JPS6379727A - Method for forming optical element - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming optical elements, such as glass lenses used in optical equipment, by precision glass molding.

2. Description of the Related Art In recent years, many attempts have been made to form optical elements such as optical lenses by one-shot molding without a polishing process. The most efficient method is to pour the glass material from a molten state into a mold and press-form it, but it is difficult to control the shrinkage of the glass during cooling, and it is not suitable for precision glass molding. Therefore,
A common method is to pre-process a glass material into a certain shape, feed it between molds, heat it, and press-form it.

(For example, JP-A-58-84134).

At that time, in order to obtain high-precision glass molded products, it is necessary to reliably transfer the shape of the molding surface of the mold to the glass, but especially during the cooling process after the deformation, the shape of the mold It is important that the surface is in close contact with the glass molding. As a means to achieve this, JP-A-60-14591
No. 9 discloses a method in which a spacing regulating member having a larger thermal expansion coefficient than glass is used between upper and lower molds.

Hereinafter, the above-mentioned conventional molding method will be explained with reference to the drawings.

FIG. 3 is a sectional view showing a lens formed by molding a glass material using a conventional method. 14 is a molded lens, 1) and 12 are a pair of molds, 13 is a spacing regulating member, and 15 is a supporting member. Glass material supporting member 15
After holding the glass and heating it by an appropriate method to a temperature near the softening point of the glass, a pair of molds 1). 1) by a pressurizing mechanism (not shown). Pressure is applied to mold No. 12 for pressure molding. In the cooling process after the deformation, the mold,
All the parts such as the lenses will shrink, and if a common material is used as the space regulating member in the configuration shown in Figure 3, the thermal shrinkage of the glass will be larger than other elements, so the upper mold 1) and lower mold 1
2 pressure is not effectively applied to the lens 14. However, if the thermal expansion coefficient of the spacing regulating member 13 is made larger than that of the lens 14 and the cooling of the spacing regulating member 13 is precisely controlled, the above drawbacks can be overcome. That is, the above-mentioned Unexamined Patent Publication No. 6
As disclosed in Japanese Patent No. 0-145919, after the deformation is completed, the pressurized state is maintained below the strain point of the glass, and the temperature of the spacing regulating member is accurately measured, and when the temperature reaches a preset temperature. If the movement of the mold is stopped, that is, the application of pressure is stopped, the movement of the mold follows the contraction of the lens during this period, so that accurate transfer can be performed.

Problems to be Solved by the Invention However, in the above method, in order to realize precise transfer of an optical surface, precise control of the temperature of the distance regulating member and therefore a long molding time are required. The main reason for this is that the thermal expansion of glass exhibits a characteristic behavior. The state of thermal expansion of glass will be explained in detail with reference to FIG. Second
In the figure, (al represents the glass thermal expansion degree. (bl
represents the thermal expansion of metal materials for comparison. Like metal materials, glass expands almost linearly with temperature rise up to its glass transition point. When the transition point is exceeded, the expansion rapidly increases and becomes several times larger than below the transition point.

As the temperature rises further and exceeds the yielding point, the expansion becomes even greater, but the glass begins to deform and no longer appears to expand.

Precision molding of glass is carried out at temperatures above the yielding point or transition point, so if you want to precisely control shrinkage during cooling, it is necessary to precisely control the temperature below the transition point, for example below the strain point, where shrinkage occurs at an almost constant rate. After molding, the mold and optical element must be cooled under pressure for a long time.

In view of the above-mentioned problems, the present invention provides a method in which the temperature of the mold can be easily controlled and a high-precision optical element can be molded in a short time by selecting a material constituting the body mold.

Means for Solving the Problems In order to solve the above problems, the optical element molding method of the present invention involves placing a glass material in a cavity formed by a pair of molds and a body mold, and molding the optical element. In the molding method, the thickness of the optical element is controlled by regulating the distance between a pair of molds using a body mold that is made of the same material as the glass material to be molded and includes a spacer with a thickness that approximates the thickness of the desired optical element. The mold and glass material are heated to a temperature higher than the glass transition point and lower than the softening point, and pressurized to form the mold. Furthermore, a method is used in which the coefficient of thermal expansion of the part that contacts the glass material is smaller than or equal to that of the glass material, and that the part that does not contact the glass material includes the above-mentioned spacer.

Function: As described above, the material used for the part of the body mold that controls the thickness of the optical element is the same material as the optical element to be molded, so that the shrinkage of the optical element is avoided during the cooling process after the glass has been deformed. Since the barrel mold contracts at the same rate, the pressure applied to the mold is effectively applied to the optical element surface, so that the optical surface shape of the mold can be accurately transferred to the optical element.

At this time, since the optical element and the barrel mold shrink at the same rate, there is no need to particularly strictly control the temperature of the spacing regulating member, and it is not necessary to cool the optical element by holding it between the molds for a long time. Nor.

Furthermore, by arranging a spacer that controls shrinkage during cooling in a portion not in contact with the optical element, it is possible to simultaneously control the outer periphery of the circular optical element.

EXAMPLE Hereinafter, lens molding will be described as an example of the optical element molding method of the present invention with reference to the drawings.

FIG. 1 is a sectional view showing a molded state of an embodiment of the present invention. 1 and 2 are molds having optical surfaces to be transferred to lenses. The material is a high-strength, high-heat-resistant material such as zirconium oxide, silicon nitride, or tungsten carbide. 6 is a molded lens. The circular mold 3 has an internal structure as shown in the figure. A deep ring-shaped groove is formed in a part of the circular shape, a spacer 5 is inserted into the groove, and a thickness control member 4 is placed on top of the spacer 5.

The circular mold 3 and the thickness control member 4 are made of the same material as the mold 1.2. The spacer 5 has approximately the same thickness as the lens 6 to be molded, and is made of the same material as the lens 6 to be molded.

FIG. 1 shows a state in which the glass has just been deformed and a lens 6 has been formed. Pressure is applied to the mold 1.2 by a pressure mechanism (not shown) in a direction to compress the lens. The optical axis of the lens is regulated by the inner circumference of the circular shape 3. The thickness of the lens is circular 3, thickness control member 4 and spacer 5
It is regulated by determining the spacing between the upper and lower molds. When forming high-precision glass lenses by pressing, the glass is deformed by applying pressure between the softening point and the yielding point.
Continue to pressurize and cool down to below the transfer point.

As can be seen from FIG. 2, the thermal expansion of the glass is extremely large during this period. When cooling is started from this state, not only the lens 6 but also everything including the mold and the circular shape starts to shrink. Generally, the coefficient of thermal expansion of glass material is 7~10X
Since the coefficient of thermal expansion is about IO-'/'C, which is larger than the coefficient of thermal expansion of about 5X10-'/'C of the mold and body material, the shrinkage is larger than that of the mold during cooling. However, in this case, the spacer 5 contracts as much or as much as the lens 6, so that the pressure applied to the mold is effectively transmitted to the lens 6. Glass can be deformed under pressure up to its transition temperature, so
Cool the glass in the state shown in the figure to the transition temperature of the glass or a temperature slightly lower than the transition temperature. In this way, the optical surface of the mold is accurately transferred to the lens, and lenses can be molded with high precision.

Even if a material with a coefficient of thermal expansion larger than that of glass at room temperature, such as a metal material, is used as a circular shape or a spacing regulating member, at the temperature at which the glass actually deforms and starts shrinking, as shown in Figure 2. As shown in Figure 2, glass shrinks more than glass, and even during the cooling process after deformation, the pressure of the mold is not effectively applied to the lens at temperatures above the transition point, as described above. Therefore, it is necessary to maintain this state even below the transition point and cool it to a temperature below the strain point as described in the above-mentioned known example. This results in a longer molding cycle.

Furthermore, if the glass material is heated separately from the mold and supplied between the molds, and molding is attempted with a temperature difference between the mold and the glass, in the conventional example, the temperature of the spacing regulating member must be precisely controlled. Therefore, it is necessary to control the pressurization of the mold. However, according to the method of the present invention, since the mold and glass are heated as one unit, there is almost no temperature difference between the mold and glass, and this, combined with the method of using the same glass material as the spacer molded glass material, makes it possible to Precise lenses can be molded without the need for temperature control. At the same time, the outer diameter of the lens is regulated by the circular shape, and centering after molding can be omitted.

Molded lenses undergo thermal contraction even at temperatures below the transition point, so the shape at which the pressure is stopped and the shape at which the lens is cooled to room temperature are naturally different, but the coefficient of thermal expansion can be considered to be approximately constant during this time. It is sufficient to design the spacer and thickness regulating member in advance with this in mind.

An example of actually molding a lens using the method shown in FIG. 1 will be described. 5F-6 was used as the material for the lens. The coefficient of thermal expansion of 5F-6 is 9.7 x 10-6/'C, the glass transition point is 435°C, the yield point is 464°C, and the softening point is 53°C.
It is 6℃. The outer diameter of the lens is 15 mm and the thickness is 41 mm. Tungsten carbide having a coefficient of thermal expansion of 5.1X10-'/'C was used as the material for the molds 1 and 2, the circular mold 3, and the thickness regulating member 4. The spacer 5 is made of the same material 5 as the lens.
F-6 was used and the thickness was 4 am. The thickness of the lens was regulated by the body mold 3, the thickness regulating member 4, and the spacer 5, so that the thickness regulating member 4 was placed in contact with the upper mold 1 as shown in the figure.

The molding temperature was set at approximately 485°C, and the pressure was cooled to 430°C. After that, the pressure was stopped and the lens was removed from the molding equipment. When the shape of the lens was measured, the optical surface of the mold was transferred with extremely high precision down to 0.1 μm. Was.

In the above embodiments, a spacer made of a glass member is arranged to form a groove in the body mold and control thermal expansion, but various modifications can be made to this structure. For example, the body mold may be formed into a double ring shape, and a structure for controlling thermal expansion may be built into the outer body mold. In either case, the portion in contact with the lens to be molded must be made of a material having a coefficient of thermal expansion smaller than or equal to that of glass. This is because if the barrel mold shrinks more during the cooling process, it will be extremely difficult to remove the lens from the barrel mold after cooling. Further, since glass is a material that easily deforms near the molding temperature, in order to maintain its thickness when used as a spacer, it is necessary to hold it in some kind of sealed structure as in the above embodiment. Further, in the above embodiments, an example of molding a glass lens has been described, but it goes without saying that other similar optical glass elements can also be precisely molded by the present invention.

Effects of the Invention As described above, the present invention makes the thermal expansion of the barrel shape that regulates the thickness almost equal to the thermal expansion of the glass when molding a glass optical element, so that the optical element can be It is possible to effectively maintain the pressure applied to the mold, accurately transfer the shape of the optical surface of the mold onto the optical element, and mold extremely high-precision optical elements with simple temperature control and a relatively short cooling time. This effect is achieved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the molding state of a lens in an embodiment of the present invention, FIG. 2 is a graph showing the thermal expansion of glass, and FIG. 3 is a sectional view showing the molding method in a conventional example. 1.2.1). 12... Molding mold, 3.4.5.
...Body type, 6.14... Molded lens, 13... Spacing regulating member, 15...
Support member. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 1 Figure 2 Number supervised exhibition Figure 3

Claims (2)

[Claims] (1) A method of molding an optical element by placing a glass material in a cavity formed by a pair of molds and a body mold, in which the lens is made of the same material as the glass material to be molded and has a desired thickness. The thickness of the optical element is controlled by regulating the distance between the pair of molds using a body mold including a spacer with a thickness similar to A method for molding an optical element characterized by molding under pressure. (2) The coefficient of thermal expansion of the portion that contacts the glass material is smaller than or equal to that of the glass material, and the portion that does not contact the glass material includes a spacer, as set forth in claim (1). A method for molding optical elements.