JP5326379B2 - Surface-treated steel sheet and resin-coated steel sheet - Google Patents

Description

  The present invention is a surface-treated steel sheet mainly used for containers such as cans after the resin is coated by laminating a resin film or the like on the surface or coating a resin-containing paint, particularly in a high temperature and humid environment. The present invention relates to a surface-treated steel sheet having excellent adhesion to a coated resin (hereinafter referred to as wet resin adhesion), and a resin-coated steel sheet in which the surface-treated steel sheet is coated with a resin.

  Various metal cans such as beverage cans, food cans, pail cans and 18 liter cans use metal plates such as electrolytic chromic acid treated steel plates called tin-plated steel plates or tin-free steel plates. Among these, tin-free steel sheets are manufactured by electrolytically treating steel sheets in a plating bath containing hexavalent Cr, and have a feature of having excellent wet resin adhesion to resins such as paints.

  In recent years, due to the increasing awareness of the environment, the use of hexavalent Cr has been regulated worldwide, and there is an alternative material for tin-free steel plates manufactured using a hexavalent Cr plating bath. It has been demanded. For example, Patent Document 1 discloses a steel plate for containers that has been subjected to electrolytic treatment in a tungstic acid solution. Patent Document 2 discloses a surface-treated steel sheet for containers having a phosphate layer formed on the surface. Furthermore, Patent Document 3 has a phenol structure containing one or more of tannic acid or acetic acid and one or more of Ti or Zr or a compound thereof on a surface treatment layer containing one or more of Sn and Ni. A steel plate for containers in which a resin film is formed has been proposed. Furthermore, Patent Document 4 proposes a surface-treated metal material that does not contain phosphate ions and has an inorganic surface treatment layer and an organic surface treatment layer mainly composed of Ti, O, and F.

On the other hand, various types of metal cans have been manufactured by processing metal cans such as tin-free steel sheets and then processing them into cans. Instead of this, a method of processing a resin-coated metal plate coated with a resin such as a resin film into a can body is frequently used. In this resin-coated metal plate, it is necessary that the resin is strongly adhered to the metal plate. In particular, the resin-coated metal plate used as a beverage can or a food can is subjected to a retort sterilization process after filling the contents. In some cases, strong wet resin adhesion is required so that the resin does not peel even in a high temperature wet environment.
JP 2004-285380 A Japanese Patent Laid-Open No. 2001-220685 JP 2002-355921 A JP 2006-009046 A

  However, a resin-coated steel sheet using a container steel plate subjected to electrolytic treatment in a tungstic acid solution described in Patent Document 1, and a container surface-treated steel sheet having a phosphate layer formed on the surface described in Patent Document 2 The steel sheet for containers in which the resin film having a phenol structure described in Patent Document 3 is formed, and the inorganic surface treatment layer and the organic surface treatment layer mainly composed of Ti, O, and F described in Patent Document 4 are formed. In any of the surface-treated metal materials, the wet resin adhesion in the retort atmosphere is insufficient.

  An object of the present invention is to provide a surface-treated steel sheet that does not use Cr, has excellent wet resin adhesion, and can be used as a substitute for a tin-free steel sheet, and a resin-coated steel sheet in which a resin is coated on the surface-treated steel sheet. .

As a result of intensive research on a surface-treated steel sheet that does not use Cr, has excellent wet resin adhesion, and can be used as a substitute for a tin-free steel sheet, the surface of the steel sheet contains Ti and contains a large number of fine protrusions. It has been found that extremely excellent wet resin adhesion can be obtained by forming a film having a uniform part and excellent wet resin adhesion (hereinafter sometimes abbreviated as an adhesive film ) .

The present invention has been made based on such knowledge, and includes at least one metal selected from Co, Fe, Ni, V, Cu, Mn, and Zn, including Ti on at least one side of the steel sheet. the steel sheet in an aqueous solution containing the ions obtained by cathodic electrolytic treatment has a film excellent wet resin adhesion, including thickness of Ti 20 to 800 nm, and the film excellent in the wet resin adhesion Is a mass ratio of Co, Fe, Ni, V, Cu, Mn and Zn to Ti contained in the film having a linear density of 1 piece / μm or more and having excellent wet resin adhesion Is a surface-treated steel sheet, characterized by being 0.01 to 10 . Here, the thickness of the film excellent wet resin adhesion, the coating section profile observed with a transmission electron microscope (TEM), and that the maximum height H of the projection measured from the film lower surface, wet resin adhesion The line density of the convex part of the film with excellent properties is the minimum height from the lower surface of the film at the bottom of the concave part, and the horizontal line at the upper and lower levels of ± 10 nm centered on the position of (H + L) / 2 When it is drawn, there is one convex part when there is at least one point where the upper level horizontal line intersects the profile curve between two adjacent points where the lower level horizontal line intersects the profile profile curve. This is the number of convex portions per unit length obtained as if.

Further, in the surface-treated steel sheet of the present invention, the distribution state of the convex portions existing in the adhesive film is 16 / μm by three-dimensionally analyzing the SEM image of the surface of the adhesive film observed with a scanning electron microscope (SEM). It can also be defined by an area density of ² or more. Here, the surface density of the convex part of the adhesive film is the average line of the unevenness obtained by performing a three-dimensional analysis of the SEM image of the film surface observed by SEM and filtering at a cutoff wavelength of 1.0 μm + 0.005 It is the number of convex portions having a height of μm or more per unit area.

  In the surface-treated steel sheet of the present invention, the cross-sectional curve is extracted from the three-dimensional data by SEM, and the root mean square roughness (Rq) defined in JIS B 0601: 2001 obtained after filtering with a cutoff wavelength of 1.0 μm and The ratio (Rq / Ra) to the arithmetic average roughness (Ra) is preferably 1.3 or less. In addition, the cross-sectional curve is extracted from the three-dimensional data by SEM, and the skewness (Rsk) specified in JIS B 0601: 2001 obtained after filtering at a cutoff wavelength of 1.0 μm is 0.6 or less, or the kurtosis (Rku) is 4 The following is more preferable.

In the surface-treated steel sheet of the present invention, the Ti amount of the adhesive film is preferably ³ to 200 mg / m ² per side.

  The present invention also provides a resin-coated steel sheet, wherein the surface-treated steel sheet of the present invention is coated with a resin.

  According to the present invention, it has become possible to produce a surface-treated steel sheet having excellent wet resin adhesion without using Cr. The surface-treated steel sheet of the present invention can be used without any problem as an alternative to conventional tin-free steel sheets without being coated with a resin on a container containing oil, organic solvent, paint, or the like. Further, even if the resin is coated to form a resin-coated steel sheet, processed into a can or can lid and exposed to a retort atmosphere, the resin does not peel at all.

1) Surface-treated steel sheet As described above, in the surface-treated steel sheet of the present invention, at least one side of the steel sheet contains Ti having a thickness of 20 to 800 nm and has convex portions with a linear density of 1 piece / μm or more. Excellent wet resin adhesion can be obtained by forming an adhesive film or an adhesive film having convex portions with an area density of 16 / μm ² or more. The details will be described below.

  As the raw steel plate, a general steel plate for cans such as low carbon steel and extremely low carbon steel can be used.

  The reason why the wet resin adhesion improves when an adhesive film containing Ti is formed on the steel sheet surface is not necessarily clear at present, but a high molecular weight film mainly composed of an oxide of Ti is not compatible with the resin. It is assumed that this is because a strong intermolecular force is generated between them. Therefore, it is preferable to contain O in the adhesive film.

The amount of Ti in the adhesive film is preferably ³ to 200 mg / m ² per side. This is because better wet resin adhesion can be obtained when the Ti content is 3 mg / m ² or more, and the effect tends to be saturated when it exceeds 200 mg / m ² . Note that the Ti amount of the adhesive film can be measured by fluorescent X-ray analysis. The amount of O is not particularly defined, but its presence can be confirmed by photoelectron spectroscopy (XPS).

  Also, the reason why the thickness of the adhesive film is 20 to 800 nm is that if the thickness is less than 20 nm, excellent wet resin adhesion cannot be obtained, and if it exceeds 800 nm, the film itself becomes brittle and the wet resin adhesion deteriorates. Because.

  Furthermore, the reason why the wet resin adhesion is improved when a convex portion is present at a linear density of 1 piece / μm or more in the adhesive film is considered as follows. That is, FIG. 1 schematically shows a cross section of the adhesive film of the surface-treated steel sheet according to the present invention. In this way, the convex portions are present uniformly and densely, specifically, a linear density of 1 piece / μm or more. In the case of being present, the surface area is increased and the adhesion area with the resin is increased as compared with a film having uneven and sparse convex portions of the surface-treated steel sheet which is a comparative example as schematically shown in FIG. At the same time, the anchor effect by the uneven portions present uniformly and densely increases, and extremely excellent wet resin adhesion can be obtained. On the other hand, if the linear density of these convex portions is less than 1 piece / μm, the area of adhesion with the resin is reduced, the anchor effect is not sufficient, and the above effect is not exhibited and excellent wet resin adhesion is achieved. I can't get it.

  Here, the thickness of the adhesive film and the linear density of the convex part of the adhesive film are defined as follows. At this time, a film cross-sectional profile observed in an arbitrary direction within the film surface can be used.

  FIG. 3 is a schematic diagram for explaining the thickness of the adhesive film of the surface-treated steel sheet according to the present invention and the linear density of the convex portions. The thickness of the adhesive film is the maximum height H of the convex part measured from the lower surface of the film cross-sectional profile observed with TEM. The linear density of the convex part of the adhesive film is the bottom of the concave part. Two points where the horizontal line of the lower level intersects the curve of the cross-sectional profile when the horizontal line of the upper and lower levels of ± 10nm is drawn centering on the position of (H + L) / 2, where L is the minimum height from the lower surface of the film This is the number of convex portions per unit length obtained by assuming that one convex portion exists when there is a point where the upper level horizontal line intersects with the profile curve at least once.

  In order to measure the thickness H of the adhesive film, the highest convex portion is selected from the film cross-sectional profile observed with TEM, and the height measured from the lower surface of the film is obtained. On the other hand, in order to measure the minimum height L of the bottom of the recess from the lower surface of the film, the lowest bottom of the recess is selected from the observed cross-sectional profile of the film, and the height measured from the lower surface of the film is obtained.

In the present invention, the three-dimensional analysis of the SEM image of the surface of the adhesive film observed with the SEM can define the distribution state of the convex portions existing in the adhesive film with an area density of 16 pieces / μm ² or more. . FIG. 4 shows SEM images of an example of the present invention (No. 2 of an example described later) and a comparative example (No. 1 of a comparative example described later). In the example of the present invention (a), a comparative example (b ), It can be seen that the convex portions of the film are uniform and dense. As described above, the presence of uniform and dense convex portions increases the surface area and increases the adhesion area with the resin, and the anchor effect by the concave and convex portions is increased to provide extremely excellent wet resin adhesion. It is done.

  Here, the surface density of the convex part of the adhesive film is obtained by three-dimensional analysis of the SEM image (6 μm × 4.5 μm region) shown in FIG. The average line of unevenness obtained by removing + the number of convex parts having a height of 0.005 μm or more can be obtained per unit area.

  The reason why the density of the convex part of the adhesive film was separately defined by the line density obtained from the film cross-sectional profile observed with TEM and the surface density obtained by three-dimensional analysis of the film surface image observed with SEM is In the former case, the adhesive film itself can be observed directly, but there is a problem that it takes time to prepare and measure the sample. In the latter case, when there is a resin coating layer on the film, it takes time to remove the resin coating layer. However, the measurement itself is simple and can be performed quickly. In the present invention, it has been confirmed that equivalent wet resin adhesion can be obtained both when defined by linear density and when defined by surface density.

  Furthermore, the cross-sectional curve is extracted from the three-dimensional data by SEM, and the ratio (Rq / Ra) of Rq and Ra specified in JIS B 0601: 2001 obtained after filtering at a cutoff wavelength of 1.0 μm (Rq / Ra) is 1.3 or less. Then, since a more uniform and dense convex part distribution is obtained, it is preferable. Similarly, when the cross-sectional curve is extracted from the three-dimensional data obtained by SEM, the Rsk specified in JIS B 0601: 2001 obtained after filtering at a cutoff wavelength of 1.0 μm is 0.6 or less, or the Rku is 4 or less. It is more preferable not only to increase the surface area when coating the resin on the adhesive film, but also to withstand the pressure at the time of molding in order to create a strong interface and to develop the anchor effect.

  As a method for forming an adhesive film, a steel plate is subjected to cathodic electrolysis in an aqueous solution containing Ti and further containing at least one metal ion selected from Co, Fe, Ni, V, Cu, Mn and Zn. A method of treating or dipping is preferred. As the aqueous solution containing Ti, an aqueous solution containing fluorotitanate ions or an aqueous solution containing fluorotitanate ions and a fluorine salt is suitable. As the compound that gives fluorotitanate ions, fluorinated titanate, ammonium fluoride titanate, potassium fluoride titanate, and the like can be used. As the fluorine salt, sodium fluoride, potassium fluoride, silver fluoride, tin fluoride, or the like can be used. In particular, the method of cathodic electrolysis of a steel sheet in an aqueous solution containing potassium fluorinated titanate or an aqueous solution containing potassium fluorinated titanate and sodium fluoride can form a uniform film efficiently. It is preferable.

  The compounds that give Co, Fe, Ni, V, Cu, Mn and Zn ions include cobalt sulfate, cobalt chloride, iron sulfate, iron chloride, nickel sulfate, copper sulfate, vanadium oxide sulfate, zinc sulfate, manganese sulfate, etc. Can be used.

  Furthermore, what is necessary is just to adjust the mass ratio of Ti ion and metal ion in the said aqueous solution so that mass ratio of these metal elements with respect to Ti of an adhesive film may be set to 0.01-10. Moreover, what is necessary is just to determine suitably the current density and electrolysis time in cathodic electrolysis processing, and the immersion time in immersion treatment according to required Ti amount. The content of these metal elements in the film can be measured by energy dispersive X-ray analysis (EDX) or electron beam energy loss spectroscopy (EELS) in the TEM observation described above.

2) Resin-coated steel sheet A resin-coated steel sheet can be obtained by coating a resin on the surface-treated steel sheet of the present invention. As described above, since the surface-treated steel sheet of the present invention is excellent in wet resin adhesion, this resin-coated steel sheet has excellent corrosion resistance and workability.

  The resin coated on the surface-treated steel sheet of the present invention may be a resin film for lamination or a resin paint for coating, and is not particularly limited, and examples thereof include various thermoplastic resins and thermosetting resins. be able to. For laminating, for example, polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, olefin resin film such as ionomer, or polyester such as polybutylene terephthalate. It may be an unstretched or biaxially stretched film or a thermoplastic resin film such as nylon 6, nylon 6,6, nylon 11, nylon 12 or other polyamide film, polyvinyl chloride film, polyvinylidene chloride film, etc. . When using an adhesive during lamination (urethane), urethane adhesive, epoxy adhesive, acid-modified olefin resin adhesive, copolyamide adhesive, copolyester adhesive (thickness: 0.1-5.0 μm) and the like are preferably used. Furthermore, a thermosetting paint may be applied to the surface-treated steel plate side or film side in a thickness range of 0.05 to 2 μm, and this may be used as an adhesive.

  For coating, modified epoxy paints such as phenol epoxy and amino-epoxy, vinyl chloride-vinyl acetate copolymer, saponified vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer Thermoplastic or thermosetting paints such as coalesced, epoxy-modified, epoxy-amino-modified, epoxyphenol-modified-vinyl paint or modified vinyl paint, acrylic paint, synthetic rubber paint such as styrene-butadiene copolymer, etc. It may be a combination of two or more.

  In the present invention, the thickness of the resin coating layer is desirably 3 to 50 μm, particularly 5 to 40 μm. When the thickness is below the above range, the corrosion resistance becomes insufficient, and when the thickness is above the above range, problems are likely to occur in terms of workability.

  In the present invention, the resin coating layer can be formed on the surface-treated steel sheet by any means. When resin coating is performed by laminating, for example, extrusion coating, cast film thermal bonding, biaxially stretched film thermal bonding, or the like can be used. In the case of the extrusion coating method, it can be produced by extrusion coating a resin on a surface-treated steel sheet in a molten state and thermally bonding the resin. That is, after melt-kneading the resin with an extruder, the resin is extruded from a T-die into a thin film, and the extruded molten resin film is pressed and integrated with a surface-treated steel sheet between a pair of laminate rolls, and then rapidly cooled. To do. When extrusion coating a multi-layer resin coating layer, use multiple extruders for each layer, merge the resin streams from each extruder in a multi-layer die, and then extrude as in the case of a single layer resin. Just coat it. Moreover, a resin coating layer can be formed on both surfaces of a surface-treated steel sheet by passing a surface-treated steel sheet vertically between a pair of laminate rolls and supplying a molten resin web to both sides thereof.

  Such a resin-coated steel sheet can be applied to three-piece cans and seamless cans (two-piece cans) having side seams. The present invention can also be applied to a stay-on-tab type easy open can lid and a full open type easy open can lid.

  The above description is merely an example of an embodiment of the present invention, and various modifications can be made within the scope of the claims.

  Cathodic electrolysis was performed on both sides of cold-rolled cold-rolled steel plate (thickness 0.2 mm) as cold-rolled steel used for the production of tin-free steel plates (TFS) under the conditions of cathodic electrolysis shown in Table 1. Then, an adhesive film is formed by drying, and surface-treated steel sheets Nos. 1 to 8 shown in Table 1 are produced.

  The Ti amount of the adhesive film is obtained by fluorescent X-ray analysis in comparison with a calibration plate obtained by chemical analysis of the adhesion amount in advance. In addition to surface analysis methods such as XPS, Auger Electron Spectroscopy (AES), and Glow Discharge Spectroscopy (GDS), metal elements detected in adhesive films are evaluated using EDX attached to TEM. Since Fe is contained in the base steel sheet, it is considered that EDX alone is insufficient to confirm that it is present in the adhesive film of the present invention, which is an ultrathin film, and is also performed by EELS attached to the TEM. For the amount of Co, Fe, Ni, V, Cu, Mn, and Zn deposited, select the appropriate measurement method from the fluorescent X-ray analysis method similar to Ti, chemical analysis method, AES, and secondary ion mass spectrometry method. The mass ratio of Co, Fe, Ni, V, Cu, Mn and Zn to Ti contained in the adhesive film is obtained. In addition, O confirms the presence by XPS about all of No. 1-8.

  As described above, the thickness of the adhesive film and the linear density of the protrusions are measured based on the cross-sectional profile obtained by TEM observation by processing the film cross section with FIB to produce a thin film sample. At this time, SEM observation is performed in advance, the evaluation site is positioned, a protective film is formed, and then cross-section processing is performed by FIB using Ga ions to perform TEM observation as a thin film of about 0.1 μm. In the present invention, FIB uses SMI-3050MS2 manufactured by SII-NT, and TEM uses JEM-2010F manufactured by JEOL.

  In addition, the SEM image is acquired by an SEM that can measure the uneven shape. In the present invention, high resolution SEM ERA-8800FE manufactured by Elionix Co., Ltd. is used. This device is equipped with four secondary electron detectors facing the sample direction, and displays an image that emphasizes the difference in composition from the sum and difference signals of secondary electrons and an image that reflects irregularities in a specific direction. can do. Based on the obtained SEM image, Rq, Ra, Rsk and Rku are calculated using the image processing software attached to the apparatus. The surface density of the convex part is calculated using the SEM image obtained by the above apparatus using the three-dimensional surface shape analysis software “SUMMIT” developed by Nagaoka Institute of Technology Yanagi Laboratory. At this time, about 10 nm of Au is deposited on the sample before observation, and SEM image observation is performed at an acceleration voltage of 5 kV and a magnification of 20000 times. Analyze each sample from five arbitrary fields of view and average the surface density of the protrusions. When calculating Rq, Ra, Rsk, Rku, extract 100 or more cross-sectional curves for each visual field, average the values obtained by evaluating the roughness curves extracted for each, and obtain the evaluation value for each visual field. Average it over 5 fields of view.

In addition, on both surfaces of these surface-treated steel sheets No. 1 to 8, an isophthalic acid copolymerized polyethylene terephthalate film having a draw ratio of 3.1 × 3.1, a thickness of 25 μm, a copolymerization ratio of 12 mol%, and a melting point of 224 ° C. was used. Lamination conditions with a degree of axial orientation (BO value) of 150, that is, steel sheet feed speed: 40 m / min, rubber roll nip length: 17 mm, and time to water cooling after crimping: 1 second Make 1-8. Here, the nip length is the length in the transport direction of the portion where the rubber roll and the steel plate are in contact. And about the produced laminated steel plates No. 1-8, the following wet resin adhesiveness evaluation is performed.
Wet resin adhesion: Wet resin adhesion is evaluated by a 180 ° peel test in a retort atmosphere at a temperature of 130 ° C. and a relative humidity of 100%. The 180 ° peel test is a test piece (size: 30 mm x 100 mm, with both sides on the front and back sides set to n = 1, leaving a film 2 as shown in Fig. 5 (a) and cutting off part 3 of the steel plate 1 , N = 2 for each laminated steel plate), and as shown in Fig. 5 (b), attach a weight 4 (100g) to one end of the test piece and turn it 180 ° to the film 2 side and leave it for 30min. This is a film peeling test. Then, the peel length 5 shown in (c) of FIG. 5 is measured and evaluated, and the average of the peel lengths (n = 2) on the front and back surfaces of each laminated steel sheet is obtained. It can be said that the smaller the peeling length 5 is, the better the wet resin adhesion is. However, if the peeling length 5 is less than 10 mm, it is evaluated that the excellent wet resin adhesion intended by the present invention is obtained.

  The results are shown in Table 2. In laminated steel sheets Nos. 2 to 8 which are examples of the present invention, all show excellent wet resin adhesion. On the other hand, laminated steel plate No. 1 as a comparative example is inferior in wet resin adhesion.

  In addition to the above examples, excellent wet adhesion and corrosion resistance are also obtained when cathodic electrolysis is performed in a treatment bath in which cobalt chloride hexahydrate or cobalt sulfate heptahydrate is added to potassium fluorotitanate. Is confirmed.

It is a schematic diagram of the adhesive film cross section of the surface treatment steel plate which is this invention. It is a schematic diagram of the film cross section of the surface treatment steel plate which is a comparative example. It is a schematic diagram for demonstrating the thickness of the adhesive film of the surface treatment steel plate which is this invention, and the linear density of a convex part. It is a figure which shows the SEM observation result of the adhesive film of this invention example, and the film surface of a comparative example. It is a figure explaining a 180 degree peel test.

Explanation of symbols

1 Steel plate
2 film
3 Parts cut from steel plate
4 weights
5 Peel length

Claims (6)

It is obtained by cathodic electrolysis treatment in an aqueous solution containing at least one metal ion selected from Co, Fe, Ni, V, Cu, Mn and Zn. and has a film excellent wet resin adhesion, including thickness of Ti 20 to 800 nm, and the film excellent in the wet resin adhesion, there is a convex portion 1 / [mu] m or more linear density And a surface-treated steel sheet, characterized in that the mass ratio of Co, Fe, Ni, V, Cu, Mn and Zn to Ti contained in the film excellent in wet resin adhesion is 0.01 to 10 ;
Here, the thickness of the film excellent wet resin adhesion, the coating section profile observed with a transmission electron microscope (TEM), and that the maximum height H of the projection measured from the film lower surface, wet resin adhesion The line density of the convex part of the film with excellent properties is the minimum height from the lower surface of the film at the bottom of the concave part, and the horizontal line at the upper and lower levels of ± 10 nm centered on the position of (H + L) / 2 When it is drawn, there is one convex part when there is at least one point where the upper level horizontal line intersects the profile curve between two adjacent points where the lower level horizontal line intersects the profile profile curve. This is the number of convex portions per unit length obtained as if. It is obtained by cathodic electrolysis treatment in an aqueous solution containing at least one metal ion selected from Co, Fe, Ni, V, Cu, Mn and Zn. and has a film excellent wet resin adhesion, including thickness of Ti 20 to 800 nm, and the film excellent in the wet resin adhesion, the convex portion 16 / [mu] m ² or more of the surface density A surface-treated steel sheet, characterized by having a mass ratio of Co, Fe, Ni, V, Cu, Mn, and Zn to Ti contained in the film having excellent wet resin adhesion and 0.01 to 10 ;
Here, the surface density of the convex part of the film with excellent wet resin adhesion means that the SEM image of the film surface observed with a scanning electron microscope (SEM) is three-dimensionally analyzed and filtered with a cutoff wavelength of 1.0 μm. It is the average line of unevenness obtained by applying + the number of convex portions per unit area having a height of 0.005 μm or more.   The root mean square roughness (Rq) and arithmetic mean roughness (Ra) defined in JIS B 0601: 2001, obtained by extracting the cross-sectional curve from the three-dimensional data by SEM and filtering it with a cutoff wavelength of 1.0 μm, 3. The surface-treated steel sheet according to claim 2, wherein the ratio (Rq / Ra) is 1.3 or less.   The cross-sectional curve is extracted from the three-dimensional data by SEM, and the skewness (Rsk) specified in JIS B 0601: 2001 obtained after filtering at a cutoff wavelength of 1.0 μm is 0.6 or less, or the kurtosis (Rku) is 4 or less. 4. The surface-treated steel sheet according to claim 2, wherein the surface-treated steel sheet is provided. The surface-treated steel sheet according to any one of claims 1 to 4, wherein the amount of Ti of the film excellent in wet resin adhesion is 3 to 200 mg / m ² per side.   A resin-coated steel sheet, wherein the surface-treated steel sheet according to any one of claims 1 to 5 is coated with a resin.