JP2783332B2 - Optical element molding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for molding an optical element in which a glass material is heated and softened, conveyed between a pair of dies, and pressed.

[Conventional technology]

In general, in a method of heating a glass material and pressing the glass material, the surface portion is rapidly cooled by removing heat from the mold when the softened glass lump is carried into the molding die and pressed. However, the inside of the glass material is still in a high temperature state during heating. Therefore, the glass material does not shrink uniformly, and a portion that shrinks greatly occurs as a sink mark.

Japanese Patent Application Laid-Open No. 61-53162 discloses an invention which has developed a measure against such sink marks. According to this publication, after unloading after press molding,
It is described that a mold and glass are cooled at a constant rate of 0.9 ° C./sec or less, and a molded product pressed at a glass viscosity of 10 ^11.5 to 10 ^12.5 poise is removed from the mold.

[Problems to be solved by the invention]

After being press-formed as described in the above publication
When cooling at 0.9 ° C./sec or less, a lens of good quality can be obtained with respect to transferability, but there is a problem that the time required for cooling becomes long and the molding cycle time becomes long.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical element molding method that shortens a cooling time while obtaining good transferability, that is, shortens a molding cycle time. is there.

[Means and actions for solving the problem]

In the present invention, the glass material is heated and softened to a temperature at which the viscosity of the glass material becomes 10 ⁶ to 10 ⁸ poise, and then conveyed between a pair of dies heated near the transition temperature of the glass material and pressed and formed. Immediately after press molding, forced cooling is performed from either one of a pair of molds, and heat transfer is cooled in the optical axis direction from the forcedly cooled mold, so that the maximum temperature of the glass material becomes less than its transition point. This is a method for molding a glass material that is released at a point in time.

According to the present invention according to the above method, by performing forced cooling from either one of the pair of molds immediately after the pressure molding, the heat of the heated glass material is brought into contact with the cooled side of the mold. More people are taken away. Therefore, the glass material contracts and solidifies while being cooled sequentially while generating a temperature gradient from the side of the forced cooling, that is, gradually contracts and solidifies in the optical axis direction. In this state, the mold temperature is maintained near the transition point, and immediately after pressing, the inside is initially hotter than the surface due to the rapid removal of heat from the heated glass material. . However, in this state, the temperature near the surface is still higher than the transition point. That is, since it is in a state where it can flow sufficiently, it is a state where it can follow the pressing action of the mold.

In a state where the temperature is maintained at or above the above-mentioned transition point, heat is taken away from one surface (forced cooling type) by forced cooling, and the temperature of the glass material is brought into contact with the mold to be cooled and the surface in contact with the mold without internal cooling. In this order.

When the temperature inside the glass material falls below the transition point as described above, the surface of the mold that does not necessarily perform forced cooling is in the state above the transition point and shrinks until the inside falls below the transition point and solidifies. Is in a state capable of following the flow. In this case, if the vicinity of the surface of the glass material in contact with the mold on which cooling is not performed becomes less than or equal to the transition point before the inside, there is no flow-followable portion corresponding to the shrinkage inside, The shrinking force acts as a force for forcibly changing the shape near the solidified surface, and the surface is formed as sink marks. Therefore, the present invention has been made in view of preventing the occurrence of sink marks due to such a state. Hereinafter, description will be made based on embodiments.

〔Example〕

FIG. 1 is a side view showing an outline of a lens forming apparatus according to the optical element forming method of the present invention.

FIG. 2 is a graph showing a temperature state during molding according to the first embodiment of the present invention.

FIG. 3 is a graph showing a temperature state during molding according to a second embodiment of the present invention.

(First Embodiment) Reference numeral 1 shown in FIG. 1 denotes a lower mold 3 having the same shape as a cylindrical upper mold 2 for molding a glass material to be molded and configured to be vertically movable and having respective molding surfaces. Is a molding chamber that is disposed opposite to and accommodated.

The vicinity of the outer peripheral surface of the lower mold 3 of the molding chamber 1, arranged a plurality of cooling nozzles (ejection holes) 4 and 5 towards the opening so as to cool the lower mold 3 at N ₂ blow Have been.

The side wall of the forming chamber 1 is provided with an opening for carrying in and out the glass material 6 to be formed, and a heating coil 7 is provided in the opening, and a heating furnace 8 for heating the glass material 6 to be formed. Are connected.

A belt-shaped transfer arm 9 for transferring the glass material 6 to be formed into the forming chamber 1 is provided in the heating furnace 8 and the forming chamber 1 so as to be transferable. A hole is formed in the tip of the transfer arm 9, and a transfer tool 10 having the glass material 6 to be formed placed in the hole.
Is mounted and transported.

Next, the glass material 6 to be molded is
A molding method for molding is described.

The glass type of the glass material to be molded 6 in this embodiment is SK11
This is a bi-convex aspheric lens with a thickness of 2.5 mm and a diameter of φ15. A method for forming the glass material 6 having the glass type shape will be described. A glass material to be formed 6 previously formed into a shape approximate to a desired shape is placed on a transfer arm 9 via a transfer tool 10. The glass material to be molded 6 is transferred to the heating furnace 8 by the transfer arm 9. The heating furnace 8 is maintained at 750 ° C. in advance. The glass material to be molded 6 is conveyed into the heating furnace 8 and heated for 60 seconds to have a viscosity of 10 ⁶ to 10 ⁸ poise.

Next, the glass material to be molded 6 heated to a predetermined temperature is
It is transported between the upper mold 2 and the lower mold 3. The lath material 6 to be molded conveyed between the upper mold 2 and the lower mold 3 is held between the upper mold 2 and the lower mold 3 at a temperature near the transition point of the glass material 6 in advance. After being reached, as shown by an arrow in FIG. 1, the lower mold 3 is pressed and formed by movement, and at the same time, N ₂ blows are ejected from the nozzles 4 and 5 to be cooled by the lower mold 3.

The heat of the glass material to be molded 6 is taken away in the direction of the optical axis toward the lower mold 3 by the cooling of the N ₂ blow.

The upper surface temperature, the internal temperature, and the lower surface temperature measured during molding of the glass material 6 will be described with reference to FIG.

As shown in the figure, immediately after the glass material to be molded 6 is heated,
Although the upper surface temperature and the lower surface temperature are slightly higher than the internal temperature, the temperature of the glass material to be molded 6 decreases with the pressing, and the lower surface temperature decreases due to forced cooling by N ₂ blow from the lower mold 3 side. Is fast after a few seconds after the top surface temperature, internal temperature,
It can be seen that a temperature gradient occurs in the order of the lower surface temperature. The end of the pressing (after molding) is the time when the upper surface temperature, which is the highest temperature of the glass material 6 to be molded, has fallen below the transition point. At that time, the lower surface temperature and the internal temperature have fallen below the transition point and solidify. It is in the state where it was done. Therefore, the surface is not solidified, the internal high temperature is not generated, and the sink is not generated due to the internal shrinkage, so that good transferability can be obtained. Due to this forced cooling method, the time required for the temperature of the glass material to be formed 6 to be equal to or lower than the transition point in a state where the above-mentioned temperature gradient is generated is as follows:
It is several seconds to several tens of seconds, so that the pressing time can be greatly reduced and the molding cycle time can be reduced.

Further, the upper mold 2 and the lower mold 3 and the glass
Since the contact time with the mold can be shortened, the life of the mold can be improved.

Second Embodiment The configuration of a molding apparatus according to the present embodiment is the same as that of the first embodiment, and a description thereof will be omitted. Therefore, only the molding method will be described.

First, the glass type of the glass material to be molded 6 in this embodiment is
This is a BaLF3, biconvex aspherical lens with a diameter of 20 mm and a thickness of 3.8 mm. The glass material to be molded 6 is transferred by a transfer arm 9 via a transfer tool 10 to a heating furnace 8 previously held at 700 ° C. and heated.

The heated glass material 6 to be molded is conveyed between the upper mold 2 and the lower mold 3, and is pressed and formed by raising the lower mold 3. In the above case, the glass material 6 to be molded has a thickness of 3.
Because the thickness is as large as 8 mm, the temperatures of the upper mold 2 and the lower mold 3 are stored in advance at the transition point or higher. Nozzle simultaneously with press molding
N ₂ is discharged from 4 and 5 and cooled by the lower mold 3. Since the glass material to be molded 6 has a large medium thickness, the cooling effect of the forced cooling by N ₂ blow is slightly reduced, and during this time, the upper surface temperature becomes lower than the transition point due to the transfer of heat by the upper mold 2. In order to prevent solidification, it is necessary to raise the temperature of the upper mold 2 to be higher than the transition point.

Therefore, the heating temperature of the glass material to be molded 6 can be lowered, and the viscosity is set to 10 ^8.5 to 10 ¹¹ poise under the above conditions. Temperature of the lower mold 3 is likewise a temperature corresponding to a viscosity of 10 ^8.5 to 10 ¹¹ poise of the glass molding material 6 (or transition)
Is held in. Therefore, the glass material to be molded 6 does not solidify spontaneously after pressing, but is solidified by forced cooling. The above case shows a temperature change as shown in FIG. It can be seen that the cooling rates are such that the temperatures of the glass material to be molded 6, the upper mold 2 and the lower mold 3 are substantially equal. As a result, a lens having no sink marks can be formed.

Although the mold temperature of the upper mold 2 and the lower mold 3 immediately after molding is higher than the transition point, the mold is released when the maximum temperature of the glass material 6 to be molded falls below the transition point due to forced cooling. It does not cause adhesion of glass to the mold by the glass material to be molded 6 and the resulting load on the mold. As described above, from the state where the mold temperature and the temperature of the molding material 6 are equal to each other, the cooling with the temperature gradient generated immediately after the press molding makes it possible to mold large-diameter, medium-thick lenses and the like. come. Needless to say, the molding cycle time is shortened by shortening the press molding time by forced cooling, and the life of each of the molds 2 and 3 is extended.

Further, in this embodiment, the temperature of the glass material 6 to be initially formed is set to be equal to the temperature of each of the molds 2 and 3.
It is self-evident that the temperature of the molded glass material may be increased in the case of a lens or the like having a large deformation amount without being limited to this.

(Third Embodiment) In this embodiment, as in the second embodiment, the configuration of the molding apparatus is the same as that of the first embodiment, and a description thereof will be omitted. However, the material of the upper mold 2 and the lower mold 3 in the structure of the molding apparatus is metal in the first and second embodiments, but in this embodiment, the upper mold 2 is made of ceramic. The difference is that the lower mold 3 is formed of a C-BN sintered body.

First, the molding method of the glass material 6 to be molded in this embodiment is SF8, and a method of molding a plano-convex aspheric lens having a thickness of 2.8 mm and a thickness of φ14 is described. The glass material to be formed 6 is transferred by a transfer arm 9 via a transfer tool 10 into a heating furnace 8 preheated and held at 680 ° C., and is heated for 60 seconds to a poise of 10 ⁶ to 10 ⁸ poise. The heated glass material to be molded 6 is conveyed between the upper mold 2 and the lower mold 3 and
Is pressed by the rise of the pressure. The upper mold 2 is a ceramic mold. The lower mold 3 is formed of a C-BN sintered body. Since the lower mold 3 has better thermal conductivity than the upper mold 2, heat transfer occurs in the direction of the lower mold 3 only by molding pressure.

Since only the above-described heat transfer causes a state of solidification of the surface and a high internal temperature, the lower mold 3 is discharged from the nozzles 4 and 5 by discharging N _2.
To cool. In this case, since heat is transferred by the mold material, the flow rate of N ₂ may be small, and the mold temperature may not fluctuate due to cooling. Further, similarly to the above embodiments, there are effects such as shortening of a molding cycle time and improvement of a mold life.

〔The invention's effect〕

By performing the shrinkage of the molded glass material by a cooling method having a temperature gradient, it is possible to obtain good transferability without sink marks. In addition, since the cooling is performed by forced cooling, the press molding time can be shortened, and there is a great effect that the life of the mold can be improved by shortening the molding cycle time and the contact time between the mold and the molded glass.

[Brief description of the drawings]

FIG. 1 is a side view showing an outline of a lens forming apparatus according to an optical element forming method of the present invention. FIG. 2 is a graph showing a temperature state during molding according to the first embodiment of the present invention. FIG. 3 is a graph showing a temperature state during molding according to a second embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Molding room 2 ... Upper mold (upper mold) 3 ... Lower mold (lower mold) 4,5 ... Nozzle 6 ... Glass material to be molded 7 ... Heating coil 8 ... Heating furnace 9 ... ... Transport arm 10 ... Transport tool

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Bunji Akimoto 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd. (56) References JP-A-2-275722 (JP, A) 57-98645 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C03B 11/00, 11/12

Claims (2)

(57) [Claims] In a method for forming an optical element, wherein a glass material is heated and conveyed between a pair of dies, and pressed and formed, one of the dies is pressed during the step of simultaneously performing the pressing and cooling of the glass material. An optical element molding method, wherein forced cooling is performed to generate a temperature gradient in the optical axis direction from the cooled mold side, and cooling and pressing are performed until the temperature of the glass material falls below the transition point. . 2. A method of forming an optical element, comprising heating a glass material, transporting the glass material between a pair of dies, and press-forming, wherein the glass material is forcibly cooled from one of the pair of dies immediately after the press-forming. An optical element molding method, wherein the glass material is cooled from the cooled mold side, and the glass material is released when the temperature of the glass material becomes lower than its transition point.