JP3131472B2 - Optical element and method for molding optical element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical element and a method for molding an optical element.

[0002]

2. Description of the Related Art Conventionally, as a method for obtaining an optical element by heating and softening a glass material and then pressing the glass material with a molding die, there is, for example, the invention described in Japanese Patent Application Laid-Open No. 2-133325.

[0003] In the above invention, when the glass material is heated and softened, the preform is heated so that the thin portion is heated to a higher temperature than the thick portion, and then molded, so that the temperature difference inside the preform during molding is reduced. However, this is a molding method for preventing reversal deterioration due to sink marks caused by uneven shrinkage in a cooling process.

[0004]

However, in the invention described in JP-A-2-133325, a temperature distribution must be forcibly applied to the preform when the preform is heated and softened. The heating method becomes complicated. Also, it is difficult to give a strict temperature distribution to the preform. Further, although it is possible to some extent in a large-diameter optical element, it is difficult to provide a temperature distribution in a small-diameter optical element.

Accordingly, the present invention has been developed in view of the above-mentioned problems in the prior art, and has as its object to provide an optical element which does not cause reversal deterioration due to sink and a method of molding the optical element.

[0006]

According to the present invention, there is provided a method for molding an optical element using a mold having an optically functional surface and a non-optically functional surface, the method comprising the steps of: By molding using a mold having a large surface roughness of the non-optical function surface, the contact area between the non-optical function surface and the optical element is made smaller than the contact area between the optical function surface and the optical element, This is a method of performing molding while slowing down the cooling speed of the contact portion between the non-optical function surface and the optical element.

Therefore, in an optical element pressed by a molding surface having a different surface roughness, the non-optical function surface has a sink mark, and the surface accuracy of the non-optical function surface is lower than the surface accuracy of the optical function surface.

[0008]

According to the present invention, since the cooling rate of the non-optical function surface is lower than that of the optical function surface of the optical element during pressing, the temperature of the non-optical function surface becomes higher than that of the optical function surface, and the heat in the optical element becomes higher. The sinks generated when the pool shrinks are concentrated on the high-temperature portion, that is, the non-optically functional surface having a low viscosity, thereby preventing the sinks on the optically functional surface.

Reference Example First, before describing a specific embodiment of the present invention, an outline of the present invention will be described. An overview of the present invention is to mold a glass optical element using a mold having a molding surface composed of an optically functional surface and a non-optically functional surface, while molding at a lower cooling rate of the non-optically functional surface than the optically functional surface. How to do. That is, when a preform is heated and softened and pressed with a mold heated to a temperature lower than that of the preform, the cooling rate during the pressing of the non-optically functional surface of the optical element is lower than that of the optically functional surface. Alternatively, it is a method in which the temperature of the non-optical function surface is higher than that of the optical function surface in the mold. Therefore, the optical element of the present invention in which the molding surface is molded using a mold including an optically functional surface and a non-optically functional surface has sink marks due to shrinkage during press molding on the non-optically functional surface of the molded surface. It is characterized by the following. In the summary of the present invention, since the cooling rate of the non-optical function surface is lower than that of the optical function surface of the optical element during pressing, the temperature of the non-optical function surface becomes higher than that of the optical function surface, and the heat pool in the optical element The sinks generated when shrinks are concentrated on the high-temperature portion, that is, the low-viscosity non-optical function surface, so that the occurrence of the sink on the optical function surface can be prevented.
1 and 2 are longitudinal sectional views showing the upper and lower molds used in the reference example.

Reference numeral 1 denotes a lower die, and an upper die 2 is disposed above the lower die 1 on the same axis. The upper mold 2 includes an upper mold 4 having an optical function surface 3 and an upper mold 6 having a non-optical function surface 5. The upper mold 6 is slidably fitted to the upper mold 4 so that the upper mold 4 can be pressed integrally with the upper mold 4 at the time of pressing and can slide in the axial direction during the pressing.

In the molding using the upper and lower dies 2 and 1 having the above-described configuration, first, the lower die 1 and the upper die 2 are heated to 550.degree. Next, the glass preform 8 held on the plate 7 is
After heating to 0 ° C., the glass preform 8 is interposed between the lower mold 1 and the upper mold 2 and
Press molding with Kgf (see Fig. 1).

After the glass preform 8 is formed into a desired optical element shape, the temperature of the non-optical function surface 9 of the glass preform 8 is reduced while maintaining the pressing of the upper mold 4 having the optical function surface 3. In order to raise the height, only the upper mold 6 is slid upward during the pressing to
Was exposed to a molding atmosphere gas (see FIG. 2).

[0013] The above-mentioned molding method uses the glass preform 8
Since the cooling speed of the non-optical function surface 9 is lower than the cooling speed of the optical function surface 10 being cooled by the upper mold 4, the viscosity of the non-optical function surface 9 is lower than the viscosity of the optical function surface 10; The sink due to shrinkage of the ball 11 is the non-optical function surface 9
Concentrated on.

As a result of actual molding, the surface accuracy of the optical function surface 10 of the optical element molded by the upper mold 4 is 0.1 μm in PV value, and that of the lower mold is 0.1 μm, which is within the design standard. Was. For reference, when the surface accuracy of the non-optical function surface 9 was measured, the PV value was 6 μm.

On the other hand, when the upper die 6 is formed integrally with the upper die 4 without sliding upward during pressing, the surface accuracy of the optical functional surfaces formed by the lower die 1 and the upper die 2 is both The PV value was 3 to 5 μm, which was outside the design standard.

According to the reference example, it is possible to obtain an optical element having excellent surface accuracy of the optical function surface.

[0017]

[Embodiment 1] FIG. 3 is a vertical sectional view of a vertical die used in the present embodiment.

Reference numeral 21 denotes a lower mold. The lower mold 21 has an entire molding surface formed on the optical function surface 22. An upper die 23 has an optical function surface 24 on a molding surface and a non-optical function surface 25 on an outer periphery thereof. The surface roughness of the optical function surface 24 of the upper die 23 is processed to Rmax = 0.03 μm, and the surface roughness of the non-optical function surface 25 is processed to Rmax = 0.2 μm.

The molding using the upper and lower dies 23, 21 having the above-described structure is performed on the non-optical function surface 2 having a large surface roughness of the molding surface.
5 is an optically functional surface 24 having a small surface roughness during molding.
On the other hand, a gap is formed between the molding surface and the optical element and the contact area is small, so that a kind of heat insulating effect is produced. As a result, the cooling speed of the optical element in contact with the non-optical function surface 25 is lower than that of the optical function surface 24, and becomes relatively high.

First, the upper and lower dies 23 and 21 were heated to 550 ° C., and a preform of BK7 heated to 850 ° C. was press-formed. As shown in the graph of FIG. 4, the surface accuracy of the optical function surface of the molded optical element was 0.38 μm in PV value, which was within the design standard. Further, as shown in FIG. 5, the surface accuracy of the non-optical function surface was 3.5 μm in the PV value, causing sink marks. Further, as shown in FIG. 6, the surface accuracy of the optical element was Rmax = 0.3 μm.

According to the present embodiment, it is possible to obtain an optical element having excellent surface accuracy of the optical function surface.

[0022]

As described above, according to the method of molding an optical element according to the present invention, the cooling rate of the non-optically functional surface is made slower than that of the optically functional surface in glass molding,
Sinks due to shrinkage of the heat pool are concentrated on the non-optical function surface, and excellent transfer accuracy of the optical function surface can be secured. Therefore, a highly accurate optical element can be easily obtained.
Further, the optical element according to the present invention has high surface accuracy of the optical function surface.
High accuracy, thereby achieving high accuracy.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a reference example.

FIG. 2 is a longitudinal sectional view showing a reference example.

FIG. 3 is a vertical sectional view showing the first embodiment.

FIG. 4 is a graph of Example 1.

FIG. 5 is a graph of Example 1.

FIG. 6 is a graph of Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lower mold 2,4,6 Upper mold 3,10 Optical functional surface 5,9 Non-optical functional surface 7 Dish 8 Glass preform 11 Heat pool

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-157130 (JP, A) JP-A-62-226827 (JP, A) JP-A-63-107822 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C03B 11/08 C03B 11/12

Claims (2)

(57) [Claims] 1. A method for molding an optical element using a mold having an optically functional surface and a non-optically functional surface, wherein the surface of the non-optically functional surface has a greater surface roughness than the surface roughness of the optically functional surface. By molding using a mold with a large roughness, the contact area between the non-optical function surface and the optical element is made smaller than the contact area between the optical function surface and the optical element, and the non-optical function surface and the optical element Molding while reducing the cooling rate of the contact portion of the optical element. 2. An optical element which is pressed by molding surfaces having different surface roughnesses and has an optically functional surface and a non-optically functional surface on its molding surface, wherein the non-optically functional surface has a sink mark and the non-optically An optical element, wherein the surface accuracy of the functional surface is lower than the surface accuracy of the optical functional surface.