JPWO2009104585A1 - Mold regeneration method - Google Patents

Abstract

A method for regenerating a mold for pressure-molding a glass material, which includes a mold substrate and at least one coating layer provided on the mold substrate. After removing at least a part of the coating layer (coating layer removing step), the oxide layer formed in the coating layer removing step is removed (oxide layer removing step), and then the coating layer is re-formed (coating layer forming step) ).

Description

  The present invention relates to a method for regenerating a mold for pressure-molding a glass material to produce a glass molded body used for an optical element or the like.

  As a method for producing a glass molded body to be used for an optical element or the like by pressure-molding a glass material, two methods of a reheat press method and a droplet forming method are known. The reheat press method is a method in which a glass preform having a predetermined mass and shape prepared in advance is heated together with a mold and pressure-molded, and is widely implemented because it does not require equipment such as a glass melting furnace. ing.

  On the other hand, the droplet molding method is a method in which molten glass droplets are dropped onto a molding die (lower mold) heated to a predetermined temperature, and the molten glass droplets dropped are pressure-molded with a molding die to obtain a glass molded body. . In this method, it is not necessary to repeat heating and cooling of a mold or the like, and a glass molded body can be produced directly from molten glass droplets. Therefore, a method attracting attention because the time required for one molding can be extremely shortened. It is.

  Forming a coating layer on a precision-worked mold base from the viewpoints of protecting the molding surface and improving mold releasability as a mold for producing glass moldings by these methods These molds are widely used.

  In general, such a mold requires a lot of time and labor for processing, and the material itself is very expensive, so that high durability is required. However, since the coating layer is easily damaged by repeated pressure molding and defects such as partial peeling are likely to occur, a mold having sufficient durability has not yet been obtained.

  For this reason, methods for regenerating the damaged coating layer and extending the life of the mold have been studied and proposed (see, for example, Patent Documents 1 and 2). Patent Document 1 describes a method in which an intermediate layer mainly composed of chromium is provided between a mold substrate and a surface layer, and the intermediate layer is removed using a chromium-soluble treatment liquid. Patent Document 2 discloses a method in which an intermediate layer is provided between a mold base and a surface layer, the uppermost portion of the surface layer and the intermediate layer is removed by ion beam irradiation, and then the intermediate layer is dissolved and removed. Is described.

Further, in the droplet forming method, air accumulation may occur on the lower surface of the molten glass droplet (contact surface with the lower die) due to collision with the lower die. In order to prevent this, a method of roughening the surface of the lower mold (Rmax is 0.05 μm to 0.2 μm) has been proposed (see Patent Document 3). Moreover, on the roughened base surface (Ra is 0.005 μm to 0.05 μm), by forming a coating layer including a dissolved layer that dissolves in a predetermined treatment liquid, air accumulation is prevented, A lower mold that can be easily regenerated by dissolving a dissolved layer has been proposed (see Patent Document 4).
Japanese Patent Laid-Open No. 1-192733 JP 2001-130918 A Japanese Patent Laid-Open No. 3-137031 JP 2005-272187 A

  However, as described in Patent Documents 1, 2, and 4, when the coating layer is dissolved and removed, and then the coating layer is formed again and the mold is regenerated, the adhesion of the coating layer is not improved. There was a problem that the required durability could not be obtained. In addition, by repeating the regeneration of the mold, the decrease in the adhesiveness of the coating layer became more remarkable. Therefore, it is difficult to regenerate and re-use the mold, which has been a major factor that hinders cost reduction of the glass molded body.

  Further, in the case of a mold used for the droplet forming method, when the surface is roughened as in Patent Documents 3 and 4, the surface roughness changes (roughness decreases) due to damage caused by pressure molding. Therefore, the lifetime is shorter than usual. For this reason, it is necessary to frequently regenerate the mold, and a decrease in the adhesion of the coating layer due to the regeneration has been a particularly serious problem.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to provide a method for regenerating a mold that can prevent a decrease in the adhesion of the coating layer due to regeneration and can be repeatedly regenerated. Is to provide.

  In order to solve the above problems, the present invention has the following features.

(1) In a method for regenerating a mold, which has a mold substrate and at least one coating layer provided on the mold substrate, and press-molds a glass material,
A coating layer removing step of removing at least a part of the coating layer;
A coating layer forming step of re-forming the removed coating layer,
A method for regenerating a mold, comprising: an oxide layer removing step of removing an oxide layer formed on a surface after removing at least a part of the coating layer prior to the coating layer forming step.

(2) The glass material is a dropped molten glass droplet,
The method for regenerating a mold according to (1), further comprising a roughening step of roughening a surface of the coating layer by etching after the coating layer forming step.

  (3) The molding die regeneration method according to (1) or (2), wherein the mold base is made of silicon carbide.

  (4) The mold regeneration method according to (3), wherein the mold base is a silicon carbide sintered body formed with a silicon carbide layer by a CVD method.

  (5) The mold regeneration method according to any one of (1) to (4), wherein the oxide layer removing step is a step of removing the oxide layer by a physical method.

  (6) The mold regeneration method according to any one of (1) to (4), wherein the oxide layer removing step is a step of removing the oxide layer by a chemical method.

  (7) The mold regeneration method according to (6), wherein the oxide layer removing step is a step of etching the oxide layer with a fluorine-based etchant.

  (8) The mold regeneration method according to any one of (1) to (7), wherein the coating layer contains at least one element of chromium, aluminum, and titanium.

  (9) The method for regenerating a mold according to any one of (1) to (8), wherein the coating layer removing step is an etching step using an acidic solution.

  (10) After the coating layer forming step, the surface of the reformed coating layer has an arithmetic average roughness (Ra) of 0.01 μm to 0.2 μm, and an average length (RSm) of roughness curve elements. The method for regenerating a mold according to any one of (1) to (9), further comprising a step of roughening the surface to 0.5 μm or less.

  According to the present invention, since there is a step of removing the oxide layer formed when removing the coating layer prior to the step of reforming the coating layer, the adhesiveness of the coating layer to be reformed is improved. The decrease can be prevented, and the mold can be regenerated repeatedly.

It is a flowchart which shows the reproduction | regeneration method of the shaping | molding die by 1st Embodiment. It is a schematic diagram (sectional drawing) which shows the state of the shaping | molding die in each process of 1st Embodiment. It is a flowchart which shows the reproduction | regeneration method of the shaping | molding die by 2nd Embodiment. It is a schematic diagram (sectional drawing) which shows the state of the shaping | molding die in each process of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 20 Mold 11 Mold substrate 12 Coating layer 13 Oxidation layer 14 Surface of coating layer 15 Molding surface S101 Coating layer removal process S102 Oxidation layer removal process S103 Coating layer formation process S104 Roughening process

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.

(First embodiment)
FIG. 1 is a flowchart showing a mold regeneration method according to the first embodiment of the present invention. FIG. 2 is a schematic view (cross-sectional view) showing the state of the mold in each step.

(Molding mold)
Fig.2 (a) has shown the shaping | molding die 10 before reproduction | regeneration. The mold 10 includes a mold base 11 and at least one coating layer 12 provided on the mold base 11. The coating layer 12 has defects (not shown) such as partial peeling and cracks due to damage caused by repeated pressure molding.

  The mold base 11 is provided with a molding surface 15 having a predetermined shape by a known precision processing method. There is no restriction | limiting in particular in the shape of the molding surface 15, According to the glass molded object to manufacture, it can be set as various shapes, such as a spherical surface, an aspherical surface, and a cylinder surface. A convex surface may be sufficient and a concave surface may be sufficient.

  The material of the mold base 11 can be appropriately selected from known materials used for a mold for pressure-molding a glass material according to conditions. For example, various heat-resistant alloys (such as stainless steel), super hard materials mainly composed of tungsten carbide, various ceramics (such as silicon carbide and silicon nitride), composite materials containing carbon, and the like can be given.

  Among them, silicon carbide (SiC) is a material that is particularly excellent in heat resistance and durability, but since the adhesiveness of the coating layer 12 after regeneration is remarkably reduced, a mold in which the mold base 11 is made of SiC is Conventionally, it has been difficult to use repeatedly by reproduction. According to the method of the present invention, even when the mold base 11 is a mold made of SiC, it is possible to effectively prevent a decrease in the adhesion of the coating layer 12 after regeneration. Can be used repeatedly. In particular, a material in which a SiC layer is formed by a CVD method on a SiC sintered body has an advantage that the material cost can be kept low.

  The coating layer 12 is provided from the viewpoint of protecting the molding surface 15 of the mold base 11 and improving the releasability from glass, and is made of various materials such as metals, nitrides, and oxides. Can do. Among these, a material containing at least one element among chromium, aluminum, and titanium is particularly preferable. Films containing these elements not only have the advantage that they can be easily formed and can be easily removed by etching, but the surface is oxidized by heating in the atmosphere, forming a stable oxide layer. There is a feature that is. Chromium, aluminum, and titanium oxides all have low standard generation free energy (standard generation Gibbs energy) and are very stable, so they do not react easily even when they come into contact with hot molten glass droplets. Has great advantages.

  Examples of the material containing at least one element of chromium, aluminum, and titanium include metal chromium, metal aluminum, metal titanium, chromium nitride, aluminum nitride, titanium nitride, chromium oxide, aluminum oxide, and titanium oxide. .

  The coating layer 12 only needs to be provided with at least one layer, and may have a multilayer structure of two or more layers. Although there is no restriction | limiting in particular in the thickness of the coating layer 12, However, Since functions, such as protection of the molding surface 15, will become insufficient when it is too thin, it is preferable normally that it is 0.05 micrometer or more. On the other hand, if the coating layer 12 is too thick, the film thickness distribution may be increased, and the shape of the molding surface 15 may be lost, or defects such as film peeling may easily occur. Therefore, the thickness of the coating layer 12 is preferably 0.05 μm to 5 μm, particularly preferably 0.1 μm to 1 μm. When the coating layer 12 has a multilayer structure, the total thickness is preferably in the above range.

(Coating layer removal step S101)
The covering layer removing step S101 is a step of removing at least a part of the covering layer 12 from the damaged mold 10. FIG. 2B shows a state in which the coating layer 12 has been removed from the mold 10 by the coating layer removing step S101.

  The removal of the coating layer 12 can be performed by etching. Etching may be wet etching using an etchant or dry etching using plasma.

  Wet etching is a method in which a reactive etching solution is brought into contact with the coating layer 12 to dissolve and remove the coating layer 12, and does not require expensive equipment, and the coating layer 12 can be easily removed. . The coating layer 12 may be immersed in the stored etching solution, or a predetermined amount of etching solution may be supplied onto the coating layer 12. Moreover, the method of spraying etching liquid in the spray form may be used.

  As the etchant, a known etchant corresponding to the material of the coating layer 12 may be selected as appropriate. When the coating layer 12 is aluminum, etching solutions that can be preferably used for aluminum, such as various acidic solutions, are commercially available. Even when the coating layer 12 is titanium, an etching solution that can be preferably used for titanium is commercially available. For example, an etching solution mainly containing a reducing acid such as hydrochloric acid or sulfuric acid can be used.

  Moreover, when the coating layer 12 is chromium, the etching liquid which can be preferably used for chromium is marketed similarly. For example, an acidic solution containing ceric ammonium nitrate can be used. An alkaline solution containing potassium ferricyanide and potassium hydroxide can also be used.

  On the other hand, dry etching using plasma is a method in which an etching gas is introduced into a vacuum chamber to generate plasma by high frequency and the like, and the coating layer 12 is removed by ions or radicals generated by the plasma. Sometimes called plasma etching or reactive ion etching (RIE). This is a preferable method because the waste liquid is not generated, the environmental load is small, the surface is less contaminated with foreign matter, and the reproducibility of the treatment is excellent.

The etching gas may be an inert gas such as Ar, or a highly reactive gas containing a halogen such as F, Cl, or Br. Among them, a gas containing a halogen such as F, Cl, Br (for example, CF ₄ , SF ₆ , CHF ₃ , Cl ₂ , BCl ₃ , HBr, etc.) is highly reactive with the coating layer 12, and can be used in a short time. Processing can be performed. Further, a mixed gas of these gases and O ₂ , N ₂ or the like may be used. The dry etching apparatus may be appropriately selected from known apparatuses such as a parallel plate type, a barrel (cylindrical) type, a magnetron type, and an ECR type, and is not particularly limited.

  In the coating layer removing step S101, it is not necessary to remove the coating layer 12 over the entire surface of the molding surface 15, and the coating layer 12 in a partial region of the molding surface 15 (for example, a region that comes into contact with glass during glass molding). Remove it. Further, when the coating layer 12 has a multilayer structure, the entire coating layer 12 may be removed by etching, or some layers of the coating layer 12 on the side close to the mold substrate 11. Alternatively, only the surface layer may be removed.

  The inventor forms an oxide layer 13 on the surface after removing the coating layer 12 by etching for removing the coating layer 12, and the presence of this oxide layer 13 is the adhesion of the coating layer 12 after regeneration. I found out that it was the cause of lowering.

For example, when the mold base 11 is SiC, the oxide layer 13 made of an oxide such as SiO ₂ is formed on the surface of the mold base 11 by contacting with the etching solution or the like during the coating layer removing step S101. It is formed. The coating layer 12 formed on such an oxide layer 13 has low adhesion, and peeling or the like easily occurs during pressure molding. In particular, when the coating layer 12 is a metal material, the adhesive compatibility with the oxide is poor, and the decrease in adhesion is remarkable. Furthermore, by repeating the regeneration, the thickness of the oxide layer 13 increases, and the adhesion of the coating layer 12 further decreases.

  In the present invention, in order to prevent such a decrease in the adhesion of the coating layer 12, the coating layer 12 was formed prior to the step of re-forming the coating layer 12 (coating layer forming step S 103). A step of removing the oxide layer 13 (oxide layer removal step S102) is performed.

(Oxide layer removal step S102)
The oxide layer removing step S102 is a step of removing the oxide layer 13 formed on the surface after removing at least a part of the coating layer 12 prior to the coating layer forming step. FIG. 2C shows the state of the mold base 11 after the oxide layer 13 is removed by the oxide layer removal step S102.

  As a method of removing the oxide layer 13, there are a physical method and a chemical method. As a physical method, there are methods such as ion bombardment and polishing in vacuum, and polishing is effective from the viewpoint that the oxide layer 13 can be easily and reliably removed. From the viewpoint of preventing the shape of the molding surface 15 from collapsing, it is preferable to use alumina rather than diamond as the abrasive. For example, when the mold base 11 is SiC, the shape of the molding surface 15 is prevented from collapsing by performing polishing for several tens of seconds to several minutes using alumina whose particle size is about 1 μm as an abrasive. The oxide layer 13 can be reliably removed.

Etching is effective as a chemical method. Etching has an advantage that the shape of the molding surface 15 is not easily broken. For example, when the mold base 11 is SiC, the oxide layer 13 can be reliably removed by performing etching for several minutes using diluted hydrofluoric acid. The etchant is not limited to diluted hydrofluoric acid, and any etchant that can remove the oxide layer 13 without damaging the mold substrate 11 can be preferably used. The oxide layer 13 here is a thin layer of about several tens of nm to one hundred nm, and the etching rate may be slow. Further, since a fluorine-based etching solution such as diluted hydrofluoric acid does not etch SiC as the mold base 11, the optical surface can be obtained even if the oxide layer 13 (SiO ₂ film) having a uniform film thickness is removed. There is an advantage that the shape hardly changes.

(Coating layer forming step S103)
The coating layer forming step S103 is a step of regenerating the mold 10 by re-forming the coating layer 12 removed in the coating layer removing step S101. FIG. 2D shows a state in which the coating layer 12 is re-formed on the surface after the oxide layer 13 is removed. Since the oxide layer 13 has been removed in the above-described oxide layer removing step S102, the coating layer 12 can be formed without reducing the adhesion.

  There is no restriction | limiting in the formation method of the coating layer 12, What is necessary is just to select suitably from well-known film-forming methods, and to use. For example, a vacuum deposition method, a sputtering method, a CVD method, and the like can be given. Among these, the sputtering method is preferable because the coating layer 12 having high adhesion can be easily formed.

  In order to further improve the adhesion of the coating layer 12, it is preferable to sufficiently remove the abrasive or the etching solution attached in the oxide layer removing step S <b> 102 before forming the coating layer 12.

(Second Embodiment)
Next, a method for regenerating a forming die having a roughened surface used in the droplet forming method will be described with reference to FIGS. FIG. 3 is a flowchart showing a method for regenerating the mold in this embodiment. FIG. 4 is a schematic view (cross-sectional view) showing the state of the molding die in each step of the present embodiment.

  FIG. 4A shows the mold 20 before regeneration in the present embodiment. As in the case of the first embodiment, the mold 20 includes a mold base 11 and at least one coating layer 12 provided on the mold base 11. The surface 14 of the coating layer 12 has been roughened so as to have a predetermined surface roughness, but the roughness becomes dull due to repeated press molding, and the surface roughness is smaller than an appropriate range. In addition, defects such as partial peeling and cracks may exist. The material of the mold base 11 and the covering layer 12 is the same as that of the mold 10 described above.

  As described above, in the droplet forming method, it is possible to prevent air pools from remaining in the glass molded body by using the mold having a roughened surface as a lower mold for receiving molten glass droplets. .

  Further, in the droplet forming method, the molten glass and the mold come into contact with each other, so that the mold and the glass are likely to be fused. However, it is possible to effectively prevent fusion with glass by using a mold having a roughened surface. Such an effect can be obtained in the same manner whether the mold having a roughened surface is used as the lower mold or the upper mold.

  The covering layer removing step S101, the oxide layer removing step S102, and the covering layer forming step S103 shown in FIG. 3 are the same as those in the first embodiment shown in FIG. FIG. 4B shows a state in which the coating layer 12 has been removed from the mold 20 in the coating layer removal step S101, and FIG. 4C shows a mold base after the oxide layer 13 has been removed in the oxidation layer removal step S102. FIG. 4 (d) shows a state in which the coating layer 12 is re-formed on the surface after the oxide layer 13 is removed.

(Roughening step S104)
The roughening step S104 is a step of roughening the surface 14 of the re-formed covering layer 12 by etching. FIG. 4E shows the mold 20 in a state where the surface 14 of the coating layer 12 is roughened and the regeneration is completed.

  The roughening is performed so that the arithmetic average roughness (Ra) of the surface 14 of the coating layer 12 is 0.01 μm to 0.2 μm, and the average length (RSm) of the roughness curve element is 0.5 μm or less. It is particularly preferred. By setting the arithmetic average roughness (Ra) and the average length (RSm) of the roughness curve elements within such ranges, it is possible to more effectively prevent the occurrence of air accumulation and fusion.

  The arithmetic average roughness (Ra) and the average length of the roughness curve element (RSm) are roughness parameters defined in JIS B 0601: 2001. These parameters are measured using a measuring machine having a spatial resolution of 0.1 μm or less, such as an AFM (Atomic Force Microscope). A general stylus type roughness measuring machine is not preferable because the radius of curvature of the stylus tip is as large as several μm or more.

There is no restriction | limiting in particular in the etching method, What is necessary is just to select suitably from the methods similar to the method demonstrated by coating layer removal process S101, and to implement. When the coating layer 12 contains a chromium element, the following method (1) or (2) does not require expensive and large-sized equipment, and can perform a process with excellent uniformity efficiently and at low cost. Particularly preferred.
(1) Wet etching using an acidic solution containing ceric ammonium nitrate (2) Wet etching using an alkaline solution containing potassium ferricyanide and potassium hydroxide Even when only the solution is used, the coating layer 12 can be roughened. However, by using the acidic solution containing ceric ammonium nitrate (Ce (NH ₄ ) ₂ (NO ₃ ) ₆ ) of (1) above, fine irregularities are formed on the surface 14 of the coating layer 12 containing chromium element. It can be formed uniformly and in a short time. As long as ceric ammonium nitrate is contained, a solution containing a plurality of acids such as nitric acid and perchloric acid may be used. What is necessary is just to select the density | concentration of ceric ammonium nitrate suitably so that a desired processing rate may be obtained, and 5 mass%-50 mass% are preferable normally.

  Moreover, the coating layer 12 can be roughened also when only normal alkaline solutions, such as sodium hydroxide and potassium hydroxide, are used as etching liquid. However, by using the alkaline solution containing potassium ferricyanide and potassium hydroxide (2) above, fine irregularities can be formed uniformly and in a short time on the surface 14 of the coating layer 12 containing chromium element. . As the alkaline solution containing potassium ferricyanide and potassium hydroxide, for example, a mixed solution of potassium ferricyanide, potassium hydroxide, and pure water can be used. Furthermore, other components may be included as long as the effects of the present invention are not hindered. The ratio of potassium ferricyanide and potassium hydroxide is preferably 0.2 to 5 parts by mass of potassium hydroxide with respect to 1 part by mass of potassium ferricyanide. The amount of pure water to be mixed is not particularly limited, and may be adjusted as appropriate so as to obtain a desired processing speed.

  In order to perform a stable process, it is preferable to maintain constant conditions such as the atmospheric temperature and illuminance of the process chamber, the temperature of the lower mold, the number of processes, the temperature, amount, and concentration of the etching solution. Conversely, by changing these conditions, the depth and period of the irregularities formed can be adjusted as appropriate.

(Examples 1 and 2)
While repeating the regeneration of the mold by the method of the present invention, a glass molded body was produced by the droplet molding method, and the durability of the mold (adhesion of the coating layer) was confirmed.

  The mold 10 (Example 1) shown in FIG. 2 was used as the upper mold, and the mold 20 (Example 2) shown in FIG. 4 was used as the lower mold. In either case, the mold base 11 was SiC (a SiC layer formed by a CVD method on a SiC sintered body), and the coating layer 12 was a single layer of chromium (metal).

  The molding die 10 (upper die) was regenerated every 2000 shots according to the flowchart shown in FIG. Further, the mold 20 (lower mold) was regenerated every 1000 shots according to the flowchart shown in FIG. In any case, the coating layer removal step S101 removed the coating layer 12 by etching using a commercially available chromium etching solution (ECR-2 manufactured by Nacalai Tesque, Inc.) containing ceric ammonium nitrate. Further, the removal of the oxide layer 13 in the oxide layer removing step S102 was performed using hydrofluoric acid. The reforming of the coating layer 12 in the coating layer forming step S103 was performed by a sputtering method.

  About the shaping | molding die 20 (lower die), the roughening of the surface 14 of the coating layer 12 was performed by wet etching after that. As the etching solution, a mixed solution (alkaline solution) in which 100 g of potassium ferricyanide, 100 g of potassium hydroxide, and 1 L of pure water were mixed was used. The arithmetic average roughness (Ra) after roughening was 0.1 μm, and the average length (RSm) of the roughness curve elements was 0.25 μm. The arithmetic average roughness (Ra) and the average length of the roughness curve element (RSm) were measured by AFM (D3100 manufactured by Digital Instruments).

  A total of 8000 shots were molded while the mold was regenerated under these conditions. The number of regenerations of the mold 10 (upper mold) was 3, and the number of regenerations of the mold 20 (lower mold) was 7. As the glass material, phosphoric acid-based glass having a Tg of 480 ° C. was used. The mold was used by heating the lower mold to 500 ° C. and the upper mold to 450 ° C. The mass of the molten glass droplet was about 190 mg, and the load during pressurization was 1800 N.

  After molding, the surface of the obtained glass molded body was observed with a 50-fold optical microscope. As a result, no defects indicating that film peeling occurred in the coating layer 12 were confirmed, and even if repeated reproduction was performed, the coating layer 12 It was found that the adhesion did not decrease. The results are shown in Table 1 (molding die 10) and Table 2 (molding die 20).

(Comparative Examples 1 and 2)
Unlike Examples 1 and 2, the mold was regenerated without performing the oxide layer removing step S102, and a total of 8000 shots were molded. Other regeneration conditions and molding conditions are the same as those in Examples 1 and 2.

  After molding, a defect indicating that film peeling occurred on the coating layer 12 was confirmed on the surface of the glass molded body. Therefore, the number of shots until film peeling occurred for each number of reproductions was investigated. The results are shown in Tables 1 and 2.

  As shown in Tables 1 and 2, the number of shots until film peeling occurs in each of the upper mold and the lower mold is shortened every time reproduction is performed. Thus, when the mold was regenerated without performing the oxide layer removing step S102, it was confirmed that the adhesiveness of the coating layer 12 was lowered by repeating the regeneration.

Claims (10)

In a method for regenerating a molding die for pressure-molding a glass material, having a mold substrate and at least one coating layer provided on the mold substrate,
A coating layer removing step of removing at least a part of the coating layer;
A coating layer forming step of re-forming the removed coating layer,
A method of regenerating a mold, comprising: an oxide layer removing step of removing an oxide layer formed on a surface after removing at least a part of the coating layer prior to the coating layer forming step. The glass material is a dropped molten glass drop,
The method for regenerating a mold according to claim 1, further comprising a roughening step of roughening a surface of the coating layer by etching after the coating layer forming step.   The method for regenerating a mold according to claim 1 or 2, wherein the mold base is made of silicon carbide.   4. The method for regenerating a mold according to claim 3, wherein the mold base is a silicon carbide sintered body formed on a silicon carbide sintered body by a CVD method.   The method for regenerating a mold according to any one of claims 1 to 4, wherein the oxide layer removing step is a step of removing the oxide layer by a physical method.   The method for regenerating a mold according to any one of claims 1 to 4, wherein the oxide layer removing step is a step of removing the oxide layer by a chemical method.   The method for regenerating a mold according to claim 6, wherein the oxide layer removing step is a step of etching the oxide layer with a fluorine-based etching solution.   The method for regenerating a mold according to any one of claims 1 to 7, wherein the coating layer contains at least one element of chromium, aluminum, and titanium.   The method for regenerating a mold according to any one of claims 1 to 8, wherein the covering layer removing step is an etching step using an acidic solution.   After the coating layer forming step, the surface of the re-formed coating layer has an arithmetic average roughness (Ra) of 0.01 μm to 0.2 μm and an average length (RSm) of the roughness curve element of 0.5 μm. The method for regenerating a mold according to any one of claims 1 to 9, further comprising a step of roughening the surface to be as follows.