JP2010072131A - Light diffusion plate, optical sheet, backlight unit and display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion plate that reduces a lamp image and obtains high front luminance, and to provide an optical sheet, a backlight unit and a display apparatus using the light diffusion plate. <P>SOLUTION: The light diffusion plate 1 contains at least one light diffusing agent having ≤2 μm average particle size and is constituted so that one surface thereof in the thickness direction is used as a light entrance surface 100 and the other surface is used as a light emission surface 101. A surface haze value on the light entrance surface 100 is ≥20% and the mean spacing Sm of the roughness profile is 300-900 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light diffusing plate for a direct type liquid crystal backlight. More specifically, the present invention relates to a light diffusing plate capable of obtaining an excellent lamp image reduction effect when used as a liquid crystal backlight member, a display backlight unit using the diffusing plate, and a display device.

  In recent years, liquid crystal display devices using TFT liquid crystal panels and STN liquid crystal panels have been commercialized mainly for color notebook PCs (personal computers) in the OA field.

  In such a liquid crystal display device, a so-called backlight method in which a light source is arranged on the back side (observer side) of the liquid crystal panel and the liquid crystal panel is illuminated with light from the light source is employed.

  As a backlight unit employed in this type of backlight system, a light source lamp such as a cold cathode fluorescent lamp (CCFT) is roughly divided within a flat light guide plate made of acrylic resin having excellent light transmittance. There are a “light guide plate light guide method” for reflecting (a so-called edge light method) and a “direct type method” that does not use a light guide plate.

  As a liquid crystal display device on which a light guide plate light guide type backlight unit is mounted, for example, the one shown in FIG. 3 is generally known.

  This is provided with a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 at the top, and a light guide plate 79 made of a transparent base material such as a substantially rectangular plate-like PMMA (polymethyl methacrylate) or acrylic on the lower surface side. Is installed, and a diffusion film (diffusion layer) 78 is provided on the upper surface (light emission side) of the light guide plate.

  Further, a scattering reflection pattern portion for efficiently scattering and reflecting the light introduced into the light guide plate 79 in the direction of the liquid crystal panel 72 is provided on the lower surface of the light guide plate 79 by printing or the like. A reflection film (reflection layer) 77 is provided below the scattering reflection pattern portion (not shown).

  Further, the light guide plate 79 is provided with a light source lamp 76 at the side end, and further covers the back side of the light source lamp 76 so that the light from the light source lamp 76 can be efficiently incident on the light guide plate 79. Thus, a high-reflectance lamp reflector 81 is provided. The scattering reflection pattern portion is formed by printing a mixture of white titanium dioxide (TiO2) powder in a solution such as a transparent adhesive in a predetermined pattern, for example, a dot pattern, and drying and forming the light guide plate. This is a device for increasing the brightness by giving directivity to the light incident in 79 and guiding it to the light exit surface side.

  Furthermore, recently, in order to increase the light utilization efficiency and increase the brightness, a prism film (prism layer) having a light condensing function between the diffusion film 78 and the liquid crystal panel 72 as shown in FIG. ) 74 and 75 are proposed. The prism films 74 and 75 are configured to collect light emitted from the light exit surface of the light guide plate 79 and diffused by the diffusion film 78 on the effective display area of the liquid crystal panel 72 with high efficiency.

On the other hand, in the direct type, a display device such as a large liquid crystal TV in which the light guide plate is difficult to use is used.
As a direct type liquid crystal display device, a device illustrated in FIG. 5 is generally known. In this, a liquid crystal panel 72 sandwiched between polarizing plates 71 and 73 is provided on the upper side, and is emitted from a light source 51 made of a fluorescent tube or the like on the lower surface side thereof and diffused by an optical sheet such as a diffusion film 82. The light is condensed on the effective display area of the liquid crystal panel 72 with high efficiency. In order to efficiently use the light from the light source 51 as illumination light, a reflector 52 is disposed on the back surface of the light source 51.

  The diffuser plate used in the direct type system is required to have the ability to scatter the light from the light source of the display device and prevent the lamp image from being visually recognized. Various developments have been made in line with the rapid increase in mold methods. Many of the developments aim at high transmission and high diffusion, and control the kind, particle size and blending amount of light scattering fine particles.

  However, even in the apparatus illustrated in FIG. 5, the control of the viewing angle is left only to the diffusibility of the diffusion film 82, and it is difficult to control, and the center of the front direction of the display is bright and becomes darker toward the periphery. This characteristic is inevitable. For this reason, when the liquid crystal screen is viewed from the side, the luminance is greatly reduced, and the light utilization efficiency is reduced.

Therefore, as one solution, as shown in FIG. 7, a brightness enhancement film (BEF) 72, which is a registered trademark of US 3M, shown in FIG. A method of arranging a light diffusion film (not shown) on the top is employed. Here, BEF is a film in which unit prisms having a triangular cross section are periodically arranged in one direction on a transparent member.
This prism has a large size pitch compared to 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 (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 the repetitive array structure of prisms is arranged in only one direction, only the direction change or recycling in the parallel direction is possible, and in order to control the luminance of the display light in the horizontal and vertical directions, the parallel direction of the prism groups Are stacked and used in combination so that they are substantially orthogonal to each other.

The adoption of BEF allows display designers to achieve the desired on-axis brightness while reducing power consumption.
As patent documents disclosing that a brightness control member having a repetitive array structure of prisms typified by BEF is adopted for a display, many are known as exemplified in Patent Documents 1 to 3. Yes.
In the optical sheet using the BEF as a luminance control member as described above, the light from the light source is finally emitted from the film at a controlled angle by the refraction action, so that the visual direction of the viewer can be improved. It can be controlled to increase the light intensity.

  However, there are unexpected light rays that are unnecessarily emitted laterally without proceeding in the visual direction of the viewer. For this reason, as shown in FIG. 8, the light intensity distribution emitted from the optical sheet using BEF has the light intensity when the viewer's visual direction, that is, the angle with respect to the visual direction F is 0 ° (corresponding to the axial direction). Although most enhanced, there is a problem that a small light intensity peak occurs in the vicinity of ± 90 ° from the front, that is, light (side lobes) emitted from the lateral direction is increased.

  Further, when only the on-axis luminance is excessively improved, the peak width of the luminance distribution curve is remarkably narrowed, and the viewing area is extremely limited. Therefore, in order to increase the peak width appropriately, the prism sheet shown in FIG. Requires the use of a separate light diffusing film 300, which is accompanied by an increase in the number of members.

  As described above, this optical sheet is required not only to improve the light utilization efficiency, but also to have various functions such as removing unevenness of the light source, erasing the lamp image, and securing the viewing area of the display. It is configured by superposing a plurality of optical sheets. However, when the number of the optical sheets is large, there is a problem that the work for assembling the display becomes complicated and the dust between the optical sheets is affected.

For this reason, it has been required that the light diffusing plate itself be provided with various functions such as removal of unevenness of the light source, extinguishing of the lamp image, and securing of the viewing zone of the display.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

  The present invention has been made in view of such problems, and a light diffusing plate capable of obtaining an excellent lamp image reduction effect by optimizing the configuration of the light diffusing plate, and the light diffusing plate. An object of the present invention is to provide a backlight unit and a display device using the display, and to achieve high display quality and low price.

In order to achieve the above object, the present invention takes the following measures.
That is, the invention of claim 1 includes at least one kind of light diffusing agent having an average particle diameter of 2 μm or less in a base material made of a translucent resin, and one surface in the thickness direction is a light incident surface. A light diffusing plate whose surface is a light emitting surface, wherein the light incident surface has a surface haze value of 20% or more, and an average interval Sm of surface irregularities of 300 to 900 μm.
According to the light diffusing plate having such characteristics, a light scattering effect on the surface irregularities of the light incident surface can be sufficiently obtained, and an excellent lamp image reduction effect can be obtained.
The invention of claim 2 is characterized in that in the light diffusion plate, a diffusion layer is constituted by the base material and the light diffusion agent, and a plurality of diffusion layers containing different light diffusion agents are laminated. And
According to the light diffusing plate having such characteristics, it is possible to have a layer having a strong diffusivity or a layer having a high reflectivity by stacking with different types of light diffusing agents, and further reducing the lamp image. An effect can be obtained.
According to a third aspect of the present invention, in the light diffusing plate, a diffusion layer is configured by the base material and the light diffusing agent, and the light diffusing agent is one type and is configured by laminating a plurality of diffusion layers having different concentrations. It is characterized by.
According to the light diffusing plate having such characteristics, a layer having a high concentration of the light diffusing agent has high diffusibility, and a layer having a low concentration of the light diffusing agent has high light transmittance. Accordingly, high diffusibility can be obtained while maintaining high light transmittance of the entire light diffusion plate, and the lamp image reduction effect is excellent.
The invention of claim 4 is characterized in that, in the light diffusing plate, an ultraviolet absorber is added to the translucent resin to the base material.
According to the light diffusing plate having such characteristics, it is advantageous in that deterioration of the transparent resin constituting the light diffusing plate can be prevented by adding an ultraviolet absorber.
The invention according to claim 5 is characterized in that, in the light diffusing plate, the surface roughness of the light incident surface is regular.
According to the light diffusing plate having such characteristics, it is possible to design a light diffusing plate having a certain light scattering effect and light transmittance, and the manufacture is facilitated.
The invention of claim 6 is disposed on the light diffusing plate according to any one of claims 1 to 5 and the light emitting surface side opposite to the light source of the light diffusing plate, An optical sheet comprising a lens sheet that converts an optical characteristic of the light of the light source that has passed through and emits the converted light characteristic.
According to such an optical sheet, the light condensing effect by the lens sheet can be expected, and it becomes possible to obtain a high front luminance as well as a reduction in the lamp image.
The invention of claim 7 is disposed on the light diffusing plate according to any one of claims 1 to 5 and the light emitting surface side opposite to the light source of the light diffusing plate. An optical sheet comprising: a light diffusion film that converts an optical characteristic of light of the light source that has passed through and emits the light.
According to such an optical sheet, it is possible to expect a light collecting effect by the diffusion film, and it is possible to obtain a high front luminance as well as a reduction in the lamp image.
The invention according to claim 8 is a backlight unit comprising the optical sheet according to claim 6 or 7 and a light source disposed on one surface side of the optical sheet.
According to such a backlight unit, 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 high front luminance is achieved. Can be obtained.
According to a ninth aspect of the present invention, an image display element that defines a display image in accordance with transmission / shielding in pixel units, and the backlight unit according to the eighth aspect are provided on the back surface of the image display element. A display device.
According to such a display device, since the backlight unit is mounted, it is possible to provide an image with a good display quality in which the lamp image is reduced and high front luminance is maintained.

  According to the light diffusing plate, the optical sheet, the backlight unit, and the display device according to the present invention, an excellent lamp image reduction effect can be obtained.

The best mode for carrying out the present invention will be described below.
First, an embodiment of the present invention is shown in FIG. The backlight unit 44 includes a plurality of cylindrical light sources 41 housed in the lamp house 43 and the light diffusing plate 1 that supplies the light H from each light source 41 to the liquid crystal panel 32. The liquid crystal panel 32 is configured by sandwiching liquid crystal 35 between polarizing plates 31 and 33, and 45 in the drawing is a light reflecting plate disposed on the back side of the plurality of light sources 41.
Further, the display device L according to the embodiment of the present invention is a device including the light source 41 and the light diffusing plate 1 and the liquid crystal panel 32 thereon.

  The direct type backlight uses the light diffusing plate 1 that scatters and collects light, and is used on the light source 41 side to increase the light use efficiency. A film is placed.

The light source 41 is a linear light source such as a fluorescent lamp in the present embodiment, and a cold-cathode tube is usually used for a liquid crystal display, but is not limited to the present embodiment. Point light sources such as EL and semiconductor lasers can also be used.
Here, when an LED is used as the light source 51 of the display device L, an array of red, green, and blue LEDs is used, and light from the array of red, green, and blue LEDs is mixed with a light guide plate or the like as white light. It can also be used for those that emit uniformly, or those that can be emitted uniformly as white light by mixing light from an array of red, green, and blue LEDs using a diffusion plate or the like.

The light diffusing plate 1 is composed of a transparent resin and a light diffusing agent (particles) dispersed in the transparent resin.
Examples of the transparent resin used for the light diffusion plate 1 include polycarbonate resin, acrylic resin, fluorine acrylic resin, silicone acrylic resin, epoxy acrylate resin, polystyrene resin, cycloolefin polymer, methylstyrene resin, fluorene resin, PET, polypropylene, etc. can be used.

  Moreover, as a light-diffusion agent disperse | distributed in the said transparent resin, the transparent particle which consists of an inorganic substance or resin can be used, for example. As the transparent particles made of an inorganic substance, for example, particles made of an oxide such as silica, alumina and titania, or other particles such as calcium carbonate and barium sulfate can be used. Transparent particles made of resin include acrylic resin, styrene resin, acrylic styrene resin, or a crosslinked product thereof; melamine formaldehyde resin; polytetrafluoroethylene, perfluoroalkoxy resin, tetrafluoroethylene-hexafluoropropylene copolymer, and polyfluorovinylidene. Fluorine resin such as ethylene-tetrafluoroethylene copolymer; or particles made of silicone resin can be used.

Here, the light diffusing plate 1 includes a transparent resin and a light diffusing agent dispersed in the transparent resin, and the refractive index of the transparent resin and the refractive index of the light diffusing agent are sufficient. Different light diffusion characteristics need to be obtained. Usually, this refractive index difference is desirably 0.02 or more.
Moreover, the said light-diffusion agent may be used only by 1 type, and may mix and use 2 or more types. Moreover, when using 2 or more types, it can also be set as the laminated structure which each made another layer.

Then, the light diffusing agent is dispersed in these transparent resins, and the plate-like light diffusing plate 1 can be manufactured by a known molding method such as extrusion molding or injection molding. The thickness of the light diffusing plate 1 is desirably 0.5 to 3 mm, and more specifically 1 to 2 mm. When the thickness is less than 1 mm, the light diffusing plate 1 is thin and does not have a stiffness, so that there is a drawback that it bends. On the other hand, if it exceeds 3 mm, there is a disadvantage that the transmittance of light from the light source 41 is deteriorated.
One surface in the thickness direction of the light diffusing plate 1 is a light incident surface 100 and the other surface is a light emitting surface 101.

FIG. 1A shows an embodiment of a light diffusing plate 1 according to the present invention. In the transparent resin, two types of first diffusing agent 7 having different sizes and types and a second diffusion are shown. Agent 8 is dispersed. The light diffusing plate 1 is manufactured by blending at least one diffusing agent having an average particle diameter of 2 μm or less in a transparent resin. This is because if the average particle diameter of the light diffusing material exceeds 2 μm, the light from the light source 41 passes through and the haze cannot be increased, and the light diffusion with an average particle diameter of 2 μm or less. Inclusion of at least one kind of agent is advantageous in adjusting the haze.
In other words, the light diffusing plate 1 contains at least one kind of light diffusing agent having an average particle diameter of 2 μm or less in a base material made of a translucent resin.

FIG. 1B shows another embodiment of the light diffusing plate 1 according to the present invention. The second diffusing agent 8 is formed on the diffusing layer in which the first diffusing agent 7 is dispersed. A layer in which the first diffusing agent 7 is dispersed is further laminated thereon.
The light diffusing plate 1 has a multilayer structure in which a plurality of diffusing layers containing different diffusing agents are laminated. In other words, the light diffusing plate 1 includes a diffusion layer composed of the base material and the light diffusing agent, and a plurality of diffusion layers containing different light diffusing agents 7 and 8 are laminated.
The type and configuration of the light diffusing agent is not particularly limited. For example, a light diffusing agent having a diffusibility such as a silicone resin or an acrylic resin, and light reflecting performance and light such as alumina, barium sulfate, and titanium oxide. Combinations having both transmission performance can also be used. Thereby, higher diffusibility and high light transmittance are easily maintained.

1C and 1D show still another embodiment of the light diffusing plate 1 according to the present invention. FIG. 1C shows a case where diffusion layers in which one kind of diffusing agent 7 is dispersed are laminated, and each layer shows a different concentration distribution. In other words, the light diffusing light 1 includes a diffusion layer composed of the base material and the light diffusing agent 7, and the light diffusing agent 7 is composed of one kind and a plurality of diffusion layers having different concentrations.
In this configuration, the light transmittance of the entire light diffusing plate 1 is not changed, but the diffusibility becomes stronger in a layer having a high diffusing agent concentration, and a desired lamp image reduction and high front luminance can be easily obtained.
FIG. 1D shows a multilayer structure in which a diffusion layer in which one kind of diffusing agent 7 is dispersed and a transparent layer not containing a light diffusing agent are laminated. In this configuration, the light transmittance can be maintained high by including the transparent layer, and the diffusion layer can provide sufficient diffusibility.
Further, by adding an ultraviolet absorber to at least one layer of the light transmissive resin of the light diffusing plate 1, in other words, by adding an ultraviolet absorber to the substrate, the light is diffused by ultraviolet rays from the light source 41. This is advantageous in preventing deterioration of the transparent resin constituting the plate 1.

The surface state of the light incident surface 100 of the light diffusion plate 1 of the present invention is a specific mat shape. The mat shape has an effect of reducing the lamp image.
Usually, the unevenness of the surface state of the light incident surface 100 is often quantified by roughness, but in the present invention, the surface state of the light incident surface 100 is represented by a surface haze value and an unevenness interval Sm value.
The surface haze value described in the present invention is defined by JIS K 7136, and is represented by an average value when measured five times using a haze meter. The unevenness interval is defined by the surface roughness standard JIS B0601-2001, This means the average value when measured using a surface roughness meter with a cut-off value of 2.0 mm.
The larger the haze value, the more scattering on the light incident surface 100, and vice versa. At the same time, if the Sm value is small, the surface unevenness becomes fine.
When the surface haze value is less than 20%, the surface scattering of light is reduced, and a sufficient lamp image reduction effect cannot be obtained.
Similarly, if the Sm value is less than 300 μm, the unevenness interval is fine but the unevenness roughness becomes insufficient, and a sufficient lamp image reduction effect cannot be obtained. If it exceeds 900 μm, the unevenness interval is wide and the roughness becomes rough. Although the surface scattering of light becomes strong, it leads to a decrease in front luminance.
Furthermore, when the surface roughness of the light incident surface 100 is regular, it is advantageous in obtaining a certain scattering effect as compared with the case where the surface roughness is irregular, and the manufacture becomes easy.

  The present invention has a surface haze value of 20% or more of the light incident surface 100 and an Sm value of 300 to 900 μm. By combining the light incident surface 100 and the diffusing agent, a lamp image reduction effect and high front luminance can be obtained. . There are several methods for adjusting the surface haze value. When physically forming irregularities, the surface condition of the mold is adjusted and transferred in-line during injection molding or extrusion molding, or offline after molding. There are methods of blasting with a press or abrasive. Moreover, when bleeding out a light-diffusion agent on extrusion conditions, it adjusts with the density | concentration and particle size of a light-diffusion agent, and the thickness of a diffusion layer.

  In the extrusion method, a thermoplastic resin is heated and melted with an extruder, extruded from a T-die, and formed into a plate shape. The co-extrusion method is used in the case of a laminated plate, and a plurality of extruders are used to carry out lamination extrusion from a lamination die such as a feed block die or a manifold die to form a multilayer plate.

On the light exit surface side of the light diffusing plate 1, a lens sheet, a prism sheet, or a diffusing sheet in which convex cylindrical unit lenses are formed in parallel are laminated and used as an optical sheet 39, brightness, light distribution characteristics, etc. Optimize the optical characteristics of A light diffusing agent may also be dispersed in the lens sheet 4. In addition, the stacking method may be only overlapping, but may be bonded via a fixing element.
In the case of pasting together via a fixing element, as shown in FIG. 2, the light diffusing plate 1 is provided between the light emitting surface 101 side of the light diffusing plate 1 and the incident surface 102 of the lens sheet 4. The holding element 3 is fixed with an adhesive or an adhesive while holding the gap 200.
As shown in FIG. 2, the lens sheet 4 is incident on the incident surface 102 where the light transmitted from the light source 41 through the light diffusing plate 1 and the air gap (air layer) 200 is incident. 1 or more.

Here, the optical gain is one of indexes indicating the diffusibility of the optical diffusing member, and is expressed as a ratio to the luminance of the light, assuming that the luminance of the diffuser that completely diffuses is 1. When the diffusivity of the diffusing member to be measured is biased depending on the direction, the diffusion characteristic of the diffusing member can be shown by obtaining the optical gain for each direction.
Also, complete diffusion refers to an ideal diffuser that has zero absorption and a constant 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.

  Examples actually performed using the backlight unit and the display device as described above will be described below.

Example 1
(Production of light diffusion plate)
As a base material, a polystyrene resin having a refractive index of 1.59 is used, a first resin layer in which 4 parts by weight of silicone having an average particle diameter of 2 μm is added to 100 parts by weight of polystyrene, and an average particle diameter of 100 parts by weight of polystyrene. A second resin layer to which 10 parts by weight of 20 μm acrylic beads were added was laminated, and at the same time, an uneven shape with a surface haze value of 20% and Sm of 300 μm was formed. In addition, the 2nd resin layer side becomes a light-incidence surface.
As a specific production method, the light diffusing plate 1 was produced by extruding a laminated sheet while adjusting the extrusion amount with a laminated extruder. At this time, the die temperature of the extruder was 200 ° C., and the cooling roll temperature (second roll) was set to 100 ° C. The surface unevenness was obtained by transferring the uneven shape on the surface of the cooling roll during extrusion and bleeding out the diffusing agent of the second resin layer.
(Production of lens sheet)
The lens sheet was obtained by melting a polycarbonate resin having a refractive index of 1.49 as a material, and then extruding the sheet with an extruder to transfer a convex cylindrical unit lens on the surface of the cooling roll. The unit lens pitch was 140 μm.

(Examples 2 to 4)
It was produced in the same manner as in Example 1 except that the uneven shape of the cooling roll for extruding the surface unevenness of the light diffusion plate was changed and the surface haze value and Sm value were adjusted as shown in Table 1.

(Example 5)
As a base material, a polystyrene resin having a refractive index of 1.59 is used, a first resin layer in which 0.5 parts by weight of silicone having an average particle diameter of 2 μm is added to 100 parts by weight of polystyrene, and an average of 100 parts by weight of polystyrene. Light is obtained by laminating a second resin layer to which 10 parts by weight of silicone having a particle size of 2 μm is added, and simultaneously transferring an uneven shape of Sm of 300 μm with a surface haze value of 20% on the surface and an uneven shape of the surface of the cooling roll during extrusion A diffusion plate was produced. In addition, the 2nd resin layer side becomes a light-incidence surface.

(Example 6)
Example 1 except that a convex cylindrical unit lens having a pitch of 300 μm is cut into a cooling roll for extrusion transfer, and the light incident surface of the light diffusion plate is extrusion transferred to give a regular uneven shape. It was produced by the same method.

(Comparative Examples 1-4)
It was produced in the same manner as in Example 1, except that the surface roughness of the cooling roll for transferring the surface irregularity of the light diffusing plate during extrusion was changed and the surface haze value and Sm value were adjusted as shown in Table 1.

(Comparative Example 5)
As a base material, a polystyrene resin having a refractive index of 1.59 is used. A first resin layer in which 0.5 parts by weight of silicone having an average particle diameter of 6 μm is added to 100 parts by weight of polystyrene, and an average of 100 parts by weight of polystyrene. A second resin layer to which 10 parts by weight of acrylic beads having a particle size of 20 μm was added was laminated, and at the same time, an uneven shape with a surface haze value of 20% and Sm of 300 μm was formed. The surface unevenness was obtained by transferring the uneven shape on the surface of the cooling roll during extrusion and bleeding out the diffusing agent of the second resin layer.

(Evaluation)
The light diffusion plates of Examples 1 to 6 and Comparative Examples 1 to 5 thus produced and the lens sheet produced in Example 1 were overlapped to form an optical sheet, and the lamp image reduction effect and brightness were evaluated. It was. The results are shown in Table 1. The lamp image was visually evaluated and the brightness was 8000 cd / m 2 or more.

From Table 1, Examples 1 to 6 which contain a light diffusing agent having an average particle diameter of 2 μm or less, the uneven shape of the light incident surface has a surface haze value of 20% or more, and an Sm value of 300 to 900 μm. 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, for Comparative Examples 1 to 5 that do not satisfy at least one of the above conditions, at least one of the lamp image and the brightness was not preferable.

  From the above, the light diffusing plate contains at least one kind of light diffusing agent having an average particle diameter of 2 μm or less, the surface haze value of the light incident surface is 20% or more, and the average interval Sm of the surface irregularities is 300 to 900 μm. In this case, it was found that it is possible to have an excellent lamp image reduction effect.

  The light diffusing plate 1 and the optical sheet 39 of the present invention can be used as a sheet for controlling the viewing angle of a display or a sheet for improving contrast, in addition to being used for a liquid crystal backlight. In addition, since the light from the illumination source can be diffused and collected, it can be used for illumination covers, signboards, building materials, and the like.

It is explanatory drawing which shows the perspective view of the light diffusing plate which concerns on embodiment of this invention. It is explanatory drawing which shows the illustrative display apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. It is explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. It is explanatory drawing which shows the structural example of the liquid crystal display device by a prior art. It is explanatory drawing which shows the perspective view of BEF by a prior art. It is explanatory drawing which shows the structural example of the optical sheet for liquid crystal displays by a prior art. It is explanatory drawing which shows the light intensity distribution radiate | emitted from the optical sheet using BEF.

Explanation of symbols

  H, F, K, P, X ... light, L ... viewing surface (display display surface), 1 ... light diffusion plate, 3 ... fixed element, 4 ... lens sheet, 7 ... first diffusing agent, 8 ... second diffusion Agent, 31, 33, 71, 73 ... polarizing plate, 32, 72 ... liquid crystal panel, 35 ... liquid crystal layer, 39 ... optical sheet, 41, 76 ... light source, 43 ... lamp house, 44 ... backlight unit, 45, 52 , 81 ... reflector, 51 ... LED light source, 74, 75 ... prism, 77 ... reflector film, 78 ... diffuser film, 79 ... light guide plate, 100 ... light entrance surface of light diffuser plate, 101 ... light exit from light diffuser plate Surface 102, light incident surface of the lens sheet, 103 light emitting surface of the lens sheet, 200, gap, 300, diffusion sheet.

Claims (9)

Light in which at least one kind of light diffusing agent having an average particle diameter of 2 μm or less is contained in a base material made of a translucent resin, and one surface in the thickness direction is a light incident surface and the other surface is a light emitting surface A diffusion plate,
The surface haze value of the light incident surface is 20% or more, and the average interval Sm between the surface irregularities is 300 to 900 μm.
A light diffusion plate characterized by that. The light diffusing plate according to claim 1,
A diffusion layer is composed of the base material and the light diffusing agent,
A light diffusing plate, wherein a plurality of diffusion layers containing different light diffusing agents are laminated. The light diffusing plate according to claim 1,
A diffusion layer is composed of the base material and the light diffusing agent,
The light diffusing plate is formed by laminating a plurality of diffusion layers having different concentrations from each other. In the light diffusing plate according to any one of claims 1 to 3,
A light diffusing plate, wherein an ultraviolet absorber is added to the substrate. In the light diffusing plate according to any one of claims 1 to 4,
A light diffusing plate, wherein the light incident surface has a regular surface roughness. The light diffusing plate according to any one of claims 1 to 5,
A lens sheet that is disposed on the light emitting 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 lens sheet.
An optical sheet characterized by that. The light diffusing plate according to any one of claims 1 to 5,
A light diffusing film that is disposed on the light emitting surface side opposite to the light source of the light diffusing plate and that 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 characterized by that. The optical sheet according to claim 6 or 7,
A light source disposed on one side of the optical sheet,
Backlight unit characterized by that. An image display element that defines a display image according to transmission / shading in pixel units;
A display device comprising the backlight unit according to claim 8 on a back surface of the image display element.

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