JP2006310150A - Direct backlight device - Google Patents

Direct backlight device Download PDF

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JP2006310150A
JP2006310150A JP2005132628A JP2005132628A JP2006310150A JP 2006310150 A JP2006310150 A JP 2006310150A JP 2005132628 A JP2005132628 A JP 2005132628A JP 2005132628 A JP2005132628 A JP 2005132628A JP 2006310150 A JP2006310150 A JP 2006310150A
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light source
linear light
light
backlight device
housing
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Keisuke Tsukada
啓介 塚田
Yasunori Takahashi
靖典 高橋
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Zeon Corp
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Nippon Zeon Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct backlight device which does not increase the number of light sources, suppresses the decrease in the periphery part brightness and the lamp appearance, and simultaneously achieves the improvements in the brightness and the brightness uniformity. <P>SOLUTION: The direct backlight device comprises an opening part, of which the shape observed from the normal direction is nearly rectangular, a case 3 whose inner surface is a reflection surface, a plurality of linear light sources 2-1, 2-2, 2-3 arranged parallelly in the case, and a light diffusion plate 1 installed on the opening part of the case. When "a" (mm) refers to the distance from the case side-wall to the linear light source nearest to the case side-wall, and "b" (mm) refers to the distance from the linear light source nearest to the case side-wall to the inner side linear light source adjacent ot that nearest to the case side-wall, "a" and "b" satisfy the relation: 0.15<a/b<2. The light diffusion plate has an unevenness structure of a maximum surface unevenness height Rz ≤200 μm at least on one major surface of the light diffusion plate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、直下型バックライト装置に関する。さらに詳しくは、輝度が高く、輝度均斉度の良い直下型バックライト装置に関する。   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.

近年、液晶ディスプレイ、プラズマディスプレイ等の、テレビなどに使用する薄型表示装置の研究開発が盛んである。その中でも、消費電力の少なさ、明るい部屋での視認性のよさから液晶ディスプレイが注目されているが、液晶ディスプレイ自体は発光しないので、バックライト装置が必要とされる。
従来、液晶ディスプレイ用バックライト装置としては、複数本の並列配置した冷陰極管と、冷陰極管の背面に設けられた反射板と、発光面をなす光拡散板とを組み合わせた構成からなる、直下型バックライト装置が広く使用されている。
しかし、直下型バックライト装置には、発光面の輝度均斉度が悪いという問題がある。特に、冷陰極管の真上で輝度が高くなることにより発生する周期的輝度むらが大きな問題となる。
一方、直下型バックライト装置に使用される光拡散板としては、透明樹脂に光拡散剤を分散させた材料が使用されることが多い。このような光拡散板においては、輝度均斉度を改良するために光拡散剤の濃度を上げると輝度が低下してしまうという問題があった。そこで、これを解決するために光拡散板表面にプリズム形状等の凹凸構造を形成し、輝度を低下させずに表面形状による拡散効果を持たせることが提案されている（特許文献１、２、３）。しかし光拡散板表面にプリズム状凹凸構造を形成するだけでは、輝度均斉度の改良は十分ではなかった。
また、直下型バックライト装置では、冷陰極管の数を増やすことで、輝度を向上することは可能である。しかしながら、冷陰極管の数を増やすと、バックライト装置の製造コストや点灯時の消費電力が上昇してしまう問題がある。
また、ＣＲＴ代替で使用される液晶ディスプレイでは、中央部の輝度を周辺部に比べて高くすることが好まれる場合があり、そのために光源をバックライト装置の筐体の中央部分に於いて狭ピッチで配設し、該筐体の上下、又は左右近傍に並設する光源を中央部分に比べて広ピッチで配設したことを特徴とするバックライト装置が提案されている（特許文献４、５）。しかし光源の間隔が比較的大きい場合には、光源の直上部が明るくなるランプ見えが発生するという欠点があった。 In recent years, research and development of thin display devices used for televisions such as liquid crystal displays and plasma displays have been actively conducted. Among them, a liquid crystal display attracts attention because of its low power consumption and good visibility in a bright room, but the liquid crystal display itself does not emit light, so a backlight device is required.
Conventionally, as a backlight device for a liquid crystal display, it comprises a combination of a plurality of cold cathode tubes arranged in parallel, a reflector provided on the back of the cold cathode tube, and a light diffusing plate forming a light emitting surface, Direct type backlight devices are widely used.
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 caused by the increase in luminance directly above the cold cathode tube is a serious problem.
On the other hand, as a light diffusing plate used in a direct type backlight device, a material in which a light diffusing agent is dispersed in a transparent resin is often used. In such a light diffusing plate, there is a problem that the luminance is lowered when the concentration of the light diffusing agent is increased in order to improve the luminance uniformity. In order to solve this problem, it has been proposed to form a concavo-convex structure 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 brightness (Patent Documents 1, 2, 3). However, it was not sufficient to improve the brightness uniformity only by forming a prismatic uneven structure on the surface of the light diffusion plate.
Further, in the direct type backlight device, it is possible to improve the luminance by increasing the number of cold cathode tubes. However, when the number of cold cathode fluorescent lamps is increased, there are problems that the manufacturing cost of the backlight device and the power consumption during lighting increase.
In addition, in a liquid crystal display used as an alternative to a CRT, it may be preferable to increase the luminance of the central portion as compared with the peripheral portion. For this reason, the light source is arranged at a narrow pitch at the central portion of the casing of the backlight device. A backlight device has been proposed in which light sources arranged in parallel at the top and bottom of the casing or in the vicinity of the left and right are arranged at a wider pitch than the central portion (Patent Documents 4 and 5). ). However, when the distance between the light sources is relatively large, there is a drawback in that a lamp appearance in which the upper part of the light source is bright is generated.

特開平５−３３３３３３号公報JP-A-5-333333 特開平８−２９７２０２号公報JP-A-8-297202 特開２０００−１８２４１８号公報JP 2000-182418 A 特開２００４−２８７２２６号公報JP 2004-287226 A 特開２００４−２２７９９１号公報JP 2004-227991 A

本発明は、光源の数を増やさずに、周辺部の輝度低下とランプ見えを抑制して、輝度と輝度均斉度の改良とを同時に実現し得る、直下型バックライト装置を提供することを目的としてなされたものである。   An object of the present invention is to provide a direct type backlight device that can simultaneously realize improvement of luminance and luminance uniformity by suppressing luminance reduction and lamp appearance at the periphery without increasing the number of light sources. It was made as.

本発明者らは、上記の課題を解決すべく、バックライト筐体側壁から該筐体側壁に一番近い線状光源までの距離と、筐体側壁に一番近い線状光源から該線状光源に隣接する内側の線状光源までの距離との関係について詳細な検討を行ったが、平板状の光拡散板を使用する限りは線状光源の間隔が比較的大きい場合にはランプ見えによる輝度ムラが発生する結果しか得られなかった。しかし、驚くべきことに、表面に凹凸構造を持つ光拡散板を使用し、バックライト筐体側壁から該筐体側壁に一番近い線状光源までの距離と、筐体側壁に一番近い線状光源から該線状光源に隣接する内側の線状光源までの距離との間を特定の関係を満たすようにすることにより、高輝度で輝度均斉度が良いバックライト装置が得られることを見いだし、この知見に基づいて本発明を完成するに至った。
すなわち、本発明は、
（１）開口面を有し、該開口面を法線方向から観察した形状が略長方形で、内面が反射面である筐体と、該筐体内に並列配置された複数の線状光源と、該筐体の開口部上に設けられた光拡散板とからなる直下型バックライト装置において、筐体側壁から筐体側壁に一番近い線状光源までの距離をａ（ｍｍ）、筐体側壁に一番近い線状光源から該線状光源に隣接する内側の線状光源までの距離をｂ（ｍｍ）とするとき、前記ａ及びｂが０．１５＜ａ／ｂ＜２の関係を満たし、かつ前記光拡散板が少なくとも一方の主面に最大高さＲｚが２００μｍ以下の凹凸構造を有するものであることを特徴とする直下型バックライト装置、
（２）光拡散板の最大高さＲｚが２００μｍ以下の凹凸構造の形状が、頂角６０〜１７０度でかつピッチが２０〜７００μｍである断面鋸歯状プリズム条列である前記（１）記載の直下型バックライト装置、
（３）光拡散板の断面鋸歯状プリズム条列の稜線方向と、線状光源の長手方向とのなす角が６０度以下である上記（２）記載の直下型バックライト装置、及び
（４）光拡散板が透明樹脂及び光拡散剤を含む樹脂組成物からなり、該樹脂組成物の全光線透過率が６０％以上９５％以下で、かつヘーズが４０％以上９４％以下である上記（１）〜（３）のいずれかに記載の直下型バックライト装置、
を提供するものである。
さらに、本発明の好ましい態様として、
（５）光拡散板に使用する透明樹脂が、吸水率０．２５％以下であることを特徴とする（４）に記載の直下型バックライト装置、
（６）光拡散剤が、ポリスチレン系重合体、ポリシロキサン系重合体又はそれらの架橋物からなる粒子である（４）または（５）に記載の直下型バックライト装置、
を挙げることができる。 In order to solve the above-mentioned problems, the inventors have made a distance from the side wall of the backlight housing to the linear light source closest to the side wall of the housing, and the linear light source closest to the housing side wall from the linear light source. Detailed investigation was made on the relationship with the distance to the inner linear light source adjacent to the light source. However, as long as a flat light diffusing plate is used, if the distance between the linear light sources is relatively large, it depends on the lamp appearance. Only the result of uneven brightness was obtained. Surprisingly, however, using a light diffusing plate with a concavo-convex structure on the surface, the distance from the backlight housing side wall to the linear light source closest to the housing side wall and the line closest to the housing side wall And finding that a backlight device having high luminance and good luminance uniformity can be obtained by satisfying a specific relationship between the distance from the linear light source to the distance between the linear light source and the inner linear light source. Based on this finding, the present invention has been completed.
That is, the present invention
(1) A housing having an opening surface, the shape of the opening surface observed from the normal direction is substantially rectangular, and the inner surface is a reflecting surface; a plurality of linear light sources arranged in parallel in the housing; In a direct type backlight device comprising a light diffusing plate provided on an opening of the housing, the distance from the housing side wall to the linear light source closest to the housing side wall is a (mm), and the housing side wall A and b satisfy the relationship of 0.15 <a / b <2, where b (mm) is the distance from the linear light source closest to the inner linear light source adjacent to the linear light source. And the light diffusing plate has a concavo-convex structure having a maximum height Rz of 200 μm or less on at least one main surface,
(2) The shape of the concavo-convex structure with a maximum height Rz of the light diffusing plate of 200 μm or less is a sawtooth-shaped prism array having a cross section with an apex angle of 60 to 170 degrees and a pitch of 20 to 700 μm. Direct type backlight device,
(3) The direct type backlight device according to the above (2), wherein the angle formed by the ridge line direction of the sawtooth prism array in the cross section of the light diffusion plate and the longitudinal direction of the linear light source is 60 degrees or less, and (4) The light diffusing plate is made of a resin composition containing a transparent resin and a light diffusing agent, the total light transmittance of the resin composition is 60% or more and 95% or less, and the haze is 40% or more and 94% or less (1 )-(3) direct type backlight device according to any one of
Is to provide.
Furthermore, as a preferred embodiment of the present invention,
(5) The direct backlight device according to (4), wherein the transparent resin used for the light diffusion plate has a water absorption of 0.25% or less,
(6) The direct type backlight device according to (4) or (5), wherein the light diffusing agent is a particle made of a polystyrene polymer, a polysiloxane polymer, or a crosslinked product thereof,
Can be mentioned.

本発明の直下型バックライト装置は、高い光束有効利用率を持ち、発光面の周期的輝度むらが抑制されているため、輝度が高く、かつ輝度均斉度が良い。   The direct type backlight device of the present invention has a high luminous flux effective utilization rate, and the periodic luminance unevenness of the light emitting surface is suppressed, so that the luminance is high and the luminance uniformity is good.

以下に図面を参照しながら、本発明の実施形態を説明する。
本発明の直下型バックライト装置は、開口面を有し、該開口面の法線方向から観察した形状が略長方形で、内面が反射面である筐体と、該筐体内に並列配置された複数の線状光源と、該筐体の開口部上に設けられた光拡散板とからなる。 Embodiments of the present invention will be described below with reference to the drawings.
The direct-type backlight device of the present invention has an opening surface, the shape observed from the normal direction of the opening surface is a substantially rectangular shape, and the inner surface is a reflective surface, and the housing is arranged in parallel in the housing It consists of a plurality of linear light sources and a light diffusing plate provided on the opening of the casing.

図１は本発明の直下型バックライト装置の一態様の模式的斜視図であり、図２は本発明の直下型バックライト装置の一態様の断面図である。
図１及び図２に示す直下型バックライト装置は、筐体３と、複数の線状光源２−１，２−２，２−３と、光拡散板１とを備えている。
筐体３内には複数本の線状光源２−１，２−２，２−３が並列配置され、線状光源からの光を反射する反射面５が筐体３の内面に設けられ、そして光源２からの直射光及び反射面５からの反射光を拡散照射するように光拡散板１が筐体の開口部上に配置されている。さらに光拡散板１は、光源から遠い側の面に頂角ｙの断面鋸歯状のプリズム条列を有している。 FIG. 1 is a schematic perspective view of an embodiment of the direct type backlight device of the present invention, and FIG. 2 is a cross-sectional view of an embodiment of the direct type backlight device of the present invention.
The direct type backlight device shown in FIGS. 1 and 2 includes a housing 3, a plurality of linear light sources 2-1, 2-2, 2-3, and a light diffusion plate 1.
A plurality of linear light sources 2-1, 2-2, 2-3 are arranged in parallel in the housing 3, and a reflection surface 5 that reflects light from the linear light source is provided on the inner surface of the housing 3. And the light diffusing plate 1 is arrange | positioned on the opening part of a housing | casing so that the direct light from the light source 2 and the reflected light from the reflective surface 5 may be diffusely irradiated. Further, the light diffusing plate 1 has a prism row with a sawtooth cross section having an apex angle y on a surface far from the light source.

本発明では、筐体側壁から筐体側壁に一番近い線状光源までの距離をａ（ｍｍ）、筐体側壁に一番近い線状光源から該線状光源に隣接する内側の線状光源までの距離をｂ（ｍｍ）とするとき、前記ａ及びｂが０．１５＜ａ／ｂ＜２の関係を満たすことが必要である。前記ａ及びｂが前記関係を満たすことにより輝度均斉度を維持しつつ、輝度を向上させることができる。前記ａとｂは、０．２＜ａ／ｂ＜１．５の関係を満たすことがより好ましい。
図２においては、内面が反射面５である筐体側壁４からこれに一番近い線状光源までの距離がａ（ｍｍ）に相当し、筐体側壁４に一番近い線状光源２−１に隣接する内側の線状光源２−２までの距離がｂ（ｍｍ）に相当する。ここで、ａは線状光源の中心から、筐体３の底面から筐体側壁４が立ち上がる点を通る筐体底面の法線までの最短距離であり、ｂは線状光源の中心間の距離である。ここで、線状光源の中心は、線状光源の長手方向に垂直な面で切断したときの断面の中心を意味する。 In the present invention, the distance from the housing side wall to the linear light source closest to the housing side wall is a (mm), and the linear light source adjacent to the linear light source from the linear light source closest to the housing side wall is used. When the distance up to b is mm (mm), it is necessary that a and b satisfy the relationship of 0.15 <a / b <2. When a and b satisfy the relationship, the luminance can be improved while maintaining the luminance uniformity. More preferably, a and b satisfy a relationship of 0.2 <a / b <1.5.
In FIG. 2, the distance from the housing side wall 4 whose inner surface is the reflecting surface 5 to the linear light source closest to this corresponds to a (mm), and the linear light source 2- The distance to the inner linear light source 2-2 adjacent to 1 corresponds to b (mm). Here, a is the shortest distance from the center of the linear light source to the normal line of the bottom surface of the housing passing through the point where the housing side wall 4 rises from the bottom surface of the housing 3, and b is the distance between the centers of the linear light sources. It is. Here, the center of the linear light source means the center of a cross section when cut along a plane perpendicular to the longitudinal direction of the linear light source.

本発明において、筐体側壁から筐体側壁に一番近い線状光源までの距離ａは、前記ａ及びｂが上記関係を満たす範囲であれば特に制限されないが、３ｍｍ以上６０ｍｍ以下であることが好ましく、５ｍｍ以上５０ｍｍ以下であることがより好ましい。
本発明において、隣接する線状光源間の距離（筐体側壁に一番近い線状光源から該線状光源に隣接する内側の線状光源までの距離ｂを含む）は光源のコストと点灯時の使用電力とを考慮して設計すればよく、特に限定されないが、１５ｍｍ以上１５０ｍｍ以下であることが好ましく、２０ｍｍ以上１００ｍｍ以下であることがより好ましい。輝度均斉度を維持するという観点からは、筐体側壁に一番近い線状光源から該線状光源に隣接する内側の線状光源までの距離ｂ以外の、隣接する線状光源間の距離をすべてｂと等しくすることが好ましい。また、筐体の中心部の輝度を高くするという観点からは、隣接する線状光源間の距離を、筐体の端部に比べて筐体の中心部において小さくすることにより、より高い輝度を得ることができるので好ましい。
線状光源の中心から光拡散板の光源側の面までの距離は、バックライト装置の厚みと輝度均斉度を考慮して設計すればよく、特に限定されないが、５ｍｍ以上３０ｍｍ以下であることが好ましく、５ｍｍ以上２５ｍｍ以下であることがより好ましい。 In the present invention, the distance a from the side wall of the casing to the linear light source closest to the side wall of the casing is not particularly limited as long as the a and b satisfy the above relationship, but may be 3 mm or more and 60 mm or less. Preferably, it is 5 mm or more and 50 mm or less.
In the present invention, the distance between adjacent linear light sources (including the distance b from the linear light source closest to the side wall of the housing to the inner linear light source adjacent to the linear light source) is the cost of the light source and the lighting time However, it is preferably 15 mm or more and 150 mm or less, and more preferably 20 mm or more and 100 mm or less. From the viewpoint of maintaining the luminance uniformity, the distance between adjacent linear light sources other than the distance b from the linear light source closest to the side wall of the housing to the inner linear light source adjacent to the linear light source is determined. All are preferably equal to b. In addition, from the viewpoint of increasing the luminance of the central portion of the housing, higher distance can be obtained by reducing the distance between adjacent linear light sources in the central portion of the housing compared to the end of the housing. It is preferable because it can be obtained.
The distance from the center of the linear light source to the light source side surface of the light diffusing plate may be designed in consideration of the thickness of the backlight device and the luminance uniformity, and is not particularly limited, but may be 5 mm or more and 30 mm or less. Preferably, it is 5 mm or more and 25 mm or less.

本発明に用いる筐体３の材質は特に限定されず、例えば樹脂、金属等を使用することができる。中でも軽量化の点からは樹脂が好ましい。
筐体の内面に反射面を設ける方法としては、筐体内面を白色または銀色で塗装する方法；筐体内面に白色または銀色の反射シートを貼り付ける方法；樹脂筐体を白色または銀色に着色する方法；等があげられる。筐体の内面に設ける反射面の色は輝度均斉度改良の観点からは白色が好ましく、輝度向上の観点からは白色部分と銀色部分とを適宜混在させることが好ましい。
本発明においては、筐体内面の反射面の複数の線状光源間に対応する領域に、光拡散板側に突出し、前記複数の線状光源の長手方向に沿った突起部を設けてもよい。該突起部を設けることにより線状光源から横方向への光を光拡散板方向へ反射することができるので、輝度と輝度均斉度をより向上することが可能となる。前記突起部は畝状に連続的でも、垂体の連なりのように断続的でもよいが、輝度均斉度がより向上できることから連続的であることが好ましい。 The material of the housing | casing 3 used for this invention is not specifically limited, For example, resin, a metal, etc. can be used. Among these, a resin is preferable from the viewpoint of weight reduction.
As a method of providing a reflective surface on the inner surface of the housing, a method of painting the inner surface of the housing with white or silver; a method of pasting a white or silver reflective sheet on the inner surface of the housing; a resin housing being colored white or silver Method; etc. The color of the reflecting surface provided on the inner surface of the housing is preferably white from the viewpoint of improving the luminance uniformity, and from the viewpoint of improving the luminance, it is preferable to mix a white portion and a silver portion as appropriate.
In the present invention, protrusions that protrude toward the light diffusing plate and extend in the longitudinal direction of the plurality of linear light sources may be provided in a region corresponding to the space between the plurality of linear light sources on the inner surface of the housing. . By providing the projection, light in the lateral direction from the linear light source can be reflected in the direction of the light diffusing plate, so that the luminance and the luminance uniformity can be further improved. The protrusions may be continuous in a bowl shape or intermittent as a series of pits, but are preferably continuous because the luminance uniformity can be further improved.

筐体内面の反射面に設ける連続的な突起部をその長手方向に垂直な面で切断したときの断面形状としては、特に限定されないが、図３（ａ）に示す二等辺三角形、図３（ｂ）に示す等脚台形、図３（ｃ）に示す円形を切断した形状、図３（ｄ）に示す楕円形を短軸に平行な線分で切断した形状、楕円形を長軸に平行な線分で切断した形状、図３（ｅ）に示す下に凸の曲線を線対象になるように連ねた形状、図３（ｆ）に示す上に凸の曲線を線対称になるように連ねた形状等があげられる。これらの形状の頂点部分は、尖っていてもよいし、丸みを帯びていてもよい。   The cross-sectional shape when the continuous protrusions provided on the reflection surface of the housing inner surface are cut by a plane perpendicular to the longitudinal direction is not particularly limited, but isosceles triangles shown in FIG. The isosceles trapezoid shown in b), the shape shown by cutting the circle shown in FIG. 3 (c), the shape shown by cutting the ellipse shown in FIG. 3 (d) along a line segment parallel to the minor axis, and the ellipse parallel to the major axis. A shape obtained by cutting with a straight line segment, a shape in which the downward convex curve shown in FIG. 3E is connected to be a line object, and an upward convex curve shown in FIG. For example, the shape of the chain. The apex portions of these shapes may be pointed or rounded.

本発明に用いる線状光源としては特に限定されず、公知の線状光源、例えば冷陰極管、熱陰極管、線状に配列したＬＥＤ、ＬＥＤと導光体との組合せ等を使用することができる。
冷陰極管又は熱陰極管の形状としては直線状以外にも、平行な２本の管が一つの略半円でつながれ一本になったＵ字状のもの、平行な３本の管が二つの略半円でつながれ一本になったＮ字状のもの、又は平行な４本の管が三つの略半円でつながれ一本になったＷ字状のものが挙げられる。
線状光源は輝度均一性の点からは冷陰極管が好ましく、色再現性の点からは線状に配列したＬＥＤ、ＬＥＤと導光体との組合せが好ましい。線状に配列したＬＥＤ、またはＬＥＤと導光体との組合せを使用する場合は、配列した一連のＬＥＤの組、またはＬＥＤと導光体との組合せ、が複数ある場合に、線状光源が複数本であるとする。 The linear light source used in the present invention is not particularly limited, and a known linear light source such as a cold cathode tube, a hot cathode tube, a linearly arranged LED, a combination of an LED and a light guide, or the like may be used. it can.
The shape of the cold cathode tube or the hot cathode tube is not limited to a straight line, but two parallel tubes are connected by a single semicircle to form a U-shape, and two parallel three tubes are used. N-shaped ones connected by two approximately semicircles, or W-shaped ones formed by connecting four parallel pipes by three approximately semicircles.
The linear light source is preferably a cold-cathode tube from the viewpoint of luminance uniformity, and from the viewpoint of color reproducibility, a linear array of LEDs, and a combination of an LED and a light guide are preferable. When using a linearly arranged LED or a combination of an LED and a light guide, when there are a plurality of arranged LED pairs or a combination of an LED and a light guide, the linear light source is Assume that there are multiple books.

本発明に用いる光拡散板は、輝度均斉度を向上するために使用される。光拡散板は光入射面と光出射面を有する。線状光源からの光は光拡散板の光源から近い側の光入射面に入射する。そして、光拡散板の光入射面に入射された光は、光拡散板内において、または、光入射面または光出射面の少なくとも一方に設けられた凹凸構造において、光が多様な方向へ拡散され、光源から遠い側の光出射面から出射される。
本発明に用いる光拡散板の少なくとも主面に有する凹凸構造は最大高さＲｚが２００μｍ以下である。前記最大高さＲｚが２００μｍを超えると加工が困難となるので、凹凸構造を均一に形成することができなくなり、ひいては輝度均斉度が悪化してしまう。バックライト装置の輝度と輝度均斉度のバランスをより改善し、光拡散板の加工をより容易にするために、光拡散板の主面に有する凹凸構造は最大高さＲｚが２μｍ以上２００μｍ以下であることが好ましく、４μｍ以上１５０μｍ以下であることがより好ましく、８μｍ以上１００μｍ以下であることが最も好ましい。本発明において、光拡散板の主面に有する凹凸構造は、主面全体に有していてもよいし、主面の光学的有効面にだけ有していてもよい。 The light diffusing plate used in the present invention is used to improve the luminance uniformity. The light diffusing plate has a light incident surface and a light exit surface. The light from the linear light source enters the light incident surface on the side closer to the light source of the light diffusing plate. The light incident on the light incident surface of the light diffusing plate is diffused in various directions in the light diffusing plate or in the concavo-convex structure provided on at least one of the light incident surface and the light emitting surface. The light is emitted from a light exit surface far from the light source.
The concavo-convex structure provided on at least the main surface of the light diffusion plate used in the present invention has a maximum height Rz of 200 μm or less. If the maximum height Rz exceeds 200 μm, the processing becomes difficult, so that the uneven structure cannot be formed uniformly, and the luminance uniformity deteriorates. In order to further improve the balance between the luminance and the luminance uniformity of the backlight device and make the processing of the light diffusing plate easier, the concavo-convex structure on the main surface of the light diffusing plate has a maximum height Rz of 2 μm or more and 200 μm or less. It is preferably 4 μm or more and 150 μm or less, and more preferably 8 μm or more and 100 μm or less. In the present invention, the concavo-convex structure on the main surface of the light diffusing plate may be provided on the entire main surface or only on the optically effective surface of the main surface.

本発明において表面の最大高さＲｚと後述する算術平均高さＲａは、ＪＩＳ Ｂ ０６０１に準拠して、対象面に直角な平面で対象面を切断したときにその切り口に現れる断面曲線から、所定の波長より長い成分を位相補償形高域フィルタで除去した粗さ曲線について求めることができ、あるいは、超深度形状測定顕微鏡などを用いて直読することもできる。
本発明に使用する光拡散板が有する凹凸構造の形状としては特に限定されないが、半球状突起、円錐状突起、角錐状突起、蒲鉾状レンチキュラーレンズ、断面鋸歯状のプリズムパターン等の光の出射方向を絞るような形状が好ましい。さらにこのような光の出射方向を絞るような形状の中でも、頂角が６０〜１７０度でかつピッチが２０〜７００μｍである断面鋸歯状プリズム条列であることが好ましい。凹凸構造の形状が、頂角６０〜１７０度でかつピッチが２０〜７００μｍである断面鋸歯状プリズム条列であることにより、輝度と輝度均斉度とのバランスを好適にすることができる。
本発明において、光拡散板が好適に有する断面鋸歯状プリズム条列の頂角は、９０〜１２０度であることがより好ましい。
本発明において、光拡散板が好適に有する断面鋸歯状プリズム条列のピッチは、３０μｍ以上５００μｍ以下であることがより好ましく、４０μｍ以上４００μｍ以下であることがさらに好ましい。前記断面鋸歯状プリズム条列のピッチが２０μｍ未満であると、形状が微細なために形状付与が難しくなったり、光拡散効果が低下したりするおそれがある。前記断面鋸歯状プリズム条列のピッチが７００μｍを超えると、光拡散が粗くなり、輝度むらを生じるおそれがある。 In the present invention, the maximum surface height Rz and the arithmetic average height Ra to be described later are determined in accordance with JIS B 0601 from a cross-sectional curve that appears at the cut surface when the target surface is cut by a plane perpendicular to the target surface. It is possible to obtain a roughness curve obtained by removing a component longer than the above wavelength with a phase compensation type high-pass filter, or to read directly using an ultradeep shape measurement microscope or the like.
The shape of the concavo-convex structure of the light diffusing plate used in the present invention is not particularly limited, but the light emission direction of hemispherical projections, conical projections, pyramidal projections, bowl-shaped lenticular lenses, prismatic patterns having a sawtooth cross section, etc. A shape that squeezes is preferable. Further, among the shapes that narrow the light emission direction, it is preferable to have a sawtooth prism array having a cross section with an apex angle of 60 to 170 degrees and a pitch of 20 to 700 μm. When the shape of the concavo-convex structure is a sawtooth prism array having a vertical angle of 60 to 170 degrees and a pitch of 20 to 700 μm, the balance between luminance and luminance uniformity can be made suitable.
In the present invention, it is more preferable that the apex angle of the cross-sectional sawtooth prism row that the light diffusion plate preferably has is 90 to 120 degrees.
In the present invention, the pitch of the cross-sectional sawtooth prism row that the light diffusing plate preferably has is 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 sawtooth prism rows in cross section is less than 20 μm, the shape may be difficult because of the fine shape, or the light diffusion effect may be reduced. When the pitch of the sawtooth prism rows in cross section exceeds 700 μm, the light diffusion becomes rough, and there is a risk of uneven brightness.

断面鋸歯状プリズム条列とは長手方向に垂直な方向に切断した断面が、三角形の突起部が連なった形状になっていることをいう。断面鋸歯状プリズム条列は、三角形の突起部のすそがつながってＶ字型の溝を形成するようになっていてもよいし、三角形突起部のすそ間に水平部が存在してもよいが、三角形のすそがつながってＶ字型の溝を形成するようになっていることが光を効率よく拡散できるので好ましい。また三角形の突起部の形状は前述した頂角の範囲内であれば、特に制限されないが、液晶ディスプレイの正面方向の輝度が最も高くなるようにするために、二等辺三角形であることが好ましい。   The section sawtooth prism array means that a section cut in a direction perpendicular to the longitudinal direction has a shape in which triangular protrusions are connected. The sawtooth prism rows in cross section may be configured such that the bases of the triangular protrusions are connected to form a V-shaped groove, or a horizontal portion may exist between the bases of the triangular protrusions. It is preferable that triangle bases are connected to form a V-shaped groove because light can be diffused efficiently. Further, the shape of the triangular protrusion is not particularly limited as long as it is within the range of the above-described apex angle, but is preferably an isosceles triangle in order to obtain the highest luminance in the front direction of the liquid crystal display.

本発明において、光拡散板の断面鋸歯状プリズム条列の表面を粗化して出射する方向を適度な範囲内でより多様にすることもできる。その場合、プリズム表面を長手に対して直角方向に２０μｍ測定したときの算術平均高さＲａが０．０８μｍ以上３μｍ以下であることが好ましく、０．０９μｍ以上２μｍ以下であることがより好ましく、０．１μｍ以上１μｍ以下であることがさらに好ましい。Ｒａを０．０８μｍ以上にすることにより光の出射方向をより多様にすることができ、３μｍ以下にすることにより、光の出射方向を多様にしすぎないようにすることができる。   In the present invention, the direction in which the light is diffused by roughening the surface of the cross-sectional sawtooth prism row of the light diffusing plate can be varied within an appropriate range. In that case, the arithmetic average height Ra when the prism surface is measured at 20 μm in the direction perpendicular to the longitudinal direction is preferably 0.08 μm or more and 3 μm or less, more preferably 0.09 μm or more and 2 μm or less. More preferably, it is 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.

本発明においては、光拡散板が断面鋸歯状プリズム条列を有する場合、光拡散板の断面鋸歯状プリズム条列の稜線方向と線状光源の長手方向とのなす角が６０度以下であることが好ましく、５０度以下であることがより好ましく、４５度以下であることがさらに好ましい。光拡散板の断面鋸歯状プリズム条列の稜線方向と線状光源の長手方向とのなす角を６０度以下とすることにより、輝度ムラを低減することができる。   In the present invention, when the light diffusing plate has a cross-sectional sawtooth prism row, the angle formed by the ridge line direction of the cross-sectional sawtooth prism row of the light diffusing plate and the longitudinal direction of the linear light source is 60 degrees or less. Is preferably 50 degrees or less, and more preferably 45 degrees or less. By setting the angle formed between the ridge line direction of the sawtooth prism array in the cross section of the light diffusion plate and the longitudinal direction of the linear light source to be 60 degrees or less, it is possible to reduce luminance unevenness.

光拡散板を構成する材料としてはガラス、混合しにくい２種以上の樹脂の混合物、透明樹脂及び光拡散剤を含む樹脂組成物等があげられ、特に限定されない。これらの中で軽量であること及び成形が容易であることから混合しにくい２種以上の樹脂の混合物、及び透明樹脂及び光拡散剤を含む樹脂組成物が好ましく、全光線透過率とヘーズの調整が容易であることから透明樹脂及び光拡散剤を含む樹脂組成物がさらに好ましい。さらに凹凸構造部分まで透明樹脂及び光拡散剤を含む樹脂組成物で形成し、光拡散板全体を同一の全光線透過率とヘーズに調整することが、光拡散板から出射する光の方向がさらに多様にできるためにより好ましい。   Examples of the material constituting the light diffusing plate include glass, a mixture of two or more resins difficult to mix, a resin composition containing a transparent resin and a light diffusing agent, and the like, and are not particularly limited. Among these, a mixture of two or more kinds of resins that are difficult to mix because of being lightweight and easy to mold, and a resin composition containing a transparent resin and a light diffusing agent are preferable, and adjustment of total light transmittance and haze Therefore, a resin composition containing a transparent resin and a light diffusing agent is more preferable. Furthermore, it is formed of a resin composition containing a transparent resin and a light diffusing agent up to the concavo-convex structure portion, and adjusting the entire light diffusing plate to the same total light transmittance and haze further increases the direction of light emitted from the light diffusing plate. It is more preferable because it can be varied.

光拡散板として、透明樹脂及び光拡散剤を含む樹脂組成物を用いる場合における光拡散剤の含有量に特に制限はなく、光拡散板の厚みやバックライトの線状光源間隔などに応じて適宜選択することができるが、樹脂組成物の全光線透過率が６０％以上９５％以下で、かつヘーズが４０％以上９４％以下であることが好ましい。樹脂組成物の全光線透過率を６０％以上、ヘーズを９４％以下とすることにより輝度をより向上することができ、全光線透過率を９５％以下、ヘーズを４０％以上とすることにより輝度均斉度をより向上させることができる。前記樹脂組成物の全光線透過率のより好ましい範囲は６５％以上９２％以下である。また、前記樹脂組成物のヘーズのより好ましい範囲は５０％以上９４％以下である。
樹脂組成物の全光線透過率はＪＩＳ Ｋ７３６１−１に準拠して両面平滑な２ｍｍ厚み板で測定した値で、樹脂組成物のヘーズはＪＩＳ Ｋ７１３６に準拠して両面平滑な２ｍｍ厚み板で測定した値とする。
光拡散板の厚みは、特に限定されないが、０．４ｍｍから５ｍｍであることが好ましく、０．８ｍｍから４ｍｍであることがさらに好ましい。光拡散板の厚みが０．４ｍｍより小さいと、支柱を多数形成する等自重によるたわみを抑えるための工夫が必要になるおそれがあり、バックライト装置のコストが上昇する。また厚みが５ｍｍを超えると成形が困難になるおそれがある。 There is no particular limitation on the content of the light diffusing agent in the case of using a resin composition containing a transparent resin and a light diffusing agent as the light diffusing plate. The total light transmittance of the resin composition is preferably 60% or more and 95% or less, and the haze is preferably 40% or more and 94% or less. The brightness can be further improved by setting the total light transmittance of the resin composition to 60% or more and the haze to 94% or less, and the brightness can be improved by setting the total light transmittance to 95% or less and the haze to 40% or more. The uniformity can be further improved. A more preferable range of the total light transmittance of the resin composition is 65% or more and 92% or less. Moreover, the more preferable range of the haze of the said resin composition is 50% or more and 94% or less.
The total light transmittance of the resin composition was a value measured with a 2 mm thick plate smooth on both sides according to JIS K7361-1, and the haze of the resin composition was measured with a 2 mm thick plate smooth on both sides according to JIS K7136. Value.
The thickness of the light diffusion 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 of the light diffusing plate is smaller than 0.4 mm, a device for suppressing the deflection due to its own weight, such as the formation of a large number of support columns, may be required, and the cost of the backlight device increases. If the thickness exceeds 5 mm, molding may be difficult.

本発明において光拡散板の材料として樹脂を用いる場合、透明樹脂としてはＪＩＳ Ｋ７３６１−１により両面平滑な２ｍｍ厚み板で測定さされる全光線透過率が７０％以上の樹脂であれば特に制限されず、例えば、ポリエチレン、プロピレン−エチレン共重合体、ポリプロピレン、ポリスチレン、芳香族ビニル系単量体と低級アルキル基を有する（メタ）アクリル酸アルキルエステルとの共重合体、ポリエチレンテレフタレート、テレフタル酸−エチレングリコール−シクロヘキサンジメタノール共重合体、ポリカーボネート、アクリル樹脂、脂環式構造を有する樹脂などを挙げることができる。これらの中でも、吸水率が０．２５％以下のものが、吸湿による変形が少ないので、反りの少ない大型の光拡散板を得ることができる点で好ましい。
吸水率が０．２５％以下の透明樹脂としては、ポリカーボネート、ポリスチレン、芳香族ビニル系単量体を１０％以上含有する芳香族ビニル系単量体と低級アルキル基を有する（メタ）アクリル酸アルキルエステルとの共重合体または脂環式構造を有する樹脂があげられる。これらの中でも脂環式構造を有する樹脂は、流動性が良好であり、大型の光拡散板を効率よく製造し得るのでさらに好ましい。脂環式構造を有する樹脂及び光拡散剤を含む樹脂組成物は、光拡散板に必要な高光透過性と高光拡散性とを兼ね備え、色度が良好なので、好適に用いることができる。 In the present invention, when a resin is used as the material of the light diffusing plate, the transparent resin is not particularly limited as long as the total light transmittance as measured with a 2 mm thick plate smooth on both sides according to JIS K7361-1 is 70% or more. For example, polyethylene, propylene-ethylene copolymer, polypropylene, polystyrene, copolymer of aromatic vinyl monomer and (meth) acrylic acid alkyl ester having a lower alkyl group, polyethylene terephthalate, terephthalic acid-ethylene glycol -A cyclohexanedimethanol copolymer, a polycarbonate, an acrylic resin, a resin having an alicyclic structure, and the like can be mentioned. Among these, those having a water absorption rate of 0.25% or less are preferable in that a large light diffusion plate with little warpage can be obtained because deformation due to moisture absorption is small.
The transparent resin having a water absorption of 0.25% or less includes polycarbonate, polystyrene, an aromatic vinyl monomer containing 10% or more of an aromatic vinyl monomer, and an alkyl (meth) acrylate having a lower alkyl group. Examples thereof include a copolymer with an ester or a resin having an alicyclic structure. Among these, a resin having an alicyclic structure is more preferable because it has good fluidity and can efficiently produce a large light diffusion plate. A resin composition containing a resin having an alicyclic structure and a light diffusing agent has both high light transmittance and high light diffusibility necessary for a light diffusing plate, and has good chromaticity, so that it can be suitably used.

脂環式構造を有する樹脂は、主鎖及び／又は側鎖に脂環式構造を有する樹脂である。機械的強度、耐熱性などの観点から、主鎖に脂環式構造を含有する樹脂が特に好ましい。
脂環式構造としては、飽和環状炭化水素（シクロアルカン）構造、不飽和環状炭化水素（シクロアルケン、シクロアルキン）構造などを挙げることができる。機械的強度、耐熱性などの観点から、シクロアルカン構造やシクロアルケン構造が好ましく、中でもシクロアルカン構造が最も好ましい。脂環式構造を構成する炭素原子数は、格別な制限はないが、通常４〜３０個、好ましくは５〜２０個、より好ましくは５〜１５個の範囲であるときに、機械的強度、耐熱性及び光拡散板の成形性の特性が高度にバランスされ、好適である。
脂環式構造を有する樹脂中の脂環式構造を有する繰り返し単位の割合は、使用目的に応じて適宜選択すればよいが、通常５０重量％以上、好ましくは７０重量％以上、より好ましくは９０重量％以上である。脂環式構造を有する繰り返し単位の割合が過度に少ないと、耐熱性が低下し好ましくない。なお、脂環式構造を有する樹脂中における脂環式構造を有する繰り返し単位以外の繰り返し単位は、使用目的に応じて適宜選択される。
脂環式構造を有する樹脂の具体例としては、（１）ノルボルネン系単量体の開環重合体及びノルボルネン系単量体とこれと開環共重合可能なその他の単量体との開環共重合体、並びにこれらの水素添加物、ノルボルネン系単量体の付加重合体及びノルボルネン系単量体とこれと共重合可能なその他の単量体との付加共重合体などのノルボルネン系重合体；（２）単環の環状オレフィン系重合体及びその水素添加物；（３）環状共役ジエン系重合体及びその水素添加物；（４）ビニル脂環式炭化水素系単量体の重合体及びビニル脂環式炭化水素系単量体とこれと共重合可能なその他の単量体との共重合体、並びにこれらの水素添加物、ビニル芳香族系単量体の重合体の芳香環の水素添加物及びビニル芳香族単量体とこれと共重合可能なその他の単量体との共重合体の芳香環の水素添加物などのビニル脂環式炭化水素系重合体；などが挙げられる。これらの中でも、耐熱性、機械的強度等の観点から、ノルボルネン系重合体及びビニル脂環式炭化水素系重合体が好ましく、ノルボルネン系単量体の開環重合体水素添加物、ノルボルネン系単量体とこれと開環共重合可能なその他の単量体との開環共重合体水素添加物、ビニル芳香族系単量体の重合体の芳香環の水素添加物及びビニル芳香族単量体とこれと共重合可能なその他の単量体との共重合体の芳香環の水素添加物がさらに好ましい。 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.

光拡散板に使用される光拡散剤は、光線を拡散させる性質を有する粒子であり、無機フィラーと有機フィラーに大別される。無機フィラーとしては、具体的には、シリカ、水酸化アルミニウム、酸化アルミニウム、酸化チタン、酸化亜鉛、硫酸バリウム、マグネシウムシリケート、又はこれらの混合物があげられる。有機フィラーの具体的な材料としては、アクリル系樹脂、アクリロニトリル、ポリウレタン、ポリ塩化ビニル、ポリスチレン系樹脂、ポリアクリロニトリル、ポリアミド、ポリシロキサン系樹脂、メラミン系樹脂、ベンゾグアナミン系樹脂又はこれらの架橋物等があげられる。これらの中で、ポリスチレン系樹脂、ポリシロキサン系樹脂又はこれらの架橋物からなる粒子は、高分散性、高耐熱性、成形時の着色（黄変）がないので、特に好適に用いることができる。またこれらの中でもポリシロキサン系樹脂の架橋物からなる粒子は、耐熱性により優れるので、さらに好適に用いることができる。光拡散剤の粒子径は、特に制限されず、平均粒径で通常０．５〜１００μｍ、好ましくは０．５〜８０μｍの範囲である。
光拡散板に使用される光拡散剤の形状としては、特に限定されず、球状、立方状、針状、棒状、紡錘形状、板状、鱗片状、繊維状などが挙げられるが、中でも光の拡散方向を等方的にすることのできる点で球状が好ましい。
前記光拡散剤は透明樹脂内部に含有された形で、巨視的に均一かつ離間的に分散されて、使用される。 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. Specific examples of the inorganic filler include silica, aluminum hydroxide, aluminum oxide, titanium oxide, zinc oxide, barium sulfate, magnesium silicate, and mixtures thereof. Specific examples of the organic filler include acrylic resin, acrylonitrile, polyurethane, polyvinyl chloride, polystyrene resin, polyacrylonitrile, polyamide, polysiloxane resin, melamine resin, benzoguanamine resin, and cross-linked products thereof. can give. Among these, polystyrene resin, polysiloxane resin, or particles made of a crosslinked product thereof can be used particularly suitably because they have high dispersibility, high heat resistance, and no coloration (yellowing) during molding. . Of these, particles made of a crosslinked product of polysiloxane resin are more excellent in heat resistance, and can be used more suitably. The particle diameter of the light diffusing agent is not particularly limited, and is usually in the range of 0.5 to 100 μm, preferably 0.5 to 80 μm as an average particle diameter.
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. A spherical shape is preferable in that the diffusion direction can be made isotropic.
The light diffusing agent is contained in a transparent resin and is used after being macroscopically dispersed uniformly and spaced apart.

本発明に用いる光拡散板を製造する方法としては、押出成形法、射出成形法、溶液キャスト法などの公知の成形方法があげられる。
光拡散板の表面に凹凸構造を形成する方法としては、特に制限されず、平板状の光拡散板を成形し、その表面に凹凸構造を形成する方法；光拡散板の成形と同時に表面に凹凸構造を形成する方法があげられる。
平板状の光拡散板を成形し、その表面に凹凸構造を形成する方法の具体例としては、平板状の光拡散板の表面に所望の構造を形成できる工具を用いて切削加工を行って凹凸構造を形成する方法；平板状の光拡散板の上に市販のプリズムシートなどの凹凸構造をもつシートを積層する方法；平板状の光拡散板の上に光硬化性樹脂を塗布し、所望の凹凸構造の型形状を転写した状態で硬化させる方法があげられる。
光拡散板の成形と同時に表面に凹凸構造を形成する方法の具体例を以下に記述する。光拡散板を押出成形により成形する場合は、所望の凹凸構造を有する異形ダイを用いて押出成形する方法；通常のダイを用いて押出成形した後にエンボス加工により凹凸構造を形成する方法があげられる。光拡散板を溶液キャスト法により成形する場合は、所望の凹凸構造を形成できるキャスティング型を用いて溶液キャストを行う方法が挙げられる。光拡散板を射出成形により成形する場合は、所望の凹凸構造を有する金型を用いて射出成形する方法があげられる。
光硬化樹脂への型形状転写、異形ダイを用いた押出成形、エンボス加工、溶液キャスト、もしくは射出成形により、凹凸構造を形成する場合に使用する型は、所望の形状を形成できる工具を用いた型の金属部材への切削加工、又は所望の形状が形成された部材上への電鋳加工により得ることができる。 Examples of the method for producing the light diffusing plate used in the present invention include known molding methods such as extrusion molding, injection molding, and solution casting.
The method for forming the concavo-convex structure on the surface of the light diffusing plate is not particularly limited, and is a method of forming a flat light diffusing plate and forming the concavo-convex structure on the surface; A method for forming the structure is mentioned.
As a specific example of a method of forming a flat light diffusion plate and forming an uneven structure on its surface, the surface of the flat light diffuser plate is cut using a tool capable of forming a desired structure to make uneven A method of forming a structure; a method of laminating a sheet having a concavo-convex structure such as a commercially available prism sheet on a flat light diffusing plate; a photocurable resin is applied on a flat light diffusing plate, and a desired There is a method of curing in a state where the mold shape of the concavo-convex structure is transferred.
A specific example of a method for forming a concavo-convex structure on the surface simultaneously with the formation of the light diffusing plate will be described below. When forming the light diffusion plate by extrusion molding, a method of extrusion molding using a deformed die having a desired concavo-convex structure; a method of forming an concavo-convex structure by embossing after extrusion using a normal die . In the case where the light diffusion plate is formed by the solution casting method, a method of performing solution casting using a casting mold capable of forming a desired uneven structure can be mentioned. When the light diffusing plate is formed by injection molding, a method of injection molding using a mold having a desired concavo-convex structure can be mentioned.
Die shape transfer to photo-curing resin, extrusion using embossed die, embossing, solution casting, or injection molding, the mold used when forming the concavo-convex structure was a tool that can form the desired shape It can be obtained by cutting a metal member of a mold or electroforming on a member having a desired shape.

本発明において、輝度と輝度均斉度向上のために、光拡散板の光源から遠い側に、拡散シートとプリズムシートのうち少なくとも一方を配置してもよい。さらに輝度を向上させるために、下記（イ）及び（ロ）に示す部材のうちいずれかを配置してもよい。
（イ）透明基材上に液晶分子の螺旋ピッチが連続的に変化するコレステリック液晶層を有する光学積層体と、式Ｒｔｈ＝｛（ｎｘ＋ｎｙ）／２-ｎｚ｝×ｄ（式中、ｎｘ、ｎｙは厚さ方向に垂直な互いに直交する２方向の屈折率を表し、ｎｘ＞ｎｙである。ｎｚは厚さ方向の屈折率を表し、ｄは膜厚を表す）で定義されるＲｔｈが−２０ｎｍ〜−１０００ｎｍである位相差素子と、１／４波長板とを含む積層体。
（ロ）特許３４４８６２６号に記載されているような複屈折を利用した反射偏光子。
上記（イ）及び（ロ）に示した部材は、拡散シートやプリズムシートの光源から遠い側に配置してもよい。 In the present invention, in order to improve luminance and luminance uniformity, at least one of a diffusion sheet and a prism sheet may be disposed on the side of the light diffusion plate far from the light source. In order to further improve the luminance, any of the members shown in the following (A) and (B) may be arranged.
(A) 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 the formula Rth = {(nx + ny) / 2-nz} × d (where nx, ny Represents a refractive index in two directions perpendicular to the thickness direction, and nx> ny, nz represents a refractive index in the thickness direction, and d represents a film thickness), and Rth defined as −20 nm A laminate including a retardation element having a wavelength of ˜−1000 nm and a ¼ wavelength plate.
(B) A reflective polarizer using birefringence as described in Japanese Patent No. 3448626.
The members shown in (a) and (b) above may be arranged on the side far from the light source of the diffusion sheet or prism sheet.

以下に、実施例を挙げて本発明をさらに詳細に説明するが、本発明はこれらの実施例によりなんら限定されるものではない。なお、部及び％は、特に制限のない限り重量基準である。   Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Parts and% are based on weight unless otherwise specified.

製造例１
透明樹脂として脂環式構造を有する樹脂の一種であるノルボルネン系樹脂［日本ゼオン（株）、ＺＥＯＮＯＲ１０６０Ｒ、吸水率０．０１％］９９．７部と、光拡散剤としてポリシロキサン系重合体の架橋物からなる粒子［ＧＥ東芝シリコーン（株）、トスパール１２０、平均粒径２μｍ］０．３部を用い、これらを混合し、次いで二軸押出機で混練してストランド状に押し出し、ペレタイザーで切断して光拡散板用ペレット１を得た。この光拡散板用ペレット１から、射出成形機［型締め力１０００ｋＮ］を用いて、両面が平滑な厚み２ｍｍで１００ｍｍ×５０ｍｍの試験板を成形した。この試験板の全光線透過率をＪＩＳ Ｋ７３６１−１にしたがって、ヘーズをＪＩＳ Ｋ７１３６にしたがって、それぞれ積分球方式色差濁度計を用いて測定した。全光線透過率は８５％であり、ヘーズは９０％であった。 Production Example 1
99.7 parts of norbornene resin [Nippon Zeon Co., Ltd., ZEONOR1060R, water absorption 0.01%] which is a kind of resin having an alicyclic structure as a transparent resin, and crosslinking of a polysiloxane polymer as a light diffusing agent Particles [GE Toshiba Silicone Co., Ltd., Tospearl 120, average particle size 2 μm] 0.3 parts are mixed together, then kneaded with a twin screw extruder, extruded into a strand, and cut with a pelletizer. Thus, a light diffusion plate pellet 1 was obtained. From this light diffusion plate pellet 1, 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 of this test plate was measured according to JIS K7361-1, and the haze was measured according to JIS K7136 using an integrating sphere color difference turbidimeter, respectively. The total light transmittance was 85% and the haze was 90%.

製造例２
透明樹脂として脂環式構造を有する樹脂の一種であるノルボルネン系樹脂［日本ゼオン（株）、ゼオノア１０６０Ｒ、吸水率０．０１％］９９．２部とポリシロキサン系重合体の架橋物からなる微粒子［ＧＥ東芝シリコーン（株）、トスパール１２０、平均粒子径２μｍ］０．８部とを使用する以外は製造例１と同様にして光拡散板用ペレット２を得、全光線透過率とヘーズを製造例１と同様に測定したところ、全光線透過率は６５％であり、ヘーズは９２％であった。 Production Example 2
Fine particles comprising 99.2 parts of norbornene resin [Nippon Zeon Co., Ltd., ZEONOR 1060R, water absorption 0.01%], which is a kind of resin having an alicyclic structure, as a transparent resin and a cross-linked product of a polysiloxane polymer [GE Toshiba Silicone Co., Ltd., Tospearl 120, average particle diameter 2 μm] Except for using 0.8 parts, a light diffusion plate pellet 2 was obtained in the same manner as in Production Example 1 to produce total light transmittance and haze. When measured in the same manner as in Example 1, the total light transmittance was 65%, and the haze was 92%.

製造例３
金型の金属部材を切削加工して、頂角１００度の二等辺三角形が連なった断面形状のプリズム条列を長手方向と平行に形成することができる金型を準備した。そしてこの金型と製造例１で得られた光拡散板用ペレット１とを用い、射出成型機（型締め力４４１０ｋＮ）を用いて、プリズム条列のピッチが７０μｍで、厚み２ｍｍで大きさが７３０ｍｍ×４２０ｍｍの光拡散板１をシリンダー温度２８０度、金型温度８５度で成形した。成形した光拡散板の表面を超深度顕微鏡で観察したところ、断面鋸歯状プリズムの頂角は１００度，プリズム状列を有する面をプリズムの長手に対して直角方向に１ｍｍ測定したときの最大高さＲｚは２９μｍで、プリズム表面を長手に対して直角方向に２０μｍ測定したときの算術平均高さＲａは０．０４μｍであった。 Production Example 3
A metal mold was prepared by cutting a metal member of the mold to form a prism row having a cross-sectional shape in which isosceles triangles having an apex angle of 100 degrees are connected in parallel to the longitudinal direction. Using this mold and the light diffusion plate pellet 1 obtained in Production Example 1, using an injection molding machine (clamping force 4410 kN), the prism row pitch is 70 μm, the thickness is 2 mm, and the size is A 730 mm × 420 mm light diffusion plate 1 was molded at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. When the surface of the molded light diffusing plate was observed with an ultra-deep microscope, the apex angle of the cross-sectional sawtooth prism was 100 degrees, and the maximum height when the surface having the prismatic row was measured 1 mm perpendicular to the length of the prism. The thickness Rz was 29 μm, and the arithmetic average height Ra was 0.04 μm when the prism surface was measured 20 μm in the direction perpendicular to the longitudinal direction.

製造例４
プリズム条列を有している金型のかわりに、プリズム条列を有しない平板状の金型を用い、光拡散板用ペレット１のかわりに製造例２による光拡散板用ペレットを用いた以外は、製造例３と同様にして光拡散板２を得た。得られた光拡散板２の表面粗さＲａは０．０４μｍであった。 Production Example 4
A plate-shaped mold not having a prism row is used in place of a mold having a prism row, and the light diffusion plate pellet according to Production Example 2 is used instead of the light diffusion plate pellet 1 Obtained the light diffusing plate 2 in the same manner as in Production Example 3. The surface roughness Ra of the obtained light diffusing plate 2 was 0.04 μm.

実施例１
底面の内側寸法が幅６９０ｍｍ奥行き３８０ｍｍ、開口部の内側寸法が幅７１０ｍｍ奥行き４００ｍｍで、深さ２０ｍｍ、側壁が底面から開口部に向かって直線状に立ち上がる乳白色プラスチック製ケースの内面に、反射シート（株式会社ツジデン製、ＲＦ１８８）を貼着して反射面を持つ筐体とし、筐体の底面から５ｍｍ離して、直径４ｍｍ、長さ４２０ｍｍの冷陰極管１０本を図４のように配置し、冷陰極管の中心間の距離を表１に示す値とし、電極部近傍をシリコーンシーラントで固定し、さらにインバーターを取り付けた。この設計のバックライト装置では、筐体側壁から筐体側壁に一番近い線状光源までの距離ａは２０ｍｍ、筐体側壁に一番近い線状光源から該線状光源に隣接する内側の線状光源までの距離ｂは３９ｍｍ、ａ／ｂは０．５１であった。
製造例３で得られた光拡散板１を、光拡散板の主面に形成された断面鋸歯状プリズム条列の稜線方向が、これと冷陰極管の長手方向とのなす角が０度（平行）になるように冷陰極管の反対側に配置し、冷陰極管を取り付けたプラスチックケース上に配置した。このとき、筐体内部からの光を直接受ける光拡散板の光源側４００×７１０ｍｍの部分と、それに相対する光拡散板の光源から遠い側の同じ寸法の部分が、光学的有効面となる。
さらにプリズムシート（住友スリーエム株式会社製、ＲＢＥＦ）を、プリズムシートのプリズム条列の長手方向が冷陰極管の長手方向と平行に、かつ光拡散板から遠い側になるように配置した。そして、その上に、複屈折を利用した反射偏光子（住友スリーエム株式会社製、ＤＢＥＦ−Ｄ）を配置し、さらに偏光板を取り付けることにより直下型バックライト装置１を作製した。
この直下型バックライト装置１を用いて、管電流６ｍＡ、管電圧３３０Ｖｒｍｓを印加して冷陰極管を点灯し、二次元色分布測定装置を用いて、光拡散板の光学的有効面の長手方向の中心線上を一方の光学的有効の面端部からもう一方の光学的有効面の端部にかけて等間隔に１５０点の輝度を測定し、下記の数式１に従ってランプ見えによる輝度むらＬＵ、数式２に従って両サイドの輝度低下率ＬＤをそれぞれ算出した。また７５点目の測定点を中央正面輝度とした。
このとき中央正面輝度は３３７３ｃｄ／ｍ２、ランプ見えによる輝度むらＬＵは０．６、両サイドの輝度低下率ＬＤは０．８８であった。
ランプ見えによる輝度むらＬＵ：値が小さい方が良好である
ＬＵ＝（Ｌ１−（Ｌ２＋Ｌ３）／２）÷（（Ｌ１＋（Ｌ２＋Ｌ３）／２）／２）×１００ （数式１）
Ｌ１：バックライト中心部の光源上の輝度（図４に示す）
Ｌ２、Ｌ３：バックライト中心部の光源と、それに隣接する両側の光源との中間点の直上の輝度（図４に示す）
両サイドの輝度低下率ＬＤ：値が１に近い方が良好である
ＬＤ＝ＬＥ／ＬＭ （数式２）
ＬＥ：エッジ部分輝度（光拡散板の光学的有効面端部から、中心方向に向かい測定長さの一割離れた位置の直上の輝度）
ＬＭ：輝度の最大値（図４ではＬ１に等しい） Example 1
The inner dimension of the bottom surface is 690 mm wide and 380 mm deep, the inner dimension of the opening is 710 mm wide and 400 mm deep, the depth is 20 mm, and the reflective sheet ( RF188) manufactured by Tsujiden Co., Ltd. is attached to form a casing having a reflective surface, and 5 cold cathode fluorescent lamps having a diameter of 4 mm and a length of 420 mm are arranged as shown in FIG. The distance between the centers of the cold cathode tubes was set to the value shown in Table 1, the vicinity of the electrode part was fixed with a silicone sealant, and an inverter was attached. In the backlight device of this design, the distance a from the housing side wall to the linear light source closest to the housing side wall is 20 mm, and the inner line adjacent to the linear light source from the linear light source closest to the housing side wall is 20 mm. The distance b to the light source was 39 mm and a / b was 0.51.
In the light diffusing plate 1 obtained in Production Example 3, the angle between the ridge line direction of the cross-sectional sawtooth prism array formed on the main surface of the light diffusing plate and the longitudinal direction of the cold cathode tube is 0 degree ( (Parallel) and placed on the opposite side of the cold cathode tube, and placed on a plastic case to which the cold cathode tube was attached. At this time, a 400 × 710 mm portion on the light source side of the light diffusing plate that directly receives light from the inside of the housing and a portion having the same dimension on the side far from the light source of the light diffusing plate corresponding thereto are optically effective surfaces.
Furthermore, a prism sheet (manufactured by Sumitomo 3M Limited, RBEF) was arranged so that the longitudinal direction of the prism row of the prism sheet was parallel to the longitudinal direction of the cold cathode tube and far from the light diffusion plate. Then, a reflective polarizer using birefringence (DBEF-D, manufactured by Sumitomo 3M Limited) was placed thereon, and a polarizing plate was attached to produce a direct type backlight device 1.
Using this direct type backlight device 1, a cold cathode tube is turned on by applying a tube current of 6 mA and a tube voltage of 330 Vrms, and a longitudinal direction of the optically effective surface of the light diffusion plate using a two-dimensional color distribution measuring device. The luminance at 150 points is measured at equal intervals from the edge of one optically effective surface to the edge of the other optically effective surface on the center line, and the luminance unevenness LU due to the lamp appearance is expressed by Equation 2 below. The luminance reduction rate LD on both sides was calculated according to the above. The 75th measurement point was set as the central front luminance.
At this time, the central front luminance was 3373 cd / m 2 , the luminance unevenness LU due to the lamp appearance was 0.6, and the luminance reduction rate LD on both sides was 0.88.
Luminance unevenness LU due to lamp appearance: smaller value is better LU = (L1− (L2 + L3) / 2) ÷ ((L1 + (L2 + L3) / 2) / 2) × 100 (Equation 1)
L1: Luminance on the light source at the center of the backlight (shown in FIG. 4)
L2, L3: Luminance immediately above the midpoint between the light source at the center of the backlight and the light sources on both sides adjacent to the light source (shown in FIG. 4)
Luminance decrease rate LD on both sides: LD = LE / LM where the value closer to 1 is better (Formula 2)
LE: Edge portion luminance (luminance directly above the position at a distance of 10% from the end of the optically effective surface of the light diffusion plate toward the center)
LM: Maximum value of luminance (equal to L1 in FIG. 4)

実施例２
筐体側壁に近い二本の線状光源の間隔をａ／ｂ＝１．２６となるようにした以外は、実施例１と同様にして直下型バックライト装置２を作製し、その評価を行った。中央正面輝度は３５７２ｃｄ／ｍ２、ランプ見えによる輝度むらＬＵは０．３、両サイドの輝度低下率ＬＤは０．７１であった。 Example 2
A direct type backlight device 2 was produced and evaluated in the same manner as in Example 1 except that the distance between the two linear light sources close to the housing side wall was a / b = 1.26. It was. The central front luminance was 3572 cd / m 2 , the luminance unevenness LU due to the lamp appearance was 0.3, and the luminance reduction rate LD on both sides was 0.71.

比較例１
筐体側壁に近い二本の線状光源の間隔をａ／ｂ＝０．０８となるようにした以外は、実施例１と同様にして直下型バックライト装置３を作製し、その評価を行った。中央正面輝度が３１６９ｃｄ／ｍ２、ランプ見えによる輝度むらＬＵは１．４、両サイドの輝度低下率ＬＤは０．９４であった。 Comparative Example 1
A direct type backlight device 3 was produced and evaluated in the same manner as in Example 1 except that the distance between the two linear light sources close to the side wall of the housing was set to a / b = 0.08. It was. The central front luminance was 3169 cd / m 2 , the luminance unevenness LU due to the lamp appearance was 1.4, and the luminance reduction rate LD on both sides was 0.94.

比較例２
筐体側壁に近い二本の線状光源の間隔をａ／ｂ＝３．１となるようにした以外は、実施例１と同様にして直下型バックライト装置４を作製し、その評価を行った。中央正面輝度は４００３ｃｄ／ｍ２、ランプ見えによる輝度むらＬＵは０．２、両サイドの輝度低下率ＬＤは０．３７であった。 Comparative Example 2
A direct type backlight device 4 was produced and evaluated in the same manner as in Example 1 except that the distance between the two linear light sources close to the housing side wall was set to a / b = 3.1. It was. The central front luminance was 4003 cd / m 2 , the luminance unevenness LU due to the lamp appearance was 0.2, and the luminance reduction rate LD on both sides was 0.37.

比較例３
製造例３で得られた光拡散板１のかわりに製造例４で得られた平板状の光拡散板２を用い、その光源の反対側に拡散シート（株式会社ツジデン社製、Ｄ１２１ＵＺ）を設置した以外は、実施例１と同様にして直下型バックライト装置５を作製し、その評価を行った。中央正面輝度は３２７５ｃｄ／ｍ２、ランプ見えによる輝度むらＬＵは２．７、両サイドの輝度低下率ＬＤは０．８９であった。 Comparative Example 3
Instead of the light diffusion plate 1 obtained in Production Example 3, the flat light diffusion plate 2 obtained in Production Example 4 is used, and a diffusion sheet (D121UZ manufactured by Tsujiden Co., Ltd.) is installed on the opposite side of the light source. Except for the above, a direct type backlight device 5 was produced in the same manner as in Example 1 and evaluated. The central front luminance was 3275 cd / m 2 , the luminance unevenness LU due to the lamp appearance was 2.7, and the luminance reduction rate LD on both sides was 0.89.

実施例１、２と比較例１、２、３の構成と測定結果を表１に示し、実施例１、２と比較例１、２の輝度測定結果を図５に示す。   The configurations and measurement results of Examples 1 and 2 and Comparative Examples 1, 2, and 3 are shown in Table 1, and the luminance measurement results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIG.

Figure 2006310150
Figure 2006310150

表１、図５において、実施例１、２と比較例１とを比べると、筐体側壁に近い二本の線状光源の間隔をａ／ｂ＞０．１５となるようにすることで、ランプ見えの輝度むらＬＵを改善できること、比較例２と比べるとａ／ｂ＜２となるようにすることで、両サイドの輝度低下を改善できることがわかる。また実施例１，２と比較例３とを比べることで、光拡散板に凹凸構造を設けることで、ランプ見えの輝度むらＬＵを大きく改善できることがわかる。   In Table 1 and FIG. 5, when Examples 1 and 2 are compared with Comparative Example 1, the distance between the two linear light sources close to the side wall of the housing is set to a / b> 0.15, It can be seen that the luminance unevenness LU of the lamp appearance can be improved, and the luminance decrease on both sides can be improved by setting a / b <2 as compared with Comparative Example 2. Further, comparing Examples 1 and 2 with Comparative Example 3, it can be seen that by providing the light diffusing plate with a concavo-convex structure, the luminance unevenness LU of the lamp appearance can be greatly improved.

本発明の直下型バックライト装置によれば、光源の数を増やさずに、周辺部の輝度低下とランプ見えを抑制して、輝度と輝度均斉度の改良とを同時に実現できるので、液晶表示装置に直下型バックライト装置を組み込んだとき、高画質の液晶表示装置を得ることができる。   According to the direct type backlight device of the present invention, it is possible to simultaneously realize improvement of luminance and luminance uniformity without increasing the number of light sources, while suppressing luminance reduction and lamp appearance at the peripheral portion. When a direct-type backlight device is incorporated in a high-quality liquid crystal display device can be obtained.

本発明の直下型バックライト装置の一態様を示す模式的斜視図である。It is a typical perspective view which shows one aspect | mode of the direct type | mold backlight apparatus of this invention. 本発明の直下型バックライト装置の一態様を示す一部の断面図である。It is a partial sectional view showing one mode of the direct type backlight device of the present invention. 本発明の直下型バックライト装置の筐体の反射面に形成してもよい連続的な突起部をその長手方向に垂直な面で切断したときの断面形状の具体例を示す図である。It is a figure which shows the specific example of a cross-sectional shape when the continuous protrusion part which may be formed in the reflective surface of the housing | casing of the direct type | mold backlight apparatus of this invention is cut | disconnected by the surface perpendicular | vertical to the longitudinal direction. 本発明の実施例の直下型バックライト装置の光源の配置と輝度測定値を示す図である。It is a figure which shows arrangement | positioning and the luminance measurement value of the light source of the direct type | mold backlight apparatus of the Example of this invention. 本発明の実施例および比較例の輝度測定値を示すグラフである。It is a graph which shows the luminance measurement value of the Example and comparative example of this invention.

符号の説明Explanation of symbols

１ 光拡散板
２−１，２−２，２−３ 線状光源
３ 筐体
４ 筐体側壁
５ 反射面
ｙ プリズム頂角
ａ 筐体側壁から筐体側壁に一番近い線状光源までの距離
ｂ 筐体側壁に一番近い線状光源から該線状光源に隣接する内側の線状光源までの距離 DESCRIPTION OF SYMBOLS 1 Light diffusing plate 2-1, 2-2, 2-3 Linear light source 3 Housing | casing 4 Housing | casing side wall 5 Reflecting surface y Prism apex angle a Distance from the housing | casing side wall to the linear light source nearest to a housing | casing side wall b Distance from the linear light source closest to the side wall of the housing to the inner linear light source adjacent to the linear light source

Claims (4)

開口面を有し、該開口面を法線方向から観察した形状が略長方形で、内面が反射面である筐体と、
該筐体内に並列配置された複数の線状光源と、
該筐体の開口部上に設けられた光拡散板とからなる直下型バックライト装置において、
筐体側壁から筐体側壁に一番近い線状光源までの距離をａ（ｍｍ）、筐体側壁に一番近い線状光源から該線状光源に隣接する内側の線状光源までの距離をｂ（ｍｍ）とするとき、前記ａ及びｂが０．１５＜ａ／ｂ＜２の関係を満たし、かつ前記光拡散板が少なくとも一方の主面に最大高さＲｚが２００μｍ以下の凹凸構造を有するものであることを特徴とする直下型バックライト装置。 A housing having an opening surface, the shape of the opening surface observed from the normal direction is substantially rectangular, and the inner surface is a reflecting surface;
A plurality of linear light sources arranged in parallel in the housing;
In a direct type backlight device comprising a light diffusing plate provided on the opening of the housing,
The distance from the housing side wall to the linear light source closest to the housing side wall is a (mm), and the distance from the linear light source closest to the housing side wall to the inner linear light source adjacent to the linear light source is When b (mm), the a and b satisfy the relationship of 0.15 <a / b <2, and the light diffusing plate has a concavo-convex structure having a maximum height Rz of 200 μm or less on at least one main surface. What is claimed is: 1. A direct type backlight device comprising: 光拡散板の最大高さＲｚが２００μｍ以下の凹凸構造の形状が、頂角６０〜１７０度でかつピッチが２０〜７００μｍである断面鋸歯状プリズム条列である請求項１記載の直下型バックライト装置。 2. The direct type backlight according to claim 1, wherein the shape of the concavo-convex structure having a maximum height Rz of the light diffusion plate of 200 [mu] m or less is a cross-sectional sawtooth prism array having an apex angle of 60 to 170 degrees and a pitch of 20 to 700 [mu] m. apparatus. 光拡散板の断面鋸歯状プリズム条列の稜線方向と、線状光源の長手方向とのなす角が６０度以下である請求項２記載の直下型バックライト装置。 The direct type backlight device according to claim 2, wherein an angle formed by a ridge line direction of the sawtooth prism array in the cross section of the light diffusing plate and a longitudinal direction of the linear light source is 60 degrees or less. 光拡散板が透明樹脂及び光拡散剤を含む樹脂組成物からなり、該樹脂組成物の全光線透過率が６０％以上９５％以下で、かつヘーズが４０％以上９４％以下である請求項１〜３のいずれかに記載の直下型バックライト装置。

2. The light diffusing plate comprises a resin composition containing a transparent resin and a light diffusing agent, the total light transmittance of the resin composition is 60% or more and 95% or less, and the haze is 40% or more and 94% or less. The direct type backlight device according to any one of?

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