JP5095564B2 - Mold, method for manufacturing glass molded body using the mold, and method for manufacturing optical element - Google Patents

Description

  The present invention relates to a mold, a method for manufacturing a glass molded body using the mold, and a method for manufacturing an optical element.

  Precision press molding as a method of producing optical elements such as aspherical lenses by heating glass materials (also called preforms) made of optical glass, press molding, and accurately transferring the shape of the molding surface of the mold to glass (Also referred to as a mold press method) is 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 addition, the preform manufacturing method used for manufacturing the optical element includes a method of grinding and polishing a glass block and a method of manufacturing from a molten glass. In addition to the method of making molten glass, the method of making a preform directly from molten glass and the molding of molten glass to make a glass molded body that approximates the shape of the preform, and polishing this molded body to form the preform There is a method to make. A method for producing a preform from molten glass has higher productivity than a method for grinding and polishing a glass block.

  In the method of directly making a preform from the molten glass disclosed in Patent Documents 1 and 2, the glass is formed in a state where the glass lump is floated by applying wind pressure to the glass lump on the mold in order to form a glass having a smooth surface. After the molding, the glass molded body is taken out from the molding die, and the molten glass lump is again supplied to the empty molding die to perform the molding. By forming a plurality of molds on the turntable and rotating the table with an index, glass molded bodies can be produced one after another from the continuously flowing molten glass.

By the way, in recent years, there is an increasing demand for lenses in which at least one optical functional surface such as a concave meniscus lens, a biconcave lens, and a plano-concave lens is concave. 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. It is characterized by using a heat-deformed one having a convex shape and a concave shape on the other surface. 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 must be increased. 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.

Therefore, the inventors have
(1) Without precisely processing the shape of the surface pressed by the mold during precision press molding,
(2) Without significantly increasing the preform volume compared to the lens volume,
(3) Without damaging the glass
(4) Various studies were conducted to provide a precision press-molding preform capable of efficiently producing an optical element having a predetermined surface accuracy. As a result, it has been found that a precision press-molding preform having a predetermined shape can solve the above problems.

  However, conventionally, there has been known a molding die suitable for molding such a precision press molding preform in the process of holding the molten glass lump in a floating state and cooling it, and a manufacturing method using such a molding die. It was not done.

Therefore, the object of the present invention is to
(1) Without precisely processing the shape of the surface pressed by the mold during precision press molding,
(2) Without significantly increasing the preform volume compared to the lens volume,
(3) Without damaging the glass
(4) To provide a molding die that can be used for producing a precision press molding preform capable of efficiently producing an optical element having a predetermined surface accuracy.

  A further object of the present invention is to provide a method for producing a molded body that can be used as a precision press-molding preform or a preform for a precision press-molding preform using the mold.

  In addition, an object of the present invention is to provide a method for producing an optical element using the precision press-molding preform produced by the above production method.

The present invention is as follows.
[1] In a mold used to mold a molten glass lump while cooling in a floating state to form a precision press-molding preform ,
The molding die includes a concave glass molding portion having a bottom portion and a side wall erected so as to surround the bottom portion,
The side wall has a gas flow path for flowing the gas ejected from the gas ejection port toward the opening direction of the glass forming part,
The gas flow path is a plurality of grooves extending perpendicularly or inclined from the bottom to the direction of the opening of the glass forming part,
The said bottom part has a some gas jet nozzle which ejects the gas for applying a wind pressure to the said glass lump and making it float.
[ 2 ] The mold according to [ 1 ], wherein the surface of the side wall having the gas flow path has a waveform formed by a continuous surface or a waveform formed by an intermittent surface.
[ 3 ] The molding die according to any one of [1] to [ 2 ], wherein the bottom portion having the plurality of gas ejection ports is made of a porous material having air permeability.
[ 4 ] The precision press-molding preform includes a rotational symmetry axis, two end faces each intersecting with the rotational symmetry axis, and one side face connected to the outer periphery of the two end faces. [1] -The shaping | molding die in any one of [ 3 ].
[ 5 ] The mold according to [ 4 ], wherein a side surface of the precision press-molding preform is molded by a side wall of the glass molding portion.
[ 6 ] The molten glass is flowed out to separate the molten glass lump, and the glass lump is molded while being cooled in a floating state in a glass forming portion provided in a mold to obtain a precision press molding preform. In the method for producing a press-molding preform ,
By using the molding die according to any one of [1] to [ 5 ] as the molding die and holding the molten glass lump in a floating state at the glass molding portion of the molding die, a, and two end surfaces and said two comprises one side that connects to the outer periphery of the end face, for precision press molding flop, which comprises molding a preform for precision press molding of the axis of rotational symmetry and each cross Reform manufacturing method.
[ 7 ] The manufacturing method according to [ 6 ], wherein the volume of the glass lump is in a range of 40 to 65% of the volume of the glass forming part.
[ 8 ] The method for producing a glass molded body according to any one of [ 6 ] to [ 7 ], comprising pressing the upper surface of the glass lump held in the glass molded part.
[ 9 ] In the precision press-molding preform , two end faces are independently convex or concave,
The side surface comprises a surface obtained by solidifying molten glass,
Assuming a virtual cylinder having an axis coinciding with the rotational symmetry axis and circumscribing the preform, the ratio (φ / h) of the diameter φ to the height h of the cylinder is 1 or more and 3 or less, wherein a ratio (V / V ₀₎ of the volume V of the preform to the volume V ₀ which cylinder is 68% or more, the production method according to any one of [6] to [8].
[10] [6] to produce a preform for precision press molding by the method according to any one of [9], the production of precision press-molding preform for polishing at least a portion of the precision press-molding preform Method.
[11] [6] to a precision press-molding preform that obtained by the production method according to any one of [10], which comprises precision press molding using a press mold, method of manufacturing an optical element .
[ 12 ] The method for producing an optical element according to [ 11 ], wherein a press molding die is configured, and at least one molding surface of an opposing mold member for pressurizing the preform is a convex surface.

  ADVANTAGE OF THE INVENTION According to this invention, the shaping | molding die used in order to manufacture the preform for precision press molding for producing a highly accurate optical element efficiently can be provided. Furthermore, according to this invention, the manufacturing method of the molded object which can be used as a preform | base_material of the precision press molding preform using the said shaping | molding die or a precision press molding preform can be provided. In addition, according to the present invention, it is possible to provide a method for manufacturing an optical element using the precision press-molding preform manufactured by the above-described manufacturing method.

[Molding mold]
The present invention relates to a molding die used for obtaining a glass molded body by molding a molten glass lump while cooling in a floating state. The molding die of the present invention includes a concave glass molding portion having a bottom portion and a side wall erected so as to surround the periphery of the bottom portion, and the bottom portion floats by applying wind pressure to the glass lump. It has a plurality of gas ejection ports for ejecting gas.

As described above, the mold of the present invention is a mold suitable for molding a molded body such as a preform having a specific shape. Such a molded body is a glass molded body having a rotational symmetry axis and having two end faces each intersecting with the rotational symmetry axis and one side surface connected to the outer periphery of the two end faces. Further, in the molded body, two end surfaces are independently convex or concave, the side surface is a surface obtained by solidifying molten glass, and has an axis coinciding with the rotational symmetry axis, and Assuming 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, and the profile with respect to the volume V ₀ of the cylinder. It is preferable that the reformed volume V ratio (V / V ₀ ) is 68% or more. This molded body will be described later.

  The shaping | molding die of this invention is equipped with the concave glass shaping | molding part which has a bottom part and the side wall standingly arranged so that the circumference | surroundings of the said bottom part may be enclosed. Furthermore, the bottom part of the glass forming part has a plurality of gas ejection ports for ejecting a gas for applying a wind pressure to the glass lump to float.

  The mold that is used for the float forming of glass preforms such as preforms that have been known so far also has a concave part having a structure in which the bottom part having a gas outlet and the side wall continues from this bottom part. A device provided with a glass forming part is described in Patent Document 2, for example. However, the molding die of the present invention is characterized in that it has a plurality of gas jets provided at the bottom and a concave glass molding having a side wall standing so as to surround the periphery of the bottom. A mold having such a glass molding part is not known.

  The bottom portion having the plurality of gas ejection ports can be made of, for example, a porous material having air permeability. Alternatively, it may be a non-porous material and regularly or irregularly provided with gas jets. Molding molds for floating molding having a plurality of gas ejection ports have been known so far.

  Specifically, the bottom of the glass molding part is made of a porous body, and a high-pressure gas is supplied to the back of the porous body, that is, the back of the surface facing the glass lump, and the glass lump is opposed to the glass lump through the porous body. It is preferable to eject the gas from the surface to be performed. By carrying out like this, gas can be uniformly ejected from the whole surface which faces the glass lump of a bottom part, and an upward wind pressure can be applied comparatively equally to the lower surface of a glass lump. Therefore, it can prevent that the wind pressure by gas ejection concentrates on the local part of the glass lump lower surface in the state where viscosity is low, and unevenness is generated on the glass lump lower surface.

  In the said shaping | molding die, in order to obtain the wind pressure for levitation | floating of a glass lump with the gas spouted from the gas spout provided in the bottom part, it is preferable to eject gas equally to the glass surface which faces a bottom part. In order to perform such gas ejection, the bottom is preferably formed of a porous body, and preferably provided with a gas flow path for supplying gas to the back surface of the porous body. By supplying a high-pressure gas to the back surface of the porous body and allowing the porous body to permeate, the gas can be uniformly ejected from the surface.

  Similar to the bottom surface, the side wall is also made of a porous material, and when high-pressure gas is supplied to the back surface of the porous material, the gas ejected from the side surface tends to block the passage of the ejected gas from the bottom surface. As a result, sufficient wind pressure on the bottom surface cannot be obtained, and the floating state of the glass may be deteriorated. Therefore, it is preferable to provide the gas outlet only on the bottom surface of the bottom surface and the side wall. By providing the gas ejection port only on the bottom surface, the glass lump can be stably floated.

  The shape of the bottom is preferably a pressed surface of a preform, which is a molded body, or a shape obtained by inverting the shape of the bottom surface of a preform base material processed into the pressed surface, or a shape that approximates the above shape.

  In addition, when the shape of the bottom part of the glass forming part is concave, the glass lump is easily shaken if there is no side wall of the above shape, but according to the present invention, the glass lump is stably floated even when the shape of the bottom part is concave. Can be made.

  The shape of the side wall can be either a side surface shape of a cylinder or a side surface shape of a truncated cone, or a shape that approximates a side surface shape of a cylinder or a shape that approximates a side surface shape of a truncated cone. Here, the shape that approximates the side surface shape of the cylinder and the shape that approximates the side surface shape of the truncated cone are because grooves and protrusions may be provided on the side wall as described above. The side wall functions to suppress the shaking of the glass lump or the glass molded body, but may be any shape that approximates the side shape of the cylinder or the shape that approximates the side shape of the truncated cone as long as such a function is exhibited. .

  In order to mold a preform having a high filling rate, a mold having a side wall that is vertical or nearly vertical is desirable. In such a mold, the side wall is opened upward so that the preform can be smoothly taken out from the glass molding part, that is, the side wall has a side face shape of the truncated cone or a shape similar to the above shape, and the opening part is larger than the bottom part. It is preferable to do. By carrying out like this, preform can be taken out smoothly from a glass forming part.

  It is preferable that the side wall has a gas flow path through which the gas ejected from the gas ejection port flows in the opening direction of the glass forming portion. Specifically, the gas flow path can be a plurality of grooves extending perpendicularly or inclined from the bottom to the direction of the opening of the glass forming part, and the surface of the side wall having the gas flow path is a continuous surface. Or a waveform consisting of intermittent surfaces. A wave consisting of a continuous surface is a shape in which grooves and mountains with no corners appear alternately, whereas a waveform having an intermittent surface is a shape in which grooves and mountains appear alternately, and It is a shape in which the tangent forms a corner. An intermediate shape between the two (for example, a waveform having an intermittent surface and a shape in which a corner tangent to a groove and a mountain range is rounded) may be used.

  As described above, the mold of the present invention is a glass mold having a rotational symmetry axis and two end faces each intersecting with the rotational symmetry axis and one side face connected to the outer periphery of the two end faces. Used to shape the body. In particular, one end face of the molded body is formed into a shape corresponding to the bottom of the mold, and the side surface is formed into a shape corresponding to the side wall of the mold. Since the molding die of the present invention has the gas flow path on the side wall, at least a part of the gas ejected from the gas ejection port reaches the opening via the gas flow path, stably stabilizes the glass lump, and glass It can be held in the molded part. Further, the gas passing through the gap between the gas channel and the side wall other than the gas channel and the glass block avoids or relaxes contact between the glass block and the side wall, and solidifies the glass in the molten state on the side surface of the glass molded body. Thus, the obtained surface can be obtained.

The mold of the present invention will be further described with reference to FIGS.
FIG. 1A shows a mold 10 which is an embodiment of the mold of the present invention. The molding die 10 includes a bottom base member 11, a bottom forming portion 12 made of a porous material provided in the central opening of the bottom base member 11, and a side wall constituting member 13. In the side wall constituting member 13, the inner wall constitutes the side wall of the molded part. Further, the side wall constituting member 13 can be divided into a plurality of parts, and when the glass molded body after molding is taken out, as shown in FIG. Can be made easier.

  FIG. 2A shows a mold 20 that is an embodiment of the mold of the present invention. The mold 20 includes a bottom base member 21, a bottom forming portion 22 made of a porous material provided in an opening at the center of the bottom base member 21, and a side wall constituent member 23. In the side wall constituting member 23, the inner wall constitutes the side wall of the molded part. The lower part of the side wall constituting member 23 has a shape corresponding to a recess provided in the upper part of the bottom base member 21, and can be assembled by being detachably incorporated into the recess. Further, a magnet 24 may be provided inside the recess provided in the upper part of the bottom base member 21 to fix the side wall constituting member 23. Further, a gas flow path including a groove cut in the vertical direction is formed on the surface 23a constituting the side wall inside the opening of the side wall constituting member 23. Furthermore, as shown in FIG. 2 (C), the inside of the opening of the side wall constituting member 23 has a truncated conical shape (the virtual apex is above the side wall constituting member 23, the lower opening being larger than the upper opening). The angle α corresponding to ½ of the apex angle of the cone is not separated when the side wall constituting member 23 is separated from the bottom base member 21 after molding. Thus, it can be appropriately determined in consideration of the size of the molded body, and can be set in the range of 2 to 3 °, for example. In addition, the said virtual vertex means the vertex of the virtual cone which makes the side surface of the said truncated cone a part of side surface, and the vertex angle of a cone means the vertex angle of the said virtual cone. When taking out the glass molded body after molding, as shown in (B), the side wall constituting member 23 can be removed, and then the glass molded body can be easily carried in.

  FIG. 3A shows a mold 30 which is an embodiment of the mold of the present invention. The mold 30 includes a bottom base member 31 and a bottom forming portion 32 made of a porous material provided in the central opening of the bottom base member 31. Above the bottom forming part 32 of the bottom base member 31, the inner wall constitutes the side wall of the molding part. The inside of the inner wall 33 of the bottom base member 31 has a truncated conical shape (the virtual vertex is above the inner wall 33) with a lower inner diameter smaller than that of the upper opening, and is 1 of the apex angle of the cone. The angle α corresponding to / 2 can be appropriately determined so as not to become a resistance due to catching when the glass molded body is taken out vertically, and considering the size of the molded body, for example, in the range of 2 to 3 °. Can be. FIG. 3B shows a cross-sectional shape of the bottom base member 31 at XX ′. Irregularities of the gas flow path consisting of grooves provided in the vertical direction appear inside the inner wall 33.

  The side wall has a rotational axis symmetric shape or a substantially rotational axis symmetric shape, but the bottom surface also has a rotational axis symmetric shape so that the symmetric axis of the side wall and the symmetric axis of the bottom surface are the same axis, that is, glass molding. It is desirable that the shape of the part is also a rotational axis symmetrical shape or a substantially rotational axis symmetrical shape.

  By carrying out like this, the shape of a glass molded object and a rotational-axisymmetric shape can be made into a substantially rotational-axisymmetric shape. When a glass molded body is polished and processed into a precision press-molding preform, that is, when the glass molded body is used as a preform base material, the rotational axis symmetry of the glass molded body is utilized, or the rotational axis symmetrical shape or substantially It is preferable to process into a precision press-molding preform having a rotational axis symmetrical shape.

  When an optical element having a rotational axis symmetry represented by a lens or the like is manufactured by precision press molding, the shape of the preform is also preferably a rotational axis symmetrical shape. By pressing the preform from the direction of the symmetry axis, the glass is spread symmetrically around the axis, and an optical element represented by a lens having no unevenness or very little can be made.

  The shape of the bottom of the glass forming part is concave, so that the gas ejected from the gas outlet provided in the bottom can smoothly escape from the gap between the bottom and glass and from the gap between the side wall and glass to the opening of the glass forming part. Is desirable. Whereas the gravity acting on the glass block attempts to narrow the gap, the gas ejected from the gas outlet tends to form the gap, and thus the upward wind pressure acts on the glass block constantly.

  As described above, since the side wall of the glass forming part stands upright, the side surface of the molten glass lump in the glass forming part is regulated by the side wall and greatly deviates from the droplet shape. In such a state, the molten glass lump tends to be in the form of droplets due to surface tension, the gap between the glass and the side wall is narrowed, and the gas ejected from the bottom tends to be difficult to escape from between the glass and the side wall. In order to eliminate such a state, it is preferable to use a molding die in which a groove is formed in the side wall from the bottom surface side toward the opening direction of the glass molding portion. Since glass does not easily enter the interior of the groove due to surface tension, a gap through which the gas flows is easily formed in the interior of the groove. By making a portion where gas easily escapes locally, it becomes difficult for glass to enter the portion more, and a gap between the glass serving as a gas flow path and the side wall is stably secured. As a result, it is possible to prevent gas from being accumulated between the glass and the glass forming portion, deforming the shape of the glass molded body, or preventing the glass from taking an unstable behavior.

A preferable shape of the side wall includes a plurality of grooves extending from the bottom side of the glass forming portion toward the opening of the glass forming portion, each groove is arranged at a constant interval, and the width and depth of each groove are equal to each other, A shape in which the grooves are parallel to each other is more preferable. In this case, the cross-sectional shape of the side wall orthogonal to the symmetry axis is a shape in which grooves having the same depth and width are formed at equal intervals on the circumference. By making the side shape into such a shape, the gas squirted from the bottom of the mold does not flow to the part where the glass lump side is located, so the axial symmetry of the glass molded body or preform does not decrease or fills The effect that the rate (V / V ₀ ) does not decrease can be obtained.

  When the groove is provided on the side wall as described above, an uneven portion or a corrugated shape reflecting the shape of the groove is formed on the side surface of the glass molded body. When there are a plurality of grooves on the side wall, a plurality of protrusions are formed on the side surface of the glass molded body, and grooves are formed between these protrusions. Such convex portions of the glass molded body serve to further suppress the shaking of the glass molded body by fitting into the grooves on the side walls of the mold.

[Method for producing glass molded body]
Hereinafter, the manufacturing method of a glass molded object is demonstrated.
According to the method for producing a glass molded body of the present invention, molten glass is flowed out to separate a molten glass lump, and the glass lump is molded while being cooled in a floating state at a glass forming portion provided in a mold. A way to get a body. A method for obtaining a glass molded body by such a process is well known. However, the present invention uses the mold of the present invention as the mold, and holds the molten glass lump in a floating state at the glass molding portion of the mold, thereby having a rotationally symmetric axis, And forming a glass molded body having two end faces each intersecting with the rotational symmetry axis and one side face connected to the outer periphery of the two end faces.

  First, the glass raw material is heated and melted in a heat-resistant container, clarified and homogenized, and then the molten glass is continuously discharged from the pipe connected to the container at a constant speed. On the other hand, a plurality of molds are arranged at regular intervals on a circumference centered on the rotation axis of the table on a turntable for index rotation, and each mold repeatedly stops at a plurality of positions including directly below the pipe. Rotate in one direction.

  When the mold is stopped at a position directly below the pipe (referred to as a cast position), the molten glass lump is supplied to the mold, and the glass lump is returned to the cast position by making a full turn by the rotation of the table. Is formed into a glass molded body and taken out of the mold. The mold that has been emptied by taking out the glass molded body is again transferred to the casting position and stopped, and the above steps are repeated. By performing the same operation for a plurality of molds, glass molded bodies are produced one after another from molten glass that flows out continuously.

  An example of the supply of the molten glass block to the mold is as follows. The mold that stays at the casting position is raised to approach the lower end of the pipe that flows out the molten glass flow, the lower end of the molten glass flow is received by the mold, a constriction is formed in the middle of the molten glass flow, and the mold is lowered rapidly The molten glass below the constricted portion is separated to obtain a molten glass lump on the mold. The amount of molten glass lump can be adjusted to a desired amount by adjusting the distance between the lower end of the pipe and the mold when receiving the lower end of the molten glass flow, the timing when the mold is rapidly lowered, and the like. In addition, the said method is an example and the other isolation | separation method of a well-known molten glass lump can be utilized suitably.

  In supplying the molten glass gob to the mold, the molten glass gob is filled in the glass forming part to a height above the lower end of the side wall, for example, to a height between the lower end and the upper end of the side wall. Then, gas is ejected from the gas outlet at the bottom, and the glass block is shaped and cooled in a state where the glass block is lifted by applying upward wind pressure. By carrying out like this, it shape | molds in the state in which the side surface of the glass lump was enclosed by the side wall.

  In the production method of the present invention, the molten glass lump is held in a floating state by the glass forming part of the mold, so that the two end surfaces each having a rotational symmetry axis and intersecting with the rotational symmetry axis, and the two A glass molded body having one side connected to the outer periphery of the end face is formed. As described above, one end surface of the molded body is formed into a shape corresponding to the bottom of the mold, and the side surface is formed into a shape corresponding to the side wall of the mold. When the ratio of the volume of the glass block to the volume of the glass forming part of the mold is not less than a certain range, the side surface of the molded body is formed into a shape corresponding to the side wall of the mold. This ratio varies depending on the flat area of the bottom of the mold, but for example, the volume of the glass block is suitably in the range of about 40% or more of the volume of the glass mold. However, even if the volume of the glass lump is less than about 40% of the volume of the glass forming part, the side surface may be formed into a shape corresponding to the side wall of the forming mold depending on the flat area of the bottom of the forming mold. .

  Further, when the ratio is less than 40%, the mold becomes unnecessarily large, and there is a problem that an excessive load is applied to the vertical movement mechanism and transfer mechanism of the mold. Further, when the volume of the glass forming part is increased, the glass forming part is deepened. As a result, when the molten glass flowing out from the outflow pipe is supplied to the glass forming part, the tip of the outflow pipe has to be inserted deep into the glass forming part. However, in order to keep the viscosity of the glass within an appropriate range, the pipe is attached with a heating device or is kept warm by a heat insulating material, so that it is difficult to put the pipe tip to the back of the glass forming portion. Therefore, it is desirable to eliminate these disadvantages by setting the ratio to 40% or more. On the other hand, if the ratio exceeds 65%, it is difficult to stably float the glass lump in the glass forming part. Therefore, the ratio is preferably set to 65% or less.

  The amount of gas ejected from the bottom of the mold is adjusted by adjusting the flow rate of the gas step by step to produce a preform or a glass molded body. Of the two end faces of the obtained prototype, the bottom of the mold Check if the curvature of the surface facing the side is in the desired range, and if it is out of the range, adjust the gas flow rate to an appropriate range and adjust the gas ejection amount corresponding to the gas flow rate. Keep manufacturing. In addition, since the gas ejection amount does not have a side wall and the gas ejection amount required to float the glass lump with the conventional molding die consisting of the bottom part in which the entire glass molding part is composed of a porous body, it does not differ greatly. First, if a trial production is performed with a conventional gas ejection amount and the gas ejection amount is adjusted as described above, a desired molding can be performed.

  Since the glass in the molten state has low viscosity, it is deformed along the bottom and side walls of the glass forming part in the floating state, and a thin gas layer made of the above gas is formed between the bottom and side walls. In this state, the side surface of the glass lump is surrounded by the side wall of the glass forming portion, and the glass lump is held while maintaining the floating state in the glass forming portion. Therefore, even if a large acceleration acts on the glass lump in the horizontal direction, the glass lump is supported by the side wall shape of the cylindrical shape or the side surface shape of the truncated cone, and the shaking of the glass lump can be suppressed.

  Since the conventional mold does not have the above-described side wall that suppresses the shaking of the glass lump, the glass lump is shaken on the mold when a large acceleration acts on the glass lump in the horizontal direction. In particular, when the turntable is index-rotated, periodic acceleration is applied to the glass lump. When this acceleration and the shaking of the glass lump on the mold resonate, the shake of the glass lump further increases. On the other hand, in the present invention, since the side wall functions to suppress the shaking of the glass lump, the shaking does not increase even when periodic acceleration is applied to the glass lump.

  As described above, the molten glass lump in the glass forming part is regulated by the side wall of the glass forming part that is sharp, and greatly deviates from the droplet shape. In such a state, the molten glass lump tends to be in the form of droplets due to surface tension, the gap between the glass and the side wall is narrowed, and the gas ejected from the bottom tends to be difficult to escape from between the glass and the side wall. If a mold with a gas flow path from the bottom side toward the opening direction of the glass forming part is used on the side wall, the glass does not easily enter the depth of the groove due to surface tension. . By making a portion where gas easily escapes locally, it becomes difficult for glass to enter the portion more, and a gap between the glass serving as a gas flow path and the side wall is stably secured. As a result, it is possible to prevent gas from being accumulated between the glass and the glass forming portion, deforming the shape of the glass molded body, or preventing the glass from taking an unstable behavior.

  The shape of the upper surface of the glass lump held in the glass forming part is a shape determined by the balance of the surface tension of the molten glass lump and its own weight, which is cooled and solidified, but if you want to change the upper surface shape to the desired shape, It is also possible to press the upper surface of the glass lump held in the glass forming part to form a desired shape. In particular, the shape determined by the balance between the surface tension of the molten glass lump and its own weight becomes a gentle convex surface.Therefore, the above method is used when making the upper surface concave, or when forming a recess near the intersection of the rotational symmetry axis of the glass lump and the upper surface. It is valid. The upper surface is a surface that becomes one of end surfaces (surfaces to be pressed) of the glass molded body, and the shape thereof is as described above. The pressing is performed while the glass on the mold is in a softened state. For example, the upper surface of the glass can be formed into a concave surface by pressing the glass from above with a press mold having a convex forming surface. The shape of the other pressed surface is formed into a shape obtained by inverting the bottom surface of the forming part of the forming die. By making the bottom surface of the forming portion concave, the other pressed surface can be formed into a convex surface, and by making the bottom surface of the forming portion convex, the other pressed surface can be formed into a concave surface. After pressing, when the press mold is separated from the glass, the glass (which has been formed into a preform) rises again, and even if the glass surface is rapidly cooled by the press to cause wrinkles, the glass surface is heated by the heat inside the glass. It can be reheated to eliminate wrinkles and produce a preform with a smooth surface. In this method, when the gas ejection pressure is high, it is preferable to adjust the gas ejection pressure at the time of pressing so that the gas does not enter the glass during pressing and the glass does not enter the porous body. However, if the glass can float and the gas does not enter the glass during pressing and the glass does not enter the porous body, the gas ejection pressure does not need to be adjusted during pressing.

  The glass molded body molded in the mold as described above is taken out from the mold. In view of the shape of the mold having the side wall, taking out from the mold is a method of adsorbing and holding the upper surface of the glass molded body and taking it out from the mold in the upward direction rather than holding the glass molded body and taking it out. Is preferred. According to such a method, the glass molded body can be taken out without being hindered by the side wall.

  Alternatively, as shown in FIGS. 1 and 2, the bottom part and the side wall of the molding die are configured as separate members, and when the molten glass lump is accommodated or when glass is molded, the bottom part and the side wall are combined to form a glass molding part. When the preform is taken out, the bottom on which the preform is placed and the side wall may be separated to take out the preform.

  At this time, as shown in FIG. 1, the side wall is composed of a plurality of members, and when the molten glass lump is accommodated or when the glass is molded, the members are combined to form a glass molding part, When taking out the reform, the member may be separated in the horizontal direction to take out the preform. Alternatively, as shown in FIG. 2, the bottom and side walls are separated in the vertical direction, but in order to leave the preform on the bottom, the shape of the side walls is a side shape of a truncated cone or a shape approximating the shape, and the opening Is preferably smaller than the bottom, that is, the side wall has a downward opening shape. By doing so, the preform can be smoothly extracted from the side wall.

  The glass molded body taken out from the mold is annealed and then cooled to room temperature.

[Glass compact]
As described above, the shape of the glass molded body obtained by the production method of the present invention is the bottom of the glass molded part, the bottom (surface facing down in the state of being in the glass molded part) and the side (similar to the shape of the side wall). The side surface is in the shape of a cylindrical side surface or the shape of a side surface of a truncated cylinder. If the upper surface (the surface facing upward in the glass molding portion) is not pressed or gas is blown, it becomes a free surface, and the central portion becomes a gently convex surface. If the upper surface is flat, concave, or the curvature of the convex surface is desired to be controlled, the upper surface may be pressed when the glass is in a deformable state, or gas may be blown into a desired shape. At the time of precision press molding, the upper surface and the bottom surface become pressed surfaces that are pressed by a press mold.

The glass molded body obtained by the manufacturing method of the present invention has, for example, 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. Furthermore, it is preferable that the two end surfaces of the glass molded body are pressed surfaces and are independently convex surfaces or concave surfaces, and the side surfaces are surfaces obtained by solidifying molten glass. Furthermore, this glass molded body has an axis coinciding with the axis of rotational symmetry, and assuming 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. Further, the ratio (V / V ₀ ) of the volume V of the preform to the volume V ₀ of the cylinder is preferably 68% or more.

  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 the glass molded body obtained by the production method of the present invention is a cylindrical shape, but it is not limited to a purely cylindrical shape, 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 convex or concave, the curvature is the curvature of 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 of the above. 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 glass molded body obtained by the production method of the present invention 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.

The side surface of the glass molded body obtained by the production method of the present invention is a side surface shape of a cylinder or a shape approximating a side shape of a cylinder, or a side surface shape of a truncated cone or a shape approximating a side shape of a truncated cone. Can do. According to the molded body 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 approximate to the side surface shape of the cylinder is not strictly the side surface shape of the cylinder from a geometrical point of view, such as when a groove to be described later is provided on the side surface of the molded body. This means a shape that can be regarded as equivalent to the side shape of a cylinder from the viewpoint of the manufacturing process. Specifically, a shape that approximates the shape of a side surface of a cylinder has irregularities and grooves (wave structures) on the surface of the side surface, but the diameter of a circle that circumscribes or inscribes these irregularities and grooves on the cylinder cross section It means a shape that is equal in position. The shape and dimensions of the unevenness and the groove can be appropriately determined in consideration of the volume of the preform to be molded, the ratio of the diameter φ to the height h of the cylinder, and the curvature on the lower surface side. By having irregularities and grooves (and mountain ranges) on the side surface of the molded body, it is possible to prevent the side surface of the molded body from becoming a gas trap in the subsequent molding process, or a smooth curved surface (curved flat surface). Compared to the case, the resistance to deformation is increased, and it is effective in suppressing the formation of surplus.

  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.

  Furthermore, the shape approximated to the side shape of the truncated cylinder is not strictly the side shape of the truncated cylinder from a geometrical point of view, such as when a groove described later is provided on the side of the preform. It means a shape that can be regarded as equivalent to the side shape of the truncated cylinder from the viewpoint of the manufacturing process of the preform. Specifically, as in the case of a shape that approximates the shape of a side surface of a cylinder, the surface of the side surface has irregularities and grooves (wave structures), but the diameter of a circle that circumscribes or inscribes these irregularities and grooves on the cylinder cross section is small. It means a shape that decreases or increases from one end face toward the other end face. The shape and dimensions of the unevenness and the groove can be appropriately determined in consideration of ease of taking out into the slow cooling process of the preform. By having irregularities and grooves (and mountain ranges) on the side surface of the preform, it is possible to prevent the side surface of the preform from becoming a gas trap in the subsequent molding process, or a smooth curved surface (curved flat surface). Compared to the case, the resistance to deformation is increased, and it is effective in suppressing the formation of surplus.

  The glass escapes in a direction orthogonal to the pressing direction, that is, when the glass is pressed, the glass spreads exclusively in the orthogonal direction, and the glass does not sufficiently spread over the molding surface. It becomes a factor. From the viewpoint of suppressing the behavior of the glass at the time of pressing, a molded body in which a plurality of grooves formed from one side to the other side of the two end surfaces is formed on the side surface is preferable. The presence of the groove on the side surface allows the glass to spread over the space in the press mold while spreading over the mold surface during pressing, so that an optical element with high surface accuracy can be manufactured more easily. The plurality of side grooves are preferably arranged at equal intervals. By doing so, it is possible to control the spread of the glass isotropically around the rotationally symmetric axis of the compact during precision press molding. The grooves may be formed parallel to the rotational symmetry axis, or may be formed in a fixed direction with respect to the rotational symmetry axis. However, during precision press molding, the groove is centered on the rotational symmetry axis. From the viewpoint of controlling the spread of the glass in an isotropic manner, the groove is preferably formed in parallel to the rotational symmetry axis. In addition, the said groove | channel can be obtained by the method mentioned later.

  In precision press molding, high-viscosity glass is pressed at high pressure. And since the molded object obtained with the manufacturing method of this invention has the large deformation amount at the time of a press, if a grinding trace and a crack exist in the molded object surface, it will be easy to break glass from the part. In order to prevent such trouble, at least the side surface of the molded body obtained by solidifying the molten glass, preferably the two end surfaces (surfaces to be pressed) in addition to the side surfaces 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 molded body or the entire 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 molded body in which the entire surface is a surface obtained by solidifying molten glass 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 there are very fine scratches called latent scratches, so the molded body having the mirror-polished surface was obtained by solidifying molten glass. Breakage resistance is lower than that of a molded body whose entire surface is constituted by a surface and a fire-making surface. Since the grinding marks and polishing marks are also removed by etching on the etched surface, the molded body 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.

  The molded body obtained by the production method of the present invention was adjusted so that the ratio of the diameter φ to the height h of the virtual cylinder circumscribing the molded body (φ / h) was 1 or more and 3 or less. Is. 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 molded body 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 molded body of the present invention is also advantageous from the viewpoint of producing a molded body whose entire surface is a surface obtained by solidifying molten glass. In the production of a molded body whose entire surface is a surface obtained by solidifying glass in a molten state, as described later, the molten glass lump is molded while being floated by applying wind pressure. 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 range of the present invention, 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.

While ensuring the amount of deformation of the glass during this manner precision press molding, reducing the amount of protrusion from the molding surface of the glass, from suppressing the ratio of the volume V of the molded body to the volume V ₀ which said cylinder ( 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, and considering the reduction of the filling rate due to the curved side grooves and end faces described later, the upper limit of the filling rate is preferably 94%, more preferably 92%, more preferably 90% More preferably, it is more preferably 88%.

When the compact is a spheroid, the filling factor (V / V ₀ ) is 2/3 (66.7%), and when the compact is a sphere, the filling factor (V / V ₀ ) is 2/3 (66 .7%). Therefore, even if scale-up is performed to increase the amount of deformation of the glass during precision press molding in the molded body of these shapes, the filling rate (V / V ₀ ) is constant, so that the amount of deformation of the glass 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 75% or more, press molding with less surplus is possible, 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 molded body and cooling the precision press-molded product can be shortened, and the throughput can be increased.

  If a molded body 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.

  In addition, the molded body of the present invention can be produced by a method of grinding and polishing glass in addition to the method described later, and a preform is produced by a method of grinding and polishing glass after press molding. Can do.

  The molded article of the present invention can be suitably used as a preform 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 preferable first specific example of a molded article obtained by the production method of the present invention, a molded article composed of optical glass having a glass transition temperature (Tg) of 540 ° C. or higher, more preferably a glass transition temperature (Tg). A molded body composed of optical glass having a temperature of 570 ° C. or higher, more preferably a molded body composed of glass having a glass transition temperature (Tg) of 590 ° C. or higher, and even more preferably a glass transition temperature (Tg) of 600 ° C. or higher. A molded body made of glass. 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.

  Preferred examples of the glass constituting the precision press-molding preform which is an embodiment of the molded body obtained by the production method of the present invention are the following optical glasses.

  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, since the amount of deformation of the glass in precision press molding is large according to the present invention, the can and crack 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 of the present invention, phosphate glass can be mentioned. 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 method for producing an optical element of the present invention comprises a precision press-molding preform comprising a molded article obtained by the production method of the present invention or a precision press-molding preform obtained by polishing the molded article, This is a method of manufacturing an optical element that 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 recess is provided in the center of the preform surface to be pressed and the surface to be pressed 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.

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

Example 1
FIG. 4 shows a cross-sectional shape (left) when a preform, which is a molded body of the present invention, is cut along a plane including a rotational symmetry axis, and a cross-sectional shape of a press-molded product obtained by precision press-molding these preforms ( Middle), the cross-sectional shape (right) of the preform which shape | molded the conventional glass lump in the floating state is shown. The outline indicated by the broken line of the press-formed product corresponds to the surplus portion.

  These preforms use a mold having grooves formed at equal intervals on the side wall shown in FIG. 3, and supply a desired amount of molten glass lump to the glass molded part, from the bottom of the glass molded part formed of a porous body. It is formed while gas is blown out and the glass lump is stably floated.

  The molten glass lump is supplied to the glass forming part by flowing the clarified and homogenized molten glass from the outflow pipe adjusted in temperature at a constant flow rate, and the glass forming part of the mold close to the glass outlet of the pipe. Receiving and supporting the lower end of the glass flow, forming a constriction due to surface tension in the middle of the molten glass flow, and by rapidly dropping the mold at a predetermined timing, the molten glass is separated at the constricted portion by the surface tension of the glass, It was carried out by a method of obtaining a molten glass lump below the separation part in the glass forming part.

  When the molded preform is taken out of the mold, if the glass forming part is spread upward, the upper surface of the preform is sucked and held and taken up and taken out.

  If the glass forming part spreads downward, the mold should be divided into a side wall part and a bottom part, and then the side wall part should be moved upward or the bottom part should be moved downward. Then, the preform is extracted from the side wall, and the preform remaining on the bottom is sucked and held. The preform taken out is annealed and then washed, and if necessary, a carbon-containing film such as a hydrogenated carbon film is formed on the surface and sent to the precision press molding process.

  Note that a plurality of grooves, not shown in the figure, are formed on the preform side surface at equal intervals and parallel to the rotational symmetry axis. This groove plays a role of controlling the spread of the glass during precision press molding.

  Table 1 below shows the weight and volume of each preform, the specific gravity of the glass constituting the preform, the diameter, height and filling rate of a virtual cylinder circumscribing the preform.

  Glass No. shown in Table 2 below by the above method. A glass molded body (preform) was prepared for each glass of 1 to 11 and phosphate glass 1 having a specific gravity of 4.421 and phosphate glass 2 having a specific gravity of 5.11. Of the glasses shown in Table 2 in FIG. The viscosity curves of 5, 9 and 12 glasses are shown.

When the heating temperature of the press mold or preform is set so that the viscosity of the glass during precision press molding is, for example, 10 ⁷ dPa · s, the absolute ratio of the viscosity change to the temperature change is clear as shown in FIG. The value (absolute value of the slope of the graph) is No. Compared to No. 12 glass, Glasses 5 and 9 are larger. That is, no. The glasses Nos. 5 and 9 have the property that the viscosity changes drastically with only a slight change in temperature. Therefore, no. Nos. 5 and 9 are No. Compared to glass No. 12, the appropriate temperature range at the time of precision press molding is narrow, and it can be said that the application of the present invention is more preferable in terms of reducing and preventing cans and cracks at the time of molding.

  These preforms are placed in a mold having a concave lower mold surface and a convex upper mold surface, precision press-molded, and annealed to remove surplus portions by centering and aspheric concave meniscus. Various aspherical lenses were obtained: lenses, aspherical convex meniscus lenses, and aspherical biconcave lenses.

The preform obtained by the above method was placed between the lower mold and the upper mold constituting the press mold, and then the quartz tube was heated by energizing the heater with a nitrogen atmosphere in the quartz tube. The temperature inside the press mold is set to a temperature at which the glass to be molded exhibits a viscosity of 10 ⁶ to 10 ¹⁰ dPa · s, and while maintaining the same temperature, the push bar is lowered and the upper mold is pushed into the mold. The set preform was pressed. The press pressure was 8 MPa, and the press time was 30 seconds. After pressing, the pressure of the press is released, and the glass molded product that has been press-molded is gradually cooled to a temperature at which the viscosity of the glass reaches 10 ¹² dPa · s or more while still in contact with the lower mold and the upper mold. Then, it was rapidly cooled to room temperature, and the glass molded product was removed from the mold to obtain an aspheric lens. The lower mold and the upper mold are aligned by the sleeve mold, and the movement of the upper mold and the lower mold is guided by the sleeve mold.

Thus, an aspherical concave meniscus lens and an aspherical biconcave lens were produced. The above lens was suitable as a lens constituting the imaging optical system. The surface accuracy of each of these lenses was within the standard in terms of PV value of 0.25 μm or less at the center and 0.35 μm or less at the periphery. Table 1 shows the surface accuracy of the aspherical concave meniscus lens obtained by using each preform as the PV value in the central portion and the PV value in the peripheral portion. The PV value is obtained by actually measuring the theoretical (x, y) coordinates represented by the aspherical expression (design formula) and the aspherical surface of the molded lens with respect to the aspherical surface of the aspherical lens (x, y). The difference in coordinates corresponds to the difference between the most protruding point and the most concave point with respect to the aspherical expression.
When these lenses were molded, the glass was not damaged. The same result as that of the aspherical concave meniscus lens was obtained for the aspherical biconcave lens. Here, when molding an aspheric concave meniscus lens, the lower mold molding surface is concave and the upper mold molding surface is convex. When molding an aspheric biconcave lens, the lower mold molding surface and the upper mold molding surface are convex. .

(Comparative example)
On the other hand, when a similar lens was manufactured using a preform with a filling rate of 66.7%, the surface accuracy was 0.25 μm or less in the center in terms of PV value, but the surface accuracy decreased to 0.4 μm in the periphery. It was seen. Glass No. shown in Table 2 1 to 11 and each glass of phosphate glass 1 and phosphate glass 2 and obtained by precision press molding a preform having a filling rate of less than 68% or a ratio (φ / h) exceeding 3. The surface accuracy of the aspherical concave meniscus lens is shown as the PV value at the center and the PV value at the periphery. The results are shown in Table 3. These lenses had a PV value of 0.25 μm or less in the central part, but a decrease in surface accuracy of 0.4 μm or more in the peripheral part. The result for the aspherical biconcave lens was the same as that of the aspherical concave meniscus lens.

(Example 2)
As in Example 1, the glass No. shown in Table 2 was used. Preforms shown in Table 4 were prepared using 1 to 11, phosphate glass 1 and phosphate glass 2. However, in this example, the glass on the molding part of the mold was pressed with an upper mold having a convex molding surface from above while the glass was softened, and the upper surface of the preform was molded into a concave surface. After press molding, the glass was cooled while being floated again. The side and bottom surfaces of the preform have the same shape as in the first embodiment. Table 4 shows data relating to the preforms thus obtained. As shown in Table 4, one preformed surface is a convex surface and the other pressed surface is a concave preform, and an upper mold having a convex molding surface and a lower mold having a concave molding surface and a sleeve mold are obtained. Precision press molding was performed with the press mold provided, and an aspheric concave meniscus lens was obtained. The surface accuracy of each lens is shown in Table 4 using the same notation as in Example 1. In precision press molding, the preform is introduced into the press mold so that the upper surface of the preform, that is, the concave surface faces the upper mold side, and the lower surface of the preform, that is, the convex surface faces the lower mold side, and at the top of the upper mold surface. The upper surface of the preform, that is, the center of the concave surface is pressed so that the preform does not deviate from the center position of the press mold. Note that when pressing the upper surface of the preform, that is, the center of the concave surface at the top of the upper mold forming surface, the force applied to the preform was only the weight of the upper mold. In this state, the preform and the press mold were heated together to perform precision press molding. Furthermore, an aspherical biconcave lens was produced by replacing the press mold with that for aspherical biconcave lens press molding. As with the aspherical concave meniscus lens, the aspherical biconcave lens was able to obtain a lens with good surface accuracy.

(Example 3)
In the same manner as in Example 2, a preform having both concave surfaces to be pressed was obtained by press molding. In this example, the molding part of the preform mold was a convex surface. Thus, the glass No. 2 shown in Table 2 was used. The preform was produced using each glass of 1-11, phosphate glass 1, and phosphate glass 2. The data regarding each preform obtained in this way is almost equal to the data shown in Table 4. Next, a preform having two concave surfaces to be pressed was heated and precision press-molded with a press mold having an upper mold and a lower mold having convex molding surfaces to obtain an aspherical biconcave lens. The surface accuracy of each lens was the same as in Example 2. In precision press molding, the center of the upper and lower surfaces of the preform was pressed at the top of the upper and lower mold surfaces to prevent the preform from shifting from the center position of the press mold. When pressing the center of the pressed surface of the preform at the top of the upper and lower mold forming surfaces, the force applied to the preform was only the weight of the upper mold. In this state, the preform and the press mold were heated together to perform precision press molding. In this way, an aspherical biconcave lens having good surface accuracy could be obtained.

  In Examples 1 to 3, since the entire surface of the preform was a surface obtained by solidifying molten glass, the preform was damaged from the time the preform was molded until the precision press molding. There was no. Moreover, even if the preform was pressed with the upper mold in Examples 2 and 3, the preform was not damaged.

  INDUSTRIAL APPLICABILITY The present invention is useful in the field of manufacturing a molding die suitable for manufacturing a precision press molding preform and a molded body such as a precision press molding preform using the molding die.

1 shows an embodiment of a mold according to the present invention. 1 shows an embodiment of a mold according to the present invention. 1 shows an embodiment of a mold according to the present invention. The cross-sectional shape when the preform of the present invention is cut along a plane including a rotationally symmetric axis (left figure), the cross-sectional shape of a preform formed with a conventional molten glass lump floated (right figure), and these profiles The cross-sectional shape (center) of a precision press-molded product (aspheric lens) obtained by precision press-molding the reform is shown. Of the glasses shown in Table 2, no. The viscosity curves of 5, 9 and 12 glasses are shown.

Claims (12)

In a mold used to mold a molten glass lump while cooling in a floating state to form a precision press-molding preform ,
The molding die includes a concave glass molding portion having a bottom portion and a side wall erected so as to surround the bottom portion,
The side wall has a gas flow path for flowing the gas ejected from the gas ejection port toward the opening direction of the glass forming part,
The gas flow path is a plurality of grooves extending perpendicularly or inclined from the bottom to the direction of the opening of the glass forming part,
The said bottom part has a some gas jet nozzle which ejects the gas for applying a wind pressure to the said glass lump and making it float. 2. The mold according to claim 1 , wherein the surface of the side wall having the gas flow path has a waveform composed of a continuous surface or a waveform composed of an intermittent surface. Bottom, mold according to any of the configured claims 1-2 of a porous material having air permeability having a plurality of gas ejection ports. The precision press-molding preform includes a rotational symmetry axis and two end faces each intersecting with the rotational symmetry axis and one side surface connected to an outer periphery of the two end faces. The mold according to any one of the above. The molding die according to claim 4, wherein a side surface of the precision press-molding preform is molded by a side wall of the glass molding portion. For precision press molding, the molten glass mass is separated by flowing out the molten glass, and the glass mass is molded while cooling in the floating state in the glass molding part provided in the molding die to obtain a precision press molding preform. In the preform manufacturing method,
As the mold, the mold according to any one of claims 1 to 5 is used, and the molten glass lump is held in a floating state by the glass molding portion of the mold, thereby having an axis of rotational symmetry. and the axis of rotational symmetry and each cross two end surfaces and said comprises one side that connects to the outer periphery of the two end faces, the precision press-molding preform, which comprises shaping a precision press molding preform Production method. The volume of the said glass lump is a manufacturing method of Claim 6 made into the range of 40 to 65% of the volume of the said glass forming part. The manufacturing method of the glass forming body in any one of Claims 6-7 including pressing the upper surface of the glass lump hold | maintained at the glass forming part. In the precision press-molding preform , the two end surfaces are independently convex or concave,
The side surface comprises a surface obtained by solidifying molten glass,
Assuming a virtual cylinder having an axis coinciding with the rotational symmetry axis and circumscribing the preform, the ratio (φ / h) of the diameter φ to the height h of the cylinder is 1 or more and 3 And
The manufacturing method according to claim 6 , wherein a ratio (V / V ₀ ) of the volume V of the preform to the volume V ₀ of the cylinder is 68% or more. A method for producing a precision press-molding preform , comprising producing a precision press-molding preform by the method according to claim 6 and polishing at least a part of the precision press-molding preform. The manufacturing method of an optical element including carrying out precision press molding of the preform for precision press molding obtained with the manufacturing method in any one of Claims 6-10 using a press molding die. 12. The method of manufacturing an optical element according to claim 11 , wherein at least one molding surface of a mold member that constitutes the press mold and presses the preform is a convex surface.