JPH01270529A - Forming mold for glass optical element - Google Patents

Abstract

PURPOSE:To prevent shrinkage, contrive high accuracy and improve shape copying properties of a forming surface by forming a thermally hardened glass material with a pair of forming molds having additionally provided heat insulating material on the outer periphery of at least one forming mold. CONSTITUTION:Outer peripheral parts (21b) and (22b) relatively adjacent to forming surfaces (21a) and (22a) of forming molds 21 and 22 in a forming device 20 are additionally provided with cylindrical heat insulating materials 27 and 28 consisting of, e.g., ZrO2 ceramic, and the top force 21 is fixed to a top plate 25. The bottom force 22 is passed through the bottom plate 26 and movably held in the vertical directions [direction of an arrow (A)] through a driving source and simultaneously constituted so as to enable temperature control at a prescribed temperature with heating heaters 23 and 24 at a controlled temperature. An optical glass material 34 is then placed in a drum type carrier 33 and fed into a heating furnace 36 with an arm 35 for conveying the drum type carrier and thermally softened through a heater 37 until a formable state is attained. The arm 35 is then advanced to convey the optical glass material 34 together with the carrier 33 to a gap between the top force 21 and the bottom force 22 and carry out press forming.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mold for forming an optical element by pressurizing a glass material heated and softened so as to be moldable.

[Conventional technology]

2. Description of the Related Art Conventionally, an optical element molding apparatus equipped with a pair of molds for heating and softening a glass material and then pressure-molding the glass material into a desired optical element has been disclosed, for example, in Japanese Patent Application Laid-Open No. 62-288119.

FIG. 9a shows the optical element molding apparatus described above, in which the upper mold 1 can be set to a predetermined temperature by a temperature control device (not shown).
A pair of molds, ie, a lower mold 2 and a lower mold 2, are arranged opposite to each other, and a transport arm 4 for transporting a glass material 3 is provided between the upper mold 1 and the lower mold 2. The glass material 3 is held by the body carrier 5 and transported into the heating furnace 6 by the transport arm 4, heated and softened to a predetermined temperature, and then transported between the upper mold 1 and the lower mold 2, as shown in FIG. As shown in the figure, the optical glass material 3 is pressed by an upper mold 1 and a lower mold 2 to form a glass optical element. In addition, the upper mold 1 and the lower mold 2 are placed in a quartz glass tube 7 to prevent oxidation of the high-temperature parts, and the inside of the quartz glass tube 7 is filled with nitrogen gas or inert gas by an atmospheric gas supply device 9. Alternatively, it is configured so that a non-oxidizing gas such as a reducing gas can be supplied.

[Problem B to be solved by the invention] However, in the conventional mold, molds 1 and 2
Since heat exchange with non-oxidizing gas takes place from the mold surface,
A large temperature distribution occurs in the radial direction symmetrically about the central axis a of the mold 1.2, with the temperature being high near the central axis a (') of the mold 1.2, and rapidly decreasing as it approaches the mold surface. It gets lower.

For this reason, when a glass material that has been heated and softened comes into contact with a mold that is kept at a lower temperature than the glass material during molding of glass optical elements, heat exchange occurs from the glass material to the mold. The temperature distribution is such that the central part of the glass material, which is difficult to escape, is ultimately the highest in temperature, resulting in a shape change due to the difference in thermal contraction, so-called "sink marks". Therefore, if the above-mentioned large temperature distribution occurs in the mold, the temperature distribution of the glass material will be promoted, and the viscosity of the outer peripheral part of the glass material will increase quickly.
By holding the glass material under pressure, the effect of removing and correcting "sink marks" is hindered, causing "sink marks" on glass optical elements.
There was a problem that occurred.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and provides a mold for a glass optical element that can reduce the temperature distribution of the mold and mold an optical element without sink marks. With the goal.

(Means for Solving the Problems) In order to achieve the above object, the mold for the glass optical element of the present invention, as shown in FIG. At least one mold outer peripheral portion 11a, 1 of the molds 11.12 arranged to face each other
It is constructed by attaching heat insulating materials 13 and 14 to 2a.

(Function) According to the mold for a glass optical element having the above configuration, the mold 1
1 and/or the surfaces of the outer peripheral portions 11a and 12a of the mold 12 and the non-oxidizing gas is relaxed, and the mold 1.
The temperature distribution of the mold 11.12 symmetrical about the central axis a of 1.12 decreases.

[Example] Hereinafter, an example of the present invention will be described in detail using one page.

(First Example) FIG. 2 shows a first example of a mold for a glass optical element according to the present invention.
This figure shows an example, and the figure shows a sectional view of a molding apparatus 20 using the mold of this example.

In the figure, 21.22 indicates a mold (upper mold 21.22).
In the lower mold 22), this mold 21.22 No. 11 is controlled to a predetermined temperature by a temperature-controlled heating heater 23.24, and the upper mold 21 is fixed to the upper plate 25, and the lower mold 2
2 penetrates the lower plate 26 and is held movably in the vertical direction (in the direction of the arrow) by a drive fi (for example, a cylinder, not shown). The settings are configured to match. Furthermore, the upper mold 21.
The lower mold 22 has a cylindrical heat insulating material 27, 28 made of zirconia ceramic on its outer circumferential portions 21b, 22b that are relatively close to its molding surfaces 21a, 22b. It is configured to weaken the heat exchange between the atmospheric gas and the mold 21.22 and reduce the temperature distribution (temperature gradient) occurring in the radial direction of the mold 21.22.

The molds 21 and 22 are surrounded by a quartz glass tube 29, and a non-oxidizing gas such as nitrogen gas, an inert gas, or a reducing gas is supplied to the inside 30 of the quartz glass tube 29 by an atmospheric gas supply device 31. However, oxidation of the high-temperature parts of the molds 21 and 22 is prevented. Note that the upper plate 25. The lower plate 26 is connected by a member not shown, so that the mutual distance 3 positions between the upper plate 25 and the lower plate 26 does not change.

Reference numeral 33 denotes a barrel-shaped carrier on which the optical glass material 34 and the optical element after press molding are placed and transported;
3 is held from the trunk wall carrier conveying arm 35,
The material is transferred through a heating furnace 36 that can be set to a predetermined temperature by a temperature control device (not shown), and is conveyed between the upper mold 21 and the lower mold 22.

Next, a method of molding a glass optical element using the molding apparatus will be described.

First, the optical glass material 34 is placed inside the body-shaped carrier 33 and transported into the heating furnace 36 by the body wall carrier transport arm 35, and the optical glass material 34 becomes ready for molding via the upper and lower heaters 37. (near the softening point temperature). Next, the arm 35 is advanced and the optical glass material 34 is transferred together with the body carrier 33 to the upper mold 21.
and the lower die 22. Thereafter, the lower mold 22 is moved upward, and the softened optical glass material 34 is press-molded through the molds 21 and 22, and the molding surface 21a of the upper mold 21 and the molding surface 22a of the lower mold 22 are Molding the element. After molding, the lower mold 22 is moved downward to release the mold, and the press-molded optical fibers are transported via the shell carrier transport arm 35 into a slow cooling furnace (not shown) provided on the opposite side of the heating section 36. After cooling the element, the optical element is taken out from the body wall carrier 33. Note that the shell carrier 33 and the optical element are transferred into the lehr by another shell carrier carrier arm (not shown) which is transferred after being press-formed from the shell carrier carrier arm 35. be able to.

FIG. 3 shows interference fringes showing the shape accuracy of the glass optical element press-molded by the molds 21 and 22 having the above configuration.
In such a glass optical element, the optical glass material 34 is L L
The optical glass material 34 is formed into a plano-convex shape with a diameter of 18 mm, a radius of curvature of the B surface of 20 mm, a flat surface of the A surface, and a thickness of 4 mm. N2 gas is used as the gas, supplied at a flow rate of 5P/min, and has an external diameter of 17 mm.

21. Stainless steel mold with mold temperature set at 450°C.
22 is press molded. Furthermore, insulation material 27.2
8 is a cylindrical zirconia ceramic with an inner diameter of 16 mm, an outer diameter of 20 mm, and a length of 15 mm (thermal conductivity of 0.007 ca).
l/cm, sec, 'C) are attached to the outer peripheral parts 21b, 22b of the mold 21.22. Note that the heat insulating material is the upper mold 21. Either of the lower molds 22 can be provided on one outer periphery.

FIG. 4 shows the mold 21 during molding of the optical element.
The distribution state of the surface temperature of the molding surfaces 24a' and 22a of the mold 22 is shown, and the temperature on the central axis of the mold 21 (22), 8 mm in diameter, and 16 mm in diameter is measured.

5 and 6 show the interference fringes of an optical element press-molded under the same conditions as above without using a heat insulator and the temperature distribution of the molding surface 40a of the mold 4o.

According to this example, as is clear from the comparison between FIG. 4 and FIG. 6, the temperature of the molding surface on the central axis of the mold is 450°
When set to
40°C and 430°C, and the temperature distribution state of this example is 10°ctt lower than that of a mold that does not use a heat insulating material. Therefore, the temperature distribution symmetrical about the central axis of the mold decreases, reducing the temperature gradient of the optical glass material during optical element molding, and slowing down the increase in viscosity at the outer periphery of the optical glass material, thereby increasing the pressure applied by the mold. The effect of correcting sink marks during holding becomes greater, and if no insulation material is used,
As shown in FIG. 5, a sink mark occurs in the central portion, but as shown in FIG. 3, a highly accurate glass optical element without sink marks can be molded.

(Second Embodiment) The mold of this embodiment is formed using a different material for the heat insulating material from the heat insulating material of the first embodiment, and the other configuration is the same as that of the first embodiment. Illustrations and explanations thereof will be omitted.

That is, the mold is constructed using quartz glass (thermal conductivity: 0.0037 cal/cm, sec, 'C) as a heat insulating material.

According to this embodiment, a temperature distribution similar to that of the first embodiment can be obtained, and a glass optical element without sink marks can be molded. Furthermore, since quartz glass, which is cheaper than zirconia ceramic, is used as the heat insulating material, it can be implemented relatively inexpensively.

(Third Example) FIG. 7 shows a third example of a mold for a glass optical element according to the present invention.
It is a sectional view showing an example.

The molds (upper mold 45 and lower mold 46) of this embodiment have heat insulating materials 47 and 48 attached to the diameters of the upper molding surface 45a and the lower molding surface 46a. The diameters of the outer peripheral portions 45b and 46b are configured to be large. That is,
The molding surfaces 45a and 46a are formed to have a diameter of 16 mm, and the outer peripheral portion 4
The diameters of 5b and 46b are 24 mm. Furthermore,
The heat insulating material 49° 50 is made of zirconia ceramic or quartz glass, as in the first and second embodiments, and has a cylindrical shape with an inner diameter of 24 mm and an outer diameter of 28 mm. It is connected to the outer peripheral parts 45b and 46b of .46.

According to the above configuration, the diameter of the outer peripheral portions 45b, 46b of the mold 45, 46 to which the heat insulating material 49, 50 is attached is set to the molding surface 45a.
, 46a (formed to constitute the mold 45, 46), the molding surfaces 45a, 46a and the outer peripheral part 45
The temperature gradient between b and 46b decreases, and furthermore, the adiabatic +A' 49 .

50 relaxes the heat exchange with the atmospheric gas, the temperature difference between the central axes (center portions) of the molding surfaces 45a, 46a and the outer peripheral portions 45b, 46b is further reduced compared to the first and second embodiments. can be reduced.

FIG. 8 shows the molding surface 4 under the same conditions as the first and second embodiments.
5a (46a), and as is clear from the figure, the temperature difference is 3.
°CX It's a little bit.

According to this example, a highly precise glass optical element without sink marks can be molded as in the previous example.

[Effects of the Invention] According to the present invention, the temperature distribution symmetrically around the central axis of the mold can be reduced, and the increase in viscosity at the outer periphery of the glass material can be delayed, so that the mold can be molded without sink marks. It is possible to mold a highly precise glass optical element with improved surface orientation.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing a mold for a glass optical element according to the present invention, FIG. 2 is a heat insulating material showing a first embodiment of a mold for a glass optical element according to the present invention, and FIG. 3 is a conceptual diagram showing a mold for a glass optical element according to the present invention. An interference fringe diagram showing the measurement results of a glass optical element molded with the example mold, FIG. 4 is a diagram showing the temperature distribution of the mold, and FIGS. 5 and 6 show the measurement results with the conventional mold. FIG. 5 is an interference fringe diagram of the optical element, FIG. 6 is a diagram showing the temperature distribution of the mold, the seventh circle is a cross-sectional view of the mold of the glass optical element according to the present invention, and FIG. 8 is the diagram of the mold. Diagram showing temperature distribution, Figure 9a
, b show the prior art, FIG. 9a is a sectional view showing a molding device, and FIG. 9 is an explanatory diagram showing the press molding of an optical element. 11.12--Molding molds 11a, 12a...-Molding molds) Periphery 13.14...Insulating material

Claims (1)

[Claims] A mold for a glass optical element, which is arranged to face each other in order to pressure-form a glass material that has been heated and softened so that it can be molded, is constructed by attaching a heat insulating material to the outer periphery of at least one of the pair of molds. A mold for glass optical elements characterized by: