JP2014086387A - Light guide plate, backlight unit including the same, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate capable of inhibiting hue changes of light emitted therefrom.SOLUTION: A light guide plate diffuses light entering from a side edge surface in a surface direction, includes an emission surface and a reflection surface having an irregular pattern on its surface and facing the emission surface, and is formed by a thermoplastic resin containing a blue pigment.

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.

  A backlight system has been proposed for display devices. The backlight system is a system in which a light source is arranged on the back side (the side opposite to the observer side) of a panel (liquid crystal panel or the like) whose design is to be changed, and the panel is illuminated with light from the back side of the panel.

  For the backlight unit used in the backlight system, a “direct type” in which a light source is disposed directly under a light guide plate, an “edge light system” in which a light source is disposed on a side end surface of the light guide plate, and the like have been proposed.

  In addition, liquid crystal display devices are strongly required as market needs to be thin, lightweight, and have low power consumption. In the edge light system, since the light source is disposed on the side end surface of the light guide plate, it is easy to reduce the thickness and weight. Further, even if the number of light sources is reduced to reduce power consumption, the dark part between the light sources does not occur unlike the direct type, so that it meets the needs of the market. For this reason, the backlight unit mounted on the liquid crystal display device is mainly an edge light system.

  In the edge light system, there is a case where a light guide plate is used in which a reflection pattern for starting up light in which a dot-like light diffusing material-containing ink is applied is formed on a reflection surface facing a light emission surface. In this case, in order to uniformly emit light on the light emitting surface of the light guide plate, the luminance in a region away from the light source is increased. As a method for improving the luminance in a region away from the light source, for example, there are a method for reducing the diameter of dots applied to a region close to the light source (for example, see Patent Document 1) and a method for reducing the density. In this way, by changing the reflection pattern according to the distance from the light source, the diffusion amount of light in the region near the light source can be reduced, and the diffusion amount of light in the region far from the light source can be increased. Light emission on the exit surface can be made uniform. Such dot application is performed by screen printing or the like.

  However, when forming a dot-like reflection pattern by printing, if the dot diameter is about 0.1 mm or less, clogging is likely to occur due to continuous printing, and the pattern becomes faint when mass-produced. Therefore, there is a problem that there is a limit to the adjustment of the luminance depending on the dot diameter (see, for example, Patent Document 2).

JP-A-5-323124 JP 2011-65970 A

  As described above, in the backlight unit, since the brightness adjustment is limited in the dot-like reflection pattern by printing, it is composed of a single material having a shape having an optical function using injection molding or extrusion molding. It is conceivable to use a light guide plate.

  However, unlike the case of forming a dot-like reflection pattern by printing, the above light guide plate cannot perform color correction with ink. Therefore, as the distance from the light source arranged on the side end face of the light guide plate increases, the light guide distance increases, and when the reflection is repeated, the yellow color changes due to absorption on the short wavelength side, and the display device As a result, a problem arises in color reproducibility. This problem appears more conspicuously in the case of increasing the size of the display device and reducing the number of light sources for cost reduction.

  Therefore, the present invention has been made to solve the above-described problems, and an object thereof is to provide a light guide plate with little color change.

  A light guide plate that diffuses light incident from a side end surface in a plane direction, and includes a light emitting surface, a thermoplastic resin that has a concavo-convex pattern on the surface and has a reflective surface facing the light emitting surface, and contains a blue pigment It is formed by.

  The first layer including the emission surface and the second layer including the reflection surface and laminated on the first layer include a blue pigment.

The absorption coefficient α (cm ⁻¹ ) at a wavelength of 400 nm and 500 nm of light guided through the light guide plate is 0.00 <α <0.10, and the absorption coefficient α (cm ⁻¹ ) at a wavelength of 600 nm is 0.05. It is desirable that the absorption coefficient α (cm ⁻¹ ) at <α <0.50 and wavelength of 700 nm satisfy 0.00 <α <0.50.

  The concavo-convex pattern formed on the reflecting surface is formed by arranging a plurality of unit dots so that the area ratio gradually increases as the distance from the light source in the direction perpendicular to the side end surface is increased. The ratio of the unit dot height h1 to the width W1 It is desirable that a certain aspect ratio h1 / W1 satisfies 0.1 ≦ h1 / W1 ≦ 0.5.

  A concavo-convex pattern is further formed on the surface of the exit surface, and the concavo-convex pattern formed on the exit surface includes a plurality of specific unit patterns arranged in a direction perpendicular to the side end surface from the light source. It is desirable that the aspect ratio h2 / W2, which is the ratio of the length h2 and the width W2, satisfies 0.2 ≦ h2 / W2 ≦ 0.5.

  The backlight unit according to the present invention includes at least the light guide plate.

  The display device according to the present invention includes at least the backlight unit described above.

  ADVANTAGE OF THE INVENTION According to this invention, a light-guide plate, a backlight unit, and a display apparatus with few color changes can be provided.

Schematic which shows the structure of the light-guide plate concerning this invention. Schematic which shows the structure of the backlight unit provided with the light-guide plate shown in FIG. Schematic which shows the structure of the display apparatus provided with the backlight unit shown in FIG. The figure which shows the result of the computer simulation of chromaticity x about the light-guide plate which concerns on this invention The figure which shows the result of the computer simulation of chromaticity y about the light-guide plate which concerns on this invention

  Hereinafter, the light guide plate according to the present invention will be described.

  FIG. 1 is a schematic view showing a configuration of a light guide plate 50 according to the present invention. The light guide plate 50 is a substantially rectangular flat plate-like member, and includes a side end surface on which a light source is disposed, an emission surface 55, and a reflection surface 52. The light guide plate 50 is used as an edge light type light guide plate that diffuses light incident from the side end face in the surface direction by arranging a light source at the side end.

  The material used for the light guide plate 50 may be any material that has optical transparency to the light emitted from the light source. Further, in view of yellowing change, any thermoplastic resin that is not reactive with light source light may be used. The resin constituting the light guide plate 50 may be a multi-layer, but if different materials are used, a light amount loss due to a difference in refractive index at the interface occurs, and therefore the same kind of material is preferable. As a material used for the light guide plate 50, 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 -Materials including styrene copolymer, styrene-butadiene-acrylonitrile copolymer, acrylic resin, PMMA (polymethyl methacrylate) and the like. An acrylic resin, particularly PMMA (polymethyl methacrylate) is preferable as a main material used for the layer of the light guide plate 50 because it has a good light transmittance with respect to visible light. Here, the main material refers to a material that occupies 90% or more of the weight ratio in the weight of the entire light guide plate 50.

  An uneven pattern 54 is formed on the surface of the emission surface 55. As the uneven pattern 54 formed on the surface of the emission surface 55, for example, a pattern in which a lenticular lens shape and a triangular prism shape are arranged in parallel is preferable, and a plurality of unit patterns are arranged in a direction parallel to the light incident from the light source. It is desirable that the aspect ratio h2 / W2, which is the ratio between the height h2 and the width W2 of the unit pattern, satisfies 0.2 ≦ h2 / W2 ≦ 0.5. Thereby, it is possible to improve the brightness | luminance as a light-guide plate and to improve the utilization efficiency of light. When the aspect ratio h2 / W2 is h2 / W2 <0.2, the light collecting effect is insufficient and the luminance cannot be improved. Further, when the aspect ratio h2 / W2 is h2 / W2> 0.5, the viewing angle is excessively narrowed, which is not preferable.

  On the other hand, a concavo-convex pattern 181 is formed on the surface of the reflecting surface 52. The concavo-convex pattern 181 is formed by arranging unit dots so as to become denser toward the center of the light guide plate 50. In the present embodiment, the dot-shaped uneven pattern 181 is composed of a plurality of recesses. The concavo-convex pattern 181 formed on the surface of the reflecting surface 52 is preferably a concavo-convex pattern (light rising pattern) that emits light incident from one side end face to the viewer side. By forming the concavo-convex pattern 181 on the reflecting surface 52, it can be used as an edge light type light guide plate. The concavo-convex pattern 181 is preferably a unit dot shape in which a plurality of unit dot shapes are arranged so that the area ratio gradually increases with distance from the light source in parallel to the light incident from the light source. The unit dot height h1 and width W1 It is desirable that the aspect ratio h1 / W1, which is a ratio of the above, satisfy a shape satisfying 0.1 ≦ h1 / W1 ≦ 0.5. Thereby, the brightness | luminance improvement as a light-guide plate is possible. When the aspect ratio h1 / W1 is h1 / W1 <0.1, the light rise is weak and it is difficult to improve the luminance. Further, when the aspect ratio h1 / W1 is h1 / W1> 0.5, the rising amount of light in the area close to the light source increases, and even if the area ratio of the uneven pattern 181 is controlled, the area away from the light source In this case, the luminance is reduced. The dot may have a convex shape, but a concave shape is more preferable in consideration of abrasion resistance.

  As the concave and convex patterns 54 and 181, depending on the desired specification of the light guide plate 50, for example, a convex cylindrical shape pattern, a lens shape pattern, a triangular prism shape pattern, a dot pattern, or the like that is appropriately optically designed is a saddle shape. You can do it.

  Further, in the present embodiment, the light guide plate 50 is composed of two layers: a first layer 58 including the emission surface 55 and a second layer 59 stacked on the first layer 58 and including the reflection surface 52. ing. In addition, the blue pigment 51 is added to the second layer 59 including the reflective surface 52. The blue pigment 51 is added for color correction and has a property of absorbing light having a wavelength in the vicinity of 500 to 700 nm. By making the blue pigment | dye 51 absorb the light of a one part wavelength, the yellow change which arises when light guides can be suppressed.

  The blue pigment 51 is added to the layer of the light guide plate 50 so that the light guided in the light guide plate 50 does not change yellow. As the blue dye 51, for example, an ultramarine blue pigment, an amber pigment, a rock group blue pigment, a bitumen pigment, a cobalt blue pigment, a manganese blue pigment, a phthalocyanine pigment, an anthraquinone-based blue dye, or the like can be used. However, since the pigments mentioned above have higher heat resistance than blue dyes such as anthraquinone, it is preferable when considering addition to a thermoplastic resin, but when considering transmittance, anthraquinone Blue dyes such as are preferred.

In addition, when the absorption coefficient α (cm ⁻¹ ) = 0.00 at wavelengths 400 nm, 500 nm, 600 nm, and 700 nm of light guided through the light guide plate having a configuration that does not include the blue pigment 51, the configuration that includes the blue pigment 51. The absorption coefficient α (cm ⁻¹ ) at 400 nm and 500 nm of the light guided through the light guide plate 50 is 0.00 <α <0.10, and the wavelength of the light guided through the light guide plate 50 is The absorption coefficient α (cm ⁻¹ ) at 600 nm is 0.05 <α <0.50, and the absorption coefficient α (cm ⁻¹ ) at a wavelength of 700 nm of light guided through the light guide plate 50 is 0.00. It is preferable to control the particle size, the addition amount, and the like of the blue pigment 51 so as to satisfy that <α <0.50. The light incident on the light guide plate 50 is guided through the light guide plate 50 while being collided and absorbed by the blue pigment 51. The absorption coefficient α (cm ⁻¹ ) is obtained by the following equation (1).

Here, T is a spectral transmittance (unit dimension is%), and x is an absorption distance of light blue pigment (unit dimension is cm).

  The light guide plate 50 is preferably manufactured by an extrusion method. In the extrusion method, the materials used for the multilayer can be laminated and extruded by the co-extrusion method. Further, by using a mold roll engraved with a concavo-convex pattern, the concavo-convex pattern 54 and the concavo-convex pattern 181 can be provided in-line on the surfaces of the emission surface 55 and the reflective surface 52. For this reason, the light-guide plate 50 can be manufactured continuously.

  In the present embodiment, the light guide plate 50 has been described as an example of a two-layer configuration in which the first layer 58 and the second layer 59 are stacked. However, the light guide plate 50 may have a single-layer configuration or three or more layers. A multi-layer structure may be used. When the light guide plate 50 has a single layer configuration, the blue pigment 51 may be dispersed throughout the light guide plate 50 or may be locally dispersed. Further, when the light guide plate 50 has a multilayer structure, the blue pigment 51 may be dispersed in at least one of the layers.

  Hereinafter, the backlight unit including the light guide plate according to the present invention will be described.

  FIG. 2 is a schematic diagram illustrating a configuration of the backlight unit 2 including the light guide plate 50. The backlight unit 2 includes a lamp house 6, a polarizing optical sheet 31, a condensing optical sheet 33, and a diffusing optical sheet 35. The lamp house 6 includes a light guide plate 50, a light source 176 provided on the light incident surfaces 56 that are side ends of the light guide plate 50, and a reflector 60 provided below the reflection surface 52 of the light guide plate 50. The light is emitted from the emission surface 55.

  As the light source 176, a known light source that emits light having desired characteristics can be appropriately used depending on the application and specifications. As the light source 176, for example, a light source such as a fluorescent tube, a cold cathode tube, a hot cathode tube, an external electrode tube, an LED, an organic EL, or an inorganic EL can be used.

  The number of light sources 176 to be arranged for the backlight unit 2 may be appropriately determined according to specifications, and it is sufficient that at least one light source is provided. In particular, when the light source 176 is a point light source such as an LED light source, it is preferable to arrange a plurality of light sources 176. As the light source 176, for example, LED groups arranged in a row or semiconductor laser groups arranged in a row can be used. When a plurality of light sources 176 are arranged, they may be arranged around the light guide plate 50. For example, 1) a configuration in which the light source 176 is disposed so as to face one side end surface of the light guide plate 50, 2) a configuration in which the light source 176 is disposed so as to face two side end surfaces of the light guide plate 50, and 3) a light guide plate. 50 may be any of a configuration in which the light source 176 is disposed so as to face the three side end surfaces of the light guide plate 50, and 4) a configuration in which the light source 176 is disposed so as to face the four side end surfaces of the light guide plate 50.

  In arranging the light source 176, the thickness of the light source 176 is preferably approximately the same as the thickness of the light guide plate 50. By making the thickness of the light source 176 equal to the thickness of the light guide plate, when the light source is arranged on the side end face of the light guide plate 50 as an edge light type light guide plate, the light from the light source 176 is not lost. The light can be guided into the light plate 50.

  In the backlight unit 2 shown in FIG. 2, three types of optical sheets are arranged. When viewed from the observation surface direction S, a polarizing optical sheet 31 having a polarization function and a prismatic pattern 43 so as to spread light uniformly. The condensing optical sheets 33 arranged in parallel and the diffusion optical sheet 35 in which the lens pattern 43a is formed on the transparent base material 41 so as to have a condensing function are arranged in this order. However, the combination, type, stacking order, and number of optical sheets are not limited. The optical sheet is not an essential component of the backlight unit 2, and the optical sheet may be provided separately from the backlight unit 2. When the backlight unit 2 is not provided with an optical sheet, the backlight unit 2 becomes the lamp house 6 itself.

  In addition, in the backlight unit 2, the optical sheet arrange | positioned above the output surface 55 of the light-guide plate 50 can combine a well-known optical sheet suitably from a viewpoint of display performance. Moreover, you may combine multiple types of optical sheets so that desired brightness | luminance and viewing angle may be acquired.

  As the optical sheet, for example, a sheet in which unit prisms having a triangular cross section are arranged at a constant pitch in one direction may be used. The unit prism has a size (pitch) larger than the wavelength of the incident light, so it collects light from “off-axis” and directs this light toward the viewer “on-axis”. (On-axis) "redirect or" recycle ".

  Further, as the optical sheet, for example, a sheet formed with a lenticular lens in which convex cylindrical lenses are arranged in parallel, a microlens arranged in a matrix, or the like may be used. At this time, the lens shape may be a well-known lens surface shape, for example, a spherical surface or an elliptical surface, depending on the required light collecting performance. Further, in order to improve the light collection efficiency, an aspherical surface having an elliptical surface as a reference surface and corrected by a higher order term may be employed.

  As the reflector 60, for example, a resin sheet in which a void is formed by kneading and stretching a filler in PET, PP, etc. to increase the reflectance, a sheet having a mirror surface formed by aluminum vapor deposition on the surface of a transparent or white resin sheet, A metal foil such as aluminum or a resin sheet carrying the metal foil, a metal thin plate having sufficient reflectivity on the surface, or the like can be used. By disposing the reflector 60 having light reflectivity, the light that has escaped from the reflecting surface 52 side can be reflected to the emitting surface side, and the light extraction efficiency can be improved. However, in FIG. 2, the reflector 60 having light reflectivity is disposed below the reflecting surface 52 of the light guide plate 50, but the reflector 60 is an essential component of the backlight unit 2 and the lamp house 6. is not.

  The display device of the present invention will be described below.

  FIG. 3 is a schematic diagram illustrating a configuration of the display device 1 including the backlight unit 2. The display device 1 includes a liquid crystal device 3 and a backlight unit 2 in order from the viewing surface direction S. The liquid crystal device 3 is configured by sandwiching an image display element 10 between two polarizing plates 9.

  A plurality of pixels are arranged in the image display element 10. A desired image can be displayed on the image display element 10 as a display image by the arranged pixels. As the image display element 10, a liquid crystal display element, a liquid crystal display element provided with a color filter, an organic EL element, an inorganic EL element, a film, etc. can be used, for example. Depending on the image display element used as the image display element 10, the display device 1 becomes a projection screen device, a plasma display, an EL display, a liquid crystal display device, or the like.

  In FIG. 3, part of the light emitted from the light source 176 directly enters the light guide plate 50, and the other light is reflected by the reflector 60 and enters the light guide plate 50. The light incident on the light guide plate 50 passes through the light guide plate 50 and is reflected directly or by the concave / convex pattern 181 to be emitted from the emission surface 55. The light emitted from the light guide plate 50 passes through the diffusion optical sheet 35, the condensing optical sheet 33, and the polarizing optical sheet 31. The light that has passed through the polarizing optical sheet 31 is, in the liquid crystal device 3, light from a predetermined pixel area corresponding to the polarization state of each pixel area controlled by a drive unit (not shown) based on an image signal. When the light is transmitted as display light and observed from the observation surface direction S, an image is displayed.

  Specific examples of the present invention will be described below. However, the present invention is not limited to the examples.

<Simulation>
In the light guide plate, a computer simulation was performed on the relationship between the light absorption coefficient α (cm ⁻¹ ) in the light guide plate, color change, luminance, and uniformity. The condition settings are shown below.

(Setting of light guide plate)
The light guide plate used for the simulation was set as follows.
Output surface: PMMA resin (refractive index: 1.49, concave / convex pattern: lenticular lens pattern, aspect ratio of height h2 and width W2: h2 / W2 = 0.33)
Reflective surface: PMMA resin (refractive index: 1.49, concave / convex pattern: dot pattern, aspect ratio of height h1 and width W1: h1 / W1 = 0.28)
Total thickness: 3 mm.

(Setting variables)
The absorption coefficient was set as a variable for the blue pigment contained in the layer constituting the reflective surface of the light guide plate. In addition, as Comparative Example 1, a light guide plate having a configuration not including a blue pigment was prepared. Table 1 shows the absorption coefficient α (cm ⁻¹ ) at the wavelengths of 400 nm, 500 nm, 600 nm, and 700 nm set in Cases 1 to 4 and Comparative Examples 1 and 2.

(Luminance evaluation by simulation)
The light guide plate set above is set to be incorporated in the backlight unit of a 40 liquid crystal television UN40D6900WF (horizontal visual field direction 890.9 mm width) made by SAMUNung, where the light source is arranged on both short sides of the screen, and the color of the observation surface The change Δxy, brightness and uniformity were evaluated. Regarding the color change, the maximum amount of change in x and y from the chromaticity x and y of the area divided into 6 in the horizontal direction of the screen at the center position in the vertical direction of the light guide plate and the chromaticity x and y at the light source side end portion. Calculated as Δxy. The front luminance of the setting incorporating the light guide plate of Comparative Example 1 is 100%, the setting incorporating the light guide plate of Cases 1 to 4 and Comparative Example 2, and the setting incorporating the light guide plate of Comparative Example 1 The difference in luminance value was calculated. The uniformity was calculated by dividing the minimum luminance of the area obtained by dividing the horizontal direction of the screen into 6 and dividing the vertical direction of the screen into 10 by the maximum luminance. As an optical sheet to be laminated, a microlens sheet, a prism sheet, and a diffusion film mounted on the liquid crystal television used for evaluation were used.

(simulation result)
The simulation results are shown in FIGS. 3 and 4 and Table 2.

FIG. 4 is a graph showing the results of computer simulation of chromaticity x in the horizontal direction of the screen. FIG. 5 is a graph showing the result of computer simulation of chromaticity y in the horizontal direction of the screen. 4 and 5, the horizontal axis indicates the horizontal direction (mm) of the screen, and 0 is the light source position. The vertical axis indicates chromaticity x and y, respectively. 4 and 5, it can be seen that, in Comparative Example 1, both the chromaticity x and y have a large color change between both ends at the center farthest from the light source. Further, in FIGS. 4 and 5, since the chromaticities x and y are increased, the color is changed to yellow. As in Cases 1 to 4, the absorption coefficient α (cm ⁻¹ ) at wavelengths of 400 nm and 500 nm is 0.00 <α <0.10, and the absorption coefficient α (cm ⁻¹ ) at a wavelength of 600 nm is 0. It can be seen that when 05 <α <0.50 and the absorption coefficient α (cm ⁻¹ ) at a wavelength of 700 nm is 0.00 <α <0.50, the color change is improved. As in Comparative Example 2, the absorption coefficient α (cm ⁻¹ ) at wavelengths of 400 nm and 500 nm is α> 0.10, the absorption coefficient α (cm ⁻¹ ) at a wavelength of 600 nm is α> 0.50, and the wavelength If the absorption coefficient α (cm ⁻¹ ) at 700 nm becomes α> 0.50, the absorption coefficient α (cm ⁻¹ ) is high (the blue dye contained in the layer constituting the reflection surface of the light guide plate is This is not preferable because x and y at the center portion are reduced and the color changes too much to the blue side.

  Table 2 shows the simulation results of the color change Δxy, the front luminance, and the uniformity in Cases 1 to 4 and Comparative Examples 1 and 2. From Tables 1 and 2, it was confirmed that Cases 1 to 4 improved the color change and further improved the uniformity while suppressing a decrease in luminance as compared with Comparative Example 1. Regarding Comparative Example 2, since the absorption coefficient is high, the uniformity is improved as compared with Comparative Example 1, but the luminance is greatly decreased, which is not preferable.

From these simulation results, the wavelength 400nm of the light incident into the light guide plate, the absorption coefficient at 500 nm alpha is (cm ^-1), a 0.00 <α <0.10, the absorption coefficient at a wavelength of 600 nm alpha (cm ^{- 1} ) 0.05 <α <0.50 and the absorption coefficient α (cm ⁻¹ ) at a wavelength of 700 nm satisfy 0.00 <α <0.50, so that the color change is suppressed while suppressing a decrease in luminance. It was suggested that it improves and also improves uniformity.

  Next, a light guide plate was actually produced and evaluated for luminance.

<Production of light guide plate>
The material of the emitting surface / reflecting surface was put into an extrusion die, and two layers were coextruded to form a concavo-convex pattern on the emitting surface and the reflecting surface, and a light guide plate was manufactured by an extrusion method. Hereinafter, the specification of the used material and a light-guide plate is shown.

<Comparative Example 3>
(Light guide plate material)
As Comparative Example 3, a light guide plate containing no blue pigment was produced with the following materials and specifications.
Output surface: PMMA resin (Product name: Acrypet (registered trademark) TF9, MFR = 20, manufactured by Mitsubishi Rayon, concavo-convex pattern: lenticular lens pattern)
Reflective surface: PMMA resin (product name: Mitsubishi Rayon Acrypet TF9, MFR = 20, uneven pattern: dot pattern)
Total thickness: 3 mm.

(Luminance evaluation)
The light guide plate produced above was placed in the backlight so that the light source was located on the end surface on the light guide plate side, and chromaticity and luminance were measured from the observation surface side. At this time, evaluation was performed using a backlight unit system of an LED light source liquid crystal TV (40 liquid crystal television UN40D6900WF manufactured by SAMSUNG). For measurement, an ultra-low luminance spectroradiometer: SR-UL2 (Topcon) was used. From the measured values, the color change, the front luminance, and the uniformity were calculated in the same manner as in the simulation.

<Comparative Example 4>
In the light guide plate produced in Comparative Example 3, when the absorption coefficient α (cm ⁻¹ ) at all wavelengths is α = 0.00, a blue pigment (manufactured by Dainichi Seika Kogyo Co., Ltd.) is present in the PMMA resin on the reflection surface of the light guide plate. A light guide plate was produced in the same manner as in Comparative Example 3 except that only the configuration of adding (bituminous pigment: 671 bitumen) was changed. In the prepared light guide plate, the pigment addition amount was adjusted so that the absorption coefficient α (cm ⁻¹ ) at light wavelengths of 400 nm, 500 nm, 600 nm, and 700 nm became the value shown in Comparative Example 4 in Table 3, and the chromaticity and The luminance was measured.

<Examples 1-3>
A light guide plate was produced in the same manner as in Comparative Example 4, and chromaticity and luminance were measured.
However, the pigment addition amount was adjusted so that the absorption coefficient α (cm ⁻¹ ) was a value shown in Table 3, and chromaticity and luminance were measured.

(Color change, front brightness, uniformity evaluation results)
Table 4 shows the color change, front luminance, and uniformity evaluation results of the light guide plates produced in Examples 1 to 3 and Comparative Examples 3 and 4.

From Table 4, the absorption coefficient α (cm ⁻¹ ) at a wavelength of 400 nm and 500 nm is 0.00 <α <0.10, and the absorption coefficient α (cm ^-1 ) is 0.05 <α <0.50, and the light guide plates of Examples 1 to 3 have an absorption coefficient α (cm ⁻¹ ) at a wavelength of 700 nm of 0.00 <α <0.50. It was confirmed that the color change was improved as compared with Comparative Example 3 which did not contain a blue pigment. Further, although it contains a blue pigment, the absorption coefficient α (cm ⁻¹ ) at wavelengths of 400 nm and 500 nm is α> 0.10, the absorption coefficient α (cm ⁻¹ ) at a wavelength of 600 nm is α> 0.50, The light guide plate of Comparative Example 4 in which the absorption coefficient α (cm ⁻¹ ) at a wavelength of 700 nm is α> 0.50 is improved in uniformity as compared with Comparative Example 3 that does not contain a blue pigment. This is not preferable because the reduction in luminance increases. As described above, the absorption coefficient α (cm ⁻¹ ) at wavelengths of 400 nm and 500 nm is adjusted to a range of 0.00 <α <0.10, and the absorption coefficient α (cm ⁻¹ ) at a wavelength of 600 nm is set to 0.05 < By adjusting α <0.50 and adjusting the absorption coefficient α (cm ⁻¹ ) at a wavelength of 700 nm to 0.00 <α <0.50, it is possible to suppress a decrease in front luminance and to ensure uniformity. It was confirmed that it could be improved.

  From the above, it was confirmed that the actually produced light guide plates of Examples 1 to 3 showed the same tendency as the simulation results.

  The light guide plate according to 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 useful for an image display device typified by a flat panel display, a liquid crystal display device, a color notebook PC (personal computer), a lighting tool, a building material, and the like.

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Backlight unit 3 Liquid crystal apparatus 6 Lamp house 9 Polarizing plate 10 Image display element 31 Polarizing optical sheet 33 Condensing optical sheet 35 Diffusing optical sheet 41 Transparent base material 43 Prism-shaped pattern 43a Lens pattern 50 Light guide plate 51 Blue pigment | dye 52 Reflecting surface 54, 181 Uneven pattern 55 Output surface 56 Light incident surface 58 First layer 59 Second layer 60 Reflector 176 Light source

Claims (7)

A light guide plate that diffuses light incident from a side end face in a plane direction,
An exit surface;
A surface having a concavo-convex pattern, and a reflective surface facing the emission surface,
A light guide plate formed of a thermoplastic resin containing a blue pigment. A first layer including the exit surface;
A second layer that includes the reflective surface and is stacked on the first layer;
The light guide plate according to claim 1, wherein the second layer contains the blue pigment. The absorption coefficient α (cm ⁻¹ ) at a wavelength of 400 nm and 500 nm of light guided through the light guide plate is 0.00 <α <0.10, and the absorption coefficient α (cm ⁻¹ ) at a wavelength of 600 nm is 0.00. The light guide plate according to claim 1, wherein an absorption coefficient α (cm ⁻¹ ) at 05 <α <0.50 and a wavelength of 700 nm satisfies 0.00 <α <0.50. The concavo-convex pattern formed on the reflective surface is formed by arranging a plurality of unit dots such that the area ratio gradually increases as the distance from the light source increases in the direction orthogonal to the side end surface,
The aspect ratio h1 / W1, which is the ratio between the height h1 and the width W1 of the unit dots, satisfies 0.1 ≦ h1 / W1 ≦ 0.5. The light guide plate described. An uneven pattern is further formed on the surface of the emission surface,
The concavo-convex pattern formed on the emission surface is formed by arranging a plurality of predetermined unit patterns in a direction perpendicular to the side end surface from a light source,
5. The aspect ratio h 2 / W 2, which is a ratio of the height h 2 and the width W 2 of the unit pattern, satisfies 0.2 ≦ h 2 / W 2 ≦ 0.5. 5. Light guide plate.   A backlight unit comprising the light guide plate according to claim 1.   A display device comprising the backlight unit according to claim 6.