JP3830363B2 - Manufacturing method of glass molded product and manufacturing method of glass press molded product - Google Patents
Manufacturing method of glass molded product and manufacturing method of glass press molded product Download PDFInfo
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- JP3830363B2 JP3830363B2 JP2001202366A JP2001202366A JP3830363B2 JP 3830363 B2 JP3830363 B2 JP 3830363B2 JP 2001202366 A JP2001202366 A JP 2001202366A JP 2001202366 A JP2001202366 A JP 2001202366A JP 3830363 B2 JP3830363 B2 JP 3830363B2
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B40/00—Preventing adhesion between glass and glass or between glass and the means used to shape it, hold it or support it
- C03B40/04—Preventing adhesion between glass and glass or between glass and the means used to shape it, hold it or support it using gas
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B11/00—Pressing molten glass or performed glass reheated to equivalent low viscosity without blowing
- C03B11/02—Pressing molten glass or performed glass reheated to equivalent low viscosity without blowing in machines with rotary tables
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B7/00—Distributors for the molten glass; Means for taking-off charges of molten glass; Producing the gob, e.g. controlling the gob shape, weight or delivery tact
- C03B7/10—Cutting-off or severing the glass flow with the aid of knives or scissors or non-contacting cutting means, e.g. a gas jet; Construction of the blades used
- C03B7/12—Cutting-off or severing a free-hanging glass stream, e.g. by the combination of gravity and surface tension forces
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Description
【０００１】
【発明の属する技術分野】
本発明は、溶融ガラスより所定重量を有するガラス成形品を成形するためのガラス成形品の製造方法、更には、前記方法によって得られたガラス成形品を再加熱しプレスしてガラスプレス成形品や光学素子を成形するための成形予備体であるガラス成形品を得る方法に関する。
【０００２】
【従来の技術】
近年、非球面ガラスレンズ等の製造法として成形型による高精度熱間プレス成形技術が開発され発展をとげている。本成形に用いる成形予備体（以下プリフォームと言う）は、ミリグラム単位の重量精度が要求され、かつ用途上、脈理、デビ、傷、泡などの欠陥や洗浄等で除去できない表面付着物の存在は許されない。
【０００３】
このようなプリフォームを安価に量産する方法としては、例えば、特開平２−１４８３９号公報に記載の方法が知られている。本方法では、流出パイプから流下する溶融ガラスを成形型の凹部で受ける際、この凹部に開口する細孔から、空気や不活性ガスを噴出させ、溶融ガラス塊と成形型凹部の内面との間にガスクッションを作り、溶融ガラス塊の少なくとも表面の一部が軟化点温度以下に達するまで、溶融ガラス塊を前記凹部内面と実質的に非接触状態で凹部内に保持し、冷却してガラス塊を作製している。本方法によれば、上下面とも自由表面となるため、表面品質の良好なプリフォームを得ることができる。
【０００４】
また上記の細孔を開けた成形型の代わりに多孔質材料からなる受け型を使用し、その受け型からガスが噴出している状態で溶融ガラスを受け、ガラス塊を得る方法が特開平６−１２２５２６号公報に開示されている。更に、多孔体型表面の凸凹の転写を確実に防止するため、流出する溶融ガラスの先端部が受け型に接触するまでに、溶融ガラス先端に低温流体を噴射して溶融ガラス表面を冷やし、凸凹の転写を防止する方法が特開平９−２２１３２９に開示されている。また多孔質材料等からなる受け型でガラス塊を成形した場合、ガラス塊の下面に凹みが発生することがある。この凹みを防止する方法として、多孔質型からの噴出ガス流量を非常に多くした状態で溶融ガラスを受け型に受け、その後で噴出ガス流量を少なくする方法が特開平９−２２１３２８に記載されている。また特開平１０−１３９４６５には、水や液状有機化合物などを含浸させた多孔質材料の受け型で溶融ガラスを受け、蒸発ガスの圧力により溶融ガラスを浮上させながら冷却し、ガラス塊を得る方法が開示されている。本方法によれば、前記したガラス塊下面の凹みを防ぐことができる。
【０００５】
【発明が解決しようとする課題】
しかしながら、上記従来例においては、それぞれ以下のような欠点があった。まず特開平２−１４８３９号公報に記載の方法では、成形型内面が研磨されているため多孔体製の受け型のように型表面の凸凹が転写される心配はない。しかし高温の溶融ガラスは非常に反応性が高いため、型と溶融ガラスが一次的に融着することがある。融着時間が短いと、融着部の痕跡は残らないが、長い場合にはこの融着部が小さな突起となり残ることがある。この一次的な融着は、細孔からの噴出ガス流量を増やすことで抑制できるが、ガスの噴出圧力でガラス塊に部分的に小さな窪み（ガス噴出痕）ができるという問題があった。また非常に低粘性の溶融ガラスを成形する場合には、浮上ガス流量を増やすと噴出圧力で溶融ガラスが揺れて溶融ガラスの流れが乱れるためにプリフォームの重量精度が悪くなるという問題もある。
【０００６】
一方、流出する溶融ガラスの先端部が受け型に接触するまでに、溶融ガラス先端に低温流体を噴射して溶融ガラス表面を冷やし、多孔体の凸凹の転写を防止するという特開平９−２２１３２９の方法では、溶融ガラスだけでなく流出ノズルが冷却される危険性がある。ノズル温度を厳密に制御している場合でも、ノズルに風が当たる状態ではノズル温度の変動幅は大きくなる。ノズル温度が変動すると溶融ガラスの流出速度が変動するため、プリフォームの重量精度が悪くなるという問題が起こる。また型表面の凸凹の転写を防止できるほど融液を冷却した場合、ガラス流の切断時に糸引きが発生しやすく、切断部を加熱する等の別の手段が必要になる。また溶融ガラスの粘性を高くすると、ガラスが伸びなくなるため、大きなガラス塊を成形しにくいという問題もある。その他、液相温度が高く失透（結晶化）しやすいガラスの場合には、ノズルの風冷により失透が誘発される危険性も増える。
【０００７】
また特開平９−２２１３２８のように、噴出ガス流量を非常に多くした状態で溶融ガラスを受け型に受け、その後で噴出ガス流量を少なくする方法においても、ノズルを冷やす危険性があり、特開平９−２２１３２９と同じ問題が発生する危険性がある。また初期の噴出ガス流量を多くすると、噴出圧力で溶融ガラスが揺れて溶融ガラスの流れが乱れるためにプリフォームの重量精度が悪くなるという問題も発生しやすい。その他、極端に低粘性の溶融ガラスを受け型で受けた場合、噴出ガスがガラスを浮上させずに、ガス噴出口を塞いでいるガラスに侵入し、ガラス中に噴出ガスの泡が閉じ込めたれ、ガラスが発泡する場合もある。このように発泡したガラスは光学素子などに使用することができない。一方、底面が平らな受け型を使用し２グラム以下の小さいガラス塊を成形する場合には、下面の中央部が凹む傾向が非常に強くなる。よって特開平９−２２１３２８の方法を用いたとしても、下面の凹みを完全になくすことは難しい。面の局部的な凹みはレンズ成形でガス溜まりとなるため非常に問題である。
【０００８】
またガスクッションに溶融ガラスを保持してガラス塊を成形する方法では、一般的に受け型のアール（曲率半径）より成形品の下面アールが大きくなる傾向がある。この傾向は成形するガラス塊の重量が軽いほど、そして型底面のアールが大きいほど顕著となる。例えば、型の底面アールが１５mm以上の成形型で２グラム以下の溶融ガラスを成形する場合、成形体下面のアールが２５〜３０mm程度まで大きくなる。つまりガラス塊下面のアールを制御することが課題となっている。
また複数の成形型を回転テーブル上に配し、間欠的にテーブルを回転させて成形するような一般的なガラス成形装置においては、底面が平らな成形型を使用いると成形品がいびつになりやすく、テイクアウトに失敗しやすいという問題もある。
【０００９】
また特開平１０−１３９４６５のように、水や液状有機化合物などを含浸させた多孔質材料の受け型で溶融ガラスを受け、蒸発ガスの圧力により溶融ガラスを浮上させながら冷却する方法では次のような問題がある。つまり型で溶融ガラスを受ける前に液体が蒸発してしまうのを防ぐため、多孔質型の温度は沸点以下にする必要がある。そのために、溶融ガラスの表面温度が急激に低下しやすく、大きめのガラス塊を成形する場合にはカン割れが起こりやすい。
【００１０】
このように従来のガスクッションを形成して、その上に溶融ガラスを受けてガラス塊を浮上成形する方法では、ガラス塊が失透してしまったり、ガラス塊中に泡が含まれたり、ガラス塊の重量精度がバラツクなどの問題があった。
【００１１】
本発明は、上記問題を解決するためになされたものであって、高品質かつ高い重量精度を有するガラス塊、特にモールドオプティクス成形用のプリフォームを製造する方法を提供すること、ならびに前記方法によって得られたガラス塊からプレス成形品を作製する方法を提供することを目的とする。
【００１２】
【課題を解決するための手段】
以下、課題を解決するための手段について説明する。
（１）
ノズルより排出される溶融ガラス流から溶融ガラス塊を分離し、分離された溶融ガラス塊は、ガラス塊成形型上に受け取られ、かつ前記ガラス塊成形型からの風圧を受けながら成形される、ガラス成形品の製造方法であって、
前記溶融ガラス塊を受けたガラス塊成形型が前記ノズル下方から移動した後に前記風圧を増加させ、
前記増加前の風圧は、前記溶融ガラス塊がガラス塊成形型と融着せず、かつ前記ノズルからの溶融ガラス流の排出を妨げない程度とし、
前記増加後の風圧は、前記溶融ガラス塊と前記ガラス塊成形型とが実質的に非接触状態を維持できる程度とすることを特徴とするガラス成形品の製造方法。
（２）
前記ガラス塊成形型は、溶融ガラスを受ける凹部を有し、かつこの凹部の表面に、前記風圧を加えるために気体を噴出する気体噴出口を有し、
前記ノズルより排出される溶融ガラス流の先端部をガラス塊成形型の凹部で受ける第１の工程、
前記先端部を溶融ガラス流から分離して得られた溶融ガラス塊をガラス塊成形型の凹部に受け取る第２の工程、及び
受け取ったガラスを気体により浮上させながら成形して成形品を得る第３の工程を含む（１）に記載の製造方法。
（３）
前記風圧の増加は、前記溶融ガラス塊の平均粘度が５０ポアズを超えた以降に行う（１）または（２）に記載の製造方法。
尚、前記風圧の増加は、前記溶融ガラス塊の平均粘度が５０ポアズ〜１０8ポアズの範囲にあるときに行うことがより好ましい。
（４）
前記ノズルより排出される溶融ガラス流の粘度が１０ポアズ以下であり、前記増加前の風圧を、風圧を作り出す気体流量を１．０Ｌ／分以下とし、前記風圧の増加を前記溶融ガラス塊の平均粘度が５０〜５００ポアズの間にある時点で行う（１）〜（３）のいずれか１項に記載の製造方法。
（５）
成形される溶融ガラス塊は、底面の曲率半径が１０ｍｍ以上であり、前記増加前の風圧は、溶融ガラス塊の底面に窪みができない程度またはガラス塊成形型の凹部と対応する溶融ガラス塊の底面が得られる程度とする（１）〜（３）のいずれか１項に記載の製造方法。
（６）
風圧の増加を行わないこと以外は（１）に記載の方法と同様の方法を実施して、前記増加前の風圧を作り出す最適な気体流量を選択する工程を含む（５）に記載の製造方法。
即ち、この方法は、前記増加前の風圧を作り出す最適な気体流量を選択する工程を含み、前記最適な気体流量は、ノズルより排出される溶融ガラス流から溶融ガラス塊を分離し、分離された溶融ガラス塊は、ガラス塊成形型上に受け取られ、かつ前記ガラス塊成形型からの風圧を受けながら成形される、ガラス成形品の製造方法を、前記風圧を増加させることなく実施することで、選択される（５）に記載の製造方法である。
（７）
前記増加後の風圧は、風圧を作り出す気体流量を１．０〜４．０Ｌ／分の範囲とする（１）〜（６）のいずれか１項に記載の製造方法。
（８）
粘度が２〜２０ポアズの溶融ガラスをノズルより排出してガラス塊を成形することを特徴とする（１）〜（３）及び（５）〜（７）のいずれか１項に記載の製造方法。
（９）
液相温度における粘度が２０ポアズ以下のガラスからなるガラス塊を作製する（１）〜（３）及び（５）〜（（８）のいずれかに記載の製造方法。
（１０）
前記ガラス成形品がプレス成形用のプリフォームである（１）〜（８）のいずれかに記載の製造方法。
（１１）
（１０）に記載された方法により作製されたプリフォームを加熱し、プレス成形型によりプレス成形してプレス成形品を作製するガラスプレス成形品の製造方法。
【００１３】
【発明の実施の形態】
以下、本発明の実施の形態について詳細に説明する。
本発明のガラス塊の製造方法では、ノズルより排出される溶融ガラス流から溶融ガラス塊を分離し、分離された溶融ガラス塊は、ガラス塊成形型上に受け取られ、かつ前記ガラス塊成形型からの風圧を受けながら成形される。
ノズルより排出される溶融ガラス流からの溶融ガラス塊の分離は、（１）ノズルから自然に滴下する溶融ガラスからガラス塊を成形する方法、（２）ノズルから排出される溶融ガラス流の先端部をガラス塊成形型によって受けた後、ガラス塊成形型とノズルとの距離を離して所定量の溶融ガラス流先端部をガラス塊成形型に受け取って成形する降下切断法を用いる方法、（３）ノズルから排出される溶融ガラス流をシアなどの切断機構によって切断する方法など、が挙げられるが、これらに限定されるものではない。
【００１４】
分離された溶融ガラス塊は、ガラス塊成形型上で、ガラス塊成形型からの風圧を受けながら成形される。ガラス塊成形型は、例えば、溶融ガラスを受ける凹部を有し、かつこの凹部の表面に、前記風圧を加えるために気体を噴出する気体噴出口を有するものであることができる。このようなガラス塊成形型については後述する。
【００１５】
さらに、本発明の製造方法は、前記溶融ガラス塊を受けたガラス塊成形型が前記ノズル下方から移動した後に前記風圧を増加させ、前記増加前の風圧は、前記溶融ガラス塊がガラス塊成形型と融着せず、かつ前記ノズルからの溶融ガラス流の排出を妨げない程度とし、前記増加後の風圧は、前記溶融ガラス塊と前記ガラス塊成形型とが実質的に非接触状態を維持できる程度とすることを特徴とする。
ノズルより排出される溶融ガラス流の粘度は、通常、数〜数十ポアズである。従って、成形初期の溶融ガラス塊も粘度が低く、ガラス塊成形型がノズル下方にある時点では、風圧は溶融ガラス塊がガラス塊成形型に融着せず、かつ前記ノズルからの溶融ガラス流の排出を妨げない程度の風圧とする。風圧が低すぎると、溶融ガラス塊がガラス塊成形型に融着してしまう。また、風圧が高すぎると、ノズル及びノズルからの溶融ガラス流が冷却され、溶融ガラス流の排出が妨げられる。次いで、溶融ガラス塊を受けたガラス塊成形型が前記ノズル下方から移動した後に、溶融ガラス塊とガラス塊成形型とが実質的に非接触状態を維持できる程度に風圧を増加させる。この時点ではガラス塊成形型からの風圧がノズルに吹き掛かることはなくなり、溶融ガラスの重量精度を維持することができる。
【００１６】
本発明の製造方法は、例えば、前記ノズルより排出される溶融ガラス流の先端部をガラス塊成形型の凹部で受ける第１の工程、前記先端部を溶融ガラス流から分離して得られた溶融ガラス塊をガラス塊成形型の凹部に受け取る第２の工程、及び受け取ったガラスを浮上させながら成形して成形品を得る第３の工程を含むことができる。
【００１７】
上記第１の工程は、ノズルより排出される溶融ガラス流の先端部をガラス塊成形型の凹部で受ける工程であり、例えば、ガラス塊成形型の凹部表面から気体を噴出させて形成したガスクッション上に流下する溶融ガラス流を受ける工程である。第２の工程は、溶融ガラス流の先端部を溶融ガラス流から分離して所定量の溶融ガラスをガラス塊成形型の凹部に受け取る工程であり、例えば、前記先端部が所定重量に達した段階で溶融ガラス流を切断して溶融ガラス塊を得る工程である。第３の工程は、受け取ったガラスを浮上させながらガラス塊を成形する工程であり、ガラス塊成形型と溶融ガラス塊を実質的に非接触の状態で保持しながら冷却固化してガラス成形品とする工程である。そして、少なくとも前記の第１と第２の工程では、ガラス塊成形型がノズル下方に有り、ガラス塊成形型内面に噴出させる気体の流量を必要最小限の量に抑える。そして、ガラス塊成形型がノズル下方から移動する第３の工程の途中から噴出させる気体の流量を増加して浮上に必要な風圧を増加させる。
【００１８】
溶融ガラスをガラス塊成形型に受ける第１の工程と溶融ガラス流を切断し溶融ガラス塊を得る第２の工程では、成形型からの噴出ガスの流量は、ガラス塊がガラス塊成形型と融着せず、かつノズルからの溶融ガラス流の排出を妨げない程度とする。より好ましくは、溶融ガラスと型表面の高範囲な融着が生じず、ノズルからの溶融ガラス流の排出を妨げず、溶融ガラス塊中に噴出ガスが侵入せず、かつ噴出ガスによりノズルから排出される溶融ガラス（ガラス融液）が震えない程度の流量を意味する。
【００１９】
ガラスに風圧を加える気体を噴出するため、受け型（ガラス塊成形型）の凹部を多孔質素材で形成し、多孔質素材を通してガスを噴出する場合、溶融ガラス塊を浮上させるのに最低限必要な上記成形型からの噴出ガスの流量の程度は、多孔質素材の気孔率と気孔径に依存するので、これらに合わせて適宜調整すれば良い。しかし、溶融ガラス流の揺れや失透現象を防ぐためにも、噴出ガス流量は１L／分以下にすることが望ましい。一方、ガスを噴出する細孔を有する型では、ガスの透過面積が小さいため多孔質型より少ないガス流量で充分量の風圧を与えることができる。また細孔を有する受け型においても、噴出ガスの流量の程度は細孔径と細孔の数に依存する。例えば、細孔径が０．２〜１．０mm程度で細孔数が７〜４３個程度の場合は、多孔体を受け型とする場合(１L／分以下)の１／３〜１／１０のガス流量であることが適当である。
【００２０】
本発明の製造方法に使用するガラス塊成形型は、溶融ガラスを受ける凹部を有し、かつこの凹部の表面に、前記風圧を加えるために気体を噴出する気体噴出口を有する。受け型成形面を多孔質素材で形成するなど、ガラス塊成形型上でガラスに風圧を加えたり、ガスクッションを形成するための手段としては、ガラス塊成形型の溶融ガラスを受ける凹部（成形面）に開口する一つまたは複数の細孔から気体を噴出させることが好ましい。また、ガラス塊成形型の前記凹部表面を溶融ガラスとの濡れ性が悪い材料から構成することが好ましい。さらにガラス塊成形型の少なくとも成形面（凹部表面）を、以下の材料で構成することが望ましい。
【００２１】
（炭素系材料）
グラファイト、ガラス状カーボン、グラファイトとガラス状カーボンの複合体、
グラファイト表面にガラス状カーボンをコーティングしたもの
グラファイト表面に化学蒸着炭素膜を被覆したもの
グラファイトとSiCとB4Cの複合材
（窒化物、炭化物）
AlN、ＢＮ、AlN／BNの複合材、SiC、TiC、WC、TiC、WCを含む超硬及び超硬合金、サイアロン （SIALON）、サイアロンとBN複合材
（薄 膜）
DLC等の硬質炭素膜
ダイヤモンド膜、非晶質炭素膜、結晶質炭素膜、両者の混合質炭素膜
Si3N4、TiAlN、TiCrN、CrN、CrXNY、AlN、TiN等の窒化物膜
上記の複合多層膜または積層膜（AlN／CrN、TiN／CrN等）
Pt-Au、Pt-Ir-Au、Pt-Rh-Auなど白金と金を含有する貴金属合金膜
（窒化処理）
耐熱金属表面を窒化処理したもの
【００２２】
本発明の製造方法では種々のガラスを成形できるが、特に近年、溶融流出時に低粘性を示すガラスの成形を良好に行う方法に対する要望が高く、本発明の製造方法は２０ポアズ以下、特に１５ポアズ以下の低粘性な溶融ガラスからの成形品の製造にも適している。このような低粘性な溶融ガラスの場合、これまでの方法では、溶融ガラス内に気体が侵入し発泡する現象や、溶融ガラスと型の界面に気体溜まりが発生し、これが界面から抜ける際に融液が振動するため、重量精度が悪くなるという問題があった。しかし、本発明の方法では、そのような問題は生じず、ノズルから排出するときの粘度が２〜２０ポアズ、特に、２〜１５ポアズの溶融ガラスを用いた成形も良好に行うことができる。
【００２３】
また第２の工程では、溶融ガラスの流出ノズルから受け型を降下する等の手段により溶融ガラスの流れを切断し、受け型上に所定重量の溶融ガラス塊を切り分ける。型を下側に移動し停める際、溶融ガラスには慣性力が加わるため、溶融ガラスが受け型内で瞬間的に扁平化する。この扁平化によりガラスと受け型の界面にあるガスクッションが一瞬乱れ、ガスの抜け道が一瞬塞がれるため、突発的に溶融ガラスが跳ねる現象も起こりやすい。このような飛び跳ねは、折れ込みによる脈理を誘発したり、ガラス融液が飛び跳ねた際にノズル先端の溶融ガラスと接触したりして大きな重量変動をまねくことがある。よってこのような現象を抑制するためにも、少なくとも第１と第２の工程においては、噴出ガスの流量を抑え、風圧を抑える。
【００２４】
特に、ノズルより排出される溶融ガラス流の粘度が１０ポアズ以下(２ポアズ以上)であり、増加前の風圧を作り出す気体流量を１．０Ｌ／分以下とし、かつ第３の工程に入った後に行う風圧の増加を、ガラス塊の平均粘度が５０〜５００ポアズの間にある時点で行うことが、低い粘性のガラスを、発泡を防止するとともに、振動と飛び跳ねによる折れ込みと脈理の発生を防止し、失透を防止し、かつ良好な重量精度でガラス塊を製造するという観点から好ましい。
【００２５】
また、底面の曲率半径が１０ｍｍ以上であるガラス塊を成形する場合、前記増加前の風圧は、ガラス塊の底面に窪みができない程度またはガラス塊成形型の凹部と対応するガラス塊の底面が得られる程度とする。即ち、底面が平らに近い受け型で小さいガラス塊を成形する場合、初期のガス噴出流量をガラス塊の底面に窪みができない程度またはガラス塊成形型の凹部と対応するガラス塊の底面が得られる程度に少なくする。底面が平らに近い受け型で小さいガラス塊を成形する場合、型底部の傾斜が緩いため型底部中央に向かう溶融ガラスの流れが殆ど起こらない。またガラス塊の外周部は浮上ガスが外側に逃げやすいため、外周部はガラス塊の中央部よりも浮上状態が悪くなる。更に溶融ガラス塊の内側は外周部より硬化が遅いため、噴出ガスが多いと内側のみが噴出圧力で凹んでしまう。逆に、底面のアールが小さく傾斜が急な受け型による成形では、受け型の底部中央に溶融ガラスが流れやすくまた厚みがある中央部が重く元々凸状であるため、少々ヒケが生じる傾向があっても凹むまでは至らない。よって凹み傾向は、受け型の底面形状が平面に近い程、そして成形するガラス塊が軽い程発生しやすい。例えば、底面アールが４０ｍｍ程度の受け型で直径が
１０ｍｍ程度のガラス塊を成形する場合、０．３L／分以上の噴出ガスを流すと
下面中央に凹みが生じる。但し底面アールが４０ｍｍの受け型による成形でも、
溶融ガラスが大きければ外周部の傾斜がきつくなり、かつ重量増により溶融ガラスが噴出圧で持ち上がらなくなるため、下面が凹むことはなくなる。この方法の場合、増加前の風圧を作り出す最適な気体流量を選択する工程を含み、前記最適な気体流量は、ノズルより排出される溶融ガラス流から溶融ガラス塊を分離し、分離された溶融ガラス塊は、ガラス塊成形型上に受け取られ、かつ前記ガラス塊成形型からの風圧を受けながら成形される、ガラス成形品の製造方法を、前記風圧を増加させることなく実施することで選択することができる。
【００２６】
ガラス塊の下面に窪みが形成されやすく、前記下面の曲率半径とガラス塊成形型の凹部の曲率半径とが大きく異なりやすいガラス塊の成形に本発明は好適である。すなわち、このようなものとしては、ガラス塊成形型の凹部の曲率半径（アール）が１０ｍｍ以上、特に１５ｍｍ以上のものであり、ガラス塊の重量が３グラム以下のもの、特に２グラム以下のものである。ガラス塊成形型の凹部の曲率半径の上限は１００ｍｍ程度である。
【００２７】
このように、本発明では、上記第１と第２の工程における噴出ガスの流量は、従来の気体浮上法に比べて少ない。そのため、ガラス塊の浮上が不完全になりやすい。浮上状態が不完全であると、溶融ガラスが成形型表面と接触する機会が増え、接触が多い部分で溶融ガラスの温度が低下する。その結果として、ガラス塊の下面にシワやゆがみが発生したり、上面から見た形が丸くならなかったり、成形体が割れやすくなったりする。また受け型上の溶融ガラス塊は、成形装置上を型が移動するたびに慣性力で揺れるが、浮上が悪いと型の中心位置から外れた位置で成形体が止まることが多くなる。この時に溶融ガラスが軟らかい状態だと、重力を受けて溶融ガラス塊の形が変形してしまう。また固化したガラス塊を真空吸着などでテイクアウトする場合、受け型の中央位置にないガラス塊はテイクアウトに失敗することも多い。特に、底面が平らなガラス塊の成形では、テイクアウトに失敗しやすく、以上説明した問題と下面の凹みの抑制を両立させることはできない。そこで本発明では、前記した第三の工程の途中から噴出ガス流量を増加させ、溶融ガラス塊の浮上状態を回復させる。
【００２８】
以下に噴出ガス増加のタイミングについて説明する。例えば多孔体素材の受け型により粘性が５ポアズ以下の低粘性の溶融ガラスよりガラス塊を成形する場合、第１と第２の工程の噴出ガス流量を０．５L／分以下と少なくし、第３の工程に入り噴出ガスを増加しても溶融ガラス塊が暴れない粘性になってから噴出ガス流量を１〜３L／分に増加させることが好ましい。なお、ガラス塊を受けたガラス塊成形型がノズル下方から移動した後であっても、増加のタイミングが早すぎる場合は溶融ガラス塊が暴れ、折れ込み等により脈理が発生することがある。また細孔を有する受け型による成形においては、細孔からの噴出ガス圧力で溶融ガラスが凹まない粘性になってから噴出ガス流量を増加すべきである。
【００２９】
また底面が平面に近い受け型による成形では、より厳密に噴出ガスの増加タイミングを調整することが好ましい。例えば、噴出ガスの増加タイミングが早すぎる場合には、噴出圧力によりガラス塊下面が平坦化し中央部が凹んでしまう。一方、増加タイミングが遅すぎる場合には、浮上不足により下面のゆがみやシワが発生する他、やはり下面が凹むことが時々ある。この場合の凹みは噴出圧力による凹みではなく、溶融ガラスが固化する際の不均一な体積収縮（所謂ヒケ）が原因であることが検討のすえ分かった。つまり底面が平坦な受け型で成形した場合に発生するガラス塊下面の凹みは、ガス噴出圧力とヒケの両方が原因と考えられる。ヒケによるガラス塊下面の凹みは、他の部分より下面の硬化が遅れることにより発生する。よってガスの噴出圧力で表面が凹まない粘性になった段階で、ガス噴出流量を増加し、ガラス塊下面の冷却を促進することで、下面の凹みを確実に防止することができる。
【００３０】
またヒケによるガラス塊下面の凹みは、下面の硬化の遅れにより発生するので、ガラス塊の上面を加熱手段で加熱することによっても抑制が可能である。但し下面の面品質を向上させるために、上面の加熱とガス噴出流量増加を同時に行うことが望ましい。例えば、ほぼ平面の受け型での成形では、浮上流量の追加のみで下面中央の凹みを無くすことは難しい場合があり、この場合には、上面の特に外周部を加熱することが適当である。加熱手段としては、ガス加熱ヒーターで４００℃以上に加熱した窒素などをガラス塊の上面に吹きかける方法や、型上面にヒーターを設置する方法が好ましい。本方法によりヒケによる下面の凹みは無くなるが、上面を加熱しすぎるとヒケが上面に出ることがある。よってヒケの状態を見ながら加熱を行うことが適当である。
【００３１】
また本発明のガラス塊の製造方法は、成形型の少なくとも成形面が溶融ガラスとの濡れ性が悪い材料で構成されていることが好ましい。多孔質素材や細孔を有する受け型によるガスクッションは、溶融ガラスとの接触を完全に防げるものではない。つまり、前記した実質的に非接触の状態という意味は、時々は接触することを意味している。実際に、溶融ガラス先端が受け型上に落下する瞬間は、落下の勢いで溶融ガラスが瞬間的に受け型に接触している。また前記した第１〜第３の工程においても、噴出ガスで溶融ガラスが暴れるような状態では、瞬間的には溶融ガラスの一部が受け型に接触している。しかし受け型からの噴出ガスの圧力で溶融ガラスが遠ざけられるため、大抵の場合は受け型への溶融ガラスの融着を防ぐことができる。また溶融ガラスが一時的に融着したとしても、溶融ガラスがまだ軟らかい状態で融着部が型から外れれば、溶融ガラスの表面張力により融着痕は消失する。つまり融着はしても良いが、直ぐ外れるような軽い融着であることが重要である。
【００３２】
但し、ガスの噴出状態が均一でない場合や、非常に反応性が高い溶融ガラスを成形する場合、そしてカン割れ等で受け型温度を高くする必要がある場合などでは、溶融ガラスが受け型表面に強く融着し、成形後のガラス塊に大きな突起状の融着痕が残ることがある。成形型の少なくとも成形面が溶融ガラスとの濡れ性が悪い材料で構成されている場合、溶融ガラスが融着しないか又は融着が外れやすいため、融着痕が格段に残りにくくなる。特に、成形初期の噴出ガス流量を少なくする方法では、融着の危険性は高まるので、成形型の少なくとも成形面が溶融ガラスとの濡れ性が悪い材料で構成されていることが、より効果的である。
【００３３】
炭素系材料は溶融ガラスの組成によらず溶融ガラスとの濡れ性が悪いのが特徴である。但しグラファイト（黒鉛）は、素材表面から離脱した炭素粉がガラス塊表面に付着する問題があるため、プリフォームの成形では付着物に注意が必要である。特に多孔質化した炭素系素材は、炭素粉の脱落の問題が起こりやすい。そこで、炭素粉が離脱しにくい炭素系素材として、ガラス状カーボン、グラファイト粒子の隙間をガラス状カーボンで埋めた複合体、グラファイト表面に化学蒸着で結晶質の炭素膜を被覆したものがより好ましい。また炭素系材料は、大気中高温下で使用すると酸化し消耗するという問題がある。よってグラファイトにＳｉＣとＢ4Ｃを少量添加した複合材のように、耐酸化性を高めた材料も好ましい。以上はバルク状の炭素系材料の例であるが、他材料の表面に炭素系膜を形成したものも使用できる。炭素膜の例としては、非晶質のダイヤモンドライクカーボン膜（ＤＬＣ）や、ダイヤモンド膜の他、前記した化学蒸着による結晶質炭素膜などが使用できる。またＤＬＣのような非晶質炭素膜に一部結晶質の炭素が含まれる膜でも良い。炭素膜のベース材料としては、炭素膜との付着強度が強いＳｉＣやＷＣやＴｉＣ等を含む超硬や超硬合金が好ましい。但し、耐熱性ステンレス等の安価な材料でも、Ｔｉ、Ｓｉ、ＳｉＣ等の中間膜を単層または複層挟むことで、実用上充分な付着強度が得られる。その結果、膜剥離による付着粉の問題も起こらなくなる。
【００３４】
また炭素系材料ほどではないが、溶融ガラスとの濡れが悪く融着しにくい材料として、ＡｌＮ、ＢＮ、Ｓｉ3Ｎ4等の窒化物やこれらの複合物、そしてＳｉＣ、ＷＣ、ＴｉＣ等の炭化物、これらを含む超硬や超硬合金も受け型用素材として好ましい。またＴｉＡｌＮ、ＣｒＮ、ＣｒXＮY、ＴｉＣｒＮ、ＴｉＮ等の窒化物膜を他材料にコーティングしたものでも同じ効果が得られる。但し、ＴｉＮは酸化により効果が薄れる場合が有る。
また上記の２種類以上の窒化物膜を積層成膜しても良い。また溶融ガラスの組成は限られるが、白金と金を含む貴金属合金膜も濡れ性を悪くする膜として使用できる。その他、耐熱製金属を窒化処理したものでも効果はある。
【００３５】
（ガラス塊成形型：受け型）
耐熱性ステンレス（ＳＵＳ３１６Ｌ）を加工し、図１のようなガスを噴出させる複数の細孔１１を有する受け型１０を作製した。受け型１０の上面には、溶融ガラスを成形する凹部１２（開口径１２．３mm、深さ６mm）が形成されている。なお凹部１２の底面１３のアールは４０mmで、凹部１２内面は鏡面仕上げしてある。また凹部底面１３には、気体を噴出させる０．３mmの細孔１１が同心円状に開けられている。
【００３６】
更に上記受け型１０の凹部１２内面に、各種コーティングを行った。コーティングの種類としては、ダイヤモンドライクカーボン（ＤＬＣ）、ＴｉＡｌＮ、ＴｉＣｒＮ、ＣｒＮ、ＣｒxＮy、ＡｌＮ、ＴｉＮ、ＳｉＣの単層膜、ＡｌＮとＣｒＮの積層膜、ＴｉＮとＣｒＮの積層膜、９５Ｐｔ５Ａｕ合金膜を試した。なおＤＬＣとＳＵＳ３１６Ｌの付着強度を持たせるため、ＴｉとＳｉの中間層を形成した。
同様に凹部の材料のみを変えて、細孔を有する同規格の受け型を作製した。なお凹部の材料としては、グラファイト、ガラス状カーボン、グラファイトとガラス状カーボンの複合体、グラファイト表面に化学蒸着炭素膜を被覆した材料、グラファイトとＳｉＣとＢ4Ｃの複合材、ＳｉＣ、ＡｌＮ、ＡｌＮとＢＮの複合材、ＷＣを主成分とする超硬、サイアロンを試した。
【００３７】
一方、図２のように、凹部２２のみを多孔質素材２１に変更した受け型２０を作製した。なお多孔質素材２１の気孔径と気孔率は、良好な浮上状態が得られる範囲（気孔径：５〜６０μm、気孔率：２０〜５０％）のものを用いた。なお多孔質素材としては、ＳＵＳ３１６Ｌ、グラファイト、グラファイト多孔体の表面に化学蒸着炭素膜を形成したもの、ＳｉＣ、サイアロンを試した。同様に、ＳＵＳ３１６Ｌ製多孔体の凹部内面に、各種コーティングを行った。コーティングの種類としては、ダイヤモンドライクカーボン（ＤＬＣ）、ＴｉＡｌＮ、ＴｉＣｒＮ、ＣｒＮ、ＣｒXＮY、ＡｌＮ、ＴｉＮ、ＳｉＣの単層膜、ＡｌＮとＣｒＮの積層膜、ＴｉＮとＣｒＮの積層膜、９５Ｐｔ５Ａｕ合金膜を試した。なおＤＬＣとＳＵＳ３１６Ｌの付着強度を持たせるため、ＴｉとＳｉの中間層を形成した。
【００３８】
（成形方法と成形装置）
図３に成形装置３０を示す。成形装置３０は、１２個の受け型３１が回転テーブル３２外周に等間隔で装着されており、溶融ガラスのキャストに合わせて間欠的に回転する。成形したガラス塊のカン割れを防ぐため、受け型はヒーターにより１００〜４００℃程度に加熱されている。受け型に溶融ガラスを受ける際は、溶融ガラスの流出ノズル（白金合金製）（図示せず）に受け型を充分接近させ、溶融ガラス流が切れない状態で溶融ガラスをキャストする。なお溶融ガラスの体積が大きい場合には、ノズル先端が溶融ガラスに埋もれないように受け型をゆっくり下降させながらキャストを行う。キャスト時においては、受け型内面から吹き出す気体の流量を広範囲な融着が起こらない程度の流量に抑える。溶融ガラス重量が所定重量に達した段階で受け型を下降させて溶融ガラス流を切断し、受け型に溶融ガラスを切り分ける。この直後に回転テーブルを回転させ、流出ノズルから受け型を退避させる。なお受け型の退避と同時に別の受け型を流出ノズルの下に配し、連続的に溶融ガラスをキャストする。キャスト後の溶融ガラスは、型からの浮上ガスにより実質的に非接触状態に保たれ、徐々に冷却されながら硬化してゆく。
【００３９】
一方、受け型へのガス供給はＡＢの二系統からなる。Ａ系統は常時流しておくもので、Ｂ系統は必要に応じて電磁弁を開き流す構造となっている。そしてＡＢ両系統の流量は流量計で個別に調整する。前記した第一と第二の工程では、Ａ系統のみを開き少量の浮上ガスを流しておき、第三の工程の途中からＢ系統の電磁弁を開きガスを追加する。つまり、第三工程の途中からはＡＢを足した流量が受け型に流れることとなる。なおＡ系統もＯＮ／ＯＦＦ可能とすれば流量調節の自由度は増えるが、装置コストは高くなる。またＢ系統をマスフローコントローラーで流量可変とすれば、よりきめ細かい流量調節が可能となるが、装置構造は非常に高くなってしまうという欠点がある。
【００４０】
（ガラス）
溶融ガラスをノズルから排出する際、ガラスを失透させないこと、粘度が高すぎても低すぎてもガラス塊の成形が困難になるので、適正な粘度範囲で排出することなどが求められる。ガラスには比較的失透しやすいものとそうでないものとがあるが、本発明は失透にくいガラスは勿論、液相温度における粘度が低いため結晶化速度が大きい、比較的失透しやすいガラスの成形にも好適である。特に従来の方法では失透しやすかった液相温度における粘度が２０ポアズ以下のガラスからなるガラス塊の成形に好適であり、液相温度における粘度が１０ポアズ以下のガラスからなるガラス塊の成形も可能である。また、ガラス塊成形型と融着しやすいガラス、例えば、リン酸塩を含有するガラスからなるガラス塊や、硼酸塩を含有するガラスからなるガラス塊の成形に好適である。
【００４１】
【実施例】
以下、実施例と比較例により本発明を更に詳しく説明する。
（実施例１）
図１の細孔を有する受け型を用い、硼酸塩系（液相温度：９１０℃、流出粘性：１０ポアズ）の溶融ガラスから１６５０mgのガラス塊を成形した。型温を２６０℃とし０．１５Ｌ／分のガスを噴出した状態で溶融ガラスを受け、第三工程の途中（キャスト開始から２９秒後）に１．５Ｌ／分の浮上ガスを追加した。そのまま受け型上で溶融ガラス塊を冷却し、約９０秒後に固化したガラス塊を受け型から取り出した。得られたガラス塊の浮上面側のアールは約３０mmで面の歪みや凹みは無かった。但し、浮上面の外周部には約１０％に小突起が見られたが、レンズ成形の結果、特に影響がないことが分かった。尚、受け型がノズル下方から移動するタイミングは、キャスト開始から８．５秒後とした。
上記条件において、浮上ガスの追加タイミングを２０秒と早くした場合には、噴出するガス圧でガラス塊の下面中央部が凹む現象が起こった。また逆に３５秒と遅くした場合には、ガラス塊の下面にシワや歪みが発生し、一部下面の中央がヒケて凹んだものがみられた。効果的な追加タイミングは、溶融ガラスの温度が低下し赤みが取れた状態を目安とすれば良い。
【００４２】
（実施例２）
実施例１と同構造の受け型を前記した各種素材で作製し、同様な成形条件でガラス塊を成形した。炭素系材料からなる型（グラファイト、ガラス状カーボン、グラファイトとガラス状カーボンの複合体、グラファイト表面に化学蒸着炭素膜を被覆した材料、グラファイトとＳｉＣとＢ4Ｃの複合材）で成形したガラス塊には小突起が全く発生せず、同様に面の歪みや凹みは無かった。但しグラファイト製の型のみは、時々グラファイト粉末がガラス表面に付着していた。洗浄によりグラファイト粉末は除去できたが、表面には点状の接触痕が残った。但しこの付着痕は小さいため、レンズ成形では特に問題にならなかった。一方、ＳｉＣ、ＡｌＮ、サイアロンからなる受け型では、小突起の発生頻度が１％以下に減少した。
【００４３】
（比較例１）
実施例１と同じ受け型を使用し、成形工程を通して一定の噴出ガス流量でガラス塊を成形した。噴出ガス流量が少ない場合は浮上面にシワや歪みが発生し、カン割れも多く発生した。噴出ガス流量を増やしてゆくと、シワや歪みやカン割れの問題は緩和されてゆくが、ガラス塊の下面中央に凹みが発生する。更に噴出ガス流量を増やした場合には、凹みが大きくなるとともにガスの噴出痕もみられた。以上のように、一定浮上流量の成形では、凹みがなく下面品質が良好なガラスを成形することは不可能であった。
【００４４】
（実施例３）
図２の多孔質素材からなる受け型を用い、硼酸塩系（液相温度：９１０℃、流出粘性：１０ポアズ）の溶融ガラスを以下のようにガラス塊に成形した。なお本実施例では、気孔径が５０μmで気孔率が３３％のグラファイト製多孔体を用いた。型温を１８０℃とし、０．5Ｌ／分のガスを噴出した状態で溶融ガラスを受け、第三工程の途中（キャスト開始から２３秒後）に２．５Ｌ／分の浮上ガスを追加した。受け型がノズル下方から移動するタイミングは、キャスト開始から８．５秒後とした。そのまま受け型上で溶融ガラス塊を冷却し、約９０秒後に固化したガラス塊を受け型から取り出した。得られたガラス塊の浮上面側のアールは約３０mmで面の歪みや凹みは無かった。但し、浮上面にグラファイト粉末の付着が約５％に見られたが、洗浄後にレンズ成形した結果、特に影響がないことが分かった。
【００４５】
（実施例４）
多孔質素材として、グラファイト製多孔体表面に化学蒸着炭素膜を１０μm形成したものを用い、実施例３と同条件でガラス塊を成形した。実施例４で見られたグラファイト粉末の付着もなく、良好なガラス塊が得られた。
【００４６】
（実施例５）
多孔質素材部分のみをＳＵＳ３１６Ｌ製の多孔体（気孔率２５％、気孔径２４μm）に変更し、実施例３と同様な条件でガラス塊を成形した。但し、初期の浮上ガス流量は０．３Ｌ／分とし、第三工程の途中（キャスト開始から２６秒後）に２．０Ｌ／分の浮上ガスを追加した。受け型がノズル下方から移動するタイミングは、キャスト開始から８．５秒後とした。得られたガラス塊の浮上面側のアールは約３０mmで、面の歪みや凹みは無かった。但し、約３％のガラス塊の下面に小突起がみられたが、レンズ成形では特に影響がないことが分かった。
【００４７】
（実施例６）
多孔質素材部分のみをサイアロン製の多孔体（気孔率２０％、気孔径１３μm）に変更し、実施例３と同様な条件でガラス塊を成形した。但し、初期の浮上ガス流量は０．２Ｌ／分とし、第三工程の途中（キャスト開始から２８秒後）に１．７Ｌ／分の浮上ガスを追加した。なおガラス塊の下面での小突起の発生頻度は１％以下であった。
【００４８】
（実施例７）
多孔質素材として、ＳＵＳ３１６Ｌ製の多孔体表面に各種コーティングを行ったものを用いて実施例６と同様な条件でガラス塊を成形した。ＤＬＣ、ＣｒＮ、ＣｒXＮY、ＴｉＡｌＮ、ＴｉＣｒＮ膜をコーティンングした受け型では、実施例６で見られた小突起が殆ど発生しなかった。
【００４９】
（実施例８）
実施例１の受け型と同じ構造で底面アールが１３mmの受け型を用い、硼酸塩系（液相温度：９１０℃、流出粘性：１０ポアズ）の溶融ガラス（１６５０mg）をガラス塊に成形した。型温を２６０℃とし０．２Ｌ／分のガスを噴出した状態で溶融ガラスを受け、第三工程の途中（キャスト開始から３１秒後）に２．０Ｌ／分の浮上ガスを追加した。そのまま受け型上で溶融ガラス塊を冷却し、約９０秒後に固化したガラス塊を受け型から取り出した。得られたガラス塊の浮上面側のアールは約１５mmで面の歪みや凹みは無かった。
【００５０】
（比較例２）
実施例８の成形型を用い、成形工程を通して一定の噴出ガス流量で１６５０mgのガラス塊を成形した。噴出ガス流量が少ない場合には、ガラス塊の下面にシワや歪みが発生した。噴出ガス流量を増やしてゆくと、シワや歪みの問題は緩和されてゆくが、次第にガラス塊の下面のアールが大きくなり、シワや歪みがない状態ではアールが２８mmと大きくなった。
【００５１】
（実施例９）
上記各実施例で得られたガラス塊をプリフォームとし、これを加熱してプレス成形型でプレス成形して非球面レンズを作製した。プレス成形によって得られたレンズの光学機能面は研削、研磨仕上げをしなくとも十分な精度を有している。なお得られたレンズ表面には必要の応じて反射防止膜などの光学薄膜を形成してもよい。また、プリフォーム表面にも必要に応じてプレス成形後の離型性等を高める膜をコートしてもよい。
【００５２】
上記のように高品質、高い重量精度を有するプリフォームを用いて、精密プレス成形を行うことにより、欠陥のない、形状精度の優れたレンズなどの光学素子を成形することができる。なお、成形品の対象はレンズに限らず各種光学素子などのガラス成形品にも適用できる。
【００５３】
【発明の効果】
以上のように本発明によれば、溶融ガラス、特に非常に低粘性で失透しやすい溶融ガラスであっても高品質で重量精度が良いガラス塊を成形できる。
また、本発明によれば、ガラス塊成形型素材と極めて融着しやすいガラスでも、融着痕を残さずにガラス塊を成形することができる。
さらに、本発明によれば、下面が平面に近い形状のガラス塊でも下面の一部が凹むことなく成形できる。特にレンズを精密プレス成形するために用いるプリフォームには、精密プレス成形の時間の短縮等を目的にプリフォームを薄くしてレンズ形状に近づけることが有効であり、底面が平坦なガラス塊成形型を使用し、薄いプリフォームを成形することになるが、このようなプリフォーム成形でも良好な形状のプリフォームを作ることができる。
さらに本発明によれば、ガラス塊成形型の底面アールに近いアールのガラス塊を成形することができるので、ガラス塊成形型のガラスを受ける凹部の形状を所定の形状に設計することにより、ガラス塊の下面の形状を目的の形状にすることができる。
【図面の簡単な説明】
【図１】ガスを噴出させる複数の細孔を有する受け型の断面図。
【図２】凹部を多孔質素材とした受け型の断面図。
【図３】成形装置の概略図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a glass molded product for molding a glass molded product having a predetermined weight from molten glass, and further a glass press molded product obtained by reheating and pressing the glass molded product obtained by the above method. The present invention relates to a method for obtaining a glass molded article which is a molding preform for molding an optical element.
[0002]
[Prior art]
In recent years, a high-precision hot press molding technique using a mold has been developed and developed as a method for manufacturing an aspheric glass lens or the like. Molding preforms (hereinafter referred to as “preforms”) used for the main molding require weight accuracy in milligram units, and are used for defects such as striae, devi, scratches, bubbles, and surface deposits that cannot be removed by cleaning. Existence is not allowed.
[0003]
As a method for mass-producing such a preform at a low cost, for example, a method described in JP-A-2-14839 is known. In this method, when the molten glass flowing down from the outflow pipe is received by the concave portion of the mold, air or an inert gas is ejected from the pores opening in the concave portion, and between the molten glass lump and the inner surface of the mold concave portion. A gas cushion is made, and the molten glass block is held in the recess in a substantially non-contact state with the inner surface of the recess until at least a part of the surface of the molten glass block reaches the softening point temperature or less, and cooled to cool the glass block. Is making. According to this method, since the upper and lower surfaces are free surfaces, a preform having a good surface quality can be obtained.
[0004]
Further, a method for obtaining a glass lump by using a receiving mold made of a porous material in place of the above-described forming mold having pores and receiving molten glass in a state in which gas is blown from the receiving mold is disclosed in Japanese Patent Laid-open No. Hei 6 (1994). -122526. Furthermore, in order to reliably prevent unevenness transfer on the surface of the porous body mold, the low temperature fluid is sprayed onto the molten glass tip to cool the molten glass surface until the flowing molten glass tip contacts the receiving mold. A method for preventing transfer is disclosed in JP-A-9-221329. Moreover, when a glass lump is formed with a receiving mold made of a porous material or the like, a dent may occur on the lower surface of the glass lump. As a method for preventing this dent, Japanese Patent Application Laid-Open No. 9-221328 describes a method in which a molten glass is received by a mold while the flow rate of gas ejected from the porous mold is extremely increased, and then the flow rate of gas ejected is reduced. Yes. Japanese Patent Application Laid-Open No. 10-139465 discloses a method for obtaining a glass lump by receiving molten glass with a porous material receiving mold impregnated with water, a liquid organic compound, etc., and cooling the molten glass while floating by the pressure of evaporating gas. Is disclosed. According to this method, the above-mentioned dent of the lower surface of the glass lump can be prevented.
[0005]
[Problems to be solved by the invention]
However, each of the conventional examples has the following drawbacks. First, in the method described in Japanese Patent Application Laid-Open No. 2-14839, since the inner surface of the mold is polished, there is no fear that the unevenness of the mold surface is transferred like a receiving body made of a porous body. However, high-temperature molten glass is very reactive, and the mold and the molten glass may be primarily fused. If the fusion time is short, no trace of the fusion part remains, but if the fusion time is long, the fusion part may remain as a small protrusion. Although this primary fusion can be suppressed by increasing the flow rate of the gas ejected from the pores, there has been a problem that a small depression (gas ejection trace) is partially formed in the glass lump by the gas ejection pressure. In addition, when molding a very low-viscosity molten glass, there is also a problem that if the flow rate of the floating gas is increased, the molten glass is shaken by the jet pressure and the flow of the molten glass is disturbed, so that the weight accuracy of the preform is deteriorated.
[0006]
On the other hand, Japanese Patent Application Laid-Open No. 9-221329 discloses that a low temperature fluid is sprayed onto the molten glass tip to cool the molten glass surface until the leading end of the molten glass flowing out contacts the receiving mold, thereby preventing uneven transfer of the porous body. In the method, there is a risk that not only the molten glass but also the outflow nozzle is cooled. Even when the nozzle temperature is strictly controlled, the fluctuation range of the nozzle temperature becomes large when the nozzle is exposed to wind. When the nozzle temperature fluctuates, the outflow speed of the molten glass fluctuates, which causes a problem that the weight accuracy of the preform is deteriorated. Further, when the melt is cooled to such an extent that the unevenness of the mold surface can be prevented from being transferred, stringing is likely to occur when the glass flow is cut, and another means such as heating the cut portion is required. Further, when the viscosity of the molten glass is increased, there is a problem that it is difficult to form a large glass lump because the glass does not stretch. In addition, in the case of glass that has a high liquidus temperature and is easily devitrified (crystallized), there is an increased risk of devitrification being induced by air cooling of the nozzle.
[0007]
Also, as in Japanese Patent Laid-Open No. 9-221328, there is a risk of cooling the nozzle even in a method of receiving the molten glass in a receiving mold with a very large flow rate of the blown gas and then reducing the flow rate of the blown gas. There is a risk that the same problem as 9-221329 occurs. Further, when the initial flow rate of the ejected gas is increased, the molten glass is shaken by the ejecting pressure and the flow of the molten glass is disturbed. In addition, when receiving extremely low-viscosity molten glass with a receiving mold, the jet gas does not lift the glass, but enters the glass closing the gas jet port, and the bubbles of the jet gas are trapped in the glass, The glass may foam. Glass thus foamed cannot be used for optical elements or the like. On the other hand, when a small glass lump of 2 grams or less is formed using a receiving mold having a flat bottom surface, the tendency of the central portion of the lower surface to be recessed becomes very strong. Therefore, even if the method disclosed in Japanese Patent Laid-Open No. 9-221328 is used, it is difficult to completely eliminate the recess on the lower surface. A local dent on the surface is a problem because it becomes a gas reservoir during lens molding.
[0008]
In the method of forming a glass lump by holding molten glass in a gas cushion, generally, the bottom surface radius of the molded product tends to be larger than the radius (curvature radius) of the receiving mold. This tendency becomes more prominent as the weight of the glass lump to be molded is lighter and as the radius of the mold bottom is larger. For example, when a molten glass of 2 grams or less is molded with a mold having a bottom surface radius of 15 mm or more, the radius of the lower surface of the molded body increases to about 25 to 30 mm. That is, it is a problem to control the radius of the lower surface of the glass lump.
Also, in a general glass forming apparatus in which a plurality of molds are placed on a rotating table and the table is rotated intermittently to form, if a mold with a flat bottom surface is used, the molded product becomes distorted. There is also a problem that it is easy and failure to take out.
[0009]
Further, as disclosed in Japanese Patent Laid-Open No. 10-139465, a method of receiving molten glass by a porous material receiving mold impregnated with water, a liquid organic compound, etc., and cooling while floating the molten glass by the pressure of evaporating gas is as follows. There is a problem. In other words, the temperature of the porous mold needs to be equal to or lower than the boiling point in order to prevent the liquid from evaporating before receiving the molten glass in the mold. For this reason, the surface temperature of the molten glass tends to rapidly decrease, and can cracking easily occurs when a large glass lump is formed.
[0010]
In this way, the conventional gas cushion is formed, and the glass lump is float-molded by receiving molten glass on the glass cushion, the glass lump is devitrified, the glass lump contains bubbles, glass There were problems such as variations in the weight accuracy of the lump.
[0011]
The present invention has been made to solve the above problems, and provides a method for producing a glass lump having a high quality and high weight accuracy, in particular, a preform for molding a mold optics, and by the above method. It aims at providing the method of producing a press-molded article from the obtained glass lump.
[0012]
[Means for Solving the Problems]
Hereinafter, means for solving the problem will be described.
(1)
Glass that separates a molten glass lump from a molten glass stream discharged from a nozzle, and the separated molten glass lump is received on a glass lump forming mold and molded while receiving wind pressure from the glass lump forming mold. A method of manufacturing a molded article,
After the glass lump mold receiving the molten glass lump has moved from below the nozzle, the wind pressure is increased,
The wind pressure before the increase is such that the molten glass lump does not fuse with the glass lump mold and does not hinder the discharge of the molten glass stream from the nozzle,
The method according to claim 1, wherein the increased wind pressure is such that the molten glass lump and the glass lump forming die can be maintained in a substantially non-contact state.
(2)
The glass lump molding die has a recess for receiving molten glass, and has a gas outlet for ejecting gas to apply the wind pressure to the surface of the recess,
A first step of receiving a tip portion of a molten glass flow discharged from the nozzle by a concave portion of a glass lump molding die;
A second step of receiving a molten glass lump obtained by separating the tip from the molten glass stream into a recess of a glass lump forming mold; and
Including a third step of obtaining a molded product by molding the received glass while floating by gas(1)The manufacturing method as described in.
(3)
The wind pressure is increased after the average viscosity of the molten glass lump exceeds 50 poise.(1) or (2)The manufacturing method as described in.
The increase in the wind pressure is caused by an average viscosity of the molten glass block of 50 poise to 10 poise.8More preferably, it is carried out when in the range of poise.
(4)
The viscosity of the molten glass stream discharged from the nozzle is 10 poises or less, the wind pressure before the increase is set to a gas flow rate for generating wind pressure of 1.0 L / min or less, and the increase in the wind pressure is an average of the molten glass lump. When the viscosity is between 50 and 500 poise(1)-(3)The manufacturing method of any one of these.
(5)
The molten glass lump to be molded has a bottom surface with a radius of curvature of 10 mm or more, and the wind pressure before the increase is such that the bottom surface of the molten glass lump cannot be recessed or the bottom surface of the molten glass lump corresponding to the recess of the glass lump forming mold. To the extent that can be obtained(1)-(3)The manufacturing method of any one of these.
(6)
Other than not increasing the wind pressure(1)The manufacturing method according to (5), further comprising a step of selecting an optimal gas flow rate that creates a wind pressure before the increase by performing a method similar to the method described in 1.
That is, the method includes a step of selecting an optimal gas flow rate that creates the wind pressure before the increase, and the optimal gas flow rate is obtained by separating a molten glass mass from a molten glass stream discharged from a nozzle and separating the molten glass mass. The molten glass lump is received on the glass lump forming mold and molded while receiving the wind pressure from the glass lump forming mold, by carrying out the manufacturing method of the glass molded product without increasing the wind pressure, It is the manufacturing method as described in (5) selected.
(7)
The increased wind pressure is the manufacturing method according to any one of (1) to (6), in which a gas flow rate for generating the wind pressure is in a range of 1.0 to 4.0 L / min.
(8)
A glass mass is formed by discharging molten glass having a viscosity of 2 to 20 poise from a nozzle.(1) to (3) and (5) to (7)The manufacturing method of any one of these.
(9)
A glass lump made of glass having a viscosity at a liquidus temperature of 20 poise or less is produced.(1) to (3) and (5) to ((8)The manufacturing method in any one of.
(10)
The glass molded product is a preform for press molding(1)-(8)The manufacturing method in any one of.
(11)
(10)A method for producing a glass press-molded product, in which a preform produced by the method described in 1 is heated and press-molded by a press mold to produce a press-molded product.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
In the method for producing a glass lump according to the present invention, the molten glass lump is separated from the molten glass stream discharged from the nozzle, and the separated molten glass lump is received on the glass lump forming die and from the glass lump forming die. Molded while receiving the wind pressure.
Separation of the molten glass mass from the molten glass stream discharged from the nozzle includes (1) a method of forming the glass mass from the molten glass dripping naturally from the nozzle, and (2) the tip of the molten glass stream discharged from the nozzle. (3) a method of using a descending cutting method in which a glass lump forming die and a nozzle are separated from each other, and a predetermined amount of a molten glass flow front end portion is received by the glass lump forming die after forming. Examples of the method include, but are not limited to, a method of cutting the molten glass flow discharged from the nozzle by a cutting mechanism such as a shear.
[0014]
The separated molten glass lump is molded on the glass lump mold while receiving the wind pressure from the glass lump mold. The glass lump molding die may have, for example, a concave portion that receives molten glass, and a gas ejection port that ejects gas to apply the wind pressure to the surface of the concave portion. Such a glass lump mold will be described later.
[0015]
Furthermore, the manufacturing method of the present invention increases the wind pressure after the glass lump forming mold that has received the molten glass lump has moved from below the nozzle, and the wind pressure before the increase is such that the molten glass lump is a glass lump forming mold. And the increase in wind pressure is such that the molten glass lump and the glass lump forming die can be maintained in a substantially non-contact state. It is characterized by.
The viscosity of the molten glass stream discharged from the nozzle is usually several to several tens of poises. Therefore, the viscosity of the molten glass lump at the initial stage of molding is also low, and when the glass lump mold is located below the nozzle, the wind pressure does not fuse the molten glass lump to the glass lump mold, and the molten glass stream is discharged from the nozzle. The wind pressure should not be disturbed. If the wind pressure is too low, the molten glass lump is fused to the glass lump mold. Moreover, when a wind pressure is too high, the molten glass flow from a nozzle and a nozzle will be cooled, and discharge | emission of a molten glass flow will be prevented. Next, after the glass lump forming mold that has received the molten glass lump has moved from below the nozzle, the wind pressure is increased to such an extent that the molten glass lump and the glass lump forming mold can be maintained in a substantially non-contact state. At this time, the wind pressure from the glass lump molding die does not spray on the nozzle, and the weight accuracy of the molten glass can be maintained.
[0016]
The manufacturing method of the present invention includes, for example, a first step of receiving a tip portion of a molten glass flow discharged from the nozzle by a concave portion of a glass lump forming mold, and melting obtained by separating the tip portion from the molten glass flow. A second step of receiving the glass lump in the concave portion of the glass lump forming mold and a third step of forming the received glass by floating while obtaining the molded product can be included.
[0017]
The first step is a step of receiving the tip of the molten glass flow discharged from the nozzle by the concave portion of the glass lump forming die, for example, a gas cushion formed by ejecting gas from the concave surface of the glass lump forming die It is a process of receiving a molten glass flow that flows down. The second step is a step of separating the tip of the molten glass flow from the molten glass flow and receiving a predetermined amount of molten glass into the concave portion of the glass lump molding die, for example, a stage where the tip reaches a predetermined weight In this step, the molten glass stream is cut to obtain a molten glass lump. The third step is a step of forming a glass lump while levitating the received glass, and cooling and solidifying while holding the glass lump forming die and the molten glass lump in a substantially non-contact state, It is a process to do. At least in the first and second steps, the glass lump mold is located below the nozzle, and the flow rate of the gas ejected to the inner surface of the glass lump mold is suppressed to the minimum necessary amount. And the flow volume of the gas ejected from the middle of the 3rd process which a glass lump shaping | molding die moves from the nozzle lower part is increased, and the wind pressure required for levitation | floating is increased.
[0018]
In the first step in which the molten glass is received by the glass lump forming mold and the second step in which the molten glass flow is cut to obtain the molten glass lump, the flow rate of the jet gas from the mold is such that the glass lump is melted with the glass lump forming mold. It is set to such an extent that it does not adhere and does not hinder the discharge of the molten glass stream from the nozzle. More preferably, high-range fusion between the molten glass and the mold surface does not occur, the discharge of the molten glass flow from the nozzle is not hindered, the injection gas does not enter the molten glass lump, and the discharge gas discharges from the nozzle. The flow rate is such that the molten glass (glass melt) is not shaken.
[0019]
In order to eject a gas that applies wind pressure to glass, if the recess of the receiving mold (glass lump molding mold) is made of a porous material and the gas is ejected through the porous material, it is at least necessary to float the molten glass lump The flow rate of the jet gas from the mold is dependent on the porosity and the pore diameter of the porous material, and may be appropriately adjusted according to these. However, in order to prevent fluctuations in the molten glass flow and devitrification, it is desirable that the flow rate of the ejected gas be 1 L / min or less. On the other hand, a mold having pores for ejecting gas has a small gas permeation area, so that a sufficient amount of wind pressure can be applied with a smaller gas flow rate than a porous mold. In the receiving mold having pores, the flow rate of the ejected gas depends on the pore diameter and the number of pores. For example, when the pore diameter is about 0.2 to 1.0 mm and the number of pores is about 7 to 43, it is 1/3 to 1/10 of the case where the porous body is a receiving type (1 L / min or less). A gas flow rate is appropriate.
[0020]
The glass lump forming mold used in the production method of the present invention has a recess for receiving molten glass, and has a gas outlet for ejecting gas to apply the wind pressure to the surface of the recess. As a means for applying wind pressure to the glass on the glass lump mold or forming a gas cushion, such as forming the receiving mold surface with a porous material, a recess (molding surface) that receives the molten glass of the glass lump mold It is preferable that gas is ejected from one or a plurality of pores that are open to (). Moreover, it is preferable to comprise the surface of the said recessed part of a glass lump shaping | molding die from a material with poor wettability with molten glass. Furthermore, it is desirable that at least the molding surface (concave surface) of the glass lump molding die is made of the following materials.
[0021]
(Carbon material)
Graphite, glassy carbon, composite of graphite and glassy carbon,
A glass surface coated with glassy carbon
Graphite surface coated with chemical vapor deposition carbon film
Graphite, SiC and BFourC composite
(Nitride, carbide)
AlN, BN, AlN / BN composites, carbides and cemented carbides including SiC, TiC, WC, TiC, WC, SIALON, sialon and BN composites
(Thin film)
Hard carbon film such as DLC
Diamond film, amorphous carbon film, crystalline carbon film, mixed carbon film of both
SiThreeNFour, TiAlN, TiCrN, CrN, CrXNY, AlN, TiN, etc. nitride films
Composite multilayer film or laminated film (AlN / CrN, TiN / CrN, etc.)
Noble metal alloy films containing platinum and gold such as Pt-Au, Pt-Ir-Au, Pt-Rh-Au
(Nitriding treatment)
Nitrided surface of refractory metal
[0022]
Various glass can be formed by the production method of the present invention, but in recent years, there has been a strong demand for a method of favorably forming glass exhibiting low viscosity at the time of melting and flowing, and the production method of the present invention is 20 poise or less, particularly 15 poise. It is also suitable for the production of molded products from the following low-viscosity molten glass. In the case of such low-viscosity molten glass, in the conventional methods, the phenomenon that gas enters into the molten glass and foams, or a gas pool is generated at the interface between the molten glass and the mold, and the molten glass is melted when it escapes from the interface. Since the liquid vibrates, there is a problem that the weight accuracy is deteriorated. However, in the method of the present invention, such a problem does not occur, and molding using molten glass having a viscosity of 2 to 20 poise when discharged from the nozzle, particularly 2 to 15 poise can be performed well.
[0023]
In the second step, the molten glass flow is cut by means such as lowering the receiving mold from the molten glass outlet nozzle, and a molten glass lump of a predetermined weight is cut on the receiving mold. When the mold is moved down and stopped, an inertial force is applied to the molten glass, so that the molten glass is flattened instantaneously in the receiving mold. Due to this flattening, the gas cushion at the interface between the glass and the receiving mold is momentarily disturbed, and the escape route of the gas is momentarily blocked, so that a phenomenon that the molten glass jumps suddenly is likely to occur. Such jumping may induce striae due to folding, or when the glass melt jumps, it may come into contact with the molten glass at the tip of the nozzle, resulting in large weight fluctuations. Therefore, in order to suppress such a phenomenon, at least in the first and second steps, the flow rate of the ejected gas is suppressed and the wind pressure is suppressed.
[0024]
In particular, after the viscosity of the molten glass flow discharged from the nozzle is 10 poises or less (2 poises or more), the gas flow rate for creating the wind pressure before the increase is 1.0 L / min or less, and after entering the third step The increase in wind pressure is performed at a time when the average viscosity of the glass block is between 50 and 500 poise.ofGlass is preferred from the viewpoint of preventing foaming, preventing folding and striae due to vibration and jumping, preventing devitrification, and producing a glass lump with good weight accuracy.
[0025]
Further, when molding a glass lump having a curvature radius of 10 mm or more at the bottom surface, the wind pressure before the increase is such that the bottom surface of the glass lump cannot be recessed or the bottom surface of the glass lump corresponding to the concave portion of the glass lump forming mold is obtained. To the extent possible. That is, when a small glass lump is formed with a receiving mold having a substantially flat bottom surface, the bottom of the glass lump corresponding to the concave portion of the glass lump forming mold can be obtained to the extent that the initial gas ejection flow rate cannot be recessed on the bottom surface of the glass lump. Reduce to a small extent. When forming a small glass lump with a receiving mold whose bottom is almost flat, the flow of molten glass toward the center of the mold bottom hardly occurs because the inclination of the mold bottom is gentle. Further, since the floating gas easily escapes to the outside at the outer peripheral portion of the glass lump, the outer peripheral portion has a worse floating state than the central portion of the glass lump. Furthermore, since the inside of the molten glass lump is slower than the outer peripheral portion, if there is a large amount of ejected gas, only the inside will be dented by the ejecting pressure. Conversely, in molding with a receiving mold having a small bottom radius and a steep slope, molten glass tends to flow in the center of the bottom of the receiving mold, and the thick central part is heavy and originally convex, so there is a tendency for slight sinking. Even if there is, it does not reach until it dents. Accordingly, the tendency to dent is more likely to occur as the shape of the bottom surface of the receiving mold is closer to a flat surface and as the glass lump to be formed is lighter. For example, the diameter of the receiving mold with a bottom radius of about 40mm
When molding a glass lump of about 10 mm, if a jet gas of 0.3 L / min or more is flowed
A dent is formed in the center of the lower surface. However, even when molding with a receiving mold with a bottom radius of 40 mm,
If the molten glass is large, the inclination of the outer peripheral portion becomes tight, and the molten glass cannot be lifted by the ejection pressure due to the increase in weight, so that the lower surface is not recessed.In the case of this method, the method includes a step of selecting an optimum gas flow rate that creates a wind pressure before increase, and the optimum gas flow rate separates the molten glass mass from the molten glass stream discharged from the nozzle, and the separated molten glass is separated. The lump is received on the glass lump mold and formed while receiving the wind pressure from the glass lump mold, and a method for producing a glass molded article is selected by performing the method without increasing the wind pressure. Can do.
[0026]
The present invention is suitable for molding a glass lump in which a depression is easily formed on the lower surface of the glass lump, and the curvature radius of the lower surface and the curvature radius of the recess of the glass lump forming die are likely to be greatly different. That is, as such, the radius of curvature (R) of the concave portion of the glass lump forming die is 10 mm or more, particularly 15 mm or more, and the weight of the glass lump is 3 g or less, particularly 2 g or less. It is. The upper limit of the radius of curvature of the concave portion of the glass gob mold is about 100 mm.
[0027]
Thus, in this invention, the flow volume of the ejection gas in the said 1st and 2nd process is small compared with the conventional gas flotation method. Therefore, the floating of the glass lump tends to be incomplete. If the floating state is incomplete, the opportunity for the molten glass to come into contact with the surface of the mold increases, and the temperature of the molten glass decreases at the part where there is much contact. As a result, wrinkles and distortion are generated on the lower surface of the glass lump, the shape seen from the upper surface is not rounded, and the molded body is easily broken. Further, the molten glass lump on the receiving mold is shaken by an inertial force every time the mold moves on the molding apparatus, but if the floating is poor, the molded body often stops at a position deviating from the center position of the mold. If the molten glass is in a soft state at this time, the shape of the molten glass lump is deformed due to gravity. When taking out the solidified glass lump by vacuum suction or the like, the glass lump that is not at the center position of the receiving mold often fails to take out. In particular, in the formation of a glass lump having a flat bottom surface, takeout is likely to fail, and the above-described problems cannot be satisfied with the suppression of the dents on the bottom surface. Therefore, in the present invention, the flow rate of the ejected gas is increased from the middle of the above-described third step to recover the floating state of the molten glass lump.
[0028]
Hereinafter, the timing of increasing the ejection gas will be described. For example, when a glass lump is formed from a low-viscosity molten glass having a viscosity of 5 poise or less by a receiving material made of a porous material, the flow rate of the ejected gas in the first and second steps is reduced to 0.5 L / min or less. It is preferable that the flow rate of the jet gas is increased to 1 to 3 L / min after the viscosity of the molten glass lump is not increased even if the jet gas is increased in step 3. Even after the glass lump forming mold that has received the glass lump has moved from the lower side of the nozzle, if the timing of increase is too early, the molten glass lump may be violated, causing striae due to folding. Further, in molding by a receiving mold having pores, the flow rate of the ejected gas should be increased after the molten glass becomes viscous so as not to be dented by the pressure of the ejected gas from the pores.
[0029]
In molding with a receiving mold whose bottom is close to a flat surface, it is preferable to adjust the increase timing of the jet gas more strictly. For example, when the increase timing of the ejection gas is too early, the lower surface of the glass lump is flattened by the ejection pressure, and the central portion is recessed. On the other hand, if the increase timing is too late, the lower surface may be distorted or wrinkled due to insufficient levitation, and the lower surface may sometimes be recessed. It was found that the dent in this case was not caused by the ejection pressure but was caused by non-uniform volume shrinkage (so-called sink) when the molten glass solidified. In other words, the dent on the bottom surface of the glass lump that occurs when the bottom surface is molded with a flat receiving mold is considered to be caused by both the gas ejection pressure and sink marks. The dent on the lower surface of the glass block due to sink marks is caused by the delay in curing of the lower surface from other portions. Therefore, at the stage where the surface becomes viscous so as not to be dented by the gas jet pressure, the gas jet flow rate is increased and the cooling of the lower surface of the glass lump is promoted, so that the lower surface can be reliably prevented from being dented.
[0030]
Moreover, since the depression of the lower surface of the glass lump due to sink marks occurs due to the delay in curing of the lower surface, it can also be suppressed by heating the upper surface of the glass lump with a heating means. However, in order to improve the surface quality of the lower surface, it is desirable to simultaneously heat the upper surface and increase the gas ejection flow rate. For example, in molding with a substantially flat receiving mold, it may be difficult to eliminate the dent at the center of the lower surface only by adding the floating flow rate. In this case, it is appropriate to heat the outer peripheral portion of the upper surface in particular. As a heating means, a method of spraying nitrogen or the like heated to 400 ° C. or higher with a gas heater on the upper surface of the glass lump or a method of installing a heater on the upper surface of the mold is preferable. Although this method eliminates dents on the bottom surface due to sink marks, if the top surface is heated too much, sink marks may appear on the top surface. Therefore, it is appropriate to perform heating while looking at the state of sink marks.
[0031]
In the method for producing a glass lump according to the present invention, it is preferable that at least the molding surface of the mold is made of a material having poor wettability with molten glass. Gas cushions using a porous material or a receiving mold having pores do not completely prevent contact with molten glass. In other words, the meaning of the substantially non-contact state described above means that contact is sometimes made. Actually, at the moment when the tip of the molten glass falls on the receiving mold, the molten glass instantaneously contacts the receiving mold with the momentum of dropping. Also in the first to third steps described above, in a state in which the molten glass is exposed by the jet gas, a part of the molten glass is instantaneously in contact with the receiving mold. However, since the molten glass is moved away by the pressure of the gas ejected from the receiving mold, in most cases, the fusion of the molten glass to the receiving mold can be prevented. Even if the molten glass is temporarily fused, if the molten glass is still soft and the fused part comes off the mold, the fusion marks disappear due to the surface tension of the molten glass. In other words, although fusion may be performed, it is important that the fusion is light and easy to come off.
[0032]
However, when the gas ejection state is not uniform, when forming a highly reactive molten glass, and when it is necessary to increase the receiving mold temperature due to can cracking, etc., the molten glass is applied to the receiving mold surface. It is strongly fused, and large projection-like fusion marks may remain on the glass lump after molding. When at least the molding surface of the mold is made of a material having poor wettability with the molten glass, the molten glass is not fused or the fusion is easily removed, so that the fusion marks are much less likely to remain. In particular, in the method of reducing the gas flow rate at the initial stage of molding, the risk of fusion increases, so it is more effective that at least the molding surface of the molding die is made of a material having poor wettability with molten glass. It is.
[0033]
Carbon-based materials are characterized by poor wettability with molten glass regardless of the composition of the molten glass. However, since graphite (graphite) has a problem that the carbon powder detached from the surface of the material adheres to the surface of the glass lump, attention must be paid to the adhered material when molding the preform. In particular, a porous carbon-based material is likely to cause a problem of carbon powder falling off. Therefore, as the carbon-based material from which the carbon powder does not easily leave, glassy carbon, a composite in which the gap between the graphite particles is filled with glassy carbon, and a graphite surface coated with a crystalline carbon film by chemical vapor deposition are more preferable. Carbon materials also have a problem that they are oxidized and consumed when used at high temperatures in the atmosphere. Therefore, graphite and SiC and BFourA material with improved oxidation resistance such as a composite material to which a small amount of C is added is also preferable. The above is an example of a bulk-like carbon-based material, but a material in which a carbon-based film is formed on the surface of another material can also be used. As an example of the carbon film, an amorphous diamond-like carbon film (DLC), a diamond film, or a crystalline carbon film formed by chemical vapor deposition described above can be used. Alternatively, a film in which crystalline carbon is partially contained in an amorphous carbon film such as DLC may be used. As the base material of the carbon film, a cemented carbide or a cemented carbide alloy containing SiC, WC, TiC or the like having a strong adhesion strength to the carbon film is preferable. However, even with inexpensive materials such as heat resistant stainless steel, practically sufficient adhesion strength can be obtained by sandwiching a single layer or multiple layers of an intermediate film such as Ti, Si, or SiC. As a result, the problem of adhered powder due to film peeling does not occur.
[0034]
Moreover, although not as much as carbon-based materials, AlN, BN, Si as materials that do not wet well with molten glass and are difficult to fuse.ThreeNFourNitrides such as these, composites thereof, carbides such as SiC, WC, and TiC, and cemented carbides and cemented carbides containing these are also preferable as receiving materials. TiAlN, CrN, CrXNYThe same effect can be obtained by coating other materials with a nitride film such as TiCrN or TiN. However, TiN may be less effective due to oxidation.
Two or more types of nitride films may be stacked. Although the composition of molten glass is limited, a noble metal alloy film containing platinum and gold can also be used as a film that deteriorates wettability. In addition, nitriding treatment of heat-resistant metal is effective.
[0035]
(Glass block mold: receiving mold)
A heat-resistant stainless steel (SUS316L) was processed to produce a receiving
[0036]
Further, various coatings were applied to the inner surface of the
Similarly, a receiving mold of the same standard having pores was produced by changing only the material of the recess. The material of the recess includes graphite, glassy carbon, a composite of graphite and glassy carbon, a material obtained by coating a graphite surface with a chemical vapor deposition carbon film, graphite, SiC and BFourA C composite material, SiC, AlN, a composite material of AlN and BN, carbide and sialon mainly composed of WC were tested.
[0037]
On the other hand, as shown in FIG. 2, a receiving
[0038]
(Molding method and molding equipment)
FIG. 3 shows the
[0039]
On the other hand, the gas supply to the receiving mold consists of two systems AB. The A system is always flowed, and the B system has a structure in which the electromagnetic valve is opened as required. The flow rates of both AB systems are individually adjusted with a flow meter. In the first and second steps described above, only the system A is opened and a small amount of floating gas is allowed to flow, and the solenoid valve of the system B is started from the middle of the third process.TheAdd opening gas. That is, from the middle of the third step, a flow rate obtained by adding AB flows into the receiving mold. If the A system can also be turned ON / OFF, the degree of freedom of flow rate adjustment increases, but the device cost increases. Further, if the flow rate of the B system is variable with a mass flow controller, finer flow rate adjustment is possible, but there is a disadvantage that the device structure becomes very high.
[0040]
(Glass)
When the molten glass is discharged from the nozzle, it is required not to devitrify the glass, and it is difficult to form a glass lump if the viscosity is too high or too low. There are glass that is relatively easily devitrified and glass that is not easily devitrified. In the present invention, not only glass that is not easily devitrified but also glass that is relatively easily devitrified because of its low viscosity at the liquidus temperature and high crystallization speed. It is also suitable for molding. In particular, it is suitable for molding a glass lump made of glass having a viscosity at a liquidus temperature of 20 poise or less, which was easily devitrified in the conventional method, and a glass lump made of glass having a viscosity at a liquidus temperature of 10 poise or less Is possible. Further, it is suitable for molding glass that is easily fused with a glass lump mold, for example, glass lump made of glass containing phosphate, or glass lump made of glass containing borate.
[0041]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
(Example 1)
A 1650 mg glass lump was molded from a borate-based (liquid phase temperature: 910 ° C., outflow viscosity: 10 poise) using a receiving mold having pores shown in FIG. Molten glass was received in a state where the mold temperature was 260 ° C. and 0.15 L / min of gas was ejected, and 1.5 L / min of floating gas was added during the third step (29 seconds after the start of casting). The molten glass lump was cooled on the receiving mold as it was, and the glass lump solidified after about 90 seconds was taken out from the receiving mold. The obtained glass lump had a radius of about 30 mm on the air bearing surface side, and there was no surface distortion or dent. However, about 10% of small protrusions were observed on the outer peripheral portion of the air bearing surface, but it was found that there was no particular influence as a result of lens molding. The timing at which the receiving mold moves from below the nozzle was 8.5 seconds after the start of casting.
Under the above conditions, when the addition timing of the floating gas was made as fast as 20 seconds, a phenomenon occurred in which the central portion of the lower surface of the glass block was dented by the gas pressure to be ejected. On the other hand, when it was delayed for 35 seconds, wrinkles and distortion occurred on the lower surface of the glass lump, and some of the center of the lower surface was indented and recessed. An effective additional timing may be determined based on a state where the temperature of the molten glass is lowered and the redness is removed.
[0042]
(Example 2)
A receiving mold having the same structure as that of Example 1 was produced from the various materials described above, and a glass lump was molded under the same molding conditions. Molds made of carbon-based materials (graphite, glassy carbon, composites of graphite and glassy carbon, materials with a chemical vapor-deposited carbon film on the graphite surface, graphite, SiC and BFourNo small protrusion was generated in the glass lump formed with the C composite material, and there was no surface distortion or dent similarly. However, only graphite molds sometimes had graphite powder adhered to the glass surface. Although graphite powder could be removed by washing, spot-like contact marks remained on the surface. However, since this adhesion mark is small, there was no particular problem in lens molding. On the other hand, in the receiving mold made of SiC, AlN, and sialon, the occurrence frequency of small protrusions decreased to 1% or less.
[0043]
(Comparative Example 1)
The same receiving mold as in Example 1 was used, and a glass lump was molded at a constant gas flow rate throughout the molding process. When the flow rate of the jet gas was small, wrinkles and distortion occurred on the air bearing surface, and many cracks occurred. Increasing the flow rate of the ejected gas will alleviate the problems of wrinkles, distortion and cracking, but a dent will occur at the center of the bottom of the glass lump. Further, when the flow rate of the ejected gas was increased, the dent increased and gas ejection marks were also observed. As described above, it has been impossible to form a glass having no dents and good bottom surface quality by molding at a constant floating flow rate.
[0044]
(Example 3)
Using a receiving mold made of the porous material shown in FIG. 2, a borate-based (liquid phase temperature: 910 ° C., outflow viscosity: 10 poise) was formed into a glass lump as follows. In this example, a graphite porous body having a pore diameter of 50 μm and a porosity of 33% was used. The mold temperature was 180 ° C., molten glass was received in a state where 0.5 L / min of gas was ejected, and a floating gas of 2.5 L / min was added during the third step (23 seconds after the start of casting). The timing at which the receiving mold moves from below the nozzle was 8.5 seconds after the start of casting. The molten glass lump was cooled on the receiving mold as it was, and the glass lump solidified after about 90 seconds was taken out from the receiving mold. The obtained glass lump had a radius of about 30 mm on the air bearing surface side, and there was no surface distortion or dent. However, although the adhesion of the graphite powder to the air bearing surface was observed at about 5%, it was found that there was no particular effect as a result of lens molding after washing.
[0045]
(Example 4)
A glass lump was molded under the same conditions as in Example 3 using a porous material having a 10 μm chemical vapor deposited carbon film formed on the surface of a graphite porous body. There was no adhesion of the graphite powder seen in Example 4, and a good glass lump was obtained.
[0046]
(Example 5)
Only the porous material portion was changed to a porous body made of SUS316L (porosity 25%, pore diameter 24 μm), and a glass lump was molded under the same conditions as in Example 3. However, the initial floating gas flow rate was 0.3 L / min, and 2.0 L / min floating gas was added during the third step (26 seconds after the start of casting). The timing at which the receiving mold moves from below the nozzle was 8.5 seconds after the start of casting. The obtained glass lump had an R of the air bearing surface side of about 30 mm, and there was no surface distortion or dent. However, although small protrusions were observed on the lower surface of about 3% of the glass lump, it was found that there was no particular effect in lens molding.
[0047]
(Example 6)
Only the porous material portion was changed to a sialon porous body (
[0048]
(Example 7)
As a porous material, a glass lump was molded under the same conditions as in Example 6 using various types of coating on the surface of a porous body made of SUS316L. DLC, CrN, CrXNYIn the receiving type coated with the TiAlN and TiCrN films, the small protrusions seen in Example 6 were hardly generated.
[0049]
(Example 8)
Using a receiving mold having the same structure as the receiving mold of Example 1 and a bottom radius of 13 mm, a borate-based (liquid phase temperature: 910 ° C., outflow viscosity: 10 poise) molten glass (1650 mg) was formed into a glass lump. The molten glass was received with a mold temperature of 260 ° C. and a gas of 0.2 L / min was ejected, and 2.0 L / min of floating gas was added during the third step (31 seconds after the start of casting). The molten glass lump was cooled on the receiving mold as it was, and the glass lump solidified after about 90 seconds was taken out from the receiving mold. The obtained glass lump had a radius of about 15 mm on the air bearing surface side, and there was no surface distortion or dent.
[0050]
(Comparative Example 2)
Using the mold of Example 8, 1650 mg of glass lump was molded at a constant gas flow rate throughout the molding process. When the flow rate of the ejected gas was small, wrinkles and distortion occurred on the lower surface of the glass block. Increasing the flow rate of the ejected gas alleviated the problem of wrinkles and distortion. However, the radius of the lower surface of the glass lump gradually increased, and in the state without wrinkles and distortion, the radius became 28 mm.
[0051]
Example 9
The glass lump obtained in each of the above examples was used as a preform, which was heated and press-molded with a press mold to produce an aspheric lens. The optical functional surface of the lens obtained by press molding has sufficient accuracy without being ground or polished. In addition, you may form optical thin films, such as an antireflection film, in the obtained lens surface as needed. Moreover, you may coat the film | membrane which improves the releasability after press molding etc. as needed to the preform surface.
[0052]
By performing precision press molding using a preform having high quality and high weight accuracy as described above, it is possible to mold an optical element such as a lens having no defect and having excellent shape accuracy. The object of the molded product is not limited to a lens, and can be applied to glass molded products such as various optical elements.
[0053]
【The invention's effect】
As described above, according to the present invention, it is possible to form a glass lump having high quality and good weight accuracy even with molten glass, particularly molten glass that is very low in viscosity and easily devitrified.
Further, according to the present invention, a glass lump can be formed without leaving a fusing mark even with a glass that is extremely easy to fuse with a glass lump forming mold material.
Furthermore, according to the present invention, even a glass lump whose bottom surface is close to a flat surface can be molded without being recessed. Especially for preforms used for precision press molding of lenses, it is effective to make the preform thinner and close to the lens shape for the purpose of shortening the time of precision press molding, etc. Is used to form a thin preform, but a preform having a good shape can be produced even by such preform molding.
Furthermore, according to the present invention, a round glass lump close to the bottom rounded radius of the glass lump forming mold can be formed. Therefore, by designing the shape of the concave portion for receiving the glass of the glass lump forming mold into a predetermined shape, The shape of the lower surface of the lump can be set to a desired shape.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a receiving mold having a plurality of pores for ejecting gas.
FIG. 2 is a cross-sectional view of a receiving mold in which a concave portion is made of a porous material.
FIG. 3 is a schematic view of a molding apparatus.
Claims (11)
前記溶融ガラス塊を受けたガラス塊成形型が前記ノズル下方から移動した後に前記風圧を増加させ、
前記増加前の風圧は、前記溶融ガラス塊がガラス塊成形型と融着せず、かつ前記ノズルからの溶融ガラス流の排出を妨げない程度とし、
前記増加後の風圧は、前記溶融ガラス塊と前記ガラス塊成形型とが実質的に非接触状態を維持できる程度とすることを特徴とするガラス成形品の製造方法。A glass that separates a molten glass lump from a molten glass stream discharged from a nozzle, and the separated molten glass lump is received on a glass lump forming mold and molded while receiving wind pressure from the glass lump forming mold. A method of manufacturing a molded article,
After the glass lump mold receiving the molten glass lump has moved from below the nozzle, the wind pressure is increased,
The wind pressure before the increase is such that the molten glass lump does not fuse with the glass lump mold and does not hinder the discharge of the molten glass stream from the nozzle,
The method according to claim 1, wherein the increased wind pressure is such that the molten glass lump and the glass lump forming die can be maintained in a substantially non-contact state.
前記ノズルより排出される溶融ガラス流の先端部をガラス塊成形型の凹部で受ける第１の工程、
前記先端部を溶融ガラス流から分離して得られた溶融ガラス塊をガラス塊成形型の凹部に受け取る第２の工程、及び
受け取ったガラスを気体により浮上させながら成形して成形品を得る第３の工程を含む請求項１に記載の製造方法。The glass lump molding die has a recess for receiving molten glass, and a gas outlet for ejecting gas to apply the wind pressure to the surface of the recess,
A first step of receiving a tip portion of a molten glass flow discharged from the nozzle by a concave portion of a glass lump molding die;
A second step of receiving the molten glass lump obtained by separating the tip from the molten glass flow into the concave portion of the glass lump forming mold, and a third step of obtaining the molded product by forming the received glass while floating with gas. The manufacturing method of Claim 1 including the process of.
ノズルより排出される溶融ガラス流から溶融ガラス塊を分離し、分離された溶融ガラス塊は、ガラス塊成形型上に受け取られ、かつ前記ガラス塊成形型からの風圧を受けながら成形される、ガラス成形品の製造方法を、前記風圧を増加させることなく実施することで、選択される
請求項５に記載の製造方法。 Look including the step of selecting an optimum gas flow to produce a wind pressure before the increase, the optimum gas flow rate,
A glass that separates a molten glass lump from a molten glass stream discharged from a nozzle, and the separated molten glass lump is received on a glass lump forming mold and molded while receiving wind pressure from the glass lump forming mold. The method of manufacturing according to claim 5 , wherein the method of manufacturing a molded product is selected by performing the method without increasing the wind pressure .
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| JP4162623B2 (en) | 2004-04-27 | 2008-10-08 | Ｈｏｙａ株式会社 | Precision press molding preform manufacturing method and optical element manufacturing method |
| CN100355679C (en) * | 2004-09-30 | 2007-12-19 | 亚洲光学股份有限公司 | Glass modelling mould taking-out device |
| JP4746995B2 (en) * | 2006-02-02 | 2011-08-10 | 株式会社オハラ | Optical glass |
| JP2007302526A (en) * | 2006-05-12 | 2007-11-22 | Ohara Inc | Glass forming apparatus, glass forming method and apparatus for manufacturing glass formed product |
| JP5414222B2 (en) * | 2007-09-25 | 2014-02-12 | Ｈｏｙａ株式会社 | Preform for precision press molding and method for manufacturing optical element |
| JP5095564B2 (en) * | 2007-09-25 | 2012-12-12 | Ｈｏｙａ株式会社 | Mold, method for manufacturing glass molded body using the mold, and method for manufacturing optical element |
| JP2009221074A (en) * | 2008-03-18 | 2009-10-01 | Unitika Ltd | Mold for molding glass lens and method for manufacturing the same |
| JP2012082096A (en) * | 2010-10-08 | 2012-04-26 | Ohara Inc | Method for manufacturing molded glass body, glass molding tool and component for glass molding tool |
| WO2013111837A1 (en) * | 2012-01-24 | 2013-08-01 | Hoya株式会社 | Glass gob molding device, method for producing glass gob, method for producing glass molded product, and method for producing optical element |
| WO2013111874A1 (en) * | 2012-01-25 | 2013-08-01 | Hoya株式会社 | Glass gob molding device, method for producing glass gob, and method for producing glass molded product |
| JP2013227211A (en) * | 2012-03-30 | 2013-11-07 | Hoya Corp | Glass forming mold and method for manufacturing glass gob |
| US11667561B2 (en) * | 2018-11-26 | 2023-06-06 | Corning Incorporated | Glass material with a high index of refraction |
| US11753347B2 (en) * | 2019-10-14 | 2023-09-12 | Corning Incorporated | Rapid forming of glass and ceramics |
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