JP2011095562A - Optical sheet combined body, backlight unit and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet combined body, a backlight unit and a display device for reducing non-uniformity and improving front brightness. <P>SOLUTION: An optical sheet combined body 10 is constituted so that first optical sheet 11 and a second optical sheet 12 to be used for illumination light path control are laminated and combined, and the refractive index of a base material of the two optical sheets 11, 12 is increased toward the display emission side from the light source side. In the optical sheets 11. 12, many unit lenses 112, 123 are arranged on at least one of the light incident surface side or the light emission surface side of the optical sheets 11, 12. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  In recent years, liquid crystal display devices using TFT (Thin Film Transistor) type liquid crystal panels and STN (Super Twisted Nematic) type liquid crystal panels are mainly commercialized mainly for color notebook PCs (personal computers) in the OA field. 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 unit employed in this type of backlight system is roughly divided into a light source lamp such as a cold cathode fluorescent tube (CCFT) and a flat plate made of an acrylic resin having excellent light transmittance. “Light guide plate light guide method” (so-called “edge light method”) for multiple reflection in the light guide plate and direct illumination with light from a light source lamp such as a cold cathode tube (CCFT) without using the light guide plate There is "type method".

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.
A liquid crystal display device 50 shown in FIG. 4 includes a liquid crystal panel 53 having upper and lower surfaces sandwiched between polarizing plates 51 and 52, and is disposed on the upper side. A light guide plate 54 made of a transparent base material such as methyl methacrylate or acrylic is installed, and a diffusion film 55 (diffusion layer) is provided on the upper surface (light emission surface 54 a side) of the light guide plate 54. Further, on the lower surface of the light guide plate 54, a scattering reflection pattern portion (not shown) for efficiently scattering and reflecting the light introduced into the light guide plate 54 toward the liquid crystal panel 53 is obtained by printing or the like. A reflection film 56 (reflection layer) is provided below the scattering reflection pattern portion.

In addition, the light guide plate 54 is provided with a light source lamp 57 at a side end portion thereof, and further covers the back side of the light source lamp 57 so that the light of the light source lamp 57 is efficiently incident on the light guide plate 54. A high-reflectance lamp reflector 58 is provided. The scattering reflection pattern portion is formed by printing, drying, and forming a mixture of white titanium dioxide (TiO ₂ ) powder in a solution such as a transparent adhesive in a predetermined pattern, for example, a dot pattern. Directivity is imparted to the light incident on the light plate 54 and guided to the light exit surface 54a side. This is a device for increasing the luminance.

  However, in the apparatus illustrated in FIG. 4, the control of the viewing angle is left only to the diffusibility of the diffusion film 55, and there is a problem that the control is difficult. For example, the display screen of the liquid crystal display is bright when viewed from the front, but the display screen may be dark when viewed from the side, and the center of the liquid crystal display is bright and the peripheral is dark There were also drawbacks. As described above, there is a problem that the light use efficiency is low.

On the other hand, in the direct type, a display device such as a large liquid crystal TV in which the light guide plate is difficult to use is used.
As a direct-type liquid crystal display device, a device illustrated in FIG. 5 is generally known.
In the liquid crystal display device 60 shown in FIG. 5, a liquid crystal panel 63 having both front and back surfaces sandwiched between polarizing plates 61 and 62 is disposed on the upper side, and a light source 64 made of a fluorescent tube or the like is provided on the lower surface side of the liquid crystal panel 63. Be placed. Further, an optical sheet such as a diffusion film 65 is provided on the upper surface side of the light source 64. In addition, a reflector 66 that reflects light traveling from the light source 64 in the direction opposite to the liquid crystal panel 63 toward the liquid crystal panel 63 is disposed on the back surface of the light source 64. Thereby, the light emitted from the light source 64 is diffused by the diffusion film 65, and this diffused light is condensed on the effective display area of the liquid crystal panel 63 with high efficiency.

  However, in the liquid crystal display device 60 shown in FIG. 5, since the control of the viewing angle is left only to the diffusibility of the diffusion film 65, there is a problem that the control is difficult. For example, when the liquid crystal display screen is viewed from the front, the display screen is bright, but when the liquid crystal display screen is viewed from the side, the display screen may be dark, and the center of the liquid crystal display screen is There were also disadvantages that were bright and the periphery was dark. As described above, there is a problem that the light use efficiency is low.

  Therefore, as one method for solving the above problem, in the liquid crystal display device 70 shown in FIG. 6, a brightness enhancement film (BEF) 71, which is a registered trademark of 3M USA, is used as the illumination light source 74 for the backlight. A method of arranging a light diffusion film (not shown) on the light emitting surface side above the BEF 71 is employed. The BEF 71 is a film in which unit prisms 73 having a triangular cross section are arranged at a constant pitch in one direction on the light emitting surface which is the upper surface of the transparent substrate 72. The unit prism 73 has a size (pitch) larger than the wavelength of light. BEF collects light from “off-axis” and redirects this light “on-axis” to the viewer, or “recycle”. To do.

  The brightness enhancement film 71 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. Here, “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 71 usually has a repetitive array structure of unit prisms arranged in only one direction, and only the 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, it is necessary to use two BEF sheets in combination so that the arrangement directions of the unit prism groups are substantially orthogonal to each other. .

  Therefore, recently, in order to increase the light use efficiency and increase the brightness, as shown in FIG. It has been proposed to provide (layer) 59 (591, 592). The prism films 591 and 592 are emitted from the light exit surface 54 a of the light guide plate 54, and concentrate the light diffused by the diffusion film 55 on the effective display area of the liquid crystal panel 53 with high efficiency. By adopting such BEF, the display designer can achieve a desired on-axis brightness while reducing power consumption. A technique in which a luminance control member having such a repetitive array structure of prisms typified by BEF is employed in a display device has been conventionally known, for example, in Patent Documents 1 to 3.

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

However, the above-described conventional liquid crystal display device has the following problems.
That is, prism sheets and lenticular sheets represented by BEF71 generally have high brightness but low concealability and have the disadvantage that the shadow of the light source on the back is easily seen through. There was a problem of being visually recognized.
Moreover, in order to improve this problem, there is a method of stacking a plurality of optical sheets such as a diffusion sheet, but since the number of members increases, if the optimum members are not stacked, it causes a decrease in luminance. There was room for improvement in that respect.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an optical sheet combination body, a backlight unit, and a display device that can reduce unevenness and improve front luminance. And

  In order to achieve the above object, the optical sheet combination according to the present invention is an optical sheet combination in which a plurality of optical sheets used for controlling an illumination optical path of a display are stacked and combined. The material is characterized in that the refractive index of the material increases from the light source side toward the display emission side.

  In the present invention, by increasing the refractive index of the plurality of optical sheets from the light source side toward the display emission side, the light can be condensed on the emission side and the front luminance can be improved. In addition, since sufficient light scattering performance can be obtained, even if a plurality of optical sheets are laminated, the concealability can be improved, and it becomes difficult to see the shadow of the light source on the back, thereby reducing unevenness. can do.

In the optical sheet combination according to the present invention, it is preferable that the optical sheet has a large number of unit lenses arranged on at least one of the light incident surface side and the light exit surface side.
In the present invention, an arbitrary refractive index can be set by changing the shape and quantity of the unit lens of the optical sheet, and an optimal combination of optical sheets can be realized.

In the optical sheet combination according to the present invention, the difference in refractive index between two overlapping optical sheets is preferably 0.01 or more larger on the exit surface side than on the incident surface side. .
Thereby, a high light-scattering performance can be given to an optical sheet combination body, and a brightness | luminance can be improved more reliably.

Further, in the optical sheet combination according to the present invention, it is more preferable that the light collecting ability of the base material of the optical sheet increases from the light source side toward the display emission side.
In the present invention, since the light can be reliably condensed on the portion where the luminance is required, the optical performance can be improved.

Further, in the backlight unit according to the present invention, the light unit is disposed on the back surface of the optical sheet combination described above, and the light emitted from the light source and the light source is incident and diffused. And a diffusing plate for emitting diffused light.
In the present invention, the optical sheet combination described above is provided, the front luminance can be improved while suppressing unevenness, and the diffusion and condensing degree can be appropriately changed according to the use by the diffusion plate. , Can enhance the optical performance.

The display device according to the present invention includes the above-described backlight unit, and an image display element that includes a backlight on the back surface and defines a display image according to transmission / light-shielding in pixel units. .
In the present invention, since the backlight unit having the above-described optical sheet combination is provided, the degree of diffusion and condensing can be appropriately changed according to the application, and the optical performance can be improved. A display quality image can be provided.

  According to the optical sheet combination body, the backlight unit, and the display device of the present invention, by laminating a plurality of optical sheets having different refractive indexes, unevenness due to the shadow of the light source can be suppressed, and the plurality of optical sheets can be refracted. By arranging from the light source side to the display emission side in ascending order of the rate, the light collecting ability is increased and sufficient light scattering performance is obtained, so that the front luminance can be improved.

It is typical sectional drawing which shows schematic structure of the display apparatus by the 1st Embodiment of this invention. It is a perspective view of the optical sheet combination used for the display apparatus shown in FIG. It is typical sectional drawing which shows schematic structure of the display apparatus by the 2nd Embodiment of this invention. It is typical sectional drawing which shows the structural example of the conventional liquid crystal display device. It is typical sectional drawing which shows the other structural example of the conventional liquid crystal display device. It is typical sectional drawing which shows an example of the conventional backlight unit. It is typical sectional drawing which shows the other structural example of the conventional liquid crystal display device.

  Hereinafter, an optical sheet combination, a backlight unit, and a display device according to a first embodiment of the present invention will be described with reference to FIGS.

In FIG. 1, reference numeral 1 denotes a display device, and reference numerals 2 and 3 denote a display backlight unit and a liquid crystal panel (image display element) provided in the display device 1, respectively.
Here, in the following description, in the display device 1 shown in FIG. 1, the liquid crystal panel 3 side is referred to as the upper side, the light guide plate 42 side described later of the backlight unit 2 is referred to as the lower side, and the normal to the plane of the liquid crystal panel 3 The direction is referred to as the vertical direction, and the upper side in the vertical direction is referred to as the emission side and the lower side is referred to as the light source side or the incident side.

  A display device 1 shown in FIG. 1 is a liquid crystal display device configured by overlapping a liquid crystal panel 3 on the light transmission side of a backlight unit 2 that emits light upward, and is directed upward from the liquid crystal panel 3. Thus, an image is displayed by sending display light whose display is controlled by the image signal.

The liquid crystal panel 3 is configured by sandwiching a liquid crystal element 33 between polarizing plates 31 and 32.
The backlight unit 2 is an edge light type light emitting device having a light emitting surface having substantially the same area as the display screen of the liquid crystal panel 3. The backlight unit 2 has an uneven shape arranged on the upper surface side of the lamp house 4. A molded optical sheet combination 10 is provided.

The lamp house 4 is arranged facing a plurality of light sources 41, 41,... Arranged on the side at a predetermined interval, and emits the light K in the normal direction. The light guide plate 42 is configured roughly.
As the light source 41, a cold cathode fluorescent lamp (CCFL), an LED, an EL, a semiconductor laser, or the like can be used.
The light guide plate 42 of the present embodiment is provided with dots 43 having a reflection pattern or a geometric structure on the back surface 42b.

  The optical sheet combination body 10 is disposed on the light exit side of the light guide plate 42 and condenses light K emitted from the light guide plate 42 on the front surface (upper surface). Then, two optical sheets (first optical sheet 11 and second optical sheet 12) are stacked and combined in the vertical direction. The optical sheet combination 10 is sized and shaped so as to be incorporated into the backlight unit 2 having a predetermined size, and has an optical shape for condensing or diffusing light on one side.

  As shown in FIG. 2, each of the first optical sheet 11 and the second optical sheet 12 has a plurality of unit lenses arranged on at least one of the light exit surface side and the incident surface side (here, the exit surface side). It is the composition to do. Thereby, it can set to arbitrary refractive indexes by changing the shape and quantity of each unit lens of optical sheets 11 and 12, and can realize the optimal combination of optical sheets.

The first optical sheet 11 positioned on the upper side (observer S side) close to the emission side has a prism shape whose surface shape is a triangular shape in cross section, has a certain thickness, and the base material 111 corresponding to the thickness. This is a structure made of a polycarbonate sheet having a refractive index of 1.59, on which a plurality of first unit lenses 112 are arranged.
The second optical sheet 12 located on the lower side near the light source side emits light on an Arton film (manufactured by JSR Corporation) substrate 121 having a surface shape of a square pyramid shape and a refractive index of 1.51. On the surface 121a side, there is a cross-stripe-shaped second unit lens 123 made of urethane acrylate ultraviolet curable resin having a refractive index after curing of 1.51.
That is, the material used as the second unit lens 123 is smaller than the refractive index of the first optical sheet 11 facing the second unit lens 123.

  The main material of each of the optical sheets 11 and 12 only needs to have a light transmittance of 88% or more. For example, polycarbonate, acrylic, acryl-styrene copolymer, polystyrene, styrene-butadiene-acrylonitrile copolymer, Examples thereof include crystalline polyarylate or polyether sulfone, bulky cyclic olefin polymer, and the like.

  Further, the refractive index difference between the first optical sheet 11 and the second optical sheet 12 facing each other in the optical sheet combination 10 is 0 for the optical sheet (here, the first optical sheet 11) that is closer to the emission surface. .01 or larger. This is because if the difference in refractive index is smaller than this, sufficient light scattering performance cannot be obtained. By making the difference in refractive index greater than 0.01 or more, the optical sheet combination 10 has high light scattering. Performance can be provided, and luminance can be improved more reliably.

  The manufacturing method of each of the optical sheets 11 and 12 and the respective unit lenses 112 and 123 is preferably manufactured by an extrusion method in consideration of the manufacturing cost. However, the base materials 111 and 121 and the unit lenses 112 and 123 are light beams. A different material may be used as long as it is a transparent material, and a unit lens may be provided on the transparent substrate with an ultraviolet curable resin.

  As described above, the backlight unit 2 includes the second optical sheet 12 and the second optical sheet 12 of the optical sheet combination 10 from the emission surface 42a of the light guide plate 42 after the light K from the light sources 41, 41,. The light La is transmitted in the order of the optical sheet 11 and emitted as light of the symbol La, the light La reaches the liquid crystal layer 33 sandwiched between the pair of polarizing plates 31 and 32, and the light La transmitted through the liquid crystal panel 3 is The light is emitted to the upper side (front side) and visually recognized by the observer S.

  By providing the optical sheet combination body 10 in this way, the refractive index of the two optical sheets 11 and 12 is increased from the light source side toward the display emission side, so that the light is condensed on the emission side and the front side. Brightness can be improved. Furthermore, since sufficient light scattering performance can be obtained, even if the two optical sheets 11 and 12 are laminated, the concealability can be improved, and the shadow of the light source on the back surface becomes difficult to see. Therefore, unevenness can be reduced.

  As described above, in the optical sheet combination body, the backlight unit, and the display device according to the first embodiment, the unevenness due to the shadow of the light source is suppressed by stacking the plurality of optical sheets 11 and 12 having different refractive indexes. In addition, by arranging a plurality of optical sheets 11 and 12 from the light source side to the display emission side in ascending order of refractive index, the light collecting ability is increased and sufficient light scattering performance is obtained, so that the front luminance is improved. Can be made.

  Next, other embodiments of the optical sheet combination, backlight unit, and display device according to the present invention will be described with reference to the accompanying drawings, but the same or similar members and parts as those of the first embodiment described above. The same reference numerals are used to omit the description, and a configuration different from that of the first embodiment will be described.

The second embodiment shown in FIG. 3 is still another embodiment of the optical sheet combination of the present invention. That is, in the optical sheet combination body 10A, the third optical sheet 13, the fourth optical sheet 14, and the first optical sheet 12 are arranged in this order from the light source side to the emission side.
The third optical sheet 13 closer to the light source side has a plurality of third unit lenses 132, 132 having a hemispherical cross section formed of urethane acrylate-based ultraviolet curable resin on the light exit surface 13a on the Arton film base 131. …have. These third unit lenses 132 are arranged over the entire surface of the base material 131.

The fourth optical sheet 14 facing the emission surface 131a of the third optical sheet 13 has a refractive index of 1.54 after curing on the light emission surface 141a of the PET film substrate 141 having a refractive index of 1.57. A plurality of fourth unit lenses 142, 142,... Formed by an epoxy acrylate-based ultraviolet curable resin and a fifth unit lens 143, 143,. Yes. As described above, the fourth unit lens 142 and the fifth unit lens 143 are mixed, so that the alignment characteristics are also mixed, and the shadow concealability of the light source on the back surface can be improved. At this time, the material of the unit lenses 142 and 143 needs to be smaller than the refractive index of the first optical sheet 12 facing on the emission side.
Note that the first optical sheet 12 on the exit surface side has the same configuration as that of the first embodiment described above, and thus detailed description thereof is omitted here.

  Next, test examples for supporting the effects of the optical sheet combination, the backlight unit, and the display device according to the first and second embodiments described above will be described below.

  In this example, as shown in Table 1, six types of optical sheets A1, B1, C1, A2, B2, and C2 were prepared, and two types of optical sheets (the light source side optical sheet 1 and the emission side in Table 2). Tests (Test Examples 1 to 12) for measuring luminance were performed on 12 optical sheet combinations in which the optical sheets 2) were appropriately combined as shown in Table 2.

  First, each optical sheet A1, B1, C1, A2, B2, C2, the optical sheet of reference A1, B1, C1 is a cross-sectional triangle, the optical sheet of reference A2, B2, C2 is a cross stripe shape, More specifically, it is as follows. Table 1 shows the structure, material, refractive index of the substrate, and refractive index of the unit lens of each of the produced optical sheets A1, B1, C1, A2, B2, and C2.

  The first optical sheet A1 is a urethane acrylate-based UV-curing using a mold having a reverse shape of a triangular section lens on an optical sheet based on a 100 μm thick Arton film (manufactured by JSR Corporation). This is produced by irradiating the resin with ultraviolet rays to give a unit lens shape. In addition, the fourth optical sheet A2 was produced by the same method using a mold having an Arton film as a base material and having a reverse shape of a unit lens having a cross-sectional cross section.

  The second optical sheet B1 is a triangular triangular cross section obtained by irradiating a urethane acrylate ultraviolet curable resin with ultraviolet rays using a mold having a reverse shape of a unit lens on an optical sheet having a PET film having a thickness of 125 μm as a base. It was produced by applying a shape unit lens shape. The fifth optical sheet B2 was produced by the same method using a mold having a PET film as a base material and having a cross-sectional cross-stripe-shaped unit lens having a reverse shape.

  The third optical sheet C1 was manufactured by extrusion using polycarbonate as a material, and was produced with a total thickness of 240 μm having a unit lens having a triangular cross section. Further, the sixth optical sheet C2 was produced by the same polycarbonate extrusion method using a mold having a reverse shape of a unit lens having a cross-stripe cross section.

Next, each of the created first to sixth optical sheets A1, B1, C1, A2, B2, C2 was appropriately combined, and as shown in Table 2, the optical sheet combination used in Test Examples 1 to 12 was set. . That is, only the first optical sheet A1 is used in Test Example 1, only the second optical sheet B1 is used in Test Example 2, only the third optical sheet C1 is used in Test Example 3, and the light source side optical sheet is used as a cross in Test Examples 4 to 12. The optical sheets A2, B2, and C2 provided with the stripe-shaped unit lenses are arranged, and the optical sheets A1, B1, and C1 provided with the triangular unit lenses are arranged on the emission side optical sheet.
In Test Examples 1 to 12, the optical sheet combination is incorporated into the display device of the first embodiment shown in FIG. 1 and a screen using a spectroradiometer SR-3A (manufactured by Topcon Corporation). The luminance was measured at a measurement angle of 0.2 ° from a distance of 50 cm in the normal direction.

  Here, the relative luminance in Table 2 is evaluated that the luminance in the configuration of only the third optical sheet C1 of Test Example 3 is 100% as a reference value, and that the relative luminance is 100% or more is improved in front luminance. did. As a result, it was confirmed that the relative luminance exceeded 100% in all the optical sheet combinations obtained by combining the two sheets used in Test Examples 4 to 12.

As described above, the first and second embodiments of the optical sheet combination, the backlight unit, and the display device according to the present invention have been described. However, the present invention is not limited to the above-described embodiments, Changes can be made as appropriate without departing from the scope.
For example, the display device 1 according to the present embodiment is a liquid crystal display device, but is not limited to this, and may be a display device that displays an image with light, such as a projection screen device, a plasma display device, or an EL display device. Any display device can be used.

And in optical sheet combination body 10 and 10A by this Embodiment, the structure which becomes large as the condensing capability of the base material of an optical sheet goes to a display output side from a light source side may be sufficient. Thereby, since it can be made to condense reliably on the part where a brightness | luminance is required, the improvement of optical performance can be aimed at.
Further, another optical sheet may be disposed between the optical sheet combination body 12 having the uneven shape and the liquid crystal panel 3.
Furthermore, the shape of the unit lens is not limited to a prism shape, a quadrangular pyramid shape, or the like.

  The optical sheet combinations 10 and 10A may be composed of a plurality of optical sheets, but it is preferable that the optical sheet combination 10 or 10A is a combination of two sheets or three sheets in consideration of a light amount loss due to an excessive increase in sheet boundary surface.

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Backlight unit 3 Liquid crystal panel (image display element)
4 lamp house 41 light source 42 light guide plate 10, 10A optical sheet combination 11 first optical sheet 12 second optical sheet 13 third optical sheet 14 third optical sheet 111, 121, 131, 141 base material 112, 123, 132, 142, 143 Unit lens K Light from light source La Light from light guide plate

Claims (6)

An optical sheet combination in which a plurality of optical sheets used for controlling an illumination optical path of a display are stacked and combined,
An optical sheet combination, wherein the refractive index of the base material of the plurality of optical sheets increases from the light source side toward the display emission side.   2. The optical sheet combination according to claim 1, wherein a plurality of unit lenses are arranged on at least one of the light incident surface side and the light emission surface side of the optical sheet.   3. The optical according to claim 1, wherein a difference in refractive index between the two overlapping optical sheets is 0.01 or more greater in the optical sheet on the exit surface side than in the optical sheet on the incident surface side. Sheet combination.   4. The optical sheet combination according to claim 1, wherein the light collecting ability of the base material of the optical sheet increases from the light source side toward the display emission side. 5. It is arranged on the back surface of the optical sheet combination according to any one of claims 1 to 4,
A backlight unit comprising: a light source; and a diffusing plate that emits diffused light by causing the light emitted from the light source to be incident and diffusing the incident light to reduce unevenness in the amount of light. The backlight unit according to claim 5;
An image display element that includes the backlight on the back surface and defines a display image according to transmission / shading in pixel units;
A display device comprising:

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