JP2008310251A - Optical sheet, back light unit, and display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently take out light from a light source and further to suppress unevenness of luminance. <P>SOLUTION: An optical sheet 3 is constituted by joining a light shielding sheet 14 in which apertures 12 and light shading parts 13 are alternately arranged to a diffusion board 11 via an adhesive layer 15 and further joining a lens sheet 16 constituted of a lens part 18 where array-shaped lenses 18A are arranged on one surface and a lens sheet base material 17 to the light shielding sheet 14. Each aperture 12 is provided so as to face each unit lens 18A. In the aperture 12, a light translucent projection 20 of a convex curved surface shape is caused to project towards the lens sheet 16 from a diffusion board 11 side and its top 20a is brought into contact with the lens sheet base material 17. The light translucent projection 20 is formed by protruding an adhesive consisting of a resin applied before hardening of the adhesive layer 15 into the aperture 12 by pressing the adhesive with the light shielding sheet 14. Air layers are provided between light shading parts 13, 13 at both sides of the light translucent projection 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to, for example, an optical sheet suitable for controlling an illumination optical path to a liquid crystal display element, a backlight unit using the optical sheet, and a display device.

In recent years, liquid crystal display devices (LCDs) using liquid crystal panels have been used for notebook personal computers, personal computer displays, image display means for information terminal devices, image display means for information appliances such as large-screen TVs, and mobile phones and personal use. It has been used in various fields as an image display means of a portable information terminal (PDA: Personal Digital Assistance).
In a display device represented by a liquid crystal display device, a type having a built-in light source necessary for recognizing provided information is remarkably widespread. Such a liquid crystal display device is, for example, a light transmission type, and a so-called backlight is used as a surface light source device in which a light source is disposed on the back side of the liquid crystal panel, and light from the light source is converted into surface light emission to irradiate the liquid crystal panel. Is adopted.

The backlight system can be broadly classified as follows: a light source such as a cold cathode fluorescent tube (CCFT) is attached to the side edge of a flat light guide plate, and the light from the light source is reflected multiple times within the light guide plate. There are a light guide method (edge light method) and a direct type method in which a light source is arranged on the back surface of a liquid crystal panel without using a light guide plate.
In a direct type backlight in which a plurality of cold cathode tubes are arranged in parallel, the shape of a cold cathode tube or an LED as a light source can be directly visually recognized through the diffusion plate. Therefore, the diffusion plate is very light scattering. A synthetic resin plate is used. For this reason, the diffusion plate usually needs to have a thickness of about 1 m to 3 m, but due to the thickness, there is a considerable amount of light absorption, and there is a problem that the amount of light from the light source is reduced and the liquid crystal screen display becomes dark.

As an optical sheet for solving this problem, for example, brightness enhancement films (BEF; DBEF; EBEF: registered trademark) shown in Patent Documents 1 to 3 are widely used. The brightness enhancement film is a film in which roof-shaped unit prisms having a triangular cross section are arranged in one direction on a sheet-like member. When the brightness enhancement film is used for a display device, the brightness in the normal direction on the axis, that is, the display screen can be increased by reducing the off-axis brightness.
In these display devices, two brightness enhancement films are stacked and combined so that the parallel directions of the prism groups are substantially orthogonal to each other. As a result, it is possible to obtain an amount of light having a desired luminance in a direction that matches the visual direction of the viewer while reducing power consumption.
In the optical sheet as described above, the light from the light source is finally refracted on the surface of the prism and emitted toward the liquid crystal panel at a controlled angle, thereby increasing the light intensity in the visual direction of the viewer. Can be controlled. However, at the same time, there is a problem that the light component due to reflection or refraction at the exit surface of the unit prism is wasted in the lateral direction away from the liquid crystal panel without proceeding in the visual direction of the viewer. In particular, when the liquid crystal panel is angled in the horizontal direction with respect to the visual direction, there is a problem in that the brightness is rapidly reduced.

In order to overcome such drawbacks, as described in Patent Document 4 below, for example, a backlight unit using an optical sheet having a repetitive array structure of unit lenses instead of a prism has been proposed.
The liquid crystal display device described in Patent Document 4 includes a liquid crystal panel and light source means for irradiating the liquid crystal panel with light from the back side, and an array for guiding light from the light source to the liquid crystal panel. A light-shielding sheet having a lens-shaped lens layer and having an opening outside the lens layer focal plane that is in a positional relationship where an image is formed inside the liquid crystal layer by the light-shielding sheet or lens layer. A backlight unit having is described.
The optical sheet of the liquid crystal display device is arranged at a position where the individual unit lenses of the lens layer and the opening of the light shielding sheet face each other at 1: 1. The light shielding sheet is configured by alternately arranging openings and light shielding portions.

According to the liquid crystal display device according to Patent Document 4, since the opening functions as a slit, light having a narrowed scattering angle passes through the lens and enters the lens. Therefore, the light that is wasted in the lateral direction by reflection or refraction can be reduced without proceeding in the viewer's visual direction.
On the other hand, the optical sheet using the brightness enhancement film described in Patent Documents 1 to 3 controls the viewing angle by refraction and total reflection of the prism, but the liquid crystal display device described in Patent Document 4 has an opening portion and a light shielding portion. In order to control the progress of light using the light shielding sheet and the lens array, the viewing angle is narrower than that of the optical sheet using the brightness enhancement film.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500 JP 2000-284268 A

Incidentally, the conventional optical sheet described in Patent Document 4 has the following problems.
That is, the light-shielding sheet is laminated opposite to the light guide plate of the light source, but when the thickness of the light-shielding sheet is thin, the lens layer facing the opening formed by the light-shielding part is easily in contact with the light guide plate. Then the air layer is lost. In this case, since the refractive index of the lens layer and the light guide plate is close to each other compared to the air layer, the influence of the refractive action is less than that of the light transmitted through the portion where the air layer is present, and the lens layer and the light guide plate are in contact with each other. The light incident through the part goes almost straight.
For this reason, there is a problem that the variation in the emission angle of the light traveling toward the lens layer increases, and the condensing performance of the lens layer deteriorates. In particular, light incident at a large incident angle from the light guide plate is not incident on the lens layer facing the opening, but is incident on other surrounding lens layers to be attenuated and light loss or transmitted through the lens layer. There is also a problem that it may cause luminance unevenness.

Further, in the optical sheet described in Patent Document 4 described above, the light shielding sheet formed by alternately arranging the air layer and the light shielding portion is disposed on the lens layer and / or the light guide plate through an adhesive layer made of a synthetic resin adhesive. May be joined. For example, when a light-shielding sheet provided on a lens layer is closely bonded to an adhesive layer applied to the entire surface of the light guide plate, the adhesive layer before curing that is pressed by the light-shielding part is adjacent to the light-shielding part. The phenomenon of being hardened in a state where the opening was filled and the air layer was lost was generated.
In this case, the opening filled with the adhesive has a smaller refractive index difference from the front and rear light guide plate, lens layer, or other adhesive layer than the case where the opening is an air layer. Incident light incident at an angle is transmitted with a small refractive index, enters the unit lens around the opposing unit lens in the same manner as described above, goes straight, attenuates and results in light loss or transmission through the lens layer. However, there is a problem similar to that described above, which causes uneven brightness.
In addition, the state of each opening varies, such as the lens layer and the light guide plate deforming and contacting at the opening, or the air layer is lost by filling the opening with the adhesive before solidification, etc. Due to the non-uniformity, there was a problem of further uneven brightness.

In addition, a light guide plate such as an edge light type surface light source is not used as a light source. For example, when a direct type backlight unit is used, a light diffusion plate or a light diffusion film is provided between the optical sheet and the light source. The arrangement is common. In this case, since the light diffusing plate and the light diffusing sheet are laminated on the light shielding sheet, problems such as non-uniform deformation and filling of individual openings occur as described above.
In particular, when a light diffusing plate or a light diffusing sheet is bonded to an optical sheet with a light-transmitting adhesive layer made of an adhesive or an adhesive, the adhesive layer is pressed against the opening side. The air layer can easily be lost.
For this reason, it is conceivable to increase the thickness of the light-shielding sheet, but there is a problem that it is difficult to stably form a sufficient thickness if the light-shielding sheet is formed by printing or transfer as in the prior art.

  The present invention has been made in view of the above-described problems, and an optical sheet that can efficiently extract light from a light source and suppress uneven luminance, and a backlight unit and a display using the optical sheet. An object is to provide an apparatus.

An optical sheet according to the present invention includes a lens member in which arrayed lenses are arranged on one surface, a light shielding member in which openings facing each of the lenses are arranged, and a lens member opposite to the lens member. An optical sheet provided with a light diffusing member provided, wherein the opening has a light transmissive protrusion projecting inward from the light diffusing member side toward the lens member side, and on both sides of the light transmissive protrusion. An air layer provided between the surface and the surface partitioning the opening is provided, and the light transmitting protrusion has a refractive index larger than that of the air layer.
According to the present invention, by providing a light-transmitting protrusion at the opening, the shape of the opening is stabilized and the light transmission characteristics at each opening are stabilized. Brightness unevenness due to the opening and the lens is less likely to occur. Moreover, since the light passing through the vicinity of the center of the opening travels substantially straight through the light-transmitting protrusion and enters the opposing lens, the central region can ensure the same high brightness as the prism type. In addition, light incident at a large incident angle from the end of the opening travels almost straight through the light-transmitting protrusion, and part of the light is totally reflected back at the interface with the air layer of the protrusion and the other one. Since the part refracts and exits the air layer having a relatively low refractive index and then refracts and enters the lens member again, it faces the opening while suppressing the spread of brightness compared to the case where the entire opening is embedded with resin. It is possible to reduce the light incident on the lenses in the vicinity of the lens, and to increase the peripheral brightness of the facing lens and broaden the brightness distribution as compared with the case where the entire opening is filled with an air layer.
Note that in order for the optical sheet according to the present invention to function effectively, it is necessary that the air layers on both sides of the light-transmitting protrusions in the opening are appropriately held. Furthermore, a desired luminance distribution can be obtained by controlling the area of the contact portion between the resin and the lens member that forms the light-transmitting protrusion that fills the opening. For example, if the contact area between the light-transmitting protrusion and the lens member is increased, the front luminance is decreased but the luminance distribution can be widened. If the contact area is decreased, the luminance distribution is narrowed but the front luminance is increased.

Moreover, it is preferable that the light-transmitting protrusion is a convex curved surface whose top is in contact with the lens member.
As a result, the luminance distribution can be distributed so that the front luminance is kept high and the decrease in peripheral luminance is suppressed. In addition, if the light-transmitting protrusion is formed in a cylindrical surface shape, a part of the light having a large incident angle incident from the end of the opening is totally reflected at the interface of the light-transmitting protrusion and the lens of the facing lens is opposed. Light emitted to the outside can be reduced.
Moreover, it is preferable that the interface with the air layer of the light transmissive protrusion in the opening is a curved surface or an inclined surface.
By forming the interface with the air layer on both sides of the light-transmitting protrusion on a curved surface or an inclined surface, the spread of the luminance distribution can be suppressed, and a decrease in the periphery of the luminance distribution through the facing lens can be suppressed.

The light shielding member has openings and light shielding portions alternately arranged, and the light shielding member and the light diffusing member are joined by an adhesive layer made of an adhesive, and the light shielding member and the light are in a stage before the adhesive is cured. You may make it form a light-transmissive protrusion by making a part of adhesive layer protrude in an opening part by mutually pressing a diffusion member.
Since the adhesive of the adhesive layer can be substantially uniformly projected into the opening and cured, the light transmissive protrusion can be easily formed in the manufacturing process of the optical sheet.
In this case, the adhesive layer preferably has a thickness before pressing of 3 μm or more and 20 μm or less.

The backlight unit according to the present invention includes any one of the optical sheets described above and a light source unit that is disposed on the opposite side of the optical sheet from the lens member and that emits light.
A display device according to the present invention includes the above-described backlight unit and a liquid crystal display unit that displays an image using light from the backlight unit as display light.
In these cases, the same effects as the above-described optical sheet are exhibited.

  According to the optical sheet, the backlight unit, and the display device according to the present invention, the light transmitting protrusions are provided in the openings so that the shape of the openings is stabilized and the light transmission characteristics in each opening are stabilized. The variation in the emission angle of the lens is suppressed, and uneven brightness due to the opening and the lens facing each other is less likely to occur. In addition, since the light passing through the vicinity of the center of the opening travels substantially straight through the light-transmitting protrusion and enters the opposing lens, a large luminance equivalent to that of the prism type can be secured. In addition, light incident at a large incident angle from the end of the opening travels almost straight through the light-transmitting protrusion, and part of the light is totally reflected back at the interface with the air layer of the protrusion and the other one. Since the portion is refracted and emitted from the air layer having a relatively low refractive index and then refracted and incident again on the lens member, the spread of luminance is suppressed and the entire opening is air-filled compared to the case where the entire opening is buried with resin. It is possible to increase the luminance distribution in the facing lens by increasing the peripheral luminance as compared with the case of filling with layers. Therefore, it is possible to efficiently extract light from the light source and to suppress luminance unevenness.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The optical sheet which concerns on embodiment of this invention is demonstrated with the backlight unit and display apparatus using the same.
1 is a schematic cross-sectional view showing a schematic configuration of a display device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the optical sheet of FIG. 1, and FIG. 3 shows an opening and a light-transmitting protrusion of the light-shielding sheet. FIG. 4 is a diagram showing a total reflection angle of light incident on the opening with a large incident angle in FIG. 3, and FIG. 5 is a path of incident light entering the opening from the end side of the opening. It is explanatory drawing which shows the relationship with the structure of an opening part, (a) is embodiment, (b) is the state with which the opening part was satisfy | filled with resin, (c) shows the state with which the opening part was satisfy | filled with air. FIG. 6 and FIG. 6 are graphs showing the luminance distribution of light transmitted through the unit lens of the optical sheet according to Examples, Comparative Examples, and Conventional Examples of the present invention.
As shown in FIG. 1, in the display device 1 according to the present embodiment, a light source unit 2, an optical sheet 3, and a liquid crystal display unit 4 are stacked in this order, and display control is performed by an image signal from the liquid crystal display unit 4 upward in the figure. By emitting the displayed light, for example, an image having a rectangular shape in plan view is displayed.
The light source unit 2 and the optical sheet 3 constitute a backlight unit 5.
Hereinafter, based on such an arrangement, the upper direction in FIG. 1 may be simply referred to as a display screen side or an emission side, and the lower direction may be simply referred to as a back side or an incident side.

In FIG. 1, a light source unit 2 includes a plurality of light sources 7 in which linear light emitting units extending in the depth direction on the paper surface are spaced apart from each other in the horizontal direction in the figure, and covers these light sources 7 from the back side and opens to the display screen side. A direct type system composed of the reflector 8 is employed.
As the light source 7, for example, a cold cathode tube or the like is used, but an LED light source in which a plurality of LED elements are arranged on a line along the depth direction of the paper surface may be employed.
However, the light source unit 2 is not limited to such a configuration as long as white light can be emitted to the back side of the optical sheet 3, and a light source unit having any known configuration may be employed. For example, an edge light type surface light source in which a line light source is arranged on the side surface of the light guide plate may be employed.

The optical sheet 3 shown in FIGS. 1 and 2 collects a part of the light emitted from the light source unit 2 to the display screen side and transmits it to the display screen side, and reflects other light to the light source unit 2 side. Then, the light is reflected again by the reflecting plate 8 and emitted to the display screen side.
The back side of the optical sheet 3 is bonded to the base material 10 for giving rigidity to the optical sheet 3, but the base material 10 may be included in the optical sheet 3. Alternatively, the base material 10 may not be provided.
The optical sheet 3 includes a light diffusing plate 11 as a light diffusing member for diffusing light incident from the back side toward the display screen side from the back side, a light shielding member in which openings 12 and light shielding portions 13 are alternately arranged. Display of the light shielding sheet 14, the adhesive layer 15 formed by applying a layer of an adhesive (adhesive) made of an ultraviolet curable synthetic resin for joining the diffusion plate 11 and the light shielding sheet 14, and the light shielding sheet 14 A lens sheet 16 as a lens member integrally formed on the screen side surface is laminated in this order.

Here, the base material 10 is formed of polycarbonate (PC), cycloolefin polymer, acrylic, polystyrene, polyethylene (PET) or the like well known in the field. Alternatively, those materials selected arbitrarily and blended in an appropriate ratio may be used.
Further, as the diffusing plate 11, glass having a total light transmittance (Tt) of 84% or more and a refractive index difference (Δn) with the adhesive layer 15 of 0.17 or less, such as polycarbonate, acrylic, polyethylene, and the like. A polymer film or sheet made of a material such as is used.
The diffuser plate 11 is a plate-like member provided at a position covering the display screen side of the light source unit 2 so as to diffuse light emitted from the light source unit 2 to the display screen side. Thereby, the uneven illuminance in the horizontal direction of the figure due to the plurality of light sources 7 can be suppressed, and an appropriate viewing angle can be given to the display light.
The diffusion plate 11 includes a transparent resin and transparent particles dispersed in the transparent resin, and the refractive index of the transparent resin is different from the refractive index of the transparent particles. The difference between the refractive index of the transparent resin and the refractive index of the transparent particles is preferably 0.02 or more. If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. Further, the difference in refractive index is preferably 0.5 or less.
The diffusion plate 11 needs to be transmitted to the display screen side while scattering the light incident on the diffusion plate 11. For this reason, the average particle diameter of the transparent particles contained in the diffusion plate 11 is desirably 0.5 μm to 10.0 μm, and more preferably 1.0 μm to 5.0 μm.

As the transparent resin of the diffusion plate 11, for example, a polycarbonate (PC) resin, an acrylic resin, a fluorine acrylic resin, a silicone acrylic resin, an epoxy acrylate resin, a methylstyrene resin, a fluorene resin, or the like can be used.
Moreover, as the transparent particles of the diffusing plate 11, 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 cross-linked products thereof; melamine-formalin condensate particles; PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetra Fluoropolymer particles such as fluoroethylene-hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer); silicone resin particles and the like. Two or more kinds of these transparent particles may be mixed and used.
And the plate-shaped diffusion plate 11 can be manufactured by disperse | distributing transparent particles in these transparent resins and extrusion-molding. The thickness of the diffusion plate 11 is desirably 1 mm to 5 mm. When the thickness is less than 1 mm, the diffusion plate 11 is thin and has no strain so that it is easily bent. On the other hand, if it exceeds 5 mm, the transmittance of light from the light source unit 2 is deteriorated.
In this embodiment, as an example, an MS (methyl methacrylate-styrene copolymer) resin having a refractive index of 1.57 is adopted as a transparent resin, and an MS resin filler having a refractive index of 1.50 is adopted as a transparent particle. The thickness of 11 is 3.0 mm.

The adhesive layer 15 is for laminating and integrating the diffusion plate 11 with the lens sheet 16 to which the light shielding sheet 14 is connected, and is made of a light-transmitting pressure-sensitive adhesive or adhesive. In this embodiment, an acrylic pressure-sensitive adhesive having a refractive index n1 = 1.54 is employed as an example, and the layer thickness T between the diffusion plate 11 and the lens sheet 16 is set to 20 μm, for example.
The light shielding sheet 14 is configured by alternately arranging openings 12 and light shielding portions 13. As shown in FIG. 2, the light shielding sheet 14 is formed in a stripe shape with a pitch P, a width (P-W), and a thickness t at the incident side interface on the back side of the lens sheet 16 in a plan view. . An opening 12 having a width W is formed between the light shielding portions 13, and constitutes a light shielding pattern that regulates the position of the incident range of scattered light incident on the lens sheet 16 from the diffusion plate 11 through the adhesive layer 15. .
In this embodiment, the light-shielding portion 13 has a stripe shape of P = 140 μm, P−W = 98 μm, and t = 10 μm as an example. For this reason, the width W of the opening 12 is 42 μm, and the ratio of the width between the opening 12 and the light shielding portion 13 is W: (P−W) = 3: 7.

As the material of the light-shielding part 13, an appropriate material can be adopted as long as at least the light-shielding property is obtained, but the light from the light source part 2 can be reused as illumination light by reflecting the light to the back side. In addition, it is preferable to use a light reflective material to form a light reflective layer. The light shielding portion 13 formed as such a light reflecting layer is formed by applying or transferring, for example, metal particles or ink obtained by dispersing and mixing high refractive index transparent particles such as titanium dioxide, and laminating a metal foil. Those formed, metal-deposited metal materials, and the like can be employed.
The reflectance of the light-shielding portion 13 is preferably a high reflectance, for example, preferably 83% or more, and more preferably 90% or more.
In the present embodiment, a configuration is adopted in which the reflectance is set to 86% by transferring and forming a white ink foil as an example of the light shielding portion 13.

In addition, the formation method of the light-shielding part 13 is not limited to the above-mentioned transfer method, You may use appropriate methods, such as a printing method, a photolithography method, and an extrusion molding method. For example, the surface on the back side of the lens sheet 16 is formed into an uneven shape corresponding to the cross-sectional shape of the light shielding part 13 by extrusion molding, and metal particles or high refractive index transparent particles are dispersed and mixed in the convex part on the back side. The light shielding part 13 can also be formed as a convex-shaped reflective film by applying the ink. In this case, since the opening 12 is formed in the concave portion formed by extrusion molding by applying the ink only to the convex portion, the manufacture becomes easy.
Also in this case, the convex shape is not limited to the convex shape having a rectangular cross section like the light shielding portion 13 in FIG. For example, a trapezoidal cross section that is reduced in width toward the back side or the display screen side, or a rectangular cross section or a cross-sectional shape obtained by rounding corners on the back side of the trapezoidal cross section can be adopted. In particular, according to the cross-sectional shape with rounded corners, when the reflective film is applied, the reflective film is also formed on the convex side surface, so that the light incident on the convex side surface can be reflected. Even if it is formed of a thin film, a light reflecting layer having a thickness in the height direction of the convex shape can be formed substantially like the light shielding portion 13.

Next, the lens sheet 16 has a light-transmitting lens sheet substrate 17 on the back side, and a lens portion 18 is arranged on the display screen side.
The lens unit 18 collects diffused light transmitted through the opening 12 and the lens sheet base material 17 to the display screen side, and thus a plurality of optical elements, for example, lenses that are unit lenses (sometimes referred to as unit lenses). 18A,... Are arranged in an array at a pitch P, facing the openings 12 at a ratio of 1: 1. The light shielding sheet 14 has a stripe shape for the purpose of preventing light transmitted through the opening 12 from entering the lens 18A adjacent to the corresponding lens 18A or further to the adjacent lens as much as possible.
The lens portion 18 has a lens surface 18a that is convexly formed on the display screen side and extends in a direction perpendicular to the paper surface of FIG. 2, and is on the incident side in the opening portion 12 on the center line of the opening portion 12 facing the focal position. It consists of a convex cylindrical lens array having a convex cylindrical lens arranged so as to be in the vicinity of the interface 12a as a unit lens 18A. That is, it is configured as a lenticular lens.
In this embodiment, the shape of the lens surface 18a is a cylindrical lens having a circular cross section with a radius of curvature of 70 μm and an opening angle of 86 ° as an example. However, a well-known appropriate lens surface shape, for example, a spherical surface or an elliptical surface, may be employed depending on the required light collecting performance. Further, in order to improve the light collection efficiency, an aspherical shape in which an ellipsoidal surface is used as a reference surface and correction is performed by a high-order term may be used.

The lens sheet base material 17 may be made of the same material as the lens portion 18, but may be formed of, for example, a fluorine polymer.
The lens unit 18 is made of, for example, a PET resin, a PC resin, PMMA (polymethyl methacrylate), COP (cycloolefin polymer), or the like, which is well known in the art, such as an extrusion molding method, an injection molding method, or a heat press. It can be formed by a molding method. Alternatively, it can be molded using an ultraviolet (UV) curable resin.

And in this embodiment, in each opening part 12 of the light shielding sheet 14, from the incident side interface 12a of the opening part 12 (the outgoing side interface of the adhesive layer 15), the outgoing side interface of the opening part 12 (the incident side interface of the lens sheet 16). ) Is provided with a light-transmitting protrusion 20 having a convex curved surface shape or a trapezoidal cross section. The light transmitting protrusion 20 advances into the opening 12 from the boundary with the light shielding parts 13, 13 which are both ends of the incident side interface 12 a of the opening 12, and the top 20 a is the lens sheet substrate 17 of the lens sheet 16. Abut or connect to
3 and 4 are enlarged views of the light transmitting protrusion 20 in the opening 12 of the light shielding sheet 14. In FIG. 3, the light transmissive protrusion 20 is a resin layer made of the same material as the adhesive layer 15 and has the same refractive index. The light-transmitting protrusion 20 has air layers 21 and 21 formed between both side portions 20b and 20b of the top portion 20a and light shielding portions 13 and 13 on both sides. Therefore, the opening 12 is filled with a resin layer composed of the light transmissive protrusion 20 and the air layers 21 and 21. The light-transmitting protrusion 20 is preferably formed so that the side portions 20b and 20b and the air layers 21 and 21 are line-symmetrical in terms of luminance balance, but may be asymmetrical.

By bringing the lens sheet base material 17 and the top 20a of the light transmitting protrusion 20 into contact with each other, the light transmitted through the center of the light transmitting protrusion 20 is transmitted almost without being refracted by the air layer and transmitted through the lens 18A. As a result, the front luminance per unit lens 18A can be increased.
Here, by controlling the contact area between the top portion 20a of the light transmitting protrusion 20 and the lens sheet substrate 17, a desired luminance distribution can be obtained per lens 18A. For example, as the contact area between the top portion 20a and the lens sheet substrate 17 increases, the front luminance decreases and the spread angle of the luminance distribution increases. However, if the area is too large, the large spread angle that does not contribute to the refractive action of the lens 18A. The front brightness is reduced by transmitting a large amount of light having the light. If the contact area between the top portion 20a and the lens sheet substrate 17 is reduced, the luminance distribution per lens 18A is narrowed and the front luminance is increased.
Therefore, when it is desired to increase the front luminance, it is necessary to set the contact surface between the lens base material and the resin layer so as not to become too large.
Further, light incident obliquely from the end of the opening 12 at an incident angle θ1 travels almost straight through the light-transmitting protrusion 20 and is refracted in the region of the air layer 21 and further refracted by the lens sheet substrate 17. Then, the light is incident on the lens portion 18 at the emission angle θ2, and the diffusion is suppressed and the light enters the lens 18A facing the opening 12 (see FIG. 5).

3 and 4 show a case where the interface between the light transmitting protrusion 20 made of a resin layer provided in the opening 12 and the air layer 21 forms a cylindrical surface.
Here, in FIG. 3, for example, the thickness t = 10 μm of the light shielding sheet 14, the width w = 50 μm of the opening 12, the refractive index n = 1.4 of the light transmitting protrusion 20, and the refractive index of the air layer 21 are n = Consider the case of 1. The radius of the cylindrical surface of the light-transmitting protrusion 20 that forms a substantially cylindrical surface is d, the angle that the light L1 that passes through one end of the opening 12 forms with the adhesive layer 15 is α, and the light-transmitting protrusion 20 Assume that the incident angle θ of the light L1 to the interface is θ.
When only the apex 20a of the light transmitting protrusion 20 is in contact with the lens sheet base material 17, θ = 0.81 + α (rad) is satisfied. Since the refractive index n of the resin of the light-transmitting protrusion 20 is 1.4 and the total reflection angle θo = 0.80 (rad) at the interface of the light-transmitting protrusion 20 is incident from the end of the light-shielding portion 13. It can be seen that the received light undergoes total reflection at the interface other than the light transmitted through the apex 20a (see FIG. 4). At this time, the emission angle of the light beam transmitted from the contact point (top portion 20a) between the light transmitting protrusion 20 and the lens sheet base material 17 is obtained as β = 68.2 °.

In the method of manufacturing the optical sheet 3, when the light shielding sheet 14 is formed integrally with the lens sheet 16, it can be formed by, for example, a transfer method. That is, after a photosensitive resin is applied on the lens sheet base material 17 side of the lens sheet 16, ultraviolet rays (UV) are irradiated from the lens portion 18 side to form exposed and unexposed portions. The exposed portion loses tackiness and the unexposed portion remains tacky. By laminating and peeling the white ink foil on this portion, the light shielding sheet 14 having the light shielding pattern in which the openings 12 and the light shielding portions 13 are alternately formed can be formed integrally with the lens sheet 16.
Next, with respect to the light shielding sheet 14 in which the light shielding portions 13 and the openings 12 are alternately arranged, an adhesive layer 15 is formed by applying an adhesive to the emission side end surface of the separately manufactured diffusion plate 11. The light shielding sheet 14 is bonded to the substrate. In this way, the optical sheet 3 is manufactured.

Here, in order to form, for example, a substantially cylindrical light transmitting protrusion 20 in the opening 12 of the light shielding sheet 14 described above, the diffusion plate 11 and the lens sheet 16 integrally joined to the light shielding sheet 14 are bonded together. At this time, this can be achieved by causing a part of the adhesive (adhesive material) of the adhesive layer 15 that joins the diffusion plate 11 and the light shielding sheet 14 to flow and bulge into the opening 12 by the bonding pressure. As the synthetic resin for the adhesive of the adhesive layer 15 that partially fills the opening 12 of the optical sheet 3, for example, an acrylic pressure-sensitive adhesive often used in this field is used.
Further, by using a resin having a high elastic modulus as the adhesive of the adhesive layer 15, the interface between the adhesive of the adhesive layer 15 protruding into the opening 12 and the air layer when the diffusion plate 11 and the light shielding sheet 14 are bonded is a cylinder. It is formed in a convex curved surface shape close to the surface, and this constitutes the light transmitting protrusion 20.
At the time of bonding, it is desirable to set the bonding pressure appropriately high so that the adhesive of the adhesive layer 15 is pushed into the opening 12 and comes into contact with the lens sheet substrate 17. In order for this adhesive to exhibit the desired characteristics described above, for example, an adhesive having a storage elastic modulus G ′ of 1.0 × 10 ⁵ Pa or more and 1.4 × 10 ⁵ Pa or less is used. The thickness of the adhesive layer 15 is suitably 3 μm or more and 20 μm or less, for example.
Here, when the storage elastic modulus G ′ is less than 1.0 × 10 ⁵ Pa, the fluidity is too high, and there is a problem that the adhesive contacts the entire surface of the lens sheet substrate 17 in the opening 12 when pressed. When the pressure exceeds 4 × 10 ⁵ Pa, the elastic modulus is too high and the adhesive cannot be sufficiently expanded into the opening 12 when pressed. Further, if the thickness of the adhesive layer 15 is less than 3 μm, the adhesive layer 15 cannot be swelled to the lens sheet base material 17 even if the pressing force is increased at the time of bonding, and the shape of the light transmitting protrusion 20 If the thickness exceeds 20 μm, an excessive amount of adhesive bulges into the opening 12 and contacts the entire surface of the lens sheet substrate 17 even with a slight pressure.

In addition, when the diffusion sheet 11 and the lens sheet 16 joined with the light shielding sheet 14 are bonded together by a roll type laminating machine, the contact pressure applied to the two rolls is in a range of 3.0 MPa to 6.0 MPa. Is desirable. If the contact pressure is less than 3.0 MPa, it is not sufficient to cause the adhesive (adhesive layer 15) to bulge in the opening 12 of the light shielding sheet 14 by pressing during bonding, and a contact pressure exceeding 6.0 MPa is applied. Since the adhesive (adhesive layer 15) is in contact with the entire surface of the opening 12, the front luminance is greatly reduced.
An example of a method for measuring the contact pressure between rolls is a method using pressure sensitive paper. In this method, the nip pressure between rolls can be measured by the color density of pressure-sensitive paper sandwiched between two rolls. By adjusting the pressure so that the color development of the pressure sensitive paper is constant over the roll width direction, the ratio of the adhesive (adhesive layer 15) that swells to the opening 12 of the light shielding sheet 14 is uniform over the entire sheet surface. An optical member free from luminance unevenness can be created.

The optical sheet 3 and the display device 1 according to the present embodiment have the above-described configuration. Next, the operation of the display device 1 will be described focusing on the operation of the optical sheet 3.
In FIG. 1, a part of the light emitted from the light source unit 2 is emitted directly from the light source 7 toward the diffusion plate 11, and the other light is reflected by the reflection plate 8 and then emitted toward the diffusion plate 11. Is done. Thereby, the back side of the optical sheet 3 is entirely illuminated. At this time, the illuminance unevenness corresponding to the arrangement pitch of the light sources 7 is mitigated by the action of the reflector 8 but remains to some extent.
The light traveling through the diffuser plate 11 is scattered by the transparent particles in the transparent resin of the diffuser plate 11 and travels as diffused light, which eliminates uneven illuminance of the light source unit 2 and has a spread angle in an appropriate angle range. The light enters the light shielding sheet 14.
In the light shielding sheet 14, the light passing through the opening 12 enters the lens sheet portion 16. The light reaching the other light-shielding part 13 is reflected to the back side according to the reflectance of the light-shielding part 13 except that part of the light is absorbed or transmitted, and is returned to the light source part 2 for reuse.

Here, all the light incident on the opening 12 enters the light transmissive protrusion 20, but the light transmissive protrusion 20, the adhesive layer 15, and the lens sheet 16 are all formed of a resin layer and are relatively refracted. Since the difference in rate is small, light having a relatively small incident angle travels almost straight and passes through the light-transmissive protrusion 20. In particular, the light L1 passing through the vicinity of the top 20a of the light transmitting protrusion 20 travels substantially straight without being emitted to the air layer 21 regardless of the incident angle.
On the other hand, as shown in FIG. 3 to FIG. 5A, the light transmitting protrusion from the diffusion plate 11 through the adhesive layer 15 in the vicinity of the large incident angle θ1 obliquely from the end of the opening 12 on the light shielding portion 13 side. The light L2 incident on the light 20 travels almost straight in the light-transmitting protrusion 20 and a part of the light L2 is totally reflected at the interface of the light-transmitting protrusion 20 and returned to the diffusion plate 11 side. After being refracted and emitted from the air layer 21, the light L2 travels straight through the air layer 21 having a relatively small refractive index and is refracted again by the lens sheet base material 17 of the lens sheet portion 16, and is thus relatively small. The light is emitted at an emission angle θ2.
Therefore, most of the light L <b> 2 is collected by the lens 18 </ b> A facing the opening 12 of the lens unit 18 of the lens sheet unit 16 and emitted toward the liquid crystal display unit 4. In this case, the ratio of incidence on the lens 18A around the lens 18A facing the opening 12 is small, and it is possible to suppress attenuation and loss of light amount, or transmission of the lens unit 18 and uneven brightness.

On the other hand, when the opening 12 is filled with a resin made of an adhesive as shown in FIG. 5B, the refractive index of the adhesive layer 15 and the refractive index of the resin are close to each other. The light L2 incident at the angle θ1 travels straight without being refracted when entering the resin layer from the adhesive layer 15. Therefore, when the opening 12 is filled with resin, light that has spread more widely than the case where the opening 12 is not filled enters the lens unit 18. For this reason, when there is no air layer in the opening 12, lateral light that is not subjected to the condensing action of the lens 18A is wasted, leading to a reduction in front luminance. And the light which injects into the lens 18A of the outer periphery of the unit lens 18A facing the opening part 12 increases, and the malfunction which raise | generates brightness nonuniformity while light quantity loss increases occurs.
Further, when the opening 12 is entirely filled with an air layer as shown in FIG. 5C, when the light L2 is incident on the air layer of the opening 12, the boundary surface between the adhesive layer 15 and the air layer The light is refracted in the direction and is then refracted toward the display screen when entering the lens sheet 16. Compared with the adhesive layer 15 and the lens sheet base material 17 which are the front and rear resin layers, the air layer having a small refractive index refracts at a relatively large refraction angle and exits to the lens sheet 16 and exits to the central region. However, since the front luminance is high and the peripheral luminance is reduced, there is a problem that uneven luminance occurs.

Note that light that has entered the surrounding lens 18A that is not opposed from the opening 12 is emitted in an oblique direction toward the display screen due to the refractive action of the unit lens 18A that has entered.
The light emitted from the optical sheet 3 enters the liquid crystal display unit 4, and the light from a predetermined pixel region is controlled according to the polarization state of each pixel region controlled by a drive unit (not shown) based on the image signal. Is transmitted as display light, and an image having a viewing angle is displayed. At this time, if the amount of light that enters the pixel area other than the pixel area at the opposite position from the opening 12 increases, the luminance of the light transmitted through the pixel area at the opposite position decreases, causing luminance unevenness in the surrounding pixel area. In addition, since the emission angle of these lights becomes large, the radiance distribution becomes distorted, which causes a reduction in image quality.
Accordingly, it is preferable that the amount of light incident on the unit lens 18A other than the unit lens 18A at the opposing position from the opening 12 is small, and it is preferable that the range is at least from the unit lens 18A adjacent to the unit lens 18A at the opposing position.

Next, examples of the present invention will be described.
For the optical sheet 3, as an example, a light-transmitting protrusion 20 having a convex curved surface having a substantially cylindrical surface shape is formed in the opening 12 of the light-shielding sheet 14 by the same material as the adhesive, and the top of the light-transmitting protrusion 20. 20a is configured to be in contact with the lens sheet substrate 17 at one point. In the comparative example, the entire opening 12 is an air layer, and the remaining configurations of these examples and the comparative example are the same as those of the present embodiment. As a conventional example, the above-described conventional optical sheet formed by laminating a brightness enhancement film (RBFF) in the orthogonal direction was used.
And the result of having measured the light intensity distribution radiate | emitted from one unit lens 18A by attaching the light source part 2 of the same structure with respect to the optical sheet by these Examples, a comparative example, and a prior art example is shown in FIG. In the luminance distribution shown in FIG. 6, the luminance distribution having a normal distribution shape in which all of the example, the comparative example, and the conventional example have a luminance that peaks at a radiation angle of 0 ° and is distributed so that the luminance gradually decreases. .
The luminance distribution of the example is slightly narrower than the luminance distribution of the prior art, but can be wider than the comparative example in which the opening 12 is filled with an air layer.

As described above, according to the optical sheet 3 according to the present embodiment, since the light transmitting protrusion 20 made of resin is provided in the opening 12 of the light shielding sheet 14, the lens 18 that faces the opening 12 is provided on the lens 18. Incident light can be efficiently incident, and light having a large incident angle with respect to the opening 12 can be prevented from entering the surrounding lens unit 18 and causing light loss and luminance unevenness.
In addition, since the light passing through the vicinity of the center of the opening 12 travels substantially straight through the light-transmitting protrusion 20 and enters the opposing lens 18A, a large brightness equivalent to that of the conventional prism type can be secured in the central region. In addition, light incident from the end side of the opening 12 travels almost straight through the light-transmitting protrusion 20, and part of the light is totally reflected back at the interface with the air layer 21 of the protrusion 20, and the other A portion of the aperture 12 is refracted and emitted after being refracted into the air layer 21 having a relatively low refractive index, so that the lens sheet 16 is refracted and incident again. The light incident on the lens 18A in the vicinity of the lens 18A facing the portion 12 is reduced, and the luminance distribution is widened by increasing the peripheral brightness of the facing lens 18A than when the entire opening 12 is filled with an air layer. Can do.
In addition, when the top portion 20 a of the light transmitting protrusion 20 contacts the lens sheet substrate 17 in the opening 12, the shape of each opening 12 of the light shielding sheet 14 is stabilized, and the light transmission characteristics in each opening 12. Therefore, unevenness in luminance due to the lens 18 </ b> A facing the opening 12 while suppressing variations in the light emission angle is less likely to occur.
In addition, since the optical sheet using the brightness enhancement film in the prior art is not employed, a part of the light traveling toward the liquid crystal display unit 4 is unnecessarily emitted out of the optical path, or the angle of the liquid crystal display unit 4 is horizontal with respect to the visual direction. It is possible to prevent a sudden decrease in luminance when the direction is shifted.

Next, a modification of the optical sheet 2 according to the present embodiment will be described. However, the same or similar parts and members as those of the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.
FIG. 7 shows the opening 22 of the light shielding sheet 14 of the optical sheet 2 according to the first modification. In FIG. 7, the wall surfaces 22a and 22a that form the boundary with the light shielding portion 23 of the opening 22 are inclined so that the width gradually decreases from the back side toward the display screen side, and the wall surfaces 22a and 22a are preferably It has a symmetrical shape. A light-transmitting protrusion 20 is formed in the opening 22 so as to protrude in a convex curved surface shape, contacts the lens sheet substrate 17 at the top 20a, and air layers 21 and 21 are formed on both sides.
By adopting such a shape, when the diffusion plate 11 and the light shielding sheet 14 integrally laminated on the lens sheet 16 are joined, the applied adhesive layer 15 is pressed with a predetermined pressure by the light shielding portion 23 of the light shielding sheet 14. This guides the adhesive before being cured by UV irradiation from bulging into the opening 22. As a result, the adhesive can be formed so as to project into a convex curve shape in the opening 22 smoothly and in a well-balanced manner, and the light-transmissive projection 20 having a convex curve shape can be formed by subsequent curing by UV irradiation or the like.
The wall surfaces 22a and 22a of the opening 22 may be formed so as to be inclined so that the width gradually increases from the back side toward the display screen side as opposed to that shown in FIG. In order to form such a light-shielding sheet 14, it may be formed by a transfer method in the same manner as the light-shielding sheet 14 shown in FIG.

  FIG. 8 shows the opening 12 and the light transmitting protrusion 25 of the light shielding sheet 14 according to the second modification, and the light transmitting protrusion 25 provided in the opening 12 is formed in a trapezoidal cross section. The top surface 25 a is in contact with or connected to the lens sheet substrate 17.

FIG. 9 shows a light shielding sheet 31 of the optical sheet 30 according to the third modification.
In FIG. 9, the light-transmitting protrusion 20 that protrudes into the opening 12 is integrally formed in advance on the exit surface of the diffusion plate 11 by molding or extrusion molding. Then, the light-transmitting protrusions 20 are formed in the openings 12 by projecting and forming the light-shielding parts 13 between the light-transmitting protrusions 20 arranged at predetermined intervals on the exit surface of the diffusion plate 11 by the transfer method described above. A light-shielding sheet 31 having a protrusion is formed. Thereafter, an adhesive is applied to the incident side end surface of the lens sheet substrate 17 in the lens sheet 16 to form the adhesive layer 32, and the light shielding sheet 14 integrally formed with the diffusion layer 11 is joined. Thereby, the optical sheet 30 can be manufactured.
The light transmitting protrusions 20 and 25 may be manufactured by integral molding with the diffusion plate 11 as described above, or may be separately molded and joined. When manufacturing the light-transmitting protrusion 20, it may be molded or extruded and may be manufactured by an appropriate manufacturing method.
Alternatively, the light-shielding sheet 14 in which the light-transmitting protrusion 20 is integrally formed in the opening 12 is formed by bonding the lens sheet base material 17 of the lens sheet 16 and the diffusion plate 11 via adhesive layers 15 and 32, respectively. May be.

  As mentioned above, although embodiment and the modification of this invention were demonstrated, this invention is not limited to these, In the range which does not deviate from the meaning of this invention, an appropriate change is possible. Further, the optical sheet according to the present invention can be applied to other flat panel displays, used for illumination, and the like.

It is typical sectional drawing which shows schematic structure of the display apparatus by embodiment of this invention. It is sectional drawing of the optical sheet part of FIG. It is explanatory drawing which shows the opening part and light transmissive protrusion of a light shielding sheet in an optical sheet in a longitudinal section. It is explanatory drawing which shows the total reflection angle of the incident light and light which inject into a light transmissive protrusion from the edge part side of the opening part in FIG. It is explanatory drawing which shows the relationship between the course of the incident light which injects into an opening part from an edge part of an opening part, and the structure of an opening part, (a) is embodiment, (b) is the state by which the opening part was filled with resin, (C) is a figure which shows the state by which the opening part was satisfy | filled with air. It is a figure which shows the luminance distribution of the unit lens in the Example shown to Fig.5 (a), the comparative example shown in FIG.5 (c), and a prior art example. It is a figure similar to FIG. 3 by the 1st modification of this embodiment. It is a figure similar to FIG. 3 by the 2nd modification of this embodiment. It is a figure similar to FIG. 2 by the 3rd modification of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Light source part 3 and 30 Optical sheet 11 Diffusing plate 12 Opening part 13 and 23 Light-shielding part 14 and 31 Light-shielding sheet 15 and 32 Adhesive layer 16 Lens sheet 17 Lens sheet base material 20 and 25 Light-transmissive protrusion

Claims (7)

A lens member in which arrayed lenses are arranged on one surface, a light shielding member in which openings facing each of the lenses are arranged, and a light diffusion member provided on the opposite side of the light shielding member from the lens member An optical sheet comprising
Air provided between the light transmissive protrusions projecting inward from the light diffusing member side toward the lens member side and the surfaces partitioning the opening parts on both sides of the light transmissive protrusions. Layers are provided,
The optical sheet, wherein the light transmitting protrusion has a refractive index larger than that of the air layer.   The optical sheet according to claim 1, wherein the light-transmitting protrusion is a convex curved surface whose top is in contact with the lens member.   2. The optical sheet according to claim 1, wherein an interface between the light-transmissive protrusion and the air layer in the opening is a curved surface or a substantially inclined surface.   In the light shielding member, openings and light shielding portions are alternately arranged, and the light shielding member and the light diffusing member are joined by an adhesive layer made of an adhesive, and the light shielding member and the light shielding member are in a stage before the adhesive is cured. 4. The light-transmitting protrusion is formed by projecting a part of an adhesive layer into the opening by pressing each other with a light diffusing member. The optical sheet described.   The optical sheet according to claim 4, wherein the adhesive layer has a thickness before pressing of 3 μm or more and 20 μm or less. The optical sheet according to any one of claims 1 to 5,
A backlight unit that includes a light source unit that is disposed on the opposite side of the optical sheet from the lens member and that emits light. A backlight unit according to claim 6;
And a liquid crystal display unit for displaying an image using light from the backlight unit as display light.

Images