JP4448078B2 - Method for producing glass preform, method for producing glass molded body, and method for producing optical element - Google Patents

Description

  The present invention relates to a glass preform lot composed of a plurality of glass preforms used when producing a glass optical element by precision press molding, a mass production method of the preform, and a method of manufacturing an optical element. About.

  A precision press molding method is known as a technique for manufacturing glass optical elements such as aspherical lenses with high accuracy. This method is also called a mold optics molding method, which uses a press mold having a precisely machined molding surface to press-mold a heated glass preform to mold the shape of the entire optical element. The optical function surface is formed by precisely transferring the surface to glass. Such a method is disclosed in Patent Document 1, for example.

Further, the glass preform used for manufacturing the optical element is, for example, disclosed in Patent Document 2, outflowing molten glass, separating a molten glass lump of a desired mass, this glass lump is It can be produced by a method of forming into a preform in the process of cooling.
JP-A-10-316448 JP 2002-121032 A

  In recent years, there has been an increasing demand for small devices incorporating an imaging device, such as mobile phones with cameras. An image pickup optical system incorporated in such an image pickup apparatus is preferably composed of ultra-small lenses, and is preferably provided with a positioning reference surface for precisely positioning and fixing each lens. For example, as a positioning reference surface for precisely determining the distance between lenses, a flat surface provided on the outer periphery of the lens surface is used, and as a positioning reference surface for aligning the optical axes of the lenses, the lens side surface is used. Can do. Precision press molding not only allows precise formation of optical functional surfaces, but also allows precise formation of the positional relationship and angle between surfaces formed by transferring the molding surface including the optical functional surface. If the mold forming surface is transferred and formed, the optical function surface and the positioning reference surface can be formed in a lump.

  In this way, by utilizing the characteristics of precision press molding, an ultra-small optical element can be efficiently manufactured. On the other hand, if the volume of the preform is not precisely controlled, the following problems occur.

  First, when the volume of the preform is larger than the volume of the space formed in a state where the press mold is closed, between the mold members constituting the press mold, for example, between the upper mold and the barrel mold or the lower mold It protrudes between the body and the body mold and becomes a molding burr, which impairs the slidability of the mold and causes production stoppage or damage to the press mold.

  On the other hand, when the volume of the preform is smaller than the volume of the space formed with the press mold closed, the glass is insufficiently filled in the space, and the surface accuracy of the optical function surface is reduced. The portion that should become the positioning reference surface of the glass does not reach the mold member, and the positioning reference surface is not formed.

  Therefore, in order to enable a method of forming the optical function surface and the positioning reference surface in a lump, it is desired to use a preform having a high volume accuracy, that is, a mass accuracy.

  As described above, as a method for producing a glass preform with high productivity, a method in which molten glass is discharged, a molten glass lump having a desired mass is separated, and the preform is formed in the process of cooling the glass lump. (Patent Document 2). If a preform is produced using this method, the optical element can be mass-produced with extremely high productivity starting from melting of glass. However, as described above, it is necessary to precisely control the volume of the preform. However, in the conventional glass preform production method, there is a slight variation in the volume of the preform. However, the volume control of the preform was not always sufficient.

  The present invention has been made in order to solve the above-described problems, and is a glass preform lot configured by a plurality of relatively lightweight preforms suitable for precision press molding of a small optical element. An object of the present invention is to provide a glass preform lot in which the volume variation between the preforms is very controlled. Another object of the present invention is to provide a method for producing a preform lot from molten glass in which the volume variation between the preforms is extremely controlled. In addition, the present invention is a glass molded product lot in which a plurality of glass molded products that are preform base materials from molten glass are collected, and the glass molded product lot in which the volume variation between the glass molded products is extremely controlled. A method for producing, a method for producing a preform from a glass molded body of the glass molded body lot, and a method for manufacturing an optical element for producing an optical element by precision press molding each preform of the preform lot. Objective.

The present invention for solving the above problems is as follows.
[ 1 ] In a method for manufacturing a glass preform for forming a glass preform for precision press molding by molding molten glass,
The molten glass flowing out from the nozzle is suspended at the lower end of the nozzle, and the molten glass suspended at a certain period is dropped to obtain a molten glass droplet,
While forming the preform in the process of cooling the molten glass droplets,
The molten glass is dropped at least at the lower end of the nozzle and the space around the nozzle side 1/3 to 1/2 of the entire path where the molten glass falls is covered with a cover , and the upper part of the cover is covered. A method for producing a glass preform, which is performed in a closed state .
[ 2 ] The method for producing a glass preform according to [ 1 ], wherein the molten glass is dropped at a constant cycle with a distance between a surface receiving the molten glass and the lower end of the nozzle being constant.
[ 3 ] Manufacturing the glass preform according to [ 1 ] or [ 2 ], in which the cover is made of an insulator, and a high-frequency current is passed through a high-frequency coil arranged around the cover to inductively heat the nozzle. Method.
[ 4 ] The method for producing a glass preform according to any one of [ 1 ] to [ 3 ], wherein a preform made of glass containing SiO ₂ in excess of 20% by mass is formed.
[ 5 ] The glass preform according to any one of [ 1 ] to [ 4 ], wherein a glass preform lot comprising a plurality of glass preforms is produced by repeating the step of forming the glass preform. Production method.
[ 6 ] In a method for producing a glass molded body in which molten glass is molded to produce a glass molded body,
The molten glass flowing out from the nozzle is suspended at the lower end of the nozzle, and the molten glass suspended at a certain period is dropped to obtain a molten glass droplet,
While forming the glass molded body in the process of cooling the molten glass droplets,
The molten glass is dropped at least at the lower end of the nozzle and the space around the nozzle side 1/3 to 1/2 of the entire path where the molten glass falls is covered with a cover , and the upper part of the cover is covered. A method for producing a glass molded body, which is performed in a closed state .
[ 7 ] The method for manufacturing a glass molded body according to [6], wherein the cover is made of an insulator, and a high-frequency current is passed through a high-frequency coil arranged around the cover to heat the nozzle by high-frequency induction.
[ 8 ] The method for producing a glass molded body according to [ 6 ] or [7] , wherein the step of molding the glass molded body is repeated to produce a glass molded body lot composed of a plurality of glass molded bodies.
[ 9 ] A glass preform comprising: producing a glass molded article by the method according to [ 6 ] or [7] ; and polishing the surface of the glass molded article to obtain a glass preform used for precision press molding. Reform manufacturing method.
[ 10 ] The method for producing a glass preform according to [ 9 ], wherein the step of polishing the surface of the glass molded body is repeated to produce a glass preform lot composed of a plurality of glass preforms.
[ 11 ] A method for producing an optical element in which a preform lot is produced by the production method described in [ 5 ] or [ 10 ], the preform is taken out from the produced preform lot, and heated and precision press-molded.
[ 12 ] Using a press mold having an upper mold, a lower mold, and a sleeve mold, each molding surface of the upper mold, the lower mold, and the sleeve mold was transferred to glass, and the upper mold molding surface was transferred to form. The ridge formed by the surface formed by transferring the surface and the sleeve mold forming surface and / or the ridge formed by the surface formed by transferring the lower mold forming surface and the surface formed by transferring the sleeve mold forming surface is a free surface. [ 11 ] The method for producing an optical element according to [ 11 ], wherein precision press molding is performed.

  ADVANTAGE OF THE INVENTION According to this invention, the glass preform lot suitable for manufacture by the precision press molding of a small optical element and a small mass variation can be provided. In addition, since the variation in mass is small, the volume in the press mold when the mold is closed is determined based on the volume of the glass determined from the average mass of the preforms constituting the lot and the specific gravity of the glass. In addition, it is possible to prevent excessive glass from entering the clearance between the members constituting the press mold and forming molding burrs.

According to the present invention, it is possible to mass-produce a glass preform that is lightweight and has a small mass variation that is suitable for manufacturing a small optical element by precision press molding. It is possible to produce a preform having a small mass variation even in a glass in which a thread-like narrow neck is formed between the nozzle and the falling glass when the molten glass falls from the lower end of the nozzle, such as glass containing more than 20% by mass of SiO ₂ it can.

  ADVANTAGE OF THE INVENTION According to this invention, the method for mass-producing the glass molded object with a small mass variation finished to the glass preform for precision press molding by grinding | polishing can be provided. Further, by polishing the glass molded body, a glass preform with small mass variation can be mass-produced.

  According to the present invention, it is possible to efficiently manufacture an optical element, particularly an optical element having a positioning reference surface composed of a mold transfer surface with a small size or a small size, using the preform with small mass variation.

  As described above, it is preferable that a small optical element incorporated in a small device incorporating an image pickup device such as a camera-equipped mobile phone includes an optical functional surface and a positioning reference surface formed together by precision press molding. As described above, when such an optical element is precision press-molded, the volume of the glass preform must be precisely controlled.

  As the optical element molding preform, one having a mass of 30 mg or less is suitable. A mass tolerance within ± 0.3% is required for the preform used when the optical functional surface and the positioning reference surface of the optical element are formed together by precision press molding.

  For the production of the preform, a method of flowing out molten glass and separating molten glass droplets of a target mass is suitable because high productivity is obtained. Specifically, a method of dropping the molten glass flowing down through the nozzle from the nozzle outlet and forming the obtained glass droplet on a preform is suitable. The mass of the glass droplet is determined by the downward acceleration acting on the glass hanging from the nozzle outlet, the outer diameter of the lower end of the nozzle, the surface tension of the molten glass, and the like. Therefore, if these conditions are made constant, it becomes possible to continue dropping glass drops having a constant mass.

  However, if it is attempted to reduce the ratio of the mass tolerance to the target preform mass, it is difficult to suppress the mass variation only by maintaining the above-mentioned conditions constant. When a high-speed camera is used to shoot a glass drop dripping from the nozzle outlet, first, a constriction occurs between the molten glass that hangs down and the molten glass that is about to flow out of the outlet, and the constriction gradually narrows and extends longer. The lower end is lowered. When the constriction is thin and long, the glass is torn at the thread-like portion, and the glass above the torn portion returns to the vicinity of the nozzle outlet due to surface tension, and becomes glass that hangs down to the nozzle outlet. On the other hand, the glass below the broken portion is taken into the separated glass droplets.

  When observed more closely, it was found that the tearing position fluctuated each time the glass was dropped. When the tearing position becomes higher, the amount taken into the glass drop in the thread-like part increases, the mass of the glass drop slightly increases, and when the tearing position becomes lower, the amount taken into the glass drop among the thread-like part decreases, The glass drop mass is slightly reduced. This mass variation has been found to increase mass tolerances.

  As a result of further detailed analysis, if the filamentous part is long, the tearing position tends to fluctuate, and as a result, the mass fluctuation of the glass droplet tends to be large.If the filamentous part is broken in a short state, the mass fluctuation of the glass drop is small. I found out. It was also found that the glass determines whether the filamentous portion is long or short under the condition of preventing devitrification when the glass flows out.

  From these results, it can be seen that if the position where the thread-like portion breaks is constant each time, the variation in the mass of the glass drops obtained can be reduced. The fluctuation of the position is mainly caused by disturbance due to the atmosphere. Since the high-temperature molten glass flows out of the nozzle, the atmosphere around the nozzle and the pipe that leads the molten glass to the nozzle is heated, and convection of the atmosphere occurs around the nozzle. Moreover, since the shaping | molding die which shape | molds a molten glass drop is moved one after another below a nozzle, atmosphere is disturbed also by operation | movement of a shaping | molding apparatus. Such a thing disperses the position where the thread-like portion breaks.

  The present invention has been realized for the first time by considering the above phenomenon in detail and adopting means for reducing the disturbance due to the atmosphere.

  The glass preform lot of the present invention is a glass preform lot composed of a plurality of glass preforms used for precision press molding of optical elements. The average mass composed of spherical preforms is 30 mg or less, relative to the mass This is a glass preform lot having a mass tolerance within ± 0.3%.

As described above, a preform used for a small optical element or the like built in a mobile device is required to be lightweight and have high mass accuracy. When assembling an imaging optical system by aligning small optical elements, the optical axes of a plurality of small optical elements are precisely aligned, and the distance between each element and the distance from the imaging element are accurately maintained. When a holder for positioning and fixing is used, assembly work is facilitated. If each element is fitted in the holder, accurate alignment and assembly can be performed without adjusting positioning. For this purpose, it is desired to form at least two positioning reference surfaces on the optical element together with the optical functional surface by precision press molding. In such precision press molding, it is necessary to fill a space called a cavity surrounded by a press mold without excess or deficiency. If the volume of the preform is too small, the glass will enter the clearance between the mold members that make up the press mold during press molding, forming a molding burr, and stopping the precision press molding process. There is a risk of damaging the molded product or the molding surface. On the other hand, if the volume of the preform is insufficient, the glass is insufficiently filled in the cavity, resulting in insufficient transfer of the optical function surface and the positioning reference surface, and the desired purpose cannot be achieved. Such a problem is likely to become more prominent as the target optical element is smaller.
Therefore, the present invention solves the above-mentioned problems by the above configuration.

  Here, the preform lot means a set of a plurality of preforms made of the same kind of glass and having the same shape and mass. For example, when mass-producing a predetermined optical element, prepare a preform lot consisting of a required number of preforms, take out the preform from the lot, and perform precision press molding using a press mold of the same shape Thus, optical elements having the same shape can be mass-produced. At this time, a plurality of sets of press molds may be used, or the preforms may be precision press molded one after another using one press mold set. A preform lot can be considered to be composed of a plurality of preform lots. For example, a lot composed of 1000 preforms can be considered to be composed of 10 lots composed of 100 preforms, or 100 lots composed of 10 preforms. It can be considered that it is constituted by. In a preferred embodiment of the present invention, the number of preforms constituting a lot is 1000 or more, more preferably 2000 or more, and further preferably 5000 or more. The upper limit of the number may be determined by the required number of optical elements.

  Whether a preform lot has a mass tolerance ratio within ± 0.3% of the average mass of the preforms constituting the preform lot should be verified by a preform lot consisting of 500 preforms. Can do. When the preform lot is composed of 500 preforms, the ratio of the mass tolerance to the average mass is preferably within ± 0.26%, more preferably within ± 0.25%. Further, even if the number of preforms constituting the preform lot is 500 or more, the ratio of the mass tolerance to the average mass is preferably within ± 0.3%, and preferably 1000 pieces as described above. As described above, even when the number is 2000 or more, and more preferably 5000 or more, the ratio of the mass tolerance to the average mass is preferably within ± 0.3%.

  A preferred embodiment of the present invention is a glass preform lot comprising a preform for precision press molding an optical element having a surface formed by transferring a molding surface of a press mold during precision press molding and a free surface. It is.

  The optical element made by the preform of the present invention has a positioning reference surface in addition to the optical functional surface. For example, the lens positioning reference surface is a reference surface for determining the distance between the lenses and a reference surface for accurately matching the optical axes of the lenses. By bringing these reference surfaces into contact with the holder, each lens can be accurately aligned. Taking a lens as an example, a bowl-shaped flat portion is formed so as to surround each lens surface, and the two bowl-shaped flat portions of the two lens surfaces are parallel to each other. The one hook-shaped flat portion is used as a positioning reference surface and is in contact with the holder. A pressure for maintaining the abutted state is applied to the other bowl-shaped flat surface to fix the lens to the holder. In such a lens, the distance between the two bowl-shaped flat portions (referred to as edge thickness) is as short as possible without causing damage to the lens during molding and without causing damage to the lens when fixed to the holder. It is desirable to reduce the thickness. In such a lens, a side surface between the two bowl-shaped flat portions, that is, a portion called an edge is used as a second positioning reference surface. The second positioning reference surface is a reference surface for aligning the optical axis of the lens. Therefore, the edge is a surface to which a press mold forming surface is transferred during precision press molding. The press mold member transferred to the edge is a member called a sleeve mold or a barrel mold. A sleeve mold used when molding a small optical element has an elongated through hole into which an upper and lower molds are inserted. A part of the inner surface of the through hole becomes a molding surface transferred to the edge. A mold release film that improves the mold releasability of the glass is provided on the upper and lower mold surfaces, but it is difficult to provide a mold release film with a uniform thickness on the inner surface of the through hole of the sleeve mold. No release film is formed. Therefore, in order to prevent the glass from fusing to the inner surface of the sleeve mold through-hole at the time of press molding, it is only necessary to reduce the area of the edge as long as the glass is not damaged and to minimize the contact area between the glass and the sleeve mold. .

  For this reason, the edge thickness is reduced, but when a lens having a thin edge thickness is precision press-molded, the glass is filled from the portion that becomes the lens surface and gradually spreads in the sleeve mold direction. At this time, since the volume of the space between the upper mold forming surface and the lower mold forming surface for transferring and molding the two bowl-shaped flat portions is small, if the amount of the glass constituting the preform is too small, If the amount of the glass is small or small, the glass does not reach the sleeve mold even when pressed, and the edge serving as the positioning reference surface is not formed.

That is, in the preform for molding the optical element, over and short of a mass of 30 mg or less is allowed within a range of ± 0.3%.
Therefore, in the present invention, the average mass of the preforms constituting the lot is 30 mg or less, preferably 28 mg or less, more preferably 1 to 26 mg, and the mass tolerance is within ± 0.3%, preferably within ± 0.28%. More preferably, it is within ± 0.26%.

The present invention is suitable for preform lots and glass molded body lots made of glass having a relatively low refractive index and SiO ₂ content exceeding 20% by mass, and methods for producing them. Since such glass is particularly effective as a small optical element among small optical elements, the mass is set to 30 mg or less. The glass preferably has a refractive index (nd) of 1.65, more preferably 1.60 or less.

  Here, the average mass is an arithmetic average value (Mav) calculated from the mass of each preform. The mass tolerance is ± (Mmax−Mmin) from the mass of the preform having the largest mass (referred to as Mmax) and the mass of the preform having the smallest mass (referred to as Mmin) in the preforms constituting the lot. This is a value calculated by the formula / 2Mav. When the number of preforms constituting a lot is large, a predetermined number of preforms may be randomly extracted from the lot, and Mav, Mmax, and Mmin may be obtained using the extracted preforms.

Next, a method for producing a glass preform will be described. The method for producing a glass preform of the present invention is a method for producing a glass preform for producing a glass preform for precision press molding by molding molten glass.
The molten glass flowing out from the nozzle is dropped at the lower end of the nozzle, and the molten glass dropped at a certain period is dropped to obtain a molten glass drop
While forming the preform in the process of cooling the molten glass droplets,
The method for producing a glass preform is characterized in that the molten glass is dropped in a state where at least the periphery of the molten glass hanging from the lower end of the nozzle is covered with a cover.

  First, molten glass obtained by heating, melting, clarifying and homogenizing a glass raw material is guided to a nozzle at the lower end of the pipe using a pipe. Although the molten glass flows out from the glass outlet at the lower end of the nozzle, the temperature of the pipe and the nozzle is controlled so that the amount of glass flowing out per unit time becomes constant.

  The molten glass that has flowed out of the glass outlet port hangs down to the lower end of the nozzle due to surface tension. The molten glass falls from the lower end of the nozzle when the downward force acting on the glass that is drooping becomes stronger than the force at which the molten glass stays at the lower end of the nozzle. Here, since the glass outflow per unit time is made constant, the fall of the molten glass occurs at a constant cycle. The mass of the molten glass falling is obtained by multiplying the glass outflow amount per unit time represented by mass by the above period.

Here, the dropping of the molten glass includes the dropping of the molten glass drop and the case where the thread-like portion is broken after the lower end of the molten glass reaches the receiving surface for receiving the molten glass.
And the said fall is performed in the state which covered the circumference | surroundings of the molten glass hanging on the nozzle lower end with the cover. The cover does not obstruct the path of the fall so as not to prevent the fall of the molten glass. And in order to weaken the upward airflow by the convection mentioned above in the nozzle lower end, the cover upper part is closed. With such a configuration, it is possible to stabilize the position where the molten glass breaks, and to reduce the mass variation of the glass droplets.

  In addition to the molten glass lump obtained by dripping, the glass drop includes a molten glass lump obtained by tearing off the filamentous portion after the lower end of the molten glass reaches the receiving surface for receiving the molten glass.

By the way, the main factor that determines the length of the thread-like portion is the content of SiO _{2 in} the glass. When the amount of SiO ₂ exceeds a certain level, the thread-like portion becomes longer, and when it is less, the thread-like portion becomes shorter. Therefore, the larger the SiO ₂ content, the greater the effect.

  In a glass having a long thread-like part, the thread-like part is broken by an impact when the lower end of the molten glass reaches the receiving surface. Therefore, it is preferable that the molten glass is dropped at a constant period with the distance between the surface receiving the molten glass and the lower end of the nozzle being constant. With such a configuration, it is possible to stabilize the length of the thread-like part and the timing at which an impact for separating the thread-like part is generated every time it is dropped, and the mass variation of the glass droplets can be reduced.

  The lower end of the cover is preferably 0.2 to 0.8 times the distance from the receiving surface to the lower end of the nozzle, and more preferably 0.3 to 0.7 times higher.

  If the diameter of the cover is too large, the workability will deteriorate and it will be difficult to stabilize the atmosphere in the cover, and if it is too small, molten glass that flows out to the cover may adhere, or it may come into contact with nozzles or pipes. is there. Moreover, in the method of applying a wind pressure to the molten glass drooping to the lower end of the nozzle, which will be described later, to promote the drop, if the aperture is too small, it becomes difficult to create a stable airflow around the nozzle. Therefore, the aperture of the cover can be appropriately set so that the mass tolerance is reduced while considering the above points.

  The cover serves to slow down the cooling speed of the molten glass depending on the lower end of the nozzle. In other words, the molten glass hanging down by the cover is kept warm, the viscosity increase speed of the glass is slowed, the viscosity of the filamentous portion is kept in a range suitable for separation, and the viscosity of the glass droplet is also in a range suitable for spheroidizing the glass. Can do.

  It is preferable that the cover is made of an insulator, a high frequency coil is arranged around the cover, a high frequency current is passed, and the nozzle is heated by high frequency induction. With such a configuration, a nozzle made of platinum or a platinum alloy can be induction-heated without induction heating of the cover, and the temperature of the nozzle is maintained so that the desired outflow amount is maintained without devitrifying the glass. Can be controlled.

  Next, the application of the present invention is not limited to the type of glass, but there is a particularly effective glass, and the glass will be described. Hereinafter, unless otherwise specified, the content of the glass component is indicated by mass%.

As described above, the length of the filamentous portion of the molten glass is determined by the amount of SiO ₂ in the glass. When the amount of SiO ₂ exceeds 20%, the filamentous portion becomes long, and the separation position tends to vary due to disturbance due to the atmosphere. Therefore, the method for producing a glass preform of the present invention is particularly effective for glass having a SiO ₂ content of more than 20%. The preferable amount of SiO ₂ is 21% or more, more preferably 23% or more, still more preferably 30% or more, still more preferably 35% or more, and still more preferably 40% or more. If the amount of SiO ₂ is excessive, glass separation will not be successful. Therefore, the state in which the glass can be separated may be considered as the upper limit of the amount of SiO _{2, and the} amount of SiO _{2 is} preferably in the above range and 65% or less, preferably 60% or less, and 55% or less. More preferably.

The glass in the present _{invention, SiO 2 21~65%, B 2} O 3 0~40%, Li 2 O 0~12%, Na 2 O 0~10%, K 2 O 0~10%, MgO 0~ 10%, CaO 0-25%, SrO 0-25%, BaO 0-40%, ZnO 0-30%, La ₂ O ₃ 0-20%, Gd ₂ O ₃ 0-10%, Y ₂ O ₃ 0 Examples thereof include glass containing 10% to 10%, ZrO ₂ 0 to 15%, TiO ₂ 0 to 30%, Ta ₂ O ₅ 0 to 10%, and Nb ₂ O ₅ 0 to 8%.

If the amount of SiO ₂ is about the same, glass having a lower specific gravity is more effective for molding a preform made of glass having a specific gravity of less than 3.3 because the filamentous portion is less likely to separate. Furthermore, it is effective by molding glass having a specific gravity of 3.2 or less.

  In the method for producing a glass preform of the present invention, a glass preform lot composed of a plurality of glass preforms can be produced by repeating the step of forming the glass preform. This glass preform lot has a small variation such that the ratio of the mass tolerance to the mass is within ± 0.3% despite the fact that the average weight of the preform is as light as 30 mg or less.

In addition, it is preferable that the shape of each preform constituting the lot is spherical. When a small optical element is precision press-molded, if a spherical preform is used and the lower mold molding surface is concave, the preform can be stably placed at the center of the molding surface. The glass with the amount of SiO _{2 in} the above range may have a viscosity higher than the viscosity suitable for spheroidization because the volume of the glass droplet is small, but according to the present invention, the heated molten glass is dropped. Therefore, glass droplets having a viscosity suitable for spheroidization can be formed, and a spherical preform can be stably produced.

  So far, the preform lot of the present invention and the method for producing the preform have been described, but in the following, a glass molded body lot comprising a plurality of glass molded bodies for processing into a glass preform to be subjected to precision press molding and The manufacturing method of a glass molded object is demonstrated.

  The glass molded body lot is a glass molded body lot comprising a plurality of glass molded bodies for processing into a glass preform to be subjected to precision press molding, and the average mass composed of spherical glass molded bodies is 30 mg or less, the mass The glass molded product lot has a mass tolerance ratio of ± 0.3% or less.

The method for producing a glass molded body of the present invention is a method for producing a glass molded body in which a molten glass is molded to produce a glass molded body.
The molten glass flowing out from the nozzle is dropped at the lower end of the nozzle, and the molten glass dropped at a certain period is dropped to obtain a molten glass drop.
While forming the glass molded body in the process of cooling the molten glass droplets,
The molten glass is dropped in a state where at least the periphery of the molten glass hanging from the lower end of the nozzle is covered with a cover.

  In the manufacturing method of the said glass molded object, the glass molded object lot which consists of a some glass molded object can be produced by repeating the process shape | molded into a glass molded object.

  The glass molded body lot is a set of a plurality of glass molded bodies. The concept of the lot is the same as the concept of the lot in the preform lot described above. A preform can be obtained by machining (for example, polishing) the surface of the glass molded body. In order to obtain a preform lot from a glass molded product lot, if each glass molded product is made to have the same removal amount by machining, a lot consisting of an equal mass preform, that is, a preform lot of the present invention is obtained. be able to. Specifically, a glass molded body is prepared by the above-described method, and a glass preform to be subjected to precision press molding for polishing the surface of the glass molded body is manufactured.

  By repeating the step of polishing the surface of the glass molded body, a glass preform lot composed of a plurality of glass preforms can be produced.

The above phenomenon occurs even when molten glass falls when forming a glass molded body, and the glass tends to increase in mass variation of the glass molded body due to a long filamentous portion, that is, the amount of SiO _{2 in} the glass is 20%. It is especially effective for super glass. The glass molded body and the preform have the same manufacturing method, preferable glass composition, and specific gravity as described above except that the preform is finished by processing.

  For both the preform production method and the glass production method, known methods may be employed for the outflow and molding of the molten glass. It flows out from a heat-resistant nozzle (for example, a nozzle made of platinum or a platinum alloy) at a constant flow rate while maintaining a clarified, stirred and homogenized molten glass in a temperature range that does not devitrify. A molding die having a recess is carried under the nozzle, receives a glass drop dripping from the nozzle at a constant period on the outer peripheral surface of the recess, and is introduced into the recess by rolling or sliding, and is provided at the bottom of the recess A preform is obtained by forming into a spherical shape while moving the glass droplet up and down in the recess by the gas jetted upward from the top. For mass production of preforms, a plurality of molds are prepared, and the molds are successively carried under the nozzle to receive glass droplets. The molds that have received the glass droplets are unloaded from below the nozzles to form an empty mold. The mold is carried down the nozzle. The mold on which the glass droplets are placed is moved, molded into a preform in the recess, cooled to a temperature range where the preform does not deform, then taken out of the mold, and again as an empty mold, below the nozzle It is carried in. By performing such a process one after another for each of a plurality of molds, a preform is mass-produced. The preform mass-produced product obtained here corresponds to a preform lot. The manufacturing method of a glass molded object is also the same.

  Since defects such as scratches and dirt on the preform surface may cause defects in the optical element, it is preferable to finish the surface of the preform to a smooth surface so that no scratches remain on the preform surface when the glass molded body is polished. Also, the preform is washed to a clean surface so that no abrasive remains after polishing.

  Next, a mass production method of optical elements will be described. The optical element manufacturing method of the present invention is a mass production method of optical elements in which preforms are taken out from the preform preforms made of glass or mass-produced by the manufacturing methods, heated, and precision press-molded. is there.

  The preforms to be taken out are all spherical preforms having a mass that precisely matches the target mass, and therefore have a surface composed of a surface formed by transferring a molding surface of a press mold during precision press molding and a free surface. A small optical element can be manufactured stably.

  Precision press molding is a method that uses a press mold including an upper mold, a lower mold, and a sleeve mold, presses the preform by heating, and accurately transfers the shape of the molding surface of the press mold to glass. is there. For the processing of the mold material of the press mold and the material of the mold material, the mold release film formed on the molding surface of the upper mold and the lower mold, the method of forming the mold release film, the type of atmosphere for performing the precision press molding, etc., apply known techniques. That's fine.

  For example, a surface formed by using a press mold having an upper mold, a lower mold, and a sleeve mold, transferring each molding surface of the upper mold, the lower mold, and the sleeve mold to glass and transferring the upper mold molding surface. And the ridge formed by the surface formed by transferring the sleeve molding surface and / or the ridge formed by the surface formed by transferring the lower mold surface and the surface formed by transferring the sleeve molding surface to the free surface Press molding to mass produce optical elements with the same shape.

As an example of the precision press molding method, a spherical preform is placed in the center of the concave lower mold surface inserted into the through hole of the sleeve mold, and the upper mold is placed so that the molding surface faces the lower mold surface. Insert into the sleeve-type through hole. In this state, when the preform and the press mold are heated together and the temperature of the glass constituting the preform rises to a temperature showing a viscosity of 10 ⁶ dPa · s, the upper mold and the lower mold are pressed. Pressurize the reform. The pressurized preform is spread out in a space (called a cavity) surrounded by the upper mold, the lower mold, and the sleeve mold. In this way, the glass preform is pressed to fill the glass in the sealed space formed with the press mold closed.

  The relative positions of the molding surfaces of the upper mold, the lower mold, and the sleeve mold in the mold closed state, and the angle formed by the surface normal are precisely formed. If the above molding is performed using such a press mold, the optical function surface and the positioning reference surface can be formed with a highly accurate positional relationship and angle.

  Taking lens molding as an example, the central portion of the upper mold molding surface is a lens surface that is an optical functional surface of the lens, and the peripheral portion is a ring-shaped flat surface that is transfer-molded with a bowl-shaped flat portion. Similarly, for the lower mold forming surface, the center portion is a surface on which the lens surface is transfer-molded, and the peripheral portion is the plane on the annular zone on which the bowl-shaped flat portion is transfer-molded. Until the press molding is completed, the upper and lower molds are accurately maintained so that the directions of the upper and lower molds face each other and the central axes of the upper and lower molds coincide with each other.

  By filling glass in a sealed space formed with the press mold closed, the inner surface of the sleeve mold through-hole is transferred to the glass. By accurately forming the angle between the central axis of the sleeve-type through hole and the inner surface of the through-hole, and maintaining the central axis of the through-hole and the upper and lower mold central axes precisely until the end of press molding, 2 It is possible to accurately form the two lens surfaces, the two bowl-shaped flat portions, the relative position of the edge of the lens on which the inner surface of the sleeve mold is transferred and formed, and the angle between the surfaces. Then, one of the two hook-shaped flat portions and the edge are used as a positioning reference surface, and one of the hook-shaped flat portions is used as a reference surface for accurately positioning the distance between the lenses, and the edge is used as the light between the lenses. It can be used as a reference plane for precisely matching the axes.

  In order to prevent glass from fusing between the inner surface of the sleeve-type through-holes, the mass of each preform is accurately determined relative to the target lens mass even if the edge thickness is reduced within a range where the lens is not damaged. As a result, the inner surface of the sleeve-type through-hole can be transferred to form an edge that functions as a positioning reference surface, and a molding burr does not occur to stop the optical element mass production process.

  In addition, it is desirable to form the ridge where the edge and the ridge-shaped flat portion intersect on the free surface. If the edge and the bowl-shaped flat part are formed, there is no risk of hindering the positioning function, and if the ridge is sharp, the ridge will be missing when it fits into the holder, the ridge will scrape the holder, It will cause dust generation. When dust adheres to the light-receiving surface of the image sensor, the image quality is greatly reduced. Therefore, in order to prevent such trouble, it is desirable to mold a precision press-molded product having a ridge composed of a free surface.

In the optical element, it is desirable to form at least two or more surfaces, specifically, two or three positioning reference surfaces by precision press molding. The two or three positioning reference surfaces are preferably formed non-parallel to each other. If the optical element is positioned using two reference planes that are not parallel to each other in this way, the positioning and orientation of the optical element in the optical system can be determined with high accuracy. An optical element having rotational symmetry like a lens only needs to have two reference surfaces. In the case of an optical element having no rotational symmetry such as a prism, three positioning reference planes are formed to accurately determine the positioning in the optical system and the orientation at that position.
An optical multilayer film such as an antireflection film may be formed on the thus produced optical element as necessary.

Examples will be described.
Example 1
First, glass raw materials are weighed, mixed and sufficiently stirred so as to obtain an optical glass having a SiO ₂ amount of more than 20% by mass shown in Table 1, introduced into a melting vessel, heated, melted, clarified, A homogeneous molten glass was prepared by stirring. A glass preform was produced from molten glass droplets using the apparatus shown in FIG.

The pipe connected to the bottom of the melting vessel is opened, and the molten glass flows out from the nozzle attached to the lower end of the pipe at a constant flow rate. The nozzle, the pipe, and the melting vessel are each temperature controlled so that the glass does not devitrify and has a viscosity that provides a desired flow rate.
As shown in FIG. 1, a gas flow path forming cover 3 is provided at the lower end of the pipe 1 and the outer periphery of the nozzle 2, and a gas flow for flowing gas into the space between the gas flow path forming cover and the pipe and nozzle. A path 4 is provided. And the opening part 3-1 is provided in the lower end of the cover for gas flow path formation, and the nozzle front-end | tip protrudes from the said opening part. The nozzle, the gas flow path forming cover, and the gas flow path forming cover opening are preferably arranged symmetrically around the central axis of the nozzle. In addition, it is desirable that the gas discharged from the gas channel forming cover opening also flow evenly around the central axis.

  In this embodiment, the outflow amount of the glass is controlled by adjusting the inner diameter of the pipe, the inner and outer diameters of the nozzle, and the temperature of the pipe and the nozzle so that the molten glass hanging from the lower end of the nozzle falls at a constant cycle. The molten glass flowing out from the glass outlet hangs down to the lower end of the nozzle, but the gas that continuously spouts downward from the gas channel forming cover opening at a constant flow rate is sprayed on the molten glass. Wind pressure is applied.

  Further, as shown in FIG. 1, a cover 5 is attached so as to surround the periphery of the nozzle 2 and the gas flow path forming cover 3. The cover 5 covers the circumference of the nozzle side 1/3 to 1/2 space (the entire circumference on the side of the path) of the molten glass hanging down from the lower end of the nozzle and the path where the molten glass falls, and also covers the upper part of the cover 5 It is peeling off. However, the lower part is opened so as not to block the molten glass falling path. The cover 5 reduces disturbance caused by the external atmosphere, for example, an upward airflow around the nozzle, and creates a stable atmosphere in the cover 5. In the cover 5, the gas ejected from the gas channel forming cover opening constantly flows stably and downward.

  A high frequency induction coil 6 is disposed outside the cover 5, and a high frequency current is supplied to heat the nozzles by high frequency induction. The cover 5 is made of a heat-resistant insulator so as not to be induction heated. As a material for the cover 5, quartz glass or the like is suitable. If the cover 5 is made of such a transparent heat-resistant insulator, the inside of the cover 5 can be observed from the outside.

  The fall of the molten glass occurs when the gravity acting on the molten glass droops more than the force at which the molten glass stays at the lower end of the nozzle. However, with this method, only glass droplets having a mass determined by the force of staying at the lower end of the nozzle can be obtained, and lighter glass droplets cannot be dropped.

  However, according to the present embodiment, the molten glass drooping receives a downward force due to the wind pressure caused by the gas, and accordingly, a lighter glass drop can be obtained. Then, if the gas flow rate is controlled by a mass flow controller or the like so that the gas flow rate becomes constant, the mass of the glass droplet can be stabilized.

  The falling molten glass is received by a molding die waiting under the nozzle. In order to stabilize the mass of the glass droplet, the mold is put on standby so that the distance between the receiving surface that receives the molten glass lower end of the mold and the lower end of the nozzle is constant, the lower end of the falling molten glass is received, and the molten glass receives The glass is separated at the thread-like portion by impact when it reaches the surface. A vertical cross section of the mold 7 is shown in FIG. A glass drop dripped is received on the glass drop receiving surface 7-1 of the mold. Since the glass drop receiving surface 7-1 is also inclined in the direction of the concave portion 7-2 provided on the upper surface of the mold, the glass droplet slides or rolls from the receiving surface 7-1 into the concave portion 7-2.

  The cross section of the recess 7-2 has a shape that spreads in a trumpet shape from the bottom to the top as shown in FIG. 2, and one gas jet port for jetting gas upward is provided at the bottom of the recess. The glass drop introduced into the recess descends while rolling on the inner wall of the recess toward the bottom of the recess. However, since the inner diameter of the recess decreases, the glass drop is strongly subjected to upward wind pressure as it falls. It will be. As a result, the glass droplet rises in the recess, but when it rises, the upward wind pressure is weakened, so that it drops while rolling along the inner wall of the recess. Then, since the upward wind pressure is strongly received again, the movement of the glass droplet ascending in the recess and descending while rolling on the inner wall of the recess is repeatedly performed in a short time. Since the direction in which the glass droplet rolls on the inner wall of the concave portion is random, the glass droplet is cooled while being spheroidized as the above movement is repeated, and formed into a spherical preform. When the temperature reaches a temperature at which the preform is not deformed by cooling, the preform in the recess is taken out and cooled to room temperature at a speed at which the glass does not break.

  By repeating the above steps using a plurality of molds, it is possible to mass produce spherical preforms of equal mass. In this way, a preform lot made of a spherical preform having a desired mass made of optical glass and a small mass tolerance was obtained.

(Example 2)
Next, spherical preform base materials were mass-produced by the same method as described above. Table 1 shows the glass used, the number of base materials obtained, the average mass, the ratio of mass tolerance to the average mass (mass tolerance / average mass), and the diameter. These preform preforms were annealed to reduce strain and then polished to obtain preform lots having values equivalent to the ratio of mass tolerance to the average mass of preform preforms shown in Table 1. .

(Example 3)
Using the preform lots obtained in Examples 1 and 2, small aspherical lenses having a cross-sectional shape shown in FIG. 3 were obtained by precision press molding. None of the lenses were damaged, and the lens had sufficient optical performance. Further, the edge 8 and the bowl-shaped flat part 9 of each lens were obtained by transferring the press-molding molding surface, and the ridge where the edge and the bowl-shaped flat part intersected was a rounded free surface. And generation | occurrence | production of the molding burr | flash was not recognized.

  These aspherical lenses function as lenses constituting an imaging optical system of an imaging device built in a mobile phone. The lens obtained in this way and a lens with a flange and a bowl-shaped flat part as a positioning reference surface produced by the same method except for the shape are assembled in the lens holder and fixed with the positioning reference surface in contact with the holder. By doing so, each lens could be accurately arranged in the holder.

[Comparative example]
Next, using the glass shown in Table 1 and using the same apparatus as shown in FIG. 1 and having the cover 5, the preform shown in Table 1 was produced. As a result, the mass tolerance was large and the mass was varied. Oops.
When this lot is used to precision press-mold a small aspheric lens in the same manner as described above, the entire edge becomes a free surface and a lens that does not function as a positioning reference surface, or a molding burr occurs, resulting in a press mold. Troubles such as no longer sliding occurred.

Explanatory drawing of the apparatus which produces a glass preform from a molten glass drop. The vertical sectional view of the shaping | molding die for producing a glass preform from a molten glass drop. Sectional explanatory drawing of the lens which is 1 aspect of the optical element of this invention.

Claims (12)

In a method for manufacturing a glass preform for forming a glass preform for precision press molding by molding molten glass,
The molten glass flowing out from the nozzle is suspended at the lower end of the nozzle, and the molten glass suspended at a certain period is dropped to obtain a molten glass droplet,
While forming the preform in the process of cooling the molten glass droplets,
The molten glass is dropped at least at the lower end of the nozzle and the space around the nozzle side 1/3 to 1/2 of the entire path where the molten glass falls is covered with a cover , and the upper part of the cover is covered. A method for producing a glass preform, which is performed in a closed state . The distance between the surface and the nozzle lower end for receiving the dropped molten glass in the fixed method for producing a glass preform according to claim 1 for dropping of the molten glass in a constant cycle. The method for producing a glass preform according to claim 1 or 2 , wherein the cover is made of an insulator, and a high-frequency current is passed through a high-frequency coil arranged around the cover to inductively heat the nozzle. The method for producing a glass preform according to any one of claims 1 to 3 , wherein a preform made of glass containing more than 20% by mass of SiO ₂ is formed. Repeat step of forming a glass preform to produce a glass preform lot comprising a plurality of glass preform, method for producing a glass preform according to any one of claims 1-4. In the method for producing a glass molded body for producing a glass molded body by molding molten glass,
The molten glass flowing out from the nozzle is suspended at the lower end of the nozzle, and the molten glass suspended at a certain period is dropped to obtain a molten glass droplet,
While forming the glass molded body in the process of cooling the molten glass droplets,
The molten glass is dropped at least at the lower end of the nozzle and the space around the nozzle side 1/3 to 1/2 of the entire path where the molten glass falls is covered with a cover , and the upper part of the cover is covered. A method for producing a glass molded body, which is performed in a closed state . The method for producing a glass molded body according to claim 6, wherein the cover is made of an insulator, and a high-frequency current is passed through a high-frequency coil arranged around the cover to heat the nozzle by high-frequency induction. The manufacturing method of the glass molded object of Claim 6 or 7 which repeats the process shape | molded to a glass molded object and produces the glass molded object lot which consists of a some glass molded object. A method for producing a glass preform, comprising: producing a glass molded body by the method according to claim 6 or 7 ; and obtaining a glass preform to be used for precision press molding by polishing the surface of the glass molded body. The method for producing a glass preform according to claim 9 , wherein the glass preform lot comprising a plurality of glass preforms is produced by repeating the step of polishing the surface of the glass molded body. Producing a preform lot in the production method according to claim 5 or 10, removed preform from the production preform lot, heating, a method of producing an optical element for precision press molding. Using a press mold with an upper mold, a lower mold, and a sleeve mold, each molding surface of the upper mold, the lower mold, and the sleeve mold is transferred to glass, and the surface and sleeve formed by transferring the upper mold molding surface Precision press molding that makes the ridge formed by the surface formed by transferring the mold forming surface and / or the surface formed by transferring the lower mold forming surface and the surface formed by transferring the sleeve mold forming surface free surface The method for producing an optical element according to claim 11 , wherein:

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