Optical glass, precision press molding preforms, and optical elements

Abstract

To provide optical glass which, in addition to having a high refractive index low dispersibility, has a low glass transition temperature and is capable of suppressing temperature dependence of image formation.SOLUTION: Optical glass has a composition comprising, 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, but being substantially free of ZnO, with the molar ratio (R / F) of contents of predetermined components being 0.8 or more and 2.0 or less, and a temperature coefficient of relative refractive index (40-60°C) being -5.0×10-6°C-1 or more and 3.0×10-6°C-1 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an optical glass, a precision press molding preform, and an optical element. [Background technology]

[0002]

[0003] Conventionally, with the widespread use and development of optical instruments, there has been a demand for optical glasses having various properties. In particular, in recent years, there has been an increasing demand for optical glasses that can achieve product miniaturization and high performance, particularly in the case of in-vehicle optical instruments, surveillance cameras, etc.

[0003] In order to achieve smaller and higher performance products, the use of high refractive index glass (for example, glass with a refractive index (nd) of 1.70 or higher) and optical design using aspherical lenses produced by precision press molding, etc., are essential elements.

[0004] Here, high-refractive-index glasses generally have high wavelength dispersion and tend to easily cause chromatic aberration, so they usually need to be combined with low-dispersion glasses to correct chromatic aberration. However, increasing the number of glasses (lenses) to be combined often becomes a disadvantage in achieving compactness. Therefore, by using optical glasses that have a high refractive index but low dispersion (refractive index (nd): approximately 1.70 to 1.80, Abbe number (νd): approximately 40 to 55), it is possible to reduce the number of lenses and, ultimately, to achieve compactness. In other words, there is a need for the above-mentioned high-refractive-index, low-dispersion optical glasses.

[0005] Furthermore, optical glass (lenses) used in projectors, automotive optical devices, and the like are often exposed to drastic changes in environmental temperature, and therefore it is desirable that temperature changes have minimal adverse effects on imaging, etc. In this regard, the high refractive index glasses described above tend to have a large positive change in refractive index with respect to temperature. Therefore, it is necessary to select such high refractive index glasses that have a small or large negative change in refractive index with respect to temperature, thereby minimizing the temperature dependency of the refractive index as much as possible.

[0006] For example, Patent Document 1 discloses an optical glass with a high refractive index and low dispersion, which has a predetermined B2O3-La2O3-Gd2O3-ZnO-based composition and optical constants of a refractive index (nd) of 1.72 to 1.83 and an Abbe number (νd) of 45 to 55.

[0007] However, the optical glass described in Patent Document 1 contains large amounts of rare earth element compounds such as La2O3 and B2O3 in order to achieve a high refractive index and low dispersion, and its substantial glass transition temperature (Tg) is high, at least around 580°C, making it disadvantageous for producing aspherical lenses by precision press molding.

[0008] On the other hand, Patent Document 2 discloses an optical glass having a predetermined SiO2-B2O3-La2O3-Gd2O3-ZnO-based composition, 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 lower. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-315954 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-111482 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the optical glass described in Patent Document 2 contains a large amount of ZnO to lower the glass transition temperature (Tg), and the amount of change in refractive index is large in the positive direction, which may cause a significant deterioration in imaging performance in response to temperature changes.

[0011] The present invention was developed in view of the above-mentioned current situation, and aims to provide an optical glass that has a high refractive index and low dispersion, a low glass transition temperature, and is capable of suppressing the temperature dependence of imaging. Another aim of the present invention is to provide a precision press molding preform and an optical element that use the above-mentioned optical glass. [Means for solving the problem]

[0012] As a result of extensive research into achieving the above-mentioned object, the inventors have found that by using SiO2, B2O3, Li2O, CaO, and La2O3 as the basic composition and optimizing the molar ratio (R / F) of the contents of predetermined components, the amount of change in refractive index (n) with respect to temperature (T) (temperature coefficient of relative refractive index (dn / dT)) is reduced or becomes negative, thereby suppressing the temperature dependency of imaging and providing an optical glass with a low glass transition temperature.

[0013] That is, the optical glass of the present invention contains, 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: 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 and 20% or less, Gd2O3: 0% or more and 15% or less, Ta2O5: 0% or more and 8% or less, WO3: 0% or more and 8% or less and a composition comprising Contains substantially no ZnO, When the total content of LiO, CaO, and BaO in mole percent is R and the total content of SiO and BO in mole percent is F, R / F is 0.8 or more and 2.0 or less; The temperature coefficient of the relative refractive index (40 to 60°C) at the d line (587.562 nm) is -5.0 × 10 -6 °C -1 Over 3.0 x 10 -6 °C -1 The optical glass has the following characteristics: In addition to having a high refractive index and low dispersion, it has a low glass transition temperature and is capable of suppressing the temperature dependency of imaging.

[0014] The optical glass of the present invention preferably has a refractive index (nd) of 1.70 or more and 1.80 or less, and an Abbe number (νd) of 40 or more and 55 or less.

[0015] The optical glass of the present invention preferably has a glass transition temperature (Tg) of 560° C. or lower.

[0016] The precision press-molding preform of the present invention is characterized by using the above-mentioned optical glass as its raw material. Such precision press-molding preform is easy to perform precision press molding, and can be used to obtain products in which the temperature dependency of imaging is suppressed.

[0017] The optical element of the present invention is characterized by using the above-mentioned optical glass as its material, and by using such an optical element, it is possible to obtain a product in which the temperature dependency of imaging is suppressed. [Effects of the Invention]

[0018] According to the present invention, an optical glass can be provided that has a high refractive index and low dispersion, a low glass transition temperature, and is capable of suppressing the temperature dependence of imaging. Furthermore, according to the present invention, a precision press molding preform and an optical element can be provided that use the above-mentioned optical glass. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be specifically described below using embodiments.

[0020] (optical glass) The optical glass of one embodiment of the present invention (hereinafter sometimes referred to as "the optical glass of this embodiment") contains, 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: 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 and 20% or less, Gd2O3: 0% or more and 15% or less, Ta2O5: 0% or more and 8% or less, WO3: 0% or more and 8% or less and a composition comprising Contains substantially no ZnO, When the total content of LiO, CaO, and BaO in mole percent is R and the total content of SiO and BO in mole percent is F, R / F is 0.8 or more and 2.0 or less; The temperature coefficient of the relative refractive index (40 to 60°C) at the d line (587.562 nm) is -5.0 × 10 -6 °C -1 Over 3.0 x 10 -6 °C -1 The present invention is characterized by the following:

[0021] The optical glass of this embodiment may contain other components (described below) in addition to the above-mentioned components (SiO2, B2O3, Li2O, CaO, BaO, Nb2O5, ZrO2, TiO2, Y2O3, La2O3, Gd2O3, Ta2O5, WO3). However, from the viewpoint of more reliably achieving the desired optical constants, reducing the glass transition temperature, and suppressing the 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. It is particularly preferable that the optical glass of this embodiment have a composition consisting solely of the above-mentioned components. Here, "consisting only of the above-mentioned components" includes cases where impurities other than the above-mentioned components are inevitably mixed in, specifically, cases where the proportion of impurities is 0.2 mass % or less.

[0022] First, the reasons for limiting the composition of the optical glass to the above ranges in this embodiment will be explained. Note that "%" indications for components refer to mass % unless otherwise specified (however, for R / F, mol % is used).

[0023] <sio2> SiO2 is an essential component of the optical glass of this embodiment, forming a network structure that serves as the skeleton of the glass. SiO2 is also a component that can enhance devitrification resistance and chemical durability. However, if the SiO2 content in the optical glass exceeds 15%, the refractive index decreases excessively. Furthermore, if the SiO2 content in the optical glass exceeds 15%, there is a risk of the glass transition temperature (Tg) and yield temperature (At) increasing excessively. On the other hand, if the SiO2 content in the optical glass is less than 1%, glass formation becomes difficult. Therefore, the SiO2 content in the optical glass of this embodiment is set to a range of 1% to 15%. 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.

[0024] <b2o3> B2O3 is an essential component of the optical glass of this embodiment, forming the glass network structure. Furthermore, B2O3 is an effective component for improving devitrification resistance, glass homogenization, and meltability. However, if the B2O3 content in the optical glass exceeds 25%, the refractive index decreases excessively. Furthermore, if the B2O3 content in the optical glass exceeds 25%, the glass transition temperature (Tg) and yield temperature (At) may increase excessively. On the other hand, if the B2O3 content in the optical glass is less than 10%, glass formation becomes difficult. Therefore, the B2O3 content in the optical glass of this embodiment is set to a range of 10% to 25%. 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.

[0025] <li2o> Li2O is an essential component of the optical glass of this embodiment, and is effective in lowering the glass transition temperature (Tg) and yield temperature (At), as well as reducing the temperature coefficient of the 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 lowered. Furthermore, if the Li2O content in the optical glass is less than 1%, the effect of reducing the temperature coefficient of the relative refractive index may not be sufficiently achieved. Therefore, the Li2O content in the optical glass of this embodiment is set to be 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.

[0026] <cao> CaO is an essential component in the optical glass of this embodiment, and is effective in reducing the temperature coefficient of the relative refractive index and increasing the 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 reducing the temperature coefficient of the relative refractive index will not be sufficiently achieved. Therefore, the CaO content in the optical glass of this embodiment is set to be in the range of 5% to 30%. 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.

[0027] <bao> BaO is a component effective for reducing the temperature coefficient of the relative refractive index. BaO is also a component effective for increasing the refractive index and improving meltability. 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% to 10%. From the same viewpoint, the BaO content in the optical glass of this embodiment is preferably 9% or less, and more preferably 8% or less.

[0028] <nb2o5> Nb2O5 is a component effective in increasing the refractive index and chemical durability of glass. However, if the Nb2O5 content in optical glass exceeds 8%, an undesirable increase in refractive index or increase in dispersion (decrease in Abbe number) may occur. Therefore, in the optical glass of this embodiment, the Nb2O5 content is set to a range of 0% to 8%. From the same viewpoint, the Nb2O5 content in the optical glass of this embodiment is preferably 7.5% or less, and more preferably 7% or less.

[0029] <zro2> ZrO2 is a component effective in increasing the refractive index and improving the chemical durability of glass. However, if the ZrO2 content in optical glass exceeds 8%, devitrification resistance decreases and an undesirable increase in refractive index or dispersion (a decrease in Abbe number) may occur. Therefore, in the optical glass of this embodiment, the ZrO2 content is set to a range of 0% to 8%. 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.

[0030] <tio2> TiO2 is a component effective in increasing the refractive index and chemical durability of glass. However, if the TiO2 content in optical glass exceeds 8%, devitrification resistance decreases and an undesirable increase in refractive index or dispersion (a decrease in Abbe number) may occur. Therefore, in the optical glass of this embodiment, the TiO2 content is set to a range of 0% to 8%. From the same viewpoint, the TiO2 content in the optical glass of this embodiment is preferably 7.5% or less, and more preferably 7% or less.

[0031] <y2o3> Y2O3 is a component effective in increasing the refractive index and chemical durability of glass. However, if the Y2O3 content in optical glass exceeds 10%, devitrification resistance decreases. Therefore, the Y2O3 content in the optical glass of this embodiment is set to a range of 0% to 10%. From the same viewpoint, the Y2O3 content in the optical glass of this embodiment is preferably 9.5% or less, and more preferably 9% or less.

[0032] <la2o3> La2O3 is an essential component of the optical glass of this embodiment and is useful for adjusting the desired optical constants (refractive index and Abbe number) of the present invention. La2O3 is also effective for improving chemical durability and reducing the temperature coefficient of the relative refractive index. However, if the La2O3 content in the optical glass exceeds 20%, 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 increased, or it becomes extremely difficult to obtain the desired optical constants even when the amounts of other components are adjusted within the specified ranges. Therefore, the La2O3 content in the optical glass of this embodiment is set to be 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.

[0033] <gd2o3> Gd2O3 is an effective component for increasing the refractive index of glass, lowering dispersion, improving chemical durability, and reducing the temperature coefficient of the 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% to 15%. 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.

[0034] <ta2o5> Ta2O5 is a component effective in increasing the refractive index and chemical durability of glass. However, if the Ta2O5 content in the optical glass exceeds 8%, devitrification resistance decreases and an undesirable increase in dispersion (a decrease in Abbe number) may occur. Therefore, in the optical glass of this embodiment, the Ta2O5 content is set to a range of 0% to 8%. 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.

[0035] <wo3> WO3 is an effective component for increasing the refractive index and improving the chemical durability of glass. However, when the content of WO3 in optical glass exceeds 8%, the devitrification resistance decreases, and an undesired increase in dispersion (decrease in Abbe number) may occur. Therefore, in the optical glass of the present embodiment, the content of WO3 is set within the range of 0% or more and 8% or less. From the same perspective, the content of WO3 in the optical glass of the present embodiment is preferably 7.5% or less, and more preferably 7% or less.

[0036] <R / F (molar ratio)> In the optical glass of the present embodiment, when the total content of the molar percentages of Li2O, CaO, and BaO is defined as R, and the total content of the molar percentages of SiO2 and B2O3 is defined as F, it is necessary that R / F is 0.8 or more and 2.0 or less. The inventor has found that by optimizing the R / F (molar ratio) while limiting the content of each component of metal ions such as Li, Ca, and Ba, the amount of use of La2O3, Gd2O3, and Y2O3 containing rare earth elements can be reduced while lowering the temperature coefficient of the relative refractive index, and an optical glass with a low glass transition temperature (Tg) can be obtained. When R / F exceeds 2.0, the devitrification resistance of the glass decreases, and high-quality glass cannot be obtained. In addition, from the perspective of further reducing the temperature coefficient of the relative refractive index and the glass transition temperature, the R / F in the optical glass of the present embodiment is preferably more than 0.9, and more preferably 1.0 or more.

[0037] <ZnO (non-containing component)> Although ZnO can lower the glass transition temperature (Tg) and the yield temperature (At), in the optical glass containing the above-described components, there is a risk that the temperature coefficient of the relative refractive index cannot be suppressed within a predetermined range. Therefore, the optical glass of the present embodiment is substantially free of ZnO. Here, in this specification, "substantially not containing" a certain component means that the component is not intentionally contained.

[0038] <Other components> The optical glass of this embodiment may contain small amounts of other components besides the components described above, such as Na2O, K2O, Cs2O, MgO, SrO, Al2O3, Ga2O3, In2O3, GeO2, Sb2O3, Bi2O3, P2O5, and MoO3, so long as the purpose is not violated (for example, such amounts that the total amount of these other components is 5 mass % or less in the optical glass). The optical glass of this embodiment preferably does not contain components that have a significant impact on the environment and adversely affect the human body, such as PbO, TeO2, As2O3, and CdO.

[0039] Next, various properties of the optical glass of this embodiment will be described.

[0040] <Refractive index (nd) and Abbe number (νd)> The optical glass of this embodiment preferably has a high refractive index and low dispersion in order to meet specific needs. More specifically, the refractive index (nd) of the optical glass of this embodiment can be 1.70 or more and 1.80 or less. The refractive index (nd) of the optical glass of this embodiment is more preferably 1.71 or more and more preferably 1.79 or less. More specifically, the Abbe number (νd) of the optical glass of this embodiment can be set to be equal to or greater than 40 and equal to or less than 55. Moreover, the Abbe number (νd) of the optical glass of this embodiment is more preferably equal to or greater than 41, and even more preferably equal to or greater than 42, and is more preferably equal to or less than 53, and even more preferably equal to or less than 50. The refractive index (nd) and Abbe number (νd) of the optical glass of this embodiment can be adjusted, for example, by appropriately adjusting the content of each of the above-mentioned components within a predetermined range.

[0041] <Temperature coefficient of relative refractive index (dn / dT)> The optical glass of this embodiment has a temperature coefficient (40 to 60°C) of the relative refractive index at the d line (587.562 nm) of -5.0 × 10 -6 °C -1 Over 3.0 x 10 -6 °C -1 The optical glass of this embodiment is thus able to suppress the temperature dependency of image formation. Here, while the component composition of the optical glass is as described above, the temperature coefficient must be −5.0×10 or less. -6 °C -1 If the temperature coefficient of the optical glass is less than 3.0×10, the minimum chemical durability of the optical glass cannot be ensured. -6 °C -1 If the temperature coefficient of the optical glass of this embodiment is greater than -4.0×10, the amount of change in refractive index with respect to temperature is large in positive direction, and therefore the temperature dependence of image formation cannot be sufficiently suppressed. -6 °C -1 It is preferable that it is equal to or greater than -3.5 x 10 -6 °C -1 From the viewpoint of more effectively suppressing the temperature dependency of image formation, the temperature coefficient of the optical glass of this embodiment is more preferably 2.7×10 -6 °C -1 Preferably, it is 2.5 x 10 or less. -6 °C -1 More preferably, it is: The temperature coefficient of the optical glass of this embodiment can be adjusted, for example, by appropriately adjusting the content of each of the above-mentioned components within a predetermined range.

[0042] <Glass transition temperature (Tg)> The optical glass of this embodiment preferably has a glass transition temperature (Tg) of 560°C or lower. When the glass transition temperature (Tg) of the optical glass is 560°C or lower, the softening temperature is also lowered, making it easier to produce aspherical lenses by precision press molding, in particular precision press molding. From the same perspective, the glass transition temperature (Tg) of the optical glass of this embodiment is more preferably 555°C or lower, and even more preferably 550°C or lower. The glass transition temperature (Tg) of the optical glass of this embodiment can be adjusted, for example, by appropriately adjusting the content of each of the above-mentioned components within a predetermined range.

[0043] <Optical glass manufacturing method> Next, a method for manufacturing the optical glass of this embodiment will be described. The optical glass of this embodiment may be produced by any conventional method, provided that the composition of each component satisfies the above-mentioned ranges. For example, first, oxides, hydroxides, carbonates, nitrates, etc., as raw materials for each component that can be contained in the optical glass of this embodiment, are weighed in predetermined proportions and thoroughly mixed to form a glass compound raw material. Next, these raw materials are placed in a melting vessel (e.g., a crucible made of a precious metal such as platinum) that is non-reactive with the glass raw materials, and heated to 1000 to 1500°C in an electric furnace to melt them. The mixture is then stirred appropriately to homogenize and clarify, and then cast into a mold preheated to an appropriate temperature. The optical glass of this embodiment can be produced by slowly cooling it in an electric furnace to remove distortion. A small amount of a fining agent such as Sb2O3 (e.g., an amount less than 2 mass% in the optical glass) can be added to degas the glass.

[0044] (Precision press molding preforms) Hereinafter, a preform for precision press molding according to one embodiment of the present invention (hereinafter sometimes referred to as "the preform of this embodiment") will be specifically described. A precision press-molding preform is a preformed glass material used in a known precision press-molding method, that is, a glass preform that is heated and subjected to precision press-molding.

[0045] Here, precision press molding, also known as mold optics molding, is a method of forming the optically functional surface of the final optical element by transferring the molding surface of a press mold. Note that the optically functional surface refers to the surface of an optical element that refracts, reflects, diffracts, or allows the light to enter or exit the element, and an example of this optically functional surface is the lens surface of a lens.

[0046] The preform of this embodiment is characterized by using the above-mentioned optical glass as its raw material. As described above, the preform of this embodiment is easy to be precision press molded, and can be used to obtain a product in which the temperature dependency of imaging is suppressed. From the viewpoint of more reliably obtaining the desired performance, the preform of this embodiment preferably satisfies the essential requirements for the composition of each component as described above for the optical glass of the present invention, and more preferably satisfies the various preferable requirements as described above for the optical glass of the present invention.

[0047] There are no particular limitations on the method for producing the preform of this embodiment, but it is desirable to produce the preform of this embodiment by the following method, taking advantage of the excellent properties of the optical glass.

[0048] The first preform production method (referred to as "preform production method I") is a method in which optical glass as a raw material is melted, the resulting molten glass is allowed to flow out to separate a molten glass gob, and the molten glass gob is shaped into a preform during the process of cooling.

[0049] The second preform manufacturing method (referred to as "preform manufacturing method II") is a method in which optical glass is melted as a raw material, the resulting molten glass is molded to produce a glass molded body, and the molded body is processed to obtain a preform.

[0050] Preform manufacturing methods I and II have in common the step of obtaining a homogeneous glass melt from optical glass as a raw material. In this step, for example, optical glass raw materials prepared by blending to obtain the desired properties are placed in a platinum melting vessel, and heated, melted, refined, and homogenized to prepare a homogeneous glass melt, which can then be discharged from a temperature-controlled platinum or platinum alloy flow nozzle or flow pipe. Alternatively, the optical glass raw materials may be roughly melted to prepare cullet, which may then be blended and heated, melted, refined, and homogenized to obtain a homogeneous glass melt, which can then be discharged from the above-mentioned flow nozzle or flow pipe.

[0051] Here, when producing small or spherical preforms, a method can be employed in which the molten glass is dropped from an outflow nozzle as molten glass droplets of a desired mass, which are then received in a mold or the like and molded into a preform. Alternatively, a method can be employed in which the molten glass droplets of a similarly desired mass are dropped from an outflow nozzle into liquid nitrogen or the like to mold a preform.

[0052] On the other hand, when producing medium to large sized preforms, for example, a method can be employed in which a molten glass flow is allowed to flow down from an outflow pipe, the tip of the molten glass flow is received by a preform mold or the like, a constricted portion is formed between the nozzle of the molten glass flow and the preform mold, the preform mold is then suddenly lowered straight down, the molten glass flow is separated at the constricted portion due to the surface tension of the molten glass, and a molten glass gob of a desired mass is received on a receiving member and molded into a preform.

[0053] In order to obtain a preform having a smooth surface free from scratches, stains, wrinkles, surface alteration, and the like, for example, a free surface, methods such as applying air pressure to a molten glass gob on a preform mold or the like to float it up and form it into a preform, or placing molten glass droplets in a medium such as liquid nitrogen that is a gaseous substance at room temperature and pressure and has been cooled to a liquid state, and then forming the molten glass into a preform, are used.

[0054] When forming a preform while floating a molten glass gob, gas (called floating gas) is blown onto the molten glass gob, applying upward wind pressure. If the viscosity of the molten glass gob is too low, the floating gas will get into the glass and remain as bubbles in the preform. However, by adjusting the viscosity of the molten glass gob to 3 to 60 dPa·s, the glass gob can be floated without the floating gas getting into the glass.

[0055] Examples of gases that can be used when blowing floating gas onto the preform include air, N2 gas, O2 gas, Ar gas, He gas, water vapor, etc. There are no particular restrictions on the air pressure, as long as it allows the preform to float without coming into contact with solid objects such as the surface of the mold.

[0056] Because precision press-molded products (e.g., optical elements) manufactured from preforms often have an axis of rotational symmetry, such as lenses, it is desirable for the shape of the preform to also have an axis of rotational symmetry. Specific examples include a sphere or a shape with one axis of rotational symmetry. Shapes with one axis of rotational symmetry include those with a smooth outline without corners or depressions in a cross section containing the axis of rotational symmetry, such as those with an ellipse whose outline in the cross section coincides with the axis of rotational symmetry. Other examples include a flattened sphere (a shape in which a single axis passing through the center of a sphere is defined and the dimensions are reduced along the axis).

[0057] In Preform Manufacturing Method I, optical glass is molded in a temperature range where it can be plastically deformed, so a preform may be obtained by press-molding a glass lump. In this case, the shape of the preform can be set relatively freely, so it can approximate the shape of the desired precision press-molded product, for example, by making one of the opposing surfaces convex and the other concave, or both concave, or one surface flat and the other convex, or one surface flat and the other concave, or both surfaces convex.

[0058] In preform manufacturing method II, for example, molten glass is cast into a mold to form it, and then distortion of the molded body is removed by annealing, and the molded body is divided into predetermined dimensions and shapes by cutting or cleaving to produce multiple glass pieces, and the glass pieces are polished to smooth their surfaces, and a preform made of glass with a predetermined mass can be obtained. The surface of the preform thus produced is also preferably coated with a carbon-containing film before use. Preform manufacturing method II is suitable for producing spherical preforms, flat preforms, etc., which can be easily ground and polished.

[0059] Next, a more preferable preform for further improving the mass productivity of molded products such as optical elements by precision press molding will be described.

[0060] In the production of the preform of this embodiment, by reducing the amount of deformation of the glass during precision press molding, it becomes possible to lower the temperatures of the glass and the mold during precision press molding, shorten the time required for press molding, reduce the press pressure, etc. As a result, the reactivity between the glass and the molding surface of the mold decreases, defects that occur during precision press molding are reduced, and mass productivity is improved.

[0061] Here, when a lens is produced by precision press molding of a preform, a preferred preform is one having press surfaces (surfaces that are pressed by opposing molding surfaces of a mold during precision press molding) that face in opposite directions, and even more preferred is a preform that has an axis of rotational symmetry that passes through the centers of the two press surfaces. Among these preforms, those suitable for precision press molding of meniscus lenses are those in which one press surface is convex and the other is concave, flat, or convex with a smaller curvature than the convex surface.

[0062] Furthermore, a preform suitable for precision press molding of a biconcave lens is a preform in which one of the surfaces to be pressed is convex, concave, or flat, and the other is convex, concave, or flat. On the other hand, a preform suitable for precision press molding of a biconvex lens is a preform in which one of the surfaces to be pressed is convex and the other is either convex or flat.

[0063] In either case, it is preferable that the preform has a shape that closely resembles the shape of the precision press-molded product.

[0064] When a molten glass gob is molded into a preform using a preform mold, the lower surface of the glass on the mold is generally determined by the shape of the molding surface of the mold. Meanwhile, the shape of the upper surface of the glass is determined by the surface tension of the molten glass and the weight of the glass itself. To reduce the amount of deformation of the glass during precision press molding, it is necessary to also control the shape of the upper surface of the glass being molded in the preform 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 itself is a convex free surface. To make the upper surface flat, concave, or a convex surface with a smaller curvature than the free surface, pressure can be applied to the upper surface of the glass. Specifically, the upper surface of the glass can be pressed with a mold having a molding surface of the desired shape, or air pressure can be applied to the upper surface of the glass to mold it into the desired shape. When pressing the upper surface of the glass with the mold, a plurality of gas outlets can be provided on the molding surface of the mold, and gas can be ejected from these gas outlets to form a gas cushion between the molding surface and the upper surface of the glass, and the upper surface of the glass can be pressed via the gas cushion. Alternatively, when it is desired to form the upper surface of the glass into a surface with a larger curvature than the free surface, the upper surface of the glass may be formed by generating a negative pressure in the vicinity thereof to raise the upper surface.

[0065] In addition, the preform is preferably a preform with a polished surface to more closely resemble the shape of the precision press-molded product. For example, a preform is preferred in which one of the pressed surfaces is polished to a flat surface or a portion of a sphere, and the other is polished to a flat surface or a portion of a sphere. Here, the portion of the sphere may be convex or concave, but whether it is convex or concave is desirably determined based on the shape of the precision press-molded product, as described above.

[0066] The above preforms can be preferably used to mold lenses having a diameter of 10 mm or more, and more preferably to mold lenses having a diameter of 20 mm or more, and can also be preferably used to mold lenses having a center thickness of more than 2 mm.

[0067] (Optical elements) An optical element according to one embodiment of the present invention (hereinafter, sometimes referred to as "the optical element of this embodiment") will be specifically described below. The optical element of this embodiment is characterized by using the above-mentioned optical glass as a material. As described above, the optical element of this embodiment uses the above-mentioned optical glass as a material, and therefore a product in which the temperature dependence of image formation is suppressed can be obtained. Note that, from the viewpoint of more reliably obtaining the desired performance, the optical element of this embodiment preferably satisfies the essential requirements for the composition of each component as described above for the optical glass of this embodiment, and more preferably satisfies the various preferred requirements as described above for the optical glass of this embodiment. The optical element of this embodiment also includes an optical element using the above-described precision press molding preform.

[0068] The type of optical element is not limited, but typical examples include lenses such as aspherical lenses, spherical lenses, plano-concave lenses, plano-convex lenses, biconcave lenses, biconvex lenses, convex meniscus lenses, and concave meniscus lenses; microlenses; lens arrays; lenses with diffraction gratings; prisms; and prisms with lens functions. Preferred examples of optical elements include lenses such as convex meniscus lenses, concave meniscus lenses, biconvex lenses, biconcave lenses, plano-convex lenses, and plano-concave lenses; prisms; and diffraction gratings. Each of the above lenses may be an aspherical lens or a spherical lens. If necessary, an anti-reflection film or a wavelength-selective partial reflection film may be provided on the surface.

[0069] <Method of manufacturing optical elements> Next, a method for manufacturing the optical element of this embodiment will be described. The optical element of this embodiment can be manufactured, for example, by precision press molding the above preform using a press mold.

[0070] Precision press molding can use a press mold whose molding surface has been precisely machined to the desired shape. A mold release film may be formed on the molding surface to prevent the glass from fusing during pressing and to facilitate smooth glass spreading along the molding surface. Examples of mold release films include films of precious metals (platinum, platinum alloys), oxides (such as oxides of Si, Al, Zr, and Y), nitrides (such as nitrides of B, Si, and Al), and carbon-containing films. Carbon-containing films are preferably those containing carbon as a major component (i.e., films in which the carbon content is higher than the other elements when the element content in the film is expressed in atomic percent). Specific examples include carbon films and hydrocarbon films. Carbon-containing films can be formed using known methods such as vacuum deposition, sputtering, and ion plating using carbon raw materials, or known methods such as pyrolysis using hydrocarbon or other source gases. Other films can be formed using methods such as vapor deposition, sputtering, ion plating, and sol-gel processes.

[0071] Furthermore, the heating of the press mold and preform and the precision press molding process are preferably carried out in a non-oxidizing gas atmosphere, such as nitrogen gas or a mixture of nitrogen gas and hydrogen gas, to prevent oxidation of the molding surface of the press mold or the release film suitably provided on the molding surface. In a non-oxidizing gas atmosphere, the release film covering the surface of the preform, particularly the carbon-containing film, is not oxidized and remains on the surface of the precision press-molded product. This film should ultimately be removed, but to remove the carbon-containing film or other release film relatively easily and completely, the precision press-molded product can be heated in an oxidizing atmosphere, for example, in air. The carbon-containing film or other release film should be removed at a temperature that does not deform the precision press-molded product due to heating. Specifically, the carbon-containing film or other release film is preferably removed at a temperature range below the glass transition temperature.

[0072] The method for manufacturing the optical element of this embodiment is not particularly limited, and the following two manufacturing methods are listed. Here, in manufacturing the optical element of this embodiment, it is preferable from the viewpoint of mass production of optical elements to repeat the step of precision press molding the above-mentioned precision press molding preform using the same press mold.

[0073] The first optical element manufacturing method (referred to as "optical element manufacturing method I") involves introducing a preform into a press mold, heating the preform and the press mold together, and performing precision press molding to obtain an optical element. The second optical element manufacturing method (hereinafter referred to as "optical element manufacturing method II") is a method in which a heated preform is introduced into a preheated press mold and precision press-molded to obtain an optical element.

[0074] In optical element manufacturing method I, a preform is placed between a pair of opposing upper and lower molds whose molding surfaces are precisely shaped. Then, the glass is heated until the viscosity of the glass reaches 10 5 ~10 9 By heating both the mold and preform to a temperature equivalent to dPa·s to soften the preform, and then pressurizing it, the molding surface of the mold can be precisely transferred to the glass. Optical Element Manufacturing Method I is recommended when improving molding precision, such as surface accuracy and decentering precision, is important.

[0075] In the optical element manufacturing method II, a glass having a viscosity of 10 4 ~10 8 By supplying a preform heated to a temperature equivalent to dPa·s and then pressurizing it, the molding surface of the mold can be precisely transferred to the glass. Optical Element Manufacturing Method II is the recommended method when improving productivity is important.

[0076] The pressure and time during pressing can be appropriately determined taking into consideration the viscosity of the glass, etc. For example, the pressing pressure can be about 5 to 15 MPa, and the pressing time can be 10 to 300 seconds. Pressing conditions such as pressing time and pressing pressure can be appropriately set within known ranges depending on the shape and dimensions of the molded product.

[0077] The mold and precision press-molded article are then cooled, and preferably when the temperature reaches or is below the strain point, they are released from the mold and the precision press-molded article is removed. Note that in order to precisely adjust the optical properties to the desired values, the annealing conditions of the molded article during cooling, such as the annealing rate, may be appropriately adjusted.

[0078] The optical element of this embodiment can be produced without going through a press molding process, for example, by casting homogeneous molten glass into a mold to form a glass block, annealing the glass to remove distortion, adjusting the annealing conditions so that the refractive index of the glass reaches a desired value, and then cutting or cleaving the glass block to produce glass pieces, which are then ground and polished to form an optical element. [Example]

[0079] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0080] The corresponding oxides, hydroxides, carbonates, and nitrates were prepared as raw materials for each component, weighed out so that the compositions after vitrification would be as shown in Tables 1 to 4, and thoroughly mixed to obtain blended raw materials. These blended raw materials were placed in a platinum crucible and melted in an electric furnace. The temperature during melting was adjusted appropriately within the range of 1000 to 1500°C to ensure sufficient degassing. The mixture was then stirred appropriately to homogenize it, clarified, and cast into a mold preheated to an appropriate temperature. The glass was then slowly cooled in an electric furnace to obtain the optical glass of each example.

[0081] Next, the optical glasses of each example obtained were evaluated for devitrification resistance and measured for refractive index (nd), Abbe number (νd), glass transition temperature (Tg), and temperature coefficient of relative refractive index (dn / dT) according to the procedures described below. The results are shown in Tables 1 to 4.

[0082] The resistance to devitrification was evaluated by visual observation, with a score of "Good" indicating that no devitrification was observed in the glass after annealing, and a score of "Poor" indicating that devitrification was observed. In addition, examples in which the resistance to devitrification was evaluated as "x" were deemed to be of insufficient quality and were not subjected to further measurements.

[0083] The refractive index (nd) and Abbe number (νd) were measured according to the method described in JOGIS01-2003 "Method for measuring the refractive index of optical glass," a standard of the Japan Optical Glass Industry Association.

[0084] The glass transition temperature (Tg) was measured according to the method described in JOGIS08-2003 "Method for measuring thermal expansion of optical glass," a standard of the Japan Optical Glass Industry Association.

[0085] The temperature coefficient of relative refractive index (dn / dT) was measured in the temperature range of 40 to 60°C using d-line (587.562 nm) in accordance with the method described in JOGIS18-1994 "Method for measuring the temperature coefficient of refractive index of optical glass," a standard of the Japan Optical Glass Industry Association.

[0086] [Table 1]

[0087] [Table 2]

[0088] [Table 3]

[0089] [Table 4]

[0090] From Tables 1 and 2, it can be seen that the optical glasses of Examples 1 to 21 all have a refractive index (nd) of 1.70 or more and 1.80 or less, and an Abbe number (νd) of 40 or more and 55 or less, i.e., they have high refractive index and low dispersion. Furthermore, the optical glasses of Examples 1 to 21 all have a temperature coefficient of relative refractive index of -5.0×10 -6 °C -1 Over 3.0 x 10 -6 °C -1 or less, and the temperature dependency of imaging is significantly suppressed.

[0091] Furthermore, the optical glasses of Examples 1 to 21 all have a glass transition temperature (Tg) of 560° C. or less, which means that the softening temperature is low and precision press molding can be carried out more easily.

[0092] In contrast, as can be seen from Table 3, the refractive index of the optical glass of Comparative Example 1 was lower than 1.70. This is thought to be due to an excessive amount of SiO2, etc. Furthermore, in Comparative Example 2, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the fact that the amount of SiO2 was too small. Furthermore, the optical glass of Comparative Example 3 had a refractive index lower than 1.70, which is thought to be due to an excessive amount of B2O3. Furthermore, in Comparative Example 4, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the fact that the amount of B2O3 was too small. Furthermore, the optical glass of Comparative Example 5 had a glass transition temperature (Tg) higher than 560° C. This is thought to be due to the fact that the amount of Li2O was too small.

[0093] Furthermore, in Comparative Example 6, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the fact that the amount of Li2O was too much. Furthermore, in Comparative Example 7, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the fact that the amount of CaO was too small. Furthermore, in Comparative Example 8, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the excessive amount of CaO, etc. Furthermore, in Comparative Example 9, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the excessive BaO content, etc. Furthermore, the optical glass of Comparative Example 10 had a refractive index (nd) higher than 1.80 and an Abbe number lower than 40. This is thought to be due to the fact that the content of Nb2O5 was too high.

[0094] Furthermore, as can be seen from Table 4, devitrification occurred and good quality glass could not be obtained in Comparative Example 11. This is thought to be due to the fact that the amount of ZrO2 was too high. In Comparative Example 12, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the presence of too much TiO2. In Comparative Example 13, devitrification occurred and good quality glass could not be obtained. This is thought to be due to the fact that the amount of Y2O3 was too high. Furthermore, the optical glass of Comparative Example 14 had an Abbe number lower than 40. This is thought to be due to the fact that the La2O3 content was too low, etc. More specifically, if the La2O3 content was too low, the refractive index could not be sufficiently increased, and so the amounts of components that contribute to increasing the refractive index (BaO, Nb2O5, ZrO2, TiO2, etc.) were increased to compensate for this, but as a result, the Abbe number could not be kept within the specified range.

[0095] In Comparative Example 15, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the fact that the amount of La2O3 was too high. Furthermore, in Comparative Example 16, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the fact that the amount of Gd2O3 was too high. Furthermore, in Comparative Example 17, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the fact that the Ta2O5 content was too high. In addition, in Comparative Example 18, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the fact that the amount of WO3 was too high.

[0096] Furthermore, in Comparative Example 19, devitrification occurred and good quality glass could not be obtained, which is thought to be due to the R / F ratio being greater than 2.0, etc. The optical glass of Comparative Example 20 has a temperature coefficient of relative refractive index of 3.0×10 -6 °C -1 The glass transition temperature (Tg) was higher than 560° C. This is thought to be due to the R / F (molar ratio) being smaller than 0.8. The optical glass of Comparative Example 21 has a temperature coefficient of relative refractive index of 3.0×10 -6 °C -1 This is thought to be due to the inclusion of ZnO. [Industrial Applicability]

[0097] According to the present invention, an optical glass can be provided that has a high refractive index and low dispersion, a low glass transition temperature, and is capable of suppressing the temperature dependence of imaging. Furthermore, according to the present invention, a precision press molding preform and an optical element can be provided that use the above-mentioned optical glass. < / bao> < / cao>

Claims

1. By mass% SiO ２ : more than 1% and less than 15%, B ２ O ３ : More than 10% but less than 25%, Li ２ O: more than 1% and less than 5%, CaO: 5% or more and 30% or less, BaO: 0% or more and 10% or less, Nb ２ O ５ :0% or more but less than 8% ZrO ２ :0% or more but less than 8% TiO ２ :0% or more but less than 8% Y ２ O ３ :0% or more but less than 10%, La ２ O ３ : More than 5% but less than 20%, Gd ２ O ３ :0% or more but less than 15%, Ta ２ O ５ :0% or more but less than 8% WO ３ :0% or more but less than 8% and a composition comprising Substantially does not contain ZnO, Li ２ The total mole percent content of O, CaO and BaO is R, and SiO ２ and B ２ O ３ where F is the total mole percent content of the above, R / F is 0.8 or more and 2.0 or less, The temperature coefficient of the relative refractive index (40 to 60°C) at the d line (587.562 nm) is -5.0 × 10 －６ °C －１ Above 3.0 x 10 －６ °C －１ An optical glass characterized by:

2. 2. The optical glass according to claim 1, having a refractive index (nd) of 1.70 or more and 1.80 or less, and an Abbe number (νd) of 40 or more and 55 or less.

3. 3. The optical glass according to claim 1, which has a glass transition temperature (Tg) of 560° C. or lower.

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

5. An optical element characterized by using the optical glass according to any one of claims 1 to 3 as a material.

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