JP7449492B2 - Optical structures and display devices - 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 an example of display devices, are used in various fields. The liquid crystal panels of liquid crystal display devices are roughly classified into TN (Twisted Nematic) type, VA (Vertical Alignment) type, and IPS (In-Plane Switching) type.

Among these, in the TN type liquid crystal panel, when the voltage is off, the liquid crystal molecules are aligned in a direction parallel to the display surface, allowing light to pass through.The voltage is gradually increased to align the liquid crystal molecules in the direction parallel to the display surface. It has a configuration in which the light transmittance is gradually reduced by rising toward the side along the line direction. In addition, in VA type liquid crystal panels, when the voltage is off, the liquid crystal molecules align along the normal direction of the display surface, blocking light, and the voltage is gradually increased to move the liquid crystal molecules onto the display surface. It has a structure that gradually increases the light transmittance by sloping it along the side. In addition, an IPS type liquid crystal panel adjusts light transmittance by rotating liquid crystal molecules aligned along a display surface in accordance with the application of a voltage.

In liquid crystal panels, it is usually important to control the amount and range of light that travels toward the front, and efforts have been made to ensure appropriate brightness, contrast ratio, and color reproducibility when viewed from the front. On the other hand, controlling light that travels in a direction tilted to the normal direction of the liquid crystal panel is relatively complicated, and it is difficult to ensure a wide viewing angle and to ensure variations in brightness, contrast ratio, and color reproducibility within the viewing angle. In order to sufficiently suppress this, the structure becomes complicated and costs may undesirably increase. To address such problems, for example, Patent Documents 1 to 4 disclose optical members that are provided on the display surface of a liquid crystal panel in order to expand the viewing angle by effects such as diffusion. With such a member, it is possible to easily improve the viewing angle.

Japanese Patent Application Publication No. 7-43704 Patent No. 3272833 Patent No. 3621959 Japanese Patent Application Publication No. 2016-126350

By the way, in a liquid crystal panel that adopts the VA method among the above-mentioned methods, black is displayed when the voltage to the liquid crystal molecules is off, and this black becomes very close to the actual black when viewed from the front. The visual contrast ratio can be made very high. On the other hand, when viewed from a direction tilted to the normal direction of the display surface, relatively more light leaks from pixels that are black when viewed from the front, compared to when viewed from the front. As a result, the contrast ratio may vary significantly within the viewing angle. If such a liquid crystal panel is provided with an optical member for simply diffusing light, the contrast ratio when viewed from the front will be undesirably lowered, and the advantages of the VA system may be impaired. Similarly, optical elements that merely diffuse light may also undesirably reduce front-view brightness.

Furthermore, when a VA type liquid crystal panel is viewed from a direction tilted with respect to the normal direction of the display surface, the shape of the emission spectrum in the tilt direction changes, resulting in a decrease in color reproducibility. The reason for this is that the change in the shape of the emission spectrum with respect to the viewing angle of blue display is strong (compared to red display or green display). Specifically, the "intensity of the wavelength component corresponding to green" is The inventor of the present invention has found that the display color tends to yellow due to a change that increases with respect to the intensity of the wavelength component. It would be useful if this problem could be solved by an optical member such as the one described above. However, it cannot be said that the above-mentioned conventional techniques have been devised to effectively suppress color changes depending on viewing angles.

The present invention has been made in consideration of the above-mentioned circumstances, and can easily suppress variations in color change within the viewing angle while maintaining good display quality when viewed from the front of the display device. An object of the present invention is to provide an optical structure and a display device equipped with the same.

An optical structure according to the present invention is an optical structure disposed on a display surface of a display device, the optical structure comprising a high refractive index layer; a low refractive index layer lower than , the interface between the high refractive index layer and the low refractive index layer has an uneven shape, and each of the concave portions and convex portions in the uneven shape and a flat part extending along the surface direction of the low refractive index layer, and the uneven side surface extending between the flat part of the recess and the flat part of the convex part is on the high refractive index layer side. The optical structure has a curved or folded surface that is convex toward the low refractive index layer, and is arranged so that the low refractive index layer faces the display surface side of the display device. .

In the optical structure according to the present invention, a difference between a maximum angle and a minimum angle that the uneven side surface makes with the normal direction of the high refractive index layer and the low refractive index layer is 3 degrees or more and 60 degrees or less. It is preferable that the

Further, in the optical structure according to the present invention, the ratio of the total length of the flat portion to the length of one period of the concave and convex portions of the uneven shape is 0.50 or more and less than 1.00. Preferably.

Further, in the optical structure according to the present invention, the uneven shape is defined by a straight line connecting both end points of the side surface of the uneven shape and a normal direction of the high refractive index layer and the low refractive index layer. The average slope angle of the side surfaces is preferably 9 degrees or more and 18 degrees or less.

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

The display device according to the present invention includes a liquid crystal panel having the display surface and a back surface disposed opposite to the display surface, and a surface light source device disposed facing the back surface of the liquid crystal panel. may have.

In the liquid crystal panel, when the voltage applied to the liquid crystal molecules is off or at a minimum value, the liquid crystal molecules are aligned along the normal direction of the display surface and light from the surface light source device is blocked, and the liquid crystal A VA type liquid crystal configured to gradually increase the transmittance of light from the surface light source device by gradually increasing the voltage applied to the molecules to gradually tilt the liquid crystal molecules toward the side along the display surface. It may also be a panel.

According to the present invention, it is possible to easily suppress variations in color change within the viewing angle while maintaining good display quality when viewed from the front of the display device.

1 is a schematic cross-sectional view of a display device including an optical structure according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of the display device for explaining the behavior of light in the display device according to the embodiment. FIG. 3 is an enlarged cross-sectional view of the optical structure according to the same embodiment. FIG. 2 is an enlarged view of an uneven shape formed at an interface between a high refractive index layer and a low refractive index layer of the optical structure according to the same embodiment. It is a figure which shows the uneven|corrugated shape of an optical structure, Comprising: It is a figure which showed the side surface of the several uneven|corrugated shape which mutually differs in curvature. FIG. 3 is a diagram showing the behavior of light reflected on each of the side surfaces of a plurality of uneven shapes having mutually different curvatures. A graph showing the color change within the viewing angle of light emitted from the optical structure via the display device according to the curvature (difference between the maximum angle and the minimum angle) of the side surface of the uneven shape of the optical structure is shown. It is a diagram. This is a graph showing the degree of color change of light emitted from an optical structure via a display device according to the curvature (difference between the maximum angle and the minimum angle) of the side surface of the uneven shape of the optical structure. be. A graph showing the radiance within the viewing angle of light emitted from the optical structure via the display device according to the curvature (difference between the maximum angle and the minimum angle) of the side surface of the uneven shape of the optical structure is shown. It is a diagram. A graph showing the degree of decrease in the radiance of light emitted from the optical structure via the display device according to the curvature (difference between the maximum angle and the minimum angle) of the side surface of the uneven shape of the optical structure is shown. It is a diagram. A diagram showing a graph showing the contrast within the viewing angle of light emitted from the optical structure via the display device according to the curvature (difference between the maximum angle and the minimum angle) of the side surface of the uneven shape of the optical structure. It is. A diagram showing a graph showing the degree of decrease in the contrast of light emitted from an optical structure via a display device according to the curvature (difference between the maximum angle and the minimum angle) of the side surface of the uneven shape of the optical structure. It is. FIG. 2 is a diagram showing a side surface of an optical structure having a concave-convex shape, and is a diagram showing a side surface of a plurality of concave-convex shapes having different average slope angles from each other. FIG. 3 is a diagram showing a graph showing a color change within a viewing angle of light emitted from an optical structure via a display device according to an average slope angle of a side surface of a concavo-convex shape of the optical structure. FIG. 7 is a diagram showing a graph showing the degree of color change of light emitted from the optical structure via the display device according to the average slope angle of the uneven side surface of the optical structure. FIG. 7 is a graph showing the radiance within the viewing angle of light emitted from the optical structure via the display device, depending on the average slope angle of the uneven side surface of the optical structure. FIG. 3 is a graph showing the degree of decrease in the radiance of light emitted from the optical structure via the display device, depending on the average slope angle of the uneven side surface of the optical structure. FIG. 7 is a diagram showing a graph showing the contrast within the viewing angle of light emitted from the optical structure via the display device according to the average slope angle of the uneven side surface of the optical structure. FIG. 7 is a diagram showing a graph showing the degree of decrease in the contrast of light emitted from the optical structure via the display device according to the average slope angle of the uneven side surface of the optical structure. FIG. 3 is a graph showing a color change within a viewing angle of light emitted from an optical structure via a display device, depending on a proportion of flat portions of an uneven shape of the optical structure. FIG. 3 is a diagram showing a graph showing the degree of color change of light emitted from the optical structure via the display device according to the proportion of the flat portion of the uneven shape of the optical structure. FIG. 7 is a diagram showing a graph showing the radiance within the viewing angle of light emitted from the optical structure via the display device, depending on the proportion of the flat portion of the uneven shape of the optical structure. FIG. 7 is a graph showing the degree of decrease in the radiance of light emitted from the optical structure via the display device, depending on the proportion of the flat portion of the uneven shape of the optical structure. FIG. 3 is a diagram showing a graph showing the contrast within the viewing angle of light emitted from the optical structure via the display device, depending on the proportion of the flat portion of the uneven shape of the optical structure. FIG. 7 is a graph showing the degree of decrease in the contrast of light emitted from the optical structure via the display device, depending on the proportion of the flat portion of the uneven shape of the optical structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

Note that in this specification, terms such as "sheet", "film", "plate", "layer", etc. are not distinguished from each other based only on the difference in name. Therefore, for example, the term "sheet" is a concept that includes members that can also be called films, plates, and layers. In addition, in this specification, "sheet surface (plate surface, film surface)" refers to the planar direction (plane direction) of the target sheet-like member when the target sheet-like member is viewed from a holistic perspective. ) refers to the surface that matches. Furthermore, in this specification, the normal direction of a sheet-like member refers to the normal direction to the sheet surface of the sheet-like member.

First, the 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. 1 is a schematic cross-sectional view of a display device 10 including 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. 3 is an enlarged sectional view of the optical structure 100, and FIG. 4 is an enlarged view of the uneven shape formed at the interface between the high refractive index layer and the low refractive index layer of the optical structure 100. Note that in each of the above cross-sectional views, hatching may be omitted for convenience of explanation. 1 to 4 are cross sections taken in a plane including a first direction _d1 , which will be described later, and a common normal direction of the liquid crystal panel 15 in the display device 10 and the sheet-like base material 101 of the optical structure 100. The figure shows. In the present embodiment, the first direction d ₁ is a direction in which the light source 24 of the edge-light surface light source device 20 in the display device 10 emits light to the light guide plate 30 as described later.

(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 disposed facing the back surface 15B of the liquid crystal panel 15 and illuminates the liquid crystal panel 15 planarly from the back surface 15B side. It includes a device 20 and a sheet-like optical structure 100 disposed on a display surface 15A of a liquid crystal panel 15. The liquid crystal panel 15 has a display surface 15A that displays an image, which is a still image or a moving image, and a back surface 15B that is disposed opposite to 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 forming a pixel (sub-pixel), and when the liquid crystal panel 15 is driven, light is transmitted onto the display surface 15A. The image is now displayed.

The illustrated liquid crystal panel 15 includes an upper polarizing plate 13 disposed on the light output side, a lower polarizing plate 14 disposed on the light input side, and a liquid crystal panel disposed between the upper polarizing plate 13 and the lower polarizing plate 14. It has a layer 12. The polarizing plates 14 and 13 separate the incident light into two orthogonal polarized components (for example, P waves and S waves), and separate the incident light into two linearly polarized components (for example, P waves) that vibrate in one direction (parallel to the transmission axis). It has a function of transmitting a linearly polarized light component (for example, an S wave) that vibrates in the other direction (parallel to the absorption axis) perpendicular 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 liquid crystal molecules in the liquid crystal layer 12 changes depending on whether or not a voltage is applied. As an example, when a polarized light component in a specific direction passes through the lower polarizing plate 14 disposed on the light entrance side, its polarized direction is rotated by 90 degrees when passing through the liquid crystal layer 12 to which no voltage is applied; , maintains its polarization direction when passing 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 light component that has passed through the lower polarizing plate 14 and vibrating in a specific direction may further pass through the upper polarizing plate 13 disposed on the light output side of the lower polarizing plate 14. Alternatively, it is possible to control whether the light is absorbed and blocked by the upper polarizing plate 13. In this manner, in the liquid crystal panel 15, transmission or blocking of light from the surface light source device 20 can be controlled for each region forming a pixel.

In this 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 aligned along the normal direction of the display surface 15A, and light from the surface light source device 20 is blocked. The structure is such that the transmittance of light from the surface light source device 20 is gradually increased by gradually increasing the voltage applied to the liquid crystal molecules and gradually tilting the liquid crystal molecules toward the side along the display surface 15A. have
Note that the liquid crystal panel 15 is not limited to the VA type, but 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 Encyclopedia (supervised by Tatsuo Uchida and Hiraki Uchiike)" published by Kogyo Kenkyukai in 2001), and we will not provide further details here. Omit detailed explanation.

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 manner, and in this embodiment is used as a device that illuminates the liquid crystal panel 15 from the back 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, for example, and includes a light guide plate 30 and a side surface on one side (the left side in FIG. 1) of the light guide plate 30. It has a light source 24 disposed at , and an optical sheet (prism sheet) 60 and a reflective sheet 28 disposed to face the light guide plate 30, respectively. In the illustrated example, the optical sheet 60 is placed facing the liquid crystal panel 15. The light emitting surface 61 of the optical sheet 60 defines the light emitting surface 21 of the surface light source device 20.

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

As shown in FIGS. 1 and 2, the light guide plate 30 includes the above-mentioned light emitting surface 31 constituted by one principal surface on the liquid crystal panel 15 side, and a back surface 32 consisting of the other principal surface opposite to the light emitting surface 31. and a side surface extending between the light exit surface 31 and the back surface 32, one of the two side surfaces facing in the first direction _d1 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 entering the light guide plate 30 from the light incident surface 33 is generally directed toward the opposite surface 34 facing the light incident surface 33 along the first direction (light guide direction) _d1 . The light is guided inside 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 such that the first direction _d1 is along the horizontal direction, that is, the left-right direction, and in this case, the light from the light source 24 is The light will be guided in the left and right directions. However, such an arrangement is not particularly limited, and the display device may be arranged in other manners. Further, in this embodiment, the surface light source device 20 is an edge light type, but the surface light source device 20 may be of other types such as a direct type or a backside illumination type.

To explain the light guide plate 30 in more detail, in this embodiment, the back surface 32 of the light guide plate 30 is 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, and a connecting 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 that it approaches the light output surface 31 as it goes from the light entrance surface 33 side to the opposite surface 34 side. Therefore, the angle of incidence of the light reflected on the inclined surface 37 when it enters the pair of main surfaces 31 and 32 becomes small. When the incident angle on the pair of main surfaces 31 and 32 becomes less than the critical angle of total reflection by reflection on the inclined surface 37, the light is emitted from the light guide plate 30 as shown at L1 in FIG. Become. That is, the inclined surface 37 functions as an element for extracting light from the light guide plate 30. Note that the light guide plate 30 is not limited to the mode according to this embodiment, and may have other modes such as a dot pattern method.

The light source 24 may be configured in various ways, such as a fluorescent lamp such as a linear cold cathode tube, a dotted LED (light emitting diode), or an incandescent lamp. The light source 24 in this embodiment is constituted by a large number of point light emitters 25, specifically, a large number of light emitting diodes (LEDs) arranged in parallel along the longitudinal direction of the light entrance surface 33.

Further, the reflective sheet 28 is a member disposed so as 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 and makes it 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 with 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 with high reflectance as a surface layer. etc., may be constructed from. The reflection on the reflective sheet 28 may be regular reflection (specular reflection) or diffuse reflection. When the reflection on the reflective sheet 28 is diffuse reflection, the diffuse reflection may be isotropic diffuse reflection or anisotropic diffuse reflection.

Further, 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 the present example includes a main body 65 formed in a plate shape, and a plurality of unit prisms (unit shape elements, unit It has an optical element (unit lens) 70. The main body portion 65 is configured as a flat member having a pair of parallel main surfaces. In the illustrated example, the unit prisms 70 are arranged side by side on the light entrance side surface 67 of the main body part 65, and each unit prism 70 is formed in a columnar shape and extends in a direction intersecting the arrangement direction. Note that in this embodiment, one optical sheet 60 is provided on the light guide plate 30, but a plurality of optical sheets may be provided on the light guide plate 30. In this case, the directions of the prism grooves of each optical sheet may be different from each other.

The above-described surface light source device 20 includes the optical sheet 60 so that the light from the light guide plate 30 is converted into a desired traveling direction and polarization state and is made to enter the liquid crystal panel 15. As described above, the light incident on the liquid crystal panel 15 is transmitted or blocked in the liquid crystal layer 12 for each pixel forming area according to the applied voltage, and as a result, an image is formed on the display surface 15A of the liquid crystal panel 15. It will be displayed.

(Optical structure)
Next, the optical structure 100 will be explained in detail with reference to FIGS. 2 to 4. As shown in FIGS. 2 and 3, the optical structure 100 according to the present embodiment includes a sheet-like base material 101 having a light exit surface 101A and a back surface 101B disposed opposite to the light exit surface 101A; A film-like high refractive index layer 102 provided on the back surface 101B of the material 101 and extending along the base material 101, and a base material 101 and has a lower refractive index than the high refractive index layer 102, and an antireflection layer 104 provided on the light exit surface 101A of the base material 101. .

The base material 101 is a transparent base material having light transmittance made of resin, glass, etc., and examples of the material include polyolefin, polycarbonate, polyacrylate, polyamide, and glass. The optical structure 100 is arranged such that the low refractive index layer 103 faces the display surface 15A side of the display device 10, and in the illustrated example, the low refractive index layer 103 faces directly toward the display device 10, that is, the display surface 15A. is in contact with Further, the antireflection layer 104 is provided to suppress surface reflection of external light incident on the optical structure 100. This can prevent the visibility of the image displayed on the display device 10 from being impaired due to surface reflection of external light.
Note that such an antireflection layer 104 may not be provided.

As shown in FIG. 3, in this embodiment, the high refractive index layer 102 has a plurality of lens parts 110 on the surface opposite to the base material 101 side, and the lens parts 110 It is formed so as to be convex toward the low refractive index layer 103 along the normal direction. That is, the high refractive index layer 102 includes a film-like layer main body 102A having a surface facing the base material 101 side and a back surface disposed opposite to the surface and facing the low refractive index layer 103 side, and a layer main body 102A having a film-like layer main body 102A having a surface facing the base material 101 side and a back surface facing the low refractive index layer 103 side. It integrally has a plurality of lens parts 110 arranged side by side. On the other hand, the low refractive index layer 103 is laminated on the high refractive index layer 102 so as to cover the lens portion 110 and fill in between the plurality of lens portions 110 . As a result, in this embodiment, the interface between the high refractive index layer 102 and the low refractive index layer 103 forms an uneven shape 120.

The concavo-convex shape 120 has one period of one concave portion 121 and one convex portion 122, and is constructed by repeatedly forming this one period of shape. Note that the portion recessed toward the high refractive index layer 102 corresponds to the recess 121 with respect to the reference line SL extending in the surface direction passing through the midpoint between the bottom of the recess 121 and the top of the convex portion 122, and the recess is lower than the reference line SL. The convex portion toward the refractive index layer 103 corresponds to the convex portion 122 . The recesses 121 and the protrusions 122 are each arranged in the first direction _d1 and extend linearly in _a direction non-parallel to, for example perpendicular to, the first direction d1. It extends linearly in a direction perpendicular to the first direction _d1 .

Here, each of the recessed part 121 and the convex part 122 in this embodiment has flat parts 121A and 122A extending along the surface direction of the high refractive index layer 102 and the low refractive index layer 103, as shown in FIG. More specifically, the bottom of the concave portion 121 is a flat portion 121A, and the top of the convex portion 122 is a flat portion 122A. Further, a side surface 120S of the uneven shape 120 extending between the flat portion 121A of the recess 121 and the flat portion 122A of the convex portion 122 is a curved surface that is convex toward the low refractive index layer 103 side. The side surface 120S is formed so as not to extend in the surface direction over a straight line extending along the normal direction from the end point of the flat portion 121A to which it is connected. This makes it possible to die-cut the high refractive index layer 102 having the lens portion 110 forming the side surface 120S. Note that in this embodiment, the side surface 120S is a curved surface, but the side surface 120S may be a folded surface (polygonal shape) that is convex toward the low refractive index layer 103 side. The uneven shape 120 as described above is displayed on the display surface 15A by exerting optical effects such as total reflection, refraction, and transmission on the light for displaying an image emitted from the display surface 15A. This is provided to improve the display quality of images.

Further, in this embodiment, the high refractive index layer 102 is adjusted such that the difference between the refractive index of the high refractive index layer 102 and the refractive index of the low refractive index layer 103 is in the range of 0.05 or more and 0.25 or less. and low refractive index layer 103 are selected. Further, the high refractive index layer 102 is arranged so as to face the front side of the display device 10, and the low refractive index layer 103 is arranged so as to face the display surface 15A side of the liquid crystal panel 15. In the illustrated example, the low refractive index layer 103 is an adhesive layer, and as shown in FIG. 2, the optical structure 100 is bonded to the display surface 15A of the liquid crystal panel 15 by the low refractive index layer 103. . These high refractive index layer 102 and low refractive index layer 103 are also members having light transmittance, and their materials are not particularly limited.

FIG. 4 is an enlarged view showing the uneven shape 120. Below, the uneven shape 120 will be explained in more detail with reference to FIG. 4. In FIG. 4, the symbol θ1 indicates the minimum angle that the side surface 120S of the uneven shape 120 makes with the normal direction of the high refractive index layer 102 and the low refractive index layer 103, and the symbol θ2 indicates that the side surface 120S of the uneven shape 120 has a high refractive index. The maximum angle made with the normal direction of the index layer 102 and the low index layer 103 is shown. Specifically, the minimum angle θ1 is the angle that a tangent passing through the end point of the side surface 120S on the concave portion 121 side makes with the normal direction of the interface between the high refractive index layer 102 and the low refractive index layer 103, and the maximum angle θ2 is the angle between the side surface 120S This is the angle that a tangent passing through the end point on the convex portion 122 side makes with the normal direction of the interface between the high refractive index layer 102 and the low refractive index layer 103. Note that when the side surface 120S is a folded surface, the minimum angle θ1 is such that a straight line passing through the element surface including the end point on the concave portion 121 side of the side surface 120S is the normal direction of the interface between the high refractive index layer 102 and the low refractive index layer 103. The maximum angle θ2 is the angle that a straight line passing through the element surface including the end point on the convex portion 122 side of the side surface 120S makes with the normal direction of the interface between the high refractive index layer 102 and the low refractive index layer 103. Further, the symbol θ0 indicates the "average slope angle" of the side surface 120S defined by the straight line connecting both end points of the uneven side surface 120S and the normal direction of the high refractive index layer 102 and the low refractive index layer 103. ing. Further, the symbol P indicates a pitch which is an interval of one period between one concave portion 121 and one convex portion 122 in the uneven shape 120. Further, the symbol H indicates the height of the uneven shape 120 along the normal direction from the concave portion 121 to the convex portion 122, and the symbol L indicates the distance in the surface direction between both end points of the side surface 120S.

A "slope angle range α" is defined by the difference between the maximum angle θ2 and the minimum angle θ1, and the larger the slope angle range α, the larger the curvature of the side surface 120S. As a result of intensive research, the inventor of the present invention has found that it is preferable that the slope angle range α is 3 degrees or more and 60 degrees or less. The inventor of the present invention also found that the above-mentioned "average slope angle θ0" is preferably 9 degrees or more and 18 degrees or less. Further, the inventor of the present invention has determined that the ratio β of the total length of the flat portions 121A and 122A to the length of one cycle of the concave portions 121 and the convex portions 122 of the uneven shape 120, that is, with reference to FIG. 4, β=(a+b). It has also been found that it is particularly preferable that /P be 0.60 or more and 0.90 or less. Note that the above a is the width (length) of the flat portion 122A of the convex portion 122, and the above b is the width (length) of the flat portion 121A of the concave portion 121. The inventor of the present invention has also found that a particularly preferable range of the slope angle range α changes depending on the ratio β. For example, as described below, it has been found that when the ratio β is 0.80, it is particularly preferable that the slope angle range α is 9 degrees or more and 16 degrees or less, but if the ratio β changes, The range of this particularly preferable slope angle range α varies.

By forming the uneven shape 120 so as to simultaneously satisfy the three types of dimensional conditions described above, it is possible to maintain good display quality when viewed from the front of the display device 10 and extremely effectively suppress color changes within the viewing angle. can be suppressed. However, even if only a part of the above-mentioned dimensional conditions are satisfied, the uneven shape 120 can effectively suppress color change within the viewing angle.

Next, an example will be described in which particularly preferable ranges of the above-described slope angle range α, average slope angle θ0, and ratio β are specifically derived.

(Relationship between slope angle range (curvature) of uneven side surface and color change)
First, as an example, it will be explained that when the ratio β is 0.80, the slope angle range α is a particularly preferable range of 9 degrees or more and 16 degrees or less. FIG. 5 shows side surfaces 120S of a plurality of (three) uneven shapes 120 having different curvatures, and the more the uneven shapes 120 are shown on the right side of the figure, the larger the slope angle range α of the side surface 120S becomes. In other words, the curvature has also increased. When the curvatures of the side surfaces 120S are different, the behavior of the light that enters from the flat portion 122A of the convex portion 122 and is totally reflected at the side surface 120S changes, as shown by the light trajectory LT in FIG. In FIG. 6, in the side surface 120S illustrated on the left side of the figure, the slope angle range α is 0 degrees, and the radius of curvature is infinite (Inf). The side surface 120S in which the slope angle range α is 0 degrees is not included in the concept of "curved surface", but is shown for convenience of explanation. Further, in the side surface 120S illustrated in the center of the figure, the slope angle range α is 12 degrees, and the radius of curvature is 55 μm. Further, in the side surface 120S shown on the right side of the figure, the slope angle range α is 22 degrees, and the radius of curvature is 31 μm. In FIGS. 5 and 6, between the different uneven shapes 120, the distance L in the surface direction between both end points of the side surface 120S is fixed to a constant value, and the distance L between both end points of the side surface 120S is fixed to a constant value. The slope length, which is , is also fixed at a constant value. Furthermore, the width a of the flat portion 122A of the convex portion 122 is also fixed to a constant value.

FIGS. 7A and 7B show evaluations of color changes within the viewing angle for the optical structure 100 corresponding to the three uneven shapes 120 (α=0 degrees, 12 degrees, and 22 degrees) shown in FIG. A graph is shown. Specifically, FIGS. 7A and 7B show the case where the ratio β of the total length of the flat portions 121A and 122A to the length of one cycle of the concave portions 121 and convex portions 122 of the uneven shape 120 is 0.80. It is a graph evaluating the color change of the optical structure 100 corresponding to each of the above-mentioned uneven shapes 120. Among them, FIG. 7A is a graph in which the horizontal axis indicates the angle in the viewing angle of the light emitted from the optical structure 100, and the vertical axis indicates the color change Δu'v'. The color change within the viewing angle of light incident from the liquid crystal panel 15 side) and emitted from the optical structure 100 under the above-mentioned conditions is shown. Note that if the angle shown on the horizontal axis is 0 degrees (deg), it means that it was viewed along the normal direction; for example, 30 degrees means that it was viewed in a direction tilted 30 degrees with respect to the normal direction. It means that it was visually recognized along the line. Further, the color change Δu'v' indicates a color difference, and is calculated from the color defined by u' and v' in the uniform color space. The value of Δu'v' at an angle θ within a certain viewing angle is expressed by the following equation (1).

The color coordinates u' and v' of the uniform color space in equation (1) are expressed by the following equations (2-1) and (2-2), respectively.

Here, in each of the above equations, x and y are color coordinates defined in the CIE 1931 color space (CIE xyY color space).

FIG. 7B is a graph in which the horizontal axis shows the value of the slope angle range α and the vertical axis shows the color change score. A color change score of light emitted from optical structure 100 is shown. Here, the smaller the color change score, the more effectively the color change is suppressed in the entire viewing angle range of 0 to 60 degrees compared to the case without the optical structure 100. It is an indicator. The color change score is calculated using the following equation (3). In formula (3), θ indicates an angle within the viewing angle, Film means the case where the optical structure 100 is provided in the display device 10, and NonFilm means the case where the optical structure 100 is provided in the display device 10. This means that it is not provided. Note that the color change score is an index uniquely created by the inventor of the present invention in order to evaluate the degree of color change. This color change score can be used in evaluating the color change of a member similar to the optical structure 100 according to the present embodiment, as long as the color change Δu'v' can be specified.

Note that in the evaluation of color change shown in FIGS. 7A and 7B, the evaluation of brightness shown in FIGS. 8A and 8B, and the evaluation of contrast shown in FIGS. A multi-domain VA type liquid crystal display device manufactured by Co., Ltd. was used. The color change when a blue image is displayed by a pattern generator without the optical structure 100 in the main body of this display device, and the same image as above when the optical structure 100 is provided in the main body of this display device. Color changes and the like when displayed were evaluated using "Spectroradiometer SR-2" manufactured by Topcon Corporation. Note that the evaluations shown in FIGS. 11A to 13B and the evaluations shown in FIGS. 13A to 16B, which will be described later, were also conducted under the same conditions as described above.

Looking at the graph of FIG. 7A created as described above, it can be seen that the optical structure 100 on which the uneven shape 120 having the side surface 120S with the slope angle range α of 0 degrees, 12 degrees, and 22 degrees is formed is mounted on the display device 10. It can be seen that when the optical structure 100 is provided, the color change within the viewing angle is suppressed compared to the case where the optical structure 100 is not provided in the display device 10. On the other hand, if the slope angle range α is 0 degrees, it cannot be said that the color change graph changes smoothly within the viewing angle within the range of 30 to 45 degrees. It becomes. Based on this tendency, the inventor of the present invention has found that if the slope angle range α is too small, the diffusion effect is weak and the color change suppressing effect may be small. In FIG. 6, on the side surface 120S where the slope angle range α is 0 degrees, the totally reflected light is emitted in a direction at a certain angle. If the slope angle range α is too small, it is thought that due to the phenomenon that the angle at which light is diffused becomes small, the diffusion effect becomes weak and the color change suppressing effect tends to become small.

It can also be seen that when the slope angle range α is 22 degrees, the effect of suppressing color change is weaker in the range of 30 to 45 degrees within the viewing angle than in the other cases. Based on this tendency, the inventor of the present invention has found that if the slope angle range α is too large, the diffusion effect is weak and the color change suppressing effect may be small. In FIG. 6, on the side surface 120S where the slope angle range α is 22 degrees, light hits the side surface 120S at an angle equal to or greater than the critical angle, and is refracted and exits. Due to such a phenomenon, if the slope angle range α is too large, the diffusion effect tends to be weak and the color change suppressing effect tends to be small.

On the other hand, the color change score in FIG. 7B is calculated by the above-mentioned formula (3), and the smaller the value, the greater the color change compared to the case without the optical structure 100, and the greater the color change within the viewing angle. This is an indicator that shows that color changes are smoothly suppressed. Here, looking at FIG. 7B, it can be seen that the color change score tends to be significantly suppressed when the slope angle range α is 9 degrees or more and 16 degrees or less. Note that the slope angle range α of 7 degrees or more and 20 degrees or less also tends to have a lower color change score than the outside range, so it can be said that this is a preferable range in terms of suppressing color change. If α is in the range of 9 degrees or more and 16 degrees or less, the value of the color change score is relatively particularly small, so it can be said to be a particularly preferable range. Focusing on this point and the findings regarding the above-mentioned changes in color change, it is found that within the range where the slope angle range α of the side surface 120S is 9 degrees or more and 16 degrees or less, variations in color change within the viewing angle are significantly suppressed. It can be evaluated as follows. Note that FIG. 7B also shows color change scores for the optical structure 100 at angles different from the slope angle range α illustrated in FIG. 7A.

Based on the above, the present inventor has determined that, as an example, when the ratio β of the flat portions 121A and 122A to one period of the uneven shape 120 is 0.80, the preferable range of the slope angle range α is 7 degrees or more and 20 degrees or less. It has been found that a particularly preferable range is 9 degrees or more and 16 degrees or less. In practice, it has been confirmed that within this range, variations in color change within the viewing angle can be more effectively suppressed than when outside this range. In addition, in the graph of FIG. 7B, when the slope angle range α exceeds the position of 9 degrees, the color score drops sharply, and when the slope angle range α falls below the position of 16 degrees, the color change score drops sharply. At a position of 16 degrees, the value of the color change score is relatively sufficiently small compared to when it is larger than that, and criticality can be found at each position. In the preferable range of the above-mentioned slope angle range α, points at which it can be evaluated that the color change score is decreasing steeply are defined as the lower limit value and the upper limit value. Note that the slope angle range α is preferably 9 degrees or more and 16 degrees or less, and more preferably 10 degrees or more and 15 degrees or less.

In addition, the inventor of the present invention found that when the value of the ratio β is changed from 0.80 to the positive side, the range in which the color change score steeply decreases as shown in FIG. 7B is the plus side of the slope angle range α. There is a tendency for the slope angle range α to spread in the horizontal axis while being displaced in the direction, and when the ratio β is changed to the negative side from 0.80, the color change score steeply decreases as shown in FIG. 7B. found that there is a tendency to shift in the negative direction in FIG. 7B. Therefore, when the ratio β is 0.80 as described above, a particularly preferable range of the slope angle range α is 9 degrees or more and 16 degrees or less, but if the ratio β changes, such a preferable range becomes It's going to change.

Further, FIG. 8A is a graph showing the radiance at a wavelength of 450 nm within the viewing angle of light incident from the main body of the display device 10 (liquid crystal panel 15 side) and emitted from the optical structure 100, where the horizontal axis is the viewing angle. The vertical axis shows the radiance. FIG. 8B is a graph showing the degree of decrease in the radiance of light incident from the main body (liquid crystal panel 15 side) of the display device 10 and emitted from the optical structure 100 under the above-mentioned conditions, where the horizontal axis is the slope. The value of the angular range α is shown, and the vertical axis shows the radiance reduction rate (denoted as "luminance reduction rate" in the figure). The radiance reduction rate is an index indicating that the smaller the value, the smaller the degree of reduction in radiance compared to the case without the optical structure 100.

Further, FIG. 9A is a graph showing the contrast within the viewing angle of light incident from the main body of the display device 10 (liquid crystal panel 15 side) and emitted from the optical structure 100, where the horizontal axis represents the angle within the viewing angle. The vertical axis shows the contrast. FIG. 9B is a graph showing the degree of decrease in the contrast of light incident from the main body (liquid crystal panel 15 side) of the display device 10 and emitted from the optical structure 100 under the above-mentioned conditions, in which the horizontal axis is the slope angle. The value of the range α is shown, and the vertical axis shows the contrast reduction rate. The contrast reduction rate is an index indicating that the smaller the value, the smaller the degree of contrast reduction compared to the case without the optical structure 100.

In the range where the above-mentioned slope angle range α is 9 degrees or more and 16 degrees or less, it can be evaluated that the brightness and contrast are not reduced excessively compared to the case where the optical structure 100 is not provided. Therefore, within this range, color changes within the viewing angle can be effectively suppressed while maintaining good display quality when viewed from the front of the display device 10. From this point as well, it can be said that the slope angle range α is preferably 9 degrees or more and 16 degrees or less. Note that such numerical ranges are merely examples of particularly preferred ranges, and the present invention can obtain useful effects even when the numerical ranges are different from the numerical ranges exemplified here.

(Relationship between the average slope angle of the uneven side surface and color change)
Next, the reason why it is preferable that the average slope angle θ0 of the side surface 120S of the uneven shape 120 is 9 degrees or more and 18 degrees or less will be explained. FIG. 10 shows side surfaces 120S of a plurality (three) of concavo-convex shapes 120 having different average slope angles θ0, and the more rightward in the figure the side surfaces 120S are, the larger the average slope angle θ0 is. Note that each side surface 120S shown in FIG. 10 is set to have the same curvature (that is, α is constant). FIGS. 11A and 11B show optical structures corresponding to uneven shapes 120 with average slope angles θ0=6.0 degrees, 8.5 degrees, 11 degrees, 15.0 degrees, 17.5 degrees, and 20 degrees. A graph is shown evaluating the color change within the viewing angle for 100°. More specifically, FIGS. 11A and 11B show the case where the ratio β of the total length of the flat portions 121A and 122A to the length of one cycle of the concave portions 121 and convex portions 122 of the uneven shape 120 is 0.80. , is a graph for evaluating the color change of the optical structure 100 corresponding to each of the above-mentioned uneven shapes 120.

FIG. 11A is a graph in which the horizontal axis indicates the angle in the viewing angle of the light emitted from the optical structure 100, and the vertical axis indicates the color change Δu'v'. The color change within the viewing angle of light incident from the side) and emitted from the optical structure 100 under the above-mentioned conditions is shown. Note that in the optical structure 100 under each condition, the curvature of the side surface 120S is set to be the same. Further, FIG. 11B is a graph in which the horizontal axis indicates the value of the average slope angle θ0 and the vertical axis indicates the color change score. A color change score of light emitted from optical structure 100 is shown. The color change score is calculated by the above-mentioned formula (3).

Looking at FIG. 11A created as described above, an optical structure 100 is displayed in which an uneven shape 120 having a side surface 120S with an average slope angle θ0 of 11 degrees, 15 degrees, 17.5 degrees, and 20 degrees is formed. It can be seen that when the optical structure 100 is provided in the display device 10, the color change within the viewing angle is suppressed compared to the case where the optical structure 100 is not provided in the display device 10. On the other hand, when the optical structure 100 in which the uneven shape 120 having the side surface 120S with the average slope angle θ0 of 6 degrees and 8.5 degrees is provided in the display device 10 is provided, It can be seen that the color changes are greater in the range of degrees than in the case where the optical structure 100 is not provided, which is undesirable. Based on this tendency, the present inventor discovered that if the average slope angle θ0 is too small, the amount of light that is totally reflected by the side surface 120S is reduced, which weakens the diffusion effect and reduces the effect of suppressing color change. found out.

On the other hand, looking at FIG. 11B, it can be seen that the color change score is suitably suppressed when the average slope angle θ0 is in the range of 9 degrees or more and 18 degrees or less. Focusing on this point and the above-mentioned knowledge regarding the change in color change, it is found that variations in color change within the viewing angle are suitably suppressed in the range where the average slope angle θ0 of the side surface 120S is 9 degrees or more and 18 degrees or less. It can be evaluated.

Based on the above, the inventor of the present invention defines a preferable range of the average slope angle θ0 to be 9 degrees or more and 18 degrees or less. In practice, it has been confirmed that within this range, variations in color change within the viewing angle can be more effectively suppressed than when outside this range. Note that the average slope angle θ0 is preferably 9 degrees or more and 18 degrees or less, and more preferably 10 degrees or more and 17.5 degrees or less. More preferably, the average slope angle θ0 is 11 degrees or more and 15 degrees or less. Further, the color change graph shown in FIG. 11B changes depending on the value of the ratio β of the total length of the flat portions 121A and 122A to the length of one cycle of the concave portions 121 and convex portions 122 of the uneven shape 120, The inventor of the present invention has found that regardless of the value of the ratio β, when the average slope angle θ0 is 9 degrees or more and 18 degrees or less, a good color change suppression effect can be obtained.

Further, FIG. 12A is a graph showing the radiance at a wavelength of 450 nm within the viewing angle of light incident from the main body (liquid crystal panel 15 side) of the display device 10 and emitted from the optical structure 100, where the horizontal axis is the viewing angle. The vertical axis shows the radiance. FIG. 12B is a graph showing the degree of decrease in the radiance of light incident from the main body (liquid crystal panel 15 side) of the display device 10 and emitted from the optical structure 100 under the above-mentioned conditions, where the horizontal axis is the average The value of the slope angle θ0 is shown, and the vertical axis shows the radiance reduction rate (denoted as "luminance reduction rate" in the figure). The radiance reduction rate is an index indicating that the smaller the value, the smaller the degree of reduction in radiance compared to the case without the optical structure 100.

Further, FIG. 13A is a graph showing the contrast within the viewing angle of light incident from the main body (liquid crystal panel 15 side) of the display device 10 and emitted from the optical structure 100, where the horizontal axis represents the angle within the viewing angle. The vertical axis shows the contrast. FIG. 13B is a graph showing the degree of decrease in the contrast of light incident from the main body (liquid crystal panel 15 side) of the display device 10 and emitted from the optical structure 100 under the above-mentioned conditions, where the horizontal axis is the average slope. The value of the angle θ0 is shown, and the vertical axis shows the contrast reduction rate. The contrast reduction rate is an index indicating that the smaller the value, the smaller the degree of contrast reduction compared to the case without the optical structure 100.

From the results shown in FIGS. 12A to 13B, it was found that when the average slope angle θ0 is 9 degrees or more and 18 degrees or less, there is a trade-off relationship between brightness and contrast and color change.

(Relationship between the proportion of the flat part of the uneven shape and color change)
Next, when the ratio β of the total width of the flat portions 121A and 122A to the length of one period of the concave portions 121 and the convex portions 122 of the uneven shape 120 is, for example, when the slope angle range α is 12 degrees, The reason why 0.74 or more and 0.83 or less is particularly preferable will be explained. As mentioned above, as a result of intensive research, the inventor of the present invention found that in the optical structure 100, the ratio β is particularly preferably in a range of 0.60 or more and 0.90 or less. As an example, it will be explained that it has been derived from experiments or simulations that when the slope angle range α is 12 degrees, the ratio β is a particularly preferable range of 0.74 or more and 0.83 or less. The graphs shown in FIGS. 14A and 14B are graphs when the slope angle range α is 12 degrees. A graph evaluating the color change within the viewing angle for the corresponding optical structure 100 is shown. FIG. 14A is a graph in which the horizontal axis indicates the angle in the viewing angle of the light emitted from the optical structure 100, and the vertical axis indicates the color change Δu'v'. The color change within the viewing angle of light incident from the side) and emitted from the optical structure 100 under the above-mentioned conditions is shown. Further, FIG. 14B is a graph in which the horizontal axis shows the value of the ratio β and the vertical axis shows the color change score. The color change score of the light emitted from the body 100 is shown. The color change score is calculated by the above-mentioned formula (3).

Looking at FIG. 14A, the display device 10 is provided with an optical structure 100 in which an uneven shape 120 having a side surface 120S with a flat portion ratio β of 0.63, 0.75, 0.80, and 0.90 is formed. It can be seen that in the case where the optical structure 100 is not provided in the display device 10, the color change within the viewing angle is suppressed compared to the case where the optical structure 100 is not provided in the display device 10. However, it can be seen that in the uneven shape 120 having the side surface 120S where the ratio β is 0.90, the degree of color change is smaller than when the optical structure 100 is not provided in the display device 10. From this tendency, the inventor of the present invention has found that if the ratio β is too large, the diffusion effect by the side surface 120S may be weak, and the effect of suppressing color change may be small.

On the other hand, looking at FIG. 14B, it can be seen that the color change within the viewing angle is suppressed when the flat portion ratio β is 0.63, 0.75, 0.80, and 0.90. However, when the ratio β is 0.90, it can be evaluated that the color change score is relatively high, that is, the color change is relatively large. In addition, when the ratio β is 0.63, although the color change score is low, that is, the color change can be evaluated as small, there is no continuity for values larger than this, and there is no stable color change. It is difficult to say that a suppressive effect can be obtained. Note that FIG. 14B also shows the color change score in the optical structure 100 having a proportion β different from the flat portion proportion β illustrated in FIG. 14A. Focusing on the above points, the present inventor has determined that when the slope angle range α is 12 degrees, the color change within the viewing angle is stable in the range where the ratio β is 0.70 or more and 0.86 or less. It was evaluated that the variation in the results was suppressed. Further, in this evaluation, considering the graph, it is considered particularly preferable that the ratio β is 0.74 or more and 0.83 or less.

Further, FIG. 15A is a graph showing the radiance at a wavelength of 450 nm within the viewing angle of light incident from the main body of the display device 10 (liquid crystal panel 15 side) and emitted from the optical structure 100, where the horizontal axis is the viewing angle. The vertical axis shows the radiance. FIG. 15B is a graph showing the degree of decrease in the radiance of light incident from the main body (liquid crystal panel 15 side) of the display device 10 and emitted from the optical structure 100 under the above-mentioned conditions, where the horizontal axis is the percentage. The value of β is shown, and the vertical axis shows the radiance reduction rate (denoted as "luminance reduction rate" in the figure). The radiance reduction rate is an index indicating that the smaller the value, the smaller the degree of reduction in radiance compared to the case without the optical structure 100.

Further, FIG. 16A is a graph showing the contrast within the viewing angle of light incident from the main body (liquid crystal panel 15 side) of the display device 10 and emitted from the optical structure 100, where the horizontal axis represents the angle within the viewing angle. The vertical axis shows the contrast. FIG. 16B is a graph showing the degree of decrease in the contrast of light incident from the main body (liquid crystal panel 15 side) of the display device 10 and emitted from the optical structure 100 under the above-mentioned conditions, where the horizontal axis is the ratio β. The vertical axis shows the contrast reduction rate. The contrast reduction rate is an index indicating that the smaller the value, the smaller the degree of contrast reduction compared to the case without the optical structure 100.

In the range where the ratio β is 0.74 or more and 0.83 or less, it can be evaluated that the reduction in brightness and contrast is not excessive compared to the case where the optical structure 100 is not provided. Therefore, within this range, color change within the viewing angle can be effectively suppressed without deteriorating the display quality of the display device 10 when viewed from the front. From this point as well, it can be said that the ratio β is preferably 0.74 or more and 0.83 or less.

Moreover, as explained above, when the slope angle range α is 12 degrees, it is particularly preferable that the ratio β is 0.74 or more and 0.83 or less. On the other hand, as explained above in "Relationship between the slope angle range (curvature) of the side surface of an uneven shape and color change," when the ratio β is 0.80, the slope angle range α is 9 degrees or more and 16 degrees. This is a particularly preferable range. As a result of intensive study of these results, the inventor of the present invention has come to the conclusion that a preferable value for the slope angle range α can be determined from the following relationship that changes depending on the value of the ratio β.
The slope angle range α is preferably 83.33β-59.67 degrees or more and 80β-44 degrees or less, more preferably 66.67β-37.33 degrees or more and 100β-71 degrees or less. However, α is greater than 0 and β is less than 1. From the above equation, it can be said that β is preferably 0.55 or more and less than 1.00, and α is preferably greater than 0 and less than 36 degrees.
If the optical structure 100 is manufactured according to such conditions, it is possible to easily and effectively suppress variations in color change within the viewing angle while maintaining good display quality when viewed from the front of the display device 10. The optical structure 100 can be obtained.

Furthermore, in the configuration of the display device 10 according to the present embodiment, light from the surface light source device 20 is incident on the back surface of the optical structure 100. At this time, even if the range of the radiation angle of the light from the surface light source device 20 is from 0 degrees to 90 degrees, the angular range of the light ray inside the optical structure 100 is the radiation angle of the light from the surface light source device 20. narrower than the range of This is because light is refracted when it enters the optical structure 100. Although it depends on the refractive index of the surface light source device 20 and the optical structure 100, in the configuration of the display device 10 according to the present embodiment, the range of the radiation angle of light from the surface light source device 20 is 0 degrees or more. When the angle is 90 degrees or less, it is assumed that the angular range of the light ray inside the optical structure 100 can be approximately 0 degrees or more and 60 degrees or less. Specifically, when the refractive index of the high refractive index layer 102 is 1.15 or more, the angular range of the light ray inside the optical structure 100 can be approximately 0 degrees or more and 60 degrees or less. Further, when the refractive index of the high refractive index layer 102 is 1.29, the angular range of the light ray inside the optical structure 100 can be suppressed to 0 degrees or more and 51 degrees or less. Furthermore, if the refractive index of the high refractive index layer 102 is 1.6 or more, as a range that is easier to manufacture, the angular range of the light ray inside the optical structure 100 is suppressed to approximately 0 degrees or more and 40 degrees or less. be able to.
Here, the light having an angle larger than the maximum angle in the angular range of the light ray inside the optical structure 100 does not need to exert an optical effect on the side surface 120S of the concavo-convex shape 120. Considering this point, considering the maximum angle of the assumed angle range of the light ray inside the optical structure 100, the slope angle range α may be greater than 0 degrees and less than or equal to 60 degrees; Depending on the value of the refractive index, the angle may be greater than 0 degrees and less than 40 degrees. Note that the inventor of the present invention has confirmed that when the slope angle range α is 3 degrees or more, the effect of suppressing color change is to the extent that it can be recognized visually. From this point of view, the slope angle range α is preferably 3 degrees or more and 60 degrees or less, and depending on the value of the refractive index of the high refractive index layer 102, it is more preferably 3 degrees or more and 40 degrees or less. Note that the high refractive index layer in the present invention is referred to as a high refractive index layer in the sense that its refractive index is higher than that of the low refractive index layer.

(Behavior of light in display device)
Next, the behavior of light in the display device 10 of this embodiment will be explained again with reference to FIG. 2 and the like. When displaying an image in the display device 10 of this embodiment, light is first emitted from the light source 24 . As a result, 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 _d1 , as shown in FIG. The light is guided inside 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 angle of incidence on the main surface 31 becomes less than the critical angle for total reflection, the guided light is reflected as shown by L1 in FIG. Light is emitted from the light plate 30. The light emitted from the light guide plate 30 is converted into a desired traveling direction and polarization state by the unit prism 70 when passing through the optical sheet 60 and enters the liquid crystal panel 15 . Next, the light incident on the liquid crystal panel 15 is transmitted or blocked in the liquid crystal layer 12 for each pixel forming area according to the applied voltage, and thereby 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. At this time, the light that enters the optical structure 100 from the liquid crystal panel 15 side is given an optical effect by transmission and total reflection by the concavo-convex shape 120. That is, at this time, the curved side surface 120S of the concavo-convex shape 120 that is convex toward the low refractive index layer 103 side causes light traveling on the high-angle side of the viewing angle to be totally reflected and reflected over a wide range in the direction including the low-angle side. In addition to being diffused, the light incident vertically on the optical structure 100 travels in the front direction due to the flat portions 121A and 122A of the uneven shape 120, and diffusion is suppressed. As a result, color changes within the viewing angle are suppressed, and reductions in brightness and contrast when viewed from the front are suppressed.

As a result, according to the present embodiment, it is possible to easily suppress variations in color change within the viewing angle while maintaining good display quality when viewed from the front of the display device 10. Further, in this embodiment, for example, the difference between the maximum angle and the minimum angle (slope angle range α) that the side surface 120S of the uneven shape 120 makes with the normal direction of the high refractive index layer 102 and the low refractive index layer 103 is determined as described above. When the ratio β is 0.80, by setting it to 9 degrees or more and 16 degrees or less, it is possible to effectively suppress variations in color change within the viewing angle, and suppress excessive reductions in brightness and contrast. can do. Further, the average slope angle θ0 of the side surface 120S defined by the straight line connecting both end points of the side surface 120S of the uneven shape 120 and the normal direction of the high refractive index layer 102 and the low refractive index layer 103 is set to be 9 degrees or more and 18 degrees. By making it less than 1°, variations in color change within the viewing angle can be effectively suppressed. Note that such numerical ranges are merely examples of preferred ranges, and the present invention can obtain useful effects even when the numerical ranges are different from the numerical ranges exemplified here.

Further, as described above, the flat portions 121A and 122A of the uneven shape 120 have a function of transmitting light that is perpendicularly incident on the optical structure 100 in the front direction. As a result, in this embodiment, the diffusion of the emitted light is suppressed, and a decrease in brightness and contrast when viewed from the front can be suppressed. On the other hand, the fact that the uneven shape 120 has the flat portions 121A and 122A has a great manufacturing advantage. Specifically, even if the ratio between the length of the flat part 121A and the length of the flat part 122A is changed arbitrarily to some extent under the condition that the shape of the side surface 120S of the uneven shape 120 is fixed, the optical characteristics hardly change. do not. Therefore, at the design stage, the ratio β of the flat portions 121A and 122A to one cycle of the concave portions 121 and the convex portions 122 of the uneven shape 120 is fixed to a desired value, and the length of the flat portion 121A and the length of the flat portion 122A is By arbitrarily changing the ratio to some extent, it is possible to manufacture the optical structure 100 having desired optical characteristics using a desired manufacturing process. Specifically, if the proportion of the flat portion 121A of the recessed portion 121 is increased, filling with the low refractive index layer 103 becomes easier. If the proportion of the flat portions 122A of the convex portions 122 is large, the high refractive index layer 102 can be easily cut out, and the problem of air being mixed in when forming the high refractive index layer 102 can be suppressed. It has been found that such manufacturing advantages can be obtained when the ratio of the flat portion 121A to the flat portion 122A is, for example, 7:4. Note that unless the ratio between the flat portion 121A and the flat portion 122A is set to an extreme ratio, the optical characteristics will hardly change. For example, when the slope angle range α=12, the ratio β=0.80, and the average slope angle θ0=11, the ratio of the flat part is changed between flat part 121A:flat part 122A=7:3 to 3:10. However, the optical properties hardly changed.

Furthermore, considering the ease of die cutting, the larger the ratio β, the easier the die cutting becomes. When considering such manufacturing advantages, the ratio β is preferably 0.50 or more and less than 1.00, and when considering that it is easy to ensure the effect of suppressing color change, the ratio β is preferably 0.60. More preferably, it is less than 0.90.

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

DESCRIPTION OF SYMBOLS 10... Display device, 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 light emitter, 28... Reflective sheet, 30... Light guide plate, 60... Optical sheet, 100... Optical structure, 101... Base material, 101A... Light output surface, 101B... Back surface, 102... High refractive index layer, DESCRIPTION OF SYMBOLS 103...Low refractive index layer, 104...Antireflection layer, 110...Lens part, 120...Irregular shape, 120S...Side surface, 121...Concave part, 121A...Flat part, 122...Convex part, 122A...Flat part

Claims (1)

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 refractive index lower than the high refractive index layer,
The interface between the high refractive index layer and the low refractive index layer has an uneven shape,
Each of the concave portions and convex portions in the uneven shape has a flat portion extending along the surface direction of the high refractive index layer and the low refractive index layer,
The side surface of the uneven shape extending between the flat part of the concave part and the flat part of the convex part is a curved or folded surface that is convex from the high refractive index layer side toward the low refractive index layer side. Ori,
The low refractive index layer is arranged so as to face the display surface side of the display device,
The ratio of the total length of the flat portion to the length of one period of the concave and convex portions of the uneven shape is 0.60 or more and 0.90 or less,
A portion recessed toward the high refractive index layer corresponds to the recess, with respect to a reference line extending in the plane direction passing through the midpoint between the bottom of the recess and the top of the convex portion, and the low refractive index layer corresponds to the recess. A portion that is convex toward the index layer 103 side corresponds to the convex portion,
The angle between the tangent passing through the end point of the side surface on the concave side and the normal direction of the high refractive index layer and the low refractive index layer, and the tangent passing through the end point of the side surface on the convex side make the high refractive index layer. and an optical structure in which the slope angle range determined by the difference between the angle and the normal direction of the low refractive index layer is 9 degrees or more and 16 degrees or less .

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