JP2016084257A - Optical glass, optical element and optical glass material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical glass having a relatively high refractive index and excellent thermal stability, an optical element and an optical glass material each composed of the optical glass.SOLUTION: There is provided the optical glass which contains 55 mass% or less in total of PO, BOand AlO, and contains BaO, one or more kind selected from MgO, CaO, ZnO and SrO and one or more kind selected from GdO, YO, LaOand YbO, and in which content of ZnO is 15 mass% or less, a mass ratio α of content of BaO to total content of MgO, CaO, ZnO and SrO is 2.1 or less, a mass ratio β of total content of PO, BOand AlOto total content of GdO, YO, LaOand YbOis less than 4.80, and which has a refractive index nd of 1.620 to 1.700 and an Abbe number νd of 53 to 65.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical glass having excellent thermal stability. The present invention also relates to an optical element and an optical glass material made of such optical glass.

  Optical glass is widely used as optical elements such as optical lenses and optical glass materials for optical elements. Glass is a viscous material above the glass transition temperature Tg (hereinafter sometimes simply referred to as “glass transition temperature”, “Tg” or “temperature Tg”), and has a property that the viscosity decreases as the temperature rises, ie, more than Tg. It has the property of softening when heated to a high temperature. As a method for forming an optical element utilizing this property, a press forming method is known in which heat-softened glass is pressed into a desired shape. Such press molding methods are roughly classified into three methods: a direct press molding method, a reheat press molding method, and a precision press molding method (also referred to as a mold press molding method).

  Among these molding methods, the direct press molding method and the reheat press molding method are press molding a melted or softened glass material in a short time to mold an optical element blank that approximates the target optical element shape, and then In this method, the optical element blank is ground and polished to finish the optical element. On the other hand, the precision press molding method is a method of producing a target optical element by transferring a precisely processed molding surface shape to glass softened in a non-oxidizing atmosphere. No grinding / polishing is required.

  The direct press molding method is a method of pressing molten glass without producing a glass material, whereas the reheat press molding method and the precision press molding method are once solidified by cooling the molten glass. After forming the glass material, the glass material is reheated and softened and press-molded.

  In general, when the glass material that has been solidified is reheated and softened, such as the reheat press method and precision press molding method, if the heating temperature is too high, defects due to crystallization occur in the molded product after pressing. There is. Therefore, if the heating temperature is too low to avoid crystallization of the glass, the viscosity of the glass is high. Therefore, the glass has a defective shape due to insufficient deformation of the glass during press molding, or the glass is increased due to an increase in press pressure for deforming the glass. Defects such as cracks may occur.

These problems are caused by precise temperature control in an open atmosphere rather than precision press molding, in which press molding is performed over a long period of time at a relatively low temperature in a non-oxidizing atmosphere under precise temperature control. Reheat press molding, which is difficult and is heated in a short time at a high temperature by heating the glass material to a relatively high temperature (for example, a temperature corresponding to a glass viscosity of 10 ⁴ to 10 ⁶ dPa · s). It becomes prominent in the case of law.

  In addition, when the glass material is reheated and softened, crystallization of the glass becomes a problem, and depending on the type of glass, crystals are formed when glass is formed by supplying (casting) molten glass to a mold or the like. There is also a problem that it tends to precipitate.

  Glass crystals include surface crystals that frequently occur on the glass surface and internal crystals that are generated throughout the glass surface. For optical glass, it is preferred that there are no or very few surface crystals and internal crystals.

  By the way, as glass for making an optical element, various kinds of glass can be selected according to target characteristics. For example, the phosphate glass described in Patent Document 1 is an attractive glass in that it exhibits low dispersibility, and a lens using this glass has high utility value.

Japanese Patent No. 4533069

  However, when the refractive index nd is increased, such phosphate glass tends to have poor thermal stability due to the influence of a glass component that increases the refractive index. Therefore, under severe reheating conditions (for example, high heating temperature) as in the reheat press molding method, there is a problem that crystals are likely to be generated in the molded body (optical element blank) after pressing. In particular, crystallization due to reheating is more remarkable when the refractive index of the optical glass is increased, and it is difficult to increase the thermal stability in the optical glass having a high refractive index.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an optical glass having a relatively high refractive index nd and excellent thermal stability. Furthermore, an object of this invention is to provide the optical element and optical glass raw material which consist of such optical glass.

  In the present invention, the thermal stability of the glass includes devitrification resistance when the glass melt is formed and devitrification resistance when the glass once solidified is reheated.

That is, the gist of the present invention is as follows.
[1] A glass having a total content [P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ] of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ of 55% by mass or less,
BaO,
Any one or more selected from MgO, CaO, ZnO and SrO;
Any one or more selected from Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ ,
The content of ZnO is 15% by mass or less,
The mass ratio α [BaO / (MgO + CaO + ZnO + SrO)] of the content of BaO to the total content of MgO, CaO, ZnO and SrO is 2.1 or less,
Mass ratio β of total content of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ with respect to the total content of Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ [(P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ) / (Gd ₂ O ₃ + Y ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ )]] is less than 4.80,
An optical glass having a refractive index nd of 1.620 to 1.700 and an Abbe number νd of 53 to 65.
[2] Total content of Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ [Gd ₂ O ₃ + Y ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ ] is 4 to 30% by mass The optical glass according to [1] above.
[3] The optical glass according to [1] or [2], wherein the content of P ₂ O ₅ is 12 to 40% by mass.
[4] The optical glass according to any one of [1] to [3], wherein the BaO content is 10 to 45% by mass.
[5] An optical element made of the optical glass according to any one of [1] to [4].
[6] An optical glass material made of the optical glass according to any one of [1] to [4].

  According to the present invention, an optical glass having a relatively high refractive index (refractive index nd is 1.620 or more), even when reheated under harsh conditions due to excellent thermal stability Thus, an optical glass that hardly causes crystallization can be obtained. Moreover, the optical element and optical glass material which consist of such optical glass are obtained.

It is a schematic diagram which shows the differential scanning calorific value curve of optical glass.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) 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 implemented with appropriate modifications within the scope of the gist thereof. In the present specification, each content is expressed in mass% unless otherwise specified.

Optical glass The optical glass of the present invention is a glass having a total content [P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ] of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ of 55% by mass or less. Any one or more selected from BaO, MgO, CaO, ZnO and SrO, and any one selected from Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ The ZnO content is 15% by mass or less, and the mass ratio α [BaO / (MgO + CaO + ZnO + SrO)] of the BaO content to the total content of MgO, CaO, ZnO and SrO is 2.1 or less. The mass ratio β of the total content of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ with respect to the total content of Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ (P _{O 5 + B 2 O 3 +} Al 2 O 3) / (Gd 2 O 3 + Y 2 O 3 + La 2 O 3 + Yb 2 O 3)] is less than 4.80, a refractive index nd of 1.620 to 1.700 The Abbe number νd is 53 to 65.

  In general, components constituting the glass can be broadly classified into a network component that forms a glass network structure and a modifying component that controls the properties of the glass. Among these components, the network component mainly contributes to the stability of the glass (for example, structural stability, thermal stability, and glass meltability). Therefore, from the viewpoint of obtaining a stable glass, it is desirable to relatively increase the proportion of network components in the glass.

  On the other hand, the modifying component mainly contributes to the functionality of the glass (for example, optical properties such as refractive index and dispersibility and chemical durability such as weather resistance). For this reason, it is desirable to appropriately select and adjust the type and amount of the modifying component depending on the function and characteristics required of the glass. However, when the ratio of the modifying component in the glass increases, the ratio of the network component decreases as a result, so that the stability as the glass may decrease. Some modifying components are effective from the viewpoint of improving the characteristics, but may significantly reduce the stability of the glass by adding a small amount.

  Thus, the stability and functionality of glass are greatly influenced by the balance between the network component and the modifying component.

  Conventionally, phosphate glass has been expected to be used as an optical element such as an optical lens because of its high refractive index and low dispersibility, but it has low weather resistance and cannot be used as a glass for press molding. It was. In order to solve such problems, in the invention described in Patent Document 1 (Reference Example 4), by adding BaO as a modifying component and increasing the proportion of BaO in the glass, a high refractive index (refractive index nd However, the weather resistance was improved.

  However, such an optical glass has improved weather resistance and is suitable as a glass for precision press molding, but crystallization due to a modifying component (for example, BaO) introduced in a large amount is likely to occur. There was a problem that the thermal stability deteriorated. Therefore, even if the glass has been solidified once, if it is softened again under severe conditions, crystals may be formed in the cooled glass. Such glass is an optical element such as a reheat press molding method. It was unsuitable for the production method.

In particular, when the proportion of network components (for example, P ₂ O ₅ ) in the optical glass decreases and the proportion of modifying components (for example, components that increase weather resistance or components that increase the refractive index) increases, the heat of the glass Stability tends to deteriorate. For this reason, crystallization of the glass occurs due to reheating in reheat press molding, and it has been difficult to obtain a high refractive index phosphate glass excellent in weather resistance and thermal stability. Such a problem becomes conspicuous when an attempt is made to obtain a relatively high refractive index (refractive index nd is 1.620 or more, further 1.630 or more).

Therefore, as a result of intensive studies to solve the above problems, the present inventors have increased the proportion of the modifying component in the glass and decreased the proportion of the network component (P ₂ O ₅ , B ₂ the total content of O ₃ and _Al 2 _{O 3} be _{[P 2 O 5 + B 2} O 3 + Al 2 O 3] is less 55 mass%), blended well balanced and BaO, and other divalent component Thus, it was found that the thermal stability of the glass can be improved, and the present invention has been completed.

  That is, the optical glass according to the present invention contains BaO and contains at least one selected from MgO, CaO, ZnO and SrO, and the content of BaO with respect to the total content of MgO, CaO, ZnO and SrO. One characteristic is that the mass ratio α of [BaO / (MgO + CaO + ZnO + SrO)] is 2.1 or less.

  By setting the mass ratio α in the above range, it is possible to prevent the specific modifying component (BaO) from being introduced excessively with respect to the other modifying components, and thus it is possible to prevent crystals caused by the specific modifying component. . Therefore, the thermal stability of the glass can be ensured.

  According to the optical glass according to the present invention, generation of internal crystals of the glass can be effectively prevented in reheat press molding performed in an air atmosphere in which precise temperature control is difficult.

In addition, the optical glass according to the present invention is made of Gd ₂ O ₃ , in order to effectively increase the refractive index (nd) while maintaining the thermal stability obtained by setting the mass ratio α within a predetermined range. Contains at least one rare earth element selected from Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ , and Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O _P 2 _O 5 to the total content of _3, B 2 _{O 3} and _Al 2 _O weight ratio of the total content of _{3 β [(P 2 O 5} + B 2 O 3 + Al 2 O 3) / (Gd 2 O 3 + Y One characteristic is that ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ )] is less than 4.80.

Total content of network components (P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ ) with respect to the total content of the rare earth elements (Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ ) By setting the amount ratio (mass ratio β) in the above range, the total content of the rare earth elements is relatively increased, so that the refractive index of the glass can be set high.

  Such an optical glass according to the present invention is particularly suitable when an optical element having a high refractive index is produced using a reheat press molding method.

  The optical glass in the present invention is a glass composition containing a plurality of metal oxides, regardless of the form (lumps, plates, spheres, etc.) and uses (materials for optical elements, optical elements, etc.). In general, it is called optical glass.

<Glass composition>
Next, the constituent components of the optical glass according to the present invention will be described in detail. The glass composition can be determined by a method such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry).

  In the ICP-AES analysis, first, quantitative analysis is performed for each element, and then converted into oxide notation based on this quantitative analysis value. The analysis value obtained by ICP-AES may include a measurement error of about ± 5% of the analysis value. Therefore, the oxide notation value converted from the analysis value may also contain an error of about ± 5%.

  In addition, in the present specification, the content of the constituent component (notation of oxide) is 0% or does not contain or is not introduced, which means that the constituent component is not substantially contained, It shall indicate that it is below the impurity level.

P ₂ O ₅ is a network component that forms a network structure of glass, and is an essential component for imparting thermal stability that can be produced to glass. However, when P ₂ O ₅ is excessively contained, the glass transition temperature, the yield point, and the melting temperature of the glass increase, and the refractive index and weather resistance tend to decrease. On the other hand, if the content of P ₂ O ₅ is too small, the Abbe number (νd) of the glass is reduced and the low dispersibility is impaired, and the tendency of the glass to become devitrified becomes strong and the glass tends to become unstable. . Therefore, in the optical glass of the present invention, the upper limit of the content of P ₂ O ₅ is preferably 40%, and more preferably in the order of 37%, 35%, 34%, and 33%. Moreover, the lower limit of the content of P ₂ O ₅ is preferably 12%, and more preferably in the order of 13%, 14%, 15%, and 16%.

B ₂ O ₃ is a very effective component for improving the meltability of glass and homogenizing the glass, and at the same time, improving the devitrification resistance and weather resistance of the glass and increasing the refractive index to promote low dispersion. It is an effective ingredient above. However, excessive introduction of B ₂ O ₃ may cause an increase in glass transition temperature and yield point, deterioration of devitrification resistance, and loss of low dispersibility. Therefore, in the optical glass of the present invention, the upper limit of the content of B ₂ O ₃ is preferably 20%, and more preferably in the order of 17%, 15%, 14%, 13%, and 12%. Further, meltability and devitrification resistance of the glass when the content of B ₂ O ₃ is too small decreases. Therefore, in the optical glass of the present invention, the lower limit of the content of B ₂ O ₃ is preferably 0.1%, and further 1.0%, 2.0%, 3.0%, 3.5% Are preferred in this order. Incidentally, B ₂ O ₃ in the optical glass of the present invention, to form a network structure of the glass together with P ₂ O _5, from the viewpoint of the stability of the glass is preferably contained.

Al ₂ O ₃ is a network component that forms a network structure of glass, and is used as an effective component for improving the weather resistance of glass. However, if the amount introduced is excessive, the glass transition temperature and the yield point increase, the stability and meltability of the glass deteriorate, and the refractive index may also decrease. Therefore, in the optical glass of the present invention, the upper limit of the content of Al ₂ O ₃ is preferably 10%, and more preferably in the order of 7%, 5%, and 3%. Moreover, the lower limit of the content of Al ₂ O ₃ is preferably 0%, and more preferably 0.5%, 1.0%, 1.3%, and 1.5% in this order.

In addition, if the total content [P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ] of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ exceeds 55%, the refractive index decreases and the glass melting temperature. There is a risk that the quality will deteriorate due to the increase of the glass and the volatilization of the glass. On the other hand, if the total content of these components is too small, devitrification resistance deteriorates and vitrification becomes difficult, and low dispersibility may be impaired. In the optical glass of the present invention, the upper limit of the total content [P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ] is 55%, and further 50%, 45%, 42%, 40%, 39%, It is preferable in the order of 38%. The lower limit of the total content [P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ] is preferably 20%, and more preferably in the order of 23%, 25%, 27%, 29%, and 30%.

Moreover, in the optical glass of the present invention, the content of P ₂ O ₅ with respect to the content of B ₂ O ₃ from the viewpoint of both imparting low dispersibility to the glass and enhancing thermal stability. The upper limit of the ratio: mass ratio [P ₂ O ₅ / B ₂ O ₃ ] is preferably 12, and more preferably in the order of 10, 9, 8, and 7. Moreover, the lower limit of the mass ratio [P ₂ O ₅ / B ₂ O ₃ ] is preferably 0.6, and more preferably 0.8, 1.0, 1.2, and 1.5 in this order. Thus, in the optical glass according to the present invention, excellent thermal performance is achieved while achieving low dispersion by balancing the proportion of P ₂ O ₅ and B ₂ O ₃ that predominantly acts on the formation of the glass network structure. Stability can be obtained.

  BaO is an essential component that is very effective for increasing the refractive index of glass and improving weather resistance by introducing an appropriate amount. However, if the amount introduced is too large, the thermal stability of the glass is remarkably impaired, the glass transition temperature rises, and the low dispersibility tends to be impaired. On the other hand, if the amount introduced is too small, the desired refractive index cannot be obtained, and the weather resistance is further deteriorated. Therefore, in the optical glass of the present invention, BaO is an essential component, and the upper limit of the content thereof is preferably 45%, and further 40%, 37%, 35%, 33%, 32%, 31%. Are preferred in this order. Moreover, the lower limit of the BaO content is preferably 10%, and more preferably 13%, 15%, 17%, 19%, and 20% in this order.

Further, from the viewpoint of enhancing the thermal stability and weather resistance of the glass, the upper limit of the total content of BaO and P ₂ O ₅ [BaO + P ₂ O ₅ ] is preferably 70%, and further 67% and 65%. 63%, 61% and 60% in this order. Moreover, the lower limit of the total content [BaO + P ₂ O ₅ ] is preferably 35%, and more preferably in the order of 38%, 40%, 42%, 44%, and 45%.

Further, the glass was lowering dispersion, and in view of enhancing the thermal stability of the _glass, the proportion of BaO content to the content of B 2 _{O 3:} upper limit of the mass ratio [BaO _/ B 2 _{O 3]} is preferably Is 30, more preferably in the order of 20, 15, 12, 10, 8, and 7. Moreover, the lower limit of the mass ratio [BaO / B ₂ O ₃ ] is preferably 0.5, and more preferably in the order of 1.0, 1.5, 1.8, 2.0, and 2.2.

  MgO is a component introduced to achieve both high weather resistance and low dispersion of glass. The introduction of a small amount of MgO has the effect of lowering the glass transition temperature, yield point or liquidus temperature. However, when introduced in a large amount, the thermal stability of the glass is remarkably deteriorated, and the liquidus temperature is increased. Therefore, in the optical glass of the present invention, the upper limit of the content of MgO is preferably 20%, and more preferably in the order of 15%, 12%, 10%, 9%, and 8%. Further, the lower limit of the content of MgO is preferably 0%, and more preferably in the order of 1%, 2%, 3%, 3.5%, and 4%.

Incidentally, MgO _is advantageous work for B ₂ O 3, Li ₂ O as well as low dispersion of the glass. Therefore, in order to obtain a desired dispersion without impairing the thermal stability in the reheat press molding, the optical glass of the present invention contains at least 2% of any one component of MgO, B ₂ O ₃ and Li ₂ O. It is preferable to introduce. In particular, the lower limit of the content of any one of MgO, B ₂ O ₃ and Li ₂ O is preferable in the order of 3%, 5% and 7%.

  CaO is a component introduced to promote low dispersion of the glass, improve the thermal stability of the glass, and lower the liquidus temperature. However, when CaO is introduced excessively, not only the chemical durability of the glass is deteriorated, but also the thermal stability of the glass is lowered and the refractive index may be lowered. Therefore, in the optical glass of the present invention, the upper limit of the CaO content is preferably 18%, and more preferably in the order of 15%, 12%, 11%, 10%, and 9.5%. Moreover, the lower limit of the CaO content is preferably 0%, and more preferably in the order of 2%, 3%, 4%, 5%, and 5.5%.

  The upper limit of the total content [MgO + CaO] of MgO and CaO in the optical glass of the present invention is preferably 30% from the viewpoint of achieving both low dispersion of glass, thermal stability, and weather resistance. Is preferred in the order of 25%, 22%, 20%, 19% and 18%. Further, the lower limit of the total content [MgO + CaO] is preferably 5%, and more preferably 7%, 9%, 10%, and 11% in this order.

  SrO is an effective component that increases the refractive index of the glass without impairing the low dispersibility of the glass. It is also effective as a component that enhances the weather resistance of glass. However, when SrO is introduced excessively, the liquidus temperature rises and the thermal stability of the glass tends to deteriorate. Therefore, in the optical glass of the present invention, the upper limit of the SrO content is preferably 15%, and more preferably in the order of 13%, 10%, 7%, and 5%. Moreover, the lower limit of the SrO content is preferably 0%, and more preferably in the order of over 0%, 1.0%, 2.0%, and 2.5%.

  ZnO is a component used to increase the refractive index of glass by appropriate introduction, improve the thermal stability of glass, and lower the liquidus temperature and glass transition temperature. However, when ZnO is introduced excessively, the low dispersibility is greatly impaired and the chemical durability of the glass deteriorates. Therefore, in the optical glass of the present invention, the upper limit of the content of ZnO is 15%, and more preferably in the order of 13%, 12%, 11%, 10%, 9%, 6%, and 5%. Moreover, when there is too little introduction amount of ZnO, it exists in the tendency for a liquidus temperature and a glass transition temperature to become high. Therefore, the lower limit of the ZnO content is preferably 0%, and more preferably in the order of over 0%, 1.0%, 2.0%, and 2.5%.

  In addition to BaO, the optical glass of the present invention contains one or more selected from MgO, CaO, ZnO and SrO as a divalent component. At that time, from the viewpoint of improving the weather resistance of the glass and obtaining desired optical properties, the upper limit of the total content R = [MgO + CaO + ZnO + SrO + BaO] of MgO, CaO, ZnO, SrO and BaO is preferably 80%, Is preferred in the order of 70%, 60%, 55%, 52%. Further, the lower limit of the total content R is preferably 25%, and more preferably in the order of 30%, 35%, 40%, 42%, and 44%.

  In the optical glass of the present invention, from the viewpoint of improving the thermal stability of the glass while increasing the refractive index, the ratio of the content of BaO to the total content of MgO, CaO, ZnO and SrO: mass ratio α [BaO / (MgO + CaO + ZnO + SrO)] is made 2.1 or less. Moreover, the upper limit with preferable mass ratio (alpha) is 2.0, Furthermore, it is preferable in order of 1.9, 1.8, 1.7, 1.6, 1.5, 1.2. Further, from the viewpoint of improving the weather resistance of the glass, the lower limit of the mass ratio α is preferably 0.4, and further in the order of 0.5, 0.6, 0.7, 0.8, 0.9. preferable. By satisfying such a condition, the BaO content is not excessively introduced with respect to the content of the other divalent components, so that the precipitation of crystals due to BaO can be suppressed. Therefore, even when BaO and other divalent components are blended in a balanced manner, the component that increases the refractive index is increased, and the component that forms the network structure is decreased. Can be improved.

  The optical glass of the present invention satisfying a mass ratio α of 2.1 or less may be referred to as a crystallization peak temperature Tc (hereinafter simply referred to as “crystallization peak temperature”, “Tc”, or “temperature Tc”). ) And the glass transition temperature Tg (Tc−Tg) is relatively wide, and both Tc−Tg are 145 ° C. or higher. By setting the mass ratio α within the above range, as a result, Tc-Tg increases, and when the glass is re-softened, it can be softened at a temperature lower than the temperature Tc. Without improving the thermal stability of the glass.

  Furthermore, from the viewpoint of improving the thermal stability of the glass, the upper limit of the ratio of the content of BaO to the total content of MgO and SrO: mass ratio [BaO / (MgO + SrO)] is preferably 12, 10, 9, 8, 7, and 6 are preferable in this order. Further, the lower limit of the mass ratio [BaO / (MgO + SrO)] is preferably 0.2, and more preferably 0.4, 0.5, 0.6, 0.65, and 0.7 in this order.

  Further, from the viewpoint of improving the thermal stability of glass and obtaining desired optical properties, the ratio of the total content of SrO and BaO to the total content of MgO and CaO: the upper limit of the mass ratio [(SrO + BaO) / (MgO + CaO)] Is preferably 5, and more preferably in the order of 4, 3.5, 3.2, 3.0, 2.8. Moreover, the lower limit of the mass ratio [(SrO + BaO) / (MgO + CaO)] is preferably 0.3, and more preferably 0.7, 1.0, 1.2, and 1.4 in this order.

  Of the divalent components composed of MgO, CaO, ZnO, SrO and BaO, BaO effectively increases the refractive index and weather resistance of the glass, but the thermal stability of the glass is significantly impaired by excessive introduction. On the other hand, ZnO improves the thermal stability of the glass, but low dispersibility is greatly impaired by excessive introduction. Therefore, from the viewpoint of obtaining the thermal stability of the glass and the desired optical constant, the upper limit of the ratio of the content of ZnO to the content of BaO: mass ratio [ZnO / BaO] is preferably 0.5, Furthermore, it is preferable in the order of 0.4, 0.35, and 0.3. Moreover, the lower limit of the mass ratio [ZnO / BaO] is preferably 0.05, and more preferably in the order of 0.1 and 0.13.

Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ are all components that contribute to improving the weather resistance and increasing the refractive index of the glass. However, if these components are introduced excessively, the thermal stability of the glass may be deteriorated. Therefore, in the optical glass of the present invention, the upper limit of the content of Gd ₂ O ₃ is preferably 30%, and more preferably 27%, 24%, and 22% in this order. Moreover, the lower limit of the content of Gd ₂ O ₃ is preferably 0%, and more preferably in the order of 1%, 2%, 4%, and 5%. The upper limit of the content of Y ₂ O ₃ is preferably 10%, and more preferably 8%, 7%, and 6% in this order. Moreover, the lower limit of the content of Y ₂ O ₃ is preferably 0%, and more preferably 0.5% and 1.0% in this order. The upper limit of the content of La ₂ O ₃ is preferably 10%, and more preferably 7%, 5%, and 4% in this order. Moreover, the lower limit of the content of La ₂ O ₃ is preferably 0%, more preferably 0.05%. The upper limit of the content of Yb ₂ O ₃ is preferably 7%, and more preferably in the order of 5%, 2%, and 1%. Further, the lower limit of the content of Yb ₂ O ₃ is preferably 0%, more preferably 0.05%. Incidentally, Yb ₂ O _3, because having absorptivity in the near infrared region, preferably not introduced when using the light in the near-infrared region.

In addition, the rare earth elements such as Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O _3, and Yb ₂ O ₃ are preferably introduced appropriately from the viewpoint of effectively increasing the refractive index. Therefore, the optical glass of the present invention contains one or more selected from Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ . However, if these components are introduced excessively, the thermal stability of the glass tends to deteriorate, so the total content of Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ Re = The upper limit of [Gd ₂ O ₃ + Y ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ ] is preferably 30%, and more preferably 25%, 23%, 22% and 21% in this order. Further, the lower limit of the total content Re is preferably 4%, and more preferably in the order of 5%, 6%, 8%, and 9%. Note that the thermal stability of the glass may be improved by introducing two or more rare earth elements rather than introducing a single rare earth element. For this reason, the optical glass of the present invention preferably contains any two or more rare earth elements selected from Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ .

In addition, the optical glass according to the present invention is a total content of the rare earth elements from the viewpoint of effectively increasing the refractive index while ensuring the thermal stability of the glass obtained by setting the mass ratio α within a predetermined range. Ratio of total content of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ with respect to amount Re: mass ratio β [(P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ) / Re] less than 4.80 And The upper limit of the mass ratio β is preferably 4.70, and more preferably 4.60, 4.50, 4.30, 4.10, 4.00 in this order. Moreover, the lower limit of the mass ratio β is preferably 1.00, and more preferably in the order of 1.20, 1.30, and 1.40.

  In the present invention, the mass ratio α and the mass ratio β are closely related from the viewpoint of obtaining desired optical characteristics and improving the thermal stability of the glass. This will be described below.

  In the optical glass according to the present invention, in consideration of increasing the refractive index of the glass, the total content Re of rare earth elements, which are components that effectively increase the refractive index, is introduced in a relatively large amount. On the other hand, when the total content Re of the rare earth elements becomes excessive, the thermal stability of the glass tends to deteriorate as described above. Therefore, there is a predetermined limit to the amount of introduction of the total rare earth element content Re, and this limit is defined by the mass ratio β (the upper limit of the mass ratio β is less than 4.80). Thus, by defining the mass ratio β within a predetermined range, desired optical characteristics (high refractive index) can be obtained. However, as the total content Re of the rare earth elements increases, the thermal stability of the glass increases. It tends to get worse.

  On the other hand, since excessive introduction of rare earth elements deteriorates the thermal stability, in the optical glass according to the present invention, the thermal stability is improved by setting the mass ratio α within a predetermined range. However, if the amount of BaO introduced relative to the total content of MgO, CaO, ZnO and SrO is too large, the thermal stability is impaired, so in the present invention, the upper limit of the mass ratio α is specified (the mass ratio α is 2. 1 or less).

  Thus, by adjusting the glass composition so that the mass ratio α and the mass ratio β are within a predetermined range, desired optical characteristics can be obtained and the thermal stability of the glass can be improved.

SiO ₂ is an effective component for improving chemical durability while maintaining low dispersibility. However, if the amount introduced is too large, the glass transition temperature and yield point tend to increase and the refractive index tends to decrease. Therefore, in the optical glass of the present invention, the upper limit of the content of SiO ₂ is preferably 3%, more preferably 2%, still more preferably 1.5%, and even more preferably 1%. Incidentally, SiO _{2 is} a network component with _{P 2 O 5, B 2 O} 3, Al 2 O 3, it is not necessarily introduced SiO ₂ in the optical glass of the present invention.

Li ₂ O is a component that lowers the glass transition temperature and the yield point and is effective for lowering the dispersion. In particular, coexistence of P ₂ O ₅ , B ₂ O ₃ and Li ₂ O is very effective for reducing the glass dispersion. However, when Li ₂ O is excessively introduced, the chemical durability (weather resistance, alkali resistance, etc.) of the glass deteriorates, and the refractive index tends to rapidly decrease. Therefore, in the optical glass of the present invention, the upper limit of the Li ₂ O content is preferably 7%, and more preferably in the order of 5%, 4%, and 3%. Moreover, the lower limit of the content of Li ₂ O is preferably 0%, and more preferably in the order of 0.1%, 0.5%, 1.0%, 1.3%, and 1.5%.

Na ₂ O and K ₂ O are optional components introduced to improve the devitrification resistance of the glass, lower the glass transition temperature, yield point, and liquidus temperature, and improve the meltability of the glass. is there. The introduction of appropriate amounts of Na ₂ O and K ₂ O improves the stability of the glass and leads to a decrease in the liquidus temperature and transition temperature. However, when excessively introduced, the chemical durability is remarkably deteriorated and the refractive index is also increased. It tends to decrease. Therefore, in the optical glass of the present invention, the upper limit of the Na ₂ O content is preferably 8%, and more preferably in the order of 5%, 3%, and 1%. Moreover, the upper limit of the content of K ₂ O is preferably 8%, and more preferably in the order of 5%, 3%, and 2%. It is particularly preferable that Na ₂ O and K ₂ O are not substantially introduced.

Further, Li 2 _O, the total content of Na 2 _O and K _{2 O,} is too small, or the glass transition temperature and sag increases, meltability is deteriorated. Therefore, in the optical glass of the present invention, the upper limit of the total content R ₂ = [Li ₂ O + Na ₂ O + K ₂ O] of Li ₂ O, Na ₂ O and K ₂ O is preferably 15%, 10%, 7% and 5% are preferable in this order. The lower limit of the total content _{R 2} is preferably 0%, further 0.1%, 0.5%, 1.0%, 1.3%, preferably in the order of 1.5%.

In addition, in the optical glass of the present invention, it is not always necessary to introduce Cs ₂ O, which is an alkali metal oxide. Further, Cs ₂ O lowers the refractive index and remarkably impairs the weather resistance, so it is preferable not to introduce Cs ₂ O.

In addition, the upper limit of the ratio of the P ₂ O ₅ content to the total content R ₂ of the alkali metal oxide: mass ratio [P ₂ O ₅ / R ₂ ] from the viewpoint of achieving both glass meltability and thermal stability. Is preferably 40, and more preferably 30, 25, and 20 in this order. The lower limit of the mass ratio [P ₂ O ₅ / R ₂ ] is preferably 2, and more preferably 3, 5, and 7 in this order.

  Moreover, it is preferable that the optical glass of this invention does not contain Pb, As, Cd, U, Th, and Tl substantially from a viewpoint of reducing the load to an environment.

The optical glass of the present invention can contain halogen, that is, F, Cl, Br, and I as optional components. The content can be represented by the mass fraction of anions (for example, [F / (O + F)]). The upper limit of the F content is preferably 8%, and more preferably 5%, 3%, 2%, 1%, 0.5%, and 0.1% in this order. Further, the upper limit of the content of Cl, Br, and I is preferably 5%, respectively, and more preferably in the order of 3%, 2%, 1%, 0.5%, and 0.1%. When halogen is contained in the glass, the upper limit of B ₂ O _{3 in} the glass is preferably 8% in order to suppress the volatilization of the glass, more preferably in the order of 5%, 3%, and 1%, and most preferably. Is substantially not contained. However, this does not apply when a small amount of halogen of 1% or less is added. In particular, in order to suppress the volatilization of components from the glass and improve the homogeneity of the glass, it is preferable that the halogen is not substantially contained.

In the optical glass of the present invention may contain readily reducing component from _{WO 3, TiO 2, Bi 2} O 3 and _Nb 2 _{O 5} as an optional component. These easily reducing components are effective components for increasing the refractive index. However, W, Ti, Bi, and Nb significantly reduce the glass Abbe number (νd). Therefore, the upper limit of the content of the easily reducing component is preferably 4%, more preferably 3%, 2%, and 1%. In addition, it is particularly preferable not to substantially introduce the easily reducing component.

The optical glass of the present invention as described above is basically composed of P ₂ O ₅ , B ₂ O ₃ , SiO ₂ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, ZnO. , SrO, BaO, Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ . The total content [P ₂ O ₅ + B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ + Li ₂ O + Na ₂ O + K ₂ O + MgO + CaO + ZnO + SrO + BaO + Gd ₂ O ₃ + Y ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ ] is 95% or more. Preferably, it is 98% or more, more preferably 99% or more, and still more preferably 100%.

  In addition, although it is preferable that the optical glass of this invention is fundamentally comprised by the said component, in the range which does not prevent the effect of this invention, it is also possible to introduce | transduce another component. In the present invention, the inclusion of inevitable impurities is not excluded.

  In addition, "substantially not containing" can be based on the content being less than 0.2% by mass. Since components and additives that are not substantially contained are preferably not contained in the glass, the content is preferably less than 0.1% by mass, more preferably less than 0.08% by mass, It is further preferably less than 0.05% by mass, more preferably less than 0.01% by mass, and even more preferably less than 0.005% by mass.

Further, when the optical glass of the present invention is composed of the above components and the total amount is 100% by mass, even if a refining agent such as Sb ₂ O ₃ , SnO ₂ , CeO _{2 is} introduced in an external ratio within 4% by mass. Good. The upper limit of the content of Sb ₂ O ₃ is preferably 4% by mass, and more preferably 3% by mass, 2% by mass, 1% by mass, 0.5% by mass, and 0.1% by mass in this order. Moreover, the lower limit of the content of Sb ₂ O ₃ is preferably 0%, and more preferably in the order of 0.01% by mass, 0.02% by mass, and 0.04% by mass. In addition, SnO ₂ and CeO ₂ may deteriorate the transmittance of the glass, so that introduction of 1% by mass or less is preferable, and it is particularly preferable not to introduce substantially.

<Optical properties of optical glass (refractive index, Abbe number)>
The upper limit of the refractive index nd of the optical glass of the present invention is 1.700, and further preferably 1.690, 1.485, 1.680, 1.670, 1.660. Moreover, the minimum of refractive index nd is 1.620, Furthermore, it is preferable in order of 1.625, 1.630, 1.635, 1.640.

  The upper limit of the Abbe number νd of the optical glass of the present invention is 65, and 62 and 61 are preferable in this order. The lower limit of the Abbe number νd is 53, and 54, 55, 56, 57, 58, and 59 are preferable in this order.

  By using such an optical element made of an optical glass having a high refractive index and low dispersion, an optical system is constructed, so that the optical system can be made compact, highly functional, and improved in chromatic aberration.

<Thermal stability of optical glass>
The thermal stability of glass includes devitrification resistance when forming a glass melt and devitrification resistance when glass that has been solidified once is reheated. The devitrification resistance when molding the glass melt is based on the liquidus temperature, and the lower the liquidus temperature, the better the devitrification resistance. In glass with a high liquidus temperature, the temperature of the glass melt must be maintained at a high temperature in order to prevent devitrification, which leads to deterioration in quality and productivity due to volatilization of glass components. May end up. Therefore, the optical glass of the present invention preferably has a liquidus temperature of 1350 ° C. or lower, more preferably 1300 ° C. or lower, further preferably 1250 ° C. or lower, and further preferably 1200 ° C. or lower. preferable.

On the other hand, regarding the devitrification resistance when the glass once solidified is reheated, the larger the temperature difference (Tc−Tg) between the crystallization peak temperature Tc and the glass transition temperature Tg, the better the devitrification resistance. . For example, in the reheat press molding method, it is necessary to heat the optical glass material to a temperature higher than the temperature Tg and soften it to an appropriate viscosity (about 10 ⁴ to 10 ⁶ dPa · s). However, when the temperature of the heated glass material reaches the temperature Tc, an internal crystal is generated, so that a glass having a small temperature difference (Tc−Tg) is disadvantageous in performing reheat press molding. On the other hand, glass having a large temperature difference (Tc−Tg) is softened at a temperature lower than the temperature Tc, so that reheat press molding can be performed without devitrification of the glass.

In general, the “softening point” of a glass is a temperature at which the glass starts to be significantly deformed by its own weight, and corresponds to a viscosity of about 10 ^7.6 dPa · s. On the other hand, in the reheat press molding method, “temperature Tp at which glass is softened” (hereinafter simply referred to as “temperature at which glass is softened”, “Tp” or “temperature Tp”) is higher than “softening point”. This is the temperature at which the viscosity of the glass corresponds to a viscosity of 10 ⁴ to 10 ⁶ dPa · s. The temperature corresponding to a viscosity of 10 ⁴ to 10 ⁶ dPa · s can be uniquely determined by a viscosity curve.

  Glass transition temperature Tg, crystallization peak temperature Tc and endothermic peak temperature Tk associated with glass transition (hereinafter simply referred to as “endothermic peak temperature”, “Tk”, or “temperature Tk”), which are indicators of the thermal stability of glass. 1), the crystallization start temperature Tx (hereinafter, simply referred to as “crystallization start temperature”, “Tx”, or “temperature Tx”) will be described with reference to FIG.

  FIG. 1 is a schematic diagram showing a differential scanning calorimetric curve of optical glass (phosphate glass). In the figure, the horizontal axis represents temperature, and the vertical axis represents the amount of differential heat corresponding to exothermic endotherm of glass. The glass transition temperature Tg, the endothermic peak temperature Tk accompanying the glass transition, the crystallization start temperature Tx, and the crystallization peak temperature Tc are all measured by a differential scanning calorimeter [DSC (Differential Scanning Calorimetry)].

  The endothermic peak temperature Tk accompanying the glass transition in the present invention means the temperature of the endothermic reaction peak that occurs in the vicinity of about Tg to (Tg + 100 ° C.). The crystallization peak temperature Tc means a temperature showing the lowest crystallization exothermic peak when glass is powdered and differential scanning calorimetry is performed from room temperature to a predetermined temperature at a heating rate of 10 ° C./min. The crystallization start temperature Tx means the rising temperature on the low temperature side of the crystallization peak.

  The glass transition temperature Tg of the optical glass of the present invention is preferably within the following range. That is, the upper limit of Tg is preferably 630 ° C, and more preferably in the order of 600 ° C, 580 ° C, 560 ° C, and 540 ° C. Moreover, although the minimum of Tg is not specifically limited, 400 degreeC is preferable and also 440 degreeC, 460 degreeC, 480 degreeC, and 490 degreeC are preferable in order.

  The crystallization peak temperature Tc of the optical glass of the present invention is preferably in the following range. That is, the lower limit of Tc is preferably 640 ° C, and more preferably in the order of 650 ° C, 660 ° C, 67 ° C, and 675 ° C. Further, the upper limit of Tc is preferably 820 ° C, and more preferably in the order of 810 ° C, 800 ° C, 790 ° C, 785 ° C, and 780 ° C.

  Usually, in the press molding method, a glass material is heated and adjusted to have a viscosity suitable for press molding. In particular, the reheat press molding method deforms the glass in a shorter time than the precision press molding method, so it is common to reheat the glass at a relatively high temperature so that good press molding can be performed, and sufficiently reduce the viscosity of the glass. Is.

In the case of press molding for a short time, if the heating temperature is insufficient and the viscosity of the glass is high, cracks may occur in the molded product due to pressure during pressing, or shape defects may occur due to insufficient deformation, There is a risk that the yield rate is reduced. Therefore, in order to perform good press molding, particularly in the reheat press molding method, it is necessary to sufficiently heat the glass material and adjust it to an appropriate temperature (temperature corresponding to a glass viscosity of 10 ⁴ to 10 ⁶ dPa · s). There is.

  On the other hand, if the glass is heated to a temperature higher than the crystallization peak temperature Tc of the glass, crystals (internal crystals and surface crystals) are generated in the glass molded product after press molding, There is a risk. Therefore, when heating the glass material, it is necessary to carry out the temperature at a temperature suitable for press molding and lower than the temperature Tc.

  However, glass that is easily crystallized in the reheat press molding method often has a small temperature difference between Tg and Tc, and when heated to a temperature suitable for press molding, the temperature Tc may be exceeded.

  Therefore, the larger the temperature difference (Tc−Tg) between the temperature Tc and the temperature Tg, the less the crystallization of the glass occurs. The optical glass of the present invention has excellent Tc-Tg of 145 ° C. or higher, no internal crystals are generated by reheating, and is excellent in thermal stability, as shown in Examples described later. That is, since the temperature Tc of the optical glass of the present invention is sufficiently higher than the temperature Tg, the glass material is softened at a temperature lower than the crystallization peak temperature Tc and no crystal is generated at the time of reheat press molding. .

  In other words, the crystallization peak temperature Tc of the optical glass of the present invention is sufficiently higher than the temperature Tp at which the glass softens. In the optical glass of the present invention, as shown in Tables 1 to 5 described later, no internal crystals were generated in any of the samples (Samples 1 to 37). Therefore, if the optical glass of the present invention is used, reheat press molding under severe reheating conditions can be performed satisfactorily.

  Further, looking at the relationship between the temperature difference (Tc−Tg) and the temperature difference (Tc−Tp), the temperature Tp is higher than the temperature Tg. Therefore, the temperature difference (Tc−Tg) is higher than the temperature difference (Tc−Tg−). It is more preferable that the temperature difference is larger than Tp). Since the optical glass of the present invention has the above-described glass composition, the temperature Tc is high and the temperature difference (Tc−Tg) is large. Accordingly, as a result, the temperature difference (Tc−Tp) also increases, and the thermal stability can be improved.

  In the optical glass of the present invention, the temperature difference (Tc−Tg) between the temperature Tc and the temperature Tg is preferably 145 ° C. or more, more preferably 150 ° C. or more, and further preferably 160 ° C. or more. Especially preferably, it is 180 degreeC or more, More preferably, it is 200 degreeC or more.

  The temperature difference (Tc−Tp) between the temperature Tc and the temperature Tp is preferably 1 ° C. or more, and the temperature difference (Tc−Tp) is preferably 5 ° C. or more, more preferably 10 ° C. or more. Yes, more preferably 20 ° C. or higher, more preferably 30 ° C. or higher, and even more preferably 50 ° C. or higher.

The optical glass of the present invention has a crystallization peak in a reheat press molding method in which a glass material is heated to a temperature higher than Tg to soften the glass material to an appropriate viscosity (about 10 ⁴ to 10 ⁶ dPa · s). Since it is sufficiently softened at a temperature lower than the temperature Tc, the generation of internal crystals can be effectively prevented. Further, since the optical glass of the present invention is excellent in thermal stability, it can be applied to a reheat press molding method in an open atmosphere where precise temperature control is difficult.

  As described above, in the optical glass of the present invention, the quantitative relationship between the content of BaO contained in the optical glass and the total content of divalent components other than BaO (mass ratio α [BaO / (MgO + CaO + ZnO + SrO)]. ) Within the range of 2.1 or less, the glass can be improved in thermal stability without devitrification even under severe reheating conditions such as reheat press molding. .

The optical glass of the present invention contains one or more rare earth elements selected from Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ , and these rare earth elements Quantitative relationship of the total content of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ with respect to the total content Re (mass ratio β [(P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ) / Re] ) Is set to less than 4.80, the refractive index can be effectively increased while ensuring the thermal stability of the glass.

  The thermal stability of the glass obtained from a differential scanning calorimeter (DSC) can also be evaluated by the peak intensity Δ of crystallization. Specifically, the smaller the crystallization exothermic peak is, the smaller the tendency of the glass to change into crystals, so that the thermal stability of the glass increases, which is preferable for the glass of the present invention. The peak intensity Δ of crystallization is B based on A when the absolute value of the calorific difference between Tk and Tg is A and the absolute value of the calorific difference between Tx and Tc is B, taking into account the sensitivity of the apparatus. , That is, a relative value such as peak intensity Δ = B / A (times). The height of the crystallization peak can be calculated from the difference between the calorific value at the peak temperature and the baseline of the differential scanning calorimeter, but depends on how the baseline is drawn. The peak intensity Δ was calculated.

  The higher the thermal stability and the less likely crystallization occurs, the smaller the peak intensity Δ because the heat generated when the glass transitions to crystals is smaller. Accordingly, the peak intensity Δ is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, still more preferably 4 or less, still more preferably 2 or less, and even more preferably 1 or less. In the most preferable glass, the crystallization peak is not observed and the peak intensity cannot be defined. Even when the peak intensity Δ is relatively large, if the temperature difference [Tc−Tg] between the temperature Tc and the temperature Tg is 145 ° C. or higher, crystallization occurs even if the glass is heated to lower the viscosity. Therefore, crystallization in reheat press molding hardly occurs.

  The optical glass of the present invention is also excellent in weather resistance. The weather resistance of glass can be expressed using a haze value (haze) as an index. The haze value is the degree of cloudiness of the glass when the glass is held for a predetermined time in a high temperature and high humidity environment. Specifically, the haze value is the ratio of the scattered light intensity to the total transmitted light intensity when white light is transmitted perpendicular to the polished surface of the glass flat plate subjected to double-side optical polishing, that is, [scattered light intensity / transmitted light intensity. ] In%. The optical glass of the present invention preferably has a haze value of 10 or less, more preferably a haze value of 5 or less, further preferably a haze value of 2 or less, more preferably a haze value of less than 1. Glass with a high haze value is a so-called chemical endurance that has a high rate at which the glass is eroded by various chemical components such as water droplets and water vapor attached to the glass, and glass in the usage environment, and a reaction product is generated on the glass surface. It is a glass with low properties. Conversely, a glass having a small haze value, such as the optical glass of the present invention, is a glass having high chemical durability (weather resistance).

Production of Optical Glass The optical glass according to the present invention may be produced according to a known glass production method by blending raw materials so as to have the above-mentioned predetermined composition.

  In addition, although it does not specifically limit as a raw material (glass raw material) of each component in glass, Each metal oxide, carbonate, nitrate, hydroxide, etc. are mentioned.

Manufacture of optical elements, etc. In order to make an optical element using the optical glass according to the present invention, a known method may be applied. For example, the optical glass according to the present invention is melted to form a plate-like glass material, and the plate-like glass material is subdivided into a predetermined volume to produce a glass material for press molding. Or the glass lump of a predetermined volume is shape | molded continuously from the state which melted the optical glass which concerns on this invention, and the glass raw material for press molding is produced. Next, this glass material is reheated and press-molded (reheat press molding) to produce an optical element blank. Further, the optical element blank is processed by a process including polishing to produce an optical element or a glass material for precision press molding.

  Alternatively, molten glass is hot-formed to produce a precision press-molding glass material (preform), and this glass material is heated and precision press-molded to produce an optical element.

  Alternatively, molten glass is directly molded (direct press molding) to produce a glass molded body, and this molded body is polished to produce an optical element.

  The optical functional surface of the manufactured optical element may be coated with an antireflection film, a total reflection film, or the like according to the purpose of use.

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

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, Of course, it can implement with a various aspect in the range which does not deviate from the summary of this invention. .

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.

(Example 1 and Comparative Example 1)
Tables 1 to 4 show optical glasses (samples 1 to 37) according to examples of the present invention, and Table 5 shows an optical glass (sample 38) according to comparative examples of the present invention. Samples 11 and 13 shown in Table 5 are the same as the samples shown in Table 2, and are shown together for comparison between Examples and Comparative Examples.

  These optical glasses were produced by the following procedures and various evaluations were performed.

[Manufacture of optical glass]
First, oxides, hydroxides, carbonates, and nitrates corresponding to glass constituent components are prepared as raw materials, and the above-mentioned raw materials are set so that the glass composition of the obtained optical glass has the compositions shown in Tables 1 to 5. Were weighed and blended to thoroughly mix the raw materials. The prepared raw material (batch raw material) thus obtained is put into a platinum crucible, melted in a temperature range of 1200 to 1400 ° C. in an electric furnace according to the meltability of the raw material, and stirred to homogenize and clarify. From the outflow nozzle, the molten glass was discharged and cast into a mold preheated to an appropriate temperature. The cast glass was put into a slow cooling furnace and cooled to room temperature according to a predetermined slow cooling schedule to obtain each optical glass (Samples 1 to 38).

[Evaluation of optical glass]
About the obtained optical glass (Samples 1 to 38), confirmation of glass composition, refractive index (nd), Abbe number (νd), glass transition temperature (Tg), crystallization start temperature ( Tx), crystallization peak temperature (Tc), and the presence or absence of internal crystals were evaluated. For samples 11, 13, and 38, the crystallization peak intensity (Δ) was also measured. Further, the sample 13 was also subjected to a weather resistance (D _H ) test.

[1] Confirmation of glass composition An appropriate amount of each optical glass obtained as described above is collected, treated with an acid and an alkali, and inductively coupled plasma mass spectrometry (ICP-AES method) is used. It measured by quantifying content and confirmed that it corresponded with the oxide composition of each sample shown to Tables 1-5.

[2] Refractive index (nd) and Abbe number (νd)
The optical glass cooled to room temperature is held again at a temperature between the glass transition temperature (Tg) and the yield point (Ts) by the refractive index measurement method of the Japan Optical Glass Industry Association standard, and the temperature is lowered at a temperature drop rate of -30 ° C / hour. The optical glass obtained by removing the strain in the glass was measured for refractive index (nd) and Abbe number (νd) ["GMR-1" sold by Shimadzu Device Manufacturing Co., Ltd. use〕. The results are shown in Tables 1-5.

[3] Glass transition temperature (Tg), crystallization peak temperature (Tc), and peak intensity (Δ)
The measurement was carried out with a differential scanning calorimeter manufactured by Bruker AXS Co., Ltd. at a heating rate of 10 ° C./min. Furthermore, the temperature difference (Tc−Tg) was calculated from the measured Tg and Tc. Moreover, the peak intensity (Δ) was calculated based on the differential scanning calorific curve shown by the differential scanning calorimeter. The results are shown in Tables 1-5.

[4] Presence / absence of internal crystals The glass is cast from the molten state into the mold in the atmosphere to produce a glass molded body having a flat free surface on the upper surface, and this glass molded body is cut to 1 × 1 × 1 cm ³ A cubic glass sample was obtained. This glass sample is put into a heating furnace, held at a temperature Tg for 10 minutes (primary heating), then held at a temperature (Tp) at which the glass softens (secondary heating) for 10 minutes, and the glass sample is taken out from the heating furnace. And allowed to cool. Next, the glass sample was polished, and the inside of the glass was observed from the polished surface with a microscope for the presence of internal crystals. According to this observation, a crystal having a diameter of 0.1 μm or more was evaluated as “without crystal”, and a crystal having a diameter of 0.1 μm or more was evaluated as “with crystal”. In addition, although temperature Tp had individual differences with each sample, it was confirmed that any sample was softened at a temperature within the range of (Tg + about 130 ° C.) to (Tg + about 180 ° C.). The results are shown in Tables 1-5.

[5] Weather resistance ( _DH ) test With respect to the obtained optical glass (sample 13), a glass sample (30 × 30 × 3 mm) whose main surface was polished face-to-face according to Japan Optical Glass Industry Association Standard JOGIS07, The treatment was performed for 48 hours in a high temperature and high humidity temperature cycle environment. Then, the haze value of the glass sample was measured using the Tokyo Denshoku haze meter (TC-HIIIDPK). In addition, a haze value can be calculated | required by scattered light intensity / transmitted light intensity x100 (unit:%). The results will be described later.

As shown in Tables 1 to 5, the optical glass (samples 1 to 37) according to the examples of the present invention has a refractive index nd of 1.620 to 1.700 and an Abbe number νd of 53 to 65. In particular, the ZnO content, the mass ratio α [BaO / (MgO + CaO + ZnO + SrO)] and the mass ratio β [(P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ) / Re] are within the desired ranges (ZnO content). The amount of the glass is 15% by mass or less, the mass ratio α is 2.1 or less, and the mass ratio β is less than 4.80.

  In the optical glass according to the embodiment of the present invention, the average value of the temperature difference (Tc−Tg) between the temperature Tg and the temperature Tc is about 210 ° C., and the temperature Tp of each sample is higher than the crystallization peak temperature Tc. (In other words, Tp <Tc), it was confirmed that no internal crystals were generated in the solidified glass and the thermal stability was high.

  In particular, the sample 11 is the sample having the lowest temperature difference (Tc-Tg) among the samples 1 to 37, but even in this case, the glass is softened, no internal crystals are generated, and thermal stability is achieved. It was confirmed that the property is high.

  Moreover, although the sample 13 is a sample very close to the sample 38 (comparative example) in terms of the refractive index and the Abbe number, the temperature difference (Tc−Tg) is 192 ° C., and the internal crystal is It did not occur and was confirmed to have high thermal stability like other samples.

  On the other hand, the sample 38 which is the optical glass according to the comparative example of the present invention has a temperature difference (Tc−Tg) of 139 ° C. and a temperature Tp (much higher than the crystallization peak temperature Tc (667 ° C.)). 710 ° C). That is, in the sample 38, the temperature Tp and the temperature Tc were in a relationship of Tp> Tc. And it was confirmed that the crystal | crystallization of the sample 38 which solidified has produced | generated the internal crystal | crystallization and is inferior to thermal stability.

  The reason why the above difference occurs is that although the sample 38 which is the optical glass according to the comparative example has a mass ratio β of 4.77, the mass ratio α serving as an index of the thermal stability of the glass is within a predetermined range ( 2.1 or less).

  As described above, the temperature difference (Tc−Tg) is sufficiently large in the optical glass according to the example of the present invention. For this reason, glass can be reliably softened at a temperature Tp lower than the temperature Tc. Therefore, the optical glass of the present invention can be applied to reheat press molding where precise temperature control is difficult.

  On the other hand, the optical glass (sample 38) according to the comparative example has a relatively small temperature difference (Tc−Tg), and the softening temperature Tp is higher than the crystallization peak temperature Tc. Therefore, the optical glass according to the comparative example is softened. When it does, an internal crystal will arise and it is difficult to apply the optical glass which concerns on a comparative example to reheat press molding.

In addition, as a result of the weather resistance ( _DH ) test, it was confirmed that the optical glass (sample 13) according to this example has no surface deterioration and excellent transparency even after being treated for a long time under high temperature and high humidity. It was. The haze value was 0.1%.

  From these results, it was confirmed that the optical glass according to the present invention has excellent weather resistance.

(Example 2)
An optical lens was manufactured using the optical glass (Samples 1 to 37) manufactured in Example 1. Specifically, each optical glass of Example 1 was processed into a predetermined shape to create an optical glass material. Next, the optical glass material is heated and softened, press-molded into a shape that approximates the shape of the target lens, and after press molding, the glass is annealed (annealed) and finished into an optical lens through processing steps including a polishing step. It was. In addition, what is necessary is just to apply a well-known method suitably for the press molding method of glass, the method of annealing, and a process process.

  It was confirmed that the optical lens thus obtained can be obtained as a good optical lens without crystallization of the glass even when heated at a relatively high temperature during reheat press molding.

(Comparative Example 2)
In the same manner as in Example 2, an attempt was made to produce an optical lens using the optical glass (sample 38) produced in Comparative Example 1.

  However, the optical glass according to the comparative example has low thermal stability, and it was confirmed that crystallization occurred due to heating during reheat press molding, and internal crystals were generated in the obtained optical lens.

The present invention is summarized below.
As shown in Tables 1 to 5, the optical glass of the present invention (Samples 1 to 37) has a total content of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ [P ₂ O ₅ + B ₂ O ₃ + Al. ₂ O ₃ ] is 55% by mass or less of glass,
BaO,
Any one or more selected from MgO, CaO, ZnO and SrO;
Any one or more selected from Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ ,
The content of ZnO is 15% by mass or less,
The mass ratio α [BaO / (MgO + CaO + ZnO + SrO)] of the content of BaO to the total content of MgO, CaO, ZnO and SrO is 2.1 or less,
P ₂ O ₅ , B ₂ O with respect to the total content [Gd ₂ O ₃ + Y ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ ] of Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O _{3 3} and the total content of _{Al 2 O 3 [P 2 O} 5 + B 2 O 3 + Al 2 O 3] mass ratio _{β [(P 2 O 5 +} B 2 O 3 + Al 2 O 3) of _{/ (Gd 2 O} 3 + Y _{2 O 3 + La 2 O 3} + Yb 2 O 3)] is less than 4.80,
It satisfies that the refractive index nd is 1.620 to 1.700 and the Abbe number νd is 53 to 65.

From another aspect, Samples 1, 6-8, 10, 13-18, and 20-22, which are examples of the optical glass according to the present invention, are selected as optical glasses that are particularly excellent in low dispersibility and thermal stability. Is done. When the present invention is viewed with reference to these samples, these optical glasses satisfy the following conditions.
The total content of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ [P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ] is 55% by mass or less glass,
BaO,
Any one or more selected from MgO, CaO, ZnO and SrO;
Any one or more selected from Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ ,
The content of ZnO is 6% by mass or less,
The mass ratio α [BaO / (MgO + CaO + ZnO + SrO)] of the content of BaO to the total content of MgO, CaO, ZnO and SrO is 1.2 or less,
P ₂ O ₅ , B ₂ O with respect to the total content [Gd ₂ O ₃ + Y ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ ] of Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O _{3 3} and _Al total content of _{2 O 3 [P 2 O 5} + B 2 O 3 + Al 2 O 3] mass ratio _{β [(P 2 O 5 +} B 2 O 3 + Al 2 O 3]) of / _(Gd 2 _{O 3} + Y ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ )]] is 4.5 or less,
An optical glass having a refractive index nd of 1.635 to 1.660 and an Abbe number νd of 59 to 62.

  According to these samples, an optical fiber having a large Tc-Tg of 180 ° C. or higher, a low peak intensity Δ, excellent thermal stability, a refractive index nd of 1.635 or higher, and an Abbe number of 59 or higher. Optical glass having characteristics can be manufactured.

Tg Glass transition temperature Tk Endothermic peak temperature Tx Crystallization start temperature Tc Crystallization peak temperature A Absolute value of the calorific difference between Tk and Tg B Absolute value of the calorific difference between Tx and Tc

Claims (6)

The total content of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ [P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ] is 55% by mass or less glass,
BaO,
Any one or more selected from MgO, CaO, ZnO and SrO;
Any one or more selected from Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ ,
The content of ZnO is 15% by mass or less,
The mass ratio α [BaO / (MgO + CaO + ZnO + SrO)] of the content of BaO to the total content of MgO, CaO, ZnO and SrO is 2.1 or less,
Mass ratio β of total content of P ₂ O ₅ , B ₂ O ₃ and Al ₂ O ₃ with respect to the total content of Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ [(P ₂ O ₅ + B ₂ O ₃ + Al ₂ O ₃ ) / (Gd ₂ O ₃ + Y ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ )]] is less than 4.80,
An optical glass having a refractive index nd of 1.620 to 1.700 and an Abbe number νd of 53 to 65. The total content [Gd ₂ O ₃ + Y ₂ O ₃ + La ₂ O ₃ + Yb ₂ O ₃ ] of Gd ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ and Yb ₂ O ₃ is 4 to 30% by mass, The optical glass according to claim 1. The content of P ₂ O ₅ is 12 to 40 wt%, the optical glass according to claim 1 or 2.   Optical glass in any one of Claims 1-3 whose content of BaO is 10-45 mass%.   An optical element made of the optical glass according to claim 1.   An optical glass material made of the optical glass according to claim 1.

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