JPH08133762A - Optical element forming die and its production - Google Patents

Abstract

PURPOSE: To improve the die releasability and durability to the tensile stress when released from the die by forming a Cr nitride film having a specified thickness on the optical element forming face formed by press-forming a glass. CONSTITUTION: A cemented carbide consisting of WC-Ni-Cr is used as the material. A forming face 2 is mirror-finished on the upper end face of the cylindrical part of a die base 1 consisting of the integrated large-diameter disk and small-diameter cylinder on the disk, the peripheral part of the disk forms a step 3 to be used when the die is mounted in a forming machine. The position of the die in the shifting direction is controlled by the side face, and the inclination of the die to the center axis is controlled by the bottom face 5. The die base 1 with the optical element forming face 2 as a concave face of 15mm curvature and having 8mm outer diameter and finished to >=0.6μm surface roughness Rmax is cleaned with surfactant, pure water, etc., and then placed in a vacuum chamber, a Cr-N coating film 6 having >=3μm thickness is formed by ion plating for ionizing metallic Cr by an arc discharge, and the obtained forming die is kept at 600 deg.C in the atmosphere for 2hr to form Cr2 O3 on the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element molding die used for producing an optical element by press-molding heat-softened glass, and more specifically, a molding surface for obtaining a good releasability. The present invention relates to an optical element molding die having a coating formed thereon.

[0002]

2. Description of the Related Art Conventionally, as this type of molding die, for example, one disclosed in Japanese Patent Laid-Open No. 2222131/1990 is known. This is a molding die whose peelability to glass is improved by coating the molding surface with a compound containing Cr and nitrogen as main components. An intermediate layer made of a material having a linear expansion coefficient between the material forming the mold base material and the material forming the coating film is interposed at the interface between the coating film and the mold base material. The thermal stress generated between them is relaxed to prevent peeling of the coating.

[0003]

However, in the above-mentioned prior art, since the thickness of the coating film is as thin as 0.3 μm as described in the examples of the above-mentioned publications, the following strength problem occurs. there were.

Tensile stress acts on the coating when the molded product is released from the mold, but with a film thickness of 0.3 μm, the stress cannot be countered and the coating may be damaged.

When a coating film is formed on the surface of a molding die base material, if the surface of the base material has minute stains or defects, the coating film will float from the base material. It is difficult to thoroughly clean the dirt and make the surface defect-free. Whether or not film peeling occurs when a releasing force acts on such a floating portion depends on the bond strength of the coating film itself, but since the coating film is thin, the strength is small and peeling easily occurs.

For the above-mentioned reasons, although the above-mentioned conventional technique is provided with the intermediate layer in order to prevent the peeling of the coating film, it was not possible to obtain sufficiently satisfactory durability.

The present invention has been made in view of the above-mentioned problems, and an optical element molding die having good mold releasability and having sufficient durability against tensile stress at the time of mold release, and its manufacture. The purpose is to provide a method.

[0008]

In order to achieve the above object, the optical element molding die of the present invention according to claim 1 is an optical element used for manufacturing an optical element by press-molding glass softened by heating. The molding die is characterized in that a Cr nitride film having a thickness of 3 μm or more is formed on at least the molding surface of the optical element.

In this case, it is preferable that Cr ₂ O ₃ is formed on the surface layer portion of the Cr nitride film as described in claim 2.

When manufacturing such an optical element molding die, as described in claim 3, the Cr nitride film may be formed by an ion plating method in which metal Cr is ionized by arc discharge.

[0011]

In the optical element molding die according to the first aspect of the present invention having the above-mentioned constitution, in the optical element molding die according to claim 1, a coating of Cr nitride having high hardness, heat resistance and oxidation resistance, and excellent releasability is formed. Since the optical element molding surface of the base material is formed with a thickness of 3 μm or more, it has good mold releasability at the time of molding, and the surface of the molding base material coated with the coating film has defects or residual cleaning liquid. However, since the coating itself has a large bonding force, peeling does not occur.

According to a second aspect, Cr is formed on the surface layer of the molding surface.
Cr ₂ O, whose standard free energy of formation is smaller than that of nitride
_{Since 3} is formed, even if the softened glass is pressed, no fusion or reaction occurs, and good mold releasability is obtained.

According to the third aspect of the present invention, since the metal is ionized by arc discharge, a Cr nitride film having an extremely high ionization rate and an extremely good crystallinity is formed.

[0014]

Embodiments of the optical element molding die according to the present invention will be described below with reference to the accompanying drawings.

(Embodiment 1) FIG. 1 is a sectional view showing the structure of an optical element molding die according to Embodiment 1 of the present invention.

(Structure) In the figure, the mold base 1 is WC-N.
It is made of a cemented carbide made of i-Cr and is integrally formed into a shape in which a small-diameter cylinder is placed on a large-diameter disk, and a desired lens shape is transferred to the upper end surface of the cylindrical portion. The optical element molding surface 2 having the above shape is mirror-finished, and the peripheral portion of the large-diameter disk serves as a step portion 3 for mounting on a molding machine (not shown). The side surface 4 is a surface that regulates the shift direction position of the molding die, and the bottom surface 5 is a surface that regulates the inclination of the molding die with respect to the central axis. In this embodiment, the optical element molding surface 2 is a concave surface having a curvature of 15 mm, the outer diameter is φ8 mm, and the surface roughness is R.
Processed to max = 0.06 μm or less.

The mold base 1 thus processed is washed with acetone, a surfactant, pure water, etc., and then placed in a vacuum chamber. After that, a Cr—N coating film 6 was formed by an ion beam sputtering method. The conditions at this time are shown in Table 1.

[0018]

[Table 1]

In this embodiment, the film forming conditions were set as follows for a film of Cr-N having good crystallinity.

Gas pressure (mixed gas of Ar and N ₂ ) Ar: 1.0 (× 10 ^-2 (Pa)) N ₂ : 7.0 (× 10 ^-2 (Pa)) Ion beam acceleration voltage: 0. 9 (KV) Anode current: 3.0 (A)

The film formation time was 5 hours and the film thickness was 5 μm. As for the crystallinity, a crystal peak of CrN appears like the analysis result by the X-ray diffraction method in FIG.

The surface roughness of the surface coated with the Cr-N film 6 was the same as that of the optical element molding surface 2.

The Cr-N film 6 covers not only the optical element molding surface 2 but also the surface other than the optical element molding surface 2 as shown in FIG. The mold obtained in this manner was used in the atmosphere at 60
Hold at 0 ° C. for 2 hours. As a result, Cr ₂ O ₃ is formed as shown in the analysis result by X-ray diffraction in FIG. This C
r ₂ O ₃ is formed on the outermost surface of the film. The surface roughness of the molding surface 7 at this time was Rmax = 0.08 µm.

(Operation) Since the optical element molding die having the above-described structure has Cr ₂ O ₃ formed on the surface thereof, it does not easily get wet with glass and is likely to be seized even if press-molded on a softened glass material. There is no such thing. Cr-N has a high hardness, and in the mold of this example, it was 1800 kgf / mm ² under a load of 10 g as measured by a micro Vickers hardness meter. Since it has such a high hardness surface, the molding surface 7 is not damaged even by a pressing load when the glass is solidified at the time of molding, and when the foreign matter such as metal powder is sandwiched and pressed at the time of pressing. However, no indentation was formed on the molding surface 7, and even if the optical element was continuously molded, it was possible to manufacture an optical element with good appearance quality.

Further, since the film thickness is 5 μm, the occurrence of film peeling can be suppressed. In this embodiment, the thickness of the Cr- film is set to 1 μm.
A comparative test of film peeling with an optical element molding die coated with the N film 6 was carried out in the actual molding of the optical element. Molded glass material is B
This glass material was heated to 770 ° C. with SL7 (manufactured by Ohara Co., Ltd.) and then molded with a pair of molding dies at a pressing pressure of 4.2 kgf / mm ² . The occurrence of film peeling was confirmed by observing the Cr-N film attached to the molded optical element with a stereoscopic microscope. The test results are shown in Table 2.

[0026]

[Table 2]

Here, No. in Table 2 is a number given to each of the tested optical element molding dies because each of them has three molds. As is clear from the results in Table 2, it is about 3 in the mold with a film thickness of 5 μm.
The film peeling occurs in 0000 shots, whereas the maximum film thickness is 7800 shots in the mold having a film thickness of 1 μm, and the film peels. Therefore, the optical element molding die of this embodiment has a long life and stable quality.

(Effects) As described above, the optical element molding die of this embodiment has a long service life against film peeling and good appearance quality.

In this embodiment, the mold base 1 is made of an alloy other than cemented carbide, cermet such as sialon, ceramics such as SiC sintered body, Cr-C sintered body and AlN sintered body. Is obtained. In this case, if the ceramic contains additives such as TiO ₂ , Y ₂ O ₃ and ZrO ₂ , heat resistance and toughness are improved.

Further, even if the Cr-N film is only CrN,
And Cr ₂ N may both be contained, and further Cr may be contained therein. In the present embodiment, Cr ₂ O ₃ is formed on the surface after heating in the atmosphere after forming the Cr-N film.
However, if it is chromium oxide, another crystal such as Cr ₅ O ₁₂ may be mixed.

In this embodiment, the Cr-N film 6 is formed on the entire surface of the molding die base material 1. However, if the material of the molding die base material 1 has good heat and oxidation resistance, the optical element molding surface 2 is formed. Alternatively, the film may be formed on only a part of the surface other than the optical element molding surface 2. Ceramics such as SiC and AlN and cermets are examples of materials having good heat and oxidation resistance. Furthermore C
Although the film thickness of the r-N film 6 is 5 μm, it may be 3 μm or more on the optical element molding surface 2. In the ion beam sputtering method of this embodiment, the film forming rate is about 8 nm / min, so that the optical element molding die Considering productivity, the film thickness is preferably 3 μm to 5 μm.

Further, in the present embodiment, the Cr-N film is formed by the ion beam sputtering method, but other PVD method may be used. For example, the magnetron sputtering method, the ion plating method or the hollow cathode method may be used. The same effect as that of the ion beam sputtering method can be obtained.

Example 2 (Structure) The structure of the mold base 1 of the optical element molding mold of Example 2 of the present invention is the same as that shown in FIG. In this embodiment, the Cr-N film 6 is formed by an ion plating method (arc ion plating method) in which a metal is ionized by arc discharge. This method is as follows. As shown in FIG. 4, the inside of the vacuum chamber 8 is exhausted from the exhaust port 9 by a vacuum pump (not shown). In this example, the vacuum was evacuated to 8.0 × 10 ⁻⁴ (Pa). The higher the degree of vacuum, the better, but 1.0 × 10 ^{-3 in} consideration of the exhaust time.
(Pa) It should be below. The mold base 1 is a turntable 1
It is set above 0 and is heated by a heater (not shown). The heating temperature was 600 ° C. The turntable 10 can be rotated by a drive unit (not shown). The material of the mold base material 1 used in this embodiment is the same as that of the first embodiment.

In this state, a current (arc current) of 150 (A) is made to flow from the arc power source 12 to the evaporation source 14 made of Cr for discharging. At the same time, a voltage (bias voltage) of −700 V was applied to the mold base 1 via the turntable 10 by the bias power supply 13. By this process, the evaporation source 14 to C
r is ionized and evaporated, and the mold base 1 is bombarded with Cr ions 21 for 60 seconds. After that, N ₂ gas was introduced from the inlet 11 while adjusting the flow rate by a valve (not shown) so that the degree of vacuum in the vacuum chamber 8 was kept constant at 1.0 (Pa). Here, a current of 100 (A) is caused to flow from the arc power source 12 to the evaporation source 14 made of Cr to be discharged. At the same time, the bias power supply 13 turns the turntable 10
A bias voltage of −50 V was applied to the mold base 1 via the.
This state was continued for 80 minutes to form the Cr-N film 6. The film thickness was 6 μm. The mold thus obtained was kept at 600 ° C. for 2 hours in the atmosphere to form Cr ₂ O ₃ on the outermost surface.

(Operation) According to the above-mentioned arc ion plating method, in the first bombarding with Cr ions 21, the arc current is concentrated on the arc spot of the evaporation source made of Cr, and the energy thereof causes the Cr to be ionized and evaporated. The surface of the mold base 1 is bombarded with Cr ions 21 by the bias voltage applied to the mold base 1. As a result, the surface of the mold base 1 is washed and the thin oxide layer formed on the surface is removed in some cases, so that the adhesion of the film can be improved. In the film forming process performed thereafter, the N ₂ gas 22 is also ionized, and the bias voltage is set to −
Since it is set to 50 V, Cr ions 21 and N (nitrogen) ions 23 adhere to the surface of the mold base material to form a Cr-N film. The Cr-N film 6 thus formed showed almost the same crystal peak as in Example 1 when analyzed by X-ray diffraction.

Further, a composition analysis by ESCA revealed that the composition ratio (the number of elements) of Cr and N (nitrogen) at the depth of 0.1 μm from the surface was Cr: N = 1: 0.88, and most of Cr was nitrided. You are doing it. The hardness of the film was also 1900 kgf / mm ² under a load of 10 g as measured by a micro Vickers hardness meter as in Example 1. This action is similar to that of the first embodiment.

The optical element molding die thus manufactured was subjected to the same test as in Example 1 by actually molding an optical element. As a result, the number of moldings in which film peeling occurred was 45,000 shots. This is because the adhesion of the Cr—N film 6 is improved by the cleaning effect of the ion bombardment before film formation in this example. As a comparative example, when the ion bombardment step was omitted, the number of moldings in which film peeling occurred was 30,000.
The shots had almost the same level of durability as the Cr-N film of Example 1.

(Effect) In this embodiment, since the Cr-N film was formed by the arc ion plating method, C
Cr-N with an element number ratio in which r and N (nitrogen) are almost 1: 1
Since it becomes a film and a substantially perfect CrN polycrystal film can be formed, it is possible to provide an optical element molding die having a high hardness and high durability, and to prevent film peeling due to a bombardment before film formation. It is possible to provide a highly durable optical element molding die.

In this embodiment, the mold base material 1 can be made of the same material as that of the embodiment 1 except the cemented carbide.

Further, the Cr-N film 6 may be made of CrN alone.
Both N and Cr ₂ N may be contained, and further Cr may be contained therein. In the present embodiment, Cr ₂ O is formed on the surface after heating in the atmosphere after forming the Cr-N film.
_{Although 3} was formed, if it is chromium oxide, another crystal such as Cr ₅ O ₇ may be mixed.

In the present embodiment, the Cr-N film 6 is formed on the entire surface of the molding die base material 1. However, if the material of the molding die base material 1 has good heat resistance and oxidation resistance, the optical element molding surface is formed. 2 may be used, or a film may be formed on a part of the surface other than the optical element molding surface 2. SiC and AlN are good materials for heat and oxidation resistance
Such as ceramics and cermet.

Further, in the present embodiment, the respective conditions of the arc ion plating method were carried out under the above conditions. However, if the respective conditions are in the following ranges, the performance as the optical element molding die is satisfied.

Arc current: 70 to 200 (A) (during bombarding) Arc current: 30 to 200 (A) (during film formation) Bias voltage: -600 to -1000 (V) (during bombarding) Bias voltage: -10 ~ -600 (V) (during film formation) N ₂ gas pressure: 6.0 x 10 ^{-3 to} 6.0 (Pa) (during film formation)

The particularly preferable range is as follows. This is a condition that the hardness of the film is relatively high and the strength is high during film formation, as long as the surface shape and roughness of the die base material are not deteriorated during bombardment.

Arc current: 70 to 100 (A) (at bombarding) Arc current: 30 to 100 (A) (at film forming) Bias voltage: -700 to -800 (V) (at bombarding) Bias voltage: -30 To -300 (V) (during film formation) N ₂ gas pressure: 0.1 to 6.0 (Pa) (during film formation)

(Embodiment 3) (Structure) FIG. 5 shows a sectional view of an optical element molding die of Embodiment 3 of the present invention. The mold base material 15 is a sintered body containing Cr ₃ O ₂ as a main component and has an average grain size of 3 μm. After being processed into the same shape as in Example 1, the surface roughness of the molded surface is Rmax = 0. 0
The mirror surface processing was performed until it became 5 μm. Cr- was formed on the formed surface by the arc ion plating method of Example 2.
The N film 17 was formed to a thickness of 60 μm. The film formation time is the same as in Example 2.
Was 13 hours and 20 minutes. Since the surface coated with the Cr-N film had a surface roughness of Rmax = 0.16 µm, it was ground with a diamond paste of # 14000 to have a surface roughness of 0.05 µm. In this embodiment, the mold substrate 1
The bottom side surface 18 and the bottom surface 19 of the No. 5 mask the Cr-N film 17 so that the Cr-N film 17 is not covered with the Cr-N film 1.
7 was deposited.

(Operation) In the case of the optical element molding die having the above-mentioned structure, in the case of the mold base material 15 such as a sintered body containing Cr ₃ O ₂ as a main component, at the time of releasing from the mold after molding the softened glass. Grains may fall off. This makes the Cr-N film 17 3 μ
When the coating is performed with a film thickness of m or less, since the bonding force of the film is weak and the part falls off together with the Cr-N film due to the effect of the particles falling off, there is a hole in that part, and when molding with such a molding surface 20 That is, an optical element having a poor appearance is manufactured. However, the Cr-N film 17 of this embodiment has a thickness of 60 μm.
Since the bonding force of the Cr-N film 17 is strong by the thickness of the Cr-N film 17, the particles of the die base material do not fall off.

(Effect) The effect of the present embodiment is to produce an optical element having a good appearance without causing particle dropout even when the mold base is made of a material obtained by sintering powder such as a sintered body. be able to.

In this embodiment, the mold base material 15 is made of Cr ₃ O ₂
However, other ceramic materials such as those containing AlN as a main component (Y
₂ O ₃ , CaO ₂ , YF ₃ , CaCO and other additives may be included), ZrO ₂ as a main component or Al
Similar effects can be obtained with ceramics such as those containing ₂ O ₃ as the main component or those containing SiC as the main component, or cermets such as sialon. Further, basically the same action and effect can be obtained if the film thickness of the Cr-N film 17 is 3 μm or more. However, in the case of a film thickness of about 3 μm, it is preferable not to polish since the Cr—N film 17 becomes thin if the molding surface is polished after the film formation.

[0050]

As described above, the optical element molding die of the present invention has the following effects.

According to the first aspect of the present invention, since the molding surface is formed of the coating film made of Cr-N, which has a high hardness and excellent heat resistance, the optical element molding die has a long life when the optical element is repeatedly molded. Is obtained. Further, since the film thickness is 3 μm or more, peeling of the film can be prevented, and appearance defects of the optical element due to the particles falling off the mold base material can be prevented.

According to the second aspect, since chromium oxide is formed on the surface of the molding surface, the releasability after molding can be further improved and seizure can be prevented.

According to the third aspect, since the Cr-N film is formed by the arc ion plating method, a Cr-N film having an element number ratio of Cr and N nitrogen close to about 1: 1 is formed, and a substantially complete CrN film is formed. Since a crystalline film can be formed, it is possible to provide an optical element molding die having high hardness and high durability, and an optical element molding die having high durability against film peeling due to a bombardment before film formation. Can be provided.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view schematically showing an optical element molding die according to Example 1 of the present invention.

FIG. 2 is a graph showing the result of analysis by an X-ray diffraction method of the state immediately after film formation of the optical element molding die of Example 1.

FIG. 3 is a graph showing the results of analysis of the optical element molding die of Example 1 after oxidation by an X-ray diffraction method.

FIG. 4 is a cross-sectional view showing a vacuum chamber used for manufacturing an optical element molding die of Example 2.

FIG. 5 is a vertical sectional view schematically showing an optical element molding die according to Example 3 of the present invention.

[Explanation of symbols]

1 type base material 2 optical element molding surface 3 step part 4 bottom side surface 5 bottom surface 6 Cr-N film 7 molding surface 8 vacuum chamber 9 exhaust port 10 turntable 11 introduction port 12 arc power supply 13 bias power supply 14 evaporation source 15 type base material 16 Formed surface 17 Cr-N film 18 Bottom side surface 19 Bottom surface 20 Formed surface 21 Cr ion 22 N ₂ gas 23 N ion

Claims (3)

[Claims] 1. An optical element molding die used for press-molding heat-softened glass to manufacture an optical element, wherein Cr has a thickness of at least 3 μm on at least the optical element molding surface.
An optical element molding die having a nitride film formed thereon. 2. The surface layer of the Cr nitride coating is Cr ₂ O.
_3. The optical element molding die according to claim 1, wherein ₃ is formed. 3. When manufacturing the optical element molding die according to claim 1, the Cr nitride film is formed by an ion plating method in which metal Cr is ionized by arc discharge. Mold manufacturing method.