating in one direction (direction parallel to the transmission axis). wave) and absorbs a linearly polarized component (for example, S wave) vibrating in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.

In the liquid crystal layer 12, a voltage can be applied to each region forming one pixel, and the alignment direction of the liquid crystal molecules in the liquid crystal layer 12 is changed depending on the presence or absence of voltage application. As an example, the polarization component in a specific direction transmitted through the lower polarizing plate 14 arranged on the light incident side rotates its polarization direction by 90° when passing through the liquid crystal layer 12 to which no voltage is applied. , maintains its polarization direction as it passes through the liquid crystal layer 12 to which a voltage is applied. In this case, depending on whether or not a voltage is applied to the liquid crystal layer 12, the polarized component that has passed through the lower polarizing plate 14 and oscillates in a specific direction is further transmitted through the upper polarizing plate 13 arranged on the light output side of the lower polarizing plate 14. , or whether the light is absorbed and blocked by the upper polarizing plate 13 can be controlled. In this manner, the liquid crystal panel 15 can control transmission or blocking of light from the surface light source device 20 for each region forming a pixel.

In the present embodiment, the liquid crystal panel 15 is, for example, a VA (Vertical Alignment) type liquid crystal panel. Therefore, in the liquid crystal panel 15, when the voltage applied to the liquid crystal molecules in the liquid crystal layer 12 is off or at the minimum value, the liquid crystal molecules are oriented along the normal direction of the display surface 15A and the light from the surface light source device 20 is blocked. In this state, the voltage applied to the liquid crystal molecules is gradually increased to gradually tilt the liquid crystal molecules along the display surface 15A, thereby gradually increasing the transmittance of light from the surface light source device 20. have. The liquid crystal panel 15 is not limited to the VA type, and may be a TN (Twisted Nematic) type liquid crystal panel or an IPS (In-Plane Switching) type liquid crystal panel. Details of the liquid crystal panel 15 are described in various known documents (for example, "Flat Panel Display Comprehensive Dictionary (supervised by Tatsuo Uchida and Heiki Uchiike)" published by the Industrial Research Institute in 2001), and further details are described here. detailed description is omitted.

Next, the surface light source device 20 will be explained. The surface light source device 20 has a light emitting surface 21 that emits light in a planar shape, and in this embodiment, is used as a device for illuminating the liquid crystal panel 15 from the rear surface 15B side. As shown in FIG. 1, the surface light source device 20 is configured as an edge light type surface light source device as an example, and includes a light guide plate 30 and one side (the left side in FIG. 1) of the light guide plate 30. and an optical sheet (prism sheet) 60 and a reflective sheet 28 which are arranged so as to face the light guide plate 30, respectively. In the illustrated example, the optical sheet 60 is arranged facing the liquid crystal panel 15 . The light emitting surface 21 of the surface light source device 20 is defined by the light emitting surface 61 of the optical sheet 60 .

In the illustrated example, the light emitting surface 31 of the light guide plate 30 has a rectangular planar shape (when viewed from above), like the display surface 15A of the liquid crystal panel 15 and the light emitting surface 21 of the surface light source device 20. formed. As a result, the light guide plate 30 as a whole is configured as a rectangular parallelepiped member having a pair of main surfaces (the light output surface 31 and the back surface 32), and the sides in the thickness direction are relatively smaller than the other sides. The sides defined between the pair of major faces include four faces. Similarly, the optical sheet 60 and the reflective sheet 28 are generally configured as rectangular parallelepiped members having relatively smaller sides in the thickness direction than other sides.

As shown in FIGS. 1 and 2, the light guide plate 30 has the above-described light exit surface 31 constituted by one principal surface on the liquid crystal panel 15 side, and a back surface 32 constituted by the other principal surface facing the light exit surface 31. and a side surface extending between the light exit surface 31 and the back surface 32 , and one side surface of the two surfaces facing the first direction d ₁ of the side surfaces forms the light entrance surface 33 . . As shown in FIGS. 1 and 2, a light source 24 is provided facing the light entrance surface 33 . As shown in FIG. 2, the light incident on the light guide plate 30 from the light incident surface 33 is directed toward the opposite surface 34 facing the light incident surface 33 along the _first direction (light guide direction) d1, and is approximately The light is guided through the light guide plate 30 along the _first direction (light guide direction) d1. Here, the display device 10 according to the present embodiment is assumed to be arranged so that the _first direction d1 is along the horizontal direction, that is, the left-right direction. In this case, the light from the light source 24 is Light is guided in the horizontal direction. However, such arrangement is not particularly limited, and the display devices may be arranged in other manners. Further, in the present embodiment, the surface light source device 20 is of the edge light type, but the surface light source device 20 may be of another type such as a direct type or a backside illumination type.

More specifically, in the present embodiment, the light guide plate 30 has a rear surface 32 formed as an uneven surface. As a specific configuration, as shown in FIG. 2, the back surface 32 includes an inclined surface 37, a stepped surface 38 extending in the normal direction of the light guide plate 30, a connection surface 39 extending in the plate surface direction of the light guide plate 30, have. Light is guided within the light guide plate 30 by total reflection on the pair of main surfaces 31 and 32 of the light guide plate 30 . On the other hand, the inclined surface 37 is inclined with respect to the plate surface of the light guide plate 30 so as to approach the light output surface 31 as it goes from the light incident surface 33 side to the opposite surface 34 side. Therefore, the light reflected by the inclined surface 37 has a small incident angle when incident on the pair of main surfaces 31 and 32 . When the angle of incidence on the pair of main surfaces 31 and 32 becomes less than the critical angle for total reflection due to reflection on the inclined surface 37, the light is emitted from the light guide plate 30 as indicated by L1 in FIG. Become. That is, the inclined surface 37 functions as an element for extracting light from the light guide plate 30 . It should be noted that the light guide plate 30 is not limited to the mode in this embodiment, and may be of another mode such as a dot pattern system.

Also, the light source 24 can be configured in various forms such as, for example, a fluorescent lamp such as a linear cold-cathode tube, a point-like LED (light-emitting diode), or an incandescent lamp. The light source 24 in this embodiment is composed of a large number of point-like light emitters 25, specifically, a large number of light emitting diodes (LEDs) arranged along the longitudinal direction of the light incident surface 33 .

The reflective sheet 28 is a member arranged to face the back surface 32 of the light guide plate 30, and reflects the light leaking from the back surface 32 of the light guide plate 30 to enter the light guide plate 30 again. It is a member for The reflective sheet 28 is a white scattering reflective sheet, a sheet made of a material having a high reflectance such as metal, or a sheet containing a thin film (for example, a metal thin film or a dielectric multilayer film) made of a material having a high reflectance as a surface layer. and so on. The reflection on the reflection sheet 28 may be regular reflection (specular reflection) or diffuse reflection. When the reflection on the reflection sheet 28 is diffuse reflection, the diffuse reflection may be isotropic diffuse reflection or anisotropic diffuse reflection.

Also, the optical sheet 60 is a member having a function of changing the traveling direction of transmitted light. As shown in FIG. 2, the optical sheet 60 according to this example includes a plate-shaped body portion 65 and a plurality of unit prisms (unit shape elements, unit and an optical element (unit lens) 70 . The body portion 65 is configured as a plate-like member having a pair of parallel main surfaces. In the illustrated example, the unit prisms 70 are arranged side by side on the light incident side surface 67 of the main body portion 65, and each unit prism 70 is formed in a columnar shape and extends in a direction intersecting the arrangement direction. Although one optical sheet 60 is provided on the light guide plate 30 in this embodiment, a plurality of optical sheets may be provided on the light guide plate 30 . In this case, the directions of the grooves of the prisms of each optical sheet may be different from each other.

By providing the optical sheet 60 , the surface light source device 20 as described above converts the light from the light guide plate 30 into a desired traveling direction and causes the light to enter the liquid crystal panel 15 . Specifically, the optical sheet 60 emits light so that most of the light incident on the liquid crystal panel 15 is parallel to the normal direction of the surface light source device 20 . Thereby, the surface light source device 20 in this embodiment is configured as a so-called parallel light backlight. As described above, the light incident on the liquid crystal panel 15 is controlled to be transmitted or blocked in the liquid crystal layer 12 in accordance with the voltage application, for each pixel forming region. will be displayed. An image displayed on the display surface 15A is visually recognized through the optical structure 100. FIG.

(Optical structure)
Next, the optical structure 100 will be described in detail with reference to FIGS. 2-4. As shown in FIGS. 2 and 3, the optical structure 100 according to the present embodiment includes a sheet-like or film-like substrate 101 having a front surface 101A and a back surface 101B arranged to face the front surface 101A, A high refractive index layer 102 provided on the surface 101A of the substrate 101 and formed in a sheet or film shape extending along the substrate 101 and having a pair of principal surfaces facing each other in the thickness direction, and a high refractive index layer 102 provided on the surface opposite to the substrate 101 side and formed in a sheet or film shape extending along the substrate 101, having a pair of principal surfaces facing each other in the thickness direction, and having a refractive index is lower than that of the high refractive index layer 102; ing. The surface material 104 in the present embodiment forms the outermost surface on the light (image) emission side, but a protective film or the like may be further laminated on the surface material 104 .

The base material 101 is a light-transmitting transparent base material made of resin, glass, or the like. Examples of the material include polyethylene terephthalate, polyolefin, polycarbonate, polyacrylate, polyamide, glass, and triacetyl cellulose. . As shown in FIG. 2, the optical structure 100 is arranged such that the high refractive index layer 102 faces the display surface 15A side of the display device 10, and in the illustrated example, the back surface 101B of the substrate 101 is the adhesive layer. The optical structure 100 is joined to the liquid crystal panel 15 , that is, the display surface 15 A of the liquid crystal panel 15 via 105 , thereby incorporating the optical structure 100 into the display device 10 .

3 more precisely shows the optical structure 100 before being bonded to the liquid crystal panel 15. FIG. As shown in FIG. 3 , in the optical structure 100 according to the present embodiment, in the state before being joined to the liquid crystal panel 15, the adhesive material layer 105 is joined to the base material 101, and the side opposite to the base material 101 side. A release film 106 is provided on the side surface.

The surface material 104 forms the outermost surface of the optical structure 100 on the side opposite to the display surface 15A side of the liquid crystal panel 15 . As an example, the surface material 104 is provided to suppress the surface reflection of external light incident on the optical structure 100, thereby improving the visibility of the image displayed on the display device 10 by the surface reflection of the external light. is suppressed from being impaired. Specifically, the surface material 104 functions as an antireflection layer for external light by setting its refractive index lower than the refractive index of the low refractive index layer 103 . Note that the surface material 104 in this embodiment functions as an antireflection layer, but it may be a simple protective layer, for example, a layer provided for anti-scratching or antifouling, or may be provided for antistatic. It may be something that can be obtained. Also, the surface material 104 may not be provided, and in this case, the low refractive index layer 103 may form the outermost surface of the optical structure 100 .

In this embodiment, the high refractive index layer 102 and the low refractive index layer 103 are provided between the substrate 101 and the surface material 104 as described above. The high refractive index layer 102 is arranged in a _first direction d1 parallel to the main surfaces of the sheet-like high refractive index layer 102 and the low refractive index layer 103, and has a plurality of convex portions 120 convex toward the low refractive index layer 103 side. , and the low refractive index layer 103 is stacked on the high refractive index layer 102 so as to enter between the plurality of convex portions 120 . The protrusions 120 linearly extend in a _second direction d2 that is non-parallel to the _first direction d1, specifically, perpendicular to the _first direction d1. The entering portion of the layer 103 also extends linearly along the _second direction d2. Further, in detail, the high refractive index layer 102 in the present embodiment is formed in a flat film shape in which a pair of flat surfaces are opposed to the plurality of convex portions 120 described above, and one of the flat surfaces is formed in a flat film shape. and a base portion 120</b>B that is integrated with and supports the convex portion 120 . In this embodiment, the low-refractive-index layer 103, like the high-refractive-index layer 102, supports the entering portion between the convex portions 120 on one flat surface of the flat film-shaped base portion. ing.

It should be noted that the above-described state of “parallel to the main surfaces of the high refractive index layer 102 and the low refractive index layer 103” corresponds to one flat main surface of each of the high refractive index layer 102 and the low refractive index layer 103 in the present embodiment. and a direction in which the projections 120 of the high refractive index layer 102 and the entrance portions of the low refractive index layer 103 are aligned, and It means a state of extending parallel to the other main surface of each of the high refractive index layer 102 and the low refractive index layer 103, which are planes including the linearly extending direction.

4, the convex portion 120 in the present embodiment has a first convex portion 121 and a second convex portion 122, and has a _first direction d1 and a high refractive index. When viewed in a cross section along a plane including the normal direction d3 of the index layer 102 and the low refractive index layer 103 (the cross section shown in FIGS. ₃ and 4), the first protrusion 121 and the second protrusion 122 are perpendicular to each other. It is line symmetrical with an axis parallel to the line direction _d3 as an axis of symmetry (for example, n1 and n2 in FIG. 4).

Specifically, the side surface 121A of the first protrusion 121 facing _one side in the first direction d1 (the left side in FIGS. 3 and 4) forms a curved surface, and the side surface 121A faces the other side in the _first direction d1 (the right side in FIGS. 3 and 4). A side surface 121B of the first convex portion 121 facing toward has a shape different from that of the side surface 121A, and is specifically flat. On the other hand, in the second convex portion 122, the side surface 122B facing the other side in the _first direction d1 forms a curved surface, and the side surface 122A facing the _one side in the first direction d1 has a different shape from the side surface 122B, Specifically, it forms a plane. As shown in FIG. 4, the curved side surface 121A of the first convex portion 121 and the curved side surface 122B of the _second convex portion 122 are symmetrical about an axis parallel to the normal direction d3. The side surface 121B of the first convex portion 121 and the side surface 122A of the second convex portion 122, which form a plane _, are symmetrical about an axis parallel to the normal direction d3.

Although the first convex portions 121 and the second convex portions 122 are arranged alternately in the _first direction d1 in the present embodiment, the arrangement of the first convex portions 121 and the second convex portions 122 is limited to this mode. Instead, the first protrusions 121 and the second protrusions 122 may be arranged randomly. In the present embodiment, the curved side surface 121A of the first convex portion 121 and the curved side surface 122B of the second convex portion 122 are curved surfaces convex toward the low refractive index layer 103 side. It may be a curved surface that is concave on the side opposite to the 103 side. In addition, the shape of the side surface formed as a curved surface is not particularly limited, and may be formed along an arc of a perfect circle, may be formed along an arc of an ellipse, or may be formed along a quadratic function. or a cubic function or the like.

By the way, in FIG. 4, the angle formed by a straight line connecting both end points of the side surface 121A of the first convex portion 121 facing _one side of the first direction d1 and the normal direction d3 is shown as an _average slope angle θ1A. An average slope angle _θ2B is an angle formed by a straight line connecting both end points of the side surface 122B of the second convex portion 122 facing the other side of the _first direction d1 and the normal direction d3. In addition, the angle formed by the normal direction d3 and the straight line connecting the two end points of the side surface 121B of the first convex portion 121 facing the other side of the _first direction d1 is indicated as the _average slope angle _θ1B . The angle between the normal direction d3 and the straight line connecting the two end points of the side surface 122A of the second convex portion 122 facing one side is shown as the average slope angle _θ2A . Here, in the present embodiment, average slope angle θ1A=average slope angle θ2B, average slope angle θ1B=average slope angle θ2A, average slope angle θ1A>average slope angle θ1B, and average slope angle θ2B>average slope angle θ2A relationship is established. Strictly speaking, the average slope angle is the smaller of the angles formed by the straight line connecting the _two end points of the side surface of the projection 120 and the normal direction d3.

The average slope angle θ1A of the side surface 121A of the first protrusion 121 and the average slope angle θ2B of the side surface 122B of the second protrusion 122 are preferably 20 degrees or more and 30 degrees or less. It's 8 degrees. In addition, the average slope angle θ1B of the side surface 121B of the first protrusion 121 and the average slope angle θ2A of the side surface 122A of the second protrusion 122 are preferably 5 degrees or more and 15 degrees or less. It is 9.0 degrees.

FIG. 4 also shows the maximum angle _θC and the minimum angle θD formed between the side surface 121A of the first convex portion 121 facing _one side of the first direction d1 and the normal direction d3. A difference between the maximum angle θC and the minimum angle θD is defined as a “slope angle range”. The maximum angle θC is the angle formed by the tip of the side surface 121A, in other words, the tangent line of the side surface 121A passing through the end point of the side surface 121A on the tip side of the projection 120 and the normal direction d3 _, and the minimum angle θD is the base of the side surface 121A. It is the angle formed by the end _, in other words, the tangent line of the side surface 121A passing through the end point of the side surface 121A on the base end side of the convex portion 120 and the normal direction d3. The slope angle range for the side surface 121A of the first convex portion 121 is preferably 5 degrees or more and 55 degrees or less, and in the present embodiment, as an example, θC=32.2° and θD=9.9°. . Similarly, the slope angle range for the side surface 122B of the second convex portion 122 is preferably 5 degrees or more and 55 degrees or less. It's becoming Strictly speaking, the maximum angle and the minimum angle are the smaller of the angles formed by the tangent to the side surface and the normal direction d3 _, like the average slope angle.

In the present embodiment, the side surface 121A of the first convex portion 121 and the side surface 122B of the second convex portion 122, which have a line-symmetrical relationship, form curved surfaces. You may form a folded surface including. When the side surface 121A of the first convex portion 121 is a bent surface, the maximum angle _θC is the angle formed by the straight line passing through the element surface including the tip of the side surface 121A and the normal direction d3. The angle formed by a straight line passing through the element surface including the base end at 121A and the normal direction _d3 .

In the present embodiment, the side surface 121B of the first convex portion 121 facing the other side in the _first direction d1 and the side surface 122A of the second convex portion 122 facing the _one side in the first direction d1 are flat. However, these side surfaces 121B and 122A may be curved surfaces or bent surfaces. In this case, the slope angle ranges of the side surface 121A of the first convex portion 121 facing _one side in the first direction d1 and the side surface 122B of the second convex portion 122 facing the other side in the _first direction d1 are It is set to a value larger than the slope angle range of the side surfaces 121B and 122A forming a curved surface or a bent surface on the opposite side.

Further, as shown in FIG. 4, the tip 121C of the first protrusion 121 in this embodiment forms a plane parallel to the _first direction d1, and the tip 122C of the second protrusion 122 forms a plane parallel to the _first direction d1. They form parallel planes. In addition, the tip of the low refractive index layer 103 entering between the adjacent convex portions 120, that is, between the first convex portion 121 and the second convex portion 122 also forms a plane parallel to the _first direction d1. . Note that the tip 121C and the tip 122C may not be planes, and may be planes that are inclined with respect to the _first direction d1.

The high refractive index layer 102 and the low refractive index layer 103 as described above exert optical effects such as reflection, refraction, and transmission on light for displaying an image emitted from the display surface 15A. It is provided to improve the display quality of the image displayed on the display surface 15A. More specifically, the curved side surface 121A of the first convex portion 121 and the curved side surface 122B of the _second convex portion 122 direct light parallel to the normal direction d3 emitted from the display surface 15A to a curved surface. , the light can be diffused over a wide range from the low angle side to the _high angle side with respect to the normal direction d3. On the other hand, on the curved side surfaces 121A and 122B _, light parallel to the normal direction d3 and the side surfaces 121A and 122B form from a certain position toward the base end side from the distal end side of the convex portion 120. The angle becomes larger than the total reflection critical angle, and the light is totally reflected. At this time, the totally reflected light gathers in a certain angle range, which is the high angle side in this embodiment, so that the intensity of the light diffused to the high angle side can be increased. At different angular ranges, specifically at lower angles, the totally reflected light is not collected, resulting in a difference in light intensity between the higher angle range and the lower angle range. A situation can arise in which a difference occurs and visibility is impaired. In contrast, in the present embodiment, the flat side surface 121B of the first convex portion 121 and the flat side surface 122A of the second convex portion 122 absorb light totally reflected by the curved side surfaces 121A and 122B. The average tilt angles .theta.1B and .theta.2A are set so that the light is totally reflected in the lower angle range than the advancing angle range to compensate for the above-described difference in light intensity. As a result, the high refractive index layer 102 and the low refractive index layer 103 make the light distribution in the wide viewing angle from the front view direction to the high angle side closer to the normal distribution, and improve the display quality in the wide viewing angle. It's like

The behavior of light in the display device 10 of the present embodiment will be described below with reference to FIGS. 2 and 5. FIG. When displaying an image on the display device 10 of the present embodiment, light is emitted from the light source 24 first. As a result, the light entering the light guide plate 30 from the light incident surface 33 is directed toward the opposite surface 34 facing the light incident surface 33 along the _first direction d1, as shown in FIG. _The light is guided through the light guide plate 30 along d1. The guided light repeats total reflection between the main surfaces 31 and 32 of the light guide plate 30, and when the incident angle on the main surface 31 becomes less than the critical angle for total reflection, as indicated by L1 in FIG. Light is emitted from the light plate 30 . When the light emitted from the light guide plate 30 passes through the optical sheet 60 , the unit prism 70 converts the light into a desired traveling direction and enters the liquid crystal panel 15 . Next, the light incident on the liquid crystal panel 15 is controlled to be transmitted or blocked by the liquid crystal layer 12 in accordance with the voltage applied to each pixel forming region, whereby an image is displayed on the display surface 15A of the liquid crystal panel 15. .

In this embodiment, light emitted from the display surface 15A of the liquid crystal panel 15 enters the optical structure 100. FIG. At this time, the light incident on the optical structure 100 from the liquid crystal panel 15 side is given an optical action by reflection and transmission (refraction) by the high refractive index layer 102 and the low refractive index layer 103 as described above. That is, the curved side surface 121A of the first convex portion 121 and the curved side surface 122B of the _second convex portion 122 reflect and reflect the light parallel to the normal direction d3 emitted from the display surface 15A over the entire curved surfaces. By being refracted, the light is diffused over a wide range from the low angle side to the _high angle side with respect to the normal direction d3.

Here, on the curved side surfaces 121A and 122B _, the light parallel to the normal direction d3 and the side surface 121A and the side surface 121A and the side surface 122B are projected from a certain position toward the base end side from the tip side of the convex portion 120 as described above. 122B becomes larger than the total reflection critical angle, and the light is totally reflected. In FIG. 5, the light flux in the area A enclosed by the two-dot chain line corresponds to the light flux totally reflected by the curved side surfaces 121A and 122B. In the present embodiment, the curved side surfaces 121A and 122B totally reflect the light as described above, so that the light gathers on the high-angle side, and as a result, the intensity of the light diffused on the high-angle side is increased. However, the total reflected light does not collect on the low angle side, and as a result, a difference in light intensity can occur between the high angle range and the low angle range. . That is, in the angle range on the lower angle side than the area A in FIG. 5, the totally reflected light does not gather, so the light intensity in that range can be lower than the light intensity on the area A side. Therefore, with the optical action of only the curved side surfaces 121A and 122B, the brightness of the image viewed from the low angle side becomes undesirably low, or the brightness of the image viewed from the high angle side decreases. A situation may occur in which the visibility is impaired because the brightness becomes higher than that when the image is viewed from the angle side.

However, in the present embodiment, the angle range in which the light travels when the side surface 121B forming the flat surface of the first convex portion 121 and the side surface 122A forming the flat surface of the second convex portion 122 are totally reflected by the side surface 121A and the side surface 122B forming the curved surface The light is totally reflected in the angle range on the lower angle side. In FIG. 5 , the light flux totally reflected by the flat side surface 121B of the first convex portion 121 and the flat side surface 122A of the second convex portion 122 is indicated by an area B surrounded by a chain double-dashed line. there is As is clear from FIG. 5, the angle range on the low angle side where the light intensity can be smaller than that on the area A side where the light totally reflected by the curved side surface 121A of the first convex portion 121 gathers includes the second The light that is totally reflected by the flat side surface 122A of the convex portion 122 travels. On the other hand, in the angle range of the low angle side where the light intensity can be smaller than the area A where the light totally reflected by the curved side surface 122B of the second convex portion 122 gathers, the first convex portion 121 forms a flat surface. The light totally reflected by the side surface 121B travels. As a result, the light from the display surface 15A is diffused over a wide range, and the intensity of the light, which changes from the front view toward the high angle side, changes uniformly.

Therefore, according to the present embodiment, it is possible to ensure good visibility by uniformly changing the luminance change and the color change in the viewing angle toward the high angle side while widening the viewing angle.

In this embodiment, the refractive index of the high refractive index layer 102 is 1.65 as an example, and the refractive index of the low refractive index layer 103 is 1.48 as an example. Further, referring to FIG. 4, the average slope angle θ1A of the side surface 121A of the first protrusion 121 and the average slope angle θ2B of the side surface 122B of the second protrusion 122 are, for example, 21.8 degrees. Further, the average slope angle θ1B of the side surface 121B of the first protrusion 121 and the average slope angle θ2A of the side surface 122A of the second protrusion 122 are, for example, 9.0 degrees. Further, the slope angle range for the side surface 121A of the first protrusion 121 and the slope angle range for the side surface 122B of the second protrusion 122 are, for example, θD=9.9° and θC=32.2°. Under such conditions, it is possible to uniformly change the brightness without significantly lowering the brightness in the front view direction up to a range where the angle from the front view direction to the front view direction is about 75 degrees. , good visibility in a wide viewing angle can be ensured.

As described above, the average slope angle θ1A of the side surface 121A of the first protrusion 121 and the average slope angle θ2B of the side surface 122B of the second protrusion 122 are preferably 20 degrees or more and 30 degrees or less. The average slope angle θ1B of the side surface 121B of the portion 121 and the average slope angle θ2A of the side surface 122A of the second convex portion 122 are preferably 5 degrees or more and 15 degrees or less. Also, the slope angle range for the side surface 121A of the first protrusion 121 and the slope angle range for the side surface 122B of the second protrusion 122 are preferably 5 degrees or more and 55 degrees or less. Assuming such an angle range, the refractive index of the high refractive index layer 102 is preferably from 1.60 to 1.67, and the refractive index of the low refractive index layer 103 is preferably from 1.46 to 1.46. It is preferably 50 or less. In this case, the inventors have confirmed that good visibility can be ensured at a wide viewing angle.

Here, FIG. 6 is a diagram showing a simulation result of the luminance distribution of the image displayed by the display device 10 including the optical structure 100 according to the present embodiment and the luminance distribution of the image displayed by the display device according to the comparative example. is. FIG. 7 is a schematic cross-sectional view of an optical sheet provided in a display device according to a comparative example in which simulation results of luminance distribution are shown in FIG. The optical sheet provided in the display device according to the comparative example includes the high refractive index layer 202 and the low refractive index layer 103 shown in FIG. A refractive index layer 203 is provided. The side surfaces of the protrusions 220 in the high refractive index layer 202 are symmetrical in the figure and form a curved surface that protrudes toward the low refractive index layer 203 side.

In FIG. 6, the horizontal axis indicates the angle tilted with respect to the front view direction, and the vertical axis indicates the image viewed in the direction tilted with respect to the front view direction with respect to the luminance when the image is viewed in the front view direction. It shows the ratio of luminance (normalized luminance) when In the simulation shown in FIG. 6, the light emitted from the display surface 15A of the liquid crystal panel 15 according to the normal distribution indicated by the solid line is the luminance distribution when emitted through the optical structure 100 and the optical sheet according to the comparative example. The luminance distribution at the time of emission is calculated. The light emitted from the display surface 15A according to the normal distribution is hereinafter referred to as reference light. The reference light has a normal distribution with a standard deviation of 13.98 in which the luminance when viewed at an angle of ±30 degrees with respect to the front viewing direction is 10% of the luminance in the front viewing direction. Also, the one-dot chain line indicates the simulation result according to the present embodiment, and the two-dot chain line indicates the simulation result according to the comparative example.

In the optical sheet according to the comparative example, the light totally reflected by the side surface of the convex portion 220 forming the curved surface in the high refractive index layer 202 can be concentrated and diffused on the high angle side, but is totally reflected on the low angle side. Since the collected light is not concentrated, the luminance near the ±30-degree angle in FIG. In such a case, when the image is viewed toward the high angle side from the front view direction, the image may be perceived to become brighter after suddenly darkening, thereby impairing visibility. On the other hand, according to the simulation results according to the present embodiment, the luminance gradually and uniformly decreases from the vicinity of the ±30-degree angle to the vicinity of the ±60-degree angle in FIG. Therefore, when the image is viewed toward the high-angle side from the front view direction, the image is perceived as gradually darkening, and the viewer does not feel discomfort.

From the simulation results as shown in FIG. 6, according to the present embodiment, while the viewing angle is widened, the luminance change and color change within the viewing angle are uniformly changed toward the high angle side. It can be confirmed that good visibility can be secured.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and further modifications can be made to these embodiments. For example, in the above-described embodiment, the surface light source device 20 is of the edge light type, but the surface light source device 20 may be of the direct type.

DESCRIPTION OF SYMBOLS 10... Display apparatus 12... Liquid crystal layer 13... Upper polarizing plate 14... Lower polarizing plate 15... Liquid crystal panel 15A... Display surface 15B... Back surface 20... Surface light source device 21... Light emitting surface 24... Light source , 25... point-like light emitters, 28... reflective sheet, 30... light guide plate, 31... light emitting surface, 32... back surface, 33... light incident surface, 34... opposite surface, 37... inclined surface, 38... stepped surface, 39... Connection surface 60 Optical sheet 61 Light output surface 65 Main body 67 Light incident side surface 70 Unit prism 100 Optical structure 101 Base material 101A Front surface 101B Back surface 102 High refractive index layer 103 Low refractive index layer 104 Surface material 105 Adhesive layer 106 Release film 120 Convex portion 120B Base portion 121 First convex portion 121A First convex portion 121B... The other side of the first protrusion 122... The second protrusion 122A... The one side of the second protrusion 122B... The other side of the second protrusion

Claims (9)

An optical structure disposed on a display surface of a display device,
a high refractive index layer;
A low refractive index layer laminated on the high refractive index layer and having a lower refractive index than the high refractive index layer,
The high refractive index layer has a plurality of protrusions arranged in a first direction parallel to the main surfaces of the sheet-like high refractive index layer and the low refractive index layer and protruding toward the low refractive index layer side. ,
The low refractive index layer is laminated on the high refractive index layer so as to enter between the plurality of protrusions,
The convex portion has a first convex portion and a second convex portion,
A side surface of the first convex portion facing one side in the first direction forms a curved surface or a bent surface, and a side surface of the first convex portion facing the other side in the first direction forms a flat surface ,
A side surface of the second protrusion facing the other side in the first direction forms a curved surface or a bent surface, and a side surface of the second protrusion facing the one side in the first direction forms a flat surface ,
When viewed in a cross section along a plane including the first direction and normal directions of the high refractive index layer and the low refractive index layer, the first convex portion and the second convex portion correspond to the high refractive index layer and the low refractive index layer. It is symmetrical with respect to an axis parallel to the normal direction of the low refractive index layer,
A straight line connecting both end points of the side surface of the first convex portion facing one side in the first direction and a straight line connecting both end points of the side surface of the second convex portion facing the other side in the first direction are the The average slope angle of each side surface to the normal direction of the high refractive index layer and the low refractive index layer is 20 degrees or more and 30 degrees or less,
A straight line connecting both end points of the side surface of the first convex portion facing the other side in the first direction and a straight line connecting both end points of the side surface of the second convex portion facing one side in the first direction are the The average slope angle of each side surface to the normal direction of the high refractive index layer and the low refractive index layer is 5 degrees or more and 15 degrees or less,
The optical structure, wherein the high refractive index layer is arranged to face the display surface side of the display device. 2. The optical structure according to claim 1, further comprising a surface material forming an outermost surface on the side opposite to the display surface side of said display device and having a refractive index lower than that of said low refractive index layer. A difference between a maximum angle and a minimum angle formed by a side surface of the first protrusion facing one side in the first direction and normal directions of the high refractive index layer and the low refractive index layer is 5 degrees or more and 55 degrees or less. The optical structure according to claim 1 , wherein A side surface of the first convex portion facing one side in the first direction and a side surface of the second convex portion facing the other side in the first direction are curved surfaces or bent surfaces convex to the low refractive index layer side. 4. The optical structure according to any one of claims 1 to 3 , comprising: 5. The optical structure according to any one of claims 1 to 4 , wherein tips of said first convex portion and said second convex portion form a plane parallel to said first direction. 6. The optical structure according to any one of claims 1 to 5 , wherein the tip of said low refractive index layer that enters between said adjacent convex portions forms a plane parallel to said first direction. 7. The optical structure according to any one of claims 1 to 6 , wherein the first protrusions and the second protrusions are arranged alternately. A display device, wherein the optical structure according to any one of claims 1 to 7 is arranged on a display surface. The display device
a liquid crystal panel having the display surface and a rear surface arranged to face the display surface;
9. The display device according to claim 8 , further comprising a surface light source device arranged to face the rear surface of said liquid crystal panel.

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