JP2008094654A - Method and apparatus for manufacturing optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing optical elements, by which optical elements each having a high precision optical surface can be manufactured at high manufacturing efficiency by uniformizing the cooling rates at the center part and the end part of molten glass. <P>SOLUTION: The method for manufacturing the optical elements includes: a heating process for heating a forming mold to a prescribed temperature; a molten glass supply process for supplying molten glass to the forming mold; a cooling process for cooling the molten glass by bringing a cooling member into contact with the upper surface of the supplied molten glass; and a forming process for press-forming the molten glass. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical element manufacturing method and apparatus for obtaining glass optical elements by pressure molding molten glass with a molding die.

  Today, glass optical elements are widely used as digital camera lenses, optical pickup lenses such as DVDs, mobile phone camera lenses, optical communication coupling lenses, various mirrors, and the like. Such glass optical elements are often manufactured by a press molding method in which a glass material is pressure-molded with a molding die. In particular, an optical element having an aspheric surface as an optical surface is not easily formed by grinding / polishing, and therefore is generally manufactured by a press molding method using a molding die. Among them, a direct press method for obtaining a glass optical element by directly pressure-molding molten glass with a molding die is attracting attention because high production efficiency can be expected.

  As a method for obtaining a glass optical element by directly pressure-molding molten glass with a molding die, the molten glass from the nozzle tip is retained in the support member, and then the support member is withdrawn from the nozzle tip. A method of pressure-molding a glass gob with an upper mold and a lower mold is known (see, for example, Patent Document 1).

  However, the speed at which the molten glass is cooled during the molding process is different between the upper and lower surfaces of the molten glass, or the center and ends, and the amount of shrinkage due to cooling becomes uneven. It was difficult to form a surface. In particular, it has been very difficult to form a highly accurate optical surface on the lower surface side where the molten glass first contacts with the support member and is rapidly cooled.

  In addition, after conveying the molten glass supplied to the receiving mold onto the lower mold, only the upper optical surface on which the temperature of the molten glass is relatively stable is formed by pressing with the upper and lower molds. There has been proposed a method of manufacturing a glass lens by forming a molding surface by transfer and forming an optical surface on the lower surface side by additional processing (grinding / polishing) (see, for example, Patent Document 2).

In Patent Document 2, the distribution of the cooling rate in the radial direction of the lens is reduced by forming the receiving surface of the lower mold so that the thickness of the molded lens is uniform over the entire surface. It is disclosed that a highly accurate optical surface can be obtained on the side.
JP-A-6-206730 JP-A-8-208248

  However, in practice, even if the lower mold receiving surface is formed so that the thickness of the optical element to be molded is uniform over the entire surface, the molten glass is melted in the state where the molten glass is stored on the lower mold receiving surface. Generally, the thickness of the central portion is larger than the end portion due to the surface tension of the glass. Therefore, at the stage where pressure molding is performed with the upper mold and the lower mold, the end portion is already cooled more than the center portion, so the amount of shrinkage during molding is not uniform, There was a problem that a highly accurate optical surface could not be obtained on the upper surface side of the optical element.

  Further, when manufacturing a relatively large optical element having an outer diameter of, for example, φ20 mm or more, it is necessary to store a large amount of molten glass on the receiving surface of the lower mold, so that the outer diameter for regulating the outer diameter of the molten glass is limited. It is necessary to use a molding die provided with an outer diameter regulating member having a diameter regulating surface. In this case, the supplied molten glass not only contacts the receiving surface of the lower mold but also contacts the outer diameter regulating surface of the outer diameter regulating member. Since the molten glass is rapidly cooled from the contact surface with these molding dies, when using a molding die having such an outer diameter regulating member, the end of the molten glass is cooled more rapidly. Will proceed to. As described above, a large difference occurs in the cooling rate between the central portion and the end portion of the molten glass, so that the amount of shrinkage of the molten glass during molding is not uniform, and a high-precision optical surface is obtained on the upper surface side of the optical element. That was even more difficult.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to provide an optical element having a high-precision optical surface by uniformizing the cooling rate of the center portion and the end portion of the molten glass. It is providing the manufacturing method of the optical element which can be manufactured with high production efficiency.

  In order to solve the above problems, the present invention has the following features.

  1. A molding die comprising a lower mold having a receiving surface for receiving molten glass and an upper mold having a molding surface for forming the first optical surface of the optical element, a predetermined temperature lower than the temperature of the molten glass A heating step for heating the molten glass, a molten glass supplying step for supplying the molten glass to the receiving surface of the lower mold, and a cooling step for cooling the molten glass by bringing a cooling member into contact with the upper surface of the supplied molten glass And a molding step of press-molding the molten glass with the molding die to form a molded body having a first optical surface to which the molding surface of the upper mold is transferred. Manufacturing method.

  2. When the diameter of the contact portion between the molten glass and the cooling member is φD, and the diameter of the contact portion between the molten glass and the lower mold receiving surface is φG, 0.3 ≦ φD / φG ≦ 0.9 2. The method for producing an optical element according to 1 above, wherein the method is satisfied.

  3. 3. The optical element according to 1 or 2, further comprising an additional processing step of forming a second optical surface on a back surface side of the first optical surface of the molded body by additional processing after the molding step. Production method.

  4). The molding die includes an outer diameter regulating member having an outer diameter regulating surface for regulating the outer diameter of the molten glass, and the molten glass supplied to the receiving surface of the lower mold in the molten glass supply step The method for manufacturing an optical element according to any one of 1 to 3, wherein the outer diameter regulating member contacts an outer diameter regulating surface of the outer diameter regulating member.

  5. A mold having a lower mold having a receiving surface for receiving molten glass and an upper mold having a molding surface for forming the first optical surface of the optical element, and the temperature of the molten glass as the mold A heating means for heating to a lower predetermined temperature, a molten glass supply means for supplying the molten glass to the receiving surface of the lower mold, and a cooling member in contact with the upper surface of the supplied molten glass To form a molded body having a first optical surface to which the molding surface of the upper mold is transferred by pressure-molding the molten glass with the cooling mold and cooling means for cooling the molten glass. An optical element manufacturing apparatus.

  According to the method for producing an optical element of the present invention, the temperature distribution of the molten glass supplied to the molding die can be made uniform by bringing the cooling member into contact with the upper surface of the molten glass prior to the molding step. The amount of shrinkage of the molten glass can be made uniform. Therefore, a molded body in which at least the optical surface on the upper surface side is formed with high accuracy by molding can be obtained, and an optical element having a high accuracy optical surface can be manufactured with high production efficiency.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Optical element)
The shape of the optical element produced by the method of the present invention is not particularly limited, and optical elements having various shapes such as a biconvex shape, a meniscus shape, a biconcave shape, and a flat surface can be produced. Here, the optical element includes a transmissive optical element such as a lens and a reflective optical element such as a mirror.

  FIG. 3 shows a meniscus lens 10 which is an example of an optical element manufactured in the present embodiment. The lens 10 has a first optical surface 11 formed by molding, a second optical surface 12 and an edge surface 13 formed by additional machining. The first optical surface 11 is a concave aspheric surface, and the second optical surface 12 is a convex spherical surface.

  There is no particular limitation as to which one of the two optical surfaces of the optical element is the first optical surface formed by molding. However, as in the lens 10, when one surface has a shape that is difficult to be formed by additional processing such as an aspherical surface or a diffractive surface, and the other surface is a general spherical surface, the former is formed by molding. It is preferable from the viewpoint of productivity that the first optical surface is a second optical surface formed by additional machining. However, when the optical element to be manufactured is a reflective optical element such as a mirror and has only one optical surface, the surface may be formed as a first optical surface by molding.

  FIG. 4 is a view showing a molded body obtained in a molding process for manufacturing the lens 10. In the present invention, the thickness of the molded body is not necessarily uniform over the entire surface. 4A shows a molded body 14a having a substantially uniform thickness over the entire surface, FIG. 4B shows a molded body 14b whose end portion is thicker than the center, and FIG. 4C shows an end portion. A molded body 14c having a larger thickness at the center is shown. In the present invention, any of the molded bodies 14a, 14b, and 14c may be used as a molded body for manufacturing the lens 10. In either case, the target lens 10 is completed by forming the second optical surface 12 and the edge surface 13 by additional machining as indicated by the wavy line in the figure.

  FIG. 5 shows a biconvex lens 20 which is another example of the optical element manufactured in the present embodiment. The lens 20 has a first optical surface 21 formed by molding, a second optical surface 22 and an edge surface 23 formed by additional machining. The first optical surface 21 is a convex aspheric surface, and the second optical surface 22 is a convex spherical surface.

  FIG. 6 is a view showing a molded body obtained in a molding process for manufacturing the lens 20. 6A shows a molded body 24a having a substantially uniform thickness, FIG. 6B shows a molded body 24b whose end portion is thicker than the center, and FIG. A molded body 24c having a larger central thickness is shown. Also in this case, any of the molded bodies 24a, 24b, and 24c may be used as the molded body for manufacturing the lens 20. In either case, the target lens 20 is completed by forming the second optical surface 22 and the edge surface 23 by additional machining as indicated by the wavy line in the figure.

(Molding mold)
FIG. 7 is a view showing a molding die 30 used in the present embodiment. The molding die 30 is a molding die for molding the molded body 14 a for the lens 10. The molding die 30 includes a lower die 31 and an upper die 32, and further includes an outer diameter regulating member 33. The lower mold 31 has a receiving surface 37 for receiving molten glass, and the upper mold 32 has a molding surface 38 for forming a first optical surface of the optical element. The outer diameter regulating member 33 has an outer diameter regulating surface 39 for regulating the outer diameter of the molten glass, and is fixed in combination with the lower mold 31. The lower mold 31, the upper mold 32, and the outer diameter regulating member 33 have heaters 34a, 34b, 34c and temperature sensors 35a, 35b, 35c as heating means, respectively.

  The outer diameter regulating member 33 is not necessarily an essential member in the manufacturing method of the present invention. However, for example, when a relatively large optical element having an outer diameter of φ20 mm or more is manufactured, a large amount is provided on the receiving surface 37 of the lower mold 31. Since it is necessary to store molten glass, it is preferable to include an outer diameter regulating member 33 having an outer diameter regulating surface 39 for regulating the outer diameter of the molten glass. As shown in FIG. 7, the outer diameter regulating member may be constituted by a member separate from the lower mold, or the receiving surface and the outer diameter regulating surface are formed on the same member, so that both the lower mold and the outer diameter regulating member function. You may use the member which combined these. Moreover, it is good also as a structure which can be attached or detached, without fixing with a lower mold | type, and it is also preferable to set it as the structure provided with the mechanism which can be moved up and down independently separately from a lower mold | type.

  The material of the lower mold 31, the upper mold 32, and the outer diameter regulating member 33 is formed by press-molding a glass optical element such as a super hard material mainly composed of tungsten carbide, silicon carbide, silicon nitride, aluminum nitride, or carbon. As a molding die for this purpose, it can be appropriately selected from known materials according to the use. Moreover, what formed protective films, such as various metals, ceramics, and carbon, on the surface of these materials can also be used. The lower mold 31, the upper mold 32, and the outer diameter regulating member 33 may all be made of the same material, or may be made of different materials.

  The molding surface 38 of the upper mold 32 has a shape corresponding to the first optical surface 11 of the lens 10. On the other hand, since the second optical surface 12 of the lens 10 is formed by additional machining after molding, the receiving surface 37 of the lower mold 31 does not need to have a shape corresponding to the second optical surface 12.

(Heating process)
The heating step is a step of heating the molding die to a predetermined temperature lower than the temperature of the molten glass. The lower mold 31, the upper mold 32, and the outer diameter regulating member 33 have heaters 34a, 34b, and 34c as heating means and temperature sensors 35a, 35b, and 35c, respectively. Thus, it is good also as a structure which can adjust temperature of each member independently, and it is good also as a structure which heats the whole shaping die collectively with one or several heaters. The heater can be appropriately selected from known various heaters. For example, a cartridge heater that is used by being embedded inside the member, or a sheet heater that is used while being in contact with the outside of the member can be used. In addition to various thermocouples, known means such as a platinum resistance thermometer and various thermistors can be used as the temperature sensor.

  Among the molding dies 30, the heating temperature of the upper mold 32 needs to be set in a temperature range in which the shape of the molding surface 38 can be satisfactorily transferred to the molten glass. Usually, it is preferable to make it the temperature range of Tg (glass transition point) -100 degreeC of glass to shape | mold to about Tg + 100 degreeC. If the heating temperature is too low, it becomes difficult to transfer the shape of the molding surface 38 to the molten glass. On the contrary, it is not preferable to raise the temperature more than necessary from the viewpoint of preventing fusion between the glass and the molding die and the life of the molding die. In practice, the appropriate temperature is determined taking into account various conditions such as the glass material to be molded, the shape and size of the molded body, the material of the molding die, the type of protective film, the position of the heater and temperature sensor, etc. To do.

  Unlike the upper mold 32, the heating temperature of the lower mold 31 and the outer diameter regulating member 33 does not need to consider the transferability of the molding surface, but it affects the cooling rate of the molten glass and is the same as the upper mold 32. Furthermore, it is preferable that the glass to be molded has a temperature range of about Tg-100 ° C to about Tg + 100 ° C.

(Molten glass supply process)
The molten glass supply step is a step of supplying molten glass to the receiving surface 37 of the lower mold 31. The supplied molten glass comes into contact with the receiving surface 37 of the lower mold 31 and is cooled. When the molding die includes the outer diameter regulating member 33 having the outer diameter regulating surface 39 for regulating the outer diameter of the molten glass, the molding die is also brought into contact with the outer diameter regulating surface 39 and cooled.

  There is no restriction | limiting in particular about the method of supplying molten glass, A well-known method can be selected suitably and can be used. FIG. 8 is a schematic diagram illustrating an example of a method for supplying molten glass. Molten glass is stored in the melting tank 41, and a molten glass droplet falls from the tip of the nozzle 42 provided in the lower part of the melting tank 41 by its own weight. At this time, the melting tank 41 and the nozzle 42 are heated to a predetermined temperature by the heater 43. In this state, the lower mold 31 is brought close to the tip of the nozzle to retain a predetermined amount of molten glass on the receiving surface 37, and then the lower mold 31 is pulled downward to cut the molten glass to supply molten glass. (See Patent Document 1). FIG. 8A is a view showing a state where the lower die 31 is brought close to the tip of the nozzle, and FIG. 8B is a view showing a state where the molten glass is cut by lowering the lower die 31 downward. is there. As another method, after a predetermined amount of molten glass is retained in the lower mold in a state where the molten glass flows out from the tip of the nozzle in a liquid line state, the molten glass is cut by a metal blade. It can also be supplied.

  As shown in FIG. 8B, the supplied molten glass 44 comes into contact with the receiving surface 37 of the lower mold 31 and the outer diameter regulating surface 39 of the outer diameter regulating member 33. Since the temperature of the lower mold 31 and the outer diameter regulating member 33 is lower than that of the supplied molten glass 44, the molten glass 44 is mainly cooled from these contact surfaces. Moreover, it is normal that the molten glass 44 becomes a shape where the center part rose by surface tension. For this reason, the supplied molten glass 44 has a temperature distribution in which the central portion has a high temperature and the end portion has a low temperature.

In addition, there is no restriction | limiting in particular in the kind of glass which can be used, The well-known glass used for an optical use can be selected and used according to a use. For example, phosphate glass, lanthanum glass, etc. (cooling process)
The cooling step is a step of cooling the molten glass by bringing a cooling member into contact with the upper surface of the supplied molten glass.

  As described above, the molten glass supplied to the molding die in the molten glass supply step has a temperature distribution in which the central part is high temperature and the end part is low temperature. If the molten glass in such a state is directly molded, the shrinkage amount of the molten glass at the time of molding is not uniform, and it is difficult to obtain a highly accurate optical surface. In the production method of the present invention, by bringing the cooling member into contact with the upper surface of the molten glass prior to the molding step, the center portion of the molten glass is cooled and the temperature distribution of the molten glass can be eliminated. An optical surface can be obtained.

  FIG. 1 is a schematic view showing a state in which a cooling member is in contact with molten glass. An outer diameter regulating member 33 is fixed to the lower mold 31. FIG. 1A is a diagram when a cylindrical cooling member 51 having a flat end is used, and FIG. 1B is a spherical surface having a convex end and a diameter larger than that of the cooling member 51. It is a figure at the time of using the cooling member 52. FIG.

  Moreover, FIG. 2 is the schematic diagram which showed another example of the state which the cooling member is contacting the molten glass. Unlike the case of FIG. 1, the outer diameter regulating member is removed after the end of the molten glass is cooled to some extent to increase the viscosity, and then the cooling member is brought into contact therewith. 2A is a diagram in the case where a cylindrical cooling member 53 having a flat end portion and a large diameter is used, and FIG. 2B uses a cooling member 54 having a truncated cone shape at the end portion. FIG.

  There is no particular limitation on the diameter φD of the contact portion between the molten glass and the cooling member. From the viewpoint of effectively cooling the center portion of the molten glass that is particularly hot, the diameter φD of the contact portion between the molten glass and the cooling member is the contact portion between the molten glass and the lower mold receiving surface. It is preferable that the diameter is smaller than the diameter φG. Furthermore, it is particularly preferable that the range satisfies 0.3 ≦ φD / φG ≦ 0.9.

  In general, the receiving surface of the molded body and the lower mold often has a circular outer diameter, and the contact portion between the molten glass and the cooling member and the contact portion between the molten glass and the lower mold receiving surface are also included. In many cases, the shape is circular, but the present invention is not limited thereto, and may be a shape other than a circle, such as a polygon. In this case, φD and φG mean the diameters of the circles when it is assumed that each part is a circle having the same area.

  The shape of the portion where the cooling member contacts the molten glass is not particularly limited, and may be various shapes such as a flat surface, a spherical surface, a cone, and a truncated cone. From the viewpoint of efficiently cooling not only near the surface of the molten glass but also to the inside, it is preferable to have a shape in which the central portion protrudes from the end portion of the contact portion such as a spherical surface, a cone, or a truncated cone.

  For the time of contact with the cooling member, an appropriate value is selected in consideration of conditions such as the type and temperature of the molten glass, the temperature of the molding die, and the diameter and thickness of the molded product to be obtained. Normally, when the cooling member is retracted and the contact with the molten glass is released, the molten glass returns to the form of a thick droplet at the center due to the surface tension, and the trace of contact with the cooling member is not a problem. However, if the contact time is too long and the cooling proceeds too much, the viscosity of the molten glass becomes too high, and the trace of contact with the cooling member may remain in the molded body as it is, which causes a problem. On the other hand, when the contact time is too short, the molten glass is not sufficiently cooled, and the temperature distribution of the molten glass may not be eliminated. Generally, about 1 to 20 seconds is a preferable range.

  The cooling member may have a temperature adjusting mechanism by providing a pipe for fluid such as water or oil, a heater, a temperature sensor, or the like. By keeping the temperature of the cooling member constant, the molten glass can be cooled stably. Although there is no restriction | limiting in particular in the temperature of a cooling member, From a viewpoint that it cools effectively and stably, 0 to 500 degreeC is preferable and 10 to 300 degreeC is still more preferable.

  The material of the cooling member is preferably one that has high heat resistance and is not easily deteriorated by contact with molten glass. Moreover, in order to take away the heat | fever of a molten glass efficiently, what has high heat conductivity and high specific heat is still more preferable. Materials that can be used as cooling members include, for example, heat-resistant steel such as stainless steel, nickel-based and cobalt-based heat-resistant alloys, superhard materials mainly composed of tungsten carbide, ceramics such as silicon carbide and silicon nitride, and carbon. Is mentioned. Moreover, what formed protective films, such as various metals, ceramics, and carbon, on the surface of these materials can also be used.

  Although the upper mold can be used as a cooling member, it is preferable that the cooling member and the upper mold are separate members. By making the cooling member a member different from the upper mold, the shape and temperature of the contact portion can be freely set, and deterioration of the upper mold can be minimized.

(Molding process)
The molding step is a step of forming a molded body having a first optical surface on which the molding surface of the upper mold is transferred by pressure-molding molten glass with a molding die.

  There is no particular limitation on the pressurizing means, and known pressurizing means such as an air cylinder, a hydraulic cylinder, and an electric cylinder using a servo motor can be appropriately selected and used.

  Cooling of the molten glass further proceeds during pressing. After being cooled to a temperature at which the molten glass is sufficiently solidified, the pressure is released and the molded body is taken out from the molding die. The temperature of the molded body at the time of releasing the pressure depends on the type of glass, the size and shape of the molded body, the required accuracy, and the like, but it may be usually cooled to a temperature in the vicinity of Tg of the glass. Necessary pressurization time and load vary depending on various conditions, but normally, an appropriate value may be selected from the range of pressurization time of 10 seconds to 300 seconds and load of 500 N to 20000 N.

  Note that pressurization may be performed while the molten glass and the outer diameter regulating member are in contact with each other, or the outer diameter regulating member is retracted before the molding process to release the contact between the molten glass and the outer diameter regulating member. After that, pressurization may be performed. In the latter case, it is necessary to retract the outer diameter regulating member after cooling until the viscosity reaches a level at which the molten glass does not flow outside.

  In addition, a step of annealing the molded body can be provided in order to remove distortion remaining in the obtained molded body and to make the quality such as the refractive index uniform and to obtain a more accurate optical element.

(Additional process)
The additional processing step is a step of forming the second optical surface on the back side of the first optical surface of the molded body after the molding step.

  In general, an optical surface can be formed by a process such as a roughing process using a high-speed grinding machine (curve generator), a fine grinding process using diamond pellets, or a polishing process for finishing the surface with an abrasive. However, the present invention is not limited to this, and a known method can be appropriately selected and used.

  Moreover, you may provide the process of forming the edge surface of an optical element by grinding etc.

(Example 1)
Using the molding die 30 shown in FIG. 7, the molded body 14a shown in FIG. 4A is produced, and the shape accuracy of the first optical surface 11 formed by transferring the molding surface of the upper mold is evaluated. went. The first optical surface 11 is usually an aspheric surface in many cases, but here a spherical surface having a curvature radius of 30 mm is used for easy evaluation.

  The outer diameter of the molded body 14a was 25 mm, and the wall thickness at the center was 6 mm. The center portion of the receiving surface 37 of the lower mold 31 is a concave surface having a curvature radius of 30 mm. The lower mold 31, the upper mold 32, and the outer diameter regulating member 33 are all made of super hard material mainly composed of tungsten carbide. The heating temperature was set to 520 ° C. for the lower die 31 and the outer diameter regulating member 33, and 430 ° C. for the upper die 32.

  As the glass material, phosphoric acid glass having a Tg of 495 ° C. was used. In a state where the nozzle is heated to 1000 ° C. and the molten glass droplet falls due to its own weight, the lower mold 31 is brought close to the tip of the nozzle and the molten glass is retained on the receiving surface 37, and then the lower mold 31 is moved downward. The molten glass was cut down to supply a predetermined amount of molten glass.

  The cooling member was brought into contact with the supplied molten glass. As the cooling member, the cooling member 51 shown in FIG. The material of the cooling member 51 was SUS310S. The cooling member 51 was not particularly equipped with a temperature control means, and the temperature before contact with the molten glass was about 28 ° C. The diameter φD of the contact portion between the molten glass and the cooling member was 10 mm, and the contact time was 5 seconds.

  When the contact with the molten glass was released by raising the cooling member, the molten glass returned to the same droplet shape as before the contact due to the surface tension. Then, the lower mold | type 31 was moved to the position facing the upper mold | type 32, and the molten glass was pressurized for 70 second with the load of 1800N.

  The shape accuracy of the optical surface 11 of the removed molded body was evaluated. For evaluation, the maximum value of the deviation from the spherical surface was obtained using a surface shape measuring instrument PGI840 manufactured by Taylor Hobson Co., Ltd., and the maximum value of the deviation from the spherical surface was 150 nm or less. The case where it was large and 300 nm or less and good was rated as ○, and the case where the problem was larger than 300 nm was marked as x.

  The evaluation results are shown in Table 1. The shape accuracy of the optical surface 11 is extremely good at 95 nm, and it was confirmed that a highly accurate optical surface can be formed by the method of the present invention.

(Example 2)
A molded body 14a was produced under the same conditions as in Example 1 except that the cooling member 52 shown in FIG. 1B was used as the cooling member. The surface of the cooling member 52 that contacts the molten glass was a convex spherical surface with a curvature radius of 20 mm. The material and temperature are the same as those of the cooling member 51 used in the first embodiment. The diameter φD of the contact portion between the molten glass and the cooling member was 15 mm, and the contact time was 3 seconds.

  The shape accuracy of the optical surface 11 of the obtained molded body was evaluated. Evaluation was performed in the same manner as in Example 1. The evaluation results are also shown in Table 1. The shape system was 70 nm, and an optical surface with higher accuracy than that of Example 1 could be formed.

(Comparative Example 1)
Without providing a cooling step, the supplied molten glass was directly molded to produce a molded body. Other conditions are the same as those in the first embodiment. The shape accuracy of the optical surface 11 of the obtained molded body was evaluated. Evaluation was performed in the same manner as in Example 1.

  The evaluation results are also shown in Table 1. Unlike the cases of Examples 1 and 2, the shape accuracy of the optical surface was larger than 300 nm, and a highly accurate optical surface could not be formed.

(Examples 3 to 7)
A molded body 24c shown in FIG. 6C was produced, and the shape accuracy of the first optical surface 21 formed by transferring the molding surface of the upper mold was evaluated. The first optical surface 21 was a spherical surface having a curvature radius of 30 mm.

  The outer diameter of the molded body 24c was φ40 mm, and the thickness of the central portion was 8 mm. The center part of the receiving surface of the lower mold is a concave surface with a curvature radius of 30 mm. The materials of the lower mold, the upper mold, and the outer diameter regulating member were all silicon carbide. The heating temperature was set to 710 ° C. for the lower mold, 730 ° C. for the outer diameter regulating member, and 680 ° C. for the upper mold.

  As the glass material, lanthanum glass having a Tg of 650 ° C. was used. After the nozzle tip is heated to 1200 ° C and molten glass flows out from the nozzle tip in a liquid line state, the molten glass is retained in the lower mold, and then the molten glass is cut with a metal blade to supply a predetermined amount of molten glass. did. About 10 seconds after cutting, the outer diameter regulating member was removed.

  The cooling member was brought into contact with the supplied molten glass. As the cooling member, the cooling member 53 shown in FIG. The material of the cooling member 53 was a super hard material mainly composed of tungsten carbide. The cooling member 53 is provided with a pipe through which oil for temperature adjustment flows. The temperature of the oil was adjusted, and the temperature of the cooling member 53 was set to 100 ° C. The diameter φD of the contact portion between the molten glass and the cooling member is 10 mm (Example 3), 12 mm (Example 4), 24 mm (Example 5), 36 mm (Example 6), and 40 mm (Example 7). Molded bodies were produced under various conditions. All contact times were 12 seconds.

  When the contact with the molten glass was released by raising the cooling member, the molten glass returned to the same droplet shape as before the contact due to the surface tension. Thereafter, the lower mold was moved to a position facing the upper mold, and the molten glass was pressurized with a load of 3200 N for 110 seconds.

  The shape accuracy of the optical surface 21 of the obtained molded body was evaluated. Evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 2. The shape accuracy of the optical surface 21 was good. In particular, when the diameter of the contact portion between the molten glass and the cooling member is φD and the diameter of the contact portion between the molten glass and the lower mold receiving surface is φG, 0.3 ≦ φD / φG ≦ 0.9 is satisfied. In Examples 4, 5, and 6, extremely good results were obtained.

(Comparative Example 2)
Without providing a cooling step, the supplied molten glass was directly molded to produce a molded body. Other conditions are the same as in Examples 3-7. The shape accuracy of the optical surface 21 of the obtained molded body was evaluated. Evaluation was performed in the same manner as in Example 1.

  The evaluation results are also shown in Table 2. Unlike the cases of Examples 3 to 7, the shape accuracy of the optical surface was larger than 300 nm, and a highly accurate optical surface could not be formed.

Schematic showing an example of the state where the cooling member is in contact with the molten glass Schematic diagram showing another example of the state in which the cooling member is in contact with the molten glass Sectional drawing which shows an example of the optical element manufactured by this embodiment Sectional drawing of the molded object for manufacturing the lens 10 Sectional drawing which shows another example of the optical element manufactured by this embodiment Sectional drawing of the molded object for manufacturing the lens 20 Sectional view of the molding die used in this embodiment Schematic diagram showing an example of a method for supplying molten glass

Explanation of symbols

10, 20 Lens (optical element)
DESCRIPTION OF SYMBOLS 11, 21 1st optical surface 12, 22 2nd optical surface 14a, 14b, 14c Molding body 24a, 24b, 24c Molding body 30 Molding die 31 Lower mold 32 Upper mold 33 Outer diameter control member 37 Receiving surface 38 Molding Surface 39 Outer diameter regulating surface 44 Molten glass 51, 52, 53, 54 Cooling member φD Diameter of contact portion between molten glass and cooling member φG Diameter of contact portion between molten glass and lower mold receiving surface

Claims (5)

A molding die comprising a lower mold having a receiving surface for receiving molten glass and an upper mold having a molding surface for forming the first optical surface of the optical element, a predetermined temperature lower than the temperature of the molten glass A heating step of heating to
A molten glass supply step of supplying the molten glass to the receiving surface of the lower mold;
A cooling step of cooling the molten glass by bringing a cooling member into contact with the upper surface of the supplied molten glass;
And a molding step of pressing the molten glass with the molding die to form a molded body having a first optical surface to which the molding surface of the upper mold is transferred. Method. When the diameter of the contact portion between the molten glass and the cooling member is φD, and the diameter of the contact portion between the molten glass and the lower mold receiving surface is φG, 0.3 ≦ φD / φG ≦ 0.9 The method for manufacturing an optical element according to claim 1, wherein the method is satisfied. 3. The optical element according to claim 1, further comprising an additional processing step of forming a second optical surface on a back surface side of the first optical surface of the molded body by additional processing after the molding step. Manufacturing method. The molding die includes an outer diameter regulating member having an outer diameter regulating surface for regulating the outer diameter of the molten glass,
The molten glass supplied to the receiving surface of the lower mold is in contact with an outer diameter regulating surface of the outer diameter regulating member in the molten glass supply step. The manufacturing method of the optical element of description. A molding die comprising a lower mold having a receiving surface for receiving molten glass, and an upper mold having a molding surface for forming the first optical surface of the optical element;
Heating means for heating the molding die to a predetermined temperature lower than the temperature of the molten glass;
Molten glass supply means for supplying the molten glass to the receiving surface of the lower mold,
Cooling means for cooling the molten glass by bringing a cooling member into contact with the upper surface of the supplied molten glass;
Pressurizing means for press-molding the molten glass with the molding die and forming a molded body having a first optical surface onto which the molding surface of the upper mold has been transferred. Device manufacturing equipment.

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