Optical glass, preform for precision press molding, and optical element

Abstract

Provided is an optical glass having a high refractive index and low dispersion, a low glass transition temperature, and an ability to suppress temperature dependence of imaging. The optical glass is characterized by having a composition containing, in mass%, SiO2: 1% or more and 15% or less, B2O3: 10% or more and 25% or less, Li2O: 1% or more and 5% or less, CaO: 5% or more and 30% or less, BaO: 10% or less, Nb2O5: 8% or less, ZrO2: 0% or more and 8% or less, TiO2: 8% or less, Y2O3: 10% or less, La2O3: 5% or more and 20% or less, Gd2O3: 15% or less, Ta2O5: 8% or less, and WO3: 8% or less, being substantially free of ZnO, a molar ratio (R / F) of the amounts of the specified components being 0.8 or more and 2.0 or less, and a temperature coefficient of the relative refractive index (40-60°C) being -5.0 x 10 ‑6 °C ‑1 or more and 3.0 x 10 ‑6 °C ‑1 or less.

Description

Technical Field

[0001] This invention relates to optical glass, preforms for precision pressure forming, and optical elements. Background Technology

[0002] With the widespread adoption and development of optical equipment, there has always been a demand for optical glass with various properties. In particular, in recent years, the demand for optical glass that enables miniaturization and high performance in products such as automotive optical equipment and surveillance cameras has further increased.

[0003] In achieving miniaturization and high performance of products, essential elements include the use of high-refractive-index glass (e.g., glass with a refractive index (nd) of 1.70 or higher) and the optical design of aspherical lenses made by precision press molding, etc.

[0004] High-refractive-index glass typically exhibits high wavelength dispersion and is prone to chromatic aberration. Therefore, it is usually necessary to combine it with low-dispersion glass to correct chromatic aberration. However, increasing the number of combined glass elements (lenses) is generally detrimental to miniaturization. Therefore, using optical glass with both high refractive index and low dispersion (refractive index (nd): approximately 1.70–1.80, Abbe number (νd): approximately 40–55) allows for a reduction in the number of lenses and even miniaturization. In other words, there is a demand for such high-refractive-index, low-dispersion optical glass.

[0005] Furthermore, optical glass (lenses) used in projectors and automotive optical devices are exposed to environments with drastic temperature changes, so it is desirable that temperature changes have minimal adverse effects on imaging. In this regard, the change in refractive index of the aforementioned high-refractive-index glass is positively correlated with temperature. Therefore, for such high-refractive-index glass, it is necessary to select glass with a small change in refractive index relative to temperature, or a refractive index change that is negatively correlated with temperature, to minimize the temperature dependence of the refractive index.

[0006] As an optical glass with high refractive index and low dispersion, for example, Patent Document 1 discloses an optical glass having a specified composition of B2O3-La2O3-Gd2O3-ZnO system and having an optical constant with a refractive index (nd) of 1.72 to 1.83 and an Abbe number (νd) in the range of 45 to 55.

[0007] However, the optical glass described in the aforementioned patent document 1 contains a large amount of rare earth element compounds such as La2O3 and B2O3 in order to achieve high refractive index and low dispersion. Even if the glass transition temperature (Tg) is low, it is still at a high temperature of around 580°C, which is not conducive to the production of aspherical lenses by means of precision pressure forming.

[0008] On the other hand, Patent Document 2 discloses an optical glass having a specified composition of SiO2-B2O3-La2O3-Gd2O3-ZnO system and a refractive index (nd) of 1.65 to 1.77, an Abbe number (νd) of 40 to 55, and a glass transition temperature (Tg) of 550°C or less.

[0009] (Existing technical literature)

[0010] (Patent Documents)

[0011] Patent Document 1: Japanese Patent Application Publication No. 2006-315954

[0012] Patent Document 2: Japanese Patent Application Publication No. 2006-111482 Summary of the Invention

[0013] (The problem the invention aims to solve)

[0014] However, the optical glass described in Patent Document 2 contains a large amount of ZnO in order to lower the glass transition temperature (Tg), which poses a risk that the change in refractive index is large in the positive direction and the imaging performance deteriorates significantly with temperature changes.

[0015] Therefore, the present invention was developed in view of the above-mentioned situation, with the aim of providing optical glass with high refractive index and low dispersion, while having a low glass transition temperature and suppressing temperature dependence of imaging. Furthermore, the present invention aims to provide preforms and optical elements for precision pressure forming using the aforementioned optical glass.

[0016] (The measures taken to solve the problem)

[0017] To achieve the aforementioned objective, the inventors conducted extensive research and discovered that by using SiO2, B2O3, Li2O, CaO, and La2O3 as basic components, and by optimizing the molar ratio (R / F) of the contents related to the specified components, it is possible to obtain optical glass with a reduced change in refractive index (n) relative to temperature (T) (temperature coefficient of relative refractive index (dn / dT)) and a low glass transition temperature. Alternatively, it is possible to obtain optical glass with a negative increase that can suppress the temperature dependence of imaging and a low glass transition temperature.

[0018] That is, the optical glass of the present invention is characterized by having a content of, by mass percent

[0019] SiO2: 1% or more and less than 15%

[0020] B2O3: 10% or more but less than 25%

[0021] Li2O: 1% or more but less than 5%

[0022] CaO: 5% or more but less than 30%

[0023] BaO: 0% or more and less than 10%

[0024] Nb2O5: 0% or more and 8% or less

[0025] ZrO2: 0% or more and 8% or less

[0026] TiO2: 0% or more and 8% or less

[0027] Y2O3: 0% or more and 10% or less

[0028] La2O3: 5% or more but less than 20%

[0029] Gd2O3: 0% or more and 15% or less

[0030] Ta2O5: 0% or more and 8% or less

[0031] WO3: 0% or more and 8% or less

[0032] The composition,

[0033] It does not actually contain ZnO.

[0034] If we define the total mol% content of Li₂O, CaO, and BaO as R, and the total mol% content of SiO₂ and B₂O₃ as F, then R / F is above 0.8 and below 2.0.

[0035] The temperature coefficient of the relative refractive index at the d-line (587.562 nm) (40–60 °C) is -5.0 × 10⁻⁵. -6 ℃ -1 Above and 3.0×10 -6 ℃ -1 The optical glass involved has a high refractive index, low dispersion, low glass transition temperature, and can suppress the temperature dependence of imaging.

[0036] Preferably, the optical glass of the present invention has a refractive index (nd) of 1.70 or higher and 1.80 or lower, and an Abbe number (νd) of 40 or higher and 55 or lower.

[0037] The glass transition temperature (Tg) of the optical glass of the present invention is preferably below 560°C.

[0038] The precision pressure forming preform of the present invention is characterized by using the aforementioned optical glass as the material. The precision pressure forming preform is easily precision pressure formed and can be used to obtain products that suppress the temperature dependence of imaging.

[0039] The optical element of the present invention is characterized by using the aforementioned optical glass as a material. Based on the optical element, a product that suppresses the temperature dependence of imaging can be obtained.

[0040] (The effect of the invention)

[0041] According to the present invention, optical glass with high refractive index, low dispersion, low glass transition temperature, and the ability to suppress temperature dependence of imaging can be provided. Furthermore, according to the present invention, precision pressure-molded preforms and optical elements using the aforementioned optical glass can be provided. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the embodiments.

[0043] (Optical glass)

[0044] An optical glass according to one embodiment of the present invention (hereinafter, there may be a case referred to as "the optical glass of this embodiment") is characterized by having a content of, by mass%, %

[0045] SiO2: 1% or more and less than 15%

[0046] B2O3: 10% or more but less than 25%

[0047] Li2O: 1% or more but less than 5%

[0048] CaO: 5% or more but less than 30%

[0049] BaO: 0% or more and less than 10%

[0050] Nb2O5: 0% or more and 8% or less

[0051] ZrO2: 0% or more and 8% or less

[0052] TiO2: 0% or more and 8% or less

[0053] Y2O3: 0% or more and 10% or less

[0054] La2O3: 5% or more but less than 20%

[0055] Gd2O3: 0% or more and 15% or less

[0056] Ta2O5: 0% or more and 8% or less

[0057] WO3: 0% or more and 8% or less

[0058] The composition,

[0059] It does not actually contain ZnO.

[0060] If the total mol% content of Li₂O, CaO, and BaO is set as R, and the total mol% content of SiO₂ and B₂O₃ is set as F, then R / F is above 0.8 and below 2.0.

[0061] The temperature coefficient of the relative refractive index at the d-line (587.562 nm) (40–60 °C) is -5.0 × 10⁻⁵. -6 ℃ -1 Above and 3.0×10 -6 ℃ -1 the following.

[0062] In addition to the aforementioned components (SiO2, B2O3, Li2O, CaO, BaO, Nb2O5, ZrO2, TiO2, Y2O3, La2O3, Gd2O3, Ta2O5, WO3), the optical glass of this embodiment may also contain other components (described later). However, from the viewpoint of reliably exhibiting the desired optical constants, a reduction in glass transition temperature, and suppression of temperature dependence of imaging, the content of these other components in the optical glass of this embodiment is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. Furthermore, the optical glass of this embodiment is particularly preferably composed of only the aforementioned components.

[0063] The phrase "consisting solely of the above-mentioned components" includes cases where impurities other than those components are unavoidably mixed in, specifically including cases where the proportion of impurity components is less than 0.2% by mass.

[0064] First, the reasons for limiting the composition of the optical glass to the above-mentioned range in this embodiment will be explained. Furthermore, unless otherwise specified, the "%" designation related to composition refers to mass % (but regarding R / F, mole % is used).

[0065] <sio2>

[0066] SiO2 is an essential component in the optical glass of this embodiment, forming the network structure that constitutes the glass framework. Furthermore, SiO2 can improve devitrification resistance and chemical durability. However, if the SiO2 content in the optical glass exceeds 15%, the refractive index decreases excessively. Moreover, if the SiO2 content in the optical glass exceeds 15%, there is a risk of an excessive increase in the glass transition temperature (Tg) and yield temperature (At). On the other hand, if the SiO2 content in the optical glass is less than 1%, it is difficult to form glass. Therefore, in the optical glass of this embodiment, the SiO2 content is set to a range of 1% or more and 15% or less. From the same viewpoint, the SiO2 content in the optical glass of this embodiment is preferably 2% or more, more preferably 3% or more, and preferably 14% or less, more preferably 13% or less.

[0067] <b2o3>

[0068] B2O3 is an essential component in the optical glass of this embodiment, forming the network structure of the glass. Furthermore, B2O3 is effective in improving devitrification resistance, glass homogenization, and melt flowability. However, if the B2O3 content in the optical glass exceeds 25%, the refractive index decreases excessively. Additionally, if the B2O3 content in the optical glass exceeds 25%, there is a risk of an excessive increase in the glass transition temperature (Tg) and yield temperature (At). On the other hand, if the B2O3 content in the optical glass is less than 10%, it is difficult to form glass. Therefore, in the optical glass of this embodiment, the B2O3 content is set to a range of 10% or more and 25% or less. From the same viewpoint, the B2O3 content in the optical glass of this embodiment is preferably 11% or more, more preferably 12% or more, and preferably 24% or less, more preferably 23% or less.

[0069] <li2o>

[0070] Li₂O is an essential component in the optical glass of this embodiment, and it is effective in reducing the glass transition temperature (Tg), yield temperature (At), and temperature coefficient of relative refractive index. However, if the Li₂O content in the optical glass exceeds 5%, chemical durability and devitrification resistance decrease. On the other hand, if the Li₂O content in the optical glass is less than 1%, the glass transition temperature (Tg) cannot be sufficiently reduced. Furthermore, if the Li₂O content in the optical glass is less than 1%, there is a risk that the effect of sufficiently reducing the temperature coefficient of relative refractive index cannot be obtained. Therefore, in the optical glass of this embodiment, the Li₂O content is set to a range of 1% or more and 5% or less. From the same viewpoint, the Li₂O content in the optical glass of this embodiment is preferably 1.5% or more, more preferably 2% or more, and preferably 4.5% or less, more preferably 4% or less.

[0071] <cao>

[0072] CaO is an essential component in the optical glass of this embodiment, and it is effective in reducing the temperature coefficient of relative refractive index and achieving a high refractive index. However, if the CaO content in the optical glass exceeds 30%, chemical durability and devitrification resistance decrease. On the other hand, if the CaO content in the optical glass is less than 5%, devitrification resistance decreases. Furthermore, if the CaO content in the optical glass is less than 5%, there is a risk that the effect of sufficiently reducing the temperature coefficient of relative refractive index cannot be obtained. Therefore, in the optical glass of this embodiment, the CaO content is set to a range of 5% or more and 30% or less. From the same viewpoint, the CaO content in the optical glass of this embodiment is preferably 7% or more, more preferably 9% or more, and preferably 28% or less, more preferably 26% or less.

[0073] <bao>

[0074] BaO is an effective component for reducing the temperature coefficient of relative refractive index. Furthermore, BaO is also effective in achieving high refractive index and improving melt flowability. However, if the BaO content in the optical glass exceeds 10%, chemical durability and devitrification resistance decrease. Therefore, in the optical glass of this embodiment, the BaO content is set to a range of 0% or more and 10% or less. From the same viewpoint, the BaO content in the optical glass of this embodiment is preferably 9% or less, more preferably 8% or less.

[0075] <nb2o5>

[0076] Nb₂O₅ is an effective component for improving the refractive index and chemical durability of glass. However, if the Nb₂O₅ content in the optical glass exceeds 8%, an undesirable increase in refractive index or dispersion (a decrease in Abbe number) may occur. Therefore, in the optical glass of this embodiment, the Nb₂O₅ content is set to a range of 0% or more and 8% or less. From the same viewpoint, the Nb₂O₅ content in the optical glass of this embodiment is preferably 7.5% or less, more preferably 7% or less.

[0077] <zro2>

[0078] ZrO2 is an effective component for improving the refractive index and chemical durability of glass. However, if the ZrO2 content in optical glass exceeds 8%, it may reduce devitrification resistance and, moreover, cause an undesirable increase in refractive index or dispersion (a decrease in Abbe number). Therefore, in the optical glass of this embodiment, the ZrO2 content is set to a range of 0% or more and 8% or less. From the same viewpoint, the ZrO2 content in the optical glass of this embodiment is preferably 7.5% or less, and more preferably 7% or less.

[0079] <tio2>

[0080] TiO2 is an effective component for improving the refractive index and chemical durability of glass. However, if the TiO2 content in optical glass exceeds 8%, it may reduce devitrification resistance and, moreover, cause an undesirable increase in refractive index or dispersion (a decrease in Abbe number). Therefore, in the optical glass of this embodiment, the TiO2 content is set to a range of 0% or more and 8% or less. From the same viewpoint, the TiO2 content in the optical glass of this embodiment is preferably 7.5% or less, more preferably 7% or less.

[0081] <y2o3>

[0082] Y₂O₃ is an effective component in improving the refractive index and chemical durability of glass. However, if the Y₂O₃ content in the optical glass exceeds 10%, the devitrification resistance decreases. Therefore, in the optical glass of this embodiment, the Y₂O₃ content is set to a range of 0% or more and 10% or less. From the same viewpoint, the Y₂O₃ content in the optical glass of this embodiment is preferably 9.5% or less, more preferably 9% or less.

[0083] <la2o3>

[0084] La2O3 is an essential component in the optical glass of this embodiment, and is useful in adjusting the optical constants (refractive index and Abbe number) desired by the present invention. Furthermore, La2O3 is also effective in improving chemical durability and reducing the temperature coefficient of relative refractive index. However, if the La2O3 content in the optical glass exceeds 20%, the devitrification resistance decreases. On the other hand, if the La2O3 content in the optical glass is less than 5%, the refractive index cannot be sufficiently improved, or even if the amounts of other components are adjusted to a specified range, it is extremely difficult to obtain the desired optical constants. Therefore, in the optical glass of this embodiment, the La2O3 content is set to a range of 5% or more and 20% or less. From the same viewpoint, the La2O3 content in the optical glass of this embodiment is preferably 7% or more, more preferably 9% or more, and preferably 19% or less, more preferably 18% or less.

[0085] <gd2o3>

[0086] Gd₂O₃ is an effective component in improving the refractive index of glass, reducing dispersion, enhancing chemical durability, and lowering the temperature coefficient of relative refractive index. However, if the Gd₂O₃ content in the optical glass exceeds 15%, devitrification resistance decreases. Therefore, in the optical glass of this embodiment, the Gd₂O₃ content is set to a range of 0% or more and 15% or less. From the same viewpoint, the Gd₂O₃ content in the optical glass of this embodiment is preferably 14% or less, and more preferably 13% or less.

[0087] <ta2o5>

[0088] Ta₂O₅ is an effective component for improving the refractive index and chemical durability of glass. However, if the Ta₂O₅ content in optical glass exceeds 8%, it may reduce devitrification resistance and, moreover, cause an undesirable increase in dispersion (a decrease in the Abbe number). Therefore, in the optical glass of this embodiment, the Ta₂O₅ content is set to a range of 0% or more and 8% or less. From the same viewpoint, the Ta₂O₅ content in the optical glass of this embodiment is preferably 7.5% or less, and more preferably 7% or less.

[0089] <wo3>

[0090] WO₃ is an effective component for improving the refractive index and chemical durability of glass. However, when the content of WO₃ in optical glass exceeds 8%, it may reduce the devitrification resistance, and additionally cause an undesired increase in dispersion (a decrease in Abbe number). Therefore, in the optical glass of the present embodiment, the content of WO₃ is set in the range of 0% or more and 8% or less. From the same viewpoint, the content of WO₃ in the optical glass of the present embodiment is preferably 7.5% or less, and more preferably 7% or less.

[0091] <R / F (molar ratio)>

[0092] In the optical glass of the present embodiment, when R represents the total content in mole percent of Li₂O, CaO and BaO, and F represents the total content in mole percent of SiO₂ and B₂O₃, R / F is required to be 0.8 or more and 2.0 or less. The inventors have found that by limiting the contents of respective components of metal ions such as Li, Ca and Ba and optimizing R / F (molar ratio), an optical glass having a low glass transition temperature (Tg) can be obtained while reducing the usage amounts of rare-earth element-containing La₂O₃, Gd₂O₃ and Y₂O₃ and lowering the temperature coefficient of relative refractive index. Furthermore, if R / F exceeds 2.0, the devitrification resistance of the glass decreases, and high-quality glass cannot be obtained.

[0093] Furthermore, from the viewpoint of further reducing the temperature coefficient of relative refractive index and the glass transition temperature, R / F in the optical glass of the present embodiment is preferably more than 0.9, and more preferably 1.0 or more.

[0094] <ZnO (Excluded component)>

[0095] ZnO can reduce the glass transition temperature (Tg) and the yield temperature (At), but in optical glass containing the aforementioned components, there is a risk that the temperature coefficient of relative refractive index cannot be suppressed within a predetermined range. Therefore, the optical glass of the present embodiment is substantially free of ZnO.

[0096] Herein, in the present specification, the expression "substantially free of" a certain component means that the component is not intentionally included.

[0097] <Other components>

[0098] Without departing from the object of the present invention, the optical glass of the present embodiment may contain other components in addition to the aforementioned components in a small amount (for example, an amount where the total of the following other components is 5 mass% or less in the optical glass), such as Na₂O, K₂O, Cs₂O, MgO, SrO, Al₂O₃, Ga₂O₃, In₂O₃, GeO₂, Sb₂O₃, Bi₂O₃, P₂O₅, MoO₃, etc.

[0099] Furthermore, the optical glass of this embodiment preferably does not contain components that are highly environmentally burdensome and have significant adverse effects on the human body, such as PbO, TeO2, As2O3, and CdO.

[0100] Next, the various properties of the optical glass in this embodiment will be explained.

[0101] <Refractive index (nd) and Abbe number (νd)>

[0102] To meet specific requirements, the optical glass in this embodiment preferably has a high refractive index and low dispersion.

[0103] More specifically, the refractive index (nd) of the optical glass in this embodiment can be 1.70 or higher and 1.80 or lower. Furthermore, the refractive index (nd) of the optical glass in this embodiment is preferably 1.71 or higher, and more preferably 1.79 or lower.

[0104] More specifically, the Abbe number (νd) of the optical glass in this embodiment can be 40 or higher and 50 or lower. Furthermore, the Abbe number (νd) of the optical glass in this embodiment is preferably 41 or higher, more preferably 42 or higher, and preferably 53 or lower, more preferably 50 or lower.

[0105] Furthermore, for example, the refractive index (nd) and Abbe number (νd) of the optical glass of this embodiment can be adjusted by appropriately adjusting the content of each of the above components within a specified range.

[0106] <Temperature coefficient of relative refractive index (dn / dT)>

[0107] The optical glass in this embodiment requires a temperature coefficient (40–60°C) of relative refractive index at the d-line (587.562 nm) of -5.0 × 10⁻⁶. -6 ℃ -1 Above and 3.0×10 -6 ℃ -1 Therefore, the temperature dependence of the imaging of the optical glass in this embodiment is suppressed. Specifically, if the composition of the optical glass is as described above while the temperature coefficient is less than -5.0 × 10⁻⁶, then... -6 ℃ -1 If the temperature coefficient of the optical glass exceeds 3.0 × 10⁻⁶, then the minimum chemical durability required for optical glass cannot be guaranteed. Furthermore, if the aforementioned temperature coefficient of the optical glass exceeds 3.0 × 10⁻⁶... -6 ℃ -1 If the refractive index changes positively with temperature, then the temperature dependence of the imaging cannot be sufficiently suppressed. Furthermore, from the viewpoint of improving chemical durability, the aforementioned temperature coefficient of the optical glass in this embodiment is preferably -4.0 × 10⁻⁶. -6 ℃ -1 The above is more preferably at -3.5×10 -6 ℃ -1 That's all. Furthermore, from the viewpoint of more effectively suppressing the temperature dependence of imaging, the temperature coefficient of the optical glass in this embodiment is preferably 2.7 × 10⁻⁶. -6 ℃ -1 Below, 2.5 × 10 is more preferred. -6 ℃ -1 the following.

[0108] Furthermore, for example, the temperature coefficient of the optical glass of this embodiment can be adjusted by appropriately adjusting the content of each of the above components within a specified range.

[0109] Glass transition temperature (Tg)

[0110] The glass transition temperature (Tg) of the optical glass in this embodiment is preferably below 560°C. By keeping the glass transition temperature (Tg) of the optical glass below 560°C, the softening temperature can also be reduced, making it easier to perform precision pressure forming. In particular, it is easier to manufacture aspherical lenses using precision pressure forming. From the same viewpoint, the glass transition temperature (Tg) of the optical glass in this embodiment is preferably below 555°C, and more preferably below 550°C.

[0111] Furthermore, for example, the glass transition temperature (Tg) of the optical glass of this embodiment can be adjusted by appropriately adjusting the content of each of the above components within a specified range.

[0112] <Methods for Manufacturing Optical Glass>

[0113] Next, the method for manufacturing the optical glass of this embodiment will be described.

[0114] In this embodiment, the optical glass can be manufactured as long as the composition of each component meets the above range. There are no special restrictions on its manufacturing method, and it can be manufactured according to existing manufacturing methods.

[0115] For example, firstly, as raw materials that may contain various components of the optical glass of this embodiment, oxides, hydroxides, carbonates, nitrates, etc., are weighed in a prescribed ratio and thoroughly mixed, and the resulting mixture is used as a glass blending raw material. Then, this raw material is placed in a melting container (e.g., a crucible made of a precious metal such as platinum) that is not reactive with the glass raw material and is heated to 1000–1500°C in an electric furnace to melt it. Then, it is stirred in a timely manner to achieve homogenization, and after clarification, it is poured into a mold preheated to an appropriate temperature. Then, it is slowly cooled in an electric furnace to remove strain, thereby manufacturing the optical glass of this embodiment. Furthermore, to defoam, a small amount (e.g., less than 2% by mass in the optical glass) of a clarifying agent such as Sb₂O₃ can be added.

[0116] (Preformed parts for precision pressure forming)

[0117] Hereinafter, a precision pressure forming preform (hereinafter referred to as "the preform of this embodiment") according to one embodiment of the present invention will be specifically described.

[0118] Precision press-molding preforms are glass materials preformed for use in known precision press-molding methods; that is, they refer to glass preforms that are heated and precisely press-molded.

[0119] As is well known, precision pressure forming, also known as mold optics forming, is a method of forming the optical functional surfaces of the final optical element by transferring the forming surface of a pressure forming mold. Furthermore, an optical functional surface refers to the surface of an optical element that refracts, reflects, diffracts, incident, or exits light from a controlled object; for example, the lens surface in a lens corresponds to this optical functional surface.

[0120] Furthermore, the preform of this embodiment is characterized by using the aforementioned optical glass as the material. Thus, since the preform of this embodiment is made of the aforementioned optical glass, it is easy to perform precision pressure molding, and can be used to obtain products that suppress the temperature dependence of imaging.

[0121] Furthermore, from the viewpoint of more reliably obtaining the desired performance, the preform of this embodiment preferably satisfies the necessary conditions related to the composition of each component as described for the optical glass of the present invention, and more preferably satisfies the various preferred conditions described for the optical glass of the present invention.

[0122] The method for manufacturing the preform of this embodiment is not particularly limited. However, it is preferable to utilize the excellent properties of the optical glass described above and manufacture the preform of this embodiment using the following method.

[0123] The first preform manufacturing method (referred to as "preform manufacturing method I") is as follows: melt optical glass as the material, allow the resulting molten glass to flow out and separate into molten glass blocks, and form a preform during the cooling process of the molten glass blocks.

[0124] The second preform manufacturing method (referred to as "Preform Manufacturing Method II") is as follows: optical glass as the material is melted, the resulting molten glass is shaped to form a glass molded body, and the molded body is processed to obtain a preform.

[0125] The common feature of preform manufacturing methods I and II is that they include a step of obtaining homogeneous molten glass from optical glass as the material. In this step, for example, optical glass raw materials, prepared by blending in a manner that yields desired properties, can be placed in a platinum melting vessel, heated, melted, clarified, and homogenized to prepare homogenized molten glass, which then flows out from a platinum or platinum alloy outlet nozzle or pipe after temperature adjustment. Alternatively, optical glass raw materials can be roughly melted to produce cullets, which can then be blended, heated, melted, clarified, and homogenized to obtain homogeneous molten glass, which then flows out from the aforementioned outlet nozzle or pipe.

[0126] In the production of small preforms or spherical preforms, for example, molten glass can be dripped from an outlet nozzle in the form of droplets of molten glass of desired mass, and the dripping droplets can be caught by a mold or the like to form a preform. Alternatively, a method can be used to drip molten glass of the same desired mass from an outlet nozzle onto liquid nitrogen or the like to form a preform.

[0127] On the other hand, in the case of manufacturing medium to large preforms, for example, a method can be adopted in which molten glass flows out from an outlet pipe, the front end of the molten glass flow is received by a preform forming mold, a neck is formed between the nozzle of the molten glass flow and the preform forming mold, and the preform forming mold is rapidly lowered directly downwards, thereby separating the molten glass flow at the neck by the surface tension of the molten glass, and a block of molten glass of the desired quality is received at the receiving part to form a preform.

[0128] In addition, in order to obtain a preform with a smooth surface, such as a free surface, free from scratches, dirt, wrinkles, and surface deterioration, a method is used to form a preform by applying air pressure to make the molten glass block float on a preform forming mold, or by dropping molten glass into a medium such as liquid nitrogen, which cools into a liquid at room temperature and pressure.

[0129] In this process, when a molten glass block is floated and simultaneously molded into a preform, a gas (called a floating gas) is blown onto the molten glass block, applying upward air pressure. If the viscosity of the molten glass block is too low, the floating gas may enter the glass and remain in the preform as bubbles. However, by setting the viscosity of the molten glass block to 3–60 dPa·s, the glass block can be floated without the floating gas entering the glass.

[0130] The gas used to blow the buoyancy gas toward the preform can be, for example, air, N2 gas, O2 gas, Ar gas, He gas, or water vapor. Furthermore, there are no particular restrictions on the air pressure, as long as it allows the preform to float without contacting the surface of the molding die or other solids.

[0131] Precision pressure-molded articles (e.g., optical elements) manufactured from preforms often have an axis of rotational symmetry, much like lenses; therefore, the shape of the preform is also preferably an axis of rotational symmetry. As a specific example, a sphere or a shape having an axis of rotational symmetry can be shown. As a shape having an axis of rotational symmetry, there are shapes with smooth, concave contours without corners in a cross-section containing the axis of rotational symmetry, such as shapes with an ellipse whose minor axis coincides with the axis of rotational symmetry in the aforementioned cross-section as the contour. An example is a shape obtained by flattening a sphere (a shape obtained by defining an axis passing through the center of the sphere and compressing the dimensions along the direction of said axis).

[0132] In preform manufacturing method I, optical glass is formed in a temperature range where plastic deformation is possible, so a preform can be obtained by pressure forming the glass block. In this case, the shape of the preform can be set more freely, so the shape of the preform can approximate the shape of the target precision pressure-formed article. For example, one of the opposing surfaces can be convex and the other concave, both surfaces can be concave, one surface can be flat and the other convex, one surface can be flat and the other concave, or both surfaces can be convex.

[0133] In preform manufacturing method II, for example, after molten glass is poured into a mold to form a shape, the strain of the formed body can be removed by annealing, and it can be cut or slit to divide it into a specified size and shape, thereby producing multiple glass sheets. The surface of the glass sheets is then ground to make it smooth, thus obtaining a preform made of glass of a specified quality. Preferably, a carbon-containing film is also coated on the surface of the preform thus produced for use. Preform manufacturing method II is suitable for manufacturing spherical preforms, flat preforms, etc., that can be easily ground and polished.

[0134] Then, from the viewpoint of further improving the mass production of molded products such as optical elements formed by precision pressure molding, a more preferred preform will be explained.

[0135] In the manufacturing of the preform in this embodiment, by reducing the amount of glass deformation during precision pressure forming, the temperature of the glass and the forming mold during precision pressure forming is reduced, the time required for pressure forming is shortened, and the pressing pressure is reduced. As a result, the reactivity between the glass and the forming surface of the forming mold is reduced, problems arising during precision pressure forming are reduced, and mass production is further improved.

[0136] In the case of manufacturing lenses by precision pressure forming of a preform, a preferred preform is one having extruded surfaces (surfaces pressed by opposing mold surfaces during precision pressure forming) facing opposite directions. More preferably, a preform has a rotational symmetry axis passing through the center of the two extruded surfaces. Among such preforms, those suitable for precision pressure forming of meniscus lenses are preforms where one extruded surface is convex, and the other is concave, flat, or a convex surface with a curvature smaller than that of the convex surface.

[0137] Furthermore, the preform suitable for precision pressure forming of biconcave lenses is a preform in which one of the extruded surfaces is any one of a convex surface, a concave surface, or a plane, and the other surface is any one of a convex surface, a concave surface, or a plane.

[0138] On the other hand, the preform suitable for precision pressure forming of biconvex lenses is a preform where one of the extruded surfaces is convex and the other is either convex or flat.

[0139] In either case, the preform is preferably one whose shape is closer to that of a precision pressure-molded part.

[0140] Furthermore, when using a preform forming mold to shape molten glass into a preform, the lower surface of the glass on the mold is largely determined by the shape of the forming surface of the mold. On the other hand, the upper surface of the glass takes on a shape determined by the surface tension of the molten glass and the weight of the glass itself. In order to reduce the amount of glass deformation during precision pressure forming, it is also necessary to control the shape of the upper surface of the glass being formed in the preform forming mold. The shape of the upper surface of the glass, determined by the surface tension of the molten glass and the weight of the glass, is a convex free surface. However, to make the upper surface flat, concave, or convex with a curvature smaller than the free surface, pressure can be applied to the upper surface of the glass. Specifically, pressure can be applied to the upper surface of the glass using a mold with a forming surface of the desired shape, or air pressure can be applied to the upper surface of the glass to shape it into the desired shape. Furthermore, when applying pressure to the upper surface of the glass using a mold, multiple gas outlets can be provided on the forming surface of the mold, from which gas is ejected to form an air cushion between the forming surface and the upper surface of the glass, and pressure can be applied to the upper surface of the glass using this air cushion. Alternatively, if it is desired to shape the upper surface of the glass into a surface with a curvature greater than that of the free surface mentioned above, it can be shaped by generating negative pressure near the upper surface of the glass to bulge the upper surface of the glass.

[0141] Furthermore, the preform is designed to more closely resemble the shape of a precision pressure-molded article; therefore, the preform is preferably a preform with a ground surface. For example, it is preferable to grind a preform such that one of the extruded surfaces is a plane or part of a sphere, while the other is a part of a sphere or a plane. The part of the sphere can be convex or concave, but it is preferable that, as described above, it is convex or concave depending on the shape of the precision pressure-molded article.

[0142] The aforementioned preforms are preferably used for molding lenses with a diameter of 10 mm or more, and more preferably for molding lenses with a diameter of 20 mm or more. Furthermore, they are also preferably used for molding lenses with a center wall thickness exceeding 2 mm.

[0143] (Optical components)

[0144] Hereinafter, an optical element according to one embodiment of the present invention will be specifically described (hereinafter, there are cases referred to as "the optical element of this embodiment").

[0145] The optical element of this embodiment is characterized by using the aforementioned optical glass as a material. Thus, according to the optical element of this embodiment, since the aforementioned optical glass is used as a material, a product that suppresses the temperature dependence of imaging can be obtained. Furthermore, from the viewpoint of more reliably obtaining the desired performance, the optical element of this embodiment preferably satisfies the necessary conditions related to the composition of each component as described for the optical glass of this embodiment, and more preferably satisfies the various preferred conditions described for the optical glass of this embodiment.

[0146] Furthermore, the optical element in this embodiment includes an optical element that uses the aforementioned precision pressure forming preform.

[0147] The types of optical elements are not limited, but typical examples include: aspherical lenses, spherical lenses or plano-concave lenses, plano-convex lenses, biconcave lenses, biconvex lenses, positive meniscus lenses, negative meniscus lenses, etc.; microlenses; lens arrays; lenses with diffraction gratings; prisms; prisms with lens functions, etc. Preferably, as optical elements, examples include: positive meniscus lenses, negative meniscus lenses, biconvex lenses, biconcave lenses, plano-convex lenses, plano-concave lenses, etc.; prisms; diffraction gratings. The above-mentioned lenses can be aspherical lenses or spherical lenses. Anti-reflective coatings, wavelength-selective partial reflective coatings, etc., can also be provided on the surface as needed.

[0148] <Methods for Manufacturing Optical Components>

[0149] Next, the manufacturing method of the optical element of this embodiment will be described.

[0150] For example, by using a pressure forming mold to precisely pressure form the preform described above, the optical element of this embodiment can be manufactured.

[0151] In precision pressure forming, a pressure forming mold with a pre-machined forming surface of high precision into the desired shape can be used. Alternatively, a release film can be formed on the forming surface to prevent glass fusion during extrusion while ensuring good glass extension along the forming surface. Examples of release films include those made of noble metals (platinum, platinum alloys), oxides (oxides of Si, Al, Zr, Y, etc.), nitrides (nitrides of B, Si, Al, etc.), and carbon-containing films. Preferably, carbon-containing films are those with carbon as the main component (films where the carbon content is higher than other elements when expressed as atomic percent). Examples include carbon films and hydrocarbon films. Methods for forming carbon-containing films include known methods such as vacuum evaporation, sputtering, and ion plating using carbon raw materials, and known methods such as pyrolysis using hydrocarbon gases. Other films can be formed using methods such as evaporation, sputtering, ion plating, and sol-gel methods.

[0152] Furthermore, to prevent oxidation of the molding surface of the pressure forming die or the release film suitably disposed on the molding surface, the heating of the pressure forming die and the precision pressure forming process of the preform are preferably performed in a non-oxidizing gas atmosphere, such as nitrogen or a mixture of nitrogen and hydrogen. In a non-oxidizing gas atmosphere, the release film covering the surface of the preform, especially the carbon-containing film, will not be oxidized, and this film remains on the surface of the precision pressure-formed article. This film should eventually be removed, and the carbon-containing film and other release films can be removed more easily and completely by heating the precision pressure-formed article in an oxidizing atmosphere, such as air. The removal of the carbon-containing film and other release films should be performed at a temperature at which the precision pressure-formed article will not deform due to heating. Specifically, it is preferable to remove the carbon-containing film and other release films in a temperature range below the glass transition temperature.

[0153] Furthermore, the manufacturing method of the optical element in this embodiment is not particularly limited, and two manufacturing methods are described below as examples. Here, in the manufacturing of the optical element in this embodiment, from the viewpoint of mass-producing optical elements, it is preferable to repeatedly perform the process of precision pressure forming the above-mentioned precision pressure forming preform using the same pressure forming mold.

[0154] The first optical element manufacturing method (referred to as "optical element manufacturing method I") is as follows: a preform is introduced into a pressure forming mold, and the preform and the pressure forming mold are heated together to perform precision pressure forming, thereby obtaining an optical element.

[0155] The second optical element manufacturing method (referred to as "Optical Element Manufacturing Method II") is as follows: The heated preform is introduced into the preheated pressure forming mold and precision pressure forming is performed to obtain the optical element.

[0156] In optical element manufacturing method I, after the preform is fed between a pair of opposing upper and lower dies whose forming surfaces have been precisely shaped, both the forming dies and the preform are heated until their viscosity with glass reaches 10. 5 ~10 9 The preform is softened at a temperature equivalent to dPa·s, and then pressure-formed by applying pressure to the preform, thereby precisely transferring the forming surface of the molding die onto the glass. Optical element manufacturing method I is a recommended method when improving forming accuracy, such as surface accuracy and eccentricity accuracy, is of paramount importance.

[0157] In optical element manufacturing method II, the material is preheated to a viscosity of 10 with the glass. 4 ~10 8 A preform at a temperature equivalent to dPa·s is supplied between a pair of opposing upper and lower dies whose forming surfaces have been precisely shaped, and the preform is then pressurized to form the glass, thereby precisely transferring the forming surface of the die onto the glass. Optical element manufacturing method II is a recommended method when increasing productivity is a priority.

[0158] The pressure and time during pressurization can be appropriately determined by considering factors such as the viscosity of the glass. For example, the pressure can be set to approximately 5–15 MPa, and the pressurization time to 10–30 seconds. The extrusion conditions, such as the pressurization time and pressure, can be appropriately set within a known range according to the shape and size of the molded product.

[0159] Then, the mold and the precision pressure-molded part are cooled, preferably demolded and removed when cooled to a temperature below the strain point. Furthermore, in order to precisely adjust the optical properties to the desired values, the annealing conditions of the molded part during cooling can be appropriately adjusted, such as adjusting the annealing speed.

[0160] Alternatively, the optical element of this embodiment can be manufactured without a pressure forming process. For example, homogeneous molten glass is poured into a mold to form a glass block. While annealing the glass block to remove strain, the annealing conditions are adjusted to make the refractive index of the glass reach a desired value, thereby adjusting the optical properties. Then, the glass block is cut or diced to produce a glass sheet, which is then ground and polished to obtain an optical element.

[0161] Example

[0162] The present invention will be specifically described below with examples and comparative examples, but the present invention is not limited to these examples.

[0163] Each corresponding oxide, hydroxide, carbonate, and nitrate was prepared as a raw material, weighed to obtain the vitrified composition as shown in Tables 1 to 4, and thoroughly mixed to obtain a blended raw material. This blended raw material was placed in a platinum crucible and melted in an electric furnace. Furthermore, to effectively defoam, the melting temperature was appropriately adjusted within the range of 1000–1500°C. Then, it was stirred in a timely manner to achieve homogenization, and after clarification, it was poured into a mold preheated to an appropriate temperature. Then, it was slowly cooled in an electric furnace, thereby obtaining the optical glass of each example.

[0164] Subsequently, for each example of optical glass, the devitrification resistance, refractive index (nd), Abbe number (νd), glass transition temperature (Tg), and temperature coefficient of relative refractive index (dn / dT) were evaluated in the following order. The results are shown in Tables 1-4.

[0165] As an evaluation of devitrification resistance, the glass is visually evaluated after slow cooling. No devitrification is identified as "A", and devitrification is identified as "B".

[0166] Furthermore, cases rated "B" for devitrification resistance are considered to be of poor quality and will not be subject to further testing.

[0167] The refractive index (nd) and Abbe number (νd) were determined according to the method described in the Japan Optical Glass Manufacturers Association standard JOGIS01-2003 "Method for determination of refractive index of optical glass".

[0168] The glass transition temperature (Tg) was determined according to the method described in the Japan Optical Glass Manufacturers Association standard JOGIS08-2003 "Method for Determination of Thermal Expansion of Optical Glass".

[0169] The temperature coefficient of relative refractive index (dn / dT) was determined according to the method described in the Japan Optical Glass Manufacturers Association standard JOGIS18-1994 "Method for determination of temperature coefficient of refractive index of optical glass", using the d-line (587.562 nm) in a temperature range of 40 to 60 °C.

[0170] [Table 1]

[0171]

[0172] [Table 2]

[0173]

[0174] [Table 3]

[0175]

[0176] [Table 4]

[0177]

[0178] As shown in Tables 1 and 2, the refractive index (nd) of the optical glasses in Examples 1 to 21 is all above 1.70 and below 1.80, and the Abbe number (νd) is all above 40 and below 55, that is, they have high refractive index and low dispersion. Furthermore, the temperature coefficient of the relative refractive index of the optical glasses in Examples 1 to 21 is all below -5.0 × 10⁻⁶. -6 ℃ -1 Above and 3.0×10 -6 ℃ -1 The temperature dependence of the imaging was significantly suppressed.

[0179] Furthermore, the glass transition temperature (Tg) of the optical glasses in Examples 1 to 21 is all below 560°C, resulting in a low softening temperature and making it easier to perform precision pressure molding.

[0180] In contrast, as shown in Table 3, the refractive index of the optical glass in Comparative Example 1 is less than 1.70. This can be attributed to excessive SiO2, etc.

[0181] Furthermore, in Comparative Example 2, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to insufficient SiO2, among other factors.

[0182] Furthermore, the refractive index of the optical glass in Comparative Example 3 is less than 1.70. This can be attributed to an excess of B2O3, etc.

[0183] Furthermore, in Comparative Example 4, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to insufficient B2O3, among other factors.

[0184] Furthermore, the glass transition temperature (Tg) of the optical glass in Comparative Example 5 is greater than 560°C. This can be attributed to insufficient Li₂O, etc.

[0185] Furthermore, in Comparative Example 6, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to factors such as excessive Li₂O.

[0186] Furthermore, in Comparative Example 7, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to insufficient CaO, among other reasons.

[0187] Furthermore, in Comparative Example 8, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to excessive CaO, etc.

[0188] Furthermore, in Comparative Example 9, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to excessive BaO, etc.

[0189] Furthermore, the optical glass of Comparative Example 10 has a refractive index (nd) greater than 1.80 and an Abbe number less than 40. This can be attributed to an excess of Nb₂O₅, etc.

[0190] Furthermore, as shown in Table 4, devitrification occurred in Comparative Example 11, making it impossible to obtain high-quality glass. This can be attributed to excessive ZrO2, etc.

[0191] Furthermore, in Comparative Example 12, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to excessive TiO2, etc.

[0192] Furthermore, in Comparative Example 13, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to excessive Y₂O₃, etc.

[0193] Furthermore, the Abbe number of the optical glass in Comparative Example 14 is less than 40. This can be attributed to insufficient La2O3, etc. More specifically, if there is insufficient La2O3, the refractive index cannot be sufficiently increased. Therefore, in order to compensate for this, the amount of components that help increase the refractive index (BaO, Nb2O5, ZrO2, TiO2, etc.) is increased, resulting in the inability to maintain the Abbe number within the specified range.

[0194] Furthermore, in Comparative Example 15, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to excessive La2O3, etc.

[0195] Furthermore, in Comparative Example 16, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to factors such as excessive Gd₂O₃.

[0196] Furthermore, in Comparative Example 17, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to excessive Ta₂O₅, etc.

[0197] Furthermore, in Comparative Example 18, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to excessive WO3, etc.

[0198] Furthermore, in Comparative Example 19, devitrification occurred, making it impossible to obtain high-quality glass. This can be attributed to factors such as an R / F ratio greater than 2.0.

[0199] Furthermore, the temperature coefficient of the relative refractive index of the optical glass in Comparative Example 20 is greater than 3.0 × 10⁻⁶. -6 ℃ -1 The glass transition temperature (Tg) is greater than 560℃. This can be attributed to factors such as an R / F (molar ratio) less than 0.8.

[0200] Furthermore, the temperature coefficient of the relative refractive index of the optical glass in Comparative Example 21 is greater than 3.0 × 10⁻⁶. -6 ℃ -1 This can be attributed to the presence of ZnO and other similar substances.

[0201] (Industry availability)

[0202] According to the present invention, optical glass with high refractive index, low dispersion, low glass transition temperature, and the ability to suppress temperature dependence of imaging can be provided. Furthermore, according to the present invention, precision pressure-molded preforms and optical elements using the aforementioned optical glass can be provided. < / bao> < / cao>

Claims

1. An optical glass, characterized in that, Contains, by mass% SiO2: 1% or more but less than 15% B2O3: 10% or more but less than 25% Li2O: 1% or more but less than 5% CaO: 5% or more but less than 30% BaO: 0% or more and 10% or less Nb2O5: 0% or more and 8% or less ZrO2: 0% or more and 8% or less TiO2: 0% or more and 8% or less Y2O3: 0% or more and 10% or less La2O3: 5% or more but less than 20% Gd2O3: 0% or more and 15% or less Ta2O5: 0% or more and 8% or less WO3: 0% or more and 8% or less The composition, It does not actually contain ZnO. If we define the total molar percentage of Li₂O, CaO, and BaO as R, and the total molar percentage of SiO₂ and B₂O₃ as F, then R / F must be greater than 0.8 and less than 2.

0. The temperature coefficient of the relative refractive index at 587.562 nm along the d-line at 40–60 °C is -5.0 × 10⁻⁶. -6 ℃ -1 Above and 3.0×10 -6 ℃ -1 the following.

2. The optical glass according to claim 1, characterized in that, The refractive index nd is above 1.70 and below 1.80, and the Abbe number νd is above 40 and below 55.

3. The optical glass according to claim 1 or 2, characterized in that, The glass transition temperature (Tg) is below 560℃.

4. A preform for precision pressure molding, characterized in that, The optical glass according to any one of claims 1 to 3 is used as the material.

5. An optical element, characterized in that, The optical glass according to any one of claims 1 to 3 is used as the material.

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