JPWO2018083784A1 - Surface-treated steel sheet - Google Patents

Abstract

A surface-treated steel sheet having excellent condensation whitening resistance and corrosion resistance is provided. A polyurethane resin having a steel plate, a plating layer containing zinc formed on a surface of the steel plate, and a coating formed on the plating layer, the coating having an average particle size of 20 nm to 200 nm. A resin component comprising resin particles comprising: P, Ti, V, and Si; P in the film 3 is contained in an amount of 2.5% by mass to 7.5% by mass; and the area of the resin component in the cross section of the film The rate is 35% or more and 80% or less, the resin particles are dispersed in the film, and 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 of the resin particles. A surface-treated steel sheet is used. [Selection] 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 the galvanized steel sheet, a technique for forming a film on the surface of the galvanized steel sheet is widely used (for example, see Patent Documents 1 to 6).

JP 2011-183307 A JP 2003-13252 A Japanese Patent No. 5642082 JP 2012-92444 A International Publication No. 2011/122119 JP 2011-225967 A

  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. In addition, the conventional galvanized steel sheet having a coating on the surface has been required to further improve the corrosion resistance.

  This invention is made | formed in view of such a situation, and makes it a subject to provide the surface treatment steel plate which has the outstanding dew condensation whitening resistance and corrosion resistance.

  The present inventor has intensively studied to solve the above problems. The present inventors first examine the components constituting the film, and that the film formed using a treatment agent containing P, Ti, V, Si and polyurethane resin improves condensation whitening resistance and corrosion resistance. I found it.

Furthermore, the present inventors further reduced the amount of the polyurethane resin into fine particles and uniformly dispersed in the film, thereby uniformly dispersing the component having corrosion inhibitory action such as V and Ti in the film. We focused on the possibility of improving the whitening resistance and corrosion resistance. Then, the present inventors have confirmed a film in which the polyurethane resin is uniformly dispersed in a particulate form for the first time in the above composition system by adopting a special manufacturing method using acetic acid as a component of the treatment chemical. Furthermore, the present inventors surprisingly found that the film formed in this way not only exhibits excellent dew condensation whitening resistance and corrosion resistance, but also stack whitening that occurs in a completely different environment from dew condensation whitening. It was also found that high resistance was developed.
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 nm or more and 200 nm or less, P, Ti, V, and Si,
In the film, containing 2.5% by mass to 7.5% by mass of P in terms of phosphoric acid,
The area ratio of the resin component in the cross section of the film is 35% or more and 80% or less,
A surface-treated steel sheet in which the resin particles are dispersed in the film, and the maximum value of the distance between the centers of gravity of the resin particles is 3.0 times or less the average particle diameter of the resin particles.

(2) The surface-treated steel sheet according to (1), wherein the surface roughness (Ra) of the film is 1 nm or more and 10 nm or less.
(3) The surface-treated steel sheet according to (1) or (2), wherein a surface roughness (Ra) of the steel sheet is 0.1 μm or more and 2 μm or less.
(4) The surface-treated steel sheet according to any one of (1) to (3), wherein the plating layer contains antimony.
(5) The surface-treated steel sheet according to any one of (1) to (4), wherein the resin component includes an olefin wax and / or a phenol resin.

(6) Si in the film is 10% by mass or more and 40% by mass or less in terms of SiO ₂ ;
Ti is 1.7% by mass or more and 2.4% by mass or less,
V is 0.70 mass% or more and 0.90 mass% or less,
The surface-treated steel sheet according to any one of (1) to (5), wherein a mass ratio (Ti / V) between Ti and V is 2.1 or more and 2.9 or less.

  As described above, the surface-treated steel sheet of the present invention has excellent condensation whitening resistance and corrosion resistance.

  In addition, the surface-treated steel sheet of the present invention has surprisingly further excellent anti-stacking whitening property by having the above-described configuration. Here, “stacking whitening resistance” indicates the corrosion resistance when the coil of the surface-treated steel sheet is transported and stored in a high-temperature and high-humidity environment. Stack whitening has a high temperature governing the reaction rate, and the amount of water that is a reaction field is small, whereas condensation whitening is different in that there is a large amount of water that is a reaction field at room temperature, and both resistances can be improved. It is a surprising effect.

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 typical sectional drawing of the membrane | film | coat for demonstrating the comparison method of the distance between the gravity centers of a resin particle, and the average particle diameter of a resin particle. It is typical sectional drawing of the membrane | film | coat for demonstrating the comparison method of the distance between the gravity centers of a resin particle, and the average particle diameter of a resin particle. 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). 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). It is the bright field (STEM-BF) image obtained by observing the cross section of the surface treatment steel plate of the comparative example 11 with a scanning transmission electron microscope (STEM). It is the bright field (STEM-BF) image obtained by observing the cross section of the surface treatment steel plate of the comparative example 11 with a scanning transmission electron microscope (STEM).

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol. In the present specification, the description of the numerical range “a to b” is a description intended to include not only the range between a and b but also the upper limit value and the lower limit value. That is, in the present specification, the description “ab” means “a to b”.

1. FIG. 1 is a schematic diagram for explaining an example of a cross-sectional structure of a surface-treated steel sheet according to 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.

1.1 Steel Plate 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 surface roughness Ra (test length: 1 inch) (hereinafter also referred to as “Ra-S”) of the steel sheet 1 is not particularly limited, but is preferably 0.1 to 2 μm. As a result of the uniform dispersion of the polyurethane resin, the coating 3 has a uniform distribution of each component in the coating 3, and therefore, irregular reflection of incident light in the coating 3 is relatively suppressed. Furthermore, the film 3 exhibits excellent corrosion resistance, anti-condensation whitening resistance and anti-stack whitening resistance even when the film 3 has a relatively small film thickness, for example, 500 nm. Thus, when a component is uniformly distributed in the film 3 and the film thickness is relatively small, an interference pattern may occur on the surface-treated steel sheet 10 depending on the composition of the film 3 and the like.

  On the other hand, the present inventors control the shape of the reflective interface on the plating layer 2 side of the coating 3 and suppress the interference pattern by making the surface roughness of the steel plate 1 within a predetermined range. I found it. Specifically, 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, Good appearance is obtained. The surface roughness (Ra-S) of the steel sheet 1 is more preferably 0.2 μm or more, and further preferably 0.3 μm or more.

On the other hand, when the surface roughness (Ra-S) (test length: 1 inch) of the steel plate 1 is 2 μm or less, the surface roughness of the steel plate 1 is large, so that a part of the steel plate 1 penetrates the coating 3. It is possible to prevent exposure more reliably. Therefore, excellent corrosion resistance can be obtained more reliably. The surface roughness (Ra-S) of the steel plate 1 is more preferably 1.5 μm or less, and even more preferably 1.0 μm or less.
In addition, the surface roughness (Ra-S) (test length: 1 inch) of the steel plate 1 is the surface 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. Roughness (Ra). Moreover, in this specification, surface roughness Ra is obtained by measuring based on JISB0601.

1.2 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 if the plating layer 2 contains antimony, excellent dew whitening resistance, stack 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.

1.3 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.

  As will be described later, in this embodiment, the water-based surface treatment chemical contains an acetic acid component. The acetic acid component can stabilize the pH of the aqueous surface treatment agent by a pH buffering action. In the aqueous surface treatment agent, it is stabilized by suppressing the condensation reaction of a silicon (Si) precursor, for example, a silane coupling agent. As a result, it contributes to the suppression of aggregation and association of the resin particles of the first component. It is thought that there is. As described above, the acetic acid component stabilizes each component of the aqueous surface treatment agent, so that the first component 31 can be present as relatively uniform and minute resin particles even in the formed film 3. On the other hand, when the aqueous surface treatment agent does not contain an acetic acid component, each component of the aqueous surface treatment agent is not stable, and the first component is uniformly and finely dispersed in the resulting coating film. I can't.

  In the coating 3 in which the first component 31 and the second component 32 are dispersed substantially uniformly, the improvement effect of the first component 31 and the second component 32 on the corrosion resistance, condensation whitening resistance, and stack whitening resistance is exerted on the entire surface of the coating. Obtained substantially uniformly. As a result, in the surface-treated steel sheet 10 of the present embodiment, excellent corrosion resistance, condensation whitening resistance and stack whitening resistance can be obtained. Although the manifestation principle of such an effect is not clear, the mechanism of manifestation of the estimated effect will be described below.

  That is, first, the film 3 is uniformly formed by the film forming action of silicon contained in the first component 31 and the second component 32, and exhibits excellent barrier properties and adhesion. For this reason, in any place of the film 3, intrusion of water, oxygen, or the like can be suppressed, and each component of the surface-treated steel sheet 10 from the film 3 is prevented from leaching onto the surface of the film 3. . As a result, the corrosion resistance is improved by the coating 3, and the condensation whitening resistance and the stack whitening resistance are improved.

  On the other hand, since titanium (Ti) and vanadium (V) are distributed substantially uniformly over the entire surface of the coating 3, even when corrosion starts in a part of the surface-treated steel sheet 10, these components are present. The said part can be accessed quickly and corrosion can be suppressed. Furthermore, since titanium (Ti) and vanadium (V) are distributed substantially uniformly over the entire surface of the coating 3, it is a case where titanium (Ti) and vanadium (V) are insufficient in a part of the surface-treated steel sheet 10. Even so, titanium (Ti) and vanadium (V) are quickly supplied to the part.

  And, by the 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), excellent corrosion resistance and dew condensation resistance Whitening resistance and stack whitening resistance can be obtained.

  In the present embodiment, the dispersion state of the first component 31 in the coating 3 is evaluated using 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 center of gravity of the resin particles is 3.0 times or less of the average particle diameter, more preferably 2.5 times or less, and further preferably 2.0 times or less. When the maximum value of the distance between the centers of gravity of the resin particles is 3.0 times or less, the effect due to the first component 31 and the second component 32 being uniformly disposed in the coating 3 is increased, and the corrosion resistance, The surface-treated steel sheet 10 is excellent in condensation whitening resistance and stack whitening resistance. On the other hand, in order to achieve both the barrier property and adhesion improvement effect by the first component 31 and the corrosion resistance improvement effect by the second component 32 as sufficiently excellent, the maximum value of the distance between the centers of gravity of the resin particles is preferably The average particle size is more than 1.0 times, more preferably 1.25 times or more, and further preferably 1.5 times or more.

The maximum value of the distance between the center of gravity of the resin particles in the film 3 can be obtained as follows.
First, the arbitrary 3rd of the film | membrane 3 by the carbon element mapping of a cross-sectional TEM-EDX (Transmission Electron Microscope-Energy dispersive X-ray spectrometry) or a high angle scattering annular dark field (STEM-HAADF, High-angle Annular Dark Field Scanning TEM) image. The resin particles are identified in the three cross sections of the component 31 of 1 and the contour is the outermost side of the resin particles. When the resin particle to be measured is a substantially perfect circle, the particle size and the center of gravity of the resin particle are the particle size and the center of gravity itself. When the resin particles to be measured are not perfect circles, the maximum diameter and the minimum diameter of the resin particles are measured, and the cross section of the resin particles is regarded as an ellipse having a major axis and a minor axis, respectively. Then, after calculating the area of the ellipse, the particle diameter and the center of gravity of the resin particle are determined as a perfect circle having the center of gravity where the maximum diameter and the minimum diameter intersect.

Then, in the three cross sections of the first component 31 in the cross section of the coating 3, the distance between the centers of gravity of the resin particles that are adjacent to each other and not in contact with each other (the center when the cross sectional shape of each resin particle is regarded as a circle) The maximum value of the distance between the centers of gravity of the resin particles is obtained by calculating the average value of the values obtained from the three cross-sections.
Note that the gravity center and the like can be calculated assuming that the specific gravity in the resin particles is constant.

FIG. 2 and FIG. 3 are schematic cross-sectional views of a film for illustrating a method of comparing the distance between the center of gravity of the resin particles and the average particle diameter of the resin particles. In FIG. 2, the maximum value of the distance between the center of gravity of the resin particles is 3.0 times or less of the average particle diameter. In FIG. 3, the maximum value of the distance between the center of gravity of the resin particles is the average particle diameter. Each example is over 3.0 times. In addition, about the plating layer and the steel plate 1, description was abbreviate | omitted.
In FIG. 2, first, the distance 1 between the centers of gravity of the resin particles 311 that are adjacent to each other and not in contact with each other in the coating 3 is obtained. Next, a ratio of the maximum value of the distance 1 between the centers of gravity of the resin particles 311 to the average particle size is obtained by comparison with the average particle size of the resin particles 311. Note that virtual resin particles 312 having an average particle diameter are indicated by broken lines.

  In FIG. 3, first, a distance lA between the centers of gravity of resin particles 311A that are adjacent to each other and are not in contact with each other in the coating 3A is obtained. Next, the ratio of the maximum value of the distance 1A between the centers of gravity of the resin particles 311A to the average particle diameter is obtained by comparison with the average particle diameter of the resin particles 311A. Note that virtual resin particles 312A having an average particle diameter are indicated by broken lines.

  In addition, 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, even if the surface roughness (Ra) of the coating 3 is used, the dispersion state of the resin particles in the coating 3 can be evaluated. 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 also 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 due to the first component 31 and the second component 32 being uniformly arranged in the film is further enhanced, and the corrosion resistance, The surface-treated steel sheet 10 is excellent in condensation whitening resistance and stack whitening 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 1 to 10 nm. In addition, an arbitrary rectangular region having four sides of 1 μm is scanned using an atomic force microscope, and arithmetic mean roughness (Ra), maximum section height (Rt), and root mean square roughness (Rq) are calculated from the measurement data. be able to.

  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 sheet 10 excellent in corrosion resistance, dew condensation whitening resistance and stack whitening 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 area ratio of the first component 31 (resin component) in the cross section of the film 3 can be obtained as follows.
First, a carbon film is deposited as a protective film on the surface of the surface-treated steel sheet 10, and a carbon film having a thickness of several μm is formed using a FIB (focused ion beam processing apparatus). 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 having a cross section of the film 3. The obtained sample was observed using a TEM (transmission electron microscope) or SEM (scanning electron microscope) having an EDS (energy dispersive X-ray spectrometer). EDS analysis (element mapping) of the cross section of the part is performed to obtain each element map of C, P, Ti, V, and Si. The obtained element map is divided into 100 squares (10 × 10), and C and other elements are binarized to calculate the area ratio of the resin component in the cross section of the film.

  The thickness of the film 3 is preferably 150 to 900 nm, but is not limited thereto. When the thickness of the film 3 is 150 to 900 nm, the effect of improving the corrosion resistance by the film 3 becomes remarkable, and even more excellent corrosion resistance is obtained.

Hereinafter, the 1st component 31 and the 2nd component 32 which comprise the membrane | film | coat 3 are demonstrated in detail.
(I) 1st component The 1st component 31 contains the resin particle which consists of a polyurethane resin with an average particle diameter of 20-200 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, condensation whitening resistance, and stack whitening 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, there is a coating 3 in which resin particles are unevenly distributed, and the corrosion resistance, condensation whitening resistance, and stack whitening resistance of the surface-treated steel sheet 10 may be insufficient. In this embodiment, since the polyurethane resin has an average particle size of 20 nm or more, excellent corrosion resistance, condensation whitening resistance and stack whitening resistance can be obtained. When the average particle size of the polyurethane resin is 50 nm or more, further excellent corrosion resistance, condensation whitening resistance and stack whitening 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 the study by the present inventors, the result of the average particle diameter of the resin particles made of the polyurethane resin calculated by the above method is the average particle diameter of the polyurethane resin used as the material of the aqueous surface treatment agent in this embodiment. It was confirmed that they were almost identical. 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 include not only polyurethane resin particles but also an olefin wax and / or a phenol resin.
The olefin-based wax is included as necessary and may not be included. 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.

(Ii) 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) are components having 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 exhibits barrier properties and adhesion, thereby improving corrosion resistance, condensation whitening resistance and stack whitening 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 on the assumption that P, Ti, V, and Si in the film 3 are present as oxides by fluorescent X-ray analysis of the film 3. 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, Si (SiO ₂ equivalent) in the film 3 is expressed as a percentage of the mass ratio of the aqueous surface treatment agent to the total solid content. Can be considered.

The film 3 may contain fluoride ions. Fluoride ions in the film 3 are derived from components containing fluoride ions contained in the aqueous surface treatment agent used when the film 3 is formed, for example. 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. Although content of the fluoride ion in the film 3 is not particularly limited, for example, when it is less than 0.3 mg · m ⁻² , the occurrence of condensation whitening due to the inclusion of fluoride ion can be more reliably prevented. 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.

2. Next, a method for manufacturing 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.

2.1 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), and titanium acetylacetone complex (D) And a vanadium compound (E), 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. , Condensation whitening resistance and stack whitening resistance are improved.

  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), X and Y each independently represent hydrogen or a Z group represented by the general formula (3) or the general formula (4), and the average number of substitution of Z groups per each benzene ring 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 salts thereof (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.

  Then, as described above, the acetic acid component (G) increases the dispersion stability of the silane coupling agent (C), thereby suppressing aggregation and association of the resin particles of the first component. On the other hand, when the aqueous surface treatment agent does not contain the acetic acid component (G), each component of the aqueous surface treatment agent is not stable, and the first component is uniform and minute in the resulting coating film. Can not be dispersed.

  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 film 3 can be prevented.

  The phosphoric acid component (H) is preferably inorganic phosphoric acid because of its stability in the drug.

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, anti-condensation whitening resistance and anti-stack whitening 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) is 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.

2.2 Method for Forming Film In this 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. Further, if the time from the formation of the coating film to the start thereof is long, the first components 31 tend to aggregate and unevenly distribute. 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, induction heating, 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.

1. Manufacture of surface-treated steel sheets Aqueous surface treatment chemicals X1 to X46 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

  The steel plate which has a plating layer on both surfaces shown below of the surface roughness (Ra-S) shown in Table 3 and Table 4 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 Tables 3 and 4 is a measurement length of 1 inch at any place on the surface of the film in the surface-treated steel sheet obtained by forming the film by the method described later. The surface roughness (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 the plating layer was formed, aqueous surface treatment agents X1 to X46 shown in Table 2 were applied to both surfaces of the steel plates having the plating layers shown in Tables 3 and 4 using a roll coater. The peripheral speed ratio of the roll coater was adjusted so that the film had an adhesion amount (weight after formation) of 700 (mg / m ² ) and a film thickness of 150 to 900 nm. 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. Further, the time shown in Tables 3 and 4 (coating film holding time) was maintained in the state of the coating film from the application to the start of drying. 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 Tables 3 and 4 using an induction heating furnace. In Comparative Example 15, no film was formed.
Through the above steps, surface treated steel sheets of Examples and Comparative Examples were obtained.

2. Evaluation About the surface treatment steel plate of the Example and comparative example which were obtained in this way, each following item was evaluated with the following method.

2.1 Evaluation of film properties (average particle diameter of resin particles made of polyurethane resin in the film)
For Example 4, Comparative Example 1, and Comparative Example 2, 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 1: 10 nm, Comparative Example 2: 200 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 to 3, Examples 5 to 47, and Comparative Examples 3 to 15 were also regarded as equivalent to the average particle diameter of the polyurethane resin used as the material for the aqueous surface treatment agent.

(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. 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) 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, using a FIB (focused ion beam processing apparatus, SMI3050SE: manufactured by Hitachi High-Tech Science Co., Ltd.) 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 X46 shown in Table 2 were obtained.

(2) Maximum value of the distance between the center of gravity of the resin particles In the three cross sections of each film observed by the area ratio of the resin component in the cross section of the film by carbon element mapping of the cross section TEM-EDX, they are adjacent to each other and in contact with each other The maximum value of the distance between the center of gravity of the resin particles that are not (the distance between the centers when the cross-sectional shape of each resin particle is regarded as a circle) is calculated, and the average value of the values obtained from the three cross-sections is obtained. The maximum distance between the centers of gravity was used. 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. Further, the identification of the resin particles and the measurement of the average particle diameter and the center of gravity of the resin particles were performed by the method described above.
1: More than 3.0 times 2: More than 2.0 times 3.0 or less 3: Less than 2.0 times

(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

2.2 Corrosion resistance evaluation (4) Corrosion resistance For the test plate, unprocessed (planar part), cross-cut to the base with an NT cutter (cross-cut part), and Erichsen 7 mm extruded (processed part) A corrosion resistance test was performed. The evaluation method is as follows.

(4) -1: Plane portion corrosion resistance Based on the salt spray test method JIS-Z-2371, the white rust generation area ratio after 72 hours from salt spray was determined and evaluated. Evaluation criteria are shown below (A to C are practical performances).
A: White rust generation area ratio is less than 10% B: White rust generation area ratio is 10% or more and less than 30% C: White rust generation area ratio is 30% or more and less than 60% D: White rust generation area ratio is 60 %more than

(4) -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 (A to C are practical performances).
A: Almost no rust generation B: Slight rust generation C: Rust generation D: Significant rust generation

(4) -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 (A to C are practical performances).
A: Almost no rust generation B: Slight rust generation C: Rust generation D: Significant rust generation

(5) 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 (4) -1.

2.3 Appearance evaluation (6) Condensation whitening resistance One test piece of ion-exchanged water was dropped on the surface of the test plate, and another test piece was superimposed on the dropping surface side so that the films face each other. With water in between. 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. The evaluation criteria are as follows (A and B are practical performances).
A: No whitening visually, no glossiness (loss of gloss) B: No whitening visually, glossiness (loss of gloss) C: Whitening, glossiness (loss of gloss) Yes

(7) 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 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 (A to D are practical performances).
A: Area ratio of the whitened portion is less than 1% (no whitening)
B: The area ratio of the whitened part is 1% or more and less than 5% C: The area ratio of the whitened part is 5% or more and less than 25% D: The area ratio of the whitened part is 25% or more, 50% Less than E: Area ratio of whitened area is 50% or more

(8) 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 (A to D are practical performances).
A: Area ratio of the blackened portion is less than 1% (no blackening)
B: Area ratio of blackened portion is 1% or more and less than 5% C: Area ratio of blackened portion is 5% or more and less than 25% D: Area ratio of blackened portion is 25% or more, 50% Less than E: Area ratio of blackened area is 50% or more

(9) Interference pattern The appearance of the steel sheet was visually confirmed under a sufficiently bright fluorescent lamp and evaluated as follows.
A: The interference pattern is clearly seen from the front.
B: The interference pattern cannot be seen from the front.
C: The interference pattern is not seen when viewed from an oblique direction.

(10) 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. The evaluation criteria are as follows (A to D are practical performances).
A: The peeled portion is completely unknown even when viewed obliquely. B: The peeled portion is slightly understood when viewed obliquely. C: The peeled portion is clearly understood when viewed obliquely. D: The peeled portion is slightly visible when viewed from the front. E: The peeled part can be clearly seen from the front.

  The above results are shown in Tables 5 and 6.

  As shown in Tables 5 and 6, each of the surface-treated steel sheets according to Examples 1 to 45, which are examples of the present invention, is in addition to (4) corrosion resistance and (5) alkali resistance (corrosion resistance after degreasing) (6) Condensation whitening resistance, (7) Stack whitening resistance, (8) Blackening resistance, and (9) Interference pattern were good. Moreover, all the surface treatment steel plates concerning Examples 1-45 which are the Examples of this invention were excellent also in (10) filament tape resistance.

  In addition, as shown in Table 6, in Example 46 where the surface roughness (Ra-S) of the steel sheet is less than 0.1 μm, in addition to (4) corrosion resistance and (5) alkali resistance (corrosion resistance after degreasing), ( 6) Condensation whitening resistance and (7) Stack whitening resistance were excellent, but (9) interference patterns were observed. Moreover, in Example 47 where the surface roughness (Ra-S) of the steel sheet exceeds 2 μm, (9) an interference pattern was observed.

In Comparative Example 1 in which the average particle size of the polyurethane resin is less than 20 nm, (2) the maximum value of the distance between the centers of gravity of the resin particles exceeds 3.0 times the average particle size, and (3) the surface roughness of the film Since (Ra-F) is more than 10 nm and the dispersion of the resin particles is not uniform, (4) the corrosion resistance is insufficient.
In Comparative Example 2 where the average particle size of the polyurethane resin exceeds 200 nm, (2) the maximum value of the distance between the centers of gravity of the resin particles exceeds 3.0 times the average particle size, and (3) the surface roughness of the film Since (Ra-F) is more than 10 nm and the dispersion of the resin particles is not uniform, (4) the corrosion resistance is insufficient.

(1) In Comparative Example 3 in which the area ratio of the resin component in the cross section of the coating 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 size, Dispersion became non-uniform and (4) corrosion resistance was insufficient.
(1) In Comparative Example 4 in which the area ratio of the resin component in the cross section of the film was more than 80%, the effect of improving corrosion resistance by Ti, V, and Si was not sufficiently obtained, and (4) the corrosion resistance was insufficient.

In Comparative Example 5 containing no Si, (4) the corrosion resistance was insufficient.
In Comparative Example 6 containing no Ti, (4) the corrosion resistance was insufficient.
In Comparative Example 7 containing no V, (4) the corrosion resistance was insufficient.

  In Comparative Example 8 not containing P, (2) the maximum value of the distance between the centers of gravity of the resin particles was more than 3.0 times the average particle size, and the dispersion of the resin particles was non-uniform, so (4) corrosion resistance and ( 5) Alkali resistance (corrosion resistance after degreasing) was insufficient. Further, in Comparative Example 8, (7) stack whitening resistance, (6) condensation whitening resistance, and (10) filament tape resistance did not satisfy practical performance.

  In Comparative Example 9 with a low P content, (2) 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. (5) Alkali resistance (corrosion resistance after degreasing) was lowered. In Comparative Example 9, (7) stack whitening resistance and (10) filament tape resistance did not satisfy practical performance.

  In Comparative Example 10 having a large P content, (4) corrosion resistance and (5) alkali resistance (corrosion resistance after degreasing) were low, and (8) blackening resistance did not satisfy practical performance.

  In Comparative Example 11 in which the acetic acid component (G) and the phosphoric acid component (H) were not used in the surface treatment agent, (2) the maximum value of the distance between the centers of gravity of the resin particles was more than 3.0 times the average particle size, Since the dispersion of the resin particles is not uniform, (4) corrosion resistance and (5) alkali resistance (corrosion resistance after degreasing) are insufficient. Further, in Comparative Example 11, (7) stack whitening resistance and (10) filament tape resistance did not satisfy practical performance.

  In Comparative Example 12 in which the titanium compound (D) and the phosphoric acid component (H) were not used in the surface treatment agent, (2) the maximum value of the distance between the centers of gravity of the resin particles was more than 3.0 times the average particle diameter, Since the dispersion of the resin particles is not uniform and the titanium compound (D) is not included, (4) corrosion resistance and (5) alkali resistance (corrosion resistance after degreasing) are insufficient. In Comparative Example 12, (7) stack whitening resistance and (10) filament tape resistance did not satisfy practical performance.

  In Comparative Example 13 in which the titanium compound (D) and the acetic acid component (G) were not used in the surface treatment agent, (4) corrosion resistance and (5) alkali resistance (corrosion resistance after degreasing) were insufficient.

  In Comparative Example 14 where the titanium compound (D), the acetic acid component (G) and the phosphoric acid component (H) were not used in the treatment agent, (2) the maximum value of the distance between the centers of gravity of the resin particles was 3. Since the dispersion of the resin particles is not uniform and the titanium compound (D) is not contained, (4) corrosion resistance and (5) alkali resistance (corrosion resistance after degreasing) are insufficient. . In Comparative Example 14, (7) stack whitening resistance and (10) filament tape resistance did not satisfy practical performance.

  In Comparative Example 15 in which no film was formed, (4) corrosion resistance and (5) alkali resistance (corrosion resistance after degreasing) were insufficient. Furthermore, the steel plate according to Comparative Example 15 did not have practical performance with respect to (8) blackening resistance.

  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. 4 is a bright-field image of Example 4. FIG. 5 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. 4, a film composed of a gray part and a plurality of substantially spherical white parts is observed, and the white part is arranged substantially uniformly in the film. I understand that. In the high-angle scattering annular dark field (STEM-HAADF) image of Example 4 shown in FIG. 5, the white portion in FIG. 4 is black. In the high-angle scattering annular dark field image, since the light element is black, the white portion shown in FIG. 4 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.

  Furthermore, the high angle scattering cyclic | annular dark field (STEM-HAADF) image which observed the cross section of the surface treatment steel plate of Example 4 with the scanning transmission electron microscope (STEM) is shown. The schematic pseudo shape of the resin particles is indicated by the solid line edge. Further, virtual resin particles having an average particle diameter are indicated by broken lines.

  In the high-angle scattering annular dark field (STEM-HAADF) image of Example 4 shown in FIG. 6, it was confirmed that the resin particles were dispersed substantially uniformly in the film in the surface-treated steel sheet of Example 4. Moreover, it has confirmed that the distance between the gravity centers of a resin particle was 3 times or less of a particle size.

  Moreover, the cross section of the surface treatment steel plate of the comparative example 11 was observed with the scanning transmission electron microscope (STEM), and the bright field (STEM-BF) image was obtained. 7 and 8 are bright field images of Comparative Example 11. FIG. The schematic pseudo shape of the resin particles is indicated by the solid line edge. Further, virtual resin particles having an average particle diameter are indicated by broken lines.

  In the bright field (STEM-BF) image of Comparative Example 11 shown in FIG. 7, 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, in the surface-treated steel sheet of Comparative Example 11, it was confirmed that the resin particles in the film were unevenly distributed. FIG. 8 is an enlarged image of the portion surrounded by the frame in FIG. 7, and it was confirmed that the distance between the gravity centers of the resin particles is more than three times the particle size.

  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, 3A film | membrane, 10 Surface treatment steel plate, 31 1st component, 311, 311A Resin particle, 32 2nd component

The maximum value of the distance between the center of gravity of the resin particles in the film 3 can be obtained as follows.
First, the arbitrary 3rd of the film | membrane 3 by the carbon element mapping of a cross-sectional TEM-EDX (Transmission Electron Microscope-Energy dispersive X-ray spectrometry) or a high angle scattering annular dark field (STEM-HAADF, High-angle Annular Dark Field Scanning TEM) image. The resin particles are identified in the three cross sections of the component 31 of 1 and the contour is the outermost side of the resin particles. When the resin particle to be measured is a substantially perfect circle, the particle size and the center of gravity of the resin particle are the particle size and the center of gravity itself. When the resin particles to be measured are not perfect circles, the maximum diameter and the minimum diameter of the resin particles are measured, and the cross section of the resin particles is regarded as an ellipse having a major axis and a minor axis, respectively. Then, after calculating the area of the ellipse, the particle diameter and the center of gravity of the resin particles are determined as a perfect circle having the center of gravity where the maximum diameter and the minimum diameter intersect.

The content of the polyurethane resin in the film 3 is preferably 25 to 45% by mass. The content of the polyurethane resin is 25 mass% or more, and more preferably is 30 wt% or more, barrier properties and tight adhesion improving effect of the polyurethane resin, a coating 3 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.

Examples of the silane coupling agent (C) include N- (aminoethyl) -3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxy. propyl methyl dimethoxy silane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-methacryloxypropyl trimethoxy silane, and the like.

<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. The titanium acetylacetone complex (D), for example, titanium di-iso-propoxide-bis acetylacetonate, and titanium tetrakis acetylacetonate.

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 Filament tape using an end portion of the coil consisting of a surface treated steel sheet 10 for temporarily fixing is prevented to be damaged by acid component (G), suppressing a decrease adhesion Filament Tape it can. 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.

<(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. There can suppress a decrease adhesion resistance condensation whitening resistance decreases and filament tapes due to residual.

[Acetylacetone complex of titanium (D)]
D1: Titanium diisopropoxy de bisacetylacetonate D2: titanium tetrakis acetylacetonate D3: titanium hydrofluoric acid (component containing a fluoride ion)
[Vanadium compound (E)]
E1: Vanadium acetylacetonate

Claims (6)

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 nm or more and 200 nm or less, P, Ti, V, and Si,
In the film, containing 2.5% by mass to 7.5% by mass of P in terms of phosphoric acid,
The area ratio of the resin component in the cross section of the film is 35% or more and 80% or less,
A surface-treated steel sheet in which the resin particles are dispersed in the film, and the maximum value of the distance between the centers of gravity of the resin particles is 3.0 times or less the average particle diameter of the resin particles.   The surface-treated steel sheet according to claim 1, wherein the film has a surface roughness (Ra) of 1 nm or more and 10 nm or less.   The surface-treated steel sheet according to claim 1 or 2, wherein a surface roughness (Ra) of the steel sheet is 0.1 µm or more and 2 µm or less.   The surface-treated steel sheet according to any one of claims 1 to 3, wherein the plating layer contains antimony.   The surface-treated steel sheet according to any one of claims 1 to 4, wherein the resin component contains an olefin wax and / or a phenol resin. In the film, Si is converted into SiO ₂ in an amount of 10% by mass to 40% by mass,
Ti is 1.7% by mass or more and 2.4% by mass or less,
V is 0.70 mass% or more and 0.90 mass% or less,
The surface-treated steel sheet according to any one of claims 1 to 5, wherein a mass ratio (Ti / V) between Ti and V is 2.1 or more and 2.9 or less.