JP2010018487A - Forming method of optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method of an optical element which forms the optical element of a concave meniscus shape up to its side part with high shape accuracy. <P>SOLUTION: The difference of the depth of a cavity in the normal-line direction to a forming surface of a spherical shape is structured as to be 15% or below between a central part and an outer peripheral part of the cavity of a forming mold used in a step of forming a formed glass lump 1 from melt glass. The formed glass lump 1 is formed using the forming mold and press molded to produce an optical element 2, that is a molded product. The more nearly the depth of the cavity of the forming mold for forming the formed glass lump 1 is uniform, the fewer a great swell is generated on the surface of the formed glass lump 1 and the less the shape accuracy of the optical element 2 to be press formed is impaired. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical element molding method for obtaining a concave meniscus optical element by press molding a molding material molded from molten glass or the like.

  As a technique for obtaining a forming material from molten glass, for example, a method disclosed in Patent Document 1 is known. In this method, molten glass is received on a convex jig, inverted, and further, this glass lump is thermally deformed, and then precision molded with a precision mold to obtain an optical element such as a lens. The reason why the molten glass is received on the convex jig is to prevent the generation of vacuum bubbles generated at the interface between the molten glass and the receiving jig. This is to smooth the wrinkled surface of the glass generated at the interface of the receiving jig.

  In this known technology, a molding material obtained by reversing the glass lump and then thermally deforming has a convex free surface, and an optical element is obtained by precisely molding the convex molding material. However, this optical element has a biconvex shape. Moreover, the side part of the optical element is not molded.

JP-A-4-77320

  In recent years, the use of molded glass optical elements in optical devices has become common, and development of glass materials and lens shapes that have not been seen in the past has progressed, and development of concave meniscus optical elements is also active. However, there are the following problems as a molding material for manufacturing a concave meniscus optical element.

  Phenomenon that glass becomes uneven during molding due to the large amount of deformation until it becomes a concave meniscus optical element when using a convex molding material with a free surface as in the conventional example above May occur. For this reason, it has been difficult to obtain a clean axisymmetric shaped concave meniscus optical element.

  Therefore, it has been considered that the shape of the molding material is close to the shape of the optical element that is a molded product. However, although it is naturally possible to produce a concave meniscus-shaped molding material by grinding and polishing, its manufacturing cost increases and it is difficult to introduce it into a product with severe product price competition.

  A technique for obtaining a concave meniscus-shaped molding material from molten glass by press molding has also been studied, but it is necessary to discharge the molten glass with low viscosity in order to prevent devitrification of the molten glass. For this reason, the shrinkage amount of the glass at the time of shaping | molding becomes large, and when obtaining a molded product with a large thickness difference like a concave meniscus shape, sink marks due to the shrinkage of the glass occur. Therefore, it has been difficult to obtain a concave meniscus molding material from molten glass.

  On the other hand, recent molded glass optical elements are required to be molded with high shape accuracy up to the side surface. That is, conventionally, as disclosed in Patent Document 1, a centering process for forming a side surface of an optical element by grinding after molding has been performed. However, from the viewpoint of manufacturing cost reduction and the environmental viewpoint for the purpose of preventing the generation of processing waste generated during grinding, molding was performed with high shape accuracy up to the side surface of the optical element, which was conventionally performed in a subsequent process. Development of technology that does not perform centering is desired.

  An object of the present invention is to provide an optical element molding method capable of molding a concave meniscus optical element up to its side surface with high shape accuracy.

  The optical element molding method of the present invention includes a first step of filling a molten mold optical material into a cavity of a molding die having a spherical molding surface, and molding the molding material, and pressing the molding material. A second step of forming a concave meniscus optical element by molding, and in the first step, a central portion of the cavity of the molding die in a direction normal to the spherical molding surface The difference between the thickness and the thickness of the outer peripheral portion of the cavity in the normal direction to the spherical molding surface is 15% or less.

  By forming a molding material using a mold having a nearly uniform cavity thickness, sink marks during cooling are reduced. By using such a molding material, it is possible to obtain a concave meniscus-shaped optical element with a high refractive index glass with high shape accuracy up to its side surface by molding alone without the need for post-centering processing. it can.

  This can greatly contribute to the improvement of the quality of the optical element, the reduction of the manufacturing cost, and the environmental measures.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 illustrates one embodiment, and the optical element molding method according to the present embodiment includes the following two steps.

  In the first step, a molded glass lump 1 that is a forming material is formed. The mold prepared in the first step includes a pair of upper and lower molds having a spherical molding surface corresponding to the optical surface of the optical element, and a cylindrical side mold for molding a portion corresponding to the side surface of the optical element. Have.

  One of the pair of upper and lower molds is a concave spherical mold having a concave spherical shaped molding surface, and the other is a convex spherical mold having a convex spherical shaped molding surface. When the thickness of the cavity formed by the concave spherical surface mold and the convex spherical surface mold is measured in the normal direction with respect to the molding surface of the spherical surface of the lower mold, The difference is 15% or less.

  The mold prepared in the first step is preferably made of a material having poor wettability with molten glass, and specific materials include carbon, ceramic, metal, and the like.

  In the first step, molten glass is filled into the above-described mold to obtain a molded glass lump 1 shown in FIG.

  There is no problem even if this process is performed in an air atmosphere.

  For the molding temperature and pressing force in this step, it is desirable to select an optimum process from the type of glass and the lens shape.

  In the second step, the molded glass lump 1 obtained in the first step is precision-molded (press-molded) with a precision mold to obtain the optical element 2 shown in FIG.

  The precision mold used in the second step preferably has a cylindrical side mold so that the side portion of the optical element 2 can be molded.

  This step is preferably performed in a non-oxidizing atmosphere.

  The mold used in this step is preferably made of a material having high temperature strength such as ceramic.

  For the molding temperature and pressing force in this step, it is desirable to select an optimum process from the type of glass and the lens shape.

  FIG. 1 shows a molded glass lump 1 that is a molding material molded in this example and an optical element 2 that is a molded product.

  The shape of the optical element 2 is a concave meniscus shape as shown in FIG. 1B, and the glass material is a high refractive index glass having a refractive index nd1.82. The specific dimensions of the optical element 2 are a concave meniscus lens having a diameter of 12.6 mm, a center height of 1.5 mm, a convex surface R40 mm, and a concave surface R5 mm.

  As a first step, a molding die having a lower concave spherical surface R12.3 mm, an upper convex spherical surface R9 mm, and a cylindrical side surface inner diameter 11.9 mm was prepared. The center height of this mold is 3.3 mm, and the thickness in the normal direction to the concave spherical surface of the lower mold, which is the molding surface of the cavity, is uniform between the center and the outer periphery of the mold. ing. This mold was made from a carbon material.

  Using this carbon mold, a molded glass lump 1 shown in FIG. 1 (a) was obtained. Molten glass, which is an optical material in a molten state, was flowed out at 1000 ° C. to obtain a glass lump having a desired weight, and this glass lump was placed in a mold and molded. The temperature of the mold was always kept at 500 ° C. The pressing force was 200N. This molding was performed in the atmosphere. The obtained glass lump 1 for molding had an inner diameter of 11.9 mm, a convex surface R of 12.25 mm, a concave surface R of 8.9 mm, and a center height of 3.25 m.

  Next, as a second step, this molded glass lump 1 was press-molded using a precision mold to obtain an optical element 2. The precision molding die is made of a cemented carbide, has a cylindrical side mold so that the side surface of the optical element 2 can be molded, and this member is also made of a cemented carbide. Precision molding in this step was performed in a nitrogen atmosphere. The press temperature was 560 ° C. At this time, the difference between the center thickness of the molded glass lump 1 and the center thickness of the optical element 2 as a press margin was 1.8 mm. The optical element 2 was a concave meniscus lens having a diameter of 12.6 mm, a center height of 1.5 mm, a convex surface R40 mm, and a concave surface R5 mm. The ridge line portion between the side surface and the optical surface was formed with a curvature radius of 0.1 mm or more and 1.2 mm or less.

  The optical element obtained in this way has high optical performance, and its side surface is molded with high shape accuracy, so it can be incorporated into the barrel of optical equipment without the need for centering. It was possible.

  According to the present embodiment, since an optical element having high optical performance can be obtained with a simple process, there is a great effect in reducing the manufacturing cost.

  As shown in FIG. 2, in this example, in order to obtain an optical element having the same shape as that of Example 1, a molded glass lump 11 having different dimensions is used.

  As a first step, a molding die having a lower concave spherical surface R of 16.43 mm, an upper convex spherical surface R of 6 mm, and a cylindrical side surface inner diameter of 11.9 mm was prepared. The center height of this mold is adjusted to 2.5 mm, and the normal thickness of the cavity with respect to the molding surface (concave spherical surface) of the lower mold is such that the difference between the center and the outer periphery is 14%. Is formed. This mold was made from boron nitride.

  A molded glass lump 11 was obtained using this boron nitride mold. The molten glass was flowed out at 1000 ° C. to obtain a glass lump having a desired weight, and this glass lump was placed in a mold and molded. The temperature of the mold was always kept at 500 ° C. The pressing force was 200N. This molding was performed in the atmosphere. The obtained molded glass lump 11 had an inner diameter of 11.8 mm, a convex surface R16 mm, a concave surface R5.5 mm, and a center height of 2.4 mm. On the surface of the molded glass lump 11, there was a concave undulation with a depth of 20 μm.

  Next, as a second step, the molded glass lump 11 was precisely molded to obtain an optical element. The precision mold is made of cemented carbide and has a cylindrical side mold so that the side part of the optical element can be molded. This member is also made of cemented carbide. The precision molding in the second step was performed in a nitrogen atmosphere. The press temperature was 560 ° C. At this time, the difference between the center thickness of the molded glass lump 11 serving as a press margin and the center thickness of the optical element serving as a molded product was 1.0 mm. The dimensions of the optical element were a concave meniscus lens having a diameter of 12.6 mm, a center height of 1.5 mm, a convex surface R40 mm, and a concave surface R5 mm. The ridge line portion between the side surface and the optical surface was formed with a curvature radius of 0.1 mm or more and 1.2 mm or less. The optical element obtained in this way has high optical performance, and its side surface is molded with high shape accuracy, and can be incorporated into the lens barrel of optical equipment without the need for centering processing. Met.

According to the present embodiment, since an optical element having high optical performance can be obtained, there is a great effect in reducing the manufacturing cost.
(Comparative example)
For comparison, an optical element having the same shape as that of Examples 1 and 2 was used, and the molded glass block having a different size was used.

  As a first step, a lower mold concave spherical surface R21.53 mm, an upper mold convex spherical surface R6 mm, and a cylindrical side surface mold having an inner diameter of 11.9 mm were prepared. The center height of the mold is adjusted to 2.3 mm. The thickness of the mold cavity in the normal direction relative to the molding surface (concave spherical surface) of the lower mold is formed such that the difference between the central portion and the outer peripheral portion is 30%. This mold was made from boron nitride.

  Using this boron nitride mold, a molded glass lump was obtained. The molten glass was allowed to flow out at 1000 ° C. to obtain a glass lump having a desired weight, and then the glass lump was placed in the mold and molded. The temperature of the mold was always kept at 500 ° C. The pressing force was 200N. This molding was performed in the atmosphere. The dimensions of the resulting molded glass block were an inner diameter of 11.8 mm, a convex surface R of 20 mm, a concave surface R of 5.5 mm, and a center height of 2.2 m. On the surface of this molded glass lump, there was a concave undulation with a depth of 80 μm.

  Next, as a second step, this molded glass lump was precisely molded to obtain an optical element. The precision mold is made of cemented carbide. A cylindrical side surface mold is provided so that the side surface portion of the optical element can be molded, and this member is also made of a cemented carbide. The precision molding in the second step was performed in a nitrogen atmosphere. The press temperature was 560 ° C. The press allowance at this time, that is, the difference between the center thickness of the formed glass lump and the center thickness of the optical element was 0.7 mm. The dimensions of the optical element thus obtained were a concave meniscus lens having a diameter of 12.6 mm, a center height of 1.5 mm, a convex surface R40 mm, and a concave surface R5 mm. The ridge line portion between the side surface portion and the optical surface is formed with a curvature radius of 0.1 mm or more and 1.2 mm or less.

  However, the concave portion of the molded glass lump remains as a gas residue on the optical surface of the optical element obtained here and cannot be used as an optical element.

1 shows Example 1, (a) is a schematic cross-sectional view showing a cross-sectional shape of a molded glass lump, and (b) is a schematic cross-sectional view showing a cross-sectional shape of an optical element that is a molded product. It is a schematic cross section which shows the cross-sectional shape of the shaping | molding glass lump by Example 2. FIG.

Explanation of symbols

1, 11 Molded glass block 2 Optical element

Claims (3)

A first step of filling the molten optical material into a cavity of a molding die having a spherical molding surface, and molding a molding material;
A second step of forming a concave meniscus optical element by press molding the molding material,
In the first step, the thickness of the central portion of the cavity of the mold in the normal direction with respect to the spherical shaped molding surface, and the thickness of the outer peripheral portion of the cavity in the normal direction with respect to the spherical shaped molding surface. A method for molding an optical element, wherein the difference in thickness is 15% or less.   The method for molding an optical element according to claim 1, wherein a ridge line portion between the side surface of the press-molded optical element and the optical surface has a curvature radius of 0.1 mm or more and 1.2 mm or less.   3. The optical element according to claim 1, wherein, in the first step, the mold includes a pair of upper and lower molds having the spherical molding surface and a cylindrical side mold. Molding method.

Images