JPS6081032A - Method for molding glass lens of high accuracy - Google Patents

Abstract

PURPOSE:To mold efficiently a glass lens of high accuracy in a short time by forming a glass blank whose weight is close to that of the end product by high- speed rough polishing, heating the blank to a temp. above the softening point, and press-molding it with a molding tool heated to a temp. above the transition point. CONSTITUTION:Glass is cut, weighed, and pressed to form a lump of glass, and this lump is ground with a curve generator and subjected to high-speed rough polishing with a polishing dish to form a glass blank 1C whose weight is close to that of a finished glass lens. The blank 1C is heated to a temp. above the softening point (10<11>-10<12> poises), and it is set in a glass molding tool heated to a temp. above the transition point (10<13>-10<14> poises) with a heating element 8. The molding tool consists of a drag 15 and a cope 16. The heated blank 1C is then press-molded by pushing up a core 12. The drag 15, the cope 16 and the core 12 each have a molding layer 10 made of a material sticking hardly to glass at high temp. such as glassy carbon, silicon carbide, silicon nitride or sialon. After the molding, the molding tool is slowly cooled to a temp. below the transition point, and the pressure is reduced to obtain a lens of high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for molding a high-precision glass lens that does not require precision polishing.

Conventionally, the first step in making a high-precision glass lens is to cut optical glass to an appropriate size and weigh it so that the weight falls within a desired range. In the second step, the glass material is heated and pressed with a mold of an appropriate shape. In the third step, the above-mentioned glass material is finished into the shape of a dog body using a curve deenerator (a grinding ring embedded with diamond particles). In the fourth step, a plurality of glass materials ground in the third step are placed on a cast iron plate and ground with abrasive sand, and the sand is gradually made finer to finish the grinding. Fifth
The process involves pitch-polishing the glass material that has been ground to give it a gloss finish, using red rosewood or cerium oxide.
Or perform rasha polishing.

In the case of lenses used in precision optical systems such as cameras, it is necessary to maintain a high level of surface quality and high level of surface precision.sb Each of the above steps requires a great deal of time, effort, and skill. In the case of aspherical glass lenses, it is necessary to polish them one by one, which requires a great deal of time, effort, and skill.

The above-mentioned surface quality relates to the finish of the lens, and indicates the degree of scratches, punctures, dents, orange peel, and other defects, and it is necessary to eliminate almost all of them in high-precision camera lenses. Surface accuracy relates to the dimensional characteristics of a surface, and relates to the value and uniformity of the radius of the curved surface of the surface, and is generally expressed in the number and shape of Newton's rings. For high-precision camera lenses, Newton's rings are considered to be 6 or less.

One way to improve the above drawbacks is to press molten glass directly, but it may leave shear marks (marks from cutting the molten glass) or the difference in thermal history between the surface and the inside of the pressed glass. It is difficult to make high-precision glass lenses without precision polishing, as wrinkles and unevenness may form on the surface. Plastic may also be considered as a substitute for glass, but currently available plastic is relatively soft and easily damaged. Furthermore, it is currently unsuitable for high-precision lenses because the LW refractive index, which has a very high coefficient of thermal expansion, tends to change. In addition, a method of using glassy carbon as a substitute for metal as a mold makes it easier to release the glass from the mold, and also eliminates the defects of surface granularity that occur in the case of metal (Japanese Patent Publication No. 1973- No. 38126, U.S. Patent No. 3.9
00.328), but glassy carbon is easily oxidized, structurally weak, scratches easily on the surface, has a low elastic modulus, easily cracks, has low impact strength, and has poor thermal conductivity. It has many drawbacks such as small size, making it unsuitable for mass production. Method of using silicon carbide or silicon nitride as a mold (U.S. Pat. No. 4,139,677)
US Pat. No. 4,168,961 discloses a method using a mixture of silicon carbide and carbon as a mold. In this case, the drawbacks of the glassy carbon material have been improved, such as high oxidation resistance, high crack resistance, high impact strength at high temperatures, physical cirrhosis, thermal conductivity and other properties. It shows satisfactory characteristics in these respects. Therefore, when molding is performed using the above-mentioned mold, a high-precision glass lens surface having high surface quality and high surface precision can be produced relatively easily.

However, in order for a high-precision glass lens to exhibit its unique characteristics, it is necessary to keep its thickness to a design value. In the case of lenses used in precision optical systems such as cameras, the tolerance range is ±0.1 degrees or less. The tolerance range of ±0.1 m is converted into weight as follows.

3 to optical glass (nd: 1.51823, Vd: 5
9.0, specific gravity 2.55 > When making a convex lens with a diameter of 10 mm, thickness of 3 mm, R1 = 21 mm, R, = 21+++ m, the weight is 0.48 rr, and the allowable range of thickness ±
The weight conversion value of 0.1 m is ±0.02 fr. When making a glass material for the above convex lens and weighing (1)
Weighing with a mass production balance, (2) Weighing with a precision balance and adjusting the weight with a rough sander, (3) Weighing with a precision balance and adjusting the weight with a hammer, (4) Grinding with a ball mill. (5) Press the molten glass directly to adjust the weight. (6) Heat one end of a glass rod of an appropriate diameter to make it into a sphere, and then directly press mold it. (7) When directly press-molding molten glass, there are methods such as pressing the shear marks at both ends outside the mold (US Patent No. 3.306.723).
The weighing accuracy of the mass-produced top balance (1) is ±0.1rr, which is insufficient. When adjusting the weight by roughening (2), part of the surface becomes a roughened surface and does not become a mirror surface after sanding.

(3) When adjusting the weight with a hammer, cracks that are difficult to detect with the naked eye tend to occur, and small bubbles are generated after press molding. (4) When using a tail mill, the surface cannot be mirror-finished. (5) When molten glass is glassed directly, shermer residue remains. (6) Cutting marks remain on the tip of the glass rod, and since the softened glass is sandwiched between the periphery of the mold, the thickness varies depending on the softening state of the glass, and cracks are likely to occur from the periphery. (7)
In this case as well, since the softened glass is sandwiched between the periphery of the mold, the thickness varies considerably, and cracks are likely to occur from the periphery. The present invention has been made to eliminate the above-mentioned drawbacks, and its objectives are firstly high-speed roughing;
To provide a method for producing a glass material having a desired weight range close to the final glass lens by polishing, and directly pressing this material to efficiently produce a high-precision glass lens in a short time.

That is, in the first step of the present invention, a glass lump is roughly polished to produce a glass material having a desired weight range close to that of the final glass lens, and in the second step, the glass material is polished to a softening point (x
As the heating intimidation mini 3rd step, the heated glass material is heated to a temperature above 1° 1 s to 1 s to a temperature of 1 s to 1 s
Made from materials that do not easily adhere to glass at high temperatures, such as glassy carbon, silicon carbide, silicon nitride, and sialon heated to a temperature of 4 poise or higher, the lens is charged into a mold for FC glass lenses, pressurized, and molded. The fourth step is to slowly cool the mold under pressure to a temperature below the transition point (10111~m4 poise), and then remove the pressure from the mold to make a glass lens. The present invention relates to a method for molding a high-precision glass lens.

The present invention will be described in detail with reference to the accompanying drawings.

In the first step, the glass is cut, weighed, and pressed in a conventional manner to produce a pressed product (Fig. 1).

Next, the pressed product 1a is pasted on a cast iron plate 2 (Fig. 2) and ground and formed by a curve cinerator 4. After grinding and forming, high-speed rough polishing is carried out using a polishing plate 5 (Fig. 3). glass material (Figure 4 1c) with a desired weight range close to the final glass lens.
)make.

In the case of high-speed roughing and polishing, the working time is very short compared to general precision roughing and the surface quality is also good, but the surface accuracy is poor and it cannot be used as it is as a high-precision glass lens.

In the second step, the glass material 1c is placed on the heat-resistant plate 11 (FIG. 4) via the mold release layer 18 (FIG. 4) and heated to a temperature 970 to 80 DEG C. higher than the softening point. 5FS3(
nd=1.78470, Vd=26.1, transition point 438°C, softening point 475°C), 550°C is sufficient. As the mold release layer, glassy carbon, silicon carbide, silicon nitride, sialon, boron nitride, or the like is used.

Furthermore, although the release layer is used in the form of a layer in this embodiment, it may be in the form of a block. It is desirable that the heating device for the glass material 1c be in a non-oxidizing atmosphere. The third step is the fifth step.
As shown in the figure, the heated glass material 1c is heated by the heating element 8 to a temperature 2o~30°C higher than the υ transition point. 14, 14&, and the guide holes 13, 13a, and are brought into close contact with the lower molding mold 15, and then the middle mold 12 is pushed up to perform pressure molding. The applied pressure is approximately 9 KlF/c11! However, the pressure varies considerably depending on the time during which the pressure is applied, the temperature of the glass material 1c, etc.

The heating element 8 is preferably a sheathed heater or the like for dust prevention. In addition, the mold has a groove 18 on the outer periphery of the mold, and a sheathed heater is passed through the mold in order to increase the heat transfer area and improve thermal efficiency. The temperature of the mold is controlled by a thermocouple 9. Further, the mold is provided with a guide pin 14.14m and a guide hole 13.13a in order to accurately fit the upper and lower parts. In addition, guide bottle 14.14m1 guide hole 13
, 13& are desirably made of aluminum oxide laminate or the like to avoid problems caused by thermal expansion. on the mold.

At least the part of the inner surface of the lower mold that comes into contact with the glass material 1C must be made of glassy carbon, silicon carbide, silicon nitride, or sialon, which is difficult to adhere to the glass at high temperatures and maintains high surface quality and surface precision. A material that can be used as a nuclide or as a block is used. Boron nitride is good as a mold release agent, but is not preferred because it is difficult to maintain high surface quality and surface precision. In order to prevent oxidation of the molded layer 10, the vicinity of the molded layer is slowly cooled to a temperature below the transition point in a non-oxidizing atmosphere.

In the case of 5FS3 mentioned above, it is slowly cooled to about 420°C. Next, the pressure is removed, and if necessary, it is briefly cooled down and taken out. In the above embodiments, the glass material 1c is described as being in the shape of a biconvex lens, but it may be in the shape of a disk without rounded surfaces on both sides, or it may be in the shape of a sphere.

In the above embodiments, the spherical lens pair is described; however, if the pair is an aspherical lens, the effects of the present invention will be even greater. That is, a spherical or flat glass material with a desired weight range close to the aspherical surface of the final 7f lath lens is made by high-speed rough polishing, and then a high-temperature glass material made of a material that is difficult to stick to the glass is prepared by high-speed rough polishing. By directly pressing with an aspherical mold with high surface quality and grain orientation accuracy, aspherical lenses can be mass-produced in a very short time and efficiently.

As described above, the present invention uses high-speed rough polishing to create a glass material with a desired weight range close to that of the final glass lens.
This method is characterized by directly pressing this into a mold with high surface quality and high surface precision made of a material that does not easily adhere to glass at high temperatures, making it possible to produce high precision glass lenses much more easily than with conventional methods. It can be made efficiently in a short time.

[Brief explanation of drawings]

Figure 1 shows a small glass block before rough polishing. Figure 2 shows how glass particles are heated by curved generake.
Schematic diagram of the process of cutting and forming Figure V00c is a schematic diagram of the process of roughening the glass/J% lump on a polishing plate. FIG. 4 is a schematic diagram of a step in which a roughly polished glass material of a desired weight range is placed on an AII type layered silicon heat-resistant press and heated. The heating device is omitted. fAE Figure 5 is a schematic diagram of the process of charging the glass material into the lower die of the mold. FIG. 6 is a schematic diagram of the process of pressure molding the final product using a mold. 1...Glass pressed product before rough polishing, 'In, 1b
...Glass pressed product during rough polishing, 1c...Glass material after rough polishing, 1d...Final high-precision glass lens, 2.2a...
Cast iron plate, 3.3a... Pitch, 4... Curve generator, 5... Polishing plate, 6... Lasha or pitch, 8... Heating element, 9... Thermocouple, 10...・Molding layer, 12...Medium size, 13.13m...Guide hole, 14
．． 14m...Guide bottle, 15...One mold of the mold, 16...Upper mold of the mold, 17...Heat-resistant press, 18...
・Sister, 2, 1 man, 2 children, 3 m, 4 men, 1, 5th country, 6th

Claims (1)

[Claims] 1. In the first step, a glass lump is roughly ground and polished to produce a glass material with a desired weight range close to that of the final glass lens; in the second step, the glass material is heated to a softening point ( roll'''''1 poise). After the above preparation, heating -f=is, and as the third step, the heated glass material is heated to a temperature above the transition point (101"44 poise) to produce high-temperature materials such as glassy carbon, charcoal-fired silicon, silicon nitride, and sialon. 1. Pressure molding.The fourth step is to pressurize the mold to the transition point (101" 4 poise). A method for molding a high-precision glass lens, which is characterized by slowly cooling the glass lens to a temperature of less than 100 ml, and then removing pressure from the mold to produce a glass lens.