JP2000247676A - Optical glass for mold press forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide optical glass for mold press forming, which has a refractive index of 1.65-1.75, a low softening point, low density and high weatherability. SOLUTION: The optical glass has a composition of, by weight, 35-50% SiO2, 0.1-5% Al2O3, 0-5% B2O3, 0-5% MgO, 0-5% CaO, 0-5% BaO, 0-5% SrO, 0-5% ZnO, 0.5-15% MgO+CaO+BaO+SrO+ZnO, 0-5% Li2O, 10-30% Na2O, 0-5% K2O, 25-35% TiO2, 0-15% ZrO2, 0-20% Nb2O5, 0-10% La2O3 and 0-10% Gd2O3, and the weight ratio of (Na2O+K2O)/Al2O3 is in the range of 6.5-40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical glass for mold press molding.

[0002]

2. Description of the Related Art CDs, MDs, DVDs and other optical discs
Optical pickup lenses, video cameras and
Refractive index for optical lenses such as shooting lenses of general cameras
An optical glass having an nd of 1.65 to 1.75 is used.
You. Conventionally, as such a glass, SiO 2_Two-PbO-
R '_TwoO (R '_TwoO is lead based on alkali metal oxides)
Glasses have been widely used, but in recent years
From problem SiO_Two-B_TwoO _Three-RO (RO is a divalent metal acid
Compound) -R '_TwoO-TiO_TwoSwitch to lead-free glass
It is being obtained.

[0003]

In molding an optical pickup lens or a photographing lens, a softened glass block is pressure-formed by a precision-worked mold, and the surface shape of the mold is transferred to glass. The so-called mold press molding method is widely used.

However, since the above-mentioned lead-free optical glass generally has a high softening point, it is suitable for mold press molding, for example, the mold is deteriorated and the molding accuracy is reduced, and the mold is contaminated by volatilization of glass components. There is no problem. In addition, there is also a part of glass that enables mold press molding at an industrial level by containing a large amount of an alkali metal oxide. However, this kind of glass has poor weather resistance, and the glass components are eluted into polishing and washing water and various cleaning solutions due to cutting, polishing, and cleaning in the manufacturing process of lenses, prisms, etc., resulting in deterioration of physical properties and surface deterioration. . Also, in the final product, there is a problem that when exposed to a high-temperature and high-humidity state for a long time, the surface is deteriorated, the optical characteristics as designed cannot be obtained, and the reliability is impaired.

[0005] Further, in the market of CD, MD, DVD, video cameras and general cameras, demands for miniaturization and weight reduction have been increasing in recent years, and lower densities are also required for lenses used. In particular, in the case of CDs, MDs and DVDs, an optical pickup system drives and reads a signal from an optical disk, and the reduction in the density of the lens reduces the load on the drive system and makes it easy to respond to high-speed access. Further, there is a further demand because the ratio of the lens weight to the total weight of the drive system is high.

An object of the present invention is to provide an optical glass for mold press molding which has a refractive index of 1.65 to 1.75, and also has a low softening point and density and high weather resistance.

[0007]

The optical glass for mold press molding of the present invention has a SiO ₂ content of 35 to 50% by weight.
_{%, Al 2 O 3 0.1~5%} , B 2 O 3 0~5%, Mg
O 0-5%, CaO 0-5%, BaO 0-5%, S
rO 0-5%, ZnO 0-5%, MgO + CaO + B
aO + SrO + ZnO 0.5~15%, Li 2 O 0~
_{5%, Na 2 O10~30%,} K 2 O 0~5%, TiO
_{2 25~35%, ZrO 2 0~15%} , Nb 2 O 5 0
_{~20%, La 2 O 3 0~10} %, Gd 2 O 3 0~10
%, And (Na ₂ O + K ₂ O) / Al ₂ O ₃ is in a range of 6.5 to 40 in weight ratio.

[0008]

The optical glass for mold press molding of the present invention comprises:
It has a refractive index nd of 1.65 to 1.75. Also CD,
In order to reduce the load on the drive system and to cope with high-speed access in MD, DVD, etc., the density is 3.0 g / c.
m ³ or less. Further, in order to prevent deterioration and contamination of the mold, the softening point needs to be 650 ° C. or less. Furthermore, in order to obtain practically sufficient weather resistance, the weight loss by powder method water resistance according to the Japan Optical Glass Industry Association standard JOGIS is less than 0.05%, and the weight loss by powder method acid resistance is 0.20%. It is important that the total alkali elution amount in an alkali elution test according to JIS R3502 satisfy the condition of 0.95 mg or less.

As an optical glass having such properties, 35 to 50% by weight of SiO _{2 and} 35% by weight of Al ₂ O ₃ .
_{1~5%, B 2 O 3 0~5} %, 0~5% MgO, Ca
O 0-5%, BaO 0-5%, SrO 0-5%,
ZnO 0-5%, MgO + CaO + BaO + SrO + Zn
_{O 0.5~15%, TiO 2 25~35%} , Li 2 O
_{0~5%, Na 2 O 10~30%} , K 2 O 0~5
_{%, Nb 2 O 5 0~20%} , ZrO 2 0~15%, L
_{a 2 O 3 0~10%, Gd} 2 O 3 has a 0-10% composition, 6.5 in weight ratio _{(Na 2 O + K 2 O} ) / Al 2 O 3
Glasses in the range of 40 are mentioned. The reasons for limiting the composition range are described below.

[0010] SiO ₂ is a component constituting the skeleton of glass and has the effect of lowering the density. Its content is 3
It is 5 to 50%, preferably 37 to 47%. SiO ₂
Exceeds 50%, the refractive index becomes too low or the softening point exceeds 650 ° C. On the other hand, if it is less than 35%, the density becomes too high, and weather resistance such as acid resistance and water resistance deteriorates remarkably.

Al ₂ O ₃ is a component constituting the skeleton of glass and has an effect of lowering the density. It also has the effect of significantly improving the weather resistance, especially the alkali elution characteristics. In this type of glass, a large amount of alkali component is contained in order to perform mold press molding, and low softening properties are imparted.However, the alkali component in the glass is easily eluted into water and exposed to high temperature and high humidity for a long time. When this occurs, an alkali component precipitates on the surface to form a carbonate or a reaction product, and the surface is altered. However, by containing Al ₂ O ₃ , this can be effectively suppressed. The content of Al ₂ O ₃ 0.1-5%, preferably 0.5-3%. If Al ₂ O ₃ exceeds 5%, the devitrification resistance deteriorates,
Meltability is remarkably deteriorated, striae and bubbles remain in the glass, and do not satisfy the required quality as glass for lenses.
If it is less than 1%, the above effects cannot be obtained.

B ₂ O ₃ acts as a flux and has the effect of assisting the melting of glass, and its content is 0 to 5%, preferably 0 to 1.9%. If B ₂ O ₃ exceeds 5%, the weather resistance will be remarkably deteriorated. Further, volatilization increases when the glass is melted, resulting in striae, and a sufficiently homogeneous glass cannot be obtained. In addition, volatilization also occurs at the time of molding to contaminate the mold, thereby greatly shortening the life of the mold.

MgO, CaO, BaO, SrO, ZnO
Increases the refractive index, imparts glass stability, and acts as a flux. The content of these components is MgO 0-5
%, Preferably 0-2.5%, CaO 0-5%, preferably 0-2.5%, BaO 0-5%, preferably 0-2.9%, SrO 0-5
%, Preferably 0-2.5%, ZnO 0-5%, preferably 0-2.5%. If each component is out of the range, the density becomes too high.

In order to achieve a refractive index of 1.65 to 1.75, low density, and stabilization of glass, MgO,
The total amount of CaO, BaO, SrO, and ZnO is 0.5 to
It is limited to 15%, preferably 0.5 to 7%. If the total amount exceeds 15%, the density becomes too high, and
%, It becomes difficult to obtain a desired refractive index even if a large amount of TiO ₂ described later is contained, and the glass stability is deteriorated, and the weather resistance is liable to be deteriorated.

Li ₂ O, Na ₂ O and K ₂ O are components for lowering the softening point, and their contents are Li ₂ O 0
5%, preferably 1 to 4.5%, Na ₂ O ten to three
0%, preferably 15-25% K ₂ O 0 to 5% and preferably from 0 to 2.9%. If the Li ₂ O and Na ₂ O contents exceed the above ranges, the weather resistance deteriorates and the devitrification increases, so that a homogeneous glass cannot be obtained. Since K ₂ O evaporates more than Li ₂ O or Na ₂ O, if it exceeds 5%, volatilization during mold press molding becomes remarkable, and as a result, the mold is contaminated and the life of the mold is increased. Shrink. Also, the weather resistance is deteriorated. On the other hand, when Na ₂ O is less than the above range, the softening point exceeds 650 ° C.

TiO ₂ is a component for increasing the refractive index, and its content is 25 to 35%, preferably 26 to 34%. Since TiO ₂ has a large effect of increasing the refractive index, M
The total amount of gO, CaO, BaO, SrO, and ZnO is 1
Even if it is limited to 5% or less, a desired refractive index can be obtained. However, if the content of TiO ₂ is more than 35%, the meltability and the devitrification resistance deteriorate, and a homogeneous glass cannot be obtained. On the other hand, if TiO ₂ is less than 25%, a desired refractive index cannot be obtained.

The ZrO ₂ and Nb ₂ O ₅ is effective to increase the refractive index, the content is ZrO ₂ 0 to 15%, preferably _{0~5%, Nb 2 O 5 0~20} %, preferably 0
10%. However, when these components exceed the range, the density becomes too high, and the devitrification resistance is remarkably deteriorated.

[0018] La ₂ O ₃ and Gd ₂ O _3, in glass system of this type is a component effective for improving the devitrification resistance, the content thereof is respectively 0 to 10%, preferably 0 to 5% It is. If these components exceed the above range, the density becomes too high.

In addition to the above, the optical glass of the present invention includes:
For example, Sb ₂ O ₃ or the like can be added as a fining agent. However, PbO and As ₂ O ₃ are not preferably used because they are not environmentally preferable, and P ₂ O ₅ is not used because it deteriorates the weather resistance.

Further, in the optical glass of the present invention, the value of (Na ₂ O + K ₂ O) / Al ₂ O ₃ is 6.5 to 40 by weight in order to achieve both prevention of alkali elution and low softening property. It is important to adjust to the range. That is, by adjusting the ratio of Na ₂ O and K ₂ O, which are particularly easy to elute among alkali components, to Al ₂ O ₃ , which has an effect of suppressing alkali elution, within the above range, JIS R3502 can be obtained.
The total alkali dissolution amount in the alkali dissolution test was 0.9
It can be reduced to 5 mg or less, and a softening point of 650 ° C. or less can be achieved. When this ratio exceeds 40, alkali elution becomes remarkable, and when the glass surface is exposed to a high temperature and high humidity state for a long time, the glass surface is deteriorated, and optical characteristics as designed cannot be obtained. On the other hand, if it becomes smaller than 6.5, it becomes 650
It becomes difficult to obtain a softening point of not more than ℃.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

Tables 1 to 5 show examples of the present invention (sample No. 1).
14 to 14) and Comparative Examples (Sample Nos. 15 to 21).

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

Each sample was prepared as follows. First, a glass raw material was prepared so as to have the composition shown in the table, and was melted at 1500 ° C. for 4 hours using a platinum crucible. After melting, the melt was poured out onto a carbon plate, and after annealing, samples suitable for each measurement were prepared.

The obtained sample was measured for refractive index nd, softening point Ts, density, water resistance, acid resistance, and alkali elution amount. The results are shown in each table.

As can be seen from the table, No. 1 of the embodiment of the present invention. Each of the samples 1 to 14 has a refractive index nd of 1.66.
79 to 1.7393, the density was 3.000 g / cm ³ or less, and the softening point Ts was 645 ° C. or less. The water resistance has a weight loss rate of 0.04% or less, the acid resistance has a weight reduction rate of 0.17% or less, and an alkali elution amount of 0.75 mg.
It was below.

On the other hand, in Comparative Example No. 15 is
Since SiO ₂ was higher than 50%, the refractive index was low, and the softening point was high. No. No. 16 had a low refractive index because TiO ₂ was less than 25%. No. 17 is SiO
Water resistance and acid resistance were poor because ₂ was less than 35%. No. Sample No. 18 was poor in water resistance and acid resistance because B ₂ O ₃ exceeded 5%. No. 19 is MgO, Ca
Since the total amount of O, BaO, SrO, and ZnO exceeded 15%, the density was high. No. 20 is 1 Na ₂ O
Since it was less than 0% and the ratio of (Na ₂ O + K ₂ O) / Al ₂ O ₃ was less than 6.5, the softening point was high. No.
Sample No. 21 had a large amount of alkali elution since the ratio of (Na ₂ O + K ₂ O) / Al ₂ O ₃ exceeded 40.

The refractive index nd is shown by a measured value with respect to a d-line (587.6 nm) of a helium lamp. The density is
A sample having a size of 1 × 1 × 2 cm was immersed in water and determined by the Archimedes method. The softening point was measured by a fiber elongation method based on JIS R3104. Water resistance and acid resistance are based on the Japan Optical Glass Industry Association Standard 06.
According to -1975, the glass sample was subjected to a particle size of 420-590.
μm, weigh the specific gravity gram, put it in a platinum basket, put it in a flask containing the reagent, treat it in a boiling water bath for 60 minutes, and determine the mass reduction rate (wt%) of the powdered glass after the treatment. It is calculated. The reagent used in the water resistance evaluation was pure water adjusted to pH 6.5 to 7.5, and the reagent used in the acid resistance evaluation was a nitric acid aqueous solution adjusted to 0.01 N. The alkali elution amount was evaluated based on JIS R3502, the amounts of eluted Li ₂ O, Na ₂ O, and K ₂ O were determined by atomic absorption analysis, and the total amount (mg) was calculated.

[0033]

As described above, the optical glass of the present invention can be used for optical lenses such as optical pickup lenses of CD, MD, DVD and other various optical disk systems, and photographic lenses of video cameras and general cameras. 1.65
It has a refractive index nd of １1.75. Moreover, it has a low density and meets recent market demands. In addition, it has good weather resistance, and does not cause deterioration of physical properties or deterioration of the surface during the manufacturing process or during use or storage of the product. Further, since the softening point is low and the mold is not deteriorated and the glass component is not volatilized, the molding accuracy is not reduced and the mold is not contaminated, so that it is suitable for mold press molding.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C03C 3/087 C03C 3/087 3/091 3/091 3/093 3/093 3/095 3/095 3/097 3 / 097 4/00 4/00 G02B 3/00 G02B 3/00 F term (reference) 4G062 AA04 BB01 DA05 DB02 DB03 DC01 DC02 DC03 DD01 DE01 DE02 DE03 DF01 EA01 EA02 EA03 EB04 EC01 EC02 EC03 ED01 ED02 ED03 EE01 EE02 EE02 EF01 EF03 EG01 EG02 EG03 FA01 FB04 FB05 FC01 FC02 FC03 FC04 FD01 FE01 FF01 FG01 FG02 FG03 FG04 FH01 FJ01 FK01 FK02 FK03 FL01 GA01 GA10 GB01 GC01 GD01 GE01 HH01 HH03 HH05 H03 HK01 JJ01 KK01 GG01 KK10 MM02 NN02 NN32 NN34

Claims (3)

[Claims] 1. The method according to claim 1, wherein the SiO _{2 is} 35 to 50% by weight and the Al _{2 is}
O ₃ 0.1-5%, B ₂ O ₃ 0-5%, MgO 0-0
5%, CaO 0-5%, BaO 0-5%, SrO
0-5%, ZnO 0-5%, MgO + CaO + BaO +
SrO + ZnO 0.5-15%, Li ₂ O 0-5%, Na ₂ O 10-10
_{30%, K 2 O 0~5%} , TiO 2 25~35%, Z
rO _{2 0 to} 15%, Nb ₂ O ₅ 0 to 20%, La ₂ O ₃
0-10%, has the composition Gd ₂ O ₃ 0-10%,
(Na ₂ O + K ₂ O) / Al ₂ O ₃ is 6.5 to 40 by weight.
An optical glass for mold press molding, wherein 2. The optical glass for mold press molding according to claim 1, which is used for an optical pickup lens or a photographing lens. 3. Weight loss by powder method water resistance according to the Japan Optical Glass Industry Association Standard JOGIS, having a refractive index nd of 1.65 to 1.75, a density of 3.0 g / cm ³ or less, and a softening point of 650 ° C. or less. Press molding, characterized in that the weight loss in acid resistance of the powder method is less than 0.05% and the total alkali elution amount in an alkali elution test according to JIS R3502 is 0.95 mg or less. For optical glass.