JPH052616B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an improvement in an ion exchange treatment method in which an elongated glass rod is brought into contact with a molten salt to exchange ions in the glass with ions in the salt.

<Description of Prior Art> As a method for manufacturing a self-focusing lens whose refractive index continuously changes from the center to the periphery,
By bringing a glass rod base material containing cations such as Tl, Cs, and Li that contribute to an increase in the refractive index into contact with molten salts such as nitrates containing cations such as K and Na that contribute to a decrease in the refractive index, A method is known in which the ions are exchanged with the ions in the salt, and the concentration distribution of the ions creates a distribution in the glass rod in which the refractive index is maximum on the central axis and gradually decreases parabolically toward the periphery. .

<Problems to be Solved by the Invention> When performing the above ion exchange treatment, the simplest method is to immerse a long glass rod of the lens base material vertically in a molten salt bath and leave it standing.

However, in the above method, if many rods are processed at once, uneven concentration of cations will occur in the molten salt, which will cause variations in the ion diffusion rate in the length direction of the lens base material rod, resulting in a large number of rods being processed. This results in large variations in optical performance between lenses manufactured by cutting the lens into different shapes.

On the other hand, if a forced stirring device is immersed in the molten salt and the ion exchange treatment is performed while mixing and stirring the molten salt, the above concentration unevenness is reduced, but a new problem arises in that the glass rod often becomes deformed such as warping. There has occurred.

As a result of examining the causes of this glass rod deformation, we found that forced stirring of the molten salt causes flows in various locations within the molten salt to flow in random directions.On the other hand, due to the need to perform ion exchange quickly, the ion exchange treatment temperature is increased. It has been found that the glass rod is deformed, especially in the lower part, by the contradictory loads applied to various parts of the glass rod by the above-mentioned turbulence in the flow of the molten salt.

The present invention was completed based on the above findings.

<Object of the invention> The main object of the invention is to achieve highly uniform ion exchange along the length of the glass rod, and
An object of the present invention is to provide an ion exchange treatment method that prevents deformation of glass rods.

<Summary of the Invention> The present invention achieves the above-mentioned objects in a glass ion exchange treatment method in which an elongated glass rod is immersed in a molten salt bath to exchange ions in the glass with ions in the salt. The gist is to continuously provide the molten salt with a laminar flow along the length direction over substantially the entire length of the glass rod.

In order to generate the laminar flow of the above-mentioned molten salt near the glass rod and to efficiently process a large amount of it, the method of the present invention has a method in which the upper and lower ends are open longer than the glass rod and the inner diameter is uniform in the length direction during the salt bath. A plurality of rectifying cylinders each made of a cylindrical body are installed in a vertical position, and each group of glass rods is held in a freely hanging state in the rectifying cylinder for each group of glass rods.
An ion exchange treatment is carried out in the salt bath by a stirring device placed outside the rectifying cylinder while giving the molten salt a circulating flow that flows downward within the rectifying cylinder and then ascends and refluxes again after exiting the cylinder. Furthermore, it is preferable to support the immersed glass rod in a freely hanging state rather than holding it fixed, since parallelism to the flow of the molten salt becomes better.

<Operations and Effects of the Invention> According to the present invention, the flow generated in random directions from the stirring device is blocked by the side wall of the rectifying cylinder and does not disturb the flow inside the cylinder, so that the molten salt that enters from the opening at the upper end of the cylinder The glass rod flows in a laminar state along the vertical side wall without receiving any lateral force until it exits from the lower end opening of the straightening cylinder, and the glass rod is held in a freely hanging state, unlike the conventional method. A large load is not applied to the rod in the radial direction, and therefore deformation can be prevented even if ion exchange treatment is performed at the same high temperature as in the prior art. moreover,
Since molten salt with uniform ion concentration and temperature is always in contact with the glass surface over the entire length of the glass rod, ion exchange conditions are maintained uniformly in the length direction of the rod, resulting in a lens matrix with uniform optical performance over the entire length. material can be obtained.

Furthermore, since multiple rectifying cylinders are installed in a common molten salt bath, a large number of glass rods can be processed simultaneously, and at the same time, the molten salt that comes into contact with the glass rods between each cylinder is the same as in the case of a conventional single bath. Unlike the method of providing a large number of independent salt baths having a small cross-sectional area, this method has the advantage that variations in ion exchange conditions due to differences in salt composition are less likely to occur.

<Example> Hereinafter, the present invention will be described in detail with regard to an example shown in the drawings.

FIG. 1 is a sectional view showing an example of an apparatus for carrying out the method of the present invention, in which 1 is a molten salt bath having a cylindrical shape, the inside of which is filled with molten salt 2 such as potassium nitrate, and the outer periphery of the bath. The temperature is maintained at a constant temperature by a heater 3 provided surrounding the area.

A double cylindrical guide partition wall 4 in which an inner cylinder 5 having a small diameter and an outer cylinder 12 having a sufficiently larger diameter are arranged concentrically is immersed in the molten salt 2.
A rotary shaft 6 passes from outside the tank through the center of the inner cylinder 5 of the guide partition wall 4, and a stirring blade 7 is provided at the lower end of the shaft 6.
The shaft 6 is supported by a rotation bearing 8 fixed to the inner cylinder 5, and a pulley 9 attached to the upper end of the shaft 6 is connected to the drive device 1 via a transmission belt 10.
1, the stirring blade 7 rotates to stir and mix the molten salt.

Further, the bottom portion 12A of the outer cylinder 12 of the guide partition wall 4 is concave in a concave shape, and its lower end faces near the outer periphery of the stirring blade 7.

The rectification shown in FIG. 2 (top view) and FIG. A cylinder unit 13 is installed. This rectifying tool 13 has a large number of rectifying cylinders 14 made of corrosion-resistant metal that have a uniform inner diameter over the entire length and a length longer than the lens base material rod, and are arranged on the circumference at regular intervals.
4... are connected by an annular flange 15.

By placing the flange 15 of the rectifying cylinder unit 13 having the above structure on the upper end of the guide partition wall 4, each rectifying cylinder 14... is vertically immersed in the molten salt in the annular space between the inner and outer cylinders 5 and 12 of the guide partition wall 4. be done.

16 is a glass rod that becomes the lens base material;
A fixed number of glass rods 16 are used as one unit, and each group of glass rods is connected to each rectifying cylinder 14 described above.
...Suspended and supported in a freely hanging state.

Specifically, as shown in an enlarged view in FIG. 4, the upper end of the glass rod 16 is melted to form a spherical head 1 with a large diameter.
6A is formed, and the rod 16 is passed through the holes 17A, which are provided at equal intervals in the rod support 17, which is made of a disk-shaped thin perforated plate, and whose diameter is larger than the diameter of the glass rod and smaller than the rod head 16A. Part 16A
The rod support 17, on which a large number of glass rods 16 are suspended, is fixed to the perforated plate by the rod head 16A using a notch partially provided at the upper end of the rectifying cylinder 14. Support it in a lower position.

To give a specific numerical example, the outer diameter is 1.1mmφ.
Tens to hundreds of glass rods 16 with a length of 1255 mm are placed in one rectifying cylinder 14, and the inner diameter of the rectifying cylinder 14 is, for example, 70 mm to 75 mm, and the length is about 1350 mm.

In the above device, when the central stirring blade 7 is rotated, the molten salt pushed down collides with the bottom wall of the salt bath, flows to the side, and the salt flows along the bottom wall 12A of the outer cylinder 12 of the guide partition wall 4. The flow rises through the annular flow path 18 formed between the inner wall of the bathtub 1 and the side wall of the outer cylinder 12 of the guide partition, flows into the upper end opening of the rectifying cylinder 14, and flows inside the cylinder 14 in a uniform laminar flow state. The molten salt flows down along the glass rod 16 and exits from the lower end opening of each rectifying cylinder 14, joins together, reaches the stirring blade 7, and is mixed there, repeating the cycle. That is, the bottom part 12A of the outer cylinder part of the guide partition wall 4 in the above embodiment prevents the flow pushed out from the stirring blade 7 and rising after hitting the bottom wall of the salt bath from directly toward the lower end opening of the rectifying cylinder 14. It plays the role of guiding molten salt outward.
Further, the outer cylinder 12 itself is connected to the rectifying cylinder unit 13.
It plays the role of supporting the flange 15 and the role of reliably guiding the rising and refluxing molten salt to the upper end of the rectifying cylinder.

In the above embodiment, the entire rectifying cylinder 14 is immersed in molten salt so that the circulating flow in the salt bath flows in from the upper end. In this case, the circulating molten salt may not flow sufficiently into the rectifying cylinder 14 located near the center.

In such a case, as shown in plan view in FIG. It is effective to forcibly force the molten salt rising in the channel 18 through a trough 19 provided in the rectifying cylinder 14 to flow into each rectifying cylinder 14 in a distributed manner.

In the embodiment described above, a plurality of cylindrical rectifying partitions 12 are provided by being immersed in a common salt bath, but the molten salt rectifying sections surrounded by these partitions 12 may be made independent.

According to the present invention, the molten salt discharged from each rectifying cylinder is mixed as a whole and then redistributed, so that the variation in concentration between each rectifying partition wall can be made as small as possible.

Furthermore, since the outer periphery of each rectifying cylinder is surrounded by molten salt having a very large heat capacity, the temperature distribution in the length direction of the rod is also uniform.

The present invention is not limited to the manufacturing process of self-focusing lenses, but can be broadly applied to processes in which ion exchange is performed by bringing an elongated glass rod into contact with molten salt.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a device implementing the present invention, FIG. 2 is a plan view showing a rectifying cylinder, and FIG.
4 is a sectional view of a main part showing an example of a method for supporting a lens base material glass rod, and FIG. 5 is a plan view of a main part showing another embodiment of the present invention. 1... Salt bath, 2... Molten salt, 3... Heater, 4... Guide partition wall, 5... Guide partition inner cylinder,
6... Rotating shaft, 7... Stirring blade, 12...
Guide bulkhead outer cylinder, 13... rectifying cylinder unit, 14... rectifying cylinder, 16... glass rod, 17... rod support, 19... trough.

Claims (1)

[Scope of Claims] 1. A glass ion exchange treatment method in which a long and thin glass rod is immersed in a molten salt bath to exchange ions in the glass with ions in the salt; A plurality of rectifying cylinders 14 each consisting of a cylindrical body whose upper and lower ends are open and whose inner diameter is uniform in the length direction are installed in a vertical position, and each group of glass rods is suspended and held within the rectifying cylinder in units of a certain number of glass rods. , performing ion exchange treatment while giving the molten salt a circulating flow that flows downward in the rectification cylinder and then rises and refluxes again after exiting the cylinder, using a stirring device placed outside the rectification cylinder in the salt bath. Characteristic glass ion exchange treatment method.