JPS6283324A - Production of optical glass - Google Patents

Abstract

PURPOSE:To obtain optical glass consisting of optional components easily by vitrifying a mixture of several kinds of oxide constituting the target optical glass on the surface of a base body by the physical vapor deposition process. CONSTITUTION:Plural kinds of oxide constituting target optical glass are evaporated separately by heating at above each evaporating temp. The plural kinds of the vapor are mixed in a mixing zone maintaining each vapor in the gaseous state and the gaseous mixture is deposited on a base material held at below a coagulation temp. of the above described optical glass in a vacuum vessel. It is preferred that each vapor evaporated from the above-described evaporation source is carried by carrier gas to a mixing zone where they are allowed to contact with the surface of the base material after they are mixed. Furthermore, it is preferred that the flow of the vapor is scanned on the surface of the base material if the area of the base material is large.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing optical glass, and in particular to a method for manufacturing a new type of optical glass that has optical properties effective for eliminating chromatic aberration in a lens system without using conventional melting. It is.

As is well known, the chromatic aberration of a lens system is Σ−□
It can be eliminated by satisfying the following condition: =0 kfk (where fk is the focal length of the th lens in the lens system, and ν is the Abbe number). Also, in order to simultaneously eliminate curvature of the image plane and chromatic aberration.

For example, if there are two constituent lenses, the condition n2 ν2 (where n is the refractive index) must also be satisfied. For this reason, an extremely wide variety of optical glasses are required, each having a different refractive index and Abbe number, and new types of glasses with different combinations of refractive index and Abbe number are being actively developed.

In particular, materials that have special optical properties such as a large refractive index and a small unidispersion are extremely important as lens materials for eliminating chromatic aberration in lens systems. Region A surrounded by a line in FIG. 1 shows the distribution range of the optical properties of new types of optical glasses that have been obtained to date, and optical glasses that have all the optical properties outside this region.

Its production is said to be extremely difficult. One of the reasons for this is that when each component is melted in a rumbo and then cooled and solidified to be vitrified, the blending ratio of each component that can be vitrified is limited to an extremely narrow range. For example, in the case of a 20% B205-La20 system optical glass, it is known that the blending ratio of each component that can be vitrified is limited to a narrow range shown by region B in the phase diagram in Figure 2. . Furthermore, even within this vitrification region, the temperature during melting and slow cooling, fc, for example, during cooling, non-uniform strain tends to remain in the glass block solidified in the crucible.
It is difficult to control and there is a great risk of devitrification.

An object of the present invention is to provide a method that enables extremely stable vitrification when producing optical glass made of arbitrary components.

In the method of this invention, an optical glass raw material mainly consisting of a mixture of two different oxides is produced by a method that does not involve melting in a crucible;
That is, it is vitrified on the surface of the substrate by a physical vapor deposition method (PVD method). The formation of the vapor deposited layer by the PVD method is as follows:
It is formed through the process in which the molecules evaporated from the evaporation source corresponding to each component are mixed uniformly in space and then attached to the substrate and instantly solidified, so it is different from the case where the molecules are melted and solidified in two crucibles. , internal distortion is less likely to occur, vitrification is reliably performed, and the risk of undesirable phenomena such as devitrification occurring is extremely small.

In addition, by changing the mixing ratio of each raw material as the vapor deposition progresses, for example, by computer control, υ,
After vapor deposition, the composition within the glass solid is changed, thereby changing the refractive index and ambe number? It is also possible to change it appropriately.

And in this case.

There is no need for the glass surface to be curved, and even a simple flat plate has the potential to perform the same functions as conventional lenses.

Formation of the evaporation layer by the PVD method can be performed by applying techniques generally known in this field, but as a factor specific to the production of optical glass, the number of evaporation sources is dependent on the number of types of raw material components. The same amount may be required, and the vapors of each component evaporated from these evaporation sources may be mixed in precise proportions depending on the composition of the desired optical glass.

Various methods can be considered to satisfy these requirements, but one of them is to prepare multiple evaporation sources that keep each component isolated from each other, and to use a gold laser or microwave for each evaporation source. Each component is evaporated by heating with a heating means such as, and the generated vapor is transported to a mixing region with an appropriate carrier gas. After mixing each component in this mixing region, the resulting optical glass has a temperature below the freezing point. A method of contacting the surface of a substrate maintained at a temperature can be adopted. Control of the mixing ratio of each component is
By strictly controlling the temperature of the evaporation sources heated by laser or microwave to maintain the evaporation t i of each evaporation source at a predetermined value, or by controlling the temperature of the evaporation source heated by laser or microwave, or by controlling the temperature of the evaporation source heated by each evaporation source. This can be achieved by controlling the flow rate of the carrier gas delivered to the mixing region.〇The substrate on which the deposited layer is formed has a small coefficient of thermal expansion.

The substrate is made of a substance that is chemically stable at high temperatures, and the most preferred substrate is a platinum plate. If the area of the substrate is relatively small, a deposited layer of uniform thickness can be obtained by simply directing the flow (beam) of the gases mixed in the mixing region to the center of the surface of this substrate, but if the area is large, If a large-area substrate is used to obtain the deposited layer, the surface of this substrate may be scanned with the beam.

As described above, according to the present invention, optical glass of a desired composition is formed from vapor as a solid vapor deposited layer on a substrate, so that even if the composition is difficult to vitrify using the method of melting and solidifying in a JV pot, Also.

It can be easily vitrified without causing any disadvantages such as devitrification.

Furthermore, the results of experiments revealed that optical glasses with compositions that could not be vitrified using conventional methods can be easily produced. For example, the 20% B O shown in Figure 2
-20%BaO-20%TaO-20, which is a composition outside the vitrification region B in the phase diagram of the La203 system.
%La20. -40% ThO2 (molar ratio) was also able to be completely vitrified (point 0 in Figure 2).
. This means that it is also possible to obtain an optical glass having characteristics of high refractive index, low dispersion, or low refractive index and large dispersion, which are far outside the region A shown in Figure 1.

Example B2O5, Ta205. Prepare all airtight containers containing La2O3 and Th02, heat the contents of each container with microwaves to evaporate, and then use argon as a carrier gas to transfer the oxide vapor in each container to the mixing pipe in the vacuum container. supplied. A flow rate adjustment mechanism is provided on the pipe that leads gas from each container to the mixing pipe, and B2O3:
The molar mixing ratio of Ta205:La2O5:ThO2 is 20
The flow rate was adjusted so that the ratio was 20:20:40.

A platinum plate measuring 10 m x 10 m x 0.5 ++ m was placed inside the vacuum vessel, and a mixed gas was discharged from a mixing pipe toward the surface of the platinum plate. The temperature of the platinum plate is 480±5
It was kept at ℃. After 70 minutes of vapor deposition, a vapor deposited layer with a thickness of 2 mm was formed.

According to fluorescent X-ray analysis, the vapor deposited layer peeled off from the platinum plate was 19% BO-22% Ta205-18% La205-
It is a homogeneous glass with a total composition of 41% ThO2, and its refractive index is 1.862. Atsbe's number was 44.3.

[Brief explanation of drawings]

Figure 1 is a graph showing the distribution area of the refractive index vs. ambe number characteristic of conventional special optical glass, and Figure 2 is a graph showing the distribution area of the refractive index - ambe number characteristic of conventional special optical glass.
It is a phase diagram of O-La O-Th02 type glass. Patent applicant Industrial Development Research Institute Agent Patent attorney 1) Hiroshi Sawa (2 others) 4-m-Dispersion・1・7-nohe Kei Dispersion 9-1! =1
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O2su5 procedural amendment power (voluntary) 60.11.14 Showa year month day

Claims (3)

[Claims] (1) Multiple types of oxides constituting the target optical glass are heated above their respective evaporation temperatures and evaporated separately, and the multiple types of vapors are mixed in a gas phase in a mixing region, and this mixed gas is A method for producing an optical glass, which comprises depositing the above-mentioned optical glass on a substrate maintained at a temperature below the freezing point of the optical glass in a vacuum container. (2) The method for manufacturing optical glass according to claim 1, wherein vapor evaporated from the evaporation source is carried by a carrier gas toward the heating region and then directed toward the surface of the substrate. (3) Claim 1, wherein the flow of the mixed gas formed in the heating region is scanned over the surface of the substrate.
A method for producing optical glass as described in Section 1.