JP2004083327A

JP2004083327A - Forming method of optical element

Info

Publication number: JP2004083327A
Application number: JP2002245627A
Authority: JP
Inventors: Masato Nakahama; 中濱　正人
Original assignee: Olympus Corp
Current assignee: Olympus Corp
Priority date: 2002-08-26
Filing date: 2002-08-26
Publication date: 2004-03-18
Anticipated expiration: 2022-08-26
Also published as: JP4090816B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method of an optical element by which a crack and a deficiency of middle thickness are not generated and melt sticking of a glass workpiece to a mold, shrinkage and the like are not generated. <P>SOLUTION: The forming method of the optical element consists of a heating step for heating the glass workpiece and the forming mold and a press forming step for press forming the glass workpiece by using the forming mold. The heating temperature of the glass workpiece and the heating temperature of the forming mold are so controlled that the heating temperature of the forming mold is lower than the heating temperature of the glass workpiece in the heating step and so set that the ratio of the viscosity of a surface part to the viscosity of a center part of the glass workpiece is more than 1 and ≤10<SP>3.5</SP>directly after the press forming step is started. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、加熱軟化したガラス素材を一対の成形型によりプレス成形してガラス光学素子を得るための光学素子の成形方法に関する。
【０００２】
【従来の技術】
ガラス光学素子を成形する方法として、特許３２０１８８７号公報、特許２９５２１８５号公報の発明が開示されている。
特許３２０１８８７号公報に記載の方法は、ガラス素材を１０^７〜１０^９ｄＰａＳの粘度になるように加熱し、ガラスの１０^１０〜１０^１２ｄＰａＳの粘度相当に加熱した成形用型でプレスして所望の光学素子を得る方法である。この特許３２０１８８７号公報に記載された実施例１には、プレス開始の瞬間にガラス温度は急激に低下し、成形用型の温度はわずかに上昇する事実が記載されている。
【０００３】
特許２９５２１８５号公報に記載の方法は、ガラス素材を１０^９ｄＰａＳ未満の粘度になるように加熱し、ガラスの１０^９〜１０^１２ｄＰａＳの粘度相当に加熱した成形用型でプレスして所望の光学素子を得る方法である。
【０００４】
【発明が解決しようとする課題】
しかしながら、特許３２０１８８７号に記載の方法の場合、成形型の温度上昇を制御していない為に、成形用型の温度上昇が少ないと所望の光学素子の中肉まで押圧できなかったり、割れたりすることがあった。また、逆に温度上昇が高すぎるとガラスと型とに融着が生じたり、ヒケを生じたりすることがあった。
【０００５】
また特許２９５２１８５号公報に記載の条件にて光学素子を成形する場合には、Φ５ｍｍ以下の小径の光学素子を成形する場合には、成形対象となるガラス素材の体積が小さいことに起因して冷却が過度に早くなり、所望の光学素子の中肉部分まで押圧することができなかったり、割れたりする問題がある。
【０００６】
本発明は以上の従来技術における問題に鑑み、割れや中肉不足や、型とガラス素材の融着やヒケなどが発生しない光学素子の成形方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
前記課題を解決する本出願第１の発明の光学素子の成形方法は、ガラス素材と成形型とを加熱する加熱工程と、前記成形型によって前記ガラス素材を押圧成形する押圧成形工程とよりなり、前記加熱工程ではガラス素材の加熱温度と成形型の加熱温度とを、成形型の加熱温度がガラス素材の加熱温度よりも低い温度であり、かつ、前記押圧工程開始直後に、ガラス素材の表面部粘度の中央部粘度に対する比が１より大きく１０^３．５以下となるようにガラス素材と成形型との加熱温度を設定することを特徴とする。
【０００８】
かかる光学素子の成形方法によれば、押圧開始直後のガラス素材の表面部粘度の中央部粘度に対する比を１０^３．５以下とすることによって短時間に所望の中肉まで押圧することができ面精度のよい、所望の光学素子を成形することができる。
ここで、ガラスの表面部の中央部に対する粘度の比が１０^３．５を超える場合にはヒケが生じ、面精度が悪化して所望の光学素子を得ることができない。
【０００９】
また、押圧成形工程開始後に冷却を行う冷却工程を有し、ガラス素材の表面部粘度の中央部粘度に対する比が１より大きく１０^２．５未満でかつガラス転移点に相当する温度にガラス素材表面温度が達する前に前記冷却工程を開始し、成形後にガラス素材の表面部粘度の中央部粘度に対する比が１０^１．５以内になるまで冷却を行う。
【００１０】
係る本発明のガラス素材の成形方法によれば、ＮＲ（ニュートンリング）、ヒケ等の欠陥のない面精度のよい、所望の光学素子を成形することができる。
ガラス表面部の中央部に対する粘度の比が１０^２．５以上である場合にはガラス素材表面部と中央部とに過剰な熱膨張差が生じ、その後冷却した場合には、その熱膨張差がヒケと称される形状劣化の原因となる。
【００１１】
ガラス素材表面部の温度がガラス素材のガラス転移点に相当する温度に達した後に冷却する場合には、ガラス素材の物性的特性から流動性が失われ、その後冷却した場合には、ガラス素材の表面部は流動性がなく、且つガラス素材表面部と中央部とに熱膨張差が生じることからヒケと称される形状の劣化が起こり、かかる欠陥が得られる光学素子における転写精度の悪化の原因となる。
【００１２】
また、成形後のガラス表面部粘度の中央部粘度に対する比が１０^１．５以内になるまで収束させながら冷却することによってガラス表面部と中央部との熱膨張差がなくすことができ、全体としてほぼ相似形の変形を進行させて、ヒケの発生をなくすることができる。成形後のガラス表面部粘度の中央部粘度に対する比が１０^１．５以内になるまで冷却しない場合にはガラス表面部と中央部との熱膨張差に起因してヒケが発生する。
【００１３】
また、本発明の光学素子の成形方法は、ガラス素材の粘度が当該ガラス素材の転移点での粘度に対して１０^−１．５倍の粘度に相当する温度以下のガラス素材表面温度で前記冷却工程を開始する。
【００１４】
係る本発明のガラス素材の成形方法によれば、より効率よくＮＲ（ニュートンリング）、ヒケ、クセ等の欠陥のない面精度のよい、所望の光学素子を成形することができる。
ここでガラス素材の表面温度がガラス転移点のガラス粘度に対して１０^−１．５倍の粘度に相当する温度を超えるガラス素材表面温度で前記冷却工程を開始する場合には、ガラス固有の物性として、ガラス転移点の粘度に対して１０^−１．５倍を超える粘度ではガラス素材表面の流動性は完全に消失しないまでも流動性は極めて小さくなり、特にガラス素材の表面部と中央部とに粘度の差がありガラス素材表面部と中央部とに熱膨張差が生じる場合には、その後冷却するとガラス素材の表面部は流動性が極めて低く、且つガラス素材表面部と中央部とに熱膨張差が生じることからヒケと称される形状の劣化が起こり、かかる欠陥が得られる光学素子における転写精度の悪化の原因となる。
【００１５】
以上においてガラス転移点のガラス粘度に対して１０^−１．５倍の粘度に相当する温度は、ガラス素材のガラス転移点が、例えばガラス粘度で１０^１３．５ｄＰａＳに相当する温度である場合には、ガラス粘度で１０^１２ｄＰａＳに相当する温度となる。したがってその場合にはガラス粘度で１０^１２ｄＰａＳに相当する温度以下のガラス素材表面温度で前記冷却工程を開始する。
【００１６】
また、本発明の光学素子の成形方法は、押圧成形工程開始後に冷却を行う冷却工程を有し、ガラス素材表面部の粘度のガラス素材中央部の粘度に対する比が１より大きく１０^２．５未満でかつガラス転移点のガラス粘度に対して１０^−１．５倍の粘度に相当する温度以下のガラス素材中心温度で前記冷却工程を開始し、成形後のガラス素材の表面部粘度の中央部粘度に対する比が１０^１．５以内になるまで冷却を行う。
【００１７】
係る本発明のガラス素材の成形方法によれば、上述の各発明と同様により効率よくＮＲ、ヒケ等の欠陥のない面精度のよい、所望の光学素子を成形することができる。
【００１８】
以上においてガラス転移点のガラス粘度に対して１０^−１．５倍の粘度に相当する温度は、ガラス素材のガラス転移点が、例えばガラス粘度で１０^１３．５ｄＰａＳに相当する温度である場合には、ガラス粘度で１０^１２ｄＰａＳに相当する温度となる。したがってその場合にはガラス粘度で１０^１２ｄＰａＳに相当する温度以下のガラス素材中心温度で前記冷却工程を開始する。
【００１９】
また、本発明の光学素子の成形方法は、ガラス素材と成形型とを加熱する第一の加熱工程と、前記成形型によって前記ガラス素材を押圧成形する押圧成形工程と、押圧成形工程開始後にガラス素材と成形型とを加熱する第二の加熱工程とよりなり、前記第一の加熱工程では成形型の温度がガラス素材の温度よりも低い温度となるように加熱温度を設定し、前記第二の加熱工程では押圧成形工程開始後の成形型表面近傍の温度上昇が３°Ｃ以上４０°Ｃ以内となるように加熱を行うことを特徴とする。
【００２０】
これにより本発明の光学素子の成形方法によれば所望の光学素子の中肉まで押圧して充分な押圧成形ができできかつその際に成形型へのガラスの融着が生じることを防止することができる。
成形型表面近傍の温度上昇が、３°Ｃ未満では、押圧成形しようとするとガラス素材自身の熱容量が不足して、所望の光学素子の中肉まで押圧成形することができない。一方、押圧開始後の成形型表面近傍の温度上昇が４０°Ｃを超える場合には成形型にガラス素材が融着し、成形を行うことができない。
【００２１】
以上の本発明の光学素子の成形方法においては、ガラス素材を押圧成形して得られる成形品の押圧される２面の最も厚い部分の厚さよりも成形型表面よりも浅い位置を測定点として、その測定点の温度上昇が３°Ｃ以上４０°Ｃ以内となるように第二の加熱工程における加熱を行うようにすることができる。
係る測定点は成形型表面近傍であり、係る測定点において測定することによって、成形型で押圧成形されるガラス素材の挙動をその温度変化として正確に把握することができ、光学素子の成形過程における加熱及び冷却制御を適切に行うことができる。
【００２２】
【発明の実施の形態】
次に本発明のガラス素材の成形方法の一実施の形態に用いるガラス素材の成形装置を図面を参照して説明する。
本実施の形態のガラス素材の成形方法に用いるガラス素材の成形装置の全体構成を図１に示す。
基台１上にはガラス素材２の加熱を行う加熱部３とガラス素材２に対する成形を行う成形部４とが隣接して配置される。前記成形部４の成形室５には、その上部に上型押さえ部材６が配置され、その上型押さえ部材６と天地方向に対向して下型押さえ部材７が設けられる。前記上型押さえ部材６は成形部４に対し固定され、一方前記下型押さえ部材７と一体な加圧軸８は図示しない駆動機構によって成形部４に対し上下動可能に摺動支持部９を介して取りつけられる。上型押さえ部材６には上型１０が固定され、係る上型１０はガラス素材２に対する上型成形機能面１０ａを有する。一方下型押さえ部材７には下型１１が固定され、係る下型１１はガラス素材２に対する下型成形機能面１１ａを有する。また下型押さえ部材７に固定された下型１１は前記加圧軸８を駆動させることによって上下駆動される。
【００２３】
また上型押さえ部材６には上型１０の外部に突出した部分の外周を取り囲んで上型加熱部１２が設けられる。その上型加熱部１２内側には上型１０側部を囲撓するように上型用ヒータ１３が取り付けられる。この上型用ヒータ１３は、上型１０を加熱するためのヒータであって係る目的から上型用ヒータ１３は上型１０を円周上に囲んで配置される。一方下型押さえ部材７には下型１１の外部に突出した部分の外周を取り囲んで下型加熱部１４が設けられる。その下型加熱部１４内側には下型１１側部を囲撓するように下型用ヒータ１５が取り付けられる。この下型用ヒータ１５は、下型１１を加熱するためのヒーターであって係る目的から下型用ヒータ１５は下型１１を円周上に囲んで配置される。
【００２４】
さらに上型押さえ部材６及び上型１０には、上型押さえ部材６及び上型１０それぞれの略中央部分を貫通する態様で上型用熱電対１６が取り付けられ、この上型用熱電対１６の基端は成形部４上面部分近傍の上型押さえ部材６基端部に固定され、一方上型用熱電対１６先端は上型１０のガラス素材２に対する上型成形機能面１０ａの近傍位置に配置される。この上型用熱電対１６によって上型１０の温度がモニターされ、したがって上型用熱電対１６の先端は、上型１０のガラス素材２に対する上型成形機能面１０ａ近傍に近いほど望ましい。
また上型１０のガラス素材２に対する上型成形機能面１０ａは凹面形状をしており、所望する球面形状に鏡面加工される。上型１０の上型成形機能面１０ａと上型１０の側部外周との連続部分１０ｂは、滑らかに連続するように上型成形機能面１０ａの球面形状の接線と、連続部分１０ｂの面取りＲの接線とが一致するように接続して加工される。連続部分１０ｂの面取りＲの接線と上型成形機能面１０ａの接線とを一致させることで滑らかにつなぐことは、非球面形状、自由曲面でも同様に可能である。
【００２５】
一方下型押さえ部材７及び下型１１には、下型押さえ部材７及び下型１１それぞれの略中央部分を貫通する態様で下型用熱電対１７が取り付けられ、この下型用熱電対１７の基端は成形部４下面部分近傍の下型押さえ部材７基端部に固定され、一方下型用熱電対１７先端は下型１１のガラス素材２に対する下型成形機能面１１ａの近傍位置に配置される。この下型用熱電対１７によって下型１１の温度がモニターされ、したがって下型用熱電対１７の先端は、下型１１のガラス素材２に対する下型成形機能面１１ａ近傍に近いほど望ましい。
【００２６】
また下型１１のガラス素材２に対する下型成形機能面１１ａは凹面形状をしており、所望する球面形状に鏡面加工される。下型１１の下型成形機能面１１ａと下型１１の側部外周との連続部分１１ｂは、滑らかに連続するように下型成形機能面１１ａの球面形状の接線と、連続部分１１ｂの面取りＲの接線とが一致するように接続して加工される。連続部分１１ｂの面取りＲの接線と下型成形機能面１１ａの接線とを一致させることで滑らかにつなぐことは、非球面形状、自由曲面でも同様に可能である。
【００２７】
前記基台１上に成形部４と隣接して配置されたガラス素材２の加熱を行う加熱部３は加熱室１８を備え、その加熱室１８を形成する加熱部３内側壁面に加熱室１８を取り囲む態様で円筒形状のヒーター１９が配置される。
また加熱部３には搬送アーム２０が設けられ、係る搬送アーム２０は加熱部３の加熱室１８内側を図示しない駆動源によって移動可能に配置される。この搬送アーム２０の先端部にはＵ字型のホルダ受け部２０ａが形成され、このホルダ受け部２０ａにガラス素材２を載置するホルダ２１が載置される。ホルダ２１はその内周面にガラス素材２を載置するための段部２１ａを備える。またホルダ２１の上端部は開放されて上型１０の上型成形機能面１０ａの外径よりも大なる径の開口部２１ｂとされ、一方ホルダ２１の段部２１ａ下方の下端部は開放されて下型１１の下型成形機能面１１ａの外径よりも大なる径の開口部２１ｃとされる。
【００２８】
一方、上型１０及び下型１１の酸化を防止することを目的として、ガラス素材２の成形を行う成形部４の前記成形室５内部は図示しない非酸化性ガス導入部材により非酸化性ガスが導入されて非酸化性雰囲気に保たれる。係る成形室５内部を非酸化性雰囲気に保つ非酸化性ガスとしては窒素ガス、アルゴンガス、ヘリウムガス等を適用することができる。また成形室５内部の酸素濃度は成形に使用される上型１０及び下型１１の型材や上型１０及び下型１１の表面を被覆する成膜材の種類に応じて適宜に調整される。例えば、上型１０及び下型１１の型材としてＷＣを用い膜厚３００Å（オングストローム）以下のＷＣ膜で被覆して構成した上型１０及び下型１１を使用する場合の成形室５内部の酸素濃度は、５ｐｐｍ〜２００ｐｐｍの範囲にするのが望ましい。この酸素濃度が２００ｐｐｍを超える場合には、上型１０及び下型１１の酸化が顕著となり、一方、この酸素濃度を５ｐｐｍ未満としても特に酸化防止効果がそれ以上向上するという利益はない。
【００２９】
以上の図１に示すガラス素材の成形装置によれば次のように本発明のガラス素材の成形方法が実施される。
先ずガラス素材２をホルダ２１の内側段部２１ａ上に載置し、その後に、ホルダ２１を搬送アーム２０のホルダ受け部２０ａに載置する。その状態で搬送アーム２０によって加熱部３の加熱室１８内にホルダ２１を搬送し、ヒータ１９によってガラス素材２を加熱する。
一方、前記基台１上に加熱部３と隣接して配置されたガラス素材２の成形を行う成形部４の成形室５内部に非酸化性ガスを導入して非酸化性雰囲気とし、上型１０及び下型１１とをあらかじめ所定温度Ｔ１に加熱する。
ガラス素材２中央部の温度が、所定温度Ｔ２に達した時に、ガラス素材２を対向配置されている上型１０及び下型１１間に搬送する。
【００３０】
次に加圧軸８を駆動させることによって下型押さえ部材７に固定された下型１１を駆動させ、上型１０の上型成形機能面１０ａと下型１１の下型成形機能面１１ａ間でガラス素材２を押圧成形する押圧工程を行う。
【００３１】
以上の工程において、ガラス素材２を押圧成形する押圧工程前にガラス素材２と上型１０及び下型１１を加熱する第一の加熱工程においてはガラス素材２の加熱温度Ｔ２と成形型である上型１０及び下型１１の加熱温度Ｔ１とを、上型１０及び下型１１の加熱温度Ｔ１がガラス素材２の加熱温度Ｔ２よりも低い温度であり（Ｔ２＞Ｔ１）、かつ押圧工程開始直後のガラス素材２表面部粘度はガラス素材２中央部粘度より高く、ガラス素材２表面部粘度とガラス素材２中央部粘度との比が１０^３．５以下となるようにガラス素材２の加熱温度Ｔ２と上型１０及び下型１１の加熱温度Ｔ１とを設定する。
【００３２】
次いで押圧成形工程開始後にガラス素材２と上型１０及び下型１１とをさらに加熱する第二の加熱工程を行う。この第二の加熱工程では押圧成形工程開始後の上型１０の上型成形機能面１０ａと下型１１の下型成形機能面１１ａの表面近傍のガラス素材２の温度上昇が３°Ｃ以上４０°Ｃ以内となるように加熱を行う。　この第二の加熱工程では、成形型表面すなわち上型成形機能面１０ａと下型成形機能面１１ａからの距離が図１に示す間隔Ａよりも浅い位置を測定点として、その測定点の温度上昇が３°Ｃ以上４０°Ｃ以内となるように加熱を行うようにする。この図１に示す間隔Ａはガラス素材２を押圧成形して得られる成形品の押圧される２面間の最も厚い部分の厚さであって上型成形機能面１０ａと下型成形機能面１１ａそれぞれの中心間距離である。
【００３３】
次に上型１０の上型成形機能面１０ａと下型１１の下型成形機能面１１ａ間でガラス素材２を押圧成形しさらに加熱する第二の加熱工程の後に冷却工程に移行する。係る冷却工程はガラス素材２のガラス転移点に相当する温度Ｔ３にガラス素材２の表面温度が達する前に開始する。この冷却工程開始温度Ｔ３は、ガラス素材２のガラス転移点がガラス粘度で１０^１３．５ｄＰａＳに相当する温度である場合には、１０^１３．５ｄＰａＳに相当する温度と設定される。またこの冷却工程開始温度Ｔ３は、実施の態様によってはガラス素材２の表面温度がガラス転移点のガラス粘度に対して１０^−１．５倍の粘度に相当する温度以下とする。したがって前述のようにガラス素材２のガラス転移点がガラス粘度で１０^１３．５ｄＰａＳに相当する温度と決定される場合には、この冷却工程開始温度Ｔ３はガラス粘度で１０^１２ｄＰａＳに相当する温度として設定する。またこの冷却工程では、成形後のガラス素材２表面部の粘度のガラス素材２中央部の粘度に対する比が１０^１．５ｄＰａＳ以内になるまで冷却を行う。
【００３４】
【実施例】
次に以上の実施の形態に示したガラス素材の成形装置を用いて本発明のガラス素材の成形方法を実施した実施例を説明する。
（実施例１）
図１に示す全体構成のガラス素材の成形装置を用いて本発明のガラス素材の成形方法を実施した。
本実施例では、上型用ヒータ１３及び下型用ヒータ１５として赤外線ランプヒータ使用した。
【００３５】
本実施例では、上型１０及び下型１１の素材にはＳｉＣ（炭化珪素）を使用し、膜厚２０００Å（オングストローム＝１０^−１０ｍ）以下のカーボン膜にて被覆した。上型１０の成形機能面１０ａ中心から上型１０基端部までの距離の９０％に相当する深さまで上型用熱電対１６を挿入し、同様に下型１１の成形機能面１１ａ中心から下型１１基端部までの距離の９０％に相当する深さまで下型用熱電対１７を挿入した。その結果、上型用熱電対１６と上型成形機能面１０ａ及び下型用熱電対１７先端と下型成形機能面１１ａとの間隔は、上型成形機能面１０ａと下型成形機能面１１ａとの間隔の最も大きな部分の間隔Ａ、すなわち成形品の最大肉厚であって、上型成形機能面１０ａと下型成形機能面１１ａとの中心間距離よりも小さくされた。
またガラス素材２の成形を行う成形部の成形室５中央部を非酸化性雰囲気に保つ非酸化性ガスとしては窒素ガスを使用し、成形室５中央部を、酸素濃度１５％以下に保った。
【００３６】
また、本実施例では、ガラス素材２の表面温度と中央部温度とをモニターする為に、ガラス素材２中央部に図示を省略した熱電対を挿入した。測定した結果を図２に示してある。図２のΔｔは、ガラス素材２の表面温度と中央部温度との差を示す。
【００３７】
先ず上型１０及び下型１１とをあらかじめガラス素材２の粘度で１０^１３．５ｄＰａＳに相当する５４０℃に加熱し、同時に、ガラス素材２を収納したホルダ２１を搬送アーム２０によって加熱部３の加熱室１８内に搬送し、ヒータ１９によってガラス素材２を加熱して、ガラス素材２中央部の温度が、ガラス素材２の粘度で１０^８．５ｄＰａＳに相当する粘度である６４５℃に達した時に、ガラス素材２を対向配置されている上型１０及び下型１１間に搬送した。
【００３８】
次に加圧軸８を駆動させることによって下型押さえ部材７に固定された下型１１を駆動させ、上型１０の上型成形機能面１０ａと下型１１の下型成形機能面１１ａ間でガラス素材２を押圧成形した。
【００３９】
以上の工程において、ガラス素材２を押圧成形する押圧工程前にガラス素材２と上型１０及び下型１１を加熱する第一の加熱工程においてはガラス素材２の加熱温度６４５℃（＝Ｔ２）と成形型である上型１０及び下型１１の加熱温度５４０℃（＝Ｔ１）とを、上型１０及び下型１１の加熱温度Ｔ１がガラス素材２の加熱温度Ｔ２よりも低い温度となるようにした。またガラス素材２の加熱温度Ｔ２と上型１０及び下型１１の加熱温度Ｔ１とを以上のように設定した結果、押圧工程開始直後のガラス素材２表面部の粘度のガラス素材２中央部の粘度に対する比は１０^３．５以下であった。具体的には、押圧工程開始直後の成形された瞬間にガラス素材２の表面温度は下がり、ガラス素材２の粘度で１０^１２ｄＰａＳに相当する温度である５７０℃となった。また、その時、ガラス素材２の中央部温度はガラス素材２の粘度で１０^８．５ｄＰａＳに相当する温度である６４５℃であった。したがって、この時、図２のΔｔすなわちガラス素材２の表面温度と中央部温度との差は７５℃であった。また、この時、上型１０及び下型１１の温度は３℃上昇した。
【００４０】
その後冷却工程に移行した。係る冷却工程はガラス素材２のガラス粘度で１０^１２ｄＰａＳに相当する温度である５７０℃にガラス素材２中央部の温度が達する前に開始した。その際、ガラス素材２表面は本実施例で使用したガラス転移点温度である１０^１３．５ｄＰａＳであった。またこの冷却工程では、成形後、ガラス素材２表面部粘度の中央部粘度に対する比が１０^１．５以内になるまで冷却を行った。
【００４１】
その後ガラス素材２から、熱電対を取り去り、上述と同じ条件でガラス素材２の成形を行い得られた光学素子の検査を行った。
検査はＮＲ（ニュートンリング）、クセにつき行った。
（１）ＮＲ：得られた光学素子の曲率半径と成形に使用した型の曲率半径の差の絶対値を干渉縞本数で記述したパラメータ。
（２）クセ：得られた光学素子の形状の誤差であり、ヒケを定量的に評価したパラメータ。
以上のＮＲとクセについてはそれぞれ成形品の仕様で許容される上限値で規格化し、許容される上限値を１００％とし、得られた結果がこれを下回る数値である場合には良好な結果であるものとして評価した。
係る検査の結果、本実施例によって得られた光学素子がＮＲ８３％、クセ５０％以下の高精度な面形状を持つ光学素子が成形できることを確認した。
【００４２】
以上の実施例において上型１０及び下型１１から離型を行う温度はガラス素材２中央部の粘度がガラス転移点温度以下になった後の方が、より望ましいが、サイクルタイムを短縮するために、ガラス中央部の温度がガラス粘度で１０^１２ｄＰａＳに相当する温度になった時に離型しても、ガラス素材２表面部粘度の中央部粘度に対する比が１０^１．５以下であれば、得られる光学素子は、十分な光学性能が得られた。
【００４３】
（実施例２）
他は実施例１と同様として、下記ｉ，ｉｉ　の２条件につき異なる数値とする制御を行い光学素子を成形した。
ｉ　　押圧工程開始直後のガラス素材２表面部粘度の中央部粘度に対する比
ｉｉ　　　押圧工程開始後、ガラス素材２中央部の粘度が１０^１２ｄＰａＳに達した際の表面部の中央部に対する粘度比
得られた光学素子につきその検査を行った。結果を表１に示す。
【００４４】
【表１】

【００４５】
表１に示されるように、押圧工程開始直後のガラス素材２表面部粘度と中央部粘度に対する比（条件ｉ）が１０^４．５に達する場合には、押圧工程開始後、ガラス素材２中央部の粘度が１０^１２ｄＰａＳに達した際の表面部の中央部に対する粘度比（条件ｉｉ　）のいかんに関わらず、上型１０及び下型１１へのガラス素材２の融着による成形不良である型融着が発生すると共に、クセが許容上限値を超えた。
【００４６】
これに対し、押圧工程開始直後のガラス素材２表面部粘度の中央部粘度に対する比（条件ｉ）が１０^３．５以下であれば原則として良好な成形結果が得られる。但し押圧工程開始後、ガラス素材２中央部の温度がガラス粘度で１０^１２ｄＰａＳに相当する温度に達した際の表面部の中央部に対する粘度比（条件ｉｉ　）が１０^２．５に達する場合には、ＮＲ、クセが許容上限値を超えた。
これは以下の理由による。
すなわちガラス固有の物性として、ガラス転移点に近い１０^１２ｄＰａＳを超える粘度では流動性すなわち変形がなくなるという事実がある。さらに詳細には１０^１２ｄＰａＳ以上でもわずかに流動性が保たれるにしろほぼガラス転移点であると認められる１０^１３．５ｄＰａＳ以上では流動性は失われる。また、ガラス素材２の表面部と中央部とに粘度の差がある場合にはガラス素材２表面部と中央部とに熱膨張差が生じる。以上のことから、ガラス素材２中央部の温度がほぼガラス転移点であると認められる１０^１３．５ｄＰａＳに対して１０^−１．５倍のガラス粘度である１０^１２ｄＰａＳに相当する温度に達すると共に、ガラス素材２の表面が中央部に対して１０^２．５倍を超える粘度の違いが生じる場合には、その後冷却すると、ガラス素材２の中央部は流動性が極めて低く、且つガラス素材２表面部と中央部とに熱膨張差が生じることからヒケが起こり、得られる光学素子における転写精度の悪化の原因となる。
【００４７】
（実施例３）
本実施例では、半径Φ２ｍｍのガラス素材２を使用した。その他、用いた成形装置等は実施例１と同様でありその記載を省略する。
尚、図３は本実施例でガラス素材２に熱電対を挿入し測定した結果であり、ΔＳは、プレス開始後の型温度の最高到達点とプレス直前の成形型の温度差を示す。
先ず上型１０及び下型１１とをあらかじめガラス素材２の粘度で１０^１３．５ｄＰａＳに相当する５４０℃に加熱し、同時に、ガラス素材２を収納したホルダ２１を搬送アーム２０によって加熱部３の加熱室１８内に搬送し、ヒータ１９によってガラス素材２を加熱して、ガラス素材２中央部の温度が、ガラス素材２の粘度で１０^８．５ｄＰａＳａｓに相当する粘度である６３０℃に達した時に、ガラス素材２を対向配置されている上型１０及び下型１１間に搬送した。
【００４８】
次に加圧軸８を駆動させることによって下型押さえ部材７に固定された下型１１を駆動させ、上型１０の上型成形機能面１０ａと下型１１の下型成形機能面１１ａ間でガラス素材２を押圧成形し、成形された瞬間にガラス素材２の表面温度は低下し、表面温度はガラス素材２の粘度で１０^１３．７ｄＰａＳに相当する温度である５４５℃となり、一方、中央部温度はガラス素材２の粘度で１０^８．８ｄＰａＳに相当する温度である６３０℃であった。この時、同時に上型用ヒータ１３と下型用ヒータ１５の出力を上げ、ガラス素材２と上型１０及び下型１１とをさらに加熱する第二の加熱工程を行った。これにより、上型１０と下型１１との温度が上昇し、上型１０と下型１１の温度は５８０℃となった。図３に示されるように本実施例ではプレス開始後の型温度の最高到達点とプレス直前の成形型の温度差ΔＳは３５℃である。
【００４９】
次に実施例１と同様に冷却工程を行い、その後ガラス素材２から、熱電対を取り去り、上述と同じ条件でガラス素材２の成形を行い得られた光学素子の外観検査を行った。その結果、得られた光学素子がＮＲ８３％、クセ５０％以下の良好な光学素子であることを確認した。
本実施例３の光学素子の成形方法によれば、割れや中肉の加圧不足等の欠陥がない光学素子を成形することができた。
【００５０】
（実施例４）
他は実施例３と同一として、ガラス素材２の中央部温度を１０^７ｄＰａＳに相当する６６０℃とし、上型１０及び下型１１の温度をガラス素材２の粘度で１０^１１ｄＰａＳに相当する５８０℃に設定して、上型１０と下型１１間でガラス素材２の押圧成形を開始した。また上型用ヒータ１３と下型用ヒータ１５による押圧成形開始後の加熱は行わなかった。しかし、上型１０と下型１１の温度は３５℃上昇し、良好な光学素子が得られた。
【００５１】
（比較例１）
他は実施例３と同様として、上型用ヒータ１３と下型用ヒータ１５の出力を調整することによってガラス素材２を押圧成形する押圧工程開始後に上型用ヒータ１３と下型用ヒータ１５の出力を上げ、上型１０及び下型１１の加熱温度を５８５℃以上とした。したがってガラス素材２押圧成形工程開始後の成形型である上型１０と下型１１の表面近傍の温度上昇は４０℃以上となった。その結果、ガラス素材２の上型１０及び下型１１への融着が起き、光学素子を得ることはできなかった。
（比較例２）
他は実施例２と同様として、ガラス素材２を押圧成形する押圧工程開始後に上型用ヒータ１３と下型用ヒータ１５による出力を行わず上型１０及び下型１１の加熱は行わなかった。この時、上型１０及び下型１１の温度は実質的には上昇せず、温度上昇は３℃未満（２℃）であった。その結果、押圧成形過程でガラス素材２は割れてしまい所望の光学素子は得られなかった。
（比較例３）
他は実施例２と同様として、ガラス素材２を押圧成形する押圧工程前にガラス素材２と上型１０及び下型１１を加熱する第一の加熱工程においてガラス素材２の加熱温度Ｔ２をガラス素材２中央部の温度を１０^５．５ｄＰａＳに相当する７００℃とし、上型１０及び下型１１の加熱温度Ｔ１をガラス素材２の粘度で１０^１１ｄＰａＳに相当する温度である５８０℃に設定した。その結果上型１０と下型１１の温度は４５℃上昇し、ガラス素材２の上型１０及び下型１１への融着が起き、光学素子を得ることはできなかった。
【００５２】
以上の実施例１、実施例３、実施例４、比較例１〜比較例３につき押圧成形工程開始後の成形型表面近傍の上昇温度と成形結果とを表２に整理して示す。
表２に示されるように、押圧成形工程開始後の成形型表面近傍の上昇温度が３℃である実施例１及び同じく上昇温度が３５℃である実施例３及び実施例４では良好な成形結果が得られた。これに対し上昇温度が４０℃以上である比較例１、比較例３では型融着が生じて良好な成形結果は得られない。また押圧成形工程開始後の成形型表面近傍の温度上昇を行わない比較例２ではガラス素材２に割れが発生し、やはり良好な成形結果は得られない。
【００５３】
【表２】

【００５４】
【発明の効果】
本発明の光学素子の成形方法によれば、ガラスが型に融着したり、割れたり、所定厚みまで押厚できなかったりすることがなく、高精度な面精度を有する光学素子を得ることができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に用いるガラス素材の成形装置の全体構成図である。
【図２】本発明の実施例１におけるガラス素材２の表面温度と中央部温度との成形過程における変化を測定した結果を示す説明図である。
【図３】本発明の実施例３におけるガラス素材２の表面温度と中央部温度との成形過程における変化を測定した結果を示す説明図である。
【符号の説明】
２・・・ガラス素材、４・・・成形部、３・・・加熱部、１０・・・上型、１１・・・下型、１６・・・上型用熱電対、１７・・・下型用熱電対。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for molding an optical element for obtaining a glass optical element by press-molding a heat-softened glass material with a pair of molds.
[0002]
[Prior art]
As methods for molding glass optical elements, the inventions of Japanese Patent Nos. 3201887 and 2952185 are disclosed.
The method described in Japanese Patent No. 3201887 uses a glass material of 10 ⁷ -10 ⁹ Heat to a viscosity of dPaS, ¹⁰ -10 ¹² In this method, a desired optical element is obtained by pressing with a molding die heated to a viscosity equivalent to dPaS. In Example 1 described in Japanese Patent No. 3201887, it is described that the glass temperature suddenly drops and the temperature of the molding die rises slightly at the start of pressing.
[0003]
The method described in Japanese Patent No. 2952185 uses 10 glass materials. ⁹ Heat to a viscosity of less than dPaS, ⁹ -10 ¹² In this method, a desired optical element is obtained by pressing with a molding die heated to a viscosity equivalent to dPaS.
[0004]
[Problems to be solved by the invention]
However, in the case of the method described in Japanese Patent No. 3201887, since the temperature rise of the molding die is not controlled, if the temperature rise of the molding die is small, the desired optical element cannot be pressed or cracked. There was a thing. On the other hand, if the temperature rise is too high, the glass and the mold may be fused or sinked.
[0005]
Further, when molding an optical element under the conditions described in Japanese Patent No. 2952185, when molding an optical element with a small diameter of Φ5 mm or less, cooling is caused by the small volume of the glass material to be molded. However, there is a problem in that it becomes too fast and the inner part of the desired optical element cannot be pressed or cracked.
[0006]
The present invention has been made in view of the above-described problems in the prior art, and an object of the present invention is to provide a method for molding an optical element which does not cause cracks, lack of thickness, fusion between a mold and a glass material, and sink.
[0007]
[Means for Solving the Problems]
The optical element molding method of the first invention of the present application that solves the above problems comprises a heating step of heating a glass material and a mold, and a press molding step of pressing the glass material by the molding die, In the heating step, the heating temperature of the glass material and the heating temperature of the mold are set such that the heating temperature of the mold is lower than the heating temperature of the glass material, and immediately after the start of the pressing step, the surface portion of the glass material The ratio of viscosity to center viscosity is greater than 1 and 10 ^3.5 The heating temperature of the glass material and the mold is set so as to be as follows.
[0008]
According to such a molding method of an optical element, the ratio of the surface part viscosity of the glass material immediately after the start of pressing to the central part viscosity is 10 ^3.5 By setting it as below, it is possible to press the desired contents in a short time, and it is possible to mold a desired optical element with good surface accuracy.
Here, the ratio of the viscosity of the surface portion of the glass to the central portion is 10 ^3.5 If the ratio exceeds 1, sink marks occur, the surface accuracy deteriorates, and a desired optical element cannot be obtained.
[0009]
Moreover, it has the cooling process which cools after the press molding process start, and the ratio with respect to the center part viscosity of the surface part viscosity of a glass raw material is larger than 1, 10 ^2.5 The cooling step is started before the glass material surface temperature reaches a temperature lower than the temperature corresponding to the glass transition point, and the ratio of the surface part viscosity of the glass material to the central part viscosity after molding is 10 ^1.5 Cool until it is within.
[0010]
According to the method for forming a glass material of the present invention, a desired optical element having good surface accuracy free from defects such as NR (Newton ring) and sink marks can be formed.
The ratio of viscosity to the center of the glass surface is 10 ^2.5 In the above case, an excessive difference in thermal expansion occurs between the glass material surface portion and the central portion, and when the glass material is subsequently cooled, the thermal expansion difference causes shape deterioration called sink.
[0011]
When cooling after the temperature of the glass material surface reaches a temperature corresponding to the glass transition point of the glass material, the fluidity is lost due to the physical properties of the glass material. The surface part has no fluidity, and a difference in thermal expansion occurs between the surface part and the central part of the glass material, resulting in deterioration of the shape called sink, causing the deterioration of transfer accuracy in the optical element from which such a defect is obtained. It becomes.
[0012]
Further, the ratio of the glass surface part viscosity after molding to the central part viscosity is 10 ^1.5 By cooling while converging until it is within the range, the difference in thermal expansion between the glass surface portion and the central portion can be eliminated, and deformation of a similar shape can be promoted as a whole, and the occurrence of sink marks can be eliminated. The ratio of the glass surface part viscosity after molding to the central part viscosity is 10 ^1.5 If it is not cooled to within the range, sink marks occur due to the difference in thermal expansion between the glass surface portion and the central portion.
[0013]
In the method for molding an optical element of the present invention, the viscosity of the glass material is 10 with respect to the viscosity at the transition point of the glass material. ^-1.5 The cooling step is started at a glass material surface temperature equal to or lower than the temperature corresponding to the double viscosity.
[0014]
According to the method for molding a glass material of the present invention, it is possible to more efficiently mold a desired optical element having good surface accuracy free from defects such as NR (Newton ring), sink marks, and peculiarities.
Here, the surface temperature of the glass material is 10 with respect to the glass viscosity at the glass transition point. ^-1.5 When the cooling step is started at a glass material surface temperature exceeding a temperature corresponding to twice the viscosity, as a physical property specific to glass, the viscosity of the glass transition point is 10%. ^-1.5 If the viscosity exceeds twice, the fluidity on the surface of the glass material will be extremely small even if it does not completely disappear.There is a difference in viscosity between the surface and center of the glass material, and there is a difference between the surface and center of the glass material. If there is a difference in thermal expansion, the surface portion of the glass material will have extremely low fluidity when cooled, and a difference in thermal expansion will occur between the surface portion and the central portion of the glass material, resulting in deterioration of the shape called sink. It occurs and causes the deterioration of transfer accuracy in the optical element from which such a defect is obtained.
[0015]
In the above, it is 10 with respect to the glass viscosity of a glass transition point. ^-1.5 The temperature corresponding to the double viscosity is such that the glass transition point of the glass material is, for example, 10 in terms of glass viscosity. ^13.5 When the temperature is equivalent to dPaS, the glass viscosity is 10 ¹² The temperature corresponds to dPaS. Therefore, in that case, the glass viscosity is 10 ¹² The cooling process is started at a glass material surface temperature equal to or lower than the temperature corresponding to dPaS.
[0016]
Moreover, the molding method of the optical element of the present invention includes a cooling step of cooling after the start of the press molding step, and the ratio of the viscosity of the glass material surface portion to the viscosity of the glass material central portion is larger than 1 and 10 ^2.5 Less than 10 for the glass viscosity at the glass transition point. ^-1.5 The cooling step is started at the glass material center temperature equal to or lower than the temperature corresponding to the double viscosity, and the ratio of the surface part viscosity of the glass material after molding to the center part viscosity is 10 ^1.5 Cool until it is within.
[0017]
According to the method for forming a glass material of the present invention, a desired optical element having a good surface accuracy free from defects such as NR and sink marks can be formed more efficiently as in the above-described inventions.
[0018]
In the above, it is 10 with respect to the glass viscosity of a glass transition point. ^-1.5 The temperature corresponding to the double viscosity is such that the glass transition point of the glass material is, for example, 10 in terms of glass viscosity. ^13.5 When the temperature is equivalent to dPaS, the glass viscosity is 10 ¹² The temperature corresponds to dPaS. Therefore, in that case, the glass viscosity is 10 ¹² The cooling process is started at the glass material center temperature equal to or lower than the temperature corresponding to dPaS.
[0019]
The optical element molding method of the present invention includes a first heating step of heating a glass material and a molding die, a press molding step of pressing the glass material with the molding die, and a glass after starting the pressing molding step. A second heating step for heating the material and the mold, and in the first heating step, the heating temperature is set so that the temperature of the molding die is lower than the temperature of the glass material, and the second heating step is performed. The heating step is characterized in that heating is performed so that the temperature rise in the vicinity of the mold surface after the start of the press molding step is 3 ° C. or more and 40 ° C. or less.
[0020]
As a result, according to the method for molding an optical element of the present invention, the inside of the desired optical element can be pressed and sufficient press molding can be performed, and at that time, the glass can be prevented from being fused to the mold. Can do.
If the temperature rise in the vicinity of the mold surface is less than 3 ° C., the heat capacity of the glass material itself is insufficient when press molding is performed, and it is impossible to press mold to the desired thickness of the optical element. On the other hand, when the temperature rise in the vicinity of the mold surface after the start of pressing exceeds 40 ° C., the glass material is fused to the mold and molding cannot be performed.
[0021]
In the method for molding an optical element of the present invention described above, a measurement point is a position shallower than the surface of the mold than the thickness of the thickest part of the two surfaces to be pressed of a molded product obtained by press molding a glass material, The heating in the second heating step can be performed so that the temperature rise at the measurement point is 3 ° C. or more and 40 ° C. or less.
The measurement point is near the surface of the mold, and by measuring at the measurement point, the behavior of the glass material that is press-molded by the mold can be accurately grasped as the temperature change, and in the process of molding the optical element Heating and cooling control can be appropriately performed.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, a glass material molding apparatus used in an embodiment of a glass material molding method of the present invention will be described with reference to the drawings.
FIG. 1 shows an overall configuration of a glass material molding apparatus used in the glass material molding method of the present embodiment.
On the base 1, a heating unit 3 that heats the glass material 2 and a molding unit 4 that molds the glass material 2 are disposed adjacent to each other. In the molding chamber 5 of the molding unit 4, an upper mold pressing member 6 is disposed at an upper portion thereof, and a lower mold pressing member 7 is provided so as to face the upper mold pressing member 6 in the vertical direction. The upper mold pressing member 6 is fixed to the molding part 4, while the pressure shaft 8 integrated with the lower mold pressing member 7 is provided with a sliding support part 9 which can be moved up and down with respect to the molding part 4 by a drive mechanism (not shown). It is attached via. An upper mold 10 is fixed to the upper mold holding member 6, and the upper mold 10 has an upper mold forming functional surface 10 a for the glass material 2. On the other hand, a lower mold 11 is fixed to the lower mold holding member 7, and the lower mold 11 has a lower mold forming functional surface 11 a for the glass material 2. The lower mold 11 fixed to the lower mold pressing member 7 is driven up and down by driving the pressure shaft 8.
[0023]
Further, the upper mold holding member 6 is provided with an upper mold heating section 12 surrounding the outer periphery of the portion protruding to the outside of the upper mold 10. An upper mold heater 13 is attached inside the upper mold heating section 12 so as to surround and bend the upper mold 10 side section. The upper die heater 13 is a heater for heating the upper die 10. For the purpose, the upper die heater 13 is disposed so as to surround the upper die 10 on the circumference. On the other hand, the lower mold holding member 7 is provided with a lower mold heating section 14 surrounding the outer periphery of the portion protruding to the outside of the lower mold 11. A lower mold heater 15 is attached to the inner side of the lower mold heating section 14 so as to surround and bend the side of the lower mold 11. The lower mold heater 15 is a heater for heating the lower mold 11. For the purpose, the lower mold heater 15 is disposed so as to surround the lower mold 11 on the circumference.
[0024]
Further, an upper mold thermocouple 16 is attached to the upper mold holding member 6 and the upper mold 10 in such a manner as to pass through substantially the central portions of the upper mold holding member 6 and the upper mold 10. The base end is fixed to the base end portion of the upper mold holding member 6 near the upper surface portion of the molding portion 4, while the tip of the upper mold thermocouple 16 is disposed in the vicinity of the upper mold forming functional surface 10 a with respect to the glass material 2 of the upper mold 10. Is done. The temperature of the upper mold 10 is monitored by the upper mold thermocouple 16, and therefore the tip of the upper mold thermocouple 16 is preferably closer to the vicinity of the upper mold forming functional surface 10 a for the glass material 2 of the upper mold 10.
Further, the upper mold forming functional surface 10a for the glass material 2 of the upper mold 10 has a concave shape and is mirror-finished into a desired spherical shape. The continuous portion 10b between the upper mold forming functional surface 10a of the upper mold 10 and the outer periphery of the side portion of the upper mold 10 has a spherical tangent to the upper mold forming functional surface 10a and a chamfer R of the continuous portion 10b. Are connected and processed so that their tangents coincide with each other. Smooth connection by matching the tangent line of the chamfer R of the continuous portion 10b with the tangent line of the upper mold forming functional surface 10a is also possible with an aspherical shape and a free-form surface.
[0025]
On the other hand, a lower mold thermocouple 17 is attached to the lower mold holding member 7 and the lower mold 11 in such a manner that the lower mold holding member 7 and the lower mold 11 pass through substantially the center portions of the lower mold holding member 7 and the lower mold 11. The base end is fixed to the base end portion of the lower mold holding member 7 in the vicinity of the lower surface portion of the molding portion 4, while the tip of the lower mold thermocouple 17 is disposed in the vicinity of the lower mold forming functional surface 11 a with respect to the glass material 2 of the lower mold 11. Is done. The temperature of the lower mold 11 is monitored by the lower mold thermocouple 17. Therefore, it is desirable that the tip of the lower mold thermocouple 17 is closer to the vicinity of the lower mold forming functional surface 11 a with respect to the glass material 2 of the lower mold 11.
[0026]
The lower mold forming functional surface 11a of the lower mold 11 with respect to the glass material 2 has a concave shape and is mirror-finished into a desired spherical shape. The continuous part 11b between the lower mold forming functional surface 11a of the lower mold 11 and the outer periphery of the side of the lower mold 11 is a tangential line of the spherical shape of the lower mold forming functional surface 11a and the chamfer R of the continuous part 11b so as to be smoothly continuous. Are connected and processed so that their tangents coincide with each other. Smooth connection by matching the tangent line of the chamfer R of the continuous portion 11b with the tangent line of the lower mold forming functional surface 11a is also possible for an aspherical shape and a free-form surface.
[0027]
The heating unit 3 for heating the glass material 2 disposed adjacent to the forming unit 4 on the base 1 includes a heating chamber 18, and the heating chamber 18 is provided on the inner wall surface of the heating unit 3 that forms the heating chamber 18. A cylindrical heater 19 is arranged in a surrounding manner.
The heating unit 3 is provided with a transfer arm 20, and the transfer arm 20 is disposed inside the heating chamber 18 of the heating unit 3 so as to be movable by a driving source (not shown). A U-shaped holder receiving portion 20a is formed at the tip of the transfer arm 20, and a holder 21 for placing the glass material 2 is placed on the holder receiving portion 20a. The holder 21 includes a step portion 21a for placing the glass material 2 on the inner peripheral surface thereof. The upper end of the holder 21 is opened to form an opening 21b having a diameter larger than the outer diameter of the upper mold forming functional surface 10a of the upper mold 10, while the lower end of the holder 21 below the step 21a is opened. The opening 21c has a diameter larger than the outer diameter of the lower mold forming functional surface 11a of the lower mold 11.
[0028]
On the other hand, in order to prevent the upper mold 10 and the lower mold 11 from being oxidized, a non-oxidizing gas is introduced into the molding chamber 5 of the molding unit 4 for molding the glass material 2 by a non-oxidizing gas introduction member (not shown). It is introduced and kept in a non-oxidizing atmosphere. Nitrogen gas, argon gas, helium gas, etc. can be applied as the non-oxidizing gas for keeping the inside of the molding chamber 5 in a non-oxidizing atmosphere. Further, the oxygen concentration inside the molding chamber 5 is appropriately adjusted according to the mold materials of the upper mold 10 and the lower mold 11 used for molding and the types of film forming materials covering the surfaces of the upper mold 10 and the lower mold 11. For example, the oxygen concentration in the molding chamber 5 when using the upper mold 10 and the lower mold 11 formed by covering the upper mold 10 and the lower mold 11 with a WC film having a film thickness of 300 Å (angstrom) or less using WC. Is preferably in the range of 5 ppm to 200 ppm. When the oxygen concentration exceeds 200 ppm, the oxidation of the upper mold 10 and the lower mold 11 becomes remarkable. On the other hand, even when the oxygen concentration is less than 5 ppm, there is no benefit that the antioxidant effect is further improved.
[0029]
According to the glass material molding apparatus shown in FIG. 1, the glass material molding method of the present invention is carried out as follows.
First, the glass material 2 is placed on the inner step portion 21 a of the holder 21, and then the holder 21 is placed on the holder receiving portion 20 a of the transfer arm 20. In this state, the holder 21 is transferred into the heating chamber 18 of the heating unit 3 by the transfer arm 20, and the glass material 2 is heated by the heater 19.
On the other hand, a non-oxidizing gas is introduced into the forming chamber 5 of the forming part 4 for forming the glass material 2 arranged adjacent to the heating part 3 on the base 1 to form a non-oxidizing atmosphere. 10 and the lower mold 11 are heated in advance to a predetermined temperature T1.
When the temperature at the center of the glass material 2 reaches a predetermined temperature T2, the glass material 2 is transported between the upper mold 10 and the lower mold 11 that are arranged to face each other.
[0030]
Next, the lower mold 11 fixed to the lower mold pressing member 7 is driven by driving the pressure shaft 8, and the upper mold forming functional surface 10 a of the upper mold 10 and the lower mold forming functional surface 11 a of the lower mold 11 are driven. A pressing step of pressing the glass material 2 is performed.
[0031]
In the above process, in the first heating process in which the glass material 2 and the upper mold 10 and the lower mold 11 are heated before the pressing process of pressing the glass material 2, the heating temperature T2 of the glass material 2 and the molding die The heating temperature T1 of the mold 10 and the lower mold 11 is the temperature at which the heating temperature T1 of the upper mold 10 and the lower mold 11 is lower than the heating temperature T2 of the glass material 2 (T2> T1) and immediately after the pressing process is started. Glass material 2 surface part viscosity is higher than glass material 2 center part viscosity, and ratio of glass material 2 surface part viscosity and glass material 2 center part viscosity is 10 ^3.5 The heating temperature T2 of the glass material 2 and the heating temperature T1 of the upper mold 10 and the lower mold 11 are set so as to be as follows.
[0032]
Next, after the press molding process is started, a second heating process for further heating the glass material 2 and the upper mold 10 and the lower mold 11 is performed. In this second heating step, the temperature rise of the glass material 2 in the vicinity of the upper mold functional surface 10a of the upper mold 10 and the lower mold functional surface 11a of the lower mold 11 after the start of the press molding process is 3 ° C. or more and 40 Heat so that it is within ° C. In this second heating step, the temperature rise at the measurement point is taken at a position where the distance between the mold surface, that is, the upper mold function surface 10a and the lower mold function surface 11a is shallower than the distance A shown in FIG. Is heated to 3 ° C or more and 40 ° C or less. The interval A shown in FIG. 1 is the thickness of the thickest portion between two pressed surfaces of a molded product obtained by pressing the glass material 2, and the upper mold forming functional surface 10a and the lower mold forming functional surface 11a. The distance between each center.
[0033]
Next, the glass material 2 is press-molded between the upper mold forming functional surface 10a of the upper mold 10 and the lower mold forming functional surface 11a of the lower mold 11, and then the process proceeds to the cooling process after the second heating process. Such a cooling process starts before the surface temperature of the glass material 2 reaches the temperature T3 corresponding to the glass transition point of the glass material 2. The cooling process start temperature T3 is such that the glass transition point of the glass material 2 is 10 in terms of glass viscosity. ^13.5 When the temperature is equivalent to dPaS, 10 ^13.5 It is set to a temperature corresponding to dPaS. Moreover, this cooling process start temperature T3 is 10 with respect to the glass viscosity of the glass transition point where the surface temperature of the glass raw material 2 depending on the aspect. ^-1.5 The temperature is equal to or lower than the temperature corresponding to the double viscosity. Therefore, as described above, the glass transition point of the glass material 2 is 10 in terms of glass viscosity. ^13.5 When it is determined that the temperature corresponds to dPaS, this cooling process start temperature T3 is 10% in terms of glass viscosity. ¹² It is set as a temperature corresponding to dPaS. In this cooling step, the ratio of the viscosity of the surface portion of the glass material 2 after molding to the viscosity of the central portion of the glass material 2 is 10 ^1.5 Cool until dPaS is reached.
[0034]
【Example】
Next, an example in which the glass material forming method of the present invention is implemented using the glass material forming apparatus shown in the above embodiment will be described.
Example 1
The glass material molding method of the present invention was carried out using the glass material molding apparatus having the overall configuration shown in FIG.
In this example, infrared lamp heaters were used as the upper mold heater 13 and the lower mold heater 15.
[0035]
In the present embodiment, SiC (silicon carbide) is used for the material of the upper mold 10 and the lower mold 11, and the film thickness is 2000 mm (angstrom = 10). ^-10 m) Covered with the following carbon film. The upper mold thermocouple 16 is inserted to a depth corresponding to 90% of the distance from the center of the molding function surface 10a of the upper mold 10 to the base end portion of the upper mold 10, and similarly, from the center of the molding function surface 11a of the lower mold 11 to the bottom. The lower mold thermocouple 17 was inserted to a depth corresponding to 90% of the distance to the mold 11 base end. As a result, the distance between the upper mold forming functional surface 10a and the upper mold forming functional surface 10a and the lower mold thermocouple 17 tip and the lower mold forming functional surface 11a is the same as the upper mold forming functional surface 10a and the lower mold forming functional surface 11a. The distance A of the largest part of the distance, that is, the maximum thickness of the molded product, was made smaller than the center-to-center distance between the upper mold functional surface 10a and the lower mold functional surface 11a.
Further, nitrogen gas was used as a non-oxidizing gas for keeping the central part of the molding chamber 5 for molding the glass material 2 in a non-oxidizing atmosphere, and the central part of the molding chamber 5 was kept at an oxygen concentration of 15% or less. .
[0036]
In this example, in order to monitor the surface temperature and the center temperature of the glass material 2, a thermocouple (not shown) was inserted in the center of the glass material 2. The measurement results are shown in FIG. Δt in FIG. 2 indicates a difference between the surface temperature of the glass material 2 and the center temperature.
[0037]
First, the upper mold 10 and the lower mold 11 are preliminarily set to 10 with the viscosity of the glass material 2. ^13.5 The glass material 2 is heated to 540 ° C. corresponding to dPaS, and at the same time, the holder 21 containing the glass material 2 is conveyed into the heating chamber 18 of the heating unit 3 by the conveying arm 20, and the glass material 2 is heated by the heater 19. 2 The temperature at the center of the glass material 2 is 10 ^8.5 When the temperature reached 645 ° C., which is a viscosity corresponding to dPaS, the glass material 2 was transported between the upper mold 10 and the lower mold 11 that are opposed to each other.
[0038]
Next, the lower mold 11 fixed to the lower mold pressing member 7 is driven by driving the pressure shaft 8, and the upper mold forming functional surface 10 a of the upper mold 10 and the lower mold forming functional surface 11 a of the lower mold 11 are driven. The glass material 2 was press-molded.
[0039]
In the above process, the heating temperature of the glass material 2 is 645 ° C. (= T2) in the first heating process of heating the glass material 2, the upper mold 10 and the lower mold 11 before the pressing process of pressing the glass material 2. The heating temperature 540 ° C. (= T1) of the upper mold 10 and the lower mold 11 which are forming molds is set so that the heating temperature T1 of the upper mold 10 and the lower mold 11 is lower than the heating temperature T2 of the glass material 2. did. Moreover, as a result of setting the heating temperature T2 of the glass material 2 and the heating temperature T1 of the upper mold 10 and the lower mold 11 as described above, the viscosity of the glass material 2 surface portion immediately after the start of the pressing process is the viscosity of the glass material 2 central portion. The ratio to 10 is ^3.5 It was the following. Specifically, the surface temperature of the glass material 2 decreases at the instant of molding immediately after the start of the pressing step, and the viscosity of the glass material 2 is 10 ¹² The temperature corresponding to dPaS was 570 ° C. At that time, the temperature at the center of the glass material 2 is 10 by the viscosity of the glass material 2. ^8.5 The temperature corresponding to dPaS was 645 ° C. Accordingly, at this time, the difference between Δt in FIG. 2, that is, the surface temperature of the glass material 2 and the central temperature was 75 ° C. At this time, the temperature of the upper mold 10 and the lower mold 11 increased by 3 ° C.
[0040]
Thereafter, the cooling process was started. The cooling process is 10 with the glass viscosity of the glass material 2. ¹² It started before the temperature of the glass material 2 center part reached 570 degreeC which is the temperature corresponded to dPaS. At that time, the surface of the glass material 2 is the glass transition temperature used in this example. ^13.5 dPaS. In this cooling step, after molding, the ratio of the viscosity of the surface of the glass material 2 to the viscosity of the center is 10 ^1.5 Cooling was performed until it was within.
[0041]
Thereafter, the thermocouple was removed from the glass material 2, and the optical element obtained by molding the glass material 2 under the same conditions as described above was inspected.
The inspection was conducted for NR (Newton ring) and habit.
(1) NR: a parameter describing the absolute value of the difference between the radius of curvature of the obtained optical element and the radius of curvature of the mold used for molding in terms of the number of interference fringes.
(2) Peculiarity: An error in the shape of the obtained optical element, and a parameter for quantitatively evaluating sink marks.
The above NR and peculiarity are standardized by the upper limit value allowed in the specification of the molded product, the allowable upper limit value is set to 100%, and when the obtained result is a numerical value lower than this, good results are obtained. Evaluated as being.
As a result of such inspection, it was confirmed that an optical element having a highly accurate surface shape with an optical element obtained by the present example of NR 83% and a habit of 50% or less can be formed.
[0042]
In the above embodiment, the temperature for releasing from the upper mold 10 and the lower mold 11 is more preferable after the viscosity of the central portion of the glass material 2 is equal to or lower than the glass transition temperature, but in order to shorten the cycle time. The glass center temperature is 10 in terms of glass viscosity. ¹² Even if the mold is released when a temperature corresponding to dPaS is reached, the ratio of the surface viscosity of the glass material 2 to the viscosity at the center is 10 ^1.5 If it was below, the obtained optical element had sufficient optical performance.
[0043]
(Example 2)
Others were the same as in Example 1, and the optical element was molded by controlling the numerical values to be different for the following two conditions i and ii.
i Ratio of the viscosity of the surface of the glass material 2 immediately after the start of the pressing process to the viscosity of the center
ii After starting the pressing step, the viscosity at the center of the glass material 2 is 10 ¹² Viscosity ratio with respect to the center of the surface when dPaS is reached
The obtained optical element was inspected. The results are shown in Table 1.
[0044]
[Table 1]

[0045]
As shown in Table 1, the ratio (condition i) to the surface viscosity of the glass material 2 and the viscosity at the center immediately after the start of the pressing process is 10 ^4.5 When the pressing process starts, the viscosity at the center of the glass material 2 is 10 ¹² Regardless of the viscosity ratio (condition ii) with respect to the central portion of the surface when dPaS is reached, mold fusion, which is a molding defect due to fusion of the glass material 2 to the upper mold 10 and the lower mold 11, occurs. At the same time, the habit exceeded the allowable upper limit.
[0046]
On the other hand, the ratio (condition i) of the glass part 2 surface part viscosity to the central part viscosity immediately after the start of the pressing step is 10 ^3.5 In principle, good molding results can be obtained if However, after starting the pressing process, the temperature at the center of the glass material 2 is 10 as the glass viscosity. ¹² When the temperature corresponding to dPaS is reached, the viscosity ratio (condition ii) to the central portion of the surface portion is 10 ^2.5 When NR is reached, NR and peculiarities exceed the allowable upper limit values.
This is due to the following reason.
That is, as a physical property unique to glass, it is close to the glass transition point. ¹² There is the fact that at viscosities above dPaS, there is no fluidity or deformation. 10 for more details ¹² Even if it is dPaS or more, it is recognized that it is almost a glass transition point even though the fluidity is kept slightly. ^13.5 Above dPaS, fluidity is lost. Further, when there is a difference in viscosity between the surface portion and the center portion of the glass material 2, a difference in thermal expansion occurs between the surface portion and the center portion of the glass material 2. From the above, it is recognized that the temperature at the center of the glass material 2 is almost the glass transition point. ^13.5 10 for dPaS ^-1.5 10 times the glass viscosity ¹² While the temperature corresponding to dPaS is reached, the surface of the glass material 2 is 10% relative to the center portion. ^2.5 When the difference in viscosity exceeds twice, when cooled after that, the central part of the glass material 2 has extremely low fluidity, and a difference in thermal expansion occurs between the surface part and the central part of the glass material 2, causing sinks. This causes deterioration of transfer accuracy in the obtained optical element.
[0047]
(Example 3)
In this example, a glass material 2 having a radius of Φ2 mm was used. In addition, the used molding apparatus and the like are the same as those in Example 1, and the description thereof is omitted.
FIG. 3 shows the results of measurement with a thermocouple inserted into the glass material 2 in this example, and ΔS indicates the temperature difference between the highest point of the mold temperature after the start of pressing and the mold immediately before pressing.
First, the upper mold 10 and the lower mold 11 are preliminarily set to 10 with the viscosity of the glass material 2. ^13.5 The glass material 2 is heated to 540 ° C. corresponding to dPaS, and at the same time, the holder 21 containing the glass material 2 is conveyed into the heating chamber 18 of the heating unit 3 by the conveying arm 20, and the glass material 2 is heated by the heater 19. 2 The temperature at the center of the glass material 2 is 10 ^8.5 When the temperature reached 630 ° C., which is a viscosity corresponding to dPaSas, the glass material 2 was transported between the upper mold 10 and the lower mold 11 arranged to face each other.
[0048]
Next, the lower mold 11 fixed to the lower mold pressing member 7 is driven by driving the pressure shaft 8, and the upper mold forming functional surface 10 a of the upper mold 10 and the lower mold forming functional surface 11 a of the lower mold 11 are driven. When the glass material 2 is press-molded, the surface temperature of the glass material 2 decreases at the moment when the glass material 2 is molded. ^13.7 The temperature corresponding to dPaS is 545 ° C., while the central temperature is 10 times the viscosity of the glass material 2. ^8.8 It was 630 degreeC which is the temperature corresponded to dPaS. At this time, the outputs of the upper mold heater 13 and the lower mold heater 15 were increased at the same time, and a second heating process for further heating the glass material 2, the upper mold 10 and the lower mold 11 was performed. Thereby, the temperature of the upper mold | type 10 and the lower mold | type 11 rose, and the temperature of the upper mold | type 10 and the lower mold | type 11 became 580 degreeC. As shown in FIG. 3, in this embodiment, the temperature difference ΔS between the highest point of the mold temperature after the start of press and the mold immediately before the press is 35 ° C.
[0049]
Next, the cooling process was performed in the same manner as in Example 1, and then the thermocouple was removed from the glass material 2, and the optical element obtained by molding the glass material 2 under the same conditions as described above was inspected. As a result, it was confirmed that the obtained optical element was a good optical element with NR 83% and peculiar 50% or less.
According to the method for molding an optical element of Example 3, it was possible to mold an optical element free from defects such as cracks and insufficient pressurization of the inner wall.
[0050]
Example 4
Others are the same as in Example 3, and the temperature of the central portion of the glass material 2 is ⁷ The temperature of the upper mold 10 and the lower mold 11 is set to 660 ° C. corresponding to dPaS, and the viscosity of the glass material 2 is 10 ¹¹ The temperature was set to 580 ° C. corresponding to dPaS, and press molding of the glass material 2 was started between the upper mold 10 and the lower mold 11. Further, heating after the start of press molding by the upper mold heater 13 and the lower mold heater 15 was not performed. However, the temperature of the upper mold 10 and the lower mold 11 increased by 35 ° C., and a good optical element was obtained.
[0051]
(Comparative Example 1)
Others are the same as in the third embodiment, and after adjusting the output of the upper die heater 13 and the lower die heater 15 to adjust the output of the glass material 2, the upper die heater 13 and the lower die heater 15 The output was increased and the heating temperature of the upper mold 10 and the lower mold 11 was set to 585 ° C. or higher. Therefore, the temperature rise in the vicinity of the surfaces of the upper mold 10 and the lower mold 11 which are molds after the start of the glass material 2 press molding process was 40 ° C. or more. As a result, the glass material 2 was fused to the upper mold 10 and the lower mold 11, and an optical element could not be obtained.
(Comparative Example 2)
Others were the same as in Example 2, and the upper mold 10 and the lower mold 11 were not heated without output by the upper mold heater 13 and the lower mold heater 15 after the pressing process of pressing the glass material 2 was started. At this time, the temperature of the upper mold 10 and the lower mold 11 did not substantially increase, and the temperature increase was less than 3 ° C. (2 ° C.). As a result, the glass material 2 was broken during the press molding process, and a desired optical element could not be obtained.
(Comparative Example 3)
Others are the same as in Example 2, and the heating temperature T2 of the glass material 2 is set to the glass material in the first heating process in which the glass material 2, the upper mold 10 and the lower mold 11 are heated before the pressing process of pressing the glass material 2. 2 Set the temperature at the center to 10 ^5.5 The heating temperature T1 of the upper mold 10 and the lower mold 11 is set to 700 ° C. corresponding to dPaS, and the viscosity of the glass material 2 is 10 ¹¹ The temperature was set to 580 ° C. corresponding to dPaS. As a result, the temperature of the upper mold 10 and the lower mold 11 increased by 45 ° C., and the glass material 2 was fused to the upper mold 10 and the lower mold 11, and an optical element could not be obtained.
[0052]
Table 2 shows the temperature rise and the molding result in the vicinity of the mold surface after the start of the press molding process for Example 1, Example 3, Example 4, and Comparative Examples 1 to 3.
As shown in Table 2, good molding results were obtained in Example 1 in which the rising temperature in the vicinity of the mold surface after the start of the press molding process was 3 ° C. and in Example 3 and Example 4 in which the rising temperature was also 35 ° C. was gotten. On the other hand, in Comparative Example 1 and Comparative Example 3 in which the rising temperature is 40 ° C. or higher, mold fusion occurs and good molding results cannot be obtained. Further, in Comparative Example 2 in which the temperature rise in the vicinity of the mold surface after the start of the press molding process is not performed, the glass material 2 is cracked, and a satisfactory molding result cannot be obtained.
[0053]
[Table 2]

[0054]
【The invention's effect】
According to the method for molding an optical element of the present invention, it is possible to obtain an optical element having high surface accuracy without causing glass to be fused to a mold, broken, or pressed to a predetermined thickness. it can.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a glass material molding apparatus used in an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing the results of measuring changes in the molding process between the surface temperature and the center temperature of the glass material 2 in Example 1 of the present invention.
FIG. 3 is an explanatory diagram showing the results of measuring changes in the molding process between the surface temperature and the center temperature of the glass material 2 in Example 3 of the present invention.
[Explanation of symbols]
2 ... Glass material, 4 ... Molding part, 3 ... Heating part, 10 ... Upper mold, 11 ... Lower mold, 16 ... Thermocouple for upper mold, 17 ... Lower Mold thermocouple.

Claims

It consists of a heating process for heating the glass material and the mold, and a press molding process for pressing the glass material by the molding mold. In the heating process, the heating temperature of the glass material and the heating temperature of the mold are The heating temperature of the mold is lower than the heating temperature of the glass material, and immediately after the start of the pressing step, the ratio of the surface viscosity of the glass material to the central viscosity is greater than 1 and 10 ^3.5 or less. A method for molding an optical element, characterized in that the heating temperature of the glass material and the mold is set.

A cooling step for cooling after the press forming process starts, the ratio to the central portion viscosity of the surface portion viscosity of the glass material with greater than 10 ^2.5 from 1, and the glass material surface temperature to the temperature corresponding to the glass transition temperature It said cooling step starts, molding of an optical element according to claim 1, wherein the ratio of the central portion viscosity of the surface portion viscosity of the glass material after the molding to cool until within 10 ^1.5 before reaching.

3. The optical element according to claim 2, wherein the cooling step is started at a glass material surface temperature equal to or lower than a temperature corresponding to a viscosity of 10 ^−1.5 times the viscosity at a transition point of the glass material. Molding method.

A cooling step of cooling after the start of the press molding step, wherein the ratio of the viscosity of the glass material surface portion to the viscosity of the glass material central portion is greater than 1 and less than 10 ^2.5 and 10 relative to the glass viscosity of the glass transition point. start the cooling step at a temperature below the glass material core temperature corresponding to ^-1.5 times the viscosity of the cooling until the ratio of the center portion viscosity of the surface portion viscosity of the glass material after forming is within 10 ^1.5 The method for molding an optical element according to claim 1.

A first heating step for heating the glass material and the mold, a press molding step for press-molding the glass material with the molding die, and a second heating for heating the glass material and the mold after the press molding process is started. The heating temperature is set so that the temperature of the mold is lower than the temperature of the glass material in the first heating process, and the mold after the press molding process is started in the second heating process. A method for molding an optical element, wherein heating is performed so that a temperature rise in the vicinity of the surface is 3 ° C. or more and within 40 ° C.

The temperature rise at the measurement point is 3 ° C. or more and 40 °, with the measurement point being a position shallower than the surface of the mold than the thickness of the two thickest surfaces to be pressed of the molded product obtained by press molding the glass material. The method for molding an optical element according to any one of claims 1 to 5, wherein the heating in the second heating step is performed so as to be within C.