JP6812147B2 - Optical glass, optics blank, and optics - Google Patents

Description

The present invention relates to optical glass, optical element blanks and optical elements.

In the design of an optical system, an optical glass having a high refractive index nd and a low Abbe number νd and having a high refractive index and a high dispersion has high utility value in correcting chromatic aberration and making the optical system highly functional and compact.

As an optical glass having a high refractive index and high dispersion, for example, phosphate based glass comprised mainly of P ₂ O ₅ are known (see Patent Document 12).

JP-A-2010-260746 Japanese Unexamined Patent Publication No. 6-345481 Japanese Unexamined Patent Publication No. 8-104537 Japanese Unexamined Patent Publication No. 9-188540 Japanese Unexamined Patent Publication No. 2003-300751 JP-A-2010-222236 JP-A-2010-260740 Japanese Unexamined Patent Publication No. 2010-260742 Japanese Unexamined Patent Publication No. 2011-195369 Japanese Unexamined Patent Publication No. 2012-17261 JP-A-2015-063460 Japanese Unexamined Patent Publication No. 2015-096468

By the way, in the phosphate-based high-refractive-index, high-dispersion optical glass, it is necessary to maintain a high temperature when melting the glass raw material. Therefore, the viscosity of the molten glass is excessively lowered, and the formability of the molten glass tends to be poor.

Further, in the production of the optical element, a method of reheating and molding the optical glass, such as a reheat press, may be used. At this time, the high-refractive-index, high-dispersion glass as described above tends to have poor devitrification resistance because crystals may precipitate.
Therefore, there has been a demand for a phosphate-based high-refractive index, high-dispersion optical glass having excellent formability and devitrification resistance of molten glass.

The present invention has been made in view of such an actual situation, and one aspect of the present invention is to provide a high refractive index high dispersion optical glass having excellent moldability and devitrification resistance.

As a result of intensive research to achieve the above object, the present inventor can achieve the object by adjusting the content ratio of various glass constituents (hereinafter referred to as glass components) constituting the glass. Was found, and the present invention was completed based on this finding.

That is, one aspect of the present invention is as follows.
In oxide-based glass composition
The total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O ₃ [P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ] is 26% by mass or more.
And the content of _{B 2 O 3, P 2 O} 5, B 2 O 3, the mass ratio of the total content of SiO ₂ and _{Al 2 O 3 [B 2 O} 3 / (P 2 O 5 + B 2 O 3 + SiO ₂ + Al ₂ O ₃ )] is 0.11 or more and 0.24 or less.
Mass ratio of the total content of Li ₂ O, Na ₂ O and K ₂ O to the total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O ₃ [(Li ₂ O + Na ₂ O + K ₂₎ O) / (P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ )] is 0.35 or more and 0.56 or less.
And the content of _{TiO 2, TiO 2, Nb 2} O 5, WO 3 and _Bi 2 mass ratio of the total content of _{O 3 [TiO 2 / (TiO} 2 + Nb 2 O 5 + WO 3 + Bi 2 O 3)] is 0.12 or more and 0.32 or less,
An optical glass having a refractive index nd of more than 1.85 and less than 1.90 and an Abbe number νd of 15 or more and 25 or less.

According to one aspect of the present invention, it is possible to provide a high refractive index and high dispersion optical glass having excellent moldability and devitrification resistance. Further, according to one aspect of the present invention, it is possible to provide an optical element blank and an optical element made of such optical glass.

It shows the relationship between the refractive index nd of glass and the crystal melting peak temperature Tl obtained in this embodiment. This is an example of a DSC chart.

Hereinafter, embodiments for carrying out the present invention (hereinafter, simply referred to as “embodiments”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be appropriately modified and implemented within the scope of the gist thereof. Further, although the description may be omitted as appropriate for the parts where the description is duplicated, the gist of the invention is not limited. In the present specification, "optical glass" is a glass composition containing a plurality of types of glass constituents (glass components), and unless otherwise specified, the form (lump, plate, spherical, etc.) or It is used as a general term regardless of the application (optical element blank, optical element, etc.) and size. That is, there is no limitation on the form, use, and size of the optical glass, and the optical glass of any form, the optical glass of any use, and the optical glass of any size are included in the optical glass of the present invention. Also, in the present specification, optical glass may be simply referred to as "glass".

In the present specification, the refractive index refers to the refractive index nd at the d-line (wavelength 587.56 nm) of helium unless otherwise specified.

Further, the Abbe number νd is used as a value representing a property related to dispersion, and is expressed by the following equation. Here, nF is the refractive index of blue hydrogen at the F line (wavelength 486.13 nm), and nC is the refractive index of red hydrogen at the C line (656.27 nm).
νd = (nd-1) / nF-nC ... (1)

In the present specification, the glass composition is displayed based on the content of each glass component in terms of mass%. Unless otherwise specified, the indication of% in each content means% by mass.

In addition, in this specification, the mass% display of a glass composition means each glass component represented by an oxide or fluoride, when the total content of all the glass components is 100% by mass. It means to display the content by mass percentage.

In this embodiment, the glass composition can be quantified by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). The analytical value obtained by ICP-AES may include, for example, a measurement error of about ± 5% of the analytical value. Further, in the present specification and the present embodiment, the content of the constituent component of the glass is 0% or not contained, which means that the constituent component is substantially not contained, and the content of the constituent component is the impurity level. It means that it is below the degree.

As will be described later, Sb ₂ O ₃ and CeO ₂ may be added in a small amount to the glass as a fining agent. However, in the mass% representation herein, the total content of all glass components does not include the contents of Sb ₂ O ₃ and Ce O ₂ . That is, each content at _Sb 2 _O 3, of CeO ₂ weight percentages of the glass components, in the case where the total content of all glass components other than _Sb 2 _{O 3} and CeO ₂ is 100 mass% Sb It is displayed as each content of ₂ O ₃ and CeO ₂ . In the present specification, such a notation is referred to as an external division.

The total content refers to the total amount of the contents (including the case where the content is 0%) of a plurality of types of glass components. Further, the mass ratio refers to the ratio (ratio) of the contents of glass components (including the total content of a plurality of kinds of components) in the mass% display.

The formability of molten glass as used herein is sometimes referred to simply as "formability". Further, in the present specification, the thermal stability and the devitrification resistance of the glass both refer to the difficulty of crystal precipitation in the glass. In particular, thermal stability refers to the difficulty of crystal precipitation when the molten glass solidifies, and devitrification resistance refers to the difficulty of crystal precipitation when the solidified glass is reheated, as in the case of reheat pressing. It shall refer to the difficulty.

In the optical glass according to the present embodiment, the refractive index nd is more than 1.85 and less than 1.90, and the Abbe number νd is 15 or more and 25 or less. Hereinafter, the optical glass according to this embodiment will be described in detail.

In the optical glass according to the present embodiment, the total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O ₃ [P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ] is 26%. That is all. The total content [P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ] is preferably 26.5% or more, more preferably 27% or more, 27.5% or more, and 28% or more. .. The total content [P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ] is preferably 45% or less, more preferably 40% or less, 37% or less, and 35% or less.

P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O ₃ are known as network forming components of glass. The network-forming components of these glasses improve devitrification resistance. Further, it has a function of suppressing an excessive decrease in the viscosity of the molten glass and facilitating the molding of the molten glass. Therefore, in the embodiment of the present invention, by setting the total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O _{3 in} the above range, the optical glass having excellent moldability and devitrification resistance Is obtained.

In the optical glass according to the present _embodiment, B and content _{2 O 3, P 2 O 5} , B 2 O 3, the mass ratio of the total content of SiO ₂ and _{Al 2 O 3 [B 2 O} 3 / ( P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ )] is 0.11 or more and 0.24 or less. The mass ratio [B ₂ O ₃ / (P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ )] is preferably 0.13 or more, and further 0.15 or more, 0.16 or more, 0. It is more preferable in the order of 17 or more. Further, the mass ratio [B ₂ O ₃ / (P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ )] is preferably 0.22 or less, and further 0.21 or less, 0.20 or less, It is more preferable in the order of 0.19 or less.

Among the network-forming components of glass, B ₂ O ₃ has a function of improving moldability. On the other hand, if the content of B ₂ O ₃ is large, the devitrification resistance may decrease. In the embodiment of the present invention, by setting the content ratio of B ₂ O ₃ in the network forming component within the above range, an optical glass having excellent moldability and devitrification resistance can be obtained.

In the optical glass according to the present embodiment, the total content of Li ₂ O, Na ₂ O and K ₂ O [Li ₂ O + Na ₂ O + K ₂ O] and P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O weight ratio of the total content of _{3 [(Li 2 O + Na} 2 O + K 2 O) / (P 2 O 5 + B 2 O 3 + SiO 2 + Al 2 O 3)] is 0.35 or more 0.56 or less .. The mass ratio [(Li ₂ O + Na ₂ O + K ₂ O) / (P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ )] is preferably 0.40 or more, and further 0.45 or more, 0. It is more preferable in the order of 48 or more and 0.50 or more. The mass ratio [(Li ₂ O + Na ₂ O + K ₂ O) / (P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ )] is preferably 0.55 or less, more preferably 0.54 or less. It is more preferable in the order of 0.53 or less.

Li ₂ O, Na ₂ O and K ₂ O all have a function of improving the meltability, but when the content thereof is increased, the devitrification resistance is lowered. In the embodiment of the present invention, by setting the content ratio of Li ₂ O, Na ₂ O and K ₂ O to the network forming component in the above range, an optical glass having excellent moldability and devitrification resistance can be obtained.

In the optical glass according to the present embodiment, the content of _{TiO 2, TiO 2, Nb 2} O 5, the mass ratio of the total content of WO ₃ and _{Bi 2 O 3 [TiO 2 /} (TiO 2 + Nb 2 O 5 + WO ₃ + Bi ₂ O ₃ )] is 0.12 or more and 0.32 or less. The mass ratio [TiO ₂ / (TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ )] is preferably 0.15 or more, and further in the order of 0.18 or more, 0.20 or more, and 0.21 or more. More preferred. Further, the mass ratio [TiO ₂ / (TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ )] is preferably 0.30 or less, and further 0.28 or less, 0.26 or less, 0.24 or less. Is more preferable in this order.

TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ are all glass components that contribute to high dispersion, but they also cause an increase in coloring. In particular, TiO ₂ greatly contributes to high dispersion as compared with Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ , but tends to increase the coloring of glass. Further, TiO ₂ has a function of easily promoting crystal formation in the glass and lowering the transparency (white turbidity) of the glass in the process of molding and slowly cooling the molten glass. Therefore, in the embodiment of the present invention, by setting the content ratio of TiO ₂ in TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ in the above range, an optical glass having high dispersion and excellent transmittance can be obtained. Be done.

(Glass component)
The glass component of the optical glass according to this embodiment will be described in detail below.

In the optical glass according to the present _embodiment, the content of P 2 _{O 5} is preferably 18% or more, further 20% or more, 21% or more, preferably in the order of 22% or more. The content of P ₂ O ₅ is preferably 32% or less, more preferably 28% or less, 26% or less, and 25% or less.

P ₂ O ₅ is an essential component in order to contain a large amount of highly dispersed components in the glass. On the other hand, if P ₂ O ₅ is excessively contained, the thermal stability deteriorates. Therefore, the content of P ₂ O ₅ is preferably in the above range.

In the optical glass according to the present embodiment, the content of B ₂ O ₃ is preferably 0.1% or more, more preferably 2% or more and 3% or more. The content of B ₂ O ₃ is preferably 12% or less, more preferably 9% or less, 7% or less, and 6% or less.

B ₂ O ₃ is a network-forming component of glass and has a function of improving the thermal stability of glass. On the other hand, if the content of B ₂ O ₃ is large, high dispersion is hindered and the devitrification resistance tends to decrease. Therefore, from the viewpoint of improving the thermal stability and devitrification resistance of the glass, the content of B ₂ O ₃ is preferably in the above range.

In the optical glass according to the present embodiment, the content of SiO ₂ is preferably 3% or less, more preferably 2% or less, and more preferably 1.5% or less. The content of SiO ₂ may be 0%.

SiO ₂ is a network-forming component of glass, and has a function of improving thermal stability, chemical durability, and weather resistance of glass, increasing the viscosity of molten glass, and facilitating molding of molten glass. On the other hand, when the content of SiO ₂ is large, the devitrification resistance of the glass tends to decrease. Therefore, from the viewpoint of improving the thermal stability and devitrification resistance of the glass, the upper limit of the content of SiO ₂ is preferably in the above range.

In the optical glass according to the present embodiment, the content of Al ₂ O ₃ is preferably 3% or less, more preferably 2% or less and 1% or less. The content of Al ₂ O ₃ may be 0%.

Al ₂ O ₃ is a glass component having a function of improving the chemical durability and weather resistance of glass, and can be considered as a network forming component. On the other hand, when the content of Al ₂ O ₃ increases, the devitrification resistance of the glass decreases. In addition, problems such as an increase in the glass transition temperature Tg and a decrease in thermal stability are likely to occur. From the viewpoint of avoiding such a problem, the upper limit of the content of Al ₂ O ₃ is preferably in the above range.

In the optical glass according to the present embodiment, the content of TiO ₂ is preferably 3% or more, more preferably 5% or more, 8% or more, and 10% or more. The TiO ₂ content is preferably 20% or less, more preferably 18% or less, 16% or less, and 14% or less in that order.

TiO ₂ greatly contributes to high dispersion. On the other hand, TiO ₂ tends to increase the coloring of glass relatively easily. Further, TiO ₂ promotes crystal formation in the glass in the process of forming and slowly cooling the molten glass to obtain optical glass, and lowers the transparency (white turbidity) of the glass. Therefore, the content of TiO ₂ is preferably in the above range.

In the optical glass according to the present embodiment, the content of Nb ₂ O ₅ is preferably 35% or more, more preferably 38% or more, 40% or more, and 42% or more. The content of Nb ₂ O ₅ is preferably 56% or less, more preferably 50% or less, 48% or less, and 46% or less.

Nb ₂ O ₅ is a component that contributes to high dispersion. It is also a glass component that improves the thermal stability and chemical durability of glass. On the other hand, if the content of Nb ₂ O ₅ is too large, the thermal stability of the glass tends to decrease and the coloring of the glass tends to increase. Therefore, in the optical glass according to the present embodiment, the content of Nb ₂ O ₅ is preferably in the above range.

In the optical glass according to the present embodiment, the lower limit of the WO ₃ content is preferably 0%. The WO ₃ content is preferably 5% or less, more preferably 3% or less and 1% or less.

WO ₃ tends to cause coloring of glass and deteriorates the transmittance. Therefore, the content of WO ₃ is preferably in the above range.

In the present embodiment, the content of Bi ₂ O ₃ is preferably 5% or less, more preferably 3% or less, and 2% or less in that order. The lower limit of the Bi ₂ O ₃ content is preferably 0%.

Bi ₂ O ₃ has a function of improving the thermal stability of glass by containing an appropriate amount. On the other hand, when the content of Bi ₂ O ₃ is increased, the coloring of the glass increases. Therefore, the content of Bi ₂ O ₃ is preferably in the above range.

In the optical glass according to the present embodiment, the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ [TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ ] is preferably 45% or more. Yes, more preferably 50% or more, 52% or more, 54% or more in that order. The total content [TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ ] is preferably 65% or less, more preferably 60% or less, and more preferably 58% or less.

TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ contribute to high dispersion of glass, and also have a function of improving the thermal stability of glass by containing an appropriate amount. On the other hand, it is also a component that increases the coloring of glass. Therefore, the total content [TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ ] is preferably in the above range.

In the optical glass according to the present embodiment, the total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O _{3 and} the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ are contained. The mass ratio to the amount [(P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ) / (TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ )] is preferably 0.40 or more and 0.60 or less. Is. The mass ratio [(P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ) / (TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ )] is more preferably 0.42 or more, and further 0. It is more preferable in the order of .44 or more, 0.46 or more, and 0.48 or more. Further, the mass ratio [(P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ) / (TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ )] is more preferably 0.58 or less, and further. Is more preferably 0.56 or less, 0.54 or less, and 0.52 or less in that order.

TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ are all glass components that contribute to high dispersion. Therefore, the content ratio of these components and the network forming component is preferably in the above range.

In the optical glass according to the present embodiment, the Li ₂ O content is preferably 5% or less, more preferably 3% or less, and 1% or less in that order. The lower limit of the Li ₂ O content is preferably 0%.

In the optical glass according to the present embodiment, the Na ₂ O content is preferably 12% or less, more preferably 10% or less, 9% or less, and 8% or less in that order. The Na ₂ O content is preferably 0% or more, more preferably 3% or more, 5% or more, and 6% or more.

In the optical glass according to the present embodiment, the content of K 2 _O is preferably 12% or less, further 10% or less, 9% or less, preferably in the order of 8% or less. The K ₂ O content is preferably 0% or more, more preferably 3% or more, 5% or more, and 6% or more.

Li ₂ O, Na ₂ O and K ₂ O have a function of improving the thermal stability of glass, but when the content thereof is high, the thermal stability, chemical durability and weather resistance are lowered. .. Therefore, the contents of Li ₂ O, Na ₂ O, and K ₂ O are preferably in the above ranges. Further, it is preferable to contain Na ₂ O in particular for improving thermal stability and devitrification resistance.

In the optical glass according to the present embodiment, the total content of Li ₂ O, Na ₂ O and K ₂ O [Li ₂ O + Na ₂ O + K ₂ O] is preferably 20% or less, and further 18% or less, 16 It is more preferable in the order of% or less. The total content [Li ₂ O + Na ₂ O + K ₂ O] is preferably 8% or more, more preferably 10% or more, 12% or more, and 13% or more.

Li ₂ O, Na ₂ O and K ₂ O all have a function of improving the thermal stability of glass. However, when these contents are increased, the chemical durability and weather resistance are lowered. Therefore, the total content of Li ₂ O, Na ₂ O and K ₂ O [Li ₂ O + Na ₂ O + K ₂ O] is preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the content of Cs ₂ O is preferably 2%. The lower limit of the Cs ₂ O content is preferably 0%.

Cs ₂ O has a function of improving the thermal stability of the glass, but as the content increases, the thermal stability, chemical durability, and weather resistance of the glass decrease. Therefore, each content of Cs ₂ O is preferably in the above range.

In the optical glass according to the present embodiment, the content of MgO is preferably 5% or less, more preferably 3% or less and 1% or less. The lower limit of the MgO content is preferably 0%. The content of MgO may be 0%.

In the optical glass according to the present embodiment, the CaO content is preferably 5% or less, more preferably 3% or less, and 1% or less in that order. The lower limit of the CaO content is preferably 0%. The CaO content may be 0%.

In the optical glass according to the present embodiment, the SrO content is preferably 5% or less, more preferably 3% or less, and 1% or less in that order. The lower limit of the SrO content is preferably 0%.

In the optical glass according to the present embodiment, the upper limit of the BaO content is preferably 5%, more preferably 3% or less and 1% or less. The lower limit of the BaO content is preferably 0%.

MgO, CaO, SrO, and BaO are all glass components having a function of improving the thermal stability and devitrification resistance of the glass. However, when the content of these glass components is increased, the high dispersibility is impaired, and the thermal stability and devitrification resistance of the glass are lowered. Therefore, the content of each of these glass components is preferably in the above range.

In the optical glass according to the present embodiment, the total content of MgO, CaO, SrO and BaO [MgO + CaO + SrO + BaO] is preferably 6% or less, more preferably 4% or less and 2% or less. The lower limit of the total content [MgO + CaO + SrO + BaO] is preferably 0%. From the viewpoint of maintaining thermal stability and devitrification resistance without hindering high dispersion, the total content [MgO + CaO + SrO + BaO] is preferably in the above range.

In the optical glass according to the present embodiment, the ZnO content is preferably 5% or less, more preferably 3% or less and 1% or less. The lower limit of the ZnO content is preferably 0%.

ZnO is a glass component having a function of improving the thermal stability of glass. However, if the ZnO content is too high, the high dispersibility of the glass is impaired. Therefore, from the viewpoint of improving the thermal stability of the glass and maintaining the desired optical properties, the ZnO content is preferably in the above range.

In the optical glass according to the present embodiment, the content of ZrO ₂ is preferably 5% or less, more preferably 3% or less and 1% or less. The lower limit of the ZrO ₂ content is preferably 0%.

ZrO ₂ is a glass component having a function of improving the thermal stability and devitrification resistance of glass. However, if the content of ZrO ₂ is too high, the thermal stability tends to decrease. Therefore, the content of ZrO ₂ is preferably in the above range from the viewpoint of maintaining good thermal stability and devitrification resistance of the glass.

In the optical glass according to the present embodiment, the content of Ta ₂ O ₅ is preferably 5% or less, more preferably 3% or less and 2% or less. The lower limit of the content of Ta ₂ O ₅ is preferably 0%.

Ta ₂ O ₅ is a glass component having a function of improving the thermal stability and devitrification resistance of glass. On the other hand, Ta ₂ O ₅ increases the refractive index and lowers the dispersion of the glass. Further, when the content of Ta ₂ O ₅ is increased, the thermal stability of the glass is lowered, and when the glass is melted, unmelted glass raw material is likely to occur. Therefore, the content of Ta ₂ O ₅ is preferably in the above range. Further, Ta ₂ O ₅ is an extremely expensive component as compared with other glass components, and as the content of Ta ₂ O ₅ increases, the production cost of glass increases. Further, since Ta ₂ O ₅ has a larger molecular weight than other glass components, it increases the specific gravity of the glass, and as a result, increases the weight of the optical element.

In the optical glass according to the present embodiment, the upper limit of the Sc ₂ O ₃ content is preferably 2%. The lower limit of the Sc ₂ O ₃ content is preferably 0%.

In the optical glass according to the present embodiment, the upper limit of the HfO ₂ content is preferably 2%. The lower limit of the HfO ₂ content is preferably 0%.

Sc ₂ O ₃ and HfO ₂ both have a function of increasing the refractive index nd and are expensive components. Therefore, the contents of Sc ₂ O ₃ and HfO ₂ are preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the content of Lu ₂ O ₃ is preferably 2%. The lower limit of the content of Lu ₂ O ₃ is preferably 0%.

Lu ₂ O ₃ has a function of increasing the refractive index nd. In addition, since it has a large molecular weight, it is also a glass component that increases the specific gravity of glass. Therefore, the content of Lu ₂ O ₃ is preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the content of GeO ₂ is preferably 2%. The lower limit of the content of GeO ₂ is preferably 0%.

GeO ₂ has a function of increasing the refractive index nd, and is a prominently expensive component among commonly used glass components. Therefore, from the viewpoint of reducing the manufacturing cost of glass, the content of GeO ₂ is preferably in the above range.

In the optical glass according to the present embodiment, the upper limit of the content of La ₂ O ₃ is preferably 2%. The lower limit of the content of La ₂ O ₃ is preferably 0%. The content of La ₂ O ₃ may be 0%.

When the content of La ₂ O ₃ is increased, the thermal stability and devitrification resistance of the glass are lowered, and the glass is easily devitrified during production. Therefore, the content of La ₂ O ₃ is preferably in the above range from the viewpoint of suppressing the decrease in thermal stability and devitrification resistance.

In the optical glass according to the present embodiment, the upper limit of the content of Gd ₂ O ₃ is preferably 2%. The lower limit of the content of Gd ₂ O ₃ is preferably 0%.

If the content of Gd ₂ O ₃ is too high, the thermal stability and devitrification resistance of the glass will decrease, and the glass will easily devitrify during production. Further, if the content of Gd ₂ O ₃ becomes too large, the specific gravity of the glass increases, which is not preferable. Therefore, the content of Gd ₂ O ₃ is preferably in the above range from the viewpoint of suppressing an increase in specific gravity while maintaining good thermal stability and devitrification resistance of the glass.

In the optical glass according to the present embodiment, the upper limit of the content of Y ₂ O ₃ is preferably 2%. The lower limit of the content of Y ₂ O ₃ is preferably 0%. The content of Y ₂ O ₃ may be 0%.

If the content of Y ₂ O ₃ is too high, the thermal stability and devitrification resistance of the glass will decrease. Therefore, from the viewpoint of suppressing a decrease in the thermal stability and devitrification resistance, the content of Y ₂ O ₃ is preferably in the range.

In the optical glass according to the present embodiment, the upper limit of the content of Yb ₂ O ₃ is preferably 2%. The lower limit of the content of Yb ₂ O ₃ is preferably 0%.

Since Yb ₂ O ₃ has a larger molecular weight than La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ , it increases the specific gravity of glass. As the specific gravity of glass increases, the mass of the optical element increases. For example, if a lens having a large mass is incorporated into an autofocus type imaging lens, the power required to drive the lens during autofocus increases, and the battery consumption increases. Therefore, it is desirable to reduce the content of Yb ₂ O ₃ to suppress the increase in the specific gravity of the glass.

Further, if the content of Yb ₂ O ₃ is too large, the thermal stability and devitrification resistance of the glass are lowered. The content of Yb ₂ O ₃ is preferably in the above range from the viewpoint of preventing a decrease in thermal stability of the glass and suppressing an increase in specific gravity.

The optical glass according to the present embodiment mainly contains the above-mentioned glass components, that is, P ₂ O ₅ , B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ , TiO ₂ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, Cs ₂ O, MgO, CaO, SrO, BaO, ZnO, ZrO ₂ , Ta ₂ O ₅ , Sc ₂ O ₃ , HfO ₂ , Lu ₂ O ₃ , GeO ₂ , la ₂ O _{3, Gd} 2 _{O 3,} Y 2 _{O 3,} and _Yb is preferably configured in 2 _{O 3,} the total content of the glass component described above is preferably larger than the 95%, 98 It is more preferably more than%, more preferably more than 99%, still more preferably more than 99.5%.

In the optical glass according to the present embodiment, the upper limit of the content of TeO ₂ is preferably 2%. The lower limit of the content of TeO ₂ is preferably 0%.

Since TeO ₂ is toxic, it is preferable to reduce the content of TeO ₂ . Therefore, the content of TeO ₂ is preferably in the above range.

The optical glass according to the present embodiment is basically composed of the above glass components, but other components may be contained as long as the effects of the present invention are not impaired. Further, in the present invention, the inclusion of unavoidable impurities is not excluded.

<Other component composition>
Pb, As, Cd, Tl, Be and Se are all toxic. Therefore, it is preferable that the optical glass according to the present embodiment does not contain these elements as a glass component.

U, Th, and Ra are all radioactive elements. Therefore, it is preferable that the optical glass according to the present embodiment does not contain these elements as a glass component.

V, Cr, Mn, Fe, Co, Ni, Cu, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm increase the coloring of glass and can be a source of fluorescence. Therefore, it is preferable that the optical glass according to the present embodiment does not contain these elements as a glass component.

Sb (Sb ₂ O ₃ ) and Ce (CeO ₂ ) are optionally additive elements that function as fining agents. Of these, Sb (Sb ₂ O ₃ ) is a fining agent having a large fining effect. However, Sb (Sb ₂ O ₃ ) is highly oxidizing, and if the amount of Sb (Sb ₂ O ₃ ) added is increased, the coloration of the glass increases due to light absorption by Sb ions, which is not preferable. Further, when the glass is melted, if Sb is present in the melt, the elution of platinum constituting the glass melting crucible into the melt is promoted, and the platinum concentration in the glass becomes high. When platinum is present as ions in the glass, the coloration of the glass increases due to the absorption of light. Further, when platinum exists as a solid substance in the glass, it becomes a scattering source of light and deteriorates the quality of the glass. Ce (CeO ₂ ) has a smaller clarification effect than Sb (Sb ₂ O ₃ ). When a large amount of Ce (CeO ₂ ) is added, the coloring of the glass is strengthened. Therefore, when adding a fining agent, it is preferable to add Sb (Sb ₂ O ₃ ) while paying attention to the amount of addition.

The content of Sb ₂ O ₃ is indicated by external division. That is, when the total content of all glass components other than Sb ₂ O ₃ and CeO ₂ is 100% by mass, the content of Sb ₂ O ₃ is preferably less than 1% by mass, more preferably 0.5% by mass. Is less than. Further, is preferably less than 0.1% by mass, less than 0.05% by mass, and less than 0.03% by mass in this order. The content of Sb ₂ O ₃ may be 0% by mass.

The content of CeO ₂ is also indicated by external division. That is, when the total content of all glass components other than CeO ₂ and Sb ₂ O ₃ is 100% by mass, the content of CeO ₂ is preferably less than 2% by mass, more preferably less than 1% by mass, and even more preferably. Is in the range of less than 0.5% by mass, more preferably less than 0.1% by mass. The content of CeO ₂ may be 0% by mass. By setting the content of CeO _{2 in} the above range, the clarity of the glass can be improved.

(Glass characteristics)
In the optical glass according to the present embodiment, the refractive index nd is more than 1.85 and less than 1.90. The refractive index nd is preferably 1.855 or more, and more preferably 1.860 or more and 1.865 or more. The refractive index nd is preferably 1.890 or less, more preferably 1.885 or less, 1.880 or less, and 1.875 or less.

In the optical glass according to the present embodiment, the Abbe number νd is 15 or more and 25 or less. The Abbe number νd is preferably 16 or more, and more preferably 17 or more, 18 or more, and 19 or more. The Abbe number νd is preferably 24 or less, more preferably 23 or less, 22 or less, and 21 or less.

<Crystal melting peak temperature Tl>
The crystal melting peak temperature Tl is the temperature at which all pseudocrystals in the glass disappear and correlates with the liquidus temperature. For example, when the crystal melting peak temperature Tl becomes high, the glass temperature at the time of molding also needs to be kept high, so that the viscosity of the molten glass is excessively lowered and the moldability is deteriorated.

The crystal melting peak temperature Tl varies depending on the components contained in the glass. In the present embodiment, in order to increase the refractive index nd of the glass, it is necessary to contain a large amount of high refractive index components such as Nb ₂ O ₅ and TiO ₂ , but these high refractive index components are the crystal melting peak temperature. It is also a component that raises Tl. Further, in order to stably contain these components in the glass, it is necessary to increase the content of network-forming components such as P ₂ O ₅ and B ₂ O ₃ at the same time. Here, the network-forming component has an effect of suppressing a decrease in the viscosity of the molten glass. That is, as the refractive index nd of the glass increases, the crystal melting peak temperature Tl apparently rises, but the decrease in the viscosity of the molten glass, that is, the deterioration of the moldability may be suppressed.

FIG. 1 shows the relationship between the refractive index nd of glass and the crystal melting peak temperature Tl (° C.) obtained in the present embodiment. In FIG. 1, glass having good moldability is shown as an example (diamond plot), and glass other than the example is shown as a comparative example (square plot). As described above, it can be seen that the preferable crystal melting peak temperature Tl tends to increase as the refractive index nd of the glass increases. From FIG. 1, the preferable crystal melting peak temperature Tl with respect to the refractive index nd of the glass is represented by the following formula (2).
Tl <1000nd-790 ... (2)
The more preferable crystal melting peak temperature Tl is represented by the following formula (3).
Tl <1300nd-1364 ... (3)

The crystal melting peak temperature Tl can be determined by differential scanning calorimetry (DSC). FIG. 2 is an example of a DSC chart. The vertical axis is the differential scanning calorimetry (DSC), and the horizontal axis is the sample temperature (T). The DSC chart has regions showing glass transition, crystallization, and crystal melting. The crystal melting peak temperature Tl is the temperature at which DSC shows a peak in the crystal melting region of FIG. The crystal melting start temperature in FIG. 2 is a temperature at which DSC begins to rise in the crystal melting region. With DSC, the crystal melting peak temperature Tl, which is an index of the liquidus temperature, can be obtained with high accuracy and relatively easily.

<Glass transition temperature Tg>
The glass transition temperature Tg of the optical glass according to the present embodiment is preferably 750 ° C. or lower, more preferably 730 ° C. or lower, and 710 ° C. or lower in that order. The glass transition temperature Tg is preferably 520 ° C. or higher, and more preferably 560 ° C. or higher and 600 ° C. or higher.

When the upper limit of the glass transition temperature Tg satisfies the above range, it is possible to suppress an increase in the annealing temperature of the glass, and it is possible to reduce the thermal damage of the annealing equipment, for example, a continuous annealing or a batch annealing furnace called a layer. ..

When the lower limit of the glass transition temperature Tg satisfies the above range, it becomes easy to maintain good thermal stability of the glass while maintaining the desired Abbe number and refractive index.

<Light transmission of glass>
In the present embodiment, the light transmittance can be evaluated by the degree of coloring λ5.
Using glass (thickness 10.0 mm ± 0.1 mm) having two planes that are parallel to each other and optically polished, light rays are incident from one of the above two planes perpendicular to this plane. Let me. Then, the ratio (Iout / Iin) of the intensity Iout of the transmitted light emitted from the other plane and the intensity Iin of the incident light, that is, the external transmittance is calculated. A spectral transmittance curve is obtained by measuring the external transmittance while scanning the wavelength of the incident light in the range of, for example, 280 to 700 nm using a spectrophotometer.

The external transmittance increases as the wavelength of the incident light goes from the absorption edge on the short wavelength side of the glass to the long wavelength side, and shows a high value.

λ5 is a wavelength at which the external transmittance is 5%. In the wavelength range of 280 to 700 nm, the external transmittance of glass on the wavelength side longer than λ5 shows a value larger than 5%.

By using an optical glass in which the wavelength of λ5 is shortened, it is possible to provide an optical element that enables suitable color reproduction.

For this reason, the range of λ5 is preferably 400 nm or less, more preferably 390 nm or less. The lower limit of λ5 is, for example, 360 nm.

(Manufacturing of optical glass)
The optical glass according to the embodiment of the present invention may be produced by blending a glass raw material so as to have the above-mentioned predetermined composition and using the blended glass raw material according to a known glass manufacturing method. For example, a plurality of kinds of compounds are mixed and sufficiently mixed to obtain a batch raw material, and the batch raw material is placed in a quartz crucible or a platinum crucible for rough melting. The melt obtained by crude melting is rapidly cooled and crushed to prepare a cullet. Further, the cullet is placed in a platinum crucible, heated and remelted to obtain molten glass, and after further clarification and homogenization, the molten glass is formed and slowly cooled to obtain an optical glass. A known method may be applied to the molding and slow cooling of the molten glass.

As long as a desired glass component can be introduced into the glass so as to have a desired content, the compound used when preparing the batch raw material is not particularly limited, and examples of such a compound include oxides and carbonates. Examples thereof include salts, nitrates, hydroxides and fluorides.

(Manufacturing of optical elements, etc.)
In order to produce an optical element using the optical glass according to the embodiment of the present invention, a known method may be applied. For example, a glass raw material is melted to obtain molten glass, and the molten glass is poured into a mold to form a plate shape to produce a glass material made of optical glass according to the present invention. The obtained glass material is appropriately cut, ground, and polished to produce a cut piece having a size and shape suitable for press molding. The cut piece is heated and softened, and press-molded (reheat-pressed) by a known method to produce an optical element blank that approximates the shape of the optical element. An optical element blank is annealed and ground and polished by a known method to produce an optical element.

The optical functional surface of the produced optical element may be coated with an antireflection film, a total reflection film, or the like, depending on the purpose of use.

Examples of the optical element include various lenses such as a spherical lens, a prism, and a diffraction grating.

The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

(Example)
[Preparation of glass sample]
Examples No. 1 and 2 shown in Tables 1 and 2. Compound raw materials corresponding to each component, that is, raw materials such as phosphates, carbonates, and oxides, were weighed and sufficiently mixed to prepare a blending raw material so as to form a glass having a composition of 1-32. The compounding raw material was put into a platinum crucible, heated to 1000 to 1350 ° C. in an air atmosphere to melt, homogenized and clarified by stirring to obtain molten glass. The molten glass was cast into a molding die, molded, and slowly cooled to obtain a block-shaped glass sample.

[Evaluation of glass sample]
For the obtained glass sample, the glass composition, specific gravity, refractive index nd, Abbe number νd, λ5, glass transition temperature Tg and crystal melting peak temperature Tl were measured by the methods shown below, and formability and loss resistance were measured. Transparency was evaluated.

[1] Glass Composition An appropriate amount of the glass sample obtained as described above was collected, treated with acid and alkali, and the content of the glass component was measured by ICP-AES. The results are shown in Tables 1 and 2.

[2] Specific gravity The measurement was performed based on the Japan Optical Glass Industry Association standard JOBIS-05. The results are shown in Tables 4 and 5.

[3] Refractive index nd and Abbe number νd
The measurement was performed based on the Japan Optical Glass Industry Association standard JOGIS-01. The results are shown in Tables 4 and 5.

[4] Glass transition temperature Tg, crystal melting peak temperature Tl
The glass transition temperature Tg and the crystal melting peak temperature Tl were determined based on a DSC chart when the temperature of glass in a solid state was raised using a differential scanning calorimeter DSC3300SA (NETZSCH Japan). The results are shown in Tables 4 and 5.

[5] λ5
The glass sample was processed so as to have a plane having a thickness of 10 mm, parallel to each other and optically polished, and the spectral transmittance in the wavelength range from 280 nm to 700 nm was measured. The spectral transmittance B / A was calculated, where the intensity of the light beam perpendicularly incident on one plane that was optically polished was defined as the intensity A and the intensity of the light beam emitted from the other plane was defined as the intensity B. The wavelength at which the spectral transmittance is 5% was defined as λ5. The spectral transmittance also includes the reflection loss of light rays on the sample surface. The results are shown in Tables 4 and 5.

[6] Formability In the present embodiment, the formability of the molten glass was evaluated by whether or not the crystal melting peak temperature Tl satisfies the following formula (2). When the crystal melting peak temperature Tl obtained in the above [4] satisfies the formula (2), it is judged as ◯, and when it does not satisfy the following formula (2), it is judged as x. The results are shown in Tables 4 and 5.
Tl <1000nd-790 ... (2)
The glass No. of Examples. All of 1-32 were judged as ◯. The glass No. of Examples. It was confirmed that Nos. 1 to 2 were glasses having excellent moldability of molten glass.

[7] Softening test (devitrification resistance)
The softening test is an evaluation method that serves as an index of devitrification resistance in the present embodiment. A 1 cm square glass sample is heated in a first test furnace set to a glass transition temperature Tg of the glass for 10 minutes, and further to a second test furnace set to a temperature 120 to 200 ° C. higher than the Tg of the glass. After heating for 10 minutes, the presence or absence of crystals or cloudiness was confirmed with an optical microscope. The observation magnification of the optical microscope was 10 to 100 times. When neither crystal nor cloudiness was confirmed, it was judged as ◯, and when at least one of crystal and cloudiness was confirmed, it was judged as x. The results are shown in Tables 4 and 5. The glass No. of Examples. All of 1-32 were judged as ◯. The glass No. of Examples. It was confirmed that Nos. 1 to 32 were glasses having excellent devitrification resistance.

(Comparison example)
(Preparation and evaluation of glass samples Nos. 33 to 41)
For the production and evaluation of glass, the glass No. The procedure was the same as in 1-32. The results are shown in Tables 3 and 6.

Comparative Example Glass No. The glasses of 33 to 41 are evaluated as x in the evaluation of the moldability or softening test. The comparative example glass was inferior in thermal stability or devitrification resistance as compared with the example glass.

(Manufacturing of optical element blank)
No. 1 shown in Tables 1 and 2. A glass sample having a composition of 1-32 was annealed, cut and ground to prepare a cut piece.
The cut piece was press-molded by a reheat press to prepare an optical element blank.

The optical element blank was precisely annealed, the refractive index was precisely adjusted to obtain the required refractive index, and then ground and polished by a known method to obtain an optical element.

Claims (5)

In oxide-based glass composition
The total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O ₃ [P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ] is 26% by mass or more.
And the content of _{B 2 O 3, P 2 O} 5, B 2 O 3, the mass ratio of the total content of SiO ₂ and _{Al 2 O 3 [B 2 O} 3 / (P 2 O 5 + B 2 O 3 + SiO ₂ + Al ₂ O ₃ )] is 0.11 or more and 0.24 or less.
Mass ratio of the total content of Li ₂ O, Na ₂ O and K ₂ O to the total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O ₃ [(Li ₂ O + Na ₂ O + K ₂₎ O) / (P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ )] is 0.35 or more and 0.56 or less.
And the content of _{TiO 2, TiO 2, Nb 2} O 5, WO 3 and _Bi 2 mass ratio of the total content of _{O 3 [TiO 2 / (TiO} 2 + Nb 2 O 5 + WO 3 + Bi 2 O 3)] is 0.12 or more and 0.32 or less,
The content of BaO is 5% by mass or less,
An optical glass having a refractive index nd of more than 1.85 and less than 1.90 and an Abbe number νd of 15 or more and 25 or less. The optical glass according to claim 1, wherein the content of Bi ₂ O ₃ is less than 5% by mass. Mass ratio of the total content of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ and Al ₂ O _{3 to} the total content of TiO ₂ , Nb ₂ O ₅ , WO ₃ and Bi ₂ O ₃ [(P ₂₎ The optical according to claim 1 or 2, wherein O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ) / (TiO ₂ + Nb ₂ O ₅ + WO ₃ + Bi ₂ O ₃ )] is 0.40 or more and 0.60 or less. Glass. An optical element blank made of the optical glass according to any one of claims 1 to 3. An optical element made of optical glass according to any one of claims 1 to 3.

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