JP2007284286A - Method for molding optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To mold a precise glass optical element by press molding. <P>SOLUTION: After the temperature of a lower mold 4 is adjusted to a temperature not higher than a glass transition temperature, then a softened glass lump 2 is dropped into the lower mold 4. The glass lump 2 is rapidly cooled by coming into contact with the lower mold 4 of the not higher than a glass transition temperature and departs from the lower mold 4. Consequently, a time for exposing the lower mold 4 to a high temperature is shortened while preventing glass from fusion-bonding to the lower mold 4. After the glass lump 2 is heated again on the lower mold 4, an upper mold 3 is lowered for press molding. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical element molding method for molding an optical element such as a glass lens by press molding.

  Conventionally, as disclosed in Patent Document 1, for example, a direct press molding method for directly molding molten glass into an optical element is known. However, since molding is performed while bringing high-temperature glass into contact with the mold for a relatively long time, the damage to the mold is increased, and the appearance of the optical element tends to deteriorate due to deterioration of the surface condition of the mold. . Furthermore, if the shape of the molded product is complicated, when the glass lump is received by the mold, gas may be caught between the glass lump and the mold, and a gas residue may be generated in the molded product. In addition, when the temperature of the mold that receives the glass lump is low, irregularities are formed on the surface of the glass lump, and a gas residue may be generated in the molded product.

Therefore, the process of creating a gob as a preform before molding a molded product is newly divided, and a method for molding high-temperature glass into a shape close to the molded product in a non-contact manner with a dedicated gob molding die is also performed. ing. However, since a mechanism for moving the gob from the dedicated gob mold to the precision molding mold is required, the apparatus configuration becomes complicated, and the gob temperature decreases during the movement, resulting in a longer cycle time. May arise. Furthermore, there is a problem that it is difficult to align the gob and the precision molding die.
Japanese Patent Publication No. 3-72016

  According to the above-described conventional technique, as described above, there is a risk that damage to the mold due to contact or defective gas residue of the molded product may occur in the process until press-molding the softened glass into an optical element. In addition, the method using the gob mold has problems such as the complexity of the positioning mechanism when the gob is transferred to the precision molding mold and the extension of the cycle time due to the decrease in the gob temperature during the transfer.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and reduces damage to the mold caused by the softened high-temperature glass, and also efficiently press-molds the optical element. An object of the present invention is to provide a method for forming an optical element that can be used.

The optical element molding method of the present invention is the optical element molding method for molding an optical element by press molding using an upper mold and a lower mold, wherein the softened glass lump is controlled at a temperature lower than the glass transition point. A cooling step of receiving and cooling with the lower die, and a reheating step of reheating the cooled glass lump on the lower die until the glass viscosity falls within the range of 10 ⁵ to 10 ¹¹ dPa · s. The reheated glass lump is press-molded by the upper mold and the lower mold.

  The softened glass lump is brought into contact with the lower mold whose temperature is controlled below the glass transition point, whereby the glass lump is rapidly cooled and instantaneously separated from the lower mold. As a result, the time during which the lower mold is exposed to a high temperature is shortened, so that the glass can be fused to the lower mold and the surface of the mold can be prevented from being rough.

  When the softened glass is dropped onto the lower mold, the glass lump that collides with the lower mold is deformed so as to follow the shape of the lower mold, so that the glass and the lower mold can be easily positioned.

  Thus, by utilizing the thermal shrinkage of the glass that occurs below the glass transition point, the glass is surely separated from the lower mold, so that the time during which the lower mold is exposed to high temperatures is shortened, and a high anti-fusion effect Thus, a highly accurate optical element can be manufactured at low cost.

  Further, by performing evacuation after the glass lump has been separated from the lower mold, the gas between the glass lump and the lower mold can be eliminated, and defective gas residues in the molded product can be prevented.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a process diagram schematically showing a method of molding an optical element according to an embodiment, and the melting furnace 1 is temperature-controlled so that the glass becomes equal to or higher than the liquidus temperature. The softened glass lump 2 is formed by dropping glass in the melting furnace 1 from a pipe extending from the melting furnace 1. In both the upper die 3 and the lower die 4 arranged in a pair in the upper and lower sides, diamond-like carbon (DLC) is formed on the press surface as a release film. The two dies 3 and 4 are precision molding dies, and the surface of the press surface of the dies is smooth to the level that the surface roughness of the pressed surface of the molded product satisfies the required value of the optical element. The heater 5 for heating the glass block 2 on the lower mold 4 may have any heat transfer mode such as conduction and radiation. The manufactured optical element 6 is made of glass such as SK12 (glass transition point Tg = 505 ° C.).

  The molding method of the optical element 6 is as follows.

  As shown in FIG. 1A, a softened glass lump 2 having a predetermined weight is dropped from a pipe extending from the melting furnace 1. When the positional relationship between the pipe and the lower mold is adjusted so that the center position deviation between the glass lump 2 and the lower mold 4 is 500 μm or less, the axial symmetry of the glass lump 2 that is a sphere due to surface tension is reduced. It can be cooled and hardened without breaking down. Thereby, a highly accurate molded product can be stably obtained especially in an axially symmetric lens.

  As shown in FIG. 1B, the dropped glass lump 2 collides with the lower mold 4, and an impact force is applied to the surface of the lower mold 4 by the kinetic energy that the glass lump 2 had. At the same time, the reaction force from the lower mold 4 acts on the glass lump 2. Due to the balance of these forces, the glass block 2 is pressed against the lower mold 4 and deformed to follow the shape of the surface of the lower mold 4. At this time, the surface temperature of the glass lump 2 is drastically lowered by controlling the temperature of the lower mold 4 that receives the dropped glass lump 2 to be equal to or lower than the glass transition point Tg and increasing the heat capacity of the lower mold 4. Can do.

  By such rapid cooling, the glass shrinks at the moment when the glass lump 2 comes into contact with the lower mold 4, and the glass lump 2 is separated from the lower mold 4 by this force. By separating them in this way, the interfacial reaction caused by the glass block 2 and the lower mold 4 coming into contact with each other at a high temperature for a long time is prevented. Further, by rapidly cooling the glass lump 2, volatilization of the glass components generated from the glass lump 2 is stopped, and damage to the surface of the lower mold 4 is prevented.

  As a result, the glass lump 2 was aligned with the lower mold 4 with high accuracy without fusing with the lower mold 4 and without deteriorating the roughness of the mold surface of the lower mold 4. It is placed on the lower mold 4 in a state.

In the step shown in FIG. 1C, the glass block 2 on the lower mold 4 is reheated by the heater 5 as it is without changing the positional relationship between the glass block 2 and the lower mold 4. Next, as shown in FIG. 1 (d), when the glass viscosity reaches, for example, 10 ⁹ dPa · s, the upper die 3 is lowered to perform press molding, and the glass lump 2 is placed on the press surface of the lower die 4. The glass is filled into the space between the upper mold 3 and the lower mold 4 by deforming while following.

  As shown in FIG. 1E, after the glass cooling step, the upper and lower molds 3 and 4 are separated as shown in FIG. 1F, and the molded optical element 6 is taken out. Before starting the next cycle, the temperature is adjusted until the temperature of the lower mold 4 reaches the set temperature.

  The optical element can be continuously formed by executing the cycle using the above steps as a repeating unit.

  FIG. 2 shows a temperature gradient for each step shown in FIGS. 1A to 1F in the above-described optical element molding method.

  In the first step shown in FIG. 1A, when the glass block is dropped, heat exchange with the atmosphere is performed, and the temperature of the glass block decreases relatively slowly. Here, the temperature of the lower mold is adjusted to a temperature 150 ° C. lower than the glass transition point Tg, for example. The temperature of the lower mold prevents excessive unevenness (PV value = 500 μm or more) from being formed on the glass surface due to rapid cooling from the lower mold, and the second step shown in FIG. The temperature at which the glass is surely separated from the lower mold.

  In the second step, the glass lump and the lower mold come into contact with each other, so that the heat of the glass lump instantaneously moves to the lower mold, and the temperature of the glass lump rapidly decreases, while the temperature of the lower mold rapidly To rise. At this time, if the heat capacity of the glass lump is set to be smaller than the heat capacity of the lower mold, the glass lump can be rapidly cooled, so that the effect of preventing fusion is increased.

  When the heat exchange caused by the contact between the glass block and the lower mold gradually approaches an equilibrium state, if the glass temperature becomes higher than the glass transition point Tg, the thermal stress that the glass tends to leave the lower mold is relaxed. . Therefore, it becomes impossible to separate the glass lump and the lower mold, and if there is a gas sealed between the glass lump and the lower mold, the gas residue is poor on the surface of the optical element that is a molded product after press molding. Can do. In order to prevent this, the temperature of the lower mold is adjusted so that the glass temperature is equal to or lower than the glass transition point Tg when approaching the above-mentioned equilibrium state, so that the glass is surely separated. For example, the temperature of the lower mold when the glass is separated from the lower mold is set to a temperature 110 ° C. lower than the glass transition point Tg.

In the third step shown in FIG. 1C, reheating with a heater is performed to increase the temperature of the glass block and the lower mold below the glass transition point Tg. The upper limit of the temperature to be raised corresponds to the glass viscosity at which the glass can be press deformed, and the lower limit corresponds to the glass viscosity at which the glass and the lower mold do not react in a short time. That is, the temperature is adjusted so that the glass viscosity is in the range of 10 ⁵ to 10 ¹¹ dPa · s.

  In the fourth step shown in FIG. 1 (d), the temperature of the glass and the lower mold is stabilized for a predetermined time, and press molding is performed.

  In the fifth step shown in FIG. 1 (e), the glass molded product is re-cooled to generate thermal stress due to the difference in thermal expansion coefficient between the upper and lower molds, and the glass molded product is released from the mold naturally. Like that.

  In the sixth step shown in FIG. 1 (f), the mold is opened and the temperature of the lower mold is adjusted to the set temperature of the first step of the next cycle while taking out the glass optical element as the molded product. To do. When the sixth step ends, the first step starts again.

  In this way, a high-quality optical element can be efficiently molded from the softened glass.

In this example, the temperature of the lower mold at the start of the second step shown in FIG. 2 was set to a temperature 200 ° C. or more lower than the glass transition point Tg, and the temperature of the glass lump was lowered more rapidly. In the third step, vacuuming is performed when the viscosity of the glass lump separated from the lower mold is 10 ¹⁵ dPa · s or more, and the gas between the unevenness of the separated glass lump and the lower mold is excluded. Then, reheating was continued and filling (press molding) in the fourth step was performed.

In this example, the temperature of the lower mold was set to a temperature 200 ° C. or more lower than the glass transition point Tg, so that vacuuming was performed even when the unevenness of the glass lump after separation in the second step became large. Thus, it was possible to press-mold a highly accurate optical element without generating a gas residue. In addition, if the glass viscosity is 10 ¹³ dPa · s or more when the vacuuming is performed, the separated glass will not be softened again due to its own weight deformation and will not adhere to the mold again, so that the same gas residue prevention effect can be obtained. .

In the third step of Example 1, the glass block was evacuated while being reheated by infrared rays from the lamp heater, and the gas between the unevenness of the separated glass block and the lower mold was excluded. Then, when the glass viscosity reached 10 ⁹ dPa · s in a vacuum state, press molding was performed to obtain an optical element.

  In this example, by performing reheating with infrared rays, even when evacuation was performed to prevent gas residue, the temperature raising time could be shortened, and the tact shortening effect was obtained. In addition, although heating was performed by infrared rays here, even if this is an electromagnetic wave having a wavelength of about a microwave, if the electromagnetic wave is in a band that is absorbed by the glass, the glass can be directly heated. An effect is obtained.

It is process drawing which shows the shaping | molding method of the optical element by one embodiment. It is a graph which shows the temperature change of the glass lump and lower mold | type in each process of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Melting furnace 2 Glass lump 3 Upper mold | type 4 Lower mold | type 5 Heater 6 Optical element

Claims (4)

In an optical element molding method in which an optical element is molded by press molding using an upper mold and a lower mold,
A cooling step of receiving and cooling the softened glass lump with the lower mold controlled to a temperature lower than the glass transition point;
A reheating step of reheating the cooled glass lump on the lower mold until the glass viscosity is in the range of 10 ⁵ to 10 ¹¹ dPa · s,
A method of molding an optical element, wherein the reheated glass block is press-molded by the upper mold and the lower mold.   The method for molding an optical element according to claim 1, wherein in the cooling step, the softened glass lump is dropped from above the lower mold.   3. The method for molding an optical element according to claim 1, wherein, in the cooling step, the glass block is separated from the lower mold by being contracted by cooling. The method for molding an optical element according to claim 3, wherein, in the cooling or reheating step, when the glass viscosity of the glass block is 10 ¹³ dPa · s or more, the periphery of the lower mold is evacuated.

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