JP2014105391A - Surface treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment method enabling quick formation of an oxide film layer.SOLUTION: A surface treatment method is based on removing grease on the surface of a metal product, removing and neutralizing the substance used in removal of grease, cleaning the metal product and surface-treating the cleaned metal product and includes a solution spraying step of spraying a surface treatment solution obtained by mixing at least ethanol, acetone and water or alcohols onto the surface of the cleaned metal product and an oxide film layer formation step of forming an oxide film layer on the surface of the metal product by burning, directly or indirectly, the metal product treated in the solution spraying step.

Description

  The present invention relates to a surface treatment method.

  In general, about 3/4 of the chemical elements known so far are metals. Representative examples of these metal elements include aluminum (Al), iron (Fe), copper (Cu), and the like. Since these metals are usually crystalline solids and have a relatively simple crystal structure, in most cases the arrangement of metal atoms is dense and highly symmetric. In addition, since the number of outermost electrons of a metal atom is half or less of the number of electrons accommodated in the metal, the metal does not easily form a compound with each other. However, metals readily form bonds with non-metals, such as oxygen and sulfur, which generally have more than half the number of outer shell electrons accommodated.

  Metals are widely used in various applications such as automobiles and aircraft parts, mobile phone cases, notebook computer cases, glasses rims, and kitchen equipment, depending on the material. Specifically, magnesium alloys, aluminum and aluminum alloys, titanium and titanium alloys, iron and iron alloys, copper and copper alloys, etc. are utilized in various fields depending on the characteristics of the materials.

  On the other hand, in order to form an oxide film layer on the surface of a metal, conventionally, a surface treatment method such as anodizing, plasma electrolytic oxidation, or the like called anodizing has been used.

  For example, conventionally, a magnesium alloy product is surface-treated by a surface treatment method such as anodizing or plasma electrolytic oxidation to form a thin film layer such as MgO.

Specifically, in the above surface treatment method, sodium hydroxide (NaOH) is mainly used as an electrolyte, and hydroxyl groups (OH ⁻ ) ionized from sodium hydroxide are bonded to the surface layer of a magnesium alloy product, An oxide film is formed. By forming a strong current field inside the oxide film thus formed, an oxide is further formed, and a thin film layer of MgO and Mg (OH) ₂ is formed on the surface layer of the magnesium alloy product.

  However, the above-described prior art has a problem that it takes time to form an oxide film layer on the surface layer of the product, and the product cannot be processed promptly.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved surface treatment method capable of quickly forming an oxide film layer. There is.

In order to solve the above problems, according to an aspect of the present invention, after removing oil and fat on the surface of a metal product, the substance used for removing the oil and fat is removed and neutralized, and the metal is removed. In the surface treatment method for cleaning a product and surface-treating the cleaned metal product, at least ethanol (C ₂ H ₅ OH), acetone (CH ₃ COCH ₃ ) and water are applied to the surface of the cleaned metal product. A solution spraying step of spraying the mixed surface treatment solution or alcohol; and an oxide film layer generating step of heating the metal product treated in the solution spraying step to form an oxide film layer on the surface of the metal product. A surface treatment method is provided.

  The surface treatment solution may be a solution in which ethanol is mixed 1 to 50 times the volume of water and acetone is mixed 0.05 to 1 times the volume of ethanol.

  In the oxide film layer generation step, the metal product has an internal space at a temperature of 200 to 260 ° C., and is placed in a direct flame apparatus that directly exposes the metal product to a heat source, and is subjected to a flame treatment for 10 to 15 seconds. Also good.

  The oxide layer generation step includes placing the metal product in a heat treatment device having an internal space at a temperature of 150 to 200 ° C. and indirectly heating the metal product without directly exposing it to a heat source, for 5 to 20 minutes. You may heat-process.

  In the surface treatment method, the metal product treated in the oxide film layer generation step is washed with ethanol and dried, and a top surface of the oxide film layer of the metal product treated in the washing and drying step. In addition, an electro-coloring step of forming an electrodeposition layer by an electro-coloring method may be further included.

  In the surface treatment method, the metal product treated in the oxide film layer generation step is washed and dried, and on the oxide film layer of the metal product treated in the washing and drying step, And a coating step of forming a coating layer by a coating operation.

  In the surface treatment method, the metal product treated in the oxide film layer generation step is washed and dried, and on the oxide film layer of the metal product treated in the washing and drying step, And a dry coating step of forming a coating layer by a dry coating method.

  As described above, according to the present invention, it is possible to quickly form an oxide film layer.

It is the photograph which expanded the surface of the magnesium alloy product processed by the surface treatment method concerning this invention. It is the photograph which expanded the cross section of the magnesium alloy product processed by the surface treatment method concerning this invention. It is the photograph which expanded the cross section of the magnesium alloy product which processed with the surface treatment method which concerns on this invention, and formed the coating layer.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  Hereinafter, preferred embodiments of the surface treatment method according to the present invention will be described in detail.

  The present invention provides a surface treatment method for quickly forming an oxide film layer.

  In recent years, a technique has been employed in which a coating layer is formed by applying a paint to the surface of a metal product, or a metal coating layer is formed by a sputtering method. However, when a paint layer or a metal coating layer is formed without surface treatment of a metal product, the adhesive force between the metal surface and the paint layer or between the metal surface and the metal coating layer decreases, and the paint layer and There arises a problem that the metal coating layer is easily peeled off. Therefore, the present invention provides a surface treatment method for forming a strong adhesive force with a paint layer and a metal coating layer.

  The present invention relates to a surface treatment method for metal products. Specifically, in the present invention, after removing oil and dirt adhering to the surface of a metal product, a surface treatment solution or alcohol is sprayed on the metal surface, and an open fire having an internal space maintained at a predetermined temperature. Surface treatment is performed by an apparatus or a heat treatment device.

  That is, in the present invention, first, the oil and fat on the surface of the metal product is removed as in the prior art. Furthermore, while removing and neutralizing the material used for removing fats and oils, the metal product is washed, and the cleaned metal product is subjected to surface treatment.

  Specifically, a degreasing step for degreasing, a removing step for removing trichlorethylene used for degreasing, a neutralizing step for neutralizing acetone, and a washing to remove oil and dirt adhered to the surface of the product The metal product is pretreated by a cleaning step.

In a degreasing step that removes oil and fat on the surface of the metal product, the metal product is treated with a trichlorethylene (C ₂ HCl ₃ : trichloroethylene (TCE)) solution.

Trichlorethylene (C ₂ HCl ₃ : trichloroethylene (TCE)) is a colorless and transparent liquid having a sweet scent. Trichlorethylene is used in factories, etc. for degreasing and cleaning metal machinery parts, drying metal surfaces, cleaning and dyeing in the textile industry, general solvents, diluents such as lacquers, glass and optical mechanism cleaners and leather fat removers. It is an organic solvent used for such as.

  The above-described trichlorethylene removes oil and the like adhering to the surface of metal products such as parts for automobiles and aircraft, mobile phone cases, notebook computer cases, glasses edges, and kitchen equipment.

  Next, in the removing step, after removing the oleaginous substance and the like in the degreasing step, the trichlorethylene remaining on the surface of the metal product is removed. Specifically, in the removing step, the metal product degreased in the degreasing step is treated with an acetone solution to remove the surface trichlorethylene solution.

  In addition, since the product treated with acetone is washed with water, it is necessary to neutralize acetone adhering to the product, and a neutralization step is performed. In such an acetone neutralization step, the acetone used in the removal step is treated with a methanol solution to neutralize the acetone present on the surface of the metal product.

Note that methanol (CH ₃ OH) is an alcohol having the simplest structure and is called methyl alcohol. Since methanol is extracted from the woody grass liquid obtained by dry distillation of wood, the alias is also referred to as wood sperm. Such methanol (CH ₃ OH) is contained in various natural products in the form of methyl esters with various carboxylic acids such as salicylic acid or various methyl ethers.

  Methanol is a colorless and transparent volatile liquid having a specific odor, and has good miscibility with solvents such as water, ethanol, benzene, and ether. In addition, methanol is mixed with gasoline and used as a cold-resistant fuel for automobiles, or mixed with ethanol and used as denatured alcohol.

  After acetone adhering to the surface of the metal product is neutralized with methanol, washing is performed in a washing step. In the washing step, the metal product treated in the neutralization step is washed with water, and then moisture is removed.

  Further, in the present invention, before the product cleaned in the cleaning step is placed in an open flame apparatus or a heat treatment device, a surface treatment solution or a solution for spraying alcohol on the surface of the product in order to smoothly treat the surface of the product. An injection step is performed.

The surface treatment solution used in the solution spraying step is obtained by mixing water, ethanol (C ₂ H ₅ OH), and acetone (CH ₃ COCH ₃ ). Here, the surface treatment solution is a solution in which ethanol is mixed at 1 to 50 times the volume of water and acetone is mixed at 0.05 to 1 times the volume of ethanol.

  Furthermore, in the solution spraying step, in addition to the surface treatment solution in which ethanol, acetone and water are mixed, alcohols may be sprayed on the surface of the metal product. You may spray on the surface. Even when alcohol is sprayed on the surface of the metal product, the oxide film layer can be formed smoothly by the method described later.

In the surface treatment solution, ethanol affects the flame stability and the removal of speckles and reduces the surface tension of water. Specifically, when ethanol is mixed in less than 1 times the volume of water, an oxide film layer cannot be smoothly formed on the surface layer of the metal product due to the lack of hydroxyl groups (OH ⁻ ). Furthermore, due to the surface tension of water, the surface treatment solution sprayed on the surface of the metal product is not uniformly distributed on the surface of the metal product, resulting in spots.

In addition, when ethanol is mixed more than 50 times the volume of water, the oxide film layer is easily formed by water, but the hydroxyl group (OH ⁻ ) becomes excessive, and the boiling points of water and ethanol become unstable. Therefore, it adversely affects the formation of a uniform oxide film layer.

Note that ethanol (C ₂ H ₅ OH), which is a kind of alcohol, is also called ethyl alcohol and is a colorless flammable compound and has a specific odor and taste. In addition, ethanol exists as a liquid at room temperature, and produces a clear, light blue flame when burned. Ethanol (C ₂ H ₅ OH) forms a hydrogen bond, its melting point is -114.5 ° C, and its boiling point is 78.32 ° C. In addition, ethanol is soluble in water, other alcohols, ethers, ketones, chloroform, etc., and since steam is explosive, it can also be used as a fuel in some internal combustion engines. Solvents, disinfectants It is often used as fuel.

  Acetone, on the other hand, affects the temperature and persistence of the flame, the uniformity of the heating power with ethanol, and the reduction of surface treatment time. When acetone is mixed in less than 0.05 times the volume of ethanol, the heating power by ethanol cannot be made uniform, so that the thickness of the oxide film layer cannot be made constant. Further, when acetone is mixed in an amount larger than 1 times the volume of ethanol, an excessive amount of acetone may adversely affect the shortening of the surface treatment time, and bubbles may be generated to reduce the surface uniformity.

Acetone (CH ₃ COCH ₃ ) has good miscibility with most solvents such as water, alcohol and ether, and is highly flammable due to high volatility at room temperature. Acetone is reduced by most reducing agents to isopropyl alcohol. In addition, acetone reacts with sodium amalgam to produce tetramethylethylene glycol, reacts with sodium dichromate and sulfuric acid to produce acetic acid and carbon dioxide, and reacts with ammonia to produce acetone amines such as diacetoneamine. Generate.

  Acetone is a kind of solvent and is generally used for the production of plastics and cellulose paints, and is also used for dissolving and storing acetylene. Furthermore, acetone can also be used as a raw material for organic synthesis, and a typical compound produced from acetone as a raw material is, for example, diacetone alcohol. Diacetone alcohol is used as a solvent, thinner, etc., and is easily soluble in both water and organic solvents. For example, diacetone alcohol is used for washing substances that cannot be washed with water, such as paint paints.

  Subsequently, in the oxide film layer generation step, an oxide film layer is formed on the surface of the product surface-treated in the solution spraying step. Specifically, in the oxide film layer generation step, the surface of the metal product is heated by directly exposing the metal product surface-treated in the solution spraying step to a heat source or indirectly without exposing to the direct heat source. The step of forming an oxide film layer.

  For example, in the oxide film layer generation step, the metal product surface-treated in the solution spraying step is placed in a direct fire apparatus having an internal space maintained at 200 to 260 ° C., and directly on the metal product for 10 to 15 seconds. Perform an open flame treatment that is exposed to a heat source. At this time, when the temperature of the direct flame treatment is lower than 200 ° C., not only the surface treatment time becomes long but also an oxide film layer is hardly formed on the surface of the product. In addition, when the temperature of the direct fire treatment is higher than 260 ° C., the surface state of the metal product is not uniform.

  Furthermore, in the direct fire equipment, since the heat source directly hits the metal product, the heat treatment time is 10 to 15 seconds. However, when the time of the direct fire treatment is shorter than 10 seconds, an oxide film is hardly generated, When the time of the open flame treatment is longer than 15 seconds, the surface quality of the metal product is deteriorated.

  As another embodiment of the present invention, instead of directly performing the direct flame treatment described above, the surface treatment solution or alcohol attached to the surface of the product by another heat treatment method is not directly exposed to a heat source, but indirectly. You may heat. Specifically, the metal product treated in the solution injection step is put into a heat treatment device having an internal space at a temperature of 150 to 200 ° C. and heat treated for 5 to 20 minutes. Here, when the temperature is lower than 150 ° C., the indirect heating state cannot be maintained, and not only the surface treatment time becomes longer, but also an oxide film layer is hardly generated on the surface of the product. Moreover, when temperature is higher than 200 degreeC, the above-mentioned direct-fire treatment method is more efficient in terms of energy and time.

  Further, in the above heat treatment apparatus that is not an open flame apparatus, the heat source indirectly hits the product, so the heat treatment time is 5 to 20 minutes. However, when the heat treatment time is shorter than 5 minutes, an oxide film is not easily formed. Further, since the surface treatment solution can be completely removed within 20 minutes, it is not necessary to perform heat treatment longer than 20 minutes.

  The indirect heat treatment method described above takes longer time than the direct fire treatment method, but the surface treatment solution or alcohol sprayed on the surface of the metal product should be removed more smoothly than the direct fire treatment method. Can do.

Here, the material of the metal product in the present invention is magnesium alloy, aluminum and aluminum alloy, titanium and titanium alloy, iron and iron alloy, copper and copper alloy, or the like. In the case of a magnesium alloy, an oxide film layer of MgO and Mg (OH) ₂ is formed by the surface treatment method according to the embodiment of the present invention. In the case of aluminum and an aluminum alloy, an oxide film of Al ₂ O ₃ is formed. In the case of titanium and titanium alloy, an oxide film layer of TiO ₂ is formed, in the case of iron and iron alloy, an oxide film layer of Fe ₃ O ₄ is formed, and in the case of copper and copper alloy Then, a Cu ₂ O oxide film layer is formed.

  For example, after removing the fats and oils on the surface of the magnesium alloy product, the substance used for removing the fats and oils is removed and neutralized, and the metal product is washed to prepare a magnesium alloy product.

  Further, the surface treatment solution is sprayed on the surface of the magnesium alloy product in the solution injection step, and the surface of the magnesium alloy product is burned by the direct flame method in the oxide film layer generation step. By such a surface treatment method, as shown in FIGS. 1 and 2, an oxide thin film layer can be rapidly formed on the surface of the magnesium alloy product, and an oxide film layer having a fine pattern can be formed. .

  1 and 2 show images of the surface of a magnesium product having an oxide film layer formed thereon. Similarly, an oxide film layer may be formed on aluminum and aluminum alloy, titanium and titanium alloy, iron and iron alloy, copper and copper alloy, etc. by the surface treatment method of the present invention. A surface can be obtained.

  Here, in FIG. 1 and FIG. 2, in the surface treatment of the present invention, after a surface treatment solution in which 20% by volume of acetone, 75% by volume of ethanol, and 5% by volume of water are mixed is sprayed on the surface of the magnesium alloy product, The result of the magnesium alloy product which performed the direct-fire process for 12 seconds at 250 degreeC is shown.

  By forming an oxide film layer having a fine pattern by the surface treatment method according to the present invention described above, an electrodeposition layer, a coating layer, or a coating layer described later can be formed firmly.

  As one embodiment of the present invention, after forming the oxide film layer on the surface of the metal product as described above, the electrodeposition layer can be formed on the oxide film layer by the washing and drying step and the electrocoloring step. Specifically, in the washing and drying step, the metal product treated in the oxide film layer generation step is washed and then dried. Further, in the electrocoloring step, an electrodeposition layer is formed on the oxide film layer of the cleaned and dried metal product.

  Here, in the washing and drying step, washing is preferably performed using ethanol, and after washing, ethanol is preferably sufficiently dried.

  In the electrocoloring step, the electrodeposition layer can be formed by a known electrocoloring method. Specifically, in the electro-coloring step, as shown in FIG. 3, an electrodeposition layer is formed by an electro-coloring method on the oxide film layer formed on the surface of the metal product treated in the washing and drying step. Form. Since the electro-coloring method is well known, detailed description thereof will be omitted.

  The magnesium alloy product of FIG. 3 is obtained by forming an electrodeposition layer on the magnesium alloy product shown in FIGS. 1 and 2 by an electrocoloring method. Since the specific conditions for generating the oxide film layer on the magnesium alloy product before the electrocoloring method are the same as those of the magnesium alloy product shown in FIGS. 1 and 2, the description thereof is omitted here.

  In the present invention, the thickness of the electrodeposition layer in the electrocoloring step is preferably 10 to 24 μm. The aforementioned thickness is an optimum thickness considering surface gloss, durability, and processing cost. By forming an oxide film layer on the surface of the metal product and forming the electrodeposition layer more uniformly on the oxide film layer, the surface of the metal product can be given gloss.

  Here, an experimental product having an oxide film layer and an electrodeposition layer formed on the surface of the product was subjected to hairline processing, surface gloss was confirmed every 24 hours by a limit test method using salt spray, and a 500 hour test was conducted. As a result, it was found that the surface gloss of the electrodeposition layer formed on the surface of the metal product was kept good even after 500 hours had elapsed.

  As another embodiment of the present invention, an oxide film layer is formed in the oxide film layer generation step on the metal product processed in the solution spraying step, and then a washing and drying step and a painting step are performed. A paint layer can be formed on the layer.

  Specifically, after forming an oxide film layer on the surface of the metal product, in the washing and drying step, the metal product treated in the oxide film layer generation step is washed and dried, and then in the coating step. Then, a coating layer is formed by a painting operation on the oxide film layer formed on the surface of the metal product.

  For example, as the above-described painting operation, baking coating, Teflon (registered trademark) coating, ceramic coating, powder coating, or the like can be used. In the coating step, the coating layer is formed on the oxide film layer by such coating operation. Can be formed. In addition, since the painting work methods, such as powder coating, are well-known, detailed description here is abbreviate | omitted.

  In the coating step, a coating layer may be formed on the oxide film layer by a coating method such as a powder coating method using a paint such as a baking paint, an epoxy paint, an enamel paint, or a powder paint. .

  The thickness of the coating layer is preferably formed to an optimum thickness in consideration of surface gloss, durability and processing cost. Furthermore, the coating step may be subdivided into a plurality of coatings in consideration of the gloss and durability of the coating layer.

  Specifically, the metal product that has been washed and dried in the washing and drying step is placed on a conveyor, the surface of the metal product is pretreated with a static elimination gun or a static elimination nozzle, and then an undercoat is applied to increase corrosion resistance. . Subsequently, after performing primary indirect drying, top coating is applied to increase the durability of the coating, and secondary indirect drying is performed. Furthermore, after performing the glossing by the clear process, the paint of the coating layer formed on the surface of the metal product is completely dried.

  The paint constituting the paint layer adheres firmly due to the fine pattern of the oxide film layer formed on the surface of the metal product, and the durability of the paint layer increases.

  Furthermore, as another embodiment of the present invention, after the product is washed and dried in the washing and drying step, a dry coating step of forming a metal coating layer on the oxide film layer by a dry coating method can be performed. .

  Specifically, as a dry coating method, an electron beam evaporation method, an ion plating method, a sputtering method, a plasma enhanced chemical vapor deposition (PECVD) method, or the like may be used. A metal coating layer can be formed on the oxide film layer by such a dry coating method. Here, for example, aluminum (Al), tin (Sn), titanium (Ti), copper (Cu), gold (Au), silver (Ag), nickel (Ni), stainless steel (SUS) and silicon (Si) Any one of them may be used to form a coating layer by a dry coating method. In addition, since dry coating methods, such as a sputtering method, are well-known, detailed description about this is abbreviate | omitted.

  In the dry coating step, aluminum (Al), tin (Sn), titanium (Ti), copper (Cu), gold (Au), silver (Ag), nickel (Ni), stainless steel (SUS) and silicon Two or more types of (Si) may be selected, and a multi-layered metal coating layer may be formed on the oxide film layer sequentially by a dry coating method, and various patterns are formed with different metals. May be. Note that the thickness of the metal coating layer can be set to an optimum thickness in consideration of surface gloss, durability, and processing cost.

  As described above, the surface treatment method according to the present invention can quickly form an oxide film layer by spraying a surface treatment solution on the surface of a metal product by a direct fire method or an indirect heat treatment method. is there.

Specifically, in the surface treatment method according to the present invention, water, ethanol (C ₂ H ₅ OH) and acetone (CH ₃ COCH ₃ ) are removed after removing and cleaning foreign matters such as oil adhering to the surface of the metal product. The surface treatment solution or alcohol mixed with is sprayed on the surface of the metal product, and an oxide film layer is formed by a direct fire method or an indirect heat treatment method. Therefore, the surface treatment method according to the present invention can rapidly form the oxide film layer on the surface of the metal product by greatly reducing the surface treatment time by direct or indirect heat treatment.

  In addition, the surface treatment method according to the present invention can form a strong coating layer, metal coating layer, or electrodeposition layer with a fine pattern of the oxide film layer formed quickly.

  Specifically, colored gloss can be realized on the surface of the metal product by forming an electrodeposition layer on the oxide film layer formed on the surface of the metal product by an electro-coloring method. When the metal product was subjected to hairline processing and tested by a limit test method using salt water spray, it was found that the surface gloss of the electrodeposition layer formed on the surface of the metal product was maintained for a long time.

  That is, when the oxide film layer formed on the surface of the metal product forms a fine pattern, the durability of the coating layer or the paint layer can be improved on the oxide film layer. Furthermore, the durability of the final product on which such a coating layer or paint layer is formed can be improved.

  As described above, in the present invention, an oxide film layer having a fine pattern can be rapidly formed. The durability of the coating layer is increased by the fine pattern of the oxide film layer, and the metallic texture and visualization of different materials of the product can be smoothly achieved by the coating layer of the metal product.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

Claims (7)

A surface treatment method for removing the fats and oils on the surface of the metal product, removing and neutralizing substances used for removing the fats and oils, washing the metal product, and surface-treating the washed metal product In
A solution spraying step of spraying a surface treatment solution or alcohol mixed with at least ethanol, acetone and water on the surface of the cleaned metal product;
An oxide film layer generating step of heating the metal product treated in the solution spraying step to form an oxide film layer on a surface of the metal product;
A surface treatment method comprising:   2. The surface treatment method according to claim 1, wherein the surface treatment solution is a solution obtained by mixing ethanol at 1 to 50 times the volume of water and acetone at 0.05 to 1 times the volume of ethanol.   In the oxide film layer generation step, the metal product has an internal space at a temperature of 200 to 260 ° C., and is placed in a direct flame apparatus that directly exposes the metal product to a heat source, and is subjected to a flame treatment for 10 to 15 seconds. The surface treatment method according to claim 1 or 2.   The oxide film layer generating step includes placing the metal product in an internal space at a temperature of 150 to 200 ° C. and placing the metal product in a heat treatment apparatus that indirectly heats the metal product without directly exposing it to a heat source for 5 to 20 minutes. The surface treatment method according to claim 1, wherein heat treatment is performed. Washing and drying step of washing the metal product treated in the oxide film layer generation step with ethanol and drying,
An electro-coloring step of forming an electrodeposition layer by an electro-coloring method on the oxide film layer of the metal product treated in the washing and drying step;
The surface treatment method according to any one of claims 1 to 4, further comprising: A washing and drying step of washing and drying the metal product treated in the oxide layer generation step;
A coating step of forming a coating layer by a coating operation on the oxide film layer of the metal product treated in the washing and drying step;
The surface treatment method according to any one of claims 1 to 4, further comprising: A washing and drying step of washing and drying the metal product treated in the oxide layer generation step;
A dry coating step of forming a coating layer by a dry coating method on the oxide film layer of the metal product treated in the washing and drying step;
The surface treatment method according to any one of claims 1 to 4, further comprising: