JP2000072456A - Optical element forming device and production of optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an optical element which is kept at a specified distance between optical function faces without the collapse of these optical function faces. SOLUTION: A spacing regulating member 12 is projected from a drum mold 13 for a lower die under a difference in coeffts. of thermal expansion by raising forming temp. and before a drum mold 14 for an upper die is brought into tight contact with the mold 13 for the lower die under a pressure by a press, the front surface of the spacing regulating member 12 is brought into tight contact with the drum mold 13 for the lower die. The spacing regulating member 12 is shrunk by gradually lowering the temp. down to 610 deg.C and the state, that the pressure by the press is applied on a glass blank 15, is attained. Further, the glass blank is taken out when the tamp. falls down to the temp. allowing the take-out. The optical element is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element molding apparatus for forming a high-precision optical element represented by an aspherical lens by press molding.

[0002]

2. Description of the Related Art In recent years, as a method of manufacturing a high-precision aspherical lens or a specially shaped optical element (such as a prism or a fly-eye lens), a method of manufacturing by press molding without requiring a polishing step has been used. . As a result, complicated steps conventionally performed in the manufacture of optical elements are omitted, and the same shape can be manufactured in large quantities at low cost.

An example of a conventional optical element molding method will be described below. FIG. 1 is a schematic diagram showing a state in which a glass material in a ball shape is formed into a biconvex shape using an optical element molding die. 1 is the upper die, 2 is the lower die, 3
Is an upper molding die, 4 is a lower molding die, 5 is a ball-shaped glass material, 6 is a press shaft, and 7 is a plate for connecting the body dies 1 and 2 to the press shaft 6. The glass material 5 polished on both sides is placed between the upper mold 3 and the lower mold 4, and the inside of the molding apparatus is replaced with a nitrogen gas atmosphere so that the mold members and the like are not oxidized.
After the glass material 5 is heated to a temperature at which the glass material 5 can be deformed, the glass material 5 is pressed and molded with a press shaft 6 for an appropriate time and pressure to transfer the mold shape to the glass material 5. Then, it is cooled to a temperature sufficiently lower than the glass transition temperature, the press pressure is removed when the transferred molding surface shape is stabilized, the atmosphere is introduced at a temperature at which it can be taken out, the mold is opened, and the biconvex optical element is opened. It has gained.

In general, the performance of an optical element is determined not only by the shape of the optical functional surface but also by the distance between functional surfaces represented by the center thickness as an important factor. In the conventional method, a method of closely contacting the upper and lower body dies and a method of controlling the moving distance of the press shaft by software have been used for adjusting the pushing amount.

[0005]

However, in the above-mentioned conventional technique, the distance between the optically functional surfaces after molding is always constant, but the pressure applied to the glass material at the moment when the upper and lower body dies are brought into close contact with each other. Is the same as the state in which is removed. In other words, the optical element in this state in the early stage of molding undergoes a surface change due to viscous flow during the cooling process up to the glass transition temperature, causing the optical functional surface to lose its shape.

In software control of the press axis moving distance, it is necessary to take into account expansion and contraction of the entire apparatus due to changes in outside temperature, cooling water temperature, etc. due to the nature of the molding apparatus that repeats heating and cooling. It was not suitable for the required high-precision lens molding. The present invention has been made in view of such a problem, and an optical element molding apparatus capable of maintaining a constant distance between optical function surfaces without disturbing the shape of the optical function surface, and an optical element manufacturing device using the same. The aim is to provide a method.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a mold structure for press-molding an optical material that has been heated and softened by using upper and lower dies, so that the distance between optical functional surfaces after molding is constant. In this case, a space adjusting member for making the optical material has a thermal expansion coefficient of α1 at the molding temperature, a thermal expansion coefficient of the molding die of α2 at the molding temperature, and a heat The expansion coefficient is α3, the thermal expansion coefficient of the gap adjusting member is α4, the maximum thickness of the optical element is h1, the total height of the upper and lower molding dies at the position where the optical element takes the maximum thickness is h2, and the total height of the upper and lower molds is h3. Then, the height of the gap adjusting member> (h1.times..alpha.1 + h2.times..alpha.2-h3.times..alpha.3) /. Alpha.4... (A) is provided.

In the present invention, the distance between the optically functional surfaces can be kept constant by first receiving a load by the spacing adjusting member during molding. Further, by using the interval adjusting member having a length suitable for the condition (a), the interval adjusting member shrinks more than the sum of the heat shrinkage of the molding die and the glass material during cooling. Pressure is always applied to the material, and the problem of deterioration of the optical function surface shape due to viscous flow is eliminated.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The thermal expansion coefficients of the materials used in the present embodiment are shown in Table 1 below, and an optical element molding apparatus and a molding method will be described based on examples with reference to the drawings. To go.

[0010]

[Table 1]

FIGS. 2 and 3 are cross-sectional views of the cemented carbide mold used in the present embodiment. FIG. 4 is a schematic view of a heavy crown optical glass element 150 produced according to the present embodiment. FIG. 5 is a sectional view of the chromium carbonaceous ceramic spacing adjusting member 12 used in the present embodiment. First, the lower molding die 1
As shown in FIG. 6, the upper mold 11 and the gap adjusting member 12 are disposed in a lower mold body 13 (height 25 mm) 13 and an upper mold body 20 (height 20 mm) 14 as shown in FIG. Set up. At this time, three space adjusting members 12 are arranged at equal intervals at a position 10 mm outside the outer periphery of the lower mold 10. At this time, the height of the gap adjusting member 12 is calculated based on the E position where the thickness of the glass element is the largest.

[0012]

(Equation 1)

It is apparent that the height 25 mm of the gap adjusting member 12 satisfies the expression (a). Subsequently, the plano-convex glass blank 15 polished on both sides is placed in the lower mold body 13 so as to be sandwiched between the lower mold 10 and the upper mold 11. The molding surfaces of the upper mold 10 and the lower mold 11 are mirror-finished into a shape of curvature R30 and R50 by grinding and polishing.
The molding surface is coated with a platinum-iridium alloy to a thickness of 2 μm by an ion plating method.
The glass blank 15, the upper and lower molds 10, 11, the upper and lower body dies 13, 14, and the space adjusting member 12 are fixed to a press shaft 16 via a plate 18 with bolts (not shown).

[0014] The nitrogen gas is replaced until the oxygen concentration inside the molding apparatus becomes 10 ppm or less. Next, it is heated to a molding temperature of 720 degrees by an infrared lamp 17 surrounding the periphery. Three
This temperature is maintained for one minute, so as to equalize the temperature of the mold and the glass material. At this time, the height of the gap adjusting member 12 is increased by thermal expansion, and the tip of the gap adjusting member 12 is slightly (for example, 0.
12mm) It is in a protruding position. Then, press shaft 16
The upper surface of the gap adjusting member 12 and the upper mold die 14
The glass blank 15 at a pressure of 1 t until the
Is formed.

In the final stage in which the lens shape is substantially formed by pressing, the pressure of 1 t is all received by the spacing adjusting member 12 to substantially determine the center thickness of the glass blank 15. After reaching the close contact position, the temperature is cooled to 610 degrees while controlling the temperature at 0.3 degrees / sec. During this time, since the heat shrinkage of the gap adjusting member 12 always exceeds the heat shrinkage of the glass blank 15 and the molding dies 10, 11, an appropriate force is continuously applied to the optical function surface to prevent the surface change due to viscous flow. Can be done. The pressure is released at 610 ° C., and when the temperature reaches a temperature at which it can be taken out, air is introduced into the molding apparatus, and the mold is opened. Thus, an optical element as shown in FIG. 3 is completed. As a result of measuring the optical element 150 formed in this way, it was found that the functional surface shape did not collapse and the variation in the center thickness was kept within 3 microns.

Although the mold shown in the embodiment has both concave and convex shapes, the mold may have a planar shape or a biconcave shape as long as it satisfies the optical performance. Absent. Further, the shape of the optical element material is not limited to the plano-convex shape, and it is also possible to use an approximate spherical surface, a ball, or the like, and it is needless to say that the type of the optical element material can be appropriately changed depending on the application. In addition, the spacing adjusting member used in the present embodiment is configured to receive a load by three chromium carbide ceramic pins. However, the spacing adjusting member may be a material that can maintain the parallelism of the upper and lower body molds and withstand the molding pressure. The number and form are not limited.

For comparison, a conventional mold having no interval adjusting member was prepared and a similar molding experiment was performed. In the conventional type mold, the shape of the optical function surface is broken due to the body-type close contact method, and about half of the molded product cannot be used. For it,
In the mold according to the present invention, all molded products can be used because the functional surface shape does not collapse. In addition, in the conventional mold, the functional surface shape collapse hardly occurred by software control of the press axis moving distance, but the variation in the center thickness widened to 100 microns. , I needed to adjust the spacing. On the other hand, according to the mold according to the present invention, since the variation width of the center thickness is within 3 μm, it is not necessary to adjust the interval.
On the other hand, according to the mold according to the present invention, since the variation width of the center thickness is within 3 μm, it is not necessary to adjust the interval.

[0018]

As described above, according to the present invention, even if there is a molding timing shift due to a variation in the weight of the material, the center thickness can be suppressed to a width of several microns without breaking the optical function surface shape. Therefore, there is an effect that high-precision optical elements can be stably mass-produced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a conventional optical element molding die.

FIG. 2 is a sectional view of a mold for molding an optical element of the present invention.

FIG. 3 is a sectional view of a mold for molding an optical element according to the present invention.

FIG. 4 is an optical element formed according to the present invention.

FIG. 5 is a sectional view of a gap adjusting member used in the present invention.

FIG. 6 is a schematic view of the device of the present invention.

[Explanation of symbols]

1: Upper die mold 2: Lower die mold 3: Upper mold 4:
Lower forming die 5: Optical element 6: Press shaft 7: Plate 10: Lower forming die 11: Upper forming die 12: Interval adjusting member 13: Lower die body die 14: Upper die trunk die 15: Glass blank 16: Press Axis 17: Infrared lamp 18: Plate 150: Optical element

Continued on the front page (72) Inventor Mitsumasa Negishi 3-2-3 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation

Claims (3)

[Claims] 1. An optical element molding apparatus for press-molding an optical material heated and softened by polishing upper and lower molds,
An optical element molding apparatus, wherein an interval adjusting member for keeping a distance between optical functional surfaces after molding is arranged in a mold structure. 2. The method according to claim 1, wherein the thermal expansion coefficient of the optical material at the molding temperature is α1, and the thermal expansion coefficient of the molding die is α1.
2. The coefficient of thermal expansion of the body member is α3, the coefficient of thermal expansion of the gap adjusting member is α4, the maximum thickness of the optical element is h1, and the total height of the upper and lower molding dies at the position where the optical element takes the maximum thickness is h.
2. Further, when the total height of the upper and lower torso is defined as h3, the height of the gap adjusting member> (h1 × α1 + h2 × α2-h3
× α3) / α4. 3. A method for manufacturing an optical element using the molding apparatus according to claim 1.