JPWO2018025844A1 - Glass material for press molding and method of manufacturing optical element using the same - Google Patents

Abstract

The glass material 1 has at least the surface of a portion that will become a pair of optical functional surfaces after molding is formed as a free surface, has a shape of a rotating body centered on the rotation axis A, and the lower surface 6 in the rotation axis A direction is outside The lower surface 6 has a first radius of curvature R1 smaller than the radius of a sphere of the same volume as the glass material 1, and the lower surface 6 has a central portion 8 around the central portion 8. The peripheral portion 10 disposed adjacent to the second portion has a second radius of curvature R2 that is larger than the first radius of curvature R1.

Description

  The present invention relates to a glass material for press molding and a method of manufacturing an optical element using the same, and more specifically, a glass material for press molding in which at least a portion to be an optically functional surface is formed of a free surface The present invention relates to a method of manufacturing an optical element using

  DESCRIPTION OF RELATED ART Conventionally, as a glass material for press molding used when manufacturing an optical element by press molding, there exists a thing as described in patent document 1, for example. The glass material for press molding described in Patent Document 1 receives molten glass in a spherical receiving mold, ejects gas from the receiving surface, holds the molten glass in a floating state, and forms the glass material. It is formed by so-called floating molding. For this reason, the glass material for press molding manufactured by this method has a lower surface formed by a curved surface having a radius of curvature substantially the same as the radius of curvature of the receiving mold and is formed with a smooth free surface as a whole.

Unexamined-Japanese-Patent No. 11-171565 gazette

  By the way, in recent years, the application field of the lens has been expanded, and along with this, diversification of the shape and size of the lens is advanced. For example, in the field of image identification sensing, strong distortion is increasing the need for a special projection type camera with a telephoto at the center and a wide angle at the periphery, and as the first lens arranged at the most object side of such a camera In the aspherical lens to be used, a complicated shape is required such that the thickness is large and the volume of the entire lens is large while the radius of curvature of the paraxial axis is small.

However, in the glass material for press molding of the conventional shape, the curvature radius of the lower surface (the surface facing the receiving mold) also increases as the volume of the glass material increases. However, the glass material for press molding of such a conventional shape is used. When pressed into an aspheric lens with a small paraxial radius of curvature, a gas trap occurs in which gas is accumulated between the glass material for press molding and the die for press, and a molded article of good shape quality is obtained I can not do it.
An object of the present invention is to provide a glass material for press-forming capable of press-forming an aspheric lens having a large volume and a complicated shape, and a method of manufacturing an optical element using the same.

  In order to achieve the above object, in the glass material for press molding of the present invention, the surface of a portion to be at least a pair of optical functional surfaces after molding is formed as a free surface, and the shape of a rotating body centered on the rotation axis And the first surface, which is the surface of the portion to be one of the optically functional surfaces in the direction of the rotation axis, is convexly formed outward, and the first surface has a central portion formed of glass for press-forming A second radius of curvature having a first radius of curvature smaller than the radius of a sphere of the same volume as the material, and a peripheral portion disposed adjacent to the central portion around the central portion has a second radius of curvature greater than the first radius of curvature It is characterized by having.

  In the present invention configured as described above, a smooth surface glass material can be obtained because the surfaces of the portions to be the pair of optical functional surfaces after forming at least the glass material for press molding are free surfaces. In addition, the central portion of the first surface of the glass material for press molding has a first radius of curvature smaller than the radius of a sphere of the same volume, and the second radius of curvature has a peripheral portion larger than the first radius of curvature. Therefore, even if the glass material for press molding has a relatively large volume, the radius of curvature of the central portion becomes relatively small and a smooth continuous overall shape can be obtained. Therefore, even in the case of press-molding a glass material for press-forming, for example, into a lens having a relatively small radius of curvature of paraxial axis, the press-forming is performed without generating a gas trap at the central portion The glass material for press molding spreads to every corner of the molding die at the time of molding, and an optical element with high shape accuracy can be obtained. Therefore, a molded product of good quality can be obtained even in the case of molding a thick and complex shaped aspheric lens.

It is a figure which shows the cross-sectional shape containing the rotating shaft of the glass raw material for press molding which concerns on one Embodiment of this invention. It is a figure which shows the relationship of the volume of the glass material for press molding which concerns on one Embodiment of this invention, and the curvature radius of center part. It is a figure which shows an example of the cross-sectional shape of the optical element which press-formed the glass raw material for press molding which concerns on one Embodiment of this invention. It is a figure which shows the cross-sectional shape of the glass material for press molding of the comparative example 1 of this invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings.
In the present specification, a glass material for press molding is a glass material mainly used for precision press molding, and refers to a so-called preform.
Further, in the present specification, the free surface refers to the surface when the molten glass solidifies without coming into contact with other members such as a mold, and the surface to which a part of the other members is transferred, and polishing・ Does not include surfaces that have been machined such as grinding.

  FIG. 1 is a view showing a cross-sectional shape including a rotation axis of a press-molding glass material 1 (hereinafter, simply referred to as “glass material 1”) according to an embodiment of the present invention. The glass material 1 has at least the surface of a portion to be an optical function surface formed as a free surface, has a shape of a rotating body centered on the rotation axis A, and one surface (lower surface 6) in the rotation axis A direction It is formed in a convex shape outward, and one surface (lower surface 6) has a first curvature radius R1 smaller than the radius of a sphere having the same volume as that of the glass material 1, and the center 8 The peripheral portion 10 disposed adjacent to the periphery of has a second radius of curvature R2 that is greater than the first radius of curvature R1. The curvature radius R7 of the other surface (upper surface 4) in the rotation axis A direction is larger than the curvature radius R1 of the lower surface 6.

  In addition, an optical function surface means the area | region in the effective diameter in optical elements, such as an optical lens. The site to be the optically functional surface in the glass material 1 varies depending on the shape and function of the optical element, but at least the center of the optical axis (rotation axis A) and the peripheral region thereof can be the optically functional surface.

  Hereinafter, the glass material 1 according to the present embodiment will be described in more detail. As shown in FIG. 1, the glass material 1 has a shape of a rotating body centering on the rotation axis A while at least the surface of a portion to be a pair of optical functional surfaces after press forming is formed as a free surface. 1 along the axis A. The diameter about the rotation axis A gradually increases from the bottom of FIG. 1 and has the largest diameter D1 at the largest diameter position 2, and then the diameter gradually decreases again. With such a shape, the upper surface 4 above the maximum diameter position 2 is formed in a convex shape that curves outward, that is, upward. In addition, the lower surface 6 below the maximum diameter position 2 is formed in a convex shape that curves outward, that is, downward. In addition, in FIG. 1, S1 is a site | part used as the optical function surface by the side of the upper surface 4, and S2 is a site | part used as the optical function surface by the side of the lower surface 6. Moreover, 4a and 6a show the surface of the part used as an optical function side, respectively, 6a is a 1st surface, 4a is a 2nd surface. The surfaces other than the surfaces 4a and 6a of the portion to be the optical function surface are surfaces which do not function optically even if they are removed by coring after pressing the glass material 1 or are not removed. It does not necessarily have to be a free surface. In the present embodiment, the entire surface of the glass material 1 is formed as a free surface.

The lower surface 6 has a central portion 8 near the rotation axis A and a peripheral portion 10 disposed adjacent to the periphery of the central portion 8.
FIG. 2 is a view showing the relationship between the volume V of the glass material 1 and the radius of curvature R1 of the central portion 8 according to an embodiment of the present invention. In FIG. 2, the horizontal axis represents the radius of curvature r, the vertical axis represents the volume V, and the curve C represents the relationship between the volume and the radius of curvature (radius) of the sphere having the volume. The radius of curvature R1 of the central portion 8 of the glass material 1 of the present embodiment is set to be located in the hatched region on the left side of the curve C. That is, the curvature radius R1 of the central portion 8 of the glass material 1 of the present embodiment is set smaller than the radius when the glass material having the same volume V as the glass material 1 is formed spherically. In FIG. 2, the symbol ■ indicates the relationship between the volume of the glass material and the radius of curvature in the example, and the symbol ○ indicates the relationship between the volume of the glass material and the radius of curvature in the comparative example 1 , And ● show the relationship between the volume of the glass material and the radius of curvature in Comparative Example 2. These will be described later.
Further, in the glass material 1, the curvature radius R 2 of the peripheral portion 10 is set larger than the curvature radius R 1 of the central portion 8.

Thus, when the glass material 1 is formed by pressing the glass material 1 to form an optical element, the surface (first surface 6 a and the first surface 6 a of the glass material 1 will form the optically functional surface of the optical element). Two surfaces 4a) are formed at least on the free surface. A free surface refers to the surface when molten glass solidifies without contacting other members, such as a mold, as mentioned above, and arithmetic mean roughness Ra is 10 ⁻³ μm or less (1 nm or less) It is a very smooth surface of The arithmetic average roughness Ra is preferably 0.7 nm or less, and more preferably 0.5 nm or less from the viewpoint of obtaining surface smoothness after press-molding the glass material 1.

Furthermore, the glass material 1 has a shape of a rotating body centering on the rotation axis A, and one surface in the direction of the rotation axis A, that is, the lower surface 6 is convexly formed outward, and the lower surface 6 is The portion 8 has a first radius of curvature R1 smaller than the radius of a sphere of the same volume, and the peripheral portion 10 disposed adjacent to the central portion 8 around the central portion 8 has a first radius of curvature R1 Also has a large second radius of curvature R2.
In addition, 1st curvature radius R1 is 2-10 mm, for example, Preferably it is 3-8 mm, More preferably, it is 4-7 mm. Moreover, although 2nd curvature radius R2 is 5-30 mm, for example, it is not limited to this range.

Further, in the glass material 1 with respect to the distance L1 from the maximum diameter position 2 to the uppermost end of the upper surface 4, ie, the point where the upper surface 4 and the rotational axis A intersect, The ratio (L2 / L1) of the distance L2 to the point of intersection with the rotation axis A is preferably set to 1.2 to 1.7. When the ratio of the distance L2 to the distance L1 is out of the above range, the stability of the glass material 1 when mounting the glass material 1 on a press forming mold is deteriorated, and the rotation axis A of the glass material 1 is formed It becomes difficult to align with the central axis of the mold. When the rotation axis A of the glass material 1 is deviated from the central axis of the forming die, the optical element obtained by press-molding will be one with uneven thickness.
The thickness T in the direction of the rotation axis A of the glass material 1 shown in FIG. 1 is the sum of the distance L1 and the distance L2.

  As a result of examining the relationship between the ratio (L2 / L1) of the distance L2 to the distance L1 and the stability of the glass material, the present inventors obtained findings as shown in Table 1.

なお、表１の安定性評価において、ガラス素材１を下面６を下にした状態で平面に載置したときに、安定性が良好で自立したものを「良好」とし、安定性に欠けガラス素材が横転するなど自立できなかったものを「不安定」とした。

In addition, in the stability evaluation of Table 1, when the glass material 1 is placed on a flat surface with the lower surface 6 down, the one having good stability and standing by itself is regarded as “good” and the glass material is chipped for stability. Those who could not stand on their own as "overturned" were considered "unstable".

  As apparent from Table 1, when the ratio (L2 / L1) of the distance L2 to the distance L1 is 1.7 or less, the stability of the glass material is good, but the above ratio (L2 / L1) It turns out that it becomes unstable when A exceeds 1.7.

  The lower limit of the ratio (L2 / L1) is preferably 1.2 or more from the viewpoint of suppressing the occurrence of gas trap during press molding.

Next, the manufacturing method of the above glass raw materials 1 is demonstrated.
The glass material 1 is formed by so-called float forming, in which molten glass is received in a mold and gas is jetted from a receiving surface of the mold to hold the molten glass in a floating state to form the glass material. Therefore, the whole surface of the glass material 1 is formed as a free surface.

  The mold is formed of, for example, a porous material. The shape of the mold is such that when the molten glass supplied to the mold is supported by floating gas rising from the surface of the mold, the distance between the mold and the molten glass becomes the smallest at the peripheral portion, and the central portion In the above, the distance between the mold and the molten glass is formed to be the largest. Further, the shape of the mold is formed such that the pressure of floating gas received by the surface of the molten glass in the mold is the highest in the peripheral portion and the lowest pressure distribution in the central portion.

  A plurality of molds are arranged at equal intervals on the circumference of the turn table, and the turn table is configured to be rotatable by a predetermined angle. A levitation gas supply source is connected below the mold. In addition, the mold is heated by a heater so that the shape of the glass material 1 may be distorted or cracked, or the glass material 1 may not stick when the glass material 1 contacts the surface of the mold. The temperature is adjusted to

When the levitation gas is supplied from the lower side of the thus configured mold, the levitation gas is ejected from the mold. When a predetermined amount of molten glass is supplied into the mold, the whole of the molten glass is lifted from the mold by the pressure of the floating gas, and the pressure of the floating gas, the surface tension of the molten glass, and the self weight balance the inner surface of the mold. The lower surface 6 of the glass material 1 is formed to face each other, and is formed into a predetermined shape as shown in FIG. 1 as a whole.
The material of the glass to be used is not particularly limited. For example, a lanthanum borate glass mainly composed of boric acid and a rare earth oxide, a phosphate glass mainly composed of phosphate, fluorine and phosphorus The fluorophosphate glass which has an acid salt as a main component, the borosilicate glass which has borosilicate as a main component, etc. can be used.

  The molten glass moves on the turntable while being molded in a mold, and is cooled to a temperature range that does not deform even when an external force is applied, thereby forming the glass material 1. Thereafter, the glass material 1 is taken out of the mold and annealed. The formed glass material 1 may be washed if necessary, or a carbon film may be formed on the entire surface as needed. Such a carbon film improves the slippage of the glass and enhances the releasability of the formed optical element when the glass material 1 is press-formed on the optical element.

  Next, a method of manufacturing an optical element using the glass material 1 will be described. The glass material 1 molded into the shape as shown in FIG. 1 is housed in a die for press molding, the mold is heated, and the glass material 1 is softened and pressed to obtain an optical element of a predetermined shape. Here, the radius of curvature R1 of the central portion 8 of the glass material 1 is smaller than the radius of curvature of the die for press molding at the position facing the central portion 8. Therefore, the softened glass material 1 comes in contact with the mold for press molding from the central portion 8 at the lower surface 6, and the shape of the mold is gradually transferred outward to be formed into a desired shape.

FIG. 3 is a view showing an example of the cross-sectional shape of an optical element obtained by press-molding a glass material for press-forming according to an embodiment of the present invention. An outer peripheral portion of a molded body obtained by press-molding the glass material 1 has a surplus thickness portion 26 as shown by a broken line, and a portion from which the surplus thickness portion 26 is removed by centering is an optical element 16. The optical element 16 shown in FIG. 3 has a relatively small radius of curvature R3 (for example, a radius of curvature of 10 mm or less) to be the central portion 18 (for example, a radius of curvature of 10 mm or less). (In the upper direction) is formed with a curved portion 22 which is recessed upward. The surface opposite to the central portion 18 (the upper surface in FIG. 3) has a paraxial radius of curvature R4 and is a concave surface 23 recessed inward (downward in FIG. 3). Thus, the optical element 16 has a generally complicated shape and is formed relatively thick compared to the prior art.
When cold working is performed on a compact obtained by press-molding the glass material 1 to obtain an optical element having a predetermined shape, the site and range to which cold working is performed differ depending on the range of the optically functional surface of the optical element. Therefore, the range and the shape of the extra thickness portion 26 shown in FIG. 3 are variously different.

According to the glass material 1 of the present embodiment, the following effects can be obtained.
Since the entire surface of the glass material 1 is formed as a free surface, a glass material 1 having a smooth surface is obtained, and when this glass material 1 is press-formed to obtain an optical element, an optical element with good appearance and shape quality You can get

The conventional glass material has a spherical shape or an elliptical shape with a radius of curvature larger than the radius of the sphere, and as the volume of the entire glass material increases, the radius of curvature naturally increases accordingly. For this reason, when trying to press-mold, for example, an aspheric lens having a complicated shape with a conventional glass material having a large volume, if the radius of curvature of the paraxial lens of the aspheric lens is small, the curvature radius of the glass material is press-formed The radius of curvature of the mold for this purpose makes the gas accumulated between the glass material and the mold, making it impossible to obtain an optical element with a good shape.
On the other hand, in the present embodiment, the radius of curvature R1 of the central portion 8 of the lower surface 6 of the glass material 1 is set smaller than the radius of a sphere having the same volume as the volume V of the glass material 1. Even with the glass material 1 having a large target volume, the curvature radius R1 of the central portion 8 can be formed small. Therefore, even in the case of molding an optical element having a thick wall and a complicated shape with a small radius of curvature of the paraxial axis, a molded article of a good shape can be obtained without generating a gas trap.

  Since the radius of curvature R2 of the peripheral portion 10 of the glass material 1 is larger than the radius of curvature R1 of the central portion 8, from the central portion 8 having a small radius of curvature R1 to the peripheral portion 10 having a larger radius of curvature R2. The transition area is smooth, resulting in a generally continuous and smooth shape.

Since the ratio of the distance L2 to the lower surface 6 to the distance L1 from the maximum diameter position 2 to the upper surface 4 of the glass material 1 is appropriately set, the first curvature of the central portion is secured while securing a relatively large volume. The radius R1 can be made relatively small, and even when the glass material 1 is press-formed into an aspheric lens having a complicated shape, an optical element of good quality can be obtained without causing a shape defect. be able to.
Further, since the ratio of the distance L2 to the distance L1 is appropriately set, when the glass material 1 is placed on a die for press molding, the glass material 1 can be stably placed in the die. it can. Therefore, the rotational axis A of the glass material 1 can be easily and reliably aligned with the central axis of the mold, and an optical element of good quality without defects such as uneven thickness can be formed.

[Example]
An embodiment of the present invention will be described.
The glass material 1 having a volume V of 547 mm ³ was produced by using the above-mentioned floating molding. The radius of curvature R1 of the central portion 8 of the glass material 1 was 4.2 mm. This glass material 1 has a relationship between the volume and the radius of curvature shown by ▪ in FIG. 2, which is in the hatched area on the left side of the curve C in FIG. Moreover, this whole glass material 1 is a free surface.
The supply and cutting method of molten glass, the floating condition on the mold surface of molten glass, etc. used a publicly known method.
The obtained glass material 1 was heated, softened, precision press-formed, and press-formed into an optical element 16 having a cross-sectional shape as shown in FIG. The radius of curvature R3 of the central portion 18 of the convex surface of the obtained optical element 16 was 4.7 mm, and the radius of curvature R4 of the concave surface 23 was 2.2 mm. The press mold was formed in a shape corresponding to the shape of the optical element 16.
As a result of heating the glass material 1 and performing precision press molding with a press molding die, an optical element 16 having a desired thickness and diameter was obtained with good reproducibility while maintaining desired curvature radii R3 and R4.

Comparative Example 1
Next, Comparative Example 1 of the present invention will be described.
FIG. 4 is a view showing the cross-sectional shape of the glass material 24 of Comparative Example 1 of the present invention. In Comparative Example 1, the glass material 24 having a volume V of 250 mm ³ was produced using float forming. The radius of curvature R5 of the central portion of the glass material 24 was 4.5 mm. This glass material 24 has a relationship between the volume and the radius of curvature indicated by ○ in FIG. 2, which is outside the hatched area on the right side of the curve C in FIG.
As a result of heating the glass material 24 and performing precision press molding with a press mold, particularly desired thickness and diameter can not be obtained, and the shape accuracy of the optical element is significantly deteriorated as compared with the example.

Comparative Example 2
Next, Comparative Example 2 of the present invention will be described.
In Comparative Example 2, a spherical glass material 24 having a volume of 550 mm ³ was produced by cold working. The radius of the obtained spherical glass material was 5.1 mm. This glass material has a relationship between the volume and the radius of curvature indicated by ● in FIG. 2, which is on the curve C of FIG. When the obtained glass material was precision press-molded using the same precision press-molding mold as that of the example, a gas trap was generated in the central portion 18 of the optical element 16. This is because the radius of curvature of the glass material is 5.1 mm while the radius of curvature R3 of the central portion 18 of the optical element 16 is 4.7 mm, so that the gas between the glass material and the press molding die It is thought that it was because of

  As mentioned above, in the glass raw material 1 by this invention, the optical element of a favorable shape was obtained like an Example. On the other hand, in the conventional glass elements described in Comparative Examples 1 and 2, a gas trap was generated, and an optical element with a good shape could not be obtained.

1 glass material for press molding 4 upper surface 4a surface of the part to be an optical function surface (second surface)
6 lower surface 6a surface (first surface) of a portion to be an optical function surface
8 central part 10 peripheral part R1, R2 radius of curvature D1 maximum diameter T thickness L1, L2 distance S1, S2 part to be an optical function surface

Claims (5)

In press forming glass materials,
At least a surface of a portion to be a pair of optical functional surfaces after molding is formed as a free surface, and has a shape of a rotating body centered on a rotation axis,
A first surface, which is a surface of a portion to be one of the optical functional surfaces in the rotation axis direction, is outwardly formed in a convex shape, and a central portion of the first surface is the glass for press molding Has a first radius of curvature smaller than the radius of a sphere of the same volume as the material,
A peripheral portion disposed around the central portion and adjacent to the central portion has a second radius of curvature greater than the first radius of curvature.
Glass material for press molding. From the position where the diameter is maximum with respect to the distance along the rotation axis from the position where the diameter of the glass material for press molding around the rotation axis is maximum to the end on the first surface side The ratio of the distance along the rotation axis to the end on the second surface side, which is the surface of the other optical function surface, is 1.2 to 1.7.
The glass material for press molding according to claim 1.   The glass material for press molding according to claim 1, wherein an arithmetic mean roughness Ra of the free surface is 1 nm or less.   The glass material for press molding according to any one of claims 1 to 3, wherein the first radius of curvature is 2 to 10 mm.   The manufacturing method of an optical element provided with the press molding process which heats and press-molds the glass raw material for press molding in any one of Claims 1-4.

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