JP2010044268A - Light diffusion plate, optical sheet, back light unit and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion plate which can reduce a lamp image and further can improve front luminance, and to provide an optical sheet, a back light unit and a display device using the same. <P>SOLUTION: A light diffusion plate 10 obtained by dispersedly mixing light scattering particles 13 into a resin 12 includes at least two layers of the first resin layer 20 having a light transmission of T1% and the second resin layer 21 having a light transmission of T2% (T1%<T2%). Concretely, as the light scattering particles, spherical particles having a particle diameter of 1 to 12 μm and also whose refractive index difference with the resin is 0.15 to 0.18 are used, the mixing amount of the light scattering particles 13 in the first resin layer 20 is controlled to 4 to 10 wt.%, the mixing amount of the light scattering particles 13 in the second resin layer is controlled to 0.1 to 0.5 wt.%, and a ratio between the layer thickness d1 of the first resin layer 20 and the layer thickness d2 of the second resin layer 21, d1/d2 is controlled to 1/19 to 1/4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light diffusing plate mounted on a liquid crystal backlight device or a lighting device having a light source such as a fluorescent tube, LED, EL, and the like, and an optical sheet, a backlight unit, and a display device using the light diffusing plate.

In recent years, display devices using TFT-type liquid crystal panels and STN-type liquid crystal panels have been commercialized mainly in color notebook PCs (personal computers) in the OA field, for example.
Such a display device employs a so-called backlight system in which a light source is arranged on the back side of the liquid crystal panel and the liquid crystal panel is illuminated with light from the light source.
The backlight units used in this type of backlight system can be broadly divided into multiple light sources such as cold cathode fluorescent lamps (CCFL) within a flat light guide plate made of acrylic resin with excellent light transmission. There are a “light guide plate light guide method” (so-called edge light method) and a “direct type method” that does not use a light guide plate.

As a display device on which a light guide plate light guide type backlight unit is mounted, for example, the display device shown in FIG. 5 is generally known.
This display device includes a liquid crystal panel 172 sandwiched between polarizing plates 171 and 173, and a light guide plate 179 made of a transparent base material such as a substantially rectangular plate-like PMMA (polymethyl methacrylate) or acrylic is installed on the back side thereof. A diffusion film (diffusion layer) 178 is provided between the upper surface (light emitting side) of the light guide plate 179 and the polarizing plate 173 on the rear side.

  On the back side of the light guide plate 179, a scattering reflection pattern portion (not shown) for scattering and reflecting the light introduced into the light guide plate 179 so as to be uniform in the direction of the liquid crystal panel 172 is printed. A reflective film (reflective layer) 177 is provided on the further back side of the scattering reflection pattern portion.

  Further, a light source lamp 176 is attached to one side end of the light guide plate 179, and covers the back side of the light source lamp 176 in order to make the light of the light source lamp 176 enter the light guide plate 179 efficiently. A high-reflectance lamp reflector 181 is provided. The scattering reflection pattern portion is formed by printing a mixture of white titanium dioxide (TiO2) powder in a transparent adhesive or the like in a predetermined pattern, for example, a dot pattern, and drying and forming the light guide plate 179. A directivity is imparted to the light incident on the inside of the light to guide it to the light exit surface side, thereby increasing the brightness.

  Recently, in order to improve the light utilization efficiency and increase the brightness, as shown in FIG. 6, a prism film (prism layer) having a condensing function between the diffusion film 178 and the liquid crystal panel 172 is used. 174, 175 have been proposed. The prism films 174 and 175 are for emitting the light emitted from the light exit surface of the light guide plate 179 and diffused by the diffusion film 178 to the effective display area of the liquid crystal panel 172 with high efficiency.

  On the other hand, a direct type backlight unit is used in a display device such as a large liquid crystal TV in which it is difficult to use a light guide plate. As an example of using this backlight unit, for example, a display as shown in FIG. Devices are generally known.

  In this display device, a liquid crystal panel 172 sandwiched between polarizing plates 171 and 173 is provided, and a light source 151 made of a fluorescent tube or the like is provided on the back side thereof. And the light radiate | emitted from the light source 151 is diffused by the diffusion film 182, and is condensed on the effective display area of the liquid crystal panel 172 with high efficiency. In order to efficiently use the light from the light source 151 as illumination light, a reflector 152 is disposed on the back surface of the light source 51.

  In a display device equipped with such a direct type backlight unit, light scattering particles are blended to prevent the occurrence of uneven brightness by preventing the light source image (lamp image) from being seen on the display screen. The formed resin plate is provided as a light diffusion plate for diffusing light emitted from the light source.

This light diffusing plate is required to have a high transmission and high diffusion function of preventing the lamp image from being visually recognized by diffusing the light while transmitting the light. Trial and error is performed by changing the type, particle size, and blending amount.
In this regard, in the case of a light diffusing plate uniformly dispersed at a certain concentration by using spherical particles as light scattering particles to be blended with the resin, it has been confirmed that the light diffusing characteristic widens the viewing angle. Yes. Therefore, since the lamp image is visually recognized in a state where only the bright part is spread, stripe-like luminance unevenness occurs between the wide bright part and the narrow dark part. Therefore, in order to suppress this luminance unevenness, it is necessary to reduce the light transmittance so that the difference between light and dark becomes difficult to be visually recognized. As a result, there is a problem that the front luminance becomes insufficient.

  Further, in the liquid crystal display device shown in FIG. 7, since the control of the viewing angle is left only to the diffusibility of the diffusion film 182, the control is difficult, and the central portion in the front direction of the liquid crystal display screen is bright, The characteristic that becomes darker toward the periphery cannot be avoided. For this reason, when the liquid crystal display screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.

Therefore, as one method for solving such a problem, as shown in FIG. 8, a brightness enhancement film (BEF) 185, which is a registered trademark of 3M USA, is placed above the illumination light source 190 for the backlight. There has been proposed a method of improving the front luminance by arranging a light diffusion film (not shown) on the light emitting surface side above the BEF 185 (see, for example, Patent Documents 1 to 5).
As shown in FIGS. 8 and 9, the BEF 185 is a film in which unit prisms 187 having a triangular cross section are arranged at a constant pitch in one direction on the upper surface of the transparent substrate 186.
The unit prism 187 has a size (pitch) larger than the wavelength of light. BEF collects light from “off-axis” and redirects this light “on-axis” to the viewer, or “recycle”. To do.

When using the display device (when observing), the BEF increases the on-axis brightness by reducing the off-axis brightness. Here, “on-axis” is a direction that coincides with the visual direction of the viewer, and is generally on the normal direction side with respect to the display screen.
When this BEF is used alone, the repetitive array structure of unit prisms is arranged in only one direction, so that only the direction change or recycling in the parallel direction is possible. Therefore, in order to control the luminance of the display light in the horizontal and vertical directions, generally, two sheets are combined and used so that the parallel directions of the unit prism groups are substantially orthogonal to each other.
Japanese Patent No. 3374316 Japanese Patent No. 3684587 Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

  By the way, when the BEF is used together with the light diffusing plate as described above, it is possible to increase the intensity of light in the viewer's visual direction and improve the front luminance, but the light component due to the refraction action is in the viewer's visual direction. There is a problem that the side lobe light is unnecessarily emitted in the lateral direction without traveling.

  For this reason, as shown in the luminance distribution diagram of FIG. 10, the luminance distribution emitted from the BEF has the highest front luminance at an angle of 0 ° with respect to the visual direction of the viewer, and is around ± 90 ° from the front. There was a problem that a small light intensity peak was generated and the light could not be collected efficiently.

  In addition, when only the luminance in the front direction is excessively improved, the peak width of the curve of the luminance distribution becomes extremely narrow, and the viewing area is extremely limited. Therefore, in order to increase the peak width appropriately, it is necessary to newly provide a light diffusion film which is a separate member from BEF (prism sheet), which increases the number of parts. Therefore, not only does it lead to an increase in material cost, but the operation for assembling the display becomes complicated, which is not preferable.

  The present invention has been made in view of such problems, and provides a light diffusing plate capable of reducing a lamp image and improving front luminance, an optical sheet using the same, a backlight unit, and a display device. The purpose is to do.

In order to solve the above problems, the present invention proposes the following means.
That is, the light diffusing plate according to the present invention is a light diffusing plate in which light scattering particles are dispersed and mixed in a resin. The first resin layer has a total light transmittance of T1% and the total light transmittance is T2%. It consists of at least two layers with the second resin layer, and the total light transmittance T1% of the first resin layer and the total light transmittance T2% of the second resin layer satisfy the relationship of T1% <T2%. It is characterized by.

In the light diffusing plate having such characteristics, the first resin layer can exhibit high light diffusibility as compared with the second resin layer while having light transmittance, and the second resin layer has While having light diffusibility, it is possible to exhibit high light transmittance as compared with the first resin layer.
Therefore, by combining the first resin layer and the second resin layer, a light diffusing plate having both light diffusing properties and light transmitting properties can be realized, and the lamp image can be accurately obtained. It is possible to improve the front brightness while reducing the brightness.

  In the light diffusing plate according to the present invention, the light scattering particles are true spherical particles having an average particle diameter of 1 to 12 μm, and a refractive index difference between the light scattering particles and the resin is 0.15 to 0. 18 and the mixing amount of the light scattering particles in the first resin layer is 4 to 10% by weight, and the mixing amount of the light scattering particles in the second resin layer is 0.1 to 0.5% by weight. The ratio d1 / d2 between the layer thickness d1 of the first resin layer and the layer thickness d2 of the second resin layer is 1/19 to 1/4.

According to the light diffusing plate having such characteristics, in the first resin layer in which the amount of light scattering particles in the resin is in the range of 4 to 10% by weight, very high light is maintained while maintaining a certain degree of light transmittance. Has diffusivity. Therefore, the bright place of the lamp on the light source 11 can be widened to obtain high light diffusibility, and the effect of reducing the lamp image can be obtained.
On the other hand, the second resin layer in which the mixing amount of the light scattering particles in the resin is in the range of 0.1 to 0.5% by weight has very high light transmittance while maintaining a certain degree of light diffusibility. Therefore, a large brightness in the front direction can be obtained.
Therefore, by combining the first resin layer and the second resin layer, it is possible to obtain high light transmittance while obtaining high light diffusivity. Can be improved.

  Furthermore, the light diffusing plate according to the present invention includes a third resin layer having a configuration similar to that of the first resin layer on a surface of the second resin layer opposite to a surface on which the first resin layer is laminated. Is characterized by being laminated.

  Even with such a three-layered light diffusing plate, as described above, high light transmittance can be obtained while obtaining high light diffusibility, and front luminance can be improved while reducing the lamp image. It becomes possible.

  An optical sheet according to the present invention is an optical sheet that emits incident light from the light source to the other surface side when the light source is disposed on one surface side, and includes any one of the light diffusing plate and the light diffusing plate. And a lens sheet that is disposed on the other surface side opposite to the light source and converts the optical characteristics of the light of the light source that has passed through the light diffusion plate and emits the light.

  According to the optical sheet having such a feature, a lens sheet having a condensing function in the front direction is laminated on the light diffusing plate. Therefore, in addition to the function of the light diffusing plate, the collecting by the lens sheet is performed. Optical function can be obtained. Therefore, it is possible to obtain a high front luminance while reducing the lamp image.

  On the other hand, the optical sheet according to the present invention is an optical sheet that emits incident light from the light source to the other surface side when the light source is disposed on the one surface side. A light diffusing film that is disposed on the other surface side opposite to the light source of the plate, converts the optical characteristics of the light of the light source that has passed through the light diffusing plate, and emits the light. Also good.

  Also in the optical sheet having such a feature, in addition to the function of the light diffusing plate, it is possible to obtain a light collecting function by the light diffusing film. Therefore, it is possible to obtain a high front luminance while reducing the lamp image.

  A backlight unit according to the present invention includes the optical sheet and a light source disposed on one surface side of the optical sheet.

  According to the backlight unit having such a feature, since the light diffusion plate and the optical sheet described above are used, the optical characteristics relating to diffusibility and transparency are optimized, the lamp image is reduced, and the front direction It is possible to emit light with improved brightness.

  The display device according to the present invention includes the backlight unit, and an image display unit that is disposed on an emission surface side of the backlight unit and displays an image using light from the backlight unit as display light. Features.

  According to the display device having such a feature, since the backlight unit is mounted, it is possible to provide an image with good display quality in which the lamp image is reduced and the front luminance is improved. .

  According to the light diffusing plate, the optical sheet, the backlight unit, and the display device according to the present invention, it is possible to reduce the lamp image and improve the front luminance.

Hereinafter, a light diffusion plate, an optical sheet, a backlight unit, and a display device according to a first embodiment of the present invention will be described in detail with reference to the accompanying drawings. Here, the light diffusing plate according to the embodiment of the present invention will be described together with an optical sheet, a backlight unit, and a display device using the same.
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of the display device according to the first embodiment.

As shown in FIG. 1, the display device 70 according to the first embodiment is configured by overlapping a liquid crystal panel (image display unit) 100 on the light emission side of the backlight unit 35 that emits light upward. The liquid crystal display device displays an image by emitting display light whose display is controlled by an image signal from the liquid crystal panel 100 upward.
Hereinafter, based on such an arrangement, the upper direction in FIG. 1 may be simply referred to as a display screen side, and the lower direction may be simply referred to as a back side.

  The display device 70 is a liquid crystal display device including the liquid crystal panel 100, but any type of display device that displays an image with light, such as a projection screen device, a plasma display, or an EL display, may be used.

The liquid crystal panel 100 includes, for example, a liquid crystal layer (display element or panel) 9 that controls a light transmission state according to an image signal for each of a plurality of pixel regions formed in a rectangular lattice shape. Glass substrates 81 and 82 are laminated on the emission surface 9b.
A polarizing plate 62 that controls the polarization direction of incident light is disposed on the light incident side of the liquid crystal panel 100, and a polarizing plate that controls the polarization direction of emitted light is disposed on the light output side of the liquid crystal panel 100. 61 is provided.

The backlight unit 35 is a light emitting device having a light emitting surface having substantially the same area as the display screen of the liquid crystal panel 100. The backlight unit 35 emits a direct light source 11 and light from the light source 11 in the light emission direction and emission. An optical sheet 25 that emits light while controlling at least one of a range and a luminance distribution.
The optical sheet 25 includes a lens sheet 17a and a light diffusion plate 10 stacked on the light incident surface side of the lens sheet 17a.

As the light source 11, for example, it is possible to use a direct type system configured by arranging lamps made of cylinder-shaped linear light sources extending in the depth direction of the drawing at a constant pitch. The light source 11 is not limited to this, and may be a so-called edge light system.
As the linear light source, a cathode ray tube (CCFL), an LED, an EL, a semiconductor laser, or the like can be used. Furthermore, light from an array of red, green, and blue LEDs is mixed with a light guide plate or a diffusing plate and emitted as white light, or a yellow fluorescent light emitter is applied to a blue LED and emitted as pseudo white light. It is also possible to use a light source such as a light source in which a light emitting material of each color is applied to a single color LED.

Such light emitted from the light source 11 for the backlight has a characteristic that the portion near the lamp is bright and the space between the lamps is dark. Therefore, there arises a problem that the shape (lamp image) of each lamp is visually recognized by an observer in the front direction (observer side) f.
However, since the backlight unit 35 has an optical sheet 25 as will be described later and is configured to diffuse light from the light source 11, either the direct type or the edge light method is used as the backlight unit 35. In such a case, the visibility problem due to the lamp image can be suppressed.

The lens sheet 17a includes a translucent base material 18 that is formed in a film shape and has light transmissivity, and a plurality of unit lenses 16 that are integrally provided on an emission surface 18b of the translucent base material. .
Each unit lens 16 extends in the depth direction of the paper surface, and has a flat surface facing the emission surface 18a of the translucent substrate 18 and a convex curved surface formed so as to protrude from the emission surface 18a. A plurality of cylindrical shapes are arranged along the emission surface 18a. As described above, the unit lens 16 has a cylindrical shape, so that a high light collecting effect can be exhibited. However, the shape is not limited to the shape, and any other shape may be used as long as the light direction is controlled and condensed. It may be a shape.

  The unit lens 16 may be molded on the translucent substrate 18 using UV or radiation curable resin. For example, PET (polyethylene terephthalate), PC (polycarbonate), PMMA (polymethyl methacrylate), COP (Cycloolefin polymer), an acrylonitrile styrene copolymer, or the like may be integrally formed with the translucent substrate 18 by a known extrusion molding method, injection molding method, or hot press molding method.

  The light diffusing plate 10 plays a role of diffusing light emitted from the light source 11 toward the display screen, and is configured to reduce a lamp image by suppressing luminance unevenness due to the light source 11. .

As shown in FIG. 1, the light diffusing plate 10 includes a first resin layer 20 and a second resin 21 in which a resin 12 in which light scattering particles 13 are dispersed and mixed is formed in a substantially plate shape. It consists of
Further, in the light diffusing plate 10, when the total light transmittance of the first resin layer 20 is T1% and the total light transmittance of the second resin layer 21 is T2%, the relationship of T1% <T2% is satisfied. Has been. Thereby, while the 1st resin layer 20 has high light diffusibility, the 2nd resin layer 21 will have high light transmittance.
In the present embodiment, the first resin layer 20 is disposed on the back side, and the second resin layer is disposed on the display screen side.

In the case where the first resin layer 20 and the second resin layer 21 are formed, the first resin layer 20 and then the second resin layer 21 are arranged in this order on the light source 11 side. Even when the two resin layers 21 and then the first resin layer 20 are arranged in this order, the same performance is exhibited.
Further, the light diffusion plate 10 in the present embodiment is not limited to a two-layer structure, and may be a three-layer structure, a four-layer structure, or a five-layer structure. For example, in the case of three layers, a combination of the first resin layer 20 and then the second resin layer 21 and then the first resin layer 20 may be used.

  The resin 12 used for the light diffusing plate 10 may be a transparent resin, a colored resin, or an opaque resin. For example, a polycarbonate resin, an acrylic resin, a fluorine acrylic resin, a silicone acrylic resin, or an epoxy acrylate resin. Polystyrene resin, acrylonitrile styrene resin, cycloolefin polymer, methyl styrene resin, fluorene resin, PET, polypropylene and the like can be used.

As the light scattering particles 13 dispersed and mixed in such a resin 12, spherical particles are used.
The refractive index difference between the light scattering particles 13 and the resin 12 is set in the range of 0.15 to 0.18. Within this range, light diffusibility can be obtained, and viewing angle distribution can be adjusted appropriately.
Furthermore, the average particle diameter of the light scattering particles 13 is set in the range of 1 to 12 μm. If the average particle diameter of the light scattering particles 13 is less than 1 μm or more than 12 μm, the light diffusibility is not sufficient and the viewing angle distribution cannot be adjusted, which is not preferable. In this regard, if the average particle diameter of the first light scattering particles 13 is in the range of 1 to 12 μm, sufficient light scattering properties can be obtained.
The average particle size of the light scattering particles 13 is more preferably 2 to 6 μm or less.

Here, the mixing amount of the light scattering particles 13 in the first resin layer 20 is set in a range of 4 to 10% by weight. Accordingly, the first resin layer 20 has a total light transmittance of T1%, and has a very high light diffusibility while maintaining a certain degree of light transmittance.
On the other hand, the mixing amount of the light scattering particles 13 in the second resin layer 21 is set in the range of 0.1 to 0.5% by weight, whereby the second resin layer 21 has a total light transmittance of T2%. Therefore, it has a very high light transmittance while maintaining a certain degree of light diffusibility.

  As a material for the light scattering particles 13, particles made of inorganic fine particles or organic fine particles are used. Examples of this include acrylic particles, styrene particles, styrene acrylic particles and crosslinked products thereof, melamine-formalin condensate particles, polyurethane particles, polyester particles, silicone particles, fluorine particles, copolymers thereof, Clay compound particles such as smectite, kaolinite, talc, inorganic oxide particles such as silica, titanium oxide, alumina, silica alumina, zirconia, zinc oxide, barium oxide, strontium oxide, calcium carbonate, barium carbonate, barium chloride, barium sulfate And inorganic fine particles such as barium nitrate, barium hydroxide, aluminum hydroxide, strontium carbonate, strontium chloride, strontium sulfate, strontium nitrate, strontium hydroxide, and glass particles.

The light diffusing plate 10 may have a plate shape, a plate shape, or a sheet shape, and the thickness thereof is preferably set within a range of 0.5 to 5 mm.
When the thickness of the light diffusing plate 10 is less than 0.5 mm, there is a problem that bending occurs because it is thin and has no stiffness. On the other hand, when the thickness of the light diffusing plate 10 exceeds 5 mm, there is a problem that the transmittance of light from the light source 11 is lowered.

Moreover, in the light diffusing plate 10 of this embodiment, when the layer thickness (thickness in the stacking direction) of the first resin layer 20 is d1, and the layer thickness of the second resin layer 21 is d2, d1 / d2 is The layer thicknesses of the first resin layer 20 and the second resin layer 21 are determined so as to be in the range of 1/19 to 1/4.
Here, when d1 / d2 is less than 1/19, the first resin layer 20 is too thin to exhibit light diffusibility. When d1 / d2 exceeds 1/4, the first resin Since the layer 20 becomes too thick, the light transmission is impaired.
In this respect, when d1 / d2 is within the above range, the first resin layer 20 can exhibit high light diffusibility while exhibiting a certain degree of light transmittance.

Such a light diffusing plate 10 can be manufactured by integrally forming the first resin layer 20 and the second resin layer 21 by an extrusion method, a coextrusion method, or the like.
The extrusion method is a method in which a thermoplastic resin is heated and melted with an extruder, extruded from a T-die, and formed into a plate shape or a sheet shape. The coextrusion method is used when forming a laminated plate or a laminated sheet. Using a plurality of extruders, a multilayer extrusion is performed from a laminated die such as a feed block die or a manifold die. It is the method of shape | molding.

The surface of the light diffusing plate 10 is preferably matted. In this case, since the light from the light source 11 is scattered on the surface, it is possible to obtain effects such as reducing the lamp image and making it difficult to confirm the pins. Further, when the light emitting surface 10b of the light diffusing plate 10 is matted, a gap can be obtained between them without contacting the member (lens sheet 17a in the present embodiment) superimposed on the display screen. Therefore, it is possible to prevent optical influences such as Newton rings due to the close contact between the light diffusion plate 10 and the lens sheet 17a.
Instead of mat processing, processing for providing discontinuous minute protrusions may be performed.

Further, the light diffusion plate 10 may be one in which an ultraviolet absorber is added to at least one layer of the first resin layer 20 disposed on the light source 11 side.
Thereby, deterioration of the light diffusing plate 10 itself due to ultraviolet rays irradiated from the light source 11 can be suppressed, and the life can be extended. Furthermore, it is possible to suppress deterioration of the lens sheet 17a and the diffusing films 61 and 62 arranged facing the light emitting surface 10b of the light diffusing plate 10 due to ultraviolet rays.
Examples of the ultraviolet absorber include benzotriazole compounds such as 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, benzophenone compounds such as 2-hydroxy-4-methoxybenzophenone, 4-t- Salicylic acid ester compounds such as butylphenyl salicylate; Oxalic acid anilide compounds such as 2-ethoxy-2'-ethyl oxalic acid bisanilide; Cyanoacrylates such as ethyl-2-cyano-3,3-diphenylacrylate A system or the like can be used.

The optical sheet 25 formed by laminating the light diffusion plate 10 and the lens sheet 17a may be bonded by a fixing element such as an adhesive or a spacer. In that case, a gap (for light transmission) is formed between the lens sheet 17a and the light diffusion plate 10.
As an example of this fixing element, an adhesive sheet obtained by, for example, applying an acrylic adhesive to a film can be mentioned.

As described above, a gap (air layer) is formed between the light diffusion plate 10 and the lens sheet 17a, so that a diffusion effect due to the gap can be obtained and a light condensing effect in the unit lens 16 can be obtained. Therefore, the light passing through the optical sheet 25 is emitted with an optical gain of 1 or more.
Here, the optical gain is one of the indexes indicating the diffusibility of the diffusing member, and is expressed as a ratio with respect to the luminance of the diffuser that completely diffuses as 1. When the diffusivity of the diffusing member is biased depending on the direction to be measured, the optical gain for each direction is obtained, and the diffusion characteristics of the diffusing member can be shown by counting them. Note that complete diffusion refers to an ideal diffusing member that has zero light absorption by the diffusing member and has a certain intensity in any direction. That is, an optical gain of 1 or more indicates that there is an effect of collecting light in the measurement direction, and that the larger the value, the stronger the light collection effect.

Next, the operation of the display device 70 having the above configuration will be described.
The light emitted from the light source 11 is incident on the incident surface 10a of the light diffusing plate 10 and is scattered by the light diffusing plate 10 and proceeds as diffused light. The light having a divergence angle reaches the emission surface 10b of the light diffusion plate 10.

  The light reaching the exit surface 10b of the light diffusing plate 10 is refracted according to Snell's law according to the refractive index of the gap between the light diffusing plate 10 and the lens sheet 17a, and enters the lens sheet 17a. . The light incident on the lens sheet 17a is refracted by the incident surface 18a, then refracted by each unit lens 16 and emitted to the display screen side. Then, after being appropriately polarized by passing through the polarizing film 62, light is transmitted as display light from a predetermined pixel region via the polarizing plate 82, the liquid crystal layer 9, and the polarizing plate 81 of the liquid crystal panel 100, and By passing through the polarizing film 61, an image having a viewing angle is displayed.

Here, in the first resin layer 20 in which the mixing amount of the light scattering particles 13 in the resin 12 is in the range of 4 to 10% by weight, the total light transmittance is T1% smaller than that of the second resin layer 20 as described above. Thus, it has a very high light diffusibility while maintaining a certain degree of light transmittance.
That is, as shown in FIG. 2, the luminance distribution of light passing through the first resin layer has a viewing angle that widens the viewing angle from the front direction f, has a high forward diffusibility, and drops sharply when the wide angle is reached. Show properties. Therefore, the bright place of the lamp on the light source 11 can be greatly widened to obtain high light diffusibility, so that the effect of reducing the lamp image can be obtained.

On the other hand, in the second resin layer 21 in which the mixing amount of the light scattering particles 13 in the resin 12 is in the range of 0.1 to 0.5% by weight, the total light transmittance is higher than that of the first resin layer 20 as described above. It has a large T2% and has a very high light transmittance while maintaining a certain degree of light diffusibility.
That is, as shown in FIG. 3, the luminance distribution of light passing through the second resin layer has a viewing angle characteristic such that it protrudes in the front direction f and is high and falls sharply when it deviates from the front direction f. Therefore, a large brightness in the front direction can be obtained.

Therefore, the light diffusing plate 10 of the present embodiment has a structure in which the first resin layer 20 and the second resin layer 21 in which a relationship of T1% <T2% is established between the total light transmittances are high. High light transmittance can be obtained while obtaining light diffusibility, and the front luminance can be improved while reducing the lamp image.
Furthermore, since a high diffusion function can be obtained only with the light diffusion plate 10 as described above, it is not necessary to provide a separate diffusion film or the like. Therefore, it is possible to reduce the number of parts and reduce the manufacturing cost.

  In addition, since the optical sheet 25 of the present embodiment is configured by laminating the lens sheet 17a having a light condensing function in the front direction (observer side) f on the light diffusion plate 10, the light diffusion plate 10 described above. In addition to the above function, the light collecting function by the lens sheet 17a can be obtained. Therefore, according to the optical sheet 25, it is possible to obtain a very high front luminance while reducing the lamp image.

The optical sheet 25 can increase the strength of the optical sheet 10 itself even when the light diffusing plate 10 is formed thin, and the display device 70 has excellent image display quality. Therefore, it is preferable to use for a large display.
Further, the optical sheet 25 is used as a sheet for controlling the viewing angle of the display or a sheet for improving the contrast, in addition to the use for improving the luminance of the light from the light source 11 for the backlight. It is also possible to do.
Furthermore, for example, it can also be used for a sheet for improving the luminance of light projected on the projection screen or a sheet for performing light control for solar cells.
Moreover, since the optical sheet 25 can uniformly diffuse and collect light from the illumination source, it can be used for illumination covers, signboards, building materials, and the like.

Furthermore, according to the backlight unit 35 of the present embodiment, since the light diffusing plate 10 and the optical sheet 25 are used, the optical characteristics related to light diffusibility and light transmittance are optimized, and Light with improved luminance in the front direction (observer side) f can be incident on the liquid crystal panel 100. Therefore, the display device 70 equipped with the backlight unit 35 can display an image with high brightness and reduced lamp image.
Further, since the lamp image reduction effect and the brightness are high, the distance to the light source 11 can be reduced, and the number of lamps of the light source 11 can be reduced, so that the backlight unit 35 and the display device 70 can be saved. It becomes.
Since the optical sheet 25 is used, a thin backlight unit 35 can be obtained, and a large display device 70 can be easily configured.

Next, the display apparatus 80 of the 2nd Embodiment of this invention is demonstrated. FIG. 4 is a schematic cross-sectional view showing a schematic configuration of the display device according to the second embodiment.
In the display device 80 according to the second embodiment, the display device 70 according to the first embodiment includes the lens sheet 17a. However, as shown in FIG. 4, a light diffusion film 17b is used instead of the lens sheet 17a. It differs from 1st Embodiment by the point provided.
Therefore, in FIG. 4, the same components as those in FIG.

  In the second embodiment, the optical sheet 25 is configured by laminating the light diffusing film 17b on the light emitting surface 10a side of the light diffusing plate 10, and the backlight unit 35 is further formed using the optical sheet 25. And the display apparatus 80 is comprised.

The light diffusing film 17b has an effect of uniformly diffusing the light emitted from the light diffusing plate 10 and an effect of condensing the emitted light, and is formed in a film shape and has a light transmitting property. A light transmissive substrate 191 and a light diffusing portion 192 formed on the light emitting surface of the light transmissive substrate 191 are provided, and the light diffusing portion 192 includes a plurality of convex portions. The shape of the convex portion is not particularly limited as long as it has a shape that exhibits light diffusibility and a light collecting effect.
The light diffusion film 17b may be configured to totally reflect a part of incident light, or may be a laminate of a plurality of sheets.

  Further, the optical sheet 25 in which the light diffusing plate 10 and the light diffusing film 17b are laminated may be joined by a fixing element such as an adhesive or a spacer, like the optical sheet 25 of the first embodiment. Good. In that case, a gap (for light transmission) is formed between the light diffusion film 17 b and the light diffusion plate 10.

In the display device 80 shown in FIG. 4 configured as described above, the light emitted from the light source 11 and transmitted through the light diffusion plate 10 is incident from the light incident surface 19a of the light diffusion film 17b, and the light is further transmitted. Is emitted from the light exit surface 19b of the light diffusion film 17b with an optical gain of 1 or more. At this time, since the light condensing effect is expressed by the light diffusion film 17b, high front luminance can be obtained.
The optical sheet 25 according to the second embodiment is formed by laminating a light diffusion film 17b having a light condensing effect on the light diffusion plate 10 in the front direction (observer side) of the light diffusion plate 10 to form the optical sheet 25. Accordingly, it is possible to reduce the lamp image by diffusing light due to the contribution of the light diffusion plate 10 described above, and it is possible to improve the front luminance by condensing the light and increasing the light use efficiency.

  The light diffusing plate 10, the optical sheet 25, the backlight unit 35, and the display devices 70 and 80 according to the embodiment of the present invention have been described above, but the present invention is not limited thereto, and the technical idea of the present invention is described. Changes can be made as appropriate without departing from the scope.

  For example, in the first and second embodiments, the light diffusion plate 10 in which the first resin layer 20 is disposed on the back surface side and the second resin layer 21 is disposed on the display screen side has been described. The second resin layer 21 may be disposed on the side, and the first resin layer 20 may be disposed on the display screen side.

  The light diffusing plate 10 is not limited to a two-layer structure, and may have a multilayer structure of three or more layers. For example, in the case of a three-layer structure, the first resin layer 20, the first resin layer 20 The two resin layers 21 and the first resin layer 20 may be laminated in combination.

  Furthermore, in order to further improve the brightness enhancement or lamp image reduction effect, a lens shape or a convex portion may be formed on one side or both sides of the light diffusing plate 10. In this case, the difference between the maximum and minimum roughness of the surface is preferably up to about 200 μm.

An optical sheet using the light diffusing plate shown in this embodiment was produced, and its physical properties were evaluated. Hereinafter, specific configurations, test methods, and test results of the produced light diffusion plate and optical sheet will be described.
As described in the first embodiment, the optical sheet was prepared by laminating a light diffusion plate and a lens sheet.

(Lens sheet)
A lens sheet constituting an optical sheet was produced using thermoplastic polycarbonate resin beads as a material. Specifically, after melting the thermoplastic polycarbonate resin beads, the sheet is extruded by an extruder, and a convex cylindrical unit lens is molded by a mold roll before the sheet is cooled and cured. . The unit lens pitch was 60 μm.

(Three-layer light diffuser)
First, a light diffusing plate having a three-layer structure including a first resin layer, a second resin layer, and a third resin layer was produced, and physical properties were evaluated. In the light diffusing plate, the thicknesses of the first resin layer and the third resin layer, the average particle diameter of the light scattering particles, the refractive index, and the mixing amount (% by weight) are the same.

(Light diffusing plate of Examples 1-7)
A three-layer structure comprising a first resin layer, a second resin layer, and a third resin layer obtained by adding one or two kinds of light scattering particles (true spherical particles) to polystyrene resin (PS) having a refractive index of 1.59. The light diffusing plate was prepared as Examples 1-7. The light diffusion plate is configured to sandwich the second resin layer between the first resin layer and the third resin layer.
Table 1 shows the thickness of each resin layer, the average particle diameter of the light scattering particles, the refractive index, and the mixing amount (% by weight).
As a specific production method, a light diffusing plate was produced by extruding a laminated sheet composed of the first resin layer and the second resin layer while adjusting the extrusion amount with a laminated extruder. At this time, the die temperature of the extruder was set to 200 ° C., and the roll temperature (temperature of the second roll) was set to 100 ° C.

(Light diffusion plate of Comparative Examples 1 to 9)
Light diffusion of a three-layer structure composed of a first resin layer, a second resin layer, and a third resin layer obtained by adding one kind of light scattering particles (true spherical particles) to polystyrene resin (PS) having a refractive index of 1.59. The board was produced as Comparative Examples 1-9. The light diffusion plate is configured to sandwich the second resin layer between the first resin layer and the third resin layer.
The specific manufacturing method is the same as in Examples 1 to 7.

(Evaluation)
Then, the light diffusion plate of Examples 1 to 7 and Comparative Examples 1 to 9 and the lens sheet were overlapped to form an optical sheet, and the lamp image effect and the brightness were evaluated. The results are shown in Table 2. In addition, the brightness set 8000 cd / m < ² > or more as the pass.

From Table 1 and Table 2, while the average particle diameter of a spherical light-scattering particle is 1-12 micrometers, the refractive index difference with a polystyrene resin is 0.15-0.18, Comprising: The mixing amount of the light scattering particles is 4 to 10% by weight, the mixing amount of the light scattering particles in the second resin layer is 0.1 to 0.5% by weight, and the layer thickness d1 of the first resin layer. The ratio d1 / d2 between the thickness d2 of the second resin layer satisfies the relationship of 1/19 to 1/4, and the third resin layer has the same configuration as the first resin layer. In Examples 1 to 7, the lamp image was not visually recognized, the image display was good, and the brightness was 8000 cd / m ² or more, which was a favorable result.
On the other hand, in Comparative Examples 1 to 9 that do not satisfy at least one of the above conditions, at least one of the lamp image and the brightness was not preferable. In Table 1, items that do not satisfy the above conditions are clearly shown by applying colors.

  From the above, in the light diffusion plate having a three-layer structure, the light scattering particles are true spherical particles having a particle diameter of 1 to 12 μm and a refractive index difference from the resin of 0.15 to 0.18. The amount of light scattering particles mixed in the resin layer is 4 to 10% by weight, the amount of light scattering particles mixed in the second resin layer is 0.1 to 0.5% by weight, and the first resin layer When the d1 / d2 between the layer thickness d1 of the second resin layer and the layer thickness d2 of the second resin layer is 1/19 to 1/4, and the third resin layer has the same configuration as the first resin layer It has been found that it is possible to reduce the lamp image and improve the front brightness.

(Light diffusion plate with two layers)
Next, a light diffusing plate having a two-layer structure composed of a first resin layer and a second resin layer was produced, and physical properties were evaluated.

(Light diffusion plate of Examples 8 to 12)
A first resin layer and a second resin layer obtained by adding one kind of light scattering particles (true spherical particles) to polystyrene resin (PS) having a refractive index of 1.59 were produced as Examples 8-12. Table 3 shows the thickness of each resin layer, the average particle diameter of the light scattering particles, the refractive index, and the mixing amount (% by weight).
As a specific production method, a light diffusing plate was produced by extruding a laminated sheet composed of the first resin layer and the second resin layer while adjusting the extrusion amount with a laminated extruder. At this time, the die temperature of the extruder was set to 200 ° C., and the roll temperature (temperature of the second roll) was set to 100 ° C.

(Light diffusion plate of Comparative Examples 10-12)
Light diffusion plates of the first resin layer and the second resin layer obtained by adding one kind of light scattering particles (true spherical particles) to polystyrene resin (PS) having a refractive index of 1.59 were produced as Comparative Examples 8-12.
The specific manufacturing method is the same as described above.

(Evaluation)
Then, the light diffusion plate of Examples 1 to 7 and Comparative Examples 1 to 9 and the lens sheet were overlapped to form an optical sheet, and the lamp image effect and the brightness were evaluated. The results are shown in Table 4. In addition, the brightness set 8000 cd / m < ² > or more as the pass.

From Tables 3 and 4, the average particle diameter of the spherical light-scattering particles is 1 to 12 μm, the refractive index difference from the polystyrene resin is 0.15 to 0.18, and in the first resin layer The mixing amount of the light scattering particles is 4 to 10% by weight, the mixing amount of the light scattering particles in the second resin layer is 0.1 to 0.5% by weight, and the layer thickness d1 of the first resin layer In Examples 8 to 12, in which the ratio d1 / d2 between the thickness d2 and the second resin layer satisfies the condition of 1/19 to 1/4, the lamp image is not visually recognized and the image display is good. The brightness was 8000 cd / m ² or more, which was a preferable result.
On the other hand, among the above conditions, in particular, Comparative Examples 10 to 11 in which the ratio d1 / d2 between the layer thickness d1 of the first resin layer and the layer thickness d2 of the second resin layer does not satisfy 1/19 to 1/4. At least one of the lamp image and the brightness resulted in an undesirable result. In Table 3, items that do not satisfy the above conditions are clearly shown by applying colors.

  From the above, in the light diffusion plate having a two-layer structure, the light scattering particles are true spherical particles having a particle diameter of 1 to 12 μm and a refractive index difference from the resin of 0.15 to 0.18, The mixing amount of the light scattering particles in the resin layer is 4 to 10% by weight, the mixing amount of the light scattering particles in the second resin layer is 0.1 to 0.5% by weight, When d1 / d2 of the layer thickness d1 and the layer thickness d2 of the second resin layer is 1/19 to 1/4, it is understood that the lamp image can be reduced and the front luminance can be improved. It was.

It is typical sectional drawing which shows schematic structure of the display apparatus which concerns on 1st Embodiment. It is a luminance distribution figure of the light which passes the 1st resin layer. It is a luminance distribution figure of the light which passes the 2nd resin layer. It is typical sectional drawing which shows schematic structure of the display apparatus which concerns on 2nd Embodiment. The It is a longitudinal cross-sectional view of the display apparatus in which the light guide plate light guide type backlight unit is mounted. It is a longitudinal cross-sectional view of the display apparatus which provided the prism film between the diffusion film and the liquid crystal panel. It is a longitudinal cross-sectional view of the display apparatus provided with the direct type backlight unit. It is a perspective view of the light control sheet provided with the brightness emphasis film. It is a longitudinal cross-sectional view of the principal part of the display apparatus by which the light control sheet provided with the brightness | luminance emphasis film is arrange | positioned. It is a figure which shows the light intensity distribution of the light control sheet provided with the brightness | luminance emphasis film.

Explanation of symbols

10 Light Diffusing Plate 11 Light Source 12 Resin 13 Light Scattering Particle (True Spherical Particle)
17a lens sheet 17b light diffusion film 20 first resin layer 21 second resin layer 25 optical sheet 35 backlight unit 70 display device 80 display device 100 liquid crystal panel (image display unit)

Claims (7)

In a light diffusing plate in which light scattering particles are dispersed and mixed in a resin,
It consists of at least two layers of a first resin layer having a total light transmittance of T1% and a second resin layer having a total light transmittance of T2%,
The light diffusion plate, wherein the total light transmittance T1% of the first resin layer and the total light transmittance T2% of the second resin layer satisfy a relationship of T1% <T2%. The light scattering particles are true spherical particles having an average particle diameter of 1 to 12 μm,
The refractive index difference between the light scattering particles and the resin is 0.15 to 0.18,
The mixing amount of the light scattering particles in the first resin layer is 4 to 10% by weight, and the mixing amount of the light scattering particles in the second resin layer is 0.1 to 0.5% by weight,
2. The light diffusing plate according to claim 1, wherein a ratio d1 / d2 between a layer thickness d1 of the first resin layer and a layer thickness d2 of the second resin layer is 1/19 to 1/4.   The third resin layer having the same configuration as that of the first resin layer is laminated on the surface of the second resin layer opposite to the surface on which the first resin layer is laminated. 3. The light diffusing plate according to 1 or 2. An optical sheet that emits incident light from the light source to the other surface side when the light source is disposed on the one surface side,
The light diffusing plate according to any one of claims 1 to 3,
An optical sheet comprising: a lens sheet that is disposed on the other surface side opposite to the light source of the light diffusing plate, converts the optical characteristics of the light of the light source that has passed through the light diffusing plate, and emits the light. . An optical sheet that emits incident light from the light source to the other surface side when the light source is disposed on the one surface side,
The light diffusing plate according to any one of claims 1 to 3,
An optical device comprising: a light diffusing film that is disposed on the other surface side opposite to the light source of the light diffusing plate, converts the optical characteristics of the light of the light source that has passed through the light diffusing plate, and emits the light. Sheet. The optical sheet according to claim 4 or 5,
And a light source disposed on one side of the optical sheet. The backlight unit according to claim 6;
A display device, comprising: an image display unit that is disposed on an emission surface side of the backlight unit and displays an image using light from the backlight unit as display light.

Images