JP3609867B2 - Optical element molding method and apparatus - Google Patents

Description

[0001]
【Technical field】
The present invention relates to a molding method and apparatus for molding an optical element material with a pair of upper and lower molds, and more particularly to a method and apparatus for facilitating removal of a molded product from the mold.
[0002]
[Prior art and problems]
In the conventional glass mold method, the heat-softened optical element material is press-molded, cooled, and then the upper mold or the lower mold is moved, and the molded optical element is picked up or taken out by a robot hand. ing. However, the molding optical element does not always adhere to a specific one of the open upper and lower molding dies. For this reason, the chucking or pinching jig of the robot hand cannot take out the molding optical element, and further, the jig may hit the mold surface without the optical element and damage the mold.
[0003]
As a countermeasure, Japanese Patent Application Laid-Open No. 5-43259 discloses that the position of a molded product is detected by a sensor, and when it is attached to the upper mold, it is further cooled and dropped onto the lower mold. It has been proposed to take out a molded article after detecting it. However, this requires a sensor and its circuit, which increases equipment costs.
[0004]
Japanese Patent Application Laid-Open No. 5-70154 proposes a method in which a temperature difference is provided between an upper mold and a lower mold, and the mold product is cooled to the temperature of the mold and then released. However, in this method, a temperature difference is generated between the upper and lower sides of the optical element, so that the shape of the molded product may be defective or distorted.
[0005]
OBJECT OF THE INVENTION
An object of this invention is to obtain the method and apparatus which can position the shaping | molding optical element after shaping | molding on a lower mold | die with high probability, without requiring a special apparatus and a sensor.
[0006]
SUMMARY OF THE INVENTION
The present invention has found the fact that when the contact area with the optical element material is different between the upper and lower molds, the mold with the larger contact area is more easily separated from the mold optical element than the mold with the smaller side. It was made.
[0007]
That is, the present invention provides an optical element in which an optical element material is sandwiched between upper and lower molds having different contact areas with the optical element material, and the optical element material is heat-softened and press-molded by the pair of molds. In the element molding method and apparatus, among the upper and lower molds, the mold having the larger contact area with the optical element material is disposed as the upper mold, and the thermal expansion coefficient α1 of the optical element material and the upper and lower molds The relationship of α1> α2 is established between the thermal expansion coefficient α2 and the upper and lower molds are both concave surfaces, and the curvature radii of the upper and lower molds are R1 and R2 (R2> R1). In this case, R2−R1> R1 · R2 / 100 is satisfied.
[0008]
Further, empirically, when the curvature radii of the upper and lower molds are R1 and R2 (R2> R1),
R2-R1> R1 / R2 / 100
When satisfying the above, more preferable results can be obtained.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to illustrated embodiments. FIG. 1 shows an optical element molding apparatus to which the present invention is applied. The apparatus includes an upper trunk mold 10 and a lower trunk mold 20, and a plurality (five in this embodiment) of the upper trunk mold 10 and the lower trunk mold 20 are associated with each other in the vertical position. Insertion fixing holes 11 and 21 of the optical element molding die are formed. The upper mold 12 and the lower mold 22 for optical element molding are inserted and fixed in the insertion fixing holes 11 and 21, respectively. The upper mold 12 has a flange 12a at its upper end, and the lower mold 22 has a flange 22a at its lower end. The flange 12 a is sandwiched and fixed between the upper end surface of the upper body mold 10 and the upper mold base 13, and the flange 22 a is connected to the lower end surface of the lower body mold 20 and the lower mold base via a spacer 24. 23 and is fixed between the two. The spacer 24 sets an interval between the upper mold 12 and the lower mold 22. The upper mold base 13 is connected to the lift cylinder rod 15, and the lower mold base 23 is connected to the lift cylinder rod 25.
[0010]
FIG. 2 shows a single shape of the lower mold 22. The base material of the lower mold 22 is made of, for example, cemented carbide tungsten carbide WC. After the molding surface is ground with an ultra-precision lathe, the surface roughness is further adjusted using a diamond abrasive, A platinum film 22b having a thickness of about 1 μm is formed by sputtering. The platinum film 22b improves the heat resistance, oxidation resistance, and wettability of the base material. The structure on the upper mold 12 side is the same.
[0011]
The molding surfaces of the upper and lower molding dies 12 and 22 are both concave in this embodiment, and their radii of curvature are different from each other. That is, the optical element (lens) to be molded is a biconvex lens having different curvature radii on the front and back sides. In the present invention, as shown in FIGS. 5 and 6, among the upper and lower molds, a mold having a large contact area with the molding optical material, that is, a mold having a smaller radius of curvature is used as the upper mold 12. It is characterized in that the lower mold 22 is a mold having a smaller area and a larger curvature radius.
[0012]
The apparatus having the above configuration molds an optical element (lens) as follows. With the upper body mold 10 and the lower body mold 20 opened as shown in FIG. 4, a preform (optical element material) 31 is placed on the platinum film 22 b of each lower mold 22, and the upper mold 12 is the preform 31. Lower the upper body mold 10 to a level where it does not come into contact with. Next, the quartz tube 32 and the heater 33 are lowered around the upper body mold 10 and the lower body mold 20. The quartz tube 32 forms a sealed chamber around the upper body mold 10 and the lower body mold 20. The quartz tube 32 is filled with nitrogen gas and heated by the heater 33. When the temperature of the lower body mold 20 reaches an appropriate temperature, the upper body mold 10 is further lowered with respect to the lower body mold 20 by the lifting cylinder rod 15. The temperatures of the upper body mold 10 and the lower body mold 20 are detected by a thermocouple 29.
[0013]
When the molding is finished, when the temperature becomes equal to or lower than the glass transition point, the nitrogen gas in the quartz tube 32 is removed, and the upper body mold 10 is raised by the elevating cylinder rod 15, so that the upper body mold 10 and the lower body mold 20. open.
[0014]
According to the present invention, at this time, the optical molded product 31M molded by the upper and lower molds 12 and 22 is always left on the lower mold 22 and does not adhere to the upper mold 12 side. The reason is inferred as follows. The optically molded product 31M immediately after molding and the upper and lower molding dies 12, 22 are attached with a slight force. The thermal expansion coefficient α1 of the preform 31 and the thermal expansion coefficient α2 of the upper and lower molds 12 and 22 have a relationship of α1> α2, and therefore, the shrinkage amount due to cooling after press molding is a molded product> It is a mold. In a glass mold lens, a large contact area between a mold and a molded product is synonymous with a small radius of curvature R, and the amount of shrinkage at the outer periphery of the optical element is large when the radius of curvature R is large and small. The one with a smaller radius of curvature R is larger. In other words, the tensile force toward the center of the molded optical element is large, and therefore it is easy to leave the mold. The broken line in FIG. 6 is an exaggerated drawing of the shape of the optical molded product 31M after shrinkage, and the shape change is larger on the upper mold 12 side with a smaller curvature radius R than on the lower mold 22 side. That is, in the optical molded product 31M, the tensile force F1 to the center of the optical molded product 31M generated on the upper mold 12 side is larger than the force F2 generated on the lower mold 22 side. Due to the difference in force, when the upper and lower molds are separated after molding, the molded product is separated from the upper mold 11 having a small curvature radius R and remains in the lower mold 22 having a large curvature radius R.
[0015]
Note that even if a mold having a large curvature radius R and a small contact area is used as the upper mold, the molded product does not always adhere to the upper mold. This is because the adhesion force between the mold having a large radius of curvature R and a small contact area and the molded product is not always so large as to overcome the weight of the molded product.
[0016]
A specific embodiment will be described.
The upper and lower molds 12 and 22 are both made of cemented carbide tungsten carbide WC (thermal expansion coefficient: 45 × 10 ⁻⁷ deg), the surface roughness of the molding surface is Rmax = 0.02 μm, and sputtering is performed thereon. Thus, a platinum film 12b having a thickness of 1 μm was formed. The radius of curvature R of the upper mold 12 was 17 mm paraxial, and the radius of curvature R of the lower mold 22 was 50 mm. As the preform 31, “VC78 glass” (thermal expansion coefficient; 95 × 10 ⁻⁷ deg, manufactured by Sumita Optical Glass Co., Ltd.) was used and molded at a molding temperature of 580 ° C. and a molding pressure of 100 kgf / cm ² . This molding was repeated 10,000 times. However, in all cases, the optical molded product 31M remained on the lower mold 22 side, and the optical molded product 31M had never adhered to the upper mold 12 side. The same was true when molding was performed under the same conditions using “PSK50 glass” (thermal expansion coefficient; 112 × 10 ⁻⁷ deg, manufactured by Sumita Optical Glass).
[0017]
As in the above-described embodiments, according to the present invention, the molded product can be left in the lower mold by using the mold having a large contact area and a small curvature radius R as the upper mold. Even if the difference in the contact area (curvature radius R) between the upper and lower molds is small, the molded product has a constant weight. Therefore, the molded product is always formed on the lower mold due to the synergistic effect of the weight and the release characteristics according to the present invention. You can expect to leave. However, in order to obtain a certain effect, when the curvature radii of the upper and lower molds are R1 and R2 (R2> R1),
R2-R1> R1 / R2 / 100
When this is satisfied, it is preferable to apply the present invention.
[0018]
【The invention's effect】
According to the present invention, the probability that the molded product after molding is left in the lower mold is the simple structure in which the mold having the larger contact area with the optical element molding material is the upper mold among the upper and lower molds. This can increase the workability of taking out the molded product.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a molding part of an optical element molding apparatus to which the present invention is applied.
FIG. 2 is a detailed longitudinal sectional view of a lower mold of the molding apparatus shown in FIG.
3 is a plan view of the lower body mold shown in FIG. 1. FIG.
FIG. 4 is a longitudinal sectional view of a molding state of the apparatus of FIG.
FIG. 5 is a longitudinal sectional view showing an example of arrangement of upper and lower molds according to the present invention.
6 is an enlarged view of a main part of FIG.
[Explanation of symbols]
12 Upper mold 22 Lower mold 31 Preform 31M Molded product

Claims (2)

In an optical element molding method in which an optical element material is sandwiched between upper and lower molds having different contact areas with the optical element material, the optical element material is heated and softened, and press-molded by the pair of molds.
Of the upper and lower molds, a mold having a larger contact area with the optical element material is molded as an upper mold,
The relationship of α1> α2 is established between the thermal expansion coefficient α1 of the optical element material and the thermal expansion coefficient α2 of the upper and lower molds.
The upper and lower molds are both concave, and
An optical element molding method characterized by satisfying R2-R1> R1 · R2 / 100, where R1 and R2 (R2> R1) are curvature radii of the upper and lower molds. In an optical element molding apparatus that sandwiches an optical element material between upper and lower molds having different contact areas with the optical element material, heat-softens the optical element material, and press-molds with the pair of molds.
Among the upper and lower molds, the mold on the side having a large contact area with the optical element material is arranged as an upper mold,
The relationship of α1> α2 is established between the thermal expansion coefficient α1 of the optical element material and the thermal expansion coefficient α2 of the upper and lower molds.
The upper and lower molds are both concave, and
An optical element molding apparatus characterized by satisfying R2-R1> R1 · R2 / 100, where R1 and R2 (R2> R1) are curvature radii of the upper and lower molding dies.

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