Press-molding die for glass optical elements

Abstract: A die for press-molding a glass optical element which includes a base material (12) having a surface to press-mold glass and a tantalum(Ta)-containing alloy thin layer (11) on the surface, the base material being heat-resistant and strong enough to withstand press-molding.

Description: This invention relates to dies for press-molding glass optical elements. More specifically, it relates to dies for press-molding fine glass optical elements which do not require a polishing process after being press-molded. Repeated press-molding fine glass optical elements needs dies mechanically strong enough not to lose their shape during press-mold processing. Such dies should be stable to high temperatures, resistant to oxidation, and inert with respect to glass. Further, the dies must be excellent in machinability so as to be machined precisely and easily. Conventional press-molding dies include, for example, a die of mixed materials including titanium carbide (TiC) and a metal, as disclosed in Japanese Unexamined Patent Publication SHO 59-121126, and a die composed of cemented carbides and a precious metal thin layer formed thereon, as disclosed in Japanese Unexamined Patent Publication SHO 62-96331. These conventional dies, however, could not satisfy all the conditions. Although the die made of TiC and a metal is hard and mechanically strong, it is very difficult to machine the dies precisely. In addition, the die has the problem of reacting with components of glass optical elements, such as lead (Pb) or alkaline metals. On the other hand, dies made of cemented carbides coated with a thin layer of a precious metal are superior in mechanical strength and easy to process. They hardly react with glass in an inert gas atmosphere, such as nitrogen gas, up to about 600 °C during repeated press-molding. However, at 650 °C or more, the surface of the dies changes in color, and becomes cloudy after about 100 times of press-moldings. Thus, the dies cannot withstand further use. At 650 °C or more, the dies show no satisfactory wetting to and releasing from glass. To improve the press-molding dies, a die composed of cemented carbides coated with a nickel (Ni) -precious metal alloy thin layer is proposed in Japanese Unexamined Patent Publication SHO 64-61327. The proposed die still has a problem of suffering grain growth after 1000 times of press-moldings at 650 °C or more, and becoming rough. Thus, the die can not repeatedly press-mold higher-melting glass. JP-A-62-017 028 relates to a precision mould covered by a thin film which can be used for moulding optical glass elements. The thin film consists of a noble metal alloy to which 0.01 - 10 wt% of a group Va element is added. Thus, this thin film is a ternary alloy. Therefore, higher-melting glass optical elements cannot be mass-produced using the conventional press-molding dies. To solve the above-noted problems, this invention aims to provide a die for press-molding glass optical elements which will not deteriorate even after repeatedly press-molding fine higher-melting glass optical elements over a long period of time. This object is achieved by the die according to claim 1. Thus the invention provides a die for press-molding a glass optical element comprising a base material having a surface to press-mold glass, and a tantalum (Ta)-containing alloy thin layer on the surface, the base material being heat-resistant to the softening point of the glass or more and being strong enough to withstand press-molding. The Ta-containing alloy thin layer consists of tantalum Ta and one element selected from the group consisting of Pt, Rh, Ir, Ru, Os, Re, W and Pd. It is preferable that the Ta content of the Ta-containing alloy thin layer is 5 to 95 wt%. It is further preferable that the Ta-containing alloy thin layer has a thickness of 1 to 5 µm. It is also preferable that the base material comprises at least one material selected from the group consisting of cemented carbides comprising tungsten carbide (WC) with at least 50 wt%, a cermet comprising titanium carbide (TiC) with at least 50 wt%, a cermet comprising titanium nitride (TiN) with at least 50 wt% and a WC sintered body. It is also preferable that the press-molding die of the invention further comprises a middle layer between the base material and the Ta-containing alloy thin film for strengthening adhesion of the base material to the Ta-containing alloy thin layer, and the middle layer comprises at least one material selected from the group consisting of tantalum carbide (TaC), tantalum nitride (TaN) and tantalum oxide (Ta 2 O 5 ), the composition of this middle layer being dependent on the principal component of the base material. Hereby the adhesion of the base material to the middle layer and adhesion of the middle layer to the Ta-containing alloy thin layer are each stronger than that of the base material to the Ta-containing alloy thin layer. It is further preferable that the base material comprises a carbide as its principal component and the middle layer comprises tantalum carbide (TaC). It is also preferable that the base material comprises a nitride as its principal component and the middle layer comprises tantalum nitride (TaN). It is also preferable that the base material is an oxide and the middle layer comprises tantalum oxide (Ta 2 O 5 ). All the carbides, nitrides or oxides are generally possible for use in forming the base material as long as they are strong enough to withstand press-molding. Combination of a carbide base material and a TaC middle layer, that of a nitride base material and a TaN middle layer, and also that of an oxide base material and a Ta 2 O 5 middle layer provide a better performance of the dies. It is also preferable that the middle layer is a heat-diffusion preventive layer to prevent metal present in the base material from diffusing into the Ta-containing alloy thin layer due to heat. It is also preferable that the heat-diffusion preventive layer comprises at least one material selected from the group consisting of Re and W. It is also preferable that the middle layer has a thickness of 1 to 3 µm. Fig. 1 is a sectional view of a press-molding die of a preferred embodiment of the invention. Fig. 2 is a sectional view of a press used in a preferred embodiment. Fig. 3 is a chart of Auger electron spectroscopy (abbreviated as AES) analysis. Fig. 4 is a sectional view of a press-molding die of another preferred embodiment. Fig. 5 is a sectional view of a press-molding die of still another preferred embodiment. Fig. 6 is a sectional view of a press-molding die of a further preferred embodiment. Fig. 7 is a sectional view of a press-molding die of a still further preferred embodiment. The press-molding die of the preferred embodiment of the invention is strong, easy to minutely process and resistant to high temperatures, so as to satisfy all of the needs for press-molding glass optical elements. Therefore, the die can mass-produce very fine higher-melting glass optical elements by repeatedly press-molding without deteriorating. Examples of the invention will be explained with reference to Tables and the accompanying drawings. Example 1 Cemented carbides comprising tungsten carbide (WC) as its principal component (20 mm diameter, 5 mm thick) was processed into a pair of a concave upper half die and a concave lower half die whose curvature diameters were 46 mm and 200 mm, respectively. The press-mold surfaces of the dies were polished to a mirror surface using an abrasive grain of ultrafine diamonds. The dies were finished by coating their mirror surfaces with a 3 µm thick alloy thin film selected from a Ta-Pt, Ta-Rh, Ta-Ir, Ta-Ru, Ta-Os, Ta-Re, Ta-W, and Ta-Pd thin films by a sputtering method. The base material temperature was 450 °C, the sputtering power was 150 W, and the pressure of argon gas was 1.1 × 10 -3 Torr. Preferable sputtering conditions include a base material temperature of 100 to 600 °C, a sputtering power of 100 to 500 W, and a pressure of argon gas of 1.0 × 10 -4 to 1.0 × 10 -2 Torr. The thin film can be formed in other ways such as vacuum evaporation or ion plating. Fig. 1 shows a die comprising WC cemented carbides base material 12 and Ta-Ir alloy thin film 11 having a thickness of 3 µm. The dies were then placed in a press as shown in Fig. 2. The press was provided with upper heater block 21, upper heater 22, upper half die 23, sample glass 24, lower half die 25, lower heater 26, lower heater block 27, cover 28, side die 29, plunger 210, locating sensor 211, and stopper 212. Schwer-Kronglass 24, which had been processed to a sphere with radius 5 mm, was placed on lower half die 25, on which upper half die 23 was then placed. They were heated up together to 700 °C. A pressure of about 40 kg/cm 2 was applied to glass 24 through the upper and lower half dies 23 and 25 in a nitrogen atmosphere for 2 min. Afterwards, glass 24 was left to cool to 600 °C, and finally taken out of the press. After 10000 repetitions of the above pressing processes, the upper and lower half dies 23 and 25 were taken out of the press, and subjected to optical microscopic observation of their press-mold surfaces. At the same time, the roughness (RMS value, nm) of the surfaces was measured to judge the accuracy of each die. Tables 2-1, 2-2, 2-3 and 2-4 show the results of various Ta contents (wt%) of the Ta-Ir alloy thin film. On the other hand, comparative embodiments were performed to judge the accuracy of conventional dies by repeating the above pressing 10000 times. The dies used were those of an SiC sintered body and those comprising cemented carbides base material and a Pt or Ir thin film thereon. Table 1 shows the results. Sample No. Die Roughness of die surface before press-moldings (RMS value) Condition and roughness of die surface after 10000 press-moldings Roughness (RMS value) Condition 1 SiC sintered body 1.03 nm Immeasurable Glass attached 2 Pt sputtered film 1.05 nm 25.56 nm White clouded 3 Ir sputtered film 1.01 nm 10.54 nm White clouded Sample No. 1, made from an SiC sintered body alone, could not withstand more than 50 press-moldings, because the glass attached to both the upper and lower half dies. In other words, the die can not mass-produce glass optical elements. Although sample Nos. 2 and 3, comprising a Pt or Ir sputtered film, were free from the glass after 10000 press-moldings, they exhibited rather high RMS values, such as 25.56 and 10.54 nm, proving their surfaces were very rough. They also became too cloudy for practical use. Observation of the die surface detected diffusion of Co, and grain growth of Pt or Ir due to heat. Fig. 3 shows the result of AES analysis revealing that Co was diffused in a die composed of cemented carbides and Ir film thereon after heat treatment at 870 °C in nitrogen gas for 1 hour. Sample No. Film composition (wt%) Roughness of die surface before press-moldings (RMS value, nm) Condition and roughness of die surface after 10000 press-moldings Ta Pt Rh Roughness Condition 4 5 95 0 1.01 2.79 Good 5 30 70 0 0.98 0.99 Good 6 50 50 0 0.97 0.98 Good 7 70 30 0 0.99 1.00 Good 8 95 5 0 1.02 2.54 Good 9 5 0 95 1.04 3.07 Good 10 30 0 70 1.01 1.02 Good 11 50 0 50 1.02 1.03 Good 12 70 0 30 1.03 1.05 Good 13 95 0 5 1.02 2.96 Good Sample No. Film composition (wt %) Roughness of die surface before press-moldings (RMS value, nm) Condition and roughness of die surface after 10000 press-moldings Ta Ir Ru Roughness Condition 14 5 95 0 0.99 2.89 Good 15 30 70 0 1.00 1.01 Good 16 50 50 0 0.98 1.00 Good 17 70 30 0 1.01 1.03 Good 18 95 5 0 0.99 2.95 Good 19 5 0 95 1.03 3.02 Good 20 30 0 70 1.00 1.02 Good 21 50 0 50 1.01 1.02 Good 22 70 0 30 1.01 1.02 Good 23 95 0 5 1.02 3.12 Good Sample No. Film composition (wt %) Roughness of die surface before press-moldings (RMS value, nm) Condition and roughness of die surface after 10000 press-moldings Ta Os Re Roughness Condition 24 5 95 0 1.02 3.01 Good 25 30 70 0 1.02 1.04 Good 26 50 50 0 0.99 1.01 Good 27 70 30 0 1.00 1.02 Good 28 95 5 0 1.03 3.25 Good 29 5 0 95 1.00 3.31 Good 30 30 0 70 0.97 1.00 Good 31 50 0 50 0.99 1.00 Good 32 70 0 30 0.99 1.05 Good 33 95 0 5 1.01 3.78 Good Sample No. Film composition (wt %) Roughness of die surface before press-moldings (RMS value, nm) Condition and roughness of die surface after 10000 press-moldings Ta W Pd Roughness Condition 34 5 95 0 1.03 2.99 Good 35 30 70 0 1.02 1.08 Good 36 50 50 0 1.04 1.08 Good 37 70 30 0 1.04 1.09 Good 38 95 5 0 1.03 2.76 Good 39 5 0 95 1.03 3.37 Good 40 30 0 70 1.05 1.06 Good 41 50 0 50 1.01 1.02 Good 42 70 0 30 1.03 1.05 Good 43 95 0 5 1.02 3.49 Good Of sample Nos. 4 to 43, all dies having Ta alloy thin films with a Ta content of 30 to 70 wt% exhibited little change in their surfaces even after 10000 press-moldings, as well as the surface roughness. The remaining dies having Ta-Ir alloy thin films with a Ta content of 5 or 95 wt% exhibited a small change in surface roughness after 10000 press-moldings, compared to conventional dies. The press-molding dies of this preferred embodiment comprising Ta-Ir alloy thin films with a Ta content of 30 to 70 wt% on the WC base material repeatedly press-mold higher-melting glass for a long time without deteriorating. It allows press-molding a large amount of fine higher-melting glass optical elements. Similar results were acheived using dies comprising a base material formed of a TiN or TiC cermet as its principal component, and dies comprising a base material of a WC sintered body. Example 2 Two cermets comprising TiC as its principal component (20 mm diameter, 5 mm thick) were provided with concave press-mold surfaces whose curvature diameter were 46 mm and 200 mm, respectively, in the same manner as in Example 1. The concave press-mold surfaces were polished to a mirror surface using an abrasive grain of ultrafine diamonds. A 1 µm thick TaC film as a middle layer was formed on each of the mirrored press-mold surfaces by sputtering in the same manner as in Example 1. Further, a 3 µm thick Ta alloy thin film selected from a Ta-Pt, Ta-Rh, Ta-Ir, Ta-Ru, Ta-Os, Ta-Re, Ta-W, and Ta-Pd alloy thin films with a Ta content of 30 to 70 wt% was similarly formed on each of the TaC sputtered films to finish the dies. Fig. 4 shows the die comprising TiC cermet base material 33, TaC thin film 32 and Ta-Ir alloy thin film 31 with the Ta content of 50 wt%. The dies were then placed in the press shown in Fig. 2. Schwer-Kronglass 24, which had been processed to a sphere with radius 5 mm, was placed on lower half die 25, on which upper half die 23 was then placed. Press-moldings were conducted 100000 times in the same manner as in Example 1 to judge the life of each die. Tables 4-1, 4-2 and 4-3 show the results. On the other hand, comparative embodiments were performed to judge the life of other dies after 80000 repetitions of the above-mentioned pressing. The dies used comprised a TiC cermet base material and a Ta-Ir alloy thin film with a Ta content of 30 to 70 wt%, and those comprising WC cemented carbides and a Ta-Ir alloy thin film with a Ta content of 30 to 70 wt% as used in Example 1. Table 3 shows the results. Sample No. Base material Film composition Adhesion of film to base material After film-forming After 10000 times After 50000 times After 80000 times 44 TiC Ta(30)-Ir ○ ○ ○ Exfoliated 45 Ta(50)-Ir ○ ○ ○ Exfoliated 46 Ta(70)-Ir ○ ○ ○ Exfoliated 47 WC Ta(30)-Ir ○ ○ ○ Exfoliated 48 Ta(50)-Ir ○ ○ ○ Exfoliated 49 Ta(70)-Ir ○ ○ ○ Exfoliated The dies of sample Nos. 44 to 49, having no middle layer between the base material and the Ta alloy thin film did not become rough and their thin films did not become exfoliated after 50000 press-moldings. After 80000 press-moldings, the film peeled off the base material. The dies could not withstand further use. Sample No. Film composition Middle layer: TaC Adhesion of film to base material After film-forming After 10000 times After 50000 times After 100000 times 50 Ta(30)-Pt ○ ○ ○ ○ 51 Ta(30)-Rh ○ ○ ○ ○ 52 Ta(30)-Ir ○ ○ ○ ○ 53 Ta(30)-Ru ○ ○ ○ ○ 54 Ta(30)-Os ○ ○ ○ ○ 55 Ta(30)-Re ○ ○ ○ ○ 56 Ta(30)-W ○ ○ ○ ○ 57 Ta(30)-Pd ○ ○ ○ ○ Sample No. Film composition Middle layer: TaC Adhesion of film to base material After film-forming After 10000 times After 50000 times After 100000 times 58 Ta(50)-Pt ○ ○ ○ ○ 59 Ta(50)-Rh ○ ○ ○ ○ 60 Ta(50)-Ir ○ ○ ○ ○ 61 Ta(50)-Ru ○ ○ ○ ○ 62 Ta(50)-Os ○ ○ ○ ○ 63 Ta(50)-Re ○ ○ ○ ○ 64 Ta(50)-W ○ ○ ○ ○ 65 Ta(50)-Pd ○ ○ ○ ○ Sample No. Film composition Middle layer: TaC Adhesion of film to base material After film-forming After 10000 times After 50000 times After 100000 times 66 Ta(70)-Pt ○ ○ ○ ○ 67 Ta(70)-Rh ○ ○ ○ ○ 68 Ta(70)-Ir ○ ○ ○ ○ 69 Ta(70)-Ru ○ ○ ○ ○ 70 Ta(70)-Os ○ ○ ○ ○ 71 Ta(70)-Re ○ ○ ○ ○ 72 Ta(70)-W ○ ○ ○ ○ 73 Ta(70)-Pd ○ ○ ○ ○ In contrast, the dies of sample Nos. 50 to 73, each comprising a TiC cermet base material, a TaC middle layer and a Ta alloy thin film thereon, were free from exfoliation of their alloy thin films even after 100000 press-moldings. In other words, the TaC middle layer causes phase diffusion at the interfaces between the base material and the middle layer, and between the thin film and the middle layer, remarkably improving adhesion of the base material and the thin film. That extends the life of the dies without the thin film peeling off. Though Example 2 used the TiC cermet base material, base materials of other carbides such as SiC, WC or TaC achieve similar results. Example 3 Two cermets comprising TiN as its principal component (20 mm diameter, 5 mm thick) were provided with concave press-mold surfaces whose curvature diameters were 46 mm and 200 mm, respectively, in the same manner as in Example 1. The concave press-mold surfaces of the dies were polished to a mirror surface using an abrasive grain of ultrafine diamonds. A 1 µm thick TaN film as a middle layer was formed on each of the mirror surfaces by sputtering in the same manner as in Example 1. Further, on each of the TaN sputtered films, was formed a 3 µm thick Ta alloy thin film selected from a Ta-Pt, Ta-Rh, Ta-Ir, Ta-Ru, Ta-Os, Ta-Re, Ta-W, and Ta-Pd alloy thin films with a Ta content of 30 to 70 wt% to finish the dies. Fig. 5 shows the die comprising TiN cermet base material 43, TaN thin film 42, and Ta-Ir alloy thin film 41 with the Ta content of 50 wt%. The dies were then placed in the press shown in Fig. 2. SK-14 glass 24 which had been processed to a sphere with radius 5 mm, was placed on lower half die 25, on which upper half die 23 was then placed. Press-moldings were conducted 100000 times in the same manner as in Example 1 to judge the life of each die. Tables 6-1, 6-2 and 6-3 show the results. On the other hand, comparative embodiments were performed to similarly judge the life of other dies by repeating the above-mentioned press-molding processes 80000 times. The dies used were those comprising a TiN cermet base material and a Ta-Ir alloy thin film with a Ta content of 30 to 70 wt% and those comprising WC cemented carbides and a Ta-Ir alloy thin film with a Ta content of 30 to 70 wt% used in Example 1. Table 5 shows the results. Sample No. Base material Film composition Condition of die surface After film-forming After 10000 times After 50000 times After 80000 times 74 TiN Ta(30)-Ir ○ ○ ○ Exfoliated 75 Ta(50)-Ir ○ ○ ○ Exfoliated 76 Ta(70)-Ir ○ ○ ○ Exfoliated 77 WC Ta(30)-Ir ○ ○ ○ Exfoliated 78 Ta(50)-Ir ○ ○ ○ Exfoliated 79 Ta(70)-Ir ○ ○ ○ Exfoliated The dies of sample Nos. 74 to 79, having no middle layer between the base material and the alloy thin film did not become rough and the thin films were not exfoliated after 50000 press-moldings. After 80000 press-moldings, the films peeled off the base material. The dies could not withstand further use. Sample No. Film composition Middle layer: TaN Adhesion of film to base material After film-forming After 10000 times After 50000 times After 100000 times 80 Ta(30)-Pt ○ ○ ○ ○ 81 Ta(30)-Rh ○ ○ ○ ○ 82 Ta(30)-Ir ○ ○ ○ ○ 83 Ta(30)-Ru ○ ○ ○ ○ 84 Ta(30)-Os ○ ○ ○ ○ 85 Ta(30)-Re ○ ○ ○ ○ 86 Ta(30)-W ○ ○ ○ ○ 87 Ta(30)-Pd ○ ○ ○ ○ Sample No. Film composition Middle layer: TaN Adhesion of film to base material After film-forming After 10000 times After 50000 times After 100000 times 88 Ta(50)-Pt ○ ○ ○ ○ 89 Ta(50)-Rh ○ ○ ○ ○ 90 Ta(50)-Ir ○ ○ ○ ○ 91 Ta(50)-Ru ○ ○ ○ ○ 92 Ta(50)-Os ○ ○ ○ ○ 93 Ta(50)-Re ○ ○ ○ ○ 94 Ta(50)-W ○ ○ ○ ○ 95 Ta(50)-Pd ○ ○ ○ ○ Sample No. Film composition Middle layer: TaN Adhesion of film to base material After film-forming After 10000 times After 50000 times After 100000 times 96 Ta(70)-Pt ○ ○ ○ ○ 97 Ta(70)-Rh ○ ○ ○ ○ 98 Ta(70)-Ir ○ ○ ○ ○ 99 Ta(70)-Ru ○ ○ ○ ○ 100 Ta(70)-Os ○ ○ ○ ○ 101 Ta(70)-Re ○ ○ ○ ○ 102 Ta(70)-W ○ ○ ○ ○ 103 Ta(70)-Pd ○ ○ ○ ○ In contrast, the dies of sample Nos. 80 to 103, comprising a TiN cermet base material, a TaN middle layer and a Ta alloy thin film thereon, were free from exfoliation of their alloy thin films even after 100000 press-moldings. In other words, the TaN middle layer causes phase diffusion at interfaces between the base material and the middle layer, and between the thin film and the middle layer, remarkably improving adhesion of the base material and the thin film. That extends the life of the dies without the thin film peeling off. Though Example 3 used the TiN cermet base material, base materials formed of other nitrides achieve similar results. Example 4 Two Al 2 O 3 materials (20 mm diameter, 5 mm thick) were provided with concave press-mold surfaces whose curvature diameters were 46 mm and 200 mm, respectively, in the same manner as in Example 1. The concave press-mold surfaces were polished to a mirror surface using an abrasive grain of ultrafine diamonds. A 1 µm thick Ta 2 O 5 film as a middle layer was formed on each of the mirror surfaces by sputtering in the same manner as in Example 1. Further, on each Ta 2 O 5 sputtered films, was formed a 3 µm thick Ta alloy thin film selected from a Ta-Pt, Ta-Rh, Ta-Ir, Ta-Ru, Ta-Os, Ta-Re, Ta-W, and Ta-Pd alloy thin films with a Ta content of 30 to 70 wt% to finish the dies. Fig. 6 shows the die comprising Al 2 O 3 cermet base material 53, Ta 2 O 5 thin film 52 and Ta-Ir alloy thin film 51 with the Ta content of 50 wt%. The dies were then placed in the press shown in Fig. 2. SK-14 glass 24 which had been processed to a sphere with radius 5 mm, was placed on lower half die 25, on which upper half die 23 was then placed. Press-moldings were conducted 100000 times in the same manner as in Example 1 to judge the life of each die. Tables 8-1, 8-2 and 8-3 show the results. On the other hand, comparative embodiments were performed similarly judge the life of other dies by repeating the above-mentioned pressing 70000 times. The dies used were those comprising an Al 2 O 3 base material and a Ta-Ir alloy thin film with a Ta content of 30 to 70 wt% and those comprising WC cemented carbides base material and a Ta-Ir alloy thin film with a Ta content of 30 to 70 wt% used in Example 1. Table 7 shows the results. Sample No. Base material Film composition Adhesion of film to base material After film-forming After 10000 times After 50000 times After 70000 times 104 Al 2 O 3 Ta(30)-Ir ○ ○ ○ Exfoliated 105 Ta(50)-Ir ○ ○ ○ Exfoliated 106 Ta(70)-Ir ○ ○ ○ Exfoliated 107 WC Ta(30)-Ir ○ ○ ○ Exfoliated 108 Ta(50)-Ir ○ ○ ○ Exfoliated 109 Ta(70)-Ir ○ ○ ○ Exfoliated The dies of sample Nos. 104 to 109, having no middle layer between the base material and the alloy thin film did not become rough and the thin films were not exfoliated after 50000 press-moldings. After 70000 press-moldings, the films peeled off the base material. The dies could not withstand further use. Sample No. Film composition Middle layer: Ta 2 O 5 Adhesion of film to base material After film-forming After 10000 times After 50000 times After 100000 times 110 Ta(30)-Pt ○ ○ ○ ○ 111 Ta(30)-Rh ○ ○ ○ ○ 112 Ta(30)-Ir ○ ○ ○ ○ 113 Ta(30)-Ru ○ ○ ○ ○ 114 Ta(30)-Os ○ ○ ○ ○ 115 Ta(30)-Re ○ ○ ○ ○ 116 Ta(30)-W ○ ○ ○ ○ 117 Ta(30)-Pd ○ ○ ○ ○ Sample No. Film composition Middle layer: Ta 2 O 5 Adhesion of film to base material After film-forming After 10000 times After 50000 times After 100000 times 118 Ta(50)-Pt ○ ○ ○ ○ 119 Ta(50)-Rh ○ ○ ○ ○ 120 Ta(50)-Ir ○ ○ ○ ○ 121 Ta(50)-Ru ○ ○ ○ ○ 122 Ta(50)-Os ○ ○ ○ ○ 123 Ta(50)-Re ○ ○ ○ ○ 124 Ta(50)-W ○ ○ ○ ○ 125 Ta(50)-Pd ○ ○ ○ ○ Sample No. Film composition Middle layer: Ta 2 O 5 Adhesion of film to base material After film-forming After 10000 times After 50000 times After 100000 times 126 Ta(70)-Pt ○ ○ ○ ○ 127 Ta(70)-Rh ○ ○ ○ ○ 128 Ta(70)-Ir ○ ○ ○ ○ 129 Ta(70)-Ru ○ ○ ○ ○ 130 Ta(70)-Os ○ ○ ○ ○ 131 Ta(70)-Re ○ ○ ○ ○ 132 Ta(70)-W ○ ○ ○ ○ 133 Ta(70)-Pd ○ ○ ○ ○ In contrast, the dies of sample Nos. 110 to 133, comprising the Al 2 O 3 base material, a TaN middle layer and a Ta alloy thin film thereon, were free from exfoliation of the alloy thin films after 100000 press-moldings. In other words, the TaN middle layer causes phase diffusion at the interfaces between the base material and the middle layer, and between the thin film and the middle layer, remarkably improving adhesion of the base material and the thin film. That extends the life of the dies without the thin film peeling off. Though Example 4 used the TiN cermet base material, base materials formed of other nitrides achieve similar results. Example 5 Two WC cemented carbides (20 mm diameter, 5 mm thick) were provided with concave press-mold surfaces whose curvature diameters were 46 mm and 200 mm, respectively, in the same manner as in Example 1. The concave press-mold surfaces were polished to a mirror surface using an abrasive grain of ultrafine diamonds. A 1 µm thick Ta 2 O 5 film as a middle layer was formed on each mirror surface by sputtering in the same manner as in Example 1. Further, on each of the Ta 2 O 5 sputtered films, was formed a 3 µm thick Ta alloy thin film selected from a Ta-Pt, Ta-Rh, Ta-Ir, Ta-Ru, Ta-Os, Ta-Re, Ta-W, and Ta-Pd alloy thin films with a Ta content of 30 to 70 wt% to finish the dies. Also, dies comprising a tungsten (W) middle layer were similarly formed. Fig. 7 shows the die comprising WC cemented carbides base material 63, Re middle layer 62 and Ta-Ir alloy thin film 61 with the Ta content of 50 wt%. The dies were then placed in the press shown in Fig. 2. Glass 24 selected from Schwer-Flint glass, SK-14 glass, aluminum zinc silicate glass and borosilicate glass, which had been processed to a sphere with radius 5 mm, was placed on lower half die 25, on which upper half die 23 was then placed. Glass 24 was press-molded at a suitable temperature, such as 600 °C for Schwer-Flint glass, 700 °C for SK-14 glass, 800 °C for aluminum zinc silicate glass and 900 °C for borosilicate glass. Press-moldings were conducted 1000 times in the same manner as in Example 1 using each glass. Afterward, the dies were observed by AES analysis to examine diffusion of Co on their surfaces. At the same time, the roughness of the die surface (RMS value, nm) was measured to judge the accuracy of the dies. Tables 10-1 through 10-6 show the results. On the other hand, comparative embodiments were performed to similarly judge the accuracy of the dies comprising WC cemented carbides and a Ta-Ir alloy thin film with a Ta content of 30 to 70 wt% used in Example 1. Table 9 shows the results. Sample No. Film composition Condition of die surface after 1000 press-moldings (RMS value, nm) 600 °C 700 °C 800 °C 900 °C 134 Ta(30)-Ir 1.43 2.04 7.14 20.17 135 Ta(50)-Ir 1.63 2.36 9.11 22.93 136 Ta(70)-Ir 1.61 2.29 8.53 21.64 Sample No. Film composition Middle layer: Re Condition of die surface after 1000 press-moldings (RMS value, nm) 600 °C 700 °C 800 °C 900 °C 137 Ta(30)-Pt 1.04 1.08 1.14 1.18 138 Ta(30)-Rh 1.03 1.06 1.08 1.18 139 Ta(30)-Ir 1.07 1.09 1.16 1.20 140 Ta(30)-Ru 1.05 1.08 1.16 1.24 141 Ta(30)-Os 1.03 1.08 1.14 1.26 142 Ta(30)-Re 1.05 1.09 1.18 1.25 143 Ta(30)-W 1.06 1.09 1.13 1.22 144 Ta(30)-Pd 1.05 1.08 1.17 1.28 Sample No. Film composition Middle layer: Re Condition of die surface after 1000 press-moldings (RMS value, nm) 600 °C 700 °C 800 °C 900 °C 145 Ta(50)-Pt 1.04 1.09 1.17 1.20 146 Ta(50)-Rh 1.06 1.08 1.17 1.28 147 Ta(50)-Ir 1.05 1.08 1.13 1.21 148 Ta(50)-Ru 1.07 1.12 1.15 1.20 149 Ta(50)-Os 1.04 1.09 1.15 1.18 150 Ta(50)-Re 1.06 1.12 1.16 1.22 151 Ta(50)-W 1.06 1.09 1.14 1.26 152 Ta(50)-Pd 1.08 1.14 1.19 1.26 Sample No. Film composition Middle layer: Re Condition of die surface after 1000 press-moldings (RMS value, nm) 600 °C 700 °C 800 °C 900 °C 153 Ta(70)-Pt 1.06 1.09 1.15 1.27 154 Ta(70)-Rh 1.04 1.08 1.11 1.23 155 Ta(70)-Ir 1.07 1.16 1.19 1.26 156 Ta(70)-Ru 1.03 1.07 1.13 1.21 157 Ta(70)-Os 1.08 1.12 1.16 1.24 158 Ta(70)-Re 1.06 1.09 1.17 1.29 159 Ta(70)-W 1.09 1.13 1.18 1.27 160 Ta(70)-Pd 1.07 1.13 1.16 1.25 Sample No. Film composition Middle layer: W Condition of die surface after 1000 press-moldings (RMS value, nm) 600 °C 700 °C 800 °C 900 °C 161 Ta(30)-Pt 1.05 1.07 1.10 1.19 162 Ta(30)-Rh 1.03 1.09 1.18 1.21 163 Ta(30)-Ir 1.05 1.08 1.11 1.25 164 Ta(30)-Ru 1.04 1.09 1.20 1.28 165 Ta(30)-Os 1.06 1.13 1.20 1.28 166 Ta(30)-Re 1.02 1.04 1.13 1.25 167 Ta(30)-W 1.04 1.07 1.13 1.24 168 Ta(30)-Pd 1.06 1.11 1.19 1.27 Sample No. Film composition Middle layer: W Condition of die surface after 1000 press-moldings (RMS value, nm) 600 °C 700 °C 800 °C 900 °C 169 Ta(50)-Pt 1.03 1.08 1.17 1.26 170 Ta(50)-Rh 1.05 1.09 1.18 1.27 171 Ta(50)-Ir 1.01 1.07 1.14 1.23 172 Ta(50)-Ru 1.03 1.08 1.16 1.27 173 Ta(50)-Os 1.05 1.09 1.12 1.22 174 Ta(50)-Re 1.03 1.08 1.13 1.23 175 Ta(50)-W 1.07 1.10 1.15 1.24 176 Ta(50)-Pd 1.05 1.08 1.13 1.20 Sample No. Film composition Middle layer: W Condition of die surface after 1000 press-moldings (RMS value, nm) 600 °C 700 °C 800 °C 900 °C 177 Ta(70)-Pt 1.04 1.09 1.13 1.21 178 Ta(70)-Rh 1.03 1.09 1.18 1.25 179 Ta(70)-Ir 1.06 1.12 1.21 1.30 180 Ta(70)-Ru 1.04 1.08 1.13 1.22 181 Ta(70)-Os 1.02 1.06 1.14 1.20 182 Ta(70)-Re 1.05 1.09 1.17 1.25 183 Ta(70)-W 1.03 1.08 1.16 1.24 184 Ta(70)-Pd 1.07 1.09 1.13 1.21 Diffusion of Co on the surfaces of the dies was also examined by AES analysis. After 1000 press-moldings at 800 °C, Co was detected on the dies of sample Nos. 134 to 136, which had no middle layer between the base material and the Ta alloy thin film, the surfaces of the dies became rough. After 1000 press-moldings at 900 °C, more Co was detected, and the die surfaces got very rough. In contrast, the dies of sample Nos. 137 to 184, which had the Re or W middle layer between the base material and the Ta alloy thin film, were free from Co diffusion even after 1000 press-moldings at 900 °C, and they kept almost the same surface as that just after sputtering. In other words, the Re or W middle layer prevents a binder metal in the base material, such as Co, from diffusing into the surfaces due to heat. Therefore, the press-molding die can mass-produce very fine higher-melting glass optical elements without deteriorating. Though Example 5 used the WC cemented carbides base material, other base materials formed of a cermet comprising TiN or TiC achieve similar results. The invention may be embodied in other specific forms without departing from the scope of the appended claims.

Claims: A die for press-molding a glass optical element comprising: a base material (12,33,43,53,63) having a surface to press-mold glass; and a tantalum (Ta)-containing alloy thin layer (11,31,41,51,61) on said surface, said base material (12,33,43,53,63) having heat-resistance and strength enough to withstand press-molding, characterized in that the tantalum (Ta)-containing alloy consists of tantalum and one element selected from the group consisting of platinum, rhodium, iridium, ruthenium, osmium, rhenium, tungsten and palladium. The die according to claim 1, wherein the Ta content of said Ta-containing alloy thin layer (11,31,41,51,61) is 5 to 95 wt%. The die according to claim 1 or 2, wherein the Ta-containing alloy thin layer (11,31,41,51,61) has a thickness of 1 to 5 µm. The die according to any of claims 1 to 3, wherein said base material (12,33,43,53,63) comprises at least one material selected from the group consisting of cemented carbides comprising tungsten carbide (WC) as its principal component, a cermet comprising titanium carbide (TiC) as its principal component, a cermet comprising titanium nitride (TiN) as its principal component and a tungsten carbide (WC) sintered body. The die according to any of claims 1 to 4, further comprising a middle layer (32,42,52,62) between said base material (12,33,43,53,63) and said Ta-containing alloy thin layer (11,31,41,51,61) for strengthening adhesion of said base material (12,33,43,53,63) to said Ta-containing alloy thin layer (11,31,41,51,61), wherein said middle layer (32,42,52,62) comprises at least one material selected from the group consisting of tantalum carbide (TaC), tantalum nitride (TaN) and tantalum oxide (Ta 2 O 5 ), the composition of this middle layer being dependent on the principal component of the base material. The die according to claim 5, wherein said base material (12,33,43,53,63) is a cemented carbide comprising WC as its principal component, a cermet comprising TiC as its principal component, or a WC sintered body and said middle layer (32,42,52,62) comprises tantalum carbide (TaC). The die according to claim 5, wherein said base material (12,33,43,53,63) is a cermet comprising TiN as its principal component and said middle layer (32,42,52,62) comprises tantalum nitride (TaN). The die according to claim 5, wherein said base material (12,33,43,53,63) is an oxide and said middle layer (32,42,52,62) comprises tantalum oxide (Ta 2 O 5 ). The die according to any of claims 1 to 4, wherein said base material (12,33,43,53,63) comprises a tungsten carbide sintered body , and wherein a middle layer (32,42,52,62) is formed between said base material (12,33,43,53,63) and said Ta-containing alloy thin layer (11,31,41,51,61) and said middle layer (32,42,52,62) is a heat-diffusion preventive layer to prevent a metal in said base material (12,33,43,53,63) from diffusing into said Ta-containing alloy thin layer (11,31,41,51,61) due to heat. The die according to claim 9, wherein said heat-diffusion preventive layer (32,42,52,62) comprises at least one material selected from the group consisting of rhenium and tungsten. The die according to any of claims 5 to 10, wherein said middle layer (32,42,52,62) has a thickness of 1 to 3 µm.

Inventors: AOKI MASAKI, KASHIWAGI YOSHINARI, UMETANI MAKOTO, AOKI, MASAKI, KASHIWAGI, YOSHINARI, UMETANI, MAKOTO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: C03B11
IPC codes: C03B11