JP2014029416A - Light diffusion plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusion plate capable of suppressing a change in color tone of light penetrating through the light diffusion plate and suppressing lowering of transmissivity, and provide a surface light source device and a transmissive image display device which include the light diffusion plate.SOLUTION: A transmissive image display device 1 comprises a light diffusion plate 40, a light source part 30 and a transmissive image display part 10. The light diffusion plate 40 is composed of translucent resin and diffuses incident light. The light diffusion plate comprises an incidence surface 40b into which light is made incident, and an emission surface 40a opposite to the incidence surface 40b and emitting light, and has an ultraviolet absorber having an addition amount of 1000 mass ppm or less for the translucent resin. The light source part 30 is arranged facing the incidence surface 40b of the light diffusion plate 40 and supplies light to the incidence surface 40b. The transmissive image display part 10 is arranged on an emission surface 40a side of the light diffusion plate 40 and is irradiated with the emission light from the light diffusion plate 40 to thereby display an image.

Description

  The present invention relates to a light diffusing plate, a surface light source device including the same, and a transmissive image display device.

  2. Description of the Related Art A transmissive image display device such as a liquid crystal display device generally includes a surface light source device that is disposed on the back side of a transmissive image display unit such as a liquid crystal display panel and supplies light to the transmissive image display unit. As such a surface light source device, a direct type surface light source device is known. The direct type surface light source device includes a light diffusing plate having translucency and a light source disposed on the back surface of the light diffusing plate to supply light to the back surface of the light diffusing plate. In a light diffusing plate formed of a translucent resin, an ultraviolet absorber is added to suppress deterioration due to ultraviolet rays emitted from a light source or the like (see, for example, Patent Document 1).

JP 2010-059441 A

  However, when an ultraviolet absorber is added to the translucent resin forming the light diffusing plate, the light diffusing plate becomes yellowish depending on the color of the ultraviolet absorber itself. If the light transmitted through the light diffusing plate is affected by yellowishness, the hue may change. Moreover, there exists a possibility that the transmittance | permeability may fall with the ultraviolet absorber added to translucent resin.

  Accordingly, a main object of the present invention is to provide a light diffusing plate capable of suppressing a change in hue of light transmitted through the light diffusing plate and suppressing a decrease in transmittance, a surface light source device including the same, and a transmission type An object is to provide an image display device.

  The light diffusing plate according to the present invention is a light diffusing plate made of a translucent resin and diffusing and emitting incident light, and includes an incident surface on which light is incident and a surface opposite to the incident surface. And an emission surface for emitting light, and the amount of the ultraviolet absorber added to the translucent resin is 1000 mass ppm or less.

  A surface light source device according to the present invention includes the light diffusing plate described above, and a light source unit that is disposed to face the incident surface of the light diffusing plate and supplies light to the incident surface.

  A transmissive image display device according to the present invention includes the above-described light diffusing plate, a light source portion that is disposed to face the incident surface of the light diffusing plate, supplies light to the incident surface, and a light diffusing plate. A transmission-type image display unit that is disposed on the emission surface side and that is illuminated by light emitted from the light diffusion plate and displays an image.

  In the light diffusing plate, the surface light source device, and the transmissive image display device configured as described above, the light incident from the incident surface of the light diffusing plate is emitted from the emitting surface. In the light diffusion plate, since the amount of the ultraviolet absorber added to the translucent resin is 1000 ppm by mass or less, the influence of the yellow color that is received between the incident on the incident surface and the emergence on the exit surface is suppressed. The Thereby, while suppressing the change of the hue of the light which permeate | transmits a light diffusing plate, the fall of the transmittance | permeability can be suppressed. In the surface light source device including this light diffusion plate, light having a natural hue and high luminance can be supplied to the transmissive image display unit. In the transmissive image display apparatus supplied with such light, the image displayed on the transmissive image display unit can be of higher quality.

  In the light diffusing plate according to the present invention, the translucent resin may be a polystyrene resin or a methyl methacrylate / styrene copolymer resin.

  Since the polystyrene resin or the methyl methacrylate / styrene copolymer resin has a relatively low hygroscopic property, a change in shape due to moisture absorption is suppressed. Thereby, a favorable emission state can be maintained. In addition, the cost for the material can be reduced in the manufacture of the light diffusing plate.

  The light diffusing plate according to the present invention can be used as a light diffusing plate for a white light emitting diode in which light from a white light emitting diode as a light source is incident on an incident surface.

  The wavelength of ultraviolet light that causes deterioration of the translucent resin is 290 to 400 nm. For this reason, in order to reduce deterioration of translucent resin, it is desired to cut the light whose upper limit of wavelength is about 410 nm. On the other hand, the wavelength of light emitted from the white light emitting diode is 400 nm or more. Therefore, in the conventional light diffusing plate in which measures against deterioration by ultraviolet rays are taken, light in the wavelength region of 400 nm to 410 nm included in the light emitted from the white light emitting diode is also cut. As a result, it has been found that the emission intensity is lowered, and this causes a further decrease in luminance. In the light diffusing plate having the above configuration, even when light from the white light emitting diode is incident, the light having a wavelength in the region of 400 nm to 410 nm peculiar to the white light emitting diode is not cut. The effect of suppressing the decrease in the increase is further increased.

  In the light diffusing plate according to the present invention, the amount of the fluorescent whitening agent added to the translucent resin can be 0 mass ppm or more and 10 mass ppm or less.

  According to the light diffusing plate having the above configuration, since the ultraviolet absorber is added as described above, it is possible to reduce the amount of the fluorescent whitening agent for suppressing the yellowness due to the addition of the ultraviolet absorber. . Thereby, since the fall of the transmittance | permeability by adding a fluorescent whitening agent is suppressed, the brightness | luminance of the light radiate | emitted from a light diffusing plate can be improved.

  The light diffusing plate according to the present invention can be used as a light diffusing plate for a color liquid crystal display device that illuminates a color liquid crystal display panel as a transmissive image display unit with light emitted from an emission surface.

  According to the light diffusing plate having this configuration, the transmissive image display is irradiated with light in which the influence of yellowishness is suppressed. As a result, the image displayed on the transmissive image display unit can be of higher quality.

  According to the light diffusing plate, the surface light source device including the light diffusing plate, and the transmissive image display device according to the present invention, it is possible to suppress a change in the hue of light transmitted through the light diffusing plate and to suppress a decrease in transmittance. It becomes possible.

It is sectional drawing which shows schematic structure of the transmissive image display apparatus to which one Embodiment of the light diffusing plate which concerns on this invention is applied. It is the schematic block diagram which showed one Embodiment of the apparatus which manufactures the light diffusing plate shown in FIG. It is the graph which showed the spectrum distribution of the light which white LED radiate | emits, and the area | region of the wavelength which an ultraviolet absorber cut | disconnects, and the graph which expanded and showed the light intensity in the wavelength vicinity of 400 nm.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or an equivalent element, and the overlapping description is abbreviate | omitted. Further, the dimensional ratios in the drawings do not necessarily match those described. Further, in the description, words indicating directions such as “up” and “down” are convenient words based on the state shown in the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a transmissive image display device to which an embodiment of a light diffusion plate according to the present invention is applied, and shows the transmissive image display device in an exploded manner.

  As shown in FIG. 1, the transmissive image display device 1 includes a transmissive image display unit 10 and a surface light source device 20 disposed to face the back side of the transmissive image display unit 10. In the following description, as shown in FIG. 1, the arrangement direction of the surface light source device 20 and the transmissive image display unit 10 is referred to as a Z-axis direction (plate thickness direction), which is two directions orthogonal to the Z-axis direction. Two orthogonal directions are referred to as an X-axis direction and a Y-axis direction.

  The transmissive image display unit 10 displays an image by being illuminated with light output from the surface light source device 20. Examples of the transmissive image display unit 10 include, for example, a color liquid crystal display panel in which polarizing plates 12 and 13 are disposed on both surfaces of a liquid crystal cell 11. In this case, the transmissive image display device 1 is a liquid crystal display device (or a liquid crystal television). As the liquid crystal cell 11 and the polarizing plates 12 and 13, those used in a transmissive image display device such as a conventional liquid crystal display device can be used. Examples of the liquid crystal cell 11 include known liquid crystal cells such as TFT (Thin Film Transistor) type liquid crystal cells and STN (SuperTwistedNematic) type liquid crystal cells.

  The surface light source device 20 is a so-called direct type surface light source device and includes a light source unit 30 including a plurality of light sources 31 arranged in parallel. Each light source 31 is a linear light source extending in a direction orthogonal to the arrangement direction of the plurality of light sources 31, and is exemplified by a straight tube like a fluorescent lamp (cold cathode ray lamp). The plurality of light sources 31 are arranged at intervals so that the central axes of the light sources 31 are located in the same plane, and when the distance between the central axes of the two adjacent light sources 31 and 31 is L1, The distance L1 is 15 mm to 150 mm, for example. Here, the light source 31 is linear, but a point light source such as an LED can also be used. 1 is a virtual plane for convenience of explanation and is a virtual plane.

  An example of the point light source is a white light emitting diode (hereinafter also referred to as “white LED”). As white LED used as the light source part 30, what has various light emission distribution can be used. It is preferable that the light intensity distribution in the normal direction is the maximum and the light emission distribution has a full width at half maximum of 40 degrees or more and 80 or less. Specific examples of the LED type include a Lambertian type, a shell type, and a side emission type.

  As shown in FIG. 1, the plurality of light sources 31 are preferably disposed in a lamp box 32, and the inner surface 32a of the lamp box 32 is preferably formed as a light scattering reflection surface. Thereby, since the light output from each light source 31 is reliably output to the transmissive image display part 10 side, it becomes possible to use the light from each light source 31 efficiently. In the present embodiment, the light source unit 30 will be described as including the lamp box 32 having the above-described preferable configuration.

  The surface light source device 20 includes a light diffusing plate 40 disposed on the front surface side (upper side in FIG. 1) of the light source unit 30, that is, on the transmissive image display unit 10 side so as to be separated from the light source unit 30. . At this time, in the light diffusing plate 40, the surface on the light source unit 30 side is the incident surface 40b, and the surface on the transmissive image display unit 10 side is the emission surface 40a. In the light diffusing plate 40 of the present embodiment, both the entrance surface 40b and the exit surface 40a are formed flat. When the distance between the light diffusion plate 40 and the plurality of light sources 31 is D, the distance D is, for example, 5 mm to 50 mm. In order to reduce the thickness of the surface light source device 20, the distance L1 between the two adjacent light sources 31, 31 is set so that L1 / D is 1.5 or more, and preferably L1 / D is 2.5 or more. And the separation distance D is selected.

  The light diffusion plate 40 is for diffusing and irradiating light from the light source unit 30, that is, direct light from each light source 31 and reflected light reflected by the inner surface 32 a of the lamp box 32 toward the transmissive image display unit 10. It is. The light diffusing plate 40 is formed in a plate shape, and the thickness d1 is usually about 1.0 mm to 4.0 mm, and preferably 1.5 mm or more. The example of the planar view shape of the light diffusing plate 40 includes a substantially rectangular shape and a substantially square shape. The size of the light diffusing plate 40 in plan view is selected so as to match the target screen size of the transmissive image display unit 10. The size of the light diffusing plate 40 is usually 270 mm × 480 mm or more and 1250 mm × 2220 mm or less, and preferably 390 mm × 700 mm or more. Further, the length of the diagonal line of the light diffusing plate 40 is usually 50 cm or more and 250 cm or less, and preferably 80 cm or more.

  The light diffusing plate 40 is composed mainly of a translucent resin (or transparent resin). Examples of the refractive index of the translucent resin are 1.46 to 1.62. Examples of the translucent resin material include polystyrene (PS) resin (refractive index: 1.59), MS (methyl methacrylate-styrene copolymer) resin (refractive index: 1.56-1.59), polymethacrylic resin. And methyl acid (PMMA) resin (refractive index: 1.49). As the translucent resin material, polystyrene resin and MS resin are more preferable from the viewpoint of hygroscopicity and cost.

  The light diffusion plate 40 is added with an ultraviolet absorber for reducing deterioration due to ultraviolet rays. In this embodiment, there is one feature in the addition amount of the ultraviolet absorber. That is, the addition amount of the ultraviolet absorber with respect to the translucent resin constituting the light diffusion plate 40 is 1000 mass ppm or less, preferably 1000 mass ppm or less, and preferably 500 mass ppm or less. For example, for the light diffusion plate 40 for a 40-inch display having a size of 514 mm × 904 mm and a diagonal length of 104 cm, the amount of the UV absorber added to the translucent resin can be 0 ppm by mass. .

  Examples of the ultraviolet absorber added to the translucent resin include, for example, a benzotriazole ultraviolet absorber, a benzophenone ultraviolet absorber, a cyanoacrylate ultraviolet absorber, a malonic ester ultraviolet absorber, and an oxalic anilide ultraviolet absorber. Agents, triazine ultraviolet absorbers, and the like, preferably benzotriazole ultraviolet absorbers and triazine ultraviolet absorbers.

  The addition amount of the fluorescent whitening agent with respect to the total mass of the translucent resin and the ultraviolet absorber is 0 mass ppm or more and 10 mass ppm or less. Conventionally, in order to suppress yellowing due to the addition of an ultraviolet absorber, a fluorescent brightening agent has been added. In this embodiment, since yellowing is suppressed by making the addition amount of the ultraviolet absorber the above addition amount, there is a case where the fluorescent whitening agent may not be added, and at most 10 ppm by mass. If a fluorescent brightening agent is added, yellowing can be sufficiently suppressed. The light emitted from the light diffusing plate can be prevented by not adding the fluorescent brightening agent, or by reducing the transmittance by adding the fluorescent brightening agent by setting the addition amount to the above addition amount. The brightness can be improved.

  In order to provide diffusion performance as the light diffusion plate 40, an additive such as a diffusion agent having an effect of diffusing light by the particles themselves is added. As the diffusing agent, powder having a refractive index different from that of the above-described thermoplastic resin mainly constituting the light diffusing plate 40 is used. For example, organic particles such as styrene resin particles and methacrylic resin particles, and inorganic particles such as potassium carbonate particles, silica particles, and silicone resin particles are used.

  In addition, additives such as an antistatic agent, an antioxidant, a processing stabilizer, a flame retardant, and a lubricant can be added to the light diffusion plate 40 without departing from the spirit of the present invention. These additives can be used alone or in combination of two or more.

  When there are those added to the translucent resin, such as the above-mentioned particle components and additives, the addition amount of the ultraviolet absorber is added to the translucent resin constituting the light diffusion plate 40 and others. And the added amount is 1000 ppm by mass or less. The same applies to the amount of fluorescent brightener added.

[Production method of light diffusion plate]
Next, an example of a method for manufacturing the light diffusing plate 40 according to the present embodiment will be described with reference to FIG. FIG. 2 is a schematic configuration diagram showing an embodiment of an apparatus for manufacturing a light diffusing plate.

  As shown in FIG. 2, the light diffusing plate manufacturing apparatus 60 includes a resin inlet 61 for feeding a thermoplastic resin as a raw material, an extruder 62 for heating and melting the thermoplastic resin, and an extruder 62. A die 63 for extruding the supplied molten resin into a sheet shape, and a first pressing roll 64, a second pressing roll 65, and a third pressing roll 66 for forming a sheet-shaped resin sheet 80 extruded from the die 63. And a cutter 68 for cutting the resin sheet 80 into a predetermined size along the width direction (direction orthogonal to the extrusion direction).

  As for the 1st press roll 64, the 2nd press roll 65, and the 3rd press roll 66, the rotating shaft of each roll is arrange | positioned substantially parallel. The 1st press roll 64 and the 2nd press roll 65, the 2nd press roll 65, and the 3rd press roll 66 are mutually spaced apart in the thickness direction of the resin sheet 80, and the interval between each peripheral surface is as follows. It is set according to the thickness of the resin sheet 80. The peripheral surfaces 64a to 66a of the first to third pressing rolls 64 to 66 are mirror surfaces.

  In such a light diffusing plate manufacturing apparatus 60, for example, 98.1 wt% polystyrene resin as a thermoplastic resin, 1.8 wt% crosslinked acrylic copolymer particles as a diffusing agent, and an ultraviolet absorber. 0.05% by weight of benzotriazole-based compound and 0.05% by weight of hindered phenol-based compound as antioxidant are charged into the resin inlet 61. Next, the polystyrene resin mixed with the ultraviolet absorber is melt-kneaded in the extruder 62 and supplied to the die 63. In the die 63, the molten resin supplied from the extruder 62 is extruded as a resin sheet 80. Next, the resin sheet 80 is sandwiched and pressed between the first pressing roll 64 and the second pressing roll 65, and then the resin sheet 80 is sandwiched and pressed between the second pressing roll 65 and the third pressing roll 66. As a result, the resin sheet 80 having a flat surface and a desired thickness is formed. And it becomes the light diffusing plate 40 which has desired thickness and size by cut | disconnecting to desired size with the cutter 68. FIG.

  Next, the function and effect of the light diffusing plate 40 will be described by taking as an example the case where the surface light source device 20 including the light diffusing plate 40 is applied to the transmissive image display device 1 as shown in FIG. . In the light diffusing plate 40, the surface light source device 20, and the transmissive image display device 1 of the above embodiment, the light incident from the incident surface 40b of the light diffusing plate 40 is emitted from the emitting surface 40a. In the light diffusing plate 40, since the amount of the ultraviolet absorber added to the translucent resin is 1000 mass ppm or less, the influence of the yellow color that is received from the time when the light diffusing plate 40 is incident on the incident surface 40b until the light is emitted to the output surface 40a. Is suppressed. Thereby, while suppressing the change of the hue of the light which permeate | transmits the light diffusing plate 40, the fall of the transmittance | permeability can be suppressed. In the surface light source device 20 including the light diffusing plate 40, light having a natural hue and high luminance can be supplied to the transmissive image display unit 10. In the transmissive image display device 1 to which such light is supplied, the image displayed on the transmissive image display unit 10 can be of higher quality.

  Furthermore, in the transmissive image display device 1 having the above-described configuration, when a white LED is applied as the light source unit 30, that is, when the light from the white LED is incident on the light diffusion plate 40, the effect is increased. 3 (a) and (b) will be used for explanation. FIG. 3A is a graph showing the spectral distribution of light emitted from the white LED and the wavelength region blocked by the UV absorber, and FIG. 3B shows the light intensity in the vicinity of the wavelength of 400 nm in an enlarged manner. It is a graph.

  The wavelength of ultraviolet light that causes deterioration of the translucent resin is 290 to 400 nm. For this reason, as shown in FIG. 3, it is desired to cut light having an upper limit of wavelength up to about 410 nm in order to suppress deterioration of the translucent resin forming the light diffusion plate 40. On the other hand, the wavelength of light emitted from the white LED is 400 nm or more as shown in FIG. Therefore, in the conventional light diffusing plate in which measures against deterioration due to ultraviolet rays are taken, light in the wavelength region of 400 nm to 410 nm included in the light emitted from the white LED is also cut. As a result, it has been found that the emission intensity is lowered, and the luminance is further reduced. In this regard, in the light diffusing plate 40 of the above-described embodiment, even when light from the white LED is incident, light having a wavelength in the region of 400 nm to 410 nm unique to the white LED is not cut. . Therefore, the effect of suppressing the decrease in luminance is further increased.

  As mentioned above, although one Embodiment and one Example of this invention were demonstrated, this invention is not limited to the said embodiment and Example, A various change is possible in the range which does not deviate from the meaning of invention.

  In the said embodiment, although the example of light diffusing plate 40 manufacture by extrusion molding was given and demonstrated using the manufacturing apparatus as shown in FIG. 2, this invention is not limited to this. The light diffusing plate 40 may be a method of obtaining a light diffusing plate 40 having an arbitrary shape by filling a mold or mold with a resin using a hot press molding machine or an injection molding machine.

  In the said embodiment, although the example in which the entrance plane 40b and the output surface 40a of the light diffusing plate 40 were both formed flat was demonstrated, this invention is not limited to this. For example, at least one surface may have irregularities formed on the surface, such as a lenticular lens, a Fresnel lens, or a prism lens. Further, at least one surface may be a matte surface (embossed surface).

  In the said embodiment, in order to provide the diffusion performance as the light diffusing plate 40, although the example which adds additives, such as a diffusing agent, was given and demonstrated, this invention is not limited to this. For example, an additive such as a matting agent having a function of forming an uneven surface for diffusing light may be added. Examples of the matting agent include cross-linked acrylic resins.

  In the said embodiment, although the light diffusing plate 40 of the single layer structure was mentioned as an example and demonstrated, this invention is not limited to this. For example, the light diffusing plate 40 having a multilayer structure in which surface layers are provided on the incident surface 40b side and the emission surface 40a side, respectively. In this case, you may add a ultraviolet absorber so that the addition amount with respect to the translucent resin which mainly comprises each layer may be 1000 mass ppm or less. Moreover, you may add a ultraviolet absorber only to the surface layer which comprises the entrance plane 40b side. In this case, an ultraviolet absorber can be added so that the addition amount with respect to the translucent resin constituting the surface layer is 1000 ppm by mass or less.

  DESCRIPTION OF SYMBOLS 1 ... Transmission type image display apparatus, 10 ... Transmission type image display part, 11 ... Liquid crystal cell, 12, 13 ... Polarizing plate, 20 ... Surface light source device, 30 ... Light source part, 31 ... Light source, 32 ... Lamp box, 40 ... Light diffusing plate, 40a ... emission surface, 40b ... incident surface, 60 ... light diffusing plate manufacturing apparatus, 61 ... resin inlet, 62 ... extruder, 63 ... die, 64 ... first pressing roll, 65 ... second pressing roll , 66 ... third pressing roll, 68 ... cutter, 80 ... resin sheet.

Claims (7)

A light diffusing plate made of a translucent resin that diffuses and emits incident light,
An incident surface on which light is incident;
An exit surface that is opposite to the entrance surface and emits the light;
With
The amount of the ultraviolet absorber added to the translucent resin is 1000 mass ppm or less.
Light diffusion plate. The translucent resin is a polystyrene resin or a methyl methacrylate / styrene copolymer resin.
The light diffusing plate according to claim 1. Used as a light diffusing plate for a white light emitting diode, in which light from a white light emitting diode as a light source is incident on the incident surface.
The light diffusing plate according to claim 1 or 2. The amount of fluorescent brightener added to the translucent resin is 0 mass ppm or more and 10 mass ppm or less.
The light diffusing plate as described in any one of Claims 1-3. Illuminating a color liquid crystal display panel as a transmissive image display unit with light emitted from the emission surface, used as a light diffusion plate for a color liquid crystal display device,
The light diffusing plate as described in any one of Claims 1-4. The light diffusing plate according to any one of claims 1 to 5,
A light source unit disposed opposite to the incident surface of the light diffusing plate, and supplying light to the incident surface;
A surface light source device. The light diffusing plate according to any one of claims 1 to 5,
A light source unit disposed opposite to the incident surface of the light diffusing plate, and supplying light to the incident surface;
A transmission-type image display unit that is disposed on the emission surface side of the light diffusion plate and is illuminated with light emitted from the light diffusion plate and displays an image;
A transmissive image display device.

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