JP4097954B2

JP4097954B2 - Optical element, optical element molding die, and optical element molding method

Info

Publication number: JP4097954B2
Application number: JP2002048424A
Authority: JP
Inventors: 利昭高野; 淳村田; 貴志森本; 晃久山田; 紀雄桐田
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2002-02-25
Filing date: 2002-02-25
Publication date: 2008-06-11
Anticipated expiration: 2022-02-25
Also published as: JP2003245946A

Description

【０００１】
【発明の属する技術分野】
本発明は、光学機器に使用されるレンズ、プリズム、ミラー等の高精度光学素子、及び該光学素子を形成するための光学素子成形型と該光学素子の成形方法に関する。
【０００２】
【従来の技術】
従来の光学素子の成形方法としては、例えば、特開平５−１７７７２５号公報に記載のように、ペレットを加熱混錬溶融し、光学素子の光学有効部を成形するためのインサート部材を備えた成形型のキャビティ内に射出充填して得る射出成形法が知られている。
【０００３】
以下に従来の成形方法及び得られる光学素子について図を用いて簡単に説明する。
【０００４】
図４は、射出成形方法に用いられる射出成形機の概略断面図である。図４において、７はホッパ、８は成形材料、９は射出シリンダ、１０は加熱シリンダ、１１はスクリュ、１２はノズル、１３は固定ダイプレート、１４は移動ダイプレート、１５は型締めシリンダ、５は光学素子成形型（固定側）、６は光学素子成形型（可動側）、４はスプル、３はランナ、２はゲート、１は光学素子である。
【０００５】
図３は前述の射出成形方法で得られた成形品の概略図であり、図３（Ａ）は上面図、図３（Ｂ）は図３（Ａ）の３Ｂ−３Ｂ線での矢視断面図である。図中、４はスプル、３はランナ、２はゲート、１は光学素子である。
【０００６】
ホッパ７に成形材料８を投入する。成形材料８はスクリュ１１の回転に伴い、ノズル１２の方向へと移動する。成形材料８は、スクリュ１１及び加熱シリンダ１０により加熱溶融混錬される。そして、ノズル１２から光学素子成形型５、６内のスプルー４、ランナ３、及びゲート２を順に通過し、所望する光学素子形状のキャビティ内に射出され充填される。光学素子成形型５，６は所定の温度、例えば、成形材料８の荷重たわみ温度近傍に設定されている。光学素子１が取り出し可能な状態に冷却されると、光学素子成形型６を開き、ゲートカットを行い、スプル４、ランナー３、及びゲート２から切り離し、光学素子１を取り出す。
【０００７】
【発明が解決しようとする課題】
前述した従来の光学素子の成形型、成形方法、及び光学素子では、射出成形条件をいかにコントロールしても、ひけ、ジェッティング、ウエルドなどの発生を十分に抑えることが困難であった。
【０００８】
また、得られる光学素子が良好な転写性、すなわち、軸対称性に優れた光学特性を有していると、光学素子を光学機器に組み付ける際に、光学素子の組み付け方向を考慮しなくて済むので、作業効率が向上する。従って、光学特性の軸対称性が優れた光学素子を安定して高い歩留まりで得ることが望まれる。
【０００９】
本発明の目的は、ひけ、ジェッティング、ウエルドなどの発生を抑えながら、良好な転写性、すなわち、軸対称性に優れた光学特性を有した光学素子を安定して高い歩留まりで得ることができる光学素子の成形型、成形方法、及び光学素子を提供することにある。
【００１０】
【課題を解決するための手段】
上記の目的を達成するために、本発明は以下の事項よりなる。
【００１１】
本発明の光学素子は、成形材料を加熱混錬溶融し、ゲートを介してキャビティ内に射出充填して得られた両面凸形状の光学素子であって、光学素子の外径をφＧ、光学素子の光学有効面径をφＬＹ、光学素子の中心厚みをＬＴ、光学素子のコバ厚みをＬＫ、光学素子の外周に接続されるゲートの円周方向の幅をＧＨ、ゲートの厚みをＧＴ、光学素子の中心厚みＬＴとコバ厚みＬＫとの比をｘ（＝ＬＴ／ＬＫ）、ゲートの厚みＧＴと光学素子のコバ厚みＬＫとの比をｙ（＝ＧＴ／ＬＫ）としたとき、下記式（１）〜式（３）を満足することを特徴とする。
【００１２】
０．８＞φＬＹ／φＧ・・・（１）
０．１＜ＧＨ／φＧ＜０．３５・・・（２）
ｙ≧０．０９７７ｘ＋０．４７・・・（３）
【００１３】
また、本発明の光学素子成形型は、加熱混錬溶融された成形樹脂を射出充填して両面凸形状の光学素子を成形するためのキャビティと、前記キャビティの一部を構成し、前記光学素子の光学有効面を形成するためのインサート部材と、前記キャビティ内に前記成形樹脂を導入するためのゲートとを備えた光学素子成形型であって、成形される前記光学素子の外径をφＧ、光学素子の光学有効面径をφＬＹ、光学素子の中心厚みをＬＴ、光学素子のコバ厚みをＬＫ、光学素子の外周に接続される前記ゲートの円周方向の幅をＧＨ、ゲートの厚みをＧＴ、光学素子の中心厚みＬＴとコバ厚みＬＫとの比をｘ（＝ＬＴ／ＬＫ）、ゲートの厚みＧＴと光学素子のコバ厚みＬＫとの比をｙ（＝ＧＴ／ＬＫ）としたとき、下記式（１）〜式（３）を満足することを特徴とする。
【００１４】
０．８＞φＬＹ／φＧ・・・（１）
０．１＜ＧＨ／φＧ＜０．３５・・・（２）
ｙ≧０．０９７７ｘ＋０．４７・・・（３）
【００１５】
また、本発明の光学素子を成形方法は、加熱混錬溶融された成形樹脂を光学素子成形型のゲートを介してキャビティ内に射出充填して両面凸形状の光学素子を成形する方法であって、前記光学素子成形型は、前記光学素子の光学有効面を形成するためのインサート部材を備え、成形される前記光学素子の外径をφＧ、光学素子の光学有効面径をφＬＹ、光学素子の中心厚みをＬＴ、光学素子のコバ厚みをＬＫ、光学素子の外周に接続される前記ゲートの円周方向の幅をＧＨ、ゲートの厚みをＧＴ、光学素子の中心厚みＬＴとコバ厚みＬＫとの比をｘ（＝ＬＴ／ＬＫ）、ゲートの厚みＧＴと光学素子のコバ厚みＬＫとの比をｙ（＝ＧＴ／ＬＫ）としたとき、下記式（１）〜式（３）を満足することを特徴とする。
【００１６】
０．８＞φＬＹ／φＧ・・・（１）
０．１＜ＧＨ／φＧ＜０．３５・・・（２）
ｙ≧０．０９７７ｘ＋０．４７・・・（３）
【００１７】
上記の本発明の光学素子、光学素子成形型及び光学素子成形方法によれば、ひけ、ジェッティング、ウエルドなどの発生を抑えながら、ゲートが光学有効面に影響を与えることがなく良好な転写性（軸対称性）を有する両面凸形状の光学素子を安定して得ることが可能となる。
【００１８】
【発明の実施の形態】
本発明者らは、光学素子を成形型内で成形する際に、その外周端に成形材料の充填や保圧のために設けられるゲートの形状の違いにより、得られる光学素子の光学性能が異なることに着目し、本発明を完成した。
【００１９】
成形して得られる光学素子が所望する光学性能を具備しないという問題は、成形材料の充填工程で成形材料がスムーズに充填ができない、あるいは、冷却工程で成形材料の適正な保圧ができないなどにより、光学素子の光学有効面を形成するインサート部材の表面形状が光学素子に良好に転写できない、あるいは、無理な成形条件を選択せざるを得ないために、ゲート近傍で生じる応力歪みなどが光学有効面に影響するなどの現象が生じ、これらの結果、光軸に対して軸対称性を損なった光学性能すなわち大きな非点収差を備えた光学素子となってしまうということに起因している。
【００２０】
このことから、本発明は、ゲートが光学有効面に影響しない、すなわち、光学素子の光学性能に影響を与えないように、光学素子の外径と光学素子の光学有効面との間隔を制御する、あるいは、光学素子の外周端に設けるゲートの形状を制御するという技術的手段を用いることにより、上記の問題を解決した。
【００２１】
以下、本発明の光学素子と光学素子成形型と光学素子成形方法の実施の形態を具体的な実施例とともに、図面及び表を参照しながら説明する。
【００２２】
図１は、本発明の一実施形態に係る光学素子及びゲートの形状を示した概略図であり、図１（Ａ）は上面図、図１（Ｂ）は図１（Ａ）の１Ｂ−１Ｂ線での矢視断面図である。図２は、光学素子成形型の形状を示した概略図であり、図２（Ａ）は概略断面図、図２（Ｂ）はパーティング面からみた可動側成形型の正面図、図２（Ｃ）はパーティング面からみた固定側成形型の正面図である。これらの図において、１は光学素子、１ａは光学素子１の周囲に形成されたコバ、２は光学素子１のコバ１ａに接続されたゲート、３はゲート２と接続されたランナー、４は周囲にランナー３を放射状に備えるスプルー、５は固定側光学素子成形型、６は可動側光学素子成形型、５ａは固定側光学素子成形型５に組み込まれたインサート部材、６ａは可動側光学素子成形型６に組み込まれたインサート部材、１８は固定側光学素子成形型５と可動側光学素子成形型６とが突き合わされるパーティング面である。
【００２３】
実施例として、図１に示す光学素子１の各部の形状、すなわち、外径φＧ（光学素子１の最外径）、中心厚ＬＴ（光学素子１の光軸方向の厚み）、コバ厚ＬＫ（コバ１ａの光軸方向の厚み）、光学素子の第１面（１面）の光学有効面径φＬＹ１、第２面（Ｒ２面）の光学有効面径φＬＹ２、第１面の加工径φＬＫ１、第２面の加工径φＬＫ２などと、ゲート２の形状、すなわち、ゲート２の幅ＧＨ（光学素子１の円周方向の寸法）とゲート２の厚みＧＴ（光学素子の光軸方向の寸法）とを変化させた光学素子成形型を製作し、その光学素子成形型で光学素子を成形して、光学特性を評価確認した。ここで言う光学有効面とは、光学素子に要求される光学特性を生み出すために最小限必要とされる光学作用面のことで、光線の経路になる。
【００２４】
射出成形条件は、それぞれの光学素子の形状、ゲートの形状などが異なることから、その都度、条件検討を行い、最適な条件、すなわち、もっとも良好な光学特性が得られる成形条件を抽出していった。
【００２５】
より具体的に、光学素子成形型、光学素子、光学素子成形方法について記述する。
【００２６】
実施例において、光学素子１の材料として、ポリオレフィン樹脂（ガラス転移点Ｔｇ＝１５０℃、熱変形温度温度Ｔｔ＝１２５℃）を用いた。光学素子成形型５、６はプリハードン鋼、ステンレス鋼（Ｓ５５Ｃ、ＨＰＭ（例えば、日立金属株式会社の商標）、ＮＡＫ（大同特殊鋼株式会社の商標））などを用いて構成し、光学素子の光学有効面を形成するインサート部材５ａ、６ａは、超硬合金を材料として製作した。言うまでもないが、本発明において光学素子成形型５、６は前述の材料以外でも射出成形に使用可能な材料であれば何ら問題はない。また、インサート部材５ａ、６ａの材料として、光学素子としての表面性を得られる材料であればステンレス鋼（例えばＳＴＡＶＡＸ（ウッデホルム社の商標））などを基材として、その表面に例えば無電解ニッケルメッキを施し加工したものをインサート部材として用いても問題はない。ただし、強度を考えた場合、超硬合金を基材として用いるのが好ましい。また、離型性の向上や、型の酸化、腐食防止のために表面に保護膜などを施しても問題はない。
【００２７】
得ようとする光学素子の主な形状寸法の一例は、外径φＧ＝φ４．８ｍｍ、第１面（Ｒ１面）有効面径φＬＹ１＝φ３．６ｍｍ、中心厚ＬＴ＝１．７ｍｍ、コバ厚ＬＫ＝０．４１２ｍｍで、両面凸形状を有し、所望の光学仕様で光学特性が得られるように設計し、製作した。また、ゲートの形状の一例は、ゲート幅ＧＨ＝１．０ｍｍ、ゲート厚みＧＴ＝０．４ｍｍで、光学素子の外周部に連接配置されるように成形型を製作、組立した。
【００２８】
次に前述の光学素子成形型を用いた成形工程を述べる。成形は図４に示した従来の射出成形機と同様の構成の射出成形機を用いて行なった。まず、ホッパ７に成形材料８を投入した。成形材料８はスクリュ１１の回転に伴い、ノズル１２の方向へと移動する。成形材料８は、スクリュ１１及び加熱シリンダ１０により、所望の温度に加熱溶融混錬される。ここでは、加熱シリンダの設定温度を２６０℃に設定した。そして、同じく２６０℃に加熱されたノズル１２から光学素子成形型５、６内のスプルー４、ランナ３、及びゲート２を順に通過し、所望する光学素子形状のキャビティ内に射出し充填した。その後、射出シリンダにて保圧した。光学素子成形型５，６は所定の一定温度（ここでは、１３０℃に設定した）に保たれており、成形材料は、キャビティ内への充填が始まると同時に、冷却されていく。適正な、射出条件、充填条件、保圧条件、光学素子成形型の温度の条件を選択しなければ、所望の光学素子の光学特性は得られない。光学素子１が取り出し可能な状態に達した後、光学素子成形型６を開き、ゲートカットを行い、スプル４、ランナー３、及びゲート２から切り離し、光学素子１を取り出した。
【００２９】
上記の成形条件は一例であり、成形材料、光学素子の形状、ゲートの形状に応じて、各種成形条件を最適化する必要があることは言うまでもない。
【００３０】
得られた光学素子の光学特性の評価は、干渉計を用いて透過波面収差（測定波長６３２．８ｎｍ）を測定して非点収差を求め、これにより光学素子の有効面の転写性および軸対称性を評価した。非点収差は小さければ小さいほど望ましいが、ここでは、非点収差が２０ｍλ以下のものを良好な光学特性であるとした。それを超える非点収差を有した光学素子では、有効面の光学特性に回転軸対称性が乏しく、光学機器に搭載する際、非点収差の方向を把握し、方向を決めて光学機器に搭載しなくては、光学機器として所望の光学特性が得られない。
【００３１】
前述の光学素子は、非点収差は８ｍλであり、非常に良好な光学特性を有していた。
【００３２】
光学素子形状とゲート形状とを種々に変更して同様に光学素子成形型を製作し、最適化した成形条件により光学素子を得た。表１，表２に各サンプルの光学素子形状とゲート形状を、表３に得られた光学素子の光学特性（非点収差）と良否評価結果を示す。
【００３３】
【表１】

【００３４】
【表２】

【００３５】
【表３】

【００３６】
表３において、「非点収差」の欄に「−」があるのは、成形条件を種々に変更してみても、上記の光学特性の評価を実施できる程度の光学素子を得ることができなかったことを示している。
【００３７】
表１〜表３から分かるように、本発明の目的とする、回転軸対称性に優れた光学特性を備えた光学素子を得るためには以下の３つの条件を満足する必要がある。
【００３８】
第１に、ゲート２を設けた光学素子１の外径φＧと光学素子１の光学有効径φＬＹ（ここで言う光学有効径φＬＹは、光学素子の第１面（Ｒ１面）光学有効径φＬＹ１と第２面（Ｒ２面）光学有効径φＬＹ２とのうちの何れか大きい方を意味する）との比φＬＹ／φＧが、φＬＹ／φＧ＜０．８を満足するように、光学素子１の光学有効径φＬＹと外径φＧとを設定することが必要である。比φＬＹ／φＧが上記の範囲を満足しないとき、如何にゲート２の形状や射出成形条件を変更しても、ゲート２部分での応力歪みなどの影響が光学素子１の光学有効面に及び、非点収差が大きな光学素子になってしまう。
【００３９】
第２に、光学素子１の外径φＧとゲート２の幅ＧＨとの比ＧＨ／φＧが、０．１＜ＧＨ／φＧ＜０．３５を満足することが必要である。比ＧＨ／φＧがこの関係を満たさない場合、如何に射出成形条件を変更しても、転写性が光軸に対して非対称になってしまう。言い換えれば、軸非対称な光学素子が必要な場合、ゲート幅ＧＨを前述の関係を満たさない関係にすればよいと言える。
【００４０】
第３に、光学素子１の偏肉比やコバに対するゲート２の厚み形状を適正な寸法にする必要がある。即ち、光学素子１の中心厚みをＬＴ、光学素子１のコバ厚みをＬＫ、ゲート２の厚みをＧＴとし、光学素子１の中心厚みＬＴとコバ厚みＬＫとの比をｘ＝ＬＴ／ＬＫ、ゲート２の厚みＧＴと光学素子１のコバ厚みＬＫとの比をｙ＝ＧＴ／ＬＫとしたとき、ｙ≧０．０９７７ｘ＋０．４７である関係を有することが必要である。
【００４１】
前述した実験結果から明らかなように、光学素子形状及び光学素子成形型が上記の３つの条件を満たしたとき、光学素子は良好な非点収差を備える。
【００４２】
即ち、光学素子及び成形型（ゲート）が上記の３つの条件を同時に備える場合には良好な光学特性を有した光学素子を得ることが出来るので、光学素子及び光学素子成形型を試行錯誤して製作する必要がなくなり、光学素子成形型及び光学素子をより安価に提供できる。
【００４３】
従って、上記の３つの条件を満たすように光学素子及び成形型を設計し、実際の射出成形において、ひけ、ジェッティング、ウエルドなどが発生しないように射出成形条件をコントロールすることにより、軸対称性に優れた光学特性を有した光学素子を安定して高い歩留まりで得ることができる。
【００４４】
尚、上記の実施例においては、成形材料として、ポリオレフィン樹脂を用いたが、これに限らず、その他の成形材料を用いても同様であることはいうまでもない。
【００４５】
また、成形における温度条件、圧力条件は、成形材料のガラス転移点、荷重たわみ温度等の特性により異なることは言うまでもない。
【００４６】
【発明の効果】
以上のように、本発明によれば、ひけ、ジェッティング、ウエルドなどの発生を抑えながら、ゲートが光学有効面に影響を与えることがなく良好な転写性（軸対称性）を有する両面凸形状の光学素子を安定して得ることが可能となる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る光学素子及びゲートの形状を示した概略図であり、図１（Ａ）は上面図、図１（Ｂ）は図１（Ａ）の１Ｂ−１Ｂ線での矢視断面図である。
【図２】本発明の一実施形態に係る光学素子成形型の形状を示した概略図であり、図２（Ａ）は概略断面図、図２（Ｂ）はパーティング面からみた可動側成形型の正面図、図２（Ｃ）はパーティング面からみた固定側成形型の正面図である。
【図３】本発明及び従来の射出成形方法で得られる成形品の概略図であり、図３（Ａ）は上面図、図３（Ｂ）は図３（Ａ）の３Ｂ−３Ｂ線での矢視断面図である。
【図４】光学素子の成形方法に用いられる射出成形機の概略断面図である。
【符号の説明】
１光学素子
１ａコバ
２ゲート
３ランナー
４スプルー
５固定側光学素子成形型
５ａインサート部材
６可動側光学素子成形型
６ａインサート部材
７ホッパ
８成形材料
９射出シリンダ
１０加熱シリンダ
１１スクリュ
１２ノズル
１３固定ダイプレート
１４移動ダイプレート
１５型締めシリンダ
１８パーティング面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to high-precision optical elements such as lenses, prisms, and mirrors used in optical equipment, an optical element molding die for forming the optical elements, and a method for molding the optical elements.
[0002]
[Prior art]
As a conventional method for molding an optical element, for example, as described in JP-A-5-177725, molding including an insert member for heating and kneading and melting pellets to mold an optically effective portion of the optical element An injection molding method obtained by injection filling into a cavity of a mold is known.
[0003]
The conventional molding method and the obtained optical element will be briefly described below with reference to the drawings.
[0004]
FIG. 4 is a schematic cross-sectional view of an injection molding machine used in the injection molding method. In FIG. 4, 7 is a hopper, 8 is a molding material, 9 is an injection cylinder, 10 is a heating cylinder, 11 is a screw, 12 is a nozzle, 13 is a fixed die plate, 14 is a moving die plate, 15 is a clamping cylinder, 5 Is an optical element mold (fixed side), 6 is an optical element mold (movable side), 4 is a sprue, 3 is a runner, 2 is a gate, and 1 is an optical element.
[0005]
FIG. 3 is a schematic view of a molded product obtained by the above-described injection molding method, FIG. 3 (A) is a top view, and FIG. 3 (B) is a cross-sectional view taken along line 3B-3B in FIG. 3 (A). FIG. In the figure, 4 is a sprue, 3 is a runner, 2 is a gate, and 1 is an optical element.
[0006]
The molding material 8 is put into the hopper 7. The molding material 8 moves in the direction of the nozzle 12 as the screw 11 rotates. The molding material 8 is heated and melted and kneaded by the screw 11 and the heating cylinder 10. Then, the nozzle 12 sequentially passes through the sprue 4, the runner 3, and the gate 2 in the

optical element molds

5 and 6, and is injected and filled into a cavity having a desired optical element shape. The

optical element molds

5 and 6 are set at a predetermined temperature, for example, near the deflection temperature under load of the molding material 8. When the optical element 1 is cooled to a state where it can be taken out, the optical element mold 6 is opened, gate cutting is performed, the optical element 1 is separated from the sprue 4, the runner 3, and the gate 2, and the optical element 1 is taken out.
[0007]
[Problems to be solved by the invention]
With the conventional optical element mold, molding method, and optical element described above, it is difficult to sufficiently suppress the occurrence of sink marks, jetting, welds, etc., no matter how the injection molding conditions are controlled.
[0008]
Further, when the obtained optical element has good transferability, that is, optical characteristics excellent in axial symmetry, it is not necessary to consider the assembly direction of the optical element when assembling the optical element in an optical device. So work efficiency is improved. Accordingly, it is desirable to obtain an optical element having excellent axial symmetry of optical characteristics with high yield.
[0009]
An object of the present invention is to stably obtain an optical element having excellent transfer properties, that is, optical properties excellent in axial symmetry, with high yield while suppressing the occurrence of sink marks, jetting, welds and the like. An object is to provide a mold for an optical element, a molding method, and an optical element.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention comprises the following items.
[0011]
An optical element of the present invention is a double-sided convex optical element obtained by kneading and melting a molding material and injection-filling it into a cavity through a gate, the outer diameter of the optical element being φG, The optical effective surface diameter is φLY, the center thickness of the optical element is LT, the edge thickness of the optical element is LK, the circumferential width of the gate connected to the outer periphery of the optical element is GH, the gate thickness is GT, and the optical element When the ratio of the center thickness LT to the edge thickness LK is x (= LT / LK), and the ratio of the gate thickness GT to the edge thickness LK of the optical element is y (= GT / LK), the following formula (1) ) To Expression (3) are satisfied.
[0012]
0.8> φLY / φG (1)
0.1 <GH / φG <0.35 (2)
y ≧ 0.0977x + 0.47 (3)
[0013]
The optical element mold according to the present invention comprises a cavity for injection-filling a heat-kneaded and melted molding resin to form a double-sided convex optical element, and a part of the cavity. An optical element molding die comprising an insert member for forming an optically effective surface of the optical element and a gate for introducing the molding resin into the cavity, wherein the outer diameter of the optical element to be molded is φG, The optical effective surface diameter of the optical element is φLY, the center thickness of the optical element is LT, the edge thickness of the optical element is LK, the circumferential width of the gate connected to the outer periphery of the optical element is GH, and the gate thickness is GT When the ratio between the center thickness LT of the optical element LT and the edge thickness LK is x (= LT / LK) and the ratio between the gate thickness GT and the edge thickness LK of the optical element is y (= GT / LK), Satisfy Formula (1) to Formula (3) It is characterized by that.
[0014]
0.8> φLY / φG (1)
0.1 <GH / φG <0.35 (2)
y ≧ 0.0977x + 0.47 (3)
[0015]
The optical element molding method of the present invention is a method for molding a double-sided convex optical element by injection-filling a mold resin melted by heating and kneading into a cavity through a gate of an optical element molding die. The optical element mold includes an insert member for forming an optically effective surface of the optical element, the outer diameter of the optical element to be molded is φG, the optically effective surface diameter of the optical element is φLY, The center thickness is LT, the edge thickness of the optical element is LK, the circumferential width of the gate connected to the outer periphery of the optical element is GH, the gate thickness is GT, the center thickness LT of the optical element and the edge thickness LK When the ratio is x (= LT / LK) and the ratio between the gate thickness GT and the edge thickness LK of the optical element is y (= GT / LK), the following expressions (1) to (3) are satisfied. It is characterized by.
[0016]
0.8> φLY / φG (1)
0.1 <GH / φG <0.35 (2)
y ≧ 0.0977x + 0.47 (3)
[0017]
According to the above-described optical element, optical element molding die, and optical element molding method of the present invention, the gate does not affect the optically effective surface while suppressing the occurrence of sink marks, jetting, welds, etc. It becomes possible to stably obtain a double-sided convex optical element having (axial symmetry).
[0018]
DETAILED DESCRIPTION OF THE INVENTION
When the optical element is molded in a mold, the present inventors differ in the optical performance of the obtained optical element due to the difference in the shape of the gate provided for filling or holding pressure of the molding material at the outer peripheral end of the optical element. In particular, the present invention has been completed.
[0019]
The problem that the optical element obtained by molding does not have the desired optical performance is that the molding material cannot be filled smoothly in the molding material filling process, or the molding material cannot be properly held in the cooling process. Because the surface shape of the insert member that forms the optically effective surface of the optical element cannot be transferred to the optical element satisfactorily or forced molding conditions must be selected, the stress strain generated near the gate is optically effective. Phenomena such as affecting the surface occur, and as a result, the optical performance is impaired in the axial symmetry with respect to the optical axis, that is, the optical element has a large astigmatism.
[0020]
Therefore, the present invention controls the distance between the outer diameter of the optical element and the optical effective surface of the optical element so that the gate does not affect the optical effective surface, that is, does not affect the optical performance of the optical element. Alternatively, the above problem was solved by using a technical means for controlling the shape of the gate provided at the outer peripheral edge of the optical element.
[0021]
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an optical element, an optical element molding die, and an optical element molding method according to the present invention will be described below together with specific examples with reference to the drawings and tables.
[0022]
1A and 1B are schematic views showing shapes of an optical element and a gate according to an embodiment of the present invention, in which FIG. 1A is a top view, and FIG. 1B is 1B-1B of FIG. It is arrow sectional drawing in a line. 2A and 2B are schematic views showing the shape of the optical element molding die, FIG. 2A is a schematic sectional view, FIG. 2B is a front view of the movable-side molding die as seen from the parting surface, and FIG. C) is a front view of the fixed-side mold as seen from the parting surface. In these figures, 1 is an optical element, 1a is an edge formed around the optical element 1, 2 is a gate connected to the edge 1a of the optical element 1, 3 is a runner connected to the gate 2, and 4 is the surroundings. Sprue provided with runners 3 radially, 5 is a fixed side optical element molding die, 6 is a movable side optical element molding die, 5a is an insert member incorporated in the fixed side optical element molding die 5, and 6a is a movable side optical element molding. An insert member 18 incorporated in the mold 6 is a parting surface on which the fixed-side optical element mold 5 and the movable-side optical element mold 6 are abutted.
[0023]
As an example, the shape of each part of the optical element 1 shown in FIG. 1, that is, the outer diameter φG (the outermost diameter of the optical element 1), the center thickness LT (the thickness of the optical element 1 in the optical axis direction), the edge thickness LK ( Thickness of the edge 1a in the optical axis direction), the optical effective surface diameter φLY1 of the first surface (one surface) of the optical element, the optical effective surface diameter φLY2 of the second surface (R2 surface), the processing diameter φLK1 of the first surface, The processing diameter φLK2 of the two surfaces, the shape of the gate 2, that is, the width GH of the gate 2 (dimension in the circumferential direction of the optical element 1) and the thickness GT of the gate 2 (dimension in the optical axis direction of the optical element) The changed optical element mold was manufactured, the optical element was molded with the optical element mold, and the optical characteristics were evaluated and confirmed. The optically effective surface referred to here is an optical action surface that is minimally required to produce optical characteristics required for the optical element, and serves as a path of light rays.
[0024]
Since the injection molding conditions differ in the shape of each optical element, the shape of the gate, etc., the conditions are examined each time, and the optimal conditions, i.e., molding conditions that provide the best optical characteristics are extracted. It was.
[0025]
More specifically, an optical element mold, an optical element, and an optical element molding method will be described.
[0026]
In the examples, polyolefin resin (glass transition point Tg = 150 ° C., heat distortion temperature Tt = 125 ° C.) was used as the material of the optical element 1. The

optical element molds

5 and 6 are made of pre-hardened steel, stainless steel (S55C, HPM (for example, trademark of Hitachi Metals, Ltd.), NAK (trademark of Daido Steel), etc. The

insert members

5a and 6a forming the effective surface were made of cemented carbide. Needless to say, in the present invention, there is no problem as long as the

optical element molds

5 and 6 are materials that can be used for injection molding other than the above-described materials. Further, as a material of the

insert members

5a and 6a, if the material can obtain surface properties as an optical element, stainless steel (for example, STAVAX (trademark of Woodeholm)) or the like is used as a base material, and the surface thereof is electroless nickel-plated, for example. There is no problem even if the processed material is used as an insert member. However, when the strength is considered, it is preferable to use a cemented carbide as the base material. Further, there is no problem even if a protective film or the like is provided on the surface in order to improve releasability, to prevent mold oxidation or corrosion.
[0027]
An example of main dimensions of the optical element to be obtained is as follows: outer diameter φG = φ4.8 mm, first surface (R1 surface) effective surface diameter φLY1 = φ3.6 mm, center thickness LT = 1.7 mm, edge thickness LK = 0.412 mm, has a convex shape on both sides, and was designed and manufactured so as to obtain optical characteristics with desired optical specifications. An example of the shape of the gate was a gate width GH = 1.0 mm and a gate thickness GT = 0.4 mm, and a mold was manufactured and assembled so as to be connected to the outer peripheral portion of the optical element.
[0028]
Next, a molding process using the above-described optical element mold will be described. Molding was performed using an injection molding machine having the same configuration as the conventional injection molding machine shown in FIG. First, the molding material 8 was put into the hopper 7. The molding material 8 moves in the direction of the nozzle 12 as the screw 11 rotates. The molding material 8 is heated, melted and kneaded to a desired temperature by the screw 11 and the heating cylinder 10. Here, the set temperature of the heating cylinder was set to 260 ° C. Then, the nozzle 12 heated to 260 ° C. was passed through the sprue 4, the runner 3, and the gate 2 in the

optical element molds

5 and 6 in that order, and injected into a cavity having a desired optical element shape. Thereafter, the pressure was maintained with an injection cylinder. The

optical element molds

5 and 6 are maintained at a predetermined constant temperature (here, set to 130 ° C.), and the molding material is cooled as soon as filling into the cavity starts. Unless proper injection conditions, filling conditions, pressure holding conditions, and temperature conditions of the optical element mold are selected, desired optical characteristics of the optical element cannot be obtained. After reaching the state where the optical element 1 can be taken out, the optical element mold 6 was opened, gate cutting was performed, and the optical element 1 was taken out from the sprue 4, the runner 3, and the gate 2.
[0029]
The above molding conditions are merely examples, and it goes without saying that various molding conditions need to be optimized according to the molding material, the shape of the optical element, and the shape of the gate.
[0030]
The optical characteristics of the obtained optical element are evaluated by measuring the transmitted wavefront aberration (measurement wavelength 632.8 nm) using an interferometer to obtain astigmatism, thereby transferring the effective surface of the optical element and its axial symmetry. Sex was evaluated. The smaller the astigmatism, the better. However, in this case, the one having astigmatism of 20 mλ or less is regarded as a good optical characteristic. Optical elements with astigmatism exceeding that range have poor rotational axis symmetry in the optical characteristics of the effective surface, and when mounted on optical equipment, the direction of astigmatism is determined, the direction is determined, and the optical equipment is installed. Otherwise, the desired optical characteristics cannot be obtained as an optical instrument.
[0031]
The aforementioned optical element had astigmatism of 8 mλ and had very good optical characteristics.
[0032]
The optical element shape and the gate shape were variously changed to produce an optical element mold in the same manner, and an optical element was obtained under optimized molding conditions. Tables 1 and 2 show the optical element shape and gate shape of each sample, and Table 3 shows the optical characteristics (astigmatism) and pass / fail evaluation results of the optical elements obtained.
[0033]
[Table 1]

[0034]
[Table 2]

[0035]
[Table 3]

[0036]
In Table 3, “-” is present in the column of “astigmatism” because an optical element capable of evaluating the above optical characteristics cannot be obtained even when various molding conditions are changed. It shows that.
[0037]
As can be seen from Tables 1 to 3, it is necessary to satisfy the following three conditions in order to obtain an optical element having an optical characteristic excellent in rotational axis symmetry, which is an object of the present invention.
[0038]
First, the outer diameter φG of the optical element 1 provided with the gate 2 and the optical effective diameter φLY of the optical element 1 (the optical effective diameter φLY referred to here is the first surface (R1 surface) of the optical element and the optical effective diameter φLY1). The optical effectiveness of the optical element 1 is such that the ratio φLY / φG with respect to the second surface (R2 surface) means the larger one of the optical effective diameters φLY2 and φLY / φG <0.8. It is necessary to set the diameter φLY and the outer diameter φG. When the ratio φLY / φG does not satisfy the above range, no matter how the shape of the gate 2 and the injection molding conditions are changed, the influence of the stress strain at the gate 2 portion affects the optically effective surface of the optical element 1. This results in an optical element with large astigmatism.
[0039]
Second, the ratio GH / φG between the outer diameter φG of the optical element 1 and the width GH of the gate 2 needs to satisfy 0.1 <GH / φG <0.35. If the ratio GH / φG does not satisfy this relationship, the transferability becomes asymmetric with respect to the optical axis no matter how the injection molding conditions are changed. In other words, when an axially asymmetric optical element is required, it can be said that the gate width GH should be a relationship that does not satisfy the above-described relationship.
[0040]
Thirdly, the thickness ratio of the optical element 1 and the thickness of the gate 2 with respect to the edge need to be set to appropriate dimensions. That is, the center thickness of the optical element 1 is LT, the edge thickness of the optical element 1 is LK, the thickness of the gate 2 is GT, and the ratio of the center thickness LT to the edge thickness LK of the optical element 1 is x = LT / LK, gate. When the ratio between the thickness GT of 2 and the edge thickness LK of the optical element 1 is y = GT / LK, it is necessary that y ≧ 0.0977x + 0.47.
[0041]
As is clear from the experimental results described above, when the optical element shape and the optical element mold satisfy the above three conditions, the optical element has good astigmatism.
[0042]
That is, when the optical element and the mold (gate) have the above three conditions at the same time, an optical element having good optical characteristics can be obtained. There is no need to manufacture the optical element molding die and the optical element at a lower cost.
[0043]
Therefore, by designing the optical element and the mold so as to satisfy the above three conditions and controlling the injection molding conditions so that sinks, jetting, welds, etc. do not occur in actual injection molding, axial symmetry is achieved. Thus, an optical element having excellent optical characteristics can be obtained stably with a high yield.
[0044]
In the above embodiment, the polyolefin resin is used as the molding material. However, the present invention is not limited to this, and it goes without saying that the same applies when other molding materials are used.
[0045]
Needless to say, temperature conditions and pressure conditions in molding differ depending on characteristics such as a glass transition point of the molding material and a deflection temperature under load.
[0046]
【The invention's effect】
As described above, according to the present invention, the double-sided convex shape having good transferability (axial symmetry) without affecting the optically effective surface while suppressing the occurrence of sink marks, jetting, and welds. It is possible to stably obtain the optical element.
[Brief description of the drawings]
1A and 1B are schematic views showing shapes of an optical element and a gate according to an embodiment of the present invention, in which FIG. 1A is a top view and FIG. 1B is 1B-1B in FIG. It is arrow sectional drawing in a line.
FIGS. 2A and 2B are schematic views showing the shape of an optical element molding die according to an embodiment of the present invention, FIG. 2A is a schematic cross-sectional view, and FIG. 2B is a movable side molding viewed from a parting surface. FIG. 2 (C) is a front view of the fixed-side mold as seen from the parting surface.
3 is a schematic view of a molded product obtained by the present invention and a conventional injection molding method, FIG. 3 (A) is a top view, and FIG. 3 (B) is a line 3B-3B in FIG. 3 (A). It is arrow sectional drawing.
FIG. 4 is a schematic cross-sectional view of an injection molding machine used in a method for molding an optical element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical element 1a Edge 2 Gate 3 Runner 4 Sprue 5 Fixed side optical element shaping | molding die 5a Insert member 6 Movable side optical element shaping | molding die 6a Insert member 7 Hopper 8 Molding material 9 Injection cylinder 10 Heating cylinder 11 Screw 12 Nozzle 13 Fixed die plate 14 Moving die plate 15 Clamping cylinder 18 Parting surface

Claims

A double-sided convex optical element obtained by kneading and melting a molding material and injection-filling it into a cavity through a gate,
The outer diameter of the optical element is φG, the optical effective surface diameter of the optical element is φLY, the center thickness of the optical element is LT, the edge thickness of the optical element is LK, and the circumferential width of the gate connected to the outer periphery of the optical element is GH, the thickness of the gate is GT, the ratio of the center thickness LT of the optical element to the edge thickness LK is x (= LT / LK), and the ratio of the gate thickness GT to the edge thickness LK of the optical element is y (= GT / LK), a double-sided convex optical element satisfying the following formulas (1) to (3):
0.8> φLY / φG (1)
0.1 <GH / φG <0.35 (2)
y ≧ 0.0977x + 0.47 (3)

A cavity for injection-filling a heat-kneaded and melted molding resin to mold a double-sided convex optical element;
An insert member for forming a part of the cavity and forming an optically effective surface of the optical element;
An optical element molding die comprising a gate for introducing the molding resin into the cavity,
The outer diameter of the optical element to be molded is φG, the optical effective surface diameter of the optical element is φLY, the center thickness of the optical element is LT, the edge thickness of the optical element is LK, and the circle of the gate connected to the outer periphery of the optical element The circumferential width is GH, the gate thickness is GT, the ratio of the center thickness LT of the optical element to the edge thickness LK is x (= LT / LK), and the ratio of the gate thickness GT to the edge thickness LK of the optical element is An optical element molding die characterized by satisfying the following formulas (1) to (3) when y (= GT / LK).
0.8> φLY / φG (1)
0.1 <GH / φG <0.35 (2)
y ≧ 0.0977x + 0.47 (3)

A method of molding a double-sided convex optical element by injection-filling a mold resin melted by heating and kneading into a cavity through a gate of an optical element molding die, wherein the optical element molding die comprises: An insert member for forming an optically effective surface;
The outer diameter of the optical element to be molded is φG, the optical effective surface diameter of the optical element is φLY, the center thickness of the optical element is LT, the edge thickness of the optical element is LK, and the circle of the gate connected to the outer periphery of the optical element The circumferential width is GH, the gate thickness is GT, the ratio of the center thickness LT of the optical element to the edge thickness LK is x (= LT / LK), and the ratio of the gate thickness GT to the edge thickness LK of the optical element is A molding method for a double-sided convex optical element, wherein y (= GT / LK) satisfies the following formulas (1) to (3):
0.8> φLY / φG (1)
0.1 <GH / φG <0.35 (2)
y ≧ 0.0977x + 0.47 (3)