JPWO2005030468A1 - Thick plate molded product and method for manufacturing the same - Google Patents

Thick plate molded product and method for manufacturing the same Download PDF

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JPWO2005030468A1
JPWO2005030468A1 JP2005514324A JP2005514324A JPWO2005030468A1 JP WO2005030468 A1 JPWO2005030468 A1 JP WO2005030468A1 JP 2005514324 A JP2005514324 A JP 2005514324A JP 2005514324 A JP2005514324 A JP 2005514324A JP WO2005030468 A1 JPWO2005030468 A1 JP WO2005030468A1
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plate molded
mold
molded product
flat plate
temperature
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林　昌彦
昌彦 林
植木　一範
一範 植木
成瀬　史博
史博 成瀬
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Zeon Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/72—Heating or cooling
    • B29C45/73—Heating or cooling of the mould
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/26—Moulds
    • B29C45/37—Mould cavity walls, i.e. the inner surface forming the mould cavity, e.g. linings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/72—Heating or cooling
    • B29C45/73—Heating or cooling of the mould
    • B29C2045/7343—Heating or cooling of the mould heating or cooling different mould parts at different temperatures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/26—Moulds
    • B29C45/37—Mould cavity walls, i.e. the inner surface forming the mould cavity, e.g. linings
    • B29C45/372—Mould cavity walls, i.e. the inner surface forming the mould cavity, e.g. linings provided with means for marking or patterning, e.g. numbering articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2011/00—Optical elements, e.g. lenses, prisms

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Mechanical Engineering (AREA)
  • Moulds For Moulding Plastics Or The Like (AREA)
  • Injection Moulding Of Plastics Or The Like (AREA)
  • Light Guides In General And Applications Therefor (AREA)

Abstract

射出成形法により製造された熱可塑性樹脂を含んでなる長方形の厚物平板成形品において、最大厚みと最小厚みとの差が、中央部の厚みの３％以下であることを特徴とする、中央部から周縁部まで厚みが均一でむらがなく、金型表面の微細な凹凸模様を正確に転写し、光学材料として好適に用いることができる厚物平板成形品、及び、前記厚物平板成形品を射出成形法により製造するに際して、射出成形用金型の長方形のキャビティの少なくとも１対の対向する２端辺の温度が、金型のキャビティの中央部の最高温度よりも２℃以上高く維持されるように金型を加熱することを特徴とする厚物平板成形品の製造方法。In a rectangular thick flat plate molded article comprising a thermoplastic resin produced by an injection molding method, the difference between the maximum thickness and the minimum thickness is 3% or less of the thickness of the central portion, Thick plate molded product that can be used as an optical material by accurately transferring a fine uneven pattern on the mold surface with a uniform and uniform thickness from the portion to the peripheral portion, and the thick plate molded product Is produced by the injection molding method, the temperature of at least one pair of opposing two sides of the rectangular cavity of the injection mold is maintained at 2 ° C. or more higher than the maximum temperature at the center of the cavity of the mold. A method for manufacturing a thick flat plate molded product, wherein the mold is heated so that

Description

本発明は、厚物平板成形品及びその製造方法に関する。さらに詳しくは、本発明は、中央部から周縁部まで厚みが均一でむらがなく、金型表面の微細な凹凸模様を正確に転写し、光学材料として好適に用いることができる厚物平板成形品及びその製造方法に関する。  The present invention relates to a thick flat plate molded article and a method for producing the same. More specifically, the present invention provides a thick flat plate molded article that can be used as an optical material by accurately transferring a fine uneven pattern on the mold surface with a uniform and uniform thickness from the central part to the peripheral part. And a manufacturing method thereof.

射出成形品は、日用品、自動車部品、家電部品、電子部品、光学機器など、汎用から精密用途に至るまで広範囲に使用されている。射出成形品の品質と生産性の良否は、金型の良否に左右されるところが大きい。射出成形用金型の製作には、工作精度、品質の均一化、生産性など、あらゆる面で高度な技術が要求される。液晶表示装置の光拡散板、導光板などは、一見すると単純な形状の平板であるが、実用上は極めて厳密な平面性が必要であり、厚みむらがないことが要求される。平板のような単純な形状であっても、厚みむらのない射出成形品を製造することは容易ではなく、厚みむらのない射出成形品を製造するためにさまざまな試みがなされている。
例えば、プラテン平行度のずれやタイバ延びの変化に起因した金型のかじりや成形体の厚みむらを低減させる射出成形方法として、固定プラテンと可動プラテンの平行度をそれぞれ実際の射出成形時のプラテン温度に相当する温度に加熱した状態で予め調整しておき、射出成形時にプラテンを平行度調整時の温度に維持する方法が提案されている（特許文献１）。しかし、射出成形においては、型締圧力や射出圧力などの力が作用して金型が変形するので、特に大型成形品の場合は、温度制御のみによって平行性を実現することは困難である。また、光磁気ディスク基盤などの寸法精度と面粗さ精度を上げ、成形体の充填密度を上げることができる射出成形金型として、固定側組立と可動側組立とを有し、円盤キャビティ中に射出された溶融樹脂材料が凝固する前にカットスリーブを押し上げて中心孔の形成と円盤キャビティ部の密閉を同時に行い、次に可動側組立を上昇させて一次成形体を再圧縮する金型が提案されている（特許文献２）。しかし、大型の長方形の成形品の厚みむらをこのような手段によって低減することは困難である。さらに、成形圧力による金型の撓みを抑えることが可能であり、パーティング面に大きな隙間が発生してバリが発生するのを抑えることができる金型として、成形圧力による金型の撓みを抑えるように、キャビティの数及び配置に応じてエジェクタスペースを複数設けた射出成形用金型が提案されている（特許文献３）。しかし、このような手段は、多数個取りの金型には有効であっても、大型成形品１個取りの金型に適用することはできない。
特開平１０−３２３８７２号公報（第２頁、図１−２） 特開平６−２７０２０８号公報（第２−３頁、図１） 特開平１０−４４１９７号公報（第２頁、図１） Injection molded products are used in a wide range from general-purpose to precision applications such as daily necessities, automobile parts, home appliance parts, electronic parts, and optical equipment. The quality of the injection-molded product and the quality of the productivity largely depend on the quality of the mold. Production of injection molds requires advanced technology in all aspects, such as machining accuracy, quality uniformity, and productivity. A light diffusing plate, a light guide plate, and the like of a liquid crystal display device are flat plates having a simple shape at first glance. However, in practical use, extremely strict flatness is required and thickness unevenness is required. Even if it is a simple shape such as a flat plate, it is not easy to produce an injection-molded product without uneven thickness, and various attempts have been made to produce an injection-molded product without uneven thickness.
For example, as an injection molding method that reduces mold galling and uneven thickness of the molded product due to deviations in platen parallelism and changes in tie bar extension, the parallelism between the fixed platen and the movable platen can be set to the platen during actual injection molding. A method has been proposed in which the platen is adjusted in advance in a state heated to a temperature corresponding to the temperature, and the platen is maintained at the temperature at the time of adjusting the parallelism during injection molding (Patent Document 1). However, in injection molding, a mold is deformed by the action of a clamping pressure, injection pressure, or the like, so that it is difficult to achieve parallelism only by temperature control, particularly in the case of a large molded product. In addition, it has a fixed side assembly and a movable side assembly as an injection mold that can increase the dimensional accuracy and surface roughness accuracy of the magneto-optical disk substrate and the like, and can increase the filling density of the molded body. A mold that pushes up the cut sleeve to form the center hole and seal the disk cavity at the same time before the injected molten resin material solidifies, then raises the movable assembly and recompresses the primary compact is proposed. (Patent Document 2). However, it is difficult to reduce the thickness unevenness of a large rectangular molded product by such means. Furthermore, it is possible to suppress the bending of the mold due to the molding pressure, and as a mold that can suppress the occurrence of burrs due to a large gap on the parting surface, the bending of the mold due to the molding pressure is suppressed. As described above, an injection mold having a plurality of ejector spaces according to the number and arrangement of cavities has been proposed (Patent Document 3). However, even if such a means is effective for a multi-cavity mold, it cannot be applied to a large-size molded article single-cavity mold.
JP-A-10-323872 (second page, FIG. 1-2) JP-A-6-270208 (page 2-3, FIG. 1) Japanese Patent Laid-Open No. 10-44197 (second page, FIG. 1)

本発明は、中央部から周縁部まで厚みが均一でむらがなく、金型表面の微細な凹凸模様を正確に転写し、光学材料として好適に用いることができる厚物平板成形品及びその製造方法を提供することを目的としてなされたものである。
本発明者らは、上記の課題を解決すべく鋭意研究を重ねた結果、熱可塑性樹脂の射出成形により厚物平板成形品を製造すると、厚物平板成形品の周縁部の厚みが中央部の厚みよりも厚くなり、そのために厚物平板成形品を液晶表示装置の導光板として用いたとき、画面の周縁部に明線や暗帯などの輝度の異なる縞状の部分が生ずること、及び、射出成形用金型の端辺を加熱して金型の中央部より高温に保つことにより、厚物平板成形品の周縁部の厚みと中央部の厚みとの差が減少し、厚物平板成形品を液晶表示装置の導光板として用いたとき、画面の周縁部に明線や暗帯などが発生しなくなることを見いだし、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）射出成形法により製造された熱可塑性樹脂を含んでなる長方形の厚物平板成形品において、以下の式
ギャップ値 ＝ ｛（ＴＭＡＸ−ＴＭＩＮ）／ＴＣＥＮＴＥＲ｝×１００
（ただし、上記式において、ＴＭＡＸは平板成形品の最大厚み、ＴＭＩＮは平板成形品の最小厚み、ＴＣＥＮＴＥＲは平板成形品の中央部の厚みをそれぞれ表す）
で表されるギャップ値が３％以下であることを特徴とする厚物平板成形品、
（２）ギャップ値が１％以下である第１項記載の厚物平板成形品、
（３）中央部の厚みが、３〜５０ｍｍである第１項又は第２項記載の厚物平板成形品、
（４）熱可塑性樹脂が、脂環式構造を有する樹脂である第１項乃至第３項のいずれか１項に記載の厚物平板成形品、
（５）熱可塑性樹脂が、メタクリル樹脂又は（メタ）アクリル酸アルキルエステル−芳香族ビニル化合物共重合体である第１項乃至第３項のいずれか１項に記載の厚物平板成形品、
（６）液晶表示装置の導光板であ第１項乃至第５項のいずれか１項に記載の厚物平板成形品、及び
（７）熱可塑性樹脂の厚物平板成形品を射出成形法により製造するに際して、射出成形用金型の長方形のキャビティの少なくとも１対の対向する２端辺の温度が、金型のキャビティの中央部の最高温度よりも２℃以上高く維持されるように金型を加熱することを特徴とする第１項乃至第６項のいずれか１項に記載の厚物平板成形品の製造方法、
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、
（８）１つの成形サイクル中に、金型内の熱媒体流路に通液する熱媒体を高温の熱媒体と低温の熱媒体に切り替えて、射出時の金型のキャビティの中央部の温度を高く、冷却時の金型のキャビティの中央部の温度を低くする第６項記載の厚物平板成形品の製造方法、
を挙げることができる。The present invention provides a thick flat plate molded product that can be used as an optical material, and can be suitably used as an optical material, by accurately transferring a fine uneven pattern on the mold surface with a uniform thickness from the central portion to the peripheral portion. It was made for the purpose of providing.
As a result of intensive studies to solve the above problems, the inventors of the present invention have produced a thick flat plate molded product by injection molding of a thermoplastic resin. When the thick flat plate molded product is used as a light guide plate of a liquid crystal display device for that reason, striped portions with different luminance such as bright lines and dark bands are generated at the peripheral edge of the screen, and By heating the edge of the mold for injection molding to a temperature higher than the central part of the mold, the difference between the thickness of the peripheral part of the thick flat plate molded product and the thickness of the central part is reduced. When the product is used as a light guide plate of a liquid crystal display device, it has been found that bright lines, dark bands and the like are not generated at the periphery of the screen, and the present invention has been completed based on this finding.
That is, the present invention
(1) In a rectangular thick flat plate molded article comprising a thermoplastic resin produced by an injection molding method, the following formula: gap value = {(T MAX −T MIN ) / T CENTER } × 100
(In the above formula, T MAX represents the maximum thickness of the flat plate molded product, T MIN represents the minimum thickness of the flat plate molded product, and T CENTER represents the thickness of the central portion of the flat plate molded product.)
A thick flat plate molded product characterized in that the gap value represented by
(2) The thick plate molded article according to the first item, wherein the gap value is 1% or less,
(3) The thick plate molded article according to the first or second item, wherein the thickness of the central part is 3 to 50 mm,
(4) The thick plate molded article according to any one of Items 1 to 3, wherein the thermoplastic resin is a resin having an alicyclic structure,
(5) The thick plate molded article according to any one of Items 1 to 3, wherein the thermoplastic resin is a methacrylic resin or a (meth) acrylic acid alkyl ester-aromatic vinyl compound copolymer,
(6) A thick plate molded product according to any one of items 1 to 5 as a light guide plate of a liquid crystal display device, and (7) a thick plate molded product of a thermoplastic resin by an injection molding method. At the time of manufacture, the mold is such that the temperature of at least one pair of opposing two sides of the rectangular cavity of the injection mold is maintained at 2 ° C. or higher than the maximum temperature at the center of the mold cavity. The method for producing a thick flat plate molded article according to any one of items 1 to 6, wherein
Is to provide.
Furthermore, as a preferred embodiment of the present invention,
(8) During one molding cycle, the heat medium flowing through the heat medium flow path in the mold is switched between a high temperature heat medium and a low temperature heat medium, and the temperature at the center of the mold cavity during injection The method for producing a thick flat plate molded article according to claim 6, wherein the temperature of the central portion of the mold cavity during cooling is lowered,
Can be mentioned.

Ｆｉｇ．１は射出成形法により製造された厚物平板成形品の模式的断面図、Ｆｉｇ．２は液晶表示装置の画面の説明図、Ｆｉｇ．３は厚物平板成形品の中央部の説明図、Ｆｉｇ．４は本発明方法におけるキャビティの端辺の加熱方法の一態様を示す説明図である。図中、符号１は中央部、２は端辺、３は明線、４は暗帯、５はキャビティ、６は棒状ヒーターである。  FIG. 1 is a schematic cross-sectional view of a thick flat plate product manufactured by an injection molding method, FIG. 2 is an explanatory diagram of a screen of a liquid crystal display device, FIG. 3 is an explanatory view of the central part of the thick flat plate molded product, FIG. 4 is an explanatory view showing one embodiment of a method for heating the edge of the cavity in the method of the present invention. In the figure, reference numeral 1 is a central portion, 2 is an edge, 3 is a bright line, 4 is a dark belt, 5 is a cavity, and 6 is a bar heater.

本発明の厚物平板成形品は、射出成形法により製造された熱可塑性樹脂の長方形の厚物平板成形品において、最大厚みと最小厚みとの差が、中央部の厚みの３％以下、より好ましくは２％以下、特に好ましくは１％以下である厚物平板成形品である。本発明の厚物平板成形品及びその製造方法を適用する対象に特に制限はないが、導光板、光拡散板、反射板などの表面に厳しい平面性が要求される大型の厚物平板成形品に好適に適用することができるが、液晶表示装置の導光板に特に好適に適用することができる。
Ｆｉｇ．１は、射出成形法により製造された厚物平板成形品の模式的断面図である。厚物平板成形品を射出成形法により製造すると、中央部１よりも端辺２の厚みが厚い成形品が得られる。このような成形品を液晶表示装置の導光板として用いると、画面の入光面の近くに、Ｆｉｇ．２に模式的に示すような、輝度の強い線状の明線３や、輝度の弱い帯状の暗帯４などが現れて、画質を低下させる。液晶表示装置の導光板として、最大厚みと最小厚みとの差が中央部の厚みの３％以下である本発明の厚物平板成形品を用いることにより、明線や暗帯などのない外観品質の良好な画面を得ることができる。
本発明において、厚物平板成形品の中央部とは、長方形の厚物平板成形品の対角線の交点である。厚物平板成形品が正確な長方形の形状でない場合は、その形状の各辺を延長して形成される長方形の対角線の交点を中央部とする。このとき、各辺の延長により補われる部分と除かれる部分の合計面積が最小になるように各辺を延長して長方形を形成する。Ｆｉｇ．３は、厚物平板成形品の中央部の説明図である。本図の３例に示すように、各例において、点線で示すように各辺を延長して長方形を形成し、例えば、中央の図の一点鎖線で示すようには各辺を延長しない。
本発明の厚物平板成形品においては、中央部の厚みが３〜５０ｍｍであることが好ましく、５〜２０ｍｍであることがより好ましい。中央部の厚みが３ｍｍ未満の平板成形品は、最大厚みと最小厚みとの差が中央部の厚みの３％を超えても、明線や暗帯などの光学的な不都合が生じにくい。中央部の厚みが５０ｍｍを超える厚物平板成形品は、冷却に長時間を要するので射出成形法により製造することは得策ではない
本発明に用いる熱可塑性樹脂に特に制限はなく、例えば、脂環式構造を有する樹脂、メタクリル樹脂、ポリカーボネート、ポリスチレン、アクリロニトリル−スチレン共重合体樹脂、（メタ）アクリル酸エステル−芳香族ビニル化合物共重合体、好ましくはメタクリル酸メチル−スチレン共重合体樹脂、ＡＢＳ樹脂、ポリエーテルスルホンなどを挙げることができる。これらの中で、脂環式構造を有する樹脂、メタクリル樹脂及び（メタ）アクリル酸エステル−芳香族ビニル化合物共重合体を好適に用いることができ、脂環式構造を有する樹脂を特に好適に用いることができる。
脂環式構造を有する樹脂は、溶融樹脂の流動性が良好なので、金型のキャビティ表面の微細な凹凸模様を正確に転写することができ、吸湿性が極めて低いので、寸法安定性に優れ、厚物平板成形品に反りを生ずることがなく、比重が小さいので、大型の厚物平板成形品を軽量化することができる。
脂環式構造を有する樹脂としては、主鎖又は側鎖に脂環式構造を有する重合体樹脂を挙げることができる。主鎖に脂環式構造を有する重合体樹脂は、機械的強度と耐熱性が良好なので、特に好適に用いることができる。脂環式構造は、飽和環状炭化水素構造であることが好ましく、その炭素数は、４〜３０であることが好ましく、５〜２０であることがより好ましく、５〜１５であることがさらに好ましい。脂環式構造を有する重合体樹脂中の脂環式構造を有する繰り返し単位の割合は、５０重量％以上であることが好ましく、７０重量％以上であることがより好ましく、９０重量％以上であることがさらに好ましい。
脂環式構造を有する樹脂としては、例えば、ノルボルネン系単量体の開環重合体若しくは開環共重合体又はそれらの水素添加物、ノルボルネン系単量体の付加重合体若しくは付加共重合体又はそれらの水素添加物、単環の環状オレフィン系単量体の重合体又はその水素添加物、環状共役ジエン系単量体の重合体又はその水素添加物、ビニル脂環式炭化水素系単量体の重合体若しくは共重合体又はそれらの水素添加物、ビニル芳香族炭化水素系単量体の重合体又は共重合体の芳香環を含む不飽和結合部分の水素添加物などを挙げることができる。これらの中で、ノルボルネン系単量体の重合体の水素添加物及びビニル芳香族炭化水素系単量体の重合体の芳香環を含む不飽和結合部分の水素添加物は、機械的強度と耐熱性に優れるので、特に好適に用いることができる。
メタクリル樹脂としては、メタクリル酸メチルに由来する繰返し単位を全繰返し単位に対し好ましくは８０モル％以上含有するものを挙げることができる。中でも、ＡＳＴＭ Ｄ１２３８に準拠して２３０℃、３７．３ｋｇの荷重下で測定したメルトフローレートが、０．５〜２０ｇ／１０分のメタクリル樹脂が好ましい。（メタ）アクリル酸アルキルエステル−芳香族ビニル化合物共重合体は、芳香族ビニル化合物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化合物とを共重合して得られる。
芳香族ビニル化合物としては、スチレン、α−メチルスチレン、ｍ−メチルスチレン、ｐ−メチルスチレン、ｏ−クロルスチレン、ｐ−クロルスチレン等が挙げられる。これらを単独若しくは２種以上併用して使用してもよい。
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化合物としては、炭素数１〜４のアルキル基、好ましくは炭素数１又は２のアルキル基を有する（メタ）アクリル酸アルキルエステルが挙げられ、具体的にはメタクリル酸メチル、メタクリル酸エチル、アクリル酸メチル、アクリル酸エチルが挙げられる。これらを単独若しくは２種以上併用して使用してもよい。
前記共重合体を構成する各成分の割合は、芳香族ビニル化合物が９５〜５重量％、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化合物が５〜９５重量％の範囲である。中でも、光学特性、成形性などの点から、上記芳香族ビニル化合物が６０〜２０重量％、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化合物が８０〜４０重量％の範囲が好ましい。
本発明に用いる熱可塑性樹脂のガラス転移温度Ｔｇは、８０℃以上、好ましくは９０〜２５０℃である＿。ガラス転移温度Ｔｇは、ＪＩＳ Ｋ ７１２１に準拠して、示差走査熱量測定（ＤＳＣ）により測定する。
なお、本発明の厚物平板成形品を導光板として用いる場合、上述した樹脂に、必要に応じて、その他のポリマー、各種配合剤又は充填剤を単独あるいは２種以上混合して用いることができる。その他のポリマーとしては、ポリブタジエン、ポリアクリレートなどのゴム又は樹脂が挙げられる。
配合剤としては、酸化防止剤、紫外線吸収剤、光安定剤、近赤外線吸収剤、染料や顔料などの着色剤、滑剤、可塑剤、帯電防止剤、蛍光増白剤などの配合剤が挙げられる。また、導光板は、必ずしも透明である必要はなく、ポリスチレン系重合体、ポリシロキサン系重合体又はこれらの架橋物からなる微粒子を配合し光散乱能を付与することもできる。
上記その他のポリマー、各種配合剤又は充填材は、単独で、あるいは２種以上を組み合わせて用いることができ、その配合量は本発明の目的を損なわない範囲で適宜選択され、熱可塑性樹脂１００重量部に対して、通常０〜５重量部、好ましくは０〜３重量部である。
本発明の厚物平板成形品の製造方法においては、熱可塑性樹脂の厚物平板成形品を射出成形法により製造するに際して、射出成形用金型の長方形のキャビティの少なくとも１対の対向する２端辺の温度が、金型のキャビティの中央部の最高温度よりも２℃以上高く維持されるように金型を加熱する。キャビティの中央部の温度とは、厚物平板成形品の中央部が接触する金型の中央部の温度をいう。また、対向する２端辺の温度とは、厚物平板成形品と接触する金型の２端辺の温度をいう。なお、２端辺に温度分布がある場合は、その最も低い部分の温度をキャビティの中央部の最高温度よりも２℃以上高く維持する必要がある。Ｆｉｇ．４は、本発明方法におけるキャビティの端辺の加熱方法の一態様を示す説明図である。本図においては、金型のキャビティ５の１対の対向する２長辺に発熱抵抗体からなる棒状ヒーター６が埋め込まれている。棒状ヒーターに通電する電圧を調節することにより、キャビティの端辺の温度を制御することができる。Ｆｉｇ．４に示す態様においては、金型のキャビティの１対の対向する２長辺を加熱しているが、さらに、他の２辺にも棒状ヒーターを埋め込んで、キャビティの２対の対向する４端辺を加熱することもできる。本発明方法において、キャビティの端辺を加熱する方法に特に制限はなく、例えば、金型内のキャビティの端辺の近傍に熱媒体の流路を設け、高温の熱媒体を通液することにより加熱することができる。
本発明方法においては、金型のキャビティの少なくとも１対の対向する２端辺の温度をキャビティの中央部の温度より高くすることにより、厚物平板成形品の周縁部が厚くなることを防ぎ、厚みむらの少ない、優れた平面性を有する厚物平板成形品を得ることができる。また、厚物平板成形品が導光板である場合、出光面には光を拡散するための微細なプリズムパターンが設けられ、反射面には光の反射方向を制御するための微細な突起などのパターンが設けられる場合が多い。ゲートからキャビティ内に送られた溶融樹脂は、キャビティ内を流動して端辺まで到達し、キャビティを充填する。しかし、キャビティ内を流動する間に溶融樹脂の温度が下がり、キャビティの端辺では金型の微細な凹凸模様の転写が不完全になりやすい。本発明方法によれば、溶融樹脂の温度が下がりやすいキャビティの端辺の温度をキャビティ中央部の最高温度より高くすることにより、金型の微細な凹凸模様の転写性を高めることができる。
本発明方法において、金型の温度調節方法に特に制限はなく、例えば、金型内の熱媒体の流路に一定温度の熱媒体を通液して、金型温度を一定に制御することができ、あるいは、射出成形の１サイクルの中で、高温の熱媒体と低温の熱媒体を切り替えて通液し、射出時には金型温度を高くして、溶融樹脂の流動性と転写性を高め、冷却時には金型温度を低くして、成形サイクルを短くし、生産性を向上することもできる。金型温度を一定に制御する場合は、その温度がキャビティ中央部の最高温度となり、高温の熱謀体と低温の熱媒体を切り替えて通液する場合は、１成形サイクル中にキャビティの中央部が到達する最も高い温度が、キャビティの中央部の最高温度である。
本発明方法において、金型のキャビティの少なくとも１対の対向する２端辺の温度は、キャビティの中央部の最高温度より２℃以上高く、より好ましくは３〜３０℃高く、さらに好ましくは５〜２０℃高く維持する。金型のキャビティの端辺の温度とキャビティの中央部の最高温度の差が２℃未満であると、厚物平板成形品の厚みむらを減少する効果と、金型の微細な凹凸模様を正確に転写する効果が十分に発現しないおそれがある。金型のキャビティの端辺の温度とキャビティの中央部の最高温度の差が大きすぎると、成形サイクルが延びて生産性が低下するおそれがある。
本発明においては、通常Ｔｇ＋１００（℃）〜Ｔｇ＋２００（℃）、好ましくはＴｇ＋１５０（℃）〜Ｔｇ＋２００（℃）の樹脂温度で、通常Ｔｇ−５０（℃）、好ましくはＴｇ−３０（℃）〜Ｔｇ（℃）の金型温度で射出成形する。なお、前記Ｔｇは、用いる熱可塑性樹脂のガラス転移温度（単位は℃）である。In the thick flat plate molded product of the present invention, the difference between the maximum thickness and the minimum thickness is 3% or less of the thickness of the central portion in the rectangular thick flat plate molded product of the thermoplastic resin manufactured by the injection molding method. It is preferably a thick flat plate molded product of 2% or less, particularly preferably 1% or less. There are no particular restrictions on the object to which the thick plate molded product of the present invention and the manufacturing method thereof are applied, but a large thick plate molded product that requires strict flatness on the surface of a light guide plate, light diffusing plate, reflector, etc. However, it can be particularly preferably applied to a light guide plate of a liquid crystal display device.
FIG. 1 is a schematic cross-sectional view of a thick flat plate product manufactured by an injection molding method. When a thick flat plate molded product is manufactured by an injection molding method, a molded product having a thicker edge 2 than the central portion 1 is obtained. When such a molded product is used as a light guide plate of a liquid crystal display device, FIG. As shown schematically in FIG. 2, a bright line 3 having a high luminance, a dark band 4 having a low luminance, and the like appear, thereby degrading the image quality. As a light guide plate of a liquid crystal display device, by using the thick flat plate molded product of the present invention in which the difference between the maximum thickness and the minimum thickness is 3% or less of the thickness of the central portion, the appearance quality free from bright lines and dark bands A good screen can be obtained.
In the present invention, the central portion of the thick flat plate molded product is an intersection of diagonal lines of the rectangular thick flat plate molded product. When the thick flat plate molded product is not an accurate rectangular shape, the intersection of the diagonal lines of the rectangle formed by extending each side of the shape is set as the central portion. At this time, each side is extended to form a rectangle so that the total area of the portion supplemented by the extension of each side and the portion removed is minimized. FIG. 3 is explanatory drawing of the center part of a thick flat plate molded product. As shown in the three examples of this figure, in each example, each side is extended as shown by a dotted line to form a rectangle, and for example, each side is not extended as shown by a one-dot chain line in the center figure.
In the thick flat plate molded article of the present invention, the thickness of the central portion is preferably 3 to 50 mm, and more preferably 5 to 20 mm. In a flat plate molded product having a thickness of less than 3 mm in the central portion, even if the difference between the maximum thickness and the minimum thickness exceeds 3% of the thickness of the central portion, optical inconveniences such as bright lines and dark bands are unlikely to occur. Thick plate molded products having a thickness of more than 50 mm in the central part are not suitable to manufacture by injection molding because it takes a long time for cooling. There is no particular limitation on the thermoplastic resin used in the present invention. Resin having formula structure, methacrylic resin, polycarbonate, polystyrene, acrylonitrile-styrene copolymer resin, (meth) acrylic acid ester-aromatic vinyl compound copolymer, preferably methyl methacrylate-styrene copolymer resin, ABS resin And polyethersulfone. Among these, a resin having an alicyclic structure, a methacrylic resin, and a (meth) acrylic acid ester-aromatic vinyl compound copolymer can be preferably used, and a resin having an alicyclic structure is particularly preferably used. be able to.
Since the resin having an alicyclic structure has good flowability of the molten resin, it can accurately transfer the fine uneven pattern on the cavity surface of the mold and has extremely low hygroscopicity, so it has excellent dimensional stability, Since the thick flat plate molded product does not warp and has a small specific gravity, a large thick flat plate molded product can be reduced in weight.
Examples of the resin having an alicyclic structure include polymer resins having an alicyclic structure in the main chain or side chain. A polymer resin having an alicyclic structure in the main chain can be particularly preferably used because it has good mechanical strength and heat resistance. The alicyclic structure is preferably a saturated cyclic hydrocarbon structure, and the carbon number thereof is preferably 4 to 30, more preferably 5 to 20, and further preferably 5 to 15. . The ratio of the repeating unit having an alicyclic structure in the polymer resin having an alicyclic structure is preferably 50% by weight or more, more preferably 70% by weight or more, and 90% by weight or more. More preferably.
Examples of the resin having an alicyclic structure include a ring-opening polymer or a ring-opening copolymer of a norbornene monomer or a hydrogenated product thereof, an addition polymer or an addition copolymer of a norbornene monomer, or Those hydrogenated products, polymers of monocyclic olefin monomers or hydrogenated products thereof, polymers of cyclic conjugated diene monomers or hydrogenated products thereof, vinyl alicyclic hydrocarbon monomers Or a hydrogenated product thereof, a polymer of a vinyl aromatic hydrocarbon monomer, or a hydrogenated product of an unsaturated bond part containing an aromatic ring of the copolymer. Among these, hydrogenated products of norbornene-based monomer polymers and hydrogenated products of unsaturated bonds containing aromatic rings of vinyl aromatic hydrocarbon-based monomer polymers have mechanical strength and heat resistance. Since it is excellent in property, it can be used especially suitably.
As a methacryl resin, what contains 80 mol% or more of repeating units derived from methyl methacrylate preferably with respect to all the repeating units can be mentioned. Among them, a methacrylic resin having a melt flow rate of 0.5 to 20 g / 10 min measured at 230 ° C. under a load of 37.3 kg in accordance with ASTM D1238 is preferable. The (meth) acrylic acid alkyl ester-aromatic vinyl compound copolymer is obtained by copolymerizing an aromatic vinyl compound and a (meth) acrylic acid alkyl ester compound having a lower alkyl group.
Examples of the aromatic vinyl compound include styrene, α-methylstyrene, m-methylstyrene, p-methylstyrene, o-chlorostyrene, p-chlorostyrene, and the like. You may use these individually or in combination of 2 or more types.
Examples of the (meth) acrylic acid alkyl ester compound having a lower alkyl group include (meth) acrylic acid alkyl esters having an alkyl group having 1 to 4 carbon atoms, preferably an alkyl group having 1 or 2 carbon atoms. Includes methyl methacrylate, ethyl methacrylate, methyl acrylate, and ethyl acrylate. You may use these individually or in combination of 2 or more types.
The proportion of each component constituting the copolymer is 95 to 5% by weight of the aromatic vinyl compound and 5 to 95% by weight of the (meth) acrylic acid alkyl ester compound having a lower alkyl group. Among them, the aromatic vinyl compound is preferably 60 to 20% by weight and the (meth) acrylic acid alkyl ester compound having a lower alkyl group is preferably 80 to 40% by weight from the viewpoint of optical properties, moldability and the like.
The glass transition temperature Tg of the thermoplastic resin used for this invention is 80 degreeC or more, Preferably it is 90-250 degreeC. The glass transition temperature Tg is measured by differential scanning calorimetry (DSC) according to JIS K7121.
In addition, when using the thick plate molding of this invention as a light-guide plate, another polymer, various compounding agents, or fillers can be used individually or in mixture of 2 or more types as needed to the resin mentioned above. . Other polymers include rubbers or resins such as polybutadiene and polyacrylate.
Examples of the compounding agents include antioxidants, ultraviolet absorbers, light stabilizers, near infrared absorbers, coloring agents such as dyes and pigments, lubricants, plasticizers, antistatic agents, fluorescent whitening agents, and the like. . Moreover, the light guide plate does not necessarily need to be transparent, and a light scattering ability can be imparted by blending fine particles comprising a polystyrene polymer, a polysiloxane polymer, or a cross-linked product thereof.
The above-mentioned other polymers, various compounding agents or fillers can be used alone or in combination of two or more thereof, and the blending amount is appropriately selected within a range not impairing the object of the present invention, and the thermoplastic resin is 100 wt. The amount is usually 0 to 5 parts by weight, preferably 0 to 3 parts by weight with respect to parts.
In the method for manufacturing a thick flat plate molded article of the present invention, when manufacturing a thick flat plate molded article of a thermoplastic resin by an injection molding method, at least one pair of opposed two ends of a rectangular cavity of an injection mold. The mold is heated so that the temperature of the side is maintained at 2 ° C. or more higher than the maximum temperature at the center of the mold cavity. The temperature of the central part of the cavity refers to the temperature of the central part of the mold with which the central part of the thick flat plate product comes into contact. Moreover, the temperature of two opposing edges means the temperature of the two edges of the mold that comes into contact with the thick flat plate molded product. In the case where there is a temperature distribution at the two end sides, it is necessary to keep the temperature of the lowest part 2 ° C. or more higher than the maximum temperature of the central part of the cavity. FIG. 4 is an explanatory view showing one embodiment of a method for heating the edge of the cavity in the method of the present invention. In this figure, a bar heater 6 made of a heating resistor is embedded in a pair of two opposing long sides of a cavity 5 of a mold. The temperature at the edge of the cavity can be controlled by adjusting the voltage applied to the rod heater. FIG. In the embodiment shown in FIG. 4, two opposing long sides of the mold cavity are heated, but a bar heater is also embedded in the other two sides to provide two opposing ends of the cavity pair. The sides can also be heated. In the method of the present invention, the method for heating the edge of the cavity is not particularly limited. For example, by providing a heat medium flow path in the vicinity of the edge of the cavity in the mold and passing a high-temperature heat medium. Can be heated.
In the method of the present invention, by making the temperature of at least one pair of two opposite sides of the cavity of the mold higher than the temperature of the central part of the cavity, it is possible to prevent the peripheral part of the thick plate molded product from becoming thick, A thick flat plate molded article having excellent flatness with little thickness unevenness can be obtained. In addition, when the thick flat plate molded product is a light guide plate, a fine prism pattern for diffusing light is provided on the light exit surface, and a fine protrusion for controlling the light reflection direction is provided on the reflective surface. A pattern is often provided. The molten resin sent from the gate into the cavity flows in the cavity, reaches the end, and fills the cavity. However, the temperature of the molten resin decreases while flowing in the cavity, and the transfer of the fine uneven pattern of the mold tends to be incomplete at the end of the cavity. According to the method of the present invention, by making the temperature of the edge of the cavity where the temperature of the molten resin tends to be lower than the maximum temperature at the center of the cavity, the transferability of the fine uneven pattern of the mold can be improved.
In the method of the present invention, there is no particular limitation on the mold temperature adjustment method. For example, the mold temperature can be controlled to be constant by passing a heat medium at a constant temperature through the flow path of the heat medium in the mold. Or, in one cycle of injection molding, switch between high temperature heat medium and low temperature heat medium and let liquid flow at the time of injection, increase the mold temperature, improve the fluidity and transferability of the molten resin, During cooling, the mold temperature can be lowered, the molding cycle can be shortened, and the productivity can be improved. When the mold temperature is controlled to be constant, the temperature becomes the maximum temperature in the center of the cavity, and when the high temperature heat shield and the low temperature heat medium are switched and passed through, the center of the cavity during one molding cycle. The highest temperature reached by is the highest temperature in the middle of the cavity.
In the method of the present invention, the temperature of at least one pair of two opposite sides of the cavity of the mold is 2 ° C. or higher, more preferably 3 to 30 ° C., more preferably 5 to 5 ° C. higher than the maximum temperature at the center of the cavity. Keep 20 ° C higher. If the difference between the temperature at the edge of the mold cavity and the maximum temperature at the center of the cavity is less than 2 ° C, the thickness unevenness of the thick flat plate molded product can be reduced and the fine uneven pattern on the mold can be accurately measured. There is a risk that the effect of transferring to the surface will not be sufficiently developed. If the difference between the temperature at the edge of the mold cavity and the maximum temperature at the center of the cavity is too large, the molding cycle may be extended and productivity may be reduced.
In the present invention, the resin temperature is usually Tg + 100 (° C.) to Tg + 200 (° C.), preferably Tg + 150 (° C.) to Tg + 200 (° C.), and usually Tg-50 (° C.), preferably Tg-30 (° C.) to Tg. Injection molding is performed at a mold temperature of (° C). The Tg is the glass transition temperature (unit: ° C.) of the thermoplastic resin used.

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、実施例及び比較例において、厚物平板成形品は下記の方法により評価した。
（１）ギャップ値
導光板の対角線の交点を中央部とし、中央部を通る短辺に平行な直線上で、導光板の端から端まで０．１ｍｍ間隔で、非接触三次元測定器［三鷹光器（株）、ＮＨ−３］を用いて厚みを測定し、次式によりギャップ値を求める。
ギャップ値 ＝ ｛（ＴＭＡＸ−ＴＭＩＮ）／ＴＣＥＮＴＥＲ｝×１００
ただし、上記式において、ＴＭＡＸは導光板の最大厚み、ＴＭＩＮは導光板の最小厚み、ＴＣＥＮＴＥＲは導光板の中央部の厚みをそれぞれ表す。
（２）転写率
短辺２７６．４ｍｍ、長辺３４４．０ｍｍの導光板の対角線の交点を中央部とし、中央部を通る短辺に平行な直線上で、中央部、中央部から６９．１ｍｍ、１０３．６ｍｍ、１３２ｍｍから１３８ｍｍまで０．５ｍｍピッチで１３点及び１３８．２ｍｍで、超深度顕微鏡［（株）キーエンス、ＶＫ−９５００］を用いて円柱状の突起の高さｈ（μｍ）を測定し、各点について下式により転写率を求め、さらに求めた数値から平均値と標準偏差を算出する。
転写率＝（ｈ／ｈｔ）×１００（％）
ただし、ｈｔは金型から計算される円柱状の突起の理論高さ（μｍ）であり、金型キャビティの円柱状の窪みの深さに等しい。
（３）外観品質
導光板の２つの長辺に、冷陰極蛍光ランプ［ハリソン東芝ライティング（株）、ＭＢＳＭ２４ＪＮ１０ＷＸ３７０ＮＬＵ］各１本を取り付けて液晶表示装置を組み立て、目視により、ランプ近傍の明線と暗帯に着目して、外観品質を検査する。
［実施例１］
熱可塑性樹脂として、脂環式構造を有する樹脂の一種であるノルボルネン系重合体［日本ゼオン（株）、ＺＥＯＮＯＲ１０６０Ｒ、ガラス転移温度１００℃］を用い、射出成形機［東芝機械（株）、ＩＳ３５０ＧＳ、スクリュー径７０ｍｍ、型締め力３，４３０ｋＮ］を用いて、射出成形法により１７インチ型導光板を製造した。
成形品の寸法は、短辺２７６．４ｍｍ、長辺３４４．０ｍｍ、厚み８．０ｍｍである。導光板の出光面となる金型の可動側のキャビティの表面には、光を拡散するプリズムパターンとして、断面が底辺５０μｍ、頂角１４０度の二等辺三角形である単位プリズムを、隣接する単位プリズム同士が下端で接する状態で、長辺に対して垂直に設けた。導光板の反射面となる金型の固定側のキャビティの表面には、直径８０μｍ、高さ８０μｍの円柱状の突起を形成する穴を、キャビティの２つの長辺の中間のピッチ１３０μｍから、長辺の近傍のピッチ３００μｍまで順次拡大して設けた。金型のキャビティの２つの長辺に隣接して、８００Ｗの棒状ヒーターを１本ずつ埋め込んだ。また、キャビティの１つの短辺に、ファンゲートを設けた。
上記の射出成形機と金型を用いて、成形温度２７０℃、金型温度８５℃、金型の長辺近傍温度９５℃とし、射出時間５秒、射出後１５ＭＰａの保圧を１０秒加え、その後冷却１２０秒、取り出し５秒、成形サイクル１４０秒で導光板の射出成形を行った。金型温度は、金型内流路に通水する温水の温度を８０℃に保つことにより調節し、金型の長辺近傍温度は、棒状ヒーターに通電する電圧を制御することにより、９５℃に保った。金型のキャビティの中央部の最高温度は８５℃、キャビティの長辺の温度は９５℃であった。
得られた導光板の最大厚みは８．０１１ｍｍ、最小厚みは７．９９５ｍｍ、中央部の厚みは８．００１ｍｍであり、ギャップ値は０．２０％であった。転写率の平均値は８９．５％であり、標準偏差は０．３４％であった。この導光板を用いて外観品質を評価したところ、液晶表示装置の画面に明線、暗帯はなく、外観品質は良好であった。
［実施例２］
取り出し５秒、射出５秒、保圧１０秒の間は、金型内流路に９０℃の温水を通水し、冷却１００秒の間は金型内流路に２５℃の冷水を通水した以外は、実施例１と同じ条件で、導光板の射出成形を行った。金型のキャビティの中央部の最高温度は９０℃、キャビティの長辺の温度は９５℃であった。
得られた導光板の最大厚みは８．０１８ｍｍ、最小厚みは７．９８９ｍｍ、中央部の厚みは８．００５ｍｍであり、ギャップ値は０．３６％であった。転写率の平均値は９３．７％であり、標準偏差は０．１８％であった。この導光板を用いて外観品質を評価したところ、液晶表示装置の画面に明線、暗帯はなく、外観品質は良好であった。
［実施例３］
熱可塑性樹脂として、脂環式構造を有する樹脂の代わりに、メタクリル樹脂［旭化成（株）、デルペット８０ＮＨ］を用い、成形温度を２６０℃とした以外は、実施例１と同じ条件で、導光板の射出成形を行った。
得られた導光板の最大厚みは８．０２５ｍｍ、最小厚みは７．９９４ｍｍ、中央部の厚みは８．０１５ｍｍであり、ギャップ値は０．３９％であった。転写率の平均値は８０．３％であり、標準偏差は１．５０％であった。この導光板を用いて外観品質を評価したところ、液晶表示装置の画面に明線、暗帯はなく、外観品質は良好であった。
［実施例４］
熱可塑性樹脂として、脂環式構造を有する樹脂の代わりに、メタクリル酸エステル−芳香族ビニル化合物共重合体［新日鐵化学（株）、エスチレンＭＳ−６００］を用いた他は、実施例１と同じ条件で、導光板の射出成形を行った。
得られた導光板の最大厚みは８．０５２ｍｍ、最小厚みは７．９７８ｍｍ、中央部の厚みは８．０４０ｍｍであり、ギャップ値は０．９２％であった。転写率の平均値は８２．４％、標準偏差は１．８２％であった。この導光板を用いて外観品質を評価したところ、液晶表示装置の画面に明線、暗帯はなく、外観品質は良好であった。
比較例１
金型のキャビティの２つの長辺に隣接して埋め込んだ棒状ヒーターを取り外し、長辺側からの加熱を行わなかった以外は、実施例１と同じ条件で、導光板の射出成形を行った。金型のキャビティの中央部の最高温度は８５℃、キャビティの長辺の温度は８５℃であった。
得られた導光板の最大厚みは８．１０２ｍｍ、最小厚みは７．８０８ｍｍ、中央部の厚みは８．００５ｍｍであり、ギャップ値は３．６７％であった。転写率の平均値は８４．９％であり、標準偏差は１１．９８％であった。この導光板を用いて外観品質を評価したところ、液晶表示装置の画面の長辺近傍に、明線と暗帯が現れ、外観品質は不良であった。
実施例１〜４及び比較例１の結果を、第１表に示す。

Figure 2005030468
第１表に見られるように、金型のキャビティの２つの長辺に隣接して棒状ヒーターを埋め込み、金型のキャビティの長辺近傍の温度を金型のキャビティ中央部の最高温度よりも高く保った実施例１〜４の導光板は、厚みむらと円柱状の突起の転写率のばらつきが小さく、液晶表示装置の画面に明線や暗帯などがなく、良好な性能を有している。特に、脂環式構造を有する樹脂を用いた実施例１〜２の導光板の性能が優れている。これに対して、金型のキャビティの端辺を加熱しなかった比較例１の導光板は、厚みむらと円柱状の突起の転写率のばらつきが大きく、液晶表示装置の画面に明線と暗帯が現れる。Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, thick plate molded products were evaluated by the following methods.
(1) Gap value The non-contact three-dimensional measuring instrument [Mitaka, with the intersection of the diagonals of the light guide plate as the center and a straight line parallel to the short side passing through the center at intervals of 0.1 mm from end to end of the light guide plate Thickness is measured using an optical apparatus, NH-3], and a gap value is obtained by the following formula.
Gap value = {(T MAX −T MIN ) / T CENTER } × 100
In the above formula, T MAX represents the maximum thickness of the light guide plate, T MIN represents the minimum thickness of the light guide plate, and T CENTER represents the thickness of the central portion of the light guide plate.
(2) Transfer rate The intersection of diagonal lines of the light guide plate having a short side of 276.4 mm and a long side of 344.0 mm is the central part, and the central part is 69.1 mm from the central part on a straight line parallel to the short side. 103.6 mm, 132 mm to 138 mm at a pitch of 0.5 mm with 13 points and 138.2 mm, and using a super depth microscope [Keyence Co., Ltd., VK-9500], the height of the cylindrical projection h (μm) Measure the transfer rate for each point using the following formula, and calculate the average value and standard deviation from the calculated values.
Transfer rate = (h / h t ) × 100 (%)
Here, ht is the theoretical height (μm) of the cylindrical projection calculated from the mold, and is equal to the depth of the cylindrical depression of the mold cavity.
(3) Appearance quality A cold-cathode fluorescent lamp [Harrison Toshiba Lighting Co., Ltd., MBSM24JN10WX370NLU] is attached to each of the two long sides of the light guide plate, and a liquid crystal display is assembled. Pay attention to the belt and inspect the appearance quality.
[Example 1]
As a thermoplastic resin, a norbornene polymer [Nippon Zeon Co., Ltd., ZEONOR 1060R, glass transition temperature 100 ° C.], which is a kind of resin having an alicyclic structure, is used, and an injection molding machine [Toshiba Machine Co., Ltd., IS350GS, A 17-inch light guide plate was manufactured by an injection molding method using a screw diameter of 70 mm and a clamping force of 3,430 kN.
The dimensions of the molded product are a short side of 276.4 mm, a long side of 344.0 mm, and a thickness of 8.0 mm. On the surface of the cavity on the movable side of the mold, which is the light exit surface of the light guide plate, as a prism pattern for diffusing light, a unit prism having an isosceles triangle with a base of 50 μm and an apex angle of 140 degrees is provided as an adjacent unit prism. In a state where they are in contact with each other at the lower end, they are provided perpendicular to the long side. Holes that form cylindrical protrusions with a diameter of 80 μm and a height of 80 μm are formed on the surface of the cavity on the fixed side of the mold, which is the reflecting surface of the light guide plate, from a pitch of 130 μm between the two long sides of the cavity. The pitch was gradually enlarged to 300 μm near the side. One 800 W bar heater was embedded adjacent to the two long sides of the mold cavity. A fan gate was provided on one short side of the cavity.
Using the above-described injection molding machine and mold, a molding temperature of 270 ° C., a mold temperature of 85 ° C., a mold near-long side temperature of 95 ° C., an injection time of 5 seconds, and a holding pressure of 15 MPa after injection was added for 10 seconds, Thereafter, the light guide plate was injection-molded in 120 seconds for cooling, 5 seconds for removal, and 140 seconds for the molding cycle. The mold temperature is adjusted by maintaining the temperature of hot water flowing through the flow path in the mold at 80 ° C., and the temperature in the vicinity of the long side of the mold is 95 ° C. by controlling the voltage applied to the rod heater. Kept. The maximum temperature at the center of the mold cavity was 85 ° C., and the temperature at the long side of the cavity was 95 ° C.
The obtained light guide plate had a maximum thickness of 8.011 mm, a minimum thickness of 7.995 mm, a thickness of the central portion of 8.001 mm, and a gap value of 0.20%. The average value of the transfer rate was 89.5%, and the standard deviation was 0.34%. When the appearance quality was evaluated using this light guide plate, the screen of the liquid crystal display device had no bright lines or dark bands, and the appearance quality was good.
[Example 2]
During extraction 5 seconds, injection 5 seconds, holding pressure 10 seconds, hot water of 90 ° C. is passed through the flow path in the mold, and cold water of 25 ° C. is passed through the flow path in the mold during cooling 100 seconds. The light guide plate was injection molded under the same conditions as in Example 1 except that. The maximum temperature at the center of the mold cavity was 90 ° C., and the temperature at the long side of the cavity was 95 ° C.
The obtained light guide plate had a maximum thickness of 8.018 mm, a minimum thickness of 7.989 mm, a thickness of the central portion of 8.005 mm, and a gap value of 0.36%. The average value of the transfer rate was 93.7%, and the standard deviation was 0.18%. When the appearance quality was evaluated using this light guide plate, the screen of the liquid crystal display device had no bright lines or dark bands, and the appearance quality was good.
[Example 3]
As a thermoplastic resin, instead of a resin having an alicyclic structure, a methacrylic resin [Asahi Kasei Co., Ltd., Delpet 80NH] was used and the molding temperature was set to 260 ° C. under the same conditions as in Example 1. An optical plate was injection molded.
The obtained light guide plate had a maximum thickness of 8.025 mm, a minimum thickness of 7.994 mm, a thickness of the central portion of 8.015 mm, and a gap value of 0.39%. The average value of the transfer rate was 80.3%, and the standard deviation was 1.50%. When the appearance quality was evaluated using this light guide plate, the screen of the liquid crystal display device had no bright lines or dark bands, and the appearance quality was good.
[Example 4]
Example 1 except that instead of a resin having an alicyclic structure, a methacrylic acid ester-aromatic vinyl compound copolymer [Nippon Steel Chemical Co., Ltd., Estyrene MS-600] was used as the thermoplastic resin. The light guide plate was injection-molded under the same conditions.
The obtained light guide plate had a maximum thickness of 8.052 mm, a minimum thickness of 7.978 mm, a thickness of the central portion of 8.040 mm, and a gap value of 0.92%. The average value of the transfer rate was 82.4%, and the standard deviation was 1.82%. When the appearance quality was evaluated using this light guide plate, the screen of the liquid crystal display device had no bright lines or dark bands, and the appearance quality was good.
Comparative Example 1
The light guide plate was injection molded under the same conditions as in Example 1 except that the bar heater embedded adjacent to the two long sides of the mold cavity was removed and no heating was performed from the long side. The maximum temperature at the center of the mold cavity was 85 ° C., and the temperature at the long side of the cavity was 85 ° C.
The obtained light guide plate had a maximum thickness of 8.102 mm, a minimum thickness of 7.808 mm, a thickness of the central portion of 8.005 mm, and a gap value of 3.67%. The average value of the transfer rate was 84.9%, and the standard deviation was 11.98%. When the appearance quality was evaluated using this light guide plate, bright lines and dark bands appeared in the vicinity of the long side of the screen of the liquid crystal display device, and the appearance quality was poor.
The results of Examples 1 to 4 and Comparative Example 1 are shown in Table 1.
Figure 2005030468
As can be seen in Table 1, a bar heater is embedded adjacent to the two long sides of the mold cavity, and the temperature near the long side of the mold cavity is higher than the maximum temperature at the center of the mold cavity. The light guide plates of Examples 1 to 4 that are kept have small variations in thickness unevenness and variations in the transfer rate of the columnar protrusions, and there are no bright lines or dark bands on the screen of the liquid crystal display device, and have good performance. . In particular, the performance of the light guide plates of Examples 1 and 2 using a resin having an alicyclic structure is excellent. On the other hand, the light guide plate of Comparative Example 1 in which the edge of the cavity of the mold was not heated has a large variation in the thickness unevenness and the transfer rate of the columnar protrusion, and the bright line and the dark on the screen of the liquid crystal display device. A band appears.

本発明の厚物平板成形品は、厚みむらが少なく、平面性が良好であり、液晶表示装置の導光板として用いることにより、画面に明線や暗帯などのない優れた外観品質を得ることができる。本発明方法によれば、射出成形用金型のキャビティの端辺を加熱して、端辺の温度をキャビティの中央部の温度より高めることにより、厚みむらが少なく、平面性の良好な厚物平板成形品を容易に製造することができる。  The thick flat plate molded product of the present invention has little thickness unevenness and good flatness, and can be used as a light guide plate of a liquid crystal display device to obtain an excellent appearance quality free from bright lines and dark bands on the screen. Can do. According to the method of the present invention, by heating the end of the cavity of the injection mold and raising the temperature of the end to be higher than the temperature at the center of the cavity, there is little thickness unevenness and good thickness. A flat plate molded product can be easily manufactured.

Claims (7)

射出成形法により製造された熱可塑性樹脂を含んでなる長方形の厚物平板成形品において、以下の式
ギャップ値 ＝ ｛（ＴＭＡＸ−ＴＭＩＮ）／ＴＣＥＮＴＥＲ｝×１００
（ただし、上記式において、ＴＭＡＸは平板成形品の最大厚み、ＴＭＩＮは平板成形品の最小厚み、ＴＣＥＮＴＥＲは平板成形品の中央部の厚みをそれぞれ表す）
で表されるギャップ値が３％以下であることを特徴とする厚物平板成形品。In a rectangular thick flat plate molded article comprising a thermoplastic resin produced by an injection molding method, the following formula: gap value = {(T MAX −T MIN ) / T CENTER } × 100
(In the above formula, T MAX represents the maximum thickness of the flat plate molded product, T MIN represents the minimum thickness of the flat plate molded product, and T CENTER represents the thickness of the central portion of the flat plate molded product.)
A thick flat plate molded product having a gap value of 3% or less. ギャップ値が１％以下である請求項１記載の厚物平板成形品、The thick plate product according to claim 1, wherein the gap value is 1% or less, 中央部の厚みが、３〜５０ｍｍである請求項１又は２記載の厚物平板成形品。The thick flat plate molded product according to claim 1 or 2, wherein the thickness of the central portion is 3 to 50 mm. 熱可塑性樹脂が、脂環式構造を有する樹脂である請求項１乃至３のいずれか１項に記載の厚物平板成形品。The thick plate molded article according to any one of claims 1 to 3, wherein the thermoplastic resin is a resin having an alicyclic structure. 熱可塑性樹脂が、メタクリル樹脂又は（メタ）アクリル酸アルキルエステル−芳香族ビニル化合物共重合体である請求項１乃至３のいずれか１項に記載の厚物平板成形品。The thick plate molded article according to any one of claims 1 to 3, wherein the thermoplastic resin is a methacrylic resin or a (meth) acrylic acid alkyl ester-aromatic vinyl compound copolymer. 液晶表示装置の導光板である請求項１乃至５のいずれか１項に記載の厚物平板成形品。The thick plate molded product according to any one of claims 1 to 5, which is a light guide plate of a liquid crystal display device. 熱可塑性樹脂の厚物平板成形品を射出成形法により製造するに際して、射出成形用金型の長方形のキャビティの少なくとも１対の対向する２端辺の温度が、金型のキャビティの中央部の最高温度よりも２℃以上高く維持されるように金型を加熱することを特徴とする請求項１乃至６のいずれか１項に記載の厚物平板成形品の製造方法。When a thermoplastic flat plate product is manufactured by an injection molding method, the temperature of at least one pair of opposite ends of the rectangular cavity of the injection mold is the highest in the center of the mold cavity. The method for producing a thick flat plate molded article according to any one of claims 1 to 6, wherein the mold is heated so that the temperature is maintained at 2 ° C or higher than the temperature.
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