JP3122236B2 - Optical glass for precision press - Google Patents

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 precision press which can be press-formed at a low temperature and does not require grinding or polishing after press-forming.

[0002]

2. Description of the Related Art Conventionally, low refractive index, high dispersion type (nd = 1.660 or less, ν
(d = 40.5 or less) optical glass containing a large amount of lead oxide. Also, as optical glass for press molding,
Phosphate-based optical glasses (Japanese Patent Application Laid-Open Nos. 60-122747 and 58-79839, European Patent No. 193)
No. 42, reference) fluorophosphate optical glass (JP-A-56-59641, JP-A-58-21745)
No. 1, reference) borosilicate optical glass (Japanese Unexamined Patent Publication No. Sho 62)
No. 1234040) is known.

[0003]

In recent years, with the advancement of lightweight and high performance of single-lens reflex cameras and video integrated cameras,
In order to reduce the weight and performance of the lens portion of these products, aspheric lenses have come to be used. The adoption of an aspherical lens has reduced the weight by reducing the number of lenses, and the aspherical surface has improved the performance by eliminating spherical aberration of the lens. However, in the conventional method of manufacturing a lens by grinding and polishing, it is very difficult to make an aspheric surface, and mass production is poor, so that it is very expensive. For this reason, a manufacturing method by precision press molding that does not require grinding and polishing using a precision processed mold material has been used at present. However,
The mold materials for precision press molding known so far are:
When the molding temperature is high, the material is deteriorated, it is difficult to maintain the surface accuracy of the mold, and it is not suitable for mass production of press lenses. Therefore, it is desirable that the glass to be pressed can be formed at the lowest possible temperature. That is, precision press molding which is usually performed is performed using the yield temperature (At) of glass.
More specifically, it is performed at a temperature higher by about 30 to 50 ° C. Therefore, it is desired that the yield temperature (At) of the glass be as low as possible.

[0004] In addition, optical glass that has been conventionally used includes:
About 10 to 50% of lead oxide is contained as a glass component. When these optical glasses are used in precision presses, they are usually performed in a reducing atmosphere in order to prevent oxidation of the mold, so that the lead oxide present on the glass surface is reduced by the atmosphere, and is deposited on the press lens surface and pressed. Evaporates by heating for forming concave parts on the press lens surface,
Evaporated lead adheres to the surface of the mold material to form a convex part, which causes minute irregularities, and cannot maintain the surface accuracy of the press-molded lens. In addition, it is necessary to remove lead adhering to the mold material, which is not suitable for mass production.
From these points, it is desired that the optical glass used for precision press molding does not contain lead oxide as a glass component and can be formed at a temperature as low as possible. In order to solve these problems, optical glasses for press molding as disclosed in the above publications have been proposed. However, some of these optical glasses do not have the optical properties aimed at by the present invention, and some contain lead oxide.

Accordingly, a first object of the present invention is to provide a low temperature of 620 ° C. or less, that is, a yield of 30 to 5 degrees below the yield temperature (At).
An object of the present invention is to provide an optical glass for precision press molding capable of performing precision press at a temperature higher by 0 ° C. A second object of the present invention is to provide a point A (1.660, 1.660) shown in FIG.
40.5), B (1.660, 32.5), C (1.5
85, 40.5) and D (1.585, 39.0) in the range surrounded by the four points.
An object of the present invention is to provide a low-refractive-index, high-dispersion optical glass having d).

[0006]

Means for Solving the Problems The present inventors have described above.
Of conventional optical glass and optical glass for press molding
In light of the drawbacks, as a result of various studies, SiO_Two, Ge
O_Two, TiO_Two, Na _TwoO, Li_TwoGala that requires O
When the optical glass having the glass composition is within the specified range,
Low refractive index and high density not found in optical glass for press molding in the open gazette
It has diffuse optical properties, and also has a mold
Glass low enough with little effect on the material
After finding that it has a softening temperature, after press forming,
Is the best optical glass for precision press that does not require polishing.
We have come to the conclusion that it is suitable.

That is, the composition of the optical glass of the present invention is
In terms of% by mass, SiO_Two10.0 to 50.0% by weight (hereinafter referred to as
Lower%), GeO_Two5.0-52.0%, TiO_Two
4.0 to 25.0%, Nb_TwoO_Five0 to 25.0%, provided
And SiO_Two+ GeO_Two45.0-67.0% of the total amount of
However, TiO_Two+ Nb_TwoO_Five10.0 to 30.0
%, Li_TwoO 1.0-5.0%, Na_TwoO5.0-1
9.0%, K_TwoO0-8.0%, Cs_TwoO0-20.0
%, But Li_TwoO + Na_TwoO + K_TwoO + Cs_TwoO
8.0 to 32.0%, ZnO 0 to 10.0%, MgO
0-8.0%, Al _TwoO_Three0-6.0, ZrO_Two0 to
1.0%, TeO_TwoHaving a composition of 0-3.0%
I have.

The reasons for limiting the range of each component of the optical glass according to the present invention as described above are as follows. SiO ₂
Is a main component constituting a glass network, and is effective for stabilizing and highly dispersing the glass. However, if the content is less than 10.0%, the glass becomes unstable. If the content is more than 50.0%, the softening temperature rises, which makes the glass unsuitable as a glass for precision press lenses and also causes unmelted material in the glass. Cause. GeO ₂ is a component constituting a glass network like SiO _2, and exhibits the highest dispersibility among components that form glass alone, and further has a softening temperature lower than that of ordinary optical glass of the same type. It is an essential component in providing. However, if the content is less than 5.0%, the effect is not obtained. If the content is more than 52.0%, the chemical durability is deteriorated and the refractive index is further increased. The total amount of SiO ₂ and GeO ₂ is 45.
If the value exceeds 0 to 67.0%, a predetermined optical constant cannot be obtained.

TiO ₂ is the most important essential component in the present invention. Usually, low refractive index and high dispersion optical glass is
In order to give the glass its low refractive index and high dispersion properties, P
The bO component is required. However, since the optical glass in the present invention is a glass for a precision press lens, PbO, which is a component that has an adverse effect on a press mold, is used.
Can not be used. Therefore, in the present invention, TiO ₂ is essential as the most effective component that imparts the same optical properties as PbO to glass and does not adversely affect the stamping die. However, if the content is less than 4.0%, the above effect cannot be obtained. If the content is more than 25.0%, the glass becomes unstable. Nb
₂ O ₅ is a component for imparting low refractive index and high dispersion to the glass instead of the PbO component like TiO ₂ . However, no effect of TiO ₂ degree, since than highly disperse better effects on the high refractive index larger, in conjunction with TiO _2, and a component for adjusting the optical constants. However, if it exceeds 25.0%, the refractive index becomes higher than a predetermined optical constant, and the tendency to devitrify further increases. TiO
₂ , Nb ₂ O ₅ falls within this range since a predetermined optical constant cannot be obtained if the total amount exceeds 10.0-30.0%.

Li ₂ O is a component which has the effect of lowering the softening temperature of the glass among the alkaline components and which does not deteriorate the chemical durability of the glass most. However, if the proportion of use increases, the glass becomes very unstable, and the tendency to crystallize increases. Therefore, in the present invention, the use amount of the small essential component within 1.0 to 5.0% is limited to 1.0 to 5.0%. Limited. Na ₂ O is Li among the alkaline components.
It is a component having an effect of lowering the softening temperature of glass after ₂ O. However, unlike Li ₂ O, even if the amount of use is increased, the stability of the glass is not impaired, so that it is the alkali essential component most used in the present invention. However, if less than 5.0%, the effect is small, and 19.0%
%, The chemical durability of the glass deteriorates. K ₂ O has no effect on lowering the softening temperature of the glass as compared with Li ₂ O and Na ₂ O, and when the amount of K ₂ O used is increased, the chemical durability of the glass is extremely deteriorated. However, since it has a property of giving glass a low refractive index and high dispersibility, it is used at 8.0% or less. Cs ₂ O is the most effective component for increasing the dispersion of the refractive index among the alkali components, and does not impair the stability of the glass even when used in large amounts. However, there is almost no effect on lowering the softening temperature, and if it exceeds 20.0%, the chemical durability deteriorates. Li ₂ O
, Na ₂ O, K ₂ O, and Cs ₂ O are components more effective in lowering the softening temperature than the other components, and are also effective in lowering the refractive index and increasing the dispersion. However, if the total amount is less than 8.0%, the effect is small, and if it exceeds 32.0%, the chemical durability of the glass is deteriorated.

[0011] ZnO is effective in lowering the softening temperature, but if it exceeds 10.0%, the refractive index will be increased. MgO is an effective component for lowering the refractive index, but if it exceeds 8.0%, the tendency to devitrify will increase. Al ₂ O ₃ is a component that makes the chemical durability of glass very good, but if it exceeds 6.0%, the softening temperature increases. ZrO ₂ improves the chemical durability similarly to Al ₂ O ₃ , but when it exceeds 1.0%, the softening temperature increases and the tendency to devitrify increases. TeO ₂ is a component effective for high refractive index and high dispersion.
For this reason, the optical constants are adjusted by adding a small amount of 3.0% or less.

The optical glass of the present invention deviates from the object of the present invention in addition to the above components, in order to adjust the optical performance, improve the melting property, expand the vitrification range and lower the softening temperature. Unless otherwise, Ca, Sr, Ba, Ga, In, Y
, La, Ta, Gd, Yb and other metal oxides and halides.

The optical glass of the present invention uses the corresponding oxides, hydroxides, carbonates, nitrates, halides and the like as the raw materials for the respective components, and becomes the ratio of the desired glass composition after vitrification. Weighed as described above, mixed well, and put into a platinum crucible as a glass blending raw material.
It can be manufactured by melting at 000 ° C. to 1400 ° C., stirring with a platinum stirring bar, clarifying and homogenizing, casting into a mold preheated to an appropriate temperature, and then gradually cooling.

[0014]

EXAMPLES Hereinafter, the optical glass of the present invention will be described specifically with reference to examples, but the present invention is not limited thereto. Examples 1 to 24 Table 1 shows the compositions (numerical values are% by weight) of the examples according to the present invention, and the refractive index (nd), Abbe number (νd) and yield temperature (At) as characteristic values thereof. The optical glass of the present invention uses the corresponding oxides, hydroxides, carbonates, nitrates, halides, and the like as the raw materials for the components, and after being vitrified, has the ratio of the composition of each example in Table 1. Weighed, mixed well and mixed as a glass blending material, put into a platinum crucible, melted in an electric furnace at 1000 ° C to 1400 ° C, stirred with a platinum stirring rod, clarified and homogenized. After casting in a mold preheated to an appropriate temperature, it is gradually cooled. In addition, a small amount of As ₂ is used to prevent coloring of the glass and to remove bubbles.
The addition of O ₃ or the addition of small amounts of defoaming components well known in the industry does not affect the effect of the present invention.

[0015] Next, a predetermined weight of glass lump is cut out of the obtained glass, polished into a sphere by a conventional polishing method, and precision-pressed at 500 to 610 ° C as a preform to obtain 24 types of products. Obtained. As a result of measuring the shape of these press lenses, all showed a shape error of 1.0 μm or less, exhibited good transferability, and did not recognize glass adherence or volatile matter adherence to the mold material.

Comparative Examples 1-2 The compositions of conventionally known optical glasses usually called F2 and BaSF4 are shown in Table 2 and produced as comparative examples.
Using this composition, a glass was produced in the same manner as in Examples 1 to 24, a preform was prepared, and the preform was placed in a heated reducing atmosphere, and the surface state was observed. As a result, the surface of the preform, which had been in a mirror surface state, was reduced without performing precision press molding, and lead precipitation was recognized and the state changed to a cloudy state.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

[Table 4]

[0021]

[Table 5]

[0022]

According to the present invention, the yield temperature (At) is 5
At 70 ° C. or lower and at the point A (1.660, 4
0.5), B (1.660, 32.5), C (1.58
5,40.5) and D (1.585,39.0) in the range surrounded by the four points of refractive index (nd) and Abbe number (νd)
Since it is stable against devitrification and can be press-formed at an extremely low temperature, it is useful as an optical glass for precision press that does not require grinding or polishing after press-forming.

[Brief description of the drawings]

FIG. 1 is an optical constant diagram (nd-νd diagram) showing an optical constant region of the glass of the present invention.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 1/00-14/00

Claims (1)

(57) [Claims] (1) SiO_Two10.0 to 50.0% by weight (hereinafter referred to as
%), GeO _Two5.0-52.0%, TiO
_Two4.0 to 25.0%, Nb_TwoO_Five0 to 25.0%, provided
And SiO_Two+ GeO_Two45.0-67.0% of the total amount of
However, TiO_Two+ Nb_TwoO_Five10.0 to 30.0
%, Li_TwoO 1.0-5.0%, Na_TwoO5.0-1
9.0%, K_TwoO0-8.0%, Cs_TwoO0-20.0
%, But Li_TwoO + Na_TwoO + K_TwoO + Cs_TwoO
8.0 to 32.0%, ZnO 0 to 10.0%, MgO
0-8.0%, Al_TwoO_Three0-6.0%, ZrO_Two0 to
1.0%, TeO_TwoYield of 0-3.0% composition
A temperature (At) of 570 ° C. or lower and a point shown in FIG. 1;
A (1.660, 40.5), B (1.660, 32.
5), C (1.585,40.5), D (1.585,
39.0), the refractive index (nd) and the refractive index (nd) within the range surrounded by the four points.
Low refractive index and high dispersion precision press with high Abbe number (νd)
Optical glass for