JPH06100323A - Method for molding glass optical device - Google Patents

Abstract

PURPOSE:To provide the subject method for press molding for a concave lens, intended to make the cooling rates for the thick and thin portions of the lens equal to each other. CONSTITUTION:During press molding of a glass material using a pair of molds 17, 22, the outer periphery of the glass material is first cooled by blowing a nitrogen gas from an outer peripheral blow ring 34. And, after stopping nitrogen gas blow, a nitrogen gas are blown through both upper and lower blow tubes 27, 31 to cool the top force 17 and bottom force 22, respectively, thus cooling the center of the glass material. Thereby, the temperature distribution throughout the glass material can be made uniform and the time to attain the transition temperature in both the thick and thin portions of the material can be shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method for obtaining a glass optical element by pressing a glass material which has been softened by heating with a pair of molding dies and cooling it, and more particularly to a molding method for obtaining a glass optical element having a concave lens shape. .

[0002]

2. Description of the Related Art Conventionally, as a molding method for obtaining a glass optical element by cooling a heat-softened glass material with a pair of molding dies while cooling it, for example, JP-A-63-159227 and JP-A-2-55235. There is an invention described in the publication. In Japanese Patent Laid-Open No. 63-159227, the mold part in contact with the thick part of the optical part and the mold part in contact with the thin part of the optical part are independently provided so that heat media of different temperatures can be introduced. The heat medium chamber is provided so that a heat medium having a temperature higher than that of the heat medium chamber provided in the mold portion in contact with the thick portion can be introduced into the heat medium chamber provided in the die portion in contact with the thin portion. Disclosed is a mold for producing a lens that does not cause a large difference between the cooling rate in the thick portion and the cooling rate in the thin portion of the optical glass product and has no uneven refractive index. It is a thing.

Further, Japanese Patent Application Laid-Open No. 2-55235 discloses that
A pair of molding dies is provided with an air heat insulating layer by subjecting a columnar shape and an arbitrary shape to the part in contact with the heat source to provide an air heat insulating layer, so that the temperature of the center of the lens optical surface with a small amount of contraction during pressure cooling can be maintained and the amount of contraction can be reduced. A molding die and a molding method are disclosed which obtain a molded lens with good shape accuracy by cooling while reducing the difference in shrinkage amount with the vicinity of a large non-optical surface portion.

[0004]

In the above prior art, since the thin wall portion having a high glass cooling rate is always kept warm or insulated from the initial stage to the end of molding, the temperature difference between the thick wall portion and the thin wall portion changes. Therefore, it is not possible to optimize the temperature control of each part. FIG. 5 shows the measurement results of the temperature changes of the thick wall portion and the thin wall portion during the molding of the concave lens having a large outer diameter. After the start of molding, the heat of the glass is taken up by the mold until T ₁ seconds, so that the temperature of the thin portion where the heat transfer is fast becomes lower. After T ₁ second when the glass temperature approaches the mold temperature, the heat of the thin-walled portion located at the center cannot move unless the thick-walled portion located at the outer periphery is cooled by the atmospheric gas. become. As described above, when the cooling rate changes during molding in the thick portion and the thin portion,
In the above conventional technique, the cooling rate of the thin portion can be reduced, but it is not possible to cool to the glass transition point in a short time while reducing the temperature difference between the thick portion and the thin portion of the glass. Therefore, in molding a concave lens shape having a large outer diameter, it is not possible to obtain an optical element with good transfer accuracy in a short time.

The present invention was developed in view of the above problems in the prior art. The temperature distribution in the lens during molding is made uniform within a short time, and the temperature is cooled to the glass transition point. It is an object of the present invention to provide a glass optical element molding method capable of improving transferability.

[0006]

In order to achieve the above object, a method of molding a glass optical element according to the present invention comprises a step of pressing a softened glass material with a pair of molding dies, while maintaining this pressed state. Obtaining an optical element by cooling a glass material In the method of forming an optical element, when cooling the glass material, first cool the glass material from the outer periphery and then correspond to the center of the glass material that is being pressed. It was decided to perform pressure molding while cooling the glass material by cooling from inside the molding die.

[0007]

According to the above construction, first, when cooling is performed from the outer peripheral portion which is the thick portion of the glass material, the transition point temperature reaching speed in the thick portion during molding is accelerated. Subsequently, when cooled from the inside of the mold, the transition temperature reaching speed in the thin portion in the center of the glass material becomes faster. As a result, the temperature difference between the outer peripheral portion and the central portion of the glass material reaches the transition point temperature almost at the same time.

[0008]

Example 1 FIG. 1 is a sectional view showing a molding die in a molding apparatus used in a method for molding a glass optical element of Example 1 of the present invention, and FIG. 2 shows a molding apparatus used in an example of the present invention. In a sectional view, a concave lens forming device is shown. In FIG. 2, reference numeral 1 denotes a molding part, which is adjacent to a heating furnace 2 which includes a heater 2a and which can be set to a predetermined temperature by a temperature control device (not shown). The periphery of the molding unit 1 and the heating furnace 2 is closed by a cover 3 made of a quartz glass tube or a stainless tube, an upper base 4 and a lower base 5,
A molding chamber 6 is formed by the cover 3, the upper base 4 and the lower base 5. A gas nozzle 7 connected to an atmospheric gas supply device (not shown) is provided through the upper and lower bases 4 and 5, and a nitrogen gas, an inert gas, or a reduction gas supplied into the molding chamber 6 through the gas nozzle 7 is provided. The oxidizing gas prevents the inside of the molding chamber 6 from being oxidized. The upper base 4 and the lower base 5 are coupled via a member (not shown),
The upper base 4 and the lower base 5 are configured such that their mutual distances and positions do not change.

In the molding chamber 6, an upper mold part 8 and a lower mold part 9 are arranged so as to be relatively close to and away from each other on the same axis. The upper mold part 8 is fixed to the upper base 4, and the lower mold part 9 is fixed to the tip of the press shaft 10. The press shaft 10
In a housing 11 fixed to the lower base 5, a bearing (sliding bearing) 12 is axially slidably held, and a lower end thereof is connected to a driving cylinder 13 so as to be vertically movable.

Reference numeral 23 indicates a carrier for mounting and carrying the optical glass material 24 and the optical element after press molding,
The carrier 23 is held by a carrier transfer arm 25 and controlled so as to be transferred into the heating furnace 2 and between the upper mold 8 and the lower mold part 9.

As shown in FIG. 1, the upper die portion 8 is composed of an upper die mount 14, an upper die heater 15 and an upper die 17. The upper mold mount 14 is made of Si ₃ N ₄ —Al ₂ O ₃ system ceramics (coefficient of linear expansion 3.5 × 10 ⁻⁶ ),
The upper end is fixed to the upper base 4, and the lower end surface (tip end surface) thereof is provided with a recess 16 for positioning and fixing the upper die 17, and the bottom surface of the recess 16 is flat-finished. There is. Further, a through hole 14a is provided at the center of the inside of the upper mold mount 14 so as to open to the bottom surface of the concave portion 16, and an exhaust hole 14b is provided at the upper part to connect the through hole 14a to the molding chamber 6. So the upper mount 1
4 is provided with an opening on the outer peripheral surface. The upper heater 15 is
The upper die mount 14 is wound around the outer periphery of the upper mount 14 and is connected to a temperature control device (not shown) to be freely controlled to a predetermined temperature.

The upper die 17 is made of cemented carbide (coefficient of linear expansion 6 × 1).
0 ^-6 ), and its molding surface 17a is precisely mirror-finished into a predetermined convex shape, and then has a low fusion property with glass C.
The rN thin film 17b is coated. On the other hand, the molding surface 17
An end surface (hereinafter, referred to as a bottom surface) 17c on the opposite side of a is finished to be a precise flat surface. Inside the upper mold 17, the bottom 17
A single hollow portion 18 is provided from the center of c toward the molding surface 17a, and the bottom surface 18a of the hollow portion 18 is formed in a planar shape near the molding surface 17a. This upper mold 1
7 is housed in the recess 16 of the upper mold mount 14 so that the cavity 18a and the through hole 14a are aligned with each other. Bottom surface 17d of upper mold 17 and inner surface 1 of recess 16
The clearance with respect to 6a is dimensioned such that when it is heated to a predetermined temperature by the upper heater 15, it is shrunk and fixed. At this time, the upper die 17 and the upper die mount 14
Are intimately intimately attached to each other so that heat transfer can take place.

The lower mold part 9 is composed of a lower mold mount 19, a lower mold heater 20 and a lower mold 22. The lower end of the lower mold mount 19 is fixed to the tip of the press shaft 10, and a concave portion 21 is formed at the front end like the upper mold mount 14, and a through hole 19a and an exhaust hole 19b are provided. . The lower die heater 20 is wound around the outer periphery of the lower die mount 19 and is connected to a temperature control device (not shown) so that it can be controlled to a predetermined temperature.

Like the upper mold 17, the lower mold 22 is made of cemented carbide (coefficient of linear expansion 6 × 10 ^-6 ) and has a molding surface 22a.
Is precisely mirror-finished into a predetermined convex shape, then coated with a CrN thin film 22b having a low fusion property with glass, and an end surface (hereinafter referred to as a bottom surface) 22c opposite to the molding surface 22a is a precise flat surface. Has been finished. Lower mold 22
Inside, a single cavity 26 is provided from the center of the bottom surface 22c toward the molding surface 22a.
Bottom surface 26a is formed in a planar shape in the vicinity of molding surface 22a. The detailed structure of the lower mold part 9 is as follows.
The description is omitted because it is similar to the above.

Inside the cavity 18 of the upper mold 17, an upper mold internal blow pipe 27 penetrates the upper base 4 from outside the molding chamber 6 and is installed through a through hole 14a. As shown in FIG. 2, the upper mold internal blow pipe 27 is connected to a nitrogen gas supply device 30 via a solenoid valve 28 and a flow rate control valve 29. On the other hand, in the cavity 26 of the lower mold 22, a lower mold internal blow pipe 31 penetrates the press shaft 10 from the outside of the molding chamber 6 and is installed through the through hole 19a. The lower mold internal blow pipe 31 includes a solenoid 32 and a flow rate control valve 3.
It is piped to the nitrogen gas supply device 30 via 3. Then, when a predetermined amount of nitrogen gas supplied from the nitrogen gas supply device 30 flows out from the tip of the upper mold internal blow pipe 27 and the tip of the lower mold internal blow pipe 31, respectively, with the mold heated, the nitrogen gas is hollow. Bottom surfaces 18a, 26 of the parts 18, 26
While exhausting the heat in the vicinity of a, the exhaust holes 14b, 19
It is exhausted into the molding chamber 6 from b.

Reference numeral 34 in FIGS. 2 and 3 denotes a ring-shaped outer peripheral blow ring, the inside of which is formed into a ring-shaped hollow portion 34a, and a plurality of discharges communicating with the hollow portion 34a on the inner peripheral surface. The holes 34b are provided at equal intervals. A hollow outer peripheral blow pipe 35 is provided on the side of the outer peripheral blow ring 34.
Are welded so as to communicate with the cavity 34a. The outer peripheral blow pipe 35 is drawn out through the cover 3 to the outside of the molding chamber 6 and bent downward, and then through the bellows pipe 36, the solenoid valve 37 and the flow rate control valve 38, and then to the nitrogen gas supply device 30. It is plumbed. The outer peripheral blow pipe 35 is connected to the end of the movable rod 39a of the air cylinder 39 fixed to the upper base 4 in the vertical direction outside the molding chamber 6, and the operation of the air cylinder 39 and the bellows pipe accompanying it. By expansion and contraction of 36, the outer peripheral blow ring 34 can be moved up and down between the middle of the upper die 17 and the lower die 22 and the height above it.

Next, an embodiment of a method of molding an optical element using the molding apparatus having the above construction will be described together with its operation. First, nitrogen gas or the like is supplied into the molding chamber 6 from the nozzles 7 of the upper and lower bases 4 and 5 to replace the oxygen concentration in the molding chamber 6 with 1% or less. Next, the heater 2a, the upper die heater 15 and the lower die heater 20 heat the heating furnace 2, the upper die 17 and the lower die 22 to a predetermined temperature. In this state, the optical glass material 24 is placed in the carrier 23, and the carrier conveying arm 2
5 is conveyed into the heating furnace 2, and the upper and lower heaters 2a heat and soften the optical glass material 24 until it becomes a moldable state (softening point).

Next, the carrier arm 25 is moved forward, and the optical glass material 24 together with the carrier 23 is moved to the upper mold 17 and the lower mold 22.
Transport between. Then, the lower mold 22 is moved upward by the cylinder 13 via the press shaft 10, and the softened optical glass material 24 is press-molded by the molding surfaces 17a and 22a of the upper and lower molds 17 and 22, respectively.

At the same time as the start of press molding, the transfer arm 2
5 is retracted, and the outer peripheral blow ring 34 is lowered with it, and is positioned on the outer periphery of the carrier 23. At this time, cooling control by nitrogen gas is performed so that the temperature inside the glass changes as shown in FIG. 3 during the press molding. That is, the nitrogen gas is supplied from the nitrogen gas supply device 30, is made to flow out from the discharge hole 34a of the outer peripheral blow ring 34, and the glass material 24 being press-molded is cooled from the outer peripheral portion, and the glass temperature of the thick wall portion on the outer periphery is adjusted. While keeping the glass temperature of the thin portion in the center close to the glass temperature of T ₃ seconds, which is shorter than T ₁ seconds of FIG. 5, the nitrogen gas supply is switched to the inside of the upper mold blow pipe 27 and the lower mold interior. Nitrogen gas is caused to flow out from the tip of the blow tube 31 to cool the glass material 24 from the inside of the mold, and a lens having a large outer diameter (for example, φ20 m
(m or more), the glass material 24 is cooled to near the glass transition point while preventing the central part of the glass from having a high temperature. By implementing the above cooling process, a short T ₄ seconds from ₂ seconds T in FIG. 5 (see FIG. 3), while a substantially thick portion of the outer periphery and the center of the thin portion is uniform Yutakaka, near the glass transition point The glass can be cooled down and pressed.

After the press molding by the upper and lower molds 17 and 22 is completed, the lower mold 22 is lowered and released, and in a slow cooling furnace (not shown) provided on the side surface of the molding chamber 6 opposite to the heating furnace 2. The optical element that has been press-molded is gradually cooled by being transported by the transport arm 25. Then, after the slow cooling is completed, the optical element is taken out from the slow cooling and the optical element is taken out from the carrier 23.

According to this embodiment, after the transition point temperature reaching speed in the thick portion on the outer periphery of the concave lens during molding is accelerated, the cooling control is subsequently performed so as to accelerate the transition point temperature reaching speed in the central thin portion. This makes it possible to make the temperature distribution in the lens during press molding uniform and cool it to the glass transition point in a short time. Therefore, a concave lens-shaped glass optical element with good shape accuracy can be obtained by molding in a short time.

As a modified example of this embodiment, in forming a concave meniscus lens, only the convex surface side can be formed by cooling the mold by inflowing nitrogen gas from the inside of the mold, and the same effect as described above can be obtained. Further, the gas to be introduced is not limited to nitrogen gas, and may be an inert gas that is not flammable at high temperatures or harmful to the human body and does not cause deterioration of the mold, for example, argon gas is used. be able to. Further, it is also possible to switch the strength of the flow rate of nitrogen gas, for example, without completely switching the outer peripheral blow and the mold internal blow. In this case,
It is desirable to increase the press pressure to increase the press amount during press forming.

[0023]

[Embodiment 2] FIG. 4 is a sectional view showing a molding apparatus used in Embodiment 2 of the present invention. The molding apparatus is provided with a temperature sensor 40 for detecting a mold temperature in the lower mold 22, and a controller 41 connected to the temperature sensor 40. The controller 41 is connected to the solenoid valves 28 and 37, respectively. Other configurations are the same as those of the molding apparatus shown in FIG.

Next, the molding method of this embodiment will be described. The feature of this embodiment is that the temperature sensor 4 for detecting the mold temperature is used to switch from the outer peripheral blow to the internal mold blow during press molding.
This is performed by the controller 41 judging the signal of 0 and controlling the operation of the solenoid valves 28, 32, 37, and the other points are the same as in the first embodiment. As shown in FIG. 3, since the change of the mold temperature corresponds to the change of the glass temperature during the press forming, the mold temperature when the temperature of the thick portion and the thin portion is equalized is measured in advance, When cooled to this mold temperature, the outer peripheral blow is switched to the mold internal blow as described above. According to the present embodiment, in-process control of cooling in the press molding process becomes possible, so that it is possible to manufacture a molded product with good shape accuracy without variation.

[0025]

As described above, according to the present invention, the transition point temperature reaching speed in the thick portion on the outer circumference of the concave lens during molding is accelerated, and subsequently, the transition point temperature reaching speed in the central thin portion is accelerated. By controlling the cooling to 2, it is possible to obtain a concave glass optical element having good shape accuracy in a short time.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a molding part of a molding apparatus used in Example 1 of the present invention.

FIG. 2 is a sectional view showing a molding apparatus used in Example 1 of the present invention.

FIG. 3 is a graph showing changes in temperature inside the glass material over time.

FIG. 4 is a sectional view showing a molding apparatus used in Example 2 of the present invention.

FIG. 5 is a graph showing changes in temperature inside the glass material with time in the prior art.

[Explanation of symbols]

 17 Upper mold 22 Lower mold 24 Optical glass material 27 Upper mold internal blow pipe 30 Nitrogen gas supply device 31 Lower mold internal blow pipe 34 Peripheral blow ring 35 Peripheral blow pipe

Claims (1)

[Claims] 1. A method of molding an optical element, comprising pressing a heated and softened glass material with a pair of molding dies, and cooling the glass material while maintaining the pressed state to obtain an optical element. First, after cooling from the outer peripheral portion of the glass material, the glass material is cooled and pressure-molded by cooling from inside the molding die corresponding to the central portion of the glass material being pressed. A method for molding a glass optical element.