JP2746454B2 - Optical element molding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming an optical element such as a glass lens or a prism. Particularly, the present invention relates to a method in which an optical glass material is heated and melted and press-molded with a molding die. The present invention relates to a molding method capable of molding an optical element having surface accuracy and surface roughness.

[Conventional technology]

Conventionally, in order to manufacture a lens, a prism, or the like, a method has been adopted in which a material is ground with a diamond grindstone or the like and then polished with cerium oxide or the like. However, the need for aspherical lenses and the like has increased, and it has become difficult to manufacture a large number of optical elements at low cost by the conventional method. Therefore, in recent years, a manufacturing method for producing an aspherical lens or the like by simply performing press molding using a mold has been proposed.

For example, in Japanese Patent Application Laid-Open No. 63-307130, a mold temperature of a molding die is maintained between a glass transition temperature and a temperature 110 ° C. lower than the glass transition temperature, and the molten glass is preformed by the preforming die. Thereafter, a method is disclosed in which a main molding die in which the mold temperature is maintained between the glass transition point temperature and a temperature lower by 50 ° C. than that temperature is used to perform the main molding on the glass after the preliminary molding. Further, in Japanese Patent Application Laid-Open No. 63-310735, glass is molded, and at the end of molding, the temperature difference between the mold and the molded article is kept within 20 ° C., and cooling is performed to the glass transition temperature. There is disclosed a method of obtaining a molded product by performing temporary cooling to be performed and then secondary cooling in which the molded product is accommodated in a mold and then cooled at a lower speed than the primary cooling to the lower limit temperature for removing strain.

[Problems to be solved by the invention]

However, in the molding method disclosed in Japanese Patent Application Laid-Open No. 63-307130, the temperature of the mold in the preforming step is near or below the glass transition point. It caused severe sink marks and heat shock applied to the glass, causing cracking.
On the other hand, in the molding method of JP-A-63-310735, after molding, the molded article is cooled to a glass transition temperature in a pressed state, and further cooled to a cooling distortion lower limit temperature, so that a molding cycle time becomes longer. Further, since the molding die is exposed to a high temperature for a long time, there is a problem that the life of the die is shortened.

Such problems have significantly reduced productivity and production efficiency.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an efficient method for molding an optical element which has a reduced cycle time while preventing a large amount of sinks and cracks.

[Means and actions for solving the problem]

In order to achieve the above object, the present invention provides a method for forming an optical element by heating and melting an optical glass and pressing to obtain an optical element, wherein the optical glass is heated and melted until its viscosity becomes 10 ² to 10 ³ poise. The molten glass is pre-press-molded in a pre-molding die maintained at a temperature corresponding to 10 ⁷ to 10 ⁹ poise with the viscosity of the optical glass, and the pre-formed glass has a viscosity of 10 ⁷ to 10 ⁸ poise. When the cooled glass has a viscosity of 10 ⁸ to 10 ⁹ poise, it is subjected to main press molding with a main mold maintained at a temperature corresponding to the viscosity of the optical glass of 10 ¹² to 10 ¹³ poise. With
Pressing was terminated after the molded glass was forcibly cooled to a temperature below the glass transition point.

In the present invention, the mold temperature of the molding die at the start of preforming is kept at a temperature corresponding to 10 ⁷ to 10 ⁹ poise in the viscosity of the optical glass. The reason for this is that, although the molten glass is pressed, sinks are likely to occur when the molten glass is press-formed, and cracks may occur due to a large heat shock. However, in the present invention, since forced cooling is performed by inert gas during molding, fusion hardly occurs. On the other hand, if the mold temperature of the mold is maintained above the above range, sink marks are less likely to occur than in the present invention, but the mold life is shortened due to the high temperature.

In addition, when the mold temperature of the main mold at the start of the main molding is kept at a temperature corresponding to 10 ¹² to 10 ¹³ poise in terms of the viscosity of the glass, if the temperature is kept below that, the glass after the preliminary molding is pressed. This is because sometimes the formed glass cannot be completely pushed out and a highly accurate surface shape cannot be obtained. On the other hand, if the mold temperature of the main mold is maintained above the above range, sink marks during cooling are large, and a highly accurate surface shape cannot be obtained.

Furthermore, in the preforming step, the viscosity of the molten glass is reduced.
The reason why the pressure is set to 10 ² to 10 ³ poise is that if press molding is performed from the viscosity or more, the difference from the mold temperature becomes large, so that fusion is likely to occur, and it cannot be suppressed even by forced cooling with an inert gas. . On the other hand, when press molding is performed from a viscosity of 10 ² to 10 ³ poise or less, fusion is difficult to occur, but it is not possible to push up to the preliminary shape in a short time molding, and the molding time is long, so holding the mold at high temperature and high pressure keeps the mold life. Is shortened.

In the main molding step, the viscosity of the molded glass is 10 ⁸
It was decided to press when the pressure reached ~ 10 ⁹ poise.Because the mold temperature of the preforming mold was equivalent to 10 ⁷ to 10 ⁹ poise, it was necessary to reheat in order to mold below the viscosity. This is because there is a possibility that the cycle time will not be shortened. On the other hand, if press molding is performed at a viscosity higher than the above, the glass viscosity is high, cracks occur, and an optical lens cannot be obtained.

FIGS. 1 (a) to 1 (e) are conceptual diagrams of a method for molding an optical element according to the present invention.

First, as shown in FIG. 1 (a), a predetermined amount of molten glass 3 flowing out of a movable molten glass outlet 2 is cut by a cutting shear 4 onto a vertically movable preforming lower mold 1. Let it fall. Reference numeral 5 denotes a body mold which is fitted to the upper end of the preform lower mold 1 so as to be freely attached, and is for taking out the glass (lens) after the preform and the main form. At this point, the molten glass 3 is heated and melted at a viscosity of 10 ² to 10 ³ poise.

The preforming lower mold 1 has a viscosity of 10%.
It is maintained at a temperature corresponding ⁷ 10 ⁹ poises.

Thereafter, as shown in FIG. 1 (b), the molten glass outflow port 2 and the like are moved, and the preform upper mold fixed to a movable upper mount (not shown) is placed above the preform lower mold 1. 6 is arranged coaxially. Here, the preforming upper mold 6
Is maintained at the same temperature as the lower preform 1.

Then, as shown in FIG.
Is raised and preformed, and cooled by an inert gas injection device (not shown), and the formed glass is
Forcible cooling is performed until the viscosity becomes 10 ⁷ to 10 ⁸ poise, and the preforming is completed.

Next, as shown in FIG. 1 (d), the body mold 5 and the preformed glass 8 are supported by the transfer arm 7, and the preformed lower mold 1 is lowered, so that the main forming lower The body mold 5 and the preformed glass 8 are transported between the mold 9 and the main molding upper mold 10. Then, the body mold 5 is set on the upper part of the main molding lower mold 9.

When the viscosity of the preformed glass 8 became 10 ⁸ to 10 ⁹ poise, as shown in FIG. 1 (e), it was maintained at a temperature corresponding to 10 ¹² to 10 ¹³ poise in the glass to be preformed. The main molding is performed by the upper and lower molds 9 and 10, and at the same time, cooling is performed by an inert gas jetting device (not shown), and forced cooling is performed until the main molding glass 11 has a viscosity of 10 ¹² to 10 ¹³ poise. Then, the main molding is completed, and when the temperature of the molded product becomes equal to or lower than the glass transition point, the entire molding is completed.

According to such a molding method, since the mold temperature at the time of the preliminary molding is high, heat shock is not applied when the molten glass 3 is press-molded, cracks are hardly generated, and sinks are suppressed to be extremely small. can do. Further, since the press molding can be performed in a short time, the life of the mold is extended.
Further, since reheating is not required between the preforming and the main forming, the cycle time can be reduced.

〔Example〕

(First Embodiment) FIG. 2 shows a molding apparatus used in the present embodiment. An upper base 12 movable in a direction perpendicular to a molding direction is provided on a preforming part capable of individually setting a temperature. The mold 13 and the main molding upper mold 14 are attached. A lower base 15 that can move in the same direction as the upper base 12 and can also move in the vertical direction is provided with a preforming lower mold 16 and a main forming upper mold 17 that can individually perform temperature setting. . 18 is both lower type 16,1
It is a torso that can be freely attached to the upper end of 7. Reference numeral 19 denotes a glass crucible for supplying the molten glass 20, and a cutting shear 21 for cutting the molten glass 20 into a predetermined amount is disposed near the lower end of the glass crucible 19. Reference numeral 22 denotes a transfer arm that mounts and transfers the body die 18, and 23 denotes a cooling jig.

The molding of the optical element was performed by the molding apparatus shown in FIG. First, the molten glass 20 of about 10 ³ poise melted by the glass crucible 19 was discharged, and cut by a cutting shear 21 into a predetermined amount. Cut the molten glass 20 is dropped onto the preforming lower mold 16 which is maintained at a temperature corresponding to 10 ⁷ to 10 ⁹ poise viscosity of the glass to be molded in advance. Thereafter, the upper base 12 was moved, and the preform upper and lower dies 13, 16 were coaxially arranged. Then, the lower base 15 was raised, and pre-press molding was performed by the pre-forming upper and lower dies 13 and 16 set at the same temperature, and N ₂ gas was ejected from the cooling jig 23 to perform forcible cooling to perform pre-forming. The glass was brought to a viscosity of 10 ⁷ to 10 ⁸ poise. After the pre-press molding, the glass is engaged and mounted on the copper mold 18 on the lower pre-mold 16 (see FIG. 1 (c)).

Next, the body die 18 is supported by the transfer arm 22 extending in a direction orthogonal to the upper and lower bases 12, 15, and the lower base 15 is lowered, and the main molding upper and lower dies 14, 17 are positioned coaxially with the body die 18. The upper and lower bases 12 and 15 were moved so that

At the time when the viscosity of the preformed glass becomes 10 ⁸ to 10 ⁹ poise, the main forming is performed by the main forming upper and lower molds 14 and 17 which are maintained at a temperature equivalent to 10 ¹² to 10 ¹³ with the viscosity of the glass to be formed in advance. , the cooling jig 23 by performing forced cooling by jetting N ₂ gas, the formed glass is cooled to a viscosity of 10 ¹² 10 ¹³ poise, and terminates the molded, shaped article continues to further cooled When the temperature reached below the glass transition point, the entire molding was completed. Thereafter, the lower base 15 was lowered, and the molded product (optical lens) was taken out by the transfer arm 22.

According to this embodiment, press molding can be performed in a short time without sink marks and cracks, and the life of the mold is prolonged. In particular, during preforming,
Burn the hot preforming die 13, 16 and the molten glass 20 is prevented by cooling with N ₂ gas.

In the molding apparatus shown in FIG.
Since the dies 13,14,16,17 are mounted on the dies, the transport accuracy of the dies 13,14,16,17 is determined only by the movement of the upper and lower bases 12,15. Can be obtained.

Second Embodiment FIG. 3 shows a molding apparatus used in the present embodiment, in which a glass crucible 19 and a cutting shear 21 are movably provided. Also, the lower base 15 can move up and down freely,
The upper base 12 is horizontally movable. In addition, the upper base 12
The upper mold revolver 24, which is rotatable by a motor (not shown), is fixed to the upper mold revolver 24, and the preform upper mold 13 and the main mold upper mold 14 are used according to the rotation. It is provided so that it can be converted. Similarly, a lower mold revolver 25 that is rotatable by a motor (not shown) is attached to the lower base 15, and the lower base 15 is rotated by the preform lower mold 16 fixed to the lower mold revolver 25. The lower mold 17 is provided so that it can be converted according to use.

Were subjected to molding of an optical element in such a molding apparatus, the viscosity of the glass to be molded, the cooling due the set temperature and the N ₂ gas of the mold 13, 14, 16, 17, similar to the first embodiment went. However, the operation of the constituent members is different from that of the first embodiment, and the different points will be described below.

That is, after cutting the molten glass 20, the glass crucible
The 19 and the cutting shear 21 move, the upper base 12 moves, and the preformed upper die 13 is positioned coaxially with the preformed lower die 16.
Then, the lower die 16 moves up, performs pre-press molding, and performs cooling.

After the completion of the pre-press forming, the body die 18 on which the pre-formed glass is mounted is taken out by the transfer arm 22, and the upper and lower revolvers 24, 25 are rotated by 90 degrees to change to the main forming dies 14, 17. Thereafter, the body die 18 is moved again by the transfer arm 22 and set on the upper part of the main molding lower die 17. Then, the lower base 15 is raised to perform the main molding, and to perform cooling. Thereafter, the molded product is taken out by the transfer arm 22.

In this embodiment, the same effects as in the first embodiment can be obtained. Further, according to the molding apparatus used in the present embodiment, the upper and lower bases 12, 15 can be made compact,
Even if two or more presses are required due to the properties of the optical glass, multistage molding can be performed without changing the size of the molding apparatus body by appropriately attaching a molding die to each of the revolvers 24 and 25.

(Third Embodiment) FIG. 4 shows a main part of a molding apparatus used in the present embodiment. The difference from the molding apparatus shown in FIG.
15 through the cooling jigs 26 and 27 respectively.
And the lower mold 17 is fixed, and the cooling jig in FIG.
23 is omitted.

The molding of the optical element by the molding apparatus having such a configuration is performed in the same manner as in the first embodiment. In particular, in this embodiment, the N ₂ gas is subjected to the pre-molding and the main molding according to each molding condition. can change the flow rate or pressure, a high pressure in a short time N ₂ gas during preforming, by a large amount set, can prevent fusion of the glass to the forming upper and lower dies 13 and 16, the low pressure during the molding, Setting a small amount can prevent sink marks.

[Effects of the Invention] As described above, according to the optical element molding method of the present invention, since the viscosity (temperature) of the glass to be molded and the mold temperature of the molding die are set under appropriate conditions, heat shock during molding can be reduced. In addition, cracks are unlikely to occur, and the occurrence of sinks can be suppressed, so that a highly accurate optical element can be obtained.
Further, the cycle time can be shortened, the work efficiency can be improved, and press molding can be performed in a short time, so that the mold life can be extended and the manufacturing cost can be reduced.

[Brief description of the drawings]

1 (a) to 1 (e) are longitudinal sectional views for respective steps conceptually showing a method for molding an optical element according to the present invention, and FIGS.
FIG. 3 and FIG. 4 are perspective views showing the molding apparatus used in the first, second and third embodiments of the present invention, respectively. 1,16… Preformed lower mold 3,20… Molten glass 6,13… Preformed upper mold 8 …… Preformed glass 9,17… Full molded lower mold 10,14… Full molded upper mold 11 …… Main mold upper mold 23,26,27 …… Cooling jig

Claims (1)

(57) [Claims] 1. A method for molding an optical element, wherein an optical glass is heated and melted and pressed to obtain an optical element, wherein the optical glass is heated and melted until its viscosity becomes 10 ² to 10 ³ poise. Pre-press molding with a pre-molding die held at a temperature equivalent to 10 ⁷ to 10 ⁹ poise with the viscosity of the optical glass, and forcibly cooling the pre-formed glass to a viscosity of 10 ⁷ to 10 ⁸ poise, 10 ⁸ cooled glass
When the viscosity reaches ~ 10 ⁹ poise, the viscosity of the optical glass is 1
0 ¹² to 10 ¹³ Positive pressure is applied to the main mold with the main mold maintained at a temperature equivalent to ¹³ poise, and the press is terminated after the molded glass is forcibly cooled to a temperature below the glass transition point. Optical element molding method.