Glass molding device and mold cleaning method

Abstract

This glass molding device (10) is provided with: a molding chamber (26a); an upper mold (15) and a lower mold (14) that are arranged vertically facing each other within the molding chamber; an infrared lamp (28) that heats the upper mold, the lower mold, and a glass material placed between the upper mold and the lower mold; a jack (21) that pressurizes and molds the glass material by moving the lower mold in a direction in which the lower mold is pressed against the upper mold; and a high-voltage pulse power supply (40) that generates plasma by applying a high-voltage pulse to the space between a metal plate (45) inserted between the upper mold and the lower mold and the upper mold and the space between the metal plate and the lower mold so that the metal plate has a higher potential than the upper mold and the lower mold, thereby cleaning the upper mold and the lower mold by the plasma, with an inert gas supplied to the interior of the molding chamber while the glass material is not being molded.

Description

Glass molding device and mold cleaning method

[0001] The present invention relates to a glass molding apparatus and mold cleaning method for molding glass products having complex shapes such as aspherical glass lenses by pressing a glass material with opposing molds.

[0002] Conventionally, a glass forming device is known in which a glass material is placed between molds installed at the ends of a fixed shaft and a moving shaft arranged opposite each other, the glass material is heated, and the moving shaft is pressed in the direction of the fixed shaft, thereby forcing the glass material against the molds and forming it into a predetermined shape (for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2005-306693

[0004] In such conventional glass molding devices, the mold surface becomes contaminated with each molding cycle, reducing mold releasability and sometimes causing fusion between the glass material and the mold (see FIG. 2 for details). When such fusion occurs on a large scale, the quality of the molded product cannot be maintained, and the mold must be replaced. Furthermore, when replacing the mold, the glass molding device must be stopped, and when mass production is resumed, the glass molding device must be operated in dummy mode until it reaches the appropriate temperature, resulting in reduced productivity. For these reasons, there has been a demand for a glass molding device that can remove the contaminants without stopping the device.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide a glass molding apparatus and a mold cleaning method that are capable of cleaning a mold without stopping the apparatus, even after repeated molding.

[0006] In order to solve the above-mentioned problems and achieve the object, the glass forming device of the present invention is characterized by comprising: a forming chamber; a fixed mold and a movable mold arranged opposite each other above and below inside the forming chamber and formed into a predetermined shape; a movable shaft that supports the movable mold so that it can move relative to the fixed mold; heating means that heats the fixed mold, the movable mold, and a glass material placed between the fixed mold and the movable mold; pressure forming means that pressurizes the glass material with the movable mold and the fixed mold by moving the movable shaft in a direction that presses the movable mold against the fixed mold; and cleaning means that, when the glass material is not being formed, generates plasma by applying a high-voltage pulse to a space between the fixed mold and the movable mold and an electrode inserted between the separated fixed mold and the movable mold, and to the space between the electrode and the movable mold, while supplying an inert gas inside the forming chamber, and then cleans the fixed mold and the movable mold with the plasma.

[0007] Furthermore, the present invention provides a mold cleaning method for cleaning the fixed mold and the movable mold in a glass molding apparatus comprising: a molding chamber; a fixed mold and a movable mold arranged opposite each other inside the molding chamber and formed into a predetermined shape; a movable shaft that supports the movable mold so that it can move relative to the fixed mold; heating means that heats the glass material placed between the fixed mold and the movable mold; and pressure molding means that moves the movable shaft in a direction that presses the movable mold against the fixed mold, thereby pressurizing the glass material placed between the movable mold and the fixed mold at a predetermined pressure for a predetermined time, the mold cleaning method being characterized in that an inert gas is supplied into the molding chamber, and a high-voltage pulse is applied to the space between the fixed mold and an electrode inserted between the separated fixed mold and the movable mold, and to the space between the electrode and the movable mold, so that the electrode has a higher potential than the fixed mold and the movable mold, thereby generating plasma, and the fixed mold and the movable mold are cleaned by the plasma.

[0008] The glass forming device according to the present invention has the effect of being able to regenerate a deteriorated mold that has been repeatedly used for forming with minimal downtime.

[0009] FIG. 1 is a diagram showing an example of a mold structure used in molding a glass material. FIG. 2 is a diagram explaining the mechanism by which fusion between a mold and a glass material occurs. FIG. 3 is a diagram showing an example of a schematic structure for realizing a glass molding function provided in a glass molding apparatus. FIG. 4 is a diagram showing an example of an installation structure for a lower mold provided in a glass molding apparatus. FIG. 5 is a diagram showing an example of a schematic structure for realizing a mold cleaning function provided in a glass molding apparatus. FIG. 6 is a diagram showing an example of the configuration of an exhaust system provided in a glass molding apparatus. FIG. 7 is a diagram showing an example of an equivalent circuit of a plasma generation circuit provided in a glass molding apparatus of an embodiment. FIG. 8 is a diagram showing an example of a voltage waveform and a current waveform applied between an upper mold and a lower mold and a metal plate. FIG. 9 is a diagram showing an example of a state between electrodes when plasma is generated. FIG. 10 is a diagram showing an example of an equivalent circuit between electrodes when plasma is generated. FIG. 11 is a diagram showing an example of a circuit in which an ammeter, a voltmeter, and a control device are connected to the equivalent circuit of a plasma generation circuit provided in a glass molding apparatus of an embodiment.

[0010] Hereinafter, embodiments of a molding apparatus according to the present disclosure will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are replaceable and easily conceivable by those skilled in the art, or those that are substantially the same.

[0011] (Embodiment) An embodiment of the present disclosure relates to a glass molding device 10 that uses a superhard mold used to mold optical elements having complex surface shapes, such as aspherical glass lenses.

[0012] (Mold Deterioration Process) The mechanism by which fusion occurs between a mold 12 (also called a core) used in a glass molding device 10 and a glass material will be described using Figures 1 and 2. Figure 1 is a diagram showing an example of the structure of a mold used in molding a glass material. Figure 2 is a diagram explaining the mechanism by which fusion occurs between a mold and a glass material.

[0013] As shown in FIG. 1, the mold 12 has a structure in which an intermediate layer 12b and a mold release film 12c are formed on the surface of a superhard material 12a.

[0014] Molding of glass materials is carried out at higher temperatures than injection molding, for example, up to 750°C for ordinary optical glass and 1500°C for quartz glass. Furthermore, during pressing, the mold is subjected to a pressure of 200 (N / cm ２ ) ~ 220 (N / cm ２ ) is applied. Therefore, a super-hard material 12a having high mechanical strength at high temperatures is used for the mold base material. The super-hard material 12a is an alloy that has very high hardness and loses less hardness at high temperatures compared to other metals. The super-hard material 12a is manufactured, for example, by sintering WC particles 12d (tungsten carbide), which are super-hard particles, with a metal such as Ni, Ti, Cr, or Co as a binder 12e.

[0015] The intermediate layer 12b is a layer containing Cr, Ni, etc., and has a thickness of about 30 nm, which is formed on the surface of the super-hard material 12a. The intermediate layer 12b is a layer provided to improve the adhesion between the super-hard material 12a and the release film 12c, which have different thermal expansion coefficients. The thermal expansion coefficient of the intermediate layer 12b is approximately intermediate between that of the super-hard material 12a and the release film 12c.

[0016] The mold release film 12c is a layer made of Pt-Ir or the like, with a thickness of, for example, about 600 (nm), to prevent reaction with the glass material. Pt (platinum) is well known as a material that is non-reactive with glass, while Ir (iridium) is highly heat-resistant and durable even at high temperatures, and is used in parts exposed to high temperatures, such as jet engines. In other words, the mold release film 12c is heat-resistant and has low reactivity with the glass material, making it a material that is unlikely to fuse with the glass material (having excellent mold release properties).

[0017] However, even with such a mold 12, it is known that the glass material gradually changes in quality as the molding cycle is repeated, the mold release properties deteriorate, and eventually the glass and the mold fuse together.

[0018] As the molding cycle of the glass material is repeated, the temperature of the mold 12 is repeatedly raised and lowered, and as a result, as shown in the left diagram of Figure 2, tungsten (W), a component of the superhard material 12a, may cross the intermediate layer 12b and the mold release film 12c, diffuse to the surface of the mold release film 12c, and become exposed. Similarly, chromium (Cr), etc., a component of the intermediate layer 12b, may cross the mold release film 12c and diffuse to the surface of the mold release film 12c. The exposed tungsten, chromium, etc. then promotes fusion between the glass material and the mold 12.

[0019] More specifically, the Ir in the Pt-Ir surface layer is oxidized and evaporated, causing a shortage of Ir in the film, and the Pt-Ir, which is originally in a solid solution state and has a uniform structure (uniform density), becomes polycrystallized and separates into high-density Pt-rich crystal grains and low-density grain boundaries between them. Because the density of these grain boundaries is low, the chromium constituting the intermediate layer 12b in FIG. 2 and the tungsten constituting the superhard material 12a in the same figure diffuse along the grain boundaries and appear on the surface of the mold release film 12c, and these are absorbed by the moisture 13c (H ２ O). As a result, chromium oxide 13a and tungsten oxide 13b are produced, as shown in the right diagram of Figure 2. The produced chromium oxide 13a and tungsten oxide 13b have good wettability with the glass material, so the glass is fused to the chromium oxide 13a and tungsten oxide 13b that are adhered to the surface of the mold 12.

[0020] This phenomenon occurs and accumulates with each molding cycle of the glass material, gradually increasing the area of ​​the fusion points and gradually worsening the mold releasability, which may ultimately result in large-scale fusion.

[0021] Since it is difficult to prevent the exposure of tungsten and chromium, the glass molding apparatus 10 of this embodiment has the function of removing these exposed materials without removing the mold from the molding apparatus, i.e., without stopping the apparatus, while the density of the tungsten and chromium exposed to the mold release film 12c is still low.

[0022] (Schematic Structure of Glass Forming Apparatus) The schematic structure of the glass forming apparatus 10 of the embodiment will be described with reference to Figures 3 and 4. Figure 3 is a diagram showing an example of a schematic structure for realizing the glass forming function of the glass forming apparatus. Figure 4 is a diagram showing an example of an installation structure of a lower mold of the glass forming apparatus.

[0023] 3, a glass material 5 (e.g., quartz glass) that is the object to be molded is placed on a lower mold 14. An upper mold 15 is disposed above the lower mold 14 in a position opposite the lower mold 14. Both the lower mold 14 and the upper mold 15 have the same structure as the mold 12 described above.

[0024] 4, the lower mold 14, with the release film 12c facing upward, is fixed to a lower joint 16 that is movable in the vertical direction (the Z-axis direction in FIG. 3) via a mold die 17 and a die plate 18. The lower mold 14 is an example of a movable mold in the present disclosure.

[0025] The bottom joint 16 is made of ceramics such as SiN, which has high mechanical strength even at high temperatures, and is connected to a jack 21 that can be moved up and down by the rotational force of a servo motor 20 via a lower shaft 19 shown in FIG. 3. This allows the bottom joint 16 to move up and down (in the Z-axis direction). The lower shaft 19 is an example of a moving shaft in the present disclosure. The jack 21 is also an example of a pressure molding means in the present disclosure.

[0026] A load cell 22 for detecting the pressing force of the lower mold 14 is installed between the lower shaft 19 and the jack 21. Although not shown, the glass forming apparatus 10 further includes a mechanism for detecting the vertical position of the lower shaft 19.

[0027] As shown in Fig. 4, the lower mold 14 on which the glass material 5 is placed is assembled into the mold die 17 with an accuracy of several micrometers. The mold die 17 is then fastened to the die plate 18 with screws 17a. Although only one screw 17a is shown in Fig. 4, the mold die 17 is screwed to the die plate 18 at multiple positions surrounding the lower mold 14.

[0028] Furthermore, the die plate 18 is fastened to the bottom joint 16 by a screw 18a. Although only one screw 18a is shown in Fig. 4, the die plate 18 is actually fastened to the bottom joint 16 by the screw at a plurality of positions.

[0029] Returning to Fig. 3, the upper mold 15 has a structure similar to the fixing structure of the lower mold 14 shown in Fig. 4. That is, the upper mold 15, with the mold release film 12c facing downward, is fixed to a ceramic upper fitting 23 via a mold die and die plate (not shown). The upper fitting 23 is then fixed to an apparatus column 25 constituting the outer housing of the glass molding apparatus 10 via an upper shaft 24, which is a fixed shaft. The upper mold 15 is an example of a fixed mold in the present disclosure.

[0030] Glass forming apparatus 10 moves lower mold 14 upward, thereby sandwiching and pressurizing glass material 5 placed on lower mold 14 between it and fixed upper mold 15. As a result, glass material 5 is formed into a shape that conforms to the mold surfaces of lower mold 14 and upper mold 15. Glass forming apparatus 10 is also called a fixed mold type forming apparatus.

[0031] The lower mold 14, upper mold 15, lower joint 16, and upper joint 23 are housed inside a quartz tube 26. O-rings 27 are installed at the top and bottom of the quartz tube 26 to maintain airtightness. As a result, a sealed molding chamber 26a is formed inside the quartz tube 26. In the glass molding device 10, O-rings 27 are installed at various sliding parts and joints to maintain airtightness.

[0032] A plurality of ring-shaped infrared lamps 28 are arranged on the outside of the quartz tube 26. A reflecting mirror 29 is arranged behind the infrared lamps 28. Light emitted from the infrared lamps 28 and light reflected from the reflecting mirror 29 heat the lower mold 14 and the upper mold 15. The temperatures of the lower mold 14 and the upper mold 15 are measured by a thermocouple 30, and the output of the infrared lamps 28 is controlled so as to obtain a desired temperature rise curve. The infrared lamps 28 are an example of a heating means in the present disclosure.

[0033] In addition, reflectors 31 are installed above and below the infrared lamp 28 to surround the bottom fitting 16 and the top fitting 23 so that the light emitted by the infrared lamp 28 does not heat the O-ring 27 .

[0034] The reflecting mirror 29 becomes hot due to the heat emitted by the infrared lamp 28. Therefore, the reflecting mirror 29 is cooled by the cooling water flowing through the cooling water passage 32 and the room temperature nitrogen gas (N ２ The cooled cooling water is discharged from a water channel (not shown). The cooled air is exhausted from an exhaust port 34. Each part of the glass forming apparatus 10 is also appropriately cooled by the cooling water flowing through the cooling water channel 35.

[0035] When the glass material 5 is formed using the glass forming apparatus 10, an inert gas such as nitrogen gas is supplied to the interior of the quartz tube 26 (i.e., the forming chamber 26a) through the gas supply port 36. This inert gas is dried to thoroughly remove moisture. A control device (not shown) then detects the temperatures of the lower mold 14 and the upper mold 15 using a thermocouple 30. The control device also controls the output of the infrared lamp 28 to heat the lower mold 14, the upper mold 15, and the glass material 5. The control device controls the speed, torque, and rotation amount of the servo motor 20 in relation to the detected temperature, thereby moving the lower shaft 19 at a predetermined speed, torque (pressing force), and position according to a preset program, thereby forming the glass material 5 into a predetermined shape. If a more precise transfer of the mold shape is required, the forming chamber is evacuated. Thereafter, the control device supplies a predetermined flow rate of inert gas to the molding chamber 26a while applying a predetermined pressing force to the lower shaft 19, thereby cooling the lower mold 14, the upper mold 15, and the molded glass product to a predetermined temperature, thereby completing molding. The inert gas supplied to the molding chamber 26a is exhausted from the gas exhaust port 37.

[0036] When glass fusion occurs between the mold and the glass in such a glass molding device, the mass production molding line and the molding operation of the glass molding device must first be stopped, the mold must be cooled with nitrogen gas, and the mold die and die plate must be removed from the joint. The mold must then be removed, the fused glass must be removed, and the mold release film and intermediate layer must be peeled off and re-formed. During this time, the glass molding device is in a stopped state, so a spare mold unit is typically prepared and replaced to shorten downtime. However, during the mold replacement process, the temperature of the vertical shaft and column drops and shrinks. If the column shrinks, the vertical position of the mold changes, resulting in a deterioration in the thickness accuracy of the molded glass product. Therefore, the glass molding device must be idled until the column temperature stabilizes, and production is halted during this time. In particular, for large-diameter lenses, for which fixed mold systems are advantageous, the molds are large and heavy, and therefore have a large heat capacity, which means it takes a long time for the temperature to stabilize. Thus, when glass fusion occurs between the mold and the glass in a fixed mold system, productivity is significantly reduced.

[0037] To solve these problems, the glass molding apparatus 10 of this embodiment has a cleaning function for removing tungsten oxide and chromium oxide fused to the mold release film 12c of the lower mold 14 and the upper mold 15. The cleaning function will be described in detail later (see FIG. 5).

[0038] (Cleaning Function of Glass Forming Apparatus) The mold cleaning function provided in the glass forming apparatus 10 of the embodiment will be described with reference to Fig. 5. Fig. 5 is a diagram showing an example of a schematic structure for realizing the mold cleaning function provided in the glass forming apparatus.

[0039] In addition to the structure shown in FIG. 3, the glass forming apparatus 10 further includes a high-voltage pulse power supply 40, a metal plate 45, and an electromagnetic wave shield 50 shown in FIG.

[0040] High-voltage pulse power supply 40 is connected to lower mold 14 by a high-voltage coaxial cable 41a and to upper mold 15 by a similar high-voltage coaxial cable 41b. Glass molding apparatus 10 simultaneously applies a high voltage of about −1 kV to lower mold 14 and upper mold 15 with a pulse width of several nanoseconds to several milliseconds while lower mold 14 and upper mold 15 are spaced apart. High-voltage pulse power supply 40 is an example of the cleaning means of the present disclosure.

[0041] When a high voltage is applied to the lower mold 14 and the upper mold 15, a metal plate 45 held at ground potential is inserted between the lower mold 14 and the upper mold 15. That is, the metal plate 45 is held at GND potential. The metal plate 45 is an example of an electrode in the present disclosure. An insulating lower insulator 52 is installed below the lower mold 14. The lower insulator 52 electrically insulates the lower mold 14 to prevent abnormal discharge. An insulating upper insulator 53 is installed above the upper mold 15. The upper insulator 53 electrically insulates the upper mold 15 to prevent abnormal discharge. The surface areas of the lower insulator 52 and the upper insulator 53 are formed as large as possible to enhance insulation.

[0042] The reason for using coaxial cables 41a and 41b to connect the high-voltage pulse power supply 40 and the mold is that the pulses generated by the high-voltage pulse power supply 40 can be applied to the mold with high responsiveness. Furthermore, the use of coaxial cables 41a and 41b provides noise countermeasures, thereby preventing malfunction of the device itself or adjacent devices. The lengths of the coaxial cables 41a and 41b are set equal and as short as possible. This prevents differences in the change over time (amount of current) in the voltage applied to the lower mold 14 and the upper mold 15. Furthermore, since even coaxial cables have a certain amount of impedance, shortening their lengths minimizes the impedance and improves responsiveness to the applied pulse waveform.

[0043] The metal plate 45 is made of, for example, stainless steel, copper, or aluminum, and has a shape larger than the outer diameters of the lower mold 14 and the upper mold 15. As will be described later, the metal plate 45 is movable in the up and down direction in the drawing, and its height is adjusted so that the distance dd to the lower mold 14 and the distance du to the upper mold 15 are equal.

[0044] One end of the metal plate 45 is fastened to a plate support shaft 46. The plate support shaft 46 can rotate the metal plate 45 around the fastening point with the plate support shaft 46 in response to the rotation of an electrode opening / closing motor 47 driven by instructions from a control device (not shown). Furthermore, the electrode opening / closing motor 47, the plate support shaft 46, and the metal plate 45 are configured to be movable in the vertical direction in the figure. That is, in FIG. 5 , the metal plate 45 can be rotated and moved along the XY plane and also in the Z-axis direction. As a result, the position of the metal plate 45 can be switched to one of two positions, position 45a and position 45b, and the distance du between the metal plate 45 and the upper mold 15 and the distance dd between the metal plate 45 and the lower mold 14 can also be adjusted by a drive mechanism (not shown).

[0045] The metal plate 45, the plate support shaft 46, and the electrode opening / closing motor 47 are all electrically grounded via a high-frequency GND line, and other metal parts (such as the device column 25, the lower shaft 19, the upper shaft 24, and the reflecting mirror 29) are also electrically grounded in a similar manner.

[0046] The corners of the lower mold 14 and the upper mold 15 are rounded to prevent abnormal discharge when a high voltage pulse is applied from the high voltage pulse power supply 40 .

[0047] After the glass forming apparatus 10 has completed forming the glass material 5 and removed the formed product, it evacuates the interior of the forming chamber 26a to a final vacuum using various pumps (see FIG. 6 ), as described below. The vacuum level is measured by a vacuum gauge 51. The glass forming apparatus 10 then switches the position of the metal plate 45 to position 45a and supplies argon (Ar) gas, an example of an inert gas, into the forming chamber 26a to a pressure of, for example, 5 Pa. Nitrogen gas is typically used as the inert gas. Although argon gas is more expensive than nitrogen gas, it has a lower electronegativity and is less reactive even at high temperatures, such as plasma. Therefore, in the glass forming apparatus 10 of this embodiment, argon gas is preferably used as the plasma gas rather than nitrogen gas. A predetermined amount of argon gas is supplied into the forming chamber 26a via a mass flow controller (MFC) 54, which measures the flow rate. Since the exhaust rate is adjusted to be equal to the supply rate, the interior of the forming chamber 26a maintains a constant pressure. Thereafter, the glass forming apparatus 10 simultaneously applies a high voltage pulse of about −1 kV (e.g., −700 V) for a short time from the high voltage pulse power supply 40 to the lower mold 14 and the upper mold 15. This generates plasma in the space between the metal plate 45 and the lower mold 14 and in the space between the metal plate 45 and the upper mold 15.

[0048] At this time, the potential of the lower mold 14 and the upper mold 15 is lower than the potential of the grounded metal plate 45, so that the argon ions (Ar ＋ ) is accelerated toward both molds and collides with the lower mold 14 and the upper mold 15. As a result, the tungsten oxide (WxOy) and chromium oxide (CrxOy) exposed on the mold release film 12c are removed.

[0049] At the moment when a high-voltage pulse is applied to the lower mold 14 and the upper mold 15, and at the moment when the high-voltage pulse is cut off, electromagnetic waves are radiated from the space between the metal plate 45 and the lower mold 14 and the space between the metal plate 45 and the upper mold 15 toward the outside of the molding chamber 26a. These electromagnetic waves penetrate the quartz tube 26 and may cause malfunction of the infrared lamp 28, other control panels, and adjacent devices. Although the impact is minimal if the infrared lamp 28 and the reflective mirror 29 are at ground potential, to further reduce the impact of the electromagnetic waves, a metal electromagnetic shield 50 is provided to surround the space between the metal plate 45 and the lower mold 14 and the space between the metal plate 45 and the upper mold 15. The electromagnetic shield 50 has an electrically grounded cylindrical shape, and during molding of the glass material 5, it is retracted by a sliding mechanism (not shown) to a position where it is not irradiated by the infrared lamp 28 (e.g., the −Z direction in FIG. 5 ).

[0050] In this way, the glass forming apparatus 10 of this embodiment can remove ions (Ar) contained in the generated plasma without removing the molds (lower mold 14 and upper mold 15). ＋ ) can remove tungsten and chromium exposed on the surfaces of both molds. This allows the molds to be cleaned in a short time without stopping the glass molding apparatus 10, and makes it possible to maintain the performance of the mold release film 12c for a long period of time.

[0051] (Schematic Structure of Exhaust System) An exhaust system 60 provided in the glass forming apparatus 10 of the embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram showing an example of the configuration of an exhaust system provided in the glass forming apparatus.

[0052] The glass forming apparatus 10 is equipped with an exhaust system 60 that exhausts the nitrogen gas supplied to the forming chamber 26a when forming the glass material 5, the argon gas supplied to the forming chamber 26a when generating plasma, and the gas generated by cleaning the mold.

[0053] 6, the exhaust system 60 includes a cryopump 61, a turbomolecular pump 62, a mechanical booster pump 63, and a dry pump 64. These multiple pumps are connected as appropriate either directly or via valves 66a, 66b, 66c, 66d, and 66e or a butterfly valve 67. Furthermore, the glass forming apparatus 10 includes a QMASS 65, which is a type of mass spectrometer, in the exhaust system. The exhaust system 60 is an example of the exhaust means in the present disclosure.

[0054] The cryopump 61 is a type of adsorption pump, and is H ２ Therefore, by performing evacuation via the cryopump 61, the H remaining inside the molding chamber 26a can be removed. ２ The O partial pressure can be reduced.

[0055] In the glass forming device 10, the forming chamber 26a is opened to the atmosphere every time the forming of the glass material 5 is completed in order to remove the formed product and set a new glass material 5. Therefore, the inner wall of the opened forming chamber 26a is exposed to the atmosphere. ２ O adheres. Adhered H ２ O vaporizes during evacuation and decomposes into H and OH when the mold (lower mold 14 and upper mold 15) is heated. The generated active oxygen OH reacts with the cemented carbide material 12a, blackening the mold. As a result, the absorption rate of near-infrared light from the infrared lamp 28 increases. In addition, OH oxidizes the chromium on the surface of the mold release film 12c, significantly reducing mold release performance.

[0056] In addition, the cryopump 61 absorbed H ２ The O is exhausted at a predetermined timing (for example, at the end of work for the day).

[0057] The turbo molecular pump 62, like a jet engine, uses a combination of turbine blades that rotate at high speed and stationary blades to exhaust, compress, and exhaust gas molecules.

[0058] The mechanical booster pump 63 is used in combination with other pumps to increase the pumping speed in pressure regions where the pumping speed of the other pumps is low.

[0059] The dry pump 64 is a mechanical vacuum pump that does not use oil or liquid inside the vacuum chamber, and because no oil or liquid is used, it can perform clean evacuation.

[0060] The opening of the butterfly valve 67 is controlled so that the exhaust speed is the same as the above-mentioned argon supply amount.

[0061] QMASS65 is a type of mass spectrometer that measures H when the ultimate vacuum is reached. ２ This is a means for managing the O partial pressure and determining the end of the plasma cleaning process. Specifically, the glass forming apparatus 10 ends the cleaning process when the QMASS 65 detects platinum (Pt) or iridium (Ir) that constitutes the mold release film 12c. This is because if platinum or iridium is detected in the gas generated inside the forming chamber 26a, it is believed that the mold release film 12c itself is being eroded by the cleaning process, which is known as over-sputtering.

[0062] (Schematic Configuration of Plasma Generation Circuit) The schematic configuration of the plasma generation circuit (not shown in Fig. 5) provided in the glass forming apparatus 10 of the embodiment will be described using Fig. 7 and Fig. 8. Fig. 7 is a diagram showing an example of an equivalent circuit of the plasma generation circuit provided in the glass forming apparatus of the embodiment. Fig. 8 is a diagram showing an example of a voltage waveform and a current waveform applied between the upper mold and the lower mold and the metal plate.

[0063] Because the thickness of the tungsten or chromium exposed in the mold release film 12c is on the order of nanometers, it is necessary to control the magnitude and duration of the applied pulse voltage with high precision. In other words, the transient state at the moment the voltage is applied and when it is released is extremely important.

[0064] More specifically, if the pulse width applied to the lower mold 14 and the upper mold 15 to generate plasma for cleaning the mold is too long, the mold release film 12c may also be removed, and the surface roughness of the lower mold 14 and the upper mold 15 may be deteriorated. Therefore, the glass molding apparatus 10 minimizes the pulse width applied to the lower mold 14 and the upper mold 15, and adjusts the amount of fused tungsten and chromium removed by adjusting the number of pulse applications, i.e., the number of times plasma is generated. Therefore, the high-voltage pulse power supply 40 is capable of controlling the pulse width generated on the order of milliseconds. Furthermore, it is desirable that the high-voltage pulse power supply 40 be able to control the pulse shape (particularly the pulse rise shape dV / dt) of the pulse generated.

[0065] 7, an equivalent circuit 70 of the plasma generating circuit provided in the glass forming apparatus 10 includes a high-voltage pulse power supply 40, capacitors Ca and Cb, cable impedances Za and Zb, diodes Da and Db, and a variable capacitance reactance L. Since plasma 100 is generated between the lower mold 14 and the upper mold 15 and the metal plate 45, the equivalent circuit 70 also includes the impedance of the plasma itself (not shown).

[0066] Capacitor Ca is a capacitor formed by the lower mold 14 and the metal plate 45. The capacitance of capacitor Ca is Cd. Capacitor Cb is a capacitor formed by the upper mold 15 and the metal plate 45. The capacitance of capacitor Cb is Cu. As described above, the distance dd between the metal plate 45 and the lower mold 14 is equal to the distance du between the metal plate 45 and the upper mold 15, so the capacitances Cd and Cu are equal.

[0067] The operation of the glass forming apparatus 10 described above is equivalent to applying the same high-voltage pulse to the capacitors Ca and Cb at the same timing in Fig. 7. Specifically, the high-voltage pulse power supply 40 is turned on to apply a high voltage of, for example, -1 kV to the metal plate 45 of the upper mold 15 and the lower mold 14.

[0068] At this time, the space between the upper mold 15 and the metal plate 45 and the space between the lower mold 14 and the metal plate 45 are filled with an inert gas such as argon adjusted to a predetermined pressure P.

[0069] Incidentally, discharge starts corresponding to the product of the pressure P and the distance (du, dd), i.e., P×du and P×dd, and plasma 100 (see FIG. 9) is generated in the space between the metal plate 45 and the upper mold 15 and in the space between the metal plate 45 and the lower mold 14. At this time, the distances du and dd are controllable, so the discharge inception voltage and plasma characteristics can be controlled.

[0070] Figure 9 shows an example of the state between electrodes when plasma is generated. Reference numeral 100 in the figure denotes plasma, which is a partially ionized gas. When plasma 100 comes into contact with a solid such as an electrode, a space charge layer called a sheath is formed on the surface of the electrode. That is, as shown in Figure 9, sheaths 101 are generated between the upper mold 15, lower mold 14, and plasma 100, and sheaths 102 are generated between the plasma 100 and the metal plate 45.

[0071] Taking the sheaths 101 and 102 into consideration, an equivalent circuit 70a of the discharge portion (between the electrodes) when the plasma 100 is generated is as shown in FIG.

[0072] As shown in Figure 10, it is known that a sheath is generally equivalent to a parallel circuit of a resistor and a capacitor. Furthermore, since the plasma 100 in Figure 9 is ionized, it is represented by a resistive element in the equivalent circuit. In Figure 10, the resistance value of resistor 103, which is the equivalent circuit of the plasma body, is set to Rp.

[0073] 9 is replaced with a parallel circuit of a sheath resistor 106 and a sheath capacitor 107, and similarly, the sheath 102 is replaced with a parallel circuit of a sheath resistor 108 and a sheath capacitor 109.

[0074] Here, the resistance value of the sheath resistor 106 is R1, the resistance of the sheath resistor 108 is R2, the electrostatic capacitance of the sheath capacitor 107 is CsA, and the electrostatic capacitance of the sheath capacitor 109 is CsB.

[0075] 10, the sheath 101, plasma 100, and sheath 102 are arranged in series, so that an equal current I flows through each of them. In other words, the voltages applied to each device (voltages VA, VP, and VB in FIG. 10) are adjusted so that this is satisfied.

[0076] As is well known, the current flowing through a capacitor is proportional to the time change (dV / dt) of the applied voltage. Conversely, if there is no time change, no current will flow.

[0077] When a negative high voltage pulse shown in FIG. 8 is applied to such a circuit, theoretically, no current flows through the sheath capacitors 107 and 109 during the time period ta-tc when the voltage v(t) does not change.

[0078] Therefore, the load at this time is only three resistors, that is, the sheath resistor 106, the resistor 103, and the sheath resistor 108.

[0079] However, since the voltage v(t) changes greatly between time ta and time tc, at that moment a spike-shaped current i(t) as shown in Fig. 8 flows through the sheath capacitors 107 and 109. In other words, there are a total of five loads: three resistors and two capacitors.

[0080] As mentioned above, theoretically, no current flows between time ta and time tc. However, in reality, a current i(t) flows between time ta and time tb, and between time tc and time td, for a period of time corresponding to the attenuation constant (time constant).

[0081] Furthermore, the direction of the spike current flowing at time ta is the direction I shown in FIG. 7, but at time tc, the spike current flows in the opposite direction.

[0082] The current flowing in the direction I is due to the Ar in the plasma. ＋ This means that ions are irradiated onto the upper mold 15 and the lower mold 14, which means that deposits on the mold surfaces are sputtered.

[0083] On the other hand, the reverse current occurs when Ar ＋ This means that ions are irradiated from the plasma 100 onto the metal plate 45, causing the metal plate 45 to be sputtered.

[0084] The sputtered material will naturally adhere to the surfaces of the upper mold 15 and the lower mold 14, which will actually worsen the mold releasability. For this reason, diodes Da and Db are provided to prevent backflow, as shown in Figure 7. The withstand voltage of diodes Da and Db is set to several times the voltage that can be applied by the high-voltage pulse power supply 40.

[0085] Furthermore, applying a stepped high voltage as shown in Fig. 8 will result in a spike-like overcurrent as described above, which may damage the power supply cable, insulators, or power supply. To avoid this, a variable capacitive reactance L shown in Fig. 7 may be inserted to control the voltage rise at time ta to be more gradual.

[0086] However, since this acts to lengthen the time difference between time tb and time ta and the time difference between time td and time tc in FIG. 8, care must be taken when setting the pulse width of the voltage.

[0087] Because the above-described overcurrent is undesirable for the power supply, the high-voltage pulse power supply 40 is often equipped with a function to prevent this. Therefore, this function may be utilized. Furthermore, since the voltage and current change rapidly as described above, it is desirable to form an equivalent circuit 70b in which a highly responsive voltmeter 111 and ammeter 110 are additionally installed, as shown in FIG. 11 . Furthermore, the voltmeter 111 and ammeter 110 have the function of outputting the measured voltage and current values ​​to the control device 112. Furthermore, the control device 112 not only collects and stores these values, but also has a database function of integrating the collected data over time, particularly for current, and storing the results for a long period of time.

[0088] The time integral value of the current is the Ar flowing into the lower die 14 and the upper die 15. ＋ The total number of ions, i.e., the number of Ar atoms required for a given cleaning ＋ By storing and saving this information, it can be used to shorten the time required to optimize cleaning conditions. For example, if the number of cycles required for cleaning is doubled, the number of Ar ＋ The number of ions can be doubled, and if it is halved, it is estimated that it will be 0.5 times.

[0089] (Cleaning Process Performed by Glass Forming Apparatus) Next, the cleaning process performed by the glass forming apparatus 10 will be described in more detail.

[0090] After a predetermined number of molding cycles (e.g., several tens of times) have been completed for the glass material 5, and the molded product has been removed, the glass molding device 10 evacuates the interior of the molding chamber 26a to an ultimate vacuum level using the exhaust system 60 shown in Figure 6, without any material being set.

[0091] At this time, the QMASS 65 removes the H remaining inside the molding chamber 26a. ２ The partial pressure of O and O ２ It is then confirmed that the partial pressure of the metal plate 45 is sufficiently small. Thereafter, the glass forming apparatus 10 adjusts the position of the lower mold 14 so that the distance between the upper mold 15 and the lower mold 14 is a predetermined size, adjusts the height of the metal plate 45 so that it is exactly midway between the upper mold 15 and the lower mold 14, and then moves the metal plate 45 from position 45b to position 45a. After this operation is completed, the electromagnetic wave shield 50 is further raised to the position shown in FIG. 5 by a moving mechanism (not shown).

[0092] After confirming that the electromagnetic wave shield 50 has reached the position shown in Fig. 5, the glass forming apparatus 10 opens the valve 66a shown in Fig. 6 and adjusts the flow rate of argon so that the interior of the forming chamber 26a reaches a predetermined pressure. Once the pressure inside the forming chamber 26a has stabilized, the glass forming apparatus 10 applies a pulse voltage of, for example, about -1 kV to each of the lower mold 14 and the upper mold 15 for several hundred milliseconds. The argon pressure in the forming chamber 26a, the voltage applied by the high-voltage pulse power supply 40, the applied pulse width, and the number of pulse applications are all set in advance.

[0093] During the cleaning process, the glass forming apparatus 10 opens the valve 66d shown in FIG. 6 to perform process analysis using the QMASS 65. If the QMASS 65 detects platinum (Pt: (mass number 195)) or iridium (Ir: (mass number 192)), which are elements constituting the mold release film 12c, during the cleaning process, the glass forming apparatus 10 forcibly terminates the cleaning process even if the set number of pulses has not been reached. This is because it is believed that the cleaning process is causing erosion of the mold release film 12c. Incidentally, because the atomic weights of Pt and Ir are larger than those of chromium and tungsten, the sputtering yields of the former are overwhelmingly lower and the former are less susceptible to sputtering.

[0094] After the cleaning process is completed and cooling is performed as necessary, the glass forming apparatus 10 moves the metal plate 45 to position 45b and further lowers the electromagnetic wave shield 50. Next, the glass forming apparatus 10 opens the interior of the forming chamber 26a to the atmosphere, sets the glass material 5, and starts a normal forming cycle.

[0095] (Specific Example of Cleaning Process) Next, a specific cleaning process carried out by the inventors and the results thereof will be described.

[0096] The inventors formed a mold (lower mold 14, upper mold 15) by forming a 20 nm thick Cr intermediate layer and a 600 nm thick Pt-Ir mold release film on an existing flat cemented carbide material.

[0097] Using this mold, glass material 5 (BK-7) was molded 120 times at 650°C, and then the mold was cleaned using the glass molding device 10. The applied pulse voltage was -670 V, the pulse application time was 100 msec, and the pulse was applied 10 times.

[0098] In parallel with the cleaning of the mold, a process analysis was carried out using QMASS65, but no Pt or Ir was detected. Furthermore, W and Cr were detected every time a pulse was applied.

[0099] Furthermore, as a result of observing the transient state of the voltage and current when the pulse voltage was applied, it was found that the time from input of the pulse voltage until the plasma was generated was about 15 msec, and a current of about 15 A flows. From this current value, the ion flux irradiated onto the mold was calculated to be about 9.4 × 10 １９ ( / sec).

[0100] Assuming that the sputtering rate of tungsten (W) is 0.5, the removal rate is approximately 4.7 × 10 １９ From this result, it was found that the partial pressure of tungsten calculated almost coincided with the analysis result of QMASS65.

[0101] The mold release force after mold cleaning was measured using the load cell 22 in Figure 5, and it was found to have improved by approximately 80% compared to before cleaning the mold. This confirmed the effectiveness of the cleaning process.

[0102] (Operation and Effect of the Embodiment) As described above, the glass forming device 10 of the present embodiment includes the forming chamber 26 a, the upper mold 15 (fixed mold) and the lower mold 14 (movable mold) that are arranged opposite each other inside the forming chamber 26 a and are formed into a predetermined shape, the lower shaft 19 (movable shaft) that supports the lower mold 14 so that it can move relative to the upper mold 15, the infrared lamp 28 (heating means) that heats the upper mold 15, the lower mold 14, and the glass material 5 placed between the upper mold 15 and the lower mold 14, and the lower shaft 19 is moved in a direction that presses the lower mold 14 against the upper mold 15, thereby pressing the glass material 5 between the lower mold 14 and the upper mold 15. The glass forming apparatus 10 includes a jack 21 (pressure forming means) for forming the glass material 5 by applying a high-voltage pulse to a space between the upper mold 15 and the lower mold 14 and a metal plate 45 (electrode) inserted between the separated upper mold 15 and the lower mold 14, and to a space between the metal plate 45 and the lower mold 14, while supplying an inert gas to the interior of the forming chamber 26a when the glass material 5 is not being formed, so that the metal plate 45 has a higher potential than the upper mold 15 and the lower mold 14, thereby generating plasma, and cleaning the upper mold 15 and the lower mold 14 with the plasma. Therefore, even after repeated forming, deteriorated molds can be cleaned (regenerated) without completely stopping the glass forming apparatus 10, thereby preventing a decrease in productivity.

[0103] In addition, in the glass forming apparatus 10 of this embodiment, the high-voltage pulse power supply 40 (cleaning means) applies a high-voltage pulse of negative potential to each of the upper mold 15 (fixed mold) and the lower mold 14 (movable mold) while the metal plate 45 (electrode) is held at GND potential. Ions in the plasma generated by this process collide with the upper mold 15 and the lower mold 14, allowing the molds to be efficiently cleaned.

[0104] In addition, in the glass forming apparatus 10 of this embodiment, when the high-voltage pulse power supply 40 (cleaning means) generates plasma, the amount of inert gas supplied to the inside of the forming chamber 26a, and the voltage, pulse width, and pulse number of the high-voltage pulse are all set to predetermined values. Therefore, the state of the plasma generated inside the forming chamber 26a can be finely adjusted, and a cleaning process tailored to the state of the mold to be cleaned can be achieved.

[0105] The glass forming apparatus 10 of this embodiment further includes an ammeter 110 that measures the value of the current flowing in the circuit that applies the high-voltage pulse, and a control device 112 that acquires and stores the current value measured by the ammeter 110. The control device 112 determines the cleaning conditions for cleaning the upper mold 15 (fixed mold) and the lower mold 14 (movable mold) based on the time integral of the current value. Therefore, the upper mold 15 and the lower mold 14 can be cleaned at an appropriate timing.

[0106] Furthermore, in the glass forming apparatus 10 of this embodiment, the metal plate 45 (electrode) has a shape that completely covers at least the upper mold 15 (fixed mold) and the lower mold 14 (movable mold), so that the entire molds can be cleaned completely.

[0107] In addition, in the glass forming apparatus 10 of this embodiment, the distance du between the metal plate 45 (electrode) and the upper mold 15 (fixed mold) and the distance dd between the metal plate 45 and the lower mold 14 (movable mold) are adjustable, so that the discharge start voltage and plasma characteristics when generating the plasma 100 can be controlled.

[0108] Furthermore, the glass forming apparatus 10 of this embodiment changes the cleaning conditions for cleaning the upper mold 15 and the lower mold 14 by adjusting the distance du between the metal plate 45 (electrode) and the upper mold 15 (fixed mold) and the distance dd between the metal plate 45 and the lower mold 14 (movable mold). Thus, the cleaning conditions for the molds can be controlled.

[0109] Furthermore, the glass forming apparatus 10 of this embodiment adjusts the distances du and dd in accordance with the values ​​of currents flowing through the upper mold 15 (fixed mold) and the lower mold 14 (movable mold), thereby enabling appropriate control of the timing of mold cleaning.

[0110] In addition, in the glass forming apparatus 10 of this embodiment, the inert gas supplied to the forming chamber 26a is argon gas. While inexpensive nitrogen gas is generally used, nitrogen has a high electronegativity and a certain level of reactivity. While this is not a problem at forming temperatures of around 500 to 700°C, the effects become unignorable at high temperatures such as plasma. Therefore, argon gas is preferable, even though it is more expensive.

[0111] The glass molding apparatus 10 of this embodiment also includes an exhaust system 60 (exhaust means) that exhausts the gas inside the molding chamber 26a, monitors whether the gas contains elements that make up the mold release film 12c that forms the surfaces of the lower mold 14 (movable mold) and the upper mold 15 (fixed mold), and terminates the operation of the high-voltage pulse power supply 40 (cleaning means) if any of the elements is detected. This makes it possible to prevent over-sputtering of the mold surfaces during the cleaning process.

[0112] Although the embodiments of the present invention have been described above, the above-described embodiments are presented as examples and are not intended to limit the scope of the present invention. This novel embodiment can be embodied in various other forms. Furthermore, various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Furthermore, this embodiment is included within the scope and spirit of the invention, and is also included in the scope of the invention and its equivalents as defined in the claims.

[0113] 5 Glass material 10 Glass molding device 12 Mold 12a Super hard material 12b Intermediate layer 12c Mold release film 12d WC particles 12e Binder 14 Lower mold (movable mold) 15 Upper mold (fixed mold) 16 Lower joint 17 Mold die 17a Screw 18 Die plate 18a Screw 19 Lower shaft (movable shaft) 20 Servo motor 21 Jack (pressure molding means) 22 Load cell 23 Upper joint 24 Upper shaft 25 Device column 26 Quartz tube 26a Molding chamber 27 O-ring 28 Infrared lamp (heating means) 29 Reflecting mirror 30 Thermocouple 31 Reflecting plate 32, 35 Cooling water channel 33 Air intake 34 Exhaust port 36 Gas supply port 37 Gas exhaust port 40 High-voltage pulse power supply (cleaning means) 41a, 41b Coaxial cable 45 Metal plate (electrode) 45a, 45b Position 46 Plate support shaft 47 Electrode opening / closing motor 50 Electromagnetic wave shield 51 Vacuum gauge 52 Lower insulator 53 Upper insulator 54 MFC 60 Exhaust system (exhaust means) 61 Cryopump 62 Turbomolecular pump 63 Mechanical booster pump 64 Dry pump 65 QMASS 66a, 66b, 66c, 66d, 66e Valve 67 Butterfly valve 70, 70a, 70b Equivalent circuit 100 Plasma 101, 102 Sheath 103 Resistor 106, 108 Sheath resistor 107, 109 Sheath capacitor 110 Ammeter 111 Voltmeter 112 Control device dd, du Distance Ca, Cb Capacitor Cd, Cu Electrostatic capacitance Da, Db Diode I Current L Capacitive variable reactance P Pressure v(t) Voltage Za, Zb Cable impedance

Claims

1. A glass forming device comprising: a forming chamber; a fixed mold and a movable mold arranged opposite each other above and below inside the forming chamber and formed into a predetermined shape; a movable shaft that supports the movable mold so that it can move relative to the fixed mold; heating means that heats the fixed mold, the movable mold, and a glass material placed between the fixed mold and the movable mold; pressure forming means that moves the movable shaft in a direction that presses the movable mold against the fixed mold, thereby forming the glass material by pressurizing it with the movable mold and the fixed mold; and cleaning means that, when the glass material is not being formed, generates plasma by applying a high voltage pulse to a space between the fixed mold and the movable mold and an electrode inserted between the separated fixed mold and the movable mold, and to the space between the electrode and the movable mold, while supplying an inert gas into the inside of the forming chamber, so that the electrode has a higher potential than the fixed mold and the movable mold, and then cleans the fixed mold and the movable mold with the plasma.

2. The glass forming device according to claim 1, wherein said cleaning means applies a high voltage pulse of negative potential to said fixed mold and said movable mold, respectively, while said electrodes are held at GND potential.

3. A glass forming apparatus according to claim 1 or claim 2, wherein when the cleaning means generates the plasma, the amount of the inert gas supplied into the forming chamber, and the voltage, pulse width and number of pulses of the high voltage pulse are each set to a predetermined value.

4. A glass molding apparatus according to claim 1 or claim 2, further comprising: an ammeter that measures the value of a current flowing in a circuit that applies the high voltage pulse; and a control device that acquires and stores the current value measured by the ammeter, wherein the control device determines cleaning conditions for cleaning the fixed mold and the movable mold based on the time integral value of the current value.

5. The glass forming device according to claim 1 or 2, wherein the electrode has a shape that completely covers at least the fixed mold and the movable mold.

6. A glass forming device according to claim 1 or 2, wherein the distance between the electrode and the fixed mold and the distance between the electrode and the movable mold are adjustable.

7. The glass forming device according to claim 6, wherein the cleaning conditions for cleaning the fixed mold and the movable mold are changed by adjusting the distance between the electrode and the fixed mold and the distance between the electrode and the movable mold.

8. The glass forming device according to claim 7, wherein the distance is adjusted according to the value of current flowing into the fixed mold and the movable mold.

9. The glass forming apparatus according to claim 1 or 2, wherein the inert gas supplied to the forming chamber is argon gas.

10. The glass forming device according to claim 1 or claim 2, further comprising an exhaust means for exhausting gas from the inside of the forming chamber, monitoring whether the gas contains elements that make up the mold release film that forms the surfaces of the movable mold and the fixed mold, and terminating the operation of the cleaning means when the elements are detected.

11. A mold cleaning method for cleaning the fixed mold and the movable mold in a glass molding device comprising: a molding chamber; a fixed mold and a movable mold arranged opposite each other inside the molding chamber and formed into a predetermined shape; a movable shaft that supports the movable mold so that it can move relative to the fixed mold; a heating means that heats a glass material placed between the fixed mold and the movable mold; and a pressure molding means that moves the movable shaft in a direction that presses the movable mold against the fixed mold, thereby pressurizing the glass material placed between the movable mold and the fixed mold at a predetermined pressure for a predetermined time, the mold cleaning method comprising: supplying an inert gas into the molding chamber; applying a high voltage pulse to a space between the fixed mold and an electrode inserted between the separated fixed mold and the movable mold, and to the space between the electrode and the movable mold, so that the electrode has a higher potential than the fixed mold and the movable mold, thereby generating plasma, and cleaning the fixed mold and the movable mold with the plasma.

12. A mold cleaning method as set forth in claim 11, wherein, when exhausting gas generated when cleaning the fixed mold and the movable mold using the mold cleaning method as set forth in claim 11, the gas is monitored for the presence of elements that make up the mold release film that forms the surfaces of the movable mold and the fixed mold, and cleaning is terminated if the elements are detected.

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