JPH11302035A - Optical glass for mold press molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical glass having a refractive index of 1.55-1.65, good weather resistance and a softening point suitable for mold press molding. SOLUTION: The optical glass has a compsn. consisting of, by weight, 53-65% SiO2 , 0-10% Al2 O3 , 0-4.9% B2 O3 , 0-5% MgO, 0-4.9% CaO, 1-15% SrO, 4.1-11.9% BaO, 1-15% ZnO (SrO+BaO+ZnO=15-30%), 1-9% TiO2 , 0-7.5% ZrO2 , 2-7% Li2 O, 1-20% Na2 O and 0-10% K2 O. The weight ratio of Li2 O to (TiO2 +ZrO2 ) is in the range of 0.95-3.5.

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 A refractive index (nd) of 1.55 to 1.65 is used for an optical lens such as an optical pickup lens of a CD, MD, DVD or other various optical disk systems and a photographing lens of a video camera or a general camera. Optical glass is used. Conventionally, as such a glass, SiO ₂ —Pb
_{O-R '2 O (R} ' 2 O is an alkali metal oxide). However lead-containing glass which is based have been widely used in recent years in -RO SiO ₂ -B ₂ O ₃ from the environmental problems (RO is being switched to the divalent metal oxide) -R 'lead-free glass such as ₂ O system.

[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.

[0005] In addition, there is a part of glass which enables mold press molding on an industrial level by containing a large amount of R ' ₂ O, but these have poor weather resistance and are difficult to produce in the process of manufacturing lenses and prisms. By the cutting, polishing and cleaning in the above, the glass component is eluted into the polishing cleaning water and various cleaning solutions, and the physical properties are degraded and the surface is deteriorated. Also, in the final product, if exposed to a high temperature and high humidity state for a long time, the surface of the glass is deteriorated, so that the optical characteristics as designed cannot be obtained, and the reliability is impaired.

An object of the present invention is to provide an optical glass having a refractive index of 1.55 to 1.65, good weather resistance, and a softening point suitable for mold press molding.

[0007]

The optical glass for mold press molding of the present invention has a SiO ₂ content of 53 to 65% by weight.
%, Al ₂ O ₃ 0 to 10%, B ₂ O ₃ 0 to 4.9
%, MgO 0-5%, CaO 0-4.9%, SrO
1 to 15%, BaO 4.1 to 11.9%, ZnO
1-15%, SrO + BaO + ZnO 15-30%,
TiO ₂ 1-9%, ZrO ₂ 0-7.5%, Li ₂
O 2-7%, Na ₂ O 1-20%, K ₂ O 0-1
It has a composition of 0%, and Li ₂ O / (TiO ₂ + ZrO ₂ )
Is in the range of 0.95 to 3.5 in weight ratio.

[0008]

The optical glass for mold press molding of the present invention comprises:
By indispensably using TiO ₂ having a large effect of increasing the refractive index, 1.5% can be obtained even if a large amount of R ′ ₂ O or RO is not contained.
A refractive index of 5 to 1.65 can be obtained. Thereby, the amount of SiO ₂ can be relatively increased, and a glass having high weather resistance can be obtained. Regarding the weather resistance, in order to obtain a highly reliable lens, the weight loss rate in the water resistance evaluation according to Japan Optical Glass Industrial Standard 06-1975 is less than 0.05%, and the weight loss rate in the acid resistance evaluation is 0.1%. 20
% Is preferred.

[0009] Also, L with respect to the total amount of TiO ₂ and ZrO ₂
By adjusting the ratio of i ₂ O to a specific range, both weather resistance and low softening characteristics can be achieved. Since the glass of the present invention has a softening point of 650 ° C. or lower, the mold does not deteriorate and the glass components hardly volatilize even when subjected to mold press molding.

Next, the reason why the composition range is limited as described above will be described.

[0011] SiO ₂ is a component constituting the skeleton of glass, and its content is 53 to 65%, preferably 55 to 6%.
2%. If SiO ₂ exceeds 65%, the refractive index will be too low, or the softening point will exceed 650 ° C. On the other hand, if it is less than 53%, weather resistance such as acid resistance and water resistance is significantly deteriorated.

Al ₂ O ₃ has an effect of improving the weather resistance of the glass, and its content is 0 to 10%, preferably 0 to 5%.
%. If the content of Al ₂ O ₃ exceeds 10%, the melting property is remarkably deteriorated, striae and bubbles remain in the glass, and the quality required for glass for lenses cannot be satisfied.

B ₂ O ₃ acts as a flux and has the effect of assisting the melting of glass, and its content is 0 to 4.9%, preferably 0 to 2%. When B ₂ O ₃ exceeds 4.9%, the weather resistance is significantly deteriorated. Further, volatilization increases when the glass is melted and striae occur, and a sufficiently homogeneous glass cannot be obtained. In addition, volatilization also occurs at the time of molding to contaminate the mold and greatly shorten the life of the mold.

MgO and CaO act as a flux, and the content of MgO is 0 to 5%, preferably 0 to 2%.
aO is 0 to 4.9%, preferably 0 to 2%. If each component is too large, the devitrification will increase and the glass will be burnt due to the elution of MgO or CaO, which is not preferable.
Note that the coexistence of CaO and MgO significantly increases the devitrification, so that the total amount of these components is preferably 5% or less.

SrO, BaO, and ZnO are components that increase the refractive index and also act as a flux. The content of SrO is 1-15%, preferably 4-10%, and BaO is 4.9-11. 9%, preferably 5.5-10%, Zn
O is 1 to 15%, preferably 4 to 10%. If each component is out of the range, the above effects cannot be obtained.

Further, in order to achieve both a refractive index of 1.55 to 1.65 and excellent weather resistance, the total amount of SrO, BaO and ZnO is limited to 15 to 30%, preferably 18 to 28%. When the total amount of these exceeds 30%, the relative content of SiO ₂
, The weather resistance deteriorates. On the other hand, 15
%, The desired refractive index cannot be obtained, and the meltability deteriorates.

TiO ₂ and ZrO ₂ are components that increase the refractive index, and the content of TiO ₂ is 1 to 9%, preferably 2 to 5%, and ZrO ₂ is 0 to 7.5%, preferably 1 to 5%.
4%. Since these components have a large effect of increasing the refractive index, a desired refractive index can be obtained even when the total amount of BaO, SrO and ZnO is limited to 30% or less. However, when TiO ₂ is more than 9%, the softening point of the glass becomes too high, and when ZrO ₂ is more than 7.5%, the softening point of the glass becomes high, and the devitrification remarkably increases to obtain a homogeneous glass. Can not be. On the other hand, if TiO ₂ is less than 1%, a desired refractive index cannot be obtained.

The total amount of TiO ₂ and ZrO ₂ is 2-9.
It is preferably in the range of 5%, especially 3-7%. If the combined amount exceeds 9.5%, the devitrification will increase and it will be difficult to obtain a homogeneous glass, and if it is less than 2%, it will be difficult to obtain a desired refractive index.

Li ₂ O, Na ₂ O and K ₂ O are components for lowering the softening point. The content of Li ₂ O is 2 to 7%, preferably 4 to 7%, and Na ₂ O is 1-20
%, Preferably 1 to 10%, K ₂ O 0-10%, preferably 0-2%. 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. If K ₂ O exceeds 10%, it will volatilize during mold press molding, causing mold contamination, and the devitrification of the glass will increase. On the other hand, when the content of Li ₂ O and Na ₂ O is less than the above range, the softening point becomes 650.
Exceeds ° C.

In addition to the above, various components can be added to the optical glass of the present invention. For example, Nb ₂ O ₅ can be added to increase or finely adjust the refractive index, and Sb ₂ O ₃ or the like can be added as a fining agent. But Nb
_{Since 2} O ₅ increases the density of glass and makes it difficult to use it for applications such as photographic lenses that require light weight, 0.3%
It is preferable to set the following. Further, PbO, As ₂ O _3, etc. are not preferable because they are not environmentally preferable.

Further, in the present invention, in order to achieve both excellent weather resistance and a low softening point, Li ₂ O / (TiO ₂ +
It is important to the range of 0.95 to 3.5 in a weight ratio values of ZrO _2). That is, if this value is smaller than 0.95, the softening point does not become 650 ° C. or lower, and if it is larger than 3.5, the weather resistance deteriorates and the devitrification increases. For the same reason, the value of Li ₂ O / TiO ₂ is 1.2 or more by weight ratio, and (Li ₂ O + Na ₂ O) / (TiO ₂ + Z
It is preferred that the value of (rO ₂ ) be 1.2 or more by weight.

Since the optical glass of the present invention having the above composition has a refractive index of 1.55 to 1.65 and a softening point of 650 ° C. or less, it has optical characteristics necessary for an optical pickup lens and a photographing lens. It is suitable for mold press molding.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

Tables 1 to 4 show examples of the present invention (sample No. 1).
13 to 13) and Comparative Examples (Sample Nos. 14 to 20).

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

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.

For the obtained sample, the refractive index (nd),
The softening point (Ts), water resistance and acid resistance were measured. The results are shown in each table.

As is clear from the table, the No. 1 of the embodiment of the present invention. Each of the samples 1 to 13 has a refractive index (nd) of 1.
5505 to 1.6324, and a softening point (Ts) of 65
It was below 0 ° C. The water resistance is 0.04% by weight.
%, Acid resistance, weight loss rate is 0.18% or less,
The weather resistance was good.

On the other hand, in Comparative Example No. 14 and No. 20 had poor weather resistance. No. Sample No. 15 had a low refractive index of 1.5174 and a high softening point of 705 ° C. No. 16 and No. 17 has a refractive index of 1.5359
And 1.5455. No. 18 and no. 1
Sample No. 9 had high softening points of 720 ° C and 743 ° C.

Incidentally, the refractive index (nd) is shown by a measured value with respect to the d line (587.6 nm) of a helium lamp. The softening point was measured by a fiber elongation method based on Japanese Industrial Standard R-3104. Water resistance and acid resistance are based on Japan Optical Glass Industry Association Standard 06-1975, and a glass sample is crushed to a particle size of 420 to 590 μm, its specific gravity gram is weighed, placed in a platinum basket, and placed in a flask containing a reagent. The glass powder was placed in a boiling water bath and treated for 60 minutes, and the mass reduction (% by weight) of the powdered glass after the treatment was calculated. The reagent used in the water resistance evaluation had a pH of 6.5 to 6.5.
Pure water adjusted to 7.5, and the reagent used in the acid resistance evaluation was an aqueous nitric acid solution adjusted to 0.01N.

[0034]

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. 1.55
It has a refractive index (nd) of １1.65. 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 use of the product. Moreover, the softening point is low,
Since 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.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02B 1/00 G02B 1/00

Claims (3)

[Claims] 1. An SiO ₂ content of 53 to 65% by weight, Al
_{2 O 3 0~10%, B 2} O 3 0~4.9%, MgO
0-5%, CaO 0-4.9%, SrO1-15
%, BaO 4.1-11.9%, ZnO 1-15
%, SrO + BaO + ZnO 15-30%, TiO _{2
1~9%, ZrO 2 0~7.5%,} Li 2 O 2~
_{7%, Na 2 O 1~20%} , having a composition of _{K 2 O 0~10%, Li 2} O / the (TiO ₂ + ZrO ₂₎ is in the range of 0.95 to 3.5 in weight ratio An optical glass for mold press molding. 2. a refractive index (nd) of 1.55 to 1.65;
2. The optical glass for mold press molding according to claim 1, wherein the optical glass has a softening point of 650 ° C. or lower. 3. The optical glass for mold press molding according to claim 1, which is used for an optical pickup lens or a photographing lens.