JP2616958B2 - Optical glass for precision press molding - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical glass for a precision press lens which can be press-formed at a relatively low temperature.

2. Description of the Related Art Conventionally, there is an optical glass of high refractive index and low dispersion type (nd = 1.65 or more, vd = 50 or more) having the same optical constant. However, since this type of glass has a high softening temperature and poor stability, it is not suitable as a glass for precision press molding.

Problems to be Solved by the Invention Conventional high refractive index and low dispersion type (nd = 1.65 or more,
νd = 50 or more) has a yield temperature (At) of 650
C. or higher, and molding could not be performed unless the pressing temperature was higher than 700 ° C. Table 1 shows examples of the high-refractive-index low-dispersion type (refractive index (nd), Abbe number (νd), yielding temperature (At)).

In a known mold material of precision press molding, when the press molding temperature is high, a problem such as oxidation of the mold material occurs, and it is difficult to maintain the surface accuracy, which is not suitable for mass production of lenses. Therefore, it is desirable that the glass to be pressed be formed at the lowest possible temperature. In order to solve these problems, in the publication of press molding glass, phosphate glass (see JP-A-55-154343, JP-A-58-79839 and JP-A-60-1222749), fluoroborate Glass (see Japanese Patent Application Laid-Open No. 59-144692) is known, and phosphoric acid and boric acid are selected as glass-forming oxides. However, the use of large amounts of phosphoric acid and boric acid, while advantageous for lowering the temperature, causes problems in the chemical durability and weather resistance of the glass. The introduction of fluorine as disclosed in the above-mentioned publication is advantageous for lowering the temperature and reducing the dispersion, but tends to cause problems in stability at the time of melting glass, mold material due to volatilization of fluorine at the pressing temperature, environment, and the like. Glass containing lead is also found in the above patent, but if lead is contained, volatiles of lead as well as fluorine will adhere to the mold material, causing problems in maintaining surface accuracy and the like.

Therefore, the first object of the present invention is to provide a relatively low temperature (60 ° C).
An object of the present invention is to provide an optical glass for a precision press lens that is precision pressed at 0 ° C. or lower.

A second object of the present invention is to provide a refractive index (nd) of 1.65 to 1.7.
The object of the present invention is to provide a high-refractive-index, low-dispersion optical glass having an Abbe number (νd) of 53.0 to 57.5.

Means for Solving the Problems The present inventors have conducted various studies and studies in view of the above-described drawbacks of the conventional optical glass and the optical glass for press molding, and found that B ₂ O ₃ , SiO ₂ , and Li ₂ O , La ₂ O ₃ and / or Gd
Optical glass with a glass composition that essentially requires ₂ O ₃ , CaO and / or BaO has almost the same optical constants as high-refractive-index low-dispersion type optical glass, and is press-molded at a lower temperature. Can be made, there is almost no effect on the mold material, and more stable than the optical glass for press molding of the above patent,
Excellent in chemical durability, weather resistance, and melting properties, can be handled like conventional optical glass, and has a low yield temperature (At), making it ideal as an optical glass for precision press lenses that does not require grinding or polishing after press molding. The present inventors have found the glass composition of the present invention, and have reached the present invention.

That is, when showing the present invention in weight percent (shown below%) B ₂ O ₃ 10~35 _{wt% SiO 2 5~30% La 2 O} 3 0~35% Gd 2 O 3 0~35% However La ₂ O ₃ + Gd ₂ O ₃ combined 20-40% Li ₂ O 3-8% CaO 0-20% BaO 0-25% However, it has a composition consisting of combined CaO + BaO 10-30%.

The reasons for limiting the component ranges of the optical glass according to the present invention as described above are as follows.

B ₂ O ₃ is a main component of the glass network, and is effective for stabilizing the glass and lowering the yield temperature (At). However, if it is less than 10%, the above effect is small, 35%
As the number increases, the chemical durability deteriorates.

SiO ₂ forms a glass network like B ₂ O ₃ and is effective in improving the chemical durability of glass. However, if it is less than 5%, the above effect is small, and if it is more than 30%, the viscosity at the time of melting increases, leading to an increase in the yield temperature (At), and the tendency to devitrify further increases.

La ₂ O ₃ and Gd ₂ O ₃ are effective components for increasing the refractive index and reducing the dispersion, but when both are more than 35%, the tendency to devitrify increases. When the total amount of La ₂ O ₃ and Gd ₂ O ₃ is less than 20%, a predetermined optical constant cannot be obtained. When the total amount is more than 40%, a temperature rise during press molding is caused. I do.

Li ₂ O is a component having an important meaning in the present invention, and Li ₂ O will be added in an appropriate amount as an essential compounding component,
This has the effect of significantly lowering the temperature during press molding without impairing the stability of the glass. However, if it is less than 3%, the above effect is small, and if it is more than 8%, the tendency of devitrification is increased, and the chemical durability is further deteriorated.

CaO is effective in increasing the refractive index and increasing the chemical durability, but when it exceeds 20%, the tendency to devitrify increases.

BaO, like CaO, increases the refractive index and is an effective component for stabilizing glass. However, if it exceeds 25%, the chemical durability deteriorates.

If the total content of CaO and BaO is less than 10%, the above effect cannot be obtained, and if it exceeds 30%, the glass tends to be devitrified.

In the optical glass of the present invention, in addition to the above components, to adjust the optical performance, improve the meltability, expand the vitrification range, and the like,
ZrO ₂ , Ta ₂ O ₅ , Y ₂ O ₃ , In ₂ O ₃ , Ga ₂ O ₃ , Al ₂ O ₃ , MgO, Na ₂
O, K ₂ O, Cs ₂ O, SrO, and the like can be contained.

Examples Next, the compositions (numerical values are% by weight) of the examples according to the present invention,
Table 2 shows the refractive index (nd), Abbe number (νd), and yield temperature (At).

The optical glass of the present invention uses the corresponding oxides, hydroxides, carbonates, nitrates, etc. as the raw materials of the components, and weighs them at a predetermined ratio and mixes them well as glass raw materials.
Pour into a platinum crucible, melt in an electric furnace at 1100 ° C to 1300 ° C, stir with a platinum stirring rod, clarify, homogenize, then cast into a mold that has been preheated to an appropriate temperature, Cool slowly and make.

The addition of a small amount of As ₂ O ₃ for preventing the coloring of the glass and defoaming, or the addition of a small amount of a defoaming component well known in the industry does not affect the effect of the present invention.

According to the present invention, the yield temperature (At) is 550 ° C. or less, the refractive index (nd) is 1.65 to 1.70, and the Abbe number (νd) is 53.0 to 5
It has an optical constant of 7.5, is stable against devitrification, can be precision pressed at a relatively low temperature, and can be obtained as an optical glass for precision press lenses that does not require grinding or polishing after press molding.

Claims (1)

(57) [Claims] 1. A B ₂ O ₃ 10~35 (shown below%) _{wt% SiO 2 5~30% La 2 O} 3 0~35% Gd 2 O 3 0~35% , however, La ₂ O ₃ + Gd ₂ Total amount of O ₃ 20-40% Li ₂ O 3-8% CaO 0-20% BaO 0-25% However, the bending temperature (At) consisting of the total amount of CaO + BaO 10-30% is below 550 ° C and refraction Rate (nd)
Is 1.65 to 1.70, and the Abbe number (νd) is 53.0 to 57.5.
An optical glass for precision press lenses with a very low softening point and a high refractive index dispersion.