JP4318681B2 - Preform for precision press molding, manufacturing method thereof, and manufacturing method of optical element - Google Patents

Description

  The present invention relates to a glass preform used as a raw material for precision press molding of an optical element such as an aspheric lens, a method for manufacturing the same, and a method for manufacturing an optical element for precision press molding the preform.

  A precision press molding method is known as a method capable of producing a glass optical element such as an aspherical lens and a microlens, which requires much labor and cost in grinding and polishing with high productivity. This method is also called mold optics molding method, which is formed by press molding without grinding and polishing the surface called optical function surface that refracts, diffracts, transmits, or reflects light such as lens surface It is attracting attention as a method that can precisely match the central axes of the two surfaces of the lens without inclining each other.

In the precision press molding method, a glass molded body called a preform is prepared, heated, and pressed using a precisely processed press molding die to shape the entire optical element, and the mold molding surface is made of glass. Precise transfer to form the optical function surface. In order to take advantage of the precision press molding method, it is necessary to increase productivity and reduce production costs not only in the process of producing optical elements from a preform but also in the process of producing a preform. In the method of producing a preform by grinding and polishing a glass piece obtained by cutting a glass block, it takes time and cost even for a preform having a shape that is relatively easy to process, such as a spherical shape. It takes as much effort and cost as processing a block to make a lens. Therefore, even if the optical element can be manufactured from the preform with high productivity, the merit of the precision press molding method cannot be fully utilized. In order to make use of the above-mentioned merits, as disclosed in Patent Document 1, the molten glass is flowed out to separate a molten glass lump corresponding to the amount of one preform, and the molten glass lump is cooled by the glass. In this process, a method of forming into a preform (referred to as hot forming method) is required.
JP-A-8-277132

  A typical shape of a preform obtained by a hot forming method is a sphere. If the radius of the sphere preform is less than the radius of curvature of the press mold surface and placed at the center of the press mold surface, the space between the mold surface and the glass during press molding is independent of the orientation of the preform. It is possible to avoid a phenomenon called a gas trap in which the atmospheric gas is trapped.

  In addition, when a lower mold having a concave molding surface with a large radius of curvature is used together with the upper mold to attempt precision press molding of a spherical preform, the preform is stably placed at the center of the lower mold molding surface. This is difficult, and the center of the preform is deviated from the center axis of the press mold, so that the thickness of the press molded product is uneven, and the desired performance as an optical element cannot be obtained.

  Even if the preform can be placed in a stable state at the center of the lower mold surface, the preform will be pressed at that pressure when the press of the preform is started on the upper mold surface. It is also caused by deviation from the central axis of the mold.

  With recent downsizing of imaging devices and higher resolution, optical elements incorporated in such devices are required to have high molding accuracy, and the demand for prevention of uneven thickness of precision press-molded products has become severe.

  As described above, the sphere preform is very useful, but has the above-mentioned problems.

  In order to expand the degree of freedom of the volume of precision press-molded products while preventing gas trapping and to prevent the above-mentioned uneven thickness, pressurization is performed by the surface pressed by the upper mold surface and the lower mold surface. What is necessary is just to make it the curvature radius of the surface to be made different. However, processing a preform having such a shape by grinding and polishing requires enormous labor and cost more than a spherical preform, and cannot take advantage of the precision press molding method. Therefore, if the preform is molded by adjusting the shape of the mold by hot molding, the preform having the above shape can be produced with high productivity.

  When forming a preform by a hot forming method, the molten glass is continuously discharged from the pipe, and the molten glass lump corresponding to one preform is separated by a so-called shearless cut without cutting with a cutting blade, Mold on the mold. In order to form a preform one after another from molten glass that continuously flows out, a plurality of molds are successively carried into the lower part of the pipe to supply the molten glass lump, and the mold on which the molten glass lump is placed is placed from below the pipe. The preform is formed on a moving mold that is unloaded and moved. At this time, the plurality of molds are moved and stopped synchronously, but inertial force is applied to the glass lump on the mold by acceleration and deceleration of the mold. When a plurality of molds are arranged on the turntable and the molds are transferred, centrifugal force is applied to the glass block on the mold by the rotation of the turntable. And since the molten glass lump on a shaping | molding die is shape | molded by such an inertia force, it is difficult to shape | mold a preform in a rotationally symmetrical shape. In particular, in the case of glass having a low viscosity at the time of outflow, the viscosity of the molten glass lump supplied onto the mold becomes low, so that the degree of deformation due to the inertial force increases.

  If the preform is deformed by the inertial force during hot forming, the symmetry of the rotating body is lost, and as a result, the glass does not spread evenly in the press mold during precision press molding, Uneven thickness occurs. Thus, it has been difficult to suppress the uneven thickness of the press-formed product and improve the productivity of the preform.

  The present invention solves the above-mentioned problems, a precision press-molding preform having a shape suitable for precision press-molding made of high-quality glass, and a method for producing the same, and precision press-molding the preform to make uneven thickness, etc. It is an object of the present invention to provide a method for manufacturing an optical element that can manufacture a highly accurate optical element free of defects with high productivity.

The present invention for achieving the above object comprises the following (1) to (11).
(1) In the precision press molding preform made of glass,
A rotating body having one rotational symmetry axis,
Of the two intersections where the rotational symmetry axis intersects the surface, the first intersection is included, the first surface is convex outside, the second intersection is included, and the second surface is convex outside. And
When the first surface is viewed in plan from the rotationally symmetric axis direction, the minimum radius of curvature of the in-circle portion having a diameter of 2/3 of the outer diameter around the first intersection is R _{1 (min)} ,
When the second surface is viewed in plan from the rotationally symmetric axis direction, the minimum curvature radius of the in-circle portion having a diameter of 1/3 of the outer diameter around the second intersection is R _{2 (min)} , the maximum curvature Let the radius be R _{2 (max)} ,
When the second surface is viewed in plan from the rotationally symmetric axis direction, the maximum radius of curvature of the outside of the circle whose diameter is 2/3 of the outer diameter around the second intersection is R _{3 (max)} ,
When the distance between the first intersection and the center of gravity is H ₁ , and the distance between the second intersection and the center of gravity is H ₂ ,
| R _{3 (max)} | <| R _{2 (min)} | <| R _{2 (max)} | <| R _{1 (min)} |
And H ₁ <| R _{1 (min)} |
Have the relationship
A precision press characterized in that the shape of a contour line in a cross section including the rotationally symmetric axis is convex outward at an arbitrary position, and the inclination of the contour line continuously changes along the contour line Preform for molding.
(2) When the length of the second intersection point and the center of gravity was H _2,
H ₂ <| R _{2 (min)} |
The precision press-molding preform according to the above (1), which has the following relationship.
(3) The precision press-molding preform as described in (1) or (2) above, wherein the entire surface is formed by solidifying the surface of the molten glass.
(4) For precision press-molding according to any one of (1) to (3) above, wherein the ratio of the center thickness to the outer diameter (center thickness / outer diameter) is 0.45 to 0.85. preform.
(5) In the process for producing a precision press-molding preform that flows out of the molten glass, separates the molten glass lump, and forms the preform on the concave portion of the mold in the process of solidifying the molten glass lump.
Molding the molten glass lump into the preform according to any one of the above (1) to (4) on the concave portion of the moving mold;
Forming the molten glass surface formed on the first surface of the preform on the concave portion in a state of facing downward,
A method for producing a precision press-molding preform.
(6) The method for producing a precision press-molding preform according to the above (5), wherein the preform is molded while the entire molten glass mass is floated on the concave portion.
(7) The concave surface has a shape that is symmetric with respect to rotation at an arbitrary angle around one central axis,
Production of a precision press-molding preform as described in (5) or (6) above, wherein a mold in which the absolute value of the radius of curvature of the concave surface decreases discretely or continuously as the distance from the central axis increases. Method.
(8) The method for producing a precision press-molding preform according to any one of (5) to (7), wherein the preform is molded while repeating the operation of moving and stopping the molding die in the horizontal direction.
(9) The preform according to any one of (1) to (4) above or the preform produced by the manufacturing method according to any one of (5) to (8) above is heated, A method for producing an optical element, comprising performing precision press molding using a press mold.
(10) The method for producing an optical element according to (9), wherein the preform is introduced into a press mold, the preform and the press mold are heated together, and precision press molding is performed.
(11) The method for producing an optical element according to (9) above, wherein the heated preform is introduced into a preheated press mold and precision press molding is performed.

  ADVANTAGE OF THE INVENTION According to this invention, the preform for precision press molding for manufacturing a highly accurate optical element stably by precision press molding, and its manufacturing method can be provided.

  Also, by performing precision press molding of the preform, a highly accurate optical element can be manufactured with high productivity.

Hereinafter, the best mode for carrying out the invention will be described, but the present invention is not limited to these modes.
[Preform for precision press molding]
The preform for precision press molding of the present invention is
In precision press molding preforms made of glass,
A rotating body having one rotational symmetry axis,
Of the two intersections where the rotational symmetry axis intersects the surface, the first intersection is included, the first surface is convex outside, the second intersection is included, and the second surface is convex outside. And
When the first surface is viewed in plan from the rotationally symmetric axis direction, the minimum radius of curvature of the in-circle portion having a diameter of 2/3 of the outer diameter around the first intersection is R _{1 (min)} ,
When the second surface is viewed in plan from the rotationally symmetric axis direction, the minimum curvature radius of the in-circle portion having a diameter of 1/3 of the outer diameter around the second intersection is R _{2 (min)} , the maximum curvature Let the radius be R _{2 (max)} ,
When the second surface is viewed in plan from the rotationally symmetric axis direction, the maximum radius of curvature of the outside of the circle whose diameter is 2/3 of the outer diameter around the second intersection is R _{3 (max)} ,
When the distance between the first intersection point and the center of gravity was H _1,
| R _{3 (max)} | <| R _{2 (min)} | <| R _{2 (max)} | <| R _{1 (min)} |
And H ₁ <| R _{1 (min)} |
Have the relationship
The shape of the contour line in the cross-section including the rotationally symmetric axis is convex outward at an arbitrary position, and the inclination of the contour line continuously changes along the contour line. is there.

  The outer diameter of the preform of the present invention corresponds to the diameter of the preform contour when the preform is viewed in plan from the rotationally symmetric axis direction. In the first surface, 1/3 of the outer diameter is the diameter, the part in the circle centered on the first intersection is called the center of the first surface, and 1/3 of the outer diameter is the diameter in the second surface. The in-circle part centering on the second intersection is called the center part of the second surface, and the non-circular part is called the peripheral part of the second surface.

  As mentioned above, the uneven thickness of precision press-molded products is to use a preform that does not have a rotationally symmetric axis. Even if the preform has a rotationally symmetric axis, the rotationally symmetric axis deviates from the center axis of the press mold. This is caused by press molding in a tilted state or tilted with respect to the center axis of the press mold, and low processing accuracy and assembly accuracy of the press mold. The direction of the central axis of the press mold coincides with the pressurizing direction during precision press molding.

In order to eliminate the cause of the above uneven thickness, in addition to using a high-precision press mold,
(1) The glass tends to spread isotropically around the central axis of the mold in the press mold,
(2) Easy to place stably on the central axis of the press mold,
(3) It is difficult to shift from the center axis of the press mold by pressurizing at the initial stage of press molding.
A shape preform is required.

  In order to satisfy the condition (1), in the present invention, the shape of the preform is a rotating body shape having one rotational symmetry axis. By doing so, the glass spreads isotropically around the central axis of the mold in the press mold.

When the molding surface of the lower mold constituting the press mold is concave and the absolute value of the radius of curvature is small, the preform easily rolls on the molding surface. As a result, in order to stably arrange the preform at the center of the lower mold forming surface, when the distance H ₁ between the first intersection and the center of gravity is set, the minimum radius of curvature R _{1 ( min)} so that H ₁ is smaller than the absolute value of
H ₁ <| R _{1 (min)} |
It is sufficient to satisfy the relationship. When the preform is placed on the lower mold with the first surface down, when the preform rolls, the preform tries to rotate around the center of the radius of curvature at the center of the first surface, but the center of gravity is the first If it is at a position lower than the height of R _{1 (min)} from the intersection, rolling is suppressed and the preform can be placed stably. As a result, even if a pressing force is applied to the first intersection and the second intersection of the preform at the initial stage of press molding, the preform is not easily displaced from the center axis of the press mold. Further, when the preform is pressed with a press mold having a convex molding surface, the preform is less likely to be displaced laterally from the central axis of the press mold when the pressed surface is nearly flat. In this way, the above conditions (2) and (3) are also satisfied.

It is sufficient that the preform can be stably placed with the first surface down on the lower mold forming surface, but the preform is stabilized with the second surface down on the lower mold forming surface. It is preferable to be able to place it. To that end, when the distance between the second intersection and the center of gravity was _{H 2,} the shape of the preform _{H 2 <| R 2 (min} ) |
It is preferable to satisfy the above relationship.

The values of R _{1 (min)} and R _{2 (min)} may be determined in consideration of the radii of curvature of the upper and lower mold surfaces of the press mold. At this time, attention should be paid so that an atmosphere gas is confined between the upper and lower mold forming surfaces and the preform so that an underfilled portion of glass called a gas trap cannot be formed. In the use of the preform of the present invention, generally, when the preform is placed on the concave lower mold forming surface, the maximum radius of curvature of the center portion of the lower surface (when the first surface is lower) R _{1 (max)} , when the second surface is on the lower side, the absolute value of R _{2 (max)} ) is used in combination with a press mold that is smaller than the absolute value of the minimum radius of curvature of the lower mold surface To do.

When the molding surface is used in combination with a concave upper mold, the maximum radius of curvature of the center portion of the upper surface when placing the preform on the lower molding surface (R ₁ when the first surface is upper) _{(Max) When} the second surface is on the upper side, the absolute value of R2 _(max) ) is used in combination with an upper die that is smaller than the absolute value of the minimum curvature radius of the molding surface.

  Next, a request from the manufacturing side of the preform and a means for responding to this request will be described.

  As described above, in order to take advantage of the precision press molding method, it is also necessary to increase productivity in the preform manufacturing process. Preforms having a shape with one rotational symmetry axis are required to be mass-produced by the hot forming method because they require much more labor and cost than grinding and polishing glass into a spherical shape.

In the hot forming method, the molten glass continuously flows out from the pipe at a constant flow rate, so the molten glass lump is separated from the flowing molten glass, received by the preform mold, and carried out from the bottom of the pipe one after another to form. There is a need to. At this time, the molten glass lump on the concave portion of the preform mold receives the inertial force as described above and swings on the concave portion, resulting in a decrease in rotational symmetry. In the present invention, the following relationship between the shape of the central portion of the second surface and the shape of the peripheral portion is suppressed in order to suppress a swing that causes a decrease in rotational symmetry even when an inertial force is applied to the concave portion. R _{3 (max)} | <| R _{2 (min)} |
In addition, the concave shape of the preform mold is made a shape that allows such a preform to be obtained (details of the concave shape will be described later).

When the preform is molded with the second surface facing down on the concave portion of the preform mold, it is obtained when a molten glass lump runs on the side wall of the concave portion due to a horizontal inertia force acting on the glass on the concave portion. The rotational symmetry (roundness when viewed from the central axis direction) of the preform is lowered. However, the shape of the preform is | R _{3 (max)} | <| R _{2 (min)} |
By satisfying the relationship, it is difficult for the molten glass lump to ride on the side wall of the recess even if the inertial force is applied.

Cooling of the molten glass block on the recess proceeds from the surface to the center of the glass. Even in this process, the inertial force in the horizontal direction acts on the glass. Then, the peripheral portion of the second surface is pressed against the side wall of the recess, and the centers of the curvature radii R _{3 (max)} and R _{3 (min)} are set. As the center of rotation, a force that lifts the portion that becomes the second intersection acts, which causes a decrease in the rotational symmetry of the preform. In particular, when deformation that impairs rotational symmetry occurs in a state where the glass is solidified, it becomes difficult to restore the shape of the glass, so it is necessary to suppress the above behavior due to inertial force. At this time, if the above relationship is satisfied between R _{3 (max)} and R _{2 (min)} , rotation about the centers of curvature radius R _{3 (max)} and R _{3 (min)} is the glass. Therefore, the above behavior is suppressed, and as a result, the rotational symmetry of the preform can be prevented from being lowered.

Furthermore, to suppress the above behavior,
| R _{2 (max)} | <| R _{1 (min)} |
It is necessary to satisfy this relationship. if,
| R _{2 (max)} | ≧ | R _{1 (min)} |
When the preform having the above relationship is molded, the preform with the second surface down becomes unstable on the mold and behaves to lower the rotational symmetry of the preform when the mold moves. Become. Therefore, in order not to reduce the rotational symmetry of the preform,
| R _{2 (max)} | <| R _{1 (min)} |
The configuration is given.

  By such molding, the first surface of the preform becomes a free surface, and the central portion of the first surface can be convex outward by the surface tension of the glass.

  When taking out the preform from the mold, a method of sucking and lifting the upper surface of the preform on the mold is used. At this time, if the shape of the preform is as in the present invention, the preform can be accurately lifted by suction, and the preform can be taken out without being rubbed against the molding die. It is possible to prevent the preform surface from being scratched. If the shape of the preform does not satisfy the conditions of the present invention, the preform is sucked to the suction nozzle in a tilted state (the preform central axis is tilted with respect to the vertical), and the nozzle suction port is in close contact with the preform surface. Therefore, it becomes easy to make a mistake when taking out the preform from the mold. Further, it is not preferable to lift the preform in an inclined state because the preform is rubbed against the mold.

  Such problems can be caused by sucking the preforms and arranging them on the tray, transferring them from the tray to a film forming apparatus for coating on the surface, arranging them on the tray after coating, or transferring them from the tray to a press molding apparatus. It can also happen. Even in such a situation, according to the preform of the present invention, the preform is reliably sucked by the suction nozzle, and the preform can be lifted right up without being rubbed against the holding member.

  In the present invention, the shape of the contour line in the cross section including the rotationally symmetric axis is convex outward at an arbitrary position, and the shape of the contour line continuously changes along the contour line, Glass can be spread evenly in the press mold.

  Moreover, the preferable aspect of the preform of this invention is a preform in which the entire surface was formed by solidifying the surface of the molten glass. Preforms can be made by mechanical processing such as polishing, but making the preform of the present invention by machining takes the same amount of effort and cost as making the final optical element by machining, The features of precision press molding will be impaired. Also, the surface of the preform made by machining has polishing scratches and latent scratches that occur during polishing, and this scratch causes damage to the glass due to thermal shock such as heating the preform during precision press molding. There is a risk of becoming. On the other hand, according to the above aspect, since the entire surface is formed by solidifying the surface of the molten glass, a surface free of abrasive scratches and latent scratches can be obtained, and a preform with excellent thermal shock resistance can be realized. can do.

  A preferred embodiment of the preform of the present invention is a preform in which the ratio of the center thickness to the outer diameter (center thickness / outer diameter) is 0.45 to 0.85, more preferably 0.55 to 0.80. is there. In precision press molding, there are many cases in which a preform having a volume equal to the volume of the molded product is used. However, when the outer diameter is increased with respect to a predetermined volume, a barrel mold constituting the press mold or a sleeve for guiding the upper and lower molds is used. It becomes impossible to arrange a preform in a member called. Therefore, in the above aspect, the volume of the preform can be set to a required value by setting the ratio to 0.45 or more and increasing the center thickness in a situation where the upper limit of the outer diameter is determined. However, if the ratio is larger than 0.85, the glass sitting on the mold becomes unstable at the time of preform molding, and the rotational symmetry is lowered. Therefore, the ratio (center wall thickness / outer diameter) is reduced. Within the above range.

There is no particular restriction on the glass forming the preform, but arsenic, which easily damages the molding surface of the press mold during precision press molding, is reduced during precision press molding and deposited on the glass surface to form the press mold molding surface. A glass that does not contain PbO, which adheres and hinders precise transfer of the molding surface to the glass, is desirable. Considering the application to an optical element, it is desirable to be an optical glass. As such optical glass, glass containing B ₂ O ₃ and La ₂ O ₃ , glass containing P ₂ O ₅ and Nb ₂ O ₅ , glass containing SiO ₂ and B ₂ O ₃ , P ₂ Examples thereof include glass containing O ₅ and Li ₂ O, fluorophosphate glass, and the like.

[Precision press molding preform manufacturing method]
Next, a method for producing a precision press-molding preform will be described.
The method for producing a precision press-molding preform of the present invention includes:
Outflowing molten glass, separating the molten glass lump, and in the process of solidifying the molten glass lump, a method for producing a precision press-molding preform that is molded into a preform on a concave portion of a mold,
Molding the molten glass lump into the preform of the present invention on the concave portion of the moving mold,
Forming the molten glass surface formed on the first surface of the preform on the concave portion in a state of facing downward,
It is characterized by.

  By forming the molten glass surface that is formed on the first surface of the preform on the recess, with the surface facing downward, the glass behavior is stably maintained on the moving recess, and the rotational symmetry is high. A reform can be formed, and as a result, it becomes possible to obtain a precision press-molded product with less uneven thickness.

  In the preform manufacturing method, it is preferable that the preform is formed into a preform while the entire molten glass ingot is floated on the recess. By floating the entire molten glass lump, the contact time between the glass and the recess can be shortened as compared with the case where the molten glass lump is not lifted. The temperature of the recess is kept relatively low so as not to be thermally fused even when the molten glass comes into contact. When the molten glass lump comes into contact with such a recess, the preform surface is wrinkled. Moreover, when the molten glass lump is cooled while the molten glass lump is in contact with the recess, breakage of the glass called can cracking occurs. According to the above aspect, these problems can be solved.

  In the present invention, the concave surface has a shape that is symmetric with respect to rotation at an arbitrary angle around one central axis, and the absolute value of the radius of curvature of the concave surface increases as the distance from the central axis increases. Alternatively, it is desirable to use a continuously decreasing mold. Here, as an example in which the absolute value of the curvature radius decreases discretely, there is a region of the curvature radius r2 outside the region of the curvature radius r1 including the central axis, and the relationship | r1 |> | r2 | is established. The case where the region of curvature radius r3 is further outside the region of curvature radius r2 and the relationship | r2 |> | r3 | There may be a portion where the absolute value of the radius of curvature of the concave surface decreases discretely and a portion where it continuously decreases as the distance from the central axis increases.

  By using such a mold, the preform of the present invention can be easily molded, and the behavior that reduces the rotational symmetry of the preform even when acceleration is applied to the glass on the recess can be suppressed. it can.

  In each of the above methods, it is desirable to mold the preform while repeating the operation of moving and stopping the mold in the horizontal direction. This method is excellent in mass productivity because the glass is molded while moving in the horizontal direction together with the mold. Such movement of the mold tends to lower the rotational symmetry of the preform, but according to the present invention, the behavior that lowers the rotational symmetry can be suppressed. Without worrying, mass productivity can be improved.

  In addition, what is necessary is just to utilize a well-known method, a structure, and a material about supply of the molten glass lump to a shaping | molding die recessed part, floating of a molten glass lump, the structure of a shaping | molding die, a material, etc.

  The preform on the recess is cooled to a temperature range that does not deform even when an external force is applied, and then taken out from the recess and gradually cooled. A known method may be used for both the preform take-out method and the slow cooling method.

  The molded preform may be washed as necessary, and a carbon film or a self-assembled film may be formed on the entire surface as necessary. Such a film works to enhance the elongation of the glass during press molding and to increase the mold releasability of the molded product by pressing.

[Method for 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 is a method in which the preform of the present invention or the preform produced by the manufacturing method of the present invention is heated and precision press-molded using a press mold.

  According to the present invention, since the preform is used, an optical element with less uneven thickness can be manufactured without causing troubles such as a gas trap.

  Preform heating, press mold structure, material, release film provided on the press molding surface as required, precision press molding method, and precision press molding atmosphere gas are known, and precision press The molding conditions may be set as appropriate according to the specifications of the target optical element.

The present invention includes the following two aspects.
The first aspect is a method of introducing a preform into a press mold, heating the preform and the press mold together, and performing precision press molding. In this method, since the mold components are assembled in a state where the preform is introduced into the press mold in advance and the preform and the press mold are heated together, it is easy to manufacture an optical element with high shape accuracy.

The second embodiment is a method for precision press molding by introducing a heated preform into a preheated press mold. This method is preferable from the viewpoint of extending the life of the mold because the heating temperature of the press mold can be made lower than the heating temperature of the preform, and with a smaller number of press molds than the first embodiment. Optical elements can also be mass-produced.
A mode to be adopted may be determined in consideration of which feature has priority.

  By optimizing the shape and dimensions of the press mold, it is possible to manufacture lenses such as biconvex lenses, biconcave lenses, convex meniscus lenses, concave meniscus lenses, various lenses such as spherical lenses, aspherical lenses, and microlenses. .

  Glass raw materials are prepared, introduced into a melting vessel, heated, melted, clarified and stirred to produce molten glass A and B that are homogeneous and free of bubbles, and each of molten glass A and glass B is supplied at a constant flow rate. Die type No. provided with a recess partly showing a vertical cross section in FIG. Then, the mold was lowered rapidly to receive a predetermined mass of molten glass lump on the recess. The recess is made of a porous material, and gas is ejected from the porous material. Since an upward wind pressure is applied to the glass lump on the recess by the gas, the glass lump is cooled in a state of floating in the recess, and a preform No. 1 having a vertical cross-sectional shape shown in FIGS. 1-No. 12 was formed. The preform cross section shown in FIGS. 2 to 4 is a cross section including the rotation center axis of the preform.

  Here, FIG. 1 and FIGS. 2 to 4 will be described. FIG. 1 is a vertical cross section of a recess of a mold as described above, and the cross section includes the center when the recess is viewed in plan. The value indicated by φ in FIG. 1 is the diameter of the surface that directly or indirectly supports the glass. Types a, c, and h have a constant radius of curvature R throughout the range of diameter φ. The types b, d, e, f, and g have recesses formed so that the radius of curvature R ′ in the range of the diameter φ ′ and the radius of curvature R outside the range of the diameter φ are different within the range of the diameter φ. Concave portions are formed so that surfaces having different radii of curvature on the circumference of diameter φ ′ are smoothly connected. The centers of the radii of curvature R ′ for the types b, d, e, f, and g are located at points deviating from the rotational symmetry axis of the recesses. The values of φ, φ ′, R, and R ′ in FIG. 1 are displayed in mm.

  2 to 4 show a cross section of the preform in a state of being placed on the recess. In the case of a small preform, it is preferable that the first intersection point be on the lower side, that is, the side facing the recess. 1-3, no. The cross sections of the preforms 7 and 8 are drawn so that the first intersection point is on the lower side. The other preforms are drawn so that the first intersection points upward. A point drawn on the right side of each preform in FIGS. 2 to 4 indicates the height of the center of gravity of each preform. Each numerical value in FIGS. 2 to 4 is also displayed in mm.

Tables 1 and 2 show preform Nos. Obtained using molten glass A and molten glass B, respectively. 1-No. 6 and preform no. 7-No. 12 represents R _{1 (min)} , R _{2 (max)} , R _{2 (min)} , R _{3 (max)} , H ₁ , H ₂ , outer diameter, center thickness, center thickness / outer diameter, and mass. .

このような工程を複数の同一の型を用いて順次、繰り返しながら、連続して流出するガラスからプリフォームを次々と成形した。複数の同一の型を回転テーブル上にテーブルの回転軸の回りに等間隔で配置し、前記テーブルをインデックス回転することにより、空の型がパイプの真下に移送、停留され、上記のようにガラス塊を受け取る。ガラス塊のプリフォームへの成形は、上記のように移動、停止を繰り返す型上で行われる。

Preforms were formed one after another from glass that continuously flowed out by repeating such steps sequentially using a plurality of identical molds. A plurality of identical molds are arranged on the rotary table at equal intervals around the rotation axis of the table, and by rotating the table with an index, the empty mold is transported and stopped directly under the pipe, and glass is used as described above. Receive a chunk. The glass block is formed into a preform on a mold that repeatedly moves and stops as described above.

  When the temperature of the preform drops to the extent that it does not deform even when external force is applied, bring the suction nozzle closer from directly above the preform, suck the center of the upper surface of the preform with the nozzle, lift it directly above, and remove it from the mold .

  According to this example, a preform having excellent rotational symmetry could be obtained even though the preform was molded on a mold that repeatedly moved and stopped. Further, even when taking out the preform from the mold using the suction nozzle, it was possible to take out the preform from the mold being carried one after another without any suction error. If the concave shape of the mold was constant, the shape of the obtained preform was also constant, and no scratches on the surface of the preform that could be caused by friction with the mold at the time of removal were observed.

  Thus, as shown in Table 1 and Table 2, respectively, from the molten glass A, the refractive index (nd) 1.69350, Abbe number (νd) 53.2, glass transition temperature (Tg) suitable for precision press molding. Preform No. made of optical glass at 520 ° C. 1 to 6 and from glass B, a preform made of optical glass having a refractive index (nd) of 1.58313, an Abbe number (νd) of 59.46, and a glass transition temperature (Tg) of 500 ° C. suitable for precision press molding. No. 7-12 were produced continuously.

  In this example, preforms made of optical glass were produced using molten glass A and B, respectively, but other optical glasses such as refractive index (nd) 1.58913, Abbe number (νd) 61.3, glass transition An optical glass having a temperature (Tg) of 515 ° C., an optical glass having a refractive index (nd) of 1.860610, an Abbe number (νd) of 40.7, and a glass transition temperature (Tg) of 560 ° C. may be used.

  Next, the above preform was precision press-molded using a precision press mold to produce an aspheric lens. The obtained lens was a high-performance aspherical lens having good surface accuracy and high rotational symmetry. Therefore, it was confirmed that no troubles such as gas traps and uneven thickness occurred between the glass and the mold surface during precision press molding.

  In this manner, various kinds of aspheric lenses, for example, high-performance lenses such as a convex meniscus lens and a concave meniscus lens could be stably produced.

  According to the present invention, it is possible to obtain a precision press-molding preform capable of stably producing a high-precision optical element by precision press molding, and to produce a high-precision optical element with a high production using the preform. Can be obtained under sex.

It is a partial vertical sectional view of the metal mold | die used in order to manufacture the preform for precision press molding of this invention. Precision press preform No. obtained in Examples It is a vertical sectional view of 1-4. Precision press preform No. obtained in Examples It is a vertical sectional view of 5-8. Precision press preform No. obtained in Examples It is a vertical sectional view of 9-12.

Claims (11)

In precision press molding preforms made of glass,
A rotating body having one rotational symmetry axis,
Of the two intersections where the rotational symmetry axis intersects the surface, the first intersection is included, the first surface is convex outside, the second intersection is included, and the second surface is convex outside. And
When the first surface is viewed in plan from the rotationally symmetric axis direction, the minimum radius of curvature of the in-circle portion having a diameter of 2/3 of the outer diameter around the first intersection is R _{1 (min)} ,
When the second surface is viewed in plan from the rotationally symmetric axis direction, the minimum curvature radius of the in-circle portion having a diameter of 1/3 of the outer diameter around the second intersection is R _{2 (min)} , the maximum curvature Let the radius be R _{2 (max)} ,
When the second surface is viewed in plan from the rotationally symmetric axis direction, the maximum radius of curvature of the outside of the circle whose diameter is 2/3 of the outer diameter around the second intersection is R _{3 (max)} ,
When the distance between the first intersection and the center of gravity is H ₁ , and the distance between the second intersection and the center of gravity is H ₂ ,
| R _{3 (max)} | <| R _{2 (min)} | <| R _{2 (max)} | <| R _{1 (min)} |
And H ₁ <| R _{1 (min)} |
Have the relationship
A precision press characterized in that the shape of a contour line in a cross section including the rotationally symmetric axis is convex outward at an arbitrary position, and the inclination of the contour line continuously changes along the contour line Preform for molding. When the distance between the second intersection and the center of gravity was H _2,
H ₂ <| R _{2 (min)} |
The precision press-molding preform according to claim 1, having the relationship:   The precision press-molding preform according to claim 1 or 2, wherein the entire surface is formed by solidifying the surface of the molten glass.   The precision press-molding preform according to any one of claims 1 to 3, wherein a ratio of a center thickness to an outer diameter (center thickness / outer diameter) is 0.45 to 0.85. In the process for producing a precision press-molding preform that flows out of the molten glass, separates the molten glass lump, and in the process of solidifying the molten glass lump, is formed into a preform on the recess of the mold.
Forming a molten glass lump into the preform according to any one of claims 1 to 4 on a concave portion of a moving mold;
Forming the molten glass surface formed on the first surface of the preform on the concave portion in a state of facing downward,
A method for producing a precision press-molding preform.   The manufacturing method of the precision press molding preform of Claim 5 which shape | molds into a preform, floating the whole molten glass lump on the said recessed part. The concave surface has a shape that is symmetric with respect to rotation at an arbitrary angle around one central axis,
The manufacturing method of the precision press molding preform of Claim 5 or 6 using the shaping | molding die in which the absolute value of the curvature radius of the said recessed part surface decreases discretely or continuously as it distances from the said central axis.   The manufacturing method of the precision press molding preform of any one of Claims 5-7 which shape | molds preform, repeating operation which moves and stops the said shaping | molding die to a horizontal direction.   The preform according to any one of claims 1 to 4 or the preform produced by the production method according to any one of claims 5 to 8 is heated and precision press using a press mold. A method for producing an optical element, comprising molding.   The optical element manufacturing method according to claim 9, wherein the preform is introduced into a press mold, the preform and the press mold are heated together, and precision press molding is performed.   The method for producing an optical element according to claim 9, wherein the heated preform is introduced into a preheated press mold and precision press molding is performed.

Images