JPH069228A - Method for forming optical element - Google Patents

Abstract

PURPOSE:To provide an optical element excellent in shape accuracy and plane accuracy, suitable for mass production at a low cost, and to provide a method for forming the optical element. CONSTITUTION:A columnar optical element material 1 is threaded into between dies 11 and 12, heated and softened, and then put to press-forming to obtain the objective optical element. In this process, about half of the total deformation is put to the press-forming, with pressure is reduced or brought to zero at least once during heating, and the rest of the total deformation is then put to the press-forming during cooling. Thereby, the objective optical element with shape as designed can be obtained.

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 and an optical element, and more particularly to an optical element molding method which is excellent in shape accuracy and surface accuracy and is suitable for mass production.

[0002]

2. Description of the Related Art In recent years, an optical element such as a lens or a prism is formed by pouring an optical element material into a mold and heating and pressing the material instead of manufacturing the optical element material such as glass by polishing. Many have been proposed. In order to control the weight accurately, the cylindrical shape which is the easiest to pre-process and is inexpensive is preferable.

A method for forming a cylindrical glass material is disclosed in, for example, Japanese Patent Laid-Open No. 60-246231. The molding method will be described below with reference to the drawings.

Generally, when an optical element is manufactured by press molding, a material for an optical element is cut into a predetermined size and preheated to near the glass softening point. Next, when the optical element material is closed, the preheated optical element material is supplied between the upper mold and the lower mold that are processed to have almost the same shape as the finished optical element, Pressure molding is performed at temperature.

As described above, the shape of the material for molding an optical element is preferably as simple as possible in view of the manufacturing process or the processing cost of the material. For example, a bar material machined to a predetermined glass material outer diameter by centerless processing is predetermined. There is a cylindrical body cut at the width of. However, when a material for this purpose is used for molding, as shown in FIG. 5, the corner portions 43 of the material are first deformed, and the portions in contact with the upper die 41 and the lower die 42 become familiar with each other to form a closed space 44. Once a closed space is created, the closed space exists until the completion of molding, and the processed surface of the mold is not sufficiently transferred to the material, resulting in a defective optical element.

A conventional method for preventing such untransferred defects will be described with reference to FIG. The lower die 32 is the connecting rod 3
It is fixed to the base 32B via 2A, and the upper mold 31
Is attached to the piston rod 31B via a connecting rod 31A. The optical element material 1 is first heated to the molding temperature by the heater 35. When the desired forming temperature is reached, the upper die 31 is lowered by the hydraulic cylinder and comes into contact with the material.

After that, the upper mold vibrates and presses up and down, and this is executed by using, for example, a servo pulser. The oscillating pressurization is performed up to 90% of the total amount of deformation, and the remaining 10% is molded at a constant pressure while being heated to the molding temperature. When all the molding for the total deformation amount is completed, the power supply is stopped, the mold is opened when the temperature is lowered to a desired temperature, and the optical element is taken out after cooling.

[0008]

In the conventional molding method, the desired molding temperature is maintained until all the moldings of the total deformation amount are completed. During the subsequent cooling to the desired temperature, the molded optical element largely changed from the desired shape due to uneven shrinkage, and it was difficult to satisfy the optical performance.

[0009]

In order to solve the above-mentioned problems, an optical element molding method and an optical element according to the present invention include a cylindrical optical member between a molding die composed of a first die and a second die. In the method of obtaining an optical element by inserting the element material, heating and softening it and press-molding, reduce the pressure at least once during heating or reduce it to zero and add about half of the total deformation amount. After the pressure molding, the remaining half of the deformation amount is pressure-molded during cooling.

[0010]

With the above-mentioned structure, the optical element after molding has excellent optical characteristics.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment will be described below with reference to FIGS. 1 to 3. In FIG. 1, the molding apparatus according to the molding method of the present invention eliminates axial misalignment between the upper mold 11 and the lower mold 12. And a vertical direction so that both end surfaces are in contact with the upper and lower dies in a space surrounded by the upper mold, the lower mold, and the body mold 14 adjusted to have an arbitrary height so as to have a predetermined optical element thickness. Optical element material 1. Further, the upper heater block 15 is connected to the cylinder rod, and the upper die 11 is connected via the upper heater block 15 by an air cylinder.
The desired pressure can be applied to.

The optical element material is a cylindrical body as shown in FIG. 2, and is an optical glass SF-8 having a diameter of 3 mm and a length of 4 mm (glass transition temperature 420 ° C., yield temperature 454 ° C., softening temperature 55.
90 ° C 10 ^-7 / at 1 ° C and linear expansion coefficient of 100 ° C to 300 ° C
℃). The side surface is finished by centerless processing, and the surface roughness is 3 μm. The end faces are mirror-finished by polishing, and the surface roughness is 0.1 μm.
The total deformation dimension until the molding of the optical element material under pressure is completed is 2 mm.

The optical element material is put into the mold so that the mold and the polishing surface face each other. At this time, the mold transfer surface 11a,
12a and an enclosed space 11b surrounded by the end face of the optical element material,
12b can be made.

Next, the mold is transferred to the molding stage 16 in the molding machine, and the upper heater block 15 is brought into contact with the upper mold 11. It is necessary to raise the temperature of the upper heater block and the lower heater block to a temperature at which the glass material can be sufficiently deformed by the pressing force of the mold, but if the temperature is raised more than necessary, it will become an optical element that does not satisfy the desired performance. It is recommended to set it between the yielding temperature and the softening temperature. In this embodiment, the temperature of the upper heater block and the lower heater block was set to 530 ° C. When the temperature of the optical element material reaches 530 ° C., the viscosity of the optical element material is 10 ¹⁰ poise.

Next, the upper heater block presses the material through the upper mold. The pressure at this time is preferably 2 kg / mm ² or more. During the molding, 1.6 mm of the total deformation dimension of 2 mm is pressure-molded. When 0.8 mm is deformed after the start of pressurization, the molding pressure is once made zero, and the upper heater block is lifted and separated from the upper mold. Immediately before the pressure is reduced to zero, the space surrounded by the mold and the end surface of the optical element material, which had been positive pressure, returns to normal pressure. Even when the molding pressure is reduced to zero, the molding die and the optical element material remain in contact with each other.

Next, the upper heater block is lowered again and brought into close contact with the upper mold. At this time, there is no space surrounded by the molding die and the end surface of the optical element material. Then, pressurization is started while cooling, and the remaining deformation amount of 0.4 mm is molded. 400 ° C
The pressurization is terminated when the temperature reaches, and the upper heater block is raised. Subsequently, the molding die is taken out of the molding machine, cooled to room temperature, opened, and the optical element is taken out. The molded optical element had a shape as designed and was excellent in optical characteristics.

The second embodiment will be described below. Figure 3
In the molding apparatus 20 shown in (1), each stage is constantly maintained at an arbitrary set temperature, and the mold is sequentially transferred to each stage by a transfer device to be preheated, molded, and cooled.

Details of this embodiment will be described. The optical element material is a cylindrical body as shown in Fig. 2, with a diameter of 4 mm and a length of 4.5 m.
m optical glass SF-8 (glass transition temperature 420 ° C., yield temperature 454 ° C., softening temperature 551 ° C., linear expansion coefficient 100 ° C.
90 × 10 ⁻⁷ / ° C. at 300 ° C.). In addition, the side surface is finished by centerless processing, and the surface roughness is 3
μm. The end face is a face formed by stress cleavage and has a surface roughness of 0.1 μm.

The total deformation dimension until the molding of the optical element material by pressure molding is completed is 2.5 mm. The above-mentioned optical element material is put into the mold so that the mold and the polishing surface face each other. At this time, a sealed space surrounded by the molding die and the end surface of the optical element material is formed.

Next, the mold is transferred to the preheating stage 21 in the molding apparatus 20 set at 500 ° C., and the upper heater stage 25 is lowered and held for 1 minute. At this time, a slight gap is provided so that the upper heater stage 25 and the mold do not come into contact with each other.

Next, after raising the upper heater stage 25, the mold is conveyed to the next molding stage 22 set at 520.degree. The upper heater stage 26 is lowered and pressurized.
The pressing force is set so that the material is deformed sufficiently. In this embodiment, the pressure is 5 kg / cm ² . 2 mm of the total deformation dimension of 2.5 mm is pressure-molded. At the time of deformation of 1 mm after the start of pressurization, the molding pressure is once raised, and then the upper heater stage 26 is raised and then lowered again to make contact with the mold and pressurize. This operation is performed in 1 minute. At this point, the space surrounded by the molding die and the end surface of the optical element material has disappeared.

Then, the upper heater stage 26 is raised and the mold is conveyed to the cooling stage 23 set at 425 ° C. Even in the cooling stage, pressure is applied by the upper heater stage 27, and the remaining deformation amount is used for molding. At this time, the material is cooled and the surface shape is adjusted. Next 16 ° C
The film is conveyed to the water-cooled stage 24 kept at the temperature of, and after 1 minute, it is taken out from the molding apparatus, the mold is opened, and the optical element is taken out.

As described above, sink marks due to shrinkage of the material can be minimized by adjusting the surface shape of the material using the remaining deformation amount during cooling. In this embodiment, 2 mm out of the total deformation dimension of 2.5 mm, that is, 8 mm
Although the crack was deformed by heating and pressing, if it is 60% or less, the closed space surrounded by the material and the mold may not be removed, which is dangerous. Further, when heating and pressurizing and deforming a dimension exceeding 90%, the amount of deformation at the time of cooling and pressurizing becomes insufficient and the accuracy of the optical element shape deteriorates, which is not desirable.

In Table 1, the amount of deviation from the design value of the surface shape of the optical element formed by using the total amount of deformation during the conventional heating and pressing using a cylindrical optical element material, and the present invention The deviation amount from the design value of the surface shape of the optical element molded by the molding method is shown.

[0025]

[Table 1]

As shown in Table 1, the deviation amount from the design value of the optical element of the present invention is much smaller than that of the conventional optical element. The optical characteristics of the optical element of the present invention were 0.025λ at the measurement wavelength of 633 nm.

[0027]

Since the present invention is the molding method described above, the following effects can be obtained. This is a molding method in which the pressure is reduced at least once during heating or reduced to zero during the heating to press-mold approximately half of the total deformation amount, and then the remaining approximately half deformation amount is pressed during cooling. ,
Since the shape of the mold was maintained with almost no sink mark due to shrinkage of the optical element during cooling, an optical element excellent in optical characteristics could be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a molding apparatus embodying a molding method of the present invention.

FIG. 2 is an external view of an optical element material used for molding using the molding apparatus.

FIG. 3 is a sectional view of another molding apparatus embodying the molding method of the present invention.

FIG. 4 is a sectional view of a conventional molding device.

FIG. 5 is an explanatory view of problems in the conventional molding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical element material 11 Upper mold 11a Mold transfer surface 11b Sealed space 12 Lower mold 12a Mold transfer surface 12b Sealed space 14 Body 15 Upper heater block 16 Lower heater block

Claims (4)

[Claims] 1. A molding method for obtaining an optical element by inserting a cylindrical optical element material between a molding die composed of a first die and a second die, heating and softening the material to perform pressure molding. While heating, the pressure is reduced at least once or more during heating or zeroed to press about half of the total deformation amount, and then the remaining about half deformation amount is pressed during cooling. And a method for molding an optical element. 2. After press molding about half of the temperature at a stage set between the yielding point temperature and the softening temperature, a molding amount of about the other half is applied on the stage set at a temperature near the glass transition temperature. The method of molding an optical element according to claim 1, wherein the molding is performed by pressure molding. 3. The method of molding an optical element according to claim 1, wherein about 80% of the total deformation amount is heated and pressed and deformed, and then the remaining deformation amount is pressed and deformed during cooling. 4. A cylindrical optical element material having a cut surface, a polished surface, or a split cross section is inserted between a molding die composed of a first die and a second die so that the end surface faces the die and heated. The optical element molding method according to claim 1, wherein the optical element is softened and pressure-molded.