JPH11116254A - Device for forming optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the internal stress due to nonuniformity of heat distribution within the optical material from being caused and to appropriately perform the forming, at the time of forming an optical material into an optical element by pressing the heated and softened optical material to form a body and thereafter cooling the formed body. SOLUTION: In this device, at the time of forming a heated optical material 19 placed within a cylindrical sleeve 8 with a pair of forming molds 6 and 7, the sleeve 8 is formed so that it consists of at least two sections, having different infrared ray absorptivity from each other, and the whole outer peripheral surface of the sleeve 8 is irradiated with infrared lamps 14 to heat the optical material 19 placed within the sleeve 8. Since the sleeve 8 has these sections, a temp. difference between the forming molds 6 and 7 is caused to reduce the nonuniformity of heat distribution within the optical material 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element molding apparatus for molding an optical element by pressing a heat-softened optical material in a sleeve.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 62-59539 describes a conventional method for molding an optical element by inserting an upper mold and a lower mold into a sleeve. In this method, the optical material provided in the sleeve is heated by heat radiation, and a halogen lamp for that purpose is arranged outside the sleeve.

[0003] A reflection plate is attached to the halogen lamp, and heat rays from the halogen lamp are reflected by the reflection plate and condensed on an optical material insertion portion in the sleeve. As a result, the optical material is heated and softened with less heat energy, and the upper and lower dies are at a lower temperature than the optical material in the heated and softened state. Therefore, in the subsequent pressure molding by the upper mold and the lower mold, generation of bubbles on the surface of the optical material in contact with the mold can be prevented.

[0004]

Incidentally, in optical elements such as lenses, the radii of curvature of two optical surfaces may be extremely different. When such an optical element is molded, the volume of the optical material that fills the space formed by the molding surface of the mold having a small radius of curvature is more extreme than that formed by the molding surface of the mold having a large radius of curvature. Become larger. When the above-described conventional heat radiation is applied to this molding, a large difference occurs in the heat capacity stored on the molding surface to be molded.

When the molded optical element is cooled from a state where the mold is heated to a uniform temperature with the mold, the heat transfer from the molding surfaces is substantially the same on both molding surfaces, so that the heat capacity is large (the radius of curvature is small). The cooling of the molding surface on the molding die side is delayed from the molding surface of the other molding die, and the heat distribution differs between the two molding surfaces. Due to this difference in heat distribution, an internal stress is generated in the optical element, and there is a problem that defective quality such as cracking of the molding surface occurs.

The present invention has been made in view of such conventional problems. In molding an optical element using a sleeve, molding can be performed without generating internal stress, thereby achieving good quality. It is an object of the present invention to provide an optical element molding apparatus capable of molding the above optical element.

[0007]

According to a first aspect of the present invention, there is provided an optical element molding apparatus for molding an optical material heated in a cylindrical sleeve with a pair of molds. The outer peripheral surface of the sleeve is formed so as to have at least two different infrared absorptances, and infrared irradiating means for irradiating the outer peripheral surface of the sleeve with infrared light to heat the internal optical material is provided outside the sleeve. It is characterized by being arranged.

In the present invention, the optical material in the sleeve is heated by irradiating infrared rays from the infrared irradiation means toward the outer peripheral surface of the sleeve. At this time, since the outer peripheral surface of the sleeve has at least two different absorptivity of infrared rays, a temperature difference is formed between a pair of molds arranged in the sleeve. Then, since the optical material heated in the sleeve is molded by a pair of molding dies having a temperature difference, molding can be performed without generating internal stress even if the optical elements have different curvatures.

According to a second aspect of the present invention, there is provided the first aspect of the present invention, wherein a limiting portion for limiting a heat transfer amount is provided at a boundary portion of the sleeve at which the infrared ray absorptivity is different. I do.

According to the present invention, since the restricting portion restricts the transfer of heat, the temperature difference between the molds is maintained for a long time. For this reason, internal stress does not occur even when molding an optical element that requires a long time for molding.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 shows a molding apparatus according to Embodiment 1 of the present invention, in which a mold 2, a moving table 3, a fixed table 23, a molding chamber 5, a driving unit 13, a heating device 4 and the like. And

The mold 2 comprises an upper mold 6, a lower mold 7, and a sleeve 8 into which the upper mold 6 and the lower mold 7 are slidably inserted, all of which are formed of tungsten carbide (WC). The molding surface 9 of the upper die 6 is the molding surface 2 of the lower die 7
It has a spherical shape whose curvature radius is extremely small as compared with zero. A thermocouple 10 for measuring the temperature of each of the dies 6 and 7 is inserted into the center of the upper and lower dies 6 and 7.

The sleeve 8 has a cylindrical shape. The sleeve 7 has an inner diameter that matches the axis of the upper and lower dies 6, 7, and the upper and lower dies 6, 7 are fitted without any gap. The outer peripheral surface of the upper half of the sleeve 8 corresponding to the upper die 6 is mirror-finished, and is subjected to a surface treatment 11 having a low infrared absorptance (hereinafter referred to as an emissivity). The surface treatment 11 is performed by coating or plating of a metal such as gold. The emissivity of gold is about 0.018. On the other hand, the outer peripheral surface of the lower half of the sleeve 8 corresponding to the lower mold 7 remains a material and is in a surface state of a ground surface, and the emissivity is about 0.2.

The moving table 3 is connected to the upper end of a main shaft 24 extending upward from the driving section 13 by screws 25.
The main shaft 24 moves up and down with respect to the molding chamber 5 by the vertical movement.
The upper end surface of the movable base 3 serves as an installation part 12 for installing the lower mold 7 and the sleeve 8.

The fixing table 23 has a screw 2
6, the lower surface of which is fixed by the upper die 6 and the sleeve 8
The contact surface 16 is in contact with the upper end surface of the contact.

The driving unit 13 includes a cylinder (not shown),
A drive source such as a motor and a guide are provided, and the main shaft 24 is moved up and down by these. Then, the movable base 3 is moved up and down by the vertical movement of the main shaft 24 to put the mold 2 in and out of the molding chamber 5, and a pressing force is applied to the upper die 6 by the upward movement of the main shaft 24.

The heating device 4 includes an infrared lamp 14 and a reflection plate 15. The infrared lamp 14 constitutes infrared irradiation means, is formed in a ring shape concentric with the sleeve 8, and is disposed outside the sleeve 7. In this embodiment, four infrared lamps 14 are arranged at an interval along the axial direction of the sleeve 7, and the two upper infrared lamps 14 face the upper die 6 and the lower two The infrared lamp 14 of the book faces the lower die 7. These infrared lamps 14 are mounted inside the molding chamber 5 by metal fittings not shown.

The reflecting plate 15 is formed by forming the inner surface of the molding chamber 5 corresponding to the infrared lamp 14 into a concave shape in a curved shape. By such molding, the reflecting plate 15 can uniformly reflect the infrared rays emitted from the infrared lamp 14 to the outer peripheral surface of the sleeve 8.

The molding chamber 5 is supported on an upper part of a gantry 22, and includes a heating device 4, a movable pedestal 3, a fixed pedestal 23, a mold 2
And are arranged inside. In the lower part of the molding chamber 5, an inert gas suction nozzle 17 and an air or gas discharge nozzle 1 are provided.
8 is inserted, and the inside becomes a non-oxidizing atmosphere when an inert gas is introduced from the suction nozzle 17.
The discharge nozzle 18 is formed to have a smaller diameter than the suction nozzle 17.

Next, molding of an optical element using this embodiment will be described. As the optical material 19, a glass material having a transition point of 381 ° C. and a sag point of 404 ° C. is used.

The upper mold 6, the optical material 19 and the lower mold 7 are inserted into the sleeve 7, and these are placed on the installation section 12 of the movable base 3. Then, the main shaft 24 is raised to seal the molding chamber 5. At this time, no pressing force is applied between the upper and lower dies 6 and 7. Then, an inert gas is introduced into the molding chamber 5 from the suction nozzle 17, and at the same time, the internal air is exhausted from the discharge nozzle 18, whereby the inside of the molding chamber 5 is set to an inert gas atmosphere.

Thereafter, the drive unit 13 is driven to drive the spindle 24
Is further raised to apply a pressing force between the upper and lower dies 6 and 7 and to cause the infrared lamp 14 to emit light.
Due to this light emission, the outer periphery of the sleeve 8 is uniformly irradiated with infrared rays and heated. In the heating, the outer surface of the upper half of the sleeve 8 is subjected to the surface treatment 11, and reflects the irradiated infrared rays. Therefore, the temperature rise at the upper part of the sleeve 8 is slower than that at the lower part of the sleeve 8. That is, the degree of temperature rise of the upper and lower dies 6 and 7 whose temperature rises due to heat conduction from the sleeve 8 is slower in the upper die 6 than in the lower die 7.

FIG. 2 shows the heating characteristic of heating by this infrared irradiation and the cooling characteristic of cooling after that. The heating device 4 is controlled so that the lower mold 7 rises to the deformation point temperature of 404 ° C., and after holding for 20 seconds or more, the emission of infrared rays is stopped, and the process proceeds to the cooling step.

At the time of completion of molding, a temperature gradient (distribution) is generated between the upper and lower dies 6 and 7, and the temperature of the upper die 6 is reduced to the lower die 7 at the center of the die into which the thermocouple 10 is inserted. On the other hand, the temperature is lower by about 30 ° C. Although the temperature of the optical material 19 is slightly different between the upper and lower molding surfaces 9 and 20, it is approximately 390 ° C. due to its small thickness.

In the cooling step, since the temperature of the upper mold 6 is relatively lower than that of the lower mold 7, the heat transferred from the molding surface 9 having a small radius of curvature to the upper mold 6 is transmitted from the molding surface 20 having a large radius of curvature. It becomes relatively large compared to the heat transferred to the lower mold 7. For this reason, the heat distribution inside the optical material 19 generated in the cooling step of molding the optical element can be reduced. After the cooling step is completed, when the temperature of the mold 2 has dropped to near normal temperature, the mold 2 and the molded optical element are taken out of the molding chamber 5 and molding is completed.

In such an embodiment, when forming an optical element having a large difference in radius of curvature and having a temperature distribution easily formed on the upper and lower surfaces of the optical element during cooling, the upper and lower dies 6 and 7 are formed. A temperature difference can be easily provided. Therefore, the heat distribution of the entire optical element is reduced, and an optical element of good quality can be formed without generating internal stress.

(Embodiment 2) FIG. 3 shows a mold 2 according to Embodiment 2 of the present invention, and the same elements as those in Embodiment 1 are assigned the same reference numerals. Also in this embodiment, the upper die 6, the lower die 7, and the sleeve 8 are formed of tungsten carbide, and the outer peripheral surface of the upper half of the sleeve 8 is subjected to a surface treatment 11. The length (width) is set at approximately half the length of the sleeve 8 in the length direction.
A groove 21 is formed in the circumferential direction as a limiting portion of L and depth D.

In this embodiment, as in the first embodiment, the infrared lamp 14 emits light, so that the outer peripheral surface of the sleeve 8 is uniformly irradiated with infrared rays. Sleeve 8
Since the surface treatment 11 is performed on the outer peripheral surface of the upper half of the sleeve 8, the amount of infrared absorption in the upper half of the sleeve 8 decreases as in the first embodiment, and the temperature rise of the upper mold 6 is lower than that of the lower mold 7. Become slow. In this embodiment, a groove 21 is formed in the sleeve 8, and the groove 21 narrows the path of heat transfer between the upper and lower dies 6, 7, so that the temperature difference between the upper and lower dies 6, 7 is maintained for a long time. be able to.

In such an embodiment, the first embodiment
In addition to the same operation as above, the function of limiting the amount of heat transfer is added to the sleeve 8 to extend the time during which the temperature difference is reduced, so that the temperature difference between the upper and lower dies 6 and 7 is maintained for a long time. Can be done. For this reason, it is possible to suitably mold an optical element having a large diameter and a large wall thickness, which requires time for molding.

In the above embodiment, the upper and lower molds 6 and 7 are inserted into the sleeve 8, and the outer periphery of the sleeve 8 is uniformly irradiated with infrared rays from the infrared lamp 14, so that the optical material 19 and the mold 2 are
When heating is performed, the upper and lower molds that are heated by heat conduction from the sleeve 8 change the absorptivity of infrared rays on the outer periphery of the sleeve 8 to thereby cause a difference in the amount of heat absorbed by the sleeve 8 depending on the location. It is possible to provide a temperature difference between 6 and 7. As a result, heat transferred from the side having a small radius of curvature, that is, the large space formed by the molding surface to the molds 6, 7 from the side having a large volume filled with the optical material is relatively faster than that of the side having the large radius of curvature. By doing
In other words, by lowering the temperature of a mold having a small radius of curvature as low as possible within the moldable range to increase the temperature difference between the optical material and the mold and thereby speeding up the heat transfer, an optical element generated in the cooling step of molding the optical element can be formed. It is possible to reduce the heat distribution inside the element.

From the above specific embodiments, the technical idea of the following configuration is derived in the present invention.

(1) A pair of dies are inserted from upper and lower openings of a cylindrical sleeve, and the pair of dies and the sleeve are heated by infrared heating to heat the optical material disposed between the pair of dies. A heating device for a molding die for softening and pressing, comprising a sleeve having at least two kinds of different absorptivity of infrared rays on an outer peripheral surface thereof, and an infrared lamp for irradiating the sleeve with infrared rays and heating the sleeve. Heating device for optical elements.

In this apparatus, since a temperature difference can be generated between the upper and lower dies, the temperature of the mold having a small radius of curvature is lower than that of the upper mold and the lower mold, thereby reducing the radius of curvature, that is, the molding surface. The heat which moves to the mold from the side having a large space formed by the optical material and having a large volume filled with the optical material can be made relatively faster than that of the side having a large radius of curvature. That is, by setting the temperature of the mold having a small radius of curvature lower than that of the other mold within the moldable range, the temperature difference between the optical element and the mold can be increased, and heat transfer can be accelerated. For this reason, the heat distribution inside the optical element generated in the cooling step of optical element molding can be reduced, and an optical element of good quality can be molded.

[0034]

As described above, according to the first aspect of the present invention, the heat distribution inside the optical element at the time of molding can be reduced, so that the optical element of good quality without cracking. Can be molded.

According to the second aspect of the present invention, since the restricting portion provided on the sleeve restricts the transfer of heat, the temperature difference between the molds is maintained for a long time, and the molding of the optical element requiring a long time for the molding is performed. In this case, no internal stress is generated.

[Brief description of the drawings]

FIG. 1 is an overall sectional view of Embodiment 1 of the present invention.

FIG. 2 is a characteristic diagram of heating and cooling when molding according to the first embodiment.

FIG. 3 is a sectional view of a mold according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molding apparatus 4 Heating apparatus 6 Upper die 7 Lower die 8 Sleeve 14 Infrared lamp 15 Reflector 19 Optical material

Claims (2)

[Claims] 1. An optical element molding apparatus for molding an optical material heated in a cylindrical sleeve with a pair of molding dies, wherein an outer peripheral surface of the sleeve has at least two different infrared absorptivity. An optical element molding apparatus, wherein an infrared irradiating means, which is formed and irradiates an outer peripheral surface of the sleeve with infrared rays to heat an internal optical material, is disposed outside the sleeve. 2. A molding device for an optical element according to claim 1, wherein a limiter for restricting the amount of heat transfer is provided at a boundary portion of the sleeve where infrared ray absorptivity is different.