JPS647013B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an optical glass having the following characteristics: nd≧1.78, νd≧38, and specific gravity<4.3. Many optical glasses that satisfy the above optical constants are already known. For example, Japanese Patent Publication No. 36-1394 teaches a glass containing ThO ₂ and CdO, and Japanese Patent Publication No. 50-6326 teaches a glass containing a large amount of Gd ₂ O ₃ . In addition, examples of products that do not contain these ingredients include, for example,
Glasses containing large amounts of La ₂ O ₃ are known, as seen in Japanese Patent Application No. 2106, and glasses containing large amounts of ZnO and Ta ₂ O ₅ , as shown in Japanese Unexamined Patent Publication No. 101414/1983. However, these conventional glasses contain La ₂ O ₃ ,
Since it contains a large amount of ZnO, Ta ₂ O ₅ , etc., it usually has a high specific gravity. However, in recent years, in the field of optical instruments, the market trend has been toward smaller and lighter lenses, and there is a strong desire to develop lightweight lens materials. The purpose of the present invention is to eliminate harmful substances such as ThO ₂ and CdO.
It does not contain Gd ₂ O ₃ , which is an expensive component, and has a specific gravity of 4.3.
The object of the present invention is to provide a high refractive index, low dispersion glass having an optical constant of less than
As shown in the glass composition of the present invention, this purpose is to include Nb ₂ O ₅ and CaO as essential components, which give a relatively small specific gravity in spite of a high refractive index, and to increase the content of components that increase the specific gravity and dispersion. This is achieved by strictly limiting the That is, the optical glass of the present invention has, in weight%,
SiO ₂ +B ₂ O ₃ 20-30, SiO ₂ 0-22, B ₂ O ₃ 3-
30, La ₂ O ₃ +Y ₂ O ₃ 18-37, La ₂ O ₃ 18-37,
_{Y2O3 0} ~8, _{Nb2O5 8} ~22, ZrO2 ₁ ~8,
CaO + MgO 10-24, CaO 10-24, MgO 0-
10, ZnO<10, BaO<5, SrO<8, PbO<5,
It has the following composition: TiO ₂ <2, Ta ₂ O ₅ <5, WO ₃ <5, alkali metal oxide <5, Al ₂ O ₃ <6, P ₂ O ₅ <6, nd≧1.78, νd≧38 , specific gravity <4.3. Regarding the optical glass of the present invention, the reason for limiting the constituent components is that SiO ₂ and B ₂ O ₃ can be used in a total amount or singly.
If it exceeds 30%, the desired high refractive index cannot be obtained, and if the total amount is less than 20%, the glass becomes unstable. Also,
Similarly, if SiO ₂ exceeds 22% or B ₂ O ₃ falls below 3%, the glass becomes unstable. La ₂ O ₃
is required to maintain a high refractive index and low dispersion, but this component increases the specific gravity, so it is reduced to 37%.
Limited to: Y ₂ O ₃ is effective because it gives optical constants equivalent to those of La ₂ O ₃ and has a lower specific gravity than La ₂ O ₃ , but since it is an expensive raw material, it should be limited to 8% or less. As mentioned above, Nb ₂ O ₅ is an essential component to obtain a high refractive index and low specific gravity, and 8% or more is required, but if it exceeds 22%, the desired high Abbe number cannot be maintained. Since ZrO ₂ gives almost the same specific gravity as Nb ₂ O ₅ and increases the Atsube number, 1% or more is required, but if it exceeds 8%, the devitrification resistance deteriorates rapidly. CaO stabilizes the glass and gives it a low specific gravity, so 10% or more is required, but if it exceeds 24%, the glass becomes unstable. MgO can partially replace CaO without increasing the specific gravity, but if it exceeds 10%, devitrification resistance deteriorates. Other components are mainly added for the purpose of adjusting optical constants, improving devitrification resistance, improving meltability, etc., but ZnO, BaO, SrO, PbO, Ta ₂ O ₅ and WO ₃ have a specific gravity. The ingredients that increase the size are 10%, 5%, and 8, respectively.
%, 5%, 5%, limited to less than 5%. or,
TiO ₂ decreases the number of pimples and strengthens the coloration, so keep it below 2%, while alkali metal oxides, Al ₂ O ₃ , P ₂ O ₅
5%, 6%, and 6%, respectively, worsen the devitrification resistance.
limited to less than %. In addition, it is not prohibited to add small amounts of As ₂ O ₃ , Sb ₂ O ₃ , F, etc. for the purpose of clarifying, decolorizing, etc. Examples of the present invention (each component is % by weight) are shown in the following table.

【table】

[Table] These glasses are made by melting a mixture of commonly used raw materials such as silica powder, boric acid, lanthanum oxide, niobium oxide, zirconium oxide, and calcium carbonate at 1300 to 1350°C in a platinum crucible and stirring the mixture. It can be manufactured by homogenizing and removing bubbles, then casting into a mold preheated to an appropriate temperature and slowly cooling.

Claims (1)

[Claims] 1% by weight SiO ₂ +B ₂ O ₃ 20-30 SiO ₂ 0-22 B ₂ O ₃ 3-30 La ₂ O ₃ +Y ₂ O ₃ 18-37 La ₂ O ₃ 18-37 Y ₂ O ₃ 0 ~ 8 Nb ₂ O _{5 8} ~ 22 ZrO ₂ 1 ~ 8 CaO + MgO 10 ~ 24 CaO 10 ~ 24 MgO 0 ~ 10 ZnO < 10 BaO < 5 SrO < 8 PbO < 5 TiO ₂ < 2 Ta ₂ O ₅ < 5 WO ₃ < 5 alkali metal oxide < 5 Al ₂ O ₃ < 6 P ₂ O ₅ < 6, nd≧1.78, νd≧38, specific gravity <4.3
Optical glass with the following characteristics.