JP5023928B2 - Optical sheet, backlight unit and display device - Google Patents

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 computers, personal computer displays, image display means for information terminal equipment, 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 has been widely used. 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. Recently, small-sized liquid crystal display devices with a screen size of 20 inches or less used for notebook computers and personal digital assistants have adopted an edge light system that can reduce power consumption and be easily thinned. Therefore, the adoption of the direct type is the mainstream in medium to large liquid crystal display devices having a screen size of 20 inches or more.

  In a battery-powered device such as a notebook personal computer that employs an edge light system, the power consumed by the light source occupies a considerable portion of the power consumed by the entire device. Therefore, in order to extend the battery life by reducing the total power, a performance capable of obtaining a desired brightness with less power is required.

  On the other hand, in a liquid crystal display device of 20 inches or more that employs a direct type, it is desirable that it is thinner, has a low viewing angle dependency, has high luminance, and consumes low power. Achievable performance is required. Further, in the direct type backlight, the shape of a cold cathode tube or LED as a light source can be directly visually recognized through the diffusion plate, and therefore a synthetic resin plate having a very strong light scattering property is used for the diffusion plate. . Therefore, the diffusion plate usually needs to have a thickness of about 1 mm to 3 mm. However, 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 decreases and the liquid crystal screen display becomes dark.

  For example, brightness enhancement films (BEF; DBEF; EBEF: registered trademark) shown in Patent Documents 1 to 3 are widely used as optical sheets corresponding to the edge light system and the direct type as described above. 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 in a display device, the brightness in the normal direction relative to the display screen can be increased by reducing the off-axis brightness.

In this display device, two brightness enhancement films are stacked and combined so that the parallel directions of the prism groups are substantially orthogonal to each other. Thereby, it is possible to obtain a desired luminance in a direction that matches the visual direction of the viewer while reducing power consumption.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

By the way, the optical sheet having the above configuration has the following problems.
That is, in the conventional optical sheet, the light from the light source is emitted at a controlled angle when passing through the optical sheet, thereby reducing the off-axis luminance, and the light on the axis, that is, the viewer's visual direction. However, at the same time, the light component due to the reflection and refraction action is unnecessarily emitted in the lateral direction as sidelobe light without proceeding in the viewer's visual direction.

  Accordingly, the luminance distribution emitted from the optical sheet has the highest front luminance when the angle with respect to the visual direction of the viewer is 0 ° as shown in the luminance distribution diagram of FIG. In the range of 45 ° and + 45 ° to + 90 °, the peak of the luminance distribution due to the sidelobe light emitted from the lateral direction is shown, and there is a problem that light cannot be collected efficiently. Furthermore, since the ratio between the luminance at the point where the luminance distribution takes a minimum value and the luminance at the point where the peak occurs due to sidelobe light is large, uneven luminance due to the viewing angle is visually recognized, which is preferable as the display quality of the display. There was no problem.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical sheet, a backlight unit, and a display device having good display quality with high light condensing properties and little unevenness in luminance distribution.

In order to solve the above problems, the present invention proposes the following means.
That is, the optical sheet according to the present invention is an optical sheet including a lens array that condenses incident light from the light source on the other sheet surface side when the light source is disposed on the other sheet surface side. When a light reflecting layer is provided on the top of the unit lens constituting the array, and two tangents at the boundary with the light reflecting layer are drawn with respect to the lens surface of the unit lens in the sectional shape of the unit lens The distance between the intersection of these two tangents and the light incident surface of the unit lens is h, the distance between the top of the light reflecting layer and the light incident surface of the unit lens is h1, and the unit lens and the light reflecting surface. When the distance between the boundary with the layer and the light incident surface of the unit lens is h2, the relationship of 0.55 ≦ (h1−h2) / (h−h2) ≦ 3 is satisfied . .

According to the optical sheet having such a feature, the sidelobe light emitted from the adjacent unit lens in the lateral direction is reflected by the light reflecting layer located on the top of the unit lens. Thereby, a part of the side lobe light is emitted on the axis, that is, in the visual direction of the viewer, and a part thereof is advanced in an oblique direction having a predetermined emission angle from the visual direction. Therefore, the light intensity in the visual direction of the viewer can be improved to increase the front luminance, and the light traveling in the oblique direction is minimized in the luminance distribution near an angle of ± 45 ° with respect to the visual direction in the luminance distribution diagram. Since the value is filled, it is possible to obtain a good display quality with little unevenness in luminance distribution depending on the viewing angle.
Here, h1-h2 represents the length of the light reflecting layer in the visual direction, and is hereinafter referred to as the thickness of the light reflecting layer, and h-h2 is referred to as the reference thickness of the light reflecting layer.
When the value of (h1-h2) / (h-h2), which is the ratio of the thickness of the light reflecting layer to the reference thickness, is smaller than 0.55, the sidelobe light from the adjacent unit lens is effectively reflected. Cannot obtain the expected characteristics. When the value of (h1-h2) / (h-h2) is larger than 3, the light beam that should be emitted from the lens surface of the unit lens and condensed in the visual direction is reflected on the unit lens itself. Since it is reflected out of the visual direction by the light reflecting layer, the front luminance is lowered. In the present invention, the front luminance is maintained high by setting the ratio (h1−h2) / (h−h2) of the thickness of the light reflecting layer to the reference thickness in the range of 0.55 to 3 as described above. In addition, the luminance unevenness can be appropriately suppressed.

In the optical sheet according to the present invention, in the cross-sectional shape of the unit lens, the length of the projection width of the light reflecting layer onto the light incident surface is 20% of the width of the light incident surface of the unit lens. It is characterized by the following settings .

  When the length of the projection width on the light incident surface of the light reflecting layer in the cross-sectional shape of the unit lens is close to the width of the light incident surface of the unit lens, that is, the base of the unit lens in the cross-sectional shape, from the adjacent unit lens Among the emitted sidelobe light, the effective light that should be reflected in the visual direction is reflected excessively, so that the brightness unevenness can be suppressed by filling in the minimum value of the brightness distribution described above, This leads to a decrease in front brightness. Therefore, as in the present invention, the length of the projection width of the light reflecting layer on the light incident surface side is somewhat smaller than the width of the light incident surface of the unit lens, that is, 20% of the width of the light incident surface of the unit lens. By setting the length within%, it is possible to maintain high front luminance while suppressing luminance unevenness.

  In the optical sheet according to the present invention, the light reflecting layer is formed by coating or transfer molding of an ink layer formed by dispersing and mixing metal fillers or metal laminate molding. Thereby, the light reflection layer having high reflection characteristics can be reliably formed on the top of the unit lens.

  In the optical sheet of the present invention, the lens array is a prism array in which prisms are arranged in parallel as the unit lenses.

  The lens array may be a cylindrical lens array in which cylindrical lenses are arranged in parallel as the unit lens.

  Furthermore, the lens array may be a microlens array in which microlenses are arranged in parallel as the unit lenses.

  In the optical sheet according to the present invention, the lens array is characterized in that the unit lenses extending in one direction on the same plane are arranged in a direction orthogonal to the one direction.

  The lens array may be formed by arranging the unit lenses in a matrix on the same plane.

A 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 array and that emits light. Yes.
In addition, a display device according to the present invention includes the above-described backlight unit and a liquid crystal display unit that displays an image by light irradiation from the backlight unit.
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 reflecting layer provided on the top of the unit lens effectively reflects the sidelobe light emitted from the adjacent unit lens, thereby collecting light. Therefore, it is possible to realize a good display quality with a high luminance distribution and less unevenness in luminance distribution.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, about the optical sheet which concerns on embodiment of this invention, it demonstrates with the backlight unit and display apparatus using the same.

  FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a display device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a unit lens and a light reflection layer. In the display device 1 according to the present embodiment, as shown in FIG. 1, 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 toward the upper side in the figure. By emitting display light, for example, a planar rectangular image 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 is simply referred to as the display screen side or the emission side, and the lower direction is simply referred to as the back side or the incident side.

  In FIG. 1, the light source unit 2 displays a plurality of light sources 7 in which linear light emitting units extending in the depth direction on the paper surface are spaced apart at a constant pitch in the horizontal direction in the figure, and covers the light sources 7 from the back side. A direct type system composed of a reflecting plate 8 opened on the screen side is adopted.

  As the light source 7, a cold cathode tube having a function of emitting white light is used. However, an LED light source in which a plurality of LED elements are arranged in a line along the depth direction of the paper surface, a cold cathode fluorescent lamp, an EL sheet, a semiconductor, and the like Etc. may be adopted.

  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 any well-known light source may be employed. For example, an edge light type surface light source in which a line light source is disposed on the side surface of the light guide surface, or the like may be employed.

  The optical sheet 3 collects a part of the light emitted from the light source unit 2 to the display screen side, transmits the light to the display screen side, reflects the other light to the light source unit 2 side, and retransmits the light to the light source unit 2. As shown in FIG. 1, a diffusion sheet 11, a bonding layer 12, and a prism sheet 13 in which a prism array 17 is arranged as a lens array are laminated in this order from the back side to the display screen side. Has been configured.

  The diffusing plate 11 is a flat 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 is suppressed, and an appropriate viewing angle can be given to the display light.

  The diffusing plate 11 includes a transparent resin and transparent particles dispersed in the transparent resin, and the difference between the refractive index of the transparent resin and the refractive index of the transparent particles is 0.02 or more. It is desirable that If the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. The refractive index difference 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 shown in FIG. 1, the bonding layer 12 is used for stacking and integrating the diffusion plate 11 and the prism sheet 13, and is made of a linear light-transmitting pressure-sensitive adhesive material or adhesive that extends in the depth direction of the paper. A plurality of joining members 14 are provided. In this embodiment, as an example, an acrylic pressure-sensitive adhesive material having a refractive index of 1.54 is employed. Note that the bonding member 14 may be an adhesive, a thermoplastic resin, or the like having a certain thickness after curing as long as it can form a certain gap by bonding the diffusion plate 11 and the prism sheet 13.

  In the present embodiment, the diffusion plate 11 and the prism sheet 13 are integrated by, for example, printing the line-shaped joining members 14 on the diffusion plate 11 in a stripe shape and attaching them to the prism sheet 13. And as shown in FIG. 1, it was surrounded by the surface in which the joining member 14 in the output surface 11a of the diffusion plate 11 is not provided, the incident surface 13a of the prism sheet 13 facing this surface, and the joining member 14. An air layer 15 is formed in the region. That is, the bonding member 14 has a function as a spacer while the diffusion plate 11 and the prism sheet 13 are laminated and integrated. The pitch of the adjacent joining members 14 is such that the air layer 15 is not crushed and moire interference fringes are not generated.

  The prism sheet 13 collects a part of the light emitted from the light source unit 2 to the display screen side and transmits it to the display surface side. The prism sheet 13 includes a base material unit 16 and a prism array 17. The base material part 16 has a flat plate shape made of a transparent resin, and has a certain rigidity. The prism array 17 is arranged on the surface 16a on the display screen side of the base member 16 with a plurality of prisms 18 extending in the illustrated depth direction in the same direction as the light source 7 as unit lenses in a direction orthogonal to the illustrated depth direction. It has been configured. Note that a surface of the prism 18 that contacts the surface 16a on the display screen side of the base member 16 is a light incident surface 18b. A light reflecting layer 19 is provided on the top 18 c of the prism 18.

  Here, the details of the configuration of the prism 18 and the light reflecting layer 19 will be described. In the present embodiment, each prism 18 has a top surface 18c that is formed to be parallel to the light incident surface 18b in the depth direction, and covers the top portion 18c of the prism 18. A light reflecting layer 19 extending in the illustrated depth direction is formed. Alternatively, the prism surface 18a may extend into the light reflecting layer 19 so as to form a triangle. As shown in FIG. 2, in the cross section orthogonal to the direction in which the prisms 18 extend, each prism 18 has an isosceles trapezoidal shape with the prism surface 18a as two oblique sides, and the light reflecting layer 19 reflects. The surface 19a has an isosceles trapezoidal shape, and the bottom surface 19b of the light reflecting layer is in contact with the top 18c of the prism 18 with the same length. Further, the inclination angle of the reflection surface 19 a of the light reflection layer 19 is set larger than the inclination angle of the prism surface 18 a of the prism 18.

  In the present embodiment, the length d1 of the bottom surface of the light reflecting layer 19b in the cross section, that is, the length d1 of the projection width on the light incident surface side of the light reflecting layer 19 is the light incident surface 18b of the prism 18. The width is set to 20% or less of the length d0. As a result, as will be described in detail in an embodiment described later, it is possible to maintain high front luminance while suppressing luminance unevenness.

  Here, in the cross-sectional shapes of the prism 18 and the light reflecting layer 19, as shown in FIG. 2, two tangents l and m at the boundary with the light reflecting layer 19 are drawn with respect to the prism surface 18a, and the intersection is P And In the present embodiment, the tangent lines l and m mean virtual extension lines of the prism surface 18a constituting the hypotenuse of the isosceles trapezoid in the cross section of the prism 18. For example, the unit lens is a cylindrical lens or the like. When the lens surface is a curved surface, it means a tangent to the curved surface. In other words, whether the lens surface is flat or curved, it is used to include straight lines connected to these.

  Further, as shown in FIG. 2, the distance between the intersection P and the light incident surface 18d of the prism 18 is h, the distance between the top 19c of the light reflecting layer and the light incident surface 18b of the prism 18 is h1, The distance between the boundary between the prism 18 and the light reflecting layer 19 and the light incident surface 18b of the prism 18 is h2. At this time, in the present embodiment, (h1−h2) / (h−h2), which is a ratio of the thickness (h1−h2) of the light reflection layer 19 based on the reference thickness (h−h2), is set to 0. The prism 18 and the light reflecting layer 19 are configured to satisfy the relationship of 55 ≦ (h1−h2) / (h−h2) ≦ 3. As a result, as will be described in detail in an embodiment described later, it is possible to maintain high front luminance and to appropriately suppress luminance unevenness.

  Further, as a method of providing the light reflecting layer 19 on the top portion 18c of each prism 18, a method of coating or forming a white pigment formed by dispersing and mixing a metal filler, or a transfer forming of a metal foil such as aluminum or silver is used. There is something. When the light reflecting layer 19 is molded with a white pigment, the reflectance at 540 nm is 80% in the reflecting layer having a layer thickness of 10 μm by mixing at least 50% of the white pigment with urethane resin or EVA resin. The above high reflection characteristics can be obtained. At this time, it is possible to obtain a higher reflectance of about 90% by adjusting the thickness of the reflective layer and the pigment concentration. As the white pigment, titanium dioxide, barium sulfate, magnesium oxide and the like well known in the technical field are used.

  The prism sheet 13 is made of, for example, a transparent resin such as polyethylene terephthalate (PET) resin, polycarbonate (PC) resin, methyl methacrylate-styrene copolymer (MS) resin, polymethyl methacrylate (PMMA), and cycloolefin polymer (COP). Using the material, it can be formed by a known extrusion molding method, injection molding method, or hot press molding method. Moreover, you may shape | mold by the ultraviolet curing shaping | molding method shape | molded using radiation curable resins, such as an ultraviolet-ray (UV) curable resin.

  The liquid crystal display unit 4 includes, for example, a display element or panel 4a that controls a light transmission state according to an image signal for each of a plurality of pixel regions formed in a rectangular lattice shape, and light incident on the display element or panel 4a. The polarizing plate 4b controls the polarization direction of the light and the polarizing plate 4c controls the polarization direction of the emitted light.

Hereinafter, the operation of the display device 1 will be described focusing on the operation of the optical sheet 3.
A part of the light emitted from the light source 7 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 directed toward the diffusion plate 11 of the optical sheet 3. Are emitted. 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 to the diffuser plate 11 is scattered by the transparent particles in the transparent resin of the diffuser plate 11 and proceeds as diffused light, and the luminance unevenness of the light source unit 2 is eliminated and the light has a spread angle in an appropriate angle range. It reaches the exit surface 11a of the diffusion plate 11.

  The light reaching the exit surface 11a of the diffusion plate 11 is subjected to a refraction action according to Snell's law according to the refractive indexes of the diffusion plate 11, the bonding layer 12, and the diffusion plate 11 and the air layer 15, and the prism sheet 13 Is incident on. The light incident on the prism sheet 13 is refracted by the incident surface 13a, travels through the base member 16 and the prism 18, is refracted by the prism surface 18a in the prism array 17, and is emitted to the display screen side. Further, the light that travels through the prism 18 and reaches the light reflecting layer 19 without being emitted to the outside is reflected back by the light reflecting layer 19 and is incident again on the light source unit 2, and reflected by the light source unit 2. Reflected to the display screen side by the plate 8 and reused.

  Of the light refracted by the prism surface 18a and emitted toward the display screen, the sidelobe light S emitted in the lateral direction toward the adjacent prism 18 is, as shown in FIG. The light is reflected by the light reflecting layer 19 located on the top of 18. Thereby, a part of the side lobe light S is emitted on the axis, that is, in the visual direction F of the viewer, and a part of the side lobe light S is advanced in the oblique direction G having a predetermined emission angle from the visual direction.

  Then, the light emitted from the optical sheet 3 is transmitted as display light from a predetermined pixel region through the polarizing plate 4b, the display element or panel 4a, and the polarizing plate 4c of the liquid crystal display unit 4, and has a viewing angle. The image it has is displayed.

  In the backlight unit 5 and the display device 1 using such an optical sheet 3, as described above, the side lobe light S emitted from the prism surface 18a is reflected by the adjacent light reflecting layer 19, It advances in the visual direction F and the diagonal direction G. Thereby, the light intensity in the visual direction F of the viewer can be improved to increase the front luminance, and the light traveling in the oblique direction G is at an angle with respect to the visual direction F in the luminance distribution diagram shown in FIG. It plays the role of filling in the local minimum of the luminance distribution around ± 45 °. Therefore, with the optical sheet 3 in the present embodiment, the luminance distribution has a higher front luminance than the conventional one, the peak due to the sidelobe light S is relaxed, as shown in FIG. It is possible to achieve good display quality without unevenness.

  Further, the length d1 of the bottom surface 19b of the light reflecting layer 19 in the cross-sectional shapes of the prism 18 and the light reflecting layer 19, that is, the length d1 of the projection width on the light incident surface side of the light reflecting layer 19 is the light incident on the prism 18. When the width d0 of the surface 18b is close to the length d0, the effective light that would otherwise be reflected in the visual direction out of the sidelobe light S emitted from the adjacent prisms 18 is excessively reflected. The Thereby, although the minimum value of the luminance distribution diagram shown in FIG. 12 is filled to suppress luminance unevenness, the front luminance is lowered.

  In the present embodiment, the length d1 of the bottom surface 19b of the light reflecting layer 19 shown in FIG. 2 is set to 20% or less of the width d0 of the light incident surface 18b of the prism 18. As a result, as will be described in detail in the embodiment, it is possible to significantly suppress luminance unevenness while maintaining high front luminance.

  Further, when the value of (h1−h2) / (h−h2), which is the ratio of the thickness of the light reflecting layer to the reference thickness described above, is smaller than 0.55, the side lobe light from the adjacent unit lens is emitted. It cannot be reflected effectively and the expected characteristics cannot be obtained. When the value of (h1-h2) / (h-h2) is larger than 3, the light beam that should be emitted from the lens surface of the unit lens and condensed in the visual direction is reflected on the unit lens itself. Since it is reflected out of the visual direction by the light reflecting layer, the front luminance is lowered.

  In the present embodiment, the ratio (h1−h2) / (h−h2) of the thickness of the light reflecting layer to the reference thickness is set in the range of 0.55 or more and 3 or less as described above. As described in the embodiments, it is possible to significantly suppress luminance unevenness while maintaining high front luminance.

  In addition, since the air layer 14 is interposed between the prism sheet 13 and the diffusion plate 11, when the diffused light from the diffusion plate 11 enters the incident surface 16 a of the prism sheet 13, the angle is reduced by refraction. Therefore, the light condensing action by the prism 18 can be effectively obtained, and the front luminance can be increased.

  The optical sheet 3, the backlight unit 5, and the display device 1 according to the embodiment of the present invention have been described above. However, the present invention is not limited thereto, and may be appropriately changed without departing from the technical idea of the present invention. Is possible. For example, in this embodiment, the cross-sectional shape of the light reflecting layer 19 is an isosceles trapezoid as shown in FIG. 2, but may be other polygonal shapes such as a square, a long diameter, a pentagon, and the reflecting surface 19a is an arc shape. It may be a semicircular shape.

  Further, in the present embodiment, the prism 18 has an isosceles trapezoidal cross section, and the light reflecting layer 19 is provided on the top portion 18c. For example, as shown in FIG. A convex portion 25 integrally formed with the prism 18 is formed on the top portion 18c of the prism 18. The convex portion 25 is formed in a simple triangular shape and covers two surfaces near the top portion with the same inclination angle. The light reflecting layer 26 may be formed. This also has the same effect as the present embodiment.

  Further, although the prism array 17 in which the prisms 18 are arranged as unit lenses is adopted as the lens array, a cylindrical lens array in which cylindrical lenses are arranged as unit lenses, or a micro lens array in which micro lenses are arranged as unit lenses may be used. .

  In the present embodiment, a prism array is described in which a plurality of prisms 18 extending in the illustrated depth direction are used as unit lenses and the prisms 18 are arranged in a direction perpendicular to the illustrated depth direction. The prisms 18 may be formed in a matrix on the same plane. Similarly, any arrangement may be employed even when a cylindrical lens array or a microlens array is used.

  The result of the optical simulation about the prism 18 and the light reflection layer 19 of the optical sheet 3 in this embodiment is shown. Here, regarding the optical sheet 3, the length of the projection width of the light reflection layer 19 on the light incident surface side in the cross-sectional shape, that is, the width of the light reflection layer 19 and the length of the light reflection layer 19 in the visual direction, that is, light reflection. In order to examine the effect of the thickness of the layer 19, an optical model 30 as shown in FIG. 5 was used.

 Here, the optical model 30 in FIG. 5 will be described. Since the optical model 30 has the same configuration as the cross section of the prism 18 and the light reflecting layer 19 shown in FIG. 2, the same reference numerals are given to the components, and detailed description thereof is omitted. The prism 18 in the optical model 30 has an angle of 45 ° with respect to the light incident surface 18b of the prism surface 18a. Further, the angle formed with respect to the bottom surface 19b of the reflection surface 19a of the light reflection layer 19 is set to 90 °, that is, the light reflection layer 19 has a rectangular or square cross section. Then, simulation was performed by incorporating the optical model 30 as a unit lens in the optical sheet 3 described in the embodiment.

  In this simulation, the calculation was performed assuming that the refractive index of the air layer 15 in the optical sheet 3 is 1, the refractive index of the prism 18 is 1.5, the reflectance of the light reflecting layer is 90%, and the transmittance is 10%. The light reflecting layer 19 is assumed to be made of a material that is relatively close to specular reflection.

  In this simulation, the front luminance and contrast are evaluated. Here, the contrast means that the luminance at the point where the luminance distribution due to the sidelobe light S takes the maximum value as shown in the luminance distribution diagram shown in FIG. 12 is M, and the luminance at the point where the luminance distribution takes the minimum value is m. Is an evaluation index given by m / M. Therefore, it can be said that the luminance unevenness is suppressed as the contrast value is smaller.

  First, in order to investigate the effect of the width of the light reflecting layer 19, a simulation was performed on the relationship between the value of d1 / d0, the front luminance, and the contrast using d1 in FIG. 5 as a parameter. Note that d1 / d0 = 0 is the case of the right-angle prism 31 as shown in FIG. 6 in which the light reflection layer 19 is not provided, and all the luminances in this simulation are specified based on the simulation result of the luminance in the right-angle prism 31. The relative luminance is evaluated.

  FIG. 7 shows the relationship between the width of the light reflection layer 19 and the relative luminance and contrast. As d1 / d0 increases from 0, the contrast value decreases, and it can be seen that increasing the width of the light reflecting layer 19 is very effective in suppressing luminance unevenness. On the other hand, the relative luminance value is 1 or more until the d1 / d0 value is close to 0.1, and the front luminance can be increased. However, as d1 / d0 is further increased, the relative luminance gradually decreases. To do.

  Further, when d1 / d0 takes a value of 0.2, the relative luminance shows a value of about 0.95, which is about 95% of the front luminance of the right-angle prism 32 without the light reflecting layer 19 provided. It is shown that. Even if d1 / d0 is further increased, the decrease in contrast is small. Therefore, it is preferable to set the width of the light reflecting layer 19 in a range of d1 / d0 ≦ 0.2 that can secure a relative luminance of 95% or more as compared with the case where the light reflecting layer 19 is not provided. Therefore, by setting d1 to a length of 20% or less of d0, it is possible to effectively suppress luminance unevenness while maintaining high front luminance.

  Next, in order to investigate the effect of the thickness of the light reflecting layer 19, the ratio of the thickness (h1-h2) of the light reflecting layer 19 based on the reference thickness (h-h2) is shown using h1 as a parameter (h1-h2). ) / (H−h2) and the relative luminance and contrast were simulated.

  FIG. 8 shows the relationship between the thickness of the light reflection layer 19 and the relative luminance and contrast. The luminance value is a curve having a peak at (h1−h2) / (h−h2) = 1. When the thickness of the light reflection layer 19 is relatively small, the side lobe light S emitted from the adjacent prism 18 can be effectively reflected, and the relative luminance is small (see FIG. 9). When the thickness of the light reflecting layer 19 is relatively large, the light L emitted from the prism 18 and directly condensed in the visual direction is reflected by the light reflecting layer 19 of the prism 18 itself. Since it proceeds out of the visual direction, the front luminance is reduced (see FIG. 10). On the other hand, when the width of the light reflecting layer 19 is appropriately set, the side lobe light S is reflected accurately and the light L emitted directly from the prism 18 to the vicinity of the visual direction is unnecessarily reflected. Therefore, uneven brightness can be suppressed while improving the front brightness (see FIG. 11).

  Based on the above, the thickness of the light reflection layer 19 can maintain a relative luminance value of 95% or more of a right-angle prism without the light reflection layer 19 0.55 ≦ (h1−h2) / (h−h2) ≦ 3 It is considered appropriate to set within the range. Thereby, it is possible to ensure a high front luminance and appropriately suppress luminance unevenness.

  Therefore, as in the present embodiment, the light reflecting layer 19 is formed on the top portion 18c of the prism 18 so as to satisfy the relationship of d1 / d0 ≦ 0.2 and 0.55 ≦ (h1-h2) / (h-h2) ≦ 3. Accordingly, it is possible to provide the optical sheet 3, the backlight unit 5 and the display device 1 having a good display quality with high light condensing property and little unevenness in luminance distribution.

It is typical sectional drawing which shows schematic structure of the display apparatus by embodiment of this invention. It is sectional drawing of the prism as a unit lens. It is a graph which shows the luminance distribution of the transmitted light of the optical sheet of this embodiment. It is sectional drawing of the prism of a modification. It is a figure which shows the advancing direction of the light in the optical sheet of this embodiment. It is sectional drawing of a right angle prism. It is a graph which shows the relationship between the width | variety of a light reflection layer, relative luminance, and contrast. It is a graph which shows the relationship between the thickness of a light reflection layer, relative luminance, and contrast. It is a figure which shows the advancing direction of light when the thickness of a light reflection layer is small. It is a figure which shows the advancing direction of light when the thickness of a light reflection layer is large. It is a figure which shows the advancing direction of the light in the optical sheet of this embodiment. It is a graph which shows the luminance distribution of the transmitted light of the conventional optical sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Light source part 3 Optical sheet 5 Backlight unit 13 Prism sheet
17 Prism array (lens array)
18 Prism (unit lens)
19 Light reflection layer l, m Tangent P Intersection

Claims (10)

An optical sheet comprising a lens array that condenses incident light from the light source on the other sheet surface side when the light source is disposed on one sheet surface side,
A light reflecting layer is provided on the top of the unit lens constituting the lens array ,
In the cross-sectional shape of the unit lens,
When two tangents at the boundary between the light reflecting layer and the lens surface of the unit lens are drawn, the distance between the intersection of these two tangents and the light incident surface of the unit lens is h,
The distance between the top of the light reflecting layer and the light incident surface of the unit lens is h1,
When the distance between the boundary between the unit lens and the light reflection layer and the light incident surface of the unit lens is h2,
0.55 ≦ (h1−h2) / (h−h2) ≦ 3
An optical sheet characterized by satisfying the relationship: In the cross-sectional shape of the unit lens, the length of the projection width on the light incident surface of the light reflecting layer is:
The optical sheet according to claim 1, wherein the optical sheet is set to 20% or less of the width of the light incident surface of the unit lens. The light reflective layer, an optical sheet according to claim 1 or 2, characterized in that it is formed by coating molding or transfer molding or lamination molding of the metal of the ink layer formed by dispersion mixing metallic filler. The lens array, an optical sheet according to any one of claims 1 to 3, characterized in that the prism array arranged in parallel prism as the unit lenses. The lens array, an optical sheet according to any one of claims 1 to 3, characterized in that the cylindrical lens array arranged in parallel cylindrical lenses as the unit lenses. The optical sheet according to any one of claims 1 to 3 , wherein the lens array is a microlens array in which microlenses are arranged in parallel as the unit lenses. The lens array according to any one of claims 1 to 6, wherein the unit lenses extending in one direction on the same plane are formed are arranged in a direction perpendicular to said one direction Optical sheet. The lens array, an optical sheet according to any one of claims 1 6, characterized in that said unit lenses are formed are arranged in a matrix in the same plane. The optical sheet according to any one of claims 1 to 8 ,
A backlight unit including a light source unit that is disposed on the opposite side of the optical sheet from the lens array and that emits light. A backlight unit according to claim 9 ;
And a liquid crystal display unit configured to display an image by light irradiation from the backlight unit.

Images