JP2008280218A - Glass flow path, and method of manufacturing optical glass formed article using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass flow path for preparing, simply and with high quality, a formed glass article of a recent glass having high refraction and low Tg for which selection of a forming condition is very difficult, and further the glass flow path capable of simply controlling at a short distance to allow a device to be small. <P>SOLUTION: The flow path for flowing out a molten glass connected to a molten glass tank has a glass flow retention part having a form in which its flow path diameter contracts after expanding. The flow path has an outlet of the glass flow retention part which is not positioned just beneath the inlet thereof. The flow path has a maximum diameter of the retention part which is not less than two times the flow path diameter of other than the retention part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a technique for producing a predetermined amount of an optical glass molded body.

  In recent years, in the field of optical devices such as digital cameras and projectors, there has been a demand for miniaturization and weight reduction, and accordingly, there is an increasing demand for aspheric lenses that can reduce the number of lenses used.

In general, the lenses constituting the optical system generally include a spherical lens and an aspheric lens. Many spherical lenses are manufactured by grinding and polishing a glass molded product obtained by reheat press molding a glass material. On the other hand, an aspheric lens is a method in which a heat-softened preform is press-molded with a mold having a high-precision molding surface, and the shape of the high-precision molding surface of the mold is transferred to a preform material, that is, It is mainly produced by precision press molding.

  As a precision press-molding preform, a spherical or flat glass molded body (glass gob) is often used. These materials are melted in a melting apparatus such as a crucible and then connected to the melting apparatus. It can be produced by allowing it to flow out from a nozzle or the like onto a mold, forming it into plate-like glass or rod-like glass, and further cold-working them. Further, in recent years, molten glass flowing out from a flow path such as a nozzle is cut by a shear or separated by using surface tension, and flows down (drops) onto, for example, a porous mold that ejects gas, and then floats. A technique for adjusting the glass gob to an appropriate size and shape by molding is used. However, in the former case, traces of cutting by the shear may remain on the glass gob, so in recent years the latter is often used.

In any of the above means, when glass is caused to flow out of the flow path, in order to control the temperature and flow rate of the glass flow, or to prevent defects such as striae and devitrification occurring during molding, Various shapes have been devised for the flow path. In recent years, various methods have been devised to cope with the increase in the liquid phase temperature and / or the decrease in the viscosity accompanying the increase in the refractive index of the optical glass, or the decrease in the viscosity associated with the decrease in the Tg. However, the current situation is not enough.

  In Patent Document 1, the diameter of the outlet is made larger than the diameter of the channel main body, for example, the molten glass outlet at the end of the channel is opened in a tapered shape so that the molten glass flow is longer than the channel outlet. A flow path is described which can be held for a period of time and the delay of glass flow-down timing can be controlled.

  In Patent Document 2, when molten glass starts to flow from a melting apparatus, passes through a pipe, and flows out from an outlet, the flow velocity distribution is made uniform by adding a constriction inside, and the modified glass in which the components are volatilized is disclosed. A method is described that suppresses retention and prevents striae. In addition, it is described that the temperature of the throttle portion is controlled to be higher than that other than the throttle portion in order to prevent the flow rate from being reduced due to the throttle.

Patent Document 3 describes a method in which a resistance member is provided inside a flow path to reduce the flow velocity of the glass flow flowing through the center of the cross section of the flow path and increase the maximum weight of the glass gob that can be obtained.
JP-A-10-36123 JP 2003-306334 A JP-A-8-26737

However, the above conventional methods have the following problems.

In general, when molten glass is flowed out of a melting tank through a flow path and molded with a molding die, temperature control is performed by gradually reducing the temperature from the melting tank to the outlet, which is suitable for molding. It is necessary to lower the molten glass temperature to the temperature. Here, for example, striae derived from the volatilization of the glass component may occur after the outflow, but in this case, it is necessary to cope with this by lowering the flow path control temperature. However, the molten glass flow is a highly viscous fluid from the high temperature side to the low temperature side, and the temperature in the flow path is low near the inner wall and high near the center of gravity of the cross section. Further, the flow velocity distribution is low near the inner wall surface and is high near the center of gravity of the cross section.

When the control based on the temperature measurement of the flow path is performed, the measured temperature in the flow path almost accurately represents the glass temperature near the inner wall surface, but the glass flow center temperature (that is, near the center of gravity of the cross section of the flow path in the flow path) The temperature of the glass flow passing through the lower temperature) shows a low temperature. Therefore, in glass with a high liquidus temperature, the flow path temperature (the glass temperature near the inner wall of the flow path) drops to the temperature at which crystals grow, the so-called devitrification temperature, before the glass flow center drops to a temperature at which no volatilization occurs. This may cause devitrification.

In the flow path described in Patent Document 1, since the outlet is tapered and the inner diameter is increased, the temperature difference and the flow velocity difference between the inner wall surface and the glass flow center are increased, and the above-described tendency is more prominent. Become.

When a flow path having a restriction as in Patent Document 2 is used, there is an effect of uniforming the flow velocity distribution of the glass flow, but a high temperature glass flow near the center of gravity of the cross section of the flow channel is taken out. Sometimes it is difficult to prevent striae from volatilization. If the control temperature is lowered to suppress volatilization, devitrification is likely to occur and grow immediately, thereby blocking the flow path of the throttle portion, and the outflow itself is likely to stop. In the example, in order to suppress the flow rate drop due to the restriction, the temperature of the restriction part is set to a temperature higher than that other than the restriction part, and it is clear that this is not a method suitable for the production of high refractive index glass in recent years. .

The flow path described in Patent Document 3 delays the flow rate of the molten glass at the center by a resistance member provided at the center of the inside, and the velocity distribution of the outflow rate is made uniform, but the heat capacity In a small resistance member mainly composed of a small noble metal, the glass flow center temperature immediately becomes high. Therefore, the effect of lowering the glass flow center temperature cannot be obtained, and there is no effect of suppressing striae derived from volatilization. Further, as shown in FIG. 3 in Patent Document 3, it is necessary to fix the resistance member using a support member, and it is extremely difficult to process the glass outlet channel mainly containing a noble metal such as platinum. Further, in claim 4 of Patent Document 3, a plurality of channels are provided at the bottom of the crucible, and tip portions of the plurality of channels are connected to each other to form one channel port. However, the high temperature glass flow is generated at the center of each of the plurality of flow paths, and the effect of lowering the glass flow center temperature flowing down cannot be obtained. Applying such a complicated structure makes it very difficult to change the structure to adapt to the temperature, viscosity, wetting, density, and fluid pressure of the glass, which also complicates the flow rate and temperature distribution. However, a simpler structure was sought.

  In the present invention, normally, in a glass flow path where the flow velocity near the center tends to increase, the temperature of the glass flow is made uniform by temporarily retaining the glass flow at a predetermined position. Reduce the occurrence. As a result, the present invention provides a flow path for easily and high-quality glass moldings of recent high refractive glass or low Tg glass, which is very difficult to select molding conditions. It is another object of the present invention to provide a flow path that enables simple and short-distance control even in conventional glass, and that can reduce the size of the apparatus.

The present inventor can obtain a desired temperature / flow velocity distribution in addition to averaging the temperature / velocity distribution of the glass flow by providing a retention portion in the flow path where the glass flow can once stay. As a result, it has been found that disadvantages such as striae can be suppressed, and the above problems have been solved.

The first configuration of the present invention is a flow path that is connected to a molten glass tank and allows molten glass to flow out, and has a glass flow retention portion that has a shape that shrinks after the flow path diameter is expanded. It is a flow path.

A second configuration of the present invention is the flow path according to the first configuration, wherein an outlet of the glass flow retention portion is not located immediately below the inlet.

A third configuration of the present invention is the flow channel according to the above configurations 1 and 2, wherein the maximum diameter of the staying portion is twice or more the diameter of the flow channel other than the staying portion.

According to a fourth aspect of the present invention, there is provided a glass molded body comprising melting a glass raw material in a melting tank, and flowing a molten glass flow into a mold through a flow path connected to the melting tank to form a glass. It is a manufacturing method, wherein the molten glass is allowed to pass through the channels having the above-described configurations 1 to 3 so that the molten glass flow is once retained in the channel and the temperature distribution is made uniform.

  Hereinafter, the flow path of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. .

In the present invention, the “flow path” is connected to a melting tank for melting and / or holding molten glass, and the entire flow path and flow path through which the glass flow passes when the molten glass flows out into a mold (for example, a mold). It is a concept that includes an exit. That is, it is a concept that encompasses so-called pipes, orifices, and nozzles.

Normally, the temperature control of the flow path is performed by heating the flow path by various methods. However, the temperature distribution of the molten glass flowing through the flow path is determined by the center of gravity of the cross section of the flow path (that is, when the cross section of the flow path is substantially circular). Is the highest near the center in the cross-sectional direction and the flow velocity is large. As described above, in the present invention, the glass flow is temporarily retained in the glass flow retention portion, whereby heat exchange occurs between the glass flows, and the temperature distribution gap due to the flow position in the flow path is to be relaxed. is there.

FIG. 1 is an example showing the flow path of the present invention. As shown in FIG. 1, the flow path 1 is provided with a glass flow retention portion 2 having a shape that contracts after the flow path diameter is expanded. In FIG. 1, the arrow shown in the flow path 1 indicates the traveling direction of the glass flow. When the molten glass flow flowing from above the flow path enters the glass flow retention portion 2, the flow temporarily stagnates. After that, when the glass flow retention part 2 is filled with a predetermined amount of glass flow, it flows out from the lower flow path. As described above, the glass flow flowing in from above has a temperature distribution in which the temperature flowing near the center of gravity of the cross section of the flow path has a high temperature and that flowing near the inner wall has a low temperature distribution. By mixing them for a predetermined time in the residence part 2, the temperature distribution which causes a disadvantage in glass forming is relaxed. And the glass flow which flows out again from the exit of the glass flow retention part 2 is changing into what has a comparatively uniform temperature distribution unlike what the glass flow had at the time of inflow.

Although the shape of the glass flow retention part 2 is not specifically limited, It is preferable that there is no outflow port directly under the inflow port of a retention part. This is because if the outlet is provided immediately below the inlet, the glass flow that has flowed in tends to flow out without being sufficiently retained, and heat exchange between the glass flows tends to be insufficient.

The glass flow retention part 2 can be formed by a curved surface, a flat surface, or a combination thereof. The size of the glass flow retention portion 2 is not particularly limited, but if it is too small, the glass flow flowing into the glass flow retention portion 2 must flow out with insufficient heat exchange.

Therefore, the maximum diameter of the glass flow retention part 2 is preferably at least twice the diameter of the flow path other than the retention part, more preferably at least 2.5 times, and most preferably at least 3 times. preferable. Here, the diameter of the glass flow retention portion 2 means the diameter when the cross section of the glass flow retention portion 2 is perpendicular to the direction in which the glass flow proceeds, and when the cross-sectional shape is substantially circular, The maximum diameter of the staying portion 2 means the largest diameter of the staying portion 2.

In addition, when the cross-sectional shape is not substantially circular, for example, in the case of a rectangle or the like, it means the diameter when the cross-sectional area is converted into a circle.

The length of the glass flow retention part 2 is not particularly limited, and the number is not limited to one and may be plural.

Although the installation position of the glass flow retention part 2 is not specifically limited, each position is determined in consideration of the thermal conductivity, heat capacity, flow path diameter, flow rate, desired temperature / temperature distribution, and the like of the glass. Of course, depending on the total length of the flow path 1, if it is too upstream, even if the temperature is made uniform by the glass flow retention part 2, it becomes easier to form a new temperature distribution as the flow proceeds. It is difficult to obtain the expected effect. Accordingly, at least one is preferably in the range of 50% downstream, more preferably 45% downstream, and most preferably 40% downstream.

The flow path of the present invention does not hinder heating and / or cooling by the flow path 1 itself and / or an external addition means. As a heating means for the flow path 1 itself, a known heating method by directly energizing the flow path can be used, and as an additional means from the outside, a known method such as a gas burner, an electric heater, infrared radiation, high frequency heating or the like can be used. Techniques may be used as appropriate. Further, by covering the vicinity of the glass outlet with a ring burner or the like and keeping it warm, defects such as devitrification and striae can be further suppressed.

The glass forming means using the flow path of the present invention is not particularly limited. As optical glass molding, it may be continuously flown out as a glass flow into a mold, and may be continuously molded into a plate-like or rod-like glass, etc., or the glass gob is separated by shear or surface tension, and on a porous mold. A glass gob may be formed by floating molding.

As the material of the flow path of the present invention, materials usually used in the glass melting process can be used, for example, platinum, reinforced platinum, gold, reinforced gold, rhodium, other noble metals and their alloys, or quartz. Can be used. Further, a material plated by a known method, for example, platinum having a gold-plated inner surface or a ceramic film such as SiC may be used.

Since the present invention defines the internal structure of the flow path 1, the atmosphere in the vicinity of the flow path outlet may be appropriately changed. For example, a nitrogen atmosphere or an inert gas atmosphere such as argon may be used. In some cases, the channel outlet may be covered with a heated atmosphere.

Specific examples of the present invention are shown below.

(Embodiment 1) In this embodiment, optical glass is melted in a platinum crucible, and the molten glass is made to flow out from its outlet through a flow path connected to the crucible, and gas is jetted out. A glass gob for use as a precision press-molding preform was obtained by flotation molding on a porous mold.

As the flow channel, a reinforced platinum flow channel having the same shape as that shown in FIG. 1 was used. Here, the inner diameter of the flow path is 3 mm (cross-sectional area 7.07 mm ² ), and the outlet is expanded to 6 mm. The total length of the channel, that is, the length from the outlet of the crucible to the outlet at the end of the channel was 2 m.

One glass flow retention part in the flow path was formed at a point (length 100 mm) from 300 mm to 400 mm from the outlet end. The shape of the staying portion is the same as that shown in FIG. 1, and the cross section is substantially circular. The maximum diameter of the cross section was 50 mm.

The receiving mold was made of porous stainless steel, and received molten glass in a state where air was blown from the receiving surface thereof. Thus, the molten glass floated from the receiving mold to receive glass gob.

The glass used was melted optical glass mainly composed of boron oxide and lanthanum oxide. The crucible was kept at about 1200 ° C., and the outflow pipe was kept at about 1100 ° C. by electric heating. From the outlet, the molten glass was separated into droplets. The amount of molten glass flowing out at this time was 80 g per minute.

When this glass gob was visually observed for optical defects such as devitrification and striae, such a defect could not be found, and it was a high-quality glass gob that could be used as a preform for molding an optical element.

Schematic diagram of the flow path of the present invention

Explanation of symbols

1 Flow path 2 Glass flow retention part

Claims (4)

A flow path that is connected to a molten glass tank and allows molten glass to flow out, and has a glass flow retention portion that has a shape that shrinks after the flow path diameter is expanded. The flow path according to claim 1, wherein an outlet of the glass flow retention portion is not located immediately below the inlet. The flow path according to claim 1 or 2, wherein the maximum diameter of the staying portion is at least twice the diameter of the flow path other than the staying portion. A method for producing a glass molded body, comprising melting a glass raw material in a melting tank, and flowing a molten glass flow into a mold through a flow path connected to the melting tank, and molding the glass. The said manufacturing method including the process of once stagnating a molten glass flow within a flow path by making the flow path in any one of Claims 1-3 pass, and making temperature distribution uniform.