JPH07291639A - Production of optical glass element - Google Patents

Abstract

PURPOSE:To obtain an optical glass element having excellent surface by washing a gob- receiving mold after a specified number of times of molding before further repeated use, dropping a preliminary molded body of an optical glass into a precision mold from the gob- receiving mold by turning it over and the preliminary molded body is subjected to press- molding. CONSTITUTION:Fused glass is dropped from an orifice into a gob-receiving mold placed in a heater block and the received fused glass is held for about 10sec on it to form a preliminary molded body of an optical glass. Subsequently, the gob-receiving mold is turned over to drop the preliminary molded body onto a lower precision mold heated in advance. Then in the preheating process, the preliminary molded body is heated up to the molding temperature together with the lower precision mold and molded by press molding with an upper mold heated in advance in the press processing zone. Then, the lower precision-mold having the molded article on it is transferred to a cooling process and the objective optical glass element. Besides, the gobreceiving mold which has been used for molding in a specified number of times and on which materials evaporated from the glass are deposited is replaced with a clean gob-receiving mold. The old mold is transferred into an ultrasonic washing apparatus, washed with an acidic or a basic aqueous solution and then rinsed with water and dried with hot air after the substitution with an organic solvent. The clean gob-receiving mold is returned to the specified position to repeatedly use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical glass element, and more particularly to a surface of a surface for receiving an optical glass preform (hereinafter referred to as a glass gob) used in a method for continuously performing from molten glass to press molding. The present invention relates to a method for newly (intermittently) supplying a clean gob receiving mold after molding a predetermined number of times.

[0002]

2. Description of the Related Art Conventionally, an optical glass element used for a camera, a video, a CD or the like has a spherical shape or a molded shape obtained by polishing a glass obtained by molding by a direct press method or cutting out from a round bar. It was manufactured by grinding into a shape similar to the product and then heat-molding this.

However, these methods have the drawbacks that the cost for polishing the glass material is high and that the glass once cooled and polished is reheated from room temperature to be molded, so that the time for obtaining the product is very long.

In order to solve such a drawback, recently, an attempt has been proposed to obtain a product by a process (hereinafter referred to as a direct molding method) for continuously obtaining an optical glass element from a molten glass without including a processing step. For example, Japanese Patent Publication No. 4-16414 discloses a method in which molten glass is naturally dropped from a nozzle in an air atmosphere, received by a lower mold for molding, and immediately press-molded by an upper mold. Further, Japanese Patent Application Laid-Open No. 4-77320 discloses a method in which a first mold receives molten glass in the air, and a second mold performs hot press molding in a non-oxidizing atmosphere.

[0005]

However, the above direct molding method has the following problems.

That is, since the temperature of the glass gob is high in the vicinity of the glass-mold contact surface of the glass mold that receives the molten glass, the volatile components of the glass adhere to the surface of the glass gob. When granular glass volatiles are deposited and a glass gob to which the glass volatiles are attached is molded, scratches are generated on the surface of the molded product, resulting in a defective product.

According to the method disclosed in Japanese Patent Publication No. 4-16414, when the glass is dropped from the orifice in the atmosphere, the glass is brought into contact with the receiving die by setting the distance between the orifice outlet and the receiving die to be about 3 m. The glass surface temperature is lowered below the glass softening point to reduce the amount of glass volatiles attached to the receiving mold.

However, even at a temperature lower than the glass softening point, glass volatiles are deposited little by little on the receiving mold. In particular, in this method, the distance between the orifice outlet and the receiving container is long, so that the position of the glass gob falling on the receiving mold varies. Is large, the glass volatiles deposited on the receiving die have a high probability of adhering to the glass gob, and since the receiving die is also used as the precision forming die, many defective products occur after the precision forming.

Further, as a result of increasing the distance between the orifice outlet and the receiving die, there is a drawback that the entire apparatus becomes large and the total equipment cost including the auxiliary equipment becomes high, and thus the cost of the optical element to be manufactured becomes high.

On the other hand, in the method described in the above-mentioned Japanese Patent Application Laid-Open No. 4-77320, after the glass is received by the first mold which is not heated in the atmosphere, it is immediately introduced into the non-oxidizing atmosphere and the second mold. It is transferred to and molded.

However, even with this method, it is unavoidable that the first mold receives high temperature glass, and if it is used continuously, volatiles from the glass will be deposited on the surface of the mold and adhere to the surface of the glass gob to cause imperfections after precision molding. A lot of good products occur.

In view of the problems of the prior art, it is an object of the present invention to efficiently produce an optical glass element having a good surface by continuously obtaining a glass gob having a clean surface in the direct molding method. It is to provide a possible method.

[0013]

The present invention for achieving the above object provides a plurality of gob receiving molds for receiving glass gobs,
Washing, drying and intermittently replacing and supplying, a step of reversing the gob receiving mold to drop the glass gob into a precision molding die, a glass gob placed on the precision molding die by press molding, and an optical glass element A method for producing an optical glass element, which comprises the step of obtaining

Further, the present invention includes, as a gob-receiving type cleaning method, using an aqueous solution of acid or alkali and / or water and applying ultrasonic vibration to the cleaning solution.

Further, the present invention includes the use of organic solvent substitution and / or hot air as a gob-receiving type drying method.

The present invention also includes at least the step of press-molding a glass gob placed on the precision mold to obtain an optical glass element in a non-oxidizing atmosphere.

In the present invention, in order to prevent the glass gob from being contaminated by the glass volatiles adhering to the gob receiving mold, a plurality of gob receiving molds which have received the glass gob about 20 times are automatically replaced with a new gob receiving mold. Prepare a gob receiving mold of No. 2, and wash and dry the dirty gob receiving mold one after another to return to a gob receiving mold with a clean surface, and then use it repeatedly to continuously clean the precision mold with a clean surface. A glass gob can be fed to continuously obtain good surface optical glass elements by a consistent process.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows a gob receiving type automatic changing mechanism and a cleaning / drying mechanism used in the present invention.

Further, FIG. 2 shows a step in which the glass gob is press-molded in the precision molding chamber. Orifice 1
The molten glass flowing out of the glass is received by the gob receiving mold 2 and held as the glass gob 3. At this time, if the gob receiving mold 2 is kept at room temperature, the temperature of the lower surface of the glass gob suddenly drops, and shrinkage or folds occur due to shrinkage, so that a defect occurs in the optical glass element when proceeding to the precision molding step as it is. More often. Therefore, in the present invention, as shown in FIG.
A mechanism in which the heater 4 is inserted in the bottom of the receiving mold is provided. Here, the heater is usually a cartridge heater capable of heating at about 500 ° C., and the member 5 into which the heater is inserted is made of a heat-resistant alloy having a high thermal conductivity and a high heat resistance.

Further, this gob receiving mold is provided with a rotatable mechanism 6, which is turned upside down and at the same time, the shutter 7 is opened to drop the glass gob into the precision molding chamber 8 and under it. It is received on the positioned precision molding lower die 9.

The gob receiving type is a heater insertion member 5
And a rotatable mechanism 6, which are integrated with each other.
There are two sets in total.

Next, the cleaning / drying mechanism of the gob receiving type will be described.

The gob receiving mold, which has been used a predetermined number of times and has glass volatiles attached, is replaced with a new gob receiving mold by rotating the column 10 by 180 degrees so that it is possible to continuously receive the glass gob. .

The used gob receiving mold is taken out from the heater insertion member by the auto hand 11 immediately after replacement,
First, it is transferred into the ultrasonic cleaning tank 1.

The ultrasonic cleaning tank 1 is filled with an aqueous solution of an acid or an alkali or a pure water, which is prepared in advance to a predetermined concentration, in an amount sufficient for the gob receiving type cleaning, and the glass adhered to the receiving type surface. Ultrasonic cleaning is performed for a predetermined time until the volatile substances are completely dissolved and removed.

Next, the gob receiving mold is transferred into the ultrasonic cleaning tank 2 by an automatic hand. The ultrasonic cleaning tank 2 is filled with pure water, and when an aqueous solution of acid or alkali is used in the ultrasonic cleaning tank 1, the dissolved matter of acid, alkali or glass volatiles attached to the gob receiver is removed. To this end, ultrasonic cleaning is performed for a predetermined time.

Next, the gob receiving mold is transferred into the organic solvent tank by an auto hand.

The organic solvent tank is filled with a sufficient amount of solvent such as isopropyl alcohol for replacing the water adhering to the gob receiving mold with the organic solvent in the previous step, and the solvent replacement is carried out for a predetermined time.

Next, the gob receiving mold is transferred into a drying chamber equipped with a mechanism (not shown) for purging hot air. As the hot air, it is desirable to use a gas heated to a temperature equal to or higher than the volatilization temperature of the organic solvent used in the previous step, and air having a temperature of 90 ° C. or higher is usually used.

The fully dried gob receiving mold is waited as a replacement gob receiving mold, then transferred by an auto hand and mounted in the member 5 for repeated use.

The number of gob receiving molds used in the above-described process is at least two or more, and usually several to 10 depending on the condition of dirt of the gob catching mold which differs depending on the glass type of glass and the tact of the gob catching. Used about individually.

Next, the precision molding process will be described.

The lower mold 9 for precision molding has a shutter 12 in advance.
After being sequentially conveyed into the molding chamber by the belt conveyor 13 through an opening having a hole, the heater 14 first performs a preheating process, preheats to a temperature close to the molding temperature, and receives the glass gob as described above. Then, it is positioned below the precision molding upper die 16 having the built-in heater 15, and then the upper die 16 descends, thereby press-molding the glass.

Then, the optical glass element (molded product) together with the lower mold 9 is cooled down to the opening with the shutter 17, and is taken out of the molding chamber through the opening. The taken out optical glass element 18 is taken out from the lower mold 9 by a suction hand 19 of a vacuum chuck system, while the lower mold 9 is returned to the position of the molding chamber inlet of the conveyor by the action of an appropriate conveying means and is again molded into the molding chamber. 8 is transferred.

The atmosphere in the molding chamber 8 is provided by continuously supplying a non-oxidizing gas from the gas introduction pipe 20. Further, the inside of the molding chamber is kept at atmospheric pressure or positive pressure to prevent introduction of the atmosphere containing oxygen from the outside when opening / closing the shutters 7, 12, 17 and the like. For this reason,
The gas discharge pipe 21 has its flow stopped at this point.

As described above, the molding system according to the present invention is realized in a continuous process. The gob-receiving type cleaning / drying method in this case will be described in detail in the following several examples.

Example 1 Here, glassy carbon was used for the gob receiving mold.

First, a block-shaped glassy carbon was cut out to obtain a disk-shaped sample of 30 mmφ and 6 mm ^t .
After that, the center part of one side of the disk is R: 22 mm, depth 3 m
After grinding to m, the R surface was mirror-polished with cerium oxide. The gob receiving mold thus obtained was mounted in a heater block made of a heat-resistant alloy.

Further, the precision molding die for receiving the gob from the gob receiving die was manufactured by the following method for both the lower die and the upper die.

A cemented carbide of tungsten carbide (90 wt.%) And cobalt (10 wt.%) Is used as the base material of this mold. The shape is 30mmφ, 6mm
After producing a disk of ^t , the surface for molding glass is R: 16
mm and depth 2.3 mm are ground and polished to a mirror surface having a surface roughness of 2 nm. Furthermore, a silicon chip is placed on a platinum target, and a platinum semiconductor whose composition (atomic%) is platinum (53%) and silicon + nitrogen (47%) is formed on a base material surface which is mirror-finished by a sputtering method in a nitrogen atmosphere. The mixture was formed to a thickness of 1 μm to obtain a precision mold.

Regarding the atmosphere, in the step of directly receiving the molten glass with the gob-receiving mold, in the atmosphere, and in the step of performing precision molding, nitrogen gas is preliminarily set to 15 in the molding chamber.
The nitrogen atmosphere was adjusted by purging with a liter / minute.

As the molten glass, glass having optical characteristics equivalent to SK12 was used. This glass has a barium borosilicate glass composition, and its softening point temperature is 630 ° C. This glass was melted at 1200 ° C., and about 1.5 g of molten glass was preliminarily mixed with 4
It was dropped into a glassy carbon receiving mold whose temperature was adjusted to 00 ° C. The dropped molten glass is held in the receiving mold for 10 seconds, and then the receiving mold is reversed, and at the same time, it drops into the precision molding chamber through the opening where the high-speed opening / closing shutter is opened, and is heated and preheated to 570 ° C on the conveyor in advance. It is put on the lower mold for precision molding.

The distance from the tip of the orifice to the glassy carbon receiving mold was 5 cm, and the distance to the precision molding lower mold was 25 cm.

Then, the lower mold was conveyed to the preheating step by the operation of the conveyor, and the glass gob was heated together with the lower mold at a temperature of 570 ° C. for 2 minutes. Next, the lower mold on which the glass gob was placed was conveyed to the pressing step by a conveyor, and immediately there, using an upper mold which had been preheated to 570 ° C., 4 × 10 ⁶ was used.
Press molding was performed at a pressure of Pa for 2 minutes. The temperature of the mold was controlled using an internal heater of the upper mold and a heater installed below the lower mold so that the temperature of the glass was constant during press molding. After that, the lower mold on which the molded product (optical glass element) is placed is conveyed to the cooling step by the conveyor and naturally cooled for 2 minutes, and then discharged from the molding chamber to the outside by the high speed opening of the shutter, and the lower mold is moved by the suction hand. Taken out.

As described above, when molding was carried out according to a series of processes, three gob receiving molds were used, and every time 20 glass gobs were received, they were replaced with new ones to prepare a total of 200 optical glass elements.

The cleaning of the gob-receiving type and the solvent replacement method were carried out under the 13 conditions shown in Table 1 to obtain a total of 2600 optical glass elements. The conditions of the ultrasonic cleaning tank 2 omitted in Table 1 are pure water at 25 ° C. for 30 seconds, and the conditions in the drying chamber are air at 90 ° C. for 30 seconds. Made by way.

Further, as an experiment of a comparative example, without changing the gob receiving mold, 200 glass gobs continuously received by one gob receiving mold were press-molded to make a total of 200 optical glass elements. Was produced.

For the evaluation of the obtained optical glass element, the surface condition was observed with an optical microscope, EPMA (electron probe / microanalyzer) and SEM, and Zygo-MARK3 manufactured by Zygo was used for surface accuracy. As a result, for every 2600 samples obtained by replacing the gob receiving mold with every 20 gob receiving molds and washing and drying under the 13 conditions shown in Table 1, observe defects on the surface. In addition, the surface accuracy was 1.5 or less in Newton number, and it was possible to continuously obtain optical glass elements having very good performance.
On the other hand, in the case of the comparative example in which 200 glass gobs were continuously received without exchanging the gob receiving die, white foreign matter was observed on the surface in all the press-molded products after the 25th glass, and good optical glass elements were obtained. Couldn't get When these foreign substances are analyzed by EPMA, B existing in the glass composition,
Na and K were detected, and it was judged that the glass volatiles deposited in the gob-receiving type adhered to the glass gob.

[0049]

[Table 1]

(Embodiment 2) Here, a HOPG (highly oriented p-type) is used as a gob receiving type material.
(yrolytic graphite: highly oriented pyrolytic graphite) was used. This material is particularly excellent in heat resistance among carbon-based materials having excellent releasability.

HOPG was produced by a thermal CVD method and used as a core member coated with isotropic graphite.

First, a block-shaped isotropic graphite was cut out to obtain a disk-shaped sample of 30 mmφ and 6 mm ^t . After that, the central portion of one surface of the disk was ground to have R: 22 mm and a depth of 3 mm, and then the R surface was mirror-polished with cerium oxide. Then, the isotropic graphite was heated to 2400 ° C., a commercially available propane gas was introduced to perform HOPG coating, and the core material was completely covered with a HOPG layer having a film thickness of 30 μm. The gob receiving mold thus obtained was mounted in a heater block made of a heat-resistant alloy.

As the precision molding die for receiving the gob from the gob receiving die, the same lower and upper molds as in Example 1 were used.

Regarding the atmosphere, in the step of directly receiving the molten glass with the gob-receiving mold, in the atmosphere, and in the step of performing precision molding, the gas is introduced into the precision molding chamber in advance from the gas introduction pipe.
The atmosphere was adjusted by purging a mixed gas of% nitrogen + 2% hydrogen at 15 liters / minute.

As the molten glass, lanthanum-based glass having optical characteristics equivalent to LaK12 was used. The softening point temperature of this glass is 655 ° C. 130 this glass
It melted at 0 ° C., and about 1.5 g of molten glass was dropped from an orifice into a HOPG receiving mold whose temperature was adjusted to 500 ° C. in advance. The HOPG receiving-type glass gob was held in the receiving mold for 10 seconds, and then when the receiving mold was turned over, it dropped into the precision molding chamber through the opening where the high-speed opening / closing shutter was opened at the same time. It is placed on a precision molding lower mold that has been heated and soaked.

The distance from the tip of the orifice to the HOPG receiving mold was 5 cm, and the distance to the precision molding lower mold was 25 cm.

Then, the lower mold was conveyed to the preheating step by the operation of the conveyor, and the glass gob was heated together with the lower mold at a temperature of 620 ° C. for 2 minutes. Next, the lower mold on which the glass gob was placed was conveyed to the pressing step by the conveyer, and immediately there, 3 × 10 ⁶ was used by using the upper mold that had been preheated to 620 ° C.
Press molding was performed at a pressure of Pa for 2 minutes. The temperature of the mold was controlled using an internal heater of the upper mold and a heater installed below the lower mold so that the temperature of the glass was constant during press molding. After that, the lower mold on which the molded product (optical glass element) is placed is conveyed to the cooling step by the conveyor and naturally cooled for 2 minutes, and then discharged from the molding chamber to the outside by the high speed opening of the shutter, and the lower mold is moved by the suction hand. Taken out.

As described above, when molding was carried out according to the series of processes, three gob receiving molds were used, and a new one was used every time 20 glass gobs were received, and a total of 200 optical glass elements were manufactured.

As the method of cleaning and melting and replacing the gob-receiving type, the same procedure as in Example 1 was carried out under the 13 conditions shown in Table 1, and a total of 26
00 optical glass elements were obtained. Regarding the conditions of the ultrasonic cleaning tank 2 omitted in Table 1, pure water was used at 25 ° C.
30 seconds, and the conditions in the drying chamber are 90 ° C using air.
The same method was performed for 13 conditions in 30 seconds.

Further, as an experiment of a comparative example, without changing the gob receiving mold, 200 glass gobs continuously received by one gob receiving mold were press-molded to make a total of 200 optical glass elements. Was produced.

The evaluation of the obtained optical glass element was carried out by observing the surface state with an optical microscope, EPMA (electron probe / microanalyzer) and SEM, and for surface accuracy, Zygo-MARK3 manufactured by Zygo was used. As a result, for every 2600 samples obtained by replacing the gob receiving mold with every 20 gob receiving molds and washing and drying under the 13 conditions shown in Table 1, observe defects on the surface. In addition, the surface accuracy was 1.5 or less in Newton number, and it was possible to continuously obtain optical glass elements having very good performance.
On the other hand, in the case of the comparative example in which 200 glass gobs were continuously received without exchanging the gob receiving die, white foreign matter was observed on the surface in all the press-molded products after the 23rd, and good optical glass elements were obtained. Couldn't get When these foreign substances are analyzed by EPMA, B existing in the glass composition,
Na was detected, and it was determined that the glass volatiles deposited in the gob-receiving mold adhered to the glass gob.

[0062]

As described above, according to the molding system of the optical glass element of the present invention, the dirty gob receiving mold is successively washed and dried to be returned to the gob receiving mold having the clean surface, and the cleaning is repeated. Depending on the method used, a glass gob having a clean surface can be continuously supplied to a precision molding die to continuously obtain an optical glass element having a good surface by a consistent process. Moreover, since the glass gob temperature is maintained at a high temperature, the molding tact can be shortened and the cost of the product can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a glass gob receiving mold replacement, cleaning and drying mechanism of the present invention.

FIG. 2 is a vertical sectional view showing a precision molding process of the present invention.

[Explanation of symbols]

 1 Orifice 2 Gob-receiving type 3 Glass gob 4, 14, 15 Heater 5 Heater insertion member 6 Rotatable mechanism 7, 12, 17 Shutter 8 Precision molding chamber 9 Precision molding lower mold 10 Rotating support 11 Auto hand 13 Belt conveyor 16 Precision Molding Upper Mold 18 Optical Glass Element 19 Adsorption Band 20 Gas Introducing Pipe 21 Gas Exhausting Pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuyuki Nakai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. A method for producing an optical glass element by dropping molten glass from an orifice to receive the glass with a gob-receiving mold and then press-molding the glass to produce an optical glass element. A plurality of receiving molds are prepared and have a step of washing and replacing them after molding a predetermined number of times, and a step of reversing the gob receiving mold and dropping the optical glass preform into a precision molding die, Next, a method for producing an optical glass element, comprising a step of press-molding the optical glass preform placed on the precision molding die to obtain an optical glass element. 2. The method of manufacturing an optical glass element according to claim 1, wherein an acid aqueous solution is used as the gob-receiving type cleaning method, and ultrasonic vibration is applied to the cleaning solution. 3. The method for manufacturing an optical glass element according to claim 1, wherein an alkaline aqueous solution is used as the gob-receiving type cleaning method, and ultrasonic vibration is applied to the cleaning solution. 4. The method of manufacturing an optical glass element according to claim 1, wherein water is used as the gob-receiving type cleaning method, and ultrasonic vibration is applied to the cleaning solution. 5. The method for producing an optical glass element according to claim 1, wherein an acid aqueous solution and water are used as the gob-receiving type cleaning method, and ultrasonic vibration is applied to the cleaning solution. 6. The method of manufacturing an optical glass element according to claim 1, wherein an alkaline aqueous solution and water are used as the gob-receiving type cleaning method, and ultrasonic vibration is applied to the cleaning solution. 7. The method for producing an optical glass element according to claim 1, wherein an organic solvent substitution and hot air are used as the gob receiving type drying method. 8. The method according to claim 1, wherein at least the step of press-molding the optical glass preform placed on the precision molding die to obtain an optical glass element is performed in a non-oxidizing atmosphere. A method for producing the optical glass element described.