CN1968904A - Optical glass and lens - Google Patents

Abstract

An optical glass exhibits a high transmittance and a high refractive index and it is reduced in the decrease of the strength of a transmitted light when the glass is continuously irradiated with a blue-violet laser diode light, and further, it is less prone to have a higher melting temperature and exhibits the chemical durability being not low. An optical glass which comprises, in mole %, 35 to 54 % of TeO<SUB>2</SUB>, 0 to 10 % of GeO<SUB>2</SUB>, 5 to 30 % of B<SUB>2</SUB>O<SUB>3</SUB>, 0 to 15 % of Ga<SUB>2</SUB>O<SUB>3</SUB>, 0 to 8 % of Bi<SUB>2</SUB>O<SUB>3</SUB>, 3 to 20 % of ZnO, 0 to 10 % of MgO + CaO + SrO + BaO, 1 to 10 % of Y<SUB>2</SUB>O<SUB>3 </SUB>+ La<SUB>2</SUB>O<SUB>3 </SUB>+ Gd<SUB>2</SUB>O<SUB>3</SUB>, 0 to 5 % of Ta<SUB>2</SUB>O<SUB>5 </SUB>+ Nb<SUB>2</SUB>O<SUB>5</SUB>, 0 to 1.8 % of TiO<SUB>2</SUB>, and 0 to 6 % of Li<SUB>2</SUB>O + Na<SUB>2</SUB>O + K<SUB>2</SUB>O + Rb<SUB>2</SUB>O + Cs<SUB>2</SUB>O; and a lens comprising the above optical glass.

Description

Optical glass and lens

technical field

The present invention relates to lenses and optical glass suitable for objective lenses used for recording or reading optical recording media such as CD, CD-R, CD-RW, DVD, and MO, collimator lenses for lasers, and the like.

Background technique

Recording to or reading from the above-mentioned optical recording medium is carried out by converting laser light into parallel light through a collimator lens and converging it with an objective lens. Such a collimator lens and an objective lens are usually produced by heating a preform made of glass or resin to a softening point, and then precision pressing it.

In recent years, in order to improve the recording density of the optical recording medium, a technical scheme of using a blue-violet laser with a wavelength of 400-415nm (typical wavelength is 405nm) has been proposed, and a lens and optical glass suitable for this technical scheme have been disclosed (see Patent Document 1).

Patent Document 1: Japanese Patent Laid-Open No. 2004-43294

disclosure of invention

Patent Document 1 discloses an optical glass having high transmittance and refractive index and having a small drop in transmitted light intensity after continuous irradiation with light of a blue-violet laser diode having a wavelength of 405 nm.

However, among these optical glasses, those whose properties are at the level currently required have a high melting temperature, making it difficult to achieve large-scale melting using a gold crucible, or may deteriorate chemical durability such as water resistance and weather resistance. The problem.

The object of this invention is to provide the optical glass and lens which can solve these problems.

The present invention achieves the above object and has the following main contents.

(1) Optical glass, characterized in that, represented by the following mole percent based on oxides, substantially composed of 35 to 54% of TeO ₂ , 0 to 10% of GeO ₂ , 5 to 30% of B ₂ O ₃ , 0 ～15% Ga ₂ O ₃ , 0～8% Bi ₂ O ₃ , 3～20% ZnO, 0～10% MgO+CaO+SrO+BaO, 1～10% Y ₂ O ₃ +La ₂ O ₃ +Gd ₂ O ₃ , 0~5% Ta ₂ O ₅ +Nb ₂ O ₅ , 0~1.8% TiO ₂ , 0~6% Li ₂ O+Na ₂ O+K ₂ O+Rb ₂ O+Cs ₂ O is formed.

(2) The optical glass according to (1) above, wherein TeO ₂ +GeO ₂ is 40 to 60%.

(3) The optical glass as described in said (1) or (2) containing _TiO2 .

(4) The optical glass as described in any one of said (1 ₎ -(3) containing _Bi2O3 .

(5) The optical glass according to any one of the above (1) to (4), wherein B ₂ O ₃ +Ga ₂ O ₃ +Bi ₂ O ₃ is 15 to 35%.

(6) The optical glass as described in any one of said (1)-(5) whose content of ZnO+MgO+CaO+SrO+BaO is 5-30%.

(7) The optical glass according to any one of the above (1) to (6), wherein the internal transmittance at a thickness of 1 mm for light having a wavelength of 405 nm is 90% or more, and the refractive index for the light is Above 1.92.

(8) The optical glass according to any one of the above (1) to (7), wherein the transmitted light at a thickness of 1 mm when irradiated with light having a wavelength of 405 nm under the condition of an energy density of 6 kW/ ^m2 The reduction ratio L after 24 hours of irradiation of the intensity is 16% or less.

(9) The optical glass according to any one of (1) to (8) above, which is meltable at 980°C or lower.

(10) A lens characterized by being formed of the optical glass described in any one of (1) to (9) above.

The optical glass of the present invention (hereinafter simply referred to as the glass of the present invention) has a small ZnO content, so the melting temperature can be lowered and stable large-scale melting can be realized. In addition, even in the case where alkali metal oxides are contained, since the total content thereof is 6% or less, the aforementioned concerns about chemical durability can be alleviated.

In addition, if the lens of the present invention is used for the aforementioned collimator lens and objective lens, blue-violet laser light and conventionally used near-infrared laser light can be used interchangeably.

In addition, in its preferred form, while maintaining high transmittance and refractive index, it is possible to suppress the above-mentioned decrease in transmitted light intensity more remarkably than the optical glass disclosed in Patent Document 1.

The best way to practice the invention

The lens of the present invention is produced by, for example, press-molding the glass of the present invention. That is, the glass of the present invention is processed into a preform, the preform is heated to soften it, and press-molded using a mold (so-called precision press) to form a lens. The aforementioned preform can be produced by directly molding the glass of the present invention in a molten state.

The glass of the present invention is preferably produced by melting at a temperature of 980°C or lower. Otherwise, it would be difficult to melt glass using a gold crucible (melting point: 1063°C), and a platinum or platinum alloy crucible would have to be used for melting. As a result, platinum would melt into the glass, reducing the transmittance of the glass.

The glass of the present invention preferably has an internal transmittance (T) of 1 mm thickness conversion for light having a wavelength of 405 nm of 90% or more. When it is less than 90%, it becomes difficult to use it as a lens as mentioned above. More preferably, it is at least 92%, particularly preferably at least 94%.

Said T is measured, for example as follows.

For two plate-shaped samples with a size of 2 cm × 2 cm and a thickness of 1 mm and 5 mm, both sides of which are mirror-polished, the transmission of light with a wavelength of 405 nm is measured using a spectrophotometer U-3500 (trade name) manufactured by Hitachi, Ltd. Rate. The measured transmittances of plate-shaped samples having a thickness of 1 mm and 5 mm were respectively denoted as T ₁ and T ₅ , and T (unit: %) was calculated by the following formula.

T=100×exp[(2/3)×log _e (T ₅ /T ₁ )]

The glass of the present invention preferably has a refractive index (n) of 1.92 or more for light having a wavelength of 405 nm. When it is less than 1.92, it is difficult to obtain an objective lens thin enough to be used for recording on an optical recording medium (typically 1.5 to 3.5 mm in thickness) and having a desired numerical aperture (typically 0.65 to 0.85). More preferably, it is above 1.94, particularly preferably above 1.97, most preferably above 1.99. n is generally below 2.1.

For the glass of the present invention, the reduction ratio L of the transmitted light intensity at a thickness of 1 mm when irradiated with light from a blue-violet laser diode (wavelength: 405 nm) at an energy density of 6 kW/m ² after 24 hours of irradiation is preferable is below 16%. When it exceeds 16%, even if T is 97% before the start of irradiation, T also drops to less than 80% after 24 hours of irradiation. For example, it is difficult to use the lens of the present invention as an objective lens for a DVD using blue-violet laser diode light.

Even if T is 95% before the start of irradiation, when T is 90% or more after 24 hours of irradiation, L is preferably at most 5%. In addition, when T is 90% or more after 24 hours of irradiation even if T was 93% before the start of irradiation, L is preferably at most 3%.

L is measured, for example, as follows. That is, a plate-shaped sample with a size of 1 cm × 1 cm and a thickness of 1 mm, which is mirror-polished on both sides, is irradiated with blue-violet light from a blue-violet laser diode NDHV310APC (trade name) manufactured by Nichia Chemical Co., Ltd. under the condition of 6 kW/m ² (Wavelength: 405 nm) After 24 hours, the transmitted light intensity I ₀ at the beginning of irradiation and the transmitted light intensity I ₁ after 1 hour of irradiation were measured using a photodiode PD-300UV (trade name) manufactured by Ophir Co., Ltd., according to the following formula Calculate L (unit: %).

L=(I ₀ -I ₁ )×100/I ₀

Hereinafter, mol% is abbreviated as %, and the composition of the glass of this invention is demonstrated.

TeO ₂ is essential as a component that forms a glass skeleton and increases n. When it is less than 35%, vitrification becomes difficult, or n becomes low. It is preferably at least 40%, more preferably at least 44%. When it exceeds 54%, L becomes larger. It is preferably at most 52%, typically at most 48%.

GeO ₂ is not essential, but it is a component that forms a glass skeleton, increases T, stabilizes the glass, and suppresses devitrification during molding, and can be contained up to 10%. If it exceeds 10%, the glass transition temperature (T _G ) will increase, the press molding temperature will also increase, the life of the die will be shortened, or it will become difficult to melt the glass at 980°C or lower. When the melting temperature is to be lowered, GeO ₂ is preferably at most 8%, typically at most 6%. When GeO ₂ is contained, its content is preferably at least 2%.

The total TeO ₂ +GeO ₂ content of TeO ₂ and GeO ₂ is preferably from 40 to 60%. When it is less than 40%, vitrification becomes difficult. More preferably, it is above 45%, especially preferably above 47%. When it exceeds 60%, L becomes larger. More preferably, it is below 55%, particularly preferably below 53%.

B ₂ O ₃ is a component that forms a glass skeleton and is essential. When less than 5%, the glass becomes unstable. It is preferably at least 10%, more preferably at least 15%. When it exceeds 30%, n becomes low, or chemical durability such as water resistance decreases. Typically below 20%.

Ga ₂ O ₃ is not essential, but can be contained up to 15% in order to increase n or increase hardness. When it exceeds 15%, the glass becomes unstable. It is preferably at most 10%, typically at most 8%. When Ga ₂ O ₃ is contained, its content is preferably at least 4%.

Bi ₂ O ₃ is not essential, but can be contained up to 8% in order to increase n. When it exceeds 8%, T becomes low.

For example, when n is to be 1.98 or more, it is preferable to contain 1% or more of Bi ₂ O ₃ . More preferably above 2%.

B ₂ O ₃ +Ga ₂ O ₃ +Bi ₂ O ₃ is preferably from 15 to 35%. When it is less than 15%, vitrification becomes difficult. More preferably, it is more than 20% and less than 30%. When it exceeds 35%, the glass becomes unstable.

ZnO is a component for stabilizing glass and is essential. When less than 3%, the glass becomes unstable. It is preferably at least 10%. When it exceeds 20%, the melting temperature cannot be lowered. It is preferably at most 19%.

None of MgO, CaO, SrO, and BaO is essential, but they can be contained up to 10% in total to stabilize the glass. When it exceeds 10%, vitrification becomes difficult, the melting temperature rises, or _TG rises. Preferably it is at most 5%.

ZnO+MgO+CaO+SrO+BaO is preferably in the range of 5 to 30%, more preferably in the range of 10 to 25%.

Y ₂ O ₃ , La ₂ O ₃ , and Gd ₂ O ₃ are components for suppressing devitrification during molding, and any one or more of them must be contained. When the total content of these three components is less than 1%, devitrification tends to occur during molding. It is preferably at least 2%. When it exceeds 10%, vitrification becomes difficult, or the melting temperature becomes high. Preferably it is at most 8%.

When Y ₂ O ₃ or La ₂ O ₃ is contained, the respective contents are preferably at most 3%. When it exceeds 3%, n will decrease. Typically, each is 1% or less.

When n is to be further increased, it is preferable to contain 1 to 5% of Gd ₂ O ₃ .

Both Ta ₂ O ₅ and Nb ₂ O ₅ are not essential, and may be contained up to 5% in total in order to increase n. When it exceeds 5%, devitrification easily occurs during molding. Preferably it is at most 4%.

When n and T are to be increased, it is preferable to contain 1% or more of Ta ₂ O ₅ .

TiO ₂ is not essential, but can be contained up to 1.8% in order to increase n or reduce L. When it exceeds 1.8%, T falls. Preferably it is at most 1.5%. When L is to be reduced, TiO ₂ is preferably at least 0.3%.

Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, and Cs ₂ O are not essential, but may be contained up to 6% in total in order to lower _TG or melting temperature. When it exceeds 6%, the chemical durability will decrease. Preferably it is at most 5%. When the chemical durability is to be further improved, the above sum is preferably less than 1%, and it is particularly preferred that no alkali metal oxide is contained.

When L is to be 9% or less, it is preferable that GeO ₂ is 3.5% or more and Bi ₂ O ₃ is 0 to 2.5%, or TiO ₂ is 0.3 to 1.8%.

The glass of the present invention is substantially composed of the above-mentioned components, but may contain other components within a range that does not impair the object of the present invention. When such components are contained, the total of these components is preferably at most 10%, more preferably at most 5%.

The glass of the present invention preferably does not contain PbO, As ₂ O ₃ , Sb ₂ O ₃ and CdO, and the glass raw material is also preferably a high-purity raw material, so that the content of Fe ₂ O ₃ is expressed in mass percentage below 0.0001%. .

Example

In examples 1 to 14, according to the composition expressed in mol% in the column from TeO ₂ to Na ₂ O in the table, the raw materials were blended, and 450 g of the blended raw materials were prepared, which were added to a gold crucible with a capacity of 300 cc. °C for 2.5 hours. At this time, stirring was carried out for 1 hour with a gold stirrer to homogenize the molten glass. The homogenized glass flows out into a carbon mold, and after being formed into a plate shape, it is gradually cooled.

In Example 15, it was formed into a plate shape in the same manner as in Examples 1 to 14, but since devitrification was remarkable, melting was performed as follows. That is, 100 g of the prepared raw material was prepared, put into a gold crucible with a capacity of 100 cc, and melted at 995° C. for 1 hour. At this time, since the melting temperature is close to the melting point of gold, the shape may not be maintained, so stirring with a gold stirrer was not performed. The insufficiently homogenized molten glass obtained in this way is flowed out and formed into a plate shape, and then gradually cooled.

Examples 1 to 13 are examples, and examples 14 and 15 are comparative examples.

As raw materials, tellurium dioxide with a purity of 99.999% or more manufactured by Shinko Chemical Co., Ltd., special-grade boron oxide and titanium oxide manufactured by Kanto Chemical Co., Ltd., and lanthanum oxide, yttrium oxide, and gadolinium oxide manufactured by Shin-Etsu Chemical Co., Ltd. with a purity of 99.9% were used. , special-grade gallium oxide manufactured by Real Metal Co., Ltd., zinc oxide manufactured by High Purity Chemical Research Institute Co., Ltd. with a purity of 99.999% or higher, germanium oxide manufactured by the same company with a purity of 99.995% or higher, tantalum oxide manufactured by the same company with a purity of 99.9% or higher, etc. .

For the obtained glass, T _G (unit: °C), T (unit: %), n, L (unit: %), and d-line refractive index _nd and Abbe number ν _d were measured. The measurement methods of T _G , n, _nd , and ν _d are as follows.

T _G : 150 mg of a sample processed into a powder form was filled in a platinum dish, and it was measured with a thermal analyzer TG/DTA6300 (trade name) from Iko Instruments Co., Ltd.

n, _nd , ν _d : Glass was processed into a triangular prism with a side of 30 mm and a thickness of 10 mm, and was measured with a precision spectrometer GMR-1 (trade name) manufactured by Karniuichi Optical Co., Ltd. For Example 15, none of n, _nd , and _νd were measured, but n revealed a value estimated based on the composition from the refractive index (=1.92) for light having a wavelength of 633 nm.

In addition, in Examples 1, 10, 13, and 15, water resistance RW and acid resistance RA were evaluated as follows according to the evaluation method established by Japan Optical Glass Industry Association. The grades are shown in the corresponding column of the table.

RW: For glass particles with a diameter of 420 to 600 μm, the mass loss ratio (%) after immersion in 80 ml of pure water at 100°C for 1 hour was measured. When the mass reduction ratio is less than 0.05 (%), it is judged as grade 1; when it is more than 0.05 and less than 0.10 (%), it is judged as grade 2; when it is more than 0.10 and less than 0.25 (%), it is judged as grade 3; When it is 0.60 (%), it is judged as grade 4, when it is more than 0.60 and less than 1.10 (%), it is judged as grade 5, and when it is more than 1.10 (%), it is judged as grade 6.

RA: For glass particles with a diameter of 420 to 600 μm, the mass loss rate (%) after immersion in 80 ml of 0.01 N nitric acid aqueous solution at 100°C for 1 hour was measured. When the mass reduction rate is less than 0.20 (%), it is judged as grade 1; when it is more than 0.20 and less than 0.35 (%), it is judged as grade 2; when it is more than 0.35 and less than 0.65 (%), it is judged as grade 3; 1.20 (%) was judged as grade 4, when 1.20 or more and less than 2.20 (%) was judged as grade 5, and when 2.20 (%) or more was judged as grade 6.

[Table 1] 1 2 3 4 5 6 7 TeO ₂ 51.0 51.0 47.0 46.8 46.0 45.0 46.0 GeO ₂ 0 4.0 3.0 3.0 3.0 5.0 5.0 B ₂ O ₃ 29.0 19.0 19.0 19.0 19.0 19.0 19.0 Ga ₂ O ₃ 0 5.0 5.0 5.0 5.0 6.0 6.0 Bi ₂ O ₃ 0 0 5.0 5.0 5.0 4.0 3.0 ZnO 15.0 15.0 15.0 15.0 15.0 15.0 15.0 Y ₂ O ₃ 2.0 0.5 0.5 0.5 0.5 0.5 0.5 La ₂ O ₃ 2.0 0.5 0.5 0.5 0.5 0.5 0.5 Gd ₂ O ₃ 1.0 3.0 3.0 3.0 3.0 3.0 3.0 Ta ₂ O ₅ 0 2.0 2.0 2.0 2.0 2.0 2.0 TiO ₂ 0 0 0 0.2 1.0 0 0 Na ₂ O 0 0 0 0 0 0 0 T _G 420 430 430 430 435 440 440 T 99 99 96.7 95.9 91.3 98.4 99.0 L 9.4 6.0 12.1 12.2 4.1 12.0 10.0 no 1.948 1.972 2.034 2.034 2.038 2.008 1.997 n _d 1.886 1.909 1.958 1.958 1.961 1.937 1.928 ν _d 26.9 26.4 23.8 23.9 23.7 24.8 25.3 RW 1 RA 2

[Table 2] 8 9 10 11 12 13 14 15 TeO ₂ 47.0 45.2 45.0 44.8 44.6 45.0 45.0 54.0 GeO ₂ 5.0 5.0 5.0 5.0 5.0 5.0 3.0 5.0 B ₂ O ₃ 19.0 19.0 19.0 19.0 19.0 18.0 19.0 0 Ga ₂ O ₃ 6.0 6.0 6.0 6.0 6.0 6.0 5.0 0 Bi ₂ O ₃ 2.0 3.0 3.0 3.0 3.0 3.0 5.0 0 ZnO 15.0 15.0 15.0 15.0 15.0 15.0 15.0 30.0 Y ₂ O ₃ 0.5 0.5 0.5 0.5 0.5 0.5 0.5 3.0 La ₂ O ₃ 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0 Gd ₂ O ₃ 3.0 3.0 3.0 3.0 3.0 3.0 3.0 0 Ta ₂ O ₅ 2.0 2.0 2.0 2.0 2.0 3.0 2.0 0 TiO ₂ 0 0.8 1.0 1.2 1.4 1.0 2.0 0 Na ₂ O 0 0 0 0 0 0 0 8.0 T _G 440 440 440 440 450 445 445 335 T 98.7 94.2 94.9 93.6 93.0 95.2 86.6 98.0 L 9.5 2.5 1.9 1.6 1.6 1.9 2.4 10.8 no 1.986 2.001 2.001 2.001 2.002 2.011 2.041 2.01 n _d 1.920 1.931 1.932 1.930 1.931 1.940 1.963 ν _d 25.7 25.1 25.1 25.3 25.3 24.8 23.5 RW 1 1 3 RA 1 1 3

Possibility of industrial use

The lens formed from the optical glass of the present invention is suitably used as an objective lens for recording or reading optical recording media such as CD, CD-R, CD-RW, DVD, MO, etc., a collimator lens for lasers, and the like.

In particular, the lens of the present invention has a small rate of decrease in transmitted light intensity even when irradiated with blue-violet laser diode light for a long time, and is suitable as an objective lens for a DVD using blue-violet laser diode light.

The lens of the present invention can be used in a collimator lens and an objective lens, and can also be used in a field requiring interchangeable use of a blue-violet laser and a conventionally used near-infrared laser.

The specifications, claims, drawings and abstracts of Japanese Patent Application No. 2004-186226 filed on June 24, 2004 and Japanese Patent Application No. 2004-233408 filed on August 10, 2004 are hereby cited in their entirety The content is adopted as the disclosure of the specification of the present invention.

Claims (10)

1. Optical glass, characterized in that, expressed in mol% based on the following oxides, substantially composed of 35 to 54% of TeO ₂ , 0 to 10% of GeO ₂ , 5 to 30% of B ₂ O ₃ , 0 to 15% Ga ₂ O ₃ , 0-8% Bi ₂ O ₃ , 3-20% ZnO, 0-10% MgO+CaO+SrO+BaO, 1-10% Y ₂ O ₃ +La ₂ O ₃ +Gd ₂ O ₃ , 0-5% Ta ₂ O ₅ +Nb ₂ O ₅ , 0-1.8% TiO ₂ , 0-6% Li ₂ O+Na ₂ O+K ₂ O+Rb ₂ O+Cs ₂ O is formed. 2. The optical glass according to claim 1, wherein TeO ₂ +GeO ₂ is 40 to 60%. 3. The optical glass according to claim 1 or 2, which contains _TiO2 . 4. The optical glass according to any one of claims ₁ to 3, which contains _Bi2O3 . 5 . The optical glass according to claim 1 , wherein B ₂ O ₃ +Ga ₂ O ₃ +Bi ₂ O ₃ is 15 to 35%. 6. The optical glass according to any one of claims 1 to 5, wherein the content of ZnO+MgO+CaO+SrO+BaO is 5 to 30%. 7. The optical glass according to any one of claims 1 to 6, wherein the internal transmittance at a thickness of 1 mm for light having a wavelength of 405 nm is 90% or more, and the refractive index for the light is 1.92 or more. 8. The optical glass according to any one of claims 1 to 7, wherein the intensity of transmitted light at a thickness of 1 mm when irradiating light with a wavelength of 405 nm under the condition that the energy density is 6 kW/ ^m2 is 24 The reduction ratio L after one hour was 16% or less. 9. The optical glass according to any one of claims 1 to 8, which is meltable at 980°C or lower. 10. A lens, characterized in that it is formed of the optical glass according to any one of claims 1 to 9.