JP7409629B2 - Optical glass, preforms for precision press molding, and optical elements - Google Patents

Description

The present invention relates to an optical glass, a preform for precision press molding, and an optical element.

BACKGROUND ART With the spread and development of optical equipment, optical glasses having various properties have been required. In particular, in recent years, there has been an increasing demand for optical glass that can achieve smaller size and higher performance products, with automotive optical equipment, surveillance cameras, and the like in mind.

In order to achieve miniaturization and high performance of products, it is necessary to use glass with a high refractive index (for example, glass with a refractive index (nd) of 1.80 or more) and a glass that can compensate for the optical properties of such high refractive index glass. It is essential to combine these.

Here, since glass with a high refractive index generally has high dispersion and tends to cause chromatic aberration, it is usually necessary to correct the chromatic aberration by combining it with glass with low dispersion. On the other hand, however, since low-dispersion glass tends to have a low refractive index, it is often disadvantageous in achieving miniaturization. Therefore, at present, as a glass to be combined with high refractive index glass, glasses that have a somewhat high refractive index and maintain low dispersion, in other words, optical glasses with medium refractive index and low dispersion (refractive index (nd): approx. 1.55 to 1.63, Abbe number (νd): approximately 50 to 65).

Furthermore, since optical glasses (lenses) used in projectors, vehicle-mounted optical equipment, and the like are sometimes exposed to severe changes in environmental temperature, it is desirable that temperature changes have little adverse effect on imaging, etc. In this regard, the high refractive index glass described above tends to have a large amount of change in refractive index with respect to temperature. Therefore, as a glass to be combined with such high refractive index glass, it is necessary to select a glass whose refractive index changes with respect to temperature is small or negatively large, so as to offset or suppress the temperature dependence of the refractive index as much as possible. It will be done.

As an optical glass with a medium refractive index and low dispersion, for example, Patent Document 1 discloses a glass having a predetermined composition of SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -ZnO-BaO-Li ₂ O system and having a refractive index of An optical glass having optical constants (nd) in the range of 1.55 to 1.63 and Abbe's number (νd) in the range of 55 to 63 is disclosed.

However, since the optical glass described in Patent Document 1 has a significantly large change in refractive index with respect to temperature, when it is combined with glass having a high refractive index, there is a risk that the imaging performance will be significantly deteriorated in accordance with temperature changes. There is.

On the other hand, Patent Document 2 discloses an optical glass that contains SiO ₂ , B ₂ O ₃ , and La ₂ O ₃ and exhibits little performance deterioration due to temperature changes.

Japanese Unexamined Patent Publication No. 10-194772 Japanese Patent Application Publication No. 2007-106611

However, the optical glass described in Patent Document 2 contains a large amount of La ₂ O ₃ and Gd ₂ O ₃ which are high refractive index components, so the refractive index (nd) is larger than 1.63. Furthermore, since La ₂ O ₃ and Gd ₂ O ₃ described above are difficult to melt, if they are blended in large amounts, there is a risk that the meltability and devitrification resistance of the glass will deteriorate.

The present invention was developed in view of the above-mentioned current situation, and has a medium refractive index and low dispersion, good meltability, and suppresses temperature dependence of imaging when combined with other glasses. The purpose is to provide optical glass that is possible. Another object of the present invention is to provide a precision press molding preform and an optical element using the above-mentioned optical glass.

In order to achieve the above object, as a result of extensive studies, the present inventor has determined that the basic composition is SiO ₂ and BaO, and the total content of Li ₂ O, Na ₂ O and K ₂ O, as well as CaO and BaO. By optimizing the total content of and not including ZnO and SrO, the amount of change in refractive index (n) with respect to temperature (T) (temperature coefficient of relative refractive index (dn/dT)) is small. It has been found that the temperature dependence of image formation can be suppressed by increasing or becoming negatively large, and an optical glass having good meltability can be obtained.

That is, the optical glass of the present invention has SiO ₂ :30% or more and 60% or less in mass %,
B ₂ O ₃ : 0% or more and 15% or less,
Li ₂ O: 0% or more and 10% or less,
Na ₂ O: 0% or more and 10% or less,
K ₂ O: 0% or more and 15% or less,
Al ₂ O ₃ : 0% or more and 7% or less,
CaO: 0% or more and 15% or less,
BaO: 12% or more and 40% or less,
Nb ₂ O ₅ : 0% or more and 5% or less,
_ZrO2 : 0% or more and 7% or less,
_TiO2 : 0% or more and 5% or less,
_Y2O3 : 0% or more and 5 _% or less,
La ₂ O ₃ : 0% or more and 5% or less,
has a composition containing
Does not contain ZnO and SrO,
The total content of Li ₂ O, Na ₂ O and K ₂ O is 12% or more and 35% or less,
The total content of CaO and BaO is 13% or more and 55% or less,
The temperature coefficient of relative refractive index (40 to 60°C) with respect to the d-line (587.562 nm) is -5.0 x 10 ^-6 °C ^-1 or more and 3.0 x 10 ^-6 °C ^-1 or less. shall be. Such optical glass has a medium refractive index and low dispersion, has good meltability, and can suppress the temperature dependence of imaging when combined with other glasses.

The optical glass of the present invention preferably has a refractive index (nd) of 1.55 or more and 1.63 or less, and an Abbe number (νd) of 50 or more and 65 or less.

The optical glass of the present invention preferably has a glass transition temperature (Tg) of 540°C or lower.

The precision press molding preform of the present invention is characterized by using the above optical glass as a material. Such a precision press molding preform can be used together with other glasses to obtain a product in which the temperature dependence of image formation is suppressed.

The optical element of the present invention is characterized in that the optical glass described above is used as a material. Such an optical element can be combined with other glasses to obtain a product in which the temperature dependence of imaging is suppressed.

According to the present invention, it is possible to provide an optical glass that has a medium refractive index and low dispersion, has good meltability, and can suppress temperature dependence of imaging when combined with other glasses. can. Further, according to the present invention, it is possible to provide a precision press molding preform and an optical element using the above-mentioned optical glass.

Hereinafter, the present invention will be specifically described using embodiments.

(optical glass)
The optical glass of one embodiment of the present invention (hereinafter sometimes referred to as "optical glass of the present embodiment") has _SiO2 : 30% or more and 60% or less in mass %,
B ₂ O ₃ : 0% or more and 15% or less,
Li ₂ O: 0% or more and 10% or less,
Na ₂ O: 0% or more and 10% or less,
K ₂ O: 0% or more and 15% or less,
Al ₂ O ₃ : 0% or more and 7% or less,
CaO: 0% or more and 15% or less,
BaO: 12% or more and 40% or less,
Nb ₂ O ₅ : 0% or more and 5% or less,
_ZrO2 : 0% or more and 7% or less,
_TiO2 : 0% or more and 5% or less,
_Y2O3 : 0% or more and 5 _% or less,
La ₂ O ₃ : 0% or more and 5% or less,
has a composition containing
Does not contain ZnO and SrO,
The total content of Li ₂ O, Na ₂ O and K ₂ O is 12% or more and 35% or less,
The total content of CaO and BaO is 13% or more and 55% or less,
The temperature coefficient of relative refractive index (40 to 60°C) with respect to the d-line (587.562 nm) is -5.0 x 10 ^-6 °C ^-1 or more and 3.0 x 10 ^-6 °C ^-1 or less. shall be.

In addition, the optical glass of this embodiment may contain other components (described later) other than the above-mentioned components. However, the optical glass of this embodiment contains the above-mentioned components (SiO ₂ , B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, Al ₂ O ₃ , CaO, BaO, Nb ₂ O ₅ , ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ ). preferable.
Here, "consisting only of the above-mentioned components" includes cases where impurity components other than the above-mentioned components are unavoidably mixed, specifically, the case where the proportion of impurity components is 0.2% by mass or less. shall be.

First, in this embodiment, the reason why the composition of the optical glass is limited to the above range will be explained. Note that "%" regarding components means mass % unless otherwise specified.

_<SiO2>
SiO ₂ is an essential component in the optical glass of this embodiment, and is a main component forming the network structure that becomes the skeleton of the glass. Moreover, SiO ₂ is a component that can improve devitrification resistance and chemical durability. However, when the content of SiO ₂ in the optical glass exceeds 60%, the refractive index decreases, the meltability deteriorates, and the glass transition temperature (Tg) and the yield temperature (At) increase. On the other hand, if the content of SiO ₂ in the optical glass is less than 30%, chemical durability and anti-devitrification stability will deteriorate. Therefore, in the optical glass of this embodiment, the content of SiO ₂ is set in a range of 30% or more and 60% or less. From the same viewpoint, the content of SiO ₂ in the optical glass of this embodiment is preferably 32% or more, more preferably 34% or more, and preferably 58% or less, 56% or more. % or less is more preferable.

<B ₂ O ₃ >
In the optical glass of this embodiment, B ₂ O ₃ is a component that forms the network structure of the glass like SiO ₂ , and is also an effective component for homogenizing the glass and improving meltability when used in an appropriate amount. be. However, when the content of B ₂ O ₃ in the optical glass exceeds 15%, the refractive index decreases, the glass transition temperature (Tg) and the yield temperature (At) increase, and the devitrification resistance stability deteriorates. Therefore, in the optical glass of this embodiment, the content of B ₂ O ₃ is set in a range of 0% to 15%. From the same viewpoint, the content of B ₂ O ₃ in the optical glass of this embodiment is preferably 14.5% or less, more preferably 14% or less.

<Li ₂ O>
Li ₂ O is an effective component for lowering the glass transition temperature (Tg) and yielding temperature (At), improving meltability, and lowering the temperature coefficient of relative refractive index. However, when the Li ₂ O content in the optical glass exceeds 10%, chemical durability and anti-devitrification stability deteriorate. Therefore, in the optical glass of this embodiment, the content of Li ₂ O is set in a range of 0% to 10%. From the same viewpoint, the content of Li ₂ O in the optical glass of this embodiment is preferably 9.5% or less, more preferably 9% or less.

<Na ₂ O>
Na ₂ O is an effective component for lowering the glass transition temperature (Tg) and yielding temperature (At), improving meltability, and lowering the temperature coefficient of relative refractive index. However, when the content of Na ₂ O in the optical glass exceeds 10%, chemical durability and anti-devitrification stability deteriorate. Therefore, in the optical glass of this embodiment, the content of Na ₂ O is set in a range of 0% to 10%. From the same viewpoint, the content of Na ₂ O in the optical glass of this embodiment is preferably 9.5% or less, more preferably 9% or less.

<K ₂ O>
K ₂ O is an effective component for lowering the glass transition temperature (Tg) and yielding temperature (At), improving meltability, and reducing the temperature coefficient of relative refractive index. However, when the content of K ₂ O in the optical glass exceeds 15%, chemical durability and devitrification resistance stability deteriorate. Therefore, in the optical glass of this embodiment, the content of K ₂ O is set in the range of 0% to 15%. From the same viewpoint, the content of K ₂ O in the optical glass of this embodiment is preferably 14% or less, more preferably 13% or less.

<Total of Li ₂ O, Na ₂ O and K ₂ O>
Here, the optical glass of this embodiment requires that the total content of Li ₂ O, Na ₂ O, and K ₂ O be 12% or more and 35% or less. If the above-mentioned total content is less than 12%, it results in a decrease in meltability, an increase in glass transition temperature (Tg) and a yield temperature (At), and an increase in the temperature coefficient of relative refractive index. On the other hand, if the total content exceeds 35%, chemical durability and devitrification resistance stability will deteriorate. Further, from the same viewpoint, the total content of Li ₂ O, Na ₂ O and K ₂ O in the optical glass of this embodiment is preferably 12.5% or more, and preferably 13% or more. More preferably, it is 32% or less, and more preferably 30% or less.

_{<Al2O3> _}
Al ₂ O ₃ is a component that, when added together with oxides such as Li ₂ O and Na ₂ O, forms a network structure of the glass and can improve the devitrification resistance stability and chemical durability of the glass. be. However, when the content of Al ₂ O ₃ in the optical glass exceeds 7%, the meltability deteriorates. Therefore, in the optical glass of this embodiment, the content of Al ₂ O ₃ is set in a range of 0% or more and 7% or less. From the same viewpoint, the content of Al ₂ O ₃ in the optical glass of this embodiment is preferably 6.5% or less, more preferably 6% or less.

<CaO>
CaO is an effective component for lowering the glass transition temperature (Tg) and yielding temperature (At), improving meltability, and reducing the temperature coefficient of relative refractive index. However, when the content of CaO in the optical glass exceeds 15%, the devitrification resistance stability decreases. Therefore, in the optical glass of this embodiment, the content of CaO is set in a range of 0% to 15%. From the same viewpoint, the content of CaO in the optical glass of this embodiment is preferably 14% or less, more preferably 13% or less.

<BaO>
BaO is an essential component in the optical glass of this embodiment, and is an effective component for reducing the temperature coefficient of relative refractive index. BaO is also an effective component for increasing the refractive index and improving meltability. However, when the BaO content in the optical glass exceeds 40%, chemical durability and devitrification resistance stability decrease. On the other hand, if the BaO content in the optical glass is less than 12%, the temperature coefficient of refractive index cannot be effectively reduced, and the meltability also deteriorates. Therefore, in the optical glass of this embodiment, the BaO content is set in a range of 12% or more and 40% or less. From the same viewpoint, the BaO content in the optical glass of this embodiment is preferably 13% or more, more preferably 14% or more, and preferably 38% or less, 36% or more. It is more preferable that it is below.

<Total of CaO and BaO>
Here, the optical glass of this embodiment requires that the total content of CaO and BaO is 13% or more and 55% or less. If the total content is less than 13%, the meltability decreases, the glass transition temperature (Tg) and the yield temperature (At) increase, and the temperature coefficient of relative refractive index increases. On the other hand, if the total content exceeds 55%, chemical durability and devitrification resistance stability will deteriorate. Further, from the same viewpoint, the total content of CaO and BaO in the optical glass of this embodiment is preferably 13.5% or more, more preferably 14% or more, and 52% or less. It is preferably 50% or less, and more preferably 50% or less.

<Nb ₂ O ₅ >
Nb ₂ O ₅ is an effective component for increasing the refractive index and chemical durability of glass. However, when the content of Nb ₂ O ₅ in the optical glass exceeds 5%, the meltability deteriorates. Therefore, in the optical glass of this embodiment, the content of Nb ₂ O ₅ is set in a range of 0% to 5%. From the same viewpoint, the content of Nb ₂ O ₅ in the optical glass of this embodiment is preferably 4.5% or less, more preferably 4% or less.

_<ZrO2>
ZrO ₂ is an effective component for increasing the refractive index of glass and improving chemical durability. However, when the content of ZrO ₂ in the optical glass exceeds 7%, the meltability deteriorates. Therefore, in the optical glass of this embodiment, the content of ZrO ₂ is set in the range of 0% to 7%. From the same viewpoint, the content of ZrO ₂ in the optical glass of this embodiment is preferably 6.5% or less, more preferably 6% or less.

_<TiO2>
TiO ₂ is an effective component for increasing the refractive index of glass and lowering the liquidus temperature. However, when the content of TiO ₂ in the optical glass exceeds 5%, the meltability deteriorates. Therefore, in the optical glass of this embodiment, the content of TiO ₂ is set in a range of 0% to 5%. From the same viewpoint, the content of TiO ₂ in the optical glass of this embodiment is preferably 4.5% or less, more preferably 4% or less.

_{<Y2O3> _}
Y ₂ O ₃ is an effective component for increasing the refractive index of glass and improving chemical durability. However, if the content of Y ₂ O ₃ in the optical glass exceeds 5%, the meltability deteriorates. Therefore, in the optical glass of this embodiment, the content of Y ₂ O ₃ is set in a range of 0% to 5%. From the same viewpoint, the content of Y ₂ O ₃ in the optical glass of this embodiment is preferably 4.5% or less, more preferably 4% or less.

<La ₂ O ₃ >
La ₂ O ₃ is an effective component for increasing the refractive index and chemical durability of glass. However, when the content of La ₂ O ₃ in the optical glass exceeds 5%, the meltability deteriorates. Therefore, in the optical glass of this embodiment, the content of La ₂ O ₃ is set in a range of 0% or more and 5% or less. From the same viewpoint, the content of La ₂ O ₃ in the optical glass of this embodiment is preferably 4.5% or less, more preferably 4% or less.

<ZnO (non-containing component)>
Although ZnO can lower the glass transition temperature (Tg) and yield temperature (At), in optical glasses containing the above-mentioned components, the temperature coefficient of relative refractive index is lower than 3.0 × 10 ^-6 °C ^-1. It became clear that there was a risk that it could not be contained. Therefore, the optical glass of this embodiment does not contain ZnO.
Here, in this specification, "not containing" a certain component means that the component is not intentionally contained, that is, the component is not substantially contained.

<SrO (non-containing component)>
SrO is an effective component for lowering the glass transition temperature (Tg) and the yield temperature (At), and for reducing the temperature coefficient of relative refractive index. However, SrO raw materials that are easily available on the market often contain a certain amount of transition metals as impurities that have absorption in the visible region, that is, cause coloration of glass. Further, reducing the impurities in the SrO raw material as described above requires a large amount of cost. Therefore, the optical glass of this embodiment does not contain SrO.

<Other ingredients>
The optical glass of this embodiment contains other components other than the above-mentioned components, for example, MgO, Ga ₂ O 3 , Sb 2 O ₃ , Gd ₂ O ₃ , Bi ₂ O ₃ , GeO ₂ , as long as it does _{not deviate} from the purpose. It may contain a small amount of SnO ₂ , P ₂ O ₅ , Ta ₂ O ₅ , MoO ₃ , WO _{3 ,} etc. (for example, in an amount of 5% by mass or less each).
Note that the optical glass of this embodiment preferably does not contain components that have a high burden on the environment and have a high adverse effect on the human body, such as PbO, TeO ₂ , As ₂ O ₃ , and CdO.

Next, various characteristics of the optical glass of this embodiment will be explained.

<Refractive index (nd) and Abbe number (νd)>
In order to meet specific needs, the optical glass of this embodiment preferably has a medium refractive index and low dispersion. More specifically, the optical glass of this embodiment preferably has a refractive index (nd) of 1.55 or more and 1.63 or less, and an Abbe number (vd) of 50 or more and 65 or less. Moreover, it is more preferable that the refractive index (nd) of the optical glass of this embodiment is 1.56 or more, and it is more preferable that it is 1.62 or less. Further, the Abbe number (vd) of the optical glass of this embodiment is more preferably 51 or more, even more preferably 53.5 or more, and more preferably 64 or less.
Note that the refractive index (nd) and Abbe number (vd) can be measured by the procedure described in Examples. Further, the refractive index (nd) and Abbe number (vd) of the optical glass of the present embodiment can be adjusted, for example, by appropriately adjusting the content of each component described above within a predetermined range.

<Temperature coefficient of relative refractive index (dn/dT)>
The optical glass of this embodiment has a relative refractive index temperature coefficient (40 to 60°C) with respect to the d-line (587.562 nm) of -5.0×10 ^-6 °C ^-1 or more and 3.0×10 ^-6 °C. Must be ^-1 or less. Here, if the composition of the optical glass is as described above and the temperature coefficient is less than -5.0×10 ^-6 °C ^-1 , it is possible to ensure the minimum chemical durability as an optical glass. Can not. Furthermore, if the above-mentioned temperature coefficient of optical glass exceeds 3.0 × 10 ^-6 °C ^-1 , the amount of change in refractive index with respect to temperature is positively large, so that the temperature dependence of imaging when combined with other glasses is Unable to fully suppress sexuality. The above-mentioned temperature coefficient of the optical glass of this embodiment is preferably -4.0×10 ^-6 °C ^-1 or higher, and -3.5×10 ^-6 °C from the viewpoint of improving chemical durability. It is more preferable that it is ^-1 or more. Further, the temperature coefficient of the optical glass of this embodiment is preferably 2.7×10 ^-6 °C ^-1 or less, and 2.5 It is more preferable that the temperature is ×10 ⁻⁶ °C ⁻¹ or less.
Note that the temperature coefficient of relative refractive index (40 to 60° C.) regarding the d-line (587.562 nm) can be measured by the procedure described in Examples. Further, the temperature coefficient of the optical glass of the present embodiment can be adjusted, for example, by appropriately adjusting the content of each component described above within a predetermined range.

<Glass transition temperature (Tg)>
The optical glass of this embodiment preferably has a glass transition temperature (Tg) of 540° C. or lower. When the glass transition temperature (Tg) of the optical glass is 540° C. or less, the softening temperature is also low, and precision press molding can be performed more easily. From the same viewpoint, the glass transition temperature (Tg) of the optical glass of this embodiment is more preferably 535°C or lower, and even more preferably 530°C or lower.
Note that the glass transition temperature (Tg) can be measured by the procedure described in Examples. Moreover, the glass transition temperature (Tg) of the optical glass of this embodiment can be adjusted, for example, by appropriately adjusting the content of each component mentioned above within a predetermined range.

<Method for manufacturing optical glass>
Next, a method for manufacturing optical glass according to this embodiment will be explained.
Here, the optical glass of this embodiment only needs to satisfy the above-mentioned ranges for the composition of each component, and the manufacturing method thereof is not particularly limited, and can be manufactured according to a conventional manufacturing method.
For example, first, oxides, hydroxides, carbonates, nitrates, etc. are weighed in predetermined proportions as raw materials for each component that can be included in the optical glass of this embodiment, and the mixture is sufficiently mixed to form a glass preparation raw material. . Next, this raw material is put into a melting container (for example, a crucible made of a noble metal such as platinum) that is not reactive with glass raw materials, and heated to 1000 to 1500° C. in an electric furnace to melt it. After that, the optical system of this embodiment is made by stirring at appropriate times to achieve homogenization and clarification, and then casting into a mold preheated to an appropriate temperature, and then slowly cooling in an electric furnace to remove distortion. Glass can be manufactured. Note that for defoaming, a very small amount (for example, an amount less than 1% by mass in the optical glass) of a fining agent such as Sb ₂ O ₃ can be added.

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

Here, precision press molding is also known as mold optics molding, and is a method in which the optically functional surface of the finally obtained optical element is formed by transferring the molding surface of a press mold. Note that the optically functional surface refers to a surface in an optical element that refracts, reflects, diffracts, or enters and outputs the light to be controlled.For example, the lens surface of a lens has this optical function. Corresponds to the functional aspect.

The preform of this embodiment is characterized by using the above-mentioned optical glass as a material. In this way, since the material of the preform of this embodiment is the above-mentioned optical glass, it is possible to obtain a product in which the temperature dependence of image formation is suppressed together with other glasses (for example, high refractive index glass). It can be used for In addition, from the viewpoint of more reliably obtaining the desired optical constants, the preform of the present embodiment preferably satisfies the essential requirements regarding the composition of each component as already described for the optical glass of the present invention. It is more preferable that the glass satisfies the various requirements already described as preferable.

The method for manufacturing the preform of this embodiment is not particularly limited. However, it is preferable that the preform of this embodiment be manufactured by the following manufacturing method, taking advantage of the excellent characteristics of the above-mentioned optical glass.

The first preform manufacturing method (referred to as "preform manufacturing method I") is to melt optical glass as a raw material, flow out the obtained molten glass, separate a molten glass lump, and separate the molten glass lump. In this method, the material is molded into a preform during the cooling process.

The second preform manufacturing method (referred to as "preform manufacturing method II") involves melting optical glass as a raw material, molding the obtained molten glass to create a glass molded body, and molding the molded body. This is a method of processing to obtain a preform.

Both preform manufacturing methods I and II have in common that they include a step of obtaining homogeneous molten glass from optical glass as a raw material. In this process, for example, optical glass raw materials prepared by blending to obtain desired properties are placed in a platinum melting container, heated, melted, clarified, and homogenized to prepare a homogeneous molten glass, and the temperature It can exit through a controlled platinum or platinum alloy outflow nozzle or outflow pipe. Note that it is also possible to roughly melt the optical glass raw material to produce a cullet, heat, melt, clarify, and homogenize the cullet to obtain a homogeneous molten glass, which then flows out from the above-mentioned outflow nozzle or outflow pipe. good.

Here, when producing a small preform or a spherical preform, for example, a method is used in which molten glass is dropped as molten glass droplets of a desired mass from an outflow nozzle, and the droplets are received by a mold or the like and formed into a preform. can be adopted. Alternatively, a method of molding a preform by dropping molten glass droplets of a desired mass into liquid nitrogen or the like from an outflow nozzle can be adopted.
On the other hand, when producing a medium-sized or large-sized preform, for example, the molten glass flow is made to flow down from an outflow pipe, the tip of the molten glass flow is received by a preform mold, etc., and the nozzle of the molten glass flow is connected to the preform mold. After forming a constriction between the preform and the mold, the preform mold is suddenly lowered, the molten glass flow is separated at the constriction by the surface tension of the molten glass, and the receiving member receives a desired mass of molten glass gob. A method of molding it into a preform can be adopted.

In addition, in order to obtain a preform with a smooth surface free from scratches, dirt, wrinkles, and surface deterioration, such as a free surface, the molten glass lump is floated by applying wind pressure on a preform mold, etc. Methods such as molding into a preform or molding into a preform by placing molten glass droplets in a medium such as liquid nitrogen, which is a gaseous substance at room temperature and pressure, is cooled and turned into a liquid, are used.

Here, when forming a molten glass gob into a preform while floating it, gas (referred to as floating gas) is blown onto the molten glass gob, and upward wind pressure is applied to the molten glass gob. At this time, if the viscosity of the molten glass lump is too low, floating gas will enter the glass and remain as bubbles in the preform. However, by setting the viscosity of the molten glass gob to 3 to 60 dPa·s, the glass gob can be floated without the floating gas entering into the glass.

Examples of the gas used when the floating gas is blown onto the preform include air, N ₂ gas, O ₂ gas, Ar gas, He gas, and water vapor. Further, there is no particular restriction on the wind pressure as long as the preform can float without coming into contact with solid objects such as the surface of the mold.

Precision press molded products (for example, optical elements) manufactured from preforms often have an axis of rotational symmetry, such as lenses, so it is desirable that the shape of the preform also has an axis of rotational symmetry. Specific examples include a sphere or one having one axis of rotational symmetry. A shape with one axis of rotational symmetry is one that has a smooth contour line without corners or depressions in the cross section that includes the axis of rotational symmetry, for example, an ellipse whose short axis coincides with the axis of rotational symmetry in the cross section. For example, a shape in which a sphere is flattened (a shape in which one axis passing through the center of the sphere is defined and the dimensions are reduced in the axial direction) can also be mentioned.

In preform manufacturing method I, since optical glass is molded in a temperature range where it can be plastically deformed, a preform may be obtained by press molding a glass gob. In that case, the shape of the preform can be set relatively freely, so it can be made to approximate the shape of the target precision press-molded product, for example, one of the opposing surfaces can be made convex and the other concave, or both. can be concave, one surface can be flat and the other convex, one surface can be flat and the other concave, or both can be convex.

In preform manufacturing method II, for example, after molten glass is cast into a mold and shaped, the distortion of the molded body is removed by annealing, and the molded body is divided into predetermined dimensions and shapes by cutting or fracturing. By making a piece and polishing the glass piece to make the surface smooth, a preform of glass of a given mass can be obtained. It is preferable that the surface of the preform thus produced is also coated with a carbon-containing film. Preform manufacturing method II is suitable for manufacturing spherical preforms, flat plate preforms, etc. that can be easily ground and polished.

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

In manufacturing the preform of this embodiment, by reducing the amount of deformation of the glass during precision press molding, the temperature of the glass and mold during precision press molding can be lowered, the time required for press molding can be shortened, and the press pressure can be reduced. This makes it possible to reduce As a result, the reactivity between the glass and the molding surface of the mold is reduced, problems that occur during precision press molding are reduced, and mass productivity is further improved.

Here, in the case where a lens is produced by precision press molding of a preform, a preferable preform is a preform having pressed surfaces facing in opposite directions (surfaces to be pressed by opposing forming surfaces of molds during precision press molding). More preferably, the preform is a reformed one and further has an axis of rotational symmetry passing through the centers of the two surfaces to be pressed. Among these preforms, those suitable for precision press molding of meniscus lenses are those in which one of the surfaces to be pressed 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.

Further, a preform suitable for precision press molding of a biconcave lens is a preform in which one of the surfaces to be pressed is a convex surface, a concave surface, or a flat surface, and the other surface is a convex surface, a concave surface, or a flat surface.
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 a convex surface and the other surface is a convex surface or a flat surface.

In either case, the preform preferably has a shape that more closely approximates the shape of the precision press-molded product.

Note that when a molten glass gob is molded into a preform using a preform mold, the lower surface of the glass on the mold is approximately determined by the shape of the molding surface of the mold. On the other hand, the top surface of the glass has a shape determined by the surface tension of the molten glass and the own weight of the glass. Here, in order to reduce the amount of deformation of the glass during precision press molding, it is also necessary to control the shape of the upper surface of the glass during molding in the preform mold. The shape of the top surface of the glass determined by the surface tension of the molten glass and the weight of the glass is a convex free surface. However, in order to make the top surface flat, concave, or convex with a smaller curvature than the free surface, the top surface of the glass pressure can be applied to. Specifically, the top surface of the glass can be pressed with a mold having a molding surface of a desired shape, or the top surface of the glass can be molded into a desired shape by applying wind pressure. In addition, when pressing the top surface of the glass with a mold, a plurality of gas jets are provided on the molding surface of the mold, and gas is jetted from these gas jets to form a gas cushion between the molding surface and the top surface of the glass. The top surface of the glass may be pressed through a gas cushion. Alternatively, if it is desired to form the top surface of the glass into a surface having a larger curvature than the free surface, negative pressure may be generated near the top surface of the glass to bulge the top surface.

Further, the preform is preferably a preform whose surface is polished so that the shape more closely approximates the shape of the precision press-molded product. For example, it is preferable to use a preform in which one of the surfaces to be pressed is polished so that it becomes a flat surface or part of a spherical surface, and the other surface is polished so that it becomes a part of a spherical surface or a flat surface. Here, a part of the spherical surface may be a convex surface or a concave surface, but it is desirable to decide whether it is a convex surface or a concave surface depending on the shape of the precision press molded product as described above.

Each of the above preforms can be preferably used for molding lenses having a diameter of 10 mm or more, and can be more preferably used for molding lenses having a diameter of 20 mm or more. Further, it can be preferably used for molding lenses having a center wall thickness exceeding 2 mm.

(optical element)
Hereinafter, an optical element according to an embodiment of the present invention (hereinafter sometimes referred to as "an optical element according to the present embodiment") will be specifically described.
The optical element of this embodiment is characterized by using the above-mentioned optical glass as a material. In this way, according to the optical element of this embodiment, since the above-mentioned optical glass is used as a material, temperature dependence of imaging can be suppressed by combining it with other glasses (for example, glass with a high refractive index). You can get the product. Note that, from the viewpoint of more reliably obtaining the desired performance, the optical element of this embodiment preferably satisfies the essential requirements regarding the composition of each component as already described for the optical glass of this embodiment. It is more preferable that the glass satisfies the various requirements already described as preferable.
Further, the optical element of this embodiment includes an optical element using the precision press molding preform described above.

The type of optical element is not limited, but typical examples include aspheric lenses, spherical lenses, or lenses such as plano-concave lenses, plano-convex lenses, biconcave lenses, biconvex lenses, convex meniscus lenses, and concave meniscus lenses; microlenses; Examples include a lens array; a lens with a diffraction grating; a prism; a prism with a lens function; and the like. Preferred examples of the optical element include lenses such as a convex meniscus lens, a concave meniscus lens, a biconvex lens, a biconcave lens, a plano-convex lens, and a plano-concave lens, a prism, and a diffraction grating. Each of the above lenses may be an aspherical lens or a spherical lens. An antireflection film, a partially reflective film with wavelength selectivity, or the like may be provided on the surface, if necessary.

<Method for 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.

Here, in precision press molding, it is possible to use a press mold whose molding surface has been processed with high precision into the desired shape in advance. A release film may be formed to allow the glass to stretch well along the surface. As the mold release film, a film of noble metal (platinum, platinum alloy), a film of oxide (oxide of Si, Al, Zr, Y, etc.), a film of nitride (nitride of B, Si, Al, etc.), Examples include carbon-containing films. As a carbon-containing film, it is desirable that the main component is carbon (when the element content in the film is expressed in atomic %, the carbon content is higher than the content of other elements). can be exemplified by a carbon film or a hydrocarbon film. The carbon-containing film can be formed using known methods such as vacuum evaporation, sputtering, and ion plating using carbon raw materials, and thermal decomposition using material gases such as hydrocarbons. Just use it. Other films can be formed using a vapor deposition method, a sputtering method, an ion plating method, a sol-gel method, or the like.

In addition, during the heating and precision press molding process of the press mold and preform, nitrogen gas or nitrogen gas is used to prevent oxidation of the molding surface of the press mold or a release film suitably provided on the molding surface. It is preferable to carry out the process in a non-oxidizing gas atmosphere such as a mixed gas of hydrogen gas. 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 must be removed eventually, but in order to remove the release film such as the carbon-containing film relatively easily and completely, the precision press molded product should be placed in an oxidizing atmosphere, for example in the air. Just heat it. Removal of a release film such as a carbon-containing film should be carried out at a temperature at which the precision press molded product will not be deformed by heating. Specifically, it is preferable to remove a release film such as a carbon-containing film at a temperature range below the transition temperature of glass.

Note that the method for manufacturing the optical element of this embodiment is not particularly limited, and includes the following two manufacturing methods. Here, in manufacturing the optical element of this embodiment, it is preferable from the viewpoint of mass production of optical elements to repeat the process of precision press molding the above-mentioned precision press molding preform using the same press mold. .

The first optical element manufacturing method (referred to as "Optical element manufacturing method I") includes introducing a preform into a press mold, heating the preform and the press mold together to perform precision press molding, This is a method for obtaining optical elements.
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, precision press molding is performed, and an optical element is obtained.

In optical element manufacturing method I, after a preform is supplied between a pair of opposing upper and lower molds whose molding surfaces are precisely shaped, the preform is heated to a temperature equivalent to a glass viscosity of 10 ⁵ to 10 ⁹ dPa・s. By heating both the mold and the preform to soften the preform and press-molding it, the molding surface of the mold can be precisely transferred to the glass. Optical element manufacturing method I is a method recommended when improving molding accuracy such as surface accuracy and eccentricity accuracy is important.

In optical element manufacturing method II, the temperature is raised in advance to a temperature corresponding to the viscosity of glass of 10 ⁴ to 10 ⁸ dPa·s between a pair of opposing upper and lower molds whose molding surfaces have been precisely shaped. By supplying a preform and press-molding it, the molding surface of the mold can be precisely transferred to the glass. Optical element manufacturing method II is a recommended method when productivity improvement is important.

The pressure and time during pressurization can be appropriately determined in consideration of the viscosity of the glass, etc., and for example, the press pressure can be about 5 to 15 MPa, and the pressing time can be about 10 to 300 seconds. Press conditions such as press time and press pressure may be appropriately set within a known range according to the shape and dimensions of the molded product.

Thereafter, the mold and the precision press-molded product are cooled, and when the temperature is preferably below the strain point, the molds are released and the precision press-molded product is taken out. Note that, in order to precisely adjust the optical properties to desired values, the annealing treatment conditions of the molded product during cooling, such as the annealing rate, etc., may be adjusted as appropriate.

Note that the optical element of this embodiment can be manufactured without going through a press molding process. For example, a glass block is formed by pouring homogeneous molten glass into a mold, annealing it to remove distortion, and adjusting the optical properties by adjusting the annealing conditions so that the refractive index of the glass reaches the desired value. After this, the glass block is then cut or fractured to produce glass pieces, which are further ground and polished to form an optical element.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Prepare the corresponding oxides, fluorides, carbonates, and nitrates as raw materials for each component, weigh them, mix them thoroughly, and prepare them so that the composition after vitrification is as shown in Tables 1 to 4. I got the raw material. This mixed raw material was put into a platinum crucible and melted in an electric furnace. Note that the temperature during melting was appropriately adjusted within the range of 1000 to 1500°C in order to ensure sufficient defoaming. Thereafter, the mixture was stirred at appropriate times to achieve homogenization, clarified, and then cast into a mold preheated to an appropriate temperature. Next, each example of optical glass was obtained by slow cooling in an electric furnace (there were some cases in which no glass was obtained).

In addition, when melting in an electric furnace, in order to evaluate meltability, after heating at 1300° C. for 30 minutes, the platinum crucible was taken out from the electric furnace without stirring, and the presence or absence of unmelted glass was checked. The meltability was evaluated as "○" if no unmelted material was observed, and as "x" if any unmelted material was observed. The results are shown in Tables 1 to 4.

Next, the refractive index (nd), Abbe number (νd), glass transition temperature (Tg), and temperature coefficient of relative refractive index (dn/dT) were measured for each of the obtained optical glasses according to the procedures shown below. I did it. In addition, these measurements were not performed for the examples in which the above-mentioned meltability evaluation was "x" and the examples in which no glass was obtained. The results are shown in Tables 1 to 4.

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

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

The temperature coefficient of relative refractive index (dn/dT) was measured using the d-line (587. 562 nm) at a temperature range of 40 to 60°C.

From Tables 1 and 2, it can be seen that the optical glasses of Examples 1 to 30 all have good meltability. Further, the optical glasses of Examples 1 to 30 all have a refractive index (nd) of 1.55 or more and 1.63 or less, and an Abbe number (νd) of 50 or more and 65 or less, that is, a medium refractive index. It can be seen that it has low dispersion. Furthermore, it can be seen that the optical glasses of Examples 1 to 30 all have temperature coefficients of relative refractive index of -5.0×10 ^-6 °C ^-1 to 3.0×10 ^-6 °C ^-1. .

Furthermore, the optical glasses of Examples 1 to 30 all have glass transition temperatures (Tg) of 540° C. or lower, which indicates that they have low softening temperatures and can be more easily precision press molded.

On the other hand, Table 3 shows that in Comparative Example 1, devitrification occurred and glass could not be obtained. This is considered to be due to the fact that the amount of SiO ₂ is too small.
Moreover, the optical glass of Comparative Example 2 had poor meltability at least. This is considered to be due to too much SiO ₂ .
Moreover, the optical glass of Comparative Example 3 had a refractive index of less than 1.55. Furthermore, the optical glass of Comparative Example 3 had a glass transition temperature (Tg) of over 540°C. This is thought to be due to too much B ₂ O ₃ .

Furthermore, in Comparative Example 4, devitrification occurred and glass could not be obtained. This is thought to be due to too much Li ₂ O.
Furthermore, in Comparative Example 5, devitrification occurred and glass could not be obtained. This is thought to be due to too much Na ₂ O.
Furthermore, in Comparative Example 6, devitrification occurred and glass could not be obtained. This is thought to be due to too much K ₂ O.

Moreover, the optical glass of Comparative Example 7 had poor meltability at least. This is thought to be due to too much Al ₂ O ₃ .
Furthermore, in Comparative Example 8, devitrification occurred and glass could not be obtained. This is considered to be due to the fact that there is too much CaO.
Further, the optical glass of Comparative Example 9 had a temperature coefficient of relative refractive index greater than 3.0×10 ⁻⁶ ° C. ⁻¹ . This is considered to be due to the fact that BaO is too small.

Furthermore, in Comparative Example 10, devitrification occurred and glass could not be obtained. This is considered to be due to the fact that there is too much BaO.
Moreover, from Table 4, the optical glass of Comparative Example 11 had poor meltability at least. This is thought to be due to too much Nb ₂ O ₅ .
Moreover, the optical glass of Comparative Example 12 had poor meltability at least. This is thought to be due to too much ZrO ₂ .

Moreover, the optical glass of Comparative Example 13 had poor meltability at least. This is thought to be due to too much TiO ₂ .
Moreover, the optical glass of Comparative Example 14 had poor meltability at least. This is thought to be due to too much Y ₂ O ₃ .
Moreover, the optical glass of Comparative Example 15 had poor meltability at least. This is thought to be due to too much La ₂ O ₃ .

Further, the optical glass of Comparative Example 16 had a temperature coefficient of relative refractive index greater than 3.0×10 ⁻⁶ ° C. ⁻¹ . This is considered to be due to the fact that the total content of Li ₂ O, Na ₂ O and K ₂ O is too small.
Further, the optical glass of Comparative Example 17 had a temperature coefficient of relative refractive index greater than 3.0×10 ⁻⁶ ° C. ⁻¹ . This is considered to be due to the fact that the total content of CaO and BaO is too small.
Further, the optical glass of Comparative Example 18 had poor meltability at least. This is considered to be due to the fact that the total content of Li ₂ O, Na ₂ O and K ₂ O is too small, and the total content of CaO and BaO is too small.
Further, the optical glass of Comparative Example 19 had a temperature coefficient of relative refractive index greater than 3.0×10 ⁻⁶ ° C. ⁻¹ . This is considered to be due to the fact that it contains ZnO.

According to the present invention, it is possible to provide an optical glass that has a medium refractive index and low dispersion, has good meltability, and can suppress temperature dependence of imaging when combined with other glasses. can. Further, according to the present invention, it is possible to provide a precision press molding preform and an optical element using the above-mentioned optical glass.

Claims (4)

SiO ₂ in mass%: 30% or more and 60% or less,
_B2O3 : 0% _or more and 15% or less,
Li ₂ O: 0% or more and 10% or less,
Na ₂ O: 0% or more and 10% or less,
_K2O : 0% or more and 15% or less,
_Al2O3 : 0% _or more and 7% or less,
CaO: 0% or more and 15% or less,
BaO: 23.00% or more and 40% or less,
_Nb2O5 : 0% _or more and 5% or less,
_ZrO2 : 0% or more and 7% or less,
_TiO2 : 0% or more and 4.5% or less,
_Y2O3 : 0% or more and 5 _% or less,
La ₂ O ₃ : 0% or more and 5% or less,
Gd ₂ O ₃ : 0% or more and 5% or less,
has a composition containing
Does not contain ZnO and SrO,
The total content of Li ₂ O, Na ₂ O and K ₂ O is 12% or more and 35% or less,
The total content of CaO and BaO is 23 % or more and 55% or less,
The temperature coefficient of relative refractive index (40 to 60 °C) with respect to the d-line (587.562 nm) is -5.0 × 10 ^-6 °C ^-1 or more and 3.0 × 10 ^-6 °C ^-1 or less ,
An optical glass characterized by having a refractive index (nd) of 1.55 or more and 1.63 or less, and an Abbe number (νd) of 50 or more and 65 or less . The optical glass according to claim 1 , having a glass transition temperature (Tg) of 540°C or less. A preform for precision press molding, characterized in that the optical glass according to claim 1 or 2 is used as a raw material. An optical element characterized by using the optical glass according to claim 1 or 2 as a material.