JP2014093266A - Light guide plate, illuminating device using the same, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate having less amount of loss, no interference fringe and having a superior external appearance.SOLUTION: A light guide plate comprises a transparent substrate including at least an incident plane for taking in light from a light source, a light emission plane for emitting light and a bottom surface facing the light emitting plane. The bottom surface has a plurality of light control elements. The light control elements are arranged side by side with prescribed intervals in a direction (direction Y) parallel to the incident plane to form rows, the plurality of rows are formed in a direction (direction X) perpendicular to the incident plane, and a ratio of a difference between a position in the direction Y of a middle point in the direction Y of an optional light control element within an optional row and a position in the direction Y of a middle point in the direction Y of the light control element within a row adjacent to the optional row and present nearest from the optional light control element, to a prescribed interval, is 1/11 to 5/11.

Description

  The present invention relates to a light guide plate, an illumination device using the same, and a display device.

  A display device such as a general liquid crystal display has an illumination device on the back of a transmissive liquid crystal panel. This backlight unit is divided into two types: a so-called edge light type using a light guide that multi-reflects light from a light source lamp within a flat light guide plate excellent in light transmission, and a direct type that directly illuminates with a light source lamp. Broadly divided.

  In this type of lighting device in which a light source is arranged near the side end portion of the light guide plate, the light that has entered the light guide plate from the side end surface of the light guide plate is totally reflected by the planar portion of the light guide plate. Go inside. In addition, the shape of this light source is not limited, For example, a linear form and a dot form may be sufficient.

  If the surface of the light guide plate facing the display device (hereinafter referred to as the light exit surface) and the opposite surface (hereinafter referred to as the bottom surface) are flat throughout, most of the incident light will be at the boundary surface between these and the outside air. Total reflection occurs, and the light emission efficiency from the light guide plate, that is, the irradiation efficiency with respect to the display device decreases. For this reason, many light guide plates have a large number of fine concavo-convex shapes on the light emission surface or light reflection surface, thereby preventing repetition of only total reflection, thereby improving light emission efficiency.

  As a method for reducing interference fringes (so-called moire) generated by the structure of a liquid crystal panel and an optical sheet or a light guide plate in a display device using this type of illumination device, the illumination device described in Patent Document 1 has been proposed. Yes. In Patent Document 1, as shown in FIG. 11, a dot-like pattern is formed on either the light exit surface or the light reflection surface of the light guide plate at an angle with respect to the pixel arrangement direction of the liquid crystal display panel. The structure to be placed is shown. In addition, a method of making the moire inconspicuous by stacking diffusion sheets is often employed.

JP 2000-162595 A

  The shape of the surface of the light guide plate causes interference with pixels arranged at regular intervals on the display screen of the liquid crystal display panel, resulting in moire. There is a method of reducing the moiré by giving an angle to the shape of the surface of the light guide plate with respect to the arrangement direction of the pixels. It must be cut with a mold that is held, is difficult to manufacture, or involves significant material loss.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a light guide plate having a good appearance with low loss, easily, high brightness, and no moire.

  One aspect of the present invention is a light guide plate made of a transparent substrate having at least an incident surface that takes in light from a light source, a light emitting surface that emits light, and a bottom surface that faces the light emitting surface. The light control element includes a plurality of light control elements, and the light control elements form a line in a direction parallel to the incident surface (Y direction) at a predetermined interval, and the line is a direction perpendicular to the incident surface (X direction). ), A Y-direction position of a midpoint in the Y direction of any light control element in any row, and a light control element in a row adjacent to any row that is closest to any light control element Is a ratio of 1/11 or more and 5/11 or less with respect to a predetermined interval.

  In addition, the light control element density representing the number of light control elements per unit area on the bottom surface increases as the distance in the X direction from the incident surface increases, and the array pattern of the light control elements is divided into a plurality of regions. In the same region, the predetermined interval is constant, the arrangement interval of the columns in the X direction changes so as to become farther away from the incident surface, and the predetermined interval is discontinuous at the boundaries of the plurality of regions. The distance from the incident surface becomes smaller, the array spacing of the columns changes discontinuously at the boundaries of the plurality of regions, and the region farther from the incident surface is closer to the incident surface. It is preferably smaller than other areas adjacent to the side.

  The plurality of regions are preferably divided in a direction perpendicular to the incident surface.

  Moreover, it is preferable that a light control element is a concave shape inside the bottom face of a light-guide plate.

  Another aspect of the present invention is an illuminating device including the above-described light guide plate and a light source unit.

  Still another aspect of the present invention is a display device including the above-described illumination device and a liquid crystal panel.

  By using the light guide plate of the present invention, the light control elements are not aligned in the direction perpendicular to the incident surface, so that moire between the lines extending in the same direction of the black matrix in the liquid crystal display panel can be reduced. Thereby, since it is not necessary to sandwich the diffusion sheet for the purpose of avoiding moire, the cost can be reduced and higher luminance can be realized compared to a configuration in which moire is substantially removed by the diffusion sheet.

The disassembled perspective view of the display apparatus of embodiment of this invention The figure which shows the course of the incident light from a light source inside the light-guide plate of embodiment of this invention. Schematic showing the arrangement of light control elements of an embodiment of the present invention The figure which shows an example of the change of the arrangement | sequence of the light control element accompanying the change of an occupation area ratio in case the deviation | shift rate of the light control element of embodiment of this invention is constant. The figure which shows an example of the division | segmentation of the bottom face of the light-guide plate of embodiment of this invention. The figure which shows an example of the shape of the light control element of the Example of this invention The figure which shows an example of the arrangement | sequence of the light control element in case a deviation | shift rate is 0 The figure which shows an example of the arrangement | sequence of the light control element in case a deviation | shift rate is 5/11 The figure which shows an example of the arrangement | sequence of the light control element in case a deviation | shift rate is 1/11 The figure which shows an example of the arrangement | sequence of the light control element in case a deviation | shift rate is 1/2 The figure which shows an example of the arrangement | sequence of the light control element in the conventional light-guide plate

  FIG. 1 is an exploded perspective view showing an example of a configuration of a display device 1 using an illumination device 2 using a light guide plate according to an embodiment of the present invention. As shown in FIG. 1, the lighting device 2 includes, for example, optical sheets 7 and 8, a light guide plate 6, a reflection sheet 5, and a light source 4 and is configured in a rectangular plate shape or a wedge shape.

  The light source 4 includes light emitting elements such as CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp), EL (Electro Luminescence), and LED (Light Emitting Diode). More preferably, the light source 4 is provided with a housing that reflects the light and efficiently enters the light guide plate 6 so as to cover the light of the light source 4. The light source 4 may be disposed only on one side of the light guide plate 6 as shown in FIG. 1, but the incident surface is not limited to one side. For example, as shown in FIG. 3, the second light source is the first light source. The light source may be arranged in contrast to the surface relative to the adjacent surface.

  The reflection sheet 5 is provided to prevent light loss due to light incident on the light guide plate coming out of the bottom surface. As the reflection sheet 5, for example, a resin sheet in which a void is formed by kneading and stretching a filler in PET, PP or the like to increase the reflectance, a transparent or white resin sheet having a mirror surface formed by aluminum evaporation or the like on the surface, A metal foil such as aluminum or a resin sheet carrying the metal foil, a metal thin plate having sufficient reflectivity on the surface, and the like can be used.

  The light guide plate 6 has a function of guiding light from the light source 4 to the entire surface of the image display panel 3. FIG. 2 shows an example of the path of incident light from the light source 4 inside the light guide plate 6. The light incident from the incident surface 61 of the light guide plate 6 travels inside the light guide plate 6 while being totally reflected by the planar portion of the light guide plate 6. There are many light control elements 63 on the bottom surface 62 of the light guide plate 6, and the path of incident light is changed at the interface of the light control elements 63.

  The light guide plate 6 is made of a material having high light transmittance and low birefringence. For example, UV or radiation curable resin is used on a substrate such as glass, or a thermoplastic resin material such as polymethyl methacrylate (OPMMA), polycarbonate (PC), or cyclic olefin copolymer (COC) is used. Then, it is molded by a known extrusion molding method or injection molding method.

  Although the thickness of the light-guide plate 6 is not specifically limited, About 0.5-3 mm is preferable. If it is thinner than 0.5 mm, it is easy to break, and the handleability is deteriorated. If it is thicker than 3 mm, the entire backlight unit becomes large, and its application is limited. For example, it is not suitable for a thin display.

  FIG. 3 shows an outline of the arrangement of the light control elements 63. On the bottom surface 62 of the light guide plate 6, the fine light control elements 63 are arranged in a row at a constant interval Py in a direction parallel to the incident surface 61 (Y direction). They are arranged side by side with an interval Px in the (X direction). Further, columns adjacent in the X direction are arranged with the Y direction position shifted. In other words, the Y-direction rows that are adjacent to the positions where the Y-direction rows composed of the light control elements 63 are shifted in both the X and Y directions are arranged.

  When a light control element 63 in a row is A, and another light control element 63 closest to A in the row adjacent to the row is B, the Y-direction midpoint of A and B in the Y-direction A difference in position of the points in the Y direction is defined as a Y direction deviation D. The Y-direction deviation D is not particularly limited, but is preferably about 1/11 to 5/11 of Py. When this ratio is set as a displacement rate t, the Y-direction displacement D is represented by tPy. If t is 1/11 or more and 5/11 or less, the arrangement of the light control elements 63 is suitably disturbed, and the effect of reducing moire is great. When t is smaller than 1/11, the arrangement of the light control elements 63 is not disturbed, and the effect of reducing moire is small. When the value exceeds 5/11 and becomes a value close to 1/2, a certain column and its two adjacent columns Since the displacement in the Y direction becomes small, the arrangement is less disturbed and the effect of reducing moire is small.

  As the light control element 63 moves away from the incident surface 61, the density, that is, the occupied area ratio d, which is the area occupied by the light control element 63 per unit area on the bottom surface 62 of the light guide plate, further increases. The change in the occupied area ratio d on the bottom surface 62 of the light guide plate may be due to a change in the area per light control element 63 or a change in the number of light control elements 63, or both. There may be. Here, in order to increase the occupied area ratio d, the pitch Py of the light control elements 63 in the Y direction row may be changed and the deviation amount D in the Y direction may be changed. For example, FIG. 4 shows an example of the arrangement of the light control elements 63 when the density d is increased by increasing the number of light control elements 63 per unit area. Further, the change in the occupied area ratio d may be continuous or discontinuous. Since the former requires complicated arrangement data and high molding accuracy, the latter is easier to manufacture. As an example of the latter, as shown in FIG. 5, the light guide plate bottom surface 62 is divided into a plurality of regions, and the occupation area ratio d is changed stepwise. In the example illustrated in FIG. 5, the plurality of regions are divided in a direction orthogonal to the arrangement direction of the Y direction column.

  An optical sheet 7 having a diffusing function is preferably disposed on the exit surface of the light guide plate 6. In the example shown in FIG. 1, two optical sheets are used, but the number is not limited. The optical sheet 7 is, for example, a prism sheet that is a resin film having a prism structure, a micro lens sheet having a micro lens structure, a diffusion sheet in which fine particles having different refractive indexes are mixed, and the like, and exhibits a light diffusing or condensing effect. Due to the light diffusion, the deviation of the light incident from the light source due to the position in the y-axis direction, the occurrence of local brightness due to scratches or dirt on the light guide plate 6, and the light control element 63 on the bottom surface 62 of the light guide plate 6 are easily visible. To prevent it. In the present invention, it is not necessary to remove moire using a diffusion sheet having a high haze value, and a diffusion sheet having a low haze value with low luminance loss may be used, or a diffusion sheet may not be used. A sheet having a light condensing effect improves luminance by narrowing the distribution of the angles of emitted light.

  In the optical sheet 7, the image display panel 3 is disposed on the surface opposite to the light guide plate 6. The arranged image display panel 3 includes two polarizing plates (polarizing films) 8 and 9 and an image display element 10 sandwiched therebetween. The image display panel 3 is constituted by a liquid crystal panel, for example, and the image display element 10 is constituted by filling a liquid crystal layer between two glass substrates. The liquid crystal display element selected as the image display element 10 is a typical element that transmits and blocks light in pixel units and displays an image, and can improve image quality compared to other display elements. .

  As described above, the light guide plate according to the embodiment of the present invention, the illumination device using the same, and the display device including the illumination device have been described. However, the illumination device is not applied only to the display device. Applicable to.

  Examples of the present invention will be described in detail below, but the present invention is not limited to the following examples.

  The light guide plate 6 of each example was a rectangular plate made of PMMA, the length in the x direction was 500 mm, the length in the y direction was 300 mm, and the thickness was 3 mm. The light control elements 63 arranged on the bottom surface 62 of the light guide plate 6 have a substantially semi-ellipsoidal shape shown in FIG. 6 and are microlenses having a length L = 200 μm, a width W = 100 μm, and a height H = 20 μm.

  The illumination device 2 uses a white LED as the light source 4 facing the side surface of one side of the light guide plate 6 as an incident surface. The reflection sheet 5 is disposed facing the bottom surface 62 of the light guide plate 6, and the optical sheet 7 is disposed facing the light exit surface 64 of the light guide plate 6.

  Examples 1 to 5 have the Y-direction deviation D = tPy determined by the respective deviation rates t. In either case, the occupied area of the light control element 63 on the bottom surface 62 increases as the distance from the incident surface 61 increases. In the light guide plate 6 of Example 1, the occupation area ratio of the light control element 63 was continuously changed over the entire bottom surface 62. In the light guide plates of Examples 2 to 5, the bottom surface 62 is divided into five regions shown in FIG. 5, and as the distance from the incident surface 61 increases, the area occupied by the bottom surface 62 of the light control element 63 discontinuously at the region boundary. Was arranged to be larger. In any case, the interval (pitch) Py of the light control elements 63 in the Y direction row was changed with the change in the occupied area ratio. In the light guide plate 6 of Example 1 in which the occupation area ratio change is continuous, the shift amount D is also continuously changed according to the distance from the incident surface 61, and the occupation area ratio change is discontinuous. In the light guide plate 6 of ˜5, the shift amount D was also changed discontinuously. FIGS. 7 to 10 show examples of the arrangement of the light control elements 63 when the deviation rates t are 0, 5/11, 1/11, and 1/2, respectively.

  On the other hand, as Comparative Example 1, a light guide plate 6 was prepared in which the light control elements 63 were arranged without shifting in the Y direction. That is, in Comparative Example 1, the Y-direction deviation D = 0. Further, also in Comparative Example 1, as in Examples 2 to 5, the bottom surface 62 is divided into five regions shown in FIG. 5, and as the distance from the incident surface increases, the bottom surface of the light control element 63 is discontinuously at the region boundary. The occupying area ratio at 62 was increased.

  About these Examples 1-5 and the comparative example 1, the presence or absence of the interference fringe was visually evaluated. The evaluation results are shown in Table 1.

  In Examples 1 and 2, the change in the occupied area ratio and the change in the Y-direction deviation D were made continuous and discontinuous, but no moire was observed in either case (appearance) ○). It was confirmed that the occurrence of moire was sufficiently suppressed regardless of whether the changes in the occupied area ratio and the Y-direction deviation D were continuous or discontinuous.

  Moreover, although moire was not seen in Examples 1-4, in Example 5, although moire was confirmed depending on the angle which looks at a display, and moire was suppressed rather than Comparative Example 1, Examples 1-4. In comparison with, the degree of suppression was inferior (appearance Δ).

  In addition, Example 6 and Comparative Example 2 were prepared by adding a diffusion sheet to the configurations of Example 5 and Comparative Example 1, respectively. The interference fringes and the luminance were evaluated for Examples 4 to 6 and Comparative Examples 1 and 2. Moire was similarly observed visually, and the luminance was measured using a spectral radiance meter SR-UL2 manufactured by Topcon at the center of the screen. The results are shown in Table 2.

  At t = 1/2, the slightly observed interference fringes were substantially removed by increasing the diffusion sheet (Example 6). At t = 0, a slight interference fringe was observed even when the diffusion sheet was increased (Comparative Example 2).

  Since the brightness | luminance of Example 4, 5 and the comparative example 1 is comparable, it turned out that the Y direction shift | offset | difference D does not affect a brightness | luminance. However, when the diffusion sheet was added, the luminance was impaired by 5% (Example 6 and Comparative Example 2).

  From these, it was found that the arrangement of the light control element 63 having the Y-direction deviation D is effective in reducing moire, and the deviation rate t is particularly preferably 1/11 to 5/11. Furthermore, since the reduction of moire due to Y deviation does not involve a reduction in luminance, it was confirmed that it is superior not only in the cost reduction but also in the reduction of light amount loss compared to the method of adding a diffusion sheet.

  The present invention is useful for a light guide, a lighting device including the light guide, a display device, and the like.

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Illumination apparatus 3 Image display panel 4 Light source 5 Reflective sheet 6 Light guide plate 7 Optical sheet 8 Polarizing plate (polarizing filter)
9 Polarizing plate (polarizing filter)
DESCRIPTION OF SYMBOLS 10 Image display element 61 Light-guide plate entrance surface 62 Light-guide plate bottom face 63 Light-guide-plate bottom face light-control element

Claims (6)

A light guide plate comprising a transparent substrate having at least an incident surface for taking in light from a light source, a light emitting surface for emitting the light, and a bottom surface facing the light emitting surface;
The bottom surface has a plurality of light control elements;
The light control elements are arranged in a row at a predetermined interval in a direction parallel to the incident surface (Y direction),
A plurality of the rows are formed in a direction (X direction) perpendicular to the incident surface,
The Y-direction position of the Y-direction midpoint of any of the light control elements in any of the columns, and the light control element in the column adjacent to the any of the columns and closest to the arbitrary light control element The light guide plate according to claim 1, wherein a difference between the light control element and a Y-direction midpoint of the light control element is a ratio of 1/11 or more and 5/11 or less with respect to the predetermined interval. A light control element density representing the number of light control elements per unit area at the bottom surface increases as the distance in the X direction from the incident surface increases;
The array pattern of the light control elements is divided into a plurality of regions,
In the same region, the predetermined interval is constant, and the arrangement interval of the columns in the X direction changes so as to become smaller as the distance from the incident surface increases.
The predetermined interval varies discontinuously at the boundary between the plurality of regions, and becomes smaller as the region moves away from the incident surface.
The arrangement interval of the rows changes discontinuously at the boundaries of the plurality of regions, and the region far from the incident surface is smaller than the other regions adjacent to the side closer to the incident surface. The light guide plate according to claim 1, wherein the light guide plate is characterized.   The light guide plate according to claim 2, wherein the plurality of regions are divided in a direction perpendicular to the incident surface.   The light guide plate according to claim 1, wherein the light control element has a concave shape inside a bottom surface of the light guide plate.   An illuminating device comprising the light guide plate according to claim 1 and a light source unit.   A display device comprising the illumination device according to claim 5 and a liquid crystal panel.