JP2013073819A - Optical sheet, backlight unit, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet capable of controlling luminous unevenness peculiar to a light guide plate in a direction where the luminous unevenness is compensated, and having contact resistance and abrasion resistance.SOLUTION: In the optical sheet, columnar prism lenses of which the cross-sectional shape is an isosceles triangle are arranged in a stripe form so that an arrangement pitch may become a bottom length of the isosceles triangle, and moreover, two or more semispherical lenses are arranged on the prism lenses. The height of the semispherical lens is higher than the prism lens and a vertex angle of the prism lens is within a range of 90°to 120°.

Description

  The present invention relates to an optical sheet used for optical path control of backlight light, and particularly relates to a surface shape of the optical sheet.

  Liquid crystal display devices using a liquid crystal panel have been widely used not only for image display means such as mobile phones, personal digital assistants and personal computers, but also for televisions as home appliances. In particular, liquid crystal display devices have become widespread in general households as display devices for large screens that have been difficult with CRT televisions. In addition, products that are thinner and lighter by utilizing the advantages of liquid crystal display devices are being supplied to the market at a very high speed.

  Such a liquid crystal display device has a built-in light source, and a backlight unit including the light source is disposed on the back side of the liquid crystal panel in order to ensure the brightness necessary for displaying an image. . In this backlight unit, a light source typified by a cold cathode tube or a light emitting diode (LED) is arranged on the side surface of the liquid crystal display device, and multiplexed in a flat light guide plate having excellent light transmittance. Reflected “light guide plate light guide method” (so-called edge light method) and multiple light sources such as cold cathode tubes and LEDs, diffuser plate and optical film with strong light scattering are arranged on the back side of the liquid crystal display device. There are two types, the “direct type”, in which the light source is not directly visible.

  In recent liquid crystal display devices, as a part of measures against global environmental problems, suppression of power consumption to reduce energy consumption 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. In this approach, a liquid crystal display device using an LED, which is said to have low power consumption, as a light source is expanding its share over the cold cathode tube type. As for this LED, either the direct type or the edge light type configuration arranged on the back side is adopted, and products with an improved contrast ratio have been put on the market, but the LED is still Issues such as the problem of heat generation and the required brightness are not obtained.

  In order to reduce the power consumption, it is necessary to increase the luminous efficiency of the LED, which is a point light source, to reduce the number, but doing so increases the brightness unevenness (lamp image) of the light source and simply reduces the number. Then the problem is not solved. Therefore, at present, 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 so that luminance unevenness does not occur even if the number is reduced. A combination of these is used.

  Conventionally, the above-described optical sheet has been provided with a function of concentrating diffused light from the backlight unit by the optical sheet to improve the front luminance in order to increase the light use efficiency of the light source. “BEF” (registered trademark: Brightness Enhancement Film) manufactured by 3M is widely used as an optical sheet. BEF is a sheet in which unit prisms having a cross section of an isosceles triangle are arranged at a constant pitch in one direction on the upper surface of a transparent base material, and collects light from off-axis. When the light incident from the flat surface of the substrate exits from the prism surface, the light is collected in the front direction and the luminance in the front direction is improved. It becomes possible.

  An optical sheet such as BEF is not only improved in luminance by improving the light utilization efficiency, but also various functions such as removal of light source unevenness, securing of a viewing area, and maintenance of rigidity of the sheet itself are added and integrated. Therefore, a plurality of optical sheets are often 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, light in the vertical direction of BEF is refracted by the flat portion of the prism slope and emitted in the normal direction, so that the vertical viewing angle is very narrow relative to the horizontal viewing angle. there were. Moreover, since the top of the prism is pointed, the BEF has a defect that the top of the prism is easily damaged 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. It was.

  Thus, attempts have been made to reduce the number of optical sheets within a range that does not impair the target function. For example, Patent Document 1 discloses a technique for imparting a diffusion function to the light collection function of a prism by dispersing diffusible fine particles in the prism lens. Further, in Patent Document 2, by arranging microlenses randomly on a base material, the same optical effect is achieved even if the light incident from the back is condensed by the microlens and emitted forward, and the number is reduced. Means 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 prism 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.

  The laminated optical sheet or an optical member having functions such as light diffusion, condensing, polarization, and discoloration is used by fixing the four sides to the frame of the device when arranged in a liquid crystal display device. In some cases, it is not completely fixed so that it does not move inside the device. Therefore, the back surface of the other optical sheet or optical member having functionality and the tip of the prism come into contact with each other due to vibration during transportation or movement of the liquid crystal display device, resulting in rubbing and scratching.

  On the other hand, since the optical sheet described in Patent Document 2 has a hemispherical lens, even if it comes into contact with another laminated optical sheet or an optical member having functionality, the rounded structure causes contact. Even if friction occurs, it has a feature that it is hard to be scratched because it slides well. However, since there is a gap between adjacent microlenses, light that is refracted and scattered at the interface between the microlens and the air layer through the inside of the microlens and collected from the front is emitted between the adjacent microlenses. There is a problem in that light is generated, and bright spots and bright lines are visually recognized from the luminance difference between these lights.

  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. In particular, in the edge type liquid crystal display device in which the LED light source is arranged on the side surface of the housing, depending on the number of LED light sources arranged and the arrangement location, simply using a light guide plate formed from a transparent acrylic resin or the like, It is difficult to make the luminance distribution of the entire screen uniform. Therefore, the luminance distribution in the screen is made uniform by using a plurality of optical sheets including an optical sheet having diffusibility. However, this LED edge type liquid crystal display device is also required to reduce the number of LEDs in order to reduce power consumption and manufacturing cost. In this case, uneven brightness tends to occur partially, and it has become more difficult to make the brightness distribution of the entire screen uniform.

In order to solve this problem, it is necessary to make the brightness in the sheet surface uniform in the direction of increasing the brightness of the specific part corresponding to the low brightness part of the optical sheet, but such control is very difficult. . In order to make this possible, a complicated shape and highly difficult resin processing are required, so that there is a high possibility that the processing yield will be reduced and the cost will be increased.
Therefore, the present situation is that the optical sheet has a big problem in luminance control within the sheet surface.

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

  The present invention has been made in view of the above problems, and is an optical sheet that can uniformly control the luminance unevenness of the light guide plate in a direction in which the luminance unevenness is compensated. An object of the present invention is to provide an optical sheet having wear properties.

  In order to achieve the above object, the invention according to claim 1 is characterized in that a prismatic prism lens having a cross-sectional shape of an isosceles triangle is provided on a light emitting surface, and a pitch is the length of the base of the isosceles triangle. The optical sheet is characterized in that a plurality of hemispherical lenses are disposed on the prism lens.

The invention according to claim 2 is the optical sheet according to claim 1, wherein the height of the hemispherical lens is higher than the height of the prism lens.
The invention according to claim 3 is the optical sheet according to claim 1 or 2, wherein the prism lens has an apex angle in a range of 90 ° to 120 °.

  The invention according to claim 4 is the optical sheet according to any one of claims 1 to 3, wherein the arrangement of the hemispherical lenses is a random arrangement.

  According to a fifth aspect of the present invention, in the optical sheet according to any one of the first to fourth aspects, the diameter of the bottom surface of the hemispherical lens is in the range of 40 μm to 150 μm. It is a thing.

  According to a sixth aspect of the present invention, in the hemispherical lens, an aspect ratio (apex part height / bottom diameter) obtained by dividing the height by the diameter at the bottom is within a range of 0.4 to 0.6. The optical sheet according to any one of claims 1 to 5, wherein the optical sheet is provided.

  The invention according to claim 7 is the optical sheet according to claim 1, characterized in that hemispherical lenses are randomly arranged on the light incident surface.

  The invention according to claim 8 is characterized in that the ratio of the total bottom area of the hemispherical lens to the entire light incident surface is in the range of 1% to 10%. The optical sheet according to any one of the above.

  The invention according to claim 9 is the optical sheet according to any one of claims 1 to 8, wherein the thickness is in the range of 0.5 mm to 4 mm.

  According to a tenth aspect of the present invention, there is provided a backlight unit comprising the optical sheet according to any one of the first to ninth aspects.

  According to an eleventh aspect of the present invention, there is provided a liquid crystal display device comprising the backlight unit according to the tenth aspect.

  The optical sheet according to the present invention has a surface shape in which a highly diffusive hemispherical lens and a columnar prism lens are laid on the surface from which light is isolated, and the apex angle of the prism lens is By changing the brightness, the brightness in the sheet surface can be controlled. By forming the apex angle of the part where you want to increase the brightness at 90 ° and making the apex angle wider than 90 ° at the part that suppresses the brightness, the light exit surface side is less likely to be scratched and the brightness control within the sheet surface Both become possible.

  Further, the height of the hemispherical lens is set to be higher than the height to the apex angle of the highly condensing prism lens. The hemispherical shape is advantageous in that it is slippery within the contact surface and hardly scratched. It is possible to protect a prism lens that is easily damaged from contact and rubbing scratches such as contact and rubbing that occur when a sheet is processed, when a sheet is handled, or when another optical member is placed on the upper surface of the light emitting surface.

  Furthermore, when the apex angle of the prism lens is set within the range of 90 ° to 120 °, the luminance can be adjusted efficiently. The prism lens has the maximum luminance when the apex angle is 90 °, and the light condensing property decreases and the luminance decreases as the angle increases from 90 °. However, when the apex angle is 120 ° or more, the luminance decreases remarkably. It is not preferable for maintaining a constant luminance.

  In addition, hemispherical lenses with high light diffusivity are randomly arranged on the sheet surface from which light is emitted. By making the arrangement of the lenses random with no regularity, it is possible to suppress the occurrence of moire and interference unevenness due to interference with optical members or liquid crystal display members having other regularity.

  In addition, by setting the diameter of the bottom surface of the hemispherical lens within the range of 40 μm or more and 150 μm or less, the lens is not visually recognized and brightness control is facilitated.

  Also, by setting the aspect ratio of the hemispherical lens (vertex part height ÷ bottom diameter) within the range of 0.4 to 0.6, the light collecting function is significantly reduced and the luminance is excessively reduced. In addition, there is no generation of scratches due to contact or rubbing. Processing is also easy.

  If a hemispherical lens is randomly arranged on the light incident surface side, even if the optical sheet and the optical member are vibrated or rubbed, it becomes difficult to be scratched. In addition, 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 close contact.

  Further, when the area ratio occupied by the hemispherical lens formed on the light incident surface is in the range of 1% to 10%, it is possible to suppress the occurrence of interference unevenness such as Newton rings and the front luminance does not decrease. Play.

  When the thickness of the optical sheet is in the range of 0.2 mm to 4 mm, if the thickness is 0.2 mm or less, the strength of the optical sheet itself is reduced, and the sheet is wrinkled and swollen by heat generated when the display is turned on. Deformation and the like occur, which is not preferable because it causes a difference in brightness on the screen and uneven brightness. In addition, in the case of 4 mm or more, it leads to an increase in the thickness of the liquid crystal display used, and is not desirable as an optical member for a liquid crystal display that emphasizes the thinness.

  The backlight unit of the above optical sheet can emit light having a uniform luminance and no viewing angle dependency to the liquid crystal display device.

  A liquid crystal display device including the backlight unit described above has uniform luminance over the entire screen and little variation in image quality due to viewing angle.

It is a cross-sectional schematic diagram explaining the structure of the liquid crystal display device containing the optical sheet which concerns on this invention. The schematic diagram showing the difference in brightness on the light guide plate surface of the edge type liquid crystal display is (a). Correspondingly, (b) is an example of the arrangement of the prism lens and the hemispherical lens of the optical sheet. It is a figure of the top view demonstrated. It is a figure which illustrates typically the surface shape of the optical sheet which becomes this invention. (A) is a perspective enlarged view, (b) is a sectional view. It is a figure of the cross-sectional view explaining the contact condition of the optical sheet and light guide plate by this invention. It is a figure of the top view explaining the surface structure of the optical sheet light emission surface which becomes this invention. It is a figure of the top view which shows the site | part which evaluated the brightness | luminance of the backlight incorporating the optical sheet which becomes this invention.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. 1 to 4 are cross-sectional views of the main part showing the configurations of the optical sheet, the backlight unit, and the liquid crystal display device according to the present invention.

  The backlight unit 2 according to the present invention includes a light source unit 7, an optical sheet 10, and a functional sheet 11, as shown in FIG. The light source unit 7 includes a light guide plate 8, an LED light source 6 in which a plurality of LEDs arranged at its end are accommodated in a housing, and a reflection sheet 5. The light guide plate 8 has a function of directing the light H from the light source 6 toward the observer side F, and is provided with a white ink dot pattern 9 formed by a printing method on the back side. The reflection sheet 5 has a function of reflecting light emitted to the back surface.

  The functional sheet 11 has a single or multiple configuration. The functional sheet member 11 is a sheet having one or a plurality of functions typified by, for example, condensing, diffusing, polarizing, and discoloring, for example, and uniformizing and increasing the luminance of light incident on the liquid crystal panel 3. It is an optical member for imparting necessary characteristics such as a polarization function. The liquid crystal panel 3 is disposed in the observer side direction F of the sheet member 11.

  According to the liquid crystal display device 1 having such a configuration, in the backlight unit 2, the light H emitted from the light source 6 is changed to the observer side direction F by the light guide plate 8, and the optical sheet 10, the incident light is converted into light K required by diffusion, light collection, polarization, color shift, or the like by the sheet member 11 having the functionality arranged in front of the light traveling direction. The The light K enters the liquid crystal panel 3 and the light of the observation image is emitted to the observer side F.

  Here, the light source 6 in the light source unit 7 supplies light to the liquid crystal panel 3. For example, an edge type in which a plurality of LEDs are arranged on the side of the apparatus, a direct type in which the LEDs are arranged on the back of the apparatus, or the like is used. Can do. Alternatively, a plurality of linear light sources can be used, and for this, a plurality of fluorescent lamps, cold cathode fluorescent lamps (CCFL) or EEFLs can be exemplified.

  The reflection sheet 5 constituting the light source unit 7 is arranged on the side opposite to the observer side F of the plurality of light sources 6 and is emitted in the direction opposite to the observer side F of the light emitted from the light guide plate 8. It plays a role of reflecting light to be emitted to the observer side F. As a result, the light H emitted to the observer side F becomes substantially equal to the amount of light emitted 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, and a reflection sheet such as a white PET sheet, a reflection plate, or the like can 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 resins are preferred. Further, in the direct type liquid crystal display device 1 in which LEDs are disposed as light sources on the back surface of the liquid crystal display, a diffusion plate 8 </ b> A for diffusing light is provided instead of the light guide plate 8.

  Next, as shown in FIG. 1, the liquid crystal panel 3 is composed of a pair of polarizing plates (polarizing films; polarizers) 14 and 15 and a liquid crystal cell 16 sandwiched therebetween. The liquid crystal cell 16 is configured, for example, by filling a liquid crystal layer between two glass substrates. The liquid crystal panel 3 is a device that transmits / shields light in pixel units and displays an image. However, the optical sheet 10 improves the luminance toward the viewer side F, and the viewing angle dependency of light intensity is reduced. High quality images can be displayed.

  Here, the result of measuring the in-plane brightness in the observer side direction F of the light guide plate 8 attached to the edge type liquid crystal display using the LED as a light source is shown in FIG. As can be seen from FIG. 2A, it has been found that the central portion of the light guide plate 8 is bright and the side surface of the light guide plate where the LEDs are not arranged tends to be dark. This unevenness in brightness (brightness unevenness) is often seen in light guide plates with specifications that increase frontal brightness, and in specifications with a reduced number of LEDs, there is a high possibility that it will become more prominent, and measures to reduce this brightness difference Is required. In this case, it is necessary not only to improve the light guide plate 8 but also to make the function of the optical sheet 10 correspond to the direction in which the luminance distribution of the light guide plate is eliminated.

  Further, in the light guide plate 8, in order to prevent light introduced from an end surface other than the end surface on which light from the light source is incident from leaking outside the light guide plate 8, the end surface may be covered with a reflective tape. In this case, the brightness of the end portion of the light guide plate where the LEDs are not arranged is improved by the effect of the reflective tape. However, it has now been found that an intermediate portion between the central portion and the end portion of the light guide plate tends to be dark. It is necessary to solve the luminance unevenness not only in the design of the light guide plate 8 but also in the entire backlight member including the optical sheet 10.

  Next, the optical sheet 10 according to the present invention will be described in detail. As shown in FIG. 1C, the optical sheet 10 has a light incident surface 10 a as a surface on which light from the light guide plate 8 is incident, and 10 b as a surface where light is emitted in the observer side direction F. . A columnar prism lens 19 having an isosceles triangle with the same cross section is laid on the light emitting surface 10b so that the pitch extends in a stripe shape with the length of the base of the isosceles triangle. On the prism lens, a hemispherical microlens 31 is laid randomly and isolated.

  The area ratio of the hemispherical microlens 31 to the light exit surface 10b is preferably 1% to 20%. When the area ratio of the hemispherical microlens 31 is higher than 20%, the area ratio of the geometric structure 110 connected in a linear shape having a high effect of improving the luminance is relatively decreased. This is not desirable because it causes a decrease in luminance. If it is 1% or less, it is not preferable because it becomes difficult to protect the sharp apex of the columnar prism lens 19.

Here, since the apex angle of the prism lens can be set to a desired angle, in the present invention, by changing the apex angle of the highly condensing prism lens 19 in the plane, the luminance in the sheet plane is changed. I have control. That is, as shown in FIG. 2A, the optical sheet 10 disposed on the light guide plate 8 compensates for the brightness level that is difficult to control only by the combination of the light source and the light guide plate 8. That is, the apex angle of the prism lens 19 immediately above the dark part is set in the vicinity of 90 ° where the luminance is highest, and conversely, the apex angle of the prism lens 19 in the bright part is made wider than 90 °. Control to make the luminance uniform on the light emitting surface 10b of the sheet 10 becomes possible.

  The apex angle of the prism lens 19 is desirably in the range of 90 ° to 120 °. This is because the 90 ° apex angle of the prism lens 19 has the highest front luminance. Further, when the apex angle is wider than 120 °, the front luminance is excessively lowered, which is not preferable. On the other hand, when the angle is 90 ° or less, the luminance other than the front surface is decreased, the viewing angle is narrowed, and the side lobe is also increased. Furthermore, the more acute the apex angle, the more undesirable the appearance of the optical sheet 10 due to glare or the like.

  As shown in FIG. 3A, the height H1 of the hemispherical microlens 31 having a high diffusibility is set to be higher than the maximum height H2 of the prism lens 19. This makes it possible to prevent the prism lens 19 that is easily scratched because the apex angle is sharp so that it does not touch other sheets and substrates, and the microlens itself is hemispherical so that it is slippery, Hard to get scratched. By making H1 higher than H2, in addition to brightness control within the sheet surface, contact occurring when the optical member 11 placed on the surface from which light is emitted during sheet processing, sheet handling, or light emission is superimposed. This means that it is possible to protect the prism lens 19 that is easily damaged from friction scratches such as rubbing. The hemisphere does not mean a hemisphere in a strict sense and includes some deformation.

  In addition, the height H1 of the hemispherical microlens 31 shown in FIG. 3A is desirably in the range of 1.2 to 6 times the maximum height H2 of the prism lens 19. If this is 1.2 times or less, the contact prevention effect of the prism lens 19 is insufficient, and if the height H1 of the micro lens 31 is 6 times or more, the size of the micro lens 31 itself becomes large. This is because 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 maximum height H2 of the prism lens 19 is preferably in the range of 10 to 100 μm. This is because when the thickness is 10 μm or less, the required luminance cannot be obtained due to the diffraction effect of light. On the other hand, if it is 100 μm or more, it is not preferable because the prism lens 19 itself is a factor in the appearance of the light exit surface side 10b due to visual observation on the light exit surface.

  The diameter L of the hemispherical microlens 31 is preferably in the range of 40 μm to 150 μm. 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 micro lens 31 within the above range, it is possible to stably provide a brightness-controllable optical sheet that is excellent in appearance.

As shown in FIG. 4, it is desirable that the protrusions 20 having a 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, it is possible to enhance the light diffusing function by imparting fine convexity to the light incident surface side 10a, and to improve the effect of concealing the pattern of the light guide plate on the light source side by expanding the viewing angle. Become. The planar portion 21 whose surface is roughened by fine convex portions can diffuse the light H from the light source 6 by 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.

  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.

  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 used not only for the liquid crystal display device 1 but also for any device that performs optical path control, such as a rear projection screen, a solar cell, and an illumination device that uses organic or inorganic EL as a light source. You can also

Next, a manufacturing process of the optical sheet 10 will be described.
The optical sheet 10 can be formed on a highly transparent sheet-like substrate using a UV curable resin or an electron beam curable resin. As an example, the female mold of the microlens 31 and the prism lens 19 is formed in advance on the mold surface by using an etching method and cutting, and this mold plate is used to form a UV on a highly transparent sheet-like substrate. The microlens 31 and the prism lens 19 can be transferred and molded on the resin.

  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.

  In addition, a transparent resin made of a thermoplastic resin is also preferable as a material constituting the optical sheet 10, for example, polycarbonate resin, acrylic resin, fluorine-based acrylic resin, silicone-based acrylic resin, epoxy acrylate resin, polystyrene resin, cycloolefin polymer, methyl Examples thereof include styrene resin, fluorene resin, PET, polypropylene, acrylonitrile styrene copolymer, acrylonitrile polystyrene copolymer, 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 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 also 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 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.

Further, the optical sheet 10 is preferably one to which an ultraviolet absorber is added. 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 prism lens 19 and the microlens 31 on the light emitting surface 10a side of the optical sheet 10, die cutting, die cutting and etching, or die cutting and blasting are used. The method of combining different processing methods is mentioned. In particular, as a method of changing the apex angle of the prism lens 19, a plurality of diamond tools having a predetermined tip angle can be used to arrange the prism lenses 19 having different apex angles on the mold surface.

  Further, examples of the method for forming the fine protrusions on the light incident surface 10a side of the optical sheet 10 include mat processing and emboss processing. Further, 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. 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.

  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 is incident on the light incident surface 10 a of the optical sheet 10. And when light injects from the incident surface 10a of the optical sheet 10, the in-plane area ratio is prescribed | regulated so that the projection part 20 provided in the light incident surface 10a may not prevent incidence of light.

  Furthermore, since the fine irregularities of the plane portion 21 have diffusibility and concealment, the lamp image of the light source 6 and the luminance unevenness of the light guide plate 8 are reduced. 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 uniformly control the in-plane luminance. The overall luminance can be made uniform.

  Hereinafter, the present invention will be described with reference to FIGS. The present invention is not limited to these examples. In particular, the optical characteristics of the optical sheet 10 and the liquid crystal display device 1 using the same will be described in Examples.

Example 1
As the optical sheet 10, a hemisphere having a diameter of 96 μm and a lens height of 48 μm provided on the light emitting surface 10b of the optical sheet 10 separately from each other (only how they are distributed. Description of density etc. is required) Extending from one short side of the optical sheet to the other short side is a microlens 31 having a shape and a columnar prism lens 19 having an isosceles triangle cross-section with a bottom width of 50 μm and a height of 25 μm. As shown in FIG. As for the apex angle, among the prismatic prism lenses, the apex angle 90 ° is the width from the long side to the inner 10% along the short side, the apex angle is 95 °, the apex angle is 95 °, and the apex angle is 20%. The angle was 100 °, the tip 30% width was apex angle 95 °, and the tip 10% width (up to the long side) was 90 ° apex angle.
The isosceles triangle does not necessarily have a strict meaning, and includes some deformation such as a processing error.

A first mold plate having a microlens 31 shape and a columnar prism lens shape having an isosceles triangular cross-section whose apex angle varies depending on the location was processed and manufactured using an etching method and a cutting method. Note that the mold was designed and processed so that the area ratio of the microlenses 31 on the light exit surface 10b of the optical sheet 10 to be manufactured was 2% as a whole.

  Next, using a UV molding machine, a UV curable resin (refractive / BR = 1.49) is applied onto a 188 μm thick PET substrate (Toyobo product), and the mold is pressed to form a substantially hemispherical micro The lens 31 and the prism lens 19 were formed to produce a 23-inch size optical sheet 10. In addition, the prism lens 19 having a stripe 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. A top view of the optical sheet 10 is shown in FIG.

(Comparative Example 1)
As Comparative Example 1, as the light exit surface 10b of the optical sheet 10, a microlens 31 having a diameter of 96 μm and a lens height of 48 μm provided separately from each other, a bottom width of 50 μm, a height of 25 μm, and an apex angle A second mold plate in which the shape of the prism lens 19 whose 90 ° cross section is an isosceles triangle is a female mold was processed and produced by the same method as in Example 1 above.
In addition, the area ratio of the microlens 31 in the light emission surface 10b of the optical sheet 10 to be manufactured was designed to be unified at 2%, and the mold processing was performed.

  Next, using a UV molding machine, a UV curable resin (refractive index = 1.49) is applied onto a PET substrate (Toyobo product) having a thickness of 188 μm, and the second mold is pressed to form a substantially hemispherical micro The lens 31 and the prism lens 19 were formed to produce a 23-inch size optical sheet 10. The prism lenses 19 having a linear structure are arranged in stripes 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 a female shape with a prism lens 19 shape in which the width of the bottom surface is 50 μm, the height is 25 μm, and the cross section with an apex angle of 90 ° is an isosceles triangle is processed by a cutting method, In the same manner as in Example 1, using a UV molding machine, a UV curable resin (refractive index = 1.49) was applied onto a PET base material (Toyobo product) having a thickness of 188 μm, and a third mold was pressed against the prism. The lens 19 was formed to produce a 23-inch size optical sheet 10. 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 was used as the optical sheet 10 in the embodiment shown in FIG. As another optical sheet 11, a light diffusion sheet, which is a product of Eiwa Co., Ltd., was used. As the liquid crystal display device 1, a 23-inch LED edge type liquid crystal display device 1 was used. Optical evaluation was performed by the following measuring method.

(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 white ink dot pattern 9 was formed, and further an optical sheet on each of them. 11 were stacked and mounted. For the measurement, the liquid crystal panel 3 was removed.
First, the brightness of the central portion of the optical sheet 11 was measured under the same conditions using a spectral radiance meter (SR-3A: manufactured by Topcon Technohouse Co., Ltd.) with the observation screen as an all white display. The measured results are shown in Table 1.

(Brightness difference evaluation)
Next, the luminance from the end to the center on the optical sheet 11 was measured sequentially. As shown in FIG. 6, the measured locations were subjected to comparative evaluation by measuring the luminance of the central portion of the short side and the central portions of 20 mm and 75 mm from the end portion of the short side. The result of Table 1 is the average brightness | luminance which performed the brightness | luminance measurement of the same location 5 times.

The following can be said from the results shown in Table 1.
When using the optical sheet 10 according to Example 1, the front luminance is 373cd / ^{m 2} in the central portion of 381cd ^/ m 2, 75mm in the central portion of 20mm from the housing end, in the central portion 410 cd ^/ m 2, 75 mm of The central part was 383 cd / m ² , the central part 20 mm from the end of the casing was 374 cd / m ² , and the luminance ratio of the central part with the highest luminance and the casing with the lowest luminance 75 mm was 9% ( ○).

When using the optical sheet 10 according to Comparative Example 1, the front luminance is 379cd / ^{m 2} in the central portion of 356cd ^/ m 2, 75mm in the central portion of 20mm from the housing end, the main site 421cd ^/ m 2, 75mm of The central part was 388 cd / m ² , the central part 20 mm from the end of the casing was 359 cd / m ² , and the luminance ratio of the central part with the highest luminance and the 20 mm from the casing with the lowest luminance was 15% ( X).

When using the optical sheet 10 according to Comparative Example 2, the front luminance is 371cd / ^{m 2} in the central portion of 355cd ^/ m 2, 75mm in the central portion of 20mm from the housing end, the main site 428cd ^/ m 2, 75mm of 402 cd / m ² at the central part, 362 cd / m ² at the central part 20 mm from the edge of the casing, and the luminance ratio of 20 mm from the central part having the highest luminance and the casing having the lowest luminance was 17% ( X).

  From the evaluation results of Example 1 and Comparative Examples 1 and 2 shown above, in the optical sheet according to the present invention, the apex angle of the prism lens which is the geometric structure is changed, so that the light exit surface of the optical sheet is changed. It became possible to control the luminance, and it was found that the in-screen luminance in the liquid crystal display can be suppressed.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Backlight unit 3 Liquid crystal panel 6 Light source 8 Light guide plate 8A Diffusion plate 9 White ink dot pattern 10 Optical sheet 10a Light incident surface 10b Light output surface 11 Optical sheet (diffusion sheet)
14, 15 Polarizing plate 16 Liquid crystal cell 20 Projection portion 21 Plane portion 19 Prism lens (geometric structure)
31 Microlens (substantially hemispherical lens)
H1 Micro lens height H2 Maximum prism lens height F Observer side

Claims (11)

  A prismatic prism lens having a cross-sectional shape of an isosceles triangle is laid in a stripe shape on the surface from which light is emitted so that the pitch is the length of the base of the isosceles triangle, and a plurality of prism lenses are disposed on the prism lens. An optical sheet comprising a hemispherical lens.   The optical sheet according to claim 1, wherein a height of the hemispherical lens is higher than a height of the prism lens.   3. The optical sheet according to claim 1, wherein an apex angle of the prism lens is in a range of 90 ° to 120 °.   The optical sheet according to any one of claims 1 to 3, wherein the arrangement of the hemispherical lenses is a random arrangement.   5. The optical sheet according to claim 1, wherein a diameter of a bottom surface of the hemispherical lens is in a range of 40 μm to 150 μm.   The aspect ratio (vertex part height / bottom diameter) obtained by dividing the height of the hemispherical lens by the diameter at the bottom is in the range of 0.4 to 0.6. The optical sheet according to claim 5.   2. The optical sheet according to claim 1, wherein hemispherical lenses are randomly arranged on a surface on which light is incident.   8. The optical device according to claim 1, wherein a ratio of a total bottom area of the hemispherical lens to a whole light incident surface is in a range of 1% to 10%. Sheet.   The optical sheet according to any one of claims 1 to 8, wherein the thickness is in a range of 0.5 mm to 4 mm.   A backlight unit comprising the optical sheet according to any one of claims 1 to 9.   A liquid crystal display device comprising the backlight unit according to claim 10.

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