JPH0733448A - Method for forming glass optical element - Google Patents

Abstract

PURPOSE:To shorten forming time and to enable fine adjustment of production quantities by separating fused glass of a specific viscosity from a vessel, supplying this glass to molds, subjecting the glass to press holding and cooling the glass down to a glass transition temp. or below. CONSTITUTION:A glass blank 33 metered to the volume corresponding to one piece of optical element is placed on the vessel 32 and is charged from an inlet 31a by a push rod 34 into a heating furnace 31 where the glass blank is heated by a coil 31c and fused glass gob 33a having <=10<7> poise viscosity is obtd. This glass gob 33a is then taken out of the heating furnace 31 by a handling arm 35 and is dropped from a dropping port 36a of a gliding table 36 standing by under an outlet 31b of the furnace 31 by rotating a revolving shaft 35a onto the lower mold 37a of the temp. lower than the glass gob 33a. The lower mold 37a is then transported onto the upper mold and the glass gob is subjected to press holding and thereafter, the glass is cooled clown to the glass transition temp or below.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently producing an optical element such as a lens by pressing molten glass with a molding die facing each other.

[0002]

2. Description of the Related Art There have been many inventions and proposals relating to a method of molding an optical element of this type, but most of them have been classified into the following two types. First method (JP-A-4-438)
A typical example of the second method (Japanese Patent Laid-Open No. 3-137030) is shown in FIG.

The first method is to heat a glass material 1 adjusted to the volume of an optical element with a heater 2 (see FIG. 12).
(A)), as shown in FIG. 12 (b), a spherical glass gob 1a is formed, and then the glass gob 1a is held in a state of being sandwiched between a pair of molding dies 3 as shown in FIG. 12 (c). At the same time, the molding die 3 and the glass gob 1a are heated to a temperature (glass softening temperature or higher) at which the glass gob 1a is softened and deformed, press-molded, and then molded into an optical element.
Is a method of solidifying by cooling. In the first method, the temperature of the glass gob 1a changes in synchronism with that of the molding die 3, and is therefore referred to as "isothermal molding method" in the present specification.

The second method, as shown in FIG. 13 (a), is a large amount of molten glass 1 melted in a crucible (container) 2.
1 is dropped from a nozzle provided in the lower part of the crucible 12 onto the lower mold 13a as a molten glass gob 11a having a volume corresponding to the target optical element, and is opposed to the lower mold 13a as shown in FIG. 13 (b). This is a method of press molding with the upper mold 13b. In this method, the upper and lower molds 13a and 13b are adjusted to a temperature lower than the glass softening temperature, and the molten glass gob 11a
Is molded by being cooled by the upper and lower molds 13a and 13b. Therefore, in this second method, since there is a temperature difference between the molten glass gob 11a and the upper and lower molds 13a and 13b,
In the present specification, the term "non-isothermal molding method" is used.

[0005]

However, each of the above-mentioned two types of molding methods has the following drawbacks.

That is, in the "isothermal molding method", since the glass material 1 is heated and cooled together with the molding die 3, there is a drawback that one molding takes time as compared with the "non-isothermal molding method". Especially, it takes time to cool. Further, since the glass material 1 and the molding die 3 are heated at the same time, if the heating temperature is increased until the rough surface of the glass material 1 is softened and has specularity, the chemical reactivity with the molding die surface is increased. It causes fusion before. Therefore, in the glass material 1, a step of improving the surface roughness such as polishing in advance is indispensable.
In addition, in order to reduce the molding tact time, it has been proposed to perform molding with a plurality of sets of molding dies to shorten the molding time per optical element. It is expensive and not economical because it requires surface shape accuracy.

On the other hand, in the "non-isothermal molding method", a molten glass gob 1 for one optical element is selected from a large amount of molten glass 11.
Since 1a is taken out and molded, the production quantity of the optical element cannot be finely adjusted, and the glass material is wasted. On the other hand, in the “isothermal molding method”, the optical element 1
Since one glass material 1 is used for each piece, the glass material is not wasted.

The present invention has been made in view of the above points, and has a short molding time and enables fine adjustment of the production quantity.
An object is to provide a method for molding a glass optical element.

[0009]

The method for molding a glass optical element of the present invention is the one in which the idea of "isothermal molding method" is added to the idea of "non-isothermal molding method". The outline of this molding method will be described based on FIG. 1 (conceptual diagram).

As in the "isothermal molding method", a glass material 1 measured in a volume equivalent to one optical element is used, and the viscosity is 10 ⁷ poise or less, which is the viscosity that can be molded in a container such as a crucible. After heating to a temperature corresponding to that of the molten glass gob 21a, the molten glass gob 21a is separated from the container and supplied between the molding dies 23.
The glass optical element is molded by pressing between the molds 23 having a temperature lower than a. With a viscosity of 10 ⁷ poise, the surface of the glass gob 21a becomes a mirror surface and can be pressed. However, considering the amount of deformation of the glass gob 21a during pressing and separating the glass gob 21a from the container, the viscosity of the glass gob 21a is 10 ⁵ poise. The following is desirable.

[0011]

According to the above-mentioned molding method, since one glass material is used for one optical element, the glass material 2
The production quantity of the optical element can be adjusted by the number of 1. In addition, since the molten glass gob 21a is heated in the container to a temperature corresponding to a viscosity of 10 ⁷ poise or less, the glass material having a rough surface can be mirror-finished while being reliably held.

[0012]

Example 1 The molding method of Example 1 will be described with reference to FIGS. First, as shown in FIG. 2, the SF of a rough surface measured by cutting or the like into a volume corresponding to one optical element.
The glass material (glass pellet) 33 of No. 11 is placed on a heating dish (container) 32 made of carbon, and charged with a push rod 34 from an inlet 31 a of the high-frequency heating furnace 31. In this case, the heating plate 3
When a metal such as platinum is used for 2, it is preferable to use a large glass material 33 in advance in consideration of the amount of molten glass that remains attached to the heating dish 32. Next, the glass material 33 is heated in the furnace to, for example, 1350 ° C. by the coil 31c to form a molten glass gob 33a having a viscosity of about 10 poise. When the viscosity of the molten glass gob 33a exceeds 10 ⁷ poise, it becomes difficult to obtain a mirror surface property. In this case, the inside of the furnace 31 and the vicinity of the outlet 31b are set to an inert gas atmosphere such as a nitrogen gas atmosphere so that the carbon heating dish 32 does not react with oxygen. Then, the heating dish 32 on which the molten glass gob 33a is placed is moved to the handling arm 3 as shown in FIG.
5, the rotary shaft 35a is rotated to remove the molten glass gob 33a from the high frequency heating furnace 31, and the molten glass gob 33a is moved to the furnace 31 as shown in FIG.
Slide 3 to the lower mold 37a waiting under the exit 31b of the
6 through the dropping port 36a. The temperature of the lower mold 37a is set to a temperature below the glass transition temperature, for example, 450 ° C. in advance. Finally, the lower mold 37a on which the molten glass gob 33a is placed is immediately conveyed below the upper mold 37b, which is also kept at a temperature of 450 ° C., and the molten glass gob 33a is pressed and held for 1 minute under a load of 5 kg, for example. After molding, as shown in FIG. 3, the handling arm 35 is retracted from the handle hole 32a of the heating dish 33, retracted into the rotary shaft 35a as shown in FIG. Since it falls to 36 and is collected, it can be used again for molding an optical element in the same manner. The surface of the molded product thus obtained has a mirror-like property without defects.

In the molding method of this embodiment, the glass material 33
Is melted by heating to form a molten glass gob 33a as a lower mold 37a.
The time until the supply to the above can be shortened as much as possible by adjusting the length of the furnace 31 and increasing the number of glass materials 33 to be heated at one time. On the other hand, the time required for cooling and solidifying the molten glass gob 33a formed into the optical element was only 1 minute. According to the knowledge of the applicant, in the conventional "isothermal molding method", it takes about 10 minutes to mold one optical element. Therefore, if the method of this embodiment is used, the "isothermal molding method" is used.
It becomes possible to perform molding in a shorter time. Further, since the glass material 33 for one optical element is used as the molten glass gob 33a and is molded into the optical element, the production quantity of the optical element can be adjusted by the number of the glass materials 33, and the glass material is wasted. Therefore, it becomes possible to manufacture the optical element in a planned manner.

[0014]

[Embodiment 2] A molding method of Embodiment 2 and a molding apparatus used for the embodiment will be described with reference to FIGS. 7 and 8.

(Structure) In FIG. 7, reference numeral 41 is a preheating furnace, which is composed of an upper heater 41a and a lower heater 41b installed vertically. A belt conveyor 42 is provided between the heaters. Reference numeral 42a is a heat-resistant belt, which can be set to a predetermined feed speed by a drive source (not shown) and can be fed from the left side to the right side in the drawing. Protrusions 42b are provided on the surface of the belt 42a at predetermined intervals so that the molten crucible (container) 43 can be moved in the preheating furnace 41 while being held at a predetermined position on the belt. The melting crucible 43 is made of a material such as Pt (platinum) so as to hold the molten glass and heat and melt it without adversely affecting the glass.
The opening 43a is provided in the upper part. Further, on the outer peripheral portion of the melting crucible 43, the upper flange 4 provided in a circumferential shape
3b and a lower flange 43c are attached. Reference numeral 44
Is a glass material preliminarily weighed corresponding to the weight of the molded product, and is a rough surface glass material obtained at low cost such as a cut product from a block material, a direct press product, and a cullet product. A high-frequency heating coil 45 is installed laterally on the right side of the preheating furnace 41 in the drawing. High frequency heating coil 45
The object to be heated in the coil can be heated to a predetermined temperature by a power supply and a control device (not shown).

Further to the right of the high frequency heating coil 45,
A pair of upper mold 46 and lower mold 47 are arranged. The lower mold 47 is fixed, and the upper mold 46 can move up and down.
In addition, the lower mold 47 can apply a predetermined pressing pressure to the glass located between them. The upper mold 46 and the lower mold 47 can be heated and maintained at a predetermined temperature by a heater (not shown). Reference numeral 48 is a ring-shaped body, which is fitted to the outer peripheral portion of the tip of the lower mold 47, and the flange 48a is hooked and lifted by a release arm (not shown).
It can be released from the lower mold 47.

A handling arm 49 provided on the further right side of the drawing is rotatable with respect to the axis a and is movable back and forth in the direction of the axis a. Further, it is movable in the direction perpendicular to the axis a. Tip 49 of handling arm 49
As shown in FIG. 8, a has a bifurcated claw shape, and has an upper flange 43b and a lower flange 43c of the melting crucible 43.
The molten crucible 43 can be held in the gap. Reference numeral 49b is a heater, which heats the vicinity of the tip end portion 49a of the handling arm 49 to raise the temperature.

Reference numeral 40 denotes a recovery belt conveyor placed in a direction perpendicular to the drawing, and the molten crucible 43 after the molten glass is supplied onto the lower mold 47 by the handling arm 49 is placed on the belt conveyor. It is placed and collected.

(Function) With the above-described structure, SF11 (transition temperature 467 ° C., softening temperature 568) which is a heavy flint type optical glass in which the glass component PbO is often volatilized by melting.
An example of molding a glass optical element using (° C.) will be described.

First, the melting crucible 43 charged with 1 g of the glass material 44, which has been weighed in advance corresponding to the weight of the molded product by cutting from the block material, is sequentially placed on the belt conveyor 42 in the preheating furnace 41. The set temperature of the upper heater 41a and the lower heater 41b of the preheating furnace 41 is set to a temperature at which the volatilization of the glass component does not substantially occur, for example, 1000 ° C. The feeding speed of the belt conveyor 42 is set so that when the molten crucible 43 reaches the outlet of the preheating furnace 41, the set temperature thereof reaches 1000 ° C.

When the melting crucible 43 reaches the outlet of the preheating furnace 42, the handling arm 49 moves the melting crucible 43.
The tip end 49a moves between the upper flange 43b and the lower flange 43c, then rises and then retreats, and is held in the center of the high-frequency heating coil 45. The heater 49b of the handling arm 49 is set to 1000 ° C. in advance and preheated. The high-frequency heating condition is such that the glass material surface becomes a mirror surface due to surface tension, and a set temperature at which the molten crucible 43 can be dropped into the lower mold 47, for example, 1350 ° C. (glass viscosity is 10 poise), and the arrival time to this temperature is The shortest time within the capability of the high-frequency heating device is set to, for example, 20 seconds.

After that, the handling arm 49 is retracted and positioned right above the lower die 47, and then the handling arm 49 is rotated 180 ° to drop all the molten glass 44a in the molten crucible 43 onto the lower die 47. The upper mold 4
6. The set temperature of the lower mold 47 is, eg, 400 ° C. The molding surface diameter of the mold is, for example, φ10. The empty melting crucible 43 that has finished dropping is placed on the recovery belt conveyor 40 and recovered, with the handling arm 49 further retracted.

After the dropping, the upper mold 46 immediately descends to cool the dropped molten glass 44a while pressing it with a predetermined pressure to form a glass optical element having φ10 and a thickness of 3.5 mm. After that, after the upper mold 46 is lifted, the flange portion 48a of the body mold 48 is hooked and lifted by a mold releasing arm (not shown) to release the mold. The strain is removed from the glass optical element by a predetermined annealing process.

(Effect) The glass optical element obtained as described above has good optical characteristics such as a shape accuracy which is not a problem as an optical element of an image pickup optical system such as a camera, has no striae and has specularity.

In the present embodiment, a preheating step of preheating to a temperature at which volatilization of glass by heating does not substantially occur,
A main heating step of supplying the molten crucible 43 to a mold and rapidly heating it to a temperature at which the glass viscosity becomes press moldable;
Since the amount of heat applied in the main heating step can be reduced by dividing into, it is possible to shorten the time to stay in the temperature range where the volatilization of the glass component occurs. Therefore, in this embodiment, it is possible to continuously manufacture SF11 optical elements in which striae easily occur.

The set temperature of the preheating step shown in this embodiment may be within a range where the glass component is not substantially volatilized, and the set temperature of the main heating step is from the rough glass material to the specular surface. It is sufficient if the temperature is equal to or higher than the temperature corresponding to a glass viscosity of 10 ⁷ poises.

[0027]

[Embodiment 3] A molding method of Embodiment 3 and a molding apparatus used for carrying out the same will be described with reference to FIGS. 9 to 11.

(Structure) The molding apparatus used in the third embodiment has a high-frequency heating furnace 51 installed vertically, a support base 55 installed at a lower portion thereof with a gap, and an electromagnet 56 arranged near the gap. It includes a shooter 57 that moves forward and backward, and a lower frame 58 located below the support base 55. A heating dish (container) 52 on which a weighed glass material (glass pellets) 54 is placed is stacked inside the high-frequency heating furnace 51. The heating plate 52 includes a bottom plate 52a and an outer peripheral regulation frame 52b.
It is composed of two bodies, both of which are made of carbon coated with P-BN as a material that does not easily get wet with molten glass. The material of the heating dish 52 is not limited to this as long as it is a material that does not easily get wet with the molten glass.

(Function) The optical element is molded by this apparatus as follows. First, the glass material 54 placed on the heating dish 52 is heated to a softening point or higher in the high-frequency heating furnace 51, and the molten glass gob 5 having a viscosity of 10 ⁵ poise or lower is obtained.
4a (FIG. 9). Next, the shooter 57 is instantly retracted forward with respect to the outer peripheral restriction frame 52b to move the outer peripheral restriction frame 52b.
b from the top of the support 55, and the molten glass gob 5
The heating dish 52 on which 4a is placed is dropped on the support base 55 (FIG. 10). At this time, when the shooter 57 is moved backward again, this time, the bottom plate 52a on which the molten glass gob 54a is placed is placed.
However, since the bottom plate 52a is made of a material that does not easily get wet with the molten glass, the molten glass gob 54a does not adhere to the bottom plate 52a.
Since it is shielded by the outer peripheral regulation frame 52b, it is separated from the bottom plate 52a without any delay and falls onto the lower mold 58 through the hole of the support base 55 (FIG. 11). That is, the molten glass gob 54 a is supplied to the lower mold 58. After that, as in the first embodiment, the molten glass gob 54a supplied thereto is pressed by an upper die (not shown) that is paired with the lower die 58 to form an optical element. In this way, the optical element can be continuously molded by repeating the series of operations.

(Effect) Regarding the operation of the apparatus of this embodiment, the mechanism is simple because the shooter 57 only moves backward. Therefore, as compared with the device of the first embodiment, there is an advantage that the device can be easily maintained. Further, by arranging the high-frequency heating furnace 51 vertically, there is an advantage that the entire apparatus can be made compact.

[0031]

EFFECTS OF THE INVENTION According to the molding method of the present invention, a molded product having a mirror surface property can be obtained from a glass material having a rough surface, which is low in cost, without wasting the glass material. It becomes possible to mold optical elements at an overwhelmingly high production speed.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a molding method of the present invention.

FIG. 2 is a vertical cross-sectional view showing the configuration of a molding apparatus used for carrying out the molding method of Example 1.

FIG. 3 is a perspective view of a handling arm and a heating dish of the molding apparatus of FIG.

FIG. 4 is an operation diagram of the molding apparatus of FIG.

FIG. 5 is an operation diagram of the molding apparatus of FIG.

FIG. 6 is an operation diagram of the molding apparatus of FIG.

FIG. 7 is a vertical cross-sectional view showing the configuration of a molding apparatus used for carrying out the molding method of Example 2;

FIG. 8 is a perspective view of a handling arm and a heating dish of the molding apparatus of FIG.

FIG. 9 is a vertical cross-sectional view showing the structure of a molding apparatus used for carrying out the molding method of Example 3;

10 is an operation diagram of the molding apparatus of FIG.

11 is an operation diagram of the molding apparatus of FIG.

FIG. 12 is a conceptual diagram of an example of a conventional molding method.

FIG. 13 is a conceptual diagram of another example of a conventional molding method.

[Explanation of symbols]

1,2,33 Glass material 1a, 11, 11a, 21a, 33a, 44a, 54a
Molten glass 3,13a, 13b, 23,37a, 37b, 46,4
7,58 type 12,43 crucible (container) 32,52 heating plate (container)

Claims (1)

[Claims] 1. A step of heating and melting a measured glass material in a container to obtain a molten glass having a viscosity of 10 ⁷ poise or less, and separating almost all of the molten glass from the container, and at least the molten glass. A method for molding a glass optical element, which comprises continuously performing a step of supplying the molten glass to a molding die at a lower temperature and a step of holding the molten glass by pressing with the molding die and cooling it to a glass transition temperature or lower.