JP5095533B2 - Mold, method for manufacturing precision press-molding preform, method for manufacturing optical element - Google Patents

Description

  The present invention relates to a molding die for molding a precision press molding preform, a preform manufacturing method using the molding die, and an optical element manufacturing method.

  A precision press molding method (also called a mold press method) is a method for producing optical elements such as aspherical lenses by heating an optical glass preform and press molding to precisely transfer the shape of the molding surface of the mold onto the glass. .)It has been known. Since optical elements such as lenses have a rotationally symmetric shape, the shape of the preform is also rotationally symmetric, and the preform is pressed from the direction of the symmetric axis to uniformly spread the glass into the press mold. Patent Documents 1 and 2 describe an example of a method for manufacturing an optical element using such a preform and a precision press molding method.

In recent years, there has been an increasing demand for lenses having a concave shape on at least one optical functional surface such as a concave meniscus lens, a biconcave lens, and a plano-concave lens. Patent Documents 3 and 4 disclose a method for manufacturing a lens in which one or both of these optical functional surfaces are concave. Patent Document 3 describes a method of manufacturing a meniscus optical element by press-molding glass under heating using a pair of molds composed of a first mold member and a second mold member. Has been. In this method, as a glass material for forming an optical element, a cylindrical glass having a flat surface as a mirror surface is heated to a temperature equal to or higher than the yield point of the glass in an atmosphere of 10 ³ Pa or less, and one surface is convex due to its own weight deformation. A shape that is thermally deformed so that the other surface has a concave shape is used. Patent Document 4 describes a method for molding an optical element in which a glass material is press-molded under heating using a pair of molding dies composed of a first mold and a second mold facing each other. The material is characterized in that two or more cylindrical glass materials having different diameters are overlapped and pressed between the two molds.
JP 2007-99529 A JP 2003-40632 A Japanese Patent Laid-Open No. 9-295817 JP-A-9-249424

  As described above, there is an increasing demand for lenses having at least one optical function surface such as a concave meniscus lens, a biconcave lens, and a plano-concave lens. In such a lens, the proportion of the volume occupied by the part (peripheral part of the lens) away from the optical axis is higher than the vicinity of the optical axis in the entire volume of the lens compared to the biconvex lens and the plano-convex lens. That is, when molding such a lens, the space in the mold is narrow near the center axis of the mold (which coincides with the optical axis of the lens to be molded) and becomes wider as the distance from the axis increases. When trying to spread the glass into this space, the glass does not spread along the molding surface and escapes in the side direction. As a result, the glass does not sufficiently spread over the entire molding surface, and a lens having high surface accuracy over the entire optical functional surface cannot be obtained. Such a tendency becomes particularly remarkable in the peripheral portion of the concave optical functional surface.

  In order to produce a lens with excellent surface accuracy, such as a concave meniscus lens that has the above-mentioned problems during molding, for example, a method of processing a preform into a shape approximating the lens shape and precision press molding Can be considered (first method). However, in this method, if the shape of the surface to be pressed of the preform, that is, the surface pressed by the mold during precision press molding is not precisely processed, atmospheric gas is trapped between the glass and the molding surface (gas This is called a strap.) Since the shape of the molding surface cannot be transferred to the glass at that portion, there is a problem that the surface accuracy is lowered.

  As another method, a method using a preform having a large center thickness can be considered (second method). In this method, the amount of glass deformation during precision press molding is positively increased to spread the glass over the entire molding surface, thereby transferring the entire molding surface to the glass. However, in this method, the volume of the preform must be significantly increased compared to the volume of the lens, and the amount of glass (referred to as surplus) that protrudes outside the molding surface increases. When such a molded product with a large surplus is cooled, the volume shrinkage of the surplus portion increases due to a phenomenon called sink, the portion close to the surplus of the optical function surface is deformed, and the surface accuracy of the lens decreases.

  Furthermore, if the surplus portion is large, the press-molded product is accommodated, so the inner diameter of the sleeve mold constituting the press mold must be increased, and the entire press mold must be increased. However, when the press mold is enlarged, the heat uniformity of the mold is lowered, and the surface accuracy of the lens cannot be sufficiently increased. Further, since the press mold is made of an expensive material such as SiC or cemented carbide, an increase in size of the mold leads to an increase in mold material cost. Further, the processing cost is increased by increasing the size of the mold.

  Furthermore, if there is a lot of surplus, the time required for the centering process increases, which increases the production cost. Furthermore, from the viewpoint of increasing the utilization rate of glass, which is one of the features of the precision press molding method, it cannot be said that molding with a large surplus is preferable.

  Also, since the preform volume must be significantly increased compared to the lens volume, the time required to heat the preform and cool the precision press-molded product must be lengthened, resulting in reduced throughput. Problems also arise.

  In light of such circumstances, the methods described in Patent Documents 3 and 4 are examined. The method described in Patent Document 3 is a method that utilizes free deformation by heating, and thus cannot increase the wall thickness relative to the diameter. . Therefore, the method described in Patent Document 3 is not suitable for the second method. Moreover, since it is a method using free deformation, it is difficult to produce a glass material having a shape very close to the lens shape, so that it is not suitable for the first method.

  In the method described in Patent Document 4, if the number of stacked glass sheets is large, the labor and cost for polishing increase. On the other hand, if the number of glass sheets is small, the surplus at the time of precision press molding increases and the surface accuracy of the lens decreases. And the labor and cost for centering increase.

  An optical element having a predetermined surface accuracy without significantly increasing the volume of the preform compared to the volume of the optical element without precisely processing the shape of the surface pressed by the mold during precision press molding, In particular, new technologies for efficiently producing optical elements having concave optical functional surfaces such as meniscus lenses and biconcave lenses are required, but there is no such technology at present.

Further, in a lens having a concave optical function surface as described above, it is preferable to use a glass having a high refractive index in terms of optical design. Examples of the glass having a high refractive index include a high refractive index medium / low dispersion glass represented by B ₂ O ₃ —La ₂ O ₃ glass, and a high refractive index / high dispersion glass represented by phosphate glass. .

  High refractive index medium and low dispersion glass has a narrow temperature range corresponding to the viscosity suitable for precision press molding, and therefore it is difficult to control the temperature during press molding. If the temperature is too low, the required lens surface accuracy may not be obtained, or cracks may occur. On the other hand, if the temperature is too high, it causes fusion with the press mold.

  The high refractive index and high dispersion glass has high reactivity with the press mold and tends to cause fusion with the mold. In addition, radial flaws that appear to be due to reaction with the mold tend to occur on the lens surface. In order to suppress the reaction between the glass and the mold, it is desirable to lower the reactivity by lowering the temperature during press molding.

  In order to eliminate such troubles (occurrence of fusion and radiation flaws), it is desirable to lower the temperature of the glass during precision press molding as much as possible. Therefore, high viscosity glass is pressed. If fine scratches such as grinding marks are present on the preform surface as described above, defects such as glass breakage are likely to occur during precision press molding. In polishing glass, polishing is performed while applying a liquid such as water to the surface of the glass. In the case of phosphate glass, a modified layer such as a hydrated layer is likely to be formed on the surface. During molding, the fusion with the mold forming surface is promoted.

  Such a tendency becomes remarkable when the glass transition temperature (Tg) exceeds 540 ° C. or higher or the refractive index (nd) exceeds 1.75 in the high refractive index medium / low dispersion glass, It becomes remarkable when the refractive index (nd) is 1.75 or more.

  In any case, in order to obtain an optical element with high surface accuracy, it is necessary to surely prevent the glass from being damaged.

The present invention has been made to solve these problems,
(1) Without precisely processing the shape of the surface of the preform pressed by the press mold during precision press molding,
(2) Without significantly increasing the preform volume compared to the lens volume,
(3) Without damaging the glass
(4) An optical element having a predetermined surface accuracy can be produced efficiently.
It is an object to provide a mold for molding a precision press-molding preform, a method for producing a preform using the mold, and a method for producing an optical element using the preform produced by the method. To do.

[1] to accommodate the separated molten glass gob from a molten glass flow a mold for precision press molding preform for molding a recess for forming the glass melt gob to precision press molding preform ,
The recess has a gas outlet at least at a part of the bottom, and at least a part of the bottom is a molding surface,
At least a part of the inner peripheral surface of the side wall of the recess is a molding surface,
Have a bottom peripheral edge and / or the gas outlet at least a portion leading to the outside the recess of the side wall portion of the lower end of at least a portion ejected from the gas ejection port ejecting gas of the recess,
At least a part of the bottom of the recess is formed of a porous body, and includes a gas supply path that guides the jet gas to the back surface of the porous body;
The gas discharge port communicates with a gas discharge path leading to the outer peripheral surface or the upper surface of the mold,
Whether the inner surface of the recess has a cylindrical shape and is used to form a precision press-molding preform having a cylindrical shape by bringing the side surface of the molten glass into contact with the inner surface of the side wall during molding. Alternatively, the shape of the inner surface of the side wall portion of the concave portion is a side shape of a truncated cone, and the side surface of the molten glass block is brought into contact with the inner surface of the side wall portion at the time of molding, and the side surface is a side shape of the truncated cone. characterized in that it is used to shape the preform, said mold.
[ 2 ] The side wall portion is detachable at a portion including the inner peripheral surface of the side wall portion, and the detachable portion of the side wall portion is a slit that continues from the upper end to the lower end that is perpendicular or inclined with respect to the upper end surface on the outer peripheral surface. have the mold according to the slit lower end communicates with the gas outlet [1].
[ 3 ] In a method for producing a precision press-molding preform, a molten glass lump separated from a molten glass stream is molded to obtain a precision press-molding preform.
Supplying a molten glass lump on the molding surface in the recess of the molding die according to [ 1] or [2] ,
While the gas is blown out from the gas outlet of the molding surface and air pressure is applied to the glass lump, the side surface of the glass lump is brought into contact with the inner surface of the side wall, and the shape of the bottom surface is transferred from the shape of the molding surface. And forming a preform having a cylindrical shape or a side surface of a truncated cone side shape ,
Precision press molding characterized in that the amount of the ejected gas is set so that the ejected gas is discharged from the gas ejection port and the molten glass lump can block the space surrounded by the side wall portion. Method for manufacturing preform.
[ 4 ] The method for producing a precision press-molding preform according to [ 3 ], wherein the molded preform has a side surface of a cylindrical shape or a truncated cone side surface shape.
[5] The method for producing a precision press-molding preform according to [ 3] or [4], wherein the molding surface is a convex surface, and the preform has a concave shape on a surface to which the shape of the molding surface is transferred.
[ 6 ] The press for precision press molding according to any one of [ 3 ] to [ 5 ], further comprising a step of press molding with the upper mold having the glass block accommodated in the concave portion of the molding mold disposed above and the mold. Reform manufacturing method.
[7] [3] - to prepare a Risei tight press-molding preform by the method according to any one of [6], and heated to produce, manufacture of optical elements precision press molding using a press mold Method.
[ 8 ] The method for producing an optical element according to [ 7 ], wherein a preform for precision press molding is introduced into a press mold, and the preform and the press mold are heated together.
[ 9 ] The method for producing an optical element according to [ 7 ], wherein the preheated precision press molding preform is introduced into a press mold and precision press molding is performed.
[ 10 ] The method for producing an optical element according to any one of [ 7 ] to [ 9 ], wherein a meniscus lens or a biconcave lens is produced by precision press molding.

  According to the present invention, there are provided a precision press-molding preform for efficiently producing a high-precision optical element, a molding die for molding the preform, and an optical element manufacturing method using the preform. can do.

[Molding mold]
The mold of the present invention is a mold having a recess for accommodating a softened glass lump and forming the glass lump into a glass molded body,
The recess has a gas outlet at least at a part of the bottom, and at least a part of the bottom is a molding surface,
At least a part of the inner peripheral surface of the side wall of the recess is a molding surface,
It has a gas discharge port for guiding at least a part of the ejected gas ejected from the gas ejection port to the outside of the recessed part at at least a part of the peripheral edge of the bottom part of the recessed part and / or the lower end of the side wall part.

Hereinafter, the embodiment of the present invention will be described based on the example of the mold shown in FIG.
FIG. 1 is a plan view (upper view) and a vertical sectional view (lower view) of the AOB in the plan view (upper view) of the mold of the present invention. In addition, the white arrow in a figure shows the flow of gas.

  The upper part 1 of the mold has a recess 2 for accommodating the glass block A, the recess 2 has an opening, a gas outlet (not shown) in at least a part of the bottom, and the bottom At least a part of 3-1 is a molding surface. For example, by forming the bottom 3-1 of the recess 2 with the porous body 3, each hole of the porous body can serve as the gas outlet. In FIG. 1, the upper surface of the porous body 3 becomes the bottom portion 3-1 of the recess 2, and at least a part thereof (the central portion of the bottom portion 3-1) becomes a molding surface for molding the lower surface of the glass lump A. In the mold shown in FIG. 1, since the entire bottom portion 3-1 of the recess 2 is formed of the porous body 3, in this embodiment, the entire bottom bottom 3-1 of the recess 2 is a gas outlet. Have

  The recess 2 includes a side wall portion 4 having an inner peripheral surface, and at least a part of the inner peripheral surface 5 of the side wall portion 4 is a molding surface. At least a part of the inner peripheral surface 5 of the side wall portion 4 functions as a molding surface for forming (molding) the side surface of the preform. The inside of the side wall portion 4 accommodates the glass lump A and becomes a space for molding. The inner peripheral surface 5 of the side wall portion 4 can be, for example, a cylindrical shape or a truncated conical side surface shape (the inner diameter increases as it goes upward, that is, an upward opening shape).

  The side wall portion 4 surrounds the space above the molding surface of the bottom portion 3-1, and is ejected from the gas outlet to at least a part of the peripheral edge portion of the bottom portion 3-1 and / or the lower end of the side wall portion 4. A gas discharge port 6 is provided for guiding at least part of the gas to the outside of the recess.

  The gas discharge port 6 communicates with a gas discharge path that communicates with the outer peripheral surface or the upper surface of the mold 1. The outer peripheral surface or upper surface of the mold 1 can be the outer peripheral surface or upper surface of the side wall 4. Specifically, as shown in FIG. 1, the side wall portion 4 is detachable from a portion 4 a including the side wall portion inner peripheral surface 5, and the side wall portion detachable portion 4 a has serrations on the outer peripheral surface (FIG. 1). (See the above figure). The serration is formed by having a slit 4b that continues from the upper end to the lower end that is perpendicular or inclined with respect to the upper end surface on the outer peripheral surface. The lower end of the slit 4b of the detachable portion 4a of the side wall portion has a structure communicating with the inner peripheral surface 5 side, whereby the lower end of the slit 4b communicates with the gas discharge port 6. The removable part 4a of the side wall part 4 and the remaining part (outer peripheral part 4c) of the side wall part 4 constitute the side wall part 4 integrally, and the outer peripheral surface having the serration (slit) of the removable part 4a and the outer peripheral part 4c. A gap 4b due to serrations (slits) is formed between the inner surface and the gas gap.

  The gas discharge port 6, which is a gap between the outer surface of the detachable part 4 a on the side wall part and the inner surface of the outer peripheral part 4 c and one end of the detachable part 4 a on the side wall part, is a porous body 3. It functions as a gas discharge passage that guides the jet gas ejected from the gas jet port of the upper surface (the concave bottom portion 3-1) to the outside of the concave portion.

  The removable part 4a of the side wall part is selected as having an inner diameter corresponding to the outer diameter of the target glass lump, and the removable part 4a of the selected side wall part 4 is attached to the outer peripheral part 4c of the side wall part 4 If used, a preform having a desired outer diameter can be formed without replacing the entire side wall.

  The bottom part 3-1 of the recessed part 2 has the gas exhaust port 6 in at least a part between the lower end of the detachable part 4a of the side wall part. In the lower view of FIG. 1 (AOB cross section), there is a gas discharge port 6 between the drawn bottom portion 3-1 and the detachable portion 4a of the side wall portion. A spacer (for example, a protrusion extending from the lower end of the detachable portion 4a on the side wall) is provided between the bottom 3-1 and the lower end of the detachable portion 4a on the side wall. There is no gap between and direct contact. However, if the inner surface of the outer peripheral portion 4c of the side wall portion has a truncated cone side surface shape and the outer surface of the detachable portion 4a of the side wall portion also has a truncated cone side surface shape corresponding to the inner surface of the outer peripheral portion 4c, the spacer Even if it does not have, the removable part 4a of a side wall part can also be hold | maintained inside the outer peripheral part 4c of a side wall part in the state which provided the clearance gap for the gas exhaust port 6. FIG.

  From the viewpoint of making the thickness of the gas cushion, which will be described later, uniform, the gas exhaust ports 6 are desirably disposed uniformly over the entire circumference, and the gaps (gas exhaust passages) 4b are desirably disposed evenly over the entire circumference. . The spacer between the porous body and the side wall not shown, and the spacer between the main body 1 and the side wall are arranged at equal intervals along the entire circumference, so that the gas discharge is axisymmetric, and the thickness of the gas cushion is increased. It is preferable from the viewpoint of getting close to each other.

  In the mold having such a structure, when the amount of the glass lump is set to a predetermined amount or more, the side surface of the glass lump can be precisely regulated by the inner peripheral surface of the side wall portion over the entire circumference. That is, unlike the regulation of the glass lump side surface via the gas cushion, the outer diameter of the glass lump can be accurately formed.

  By making the inner peripheral surface of the side wall part into an open shape such as a cylindrical shape or a side surface shape of a truncated cone as described above, the glass can be lifted upward after molding to facilitate smooth extraction from the side wall part. For example, the side wall portion can be made of stainless steel, and the surface is preferably plated. In particular, it is preferable to perform plating such as chrome plating on the inner peripheral surface of the side wall portion because fusion with high-temperature glass can be prevented. Furthermore, such plating is effective not only for preventing fusion but also for taking out the molded glass smoothly.

  A cavity 7 can be provided in the lower part of the porous body 3, and the cavity 7 can have a structure in which high-pressure gas is supplied from a gas supply path (not shown). The lower surface 3-2 of the porous body 3 is in contact with the cavity 7, and the side surface 3-3 and the peripheral portion 3-4 of the upper surface are in close contact with the lower portion of the side wall portion 4.

  When high pressure gas is supplied to the cavity 7, the gas is ejected from the bottom (molding surface) 3-1. In this state, the space surrounded by the inner peripheral surface 5 of the side wall 4 on the bottom (molding surface) 3-1. When the glass lump A in a softened state is supplied, the glass lump A is deformed by its own weight, the side surface of the glass lump A is in contact with the inner peripheral surface 5 of the side wall, and the gas ejected from the porous body is formed in the bottom 3-1. While forming a gas cushion between the surface and the glass lump A, the gas is discharged out of the recess 2 from the gas discharge port 6 through the gap (gas discharge path) 4b. Thus, the gas discharge port 6 and the gap 4b function as a discharge path for the gas ejected from the porous body.

  It is desirable to optimize the pressure distribution of the gas ejected from the molding surface according to the shape of the bottom (molding surface) 3-1. For example, when the bottom (molding surface) 3-1 is an axisymmetric convex surface, the jet gas is not smoothly discharged near the center of the molding surface, and is easily trapped between the molding surface and the lower surface of the glass lump. When such gas confinement occurs, the shape of the lower surface of the glass lump deviates from the intended shape. In such a case, the amount of gas ejection per unit area at the center of the bottom (molding surface) 3-1 can be adjusted to be less than the amount at the periphery of the bottom (molding surface) 3-1. This adjustment can be performed, for example, by forming a recess 3-5 in the center of the lower surface 3-2 of the porous body, and closing the bottom 3-6 of the recess 3-5. By doing so, the high-pressure gas cannot pass through the bottom 3-6, and only the gas that has entered the porous body from the periphery of the bottom 3-6 is ejected from the center of the bottom (molding surface) 3-1. To do. Moreover, the deeper the depth of the recess 3-5, the smaller the amount of gas that goes around the perimeter of the bottom 3-6 that has been sealed, and the lesser the amount of gas that is ejected from the center of the bottom (molded surface) 3-1. If the depth of the recess 3-5 is reduced, the reduction in the amount of gas ejected from the center of the bottom (molding surface) 3-1 is reduced. Thus, by adjusting the depth together with the inner diameter of the recess 3-5, the distribution of the amount of gas ejected from the molding surface can be controlled, and gas confinement at the center of the molding surface can be avoided.

  Such control of the gas ejection amount distribution is also effective when the shape of the bottom (molding surface) 3-1 is a plane. In addition, even when the shape of the bottom portion (molding surface) 3-1 is concave, it is effective although it is less remarkable than the case of a convex surface or a flat surface.

  In this way, an upward wind pressure is applied to the glass lump by the gas ejected from the porous body, the glass lump floats and is molded in a non-contact state with the porous body. When the high-temperature glass lump comes into direct contact with the mold, the contact portion with the mold is locally quenched to cause wrinkles on the glass surface. If the glass lump is floated as described above so that the high-temperature glass does not substantially contact the molding surface of the mold, a preform having a smooth surface without wrinkles can be molded. The lower surface of the glass lump does not continuously come into contact with the molding surface of the porous body, but if the flow rate of the jet gas is adjusted so that the gas cushion has a uniform thickness, the shape of the molding surface is glass. Transfer molded on the bottom surface of the lump. Therefore, the glass having the lower surface of the desired shape can be formed by processing the molding surface into the inverted shape of the lower surface shape of the target glass lump. The molding surface of the mold shown in FIG. 1 is a convex surface. By using this mold, a preform having a concave bottom surface can be molded.

  FIG. 2 is a plan view (upper view) and a vertical cross-sectional view (lower view) of A-O-B in the plan view (upper view) of the molding die of the present invention having a concave molding surface. When this mold is used, the lower surface of the glass block can be formed into a convex surface. The configuration of the molding die is substantially the same as that of the molding die shown in FIG. 1 except that the molding surface is a concave surface and no depression or seal is provided in the central portion of the lower surface of the porous body.

  FIG. 3 is a vertical sectional view of the molding die of the present invention in which the molding surface is convex as in FIG. In this molding die, the side wall 4 is an integral type, and the gas discharge path 8 is provided between the bottom of the side wall 4 and the upper surface of the porous body 3. The end of the gas discharge path 8 on the inside of the recess 2 is a gas discharge port 6. The configuration of the mold is shown in FIG. 1 except that the side wall 4 is an integral type and the gas discharge path 8 is a concave surface provided between the bottom of the side wall 4 and the upper surface of the porous body 3. It is substantially the same as the mold shown. It is preferable to provide the gas exhaust passages 8 at radially equal intervals from the viewpoint that the gas cushion has a uniform thickness.

[Precision press molding preform manufacturing method]
Next, the manufacturing method of the precision press molding preform of this invention is demonstrated.
The method for producing a precision press-molding preform according to the present invention is a method for producing a precision press-molding preform by molding a molten glass lump to obtain a precision press-molding preform.

The production method of the present invention comprises:
(1) Using the mold of the present invention described above, supplying a molten glass lump to the space surrounded by the side wall on the molding surface of the mold, and (2) ejecting gas from the molding surface While applying wind pressure to the glass lump,
A step of bringing a side surface of the glass block into contact with the inner surface of the side wall portion and molding a preform having the side surface;

(1) Supply of molten glass lump In the manufacturing method of this invention, a molten glass lump is supplied to the space (molding space) enclosed by the internal peripheral surface of the side wall part on a molding surface. For example, molten glass that has been melted, clarified, and homogenized by a known method flows out from a pipe at a constant flow rate, and the lower end of the molten glass flow is received by the molding surface of the mold. At this time, gas may be ejected from the molding surface and the molten glass may be received via a gas cushion, or may be received directly on the molding surface. In this state, the molten glass flow is constricted by surface tension. Next, the mold is lowered rapidly, and the molten glass is separated by the constriction by surface tension. In this way, the molten glass below the constriction is supplied to the concave portion of the mold. Even if a receiving tool that receives the lower end of the molten glass flow is used instead of the forming mold, the receiving glass is rapidly lowered at a predetermined timing to separate the molten glass lump, and the obtained molten glass lump is supplied to the recess of the forming mold. Good.

(2) Floating molding The viscosity of the molten glass lump supplied to the recess is low and spreads in the space surrounded by the inner peripheral surface of the side wall. Since gas is ejected from the bottom of the recess, the glass lump is floated as described above, and a gas cushion is formed between the molding surface and the glass. However, since the jet gas is preferentially discharged from the gas discharge path, a gas cushion is not substantially formed between the glass and the inner peripheral surface of the side wall, and the glass side surface and the side wall are in direct contact. Thus, the molten glass lump is molded into a preform having a shape obtained by transferring the shape of the molding surface on the bottom surface and having a side surface. The shape of the side surface molded into the preform can be selected as appropriate by selecting the shape of the inner peripheral surface of the side wall, and the height of the side surface is the same as that of the molten glass lump supplied when the mold including the side wall is the same. Increase or decrease depending on the amount.

  The amount of the ejection gas is set so that the ejection gas is discharged from the gas ejection port and the molten glass lump can block the space surrounded by the side wall portion. The ejected gas is discharged out of the recess (mold) from a gas discharge port which is a gap provided between the bottom of the recess of the mold and the lower end of the side wall. If the gas ejection amount is excessive, the gas that cannot be exhausted from the gas discharge passage enters between the molten glass lump and the side wall, or enters the molten glass lump, causing deformation of the glass lump and mixing of bubbles. , Will reduce the quality. Therefore, the gas ejection amount is set to an amount suitable for the space (molding space) surrounded by the inner surface 5 of the side wall portion being closed by the molten glass lump, and for the molten glass lump to float in the molding space. Is appropriate. In order to maintain such a state, it is preferable to control the ejection amount of the gas from the viewpoint of stably producing a target glass lump with high quality.

In the production method of the present invention, the amount of molten glass lump and the space (molding space) surrounded by the inner peripheral surface of the side wall portion are constant for molding a preform having side surfaces. It is necessary to have the relationship of Even if at least a small amount of molten glass ingot is supplied to the space (molding space) surrounded by the inner peripheral surface of the side wall portion, a preform having side surfaces cannot be molded. Therefore, the molten glass lump supplied to the mold is set to an amount capable of closing the space surrounded by the inner peripheral surface of the side wall and ejecting the gas from the gas outlet. Specifically, for example, when the capacity of the space (molding space) surrounded by the inner peripheral surface of the side wall is 100, the capacity of the molten glass lump can be in the range of 65 to 111. However, the appropriate range of this ratio varies depending on the opening size and depth of the space (molding space) surrounded by the inner peripheral surface of the side wall. The said range is a case where ratio of the opening dimension and depth of the space (molding space) enclosed by the inner peripheral surface of the side wall part is in the range of 1.75 to 2.72. Even when the ratio between the opening dimension and the depth is out of consideration, if the ratio between the opening dimension and the depth is taken into consideration, the capacity of the space (molding space) surrounded by the inner peripheral surface of the side wall and the capacity of the molten glass lump The ratio can be set as appropriate.

  When the special operation for controlling the shape is not performed, the upper surface of the glass block is formed into a convex curved surface by gravity and surface tension acting on the glass. If you want to shape the upper surface of the glass lump in addition to these shapes, for example, suction the upper surface of the glass in a non-contact manner, apply a negative pressure to the center of the upper surface of the glass to raise the center, and blow a gas on the upper surface. Such as pressing the upper surface and pressing the upper surface.

  Among these, from the viewpoint of forming the upper surface shape most precisely, a method of pressing the glass block accommodated in the forming die using the upper die is preferable. FIG. 4 is an example in which the glass block accommodated in the mold shown in FIG. 1 is pressed using the upper mold 10. The molding surface 10-1 of the upper mold 10 is a convex curved surface, and the shape of the upper surface of the glass lump is molded into the inverted shape of the molding surface 10-1 by the press.

The viscosity of the molten glass at the time of outflow in the process of supplying molten glass to the mold can be, for example, in the range of 3.8 to 4.5 dPa · s, and the viscosity of the molten glass lump supplied to the recess of the mold. The viscosity can range from 9 to 60 dPa · s. Moreover, the viscosity of the glass lump at the time of float forming can be in the range of 60 to 10 ³ dPa · s. Furthermore, the viscosity of the glass lump at the time of pressing is 1.2 × 10 ^{2 to} 1.1 × 10 ⁴ dPa · s, preferably 1.2 × 10 ² to 10 ³ dPa · s. It is desirable for improving accuracy. By pressing in a state where gas is ejected from the porous body, glass can be prevented from entering the micropores of the porous body. However, if the amount of gas ejected from the porous body is too large, gas may be trapped between the lower surface of the glass lump and the molding surface, and the shape of the lower surface may deviate from the desired shape. Therefore, it is desirable to reduce the gas ejection amount from the porous body at the time of pressing than before the start of pressing, and it is desirable to increase the gas ejection amount after the pressing from the time of pressing.

  As for the increase and decrease of the gas ejection amount, the molding is actually performed and the ejection amount is changed so that the fine irregularities on the porous body surface are not transferred to the glass underside of the glass lump (so that the preform surface becomes smooth) The increase / decrease amount is adjusted so that the surface is not wrinkled by contact between the hot glass block and the mold.

  When pressing the glass lump in the molding process, the side surface of the glass lump is regulated by the inner peripheral surface of the side wall, and the inner peripheral surface is a curved surface (preferably a cylindrical shape or a truncated conical side shape). Glass does not enter the dent of the inner peripheral surface. Therefore, when the preform is taken out from the concave portion, the glass that has entered the dent on the inner peripheral surface does not hinder the taking out and can be taken out smoothly.

  In this way, it is possible to form a preform having a cylindrical side surface or a truncated cone side surface and two opposing end surfaces being flat or curved. The shape of the end surface is the shape of the molding surface of the mold, and in the case of pressing, the shape of the upper mold surface is reversed. Therefore, by appropriately selecting the shape of the molding surface, both the end surfaces are either a convex curved surface, a concave curved surface, or a flat preform, or one end surface is a convex curved surface and the other end surface is a concave curved surface. It is possible to form a preform having an end surface that is a convex curved surface, the other end surface is a flat surface, one end surface is a flat surface, and the other end surface is a concave curved surface.

  When taking out the preform from the mold, the upper surface of the preform is sucked and held with a suction tool, lifted right above, taken out from the mold, and slowly cooled. If necessary, a part or all of the preform surface may be polished.

[Preform for precision press molding]
Next, specific examples of the preform manufactured by the method of the present invention will be described.
An example of the above preform is a glass precision press-molding preform having two end faces each having a rotational symmetry axis and one side face connected to the outer periphery of each of the two end faces. It is a reform. Furthermore, the two end surfaces of the preform of the present invention are pressed surfaces and are independently convex surfaces or concave surfaces, and the side surfaces are surfaces obtained by solidifying molten glass. Furthermore, when the preform has an axis that coincides with the rotational symmetry axis and is assumed to be a virtual cylinder circumscribing the preform, the ratio of the diameter φ to the height h of the cylinder (φ / h) is 1 or more and 3 or less. Furthermore, the ratio (V / V ₀ ) of the volume V of the preform to the volume V ₀ of the cylinder is 68% or more.

  The preform includes two end faces each having a rotational symmetry axis and intersecting the rotational symmetry axis, and one side face connected to the outer periphery of the two end faces.

  In order to form an optical element having an extremely high rotational symmetry such as a lens and having a very high optical function surface shape, it is appropriate to use a preform having a rotationally symmetric axis. The contour of the preform before and after the rotation can be superimposed on the operation of rotating by an arbitrary angle around the rotational symmetry axis. However, this rotational symmetry does not need to be exact geometrically, and it is sufficient if it can produce a desired optical element by precision press molding.

  The typical shape of this preform is cylindrical, but not purely cylindrical, and one or both of the two end faces can be convex. Further, the side surface can be either parallel or non-parallel to the rotational symmetry axis.

  In order to obtain an optical element that spreads the glass evenly by precision press molding and has a small thickness deviation, the surface facing the direction of the rotational symmetry axis, that is, the end surface is used as a surface to be pressed during precision press molding. The end face can be convex or concave. For example, both end surfaces are convex surfaces, two end surfaces and concave surfaces, or one of the two end surfaces is convex and the other is concave. Whether the end surface is a convex surface or a concave surface may be determined in consideration of the shape of an optical element such as a lens to be molded. For example, when molding a concave meniscus lens or a convex meniscus lens, both end surfaces are convex surfaces. It is preferable that one of the two end surfaces is a convex surface and the other is a concave surface. When a biconcave lens is molded, either the two end surfaces are convex surfaces or the two end surfaces are concave surfaces. Of the end surfaces, it is preferable that one is a convex surface and the other is a concave surface. And the gas trap at the time of precision press molding can be prevented by determining the curvature of the end face according to the shape of the molding surface of the press mold.

  When the end surface is a convex surface or a concave surface, the curvature is the spherical surface when the molding surface of the press mold is a spherical surface, and the aspherical reference curvature of the aspherical surface when the molding surface is an aspheric surface. It can be determined as appropriate in consideration. The curvatures of the two end faces can be the same or different.

  Further, the convex surface may be provided with a concave portion in a region including an intersection with the rotational symmetry axis of the convex surface. The size of the concave portion (ratio to the convex surface) can be appropriately determined in consideration of the curvature of the spherical surface if the optical functional surface of the lens is a spherical surface, and the reference curvature of the aspherical surface of the aspherical surface if the surface is aspherical. For example, when the diameter of the optical functional surface of the lens is d, the diameter of the concave portion can be in the range of d / 3 to d / 2. The depth of the concave portion can be determined as appropriate in consideration of a lens notch or the like. For example, when the height is h, the depth of the recess can be set to h / 5 to h / 4.

  Further, when the end surface (surface to be pressed) is a convex surface, a concave surface is provided in a region including the intersection with the rotational symmetry axis of the end surface, so that when the surface to be pressed is pressed with a convex mold surface, the molding surface It becomes easy to align the center of the preform and the center of the preform. Also, during mass production of precision press-molded products, the preform is introduced into the press mold, and the press mold with the preform introduced is moved by pressing the concave portion of the pressed surface with the top of the convex molding surface. Even so, the position of the preform in the mold can be kept fixed. Such an effect can also be obtained when the end surface is concave and the center of the concave surface, that is, the most depressed portion is a region including the intersection with the rotational symmetry axis of the end surface.

  The two outer peripheral edges of the side surface of the preform are connected to the outer peripheries of the two end faces. The connecting portion may form a corner or may be a curved surface. Alternatively, a connection surface connected to each of the two outer peripheral edges of the side surface and the outer periphery of the end surface may be formed between the two outer peripheral edges of the side surface and the outer periphery of the end surface.

Further, the side surface of the preform can be a side surface shape of a cylinder or a shape approximating a side surface shape of a cylinder, or a shape approximating a side shape of a truncated cone or a side shape of a truncated cone. According to the preform having such a shape, the filling rate (V / V ₀ ) can be further increased. The side surface shape of the cylinder is a smooth curved surface (curved flat surface) in which the diameter of the cylinder cross section is equal at any position in the cross section and the surface of the side surface conforms to a smooth cylinder. On the other hand, the shape that approximates the shape of the side surface of the cylinder is not strictly the shape of the side surface of the cylinder from a geometrical point of view, such as when a groove that will be described later is provided on the side surface of the preform. This means a shape that can be regarded as equivalent to the side shape of a cylinder from the viewpoint of the manufacturing process.

  In addition, the side shape of the truncated cone is such that the diameter of the cross section of the cylinder decreases or increases from one end face to the other end face, and the side surface is a smooth curved surface (curved flat surface conforming to a smooth cylinder). ). The degree of decrease or increase in the diameter of the cylindrical section is appropriately determined in consideration of the shape required for the preform, but the apex angle (full angle) of a virtual cone with the side face of the truncated cone as a part of the side face It is appropriate that 2α) be in the range of 4 ° to 6 ° from the viewpoint of easy removal into the slow cooling step of the preform. Note that α is an angle (inner angle) formed by a central axis of a virtual cone and a generatrix.

  In precision press molding, high-viscosity glass is pressed at high pressure. And since this preform has a large amount of deformation at the time of pressing, if there are grinding marks or scratches on the surface of the preform, the glass tends to be damaged starting from that portion. In order to prevent such troubles, at least the side surface of the preform is obtained by solidifying the molten glass, preferably the two side surfaces (surfaces to be pressed) in addition to the side surface also solidify the molten glass. The obtained surface. The surface obtained by solidifying molten glass means the glass surface obtained by cooling and solidifying the entire preform or the glass molded body that is the preform base material. However, it is different from the fire-making surface described later, that is, the surface obtained by heating and remelting only the glass surface and then solidifying. Since the surface obtained by solidifying the glass in the molten state is not subjected to cold working such as grinding and polishing, there is no grinding mark or polishing mark, and there is no origin of the destruction. In particular, a preform whose surface is obtained by solidifying glass in a molten state is preferable from the above viewpoint. In addition, after re-melting the glass surface, the fire-making surface obtained by cooling and solidifying the ground surface will be repaired by re-melting, so that the surface becomes microscopically smooth. There is no starting point.

The fire-making surface is obtained by a method called fire polish. However, since the glass surface is reheated to a high temperature on the fire-making surface, the glass surface may be altered. In particular, in a glass containing a component that tends to volatilize such as B ₂ O ₃ , alkali metal, fluorine, and chlorine, the glass surface is likely to be altered by volatilization during fire polishing. Moreover, since the glass shape | molded at the end and the desired shape is reheated and remelted, glass will deform | transform from a desired shape. For this reason, when comparing the fire-making surface with the surface obtained by solidifying glass in the molten state, the latter is much better. The mirror-polished surface is a polished surface after a lapping process such as roughening or sanding. There are a number of grinding marks and polishing marks on the lapped surface, and these are the starting points of the destruction. On the mirror-polished surface, large ones of these starting points are removed, but because there are very fine scratches called latent scratches, a preform having a mirror-polished surface was obtained by solidifying molten glass. Breakage resistance is lower than a preform whose entire surface is composed of a surface and a fire-making surface. Since the grinding marks and polishing marks are also removed by etching on the etched surface, the preform whose surface is the etched surface is also excellent in fracture resistance. However, if a surface having a latent flaw is etched, the flaw resistance may be reduced due to the appearance of the flaw. In any case, it is particularly preferable to obtain a surface obtained by solidifying molten glass.

  Examples of the surface obtained by solidifying the molten glass include a free surface and a mold transfer surface obtained by transferring the mold forming surface to the molten glass. The free surface can be formed, for example, by forming a molten glass lump while floating. The mold transfer surface can be formed by pressing glass with a press mold or pouring molten glass into a mold.

  In this preform, the shape is adjusted so that the ratio (φ / h) of the diameter φ to the height h of a virtual cylinder circumscribing the preform is 1 or more and 3 or less. When the ratio (φ / h) is smaller than 1, the side surface portion or the boundary portion between the side surface and the end surface (pressed surface) falls within the effective diameter of the lens, and there is a high possibility that the quality of the lens surface is deteriorated. On the other hand, if the ratio (φ / h) is larger than 3, the amount of deformation of the glass during precision press molding becomes small, and it becomes difficult to spread the glass over the entire molding surface. In addition, the preform may be tilted in the press mold, which may cause lens thickness deviation or eccentricity. Therefore, the ratio (φ / h) is set to the above range, but the preferable range of the ratio (φ / h) is 1 to 2.6, more preferably 1 to 2.4, and still more preferably 1 to 2.0.

  The shape of the preform of the present invention is also advantageous from the viewpoint of producing a preform whose entire surface is a surface obtained by solidifying molten glass. In preparation of a preform whose entire surface is a surface obtained by solidifying glass in a molten state, the molten glass lump is molded while being floated by applying wind pressure as described later. At this time, a wind pressure is obtained by blowing a gas to the bottom surface of the glass lump to obtain a wind pressure. However, if φ / h is too large, the gas is difficult to escape from the bottom surface of the glass lump along the side surface, and the glass lump is stably floated. Becomes difficult. On the other hand, if φ / h is too small, it is difficult to float the glass lump only by the wind pressure applied to the bottom surface of the glass lump. When φ / h is in the above range, the glass lump can be molded while being stably floated. From the viewpoint of stabilizing the floating of the glass lump, the preferable range of φ / h is the above-described range.

The ratio of the volume V of the preform to the volume V ₀ of the cylinder (from the viewpoint of reducing and suppressing the amount of protrusion of the glass from the molding surface while ensuring the amount of deformation of the glass during precision press molding in this way ( V / V ₀ ) is set to 68% or more. The ratio (V / V ₀ ) is an amount that can be said to be the filling rate of the glass in the virtual cylinder, and can be considered as an index for reducing the amount of glass to be used while improving the surface accuracy of the entire optical functional surface. it can. In order to enhance the above effect, the ratio (V / V ₀ ) is preferably 69% or more, more preferably 70% or more, further preferably 71% or more, and 72% or more. Is more preferable. The upper limit of the filling rate (V / V ₀ ) is about 96%, and the upper limit of the filling rate may be set to 94% in consideration of the reduction of the filling rate due to the side grooves and end faces described later being curved. Preferably, it is 92%, more preferably 90%, still more preferably 88%.

When the preform is a spheroid, the filling rate (V / V ₀ ) is 2/3 (66.7%), and when the preform is a sphere, the filling rate (V / V ₀ ) is 2/3 (66 .7%). Therefore, with preforms of these shapes, even if scaled up to increase the amount of glass deformation during precision press molding, the filling rate (V / V ₀ ) is constant, so the amount of glass deformation can be increased. However, the amount of glass that protrudes from the molding surface, that is, the amount of surplus, also increases. As a result, the surface accuracy of the lens decreases due to sink marks in the surplus part. In addition, if the surplus portion is large, the sleeve mold that accommodates the glass must be enlarged, and the entire press mold becomes large, so that the heat uniformity of the mold is reduced, and high surface accuracy is achieved over the entire optical functional surface. It becomes difficult to make optical elements.

On the other hand, in the present invention, since the ratio (φ / h) is 1 or more and 3 or less and (V / V ₀ ) is 68% or more, it is possible to perform press molding with less surplus, and as a result, optical An optical element with high surface accuracy can be obtained over the entire functional surface. Moreover, since the enlargement of the press mold can be suppressed with respect to a predetermined optical element, the mold material cost and the mold processing cost can be reduced. Furthermore, the amount of glass removed by the centering process can be reduced, the time required for the centering process can be shortened, and the utilization rate of the glass can be increased. In addition, the time required for heating the preform and cooling the precision press-molded product can be shortened, and the throughput can be increased.

  If a preform having a diameter φ smaller than the diameter when the molding surface is viewed in plan is used, the side surface of the preform may become an optical functional surface by precision press molding. Even in such a case, a smooth and highly accurate optical functional surface can be formed by making the side surface a mirror surface. However, from the viewpoint of molding a smooth and highly accurate optical function surface and reducing or preventing glass breakage during precision press molding, the ridge where the pressed surface and the side surface intersect is a curved surface, and the curved surface is also a mirror surface. It is desirable to keep it. However, it is desirable that φ be larger than the diameter when the molding surface is viewed in plan, from the viewpoint of molding a smooth and highly accurate optical functional surface.

  It is preferable that the maximum height Ry of the pressed surface is smaller than the maximum height Ry of the side surface (according to JIS B0601-1994) from the viewpoint of forming a smooth optical functional surface. Specifically, the maximum height Ry of the side surface is preferably 1 μm or less, generally in the range of 0.3 μm to 1 μm, and the maximum height Ry of the end surface that is the pressed surface is 0.02 μm or less, generally 0.01 μm to 0.02 μm. The range.

  The preform can be suitably used for molding a concave meniscus lens, a convex meniscus lens, and a biconcave lens, and is particularly suitable for molding a concave meniscus lens and a biconcave lens.

A preferable glass as a material for a concave meniscus lens, a convex meniscus lens, a biconcave lens, or the like is a glass containing B ₂ O ₃ and La ₂ O ₃ as glass components. Such a glass is a high refractive index low dispersion glass or a high refractive index medium dispersion glass. As described above, the temperature range in which a viscosity suitable for precision press molding can be obtained is narrow, and the glass transition temperature is also high. Therefore, even if the press molding temperature fluctuates slightly, the breakage easily occurs from the starting point of breakage existing on the side surface of the preform. In addition, glass with a high glass transition temperature increases the preform heating temperature during precision press molding and the heating temperature of the press mold, but reduces and prevents wear of the release film provided on the press mold and mold surface. From the top, it is preferable to keep both the heating temperatures of the preform and the press mold as low as possible. In response to such a demand, high-viscosity glass is pressed in precision press molding with a large amount of glass deformation. At that time, an optical element such as a concave meniscus lens, a convex meniscus lens, and a biconcave lens can be molded without being damaged if the preform does not have the above-described destruction starting point.

  As a preferred first specific example of the preform, a preform composed of an optical glass having a glass transition temperature (Tg) of 540 ° C. or higher, more preferably an optical glass having a glass transition temperature (Tg) of 570 ° C. or higher. Preforms constituted, more preferably preforms made of glass having a glass transition temperature (Tg) of 590 ° C. or higher, and even more preferably preforms made of glass having a glass transition temperature (Tg) of 600 ° C. or higher It is. However, if the glass transition temperature (Tg) is too high, precision press molding may be difficult, and therefore the glass transition temperature (Tg) is preferably 690 ° C. or lower.

  A preferable example of the glass constituting the precision press-molding preform is the following optical glass.

  The preform is suitable for molding a lens having a concave lens surface such as a meniscus lens or a biconcave lens, but is particularly suitable for molding a lens having negative refractive power such as a concave meniscus lens or a biconcave lens. Such a lens is suitable for achromatization in combination with a lens having a positive refractive power, and it is desirable to use a glass having a lower dispersion than the glass constituting the lens having a positive refractive power. In addition, a glass having a high refractive index is desirable in order to make the optical system compact and to reduce the absolute value of the curvature of the lens surface, thereby facilitating mold processing of the precision press mold and precision press molding.

From this point of view, the glass constituting the preform has a refractive index satisfying the following formula (1) when the Abbe number νd is 35 or more and the refractive index nd is 1.70 or more and the Abbe number νd is less than 35: An optical glass having nd is preferred.
nd ≧ 2.4−0.02 × νd (1)

  More preferably, a glass having a refractive index nd of 1.75 or more within the above range is preferable. However, if the refractive index is further increased while maintaining low dispersibility, the glass stability is lowered. Therefore, among the optical characteristics within the above range, the range satisfying the following formula (2) is preferable, and the following (3) More preferably, the range satisfies the formula.

nd ≦ 2.48−0.012 × νd (however, the refractive index nd is 2.2 or less) (2)
nd ≦ 2.42−0.012 × νd (however, the refractive index nd is 2.2 or less) (3)
(note)
Formula (1) is nd = 1.90, straight line connecting νd = 25 and nd = 1.7, νd = 35. Formula (2) is nd = 2.00, νd = 45, nd = 1.7, νd = A straight line connecting 65 (3) is a straight line connecting nd = 2.00, νd = 35, nd = 1.7, νd = 60.

In addition to the optical properties, a glass exhibiting a relatively low glass transition temperature is preferred as the glass for precision press molding. As a glass that realizes these properties, as a glass component in mol% display,
B ₂ O ₃ 5~70%,
SiO ₂ 0-50%,
ZnO 1-50%,
La ₂ O ₃ 5-30%,
Gd ₂ O ₃ 0-22%,
Y ₂ O ₃ 0-10%,
Yb ₂ O ₃ 0-10%,
Li ₂ O 0-20%,
Na ₂ O 0-10%,
K ₂ O 0-10%,
MgO 0-10%,
CaO 0-10%,
SrO 0-10%,
BaO 0-10%,
ZrO ₂ 0-15%,
Ta ₂ O ₅ 0-20%,
WO ₃ 0~20%,
Nb ₂ O ₅ 0-15%,
TiO ₂ 0-40%,
Bi ₂ O ₃ 0-10%,
GeO ₂ 0-10%,
Ga ₂ O ₃ 0~10%,
Al ₂ O ₃ 0-10%,
The optical glass containing can be illustrated.

  The optical glass will be described below. Hereinafter, unless otherwise specified, the amount of each component is expressed in mol%.

B ₂ O ₃ is an essential component and serves as an oxide that forms a glass network. When a large amount of high refractive index component such as La ₂ O ₃ is introduced, 5% or more of B ₂ O ₃ is introduced as a main network component for forming glass, and sufficient stability against devitrification is given. At the same time, it is necessary to maintain the meltability of the glass. However, if it is introduced in excess of 70%, the refractive index of the glass is lowered, and it is not suitable for the purpose of obtaining a high refractive index glass. Therefore, the amount of B ₂ O ₃ introduced is 5 to 70%, preferably 10 to 65%, more preferably 10 to 60%, and still more preferably 15 to 60%.

SiO ₂ is an optional component, and lowers the liquidus temperature of glass, improves high-temperature viscosity, and increases the stability of glass relative to glass containing a large amount of rare-earth oxide components such as La ₂ O _3. Although it is improved, in addition to the decrease in the refractive index of the glass due to the excessive introduction, the glass transition temperature becomes high and precision press molding becomes difficult. Therefore, the amount of SiO ₂ introduced is 0 to 50%, preferably 0 to 40%, more preferably 0 to 30%, and still more preferably 0 to 25%.

  ZnO is an essential component and is indispensable for adjusting the refractive index by lowering the melting temperature, liquidus temperature and transition temperature of glass. When the content is less than 1%, the above effect is weak. When the content exceeds 50%, the dispersion increases, the stability against devitrification deteriorates, and the chemical durability also decreases. The preferred range is 3 to 45%, the more preferred range is 5 to 40%, and the still more preferred range is 10 to 35%.

La ₂ O _{3 is} also an essential component, and increases the refractive index and improves the chemical durability without decreasing the stability of the glass against devitrification or without increasing the dispersion. However, if it is less than 5%, a sufficient effect cannot be obtained, and if it exceeds 30%, the stability against devitrification is remarkably deteriorated. Therefore, the introduction amount is 5 to 30%, preferably 5 to 25%, more preferably 5 -22%, more preferably 5-20%.

Gd ₂ O ₃ , like La ₂ O ₃ , is a component that improves the refractive index and chemical durability of glass without deteriorating the stability to glass devitrification and low dispersibility. When Gd ₂ O ₃ is introduced in excess of 22%, the stability against devitrification deteriorates, and the glass transition temperature tends to increase and precision press formability tends to deteriorate. Preferably it is 0 to 20%, more preferably 0 to 18%, still more preferably 0 to 15%.

Y ₂ O ₃ and Yb ₂ O ₃ are optional components that realize a glass having a high refractive index and low dispersion. When introduced in a small amount, the stability of the glass is improved and the chemical durability is improved. By introducing it, the stability of the glass against devitrification is greatly impaired, and the glass transition temperature and yield point temperature are increased. Therefore, the Y ₂ O ₃ content is 0 to 10%, and the Yb ₂ O ₃ content is 0 to 10%.

Li ₂ O has a great effect of lowering the glass transition temperature. However, when it is excessively introduced, the refractive index is lowered and the glass stability is also lowered. Therefore, the amount of Li ₂ O is 0 to 20%, preferably 0 to 15%, more preferably 0 to 10%, and still more preferably 0 to 8%. Incidentally, the amount of Li ₂ O is the case of prioritizing the low-temperature softening property of imparting to 0.1% or more.

Na ₂ O and K ₂ O have a function of improving the meltability. However, since the refractive index and the glass stability are reduced by excessive introduction, the respective introduction amounts are set to 0 to 10%.

  MgO, CaO, and SrO also have a function of improving the meltability. However, since the refractive index and the glass stability are reduced by excessive introduction, the respective introduction amounts are set to 0 to 10%.

  BaO functions to increase the refractive index, but the glass stability decreases due to excessive introduction, so the amount introduced is 0 to 10%.

ZrO ₂ is an essential component used to realize a glass having a high refractive index and maintain the low dispersibility of the glass. By introducing ZrO ₂ , the effect of improving the stability against high temperature viscosity and devitrification can be obtained without lowering the refractive index of the glass, but when introduced over 15%, the liquidus temperature rises rapidly. Since the stability against devitrification is also deteriorated, the introduction amount is 0 to 15%, preferably 0 to 12%, more preferably 0 to 10%, and further preferably 0 to 8%.

Ta ₂ O ₅ is an optional component that realizes a glass having a high refractive index and low dispersion. By introducing Ta ₂ O ₅ , there is an effect of improving the stability against high temperature viscosity and devitrification without lowering the refractive index of the glass, but when introduced over 20%, the liquidus temperature rapidly increases. Since the dispersion increases, the introduction amount is 0 to 20%, preferably 0 to 17%, more preferably 0 to 14%, and still more preferably 0 to 10%.

WO ₃ is a component that is introduced as appropriate in order to improve the stability and meltability of the glass and improve the refractive index. However, if the amount introduced exceeds 20%, the dispersion becomes large and the necessary dispersion characteristics are required. Is not obtained, and the coloration of the glass also increases. Therefore, the introduction amount is 0 to 20%, preferably 0 to 18%, more preferably 0 to 16%, and still more preferably 0 to 14%.

Nb ₂ O ₅ is an optional component that increases the refractive index while maintaining the stability of the glass. However, since dispersion increases due to excessive introduction, the introduction amount is 0 to 15%, preferably 0 to 13%. Preferably it is 0 to 10%, more preferably 0 to 8%.

TiO ₂ is an optional component that can be introduced to improve the refractive index of the glass, but excessive introduction increases the dispersion, making it impossible to obtain the desired optical constant or increasing the coloration of the glass. Therefore, the introduction amount is 0 to 40%. Preferably it is 0 to 35%, more preferably 0 to 30%, and still more preferably 0 to 25%.

Bi ₂ O ₃ is an optional component that functions to increase the refractive index of the glass and improve the stability of the glass. However, excessive introduction reduces the stability of the glass and raises the liquidus temperature. Therefore, the introduction amount is set to 0 to 10%.

GeO ₂ is an optional component that functions to increase the refractive index of the glass and improve the stability of the glass, and its introduction amount is 0 to 10%, preferably 0 to 8%. However, it is more preferable not to introduce since it is extremely expensive compared with other components.

Ga ₂ O _{3 is} also an optional component that functions to increase the refractive index of the glass and improve the stability of the glass, and its introduction amount is 0 to 10%, preferably 0 to 8%. However, it is more preferable not to introduce since it is extremely expensive compared with other components.

Al ₂ O ₃ is an optional component that increases the high temperature viscosity of the glass and lowers the liquidus temperature, improves the moldability of the glass, and also improves the chemical durability. However, the refractive index decreases due to excessive introduction, and the stability against devitrification also decreases, so the introduction amount is set to 0 to 10%.

In addition, Sb ₂ O ₃ is optionally added as a defoaming agent. However, if the amount of Sb ₂ O ₃ added exceeds 1% by weight with respect to the total content of all glass components, press molding is performed during precision press molding. Since the molding surface of the mold may be damaged, Sb ₂ O ₃ is preferably added in an amount of 0 to 1% by weight, preferably 0 to 0.5% by weight, based on the total content of all glass components. It is more preferable to add 0 to 0.1% by weight.

  On the other hand, PbO is mentioned as a preferable material that is not introduced as a glass component. PbO is harmful, and when a preform made of glass containing PbO is precision press-molded in a non-oxidizing atmosphere, lead is deposited on the surface of the molded body and transparency as an optical element is impaired or deposited. There arises a problem that metallic lead adheres to the press mold.

Lu ₂ O ₃ can be introduced as little as 0 to 3%. However, in general, the component of the optical glass is less frequently used than the other components, and is rare and expensive as an optical glass raw material.

  It is desirable not to introduce environmental elements such as cadmium and tellurium, radioactive elements such as thorium, and toxic elements such as arsenic. Moreover, it is desirable not to introduce fluorine because of problems such as volatilization during glass melting.

  In order to obtain desired optical characteristics within the above range, the amount of each component introduced may be determined within the above composition range in accordance with the above description.

  In the case of precision press-molding a glass having a high refractive index as described above, when the temperature of the mold or the temperature of the glass increases, the components in the glass, particularly the high refractive index imparting component and the molding surface of the mold, The film coated on the preform surface undergoes a chemical reaction, and troubles such as spiders and scratches on the glass surface and glass sticking to the mold are likely to occur. In order to avoid such troubles, it is desired to keep the temperature of the mold or glass at the time of press molding low, that is, press-mold glass having a relatively high viscosity. Accordingly, the above glass has a narrow allowable temperature range during press molding compared to a glass having a low refractive index. In addition, the glass has a large viscosity change with respect to the temperature change compared to a glass having a low refractive index, and the viscosity is greatly increased only by a slight decrease in the temperature, and the hard glass is pressed. Easy to make. In addition, if the amount of deformation of the glass in precision press molding is large, the cans and cracks are more likely to occur. Therefore, it is desired to reduce or prevent cans and cracks by eliminating scratches and latent scratches on the preform surface.

  As described above, the glass containing a high refractive index-imparting component is desired to have a low glass transition temperature Tg in order to suppress a chemical reaction with the molding surface of the mold and a film with the film coating the preform surface. . The preferable range of the glass transition temperature is 650 ° C. or lower, more preferably 630 ° C. or lower. Further, as described above, since the glass contains a component having a high refractive index, the glass transition temperature is relatively high in the optical glass for precision press molding, and the transition temperature is 520 ° C. or more as a guide. A glass having a higher refractive index or a glass having a lower dispersion has a higher glass transition temperature and is 540 ° C. or higher, and depending on the glass, 550 ° C. or higher, further 580 ° C. or higher, and 600 ° C. or higher.

As the glass, in _{mol%, B 2 O 3 20~43%,} La 2 O 3 5~24%, ZnO 22~42%, Li 2 O 0~15%, Gd 2 O 3 0~20 %, SiO ₂ 0-20%, ZrO ₂ 0-10%, Ta ₂ O ₅ 0-10%, WO ₃ 0-10%, Nb ₂ O ₅ 0-10%, TiO ₂ 0-10%, Bi ₂ O ₃ 0-10%, GeO ₂ 0-10%, Ga ₂ O ₃ 0-10%, Al ₂ O ₃ 0-10%, BaO 0-10%, Y ₂ O ₃ 0-10%, Yb ₂ O ₃ 0 to 10%, it can be exemplified glass containing Sb ₂ O ₃ 0~1%.

  With the above-mentioned preform using the optical glass having the composition in the above range and having a high glass transition temperature as described above, an optical element such as a concave meniscus lens and a biconcave lens made of high refractive index and low dispersion glass can be precision press molded. It can be manufactured with high accuracy.

  The above glass is suitable as a glass that realizes optical characteristics having a refractive index (nd) of 1.75 or more and an Abbe number (νd) of 25 to 55.

As a second specific example of the glass constituting the preform, phosphate glass can be exemplified. To obtain a high refractive index and high dispersion characteristics, other _{P 2 O 5, Nb 2 O} 5, TiO 2, Bi 2 O 3, WO 3, phosphate glass containing _{Li 2 O, P 2 O 5} , Nb 2 Phosphate glass containing O ₅ , Bi ₂ O ₃ , Li ₂ O, P ₂ O ₅ , Nb ₂ O ₅ , TiO ₂ , Bi ₂ O ₃ , phosphate glass containing Li ₂ O, P ₂ O ₅ , Nb Examples thereof include phosphate glass containing ₂ O ₅ , TiO ₂ , WO ₃ , and Li ₂ O. Since these phosphate glasses contain high refractive index and high dispersion imparting components such as Nb ₂ O ₅ , TiO ₂ , Bi ₂ O ₃ , WO ₃ , they react with the press mold, and as described above Fusing with the mold and radial flaws on the optical element surface are likely to occur.

  In order to eliminate such troubles (occurrence of fusion and radiation flaws), it is desirable to lower the temperature of the glass during precision press molding as much as possible. Therefore, high viscosity glass is pressed. If fine scratches such as grinding marks are present on the preform surface as described above, defects such as glass breakage are likely to occur during precision press molding. In polishing glass, polishing is performed while applying a liquid such as water to the surface of the glass. In the case of phosphate glass, a modified layer such as a hydrated layer is likely to be formed on the surface. During molding, the fusion with the mold forming surface is promoted. According to the present invention, the side surface of the preform, preferably one of the two end surfaces in addition to the side surface, more preferably the side surface and the two end surfaces, more preferably the entire surface is formed by solidifying molten glass. By adopting the surface to be processed, it is possible to reduce and eliminate problems during precision press molding due to the grinding marks and the altered layer. Note that phosphate glass is suitable as a glass that realizes optical characteristics with a refractive index (nd) of 1.75 or more and an Abbe number (νd) of less than 25.

[Method for Manufacturing Optical Element]
The optical element manufacturing method of the present invention is an optical element manufacturing method in which the above precision press molding preform is precision press molded using a press mold.

  The press mold is constituted by, for example, a pressing mold that presses the preform and a molding surface of the pressing mold that are opposed to each other, and a sleeve mold that guides the pressing mold during pressing. Of the pair of pressing dies, when one is an upper mold and the other is a lower mold, one of the pressed surfaces of the preform faces the upper mold forming surface, and the other of the pressed surfaces faces the lower mold forming surface, In addition, the preform is placed in the press mold so that the axis of rotational symmetry of the preform is parallel to the pressing direction and coincides with the center of the molding surface of the upper and lower molds, and press molding is performed.

  As mentioned above, the smaller the surplus, the less adverse effects caused by the sinking of the surplus part can be reduced, but the entire molding surface is precisely transferred to the glass even if the glass does not protrude from the upper and lower mold surfaces. It becomes difficult. Therefore, it is desirable to provide a space for accommodating the glass protruding from the molding surface, that is, the surplus portion, outside the upper and lower mold molding surfaces inside the sleeve mold. However, if this space is made larger than necessary, the entire press mold becomes large, which is undesirable from the standpoint of soaking the die, so it is desirable to reduce the space for accommodating the surplus portion.

  The present invention is suitable for manufacturing a lens, particularly a concave meniscus lens, a convex meniscus lens, and a biconcave lens, and particularly suitable for manufacturing a concave meniscus lens and a biconcave lens. Lenses with at least one optical functional surface being concave, especially lenses with a thickened peripheral part called the edge thickness compared to the thickness at the center of the lens, such as concave meniscus lenses and biconcave lenses, go from the center to the periphery. Although it becomes difficult to accurately transfer the molding surface, according to the present invention, the entire molding surface can be precisely transferred to the glass, and the deterioration of surface accuracy due to sink marks in the subsequent cooling process can be reduced and prevented. Can do. Accordingly, a preferred embodiment of the present invention is a method for manufacturing such an optical element, and is a method in which at least one molding surface of a facing mold member for forming a press mold and pressurizing a preform is a convex surface. It is.

  In this method, it is preferable that a concave portion is provided in the center of the pressed surface (end surface) of the preform, and the pressed surface is pressed with a convex molding surface. When the convex surface of the pressed surface is pressed with the convex molding surface, the preform escapes from the proper position and direction in the press mold, and the pressing direction and the rotational symmetry axis of the preform are shifted, or the center of the molding surface There is a possibility of causing uneven thickness and eccentricity due to deviation of the rotational symmetry axis of the preform. According to the preferable aspect, such a problem can be prevented. However, from the standpoint of preventing gas trapping, it is preferable that the absolute value of the radius of curvature of the convex molding surface be smaller than the absolute value of the radius of curvature of the concave portion of the preform pressed surface.

  In order to prevent the preform from being displaced from the proper position and direction when the preform is set in the press mold and transported, the weight of the upper mold or the weight of the upper mold and the preform is reduced. You may make it hold | suppress the recessed part of a press surface with a convex shaped surface.

  As press molds, SiC molds, molds using carbide molds such as tungsten carbide, cermet molds, etc. are used as mold release films with carbon-containing films and noble metal alloy films such as platinum alloys on the molding surface. What is necessary is just to use what was formed into a film, but it is preferable to use the SiC mold | die which has high heat resistance, and what provided the carbon containing film | membrane in the molding surface is preferable. In the process of exposing the press mold to a high temperature in a series of steps of precision press molding, it is preferable to perform the above process in a non-oxidizing atmosphere such as forming gas in order to prevent deterioration of the press mold due to oxidation.

  Next, a precision press molding method particularly suitable for the method for producing an optical element of the present invention will be described.

(Precision press molding method 1)
In this method, a preform is introduced into a press mold, the press mold and the preform are heated together, and precision press molding is performed (referred to as precision press molding method 1). In precision press molding method 1, both the temperature of the press mold and the preform are heated to a temperature at which the glass constituting the preform exhibits a viscosity of 10 ⁶ to 10 ¹² dPa · s to perform precision press molding. preferable. The glass is cooled to a temperature showing a viscosity of 10 ¹² dPa · s or more, more preferably 10 ¹⁴ dPa · s or more, more preferably 10 ¹⁶ dPa · s or more, and then a precision press-molded product is formed into a press mold. It is desirable to remove from. Under the above conditions, the shape of the molding surface of the press mold can be accurately transferred with glass, and the precision press molded product can be taken out without being deformed.

(Precision press molding method 2)
This method is characterized by introducing a preheated preform into a press mold and performing precision press molding (referred to as precision press molding method 2). In this method, it is preferable that the press mold and the press molding preform are separately preheated, and the preheated preform is introduced into the press mold and precision press molding is performed. According to this method, since the preform is preliminarily heated before being introduced into the press mold, it is possible to manufacture an optical element with good surface accuracy free from surface defects while shortening the cycle time.

The preheating temperature of the press mold is preferably lower than the preheating temperature of the preform. Since the heating temperature of the press mold can be kept low by such preheating, the consumption of the press mold can be reduced. In the precision press molding method 2, it is preferable to preheat the glass constituting the preform to a temperature exhibiting a viscosity of 10 ⁹ dPa · s or less, more preferably 10 ⁹ dPa · s. The preform is preferably preheated while floating, and the glass constituting the preform has a viscosity of 10 ^5.5 to 10 ⁹ dPa · s, more preferably 10 ^5.5 dPa · s to 10 ⁹ dPa · s. It is more preferable to preheat to a temperature indicating

  Moreover, it is preferable to start cooling the glass simultaneously with the start of pressing or in the middle of pressing.

The temperature of the press mold is adjusted to a temperature lower than the preheating temperature of the preform, and the temperature at which the glass exhibits a viscosity of 10 ⁹ to 10 ¹² dPa · s may be used as a guide.

In this method, it is preferable that after the press molding, the glass is cooled to a viscosity of 10 ¹² dPa · s or more and then released.

  The precision press-molded optical element is taken out from the press mold and gradually cooled as necessary. When the molded product is an optical element such as a lens, an optical thin film may be coated on the surface as necessary.

  The optical element such as an aspheric lens is suitable as a component of a high-performance and compact imaging optical system, and is suitable for an imaging optical system such as a digital still camera, a digital video camera, a mobile phone camera, and an in-vehicle camera.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
The lower diagram of FIG. 1 schematically shows a vertical cross section of a mold during molding of glass as described above. The method using this mold is a molding method in which the floating molding surface side of the pressed surface of the glass block is a concave or flat lower surface, and the opposite free curved surface is a convex surface. The mold is composed of the outer frame 4c, the side wall 4 provided with a gap (slit) 4b, and the floating mold 3. The levitation mold 3 is made of a porous material, and the bottom surface 3-1 is slightly raised from the glass floating surface and the doughnut-shaped portion 3-2 around the opposite cylindrical depression, except for the surface through which the gas can pass Nos. 3-2, 3-3, and 3-4 crush pores on the surface of the porous body. A cylindrical recess 3-5 is provided in the center on the back side. The surface 3-6 of the cylindrical recess 3-5 is subjected to a process of crushing the surface of the porous body or reducing the passage amount of the jet gas. The diameter and depth are changed according to the capacity of the preform to be molded and the shape of the pressed surface. With this structure, when the glass lump A is filled in the recessed part, the jet gas 5 supplied from the lower side of the floating mold enters more than the central part of the glass floating surface 3-1 from the part 3-2. Pass through the part and float the glass in a stable state. At this time, the gas ejected from the lower surface of the glass lump and the glass floating surface 3-1 outwards to the gas outlet 6 without any gas accumulation, and smoothly escapes upward from the gas exhaust path 4b. In addition, since the jet gas does not pass between the inner peripheral surface 5 of the side wall 4 and the glass block A, the portion in contact with the inner peripheral surface 5 of the side wall 4 can accurately transfer the surface and shape of the preform. An accurate side shape and size can be obtained.

  Thus, without opening the upper surface and pressing the glass, one pressed surface (the lower surface of the glass lump A in FIG. 1) is a concave surface, the side surface is a cylindrical side surface, and the other pressed surface (FIG. 1). A preform was produced in which the upper surface of the glass lump A was formed into a convex surface. The preform molding conditions were as follows.

(1) Mold The capacity of the molding space is 756.5 mm ³ . The dimensions were such that the upper diameter of the truncated cone was 14.68 mm, the taper was 4 degrees on one side, and the depth to the lowest position of the taper was 5 mm. A porous body having a height convex shape (SR 32 mm) of 0.85 mm is incorporated at the center from the position upward.

(2) Glass composition of glass lump The composition of the glass constituting the glass lump is as follows. The content of B ₂ O ₃ is 38 mol%, the content of SiO ₂ is 5 mol%, the content of ZnO is 23 mol%, the content of La ₂ O ₃ is 19 mol%, and the content of ZrO ₂ is 5 The content of mol%, the content of Ta ₂ O ₅ is 4%, the content of WO ₃ is 6%, and the total content of these components is 100 mol%.

(3) Viscosity of glass lump The viscosity of glass is as follows.
The viscosity at the time of outflow is 3.8 to 4.5 dPa · s,
The viscosity at the time of supply to the mold recess is 9 to 60 dPa · s,
The viscosity at the time of molding while floating with a molding die is 60 to 10 ³ dPa · s.

(4) Floating molding The molding tact per piece was about 7.9 seconds, and the gas ejection rate was 0.3 liter / min.

(5) Preform The volume of the preform is 560 mm ³ , and the dimensions and the radius of curvature of the curved surface are approximately the values shown in FIG. FIG. 5 shows a cross section of a preform including an axis of symmetry. In addition, the dimension shown in FIG. 5 is a mm unit. Convex shape (curvature R15), concave shape (curvature R22). However, there is a tendency to be slightly smaller than the curvature of the mold due to shrinkage and return. (The same applies hereinafter)

(Example 2)
FIG. 2 is a configuration diagram of an embodiment in which the floating molding surface is concave as described above, and both the pressed surfaces of the preform are molded into a convex surface. The side wall portion 4 including the configuration of FIG. 1 is in the form of a cylinder or a truncated cylinder whose upper side is opened for easy removal after completion of cooling, and has a replaceable structure. This makes it possible to mold preforms having various outer diameters.

  Using this mold, the one pressed surface (the lower surface of the glass lump A in FIG. 2) is a convex surface, the side surface is in a cylindrical side surface shape, and the other pressed surface (the upper surface 2 of the glass lump A in FIG. 2) is A preform formed on a convex surface was prepared. The preform molding conditions were as follows.

(1) Mold The capacity of the molding space is 945.8 mm ³ . The dimensions were such that the upper diameter of the truncated cone was 14.68 mm, the taper was 4 degrees on one side, and the depth to the lowest position of the taper was 5 mm. A concave SR18 mm porous body having a depth of 1.46 mm at the center is incorporated downward from this position.

(2) Glass composition of glass lump The same glass as Example 1 was used.

(3) Viscosity of glass lump The viscosity of the glass at the time of outflow is 3.8 to 4.5 dPa · s,
The viscosity at the time of supply to the mold cavity is 9 to 60 dPa · s,
The viscosity when molding while floating is 60 to 10 ³ dPa · s.

(4) Floating forming The forming tact per piece was about 7.9 seconds, and the gas ejection rate was 0.35 liter / min.

(5) Preform The volume of the preform is 689.5 mm ³ , and the dimensions of each part are approximately the values shown in FIG. FIG. 6 shows a cross section of the preform including the axis of symmetry, and the dimensions are in mm. Upper convex shape (curvature R44), lower convex shape (curvature R20)

(Example 3)
Example 1 was an example in which a preform was molded in a state where the upper portion of the glass block on the mold was open throughout. On the other hand, in the third embodiment, in addition to the operation as in the first embodiment, the upper portion of the glass block is pressed and both the upper and lower surfaces of the glass block are made concave. FIG. 4 schematically shows, as a vertical cross-sectional view, the state after the upper surface of the glass lump on the mold is pressed to form the upper surface of the glass lump and then the upper mold 10 is separated from the glass. In the above press, the upper surface of the glass lump that is a free-form surface is molded into a concave shape that follows the shape of the upper mold forming surface 10-1 using a dense upper mold 10, and both pressed surfaces are concave. The preform is molded. As a result of press molding by this method, a preform having a good shape could be obtained without affecting the surface to be pressed due to gas accumulation. The preform molding conditions were as follows.

(1) Pressing the upper surface of the glass After the glass is supplied to the concave portion of the mold until a desired amount is reached and moved and indexed to the next section 2, the press pressure is 0.2 MPa and the timing after 0.05 seconds. Press was performed for 2 seconds.

(2) Preform The volume of the preform is 622.6 mm ³ , and the dimensions are approximately the values shown in FIG. FIG. 7 shows a cross section of the preform including the axis of symmetry, and the dimensions are in mm. Note that the upper concave surface shape is approximated as a spherical surface of SR 18 mm, and the lower concave surface shape is approximated as a spherical surface of SR 22 mm.

  In all of Examples 1 to 3, outflow of the molten glass, separation of the molten glass lump (supporting the lower end of the molten glass flow, forming a constriction due to the surface tension of the glass in the middle of the molten glass flow, removing the support and lowering from the constricted portion ), Rotate the table using a plurality of molds placed on the turntable, produce the preforms one after another, and after the mold rises to a viscosity that does not deform the molds The preform can be taken out from. The preform thus taken out can be further annealed, and in the subsequent step, a carbon film coat can be applied to the surface of the preform. For the preparation of the molten glass ingot from the spilled molten glass, a known method can be used as appropriate, for example, the method described in JP-A-2004-300020 or the method described in JP-A-8-81228. It can be used as appropriate.

Example 4
Example 4 is an example of producing an aspherical meniscus lens by precision press-molding the preform obtained in Example 1. In precision press molding, a precision press mold having one concave surface and the other convex surface is used among a pair of opposed molding surfaces (generally, a mold having a concave molding surface is a lower mold and a convex mold is an upper mold). ), An aspherical concave meniscus lens was molded so as to be a free surface without restricting the side surface.

Specifically, the preform molded in Example 1 was washed and dried, and then precision press molding was performed to produce an aspheric lens. In the press molding, a press mold in which a carbon film was formed on the surface of a SiC mold material was used, and the atmosphere was a nitrogen atmosphere. The press molding was performed by heating the preform to 635 ° C. and pressing it at a pressure of 100 kgf / cm ² for 60 seconds. After press molding, the aspheric lens was removed from the mold and allowed to cool slowly. The obtained lens was in good condition both on the inside and on the surface. The lens may be centered as necessary to form an antireflection film on the surface. Although this example relates to a method for manufacturing an aspheric lens, it can also be applied to the manufacture of other optical elements such as prisms and diffraction gratings.

  Since the preform formed in Example 1 has a cylindrical side surface, the surplus that protrudes to the side by the precision press molding is small, and accordingly the sink of the surplus portion (volume at the time of glass cooling) Since the shrinkage is small, it is possible to prevent the surface accuracy of the lens from being lowered due to the sink marks.

  The basic structure of the mold shown in FIG. 1 is left as it is, and the inner diameter of the side wall 4 and the curvature of the convex glass floating surface of the floating mold 3 are changed, and the upper surface is convex and the lower surface is concave in the same manner as the previous method. A preform having a cylindrical side surface is prepared, and a precision press mold having one concave surface and the other convex surface is used among a pair of opposing molding surfaces (generally, a concave mold is a lower mold, a convex surface is The aspherical convex meniscus lens was molded so as to be a free surface without regulating the side surface.

  Since the preform has a cylindrical side surface, there is little surplus that protrudes to the side in the precision press molding, and accordingly, there is less sink marks (volume shrinkage during glass cooling) of the surplus part. It was possible to prevent the surface accuracy of the lens from being lowered due to sink marks.

  The two types of aspheric meniscus lenses were centered, and the lens surface was coated with an antireflection film to complete the lens.

(Example 5)
Example 5 is an example in which the preform obtained in Example 2 is precision press-molded to produce an aspherical convex meniscus lens and an aspherical biconvex lens. Precision press molding was performed in the same manner as in Example 4.

  In precision press molding, a precision press mold having one concave surface and the other convex surface is used among a pair of opposed molding surfaces (generally, a mold having a concave molding surface is a lower mold and a convex mold is an upper mold). ), An aspherical convex meniscus lens was molded so as to be a free surface without restricting the side surface.

  Next, an aspherical biconvex lens was molded using a precision press mold in which a pair of opposed molding surfaces were both concave, and the side surfaces were free surfaces without restriction.

  Since the preform has a cylindrical side surface, there is little surplus that protrudes to the side in the precision press molding, and accordingly, there is less sink marks (volume shrinkage during glass cooling) of the surplus part. It was possible to prevent the surface accuracy of the lens from being lowered due to sink marks.

  The aspherical convex meniscus lens and the aspherical biconvex lens were centered, and the lens surface was coated with an antireflection film to complete the lens.

(Example 6)
Example 6 is an example in which an aspherical biconcave lens is manufactured by precision press-molding the preform obtained in Example 3. Precision press molding was performed in the same manner as in Example 4.

  In precision press molding, an aspherical biconcave lens was molded such that a pair of opposing molding surfaces was a convex precision press molding die, and the side surfaces were free surfaces without restriction.

  Since the preform has a cylindrical side surface, there is little surplus that protrudes to the side in the precision press molding, and accordingly, there is less sink marks (volume shrinkage during glass cooling) of the surplus part. It was possible to prevent the surface accuracy of the lens from being lowered due to sink marks.

  Since the preform has a cylindrical side surface, there is little surplus that protrudes to the side in the precision press molding, and accordingly, there is less sink marks (volume shrinkage during glass cooling) of the surplus part. It was possible to prevent the surface accuracy of the lens from being lowered due to sink marks.

  The aspherical biconcave lens was centered, and the lens surface was coated with an antireflection film to complete the lens.

  This is useful in the field of manufacturing optical elements such as glass lenses.

FIG. 2 is a plan view (upper view) and a vertical sectional view (lower view) of A-O-B of the plan view (upper view) of the molding die of the present invention. FIG. 2 is a plan view (upper view) and a vertical cross-sectional view (lower view) of A-O-B of the plan view (upper view) of the molding die of the present invention having a molding surface as a concave surface. It is a vertical sectional view of another aspect (side wall unit integrated type) of the molding die of the present invention. It is explanatory drawing of the example which pressed the glass lump A accommodated in the shaping | molding die of FIG. The cross-sectional shape including the symmetry axis of the preform produced in Example 1 and dimensions are shown. The cross-sectional shape and dimension including the symmetry axis of the preform produced in Example 2 are shown. The cross-sectional shape and dimension including the symmetry axis of the preform produced in Example 3 are shown.

Claims (10)

Accommodates a molten glass gob separated from the molten glass flow to a mold for precision press molding preform for molding a recess for forming the glass melt gob to precision press molding preform,
The recess has a gas outlet at least at a part of the bottom, and at least a part of the bottom is a molding surface,
At least a part of the inner peripheral surface of the side wall of the recess is a molding surface,
Have a bottom peripheral edge and / or the gas outlet at least a portion leading to the outside the recess of the side wall portion of the lower end of at least a portion ejected from the gas ejection port ejecting gas of the recess,
At least a part of the bottom of the recess is formed of a porous body, and includes a gas supply path that guides the jet gas to the back surface of the porous body;
The gas discharge port communicates with a gas discharge path leading to the outer peripheral surface or the upper surface of the mold,
Whether the inner surface of the recess has a cylindrical shape and is used to form a precision press-molding preform having a cylindrical shape by bringing the side surface of the molten glass into contact with the inner surface of the side wall during molding. Alternatively, the shape of the inner surface of the side wall portion of the concave portion is a side shape of a truncated cone, and the side surface of the molten glass block is brought into contact with the inner surface of the side wall portion at the time of molding, and the side surface is a side shape of the truncated cone. characterized in that it is used to shape the preform, said mold. The side wall portion is detachable at a portion including the inner peripheral surface of the side wall portion, and the detachable portion of the side wall portion has a slit continuous from the upper end to the lower end perpendicular or inclined with respect to the upper end surface on the outer peripheral surface. The mold according to claim 1, wherein a lower end of the slit communicates with the gas discharge port. In a method for manufacturing a precision press molding preform, which obtains a precision press molding preform by molding a molten glass lump separated from a molten glass stream ,
A molten glass lump is supplied onto the molding surface in the recess of the mold according to claim 1 or 2 ,
While the gas is blown out from the gas outlet of the molding surface and air pressure is applied to the glass lump, the side surface of the glass lump is brought into contact with the inner surface of the side wall, and the shape of the bottom surface is transferred from the shape of the molding surface. And forming a preform having a cylindrical shape or a side surface of a truncated cone side shape ,
Precision press molding characterized in that the amount of the ejected gas is set so that the ejected gas is discharged from the gas ejection port and the molten glass lump can block the space surrounded by the side wall portion. Method for manufacturing preform. 4. The method for producing a precision press-molding preform according to claim 3 , wherein the molded preform has a side surface of a cylindrical shape or a truncated conical side shape. The method for producing a precision press-molding preform according to claim 3 or 4, wherein the molding surface is a convex surface, and the preform has a concave surface on which the shape of the molding surface is transferred. The method for producing a precision press-molding preform according to any one of claims 3 to 5 , further comprising a step of press-molding with an upper mold in which a glass lump accommodated in a concave portion of the mold is arranged and the mold. The method for manufacturing an optical element to produce a Risei tight press-molding preform by the method according to any one of claims 3 to 6, and heated to prepare, for precision press molding using a press mold. The method for manufacturing an optical element according to claim 7 , wherein a preform for precision press molding is introduced into a press mold, and the preform and the press mold are heated together. The optical element manufacturing method according to claim 7 , wherein the preheated precision press molding preform is introduced into a press mold and precision press molding is performed. The method for producing an optical element according to any one of claims 7 to 9 , wherein the meniscus lens or the biconcave lens is produced by precision press molding.

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