JP2011150077A - Optical sheet, backlight unit and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet having high scratch-resistance and excellent light condensing/diffusing properties, and to provide a backlight unit and a display device. <P>SOLUTION: The optical sheet 25 has on a light emission surface 10 for emitting light, a plurality of projections projecting from an emission plane as a reference toward an emission side. The plurality of projections includes: semi-spherical or nearly semi-spherical microlenses 100 which are independent from one another; and a geometric structure continuously forming ruggedness along a predetermined direction. In the cross section obtained by cutting the geometric structure along the continuing direction of the ruggedness formed by the geometric structure, a base angle formed between the tangent of the microlens and the emission plane at the connection part of the microlens with the geometric structure is larger than a base angle formed between the ruggedness formed by the geometric structure and the emission plane. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical sheet used for optical path control, a backlight unit using the optical sheet, and a display device.

  Liquid crystal display devices using liquid crystal panels are widely used not only as image display means for mobile phones, personal digital assistants, and personal computer displays, but also as image display means for televisions as home appliances. The liquid crystal display device is also used as an image display device for information appliances for large screens, which has been difficult with conventional cathode ray tube (CRT) televisions, and has spread to general households. In addition, in order to make better use of the advantages of liquid crystal display devices, products that not only increase in size but also increase brightness, reduce thickness, and reduce weight are being developed and supplied to the market at a very high speed.

  In such a liquid crystal display device, a light source is often built in the device. In order to obtain the brightness necessary for displaying an image, a backlight unit including a light source is arranged on the back side of the liquid crystal panel. The light sources employed in the backlight unit can be broadly divided into two types: a “light guide plate light guide method” (so-called edge light method) and a “direct type”. In the edge light system, a light source represented by a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) is arranged on the side of the liquid crystal display device, and it is a flat plate made mainly of resin with excellent light transmission. Multiple reflection in the light guide plate. In the “direct type”, a diffuser plate and an optical film having a strong light scattering property are arranged between the image display element and the light source arranged on the back side of the liquid crystal display device, so that the CCFL, the LED, etc. are directly visible. It has a configuration that is not.

  In recent liquid crystal display devices, suppression of power consumption for the purpose of reducing energy consumption, which is a part of measures against global environmental problems, has become a major issue. In the case of a liquid crystal display device, the power consumption of the backlight serving as the light source is the largest, and efforts to suppress the power consumption of this backlight have been made in a wide range of fields.

  One approach is to reduce the number of cold-cathode tubes, which are light sources, to reduce power consumption, and the effect of reducing power consumption is widely recognized by society. However, reducing the number of cold-cathode tubes will increase the brightness unevenness (lamp image), which is the brightness of the light source, and it will be difficult to completely erase the lamp image with the conventional combination of the diffusion plate and the optical sheet. It is coming. Further, when diffusing particles are increased in the diffuser plate in order to erase the lamp image, the total light transmittance of the diffuser plate is lowered, and the luminance necessary for image display cannot be obtained. The required luminance can be obtained by strengthening the light from the cold cathode tube, which is a light source, but the problem remains that strengthening the light greatly reduces the effect of reducing power consumption.

  In addition, even when an LED, which is said to have low power consumption, is used as a light source, a direct type configuration in which the light source is arranged on the back side of the liquid crystal display device or an edge light type configuration in which the light source is arranged on the side surface side of the liquid crystal display device. Two methods are adopted, and products with improved contrast ratios are being introduced to the market. However, there remain problems such as suppression of heat generation around the LED light source and a required luminance not being obtained. For this reason, in order to suppress heat generation and reduce power consumption, it is required to reduce the number of LEDs that are point light sources. However, as described above, the required luminance cannot be obtained, and the brightness unevenness of the light source is dark. It is necessary to solve problems such as (lamp image) becoming stronger.

  At present, as an approach to solve these problems, diffuser plates, light guide plates, and condensing, diffusing and polarizing functions used in liquid crystal display devices, or functions of changing emission colors and absorbing some wavelengths By improving the performance of each of the functional members and using them in combination, the required brightness is ensured and the lamp image and brightness unevenness are reduced.

  In the above-mentioned optical sheet, conventionally, as a method for increasing the light use efficiency of the light source, a method of collecting diffused light from the backlight unit by the optical sheet and improving the front luminance is taken, for example, A brightness enhancement film (BEF: Brightness Enhancement Film), which is a registered trademark of US 3M, is widely used as an optical sheet. The BEF is a sheet in which unit prisms having a triangular cross section are arranged in a predetermined direction at a constant pitch on the upper surface (outgoing light side) of a transparent substrate, and light from “off-axis”. The light incident on the flat surface of the substrate is re-directed or “recycled” “on-axis” toward the viewer. When exiting from the prism surface, it has the effect of collecting light in the front direction, and the luminance in the front direction can be improved.

  Here, the optical sheet used in the liquid crystal display device has various functions such as not only improving luminance by improving light utilization efficiency but also removing unevenness of the light source, securing the viewing area of the display, and maintaining the rigidity of the display. Is required. For this reason, in order to realize desired optical characteristics, a plurality of optical sheets are often laminated on the diffusion plate (liquid crystal panel side). However, when the BEF is used as an optical sheet, since the BEF refracts light in the vertical direction on the prism surface and emits it in the normal direction, the viewing angle in the vertical direction becomes very narrow relative to the viewing angle in the horizontal direction. . In addition, since the top of the prism is sharp, it has drawbacks such as being easily damaged when contacted with another optical sheet or a functional member disposed on the prism, or a liquid crystal panel. .

Attempts have been made to reduce the number of optical sheets to be used while making up for these drawbacks and maintaining equivalent optical characteristics and environmental characteristics. For example, Patent Document 1 describes a method of imparting a diffusing function to the condensing function of a prism by dispersing diffusible fine particles in the prism lens.
Further, in Patent Document 2, by arranging microlenses randomly on a base material, light incident from the back surface is condensed by the microlens and emitted forward, and the same optical performance is achieved with fewer optical sheets than in the past. A method for achieving the above has been proposed.

JP-A-10-246805 JP 2006-301528 A

  The optical sheet described in Patent Document 1 has a diffusion function in addition to a light condensing function. However, since the optical sheet described in Patent Document 1 has diffusible fine particles dispersed in the prism, the light collected in the front is diffused again by the diffusible fine particles, and the amount of light in the front direction is small. Become. Further, there is a problem that glare due to refraction and reflection at a specific angle of the lens is visually recognized.

  Furthermore, since the tip of the prism is sharp, the back surface of the functional member disposed at the top, and further, damage due to contact with the liquid crystal panel is likely to occur, and there is a problem that foreign matter is generated due to contact or friction. In particular, optical sheets or functional members that are used in a stacked manner may be used with their four sides fixed to the frame of the device when placed in a liquid crystal display device, but are fixed without moving completely inside the device. It has not been done. For this reason, the optical sheet may come into contact with another optical sheet or a functional optical member due to vibration during conveyance or movement, and may be rubbed and scratched. Further, when driving the liquid crystal display device, the optical sheet and the functional member are warmed by the heat generated from the light source, and as a result, expansion and contraction depending on the physical properties unique to the constituent material occurs in the surface, and the dimensional change or Since bending occurs, contact with other optical sheets or functional members may cause rubbing and scratching.

Here, as a measure for improving the scratch resistance and preventing the generation of foreign matter, it is conceivable to round the prism top. However, since the width at which the top of the prism is rounded and the front luminance are in an inversely proportional relationship, in order to achieve the desired scratch resistance, the front luminance is reduced.
On the other hand, since the optical sheet described in Patent Document 2 has a hemispherical lens, even when it comes into contact with an optical sheet or a functional member that is used in a stacked manner, the hemispherical lens has a rounded structure. Even if friction due to contact occurs, it has a feature that it is hard to be scratched due to good sliding. However, a gap is generated between adjacent microlenses. For this reason, light that is refracted and scattered at the interface between the microlens and the air layer through the inside of the microlens and condensed on the front, and light that is emitted without being refracted and scattered from the gap between adjacent microlenses. Two types of light are generated. And there exists a subject that a bright spot and a bright line will be visually recognized from the brightness | luminance difference of these lights.

  The present invention has been made in view of the above-described problems, and has excellent light condensing / diffusing characteristics, and is hardly damaged when used in combination with a plurality of optical sheets and functional members. An object of the present invention is to provide an optical sheet having high scratch resistance. Furthermore, it aims at providing the backlight unit and display apparatus using this optical sheet.

In order to solve the above problems, the present invention proposes the following means.
That is, the invention according to claim 1 of the present invention is the optical sheet having a plurality of convex portions protruding from the reference emission plane to the emission side on the light emission surface that emits light. The shape portion includes a hemispherical shape or a substantially hemispherical shape and independent microlenses, and a geometric structure continuously forming irregularities along a predetermined direction,
In the cross-section cut along the continuous direction of the unevenness formed by the geometric structure, the base angle of the tangent line of the microlens with respect to the emission plane at the connection portion between the microlens and the geometric structure is the geometric structure. The unevenness formed by the body is larger than the base angle with respect to the emission plane.

Here, the base angle of the tangent line of the microlens with respect to the emission plane is the angle on the smaller angle side (the side where the optical element is present, which is 90 degrees or less) of the intersection angle with the emission plane. .
By adopting the above-described configuration, the microlens having a structure with no corners on the top side and hardly scratched has a structure that protects the easily damaged geometric structure. As a result, when used in combination with a plurality of optical sheets and functional members, the light exit surface of the optical sheet is provided with high scratch resistance that can prevent the occurrence of scratches due to contact or rubbing. I can do it.
In addition, it is possible to provide an optical sheet having both excellent optical characteristics (condensing / diffusion characteristics) of the microlens and the geometric structure.

  Next, in the invention described in claim 2, in the configuration described in claim 1, the unevenness formed by the geometric structure is a triangle having a triangular cross section and an apex angle in the range of 80 degrees to 100 degrees. The base angle of the tangent line of the microlens with respect to the emission plane is greater than 45 degrees. That is, the base angle of the tangent line of the microlens is larger than the base angle of the prism shape.

  By adopting the above configuration, a microlens having a structure that is hard to be scratched becomes a structure that protects a prism that is easily scratched, and high scratch resistance that can prevent scratches due to contact or rubbing on the light emitting surface of the present invention. Sex can be imparted. In addition, it is possible to provide an optical sheet having both the excellent hemispherical microlens and the excellent optical characteristics of the prism.

  Next, in the invention described in claim 3, the area ratio in the entire light exit surface of the microlens is in the range of 5% to 40% with respect to the configuration described in claim 1 or claim 2. It is characterized by this.

  By defining the area ratio of the microlens as described above, it is possible to control the effect of preventing scratches, the effect of widening the viewing angle, and the brightness enhancement effect of having the geometric structure. As a result, it is possible to provide an optical sheet that can achieve both high scratch resistance and excellent optical properties.

  Next, in the invention described in claim 4, in the configuration described in any one of claims 1 to 3, the diameter of the exit plane of the micro lens is in the range of 40 μm to 150 μm. It is characterized by.

  By defining the diameter of the microlens as described above, in the microlens that can be stably formed, the appearance of the optical sheet light exit surface, such as roughness or glare, due to the microlens itself being visually prevented can be prevented. Thus, it is possible to provide an optical sheet having both good scratch resistance and excellent optical properties and a good appearance.

Next, in the invention described in claim 5, the surface of the microlens and the surface of the geometric structure that form the convex portion are added to the configuration described in any one of claims 1-4. It is characterized in that an uneven shape having a surface roughness Ra in the range of 0.5 μm or more and 10 μm or less is imparted to at least one of the surfaces.
By imparting a fine uneven shape within the above range to the surface on the light emitting surface side, it is possible to control the light diffusion function and to improve the viewing angle and concealment.

  Next, the invention described in claim 6 is a hemispherical shape or a substantially projecting shape toward the light incident side on the light incident surface on which light is incident on the configuration described in any one of the first to fifth aspects. A hemispherical convex structure is provided.

  By providing a substantially hemispherical convex structure on the light incident surface side, not only the light exit surface side but also the light incident surface side is in contact with or rubbed with the light exit surface side of the diffusion plate or other functional sheet. It is possible to prevent the occurrence of scratches due to. At the same time, since the gap is generated by the substantially hemispherical structure, it is also possible to suppress the occurrence of interference unevenness such as Newton rings caused by the close contact.

Next, the invention described in claim 7 is characterized in that, with respect to the configuration described in claim 6, the light incident surface is provided with unevenness finer than the convex structure portion.
By providing fine irregularities along with the hemispherical convex structure on the light incident surface side, scratches due to contact or rubbing with the light emitting surface side of the diffuser plate or other functional sheet on the light incident surface side are prevented. prevent. At the same time, by imparting a fine uneven shape to the surface on the light emitting surface side, it is possible to enhance the light diffusing function and to improve the viewing angle and concealment.

Next, the invention described in claim 8 is characterized in that, in the configuration described in claim 7, the fine unevenness is an unevenness having a surface roughness Rz in a range of 0.1 μm to 5 μm. To do.
By providing a substantially hemispherical structure and irregularities within the above range on the light incident surface side, it is possible to prevent scratches due to contact or rubbing with the light emitting surface side of the diffusion plate on the light incident surface side or other functional sheets. prevent. At the same time, it is possible to control the light diffusing function to improve the viewing angle and concealment.

  Next, an invention described in claim 9 includes the optical sheet described in any one of claims 1 to 8 and a light source disposed on a light incident surface of the optical sheet. A backlight unit is provided.

  Next, an invention described in claim 10 includes a display device comprising: an image display element that transmits / shields light in pixel units to display an image; and a backlight unit according to claim 9. It is to provide.

A microlens with a structure that has a wide viewing angle on the light-emitting surface side where light exits, is easy to slip and is not easily scratched, and a linear geometric structure with high light-collecting properties and excellent brightness. A structure having both bodies can be formed.
And, by adopting a configuration in which the base angle of the tangent line of the microlens is larger than the base angle of the geometric structure, it has high scratch resistance that can prevent the occurrence of scratches due to contact or rubbing on the light emitting surface side. At the same time, it is possible to provide an optical sheet having both the excellent optical characteristics of a geometric structure represented by a substantially hemispherical microlens and a prism structure.

In addition, as described in claim 3 and claim 4, by specifying the specifications of the microlens, it is possible to achieve both scratch resistance and optical characteristics.
Further, as described in claim 4 and claim 7, by providing fine irregularities on the light exit surface side, or by providing a substantially hemispherical structure and fine irregularities on the light incident surface side, Scratch resistance on the incident surface side can be improved, and at the same time, a light diffusing function can be improved, and the viewing angle can be expanded and concealed.

  Furthermore, by combining the optical sheet of the present invention with an optical member having a function, or a diffusion plate or a light guide plate, a liquid crystal display image excellent in luminance, viewing angle, and concealment property is emitted in the viewer side direction. A backlight unit and a display device that can be provided can be provided.

It is a cross-sectional schematic diagram of the display apparatus which is embodiment of this invention. It is a figure explaining the optical sheet which is embodiment of this invention, (a) is a cross-sectional schematic diagram of an optical sheet, (b) is an expanded cross-sectional schematic diagram of an optical sheet. It is the cross section and upper surface schematic diagram of the optical sheet which is embodiment of this invention. It is a cross-sectional schematic diagram of the optical sheet which is embodiment of this invention. It is a cross-sectional schematic diagram of the geometric structure connected to the linear form of the optical sheet which is embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 to FIG. 5 are examples of cross-sectional schematic diagrams illustrating the configuration of the optical sheet, the backlight unit, and the display device according to the present embodiment, and the mode of use thereof. However, the scale or ratio of each part does not match the actual. Moreover, it is not limited to this.

(Display device)
FIG. 1 is a schematic cross-sectional view showing an example of an optical sheet, a backlight unit, and a display device of the present invention.
As shown in FIG. 1, the display device 70 of this embodiment includes an image display element 35 and a backlight unit 55.
As shown in FIG. 1, the image display element 35 includes a liquid crystal panel 32 and deflecting plates 31 and 33 disposed on both surfaces thereof. The image display element 35 is an element that displays an image by transmitting / blocking light in pixel units.

  As shown in FIG. 1, the backlight unit 55 includes a light source unit 45, a diffusion plate 50, an optical sheet 25 that is an embodiment of the present invention, and a functional member 2. The light source unit 45 is configured by arranging a plurality of light sources 41 in a lamp house (reflecting plate) 43. The diffusion plate 50 is disposed on the light source unit 45 (observer side direction F) and diffuses the light H emitted from the light source 41. The optical sheet 25 is disposed on the diffusion plate 50. A single functional member 2 or a plurality of functional members 2 are arranged on the optical sheet 25. The functional member 2 is a member having a function of condensing, diffusing or polarizing light, or a function of changing a color or absorbing a specific color.

  The light H emitted from the light source 41 is diffused by the diffusion plate 50 and diffused / reflected / condensed / reflected by the optical sheet 25 and the single or plural optical sheets or functional members 2 disposed thereon. Color shifted. Subsequently, the light K reaching the necessary function emitted from the backlight unit 55 enters the image display element 35 and is emitted to the observer side F.

  The light source 41 supplies light to the image display element 35. As the light source 41, for example, a plurality of linear light sources can be used. As the plurality of linear light sources, a plurality of fluorescent lamps, CCFLs, external electrode fluorescent lamps (EEFL), linearly arranged LEDs, or the like can be used as an example. The reflection plate 43 is disposed on the opposite side of the plurality of light sources 41 from the observer side F, and reflects the light emitted in the direction opposite to the observer side F out of the light emitted from the light source 41 in all directions. It plays a role of letting it be emitted to the observer side F. As a result, the light H emitted to the observer side F becomes light emitted almost in all directions from the light source 41. By using the reflection plate 43 in this way, the light utilization efficiency can be increased. The reflection plate 43 may be any member that reflects light with high efficiency. For example, a general reflection sheet, reflection plate, or the like can be used.

(Optical sheet)
As shown in FIG. 1, the optical sheet 25 according to the embodiment of the present invention has a plurality of convex portions protruding from the reference emission plane to the emission side on the light emission surface that emits light. The plurality of convex portions includes a microlens 100 that is hemispherical or substantially hemispherical and independent of each other, and a geometric structure 110 that continuously forms irregularities along a predetermined direction. Hereinafter, “a geometric structure that continuously forms irregularities along a predetermined direction” is also referred to as a “linear geometric structure”. The microlens 100 has, for example, a plan view, a circular shape or a substantially circular outline shape. The plan view refers to, for example, a state viewed from the emission side.

Here, the geometric structure 110 that forms unevenness continuously along a predetermined direction is an optical element, and each apex formed by the continuous unevenness is linear in a direction intersecting the predetermined direction. Or it extends in the shape of a curve. A plurality of top portions are arranged in the predetermined direction.
Further, the microlens 100 is an optical element having an arc shape or a substantially arc-shaped contour shape when cut in any thickness direction when cut in the thickness direction of the optical sheet.

  Then, the microlens 100 and the geometric structure 110 on the light exit surface side 10 improve the luminance by condensing and diffusing the light H incident through the diffusion plate 50 according to the structure, thereby displaying an image. Light is emitted to the element 35 side. Further, the microlens 100 has a function of preventing the occurrence of frictional scratches due to contact with or rubbing with another optical sheet or the functional member 2 disposed on the light emitting surface side 10 or the image display element 35. .

Here, the optical sheet 25 described above may be used not only for a liquid crystal device but also for any device that performs optical path control, such as a rear projection screen, a solar cell, an organic or inorganic EL, and an illumination device. it can.
The optical sheet 25 collects strong front light H incident from the light source 41 according to its structure by providing fine irregularities on at least one of the light exit surface side 10 and the light incident surface side 20. At the same time, it is possible to widen the viewing angle by diffusing with a fine uneven shape on the surface.

  Further, the fine unevenness has an effect of reducing luminance unevenness, a lamp image, a light / dark difference and the like due to the light source 41 when viewing the light source 41 side through the image display element 35 from the observer side F side. Uniform light can be emitted to the observer side F. Further, a predetermined pattern provided for the purpose of reducing the lamp image on the front or back surface of the diffusion plate 50 or a structure showing a required function is prevented from being seen through from the observer side F. It is also possible to do.

FIGS. 2A and 2B are diagrams for explaining the structure of the optical sheet 25 according to the embodiment of the present invention in a vertical cross section of the geometric structure 110 that is linearly connected. That is, FIGS. 2A and 2B are cross-sectional views cut in the continuous direction of the unevenness formed by the geometric structure 110.
As shown in FIG. 2A, the microlens 100 and the geometric structure 110 are provided together on the light emitting surface side 10 of the optical sheet 25. The extension line L3 is a line that is perpendicular to the perpendicular passing through the apex that bisects the apex angle of the geometric structure adjacent to the microlens that continuously forms unevenness, or the geometric structure that continuously forms unevenness. Represents a line parallel to the tangent at the top of the body. The position of the extension line L3 represents, for example, the position of the emission plane as a reference.

  Here, as illustrated in FIG. 2B, there is an angle θ <b> 1 that is a base angle formed by the tangent line L <b> 1 and the extension line L <b> 3 of the cross section at a portion where the microlens 100 and the geometric structure 110 are in contact with each other. On the other hand, there is a base angle θ2 formed by the extension line L2 and the extension line L3 of the exit surface of the geometric structure 110. In this embodiment, the angle θ1 is set to be always larger than the base angle θ2.

By defining that the angle θ1 is always larger than the base angle θ2, the height ratio between the microlens 100 and the geometric structure 110 is limited. As a result, it is possible to protect the geometric structure 110 that is easily damaged while maintaining high scratch resistance by the microlens 100.
Further, by keeping the angle θ1 high, the rising angle of the substantially hemispherical microlens 100 can be defined high. In this case, this leads to an increase in light collecting performance and an improvement in luminance. It has been confirmed by optical simulation analysis that the higher the rising angle and height of the microlens 100, the higher the luminance.

  Here, from the optical simulation analysis and the knowledge obtained so far, when the angle θ1 is smaller than the base angle θ2, the height of the substantially hemispherical microlens 100 is limited, which contributes to light collection. As a result, the rise angle from the bottom surface that improves the brightness can be suppressed to a low level, so that the brightness of the entire optical sheet 25 is confirmed to decrease.

  In addition, when the height of the microlens 100 is restricted, a difference in height from the geometric structure 110 that is linearly connected is reduced. In this case, it is not desirable because it becomes difficult to achieve protection of the geometric structure 110 that is easily damaged.

  The area ratio that the microlens 100 occupies in the light emitting surface 10 is a value that affects the optical characteristics of the optical sheet 25. When the area ratio of the microlens 100 is higher than 40%, the area ratio of the geometric structure 110 connected in a linear shape having a high effect of improving the luminance is relatively decreased, so that the luminance of the entire optical sheet 25 is decreased. Invite them to In addition, when the microlenses 100 are randomly arranged, if the area ratio becomes higher, it tends to have some regularity in the arrangement, and the image display element 35 or other structural body or functionality having regularity. Since it becomes easy to produce the interference fringe with the member 2, it is not preferable.

On the other hand, when the area ratio of the microlens 100 is as low as less than 5%, the area occupied by the linear geometric structure 110 increases, and the viewing angle decreases while the luminance is improved. Moreover, since the number of the substantially hemispherical microlenses 100 that exist independently decreases, it is not desirable because the required scratch resistance cannot be obtained.
From the above, in order to exhibit high luminance and necessary scratch resistance, it is preferable that the area ratio occupying the entire light exit surface 10 of the microlens 100 is in a range of 5% to 40%.

The above-described area ratio is a numerical value determined by setting the number and diameter of the microlenses 100 in the light exit surface. In the present embodiment, in FIG. 3, the diameter R on the emission plane of the microlens that determines the area ratio of the microlens 100 is in the range of 40 μm to 150 μm. The diameter R of the microlens is the diameter at the reference emission plane.
The reason why the diameter R of the microlens is in the range of 40 μm to 150 μm is as follows.

  When the diameter R exceeds 150 μm, the microlens itself is easily visible, and this is not preferable because it increases the possibility of leading to unevenness, roughness, and bright spots on the light exit surface. On the other hand, when the diameter R of the microlens 100 is less than 40 μm, the height of the geometric structure 110 is limited to be low, and the luminance decreases due to the light diffraction effect and the accuracy of the shape of the geometric structure 110 being reduced. Therefore, it is not preferable. Furthermore, it is difficult to form a microlens having a diameter of less than 40 μm, which is not preferable because of a large variation in shape, diameter, and height.

  Moreover, it is desirable that the microlens 100 exists over a plurality of projections and depressions that form the linear geometric structure 110. This arises from the fact that the height of the microlens 100 is higher than that of the geometric structure 110 in order to protect the easily damaged geometric structure 110. In addition, the planar view shape seen from the upper surface of the microlens 100 may be circular or substantially circular, and may be elliptical. In the case of other than a circle, both the maximum diameter and the minimum diameter are in the range of 40 μm to 150 μm.

  With respect to the shape of the microlens 100, the sliding of the functional member 2 laminated on the light emitting surface 10 with the portion where the light incident surface is in contact is good, and the contact area is low. It leads to the functional member 2 laminated | stacked on the upper part of the surface 10 being hard to be damaged. Therefore, as for the shape of the microlens 100, it is desirable that the shape of the top part to be contacted is close to a hemisphere. Furthermore, the area in contact with the light incident surface of the functional member 2 laminated on the light emitting surface 10 is preferably 10% or less of the bottom area of the microlens. By using a microlens structure that reduces the contact area with the functional member 2 laminated on the upper part, it is possible to suppress the occurrence of frictional flaws due to contact.

  At least one of the surfaces of the geometric structure 110 linearly connected to the surface of the microlens 100 may have fine irregularities. This is because fine irregularities can enhance the diffusion characteristics of the emitted light. At this time, the surface roughness Ra (arithmetic average roughness) is preferably in the range of 0.1 μm to 10 μm. In the uneven structure below 0.1 μm, it is difficult to obtain the diffusion effect. In addition, a concavo-convex structure exceeding 10 μm may cause a significant reduction in luminance, and at the same time, a smooth state in which the top of the substantially hemispherical microlens 100 is hard to be damaged is damaged, thereby reducing the damage prevention effect. Because that happens. As a method for forming fine irregularities, for example, the surface of a mold in which the shapes of the substantially hemispherical microlens 100 and the geometric structure 110 are first molded are etched or sandblasted by chemical treatment or physical treatment. Examples of the roughening method include a method of cutting a fine uneven shape into a mold in which the shapes of the substantially hemispherical microlens 100 and the geometric structure 110 are first formed.

  On the other hand, it is desirable that the light incident surface side 20 of the optical sheet 25 of the present invention is also provided with a substantially hemispherical convex structure portion 120 as shown in the sectional view of FIG. By providing a substantially hemispherical convex structure portion 120 on the light incident surface side 20, not only the light exit surface side 10, but also the diffuser plate 50 on the light incident surface side 20 or the light exit surface side of another functional member 2. It is possible to prevent the occurrence of scratches due to contact with or rubbing against the surface. At the same time, since a gap is formed by the substantially hemispherical convex structure 120, it is possible to suppress the occurrence of Newton rings, which are interference fringes caused by close contact. The substantially hemispherical structure is desirably formed in a range that does not interfere with the incidence of light from the light source 41, and the area ratio for installing the substantially hemispherical convex structure portion 120 on the light incident surface 20 is 1 It is desirable to be within the range of not less than 20% and not more than 20%. If it is less than 1%, the effect of preventing the occurrence of scratches due to contact or rubbing cannot be expected. If it exceeds 20%, the light from the light source 41 is prevented from being taken into the optical sheet 25, and the brightness is reduced. Will cause.

  Further, by providing substantially hemispherical structures (microlenses 100) and 120 on the front and back surfaces of the optical sheet 25 of the present invention, when wound on a roll during production or the like, scratches are caused by contact or friction by the front and back surfaces. It becomes possible to prevent this. As a result, since it is possible to omit the protective film required for preventing scratches, the manufacturing process can be omitted and the cost can be reduced.

  Furthermore, it is preferable that the substantially hemispherical convex structure portion 120 formed on the light incident surface side 20 of the optical sheet 25 has a diameter in the range of 20 μm to 150 μm. When the diameter is less than 20 μm, the effect of preventing the occurrence of scratches due to contact or rubbing is too low, and it is not desirable because it is difficult to process and mold. Further, when it exceeds 200 μm, there is a disadvantage that the substantially hemispherical convex structure portion 120 is of a size that can be visually observed, and that there is a high possibility that the incidence of light from the light source 41 is prevented and the luminance is lowered. Arise. Moreover, although the height of the substantially hemispherical convex structure portion 120 depends on the diameter thereof, the aspect ratio obtained by dividing the height by the diameter is preferably in the range of 0.1 to 0.3. This is because if the height is too low, the effect of preventing the occurrence of scratches due to contact or rubbing cannot be obtained, and if it is too high, the incidence of light from the light source 41 is hindered to lower the luminance. The substantially hemispherical convex structure portion 120 may have a circular shape or a substantially circular shape as viewed from above, and may be an elliptical shape, a triangular shape or a rectangular shape with rounded corners, or a high shape.

  It is preferable that the light incident surface side 20 of the optical sheet 25 has a fine uneven shape. By providing a fine uneven shape on the light incident surface side 20 of the optical sheet 25, it is possible to improve the concealability in addition to preventing the occurrence of scratches due to contact and rubbing, suppressing the occurrence of Newton rings. I can do it. Thus, a predetermined pattern provided for the purpose of reducing the lamp image on the front surface or the back surface of the diffusion plate 50, or a required function, while reducing luminance unevenness due to the light source, lamp image, brightness difference and the like. It is also possible to suppress the structure to be seen from the viewer side F. The surface roughness Rz (ten-point average roughness) of the fine concavo-convex shape is desirably in the range of 0.5 μm or more and 5 μm or less. Diffusing and concealing effects are difficult to obtain with a concavo-convex structure of less than 0.5 μm, and a concavo-convex structure of more than 5 μm may cause a significant reduction in brightness, and at the same time, scratches on the top of the substantially hemispherical convex structure 120. This is because a smooth state that is difficult to be damaged is impaired, and the effect of preventing scratches is reduced. As a method for forming fine irregularities, for example, a method of roughening the surface of a mold obtained by molding the substantially hemispherical convex structure portion 120 by etching or sandblasting first, the substantially hemispherical convex structure portion 120 first. Examples of the method include cutting a finer uneven shape on the molded mold.

  The substantially hemispherical convex structure portion 120 formed on the light incident surface side 20 of the optical sheet 25 is the same as the front and back in the extrusion molding process for forming the substantially hemispherical microlens 100 and the geometric structure 110 on the light emitting surface side. It can be formed by processing on both sides. Furthermore, it can also be obtained by bonding sheets obtained by processing separately.

  Furthermore, the light incident surface side 20 of the optical sheet 25 may be processed to provide discontinuous minute protrusions. Examples of the method for forming such irregularities include mat processing and embossing. According to these methods, it is possible to obtain a concavo-convex shape by pressing the transparent resin softened by heating to the concavo-convex member to transfer the shape of the member and then curing the transparent resin. . As another method, transparent particles having a particle size of about 30 to 100 μm may be blended in a molten transparent resin, and the transparent particles may be extruded to the outermost layer side to cause unevenness on the surface. When this method is used, it is preferable that the refractive indexes of the transparent resin and the transparent particles are equal.

  As the linear geometric structure 110, it is desirable that the cross-sectional shape as shown in FIG. 5 (a) is a continuous body having a triangular prism shape, and the apex angle is particularly in the range of 80 to 100 degrees. A triangular prism is particularly preferred. The reason for this is that lens molding is easy and the brightness is improved by controlling the direction of the emitted light.

Further, the geometric structure 110 connected in a linear shape may have a convex curved lens shape as shown in FIG. This is because the emission performance can be improved because the exit surface can be set at various angles. The convexly curved lens shape may be an aspherical shape as shown in FIG. 5 (c), and the reason is that the diffusion performance can be increased because the radius of curvature of the top can be reduced. .
Furthermore, the linearly connected geometric structure 110 may be a curved triangular prism as shown in FIG. 5D, and the light exit surface can be set at various angles, so that the diffusion performance is improved. Further, the geometric structure 110 may be configured by combining a plurality of the above-described cross-sectional shapes. This is because the optical performance can be expected to be improved by combining the condensing and diffusing effects of two or more linear geometric structures.

  The width and height of the linear geometric structure 110 are determined by the relationship with the substantially hemispherical microlens 100, and the width is preferably 20 μm or more and 100 μm or less. This is because, when the thickness is less than 20 μm, the brightness is lowered due to the diffraction effect of light, and it becomes difficult to maintain high shape accuracy when the geometric structure 110 is processed and molded, leading to a reduction in brightness. It is. In addition, when the thickness exceeds 100 μm, the height and area ratio of the geometric structure 110 increase, so that it comes into contact with the light incident surface side of an optical sheet or the like having a function of being stacked on the light emitting surface. There is the possibility that the image display element 35 or other functional optical sheet or the like has a regular structure and interference fringes easily, and that the viewing angle is narrow. It is not preferable to occur.

  On the other hand, the height of the geometric structure 110 is desirably 20% or more and 60% or less of the height of the substantially hemispherical microlens 100. When the height of the geometric structure 110 is less than 20% of the height of the substantially hemispherical microlens 100, the width and height of the geometric structure 110 itself are reduced, and the luminance is reduced as described above. May cause. Further, if it exceeds 60%, there is a possibility that the functional member 2 arranged in a laminated manner on the upper surface of the light emitting surface may come into contact with the light incident surface side, and may be damaged, the image display element 35 or other functions. It becomes easy to produce interference fringes with a structure having regularity possessed by an optical sheet or the like. Furthermore, it is not preferable because a disadvantage that the viewing angle becomes narrow occurs.

  The geometric structure 110 linearly connected to the substantially hemispherical microlens 100 described so far can be formed on a highly transparent sheet using an electron beam curable resin typified by a UV curable resin. it can. As an example, UV molding can be performed using a mold in which a microlens 100 having a substantially hemispherical shape with a dimension designed in advance and a geometric structure 110 are formed. Here, as the material of the highly transparent sheet, PET (polyethylene terephthalate), PC (polycarbonate), PMMA (polymethyl methacrylate), COP (cycloolefin polymer), acrylonitrile styrene copolymer, acrylonitrile polystyrene copolymer Etc. can be cited as an example.

  Further, the material used for the substantially hemispherical microlens 100 and the geometric structure 110 is preferably a transparent resin made of a thermoplastic resin. For example, a polycarbonate resin, an acrylic resin, a fluorine acrylic resin, a silicone acrylic resin, An epoxy acrylate resin, a polystyrene resin, a cycloolefin polymer, a methylstyrene resin, a fluorene resin, PET, polypropylene, an acrylonitrile styrene copolymer, an acrylonitrile polystyrene copolymer, and the like can be given. It can also be formed by an extrusion molding method using these materials, an injection molding method, or a hot press molding method.

  The geometric structure 110 linearly connected to the substantially hemispherical microlens 100 can be used by adding inorganic fine particles or organic fine particles for the purpose of improving diffusibility. Examples include acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof, melamine-formalin condensate particles, polyurethane particles, polyester particles, silicone particles, fluorine particles, copolymers thereof, smectites. , Clay compound particles such as kaolinite, talc, inorganic oxide particles such as silica, titanium oxide, alumina, silica alumina, zirconia, zinc oxide, barium oxide, strontium oxide, calcium carbonate, barium carbonate, barium chloride, barium sulfate, Examples thereof include inorganic fine particles such as barium nitrate, barium hydroxide, aluminum hydroxide, strontium carbonate, strontium chloride, strontium sulfate, strontium nitrate, strontium hydroxide, and glass particles.

  The geometric structure 110 linearly connected to the substantially hemispherical microlens 100 is preferably added with an ultraviolet absorber. By adding the ultraviolet absorber, deterioration of the substantially hemispherical microlens 100 and the geometric structure 110 itself due to ultraviolet rays irradiated from the light source 41 can be suppressed, and the life can be extended. . Examples of the ultraviolet absorber include benzotriazole compounds such as 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, benzophenone compounds such as 2-hydroxy-4-methoxybenzophenone, and 4-t- Salicylic acid ester compounds such as butylphenyl salicylate, oxalic acid anilide compounds such as 2-ethoxy-2′-ethyl oxalic acid bisanilide, and cyanoacrylates such as ethyl-2-cyano-3,3-diphenylacrylate A system or the like can be used.

  The thickness of the optical sheet 25 according to the present invention is preferably in the range of 50 μm or more and 600 μm or less, although it varies depending on the material and material used and the environment and situation of use. When the thickness is less than 50 μm, the size of the substantially hemispherical microlens 100 and the geometric structure 110 to be formed is limited, and it is difficult to achieve the required optical characteristics and to make the thickness uniform during manufacturing. Become. In addition, since the strength of the sheet itself cannot be obtained, bending or deformation due to heat or the like is likely to occur, resulting in a problem that wrinkles or luminance unevenness is likely to occur. On the other hand, when the thickness exceeds 600 μm, inconveniences such as a decrease in transmittance of the entire optical sheet, an increase in material cost, and an increase in weight in the molding process occur.

As described above, since the optical sheet 25 of the present invention has a structure in which the microlens 100 and the linearly-structured geometric structure 110 are combined on the light emitting surface side 10, the generation of scratches due to contact or rubbing is prevented. An optical sheet having both scratch resistance that can be prevented and excellent optical characteristics of the substantially hemispherical microlens 100 and the geometric structure 110 can be provided.
Further, by providing fine irregularities on the light emitting surface side 10 and imparting a substantially hemispherical convex structure portion 120 and fine irregularities on the light incident surface side 20, the scratch resistance on the light incident surface side is improved. At the same time, it is possible to enhance the light diffusing function and increase the viewing angle and concealment. Fine irregularities may also be formed on the surface of the convex structure 120.

Furthermore, by combining the optical sheet of the present invention with an optical member having a function or a diffusing plate, a liquid crystal display image excellent in luminance, viewing angle, and concealability can be emitted in the viewer side direction. A backlight unit and a display device can be provided.
As described above, in the display device 70 of the present invention, the image display element 35 is a liquid crystal display element, and the light K whose light collection / diffusion characteristics are improved by the backlight unit 55 described above is used. Therefore, the brightness on the viewer side F is improved, the distribution of the light intensity in the viewing angle direction is smoothed, and the lamp image that is the light source and the unevenness of the diffusion plate are reduced, thereby improving the brightness of the entire screen. A uniform image can be obtained.

Here, the geometrical structures 110 that are linearly connected do not have to be repeated in the same shape and the same size.
Hereinafter, the present invention will be described in detail based on examples. In addition, this invention is not limited only to these Examples.

  Hereinafter, in an Example, the optical characteristic evaluation of the optical sheet 25 of this invention and the display apparatus 70, the abrasion test of the optical sheet 25 of this invention and the functional member 2, and its evaluation are demonstrated.

"Example 1"
As the microlens 100 on the emission surface side 10, a hexagonal hemispherical microlens having an area ratio of 30%, a diameter of 110 μm, and a lens height of 54 μm was formed. Further, as the geometric structure 110 that is linearly connected, a metal mold was formed on which a prism with a vertex angle of 90 degrees having a width of 30 μm and a lens height of 15 μm was formed. Using this mold, a substantially hemispherical microlens 100 and a geometric structure 110 made of a UV curable resin (refractive index = 1.52) are formed on a PET substrate (Toyobo product) having a thickness of 250 μm. An optical sheet 25 was produced. In addition, the produced prism was set as the structure arrange | positioned linearly in the horizontal direction seeing from the observer side.

"Comparative Example 1"
Using the same UV curable resin as the optical sheet of Example 1 described above, the microlens 100 was arranged on the same PET base material in a hexagonal manner with an area ratio of 30%, a diameter of 110 μm, and a lens height of 54 μm. An optical sheet in which a prism having a 90 ° apex having a width of 80 μm and a lens height of 40 μm was produced as the substantially hemispherical microlens 100 and the geometric structure 110.

"Angle measurement"
The cross section of the manufactured optical sheet 25 is observed, and perpendicular to the tangent line L1 of the cross section at the portion where the substantially hemispherical microlens 100 and the geometric structure 110 are in contact with the perpendicular line that bisects the apex angle of the prism. The angle θ1 formed by the extended line L3 representing the line to be measured and the base angle θ2 formed by the extended line L2 and the extended line L3 of the exit surface of the geometric structure 110 were measured.

First, the optical sheet was cut into small pieces, covered with a thermosetting transparent resin and cured, and a sample for cross-sectional observation was prepared using a glass knife and a diamond knife. The angle θ1 and the base angle θ2 were measured from the result of microscopic observation of the prepared sample.
"Optical evaluation"
The display device of this example was evaluated by the following measurement method.

(Front brightness evaluation)
The produced two types of optical sheets 25 were arranged on the diffusion plate 50, and the display device 70 having the image display element 35 on the observer side was assembled. The brightness of the center of the screen was measured under the same conditions using a spectral radiance meter (SR-3A: manufactured by Topcon Technohouse Co., Ltd.) with the screen of this display device being displayed as all white.
"Abrasion assessment"
The wear evaluation of this example and the comparative example was evaluated by the following measuring method.

(Gakushin style wear test)
The scratch resistance was evaluated using a Gakushin type abrasion tester under the following conditions. First, the surface of the optical sheet 25 to be evaluated on which the substantially hemispherical microlens 100 and the geometric structure 110 are formed is fixed to the Gakushin abrasion tester as the upper surface, and then the light diffusion sheet is used as the functional member 2 to be laminated. (Ewa product) The back side (light incident surface side) is placed facing each other, pressed under the condition that the load is 100 g / cm 3, and the substantially hemispherical microlens 100, the geometric structure 110, and the back side of the diffusion sheet These were reciprocated 20 times with an amplitude of 50 mm and a speed of 120 mm / sec and rubbed together, and the presence or absence of scratches and the extent of the scratches on the rubbed surfaces were visually evaluated.

"Measurement result"
Table 1 shows the measurement results of this example and the comparative example.

  As can be seen from Table 1, in Example 1, the angle θ1 formed by the tangent line L1 and the extension line L3 of the cross section at the portion where the microlens 100 and the geometric structure 110 that is linearly connected are in contact with each other, Varies depending on the observed location. The angle θ1 is maximum at a portion where the apex of the geometric structure 110 is in contact with the substantially hemispherical microlens 100, and the value is 90 degrees. Further, the angle θ1 is the smallest at the portion where the bottom of the geometric structure 110 is in contact with the substantially hemispherical microlens 100, and the value thereof is 59 degrees. On the other hand, the angle of the base angle θ2 formed by the extension line L2 and the extension line L3 of the exit surface of the geometric structure 110 was 45 degrees as designed. From the above results, it was found that the optical sheet of Example 1 had a structure satisfying the present invention. The front luminance of the display of Example 1 was 543 cd / m 2, the viewing half value angle in the vertical direction was 34.6 degrees, and the viewing half value angle in the horizontal direction was 48.1 degrees.

In the Gakushin abrasion test, no flaws were observed on the lens surface of the optical sheet of Example 1 and the back surface of the light diffusion sheet, and a good damage prevention effect could be confirmed.
On the other hand, in Comparative Example 1, the angle θ1 formed by the tangent line L1 and the extension line L3 of the cross section at the portion where the substantially hemispherical microlens 100 and the geometric structure 110 that is linearly connected contact each other was observed. Depending on the location, the apex of the geometric structure 110 is maximum at the portion that contacts the substantially hemispherical microlens 100, the value is 90 degrees, and the bottom of the geometric structure 110 corresponds to the substantially hemispherical microlens 100. The value was minimum at the contact area, and the value was 34 degrees. The angle of the base angle θ2 formed by the extension line L2 and the extension line L3 of the exit surface of the geometric structure 110 was 45 degrees. From the above results, it was found that the optical sheet of Example 1 has a structure in which the value of the angle θ1 is lower than the base angle θ2 and does not satisfy the specifications of the present invention. The front luminance of the display of Comparative Example 1 was 547 cd / m 2, the viewing half-value angle in the vertical direction was 33.3 degrees, and the viewing half-value angle in the horizontal direction was 47.7 degrees. In the Gakushin type abrasion test, partial streak-like scratches in the amplitude direction were observed on a part of the lens surface of the optical sheet of Comparative Example 1. This was found to be due to the fact that the top of the prism was shaved and that the shavings generated by shaving were damaging other parts.

  From the results of the examples and comparative examples described above, no difference was observed in the optical characteristics indicated by the front luminance and the viewing angle, but a large difference was observed in the wear test. Therefore, in the optical sheet 25 in which the microlens 100 on the light emitting surface side and the geometric structure 110 linearly connected are combined, the tangent line L1 and the extension line L3 where the substantially hemispherical microlens 100 and the geometric structure 110 are in contact with each other. The relationship between the angle θ1 that is the base angle formed and the base angle θ2 formed by the extension line L2 and the extension line L3 of the exit surface of the geometric structure 110 is such that the angle θ1 is always larger than the base angle θ2. By providing the above, it is possible to provide an excellent optical sheet 25 that has both high scratch resistance and excellent optical characteristics of a substantially hemispherical microlens and a linear geometric structure having a linear structure. I found it possible.

  The optical sheet 25 of the present invention has a wide viewing angle on the light-emitting surface side, a hemispherical or substantially hemispherical microlens that is slippery and hardly scratched, and has a high light collecting property and a high luminance. It is an optical sheet having both linear geometric structures that are excellent in improvement. And, in a cross section perpendicular to the geometric structure, by taking a cross-sectional structure in which the base angle of the tangent line of the micro lens at the position where the micro lens and the geometric structure are in contact is larger than the base angle of the geometric structure, It is possible to impart high scratch resistance that can prevent generation of scratches due to contact or rubbing. At the same time, it is possible to provide an optical sheet having both the substantially hemispherical microlens and the excellent optical characteristics of the geometric structure.

  In addition, by defining the specifications of the microlens as described above, it is possible to achieve both scratch resistance and optical characteristics. Furthermore, by imparting fine irregularities on the light exit surface side and imparting a substantially hemispherical structure and fine irregularities on the light incident surface side, it is possible to improve the scratch resistance on the light incident surface side, It is possible to enhance the light diffusing function and increase the viewing angle and concealment.

  By combining this optical sheet of the present invention with an optical member having a function, or a diffusion plate and a light guide plate, it is possible to emit a liquid crystal display image excellent in luminance, viewing angle, and concealment in the viewer side direction. A backlight unit and a display device can be provided.

H, K ... light, F ... observer side, H ... microlens height, R ... bottom diameter of the microlens, L1 ... tangent of the portion where the linear geometric structure contacts the microlens, L2 ... linear An extension line of the light emission surface of the geometric structure connected to L3, a line orthogonal to a perpendicular passing through the apex that bisects the apex angle of the geometric structure adjacent to the microlens that continuously forms irregularities, or , A line parallel to the tangent at the apex of the geometric structure that continuously forms irregularities, θ1... The angle at the intersection of the tangent of the microlens and the line L3 (base angle), θ2 the base angle of the geometric structure, DESCRIPTION OF SYMBOLS 2 ... Functional member, 10 ... Light-emitting surface side, 20 ... Light incident surface side, 25 ... Optical sheet, 31, 33 ... Polarizing plate, 32 ... Liquid crystal panel, 35 ... Image display element, 41 ... Light source, 43 ... Reflection Plate (reflection film), 45 ... light source unit, 50 ... diffusion Plate (light guide plate), 55 ... Backlight unit, 70 ... Display device, 100 ... Microlens, 110 ... Geometric structure linearly connected, 120 ... Substantially hemispherical structure

Claims (10)

In the optical sheet having a plurality of convex portions protruding from the emission plane as a reference to the emission side on the light emission surface that emits light,
The plurality of convex portions include a hemispherical shape or a substantially hemispherical shape and independent microlenses, and a geometric structure that continuously forms irregularities along a predetermined direction,
In the cross section cut along the continuous direction of the irregularities formed by the geometric structure,
The base angle of the tangent line of the microlens with respect to the exit plane at the connection portion between the microlens and the geometric structure is larger than the base angle with respect to the exit plane of the unevenness formed by the geometric structure. Optical sheet. The unevenness formed by the geometric structure is formed by a triangular prism having a triangular cross section and an apex angle in the range of 80 degrees to 100 degrees.
The optical sheet according to claim 1, wherein a base angle of a tangent line of the microlens with respect to the emission plane is greater than 45 degrees.   3. The optical sheet according to claim 1, wherein an area ratio occupying the entire light exit surface of the microlens is in a range of 5% to 40%.   4. The optical sheet according to claim 1, wherein a diameter of the microlens at an emission plane is in a range of 40 μm to 150 μm.   Providing a concavo-convex shape having a surface roughness Ra in the range of 0.5 μm or more and 10 μm or less to at least one of the surface of the microlens and the surface of the geometric structure forming the convex part. The optical sheet according to any one of claims 1 to 4, wherein the optical sheet is characterized.   The optical sheet according to any one of claims 1 to 5, wherein a hemispherical or substantially hemispherical convex structure portion protruding toward the light incident side is provided on a light incident surface on which light is incident. .   The optical sheet according to claim 6, wherein the light incident surface is provided with unevenness finer than the convex structure portion.   The optical sheet according to claim 7, wherein the fine unevenness is an unevenness having a surface roughness Rz in a range of 0.1 μm to 5 μm.   A backlight unit comprising: the optical sheet according to any one of claims 1 to 8; and a light source disposed on a light incident surface of the optical sheet.   A display device comprising: an image display element that transmits and blocks light in pixel units to display an image; and the backlight unit according to claim 9.

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