JP2012098409A - Optical sheet, backlight unit, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet with excellent condensation property, diffusion characteristic and a configuration inhibiting interference fringe, that can protect the optical sheet itself from damage due to warping or twisting even when another optical sheet is laminated on a light emission surface.SOLUTION: An optical sheet 10 includes a substantially hemispherical microlens 31 and a prism lens 19 provided on a light emission surface 10b where a cross section height h of the microlens 31 in a cross section along a top part of the prism lens 19 is randomly varied in a range of a height H1 at the highest.

Description

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

  Liquid crystal display devices using a liquid crystal panel are widely used not only for image display means such as mobile phones, personal digital assistants, and personal computer displays, but also for televisions as home appliances. Under such circumstances, liquid crystal display devices are also spreading to general households as image display devices for information home appliances for large screens that have been difficult with conventional CRT (cathode ray tube) televisions. Furthermore, in order to make better use of the advantages of liquid crystal display devices, not only large-size products, but also products that are compatible with high brightness, thinness and light weight are being supplied to the market at a very high speed.

  Such a liquid crystal display device often incorporates a light source inside the device, and a backlight unit including the light source is arranged on the back side of the liquid crystal panel in order to ensure the brightness necessary for displaying an image. is doing. The light source means employed in this backlight unit can be broadly classified by placing a light source typified by a cold cathode tube or a light emitting diode (LED) on the side surface of the liquid crystal display device to make it light transmissive. "Light guide plate light guide method" (so-called edge light method) that makes multiple reflections within an excellent flat light guide plate, and multiple cold cathode tubes and LEDs facing the back side of image display elements and liquid crystal display devices The “direct type” with a configuration in which a light source such as a cold-cathode tube or LED is not directly visible by disposing a light diffusing plate and an optical film between them. Two are adopted.

  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. As one of these efforts, attempts have been made to reduce power consumption by reducing the number of cold cathode tubes, which are light sources, 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. If diffusing particles inside the diffusing plate are increased in order to erase the lamp image, the light transmittance of the diffusing plate is lowered, and the luminance necessary for image observation cannot be obtained. In this case, the required luminance can be obtained by intensifying the light from the cold-cathode tube as the light source. However, intensifying the light causes a problem that the effect of reducing power consumption is greatly reduced.

  In addition, even when an LED, which is said to have low power consumption, is used as a light source, a direct light 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 And products with improved contrast ratios are being introduced to the market. However, there are still problems such as heat generation around the LED light source and required brightness 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 luminance unevenness (the brightness of the light source) ( It is necessary to solve problems such as uneven brightness due to the deformation of the optical sheet due to the temperature environment inside the display. At present, as efforts to solve these problems, the performance of each of the diffusion plate, the light guide plate and the optical sheet having the light collecting, diffusing and polarizing functions used in the liquid crystal display device is improved, and a plurality of them are used. By using them in combination, the required luminance can be ensured, and the lamp image and luminance unevenness can be reduced.

  In the above-described optical sheet, conventionally, as a method for improving 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 has been taken. “BEF” (Brightness Enhancement Film), which is a registered trademark of 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 one direction at a constant pitch on the upper surface of a transparent base material, condensing off-axis light and viewing this light. When the light incident from the flat surface of the base material is emitted from the prism surface by turning or recycling on-axis toward the person, it has the effect of collecting the light in the front direction. The luminance in the direction can be improved.

  Optical sheets such as BEF used in liquid crystal display devices not only improve brightness by improving the light utilization efficiency, but also various functions such as removing unevenness of the light source, securing the viewing area of the display, and maintaining the rigidity of the display. Is required. In many cases, a plurality of such optical sheets are laminated on the front side (liquid crystal panel side) of the light diffusing plate in order to realize desired optical characteristics. However, when BEF is used as an optical sheet, the vertical viewing angle becomes very narrow with respect to the horizontal viewing angle because light in the vertical direction of BEF is refracted by the prism plane portion and emitted in the normal direction. was there. In addition, since the top of the prism is pointed, the BEF has a drawback that scratches are likely to occur when it comes into contact with an optical sheet, a functional sheet member, or a liquid crystal panel disposed on the top of the prism.

Attempts have been made to reduce the number of optical sheets to be used while compensating for these drawbacks and maintaining equivalent optical characteristics and environmental characteristics. For example, Patent Document 1 discloses a method of imparting a diffusion function to the light collecting function of a prism by dispersing diffusible fine particles in a prism lens that is a geometric structure.
Moreover, in patent document 2, the microlens is arrange | positioned at random on a base material, the light which injected from the back surface is condensed with a microlens, and is radiate | emitted ahead, and it is equivalent optically with a smaller number of optical sheets than before. Means to achieve performance have been proposed.

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

  The optical sheet described in Patent Document 1 has a diffusing function in addition to a condensing function. On the other hand, the diffusible fine particles are dispersed in the prism. The amount of light in the front direction is reduced. Further, there remains a problem that glare due to refraction or reflection at a specific angle of the lens is visually recognized. Furthermore, since the tip of the prism is sharp, scratches are likely to occur due to contact with the optical sheet disposed at the top or the back surface of the functional optical member or the liquid crystal panel, and foreign matter is generated due to contact or friction. I also have problems. In particular, an optical sheet used in a laminated manner or an optical member having functionality typified by light diffusion, condensing, polarization, discoloration, etc., is fixed to the frame of the device when arranged in a liquid crystal display device. It is not fixed without moving completely inside the device. Therefore, the liquid crystal display device may come into contact with another optical sheet or an optical member having functionality due to vibration during conveyance or movement, and may be scratched.

  Further, when driving the liquid crystal display device, the optical sheet and the optical member having functionality are warmed by the heat generated from the light source, and as a result, the expansion and contraction depending on the physical properties specific to the material constituting each member is in-plane. Since it occurs and changes in dimensions and bending occurs, it may be rubbed and scratched by contact with another optical sheet or an optical member having functionality. As a measure to improve the scratch resistance and prevent the generation of foreign matter, it is conceivable to round the prism top, but the width to cut the prism top and the front luminance are inversely proportional, so the desired scratch resistance In order to achieve this, the front brightness is reduced.

  On the other hand, since the optical sheet described in Patent Document 2 has a hemispherical lens, even if it comes into contact with an optical sheet that is used in a stacked manner or an optical member having functionality, it has a rounded structure and friction due to contact. Even if this occurs, it has a feature that it is difficult to be scratched due to good sliding. However, since a gap is formed between adjacent microlenses, light that is refracted and scattered at the microlens / air interface through the microlens and collected from the front and the gap formed between the adjacent microlenses. There is a problem that light that is emitted without being refracted or scattered is generated, and a bright spot or a bright line is visually recognized from a luminance difference between these lights.

  The present invention has been made in view of the above problems, and has both a hemispherical microlens and an excellent light condensing / diffusion characteristic of a geometric structure and a structure in which interference fringes are difficult to be generated. An object of the present invention is to provide an optical sheet having an effect of preventing damage due to deformation such as warpage or twisting of the optical sheet itself even when another optical sheet is laminated. Furthermore, it aims at providing the backlight unit and display apparatus using this optical sheet.

  In order to solve the above-mentioned problem, the invention according to claim 1 of the present invention includes a plurality of microlenses arranged on a light emitting surface for emitting light and spaced apart from each other, and extending in one direction. An optical sheet formed with a plurality of geometric structures in which a plurality of geometric shapes are arranged in a direction intersecting the extending direction, and approximately half of the microlens protruding in the light emitting direction from the geometric structure. The protruding height of the circular portion is characterized in that at least a part of the substantially semicircular portion is different from other semicircular portions.

  According to the present invention, the substantially hemispherical microlens having a structure that is hard to be scratched is provided to protrude from the top of the geometric structure at different heights, thereby simultaneously protecting the geometric structure from frictional scratches caused by contact. In addition, it is possible to eliminate the regularity of the arrangement of the microlenses, and to suppress the occurrence of moire due to interference with the other optical sheet or the regular structure of the image display element.

  Further, in the invention described in claim 2, a plurality of microlenses that are spaced apart from each other and arranged irregularly on a light emitting surface that emits light, and a geometric shape extending in one direction extend the above-described shape. In the optical sheet formed with a plurality of geometric structures arranged in a direction intersecting the present direction, the height of the plurality of microlenses is set in a range of 70 μm or less and 20 μm or more. The ratio of the maximum height to the minimum height is in the range of 1.2 to 1.8, and the minimum height of the microlens is higher than that of the geometric structure.

  “The height of the plurality of microlenses is set in a range of 70 μm or less and 20 μm or more, and the ratio of the maximum height and the minimum height of the microlenses is in a range of more than 1.2 and less than 1.8. `` Within '' is made possible by matching the construction method and the conditions for forming the microlens, and by changing the height of the substantially hemispherical microlens within the above range, According to the invention, it becomes possible to follow the deformation of the optical sheet to be laminated or the optical sheet of the present invention itself, such as warping and twisting, and at the same time protecting the geometric structure from frictional scratches due to contact, and at the same time the laminated optical sheet Since the contact location between the sheet surface and the microlens is not limited, it is possible to prevent the microlens from being partially damaged. Furthermore, it is possible to provide an optical sheet having both the substantially hemispherical microlens and the excellent optical characteristics of the geometric structure.

  When the maximum height of the microlens is higher than 70 μm, the diameter of the microlens increases accordingly, and it is not preferable because the microlens itself is easily visible. Further, when the minimum height is less than 20 μm, it is not preferable because it becomes difficult to form a substantially hemispherical shape. In addition, when the ratio of the maximum height and the minimum height of the microlens is less than 1.2, the same portion is always in contact with the laminated optical sheet or the optical sheet of the present invention due to deformation such as warpage or twist. This is undesirable because the part is limited and damaged. Further, when the ratio of the maximum height to the minimum height is larger than 1.8, a difference in characteristics due to condensing and diffusion of the microlens appears remarkably, and luminance unevenness may occur in the light exit surface. Furthermore, since the difference due to the shape and size also increases, it is not preferable because unevenness due to the shape and size is visually observed in the appearance on the light exit surface.

Next, in the invention described in claim 3, the area ratio occupying the entire light exit surface of the microlens is in the range of 1% to 10% with respect to the configuration described in claim 1 or claim 2. It is characterized by that.
When the area ratio is less than 1%, the required effect of preventing scratching of the microlens cannot be obtained. When the area ratio is greater than 10%, the effect of improving the front luminance by condensing the geometric structure is reduced and necessary. The brightness that is assumed is not exhibited. By defining the area ratio of a substantially hemispherical microlens, it is possible to control the scratch prevention effect of the microlens, the effect of widening the viewing angle, and the brightness enhancement effect of having a geometric structure, which is high. It is possible to provide an optical sheet capable of satisfying both scratch resistance and excellent optical properties.

Next, the invention described in claim 4 is different from the structure described in any one of claims 1 to 3 in that the height H1 of the microlens is 1 of the height H2 of the geometric structure. It is in the range of 2 times to 6 times.
This is because if it is less than 1.2 times, the required scratch resistance against deformation of the optical sheet cannot be secured, and if it is more than 6 times, the size of the microlens becomes too large on the light exit surface. This is because an appearance defect may be caused by visual observation. Setting the cross-sectional height h of the microlens to the above-described range makes it possible to obtain necessary scratch resistance and a good appearance.

Next, the invention described in claim 5 has a substantially hemispherical shape on the light incident surface side opposite to the light emitting surface with respect to the configuration described in any one of claims 1 to 4. The structure is provided in a random arrangement, and at the same time, fine irregularities are imparted to the light incident surface.
Because the substantially hemispherical structure provided on the light incident surface of the optical sheet makes only the top part contact an optical member such as a diffusion plate or a light guide plate, the optical sheet and the optical member are relatively vibrated or rubbed. In addition, since only the smooth top portion of the protruding portion comes into contact and rubs, it is difficult to be scratched and has high scratch resistance. In addition, since the gap is generated by the substantially hemispherical structure, by suppressing the occurrence of interference unevenness such as Newton ring caused by the close contact, while providing a substantially hemispherical structure and fine irregularities on the light incident surface side, Prevents scratches due to contact or rubbing with the light exit surface side of the diffuser plate on the light incident surface side or other optical sheets, and provides a light diffusing function by providing a fine uneven shape on the surface of the light exit surface side It is possible to increase the viewing angle and to improve the effect of concealing the light guide plate pattern on the light source side.

Next, in the invention described in claim 6, with respect to the configuration described in any one of claims 1 to 5, the substantially hemispherical structure formed on the light incident surface occupies the entire light incident surface. The area ratio is in the range of 1% to 10%.
This is because when it is less than 1%, it becomes difficult to suppress the occurrence of interference unevenness such as Newton's ring caused by adhesion, and when it exceeds 10%, the front luminance of the optical sheet of the present invention is increased. It is not preferable because of lowering. By controlling the area ratio of the substantially hemispherical structure with respect to the light incident surface, the required scratch resistance can be exhibited, and at the same time, a decrease in luminance can be suppressed.

Next, the invention described in claim 7 is the configuration described in any one of claims 1 to 6, wherein the fine unevenness formed on the uneven surface portion of the light incident surface has a roughness of Rz. It is characterized by being in the range of 0.5 μm or more and 5.0 μm or less in (10-point average roughness).
When the roughness Rz of the fine irregularities is less than 0.5 μm, the diffusibility and concealment are insufficient, and when it is greater than 5.0 μm, the diffusion performance becomes too strong, and the optical sheet of the present invention has a front surface. This is not preferable because the luminance is lowered. The unevenness of the uneven surface portion on the light incident surface has the roughness within the above-mentioned range, and at the same time exhibits the required diffusibility and concealment, and at the same time, suppresses the decrease in luminance due to the uneven shape of the uneven surface portion. Can do.

Next, the invention described in claim 8 is the configuration described in any one of claims 1 to 7, in which the geometric shape forming the geometric structure has an apex angle of 80 °. It is a prism lens having a triangular cross section in the range of 100 ° or less.
This is because a prism lens having a triangular cross section whose apex angle is in the range of 80 ° to 100 ° exhibits the highest front luminance.

Next, an invention described in claim 9 includes a light source, the optical sheet according to any one of claims 1 to 8, and an optical member disposed on the light incident surface side of the optical sheet. A backlight unit characterized by comprising:
The backlight unit according to the present invention includes a light source and a diffusion plate or a light guide plate, the optical sheet described in any of the above, or the optical sheet and another optical sheet. By providing the backlight unit with the optical sheet of the present invention, the light from the light source can be converted into light having excellent luminance, viewing angle, and concealment, and emitted to the image display element.

Next, an invention described in claim 10 includes the backlight unit described in claim 9, and an image display element that displays an image by transmitting or blocking light emitted from the backlight in units of pixels. A person who provides a display device characterized by the above.
A display device according to the present invention includes the above-described backlight unit and an image display element that displays an image by transmitting or blocking light emitted from the backlight in units of pixels. By including the optical sheet of the present invention, it is possible to reduce the lamp image and brightness unevenness of the light source, and the unevenness and pattern of the optical member such as the diffusion plate, thereby providing an image in which the brightness of the entire screen is made uniform. .

  According to the optical sheet of the present invention, a substantially hemispherical microlens having a structure that is difficult to be scratched is provided at a height within a certain range at the top portion of the geometric structure that is continuously arranged. It is possible to follow deformation such as warpage and twist of the laminated optical sheet, and protect the geometric structure from frictional scratches caused by contact, and at the same time, limit the contact point between the laminated optical sheet surface and the microlens. Therefore, it is possible to prevent the microlens from being partially damaged. Furthermore, it is possible to provide an optical sheet having both the substantially hemispherical microlens and the excellent optical characteristics of the geometric structure. Further, by making the microlenses provided on the top of the geometric structure different in height, the regularity of the arrangement of the microlenses is eliminated, and there is regularity that other optical sheets or image display elements have. Generation of moire due to interference with the structure can be suppressed.

Since the light incident surface is provided with a substantially spherical protrusion and an uneven surface portion provided with fine unevenness, an optical member such as a diffuser arranged on the light incident surface side contacts the protrusion on the light incident surface of the optical sheet. Even if it vibrates or vibrates, the contact is made only at the top of the substantially spherical shape that is slippery and hardly scratched, so that it is possible to prevent the occurrence of scratches due to contact or rubbing of the optical member, and to exhibit scratch resistance. In addition, by providing fine irregularities on the irregular surface portion of the light incident surface, it is possible to exhibit light diffusibility and concealment required for light source images, scratches, luminance unevenness, and the like.
Furthermore, the optical sheet according to the present invention, a backlight unit including an optical member such as a diffusion plate on its light incident surface, and a display device in which an image display element is added to the backlight unit are high. Light or a display image that can obtain brightness and a wide viewing angle can be emitted toward the viewer side.

It is a cross-sectional schematic diagram of the display apparatus containing the optical sheet which concerns on embodiment based on this invention. The optical sheet which concerns on embodiment based on this invention is shown, (a) is the enlarged view, (b) is sectional drawing of (a). The optical sheet which concerns on embodiment based on this invention is shown, and is a top view of the incident surface and output surface of light. It is sectional drawing of the geometric structure formed in the optical sheet light emission surface which concerns on embodiment based on this invention.

Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
"Display device"
As shown in FIG. 1, the display device 1 according to this embodiment based on the present invention includes a backlight unit 2 and an image display element 3. The display device 1 can observe an image of the image display element 3 by the light K emitted from the backlight unit 2 being transmitted through the image display element 3.

The backlight unit 2 includes a light source unit 7 in which a plurality of light sources 6 are arranged at predetermined intervals in a reflection plate 5 forming a lamp house. In the observer side direction F of the light source unit 7, a diffusion plate, a light guide plate, or other optical sheets are arranged as a single member or a plurality of optical members 8 for diffusing the light of the light source 6. In the example illustrated in FIG. 1, a case where a diffusion plate 8 </ b> A is provided as the optical member 8 is illustrated.
The optical sheet 10 of the present embodiment is arranged in the observer side direction F of the diffusion plate 8A, and the functional sheet 11 is arranged in a single or a plurality of configurations in the observer side direction F. It is configured.

  Here, the functional sheet member 11 is a sheet having one or more functions represented by, for example, condensing, diffusing, polarizing, and discoloring, and the luminance distribution of light incident on the image display element 3. And an optical member having various condensing, diffusing, or polarizing characteristics for imparting necessary characteristics such as high brightness and polarization function. An image display element 3 made of, for example, a liquid crystal display element is disposed in the observer side direction F of the sheet member 11.

  According to the display device 1 having such a configuration, in the backlight unit 2, the light H emitted from the light source 6 is diffused by the diffusion plate 8 </ b> A and condensed by the optical sheet 10 to become luminance. Incident light is converted into required light by diffusion, condensing, polarization, color shift, or the like by a functional sheet member 11 disposed in front of the light traveling direction. Then, the light transmitted through the functional sheet member 11 enters the image display element 3 as light K reaching the necessary function emitted from the backlight unit 2, and the light of the observation image is observed on the observer side F. It is injected into.

  Here, the light source 6 in the light source unit 7 supplies light to the image display element 3. As the light source 6, for example, a plurality of linear light sources or point light sources can be used. As the plurality of linear light sources, for example, a plurality of fluorescent lamps, cold cathode fluorescent lamps (CCFL), or EEFL can be used. Moreover, LED etc. can be used as a point light source. The reflector 5 forming the lamp house is disposed on the opposite side of the plurality of light sources 6 from the observer side F, and is emitted in the direction opposite to the observer side F of the light emitted from the light sources 6 in all directions. The reflected light is reflected and emitted to the observer side F. As a result, the light H emitted to the observer side F becomes light emitted in almost all directions from the light source 6. Thus, the use efficiency of light can be improved by using the reflecting plate 5. The reflection plate 5 may be any member that reflects light with high efficiency. For example, a general reflection sheet or reflection plate may be used.

  The diffusion plate 8A disposed on the light emitting side of the light source unit 7 is formed by dispersing light diffusing particles in a transparent resin. As the transparent resin, a thermoplastic resin, a thermosetting resin, or the like can be used. Suitable diffusion performance can be easily obtained by the light diffusion particles contained in the diffusion plate 8A. As the light diffusing particles, transparent particles made of an inorganic oxide or a resin can be used. As the transparent particles made of an inorganic oxide, for example, silica, alumina or the like can be used. As the transparent particles made of resin, acrylic particles, styrene particles, styrene acrylic particles and cross-linked products thereof, melamine / formalin condensate particles, fluoropolymer particles, silicone resin particles, and the like can be used. Moreover, you may use combining 2 or more types of transparent particles from the transparent particle mentioned above. Furthermore, the size and shape of the transparent particles are not particularly defined. Further, in the display device 1 using LEDs as light sources, a light guide plate 8 that guides light may be provided between the LED light sources and the optical sheet 10.

  Further, as shown in FIG. 1, the image display element 3 includes a pair of polarizing plates (polarizing films; polarizers) 14 and 15 and a liquid crystal panel 16 sandwiched between the pair of polarizing plates 14 and 15. It consists of and. The liquid crystal panel 16 is configured, for example, by filling a liquid crystal layer between two glass substrates. The image display element 3 is preferably an element that displays an image by transmitting / blocking light in pixel units. If the image is displayed by transmitting / blocking light in pixel units, the optical sheet 10 improves the luminance toward the viewer side F and reduces the viewing angle dependency of the light intensity. Furthermore, it is possible to display an image with high image quality by effectively using light with a reduced lamp image. The image display element 3 is preferably a liquid crystal display element. A liquid crystal display element is a typical element that transmits and blocks light in pixel units and displays an image, and can improve image quality and reduce manufacturing cost compared to other display elements. it can.

"Optical sheet"
Next, the optical sheet 10 of this embodiment will be described in detail.
As shown in FIG. 2A, the optical sheet 10 has a light incident surface 10a as a light incident surface 10a and a light exit surface 10b as a light emitting surface 10b. The light exit surface 10b includes a plurality of substantially hemispherical microlenses 31 whose apex height is H1, and a plurality of geometric shapes extending in one direction in the extending direction (for example, orthogonal directions). There are formed continuous geometric structures that are arranged, that is, a plurality of arranged geometric structures. In the present embodiment, a plurality of continuous geometric structures arranged in a row are configured by extending prism lenses 19 having a height H2 in a triangular section in one direction. Here, the micro lens 31 is provided with different specifications in which the height H1 is within a predetermined range, and the apex angle θ of the apex portion forming the cross-sectional triangle of the prism lens 19 is, for example, in the range of 80 ° to 100 °. It has become.

  Further, as shown in FIG. 2B, which shows a cross-section of the apex of the prism lens 19 having a triangular section having a height H2, which is a continuous geometric structure, the cross-sectional height h of the microlens from the top of the prism lens 19 is In the range where the height H1 of the microlens 31 changes. As a result, in addition to the effect of preventing the prism lens 19 from being damaged, the microlens 31 interferes with the regular structure of the other optical sheet 11, the image display element 3, or the optical member 8. It is possible to prevent the generated interference fringes (moire). Furthermore, it becomes possible to omit the protective film required when producing the optical sheet 10 by being excellent in the damage prevention effect.

  In the configuration in which the optical sheet 11 is laminated on the light emitting surface side 10b of the substantially hemispherical microlens 31, when the height H1 and the cross-sectional height h of the microlens 31 are always the same, almost all the microlens apex portions Is considered to be in contact with the light incident surface of the optical sheet 11. However, inside the display, the optical sheet itself is deformed by a temperature change caused by power ON / OFF, a light source, a drive circuit, an external environment, or the like. When deformation such as warpage or undulation occurs in the optical sheet 10 and the optical sheet 11 laminated thereon, the microlens 31 comes into contact with the optical sheet 11 laminated in a limited portion depending on these deformations. . When only a limited part contacts, the possibility that only the part will be damaged becomes high.

  However, in the optical sheet 10 of the present embodiment, the height H1 of the substantially hemispherical microlens 31 is in a range where the maximum height is 70 μm or less and the minimum height is 20 μm or more. By making the ratio between the height and the minimum height in the range of 1.2 or more and 1.8 or less, it becomes possible to follow complicated deformation of the optical sheet 10 and the optical sheet 11 laminated thereon. Therefore, the prism lens 19 is protected from frictional scratches due to contact, and at the same time, the contact position between the laminated optical sheet surface and the microlens 31 is not limited, and complicated deformation can be followed. It is possible to prevent the microlens 31 from being partially damaged on the surface, and it is possible to provide an optical sheet having the excellent optical characteristics of the substantially hemispherical microlens 31 and the prism lens 19 that are hardly damaged. By changing the height H1 of the substantially hemispherical microlens within a certain range, according to the present invention, the substantially hemispherical microlens having a structure that is hardly scratched is easily damaged at different heights. By being provided at the top portion of 19, it becomes possible to follow deformation such as warpage and twist of the laminated optical sheet, and protect the prism lens 19 from frictional scratches caused by contact, and at the same time, the laminated optical sheet surface and Since the contact location of the microlens is not limited, it is possible to prevent the microlens from being partially damaged. Furthermore, it is possible to provide an optical sheet having both the excellent optical characteristics of the substantially hemispherical microlens and the prism lens 19.

  Further, deformation such as warpage and undulation of the optical sheet itself caused by temperature changes caused by a light source, a drive circuit, an external environment, or the like also causes luminance unevenness in the surface of the optical sheet 10. That is, a gap is generated due to deformation such as warpage or undulation, and brightness is lowered and unevenness of brightness is generated compared to a portion where only this portion is close. However, when the height H1 and the cross-sectional height h formed on the optical sheet 10 change randomly within a predetermined range, it becomes possible to follow these deformations more flexibly and reduce unevenness in brightness and brightness. It leads to letting.

  The area ratio of the substantially hemispherical microlens 31 of the present embodiment to the entire light exit surface is desirably in the range of 1% to 10%. This is because when the area ratio is less than 1%, the required microlens damage prevention effect cannot be obtained. When the area ratio is greater than 10%, the ratio of the prism lens 19 decreases, and the front luminance improvement effect is obtained. This is because the required brightness is not obtained. By defining the area ratio of the substantially hemispherical microlens 31, it becomes possible to control the scratch-preventing effect of the microlens, the effect of widening the viewing angle, and the luminance improvement effect of the prism lens 19. It is possible to provide an optical sheet capable of satisfying both scratch resistance and excellent optical properties.

  The interval L between the substantially hemispherical microlenses 31 provided on the top of the prism lens 19 depends on the area ratio of the microlens on the light exit surface. The distance L between the substantially hemispherical microlenses 31 provided on the top of the prism lens 19 shown in FIG. 2B is desirably 800 μm or less when the area ratio is 1%. This is because if the spread is larger than 800 μm, the necessary effect of preventing the prism lens 19 from being damaged may not be sufficiently obtained. Since the intervals L between the substantially hemispherical microlenses 31 are different, it is possible to follow complicated deformations of the optical sheet 10 and the optical sheet 11 laminated thereon due to a temperature change or the like. It is possible to prevent the occurrence of scratches due to contact and rubbing, to widen the viewing angle, and at the same time to suppress the occurrence of moire due to interference with other optical sheets or regular structures of the image display element.

The height H1 of the microlens 31 shown in FIG. 2A is desirably in the range of 1.2 times to 6 times the height H2 of the prism lens 19. This is because when the ratio is less than 1.2 times, the effect of preventing the prism lens 19 from being scratched becomes low, and the required scratch resistance against deformation of the optical sheet cannot be secured. Further, when the height H1 of the microlens 31 is larger than 6 times, the size of the microlens 31 itself becomes too large, and an appearance defect may be caused by being visually observed on the light emitting surface. By setting the height H1 of the microlens 31 in the above-described range, it is possible to obtain necessary scratch resistance and a good appearance.
The height H2 of the prism lens 19 is preferably in the range of 10 μm to 100 μm. This is because if it is less than 10 μm, the required luminance cannot be obtained due to the light diffraction effect. If it is more than 100 μm, the prism lens 19 itself is visually observed on the light exit surface. This is because it may cause defects.

  It is desirable that the protrusions 20 having a substantially hemispherical structure are randomly arranged on the light incident surface side 10a opposite to the light emitting surface side 10b described above. The projection 20 exhibits a function of suppressing the occurrence of scratches due to contact with or rubbing with the optical member 8 such as the diffusion plate 8A or the light guide plate disposed on the light incident surface 10a side due to the substantially spherical shape. Since the gap is generated by the substantially hemispherical structure, it is possible to suppress the occurrence of interference unevenness such as Newton rings caused by the close contact. Furthermore, it becomes possible to omit the protective film required when producing the optical sheet 10 by giving the damage prevention effect.

  Furthermore, by providing fine irregularities on the light incident surface side 10a, it is possible to enhance the light diffusion function, and to improve the effect of expanding the viewing angle and concealing the pattern of the light guide plate on the light source side. . The planar portion 21 whose surface is roughened with fine irregularities can diffuse the light H from the light source 6 in the roughened planar portion 21 and take it into the optical sheet 10. Therefore, the optical sheet 10 is emitted to the observer side F from the light emitting surface 10b and the function of concealing the lamp image of the light source 6 on the light incident surface 10a and the pattern formed on the diffusion plate 8A from the observer. It has the role of converging and diffusing the light to be expanded by the prism lens group 19 to widen the viewing angle.

  As for the area ratio of the projection part 20 which occupies the light-incidence surface 10a of the optical sheet 10 mentioned above, it is desirable to exist in the range of 1% or more and 10% or less. If the area ratio of the bottom surface 20a of the protrusion 20 is within the above range, it is possible to suppress the occurrence of scratches by rubbing due to contact with the diffuser plate 8A, and to suppress a decrease in luminance of incident light. However, when the area ratio is less than 1%, the effect of preventing scratches due to contact or rubbing of the top 20b of the protrusion 20 with the diffusion plate 8A cannot be expected. This is because it prevents the light H from being taken into the optical sheet 20 and causes the brightness of the optical sheet 10 to decrease.

  Further, in the optical sheet 10 according to the present embodiment, it is desirable that the roughness of the fine irregularities formed on the incident surface 10a is in the range of 0.5 μm or more and 5.0 μm or less in Rz (10-point average roughness). . If the roughness Rz of the flat surface portion 21 of the light incident surface 10a is in the range of 0.5 μm or more and 5.0 μm or less, the required diffusibility of transmitted light and the concealment property for the observation image are exhibited, and the luminance caused by the uneven shape Can be suppressed. However, when the roughness Rz roughness is less than 0.5 μm, it is difficult to obtain the diffusion and concealment effect, and when the Rz roughness exceeds 5.0 μm, the front luminance of the optical sheet 10 is greatly reduced. . As a method for forming fine irregularities, for example, a method of roughening a mold surface used for manufacturing the optical sheet 10 by etching or sandblasting, or a method of forming a substantially spherical shape after forming fine irregularities on the mold. A method of forming the protrusion 20 is a typical example.

  The outer diameter (diameter) of the protrusion 20 formed on the light incident surface 10a of the optical sheet 10 is preferably in the range of 30 μm to 150 μm. The ratio of the height of the protrusion 20 of the optical sheet 10 to the outer diameter is preferably in the range of 3% to 30%. When the outer diameter of the protruding portion 20 exceeds 150 μm, the protruding portion 20 itself is easily seen by an observer, and this causes unevenness, roughness, and bright spots on the light emitting surface 10b in appearance. On the other hand, when the outer diameter of the protrusion 20 is less than 30 μm, the effect of preventing damage by the protrusion 20 is lowered, and it becomes difficult to manufacture the mold and the optical sheet 10. In addition, if the projection 20 of the optical sheet 10 has a substantially spherical shape with a top 20b that is in contact with the diffuser plate 8A and is not easily scratched, the planar shape of the projection 20 viewed from the light source 6 side may be circular. It may be a substantially circular shape, or may be an elliptical shape, a triangular pyramid shape with a rounded top, a quadrangular pyramid shape, or another polygonal pyramid shape. The smooth substantially spherical protrusion 20 is formed on the flat surface portion 21a of the light incident surface 10a within the range of the above-described conditions, thereby exhibiting the required scratch resistance and at the same time resulting from the substantially spherical shape. It is possible to suppress a decrease in luminance.

  Further, if the ratio of the height of the optical sheet 10 to the outer diameter of the protrusion 20 is within a range of 3% or more and 30% or less, the top of the protrusion 20 is damaged due to contact or rubbing with the diffusion plate 8A. It is possible to prevent the brightness from being reduced by preventing the incidence of light. On the other hand, if the ratio of the protrusions 20 is less than 3%, the effect of preventing the occurrence of scratches due to contact or rubbing cannot be obtained. If the ratio exceeds 30%, the protrusions 20 themselves prevent light H from being incident. In addition, this is not preferable because the luminance of the optical sheet 10 is significantly reduced.

  As the geometric structure of the optical sheet 10, it is preferable to employ a configuration in which a plurality of prism lenses 19 are arranged in one direction on the light exit surface 10b as shown in FIGS. Alternatively, geometric structures having a cross-sectional shape as shown in FIG. 4 may be formed singly or in combination. In the prism lens 19 described above, it is most desirable that the apex angle be 90 ° in order to collect light and improve the front luminance. Further, when optimizing the luminance and the viewing angle, the apex angle is preferably in the range of 80 ° to 100 °. This is a particularly desirable range for taking an optimum structure for the performance and characteristics of the optical sheet 11 and the optical member 8 used in combination.

  The optical sheet 10 described so far can be used not only for the display device 1 such as a liquid crystal display device but also for a light projection control such as a rear projection screen, a solar cell, and an illumination device equipped with organic or inorganic EL. Any of them can be used. Moreover, the optical sheet 10 according to the present embodiment diffuses the strong front light H incident from the light source 6 by widening the viewing angle by providing the fine irregularities 21a to the substantially flat portion 21 on the light incident surface 10a side. be able to. Further, when observing a transmission image from the observer side F through the image display element 3, the luminance unevenness, lamp image, light / dark difference reduction by the light source 6, and the pattern or structure on the flat surface or the back surface of the diffusion plate 8A are reduced. However, it is also possible to suppress seeing through to the observer side F side. Furthermore, with respect to deformation caused by the environment in which the other optical sheet 11 used in combination is used, the temperature of the microlens 31 and the protrusions 20 that are substantially hemispherical structures are made random by changing the temperature, etc. It becomes possible to cope with.

"Optical sheet manufacturing process"
Next, a manufacturing process of the optical sheet 10 will be described.
The optical sheet 10 can be molded using an electron beam curable resin represented by a UV curable resin on a highly transparent sheet-like substrate. As an example, a substantially spherical projection 20 having a design dimension was formed on a mold whose surface 21 was previously roughened by an etching method or a sandblasting method. The protrusion 20 can be formed on the base material 18 using this mold. Here, as the material of the highly transparent sheet-like base material 18, PET (polyethylene terephthalate), PC (polycarbonate), PMMA (polymethyl methacrylate), COP (cycloolefin polymer), acrylonitrile styrene copolymer, Examples thereof include acrylonitrile polystyrene copolymer.

  Furthermore, a transparent resin made of a thermoplastic resin is preferable as a material constituting the optical sheet 10 according to the present embodiment. For example, a polycarbonate resin, an acrylic resin, a fluorine acrylic resin, a silicone acrylic resin, an epoxy acrylate resin, a polystyrene resin, a cyclo resin, and the like. Examples thereof include olefin polymers, methylstyrene resins, fluorene resins, PET, polypropylene, acrylonitrile styrene copolymers, acrylonitrile polystyrene copolymers, and the like. It is also possible to manufacture the optical sheet 10 having the incident surface 10a by an extrusion molding method using these materials, an injection molding method, or a hot press molding method.

  The optical sheet 10 according to the present embodiment can be formed by processing the light incident surface 10a and the light emitting surface 10b on both sides simultaneously. Alternatively, the optical sheet 10 can be obtained by laminating the single-sided sheets each having a half thickness obtained by separately processing the light incident surface 10a and the light emitting surface 10b which are the front and back surfaces of the substrate 18. . Further, in the method of forming the microlens 19, the height H1 of the microlens 19 to be formed is within the range of 90% to 110% of H1 by optimizing the etching conditions, the sandblasting conditions, and the cutting method. Can be controlled.

  The optical sheet 10 according to the present embodiment 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.

  In addition, the optical sheet 10 according to the present embodiment preferably has an ultraviolet absorber added thereto. By adding the ultraviolet absorber, it is possible to suppress degradation of the prism lens group 19 formed on the light emitting surface 10b by light including ultraviolet rays emitted from the light source 6, and to extend the life of the optical sheet 10. be able to. 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.

  In addition, as a method of forming the fine unevenness formed on the flat surface portion 21 on the light incident surface 10a side of the optical sheet 10, mat processing, embossing, and the like can be given. With respect to the fine irregularities in the flat surface portion 21 of the light incident surface 10a, a process of providing discontinuous minute protrusions may be performed instead of the production by mat processing. According to these methods, the transparent resin softened by heating is pressed against a transfer member formed with fine irregularities to transfer the shape of the transfer member, and then the transparent resin is cured to obtain a fine An uneven shape can be obtained. In addition, as another method, transparent particles having a particle size of about 30 to 100 μm are blended with a molten transparent resin, and fine irregularities are formed on the flat surface portion 21 by extruding these transparent particles to the outermost layer side. Also good. When this processing method is used, it is preferable that the refractive indexes of the transparent resin and the transparent particles are adjusted equally.

  The thickness of the optical sheet 10 according to the present embodiment 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, the environment used, and the situation. If the thickness is less than 50 μm, the size of the prism lens 19 formed on the light exit surface 10b is limited, and it becomes difficult to exhibit the required optical characteristics. Further, since the strength of the base material 18 itself cannot be obtained, bending and deformation due to heat or the like are likely to occur, resulting in a problem that wrinkles and luminance unevenness are likely to occur. On the other hand, when the thickness exceeds 600 μm, in addition to a decrease in the transmittance of the entire optical sheet 10 and an increase in material cost, there is a problem in handling due to an increase in weight in the molding process.

  Since the display device 1 according to the present embodiment has the above-described configuration, the light H emitted from the light source 6 of the light source unit 7 is diffused by the diffusion plate 8A and is incident on the light incident surface 10a of the optical sheet 10. . And when light injects from the incident surface 10a of the optical sheet 10, since the projection part 20 provided in the light incident surface 10a has prescribed | regulated the area ratio in a surface, it is less likely to prevent the incidence of light. Furthermore, the light transmitted through the fine irregularities of the flat surface portion 21 imparts diffusibility and concealment, and reduces the lamp image and luminance unevenness of the light source 6 and the unevenness and pattern of the optical member 8. Then, when the light is transmitted through the optical sheet 10 and emitted from the light emitting surface 10b, it is condensed and diffused by the microlens 31 group and the prism lens 19 group to improve the optical characteristics, and is transmitted through the image display element 3. An image in which the luminance of the entire screen is made uniform can be displayed on the viewer side F. Here, the image display element 3 is a liquid crystal display element, and is configured to use the light K whose light collection / diffusion characteristics are improved by the backlight unit 2. It is possible to obtain an image in which the luminance of the entire screen is made uniform by smoothing the distribution of the intensity in the viewing angle direction and reducing the lamp image and luminance unevenness of the light source, and the unevenness and pattern of the diffusion plate or light guide plate.

Hereinafter, an embodiment of the present invention will be described in detail based on Example 1. In addition, this invention is not limited only to these Examples. Hereinafter, the optical characteristics of the optical sheet 10 according to the present embodiment and the display device 1 using the same will be described in Examples.
Example 1
As the optical sheet 10 according to Example 1, as the light emitting surface 10b of the optical sheet 10, the microlens 31 having a diameter within a range of 59 μm to 75 μm and a lens height of 28 μm to 38 μm provided separately from each other; A plate of a plurality of prism lenses 19 having a linear structure having a cross-sectional triangle with an apex angle of 90 ° having a width of 30 μm and a lens height of 15 μm was formed on the first mold surface. For the microlens 31, a first mold having a different microlens height and diameter was manufactured by optimizing the processing conditions. Next, using a UV molding machine, a substantially hemispherical microlens 100 and a prism lens 19 are formed of a UV curable resin (refractive index = 1.51) on a PET substrate (Toyobo product) having a thickness of 188 μm. Thus, an optical sheet 10 was produced. The diameter and height of the microlens 31 on the light emitting surface 10b of the obtained optical sheet 10 were measured, and it was confirmed that the height was in the range of 29 μm to 37 μm (40 measurement results). Further, it was derived from the average value of the diameter that the area ratio of the light exit surface of the microlens 31 was 6%. In addition, the prism lens 19 having a linear structure is configured to be linearly arranged in the horizontal direction when viewed from the observer side. The optical sheet 10 thus obtained is referred to as Example 1.

(Comparative Example 1)
As Comparative Example 1, a microlens 31 having a diameter of 78 μm to 84 μm and a lens height in a range of 38 μm to 42 μm provided separately from each other, and an apex angle 90 with a bottom width of 30 μm and a lens height of 15 μm. A plate of a plurality of prism lenses 19 having a linear structure having a triangular cross section was processed and produced on the second mold surface. The microlens 31 was devised in advance when producing the second mold so as to have a regular hexagonal arrangement. Next, as in Example 1, using a UV molding machine, a substantially hemispherical microlens 100 made of a UV curable resin (refractive index = 1.51) on a PET substrate (Toyobo product) having a thickness of 188 μm. A prism lens 19 was formed to produce an optical sheet 10. The diameter and height of the microlens 31 on the light exit surface 10b of the obtained optical sheet 10 were measured, and it was confirmed that the height was in the range of 38 μm to 42 μm (40 measurement results). Further, it was derived from the average value of the diameter that the area ratio of the light exit surface of the microlens 31 was 21%. In addition, the prism lens 19 having a linear structure is configured to be linearly arranged in the horizontal direction when viewed from the observer side. The optical sheet thus obtained is referred to as Comparative Example 1.

(Comparative Example 2)
As Comparative Example 2, a plate having only a plurality of prism lenses 19 with a linear structure having a cross-sectional triangle with an apex angle of 90 ° having a bottom width of 30 μm and a prism height of 15 μm is processed into a third mold surface, Similarly to Example 1, a prism lens 19 made of a UV curable resin (refractive index = 1.51) was formed on a PET substrate (Toyobo product) having a thickness of 188 μm using a UV molding machine to form an optical sheet 10. Was made. In addition, the prism lens 19 having a linear structure is configured to be linearly arranged in the horizontal direction when viewed from the observer side. The optical sheet thus obtained is referred to as Comparative Example 2.

(Optical evaluation)
The optical sheet 10 according to Example 1 and Comparative Examples 1 and 2 is mounted on the display device 1 according to the embodiment shown in FIG. 1 described above, a cold cathode tube is used as the light source 6, and the optical evaluation thereof is shown below. The method was evaluated. In addition, in order to evaluate brightness nonuniformity and brightness nonuniformity, it evaluated using the light-diffusion sheet | seat which is a product of Eiwa Co., Ltd. as the optical sheet 11. FIG.

(Front brightness evaluation)
Three types of optical sheets 10 produced as Example 1 and Comparative Examples 1 and 2 were placed on a diffuser plate 8A made of Sumitomo Chemical Co., Ltd., and liquid crystal as an image cover element 3 on the observer side F. A display device 1 using the display element was assembled. The light source used for the evaluation was CCFL. Using the display device 1 to which the optical sheet 10 according to each Example 1 and Comparative Examples 1 and 2 was respectively mounted, and using the spectral radiance meter (SR-3A: manufactured by Topcon Technohouse Co., Ltd.) with the observation screen as all white display. Then, the luminance at the center of the observation screen of the image cover element 3 was measured under the same conditions.

(Interference fringe evaluation)
Three types of optical sheets 10 produced as Example 1 and Comparative Examples 1 and 2 were placed on a diffuser plate 8A made of Sumitomo Chemical Co., Ltd., and liquid crystal as an image cover element 3 on the observer side F. A display device 1 using the display element was assembled. The light source used for the evaluation was CCFL. Using the display device 1 on which the optical sheets 10 according to each of Example 1 and Comparative Examples 1 and 2 were respectively mounted, the presence / absence of interference fringes appearing on the observation screen with all white display and the degree thereof were visually observed and evaluated.

(Luminance unevenness evaluation)
Three types of optical sheets 10 produced as Example 1 and Comparative Examples 1 and 2 are respectively arranged on a polystyrene diffusion plate 8A manufactured by Sumitomo Chemical Co., Ltd., and the light diffusion sheet is provided on the light exit surface 10b side of the optical sheet 10. No. 11, a light diffusion sheet, which is a product of Eiwa Co., Ltd., was placed. A display device 1 using a liquid crystal display element as an image cover element 3 was assembled on the observer side F. The light source used for the evaluation was CCFL. In the evaluation, after assembling the display device, generation of luminance unevenness and light / dark unevenness in 60 minutes after lighting and changes thereof were evaluated.

(Abrasion evaluation)
The wear evaluation of Example 1 and Comparative Examples 1 and 2 was evaluated by the following measurement methods.
(Gakushin style wear test)
The scratch resistance of the optical sheets 10 of Example 1 and Comparative Examples 1 and 2 was evaluated under the conditions shown below using a Gakushin type abrasion tester. First, the light emitting surface 10b of the optical sheet 10 was faced up and fixed to the shaking table of the Gakushin type abrasion tester. Next, as the back surface of the optical sheet 11, the light incident surface side of the light diffusing sheet (Ewa product) is placed facing the light emitting surface 10b of the optical sheet 10, and the pressure is applied under the condition that the load is 300 g / cm ^3. Then, the light emitting surface 10b of the optical sheet 10 and the light incident surface side of the light diffusing sheet are rubbed back and forth 20 times at an amplitude of 120 mm and a speed of 120 mm / sec. The light emission surface 10b was visually evaluated for the presence or absence of scratches and the extent of the scratches. Table 1 shows the optical evaluation test results and wear evaluation test results of Example 1 and Comparative Examples 1 and 2 described above.

The following can be said from the results shown in Table 1.
When the optical sheet 10 according to Example 1 was used, the front luminance was 441 cd / m ² , the vertical half-field angle was 34.1 °, and no visible interference fringes were observed on the screen ( ○). As a result of observing luminance unevenness and light / dark unevenness in 60 minutes after lighting, a strip-like low-brightness portion was seen in the lower right of the screen immediately after lighting, but it became invisible after a few minutes, and then on the screen until 60 minutes later. Neither unevenness nor light and dark unevenness was observed (◯). In the results of the Gakushin abrasion test, no scratches were observed on the light emitting surface 10b of the optical sheet 10 and the light incident surface of the optical sheet 11 facing each other, and high scratch resistance could be confirmed (◯). .

In Comparative Example 1, the front luminance was 417 cd / m ² , and a decrease in luminance was observed compared to Example 1 (Δ). In addition, the half-value angle in the vertical direction was 36.2 °, and no visible interference fringes were observed on the screen (◯). As a result of observing luminance unevenness and brightness / darkness unevenness in 60 minutes after lighting, a band-like low luminance portion is seen in the lower right corner and lower left corner of the screen immediately after lighting, and the position of the band-like unevenness changes with time. It was recognized that When about 5 minutes have elapsed since the start of lighting, thin luminance unevenness on a part of the screen was not visible, and no luminance unevenness and light / dark unevenness were observed on the screen until 60 minutes passed (Δ). In the results of the Gakushin abrasion test, no scratches were observed on the light emitting surface 10b of the optical sheet 10 and the light incident surface of the optical sheet 11 facing each other, and high scratch resistance could be confirmed (◯). .

In Comparative Example 2, the front luminance was 449 cd / m ² , the vertical half-field angle was 31.8 °, and visible interference fringes were observed on the screen (×). In addition, as a result of observing luminance unevenness and light / dark unevenness, a vertical strip-like region with low luminance was recognized on the right side of the center of the screen immediately after lighting. The vertical band-like luminance unevenness became thin after about 10 minutes and became invisible. Brightness unevenness and light / dark unevenness were not recognized on the screen until 60 minutes passed (Δ). In the Gakushin abrasion test, a wide range of visible scratches were observed on the prism lens, and rubbing marks were also observed on the light incident surface of the light diffusion sheet (×).

  From the evaluation results of Example 1 and Comparative Examples 1 and 2 shown above, the optical sheet according to the present invention has a substantially hemispherical microlens having a structure that is difficult to be scratched, and the top of the geometric structure at different heights. It is possible to follow deformations such as warping and twisting of the laminated optical sheet by protecting the geometric structure from frictional scratches caused by contact, and at the same time, the laminated optical sheet surface and the microlens Therefore, it is possible to prevent the microlens from being partially damaged. Furthermore, it is possible to provide an optical sheet having both the substantially hemispherical microlens and the excellent optical characteristics of the geometric structure. Further, by making the microlenses provided on the top of the geometric structure different in height, the regularity of the arrangement of the microlenses is eliminated, and there is regularity that other optical sheets or image display elements have. It was found that the generation of moire due to interference with the structure can be suppressed.

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Backlight unit 3 Image display element 6 Light source 8 Optical member 8A Diffuser 10 Optical sheet 10a Light incident surface 10b Light output surface 20 Projection part 21 Plane part 19 Prism lens (geometric structure)
31 Microlens H1 Microlens height H2 Prism lens height h Microlens height from the top of the prism lens (substantially semicircular portion of the microlens protruding in the light emission direction from the geometric structure)

Claims (10)

Geometry formed by arranging a plurality of microlenses spaced apart from each other on the light emitting surface for emitting light and a plurality of geometric shapes extending in one direction in a direction intersecting the extending direction. In the optical sheet formed with the structure,
The protrusion height of the substantially semicircular portion of the microlens that protrudes in the light emission direction from the geometric structure is characterized in that at least some of the substantially semicircular portions are different from other semicircular portions. An optical sheet. A plurality of microlenses that are spaced apart and irregularly arranged on a light emitting surface that emits light, and a plurality of geometric shapes extending in one direction are arranged in a direction intersecting the extending direction. In an optical sheet formed with a geometric structure
The height of the plurality of microlenses is set in the range of 70 μm or less and 20 μm or more, and the ratio of the maximum height to the minimum height of the microlens is in the range of 1.2 or more and 1.8 or less. An optical sheet characterized in that the minimum height of the microlens is higher than that of the geometric structure.   3. The optical sheet according to claim 1, wherein an area ratio of the microlens to the entire light exit surface is in a range of 1% to 10%.   4. The optical device according to claim 1, wherein a height of the microlens is in a range of 1.2 times to 6 times a height of the geometric structure. Sheet.   A substantially hemispherical structure is provided in a random arrangement on the light incident surface side opposite to the light emitting surface, and at the same time, fine irregularities are imparted to the light incident surface surface. The optical sheet according to claim 4.   The area ratio of the substantially hemispherical structure formed on the light incident surface to the entire light incident surface is in a range of 1% to 10%. The optical sheet described in the item.   The fine unevenness formed on the uneven surface portion of the light incident surface has a roughness in the range of 0.5 μm or more and 5.0 μm or less in Rz (10-point average roughness). Item 7. The optical sheet according to any one of Items 6.   The geometric shape constituting the geometric structure is a prism lens having a triangular cross section whose apex angle is in a range of 80 ° to 100 °. The optical sheet described in 1.   A backlight unit comprising: a light source; the optical sheet according to any one of claims 1 to 8; and an optical member disposed on a light incident surface side of the optical sheet.   A display device comprising: the backlight unit according to claim 9; and an image display element that displays an image by transmitting or shielding light emitted from the backlight in units of pixels.

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