JPS6227335A - Method for press-forming optical element - Google Patents

Abstract

PURPOSE:To increase the rate of forming and to prolong the life of a pair of dies while maintaining prescribed forming accuracy when a glass block is pressed between the dies to obtain a formed article, by giving a specified temp. gradient to the glass block and specifying the temp. of the dies. CONSTITUTION:A preformed glass block 1 heated to a certain low temp. at which the block 1 has <=10<14.5> P viscosity is put on a support member 2. The block 1 has regulated weight and smoothened principal faces. The block 1 is heated continuously and rapidly with an infrared concentric heater until the surface layer part attains a prescribed temp. corresponding to 10<9>-10<4.5> P viscosity and the internal part attains a prescribed temp. corresponding to a higher viscosity of 10<14.5>-10<9> P. The former temp. is measured with an infrared radiation thermometer and the latter temp. can be experientially estimated with a thermocouple embedded in a glass block of the same shape. The heated block 1 is rapidly put between a pair of upper and lower dies 3, 4 kept at a prescribed temp. below the glass transition temp. with thermocouples 5 and the dies 3, 4 are moved to press-form the block 1 as shown by the figures.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a novel method for directly molding optical elements by pressing a heated glass gob.

``Prior art'' In order to obtain various optical elements made of glass, a glass lump is pressed between the molding surfaces of a pair of molds, and a press press is used. (According to this type of method, the desired surface accuracy, surface performance, and dimensional accuracy including wall thickness of the optical surface cannot be obtained only by press forming, so rough polishing and precision polishing are performed after that.) Complicated post-processes such as polishing were required, and the time and effort involved were immeasurable.

Therefore, technologies that can omit the above-mentioned post-processes have been proposed and put into practice, but the general final molded products have poor surface performance, that is, surface roughness of the optical surface.
It is desirable that the surface accuracy is within 6 Newton rings, the irregularity is within /2, and the wall thickness accuracy is within about ±501L11.

In order to meet the above requirements, the measurement, size and shape of the glass ingots to be pressed must be measured to allow for an appropriate amount of surplus.

Surface condition, temperature distribution inside the glass gob just before pressing,
How to support the glass gob, material of the molding surface of the mold, surface performance and surface accuracy, dimensional design that takes into account shrinkage and deformation of the molded product after molding, temperature of the mold, timing of contact and adhesion of the mold to the glass gob, depending on the mold Much effort is required regarding the pressing pressure, the holding time of the molded glass in the mold, etc.

Among these many considerations, the temperature conditions of the glass gob and mold immediately before pressing have a large effect on the molding accuracy of the glass gob.

Therefore, in order to obtain a molded product with the desired precision, a softened glass gob is heated to a high temperature above the glass transition point and then pressed until the glass gob and the mold reach a temperature at or below the glass transition point. Although techniques are known, they all require a large amount of molding time and have the disadvantage that control of the temperature cycle of the mold is complicated, and the mold is easily damaged under these conditions.

"Problems to be Solved by the Invention" The purpose of the present invention is to eliminate the various drawbacks of the conventional optical element molding techniques described above, improve the molding speed while maintaining a predetermined molding accuracy, and An object of the present invention is to provide a novel optical element molding method that improves the life of the mold.

"Means for Solving the Problems" The structure of the optical element molding method of the present invention that achieves the above object has a low constant temperature below a temperature equivalent to 1014.5 poise (viscosity), a weight-adjusted surface A preformed glass gob that has been given smoothness is heated continuously to bring the surface of the glass gob to a predetermined temperature equivalent to 108 to 104.5 poise (viscosity), and the inside to a temperature that is higher in viscosity than the surface. 1014.5
After reaching a predetermined temperature equivalent to ~109 poise (viscosity) to create a temperature gradient between the surface and interior of the glass gob, press this glass gob with a mold that is maintained at a predetermined temperature below the glass transition point. It lies in shaping.

In addition, the temperature of the above-mentioned surface part is 107.5~lO4°5
It is more desirable that the temperature is equivalent to poise.

"Example" Hereinafter, as a preferred example of the method for molding an optical element according to the present invention, lead silicate glass [transition point (viscosity 1013°
4 poise), 425°C1 yield point (viscosity 1012~10
11 poise) and 475° C.] will be described with reference to the drawings.

As shown in Figure 1(a), a glass disc (1) (dotted line), which is at room temperature and has been preformed, that is, its weight has been adjusted and smoothness has been imparted to its main surface, is coated with a poron nitride mold release agent. It is placed on the coated support member (2). This glass disk (1) is heated using an infrared concentrated heating device (not shown).
The glass disk (1) is heated rapidly so as to continuously raise the temperature so that the surface layer reaches 675° C., which is equivalent to 106·3 poise. This temperature is measured with an infrared radiation thermometer (not shown). Also, at this point, the inside of the disk (1) is 101
The temperature has reached 475°C, which is equivalent to 1°5 poise.

This internal temperature can be determined empirically by embedding a thermocouple thermometer in the center of a glass disk of the same shape and measuring the internal temperature when the surface layer reaches a predetermined temperature under the same heating conditions. can be known. As a result of this rapid heating, the shape of one periphery of the glass disk (1) is softened and rounded, as shown by the solid line. Next, as shown in FIG. 1(b), the glass disk (1) on the support member (2) is precision polished to form a FiG'5rrs#bI--bxs type G,1
l-19・-I-4r 1. Dream-1,-...1A^G"
If+/-+1 quickly transfer the glass disk between a pair of heated upper molds (3) and lower molds (4), and immediately move these molds to remove excess glass from the mold. 1. Using a mold spacing regulating device (not shown), the molds are pressed to a predetermined distance between the molds, and then the press is stopped.

During this pressing, especially at the beginning, the temperature of the surface of the glass gob drops rapidly due to heat transfer to the mold, and the temperature of the surface of the mold temporarily rises, but the temperature inside the glass gob and of the mold remains constant. Because the temperature is relatively low, both the molded glass gob and the mold can reach an almost uniform temperature below the glass transition point in a short time, and during this time, the transfer of the mold surface shape to the glass molding surface is rapidly completed. , the shaped glass article can be immediately removed from the mold and annealed.

In this example, in the case of 5 cranes and turtles, the center wall thickness of the lens is 15
Pressing can be completed in seconds, but in the conventional molding method described above, a glass gob with a large amount of heat is pressed at an even temperature using a mold held at a high temperature, so it is necessary to soak the mold and the glass gob and to release the glass gob from the mold. It takes 2 to 3 times or more time to take out the molded product, so in order to obtain the specified quantity of molded products,
The number of molds used also increases. In addition, under the high temperature conditions of the conventional method, the mold is quickly damaged by oxidation, so it is necessary to adjust the atmosphere to make it non-oxidizing, but in this example, this kind of atmosphere adjustment is not necessarily required. The temperature of the mold only needs to be controlled to a constant temperature below the transition point, and there is no need to control the temperature cycle up and down for each press, so the operation is easy.

"Effects of the Invention" As mentioned above, the press molding method for an optical element of the present invention has the following effects:
Compared to the conventional method, the preformed glass gob is heated continuously to form a temperature gradient corresponding to a predetermined viscosity on the surface and inside, and then press-formed using a mold with a temperature below the transition point. , it is possible to improve the molding speed while maintaining a predetermined accuracy, and also to prevent damage to the mold. moreover,
The temperature control operation of the mold is simple, and the number of molds used can be reduced.

In addition, heating methods other than the heating step of the glass gob in the method of the present invention, for example, after heating and holding the glass gob at a predetermined temperature between the glass transition point and the yield point, only the outer surface portion is further heated to a fluid state. If the glass gob is thin, it is difficult to form the desired temperature gradient between the surface and the inside.However, in the method of the present invention, since the above heating step is adopted, Since it is possible to easily form a desired temperature gradient even in a relatively thin glass lump of about 2, it is possible to easily mold an optical element with a wide shape.

The method of the present invention is not limited to the above-mentioned embodiments, and various changes can be made without departing from the basic concept thereof.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the method of the present invention.

Claims (1)

[Claims] (1) 10^1^4^. A preformed glass gob with a temperature below the equivalent of ^5 poise (viscosity) is heated continuously, and the surface and inside of this glass gob are heated to a temperature of 10
＾9〜10＾4＾. ^5 poise (viscosity) and 10^1
^4^. After reaching a predetermined temperature equivalent to ^5 to 10^9 poise (viscosity) and creating a temperature gradient between the surface and the inside of the glass gob, the glass gob is heated to a predetermined temperature below the transition point of the glass. A press-molding method for an optical element, characterized by pressing with a mold.