Method for manufacturing preform, method for manufacturing optical element, and preform for optical element

Abstract

To provide a preform for an optical element that has excellent volume accuracy and surface roughness of a peripheral surface and can be manufactured with a simple process.SOLUTION: A method for manufacturing a preform 10 includes the steps of: providing a molding tool 20 including a lower mold 22 including a lower pressing surface 22S in an upper surface, an upper mold 24 including an upper pressing surface 24S facing the lower pressing surface in a lower surface, and a cylindrical side mold 26 provided between the lower mold and the upper mold; placing a spherical substrate 10B on the lower pressing surface in a recessed part surrounded by the lower mold and the side mold; and reheat-pressing the spherical substrate by bringing the spherical substrate close to the upper mold and the lower mold relatively while the lower pressing surface and the upper pressing surface are heated to shape the spherical substrate into a preform in a region surrounded by the lower pressing surface, the upper pressing surface, and an inner peripheral surface (regulation surface 26S) of the side mold, where a filling factor of the preform to the region is 77% or more and an arithmetic average roughness of the inner peripheral surface of the side mold is 0.2 μm or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a preform, a method for manufacturing an optical element, and a preform for an optical element. [Background technology]

[0002] Conventionally, optical elements such as aspherical lenses are manufactured by reheat-pressing a preform of a glass material, such as a fine gob molded directly from a glass melt, a polished ball preform, or a polished preform of an approximate lens shape, in a molding die. In particular, for optical elements in which at least one optically functional surface is concave, such as concave meniscus lenses, biconcave lenses, and plano-concave lenses, polished preforms are applicable, which are processed from a plate material and manufactured by physical grinding and polishing. For example, Patent Document 1 discloses a method for molding a meniscus lens from a cylindrical glass material.

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-295817 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional polished preforms have low volumetric accuracy because the outer periphery is ground by centering and grinding, and the roughness generated by the sanded surface remains even after molding into optical elements such as lenses, which may affect the optical surface. If the entire product is molded by polishing, it takes a long time and reduces productivity.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide a method for manufacturing a preform that has excellent volumetric accuracy and surface roughness of the peripheral surface and can be manufactured by a simple process, a method for manufacturing an optical element, and a preform for an optical element. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the preform manufacturing method according to the present disclosure is a method for manufacturing a preform for a cylindrical optical element by reheat-pressing a spherical substrate in a molding die, the method including: preparing a molding die including a lower die having a lower pressing surface on its upper surface, an upper die having an upper pressing surface on its lower surface opposite the lower pressing surface, and a cylindrical side die provided between the lower die and the upper die; placing the substrate on the lower pressing surface in a concave portion surrounded by the lower die and the side die; and, with the lower pressing surface and the upper pressing surface heated, bringing the upper die relatively close to the lower die to reheat-press the substrate, thereby molding it into a preform in a region surrounded by the lower pressing surface, the upper pressing surface, and the inner surface of the side die; wherein the filling rate of the preform in the region is 77% or more, and the arithmetic mean roughness of the inner surface of the side die is less than 0.2 μm.

[0007] The method for manufacturing an optical element according to the present disclosure manufactures an optical element using the preform manufactured by the preform manufacturing method.

[0008] The preform for an optical element according to the present disclosure has a cylindrical shape having a first end face, a second end face, a peripheral surface, a first outer peripheral edge connecting the first end face and the peripheral surface, and a second outer peripheral edge connecting the second end face and the peripheral surface, wherein the first outer peripheral edge and the second outer peripheral edge have rounded corners, the arithmetic mean roughness of the peripheral surface is less than 0.2 μm, the standard deviation of the rounded corner radii at the first outer peripheral edge at positions divided into four or more circumferential positions is less than 40 μm, and the standard deviation of the rounded corner radii at the second outer peripheral edge at the same positions is less than 40 μm. [Effects of the Invention]

[0009] According to the present invention, a preform for an optical element having excellent volume accuracy and peripheral surface roughness can be manufactured by a simple process. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is a schematic diagram of an optical element preform according to this embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along the line AA shown in FIG. [Figure 3] FIG. 3 is a schematic diagram illustrating the method for producing a preform according to this embodiment. [Figure 4] FIG. 4 is a graph showing an example of the evaluation results of thickness deviation. [Figure 5] FIG. 5 is a schematic diagram illustrating a method for suppressing uneven thickness by adjusting the filling rate. [Figure 6] FIG. 6 is a schematic diagram illustrating a method for suppressing uneven thickness by adjusting the filling rate. [Figure 7] FIG. 7 is a schematic diagram illustrating a method for suppressing thickness deviation by inverted molding. [Figure 8] FIG. 8 is a schematic diagram illustrating a method for suppressing thickness deviation by positioning molding. [Figure 9] FIG. 9 is a schematic exploded view showing another example of the molding die. [Figure 10] FIG. 10 is a schematic diagram illustrating a method for producing a preform using the molding die shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments, and when there are multiple embodiments, the present invention also includes configurations that are made by combining the respective embodiments. Furthermore, numerical values ​​include the range of rounding.

[0012] (Optical element preforms) FIG. 1 is a schematic diagram of a preform for an optical element according to this embodiment. FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1. In this embodiment, the optical element is assumed to be a lens with at least one optically functional surface having a concave shape, such as a concave meniscus lens, a biconcave lens, or a plano-concave lens, but other optical elements may also be used. Furthermore, the optical element is mounted, for example, on an imaging device that captures images, but its use is arbitrary and it is not limited to being used in imaging devices. Furthermore, a preform 10 for an optical element according to this embodiment (hereinafter simply referred to as "preform 10") is a material before being molded into an optical element by reheat pressing.

[0013] As shown in FIGS. 1 and 2, the preform 10 has a generally cylindrical shape and includes a first end face 12, a second end face 14, and a peripheral surface 16. The first end face 12 is circular and is one end face of the generally cylindrical preform 10. The second end face 14 is circular and is the end face opposite the first end face 12 of the generally cylindrical preform 10. In the following description, the second end face 14 is treated as the bottom face of the preform 10, but the first end face 12 may also be the bottom face of the preform 10. In addition, although the first end face 12 and the second end face 14 are flat in this embodiment, they do not necessarily have to be flat and may be concave, for example. The first end face 12 and the second end face 14 preferably have a rotationally symmetric shape about the central axis of the cylinder.

[0014] The peripheral surface 16 is a surface that is continuous with a first outer peripheral edge 12C of the first end face 12 and a second outer peripheral edge 14C of the second end face 14. More specifically, in this embodiment, the first outer peripheral edge 12C is formed between the first end face 12 and the peripheral surface 16, and the first end face 12 and the peripheral surface 16 are connected via the first outer peripheral edge 12C. In addition, in this embodiment, a second outer peripheral edge 14C is formed between the second end face 14 and the peripheral surface 16, and the second end face 14 and the peripheral surface 16 are connected via the second outer peripheral edge 14C. The peripheral surface 16 corresponds to a side surface of the cylindrical shape, and preferably extends in a direction intersecting the first end face 12 and the second end face 14, and in a direction perpendicular to the first end face 12 and the second end face 14. In addition, the peripheral surface 16 preferably has a perfect circular shape in a plan view. The arithmetic mean roughness Ra of the peripheral surface 16 is Ra<0.2, preferably Ra<0.1, and more preferably Ra<0.05. The arithmetic mean roughness Ra here refers to the arithmetic mean roughness Ra specified in JIS B 0601:2001, and can be measured, for example, using an OLYMPUS OLS4000.

[0015] The preform 10 is molded into an optical element by being reheat-pressed in a direction perpendicular to the first end face 12 and the second end face 14. At this time, the direction perpendicular to the first end face 12 and the second end face 14 becomes the optical axis, which is the central axis of the optical element.

[0016] Because the preform 10 is molded by reheat pressing, the first outer peripheral edge 12C of the first end face 12 and the second outer peripheral edge 14C of the second end face 14 are curved, in other words, have a corner radius of radius R. Hereinafter, the radius R of the corner radius of the first outer peripheral edge 12C and the second outer peripheral edge 14C refers to the radius of curvature of the first outer peripheral edge 12C and the second outer peripheral edge 14C when the preform 10 is viewed in a direction perpendicular to the optical axis.

[0017] The standard deviation σ, which is the variation in the radius R1 of the corner at each of the four positions obtained by dividing the first outer peripheral edge 12C circumferentially, is preferably σ<40 μm, more preferably σ<30 μm, and even more preferably σ<15 μm. Similarly, the standard deviation σ, which is the variation in the radius R2 of the corner at each of the four positions obtained by dividing the second outer peripheral edge 14C circumferentially, is preferably σ<40 μm, more preferably σ<30 μm, and even more preferably σ<15 μm.

[0018] Moreover, the preform 10 is preferably made of glass. Examples of glass for the preform 10 include transparent glass substrates such as soda-lime glass such as blue plate, low-alkali borosilicate glass, borosilicate crown glass, crown glass, borosilicate glass, alkali-free glass, optical glass (e.g., barium glass, phosphosilicate glass, fluoride glass, lanthanum glass, flint glass, etc.), chemically strengthened aluminosilicate glass, and calcium fluoride glass (glass made from CaF2). By making the preform 10 from glass, the optical properties of the optical element after molding can be properly maintained. However, the material of the preform 10 may be any material.

[0019] (spherical base material) Fig. 3 is a schematic diagram illustrating a method for producing a preform according to this embodiment. As shown in Fig. 3, the preform 10 according to this embodiment is formed by reheat-pressing a spherical substrate 10B using a molding die 20. In this embodiment, the spherical substrate 10B is a polished ball preform. That is, the spherical substrate 10B is a spherical substrate whose surface is mirror-polished, has high sphericity, and has a known diameter φ and volume.

[0020] (molding mold) 3, the molding die 20 includes a lower die 22, an upper die 24, and a side die 26. The molding die 20 preferably has rotational symmetry about an axis of rotational symmetry parallel to the vertical direction. The molding die 20 molds a preform 10 having a central axis that coincides with the axis of rotational symmetry.

[0021] The lower mold 22 has a lower pressing surface 22S on its upper surface. The lower mold 22 presses the spherical substrate 10B from below with the lower pressing surface 22S to form either the first end face 12 or the second end face 14 of the preform 10. The lower pressing surface 22S is formed into a shape corresponding to either the first end face 12 or the second end face 14 of the preform 10. In the present embodiment shown in FIG. 3, the lower mold 22 is flat, and the lower pressing surface 22S is a flat surface. The lower pressing surface 22S is preferably mirror-finished.

[0022] The lower mold 22 has a lower heating unit 22H that heats the lower pressing surface 22S. The lower heating unit 22H is, for example, a heater. The lower heating unit 22H heats and softens the spherical substrate 10B via the lower pressing surface 22S. Note that, although the lower heating unit 22H is built into the lower mold 22 in the example of FIG. 3, this is not limiting and the lower heating unit 22H may be attached to the surface of the lower mold 22 or may be located at a position away from the lower mold 22.

[0023] The upper mold 24 has an upper pressing surface 24S on its lower surface. The upper pressing surface 24S faces the lower pressing surface 22S of the lower mold 22. The upper mold 24 can move relatively close to and away from the lower mold 22 in the vertical direction. The upper mold 24 presses the spherical substrate 10B from above with the upper pressing surface 24S to form the other of the first end face 12 and the second end face 14 of the preform 10. The upper pressing surface 24S is formed in a shape corresponding to the other of the first end face 12 and the second end face 14 of the preform 10. In the present embodiment shown in Figure 3, the upper mold 24 is flat, and the upper pressing surface 24S is a flat surface. The upper pressing surface 24S is preferably mirror-finished. The upper mold 24 has an upper heating unit 24H that heats the upper pressing surface 24S. The upper heating unit 24H is, for example, a heater. The upper heating unit 24H heats and softens the spherical substrate 10B via the upper pressing surface 24S. Note that, although the upper heating unit 24H is built into the upper mold 24 in the example of FIG. 3, this is not limiting and the upper heating unit 24H may be attached to the surface of the upper mold 24 or may be located at a distance from the upper mold 24.

[0024] The side mold 26 is a cylindrical spacer provided between the lower mold 22 and the upper mold 24. The side mold 26 has a regulating surface 26S on its inner peripheral surface. The circumferential surface 16 of the preform 10 is inscribed on the regulating surface 26S. The inner diameter Φ of the side mold 26 is equal to or greater than the diameter φ of the spherical substrate 10B and is equal to the diameter of the preform 10 after molding. The inner diameter Φ of the side mold 26 refers to the diameter of the inner peripheral surface (regulating surface 26S) of the side mold 26 when viewed from the direction in which the lower mold 22 and the upper mold 24 overlap.

[0025] The restricting surface 26S restricts deformation of the spherical substrate 10B, which expands laterally when crushed between the lower pressing surface 22S of the lower mold 22 and the upper pressing surface 24S of the upper mold 24, thereby forming the peripheral surface 16 of the preform 10. The restricting surface 26S is preferably mirror-finished. The arithmetic mean roughness Ra of the restricting surface 26S is Ra<0.2, preferably Ra<0.1, and more preferably Ra<0.05. The restricting surface 26S is continuous with the lower pressing surface 22S of the lower mold 22. The height H of the side mold 26 is equal to the thickness of the preform 10 after molding.

[0026] The molding die 20 preferably has a filling rate of 77% or more, more preferably 88% or more, and even more preferably 95% or more. The filling rate refers to the volume of the preform 10 relative to the volume of the space surrounded by the lower die 22, upper die 24, and side die 26 of the molding die 20.

[0027] The side mold 26 may be separable into multiple parts, which can be moved radially outward when removing the molded preform 10 from the molding die 20, making it easier to remove. The molding die 20 is preferably made of cemented carbide, ceramics, stainless steel, or quartz. The material of the molding die 20 is preferably a material with a high melting point, a low thermal expansion coefficient, and low reactivity with the spherical substrate 10B, but is not particularly limited thereto. Examples of materials for the molding die 20 include binderless cemented carbide, general cemented carbide, silicon carbide (SiC), silicon nitride (SiN), improved SUS420J2 such as STAVAX and HPM38, ceramics, and quartz.

[0028] (Preform manufacturing method) An outline of the procedure for manufacturing a preform 10 from a spherical substrate 10B using a molding die 20 will be described. As shown in Figure 3, in this manufacturing method, first, the molding die 20, which includes the above-mentioned lower die 22, upper die 24, and side die 26, and the spherical substrate 10B are prepared. Then, in the concave space surrounded by the lower die 22 and the side die 26, the spherical substrate 10B is placed on the lower pressing surface 22S (step S10). Here, it is preferable to place the spherical substrate 10B so that it is positioned above the center of the lower pressing surface 22S (so that the central axis of the spherical substrate 10B passes through the center of the lower pressing surface 22S). Next, the lower pressing surface 22S is heated to a predetermined temperature by the lower heating section 22H, and the upper pressing surface 24S is heated to a predetermined temperature by the upper heating section 24H. With this state, the upper mold 24 is brought relatively close to the lower mold 22, and the spherical substrate 10B is sandwiched between the lower pressing surface 22S and the upper pressing surface 24S.

[0029] The spherical substrate 10B is heated and softened by the heated lower pressing surface 22S and upper pressing surface 24S, and is crushed and deformed between the lower pressing surface 22S and the upper pressing surface 24S. The lower side of the spherical substrate 10B deforms along the shape of the lower pressing surface 22S (deforms flat in this example), and the upper side deforms along the shape of the upper pressing surface 24S (deforms flat in this example). As the spherical substrate 10B is crushed from above and below, the center portion in the height direction expands radially outward until it reaches the restricting surface 26S of the side mold 26, and then deforms along the restricting surface 26S.

[0030] By moving the upper mold 24 relatively closer to the lower mold 22 until the upper pressing surface 24S of the upper mold 24 reaches the upper surface of the side mold 26, the spherical substrate 10B is molded into the preform 10 in the space surrounded by the lower pressing surface 22S, the upper pressing surface 24S, and the restricting surface 26S of the molding mold 20 (step S12). The spherical substrate 10B is molded so that its upper portion becomes the first end surface 12 of the preform 10, its lower portion becomes the second end surface 14, and its side portion becomes the circumferential surface 16.

[0031] At this time, the deformed spherical substrate 10B does not spread throughout the portion where the upper pressing surface 24S and the restricting surface 26S are continuous, and the portion where the lower pressing surface 22S and the restricting surface 26S are continuous, leaving spaces. That is, a roundness is formed along the first outer peripheral edge 12C of the first end surface 12 between the first end surface 12 molded on the upper pressing surface 24S and the circumferential surface 16 molded on the restricting surface 26S, and a roundness is formed along the second outer peripheral edge 14C of the second end surface 14 between the second end surface 14 molded on the lower pressing surface 22S and the circumferential surface 16 molded on the restricting surface 26S.

[0032] (Method for evaluating thickness deviation) Here, a method for evaluating thickness deviation will be described. In this embodiment, thickness deviation refers to the variation in the magnitude of the roundness formed on the first outer peripheral edge 12C of the first end face 12 and the second outer peripheral edge 14C of the second end face 14. The roundness is approximated to an arc in a circumferential cross-sectional view of the preform 10. That is, thickness deviation refers to the variation in the radius R of the corner radius on the first outer peripheral edge 12C and the second outer peripheral edge 14C. The radius R is defined by measuring the vertical distance from the boundary 16A, 16B between the flat surface of the peripheral surface 16 formed by the side mold 26 and the curved surface above or below the flat surface to the first end face 12 or the second end face 14.

[0033] In this embodiment, the radius R1 of the corner of the first outer peripheral edge 12C and the radius R2 of the corner of the second outer peripheral edge 14C are measured every 90° in the circumferential direction. The standard deviation σ, which represents the variation in the values ​​measured at four points for the radius R1 of the corner of the first outer peripheral edge 12C, is calculated. Similarly, the standard deviation σ, which represents the variation in the values ​​measured at four points for the radius R2 of the corner of the second outer peripheral edge 14C, is calculated. Each of these standard deviations σ is compared with a predetermined threshold.

[0034] 4 is a graph showing an example of the evaluation results of thickness deviation. In this embodiment, the threshold value is set to σ=40 μm. If the standard deviation σ of the radius R1 of the corner radius of the first outer peripheral edge 12C and the standard deviation σ of the radius R2 of the corner radius of the second outer peripheral edge 14C are both below the threshold value, the lens is judged to have little effect on thickness deviation during molding and is judged to be good. If at least either of them is above the threshold value, the lens is judged to be unacceptable.

[0035] The predetermined threshold is preferably set in the range of 0 μm to 40 μm, more preferably 0 μm to 30 μm, and even more preferably 0 μm to 15 μm. The measurement positions for the radius R of the rounded corner are not limited to positions every 90° divided into four circumferential positions, but may be divided into three, five or more positions.

[0036] Furthermore, in the above evaluation method, the standard deviation σ is calculated and evaluated separately for the first outer peripheral edge 12C of the first end face 12 and the second outer peripheral edge 14C of the second end face 14, but the standard deviation σ may also be calculated and evaluated for both. In this case, even if the standard deviation σ of the radius R1 of the corner radius of the first outer peripheral edge 12C and the standard deviation σ of the radius R2 of the corner radius of the second outer peripheral edge 14C are both below their thresholds, it can be determined to be unacceptable if the difference between radius R1 and radius R2 is large.

[0037] (Manufacturing method that suppresses thickness deviation) Next, a method for manufacturing a preform 10 that suppresses thickness deviation will be described. Because the spherical substrate 10B is spherical, if it rolls inside the side mold 26 and is positioned off-center relative to the central axis, the molded shape will also have thickness deviation. That is, the radius R of the corner radius on the off-center side may be small and the radius R of the corner radius on the opposite side may be large. Furthermore, frictional resistance with the restricting surface 26S of the side mold 26 may suppress deformation in the lower part relative to deformation in the upper part, resulting in a small radius R1 of the corner radius at the first outer peripheral edge 12C and a large radius R2 of the corner radius at the second outer peripheral edge 14C.

[0038] Methods for suppressing such uneven thickness include adjusting the temperature during reheat pressing, adjusting the filling rate of the preform 10 (spherical substrate 10B) in the molding die 20, inversion molding, positioning molding, and combinations of these. Each method will be described in detail below.

[0039] (Temperature adjustment) The spherical substrate 10B softens when heated to a predetermined temperature above its softening point and below its melting point. Therefore, the higher the temperature of the upper pressing surface 24S or the longer the heating time, the more the deformation of the upper portion of the spherical substrate 10B is promoted, and the smaller the radius R1 of the corner at the first outer peripheral edge 12C becomes. Furthermore, the higher the temperature of the lower pressing surface 22S or the longer the heating time, the more the deformation of the lower portion of the spherical substrate 10B is promoted, and the smaller the radius R2 of the corner at the second outer peripheral edge 14C becomes.

[0040] Methods for adjusting the temperature include adjusting the temperature of at least one of the lower pressing surface 22S and the upper pressing surface 24S, or adjusting the temperatures of both the lower pressing surface 22S and the upper pressing surface 24S. For example, adjusting the temperature difference between the lower pressing surface 22S and the upper pressing surface 24S within a predetermined range, or adjusting the heating time for the lower pressing surface 22S and the upper pressing surface 24S within a predetermined range. The molding die 20 can adjust the temperature of the lower pressing surface 22S using the lower heating section 22H, and the temperature of the upper pressing surface 24S using the upper heating section 24H. By adjusting the temperature in this manner, the radius of the upper and lower corners of the preform 10 can be adjusted. The heating temperature may also be changed during reheat pressing. For example, the lower pressing surface 22S may be heated to a high temperature and the upper pressing surface 24S may be cooled in the early stages, and the lower pressing surface 22S may be cooled and the upper pressing surface 24S may be heated in the final stages. In this way, thickness deviation in the thickness direction can be suppressed by adjusting the temperature profile of the lower pressing surface 22S and the upper pressing surface 24S during the process from the spherical substrate 10B to the molding of the preform 10. Furthermore, suppressing thickness deviation can increase the filling rate, which also contributes to suppressing thickness deviation in the radial and circumferential directions.

[0041] (Filling rate adjustment) 5 and 6 are schematic diagrams illustrating a method for suppressing uneven thickness by adjusting the filling rate. The filling rate can be adjusted by changing the dimensions of the inner diameter Φ and height H of the side mold 26.

[0042] For example, as shown in Figure 5, when the difference between the diameter φ of the spherical substrate 10B and the inner diameter Φ of the side mold 26 is small, the undeformed spherical substrate 10B can be prevented from rolling inside the side mold 26, and the undeformed spherical substrate 10B can be positioned at the center of the side mold 26, thereby suppressing thickness deviations in the radial and circumferential directions. That is, at the first outer peripheral edge 12C, thickness deviations between the radius R1a of the corner radius at a predetermined position in the circumferential direction and the radius R1b of the corner radius at the opposite position are suppressed. Also, at the second outer peripheral edge 14C, thickness deviations between the radius R2a of the corner radius at a predetermined position in the circumferential direction and the radius R2b of the corner radius at the opposite position are suppressed.

[0043] To achieve this effect, the ratio of the diameter φ of the spherical substrate 10B to the inner diameter Φ of the side mold 26 is preferably 95% or more and 100% or less, more preferably 98% or more and 100% or less, and even more preferably 99% or more and 100% or less. The temperature of the forming mold 20 may be adjusted as described above while the ratio of the diameter φ of the spherical substrate 10B to the inner diameter Φ of the side mold 26 is set within the above range. This reduces thickness deviations in the thickness direction due to the frictional resistance between the side mold 26 and the restricting surface 26S, which suppresses deformation in the lower part relative to deformation in the upper part.

[0044] Furthermore, for example, as shown in FIG. 6, if the diameter φ of the spherical substrate 10B is too small compared to the inner diameter Φ of the side mold 26, i.e., if there is a large gap S between the spherical substrate 10B and the regulating surface 26S, the spherical substrate 10B before deformation may roll inside the side mold 26, resulting in thickness variations in the radial and circumferential directions. On the other hand, in the early stages of deformation, the spherical substrate 10B does not come into contact with the regulating surface 26S of the side mold 26, resulting in uniform deformation in the thickness direction and reduced thickness variations. This also allows for the preform 10 to be thinned and improves the degree of freedom in shape. In this case, by lowering the height H of the side mold 26 and adjusting the filling rate, the radius R of the corner radius can be reduced, thereby reducing the standard deviation σ of the radius R of the corner radius in the circumferential direction at the first outer peripheral edge 12C and the second outer peripheral edge 14C.

[0045] (inversion molding) FIG. 7 is a schematic diagram illustrating a method for suppressing thickness deviation using inversion molding. Inversion molding, two types of molding dies 20A and 20B are used. The molding dies 20A and 20B may have the same lower die 22 and upper die 24, but at least the shapes of the side dies 26A and 26B are different. Specifically, the height H1 of the side die 26A is higher than the height H2 of the side die 26B. This allows the spherical substrate 10B to be reheat-pressed in two stages. Note that in the procedure shown in FIG. 7, the heating temperatures of the lower pressing surface 22S and the upper pressing surface 24S are assumed to be the same.

[0046] As shown in Fig. 7, first, a first molding die 20A including the above-described lower die 22, upper die 24, and side die 26A, and a spherical substrate 10B are prepared. Then, the spherical substrate 10B is placed at the center of the lower pressing surface 22S in the concave portion surrounded by the lower die 22 and side die 26A of the first molding die 20A (step S20). Next, the lower pressing surface 22S is heated to a predetermined temperature by the lower heating unit 22H, and the upper pressing surface 24S is heated to a predetermined temperature by the upper heating unit 24H. With this state, the upper die 24 is brought relatively close to the lower die 22, and the spherical substrate 10B is sandwiched between the lower pressing surface 22S and the upper pressing surface 24S.

[0047] The spherical substrate 10B is heated and softened by the heated lower pressing surface 22S and upper pressing surface 24S, and is crushed and deformed between the lower pressing surface 22S and the upper pressing surface 24S. By moving the upper mold 24 relatively closer to the lower mold 22 until the upper pressing surface 24S of the upper mold 24 reaches the upper surface of the side mold 26A, the spherical substrate 10B is molded into the intermediate molded product 10I in the area surrounded by the lower pressing surface 22S and upper pressing surface 24S of the molding mold 20A and the restricting surface 26S of the side mold 26A (step S22).

[0048] The thickness of the intermediate molded product 10I is equal to the height H1 of the side mold 26A, and the diameter is equal to the inner diameter Φ of the side mold 26A. At this time, uneven thickness occurs in the intermediate molded product 10I. Specifically, because the deformation on the lower side is suppressed relative to the deformation on the upper side, the radius R2 of the corner radius of the lower second outer peripheral edge 14C becomes larger than the radius R1 of the corner radius of the upper first outer peripheral edge 12C.

[0049] Next, a second molding die 20B is prepared, which includes the lower die 22, upper die 24, and side die 26B described above. Then, the intermediate molded product 10I is turned upside down and stored in a recessed portion surrounded by the lower die 22 and side die 26B of the second molding die 20B (step S24). That is, the radius R2 of the corner radius of the second outer peripheral edge 14C located on the upper side is greater than the radius R1 of the corner radius of the first outer peripheral edge 12C located on the lower side. Furthermore, because the height H2 of the side die 26B of the molding die 20B is lower than the height H1 of the side die 26A of the molding die 20A, a portion of the intermediate molded product 10I protrudes upward from the upper end of the side die 26B. Then, the lower heating section 22H heats the lower pressing surface 22S to a predetermined temperature, and the upper heating section 24H heats the upper pressing surface 24S to a predetermined temperature. With this state, the upper mold 24 is brought relatively close to the lower mold 22, and the intermediate molded product 10I is sandwiched between the lower pressing surface 22S and the upper pressing surface 24S.

[0050] Intermediate molded article 10I is heated and softened by heated lower pressing surface 22S and upper pressing surface 24S, and is crushed and deformed between lower pressing surface 22S and upper pressing surface 24S. By moving upper mold 24 relatively closer to lower mold 22 until upper pressing surface 24S of upper mold 24 reaches the upper surface of side mold 26B, intermediate molded article 10I is molded into preform 10 in the area surrounded by lower pressing surface 22S and upper pressing surface 24S of molding mold 20B and restriction surface 26S of side mold 26B (step S26).

[0051] The thickness of the preform 10 is equal to the height H2 of the side mold 26B. Because deformation on the lower side is suppressed relative to deformation on the upper side, the deformation amount of the radius R2 of the corner radius of the upper second outer peripheral edge 14C is greater than the deformation amount of the radius R1 of the corner radius of the lower first outer peripheral edge 12C. That is, by causing greater deformation on the first end face 12 side in the reheat press in step S22 and greater deformation on the second end face 14 side in the reheat press in step S26, thickness deviation can be suppressed. Furthermore, the effect of suppressing radial and circumferential thickness deviations on the lower side during reheat press has also been confirmed. Inverted molding suppresses the variation in the standard deviation σ on both the first outer peripheral edge 12C of the first end face 12 and the second outer peripheral edge 14C of the second end face 14.

[0052] (Positioning molding) 8 is a schematic diagram illustrating a method for suppressing thickness deviation by positioning molding. In positioning molding, two types of molding dies 20C and 20D are used. The molding dies 20C and 20D may have a common upper die 24, but the shapes of at least the lower dies 22C and 22D and the side dies 26C and 26D are different.

[0053] Specifically, a recess 22P is formed in a lower pressing surface 22S of a lower mold 22C of a molding die 20C. The recess 22P is a depression formed in the lower pressing surface 22S, and may be formed at any position on the lower pressing surface 22S, but in this embodiment, the recess 22P is formed at the center of the lower pressing surface 22S. The recess 22P can accommodate a portion of the lower side of the spherical substrate 10B and prevents the spherical substrate 10B from rolling in the radial direction. The recess 22P may have, for example, the same radius of curvature as the radius of the spherical substrate 10B. Meanwhile, the lower mold 22D of the molding die 20 is flat, and the lower pressing surface 22S is a flat surface. Furthermore, the height H1 of the side mold 26C is higher than the height H2 of the side mold 26D. This allows the spherical substrate 10B to be reheat-pressed in two stages. Note that in the procedure shown in Figure 8, the heating temperatures of the lower pressing surface 22S and the upper pressing surface 24S are assumed to be the same.

[0054] As shown in Figure 8, first, a first molding die 20C including the above-mentioned lower die 22C, upper die 24, and side die 26C, and a spherical substrate 10B are prepared. Then, the spherical substrate 10B is placed on the recess 22P of the lower die 22C of the first molding die 20C (step S30). Then, the lower pressing surface 22S is heated to a predetermined temperature by the lower heating unit 22H, and the upper pressing surface 24S is heated to a predetermined temperature by the upper heating unit 24H. With this state, the upper die 24 is brought relatively close to the lower die 22C, and the spherical substrate 10B is sandwiched between the lower pressing surface 22S and the upper pressing surface 24S.

[0055] The spherical substrate 10B is heated and softened by the heated lower and upper pressing surfaces 22S and 24S, and is crushed and deformed between the lower and upper pressing surfaces 22S and 24S. By moving the upper mold 24 relatively closer to the lower mold 22C until the upper pressing surface 24S of the upper mold 24 reaches the upper surface of the side mold 26C, the spherical substrate 10B is molded into an intermediate molded product 10I in the space surrounded by the lower and upper pressing surfaces 22S and 24S of the molding mold 20C and the restricting surface 26S of the side mold 26C (step S32). At this time, a convex portion 18 is formed in the intermediate molded product 10I along the recess 22P of the lower mold 22C.

[0056] Next, a molding die 20D is prepared, which includes the above-mentioned lower die 22D, upper die 24, and side die 26D. Then, the intermediate molded product 10I is placed upside down in a recessed space surrounded by the lower die 22D and side die 26B of the second molding die 20D (step S34). That is, the convex portion 18 of the intermediate molded product 10I faces the upper pressing surface 24S of the upper die 24. Furthermore, because the height H2 of the side die 26D of the molding die 20D is lower than the height H1 of the side die 26C of the molding die 20C, a portion of the intermediate molded product 10I protrudes upward from the upper end of the side die 26D. Then, the lower heating section 22H heats the lower pressing surface 22S to a predetermined temperature, and the upper heating section 24H heats the upper pressing surface 24S to a predetermined temperature. With this state, the upper mold 24 is brought relatively close to the lower mold 22D, and the intermediate molded product 10I is sandwiched between the lower pressing surface 22S and the upper pressing surface 24S.

[0057] Intermediate molded article 10I is heated and softened by heated lower pressing surface 22S and upper pressing surface 24S, and is crushed and deformed between lower pressing surface 22S and upper pressing surface 24S. By moving upper mold 24 relatively closer to lower mold 22D until upper pressing surface 24S of upper mold 24 reaches the upper surface of side mold 26D, intermediate molded article 10I is molded into preform 10 in the area surrounded by the flat lower pressing surface 22S and upper pressing surface 24S of molding mold 20D and restriction surface 26S of side mold 26D (step S36).

[0058] The thickness of the preform 10 is equal to the height H2 of the side mold 26D. In the procedure shown in Fig. 8, in addition to inversion molding, the spherical substrate 10B is prevented from rolling in the radial direction during the first reheat press, which prevents uneven thickness in the thickness direction as well as in the radial and circumferential directions.

[0059] (Another example of a mold) Figure 9 is a schematic exploded view showing another example of a molding die. The molding die 30 of this example shown in Figure 9 includes a lower die 32, an upper die 34, a side die 36, and a guide member 38. The molding die 30 molds a plurality of spherical substrates 10B together into a preform 10.

[0060] The basic configuration and function of the lower mold 32 are similar to those of the lower mold 22 of the molding die 20 shown in Figure 3. The lower mold 32 has a lower pressing surface 32S on its upper surface. The lower mold 32 presses the plurality of spherical substrates 10B from below with the lower pressing surface 22S, thereby forming either the first end surface 12 or the second end surface 14 of the plurality of preforms 10. The lower mold 32 also has a lower heating section 32H that heats the lower pressing surface 32S (see Figure 10). The lower heating section 32H heats and softens the plurality of spherical substrates 10B via the lower pressing surface 32S.

[0061] The basic structure and function of the upper mold 34 are similar to those of the upper mold 24 of the molding die 20 shown in FIG. 3. The upper mold 34 has an upper pressing surface 34S on its lower surface. The upper pressing surface 34S faces the lower pressing surface 32S of the lower mold 32. The upper mold 34 can move relatively close to and away from the lower mold 32 in the vertical direction. The upper mold 34 presses the plurality of spherical substrates 10B from above with the upper pressing surface 34S, thereby forming the other of the first end surface 12 and the second end surface 14 of the preform 10. The upper mold 34 also has an upper heating section 34H that heats the upper pressing surface 34S (see FIG. 10). The upper heating section 34H heats and softens the spherical substrates 10B via the upper pressing surface 34S.

[0062] The side mold 36 is a disk-shaped spacer provided between the lower mold 32 and the upper mold 34. The side mold 36 has multiple through holes 36S penetrating vertically. Each through hole 36S is inscribed in the peripheral surface 16 of the preform 10. That is, the inner peripheral surface of the through hole 36S in the molding mold 30 corresponds to the restricting surface 26S of the side mold 26 of the molding mold 20 shown in FIG. 3 and elsewhere. The inner diameter of the inner peripheral surface of the through hole 36S is equal to or greater than the diameter φ of the spherical substrate 10B and equal to the diameter of the molded preform 10. The inner peripheral surface of the through hole 36S restricts deformation of the spherical substrate 10B, which expands laterally when crushed by the lower pressing surface 32S of the lower mold 32 and the upper pressing surface 34S of the upper mold 34, thereby forming the peripheral surface 16 of the preform 10. The inner peripheral surface of the through hole 36S is mirror-finished. The inner peripheral surface of the through hole 36S is continuous with the lower pressing surface 32S of the lower mold 32. The height of the side mold 36 is equal to the thickness of the preform 10 after molding.

[0063] The guide member 38 is a cylindrical member disposed radially outward of the side mold 36. The guide member 38 is inscribed in a portion including the upper end of the lower mold 32, a portion including the lower end of the upper mold 34, and the outer peripheral surface of the side mold 36, and restricts their radial movement and guides their relative movement in the vertical direction.

[0064] FIG. 10 is a schematic diagram illustrating a method for manufacturing a preform using the molding die shown in FIG. 9. The basic procedure is the same as that of the method for manufacturing a preform 10 using the molding die 20 shown in FIG. 3. As shown in FIG. 10, in this manufacturing method, first, a molding die 30 including the lower die 32, upper die 34, and side die 36 described above, and multiple spherical substrates 10B are prepared. Then, the spherical substrates 10B are placed in multiple through holes 36S of the side die 36, each of which is closed at the bottom by the lower pressing surface 32S of the lower die 32 (step S40). Then, with the lower pressing surface 32S heated to a predetermined temperature by the lower heating unit 32H and the upper pressing surface 34S heated to a predetermined temperature by the upper heating unit 34H, the upper die 34 is brought relatively close to the lower die 32, and the spherical substrate 10B is sandwiched between the lower pressing surface 32S and the upper pressing surface 34S.

[0065] Each spherical substrate 10B is heated and softened by the heated lower pressing surface 32S and upper pressing surface 34S, and is crushed and deformed between the lower pressing surface 32S and the upper pressing surface 34S. By moving the upper mold 34 relatively closer to the lower mold 32 until the upper pressing surface 34S of the upper mold 34 reaches the top surface of the side mold 36, the spherical substrate 10B is molded into a preform 10 in the area surrounded by the lower pressing surface 32S and the upper pressing surface 34S of the molding mold 30 and the inner peripheral surface of the through hole 36S (step S42). Each spherical substrate 10B is molded so that its upper portion becomes the first end surface 12 of the preform 10, its lower portion becomes the second end surface 14, and its side portion becomes the peripheral surface 16. In this molding method, by making the molding die 30 even larger or by reducing the distance between the through holes 36S, it is possible to simultaneously mold not only the nine preforms 10 shown in Figure 9, but on the order of 100. This makes it possible to create a PF that can be used to mold multiple lenses in the same molding time that it normally takes to deform a single ball PF. Also, since only one lens can normally be made per mold, multiple molds must be prepared to mold multiple lenses simultaneously, but in this example, the number of molding dies 30 can be significantly reduced, which shortens the molding time and therefore the amount of time the equipment is occupied, and also makes it possible to significantly reduce costs.

[0066] (Yet another example of a mold) In this embodiment, the first end surface 12 and the second end surface 14 of the preform 10 are described as flat surfaces, but they may have a shape that more closely resembles the lens molded from the preform 10. Specifically, they may be a preform approximating a plano-convex lens with one convex surface, a preform approximating a biconvex lens with both convex surfaces, a preform approximating a plano-concave lens with one concave surface, a preform approximating a biconcave lens with both concave surfaces, or a preform approximating a meniscus lens with one convex surface and the other concave surface. When producing a preform whose end surfaces are not flat in this way, the pressing surface of the mold used in the final reheat press may be shaped to match the desired shape of the preform.

[0067] (Effects of the present disclosure) A method for manufacturing preform 10 according to the first embodiment of the present disclosure is a method for manufacturing preform 10 for a cylindrical optical element by reheat pressing spherical substrate 10B with molding dies 20, 20A, 20B, 20C, 20D, and includes preparing molding dies 20, 20A, 20B, 20C, 20D each including lower dies 22, 22C, 22D having a lower pressing surface 22S on their upper surface, upper dies 24 having an upper pressing surface 24S facing lower pressing surface 22S on their lower surface, and cylindrical side dies 26, 26A, 26B, 26C, 26D provided between lower dies 22, 22C, 22D and upper dies 24; and placing a spherical substrate 10B on the lower pressing surface 22S in the concave portion surrounded by B, 26C, and 26D, and while the lower pressing surface 22S and the upper pressing surface 24S are heated, the upper mold 24 is brought relatively close to the lower molds 22, 22C, and 22D to reheat-press the spherical substrate 10B, thereby molding it into a preform 10 in the area surrounded by the lower pressing surface 22S, the upper pressing surface 24S, and the inner surfaces of the side molds 26, 26A, 26B, 26C, and 26D, wherein the filling rate of the preform 10 in this area is 77% or more, and the arithmetic mean roughness Ra of the inner surfaces (regulating surfaces 26S) of the side molds 26, 26A, 26B, 26C, and 26D is less than 0.2 μm. The method for manufacturing preform 10 of the present disclosure uses only a reheat press to form the preform, and therefore can achieve higher volumetric accuracy and a simpler manufacturing process than when shaping peripheral surface 16 by grinding. Furthermore, since the surface roughness of peripheral surface 16 depends solely on the surface roughness of the inner peripheral surface (regulating surface 26S) of side mold 26, the surface roughness can be reduced by, for example, mirror-finishing the inner peripheral surface of side mold 26.

[0068] The method for manufacturing a preform 10 according to a second embodiment of the present disclosure is the same as the method for manufacturing a preform 10 according to the first embodiment, but preferably adjusts the temperature profile of the lower pressing surface 22S and the temperature profile of the upper pressing surface 24S during the process of molding the spherical substrate 10B into the preform 10 by reheat pressing. The method for manufacturing a preform 10 according to the present disclosure adjusts the temperature profiles of the lower pressing surface 22S and the upper pressing surface 24S, respectively, to promote or suppress deformation of the upper and lower parts of the spherical substrate 10B during reheat pressing, thereby suppressing thickness deviation in the thickness direction of the preform 10. Furthermore, suppressing thickness deviation can increase the filling rate, which also contributes to suppressing thickness deviation in the radial and circumferential directions.

[0069] The method for manufacturing preform 10 according to the third aspect of the present disclosure is the method for manufacturing preform 10 according to the first or second aspect, and it is preferable that the diameter of spherical substrate 10B is 95% or more of the inner diameter of side molds 26, 26A, 26B, 26C, and 26D. The method for manufacturing preform 10 according to the present disclosure can prevent spherical substrate 10B from being reheat-pressed in a radially biased position inside side molds 26, 26A, 26B, 26C, and 26D, and therefore can prevent uneven thickness of preform 10 in the radial and circumferential directions.

[0070] A manufacturing method for preform 10 according to a fourth aspect of the present disclosure is a manufacturing method for preform 10 according to any one of the first to third aspects, and preferably includes, when forming preform 10 by reheat pressing spherical substrate 10B into preform 10, reheat pressing spherical substrate 10B to a predetermined thickness greater than the thickness of preform 10 to form intermediate molded product 10I, and inverting intermediate molded product 10I and reheat pressing it again to form preform 10. In the manufacturing method for preform 10 according to the present disclosure, deformation on the lower side during reheat pressing tends to be suppressed relative to deformation on the upper side, so by inverting the upper side midway, thickness deviation in the thickness direction of preform 10 can be suppressed. Furthermore, since thickness deviation in the radial and circumferential directions is also suppressed on the lower side during reheat pressing, variation in standard deviation σ is suppressed both at first outer peripheral edge 12C of first end face 12 and at second outer peripheral edge 14C of second end face 14.

[0071] The manufacturing method of the preform 10 according to the fifth aspect of the present disclosure is a manufacturing method of the preform 10 according to any one of the first to third aspects, wherein the molding die includes a first molding die 20C in which the lower pressing surface 22S of the lower die 22C has a recess 22P capable of accommodating a portion of the spherical substrate 10B, and a second molding die 20D in which the lower pressing surface 22S of the lower die 22D has a flat shape, and when molding the spherical substrate 10B into the preform 10 by reheat pressing, it is preferable to include using the first molding die 20C to reheat press the spherical substrate 10B to a predetermined thickness greater than the thickness of the preform 10 to mold it into an intermediate molded product 10I, and using the second molding die 20D to invert the intermediate molded product 10I upside down and reheat press it again to mold it into a preform. The manufacturing method of the preform 10 of the present disclosure can prevent the spherical substrate 10B from being reheat pressed in a radially biased position inside the side mold 26C, thereby suppressing uneven thickness of the preform 10 in the radial and circumferential directions.

[0072] A method for producing a preform 10 according to a sixth aspect of the present disclosure is a method for producing a preform 10 according to any one of the first to fifth aspects, in which the molding die has a disk-shaped side die 36 having a plurality of through-holes 36S penetrating vertically, instead of the cylindrical side dies 26, 26A, 26B, 26C, and 26D, and it is preferable that a spherical substrate 10B is placed in each of the through-holes 36S, and the plurality of spherical substrates 10B are molded into a plurality of preforms 10. The method for producing a preform 10 according to the present disclosure can produce a plurality of preforms 10 from a plurality of spherical substrates 10B in a series of reheat presses, and can reduce the number of molding dies 30, thereby shortening the manufacturing time, thereby shortening the equipment occupancy time, and reducing costs.

[0073] A method for manufacturing an optical element according to a seventh aspect of the present disclosure manufactures an optical element using a preform 10 manufactured by the method for manufacturing a preform 10 according to any one of the first to sixth aspects. Because the method for manufacturing an optical element according to the present disclosure manufactures from a cylindrical preform 10, the preform 10 can be stably placed in a mold when molding an optical element such as a lens using a reheat press, and is applicable not only to convex lenses but also to optical elements having at least one optically functional surface that is concave. Furthermore, because the method manufactures from a preform 10 with high volumetric accuracy and low surface roughness of the peripheral surface 16, it is possible to prevent overfilling or underfilling of the mold when molding an outer diameter-restricted lens or the like, and to prevent abnormal appearance of the molded optical element.

[0074] A preform 10 according to an eighth aspect of the present disclosure has a cylindrical shape including a first end face 12, a second end face 14, a peripheral surface 16, a first outer peripheral edge 12C connecting the first end face 12 and the peripheral surface 16, and a second outer peripheral edge 14C connecting the second end face 14 and the peripheral surface 16. The first outer peripheral edge 12C and the second outer peripheral edge 14C have rounded corners. The arithmetic mean roughness Ra of the peripheral surface 16 is less than 0.2 μm. The standard deviation σ of the radius R1 of the rounded corners at the first outer peripheral edge 12C at four or more positions in the circumferential direction is less than 40 μm. The standard deviation σ of the radius R2 of the rounded corners at the second outer peripheral edge 14C at these positions is less than 40 μm. Because the preform 10 according to the present disclosure has a cylindrical shape, it can be stably placed in a mold when molding optical elements such as lenses using a reheat press. Furthermore, the preform can be applied not only to convex lenses but also to optical elements having at least one concave optical functional surface. Furthermore, since the surface roughness of the peripheral surface 16 is low, it is possible to prevent abnormalities in the appearance of the molded optical element. Furthermore, since the uneven thickness is low, it is possible to prevent overfilling or underfilling of the molding die when molding a lens with a restricted outer diameter, etc.

[0075] Preform 10 according to a ninth aspect of the present disclosure is preform 10 according to the eighth aspect, and preferably has a squareness of less than 20 μm for peripheral surface 16. Preform 10 according to the present disclosure can further prevent appearance abnormalities from occurring in molded optical elements and prevent overfilling or underfilling of the molding die when molding outer diameter-regulated lenses and the like.

[0076] Preform 10 according to a tenth aspect of the present disclosure is preform 10 according to the eighth or ninth aspect, and it is preferable that the standard deviation of radius R1 of the corner radius of first outer peripheral edge 12C when measured at four or more locations in the circumferential direction, and radius R2 of the corner radius of second outer peripheral edge 14C when measured at four or more locations in the circumferential direction, are less than 40 μm. Preform 10 according to the present disclosure can further prevent overfilling or underfilling of a molding die when molding into an outer diameter-regulated lens or the like.

[0077] The preform 10 according to an eleventh aspect of the present disclosure is the preform 10 according to any one of the eighth to tenth aspects, and is preferably made of glass. By making the preform 10 of the present disclosure from glass, the optical element molded from the preform 10 can exhibit appropriate optical properties.

[0078] (Example) Next, examples will be described. Table 1 shows the preforms of each example. Note that the embodiment may be modified as long as the effects of the invention are achieved.

[0079] [Table 1]

[0080] (Examples 1 to 5) Examples 1 to 5 were produced using the production method of this embodiment. In Example 1, the mold 20 shown in FIG. 5 of this embodiment was used, and production was carried out without adjusting the filling rate, positioning molding, or inversion molding. In Example 2, the molds 20C and 20D shown in FIG. 8 of this embodiment were used, and production was carried out without adjusting the filling rate, and positioning molding and inversion molding. In Example 3, the molds 20A and 20B shown in FIG. 7 of this embodiment were used, and production was carried out without positioning molding, and adjustment of the filling rate and inversion molding. In Example 4, the mold 20 shown in FIG. 6 of this embodiment was used, and production was carried out with adjustment of the filling rate, but without positioning molding and inversion molding. In Example 5, the mold 20 shown in FIG. 6 of this embodiment was used, and production was carried out without adjusting the filling rate, positioning molding, or inversion molding. The results after molding are shown in Table 1.

[0081] (Example 6) In Example 6, the molding was performed using a molding die that did not include the side die of this embodiment and that only included a lower die and an upper die. Table 1 shows the results after molding.

[0082] (Example 7) In Example 7, the mold was reheat pressed using a mold that did not include the side molds of this embodiment and included only a lower mold and an upper mold, and then the peripheral surface was ground and polished. The results after molding are shown in Table 1.

[0083] (evaluation) The preforms of each example were evaluated for volume accuracy, diameter accuracy, thickness deviation, surface roughness of the peripheral surface, squareness of the peripheral surface, and manufacturing time.

[0084] In assessing volumetric accuracy, a volumetric accuracy of less than ±0.1% was rated as excellent, a volumetric accuracy of ±0.1% or more but less than 0.5% was rated as good, a volumetric accuracy of ±0.5% or more but less than 1% was rated as acceptable, and a volumetric accuracy of ±1% or more was rated as poor.

[0085] To evaluate the diameter accuracy, the diameter at the center of the preform's thickness direction was measured, and the accuracy relative to the target value was calculated. A diameter accuracy of less than ±0.1% was rated as excellent, a diameter accuracy of ±0.3% to less than 0.5% was rated as good, a diameter accuracy of ±0.5% to less than 1% was rated as acceptable, and a diameter accuracy of ±1% or more was rated as poor.

[0086] To evaluate the thickness deviation, the radius of the corners of the upper and lower outer edges was measured every 90° around the circumference of the preform, and the standard deviation, which is the variation in the values ​​measured at each of the four points, was used to evaluate. A standard deviation of less than 15 μm was rated as excellent, a standard deviation of 15 μm or more but less than 30 μm was rated as good, a standard deviation of 30 μm or more but less than 40 μm was rated as acceptable, and a standard deviation of 40 μm or more was rated as poor.

[0087] The squareness of the peripheral surface was measured at every 90° in the circumferential direction of the preform and evaluated based on the maximum value. A squareness of less than ±10 μm was rated as excellent, a squareness of ±10 μm or more but less than 15 μm was rated as good, a squareness of ±15 μm or more but less than 25 μm was rated as acceptable, and a squareness of ±25 μm or more was rated as poor.

[0088] As shown in Table 1, in Examples 1 to 5, which are working examples, the volume accuracy, diameter accuracy, and squareness of the peripheral surface are all excellent, indicating that the volume accuracy and diameter accuracy are high and the squareness is low. Furthermore, in Examples 1 and 2, the thickness deviation is excellent, and in Example 3, the thickness deviation is also good, indicating that the thickness deviation is low. In Example 4, the thickness deviation is acceptable, but because a molding die is used, it is expected that the thickness deviation can be suppressed by adjusting the temperature.

[0089] On the other hand, in Example 6, which is a comparative example, the volumetric accuracy and thickness deviation are excellent, but the diameter accuracy and squareness of the peripheral surface are poor, indicating that the volumetric accuracy is high and the thickness deviation is low, but the diameter accuracy and squareness are low. Also, in Example 7, which is another comparative example, the thickness deviation and squareness of the peripheral surface are good, but the diameter accuracy is fair and the volumetric accuracy is poor, indicating that the thickness deviation is low, but the volumetric accuracy, diameter accuracy and squareness are low.

[0090] Although the embodiments of the present invention have been described above, the embodiments are not limited to the contents of these embodiments. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the scope of what is called equivalents. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments. [Explanation of symbols]

[0091] 10 Preform 10B Spherical base material 10I intermediate molded product 12 First end surface 12C First outer edge 14 Second end face 14C Second outer edge 16 Circumferential surface 16A, 16B boundary 18 Convex part 20, 20A, 20B, 20C, 20D, 30 molds 22, 22C, 22D, 32 lower mold 22H, 32H Lower heating section 22S, 32S lower pressure surface 22P Sungai 24, 34 (Upper Type) Upper heating section of 24H and 34H 24S, 34S upper pressure side Side profiles: 26, 26A, 26B, 26C, 26D, 36 26S Specifications 36S Through Hole 38 ガイド parts H, H1, H2 high Radius of R, R1, R1a, R1b, R2, R2a, R2b S gap φ Diameter Φ Inner Diameter

Claims

1. A method for manufacturing a preform for a cylindrical optical element by reheat pressing a spherical substrate in a molding die, comprising: Preparing a molding die including a lower die having a lower pressing surface on its upper surface, an upper die having an upper pressing surface on its lower surface facing the lower pressing surface, and a cylindrical side die provided between the lower die and the upper die; placing the substrate on the lower pressing surface in a concave portion surrounded by the lower mold and the side mold; In a state where the lower pressing surface and the upper pressing surface are heated, the upper mold is brought relatively close to the lower mold to reheat-press the base material, thereby molding the base material into a preform in an area surrounded by the lower pressing surface, the upper pressing surface, and an inner peripheral surface of the side mold; Including, The filling rate of the preform in the region is 77% or more, The arithmetic mean roughness of the inner peripheral surface of the side mold is less than 0.2 μm. Preform manufacturing method.

2. Adjusting the temperature profile of the lower pressing surface and the temperature profile of the upper pressing surface during the period from when the substrate is molded into the preform by the reheat press. A method for producing the preform according to claim 1.

3. The diameter of the substrate is 95% or more of the inner diameter of the side mold. A method for producing the preform according to claim 1.

4. When the substrate is reheat-pressed to form a preform, Reheat pressing the substrate to a predetermined thickness greater than the thickness of the preform to form an intermediate molded product; Inverting the intermediate molded product upside down and reheat pressing it again to form a preform; Including, A method for producing the preform according to claim 1.

5. The mold is a first molding die in which the lower pressing surface of the lower die has a recess capable of accommodating a part of the base material; a second molding die in which the lower pressing surface of the lower die is flat; Including, When the substrate is reheat-pressed to form a preform, In the first mold, the substrate is reheat-pressed to a predetermined thickness greater than the thickness of the preform to form an intermediate molded product; In the second mold, the intermediate molded product is turned upside down and reheat-pressed again to form a preform; Including, A method for producing the preform according to claim 1.

6. The mold is a disk-shaped side mold having a plurality of through holes extending vertically therethrough is provided instead of the cylindrical side mold, The substrate is placed in each of the through holes, A plurality of preforms are formed from the plurality of substrates. A method for producing the preform according to claim 1.

7. An optical element is manufactured using the preform manufactured by the preform manufacturing method according to any one of claims 1 to 6. A method for manufacturing an optical element.

8. a cylindrical shape having a first end surface, a second end surface, a peripheral surface, a first outer peripheral edge connecting the first end surface and the peripheral surface, and a second outer peripheral edge connecting the second end surface and the peripheral surface, The first outer peripheral edge and the second outer peripheral edge have rounded corners, The arithmetic mean roughness of the peripheral surface is less than 0.2 μm, The standard deviation of the radius of the corner radius at the first outer peripheral edge at positions divided into four or more in the circumferential direction is less than 40 μm, The standard deviation of the radius of the corner radius at the second outer peripheral edge at the position is less than 40 μm. Preforms for optical elements.

9. The perpendicularity of the peripheral surface is less than 20 μm. The preform for an optical element according to claim 8 .

10. The standard deviation of the radius of the corner radius of the first outer peripheral edge when measured at four or more points in the circumferential direction and the standard deviation of the radius of the corner radius of the second outer peripheral edge when measured at four or more points in the circumferential direction are less than 40 μm. The preform for an optical element according to claim 8 .

11. It is made of glass, The preform for an optical element according to claim 8 .

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