Glass molding mold

Abstract

This invention relates to a glass forming mold. The problem to be solved by this invention is to obtain a glass forming mold with excellent forming performance. The solution is to form a glass forming mold for pressing and forming glass to be formed from glass that meets the following conditions: (1) Young's modulus is above 85 GPa, (2) Glass transition temperature is above 650℃, (3) Average coefficient of thermal expansion between 100℃ and 300℃ is 30 × 10⁻⁶. ‑7 / ℃~80×10 ‑7 / ℃.

Description

Technical Field

[0001] This invention relates to a glass forming mold for pressing glass to be formed. Background Technology

[0002] In the manufacture of optical components such as lenses, the traditional method involves shaping glass into a rough form and then grinding or polishing it. In recent years, a method for manufacturing optical components without grinding or polishing has been put into practical use: pressing softened glass using a molding die (hereinafter referred to as a molding die). By using this molding die, not only can spherical lenses be mass-produced at low cost, but also complex-shaped aspherical lenses can be manufactured.

[0003] In compression molding, the surface shape of the molding die (forming surface) is transferred to the workpiece, thus requiring very high precision from the molding die. For example, the molding die must have high rigidity and heat resistance to prevent deformation due to the load or heating applied during pressing. Furthermore, to prevent the workpiece from adhering to the molding die or from cracking, the molding die must have an appropriate coefficient of thermal expansion relative to the workpiece.

[0004] As materials that meet the above conditions, molding dies made of metal and ceramic are widely used. However, manufacturing such molding dies separately to avoid precision differences during cutting and other processes is costly and time-consuming. In particular, when mass-producing glass lenses for optical instruments, many molding dies are required. As a countermeasure, technologies using glass molding dies have been proposed (for example, Patent Documents 1 to 12).

[0005] Specifically, a master mold with a reference forming surface is prepared, and a forming mold softened by heating is pressed into shape using glass material using the master mold, thereby obtaining a glass forming mold (replica mold) that transfers the forming surface of the master mold. The glass forming mold has the following advantages: once a high-precision master mold is manufactured, mass production is easy, and the degree of freedom in shape setting is high.

[0006] [Existing technical documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 62-226825

[0008] [Patent Document 2] Japanese Patent Application Publication No. 1-239030

[0009] [Patent Document 3] Japanese Patent No. 2616964

[0010] [Patent Document 4] Japanese Patent No. 2723497

[0011] [Patent Document 5] Japanese Patent No. 4832939

[0012] [Patent Document 6] Japanese Patent Application Publication No. 2007-284300

[0013] [Patent Document 7] Japanese Patent Application Publication No. 2006-206394

[0014] [Patent Document 8] Japanese Patent Application Publication No. 2005-97009

[0015] [Patent Document 9] Japanese Patent Application Publication No. 2004-210550

[0016] [Patent Document 10] Japanese Patent Application Publication No. 2008-56540

[0017] [Patent Document 11] Japanese Patent Application Publication No. 2007-254234

[0018] [Patent Document 12] Japanese Patent Application Publication No. 2005-15266 Summary of the Invention

[0019] [The problem the invention aims to solve]

[0020] Even in glass forming molds, conditions such as rigidity, heat resistance, and coefficient of thermal expansion, as described above, are required; however, it is difficult to meet all these conditions at a high level and put them into practical use. In particular, there is a need for a high-performance glass forming mold that possesses excellent forming performance for the glass to be formed, and is also easy to manufacture. Therefore, the object of the present invention is to provide a glass forming mold with excellent forming performance.

[0021] [Solutions to the problem]

[0022] The applicant designed this invention based on the idea that, by satisfying specific conditions, a glass forming mold with practical application capabilities and excellent forming performance can be obtained. Specifically, this invention relates to a glass forming mold for pressing and forming glass to be formed, characterized by being formed from glass that meets the following conditions: (1) Young's modulus above 85 GPa, (2) Glass transition temperature above 650°C, (3) Average coefficient of thermal expansion from 100°C to 300°C is 30 × 10⁻⁶. -7 / ℃ to 80×10 -7 / ℃.

[0023] By satisfying condition (1), the rigidity to withstand the load during the pressing and molding of the glass to be formed can be ensured. By satisfying condition (2), the glass transition temperature of the glass to be formed is higher than that of the material to be formed, such as optical components, which can prevent deformation of the glass forming mold at the forming temperature (the temperature at which the glass to be formed softens). By satisfying condition (3), the effects of preventing the glass to be formed from adhering to the glass forming mold, preventing the glass to be formed from breaking, and preventing the glass material of the forming mold from adhering to the master mold and breaking of the glass material of the forming mold can be obtained. Therefore, by preventing the glass to be formed from adhering and breaking without causing the glass forming mold to deflect, excellent forming results can be obtained.

[0024] When the glass transition temperature of the glass (glass material for forming mold) constituting the glass forming mold is set to Tg(A) and the glass transition temperature of the glass to be formed is set to Tg(B), it is preferable that Tg(A)-Tg(B) is 30°C or higher.

[0025] When the average coefficient of thermal expansion of the glass constituting the glass forming mold (glass material for the forming mold) is set to α(A) at 100℃~300℃, and the average coefficient of thermal expansion of the glass to be formed at 100℃~300℃ is set to α(B), it is preferable that α(A)-α(B) is +20×10 -7 / ℃~-120×10 -7 / ℃.

[0026] This invention is applicable to glass molding molds for pressing and shaping glass to form optical elements.

[0027] [Invention Effects]

[0028] As described above, the present invention provides a glass molding mold with excellent molding performance. Attached Figure Description

[0029] Figure 1 A cross-sectional view of a glass forming apparatus with a glass forming mold.

[0030] Explanation of reference numerals in the attached figures

[0031] 10: Glass forming apparatus

[0032] 11: Upper mold (glass molding mold)

[0033] 12: Lower mold (glass molding mold)

[0034] 13: Guiding Module

[0035] 14: Molded surface

[0036] 15: Molded surface

[0037] 16: Coating layer

[0038] 17: Coating layer

[0039] 20: Lens

[0040] 21: Glass block (glass to be formed). Detailed Implementation Plan

[0041] Figure 1 An example of a glass forming apparatus having a glass forming mold according to the present invention is shown. Figure 1 The glass forming apparatus 10 is manufactured by pressing a lens 20, which is an optical element, from a glass block 21 to be formed, and includes an upper mold 11 and a lower mold 12 as glass forming molds. The upper mold 11 and the lower mold 12 are movably supported in a guide mold 13, and the distance between them can be changed. Both the upper mold 11 and the lower mold 12 can be movable molds, or one can be a movable mold and the other a non-movable fixed mold.

[0042] The upper mold 11 and the lower mold 12 have forming surfaces 14 and 15 on opposite sides. The lens 20 is a biconvex lens with aspherical surfaces on both sides, and the forming surfaces 14 and 15 are concave surfaces (aspherical surfaces) corresponding to the shapes of the respective convex (aspherical) surfaces of the lens 20. That is, the shapes of the forming surfaces 14 and 15 are transferred through forming and form the convex surfaces of the lens 20. In addition, the glass forming mold of the present invention can also be applied to the forming of objects other than biconvex lenses, and the shape of the forming surfaces of the glass forming mold is appropriately set according to the shape of the object to be formed. For example, it can also be applied as an optical element to manufacture lenses or prisms with concave surfaces.

[0043] Coating layers 16 and 17 are formed on the forming surfaces 14 and 15. Coating layers 16 and 17 are made of carbon film or the like and have the effect of inhibiting the fusion (adhesion) of the glass to be formed. Furthermore, although... Figure 1 The coating layers 16 and 17 shown are single-layer structures, but multi-layer structures composed of different compositions can also be provided. Alternatively, a structure can be selected that does not provide coating layers 16 and 17 and exposes the molding surfaces 14 and 15.

[0044] A heater (not shown) is provided on the outside of the guide mold 13. During molding, the heater heats the glass to be molded (glass block 21) to a molding temperature that softens it.

[0045] Although not shown in the diagram, the upper mold 11 and the lower mold 12 are manufactured by pressing and forming using a master mold (mother mold). Master molds are prepared for manufacturing the upper mold 11 and the lower mold 12, respectively. These master molds are formed of metal or the like and have reference molding surfaces that serve as the basis for molding surfaces 14 and 15. The upper mold 11 and the lower mold 12 are formed by pressing a heated and softened molding die material (glass that meets various conditions described later, different from the glass to be molded used for lens 20) onto the reference molding surfaces of each master mold, thereby transferring the reference molding surfaces as molding surfaces 14 and 15.

[0046] Furthermore, the glass molding mold in this invention refers to the portion having a shape transfer surface corresponding to the forming surfaces 14 and 15. For example, the upper mold 11 and lower mold 12, except for the coating layers 16 and 17, can be made entirely of glass. Alternatively, the upper mold 11 and lower mold 12 may consist only of the forming surfaces 14 and 15 as the glass molding mold, and other base portions such as metal (not shown) may be joined to the glass molding mold to form the upper mold 11 and lower mold 12.

[0047] As a result of research and experimentation, the applicant has found that glass that meets the following conditions (1), (2) and (3) is suitable as a glass material for constituting glass forming molds such as upper mold 11 and lower mold 12.

[0048] (1) Young's modulus is above 85 GPa.

[0049] (2) The glass transition temperature (Tg) is above 650℃.

[0050] (3) The average coefficient of thermal expansion (α100-300) from 100℃ to 300℃ is 30×10⁻⁶. -7 / ℃ to 80×10 -7 / ℃.

[0051] Condition (1) relates to the rigidity of the glass forming mold. If the glass forming mold deflects during pressing, the shape of the forming surface cannot be maintained, and the forming accuracy of the glass to be formed is affected. When the Young's modulus is above 85 GPa, even if a predetermined pressure is applied during the forming of the glass to be formed, deflection of the glass forming mold due to load can be prevented, and forming can be carried out without compromising the accuracy of the forming surface.

[0052] Condition (2) relates to the effect of heating during molding on the glass forming mold. By using glass with a glass transition point higher than that of the glass to be molded as the glass material for the forming mold, and setting the temperature lower than the glass transition point of the glass material for the forming mold as the molding temperature, it is possible to soften only the glass to be molded without softening the glass material for the forming mold.

[0053] More specifically, when the glass transition temperature of the glass material used for the molding die is set to Tg(A) and the glass transition temperature of the glass to be molded is set to Tg(B), it is preferable that Tg(A)-Tg(B) ≥ 30°C. Further, it is preferable that Tg(A)-Tg(B) ≥ 50°C, and more preferably that Tg(A)-Tg(B) ≥ 100°C.

[0054] For example, in the glass material for glass molding lenses manufactured by the applicant, the highest glass transition point is 612°C (glass material name M-TAFD305). Therefore, by satisfying condition (2), an effective molding temperature for glass of various optical components can be set while preventing thermal deformation of the glass molding mold.

[0055] Condition (3) is to properly control the difference in thermal expansion coefficients between the glass forming mold and the glass to be formed, so as to prevent adhesion and cracking of the glass to be formed and to achieve good forming. If the thermal expansion coefficient of the glass forming mold is too large for the glass to be formed, the glass to be formed is prone to cracking during forming. In addition, if the difference in thermal expansion coefficients between the glass forming mold and the glass to be formed is too small, the glass to be formed is prone to adhere to the glass forming mold.

[0056] More specifically, when the average coefficient of thermal expansion (100℃~300℃) of the glass material used for the molding die is set as α(A), and the average coefficient of thermal expansion (100℃~300℃) of the glass to be molded is set as α(B), then α(A)-α(B) is +20×10 -7 / ℃~-120×10 -7 / ℃. Further, it is preferred that α(A)-α(B) is +10×10 -7 / ℃~-120×10 -7 / ℃, more preferably α(A)-α(B) is 0×10 -7 / ℃~-100×10 -7 / ℃. The α(B) of the glass material used for glass molding lenses is mostly about 70 × 10⁻⁶. -7 / ℃~90×10 -7 / ℃, by satisfying condition (3), the effect of preventing the glass to be formed from cracking and adhering to the glass forming mold can be obtained.

[0057] Furthermore, condition (3) is also related to the formability of the glass material used in the molding die when pressed into shape using a master mold. As an example, when silicon carbide (SiC) is used as the main material to form the master mold, the average coefficient of thermal expansion of silicon carbide (from 100°C to 300°C) is approximately 40 × 10⁻⁶. -7 / ℃, therefore, by satisfying condition (3), a glass molding die that can be well formed from glass material can be obtained. In particular, by satisfying the lower limit of condition (3), the coefficient of thermal expansion of the master mold will not be relatively large, and it is difficult for the glass molding die to break.

[0058] For example, glass material for molding dies that meets conditions (1), (2) and (3) can be obtained based on the following raw material composition.

[0059] The glass, expressed in mol%, contains:

[0060] 50-75% SiO2,

[0061] 0-5% Al2O3,

[0062] 0-5% ZnO,

[0063] The total amount of Na₂O and K₂O is 3-15%.

[0064] The total content is 14-35% MgO, CaO, SrO and BaO.

[0065] The total content of ZrO2, TiO2, La2O3, Y2O3, Yb2O3, Ta2O5, Nb2O5, and HfO2 is 2-9%.

[0066] The molar ratio {(MgO+CaO) / (MgO+CaO+SrO+BaO)} is in the range of 0.85 to 1, and the molar ratio {Al2O3 / (MgO+CaO)} is in the range of 0 to 0.30.

[0067] <Example>

[0068] In the glass forming apparatus 10, a glass block 21, which is the glass to be formed, is disposed between the forming surfaces 14 and 15 of the upper mold 11 and the lower mold 12, which are glass forming molds. It is heated to the forming temperature by a heater. Tables 1-3 show embodiments and comparative examples of glass forming molds applicable to the present invention. Tables 1-3 show one embodiment in which the upper mold 11 and the lower mold 12 are moved close together, and the lens 20 is formed by pressing 21 with a predetermined pressure. Examples 1 and 2 show the results of forming two types of glass using glass forming molds made of three glass materials, GA, GB, and GC, to which the present invention is applicable.

[0069] • Glass material GA (sample name) for molding dies

[0070] Young's modulus (GPa): 85

[0071] Glass transition temperature (Tg): 682℃

[0072] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 77×10 -7 / ℃

[0073] Specific gravity: 2.96 g / cm³ 3

[0074] • Glass materials for molding dies GB (sample name)

[0075] Young's modulus (GPa): 95

[0076] Glass transition temperature (Tg): 691℃

[0077] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 51×10 -7 / ℃

[0078] Specific gravity: 2.59 g / cm³ 3

[0079] • Glass material GC for molding dies (sample name)

[0080] Young's modulus (GPa): 87

[0081] Glass transition temperature (Tg): 720℃

[0082] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 32×10 -7 / ℃

[0083] Specific gravity: 2.60 g / cm³ 3

[0084] Table 1

[0085]

[0086] Table 2

[0087] Example 1

[0088] Molding result

[0089] Glass to be formed: M-NBFD130

[0090] (Tg: 567℃, α(100-300)74×10 -7 / ℃)

[0091]

[0092]

[0093] ※1 ※2 ※3

[0094] ○ No deformation ○ Suitable shape ○ No cracks

[0095] × Deformation × Poor shape × Crack

[0096] —Unable to form due to mold deformation—Unable to form due to mold deformation

[0097] Table 3

[0098] Example 2

[0099] Molding result

[0100] Glass to be formed: M-BACD5N

[0101] (Tg: 521℃, α(100-300)88×10 -7 / ℃)

[0102]

[0103] ※1 ※2 ※3

[0104] ○ No deformation ○ Suitable shape ○ No cracks

[0105] × Deformation × Poor shape × Crack

[0106] —Unable to form due to mold deformation—Unable to form due to mold deformation <Example 1>

[0107] • Glass to be formed, M-NBFD130 (manufactured by HOYA Co., Ltd.)

[0108] Glass transition temperature (Tg): 567℃

[0109] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 74×10 -7 / ℃

[0110] <Example 2>

[0111] • Glass to be formed M-BACD5N (manufactured by HOYA Co., Ltd.)

[0112] Glass transition temperature (Tg): 521℃

[0113] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 88×10 -7 / ℃

[0114] [Molding Result]

[0115] As shown in Tables 1-3, in each of Examples 1 and 2, in each glass forming mold made of glass materials GA, GB, and GC for forming molds, no harmful deformation occurs during pressing at the forming temperature, the surface shape of the surface to be formed in the glass to be formed is appropriate, no cracking of the glass to be formed occurs, and good forming results are obtained.

[0116] Subsequently, a comparative example is shown, in which the same glass to be formed as in Examples 1 and 2 is formed using a glass forming mold made of a different glass material than that in the examples.

[0117] <Comparative Example 1>

[0118] • Glass material for molding dies: ZnSF8 (Made by Sumida Optical Glass Co., Ltd.)

[0119] Young's modulus (GPa): 87

[0120] Glass transition temperature (Tg): 518℃

[0121] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 60×10 -7 / ℃

[0122] Specific gravity: 3.72 g / cm³ 3

[0123] Japanese Patent Application Publication No. 2004-210550 describes a glass molding mold made of ZnSF8.

[0124] [Molding Result]

[0125] The glass transition temperature of ZnSF8 is lower than that of condition (2) of the present invention. Furthermore, the glass transition temperature of ZnSF8 is lower than that of M-NBFD130 and M-BACD5N, which are the glass to be formed. Moreover, even when forming either M-NBFD130 or M-BACD5N, the deformation of the glass forming mold exceeds the allowable range, resulting in poor forming.

[0126] <Comparative Example 2>

[0127] • Glass material S-BSL7 for molding dies (manufactured by Ohara Co., Ltd.)

[0128] Young's modulus (GPa): 80

[0129] Glass transition temperature (Tg): 576℃

[0130] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 86×10 -7 / ℃

[0131] Specific gravity: 2.52 g / cm³ 3

[0132] Japanese Patent Application Publication No. 2008-56540 describes a glass molding mold made of S-BSL7 material.

[0133] [Molding Result]

[0134] The Young's modulus of S-BSL7 is lower than that of condition (1) of this invention, its glass transition temperature is lower than that of condition (2) of this invention, and its coefficient of thermal expansion exceeds the upper limit of condition (3) of this invention. Furthermore, even when molding either M-NBFD130 or M-BACD5N, the deformation of the glass molding die exceeds the allowable range, resulting in poor molding.

[0135] <Comparative Example 3>

[0136] • Glass material S-BSM14 for molding dies (manufactured by Ohara Co., Ltd.)

[0137] Young's modulus (GPa): 84.9

[0138] Glass transition temperature (Tg): 663℃

[0139] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 73×10 -7 / ℃

[0140] Specific gravity: 3.43 g / cm³ 3

[0141] Japanese Patent Application Publication No. 2007-254234 describes a glass molding mold made of S-BSL14 material.

[0142] [Molding Result]

[0143] The Young's modulus of S-BSL14 is lower than that of the present invention (1). Furthermore, even when molding either M-NBFD130 or M-BACD5N, the surface shape accuracy of the molded surface cannot meet the reference.

[0144] <Comparative Example 4>

[0145] ·Glass material for molding molds NA32SG (manufactured by Atomtronics Co., Ltd.)

[0146] Young's modulus (GPa): 74

[0147] Glass transition temperature (Tg): 705℃

[0148] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 34×10 -7 / ℃

[0149] Specific gravity: 2.41 g / cm³ 3

[0150] [Molding Result]

[0151] The Young's modulus of NA32SG is lower than that of the present invention (1). Furthermore, even when molding either M-NBFD130 or M-BACD5N glass, the surface shape accuracy of the molded surface cannot meet the reference.

[0152] <Comparative Example 5>

[0153] • Glass material GD (sample name) for molding dies

[0154] Young's modulus (GPa): 69

[0155] Glass transition temperature (Tg): 670℃

[0156] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 46×10 -7 / ℃

[0157] [Molding Result]

[0158] The Young's modulus of GD (sample name) is lower than that of the present invention (1). Furthermore, even when molding either M-NBFD130 or M-BACD5N glass, the surface shape accuracy of the molded surface cannot meet the reference.

[0159] <Comparative Example 6>

[0160] • Glass material for molding dies (GE sample name)

[0161] Young's modulus (GPa): 70.2

[0162] Glass transition temperature (Tg): 705℃

[0163] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 37×10 -7 / ℃

[0164] [Molding Result]

[0165] The Young's modulus of GE (sample name) is lower than that of the present invention (1). Furthermore, the glass to be formed will crack even when either M-NBFD130 or M-BACD5N is being formed.

[0166] In addition, the following patent documents describe techniques for obtaining glass molding dies using barium borosilicate glass or borosilicate glass as materials.

[0167] • Barium borosilicate glass (Japanese Patent Application Publication No. 2007-284300, Japanese Patent Application Publication No. 2006-206394)

[0168] Glass transition temperature (Tg): 690℃

[0169] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 64×10 -7 / ℃

[0170] • Barium borosilicate glass (Japanese Patent Application Publication No. 2005-97009)

[0171] Glass transition temperature (Tg): 679℃

[0172] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 55.6 × 10⁻⁶ -7 / ℃

[0173] • Barium borosilicate glass (Japanese Patent Application Publication No. 2005-97009)

[0174] Glass transition temperature (Tg): 679℃

[0175] Average coefficient of thermal expansion (α100-300) between 100℃ and 300℃: 55.6 × 10⁻⁶ -7 / ℃

[0176] • Borosilicate glass (Japanese Patent Application Publication No. 2005-15266)

[0177] Glass transition temperature (Tg): 540℃

[0178] These patent documents do not describe the Young's modulus of barium borosilicate glass or borosilicate glass used as glass materials for forming molds. That is, they do not possess the following technical concept of the present invention: setting conditions for all Young's modulus, glass transition temperature and coefficient of thermal expansion for the glass constituting the glass forming mold to prevent deformation or damage to the glass forming mold and to enable high-precision forming.

[0179] As described above, according to the glass forming mold of the present invention, since the glass forming mold has both high rigidity and heat resistance, it can maintain the surface shape of the forming surface without deformation when pressing and forming the glass to be formed. Furthermore, by appropriately controlling the coefficient of thermal expansion between the glass forming mold and the glass to be formed, adhesion of the glass to be formed to the glass forming mold and breakage of the glass to be formed can be prevented. Therefore, compared with conventional glass materials for forming molds, a glass forming mold with superior forming performance can be obtained.

Claims

1. A glass forming mold, characterized in that, It is a glass forming mold used to press and shape glass to be formed. The glass forming mold is formed from glass that meets the following conditions: 1) Young's modulus above 85 GPa, 2) Glass transition temperature above 650℃ and below 720℃, 3) Average coefficient of thermal expansion of 30×10⁻⁶ between 100℃ and 300℃. -7 / ℃~80×10 -7 / ℃; the highest glass transition point of the glass to be formed is 612℃; The glass used to form the glass molding mold comprises, expressed in mol%,: 50~75% SiO2, 0~5% Al2O3, 0~5% ZnO, The total amount of Na2O and K2O is 3-15%. The total content is 14-35% MgO, CaO, SrO and BaO. The total content is 2-9% of ZrO2, TiO2, La2O3, Y2O3, Yb2O3, Ta2O5, Nb2O5, and HfO2. The molar ratio {(MgO + CaO) / (MgO + CaO + SrO + BaO)} is in the range of 0.85 to 1, and the molar ratio {Al2O3 / (MgO + CaO)} is in the range of 0 to 0.

30.

2. The glass forming mold according to claim 1, wherein, When the glass transition temperature of the glass constituting the glass forming mold is set to Tg(A) and the glass transition temperature of the glass to be formed is set to Tg(B), Tg(A) - Tg(B) is above 30°C.

3. The glass forming mold according to claim 1 or 2, wherein, When the average coefficient of thermal expansion of the glass constituting the glass forming mold is set to α(A) at 100℃~300℃, and the average coefficient of thermal expansion of the glass to be formed at 100℃~300℃ is set to α(B), then α(A)-α(B) is +20×10⁻¹⁰. -7 / ℃~-120×10 -7 / ℃.

4. The glass forming mold according to claim 1 or 2, wherein, The glass to be formed is pressed into shape to form an optical element.

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