JPH0361614B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing optical glass elements, and in particular to press molding of optical glass elements that can be used to directly press mold high-precision optical glass elements that do not require a polishing process after press molding. It is related to usage patterns. Conventional Structures and Their Problems In recent years, optical glass lenses have been trending toward aspheric surfaces that can simultaneously simplify the lens structure of optical equipment and reduce the weight of the lens portion. When manufacturing this aspherical lens, the optical polishing method, which is a conventional method for manufacturing optical lenses, has difficulty in processing and mass production, so direct press molding is viewed as promising. This direct press molding method involves heating and molding a lump of optical glass on an aspherical mold that has been finished to the desired surface quality and surface precision, or heating a lump of glass that has been heated in advance. This is a method of manufacturing optical lenses by pressing and molding without requiring any further polishing process. However, the above method for producing an optical glass lens must be excellent to the extent that the image forming quality of the obtained lens is not impaired after press molding. In particular, in the case of an aspherical lens, it is required that it can be molded with high surface accuracy. Therefore, the mold material must have minimal chemical action on the glass at high temperatures, be resistant to damage such as scratches on the glass pressing surface of the mold, and have good fracture resistance against thermal shock. It must have a quality such as being tall. For this purpose, molds made of silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), etc., molds made of high-density carbon coated with silicon carbide (SiC), or molds made of cemented carbide are used. It is believed that molds coated with precious metals such as platinum are suitable, and various studies are being conducted. However, since materials such as SiC and Si ₃ N ₄ have extremely high hardness, it is extremely difficult to process these materials into spherical or aspherical molds with high precision. Moreover, these materials are all sintered types, so they can be used as sintering aids.
Substances such as Al ₂ O ₃ and B ₂ O ₃ that react relatively easily with glass containing lead and alkalis are used, and as press molding is repeated, the reaction between the mold and the glass progresses, resulting in highly accurate lenses. The disadvantage was that it could not be molded. Furthermore, in the case of high-density carbon coated with silicon carbide (SiC), the coating film is beta-silicon carbide (β-SiC), so it easily reacts with glass that contains large amounts of lead and alkali elements. This method has the disadvantage that it is difficult to mold a glass lens with precision. In addition, molds made of cemented carbide coated with precious metals have the problem that when optical glass is molded at high temperatures for a long period of time, the base material of cemented carbide is oxidized and the surface precision deteriorates. It was found that it has Purpose of the Invention It is an object of the present invention to easily perform the high-precision mold processing required for a mold for direct press molding of glass lenses, and to achieve good image forming quality by using the mold produced in this way. The present invention provides a press-molding mold for an optical glass element that enables direct press-molding of an optical glass lens having the following properties. Structure of the Invention The press molding mold for an optical glass element of the present invention includes:
A cermet whose main component is titanium carbide (TiC) is used as a base material, and this is processed into the shape of the lens to be molded, and on top of that, iridium (Ir), osmium (Os), palladium (Pd), and rhodium (Rh) are added. It is characterized by being coated with a noble metal alloy layer consisting of platinum (Pt) and at least one element selected from the group consisting of ruthenium (Ru) and ruthenium (Ru). The cermet whose main component is titanium carbide used here as a base material is easier to grind than SiC and Si ₃ N ₄ , which were conventionally used as press molding molds for glass lenses, even when performing general grinding. It is characterized by high precision mold processing, and the maximum surface roughness (Rmax) of the mold surface is 0.02μm.
It has the characteristic that it can be easily finished to the following precision. Also, compared to cemented carbide whose main component is tungsten carbide (WC),
It is possible to finish the maximum surface roughness (Rmax) of the mold surface to an accuracy of 0.02 μm or less in approximately the same amount of time. Furthermore, the thermal expansion coefficient of the thermite used as the base material is 8 to 9 × 10 ^-6 /℃, and it is composed of iridium (Ir), osmium (Os), palladium (Pd), rhodium (Rh), and ruthenium (Ru). The thermal expansion coefficient of the noble metal layer consisting of at least one element selected from the group and platinum (Pt) is 9 to 11.
×10 ^-6 /℃, and the thermal expansion coefficients of the base material and the precious metal layer match well, so it is strong enough to withstand thermal shock during press molding of glass and thermal cycles during repeated molding. Provides strong adhesion. Therefore, by using the mold of the present invention, SiC and
We have overcome the difficulty of high-precision mold processing, which was a drawback of Si ₃ N ₄ molds, and the mold and glass can be molded even when molding glass containing a large amount of alkali elements such as sodium and potassium, or lead. Needless to say, this method has the advantage that there is no peeling between the base material and the precious metal layer coated thereon, even during thermal cycles during repeated molding. In addition, in the noble metal layer formed on the cermet, the alloy composition is 60 to 99% by weight of platinum (Pt),
The reason for specifying that the remaining alloy is an alloy consisting of at least one element selected from the group consisting of iridium (Ir), osmium (Os), palladium (Pd), rhodium (Rh), and ruthenium (Ru) is that each composition amount ( This is because the suitability as a mold material for press molding of various optical glass elements differs depending on the weight percentage). In other words, if the alloy composition amount (wt%) is within the scope of the claims of the present invention, it is possible to press-form an optical glass element well, but if the alloy composition amount (wt%) is less than the specified amount, the strength of the noble metal layer or This is because the low hardness causes minute scratches on the die surface after press molding, and the noble metal layer formed on the cermet undergoes plastic deformation, resulting in a loss of highly accurate surface shape. Moreover, if the composition amount (wt%) is more than the specified amount, the press-molded glass will be colored and the noble metal layer will easily volatilize at high temperatures. Description of Examples Examples of the present invention will be described below. Example TiC-10Mo- on a cylinder with a diameter of 30 mm and a length of 50 mm
A cermet rod with a 9Ni composition is prepared, and a notch 1 is formed around the periphery as shown in Figure 1 by electrical discharge machining.
An upper mold 11 having a concave shape with a radius of curvature of 46 mm and a radius of curvature of 1";
It was processed into a pair of press molding molds consisting of a concave lower mold 12 with a radius of curvature of 200 mm. The press-molded surface of this mold was mirror-polished using ultrafine diamond abrasive grains. As a result, it was possible to perform mirror finishing with an accuracy of maximum surface roughness of 0.02 μm within one hour. Next, a binary alloy such as a platinum-rhodium (Pt-Rh) alloy layer or a ternary alloy such as a platinum-rhodium-iridium (Pt-Rh-Ir) alloy layer is deposited on this mirror surface to a thickness of 2 μm using a sputtering method. , quaternary alloys such as platinum-rhodium-iridium-palladium (Pt-Rh-Ir-Pd) alloy layer, platinum-rhodium-iridium-palladium-osmium (Pt-Rh-Ir-Pd-Os-Ru) alloy layer Five-element alloys such as and six-element alloys such as platinum-rhodium-iridium-palladium-osmium-ruthenium (Pt-Rh-Ir-Pd-Os-Ru) alloy layers were formed. The molds 11 and 12 produced in this way are used in a piston cylinder 15 of a press machine shown in FIG.
and 16, and in a nitrogen atmosphere, PbO
A block 17 made of a lead oxide-based optical glass consisting of 70% SiO ₂ , 27% SiO 2 , and trace components processed into a spherical shape with a radius of 20 mm was hot-pressed and formed into a lens shape with convex surfaces on both sides. During glass press molding, the mold temperature was 500℃ and the press pressure was 40Kg/ ^cm2 , which was held for 2 minutes, then cooled to 300℃ together with the mold, and the molded glass was taken out from the molded glass outlet 19, and the molded glass and mold were separated. Each was evaluated. After repeating this pressing process 1000 times, the mold used was removed and the surface condition of the mold after 1000 press moldings was observed. The above pressing experiment was repeated on a pair of molds having different alloy compositions as shown in Table 1, and the molded glass and mold after pressing were evaluated, and the results are shown in Table 1. For comparison, we created a conventionally used silicon carbide mold, a mold with silicon carbide coated on high-density carbon, and a mold with a noble metal layer formed on cemented carbide, as shown in Figure 2. It was set in a press machine instead of the mold of the present invention, and glass was press-molded under the same press conditions as described above. These silicon carbide and high-density carbon molds were prepared by grinding in the same manner as the cermet mold described above, and the surfaces of the molds were polished to a mirror finish using diamond abrasive grains. Even in this mirror polishing step alone, the time required to finish the mold surface to a maximum surface roughness of 0.02 .mu.m was 2 to 50 times longer than when mirror polishing cermet. As a result of press molding under the same conditions as described above using a silicon carbide mold and a mold in which silicon carbide was coated on high-density carbon, the press-formed glass became cloudy and left traces of reaction with the glass on the mold surface. Ivy. When similar press molding was performed using a mold with a noble metal layer formed on cemented carbide, the noble metal film peeled off after about 800 presses. In contrast, the press molding mold for the optical glass element of the present invention has a noble metal layer formed on the cermet that does not react with the lead oxide optical glass even after press molding the lead oxide optical glass 1000 times. It has the advantage of not peeling off or causing minute scratches on the mold surface, which is superior to conventional press molding molds, and the maximum surface roughness of the mold surface has been reduced to 0.02 μm. It was found that the time required for processing was 1 hour, and that the mold could be easily manufactured in the same way as in the case of cemented carbide, and that optical glass elements could be precisely press-molded. In addition, the Vickers hardness (Hv) of cermet and cemented carbide at room temperature is approximately the same, 1600 to 1800, but the Vickers hardness at 550°C is approximately 1000 and 700, respectively. The hardness of cermet is considerably higher than that of cemented carbide at the temperature (500°C), so it can be seen that the high surface precision of the base material is maintained even when press-formed for a long time. . Furthermore, in molds with a precious metal layer formed on a cemented carbide, oxidation of the base material of the cemented carbide progressed and the surface accuracy of the mold material decreased, but in molds with a precious metal layer formed on a cermet. Because oxidation of the base material cermet hardly progresses at 550°C, no change in the surface precision of the mold surface was observed even after 1000 press moldings. In Table 1, the press molding molds marked with * to the upper right of the sample numbers are described as comparative examples and outside the scope of the claims of the present application. In this example, the composition of the cermet used as the base material of the press molding mold for the optical glass element was TiC-
Although it was 10Mo-9Ni, the composition of the cermet as the base material is not limited to the above composition.
The main component is TiC, with other additives such as TiN, TaC, WC, NbC, Mo ₂ C, Cr ₃ C ₂ ,
Cermets containing VC, ZrC, Mo, Ni, Co, Cr, etc. can be used. Furthermore, although a concave press molding die was used to explain the present invention, the shape of the die surface is not limited to the shape of this example, and may be adapted to the shape of an optical glass element such as a prism. Needless to say, anything is fine.

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[Table] The * mark in the upper right corner of the sample number indicates a comparative example.
Effects of the Invention As is clear from the above description, the press molding mold for an optical glass element of the present invention uses cermet as a base material, processes this into a pressing mold for molding, and forms a noble metal layer thereon. This is a press-molding mold for optical glass elements that is characterized by the following characteristics: It has the advantage that not only is there little reactivity when processing, but also that it can be easily formed into a highly accurate mold shape even in general grinding and mirror finishing. Furthermore, it has the advantage of having better oxidation resistance and heat shock resistance than a mold with a noble metal layer formed on a cemented carbide, as well as high hardness at high temperatures. Therefore, by using the press-molding mold for optical glass elements of the present invention, it is easier to obtain optical glass elements with high precision than with conventional press-molding molds for optical glass elements. I see what's possible.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a press-molding mold for an optical glass element in an embodiment of the present invention, and FIG. 2 is a partially cutaway front view of a press machine used in the same embodiment. 11...Upper die, 12...Lower die, 11'...Press surface of upper die, 12'...Press surface of lower die, 11''...
...Cut portion, 13...Heating heater for upper mold, 14
... Heater for lower mold, 15 ... Piston cylinder for upper mold, 16 ... Piston cylinder for lower mold, 1
7... Raw glass lumps, 18... Raw glass supply jig, 19... Molded glass outlet, 20...
...Raw material glass preheating furnace, 21...Shell.

Claims (1)

[Scope of Claims] 1. A mold for press-molding an optical glass element, characterized in that the base material is a cermet containing titanium carbide (TiC) as a main component, and a noble metal layer is formed on the base material. 2. The noble metal is an alloy consisting of platinum (Pt) and at least one element selected from the group consisting of iridium (Ir), osmium (Os), palladium (Pd), rhodium (Rh), and ruthenium (Ru). A press-molding mold for an optical glass element according to claim 1, characterized in that: 3 The noble metal layer contains 60 to 99% by weight of platinum (Pt),
A patent claim characterized in that the remainder is an alloy consisting of at least one element selected from the group consisting of iridium (Ir), osmium (Os), palladium (Pd), rhodium (Rh) and ruthenium (Ru). A press-molding mold for an optical glass element according to item 1.