JPH0741327A - Optical element forming method - Google Patents

Abstract

PURPOSE:To provide an inexpensive optical element excellent in shape precision and surface precision. CONSTITUTION:An optical element material 4 is inserted between the upper die 1 and lower die 2 of a mold M in the first stage. The material is heated and softened in the second stage. The softened material is press-formed in the third stage. The pressure except the gravity of the upper die 1 is released, a temp. difference is developed between the upper die 1 and lower die 2, and the material is cooled in the fourth stage. A pressure except the gravity of the upper die 1 is again applied, and a temp. is uniformly exerted between the upper die 1 and lower die 2 to cool the material in the fifth stage to form an optical element. Meanwhile, the optical element is formed by the fourth stage after the third stage and the fifth stage with the pressure increased in comparison with at least the fourth stage, or the element is formed by the fourth stage after the third stage and again by the fifth stage.

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 method which is excellent in shape accuracy and surface accuracy, is inexpensive, and is suitable for mass production.

[0002]

2. Description of the Related Art In recent years, optical elements such as lenses and prisms are manufactured by polishing an optical element material such as glass instead of polishing the material for an optical element. It is publicly known that the material is supplied, heated, and then pressure-molded (for example, JP-A-58-84134).

At this time, in order to obtain a highly accurate optical element, it is necessary to reliably transfer the molding surface shape of the mold to the optical element. In particular, it is important that the molding surface of the mold is in close contact with the optical element in the cooling process after the completion of deformation. As means for achieving this, JP-A-63-2658
There is a method disclosed in Japanese Patent No. 33. A conventional molding method will be described below with reference to the drawings.

FIG. 1 shows the structure of a molding apparatus used in a conventional optical element molding method. In FIG. 1, 1 is an upper die, 2
Is a lower mold, 3 is a barrel mold, M is a mold including the upper mold, lower mold, and barrel mold, 4 is a molded glass lens, 5 is an upper heater block, 6 is a lower heater block, and 7 is a stopper. , 8 is a pressure shaft, 9 is a cylinder, and 10 is an outer frame.

Next, a conventional optical element molding method using a molding apparatus composed of the above members will be described.

First, the glass material 4 is supplied into the molding die M,
Set on the lower heater block 6. Next, nitrogen gas is supplied into the outer frame 10 to make the molding atmosphere a non-oxidizing atmosphere.
After that, the cylinder 9 is lowered (the lowering mechanism is not shown), and the upper die 1 is vertically pressed by the upper heater block 5. The glass material 4 is gradually deformed and the molding is completed when the cylinder 9 comes into close contact with the stopper 7.

The thickness of the molded glass lens 4 is regulated by the height of the stopper 7 and is always molded to a constant size. When cooled as it is, the mold M and the glass lens 4
However, since the upper heater block 5 is restricted by the stopper 7, the upper heater block 5 cannot be lowered and the upper mold 1 cannot be pressurized. Therefore, the pressurization is temporarily stopped, the stopper 7 is removed, and then the pressurization is performed again, and at the same time, the heater is turned off to pressurize and cool to form the optical element.

[0008]

However, in the conventional molding method as described above, since the upper and lower molds are regulated under pressure with an unnecessarily high pressure in the cooling process after the molding is completed, the optical element material is molded into the mold. When trying to shrink while closely contacting, the shrinking speed of the optical element material is faster than the shrinking speed of the upper mold or the lower mold, so the optical element material cannot shrink as expected, cracking or chipping and the desired lens performance Had a problem that was not obtained.

The present invention solves such a problem by controlling the pressure and temperature of the cooling process after completion of molding so that the optical element material can be contracted while closely adhering to the mold, thereby achieving shape accuracy and surface accuracy. It is an object of the present invention to provide an optical element molding method which is excellent, inexpensive and suitable for mass production.

[0010]

In order to achieve the above object, the first means of the present invention is to insert an optical element material between a molding die composed of an upper die and a lower die, and heat and soften it. After pressure molding, remove the pressure other than the weight of the upper mold, cool with a temperature difference between the upper mold and the lower mold, and apply pressure other than the weight of the upper mold again to separate the upper mold and the lower mold. The temperature is evenly applied during the cooling.

The second means is to insert an optical element material between a molding die composed of an upper die and a lower die, heat and soften it, press-mold it, and then cool while applying a pressure other than the weight of the upper die. Then
The pressure is increased on the way to cool it.

A third means is to insert an optical element material between a molding die composed of an upper die and a lower die, heat and soften it, and press-mold it. The cooling is performed while providing a difference, and the temperature is evenly applied between the upper die and the lower die during the cooling.

[0013]

According to the above method, the upper and lower molds are pressure-controlled in the cooling process after molding the optical element material, and the contraction speed of the upper and lower molds is faster than the contraction speed of the optical element material. , The optical element material always cools and shrinks while closely contacting the upper and lower molds. Therefore, it is possible to mass-produce optical elements having excellent surface accuracy and shape accuracy with good reproducibility.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for molding an optical element according to an embodiment of the present invention will be described below with reference to the drawings.

(Example 1) FIG. 1 shows a schematic structure of a molding machine used. In FIG. 1, 1 is an upper die, 2 is a lower die, 3 is a barrel die, M is a forming die consisting of the upper die, the lower die and the barrel die, and a superhard material is used as the die material, and its thermal expansion Coefficient is about 5
It is 0 × 10 ⁷ / ° C. Reference numeral 4 is a molded glass lens, and the glass applied has a glass transition temperature of 530 ° C. and a thermal expansion coefficient of about 99 × 10 ⁷ / ° C. The final lens shape is a spherical meniscus lens having an outer diameter of 26 mm and a maximum inclination angle of 40.5. 5 is an upper heater block, 6 is a lower heater block, 7 is a stopper, 8 is a pressing shaft, 9 is a cylinder, and 10 is an outer frame.

First, in the molding die M (the upper die 1 is a convex die)
The glass material 4 is supplied to and is set on the lower heater block 6. Next, nitrogen gas is supplied into the outer frame 10 to make the molding atmosphere a non-oxidizing atmosphere. After that, the cylinder 9 is lowered (the lowering mechanism is not shown), and the upper heater block 5 is moved to the upper mold 1.
The upper and lower molds are evenly heated by the heated upper and lower heater blocks. Until then, the temperature of the glass material 4 was raised to 575 ° C., and when the temperature became constant, pressure was applied with a pressure of 300 kgf, and the molding was completed when the cylinder 9 was brought into close contact with the stopper 7. The thickness of the molded glass lens 4 is regulated by the height of the stopper 7, and is always molded to a constant size. Then, the cylinder 9 is raised to separate the upper heater block 5 from the upper mold 1,
Excludes pressures other than the weight of upper mold 1. The upper and lower heater blocks cool at a rate of 7.5 ° C./min, but since the upper heater block 5 is separated from the upper mold 1, the upper mold 1 and the lower mold 2
Are cooled with a temperature difference between them. The temperature of the upper and lower heater blocks is 529 ° C, and the temperature of the glass lens 4 is 5
When the temperature reaches 33 ° C., the cylinder 9 is lowered again to bring the upper heater block 5 into contact with the upper mold 1 and pressurize it with a pressure of 20 kgf to keep the upper and lower molds evenly heated to 500 ° C. Allow to cool. After that, the mold is slowly cooled to a temperature at which the mold can be taken out, and the molded glass lens 4 is taken out.

Regarding the surface accuracy of this glass lens 4, the difference in surface accuracy with the mold was 44 nm as measured by an optical interferometer.

The surface accuracy of the lens 4 made at a temperature of around 533 ° C. is shown in Table 1 as a difference from the surface accuracy of the mold. From this result, it is understood that the lens accuracy is deteriorated unless the temperature at the time of pressure increase is higher than the glass transition temperature by 3 ° C. or more.

[0019]

[Table 1]

On the other hand, under the cooling conditions of the above-described molding method, after the molding which is the conventional molding method is completed, the upper heater block 5 is not separated from the upper mold 1 and the pressure other than the weight of the upper mold 1 is 20.
The surface accuracy of the glass lens 4 by the molding method in which kgf is applied and the temperature of the upper and lower heater blocks is cooled to 500 ° C. while the uniform temperature is applied, the surface accuracy of the glass lens 4 is different from that of the mold when measured by an optical interferometer. The average was 228 nm. On the other hand, under the cooling conditions of the above molding method, after the completion of molding,
The upper heater block 5 is separated from the upper mold 1 to remove the pressure other than the weight of the upper mold 1 until the temperature of the upper and lower heater blocks reaches 500 ° C. with a temperature difference between the upper mold 1 and the lower mold 2. Regarding the surface accuracy of the glass lens 4 when cooled, the difference in surface accuracy with the mold is 196 nm on average when measured by an optical interferometer, and in any method, the molding method of this embodiment is the conventional molding method. An excellent glass lens was obtained as compared with.

Although the molding of the spherical meniscus lens has been described in the present embodiment, the present invention is not limited to the spherical surface, and the same effect can be obtained for an aspherical lens, a convex lens, a concave lens and a prism. Further, similar effects can be obtained with optical element materials having different glass transition temperatures, but it goes without saying that the conditions of pressure and temperature are different for each optical element material.

Example 2 In this example, an optical element was molded by using the molding apparatus shown in FIG. 1 as in Example 1.
Since the configuration of FIG. 1 is the same as that of the first embodiment, the description thereof will be omitted.

First, in the molding die M (the upper die 1 is a convex die)
The glass material 4 is supplied to and is set on the lower heater block 6. Next, nitrogen gas is supplied into the outer frame 10 to make the molding atmosphere a non-oxidizing atmosphere. After that, the cylinder 9 is lowered (the lowering mechanism is not shown) so that the upper heater block 5 comes into vertical contact with the upper mold 1, and the upper and lower molds are uniformly heated by the upper and lower heater blocks. The glass material 4 is heated to 575 ℃, and when the temperature becomes constant, 300kg
Pressing with the pressure of f, the molding is completed when the cylinder 9 comes into close contact with the stopper 7. The thickness of the molded glass lens 4 is regulated by the height of the stopper 7, and is always molded to a constant size. When cooled as it is, the molding die M and the glass lens 4 shrink, but the upper heater block 5 cannot be lowered because it is regulated by the stopper 7, and the upper die 1
Cannot be pressurized. Therefore, the cylinder 9 is once raised and the stopper 7 is removed, and then the cylinder 9 is lowered and pressurized again, but the pressure is reduced to 2 kgf and the upper and lower heater blocks are cooled at a rate of 7.5 ° C./min. The temperature of the upper and lower heater blocks is 531 ° C, and the temperature of the glass lens 4 is 53
When the temperature reaches 6 ° C. (the temperature of the fifth step of increasing the pressure is in accordance with Example 1), the pressure of the cylinder 9 is again raised to 20 kgf, and the temperature of the upper and lower heater blocks becomes 500 ° C. while heating the upper and lower molds evenly. Cool down. After that, the glass lens 4 is gradually cooled to a temperature at which the mold can be taken out and molded.
Take out.

Regarding the surface accuracy of the glass lens 4, the difference in surface accuracy with the mold was 101 nm as measured by an optical interferometer.

On the other hand, under the cooling conditions of the above molding method, after the molding is completed and the stopper 7 is removed, which is a conventional method, the pressure when the cylinder 9 is lowered and pressurized again is not reduced, and the pressure other than the weight of the upper mold 1 is reduced. The surface accuracy of the glass lens 4 according to the molding method in which the pressure is maintained at 20 kgf and the temperature of the upper and lower heater blocks is cooled to 500 ° C. while the uniform temperature is being applied, the surface accuracy of the glass lens 4 can be determined by measuring with an optical interferometer. The average difference was 228 nm, and the molding method of this example provided a glass lens superior to the conventional molding method.

Although the method of forming the spherical meniscus lens has been described in the present embodiment, the same effect can be obtained not only for the spherical lens but also for the aspherical lens, the convex lens, the concave lens and the prism. Further, similar effects can be obtained with optical element materials having different glass transition temperatures, but it goes without saying that the conditions of pressure and temperature are different for each optical element material.

Example 3 In this example, an optical element was molded using the molding apparatus shown in FIG. 1 as in Example 1. Since the configuration of FIG. 1 is the same as that of the first embodiment, the description thereof will be omitted.

First, in the molding die M (the upper die 1 is a convex die)
The glass material 4 is supplied to and is set on the lower heater block 6. Next, nitrogen gas is supplied into the outer frame 10 to make the molding atmosphere a non-oxidizing atmosphere. After that, the cylinder 9 is lowered (the lowering mechanism is not shown) so that the upper heater block 5 comes into vertical contact with the upper mold 1, and the upper and lower molds are uniformly heated by the upper and lower heater blocks. The glass material 4 is heated to 575 ℃, and when the temperature becomes constant, 300kg
The molding is completed when pressure is applied by the pressure f and the cylinder 9 comes into close contact with the stopper 7. The thickness of the molded glass lens 4 is regulated by the height of the stopper 7, and is always molded to a constant size. When cooled as it is, the molding die M and the glass lens 4 shrink, but the upper heater block 5 cannot be lowered because it is regulated by the stopper 7, and the upper die 1
Cannot be pressurized. Therefore, the cylinder 9 is once raised, the stopper 7 is removed, and then the cylinder 9 is lowered again to
Pressurize with a pressure of 0 kgf. Then, the upper heater block 5 is cooled at a rate of 568 ° C. to 7.5 ° C./min, and the lower heater block 6 is cooled at a rate of 575 ° C. to 7.5 ° C./min. The temperature of the upper heater block 5 is 530 ° C,
When the temperature of the glass lens 4 reaches 535 ° C. (the temperature of the fifth step for applying the temperature evenly is according to the first embodiment), the temperature of the upper heater block 5 is returned to the same temperature as the temperature of the lower heater block 6, After that, the upper and lower molds are uniformly heated and cooled at the above rate until the temperature of the upper and lower heater blocks reaches 500 ° C. After that, the mold is slowly cooled to a temperature at which the mold can be taken out, and the molded glass lens 4 is taken out.

Regarding the surface accuracy of this glass lens 4, the difference in surface accuracy with the mold was 107 nm as measured by an optical interferometer.

Lens 4 cooled from a temperature around this temperature
The surface accuracy of is shown in Table 2 as a difference in surface accuracy from the mold. From this result, it is understood that the lens accuracy is deteriorated unless the temperature difference between the upper and lower molds is 7 ° C. or more.

[0031]

[Table 2]

On the other hand, under the cooling conditions of the above-mentioned molding method, after the molding is completed and the stopper 7 is removed, when the cylinder 9 is lowered and pressed again, the upper and lower heater blocks 5 are heated with no temperature difference. The surface accuracy of the glass lens 4 according to the conventional molding method for uniformly cooling under temperature conditions is
The difference in surface accuracy with the mold is 22 on average when measured with an optical interferometer.
The thickness was 8 nm, and the glass lens obtained by the molding method of this example was superior to the conventional molding method.

Although the method of forming the spherical meniscus lens has been described in the present embodiment, the same effect can be obtained not only for the spherical surface but also for the aspherical lens, the convex lens, the concave lens and the prism. Further, similar effects can be obtained with optical element materials having different glass transition temperatures, but it goes without saying that the conditions of pressure and temperature are different for each optical element material.

[0034]

As is apparent from the above description of the embodiments, according to the present invention, after the pressure molding of the optical element material is completed, the pressure and temperature at the time of cooling are controlled to form the optical element material in the molding die. Since it shrinks in close contact with, it is possible to mass-produce optical elements with excellent shape accuracy and surface accuracy at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of the present invention and a conventional optical element molding apparatus.

[Explanation of symbols]

 1 Upper Mold 2 Lower Mold 3 Body 4 Glass Lens 5 Upper Heater Block 6 Lower Heater Block 7 Stopper 8 Pressure Shaft 9 Cylinder 10 Outer Frame M Mold

Claims (12)

[Claims] 1. A first step of inserting an optical element material between a molding die having an upper die and a lower die, a second step of heating and softening the optical element material, and the softened optical element material. A third step of pressure molding, a fourth step of removing pressure other than the weight of the upper mold and cooling while providing a temperature difference between the upper mold and the lower mold, and the upper mold again An optical element molding method comprising a fifth step of applying a pressure other than its own weight to and cooling while uniformly applying a temperature between the upper mold and the lower mold. 2. The optical element molding method according to claim 1, wherein the temperature at which cooling is started again while applying pressure and temperature is when the optical element material reaches a temperature near the glass transition point. 3. A first step of inserting an optical element material between a molding die having an upper die and a lower die, a second step of heating and softening the optical element material, and the softened optical element material. Pressure molding, a fourth step of cooling while applying a pressure other than the weight of the upper mold, and a fifth step of cooling at a pressure higher than at least the fourth step. Optical element molding method. 4. The optical element molding method according to claim 3, wherein the temperature at which the pressure is increased more than in the fourth step is a temperature near the glass transition point of the optical element material. 5. The optical element molding method according to claim 2, wherein the lower limit of the temperature near the glass transition point is 3 ° C. or more higher than the glass transition point. 6. At least one of the upper die and the lower die,
The optical element molding method according to claim 1, which is a mold having a convex surface. 7. A first step of inserting an optical element material between a molding die having an upper die and a lower die, a second step of heating and softening the optical element material, and the softened optical element material. The third step of pressure molding, the fourth step of cooling while providing a temperature difference between the upper mold and the lower mold, and the temperature of the upper mold and the lower mold is evenly adjusted again. An optical element molding method comprising a fifth step of cooling while applying. 8. The method for molding an optical element according to claim 7, wherein the temperature at which the cooling is started while the temperature is evenly applied again is when the optical element material reaches a temperature near the glass transition point. 9. The optical element molding method according to claim 8, wherein the lower limit of the temperature in the vicinity of the glass transition point is a temperature higher by 3 ° C. or more than the glass transition point. 10. The optical element molding method according to claim 7, wherein a temperature difference between the upper mold and the lower mold is at least 7 ° C. or more. 11. The optical element molding method according to claim 7, wherein at least one of the upper mold and the lower mold is a mold having a convex surface. 12. The optical element molding method according to claim 11, wherein the side on which the temperature is lowered is the side having a convex surface.