JPH1160251A - Formation of optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for forming an optical element free from appearance defect and having excellent optical performance even from a glass preform having a polyhedral form and a boundary part at the connection part of the faces. SOLUTION: This forming process of an optical element includes a step to heat and deform a preform holding a forming face and a side face and having a boundary part at the connection part of the faces and a step to press the preform between molds. In the above process, the boundary part of the preform is locally heated at a temperature corresponding to the viscosity of 10<3> to 10<6> poise to form a free surface at the part constituting the boundary part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an optical glass element such as an optical lens or prism having a spherical or aspherical surface. More specifically, the present invention relates to a method of forming an optical glass element by heating and deforming a glass block processed into a shape such as a rod, a column, a cone, a triangle, and a block, and then forming the mold between molds. .

[0002]

2. Description of the Related Art As a conventional molding method of an optical element, a press molding method in which pressure molding is performed using a pair of mirror-finished dies is a typical method. In this press molding method, a glass lump is previously processed into a predetermined shape to form a preform having a certain degree of surface accuracy, and the preform is reheated and molded with a metal mold to give a desired surface accuracy. The "reheating method" is common, and mass production is possible even for glass lenses that require high precision.

According to the reheating method, since the shape of the preform is an important factor in molding, various proposals have been made on the production of the preform.
The preforms are roughly classified into a gob preform formed by cutting or dropping a molten glass flow while controlling it to a predetermined volume, and a polishing preform obtained by grinding and polishing a glass lump. A polished product whose shape is relatively easy to manage is suitable for molding a high-precision or large-diameter optical element. A typical example of the polishing preform is a cylindrical preform. A cylindrical preform is generally obtained by cutting a glass rod having a diameter corresponding to the diameter of the preform, and grinding and polishing the end surface into a curved surface or a planar shape according to the shape of the optical element to be molded. In particular, since they are relatively inexpensive and can be mass-produced, they are widely used for molding optical elements.

However, when a polished product is used, the surface of the preform is almost mirror-finished, that is, the surface roughness is Rmax.
It is necessary to finish the surface to a level of 0.02 μm or less to eliminate surface irregularities. If this finish is insufficient, confine the surface between the irregularities on the preform surface and the mold during press molding. Due to the generated air, an air pocket or a crater-shaped concave portion is generated on the surface of the optical element, and a desired mirror surface cannot be obtained.
In Japanese Patent Publication No. 2 and the like, the glass material is heated to a softening point or higher, and the surface of the glass material having an Rmax of about 0.1 to 5 μm is mirror-finished to about Rmax of about 0.05 μm.
A method of pressing has been proposed.

[0005] However, among the preforms obtained by grinding and polishing a glass block, if the above method is applied as it is to a preform having a square portion at a connecting portion between the surfaces, it is difficult to obtain a mirror-finished surface. Even if there is, a portion corresponding to the horn portion still remains in a horn shape, and at the time of forming a convex surface, this portion comes into contact with the surface of the mold first and molding starts before other portions. Then, undulation occurs between the preformed part and a part that has not yet contacted, or the preformed part solidifies first, so that a fold that causes an interface with another part whose solidification is delayed is generated. Occur. In addition, the previously solidified portion is chipped, causing linear scratches and the like, which causes a problem of poor appearance. Also, in order to heat the entire preform uniformly, if the heating temperature is further increased, the entire preform fluidizes,
It is difficult to control its shape. These problems have a problem that even when the corner portion is chamfered by about 1 mm, the same problem occurs near the chamfered portion. Furthermore, if a horn-shaped portion remains on the preform surface, this portion is cooled and solidified first and loses its elasticity.
If the glass surface has viscoelasticity, as the molding proceeds, a small amount of gas trapped between the mold and the glass is sent out from the end of the mold, but when the angular portion solidifies first, The discharged air is blocked from being discharged, and is trapped in the vicinity of the angular portion, so that air accumulation occurs.

Japanese Patent Application Laid-Open No. Hei 4-187528 discloses a technique for thermally deforming a corner of a preform by preheating. In this embodiment, the corner is formed with a curvature R.
It only describes that the surface is curved to 0.1 mm, but does not completely solve the problems of appearance defects such as undulation, breakage, linear scratches, and air pockets.

Japanese Patent Application Laid-Open No. 4-108620 discloses a technique of chamfering or spheroidizing an edge portion of a preform, and then heating and deforming the glass at a temperature at which the viscosity of the glass becomes about 10 ¹³ poise. in -73228 discloses in its examples, a technique of softening by heating to a temperature at which the viscosity of the glass is more than about 10 ⁶ poise is disclosed,
In any of the techniques, in the heating step, to uniformly heat the entire preform to each of the above temperatures,
Since the entire preform is fluidized and collapses in shape due to its own weight, it has been very difficult to form an optical element by this technique.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. Even if the glass preform has a polyhedral shape and has a boundary portion at a connecting portion between the surfaces, the appearance is poor. It is an object of the present invention to provide a molding method capable of obtaining an optical element having excellent optical performance without the above.

[0009]

According to the present invention, there is provided a step of heating and deforming a preform having a molding surface and side surfaces and having a boundary portion at a connection portion between the surfaces and pressure molding between molds. In the method of molding an optical element, the boundary portion of the preform is made to have a viscosity in the heating deformation step.
^3-10 was locally heated at the corresponding temperatures ⁶ poise relates molding method for an optical element, which comprises the free surface of the surfaces constituting the boundary portion.

According to the present invention, in the heating deformation step, the boundary between the molding surface and the side surface of the preform is made to have a viscosity of 10 ³ to 10 ⁶ poise instead of heating the entire preform uniformly. Is locally heated at a temperature corresponding to By locally heating and softening and deforming the boundary portion in this way, the surface constituting the boundary portion is free-formed, so that pressure molding can be performed in a state where there is no square portion on the surface of the preform. It becomes possible. As a result, it is possible to obtain an optical element having excellent optical performance without poor appearance by press molding.

In the present specification, the term “boundary portion” refers to, for example,
In the connecting portion between the molding surface and the side surface of the polyhedral preform, it refers to a horn-like portion (discontinuous surface portion) which may cause undulation or folding on the surface of the optical element after the subsequent pressure molding, The term “free surface formation” means that the surface forming the boundary portion is continuously curved to such an extent that the above-mentioned problem does not occur by the subsequent pressure molding.

The glass that can be used in the present invention may be made of any glass material, for example, white plate glass B270, BK7, SF14 glass, Pyrex (heat-resistant glass), or the like. Rods made of these glasses are cut to the desired thickness, and one or both end faces are cut into a curved or flat shape,
It is ground and used as a preform. If the surface roughness is within the range of Rmax 0.1 to 5 μm, the cost is not too high, and the irregularities on the glass surface can be eliminated by a subsequent heat treatment. Usually, the surface roughness of the cut surface in this case is about Rmax 3 μm.

[0013] The preform used in the method of the present invention has a polyhedral shape, and has at least a boundary portion at a connecting portion between the surfaces. Further, the method of the present invention can be usefully applied to a preform in which the boundary portion is chamfered, and further to a preform in which the boundary portion is curved to a radius of curvature of about 5 mm or less. Specifically, a preform having a shape such as a rod, a cylinder, a cone, a triangular prism, a block, or the like obtained by cutting out a rod-shaped glass is used.

In the method of forming an optical element according to the present invention, at least the boundary portion of such a glass preform is set to 10 ³ to 10 ³ .
The method includes a step of locally deforming by heating at a temperature corresponding to 10 ⁶ poise and a step of pressure-forming the preform that has been deformed by heating. It is preferable that the preform be subjected to a step of removing fine glass fragments on the surface generated by cutting and grinding before the heating deformation step. For example, the method of the present invention is applied by a series of manufacturing steps as shown in FIG. Hereinafter, the case where the preform has a cylindrical shape will be described with reference to FIG.

In the present invention, first, preform 1
Is transported to the washing / drying device 2 for cutting the preform,
The small glass fragments on the surface generated by the grinding are removed and dried. The removal method is not particularly limited, as long as the small glass pieces remaining on the glass surface can be completely removed without substantially changing the surface of the glass.

For example, there is a method using a cleaning solution containing a synthetic detergent. In general, the cleaning liquid is preferably a cleaning liquid used for cleaning a completed optical element with an ultrasonic cleaning machine. The cleaning liquid removes stains such as machine oil and dust by a surface active effect, and at the same time, cleans the glass surface and fine glass fragments. Slightly dissolves the surface of the area where
It is considered that the separation from the surface of the fine glass piece is promoted in combination with the cavitation effect by the ultrasonic wave. Therefore, in the step of removing the small glass pieces, it is desirable to perform ultrasonic cleaning while immersing the preform to which the glass pieces are attached in a cleaning solution.

As a drying method, there is a method of heating to 100 ° C. or more in a heating furnace, or a method of drying by volatilization of a solvent.

The preform 1 thus washed and dried is subjected to a heating deformation step. More specifically inserted in an electric furnace 3 by placing the said preform 1 carrying support member (cemented carbide) 4, the boundary portions in the viscosity of 10 ³ to 10 ⁶
Heat locally with a heater at a poise temperature for 5-20 minutes. With respect to the heating temperature, if the glass viscosity at the boundary is higher than the temperature corresponding to 10 ³ poise, the whole glass is fluidized, and it is difficult to control the shape. On the other hand, if the temperature is lower than 10 ⁶ poise, not only the desired surface accuracy cannot be obtained on the preform surface, but also the thermal deformation is limited to a small part of the surface, and the preform shape is not deformed. Therefore, the top and side surfaces are free surfaces, that is, both surfaces are not continuously curved over the entire surface.

In the present invention, in order to set the viscosity at the boundary of the preform within the above specified range,
The entire preform is fluidized so that the shape of the preform cannot be controlled, and the surface of the part other than the boundary part of the preform is moderately softened in the vicinity of a depth of 10 to 20%, so that the preform surface has a desired surface. It is possible to reduce the accuracy and the surface roughness to Rmax 0.05 μm or less. As a result, deformation occurs around the initial boundary portion of the preform, and the entire surface (referred to as “molding surface”) on which desired surface accuracy is to be transferred in a pressure molding step described later is continuously curved. . For this reason, it is considered that the optical element manufactured by using the preform does not generate undulation or breakage, and linear scratches and air pools, which have conventionally been problems.

In the method of the present invention, the boundary portion is locally heated to a high temperature and softened so that the viscosity of the boundary portion falls within the above range. “Locally heating the boundary portion” intends to locally heat the boundary portion and its vicinity, and does not exclude heating of the preform other than the boundary portion. The specific method of locally heating the boundary portion in the heating furnace is roughly divided into: 1. a method of heating the entire preform in the same step as the step of heating the entire preform to impart a desired surface accuracy to the preform surface by applying a temperature gradient with a heating force; A method of separately providing a step of intensively heating only the boundary portion before and after the step of heating the entire preform is exemplified. The specific method of the former is as follows. 1. Increasing the number of turns of the heating heater coil for heating a portion to be locally heated (boundary portion) among a plurality of heating heater coils installed in the heating furnace; There is a method in which a heater coil for heating a portion to be heated locally (boundary portion) is closer to a preform than an other heater coil. Also, if the output of the heater is sufficiently high, it is necessary to arrange the heater only at the position facing the boundary of the preform, and if a sufficient temperature gradient occurs, it is not necessary to arrange the heater in other parts. Absent. As a specific method of the latter, a method of separately providing a step of heating a boundary portion with an infrared lamp or the like before or after the step of heating the entire preform in a heating furnace is exemplified.

In the heating deformation step in FIG. 1, a heating heater coil 31 for heating a portion to be heated locally (boundary portion) in order to impart a temperature gradient with a heating force.
A method in which the installation position of E is closer to the preform than the other heater coils 31 is adopted. In the electric furnace 3 employing this method, the preform 1 is heated by the heater coils 31 and 31E for 5 to 20 minutes at a temperature at which the boundary portion Z has a viscosity of 10 ³ to 10 ⁶ poise. In this case, “locally heating” specifically means that the temperature of the boundary portion of the preform should be about 50 to 150 ° C. higher than other parts of the preform, and preferably 90 to 150 ° C. It is about 120 ° C higher. If the temperature is lower than 50 ° C., the effect of locally heating is not obtained even when heating, that is, the entire preform may be fluidized or the boundary may remain in a square shape. There is a possibility that the shape of only the boundary portion to be heated is extremely deformed. Specifically, FIG. 2 shows the temperature difference (x) between the temperature of the boundary portion of the preform and the temperature of the other portion of the preform. FIG. 2 is a temperature distribution diagram in which the height inside the electric furnace near the glass preform is plotted on the horizontal axis. Such temperature control can be achieved by arranging a thermocouple or a radiation thermometer near the boundary portion and other portions of the preform and monitoring the temperature.

The temperature of the boundary portion set in the heating deformation step, that is, the temperature at which the viscosity becomes 10 ³ to 10 ⁶ poise differs depending on the glass material.
About 890-1030 ° C. for SF14, about 7 for SF14
50 to 840 ° C, about 800 to 1100 ° C for BK7
Is appropriate. Therefore, the temperature of the portion other than the boundary portion is, for example, about 740 to 9 in the case of glass B270.
50 ° C, about 650-750 ° C for SF14, BK7
In the case of the above, about 650-950 ° C. is appropriate.

When the upper surface and the side surface of the cylindrical preform are formed as free surfaces as described above, the curvature of the formed free surface is at least the metal used to face the surface in the subsequent pressure molding step. It must be larger than the curvature of the mold.

After the heating is completed, the preform 1 is taken out of the support member 4 after being left to cool. When the preform 1 is taken out from the support member, a gentle free surface 8 is formed on the opposite surface of the support member by thermal deformation, and the surface roughness Rmax is set at 0. 01-0.05 μm, preferably Rm
ax secures 0.02 to 0.03 μm.

Next, the preform is further subjected to a press molding step to precisely control the shape. In the case where the supporting member 4 in the heating deformation step can be used as a lower mold in press molding, the preform can be subjected to the press molding step only by transporting the preform placed on the lower mold after the heat deformation processing. On the other hand, when the supporting member does not double as the lower mold, the preform after the heat deformation treatment is transferred while being placed on the supporting member and then transferred between the molds, or the preform on the supporting member is First transferred to the lower mold and transported,
It is necessary to provide for a press forming process.

The press molding is performed by a conventionally used press molding machine. For example, before the obtained preform is almost cooled, the preform is transferred between a mold having a desired surface accuracy as described above. Install and apply pressure to the mold to transfer the surface accuracy and shape of the mold surface.

Specifically, when the preform 1 shown in FIG. 1 is press-formed, an optical glass element can be produced by a reheat press method using a general press-forming apparatus. The illustrated example shows an example in which the support member also serves as a lower mold. An upper mold 14 (made of tungsten carbide) having a concave aspherical precision mirror-finished mold surface and a holding mold 16A for holding the same, a support member 4 precision-machined in a planar shape, and a holding for holding the same Mold 16B (made of carbon). Holding die 16 by push rod 17
A moves downward integrally with the upper mold 14 and engages with the holding mold 16B integrated with the support member 4. The above-mentioned mold structure is composed of a heating element 19 installed on the outer periphery of a transparent quartz tube 18.
Thermocouple 20 is embedded in the holding mold 16B.
And the temperature is controlled.

After the preform 1 is placed on the support member 4, the preform 1 is heated to the transition point +80 to 120 ° C. by the heating element 19 under a nitrogen atmosphere, and the push rod 17 is lowered. A pressure is applied to the mold 14 and the holding mold 16A for holding the mold 14 by applying a load (load: 20 to
200 kgf, pressurization time: 30 to 180 seconds). Next, the pressure of the push rod 17 is removed, and each mold (14, 16A, 16
In B), the pressure molded product, that is, the optical glass element is allowed to cool while being surrounded, and then the glass element is taken out.
The shape of the mold surface is accurately transferred onto the surface of the optical glass element.

The surface accuracy of the mold is about the same as the surface accuracy of the transfer surface of the support member (excluding the case of a mold).
Or higher. This is because the surface accuracy of the mold is given to the surface of the optical glass element as a result, so that even if both precisions of the preform are high, it is meaningless if both precisions of the mold are low. That is, the surface roughness is set to Rmax0.
About 0.01 to 0.05 μm, particularly Rmax 0.01 to 0.0 μm.
03 μm is preferred.

The mold shape is designed according to the desired shape of the optical element. The heating temperature in press molding is not particularly limited as long as the preform surface has a desired mirror surface due to the previous heating deformation treatment, so long as the preform shape can be finely adjusted. Specifically, it is desirable to set the viscosity near the preform surface to be 10 ⁶ to 10 ⁹ poise, preferably 10 ⁷ to 10 ⁸ poise.

In the press forming as described above, the boundary portion at the connecting portion between the upper surface of the cylindrical preform and the cylindrical surface is blunted by the heat deformation and becomes a continuous curved surface. It is possible to form a convex optical element having excellent appearance quality without causing any scratches. The present invention is described in more detail by the following examples.

[0032]

EXAMPLE 1 Example 1 will be described with reference to FIG. In this embodiment,
A plano-convex optical glass element having an effective diameter of 30 mm, a core thickness of 25 mm, a convex aspheric surface having an approximate curvature of R = 40 mm on one surface, and a flat surface on the other surface was formed.

First, the rod material of the white sheet glass B270 was cut into a substantially columnar shape to have a diameter of 40 mm and a thickness of 40 mm.
When the roughness of the cut surface and other surfaces of the preform was measured by a commercially available surface roughness meter (manufactured by Waiko Co., Ltd.), the cut surface was Rmax 3 μm, and the other surfaces were Rmax1 μm.

The preform 1 was supplied to a washing / drying device 2 to remove fine glass fragments remaining on the surface of the preform. When the surface roughness was measured again, the cut surface was Rmax 2.9 μm, and the other surfaces were Rmax 1 μm.

Next, the preform 1 from which the fine glass pieces have been removed in this manner is placed on a support member 4 which is planar and also serves as a lower mold as shown in FIG. It was subjected to deformation processing. Inside the electric furnace 3, heating elements 31, 31E (manufactured by Kanthal Gadelius: Kanthal Super Heater 1) assembled in a heating coil shape are installed.
In the vicinity of the boundary portion Z between the upper surface (molding surface) and the cylindrical surface (side surface), the structure is such that the distance between the coil and the preform surface is closer than other portions. That is,
The distance between the cylindrical surface portion and the heating element 31 was 30 mm, and the distance between the cylindrical portion and the heating element 31E was 15 mm. With this distance, the temperature of the boundary portion can be set to a desired temperature, that is, about 50 to 150 ° C. higher than the temperature of the other portions, and the boundary portion is softened and deformed by heat to form the molding surface. And the side surface could be a free surface with an approximate curvature of R = 35 mm. In the electric furnace 3, the temperature of the boundary portion of the preform made of B270 becomes 10 ⁴ poise.
Maintained at 000 ° C. for 7 minutes. FIG. 2 (x = 150 ° C.) shows the temperature distribution in which the horizontal axis represents the height inside the electric furnace near the glass preform during the maintenance.

After the heating, the preform 1 is supported
Is transported to the molding position, that is, the lower part of the upper mold 14, and is pressure-formed at a pressure of 20 kg / cm ^{2 for} 120 seconds between the support member 4 also serving as the lower mold and the upper mold 14. did. The molded product was cooled and taken out.

The upper mold 14 is an aspherical concave mold having a transfer surface with Rmax of 0.03 μm and an approximate curvature of R = 40 mm.
The support member 4 is a flat surface having a transfer surface with a surface combination Rmax of 0.03 μm. When the surface assembly of the pressure molded product taken out, that is, the surface of the optical glass element 12 which was in contact with the upper mold 14 was measured by a stylus type surface roughness meter (manufactured by Waiko Co., Ltd.), the surface roughness Rmax0. 03 μm. The optical glass element had a transfer surface shape transferred accurately, and had a convex aspheric surface with an approximate curvature R = 40 mm. On the opposite surface, a plane having a surface set of Rmax 0.03 μm was transferred. Further, when these curved surfaces and flat surfaces were observed with a differential interference microscope at a magnification of 50 times, no circumferential scratches were observed at all. From the above, it can be seen that the shape is accurately controlled.

Thus, the effective diameter is 30 mm, the core thickness is 25 mm, and one surface has an approximate curvature of R = 40 mm.
A plano-convex optical glass element having a convex aspheric surface and the other surface being a flat surface was obtained.

Embodiment 2 A description will be given with reference to FIGS. In this embodiment, the effective diameter is 33 mm, the core thickness is 25 mm,
A biconvex optical glass element was formed in which one surface was a convex aspheric surface having an approximate curvature of R = 25 mm and the other surface was a convex aspheric surface having an approximate curvature of R = 30 mm.

First, the rod material of the optical glass BK7 was cut into a substantially cylindrical shape to have a diameter of 38 mm and a thickness of 33 mm.

Next, one end is ground into a spherical shape of about R = 28 mm, and the other end is a chamfered portion 1 inclined 30 ° with respect to the center axis of the preform over a width of 5 mm.
11 is formed by grinding, and about R =
A 35 mm spherical surface was ground to obtain a preform 11 shown in FIG.

The preform 11 is washed and dried by the
To remove fine glass fragments remaining on the surface of the preform.

On the other hand, as shown in FIG. 3, the support member 41 is a ring-shaped member made of cemented carbide and having an inner diameter of 36 mm, and the chamfered portion 111 of the preform 11 has a width of about 1 mm on the inner peripheral surface of the support member. A contact surface 411 was formed.

The reason why the ring-shaped support member is used is that the surface on the side in contact with the support member can also be softened by heating. Also, the reason why the chamfered portion 111 is made to have a width of about 1 mm is that the chamfered portion 111 and the inside of the chamfered portion 111 are about
This is because, similarly to the opposite side, the boundary portion between the m and the spherical surface is directly exposed to the heating coil to be softened and deformed to form a continuous curved surface.

In this state, the preform 11 was set on the support member 41, inserted into the electric furnace 5 (FIG. 4), and subjected to a heat deformation process. Inside the electric furnace 5, as shown in FIG.
Upper and lower heating elements (Kanthal supermarket: Kanthal super) 52, 53 are installed in a panel heater shape at positions 20 mm apart from the apexes of both spherical surfaces in the horizontal direction, and no heating elements are provided on the cylindrical surface side. Was.

With such a configuration, the temperature cannot be controlled as accurately as in the above embodiment, but a temperature distribution of about 50 to 150 ° C. can be formed near the center of the cylindrical surface and both end surfaces. Was.

In the electric furnace 5, 800 ° C., at which the corners (boundaries) of the preform made of BK7 become 10 ⁴ poise
For 7 minutes. FIG. 5 (x = 150 ° C.) shows the temperature distribution with the horizontal axis representing the height inside the electric furnace near the glass preform during this maintenance.

After the completion of the heating, the preform 11 was conveyed to the molding position, that is, the lower part of the upper mold 14 while the preform 11 was placed on the support member 41.

In this embodiment, after the preform is transported to the molding position by the support member 41, the preform is transferred onto a lower mold (not shown) and is pressure-formed with the upper mold.

The upper mold is an aspherical concave mold having a transfer surface with Rmax = 0.03 μm and an approximate curvature R = 25 mm, and the lower mold is ground and polished to a concave aspherical surface with an approximate curvature R = 30 mm. It is.

Here, the mold was pressurized at a pressure of 1.0 kg / cm ^{2 for} 120 seconds, and the molded product was taken out after cooling. The pressure-molded product taken out, that is, the surface assembly of the surface of the optical glass element that was in contact with the upper and lower molds was measured by a stylus type surface roughness meter (manufactured by Waiko Co., Ltd.). Rmax = 0.03 μm and approximate curvature R = 25
mm (upper mold surface) and R = 30 mm (lower mold surface).

Further, when these two curved surfaces were observed with a differential interference microscope at a magnification of 50 times, no circumferential scratch was observed.

In this way, the shape is accurately controlled, the effective diameter is 33 mm, the core thickness is 25 mm, one surface has a convex aspheric surface with an approximate curvature of R = 25 mm, and the other surface has an approximate curvature. A biconvex aspheric optical glass element having a convex aspheric surface of R = 30 mm was obtained.

Comparative Example 1 A general heating coil was used in place of the coil of Example 1 above.
That is, when the preform was heated and deformed in an electric furnace provided with a uniform temperature distribution and the boundary of the preform was inspected, the corners were clearly left in a ring shape as shown in FIG. .

The preform was pressed under the same conditions as in Example 1 to obtain an optical glass element.
When the appearance quality of the optical glass element was confirmed, undulations, breaks, and linear scratches were found, and such poor appearance could be easily discriminated visually.

[0056]

According to the method of the present invention, at least the boundary portion of the preform which has been ground and polished is heated and deformed at a temperature corresponding to 10 ⁶ to 10 ³ poise by making the viscosity of the glass into a glass, and the surface is made almost continuous. By having a curved surface, even in the case of a preform having a boundary portion, there is no occurrence of a square portion on the surface of the preform after press molding, and as a result, undulation or folding in the molded optical glass element, ring An optical element having excellent appearance quality and optical performance can be easily provided without causing linear scratches or air accumulation.

If the present invention is applied to a cylindrical preform, it is possible to mold an optical element using the cylindrical preform without cutting the glass rod and grinding and polishing both end surfaces without special chamfering or the like. it can.

At least one end of the glass preform is formed into a curved surface, and the boundary between the curved portion and the cylindrical surface is heated to a temperature corresponding to 10 ⁶ to 10 ³ poise by setting the viscosity of the glass to a continuous curved surface. By doing so, molding can be performed using a glass preform that is more similar to the shape of the desired optical element.

Before or after uniformly heating the glass preform, the boundary portion is concentrated and heated again, whereby the configuration of the heating device can be simplified.

A temperature distribution is formed such that the heating force of the portion facing the boundary portion of the preform is higher than that of the other portions, and the glass in the vicinity of the boundary portion has a viscosity of 10 ⁶ -1.
By setting the temperature to be equal to 0 ³ poise, the edge portion can be heated without providing a separate reheating step.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a step of performing a method of the present invention.

FIG. 2 is a diagram showing a temperature distribution inside an electric furnace in a heating deformation processing step of Example 1.

FIG. 3 is an explanatory view of a preform and a support member according to a second embodiment.

FIG. 4 is a schematic diagram showing an internal state of an electric furnace immediately before the start of a heating deformation process in Example 2.

FIG. 5 is a diagram showing a temperature distribution inside an electric furnace in a heating deformation processing step of Example 2.

FIG. 6 is a schematic diagram of an appearance shape of a preform after a heat deformation treatment in a comparative example.

[Explanation of symbols]

1: Preform 2: Cleaning / drying device 3: Electric furnace
4: support member, 5: electric furnace, 8: free surface, 11: preform, 12: optical glass element, 14: upper mold, 16
A: holding type, 16B: holding type, 17: push rod, 18: transparent quartz tube, 19: heating element, 20: thermocouple, 31: heating element, 31E: heating element for boundary portion, 41: support member, 5
2: upper heating element, 53: lower heating element, 111: chamfered part, 4
11: contact surface, Z: boundary portion

Claims (5)

[Claims] 1. An optical element molding method comprising: a step of heating and deforming a preform having a molding surface and side surfaces and having a boundary portion at a connection portion between the surfaces, and a step of pressure molding between molds. The method is characterized in that the boundary portion of the preform is locally heated at a temperature corresponding to 10 ³ to 10 ⁶ poise in a heating deformation step to make the surface constituting the boundary portion a free surface. Optical element molding method. 2. The method according to claim 1, wherein the preform has a cylindrical shape. 3. The method for molding an optical element according to claim 2, wherein at least one end of the cylindrical preform is subjected to a curved surface processing. 4. The method according to claim 1, wherein in the step of heating and deforming the glass preform, a temperature gradient is applied so that a heating force at a boundary portion of the preform is higher than that at other portions. A method for forming an optical element according to any one of the above. 5. An optical element molding method including a step of heating and deforming a preform having a molding surface and a side surface and having a boundary portion at a connection portion between the surfaces, and a step of pressure molding between molds. In the method, before the surface forming the boundary portion is free-surfaced by locally concentrated heating at a temperature corresponding to 10 ³ to 10 ⁶ poise by making only the boundary portion of the preform into a viscosity in the heating deformation step, or A method for forming an optical element, comprising: uniformly heating the entire preform after forming a free surface.