JP5810481B2 - Optical sheet, backlight unit, display device, and optical sheet manufacturing mold - Google Patents

Description

  The present invention relates to an optical sheet, a backlight unit, a display device, and a mold for manufacturing an optical sheet.

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

The backlight unit employed in this type of backlight system is roughly divided into a light source lamp such as a cold cathode fluorescent lamp (CCFL, LED), and a flat light guide plate made of acrylic resin having excellent light transmittance. There are a “light guide plate light guide method” (so-called edge light method) that makes multiple reflections, 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. 7 is generally known.

  This is provided with a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 at the top, and a light guide plate 79 made of a transparent base material such as a substantially rectangular plate-like PMMA (polymethyl methacrylate) or acrylic on the lower surface side. Is installed, and a diffusion film (diffusion layer) 78 is provided on the upper surface (light emission side) of the light guide plate.

  Further, on the lower surface of the light guide plate 79, a scattering reflection pattern portion for scattering and reflecting the light introduced into the light guide plate 79 so as to be uniform in the direction of the liquid crystal panel 72 is provided by printing or the like ( A reflection film (reflection layer) 77 is provided below the scattering reflection pattern portion.

  In addition, a light source lamp 76 is attached to the light guide plate 79 at the side end, and further, the light source lamp 76 is covered so that the light from the light source lamp 76 is incident on the light guide plate 79 efficiently. A high-reflectance lamp reflector 81 is provided. The scattering reflection pattern portion is formed by printing a mixture of white titanium dioxide (TiO2) powder mixed with a transparent adhesive solution or the like in a predetermined pattern, for example, a dot pattern, and drying and forming the light guide plate 79. This is a contrivance for increasing the brightness by imparting directivity to the light incident inside and guiding it to the light exit surface side.

  Furthermore, recently, in order to increase the light utilization efficiency and increase the brightness, as shown in FIG. 8, a prism film (prism layer) having a light condensing function between the diffusion film 78 and the liquid crystal panel 72 is used. ) 74 and 75 are proposed. The prism films 74 and 75 are configured 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 apparatus illustrated in FIG. 7, the control of the viewing angle is entrusted only to the diffusibility of the diffusion film 78, which is difficult to control, and the center in the front direction of the display is bright and becomes darker toward the periphery. This characteristic 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.

  Furthermore, in the apparatus using the prism film illustrated in FIG. 8, two prism films are required, which not only greatly reduces the amount of light due to the absorption of the film but also increases the cost due to the increase in the number of members. It was also.

  On the other hand, in the direct type, a display device such as a large liquid crystal TV in which the light guide plate is difficult to use is used.

  As a direct type liquid crystal display device, a device illustrated in FIG. 9 is generally known. In this, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper side, and is emitted from a light source 51 made of a fluorescent tube or the like on the lower surface side thereof and diffused by an optical sheet such as a diffusion film 82. The light is 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, a reflector 52 is disposed on the back surface of the light source 51.

  However, even in the apparatus illustrated in FIG. 9, the control of the viewing angle is left only to the diffusibility of the diffusion film 82, which is difficult to control, and the center in the front direction of the display is bright and becomes darker toward the periphery. This characteristic 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. Furthermore, in the case of using a prism film, since the number of prism films is two, not only the light amount is greatly decreased due to absorption of the film but also the cost is increased due to an increase in the number of members.

  Further, if the interval between the light sources 51 is too wide, uneven brightness tends to occur on the screen, and the number of the light sources 51 cannot be reduced, leading to an increase in power consumption and an increase in cost.

  By the way, in such a liquid crystal display device, light weight, low power consumption, high brightness, and thinness are strongly demanded as market needs, and accordingly, the backlight unit mounted on the liquid crystal display device is also light weight, Low power consumption and high brightness are required.

  In particular, in a color liquid crystal display device that has recently made remarkable progress, the panel transmittance of the liquid crystal panel is remarkably lower than that of a monochrome-compatible liquid crystal panel. It is essential to obtain power consumption.

However, as described above, it is difficult to say that the conventional device sufficiently satisfies the demand for high luminance and low power consumption, and the user has low price, high luminance, high display quality, and low power consumption. The development of a backlight unit capable of realizing a power liquid crystal display device is awaited.
On the other hand, for the purpose of improving the performance of optical sheets, there have been proposals for various optical patterns as shown in Patent Documents 1 to 5 in addition to prisms, lenticular lenses, microlenses, and polygonal pyramids that have been conventionally used. New shapes are expected to increase.

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

  By the way, the optical sheet used for the backlight unit of a display apparatus has a big influence on the external appearance of a display apparatus, ie, commercial value, by optical performance. As the optical performance, those having a high brightness improvement effect are preferable.

  Among conventionally used dot-shaped optical element arrays such as microlenses, the higher the density of each optical element, the higher the luminance improvement effect. Further, the effect of improving luminance is higher when there is less overlap between optical elements. When considering a microlens shape with excellent brightness enhancement effect, the filling ratio of the microlens area in the total area of the optical sheet is 78.5% as long as the hexagonal arrangement, which is usually considered as a fine arrangement, does not overlap. It becomes. In order to achieve a filling rate higher than this, it is necessary to appropriately overlap the microlenses or to fill the gaps with small microlenses.

  On the other hand, the arrangement of the microlenses is limited by the method of manufacturing the optical sheet. When making beads side by side or creating a mold from beads, the filling rate cannot reach the ideal value because the overlap cannot be made and the arrangement is random. The method of filling the gaps with small microlenses is extremely difficult to arrange well.

  On the other hand, methods that do not rely on beads, such as a method using a machined die or a corrosive die, or a direct processing of an optical sheet, can form an ideal arrangement and can easily form an overlap. However, an arrangement that creates a moderate overlap has not yet been disclosed. In addition, it is very troublesome to make an optical sheet by mixing microlenses of different sizes.

  In addition to this, the hexagonal arrangement based on the vertical and horizontal biaxial coordinates based on the conventional plane and the random pattern created by slightly shifting these arrangements are the same for other optical sheets, light guide plates, and even liquid crystal panels. Since it is created in the coordinate system, there is a big problem that moire occurs.

  An object of the present invention is to optimally arrange a plurality of optical elements on one surface of an optical sheet with respect to the above problem.

In order to solve the problem, the invention according to claim 1 is an optical sheet that collects and / or diffuses incident light, and has a plurality of optical elements that are spaced apart from each other on one surface. The plurality of optical elements include any one optical element, and another optical element arranged so as to satisfy the following (a) and (b) if the one surface has a cylindrical surface shape: If the one surface has a cylindrical surface shape, the plurality of optical elements are arranged so as to be connected by screw-like lines on the cylindrical surface. When the distance between the position of the one optical element and the position of the other optical element in the central axis direction is D, the diameter of the cylindrical surface is R, and the maximum width of the optical element is P,
P ² /(R·π)·0.5≦D≦P ² / (R · π) · 2
It is an optical sheet characterized by satisfying

(A) The smaller of the angles formed by the straight line connecting the position of the one optical element and the central axis of the cylindrical surface and the straight line connecting the position of the other optical element and the central axis of the cylindrical surface When the angle is θ1 and the larger angle is θ2, 360: θ2 = θ2: θ1 (b) The position of the one optical element and the position of the other optical element in the central axis direction of the cylindrical surface The position is different

The invention according to claim 2 is the optical sheet according to claim 1, wherein the optical element is a microlens or a lens having a polygonal pyramid shape.
The invention according to claim 3 is the invention described in claim 1 or 2 , wherein the other surface is formed as a flat surface, the optical element is disposed, or fine irregularities are formed, or a combination thereof. An optical sheet characterized by the above.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the portion other than the arrangement portion of the optical element on the one surface is formed on a plane, and fine irregularities are formed. Or an optical sheet on which other optical elements are arranged.
The invention according to claim 5 is the optical sheet according to any one of claims 1 to 4 , wherein the thickness is 0.2 mm or more and 4.0 mm or less.

The invention according to claim 6 is provided with the optical sheet according to any one of claims 1 to 5 , and the light source and the light emitted from the light source are incident and diffused to be emitted as diffused light. A backlight unit characterized in that the light emitted from the diffusion plate is incident on the optical sheet to be transmitted and emitted.

The invention according to claim 7 is provided with an optical sheet according to any one of claims 1 to 5, the light source and guide the light source is emitted by the light guide incident light emitted And a light plate, wherein the light emitted from the light guide plate is incident on the optical sheet to be transmitted and emitted.

An invention according to claim 8 includes the backlight unit according to claim 6 or 7 , and includes an image display element that defines a display image according to transmission or non-transmission in pixel units, and the image The display device is characterized in that the backlight unit is arranged so that light emitted from the optical sheet is incident on the back surface of the display element.

According to a ninth aspect of the present invention, in the method of manufacturing an optical sheet that performs at least one of condensing and diffusing incident light, a plurality of optical elements arranged on one surface of the optical sheet are separated from each other. The plurality of optical elements are any one optical element and another optical element arranged so as to satisfy the following (a) and (b) if the one surface has a cylindrical surface shape: If the one surface has a cylindrical surface shape, the plurality of optical elements are arranged so as to be connected by screw-like lines on the cylindrical surface, and the cylinder When the distance between the position of the one optical element and the position of the other optical element in the central axis direction of the surface is D, the diameter of the cylindrical surface is R, and the maximum width of the optical element is P,
P ² /(R·π)·0.5≦D≦P ² / (R · π) · 2
It is a manufacturing method of an optical sheet characterized by satisfying .

(A) The smaller of the angles formed by the straight line connecting the position of the one optical element and the central axis of the cylindrical surface and the straight line connecting the position of the other optical element and the central axis of the cylindrical surface When the angle is θ1 and the larger angle is θ2, 360: θ2 = θ2: θ1 (b) The position of the one optical element and the position of the other optical element in the central axis direction of the cylindrical surface The position is different

According to a tenth aspect of the present invention, there is provided an optical sheet manufacturing mold for manufacturing an optical sheet that performs at least one of condensing and diffusing incident light. And a plurality of optical element forming portions for forming a plurality of optical elements disposed on one surface of the optical sheet so as to be spaced apart from each other, wherein the plurality of optical element forming portions is an arbitrary optical element. A pair of optical element forming parts configured to include a forming part and another optical element forming part arranged so as to satisfy the following (a) and (b) when the forming surface has a cylindrical surface shape: If the one surface has a cylindrical surface shape, the plurality of optical element forming portions are arranged so as to be connected by screw-like lines on the cylindrical surface, and the one surface in the central axis direction of the cylindrical surface The position of the optical element forming portion and the other optical element When the distance between the position of the forming section is D, the diameter of the cylindrical surface and R2, the maximum width of the optical element forming portion was set to P2,
P2 ² /(R2·π)·0.5≦D≦P2 ² / (R2 · π) · 2
An optical sheet manufacturing mold satisfying the above requirements .

(A) An angle formed by a straight line connecting the position of the one optical element forming portion and the central axis of the cylindrical surface and a straight line connecting the position of the other optical element forming portion and the central axis of the cylindrical surface. When the smaller angle is θ1 and the larger angle is θ2, 360: θ2 = θ2: θ1 (b) The position of the one optical element forming portion in the central axis direction of the cylindrical surface The position of the other optical element forming portion is different

According to the present invention, a plurality of the optical element, by arranging so as to spaced apart from one another on one surface of the optical sheet, and satisfy (a) and (b), one surface of the optical sheet A plurality of optical elements are optimally arranged.

It is a side view which shows the structure of the display apparatus of this embodiment. It is a perspective view which shows the shape of an optical sheet. It is a figure explaining the arrangement | sequence of the optical element in an optical sheet. It is a perspective view which shows the other shape of an optical sheet. It is a side view which shows the other structure of the display apparatus of this embodiment. It is a figure which shows the conditions of an Example, and a result. It is a side view which shows the structural example of the conventional liquid crystal display device. It is a side view which shows the other structural example of the conventional liquid crystal display device. It is a side view which shows the further another structural example of the conventional liquid crystal display device.

(Constitution)
FIG. 1 shows a configuration of a display device (liquid crystal display device) 1 of the present embodiment. As shown in FIG. 1, the display device 1 illuminates the liquid crystal panel 20 from the back side with the backlight unit 10.
In the following description, the upper side in FIG. 1 is expressed as the upper side, the lower side is expressed as the lower side, the surface facing the upper side is expressed as the front surface, and the surface facing the lower side is expressed as the back surface.

  The backlight unit 10 is an edge light type (edge light type) backlight unit. The backlight unit 10 includes a light source 11, a light guide plate 12, a diffusion sheet 13, an optical sheet 30, and a reflective polarization separation sheet 14.

  With such a configuration, in the backlight unit 10, the light K from the light source 11 is incident on the light guide plate 12. The incident light is emitted from the exit surface 12 a of the light guide plate 12, and the emitted light passes through the diffusion sheet 13, the optical sheet 30, and the reflective polarization separation sheet 14. Finally, the light transmitted through the reflective polarization separation sheet 14 is emitted as L from the exit surface 14a. The emitted light L is incident on the liquid crystal panel 20.

  The liquid crystal panel 20 includes a display element in which a display pattern is defined according to transmission / non-transmission or transparency / scattering in pixel units. Specifically, the liquid crystal panel 20 is configured by sandwiching the liquid crystal layer 23 between two polarizing plates 21 and 22. With such a configuration, in the liquid crystal panel 20, the outgoing light L from the reflective polarization separation sheet 14 passes through the polarizing plate 21 and reaches the liquid crystal layer 23. And the light which permeate | transmitted the liquid crystal layer 23 permeate | transmits the polarizing plate 22, is inject | emitted by S, and is visually recognized by an observer.

Next, the configuration of the optical sheet 30 will be described in detail.
FIG. 2 shows a configuration example of the optical sheet 30.
As shown in FIG. 2, the optical sheet 30 has a plurality of optical elements 33 formed at predetermined positions on a substantially planar surface 31 a of a substantially flat substrate 31. That is, the portion other than the portion where the optical element 33 is arranged on the surface 31a of the optical sheet 30 is formed in a substantially flat surface. The optical element 33 here is a microlens or a polygonal pyramid shaped lens. The optical element 33 may be other than these lenses.

Here, the arrangement of the optical element 33 will be described with reference to FIG.
The plurality of optical elements 33 are two-dimensionally independent on the surface of the optical sheet 30. This means that when assuming the same plane along or parallel to the surface 31a, the plurality of optical elements 33 are positioned apart from each other in the assumed same plane. Furthermore, in the plurality of optical elements 33, if the surface 31a is formed into a cylindrical surface shape, the position of the other optical element 33 satisfies the following first and second conditions with respect to the position of any one optical element 33. Are arranged (becomes a set).

(First condition)
360: θ2 = θ2: θ1 (1)
Here, as shown in FIG. 3, θ1 is a straight line connecting the position of any one optical element 33 (the coordinates of the point A) and the central axis of the cylindrical surface, and the position (point B) of the other optical element 33. ) And a straight line connecting the central axis of the cylindrical surface. θ2 (= 360−θ1) is the larger angle.

(Second condition)
The position of one optical element 33 and the position of another optical element 33 are different on a coordinate axis (in the direction of the central axis) parallel to the central axis of the cylindrical surface.
In the first and second conditions described above, the expression (1) indicates the positional relationship between the optical elements 33 that have the least useless overlap. This positional relationship is often seen as an array with little overlap in the natural world. The arrangement of the optical elements 33 arranged so as to satisfy the first and second conditions finally becomes an arrangement connected with screw-like lines on the cylindrical surface.

As a matter of course, if the coordinates of the point A and the point B are the same on the coordinate axis parallel to the central axis of the cylinder, the optical element 33 overlaps infinitely in the circumferential direction. Further, it is necessary to adjust the coordinates of the points A and B to obtain an appropriate filling rate. Further, when randomness is desired in the arrangement, it is necessary to set the coordinates of the points A and B individually.
Further, preferably, the following third condition (formula (2)) is satisfied.

(Third condition)
P ² /(R·π)·0.5≦D≦P ² / (R · π) · 2 (2)
Here, D is the distance between point A and point B on a coordinate axis parallel to the central axis of the cylindrical surface. R is the diameter of the cylindrical surface. P is the maximum width of the optical element 33.

  As in the third condition, it is desirable that the distance D is in a range satisfying the expression (2). Here, the filling rate (the ratio at which the optical element 33 is disposed on the surface 31a of the optical sheet 30) varies depending on the shape of the optical element 33, for example, whether it is a perfect circle. However, if the distance D between the two optical elements 33 for all the optical elements 33 is the left side of the equation (2), the filling rate is 90% or more. If the distance D is the right side of the equation (2), the filling rate is about 30%. Thus, the filling rate can be adjusted in the range of 30% to 90%.

  Even if it is desired to be random, it is preferable to vary the distance D within the range of the above-mentioned formula (2) because the arrangement is less biased and the appearance is good.

The optical element 33 is disposed as described above.
In addition, portions other than the arrangement portion of the optical element 33 on the surface 31a of the optical sheet 30 in which the plurality of optical elements 33 are arranged in this way have fine irregularities formed as an aspect other than the above-described substantially flat surface, or Other optical elements (optical elements other than microlenses or polygonal pyramid-shaped lenses) are arranged. Specifically, as shown in FIG. 4, a plurality of prism unit lenses 32 are arranged. Further, it may be a mirror surface, and may be roughened by blasting, polishing, bead application, hairline or the like as long as it is substantially flat.

  Further, the back surface 31b of the optical sheet 30 is required to function as an incident surface. That is, a simple mirror surface hardly contributes to the performance of the optical sheet 30. For this reason, the back surface 31b of the optical sheet 30 is formed in a plane in order to function as an incident surface, the optical element 33 is disposed, or fine irregularities are formed, or a combination thereof. . Specifically, the back surface 31b of the optical sheet may be roughened by blasting, polishing, bead application, hairline, or the like as long as it is substantially flat. Alternatively, the back surface 31b of the optical sheet may be provided with irregularities, dots, and optical elements 33 for preventing adhesion, preventing charging, and improving concealment. And you may use combining these shapes suitably.

Moreover, it is desirable that the thickness of the optical sheet 30 is 0.2 mm or more and 4.0 mm or less.
Further, as the main material of the optical sheet 30, for example, polycarbonate, acrylic-styrene copolymer, polystyrene, styrene-butadiene-acrylonitrile copolymer, or cycloolefin polymer may be used. Moreover, you may have the transparent particle disperse | distributed in the main material, and the refractive index of these main materials and the refractive index of a transparent particle differ. Here, the difference between the refractive index of the main material and the refractive index of the transparent particles is preferably 0.01 or more and 0.5 or less. The average particle size of the transparent particles is desirably 0.5 μm or more and 30.0 μm or less.

  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. Two or more kinds of these transparent particles may be mixed and used. 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.

  In particular, the substrate 31 of the optical sheet 30 may have a single layer structure or a multilayer structure, and may include a transparent layer. The optical sheet 30 may be manufactured by an extrusion method, a casting method, or an injection method, or may be manufactured by a UV curing method. When prepared by the UV curing method, a UV curable resin is applied on the substrate 31, a mold having a desired shape is pressed, and UV irradiation is performed to obtain an optical layer. As the base material 31, a film of PET (polyethylene terephthalate), polycarbonate, acrylic, or polypropylene well known in the art can be used.

  The diffusion sheet 13 and the light guide plate 12 can use the same main material as that of the optical sheet 30 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 optical layer while scattering, it is desirable that the average particle diameter of the transparent particles is 0.5 μm or more and 30.0 μm or less. Alternatively, the main material may have a structure having fine cavities containing air, and the diffusion performance may be obtained by the difference in refractive index between the main material and air. Further, a reflection pattern or a geometric structure may be provided on the surface.

Next, a method for forming the surface shape of the optical sheet 30 will be described in detail.
In the present embodiment, the surface shape of the optical sheet 30 is formed using a cylindrical mold (mold roll). That is, the reverse shape (inverted shape) of the surface shape of the optical sheet 30 shown in FIG. 2 formed on the surface of the cylindrical mold is transferred (replicated) to the surface of the optical sheet. The optical sheet 30 of the backlight unit 10 is obtained by cutting out an optical sheet itself having a surface formed by a mold in this way, or a part of the optical sheet.

Further, the surface shape of the cylindrical mold is a shape corresponding to the surface shape of the optical sheet 30, and therefore satisfies the following conditions.
A plurality of optical elements for forming a plurality of optical elements 33 that are spaced apart from each other on one surface of the optical sheet 30 are formed on the mold forming surface for forming the optical elements 33 on the surface 31 a of the optical sheet 30. It has a formation part. The plurality of optical element forming portions are arranged so that the position of the other optical element forming portion satisfies the following first and second conditions with respect to the position of any one optical element forming portion (is a set) ).

(First condition)
360: θ2 = θ2: θ1
Here, the cylindrical shape of FIG. 3 may be considered as the shape of the mold itself, and θ1 is a straight line connecting the position (coordinate of point A) of any one optical element forming portion and the central axis of the cylinder, This is the smaller angle among the angles formed by the position of the other optical element forming portion (the coordinates of point B) and the straight line connecting the central axis of the cylinder. θ2 (= 360−θ1) is the larger angle.

(Second condition)
The position of one optical element forming portion and the position of another optical element forming portion are different on a coordinate axis (coordinate axis direction) parallel to the central axis of the cylinder.
Further, preferably, the following third condition is satisfied.

(Third condition)
P2 ² /(R2·π)·0.5≦D≦P2 ² / (R2 · π) · 2
Here, D is a distance on a coordinate axis parallel to the central axis of the cylinder of point A and point B. R2 is the diameter of the cylinder. P2 is the maximum width of the optical element forming portion.

In addition, when copying directly from the mold in this way, the mold has a reverse shape of the surface shape of the optical sheet 30. Furthermore, when passing through a plurality of intermediate plates, the reverse shape of the surface shape (concave shape) ) Or the same surface shape (convex shape) is formed on the mold surface.
Moreover, as a processing method of the mold surface, generally known methods such as engraving and corrosion methods are exemplified.

(Effect of this embodiment)
(1) The optical sheet 30 is an optical sheet that collects and / or diffuses incident light, and is a plurality of optical elements 33 arranged on one surface (front surface in the present embodiment) spaced apart from each other. Have If the plurality of optical elements 33 has a cylindrical surface on one surface 31a, the positions of the other optical elements 33 relative to the position of any one optical element 33 are the following (a) and (b). Arranged to meet.

(A) The smaller angle among the angles formed by the straight line connecting the position of one optical element 33 and the central axis of the cylindrical surface and the straight line connecting the position of the other optical element 33 and the central axis of the cylindrical surface. When θ1 is set and the larger angle is θ2, 360: θ2 = θ2: θ1 (first condition)
(B) The position of one optical element 33 differs from the position of another optical element 33 in the direction of the central axis of the cylindrical surface (second condition)

  Thereby, the optical sheet 30 has a plurality of optical elements 33 optimally arranged on one surface 31a. More specifically, in the optical sheet 30, the optical elements 33 are arranged at a preferable filling rate, and the optical sheet 30 becomes a high-intensity optical sheet. Furthermore, when the optical sheet 30 has such a shape, the mold can be easily created.

  Further, the optical sheet 30 does not have a biased overlapping portion when viewed with a single optical element, such as when a planar arrangement such as a hexagonal arrangement is overlapped, or a biased change in optical characteristics due to this. Moreover, there is no useless gap and excessive overlap as in the case of random arrangement.

Furthermore, since the optical sheet 30 has an arrangement of optical elements with a different concept from the conventional coordinate system, moire with other optical sheets (such as a diffusion sheet) and a liquid crystal panel can be avoided. In addition, in the optical sheet, an effect of seamless processing and moiré avoidance is exhibited even in an arrangement with a low filling rate where no overlap occurs.
Furthermore, by using a cylindrical mold, it is possible to easily process an array of optical elements having a preferable filling rate without joints.

(2) When the distance between the position of one optical element 33 and the position of the other optical element 33 in the central axis direction of the cylindrical surface is D, the diameter of the cylinder is R, and the maximum width of the optical element is P,
P ² /(R·π)·0.5≦D≦P ² / (R · π) · 2
Is satisfied (the third condition is satisfied).
As a result, the optical sheet 30 has a better arrangement of the optical elements 33. Further, the optical sheet 30 can enjoy the effect (1) described above while avoiding moire even when the optical elements 30 are arranged to satisfy the distance D.

(3) The optical element 33 is a microlens or a polygonal pyramid lens.
Accordingly, the optical sheet 30 is configured using a micro lens or a polygonal pyramid-shaped lens having high performance.
(4) The other surface (back surface in the present embodiment) 31b of the optical sheet 30 is formed in a flat surface, optical elements are arranged, fine irregularities are formed, or a combination thereof.
Thereby, the other surface 31b can exhibit the function as an incident surface.

(5) A portion other than the arrangement portion of the optical element 33 on the one surface 31a of the optical sheet 30 is formed on a flat surface, fine irregularities are formed, and other optical elements are arranged.
Thereby, the unit lens 32 such as a prism can be arranged, and the other surface can be provided with a required function.

(6) The thickness of the optical sheet is 0.2 mm or more and 4.0 mm or less.
Here, in recent years, there has also been a movement in the light guide plate that shifts from the conventional printing method to a method in which optical elements are arranged. The arrangement of the optical elements of the optical sheet 30 as in the present embodiment can be expected to bring about the same effect also in the light guide plate 12. Therefore, the thickness of the optical sheet to be manufactured is set to 0.2 mm or more suitable for the thickness of the optical sheet 30 and 4.0 mm or less suitable for the thickness of the light guide plate 12. This does not limit the thickness due to the arrangement of the optical elements 33, but when considered as a final product, if the thickness is less than 0.2 mm, there is a high possibility that the optical sheet 30 cannot withstand bending use. This is because if the thickness exceeds 0.0 mm, the film is too thick and cannot be incorporated into the display device.

(7) The difference between the refractive index of the main material and the refractive index of the transparent particles is 0.01 or more and 0.5 or less. This is because if the difference in refractive index is smaller than 0.01, there is a high possibility that sufficient light scattering performance will not be obtained, and if the difference in refractive index is higher than 0.5, the collection of optical sheets is caused by unexpected stray light. This is because there is a high possibility that the optical function is lowered.

(Modification of the embodiment)
(1) The backlight unit 10 may be configured as shown in FIG.
FIG. 5 shows a configuration example of the direct-type backlight unit 10. In this configuration, the light K from the light source 11 enters the diffusion plate 15. The incident light is emitted from the exit surface 15 a of the diffusion plate 15 and passes through the optical sheet 30. Finally, the light transmitted through the optical sheet 30 is emitted as L from the emission surface and is incident on the liquid crystal panel 20. It should be noted that the number of optical sheets may be increased or decreased as appropriate, not just those listed in this configuration example.

(2) As the optical sheet on the light source side used in combination with the optical sheet 30, a reflective polarization separation sheet, a diffusion sheet, a prism sheet, or the like can be used as appropriate.
(3) The mold for manufacturing an optical sheet is not limited to a cylindrical shape, and may be a flat plate shape. In this case, the formation surface of the surface of the optical sheet 30 in the flat plate-shaped mold is such that a plurality of optical element forming portions satisfy the first to third conditions if the formation surface is a cylindrical surface shape. It becomes.

(Optical sheet manufacturing method)
As shown in FIG. 6 (items of “optical element” and “arrangement”), a mold roll engraved with an array of various microlenses was prepared.
A mold roll was placed close to the extruder. The thermoplastic polycarbonate resin sheet was melted and molded by an extruder, and the sheet was molded by a mold roll before being cooled and cured to obtain an extruded sheet having a shape on the surface. Here, M1201 from Teijin Chemicals Ltd. was used as the thermoplastic polycarbonate. The extruded sheet for an optical sheet had a thickness of 320 μm and was cut into a square of 415 mm × 730 mm and used for evaluation. In addition, the extruded sheet assuming the light guide plate had a thickness of only 2.0 mm without changing the surface shape.

(Evaluation of optical sheet)
The obtained optical sheet was incorporated into a simple display, a white screen was displayed, and the brightness of the center was measured from the normal direction of the screen at a distance of 50 cm with SR-3A manufactured by Topcon. The configuration of the backlight unit is an edge light system, and a light guide plate on which white dots are printed in order from the bottom, a diffusion film of Hz89, an optical sheet, and a polarization separation reflection sheet DBEF. When measuring the extrusion sheet supposing a light guide plate, it was set as the structure of the optical sheet, the diffusion film of Hz89, a commercially available microlens sheet | seat, and the polarization separation reflection sheet DBEF. The brightness is set to a range where 0.80 or more can be used as compared with the conventional one.

  Also, the moire was confirmed by using only a diffuser plate and an optical sheet having a total light transmittance of 65% using a direct type backlight unit in order to see interference with the liquid crystal panel. In the extruded sheet assuming the light guide plate, moire was confirmed with the configuration of only the optical sheet using an edge light type backlight unit. Since moiré is visually confirmed, it was evaluated based on the number of subjects determined to be no problem among the five subjects.

  In cases other than random (Example 5), the microlenses are overlapped at a filling rate of 78.5% or more. In addition, in the case of random, the microlenses overlap regardless of the filling rate.

(Evaluation results)
As shown in FIG. 6, in Examples 1 to 7 related to the optical sheet, moiré was greatly improved compared to Comparative Example 1 in the conventional arrangement. Strictly speaking, in Example 2 in which the coefficient of the formula (2) is an unfavorable value (0.4), it is impossible to say that there is no moire. Also, in all of Examples 1 to 7 except Example 3, since the overlap between the microlenses is moderate, the luminance ratio is good within a range of 0.80 to 1.10. As a result. On the other hand, in Example 3, although the coefficient of the formula (2) was an unsuitable value (2.1), there was no problem with moire, and the luminance was reduced to 0.75.

  Example 6 is an example in which a portion other than the optical element of Example 1 is formed into a prism shape. In Example 6, a higher luminance than that in Example 1 was obtained, which was good. If it is not a prism but a simple rough surface, a non-uniformity eliminating effect can be imparted.

  Moreover, Example 7 is an example which provided the uneven | corrugated shape to the back surface (opposite surface which has an optical element) of an optical sheet. In Example 7, since the uneven shape exhibited the effect of improving the brightness, a higher brightness than that in Example 1 was obtained. Although not shown in FIG. 6, in addition, a non-uniformity eliminating effect can be imparted, and the moire improving effect was not impaired.

  Example 8 is an example assuming a light guide plate. In Example 8, a uniform appearance without moire was obtained. Further, in Example 8, a higher luminance improvement effect was obtained as compared with the conventional printed dot type light guide plate.

  As described above, by using the optical sheet of the present embodiment (Examples 1 to 8), it does not cause moiré with other display parts such as a panel using the existing arrangement in an array with a wide filling rate. High brightness can be obtained.

  DESCRIPTION OF SYMBOLS 1 Display apparatus, 10 Backlight unit, 11 Light source, 12 Light guide plate, 13 Diffusion sheet, 14 Reflective polarization separation sheet, 20 Liquid crystal panel, 30 Optical sheet, 31 Substrate, 31a Surface, 31b Back surface, 32 Unit lens, 33 Optics element

Claims (10)

In an optical sheet that collects and diffuses incident light,
A plurality of optical elements arranged on one surface and spaced apart from each other;
The plurality of optical elements include any one optical element, and another optical element arranged so as to satisfy the following (a) and (b) if the one surface has a cylindrical surface shape: Comprising a pair of configured optical elements,
If the one surface has a cylindrical surface shape, the plurality of optical elements are arranged so as to be connected by screw-like lines on the cylindrical surface ,
When the distance between the position of the one optical element and the position of the other optical element in the central axis direction of the cylindrical surface is D, the diameter of the cylindrical surface is R, and the maximum width of the optical element is P ,
P ² /(R·π)·0.5≦D≦P ² / (R · π) · 2
An optical sheet characterized by satisfying
(A) The smaller of the angles formed by the straight line connecting the position of the one optical element and the central axis of the cylindrical surface and the straight line connecting the position of the other optical element and the central axis of the cylindrical surface When the angle is θ1 and the larger angle is θ2, 360: θ2 = θ2: θ1 (b) The position of the one optical element and the position of the other optical element in the central axis direction of the cylindrical surface The position is different The optical sheet according to claim 1, wherein the optical element is a microlens or a polygonal pyramid-shaped lens. 3. The optical sheet according to claim 1, wherein the other surface is formed as a flat surface, optical elements are arranged, fine irregularities are formed, or a combination thereof. Portion other than the arrangement portion of the optical element in said one surface is formed into a flat, fine irregularities are formed, or any one of claims 1 to 3 other optical elements, characterized in that is placed The optical sheet according to Item. The optical sheet according to any one of claims 1 to 4 , wherein the thickness is 0.2 mm or more and 4.0 mm or less. Comprising the optical sheet according to any one of claims 1 to 5 ,
A light source, and a diffuser plate that diffuses the light emitted from the light source and emits the diffused light; and
With
The backlight unit characterized in that the light emitted from the diffusion plate is incident on the optical sheet to be transmitted and emitted. Comprising the optical sheet according to any one of claims 1 to 5 ,
A light source, and a light guide plate that enters and guides the light emitted from the light source, and emits the light.
The backlight unit, wherein the light emitted from the light guide plate is incident on the optical sheet to be transmitted and emitted. The backlight unit according to claim 6 or 7 is provided,
An image display element that defines a display image according to transmission or non-transmission in pixel units,
The display device, wherein the backlight unit is arranged so that light emitted from the optical sheet is incident on a back surface of the image display element. In the method of manufacturing an optical sheet that collects and diffuses incident light,
Forming a plurality of optical elements spaced apart from each other on one surface of the optical sheet;
The plurality of optical elements include any one optical element, and another optical element arranged so as to satisfy the following (a) and (b) if the one surface has a cylindrical surface shape: Comprising a pair of configured optical elements,
If the one surface has a cylindrical surface shape, the plurality of optical elements are arranged so as to be connected by screw-like lines on the cylindrical surface ,
When the distance between the position of the one optical element and the position of the other optical element in the central axis direction of the cylindrical surface is D, the diameter of the cylindrical surface is R, and the maximum width of the optical element is P ,
P ² /(R·π)·0.5≦D≦P ² / (R · π) · 2
The manufacturing method of the optical sheet characterized by satisfy | filling .
(A) The smaller of the angles formed by the straight line connecting the position of the one optical element and the central axis of the cylindrical surface and the straight line connecting the position of the other optical element and the central axis of the cylindrical surface When the angle is θ1 and the larger angle is θ2, 360: θ2 = θ2: θ1 (b) The position of the one optical element and the position of the other optical element in the central axis direction of the cylindrical surface The position is different In an optical sheet manufacturing mold for manufacturing an optical sheet that performs at least one of condensing and diffusing incident light,
The forming surface that forms one surface of the optical sheet has a plurality of optical element forming portions for forming a plurality of optical elements that are spaced apart from each other on the one surface of the optical sheet,
The plurality of optical element forming portions include any one optical element forming portion and another optical element arranged so as to satisfy the following (a) and (b) when the forming surface has a cylindrical surface shape: And a pair of optical element forming parts composed of a forming part,
If the one surface has a cylindrical surface shape, the plurality of optical element forming portions are arranged so as to be connected by screw-like lines on the cylindrical surface ,
The distance between the position of the one optical element forming portion and the position of the other optical element forming portion in the central axis direction of the cylindrical surface is D, the diameter of the cylindrical surface is R2, and the outermost of the optical element forming portion is When the major is P2,
P2 ² /(R2·π)·0.5≦D≦P2 ² / (R2 · π) · 2
A mold for producing an optical sheet characterized by satisfying the above.
(A) An angle formed by a straight line connecting the position of the one optical element forming portion and the central axis of the cylindrical surface and a straight line connecting the position of the other optical element forming portion and the central axis of the cylindrical surface. When the smaller angle is θ1 and the larger angle is θ2, 360: θ2 = θ2: θ1 (b) The position of the one optical element forming portion in the central axis direction of the cylindrical surface The position of the other optical element forming portion is different

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