Method for peeling metal multilayer coating

Abstract

To provide a novel method for efficiently peeling a metal multilayer coating.SOLUTION: A method for peeling a metal multilayer coating comprises a step of peeling a multilayer coating from a metal article having, on its surface, the multilayer coating, in which a first metal layer to dissolve in a dissolution solution and a second metal layer to be passive in the dissolution solution are alternately laminated, the dissolution solution containing nitric acid and a water-soluble metal chloride, under ultrasonic irradiation in the dissolution solution. This method enables efficient peeling of the metal multilayer coating.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a technique for efficiently stripping a multi-layer metal coating. [Background technology]

[0002] There are two known methods for removing metal films: physical and chemical. Chemical removal is a method in which the metal film is chemically dissolved using a remover. In chemical removal, the types of metal that can be dissolved are limited depending on the type of remover, and when removing a metal laminate film, residual metal is likely to remain, so physical removal must be used in combination to completely remove the film.

[0003] As a method for shortening the peeling time of a metal laminate film, Patent Document 1 discloses a method for peeling a laminate film by irradiating ultrasonic waves in an etching solution containing a cyanide salt or the like, and Patent Document 2 describes a method for peeling a metal laminate film in a cyanide-based alkaline solution using an electrolysis device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-104736 A [Patent Document 2] Patent Publication No. 2021-046567 Summary of the Invention [Problem to be solved by the invention]

[0005] The method described in Patent Document 1 does not shorten the peeling time sufficiently for practical use. In addition, the technique described in Patent Document 2 is excellent in shortening the peeling time of the metal laminated film, but since it requires repeated electrical control to change the magnitude of the current, it is desired to use another means to more easily perform the peeling.

[0006] Therefore, an object of the present invention is to provide a new method for efficiently stripping a multi-layer metal coating. [Means for solving the problem]

[0007] As a result of intensive research, the present inventors unexpectedly discovered that by immersing a metal article having a multilayer coating in which a first metal layer that dissolves in a solution containing nitric acid and a water-soluble metal chloride and a second metal layer that is passive in the solution are alternately laminated, and irradiating the metal article with ultrasonic waves, the multilayer coating can be efficiently peeled off while suppressing corrosion of the base metal. The present invention was completed based on this finding and through further research.

[0008] That is, the present invention provides the following aspects. Item 1. A method for stripping a multi-layer metal coating, comprising the step of stripping, under ultrasonic irradiation in a dissolution solution containing nitric acid and a water-soluble metal chloride, a multi-layer coating formed by alternating lamination of a first metal layer that dissolves in the dissolution solution and a second metal layer that remains passive in the dissolution solution from a metal article having such a multi-layer coating on its surface. Item 2. The method according to Item 1, wherein the material of the surface of the metal article in contact with the multilayer coating is stainless steel. Item 3. The method according to item 1 or 2, wherein the multilayer coating includes 1 to 50 combinations of the first metal layer and the second metal layer. Item 4. The method according to any one of Items 1 to 3, wherein the multilayer coating has a total thickness of 2 μm to 3 mm. Item 5. The method according to any one of Items 1 to 4, wherein the nitric acid is contained in the dissolving solution in an amount of 0.2 to 30 mol per 1 mol of chlorine atoms of the metal chloride. Item 6. The method according to any one of Items 1 to 5, wherein the metal chloride has a concentration of 0.1 to 2 M in the dissolution solution. Item 7. The method according to any one of Items 1 to 6, wherein the second metal layer is made of a metal selected from the group consisting of Cr, Ti, and Ni. Item 8. The method according to any one of Items 1 to 7, wherein the first metal layer is made of a metal selected from the group consisting of Au, Ag, Pd, and Pt. Item 9. The method according to any one of Items 1 to 8, wherein the metal chloride is an alkali metal chloride. Item 10. The method according to any one of Items 1 to 9, wherein the dissolution solution does not contain aqua regia. Item 11. The method according to any one of Items 1 to 10, wherein the dissolution solution does not contain an inhibitor. Effect of the Invention

[0009] According to the present invention, a metal article having a multilayer coating in which a first metal layer that dissolves in the solution and a second metal layer that becomes passive in the solution are alternately laminated is immersed in a solution containing nitric acid and a water-soluble metal chloride, and ultrasonic waves are applied to the metal article, thereby making it possible to efficiently peel off the multilayer coating while suppressing corrosion of the base metal. [Brief description of the drawings]

[0010] [Figure 1] 1 shows the results of comparing the gold dissolution rates in dissolution solutions A and B in Test Example 1. [Diagram 2] FIG. 2 is a schematic diagram showing a specific embodiment of a method for removing a multi-layer metal coating. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The method for peeling off a metal multilayer coating of the present invention is characterized by comprising a step of peeling off the multilayer coating from a metal article having a surface thereof, the multilayer coating being composed of alternating layers of a first metal layer that dissolves in a solution containing nitric acid and a water-soluble metal chloride, under ultrasonic irradiation. The first metal layer is dissolvable in the solution, and a second metal layer is passive in the solution.

[0012] 1. Metal articles The predetermined multilayer coating to be peeled off in the present invention constitutes the surface layer of a metal article. The predetermined multilayer coating has a structure in which a first metal layer and a second metal layer are alternately laminated. The metal article is not particularly limited as long as it has the predetermined multilayer coating, and examples thereof include parts inside a vacuum film-forming apparatus such as an evaporation apparatus or a sputtering apparatus in a semiconductor manufacturing process, and an adhesion prevention plate that is a jig used when forming a film on a film-forming object. The size and / or shape of these metal articles vary depending on the size and type of the apparatus or the film-forming object, but any size and shape can be applied in the present invention.

[0013] The metal constituting the first metal layer is not particularly limited as long as it dissolves in the dissolving solution described in "2. Dissolving Solution" below, and examples thereof include gold (Au), silver (Ag), palladium (Pd), platinum (Pt), copper (Cu), and iron (Fe). The first metal layer may contain one of these metals alone (i.e., the first metal layer may be a layer made of a metal element) or may contain a plurality of metals (i.e., the first metal layer may be a layer made of a metal alloy). Preferred examples of the first metal layer include layers containing gold (Au), silver (Ag), palladium (Pd) and / or platinum (Pt), more preferably layers containing gold (Au), and even more preferably layers made of gold (Au) alone (Au layer).

[0014] The metal constituting the second metal layer is not particularly limited as long as it forms an oxide film in the dissolving solution described in "2. Dissolving Solution" below, becomes passive, and is insoluble or hardly soluble in the dissolving solution, and examples thereof include chromium (Cr), titanium (Ti), nickel (Ni), cobalt (Co), tantalum (Ta), tungsten (W), antimony (Sb), niobium (Nb), aluminum (Al), etc. The second metal layer may contain one of these metals alone (i.e., the second metal layer may be a layer made of a metal element) or may contain a plurality of metals (i.e., the second metal layer may be a layer made of a metal alloy). A preferred example of the second metal layer includes a layer containing chromium (Cr), titanium (Ti), and / or nickel (Ni), more preferably a layer containing chromium (Cr), and even more preferably a layer made of chromium element (Cr layer).

[0015] The number of combinations of the first metal layer and the second metal layer is not particularly limited, but may be, for example, 1 to 50 pairs (i.e., the total number of the first metal layer and the second metal layer is 2 to 100 layers). Since the method of the present invention enables high-speed peeling, peeling can be efficiently performed even if a plurality of second layers that are inherently difficult to peel are laminated. From this viewpoint, suitable examples of the number of combinations of the first metal layer and the second metal layer include preferably 3 to 50 pairs, more preferably 5 to 50 pairs, even more preferably 7 to 50 pairs, and even more preferably 9 to 50 pairs. In addition, from the viewpoint of increasing the peeling speed, the number of combinations of the first metal layer and the second metal layer is preferably 2 to 40 pairs, 2 to 30 pairs, 2 to 20 pairs, 2 to 15 pairs, 2 to 10 pairs, or 2 to 8 pairs.

[0016] The thickness of the first metal layer is not particularly limited, but may be, for example, 1 to 1000 μm, preferably 10 to 500 μm, more preferably 30 to 300 μm, and further preferably 50 to 100 μm.

[0017] The thickness of the second metal layer is not particularly limited, but may be, for example, 1 to 50 μm. Since the method of the present invention can rapidly peel off the second layer, which is inherently difficult to peel off, peeling can be effectively performed even when the second layer is relatively thick. From this viewpoint, suitable examples of the thickness of the second layer include preferably 5 to 50 μm, more preferably 8 to 30 μm, and even more preferably 10 to 15 μm or 12 to 15 μm.

[0018] The total thickness of the predetermined multilayer coating is not particularly limited, but may be, for example, 2 μm to 3 mm. Since the method of the present invention enables high-speed peeling, peeling can be efficiently performed even if the total thickness of the predetermined multilayer coating is relatively large. From this viewpoint, suitable examples of the total thickness of the predetermined multilayer coating are preferably 20 μm to 3 mm, more preferably 200 μm to 3 mm, even more preferably 400 μm to 3 mm, even more preferably 600 μm to 3 mm, even more preferably 800 μm to 3 mm, and particularly preferably 1 to 3 mm. In addition, from the viewpoint of increasing the peeling speed, the total thickness of the predetermined multilayer coating is preferably 2 μm to 2.5 mm, more preferably 2 μm to 2 mm, even more preferably 2 μm to 1.5 mm, even more preferably 2 μm to 1 mm, and even more preferably 2 μm to 400 μm.

[0019] The base material of a metal article having a predetermined multilayer coating is not particularly limited. Therefore, the material of the surface in contact with the multilayer coating is not particularly limited as long as it is a metal different from the metal constituting the first metal layer and the metal constituting the second metal layer. The method of the present invention enables high-speed peeling, while effectively suppressing corrosion of the base material even when applied to a metal article having a base material made of a metal that would corrode if a dissolving solution that does not contain water-soluble metal chlorides is used. From this perspective, stainless steel is a suitable example of a material for the surface in contact with the multilayer coating. More specifically, it is preferable that the metal article is one in which a predetermined multilayer coating is laminated on the surface of a stainless steel base material.

[0020] 2.Solution solution A dissolving solution for stripping multi-layer coatings from metal articles in combination with ultrasonic irradiation includes nitric acid and a water-soluble metal chloride.

[0021] The water-soluble metal chloride is not particularly limited as long as it is a salt that generates chloride ions in water, and examples thereof include alkali metal (lithium, sodium, potassium, etc.) chlorides and alkaline earth metal (calcium, magnesium, etc.) chlorides, preferably alkali metal chlorides, and more preferably sodium chloride.

[0022] The content of nitric acid in the dissolving solution is not particularly limited, but may be, for example, 0.2 to 30 moles per mole of chlorine atom of the metal chloride. From the viewpoint of enabling high-speed peeling and enhancing corrosion inhibition of the base material of the metal article, the preferred content of nitric acid in the dissolving solution is preferably 1 to 20 moles, more preferably 3 to 15 moles, and even more preferably 5 to 10 moles per mole of chlorine atom of the metal chloride.

[0023] The specific content of nitric acid contained in the dissolution solution is, for example, 0.05 to 17M, preferably 0.1 to 17M, more preferably 1 to 14M, and further preferably 5 to 11M.

[0024] The content of the metal chloride contained in the solution is not particularly limited, but may be, for example, 0.1 to 2 M in terms of chlorine atoms of the metal chloride. From the viewpoint of enhancing the corrosion inhibition of the base material of the metal article, the content of the metal chloride contained in the solution is preferably 0.3 to 1.7 M, more preferably 0.5 to 1.5 M, and even more preferably 0.8 to 1.2 M in terms of chlorine atoms of the metal chloride.

[0025] The dissolving solution used in the present invention is allowed to contain other components than nitric acid, water-soluble metal chlorides and water, but may not contain other components. Preferably, the dissolving solution used in the present invention does not contain aqua regia (CAS registration number: 8007-56-5). Preferably, the dissolving solution used in the present invention is not prepared using hydrochloric acid. Preferably, the dissolving solution used in the present invention does not contain cyanide ions from the viewpoint of increasing the dissolution rate of the first metal layer. Preferably, the dissolving solution used in the present invention does not contain iodine and / or iodide salts. Preferably, the dissolving solution used in the present invention does not contain sulfuric acid and sulfate salts. Preferably, the dissolving solution used in the present invention does not contain copper ions and iron ions.

[0026] Since the method of the present invention can suppress the corrosion of the base metal of the multi-layer coating, it is not necessary to add an inhibitor to the dissolving solution. Therefore, the dissolving solution used in the present invention preferably does not contain an inhibitor. Inhibitors are generally known as substances added to metal stripping solutions for the purpose of suppressing corrosion, and examples of such inhibitors include nitrites such as sodium nitrite and potassium nitrite, chromates such as potassium chromate and ammonium chromate, molybdates such as potassium molybdate, and tungstates such as potassium tungstate.

[0027] 3. Peeling conditions The multi-layer coating is stripped by subjecting the metal article to ultrasonic irradiation in a dissolving solution containing nitric acid and a water-soluble metal chloride.

[0028] The conditions for ultrasonic irradiation are not particularly limited, but the frequency may be, for example, 20 to 100 kHz, and from the viewpoint of compatibility between dissolution of the first metal layer and peeling off of the second metal layer, preferably 30 to 80 kHz, more preferably 40 to 60 kHz. The output of ultrasonic irradiation may vary depending on the scale of the dissolving solution in which the metal article is immersed, and may be, for example, 10 to 300 W, preferably 50 to 200 W, more preferably 100 to 150 W.

[0029] The temperature of the dissolving solution during ultrasonic irradiation is not particularly limited, and may be, for example, 20 to 50°C, preferably 30 to 45°C or 35 to 45°C.

[0030] The time required for peeling off the multi-layer coating may vary depending on the number of layers and / or the total thickness of the multi-layer coating, but may be, for example, 5 to 20 hours. Since the method of the present invention is excellent in peeling speed, suitable examples of the time required for peeling off the multi-layer coating include preferably 5 to 13 hours, more preferably 5 to 7 hours.

[0031] In the present invention, in order to further increase the peeling speed during the peeling step, a step of rubbing the surface of the multilayer coating (hereinafter also referred to as a "rubbing step") can be used in combination. In the rubbing step, the surface of the multilayer coating is rubbed with an abrasive sponge or the like to assist the peeling of the second metal layer. On the other hand, since the present invention has an excellent peeling speed, it is not necessary to use the rubbing step in combination during the peeling step. Furthermore, since the present invention has an excellent peeling speed, even if the above-mentioned rubbing step is used in combination, the frequency and / or time can be reduced. For example, the frequency of applying the rubbing step is once every 0.5 to 2 days, preferably once every 1 to 2 days. Furthermore, the total time for applying the rubbing step is 0.03% or less, preferably 0.025% or less, more preferably 0.02% or less of the time for the entire peeling step. EXAMPLES

[0032] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0033] [Test Example 1] Dissolution solution A and dissolution solution B (for comparison) having the following compositions were prepared. [Table 1]

[0034] Dissolving solution A or dissolving solution B was placed in a container, and the Au lump was immersed in it. The tank of an ultrasonic cleaner was filled with water, and the container was immersed in it. The container was irradiated with ultrasonic waves at 35 kHz or 44 kHz and 130 W. The Au concentration (g / L) in the dissolving solution was measured over time using ICP optical emission spectroscopy. The results are shown in Figure 1. Figure 1 also shows the Au concentration (g / L) in the dissolving solution when stirring was performed instead of ultrasonic irradiation.

[0035] As shown in Figure 1, when solution A was used, the Au dissolution efficiency was significantly improved when ultrasonic irradiation was performed compared to when ultrasonic irradiation was not performed. On the other hand, when solution B was used, the Au dissolution efficiency was significantly worse when ultrasonic irradiation was performed compared to when ultrasonic irradiation was not performed. Comparing solution A and solution B, although solution B had a higher Au dissolution efficiency, when ultrasonic irradiation was combined, it was found that solution A had a significantly higher Au dissolution efficiency, while solution B had a significantly worse Au dissolution efficiency. This is thought to be due to the fact that ultrasonic irradiation caused a decomposition reaction of cyanide ions, resulting in a decrease in the cyanide ion concentration.

[0036] [Test Example 2] The following solutions A and B and metal objects 1 and 2 were prepared. Metal objects 1 and 2 were used as adhesion prevention plates in vacuum deposition.

[0037] [Table 2]

[0038] As shown in FIG. 2, a container (13) was filled with dissolving solution A (2) and a metal article 1 or metal article 2 (1) was immersed in the solution. A tank of an ultrasonic cleaner (11) equipped with a transducer (12) was filled with water (14) and the container (13) was immersed in the solution. The container was irradiated with ultrasonic waves at 50 kHz and 130 W to peel off the multi-layer coating. The temperature of the dissolving solution A during peeling was 30 to 40°C. A rubbing process was not used. As a result, even though a rubbing process was not used, peeling of the multi-layer coating was completed in 6.5 hours for metal article 1 and in 16 hours for metal article 2. Furthermore, no corrosion was observed on the stainless steel surface of the base material of metal articles 1 and 2 after peeling was completed.

[0039] Similarly to the above, dissolving solution B was placed in a container, and metal article 1 or metal article 2 was immersed in it. Water was poured into the tank of an ultrasonic cleaner, and the container was immersed in it. The container was irradiated with ultrasonic waves at 50 kHz and 130 W, thereby peeling off the multi-layer coating. The temperature of dissolving solution B during peeling was 30 to 40°C. A rubbing process was not used in combination. As a result, although peeling progressed for both metal article 1 and metal article 2, the dissolution rate of the Au layer gradually slowed, and peeling of the multi-layer coating could not be completed even after 16 hours had passed.

[0040] When the multi-layer coating was peeled off in the same manner, except that stirring was used instead of ultrasonic irradiation, an oxide coating was formed when the Cr layer was exposed, and the peeling did not proceed any further, so that the peeling of the multi-layer coating could not be completed, even when solution A was used.

[0041] [Test Example 3] A dissolving solution A having the following composition and a metal article 3 were prepared. The metal article 3 was a used anti-adhesive plate for vacuum deposition. Thirty-five identical metal articles 3 were prepared per lot, and one lot was treated with both ultrasonic peeling and non-ultrasonic peeling. [Table 3]

[0042] The solution A was placed in a container, and one metal article 3 was immersed in it. The tank of an ultrasonic cleaner was filled with water, and the container was immersed in it. The container was irradiated with ultrasonic waves at 50 kHz and 130 W to peel off the multi-layer coating. The temperature of the solution A during peeling was 30 to 40°C. The metal article 3 was taken out of the solution A once a day, and if a Cr layer was present on the surface, it was rubbed with an abrasive sponge and immersed in the solution A again. After the peeling of the multi-layer coating was completed, another metal article 3 was immersed in the solution A and peeled in the same manner. By repeating this operation, the peeling of the multi-layer coating was completed for all of the metal articles 3 in one lot (35 pieces). Furthermore, no corrosion was observed on the stainless steel surface of the base material of the metal article 3 after the peeling was completed. The results are shown in Table 4.

[0043] For comparison, the multi-layer coating of one lot (35 pieces) of metal articles 3 was peeled off in the same manner as above, except that stirring was performed instead of ultrasonic irradiation and the frequency of the scrubbing work was increased to four times a day. The results are shown in Table 4.

[0044] [Table 4]

[0045] As shown in Table 4, when peeling was performed using ultrasonic irradiation in solution A, the peeling speed of the multi-layer coating was 1.8 times faster than when ultrasonic irradiation was not performed, even though the frequency of the rubbing process was 1 / 4 and the total time for which the rubbing process was applied was extremely short at 1 / 7.2. [Explanation of symbols]

[0046] 1 Metal articles 2 Lysis solution 11 Ultrasonic Cleaner 12 Transducer 13 Container 14 water

Claims

1. A method for peeling off a metal multilayer coating, comprising the step of peeling off a multilayer coating from a metal article having a surface thereof, the multilayer coating being formed by alternatingly stacking a first metal layer that dissolves in a solution containing nitric acid and a water-soluble metal chloride under ultrasonic irradiation in the solution.

2. The method according to claim 1 , wherein the material of the surface of the metal article in contact with the multi-layer coating is stainless steel.

3. The method of claim 1, wherein the multi-layer coating includes 1 to 50 combinations of the first metal layer and the second metal layer.

4. The method according to claim 1, wherein the multi-layer coating has a total thickness of 2 μm to 3 mm.

5. 2. The method according to claim 1, wherein the nitric acid is contained in the dissolving solution in an amount of 0.2 to 30 moles per mole of chlorine atom of the metal chloride.

6. 2. The method according to claim 1, wherein the metal chloride has a concentration of 0.1 to 2 M in the solution.

7. The method of claim 1 , wherein the second metal layer comprises a metal selected from the group consisting of Cr, Ti, and Ni.

8. The method of claim 1 , wherein the first metal layer comprises a metal selected from the group consisting of Au, Ag, Pd, and Pt.

9. The method of claim 1 , wherein the metal chloride is an alkali metal chloride.

10. The method of claim 1 , wherein the dissolution solution does not include aqua regia.

11. The method of claim 1 , wherein the lysis solution is inhibitor-free.

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