JP2006164890A - Direct backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct backlight device which can achieve a high brightness and excellent uniformity by suppressing a periodical brightness unevenness on a light-emitting surface, with a light utilization ratio keeping at a high level by devising the structure components of the direct backlight device. <P>SOLUTION: This direct backlight device comprises a plurality of paralleled linear lamps, a reflection plate, a light-diffusing plate, and a diffusion sheet. Wherein it is desirable to have a group of prism rows having a sawtooth shape in cross-section at least on either main face of the light-diffusion plate, and the vertex angle of the prism is not less than 60° and not more than 170°, the pitch of that is not less than 20 μm and not more than 700 μm, and further to have 2-4 sheets of the diffusion sheet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a direct type backlight device. More specifically, the present invention relates to a direct type backlight device having high luminance and good luminance uniformity.

Conventionally, as a backlight device for a liquid crystal display, a device using a cold cathode tube as a light source has been widely used, and there are a method called an edge light type and a method called a direct type. The edge light type is a backlight device having a structure in which a cold cathode tube of a thin tube is arranged on the end side of a light guide plate, and light incident from the end surface is repeatedly reflected in the light guide plate and emitted to the main surface of the light guide plate.
On the other hand, the direct type backlight device has a configuration in which a plurality of cold-cathode tubes arranged in parallel, a reflector provided on the back surface of the cold-cathode tube, and a light diffusing plate forming a light emitting surface are combined. In contrast to the edge light type, since the number of cold cathode fluorescent lamps can be increased, the light emitting surface can be easily brightened.
However, the direct type backlight device has a problem that the luminance uniformity of the light emitting surface is poor. In particular, the periodic luminance unevenness that occurs because the luminance is increased directly above the cold cathode tube is a serious problem.
That is, when the luminance uniformity of the light emitting surface of the backlight device is poor, display unevenness occurs on the display screen of the liquid crystal display.
Conventionally, various measures have been taken to improve the luminance uniformity. For example, a striped pattern or dot-shaped light quantity correction pattern is printed on a light diffusing plate, and a method (illustrated in Patent Document 1) for reducing a light beam emitted directly above a fluorescent tube, or a wave-shaped reflecting plate is used. There has been proposed a technique (Patent Document 2) for focusing the reflected light from the reflecting plate to a region corresponding to the middle between the fluorescent tube and the fluorescent tube.
However, when the light intensity correction pattern is printed as a means of improving the luminance uniformity, a part of the light beam is cut off, so that the utilization rate of the light beam emitted from the fluorescent tube is reduced and sufficient luminance cannot be obtained. was there. In addition, when the corrugated reflector is used, there is a problem that the configuration of the device becomes complicated and the manufacturing cost of the backlight device increases.
In addition, the light diffusing plate used for direct type backlights often uses a material in which a light diffusing agent is dispersed in a transparent resin. However, if the concentration of the light diffusing agent is increased in order to improve the luminance uniformity, There was a problem that the luminance was lowered. In order to solve this problem, it has been proposed to form a pattern such as a prism shape on the surface of the light diffusing plate so as to have a diffusion effect due to the surface shape without lowering the luminance (Patent Documents 3, 4, and 5). However, the luminance uniformity cannot be improved by simply forming a prismatic pattern on the surface of the light diffusion plate.
Conventionally, in order to improve the luminance uniformity, a diffusion sheet obtained by imparting a light diffusion effect to a sheet having a thickness of about 50 μm to 300 μm is used. This diffusion sheet is often used in combination with a prism sheet having a brightness enhancement effect having a prism array with a fine cross-sectional sawtooth shape on a transparent sheet.
However, in order to form a fine and precise prism row, the prism sheet uses an expensive shape imparting roll because it requires precision processing, and further presses the roll against the sheet to accurately shape the prism sheet. The manufacturing cost is high for two reasons, that is, it is difficult to improve the production speed and the yield, such as transferring the light, and there is a problem that the cost of the backlight device and thus the liquid crystal display increases.
Japanese Patent Laid-Open No. 6-273760 FIG. JP 2001-174813 A JP-A-5-333333 JP-A-8-297202 JP 2000-182418 A

  The present invention relates to an improvement of a direct type backlight device, obtains a high luminous flux effective utilization rate, further suppresses periodic luminance unevenness of a light emitting surface, and simultaneously improves luminance and luminance uniformity, and The present invention has been made for the purpose of providing a direct type backlight device that can be realized at low cost.

In order to solve the above-mentioned problems, the present inventors have studied a backlight device in which a flat light diffusion plate, a prism sheet, and two or more diffusion sheets are stacked, but it has been found that the luminance decreases. . Therefore, as a result of further earnest research, the present inventors have surprisingly found that a direct-type backlight device has a sawtooth cross-section on at least one main surface of a light diffusing plate that is not sufficiently effective in improving luminance uniformity. By combining the technology to provide a prism row with a specific pattern and the technology to arrange two or more diffusion sheets that may reduce the brightness, a high brightness and good brightness uniformity can be achieved without an expensive prism sheet. It has been found that a light device can be obtained, and the present invention has been completed based on this finding.
That is, the present invention
(1) A plurality of linear light sources arranged in parallel, a reflective plate that reflects light from the linear light source, and a light diffusion plate that diffuses and irradiates direct light from the linear light source and reflected light from the reflective plate In the direct type backlight device provided, the light diffusing plate has a prism row having a sawtooth cross section on at least one main surface thereof, and the apex angle of the prism row of the light diffusing plate is 60 degrees or more and 170 degrees or less. A direct-type backlight device having a pitch of 20 μm or more and 700 μm or less, and further comprising 2 or more and 4 or less diffusion sheets for adjusting the light diffused and irradiated from the light diffusion plate,
(2) The angle between the longitudinal direction of the prism row of the light diffusing plate and the longitudinal direction of the linear light source is 60 degrees or less, and the direct type backlight device according to (1),
(3) The light diffusion plate is made of a material in which a light diffusing agent is dispersed in a transparent resin, and the total light transmittance of the dispersion is 60% or more and 92% or less, and the haze is 40% or more and 94% or less (1 ) Or (2) direct type backlight device,
Is to provide.
Furthermore, as a preferred embodiment of the present invention,
(4) The direct type backlight device according to (3), wherein the transparent resin used for the light diffusing plate has a water absorption of 0.25% or less,
(5) The direct type backlight device according to (3) or (4), wherein the light diffusing agent is a polystyrene-based polymer, a polysiloxane-based polymer, or a cross-linked product thereof,
Can be mentioned.

The direct type backlight device of the present invention does not use an expensive prism sheet, has a high effective luminous flux utilization rate, and suppresses periodic luminance unevenness of the light emitting surface. According to the present invention, it is possible to provide a backlight device with high luminance and good luminance uniformity at low cost.

The direct type backlight device of the present invention includes a plurality of linear light sources arranged in parallel, a reflecting plate that reflects light from the linear light source, direct light from the linear light source and reflected light from the reflecting plate. In a direct type backlight device having a light diffusing plate for diffusing irradiation, the light diffusing plate has a prism row with a sawtooth cross section on at least one main surface thereof, and an apex angle of the prism row of the light diffusing plate Is a direct type backlight device having 60 to 170 degrees and a pitch of 20 to 700 μm, and further comprising 2 to 4 diffusion sheets for adjusting the light diffused and irradiated from the light diffusion plate.

FIG. 1 is a schematic perspective view of an embodiment of a direct type backlight device of the present invention. The direct type backlight device of this aspect includes a plurality of linear light sources 3 arranged in parallel, a reflecting plate 4 that reflects light from the light source 3, direct light from the light source 3, and reflected light from the reflecting plate. A light diffusing plate 2 for diffusing irradiation is provided. The light diffusing plate 2 has a prism array having a sawtooth cross section having an apex angle 5 on the side far from the light source, and further on the side far from the light source 3 of the light diffusing plate 2 1-1 and 1-2 are arranged. Further, as the optical member 6 for improving the luminance, any one of the following two types of members may be installed on the side far from the light source 3 of the diffusion sheet 1-2.
(1) An optical laminate having a cholesteric liquid crystal layer in which the helical pitch of liquid crystal molecules continuously changes on a transparent substrate, and a formula Rth = [(nx + ny) / 2−nz] × d (wherein nx, ny Represents a refractive index in two directions perpendicular to each other perpendicular to the thickness direction, and nx> ny, nz represents a refractive index in the thickness direction, and d represents a film thickness). A laminate including a retardation element having a thickness of 20 nm to -1000 nm and a quarter-wave plate.
(2) A reflective polarizer using birefringence proposed in Japanese Patent No. 3448626.

The linear light source used in the device of the present invention is not particularly limited, and a cold cathode tube, a hot cathode tube, a linearly arranged LED, a combination of an LED and a light guide, and the like can be used. At this time, the cold cathode tube or the hot cathode tube may be U-shaped or W-shaped in addition to the linear shape. A cold cathode tube is preferred from the viewpoint of luminance uniformity as a linear light source, and a combination of LEDs arranged in a linear form, LED and a light guide is preferred from the viewpoint of luminous efficiency. When using a linear array of LEDs, or a combination of LEDs and light guides, if there are multiple series of LED pairs or combinations of LEDs and light guides, there are multiple linear light sources. Suppose that
The reflecting plate is not particularly limited, but a white or silver colored resin, metal, or the like can be used. The color is preferably white from the viewpoint of improving the brightness uniformity, and the material is preferably a resin from the viewpoint of weight reduction.
The distance between the centers of the linear light sources is not particularly limited, but is preferably 15 mm or more and 150 mm or less, and more preferably 20 mm or more and 100 mm or less. The distance between the center of the linear light source and the surface of the light diffusing plate closer to the light source is not particularly limited, but is preferably 5 mm or more and 30 mm or less, and more preferably 5 mm or more and 25 mm or less.

The light diffusing plate used in the device of the present invention is used to improve the luminance uniformity. The light diffusing plate has a light incident surface and a light emitting surface, and light from the linear light source is incident on the light incident surface on the side closer to the light source, and within the light diffusing plate or at least of the light incident surface or the light emitting surface. In the prism array having a sawtooth cross section provided on one side, the light is diffused in various directions and emitted from the light exit surface far from the light source. The material of the light diffusing plate may be glass, a mixture of two or more resins that are difficult to mix, a material in which a light diffusing agent is dispersed in a transparent resin, and the like, but is not particularly limited. Among these, a resin is preferable because of light weight and easy molding, and a material in which a light diffusing agent is dispersed in a transparent resin is preferable because adjustment of total light transmittance and haze is easy. Furthermore, it is formed with a material in which a light diffusing agent is dispersed in a transparent resin up to the prism row portion, and adjusting the entire light diffusing plate to the same total light transmittance and haze, the direction of the light emitted from the light diffusing plate is It is more preferable because it can be further varied.

The content of the light diffusing agent in which the light diffusing agent is dispersed in a transparent resin is not particularly limited, and can be appropriately selected according to the thickness of the light diffusing plate, the linear light source interval of the backlight, etc. The content of the light diffusing agent is preferably adjusted so that the total light transmittance of the dispersion is 60% or more and 92% or less, and the content of the light diffusing agent is adjusted so that it is 65% or more and 92% or less. More preferably. It is preferable to adjust the content of the light diffusing agent so that the haze is 40% or more and 94% or less, and it is more preferable to adjust the content of the light diffusing agent so as to be 50% or more and 94% or less. The brightness can be further improved by setting the total light transmittance to 60% or more and the haze to 94% or less, and the brightness uniformity can be further improved by setting the total light transmittance to 92% or less and the haze to 40% or more. Can be improved.
The total light transmittance in this case is a value measured with a 2 mm thick plate smooth on both sides according to JIS K7361-1, and the haze is a value measured with a 2 mm thick plate smooth on both sides according to JIS K7136.
The thickness of the light diffusing plate is not particularly limited, but is preferably 0.4 mm to 5 mm, and more preferably 0.8 mm to 4 mm. If the thickness is smaller than 0.4 mm, a device for suppressing deflection due to its own weight, such as forming a large number of support columns, is required, and the cost of the backlight increases. If the thickness exceeds 5 mm, molding becomes difficult.

In the present invention, light emitted from the light diffusing plate is refracted and diffused in a specific direction by a light diffusing plate having a sawtooth prism shape with an apex angle of 60 degrees or more and 170 degrees or less on at least one main surface. . Further, the light is adjusted by the diffusion sheet. At this time, by setting the apex angle of the prism of the light diffusing plate in the above-described range, it is possible to suitably adjust the light incident direction to the diffusing sheet, and to simultaneously improve the luminance and the luminance uniformity.
A sawtooth-shaped prism array is a cross-section cut in a direction perpendicular to the longitudinal direction, and is a shape in which triangular protrusions are connected, and the bases of the triangular protrusions are connected to form a V-shaped groove. There may be a horizontal portion between the triangle projections, but the triangle skirts are connected to form a V-shaped groove in order to diffuse light appropriately It is preferable that The shape of the triangle is not particularly limited as long as it is within the range of the above-described apex angle, but is preferably an isosceles triangle so that the luminance in the front direction of the liquid crystal display is the highest.

The prism apex angle of the prism row on the light diffusion plate is preferably 60 ° or more and 170 ° or less, more preferably 65 ° or more and 165 ° or less, and further preferably 70 ° or more and 160 ° or less. . If the prism apex angle on the light diffusion plate is less than 60 degrees, the brightness unevenness may increase, and if it exceeds 170 degrees, the brightness unevenness may increase.
In the device of the present invention, the pitch of the prism rows of the light diffusion plate is preferably 20 μm or more and 700 μm or less, more preferably 30 μm or more and 500 μm or less, and further preferably 40 μm or more and 400 μm or less. If the pitch of the prism rows of the light diffusing plate is less than 20 μm, the shape may be difficult because of the fine shape, or the light diffusing effect may be reduced. If the pitch of the prism rows exceeds 700 μm, the light diffusion becomes rough and there is a risk of uneven brightness.
The surface of the prism array of the light diffusing plate can be roughened and the direction in which the light is emitted can be more varied within an appropriate range. In that case, the centerline average surface roughness (Ra) when the prism surface is measured at 20 μm in a direction perpendicular to the longitudinal direction is preferably 0.08 μm or more and 3 μm or less, and preferably 0.09 μm or more and 2 μm or less. More preferably, it is 0.1 μm or more and 1 μm or less. By making Ra 0.08 μm or more, the light emission direction can be made more diverse, and by making it Ra 3 μm or less, the light emission direction can be prevented from being made too diverse.

In the backlight device of the present invention, the angle formed by the longitudinal direction of the prism row of the light diffusing plate and the longitudinal direction of the linear light source is preferably 60 degrees or less. This angle is more preferably 50 degrees or less, and further preferably 45 degrees or less. By setting the angle between the linear light source and the prism row to 60 degrees or less, it is possible to reduce luminance unevenness.

There is no particular limitation on the method of forming the prism array having a sawtooth cross section on the surface of the light diffusion plate used in the apparatus of the present invention, for example, the prism array can be formed on the surface of the flat light diffusion plate, or A prism row can be formed simultaneously with the formation of the light diffusing plate. The method for forming the prism row on the surface of the flat light diffusion plate is not particularly limited. For example, it can be performed by cutting, or a photo-curing resin is applied and cured in a state where the shape of the mold is transferred. You can also. When a light diffusion plate is produced by extrusion molding and a prism row is formed at the same time, it can be extruded by using a deformed die having the shape of the prism row, or the prism row can be formed by embossing after extrusion. It can also be formed. When the light diffusing plate is produced by casting and the prism row is formed at the same time, a casting mold having the prism row shape can be used. In the case where the light diffusion plate is produced by injection molding and the prism row is formed at the same time, a mold having the prism row shape can be used.

In the present invention, the transparent resin means a resin having a total light transmittance of 70% or more measured with a 2 mm thick plate smooth on both sides according to JIS K7361-1.
Examples of the transparent resin constituting the light diffusion plate used in the present invention include polyethylene, propylene-ethylene copolymer, polypropylene, polystyrene, an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester having a lower alkyl group. Copolymer, polyethylene terephthalate, terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymer, polycarbonate, acrylic resin, resin having an alicyclic structure, and the like. Among these, polycarbonate, polystyrene, a copolymer or an alicyclic ring of an aromatic vinyl monomer containing 10% or more of an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester having a lower alkyl group A resin having a water absorption rate of 0.25% or less, such as a resin having a formula structure, is preferable in that a large light diffusing plate with little warpage can be obtained because deformation due to moisture absorption is small. A resin having an alicyclic structure is more preferable because it has good fluidity and can efficiently produce a large light diffusion plate. A compound in which a resin having an alicyclic structure and a light diffusing agent are mixed has both high permeability and high diffusibility necessary for a light diffusing plate, and has good chromaticity, so that it can be suitably used.

The resin having an alicyclic structure is a resin having an alicyclic structure in the main chain and / or side chain. From the viewpoint of mechanical strength, heat resistance, etc., a resin containing an alicyclic structure in the main chain is particularly preferred.
Examples of the alicyclic structure include a saturated cyclic hydrocarbon (cycloalkane) structure and an unsaturated cyclic hydrocarbon (cycloalkene, cycloalkyne) structure. From the viewpoint of mechanical strength, heat resistance, etc., a cycloalkane structure or a cycloalkene structure is preferable, and among them, a cycloalkane structure is most preferable. The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is usually 4 to 30, preferably 5 to 20, more preferably 5 to 15 in the mechanical strength, The properties of heat resistance and moldability of the light diffusing plate are highly balanced and suitable.
The proportion of the repeating unit having an alicyclic structure in the resin having an alicyclic structure may be appropriately selected according to the purpose of use, but is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90%. % By weight or more. When the ratio of the repeating unit having an alicyclic structure is too small, the heat resistance is lowered, which is not preferable. In addition, repeating units other than the repeating unit which has an alicyclic structure in resin which has an alicyclic structure are suitably selected according to the intended purpose.
Specific examples of the resin having an alicyclic structure include (1) a ring-opening polymer of a norbornene monomer and a ring-opening of the norbornene monomer and other monomers capable of ring-opening copolymerization with this. Norbornene polymers such as copolymers, addition products of these hydrogenated products, norbornene monomers, and addition copolymers of norbornene monomers with other monomers copolymerizable therewith (2) a monocyclic olefin polymer and a hydrogenated product thereof; (3) a cyclic conjugated diene polymer and a hydrogenated product thereof; (4) a polymer of a vinyl alicyclic hydrocarbon monomer and Copolymers of vinyl alicyclic hydrocarbon monomers and other monomers copolymerizable therewith, as well as hydrogenated products thereof, aromatic ring hydrogen of polymers of vinyl aromatic monomers Additives and other vinyl aromatic monomers copolymerizable therewith Vinyl alicyclic hydrocarbon polymers such as hydrogenated products of the aromatic rings of the copolymer and the amount thereof; and the like. Among these, from the viewpoints of heat resistance, mechanical strength, and the like, norbornene-based polymers and vinyl alicyclic hydrocarbon-based polymers are preferable, ring-opening polymer hydrogenated norbornene-based monomers, norbornene-based single monomers Ring-opening copolymer hydrogenated product of this product with other ring-opening copolymerizable monomers, vinyl aromatic monomer hydrogenated aromatic vinyl monomer and vinyl aromatic monomer More preferred is a hydrogenated aromatic ring of a copolymer of the above and other monomers copolymerizable therewith.
The light diffusing agent used for the light diffusing plate is a particle having a property of diffusing light, and is roughly classified into an inorganic filler and an organic filler. Specifically, silica, aluminum hydroxide, aluminum oxide, titanium oxide, zinc oxide, barium sulfate, magnesium silicate, or a mixture thereof can be used as the inorganic filler. Specific examples of the organic filler include acrylic resin, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene resin, polyacrylonitrile, polyamide, polysiloxane resin, melamine resin, and benzoguanamine resin. Among these, fine particles made of polystyrene resin, polysiloxane resin, or cross-linked products thereof can be used particularly suitably because they have high dispersibility, high heat resistance, and no coloration (yellowing) during molding. . Fine particles made of a cross-linked product of polysiloxane resin are more suitable for use because they are superior in heat resistance.
The shape of the light diffusing agent used in the light diffusing plate is not particularly limited, and examples thereof include a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scale shape, and a fiber shape. Spherical beads that can be isotropic are preferred.
The light diffusing agent is contained in a transparent resin and is used after being macroscopically dispersed uniformly and spaced apart.

The diffusion sheet used in the apparatus of the present invention is a sheet having a thickness of 500 μm or less that has a function of diffusing light, and its configuration is not particularly limited, but on at least one surface of a transparent resin base material sheet that does not contain a light diffusing agent. What apply | coated the layer containing a light-diffusion agent is used suitably. A commercially available diffusion sheet can also be used.
Although it will not be limited if the thickness of this diffusion sheet is 500 micrometers or less, it is preferred that it is 50 micrometers or more and 300 micrometers or less. If the thickness is 50 μm or less, wrinkles occur due to the influence of temperature and humidity, which may cause display unevenness of the liquid crystal display. If the thickness is 300 μm or more, the liquid crystal display becomes too thick. The haze of the diffusion sheet is preferably 10% or more, more preferably 15% or more, and further preferably 30% or more. If the haze is less than 10%, the luminance uniformity improvement effect may not be sufficient. The total light transmittance of the diffusion sheet is preferably 40% or more, more preferably 50% or more, and further preferably 60% or more. If the total light transmittance is less than 40%, the luminance may decrease. The total light transmittance in this case is a value obtained by measuring the diffusion sheet according to JIS K7361-1, and the haze is a value obtained by measuring the diffusion sheet according to JIS K7136.
The resin used for the base sheet of the diffusion sheet is not particularly limited, but polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyethylene, polypropylene, resin having an alicyclic structure, cellulose acetate, weather resistant vinyl chloride Etc. Among these, polyethylene terephthalate, polycarbonate, polypropylene, a resin having an alicyclic structure, and cellulose acetate are preferable because both transparency and film forming property are excellent.

The layer containing the light diffusing agent constituting the diffusion sheet of the present invention is composed of a binder and a light diffusing agent dispersed in the binder in a separated state. The light diffusing agent dispersed in this way can diffuse the light beam transmitted through the layer containing the light diffusing agent. Moreover, a light beam can be more diffused by making the upper end of a light-diffusion agent protrude from a binder. The thickness of the layer containing the light diffusing agent is not particularly limited, but is preferably about 1 μm or more and 50 μm or less, for example.

The polymer used for the binder is not particularly limited, and examples thereof include acrylic resins, polyurethanes, polyesters, fluorine resins, silicone resins, polyamide imides, and epoxy resins. In addition to the above-mentioned polymer, for example, a reinforcing filler, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, an antistatic agent, and the like may be blended in the binder.

The light diffusing agent used in the diffusion sheet is a particle having a property of diffusing light, and is roughly classified into an inorganic filler and an organic filler. Specifically, silica, aluminum hydroxide, aluminum oxide, titanium oxide, zinc oxide, barium sulfate, magnesium silicate, or a mixture thereof can be used as the inorganic filler. Specific examples of the organic filler include acrylic resin, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene resin, polyacrylonitrile, polyamide, polysiloxane resin, melamine resin, and benzoguanamine resin.
The shape of the light diffusing agent used in the diffusion sheet is not particularly limited, and examples thereof include a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scale shape, and a fiber shape. Spherical beads that can improve the brightness in the front direction when the upper end protrudes from the binder are preferred.
Although the method of manufacturing the diffusion sheet of this invention is not specifically limited, The following method can be mentioned. Since these are easier than the method of manufacturing the prism sheet, the diffusion sheet can be obtained at a low cost.
(1) Extruding the resin used for the base sheet or forming a solution cast to obtain a base sheet, and coating the transparent resin base sheet with the light diffusing agent dispersed in the binder how to.
(2) A method of extruding a resin used for the base sheet and a mixture of the resin used for the binder and the light diffusing agent in two layers.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Production Example 1
Resin having an alicyclic structure as a transparent resin [Nippon Zeon Co., Ltd., ZEONOR 1060R, water absorption 0.01%] 99.7 parts by weight, and fine particles comprising a cross-linked product of a polysiloxane polymer as a light diffusing agent [ GE Toshiba Silicone Co., Ltd., Tospearl 120] 0.3 parts by weight was mixed, kneaded with a twin screw extruder, extruded into a strand, and cut with a pelletizer to produce pellets 1 for a light diffusion plate. From this light diffusion plate pellet, a 100 mm × 50 mm test plate having a smooth thickness of 2 mm on both sides was molded using an injection molding machine [clamping force 1000 kN]. The total light transmittance and haze of this test plate were measured using an integrating sphere color difference turbidimeter according to JIS K7361-1 and JIS K7136. The total light transmittance was 78%, and the haze was 92%.
Production Example 2
Resin having an alicyclic structure [Nippon ZEON Co., Ltd., ZEONOR 1060R water absorption 0.01%] fine particles composed of 99.9 parts by weight and a crosslinked product of a polysiloxane polymer [GE Toshiba Silicone Co., Ltd., Tospearl 120 The light diffusion plate pellet 2 was produced in the same manner as in Production Example 1 except that 0.1 part by weight was used, and the total light transmittance and haze were measured in the same manner as in Production Example 1. Was 86% and haze was 91%.
Production Example 3
Resin having an alicyclic structure [Nippon ZEON Co., Ltd., ZEONOR 1060R water absorption 0.01%] fine particles composed of 99.6 parts by weight and a crosslinked product of a polysiloxane polymer [GE Toshiba Silicone Co., Ltd., Tospearl 120 A pellet 3 for a light diffusion plate was produced in the same manner as in Production Example 1 except that 0.4 part by weight was used, and the total light transmittance and haze were measured in the same manner as in Production Example 1. Was 75% and haze was 92%.
Production Example 4
Resin having an alicyclic structure [Nippon ZEON Co., Ltd., ZEONOR 1060R water absorption 0.01%] fine particles comprising 99.2 parts by weight and a cross-linked product of a polysiloxane polymer [GE Toshiba Silicone Co., Ltd., Tospearl 120 The pellet 4 for light diffusing plate was produced in the same manner as in Production Example 1 except that 0.8 part by weight was used, and the total light transmittance and haze were measured in the same manner as in Production Example 1. Was 65% and haze was 92%.

Example 1
From the light diffusion plate pellets 1, a prism row having a cross-sectional shape in which isosceles triangles having a pitch of 50 μm and an apex angle of 110 degrees are connected is formed in parallel with the longitudinal direction using an injection molding machine (clamping force: 4,410 kN). A light diffusion plate having a thickness of 2 mm and a thickness of 250 mm × 310 mm was molded at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. When the surface of the molded light diffusion plate was observed with an ultra-deep microscope, the pitch of the prism portions was 50 μm, the apex angle was 110 degrees, and the surface roughness Ra was 0.04 μm.
A reflective sheet (RF188, manufactured by Tsujiden Co., Ltd.) is attached to the bottom of a milky white plastic case with an inner width of 300 mm, a depth of 240 mm, and a depth of 18 mm. The reflector is 4 mm away from the reflector and has a diameter of 4 mm. Eight 360 mm cold-cathode tubes were arranged with a distance between the centers of the cold-cathode tubes being 25 mm, the vicinity of the electrode portion was fixed with a silicone sealant, and an inverter was attached. The above light diffusion plate is arranged such that the prism row is parallel to the cold cathode tube and on the opposite side, and the distance between the cold cathode tube center and the surface of the light diffusion plate closer to the cold cathode tube is 14 mm. Installed. Furthermore, two diffusion sheets (Kimoto Lightup 100GM3, Inc.) having a total light transmittance of 75.5%, a haze of 87% and a thickness of 137 μm are installed so that the layer containing the light diffusing agent is on the side far from the light diffusion plate. did. On top of that, a reflective polarizer (DBEF-M manufactured by Sumitomo 3M Limited) using birefringence was installed, and a polarizing plate was further attached.
Next, a tube current of 6 mA and a tube voltage of 330 Vrms were applied to light the cold cathode tube, and using a two-dimensional color distribution measuring device, the luminance at 100 points was measured at equal intervals on the short direction center line. The luminance average value La and the luminance uniformity Lu were obtained according to 1 and Equation 2. At this time, the luminance average value was 4380 cd / m ² and the luminance uniformity was 0.8.
Luminance average value La = (L1 + L2) / 2 (Formula 1)
Luminance uniformity Lu = ((L1-L2) / La) × 100 (Formula 2)
L1: Average luminance maximum value just above a plurality of cold-cathode tubes installed L2: Average minimum value sandwiched between local maximum values The luminance uniformity is an index indicating the uniformity of luminance. When it is bad, the figure increases.
Example 2
A light diffusion plate was molded and evaluated in the same manner as in Example 1 except that four diffusion sheets were installed. The pitch of the prism portion of the diffusion plate was 50 μm, the apex angle was 110 degrees, and the surface roughness Ra was 0.04 μm. The luminance average value was 4150 cd / m ² and the luminance uniformity was 1.0.
Example 3
A light diffusing plate was molded and evaluated in the same manner as in Example 1 except that a mold member capable of forming a prism apex angle of 70 degrees was used. The pitch of the prism portions of the diffusion plate was 50 μm, the apex angle was 70 degrees, and the surface roughness Ra was 0.04 μm. The luminance average value was 4120 cd / m ² and the luminance uniformity was 3.8.
Example 4
A light diffusing plate was molded and evaluated in the same manner as in Example 1 except that a mold member capable of forming a prism apex angle of 170 degrees was used. The pitch of the prism portions of the diffusion plate was 50 μm, the apex angle was 170 degrees, and the surface roughness Ra was 0.04 μm. The average luminance value was 3940 cd / m ² , and the luminance uniformity was 4.0.
Example 5
A light diffusion plate was molded and evaluated in the same manner as in Example 1 except that the light diffusion plate pellet 2 containing 0.1 part by weight of polysiloxane fine particles was used. The pitch of the prism portion of the diffusion plate was 50 μm, the apex angle was 110 degrees, and the surface roughness Ra was 0.04 μm. The luminance average value was 4560 cd / m ² and the luminance uniformity was 3.9.
Example 6
A light diffusion plate was molded and evaluated in the same manner as in Example 1 except that the light diffusion plate pellet 3 containing 0.4 parts by weight of polysiloxane fine particles was used. The pitch of the prism portions of the diffusion plate was 50 μm, the apex angle was 110 degrees, and the surface roughness Ra was 0.04 μm. The luminance average value was 4300 cd / m ² and the luminance uniformity was 1.0.

Comparative Example 1
Using a light diffusion plate pellet 4 containing 0.8 parts by weight of polysiloxane fine particles, using an injection molding machine (clamping force 4,410 kN), a die having no prism row and a smooth surface, and having a thickness of 2 mm A flat light diffusion plate of 250 mm × 310 mm was molded at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees.
The obtained light diffusing plate was placed in a plastic case in which the same cold cathode fluorescent lamps as those in Example 1 were placed, and a diffusion sheet (Kimoto Lightup 100GM3 ) Is placed so that the layer containing the light diffusing agent is on the side far from the light diffusing plate, a prism sheet (RBEF manufactured by Sumitomo 3M Limited) is placed on it, and the longitudinal direction of the prism array is a cold cathode A reflective polarizer (DBEF-M manufactured by Sumitomo 3M Limited) and a polarizing plate using birefringence and a polarizing plate were attached in the order described in parallel with the tube and on the side far from the light diffusion plate.
Subsequently, the cold cathode tube was turned on by applying a tube current of 6 mA and a tube voltage of 330 Vrms, and the luminance and the luminance uniformity were measured in the same manner as in Example 1. At this time, the luminance average value was 4420 cd / m ² and the luminance uniformity degree was 1.1.
Comparative Example 2
A light diffusing plate is used in the same manner as in Example 1 except that the light diffusing plate pellet 4 is used and a mold capable of forming a prism row having a cross-sectional shape in which isosceles triangles having apex angles of 40 degrees are connected is used. Was molded and evaluated. The pitch of the prism portions of the diffuser plate was 50 μm, the apex angle was 40 degrees, and the surface roughness Ra was 0.04 μm. The luminance average value was 3460 cd / m ² and the luminance uniformity was 10.2.
Comparative Example 3
A flat light diffusion plate was molded and evaluated in the same manner as in Example 1 except that a mold having no prism array and a smooth surface was used. The luminance average value was 3680 cd / m ² and the luminance uniformity was 19.7.
Comparative Example 4
Evaluation was performed in the same manner as in Example 1 except that only one diffusion sheet was used. The luminance average value was 4300 cd / m ² and the luminance uniformity was 12.2.
Comparative Example 5
Evaluation was performed in the same manner as in Example 1 except that five diffusion sheets were used. The luminance average value was 3400 cd / m ² and the luminance uniformity was 0.6.

The configurations and measurement results of Examples 1 to 6 are shown in Table 1, and the configurations and measurement results of Comparative Examples 1 to 5 are shown in Table 2. In Examples 1 to 6, an expensive prism sheet is not used, and the average brightness is 3800 cd / m ² or more and the brightness uniformity is 4.0 or less, which is not much different from Comparative Example 1 using a prism sheet. It has been.
When the prism apex angle of the light diffusing plate is outside the specified range of the present invention as in Comparative Examples 2 and 3, both the average luminance and the luminance uniformity are bad values, and as in Comparative Example 4, the diffusion sheet When the number of sheets is small, the luminance uniformity is bad, and when the number of diffusion sheets is large as in Comparative Example 5, the average luminance is a bad number.

According to the direct type backlight device of the present invention, it is possible to improve the average luminance and the luminance uniformity, so that when a direct type backlight is incorporated in the liquid crystal display device, a high-quality liquid crystal display screen can be obtained. it can.

It is the perspective view of the direct type backlight apparatus of this invention, and its one part enlarged view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diffusing sheet 2 Light diffusing plate 3 Linear light source 4 Reflecting plate 5 Vertical angle 6 of prism row | line | column of a prism sheet Optical member for brightness improvement

Claims (3)

Directly provided with a plurality of linear light sources arranged in parallel, a reflecting plate that reflects light from the linear light source, and a light diffusion plate that diffuses and irradiates direct light from the linear light source and reflected light from the reflecting plate In the type backlight device, the light diffusing plate has a prism row having a sawtooth cross section on at least one main surface, and the apex angle of the prism row of the light diffusing plate is not less than 60 degrees and not more than 170 degrees and pitch Is a direct type backlight device comprising 20 to 700 μm, and further comprising 2 to 4 diffusion sheets for adjusting the light diffused and irradiated from the light diffusion plate. 2. The direct type backlight device according to claim 1, wherein an angle formed by the longitudinal direction of the prism row of the light diffusion plate and the longitudinal direction of the linear light source is 60 degrees or less.
The light diffusing plate is made of a material in which a light diffusing agent is dispersed in a transparent resin, and the total light transmittance of the dispersion is 60% or more and 92% or less, and the haze is 40% or more and 94% or less. The direct type backlight device described in 1.

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