JP2011242419A - Optical sheet, metal mold, backlight unit and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet capable of suppressing the manufacturing cost and the number of manufacturing steps and concealing defects and shadow of a light source while maintaining brightness.SOLUTION: In the optical sheet 1 used for illumination optical path control of a display optical system, a light transmissive substrate 31 is provided of which one surface in the thickness direction severs as a light incident surface 31a and the other surface in the thickness direction serves as a light emission surface 31b. A plurality of micro lenses 32 and a plurality of minute recesses and projections having depth and height formed at random are randomly mixed over the whole area of the light incident surface 31a and formed on the light incident surface 31a.

Description

  The present invention uses an optical sheet for display composed of a light-transmitting / non-transmitting lens sheet in pixel units, a molding die for the same, and an optical sheet, and a display pattern according to a transparent state / scattering state. The present invention relates to a backlight unit that illuminates a liquid crystal panel on which a prescribed display element is arranged from the back side thereof, and a display device using the backlight unit.

In recent years, liquid crystal display devices using TFT liquid crystal panels and STN liquid crystal panels have been commercialized mainly for color notebook PCs (personal computers) in the OA field.
In such a liquid crystal display device, a so-called backlight method is employed in which a light source is arranged on the back side (counter-viewer side) of the liquid crystal panel and the liquid crystal panel is illuminated with light from the light source.

  The backlight unit employed in this type of backlight system can be broadly divided into a light source such as a cold cathode fluorescent lamp (CCFT), and multiple reflection within a flat light guide plate made of acrylic resin having excellent light transmission properties. There are a “light guide plate light guide method” (so-called edge light method) and a “direct type method” that does not use a light guide plate.

As a liquid crystal display device on which a light guide plate light guide type backlight unit is mounted, for example, the one shown in FIG. 9 is generally known.
As shown in FIG. 9, the liquid crystal display device is provided with a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 at the top, and a substantially rectangular plate-like PMMA (polymethyl methacrylate) on the lower surface side of the liquid crystal panel 72. ) Or a transparent base material such as acrylic is installed, and a diffusion film (diffusion layer) 78 is provided on the upper surface (light emission side) of the light guide plate 79.
Further, a scattering reflection pattern portion (not shown) is printed on the lower surface of the light guide plate 79 so that the light introduced into the light guide plate 79 is efficiently scattered and reflected in the direction of the liquid crystal panel 72. The reflection film (reflection layer) 77 is provided below the scattering reflection pattern portion.

A light source 76 is provided at the side end of the light guide plate 79. Further, a high-reflectance light source reflector 81 is provided on the back side of the light source 76 so as to cover the back side of the light source 76 so that the light from the light source 76 can be efficiently incident on the light guide plate 79.
The scattering reflection pattern part is formed by printing a mixture of white titanium dioxide (TiO ₂ ) powder in a solution such as a transparent adhesive in a predetermined pattern, for example, a dot pattern, and drying. The light incident on the light guide plate 79 is provided with directivity and guided to the light exit surface side, which is a device for increasing the brightness.

  Furthermore, recently, a liquid crystal display device having a configuration as shown in FIG. 10 has been proposed in order to increase the light utilization efficiency and increase the luminance. In this liquid crystal display device, prism films (prism layers) 74 and 75 having a light condensing function are provided between a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 and a diffusion film 78. . The prism films 74 and 75 are used to collect light emitted from the light exit surface of the light guide plate 79 and diffused by the diffusion film 78 on the effective display area of the liquid crystal panel 72 with high efficiency.

However, in the liquid crystal display device shown in FIG. 9, since the control of the viewing angle is left only to the diffusibility of the diffusing film 78, the control is difficult, the central portion of the liquid crystal screen in the front direction is bright, and the peripheral portion The characteristic of getting darker as you go is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.
Further, in the liquid crystal display device using the prism film shown in FIG. 10, since the number of prism films is two, not only the light amount is greatly reduced due to light absorption of the film but also the cost increases due to the increase in the number of members. It was also a cause.

On the other hand, the direct type is used in a liquid crystal display device such as a large liquid crystal TV in which it is difficult to use a light guide plate.
As a direct type liquid crystal display device, a liquid crystal display device having a structure as shown in FIG. 11 is generally known. In this liquid crystal display device, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided at the upper part, and a plurality of light sources 51 composed of fluorescent tubes and the like on the lower surface side of the liquid crystal panel 72 and the back surfaces of the respective light sources 51 A light source unit composed of the reflector 52 arranged in the above is disposed.
In such a liquid crystal display device, the light emitted from the light source 51 and diffused by the optical sheet such as the diffusion film 82 can be condensed on the effective display area of the liquid crystal panel 72 with high efficiency. In order to efficiently use the light from the light source 51 as illumination light, the reflector 52 is disposed on the back surface of the light source 51.

However, also in the liquid crystal display device shown in FIG. 11, since the control of the viewing angle is left only to the diffusibility of the diffusion film 82, the control is difficult, and the central portion in the front direction of the liquid crystal screen is bright and the peripheral portion is The characteristic of getting darker as you go is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced. Further, in the case of using a prism film, since the number of prism films is two, not only the light amount is greatly reduced due to absorption of the film, but also the cost is increased due to an increase in the number of members.
In the liquid crystal display device shown in FIG. 11, if the interval between the light sources 51 is too wide, uneven brightness tends to occur on the screen. Therefore, the number of the light sources 51 cannot be reduced, resulting in an increase in power consumption and cost. It was a cause of increase.

  By the way, in such a liquid crystal display device, there is a strong demand as market needs for light weight, low power consumption, high luminance, and thinning. Accordingly, the backlight unit mounted on the liquid crystal display device is also required to be lightweight, low power consumption, and high luminance. In particular, in color liquid crystal display devices that have recently made remarkable progress, the panel transmittance of the liquid crystal panel is much lower than that of a monochrome-compatible liquid crystal panel. It is essential to obtain low power consumption.

  However, as described above, it is difficult to say that the conventional liquid crystal display device sufficiently satisfies the demand for high luminance and low power consumption, and the user has low price, high luminance, high display quality, and The development of a backlight unit that can realize a low power consumption liquid crystal display device is awaited.

As an attempt to impart other functions to the optical sheet in addition to the optical functions, the technique shown in Patent Document 1 is known, but is limited to a case where the sheet is wound into a roll and applied to various processes. It is not something that can be done.
In addition to the conventionally used prisms, lenticular lenses, microlenses, and polygonal pyramids, various types of optical sheets as shown in Patent Documents 2 to 5 have been proposed for the purpose of improving the performance of optical sheets. It is thought that the number of optical sheets with new shapes will increase in the future.

JP 2008-203776 A Special table 2008-515026 gazette JP 2007-3571 A JP 2007-304565 A JP 2008-102497 A

The optical sheet used for the backlight of the display device has a great influence on the appearance of the display device, that is, the commercial value, depending on the optical performance.
In general, high brightness is desired, but diffusion performance is also required to hide minute defects or to eliminate the shadow of the light source. Since the light diffusion performance also causes a decrease in luminance, it is very difficult to achieve both. As a method for imparting light diffusing performance, it is widely known that a diffusion layer using a light diffusing material is combined, or that an optical sheet is roughened. An increase in the number of manufacturing steps will occur.

  The present invention has been made in view of the above points, an optical sheet capable of concealing defects and light source shadows while maintaining luminance and suppressing the manufacturing cost and the number of manufacturing steps, and a mold for molding the optical sheet. And a backlight unit using an optical sheet and a display device using the same.

  The invention of claim 1 is an optical sheet used for illumination optical path control of a display optical system, wherein one surface in the thickness direction is a light incident surface and the other surface in the thickness direction is a light emission surface. The light incident surface includes a plurality of single lenses and a plurality of concave and convex portions having random depths and heights randomly mixed over the entire area of the light incident surface. It is characterized by being formed.

  According to a second aspect of the present invention, in the optical sheet according to the first aspect, the surface roughness Rz of the light incident surface is in the range of 4 μm to 10 μm.

  According to a third aspect of the present invention, in the optical sheet according to the first or second aspect, the plurality of unit lenses are hemispherical, and the diameter of the unit lenses is in the range of 50 μm to 130 μm.

  According to a fourth aspect of the present invention, in the optical sheet according to any one of the first to third aspects, a concavo-convex portion for diffusion for diffusing a light beam emitted from the light exit surface is formed on the light exit surface. It is characterized by that.

  The invention according to claim 5 is a mold, wherein the light incident surface of the optical sheet according to any one of claims 1 to 3 is transfer-molded.

  The invention according to claim 6 is a mold, wherein the light emission surface of the optical sheet according to claim 4 is transfer-molded.

  Invention of Claim 7 is a backlight unit, Comprising: The light source and the light irradiation surface of the said light source are arrange | positioned so that the said light emission surface may be faced to the said light source. The optical sheet is provided.

  The invention according to claim 8 is a display device, the image display element defining a display image according to transmission / shading in pixel units, and the backlight according to claim 7 disposed on the back of the image display element. And a unit.

  According to the present invention, the light incident surface of the light transmissive substrate is formed with a plurality of light uneven portions and a plurality of single lenses randomly mixed over the entire light incident surface, so that the luminance is maintained. It is possible to conceal defects and light source shadows. Furthermore, since the light incident surface of the optical sheet is transferred and molded by the mold, the manufacturing cost and the number of manufacturing steps of the optical sheet can be suppressed.

The schematic diagram which shows one structural example of the liquid crystal display device incorporating the optical sheet concerning this invention, and a backlight unit using the same. The schematic diagram which shows the other structural example of the liquid crystal display device incorporating the optical sheet concerning this invention, and a backlight unit using the same. (A) is an external view of the optical sheet concerning this invention, (b) is a perspective view for description which expanded a part of optical sheet and was seen from the light-incidence surface side. The expanded sectional view which follows A-A 'of FIG.3 (b). (A)-(d) is a perspective view for description which shows the example of a shape of the uneven | corrugated | grooved part formed in the light emission surface of the optical sheet in this invention. Explanatory drawing of the metal mold | die roll for manufacturing the optical sheet concerning this invention. The expansion perspective view of the fine recessed part provided in the metal mold | die roll for manufacturing the optical sheet concerning this invention. The figure which shows the result when incorporating the optical sheet concerning this invention in a display apparatus, displaying a white screen on the display apparatus, and observing visually. The schematic diagram which shows the structural example of the liquid crystal display device by a prior art. Schematic which shows the other structural example of the liquid crystal display device by a prior art. Schematic which shows the further another structural example of the liquid crystal display device by a prior art.

(Embodiment)
Hereinafter, embodiments of a liquid crystal display device using an optical sheet according to the present invention will be described with reference to FIGS.
The liquid crystal display device shown in FIG. 1 includes a light guide plate light guide type backlight unit, and a liquid crystal panel sandwiched between polarizing plates 21 and 21 (corresponding to the image display element described in claims) 19. A backlight 23 disposed opposite to and parallel to the light incident side of the liquid crystal panel 19, an optical sheet 1 disposed between the liquid crystal panel 19 and the backlight 23, and light emission of the optical sheet 1 The reflection type deflection separation sheet 2 disposed opposite to the surface 1b and the light diffusion sheet 3 disposed opposite to the light incident surface 1a of the optical sheet 1 are configured.
As shown in FIG. 1, the backlight 23 includes a light guide plate 5 disposed opposite to the lower surface of the light diffusing sheet 3, and a light source provided to face opposite side end surfaces of the light guide plate 5. 15. In FIG. 1, K is light from the light source 15, L is light emitted from the optical sheet 1, and S represents the viewing direction of the liquid crystal display device.

The liquid crystal display device shown in FIG. 2 includes a direct-type backlight unit, a liquid crystal panel (corresponding to an image display element described in claims) 19 sandwiched between polarizing plates 21 and 21; A backlight 24 disposed opposite to and parallel to the light incident side of the liquid crystal panel 19, the optical sheet 1 disposed between the liquid crystal panel 19 and the backlight 24, and a light incident surface 1 a of the optical sheet 1. The light diffusing plate 6 is disposed to face each other. The light emission surface 1 b of the optical sheet 1 faces the liquid crystal panel 19.
As shown in FIG. 2, the backlight 24 includes a reflection plate 17 formed by depositing a mirror surface forming metal such as aluminum on the inner wall surface, and a light incident surface of the light diffusion plate 6 in the reflection plate 17. On the other hand, the light source 15 is composed of a plurality of cold-cathode tubes and the like arranged in an orientation at a constant pitch. In FIG. 2, K is the light from the light source 15, L is the light emitted from the optical sheet 1, and S represents the viewing direction of the liquid crystal display device.

Next, the structure of the optical sheet 1 shown in FIGS. 1 and 2 will be described in detail with reference to FIGS. 3, 4, and 5.
The optical sheet 1 includes a light-transmitting substrate 31 in which one surface in the thickness direction is a light incident surface 31a and the other surface in the thickness direction is a light emission surface 31b. As shown in FIGS. 3 and 4, the light incident surface 31 a of the light transmissive substrate 31 has a plurality of hemispherical microlenses (corresponding to a single lens described in claims) 32, and a depth. A plurality of fine concavo-convex portions 34 for roughening whose surface and height are random are formed so as to be randomly mixed over the entire area of the light incident surface 31a.

A light control element for controlling the direction of the emitted light as shown in FIGS. 5A to 5D is provided on the light emitting surface 31 b of the light transmissive substrate 31.
That is, the light control element 35 shown in FIG. 5A includes a plurality of prisms (or cylindrical lenses) 35 arrayed on the light emitting surface 31b of the light transmissive substrate 31 at intervals in the plane direction, The prism 35 includes a plurality of hemispherical microlenses 36 that are randomly mixed in the arrangement region of the prisms 35.
The light control element 36 shown in FIG. 5B includes a plurality of prisms (or cylindrical lenses) 36a arranged on the light emitting surface 31b of the light transmissive substrate 31 at intervals in the plane direction. Has been.

The light control element 37 shown in FIG. 5C includes a plurality of prisms (or cylindrical lenses) 37a arranged on the light emitting surface 31b of the light transmissive substrate 31 at intervals in the plane direction, An uneven portion 37b is formed on the top of the prism 37a at intervals along the length of the prism 37a.
Further, the light control element 38 shown in FIG. 5D includes a plurality of prisms (or cylindrical lenses) 38a arranged on the light emitting surface 31b of the light transmissive substrate 31 at intervals in the plane direction, An uneven portion 38b is formed between the adjacent prisms 38a at intervals along the length direction of the prism 38a.
The light control element formed on the light exit surface 31b of the light transmissive substrate 31 may be other than the structure shown in FIG. The shape of the light incident surface of the optical sheet in the present invention is not particularly limited to the structure of the light exit surface.

In the edge light type liquid crystal display device shown in FIG. 1, the light K from the light source 15 enters the light guide plate 5. Thereafter, the light diffusion sheet 3, the optical sheet 1, and the reflective polarization separation sheet 2 are transmitted through the light exit surface of the light guide plate 5. Finally, the light is emitted as light L from the light exit surface of the reflective polarization separation sheet 2. The light L reaches the liquid crystal panel 19 sandwiched between the polarizing plates 21. The light transmitted through the liquid crystal panel 19 is emitted to S and visually recognized by an observer.
In the liquid crystal display device having a direct type backlight shown in FIG. 3, the light K from the light source 15 enters the light diffusion plate 6. Thereafter, the light reaches the optical sheet 1 from the light emission surface of the light diffusion plate 6, and finally the light is emitted as light L from the emission surface of the optical sheet 1. The light L reaches the liquid crystal panel 19 sandwiched between the polarizing plates 21. The light transmitted through the liquid crystal panel 19 is emitted to S and visually recognized by an observer.
In addition, the liquid crystal display device of this invention is not restricted to the thing of the structure shown in FIG.1 and FIG.2, You may increase / decrease an optical sheet suitably.

In the optical sheet 1 shown in the present embodiment, the microlens 32 formed on the light incident surface is for improving the abrasion resistance of the light incident surface 31a. Further, when the microlens 32 is also received by the light incident surface 31a, the reflected light on the light incident surface is reduced by the lens effect, and the amount of light incident on the optical sheet 1 can be increased.
It is the inclined spherical surface portion of the microlens 32 that exhibits the lens effect. The optical sheet 1 has a thickness, and the thickness portion is shown as a light-transmitting substrate 31 in the drawing. Further, the light-transmitting base material 31 constituting the optical sheet 1, the microlens 32 and the concavo-convex portion 34 formed on the light incident surface 31a, and the light control elements 35, 36 and 37 formed on the light exit surface 31b are different. It may be made of a material or may be made of the same material.

  The diameter of the microlens 32 formed on the light incident surface 31a of the light transmissive substrate 31 is preferably in the range of 50 μm to 130 μm. If it is smaller than 50 μm, it is difficult to manufacture, and if it is larger than 130 μm, the microlens 32 itself looks like a point defect. The arrangement of the microlenses 32 may be regular or irregular. The area ratio of all the microlenses formed on the light incident surface 31b to the light incident surface is preferably in the range of 3% to 10%. If it is less than 3%, the rubbing resistance of the light incident surface is lowered, and if it is more than 10%, it is conspicuous from the light emitting surface, which is not preferable in appearance.

According to the optical sheet 1 shown in the present embodiment, the fine uneven portion 34 formed on the light incident surface 31a maintains a concealing performance for erasing the shadow of the light source, and exhibits a lens effect. The lens 32 can reduce the reflected light on the light incident surface and increase the amount of light incident on the optical sheet.
Further, when the surface roughness of the light incident surface 31a generated by forming the uneven portion 34 is Rz, the surface roughness Rz is preferably in the range of 4.0 μm to 10.0 μm. If the surface roughness Rz is smaller than 4.0 μm, the production is difficult and the hiding performance is not exhibited. If the surface roughness Rz is larger than 10 μm, the luminance is significantly reduced. It is easy to measure the surface roughness Rz at the flat part.

Next, the manufacturing method of the optical sheet in this invention is demonstrated.
First, a mold for forming the optical sheet according to the present invention is prepared. Here, if a roll-shaped mold 25 as shown in FIG. 6 is used, a continuous optical sheet can be formed. If a flat mold is used, a plate by a press method or an injection method is used. And sheet formation are possible.
When a roll-shaped mold is used, an optical sheet can be continuously produced, and a continuous pattern film can be obtained by using a mold material without a pattern seam. For this reason, it is possible to cope with many screen sizes by adjusting the cut-out dimensions, and the productivity is good. Further, when a flat metal mold is used, the optical sheet becomes a single sheet, but shape transfer onto the plate material is easy, and it is suitable for small lot multi-product production. In addition, the mold base material is made of iron, SUS, aluminum or the like in consideration of durability and handling, and copper or brass is plated as a surface layer for forming the fine irregularities 34 and the microlenses 32. It is common.

  The material of the surface layer of the mold is not particularly limited as long as transfer molding can be performed, but when using it for molding of an optical sheet, it is generally necessary to use copper or brass because a certain degree of smoothness is required. . Also, when forming a hemispherical microlens or a reversal shape of fine irregularities on the surface of the mold, place the mold on a high-precision precision cutting machine and use a diamond tool to achieve the desired position and depth. Then, the inverted shape is processed so as to be a notch. The mold having the inverted shape may be subjected to Cr plating or Ni plating on the surface of copper or brass in consideration of abrasion resistance.

The optical sheet 1 is manufactured by an extrusion method, a casting method, or an injection method, and the thickness thereof is in the range of 12 μm or more and 1 mm or less. When the thickness is less than 12 μm, there is no rigidity that can withstand processing, and when the thickness is more than 1 mm, there is no flexibility that can withstand processing.
The optical sheet 1 may be manufactured by a UV curing method. In the case of producing by the UV curing method, a UV curable resin is applied on a light transmissive substrate, a mold having a desired shape is pressed, and UV irradiation is performed to obtain an optical layer. As the light transmissive substrate, PET (polyethylene terephthalate), polycarbonate, acrylic, polypropylene films and the like well known in the art can be used.

  As shown in FIG. 5, the roll-type mold 25 used when the optical sheet 1 is molded has a hemispherical shape that is an inverted shape of a hemispherical microlens 32 formed on the light incident surface of the optical sheet 1. What formed the fine uneven part 26 which is the reverse shape of the recessed part 27 and the uneven part 34 in the outer peripheral surface of the metal mold | die 25 is applied. In this case, the surface of the mold is obtained by plating an iron core with copper, chromium, or nickel, and any of an extrusion method, a casting method, an injection method, and a UV curing method can be used for manufacturing an optical sheet. In addition, the fine uneven | corrugated | grooved part 26 formed in the outer peripheral surface of the metal mold | die 25 is a thing of a shape as shown, for example in FIG.

  As the main material of the light-transmitting substrate constituting the optical sheet 1, for example, polycarbonate, acrylic-styrene copolymer, polystyrene, styrene-butadiene-acrylonitrile copolymer, or cycloolefin polymer may be used. . Further, transparent particles dispersed in the main material may be provided, and the refractive index of these main materials and the refractive index of the transparent particles are different. The difference between the refractive index of the main material and the refractive index of the transparent particles is preferably 0.01 or more. If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. Further, the refractive index difference is 0.5 or less. The average particle size of the transparent particles is desirably in the range of 0.5 to 30.0 μm. In particular, the light transmissive substrate 31 may have a single layer structure or a multilayer structure, and may include a transparent layer.

  As the transparent particles, transparent particles made of an inorganic oxide or transparent particles made of a resin can be used. For example, examples of the transparent particles made of an inorganic oxide include particles made of silica, alumina or the like. The transparent particles made of resin include acrylic particles, styrene particles, styrene acrylic particles and crosslinked products thereof; melamine-formalin condensate particles, PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetra Examples thereof include fluorine-containing polymer particles such as fluoroethylene-hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer), and silicone resin particles. These transparent particles may be used as a mixture of two or more. Alternatively, the plate-like member has a structure in which a main material has a fine cavity containing air, and diffusion performance may be obtained by a difference in refractive index between the main material and air.

  The light diffusing plate 6 and the light guide plate 5 may be made of the same main material as that of the optical sheet 1 and may be configured to include the above-described transparent particles. The refractive index of these main materials and the refractive index of transparent particles need to be different. The difference between the refractive index of the main material and the refractive index of the transparent particles is preferably 0.01 or more. If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. Further, the refractive index difference may be 0.5 or less. Moreover, since it is necessary to transmit the light incident on the light diffusing plate 6 and the light guide plate 5 while scattering, it is desirable that the average particle size of the transparent particles be in the range of 0.5 μm to 30.0 μm. Alternatively, as a structure having a fine cavity containing air in the main material, diffusion performance may be obtained by a difference in refractive index between the main material and air. Further, a reflection pattern or a geometric structure may be provided on the surface.

  As the optical component on the light source side used in combination with the optical sheet of the present invention, a reflection type polarization separation sheet, a diffusion sheet, a prism sheet and the like well known in the art are appropriately used.

Example 1
Next, the Example of the manufacturing method of the optical sheet concerning this invention is described.
First, as shown in FIG. 6, the mold 25 was set on a high-precision precision cutting machine, and fine uneven portions 26, which are the inverted shapes of the uneven portions 34, were randomly processed on the surface thereof. Next, a hemispherical concave portion 27 that is the inverted shape of the microlens 32 was processed using the same diamond tool on the surface of the same mold.
FIG. 7 shows an example of the shape of the fine uneven portion 26. The shape shown in FIG. 7 is easy to process and can be produced in a short time. The shape of such a roughening process is not limited to the said shape. As the mold for molding, a plate making process for gravure printing was used, and a mold having a pattern formed on copper plating was used.
As the mold roll on the light incident surface side of the optical sheet, the mold 25 in which the fine uneven portion 26 and the hemispherical concave portion 27 are processed is used, and as the mold roll on the light exit surface side of the optical sheet, FIG. A prism in which the prism shown in (c) is engraved orthogonally was prepared. The area ratio of the hemispherical microlens engraved on the mold surface is 4%, the prisms on the light exit surface side each have an apex angle of 90 °, and the engraving pitch is in the range of 22 μm and 66 μm.
The mold roll is placed close to the extruder, the thermoplastic polycarbonate resin sheet is melted, and the resin sheet is molded by the mold roll before the resin sheet is cooled and cured by the extruder. An extruded sheet having a surface shape in which the portions 34 are mixed at random was obtained. The thickness was 320 μm. M1201 from Teijin Chemicals Ltd. was used as the thermoplastic polycarbonate. For comparison, a smooth surface sheet (No. 0) and a rough surface sheet (No. 1) were prepared. All extruded sheets were cut into 730 mm × 310 mm squares and used for evaluation.

Next, luminance measurement and concealment evaluation of the optical sheet will be described.
The obtained optical sheet was incorporated into a display device, a white screen was displayed, and the brightness of the center was measured from a distance of 50 cm in the normal direction of the screen with SR-3A manufactured by Topcon. The configuration of the backlight was a Teijin Chemicals diffusion plate 65HLW and an optical sheet. The hiding property was evaluated by evaluating the hiding property of the light source using a direct type backlight. The optical sheet was incorporated into the display with the same configuration as the luminance measurement, and a white screen was displayed for visual observation. Visual evaluation was performed by three or more subjects because there were individual differences. The result is shown in FIG.

From FIG. 8, it was found that when the surface roughness of the light incident surface due to the fine irregularities is 2.0 μm or less, the concealing property is impaired as indicated by the x mark. In addition, it was found that when the surface roughness of the light incident surface due to the fine irregularities was 10 μm or more, the luminance was significantly reduced. When the diameter of the micro lens is 140 μm or more, it is visually recognized from the light exit surface as roughness unevenness.
From the above, it was found that the optical sheet composed of a combination of a surface having fine irregularities and a hemispherical microlens molded under suitable conditions maintains the concealment performance of defects and light source shadows without causing a decrease in luminance. . In the examples, for the simplest comparison, the backlight is composed of a Teijin Chemicals diffusion plate 65HLW and an optical sheet. However, the optical sheet of the present invention is impaired in performance even when used in combination with other optical sheets. There is no.

  DESCRIPTION OF SYMBOLS 1 ... Optical sheet, 2 ... Reflection type polarization separation sheet, 3 ... Diffusing sheet, 5 ... Light guide plate, 6 ... Light diffusing plate, 15 ... Light source, 17 ... Reflecting plate, 19 ... Liquid crystal panel , 21... Polarizing plate, 23, 24... Backlight, 25... Molding mold, 26... Fine uneven portion, 27 .. Hemispherical recess, 31. Incident surface, 31b: Light exit surface, 32: Microlens, 34: Fine uneven portion, 35, 36, 37: Light control element.

Claims (8)

An optical sheet used for illumination optical path control of a display optical system,
A light-transmitting substrate in which one surface in the thickness direction is a light incident surface and the other surface in the thickness direction is a light emission surface;
On the light incident surface, a plurality of single lenses and a plurality of concave and convex portions whose depth and height are random and fine are randomly mixed over the entire area of the light incident surface.
An optical sheet characterized by that.   The optical sheet according to claim 1, wherein the light incident surface has a surface roughness Rz in a range of 4 μm to 10 μm.   The optical sheet according to claim 1 or 2, wherein the plurality of unit lenses have a hemispherical shape, and the diameter of the unit lenses is in a range of 50 µm to 130 µm.   The optical sheet according to any one of claims 1 to 3, wherein a concavo-convex portion for diffusion that diffuses light emitted from the light exit surface is formed on the light exit surface. The light incident surface of the optical sheet according to any one of claims 1 to 3 is transfer molded.
A mold characterized by that. The light emission surface of the optical sheet according to claim 4 is transferred and molded.
A mold characterized by that. A light source;
The optical sheet according to any one of claims 1 to 4, wherein the optical sheet is disposed on the light irradiation surface of the light source with the light emission surface facing the light source.
A backlight unit comprising: An image display element that defines a display image according to transmission / shading in pixel units;
The backlight unit according to claim 7 disposed on the back surface of the image display element,
A display device comprising:

Images