JP2017087501A - Surface-treated steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-treated steel plate which has a sufficient practical performance as a surface-treated steel plate, and in particular has a good appearance with the suppressed occurrence of an interference pattern and has excellent resistance to dew-condensation/whitening and corrosion resistance.SOLUTION: A surface-treated steel plate 10 is provided which has a steel plate 1, a plating layer 2 that is formed on the surface of the steel plate 1 and contains zinc, and a film 3 formed on the plating layer 2. The film 3 contains a resin component containing resin particles made from a polyurethane resin having an average particle size of 20-200 nm, P, Ti, V and Si, an area ratio of the resin component in the cross section of the film 3 is 35-80%, 2.5-7.5 mass% of P is contained in the film 3, surface roughness (Ra) of the steel plate 1 is 0.1-2 μm, and the resin particles are dispersed in the film.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface-treated steel sheet having a coating on the surface.

  Conventionally, galvanized steel sheets are used in various fields such as home appliances, building materials, and automobiles. Moreover, as a method for improving the corrosion resistance of a galvanized steel sheet, a technique of forming a film on the surface of the galvanized steel sheet is widely used (for example, see Patent Documents 1 to 4).

Japanese Patent No. 522050 Japanese Patent No. 4078044 Japanese Patent No. 5642082 Japanese Patent No. 5720522

Condensation whitening resistance is one of the important required characteristics regarding the surface appearance quality of surface-treated steel sheets used without coating. Condensation whitening (white rust) is a phenomenon in which a contact portion with dew condensation water generated on the surface of a surface-treated steel sheet is whitened. However, the conventional galvanized steel sheet having a coating on its surface cannot sufficiently suppress dew whitening.
Moreover, in the conventional surface-treated steel sheet, an interference pattern that causes a reduction in surface appearance quality may occur on the surface.
In addition, the conventional galvanized steel sheet having a coating on the surface has been required to further improve the corrosion resistance.

  The present invention has been made in view of such circumstances, has sufficient practical performance as a surface-treated steel sheet, and in particular, has a good appearance in which the occurrence of interference patterns is suppressed, and excellent condensation whitening resistance. It is another object of the present invention to provide a surface-treated steel sheet having corrosion resistance.

The present inventor has intensively studied to solve the above problems.
As a result, an area ratio of the resin component in the cross section of the coating, including a resin component including resin particles made of a polyurethane resin having an average particle diameter of 20 to 200 nm on a zinc-based plated steel sheet, and P, Ti, V, and Si. Then, the present inventors have found that the P content in the film and the surface roughness (Ra) of the steel sheet are within a predetermined range, and a film in which the resin particles are arranged substantially uniformly may be formed. .
The gist of the present invention is as follows.

[1] It has a steel plate, a plating layer containing zinc formed on the surface of the steel plate, and a film formed on the plating layer,
The film includes a resin component including resin particles made of a polyurethane resin having an average particle diameter of 20 to 200 nm, P, Ti, V, and Si,
The area ratio of the resin component in the cross section of the film is 35 to 80%,
In the film, P is contained in an amount of 2.5 to 7.5% by mass in terms of phosphoric acid, the steel sheet has a surface roughness (Ra) of 0.1 to 2 μm, and the resin particles are dispersed in the film. A surface-treated steel sheet characterized by comprising:

[2] The surface-treated steel sheet according to [1], wherein the maximum value of the distance between the centers of gravity of the resin particles is 3.0 times or less of the average particle diameter.
[3] The surface-treated steel sheet according to [1] or [2], wherein the film has a surface roughness (Ra) of 1 to 10 nm.
[4] The surface-treated steel sheet according to any one of [1] to [3], wherein the film has a thickness of 150 to 900 nm.
[5] The surface-treated steel sheet according to any one of [1] to [4], wherein the plating layer contains antimony.

[6] The surface-treated steel sheet according to any one of [1] to [5], wherein the resin component includes an olefin wax and / or a phenol resin.
[7] 10 to 40 wt% of Si in terms of SiO ₂ in the film in,
1.7 to 2.4% by mass of Ti,
V is 0.70-0.90 mass%,
The surface-treated steel sheet according to any one of [1] to [6], wherein a mass ratio (Ti / V) between Ti and V is 2.1 to 2.9.

  The surface-treated steel sheet of the present invention has a steel sheet, a plating layer containing zinc formed on the surface of the steel sheet, and a film formed on the plating layer, and the film is a polyurethane having an average particle diameter of 20 to 200 nm. A resin component containing resin particles made of resin, P, Ti, V, and Si, the area ratio of the resin component in the cross section of the coating is 35 to 80%, and P is converted to phosphoric acid in the coating The surface roughness (Ra) of the steel sheet is 0.1 to 2 μm, and the resin particles are dispersed in the coating. For this reason, the surface-treated steel sheet of the present invention has sufficient practical performance as a surface-treated steel sheet for coating adhesion, workability, blackening resistance, stack whitening resistance, filament tape resistance, chemical stability, and actual machine operability. Have. In particular, the surface-treated steel sheet of the present invention has a good appearance in which the generation of interference patterns is suppressed, and excellent dew whitening resistance and corrosion resistance.

It is a schematic diagram for demonstrating an example of the cross-sectional structure of the surface treatment steel plate of this embodiment. It is the bright field (STEM-BF) image obtained by observing the cross section of the surface-treated steel plate of Example 4 with a scanning transmission electron microscope (STEM). It is a high angle scattering annular dark field (STEM-HAADF) image obtained by observing the cross section of the surface-treated steel sheet of Example 4 with a scanning transmission electron microscope (STEM).

Hereinafter, the present invention will be described in detail.
"Surface-treated steel sheet"
Drawing 1 is a mimetic diagram for explaining an example of the section structure of the surface treatment steel plate of this embodiment.
A surface-treated steel plate 10 shown in FIG. 1 includes a steel plate 1, a plating layer 2 containing zinc formed on the surface 1 a of the steel plate 1, and a coating 3 formed on the plating layer 2.
In the surface-treated steel sheet 10 shown in FIG. 1, the case where the plating layer 2 and the coating 3 are formed only on the surface 1a side of one surface of the steel sheet 1 will be described as an example. A plating layer and a film may be formed on both sides of the film. Moreover, when the plating layer 2 is formed on both surfaces of the steel plate 1, the film 3 may be formed only on one surface, or may be formed on both surfaces.

(steel sheet)
In the present embodiment, the steel plate 1 on which the plating layer 2 is formed on the surface 1a is not particularly limited. For example, as the steel sheet 1, an extremely low C type (ferrite main structure), Al-k type (structure containing pearlite in ferrite), two-phase structure type (for example, structure containing martensite in ferrite, bainite in ferrite) Any type of steel sheet may be used, such as a processing induced transformation type (structure containing residual austenite in ferrite), a fine crystal type (ferrite main structure), and the like.

The steel sheet 1 has a surface roughness Ra (test length: 1 inch) (hereinafter sometimes referred to as “Ra-S”) of 0.1 to 2 μm. When the surface roughness (Ra-S) (test length: 1 inch) of the steel sheet 1 is 2 μm or less, the surface roughness of the steel sheet 1 is so rough that a part of the steel sheet 1 is exposed through the coating 3. Can be prevented. Therefore, excellent corrosion resistance can be obtained. The surface roughness (Ra-S) of the steel plate 1 is preferably 1.5 μm or less, and more preferably 1.0 μm or less. Further, when the surface roughness (Ra-S) (test length: 1 inch) of the steel plate 1 is 0.1 μm or more, it is possible to avoid the occurrence of an interference pattern on the surface-treated steel plate 10 and to obtain a good appearance. It is done. The surface roughness (Ra-S) of the steel sheet 1 is preferably 0.2 μm or more, and more preferably 0.3 μm or more.
The surface roughness (Ra-S) (test length: 1 inch) of the steel plate 1 is the surface roughness on the surface of the coating 3 of the surface-treated steel plate 10 in which the plating layer 2 and the coating 3 are formed on the surface 1a of the steel plate 1. (Ra).

(Plating layer)
The plating layer 2 contains zinc and is formed on one or both surfaces of the steel plate 1. The zinc-containing plating layer is meant to include a pure zinc-based plating layer and a zinc alloy plating layer having a zinc content of 40% by mass or more. Examples of the zinc alloy plating layer include a 55% Al—Zn alloy plating layer, a 5% Al—Zn alloy plating layer, an Al—Mg—Zn alloy plating layer, and a Ni—Zn alloy plating layer.

The plating layer 2 may contain antimony. In the plating layer 2 containing antimony, the corrosion resistance of the surface-treated steel sheet 10 tends to be lower than in the case where no antimony is contained. In the present embodiment, even when the plating layer 2 contains antimony, excellent dew whitening resistance and corrosion resistance can be obtained by the coating 3 formed on the plating layer 2.
The plating adhesion amount of the plating layer 2 is not particularly limited and may be within a conventional general range.

(Film)
The film 3 is formed on the plating layer 2.
As shown in FIG. 1, the coating 3 includes a first component 31 (resin component) including resin particles made of polyurethane resin having an average particle diameter of 20 to 200 nm, and a second component 32 excluding the first component 31. The area ratio of the first component 31 in the cross section of the coating 3 is 35 to 80%. The second component 32 includes phosphorus (P), titanium (Ti), vanadium (V), and silicon (Si). The coating 3 contains 2.5 to 7.5% by mass of P in terms of phosphoric acid. In the film 3, the first component 31 and the second component 32 are dispersed substantially uniformly.

  The coating 3 is obtained by applying an aqueous surface treatment agent containing each component contained in the coating 3 in a predetermined ratio on the plating layer 2 and drying it. Below, the mechanism in which the membrane | film | coat 3 of this embodiment is formed is demonstrated.

  When an aqueous surface treatment agent containing each component contained in the film 3 at a predetermined ratio is applied on the plating layer 2, phosphorus (P) in the aqueous surface treatment agent is deposited on the surface of the plating layer 2, and the first component 31. A coating film in which (resin component) is dispersed substantially uniformly in a self-aligning manner is formed. The balance between the surface energy of the aqueous surface treatment agent and the plating layer 2 on which phosphorus in the aqueous surface treatment agent is deposited and the balance of the specific gravity of the first component 31 present in the aqueous surface treatment agent are appropriate. It is presumed to be due to some. And if the coating film obtained by apply | coating an aqueous surface treatment chemical | medical agent is dried, the 1st component 31 and the adjacent 1st component 31 will be maintained, maintaining the substantially uniform dispersion state of the 1st component 31 in a coating film. , 31 is presumed to be formed as a film 3 in which the second components 32 existing between them are substantially uniformly arranged.

  In the coating 3 in which the first component 31 and the second component 32 are dispersed substantially uniformly, the effect of improving the corrosion resistance by the first component 31 and the second component 32 is obtained substantially uniformly over the entire coating. As a result, in the surface-treated steel sheet 10 of the present embodiment, excellent corrosion resistance is obtained. More specifically, excellent corrosion resistance is achieved by a synergistic effect of the film forming action by silicon (Si) contained in the first component 31 and the second component 32 and the corrosion inhibiting action by titanium (Ti) and vanadium (V). Is obtained.

  The dispersion state of the first component 31 in the film 3 can be evaluated using, for example, the maximum value of the distance between the centers of gravity of the resin particles. In the present embodiment, the maximum value of the distance between the centers of gravity of the resin particles is preferably 3.0 times or less of the average particle diameter, more preferably 2.5 times or less, and even more preferably 2.0 times or less. . When the maximum value of the distance between the center of gravity of the resin particles is 3.0 times or less, the effect of improving the corrosion resistance due to the uniform arrangement of the first component 31 and the second component 32 in the coating 3 is further enhanced. Thus, the surface-treated steel sheet 10 having more excellent corrosion resistance is obtained.

  The smoothness of the surface 33 of the coating 3 has a correlation with the dispersion state of the resin particles 31 in the coating 3. Therefore, the dispersion state of the resin particles in the film 3 can be evaluated using the surface roughness (Ra) of the film 3. In addition, the dispersion state of the resin particles in the film 3 is determined together with the surface roughness (Ra) of the film 3 or instead of the surface roughness (Ra) of the film 3 and the maximum cross-sectional height (Rt) of the roughness curve and You may evaluate using a root mean square roughness (Rq).

  The surface roughness (Ra) (hereinafter sometimes referred to as “Ra-F”) of the film 3 is preferably 1 to 10 nm. When the surface roughness (Ra-F) of the film 3 is 1 nm or more, it can be easily manufactured and the productivity is excellent. When the surface roughness (Ra-F) of the film 3 is 10 nm or less, the effect of improving the corrosion resistance due to the uniform arrangement of the first component 31 and the second component 32 in the film is further enhanced. The surface-treated steel sheet 10 is excellent in corrosion resistance. The surface roughness (Ra-F) of the film 3 is preferably 5 nm or less.

  For the same reason that the surface roughness (Ra-F) of the film 3 is preferably 1 to 10 nm, the maximum cross-sectional height (Rt) of the roughness curve of the film 3 is preferably 20 to 200 nm. The root mean square roughness (Rq) of the film 3 is more preferably 10 to 100 nm.

  The area ratio of the first component 31 (resin component) in the cross section of the film 3 is 35 to 80%. In the present embodiment, since the area ratio of the first component 31 of the film 3 is 35% or more, the film forming function by the first component 31 is sufficiently obtained, and the film 3 is excellent in barrier properties and adhesion. For this reason, the surface-treated steel plate 10 excellent in corrosion resistance is obtained. The area ratio of the first component 31 is preferably 40% or more in order to further improve the barrier property and adhesion improving effect of the first component 31. Moreover, in this embodiment, since the area ratio of the 1st component 31 of the membrane | film | coat 3 is 80% or less, the corrosion-resistance improvement effect by the 2nd component 32 is fully acquired, and the outstanding corrosion resistance is acquired. The area ratio of the first component 31 is preferably 60% or less in order to further improve the corrosion resistance improvement effect by the second component 32.

  The thickness of the film 3 is preferably 150 to 900 nm. When the thickness of the film 3 is 150 nm or more, the effect of improving the corrosion resistance by the film 3 becomes remarkable, and even more excellent corrosion resistance is obtained. When the thickness of the film 3 is more than 900 nm, the corrosion resistance improving effect due to the first component 31 and the second component 32 being dispersed substantially uniformly is saturated.

"First ingredient"
The first component 31 includes resin particles made of a polyurethane resin having an average particle diameter of 20 to 200 nm. The polyurethane resin forms a film having a good balance between tensile strength and elongation. For this reason, the membrane | film | coat 3 containing the 1st component 31 containing a polyurethane resin is excellent in barrier property and adhesiveness. Therefore, the surface-treated steel sheet 10 of this embodiment has excellent corrosion resistance.

  The content of the polyurethane resin in the film 3 is preferably 25 to 45% by mass. When the content of the polyurethane resin is 25% by mass or more, and more preferably 30% by mass or more, the barrier property and non-adhesion improvement effect by the polyurethane resin can be obtained more effectively. When the content of the polyurethane resin is 45% by mass or less, more preferably 40% by mass or less, the content of other components can be sufficiently ensured, so that more excellent corrosion resistance can be obtained.

  When the average particle size of the polyurethane resin is less than 20 nm, the resin particles made of the polyurethane resin are likely to aggregate, and the resin particles are difficult to uniformly disperse in the coating 3. As a result, the coating 3 is arranged in which the resin particles are unevenly distributed, and the corrosion resistance of the surface-treated steel sheet 10 may be insufficient. In this embodiment, since the average particle diameter of the polyurethane resin is 20 nm or more, excellent corrosion resistance is obtained. When the average particle size of the polyurethane resin is 50 nm or more, further excellent corrosion resistance can be obtained. Moreover, in this embodiment, since the average particle diameter of a polyurethane resin is 200 nm or less, the membrane | film | coat 3 by which the resin particle was disperse | distributed substantially uniformly is formed by forming the membrane | film | coat 3 by the method mentioned later. The average particle size of the polyurethane resin is more preferably 100 nm or less.

The average particle diameter of the resin particles made of polyurethane resin in the film can be calculated by a method of observing the film cross section shown below. First, a carbon film is deposited as a protective film on the surface of the steel plate. Subsequently, a carbon film of several μm is formed using FIB (focused ion beam processing apparatus, SMI3050SE: manufactured by Hitachi High-Tech Science Co., Ltd.). Thereafter, microsampling is performed using an FIB at an acceleration voltage of 30 kV (finishing process: 5 kV), and this is thinned to obtain a sample of a film cross section. The obtained sample is observed using TEM (transmission electron microscope) or SEM (scanning electron microscope). Ten resin particles having a large equivalent circle diameter are selected from the observed resin particles, and the average value is set as the average particle diameter of the resin particles made of polyurethane resin.
As a result of investigation by the present inventor, it was confirmed that the result of the average particle diameter of the resin particles made of the polyurethane resin calculated by the above method substantially coincides with the average particle diameter of the polyurethane resin used as the material of the aqueous surface treatment agent. did it. Therefore, the average particle diameter of the resin particles made of the polyurethane resin in the film can be regarded as the same as the average particle diameter of the polyurethane resin used as the material for the aqueous surface treatment agent.

The first component 31 (resin component) may contain not only polyurethane resin particles but also olefin wax and / or phenol resin.
The olefin wax is contained as necessary, and may not be contained. The olefin wax is preferably contained in the resin component in order to impart lubricity to the coating 3. Examples of the olefin wax include polyethylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and the like. The olefin wax is preferably resin particles having an average particle size of 20 to 200 nm.

  When the 1st component 31 contains an olefin wax, it is preferable that content of the olefin wax in the membrane | film | coat 3 is 3.5-6.0 mass%. When the content of the olefinic wax is 3.5% by mass or more, and more preferably 4.0% by mass or more, the film 3 can sufficiently obtain the lubricity improvement effect by the olefinic wax, and has excellent workability. The surface-treated steel sheet 10 is obtained. When the content of the olefin-based wax is 6.0% by mass or less, more preferably 5.5% by mass or less, the content of other components can be sufficiently secured, so that more excellent corrosion resistance can be obtained.

  The first component 31 may contain a phenol resin as necessary. When the phenol resin is contained in the film 3, the adhesion of the film 3 is further improved.

"Second component"
The second component 32 includes P, Ti, V, and Si.
Phosphorus (P) contained in the second component 32 suppresses zinc that causes white rust in the coating 3 from eluting from the plating layer 2 and suppresses the generation of white rust.

  The P content in the film 3 is 2.5 to 7.5% by mass in terms of phosphoric acid. The coating 3 in which the P content in the coating 3 is 2.5% by mass or more in terms of phosphoric acid is formed using an aqueous surface treatment agent that sufficiently contains phosphorus. Therefore, at the stage where the aqueous surface treatment agent is applied on the plating layer 2, phosphorus in the aqueous surface treatment agent is deposited on the surface of the plating layer 2, and the surface energy of the plating layer 2 becomes appropriate, so that the first component A coating film is formed in which 31 is dispersed substantially uniformly in a self-aligning manner. As a result, by drying the coating film, the coating film 3 in which the first component 31 and the second component 32 are arranged substantially uniformly is formed. Moreover, in this embodiment, since P content in the membrane | film | coat 3 is 2.5 mass% or more, favorable stack whitening resistance and filament tape-proof property are obtained. The P content in the film 3 is improved in terms of stack whitening resistance and filament tape resistance, and in order to obtain the film 3 in which the first component 31 and the second component 32 are more uniformly arranged, in terms of phosphoric acid. It is preferable that it is 3.0 mass% or more. When the P content in the film 3 is 7.5% by mass or less, preferably 7.0% by mass or less in terms of phosphoric acid, good blackening resistance is obtained, and the content of other components is sufficient. Since it can ensure, more excellent corrosion resistance is obtained.

  Titanium (Ti) and vanadium (V) have a corrosion inhibiting action and improve the corrosion resistance of the surface-treated steel sheet 10. Ti and V have different corrosive environments in which the function as a corrosion inhibitor is effectively exhibited. For this reason, by containing two types of Ti and V as corrosion inhibitors, corrosion under various corrosive environments can be suppressed by the synergistic effect of Ti and V, and more excellent corrosion resistance can be obtained.

  The Ti content in the film 3 is preferably 1.7 to 2.4% by mass. When the Ti content is 1.7% by mass or more, and more preferably 1.9% by mass or more, the surface treated steel sheet having a corrosion resistance improving effect due to containing Ti is sufficiently obtained, and the surface-treated steel sheet is more excellent in corrosion resistance. 10 When the Ti content is 2.4% by mass or less, more preferably 2.3% by mass or less, the content of other components can be sufficiently ensured, so that more excellent corrosion resistance can be obtained.

  The V content in the film 3 is preferably 0.70 to 0.90% by mass. When the V content is 0.70% by mass or more, and more preferably 0.75% by mass or more, the coating 3 can sufficiently obtain the effect of improving the corrosion resistance by vanadium, and the surface-treated steel sheet 10 having more excellent corrosion resistance is obtained. When the V content is 0.90% by mass or less, the content of other components can be sufficiently ensured, so that more excellent corrosion resistance can be obtained.

  The mass ratio (Ti / V) between Ti and V in the film 3 is preferably 2.1 to 2.9. When (Ti / V) is 2.1 or more, more preferably 2.2 or more, the coating 3 can sufficiently obtain an effect of improving corrosion resistance by titanium, and the surface-treated steel sheet 10 having excellent workability is obtained. When (Ti / V) is 2.9 or less, and more preferably 2.8 or less, the effect of improving corrosion resistance by vanadium can be sufficiently obtained, and therefore, more excellent corrosion resistance can be obtained.

Silicon (Si) has a film-forming action and improves corrosion resistance.
Si content in the film 3 is preferably from 10 to 40 wt% in terms of SiO _2. The coating 3 in which the Si content in the coating 3 is 10% by mass or more, preferably 20% by mass or more in terms of SiO ₂ is formed using an aqueous surface treatment agent that sufficiently contains Si. For this reason, it becomes the membrane | film | coat 3 excellent in the barrier property in which the three-dimensional bridge | crosslinking by a siloxane bond was formed by apply | coating and drying an aqueous surface treatment chemical | medical agent. As a result, it is possible to obtain the coating 3 having a further excellent effect of improving corrosion resistance. When the Si content in the film 3 is 40% by mass or less, preferably 30% by mass or less in terms of SiO ₂ , the content of other components can be sufficiently ensured, so that more excellent corrosion resistance can be obtained.

The contents of P, Ti, V, and Si in the film 3 can be calculated by analyzing the film 3 by fluorescent X-ray analysis and assuming that P, Ti, V, and Si in the film exist as oxides. As a result of examination by the present inventors, each component of P (phosphoric acid equivalent), Ti, V, Si (SiO ₂ equivalent) in the film calculated by the above method is a mass ratio with respect to the total solid content of the aqueous surface treatment agent. It was confirmed that it corresponds to (phosphoric acid, Ti, V, Si (in terms of SiO ₂ )). Therefore, the content (mass%) of P (phosphoric acid equivalent), Ti, V, and Si (SiO ₂ equivalent) in the film is regarded as a percentage of the mass ratio of the aqueous surface treatment agent to the total solid content. be able to.

The film 3 may contain fluoride ions of less than 0.3 mg · m ⁻² . The fluoride ion in the film 3 is derived from a component containing fluoride ions contained in the aqueous surface treatment agent used when forming the film 3 as necessary. The component containing fluoride ions may be used for water-solubilizing or solubilizing each component to be the film 3 in the aqueous surface treatment agent. Generation | occurrence | production of the condensation whitening resulting from containing fluoride ion can be prevented as content of the fluoride ion in the film | membrane 3 is less than 0.3 mg * m ^<-2 >. More specifically, when the content of fluoride ions is less than 0.3 mg · m ⁻² , the amount of fluoride ions eluted in the condensed water becomes small. For this reason, even if fluoride ions are concentrated and deposited on the film 3 during the drying process of the dew condensation water, the amount is not shown as dew condensation whitening. Therefore, it is possible to prevent deterioration of the appearance (white rust generation) due to whitening of condensation.

"Production method of surface-treated steel sheet"
Next, a method for producing the surface-treated steel sheet according to the present embodiment will be described with an example.
First, the steel plate 1 is prepared, and the plating layer 2 containing zinc is formed on one or both surfaces of the steel plate 1 by a conventionally known method.
Next, in this embodiment, the coating system 3 is formed on the plating layer 2 by applying an aqueous surface treatment agent containing the respective components contained in the coating film 3 in a predetermined ratio on the plating layer 2 and drying it. A method of forming will be described.

(Aqueous surface treatment agent)
In this embodiment, for example, as an aqueous surface treatment agent, polyurethane resin (A), phenol resin (B), silane coupling agent (C), titanium acetylacetone complex (D), and vanadium compound (E) And an olefin wax (F), an acetic acid component (G), a phosphoric acid component (H), and water.

<Polyurethane resin (A)>
The polyurethane resin (A) contained in the aqueous surface treatment agent exists as water-dispersible resin particles (dispersion) having an average particle diameter of 20 to 200 nm dispersed in water. As the polyurethane resin (A), a cationic polyurethane resin is preferable. As the cationic polyurethane resin, a resin particle whose surface is modified with an amine is preferable. The modification with amine is preferably modification with a tertiary or lower amine. In the case of modification with a quaternary amine, the water resistance deteriorates due to a positive charge present in the film 3 formed by applying and drying an aqueous surface treatment agent. The modification with amine is preferably modification with a tertiary amine from the viewpoint of achieving both the dispersibility of the resin particles in the film 3 and the water resistance of the film 3.

  The cationic polyurethane resin is preferably a polycarbonate-based cationic polyurethane resin containing a structural unit represented by the following general formula (1). When the cationic polyurethane resin contains a structural unit represented by the following general formula (1), the coating film 3 formed by applying and drying an aqueous surface treatment agent is given more excellent barrier properties, so that it has corrosion resistance. Will improve.

  In the general formula (1), R is an aliphatic alkylene group having 4 to 9 carbon atoms, and n is a number average molecular weight of a carbonate-based polyol which is a raw material of the polycarbonate-based cationic polyurethane resin is 500 to 5000. An integer corresponding to the range.

<Phenolic resin (B)>
The phenol resin (B) is contained in the aqueous surface treatment agent as necessary, and may not be contained. When the phenolic resin (B) is contained in the aqueous surface treatment agent, the stability of the aqueous surface treatment agent is improved.

As the phenol resin (B), a cationic phenol resin (B) is preferable. The cationic phenol resin preferably has a repeating unit represented by the following general formula (2). The cationic phenol resin is more preferably a polymer molecule having an average degree of polymerization of a repeating unit represented by the following general formula (2) of 2 to 50. When the average degree of polymerization is within the above range, the coating 3 having excellent water resistance can be obtained, so that more excellent corrosion resistance can be obtained. In addition, the average polymerization degree of the repeating unit of General formula (2) can be calculated | required from an integral ratio by < ¹ > H-NMR.

In the general formula (2), Y ₁ and Y ₂ each independently represent hydrogen or a Z group represented by the general formula (3) or the general formula (4), and the average of Z groups per each benzene ring The number of substitutions is 0.2 to 1.0. In addition, the average number of substitution of Z group can be calculated | required from an integration ratio by < ¹ > H-NMR.

In the above general formula (3) and general formula (4), R1, R2, R3, R4 and R5 are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms. A ⁻ represents a hydroxide ion or an oxo acid (eg, nitric acid, sulfuric acid, phosphoric acid, carbonic acid, carboxylic acid, etc.) ion.

  In the aqueous surface treatment agent, it is preferable to use an anion that volatilizes during dry film formation as the counter anion of the cationic polyurethane resin and the cationic phenol resin. Specifically, formic acid or acetate ion is preferred as the anion that volatilizes during dry film formation.

<Silane coupling agent (C)>
The silane coupling agent (C) is a process of drying (baking) a coating film formed by applying an aqueous surface treatment agent to form silanol by hydrolysis and forming a three-dimensionally crosslinked siloxane type coating by siloxane bonds. .
As the silane coupling agent (C), it is preferable to use an alkoxysilane having 2 or more, preferably 3 or more alkoxy groups. As the silane coupling agent (C), a partial hydrolyzate of the above alkoxysilane may be used.

  The alkoxy group of the silane coupling agent (C) is hydrolyzed in an aqueous surface treatment agent to form silanol (—Si—OH). When the pH of the aqueous surface treatment agent is 6.5 or less, the dispersion stability of silanol in the aqueous surface treatment agent is good.

  Examples of the silane coupling agent (C) include N- (aminoethyl) -3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxy. Examples thereof include propylmethyldimethoxysilane, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-methacryloxypropyltrimethoxysilane.

Among the above, the silane coupling agent (C) is preferably one having a functional group reactive with the polyurethane resin (A) and the phenol resin (B). As such a silane coupling agent (C), for example, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane and the like are preferable, and 3-aminopropyltriethoxysilane is preferable. Silane, 3-glycidoxypropyltrimethoxysilane is particularly preferred.
The type of reaction between the polyurethane resin (A) and the phenol resin (B) and the silane coupling agent (C) may be a polymerization reaction, a condensation reaction, an addition reaction, or the like, and is not particularly limited.

<Titanium acetylacetone complex (D)>
The titanium acetylacetone complex (D) in the aqueous surface treatment agent reacts with the plating layer 2 in the process of drying (baking) the coating formed by applying the aqueous surface treatment agent, and precipitates in the coating 3 as a titanium compound. To do. Even if acetylacetonate and acetylacetone resulting from the acetylacetone complex (D) of titanium are present in the coating 3, they are weakly ionic and do not adversely affect the condensation whitening property. Examples of the titanium acetylacetone complex (D) include titanium diisopropoxybisacetylacetonate and titanium tetrakisacetylacetonate.

<Vanadium compound (E)>
As the vanadium compound (E), a compound containing no strong electrolyte or a salt with a volatile acid is preferably used. Examples of the vanadium compound (E) that does not include a strong electrolyte include vanadium pentoxide, metavanadate and its salt (for example, ammonium metavanadate), vanadium trioxide, vanadium dioxide, vanadium oxyacetylacetonate, vanadium acetylacetonate, and the like. Can be mentioned. Examples of the salt with a volatile acid include vanadium acetate. Considering the effect of improving corrosion resistance, it is preferable to use an acetylacetone complex of vanadium such as vanadium acetylacetonate and vanadium oxyacetylacetonate among the vanadium compounds (E).

<Olefin wax (F)>
The olefin wax (F) is contained in the aqueous surface treatment agent as necessary, and may not be contained. The olefin wax (F) is preferably contained in the aqueous surface treatment agent in order to impart lubricity to the coating 3.
Examples of the olefin wax (F) include polyethylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and the like.

  The resin particles made of the olefin wax (F) are preferably surface-modified with the silane coupling agent (I). When the olefin wax (F) is surface-modified with the silane coupling agent (I), the wettability of the olefin wax (F) in the aqueous surface treatment agent is increased. For this reason, the coating film 3 obtained by applying and drying the aqueous surface treatment agent has resin particles made of olefin wax (F) dispersed more uniformly.

  As the silane coupling agent (I) used for the surface modification of the olefin wax (F), it is preferable to use a silane coupling agent having a reactive functional group. As the olefin wax (F) surface-modified with the silane coupling agent (I), a polyethylene wax emulsion having a carboxyl group is used as a silane coupling agent containing an epoxy group (for example, 3-glycidoxypropyltrimethoxy). It is preferable that the surface is modified with (silane).

  The ratio (I / F) of the mass of the silane coupling agent (I) to the mass of the olefin wax (F) is preferably 0.025 to 0.035. The addition amount of the silane coupling agent (I) is preferably equal to or greater than the acid value of the dispersion of the olefin wax (F) used for the aqueous surface treatment agent.

<Acetic acid component (G)>
The acetic acid component (G) improves the stability of the aqueous surface treatment agent. This effect is stabilized by the pH buffering action of the acetic acid component (G) when the pH of the aqueous surface treatment agent is stabilized at 3.5 to 4.0, and the dispersion stability of the silanolated silane coupling agent (C) is increased. It is presumed that the condensation reaction of the silane coupling agent (C) is slow. In addition, it is known from the investigation by the present inventors that the pH at which the condensation reaction of the silane coupling agent (C) is the slowest is 3.5 to 4.0.

  Examples of the acetic acid component (G) include acetic acid, ammonium acetate, potassium acetate, sodium acetate and the like. In view of the chemical stability of the aqueous surface treatment chemical, acetic acid is particularly preferred. In addition, acetic acid has a boiling point of 118 ° C., and has a low boiling point among organic acids having a buffering action and hardly remains in the film 3. For this reason, acetic acid is suitable as an acetic acid component (G) contained in the aqueous surface treatment agent.

<Phosphoric acid component (H)>
Examples of the phosphoric acid component (H) include inorganic phosphoric acid compounds such as phosphoric acid, ammonium phosphate, potassium phosphate, sodium phosphate, and monosodium dihydrogen phosphate. Among these, the phosphoric acid component (H) is considered in consideration of the effect of improving the stack whitening resistance and the filament tape resistance and obtaining the coating 3 in which the first component 31 and the second component 32 are more uniformly arranged. ) Is preferably phosphoric acid.

  The phosphoric acid component (H) contained in the aqueous surface treatment agent reacts with the plating layer 2 to form a zinc phosphate film on the surface of the plating layer 2. The zinc phosphate coating suppresses the elution of zinc from the plating layer 2 and suppresses the occurrence of white rust. Further, the phosphoric acid component (H) reduces the amount of the acetic acid component (G) remaining in the coating 3. As a result, the adhesive layer of the filament tape used to temporarily fix the end of the coil made of the surface-treated steel sheet 10 can be prevented from being attacked by the acetic acid component (G), and the decrease in the adhesion of the filament tape can be suppressed. Moreover, the fall of the dew condensation whitening resistance by the acetic acid component (G) which remains in the membrane | film | coat 3 can be prevented.

The preferable compounding ratio of each component contained in the aqueous surface treatment agent used in the present embodiment is as follows.
(1) The ratio (NC) / (NV) of the silane coupling agent (C) to the mass in terms of SiO _{2 with} respect to the mass of the solid content (V) of the aqueous surface treatment agent is 0.10 to 0.40.
(2) The ratio (ND) / (NV) of the titanium acetylacetone complex (D) to the mass (ND) in terms of Ti with respect to the mass of the solid content (V) is 0.017 to 0.024.
(3) Ratio (NE) / (NV) of the vanadium compound (E) to the mass (NE) in terms of V with respect to the mass of the solid content (V) is 0.007 to 0.009.
(4) Ratio (NF) / (NV) of the olefin wax (F) to the mass of the solid content (V) is 0.035 to 0.060.
(5) Ratio (NG) / (NV) of the mass of the acetic acid component (G) to the mass of the solid content (V) is 0.04 to 0.14.
(6) The ratio (NH) / (NV) of the phosphoric acid component (H) to the mass of the solid content (V) is 0.025 to 0.075.
(7) The ratio (ND) / (NE) of the mass of the acetylacetone complex (D) of titanium to the mass of Ti of the vanadium compound (E) in terms of V is 2.1 to 2.9.
(8) The ratio (NH) / (NG) of the mass of the phosphoric acid component (H) to the mass of the acetic acid component (G) is 0.25 to 1.1.

<(NC) / (NV)>
The ratio (NC) / (NV) of the silane coupling agent (C) to the mass in terms of SiO _{2 with} respect to the mass of the solid content (V) of the aqueous surface treatment agent is 0.10 to 0.40. Preferably, it is 0.16-0.19. When (NC) / (NV) is 0.40 or less, the content of other components can be sufficiently ensured, so that the effect of improving corrosion resistance by the other components can be sufficiently obtained. When (NC) / (NV) is 0.10 or more, three-dimensional crosslinking due to a siloxane bond is sufficiently formed, and the coating 3 having excellent corrosion resistance is obtained.

<(ND) / (NV)>
The ratio (ND) / (NV) of the mass of acetylacetone complex (D) of titanium with respect to the mass of solid content (V) (ND) / (NV) is 0.017 to 0.024, preferably 0. .019 to 0.023. When (ND) / (NV) is 0.017 or more, the coating film 3 can sufficiently obtain the effect of improving the corrosion resistance by the titanium compound (D). When (ND) / (NV) is 0.024 or less, the content of other components can be sufficiently ensured, so that the effect of improving corrosion resistance by the other components can be sufficiently obtained.

<(NE) / (NV)>
The ratio (NE) / (NV) of the vanadium compound (E) to the mass (NE) in terms of V with respect to the mass of the solid content (V) is 0.0070 to 0.0090, preferably 0.0075. ~ 0.0090. When (NE) / (NV) is 0.0070 or more, the coating 3 can sufficiently obtain the effect of improving the corrosion resistance by the vanadium compound (E). When (NE) / (NV) is 0.0090 or less, the content of other components can be sufficiently secured, so that the effect of improving the corrosion resistance by the other components can be sufficiently obtained.

<(NF) / (NV)>
The ratio (NF) / (NV) of the mass of the olefin wax (F) to the mass of the solid content (V) is 0.035 to 0.060, preferably 0.040 to 0.055. is there. When (NF) / (NV) is 0.035 or more, the film 3 having sufficient lubricity is obtained, and the surface-treated steel sheet 10 having good workability is obtained. Further, when (NF) / (NV) is 0.060 or less, the surface-treated steel sheet 10 having good handleability can be obtained.

<(NG) / (NV)>
The ratio (NG) / (NV) of the mass of the acetic acid component (G) to the mass of the solid content (V) is 0.04 to 0.14, preferably 0.05 to 0.13. More preferably, it is 0.06-0.12. When (NG) / (NV) is 0.04 or more, the stability of the aqueous surface treatment agent is further improved. When (NG) / (NV) is 0.14 or less, it is possible to prevent a decrease in condensation whitening resistance due to the acetic acid component (G) remaining in the coating 3.

<(NH) / (NV)>
The ratio (NH) / (NV) of the mass of the phosphoric acid component (H) to the mass of the solid content (V) is 0.025 to 0.075, preferably 0.030 to 0.070. Yes, more preferably 0.035 to 0.065. Since (NH) / (NV) is 0.025 or more, elution of zinc from the plating layer 2 can be suppressed. In addition, when the aqueous surface treatment agent is applied on the plating layer 2, the phosphoric acid component (H) in the aqueous surface treatment agent is deposited on the surface of the plating layer 2, and the surface energy of the plating layer 2 becomes appropriate. A coating film in which the first component 31 is dispersed substantially uniformly in a self-aligning manner is formed. When (NH) / (NV) is 0.075 or less, the content of other components can be sufficiently secured, so that the effect of improving the corrosion resistance by the other components can be sufficiently obtained.

<(ND) / (NE)>
The ratio (ND) / (NE) of the mass in terms of Ti of the acetylacetone complex (D) of titanium to the mass in terms of V of the vanadium compound (E) is 2.1 to 2.9, preferably 2. It is 2-2.8, More preferably, it is 2.3-2.7. When (ND) / (NE) is 2.1 or more, the coating 3 can sufficiently obtain the corrosion resistance improvement effect of the titanium compound (D). When (ND) / (NE) is 2.9 or less, the coating 3 can sufficiently obtain the effect of improving the corrosion resistance by the vanadium compound (E). When (ND) / (NE) is 2.1 to 2.9, corrosion under various corrosive environments can be suppressed due to the synergistic effect of Ti and V, and the coating 3 has more excellent corrosion resistance.

<(NH) / (NG)>
The ratio (NH) / (NG) of the mass of the phosphoric acid component (H) to the mass of the acetic acid component (G) is 0.25 to 1.1, and is 0.30 to 1.0. Preferably, it is 0.35-0.9. When (NH) / (NG) is 0.25 to 1.1, the effect of improving the stability of the aqueous surface treatment agent by the acetic acid component (G) is sufficiently obtained, and the acetic acid component (G) is contained in the coating 3. Decrease in condensation whitening resistance and decrease in adhesion of the filament tape can be suppressed due to the residual.

The aqueous surface treatment agent can be prepared by dissolving or dispersing the above components in an aqueous solvent at the above mixing ratio. Each component is adjusted to have a predetermined ratio with respect to the mass of the nonvolatile content (solid content (V)) excluding the solvent and the volatile component (the mass of the film) so as to have a predetermined ratio in the film 3. To do.
The aqueous solvent used for the aqueous surface treatment agent can be water only. The water-based solvent used for the water-based surface treatment agent is a water-soluble organic solvent (for example, alcohols) that does not contain a strong electrolyte for the purpose of improving the drying property of the coating film formed by applying the water-based surface treatment agent. ) May be contained, for example, at a content of 30% by mass or less of the entire aqueous solvent.

<PH>
The pH of the aqueous surface treatment agent is preferably 2.0 to 6.5. When the pH of the aqueous surface treatment agent is 6.5 or less, the dispersion stability of the silane coupling agent (c) becomes good. It is preferable that the pH of the aqueous surface treatment agent is 2.0 or more because the aqueous surface treatment agent can be easily handled and the aqueous surface treatment agent can be prevented from damaging the equipment. The pH of the aqueous surface treatment agent can be adjusted, for example, by adding a volatile acid such as acetic acid or formic acid to the aqueous surface treatment agent.

<Components containing fluoride ions>
The water-based surface treatment agent may contain a component containing fluoride ions as necessary. The component containing fluoride ions is used for water-solubilizing or solubilizing each component to be the film 3 in the aqueous surface treatment agent.
Examples of the component containing fluoride ions contained in the aqueous surface treatment agent include sodium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, titanium hydrofluoric acid, zircon hydrofluoric acid, and the like.

  Additives commonly used in coating treatment liquids such as leveling agents and antifoaming agents may be added to the aqueous surface treatment agent.

  In the present embodiment, a coating film is formed by applying the aqueous surface treatment agent thus obtained onto the plating layer 2. As a method of applying the aqueous surface treatment agent on the plating layer 2, it is preferable to use a roll coater. When coating using a roll coater, the film thickness can be easily controlled by adjusting the peripheral speed ratio, and excellent productivity can be obtained.

  In this embodiment, the aqueous surface treatment agent is applied on the plating layer to form a coating film and then held for 0.1 to 10 seconds until drying is started. By holding for 0.1 second or more, more preferably 0.2 seconds or more in the state of the coating film, the first component 31 in the coating film is stably dispersed substantially uniformly in a self-aligning manner. In addition, even if it exceeds 10 seconds after forming a coating film until it starts drying, the effect that the 1st component 31 in a coating film disperse | distributes uniformly is not improved, and productivity falls. Therefore, it is preferable that the time for maintaining the state of the coating film is 10 seconds or less, and more preferably 5 seconds or less.

  Next, the coating film held for a predetermined time is dried. The temperature at which the coating film is dried is selected such that the counter anion and acetic acid component (G) of the cationic polyurethane resin and the cationic phenol resin, which are volatile components in the aqueous surface treatment agent, are volatilized. Specifically, it is preferable that the maximum ultimate plate temperature (PMT) when the coating film is dried be in the range of 60 to 150 ° C. Examples of the drying method for drying the coating film include hot air drying and oven drying.

When the volatile component in the coating film is volatilized by drying the coating film, the pH in the coating film increases. Thereby, while maintaining the state in which the first component 31 is substantially uniformly dispersed, the plating layer 2, the acetylacetone complex of titanium (D), the silane coupling agent silanolized by hydrolysis (C), Cationic polyurethane resin reacts with cationic phenol resin. As a result, the surface of the plating layer 2 and polyurethane resin, phenol resin, siloxane compound, and titanium compound form a strong network by ionomer bond, metalloxane bond, or siloxane bond, and the vanadium compound and olefin wax are fixed there. Thus, the film 3 in which the first component 31 and the second component 32 are dispersed substantially uniformly is formed.
The surface-treated steel sheet of this embodiment is obtained by the above process.

  In the present embodiment, the case where an aqueous surface treatment agent containing a phenol resin (B) and an olefin wax (F) is used when forming the coating 3 has been described as an example, but the phenol resin (B) Alternatively, the film 3 may be formed using an aqueous surface treatment agent that does not contain the olefin wax (F).

  Next, examples of the present invention will be described. In addition, this invention is not limited to the Example shown below.

  Aqueous surface treatment chemicals X1 to X42 containing the contents shown in Table 1 and the components shown below in Table 2 were prepared. The solid content in the aqueous surface treatment agent was adjusted to 11 mass%.

(Components of aqueous surface treatment chemicals)
[Polyurethane resin (A)]
A1: Polyurethane resin (average particle size 60 nm)
A2: Polyurethane resin (average particle size 10 nm)
A3: Polyurethane resin (average particle size 300 nm)

[Phenolic resin (B)]
B1: Cationic phenol resin Average polymerization degree n of repeating units of general formula (2) n = 5, X = —CH ₂ N (CH ₃ ) ₂ of general formula (2), Y = H of general formula (2), Z substitution degree of general formula (2) = 0.5

[Silane coupling agent (C)]
C1: 3-aminopropyltriethoxysilane C2: 3-glycidoxypropyltrimethoxysilane C3: 3-mercaptopropyltrimethoxysilane

[Acetylacetone complex of titanium (D)]
D1: Titanium diisopropoxybisacetylacetonate D2: Titanium tetrakisacetylacetonate D3: Titanium hydrofluoric acid (component containing fluoride ion)
[Vanadium compound (E)]
E1: Vanadium acetylacetonate

[Olefin wax (F)]
F1: Olefin wax having an average particle diameter of 0.05 μm F2: Olefin wax having an average particle diameter of 0.05 μm and surface-modified with a silane coupling agent (3-glycidoxypropyltrimethoxysilane). Content of silane coupling agent contained in olefin wax [mass of silane coupling agent / mass of olefin wax] = 0.030

[Acetic acid component (G)]
G1: Acetic acid [phosphoric acid component (H)]
H1: Phosphoric acid

  A steel sheet having plating layers on both surfaces shown below in the surface roughness (Ra-S) shown in Table 3 was prepared. A steel sheet having plating layers on both sides also has a plating layer having a zinc content of 40% by mass or more. In addition, the surface roughness (Ra-S) of the steel sheet shown in Table 3 is the surface roughness of the surface-treated steel sheet obtained by forming a film by the method described later at a measurement length of 1 inch at an arbitrary position on the surface of the film. The thickness (Ra) was determined by measuring using a contact-type roughness meter.

(Steel plate with plating layers on both sides)
"EG"
NS JINCOAT (registered trademark), manufactured by Nippon Steel & Sumikin Co., Ltd., electrogalvanized steel sheet, plate thickness 0.8 mm, single-sided plating coverage 20 g / m ²
"GI"
NS Silver Zinc (registered trademark), manufactured by Nippon Steel & Sumitomo Metal Corporation, hot-dip galvanized steel sheet, plate thickness 0.8 mm, single-sided plating coverage 60 g / m ²
"GI (Sb)"
NS Silver Zinc (registered trademark), manufactured by Nippon Steel & Sumikin Co., Ltd., antimony-containing hot dip galvanized steel sheet, plate thickness 0.8 mm, single-sided plating coverage 60 g / m ²

"GA"
NS Silver Alloy (registered trademark), manufactured by Nippon Steel & Sumikin Co., Ltd., alloyed hot dip galvanized steel sheet, plate thickness 0.8 mm, single-sided plating coverage 60 g / m ²
"SD"
Superdimer (registered trademark), manufactured by Nippon Steel & Sumikin Co., Ltd., zinc-aluminum-magnesium-silicon alloy-plated steel sheet, plate thickness 0.8 mm, single-sided plating coverage 60 g / m ²
"ZL"
NS Zinclite (registered trademark), manufactured by Nippon Steel & Sumikin Co., Ltd., zinc-nickel alloy plated steel sheet, plate thickness 0.8 mm, plating coating amount 20 g / m ^{2 on} one side, nickel content 12% by mass in the plating layer

Immediately after forming the plating layer, aqueous surface treatment agents X1 to X42 shown in Table 2 were applied to both surfaces of the steel sheet having the plating layer shown in Table 3 using a roll coater. The peripheral speed ratio of the roll coater was adjusted so that the adhesion amount and film thickness shown in Table 4 were obtained. The thickness of the film was determined by observing the cross section of the surface-treated steel sheet using TEM or SEM, measuring the film thickness of the film at any five locations, and calculating the average value. Moreover, from application | coating to drying start, it hold | maintained for 0.5 to 4 second (coating film holding time) in the state of the coating film. The coating film holding time was adjusted by controlling the conveying speed of the steel plate from the roll coater to the heating furnace. The coating film was dried at the maximum plate temperature (PMT) shown in Table 4 using an induction heating furnace.
Through the above steps, surface treated steel sheets of Examples and Comparative Examples were obtained.

  The following items were evaluated by the following methods for the surface-treated steel sheets of Examples and Comparative Examples thus obtained. The results are shown in Table 5.

(Average particle size of resin particles made of polyurethane resin in the film)
For Example 4, Comparative Example 3, and Comparative Example 4, the average particle diameter of the resin particles made of the polyurethane resin in the film was measured using the above-described method of observing the film cross section. The result was equivalent to the average particle size (Example 4: 60 nm, Comparative Example 3: 10 nm, Comparative Example 4: 300 nm) of the polyurethane resin used as the material for the aqueous surface treatment agent. Therefore, the average particle diameters of the polyurethane resins of Examples 1-3, Examples 5-45, and Comparative Examples 1, 2, 5-12 are also equivalent to the average particle diameter of the polyurethane resin used as the material for the aqueous surface treatment agent. I reckon.

(Contents of P, Ti, V, Si (SiO ₂ equivalent) in the film)
Content (mass%) of P (phosphoric acid equivalent), Ti, V, and Si (SiO ₂ equivalent) in the film is expressed as a percentage of the total solid content of the aqueous surface treatment agent shown in Table 2. It is considered.

(Content of fluoride ion in the film)
Twenty sets of 100 mm × 200 mm samples cut out from each surface-treated steel plate were prepared. Next, each sample was immersed in 100 mL of water at 60 ° C. for 10 minutes. Next, 2000 mL of water in which the sample was immersed was collected, concentrated with an evaporator, and analyzed by ion chromatography. Using the result, the content (mg · m ⁻² ) of fluoride ions in the film was calculated. The results are shown in Table 2.

(1) Appearance Evaluation The appearance of the steel sheet was visually confirmed under a sufficiently bright fluorescent lamp and evaluated as follows (2 or more are practical performances).
1: The interference pattern is clearly seen from the front.
2: The interference pattern cannot be seen from the front.
3: The interference pattern cannot be seen from an oblique direction.

(2) Area ratio of resin component in the cross section of the film A carbon film is deposited as a protective film on the surface of the steel plate, and further, FIB (focused ion beam processing apparatus, SMI3050SE: manufactured by Hitachi High-Tech Science Co., Ltd.) is used. A film was formed. Thereafter, microsampling was performed using FIB at an acceleration voltage of 30 kV (finishing process: 5 kV), and this was thinned to obtain a sample having a cross section of the film. The obtained sample was observed using a TEM or SEM having an EDS (energy dispersive X-ray spectrometer). The EDS analysis (element mapping) of the cross section of 3 places was performed about the film | membrane of each steel plate, and each element map of C, P, Ti, V, and Si was obtained. The obtained element map is divided into 100 squares (10 × 10), C and other elements are binarized, the area ratio of the resin component (C) in the cross section of the film is calculated, and evaluated as follows. did.
1: Less than 35%, more than 80% 2: 35% or more and 80% or less 3: 40% or more and 60% or less

Moreover, the film was peeled off from each steel plate by acid treatment, and infrared spectroscopic analysis and pyrolysis GC-MS (gas chromatograph-mass spectrometer) analysis were performed. And from the result analyzed from the attribution of the observed absorption derived from the resin component in the infrared absorption spectrum of the film obtained by infrared spectroscopic analysis, and the result of pyrolysis GC-MS, urethane resin, phenol resin, olefin in the film It was confirmed that the system wax was contained.
As a result, results corresponding to the contents of the aqueous surface treatment agents X1 to X42 shown in Table 2 were obtained.

(3) Surface roughness of the film (Ra-F)
With an atomic force microscope (AFM), the surface roughness (Ra) was measured in a measurement range of 1 μm × 1 μm at an arbitrary location on the surface of the film formed on the steel sheet having the plating layer, and evaluated as follows.
1: Over 10 nm 2: 1 nm to 10 nm

(4) Maximum value of distance between center of gravity of resin particles (2) Center of gravity of resin particles which are adjacent to each other and are not in contact with each other in three sections of each film observed by the area ratio of the resin component in the section of the film The maximum value of the distance between the centers of gravity of the resin particles is obtained by calculating the maximum value of the distance between the centers (the distance between the centers when the cross-sectional shape of each resin particle is considered to be a circle) It was. The maximum value of the distance between the centers of gravity of the obtained resin particles was evaluated as follows using a multiple of the average particle diameter. The specific gravity within the resin particles was considered constant.
1: More than 3.0 times 2: More than 2.0 times 3.0 or less 3: Less than 2.0 times

(5) Corrosion resistance Corrosion resistance tests were performed on unprocessed (planar part), cross-cut with a NT cutter (cross-cut part), and Erichsen 7 mm extruded (processed part) on the test plate. . The evaluation method is as follows.

(5) -1: Plane portion corrosion resistance Based on the salt spray test method JIS-Z-2371, the white rust generation area rate 72 hours after salt spray was determined and evaluated. Evaluation criteria are shown below (Δ or higher is practical performance).
◎: White rust generation area ratio is less than 10% ○: White rust generation area ratio is 10% or more and less than 30% △: White rust generation area ratio is 30% or more and less than 60% ×: White rust generation area ratio is 60 %that's all

(5) -2: Corrosion resistance of the cross-cut part Based on the salt spray test method JIS-Z-2371, the white rust generation situation 72 hours after salt spray was evaluated with the naked eye. Evaluation criteria are shown below (Δ or higher is practical performance).
◎: Almost no rust generated ○: Slight rust generated △: Rust generated ×: Rust generated significantly

(5) -3: Processed part corrosion resistance Based on the salt spray test method JIS-Z-2371, the occurrence of white rust 72 hours after salt spray was evaluated with the naked eye. Evaluation criteria are shown below (Δ or higher is practical performance).
◎: Almost no rust generated ○: Slight rust generated △: Rust generated ×: Rust generated significantly

(6) Alkali resistance (corrosion resistance after degreasing)
Fine cleaner E6406 (manufactured by Nihon Parkerizing Co., Ltd.) was bathed at 20 g / L, the test plate was immersed in a degreasing aqueous solution adjusted to 65 ° C. for 2 minutes, washed with water, and dried at 80 ° C. About this board | substrate, corrosion resistance was evaluated by the conditions and evaluation method of a plane part corrosion resistance described in said (5) -1.

(7) Coating adhesion The coating was applied to the test plate under the following conditions, and a coating film adhesion test was conducted.
(Painting conditions)
Paint condition paint: Amirac # 1000 (registered trademark) (white paint) manufactured by Kansai Paint Co., Ltd.
Coating method: Bar coating method Baking and drying conditions: 140 ° C., 20 minutes Coating thickness: 25 μm
The evaluation method is as follows.

(7) -1: Cross-cut primary adhesion The 1 mm square and 100 cross-cuts were cut into the test plate with an NT cutter, a peel test with an adhesive tape was performed, and the number of peeled coating films was evaluated. Evaluation criteria are shown below (Δ or higher is practical performance).
Here, the “peeling number” means the number of pieces where more than half of each grid is peeled (the “peeling number” described below has the same meaning).
◎: Number of peels less than 1 ○: Number of peels of 1 or more and less than 10 △: Number of peels of 10 or more and less than 50 ×: Number of peels of 50 or more

(7) -2: Cross grid secondary adhesion Immerse the test plate in boiling water for 2 hours, leave it for a whole day and night, cut 1 mm square, 100 grids with an NT cutter, and perform a peel test with an adhesive tape. Evaluation was based on the number of peeled coating films. Evaluation criteria are shown below (Δ or higher is practical performance).
◎: Number of peels less than 1 ○: Number of peels of 1 or more and less than 10 △: Number of peels of 10 or more and less than 50 ×: Number of peels of 50 or more

(8) Post-degreasing coating adhesion Fine cleaner E6406 (manufactured by Nihon Parkerizing Co., Ltd.) at 20 g / L, immersed in a degreasing aqueous solution adjusted to 65 ° C. for 2 minutes, washed with water, and then 80 Dried at ℃. About this board, the coating was given with respect to the test board on the following conditions, and the coating-film adhesiveness test was done.
(Painting conditions)
Paint: Amirac # 1000 (registered trademark) (white paint) manufactured by Kansai Paint Co., Ltd.
Coating method: Bar coating method Baking and drying conditions: 140 ° C., 20 minutes Coating thickness: 25 μm
The evaluation method is as follows.

(Crosscut primary adhesion after degreasing)
With respect to the test plate, 100 mm grids of 1 mm square were cut with an NT cutter, a peel test with an adhesive tape was performed, and the number of coating films peeled was evaluated. Evaluation criteria are shown below (Δ or higher is practical performance).
◎: Number of peels less than 1 ○: Number of peels of 1 or more and less than 10 △: Number of peels of 10 or more and less than 50 ×: Number of peels of 50 or more

(9) Workability A test plate is fixed on a turntable, the turntable is rotated at a rotational speed of 100 mm / s, a pin-on-disk slider (f5 tool steel) is pressed against the test piece with a pressing load of 30 N, and the generated friction is A pin-on-disk test to measure was performed. According to this test, the minimum value (dynamic friction coefficient) of the coefficient of friction of the uncoated oil test piece (measured average of 6 friction coefficients measured every 0.1 seconds) and the number of turns in which the friction coefficient exceeds 0.20 for the first time ( The number of seizure occurrence sliding was evaluated.
In addition, this evaluation was implemented only with the processing chemical | medical agent containing an olefin type wax (F). Evaluation criteria are shown below (Δ or higher is practical performance).

◎: Dynamic friction coefficient is less than 0.16, and seizure occurrence sliding frequency is 25 times or more. ○: Dynamic friction coefficient is less than 0.16, seizure occurrence sliding frequency is 20 times or more and less than 25 times, or dynamic friction coefficient. Is 0.16 or more and less than 0.18, and seizure occurrence sliding frequency is 25 times or more. ○-: Dynamic friction coefficient is 0.16 or more and less than 0.18, seizure occurrence sliding frequency is 20 times or more and less than 25 times. : Dynamic friction coefficient is 0.18 or more and seizure occurrence sliding number is 20 times or more, or dynamic friction coefficient is less than 0.18 and seizure occurrence number is less than 20 times ×: Dynamic friction coefficient is 0.18 or more, And the seizure occurrence sliding frequency is less than 20 times.

(10) Blackening resistance After holding the test plate in a wet box at a temperature of 70 ° C. and a relative humidity of 80% for 6 days, the test plate was taken out and the blackening state of the test plate was visually determined. The evaluation criteria are as follows (Δ or higher is practical performance).
◎: Area ratio of blackened area is less than 1% (no blackened)
○: Area ratio of blackened portion is 1% or more and less than 5% ○-: Area ratio of blackened portion is 5% or more and less than 25% Δ: Area ratio of blackened portion is 25% or more, 50 Less than% ×: Area ratio of blackened portion is 50% or more

(11) Stack whitening resistance 5-10 pairs of two test plates facing each other so that the painted surfaces face each other are piled up, bolted at four corners, and a torque wrench. The load was applied to a scale of 7 N · m. And after hold | maintaining for 6 days in the humidity box of the temperature of 70 degreeC and 80% of relative humidity, it took out and determined the whitening condition of the overlapping part visually. The evaluation criteria are as follows (Δ or higher is practical performance).
◎: Area ratio of whitened area is less than 1% (no whitening)
○: Area ratio of whitened portion is 1% or more and less than 5% ○-: Area ratio of whitened portion is 5% or more and less than 25% Δ: Area ratio of whitened portion is 25% or more, 50 Less than% ×: Area ratio of whitened area is 50% or more

(12) Filament tape resistance Filament tape (registered trademark) no. After attaching 9514, it was peeled off after being held in a wet box at a temperature of 40 ° C. and a relative humidity of 80% for 7 days, and the appearance was evaluated. Evaluation criteria are as follows (Δ or higher is practical performance).
◎: The peeled portion is not understood even when viewed from an angle. ○: The peeled portion is slightly understood when viewed from an angle. ○-: The peeled portion is clearly seen when viewed from an angle. △: The peeled portion is viewed from the front. Slightly understood ×: The peeled portion can be clearly seen from the front

(13) Condensation whitening resistance One drop of ion-exchanged water is dropped on the surface of the test plate, and another test piece is superimposed on the dropping surface side so that the films face each other, and water is sandwiched between the two test pieces. It was in a state. Subsequently, the test piece was wrapped, the four corners were clipped, and the presence or absence of whitening of the water droplet dropping portion after storage in a dryer at 50 ° C. for 72 hours was visually evaluated. Evaluation criteria are as follows (Δ or higher is practical performance).
◎: No whitening visually, no glossiness (loss of gloss) △: No whitening visually, but glossiness (loss of gloss) ×: Visually whitening, glossiness (loss of gloss) Yes

(14) Drug stability 200 ml of the treated drug immediately after preparation was placed in a sealed container and kept at 40 ° C., and the solidification (gelation) state was observed at regular intervals to evaluate the period until solidification. The evaluation criteria are as follows (Δ or higher is practical performance).
◎: not solidified for 60 days or more ○: solidified for 30 days or more and less than 60 days △: solidified for 14 days or more and less than 30 days ×: solidified in less than 14 days

(15) Actual machine operability (Zn elution amount)
Ten hot-dip galvanized plates (75 × 40 mm) were immersed in 300 ml of a treatment chemical at 25 ° C., and the amount of Zn in the treatment chemical after 6 hours was evaluated. The evaluation criteria are as follows (Δ or higher is practical performance).
A: Zn content is less than 700 mg / L. O: Zn content is 700 mg or more and less than 850 mg / L. Δ: Zn content is 850 mg or more and less than 1000 mg / L. X: Zn content is 1000 mg / L or more.

  As shown in Table 5, Examples 1 to 45, which are examples of the present invention, are all (7) coating adhesion, (8) coating adhesion after degreasing, (9) workability, and (10) resistance. Blackening, (11) Anti-stack whitening, (12) Filament tape resistance, (14) Chemical stability, (15) Practical performance (Zn elution), and (1) Appearance evaluation (5) Corrosion resistance and (6) Alkali resistance (corrosion resistance after degreasing) and (13) Condensation whitening resistance were also excellent.

  On the other hand, as shown in Table 5, in Comparative Example 1 in which the surface roughness (Ra-S) of the steel sheet was less than 0.1 μm, (1) the appearance evaluation was insufficient. Further, in Comparative Example 2 in which the surface roughness (Ra-S) of the steel plate exceeded 2 μm, (5) corrosion resistance and (6) alkali resistance (corrosion resistance after degreasing) were insufficient. This is presumably because, in Comparative Example 2, the surface roughness of the steel sheet was rough, so that the surface of the steel sheet was exposed at a part of the coating surface.

In Comparative Example 3 in which the average particle size of the polyurethane resin is less than 20 nm, (3) the surface roughness (Ra-F) of the film is more than 10 nm, and (4) the maximum value of the distance between the centers of gravity of the resin particles is the average particle size. Since the diameter was over 3.0 times and the dispersion of the resin particles was uneven, (5) the corrosion resistance was insufficient.
Further, in Comparative Example 4 in which the average particle diameter of the polyurethane resin exceeds 200 nm, (3) the surface roughness (Ra-F) of the film exceeds 10 nm, and (4) the maximum value of the distance between the centers of gravity of the resin particles is average. Since the particle size exceeded 3.0 times and the dispersion of the resin particles was uneven, (5) the corrosion resistance was insufficient.

(2) In Comparative Example 5 in which the area ratio of the resin component in the cross section of the film is less than 35%, (4) the maximum value of the distance between the centers of gravity of the resin particles is more than 3.0 times the average particle diameter, Dispersion became non-uniform, and (5) corrosion resistance was insufficient.
(2) In Comparative Example 6 in which the area ratio of the resin component in the cross section of the film was more than 80%, the corrosion resistance improvement effect by Ti, V and Si was not sufficiently obtained, and (5) the corrosion resistance was insufficient.

In Comparative Example 7 containing no Si, (5) corrosion resistance was insufficient.
In Comparative Example 8 not containing Ti, (5) corrosion resistance was insufficient.
In Comparative Example 9 containing no V, (5) corrosion resistance was insufficient.

  In Comparative Example 10 containing no P, (4) the maximum value of the distance between the center of gravity of the resin particles is more than 3.0 times the average particle size, and the dispersion of the resin particles is non-uniform, so (5) corrosion resistance and ( 6) Alkali resistance (corrosion resistance after degreasing) was insufficient. Further, in Comparative Example 10, (11) stack whitening resistance, (12) filament tape resistance, and (15) actual machine operability (Zn elution amount) did not have practical performance.

In Comparative Example 11 with a low P content, (4) the maximum value of the distance between the centers of gravity of the resin particles is more than 3.0 times the average particle size, and the dispersion of the resin particles is non-uniform. (6) Alkali resistance (corrosion resistance after degreasing) was lowered. Further, in Comparative Example 11, (11) stack whitening resistance and (12) filament tape resistance did not have practical performance.
In Comparative Example 12 having a high P content, (10) anti-blackening property did not have practical performance.

  Moreover, the cross section of the surface-treated steel sheet of Example 4 was observed with a scanning transmission electron microscope (STEM), and a bright field (STEM-BF) image and a high angle scattering annular dark field (STEM-HAADF) image were obtained. FIG. 2 is a bright field image of Example 4. FIG. 3 is a high-angle scattering annular dark field image of Example 4.

  In the bright field (STEM-BF) image of Example 4 shown in FIG. 2, a film composed of a gray part and a plurality of substantially spherical white parts is observed, and the white part is substantially uniformly arranged in the film. I understand that. In the high-angle scattering annular dark field (STEM-HAADF) image of Example 4 shown in FIG. 3, the white portion in FIG. 2 is black. In the high-angle scattering annular dark field image, since the light element is black, the white portion shown in FIG. 2 is resin particles. From this, in the surface-treated steel sheet of Example 4, it has confirmed that the resin particle was disperse | distributing substantially uniformly in the membrane | film | coat.

  Moreover, the surface-treated steel sheet of the comparative example which is the same as Example 4 was produced except having formed the membrane | film | coat whose resin particle is an acrylic resin particle. And the cross section of the surface treatment steel plate of a comparative example was observed with the scanning transmission electron microscope (STEM), and it carried out similarly to Example 4, and obtained the bright field (STEM-BF) image. As a result, in the bright field (STEM-BF) image of the comparative example, a film composed of a gray part and a plurality of substantially spherical white parts was observed, and the white part was unevenly arranged in the film. From this, it was confirmed that the resin particles in the film were unevenly distributed in the surface-treated steel sheet of the comparative example.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment. That is, it is understood that other forms or various modifications that can be conceived by those skilled in the art within the scope of the invention described in the claims belong to the technical scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 Steel plate, 2 plating layer, 3 film | membrane, 10 surface-treated steel plate, 31 1st component, 32 2nd component.

Claims (7)

A steel plate, a plating layer containing zinc formed on the surface of the steel plate, and a coating formed on the plating layer,
The film includes a resin component including resin particles made of a polyurethane resin having an average particle diameter of 20 to 200 nm, P, Ti, V, and Si,
The area ratio of the resin component in the cross section of the film is 35 to 80%,
In the film, P is contained in an amount of 2.5 to 7.5% by mass in terms of phosphoric acid, the steel sheet has a surface roughness (Ra) of 0.1 to 2 μm, and the resin particles are dispersed in the film. A surface-treated steel sheet characterized by comprising:   2. The surface-treated steel sheet according to claim 1, wherein the maximum value of the distance between the centers of gravity of the resin particles is 3.0 times or less of the average particle diameter.   The surface-treated steel sheet according to claim 1 or 2, wherein the film has a surface roughness (Ra) of 1 to 10 nm.   The surface-treated steel sheet according to any one of claims 1 to 3, wherein the film has a thickness of 150 to 900 nm.   The surface-treated steel sheet according to any one of claims 1 to 4, wherein the plating layer contains antimony.   The surface-treated steel sheet according to any one of claims 1 to 5, wherein the resin component contains an olefin wax and / or a phenol resin. 10 to 40 wt% of Si in terms of SiO ₂ in the film in,
1.7 to 2.4% by mass of Ti,
V is 0.70-0.90 mass%,
The mass ratio (Ti / V) of Ti and V is 2.1-2.9, The surface-treated steel sheet as described in any one of Claims 1-6 characterized by the above-mentioned.