JP2001287919A - Spherical glass material nd method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spherical glass material having high volume accuracy and prescribed optical performance and suitable for the press molding of an optical part at a low cost. SOLUTION: The spherical glass material is composed of an optical glass and has the deviation of diameter falling within the range of 1/50 to 1/5 relative to the diameter of true sphere calculated from the prescribed volume, the volume deviation of within ±1% from the prescribed volume. The number of particles having a particle diameter of >=10 μm and welded to 1 mm2 of the surface is <=1. The spherical glass material is produced by supplying the molten glass composed of the optical glass in the form of a glass droplet 3 having a volume deviation of ±1% or less relative to the prescribed volume in a clean booth 10 maintained to the cleanliness of 7 or higher and forming the glass droplet 3 in the form of glass sphere 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a spherical glass material for press-molding an optical glass part.

[0002]

2. Description of the Related Art Generally, a spherical glass material for press-molding an optical glass part, particularly an aspherical lens, has a high surface cleanness and an accurate focal length so as not to stain the light-transmitting portion of the aspherical lens. In addition, high volume accuracy is required to obtain a transmitted wavefront aberration within a desired level.

Heretofore, there have been proposed spherical glass materials molded by receiving a gob of molten glass in a mold and rounded in a mold using the surface tension of molten glass.

[0004]

However, since the spherical glass material is molded in an ordinary atmosphere in which a large amount of suspended particles such as dust are present, many particles are deposited on the surface when observed under magnification. However, optical glass parts such as aspheric lenses molded from such a spherical glass material have a problem that desired optical characteristics cannot be obtained.

The present invention has been made in view of the above problems, and has as its object to provide a spherical glass material having high volume accuracy and predetermined optical performance and suitable for press molding optical components at low cost.

[0006]

The spherical glass material according to the present invention is made of optical glass, and the diameter difference is 1/50 to 1/5 of the diameter of a true sphere calculated from a predetermined volume. A volume of within ± 1% with respect to a predetermined volume, and no more than one particle having a particle size of 10 μm or more deposited per 1 mm ^{2 of} the surface, It is preferable that the Rmax value is 10 nm or less.

In order to maintain the optical characteristics of the spherical glass material of the present invention as a lens after being molded, it is important that no more than 1 particle of 10 μm or more adheres per 1 mm ^{2 of} surface. . Also, in order to maintain the cleanliness of the surface of the spherical glass material and maintain the optical surface after press molding, JI
It is preferable that the maximum height of the surface roughness defined in SB0601, that is, the value of Rmax is 10 nm or less.

Usually, the convex lens is thickest at the center and symmetrical with respect to the optical axis. Therefore, a mold for molding such a lens has a shape with the central portion most depressed. When press molding a spherical glass material into a convex lens, if the glass material is located in the center of the mold, it will be evenly crushed in the mold during press molding, forming a lens with high dimensional accuracy without distortion can do. When the spherical glass material having a high sphericity of the present invention is used, the mold surface rolls itself and is self-centered in the depression in the center of the mold, so that it is not necessary to supply the glass material to the center of the mold. .

When the spherical glass material of the present invention is supplied to a mold for press molding, if the diameter difference of the spherical glass material exceeds 1/5 of the diameter of a true sphere calculated from a predetermined volume, the spherical glass material cannot be rolled smoothly and the metal cannot be rolled. If it is not necessarily self-centered in the center of the mold, and if it is placed a little off the center of the mold, the spherical glass material will not evenly collapse in the mold during press molding, causing optical distortion of the molded lens Is expected to occur, and desired optical characteristics cannot be obtained. In addition, the diameter difference of the spherical glass material from the molten glass droplet is calculated as 1/1 of the diameter calculated from the predetermined volume.
It is difficult to mold to less than 50 in a short time. As the diameter difference of the spherical glass material of the present invention, 1/50 to 1/5 of the diameter of a true sphere calculated from a predetermined volume is suitable.

As for the accuracy of the volume of the spherical glass material, if it exceeds + 1% with respect to the predetermined volume of an optical glass component, for example, a lens to be press-molded, that is, the volume of a mold, the lens becomes too thick or extra glass. However, an overpacking phenomenon that sticks out of the mold occurs. On the other hand, if it deviates from -1%, the volume becomes too smaller than the mold, the lens becomes too thin, and a so-called underpacking phenomenon in which the shape of the mold cannot be accurately transferred occurs. In either case, optical performance such as a predetermined focal length and numerical aperture cannot be obtained. The volume accuracy of spherical glass material is ± 1% of the specified volume
It is important that it is within the range in order to maintain the molding accuracy of the lens and the like. The required volume accuracy varies depending on the aspherical lens to be press-molded. For a severe product, it is required to be within ± 0.3%.

Further, the softening point for determining the molding temperature of the spherical glass material is preferably 650 ° C. or less.

The method for producing a spherical glass material according to the present invention is described in JIS.
Among the cleanliness classes defined by B 9920, the number of suspended particles having a particle size of 0.5 μm or more is 1 m ^3.
In an environment in which the cleanliness is higher than Class 7, which is 350,000 or less per unit, molten glass made of optical glass is supplied as droplets having a volume within ± 1% of a predetermined volume, and the liquid is supplied. The method is characterized in that the droplet is made spherical to form a glass ball.

[0013]

The spherical glass material of the present invention is made of optical glass, and the difference in diameter is 1 to the diameter of a true sphere calculated from a predetermined volume.
/ 50 to 1/5, having a volume within ± 1% of a predetermined volume, and one or less particles having a particle diameter of 10 μm or more deposited per 1 mm ^{2 of} the surface. Therefore, it is possible to satisfy the cleanliness accuracy of the surface and predetermined optical characteristics required for press molding of the optical glass component, and to produce the optical glass component at low cost.

The spherical glass material of the present invention has a surface roughness R.
Since the max value is 10 nm or less, the surface quality of the optical component press-formed using the present spherical glass material is high, and no optical problem occurs.

Further, the spherical glass material of the present invention has a softening point of 6
Since the temperature is 50 ° C. or lower, it is possible to reduce damage to a mold for molding an aspheric lens due to high temperature.

According to the method for producing a spherical glass material of the present invention, the number of suspended particles having a particle size of 0.5 μm or more is 1 m ^3.
In an environment in which the cleanliness is higher than Class 7, which is 350,000 or less per unit, molten glass made of optical glass is supplied as droplets having a volume within ± 1% of a predetermined volume, and the liquid is supplied. Since the droplets are spheroidized to form glass spheres, the spherical glass material of the present invention can be manufactured with high efficiency.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The spherical glass material of the present invention comprises, for example, an optical glass having an alkali metal oxide and boric acid of 15% by mass, a softening point of 600 ° C. and a specific gravity of 3.0, and a diameter of 5 mm. Is spherical. The predetermined volume of the spherical glass material is 65.
45 mm ^3, which is 64.8 within ± 1%.
It has a volume of 0～66.11Mm ^3, following one is 10μm or more particles that are welded to 1 mm ² per surface, i.e. 10μm on the surface of the spherical glass material diameter 5mm having a surface area of 78.5 mm ² Three to ten of the above particles were observed.

The diameter of the spherical glass material is 200 μm.
m, and the diameter obtained by converting a predetermined volume of 65.45 mm ³ into a true sphere is 5 mm.
/ 25. Here, since the volume of a spherical glass material having a diameter difference of 200 μm cannot be easily measured from the dimensions,
Often measured by mass. Also in this case, it is substituted with a mass accuracy within ± 1% which is the same as the predetermined volume. Since the predetermined volume of the spherical glass material of the present invention is 65.45 mm ³ , the predetermined mass is 196.35 mg, which is 194.39 to 198.3.
It has a mass of 1 mg.

Incidentally, the diameter difference is determined according to JIS B 1501.
As described in the above, the diameters of four equatorial planes of a spherical glass material forming 45 degrees with each other were measured a plurality of times, and the difference between the maximum value and the minimum value was adopted.

Next, the method for producing the spherical glass material of the present invention will be described.

In the process of manufacturing the spherical glass material of the present invention, a glass ball forming apparatus shown in FIG. 1 is used. Within ± 1% of the predetermined volume 65.45 mm ₃ from the tip nozzle 2, preferably ±
A glass droplet 3 having a volume within 0.3% is dropped.
The dropped glass droplets 3 are collected by a funnel-shaped tray 5 and rolled over a sloped U-shaped groove 6 while cutting a spiral groove on the surface of a pair of rollers 7, 7. It is led to 8. At this time, the glass droplet 3 is
While rolling, is adjusted to a viscosity suitable for spheroidization. The rollers 7, 7 are provided side by side with a slant in a horizontal direction, and the glass droplets 3 guided to the glass introduction unit 8 by the rotation of the rollers 7, 7 spirally rotate with the rotation of the rollers 7, 7. Rolling in the shape of a groove, gradually becoming spherical,
Eventually it solidifies and is molded into a glass sphere 12 with a diameter of 5 mm,
It is discharged from the glass discharge section 9.

The glass spheres 12 thus molded have an Rmax value of surface roughness of about 5 nm, and about 0.1 particles of 10 μm or more deposited per 1 mm ^{2 of} the surface. The mass variation in the continuous production of the individual pieces falls within the predetermined mass of 196.35 ± 0.5 mg, and the predetermined mass ±
It has a mass accuracy within 0.3%. This mass accuracy satisfies the strictest mass accuracy currently required as a spherical glass material. For example, a product requiring an accuracy within a predetermined mass ± 1% can be more easily manufactured.

On the other hand, when a spherical glass material is produced in a normal atmosphere, more than one particle having a particle size of 10 μm or more is deposited per 1 mm ^{2 of the} surface, and
In a glass sphere of mm, 79 or more particles are welded to the surface. Such spherical glass materials cannot be used for press molding of lenses unless the surface is removed by polishing or the like.

In another embodiment, JIS B
Of the cleanliness classes specified by 9920,
The spherical glass material molded in the clean booth 10 maintaining a higher cleanness than class 6 in which the number of suspended particles having a particle size of 0.5 μm or more is 35,000 or less per m ³ is:
Less than 3 particles having a diameter of 5 mm and having a particle diameter of 10 μm or more were deposited on the surface, and 0.05 or less particles of 10 μm or more deposited per 1 mm ^{2 of} the surface.

The spherical glass material of the present invention is one-third of the conventional one.
And the time required from melting of the glass material to completion of the production of the spherical glass material is 1
With the reduction of time and man-hours, the total cost of processing can be reduced to 1/3 or less of the conventional cost.

The Rmax value, which is the maximum height of the surface roughness defined in JIS B 0601, is measured by a stylus type surface roughness measuring device manufactured by Rank Taylor Hobson, trade name “Taristep” And a vertical magnification of 1,000,000
The measurement was performed under the condition of 0 times and a filter for measuring roughness 0.33 Hz.

[0027]

According to the present invention, a spherical glass material having high volume accuracy, high surface cleanliness accuracy and predetermined optical characteristics and suitable for press molding of optical glass parts such as aspherical lenses can be obtained. This is a practically excellent effect that can be provided at a cost.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a glass ball forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Platinum pot 2 Nozzle 3 Glass droplet 4 Heater 5 Funnel-shaped saucer 6 U-shaped groove 7 Roller with spiral groove 8 Glass introduction part 9 Glass discharge part 10 Clean booth

Claims (3)

[Claims] 1. An optical glass, wherein the diameter difference is 1/50 to 1/5 of the diameter of a true sphere calculated from a predetermined volume.
Having a volume within ± 1% with respect to a predetermined volume, and one or less particles having a particle diameter of 10 μm or more deposited per 1 mm ^{2 of} the surface are spherical. Glass material. 2. The spherical glass material according to claim 1, wherein the Rmax value of the surface roughness is 10 nm or less. ^3. Class 7 wherein the number of suspended particles having a particle size of 0.5 μm or more is 350,000 or less per m ^3.
In an environment in which higher cleanliness is maintained, molten glass made of optical glass is supplied in the form of droplets having a volume within ± 1% of a predetermined volume, and the droplets are spheroidized to form glass spheres. A method for producing a spherical glass material, characterized in that: