JP2975167B2 - Glass optical element molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an optical element by softening a glass material by heating and pressing the glass material with a pair of molding dies.

[0002]

2. Description of the Related Art Conventionally, there has been known an optical element molding method in which a glass material is heated and softened, conveyed between a pair of molding dies, and then pressed by a molding die to obtain an optical element.

[0003] For example, in the invention described in Japanese Patent Application Laid-Open No. 62-27335, when a glass material is heated, the surface portion and the inside of the glass material are respectively 10 ⁹ to 10.
^A method is disclosed in which a predetermined temperature equivalent to ^4.5 poise and 10 ^14.5 to 10 ⁹ poise is set to give a temperature gradient between the surface portion and the inside. According to this method, both the glass material and the molding die can reach the temperature below the transition point in a short time, the transfer is rapidly completed, and the molded product can be immediately taken out of the molding die. .

[0004] However, the above prior art has the following disadvantages.

That is, when a glass material finished in advance to a shape close to the final shape by grinding and polishing is used, for example, when obtaining an optical element having only one aspherical surface,
What is necessary is just to shape the glass material pressing surface on the side to be aspherical,
The glass material pressing surface on the spherical surface side does not necessarily need to be heated in the same manner as the aspherical surface side.

Therefore, only by providing a temperature difference between the surface portion and the inside of the glass material as in the prior art, the glass material pressing surface on the side not required for molding is also softened and fluidly deformed. In addition, the durability of the molding die was significantly deteriorated.

That is, since the glass material is softened and deformed by heating, if the heating is performed more than necessary, the shape of the glass material immediately before pressing changes, and a large amount of glass flow is generated. This has an adverse effect on the durability of the molding die.

Further, even when an optical element having a double-sided aspherical surface is obtained, both sides (both glass material pressing surfaces) are conventionally uniformly heated and softened regardless of the amount of aspherical surface.
There is the same problem as in the case of the single-sided aspherical optical element. In other words, the necessary deformation amount is determined for each surface according to the aspherical amount, but since heating is performed evenly on both surfaces according to one required deformation amount, there is a side that is heated more than necessary, This had an adverse effect on the transferability and the durability of the molding die. Further, performing unnecessary heating hinders reduction in cycle time.

Therefore, there is an invention described in Japanese Patent Application No. Hei 1-206490 previously proposed by the present applicant to solve the above-mentioned drawbacks. According to the invention, it is possible to prevent the shape of the glass material immediately before being pressed from being largely deformed by unnecessary heating, to have excellent transferability and durability of the molding die, and to reduce the cycle time. .

That is, after the glass material is heated and softened, and the glass material is conveyed between a pair of molding dies,
In the method of molding an optical element to obtain an optical element by press molding with a molding die, when heating the glass material,
The heating of each glass material pressing surface is independently controlled according to the required deformation amount on the glass material pressing surface.

According to the invention having the above construction, when heating the glass material, the amount of heat applied to the upper glass material pressing surface and the lower glass material pressing surface depends on the amount of molding deformation on the glass material pressing surface. To change. That is, the relative distance between the glass material and the heater is adjusted, or the amount of heat generated by the upper and lower heaters is adjusted, so that the amount of deformation is increased for the glass material pressing surface having a larger deformation amount, The heating amount is reduced for a smaller glass material pressing surface.

[0012]

However, the invention described in Japanese Patent Application No. 1-206490 has the following problems.

That is, as shown in FIG. 7, the shape of the glass material 51 immediately before pressing is prevented from being largely deformed by unnecessary heating, and the glass can be sufficiently flown over the entire surface of the molding die to secure the contact. , High temperature heating side 51a
In the glass surface of the above, a delay in cooling during the press molding causes a temperature difference between the high-temperature heating side 51a and the low-temperature heating side 51b, and the amount of shrinkage of the glass on the high-temperature heating side 51a is larger. 52. The warp 52 may adversely affect optical performance.

As shown in FIG. 8, if the pressing time is sufficiently extended, the glass temperature is equalized with the temperature of the molding die, and the temperature difference between the high-temperature heating side 51a and the low-temperature heating side 51b becomes sufficiently small. , The sled 52 becomes smaller.

However, for example, in a short press in which the pressing time is 20 seconds or less, it is difficult to sufficiently reduce the temperature difference between the high-temperature heating side 51a and the low-temperature heating side 51b.

Therefore, in order to reduce the warpage, it is necessary to extend the press time, which limits the productivity.

Accordingly, the present invention has been developed in view of the above problems, and has as its object to provide a method of molding a glass optical element which can shorten the press time and reduce the occurrence of sink marks and warpage. I do.

[0018]

SUMMARY OF THE INVENTION The present invention relates to a method for forming an optical element by transferring a glass material which has been heated and softened between a pair of molding dies to obtain an optical element by press molding. Heating the surface on the side where the shape difference between the mold and the glass material surface is large to a higher temperature in accordance with the amount of deformation, and contacting the glass material surface with the side heated to a higher temperature when pressing the glass material. Forcibly cooling the molding die to be performed, a step of reducing the temperature difference between the two molding surfaces when the optical element has dropped to the transition point temperature, and a step of releasing the mold after the optical element has fallen below the transition point temperature. Is a molding method.

After the step of reducing the temperature difference between the two molding surfaces at the time when the temperature of the optical element falls to the transition point temperature, a step of forcibly cooling one of the molding dies and then releasing the mold is carried out. This is the molding method provided.

[0020]

According to the present invention, the cooling delay on the side heated to a high temperature on the glass material surface is corrected in a short time by forcibly cooling the molding die in contact with the glass material surface, and the glass transition point is reduced. The temperature difference between the two surfaces of the glass when the temperature is reached can be reduced.

[0021]

Embodiment 1 FIGS. 1 and 2 are cross-sectional views of an apparatus used for a method for molding a glass optical element of this embodiment.

Reference numeral 1 denotes a glass material which has been finished to a shape close to the final shape by grinding and polishing in advance. The glass material 1 is mounted on a transfer arm 3 via a transfer tool 2.
The transfer arm 3 can move forward and backward in the longitudinal direction, can transfer the glass material 1 through the heating furnace 4 into the forming chamber 5, and is provided so as to be able to move up and down.

The heating furnace 4 has an upper heater plate 7 on which an upper heater 6 is installed on the inner surface, a lower heater plate 9 on which a lower heater 8 is installed on the inner surface, and both upper and lower heater plates 7,
9 comprises two side plates 10 and 11 for closing the side plate 9 from the side. The upper heater plate 7 and the lower heater plate 9 are connected to a driving device (not shown) such as a cylinder via supporting rods 12 and 13, respectively, and are provided so as to be independently movable up and down. Thus, the upper and lower heaters 6 and 8 can freely move toward and away from the glass material 1 independently of each other, in conjunction with the vertical movement of the transfer arm 3. The heating amount can be adjusted by changing the relative distance 8.

Further, a thermocouple (not shown) for controlling the temperature is separately provided at the center of each of the upper and lower heaters 6 and 8, so that the heaters 6 and 8 can be controlled independently of the temperature. It is provided so that it can be controlled and the temperature can be set according to the required heating amount.

On the other hand, a forming chamber 5 for press-forming the glass material 1 heated and softened in the heating furnace 4 is connected to the heating furnace 4. The molding chamber 5 contains an upper mold 1 for molding.
4 and a lower molding die 15 are provided coaxially and opposed to each other. The lower molding die 15 is connected to a driving device (not shown), and is provided to be vertically movable.

A ring-shaped hollow forced cooling pipe 16 is loosely fitted on the outer peripheral portion of the upper mold 14 for molding, and a plurality of nozzle portions 16a are provided on the inner peripheral surface of the forced cooling pipe 16 at equal intervals. Have been.

The forced cooling pipe 16 is fixed to the introduction pipe 17. The introduction pipe 17 is connected to an external N ₂ gas generator (not shown), and the N ₂ gas from the N ₂ gas generator is formed from the nozzle 16 a of the forced cooling pipe 16 via the introduction pipe 17. The upper mold 14 is configured to be able to flow out toward the outer peripheral surface.

The N ₂ gas is configured to be controlled at a preset operation timing by a valve provided and a control device (not shown).

In the present embodiment, a single-sided aspherical lens made of glass type SK11 having an aspherical surface amount of 100 μm was formed by using the apparatus having the above configuration.

First, the glass material pressing surface 1 on the aspherical surface side
The glass material 1 was placed on the transfer arm 3 via the transfer tool 2 with a facing upward. Here, the glass material 1 is processed in advance by grinding and polishing, the glass material pressing surface 1a on the aspherical surface is processed into an approximate spherical surface, and the glass material pressing surface 1b on the spherical surface is processed into a substantially designed value. Have been. Therefore, the glass material pressing surface 1a on the aspherical surface requires a heating amount corresponding to the amount of deformation of the aspherical amount of 100 μm, and the glass material pressing surface 1b on the spherical surface does not need to be deformed. For this reason, the relative distance between the glass material pressing surface 1a on the aspherical surface side of the glass material 1 and the upper heater 6 is 10 mm, and the glass material pressing surface 1b on the spherical surface side of the glass material 1 and the lower heater 8 are set.
Was set to 30 mm.

In this embodiment, the glass material 1
The heating amounts were made different by independently changing the relative distances between the heaters 6 and 8, so that the heaters 6 and 8 were set at 680 ° C. for both the upper and lower sides.

After the glass material 1 was heated in the heating furnace 4 for 1 minute, it was conveyed between the forming dies 14 and 15 by the transfer arm 3 and the lower forming die 15 was raised to perform press forming. . As a result of a measurement using a thermocouple, the upper surface of the glass material 1 was approximately 655 ° C., and the lower surface was approximately 600 ° C.

Immediately after pressure molding, N ₂ gas was injected into the upper mold 1 for molding.
4 to lower the temperature of the upper mold 14. At this time, the flow rate of the N ₂ gas is as shown in the graph of FIG.
When the pressing time has elapsed for 15 seconds and the optical element has almost reached the transition point temperature (535 ° C.), each glass material pressing surface 1
The molding was performed while adjusting so that the temperature difference between a and 1b was eliminated.

According to the present embodiment, the conventional technique requires a press time of 25 seconds or more, but the same level of transferability can be obtained with a press time of 15 seconds. Could be molded.

In this embodiment, a preform having a nearly spherical shape is used as the glass material. However, the present invention is not limited to this, and glass materials on both surfaces can be formed in the same manner.

[0036]

[Embodiment 2] The apparatus used in this embodiment is the same as the apparatus used in Embodiment 1 and the description of the structure of the apparatus will be omitted.

In the method of forming a glass optical element in this embodiment, as shown in the graph of FIG.
The upper die for molding is continuously cooled even after a press time of 15 seconds when the temperature between the glass material pressing surfaces 1a and 1b of the glass material becomes substantially equal in the vicinity of the transition point temperature. Then, the mold is released after the temperature of the molding upper mold becomes lower than the temperature of the molding lower mold.

The optical element molded by the molding method of this embodiment temporarily warps due to the temperature difference between the two surfaces of the optical element that is lower than the transition point temperature, but the mold is easily released from the mold. . The warpage is generated at a temperature at which viscous flow of the glass does not occur at all, and is caused by a so-called temporary strain. The warpage disappears when cooled to room temperature and equalized to obtain an optical element free of warpage.

In this embodiment, the upper mold for molding is cooled even after the temperature near the transition point temperature. However, the present invention is not limited to this, and as shown in FIG. The same effect can be obtained by providing a second forced cooling pipe 21 and a pipe 22 for introducing N ₂ gas, and switching the cooling after the temperature near the transition point from the upper molding die 14 to the cooling of the lower molding die 15. Can be

[0040]

[Embodiment 3] The apparatus used in this embodiment is different from Embodiment 1 in that the forced cooling pipe 16 and the introduction pipe 17 for outflow of N ₂ gas are eliminated and a cooling jig 31 is provided instead. Differently, the other components have the same configuration, and the same components are denoted by the same reference numerals and description thereof will be omitted.

The method for molding the glass optical element of this embodiment is as follows.
Instead of cooling by blowing N ₂ gas in each of the above embodiments, cooling is performed by bringing the cooling jig 31 into contact with the upper mold 14.

The functions and effects are the same as those of the above embodiments, and the description of the functions and effects will be omitted.

[0043]

As described above, according to the method for molding a glass optical element of the present invention, it is possible to prevent the deterioration of transferability due to shrinkage of glass such as sink marks and warpage. Further, the durability of the molding die is improved. Further, the cycle time can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first embodiment.

FIG. 2 is a cross-sectional view of the first embodiment.

FIG. 3 is a graph of Example 1.

FIG. 4 is a graph of Example 2.

FIG. 5 is a sectional view showing a modification of the second embodiment.

FIG. 6 is a sectional view of a third embodiment.

FIG. 7 is a sectional view of a conventional example.

FIG. 8 is a graph of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass material 2 Carrier 3 Transfer arm 4 Heating furnace 5 Molding chamber 6 Upper heater 8 Lower heater 14 Upper mold for molding 15 Lower mold for molding 16 Forced cooling pipe

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C03B 11/00 C03B 11/12

Claims (2)

(57) [Claims] 1. A method for forming an optical element by conveying a glass material heated and softened between a pair of molding dies to obtain an optical element by press molding, wherein the shape of the molding die and the glass material surface in the glass material is A step of heating the surface having a large difference to a higher temperature in accordance with the amount of deformation thereof, and forcibly pressing a molding die in contact with the side heated to a higher temperature in the glass material surface when pressing the glass material. A glass characterized by comprising a step of cooling and reducing the temperature difference between the two molding surfaces when the optical element has cooled to the transition point temperature, and a step of releasing the mold after the optical element has fallen below the transition point temperature. Optical element molding method. 2. A step of forcibly cooling one of the molding dies and then releasing the mold after the step of reducing the temperature difference between the two molding surfaces when the optical element has cooled to the transition point temperature. The method for forming a glass optical element according to claim 1, wherein the glass optical element is provided.