JP2009007221A - Method for forming optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming an optical element where high optical performance can be achieved and the shape transfer accuracy of a mold, releasing property and durability are not spoiled, even when an optical raw material containing a volatile ingredient is used. <P>SOLUTION: The method for forming the optical element where a glass material 5 containing the volatile ingredient is heated, softened and press-formed with an upper die 8 and a lower die 9 located to be opposed in a pressing direction comprises a heating step to heat the glass material 5 to a first temperature at which its viscosity becomes less than 10<SP>7</SP>dPa s and to volatilize the volatile ingredient and a forming step to press-form the glass material 5 using the upper die 8 and the lower die 9 after the heating step. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical element molding method in which an optical material is softened by heating and press-molded with a molding die.

2. Description of the Related Art Conventionally, for example, various optical element molding methods are known in which an optical material such as a glass material is softened by heating and press-molded with a mold.
As such an optical element molding method, for example, in Patent Document 1, a molding block in which a molding die and a glass material that is an optical material are integrated in a body mold is used, and two molding blocks are preheated. A pressure stage capable of pressure forming and pressure cooling of the optical material through a stage, a preheated molding block mold, and a cooling stage for cooling the entire pressure block cooled to near room temperature. And heating, pressurizing, and cooling blocks that are vertically opposed to each of these stages. These stages and blocks are arranged in the same chamber, and the molding blocks are allowed to wait for a desired time in each stage. Then, a method using a glass lens molding apparatus that heats, presses, and cools the molding block by repeatedly moving the molding block to the next stage is described. It has been.
Patent Document 2 discloses a process of heating and softening a glass material at a temperature within a viscosity range where an easily volatile component does not volatilize, and a process of heating a mold to a temperature corresponding to a viscosity at which the glass material can be deformed before starting molding. Is described.
Patent Document 3 discloses an optical element in which a surface layer is formed twice on the surface of a preformed core glass, and the first surface layer closer to the core glass has a core glass material, A preheat treatment is performed at a temperature equal to or higher than the glass transition point under a reduced pressure state of 10 Pa or less, and the second surface layer far from the core glass is used for vapor deposition. An optical element characterized by being formed into a first surface layer by coating a glass material by vacuum deposition, sputtering, or CVD, and a method for manufacturing the same are described. That is, a method is described in which a volatile matter from an optical material is sealed with a glass coat on the surface of the optical material by coating the surface of the optical material that is easily volatile with a glass that is difficult to volatilize.
Japanese Examined Patent Publication No. 7-64571 JP 2003-73132 A JP-A-8-198631

However, the conventional optical element molding method as described above has the following problems.
In recent years, optical material manufacturers have begun to supply optical materials in the optical characteristic region, such as glass having a high refractive index and a low Abbe number region, which could not be used for molding, as molding optical materials. In addition, even in the conventional optical material for molding, there is a glass material that is difficult to be molded due to generation of volatile matter. In these optical materials, in the conventional optical element molding method, spiders of molded products due to volatiles, spiders of molded products due to volatiles adhering to the mold and transferred to the molded products, etc. The volatile gas generated from the optical material during the molding process is confined in the optical function surface of the molded product, resulting in a fine and large amount of foam shape, resulting in a decrease in optical performance, and volatiles accumulating on the mold. This increases the affinity between the mold surface and the optical material, and causes problems such as seizure. For this reason, it is difficult to obtain a molded product with high accuracy and excellent optical performance.
The above defects are likely to occur in optical materials containing one or more of lead oxide, bismuth oxide, boron oxide, zinc oxide, molybdenum oxide, fluorophosphate, phosphoric acid, borophosphoric acid or fluoride. The degree of volatilization of the components varies depending on the composition of the optical material, the shape of the molded product, and the molding conditions. Therefore, the amount of change in shape due to molding is small, and even if there is no problem due to volatile matter in molded products that can be produced under low molding temperature conditions, the amount of change in shape due to molding is large, or the molding temperature must be increased. If this happens, a problem may occur.
In the technique described in Patent Document 1, since the molding block in which the molding die and the glass material are integrally stored in the body mold is preheated, if volatiles are generated during the preheating, spider due to the volatiles as described above, etc. There is a problem that this problem occurs.
Further, in the technique described in Patent Document 2, in the process of softening by heating, heating is performed at a temperature in a viscosity range where easily volatile components do not volatilize, and at the time of molding, molding is performed at a low temperature where the viscosity becomes larger. Although it does not occur, depending on the type of the volatile component, there is a problem that in the temperature range where the volatile component does not volatilize, the viscosity is too large to perform the press molding well. Therefore, there is a problem that the material of the glass material is limited.
Examples of such a glass material that volatilizes at a low temperature include a glass material having a high refractive index and a low Abbe number that has been increasing in recent years, such as K-PSFn2 (made by Sumita Optical Glass Co., Ltd.) containing bismuth oxide and phosphoric acid. .
Moreover, in the technique described in Patent Document 3, the glass material surface is coated with a glass material for vapor deposition to form a second surface layer and contain volatiles generated from the glass material. Can be prevented from adhering to the mold or surrounding members, but the volatiles volatilized from the glass material are confined between the glass material and the second surface layer, and the glass material and the second There is a problem that spiders and bubbles are generated at the interface of the surface layer, or the second surface layer is finely peeled off to deteriorate the optical characteristics of the molded optical element.

  The present invention has been made in view of the above problems. Even when an optical material containing a volatile component is used, high optical performance can be obtained, and mold shape transfer accuracy, mold release property and durability can be obtained. It aims at providing the optical element shaping | molding method which does not impair.

In order to solve the above-described problems, the optical element molding method of the present invention is an optical element molding method in which an optical material containing a volatile component is heated and softened and press-molded with a mold placed opposite to the pressing direction to obtain an optical element. A heating step of heating the optical material to a first temperature at which the viscosity of the optical material is less than 10 ⁷ dPa · s to volatilize the volatile component, and after the heating step, the molding And a molding step of press-molding the optical material using a mold.
According to the present invention, in the heating step, the viscosity of the optical material is heated to the first temperature that is less than 10 ⁷ dPa · s, so that the volatile component is volatilized and separated from the optical material and diffuses into the surrounding space. It is possible to substantially remove volatile components that become an obstacle during molding from the surface of the optical material. And since a shaping | molding process is performed after that, the volatilization amount of the volatile component which generate | occur | produces from an optical raw material in a shaping | molding process falls remarkably. Therefore, adhesion of volatile components to the optical material surface and adhesion of volatile components to the mold can be reduced.

In the optical element molding method of the present invention, the volatile component contains at least one of lead oxide, bismuth oxide, boron oxide, zinc oxide, molybdenum oxide, fluorophosphate, phosphoric acid, borophosphoric acid, and fluoride. It is preferable.
In this case, all of these volatile components are volatilized well from the optical material when heated to a first temperature at which the viscosity of the optical material is less than 10 ⁷ dPa · s, so that the volatile components can be easily reduced. It is.

Further, in the optical element molding method of the present invention, the second optical material that is lower than the first temperature and can be press-molded between the heating step and the molding step, the optical material from which the volatile component is volatilized by the heating step. It is preferable to further include a temperature setting step for setting the temperature.
In this case, since the temperature of the optical material when performing the molding process is lower than the first temperature at which the volatile component volatilizes, there is substantially no volatile component that volatilizes from the optical material in the molding process. It is possible to further reduce adhesion of volatile components to the surface and adhesion of volatile components to the mold.

In the optical element molding method of the present invention, in the temperature setting step, it is preferable that the temperature of the mold is set to a third temperature lower than the second temperature at least on the mold surface.
In this case, at least the mold surface of the mold is set to a temperature lower than the temperature of the optical material by the temperature setting process, and then the molding process is performed, so that the press molding is performed with the surface of the optical material cooled. Is called.
The component volatilization / bubble generation from the optical material mostly occurs when the temperature is raised. When molding an optical material having a second temperature higher than the third temperature of the mold surface in the molding process, heat flows from the optical material to the molding die, and the optical material is cooled. Therefore, it is possible to reliably suppress the volatilization of components from the optical material and the generation of bubbles during molding.

In the optical element molding method of the present invention, the third temperature is preferably a temperature at which the viscosity of the optical material is 10 ¹² dPa · s or more and 10 ¹⁴ dPa · s or less.
In this case, a highly accurate molding surface can be obtained while suppressing generation of volatile substances and bubbles from the optical material.
When the third temperature is a temperature at which the viscosity of the optical material is less than 10 ¹² dPa · s, the optical material is easily baked on the mold. Further, when the temperature is higher than 10 ¹⁴ dPa · s, the molding load becomes too large.

Further, in the optical element molding method of the present invention, between the heating step and the molding step, the molding material and the optical material are sandwiched between the molding materials arranged opposite to each other. A temperature setting for setting a temperature of the molding die and the optical material by forming a die assembly in which a sleeve for regulating the position in a direction orthogonal to the pressing direction is externally fitted and heating the die assembly It is preferable to further include a step, and in the molding step, press molding is performed by pressing the molding die of the mold assembly along the axial direction of the sleeve.
In this case, since the optical material after the heating process is assembled in the mold assembly and the temperature adjustment process is performed, the volatile components from the optical material are not volatilized in the mold assembly, and the mold assembly is efficiently used. Can be molded easily.

Further, in the optical element molding method of the present invention, at least in the heating step, an air flow is formed between the optical material and the mold so that the volatile components volatilized from the optical material are removed from the mold metal mold. It is preferable to exclude from the vicinity of the mold surface.
In this case, at least in the heating process, an air flow is formed between the optical material and the mold, and volatile components are excluded from the vicinity of the mold surface of the mold, so the place to perform the heating process is set near the mold It is possible to perform optical element molding with a compact apparatus.
In addition, by bringing the heating process and the molding process close to each other in this manner, the movement time of the optical material can be shortened and the optical material can be prevented from being cooled more than necessary, thereby improving the manufacturing efficiency. be able to.
For this reason, the optical material heating temperature in the heating process can be lowered, and problems such as devitrification and crystallization of the optical material due to the temperature can be prevented.

In the optical element molding method of the present invention, it is preferable that the optical material is heated in a state isolated from the mold at least in the heating step.
In this case, at least the optical material in the heating step is isolated from the mold, so that the molding unit and the heating unit can be installed in the very vicinity, so that molding can be performed with a compact apparatus.
In addition, by bringing the heating process and the molding process close to each other in this manner, the movement time of the optical material can be shortened and the optical material can be prevented from being cooled more than necessary, thereby improving the manufacturing efficiency. be able to.
For this reason, the optical material heating temperature in the heating process can be lowered, and problems such as devitrification and crystallization of the optical material due to the temperature can be prevented.

  According to the optical element molding method of the present invention, since the molding process is performed after the optical material is heated to the first temperature at which the volatile component is volatilized, high optical performance can be obtained even if the optical material containing the volatile component is used. In addition, there is an effect that the shape transfer accuracy, mold releasability and durability of the mold can be maintained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In all the drawings, even if the embodiments are different, the same or corresponding members are denoted by the same reference numerals, and common description is omitted.

[First Embodiment]
An optical element molding method according to the first embodiment of the present invention will be described.
FIG. 1 shows a schematic configuration of an optical element molding apparatus used in the optical element molding method according to the first embodiment of the present invention.

A schematic configuration of the optical element molding apparatus 100 used in the optical element molding method of the present embodiment will be described. As shown in FIG. 1, the schematic configuration of the optical element molding apparatus 100 includes a heating furnace 1 and a molding chamber 7.
The heating furnace 1 is, for example, a heating means for heating a glass material 5 that is an optical material for molding an optical element such as a lens to a temperature T ₁ (first temperature), and a wall that surrounds the heating space 1a. A heater 20 is provided in the body.
The temperature T ₁ is a temperature at which a volatile component contained in the glass material 5 is volatilized, and the glass material 5 is composed of lead oxide, bismuth oxide, boron oxide, zinc oxide, molybdenum oxide, fluorophosphate, phosphoric acid, borophosphoric acid, and In the case of containing at least one kind of fluoride, the temperature is set so that the viscosity of the optical material is less than 10 ⁷ dPa · s.
In the following, the glass material 5 has a glass transition point (T _g) 480 ° C., yield point (A _t) is phosphoric acid 514 ° C. - described in example using a bismuth-based glass material. This glass material contains bismuth oxide as a volatile component.
Moreover, the magnitude | size of the glass raw material 5 demonstrates below as an example in case the outer diameter is 36 mm and thickness is 8 mm.

The side of the left side of the heating furnace 1 is provided with an opening that can advance and retreat in the horizontal direction (left and right in the figure, see arrows a and b) with the arm 3 holding the transport tray 2 at the tip. Further, the right end side of the heating furnace 1 in the figure is connected to the molding chamber 7 via the shutter 4.
The transport tray 2 is a transport member for accommodating and transporting the glass material 5, and has an opening 2 a provided on the bottom so that an outer edge portion of the glass material 5 can be placed, and an arm 3 serving as a transport member. It is placed on the tip of the. The inner diameter of the opening 2a is set to be slightly larger than φ35 mm so that a rod-shaped portion of the lower mold 9 described later can be inserted vertically.
The arm 3 is driven by a drive mechanism (not shown) so as to move in the horizontal direction (see the arrows a and b in the drawing), and the transport tray 2 containing the glass material 5 is moved to the outside on the left side of the heating furnace 1 in the heating space 1a. , And the inside of the molding chamber 7 can be conveyed.

The shutter 4 can selectively switch between a closed state in which heat in the heating furnace 1 is blocked so that it is not transmitted to the inside of the molding chamber 7 and an open state in which the space between the heating furnace 1 and the molding chamber 7 is opened. it can. In the present embodiment, the closed state and the open state can be switched by being pivotally supported by the rotating shaft 6 and rotating in the depth direction of the drawing.
In the open state of the shutter 4, the arm 3 advances from the heating space 1 a to the inside of the molding chamber 7, and carries the transport tray 2 on which the glass material 5 is placed, or removes the glass material 5 after molding. It can be carried out of the apparatus through the heating space 1a from the molding chamber 7.
Further, in the closed state of the shutter 4, the heating space 1 a is isolated from the molding chamber 7, so there is no air flow and even if volatile components volatilize from the glass material 5, Volatile components are prevented from entering.

The molding chamber 7 can perform molding by forming a non-oxidizing atmosphere inside by introducing a non-oxidizing gas, for example, nitrogen gas, from the outside by a non-oxidizing gas supply device (not shown). The upper die 8 (molding die) and the lower die 9 (molding die) are installed in the interior facing each other in the vertical direction.
The oxygen concentration inside the molding chamber 7 can be appropriately selected depending on the mold material and film forming material used for molding. In the present embodiment, the upper mold 8 and the lower mold 9 are made of tungsten carbide (WC) coated with a chromium oxide film, so that the oxygen concentration inside the molding chamber 7 is kept at 15% or less. ing. However, for example, when using a mold in which a WC substrate is covered with a WC film, the oxygen concentration is preferably in the range of 5 ppb to 200 ppm.

The upper die 8 corresponds to the shape of the optical element to be molded, for example, after polishing the tip 8a (mold surface) of the rod-shaped portion having an outer diameter of 35 mm to a convex aspherical mirror surface, A flange portion 8b extending outward in the radial direction is provided at the end opposite to the tip portion 8a. The upper die 8 is fixed to the upper inner side of the molding chamber 7 with the flange 8b locked by the upper die retainer 10 and the tip 8a facing vertically downward.
The upper mold retainer 10 is formed of a cylindrical member to hold the upper mold 8 and is fixed to the upper part of the molding chamber 7. At the lower end of the upper mold retainer 10, there is provided a hole 10a through which the rod-shaped portion of the upper mold 8 is inserted and the flange 8b is locked.
Inside the upper mold retainer 10, an upper mold heater 11 that constitutes a mold heating means for heating the upper mold 8 is provided in contact with the upper surface of the upper mold 8. Is retained.

The lower die 9 has a mirror surface with a concave spherical surface, which is a molding surface having a curvature radius of 18 mm, corresponding to the shape of the optical element to be molded, for example, the tip portion 9a (mold surface) of the rod-shaped portion having an outer diameter of 35 mm. After the polishing, the mold is covered with a chromium oxide film, and has a base portion 9b that vertically erects the lower die 9 at the end opposite to the tip portion 9a. A base portion 9b is disposed on the lower heater 12 held by the pressurizing shaft 13 so as to be movable up and down, and the rod-shaped portions of the lower die 9 and the upper die 8 are coaxially connected to the tip portions 9a and 8a. Are arranged in an opposing positional relationship.
The lower mold heater 12 constitutes a mold heating means for heating the lower mold 9 through the abutted base portion 9b.
The pressure shaft 13 is vertically driven by a drive mechanism (not shown). The lower mold heater 12 and the lower mold 9 are moved up and down with respect to the upper mold 8 so that a predetermined optical element inner wall, book In the embodiment, it is possible to reciprocate between a molding position in which the glass material 5 is pressed by the lower mold 9 and the upper mold 8 to obtain 2.5 mm, and a separation position in which the molded product is released by releasing the pressing. It has become.

Next, operation | movement of the optical element shaping | molding apparatus 100 for performing the optical element shaping | molding method of this embodiment is demonstrated.
In the optical element molding apparatus 100, the glass material 5 is press-molded by sequentially performing a heating process, a temperature setting process, and a molding process, and the optical corresponding to the shapes of the tip portions 8 a and 9 a of the upper mold 8 and the lower mold 9. An optical element having a surface can be molded.

First, in the heating step, after the glass material 5 is placed on the transport tray 2 and stored outside the heating furnace 1, the transport tray 2 is supported by the arm 3. Then, the arm 3 is driven in the direction of arrow a, and the glass material 5 and the transport tray 2 are carried into the heating furnace 1.
Then, the heating furnace 1, by heating the glass material 5 until the temperature T _1, to maintain this heating condition for 2 minutes. In the present embodiment, the temperature T ₁ is set according to the material of the glass material 5 such that the viscosity of the glass material 5 is less than 10 ⁷ dPa · s.
Such temperature T ₁ or to be heated, the volatile component in the glass material 5 is satisfactorily volatilized and diffused into the heating space 1a from the surface of the glass material 5.
In this heating process, since the heating furnace 1 and the molding chamber 7 are separated by the shutter 4, the volatile matter generated from the glass material 5 is the upper mold 8 installed in the molding chamber 7 and its tip. It does not adhere to the portion 8a, the lower mold 9 and the tip 9a.

Next, in the temperature setting step, the temperature of the upper die 8 and the lower die 9 is set to T ₂ (second temperature) before the next forming step in order to perform good forming. Are set to a temperature T ₃ (third temperature), respectively. In the present embodiment, the upper mold 8 and the lower mold 9 may start temperature setting in parallel with the heating process because the molding chamber 7 is isolated. Further, the upper die 8, the temperature of the lower mold 9, the upper die 8 in pressing in the molding step, as the forming surface of the glass material 5 by the lower die 9 is cooled, has become a temperature T ₃ at least the mold surface What is necessary is just to have a temperature distribution in the direction away from the mold surface.
Temperature T ₂ is lower than the temperature T _1, a temperature higher than the temperature T _3, is set to T _g above the temperature of the glass material 5 which press forming is performed satisfactorily. Temperature temperature T _2, since it is sufficient that the set temperature immediately before the molding, when the heat dissipating reduced temperature during transport to the molding chamber 7, in the heating furnace 1, obtained by adding the advance temperature decrease amount T ₂ ′ (however, T ₁ ≧ T ₂ ′> T ₂ ) is set.
The temperature T ₃ corresponds to a glass viscosity of the glass material 5 of 10 ¹² dPa · s or more and 10 ¹⁴ dPa · s or less for the purpose of delaying the cooling time of the glass material 5 in order to obtain a desired thickness in the optical element. It is preferable that the temperature is set.

Next, the glass material 5 is moved to the molding chamber 7. First, the shutter 4 is rotated about the rotating shaft 6 as a support shaft. Immediately after the shutter 4 is rotated to a range where the shutter 4 does not come into contact with the transporting tray 2 and the arm 3, the arm 3 is driven in the direction of arrow a, and the glass material 5 and transported. The dish 2 is carried into the molding chamber 7.
Then, the driving of the arm 3 is stopped when the center of the transport tray 2 and the center of the upper mold 8 and the lower mold 9 coincide with each other in the horizontal direction. In this case, the glass material 5 is a temperature T _2, the upper die 8, at least the mold surface of the lower die 9 has a temperature T _3.
Above, a temperature setting process is complete | finished.

Next, in the molding process, the pressurizing shaft 13 is driven up to raise the lower mold 9. Thereby, the front-end | tip part 9a of the lower mold | type 9 contact | abuts to the lower surface of the glass raw material 5, and the glass raw material 5 is lifted from the conveyance tray 2 by continuing a raise. The glass material 5 is sandwiched between the upper mold 8 and the lower mold 9 and further pressed. The press load of the pressure shaft 13 at this time can be set as appropriate depending on the viscosity of the glass material 5 and the like. In the present embodiment, 1470N (150 kgf) is suitable.
When the distance between the upper mold 8 and the lower mold 9 reaches the molding position, the pressing shaft 13 is stopped. Thus, the glass material 5 is press-molded by pressurizing the glass material 5. In the molding position of the present embodiment, the inner thickness of the optical element is set to 2.5 mm.
Next, the glass material 5 pressed by the upper mold 8 and the lower mold 9 is cooled at a cooling rate of 0.6 ° C./second. When the temperature of the glass material 5 reaches a temperature at which it reaches 10 ¹⁴ dPa · s or more, the pressure shaft 13 is lowered. At this time, the glass material 5 that has been molded is placed on the lower mold 9 and lowered. And if the lower mold | type 9 continues further descend | falling, the glass raw material 5 which complete | finished shaping | molding will be mounted on the conveyance tray 2 from the lower mold | type 9 on. After the tip of the lower mold 9 is further lowered from the lower end of the transport tray 2, the pressure shaft 13 is stopped.

Next, the arm 3 is moved in the direction of the arrow b in the figure, and the conveying tray 2 on which the glass material 5 that has been molded is placed is carried out of the heating furnace 1. Then, the said glass raw material 5 is taken out as an optical element which is a molded article from the conveyance tray 2, and a shaping | molding process is complete | finished.
This optical element has a lens thickness of 2.5 mm having an aspheric concave surface corresponding to the shape of the tip portion 8 a of the upper mold 8 and a convex spherical surface having a curvature radius of 18 mm corresponding to the shape of the tip portion 9 a of the lower mold 9. It is a convex / concave lens.

  The operation of the optical element molding method of this embodiment will be described with reference to specific examples shown in Table 1.

Example 1 shown in Table 1 is formed by the optical element molding method of the present embodiment described above, and is an example in the case where T ₁ = 630 ° C. (= T _g +150) is set. In this case, the viscosity of the glass material 5 at the temperature T ₁ is about 10 ^6.5 dPa · s. In this embodiment, T ₂ = 580 ° C. and T ₃ = 470 ° C. are set. This temperature T ₃ is a temperature corresponding to 10 ¹² dPa · s in terms of the viscosity of the glass material 5.
Example 2 is an example of what happens when the temperature _{T 1 = 580 ℃ (= T} g +100). In this case, the viscosity of the glass material 5 at the temperature T ₁ is about 10 ^6.9 dPa · s and less than 10 ⁷ dPa · s. Further, the temperatures T ₂ and T ₃ in the molding step were set to T ₂ = 540 ° C. and T ₃ = 470 ° C., respectively. Under such conditions, 1764N (180 kgf), which is 20% higher than that in Example 1, was suitable as the press load in the molding process.
Comparative Example 1 is an example in which the temperature T ₁ is set to a temperature T ₁ = 574 ° C. that is slightly lower than that of Example 2. In this case, the viscosity of the glass material 5 at the temperature T ₁ is 10 ⁷ dPa · s.

In Examples 1 and 2 and Comparative Example 1, the presence or absence of defects due to volatile substances such as spiders and seizures on the lens surfaces of the molded optical elements and the mold surfaces of the upper mold 8 and the lower mold 9 was evaluated.
As shown in Table 1, in Examples 1 and 2 in which the temperature T ₁ of the heating process was set to a temperature at which the viscosity of the glass material 5 was less than 10 ⁷ dPa · s, the lens surface or the mold surface Although no spider was seen, in Comparative Example 1 in which the temperature T ₁ was set to a temperature at which the viscosity of the glass material 5 was 10 ⁷ dPa · s, some spider was seen on the lens surface and the mold surface. It was.
That is, it is understood that by appropriately setting the temperature of the heating process, volatile components are volatilized during the heating process and hardly volatilized in the molding process, so that it is possible to prevent the occurrence of defects due to volatile substances. .
Further, according to the result of Example 2, the temperature setting in the molding process is set such that the temperature T ₂ of the glass material 5 is lower than the temperature T ₁ in the heating process and can be pressed, and the upper mold 8 and the lower mold 9. of by the temperature T ₃ of the mold surface lower than the temperature T ₂ of the glass material 5, the shape transfer accuracy, it allows a good molding having excellent releasability can be seen in the appropriate pressing load. In addition, the molding conditions such as the heating time of the heating step, the temperature of the mold, and the pressurizing pressure at the time of molding are not limited to the set values of the first embodiment, but in the preferred range described above. It can be set appropriately.

Table 2 shows examples 3 to 8 of the case where the optical element molding method of the present embodiment is applied to a material having a volatile component different from the above as the glass material 5.
The materials used in Examples 3 to 8 include bismuth oxide, boron oxide, fluorophosphate, phosphoric acid, borophosphoric acid, and fluoride as volatile components, respectively. The fluoride of Example 8 is a fluoride of Al, Ca, and Ba.
The heating temperature was T ₁ = T _g +150. This temperature T ₁ is a temperature at which the viscosity is less than 10 ⁷ dPa · s for any glass material 5.

  As shown in Table 2, all the examples show good results with no defects due to volatile substances.

Thus, according to the optical element molding apparatus 100, the glass material 5 is heated in the heating furnace 1 at a temperature at which the contained volatile components can be sufficiently volatilized, and the glass material 5 is heated to a temperature corresponding to the viscosity at which the glass material 5 can be deformed. Since the mold 8 and the lower mold 9 can be molded by controlling the mold temperature, an optical element that is free from defects caused by volatiles such as spiders on the surface and is pressure-molded to a desired inside dimension Obtainable.
Therefore, even if an optical material containing a volatile component is used, high optical performance can be obtained, and the shape transfer accuracy, mold releasability, and durability of the mold can be maintained.

[Second Embodiment]
Next, an optical element molding method according to the second embodiment of the present invention will be described.
FIG. 2 is a schematic cross-sectional view showing a schematic configuration of a heating furnace in an optical element molding apparatus used in an optical element molding method according to the second embodiment of the present invention. FIG. 3 is a plan view of FIG. FIGS. 4A and 4B show the optical material supporting portions inside the heating furnace of the optical element molding apparatus used for the optical element molding method according to the second embodiment of the present invention, respectively, supporting the optical material. It is a top view which shows a state when the support of an optical material is cancelled | released. FIG. 5 is a schematic cross-sectional view showing a schematic configuration of a molding apparatus used in an optical element molding method according to the second embodiment of the present invention.

The optical element molding method of the present embodiment sequentially performs a heating step, a temperature setting step, and a molding step in the same manner as the optical element molding method of the first embodiment, but the optical material is placed between the opposing molds. A mold assembly is formed in which a sleeve that restricts the position of the molding die and the optical material in a direction orthogonal to the pressing direction is fitted, and a temperature setting process is performed on the mold assembly. The difference is that the molding process is performed by pressing the mold of the mold assembly. Hereinafter, a description will be given centering on differences from the first embodiment.
The optical element molding apparatus used in this embodiment includes a heating furnace 35 (see FIG. 2) for performing a heating process and an upper mold 21 (molding die) for forming a molding block 70 (see FIG. 5) that is a mold assembly. ), A lower mold 22 (molding mold), a body mold 23 (sleeve), and a molding apparatus 40 (see FIG. 5) that performs a temperature setting process and a molding process in the state of the molding block 70.
Here, the heating furnace 35 and the molding apparatus 40 may be disposed adjacent to each other, or may be disposed at positions separated as necessary.

Furnace 35, as shown in FIG. 2, for heating glass material support 32 glass material 33 which is the lower surface of the outer edge portion supported by the (optical material) to the same temperature T ₁ of the first embodiment described above belongs to.
As shown in FIGS. 2 and 3, the schematic configuration of the heating furnace 35 includes a heater unit 25 including substantially semi-cylindrical heaters 25 a and 25 b whose central axes are arranged along the vertical direction, and a heater unit 25. It comprises two shutters 26 that open and close the upper and lower openings, and a shutter drive mechanism 30 that opens and closes each shutter 26.

The heaters 25a and 25b are held by a drive mechanism (not shown) so as to be able to contact and separate in the horizontal direction (see arrows c and d in FIG. 3).
At the time of joining, a cylindrical body is formed as shown in FIG. 3, and the glass material support portion 32 can be accommodated inside thereof. In addition, a cutout portion 25c penetrating in the radial direction is formed in one of the joining portions of the heaters 25a and 25b so that the transport arm 24 supporting the glass material support portion 32 can be inserted in the direction of arrow e. .
At the time of separation, a gap is formed between the heaters 25a and 25b so that the glass material support portion 32 can be advanced and retracted in the horizontal direction.

  As shown in FIG. 4A, the glass material support portion 32 has semicircular support arms 32 a and 32 b in one end of a semicircle in a plan view and can be rotated in the horizontal direction by the transfer arm 24. It is supported. Each support arm 32a, 32b has an L-shaped cross section, supports the outer edge portion of the glass material 33 from below by a receiving portion 32c extending in the horizontal direction, and the glass material by a side portion standing on the receiving portion 32c. 33 can be gripped in the radial direction.

  The transport arm 24 can be moved back and forth in the horizontal direction and moved up and down by a drive mechanism (not shown), and the tip portion connected to the glass material support portion 32 can be rotated. For this reason, the transfer arm 24 moves the glass material support portion 32 in and out of the heater portion 25 or rotates the support arms 32a and 32b of the glass material support portion 32 when the heater portion 25 is separated. The glass material 33 can be gripped and released. FIG. 4B shows a state of the glass material support portion 32 when the tip of the transfer arm 24 is rotated to release the grip of the glass material 33.

As the shutter driving mechanism 30, an appropriate mechanism can be adopted, but in the present embodiment, as shown in FIG. 2, the arms 27 are respectively extended in the same horizontal direction from the sides of the upper and lower shutters 26. The rotary shutter mechanism is composed of a rotary arm 30a that rotates in a horizontal plane and a motor 30b that rotates the rotary arm 30a.
The shutter drive mechanism 30 can open and close the shutter 26 at an appropriate timing by a control unit (not shown).

As shown in FIG. 2, the upper die 21 has a flange portion 21b at the upper end, a rod-shaped portion having the same diameter as the outer diameter of the optical element extends downward, and the lens surface of the optical element is molded at the lower end. A mold surface 21a is formed. The side surface of the rod-shaped portion can be slidably fitted to the inner surface of the trunk mold 23, and the flange portion 21 b constitutes a locking surface for the end portion of the trunk mold 23.
As shown in FIG. 2, the lower die 22 has a flange 22b at the lower end, a rod-shaped portion having the same diameter as the outer diameter of the optical element extends upward, and the lens surface of the optical element is molded at the upper end. A mold surface 22a is formed. The side surface of the rod-like portion can be slidably fitted to the inner surface of the trunk mold 23, and the flange portion 22 b constitutes a locking surface for the end portion of the trunk mold 23.
The material of the upper mold 21 and the lower mold 22 and the shapes of the mold surfaces 21a and 22a can be appropriately set according to the molding conditions and the shape of the optical element. For example, the same material and shape as those of the upper mold 8 and the lower mold 9 of the first embodiment can be employed.
The body mold 23 is a cylindrical member that is slidably fitted to the rod-shaped portions of the upper mold 21 and the lower mold 22, and constitutes a mold surface for molding the radial side surface of the glass material 33.

Further, in the present embodiment, the upper mold 21 is disposed coaxially with the central axis of the heater section 25 above the heating furnace 35 with the body mold 23 being externally fitted, and is vertically moved by a support mechanism (not shown). Is supported so as to be movable.
Further, the lower die 22 is disposed on the lower side of the heating furnace 35 at a position coaxial with the upper die 21.

The molding apparatus 40 carries a plurality of mold assemblies into the apparatus and sequentially performs preheating, press molding, and cooling. FIG. 5 shows a state where molding blocks 71 and 72 each having the same configuration as the molding block 70 are carried in as a mold assembly.
As shown in FIG. 5, the molding apparatus 40 includes a chamber 41 in which a non-oxidizing atmosphere is formed, and preheating stages 43 and 44, a pressure stage 45, and a cooling stage on a gantry 42 provided in the chamber 41. 46 (hereinafter, these may be collectively referred to as each stage) are arranged in a row in the horizontal direction (the left-right direction in the drawing).
In each of these stages, the upper surface of each stage is installed on the same surface so that the molding block can be conveyed between them, and although not particularly illustrated, a conveyance mechanism having a movable arm or the like is provided. .
The preheating stage 43 and the outside of the chamber are connected to each other by a preparation base 60 that waits and moves the molding block conveyed into the chamber 41. A transfer mechanism 66 that transfers the molding block 70 toward the inside of the chamber 41 is provided on the side of the preparation table 60.
As the transfer mechanism 66, for example, a mechanism can be employed in which the push rod member is advanced and retracted in the direction indicated by the arrow g by a cylinder or the like, and the side portion of the molding block 70 is pressed and slid in the horizontal direction. .
In addition, the cooling stage 46 and the outside of the chamber are connected by a cradle 61 that discharges the molding block from the inside of the chamber 41.

  Further, above the preheating stages 43 and 44 and the pressurizing stage 45, the preheating blocks 47 and 48 and the pressurizing block 49 (hereinafter collectively referred to as each block in some cases) are opposed to each other. ) Are arranged in the vertical direction with an interval larger than the height of the molding blocks 71, 72 and the like.

A press cylinder 54 is connected to the upper end of the pressurizing block 49 and is supported so as to move up and down within a required stroke range as indicated by an arrow f.
The preheating blocks 47 and 48 are respectively connected to the upper ends of the cylinders 53 and supported by the cylinders 53 so as to be movable up and down so that they can come into contact with the upper ends of the forming blocks carried on the preheating stages 43 and 44.
In the preheating stages 43 and 44, the pressurizing stage 45, the preheating blocks 47 and 48, and the pressurizing block 49, a heater 55 capable of independently controlling the temperature is embedded together with a temperature sensor for temperature control such as a thermocouple. Has been.
Preheating stage 43, pre-heating block 47 is adapted to respectively be controlled to a temperature T ₂₁ is a first preheating temperature by the heater 55. Further, the preheating stage 44 and the preheating block 48 can be controlled to a temperature T ₂₂ which is a second preheating temperature by the heater 55 (where T ₂₂ > T ₂₁ > 300 ° C.).
The cooling stage 46 is provided with a temperature controllable cooling mechanism 56 in order to efficiently cool the entire conveyed forming block. As the cooling mechanism 56, for example, a mechanism that circulates cooling water adjusted in temperature in the cooling stage 46 can be employed.

The atmosphere in the chamber 41 is controlled by an inert gas supply mechanism (not shown) connected to an inlet 58 and an outlet 59 for inert gas or the like.
An inlet 62 for carrying a molding block is provided on the right side of the chamber 41, and an outlet 64 for carrying out the molding block is provided on the left side. A shutter for closing the inlet 62 and the outlet 64 except when the molding block is carried in and out. 63 is installed.

Next, an optical element molding method using the heating furnace 35, the molding block 70, and the molding apparatus 40 will be described.
First, in the heating process, the glass material 33 is supported on the glass material support portion 32, the heaters 25 a and 25 b are separated in the horizontal direction in the heater portion 25, and the transfer arm 24 advances to the center position of the heater portion 25. Let And the heater part 25 is joined and the side of the glass raw material 33 is surrounded by the heater part 25. Further, the shutter drive mechanism 30 is driven to rotate the upper and lower shutters 26 so as to shield the upper and lower openings of the heater unit 25. Thereby, the glass material 33 is arrange | positioned in the heating space 35a covered with the heater part 25 and shutter 26,26. The atmosphere at this time is an air atmosphere.

In this state, the heater 25 is used to heat the glass material 33 to a temperature T ₁ = T _g +150 (T _g is the glass transition point of the glass material 33) at which the viscosity of the glass material 33 is less than 10 ⁷ dPa · s. Holding at this temperature for 10 minutes, the volatile components of the glass material 33 are volatilized to the atmosphere.
At this time, the volatile matter diffuses in the heating space 35 a, but the heating space 35 a is covered by the heater unit 25 and the shutter 26, and from the upper mold 21 and the lower mold 22 located in the vicinity of the heating furnace 35. Since they are isolated, volatile substances do not adhere to the upper mold 21 and the lower mold 22. Further, the volatile matter in the heating space 35 a flows to the side of the heating furnace 35 through the notch 34 due to the airflow in the heating furnace 35, and therefore does not reattach to the glass material 33. Moreover, the volatile matter on the surface of the glass material 33 can be almost volatilized by heating for 10 minutes.
Then, electricity supply of the heater 25 is interrupted | blocked, the glass raw material 33 is cooled until it becomes 300 degreeC, and a heating process is complete | finished.
In the process in which the temperature of the glass material 33 is cooled from T ₁ to 300 ° C., the viscosity of the glass material 33 increases, and when the viscosity becomes 10 ⁷ dPa · s or more, the volatile components hardly volatilize.

Thereafter, the motor 30b of the shutter drive mechanism 30 is rotated, the upper and lower shutters 26 are rotated, and the upper and lower openings of the heater unit 25 are fully opened. Then, the heaters 25a and 25b are separated.
Then, the transport arm 24 is lowered by a driving mechanism (not shown), and the glass material support portion 32 is moved to a position directly above the lower mold 22. In this state, the support arms 32a and 32b are rotated to bring the glass material support portion 32 into a grip release state as shown in FIG. As a result, the glass material 33 falls onto the lower mold 22.
Then, the transfer arm 24 is moved in the horizontal direction from the lower mold 22 to the fully retracted position.

Next, the body mold 23 and the upper mold 21 held by a holding mechanism (not shown) are lowered, the body mold 23 is externally fitted to the lower mold 22, and the upper mold 21, the lower mold 22, and the trunk mold 23 are used to make glass. A forming block 70 in which the material 33 is sealed is completed.
Further, since this sealing is performed in a state where volatile components are not scattered around the glass material 33, there is no possibility that volatile materials are sandwiched between the glass material 33 and the mold surfaces 21a and 22a. In addition, since the glass material 33 has a low temperature of 300 ° C. or lower, there is no possibility that new volatile matter is generated from the glass material 33.

Next, the forming block 70 is transferred onto the preparation table 60 of the forming apparatus 40 by an appropriate transfer means. In this conveyance process, since the glass material 33 is in a sealed state, it is possible to prevent adhesion of dust and the like.
Moreover, the glass material 33 is covered and kept warm by the upper mold | type 21, the lower mold | type 22, the trunk | drum 23, etc., and a temperature fall can be reduced compared with the case where only the glass raw material 33 is conveyed in the air.
In order to improve the molding efficiency, it is preferable that the temperature drop in the transport process is small. For example, it is preferable to transport the glass material 33 to the molding apparatus 40 so that the temperature of the glass material 33 does not drop below 200 ° C. However, when the glass material 33 breaks due to thermal shock when placed on the lower mold 22, the temperature of the glass material 33 is set to 200 ° C. or lower, or the temperature of the lower mold 22 is set to about 200 ° C. It is necessary to avoid thermal shock by heating to a high temperature.

When the forming block 70 is transported onto the preparation table 60, the shutter 63 that opens and closes the inlet 62 is opened, and the forming block 70 is transferred into the chamber 41 by the transfer mechanism 66 and placed on the preheating stage 43. At this time, each stage and each block of the molding apparatus 40 are set to a predetermined temperature.
Then, the transfer mechanism 66 is retracted outside the chamber 41 and the shutter 63 is closed. And the temperature setting process is started by the molding apparatus 40.

After the forming block 70 is transferred onto the preheating stage 43, the preheating block 47 is lowered by the cylinder 53, and the preheating block 47 is brought into contact with the upper surface of the forming block 70, that is, the end surface of the upper die 21. Thus, the forming blocks 70 are subjected to preheating preheating stage 43, from the preheating block 47, to a temperature _{T 21.} After holding in this state for a predetermined time, the preliminary heating block 47 is raised.
Thereafter, the forming block 70 is transported to the preheating stage 44 by a transport mechanism (not shown), and the preheating block 48 is brought into contact from above. Thus, the forming blocks 70 are subjected to preheating preheating stage 44, from the preheating block 48, to a temperature _{T 22.} After holding in this state for a predetermined time, the preheating block 48 is raised.
In this way, by performing the two-stage preheating from the low temperature to the high temperature, it is possible to raise the temperature stepwise from the low temperature to the high temperature without excessive heat storage. The temperatures T ₂₁ , T ₂₂ , and the respective heating times are set so that the temperature of the glass material 33 in the molding block 70 becomes a temperature T ₂ (T _g or more) at which press molding can be performed at the end of the above preheating. Keep it.
Then, to convey the molded block 70 the temperature of the glass material 33 becomes T ₂ on the pressing stage 45. In this embodiment, pressure stage 45, the pressure block 49, by the respective heaters 55, substantially equal to the temperature T _2, is set to T _g or higher.
Thus, the temperature setting process ends.

Next, in the forming step, the pressurizing block 49 is lowered by the press cylinder 54, the upper mold 21 is pressed, and the glass material 33 is press-formed. When the pressure block 49 is lowered to the molding position, the glass block 33 in the molding block 70 is held for a predetermined time until it is cooled to some extent. Thereafter, the pressure block 49 is raised, and the forming block 70 is transferred to the cooling stage 46.
In the cooling stage 46, the molding block 70 is cooled to a temperature at which the molded glass material 33 can be taken out by the cooling mechanism 56.
This completes the molding process.
Thereafter, the shutter 63 is opened, and the cooled molding block 70 is carried out from the outlet 64 onto the cradle 61, and the shutter 63 is closed. And the molding block 70 is decomposed | disassembled in air | atmosphere, and the shape | molded glass raw material 33 is demolded.
In this way, the optical element molding apparatus including the heating furnace 35, the molding block 70, and the molding apparatus 40 has lens surfaces corresponding to the shapes of the mold surface 21a of the upper mold 21 and the mold surface 22a of the lower mold 22. An optical element can be manufactured.

  The operation of the optical element molding method of this embodiment will be described with reference to specific examples shown in Table 3.

Example 9 shown in Table 3 was molded by the optical element molding method of the present embodiment described above, and a phosphate-bismuth-based glass material containing bismuth oxide similar to Examples 1 and 2 as the glass material 33. The case where is used is shown. In Examples 10 to 15, the material of the glass material 33 is changed and molded in the same manner, and each corresponds to the materials of Examples 3 to 8 of the first embodiment.
In Examples 9 to 15, the heating temperature in the heating step was T ₁ = T _g +150.
On the other hand, Comparative Examples 2 to 8 were molded from the materials of Examples 9 to 15 without performing a heating step, that is, in Comparative Examples, they were not heated above the molding temperature.
The mold surfaces 21a and 22a of Examples 9 to 15 and Comparative Examples 2 to 8 have the same shape as the tip portions 8a and 9a of the first embodiment, and the target value of the lens inner thickness is 2.50 mm. It is. Further, in the molding step, the temperature of the pressing block 49, _{T g} above the temperature of the glass material 33, i.e. to a temperature such that the viscosity of the glass material 33 is less than ¹⁰ 13.3 dPa · s, the press load, All were set to 1470N (150 kgf).

  As shown in Table 3, in Examples 9 to 15 in which the heating step was provided, molding was possible without problems, but in Comparative Examples 2 to 8 in which the heating step was not provided, the molding surface of the molded product and the mold surface 21a, Clouding (spider) occurred in 22a, or seizure of the glass material 33 occurred.

  As described above, according to the present embodiment, an optical material that is likely to generate volatiles is heat-treated in advance to remove the volatiles, and thus can be easily molded by a general molding apparatus.

In the description of the first embodiment, an example in which the heating furnace 1 and the molding chamber 7 are separated by the shutter 4 has been described. However, if volatiles can be excluded from the vicinity of the mold surface of the mold. Such a shielding mechanism may not be provided.
For example, by adding means for directing the airflow between the heating furnace 1 and the molding chamber 7 from the molding chamber 7 side to the heating furnace 4 side, volatiles generated from the glass material 5 are prevented from flying to the molding chamber 7 side. It may be.
In this case, the effect is remarkably generated by setting the flow velocity of the airflow to about 5 cm / s or more, but if the flow velocity is too high, the temperature distribution in the heating furnace may be shifted, or the heating efficiency may be deteriorated. The flow rate of the airflow is desirably 1 m / s or less.
If there is no problem in the oxidizing atmosphere, the air current can be the same effect by using an inert gas such as nitrogen gas or argon gas or a rare gas if it is necessary to be an inert atmosphere such as air or oxygen gas. Obtainable.

  In the description of the second embodiment, the heating space 35a is shielded by the shutter 26, so that the glass material 33 and the upper mold 21 and the lower mold 22 in the heating process are isolated from each other. An air flow may be generated between the glass material 33 and the upper mold 21 and between the glass material 33 and the lower mold 22 so that the volatile substances are eliminated before reaching the upper mold 21 and the lower mold 22.

  In the description of the second embodiment, an example in which the glass material 33 heated in the heating process is incorporated into a molding block 70 including the upper mold 21, the lower mold 22, and the body mold 23 that are not temperature-controlled. As described above, the upper mold 21, the lower mold 22, and the trunk mold 23 may be heated so that the glass material 33 is not broken by a thermal shock caused by rapid cooling. In this case, since the yield can be increased even if a material that is vulnerable to rapid cooling is used as the glass material 33, the number of applied optical material types can be increased.

  Further, the machine configuration, setting conditions, mold material, protective film, atmosphere, and the like in the above description do not limit the scope of the present invention and can be changed without departing from the technical idea of the present invention. .

1 shows a schematic configuration of an optical element molding apparatus used in an optical element molding method according to a first embodiment of the present invention. It is typical sectional drawing which shows schematic structure of the heating furnace in the optical element shaping | molding apparatus used for the optical element shaping | molding method which concerns on the 2nd Embodiment of this invention. It is a top view of A view of FIG. When the optical material support part of the heating furnace of the optical element molding apparatus used in the optical element molding method according to the second embodiment of the present invention supports (a) the state when supporting the optical material, (b) when the support is released It is a top view which shows the state of. It is typical sectional drawing which shows schematic structure of the shaping | molding apparatus used for the optical element shaping | molding method which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

1, 35 Heating furnace 1a, 35a Heating space 4 Shutter 5, 33 Glass material (optical material)
7 Molding chamber 8, 21 Upper mold (mold)
8a, 9a Tip (mold surface)
9, 22 Lower mold (molding mold)
21a, 22a Mold surface 23 Body type (sleeve)
25 Heating heater section 25c Notch section 26 Shutter 40 Molding device 41 Chamber 43, 44 Preheating stage 45 Pressure stage 47, 48 Preheating block 49 Pressure block 70, 71, 72 Molding block (mold assembly)
100 Optical element molding apparatus

Claims (8)

An optical element molding method for obtaining an optical element by heat-softening an optical material containing a volatile component and press-molding with a molding die arranged opposite to the pressing direction,
A heating step of heating the optical material to a first temperature at which the viscosity of the optical material is less than 10 ⁷ dPa · s to volatilize the volatile component;
An optical element molding method comprising: a molding step of press molding the optical material using the molding die after the heating step.   The volatile component includes at least one of lead oxide, bismuth oxide, boron oxide, zinc oxide, molybdenum oxide, hydrofluoric acid, phosphoric acid, borophosphoric acid, and fluoride. Optical element molding method.   A temperature setting step is further provided between the heating step and the molding step to set the optical material from which the volatile component has been volatilized by the heating step to a second temperature lower than the first temperature and capable of being press-molded. The optical element shaping | molding method of Claim 1 or 2 characterized by the above-mentioned.   4. The optical element molding method according to claim 3, wherein in the temperature setting step, the temperature of the mold is set to a third temperature lower than the second temperature at least on the mold surface. The optical element molding method according to claim 4, wherein the third temperature is a temperature at which the viscosity of the optical material is 10 ¹² dPa · s or more and 10 ¹⁴ dPa · s or less. Between the heating step and the molding step, the position of the molding die and the optical material is regulated in a direction orthogonal to the pressing direction with the optical material sandwiched between the opposingly arranged molding dies. Further comprising a temperature setting step of forming a mold assembly in which a sleeve is fitted and setting the temperature of the mold and the optical material by heating the mold assembly;
3. The optical element molding method according to claim 1, wherein in the molding step, press molding is performed by pressing the mold of the mold assembly along the axial direction of the sleeve.   At least in the heating step, by forming an air flow between the optical material and the mold, the volatile components volatilized from the optical material are excluded from the vicinity of the mold surface of the mold. The optical element shaping | molding method in any one of Claims 1-6 characterized by these.   The optical element molding method according to claim 1, wherein at least in the heating step, the optical material is heated while being isolated from the mold.

Images