Optical glass, precision press molding preforms, and optical elements

Abstract

To provide a low-dispersion optical glass which is lightweight, has small changes of optical properties by temperature, and has excellent chemical durability and low-temperature moldability.SOLUTION: An optical glass has a composition including, by mol%, B2O3: 0% or over and 15% or under, P2O5: 25% or over and 40% or under, however the sum total of B2O3 and P2O5 is 35% or over and 45% or under, Al2O3: 0% or over and 10% or under, Li2O: 5% or over and 15% or under, Na2O: 0% or over and 15% or under, K2O: 0% or over and 5% or under, MgO: 0% or over and 35% or under, CaO: 0% or over and 35% or under, however the sum total of MgO and CaO is 20% or over, ZnO: 0% or over and 5% or under, ZrO2: 0% or over and 3% or under, Y2O3: 0% or over and 3% or under, La2O3: 0% or over and 3% or under, and Gd2O3: 0% or over and 3% or under, and not including SrO and BaO.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] Glass having optical constants of a refractive index (nd) of 1.50 to 1.60 and an Abbe number (νd) of about 60 to 70 (so-called low dispersion glass) is used in various optical devices because optical elements made of the glass are useful for correcting chromatic aberration. In recent years, due to the increasing demand for optical devices that are expected to be used outdoors, such as in-vehicle cameras and drone aerial photography cameras, optical elements are also required to have characteristics suitable for such usage environments. One such characteristic is that the optical characteristics change little due to temperature. Furthermore, the glass is also required to be lightweight from the viewpoint of improving the energy efficiency of automobiles, drones, etc.

[0003] Here, as an example of low dispersion glass that satisfies the above-mentioned optical constants, Patent Documents 1 and 2 disclose optical glasses that contain P2O5 and Li2O, and also contain at least one of SrO and BaO. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-052119 A [Patent Document 2] JP 2011-241128 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, after investigations by the present inventors, it was found that the optical glasses described in Patent Documents 1 and 2 were unable to simultaneously reduce changes in optical properties due to temperature and be sufficiently lightweight, and there was room for improvement at least in this regard.

[0006] In addition, it is essential that the low-dispersion glass satisfying the above-mentioned optical constants has excellent chemical durability from the viewpoint of reliability, and also has excellent moldability at low temperatures from the viewpoints of mass production and cost reduction.

[0007] The present invention has been developed in view of the above-mentioned current situation, and aims to provide a low-dispersion optical glass that is lightweight, exhibits minimal change in optical properties due to temperature, and has excellent chemical durability and low-temperature moldability. 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]

[0008] As a result of extensive investigations in order to achieve the above-mentioned object, the present inventors have found that in a phosphate glass composition, particularly one that does not contain SrO or BaO, the desired optical glass can be produced with high productivity by setting the total content of B2O3 and P2O5 within a prescribed range, and further setting the total content of MgO and CaO to be equal to or greater than a prescribed amount, and further including Li2O in a prescribed proportion.

[0009] That is, the optical glass of the present invention contains, in mol %, B2O3: 0% or more and 15% or less, P2O5: 25% or more and 40% or less, However, the total of B2O3 and P2O5: 35% to 45%. Al2O3: 0% or more and 10% or less, Li2O: 5% or more and 15% or less, Na2O: 0% to 15%, K2O: 0% or more and 5% or less, MgO: 0% or more and 35% or less, CaO: 0% or more and 35% or less, However, the total content of MgO and CaO is 20% or more. ZnO: 0% or more and 5% or less, ZrO2: 0% or more and 3% or less, Y2O3: 0% or more and 3% or less, La2O3: 0% to 3% Gd2O3: 0% or more and 3% or less and The optical glass of the present invention is characterized by being free of SrO and BaO. The optical glass of the present invention is a low-dispersion optical glass that is lightweight, exhibits minimal change in optical properties due to temperature, and has excellent chemical durability and low-temperature moldability.

[0010] The optical glass of the present invention preferably has a refractive index (nd) of 1.50 or more and 1.60 or less, and an Abbe number (νd) of 60 or more and 70 or less.

[0011] The optical glass of the present invention preferably has a specific gravity of 2.90 or less.

[0012] The optical glass of the present invention has an absolute value of the temperature coefficient of relative refractive index (0°C / 20°C, wavelength 587.6 nm) of 2.0×10 -6 ℃ -1 It is preferable that:

[0013] The optical glass of the present invention preferably has a chemical durability (surface method) rank (DW) of 1 or 2 as measured in accordance with JOGIS07-2019.

[0014] The optical glass of the present invention preferably has a glass transition temperature (Tg) of 500° C. or lower and a yield temperature (At) of 540° C. or lower.

[0015] The precision press molding preform of the present invention is characterized in that it uses the above-mentioned optical glass as its raw material.

[0016] The optical element of the present invention is characterized in that it uses the above-mentioned optical glass as its material. Effect of the Invention

[0017] According to the present invention, it is possible to provide a low-dispersion optical glass that is lightweight, exhibits little change in optical properties due to temperature, and has excellent chemical durability and low-temperature moldability. Furthermore, according to the present invention, it is possible to provide a precision press molding preform and an optical element using the above optical glass. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, the present invention will be described in detail with reference to embodiments.

[0019] (Optical Glass) The optical glass of one embodiment of the present invention (hereinafter sometimes referred to as "the optical glass of the present embodiment") contains, in mol %, B2O3: 0% or more and 15% or less, P2O5: 25% or more and 40% or less, However, the total of B2O3 and P2O5: 35% to 45%. Al2O3: 0% or more and 10% or less, Li2O: 5% or more and 15% or less, Na2O: 0% to 15%, K2O: 0% or more and 5% or less, MgO: 0% or more and 35% or less, CaO: 0% or more and 35% or less, However, the total content of MgO and CaO is 20% or more. ZnO: 0% or more and 5% or less, ZrO2: 0% or more and 3% or less, Y2O3: 0% or more and 3% or less, La2O3: 0% to 3% Gd2O3: 0% or more and 3% or less and It is characterized by not containing SrO and BaO.

[0020] The optical glass of this embodiment may contain other components (described later) in addition to the above-mentioned components. However, from the viewpoint of reducing the change in optical properties due to temperature (hereinafter also referred to as improvement of optical stability), and more reliably bringing about high lightness, chemical durability, low-temperature moldability, and low dispersion, the optical glass of this embodiment preferably has a composition consisting of only the above-mentioned components (essential components P2O5 and Li2O, and components selected from B2O3, Al2O3, Na2O, K2O, MgO, CaO, ZnO, ZrO2, Y2O3, La2O3, and Gd2O3). Here, "consisting only of the above-mentioned components" includes cases where impurity components other than the above-mentioned components are inevitably mixed in, specifically, the proportion of impurity components is 0.2 mass % or less.

[0021] First, the reasons for limiting the composition of the optical glass in this embodiment to the above range will be described. Note that "%" indications relating to components refer to mol % unless otherwise specified.

[0022] <b2o3> In the optical glass of this embodiment, B2O3 is a component that forms the network structure of the glass, provides stability to the glass so that it can be manufactured, and is an effective component for improving the meltability of the glass. However, if the content exceeds 15%, the stability against devitrification decreases, and there is a risk that the basic quality of the optical glass may deteriorate. Therefore, in the optical glass of this embodiment, the content of B2O3 is set to a range of 0% or more and 15% or less. From the same viewpoint, the content of B2O3 in the optical glass of this embodiment is preferably 14% or less, and more preferably 13% or less.

[0023] <p2o5> P2O5 is an essential component that forms the network structure of the glass and provides the stability necessary for glass production in the optical glass of this embodiment. However, if its content exceeds 40%, the chemical durability deteriorates significantly. On the other hand, if its content is less than 25%, there is a risk of deterioration in devitrification resistance stability and low-temperature formability. Therefore, in the optical glass of this embodiment, the content of P2O5 is in the range of 25% or more and 40% or less. From the same perspective, the content of P2O5 in the optical glass of this embodiment is preferably 26% or more, more preferably 27% or more, and preferably 39% or less, more preferably 38% or less.

[0024] <Total of B2O3 and P2O5> Here, the optical glass of this embodiment requires that the total amount of B2O3 and P2O5 is 35% or more and 45% or less. This is because if the total amount of B2O3 and P2O5 exceeds 45%, the chemical durability deteriorates significantly, while if it is less than 35%, there is a risk of deterioration in devitrification resistance stability and low-temperature formability. Also, from the same perspective, the total amount of B2O3 and P2O5 in the optical glass of this embodiment is preferably 36% or more, more preferably 37% or more, and preferably 44% or less, more preferably 43% or less.

[0025] <al2o3> In the optical glass of this embodiment, Al2O3 is a component effective in improving chemical durability. However, if the content exceeds 10%, there is a risk that the devitrification resistance and optical stability may deteriorate. Therefore, in the optical glass of this embodiment, the content of Al2O3 is set to a range of 0% or more and 10% or less. From the same viewpoint, the content of Al2O3 in the optical glass of this embodiment is preferably 9% or less, and more preferably 8% or less.

[0026] <li2o> In the optical glass of this embodiment, Li2O is an essential component that is effective in improving meltability and low-temperature moldability, and also contributes to improving optical stability (particularly, the refractive index tends to decrease with increasing temperature). However, if the content exceeds 15%, the devitrification resistance stability may decrease, and the basic quality of the optical glass may deteriorate. If the content is less than 5%, the effect of improving meltability and low-temperature moldability may not be sufficiently obtained. Therefore, in the optical glass of this embodiment, the content of Li2O is set to a range of 5% to 15%. From the same viewpoint, the content of Li2O in the optical glass of this embodiment is preferably 6% or more, more preferably 7% or more, and preferably 14% or less, and more preferably 13% or less.

[0027] <na2o> In the optical glass of this embodiment, Na2O is a component that is effective in improving meltability and low-temperature moldability, and also contributes to improving optical stability (particularly, brings about a tendency for the refractive index to decrease with increasing temperature). However, if the content exceeds 15%, there is a risk that the refractive index will decrease excessively with increasing temperature. Therefore, in the optical glass of this embodiment, the Na2O content is set to a range of 0% to 15%. From the same viewpoint, the Na2O content in the optical glass of this embodiment is preferably 14% or less, and more preferably 13% or less.

[0028] <k2o> In the optical glass of this embodiment, K2O is a component that is effective in improving meltability and low-temperature moldability, and also contributes to improving optical stability (particularly, brings about a tendency for the refractive index to decrease with increasing temperature). However, if the content exceeds 5%, the stability against devitrification decreases, and there is a risk of the basic quality of the optical glass being deteriorated. Therefore, in the optical glass of this embodiment, the content of K2O is set to a range of 0% or more and 5% or less. From the same viewpoint, the content of K2O in the optical glass of this embodiment is preferably 4% or less, and more preferably 3% or less.

[0029] <mgo> In the optical glass of this embodiment, MgO is a component that improves chemical durability and low dispersion, and is also effective in reducing weight. However, if the content exceeds 35%, the melting property of the glass deteriorates, and the stability against devitrification decreases, which may deteriorate the basic quality of the optical glass. Therefore, in the optical glass of this embodiment, the content of MgO is set to a range of 0% to 35%. From the same viewpoint, the content of MgO in the optical glass of this embodiment is preferably 34% or less, and more preferably 33% or less.

[0030] <cao> CaO is an effective component for improving chemical durability and devitrification resistance stability in the optical glass of this embodiment. However, if its content exceeds 35%, the devitrification resistance stability and low-temperature formability may deteriorate. Therefore, in the optical glass of this embodiment, the content of CaO is set in the range of 0% or more and 35% or less. From the same perspective, the content of CaO in the optical glass of this embodiment is preferably 34% or less, and more preferably 33% or less.

[0031] <Total of MgO and CaO> Here, the optical glass of this embodiment requires that the total amount of MgO and CaO is 20% or more. This is because if the total amount of MgO and CaO is less than 20%, the chemical durability may decrease. Also, from the same perspective, the total amount of MgO and CaO in the optical glass of this embodiment is preferably 22% or more, more preferably 24% or more, and even more preferably 26% or more. On the other hand, from the perspective of better maintaining the devitrification resistance stability and low-temperature formability, the total amount of MgO and CaO in the optical glass of this embodiment is preferably 60% or less, more preferably 55% or less, even more preferably 53% or less, and still more preferably 51% or less.

[0032] <zno> ZnO is an effective component for improving chemical durability in the optical glass of this embodiment. However, if the content exceeds 5%, there is a risk that the devitrification resistance stability and low dispersion will deteriorate. Therefore, in the optical glass of this embodiment, the content of ZnO is set to a range of 0% to 5%. From the same viewpoint, the content of ZnO in the optical glass of this embodiment is preferably 4% or less, more preferably 3% or less.

[0033] <zro2> ZrO2 is an effective component for improving chemical durability in the optical glass of this embodiment. However, if the content exceeds 3%, there is a risk that devitrification resistance and low-temperature moldability may deteriorate. Therefore, the content of ZrO2 in the optical glass of this embodiment is set to a range of 0% to 3%. From the same viewpoint, the content of ZrO2 in the optical glass of this embodiment is preferably 2% or less, and more preferably 1% or less.

[0034] <y2o3> In the optical glass of this embodiment, Y2O3 is a component effective in improving chemical durability. However, if the content exceeds 3%, there is a risk that the devitrification resistance stability and light weight may deteriorate. Therefore, in the optical glass of this embodiment, the content of Y2O3 is set to a range of 0% to 3%. From the same viewpoint, the content of Y2O3 in the optical glass of this embodiment is preferably 2% or less, and more preferably 1% or less.

[0035] <la2o3> In the optical glass of this embodiment, La2O3 is a component effective in improving chemical durability. However, if the content exceeds 3%, there is a risk that the devitrification resistance stability and light weight may deteriorate. Therefore, in the optical glass of this embodiment, the content of La2O3 is set to a range of 0% to 3%. From the same viewpoint, the content of La2O3 in the optical glass of this embodiment is preferably 2% or less, and more preferably 1% or less.

[0036] <gd2o3> Gd2O3 is a component effective in improving chemical durability in the optical glass of this embodiment. However, if its content exceeds 3%, there is a risk of deterioration in devitrification resistance stability and light weight. Therefore, in the optical glass of this embodiment, the content of Gd2O3 is set in the range of 0% or more and 3% or less. From the same perspective, the content of Gd2O3 in the optical glass of this embodiment is preferably 2% or less, and more preferably 1% or less.

[0037] <SrO and BaO> Both SrO and BaO tend to cause a decrease in refractive index with an increase in temperature. Furthermore, it has been found that in the optical glass of this embodiment containing the above-described components, there is a risk of deteriorating light weight (increasing the specific gravity). Therefore, the optical glass of this embodiment does not contain SrO and BaO. Here, "not containing SrO and BaO" means not intentionally containing SrO and BaO, that is, substantially not containing SrO and BaO.

[0038] <Other components> The optical glass of this embodiment may contain other components other than the above-described components as long as the purpose is not deviated. Examples of other components include SiO2, GeO2, Nb2O5, Ta2O5, WO3, Bi2O3, etc. However, from the perspective of more surely obtaining the desired effect, the proportion of the above-described other components in the optical glass of this embodiment is preferably 10 mol% or less, more preferably 5 mol% or less, still more preferably 3 mol% or less, even more preferably 1 mol% or less, and particularly preferably substantially 0 mol% (the optical glass has a composition consisting only of the above-described components).

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

[0040] <Refractive index (nd) and Abbe number (νd)> From the viewpoint of obtaining the desired low dispersion, the optical glass of this embodiment preferably has a refractive index (nd) of 1.50 or more and 1.60 or less, and an Abbe number (νd) of 60 or more and 70 or less. The refractive index (nd) of the optical glass of this embodiment is more preferably 1.51 or more, and even more preferably 1.52 or more. The Abbe number (νd) of the optical glass of this embodiment is more preferably 61 or more, and even more preferably 62 or more.

[0041] <Specific gravity (Sg)> From the viewpoint of achieving a desired light weight, the optical glass of this embodiment preferably has a specific gravity (Sg) of 2.90 or less. The specific gravity of the optical glass of this embodiment is more preferably 2.85 or less, and even more preferably 2.80 or less.

[0042] <Temperature coefficient of relative refractive index (0℃ / 20℃, wavelength 587.6nm)> From the viewpoint of obtaining the desired optical stability, the optical glass of this embodiment has an absolute value of the temperature coefficient of relative refractive index (0° C. / 20° C., wavelength 587.6 nm) of 2.0×10 -6 ℃ -1 In addition, the absolute value of the optical glass of the present embodiment is preferably 1.8×10 -6 ℃ -1 More preferably, it is 1.6×10 -6 ℃ -1 It is even more preferable that:

[0043] <Chemical durability> From the viewpoint of obtaining a desired chemical durability, the optical glass of this embodiment preferably has a chemical durability (surface method) rank (DW) of 1 or 2 as measured in accordance with JOGIS07-2019.

[0044] <Glass transition temperature (Tg) and yield temperature (At)> From the viewpoint of obtaining the desired low-temperature formability, the optical glass of this embodiment preferably has a glass transition temperature (Tg) of 500° C. or less and a yield temperature (At) of 540° C. or less. The glass transition temperature (Tg) of the optical glass of this embodiment is more preferably 490° C. or less, and even more preferably 480° C. or less. The yield temperature (At) of the optical glass of this embodiment is more preferably 530° C. or less, and even more preferably 520° C. or less.

[0045] The above-mentioned various properties can be measured by the procedures described in the Examples. The above-mentioned various properties of the optical glass of this embodiment can be adjusted, for example, by appropriately adjusting the contents of the above-mentioned components within predetermined ranges.

[0046] <Method of manufacturing optical glass> Next, a method for producing the optical glass of this embodiment will be described. Here, the optical glass of the present embodiment only needs to have the composition of each component satisfying the above-mentioned range, and the method of production thereof is not particularly limited, and it can be produced according to a conventional production method. For example, first, oxides, hydroxides, carbonates, nitrates, phosphates, etc. are weighed in a predetermined ratio as raw materials of each component that can be contained in the optical glass of this embodiment, and mixed thoroughly to obtain a glass compound raw material. Next, this raw material is put into a melting vessel (for example, a crucible made of a precious metal) that is not reactive with the glass raw materials, etc., and heated to 1000 to 1300 ° C in an electric furnace to melt, and stirred appropriately. Next, the mixture is clarified and homogenized in an electric furnace, cast into a mold preheated to an appropriate temperature, and then slowly cooled in the electric furnace to remove distortion, thereby producing the optical glass of this embodiment. Note that, in order to improve coloration and defoaming of the glass, a very small amount (for example, an amount of 0.5 mass % or less in the optical glass) of a component well known in the industry, such as Sb2O3, can be added.

[0047] The optical glass of this embodiment can be used as a material for precision press molding preforms and optical glass, as described below.

[0048] (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. Here, the precision press-molding preform refers to 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.

[0049] Here, precision press molding, also known as mold optics molding, is a method for 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 means a surface of an optical element that refracts, reflects, diffracts, or allows the light to enter or exit the optical element, and for example, the lens surface of a lens corresponds to this optically functional surface.

[0050] The preform of this embodiment is characterized by using the above-mentioned optical glass as a material. In this way, the preform of this embodiment uses the above-mentioned optical glass as a material, so it is lightweight, has small changes in optical properties due to temperature, and has excellent chemical durability and low-temperature moldability. From the viewpoint of 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.

[0051] There is no particular limitation on the method for producing the preform of this embodiment, however, it is preferable to produce the preform of this embodiment by the following production method, taking advantage of the excellent properties of the optical glass described above.

[0052] 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 lump, and the molten glass lump is cooled and molded into a preform.

[0053] The second preform production method (hereinafter referred to as "preform production method II") is a method in which optical glass as a raw material is melted, the resulting molten glass is molded to produce a glass molded body, and the molded body is processed to obtain a preform.

[0054] Both preform manufacturing methods I and II have in common the step of obtaining a homogeneous molten glass from optical glass as a raw material. In this step, for example, optical glass raw materials prepared by blending to obtain desired characteristics are placed in a platinum melting vessel, and heated, melted, refined, and homogenized to prepare a homogeneous molten glass, which can then be discharged from a temperature-adjusted outflow nozzle or outflow pipe made of platinum or a platinum alloy. Alternatively, optical glass raw materials may be roughly melted to prepare cullet, which may then be blended, heated, melted, refined, and homogenized to obtain a homogeneous molten glass, which can then be discharged from the outflow nozzle or outflow pipe.

[0055] Here, when producing a small preform or a spherical preform, for example, a method can be employed in which 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 molten glass droplets of a desired mass are dropped from an outflow nozzle into liquid nitrogen or the like to mold a preform.

[0056] On the other hand, when producing medium to large sized preforms, 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 desired mass of molten glass gob is received on a receiving member and molded into a preform.

[0057] These methods are all classified as dropping methods. Since the optical glass of the present embodiment used as the material has a low viscosity in the melt, these dropping methods can be suitably carried out.

[0058] In order to obtain a preform having a smooth surface, for example a free surface, free from scratches, stains, wrinkles, surface alteration, etc., methods that can be used include molding a molten glass lump into a preform while floating it up by applying air pressure to the molten glass lump on a preform molding die or molding the molten glass droplets into a medium such as liquid nitrogen, which is a gaseous substance at room temperature and pressure, by cooling it to a liquid, and molding the molten glass droplets into a preform.

[0059] 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 setting the viscosity of the molten glass gob to 3-60 dPa s, the glass gob can be floated without the floating gas getting into the glass.

[0060] Examples of the gas used when blowing the floating gas onto the preform include air, N2 gas, O2 gas, Ar gas, He gas, water vapor, etc. There are no particular limitations on the air pressure, so long as the preform can be floated without coming into contact with solid objects such as the surface of the mold.

[0061] Many precision press molded products (e.g., optical elements) manufactured from preforms have an axis of rotational symmetry, such as lenses, and so the shape of the preform is desirably one that also has an axis of rotational symmetry. Specific examples include a sphere or one with one axis of rotational symmetry. Shapes with one axis of rotational symmetry include those that have a smooth contour line without corners or depressions in a cross section including the axis of rotational symmetry, such as those that have an ellipse whose minor axis coincides with the axis of rotational symmetry in the cross section, and also include a flattened sphere shape (a shape in which an axis is defined that passes through the center of a sphere and the dimensions are reduced in the direction of the axis).

[0062] In Preform Manufacturing Method I, optical glass is molded in a temperature range where it is plastically deformable, 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 be made to approximate the shape of the intended 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.

[0063] In the preform manufacturing method II, for example, after casting molten glass into a mold to mold it, the molded body is annealed to remove distortion, cut or broken to divide it into a predetermined size and shape, and a plurality of glass pieces are produced, and the glass pieces are polished to smooth the surface, and a preform made of glass with a predetermined mass can be obtained. It is preferable to use the surface of the preform thus produced by coating it with a carbon-containing film. The preform manufacturing method II is suitable for producing a spherical preform, a flat preform, etc., which can be easily ground and polished.

[0064] Either manufacturing method can stably produce high-quality preforms and can also improve the mass productivity of the entire manufacturing process of optical elements.

[0065] 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.

[0066] The optical glass of this embodiment provides excellent precision press moldability from the viewpoint of glass material, and by reducing the amount of deformation of the glass during precision press molding, it becomes possible to lower the temperature 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, the above-mentioned problems that occur during precision press molding are reduced, and mass productivity is improved.

[0067] Here, when a lens is produced by precision press molding of a preform, a preferred preform is one having pressed surfaces (surfaces pressed by opposing mold surfaces during precision press molding) facing in opposite directions, and a preform having an axis of rotational symmetry passing through the centers of the two pressed surfaces is even more preferred. Among these preforms, those suitable for precision press molding of meniscus lenses are those in which one of the pressed surfaces is a convex surface and the other is a concave surface, a flat surface, or a convex surface with a smaller curvature than the convex surface.

[0068] Moreover, 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.

[0069] In either case, it is preferable that the preform has a shape that closely resembles the shape of the precision press-molded product.

[0070] 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. On the other hand, the upper surface of the glass has a shape determined by the surface tension of the molten glass and the weight of the glass. In order to reduce the amount of deformation of the glass during precision press molding, it is necessary to 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 is a convex free surface, but pressure can be applied to the upper surface of the glass to make the upper surface flat, concave, or a convex surface with a smaller curvature than the free surface. Specifically, the upper surface of the glass can be pressed with a mold having a molding surface of a desired shape, or the upper surface of the glass can be molded into a desired shape by applying air pressure to the upper surface of the glass. 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 shape the upper surface of the glass into a surface having a larger curvature than the free surface, the upper surface of the glass may be shaped so as to be raised by generating a negative pressure in the vicinity of the upper surface of the glass.

[0071] In addition, the preform is preferably a preform with a polished surface to approximate the shape of the precision press-molded product. For example, a preform is preferably one in which one of the pressed surfaces is polished to be a flat surface or a part of a sphere, and the other is polished to be a part of a sphere or a flat surface. Here, the part of the sphere may be a convex or concave surface, but it is desirable to determine whether it is a convex or concave surface depending on the shape of the precision press-molded product as described above.

[0072] The above preforms can be preferably used for molding lenses having a diameter of 10 mm or more, and more preferably for molding lenses having a diameter of 20 mm or more, and can also be preferably used for molding lenses having a center thickness of more than 2 mm.

[0073] (Optical elements) An optical element according to one embodiment of the present invention (hereinafter, may be referred to as "the optical element according to this embodiment") will be specifically described below. The optical element of this embodiment is characterized by using the above-mentioned optical glass as its material. In this way, the optical element of this embodiment uses the above-mentioned optical glass as its material, and therefore is lightweight, has small changes in optical properties due to temperature, and has excellent chemical durability. From the viewpoint of obtaining desired performance, the optical element of this embodiment preferably satisfies the essential requirements for the composition of each component already described for the optical glass of this embodiment, and more preferably satisfies the various preferable requirements already described for the optical glass of this embodiment.

[0074] 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. As optical elements, preferred examples 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 aspherical lenses or spherical lenses. If necessary, an anti-reflection film or a wavelength-selective partial reflection film may be provided on the surface.

[0075] <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 molding die.

[0076] Here, in precision press molding, a press mold whose molding surface has been processed to a desired shape with high precision can be used, and a mold release film may be formed on the molding surface to prevent the glass from fusing during pressing while allowing the glass to stretch well along the molding surface. Examples of mold release films include films of precious metals (platinum, platinum alloys), films of oxides (such as oxides of Si, Al, Zr, and Y), films of nitrides (such as nitrides of B, Si, and Al), and carbon-containing films. Carbon-containing films are preferably those containing carbon as the main component (films in which the carbon content is greater than the content of other elements when the element content in the film is expressed in atomic %), and specifically include carbon films and hydrocarbon films. Examples of the carbon-containing film include known methods such as vacuum deposition, sputtering, and ion plating using carbon raw materials, and known methods such as pyrolysis using material gas such as hydrocarbon. Other films can be formed using deposition, sputtering, ion plating, sol-gel, and the like.

[0077] In addition, the heating of the press mold and the preform and the precision press molding process are preferably carried out in a non-oxidizing gas atmosphere such as nitrogen gas or a mixed gas of nitrogen gas and hydrogen gas in order 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 the film remains on the surface of the precision press molded product. This film should be removed eventually, but in order to relatively easily and completely remove the release film such as the carbon-containing film, the precision press molded product may be heated in an oxidizing atmosphere, for example, in the air. The removal of the release film such as the carbon-containing film should be carried out at a temperature at which the precision press molded product is not deformed by heating. Specifically, the removal of the release film such as the carbon-containing film is preferably carried out in a temperature range below the glass transition temperature.

[0078] The method for producing the optical element of this embodiment is not particularly limited, and includes the following two methods. Here, in the production of 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.

[0079] 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 to perform 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.

[0080] In the optical element manufacturing method I, a preform is placed between a pair of opposing upper and lower dies 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 the recommended method when improving molding precision, such as surface accuracy and decentering precision, is important.

[0081] 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 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.

[0082] The pressure and time during pressing can be appropriately determined taking into consideration the viscosity of the glass, etc., and 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 according to the shape and dimensions of the molded product.

[0083] After this, the mold and the precision press-molded product are cooled, preferably to a temperature below the strain point. In order to precisely adjust the optical properties to desired values, the annealing conditions of the molded product during cooling, such as the annealing speed, may be appropriately adjusted.

[0084] The optical element of this embodiment can be produced without going through the press molding process, for example, by casting homogeneous molten glass into a mold to form a glass block, annealing it to remove distortion, adjusting the annealing conditions so that the refractive index of the glass is a desired value, adjusting the optical properties, and then cutting or breaking the glass block to produce glass pieces, which are then ground and polished to finish into an optical element. EXAMPLES

[0085] EXAMPLES The optical glass of 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.

[0086] As raw materials for each component, oxides, hydroxides, carbonates, nitrates, etc. corresponding to each component were prepared, and the raw materials were weighed and thoroughly mixed so that the composition shown in Tables 1 and 2 would be obtained after vitrification and the total weight would be 100 g, to obtain a blended raw material. The blended raw material was placed in a platinum crucible and melted in an electric furnace at 1000 to 1300°C for 1 to 2 hours. Thereafter, the mixture was appropriately stirred to homogenize, clarified, and cast into a mold preheated to an appropriate temperature, and then slowly cooled in an electric furnace to remove distortion, to obtain the optical glasses of the examples and comparative examples. The properties of each optical glass were evaluated according to the procedure shown below. The results are shown in Tables 1 and 2.

[0087] <Devitrification resistance stability> The optical glass block (glass block) was visually inspected for the presence or absence of devitrification matter, and the stability against devitrification was evaluated according to the following criteria. ○: No devitrified matter was observed △: Devitrified matter was observed only on the glass surface ×: Devitrified matter was observed inside the glass

[0088] <Refractive index (nd) and Abbe number (νd)> The refractive index (nd) and Abbe number (νd) of optical glass were measured in accordance with the Japanese Industrial Standard JIS B 7071-1:2018 "Method of measuring the refractive index of optical glass - Part 1: Minimum deviation method."

[0089] <Temperature coefficient of relative refractive index (0℃ / 20℃, wavelength 587.6nm)> The temperature coefficient of the relative refractive index of optical glass was measured in accordance with the Japanese Industrial Standard JIS B 7072-1:2020 "Method of measurement of the temperature coefficient of the relative refractive index of optical glass - Part 1: Minimum deviation angle method." The smaller the absolute value of this value, the smaller the change in optical properties due to temperature.

[0090] <Chemical durability> Optical glass was measured in accordance with the Japan Optical Glass Industry Association standard JOGIS07-2019 "Method for measuring chemical durability of optical glass (surface method)" and evaluated as to which of grades 1 to 5 it fell into. The smaller the grade number, the better the chemical durability.

[0091] <Specific gravity (Sg)> The specific gravity of optical glass was measured in accordance with the Japan Optical Glass Industry Association standard JOGIS05-2019 "Method for measuring the specific gravity of optical glass." The smaller the specific gravity value, the more lightweight the glass is.

[0092] <Glass transition temperature (Tg) and yield temperature (At)> The glass transition temperature (Tg) of optical glass was measured in accordance with the Japan Optical Glass Industry Association standard JOGIS08-2019 "Method for measuring thermal expansion of optical glass." In the above measurement, the temperature at which the optical glass sample stops elongating and starts shrinking was confirmed as the yield temperature (At). For both the glass transition temperature (Tg) and yield temperature (At), the smaller the value, the better the low-temperature moldability.

[0093] [Table 1]

[0094] [Table 2]

[0095] From Table 1, it can be seen that all of the optical glasses of the Examples have low dispersion, since they have an Abbe number (νd) of 60 or more. In addition, all of the optical glasses of the Examples have a specific gravity of 2.90 or less, so they are lightweight. In addition, all of the optical glasses of the Examples have an absolute value of the temperature coefficient of the relative refractive index of 2.0×10 -6 ℃ -1 It is clear that the change in optical properties due to temperature is small, as shown in Table 1. All of the optical glasses in the Examples have chemical durability grades of 1 or 2, which indicates that they have excellent chemical durability. Furthermore, all of the optical glasses in the Examples have glass transition temperatures (Tg) of 500°C or less and yield temperatures (At) of 540°C or less, which indicates that they have excellent low-temperature formability.

[0096] In contrast, Table 2 shows that the optical glass of Comparative Example 1 has poor resistance to devitrification. This is believed to be due to the B2O3 content being too high. Moreover, the optical glass of Comparative Example 2 has low stability against devitrification and a high glass transition temperature (Tg) and yield temperature (At), which is believed to be due to the P2O5 content being too low. Moreover, the optical glass of Comparative Example 3 has a chemical durability of grade 3, which is low. This is believed to be due to the P2O5 content being too high.

[0097] Moreover, the optical glass of Comparative Example 4 has low stability against devitrification and a large absolute value of the temperature coefficient of the relative refractive index, which is believed to be due to the Al2O3 content being too high. Moreover, the optical glass of Comparative Example 5 has a high glass transition temperature (Tg) and a high yield temperature (At), which is believed to be due to the fact that the Li2O content is too low. Moreover, the optical glass of Comparative Example 6 has low stability against devitrification, which is believed to be due to the Li2O content being too high.

[0098] Moreover, the absolute value of the temperature coefficient of the relative refractive index is large in the optical glass of Comparative Example 7. This is believed to be due to the Na2O content being too high. Moreover, the optical glass of Comparative Example 8 has low stability against devitrification, which is believed to be due to the MgO content being too high. Moreover, the optical glass of Comparative Example 9 has low stability against devitrification, and has a high glass transition temperature (Tg) and a high yield temperature (At), which is believed to be due to the excessive CaO content.

[0099] Moreover, the optical glass of Comparative Example 10 has low stability against devitrification and a high specific gravity, which is believed to be due to the Gd2O3 content being too high. Moreover, the optical glass of Comparative Example 11 has low stability against devitrification, and a high glass transition temperature (Tg) and yield temperature (At), which is believed to be due to the total amount of B2O3 and P2O5 being too small. Moreover, the optical glass of Comparative Example 12 has low chemical durability, with a chemical durability grade of 3. This is believed to be due to the total amount of B2O3 and P2O5 being too high.

[0100] Moreover, the optical glass of Comparative Example 13 has low chemical durability, with a chemical durability grade of 3. This is believed to be due to the total amount of MgO and CaO being too small. Moreover, the optical glass of Comparative Example 14 has a high specific gravity, which is believed to be due to the inclusion of SrO. Moreover, the optical glass of Comparative Example 15 has a high specific gravity, which is believed to be due to the inclusion of BaO.

[0101] Moreover, the optical glass of Comparative Example 16 has a high specific gravity, which is believed to be due to the inclusion of SrO and BaO. The optical glass of Comparative Example 17 has a chemical durability of Class 3, which means that the chemical durability is low, the absolute value of the temperature coefficient of the relative refractive index is large, and furthermore, the specific gravity is high. This is believed to be due to the small total amount of MgO and CaO and the inclusion of SrO and BaO. [Industrial Applicability]

[0102] According to the present invention, it is possible to provide a low-dispersion optical glass that is lightweight, exhibits little change in optical properties due to temperature, and has excellent chemical durability and low-temperature moldability. Furthermore, according to the present invention, it is possible to provide a precision press molding preform and an optical element using the above optical glass. < / zno> < / cao> < / mgo>

Claims

1. In mole percent, B ２ O ３ :0% or more but less than 15% P ２ O ５ : 25% or more but less than 40% However, B ２ O ３ and P ２ O ５ Total: 35% or more and 45% or less, A ２ O ３ :0% or more but less than 10% Li ２ O:5% or more but less than 15% Na ２ O:0% or more but less than 15% K ２ O:0% or more but less than 5% MgO: 0% or more and 35% or less, CaO: 0% or more and 35% or less, However, the total content of MgO and CaO is 20% or more. ZnO: 0% or more and 5% or less, ZrO ２ :0% or more but less than 3% Y ２ O ３ :0% or more but less than 3% La ２ O ３ : 0% or more and 3% or less, and Gd ２ O ３ :0% or more but less than 3% and Does not contain SrO or BaO; The proportion of other components other than the above-mentioned components is 1 mol % or less, An optical glass having an Abbe number (νd) of 61 or more.

2. 2. The optical glass according to claim 1, having a refractive index (nd) of 1.50 or greater and 1.60 or less, and an Abbe number (νd) of 61 or greater and 70 or less.

3. 3. The optical glass according to claim 1, which has a specific gravity of 2.90 or less.

4. The absolute value of the temperature coefficient of relative refractive index (0° C. / 20° C., wavelength 587.6 nm) is 2.0×10 －６ ℃ －１ 4. The optical glass according to claim 1, wherein:

5. 5. The optical glass according to claim 1, wherein the chemical durability (surface method) measured in accordance with JOGIS07-2019 is ranked (DW) as 1 or 2.

6. 6. The optical glass according to claim 1, which has a glass transition temperature (Tg) of 500° C. or lower and a yield temperature (At) of 540° C. or lower.

7. A precision press molding preform, characterized in that the optical glass according to any one of claims 1 to 6 is used as a material.

8. An optical element, characterized in that the optical glass according to any one of claims 1 to 6 is used as a material.

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