JP7633630B2 - Film remover and film removal method - Google Patents

Description

The present invention relates to a coating remover and a coating removal method.

Metalworking tools such as dies generally have a specified coating applied to a tool steel base material such as die steel or cemented carbide to improve wear resistance and machinability. When the coating is worn and damaged, it is selectively dissolved and removed, and the tool is reused. However, because such coatings have good corrosion resistance, they are difficult to remove, which is an obstacle when reusing dies.

The first method for removing the coating is a physical method. In Patent Document 1, the coating is removed by spraying a powder onto the workpiece. However, this method has the problem that the base material is damaged and the dimensions change.

Another method is to remove the coating by electrolytic stripping. In Patent Document 2, the coating is removed by electrolyzing the workpiece in an alkaline aqueous solution using the workpiece as the anode. This method allows only the coating to be selectively removed, so there is no change in dimensions. However, electrolysis causes the metal in the base material to dissolve, which corrodes the tool steel, raising concerns about a decrease in the strength of the base material and a deterioration in workability when used as a tool. In addition, there are problems in that the equipment investment costs are high because a power source is required for electrolysis, and when treating a workpiece with a complex shape, the current density distribution becomes biased according to the shape, causing the coating to remain in the areas of low current density.

One method for completely removing the coating without leaving any residual coating even on processed objects with complex shapes is to immerse the workpiece in a chemical coating remover. Patent Document 3 discloses an acidic coating remover whose main component is ceric ammonium nitrate. However, because the coating remover used here is strongly acidic, there is a problem in that the base material, tool steel, is corroded, just as with coating removal methods using electrolysis.

One method for removing a coating without damaging the substrate is to use an alkaline chemical coating remover, as described in Patent Document 4. The treatment solution in Patent Document 4 has an alkaline treatment pH, so the substrate is not corroded. However, because this treatment solution is intended for coatings on a substrate made of glass, there is a problem that when a coating is removed from tool steel, the strong oxidizing power of the solution causes rust to form on the substrate, the tool steel.

In response to these problems, Patent Document 5 discloses a method for removing a film formed on a substrate by simply immersing the substrate in a film remover that contains a bromate, an alkaline alkali metal salt, a halide, and a reducing sugar, while effectively suppressing the erosion of the substrate and the generation of rust from the substrate.

JP 2003-200350 A JP 2001-064800 A JP 2007-321186 A JP 1994-024240 A Patent No. 6528092

If it were possible to remove a film formed on a substrate while effectively suppressing corrosion of the substrate, the film could be recoated onto the substrate and reused, reducing the total cost of production. This demand is expected to increase in the future as more films are developed to be formed on substrates, but there is still room for development in film removers that are effective at suppressing corrosion of substrates.

The present invention aims to provide a film remover and a film removal method that can effectively suppress corrosion of the substrate while removing a film formed on the substrate.

As a result of intensive research conducted by the present inventors to solve the above problems, it was found that the above problems can be solved by using a film remover that contains (A) bromate, (B) one or more members selected from the group consisting of alkaline alkali metal salts, alkaline alkaline earth metal salts, and alkali hydroxides, (C) a halide, (D) one or more members selected from the group consisting of reducing sugars, reducing sulfur compounds, and aldehydes, (E) a carboxylic acid, and (F) an azole compound.

The present invention, which was completed based on the above findings, is defined by the following (1) to (12).
(1) A film remover containing (A) a bromate, (B) one or more members selected from the group consisting of an alkaline alkali metal salt, an alkaline alkaline earth metal salt, and an alkali hydroxide, (C) a halide, (D) one or more members selected from the group consisting of a reducing sugar, a reducing sulfur compound, and an aldehyde, (E) a carboxylic acid, and (F) an azole compound.
(2) The coating remover according to (1) above, wherein (A) is one or more selected from the group consisting of sodium bromate, potassium bromate, ammonium bromate, aluminum bromate, potassium bromide, and sodium bromide.
(3) The coating remover according to (1) or (2), wherein (B) is one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, calcium hydroxide, barium carbonate, aluminum hydroxide, and ammonium hydroxide.
(4) The coating remover according to any one of (1) to (3), wherein (C) is one or more selected from the group consisting of hydrogen chloride, sodium chloride, potassium chloride, ammonium chloride, sodium bromide, and sodium fluoride.
(5) The coating remover according to any one of (1) to (4), wherein (D) is one or more selected from the group consisting of sulfur dioxide, sodium sulfite, sodium thiosulfate, thiourea, formaldehyde, vanillin, formic acid, glucose, fructose, and maltose.
(6) The coating remover according to any one of (1) to (5), wherein (E) is one or more selected from the group consisting of acetic acid, tartaric acid, Rochelle salt, citric acid, malic acid, gluconic acid, benzoic acid, sodium benzoate, phthalic acid, and salicylic acid.
(7) The coating remover according to any one of (1) to (6), wherein (F) is one or more members selected from the group consisting of tolyltriazole, mercaptobenzothiazole, benzotriazole, 2-mercaptobenzimidazole, 1,3,4-thiodiazole-2,5-dithiol, 2-isopropylimidazole, and 2-mercaptobenzothiazole sodium salt.
(8) The coating remover according to any one of (1) to (7) above, wherein the coating to be treated is a coating formed by physical vapor deposition.
(9) The coating remover according to any one of (1) to (8) above, wherein the coating to be treated is formed on the surface of a substrate made of steel or cemented carbide.
(10) A method for removing a coating on a substrate surface, comprising the steps of:
A film removal method for removing a film from a substrate surface by adjusting the ORP to 350 to 800 mV using a liquid composition containing (A) a bromate, (B) one or more members selected from the group consisting of an alkaline alkali metal salt, an alkaline alkaline earth metal salt, and an alkali hydroxide, (C) a halide, (D) one or more members selected from the group consisting of a reducing sugar, a reducing sulfur compound, and an aldehyde, (E) a carboxylic acid, and (F) an azole compound.
(11) The method for removing a film according to (10) above, wherein the film to be treated is a film formed by physical vapor deposition.
(12) The method for removing a coating according to (10) or (11) above, wherein the coating to be treated is formed on the surface of a substrate made of steel or cemented carbide.

The present invention provides a film remover and a film removal method that can effectively suppress corrosion of the substrate while removing a film formed on the substrate.

Next, a detailed description of the embodiment of the present invention will be given. The present invention is not limited to the following embodiment, and it should be understood that appropriate design changes, improvements, etc. may be made based on the ordinary knowledge of a person skilled in the art without departing from the spirit of the present invention.

<Film remover>
The film remover according to an embodiment of the present invention contains (A) a bromate, (B) one or more compounds selected from the group consisting of an alkaline alkali metal salt, an alkaline alkaline earth metal salt, and an alkali hydroxide, (C) a halide, (D) one or more compounds selected from the group consisting of a reducing sugar, a reducing sulfur compound, and an aldehyde, (E) a carboxylic acid, and (F) an azole compound.

(Coating to be treated)
The film remover according to the embodiment of the present invention removes a film formed on a substrate (hereinafter, also referred to as a treated film). The treated film is preferably a film produced by physical vapor deposition. The treated film is a chromium-based film, a titanium-based film, an aluminum-based film, etc. Examples of the chromium-based film include a chromium nitride film, an aluminum nitride chromium film, an aluminum nitride chromium titanium film, an aluminum nitride chromium titanium silicon film, and single-layer films and laminated films thereof. Examples of the titanium-based film and the aluminum-based film include a titanium carbonitride film, an aluminum nitride titanium film, and a titanium nitride film. The film remover according to the embodiment of the present invention contains (E) a carboxylic acid and (F) an azole compound, and can remove a chromium-based film while effectively suppressing corrosion of the substrate.

The thickness of the treated film is not particularly limited, but may be 0.5 to 10 μm or 1 to 5 μm.

(Substrate)
Examples of substrates on which the coating is formed include steels such as high speed tool steel (SKH), alloy tool steel (SKD), and stainless steel (SUS), and cemented carbide.

Here, the film remover according to the embodiment of the present invention is preferably used when the substrate is a metal containing tungsten, such as a cemented carbide or SKH material. Conventionally, when a film is removed using a film remover, the substrate is corroded. This corrosion is caused by the fact that the film remover is alkaline, and therefore, when the substrate is a metal containing tungsten, such as a cemented carbide or SKH material, the tungsten dissolves in the chemical solution, causing corrosion of the substrate metal. If the substrate metal is highly corroded, there is concern about the effect on the machining accuracy and strength required for a cutting tool. In response to this, the use of the corrosion-inhibiting components (E) carboxylic acid and (F) azole compound makes it possible to remove the film while suppressing the dissolution of tungsten contained in the cemented carbide or SKH material.

(Bromate)
As the (A) bromate, which is a component of the film remover of the present invention, bromates such as sodium bromate, potassium bromate, ammonium bromate, and aluminum bromate, and bromates synthesized from bromides such as potassium bromide and sodium bromide with an oxidizing agent such as ozone can be used. As long as it is a bromate compound, substances other than those mentioned above can also be used as the bromate. As the (A) bromate, sodium bromate and potassium bromate are particularly preferred. These bromates can be used alone or in combination.

The concentration of bromate is preferably 1 to 200 g/L, more preferably 20 to 200 g/L, in terms of bromate ion concentration. If the bromate ion concentration is less than 1 g/L, this may result in a decrease in film removal performance. If the bromate ion concentration exceeds 200 g/L, this may result in a decrease in cost benefit as well as a decrease in solution stability.

(Alkaline alkali metal salts, alkaline alkaline earth metal salts, and alkali hydroxides)
As the (B) alkaline alkali metal salt, alkaline alkaline earth metal salt, and alkali hydroxide, which are components of the film remover of the present invention, various alkaline alkali metals and alkaline alkaline earth metal salts such as sodium hydroxide, potassium hydroxide, sodium carbonate, calcium hydroxide, barium carbonate, etc., and alkali hydroxides such as aluminum hydroxide and ammonium hydroxide can be used. These alkaline alkali metal salts, alkaline alkaline earth metal salts, and alkali hydroxides can be used alone or in combination of two or more. As the (B) alkaline alkali metal salts, alkaline alkaline earth metal salts, and alkali hydroxides, sodium hydroxide, potassium hydroxide, and sodium carbonate are particularly preferred.

The concentrations of the alkaline alkali metal salts, alkaline alkaline earth metal salts, and alkali hydroxides are preferably 0.1 to 100 g/L, and more preferably 1 to 50 g/L. If the concentrations of the alkaline alkali metal salts, alkaline alkaline earth metal salts, and alkali hydroxides are less than 0.1 g/L, this may result in a decrease in film removability. If the concentrations of the alkaline alkali metal salts, alkaline alkaline earth metal salts, and alkali hydroxides exceed 100 g/L, this may result in a decrease in both cost benefit and solution stability.

(Halide)
As the (C) halide, which is a component of the film remover of the present invention, hydrogen chloride, sodium chloride, potassium chloride, ammonium chloride, sodium bromide, sodium fluoride, etc. can be used. These halides can be used alone or in combination. As the (C) halide, hydrogen chloride, sodium chloride, sodium bromide, and potassium chloride are particularly preferred.

The halide concentration is preferably 0.1 to 100 g/L, and more preferably 1 to 50 g/L. If the halide concentration is less than 0.1 g/L, it may result in a decrease in film removability. If the halide concentration exceeds 100 g/L, it may result in a decrease in cost benefit and a decrease in solution stability.

(Reducing sugars, reducing sulfur compounds, and aldehydes)
When removing a film using the film remover according to the embodiment of the present invention, the ORP of the treatment liquid is adjusted by preparing an alkaline liquid composition containing (A) bromate and (B) one or more of the group consisting of an alkaline alkali metal salt, an alkaline alkaline earth metal salt, and an alkali hydroxide, and adding (D) one or more of the group consisting of reducing sugar, reducing sulfur compound, and aldehydes to lower the ORP. When the ORP is lowered too much, the ORP can be increased by using (A) bromate. As the (D) reducing sugar, which is a component of the film remover of the present invention, reducing sugars generated by the decomposition of glucose, fructose, maltose, and starch can be used. As long as it is a reducing sugar, substances other than those mentioned above can also be used as a source of reducing sugar. As the (D) reducing sulfur compound, which is a component of the film remover of the present invention, reducing sulfur compounds such as sulfur dioxide, sodium sulfite, sodium thiosulfate, and thiourea, and reducing sulfur compounds obtained by synthesis from elemental sulfur and sulfur compounds can be used. In addition, as the (D) aldehydes, which are components of the film remover of the present invention, formaldehyde, vanillin, formic acid, and aldehydes generated by oxidation of alcohols or reduction of carboxylic acids can be used. Substances other than the above can also be used as sources of aldehydes. One or more of these reducing sugars, reducing sulfur compounds, and aldehydes can be used. As the (D) reducing sugars, reducing sulfur compounds, and aldehydes, glucose, fructose, thiourea, and vanillin are particularly preferred.

(Carboxylic Acid)
The (E) carboxylic acid, which is a component of the film remover of the present invention, can be acetic acid, tartaric acid, Rochelle salt, citric acid, malic acid, gluconic acid, benzoic acid, sodium benzoate, phthalic acid, or salicylic acid. These carboxylic acids can be used alone or in combination. As the (E) carboxylic acid, Rochelle salt, citric acid, gluconic acid, or sodium benzoate is particularly preferred.

The concentration of the carboxylic acid is preferably 0.01 to 50 g/L, and more preferably 0.1 to 10 g/L. If the concentration of the carboxylic acid falls below 0.01 g/L, corrosion of the substrate may progress. If the concentration of the carboxylic acid exceeds 50 g/L, the oxidizing power of the treatment liquid may decrease, and the film removal reaction may not proceed.

(Azole Compounds)
As the (F) azole compound which is a component of the film remover of the present invention, tolyltriazole, mercaptobenzothiazole, benzotriazole, 2-mercaptobenzimidazole, 1,3,4-thiodiazole-2,5-dithiol, 2-isopropylimidazole, and 2-mercaptobenzothiazole sodium salt can be used. These azole compounds can be used alone or in combination. As the (F) azole compound, mercaptobenzothiazole, benzotriazole, and 2-mercaptobenzimidazole are particularly preferred.

The concentration of the azole compound is preferably 0.1 to 100 g/L, and more preferably 1 to 50 g/L. If the concentration of the azole compound is less than 0.1 g/L, corrosion of the substrate may progress. If the concentration of the azole compound is more than 100 g/L, the oxidizing power of the treatment liquid may decrease, and the film removal reaction may not proceed.

The film is dissolved and removed by preparing an alkaline liquid composition containing (A) bromate and one or more of the group consisting of (B) alkaline alkali metal salts, alkaline alkaline earth metal salts, and alkali hydroxides, and adjusting the liquid composition containing (C) a halide to a predetermined pH. However, if the above liquid composition is used as is, rust will form on the substrate, so the oxidizing power can be adjusted by further controlling the ORP using one or more of the group consisting of (D) reducing sugars, reducing sulfur compounds, and aldehydes, and the generation of rust can be effectively suppressed. Furthermore, due to the various effects of (E) corrosion inhibition of the substrate metal by carboxylic acid (reducing effect), promotion of film removal (chelating effect), and (F) corrosion inhibition of the substrate metal by azole compound (generation of protective film), the film formed on the substrate can be removed while effectively suppressing corrosion of the substrate.

<Method of removing the coating>
In the film removing method according to the embodiment of the present invention, first, a film remover is prepared. The film remover may be the film remover according to the embodiment of the present invention described above. On the other hand, a substrate having a film formed thereon (also called a processing target) is prepared.
Next, the object to be treated is immersed in a bath containing a film remover, with the bath being controlled to a treatment temperature, treatment pH, and ORP as described below.

(Processing Temperature)
The treatment temperature of the above-mentioned film remover is preferably in the range of 10 to 80° C., more preferably 20 to 80° C. If the treatment temperature is lower than 10° C., the film removal rate may decrease significantly, while if it is higher than 80° C., the treatment liquid level may decrease due to evaporation, or costs may increase due to maintaining the temperature.

(Treatment pH)
The pH of the film remover is controlled to 8.0 to 14.0, and more preferably 11.0 to 13.0. If the pH is lower than 8.0 or higher than 14.0, the film removal rate may be significantly reduced. As a pH adjuster for the treatment solution, inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and alkalis such as caustic soda, caustic potash, and ammonia water can be used.

(ORP)
The ORP (oxidation-reduction potential) is adjusted to 350 mV to 800 mV (vs. Ag/AgCl), and preferably to 400 mV to 800 mV (vs. Ag/AgCl). If the ORP is lower than 350 mV, the film removal rate will drop significantly, and if it is higher than 800 mV, rust may form on the substrate.

The treated object may be degreased, activated, and surface-conditioned in advance to improve the film removal rate of the present invention and to further suppress rust generation from the substrate and corrosion related to erosion of the substrate. After the film removal, it may be washed with water and dried as necessary. Film removal may also be performed by a coating or spraying process.

The above-mentioned immersion is preferably carried out for 2 to 24 hours to remove the coating, after which the piece is removed from the bath, washed with water, and dried.

This method of film removal makes it possible to remove a film formed on a substrate while effectively suppressing corrosion of the substrate.

The following examples of the present invention are provided to aid in better understanding of the present invention and are not intended to limit the present invention.

A chromium nitride film was formed on the surface of a cemented carbide alloy (Japan Carbide Tool Association standard VM-50) using ion plating to a thickness of 0.8 to 1.2 μm to prepare a test specimen. The test specimen was degreased as a pretreatment.

Example 1:
In the bath, a liquid composition containing (A) 50.0 g/L potassium bromate as bromate, (B) 20.0 g/L sodium hydroxide as alkaline alkali metal salt, alkaline alkaline earth metal salt, and alkali hydroxide, (C) 20.0 g/L sodium chloride as halide, (E) 2.0 g/L gluconic acid as carboxylic acid, and (F) 20.0 g/L mercaptobenzothiazole as azole compound was prepared, and then the pH was adjusted to 12.0 using sulfuric acid and sodium hydroxide to obtain a film remover. Then, the ORP was adjusted to 500 mV using (D) sodium thiosulfate as reducing sugar, reducing sulfur compound, and aldehyde. In this state, the above-mentioned test piece was placed in the film remover in the bath. The test piece was immersed for 24 hours while the temperature of the film remover was maintained at 40°C, and then removed from the bath, washed with water, and dried. Next, the film removability, roughening of the substrate, and rust formation were evaluated under the conditions described below.

Examples 2 to 17:
A liquid composition containing (A) potassium bromate, (B) sodium hydroxide, (C) sodium chloride, (E) gluconic acid, and (F) mercaptobenzothiazole at the concentrations shown in the table below was prepared, and then sulfuric acid and sodium hydroxide were used to adjust the pH to the pH shown in the table below to obtain a film remover. Then, (D) sodium thiosulfate was used to adjust the ORP to the pH shown in the table below. In this state, the above-mentioned test piece was placed in the film remover in the bathtub. The test piece was immersed in the film remover for 24 hours while the temperature of the film remover was maintained at 40°C, and then removed from the bathtub and washed with water and dried. Next, the film removability, roughness of the substrate, and rust generation were evaluated under the conditions described below.

Comparative Example 1:
A liquid composition containing (A) potassium bromate, (B) sodium hydroxide, (C) sodium chloride, and (E) gluconic acid at the concentrations shown in the table below was prepared, and then sulfuric acid and sodium hydroxide were used to adjust the pH to the pH shown in the table below to obtain a film remover. Then, (D) sodium thiosulfate was used to adjust the ORP to the pH shown in the table below. In this state, the above-mentioned test piece was placed in the film remover in the bathtub. The test piece was immersed in the film remover for 24 hours while the temperature of the film remover was maintained at 40°C, and then removed from the bathtub and washed with water and dried. Next, the film removability, roughness of the substrate, and rust generation were evaluated under the conditions described below.

Comparative Example 2:
A liquid composition containing (A) potassium bromate, (B) sodium hydroxide, (C) sodium chloride, and (F) mercaptobenzothiazole at the concentrations shown in the table below was prepared, and then sulfuric acid and sodium hydroxide were used to adjust the pH to the pH shown in the table below to obtain a film remover. Then, (D) sodium thiosulfate was used to adjust the ORP to the pH shown in the table below. In this state, the above-mentioned test piece was placed in the film remover in the bathtub. The test piece was immersed in the film remover for 24 hours while the temperature of the film remover was maintained at 40°C, and then removed from the bathtub and washed with water and dried. Next, the film removability, roughness of the substrate, and rust generation were evaluated under the conditions described below.

Comparative Example 3:
A liquid composition containing (A) potassium bromate, (B) sodium hydroxide, and (C) sodium chloride at the concentrations shown in the table below was prepared, and then sulfuric acid and sodium hydroxide were used to adjust the pH to the pH shown in the table below to obtain a film remover. Then, (D) sodium thiosulfate was used to adjust the ORP to the pH shown in the table below. In this state, the above-mentioned test piece was placed in the film remover in the bathtub. The test piece was immersed in the film remover for 24 hours while the temperature of the film remover was maintained at 40°C, and then removed from the bathtub and washed with water and dried. Next, the film removability, roughness of the substrate, and rust generation were evaluated under the conditions described below.

(evaluation)
The removability of the coating was evaluated based on the weight ratio of chromium (the ratio of the chromium content after the test to the chromium content before the coating of the test piece was removed) detected on the surface of the test piece by observing the surface of the test piece with a scanning electron microscope (SEM) and by energy dispersive X-ray (EDS) analysis. The specific evaluation was performed according to the following criteria A to C.
A: The weight ratio of chromium detected on the surface of the test piece was 0% (100% of the coating was removed).
B: The weight ratio of chromium detected on the surface of the test piece is 30% or more (there is 30% or more of coating residue)
C: The weight ratio of chromium detected on the surface of the test piece is 90% or more (90% or more of the coating residue is present)

The roughness and rusting of the substrate were visually observed and evaluated according to the following criteria A to C.
A: Compared to Comparative Example 1, roughening and rusting of the substrate were suppressed.
B: Roughness and rust on the substrate were about the same as in Comparative Example 1.
C: Compared to Comparative Example 1, the substrate was roughened and rusted to a greater extent.
The above test conditions and test results are shown in Tables 1 and 2.

(Discussion)
In all of Examples 1 to 17, a film remover containing (A) a bromate, (B) one or more selected from the group consisting of an alkaline alkali metal salt, an alkaline alkaline earth metal salt, and an alkali hydroxide, (C) a halide, (D) one or more selected from the group consisting of a reducing sugar, a reducing sulfur compound, and an aldehyde, (E) a carboxylic acid, and (F) an azole compound was used, and therefore it was possible to remove a film formed on a substrate while effectively suppressing corrosion of the substrate.
In Comparative Example 1, since the film remover did not contain the (F) azole compound, the film formed on the substrate could be removed, but the corrosion of the substrate could not be effectively suppressed.
In Comparative Example 2, since the film remover did not contain (E) a carboxylic acid, the film formed on the substrate could be removed, but the corrosion of the substrate could not be effectively suppressed.
In Comparative Example 3, since the film remover did not contain (E) a carboxylic acid or (F) an azole compound, the film formed on the substrate could be removed, but corrosion of the substrate could not be effectively suppressed.

Claims (6)

(A) one or more selected from the group consisting of sodium bromate, potassium bromate, ammonium bromate, and aluminum bromate, in a bromate ion concentration of 50 to 200 g/L ;
(B) 5.0 to 50 g/L of one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, and calcium hydroxide ;
(C) 5.0 to 50 g/L of one or more selected from the group consisting of hydrogen chloride, sodium chloride, potassium chloride, and ammonium chloride;
(D) one or more selected from the group consisting of sodium sulfite, sodium thiosulfate, thiourea, glucose, fructose, and maltose;
(E) 0.5 to 10 g/L of one or more selected from the group consisting of tartaric acid, Rochelle salt, citric acid, malic acid, gluconic acid, benzoic acid, and sodium benzoate, and
(F) A film remover containing 5.0 to 20 g/L of one or more selected from the group consisting of tolyltriazole, mercaptobenzothiazole, benzotriazole, 2-mercaptobenzimidazole, and 2-mercaptobenzothiazole sodium salt . The film remover according to claim 1, wherein the film to be treated is a film formed by physical vapor deposition. The coating remover according to claim 1, wherein the coating to be treated is formed on the surface of a substrate made of steel or cemented carbide. A coating removal method for removing a coating on a substrate surface, comprising the steps of:
(A) one or more selected from the group consisting of sodium bromate, potassium bromate, ammonium bromate, and aluminum bromate, in a bromate ion concentration of 50 to 200 g/L ;
(B) 5.0 to 50 g/L of one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate, and calcium hydroxide ;
(C) 5.0 to 50 g/L of one or more selected from the group consisting of hydrogen chloride, sodium chloride, potassium chloride, and ammonium chloride;
(D) one or more selected from the group consisting of sodium sulfite, sodium thiosulfate, thiourea, glucose, fructose, and maltose;
(E) 0.5 to 10 g/L of one or more selected from the group consisting of tartaric acid, Rochelle salt, citric acid, malic acid, gluconic acid, benzoic acid, and sodium benzoate, and
(F) A film removal method for removing a film on a substrate surface by using a liquid composition containing 5.0 to 20 g/L of one or more members selected from the group consisting of tolyltriazole, mercaptobenzothiazole, benzotriazole, 2-mercaptobenzimidazole, and 2-mercaptobenzothiazole sodium salt , and adjusting the ORP to 350 to 800 mV. The method for removing a film according to claim 4 , wherein the film to be treated is a film formed by physical vapor deposition. 5. The method for removing a coating according to claim 4 , wherein the coating is formed on the surface of a substrate made of steel or cemented carbide.