JPH05294650A - Mold for optical element and its production - Google Patents

Abstract

PURPOSE:To provide a mold designed to produce optical elements of good shape accuracy free from sink marks by making the respective porosities in the mold substrates constituting top force and bottom force differ from each other corresponding to the thin-wall part and thick-wall part of an optical element to be molded. CONSTITUTION:The respective porosities in the mold substrates constituting top force and bottom force corresponding to the thin-wall part and thick-wall part of an optical element to be molded. Specifically, the process is as follows: glass powder consisting mainly of SiO2 and also containing B2O3, Na2O and Al2O3 is melted to make a glass lump 3, which is then ground to a desired shape and immersed in an aqueous sulfuric acid solution 2 in a vessel 1 to dissolve the B2O3 and Na2O phases in the lump 3 into the solution, thus forming numerous pores in the lump. Thence, the resulting glass rod 3 is processed to make both top and bottom forces, and the porosity in a part corresponding to the thin-wall part of a molded product is made lower to effect higher thermal conductivity, while the porosity in a part corresponding to the thick-wall part is made higher to lower thermal conductivity, thereby narrowing the temperature distribution in the molded product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for press-molding an optical element and a method for manufacturing the mold.

[0002]

2. Description of the Related Art A technique for heating and softening a glass material to press-mold an optical element is known. It is important to accurately transfer the shape of the mold for pressure molding to the glass material, but when molding a molded product with a large difference in wall thickness, the difference in temperature distribution inside the glass material becomes large. However, a phenomenon called so-called sink occurs. In order to prevent such a phenomenon, as a conventional example, for example, Japanese Patent Laid-Open No. 1-14
There is an 8716 publication. The technique described in this publication is a technique in which the mold surface portion is divided into several members concentrically and the temperature is controlled independently of each other to make a difference in the glass cooling rate. The details will be described with reference to FIG.

FIG. 8 is a diagram shown in FIG.
It is a sectional view from the front showing the state of the molding die during molding. The pressing die 30 includes an upper molding die 31 and an upper molding die 31.
And a lower mold member 32 that is disposed so as to face the above. The lower die member 32 is composed of a split die 33 and a split die 34 that are concentrically split in the axial direction.
When the glass material 35 is press-molded by the pressing die 30 having the above structure, the temperature of each of the split dies 33 and 34 is controlled independently, so that a temperature difference is concentrically applied to the glass material 35. It is a technology of the configuration.

[0004]

In carrying out the molding method using the pressing mold described in the above publication, there is a problem that the temperature control means of the molding apparatus and the structure thereof are complicated and the cost is high. Further, there is a problem in that it is extremely difficult to manufacture a mold divided into concentric circles. That is, if a gap or a level difference is generated between the divided molds, there is a problem in that the glass bites into the mold and burrs are generated in the molded optical element.

Further, in order to make the above-mentioned gaps and steps small, it is necessary to form tolerances such as inner and outer diameters and cylindrical precision of the concentric portions to be combined with each other in extremely severe dimensions, which is extremely difficult. It is difficult to process. In particular, the heat-resistant material used as a mold for molding a glass optical element is a cemented carbide or various ceramics, and it is substantially difficult to process these difficult-to-cut materials with severe tolerances as described above. .. Even if the above-mentioned processing is possible, it is extremely difficult to combine them because the gaps between the respective members are very small, and the workability is poor. If there is, there is a risk that both members will be kogitte, and it is actually impossible to construct them by combining them without any gap.
Therefore, it is possible to mold with the mold of the method described in the above publication, although it is possible to use it even if a small amount of burr is generated, it is possible to mold the optical element or perform various processes after molding to significantly increase the cost. There is a restriction that the optical element is limited to the case where it can be.

The present invention has been made in view of the above problems, and is a mold for an optical element for molding a high quality optical element with a simple structure and an inexpensive molding die in which sink marks are prevented, and its manufacture. It is intended to provide a method.

[0007]

According to the present invention, there is provided a mold comprising an upper mold and a lower mold, which are provided in respective mold bases corresponding to the thin portion and the thick portion of an optical element to be molded. It is an optical element molding die having different ratios of pores.

[0008]

When the optical element molding die having the above structure is used for molding, the porosity changes and the thermal conductivity greatly changes. The thermal conductivity of gas is, for example, air = 0.
02w / m ・ k, graphite = 100w / m ・ k,
Since it is as small as 2 to 4 digits, the thermal conductivity is significantly reduced due to the presence of pores. That is, the larger the porosity, the smaller the thermal conductivity. Therefore, when molding an optical element, the porosity of the part corresponding to the thick part of the molded product is increased, and the porosity of the part corresponding to the thin part is decreased to reduce the temperature distribution inside the molded product. I tried to prevent. Based on the above concept, by using a method of etching a specific component of the mold base material or impregnating it with an impregnating agent, it is possible to produce a single structure with different porosities on the inner and outer circumferences, and with a simple structure. Moreover, molding can be manufactured at low cost, and by molding an optical element using the mold, a high-quality optical element without sink marks can be molded with high productivity.

[0009]

Embodiment 1 A specific example of the optical element molding die of the present invention and its manufacturing method will be described with reference to the drawings. 1 to 3 show manufacturing steps of a molding die of Example 1 relating to a method of manufacturing an optical element molding die of the present invention. FIG. 1 is a front sectional view showing a state in which a mold base material is immersed in a container filled with a solution. FIG. 2 is a sectional view from the front showing the step following FIG. FIG. 3 is a cross-sectional view from the front showing a main part in a state where the molding die manufactured according to this example is mounted on a molding machine.

To make a mold substrate, SiO ₂ 76 wt%,
_{B 2 O 3 13wt%, Na} 2 O6wt%, Al 2 O 3 4
Glass powder having a composition of wt% and other unavoidable impurities is put into a crucible, mixed and melted at 1100 ° C. for 1 hour, and then the crucible is tilted and the melted glass is put into a water tank and placed in water. A glass lump of indefinite shape is obtained by rapid cooling. Further, the quenched glass lump is heated to 510 in a heating furnace.
Heat treatment is performed at 100 ° C. for 100 hours to cause phase separation. Next, in order to form the glass gob into a desired size, it is sent to a grinding step and is ground. In this embodiment, for example, the round bar 3 having a diameter of 8 mm and a length of 20 mm is ground and formed.

The glass material (round bar) 3 formed by the above grinding step is put into a container 1 filled with H ₂ SO ₄ solution 2 as shown by an arrow in FIG. Soak. By this immersion, the B ₂ O ₃ phase and Na ₂ O phase contained in the glass gob 3 are eluted into the solution. When the cross section of the manufactured glass rod 3 manufactured by the elution method was cut in the radial direction, a large number of pores were formed from the outer periphery to a depth of about 3 mm. However, no pores were observed in the range of φ2 from the center (axial center). Further, when the central part and the outer peripheral part were cut out from the glass material 1 and the thermal conductivity was measured, the central part was 1.1.
It was 3 w / m · k and the outer peripheral portion was 0.77 w / m · k.

As shown in FIG. 2, one of the pair of glass rods 3 manufactured by the above method is sent to the grinding step to form a molding surface corresponding to the shape of the optical element molded on one glass rod 3. To be done. In this grinding step, first, the lower end portion 5 of the eluted glass gob 3 is cut into 5 mm, and a concave aspherical surface 6 of, for example, R10.3 is paraxially ground to the surface. The aspherical surface 6 that has been ground and polished is coated with a thin film of CrN, BN or the like having a high fusion preventing effect during the glass molding through an intermediate layer for strengthening the adhesive force, and the manufacturing of the molding die is completed. To do.

The structure of a molding apparatus for molding a plano-convex glass optical element using the molding die manufactured by the above method will be described with reference to FIG. The pair of molding dies 10 and 14 manufactured by the above-mentioned method respectively has base end portions 7 and 16 thereof.
Is fixedly mounted on the upper mold mount 11 and the lower mold mount 17 which are disposed so as to face the apparatus, with their molding surfaces facing each other. An upper die heater 13 for heating the upper die 10 is embedded in the upper die mount 11 on which the upper die 10 is mounted, and is fixedly mounted on the apparatus. Further, a lower die heater 18 for heating the lower die 14 is also embedded in the lower die mount 17 having the lower die 14 mounted thereon, and the lower die mount mounts and raises a glass material to be formed. , So that it can be moved up and down so as to come into contact with the upper mold 10 and be pressed.

That is, a glass material that has been heated and softened near the transition point of the glass molding material is conveyed between the upper mold 10 and the lower mold 14, and as the lower mold 14 rises, it abuts and presses against the upper mold 10. Molded. As a result of this press molding, an optical element having a good shape accuracy without sink marks was obtained. In addition, although an example in which the glass material is made porous to be used as a mold is shown in the present embodiment, the present embodiment is not limited to this, and even a heat resistant material such as ceramics can be used as the present embodiment. It has been found that similar results are obtained.

According to the above molding die and the method for producing the same,
By increasing the porosity of the outer peripheral part of the upper die, the cooling rate becomes slower as the thinner part (outer peripheral part) of the optical element to be molded, so that the thicker part (center part) of the molded product and the thinner part of the molded product. It is possible to suppress the difference in cooling rate between the parts (outer peripheral part), and it is possible to obtain an optical element without sink marks.

[0016]

[Embodiment 2] Embodiment 2 of an optical element molding die and its manufacturing method of the present invention will be described with reference to FIGS. Figure 4
It is sectional drawing from the front which shows the manufacturing process of Example 2 regarding the optical element shaping | molding die of this invention, and its manufacturing method. Figure 5
FIG. 5 is a cross-sectional view from the front of the optical element molding die manufactured according to Example 2. In the drawings of the present embodiment, the same members, the same shapes, the same configurations and the same methods as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this example, the elements of the glass substrate described in Example 1 above were melted and cooled to obtain a glass lump of indefinite shape, and the glass lump was heated at a temperature of 510 ° C. for 100 ° C. The steps of heat-treating for a period of time to cause phase separation in the glass gob and the steps of grinding this glass gob to a desired size in the grinding step to obtain a glass round bar are the same and therefore omitted.

As shown in FIG. 4, a hole 21 of φ2 is formed from the center position of the upper end surface of the glass rod 20 to a depth of 15 mm, for example, and the H ₂ So ₄ solution 22 is injected into the hole 21. Then, the glass round bar 20 filled with the solution 22 is filled with 100
Store in a box (not shown) kept at ℃ and leave it for 240 hours. B ₂ O in the glass rod 20 is left in this state.
_{The 3} phase and the Na ₂ O phase are eluted in the solution 22. Due to this elution, the porosity in the vicinity of the central portion (axial center portion) in the glass rod 20 becomes large, and the glass rod 2 having the porosity OVo1% is formed on the outer peripheral portion. The above glass round bar 20 is shown in FIG.
As shown in FIG. 5, the lower end surface is ground and polished into a convex aspherical surface 23 of paraxial R12.1. The subsequent steps are the same as those in the first embodiment and will not be described.

[0019]

Third Embodiment A third embodiment of the optical element molding die and method of manufacturing the same according to the present invention will be described with reference to FIGS. 6 and 7. Figure 6
It is sectional drawing from the front which shows the manufacturing process of Example 3 regarding the optical element shaping | molding die of this invention, and its manufacturing method. Figure 7
7 is a sectional view from the front showing an optical element molding die manufactured according to Example 3. FIG. In the drawings of the present embodiment, the same members, shapes and configurations as those of the first and second embodiments are designated by the same reference numerals and the description thereof will be omitted. Further, the description of the same method will be omitted as well.

In FIG. 6, a cylindrical member indicated by reference numeral 24 is obtained by grinding a base material made of an Al ₂ O ₃ sintered body having a desired shape. For example, φ11 is ground to a length of 20 mm. This grinding-processed sintered base material 24
To SiO ₂ 69%, B ₂ O ₃ 10%, Na ₂ O 9%,
FIG. 6 shows a state in which the glass is melted by suspending it in the melting vessel 1 filled with the glass melt 25 consisting of K ₂ O 8% and BaO 3% and non-evading impurities. The glass melt 25 in which the sintering base material 24 has been dipped is always kept at 1500 ° C., and the glass melt 25 is dipped in this glass melt 25 for 2 hours, so that the glass melt 25 is melted as shown by the arrow in FIG. , Penetrates into the sintered base material 24. Penetrated glass melt 2
5 and Al ₂ O ₃ in the sintered base material 24 are fused and completely integrated to form a glass round bar 27. The integrated glass round bar 27 is again ground into a φ11 length 20 mm shape.

Glass round bar 2 manufactured by the above-mentioned embodiment
Looking at the cross-sectional shape of No. 7, the porosity was 3% in the outer peripheral portion and 24% in the central portion, and the porosity gradually increased from the outer peripheral to the center. Further, the thermal conductivity of the central part is 10 w / m. k, 18 w / m at the outermost periphery. It was k.
One end surface (upper end surface of reference numeral 27) of the glass round bar 27 manufactured by the above method was ground into a convex spherical surface 28 of R20.9. Further, when a thin film of CrN, BN or the like was laminated on the upper surface of the convex spherical surface 28 and a glass optical element was molded by a molding apparatus, an optical element with good shape accuracy without sink marks could be obtained.

[0022]

According to the present invention having the above structure and method,
The molding die corresponding to the shape of the optical element to be molded can be manufactured at a low cost by a simple method. Therefore, the optical element molded by the molding die has high quality with no sink mark and good cost performance. In addition, various effects such as molding with high productivity can be achieved.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a manufacturing process of a molding die of Example 1 according to a method for manufacturing an optical element molding die of the present invention.

FIG. 2 is a sectional view from the front showing the manufacturing process following FIG.

FIG. 3 is a cross-sectional view from the front showing a main part in a state where the molding die manufactured according to Example 1 is mounted on a molding device.

FIG. 4 is a sectional view from the front showing the manufacturing process of Example 2 relating to the optical element molding die of the present invention and the manufacturing method thereof.

5 is a front sectional view showing an optical element molding die manufactured in Example 2. FIG.

FIG. 6 is a front sectional view showing a manufacturing process of Example 3 relating to the optical element molding die and the manufacturing method thereof according to the present invention.

FIG. 7 is a cross-sectional front view showing an optical element molding die manufactured according to a third embodiment.

FIG. 8 is a sectional view from the front showing a main part of a conventional optical element in a molding state by a molding die.

[Explanation of symbols]

1 container 2 H ₂ So ₄ solution 3, 20, 27 glass rod _4, 26 arrow 5 lower end 6, 23, 28 aspherical surface 7 upper end 8 lower end 11 upper die mount 13 upper die heater 14 lower die 15 upper end surface 16 Bottom surface 17 Lower mount 18 Lower heater 21 Hole 22 H ₂ So ₄ solution 24 Al ₂ O ₃ sintering base material 25 Glass solution

Claims (3)

[Claims] 1. A forming die comprising an upper die and a lower die, wherein the ratio of pores provided in each of the die substrates is made to correspond to the thin portion and the thick portion of the optical element to be formed. Characteristic optical element molding die. 2. A method for producing a mold comprising an upper mold and a lower mold, wherein a specific component contained in the mold base material is selected in accordance with the shape of an optical element to be molded, and its porosity is adjusted by etching. A method for manufacturing an optical element molding die, which is formed by changing the shape. 3. A method for producing a mold comprising an upper mold and a lower mold, wherein the base material is impregnated with an impregnating agent in accordance with the shape of an optical element to be molded in the mold base material. A method for manufacturing an optical element molding die, which is formed by fusing with a sintered body and changing the porosity.