JP2015105221A - Optical element molding method, and optical element molding apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element molding method and an optical element molding apparatus exhibiting improved shape stability and maintaining excellent yield in a mold movement method, when manufacturing optical elements.SOLUTION: An optical element molding method comprises: a heating step for heating a mold 50 containing an optical material by a heating plate 3b to soften the optical material; a press step for pressing the softened optical material by a press plate 4b to apply a shape of an optical element to the optical material; and a cooling step, after the press step, for cooling the optical material by a cooling plate 5b to solidify the optical material. When the mold 50 is transferred in the cooling step, a preset temperature of the cooling plate 5b is raised from a reference temperature Tto a hunting suppression temperature T(where, T>T>T, and Tis a preset temperature of the plate in the preceding position). Then the temperature is lowered to the reference temperature Tat a predetermined temperature lowering speed.

Description

  The present invention relates to a molding method and a molding apparatus for an optical element, and in particular, suppresses a hunting phenomenon that occurs when an optical material is cooled and solidified after press molding the optical material, so that the temperature fluctuation (temperature of The present invention relates to a molding method and a molding apparatus for an optical element that suppresses the occurrence of shape defects by performing stable cooling with controlled vertical movement.

  In recent years, a method for molding an optical element with high accuracy has been generalized, in which an optical material is accommodated in a molding die for an optical element, heated and softened, and press-molded. In such a situation, in order to improve productivity, an optical element molding apparatus has been proposed in which a mold is conveyed to each processing stage of heating, pressing and cooling, and a plurality of optical elements are continuously manufactured. Yes.

  In these optical element molding equipment, when the optical material is softened by heating, it is heated to a high temperature condition sufficient to process the optical material, and during pressing, the pressed state is maintained and the optical material is cooled after pressing. And solidify to obtain an optical element. Therefore, in each processing stage in the molding apparatus, each stage is managed at a predetermined temperature.

  Each processing stage is generally composed of a pair of upper and lower plates provided with cartridge heaters therein, and these upper and lower plates usually have a plurality of bar-shaped cartridge heaters in the plate at a predetermined interval in the horizontal direction. It is arranged and arranged. However, the plate temperature when arranged in this way is likely to decrease at the periphery of the plate, and the temperature at the center of the plate is likely to increase due to being surrounded by the heater. Therefore, the temperature distribution in which the heating state in the plate varies depending on the location occurs. Thus, when temperature distribution arises in a plate, it will affect even the temperature of the shaping | molding die on the plate and by extension, the shaping | molding surface which shape | molds an optical raw material.

  Therefore, in order to improve the temperature distribution on the plate, a soaking plate having a specific size in which the surface of the cemented carbide is coated with a predetermined alloy thin film is provided on the plate (see Patent Document 1), or the plate surface. Temperature control means for controlling the output of the inner and outer cartridge heaters is provided to keep the temperature difference between the peripheral part and the inner part corresponding to molding of the inner part within a predetermined range (see Patent Document 2), or a heater is provided. A technique for minimizing a temperature difference between a plurality of molds by attaching a cemented carbide plate on which a thermocouple is arranged on a temperature control block has been proposed (see Patent Document 3).

JP-A-8-259240 JP 2008-69019 A JP 2010-89970 A

  However, even if the temperature uniformity is increased in this way, the surface shape may not be stable. As a result of various studies, the present inventors have found that when the mold is transferred to each temperature-controlled plate, the temperature of the mold converges to the set temperature while going up and down in the cooling process to the set temperature in the cooling stage. However, it was thought that the cause was that a slight temperature change occurred.

That is, when the mold moves from a hot front plate (eg, a press plate) to a cold plate (eg, a cooling plate), the mold is rapidly cooled while the cooling plate is removed from the mold. The temperature rises slightly with heat. Therefore, in the conventional control method, the heater output is lowered by this temperature rise so as to maintain the temperature of the cooling plate itself at a predetermined temperature. In this way, the mold is cooled, and when the temperature reaches the set temperature of the cooling plate, the temperature becomes lower than the temperature of the cooling plate as it is. At this time, the cooling plate is also lower than the set temperature. As the cooling plate is heated, the mold temperature rises accordingly. When the heater output increases, the cooling plate then becomes higher than the set temperature, so the heater output is lowered to cool the cooling plate. At this time, such up and down movement of the temperature is repeated in the vicinity of the set temperature, and the amplitude gradually decreases and is stably maintained at the set temperature. This vertical movement of temperature is called temperature hunting phenomenon. 5A and 5B are diagrams illustrating the hunting phenomenon at this temperature. FIG. 5B is an enlarged view of a portion where the hunting phenomenon of FIG. 5A occurs. In these drawings, when the mold is transferred from the press plate, which is the previous position, to the cooling plate, the mold in the cooling process from the set temperature (T _p ) of the press plate to the set temperature (T ₀ ) of the cooling plate. FIG. 5B shows a temperature change, and as shown in FIG. 5B, the temperature rises and falls near the set temperature (T ₀ ) of the cooling plate. Note that the magnitude of the temperature change amplitude in this phenomenon depends on the heat capacity of the mold, the temperature at the front plate, and the like.

  By the way, in the mold moving type molding apparatus, since a plurality of molds are used, it is difficult to equalize the heat capacities of all the molds. Even if the dimensions of all the molds are the same in units of μm, it is extremely difficult to make the heat capacities the same because there are variations in the material of the mold material (such as cemented carbide or SiC). For example, in cemented carbide, there is a variation in specific gravity of about ± 0.01.

  Also, it is difficult to make the volume of the optical material (preform) accommodated in the mold completely the same every time. The preform includes a method of grinding and polishing an optical material, and a method of molding a molten material that flows out without being ground and polished by gas. The mass tolerance is at least ± 0.01% for grinding and polishing, and at least ± 0.05% for direct production by melting, so it is extremely difficult to keep the volume of the optical material used constant. .

  Therefore, even if an optical element is manufactured under the same conditions, it is difficult to make a plurality of molds and optical materials completely the same as described above, thereby changing the temperature history and affecting the shape of the optical element. For this reason, defective products have been produced at a certain rate.

  Accordingly, in order to solve the above-described problems, the present invention has an object to provide a molding method and a molding apparatus for an optical element with a high yield by improving the shape stability of the optical surface in the mold movement method in the production of the optical element. And

  As a result of intensive studies, the present inventors have found that the above problem can be solved by the optical element molding method and molding apparatus of the present invention, and have completed the present invention.

That is, the method for molding an optical element of the present invention includes a heating step of storing an optical material in a molding die composed of an upper die, a lower die, and a body die, and heating the molding die with a heating plate to soften the optical material. A press process in which a softened optical material is pressed with the mold using a press plate to give an optical element shape; and after the press process, the mold is cooled by a cooling plate to give an optical element shape A cooling step for solidifying the material, and in the cooling step, when the mold containing the optical material is transferred, the set temperature of the cooling plate is set as a reference temperature. It increased from T ₀ to hunting suppressing temperature _{T 1 (where} a _{T p> T 1> T 0} , T p denotes the set temperature of the plate before the position.), the mold is After reaching Nchingu suppress the temperature T _1, wherein the temperature is lowered to a reference temperature T ₀ at a predetermined temperature lowering rate.

Further, the optical element molding apparatus of the present invention sequentially conveys a molding die in which an optical material is placed between an upper die and a lower die to each heating, pressing, and cooling stage provided in the chamber. A molding apparatus for an optical element to be molded, wherein the molding die is mounted at each stage of heating, pressing and cooling, and the heating, pressing and cooling processes are performed on the mounted molding die, respectively. A plurality of sets of a pair of heating plates, a press plate and a cooling plate, a driving means for performing the heating, pressing and cooling processes by bringing the pair of plates in each set close to or away from each other, the above processes and the above Control means for controlling conveyance of the mold, and the control means transfers the set temperature of the cooling plate to the mold in which the optical material is accommodated. When raising the reference temperature _{T 0} in the hunting suppressing temperatures _{T 1} to which has been _(here, a _{T p> T 1> T 0} , T p denotes the set temperature of the plate before the position.), The mold There after reaching hunting suppressing temperature T _1, and further comprising a temperature control unit for decreasing the temperature to the reference temperature T ₀ at a predetermined temperature lowering rate.

  According to the method and apparatus for molding an optical element of the present invention, in the cooling process of a pressed optical material, the hunting phenomenon at the time of cooling the optical material is suppressed to be short, the temperature history after pressing is stabilized, and the shape of the optical element is reduced. Stability (reproducibility) can be improved.

It is a schematic block diagram of the shaping | molding apparatus of the optical element which is one Embodiment of this invention. FIG. 2 is a front view showing a thermocouple in perspective in the cooling plate in the optical element molding apparatus of FIG. 1. It is a top view of the cooling plate shown in FIG. 2A. It is the figure which showed the change of the shaping | molding die temperature at the time of being transferred from the press plate to the cooling plate in the shaping | molding method of this invention. FIG. 3B is a partially enlarged view of FIG. 3A. It is a schematic block diagram of the shaping | molding apparatus of the optical element which is other embodiment of this invention. It is the figure which showed the change of the shaping | molding die temperature at the time of being transferred from the press plate to the cooling plate in the conventional shaping | molding method. FIG. 5B is a partially enlarged view of FIG. 5A.

Hereinafter, the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic configuration diagram of an optical element molding apparatus according to an embodiment of the present invention (only a chamber 2 is shown in cross section).
An optical element molding apparatus 1 according to the present invention softens an optical material by heating a chamber 2 serving as a molding chamber for molding the optical element and a mold containing the optical material provided in the chamber 2. It has a heating stage 3, a press stage 4 for pressing the heat-softened optical material, and a cooling stage 5 for cooling the optical material to which the optical element shape is given by the pressing.

  Here, the chamber 2, which is a molding chamber, provides a place for performing an optical element molding operation. The chamber 2 is provided with an inlet for taking in the optical element molding die 50 and an outlet for taking out the molding die 50 after the molding of the optical element is finished. An intake shutter 6 and an extraction shutter 7 are provided. If necessary, these shutters can be opened and closed to allow the mold 50 to be taken in and out of the chamber 2 and the atmosphere in the chamber 2 is maintained. In addition, the mold inlets 8 and 9 are provided at the inlet and the outlet, respectively, on which the molding die 50 can be placed outside the chamber 2.

  Inside the chamber 2, a heating stage 3, a press stage 4 and a cooling stage 5 for molding the optical element are provided, and a molding operation is performed by each of these stages. Actually, the mold 50 containing the optical material is taken into the chamber 2 from the intake port, and is subjected to predetermined processing while being sequentially moved to each of the above stages. 50 is taken out of the chamber 2 from the take-out port.

  Inside the chamber 2, when the optical material is press-molded, the mold 50 is heated to a high temperature. Therefore, the atmosphere in the chamber is preferably an inert gas atmosphere such as nitrogen so that the mold 50 is not oxidized. An inert gas atmosphere can be achieved by replacing the internal atmosphere with the chamber 2 as a sealed structure. However, by providing a semi-sealed structure, the inert gas is always supplied into the chamber 2 and the inside of the chamber is set to a positive pressure. An inert gas atmosphere may be maintained by preventing external air from flowing in. The intake shutter 6 and the extraction shutter 7 described above are effective for making the inside of the chamber 2 a semi-sealed state with a simple configuration. The chamber 2 and the shutters 6 and 7 are preferably made of a material that does not precipitate gas and impurities at high temperatures such as stainless steel and alloy steel.

  Next, each stage that performs the molding operation of the present invention will be described. Note that the mold 50 used to describe each stage is generally a set of molds composed of an upper mold that forms the upper optical surface of the optical element and a lower mold that forms the lower optical surface. Furthermore, it has a body mold for aligning the upper mold and the lower mold. The body mold is a hollow cylindrical inner cylinder that regulates the optical axis of the upper mold and the lower mold on the same axis and a hollow cylindrical shape that is provided on the outer periphery of the inner cylinder and regulates the distance between the upper mold and the lower mold during pressing It is preferable that the outer shell is constructed.

  The mold 50 is made of a material such as cemented carbide or ceramics, and the upper mold and the lower mold each have a molding surface for transferring the surface shape of the optical element to be molded. The shape of the optical element formed may be a mold that molds any lens shape of biconvex, biconcave, plano-convex, plano-concave, convex meniscus, or concave meniscus. In the case of using an outer shell, a material having durability at high temperature, corrosion resistance, and high mechanical strength is preferable, a material having a high thermal expansion coefficient is preferable, and specifically, stainless steel such as SUS is preferable. .

  The heating stage 3 of the present invention is composed of a pair of upper and lower heating plates 3b in which an optical material accommodated in a mold 50 is softened and a cartridge heater 3a is embedded therein. This heating plate 3b is means for bringing the upper and lower heating plates 3b into contact with the upper and lower molds of the mold and heating the upper and lower molds, and is further accommodated inside the mold by heat conduction. Optical materials can also be heated.

  In the heating stage 3, the lower heating plate 3 b is fixed to the bottom plate of the chamber 2 by laminating the heat insulating plate 3 c and the heating plate 3 b in this order, and the heat of the lower heating plate 3 b is transferred to the chamber 2. Do not communicate to.

  The upper heating plate 3b can be moved up and down, and is also connected to the shaft 3d via the heat insulating plate 3c so as not to transmit the heat of the upper heating plate 3b itself. The shaft 3d can move the heating plate 3b up and down by a cylinder (not shown). In this way, if the heating plate 3b can be moved up and down, contact / non-contact of the upper heating plate 3b with the upper die of the molding die 50 can be controlled, and the molding die 50 and the optical material can be heated at a desired timing. .

  In the press stage 4 of the present invention, the distance between the upper and lower press plates 4b is reduced to reduce the distance between the upper mold and the lower mold of the mold 50, and the optical material accommodated in the mold 50 is pressed in a softened state. Then, the optical element is formed into a desired shape by imparting molding surface shapes of the upper die and the lower die to the optical material. It consists of a pair of upper and lower press plates 4b in which a cartridge heater 4a is embedded. The press using the press plate 4b is performed while maintaining the heating temperature in the previous stage.

  In this press stage 4, the lower press plate 4 b is fixed to the bottom plate of the chamber 2 by laminating the heat insulating plate 4 c and the press plate 4 b in this order, and the heat of the lower press plate 4 b is transferred to the chamber. 2 is not transmitted.

  The upper press plate 4b can move up and down, and is also connected to the shaft 4d via the heat insulating plate 4c so as not to transmit the heat of the upper press plate 4b itself. The shaft 4d can move the press plate 4b up and down by a cylinder (not shown). In this way, if the press plate 4b can be moved up and down, the upper press plate 4b can be lowered and press molding using the molding die 50 placed on the lower press plate 4b can be performed. At this time, the press plate 4b operates so that pressing can be performed with a predetermined pressure, and an optical element shape can be imparted to the optical material with high accuracy.

  The cooling stage 5 of the present invention cools the mold 50 and cools and solidifies the optical material to which the optical element shape is given. Therefore, the cooling stage 5 includes a pair of upper and lower cooling plates 5b in which cartridge heaters 5a are embedded. Composed. The cooling plate 5b can cool the upper mold and the lower mold by bringing the pair of upper and lower cooling plates 5b into contact with the upper mold and the lower mold of the mold, and also cools the optical material accommodated in the mold. it can.

  More specifically, in this cooling stage 5, the lower cooling plate 5b is fixed to the bottom plate of the chamber 2 by laminating and fixing the heat insulating plate 5c and the cooling plate 5b in this order. This heat is not transmitted to the chamber 2.

  The upper cooling plate 5b can be moved up and down, and is also connected to the shaft 5d via the heat insulating plate 5c so as not to transmit the heat of the upper cooling plate 5b itself. The shaft 5d can move the cooling plate 5b up and down by a cylinder (not shown). In this way, if the cooling plate 5b can be moved up and down, contact / non-contact of the upper cooling plate 5b with the upper mold of the mold 50 can be controlled, and the mold 50 and the optical material can be cooled at a desired timing. it can.

  The solidification of the optical material on the cooling plate 5b may be performed by cooling the glass material below the glass transition point, more preferably below the strain point. When sufficiently cooled, the optical element shape of the optical material is stabilized and deformed. Is suppressed. The cooling here means that the temperature is lowered to a temperature at which the optical material is solidified so that the shape of the optical element is stably provided. The temperature is only about 50 to 150 ° C. lower than the press plate and is still high. Therefore, the heater 5a is embedded in the cooling plate 5b.

  As described above, the heating plate 3b, the press plate 4b, and the cooling plate 5b on the upper side of each stage are fixed to the shaft via the heat insulating plate, and this shaft is connected to the cylinder. Here, the cylinder only needs to be able to move each plate up and down, and examples thereof include an air cylinder, an electric servo cylinder, a hydraulic cylinder, an electric hydraulic cylinder, and the like.

  The heating plate 3b, the press plate 4b, and the cooling plate 5b described above have a horizontal contact surface with the mold, and in particular, the press plate 4b has a tilted contact surface with the press plate 4b. In such a case, the central axes of the upper mold and the lower mold of the mold 50 may not coincide with each other, and the optical element manufactured at this time may have a defective product because the optical axes thereof do not coincide with each other. Therefore, the management of the parallelism and flatness of the plates at each stage is strictly performed.

  The plate in each of these stages is one in which a cartridge heater is inserted and fixed inside a material such as stainless steel, cemented carbide, alloy steel, etc., and the temperature of the plate is raised by heating the cartridge heater to maintain a desired temperature. It is.

  In addition, the plate of each stage may be configured by providing a soaking plate on the surface of the mold mounting surface in order to make the plate temperature as uniform as possible. The soaking plate can be made of a known heat-resistant material such as cemented carbide or stainless steel, and has a high hardness and good heat conduction. Furthermore, it is preferable to coat the surface of the soaking plate with an anti-oxidation film, and specific examples of this coating include coating films such as CrN, TiN, and TiAlN.

  Moreover, the heat insulating plates 3c, 4c, 5c of each stage may be a known heat insulating plate such as ceramics, stainless steel, die steel, high-speed steel, etc., which has high hardness and is difficult to be deformed by pressure during press molding. Ceramics that are less likely to cause erosion are preferred.

  The heating stage 3, the press stage 4, and the cooling stage 5 described above form a place (stage) where predetermined processing is performed, and the molding die 50 is provided with a conveying means so that the processing by each stage can be performed sequentially and smoothly. (Not shown) is controlled by the control means 10 so as to be transferred to and mounted on each stage at a predetermined timing.

  More specifically, the processing by the heating plate 3b, the press plate 4b, and the cooling plate 5b is performed while the mold 50 is sequentially transported and moved onto each plate in the above order. When the molding die 50 moves to the next stage, the stage after processing becomes empty, and further, the molding die 50 containing another optical material is transported there, and the molding operation of a plurality of optical elements is continued. Is efficient.

  Although the conveying means for performing this processing is not shown in the figure, for example, a robot arm or the like can be cited, and thereby, a press from the mold mounting table 8 to the heating plate 3b, and from the heating plate 3b to the press plate 4b is performed. The plate 4b is moved to the cooling plate 5b, and the cooling plate 5b is moved to the mold mounting table 9.

 The control means 10 also controls the temperature of a pair of upper and lower plates in each stage of heating, pressing, and cooling, timing of vertical movement, etc., so that a series of molding operations can be performed smoothly and continuously. Is controlled to be performed. At this time, the opening and closing of the taking-in shutter and the taking-out shutter are also controlled. Furthermore, it is preferable to control the supply amount and timing of nitrogen so that the atmosphere in the chamber 2 is filled with an inert gas.

  In other words, the optical element molding apparatus 1 is an optical element molding apparatus that carries out a predetermined process while raising and lowering the temperature at one or more positions, by conveying a molding die.

And in this invention, it has the characteristics in the temperature management of the cooling plate 5b. That is, the control means 10 has a cooling plate temperature control unit 10a for adjusting the temperature of the cooling plate 5b by a unique control method. In the cooling plate 5b according to the present invention, a molding die 50 in which an optical material is accommodated. , The set temperature is raised from the reference temperature T ₀ to the hunting suppression temperature T ₁ (where T _p > T ₁ > T ₀ , where T _p is the plate set temperature in the previous position) After that, temperature control is performed to lower the temperature to the reference temperature T ₀ at a predetermined temperature decrease rate.

  Since each of the heating plate 3b and the press plate 4b is also managed at a predetermined temperature, the temperature is managed by the control means 10 based on the plate temperature measuring means and the measured temperature obtained from the measuring means. However, the temperature control in these plates is basically managed with the set temperature of each plate being fixed to a predetermined temperature.

  On the other hand, as described above, the cooling plate 5b of the present invention is characterized in that the temperature is adjusted while changing the set temperature in conjunction with the timing of the molding operation. Specific temperature adjustment will be described later.

  The temperature management of the plate including the heating plate 3b and the press plate 4b in addition to the cooling plate 5b is performed by measuring the temperature of the plate by a known temperature measuring means and feeding back the obtained measured temperature to the control means 10. To maintain the plate at a predetermined temperature. At this time, the temperature of the plate is generally measured using a thermocouple disposed inside the plate. In the present case, for example, as shown in FIGS. 2A and 2B, the lower cooling plate 5b is composed of a cooling plate body 5b-1 and a soaking plate 5b-2, and the soaking plate 5b- It is preferable that the thermocouple 5e is inserted and arranged in the vicinity of the mounting portion of the mold, and more preferably an arrangement in contact with the placed mold. The thermocouple 5e is disposed, for example, at the center of the mounting surface at a position of 0 mm to 0.05 mm toward the inside of the plate, and the tip of the thermocouple is disposed on the same plane as the mounting surface (contact surface) of the molding die. It is only necessary to provide a through hole in the center of the soaking plate and insert a thermocouple. 2A and 2B, the thermocouple 5e is disposed on substantially the same plane as the mold contact surface from a through hole provided in the center through a groove provided in the lower part of the soaking plate 5b-2.

  2A and 2B show an example in which one thermocouple 5e is provided at the center of the plate when viewed in plan, but a plurality of these are provided, and the temperature at each measured position is controlled by the temperature of the cooling plate. It may be fed back to the unit 10a and managed by an average value thereof or a temperature calculated by a predetermined calculation formula.

Next, an optical element molding method using the optical element molding apparatus 1 will be described.
First, the molding die 50 is placed on the molding die placing table 8 on the inlet side, and the optical material is accommodated in the molding die 50. The intake shutter 6 is opened to open the intake port, and the mold 50 is conveyed onto the heating plate 3b by the conveying means. When conveyed, the lower mold of the mold 50 is brought into contact with the lower heating plate 3b so that the temperature is raised to the same temperature as the heating plate 3b. At the same time, the upper die is brought into contact with the upper heating plate 3b from above and heated similarly.

  When the upper mold and the lower mold are heated in this way, the optical material housed therein is also heated, and when this optical material is heated above the yield point, the deformation becomes easy. Generally, the heating temperature is set to a temperature between the yield point (At) and the softening point because the lens surface becomes clouded when the temperature is raised to the softening point. At this time, the temperature rising rate is preferably about 0.5 to 2.5 ° C./sec.

  In this way, the mold 50 and the optical material sufficiently heated by the heating stage 3 are conveyed and placed on the lower press plate 4b by the conveying means.

  The press plate 4b is also heated to the same temperature as the heating plate 3b, and maintains the optical material in a softened state. Further, the upper press plate 4b is lowered to narrow the distance between the press plates 4b, the distance between the upper mold and the lower mold is also narrowed, and pressure is applied to the optical material housed in the molding die 50, so that the optical Deform the material.

  In this pressing step, as described above, the optical material is press-molded by applying pressure from above and below the mold 50, whereby the optical forming surfaces of the upper die and the lower die are transferred to the optical material, and the optical element shape is changed. Is granted.

In the press in this pressing step, the heating temperature is about the same as the temperature heated in the preceding heating stage, and the pressure during pressing is 2.5 to 37.5 N / mm ² per unit area of the lens molded body. Is more preferable, and 10 to 20 N / mm ² is particularly preferable.

  Then, through such a pressing step, the molding die 50 that has been subjected to the press-cutting is conveyed from the press plate 4b to the cooling plate 5b by the conveying means.

  Next, the mold 50 is cooled by the cooling plate 5b. This is similar to the above heating process. The lower mold is brought into contact with the lower cooling plate 5b, and the upper mold is brought into contact with the upper cooling plate 5b being lowered. Let cool. This cools and solidifies the optical material. This cooling is preferably performed to a temperature below the glass transition point (Tg) of the optical material, and more preferably to a temperature below the strain point of the optical material. At this time, the cooling rate is preferably 0.1 to 2.5 ° C./sec, more preferably 0.5 to 1.0 ° C./sec.

In the present invention, the set temperature of the cooling plate 5b is set to a higher hunting suppression temperature T ₁ than the reference temperature T ₀ that is the temperature of the mold 50 that is finally desired to reach the cooling plate. Manage while changing. This temperature management will be described with reference to FIGS. 3A and 3B.

  3A and 3B are diagrams showing a change in temperature of the mold when the mold 50 is transferred from the press plate 4b to the cooling plate 5b and a change in the set temperature of the cooling plate 5b at that time. In these drawings, the temperature of the mold 50 is indicated by a solid line, and the change in the set temperature of the cooling plate 5b is indicated by a one-dot chain line.

First, the cooling plate 5b is before the mold 50 come transported manages the reference temperature T ₀ is the temperature of the mold 50 to be finally allowed to reach the setting temperature. However, the mold 50 is finished processing in the press plate 4b, when coming transferred to the cooling plate 5b, it raises the setting temperature to a high hunting suppressing temperatures T ₁ than the reference temperature T _0.

At this time, the heat of the molding die 50 heated to a high temperature by the press plate 4b moves to the cooling plate 5b by coming into contact with the cooling plate 5b, so that the temperature of the molding die 50 decreases, and the temperature of the cooling plate 5b Rises. At this time, the temperature of the cooling plate 5b, since relatively quickly rises to a temperature exceeding the hunting suppressing temperature T _1, then the heat transfer is continued from the mold 50 to the cooling plate 5b, the cooling plate The temperature controller 10a reduces the heater output of the cooling plate 5b. When the temperature of the mold 50 is lowered to the hunting suppressing temperatures T _1, as it is below the hunting suppressing temperatures T _1, the same order below the temperature hunting suppressing the temperature T ₁ of the cooling plate 5b simultaneously, hunting the temperature of the cooling plate 5b When attempting to hold the suppression temperature T _1, the temperature control section 10a raises the heater output.

At this time, the temperature in the hunting suppressing temperatures T ₁ as in the prior art is vertically moved, in the present invention, at a timing when the vertical movement occurs continuously based on the set temperature of the cooling plate 5b from hunting suppressing temperatures T ₁ gradually lowered to a temperature T _0. That is, vertical movement occurs because the mold 50 means that you have reached the hunting suppressing temperature T _1, if followed, suitable for going slowly lowering the temperature of the mold 50, the optical element This is because the shape is easy to stabilize. Timing going the set temperature is lowered from hunting suppressing temperatures T ₁ to the reference temperature T ₀ is preferably a timing capable of suppressing the hunting phenomenon, for example, shown in FIG. 3B, the temperature of the cooling plate 5b is hunting suppressing temperatures T ₁ upon sensing that lower than or (P point in the figure), then, upon sensing that rises above hunting suppressing temperatures T ₁ again (Q point in the drawing), setting at any time equal Change the temperature. 3A and 3B, the change in the set temperature is indicated by a one-dot chain line, but here, the case where the set temperature is changed at the timing of the point Q is illustrated. Note that the number of times of vertical movement can be counted as one when an extreme value is taken in a temperature change, such as point P or point Q in FIG. 3B.

The change in the set temperature of the cooling plate 5b so as not rapidly changed the plate temperature, it is preferable to continuously change from the hunting suppressing temperatures T ₁ to the reference temperature T _0, the cooling rate of the cooling plate, for example, 0.05 ° C./sec to 0.5 ° C./sec is preferable. Cooling rate from hunting suppressing temperatures T ₁ to the reference temperature T ₀ is a time zone of hunting suppression time zone of temperatures T ₁ toward the reference temperature T ₀ close, in may be different, since the temperature history is stabilized It is preferable to make the temperature drop rate constant.

By changing the set temperature in this way, the number of temperature vertical movements based on the hunting phenomenon can be reduced, and the hunting phenomenon can be suppressed in a short time. Moreover, since the reference temperature T ₀ can be reached while being slowly cooled, the occurrence of the hunting phenomenon itself can be suppressed.

Incidentally, hunting suppressing temperatures _{T 1 is} set so as to satisfy the relation _{T p> T 1> T 0} . Here, T _p represents the setting temperature of the plate before the position, in the present embodiment, T _p is the set temperature of the press plate 4b.

Further, the hunting suppression temperature T ₁ is preferably {(T _p −T ₀ ) × 0.8 + T ₀ } or less, more preferably {(T _p −T ₀ ) × 0.5 + T ₀ } or less, and {(T _p -T ₀ ) × 0.25 + T ₀ } or less is more preferable. That is, in between the reference temperature T ₀ of the previous position of the plate set temperature T _P, to set the hunting suppressing temperatures T ₁ as possible to the reference temperature T ₀ side preferred. When the hunting suppression temperature T ₁ is a temperature equal to or lower than {(T _p −T ₀ ) × 0.8 + T ₀ }, the hunting phenomenon that occurs in the temperature of the mold 50 that has been transferred to the cooling plate 5b is suppressed. This is preferable. Further, when the hunting temperature T ₁ is a temperature of {(T _p −T ₀ ) × 0.5 + T ₀ } or lower, cooling from the hunting suppression temperature T ₁ to the reference temperature T ₀ is desired while suppressing the hunting phenomenon. It is more preferable because the temperature can be stably cooled at a lowering rate of temperature and the tact time can be shortened. Furthermore, if the hunting temperature T ₁ is a temperature of {(T _p −T ₀ ) × 0.25 + T ₀ } or lower, more stable and gentle cooling can be achieved while suppressing the hunting phenomenon, and the tact time can be shortened. Particularly preferred.

Further, the hunting suppression temperature T ₁ is preferably in a temperature range that is + 1 ° C. to + 60 ° C. higher than the reference temperature T ₀ . This temperature range can be applied when adjusting the temperature of the plate in the cooling process, but in particular, when the set temperature difference of each plate is 5 ° C. to 70 ° C. as in the case of transferring from the press plate 4b to the cooling plate 5b. Suitable for

  In the heating process and the cooling process described above, the temperature may be gradually increased and gradually increased or decreased. In this case, one or more heating stages are provided as the heating process, and the temperature of the optical material is gradually increased. Is raised to the molding temperature in the heating stage immediately before the press stage. Also in the cooling process, one or more cooling stages may be provided, and the temperature of the optical material may be lowered stepwise to cool to a temperature of 200 ° C. or lower. As described above, when heating and cooling are performed step by step, a rapid temperature change of the optical material is suppressed, and control that does not deteriorate the characteristics of the optical element such as distortion or surface cracking can be easily performed. . Here, surface cracking means that when an optical element is released from a mold, only a part is released first, and then the rest is released, and an optical surface with a discontinuous curvature is formed. A mold release abnormality that causes a defect in which the accuracy of the aspheric shape deteriorates.

  FIG. 4 shows an example of an optical element molding apparatus having a plurality of heating stages and cooling stages in order to perform such a heating process and a cooling process. The optical element molding apparatus 11 shown in FIG. 4 includes a chamber 12, a first heating stage 13, a second heating stage 14, a third heating stage 15, a press molding stage 16, a first cooling stage 17, The apparatus has a second cooling stage 18 and a third cooling stage 19, and in the chamber 12, as with the optical element molding apparatus 1, an inlet for the molding die 50 and an inlet that can be opened and closed. The shutter 20, the take-out port and the take-out shutter 21 that can be opened and closed, and the mold mounting tables 22 and 23 are provided outside the take-in port and the take-out port. Further, this molding apparatus has a control means 24, and the control means 24 controls the temperature of a pair of upper and lower plates in each stage of heating, pressing and cooling, timing of vertical movement, etc. A series of molding operations are performed smoothly and continuously. The control means 24 includes a cooling plate temperature control unit 24a for controlling the cooling plate by a predetermined control method, and the cooling plate is managed by temperature control similar to the temperature control described in the first embodiment. .

  The optical element molding apparatus 11 has the same configuration as the optical element molding apparatus 1 of FIG. 1 except that three heating stages and three cooling stages are provided to enable heating and cooling in stages. is there.

  For example, in the first heating stage 13, preliminary heating is performed to once heat the optical material to a temperature lower than the glass transition point and about 200 to 400 ° C., and in the second heating stage 14, to a temperature near the glass transition point, In the 3rd heating stage 15, it heats to the temperature of a yield point + 10-30 degreeC. Further, for example, while maintaining the molding temperature at the press stage 16, an optical element shape is imparted by a molding operation using a molding die, and the first cooling stage 17 is cooled to about the glass transition point of the optical material + 20 ° C. The cooling stage 18 may be further cooled to below the glass transition point or further below the strain point, and the third cooling stage 19 may be cooled to a temperature of 200 ° C. or lower at which the mold is not oxidized.

  Here, the third cooling stage can be efficiently cooled if the plate to be used is a water cooling plate provided with a pipe 19a so that the cooling water circulates in place of the heater in the other stage.

  In this optical element molding apparatus 11, the set temperature of at least one cooling plate of each of the first, second, and third cooling stages may be cooled by the temperature control described above. In particular, the first cooling plate 17b is a plate where the press plate 16b, which is the previous position, has the highest temperature during molding and the temperature difference tends to increase. Therefore, the first cooling plate 17b is used as a temperature control unit for the cooling plate. Preferably, the temperature is controlled by 24a, and a plurality of sets of cooling plates, for example, the first and second cooling plates are sequentially controlled from the position close to the press plate 16b by the temperature control unit 24a of the cooling plate. Is more preferable. Further, all the cooling plates in a plurality of sets may be temperature-controlled by the cooling plate temperature control unit 24a. In the last cooling plate of the plurality of sets, the temperature is sufficiently low as in the case of cooling by water cooling, so that if the hunting phenomenon does not affect the optical element shape, the characteristic described above There is no need to control the temperature, and the temperature may be controlled while being fixed to a predetermined temperature as in the prior art. This is the same when four or more sets of cooling plates are provided, and it is preferable to manage one or more sets of cooling plates from a position close to the press plate by the temperature control of the present invention. It may be applied to all the cooling plates other than the cooling plate using

  The optical element obtained by cooling as described above is then formed into an optical element shape by centering the surplus portion in order to obtain an optical element shape, or subjected to an annealing process to remove distortion. The final product is made by post-processing such as.

  As described above, by changing the set temperature of the cooling plate according to the transfer of the mold and the timing of temperature change, variations in the temperature history due to the hunting phenomenon can be reduced, and the occurrence of defective optical elements can be suppressed.

  Hereinafter, the present invention will be described in more detail with reference to Examples (Examples 2 to 7, Examples 9 to 13, Example 15 to Example 19) and Comparative Examples (Examples 1, 8, and 14).

(Example 1)
The optical element was molded as follows using the optical element molding apparatus 11 of FIG.
The optical element molding apparatus used here is a mounting surface of a mold for a plate body having three 500 W cartridge heaters inside a stainless steel 100 mm × 78 mm × 18 mm cuboid as a heating plate, a press plate, and a cooling plate. A plate with a 100 mm x 78 mm x 5 mm soaking plate made of cemented carbide made of tungsten carbide on the side is used. A laminate of × 9 mm plate-like bodies was used. The thermocouple in the cooling plate is provided with a through hole at one central portion of the soaking plate forming mold mounting portion so that the tip of the thermocouple is the same surface (height) as the soaking plate mounting die mounting surface. And placed in.

The cylinder that moves the upper plate up and down uses an air cylinder, and a shaft having a shaft diameter of 40 mm is connected and fixed to the upper plate. The chamber was a box shape of 440 mm × 592 mm × 240 mm made of SS400, and a lower plate of this chamber was 440 mm × 592 mm × 20 mm.
The mold 50 is composed of an upper mold, a lower mold, and a trunk mold having an inner cylinder and an outer cylinder. The upper mold, the lower mold, and the inner cylinder are made of cemented carbide made of tungsten carbide, and the outer cylinder is made of SUS. Thus, by press molding, a bi-concave concave meniscus shaped product having a diameter of 30 mm, a center thickness of 1.3 mm, a peripheral thickness of 8 mm, and an aspherical approximate curvature radius of 1200 mm and 15 mm, respectively, is obtained. An optical element having a diameter of 27 mm was obtained by machining.

  First, a diameter φ of 28 mm, a center thickness of 3.93 mm, a peripheral thickness of 7.75 mm, and a radius of curvature of 500 mm concave on the convex side are formed on the molding surface of the lower mold of the molding die 50 described above by grinding and polishing made of lanthanum borate glass. An optical material of a 20 mm concave meniscus spherical lens was placed. This optical material has a strain point of 580 ° C., a glass transition point (Tg) of 616 ° C., and a yield point (At) of 662 ° C.

The mold containing the optical material is conveyed and placed on the first heating plate by the conveying means, and at the same time, the upper first heating plate is lowered to contact the upper mold, and the molding die and the optical material are held for 215 seconds. Next, the upper second heating plate is lowered and brought into contact with the upper die, and the molding die and the optical material are heated for 215 seconds. The upper press plate was lowered and brought into contact with the upper die at the same time as being transported and placed on the upper die, and the molding die and the optical material were heated to press-mold the optical material in a softened state. The pressing pressure at the time of molding was 10 N / mm ² and the pressing time was 215 seconds. The first heating plate was set to 600 ° C., the second heating plate was set to 650 ° C., and the third heating plate and the press plate were set to 700 ° C.

  After pressing, the mold is transported and placed on the first cooling plate, and at the same time, the upper first cooling plate is lowered to contact the upper mold and cooled, and then the mold is placed on the second cooling plate. At the same time, the upper second cooling plate is lowered and brought into contact with the upper mold, cooled, and further transferred and placed on the third cooling plate, and at the same time, the upper third cooling plate is moved to the upper mold. It was lowered and brought into contact with the upper mold and cooled. At this time, the first cooling plate was set to 630 ° C., the second cooling plate was set to 615 ° C., and the third cooling plate was set to 20 ° C. (cooling water temperature).

  The optical material was cooled to room temperature, and when it was sufficiently cooled, it was removed from the mold and an optical element was obtained.

(Examples 2 to 7)
Using the same optical element molding apparatus as in Example 1, an optical element was obtained in the same manner. However, in Examples 2 to 7, in the first to second cooling plates, a hunting suppression temperature T ₁ higher than the reference temperature T ₀ of each cooling plate is set, and when the mold is transferred, the (cooled) temperature setting and hunting suppressing temperatures T _1, then the optical element by changing only in that cooling at a constant speed at a predetermined timing (point in Fig. 3B Q) from hunting suppressing temperatures T ₁ to the reference temperature T ₀ Manufactured. Here, the hunting suppressing temperature T ₁ of the first cooling plate, as shown in Table 1 (T 1 _{-T 0)} is subjected to molding of an optical element by changing the range of up to from 10 to 56 ° C.. In each example, the plate temperature is from reaching the reference temperature T ₀ so as to move to the next position. The temperature of the hunting suppressing the temperature T ₁ of the second cooling plate, was T 0 _{+ 4} ℃. Third cooling plate is for a water-cooled, setting the hunting suppressing temperatures T ₁ was not performed.

(Example 8, Example 14)
Except for changing the reference temperature of the first cooling plate so that the temperature difference between T _P and T ₀ between the press plate and the first cooling plate is 50 ° C. (Example 8) and 20 ° C. (Example 14), An optical element was obtained in the same manner as in Example 1.

(Example 9 to Example 13, Example 15 to Example 19)
The temperature difference between T _P and _{T 0} 50 ° C. (Examples 9 to 13), and 20 ° C. with (Example 15 Example 19), the temperature of the hunting suppressing the temperature _{T 1,} as shown in Table 1 _{(T 1} - Except for changing the reference temperature of the first cooling plate so that T ₀ ) is in the range of 5 ° C. to 30 ° C. (Examples 9 to 13), 2 ° C. to 14 ° C. (Examples 15 to 19). An optical element was obtained in the same manner as in Examples 2-7.

(Test Example 1)
In Examples 1 to 19, the relationship between the reference temperature (T ₀ ) of the first cooling plate, the hunting suppression temperature (T ₁ ), and the set temperature (T _P ) of the press plate that is the previous position, T ₁ to T ₀ Table 1 shows the cooling rate up to, the time until the hunting is settled, and the tact required for the first cooling. Further, in each _example, T 1 = calculates X from _{{(T P -T 0) ×} X + T 0}, shown together. In the conventional examples (Example 1, Example 8, Example 14) in which (T ₁ -T ₀ ) is 0, the cooling rate from _TP to T ₀ is not controlled, but it is approximately 0 on average. 4 ° C./sec.

From Table 1, Examples 2 to 7 was set hunting suppressing temperature _{T 1,} Examples 9 to 13, Example 15 to Example 19, Example 1, Example 8, hunting than Example 14 which is a conventional example corresponding respectively The time to fit is shortened. Therefore, it is considered that the number of vertical movements can be suppressed accordingly.

Table 2 also shows information equivalent to that in Table 1 for the second cooling plate. That is, in Examples 1 to 19, the relationship between the reference temperature (T ₀ ) of the second cooling plate, the hunting suppression temperature (T ₁ ), and the set temperature (T _P ) of the first cooling plate as the previous position, cooling rate from T ₁ to _{T 0,} the time until hunting fit, respectively table X, the calculated from the tact necessary for the second _{cooling, T 1 = {(T P} -T 0) × X + T 0} It was shown in 2.

From Table 2, also in the second cooling plate, Examples 2 7 set the hunting suppressing temperature _{T 1,} Examples 9 to 13, Example 15 to Example 19, Example 1 is a conventional example corresponding Examples 8. Compared with Example 14, the time until the hunting is settled can be shortened. Therefore, it is considered that the number of vertical movements can be suppressed accordingly.

(Test Example 2)
For Examples 1 and 3, ten sets of molds were used to continuously produce 500 optical elements. When it was confirmed whether or not the finally obtained optical element had a shape defect, as shown in Table 3, in Example 1, the shape defect was 48%, the appearance defect was 2%, and the yield was 50%. On the other hand, in Example 3, the shape defect was 0%, the appearance defect was 2%, and the yield was as good as 98%.

  It should be noted that, in Examples 1 and 3 at this time, the temperature of the molding die was the same as that of the molding die used, and a thermocouple was provided at the center of the bottom surface of the lower die at a depth of 0.5 mm. The results of measuring the temperature of the mold (lower mold) during the molding operation using the tool are shown below.

In Example 1, the mold in the first cooling plate reached 647 ° C. in 133 seconds after movement (X = 0.24), although becomes 630 ° C. _{(T 0)} in 175 seconds, than _{T 0} in 185 seconds After 195 seconds, the temperature becomes 2 ° C. higher than T ₀ , and after 200 seconds, the temperature becomes 1 ° C. lower than T ₀ , and then hunting is repeated within a range of ± 0.2 ° C. _It was 205 seconds when it stabilized to ₀ .

On the other hand, in Example 3, the mold reaches 647 ° C. (X = 0.24) in 133 seconds after moving to the first cooling plate, and reaches 645 ° C. (temperature lower by 2 ° C. than T ₁ ) in 138 seconds. After 143 seconds, the temperature became 648 ° C. (temperature higher by 1 ° C. than T ₁ ), and after 153 seconds, the temperature became 647 ° C. (T ₁ ). Thereafter, the cooling was stably performed along the cooling gradient, and the time when T ₀ was stabilized was 209 seconds.

Until hunting of the mold temperature falls, whereas it took 205 seconds for example 1, an example 3 in 153 seconds, then, since that could be gently cooled to T _0, hunting in the vicinity of T ₀ did not produce . Also in the second cooling plate, since that could be gently cooled to T _0, hunting in T ₀ it did not occur.

As shown above, the history at a temperature variation of the volume or the press position of the mold the heat capacity and the glass to reduce the temperature hunting time when dependent cooling, further heat capacity of the mold from T ₁ to T ₀ It was possible to cool each time at a constant speed regardless of the volume of the glass. Therefore, the optical element molding apparatus and molding method of the present invention suppresses and eliminates factors that make the temperature of the mold instability in the manufacture of optical elements unstable, and suppresses a rapid temperature change of the mold to reduce the shape of the optical element. It was found that it can stabilize the yield and improve the yield.

  The optical element molding apparatus of the present invention is used when manufacturing optical elements continuously by press molding while sequentially moving a mold.

DESCRIPTION OF SYMBOLS 1 ... Optical element shaping | molding apparatus, 2 ... Chamber, 3 ... Heating stage, 4 ... Press stage, 5 ... Cooling stage, 6 ... Taking-in shutter, 7 ... Taking out shutter, 8, 9 ... Mold mounting base, 10 ... Control means DESCRIPTION OF SYMBOLS 10a ... Temperature control part of cooling plate, 50 ... Mold, 3a, 4a, 5a ... Heater, 3b ... Heating plate, 4b ... Press plate, 5b ... Cooling plate, 3c, 4c, 5c ... Heat insulation plate, 3d, 4d , 5d ... Shaft, 5e ... Thermocouple

Claims (9)

An optical material is accommodated in a mold composed of an upper mold, a lower mold, and a body mold, and the heating mold is heated by a heating plate to soften the optical material, and the softened optical material is pressed using a press plate. An optical element comprising: a pressing step for applying an optical element shape by pressing with the molding die; and a cooling step for cooling the molding die with a cooling plate after the pressing step to solidify the optical material provided with the optical element shape. A molding method of
In the cooling step, when the mold containing the optical material is transferred, the set temperature of the cooling plate is raised from the reference temperature T ₀ to the hunting suppression temperature T ₁ (where T _p > T ₁ > T ₀ , and T _p represents the set temperature of the plate in the previous position.) After the mold reaches the hunting suppression temperature T ₁ , the temperature is lowered to the reference temperature T ₀ at a predetermined temperature drop rate. An optical element molding method. The method for molding an optical element according to claim 1, wherein the hunting suppression temperature T ₁ is {(T _p −T ₀ ) × 0.8 + T ₀ } or less. The method for molding an optical element according to claim 2, wherein the hunting suppression temperature T ₁ is {(T _p −T ₀ ) × 0.5 + T ₀ } or less. The method for molding an optical element according to claim 3, wherein the hunting suppression temperature T ₁ is {(T _p −T ₀ ) × 0.25 + T ₀ } or less. The hunting suppressing temperature T ₁ is, molding of an optical element according to any one of claims 1 to 4 than T ₀ is a high temperature range of + 1 ℃ ~ + 60 ℃. Method of forming the cooling rate from the hunting suppressing temperatures _{T 1} to said reference temperature _{T 0} is, 0.05 ℃ / sec~0.5 ℃ / sec optical element of any one of claims 1 to 5, . Method of forming the cooling rate from the hunting suppressing temperatures T ₁ to said reference temperature T ₀ is, the optical element described in any one of claims 1-6 which is a constant speed. An optical element molding apparatus for forming an optical element by sequentially transporting a molding mold in which an optical material is placed between an upper mold and a lower mold to heating, pressing and cooling stages provided in the chamber,
The mold is mounted on each of the heating, pressing and cooling stages, and a pair of upper and lower heating plates, a press plate and a cooling plate, which perform heating, pressing and cooling processes on the mounted molding mold, respectively. A plurality of sets of plates, drive means for causing the pair of plates in each set to approach or separate to perform the heating, pressing and cooling processes, and control means for controlling the transport of the processes and the mold, With
The control means raises the set temperature of the cooling plate from the reference temperature T ₀ to the hunting suppression temperature T ₁ when the mold containing the optical material is transferred (where T _p > T ₁ > T ₀ , and T _p represents the temperature of the plate at the previous position.) After the mold reaches the hunting suppression temperature T ₁ , a temperature control unit that lowers the temperature to the reference temperature T ₀ at a predetermined temperature lowering rate. An optical element molding apparatus comprising the optical element.   The optical element molding apparatus according to claim 8, wherein the temperature control by the temperature control unit is performed while feeding back a temperature measured by a thermocouple disposed in the vicinity of a mounting portion of the mold for cooling plate.

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