JP7773521B2 - Method for manufacturing surface-treated metal members - Google Patents

Description

The present invention relates to a method for manufacturing a surface-treated metal member.

Conventionally, when painting the surface of metal components, chemical conversion treatment is typically carried out to form a chemical conversion coating on the surface of the metal component before painting, with the aim of imparting corrosion resistance, paint film adhesion, etc. to the metal component.

Conventional chemical conversion treatments have involved the use of phosphate-based surface treatment agents or zirconium-based surface treatment agents that do not contain harmful heavy metals such as nickel. However, these conventional surface treatment agents have had issues, such as the inability to be used at room temperature, the generation of chemical conversion sludge as a by-product, and the need for one or more water washing steps after chemical conversion treatment, which increases treatment time and costs. Therefore, in recent years, paint-type surface treatment agents that can solve these issues have been proposed (see, for example, Patent Document 1).

International Publication No. 2022/264949

When a paint-type surface treatment agent such as that disclosed in Patent Document 1 is used, if the time interval between contacting the surface treatment agent with the metal component and drying is long, the surface treatment agent may drip or pool in the processed portion of the metal component. Dripping of the surface treatment agent poses a risk of partially reducing the corrosion resistance of the metal component. Pooling of the surface treatment agent poses a risk of causing a poor appearance of the metal component.

The present invention was made in consideration of the above, and aims to provide a method for manufacturing surface-treated metal members that can achieve desirable corrosion resistance and suppress poor appearance.

(1) The present disclosure relates to a method for producing a surface-treated metal member, the method comprising: a degreasing and water-washing step of degreasing a metal member and then rinsing it with water to form a degreased and water-washed metal member; a surface-treatment-agent contacting step of contacting the degreased and water-washed metal member with an aqueous surface treatment agent to form a metal member having a liquid film on its surface; and a drying step of drying the liquid film on the metal member having the liquid film on its surface to form a coating, the aqueous surface treatment agent comprising a silicon-containing compound (A) containing no polar functional groups other than silanol groups, a water-soluble amino group-containing compound (B), and a water-soluble amino group-containing compound (C). and water, wherein the total mass concentration of the silicon-containing compound (A) and the water-soluble amino group-containing compound (B), that is, the mass concentration of (A+B), in the aqueous surface treatment agent is within the range of 1 to 30 g/L, and the mass concentration ratio of the silicon-containing compound (A) to the total mass concentration (A+B) of the silicon-containing compound (A) and the water-soluble amino group-containing compound (B) in the aqueous surface treatment agent, {A/(A+B)}, is within the range of 45 to 95%.

(2) The method for manufacturing a surface-treated metal member described in (1), wherein the metal member is a processed and molded member.

(3) The method for producing a surface-treated metal member according to (1) or (2), wherein the silicon-containing compound (A) is a silicon-containing compound having two or more silanol groups per molecule.

(4) The method for producing a surface-treated metal member according to any one of (1) to (3), wherein the silicon-containing compound (A) is 1,2-bis(triethoxysilyl)ethane.

(5) The method for producing a surface-treated metal member according to any one of (1) to (4), wherein the water-soluble amino group-containing compound (B) is an aminosilane or an amine-modified epoxy resin.

(6) The method for producing a surface-treated metal member according to any one of (1) to (5), wherein the time interval between the end of the surface treatment agent contact step and the start of the drying step is 30 seconds or longer.

(7) The method for producing a surface-treated metal member according to any one of (1) to (6), wherein the coating formed from the aqueous surface treatment agent has a coating amount after drying in the range of 1 to 100 mg/ ^m2 .

The present invention provides a method for manufacturing surface-treated metal members that achieves desirable corrosion resistance and suppresses poor appearance.

The following describes a method for manufacturing a surface-treated metal member according to an embodiment of the present invention. The present invention is not limited to the following embodiment.

[Method of manufacturing surface-treated metal member]
The method for producing a surface-treated metal member according to this embodiment includes a degreasing and water-washing step, a surface treatment agent contact step, and a drying step. Because the method for producing a surface-treated metal member according to this embodiment includes a surface treatment agent contact step using a coating-type aqueous surface treatment agent, unlike zinc phosphate treatment, the water-washing step after the surface treatment agent contact step can be omitted. This reduces processing time and costs. A topcoat coating may be further formed on the surface of the surface-treated metal member obtained by the above-described production method using a topcoat paint. The surface-treated metal member according to this embodiment exhibits favorable adhesion to the topcoat coating. The topcoat paint is not particularly limited and may be a powder paint, a water-based paint, or a solvent-based paint.

<Metallic parts>
The metal member to be surface-treated by the method for producing a surface-treated metal member according to this embodiment is not particularly limited, and examples thereof include known metal members. Examples of metal members include iron-based substrates, aluminum-based substrates, zinc-based substrates, and magnesium-based substrates. Iron-based substrates refer to substrates containing at least one of iron and iron alloys. Specific examples of iron-based substrates include cold-rolled steel, hot-rolled steel, stainless steel, electrogalvanized steel, hot-dip galvanized steel, zinc-aluminum alloy-plated steel, zinc-iron alloy-plated steel, zinc-magnesium alloy-plated steel, zinc-aluminum-magnesium alloy-plated steel, aluminum-plated steel, aluminum-silicon alloy-plated steel, tin-plated steel, lead-tin-plated steel, chromium-plated steel, and Ni-plated steel. Aluminum-based substrates refer to substrates containing at least one of aluminum and aluminum alloys. Zinc-based substrates refer to substrates containing at least one of zinc and zinc alloys. The magnesium-based substrate means a substrate containing at least one of magnesium and a magnesium alloy.

In this embodiment, the metal component may be a processed and molded component. According to the method for manufacturing a surface-treated metal component according to this embodiment, even if the metal component to be treated is a processed and molded component, the surface-treated metal component produced can have favorable corrosion resistance and can suppress defects in appearance. A processed and molded component refers to a metal component that has been processed, for example, by laser processing, press processing, or the like.

(Degreasing and washing process)
The degreasing and water-washing process is a process in which a metal member is degreased and then washed with water to form a degreased and water-washed metal member. By degreasing the metal member, oil and/or dirt adhering to the surface of the metal member is removed. The method for degreasing the metal member is not particularly limited, and examples include a method of immersion treatment in a degreasing agent such as a phosphorus-free, nitrogen-free degreasing cleaning solution at 30 to 55°C for about several minutes. A preliminary degreasing treatment may be performed before the degreasing method. By rinsing the metal member after degreasing with water, the degreasing agent on the surface of the degreased metal member is removed. The method for water-washing is not particularly limited, and examples include a method of spraying a large amount of washing water one or more times.

(Surface treatment agent contact step)
The surface treatment agent contacting step is a step in which the degreased and washed metal member obtained in the degreasing and washing step is promptly contacted with an aqueous surface treatment agent to form a metal member having a liquid film on its surface. The time interval between the end of the degreasing and washing step and the start of the surface treatment agent contacting step is preferably 30 seconds or less. The method for contacting the degreased and washed metal member with the aqueous surface treatment agent is not particularly limited, and examples include immersion, spraying, roll coating, and bar coating. Alternatively, the aqueous surface treatment agent may be poured over the degreased and washed metal member to contact it. The conditions for contacting the degreased and washed metal member with the aqueous surface treatment agent are not particularly limited, including both temperature and time. The temperature of the aqueous surface treatment agent during contact can be, for example, 10 to 40°C. The contact time can be set arbitrarily depending on the conditions of the equipment and members to be used, and can be, for example, 10 to 30 seconds. In the surface treatment agent contacting step, if the aqueous surface treatment agent may freeze in a cold environment, the aqueous surface treatment agent may be heated to the minimum extent necessary to prevent freezing, but in a normal environment, the aqueous surface treatment agent does not need to be heated. In the surface treatment agent contacting step, the degreased and water-washed metal member may be brought into contact with the aqueous surface treatment agent once, for example.

<Water-based surface treatment agent>
The aqueous surface treatment agent used in the surface treatment agent contact step contains a silicon-containing compound (A) (hereinafter sometimes simply referred to as "silicon-containing compound (A)") that does not contain any polar functional groups other than silanol groups, a water-soluble amino group-containing compound (B), and water. The inclusion of the silicon-containing compound (A) in the aqueous surface treatment agent allows the silicon-containing compound (A) to be adsorbed onto the metal substrate, forming a film. Furthermore, the silicon-containing compound (A) functions as the main binder for the film formed by the aqueous surface treatment agent. The inclusion of the water-soluble amino group-containing compound (B) in the aqueous surface treatment agent improves adhesion between the film formed by the aqueous surface treatment agent and the topcoat coating.

The silicon-containing compound (A) is a compound that does not contain any polar functional groups other than silanol groups; in other words, it is a compound that may contain non-polar functional groups other than silanol groups. Examples of non-polar functional groups include hydrocarbon groups. In this specification and claims, the concept of silanol groups includes not only silanol groups but also silyl groups that can generate silanol groups upon hydrolysis. The silicon-containing compound (A) preferably has two silanol groups per molecule. Examples of such silicon-containing compounds (A) include compounds represented by the following formula (I):

In the above formula (I), R ¹ , R ² , R ³ , and R ⁴ each independently represent a hydrogen atom or a monovalent organic group having 1 to 30 carbon atoms. Examples of the monovalent organic group include hydrocarbon groups such as alkyl groups, alkenyl groups, cycloalkyl groups, and aryl groups. Preferred examples of the monovalent organic group include alkyl groups having 1 to 4 carbon atoms, such as methyl groups and ethyl groups.

In the above formula (I), Y represents a divalent organic group. Examples of the divalent organic group include an alkylene group or a group containing the above divalent organic group as a partial structure. The above divalent organic group preferably has 2 to 30 carbon atoms, and more preferably 2 to 12 carbon atoms.

In the above formula (I), ^X1 and ^X2 each independently represent a hydrolyzable group. Examples of the hydrolyzable group include a hydroxyl group and an alkoxy group having 1 to 4 carbon atoms. ^X1 and ^X2 are preferably hydroxyl groups. When ^X1 and ^X2 are alkoxy groups, the alkoxy groups are preferably methoxy groups or ethoxy groups.

In the above formula (I), a and b each independently represent an integer of 0 to 2, with 0≦a+b≦2. Furthermore, c and d each independently represent an integer of 0 to 2, with 0≦c+d≦2. It is preferable that a+b and c+d are both 0 or 1.

Specific examples of the silicon-containing compound (A) represented by formula (I) above include bis(trimethoxysilyl)methane, 1,2-bis(trimethoxysilyl)ethane, 1,2-bis(triethoxysilyl)ethane, 1,6-bis(trimethoxysilyl)hexane, 1,6-bis(triethoxysilyl)hexane, 1,8-bis(trimethoxysilyl)octane, 1,8-bis(triethoxysilyl)octane, 1,9-bis(trimethoxysilyl)nonane, and 1,9-bis(triethoxysilyl)nonane. Among these, 1,2-bis(triethoxysilyl)ethane is preferred from the standpoints of safety in handling and the corrosion resistance and adhesion of the resulting coating.

In addition to the compounds represented by formula (I) above, silicon-containing compound (A) may also be tetraethoxysilane, tetramethoxysilane, trimethoxysilylsilane, or condensates thereof.

The silicon-containing compound (A) may be used alone or in combination of two or more types. The silicon-containing compound (A) may be partially hydrolyzed or may be condensed by hydrolysis.

The water-soluble amino group-containing compound (B) is a water-soluble compound having one or more amino groups in its molecule. The water-soluble amino group-containing compound (B) may have a silanol group in addition to the amino group.

Specific examples of the water-soluble amino group-containing compound (B) include aminosilanes such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane, and 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, as well as amine-modified epoxy resins. The water-soluble amino group-containing compound (B) may be used alone or in combination of two or more.

Amine-modified epoxy resins can be obtained by any modification method that modifies an epoxy resin with an amine. Examples of such modification methods include adding a primary amino group-containing compound to an epoxy resin, or adding a ketiminated amino group-containing compound to an epoxy resin. Examples of such epoxy resins include bisphenol A epoxy resins and bisphenol F epoxy resins.

The total mass concentration (A+B) of the silicon-containing compound (A) and the water-soluble amino group-containing compound (B) in the aqueous surface treatment agent is within the range of 1 to 30 g/L. If the total mass concentration (A+B) is less than 1 g/L, the metal substrate will not be sufficiently covered by the film formed, resulting in reduced corrosion resistance of the surface-treated metal part. If the total mass concentration (A+B) exceeds 30 g/L, liquid pools will form, forming a thick film in those areas, resulting in poor appearance of the surface-treated metal part. It is preferable that the total mass concentration (A+B) be within the range of 3 to 30 g/L.

In the aqueous surface treatment agent, the mass concentration ratio of the silicon-containing compound (A) to the total mass concentration (A+B) of the silicon-containing compound (A) and the water-soluble amino group-containing compound (B) {A/(A+B)} is within the range of 45 to 95%. Here, the concentrations used in the calculation of {A/(A+B)} all refer to mass concentrations. If the concentration ratio {A/(A+B)} is less than 45%, the long interval between the end of the surface treatment agent contact step and the start of the drying step will cause liquid runout, resulting in insufficient adsorption of the aqueous surface treatment agent to the metal substrate surface and the failure to form a continuous film. If the concentration ratio {A/(A+B)} is greater than 95%, the content of the water-soluble amino group-containing compound (B) will decrease, resulting in reduced adhesion to the topcoat film.

The aqueous surface treatment agent according to this embodiment contains water in addition to the silicon-containing compound (A) and the water-soluble amino group-containing compound (B). The water content can be an amount such that the total mass concentration (A + B) falls within the range of 1 to 30 g/L. The aqueous surface treatment agent may also contain substances other than those mentioned above, as long as the effects of the present invention are not impaired. For example, it may also contain organic solvents, crosslinking agents that accelerate resin curing, surface conditioners used for leveling purposes, antifoaming agents used for foam suppression, and the like.

(drying process)
The drying step is a step in which the liquid film on the metal member having the liquid film on its surface obtained in the surface treatment agent contact step is dried to form a coating. The aqueous surface treatment agent used in the surface treatment agent contact step is non-reactive, so the formation of the surface treatment film does not involve a chemical conversion reaction and no sludge is generated. Therefore, unlike conventional chemical conversion treatments, the manufacturing method according to this embodiment does not require a water washing step between the surface treatment agent contact step and the drying step. This reduces the manufacturing time and manufacturing costs of the surface-treated metal member.

The drying temperature and drying time in the drying process are not particularly limited, as long as they are sufficient to evaporate components not required for the coating (e.g., water, organic solvents, etc.). For example, the drying temperature can be 100°C and the drying time can be 10 minutes. The drying method is also not particularly limited, and for example, a commercially available hot air dryer can be used. Prior to the drying process, air blowing or the like can be used to remove excess aqueous surface treatment agent.

The time interval between the end of the surface treatment agent contact step and the start of the drying step may be 30 seconds or more. The aqueous surface treatment agent according to this embodiment can ensure favorable corrosion resistance and adhesion of the surface-treated metal component even if the time interval is long and dripping or pooling occurs. The time interval may be 5 minutes or more, or 30 minutes or more. It is also preferable that it be less than 180 minutes. Here, during the period from the end of the surface treatment agent contact step to the start of the drying step, the surface-treated metal component is transported to the drying furnace without being heated, so the temperature of the surface-treated metal component is maintained at room temperature or below.

<Surface treatment film>
The amount of the coating formed by the aqueous surface treatment agent after the drying step is preferably in the range of 1 to 100 g/m ^2. This allows the surface-treated metal member to have favorable corrosion resistance and adhesion.

The method for producing a surface-treated metal member according to this embodiment may optionally include other processes as long as the effects of the present invention are not impaired. For example, after the drying process, a coating process may be included in which a topcoat coating film is formed using a topcoat coating. The topcoat coating used in the coating process is not particularly limited, and examples include powder coatings such as BI-curing powder coatings and HAA-curing powder coatings, water-based coatings, and solvent-based coatings. The coating method used in the coating process is not particularly limited, and known coating methods such as dipping, spraying, roll coating, bar coating, brush coating, and roller coating can be used.

The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. However, Example 7 is a reference example.

[Preparation of aqueous surface treatment agent]
<Examples 1 to 19, Comparative Examples 1 to 8>
Aqueous surface treatment agents according to each Example and Comparative Example were prepared according to the formulation shown in Table 1 below. The numbers indicating the blending amounts of component (A) and component (B) in Table 1 refer to parts by mass (solid content). In addition to the components shown in Table 1, the aqueous surface treatment agents according to each Example and Comparative Example also contain water. Details of the components and materials shown in Table 1 are provided below.

(A): Silicon-containing compound (A) and its corresponding components A-1: 1,2-bis(triethoxysilyl)ethane (BTSE) KBE-3026 (manufactured by Shin-Etsu Chemical Co., Ltd.)
A-2: Tetraethoxysilane (TEOS) KBE-04 (manufactured by Shin-Etsu Chemical Co., Ltd.)
A-3: Bis(triethoxysilyl)amine Dynasylan 1124 (manufactured by Evonic)

(B): Water-soluble amino group-containing compound (B) and its corresponding components B-1: 3-aminopropyltrimethoxysilane KBM-903 (manufactured by Shin-Etsu Chemical Co., Ltd.)
B-2: N-2-(aminoethyl)-3-aminopropyltrimethoxysilane KBM-603 (Shin-Etsu Chemical Co., Ltd.)
B-3: N-phenyl-3-aminopropyltrimethoxysilane KBM-573 (manufactured by Shin-Etsu Chemical Co., Ltd.)
B-4: Amine-modified epoxy resin B-5: 3-glycidoxypropyltrimethoxysilane KBM-403 (Shin-Etsu Chemical Co., Ltd.)

(B-4: Method for producing amine-modified epoxy resin)
A reaction vessel equipped with a stirrer, a cooler, a nitrogen inlet tube, and a thermometer was charged with 702 parts of an epoxy resin synthesized from bisphenol A and epichlorohydrin with an epoxy equivalent weight of 188, 269 parts of bisphenol A, 108 parts of dimer acid, and 190 parts of methyl isobutyl ketone (hereinafter referred to as "MIBK"). The mixture was reacted in the presence of 1 part benzyldimethylamine at 117°C until the epoxy equivalent weight reached 1270. Subsequently, 255 parts of an aminoethylethanolamine ketimine compound (73% by mass MIBK solution) was added, and the mixture was reacted at 117°C for 1 hour. The mixture was then diluted with MIBK to a nonvolatile content of 75%, yielding an amine-modified epoxy resin with a number average molecular weight of 2400 and an amine equivalent weight of 1184. Acetic acid was added to the amine-modified epoxy resin to a neutralization rate of 20.0% (neutralization rate relative to the amine groups in the resin), and the mixture was diluted with ion-exchanged water. Thereafter, the mixture of MIBK and water was removed under reduced pressure until the solid content reached 40% by mass, thereby preparing an emulsion of an amine-modified epoxy resin.

(C): Metal substrate C-1: Cold-rolled steel plate SPCC-SD (manufactured by Paltec Co., Ltd.)
C-2: Hot-dip galvanized steel sheet GI (manufactured by Nippon Test Panel Co., Ltd.)
C-3: Galvanized alloy steel sheet GA (manufactured by Paltec)
C-4: Electrogalvanized steel sheet SECC (manufactured by Paltec)
C-5: Stainless steel plate SUS316 (manufactured by Standard Test Piece Co., Ltd.)

(D): Topcoat paint D-1: BI curing powder paint Bilyusia PL1000 (manufactured by Nippon Paint Industrial Coatings Co., Ltd.)
D-2: HAA curing powder paint Bilyusia Ecorea PL7000 (manufactured by Nippon Paint Industrial Coatings Co., Ltd.)
D-3: One-component water-based paint, Ode Ecoline S-130 (manufactured by Nippon Paint Industrial Coatings Co., Ltd.)
D-4: Unipon 2700, a one-component urethane paint (manufactured by Nippon Paint Industrial Coatings Co., Ltd.)

[Degreasing and washing process]
Each of the metal substrates (C) shown in Table 1 below was degreased by immersion for 120 seconds in a degreasing agent (trade name "Surf Cleaner 53NF" manufactured by Nippon Paint Surf Chemicals Co., Ltd.) heated to a temperature of 40°C, and then thoroughly rinsed with tap water to obtain a degreased and water-washed metal member.

[Surface treatment agent contact step]
The aqueous surface treatment agents according to each of the Examples and Comparative Examples were sprayed onto the degreased and water-washed metal members for 30 seconds at room temperature of 25°C, bringing the metal members into contact with the aqueous surface treatment agents, and forming a liquid film of the aqueous surface treatment agent on the surface of the metal members.

In the surface treatment agent contact step, the metal component was brought into contact with the surface treatment agent while it was suspended. This makes it possible to evaluate dripping on flat surfaces and puddling on edges of processed and molded components after surface treatment. Hanging the metal component can cause dripping on the upper and middle parts of the component after contact with the surface treatment agent. In addition, puddles (thick liquid film areas) can form on the edges, which are the lowest part. This makes it possible to evaluate dripping on flat surfaces and puddling on edges of processed and molded components.

[Drying process]
After the surface treatment agent contact step, the metal substrate was left at room temperature for 30 minutes without heating, and then a drying step was started in which the metal substrate according to each Example and Comparative Example was dried in a dryer at a temperature of 100°C. The drying step was continued for 10 minutes to obtain a metal member having a surface treatment film. 30 minutes after treatment, the average amount of wet film on each steel plate was 8 g/ ^m2 .

[Painting process]
The surface-treated metal members according to each of the Examples and Comparative Examples that had undergone the drying step were spray-painted with the topcoat paint (D) shown in Table 1 below, and dried to form a coating film. The surface-treated metal members (test plates) according to each of the Examples and Comparative Examples on which the coating film had been formed were evaluated as follows.

<Corrosion resistance (SST) test>
The test panels were subjected to a salt spray test (SST) for 500 hours under the conditions of JIS Z 2371:2015. Cellophane tape was then applied to the cross-cut area, and the cellophane tape was peeled off to check for peeling from the cross-cut area. Evaluation was performed according to the following criteria. The results are shown in Table 1.
3: No peeling occurred after 500 hours.
2: No peeling occurred after 250 hours, but peeling occurred after 500 hours.
1: Peeling occurred after 250 hours.

<Film appearance evaluation>
The appearance of the surface-treated metal members according to the examples and comparative examples after the painting step was visually evaluated according to the following evaluation criteria. The results are shown in Table 1.
2: No abnormality 1: Poor appearance

As shown in Table 1, it was confirmed that the surface-treated metal members of each Example exhibited better corrosion resistance and coating appearance than the surface-treated metal members of each Comparative Example.

Claims (7)

A method for manufacturing a surface-treated metal member, comprising:
a degreasing and water-washing step of degreasing the metal member and then rinsing it with water to form a degreased and water-washed metal member;
a surface treatment agent contacting step of contacting the degreased and water-washed metal member with an aqueous surface treatment agent to form a metal member having a liquid film on its surface; and a drying step of drying the liquid film on the metal member having the liquid film on its surface to form a coating,
The aqueous surface treatment agent is
A water-soluble composition comprising a silicon-containing compound (A) containing no polar functional groups other than silanol groups, a water-soluble amino group-containing compound (B), and water,
the total mass concentration of the silicon-containing compound (A) and the water-soluble amino group-containing compound (B), i.e., the mass concentration of (A+B), in the aqueous surface treatment agent is within the range of 1 to 10.3 g/L;
the value of the mass concentration ratio {A/(A+B)} of the silicon-containing compound (A) to the total mass concentration (A+B) of the silicon-containing compound (A) and the water-soluble amino group-containing compound (B) in the aqueous surface treatment agent is within the range of 45 to 95%;
A method for manufacturing a surface-treated metal member. The method for manufacturing a surface-treated metal member according to claim 1, wherein the metal member is a processed and molded member. The method for producing a surface-treated metal member according to claim 1, wherein the silicon-containing compound (A) is a silicon-containing compound having two or more silanol groups per molecule. The method for producing a surface-treated metal member according to claim 1, wherein the silicon-containing compound (A) is 1,2-bis(triethoxysilyl)ethane. The method for producing a surface-treated metal member according to claim 1, wherein the water-soluble amino group-containing compound (B) is an aminosilane or an amine-modified epoxy resin. The method for producing a surface-treated metal member according to claim 1, wherein the time interval between the end of the surface treatment agent contact step and the start of the drying step is 30 seconds or more. 2. The method for producing a surface-treated metal member according to claim 1, wherein the coating formed from the aqueous surface treatment agent has a coating weight after drying in the range of 1 to 100 mg/ ^m2 .