JP2015054795A - Manufacturing method and apparatus of preform for press molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method and apparatus of a preform for press molding that suppress deposition of a molten glass crystal on a tip of an outflow pipe while effectively suppressing striae caused by vaporization of components, and improve production efficiency and maintainability.SOLUTION: In a manufacturing method of a preform for press molding, molten glass is discharged from an outflow pipe 2 and the molten glass lump is separated and molded on a molding die 3 into a preform. The manufacturing method and apparatus 1 of a preform for press molding include a cooling gas supply step for cooling the molten glass discharged from the outflow pipe 2 immediately after the outflow by cooling gas supply means 4, and a hot gas supply step for keeping the outflow pipe 2 at the liquid phase temperature of the molten glass-50°C or higher by a hot gas supply means 5.

Description

  The present invention relates to a method and an apparatus for manufacturing a press-molding preform, and in particular, manufacturing of a press-molding preform suitable for manufacturing a glass preform such as fluorophosphate glass that is likely to cause component volatilization at high temperatures. The present invention relates to a method and a manufacturing apparatus.

  In recent years, methods for manufacturing optical elements by press molding have become mainstream due to improvements in press molding technology. In press molding, a glass for press molding (hereinafter referred to as a preform) having a predetermined shape such as a spherical shape or a disk shape is heated to a glass transition point (Tg) or a yield point or higher in a mold and pressed. This is a technique for forming a specific shape.

  The optical glass used for the optical element has different glass main components for each desired optical property. As a glass having low refractive index and low dispersion optical properties, fluorophosphate glass is mainly used since it exhibits high visible light transmittance and anomalous dispersion (for example, see Patent Document 1). Low dispersion and anomalous dispersion are effective for correcting chromatic aberration, and a high visible light transmittance is an advantageous characteristic as an optical element material constituting an imaging optical system.

  On the other hand, fluorophosphate glass contains fluorine, which is an easily volatile component, as an essential component. When such components are contained, the components volatilize even at the temperature at which the preform is produced, causing the glass composition to fluctuate, causing striae and reducing the product yield. There's a problem.

  As a method for producing a press-forming preform that suppresses the occurrence of striae due to such component volatilization, a method of promoting cooling of the surface by blowing a cooling gas to the molten glass block that has flowed out of the outflow pipe is known. (For example, see Patent Documents 2 and 3).

  Also, it is not intended to suppress the occurrence of striae due to component volatilization, but to prevent the underside of the glass lump from being rapidly cooled at the time of contact with the receiving mold at the time of forming the preform and causing a gob in mark. However, in the production of a similar preform, a method is known in which the surface temperature on the contact surface side with the receiving mold is lowered in advance by injecting a cooling gas to the tip of the molten glass flow. (For example, see Patent Document 4).

JP-A-10-139454 Japanese Patent No. 4359169 Japanese Patent No. 4834756 JP 09-221329 A

  However, in a glass such as fluorophosphate glass that tends to cause component volatilization, the volatilization of the component occurs when the molten glass begins to flow out of the outflow pipe. Once the glass lump is cut and then the cooling gas is blown upward or obliquely above the glass lump, the occurrence of striae due to component volatilization may not be sufficiently suppressed.

  Also, as in Patent Document 4, when the glass flow of the molten glass is cooled, the temperature of the outflow pipe is also lowered, and the crystal of the molten glass is precipitated at the tip of the pipe, causing striae in the preform. In addition, there is a problem that manufacturing efficiency is lowered because maintenance of the pipe tip must be frequently performed.

  Therefore, the present invention is a method for producing a preform suitable for press molding of a glass optical element, and effectively suppresses the occurrence of striae due to component volatilization, while the molten glass is formed at the tip of the outflow pipe. It is an object of the present invention to provide a method and an apparatus for producing a preform for press molding that suppresses the precipitation of crystals and improves the production efficiency and maintainability.

  The method for producing a preform for press molding of the present invention is for press molding in which molten glass is allowed to flow out from an outflow pipe, the molten glass lump is separated, and the obtained molten glass lump is molded into a preform on a mold. A method for manufacturing a preform, the step of supplying a cooling gas so as to cool the molten glass flowing out of the outflow pipe immediately after the outflow, and the outflow pipe with the liquid phase temperature of the molten glass- And a heating gas supply step of supplying a heating gas so as to be maintained at a temperature of 50 ° C. or higher.

  An apparatus for manufacturing a preform for press molding according to the present invention includes an outflow pipe for flowing molten glass as a glass lump, a mold for receiving the molten glass lump flowing out from the outflow pipe and forming the preform into a preform, and the outflow pipe. Cooling gas supply means for supplying a cooling gas so that the molten glass flowing out can be cooled immediately after the flowing out, and a heating gas so as to maintain the outflow pipe at a liquid phase temperature of −50 ° C. or higher. And heated gas supply means for supplying.

  According to the method and apparatus for manufacturing a preform for press molding according to the present invention, the component volatilization from the molten glass is suppressed to prevent striae from occurring in the preform, and the molten glass is melted at the outflow nozzle of the molten glass. Precipitation of glass crystals can be prevented. Therefore, the manufacturing yield of preforms can be improved, maintenance work and the like can be reduced, and the manufacturing operation can be performed stably, so that the manufacturing efficiency of glass preforms can be greatly improved.

It is the figure which showed schematic structure of the manufacturing apparatus of the preform which is one Embodiment of this invention. It is a figure explaining arrangement | positioning of a cooling gas supply means. It is the sectional side view which showed the other structural example of the heating gas supply means. It is the bottom view which showed the other structural example of the heating gas supply means. It is a figure explaining the manufacturing method of the preform which is one embodiment of the present invention.

  Hereinafter, the preform manufacturing method and manufacturing apparatus of the present invention will be described in detail with reference to the drawings.

[Preform manufacturing equipment]
As an embodiment of the preform manufacturing apparatus of the present invention used here, there is a preform manufacturing apparatus 1 having the configuration shown in FIG. The preform manufacturing apparatus 1 receives an outflow pipe 2 that flows out molten glass, a molten glass that flows out from the outflow pipe 2, and cools the molten glass that flows out from the outflow pipe 2. A cooling gas supply means 4 for supplying a cooling gas for heating, and a heating gas supply means 5 for supplying a heating gas so as not to lower the temperature of the tip portion of the outflow pipe 2. FIG. 1 is a side view showing only the mold 3 as a sectional view. Further, the cooling gas supply means 4 and the warming gas supply means 5 are actually around the outflow pipe (molten glass flow). Although it arrange | positions so that it may surround, what was arrange | positioned in the front and back is abbreviate | omitted and illustrated for description.

  The outflow pipe 2 used here is not particularly limited as long as it allows molten glass to flow out and supply the molten glass as a glass lump, and a known outflow pipe can be used. As the outflow pipe, generally, a pipe made of platinum alloy or gold alloy controlled to a predetermined temperature is used.

  The mold 3 used here receives molten glass that has flowed out from the outflow pipe 2 and molds it into a preform shape, and includes a known mold 3. For example, the mold 3 is formed of a porous material having pores, and gas is discharged from the pores or by providing a gas jet on the surface holding the glass block on the mold. By spraying, an upward wind pressure is applied to the molten glass lump (hereinafter also referred to as gob), and the molten glass lump can be floated in a mold so that a glass molded body having a smooth surface can be formed. preferable.

  As this mold 3, for example, the receiving surface of the molten glass is formed of a porous material having a radius of curvature R of 2 to 200 mm and an R portion depth of 0.1 to 20 mm, and a floating gas only from the R portion. Is used that is configured to erupt. An inert gas such as nitrogen gas is ejected only from the R portion. An inert gas such as nitrogen gas may not only float the gob but also fill it around the gob. By increasing the size of the mold, a preform having a larger volume can be formed.

  Next, the cooling gas supply means 4 cools the molten glass flowing out from the outflow pipe 2, and lowers the surface temperature of the molten glass by filling the periphery of the flowing molten glass with the cooling gas. .

  The cooling gas supplied from the cooling gas supply means 4 is preferably jetted through a nozzle and cooled by colliding with the molten glass flow in a jet state. By cooling in this way, the heat transfer boundary film layer can be made very thin, and since the jet flows so as to adhere to the molten glass flow surface, there is an effect of increasing the effective cooling area. It is possible to obtain a high cooling effect. In order to supply the cooling gas so as to collide with the molten glass flow in a jet state, the supply direction of the cooling gas may be formed toward the axis of the outflow pipe 2 (molten glass flow). At this time, in order to maximize the cooling effect by the impinging jet, the angle between the cooling gas supply direction and the horizontal plane is within ± 10 degrees, and the cooling gas collides with the molten glass flow at an angle close to vertical. It is preferable to configure so as to. Here, the jet flow refers to a cooling gas flow that flows at a speed of 0.5 m / s or more.

  Further, in order to uniformly cool the surface of the molten glass, it is preferable that a plurality of the cooling gas supply means 4 be evenly arranged around the molten glass flow. For example, as shown in FIG. 2, when eight cooling gas supply means 4 are provided, the cooling gas supply means 4 is arranged on the circumference around the axis of the outflow pipe 2 so as to surround it. In addition, the supply means are arranged uniformly so that the gas supply direction from the adjacent supply means is at an angle of 45 degrees on the arranged plane so that the cooling gas can be supplied toward the molten glass flow. do it.

  If it is desired to start cooling immediately after the molten glass starts to flow out of the outflow pipe 2, the molten glass is melted immediately after it comes out from the end of the outflow pipe 2 with the cooling gas supply direction being higher than the horizontal direction. It is preferable that the cooling gas strikes the glass. However, in this case, since the temperature at the front end portion of the outflow pipe 2 is likely to be lowered by the cooling gas, care is taken so that the temperature at the front end portion of the outflow pipe 2 is sufficiently maintained.

  The cooling gas supply means 4 is preferably provided at a position where the cooling gas supply port is 0 to 5 mm below the front end surface (horizontal surface at the front end) of the outflow pipe 2, and as much as possible on the front end surface of the outflow pipe 2. It is more preferable that they are close.

  Next, the heated gas supply means 5 supplies a heated gas to the tip portion of the outflow pipe 2 to prevent a temperature drop so that a crystal of molten glass does not precipitate at the tip portion of the outflow pipe 2. . At this time, the temperature of the outflow pipe 2 may be set to a temperature at which the crystal of the molten glass does not precipitate. For example, it is preferable to maintain the liquid phase temperature of the molten glass at −50 ° C. or higher.

  In order to prevent the temperature from being lowered in this way, the heated gas is supplied. The heated gas also has the effect of directly heating the outflow pipe 2, but the main effect is to prevent the temperature from being lowered by the cooling gas. It is. In other words, the cooling gas that cools the molten glass fulfills a shielding function that prevents it from coming into contact with the outflow pipe 2.

  In order to exhibit such a shielding function, the heated gas is discharged at a predetermined discharge pressure to prevent contact between the outflow pipe 2 and the cooling gas. At this time, in order to make the shield function more effective, it is preferable to supply the warming gas to the tip of the outflow pipe 2 over the entire circumference.

  In order to supply the heated gas over the entire circumference in this way, a configuration in which a plurality of the heated gas supply means 5 are evenly arranged so as to surround the outflow pipe 2, for example, the cooling gas supply in FIG. Similarly to the means, when eight warming gas supply means are provided, the warming gas supply means 5 is arranged on the circumference around the outflow pipe 2 so as to surround it, and the arrangement is arranged. In this plane, the gas supply directions of the adjacent supply means may be evenly arranged so as to be at an angle of 45 degrees so that the heated gas can be supplied.

  Moreover, it is preferable that the supply direction of the heating gas is directed downward along the outflow pipe 2. By doing in this way, the front-end | tip part of the outflow pipe 2 can be surrounded by a heating gas flow, and exclusion of a cooling gas can be performed effectively.

  This heated gas supply means 5 is provided with its supply port above the front end surface of the outflow pipe 2 (horizontal plane at the outflow port), preferably 2 to 20 mm above the front end surface. 5 to 10 mm above. If it is too close to the outlet of the molten glass, the maintainability of the tip of the outflow pipe 2 at the time of glass wetting and troubles becomes worse. On the other hand, if it is provided above 20 mm, in order to obtain a sufficient shielding effect, it is necessary to set the discharge pressure and the flow rate high, and the efficiency is lowered. The warming gas supply means 5 is preferably installed along the outer periphery of the outflow pipe, or is installed within a distance of about 5 mm from the outer periphery to the outside.

  As the warming gas supply means 5, a plurality of gas supply ports may be provided as described above. However, as shown in FIGS. A hollow pipe 15 may be provided, and the heated gas may be supplied between the outflow pipe 2 and the hollow pipe 15. With such a configuration, it is not necessary to provide a plurality of gas supply ports, it is easy to discharge the heated gas downward along the outflow pipe 2, and the heated gas is supplied over the entire circumference. it can. Here, FIG. 3A is a side sectional view of the outflow pipe 2 and the hollow pipe 15, and FIG. 3B is a bottom view of the outflow pipe 2 as viewed from the front end side (outflow side).

[Preform manufacturing method]
Next, the preform manufacturing method of the present invention will be described with reference to FIG. 4 by taking as an example the case of using the preform manufacturing apparatus 1 of FIG. FIG. 4 is a diagram for explaining a preform manufacturing method, and these drawings show stepwise from the outflow of molten glass to the manufacture of the preform.

  First, in the production of the preform of the present invention, the molten glass is caused to flow out of the outflow pipe, the molten glass lump is separated, and the obtained molten glass lump is formed into a preform on the mold, as in the prior art. It has each process of doing.

  That is, first, the outflow of the molten glass flow 50 from the outflow pipe 2 is started (FIG. 4A), and the molten glass 50 that has flowed out is received by the mold 3 (FIG. 4B). A predetermined amount of outflow glass 50 is supplied, the glass flow is cut, and the molten glass lump is cooled and solidified while forming a predetermined shape on the mold 3 to form a preform 50a (FIG. 4 ( c)). Each of these steps is basically performed under the same conditions as conventionally known methods.

  For example, a glass raw material is melted in a tank to prepare a molten glass, and this molten glass is discharged from the tip of an outflow pipe 2 attached to the tank to a molding die 3 to produce a molten glass lump (gob). At that time, the molten glass 50 is received and collected by the receiving surface of the mold 3, but the mold 3 is slowly lowered so that the tip of the outflow pipe 2 is not wetted by the molten glass. When the gob reaches the target volume, the mold 3 is quickly lowered, and the glass flow is cut by the surface tension. In order to produce a preform with a desired volume, during the production of the gob, an inert gas such as nitrogen gas is passed through the porous mold 3, and the gob is lifted by the force of the outflow of gas to make it oval or spherical. Then, it is cooled and a preform is formed.

  In order to suppress component volatilization, it is preferable that the outflow temperature of the molten glass is in the range of ± 50 ° C. with respect to the liquidus temperature. The viscosity of the molten glass at the outflow temperature is preferably in the range of log η of 0.5 to 2.5, more preferably in the range of 1.0 to 2.0, where η is the viscosity. If the viscosity is too high, the balance between the viscosity and the surface tension will be lost, it will be difficult to separate the molten glass flow as a gob, and a stringing phenomenon will occur. On the other hand, if the viscosity is too low, it is difficult to form an axisymmetric shape by losing the pressure of the floating gas when the gob is float formed.

  And in this invention, in addition to such operation similar to the past, it has the characteristics in the point which added two processes demonstrated below.

<Cooling gas supply process>
One of the features of the present invention is that it has a cooling gas supply process that allows the molten glass 50 flowing out from the outflow pipe 2 to be cooled immediately after the outflow. In this cooling gas supply step, the surface temperature of the molten glass 50 flowing out from the outflow pipe 2 is cooled as soon as possible, and component volatilization from the molten glass 50 is suppressed.

  That is, the surface of the molten glass 50 can be cooled immediately after the molten glass 50 flows out from the outflow pipe 2 shown in FIG. At this time, it is preferable to supply the cooling gas by the cooling gas supply means 4 before the molten glass 50 flows out so that the periphery of the molten glass 50 is filled with the cooling gas.

  At this time, it is preferable from the viewpoint of efficient cooling that the cooling gas is supplied to the molten glass 50 flowing out from the outflow pipe 2 so as to directly collide with the molten gas. Therefore, the cooling gas is preferably supplied toward the molten glass flow (the axis of the outflow pipe 2), and the cooling gas discharge direction is a horizontal plane so that the cooling gas collides perpendicularly to the molten glass flow. The formed angle is preferably ± 10 degrees or less. Further, at this time, the cooling gas is preferably a jet that flows at a speed of 0.5 m / s or more.

  In addition, you may supply so that the discharge direction of a cooling gas may face the upper direction from a horizontal surface so that the molten glass which flows out from the front-end | tip part of the outflow pipe 2 may be cooled immediately. However, since the tip end portion of the outflow pipe 2 is easily cooled in this manner, sufficient attention is paid to temperature control (cooling gas and heating gas supply conditions, etc.) so that crystals do not precipitate.

  The cooling gas used here is not particularly limited as long as it can lower the surface temperature of the molten glass, and examples thereof include nitrogen, oxygen, air, argon, helium, and carbon dioxide gas. The temperature of the cooling gas is set to a temperature not higher than the glass transition point (Tg) of the molten glass in order to cool the molten glass to such an extent that no component volatilization occurs from the surface. This is preferable because it increases the required cooling capacity. From the viewpoint of cost, it is advantageous not to perform temperature control, and it is preferable to set the temperature to about room temperature (25 ° C.).

  The supply flow rate of the cooling gas may be an amount that can sufficiently cool the surface of the molten glass, and for example, a range of 10 L / min to 30 L / min is preferable. From the viewpoint of efficiently performing cooling, it is preferable that the flow rate is large, but if it exceeds 30 L / min, there is a possibility that the cutting of the molten glass flow becomes unstable due to the oscillation of the molten glass suspended from the outflow pipe 2, and If it is less than 10 L / min, the cooling effect may not be sufficiently obtained. The cooling gas supply flow rate is more preferably 15 L / min or more, and even more preferably 18 L / min or more.

<Heating gas supply process>
Furthermore, one of the features of the present invention is that it has a heated gas supply step that makes it possible to maintain the outflow pipe 2 at a liquid phase temperature of the molten glass of −50 ° C. or higher. This warming gas supply step prevents the tip portion of the outflow pipe 2 from being cooled by the cooling gas, and maintains the temperature at which the molten glass does not crystallize at the tip portion.

  That is, as described above, in order to cool the molten glass 50, the cooling gas is supplied from the cooling gas supply means 4, and the periphery of the molten glass 50 is filled with a gas having a temperature equal to or lower than the glass transition point. However, at this time, the heating gas is supplied from the heating gas supply means 5 to prevent the cooling gas from coming into contact with the outflow pipe 2 so that the tip portion is not cooled.

  In order to prevent the cooling gas from coming into contact with the outflow pipe 2, the heating gas supplied here may be set at a predetermined discharge pressure so that the cooling gas does not approach the outflow pipe 2. At this time, the discharge pressure of the warming gas is preferably 0.05 MPa or more, and preferably in the range of 0.1 to 0.5 MPa. If the discharge pressure is less than 0.05 MPa, the shielding effect is not sufficiently obtained, and the cooling gas may come into contact with the outflow pipe 2 to cause a temperature drop. Further, when the discharge pressure is 0.5 MPa or more, the contact between the molten glass 50 and the cooling gas may be hindered to prevent the cooling of the surface temperature of the molten glass 50.

  The heating gas is preferably supplied from a position higher than the front end surface of the outflow pipe 2 (horizontal plane at the outflow port) downward along the outflow pipe 2 and over the entire circumference. By doing so, the outer periphery of the outflow pipe 2 can be covered with a heated gas flow so that the outflow pipe 2 and the cooling gas do not come into contact with each other.

  The warming gas used here is not particularly limited as long as the temperature drop of the outflow pipe 2 can be prevented by the shielding effect, and examples thereof include nitrogen, oxygen, air, argon, helium, and carbon dioxide gas. In the present invention, the temperature of the heated gas is such that the outflow pipe 2 is maintained at a temperature equivalent to that of the heated gas so that crystals do not precipitate from the molten glass. Is preferable, the range of the liquidus temperature ± 50 ° C is more preferable, and the range of the liquidus temperature ± 20 ° C is more preferable.

  In addition, it can confirm by measuring with a radiation thermometer whether the temperature of the outflow pipe front-end | tip can be hold | maintained to predetermined temperature. Since the metal surface has a low emissivity and a high reflectivity, it is difficult to accurately measure the radiation temperature only by the measurement. However, a highly reliable measurement is possible by calibrating in advance in consideration of the influence of the measurement environment. Moreover, about temperature control of warming gas, warming gas temperature can be measured by providing a thermocouple in the nozzle exit of a warming gas supply means. At this time, the measurement accuracy can be improved by using a thin wire having a low heat capacity as the thermocouple element. Thus, by monitoring at least one of the temperature of the tip of the outflow pipe and the temperature of the heated gas, the preform manufacturing operation can be performed stably.

(Optical glass)
In the present invention, the glass to be used is not particularly limited, and a known optical glass is used. Among them, a glass containing a component that easily volatilizes is preferable.

  The yield point of the glass used here is preferably 420 ° C. or lower. In order to prevent deterioration of the mold during press molding and volatilization of components from the preform to prevent a decrease in productivity, a lower yield point is preferable. Therefore, the yield point is more preferably 410 ° C. or lower, further preferably 400 ° C. or lower, and particularly preferably 380 ° C. or lower.

  The liquidus temperature of the glass used here is preferably 750 ° C. or lower for good preform molding. If the liquidus temperature is higher than 750 ° C., components may volatilize from the surface of the molten glass during preform molding, which may cause striae. Therefore, the lower the liquidus temperature is, the more preferable, 730 ° C. or lower is more preferable, 670 ° C. or lower is further preferable, and 650 ° C. or lower is even more preferable. In the present specification, the liquidus temperature is the lowest temperature at which crystals are not generated from molten glass when held at that temperature for 1 hour.

The linear expansion coefficient of the glass used here is preferably 140 to 200 × 10 ⁻⁷ / ° C. If the thermal expansion coefficient exceeds 200 × 10 ⁻⁷ / ° C., a problem that the glass surface may be lost during molding may occur.

  A preferred example of the glass used in the present invention is a fluorophosphate glass that can effectively suppress the occurrence of striae due to component volatilization and can stably produce a preform. Hereinafter, the fluorophosphate glass will be described in more detail. In the present specification, unless otherwise specified, “%” represents the ratio of the cation component in terms of cation% based on the molar ratio, and the ratio of each anion component is based on the molar ratio based anion. It shall be displayed in%.

The fluorophosphate glass suitable for the present invention is expressed as cation%, P ⁵⁺ 10 to 45%, Al ³⁺ 1 to 40%, Mg ²⁺ 0 to 20%, Ca ²⁺ 0 to 25%, Sr ²⁺ 0 to 25%. Ba ²⁺ 0 to 35%, Li ⁺ 24 to 60%, Na ⁺ 0 to 10%, K ⁺ 0 to 10%, Y ³⁺ 0 to 10%, B ³⁺ 0 to 15%, and F ⁻ F ^- and ^{O 2-} as anionic ratio to the total amount of ^{(F - / (F - +} O 2-)) those containing at 0.25 to 0.85 is particularly desirable.

In this fluorophosphate glass, P ⁵⁺ is a glass network former and is an essential component. The content of P ⁵⁺ is 10 to 45%. If it is less than 10%, the stability of the glass may be lowered. In order to increase the content of P ⁵⁺ , it must be introduced with normal phosphoric acid as a raw material. If P ⁵⁺ exceeds 45%, the water in orthophosphoric acid may react with fluorine and volatilize as HF gas. Moreover, when it introduce | transduces with an oxide raw material, since an oxygen ratio becomes large too much, a desired optical characteristic is not satisfy | filled. The upper limit of P ⁵⁺ is preferably 40% or less, more preferably 35% or less, and even more preferably 33% or less. Further, the lower limit is preferably 12% or more, and more preferably 15% or more. In addition, the use of phosphate is preferable as the P ⁵⁺ raw material from the viewpoint of suppressing the erosion of the platinum crucible and suppressing the volatilization of the components.

In this glass, Al ³⁺ is a component that improves the stability of the glass and is an essential component. The content of Al ³⁺ is 1 to 40%. If it is less than 1%, the stability of the glass is lowered, and if it exceeds 40%, the glass transition point (Tg) and the liquidus temperature may be increased. The upper limit of Al ³⁺ is preferably 37% or less, more preferably 35% or less, still more preferably 33% or less, and even more preferably 30% or less. Further, the lower limit of Al ³⁺ is preferably 3% or more, and more preferably 5% or more.

In this glass, Mg ²⁺ is a component that improves the stability of the glass and is not an essential component. The content of Mg ²⁺ is 0 to 20%. The upper limit of Mg ²⁺ is preferably 15% or less, more preferably 10% or less, and even more preferably 7% or less. Further, the lower limit of Mg ²⁺ is preferably more than 0%, more preferably 1% or more.

In this glass, Ca ²⁺ is a component that improves the stability of the glass and is not an essential component. The content of Ca ²⁺ is 0 to 25%. The upper limit of Ca ²⁺ is preferably 22% or less, more preferably 15% or less, and still more preferably 10% or less. Further, the lower limit of Ca ²⁺ is preferably more than 0%, more preferably 1% or more.

In this glass, Sr ²⁺ is a component that improves the stability of the glass and is not an essential component. The content of Sr ²⁺ is 0 to 25%. The upper limit of Sr ²⁺ is preferably 22% or less, more preferably 15% or less, and even more preferably 10% or less. Further, the lower limit of Sr ²⁺ is preferably more than 0%, more preferably 0.5% or more, and further preferably 1% or more.

In this glass, Ba ²⁺ is a component capable of improving the stability of the glass and realizing a high refractive index while maintaining low dispersion, and is not an essential component. The content of Ba ²⁺ is 0 to 35%. The upper limit of Ba ²⁺ is preferably 31% or less, more preferably 30% or less, still more preferably 29% or less, and even more preferably 25% or less. Further, the lower limit of Ba ²⁺ is preferably more than 0%, more preferably 1% or more, and further preferably 3% or more.

In this glass, in order to enhance the effect due to the inclusion of the alkaline earth metal cation component (R ²⁺ ), these contents are preferably 1 to 31% in terms of the total amount (Mg ²⁺ + Ca ²⁺ + Sr ²⁺ + Ba ²⁺ ). . When the content is 1% or more, the effect of increasing the stability of the glass is enhanced. On the other hand, if it exceeds 31%, the stability of the glass is rather lowered. The upper limit of the total amount of R ²⁺ is preferably 30% or less, and more preferably 29% or less.

^Further, when containing ^{R 2+} above total ^amount, Mg ^2+, Ca 2+, 2 or more used is preferably selected from ^{Sr 2+} and ^{Ba 2+.} Furthermore, from the viewpoint of enhancing the effect due to the inclusion of the alkaline earth metal, it is preferable to use Ba ²⁺ as an essential component and to use one or more selected from Mg ²⁺ , Ca ²⁺ and Sr ²⁺ . Although Ca ²⁺ and Sr ²⁺ can be introduced in a relatively large amount, the introduction of a large amount of Mg ²⁺ and Ba ²⁺ may reduce the stability of the glass.

In this glass, Li ⁺ is a component that lowers the glass transition point (Tg) without impairing stability, and is an essential component. The content of Li ⁺ is 24 to 60%. If the content of Li ⁺ is less than 24%, the glass transition point (Tg) cannot be lowered sufficiently and the stability is also lowered. On the other hand, if it exceeds 60%, the durability of the glass is impaired, and at the same time, the workability is lowered. Although the effect of lowering the glass transition point (Tg) can be obtained even when the following alkali metal component is contained, it is preferable to contain Li ⁺ because the water resistance of the glass is excellent. The upper limit of Li ⁺ is preferably 50% or less, more preferably 45% or less, still more preferably 43% or less, still more preferably 41% or less, and particularly preferably less than 40%. The lower limit of Li ⁺ is preferably more than 25%, more preferably 27% or more, and even more preferably more than 30%. Moreover, when importance is attached to the stability of glass, it is preferable to make content of Li ^<+> more than 30%-60%. At this time, the upper limit of Li ⁺ is more preferably 59% or less, still more preferably 57% or less, and even more preferably 55% or less. The lower limit of Li ⁺ is more preferably 31% or more and even more preferably 32% or more. Moreover, when importance is attached to striae suppression of glass, the content of Li ⁺ is preferably 24 to 30%. At this time, the upper limit of Li ⁺ is more preferably 29% or less, even more preferably 28% or less, and even more preferably 27% or less. The lower limit of Li ⁺ is more preferably more than 24% and even more preferably 25% or more.

Further, in the glass, in order to obtain the effect of the stability and striae suppression of glass, the total amount for the Li ⁺ ratio Li ⁺ / .SIGMA.R ²⁺ content of the alkaline earth metal component, i.e. ^Li + / ^{(Mg 2+} + Ca ²⁺ + Sr ²⁺ + Ba ²⁺ ) is preferably more than 0.8 and less than 16. In particular, when importance is attached to the stability of the glass, it is preferable that Li ⁺ / ΣR ²⁺ be 1 or more and less than 16. By stabilizing the glass, it is possible to produce a preform having a large volume, and it is also possible to produce a large-diameter lens by a press molding method. The upper limit of Li ⁺ / ΣR ²⁺ is more preferably 15 or less, even more preferably 14 or less, and even more preferably 13 or less. The lower limit of Li ⁺ / ΣR ²⁺ is more preferably more than 1, and even more preferably 2 or more. Further, when importance is attached to striae suppression of glass, it is preferable that Li ⁺ / ΣR ²⁺ be more than 0.8 and less than 1. In this case, the upper limit of Li ⁺ / ΣR ²⁺ is more preferably 0.98 or less, and even more preferably 0.97 or less. The lower limit of Li ⁺ / ΣR ²⁺ is more preferably 0.82 or more, and even more preferably 0.85 or more.

In this glass, Na ⁺ and K ⁺ are components that lower the glass transition point (Tg) as in Li ⁺ , but are not essential components. The contents of Na ⁺ and K ⁺ are both 0 to 10%. Since Na ⁺ and K ⁺ have a larger thermal expansion coefficient than that of Li ⁺ , a low content is preferable, and it is more preferable that they are not substantially contained. In the present specification, the phrase “not substantially contained” means that it is not actively contained, but is allowed to be mixed due to inevitable impurities.

In this glass, Y ³⁺ is a component that improves the stability or durability of the glass, but is not an essential component. The content of Y ³⁺ is 0 to 10%. If it exceeds 10%, the stability of the glass is lowered, and the glass transition point (Tg) is increased. The upper limit of Y ³⁺ is preferably 7% or less, and more preferably 5% or less.

In this glass, B ³⁺ is a vitrification component and has an effect of stabilizing the glass, but is not an essential component. The content of B ³⁺ is 0 to 15%. From the viewpoint of ensuring the durability of the glass and suppressing the volatilization of the components, it is preferably 15% or less. The upper limit of B ³⁺ is preferably 10% or less, more preferably 5% or less, more preferably 0.5% or less, and still more preferably substantially not contained in order to reduce volatilization of components. The B ³⁺ raw material is preferably B ₂ O ₃ from the viewpoint of suppressing the volatilization of the components and preventing the striae of the glass.

This glass may contain components other than those described above as long as the object of the invention is not impaired, but P ⁵⁺ , Al ³⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Li may be used as the cation component. The total amount of ⁺ and Y ³⁺ is preferably 95% or more from the viewpoint of stably producing a high-quality optical glass. Furthermore, the total amount of the above-described cation component is preferably 98% or more, more preferably 99% or more, and substantially P ⁵⁺ , Al ³⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Li ⁺ and It is particularly preferred that it consists of Y ³⁺ .

In this glass, lanthanoids such as Ti ⁴⁺ , Zr ⁴⁺ , Zn ²⁺ , Bi ⁵⁺ , W ⁵⁺ , Nb ⁵⁺ , Sb ³⁺ , La ³⁺ , Gd ³⁺ and the like can be cited as components other than those described above. The total content of these is preferably 5% or less, more preferably 2% or less, and even more preferably 1% or less.

Si ⁴⁺ may be contained for the purpose of stabilizing the glass. However, in the production of fluorophosphate glass, since the melting temperature of the glass is low, if it is introduced excessively, the raw material remains undissolved in the glass melt, and volatilization increases during melting, thereby impairing the production stability. Therefore, the content of Si ⁴⁺ is preferably 0 to 10%, more preferably 0 to 8%, and still more preferably 0 to 5%.

In this glass, it is preferable that Sn ²⁺ is not substantially contained since the glass may be colored. Moreover, in order to suppress environmental load, it is preferable not to contain Pb2 ⁺ substantially.

In this glass, the proportion of the anionic component, while achieving the desired optical properties, in order to obtain a glass having excellent stability, F ^- the F ^- and anion ratio to the total amount of the O ^2-( F ⁻ / (F ⁻ + O ²⁻ )) and contained at 0.25 to 0.85. The anion ratio is preferably 0.3 to 0.8, and more preferably 0.35 to 0.75. Further, the total amount of F ⁻ and O ²⁻ in the anion is preferably 99% or more, and more preferably substantially consists of F ⁻ and O ²⁻ .

As an anion component, halogen content is allowed in addition to F ⁻ and O ²⁻ . However, the chloride raw material has higher deliquescence than the fluoride raw material and is likely to contain moisture. Therefore, when used together with the fluoride raw material, it may become hydrogen fluoride and promote volatilization of fluorine. In general, a chloride raw material has a high vapor pressure and is likely to volatilize. Therefore, in this glass, it is preferable that Cl ⁻ is not substantially contained.

The optical constant of the glass is preferably 1.4 to 1.58 for the refractive index (n _d ) and 60 to 90 for the Abbe number (ν _d ). The refractive index is more preferably 1.45 to 1.575, and particularly preferably 1.48 to 1.56. The Abbe number is more preferably 65 to 85, and particularly preferably 70 to 82.

Since this glass has a large content of Li ⁺ , the glass transition point can be lowered. In this glass, the glass transition point (Tg) is preferably 380 ° C. or lower. In order to prevent deterioration of the mold during press molding and volatilization of components from the preform and prevent a decrease in productivity, the lower the glass transition point (Tg), the better. Therefore, the glass transition point (Tg) is more preferably 370 ° C. or less, further preferably 360 ° C. or less, and particularly preferably 350 ° C. or less.

In this glass composition range, the fluorophosphate glass (Glass I) with emphasis on stability is expressed in terms of cation%,
P ⁵⁺ 10-45%,
Al ³⁺ 1-40%,
Mg ²⁺ 0-20%,
Ca ²⁺ 0-25%,
Sr2 ⁺ 0-25%,
Ba ²⁺ 0-35%,
Li ⁺ more than 30-60%,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-10%,
B ³⁺ 0-15%,
Containing
F ⁻ is contained in an anion ratio (F ⁻ / (F ⁻ + O ²⁻ )) of 0.25 to 0.85 with respect to the total amount of F ⁻ and O ²⁻ .

In addition, in this glass composition range, fluorophosphate glass (glass II) that emphasizes striae suppression is expressed in terms of cation%,
P ⁵⁺ 10-45%,
Al ³⁺ 1-40%,
Mg ²⁺ 0-20%,
Ca ²⁺ 0-25%,
Sr2 ⁺ 0-25%,
Ba ²⁺ 0-35%,
Li ⁺ 24-30%,
Na ⁺ 0-10%,
K ⁺ 0-10%,
Y ³⁺ 0-10%,
B ³⁺ 0-15%,
Containing
F ⁻ is contained in an anion ratio (F ⁻ / (F ⁻ + O ²⁻ )) of 0.25 to 0.85 with respect to the total amount of F ⁻ and O ²⁻ .

In such a fluorophosphate glass, since the glass composition is thermally stable and exhibits high liquid phase viscosity, even inside a large preform having a volume of 1 to 1.5 cm ³ , the inside of devitrification, foreign matter, etc. A defect-free product is obtained. Considering the glass composition used in this way, a preform free from striae, surface wrinkles and scratches can be obtained. If the preform has a volume of 1.5 cm ³ , a lens having a diameter of about 25 mm can be manufactured by press molding.

(Optical element)
An optical element can be obtained by molding the preform manufactured as described above. The fluorophosphate glass described above has the optical characteristics described above, and therefore, when used as an optical element, optical design is easy. Examples of such optical elements include aspherical lenses and spherical lenses used in digital cameras and the like.

As a manufacturing method of the optical element, a press molding method is preferable from the viewpoint of improving mass productivity. In the press molding method, a press molding die whose molding surface is processed into a desired shape in advance is used. A pair of molds face each other, and the above-mentioned preform is placed between them, and both the mold and preform are heated to a temperature at which the glass drops to a viscosity suitable for molding, thereby softening the preform. To do. And by pressing this, the shaping | molding surface of a shaping | molding die is precisely transcribe | transferred to glass. Since the above-mentioned fluorophosphate glass has a sufficiently low glass transition point (Tg), the heating temperature of the preform can be lowered. Therefore, the durability of the mold can be increased, and the volatilization of components from the glass surface during pressing can be suppressed. In addition, as described above, this glass is free from internal defects such as devitrification and foreign matter, and is free from striae and surface wrinkles and scratches, even in a large preform having a volume of 1 to 1.5 cm ^3. Since a preform can be obtained, it is possible to manufacture a lens having a large aperture, which has been difficult in the past, by a press molding method. That is, a lens with a diameter of 8 mm from a preform with a volume of about 0.6 cm ³ , a lens with a diameter of 15 mm from a preform with a volume of about 1.0 cm ³ , a lens with a diameter of about 25 mm from a preform with a volume of about 1.5 cm ³ Each is obtained by press molding.

  The atmosphere during press molding is preferably non-oxidizing in order to protect the mold surface and the preform surface. As the non-oxidizing atmosphere, an inert gas such as argon or nitrogen, a reducing gas such as hydrogen, or a mixed gas of an inert gas and a reducing gas can be used. Preferably, nitrogen gas or nitrogen gas mixed with a small amount of hydrogen gas can be used. Moreover, the pressure and time at the time of pressurization can be suitably changed according to the viscosity etc. of glass. And after heating and pressurizing, a shaping | molding die and a press-molded product are cooled, When it becomes the temperature below a strain point, Preferably, it molds and takes out a press-molded product.

  The present invention will be described below with reference to examples. However, the present invention is not construed as being limited to these.

  In the preform manufacturing apparatus of FIG. 1, a preform was manufactured as follows using the apparatus to which the heated gas supply means shown in FIGS. 3A and 3B was applied.

First, as a glass material to be used, a fluorophosphate glass having a liquidus temperature of 730 ° C. and a glass transition point (Tg) of 375 ° C. was prepared. This glass material is heated to 800 to 950 ° C. in a tank (not shown) to be in a molten state, sufficiently clarified, then cooled to about 730 to 830 ° C., stirred and homogenized, and set. An outflow pipe (inner diameter: 3 mm) at a temperature of 700 ° C. was flowed out at a flow rate of about 4 L / D, and supplied so as to form a molten glass lump on the mold so that the gob size was 0.3 cm ³ .

  At this time, the cooling gas supply means is arranged evenly in 10 degree increments on the circumference of the diameter of 35 mm around the axis of the outflow pipe on the horizontal plane 2 mm below the front end surface of the outflow pipe. It was made to feed horizontally toward the axis of the outflow pipe. As the cooling gas, nitrogen gas at room temperature was used, and the supply flow rate was in the range of 0 to 30 L / min.

  The warming gas uses a hollow pipe having an inner diameter of +1 mm with respect to the outer diameter of the outflow pipe, covers the outer periphery of the outflow pipe with this hollow pipe, and warms in a horizontal plane 10 mm above the tip plane of the outflow pipe. Gas was discharged. Nitrogen gas at 700 ° C. was used as the heating gas, and the discharge pressure was set to 0.1 MPa.

  The molten glass lump on the mold was float formed while supplying nitrogen gas from the molding surface, and cooled and solidified to produce a preform having an elliptical cross section.

  As a result, when the cooling gas supply flow rate was 0 L / min or more and 15 L / min or less, the surface of the preform was devitrified, and at 20 L / min, devitrified material was not observed, but striae ) Was observed, and at 25 L / min or higher, there was no devitrified substance or striae, and a preform having a smooth surface shape was obtained.

  The preform manufacturing method and manufacturing apparatus of the present invention can provide the manufacturing efficiency of a preform for an optical element used in an optical system such as a digital camera in a favorable and stable manner.

DESCRIPTION OF SYMBOLS 1 ... Preform manufacturing apparatus, 2 ... Outflow pipe, 3 ... Mold, 4 ... Cooling gas supply means, 5 ... Heating gas supply means, 50 ... Molten glass, 50a ... Preform

Claims (13)

A method for producing a preform for press molding, in which molten glass is caused to flow out from an outflow pipe, the molten glass lump is separated, and the obtained molten glass lump is formed into a preform on a mold,
A cooling gas supply step of supplying a cooling gas so as to cool the molten glass flowing out of the outflow pipe immediately after the outflow;
A heated gas supply step of supplying a heated gas so as to maintain the outflow pipe at a liquid phase temperature of the molten glass of −50 ° C. or higher;
A method for producing a press-molding preform, comprising:   The press molding according to claim 1, wherein the warming gas supply step discharges the warming gas from a position higher than the tip end surface of the outflow pipe downward along the outflow pipe and over the entire circumference. Method for manufacturing preform.   The method for producing a preform for press molding according to claim 1 or 2, wherein a discharge pressure of the warming gas is 0.1 MPa or more.   The manufacturing method of the preform for press molding of any one of Claims 1-3 in which the said cooling gas supply process supplies the said cooling gas so that it may collide with the molten glass flow which flowed out from the said outflow pipe.   The method for producing a press-molding preform according to any one of claims 1 to 4, wherein a supply flow rate of the cooling gas is 10 L / min to 30 L / min.   The method for producing a press-molding preform according to any one of claims 1 to 5, wherein a glass transition point (Tg) of the molten glass is 380 ° C or lower.   The yield point (At) of the molten glass is 420 ° C or lower. The method for producing a press-molding preform according to any one of claims 1 to 6.   The said glass is a fluorophosphate glass, The manufacturing method of the preform for press molding of any one of Claims 1-7. The fluorophosphate glass is expressed in terms of cation%, P ⁵⁺ 10-45%, Al ³⁺ 1-40%, Mg ²⁺ 0-20%, Ca ²⁺ 0-25%, Sr ²⁺ 0-25%, Ba ²⁺ 0 ^{35%, Li + 24~60%,} Na + 0~10%, K + 0~10%, Y 3+ 0~10%, containing B 3+ 0 to 15%, a, F ^- the F ^- and ^{O 2 The} method for producing a preform for press molding according to claim 8, which is contained in an anion ratio (F ⁻ / (F ⁻ + O ^{2 −} )) of 0.25 to 0.85 with respect to the total amount of . The method for producing a press-molding preform according to any one of claims 1 to 9, wherein the preform has a volume of 1 cm ³ or more and does not contain devitrification. An outflow pipe for flowing molten glass as a glass lump,
A mold for receiving a molten glass lump that has flowed out of the outflow pipe and forming it into a preform,
A cooling gas supply means for supplying a cooling gas so as to cool the molten glass flowing out from the outflow pipe immediately after the outflow;
A heated gas supply means for supplying a heated gas so as to maintain the outflow pipe at a liquid phase temperature of the molten glass of −50 ° C. or higher;
A preform manufacturing apparatus characterized by comprising:   The press-molding according to claim 11, wherein the warming gas supply means supplies the warming gas from a position higher than the front end surface of the outflow pipe downward along the outflow pipe and over the entire circumference. Preform manufacturing equipment.   The preform according to claim 11 or 12, wherein a discharge direction of the cooling gas by the cooling gas supply means is toward a molten glass flow flowing out of the outflow pipe and an angle formed with a horizontal plane is ± 10 degrees or less. manufacturing device.

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