JP5414222B2 - Preform for precision press molding and method for manufacturing optical element - Google Patents

Description

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

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

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

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

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

  As another method, a method using a preform having a large center thickness can be considered (second method). In this method, the amount of glass deformation during precision press molding is positively increased to spread the glass over the entire molding surface, thereby transferring the entire molding surface to the glass. However, in this method, the volume of the preform must be significantly increased compared to the volume of the lens, and the amount of glass (referred to as surplus) that protrudes outside the molding surface 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.

The present invention has been made to solve these problems,
(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) An object of the present invention is to provide a precision press-molding preform capable of efficiently producing an optical element having a predetermined surface accuracy.

  Furthermore, this invention aims at providing the manufacturing method of the optical element using the said preform for precision press molding.

The present invention is as follows.
[1] A precision press-molding preform made of glass having a rotational symmetry axis and comprising two end faces each intersecting with the rotational symmetry axis and one side face connected to the outer periphery of the two end faces. ,
The two end surfaces are pressed surfaces and are independently convex or concave surfaces,
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 ratio of the volume V of the preform to the volume V ₀ of the cylinder (V / V ₀ ) is 68% or more,
A plurality of grooves formed from one side of the two end surfaces to the other side are formed on the side surface , and
The side surface is a precision press-molding preform having a shape approximating a side shape of a truncated cone .
[2] The precision press-molding preform according to [1], wherein the side surface is a surface obtained by solidifying molten glass.
[3] The precision press-molding preform according to [1] or [2], wherein the glass transition temperature (Tg) of the glass is 540 ° C. or higher.
[4] The precision press-molding preform according to any one of [1] to [3], wherein the refractive index (nd) of the glass is 1.75 or more.
[5] One or both of the two end faces are made of a surface obtained by solidifying molten glass, and the precision press molding process according to any one of [1] to [4] Renovation.
[6] One or both of the two end surfaces are convex surfaces, and a concave portion is provided in a region including an intersection with the rotational symmetry axis of the convex surface, according to any one of [1] to [5] Preform for precision press molding.
[7] The precision press-molding according to any one of [1] to [6], wherein an apex angle of a virtual cone having a side surface of the truncated cone as a part of the side surface is in a range of 4 ° to 6 °. Preform for.
[8] Any one of [1] to [7], which is used for molding any one of a concave meniscus lens, a convex meniscus lens, and a biconcave lens using a molding die having a convex shape on at least the upper mold surface. Preform for precision press molding according to crab. [9] A method for producing an optical element, comprising: performing precision press molding of the precision press molding preform according to any one of [1] to [8] using a press mold.
[10] The method for manufacturing an optical element according to [9], wherein at least one of a concave meniscus lens, a convex meniscus lens, and a biconcave lens is molded using a molding die having a convex molding surface of at least the upper mold.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the optical element using the preform for precision press molding for producing a highly accurate optical element efficiently, and this preform can be provided.

  In the present invention, when specifying the range as described below, the upper limit is also included in the range, and when specifying the range as described above, the lower limit is also included in the range.

[Preform for precision press molding]
The precision press-molding preform of the present invention has a rotational symmetry axis, and has two end faces each intersecting with the rotational symmetry axis and one side connected to the outer periphery of the two end faces. This is a preform for press molding. Furthermore, the two end surfaces of the preform of the present invention are pressed surfaces and are independently convex or concave surfaces. Furthermore, when the preform of the present invention is assumed to be a virtual cylinder having an axis coinciding with the rotational symmetry axis and circumscribing the preform, the ratio of the diameter φ to the height h of the cylinder ( φ / h) is 1 or more and 3 or less. Furthermore, the ratio (V / V ₀ ) of the volume V of the preform to the volume V ₀ of the cylinder is 68% or more.

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

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

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

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

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

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

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

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

  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 glass behavior during pressing, a preform in which a plurality of grooves formed from one side of the two end faces toward the other side 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 rotational symmetry axis of the preform 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 preform of the present invention has a large amount of deformation at the time of pressing, if there are grinding marks or scratches on the surface of the preform, the glass tends to be damaged starting from that portion. In order to prevent such troubles, it is preferable that at least the side surface of the preform is obtained by solidifying the molten glass, and more preferably, in addition to the side surface, two end surfaces (surfaces to be pressed) are also made of molten glass. The surface obtained by solidification. The surface obtained by solidifying molten glass means the glass surface obtained by cooling and solidifying the entire preform or the glass molded body that is the preform base material. However, it is different from the fire-making surface described later, that is, the surface obtained by heating and remelting only the glass surface and then solidifying. Since the surface obtained by solidifying the glass in the molten state is not subjected to cold working such as grinding and polishing, there is no grinding mark or polishing mark, and there is no origin of the destruction. In particular, a preform whose surface is obtained by solidifying glass in a molten state is preferable from the above viewpoint. In addition, after re-melting the glass surface, the fire-making surface obtained by cooling and solidifying the ground surface will be repaired by re-melting, so that the surface becomes microscopically smooth. There is no starting point.

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

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

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

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

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

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

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

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

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

  In addition, the preform of the present invention can be produced by a method to be described later, can be produced by a method of grinding and polishing glass, or can be produced by a method of grinding and polishing glass after press molding.

  The preform of the present invention can be suitably used for molding concave meniscus lenses, convex meniscus lenses, and biconcave lenses, and is particularly suitable for molding concave meniscus lenses and biconcave lenses.

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.

  A preferred first specific example of the preform of the present invention is a preform composed of an optical glass having a glass transition temperature (Tg) of 540 ° C. or higher, more preferably an optical having a glass transition temperature (Tg) of 570 ° C. or higher. A preform made of glass, more preferably a preform made of glass having a glass transition temperature (Tg) of 590 ° C. or higher, and even more preferably made of glass having a glass transition temperature (Tg) of 600 ° C. or higher. It is a preform. 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 of the present invention include the following optical glasses.

  The preform of the present invention 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, as the glass constituting the preform of the present invention, when the Abbe number νd is 35 or more, the refractive index nd is 1.70 or more and the Abbe number νd is less than 35, the following formula (1) is satisfied. An optical glass having a refractive index nd that satisfies is preferable.
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, or the above components 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 with a higher refractive index or a glass with lower dispersion has a higher glass transition temperature, 540 ° C. or higher, and 550 depending on the glass.
More than ℃, further 580 ℃ or more, 600 ℃ or more.

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.

[Precision press molding preform manufacturing method]
The precision press-molding preform of the present invention comprises a concave glass molding part having a bottom part and a side wall erected so as to surround the bottom part, and the bottom part applies wind pressure to the glass lump. It can manufacture using the shaping | molding die which has several gas jet nozzle which ejects the gas for making it float.

  More specifically, the entire molding die is a concave glass molding part constituted by a bottom part having a gas ejection port for ejecting a gas for applying a wind pressure to the glass lump to float and a side wall surrounding the periphery of the bottom part. And the shape of the side wall is a side surface shape of a cylinder or a shape that approximates the side surface shape of a cylinder, or a shape that approximates a side surface shape of a truncated cone or a side surface shape of a truncated cone, and the side wall has the gas It can be a molding die provided with a gas flow path for flowing gas ejected from the ejection port toward the opening direction of the glass molding part.

  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.

  In the above mold, the shape of the side wall or the shape approximating the side shape of the cylinder, or the shape approximating the side shape of the truncated cone or the side shape of the truncated cone. 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.

  Alternatively, when the bottom and side walls of the mold are made of separate members and when the molten glass lump is accommodated, or when glass is being molded, the bottom and side walls are combined to form the glass molding part and the preform is taken out. The preform may be separated from the bottom and the side wall, and the preform may be taken out. At this time, the bottom and the side wall are separated in the vertical direction, but in order to leave the preform on the bottom, the shape of the side wall is the side shape of the truncated cone or a shape approximating the shape, and the opening is made smaller than the bottom. That is, it is preferable to make the side wall open downward. By doing so, the preform can be smoothly extracted from the side wall.

  Alternatively, the side wall is composed of a plurality of members, and when the molten glass lump is accommodated or when glass is formed, the members are combined to form a glass molded part, and when the preform is taken out, You may make it isolate | separate and take out a preform.

  By using such various molds, the preform of the present invention or the preform base material can be manufactured with high productivity.

  The side wall of the molding die is preferably provided with a gas flow path for letting gas ejected from a gas ejection port provided at the bottom part toward the opening direction of the glass molding part. This gas flow path is for allowing the gas ejected from the outlet on the bottom surface between the glass mass and the side wall to escape from the opening of the glass molding portion when the glass mass is introduced into the glass molding portion. A preferred gas flow path is obtained by making the side walls serrated. It should be noted that no gas outlet or gas inlet is formed on the side wall of such a mold.

  Examples of molds other than the above include molds in which the side walls are formed of a porous body. This aspect is roughly divided into two. One is a system in which gas is ejected from the porous body constituting the side wall, similarly to the bottom of the mold. According to this method, it is possible to prevent the glass and the side wall from being fused and to ensure a passage for the gas ejected from the bottom. For this purpose, it is preferable that the gas ejection pressure at the bottom is larger than the gas ejection pressure at the side wall. The gas ejected from the bottom generates a large wind pressure for floating the glass, whereas the gas ejected from the side wall is an auxiliary material for obtaining the above effect. In the first method, while the glass on the mold is in a softened state, it can be pressed from above to form one shape of the upper surface of the preform, that is, the pressed surface into a desired shape. 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 second method utilizes a phenomenon in which the gas present in the fine pores of the porous body is heated when high-temperature glass is supplied and rapidly expands, thereby ejecting from the sidewall surface. Also in this method, as in the first method, the softened glass can be pressed from above and the pressed surface can be formed into a desired shape.
However, from the viewpoint of performing more reliable molding, a molding die having a gas flow path on the side wall is most preferable.

  The gas flow path is preferably formed by providing a plurality of grooves at equal intervals on the side wall. By providing grooves at equal intervals, gas can escape evenly from around the glass in the glass forming part, enabling more stable floating of the glass and more stable high-quality glass moldings such as preforms. Can be produced.

  As for the bottom part and side wall of a glass forming part, it is desirable for it to be an axisymmetric shape. This is because it is easy to form an axisymmetric preform or glass molded body. It is preferable that the groove on the side wall is formed so as to be parallel to the axis of symmetry or directed in a certain direction with respect to the axis. This makes it possible to float the glass more stably.

  By using such a mold, the gas flows in the back of the groove on the side wall, so that the glass does not easily enter the back of the groove, but the glass in the molten state enters a part of the groove, and the shape of the side wall is Roughly transferred to glass. Therefore, on the side surface of the preform or glass molded body, the portion where the groove on the side wall is transferred becomes a peak from one end face to the other end face, and the valley between the peaks becomes the aforementioned groove, and the press It will play a role in controlling the elongation of the glass.

  When a preform for a precision press-molding preform is produced by the above production method, at least a part of the preform can be polished to produce a precision press-molding preform. Polishing may be performed only on both end surfaces or only one end surface. Such polishing is used as a mass adjustment step in which a glass molded body is produced in advance, and then the preform mass is determined from the specifications of the optical element, and then the glass mass is accurately matched to the preform mass. You can also For polishing, a known method may be applied.

  Precise press molding preform or manufacturing method of precision press molding preform, molten glass is flowed out to separate molten glass lump, and the glass lump is floated in the glass forming part provided in the mold It is carried out by molding into a preform for precision press molding or a preform for precision press molding in the course of cooling the glass lump.

  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 the end surfaces (pressed surfaces) of the preform or the glass molded body, and the shape thereof is as described above.

  In addition, it is desirable that the ratio of the volume of the glass lump to the volume of the glass forming portion (volume of the glass lump / volume of the glass forming portion) is in the range of 40 to 65%. If the ratio is less than 40%, the molding die becomes unnecessarily large, and problems such as excessive load on the vertical movement mechanism and transfer mechanism of the die arise. 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.

[Method for Manufacturing Optical Element]
The optical element manufacturing method of the present invention is a method for manufacturing an optical element in which the precision press-molding preform of the present invention 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. 1 shows a cross-sectional shape (left) when the preform of the present invention is cut along a plane including a rotationally symmetric axis, a cross-sectional shape (right) of a preform formed by floating a conventional molten glass lump, and these The cross-sectional shape (middle) of a press-molded product (aspherical concave meniscus lens) obtained by precision press-molding a preform 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 on the side wall shown in FIG. 2 at equal intervals, 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.

  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.

  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 shows the mass and volume of each preform, the specific gravity of the glass constituting the preform, the diameter, height, volume, 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 and 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 from 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 of P-V 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 a PV value in the central portion and a 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. In Examples 2 and 3, even if the preform was pressed with the upper mold, 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.

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 of a precision press-molded product (aspherical lens) obtained by precision press-molding the reform is shown. A mold for preform molding is shown. Of the glasses shown in Table 2, no. The viscosity curves of 5, 9 and 12 glasses are shown.

Claims (10)

A precision press-molding preform made of glass, comprising two end faces each having a rotationally symmetric axis and one side face connected to the outer periphery of each of the two end faces,
The two end surfaces are pressed surfaces and are independently convex or concave surfaces,
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 ratio of the volume V of the preform to the volume V ₀ of the cylinder (V / V ₀ ) is 68% or more,
A plurality of grooves formed from one side of the two end surfaces to the other side are formed on the side surface , and
The side surface is a precision press-molding preform having a shape approximating a side shape of a truncated cone . The preform for precision press molding according to claim 1, wherein the side surface is a surface obtained by solidifying molten glass. The precision press-molding preform according to claim 1 or 2, wherein the glass has a glass transition temperature (Tg) of 540 ° C or higher. The precision press-molding preform according to any one of claims 1 to 3, wherein the glass has a refractive index (nd) of 1.75 or more. The preform for precision press molding according to any one of claims 1 to 4, wherein one or both of the two end faces are made of a surface obtained by solidifying molten glass. 6. The precision press molding process according to claim 1, wherein one or both of the two end surfaces are convex surfaces, and a concave portion is provided in a region including an intersection with the rotational symmetry axis of the convex surface. Renovation. The precision press-molding preform according to any one of claims 1 to 6 , wherein an apex angle of a virtual cone having a side surface of the truncated cone as a part of the side surface is in a range of 4 ° to 6 ° . The precision according to any one of claims 1 to 7, which is used for molding any one of a concave meniscus lens, a convex meniscus lens, and a biconcave lens using a molding die having a convex molding surface at least. Preform for press molding. The manufacturing method of an optical element including carrying out precision press molding of the preform for precision press molding in any one of Claims 1-8 using a press molding die. The method for manufacturing an optical element according to claim 9, wherein at least one of a concave meniscus lens, a convex meniscus lens, and a biconcave lens is molded using a molding die having a convex molding surface of at least the upper mold.