JP2004231477A - Method and apparatus for molding optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for molding an optical element which can especially mold a small optical element with a high precision in a short cycle. <P>SOLUTION: The method has a step wherein at least the surface temperature of a glass material is cooled in a rate of change calculated by dividing the total temperature variation by the temperature changing time of ≥3°C/sec during a step wherein the glass material is cooled at least to the glass transition point (Tg) after pressing. Provided that the molding temperature is e.g. 30°C higher than the glass transition point (Tg), the method enables annealing of the glass material within about 10 sec , which realizes a molding cycle of within 1 min. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and apparatus for molding an optical element, and more particularly, to a method and apparatus for molding an optical element suitable for molding a small optical element.
[0002]
[Prior art]
The heat-softened glass material is pressed (for example, pressed between upper and lower dies, also called a press) by a molding die (hereinafter, also referred to as a die) to be cooled and solidified. An optical surface can be formed by molding and transferring the transfer optical surface shape and surface roughness of the mold to an optical material, thereby efficiently producing an optical element. For example, Patent Document 1 below discloses that a glass preform (a glass molding intermediate having a cross section close to a molded product having a circular or elliptical shape) has a viscosity of about 10₈-10₁₀The mold cavity and the glass preform are preheated to a temperature such that they become poise, and the glass preform is pressed in the mold cavity within the temperature range of the preheating, and the viscosity of the glass becomes about 10₁₁-10₁₂Exposing the mold cavity and the glass preform to a second temperature such as poise, pressing the glass preform under isothermal conditions in the mold cavity while placing the glass preform and the mold cavity at the second temperature. A glass lens molding method is disclosed which comprises removing a lens from a mold cavity. Further, Patent Document 2 below discloses a technique in which a mold is heated at a temperature lower than that of a glass material to prevent the heat-softened glass material from sticking to the mold and to eliminate warpage. . In addition, 10^4.6There has also been disclosed a technique of forming a preform by placing it in a mold from a low viscosity state of poise or less and rapidly cooling and molding it.
[Patent Document 1]
JP-A-6-215528
[Patent Document 2]
JP-A-4-338120
[Patent Document 3]
JP-A-7-29781
[0003]
[Problems to be solved by the invention]
By the way, a glass lens used for a conventional optical device has a relatively large diameter, and therefore, it is common to heat and soften a glass material having a certain large volume and mold it with a mold. On the other hand, in recent years, for example, an imaging lens of a micro camera mounted on a cellular phone or the like has a volume of 10 mm.³In a pickup lens or the like used for recording / reproduction of an optical disk or the like, the center radius of curvature of the aspherical optical surface is as extremely small as 2 mm or less, and the miniaturization of an optical element is rapidly progressing. As described above, in order to form a glass optical element such as a minute glass lens and a glass prism, it is necessary to use a preform of a small volume of glass material.However, such a small volume of glass material is heated and softened, In embossing and cooling, it is necessary to handle the glass material differently from a large volume glass material.
[0004]
For example, according to the technique described in Patent Literature 1, molding is performed while the viscosity of a preform of a glass material is high. Therefore, since the material is still hard, it is necessary to perform molding with constant pressure and a long time. Therefore, the time for heating and cooling can be shortened. However, since the viscosity of the glass material is high, it is necessary to take enough time for embossing in order to perform high-precision molding without distortion. It is not always advantageous in terms of time reduction.
[0005]
Further, according to the technique described in Patent Document 2, the mold releasability between the mold and the glass material can be increased in a short time by using a technique of making the temperature of the mold and the glass material different, but the lens is small. As the heat of the mold is instantaneously transmitted to the glass material, there is a problem that it cannot be applied to molding of a small-diameter glass lens with precise temperature control. According to the technology described in Patent Document 3, molten glass is heated to a high temperature,^4.6Although it is placed in a mold from a low viscosity state of poise or less and rapidly cooled and molded, there is a drawback that large sink occurs.
[0006]
The present invention has been made in view of such a problem, and an object of the present invention is to provide an optical element molding method and an molding apparatus that can mold a small optical element with high accuracy and in a short cycle.
[0007]
[Means for Solving the Problems]
The volume of the optical element molding method according to claim 1 is 10 mm.³The following glass material is heated and softened, and has a viscosity of 10 using a mold so as to obtain an optical element having a desired shape.⁷An optical element molding method for embossing with poise or more,
In the step of cooling from the embossing temperature to the glass transition point (Tg), a value obtained by dividing a temperature change amount by a total temperature change time of the surface temperature of the glass material is 3 ° C./sec or more. And
[0008]
According to the research results of the inventor, the volume is 10 mm₃The following glass materials can raise their surface temperature from room temperature to 500 ° C. within at least 10 seconds, can be cooled quickly, and hardly break even if the temperature is rapidly raised and cooled in such a manner. It turned out that there was a characteristic. It was also found that low-melting glass materials (materials) were flat and had very few sink marks. Here, the optical element made of glass is generally more expensive than the optical element made of plastic. This is because the molding process takes a long time. On the other hand, the optical element made of glass can be manufactured at lower cost by, for example, keeping the molding time within 1 minute.
[0009]
Furthermore, the volume is 10mm₃The following glass materials enable rapid heating and cooling with a small amount of heat transfer. Utilizing this characteristic, the volume is 10mm₃By using the following glass materials, molding can be performed in a short cycle time. On the other hand, some direct molding methods use³Melted below poise and above glass softening point 10^{4 . 6}There is a molding method in which embossing is started from near the poise, and the mixture is rapidly cooled and molded. However, sink marks of about 10 μm are generated, which is not suitable for molding a high-precision optical component. In order to enable high-precision molding with little sink, for example, a small-diameter optical element is set to a temperature and a viscosity near the softening point by 10%.^7.5It is preferable to start embossing near the poise. In both the direct molding method and the repeat press molding method in which the preform is reheated, the embossing is carried out at a softening point of 10.^7.5It is good to start near. On the other hand, it takes the longest time in this high-precision molding for a normal large glass part.^7.5Although the process is usually a process of lowering the temperature from the temperature at the time of molding to a glass transition point near the temperature, the present invention relates to a process of cooling a heated and molten glass material to at least a glass transition point (Tg) after embossing. And a step of cooling at a high rate of change of at least the surface temperature at which the total temperature change is divided by the temperature change time at 3 ° C./sec or more. Molding while maintaining high accuracy by this method can be realized in a small-diameter lens. Here, the “total temperature change amount” is the temperature from the temperature at which the temperature starts to change in one direction of cooling or heating in one process such as heating, pressing, and cooling to the end of the change in the process. Defined as width. In addition, the term “temperature change time” is defined here as a time width from the time when the change in one direction of cooling or heating starts to the end of the change in the process. If the cooling is started from the start of the pressing, the calculation is performed including that from the time. For example, assuming that there is a glass material having a transition point temperature of 500 ° C. and a softening point of 570 ° C., the preform is heated from room temperature to 600 ° C. in 10 seconds, and after 5 seconds, cooled to 570 ° C. near the softening point at the start of embossing. Assuming that the annealing process was started at 570 ° C. during the embossing, the temperature began to decrease and then decreased at a constant rate, and finally the annealing process to the glass transition point of 500 ° C. was decreased 25 seconds after the start. . The temperature change of 70 ° C. from the time of the stamping is defined as the total temperature change. The time 25 seconds is defined as a temperature change time. “Embossing temperature” refers to, for example, the temperature at which embossing can be performed with a molding die, and differs depending on the material. As another example, assuming that the speed of the above-mentioned temperature change is 70 ° C. from the embossing temperature to the glass transition point (Tg), according to the present invention, slow cooling can be performed in about 23 seconds. If the slow cooling step can be performed in 23 seconds, a molding cycle time within 1 minute can be realized.
[0010]
The volume of the optical element molding method according to claim 2 is 10 mm.³A glass material having the following optical surface is heated and softened, and has a viscosity of 10 using a mold so as to obtain an optical element having a desired shape.⁷An optical element molding method for embossing with poise or more,
A first step of heating the glass material to an embossing temperature, a second step of pressing the glass material with the mold, and a third step of cooling the glass material to a temperature at which the glass material is removed from the mold. In the third step, a value obtained by dividing a temperature change amount of a surface temperature of the glass material by a total temperature change time is 30 ° C./sec or more. However, as in the case described above, when cooling is performed from the start of pressing, the calculated value from that point is used.
[0011]
An optical element molding method including a step of changing the temperature at a rate of change faster than the invention according to claim 1, that is, a value obtained by dividing the total temperature change amount by the temperature change time of the surface temperature at 30 ° C./sec or more. explain. Volume is 10mm₃The present inventors have found that the following glass materials are hardly broken even when the temperature is changed at a rate of change of 30 ° C./sec or more, and the sink is small. By utilizing such characteristics, it becomes possible to remove surface defects of the optical surface.
[0012]
For example, when there is a defect such as sink marks, when heating and pressing once, and then reheating and correcting a cooled glass material (here, a glass material), heating is rapidly performed at a rate of change of 30 ° C./sec or more. Then, only at least the surface layer (that is, the optical surface) is softened. However, since the sink correction is sufficient by applying pressure to the surface layer, there is an advantage that the sink correction can be quickly performed. If the volume is smaller, the whole may change. That is, in the optical element molding method according to the second aspect, the temperature of the glass material is raised beyond the glass transition point (Tg) by, for example, heat transfer from the upper and lower molds constituting the molding die, and the mold is pressed. First, the glass material is manufactured by lowering the temperature of the upper and lower molds. Then, only the formed optical surface is heated at a rate of change of 30 ° C./sec or more, and the pressure is quickly applied for sink correction. Then, the glass material is cooled rapidly at a rate of change of 30 ° C./sec or more so as to fall below the glass transition point (Tg), whereby the glass material can be stabilized. In the case of a small-diameter lens, when a small distance from the surface cools and becomes equal to or less than the glass transition point (Tg), the surface shape is determined. It is not necessary to slowly cool the whole, and rapid cooling is possible. If the rate of change is 30 ° C./sec or more, heating from room temperature to 500 ° C. and cooling from 500 ° C. to room temperature can be performed in 18 seconds each. However, in practice, both heating and cooling can be performed at 100 ° C./sec by contact with the mold. Thereby, it can be achieved from room temperature to 500 ° C. in 5 seconds and from 500 ° C. to room temperature in 5 seconds. With these methods, it is easier to mold the optical element with a cycle time of one minute or less.
[0013]
In the optical element molding method according to the third aspect, in the invention according to the second aspect, in addition to the third step, in the first step, a temperature change amount of a surface temperature of the glass material is calculated by a total temperature change time. Characterized in that the value divided by is not less than 30 ° C./sec. According to such a feature, the volume is 10 mm₃If it is a glass material of the following small volume, it can be heated and cooled quickly with little distortion, but especially in the so-called reheat molding, in which molding is performed from a preform with a small amount of crushing, only the surface necessary for crushing is softened. Therefore, high-speed molding can be performed.
[0014]
The conventional optical element molding method targets an optical element larger than the optical element described here, and a short cycle time often causes large sink marks. Therefore, in order to avoid this, the glass material is pressed slowly (embossing) over a relatively long time in a slightly hard state. On the other hand, the volume is 10 mm₃The following small-diameter glass materials have a small heat capacity, and thus have characteristics such as a very easy temperature change, a difficulty in breaking even if a sudden temperature change occurs, and a small absolute value of sink mark. Therefore, there are few disadvantages due to pressing in a state where the viscosity of the glass material is lower than before, and the advantage that heating, slow cooling, and cooling can be performed quickly is effective. For example, an optical element is molded with a cycle time of 1 minute or less. be able to.
[0015]
When the glass preform is a sphere, the volume is 10mm₃Gives a sphere with a radius of about 1.34 mm. In experiments conducted by the present inventors, it was found that heating a sphere having a diameter of 2.7 mm can raise the surface temperature from room temperature to 500 ° C. within at least 10 seconds from the start of heating. This means that the volume is 10mm₃The possibility of realizing a high-speed series of processes for rapidly heating, forming, and rapidly cooling the following small-diameter glass materials is shown.
[0016]
In another experiment conducted by the present inventors, it was found that when high-temperature air was blown onto a glass sphere having a diameter of 1 mm at a high speed, the temperature at least near the surface became equal to the temperature of the air in a few seconds. . Further, when a small-diameter glass material is in contact with a solid, the temperature of the contact point becomes almost equal to that of the solid within a short time. In other words, since the small-diameter glass material has a small heat capacity, the temperature of the mold is not affected by the glass material, and the upper and lower molds are heated with the small-diameter glass material interposed therebetween. In this case, it can be said that the temperature of the glass material can be quickly made equal to the mold temperature, and the temperature control is easy. Also, it can be said that the temperature can be efficiently and accurately controlled by the contact.
[0017]
According to the research results of the inventor, it has been found that, in terms of the structure of the molding apparatus, it is most efficient to heat the glass element by contacting the mold. For example, in a method of heating an optical element using a heating furnace as in a conventional technique (for example, Japanese Unexamined Patent Publication No. 4-338120, "Method of Forming a Glass Optical Element"), a mold and a small-diameter optical element such as a lens or a prism are required. Therefore, the effect cannot be fully exhibited. That is, if the temperature of the small-diameter glass material is different from the temperature of the molding die, a sharp temperature distribution can occur in the small-diameter glass, and the viscosity of the portion to be molded cannot be controlled, which may result in poor molding. . In other words, if the temperature of the mold changes, the temperature of the glass material follows even if the rate of change is large. This also means that the temperature of the glass material can be precisely controlled by precisely controlling the temperature of the mold. In the prior art, the same process can be performed in several tens of seconds or less, while the pressure molding time also takes several minutes or more, and two-stage molding or three-stage molding in which heating and cooling are repeated can be performed more quickly. Become like The present invention utilizes the above features to mold an optical element with high accuracy in a short cycle time. It is preferable to use a mold having good heat conductivity for the molding die. Examples of such a mold material include metals such as Ni and W, and SiC having good thermal conductivity. Since the temperature of the glass material rises in a few seconds, in the case of a small diameter, the glass material may be put into a molding die without heating.
[0018]
According to a fourth aspect of the present invention, in the optical element molding method according to any one of the first to third aspects, the temperature of the glass material is controlled by bringing the glass material into contact with the molding die. Has become
The glass material is put into the molding die controlled in advance at a predetermined temperature, and brought into contact with the mold, so that the temperature of the glass material is reduced to about 10⁷Poise more than 10¹²A step of raising the temperature of the glass material by raising the temperature of the glass material to a first temperature that is lower than the poise, pressing the glass material, and contacting the mold with the glass material. Having a viscosity of about 10¹²And a step of reducing the temperature to the second temperature as described above. According to the prior art, since a glass material having a larger volume was formed, the temperature of the mold and the temperature of the glass material were different, and rapid heating / cooling and accurate temperature control could not be performed. On the other hand, according to the present invention, a glass material having a smaller volume quickly follows the temperature of the mold, so that rapid heating / cooling and accurate temperature control can be performed.
[0019]
According to a fifth aspect of the present invention, there is provided the optical element molding method according to any one of the first to fourth aspects, wherein the glass material has a viscosity of about 10%.⁵Poise more than 10¹²The method has a step of preheating to a third temperature lower than the poise, and thereafter, is charged into the mold and pressed. In addition to the invention according to any one of claims 1 to 4, the volume is 10 mm₃For the following glass elements, the viscosity is about 10₅-10₁₂The step of preheating to a temperature that causes poise can be performed independently and in parallel with the preceding molding step, so that the molding cycle is shortened in total. This means that the volume is 10mm₃It is effective for nearby glass materials.
[0020]
According to a sixth aspect of the present invention, in the optical element molding method according to any one of the first to fifth aspects, the glass material is put into the molding die, the glass material is pressed, and the molding die is moved to a predetermined position. After the main molding step, the mold is heated to a temperature at which molding can be performed again, pressed, and the molding die is cooled to a predetermined temperature to increase molding accuracy. It has a molding step, and the correction molding step is repeated at least once. With such a feature, molding defects such as sink marks can be corrected, so that a more accurate optical element can be obtained.
[0021]
An optical element molding method according to claim 7, wherein in the invention according to claim 6, in the correction molding step, a first step of heating the glass material to an embossing molding temperature; A second step of pressing the material; and a third step of cooling the glass material to a temperature at which the glass material is removed from the molding die. In the first step and / or the third step, the surface of the glass material is A value obtained by dividing a temperature change amount of the temperature by a total temperature change time is 30 ° C./sec or more. If cooling is performed from the second step, the second step is also excluded. With such features, high-speed molding can be performed as compared with conventional multi-stage molding, and molding defects such as sink marks can be corrected, and a more accurate optical element can be obtained.
[0022]
The optical element molding method according to claim 8 is the method according to claim 7, wherein the maximum temperature of the glass material in the first step in the correction molding step is changed each time the correction molding step is repeated a plurality of times. The temperature is set so as to be equal to or lower than the maximum temperature of the glass material in the correction molding step before that. In the conventional multi-stage molding, the number of stages is small and the temperature cannot be set in small increments, so it was necessary to take a long pressing time, but in the present invention, the maximum temperature of the glass material in the correction molding step is gradually reduced. Therefore, the precision defects such as sink marks generated in each correction molding step gradually decrease, and the correction amount corresponding to the correction is performed each time, thereby finally bringing the shape closer to a high precision shape. Also, since the glass material is gradually brought closer to the ideal shape in small increments, the pressing time can be shortened, and high-speed molding can be performed.
[0023]
In the optical element molding method according to the ninth aspect, in the invention according to the eighth aspect, in each of the correction molding steps, the viscosity of the surface of the glass material is 10%.^13.4It is characterized by applying pressure in a certain range of poise or less. The viscosity of the surface of the glass material is 10^13.4Efficiency can be achieved by applying pressure within the range of less than poise and more easily deformed.
[0024]
An optical element molding method according to a tenth aspect is characterized in that, in the invention according to the eighth or ninth aspect, each of the correction molding steps is performed within 30 seconds. Volume is 10mm₃With the following glass material, the correction molding step within 30 seconds can be realized, and high-precision and high-speed molding can be performed.
[0025]
An optical element molding method according to an eleventh aspect is characterized in that, in the invention according to any one of the sixth to tenth aspects, the total time of the main molding step and the correction molding step is 60 seconds or less. Volume is 10mm₃With the following glass material, the main molding step and the correction molding step in a total of 60 seconds or less can be realized, and high-precision and high-speed molding can be performed.
[0026]
In the optical element molding method, by performing a series of cycles from the injection of the preform to the release in 60 seconds or less, the unit price can be lower than that of a plastic lens even when a glass material is used. For example, the volume at a glass transition point (Tg) of 500 ° C. is 10 mm.₃When molding the following glass material at 570 ° C., the glass material is first preheated to 490 ° C. Next, the glass material is put into the upper and lower molds, and at the same time, the temperature is raised at a rate of 10 ° C./sec, and the temperature is raised to about 570 ° C. near the glass softening point in about 8 seconds. Pressurized for 20 seconds, then cooled at a temperature of 10 ° C./sec, lowered in about 8 seconds, and removed from the mold at around 490 ° C. As described above, even if a normal glass material having a high glass transition point at an average of 10 ° C./sec is used, molding within 60 seconds can be achieved within a practical range. In another example, the preheating temperature is raised to 600 ° C. or higher, which is equal to or higher than the softening point, then dropped into an upper and lower mold, cooled by heat conduction to 570 ° near the softening point, molded at 570 ° C., and taken in about 8 seconds. The temperature may be lowered and the mold may be removed at around 490 ° C. In this cycle, if, for example, a plurality of pairs of upper and lower dies are provided in one molding apparatus so that a large number of optical elements can be molded by one molding, the cost can be further reduced. In this case, the cooling may be performed at a rate of change of, for example, 3 ° C./sec.
[0027]
According to a twelfth aspect of the present invention, in the optical element molding method according to any one of the first to eleventh aspects, the molding die includes an upper die and a lower die, and a temperature difference between the upper die and the lower die. Is maintained within 5 ° C.
[0028]
Volume is 10mm₃When the following glass material is molded, if the temperature of the molding die is largely different between the upper and lower dies, heat conduction is fast, which is disadvantageous in controlling the temperature of the glass material. This is because a temperature gradient is formed in the glass material, and one surface can be formed, but the other surface cannot be formed. If the upper and lower mold temperatures are different, it is difficult to control at least the glass material surface within several degrees. Therefore, it is desirable to equalize the temperatures of the upper and lower molds within about 5 ° C. By always heating and cooling both surfaces of the glass material at substantially the same temperature, a highly accurate optical element can be formed.
[0029]
The optical element molding method according to a thirteenth aspect is characterized in that, in the invention according to any one of the first to twelfth aspects, the pressure of the atmosphere is set to 1000 Pa or less in at least a part of the steps.
[0030]
An optical element such as a normal lens having a large NA (numerical aperture) has an optical surface with a small curvature, so that air is trapped at the top of the optical surface during molding, causing a large sink. According to the present invention, since molding is performed under a reduced pressure of 1000 Pa or less, accumulation of air at the top of the optical surface of the optical element during molding is avoided, and a highly accurate optical element can be molded.
[0031]
An optical element molding method according to claim 14 is characterized in that the glass material is made of a low melting glass material having a glass transition point (Tg) of 400 ° C. or less. With such a low-melting glass material, the molding cycle can be further shortened.
[0032]
It is preferable that the method further includes a step of changing a pressure for pressing the glass material between the upper mold and the lower mold according to a temperature change of the upper mold and / or the lower mold. Even with a small volume glass material, some sink marks may occur depending on the molding, and a highly accurate optical element may not be obtained. In such a case, a glass material having a viscosity of about 10₅-10₁₂Heating to a temperature that causes poise, embossing, and lowering the temperature of the upper and lower molds causes the degree of adhesion between the upper and lower molds to decrease due to the shrinkage of the glass material. The mold temperature is rapidly increased while the contact area is slightly increased. Then, the temperature of the surface of the glass material also rises rapidly, and the surface is softened again, so that the surface is shaped like a mold and sink is corrected. Then, when cooled, the sinks become smaller or disappear. Even a relatively large sink mark can be removed by repeating this cycle. Therefore, such a sink correction operation should be performed at least once, preferably two or three times.
[0033]
Further, the step of changing the pressure is an operation of increasing the pressure when at least the surface temperature of the glass material is equal to or higher than the glass transition point (Tg), and relaxing the pressure when the surface temperature is lower than the glass transition point (Tg). Preferably, the cycle time is 30 seconds or less, and the pressure is repeatedly increased and decreased. At least when the surface temperature of the glass material is equal to or higher than the glass transition point (Tg), pressurization is performed, and when the temperature is lower than the glass transition point (Tg), the pressure is reduced, and the cycle time is set to 30 seconds or less. If it is held at least once, molding can be performed more quickly while solving the sink problem. For example, the volume at a glass transition point (Tg) of 500 ° C. is 10 mm.₃When molding the following glass material at 570 ° C., the glass material is first preheated to 580 ° C. Next, the glass material is put into the upper and lower molds, and at the same time, cooled at a rate of 10 ° C./sec, and the temperature is raised to 570 ° C. within one second. Thereafter, the glass material is pressurized for 15 seconds and cooled at an average rate of change of 20 ° C./sec for 4 seconds. Then, the temperature of the glass material is raised at a rate of change of 60 ° C./sec and the temperature is raised to 550 ° C. within 1 second. increase. Thereafter, the glass material is pressurized for 5 seconds, cooled at an average temperature change of 20 ° C./sec for 3 seconds, and depressurized. Next, the temperature of the glass material is raised at a rate of 50 ° C./sec, and the temperature is raised to 540 ° C. within one second. Thereafter, the glass material is pressurized for 5 seconds, cooled at an average rate of change of 25 ° C./sec for 2 seconds, depressurized, and removed from the mold at 490 ° C. Thus, the molding cycle is performed within 30 seconds, and all the steps are performed within 60 seconds. Even if the temperature changes at a high speed, by performing the process many times while changing the conditions, it is possible to form an optical element having no sink even with a small-diameter lens, a prism, or a parallel flat plate in a short time. However, the pressing of the mold is performed from near the softening point.
[0034]
A molding apparatus according to claim 15 is a molding apparatus used to execute the optical element molding method according to any one of claims 1 to 10, wherein the molding apparatus includes an upper mold and a lower mold, It is characterized by having temperature adjusting means for individually controlling the temperature of the upper mold and the lower mold.
[0035]
In order to heat the glass material with high precision and high speed by the molding die by performing the above-described optical element molding method, as the temperature adjusting means inside the molding die, for example, a heating mechanism and / or Preferably, a cooling mechanism is provided. More preferably, a heating mechanism and / or a cooling mechanism may be provided near the surface. Especially when cooling, in order to rapidly lower the temperature of the mold as well as the glass material to be molded, it is highly effective to arrange an air-cooled pipe or the like between the heating mechanism, for example, a heater and the surface of the mold. .
[0036]
According to a sixteenth aspect of the present invention, in the molding apparatus according to the fifteenth aspect, the temperature adjusting unit is a heating unit.
[0037]
According to a seventeenth aspect of the present invention, in the molding apparatus according to the fifteenth or sixteenth aspect, the temperature adjusting means has a cooling means.
[0038]
In a molding apparatus according to claim 18, in the invention according to any one of claims 15 to 18, at least a part of the upper mold and / or the lower mold is formed of a porous member, and is provided by a delivery unit. A predetermined gas sent from the outside is configured to pass through the porous member and collide with the glass material in the mold. Here, the “mold” includes the holding member.
[0039]
According to the study of the present inventors, for example, at least a part of the upper mold and / or the lower mold is formed of a porous member, and a fluid such as a gas that has passed through the porous member is sprayed on the glass material. It was found that the temperature change of the glass material was faster than in the case where heat was directly conducted from the mold surface. According to a specific experiment conducted by the inventors, by blowing high-temperature air onto a glass sphere having a diameter of 1 mm at high speed, the temperature at least near the surface became equal to the temperature of air in a few seconds. Particularly when cooling, not only the temperature of the glass material but also the temperature of the mold can be rapidly lowered. This has advantages such as shortening of the molding cycle and easy temperature control. When forming the optical element, the effective range of the optical surface that transmits, reflects, diffracts, and the like light is preferably formed on the surface of the non-porous member, and otherwise, the surface is preferably formed on the surface of the porous member. As the porous member, silicon nitride, silicon carbide, alumina oxide, or the like can be used.
[0040]
A molding apparatus according to a nineteenth aspect is characterized in that, in the invention according to the eighteenth aspect, the porous member includes a temperature adjusting unit. The temperature of the gas passing through the porous member can be adjusted by the temperature control means, so that the temperature of the glass material can be controlled.
[0041]
According to a twentieth aspect of the present invention, in the invention according to the eighteenth or nineteenth aspect, the gas delivery means is provided with a separate temperature control means such as a heater or a water-cooled tube or an air-cooled tube. By adjusting the temperature of the gas by the temperature adjusting means, the temperature of the glass material can be quickly controlled by changing the flow rate of the gas whose temperature has been adjusted.
[0042]
In a molding apparatus according to a twenty-first aspect, in the invention according to any one of the eighteenth to twentieth aspects, the upper mold and / or the lower mold formed of the porous member surrounds the outer periphery thereof and faces each other. It has an outer wall portion extending in the direction of the mold. Since the gas that has passed through the porous member is effectively directed to the glass material by the outer wall portion, a fluid whose temperature is controlled can be effectively used.
[0043]
In the molding apparatus according to claim 22, in the invention according to any one of claims 18 to 20, the upper mold and / or the lower mold having the porous member has an outer periphery formed by a separate cylinder. It is characterized by being surrounded. Since the gas passing through the porous member is effectively directed to the glass material by the separate cylinder, a fluid whose temperature is controlled can be effectively used.
[0044]
According to a twenty-third aspect of the present invention, in the molding apparatus according to any one of the eighteenth to twenty-second aspects, the upper mold and / or the lower mold are formed of a conductive material having a predetermined resistance value. And heat is generated by receiving a current from the power supply, and the temperature can be controlled by electric control. If the molding die itself is used as the heating device in this way, there is no need to provide a separate heater, and the number of parts and cost can be reduced.
[0045]
Further, when a cooling device such as a cooling air pipe is disposed inside the mold, not only heating but also cooling can be performed, so that temperature control of the mold can be performed more quickly. Since the glass material is heated directly instead of indirectly, the temperature change is quickened. When the thickness of the conductive portion in the mold is reduced, the heat capacity is reduced. This is more advantageous in preventing overheating or when heating and cooling only the surface of the glass material.
[0046]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of an optical element molding apparatus according to a first embodiment that can carry out the optical element molding method of the present invention. In FIG. 1, a cylindrical upper mold 2 has a cylindrical portion 13 made of conductive SiC arranged in the center thereof, a circular tube portion 8 made of porous SiC arranged therearound, and a thin cylinder formed around the cylindrical portion 8. An outer wall portion 14 (which is also a separate tube) is arranged. On the other hand, the cylindrical lower mold 3 has a cylindrical portion 12 made of conductive SiC arranged in the center thereof, a circular tube portion 9 made of porous SiC arranged around the cylindrical portion 12, and a thin cylindrical shape formed around the cylindrical portion 9. An outer wall (also a separate cylinder) 15 is arranged. The cylindrical portions 13 and 12 are arranged in an effective range of an optical surface of an optical element to be formed from the glass material 1. The upper mold 2 and the lower mold 3 can be relatively moved in the vertical direction by a driving device (not shown).
[0047]
Since the cylindrical portions 13 and 12 are conductive, they generate heat when supplied with power from the outside. Further, the circular pipe portions 8 and 9 are provided with N supplied from a sending means (not shown) such as an external pump.₂The gas is released toward the glass material 1 with the temperature controlled. The outer wall portions 14 and 15 are formed by N₂It has a function of directing the gas toward the glass material 1.
[0048]
A method for molding an optical element using the optical element molding apparatus of FIG. 1 will be described. In the following description, the temperature of the glass material at the time of molding is substantially equal to the temperature of the mold. The most common molding method will be described. First, the cylindrical portions 13 and 12 are heated, and N₂In a state where the gas is released, the glass material 1 having a glass transition point (Tg) of 500 ° C. is charged between the upper mold 2 and the lower mold 3, and both are moved close to each other and heated (first step). Then, as shown in FIG. 2, the surface temperature of the glass material 1 increases at a rate of change of 60 ° C./sec in total temperature change / temperature change time, and the first temperature exceeds the glass transition point (Tg) in about 10 seconds. (For example, 570 ° C.). At this time, the viscosity of the glass material 1 is 10₅Since the pressure decreases to Poise, the upper mold 2 and the lower mold 3 are further brought closer to each other and pressurized (second step), and then gradually cooled for 30 seconds, and rapidly cooled when the temperature falls below the glass transition point (Tg). To a second temperature (for example, 480 ° C.) (third step). At this time, the viscosity of the glass material 1 is 10₁₂Rise above Poise. As described above, a molding cycle time of 60 seconds can be realized.
[0049]
Next, another molding method of the optical element will be described. In the present molding method, a glass material is similarly molded without preheating. As shown in FIG. 3, the surface temperature of the glass material 1 is first increased at a rate of change of 100 ° C./sec. In the vicinity of (Tg), the surface temperature of the glass material 1 is increased at a rate of change of 50 ° C./sec, and about 10 seconds after the pressurization, the surface temperature of the glass material 1 is reduced at a rate of change of 100 ° C./sec. . Thereby, a molding cycle time of 30 seconds can be realized.
[0050]
Another molding method for an optical element will be described. In the present molding method, the glass material 1 is preheated. As shown in FIG. 4, first, the surface temperature of the glass material 1 is raised to near the glass transition point (Tg) (third temperature) by performing preliminary heating (preferably performed during transportation) for 10 seconds (preliminary heating). Step) Then, after charging between the upper mold 2 and the lower mold 3, the glass transition point (Tg) is exceeded in 1 second, and after pressurizing and slowly cooling for about 9 seconds, a rate of change of 100 ° C./sec. Reduces the surface temperature of the glass material 1. Thereby, a molding cycle time of 20 seconds can be realized.
[0051]
Another molding method for an optical element will be described. This molding method also performs sinking while molding. As shown in FIG. 6, the feature of the present molding method is that, in addition to the features of the molding method shown in FIG. 5, the molding (maximum) temperature upon repeated heating and pressing is gradually lowered. More specifically, a small-diameter preform having a glass transition point (Tg) of 500 ° C. and a diameter of 1 mm is conveyed while being preheated to 480 ° C., and placed on a mold maintained at 580 ° C. The heat transferred from the mold and the high temperature N released through the porous ceramic₂The temperature of the preform is raised at a rate of 100 ° C./sec or more by the gas to reach 570 ° C. or more within 1 second. In addition, high temperature N₂Bring the gas piping close to the mold and add N to the preform placed in the mold.₂Gas may be sprayed directly.
[0052]
Next, when the atmosphere near the shielded mold is sucked by a vacuum pump, the volume near the shielded mold is several cm.₃In this case, the pressure immediately becomes 1000 Pa or less. The first pressing is performed for 10 seconds while lowering the temperature by combining the upper and lower molds, and the heating of the conductive SiC heater (not shown in FIG. 1), which is the base material of the mold itself, is stopped.₂A gas is supplied to break the vacuum atmosphere, and cooling air is released through porous silicon carbide or alumina oxide to lower the temperature to below the glass transition point (Tg) and cool the preform. At this time, the preform is pressed to a final thickness of +20 μm.
[0053]
Next, the temperature is lowered until the mold temperature becomes equal to or lower than the glass transition point (Tg). When the mold temperature falls below the glass transition point (Tg), the upper and lower molds are separated to reduce the pressure, and the temperature is raised at a rate of change of 100 ° C./sec or more, to around 550 ° C. within one second. While further lowering the temperature, the upper and lower molds are brought close to each other, and the second pressurization is performed for 5 seconds. At this time, the preform is pressed to a final thickness of + 4μ.
[0054]
Next, the temperature is lowered until the mold temperature becomes equal to or lower than the glass transition point (Tg). When the mold temperature falls below the glass transition point (Tg), the upper and lower molds are separated to reduce the pressure, and the temperature is raised at a rate of change of 100 ° C./sec or more, and brought to around 540 ° C. within one second. While lowering the temperature further, the upper and lower molds are brought close to each other to perform the third pressurization for 3 seconds. At this time, the preform is pressed to a final thickness of + 1μ.
[0055]
Next, the temperature is lowered until the mold temperature becomes equal to or lower than the glass transition point (Tg). When the mold temperature becomes lower than the glass transition point (Tg), the upper and lower molds are separated to reduce the pressure, and the temperature is raised at a rate of change of 100 ° C./sec or more, and brought to around 515 ° C. within one second. While further lowering the temperature, the upper and lower dies are brought closer to each other to perform a fourth press for 3 seconds. At this time, the preform is pressed to a final thickness of + 0.2μ.
[0056]
Next, the temperature is lowered until the mold temperature becomes equal to or lower than the glass transition point (Tg). When the mold temperature falls below the glass transition point (Tg), the upper and lower molds are separated to reduce the pressure, and the temperature is increased at a rate of 100 ° C./sec or more, and the temperature is raised to around 510 ° C. within one second. While further lowering the temperature, the upper and lower dies are brought closer to each other to perform a fifth press for 3 seconds. Thus, it is pressed to the final thickness. Thereafter, the mold temperature is lowered to the glass transition point (Tg) or lower, and when the mold temperature becomes lower than the glass transition point (Tg), the upper and lower molds are separated to reduce the pressure. Thus, a highly accurate optical element can be formed within 35 seconds. Also, by repeating such a cycle, the sink mark at the center is gradually corrected. Thus, an optical element having no sink mark and having a surface accuracy within 0.1 μm of the design value can be formed in a short cycle. In this case, it is not always necessary to lower the temperature below the glass transition point (Tg) depending on the type of the glass material and the target accuracy. Also, the pressing may be performed once instead of three times. In that case, molding can be performed at a high speed of 10 seconds or less.
[0057]
When molding is performed in an atmosphere of atmospheric pressure, as shown in FIG. 7, air remains between the mold 2 and the glass material 1, which causes sink marks. Therefore, as shown in this embodiment, the pressure of the atmosphere is reduced. It is desirable that the pressure be 1000 Pa or less.
[0058]
FIG. 8 shows an optical element molding apparatus according to another embodiment, which can carry out the molding method described above. In FIG. 8, the upper mold 2 and the lower mold 3 have a mold base material whose optical surface is a non-porous ceramic, and a DLC (diamond-like carbon) film is laminated on the surface by 0.5 μm. Because the membrane is thin, it does not block the porous ceramic holes. Further, the upper mold 2 and the lower mold 3 are each hollow, and heaters 5 and 5 are respectively disposed therein, and a cooling pipe 4 is provided on a side closer to the glass material 1 formed by the heaters 5 and 5. , 4 are arranged respectively. Temperature-controlled N₂Gas is flowing. In addition, thermocouples 6 and 6 are arranged in the upper mold 2 and the lower mold 3 in the vicinity of the glass material 1 to be molded, respectively, and the temperature can be controlled with high accuracy based on the signals. . In this case, it is preferable that there is no difference between the upper and lower molds, and it is preferable that the difference be at most 5 ° C.
[0059]
According to the present embodiment, the cooling pipe 4 as the cooling device (means) is disposed between the heater 5 as the heating device (means) and the glass material 1 to be formed. Cooling can be performed more efficiently. The heater 5 and the cooling pipe 4 constitute temperature adjusting means for individually controlling the temperature of the upper mold 2 and the lower mold 3.
[0060]
As described above, the present invention has been described with reference to the embodiments. However, the present invention should not be construed as being limited to the above embodiments, and it is needless to say that modifications and improvements can be made as appropriate. For example, it is preferable to use a low-melting glass having a glass transition point (Tg) of 400 ° C. or lower, because the molding cycle time becomes shorter and the sink becomes smaller.
[0061]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an optical element molding method and a molding apparatus capable of molding a particularly small optical element with high accuracy and in a short cycle.
[Brief description of the drawings]
FIG. 1 is a sectional view of an optical element molding apparatus according to a first embodiment.
FIG. 2 is a diagram showing a relationship between a molding time, a temperature of a mold (or a glass material), and a viscosity of a glass material.
FIG. 3 is a diagram showing a relationship between a molding time and a temperature of a mold (or a glass material).
FIG. 4 is a diagram showing a relationship between a molding time and a temperature of a mold (or glass material).
FIG. 5 is a diagram showing the relationship between the molding time and the temperature and pressure of a mold (or glass material).
FIG. 6 is a diagram showing a relationship between a molding time and a temperature of a mold (or a glass material).
FIG. 7 is a diagram showing the appearance of sinking;
FIG. 8 is a sectional view of an optical element molding apparatus according to a second embodiment.
[Explanation of symbols]
1 Glass material
2 Upper type
3 lower mold
13,12 cylindrical part
8, 9 pipe section
14, 15 outer wall

Claims (23)

An optical element molding method in which a glass material having a volume of 10 mm ³ or less is heated and softened, and embossed with a viscosity of 10 ⁷ poise or more using a molding die so as to obtain an optical element having a desired shape,
In the step of cooling from the embossing temperature to the glass transition point (Tg), a value obtained by dividing a temperature change amount by a total temperature change time of the surface temperature of the glass material is 3 ° C./sec or more. Optical element molding method. Volume is heated and softened glass material having a 10 mm ³ or less of the optical surface is an optical element molding method of embossing mold with a viscosity of 10 ⁷ poises or more by using a mold so that the optical element of the desired shape,
A first step of heating the glass material to an embossing temperature, a second step of pressing the glass material with the mold, and a third step of cooling the glass material to a temperature at which the glass material is removed from the mold. An optical element molding method, wherein in the third step, a value obtained by dividing a temperature change amount of a surface temperature of the glass material by a total temperature change time is 30 ° C./sec or more. 3. The method according to claim 2, wherein, in addition to the third step, in the first step, a value obtained by dividing a temperature change amount of a surface temperature of the glass material by a total temperature change time is 30 ° C./sec or more. The optical element molding method according to the above. By bringing the glass material into contact with the mold, the temperature of the glass material is controlled,
The glass material is put into the mold controlled at a predetermined temperature in advance, and brought into contact with the mold, so that the temperature of the glass material is reduced to a first viscosity of about 10 ⁷ poise or more and less than 10 ¹⁰ poise. Increasing the temperature of the glass material, pressing the glass material, and lowering the temperature of the mold while contacting the mold with the glass material. ^The method according to any one of claims 1 to 3, further comprising a step of reducing the temperature to a second temperature of ¹² or more. 2. The method according to claim 1, further comprising a step of preheating the glass material to a third temperature at which the viscosity is about 10 ⁵ poise or more and less than 10 ¹² poise, and thereafter, the glass material is put into the mold and pressed. 5. The method for molding an optical element according to any one of items 1 to 4. A main molding step of charging the glass material into the molding die, pressing the glass material, and cooling the molding die to a predetermined temperature, and a temperature at which the molding die can be molded again after the main molding step. The method according to claim 1, further comprising: a correction molding step of increasing the molding accuracy by heating, pressing, and cooling the mold to a predetermined temperature, and repeating the correction molding step at least once. The optical element molding method according to any one of the above. In the correction molding step, a first step of heating the glass material to an embossing temperature, a second step of pressing the glass material with the molding die, and cooling to a temperature at which the glass material is removed from the molding die. A third step of performing the first step and / or the third step, wherein a value obtained by dividing a temperature change amount of a surface temperature of the glass material by a total temperature change time is 30 ° C./sec or more. The optical element molding method according to claim 6, wherein The maximum temperature of the glass material in the first step in the correction molding step is set to be equal to or lower than the maximum temperature of the glass material in the previous correction molding step every time the correction molding step is repeated a plurality of times. The method for forming an optical element according to claim 7, wherein: 9. The optical element molding method according to claim 8, wherein in each of the correction molding steps, the pressure is applied within a certain range where the viscosity of the surface of the glass material is 10 ^13.4 poise or less. The optical element molding method according to claim 8, wherein each of the correction molding steps is performed within 30 seconds. The optical element forming method according to any one of claims 6 to 10, wherein a total time of the main molding step and the correction molding step is 60 seconds or less. The optical element molding according to any one of claims 1 to 11, wherein the mold comprises an upper mold and a lower mold, and a temperature difference between the upper mold and the lower mold is maintained within 5 ° C. Method. The method for molding an optical element according to claim 1, wherein the pressure of the atmosphere is set to 1000 Pa or less in at least a part of the steps. 14. The method according to claim 1, wherein the glass material is a low melting glass material having a glass transition point (Tg) of 400 [deg.] C. or less. A molding apparatus used for performing the optical element molding method according to any one of claims 1 to 14, wherein a molding die including an upper die and a lower die, and the upper die and the lower die are individually formed. A molding apparatus, comprising: a temperature adjusting means for controlling a temperature. The molding apparatus according to claim 15, wherein the temperature adjusting unit is a heating unit. 17. The molding apparatus according to claim 15, wherein the temperature adjusting unit has a cooling unit. At least a part of the upper mold and / or the lower mold is formed of a porous member, and a predetermined gas delivered from the outside by a delivery unit passes through the porous member, and the inside of the mold is The molding apparatus according to any one of claims 15 to 17, wherein the molding apparatus is configured to collide with the glass material. The molding apparatus according to claim 18, wherein the porous member includes a temperature adjusting unit. 20. The molding apparatus according to claim 18, wherein the gas sending means includes a temperature adjusting means. The said upper mold | die and / or the said lower mold | type comprised from the said porous member have the outer wall part surrounding the outer periphery and extending in the direction of the opposing mold | die. The molding device as described in the above. The molding apparatus according to any one of claims 18 to 20, wherein the upper mold and / or the lower mold having the porous member are surrounded by a separate cylinder. The upper mold and / or the lower mold are made of a conductive material having a predetermined resistance value, generate heat when supplied with electric current from the outside, and can control the temperature by electric control. Item 21. The molding apparatus according to any one of Items 18 to 20.

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