JP2012242649A - Optical sheet, backlight unit, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet which is capable of uniformly controlling a brightness distribution of an entire screen without the occurrence of parts partially high or low in brightness even in the case of the reduction in the number of arranged LED light sources and in the quantity of light of the LED light sources, and a backlight unit and a display device using the optical sheet.SOLUTION: The optical sheet is configured so that a light emission surface has a structure including substantially hemispherical lenses existing independently of one another and a plurality of arrays of continuous geometrical structures, and a ratio of the substantially hemispherical lenses having high diffusivity and the geometrical structures having high light-harvesting properties varies within the sheet surface, whereby brightness within the sheet surface can be controlled.

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. doing. As a light source means employed in this backlight unit, a light source typified by a cold cathode tube or a light emitting diode (LED) is arranged on the side of the liquid crystal display device, and it has excellent light transmittance. “Light guide plate light guide method” (so-called edge light method) for multiple reflection in a flat light guide plate and a plurality of light sources such as cold cathode tubes and LEDs facing the back side of the image display element and the liquid crystal display device There are two types of "direct type" with a structure in which a diffuser plate and an optical film having a strong light scattering property are arranged between the two so that a light source such as a cold cathode tube or an LED is not directly visible. It has been 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 are increased inside the diffusing plate 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 unevenness in brightness and darkness caused by 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), a registered trademark of 3M
An enhancement film (brightness enhancement film) 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 collection function of a prism by dispersing diffusible fine particles in the prism lens. 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.

  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.

  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.

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

  Further, as described above, the optical sheet is also required to have a function of making the luminance distribution of the entire screen of the liquid crystal display device uniform, and in particular, an edge type liquid crystal display device in which an LED light source is arranged on the side surface of the casing. Depending on the characteristics of the light guide plate formed from a transparent acrylic resin or the like that plays a role of vertically raising the light from the LED light source incident from the side surface side or the number of LED light sources arranged, the entire screen It is difficult to make the luminance distribution uniform, and therefore, the luminance distribution in the screen is made uniform by using a plurality of optical sheets including an optical sheet having diffusibility. However, in this LED edge type liquid crystal display device, as part of reduction of power consumption and manufacturing cost, reduction of the number of LED light sources and reduction of light quantity are required. It tends to be generated easily, and it has become more difficult to make the luminance distribution of the entire screen uniform.

  Even in the optical sheet used to solve these problems, even if it is possible to alleviate the brightness unevenness of the entire screen by using the diffusion characteristics, the brightness is increased only at a specific part in the sheet surface. In addition, it is very difficult to control the brightness in the sheet surface, and in order to make this possible, complicated shapes and difficult processing steps are required. There is a high possibility that it will cause up, and the existing optical sheets have a great problem in brightness control within the sheet surface.

  The present invention has been made in view of the above problems, and even in an LED light source in which the number of arrangements and the amount of light are reduced, the luminance distribution of the entire screen can be obtained without causing a portion with high or low luminance partially. It is an object of the present invention to provide an optical sheet that can be uniformly controlled, a backlight unit using the optical sheet, and a display device.

  An optical sheet according to the present invention has a structure having both a substantially hemispherical lens that is independently present on a surface that emits light and a plurality of continuous geometric structures arranged in series, and has a high diffusibility. The brightness in the sheet surface can be controlled by changing the ratio of the hemispherical lens and the highly condensed geometric structure in the sheet surface. That is, according to the present invention, the ratio of a highly condensing geometric structure is increased in a portion where brightness is desired to be improved in the sheet surface, and the ratio of a substantially hemispherical lens having high diffusivity is increased in a portion where luminance is to be suppressed. By increasing the brightness, it is possible to control the brightness within the sheet surface.

  The invention according to claim 1 of the present invention is an optical sheet in which one surface of a substrate is a light exit surface and the other surface is a light entrance surface, and the exit surface has a light-collecting geometry. An optical sheet comprising an optical structure and a substantially hemispherical lens having diffusivity, wherein the light emission luminance is controlled by a difference in distribution ratio of the approximate hemispherical lens to the geometric structure. .

  The invention according to claim 2 of the present invention is the optical sheet according to claim 1, wherein the height of the substantially hemispherical lens is made higher than that of the geometrical structure having a high light collecting property. is there.

  The invention according to claim 3 of the present invention is the optical sheet according to claim 1 or 2, wherein the substantially hemispherical lens has a random arrangement without regularity.

In the invention according to claim 4 of the present invention, the diameter of the bottom surface of the substantially hemispherical lens is
It is 40 micrometers-150 micrometers, It is an optical sheet in any one of Claims 1-3 characterized by the above-mentioned.

  In the invention according to claim 5 of the present invention, an aspect ratio (vertex part height / bottom diameter) of the substantially hemispherical lens is 0.4 to 0.6. 4. The optical sheet according to any one of 4 above. When the aspect ratio is 0.4 or less, the light collecting function is greatly reduced, so that the luminance is excessively lowered. Further, since the effect of preventing scratches due to contact or rubbing cannot be obtained, it is not desirable. An aspect ratio of 0.6 or more is not preferable because processing becomes difficult, and variations in height and shape increase, leading to difficulty in controlling brightness within the sheet surface.

  Further, in the invention according to claim 6 of the present invention, the light incident surface of the optical sheet is formed in a substantially hemispherical shape at random, and the optical according to any one of claims 1 to 5 It is a sheet.

  In the invention according to claim 7 of the present invention, the proportion of the optical sheet in the substantially hemispherical plane formed on the light incident surface is 1% to 10 as an area ratio with respect to the entire light incident surface. The optical sheet according to claim 1, wherein the optical sheet is%.

  The invention according to claim 8 of the present invention is the optical sheet according to any one of claims 1 to 7, wherein the optical sheet has a thickness of 0.5 mm to 4 mm.

  An invention according to claim 9 of the present invention is a backlight unit comprising the optical sheet according to any one of claims 1 to 9. By providing the above-described optical sheet or optical member in the backlight unit, light from the light source can be converted into light having excellent luminance, viewing angle, and concealment, and can be emitted to the image display element.

  According to a tenth aspect of the present invention, there is provided a display device comprising the backlight unit according to the ninth aspect. By providing the optical sheet or optical member described above, it is possible to reduce the lamp image and luminance unevenness of the light source, the unevenness and pattern of the optical member such as the diffusion plate, and provide an image in which the luminance of the entire screen is made uniform. It becomes.

  According to the optical sheet of the present invention, the ratio of the substantially hemispherical lens and the geometric structure in the sheet plane can be obtained by utilizing the light collecting / diffusion characteristics of the substantially hemispherical lens and the geometric structure. By changing the brightness, it is also possible to control the brightness within the optical sheet surface and the brightness within the surface of the backlight unit and display device using the optical sheet. Further, by eliminating the regularity of the substantially hemispherical lens arrangement in the sheet surface, the occurrence of moire due to interference with other optical sheets, optical members, or structures such as regular image display elements is suppressed. You can also Furthermore, by making the height of this highly diffusible substantially hemispherical lens higher than that of a highly condensing geometric structure, the optical structure protects the geometric structure from frictional scratches caused by contact. The friction scratch resistance of the entire light exit surface can be improved.

1 is a schematic cross-sectional view of a display device including an optical sheet according to an embodiment of the present invention. It is the schematic diagram seen from the observer side which shows the difference in the brightness on the light-guide plate surface of the edge-type liquid crystal display which has arrange | positioned conventional LED on the upper and lower sides of a housing | casing. It is a schematic diagram which shows the optical sheet by embodiment of this invention. It is a top view of the entrance plane and exit plane of the light of the optical sheet by the embodiment of the present invention. It is sectional drawing of the geometric structure formed in the optical sheet light emission surface of this invention. It is a top view of the display incorporating the optical sheet of this invention.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. 1 to 4 are cross-sectional views of the main parts showing the configurations of the optical sheet, the backlight unit, and the display device according to each embodiment. 1 to 4 show an embodiment of the present invention. A display device 1 according to an embodiment of the present invention shown in FIG. 1 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 transmitting the image display element 3 with the light K emitted from the backlight unit 2.

  The backlight unit 2 according to the embodiment of the present invention is provided with a light source unit 7 having a specification in which a plurality of LEDs are arranged on the two side edges of the housing as the light source 6. A light guide plate 8 having a function of directing light H from the light source 6 toward the observer side F is provided between the LED light sources 6, and is formed on the opposite surface of the light guide plate from the observer side F by a printing method. A white ink dot pattern 9 is provided. Further, a reflection sheet 5 that reflects light on the surface of the white ink pattern is provided. In the example illustrated in FIG. 1, a plurality of optical sheets are provided as the backlight unit 2.

  An optical sheet 10 according to an embodiment of the present invention is arranged in the observer side direction F of the light guide plate 8, and the functional sheet 11 is arranged in a single or plural configuration in the observer side direction F. Has been 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 changed by the light guide plate 8 in the direction of the observer's direction F, and the optical sheet 10. The incident light is converted into light required by diffusion, condensing, polarization, color shift, etc. by the sheet member 11 having the functionality arranged in front of the light in the traveling direction. Is done. 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, an edge type in which a plurality of LEDs are arranged on the end face of the display or a plurality of LEDs is displayed. A direct type disposed on the back surface can be used. Alternatively, 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. 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 the light emitted from the light guide plate 8 in the direction opposite to the observer side F. 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 light guide plate 8 disposed on the light emitting side of the light source unit 7 is formed of a transparent resin. As the transparent resin, a thermoplastic resin, a thermosetting resin, or the like can be used. High acrylic resin is used. Further, in the direct type display device 1 in which LEDs are arranged as the light source on the back of the display, a diffusion plate 8A for diffusing light is provided instead of the light guide plate 8.

  Next, as shown in FIG. 1, the image display element 3 is composed of a pair of polarizing plates (polarizing films; polarizers) 14 and 15 and a liquid crystal panel 16 sandwiched therebetween. 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. 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.

  Here, the LED edge type liquid crystal display in which LEDs as the light source 6 are arranged on the upper and lower sides of the display housing is disassembled to obtain the in-plane brightness in the viewer side direction F of the light guide plate 8. The measurement results are shown in FIG. As shown in FIG. 2A, it has been found that the central portion of the light guide plate 8 is bright and tends to be darker toward the side of the casing where the LED as the light source 6 is not arranged. This brightness unevenness is likely to become more prominent in the specification with a reduced number of LEDs, and measures to reduce this brightness unevenness are required.

  FIG. 2B is a schematic view in which the luminance unevenness is reduced by the optical sheet of the present invention. The optical sheet 10 of the present invention has a light incident surface 10a as a light incident surface 10a and a light incident surface 10b as a light incident surface 10a. The microlens 31 of substantially hemispherical shape which exists independently, respectively, and the prism lens 19 of the cross-sectional triangle which is a continuous geometric structure arranged in plurality extend in one direction. Here, the luminance within the sheet surface can be controlled by changing the ratio of the highly diffusible microlenses 31 within the sheet surface.

  That is, in the optical sheet 10 arranged on the light guide plate 8 in order to compensate for the dark portion generated by the specifications of the display light source and the light guide plate 8 as shown in FIG. On the other hand, by increasing the ratio of the microlenses 31 in the bright part, the brightness can be controlled on the light exit surface 10b of the optical sheet 10. In particular, since the luminance tends to be lower at the end on the side where the LED that is the light source 6 is not disposed, the ratio of the microlens 31 having a higher diffusibility than the central portion of the screen is reduced. By improving the luminance, it is possible to reduce the luminance difference from the central portion.

  Further, as shown in FIG. 3 (a), a plurality of prisms having a triangular section, which is a continuous geometrical structure having a high light-condensing property, is arranged with the height H1 of a substantially hemispherical microlens 31 having a high diffusivity. By making the height higher than the height H2 of the lens 19, the prism lens 19 which is easily scratched because the apex angle is sharp is replaced with a microlens 31 which has a characteristic of being slippery and hardly scratched due to the substantially hemispherical shape. It becomes possible to protect. By making the height H1 of the microlens 31 higher than the height H2 of the prism lens 19, in addition to controlling the brightness in the sheet surface, the microlens 31 is disposed on the surface that emits light during sheet processing, sheet handling, or light emission. It is possible to protect the prism lens 19 that is easily scratched from frictional scratches such as contact and rubbing that occur when the optical members 11 are stacked.

In addition, the height H1 of the substantially hemispherical microlens 31 shown in FIG. 3A is preferably in the range of 1.2 to 6 times the height H2 of the prism lens 19. If this is 1.2 times or less, the damage prevention effect of the prism lens 19 is insufficient, and if the height H1 of the microlens 31 is 6 times or more, the size of the microlens 31 itself is large. This is because the 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 within a range of 10 to 100 μm. This is because if it is 10 μm or less, the required luminance cannot be obtained due to the light diffraction effect. If it is 100 μm or more, the prism lens 19 itself is visually observed on the light exit surface, which causes poor appearance. This is because it may happen.

  The diameter L of the substantially hemispherical microlens 31 is preferably in the range of 40 μm or more and 150 μm or less. A diameter of 150 μm or more is not preferable because the microlens 31 itself can be easily seen, leading to the appearance of unevenness, roughness, and bright spots on the light exit surface. In addition, when the diameter of the microlens 31 is 40 μm or less, it is difficult to form the microlens 31, and at the same time, the variation in shape, diameter, and height increases, which may cause trouble in luminance control. It is not preferable because it increases. By setting the diameter of the microlens 31 within the above range, it is possible to provide an optical sheet capable of controlling brightness with excellent appearance in a stable and substantially hemispherical shape.

  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 has a substantially spherical shape, and at the same time exhibits a function of suppressing the occurrence of scratches due to contact with or rubbing with the light guide plate 8 or other optical member 8A disposed on the light incident surface 10a side. Since the gap is generated by the hemispherical structure, it is possible to suppress the occurrence of uneven interference 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 has a function of concealing the lamp image of the light source 6 and the dot pattern 9 formed on the light guide plate 8 on the light incident surface 10a from the observer, and from the light emitting surface 10b to the observer side F. The emitted light is condensed and diffused by the prism lens 19 to expand 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%-10%. If the area ratio of the bottom surface 20a of the protrusion 20 is within the above range, it is possible to suppress the generation of scratches by rubbing due to contact with the light guide plate 8 and to suppress a decrease in the brightness 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 unevenness formed on the incident surface 10a is in the range of 0.5 μm to 5.0 μm 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 to 5.0 μm, the necessary diffusibility of transmitted light and the concealment property for the observation image are exhibited, and the luminance due to the uneven shape is reduced. Reduction 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.

  As for the outer diameter (diameter) of the projection part 20 formed in the light-incidence surface 10a of the optical sheet 10, the range of 30 micrometers-150 micrometers is preferable. And it is desirable for the ratio with respect to the outer diameter of the height of the projection part 20 of the optical sheet 10 to be 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. If the projection 20 of the optical sheet 10 has a substantially spherical shape where the top 20b that contacts the light guide plate 8 is smooth and hardly scratched, the planar view shape of the projection 20 may be circular or substantially circular, Alternatively, an elliptical shape, a triangular pyramid shape with a rounded top, a quadrangular pyramid shape, or another polygonal pyramid shape may be used. 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 projection 20 of the optical sheet 10 to the outer diameter is in the range of 3% to 30%, the top of the projection 20 is damaged by contact with or rubbing with the light guide plate 8. In addition to preventing light from entering, it is possible to prevent a decrease in luminance 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, as the second embodiment, geometric structures having a cross-sectional shape as shown in FIG. 5 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. In addition, 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 apply the lens specifications to the light guide plate. By optimizing the lens specifications of the microlens 31 and the prism lens 19, it is possible to control the light rising effect of the light guide plate, and it is possible to eliminate the brightness difference between the light emission surfaces of the light guide plate.

  The optical sheet 10 is not limited to the display device 1 such as a liquid crystal display device, but may be any one that performs optical path control, such as a rear projection screen, a solar cell, and an illumination device equipped with an organic or inorganic EL. Can also be used.

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, the microlens 31 and the prism lens 19 are formed on the mold surface in advance by using an etching method and cutting, and this mold plate is used to form a UV resin on a highly transparent sheet-like substrate. In addition, the microlens 31 and the prism lens 19 can be formed. Here, the material of the highly transparent sheet-like substrate 18 is PET (polyethylene terephthalate), PC (polycarbonate), PMM.
A (polymethyl methacrylate), COP (cycloolefin polymer), acrylonitrile styrene copolymer, acrylonitrile polystyrene copolymer and the like can be mentioned.

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. Using these materials, it can be produced by the extrusion molding method using the mold plate described above. Further, the optical sheet 10 having the incident surface 10a can be manufactured by 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 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 front and back surfaces.

  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; 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 | corrugation by the side of the light-incidence surface 10a of the optical sheet 10, mat processing, embossing, etc. are mentioned. Further, regarding the fine unevenness on the light incident surface 10a, a process of providing discontinuous minute protrusions may be performed instead of the production by the mat process. 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. As another method, fine irregularities may be formed by blending transparent particles having a particle size of about 30 to 100 μm in a transparent resin in a molten state and extruding these transparent particles to the outermost layer side. When using this processing method, it is preferable that the refractive indexes of the transparent resin and the transparent particles are equal.

  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 changed in the direction of light by the light guide plate 8 and the light incident surface 10 a of the optical sheet 10. Is incident on. 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 prescribes | regulates the area ratio in a surface, it is less likely to prevent 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, the ratio of the microlens 31 group and the prism lens 19 group is changed to control the in-plane luminance, thereby transmitting the image display element 3. Thus, an image in which the brightness 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 of 96 μm and a lens height of 48 μm provided separately from each other, the bottom width of 50 μm, and the lens height. A first mold plate having a plurality of prism lenses 19 each having a linear structure having a cross-sectional triangle with an apex angle of 90 ° with an apex angle of 25 ° was processed and manufactured using an etching method and a cutting method. In addition, the layout design was performed so that the area ratio of the microlens 31 on the light emitting surface 10b of the optical sheet 10 to be manufactured was 12% at the central portion and 2% at the short side end portion, and the mold processing was performed. Next, using a UV molding machine, a substantially hemispherical microlens 31 and 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 having a 40 inch size was produced. 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, as the light emitting surface 10b of the optical sheet 10, the microlens 31 having a diameter of 96 μm and a lens height of 48 μm provided separately from each other, the bottom surface width of 50 μm, and the lens height of 25 μm. A second mold plate having a plurality of prism lenses 19 having a linear structure having a triangular cross section with an apex angle of 90 ° was processed and produced by the same method as in Example 1 above. In addition, the area design of the microlens 31 in the light emission surface 10b of the optical sheet 10 to be manufactured was arranged at a uniform ratio of 2%, and the mold processing was performed. Next, using a UV molding machine, a substantially hemispherical microlens 31 and 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 having a 40 inch size was produced. 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 Comparative Example 1.

(Comparative Example 2)
As Comparative Example 2, a third mold plate having only a plurality of prism lenses 19 having a linear structure having a cross-sectional triangle with an apex angle of 90 ° with a bottom width of 50 μm and a prism height of 25 μm is processed by a cutting method. In the same manner as in Example 1, using a UV molding machine, a PET substrate having a thickness of 188 μm (
A prism lens 19 made of UV curable resin (refractive index = 1.51) was formed on Toyobo Co., Ltd., and a 40 inch size optical sheet 10 was produced. 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)
40-inch LED edge type display device 1 in which LEDs are arranged on the upper and lower sides of a display casing as optical source 10 according to Example 1 and Comparative Examples 1 and 2 as light source 6 in the embodiment shown in FIG. The optical evaluation was evaluated by the measurement method shown below. In addition, in order to evaluate front luminance and luminance unevenness, a light diffusion sheet, which is a product of Eiwa Co., Ltd., was used as the optical sheet 11.

(Front brightness evaluation)
Three types of optical sheets 10 produced as Example 1 and Comparative Examples 1 and 2 were respectively arranged on a light guide plate 8 made of acrylic resin on which a dot pattern 9 of white ink was formed, and liquid crystal as an image cover element 3 The display device 1 in a form in which the display element was removed was assembled. Spectral radiance meter using the display device 1 in which the light diffusing sheet as the optical sheet 11 is mounted on each of the optical sheets 10 according to each Example 1 and Comparative Examples 1 and 2 and using the display screen as an all white display. The brightness at the center of the observation screen of the optical sheet 11 was measured under the same conditions using (SR-3A: Topcon Technohouse). The measured results are shown in Table 1.

(Brightness difference evaluation)
Three types of optical sheets 10 produced as Example 1 and Comparative Examples 1 and 2 were respectively arranged on a light guide plate 8 made of acrylic resin on which a dot pattern 9 of white ink was formed, and liquid crystal as an image cover element 3 The display device 1 in a form in which the display element was removed was assembled. Spectral radiance meter using the display device 1 in which the light diffusing sheet as the optical sheet 11 is mounted on each of the optical sheets 10 according to each Example 1 and Comparative Examples 1 and 2 and using the display screen as an all white display. (SR-3A: Topcon Technohouse Co., Ltd.) was used to measure the luminance from the display edge to the center on the optical sheet 11 under the same conditions. The measured location was a comparative evaluation by measuring the luminance of the central portion of the long side and the central portion of 5 cm, 10 cm, 15 cm, and 20 cm from the end. FIG. 6 shows the measurement locations, and Table 1 shows the measurement results.

The following can be said from the results shown in Table 1.
When the optical sheet 10 according to Example 1 is used, the front luminance is 426 cd / m 2 at the central portion of 5 cm from the edge of the housing, 435 cd / m 2 at the central portion of 10 cm, 442 cd / m 2 at the central portion of 15 cm, and the center of 20 cm. The area was 448 cd / m 2 and the center area was 457 cd / m 2, and the luminance ratio of 5 cm from the central portion with the highest luminance and the casing with the lowest luminance was 7% (◯).

  When the optical sheet 10 according to Comparative Example 1 is used, the front luminance is 409 cd / m 2 at the central part of 5 cm from the end of the housing, 424 cd / m 2 at the central part of 10 cm, 439 cd / m 2 at the central part of 15 cm, and the center of 20 cm. It was 453 cd / m 2 at the site and 475 cd / m 2 at the center site, and the luminance ratio of 5 cm from the central region with the highest luminance and the housing with the lowest luminance was 14% (×).

When the optical sheet 10 according to Comparative Example 2 is used, the front luminance is 405 cd / m 2 at the central part of 5 cm from the edge of the housing, 419 cd / m 2 at the central part of 10 cm, 433 cd / m 2 at the central part of 15 cm, and the center of 20 cm. 455 cd / m2 at the site, 479 cd / m at the central site
The luminance ratio of 5 cm from the central portion with the highest luminance and the casing with the lowest luminance was 15% (×).

  From the evaluation results of Example 1 and Comparative Examples 1 and 2 shown above, the optical sheet according to the present invention can be obtained by changing the ratio of a substantially hemispherical microlens and a prism lens that is a geometric structure. It has been found that the luminance on the light exit surface of the sheet can be controlled, and the luminance in the screen of the display can be suppressed.

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Backlight unit 3 Image display element 6 Light source 7 Light source unit 8 Light guide plate 8A Diffusion plate 9 White ink dot pattern 10 Optical sheet 10a Light incident surface 10b Light output surface 20 Projection part 21 Plane part 19 Prism lens (geometric) Academic structure)
31 Microlens (substantially hemispherical lens)
H1 Micro lens height H2 Prism lens height F Observer side

Claims (10)

  An optical sheet having one surface of a substrate as a light exit surface and the other surface as a light entrance surface, wherein the exit surface is a geometric structure having a light collecting property and a substantially hemisphere having a diffusibility. An optical sheet comprising a shape lens, wherein light emission luminance is controlled by a ratio of a plane occupation area of a substantially hemispherical lens to a plane occupation area of the geometric structure.   2. The optical sheet according to claim 1, wherein the height of the substantially hemispherical lens is higher than that of the geometric structure having a high light collecting property.   The optical sheet according to claim 1, wherein the substantially hemispherical lens has a random arrangement without regularity.   The optical sheet according to any one of claims 1 to 3, wherein a diameter of a bottom surface of the substantially hemispherical lens is 40 µm to 150 µm.   The optical sheet according to any one of claims 1 to 4, wherein the substantially hemispherical lens has an aspect ratio (apex portion height / bottom diameter) of 0.4 to 0.6.   6. The optical sheet according to claim 1, wherein the light incident surface of the optical sheet is formed in a substantially hemispherical shape at random.   The ratio of the substantially hemispherical plane formed on the light incident surface of the optical sheet is 1% to 10% as an area ratio with respect to the entire light incident surface. An optical sheet according to any one of the above.   The optical sheet according to claim 1, wherein the optical sheet has a thickness of 0.5 mm to 4 mm.   A backlight unit comprising the optical sheet according to claim 1.   A display device comprising the backlight unit according to claim 9.