JP3550461B2

JP3550461B2 - Plastic molding method and optical disk manufacturing method

Info

Publication number: JP3550461B2
Application number: JP15367696A
Authority: JP
Inventors: 正樹吉井; 浩樹蔵本; 和弘藤川
Original assignee: Hitachi Ltd; Hitachi Maxell Energy Ltd
Current assignee: Hitachi Ltd; Hitachi Maxell Energy Ltd
Priority date: 1996-06-14
Filing date: 1996-06-14
Publication date: 2004-08-04
Anticipated expiration: 2016-06-14
Also published as: JPH10626A

Description

【０００１】
【発明の属する技術分野】
本発明は、プラスチック成形方法及びその装置に関する。
【０００２】
【従来の技術】
プラスチック射出成形において、成形転写性の向上を図る一つの方法として、金型キャビティに充填される溶融樹脂のキャビティ表面に接する部分を高温でかつ該部分全域にわたって均一に保持することが挙げられる。具体的な温度条件としては、充填樹脂と金型キャビティ表面との境界面温度を成形樹脂の熱変形温度以上、場合によってはガラス転移点温度以上に保持する必要がある。
【０００３】
光ディスク基板の成形においては、サブミクロンオーダの情報ピットやレーザ案内溝の精密転写が最重要課題である。一般に、光ディスク基板の射出成形では、図１に示すように情報ピットやレーザ案内溝の成形転写のためのニッケル製のスタンパを金型キャビティ内に装着し、キャビティの中心に設けたゲートより溶融樹脂を注入・充填し、冷却・固化したあと離型して成形を完了する。
【０００４】
射出成形においては、溶融樹脂は充填中に金型によって冷却される（後述の成形条件では、約２０〜３０℃低下）ため、ポリカーボネート樹脂による光ディスク基板の従来技術では、図８中の▲１▼に示されるようにスタンパの溝深さに対してほとんど転写しておらず、しかもゲートから遠ざかるに従って転写量が減少する傾向を示す。
【０００５】
光ディスク基板成形の場合、光学歪み（複屈折）の増大を避けるために圧力を大きくしないで転写性を向上させるための技術として、（１）溶融樹脂を高速充填する、（２）金型温度を高くして成形される。
【０００６】
上記した従来技術（１）の高速充填成形では、図８▲２▼に示されるように転写性はある程度改善されるものの完全な成形転写を得ることはできない。しかも、ゲートから遠ざかるに従って転写性が低下するという問題も解決されない。射出成形機の性能から云うと図８に示した例よりも高速充填は可能であるが、バリ等の発生などのために高速充填化には限界がある。
【０００７】
従来技術の（２）においても、離型時の成形品の変形防止の点から金型温度はせいぜい成形樹脂の熱変形温度近くまで（熱変形温度以下：ポリカーボネート樹脂の熱変形温度は１２６℃）しか上げられないため、上記と同様に転写性は図８▲３▼に示すように満足できるものでなく、しかも従来技術（１）と同様にゲートから遠ざかるに従って転写性が低下するという問題は残されたままとなっている。
【０００８】
転写性の低下を防止する方法として、特開平１ー２７８３２２号公報に記載されているように、ゲートから遠い部分の金型温度（キャビティ温度）を高くして成形する方法が提案されている。しかし、この方法では基板を離型して取り出す時も金型温度が高い（転写性向上のために熱変形温度以上に設定してある）ので基板の変形を生じ、光ディスク基板としてのチルト（基板反り）の仕様を満足しない。しかも、設備的にも複数の金型温度調節機構が必要である。さらに、この問題を解決する方法の一つとして、樹脂充填時には金型温度を熱変形温度以上にし、離型時には金型温度を熱変形温度以下にするという金型温度冷熱サイクル法が開発されている。しかし、この方法では、さらに設備上複雑になり、しかも成形サイクルが長くなるという問題が新たに発生する。
【０００９】
【発明が解決しようとする課題】
上記したように従来技術では、均一な転写性を得るには複数の金型温度調節機構が必要で、しかも得られる成形品は離型・取り出しによる変形を余儀なくされる。本発明の課題はこれらの問題を解決することにある。
【００１０】
【問題を解決するための手段】
前記課題を解決するために、温度的に不均一な状態で充填完了された溶融樹脂の冷却速度を遅くするとともに均一な冷却速度を実現するために、金型キャビティ表面あるいは金型キャビティ表面から金型冷却路までの間に断熱部を設け、かつ熱伝達効率を金型キャビティ内の場所によって変化させ、冷却速度が遅くかつ均一な成形を実現する。
【００１１】
【発明の実施の形態】
以下、本発明にかかる実施例を光ディスク基板成形型を例に図面を用いて説明する。
【００１２】
実施例１：先ず、セラミックス断熱材１３を用い、該厚みをゲートからの距離に応じて変化させた本発明による実施例を図２に示す。
【００１３】
事前に、成形転写性を決定する主要因子である充填された樹脂とスタンパ４の表面での温度が、断熱材の厚みによってどう変化するかをシミュレートした。シミュレーションに用いた各々の諸元は表１の通りで、その結果を図３に示した。
【００１４】
【表１】

【００１５】
図３に示した計算結果をもとに、樹脂温度３８０℃、離型時に変形を生じない金型温度１１０℃という条件で、樹脂充填直後の樹脂とスタンパ４の表面との境界温度が熱変形温度（１２６℃）以上の温度として１３０℃とすると、該温度なる断熱材の厚みは０．１３ｍｍとなる。一方、樹脂流動解析によるとゲートから遠い基板外周部までに約３０℃の低下がある。そこで、外周部の樹脂温度を３５０℃とすると、断熱材の厚みは０．６ｍｍとなる。この結果に基づいて、断熱材の厚みをゲートから遠ざかるに従って厚くして、基板内周部で０．１３ｍｍ，外周部で０．６ｍｍとした。該断熱材１３は可動型コア５にエポキシ系接着材により取り付け・固定される。
これによって、充填直後の溶融樹脂温度がゲートに近い基板内周部より低くなる基板外周部でも、樹脂充填直後のスタンパとの境界面温度が樹脂の熱変形温度以上となり、しかも基板内周部と外周部とで同じ温度となる。このような成形型で成形することによって、図８中▲４▼に示すように内・外周部とも良好な転写性を得ることができる。しかも、この成形型では樹脂の冷却速度が遅くなっているので、成形品の内部応力（複屈折）も小さく抑えることができる。
【００１６】
実施例１では、断熱材としてジルコニアを用いたが、表２に示すように熱伝導率の小さいチタニア系でもよい。ちなみに、断熱層として一般によく用いられる樹脂材料に比べ、本発明で採用したセラミックスは樹脂材料よりもはるかに硬度が高く、射出成形圧による変形もなく成形品の平面精度を低下させることがない。
【００１７】
実施例２：次に、熱伝導率の大きいものと小さいものの２種類の材料を組み合わせて、断熱材層の熱伝導率をゲートからの距離に応じて変化させた本発明による実施例を図４に示す。実施例の図２では、断熱材の厚みが内周部と外周部が異なるため、該断熱材を取り付ける可動型コア５は円錐形状となり、加工上の問題が生じる。そこで、図４に示す実施例では、内周部では熱伝導率の大きいセラミックス材１４を、熱伝導率が小さいセラミックス断熱材１３よりも厚み構成比率を大にし、外周部ではその逆になるように構成して、該構成体の厚みが一様になるようにする。このことによって、可動型コアを円錐状に加工しなくとも該断熱材の取り付けが可能で、しかも基板内周部では熱伝導率が大きく、外周部では熱伝導率が小さい断熱層が構成される。これによって、充填された溶融樹脂の冷却効果は前述の実施例と同様で、光ディスク基板成形において内外周部とも転写性の均一な基板を得ることができる。特に、可動型コア材より熱伝導率の大きい窒化珪素系のセラミックス（表２）を用い、
【００１８】
【表２】

【００１９】
熱伝導率の小さい断熱材１３として前出のジルコニアを用いれば、熱伝導の計算値から該ジルコニア断熱材の厚み仕様は実施例と同様で良い。また、熱伝導率の小さい断熱材１３としてチタニア系を用いても良い。このような成形型で成形することによっても、実施例１と同様に図８中▲４▼に示すように内・外周部とも良好な転写性を得ることができる。
【００２０】
実施例３：次に、断熱層として空気断熱部を設けた実施例を図５に示す。図５に示すように、キャビティ表面から冷却回路までの間に空気断熱部を設け、しかも該空気断熱部をゲートからの距離に対応して大きくして金型冷却路までの断熱効果を大きくする。これによって、図１で実施例１として示した同様の効果を得ることができる。
【００２１】
実施例４：さらに、断熱材として空隙部をもつ焼結金属による実施例を図６に示す。焼結金属を実施例１に示したように、該焼結金属の厚みをゲートからの距離に対応して厚くする。
【００２２】
実施例５：また、図７に示すように焼結合金の空隙率をゲートからの距離に応じて大きくして断熱効果を大きくする。
【００２３】
これらにより、先にのべてた実施例１と同様の効果を得ることができる。
【図面の簡単な説明】
【図１】従来技術によるプラスチック成形型の断面図である。
【図２】本発明による第１の実施例によるプラスチック成形型の可動型コア部の断面図である。
【図３】本発明の第１の実施例の基礎となる断熱材の厚みとスタンパ表面温度との関係を示す図である。
【図４】本発明による第２の実施例によるプラスチック成形型の可動型コア部の断面図である。
【図５】本発明による第３の実施例によるプラスチック成形型の可動型コア部の断面図である。
【図６】本発明による第４の実施例によるプラスチック成形型の可動型コア部の断面図である。
【図７】本発明による第５の実施例によるプラスチック成形型の可動型コア部の断面図である。
【図８】従来技術及び本発明による光ディスク基板の成形転写性を示す図である。
【符号の説明】
１、…光ディスク基板成形型、２…固定型、３…可動型、４…スタンパ、５…可動型コア、６…光ディスク基板、７…スタンパ内周ホルダ、８…スタンパ外周ホルダ、９…中心穴形成ポンチ、１０…エジェクタ、１１…情報ピット及びレーザ光案内溝、１２…冷却回路、１３…セラミックス断熱材、１４…セラミックス材、１５…空気断熱部、１６、１６´…焼結金属断熱材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a plastic molding method and an apparatus therefor.
[0002]
[Prior art]
In plastic injection molding, one of the methods for improving mold transferability is to keep a portion of a molten resin filled in a mold cavity in contact with the cavity surface at a high temperature and uniformly over the entire region. As a specific temperature condition, it is necessary to maintain the boundary surface temperature between the filling resin and the surface of the mold cavity at a temperature equal to or higher than the thermal deformation temperature of the molding resin, and in some cases, equal to or higher than the glass transition temperature.
[0003]
In forming an optical disk substrate, the most important issue is precise transfer of information pits and laser guide grooves on the order of submicrons. Generally, in injection molding of an optical disk substrate, a nickel stamper for forming and transferring information pits and laser guide grooves is mounted in a mold cavity as shown in FIG. 1, and molten resin is injected from a gate provided in the center of the cavity. Is injected and filled, cooled and solidified, and then released to complete the molding.
[0004]
In injection molding, the molten resin is cooled by a mold during filling (under the molding conditions described below, the temperature is reduced by about 20 to 30 ° C.). As shown in (1), almost no transfer is performed with respect to the groove depth of the stamper, and the transfer amount tends to decrease as the distance from the gate increases.
[0005]
In the case of optical disc substrate molding, techniques for improving transferability without increasing pressure to avoid an increase in optical distortion (birefringence) include (1) high-speed filling with molten resin, and (2) mold temperature. Molded higher.
[0006]
In the high-speed filling molding of the prior art (1) described above, although the transferability is improved to some extent as shown in FIG. 8 (2), complete molding transfer cannot be obtained. In addition, the problem that the transferability decreases as the distance from the gate increases cannot be solved. In terms of the performance of the injection molding machine, high-speed filling is possible as compared with the example shown in FIG. 8, but there is a limit to high-speed filling due to generation of burrs and the like.
[0007]
Also in the conventional technique (2), the mold temperature is at most close to the thermal deformation temperature of the molding resin from the viewpoint of preventing deformation of the molded product at the time of mold release (below the thermal deformation temperature: the thermal deformation temperature of the polycarbonate resin is 126 ° C.). As shown in FIG. 8 (3), the transferability is not satisfactory as described above, and the problem that the transferability decreases with distance from the gate as in the prior art (1) remains. Has been done.
[0008]
As a method for preventing a decrease in transferability, a method has been proposed in which molding is performed by increasing a mold temperature (cavity temperature) in a portion far from a gate, as described in Japanese Patent Application Laid-Open No. 1-278322. However, in this method, even when the substrate is released from the mold, the mold temperature is high (the temperature is set to be equal to or higher than the thermal deformation temperature in order to improve transferability). (Warpage) specification is not satisfied. In addition, a plurality of mold temperature control mechanisms are required in terms of equipment. Further, as one method of solving this problem, a mold temperature cooling / heating cycle method has been developed in which the mold temperature is set to be equal to or higher than the heat deformation temperature when filling the resin and the mold temperature is equal to or lower than the heat deformation temperature when releasing the mold. I have. However, in this method, there is a new problem that the equipment becomes more complicated and the molding cycle becomes longer.
[0009]
[Problems to be solved by the invention]
As described above, in the related art, a plurality of mold temperature adjusting mechanisms are required to obtain uniform transferability, and the obtained molded product is inevitably deformed by releasing and removing. An object of the present invention is to solve these problems.
[0010]
[Means to solve the problem]
In order to solve the above-mentioned problem, in order to reduce the cooling rate of the molten resin that has been filled in a non-uniform state in terms of temperature and to realize a uniform cooling rate, the mold cavity surface or the mold cavity surface has to be cooled. A heat insulating portion is provided between the mold cooling passages, and the heat transfer efficiency is changed depending on the location in the mold cavity, so that the cooling speed is slow and uniform molding is realized.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings, taking an optical disk substrate mold as an example.
[0012]
Embodiment 1 First, FIG. 2 shows an embodiment according to the present invention in which a ceramic heat insulating material 13 is used and the thickness is changed according to the distance from a gate.
[0013]
In advance, how the temperature at the surface of the stamper 4 and the filled resin, which is a main factor determining the mold transferability, was simulated as to how the thickness varies with the thickness of the heat insulating material. Table 1 shows the specifications used in the simulation, and the results are shown in FIG.
[0014]
[Table 1]

[0015]
Based on the calculation results shown in FIG. 3, the boundary temperature between the resin immediately after resin filling and the surface of the stamper 4 is thermally deformed under the conditions of a resin temperature of 380.degree. Assuming that the temperature is 130 ° C. or higher than the temperature (126 ° C.), the thickness of the heat insulating material at that temperature is 0.13 mm. On the other hand, according to the resin flow analysis, there is a drop of about 30 ° C. from the gate to the outer peripheral portion of the substrate. Therefore, when the resin temperature at the outer peripheral portion is 350 ° C., the thickness of the heat insulating material is 0.6 mm. Based on this result, the thickness of the heat insulating material was increased as the distance from the gate was increased, and was set to 0.13 mm at the inner peripheral portion and 0.6 mm at the outer peripheral portion. The heat insulating material 13 is attached and fixed to the movable core 5 with an epoxy-based adhesive.
As a result, even at the outer peripheral portion of the substrate, where the molten resin temperature immediately after filling is lower than the inner peripheral portion of the substrate near the gate, the boundary surface temperature with the stamper immediately after filling the resin becomes equal to or higher than the thermal deformation temperature of the resin. The temperature is the same at the outer periphery. By molding with such a mold, good transferability can be obtained for both the inner and outer peripheral portions as shown by (4) in FIG. In addition, since the cooling rate of the resin is slow in this mold, the internal stress (birefringence) of the molded article can be suppressed to a small value.
[0016]
In the first embodiment, zirconia is used as a heat insulating material. However, as shown in Table 2, a titania-based material having a small thermal conductivity may be used. Incidentally, as compared with a resin material generally used as a heat insulating layer, the ceramics employed in the present invention have a much higher hardness than the resin material, do not deform due to injection molding pressure, and do not lower the planar accuracy of the molded product.
[0017]
Embodiment 2 Next, an embodiment according to the present invention in which two kinds of materials having a large thermal conductivity and a small thermal conductivity are combined and the thermal conductivity of the heat insulating material layer is changed according to the distance from the gate is shown in FIG. Shown in In FIG. 2 of the embodiment, since the thickness of the heat insulating material is different between the inner peripheral portion and the outer peripheral portion, the movable core 5 to which the heat insulating material is attached has a conical shape, which causes a processing problem. Therefore, in the embodiment shown in FIG. 4, the thickness ratio of the ceramic material 14 having a large thermal conductivity in the inner peripheral portion is made larger than that of the ceramic heat insulating material 13 having a small thermal conductivity, and vice versa in the outer peripheral portion. And the thickness of the structure is made uniform. This makes it possible to attach the heat insulating material without machining the movable core into a conical shape, and furthermore, a heat insulating layer having a high thermal conductivity at the inner peripheral portion of the substrate and a small thermal conductivity at the outer peripheral portion is formed. . As a result, the effect of cooling the filled molten resin is the same as that of the above-described embodiment, and a substrate having uniform transfer properties at the inner and outer peripheral portions can be obtained in molding the optical disk substrate. In particular, using silicon nitride ceramics (Table 2) having higher thermal conductivity than the movable core material,
[0018]
[Table 2]

[0019]
If the above-mentioned zirconia is used as the heat insulating material 13 having a small heat conductivity, the thickness specification of the zirconia heat insulating material may be the same as that of the embodiment from the calculated value of the heat conduction. Further, a titania-based heat insulating material 13 having a small thermal conductivity may be used. Also by molding with such a molding die, good transferability can be obtained in both the inner and outer peripheral portions as shown by (4) in FIG.
[0020]
Embodiment 3: Next, FIG. 5 shows an embodiment in which an air heat insulating portion is provided as a heat insulating layer. As shown in FIG. 5, an air heat insulating portion is provided between the cavity surface and the cooling circuit, and the air heat insulating portion is increased corresponding to the distance from the gate to increase the heat insulating effect up to the mold cooling path. . As a result, the same effect as the first embodiment shown in FIG. 1 can be obtained.
[0021]
Embodiment 4: FIG. 6 shows an embodiment using a sintered metal having a void as a heat insulating material. As shown in Example 1, the thickness of the sintered metal is increased corresponding to the distance from the gate.
[0022]
Embodiment 5: Further, as shown in FIG. 7, the porosity of the sintered alloy is increased according to the distance from the gate to increase the heat insulating effect.
[0023]
Thus, the same effect as that of the first embodiment can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a conventional plastic mold.
FIG. 2 is a sectional view of a movable mold core of a plastic molding die according to a first embodiment of the present invention.
FIG. 3 is a diagram showing a relationship between a thickness of a heat insulating material and a stamper surface temperature, which are the basis of the first embodiment of the present invention.
FIG. 4 is a sectional view of a movable mold core of a plastic molding die according to a second embodiment of the present invention.
FIG. 5 is a sectional view of a movable mold core of a plastic molding die according to a third embodiment of the present invention.
FIG. 6 is a sectional view of a movable mold core of a plastic molding die according to a fourth embodiment of the present invention.
FIG. 7 is a sectional view of a movable mold core of a plastic molding die according to a fifth embodiment of the present invention.
FIG. 8 is a diagram showing the mold transferability of an optical disk substrate according to the related art and the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, ... Optical disk board shaping | molding die, 2 ... fixed type, 3 ... movable type, 4 ... stamper, 5 ... movable core, 6 ... optical disk substrate, 7 ... stamper inner peripheral holder, 8 ... stamper outer peripheral holder, 9 ... center hole Forming punch, 10 ... Ejector, 11 ... Information pit and laser light guide groove, 12 ... Cooling circuit, 13 ... Ceramic insulation, 14 ... Ceramics, 15 ... Air insulation, 16, 16 '... Sintered metal insulation

Claims

Providing a heat insulating portion combining a plurality of materials having different thermal conductivity from the cavity surface or from the cavity surface to the mold cooling path, and forming the heat insulating portion by changing the heat conductivity of the heat insulating portion depending on the position in the cavity. A plastic molding method.

In claim 1,
Plastic molding method, wherein the heat insulating portions using a member by sintering metal and molded the porosity of the member is changed depending on the position in the cavity.

On the lower surface of the stamper, between the cavity surface or from the cavity surface to the mold cooling path, a heat insulating portion combining a plurality of materials having different heat conductivity is provided, and the heat conductivity of the heat insulating portion is changed depending on the position in the cavity. A method for manufacturing an optical disk, comprising molding.

In claim 3,
A method for manufacturing an optical disk, characterized in that a member made of a sintered metal is used for the heat insulating portion, and the porosity of the member is changed according to the position in the cavity.