JP4646074B2 - Method for producing glass preform group and method for producing optical element - Google Patents

Description

The present invention relates to a process for the preparation of a manufacturing method and an optical element of glass-made preforms group.

  As a technique for manufacturing a glass optical element such as an aspheric lens with high accuracy, a precision press molding method is known. 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. In this method, the surface is precisely transferred to glass to form an optical functional surface (see, for example, Patent Document 1).

The glass preform used for manufacturing the optical element is formed into a preform in the process of, for example, flowing out molten glass, separating a molten glass lump of a desired mass, and cooling the glass lump. It can produce by the method to do (for example, refer patent document 2).
Japanese Patent Laid-Open No. 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 composed of ultra-small lenses, and each lens preferably has a positioning reference surface in order to precisely position and fix 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. In the precision press molding method, by transferring the molding surface of the mold to glass, not only the optical function surface but also the positional relationship and angle between the surfaces to be formed can be precisely defined. The reference surface can be formed in a lump.

  As described above, if the characteristics of precision press molding are utilized, 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 by closing the press mold having the upper mold, the lower mold, and the body mold, between the molds constituting the press mold, for example, , Protruding between the upper mold and the barrel mold, and between the lower mold and the barrel mold, forming a burr, impairing the slidability of the mold, causing production stoppage and causing damage to the press mold It becomes. 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 glass does not reach the portion that should be the positioning reference surface of the glass, and the positioning reference surface is not formed.

  Therefore, in order to collectively form the optical function surface and the positioning reference surface, it is desired to use a preform having high volume accuracy, that is, mass accuracy.

  As described above, as a method for producing a glass preform with high productivity, the molten glass is discharged from a nozzle, a molten glass lump having a desired mass is separated, and the glass lump is cooled to form a preform. There is a method of molding, and if a preform is produced using this method, optical elements can be mass-produced with extremely high productivity starting from melting of glass. However, in the conventional glass preform production method, there is a slight variation in the volume of the preform, and volume accuracy, that is, mass accuracy is not always satisfactory for use in the precision press molding. Such a problem was particularly noticeable when producing a lightweight preform.

Under these circumstances, the present invention manufactures glass preforms for precision press molding with extremely controlled volume variation between preforms from molten glass with extremely high productivity. It is an object of the present invention to provide a method for producing an optical element from a preform constituting the preform group or the preform group obtained by the method.

In order to improve the mass accuracy of the preform, as a result of repeated studies by the present inventors, the following knowledge has been obtained.
(A) The mass of a molten glass droplet obtained as a preform base material obtained by dripping molten glass from the nozzle outlet is generally the downward acceleration acting on the glass depending on the nozzle outlet, the lower end of the nozzle Although it depends on the outer diameter, the surface tension of the molten glass, and the like, if it is attempted to reduce the ratio of the mass tolerance with respect to the target preform mass, it is not possible to suppress the variation in the mass only by maintaining the above conditions constant.
(B) The variation in the mass is considered to be because the molten glass wets the outlet of the nozzle when the molten glass droplet is dropped, and the dripping amount of the molten glass slightly changes depending on the amount of the wet glass.
(C) When the nozzle is observed in detail, the tip of the nozzle vibrates slightly, and this slight vibration causes fluctuations in the dripping amount of the molten glass.
(D) Further, the wettability of the nozzle outer peripheral surface with respect to the glass slightly changes due to the temperature change and humidity change of the nozzle outlet atmosphere, and this slight change causes fluctuations in the dripping amount of the molten glass.

  Based on these findings, the present inventor has further studied, and as a result, the molten glass flowing out was dripped in order from the outlet that was damped and / or the temperature and humidity of the atmosphere were controlled at a constant flow rate. The inventors have found that a glass preform group in which the volume variation between the preforms is extremely controlled can be obtained, and the present invention has been completed based on this finding.

That is, the present invention
(1) A method for producing a glass preform group comprising a plurality of glass preforms for precision press molding,
A glass melting apparatus including a container for storing molten glass is placed on a vibration isolation table, and a pipe and a nozzle for discharging the molten glass from the container are suspended, or the glass melting apparatus is supported. By providing an anti-vibration mechanism in the structure, while preventing vibration at the outlet of the molten glass,
The molten glass flowing out from the nozzle at a constant flow rate is dropped sequentially from the outlet in an atmosphere in which the temperature is controlled and further controlled to a constant humidity corresponding to a humidity within the range of 10 to 95% relative humidity at 25 ° C. By molding ,
Characterized <br/> to produce an average mass M ± 0.5 [%] the ratio of the mass tolerance of glass preform for _AV × M within a glass-made preforms group _AV glass preform Manufacturing method of glass preform group,
( 2 ) The method for producing a glass preform group according to the above (1 ), wherein the molding after dropping of the molten glass is performed while applying air pressure to the obtained molten glass droplet and allowing it to float,
( 3 ) An optical system characterized in that a glass preform group is produced by the method described in the above (1) or (2) , the glass preform constituting the preform group is heated and precision press-molded. Device manufacturing method,
( 4 ) Precision press molding is performed by transferring each molding surface of a press mold having an upper mold, a lower mold, and a body mold to glass,
The surface formed by transferring the molding surface of the upper mold and the surface formed by transferring the molding surface of the cylinder mold and / or the surface formed by transferring the molding surface of the lower mold and the molding surface of the cylinder mold The method for producing an optical element according to the above ( 3 ), in which precision press molding is performed with a ridge formed by a surface formed by transfer as a free surface.

According to the present invention, a method for producing a glass preform group for precision press molding in which volume variation between the preforms is very controlled from molten glass with extremely high productivity, the preform group Or the method of manufacturing an optical element from the preform which comprises the preform group obtained by the said method can be provided.

[Glass preform group]
First, a glass preform group obtained by the production method of the present invention will be described.
The glass preform group of the present invention is a glass preform group composed of a plurality of glass preforms subjected to precision press molding, and the mass tolerance of the glass preform with respect to the average mass _MAV of the glass preform. ratio is equal to or is ± 0.5 [%] × the _{M a V} or less.

  In the present invention, the glass preform group means an assembly of a plurality of glass preforms that are made of the same kind of glass and that have the same shape and mass and are subjected to precision press molding. Further, in the present invention, the glass preform group does not necessarily need to be composed only of preform lots manufactured in a batch on the same day in the same apparatus, and may be constituted by a plurality of preform lots. For example, for a preform group consisting of 1000 preforms, it can be considered that 10 lots consisting of 100 preforms are assembled, or 100 lots consisting of 10 preforms. It can also be thought of as a collection.

  The number of preforms constituting the preform group is preferably 1000 or more, more preferably 2000 or more, and even more preferably 5000 or more. The upper limit of the number may be determined by the required number of optical elements.

M _AV means the arithmetic mean of the glass preform constituting the preform group, for example, when a glass preform is a preform for a micro lens used in an imaging device such as a mobile phone, M _AV is about 1 mg to 200 mg, preferably about 5 to 200 mg, more preferably about 8 to 160 mg.

Glass preform group of the present invention _is a glass proportion of the mass tolerance of the preform _{± 0.5 [%] × M A} V in than for _{M AV.}

Ratio of the mass tolerance of glass preform to the average mass _{M AV} glass preform is preferably in the _{± 0.4 [%] × M A} V in _{than, ± 0.38 [%] × M} A and more preferably in a _V in the following.

If the number of preform constituting the preform group of 500 or more, the ratio of the mass tolerance of the preform to the average mass M _AV and M _AV of the preform 500 flop extracted arbitrarily from the preform group It is sufficient to verify by renovation.

As described above, small optical elements incorporated in mobile devices such as mobile phones are precision press-molded with optical functional surfaces and positioning reference surfaces so that accurate alignment and assembly are possible. The preforms that constitute the group of preforms used for the precision press molding are required to be lightweight and have a small mass tolerance. Meanwhile, when the average mass M _AV preform is large, it is relatively easy to reduce the ratio of the mass tolerance of the preform (mass tolerance / average mass M _AV) for M _AV, the average mass of the preform When M _AV is small, even if a slight mass fluctuation occurs, the ratio of the mass tolerance of the preform to M _AV (mass tolerance / average mass M _AV ) becomes large. It has been difficult to provide a preform group composed of preforms having mass accuracy. In contrast, the glass preform group of the present invention is a glass-flop average mass M ratio is ± 0.5 [%] of a mass tolerance of glass preform for _AV remodeling × M _{A V} in more than Therefore, a preform group consisting of preforms having high mass accuracy can be provided even when it is ultralight.

The glass preform group obtained by the production method of the present invention is preferably composed of a spherical glass preform formed by solidifying glass whose entire surface is in a molten state.

  By making the entire surface of the preform a surface formed by solidifying molten glass, the entire surface can be a free surface, and latent scratches on the surface can be eliminated. As a result, each preform obtained can have a higher weather resistance than the polished preform. If the weather resistance is not sufficiently high, an altered layer called burn may be formed on the preform surface. If this altered layer is removed, the mass of the preform will slightly decrease and mass accuracy will be reduced. . According to this aspect, since the entire surface of the preform is formed by solidifying glass in a molten state, latent scratches on the surface can be eliminated, and the above inconvenience can be eliminated.

  In addition, if the shape of the preform is made spherical, if the glass used is the same type, the diameter of the preform will increase or decrease with the increase or decrease of the preform mass, and the mass and diameter of each preform will correspond one to one. It will be. Therefore, the mass accuracy of the preform can be managed by managing the variation in the diameter of the preform. In addition, when a preform is precision press-molded to obtain a compact optical element, if a spherical preform is used, the preform can be stably placed at the center of the molding surface if the lower mold molding surface is concave. become.

The glass preform group described above can be preferably manufactured by the method for manufacturing the glass preform group of the present invention described below.

[Production method of glass preform group]
Next, the manufacturing method of the glass preform group of this invention is demonstrated.
The method for producing a glass preform group according to the present invention is a method for producing a glass preform group comprising a plurality of glass preforms used for precision press molding, wherein the molten glass flowing out at a constant flow rate is damped. And / or is sequentially dropped from an outlet having a controlled temperature and humidity of the atmosphere and molded.

Hereinafter, the preferable aspect in the manufacturing method of the glass preform group of this invention is demonstrated based on drawing.

  As shown in FIG. 1, in order to produce a preform group, molten glass obtained by heating, melting, refining, and homogenizing a glass raw material is guided to a nozzle 2 provided at the lower end of a pipe 1. Although the molten glass flows out from the outlet provided at the lower end of the nozzle 2, the temperatures of the pipe 1 and the nozzle 2 are controlled so that the glass outflow amount per unit time is constant.

  The molten glass that has flowed out of the outlet hangs down to the lower end of the nozzle 2 due to surface tension. The molten glass falls from the lower end of the nozzle 2 when the downward force acting on the glass drooping becomes stronger than the force at which the molten glass tries to stay at the lower end of the nozzle 2. Here, since the glass outflow amount per unit time is made constant, the molten glass falls at a constant cycle. The total mass of the falling molten glass droplets is obtained by multiplying the glass outflow per unit time expressed by mass by the above period.

  Thus, the mass of the molten glass droplet is determined by the balance between the force that the molten glass tries to stay at the lower end of the nozzle 2 and the downward force that acts on the glass that hangs down. The outlet portion at the tip vibrates slightly, and this slight vibration causes fluctuation of the dripping amount of the molten glass. For this reason, it is possible to reduce the mass tolerance between the preforms by applying a vibration-proof measure to the nozzle 2 and performing the dropping.

  Specifically, as shown in FIG. 2, a glass melting apparatus 10 including a container for accumulating molten glass, which is connected to a nozzle 2 through a pipe 1, is placed on an anti-vibration table 11, and the pipe is removed from the container. 1 and the nozzle 2 are suspended. If it does in this way, it can prevent that the vibration from a building is transmitted to the nozzle 2 via the glass melting apparatus 10 and the pipe 1, and the vibration of the nozzle 2 can be suppressed. Or you may provide the anti-vibration mechanism which interrupts | blocks propagation of a vibration between the structure which supports a glass fusing device, and a building.

  The glass melting apparatus 10 may include a means for heating the molten glass in the container, a means for keeping the container warm, a stirring means for homogenizing the molten glass in the container, and the pipe 1 is, for example, Further, it may have an electrode for energization heating, a heat retaining means for retaining the pipe, and the like.

  In the method of the present invention, the molten glass is sequentially dropped while controlling the temperature and humidity of the outlet atmosphere together with or in place of the above-mentioned vibration-proof measures.

  As described above, the wettability of the nozzle outer peripheral surface with respect to the glass slightly changes due to the temperature change and humidity change of the nozzle outlet atmosphere, and this slight change causes the fluctuation of the dripping amount of the molten glass. By controlling the temperature and humidity of the atmosphere in the vicinity of the outlet of the nozzle 2, the mass tolerance between the preforms can be reduced.

  Specifically, as shown in FIG. 2, a booth (constant temperature chamber) 12 is installed below the glass melting apparatus 10, and the pipe 1 and the nozzle 2 connected to the glass melting apparatus 10 are accommodated in the booth 12. In the booth 12, a mold 13 to be described later is installed. When a preform is continuously produced using a plurality of molds, a plurality of molds, a turntable for mounting the molds, and a drive device for rotating the turntable are installed in the booth 12, And forming the preform from the molten glass droplet into the preform is performed in the booth.

The temperature and humidity in the booth are kept constant in a required state by a temperature control device and a humidity control device (hereinafter referred to as a temperature / humidity control device) (not shown). By such an operation, the temperature and humidity of the atmosphere around the outlet of the nozzle 2 are controlled. The temperature / humidity adjuster has temperature and humidity sensors, and feeds back the results detected by the sensors to maintain the atmosphere in the booth 12 at the set temperature and set humidity. For example, humidification is performed to prevent excessively low humidity during drying in winter, or dehumidification during humid periods such as the rainy season to prevent excessively high humidity. The temperature is also controlled so that the air temperature in the booth 12 does not deviate from the set temperature with respect to fluctuations in the outside air temperature. In this way, the mass tolerance between preforms obtained can be reduced by controlling the amount of wetting of the glass on the outer periphery of the nozzle 2 to be constant.

  In the method of the present invention, the dropping of the molten glass means that the molten glass lump falls from the nozzle outlet, and the nozzle outlet after the tip of the molten glass reaches the receiving surface of the mold that receives the molten glass. It includes both the phenomenon in which the thread-like portion formed between the molten glass flow and the tip of the molten glass flow is broken and dropped.

  And in the said method of isolate | separating a molten glass drop after the front-end | tip of a molten glass flow reaches the receiving surface of the said shaping | molding die, as shown in FIG. It is desirable to perform the dropping in a state where the periphery of the glass is covered with a cover 5 in order to keep the mass of the molten glass droplet constant. The cover 5 is preferably a hollow cylinder, and is installed so as not to block the dropping path of the molten glass droplets as shown in FIG. And it is desirable to block the upper part of the cover 5 in order to weaken the updraft caused by the convection generated at the nozzle tip. With such a configuration, it is possible to stabilize the position where the molten glass breaks, and to further reduce the mass variation of the glass droplets.

Incidentally, the main factors that determine the length of the thread part is the content of SiO ₂ in the glass, the content of SiO ₂ is increased (e.g., 20 wt percent) becomes long and filamentous portion, containing SiO ₂ When the amount decreases (for example, 20% by mass or less), the thread-like portion becomes shorter. The content of SiO ₂ is large, the glass forming the long thread-like portion, the impact when the leading end of the molten glass flow reaches the receiving surface of the mold, since the thread-like portions easily torn off, dripping efficiency of the molten glass improves.

  Therefore, it is preferable to drop the molten glass at a constant cycle with the distance between the receiving surface of the mold receiving the molten glass dropped and the tip of the nozzle constant. With such a configuration, the length of the thread-like portion and the timing of impact generation when the tip of the molten glass flow reaches the receiving surface of the mold can be stabilized for each dropping, and the variation in mass of the glass droplets can be reduced. can do.

  The cover 5 does not necessarily need to cover the entire molten glass droplet dropping path as long as it covers the periphery of the lower end (outlet) of the nozzle 2, and the length of the cover 5 extends from the lower end (outlet) of the nozzle 2 to the molding die. It is preferable to have a length that covers a portion corresponding to 1/5 to 4/5 of the distance to the receiving surface, and 3/10 to 10/10 of the distance from the lower end (outlet) of the nozzle 2 to the receiving surface of the mold. More preferably, the length covers a portion corresponding to 7/10.

  When the cover 5 has a hollow cylindrical shape, if the diameter is too large, the workability is lowered, and it is difficult to stabilize the atmosphere in the cover 5, and if it is too small, the molten glass that flows out adheres to the surface of the cover 5. Or, it may come into contact with the nozzle 2 or the pipe 1. Further, as will be described later, when applying a wind pressure to the molten glass that hangs down at the lower end of the nozzle 2 to promote a drop, if the aperture is too small, it becomes difficult to create a stable airflow around the nozzle. The diameter of the cover 5 is appropriately set in consideration of the above points so that the mass tolerance is reduced.

  The cover 5 has a function of slowing down the cooling speed of the molten glass hanging from the lower end of the nozzle 2. That is, the molten glass drooping by the cover 5 is kept warm, the speed of increase in the viscosity of the glass is slowed, the viscosity of the thread-like portion is maintained in a range suitable for separation, and the viscosity of the glass droplet is also in a range suitable for spheroidizing the glass. be able to.

  It is preferable that the cover 5 is made of an insulator and, as shown in FIG. 1, a high-frequency coil 6 is disposed around the cover so that a high-frequency current flows and the nozzle is subjected to high-frequency induction heating. With such a configuration, the nozzle made of platinum or a platinum alloy can be induction-heated without inductively heating the cover 5, and the nozzle can be maintained without devitrifying the glass and maintaining a desired outflow amount. The temperature of 2 can be controlled.

  A gas flow path forming cover 3 is preferably provided at the lower end of the pipe 1 and the outer periphery of the nozzle 2 as shown in FIG. By providing the gas flow path forming cover 3, the gas flow path 4 can be formed in the space between the pipe 1 and the nozzle 2 and the gas flow path forming cover 3. And the opening part 3-1 is provided in the lower end of the cover 3 for gas flow path formation, and the front-end | tip of the nozzle 2 protrudes from this opening part. The gas flow path forming cover 3 and the gas flow path forming cover opening 3-1 are preferably arranged coaxially around the central axis of the nozzle 2, respectively. Further, it is desirable that the gas discharged from the gas flow path forming cover opening 3-1 also flows evenly around the central axis.

  The dripping of 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. In this method, the mass determined by the force at which the molten glass tries to stay at the lower end of the nozzle is increased. Only glass drops can be obtained, and lighter glass drops cannot be dropped. On the other hand, when the gas is continuously ejected downward at a constant flow rate from the gas flow path forming cover opening 3-1 by the above method, the molten glass that is suspended receives a downward force due to the wind pressure of the gas, Accordingly, it is possible to obtain lighter glass droplets. 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.

  It is preferable to perform the molding after dropping the molten glass while applying a wind pressure to the obtained molten glass droplet and allowing it to float.

  A molding die 13 having a concave section as shown in FIG. 3 is carried under the nozzle, receives glass droplets 14 dropped from the nozzle at a constant period in the concave portion, and is introduced into the concave portion by rolling or sliding. The preform is obtained by forming the glass droplet 14 into a spherical shape while moving the glass droplet 14 up and down in the recess by the gas jetted upward from the gas outlet provided at the bottom of the recess. For mass production of preforms, a plurality of molds 13 are prepared, and the molds are successively carried under the nozzles to receive glass droplets 14, and the molds 13 that have received the glass droplets 14 are unloaded from below the nozzles. It is preferable to carry out by a method of carrying the empty molding die 13 below the nozzle. While the mold 13 moves, the glass droplets 14 are molded into a preform in the recess, cooled to a temperature range where the preform does not deform, and then the preform is taken out of the mold 13 and re-nozzled as an empty mold. It is carried downward. By performing such processes one after another for each of a plurality of molds, it is possible to mass-produce preforms and obtain a preform group.

  As described above, according to the method of the present invention, it is possible to suppress the fluctuation of the nozzle outlet vibration and the glass wetting amount, which are the cause of the mass fluctuation of the preform, and the preform having a small mass tolerance between the preforms. It becomes possible to produce groups.

[Method of manufacturing optical element]
Next, the manufacturing method of the optical element of this invention is demonstrated.
The optical element manufacturing method of the present invention comprises heating a preform constituting the glass preform group of the present invention or the glass preform group obtained by the manufacturing method of the glass preform group of the present invention, and performing precision press. It is characterized by molding.

  Precision press molding is a method in which a press mold including an upper mold, a lower mold, and a body mold is used, a preform is heated, press molded, and the shape of the molding surface of the press mold is accurately transferred to glass. is there. The manufacturing method and materials of each mold such as the upper mold, the lower mold, and the body mold, the release film formed on the molding surface of the upper mold and the lower mold, the forming method thereof, the type of atmosphere for performing the precision press molding, and the like are publicly known You can apply this technique.

As an example of the precision press molding method, as shown in FIG. 4, a spherical preform 19 is arranged at the center of the molding surface of the concave lower die 16 inserted into the body die 15, and the molding surface of the lower die 16 is arranged. The upper mold 17 is inserted into the body mold 15 so that the molding surfaces face each other. In this state, the preform 19 and the press mold (the barrel mold 15, the lower mold 16, the upper mold 17) are heated together, and the temperature of the glass constituting the preform 19 has a viscosity of, for example, 10 ⁶ dPa · s. When the temperature rises to the temperature indicated by, the push rod 18 is lowered and the preform 19 is pressurized with the upper die 17 and the lower die 16. The pressurized preform 19 is spread out in a space (referred to as a cavity) surrounded by the upper mold 17, the lower mold 16, and the body mold 15. In this way, the glass preform 19 is pressed, and the glass is filled into the sealed space formed in a state where the press mold is closed.

  The relative positions of the molding surfaces of the upper mold 17, the lower mold 16, and the body mold 15 in the mold-closed state, and the angle formed by the surface normal lines are formed in advance precisely. 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 part of the upper mold molding surface is the part to be transferred and molded with the lens surface which is the optical functional surface of the lens, and the peripheral part of the upper mold molding surface is transfer molded with the bowl-shaped flat part. As a part, it will be in the shape of a ring. Similarly, for the lower mold forming surface, the center portion of the molding surface is a portion for transferring and molding the lens surface, and the peripheral portion of the forming surface is a ring-shaped portion for transferring and molding the bowl-shaped flat portion. 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.

  By filling glass in a sealed space formed in a state where the press mold is closed, the inner surface of the barrel die through-hole is transferred to the glass. By accurately forming the angle between the central axis of the barrel-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, for example, 5, the two lens surfaces 20, 21, the two bowl-shaped flat portions 22, 23 and the edge 24 (side surfaces of the bowl-shaped flat portions 22, 23) formed by transferring the inner surface of the trunk mold. Can be formed precisely, and the relative positions of the above portions and the angles formed by the surfaces can be formed accurately.

  The optical element obtained by the method 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 the reference surface for accurately matching the optical axes of the lenses, and by bringing these reference surfaces into contact with the holder, Accurate alignment is possible. In the above example, the distance between the lenses can be accurately positioned by setting one of the bowl-shaped flat portions 22 and 23 as the first positioning reference surface and contacting the reference surface with the holder. . It is preferable that a pressure for maintaining the abutted state is applied to the other bowl-shaped flat surface to maintain the lens fixed to the holder. Further, the edge 24 is used as a second positioning reference surface, which is used as a reference surface for accurately matching the optical axes of the lenses.

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 surfaces 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 positioning reference surfaces. In the case of an optical element having no rotational symmetry such as a prism, the positioning in the optical system and the orientation at the position can be accurately determined by forming three positioning reference surfaces.

  A mold release film is provided on the upper and lower mold surfaces for the purpose of improving the mold releasability of the glass, but a mold release film having a uniform thickness is provided on the inner surface of the barrel mold (the inner surface of the through hole into which the upper mold and the lower mold are inserted). Since it is difficult to provide, a mold release film is usually not provided on the molding surface transferred to the edge. Therefore, in order to prevent the glass from fusing to the inner surface of the barrel mold during press molding, it is necessary to reduce the area of the edge 24 as long as the glass is not damaged and to minimize the contact area between the glass and the barrel mold. preferable. By the way, when precision press-molding a lens having a thin edge thickness (distance between the bowl-shaped flat portions 22, 23), the glass is filled from the portion that becomes the lens surface and gradually spread out in the body mold direction. Since the volume of the space between the upper mold forming surface and the lower mold forming surface on which the two bowl-shaped flat portions 22 and 23 are transferred and molded 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. In other words, the preform for molding the optical element is allowed to have a very small amount of the total mass, but in the method of the present invention, the preform obtained with respect to the target lens mass is obtained. Since the mass of the reform is accurately determined, even when the edge thickness is thin, the inner surface of the body mold can be transferred to form an edge that functions as a positioning reference surface, and molding burrs are generated. Thus, the mass production process of the optical element is not stopped.

  In the method of the present invention, the surface formed by transferring the surface formed by transferring the molding surface of the upper mold and the surface formed by transferring the molding surface of the body mold and / or the surface formed by transferring the molding surface of the lower mold It is preferable to precisely press-mold the glass preform with the ridge formed by the surface formed by transferring the molding surface of the body mold as a free surface.

  If the edge and the bowl-shaped flat portion are precisely formed as described above, there is no risk of hindering the positioning function. For example, in the lens shown in FIG. 5, the ridge 25 or the ridge 26 is sharp. Then, when fitting into the holder, the ridge is missing, or the ridge scrapes the holder, causing dust generation. When dust adheres to the light-receiving surface of the image sensor, the image quality is greatly lowered. Therefore, in order to prevent such trouble, it is desirable to mold an optical element having a ridge composed of a free surface. In addition, by making the ridge a free surface, even if some mass tolerance occurs between the preforms, the ridge portion plays a role in volume adjustment, which may cause problems such as forming burr and insufficient glass filling. It can be avoided.

  An optical multilayer film such as an antireflection film may be formed on the thus produced optical element as necessary.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

Example 1 (Production example of glass preform group)
First, glass raw materials are weighed, mixed and stirred sufficiently so that an optical glass having desired optical characteristics and glass transition temperature can be obtained, introduced into a melting vessel, heated, melted, clarified, stirred and homogenized. A molten glass was prepared. This glass contains B ₂ O ₃ , SiO ₂ , BaO, Li ₂ O, and has a refractive index nd of 1.58313 and an Abbe number νd of 59.46.

Using the apparatus shown in FIG. 1, 3000 glass preforms having a target mass of 100 mg were produced from the molten glass.
Here, the glass melting apparatus including the melting container is placed on a vibration isolation table. The anti-vibration table is provided with an opening through which the pipe 1 for flowing down the glass is passed, and the pipe 1 is suspended from the container through the opening, and the lower end of the pipe 1 is melted. A nozzle 2 for flowing out the glass is attached. With the above structure, the vibration from the building where these facilities are installed is blocked by the vibration isolation table and is not transmitted to the nozzle 2.

  A molding die is arranged below the nozzle 2, and the lower end portion of the pipe 1, the nozzle 2 and the molding die are booths in which the internal atmosphere is controlled to a temperature of 25 ° C. and a relative humidity of 10 to 95%. Is placed inside. With the above structure, the temperature and humidity in the vicinity of the molten glass outlet provided at the lower end of the nozzle 2 can be controlled, and the wettability of the molten glass on the outer peripheral surface of the nozzle can be controlled to be constant.

  Through the pipe 1 connected to the bottom of the melting vessel, the molten glass flows out from the nozzle 2 attached to the lower end of the pipe 1 at a constant flow rate. The nozzle 2, the pipe 1, and the melting container 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 the gas flows in the space between the pipe 1 and the nozzle 2 and the gas flow path forming cover 3. A path 4 is formed. And the opening part 3-1 is provided in the lower end of the cover 3 for gas flow path formation, and the front-end | tip of the nozzle 2 protrudes from this opening part. The nozzle 2, the gas flow path forming cover 3, and the gas flow path forming cover opening 3-1 are preferably arranged coaxially and symmetrically around the central axis of the nozzle 2. Further, it is desirable that the gas discharged from the gas flow path forming cover opening 3-1 also flows evenly around the central axis.

  In this embodiment, the outflow amount of the glass is adjusted by adjusting the inner diameter of the pipe 1, the inner and outer diameters of the nozzle 2, and the temperatures of the pipe 1 and the nozzle 2 so that the molten glass hanging from the lower end of the nozzle 2 falls at a constant cycle. Is controlling. The molten glass that flows out from the outlet of the nozzle 2 hangs down to the lower end of the nozzle, but the gas that continuously blows downward from the gas channel forming cover opening 3-1 at a constant flow rate is dropped on the molten glass. It is possible to obtain lighter glass droplets by spraying and applying downward wind pressure. 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.

  As shown in FIG. 1, a cover 5 is attached around the nozzle 2 and the gas flow path forming cover 3. The cover 5 covers a portion corresponding to 1/3 to 1/2 of the distance from the lower end (outlet) of the nozzle 2 to the receiving surface of the mold described later, and the upper portion of the cover 5 is also closed. Yes. However, the lower part is opened so as not to block the dropping route of the molten glass. The cover 5 can reduce disturbances caused by the external atmosphere, for example, the rising airflow around the nozzles, create a stable atmosphere in the cover 5, and the gas ejected from the gas channel forming cover opening 3-1 is also steady. Can flow stably downward.

  A high frequency induction coil 6 is disposed outside the cover 5, and a high frequency current is passed to heat the nozzle 2 by high frequency induction. The cover 5 is preferably made of a heat-resistant insulator in advance so as not to be induction-heated, and quartz glass or the like is suitable as such an insulator. Thus, if the cover 5 is made of a transparent heat-resistant insulator, the inside of the cover 5 can be observed from the outside.

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. FIG. 3 shows a vertical sectional view of the mold. The molten glass droplet 14 is received by the receiving surface 13-1 of the mold 13. Since the receiving surface 13-1 is inclined toward the bottom of the recess 13-2 provided on the upper surface of the mold 13, the molten glass droplet 14 slides (rolls) from the receiving surface 13-1 into the recess 13-2. ).

  The cross section of the recess 13-2 has a shape that spreads in a trumpet shape from the bottom to the top as shown in FIG. 3, and one gas jet port for jetting gas upward is provided at the bottom of the recess 13-2. ing. The molten glass droplet 14 introduced into the concave portion 13-2 descends while rolling on the inner wall of the concave portion toward the bottom of the concave portion. However, since the inner diameter of the concave portion decreases, the glass droplet 14 descends as it falls. It will be strongly subjected to upward wind pressure. As a result, the glass droplet 14 rises in the recess 13-2. However, when the glass drop 14 rises, the upward wind pressure is weakened, so that the glass droplet 14 falls again while rolling along the inner wall of the recess. Thus, the movement of the glass droplet 14 rising in the recess and descending while rolling is repeated in a short time. Since the direction in which the molten glass droplet rolls on the inner wall of the concave portion is random, the glass droplet 14 is cooled while being spheroidized as the above movement is repeated, and is formed into a spherical preform. When the preform is cooled to a temperature at which it is not deformed, the preform in the recess 13-2 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, the average mass _{M AV} is in 100.16Mg, percentage ± 0.21 [%] of a mass tolerance × within _{M A V} or more, the preform group consisting of 3000 spherical optical glass preform Got. The average mass _MAV and the mass tolerance ratio are values obtained by taking out 500 pieces from the obtained preforms.

Example 2 (Production example of glass preform group)
Example 1 except that optical glass containing B ₂ O ₃ , SiO ₂ , La ₂ O ₃ , ZnO, CaO, Li ₂ O, having a refractive index nd of 1.69350 and an Abbe number νd of 53.20 was used. to prepare a preform group in the average mass _{M AV} is in 99.88Mg, percentage ± 0.27 [%] of a mass tolerance × within _{M a V} or more, from 3000 spherical optical glass preform A preform group was obtained.
The average mass _MAV and the mass tolerance ratio are values obtained by taking out 500 pieces from the obtained preforms.

Example 3 (Production example of glass preform group)
Except for using optical glass containing P ₂ O ₅ , Nb ₂ O ₅ , TiO ₂ , BaO, Li ₂ O, having a refractive index nd of 1.82114, and an Abbe number νd of 24.06, the same as in Example 1. to prepare a preform group, with average mass _{M AV} is 99.81Mg, the ratio of the mass tolerance is ± 0.31 [%] × the _{M a V} or more, consisting of 3,000 spherical optical glass preform flop Reform group was obtained.
The average mass _MAV and the mass tolerance ratio are values obtained by taking out 500 pieces from the obtained preforms.

Example 4 (Production example of glass preform group)
But without controlling the temperature and humidity of the lower end of the nozzle 2 (outlet) is to prepare a preform group in the same manner as in Example 1-3, both the average mass M _AV is 100.25 mg, the ratio of the mass tolerance There is ± 0.43 [%] × the _{M a V} or less, to obtain a plurality of preforms group consisting of 3000 spherical optical glass preform.
The average mass _MAV and the mass tolerance ratio are values obtained by extracting 500 pieces from the obtained plurality of preform groups.

Example 5 (Production Example of Glass Preform Group)
Except that no provided vibration isolation, to produce the preform group in the same manner as in Example 1-3, both average mass _{M AV} is in 100.38Mg, percentage ± 0.47 [%] of a mass tolerance × is within M _{a V} or less, to obtain a plurality of preforms group consisting of 3000 spherical optical glass preform.
The average mass _MAV and the mass tolerance ratio are values obtained by extracting 500 pieces from the obtained plurality of preform groups.

Comparative Example 1 (Production example of glass preform group)
Without controlling the temperature and humidity of the lower end of the nozzle 2 (outlet), except that was not provided with vibration isolation is to prepare a preform group in the same manner as in Example 1-3, both average mass M _AV is in 100.74Mg, the ratio of the mass tolerance is ± 0.79 [%] × the _{M a V} or less, to obtain a plurality of preforms group consisting of 3000 spherical optical glass preform.
The average mass _MAV and the mass tolerance ratio are values obtained by extracting 500 pieces from each of the obtained preform groups.

Example 6 ( Example of optical element production)
Using each of the preform groups obtained in Examples 1 to 5, small aspheric lenses having a cross-sectional shape shown in FIG. 5 were produced by precision press molding. None of the lenses were damaged, and the lens had sufficient optical performance. The edge 24 and the bowl-shaped flat part 22 of each lens are formed by transferring the molding surface of the press mold, and the ridge 25 where the edge 24 and the bowl-shaped flat part 22 intersect is a rounded free surface. The occurrence of molding burrs was not observed in each lens.
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.

  By comparing the above Examples 1 to 5 with Comparative Example 1, the preforms constituting the preform group obtained by controlling the ambient temperature and humidity by preventing the molten glass from flowing out and / or controlling the ambient temperature and humidity. It can be seen that the mass tolerance between the preforms can be reduced even when the average mass of is as small as about 100 mg. In addition, it can be seen from Example 6 that a highly accurate optical element can be manufactured from each of the preform groups with high productivity.

According to the present invention, a method for producing a glass preform group for precision press molding in which volume variation between the preforms is very controlled from molten glass with extremely high productivity, the preform group Or the method of manufacturing an optical element from the preform which comprises the preform group obtained by the said method can be provided.

It is the schematic for demonstrating the manufacturing method of the glass preform groups of this invention. It is the schematic for demonstrating the manufacturing method of the glass preform groups of this invention. It is the schematic for demonstrating one example of the shaping | molding die used for the manufacturing method of the glass preform group of this invention. It is the schematic for demonstrating the manufacturing method of the optical element of this invention. It is the schematic for demonstrating an example of the optical element obtained by the method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pipe 2 Nozzle 3 Gas flow path formation cover 3-1 Opening part 4 Gas flow path 5 Cover 6 High frequency induction coil 10 Melting apparatus 11 Antivibration table 12 Constant temperature chamber 13 Mold 13-1 Receiving surface 13-2 Recessed part 14 Melting Glass drop 15 Body 16 Lower mold 17 Upper mold 18 Push rod 19 Glass preform 20, 21 Lens surface 22, 23 Gutter-shaped flat section 24 Edge 25, 26 Ridge

Claims (4)

A method for producing a glass preform group comprising a plurality of glass preforms for precision press molding,
A glass melting apparatus including a container for storing molten glass is placed on a vibration isolation table, and a pipe and a nozzle for discharging the molten glass from the container are suspended, or the glass melting apparatus is supported. By providing an anti-vibration mechanism in the structure, while preventing vibration at the outlet of the molten glass,
The molten glass flowing out from the nozzle at a constant flow rate is dropped sequentially from the outlet in an atmosphere in which the temperature is controlled and further controlled to a constant humidity corresponding to a humidity within the range of 10 to 95% relative humidity at 25 ° C. By molding ,
Characterized <br/> to produce an average mass M ± 0.5 [%] the ratio of the mass tolerance of glass preform for _AV × M within a glass-made preforms group _AV glass preform Manufacturing method of glass preform group. The manufacturing method of the glass preform group of Claim 1 which performs shaping | molding after the said molten glass dripping, applying a wind pressure to the obtained molten glass droplet, and making it float. A method for producing an optical element, comprising: producing a glass preform group by the method according to claim 1 ; and heating the glass preform constituting the preform group to perform precision press molding. . Precision press molding is performed by transferring each molding surface of a press mold having an upper mold, a lower mold, and a body mold to glass,
The surface formed by transferring the molding surface of the upper mold and the surface formed by transferring the molding surface of the cylinder mold and / or the surface formed by transferring the molding surface of the lower mold and the molding surface of the cylinder mold 4. The method of manufacturing an optical element according to claim 3 , wherein a precision press molding is performed with a ridge formed by a surface formed by transfer as a free surface.

Images