JPH0733481A - Ion exchange treatment of rod-shaped glass - Google Patents

Abstract

PURPOSE:To prevent deformation and to increase a refractive index difference by immersing glass contg. thallium oxide into a fused salt contg. univalent cations contg. a prescribed titanium dioxide. CONSTITUTION:Potassium nitrate, etc., and >=10wt.% powdery titanium dioxide 3 are put into a stainless steel vessel 4 of a desired capacity and are heated to obtain the fused salt 2. The upper part of rod-shaped glass 1 contg. 15 to 25mol% thallium oxide is then lanced 11 and is hung to a quartz rod 5 by means of a stainless steel wire 6. After the hung down rod-shaped glass 1 is preheated, the rod-shaped glass is immersed into the fuse salt 2 kept at a desired ion exchange temp. and is subjected to an ion exchange treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of ion-exchange glass to give a refractive index distribution, and more particularly to an ion-exchange processing technique for producing a gradient index rod lens.

[0002]

2. Description of the Related Art As a method of providing a refractive index distribution on glass, an ion exchange method can be mentioned. What is ion exchange?
By immersing the glass body in a molten salt maintained at a temperature near the glass transition point for a long time, the monovalent cations present in the glass body and the monovalent cations contained in the molten salt interdiffuse. It is to be.

By this method, the composition inside the obtained glass body is continuously changed, and accordingly, the refractive index inside the glass body can be continuously changed.

For example, when a rod-shaped glass containing thallium ions is immersed in molten potassium nitrate to ion-exchange the monovalent cations thallium ions and potassium ions, the thallium ions in the rod-shaped glass are rod-shaped. Since it goes out from the surface into the molten salt, the concentration of the thallium component decreases continuously from the central portion to the peripheral portion in the rod-shaped glass after ion exchange. On the contrary,
Potassium ions continuously increase from the periphery to the center.

Since this thallium ion has a larger refractive index than potassium ion, the central part of the rod-shaped glass has the largest refractive index, and the refractive index continuously decreases toward the peripheral part. It has a refractive index distribution. Rod-shaped glass with such a refractive index distribution,
Even if both end surfaces are flat, it functions as a convex lens.

One of the uses of such a rod-shaped lens is an objective lens of an endoscope. This objective lens is required to have a large field of view. The field of view of the objective lens can be increased by increasing the difference in refractive index between the center and the periphery of the gradient index rod lens. Therefore, in order to increase the difference in refractive index, it is necessary to make the matrix glass contain a large amount of thallium oxide, which is a component for increasing the refractive index.

[0007]

However, according to the research conducted by the present inventors, a rod-shaped glass containing 15 mol% or more of thallium oxide (hereinafter referred to as thallium-based rod glass) is immersed in molten potassium nitrate. Then, when thallium ions and potassium ions are ion-exchanged, a problem that the cross-sectional shape of the thallium-based rod glass during ion exchange is deformed from a circular shape to an elliptical shape has been discovered.

The situation is shown in FIG. The magnitude of this deformation is, for example, when the rod-shaped glass having a diameter of 2 mm, which originally has a difference between the major axis and the minor axis of 1 to 2 μm, is subjected to an ion exchange treatment, the difference between the major axis and the minor axis of the treated rod-shaped glass. Is about 1
It reaches 50 μm. This corresponds to 7.5% of the original diameter.

Since this elliptical deformation is asymmetric with respect to the optical axis, it causes remarkable astigmatism and causes deterioration of lens performance.

An object of the present invention is to provide a method for preventing the above-mentioned deformation occurring in a high thallium-based rod glass in an ion exchange treatment.

[0011]

In the present invention, a glass containing thallium oxide as a glass composition is immersed in a molten salt containing a monovalent cation to perform an ion exchange treatment. Ion exchange treatment of the rod-shaped glass is performed by adding 10% by weight or more of powdery titanium dioxide.

[0012]

The present invention will be described in detail below.

The inventors have found that the addition of powdered titanium dioxide or activated alumina into the molten salt can suppress the elliptical deformation generated in the high thallium rod glass.

However, when activated alumina is added to the molten salt, NO _x which deteriorates the working environment is generated. On the other hand, in the case of titanium dioxide, such a phenomenon does not occur, so it is preferable to add titanium dioxide to the molten salt. The titanium dioxide is present in the molten salt in the form of being precipitated at the bottom of the container.

(Specific Example) Hereinafter, specific examples of the present invention will be described in detail. First, the diameter is 100 mm and the depth is 100
1200g potassium nitrate in mm stainless steel container (4)
And a predetermined amount of powdery titanium dioxide (3) are charged, the temperature is raised to 550 ° C. in an electric furnace, and the molten salt (2) is kept for several hours.

The composition of the thallium-based rod glass used is SiO ₂ —ZnO—R ₂ O system, and Na ₂ O is 5 to 10 mol% and Tl ₂ O component is 15 to 10 mol% as the R ₂ O component.
25 mol% is contained. The Tl ₂ O component is 25mo
If it exceeds 1%, vitrification is difficult. The thallium rod glass (1) had a diameter of 6 mm and a length of 65 mm.

Next, as shown in FIG. 1, a notch (11) is made in the upper part, and the wire is hung on a quartz rod (5) with a stainless wire (6).
Ion exchange was performed by immersing the preheated thallium-based rod glass in the molten salt (2) kept at the ion exchange temperature for 0 minute.

FIG. 3 shows the relationship with the deformation of the rod glass (difference between the long axis and the short axis) when the amount of titanium dioxide added to the molten salt was changed. In this case, the amount of titanium dioxide added is the amount with respect to potassium nitrate. Table 1 shows the composition of the thallium-based rod glass and the ion exchange conditions at that time.

[0019]

[Table 1]

From these results, it can be seen that the degree of deformation of the rod glass greatly changes when the amount of titanium dioxide added is about 9% within the range of the composition of the rod glass and the ion exchange conditions. It was found that the amount of titanium dioxide added should be 10% by weight or more based on the amount of molten salt. The desirable addition amount of titanium dioxide is about 15 to 20%.

It should be noted that if the magnitude of deformation is 3 μm or less in terms of axial and minor axis difference, the performance as a lens is not significantly affected, but if it is 3 μm or more, the effect is large and lens performance is affected.

(Comparative Examples 1 to 3) The composition of thallium-based rod glass, ion exchange conditions, and
Table 2 shows the addition amount of titanium dioxide and the presence or absence of deformation of the rod glass.

[0023]

[Table 2]

In the case of this comparative example, since the composition of thallium oxide is 10% or less, it is understood that the rod glass is not deformed even if titanium dioxide is not added to the molten salt.

[0025]

According to the present invention, by preliminarily containing 10% by weight or more of titanium dioxide in the molten salt before the ion exchange, it is possible to prevent the elliptical deformation of the high thallium system rod glass, and thus the rod-shaped glass lens. It is possible to obtain a lens having a large difference in refractive index between the central portion and the peripheral portion.

Therefore, the gradient index lens having a wide viewing angle does not cause deterioration of optical characteristics due to deformation,
It can be stably obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a method of ion exchange treatment.

FIG. 2 is a cross-sectional view of a deformed glass rod.

FIG. 3 is a diagram showing the relationship between the amount of titanium dioxide added and deformation.

[Explanation of symbols]

 1 Thallium-based rod glass 1a Short axis of rod glass cross section 1b Short axis of rod glass cross section 11 Cut portion of rod glass 2 Potassium nitrate molten salt 3 Powdered titanium dioxide 4 Stainless steel container 5 Quartz rod 6 Stainless wire-

Claims (2)

[Claims] 1. A method of immersing a glass containing thallium oxide as a glass composition in a molten salt containing a monovalent cation to perform an ion exchange treatment, wherein 10 parts of the molten salt are contained in the molten salt.
A method for ion-exchange treatment of rod-shaped glass, which comprises containing powdery titanium dioxide in an amount of at least wt%. 2. The ion exchange treatment method for a rod-shaped glass according to claim 1, wherein the glass contains thallium oxide in an amount of 15 to 25 mol%.