JPS6228090B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a glass press-molding method, and in particular, the surface of a ground product is made into a mirror surface close to the final desired lens shape using a carbon dioxide gas laser beam, and this is finally transformed into a desired optical mirror surface. The present invention relates to a method of press working into a lens having a surface precision of . [Prior art and its problems] Conventionally, the manufacturing method for glass lenses involves melting or softening glass, putting it into a mold, press-molding it into the approximate shape of the lens, and then grinding and
It has been manufactured by polishing, but it requires time and labor and is expensive. However, recent patent publications use a special mold material, process it into a mold with the desired lens shape, finish the mold surface to an optical mirror surface, and press-form the glass in a non-oxidizing atmosphere to grind it. - It is disclosed that a lens having an optical mirror surface and surface precision that does not require polishing can be obtained. For example, in JP-A-47-11277, glassy carbon is used as the mold material, the glass is placed on the mold, the mold is heated to soften the glass, and pressing is started. However, a method is described in which a lens is obtained by continuing pressing until the glass becomes below the glass transition point. Manufacturing lenses using this method eliminates the need for grinding and polishing processes, which is expected to result in significant cost reductions, but the press molding cycle time is significantly longer and the glass is in constant contact with the mold. Therefore, the chemical reaction between the glass and the mold material tends to cause the surface of the mold to become rough, which poses the problem of adversely affecting the life of the mold (mold life). [Objective of the Invention] The present invention has been made in view of these problems, and aims to omit the polishing process, simplify the grinding process, save time and labor, and improve the life of the mold. The purpose of the present invention is to provide a high-precision glass press-forming method that can shorten the press-forming cycle time. [Means for Solving the Problems] The present invention, prior to press molding, places a ground product close to the final lens shape on a holder, and irradiates it with carbon dioxide laser light to grind the glass shape without substantially deforming it. After making the surface a mirror surface, this is heated and softened as a preform.
It is characterized by press molding using a mold to finally form the desired lens. A ground product close to the final lens shape is adjusted by spherical grinding and does not require fine grinding with diamond pellets. This ground product is placed in a holder and preheated to a temperature above the glass transition point. Next, the surface of this ground product is heated and softened by irradiating a defocused carbon dioxide gas laser beam to obtain a mirror surface. In this case, a slit-shaped carbon dioxide gas laser beam may be scanned to heat and soften it, or a defocused carbon dioxide gas laser beam itself may be scanned. The wavelength of carbon dioxide laser light is as long as 10.6 μm, and it is absorbed by the extremely shallow surface layer of several μm to over 10 μm on the glass surface, causing heat generation and softening, smoothing out the unevenness of the ground surface and forming a mirror surface. Because the amount of glass deformation is small and a surface with very good surface precision can be obtained,
A desired optical lens can be obtained by subjecting the preform to a very small amount of deformation during press molding using a mold. The preform press molding method using a mold is as follows:
The preform obtained by the above method is preheated to a predetermined temperature and pressed using a similarly preheated mold capable of obtaining the final lens shape. Since the preform can be press-molded in a high viscosity range of 10 ⁸ to 10 ¹¹ poise, it can be press-molded in a short time while maintaining the preform and mold temperature at a relatively low temperature corresponding to its viscosity. Therefore, roughening of the mold surface is less likely to occur, and press molding time can be shortened. When irradiating a grinding surface with a defocused carbon dioxide laser beam, it is desirable to heat a shallow portion of the surface to a high temperature in as short a time as possible in order to obtain a surface with good surface precision. However, if the surface temperature is too high, a foaming phenomenon will occur due to the volatilization of the glass, so the temperature cannot be raised too high. Furthermore, when the ground surface is irradiated with defocused carbon dioxide laser light to make it a mirror surface, microscopic bubbles are generated due to microscopic cracks generated during grinding. This type of bubble is generated when the upper part of the crack softens first and blocks the crack, trapping air inside the crack. The width of such a crack is approximately 1~
2 μm, and the depth is approximately several μm to 20 μm. Therefore, the size of the generated bubbles is extremely small, with a diameter of several micrometers, and is hardly observed with the naked eye, but can be observed with an optical microscope, and if there are a large number of bubbles, they can be observed with the naked eye. In order to solve these bubbling phenomena, it is desirable to reduce the intensity of the defocused carbon dioxide gas laser light to 2 to 30 W/cm ² and irradiate the glass surface with it. If the glass surface is irradiated with carbon dioxide laser light at an intensity lower than 2w/cm ² , the glass will not be heated or softened much due to the heat balance between the glass and the surrounding atmosphere, and a mirror surface will not be obtained. 30w/
When a glass surface is irradiated with carbon dioxide laser light at an intensity higher than cm ² , the above-mentioned fine bubbles can be clearly seen with the naked eye. Furthermore, when similarly irradiated with an intensity higher than 100w/cm ² , volatilization begins instantaneously and a foaming phenomenon occurs. Therefore, it is desirable to irradiate the glass surface with a defocused carbon dioxide laser beam at an intensity of 2 to 30 w/cm ² . At this time, the irradiation time must be at least 30 seconds or more. In order to prevent the generation of fine bubbles, it is also desirable to irradiate the ground surface with defocused carbon dioxide laser light after removing fine cracks by etching the ground surface with hydrofluoric acid or a mixed acid such as hydrofluoric acid and sulfuric acid. This pretreatment is
Applicable to sanded surfaces with loose abrasive grains. Usually, free abrasive grains remain on the sanded surface even after ultrasonic cleaning, and when the surface is softened by carbon dioxide laser light, the free abrasive grains become stains on the glass surface. However, when treated with hydrofluoric acid, fine cracks and abrasive grains are removed from the surface, so no stains are generated even when irradiated with carbon dioxide laser light. Furthermore, in order to prevent the generation of fine bubbles, it is also desirable to place the ground product in a vacuum chamber and irradiate the ground surface with carbon dioxide laser light in a vacuum. The upper part of the crack softens first, and even when the crack closes, there is no air inside the crack, so the glass inside flows naturally after that, closing the crack and softening, so no bubbles are generated. Under these conditions, the intensity of the defocused carbon dioxide laser light was
It may be irradiated at 100w/cm ² . Since the carbon dioxide laser light is defocused, it may be single mode or multimode. The oscillation form of the laser beam may be continuous or pulsed. The holder on which the ground product is placed may be a flat tray made of SUS stainless steel, a curved tray, or a donut-shaped ring. When a donut-shaped ring is used as a holder, carbon dioxide laser light may be irradiated from both sides of the grinding surface. In addition, the preform can be adjusted by irradiating the grinding surface with a defocused carbon dioxide laser beam, and the preform can be press-formed continuously, or the preform adjustment and press-forming can be performed separately and the preform can be press-formed discontinuously. good. The surface accuracy of the preform before press forming is more than 10 Newtons, but the surface accuracy after press forming is 1 Newtons.
~2 pressed lenses are obtained. [Example] Next, the content of the present invention will be explained in more detail based on an example. Fig. 1 shows a state in which a ground product 1 close to the final lens shape is placed on a ring-shaped holder 2, Fig. 2 shows a state in which the ground product on the holder is irradiated with a defocused carbon dioxide laser beam, and Fig. 3 shows a state in which the ground product 1, which has a final lens shape, is placed on a ring-shaped holder 2. FIG. 4 is a sectional view showing a state in which a preform is being pressed and a state in which a ground product is irradiated with a laser beam in a vacuum. First, a ground product 1 close to the final lens shape is placed on a ring-shaped holder 2 with a step. At this time, the holder 2 is maintained at a temperature higher than the glass transition temperature. The ground product 1 is placed on the holder 2 and moved to a carbon dioxide laser beam irradiation position in an electric furnace kept above the glass transition temperature, where it is irradiated and heated by the laser beam 4 emitted from the laser beam output end 3, and is The surface softens and becomes a mirror surface without deformation. The preform thus obtained is transferred into a cylindrical sleeve that guides the upper mold 5 and the lower mold 6, and is press-molded by the upper mold 5 and the lower mold 6 at a predetermined temperature. In addition, as shown in FIG. 4, a grinding product 8 is placed in a vacuum chamber 9, and a laser beam 4 emitted from a laser beam output end 3 is passed through a window 10 made of a material that transmits carbon dioxide laser beam.
This shows the state in which the material is heated and softened by irradiation. The ground product 8 is placed on a plate-shaped holder 11, and both are placed on an XY table 12 to determine the irradiation position. The vacuum chamber 9 is evacuated by a vacuum pump 14 through a vacuum valve 13 to obtain a stable vacuum state of 10 ^-6 torr. The following table lists the carbon dioxide laser light irradiation conditions and pretreatment conditions in each example.

【table】

[Table] As is clear from the table, the present invention can be applied regardless of the type and shape of glass. There are optimum conditions for irradiation of carbon dioxide laser light depending on the type of glass. With a glass material having a low softening temperature (Sp), a mirror surface can be obtained in a relatively short time with a strength of 2 to 10 w/cm ² . For glass materials with a high softening temperature (Sp)
A mirror surface can be obtained with relatively long irradiation at an intensity of 15-30w/ ^cm2 . Furthermore, the irradiation time after the hydrofluoric acid treatment and the irradiation in a vacuum chamber can be shortened. [Effects of the Invention] According to the present invention, the polishing process is omitted, the grinding process is simplified, time and labor are saved, and the mold life of the mold is improved to shorten the cycle time of press molding. be able to.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a ground product with a final lens shape placed on a ring-shaped holder, Figure 2 is a cross-sectional view showing the laser irradiation process, Figure 3 is a cross-sectional view showing the press forming process, FIG. 4 is a cross-sectional view showing the process of turning a ground product into a mirror-finished product in a vacuum chamber. 1...Grinded product, 2...Ring-shaped holder, 3...
...Carbon dioxide laser light output end, 4...Die-focused laser light, 5...Upper mold, 6...Lower mold, 7
... Cylindrical sleeve, 8 ... Ground product, 9 ... Vacuum chamber, 10 ... Carbon dioxide laser light transmitting material window, 11 ... Plate-shaped holder, 12 ... X-
Y table, 13... vacuum valve, 14... vacuum pump.

Claims (1)

[Claims] 1. Before press molding, a ground product close to the final lens shape was subjected to laser polishing using defocused carbon dioxide laser light to make the ground surface a mirror surface, and then this was heated and softened as a preform. A method for forming a press lens, characterized in that the lens is then press-molded. 2. The press lens according to claim 1, wherein the day-focused carbon dioxide gas laser beam is irradiated with an intensity of 2 to 30 w/cm ² for 30 seconds or more on a ground product close to the final lens shape to make the ground surface a mirror surface. molding method. 3 A ground product close to the final lens shape is polished with hydrofluoric acid and irradiated with defocused carbon dioxide laser light to make the ground surface mirror-like.Claim 1
2. Method for forming press lenses as described in Section 1. 4. The press lens forming method according to claim 1, wherein the ground product having a final lens shape is irradiated with defocused carbon dioxide laser light in a vacuum to make the ground surface a mirror surface.