JP2002128532A - Devise and method for forming optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a devise and method that can stably produce an optical element having excellent thickness and surface accuracies with compact and easy constitution. SOLUTION: This device is comprised of a pair of upper and lower metal molds 1 and 2, the former having a flange part 7 that restricts movement of the mold, the latter supported/fixed to a bottom end, cylinder mold 3 containing the metal molds and a control member 4 surrounding the exterior of the cylinder mold with longer axial length, restricting approach/movement of the upper/lower metal molds by having bottom end supported/fixed and upper end contacting the flange. Shrinkage amount of the control member is not smaller than that of upper/lower metal molds and glass material 6 combined. Using this forming devise, a heated glass material that keeps a fixed temperature between upper/ lower metal molds is pressed by lowering the upper metal mold. After the lowering movement of the mold is restricted by the control member, the glass is cooled to form an optical element while keeping the pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical element molding apparatus.

[0002]

2. Description of the Related Art An apparatus for molding an optical glass element includes a body mold that slidably accommodates an upper mold having a flange formed on an upper part and a lower mold having a flange formed on a lower part. The device is common. In the apparatus having such a configuration, when at least one of the upper and lower molds is moved during molding, the flange portion of the moved mold is brought into contact with the upper end face or the lower end face of the body mold to thereby form the mold. The movement was regulated and the thickness of the molded product was regulated. However, when cooled after molding, the glass molded product shrinks slightly, and the surface of the molded product is released from the mold molding surface, so that the surface accuracy of the molded product is deteriorated.

Various devices have been proposed for obtaining an optical element having good thickness accuracy and surface accuracy. For example, JP-A-4-
No. 74727 discloses a configuration in which one or more through-holes are provided in a vertical direction in a body mold that slidably accommodates an upper and lower mold, a pin is arranged in the through-hole, and a driving means for the pin is further provided. Is disclosed. In such an apparatus, the length of the pin is set to be longer than the length in the vertical direction of the body mold, and the upper end surface of the pin is brought into contact with the flange portion of the upper mold to move the upper mold downward. And the thickness was regulated. Further, the pressing force applied to the upper mold in the cooling step is released, the pin is moved downward, the restriction of the downward movement of the upper mold by the pin is released, and the upper mold is substantially molded by its own weight. In the mold, and the mold is prevented from being released from the mold surface. However, the above apparatus has a complicated structure, and it is actually difficult to stably move the upper mold to follow the contraction of the molded product.

Japanese Patent Application Laid-Open No. 7-215721 discloses an apparatus having a structure in which a top portion having a larger expansion coefficient than that of a glass material is provided at an upper portion, a center portion, or a lower portion of a body which slidably accommodates upper and lower molds. Is disclosed. In such an apparatus, the upper mold is brought into contact with the upper end surface of the body mold or the refilling part to restrict the downward movement of the upper mold so as to regulate the thickness. Further, in the above-described apparatus, the replenishing portion is configured to contract more greatly than the glass material in the cooling step based on the difference in expansion coefficient between the glass material and the replenishing portion, and the glass material is constantly pressed on the upper mold forming surface to improve surface accuracy. Had prescribed. However, there are actually the following problems. In order to make the shrinkage amount of the refill portion larger than the shrinkage amount of the glass material in the cooling process from the glass yielding point (At) to the glass transition point (Tg), the length of the refill portion must be set to be considerably longer. The molding equipment was too large as a whole. Further, as described above, if the replenishment part is long, it is difficult to control the temperature of the replenishment part and the glass material away from the heater whose temperature has been adjusted, and the amount of expansion and contraction of the material varies with each molding cycle. An optical element having thickness accuracy and surface accuracy could not be stably obtained.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is directed to an optical element capable of obtaining an optical element having excellent thickness accuracy and surface accuracy while having a compact and simple structure. An object is to provide a molding device and a molding method.

Another object of the present invention is to provide a molding apparatus and a molding method for an optical element capable of stably obtaining an optical element having excellent thickness accuracy and surface accuracy while having a compact and simple structure. I do.

[0007]

According to the present invention, there is provided a pair of upper and lower molds each having one mold supported and fixed at an end and a flange for restricting movement of the other mold at the end. A mold, a cylindrical body mold for accommodating the mold, and disposed outside the outer peripheral surface of the body mold while having a mold axial length equal to or greater than the mold axial length of the body mold, and supported at one end. A regulating member for restricting approach movement of the upper and lower molds by being in contact with the flange portion at the other end while being fixed, wherein the amount of contraction of the regulating member is the difference between the amount of contraction of the upper and lower molds and the amount of contraction of the glass material. The present invention relates to an optical element molding apparatus characterized by being equal to or greater than the sum.

The present invention also relates to a method for molding an optical element using the molding apparatus, wherein the upper mold is moved downward while the glass material heated between the upper and lower molds is maintained at a constant temperature. The present invention relates to a method for molding an optical element including a step of pressing and a step of cooling while continuing to press after the downward movement of an upper mold is restricted by a regulating member.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A molding apparatus according to the present invention will be described with reference to the drawings. FIG. 1 (a) shows a schematic configuration diagram of an example of the molding apparatus of the present invention, and FIG. 1 (b) shows a schematic cross-sectional view of a horizontal plane AB of the apparatus of FIG. 1 (a). The apparatus shown in FIG. 1 includes a pair of upper and lower dies (1, 2) for press-molding a glass material (preform) 6, a cylindrical body mold 3 for accommodating the dies, and an upper mold. It comprises a regulating member 4 for restricting downward movement, and usually further comprises a heating element 5.

The upper mold 1 has a flange portion 7 at the upper end, and the downward movement is restricted by the lower surface of the flange portion 7 contacting the upper end of the regulating member 4 when moving downward. The lower mold 2 has a flange portion 8 at the lower end, and the flange portion 8
The holding member 4 and the body mold 3 are held and fixed on the upper surface of the member. The molding surfaces of the upper and lower molds may have any shape, and are processed to a desired surface accuracy. Known materials can be used for the upper and lower molds, and examples thereof include aluminum oxide and cemented carbide.

The body mold 3 accommodates the upper and lower molds while suppressing the displacement and inclination of the center axis of the upper and lower molds.
Known materials can be used as the material of the body, and examples thereof include a cemented carbide and silicon carbide.

The lower end of the regulating member 4 is a flange of the lower mold 2.
The upper mold 8 is supported and fixed, and when the upper mold 1 is moved downward, the lower surface of the flange 7 of the upper mold 1 is brought into contact with the upper end of the regulating member 4 to limit the downward movement of the upper mold 1. It is supposed to. In addition, the regulating member 4 is arranged outside the outer peripheral surface of the body mold 3 while having a length in the mold axis direction longer than the length of the body mold 3 in the mold axis direction when not heated. By appropriately selecting the length within a range in which the lower surface of the flange portion 7 of the upper mold 1 can be in contact with the upper end of the regulating member 4 when not heated, the thickness of the obtained optical element (molded product) is reduced. Can control. The regulating member is located inside the outer peripheral surface of the body mold, for example,
If it is arranged between the inner peripheral surface and the outer peripheral surface of the body mold, heat is less likely to be transmitted to the regulating member and a temperature distribution occurs, so that an optical element having sufficient thickness accuracy and surface accuracy cannot be obtained.

The amount of contraction of the regulating member 4 is equal to or greater than the sum of the amount of contraction of the upper and lower molds (1, 2) and the amount of contraction of the glass material 6. For this reason, after the lower surface of the flange portion 7 of the upper mold 1 is in contact with the upper end of the regulating member 4 and the thickness of the optical element is defined,
In the cooling step, the upper mold 1 can follow the shrinkage of the formed glass material (molded product), and can avoid mold release between the upper mold forming surface and the molded product surface. If the amount of contraction of the regulating member is smaller than the sum of the amount of contraction of the upper and lower molds and the amount of contraction of the glass material, mold release occurs between the upper mold molding surface and the surface of the molded product in the cooling step, and the obtained optical The surface accuracy of the element decreases.

In the present specification, the "shrinkage amount" means the displacement length in the mold axis direction during cooling, more specifically, the displacement length in the mold axis direction when cooling from the molding temperature to room temperature. Since the above-mentioned shrinkage amount also depends on the thermal expansion coefficient of the material, the temperature difference during cooling, and the length in the axial direction of the mold during non-heating, the shrinkage amount of the regulating member is the shrinkage amount of the upper and lower molds and the shrinkage amount of the glass material. It is necessary to appropriately select the material of the regulating member and the upper and lower molds, the axial length of the mold, the type of glass material, the maximum thickness of the desired molded product, and the temperature difference in the cooling step so as to be equal to or more than the sum of However, in the present invention, it is sufficient that the thermal expansion coefficient of the regulating member is larger than the thermal expansion coefficients of the upper mold, the lower mold, and the glass material. If a regulating member having such a relationship of thermal expansion coefficient, upper and lower molds and a glass material are used,
Usually, the amount of contraction of the regulating member is equal to or more than the sum of the amount of contraction of the upper and lower molds and the amount of contraction of the glass material. As a combination of materials having the above relationship, for example, stainless steel (coefficient of thermal expansion: 18 × 10 ⁻⁶ ) as a regulating member, aluminum oxide (coefficient of thermal expansion; 5 × 10 ⁻⁶ ) as upper and lower molds, and glass material Lanthanum-based glass (thermal expansion coefficient: 8 × 10 ⁻⁶ ).

In FIG. 1 (a), the regulating member 4 has a cylindrical shape and is arranged so as to accommodate the body mold 3, but it can restrict the downward movement of the upper mold, and the outer peripheral surface of the body mold. If it is arranged outside, the shape and the installation position are not particularly limited.

It is preferable that the regulating member having a cylindrical shape has a gap 9 (see FIG. 1B) continuously formed over the entire length in the axial direction of the mold. Since the cylindrical regulating member has the “C” -shaped cross-sectional shape, the contact with the outer peripheral surface of the barrel mold is effectively secured, so that the transmitted heat can be further effectively transmitted to the barrel mold. And heat conduction efficiency is improved.

The upper and lower ends of the regulating member 4 having a cylindrical shape are each located within one horizontal plane. A regulating member having a cylindrical shape is relatively easy to process as such.

Since the heating is performed by induction heating, the heating body is arranged outside the outer peripheral surface of the barrel mold. From the viewpoint of stably obtaining an optical element having sufficient thickness accuracy and surface accuracy, it is preferable that the restricting member is disposed outside the outer peripheral surface of the body mold and is in contact with the restricting member. When the regulating member has a cylindrical shape and is arranged so as to accommodate the body mold, it is more preferable that the heating member 5 be arranged as shown in FIG.
Also has a cylindrical shape, and is arranged to accommodate the regulating member 4. As the heating body, for example, a conductive material that can be induction-heated, such as carbon or a tungsten alloy, is preferably used.

As shown in FIG. 1 (a), the inner peripheral surface of the regulating member 4 is in contact with the outer peripheral surface of the body mold 3, and the inner peripheral surface of the heating element 5 is in contact with the outer peripheral surface of the regulating member 4. preferable. This is because heat conduction during heating and cooling is performed efficiently.

The operation procedure of the apparatus shown in FIG. 1A will be described. First, the glass material (preform) 6 is heated between the upper and lower molds (1, 2), and when the glass material 6 reaches a predetermined temperature (forming temperature), the temperature is maintained for a while. FIG. 1A shows this state. Then, the glass material 6
While maintaining the temperature at the above temperature, the upper mold 1 is moved downward by a driving means (not shown) to apply pressure. And the upper mold
After the downward movement of 1 is restricted by the regulating member 4, that is, after the lower surface of the flange portion 7 of the upper mold 1 comes into contact with the upper end of the regulating member 4, cooling is performed while the pressurization is continued. At this time,
The amount of shrinkage of the regulating member 4 is equal to or more than the sum of the amount of shrinkage of the upper and lower molds (1, 2) and the amount of shrinkage of the glass material 6, and the upper mold 1 follows the shrinkage of the formed glass material (molded product). Therefore, contact between the upper mold forming surface and the surface of the molded product can be ensured, and as a result, the surface accuracy of the molded product is excellent.

The cooling may be natural cooling achieved simply by stopping the heating, or forced cooling achieved by blowing the cooling air to the heating body after the heating is stopped. .

The pressurization is preferably continued until the temperature of the molded article reaches room temperature, but from the viewpoint of shortening the molding time, the pressure is continued until the temperature of the molded article becomes about (glass transition point -100) ° C. I just need. The pressure range varies depending on the size of the lens, but may be maintained within a range of about 0.5 to 3 kgf / cm ² until the downward movement of the upper mold 1 is restricted by the regulating member 4. After the restriction by the regulating member, about 0.5-4kgf /
It may be maintained constant within the range of cm ² .

This operation procedure does not prevent the cooling from being performed after the pressurization is finished after the downward movement of the upper mold 1 is restricted by the regulating member 4, but the surface accuracy and the thickness accuracy are further improved. From the viewpoint of, it is preferable to perform cooling while continuing pressurization.

Another embodiment of the present invention will be described with reference to FIG. FIG. 2 (a) shows a schematic configuration diagram of an example of the molding apparatus of the present invention, and FIG. 2 (b) shows a horizontal plane A- of the apparatus shown in FIG. 2 (a).
1 shows a schematic cross-sectional view at B. The apparatus shown in FIG. 2 has a configuration in which the heating element 5 having a cylindrical shape is disposed so as to directly accommodate the body mold 3, the regulating member 14 has a pin shape, and the regulating member 14 is This is the same as the apparatus of FIG. 1 except that the hole is formed in a hole formed penetrating in the direction of the center axis of the mold. Therefore, the same reference numerals in FIG.
Are the same as those described above, and the description thereof is omitted.

In FIG. 2B, a pin 3
The two regulating members 14 are arranged at equal intervals on the circumference of one around the mold axis in the cross section of the heating body, but two or more regulating members having a pin shape when the upper mold 1 moves downward. As long as the members can contact the lower surface of the flange portion 7 of the upper mold 1 at their upper ends, the number and the installation positions of the regulating members are not particularly limited.
From the viewpoint of more effectively suppressing the deviation and inclination of the central axis of the upper and lower molds, and from the viewpoint of more easily obtaining a molding device, two or more, preferably 3 to 4 regulating members having a pin shape are provided in the heating element cross section. It is desirable that they are arranged at substantially equal intervals on one circumference centered on the mold axis. Note that the regulating member 14 having a pin shape is fitted in the hole of the heating element 5. In addition, all the regulating members 14 used have their upper ends and lower ends located in one horizontal plane.

The regulating member 14 is different from that of FIG.
Therefore, the description of “length”, “shrinkage amount”, “material”, etc., except for “shape”, apply the description of FIG. 1 mutatis mutandis.

As shown in FIG. 2A, it is preferable that the inner peripheral surface of the heating element 5 is in contact with the outer peripheral surface of the drum mold 3. This is because heat conduction during heating and cooling is performed efficiently.

The operation procedure of the apparatus shown in FIG. 2A is shown in FIG.
FIG. 2 (a), the regulating member 4 is replaced with the regulating member 14,
The operation procedure of the device shown in FIG.

In FIGS. 1A and 2A, the lower end of the body die 3 and the regulating member (4 or 14) is connected to the lower die 2.
Although the configuration for supporting and fixing is shown by the upper surface of the flange portion 8, a new fixing plate is newly provided without providing the flange portion on the lower mold, and the body mold, the regulating member and the lower mold are provided by the upper surface of the fixing plate. May be configured to support and fix the lower end of the.

Among the specific examples described above, an apparatus in which the regulating member has a cylindrical shape is most preferable. This is because an optical element having excellent thickness accuracy and surface accuracy can be more stably obtained.

In the molding apparatus of the present invention as described above, the regulating member can secure a length in the mold axial direction substantially equal to "the sum of the lengths of the upper and lower dies in the axial direction of the mold". It is relatively easy to control the sum of the shrinkage of the upper and lower molds and the shrinkage of the glass material. Therefore, the entire device can be easily made compact.

[0032]

(Example 1) A spherical glass preform having a diameter of 7 mm (material; L) was formed by using a molding apparatus having the structure shown in FIG.
Based on aF71 and a coefficient of thermal expansion of 7.5 × 10 ⁻⁶ ), a biconvex lens having a core thickness of 2.5 mm, an upper convex surface curvature radius of 9 mm, and a lower convex surface curvature radius of 10 mm was molded. In FIG. 1A, the material of the upper mold 1 and the lower mold 2 was aluminum oxide, the diameter was 10 mm, and the length in the mold axial direction was 25 mm. The material of the torso 3 is cemented carbide,
The inner diameter was 10 mm, and the length in the mold axial direction was 20 mm. Control member
The material of No. 4 was stainless steel, the inner diameter was 18 mm, and the length in the mold axial direction was 21 mm. The material of the heating element 5 was carbon, the inner diameter was 21 mm, and the length in the mold axial direction was 20 mm.

First, the heating element 5 is induction-heated to heat the glass material (preform) 6 between the upper and lower molds (1, 2).
When the temperature of the glass material 6 reached about 715 ° C., the temperature was maintained for a while. Heat from the heating body was transmitted to the glass material 6 via the regulating member 4 and the body mold 5. Next, while maintaining the glass material 6 at the above-mentioned temperature, the upper mold 1 was moved downward by a driving means (not shown) and pressed at 0.5 kgf / cm ² . And
After the lower surface of the flange portion 7 of the upper mold 1 came into contact with the upper end of the regulating member 4, natural cooling was performed while continuing to apply a pressure of 0.5 kgf / cm ² . Pressing and cooling are continued until the temperature of the molded article reaches about 580 ° C, and after further cooling to 80 ° C with no load,
The upper mold 1 was moved upward to take out the molded product.

When 100 preforms were molded and all the obtained lenses were evaluated, the variation of the core thickness was σ =
It was very small, 0.0005mm. When the molded surface was measured with an interferometer, the ratio of lenses with surface accuracy of λ / 6 or more was 92%.
% Or more.

Example 2 A biconvex lens similar to that of Example 1 was molded from the same preform as that of Example 1 using a molding apparatus having the structure shown in FIG. 2A. In FIG. 2A, the material of the upper mold 1 and the lower mold 2 was aluminum oxide, the diameter was 20 mm, and the length in the mold axial direction was 35 mm. The material of the barrel mold 3 was a cemented carbide, the inner diameter was 20 mm, and the length in the mold axial direction was 30 mm. The material of the regulating member 14 was stainless steel, the diameter was 3 mm, and the length in the mold axial direction was 32 mm. The material of the heating element 5 was carbon, the inner diameter was 30 mm, and the length in the mold axial direction was 30 mm.

First, the heating element 5 is induction-heated to heat the glass material (preform) 6 between the upper and lower molds (1, 2).
When the temperature of the glass material 6 reached about 715 ° C., the temperature was maintained for a while. The heat from the heating body was transmitted to the glass material 6 via the shell 5. Next, while maintaining the glass material 6 at the above-mentioned temperature, the upper mold 1 was moved downward by a driving means (not shown) and pressed at 1.5 kgf / cm ² . Then, after the lower surface of the flange portion 7 of the upper mold 1 contacts the upper end of the regulating member 14, 2 kgf /
Natural cooling was performed while the pressurization of cm ² was continued. Pressing and cooling were continued until the temperature of the molded article reached about 580 ° C., and after further cooling to 80 ° C. with no load, the upper mold 1 was moved upward to take out the molded article.

When 150 preforms were molded and all the obtained lenses were evaluated, the variation of the core thickness was σ =
It was very small, 0.0006mm. The ratio of lenses having a surface accuracy of λ / 6 or more of the molded surface was 90% or more.

(Comparative Example 1) Except for the absence of the regulating member 14,
When 150 preforms were molded using the same apparatus as the molding apparatus used in Example 2, the variation in core thickness was σ
= 0.012mm. The ratio of lenses having a surface accuracy of λ / 6 or more of the molded surface was 78% or less.

[0039]

According to the present invention, the thickness accuracy of the molded lens is improved by setting the expansion coefficient of the regulating member larger than the expansion coefficient of the lens material and the mold, and by forming the regulating member different from the body mold. And surface accuracy can be improved. Furthermore, by contacting the regulating member with the heating element, the amount of expansion of the regulating member can be made uniform, and a molded lens having excellent thickness accuracy and surface accuracy can be stably obtained.

[Brief description of the drawings]

FIG. 1A is a schematic configuration diagram of an example of a molding apparatus of the present invention, and FIG. 1B is a schematic cross-sectional view of a horizontal plane AB of the apparatus of FIG.

2A is a schematic configuration diagram of an example of a molding apparatus of the present invention, and FIG. 2B is a schematic cross-sectional view of the apparatus of FIG.

[Explanation of symbols]

1: upper mold, 2: lower mold, 3: body mold, 4: regulating member, 5: heating element, 6: preform, 7: flange, 8: flange, 9: gap, 14: regulating member .

Claims (8)

[Claims] 1. A pair of upper and lower dies having one flange fixedly supported at an end and a flange for restricting movement of the other die to the end, and accommodating the dies. A cylindrical body die, and disposed outside the outer peripheral surface of the body die while having a length in the mold axial direction not less than the length of the body die in the axial direction, and supported and fixed at one end while the flange at the other end. A restricting member that restricts the approaching movement of the upper and lower molds by contacting the upper and lower portions, wherein the amount of contraction of the restricting member is equal to or more than the sum of the amount of contraction of the upper and lower molds and the amount of contraction of the glass material. For forming optical elements. 2. The molding device for an optical element according to claim 1, wherein the regulating member is made of a material having a thermal expansion coefficient larger than that of the upper and lower molds and the glass material. 3. The molding device for an optical element according to claim 1, further comprising a heating element disposed outside the outer peripheral surface of the body mold, wherein the regulating member is in contact with the heating element. 4. The optical element according to claim 3, wherein the regulating member having a cylindrical shape is arranged to accommodate the body mold, and the heating element having a cylindrical shape is arranged to accommodate the regulating member. Molding equipment. 5. The molding device for an optical element according to claim 4, wherein the regulating member has a gap formed continuously over the entire length in the axial direction of the mold. 6. A heating element having a cylindrical shape is arranged so as to accommodate a body mold, and at least two or more regulating members having a pin shape are formed by penetrating the heating element in a central axis direction of the mold. 4. The optical element molding apparatus according to claim 3, wherein the apparatus is arranged in a hole. 7. The optical element according to claim 6, wherein at least two or more regulating members having a pin shape are arranged at substantially equal intervals on one circumference centered on a mold axis in a cross section of the heating body. Molding equipment. 8. A method of molding an optical element using the optical element molding apparatus according to claim 1, wherein the glass material heated between the upper and lower molds is maintained at a constant temperature. An optical element forming method comprising: a step of moving the upper mold downward to pressurize; and a step of cooling while continuing to pressurize after the downward movement of the upper mold is restricted by the restricting member.