JP2011242633A - Optical sheet, optical sheet laminate, backlight unit, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet for providing an improved concealment performance and a high front luminance, and a backlight unit and a display device including the optical sheet.SOLUTION: An optical sheet 1 is such that a plurality of convex lenses 4 extending in the same direction is arranged in parallel on at least one of a light incident surface and a light emission surface, and a boundary between the adjacent convex lenses 4 is formed in the shape of curve with a curvature that continuously changes along the extension direction of the convex lenses 4 viewed from an arrangement direction of the plurality of convex lenses 4.

Description

  The present invention relates to an optical sheet having a concavo-convex shape, a light source unit, and a display device used for illumination light path control, and particularly used for illumination light path control in an image display device typified by a flat panel display. The present invention relates to an optical sheet, an optical sheet laminate, a backlight unit, and a display device.

In recent years, TFT (Thin Film Transistor) type liquid crystal panels and liquid crystal display devices using STN (Super Twisted Nematic) type liquid crystal panels have been commercialized mainly in color office PCs (personal computers) in the OA field. ing.
Such a liquid crystal display device employs a so-called backlight method in which a light source is disposed on the back side of the liquid crystal panel (opposite to the observer side) and the liquid crystal panel is illuminated with light from the light source. ing.

The backlight units employed in this type of backlight system can be broadly classified into a “light guide plate light guide system” (edge light system) backlight unit and a “direct type” backlight unit.
Here, the “light guide plate light guide method” means that a light source lamp such as a cold cathode fluorescent tube (CCFT) is multiplexed within a flat light guide plate made of an acrylic resin having excellent light transmittance. This is a reflection method.

On the other hand, the “direct type” is a method of directly illuminating with light from a light source lamp such as a cold cathode tube (CCFT) without using a light guide plate.
As a liquid crystal display device on which a light guide plate light guide type backlight unit is mounted, for example, the one shown in FIG. 4 is generally known. FIG. 4 is a diagram showing a schematic configuration of a display device on which a light guide plate light guide type backlight unit is mounted.

As shown in FIG. 4, the display device 8 equipped with the light guide plate light guide type backlight unit is provided with a liquid crystal panel 14 sandwiched between a front-side polarizing plate 10 and a back-side polarizing plate 12. A light guide plate 16 is installed on the lower surface (light incident surface) side of 14.
The light guide plate 16 is formed from a transparent base material such as substantially rectangular plate-like PMMA (polymethyl methacrylate) or acrylic.

An optical sheet made of a diffusion film 18 (diffusion layer) is provided between the upper surface (light emitting surface 16 a) side of the light guide plate 16 and the back side polarizing plate 12.
Further, on the lower surface of the light guide plate 16, a scattering reflection pattern portion (not shown) for scattering and reflecting the light introduced into the light guide plate 16 so as to be uniformly uniform in the direction of the liquid crystal panel 14. ) Is provided by printing or the like. A reflective film 20 (reflective layer) is provided below the scattering reflection pattern portion.

A light source 22 is attached to one side end of the light guide plate 16, and a high-reflectivity reflecting plate 24 is provided so as to cover the back side of the light source 22. The reflection plate 24 is a member for efficiently allowing the light from the light source 22 to enter the light guide plate 16.
The above-mentioned scattering reflection pattern portion is formed by printing a mixture obtained by mixing white titanium dioxide (TiO2) powder in a solution such as a transparent adhesive in a predetermined pattern (for example, a dot pattern) and drying it. In this case, the light incident on the light guide plate 16 is given directivity and guided to the light exit surface 16a side, thereby increasing the brightness.

Further, as shown in FIG. 5, the diffusion film 18 (optical sheet) is formed on the light emitting surface of the translucent substrate 2 using a prism, and a plurality of convex lenses 4 extending in the same direction, They are arranged in parallel. FIG. 5 is a perspective view showing a conventional optical sheet.
Further, in the diffusion film 18 (optical sheet) shown in FIG. 5, the boundary 6 between the adjacent convex lenses 4 is formed in a straight line.

  However, the display device 8 shown in FIG. 4 has a problem that the control of the viewing angle is entrusted only to the diffusibility of the diffusion film 18, and that control is difficult. Specifically, for example, when viewed from the front direction, the display screen of the liquid crystal display is bright, but when viewed from the horizontal direction, the display screen of the liquid crystal display may be darkened. The center part was bright and it had the fault of becoming dark as it went to a peripheral part. For this reason, there is a problem that the light use efficiency is poor.

  On the other hand, the direct type backlight unit is used in a display device such as a large liquid crystal TV in which it is difficult to use a light guide plate. As a liquid crystal display device on which a direct type backlight unit is mounted, for example, the one shown in FIG. 6 is generally known. FIG. 6 is a diagram showing a schematic configuration of a display device on which a direct type backlight unit is mounted.

  As shown in FIG. 6, the display device 8 on which the direct type backlight unit is mounted is provided with a liquid crystal panel 14 sandwiched between a front-side polarizing plate 10 and a back-side polarizing plate 12. A plurality of light sources 22 made of a fluorescent tube or the like are provided on the lower surface (light incident side) side. The plurality of light sources 22 are arranged in a direction orthogonal to the thickness direction (vertical direction in FIG. 6) of the liquid crystal panel 14.

A diffusion film 18 (diffusion layer) is provided between the light source 22 and the back side polarizing plate 12.
And the light radiate | emitted from the light source 22 is diffused by the diffusion film 18, and this diffused light can be condensed on the effective display area of the liquid crystal panel 14 with high efficiency. A reflector 24 is disposed on the back surface of the light source 22 in order to efficiently use light from the light source 22 as illumination light.

  However, in the display device 8 shown in FIG. 6, similarly to the display device 8 shown in FIG. 4, the control of the viewing angle is left only to the diffusibility of the diffusion film 18, and the control is difficult. There was a problem. Specifically, for example, when viewed from the front direction, the display screen of the liquid crystal display is bright, but when viewed from the horizontal direction, the display screen of the liquid crystal display may be darkened. The center part was bright and it had the fault of becoming dark as it went to a peripheral part. For this reason, there is a problem that the light use efficiency is poor.

As a method for solving these problems, for example, there is a display device 8 having a configuration shown in FIG. FIG. 7 is a schematic cross-sectional view showing an example of a conventional backlight unit.
In the display device 8 shown in FIG. 7, a brightness enhancement film 26 (BEF: Brightness Enhancement Film), which is a registered trademark of 3M USA, is disposed above the illumination light source 22 for the backlight, and further brightness enhancement is performed. A method of arranging a light diffusion film (not shown) on the light emitting surface side above the film 26 is employed.

The brightness enhancement film 26 is a film in which unit prisms 28 having a triangular cross section are arranged at a constant pitch in one direction on the light emitting surface that is the upper surface of the translucent substrate 2. Here, the unit prism 28 has a size (pitch) larger than the wavelength of light.
Also, the brightness enhancement film 26 collects light from “off-axis” and redirects this light “on-axis” to the viewer. “Recycle”.

  As described above, the brightness enhancement film 26 increases the on-axis brightness by reducing the off-axis brightness when using the display device (during observation), and improves the display quality of the display device 8. The above “on-axis” is a direction that coincides with the visual direction of the viewer, and is generally a normal direction to the display screen.

  In addition, the brightness enhancement film 26 is generally configured such that the repetitive array structure of unit prisms is arranged in only one direction, and only direction change or recycling in the arrangement direction is possible. Therefore, in order to control the luminance of the display light in both the horizontal direction and the vertical direction, two BEF sheets (luminance enhancement film 26) are stacked so that the arrangement directions of the unit prism groups are substantially orthogonal to each other. Must be used in combination.

  Therefore, recently, in order to increase the light use efficiency and increase the brightness, for example, as shown in FIG. 8, a prism having a light condensing function between the diffusion film 18 and the liquid crystal panel 14 is used. It has been proposed to provide a film 30 (prism layer) (30a, 30b). FIG. 8 is a schematic cross-sectional view showing a configuration example of a conventional liquid crystal display device.

  The prism films 30a and 30b are for condensing the light emitted from the light emitting surface 16a of the light guide plate 16 and diffused by the diffusion film 18 on the effective display area of the liquid crystal panel 14 with high efficiency. By adopting such BEF, it becomes possible for a display designer to achieve a desired on-axis brightness while reducing power consumption.

  A technique in which such a brightness control member having a repetitive array structure of prisms typified by BEF is employed in a display device is conventionally known in Patent Documents 1 to 3, for example.

Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

However, in the conventional liquid crystal display device as described above, when a prism sheet represented by BEF or a general lenticular sheet is used, there is a problem that the luminance is high but the concealment performance is low.
Note that “the concealment performance is low” means that when the light from the light source reaches the observer, the brightness of the light is seen through and the brightness is visually recognized as unevenness.

  In order to improve this problem, there is a method of stacking a plurality of optical sheets such as a diffusion sheet, but this increases the number of members, leading to an increase in cost, and causing a decrease in luminance unless the optimal members are stacked. May occur. Further, when the members are laminated, there is a possibility that a problem that light loss cannot be avoided occurs.

  The present invention has been made in view of the above circumstances, and an object of the present invention is an optical sheet that has a higher hiding performance than a conventional one, and a backlight unit and a display device using the optical sheet. The purpose is to provide.

Of the present invention, the invention described in claim 1 is an optical sheet in which a plurality of convex lenses extending in the same direction are arranged in parallel on at least one of the light incident surface and the light emitting surface,
The boundary between the adjacent convex lenses is formed in a curved shape whose curvature continuously changes along the extending direction of the convex lenses when viewed from the arrangement direction of the plurality of convex lenses. is there.

Next, among the present inventions, the invention described in claim 2 is the invention described in claim 1, wherein the boundary forms a regular uneven shape when viewed from the arrangement direction of the plurality of convex lenses. It is characterized by that.
Next, of the present invention, the invention described in claim 3 is the invention described in claim 1 or 2, wherein the boundary has a coordinate X in the extending direction of the convex lens, and the thickness of the optical sheet. It is a sine curve represented by a relational expression of Y = a · sin (bX) (where a ≠ 0), where Y is a coordinate in the vertical direction and a and b are coefficients. It is.

Next, of the present invention, the invention described in claim 4 is the invention described in claim 1 or 2, wherein the boundary has a coordinate X in the extending direction of the convex lens, and the thickness of the optical sheet. When the coordinate in the vertical direction is Y and the coefficient is a, it is a sine curve represented by a relational expression of Y = a · sin (X / a) (where a ≠ 0),
The absolute value of the coefficient a every half cycle or every cycle increases or decreases according to an arithmetic sequence.

Next, of the present invention, the invention described in claim 5 is the invention described in claim 1 or 2, wherein the boundary has a coordinate X in the extending direction of the convex lens, and the thickness of the optical sheet. When the coordinate in the vertical direction is Y and the coefficient is a, it is a sine curve represented by a relational expression of Y = a · sin (X / a) (where a ≠ 0),
The absolute value of the coefficient a every half cycle or every cycle increases or decreases according to a geometric progression.

Next, of the present invention, the invention described in claim 6 is the invention described in claim 1, wherein the boundary has a non-periodic uneven shape when viewed from the arrangement direction of the plurality of convex lenses. It is characterized by forming.
Next, of the present invention, the invention described in claim 7 is the invention described in claim 1 or 6, wherein the boundary has a coordinate X in the extending direction of the convex lens, and the thickness of the optical sheet. When the coordinate in the vertical direction is Y and the coefficient is a, it is a sine curve represented by a relational expression of Y = a · sin (X / a) (where a ≠ 0),
The absolute value of the coefficient a every half cycle or every cycle increases or decreases irregularly.

Next, among the present invention, the invention described in claim 8 is an optical sheet laminate formed by laminating a plurality of optical sheets,
The plurality of optical sheets include at least one optical sheet according to any one of claims 1 to 7.
Next, among the present inventions, the invention described in claim 9 is the optical sheet described in any one of claims 1 to 7 and a light source disposed on the light incident surface side of the optical sheet. The backlight unit is characterized by comprising:

Next, among the present inventions, the invention described in claim 10 includes the optical sheet laminate described in claim 8 and a light source disposed on the light incident surface side of the optical sheet included in the optical sheet laminate. And a backlight unit.
Next, among the present inventions, the invention described in claim 11 is the backlight unit described in claim 9 or 10 and the light transmission surface side of the backlight unit. Alternatively, the display device includes an image display element that defines a display image according to light shielding.

In the following description, the extending direction of the convex lens is referred to as the x axis, the thickness direction of the optical sheet is referred to as the y axis, and the normal direction to the x axis and the y axis is referred to as the z axis.
Conventionally, when using a sheet in which the boundary between convex lenses is linear along the x-axis, light collection and diffusion are efficiently performed in the z-axis direction, but hardly performed in the y-axis direction. This was one of the causes that reduced the concealment performance.

On the other hand, according to the present invention, a plurality of convex lenses are formed using a prism, and the boundary between adjacent convex lenses is formed in a curved shape along the x-axis, so that not only the z-axis direction is formed. Condensation and diffusion are also caused in the y-axis direction, and the concealment performance can be improved.
Moreover, even if a microlens sheet or a diffusion sheet capable of condensing and diffusing in all directions can be used, high concealment performance can be realized, but these often cause a decrease in front luminance.

  On the other hand, in the present invention, the triangular prism is used as the basic skeleton of the convex lens, so the light collecting ability in a specific direction is very high, and high front luminance is obtained compared to the microlens sheet or the diffusion sheet. Is possible.

It is a figure which shows the structure of the optical sheet in 1st embodiment, Fig.1 (a) is a perspective view of an optical sheet, FIG.1 (b) is BB sectional drawing of Fig.1 (a). It is a figure which shows the structure of the optical sheet in 2nd embodiment, Fig.2 (a) is a perspective view of an optical sheet, FIG.2 (b) is BB sectional drawing of Fig.2 (a). It is a figure which shows the structure of the optical sheet in 3rd embodiment, Fig.3 (a) is a perspective view of an optical sheet, FIG.3 (b) is a BB sectional drawing of Fig.3 (a). It is a figure which shows schematic structure of the display apparatus by which the backlight unit of a light-guide plate light guide system is mounted. It is a perspective view which shows the optical sheet of a prior art example. It is a figure which shows schematic structure of the display apparatus by which the direct type backlight unit is mounted. It is typical sectional drawing which shows an example of the backlight unit of a prior art example. It is typical sectional drawing which shows the structural example of the liquid crystal display device of a prior art example.

(First embodiment)
Hereinafter, a first embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described with reference to the drawings.
(Constitution)
Hereinafter, the optical sheet according to the present embodiment will be described together with a backlight unit and a display device including the optical sheet.

(Configuration of optical sheet)
First, the structure of the optical sheet 1 of this embodiment is demonstrated using FIG.
FIG. 1 is a diagram illustrating a configuration of an optical sheet 1 according to the present embodiment. FIG. 1A is a perspective view of the optical sheet 1, and FIG. 1B is a BB line in FIG. It is sectional drawing.
As shown in FIG. 1, the optical sheet 1 is a sheet having a plurality of convex lenses 4 on one surface of a translucent substrate 2. In addition, the optical sheet 1 may have a single layer structure or a multilayer structure, and may include a transparent layer.

  In the present embodiment, as an example, a case where a plurality of convex lenses 4 are formed on the light emitting surface side of the optical sheet 1 that is the surface side of the translucent substrate 2 will be described. The configuration is not limited to this, and a plurality of convex lenses 4 may be formed on the light incident surface side of the optical sheet 1.

The translucent substrate 2 is formed in a plate shape using a translucent resin material.
Each convex lens 4 is formed using a triangular prism, and one piece thereof faces the surface of the translucent substrate 2. In the present embodiment, as an example, as shown in FIG. 1B, when the angle formed by the top (tip) of the convex lens 4 is α, α is 70 in any cross section at any position. A case where the angle is in the range of not less than 110 ° and not more than 110 ° will be described.

  Moreover, each convex lens 4 is extended along the same direction, and is arranged in parallel. In FIG. 1, the extending direction of the convex lens 4 is indicated by an arrow x, the thickness direction of the optical sheet 1 is indicated by an arrow y, and the normal direction relative to the arrow x and the arrow y is indicated by an arrow z. Therefore, in FIG. 1, the arrangement direction of the convex lenses 4 is the direction indicated by the arrow z.

In addition, each convex lens 4 is formed on the light exit surface of the optical sheet 1 with a fine uneven shape having light diffusibility.
Examples of the fine uneven shape include a convex cylindrical shape, a lens shape, and a triangular prism shape, but the uneven shape type is not limited to these. That is, the shape of the uneven shape is not limited to the above as long as it has a shape capable of improving the light diffusion function as compared with the case where the fine uneven shape is not formed.

As described above, it is possible to improve appearance characteristics such as optical adhesion, unevenness, and Newton's ring by forming a fine uneven shape on the light emitting surface of the optical sheet 1 by each convex lens 4.
Further, the boundary 6 between the adjacent convex lenses 4 is formed in a curved shape in which the curvature continuously changes along the extending direction of the convex lenses 4 when viewed from the arrangement direction of the convex lenses 4.

In the present embodiment, a case will be described in which the boundary 6 between the adjacent convex lenses 4 forms a regular uneven shape when viewed from the arrangement direction of the convex lenses 4.
In the present embodiment, when the boundary 6 between the adjacent convex lenses 4 is X, the coordinate in the extending direction of the convex lens 4 is Y, the coordinate in the thickness direction of the optical sheet 1 is Y, and the coefficients are a and b. , Y = a · sin (bX) (where a ≠ 0), a case of a sine curve represented by a relational expression will be described.

(Resin material used as optical sheet material)
The optical sheet 1 is made of a resin material.
Examples of the resin material used as the material of the optical sheet 1 include polycarbonate resin, polystyrene resin, acrylic resin, fluorine-based acrylic resin, epoxy acrylate resin, methylstyrene resin, fluorene resin, cycloolefin polymer, polyethylene terephthalate, polypropylene, and acrylic. -Various commonly used materials such as a styrene copolymer and an acrylonitrile-butadiene-styrene copolymer can be used.

  Further, transparent particles may be dispersed and contained in the resin material used as the material of the optical sheet 1.

(Optical sheet manufacturing method)
When the optical sheet 1 is manufactured, first, the resin material used as the material of the optical sheet 1 as described above is poured into a mold in a melted state to be formed into a plate shape or a belt shape, and then formed. Before the resin material is cured, the resin material is sandwiched between base sheets having concave portions corresponding to the desired convex lenses 4. And after the resin material shape | molded in plate shape or strip | belt shape hardens | cures, a base sheet is peeled from this hardened resin material, and the optical sheet 1 which has the desired convex lens 4 is manufactured.

  At this time, the thickness of the optical sheet 1 is preferably 20 [μm] or more and 2000 [μm] or less. This is because when the thickness of the optical sheet 1 is less than 20 [μm], there is almost no difference due to the presence or absence of undulations along the extending direction of the convex lens 4, so that the optical sheet 1 of the present embodiment exhibits the advantage. This is because, when the thickness of the optical sheet 1 exceeds 2000 [μm], it is difficult to wind it with a roll in the manufacturing process of the optical sheet 1.

But since the effect which the optical sheet 1 of this embodiment shows depends on a surface shape, about the thickness of the optical sheet 1, it does not restrict | limit in particular.
The production of the optical sheet 1 is not limited to the above-described procedure, and other materials and structures other than those described above can be used as long as the optical characteristics required for the optical sheet 1 of the present embodiment can be achieved. It is also possible to manufacture the optical sheet 1 using a process or the like.

(Configuration of backlight unit)
The backlight unit including the optical sheet 1 of the present embodiment is formed by including the above-described optical sheet 1 and a light source disposed on the light incident surface side of the optical sheet 1 (for example, from FIGS. 4 and 6). 8). As a light source, a cold cathode tube (CCFL), an LED, an organic or inorganic EL, a semiconductor laser, or the like can be used.

  The backlight unit including the optical sheet 1 of the present embodiment may be a light guide plate light guide method or a direct type.

(Configuration of display device)
The display device including the backlight unit of the present embodiment is arranged on the light emission surface side of the above-described backlight unit and the optical sheet 1 included in the backlight unit, and displays according to transmission or light shielding in pixel units. An image display element that defines an image is formed (see, for example, FIGS. 4 and 6 to 8).

(Effects of the first embodiment)
If it is the optical sheet 1 of this embodiment, it will become possible to improve concealment performance compared with the conventional optical sheet 1 (for example, refer FIG. 5). In addition to this, with the optical sheet 1 of the present embodiment, the front luminance can be improved as compared with a microlens sheet or a diffusion sheet.
In addition, when using the optical sheet 1 of this embodiment for a backlight unit, it is possible to provide a display device having desired display performance by using it in combination with various optical members such as a commercially available diffusion plate. It becomes possible.

(Application examples)
Hereinafter, application examples of the first embodiment will be listed.
(1) In the first embodiment, the case has been described in which the boundary 6 between the adjacent convex lenses 4 is a sine curve represented by the relational expression Y = a · sin (bX) (where a ≠ 0). However, the present invention is not limited to this. That is, the boundary 6 between the adjacent convex lenses 4 is a sine curve represented by a relational expression of Y = a · sin (X / a) (where a ≠ 0), and further, every half cycle of the coefficient a or The absolute value for each period may increase or decrease according to the arithmetic progression.
Further, the boundary 6 between the adjacent convex lenses 4 is a sine curve represented by a relational expression of Y = a · sin (X / a) (where a ≠ 0), and further, every half cycle of the coefficient a or The absolute value for each period may increase or decrease according to the geometric progression.

(2) In 1st embodiment, although the structure of the backlight unit was set as the structure provided with the one optical sheet 1 and a light source, it is not limited to this. That is, the configuration of the backlight unit may be configured to include an optical sheet laminate formed by laminating a plurality of optical sheets and a light source. In this case, at least one optical sheet 1 of the present embodiment is included in the plurality of optical sheets forming the optical sheet laminate.
The number of optical sheets used when forming the optical sheet laminate may be appropriately increased according to the required performance, etc., but considering the loss of light amount due to the excessive increase of the sheet boundary surface, It is preferable that the number is not more than one.

(3) In 1st embodiment, although the structure of the optical sheet 1 was set as the structure which has the some convex lens 4 in one surface of the translucent base material 2, it is not limited to this, The optical sheet 1 It is good also as a structure which has the some convex lens 4 on both surfaces of the translucent base material 2.

(Second embodiment)
Hereinafter, a second embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described with reference to the drawings.
(Constitution)
Hereinafter, the optical sheet according to the present embodiment will be described. In addition, about the structure of a backlight unit and a display apparatus, since it is the same as that of 1st embodiment mentioned above, the description is abbreviate | omitted.

(Configuration of optical sheet)
Hereinafter, the configuration of the optical sheet 1 of the present embodiment will be described with reference to FIG. In addition, about the structure similar to 1st embodiment mentioned above, the same code | symbol is attached | subjected and demonstrated. Moreover, the description of the same configuration as that of the first embodiment described above may be omitted. Moreover, since the resin material used as the material of the optical sheet and the method for manufacturing the optical sheet are the same as those in the first embodiment described above, the description thereof is omitted.

2A and 2B are diagrams showing the configuration of the optical sheet 1 in the present embodiment. FIG. 2A is a perspective view of the optical sheet 1, and FIG. 2B is a BB line in FIG. It is sectional drawing.
As shown in FIG. 2, the optical sheet 1 is a sheet having a plurality of convex lenses 4 on one surface of the translucent substrate 2.
The translucent substrate 2 is formed in a plate shape using a translucent resin material.

Each convex lens 4 is formed using a triangular prism, and one piece thereof faces the surface of the translucent substrate 2.
Moreover, each convex lens 4 is extended along the same direction, and is arranged in parallel. 2, the extending direction of the convex lens 4 is indicated by an arrow x, the thickness direction of the optical sheet 1 is indicated by an arrow y, and the normal direction with respect to the arrow x and the arrow y is indicated by an arrow z. Therefore, in FIG. 2, the arrangement direction of the convex lenses 4 is the direction indicated by the arrow z.

Further, the boundary 6 between the adjacent convex lenses 4 is formed in a curved shape in which the curvature continuously changes along the extending direction of the convex lenses 4 when viewed from the arrangement direction of the convex lenses 4.
In the present embodiment, a case will be described in which the boundary 6 between adjacent convex lenses 4 forms a non-periodic uneven shape when viewed from the direction in which the convex lenses 4 are arranged.

(Effect of the second embodiment)
If it is the optical sheet 1 of this embodiment, it will become possible to improve concealment performance compared with the conventional optical sheet 1 (for example, refer FIG. 5) similarly to 1st embodiment mentioned above. In addition to this, with the optical sheet 1 of the present embodiment, the front luminance can be improved as compared with a microlens sheet or a diffusion sheet.

(Third embodiment)
Hereinafter, a third embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described with reference to the drawings.
(Constitution)
Hereinafter, the optical sheet according to the present embodiment will be described. In addition, about the structure of a backlight unit and a display apparatus, since it is the same as that of 1st embodiment mentioned above, the description is abbreviate | omitted.

(Configuration of optical sheet)
Hereinafter, the configuration of the optical sheet 1 of the present embodiment will be described with reference to FIG. In addition, about the structure similar to 1st embodiment mentioned above, the same code | symbol is attached | subjected and demonstrated. Moreover, the description of the same configuration as that of the first embodiment described above may be omitted. Moreover, since the resin material used as the material of the optical sheet and the method for manufacturing the optical sheet are the same as those in the first embodiment described above, the description thereof is omitted.

3A and 3B are diagrams showing a configuration of the optical sheet 1 in the present embodiment, in which FIG. 3A is a perspective view of the optical sheet 1, and FIG. 3B is a BB line in FIG. It is sectional drawing.
As shown in FIG. 3, the optical sheet 1 is a sheet having a plurality of convex lenses 4 on one surface of the translucent substrate 2.

The translucent substrate 2 is formed in a plate shape using a translucent resin material.
Each convex lens 4 is formed using a triangular prism, and one piece thereof faces the surface of the translucent substrate 2.
Moreover, each convex lens 4 is extended along the same direction, and is arranged in parallel. In FIG. 3, as in FIG. 1, the extending direction of the convex lens 4 is indicated by an arrow x, the thickness direction of the optical sheet 1 is indicated by an arrow y, and the normal direction to the arrow x and the arrow y is indicated by an arrow z. Therefore, in FIG. 3, the arrangement direction of the convex lenses 4 is the direction indicated by the arrow z.

Further, the boundary 6 between the adjacent convex lenses 4 is formed in a curved shape in which the curvature continuously changes along the extending direction of the convex lenses 4 when viewed from the arrangement direction of the convex lenses 4.
In the present embodiment, a case will be described in which the boundary 6 between adjacent convex lenses 4 forms a non-periodic uneven shape when viewed from the direction in which the convex lenses 4 are arranged.

  In the present embodiment, when the boundary 6 between the adjacent convex lenses 4 is X, the coordinate in the extending direction of the convex lens 4 is X, the coordinate in the thickness direction of the optical sheet 1 is Y, and the coefficient is a. = A · sin (X / a) (where a ≠ 0), and the absolute value of the coefficient a every half cycle or every cycle increases irregularly or The case of decreasing will be described.

(Effect of the third embodiment)
If it is the optical sheet 1 of this embodiment, it will become possible to improve concealment performance compared with the conventional optical sheet 1 (for example, refer FIG. 5) similarly to 1st embodiment mentioned above. In addition to this, with the optical sheet 1 of the present embodiment, the front luminance can be improved as compared with a microlens sheet or a diffusion sheet.

(Example)
1 to 3 and FIG. 5, the optical sheet described in the first to third embodiments (see FIGS. 1 to 3) and the optical of the comparative example having the same configuration as the conventional example. The result of manufacturing a sheet (see FIG. 5) and evaluating the physical properties of both will be described.

(Optical sheet manufacturing method)
Since the manufacturing method of the optical sheet is the same as the method described in the first embodiment, the description thereof is omitted.

(Concealment performance evaluation)
To evaluate the concealment performance, remove the liquid crystal panel of the liquid crystal television (manufactured by Sony: KDL-40ZX1), place the television still with the light exit surface facing upward, and lay the diffusion film and optical sheet on the light guide plate. Turn on the TV while In this state, the difference in concealment performance was visually confirmed in the dark with respect to the optical sheet described in the first to third embodiments and the optical sheet of the comparative example. In that case, it confirmed from the position whose distance with a television is 10 cm or less.

The evaluation results are shown in Table 1.
Table 1 is a table showing the evaluation results. In Table 1, the optical sheet described in the first embodiment is the “first embodiment”, the optical sheet described in the second embodiment is the “second embodiment”, and the optical sheet described in the third embodiment. Is shown as “third embodiment”, and is shown as an optical sheet “comparative example” of a comparative example having the same configuration as the conventional example. The same applies to the evaluation of front luminance described later.

  Further, as shown in Table 1, the hiding performance was evaluated by manufacturing three or four kinds of optical sheets having different angles α formed by the tops of the convex lenses and different optical sheets having different angles α. The same applies to the evaluation of front luminance described later.

  However, the evaluation results shown in Table 1 evaluate whether or not the dot pattern of the light guide plate can be visually recognized, and “×” indicates that the dot pattern can be visually recognized at the most sparse position on the light guide plate. The dot pattern cannot be visually recognized at any position on the light guide plate.

  As shown in Table 1, the optical sheet according to the present invention, that is, the first to third embodiments, does not depend on the angle α formed by the top of the convex lens as compared with the optical sheet of the comparative example. It was confirmed that the hiding performance is high.

(Front brightness evaluation)
The evaluation of the front luminance was performed by installing a diffusion film and an optical sheet on a liquid crystal television (manufactured by Sony Corporation: KDL-40ZX1), similarly to the evaluation of the concealment performance described above. In addition, SR-3 (made by Topcon Co., Ltd.) was used for the measuring device, and it was carried out in the form of an overhead view from a distance of 50 cm from the TV in a dark place.

In this optical evaluation, as shown in Table 1, when the luminance that can be judged by actual visual observation is reduced by 20% or more, it is evaluated as “X”, and when the luminance is less than 20%, it is evaluated as “◯”. evaluated.
As shown in Table 1, it was confirmed that the optical sheet of the present invention, that is, the first to third embodiments has the same front luminance as the optical sheet of the comparative example.
As described above, the optical sheet according to the present invention can be suitably used in various applications. In addition, since the backlight unit and the display device provided with the optical sheet according to the present invention are also included in the technical scope of the present invention, they are preferably used in various applications as with the optical sheet according to the present invention. It is possible.

DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Translucent base material 4 Convex lens 6 Boundary 8 Display apparatus 10 Front side polarizing plate 12 Back side polarizing plate 14 Liquid crystal panel 16 Light guide plate 16a Light emission surface 18 Diffusion film 20 Reflective film 22 Light source 24 Reflector 26 Brightness enhancement film 28 Unit prism 30 Prism film α Angle formed by the top of convex lens 4

Claims (11)

An optical sheet in which a plurality of convex lenses extending in the same direction are arranged in parallel on at least one of the light incident surface and the light emitting surface,
The optical sheet characterized in that the boundary between the adjacent convex lenses is formed in a curved shape whose curvature continuously changes along the extending direction of the convex lenses when viewed from the arrangement direction of the plurality of convex lenses. .   2. The optical sheet according to claim 1, wherein the boundary forms a regular uneven shape when viewed from an arrangement direction of the plurality of convex lenses.   The boundary is defined as Y = a · sin (bX) (where a is the coordinate in the extending direction of the convex lens, Y is the coordinate in the thickness direction of the optical sheet, and the coefficients are a and b). The optical sheet according to claim 1, wherein the optical sheet is a sinusoidal curve represented by a relational expression of ≠ 0). The boundary is defined as Y = a · sin (X / a) (where a is a coordinate in the extending direction of the convex lens, Y is a coordinate in the thickness direction of the optical sheet, and a is a). ≠ 0) is a sine curve represented by the relational expression,
3. The optical sheet according to claim 1, wherein an absolute value of the coefficient a every half cycle or every cycle increases or decreases according to an arithmetic sequence. The boundary is defined as Y = a · sin (X / a) (where a is a coordinate in the extending direction of the convex lens, Y is a coordinate in the thickness direction of the optical sheet, and a is a). ≠ 0) is a sine curve represented by the relational expression,
3. The optical sheet according to claim 1, wherein the absolute value of the coefficient a every half cycle or every cycle increases or decreases according to a geometric progression.   2. The optical sheet according to claim 1, wherein the boundary forms a non-periodic uneven shape when viewed from an arrangement direction of the plurality of convex lenses. The boundary is defined as Y = a · sin (X / a) (where a is a coordinate in the extending direction of the convex lens, Y is a coordinate in the thickness direction of the optical sheet, and a is a). ≠ 0) is a sine curve represented by the relational expression,
The optical sheet according to claim 1 or 6, wherein the absolute value of the coefficient a every half cycle or every cycle increases or decreases irregularly. An optical sheet laminate formed by laminating a plurality of optical sheets,
The optical sheet laminate, wherein the plurality of optical sheets include at least one optical sheet according to any one of claims 1 to 7.   A backlight unit comprising: the optical sheet according to claim 1; and a light source disposed on the light incident surface side of the optical sheet.   9. A backlight unit comprising: the optical sheet laminate according to claim 8; and a light source disposed on the light incident surface side of the optical sheet included in the optical sheet laminate.   A backlight unit according to claim 9 or 10, and an image display element that is disposed on the light emission surface side of the backlight unit and defines a display image according to transmission or shading in pixel units. A display device.

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