JP3130610B2 - Optical element molding die and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In general, there is known a method of manufacturing a glass optical element by inserting a heated glass material between a pair of molding dies including an upper mold and a lower mold and press-molding the same.
Hitherto, many proposals have been made as molding dies for use in this manufacturing method. In particular, Japanese Patent Laid-Open Publication No.
No. 635 discloses this.

[0003] This mold for molding an optical element includes (1) a concave first mold.
A first mold having an optical surface of (1), (2) a second mold having a concave second optical surface, and (3) the first and second molds.
(4) for forming a press lens, wherein a concave portion is provided on an outer peripheral portion of a back surface of at least one of the optical surfaces of the first and second molding dies. A mold (applied to a convex lens and a convex meniscus lens), and (1) a first mold having a convex first optical surface; and (2) a convex second optical surface. Having a second
And (3) a barrel mold for guiding the first and second molding dies, and (4) a central portion of the back surface of at least one of the optical surfaces of the first and second molding dies. A press lens forming mold (applied to a concave lens and a concave meniscus lens), characterized in that a concave portion is provided in the press lens.

According to the optical element molding die having the above structure,
The heating stage in each step does not contact the concave portion of the molding die, heat transfer is suppressed, and it is possible to make it difficult for a temperature difference to occur inside the glass. Therefore, a highly accurate press lens can be manufactured.

[0005]

In the above-mentioned conventional mold for molding an optical element, a concave portion is provided on the back surface of the mold to form an air heat insulating layer, thereby suppressing heat transfer and reducing a temperature difference inside the lens. Less likely to occur. However, the movement speed of the amount of heat moving from the lens to the molding die is necessarily slow due to the presence of the air heat insulating layer, so that the pressurizing and cooling time becomes long, and there is a disadvantage that efficient molding cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to obtain a glass optical element having a good shape precision even when a relatively short pressurizing and cooling time is less likely to cause a temperature difference inside a lens. It is an object of the present invention to provide an optical element molding die capable of performing the above-mentioned.

[0007]

In order to achieve the above-mentioned object, the present invention provides a method for producing a product, in which the crystal orientation of the molding surface differs in the radial direction, and the region corresponding to the thick part of the product has the thinner thickness in the direction having large heat conduction. An area corresponding to the portion was selectively formed in an orientation having a small thermal conductivity to form an optical element molding die.

Further, the present invention provides a mold base made of a heat-resistant material, which is formed into a flat or concave surface, and then a hexagonal material is laminated so as to be oriented along the c-axis. Processing was performed to produce an optical element molding die.

Further, the present invention provides a mold base made of a heat-resistant material, which is formed into a concave or convex surface, and then a hexagonal material is laminated so as to be oriented along the c-axis. Processing was performed to produce an optical element molding die.

[0010]

According to some materials, the thermal conductivity differs greatly depending on the crystal orientation. Therefore, even if the molding surface is formed of the same material, the heat conduction can be freely controlled if the crystal orientation of the molding surface can be changed in the radial direction. As a material having such anisotropy of heat conduction, there is a material having a hexagonal crystal form. Generally, a material having a hexagonal crystal form exhibits anisotropy in the a-axis direction and the c-axis direction. For example, in the case of BN, the thermal conductivity is significantly different from about 0.17 cal / sec · cm · ° C. in the a-axis direction and about 0.02 cal / sec · cm · ° C. in the c-axis direction.

Therefore, as shown in FIG. 1, for example, a region (center portion) 3 of the molding surface 2 of the molding die 1 corresponding to the thick portion of the product is a-axis oriented, and the region (central portion) corresponding to the thin portion ( If the outer peripheral portion 4 is oriented along the c-axis, the cooling rate of the thin portion of the product can be relatively slowed, so that an optical element having good shape accuracy can be obtained by molding in a short time.

To control the orientation, there is a method of growing a single crystal while pulling up a molten material. However, as a simpler method, a film forming method such as a CVD method is suitable. According to this method, a hexagonal film oriented in the c-axis can be produced relatively easily. In order to manufacture a mold having a convex molding surface, FIGS.
As shown in (1), the mold bases 7, 8 of the molding dies 5, 6 are processed into flat or concave surfaces, and then films 9, 10 oriented in the c-axis are grown. Thereafter, when the molding surfaces 11 and 12 are processed into convex surfaces, heat is transmitted completely along the c-axis at the center of the mold, so that the thermal conductivity becomes lowest. Therefore, heat is transmitted along the middle direction between the center and the a-axis, so that the heat conductivity is higher than that in the central portion.

In order to manufacture a mold having a flat molding surface,
As shown in FIGS. 3 and 4, the mold bases 8, 14 of the molding dies 6, 13 are processed into concave or convex surfaces, and then films 10, 15 oriented in the c-axis are grown. Then, molding surface 1
When 2, 16 are machined into a plane, the center of the mold is completely c
Since heat is transmitted along the axis, the thermal conductivity is lowest, while heat is transmitted along the middle direction between the c-axis and the a-axis at the outer periphery of the mold, Also has a high thermal conductivity.

[0014]

EXAMPLE 1 As shown in FIGS. 5 and 6, two mold bases 17 and 18 made of isotropic graphite were prepared, and the tip portions corresponding to the molding base surfaces 19 and 20 were formed. ,
On the concave spherical surface of curvature R100, the other is outer diameter ф15, curvature R1
5 was processed into a concave spherical surface.

Next, BN films 21 and 22 were formed with a total thickness of 2.2 mm on the molding base surfaces 19 and 20 of the mold bases 17 and 18 by a thermal CVD method. The source gas is BCl
₃ and NH ₃ , pressure 5 torr, substrate temperature 1800
Prepared at ° C. FIG. 7 shows the result of examining the crystal state of the BN films 21 and 22 by the X-ray diffraction method. In FIG.
The horizontal axis represents the angle (2θ) between the center of the direct beam and the diffracted X-ray, and the vertical axis represents the X-ray intensity. The peak of the (002) plane of hexagonal BN is seen in addition to the peak of graphite as the substrate, but the peak of the other plane is hardly seen.
It was confirmed that the c-axis oriented BN films 21 and 22 were formed.

Next, the BN film 21 after the lower working to the curvature R100
(FIG. 5) is ground and polished to obtain R20.0
Twelve convex spherical surfaces were formed, and a molding surface 23 was formed. Also,
Curvature R15 with BN film 22 after lower processing (Fig. 6)
Was ground and polished to finish it into a flat surface to form a molding surface 24.

The molding die 25 manufactured as described above,
26 was set in a forming apparatus as shown in FIG. 8, and a plano-concave lens was formed. In FIG. 8, the molding dies 25, 26
Are slidably fitted in the body mold 27, and the
5 is used for the lower die, and the molding die 26 is used for the upper die. According to this molding apparatus, a lens with extremely good shape accuracy could be obtained in a short time.

[0018]

Embodiment 2 Molybdenum is used as a mold base material, AlBr ₃ , N ₂ , and H ₂ are used as source gases at a pressure of 1 torr.
r, an AlN film was formed at a substrate temperature of 900 ° C. by a CVD method. The pre-processing and post-processing of the mold base were exactly the same as in Example 1.

When a plano-concave lens was molded using the molding die manufactured as described above, a lens having extremely good shape accuracy could be obtained in a short time in the same manner as in Example 1.

[0020]

Embodiment 3 Unlike Embodiments 1 and 2, an example in which the orientation is controlled by sputtering will be described.

The molding surface of the mold substrate made of a cemented carbide has an outer diameter of Δ
It processed into the concave spherical surface of 11.8 and curvature R38.375. Next, on this molded surface, AlN was formed to a thickness of 1 μm by reactive RF sputtering using Al as a target and N ₂ and Ar as reactive gases. in this case,
When the pressure at the time of film formation is low, a film with little orientation (thermal conductivity is 0.21 cal / cm · sec · ° C.), and when the pressure at the time of film formation is high, a film that is strongly oriented along the c-axis. (A thermal conductivity of 0.13 cal / cm · sec · ° C.) is obtained. For example, assuming that the ratio of N ₂ to Ar is 3: 1 and the total pressure is 4
9 and 10 show X-ray diffraction patterns of the films formed at × 10 ⁻³ torr and 4 × 10 ⁻² torr. In both cases, the peak of AlN is clearly seen, but in FIG. 9, the crystal grows in various directions and is hardly oriented, whereas in FIG. 10, only the peak in the (002) plane appears strongly. , C-axis. Therefore, masking is performed on the area outside the center # 5 of the molding surface to form a film under the condition of a total pressure of 4 × 10 ⁻³ torr.
The central portion of the molding surface (the portion where the film was already attached) was masked, and a film was formed under the condition of a total pressure of 4 × 10 ⁻² torr.

In the molding die prepared as described above, the center portion corresponding to the thick portion of the product has relatively good heat conductivity, and the outer peripheral portion corresponding to the thin portion has poor heat conductivity. A good lens was produced efficiently in a short time.

According to this embodiment, since the film thickness is smaller than those of the first and second embodiments, the film formation time can be extremely short. In addition, since the mold is a mold for forming a convex lens, post-processing after film formation is not required, so that the manufacturing cost of the mold is reduced. On the other hand, the effect of preventing sink marks is slightly reduced because the film thickness is small and the difference in thermal conductivity between the center and the outer periphery is small.
A sufficient effect can be obtained depending on the lens shape.

[0024]

As described above, according to the present invention, the crystal direction of the molding surface of the mold is different in the radial direction, and the region corresponding to the thick portion of the glass product is oriented in the direction of large heat conduction and the thin portion is formed in the thin portion. Since the corresponding region is selected and formed in a direction with small heat conduction, the cooling speed of the thin glass part can be relatively delayed without delaying the cooling speed of the entire glass, and the shape accuracy can be reduced by molding in a short time. A good optical element can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing the concept of an optical element molding die of the present invention.

FIG. 2 is a front view illustrating a method of manufacturing an optical element molding die according to the present invention.

FIG. 3 is a front view showing the method for manufacturing the optical element molding die of the present invention.

FIG. 4 is a front view showing a method for manufacturing an optical element molding die of the present invention.

FIG. 5 is a front view illustrating the method for manufacturing the optical element molding die according to the first embodiment of the present invention.

FIG. 6 is a front view illustrating the method for manufacturing the optical element molding die according to the first embodiment of the present invention.

FIG. 7 is an X-ray diffraction diagram showing a crystal state of a BN film in the optical element molding die according to the first embodiment of the present invention.

FIG. 8 is a longitudinal sectional view of a main part of a molding apparatus using the optical element molding die according to the first embodiment of the present invention.

FIG. 9 is an X-ray diffraction diagram showing a crystal state of an AlN film when a film forming condition is set to 4 × 10 ⁻³ torr in the optical element molding die of Example 3 of the present invention.

FIG. 10 is an X-ray diffraction diagram showing a crystal state of an AlN film when a film forming condition is set to 4 × 10 ⁻² torr in an optical element molding die of Example 3 of the present invention.

[Explanation of symbols]

 1,5,6,13,25,26 Mold 2,11,12,16,23,24 Molding surface 3 Area corresponding to thick part 4 Area corresponding to thin part 7,8,14,17, 18 type substrate 9,10,15 film 21,22 BN film

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C03B 11/00

Claims (3)

(57) [Claims] 1. The crystal orientation of a molding surface differs in the radial direction, and a region corresponding to a thick portion of a product is selectively formed in a direction having a large thermal conductivity, and a region corresponding to a thin portion is formed in a direction having a small thermal conductivity. A mold for molding an optical element. 2. Forming a molding base of a heat-resistant material into a flat or concave surface, stacking hexagonal materials so as to be oriented along the c-axis, and then processing the molding surface into a convex surface. A method for producing a mold for molding an optical element, which is characterized by the following. 3. A method in which a molding surface of a mold base made of a heat-resistant material is processed into a concave surface or a convex surface, and then a hexagonal material is laminated so as to be oriented along the c-axis, and then the molding surface portion is processed into a flat surface. A method for producing a mold for molding an optical element, which is characterized by the following.