JPH051218B2 - - Google Patents

Description

Detailed Description of the Invention "Industrial Application Field" The present invention involves pressing a heated glass gob,
A novel method for directly molding optical elements.

"Prior art" In obtaining various optical elements made of glass,
A method has been used to obtain a press-molded product by pressing a glass gob with the molding surfaces of a pair of molds, but according to this conventional method, it is difficult to achieve the desired surface precision of the optical surface by press-molding alone. Since surface performance and dimensional accuracy including wall thickness cannot be obtained, complicated post-processes such as rough sanding and precision polishing are required, and the time and effort involved are immeasurable.

Therefore, technologies that can omit the above-mentioned post-processes have been proposed and are being put into practice, but the general final molded products require that the surface performance of the optical surface, that is, the surface roughness, be within ±0.02 μm, and the surface accuracy It is desirable that the irregularity is within λ/2 and the thickness accuracy is within about ±50 μm with six Newton rings or less.

In order to meet the above requirements, it is necessary to measure the glass gob that takes into account the appropriate surplus amount of the glass gob to be pressed, its dimensions, shape, surface condition, temperature distribution within the glass gob just before pressing, support method for the glass gob, and molding surface of the mold. Dimensional design that takes into account the material, surface performance and surface accuracy of the molded product, shrinkage and deformation after molding, temperature of the mold, timing of contact and adhesion of the mold to the glass lump, press pressure by the mold, and the shape of the formed glass in the mold. Much effort is required regarding retention time, 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, techniques such as pressing a softened glass gob using a mold heated to a high temperature above the glass transition point until the glass gob reaches the transition point or below have been developed. However, all of these methods require a large amount of molding time, are complicated to control the temperature cycle of the mold, and have the disadvantage of easily causing damage to the mold.

"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 is to mold a preformed glass gob whose weight has been adjusted and surface smoothness has been adjusted to 10 ¹⁵ to 10 ¹⁰ poise (viscosity )
After heating to an equivalent predetermined temperature and then rapidly heating only the surface portion of this glass gob to a temperature equivalent to 10 ⁹ to ^{10 4.5} poise (viscosity) to create a temperature gradient between the inside and surface of the glass gob. , the glass gob is press-molded in a mold held at a predetermined temperature below the glass transition point.

Note that the temperature of the surface portion is preferably 10 ^7.5 to 10 ^4.5 , which is equivalent to poise.

"Example" Hereinafter, a method for molding an optical element according to the present invention will be described using lead silicate glass [transition point (viscosity: ^10-13.4 poise);
425℃, softening point (viscosity 10 ¹² to 10 ¹¹ poise); 475℃]
The case of molding a meniscus lens using the following will be explained with reference to the drawings.

As seen in Figure 1a, a glass disk 1 (dotted line), which has been preformed, that is, its weight has been adjusted and smoothed on its major surface, is placed on a hollow support member 2 coated with a boron nitride mold release agent. ing. First, after uniformly heating this glass disk 1 to 435°C, the surface layer portion of the glass disk 1 is heated to a temperature equivalent to 10 ^6.5 poise using a known rapid heating means (not shown), that is, an infrared concentrated heating device. Rapidly heat to 650℃.
By this rapid heating, the glass disk 1 on the support member 2 is precisely polished to have a predetermined aspherical shape, and the glass disk 1 is heated at 405°C as shown in the experiment.
The glass disk 1 is transferred between the upper mold 3 and the lower mold 4 which are heated evenly, and these molds are immediately moved.
is pressed while allowing the excess glass to protrude from between the molds, and a mold spacing regulating device (not shown) is used to allow the molds to reach a predetermined distance between the molds, and then the pressing is stopped.

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

In this example, if the center wall thickness of the lens is 10 mm, pressing can be completed in less than 1 minute, but in the earlier conventional molding method, a mold kept at high temperature was used to press a glass lump with a large amount of heat at a uniform temperature. In order to
It takes more than twice as long to soak the mold and the glass gob and to remove the glass gob from the mold, and the number of molds used also increases. Furthermore, 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. moreover,
In this embodiment, 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.

Note that the method of the present invention is not limited to the above embodiments, and various changes can be made based on the basics thereof.

"Effects of the Invention" As described above, in the press-molding method for an optical element of the present invention, a preformed glass gob whose entire outer periphery is heated to a higher temperature than its interior is press-molded using a mold having a temperature below the transition point. Therefore, molding speed can be increased while maintaining a predetermined accuracy, and damage to the mold can be prevented. Furthermore, the temperature control operation of the mold is simple and the number of molds used can be reduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the method of the present invention. In the figure, 1... glass lump, 2... support member, 3...
...Upper mold, 4...Lower mold, 5...Thermocouple.

Claims (1)

[Claims] 1 Heat the preformed glass gob to a predetermined temperature equivalent to 10 ¹⁵ to 10 ¹⁰ poise (viscosity), then heat the surface part of this glass gob to a temperature equivalent to 10 ⁹ to 10 ^4.5 poise (viscosity) to make the glass gob 1. A press-molding method for an optical element, which comprises applying a temperature gradient between the inside and the surface, and then pressing the glass gob with a mold heated to a predetermined temperature below the transition point of the glass.