JPH06321566A - Production of raw material for forming optical element - Google Patents

Abstract

PURPOSE:To reduce the production cost by feeding optical glass mass to liquid surface of specific molten metal heated to softening temperature of a raw material for forming optical element to soften the optical glass mass and cooling the glass mass to a temperature not higher than annealing point while flowing together with the molten metal. CONSTITUTION:A molten metal 1 of Sn, etc., having a melting point lower than the transition point of a raw material 12 for forming optical element, a boiling point higher than the softening point of the raw material 12 and a specific gravity higher than that of the raw material 12 is heated in a metal melting furnace 2 and fed from the outlet 4 to a molten metal tank 5. The molten metal 1 in the molten metal tank 5 is heated so as to successively become low at points 13, 14 and 15 by heaters 6, 7 and 8 and points 16, 17 and 18 are cooled to prescribed temperature zones by a cooling water pipe 9. Then, an optical glass mass 11 is fed to the molten metal 1 in the molten metal tank 5 and moved along the flow of the molten metal 1 and simultaneously softened to form the surface to mirror face and form the outer figure to circle. When the molten metal 1 reaches right end of the molten metal tank 5, the optical glass mass 11 is cooled to the annealing point and dropped from the right end onto a conveyer 10 and taken out as the raw material 12 for forming optical element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of a material for molding an optical element having a mirror-finished surface and a spherical surface required for obtaining an optical element such as a lens, a prism and a filter by press molding.

[0002]

2. Description of the Related Art In recent years, optical elements such as lenses, prisms and filters have come to be obtained by heating and softening a material for optical element molding which has been subjected to polishing and press-molding it with a pair of upper and lower molds. However, the above method requires a step of polishing an optical element molding material before press molding, which causes a high cost.

Therefore, in order to solve the above problem, for example, Japanese Patent Laid-Open No. 61-232236 proposes the following invention. The above invention is for molding an optical element having a smooth surface and a spherical surface by vertically standing an optical glass block having a predetermined volume by cutting or grinding and dropping it into an S-shaped tube through which heated gas flows from below. It is a method of obtaining materials.

[0004]

However, in the invention described in the above-mentioned JP-A-61-2232236, the optical glass lumps are heated and softened by the heated gas flowing from below, and the spheres are formed by the surface tension. Since a spherical preform is obtained by self-deforming into a shape close to, it takes a long time for heating and cooling, which results in a long cycle time and a high cost.

Therefore, the present invention was developed in view of the above-mentioned drawbacks of the prior art, and a continuous and low-cost production of a biplanar or biconvex optical element molding material having a mirror-finished surface by a simple structure. It is an object of the present invention to provide a method for producing a material for molding an optical element that can be produced by.

[0006]

The present invention has a melting point lower than a transition point of an optical element molding material to be produced, a boiling point higher than a softening point of an optical element molding material, and a specific gravity for optical element molding. Using a molten metal larger than the specific gravity of the material, the molten metal is higher than the transition point of the optical element molding material,
It is heated to a temperature at which the optical element molding material melts. An optical glass block of a material for forming an optical element, which has been weighed in advance, is supplied to the liquid surface of the molten metal in this state. Then, a flow is created in the molten metal, and the lump of optical glass is softened and made to flow together with the molten metal. Next, the optical glass gob is gradually cooled to a temperature below the annealing point while flowing the optical glass gob and the molten metal. After cooling, the optical glass gob is taken out of the molten metal.

[0007]

In the present invention, the optical glass block is supplied to the liquid surface of the molten metal heated to the temperature at which the optical glass block softens. Since the specific gravity of the supplied optical glass lump is smaller than the specific gravity of the molten metal, it floats on the liquid surface of the molten metal. The surface of the optical glass lump facing the liquid surface of the molten metal has a flat surface or a convex shape close thereto, and the upper surface has a flat surface or a convex surface. At this time, the surface of the optical glass lump becomes a mirror surface due to the surface tension.
Next, the lump of optical glass having the above-mentioned shape and the molten metal are introduced into the flow path, where they are gradually cooled to a temperature below the annealing point of the material for forming an optical element. As described above, by making the volume of the optical glass block constant, a mirror-shaped optical element molding material having a constant shape is obtained.

[0008]

Embodiment 1 FIG. 1 is a vertical sectional view of an apparatus used in this embodiment. A heater 3 is provided on the outside of the metal melting furnace 2 so that the contained molten metal 1 can be heated to a temperature at which the optical glass block 11 can be softened. 4 are provided. A molten metal tank 5 is installed below the outlet 4. The molten metal tank 5 is shown in FIG.
The surface of the molten metal 1 is gently inclined from left to right, and is installed so that the molten metal 1 slowly flows from left to right.
Is installed so as to overflow from the right end of the molten metal tank 5.

Three heaters 6, 7, and 8 are provided on the left side of the molten metal tank 5 in the figure, and the heaters 6, 7, and 8 are set so that the temperature becomes lower sequentially from the left side. The temperature of the heater 6 is set to a temperature at which the molten metal 1 can soften the optical glass block 11. Further, a cooling water pipe 9 is provided on the right side of the molten metal tank 5, and is configured so that the molten glass 1 can be cooled to cool the optical glass block 11 to a temperature below the annealing point.

A conveyor 10 is provided near the right end of the molten metal tank 5.
Is installed. The conveyor 10 takes out and conveys the optical element molding material 12 floating on the liquid surface of the molten metal 1 overflowing from the right end of the molten metal tank 5, and is formed in a mesh shape so that the molten metal 1 can flow downward. Has been done.

A method of manufacturing a material for molding an optical element using the apparatus having the above structure will be described below. In this example, tin (Sn) was used as the molten metal 1, and SK11 was used as the glass material of the optical glass block 11. First, the molten metal 1 is heated to 950 ° C. in the metal melting furnace 2 and supplied from the outlet 4 to the molten metal tank 5. Molten metal 1 in molten metal tank 5
Is 950 ° C. and 950 at points 13, 14, and 15 on the heaters 6, 7, and 8 by the heaters 6, 7, and 8, respectively.
It is heated to ℃ and 880 ℃. Also, the cooling water pipe 9
Thus, at points 16, 17, and 18, the molten metal 1 is cooled to 750 ° C., 600 ° C., and 450 ° C., respectively.

Optical glass block 11 is supplied to molten metal 1 in molten metal tank 5. The optical glass block 11 is a cube with each side cut into a cube of 5 mm. The optical glass lump 11 moves rightward along the flow of the molten metal 1 and at the same time softens, the surface becomes a mirror surface due to surface tension, floats on the molten metal 1 due to its own weight and buoyancy, and both surfaces become a convex shape close to a plane, The outer shape is circular.

When the optical glass gob 11 reaches the right end of the molten metal tank 5, it becomes a temperature below the annealing point and solidifies to become an optical element molding material 12. The optical element molding material 12 drops onto the conveyor 10 together with the molten metal 1 overflowing from the right end of the molten metal tank 5, and is taken out to the outside. The optical element molding material 12 has an outer diameter of 9 mm,
The thickness (medium thickness) was 2 mm, the paraxial R of the surface facing the molten metal 1 was 20 mm, and the paraxial R of the upper surface was 12 mm, forming a biconvex shape. Further, the surface roughness is Rmax = 0.032 μm, which can be sufficiently used as a material for molding an optical element.

Molten metal 1 tin (S
In n), since the boiling point is higher than the softening point of the optical element molding material 12 (SK11), the optical element molding material 12 can be sufficiently softened in a liquid state. Also, molten metal 1
Since its melting point is lower than the transition point of the optical element molding material 12, the optical element molding material 1 formed by cooling is
Even when 2 is taken out, it is in a molten state, and separation is easily performed.

According to this embodiment, a satisfactory material for molding an optical element can be continuously manufactured by a simple method. Further, a material for molding a mirror-like optical element can be manufactured by self-weight transfer to the surface of a molten metal and the surface tension of optical glass.
The manufacturing cost of the optical element can be significantly reduced.

[0016]

Embodiment 2 FIGS. 2 to 4 show an apparatus used in this embodiment, FIG. 2 is a plan view, and FIGS. 3 and 4 are partial sectional views. The molten metal 22 is filled in the ring-shaped molten metal tank 21. Molten metal 2 is placed inside the molten metal tank 21.
The propeller 30 is provided so that 2 flows in the arrow direction (counterclockwise direction) in FIG. An arm 31 for supplying the optical glass block 29 is provided near the left side of the molten metal tank 21.
However, an arm 33 for taking out the optical element molding material 36 is installed near the right side.

A heater 23 is provided around the arm 31 of the molten metal tank 21. In addition, the molten metal tank 21
A cooling water pipe 28 is provided on the outer periphery in the vicinity of the arm 33. As a result, the molten metal 22 is heated by the heater 23 to a temperature at which the optical glass gob 29 softens at a point 24 near the position where the optical glass gob 29 is supplied. At a point 27 near the position where the optical element molding material 36 is taken out, the molten metal 22 is cooled by the cooling water pipe 28 to a temperature below the annealing point of the optical element molding material 36.

The optical glass block 29 can be supplied to the molten metal 22 by the rotation of the arm 31 and the claw 32 provided at the tip of the arm 31. In addition, the cooled optical element molding material 36 is taken out from the arm 3
3 rotation and suction jig 3 attached to the tip of arm 33
It is constructed so that it can be taken out by using. A glass stopping jig 35 for stopping the flowing optical element molding material 36 under the suction jig 34 is provided on the liquid surface near the point 27 of the molten metal tank 21.

A method of manufacturing a material for molding an optical element using the apparatus having the above structure will be described below. In this example, tin (Sn) was used as the molten metal 22, and SF11 was used as the glass material of the optical glass block 29. Molten metal 22
Is 90 at each point 24, 25, 26, 27
The temperature is adjusted by the heater 23 and the cooling water pipe 28 so that the temperatures become 0 ° C., 900 ° C., 700 ° C., and 300 ° C.

To this molten metal 22, an optical glass block 29 cut into a cube of 8 mm on each side was supplied by an arm 31. The optical glass gob 29 flows in the direction of the arrow in FIG. 2 along with the flow of the molten metal 22 and is softened at the same time, and the surface becomes a mirror surface due to the surface tension and has the same shape as that in the first embodiment.
The optical element molding material 36 taken out by the arm 33 at the point 27 has an outer diameter of 15 mm, a thickness (medium thickness) of 4.3 mm, an upper surface paraxial R of 18 mm, and a lower surface paraxial R of 25 mm. Became biconvex. The surface roughness is R
When max = 0.033 μm, the same specularity as in Example 1 was obtained.

According to this embodiment, the molten metal is circulated in the ring-shaped molten metal tank as compared with the first embodiment.
It can be manufactured with a simple structure.

Although the cut optical glass block was supplied to the molten metal in each of the above-mentioned embodiments, the present invention is not limited to this, and the optical glass supplied to the molten metal is melted in a crucible, Similar results can be obtained with the dropped optical glass.

[0023]

As described above, according to the method for producing an optical element molding material of the present invention, the optical element molding material having both surfaces which are biconvex close to a plane and whose surface is a mirror surface is continuously formed. It can be manufactured. Further, since a desired shape and specularity can be obtained along the flow of the molten metal, the cycle time is short, and the optical element molding material can be manufactured at a very low cost.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a first embodiment.

FIG. 2 is a plan view showing a second embodiment.

FIG. 3 is a partial cross-sectional view showing a second embodiment.

FIG. 4 is a partial cross-sectional view showing a second embodiment.

[Explanation of symbols]

 1 Molten Metal 2 Metal Melting Furnace 3, 6, 7, 8 Heater 4 Outlet 5 Molten Metal Tank 9 Cooling Water Pipe 10 Conveyor 11 Optical Glass Lump 12 Optical Element Molding Material

Claims (1)

[Claims] 1. A molten metal having a melting point lower than a transition point of an optical element molding material to be produced, a boiling point higher than a softening point of the optical element molding material, and a specific gravity higher than a specific gravity of the optical element molding material. Using a step of supplying an optical glass block of the optical element molding material to the liquid surface of the molten metal heated to a temperature at which the optical element molding material softens, together with the molten metal while softening the optical glass block. Optical element molding comprising a step of flowing, a step of cooling the optical glass gob below the annealing point while flowing the optical glass gob and molten metal, and a step of taking out the cooled optical glass gob Method of manufacturing materials.