JP2012204136A - Light guide plate, backlight unit, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate with high light extraction efficiency in which incident efficiency of light incident to the light guide plate from a light source is improved.SOLUTION: The light guide plate is for diffusing light from a light source toward a plane direction, and has a light-incident surface with unevennesses formed, and further, total reflection of light from the light source is restrained by providing fine unevennesses on the light-incident surface. Therefore, light reflecting to a light source side can be restrained, and incident efficiency of light incident to the light guide plate from the light source can be improved. With this, the display device with high luminance can be provided.

Description

  The present invention relates to a light guide plate used for optical path control, a backlight unit using the light guide plate, and a display device incorporating the backlight unit.

  In recent years, display devices using TFT (Thin Film Transistor) type liquid crystal panels and STN (Super Twisted Nematic) type liquid crystal panels have been proposed. In such a display device using a liquid crystal display, a light source is arranged on the back side of the liquid crystal panel (opposite to the viewer side), and the liquid crystal panel is illuminated with light from the light source, a so-called backlight. The method is adopted.

  In addition, liquid crystal display devices are strongly demanded as market needs to be thin, high brightness, light weight, and low power consumption. Accordingly, backlight units mounted on liquid crystal display devices are also light weight, high brightness, low power. It is required to be power consumption. In particular, in a color liquid crystal display device, the transmittance of the liquid crystal panel is much lower than that of a monochrome-compatible liquid crystal panel. Therefore, it is essential to improve the luminance of the backlight unit in order to obtain low power consumption of the device itself. It has become.

  In addition, with the diversification of video media, the demand for liquid crystal display devices capable of 3D display is increasing due to the need for higher image quality and the desire to experience the realism of video. In the case of performing 3D display with a liquid crystal display device, an “active shutter system” that requires special glasses has been proposed. In the active shutter method, right-eye and left-eye images are alternately displayed, and the shutter in dedicated glasses is opened and closed, so that the images are distributed and displayed three-dimensionally for the right-eye and left-eye. For this reason, in the active shutter system, the light emission time is reduced to half of the normal time, and the luminance is reduced to 1/10 compared to the normal 2D display due to the loss of the polarizing plate and reflection of the dedicated glasses. It has been. For this reason, the liquid crystal display device for 3D is required to have higher luminance than a normal liquid crystal display device for 2D display.

  For example, for the purpose of increasing the brightness of a liquid crystal display device, a triangular prism sheet (see Patent Document 1) having an apex angle of 90 ° is incorporated as a brightness adjustment sheet in a backlight unit, thereby improving the brightness of the display screen. Has been proposed (see Patent Document 2 and Patent Document 3).

  As a backlight unit employed in the backlight system, a “light guide plate light” in which a light source lamp such as a cold cathode fluorescent tube (CCFT) is subjected to multiple reflection within a flat light guide plate having excellent light transmittance. A “guide method” (so-called “edge light method”) has been proposed.

  In a display device using a conventional light guide plate light guide method, light emitted from a light source is first incident from the light incident surface of the light guide plate, scattered and reflected by the light reflecting surface, and emitted from the light emitting surface of the light guide plate. The For this reason, if the incident efficiency of light entering the light incident surface of the light guide plate from the light source is poor, the amount of light emitted from the light emitting surface of the light guide plate is reduced, and the luminance of the entire screen is reduced.

JP 60-70601 A JP-A-6-102506 Japanese National Patent Publication No. 10-506500

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a light guide plate with high light extraction efficiency that improves the incident efficiency of light entering the light guide plate from the light source.

  One embodiment of the present invention is a light guide plate that diffuses light from a light source in a surface direction, a light incident surface on which light from the light source is incident, a light reflecting surface that is substantially orthogonal to the light incident surface, A light guide plate comprising a light emitting surface facing the light reflecting surface, wherein irregularities are formed on the light incident surface.

  Further, the convex and concave portions of the unevenness may have a shape extending in a substantially vertical direction with respect to the light emitting surface.

  The ten-point average roughness Rz of the unevenness is in the range of 0.45 ≦ Rz ≦ 1.50, and the arithmetic average roughness Ra of the unevenness is in the range of 0.06 ≦ Ra ≦ 0.23. It is preferable that it exists in.

  The area ratio Rf of the flat portion on the light incident surface is preferably in the range of 0.00 ≦ Rf ≦ 94.75.

  One embodiment of the present invention is a backlight unit including the light guide plate described above and a light source arranged so that light is incident on a light incident surface of the light guide plate.

  The backlight unit may further include an optical sheet disposed on the exit surface of the light guide plate.

  One embodiment of the present invention includes the above-described backlight unit, and an image display element arranged so that light emitted from the backlight unit is incident from the back side. Device.

  In the display device described above, the image display element may define a display image according to transmission / shading in pixel units.

  The light guide plate of the present invention suppresses total reflection of light from the light source by providing fine irregularities on the light incident surface. For this reason, the light reflected toward the light source can be suppressed, and the incident efficiency of light entering the light guide plate from the light source can be improved. Therefore, a display device with high luminance can be provided.

It is the schematic which shows an example of the light-guide plate of this invention. It is the schematic which shows an example of the light-guide plate of this invention. It is the schematic which shows an example of the light-guide plate of this invention. It is the schematic which shows an example of the backlight unit of this invention. It is the schematic which shows an example of the display apparatus of this invention. It is the schematic which shows an example of the display apparatus of this invention. It is a correlation diagram of the front luminance ratio and ten-point average roughness Rz of the light-guide plate shown in an Example. It is a correlation diagram of front luminance ratio and arithmetic mean roughness Ra of the light-guide plate shown in an Example.

Hereinafter, the light guide plate of the present invention will be described.
The light guide plate of the present invention is a light guide plate that diffuses light from a light source in a surface direction, a light incident surface on which light from the light source is incident, a light reflecting surface substantially orthogonal to the light incident surface, and the light A light emitting surface facing the reflecting surface, and the light incident surface has irregularities.

  The light guide plate of the present invention suppresses total reflection of light from the light source by providing fine irregularities on the light incident surface. For this reason, the light reflected toward the light source can be suppressed, and the incident efficiency of light entering the light guide plate from the light source can be improved. Therefore, a display device with high luminance can be provided.

  Light from the light source is emitted so as to be distributed in a certain range. When the light incident surface is a perfectly flat surface, light rays with a certain angle or less with respect to the light incident surface enter the light guide plate with transmission and refraction, but light with a certain angle or more is light. It cannot penetrate into the light guide plate due to total reflection on the incident surface. When the light incident surface has a structure with fine irregularities, the angle of the light from the light source with respect to the light incident surface varies depending on the part, so that total reflection of incident light can be suppressed, and light from the light source can be efficiently The light can enter the light guide plate.

  The unevenness may be formed on at least one of the side end surfaces substantially orthogonal to the light reflecting surface and the light emitting surface. If at least one end face of the light guide plate is uneven, the uneven surface acts as the light incident surface of the present invention. In addition, irregularities may be formed on a plurality of side end surfaces substantially orthogonal to the light reflecting surface and the light emitting surface. When unevenness is formed on a plurality of side end surfaces, all of the side end surfaces on which the unevenness is formed can be used as a light incident surface, and light is emitted more efficiently when configured to introduce light from a light source from multiple directions. It can be introduced into the light guide plate.

In FIG. 1, one Embodiment of the light-guide plate of this invention is shown.
FIG. 1 shows a light guide plate of the present invention in which irregularities having a shape extending in a substantially vertical direction with respect to a light emitting surface are formed on a light incident surface.
FIG. 1A is an overall perspective view of the light guide plate 3. The light guide plate 3 has a light incident surface 1 in which unevenness is formed on one end surface 4 and light is incident on the light incident surface 1. And a light reflecting surface 2 that is substantially orthogonal to the light incident surface 1, and a light emitting surface 3 that faces the light reflecting surface 2.
FIG. 1B is a schematic cross-sectional view viewed from the Y-axis. In the unevenness formed on the light incident surface 1, the apex angle A of the unevenness, the base B of the unevenness, the flat portion G of the unevenness, and the height of the unevenness. H and the height P of the unevenness are shown.

FIG. 2 shows another embodiment of the light guide plate of the present invention.
FIG. 2 shows the light guide plate of the present invention in which irregularities having a shape extending in a substantially horizontal direction with respect to the light emitting surface are formed on the light incident surface.
FIG. 2A is an overall side view of the light guide plate 3. The light guide plate 3 has a light incident surface 1 in which unevenness is formed on one end surface 4 and light is incident on the light incident surface 1. And a light reflecting surface 2 that is substantially orthogonal to the light incident surface 1, and a light emitting surface 3 that faces the light reflecting surface 2.
FIG. 2B is a schematic cross-sectional view viewed from the Z-axis. In the unevenness formed on the light incident surface 1, the apex angle A of the unevenness, the base B of the unevenness, the flat portion G of the unevenness, and the height of the unevenness. H and the height P of the unevenness are shown.

Moreover, it is preferable that the said uneven | corrugated convex part is a shape extended in a substantially perpendicular direction with respect to the said light-projection surface.
The shape of the light guide plate of general specifications is a plate shape. As shown in FIGS. 1 and 2, when the length of the side in the Y-axis direction and the length of the side in the Z-axis direction are compared on the light incident surface 1, the length of the side in the Z-axis direction is larger. For this reason, in the case of a shape in which the unevenness extends one-dimensionally, the unevenness in the shape extending in the Z-axis direction (see FIG. 2) is formed by forming the unevenness in the shape extending in the Y-axis direction (see FIG. 1). ), The area of the light incident surface facing the light source is increased, and the light extraction efficiency can be further improved. The improvement of the light extraction efficiency when the unevenness extending in the Y-axis direction is formed is particularly remarkable when the light source is a point light source. Since the LED light source is a point light source, when the LED light source is used, it is particularly preferable to form unevenness extending in the Y-axis direction. When forming irregularities extending in the Y-axis direction, the irregularities need only be substantially parallel to the Y-axis direction and may not be exactly parallel.

  Further, when the light incident surface has a shape in which fine unevenness extends, the unevenness does not necessarily need to be linear, and the unevenness may be curved.

The ten-point average roughness Rz of the unevenness is in the range of 0.45 ≦ Rz ≦ 1.50, and the arithmetic average roughness Ra of the unevenness is in the range of 0.06 ≦ Ra ≦ 0.23. It is preferable that it exists in.
When the surface roughness of the light incident surface is too small, the reflection of the light incident surface cannot be suppressed and it is difficult to obtain the effect of the present invention. Further, when the surface roughness of the light incident surface is too large, the light diffusibility of the light incident surface is increased, and the amount of light leaking from a surface other than the light emitting surface is increased, thereby causing a reduction in front luminance of the light emitting surface. In addition, the distribution of fine irregularities on the light incident surface does not necessarily have to be constant within the light incident surface, but if the gradient of the surface roughness of the irregularities depending on the position of the light incident surface is too steep, There may be a site where the efficiency changes locally, and as a result, the display quality may be lowered. For this reason, it is preferable that the surface roughness of fine irregularities on the light incident surface is not significantly different throughout the light incident surface.

  The area ratio Rf of the flat portion on the light incident surface is preferably in the range of 0.00 ≦ Rf ≦ 94.75. Even when the area ratio Rf of the flat portion on the light incident surface exceeds 94.75%, the effect of the present invention is exhibited. However, as the area ratio Rf approaches 100, the superiority of the light guide plate according to the present invention becomes difficult. Specifically, when the area ratio Rf of the flat portion on the light incident surface is 0 or more and 94.75 or less, the light guide plate of the present invention realizes an improvement in incident efficiency of 3% or more compared to when Rf = 100. it can.

The light reflecting surface is provided with a scattering reflection pattern for uniformly scattering and reflecting the light incident from the light incident surface toward the light emitting surface. The scattering reflection pattern may be appropriately selected from known pattern materials and pattern shapes according to the light source to be used, application, and the like. In addition, for the formation of the scattering reflection pattern, a known pattern forming method may be appropriately selected according to the selected pattern material and pattern shape. For example, the scattering reflection pattern may be formed using a printing method, a laser method, an ink jet method, an injection method, an extrusion shaping method, or the like. For example, the scattering reflection pattern may be formed by printing a mixture of white titanium dioxide (TiO ₂ ) powder in a transparent adhesive solution or the like, printing it in a dot pattern, and drying it.

  In the light guide plate of the present invention, a lens shape may be formed on the light reflecting surface and / or the light emitting surface. By forming the lens shape, it is possible to control optical characteristics such as light reflectivity / light collecting property / diffusivity. The lens shape can also improve appearance characteristics such as optical adhesion, unevenness, and Newton ring. At this time, the lens shape may be appropriately selected from known shapes according to desired characteristics. For example, a convex cylindrical shape, a lens shape, a triangular prism shape, or the like may be used.

  When forming lens shapes on both the light reflecting surface and the light emitting surface, the lens shape of the light reflecting surface and the lens shape of the light emitting surface may be the same shape or different shapes. In addition, when both the light reflecting surface and the light emitting surface have a lens array shape extending in one direction, the light reflecting surface / light is considered in consideration of suppressing the occurrence of moire due to the shape of both surfaces. It is preferable that the minute lens shapes on the emission surface are substantially orthogonal to each other.

  FIG. 3 shows an example of the light guide plate of the present invention in which a lens shape is specifically formed. The lens shape of the light guide plate shown in FIG. 3A is a triangular prism shape with an apex angle of 90 °. The lens shape of the light guide plate shown in FIG. 3B is a shape in which polygonal prisms are arranged in parallel. The lens shape of the light guide plate shown in FIG. 3C is a shape in which triangular prisms having different heights are arranged in parallel. The lens shape of the light guide plate shown in FIG. 3D is a shape in which triangular prisms having different pitches are arranged in parallel. The lens shape of the light guide plate shown in FIG. 3E is a curved lenticular shape. The lens shape of the light guide plate shown in FIG. 3F is a non-curved surface lenticular shape. The lens shape of the light guide plate shown in FIG. 3G is a shape in which curved lenticular lenses having different heights are arranged in parallel. The lens shape of the light guide plate shown in FIG. 3 (h) is a shape in which curved lenticular lenses having different pitches are arranged in parallel.

  The light guide plate of the present invention may have a structure in which a plurality of layers are laminated. For example, it may be a laminate including an optical sheet layer, a transparent layer, and the like. At this time, if the sheet boundary surface increases too much, a light quantity loss occurs at the boundary surface, so that the laminate is preferably four layers or less. However, it is sufficient if the amount of light satisfying the specifications is obtained, and a multilayered body having more than four layers may be used.

  The material for forming the light guide plate of the present invention may be any material that has optical transparency to the light emitted from the light source. For example, when the light source is visible light, polycarbonate resin, polystyrene resin, fluorine-based acrylic resin, epoxy acrylate resin, methylstyrene resin, fluorene resin, cycloolefin polymer, polyethylene terephthalate, polypropylene, acrylic-styrene copolymer, styrene-butadiene -Materials including acrylonitrile copolymer, acrylic resin, PMMA (polymethyl methacrylate), and the like may be used. An acrylic resin, particularly PMMA (polymethyl methacrylate) is preferable as a main material used for the light guide plate of the present invention because it has a good light transmittance to visible light. Here, the main material means a material having a weight ratio of 90% or more in the weight of the entire light guide plate.

Moreover, you may disperse | distribute transparent particles in the material which forms a light-guide plate, and rigidity and toughness can be provided to a light-guide plate with a transparent particle. Transparent particles are roughly classified into organic fine particles and inorganic fine particles. For example, organic fine particles such as acrylic resin and polycarbonate, inorganic fine particles such as glass beads, and the like can be used.
These transparent particles are not particularly limited as long as they are known transparent particles, and can be suitably used regardless of the shape and particle size.

One kind of transparent particles may be used, or two or more kinds of mixtures may be used, but it is most preferable that the transparent particles are uniformly dispersed in the light guide plate.
In consideration of a decrease in front luminance due to light diffusion due to the transparent particles, the transparent particles preferably have a weight ratio of 1% or less in the weight of the entire light guide plate.

  The manufacturing method of the light guide plate of the present invention may use a known processing method as appropriate according to the dimensions / specifications of the light guide plate. For example, melt the resin pellets that are the material of the light guide plate, extrude the resin into a plate shape with a certain thickness from the die with an extruder, and mold the shape of the desired lens inverted before the resin plate cools and hardens Laminated with a base material sheet, and the cooled resin is peeled off from the base material sheet, the resin is cut according to the specifications of the desired light guide plate, and it is extended one-dimensionally by polishing or the like on the side surface that becomes the light incident surface. By forming irregularities with existing shapes, the light guide plate of the present invention made of resin and having a desired lens shape can be manufactured.

Hereinafter, the backlight unit of the present invention will be described.
The backlight unit of the present invention includes the light guide plate described above and a light source arranged so that light is incident on the light incident surface of the light guide plate.

  What is necessary is just to arrange | position a light source so that light may inject into the light-incidence surface in which the unevenness | corrugation of the light-guide plate was formed. At this time, if the distance between the light incident surface of the light guide plate and the light source is extremely large in the backlight unit, the amount of light that leaks to the side without ever hitting the light incident surface increases. This causes a decrease in front brightness of the exit surface. For this reason, it is preferable to make the gap between the light incident surface of the light guide plate and the light source small enough to prevent the light guide plate from being warped or distorted by heat.

  As the light source, a known light source that emits light having a desired characteristic may be used depending on the application and specifications. For example, a light source such as CCFL, LED, organic EL, or inorganic EL may be used.

The number of light sources arranged for one backlight unit may be appropriately determined according to specifications, and it is sufficient that at least one light source is provided. In particular, in the case of a point light source such as an LED light source, it is preferable to arrange a plurality of light sources.
When arranging a plurality of light sources, they may be arranged around the light guide plate. For example, in the case of a quadrilateral light guide plate, 1) a configuration in which light sources are arranged on one side, 2) a configuration in which light sources are arranged on two sides, 3) a configuration in which light sources are arranged on three sides, and 4) light sources on four sides. Any of the arrangement to arrange may be sufficient.
When the light source is arranged so that light is incident from a plurality of directions so as to surround the light guide plate, if the end surface of at least one direction of the light guide plate is uneven, the uneven portion acts as the light incident surface of the present invention. .

  Moreover, the above-described backlight unit may further include an optical sheet disposed on the emission surface of the light guide plate. A display device having desired display performance can be provided by appropriately combining with a known optical sheet.

FIG. 4 shows an example of the backlight unit of the present invention incorporating an optical sheet.
In the backlight unit 4 shown in FIG. 4, an optical sheet 71 is disposed in the light exit surface direction of the light guide plate 74. The optical sheet 71 is a sheet in which unit prisms 73 having a triangular cross section are arranged at a constant pitch in one direction on a light emitting surface which is the upper surface of the transparent base material 72, and the unit prism 73 has a wavelength of incident light. The size (pitch) is larger than This condenses light from “off-axis” and directs this light “on-axis” to the viewer, or “recycle”. I can do it.

In the optical sheet 71 shown in FIG. 4, when the repetitive array structure of the unit prisms 73 is arranged in only one direction, the two optical sheets 71 are arranged so that the arrangement directions of the unit prism groups are substantially orthogonal to each other. Is preferred.
The optical sheet 71 shown in FIG. 4 increases the on-axis luminance by reducing the off-axis luminance when using the display device (when observing), 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. Therefore, by arranging the two optical sheets 71 so that the arrangement directions of the unit prism groups are substantially orthogonal to each other, it is possible to control the luminance of the display light in both the horizontal direction and the vertical direction.

The display device of the present invention will be described below.
The display device of the present invention includes the above-described backlight unit and an image display element arranged so that light emitted from the backlight unit is incident from the back side.

  The image display element can display a desired image as a display image by switching a plurality of pixels. As the image display element, for example, a liquid crystal display element, a liquid crystal display element provided with a color filter, an organic EL element, an inorganic EL element, or the like may be used.

  Further, it is preferable that the image display element defines a display image in accordance with transmission / shielding in pixel units.

FIG. 5 shows an example of a display device 50 using the light guide plate of the present invention.
In the display device 50 shown in FIG. 5, the first polarizing plate 51 and the second polarizing plate 52 are disposed on the front and back surfaces of the liquid crystal panel 53, the diffusion film 55 is disposed on the lower surface side of the liquid crystal panel 53, and the lower part of the diffusion film 55 The light guide plate 54 is disposed, the reflection film 56 is disposed below the light guide plate 54, the light source lamp 57 is disposed at the side end of the light guide plate 54, and the back side of the light source lamp 57 of the light source lamp 57 is covered. A reflection plate 58 is provided. At this time, the light guide plate 54 has a scattering reflection pattern printed on the opposite side of the light emitting surface 54a, imparts directivity to the light incident in the light guide plate 54, and guides it to the light emitting surface 54a side. It has become.

FIG. 6 shows another example of the display device 50 using the light guide plate of the present invention.
In the display device 50 shown in FIG. 6, the first polarizing plate 51 and the second polarizing plate 52 are disposed on both the front and back surfaces of the liquid crystal panel 53, the diffusion film 55 is disposed on the lower surface side of the liquid crystal panel 53, and the lower part of the diffusion film 55. The light guide plate 54 is disposed on the light guide plate 54, the reflective film 56 is disposed below the light guide plate 54, and the prism layer 59 including the first optical sheet 591 and the second optical sheet 592 is disposed between the polarizing plate 52 and the diffusion film 55. The light source lamp 57 is disposed at the side end of the light guide plate 54, and the reflection plate 58 is provided so as to cover the back side of the light source lamp 57 of the light source lamp 57. Here, the first optical sheet 591 and the second optical sheet 592 are optical sheets in which the repetitive array structure of unit prisms is arranged in only one direction, and the first optical sheet 591 and the second optical sheet 592 are units. The prism groups are arranged so that the arrangement directions thereof are substantially orthogonal to each other.

<Example 1>
First, the resin pellets were melted, and the resin was extruded in a plate shape from a die using an extruder, and laminated with a base sheet having a mold shape in which the lens shape was inverted before the resin plate was cooled and cured.
At this time, PMMA resin pellets were used as resin pellets.

  Next, the cooled resin was peeled from the base sheet, and the resin was cut.

  Next, unevenness having a shape extending one-dimensionally by polishing was formed on the side surface portion serving as the light incident surface. At this time, the polishing direction was the Y-axis direction.

  Next, the reflective dot by white ink was printed on the flat part used as a light-incidence surface. At this time, the reflective dots were arranged in parallel so as to form a hexagonal close-packed arrangement, and the diameter of the reflective dots was increased as the distance from the light incident surface was increased.

  As described above, side in the X-axis direction: 1045 mm, side in the Z-axis direction: 596 mm, thickness in the Y-axis direction: 4 mm, extending direction of the light emitting surface: X-axis direction, lens shape of the light emitting surface: triangular prism shape The direction in which the unevenness of the light incident surface extends: the Y-axis direction, the ten-point average roughness Rz of the light incident surface: 1.13, and the arithmetic average roughness Ra of the light incident surface: 0.19. A light plate was obtained.

<Example 2>
The light guide plate of the present invention was produced in the same manner as in Example 1. However, ten-point average roughness Rz: 0.55 and arithmetic average roughness Ra: 0.09.

<Example 3>
The light guide plate of the present invention was produced in the same manner as in Example 1. However, ten-point average roughness Rz: 0.45 and arithmetic average roughness Ra: 0.06.

<Example 4>
The light guide plate of the present invention was produced in the same manner as in Example 1. However, ten-point average roughness Rz: 1.50 and arithmetic average roughness Ra: 0.23.

<Example 5>
The light guide plate of the present invention was produced in the same manner as in Example 1. However, ten-point average roughness Rz: 2.15 and arithmetic average roughness Ra: 0.44.

<Example 6>
The light guide plate of the present invention was produced in the same manner as in Example 1. However, the ten-point average roughness Rz: 0.35 and the arithmetic average roughness Ra: 0.05.

<Example 7>
The light guide plate of the present invention was produced in the same manner as in Example 1. However, the ten-point average roughness Rz: 0.39 and the arithmetic average roughness Ra: 0.04.

<Front brightness evaluation>
The light guide plate is allowed to stand so that the light exit surface faces upward, and light from the LED light source is incident through a 1 mm × 40 mm slit placed at a distance of 0.3 mm from the light entrance surface, and from the vertical direction of the light exit surface. A luminance measuring device was placed in a shape of looking down on the light guide plate, and the measurement was performed in a dark place.
Hereinafter, Table 1 shows the evaluation results of Examples 1 to 7.
For the reference sample in the optical evaluation, the surface roughness of the light incident surface having the same front luminance as that in the case where the light incident surface is completely flat in the simulation was calculated and adjusted to be the surface roughness. A light guide plate was used. Here, “the surface roughness of the light incident surface having the same front luminance as that when the light incident surface is completely flat” is the ten-point average roughness Rz: 3.81, the arithmetic average roughness Ra = 0. 78. In Table 1, it is shown as “Ref.”.

  FIG. 7 shows a correlation diagram between the front luminance ratio and the ten-point average roughness Rz of the light guide plate shown in the example. From FIG. 7, the graph shows a convex shape upward, and the front luminance is 3% or more as compared with the reference sample in the optical evaluation when the ten-point average roughness Rz is in the range of 0.45 ≦ Rz ≦ 1.50. It was confirmed that it would be higher.

  FIG. 8 is a correlation diagram between the front luminance ratio and the arithmetic average roughness Ra of the light guide plate shown in the example. From FIG. 8, the graph shows a convex shape upward, and the arithmetic average roughness Ra is higher than the reference sample in the optical evaluation by 3% or more in the range of 0.06 ≦ Ra ≦ 0.23. It was confirmed that

  As described above, the ten-point average roughness Rz of the unevenness is in the range of 0.45 ≦ Rz ≦ 1.50, and the arithmetic average roughness Ra of the unevenness is in the range of 0.06 ≦ Ra ≦ 0.23. It was confirmed that the front brightness was significantly improved.

<Example 8>
A light guide plate having the same 10-point average roughness and arithmetic average roughness as those of Examples 1 to 7 was manufactured, and the <front luminance evaluation> was performed in the same manner as described above. However, the extending direction of the unevenness of the light incident surface was defined as the Z-axis direction.

  Similarly to Examples 1 to 7, the light guide plate having the unevenness of the light incident surface extending in the Z-axis direction has a ten-point average roughness Rz in the range of 0.45 ≦ Rz ≦ 1.50. In addition, it was confirmed that the front luminance is significantly improved when the arithmetic average roughness Ra of the unevenness is in the range of 0.06 ≦ Ra ≦ 0.23. However, the overall brightness of the light guide plate with the Y-axis direction as the extending direction of the unevenness of the light incident surface is higher than that of the light guide plate with the extending direction of the unevenness of the light incident surface as the Z-axis direction. A trend was observed.

<Example 9>
The light guide plate of the present invention was produced in the same manner as in Example 1, and <Front luminance evaluation> was performed as described above. However, as shown in FIG. 1B, the projections and depressions on the light incident surface were triangular prisms. Further, the uneven flat portion G, the uneven height H, and the uneven height P shown in FIG. 1B are fixed, and the apex angle A of the unevenness and the base B of the unevenness are set as variables. A plurality of samples having different point average roughness and arithmetic average roughness were produced.

  Even if the concavo-convex shape is a triangular prism shape, the ten-point average roughness Rz of the concavo-convex is in the range of 0.45 ≦ Rz ≦ 1.50 as in Examples 1 to 7, and the arithmetic average of the concavo-convex It was confirmed that the front brightness was significantly improved when the roughness Ra was in the range of 0.06 ≦ Ra ≦ 0.23. Therefore, it was confirmed that the light guide plate of the present invention is effective even when it has a certain pattern.

  The light guide plate of the present invention can be widely used for applications in which incident light from a light source is diffused in the surface direction. For example, it is expected to be used for applications such as image display devices typified by flat panel displays, 3D liquid crystal display devices, color notebook PCs (personal computers), lighting fixtures, and building materials.

DESCRIPTION OF SYMBOLS 1 ... Light incident surface 2 ... Light reflective surface 3 ... Light-emitting surface 4 ... End surface 5 ... Light source 50 ... Display apparatus 51 ... First polarizing plate 52 ... Second polarizing plate 53 ... Liquid crystal panel 54 …… Light guide plate 55 …… Diffusion film 56 …… Reflection film 57 …… Light source lamp 58 …… Reflection plate 59 …… Prism layer 591 …… First optical sheet 592 …… Second optical sheet 70 …… Backlight unit 71 …… Optical sheet 72 …… Transparent substrate 73 …… Unit prism 74 …… Light guide plate

Claims (8)

A light guide plate that diffuses light from a light source in a plane direction,
A light incident surface on which light from the light source is incident;
A light reflecting surface substantially orthogonal to the light incident surface;
A light exit surface facing the light reflecting surface,
A light guide plate having irregularities formed on the light incident surface. 2. The light guide plate according to claim 1, wherein the uneven convex portion has a shape extending in a substantially vertical direction with respect to the light emitting surface. The ten-point average roughness Rz of the unevenness is in a range of 0.45 ≦ Rz ≦ 1.50, and
The light guide plate according to claim 1, wherein the arithmetic average roughness Ra of the unevenness is in a range of 0.06 ≦ Ra ≦ 0.23.   4. The light guide plate according to claim 1, wherein an area ratio Rf of the flat portion on the light incident surface is in a range of 0.00 ≦ Rf ≦ 94.75. 5. A light guide plate according to any one of claims 1 to 4,
A light source disposed so that light is incident on a light incident surface of the light guide plate;
A backlight unit characterized by comprising An optical sheet disposed on the exit surface of the light guide plate;
The backlight unit according to claim 5, further comprising: The backlight unit according to claim 5 or 6,
And an image display element arranged so that light emitted from the backlight unit is incident from the back side. The display device according to claim 7, wherein the image display element defines a display image according to transmission / shielding in pixel units.