Technical Field The present invention relates to a surface treated steel sheet for a fuel tank. Background Art With tightening environmental regulation in recent years, market needs for materials that do not contain harmful metals have been increased. For example, in the field of automobiles, the switching from a lead-tin alloy plated steel sheet, which 15 has been a main ingredient of fuel tanks, to a material not containing lead has been promoted. Here, to a unique required performance of the fuel tanks, which is high irmer corrosion resistance under the environment in which a fuel is enclosed (hereinafter, referred to as fuel corrosion resistance), many suggestions are given involving using zinc-based plated steel sheets, which achieve steady success as irmer 20 and outer sheets of automobiles (for example, see the following Patent Literatures 1 to 3). Patent Literature 25 [0003] Patent Literature 1: Patent Literature 2: Patent Literature 3: Patent Literature 4: 30 Patent Literature 5: Patent Literature 6: Citation List JP H5-106058A JP H9-324279A JP 2004-169122A JP 2007-186745A wo 2010/061964 wo 2008/059890 5 Technical Problem [0004] 2/33 Summary of Invention PCT/JP20 16/051559 However, the technologies according to Patent Literatures 1 to 3 each have an assumption that chromate treatment is performed, and therefore are incompatible with the recent market needs for materials that do not contain harmful metals. For this reason, a chromate-free zinc-based plated steel sheet for a fuel tank is disclosed (for example, see Patent Literatures 4 to 6). Compared to the conventional zinc- 10 based plated steel sheet subjected to the chromate treatment, the chromate-free zincbased plated steel sheet is not sufficient in fuel corrosion resistance under a severer environment (for example, corrosion resistance over a longer time period, and corrosion resistance in the case where damage in the coating film has occurred during processing), and requires improvement. 15 [0005] Patent Literature 4 discloses a chromate-free coating film mainly containing an organic resin. However, when such a chromate-free coating film mainly containing an organic resin is exposed to a fuel environment for a long time period, the organic resin is swelled by the fuel, and adhesion between surfaces of plating 20 decreases. It is assumed that such swelling of the organic resin is a factor in insufficient corrosion resistance. [0006] Patent Literature 5 discloses a galvanized steel sheet having a coating film formed by applying an aqueous treatment agent containing an organosilicon 25 compound and an organofluorine compound to a zinc-based plated steel sheet and drying or baking the resultant. Further, Patent Literature 6 discloses a galvanized steel sheet having a composite coating film containing an organosilicon compound, a fluorocompound, a vanadium compound, and a lubricant. However, those steel sheets are improved in corrosion resistance, but are not imparted with corrosion 30 resistance with respect to deteriorated gasoline. [0007] PCT/JP2016/051559 3/33 Accordingly, the present invention aims to provide a surface treated steel sheet for a fuel tank, which exhibits excellent corrosion resistance under an environment in which various fuels are enclosed, the fuels including a fuel containing an organic acid such as deteriorated gasoline and a fuel containing dew 5 condensation water in addition to an organic acid, and which has satisfactory press workability. The present invention also aims to obtain the above characteristics without using lead and chromate treatment. Solution to Problem 10 [0008] The inventors of the present invention have investigated the improvement in fuel corrosion resistance in a chromate-free zinc-based plated steel sheet, and have found that the fuel corrosion resistance can be remarkably improved by making a zinc-based plated layer to be a Zn plated layer or a Zn-Ni alloy plated layer, and 15 imparting not only water repellency but also oil repellency to a surface of the plated layer. Further, the inventors of the present invention have found that, on the contrary, in the case where the oil repellency is excessively imparted, the fuel corrosion resistance decreases and the press workability also remarkably decreases. As a result of carrying out investigation on the basis of those findings, the inventors 20 of the present invention have found that a steel sheet which is excellent in fuel corrosion resistance and press workability can be obtained by forming a coating film having predetermined water repellency and oil repellency on a surface to be an inner surface of a fuel tank. That is, the gist of the present invention is as follows. [0009] 25 (1) A surface treated steel sheet for a fuel tank, the surface treated steel sheet including: a Zn plated layer or a Zn-Ni alloy plated layer which is placed on a surface to be an inner surface of the fuel tank, the surface being a base metal, or on the 30 surface to be the inner surface of the fuel tank and a surface to be an outer surface of the fuel tank, the surface being the base metal; and -- ---- --1 PCT/JP2016/051559 4/33 a chromate-free chemical conversion coating layer containing a water-andoil repellent, the chromate-free chemical conversion coating layer being placed over the Zn plated layer or the Zn-Ni alloy plated layer, wherein a water contact angle on a surface of the chromate-free chemical 5 conversion coating layer is more than or equal to 70 degrees and an n-hexadecane contact angle on the surface of the chromate-free chemical conversion coating layer is more than or equal to 30 degrees and less than or equal to 70 degrees. 10 (2) The surface treated steel sheet for a fuel tank according to (1 ), wherein only the surface to be the inner surface of the fuel tank, the surface being the cold-rolled steel sheet, is provided with the chromate-free chemical conversion coating layer and one of the Zn plated layer and the Zn-Ni alloy plated layer, and the surface to be the outer surface of the fuel tank, the surface being the cold-rolled steel sheet, is not provided with the chromate-free chemical conversion 15 coating layer and the one of the Zn plated layer and the Zn-Ni alloy plated layer. (3) The surface treated steel sheet for a fuel tank according to (2), wherein a deposition amount of Zn and/or Ni on one surface of the fuel tank, the surface being the cold-rolled steel sheet, is 0.01 to 0.5 g/m2 • 20 (4) The surface treated steel sheet for a fuel tank according to any one of (1) to (3), wherein a deposition amount of the Zn plated layer or the Zn-Ni alloy plated layer is 5 to 40 g/m2 per surface. 25 (5) The surface treated steel sheet for a fuel tank according to any one of (1) to (4), wherein aNi content in the Zn-Ni alloy plated layer is 9 to 14 mass% with respect to a total mass of the Zn-Ni alloy plated layer. 30 (6) The surface treated steel sheet for a fuel tank according to any one of (1) to 5 PCT/JP2016/051559 5/33 ( 5), wherein a deposition amount of the chromate-free chemical conversion coating layer is 0.1 to 2 g/m2 . (7) The surface treated steel sheet for a fuel tank according to any one of (1) to (6), wherein the chromate-free chemical conversion coating layer contains, as the waterand- oil repellent, a fluorine-based water-and-oil repellent. (8) 10 The surface treated steel sheet for a fuel tank according to any one of (1) to (7), wherein the chromate-free chemical converswn coating layer further contains a polyolefin lubricant. (9) 15 The surface treated steel sheet for a fuel tank according to any one of (1) to (7), wherein the chromate-free chemical conversion coating layer is an inorganic coating film, and does not contain an organic resin component other than the water-and-oil repellent. 20 (10) 25 The surface treated steel sheet for a fuel tank according to (8), wherein the chromate-free chemical conversion coating layer is an inorganic coating film, and does not contain an organic resin component other than the water-and-oil repellent and the polyolefin lubricant. Advantageous Effects of Invention [0010] According to the present invention, there can be provided a surface treated steel sheet for a fuel tank, which exhibits excellent corrosion resistance under an 30 environment in which various fuels are enclosed, the fuels including a fuel containing an organic acid such as deteriorated gasoline and a fuel further containing PCT/JP2016/051559 6/33 dew condensation water in addition to an organic acid, and which has satisfactory press workability. Description of Embodiments 5 [0011] The present invention relates to a zinc-based steel sheet for a fuel tank, which is excellent in corrosion resistance to various fuels and press workability, is not subjected to lead and chromate treatment, and is environmentally friendly. The present invention also relates to a steel sheet used for an automobile, a motorcycle, 10 industrial machinery, and construction machinery, and in addition, used for a tank in which a fuel is enclosed and a part of the tank. [0012] The steel sheet for a fuel tank according to the present invention includes: a Zn plated layer or a Zn-Ni alloy plated layer (hereinafter, also referred to as plated 15 layer) which is placed on a surface to be an inner surface of the fuel tank, the surface being a base metal (one surface), or on the surface to be the inner surface of the fuel tank and a surface to be an outer surface of the fuel tank (both surfaces); and a chromate-free chemical conversion coating layer (hereinafter, also referred to as chemical conversion coating layer) containing a water-and-oil repellent, the chemical 20 conversion coating layer being placed over the Zn plated layer or the Zn-Ni alloy plated layer. Further, a water contact angle on a surface of the chemical conversion coating layer is more than or equal to 70 degrees, and an n-hexadecane contact angle on the surface of the chemical conversion coating layer is more than or equal to 30 degrees and less than or equal to 70 degrees. 25 [0013] In the steel sheet of the present invention, the surface to be the outer surface of the fuel tank (hereinafter, referred to as outer surface) may have the Zn plated layer or the Zn-Ni alloy plated layer, or does not necessarily have the Zn plated layer or the Zn-Ni alloy plated layer. However, in order to make the weldability of the 30 steel sheet satisfactory, it is preferred that the surface to be the outer surface of the fuel tank do not have the plated layer. Further, for example, in the case where the PCT/JP20 16/051559 7/33 steel sheet is used as a fuel tank for a motorcycle which places importance on the visual quality of the coating of the outer surface of the fuel tank, it is preferred that the outer surface of the fuel tank do not have the plated layer in order to make the external appearance of the coating satisfactory. On the other hand, in the case 5 where the steel sheet is used for the case where the outer surface of the fuel tank also requires high corrosion resistance, it is preferred that the outer surface of the fuel tank have the plated layer. In the steel sheet according to the present invention, the presence and absence of the plated layer on the outer surface and the inner surface can be controlled in accordance with the use. Note that the chromate-free chemical 10 conversion coating layer is not formed over: the Zn plated layer or the Zn-Ni alloy plated layer on the surface to be the outer surface of the fuel tank; or the steel sheet surface which does not have the Zn plated layer or the Zn-Ni alloy plated layer. The water contact angle and the n-hexadecane contact angle can be measured by a known measurement method using a contact angle meter. 15 [0014] It is necessary that the water contact angle and the n-hexadecane contact angle on the surface of the chromate-free chemical conversion coating layer at the surface to be the inner surface of the fuel tank be more than or equal to 70 degrees, and more than or equal to 30 degrees and less than or equal to 70 degrees, 20 respectively. In the case where the water contact angle is less than 70 degrees, the corrosion resistance with respect to deteriorated gasoline is insufficient. It is preferably more than or equal to 80 degrees. The upper limit of the water contact angle is not particularly defmed (which does not exceed 180 degrees theoretically), but the level of the upper limit that can be achieved on the chromate-free chemical 25 conversion coating layer placed over an ordinary Zn plated layer or Zn-Ni alloy plated layer is around 120 degrees. In the case where the water contact angle is large, it is assumed that the corrosion resistance improves, since isolation effects are large owing to dew condensation water in which corrosion factors such as organic matters in the deteriorated gasoline are concentrated. In order to obtain sufficient 30 corrosion resistance with respect to deteriorated gasoline, it is not sufficient only to PCT/JP2016/051559 8/33 defme the water contact angle to the above range, and it is also necessary to control an oil contact angle. [0015] Further, in the present invention, the n-hexadecane contact angle on the 5 surface of the chromate-free chemical conversion coating layer at the surface to be the inner surface of the fuel tank is more than or equal to 30 degrees and less than or equal to 70 degrees. The n-hexadecane contact angle on the surface of the chromate-free chemical conversion coating layer is more preferably more than or equal to 55 degrees and less than or equal to 70 degrees. Here, n-hexadecane is 10 used as an imitation component of fuel oil. In the case where the n-hexadecane contact angle on the surface of the chemical conversion coating layer is less than 30 degrees, corrosion resistance with respect to deteriorated gasoline is insufficient. The reason therefor is not necessarily clear, but it can be considered that, in the case where the contact angle is small, the deteriorated gasoline erodes the coating film 15 from a point at which a flaw caused by press working or the like occurs. Further, in the case where the n-hexadecane contact angle on the surface of the chemical conversion coating layer exceeds 70 degrees, primary rust resistance of the opposite surface of the steel sheet (the surface to be the outer surface of the fuel tank) remarkably decreases. The reason therefor is that the steel sheet for a fuel tank is 20 generally shipped after: the plated layer and the chemical conversion coating layer are formed in a production line; then rust -resistant oil for the primary rust resistance is applied; and the resultant is wound in a coil shape. To be specific, in the case where the steel sheet is wound in a coil shape, the surface to be the outer surface of the fuel tank (that is, the Zn plated surface or the Zn-Ni alloy plated surface which 25 does not have the chemical conversion coating layer, or the non-plated surface) faces the surface to be the inner surface of the fuel tank (that is, the surface of the chromate-free chemical conversion coating layer having water repellency and oil repellency). Here, in the case where the n-hexadecane contact angle on the surface to be the inner surface of the fuel tank exceeds 70 degrees, the surface of the 30 chemical conversion coating layer excessively repels the rust-resistant oil. Since such an effect influences the surface to be the outer surface of the fuel tank that faces PCT/JP2016/051559 9/33 the surface to be the inner surface of the fuel tank in the state of being stacked in the coil shape, under the high-temperature and high-humidity condition, rust occurs from the part that lacks the rust-resistant oil on the surface that faces the surface to be the inner surface of the fuel tank (that is, on the surface to be the outer surface of the fuel 5 tank). This phenomenon is fatal particularly in the case where the surface to be the outer surface of the fuel tank is a non-plated surface. [0016] In addition, the above-mentioned steel sheet having poor primary rust resistance also has a poor coating property in the case where a fuel tank is produced 10 after the steel sheet is kept in the coiled state for a long period of time. In the fuel tank produced using the steel sheet, the inner surface is generally the steel sheet as it is whose surface has been treated, but the outer surface is generally coated. Particularly in a tank for a motorcycle, since the importance is placed on the visual quality of the coating of the surface to be the outer surface of the fuel tank, the 15 coating property of the outer surface is an important characteristic. Here, although no abnormality such as rust that can be visually recognized is found through a primary rust resistance test, there is a case where a slight surface layer oxide filmunevenness may cause coating unevenness. Therefore, the n-hexadecane contact angle on the surface to be the inner surface being less than or equal to 70 degrees can 20 suppress the decrease in the rust resistance and the coating property. In addition, it is more preferred that the surface to be the outer surface be a non-plated surface. This is because, in the case where the Zn plated layer or the Zn-Ni alloy plated layer is provided as the surface to be the outer surface, although the n-hexadecane contact angle on the surface to be the inner surface is more than or equal to 3 0 degrees, 25 which is within the range of the present invention, and no rust occurs in the primary rust resistance test, a slight zinc oxide film-unevenness is likely to occur and the coating property may decrease. [0017] Further, in the case where the n-hexadecane contact angle exceeds 70 30 degrees, the corrosion resistance with respect to the deteriorated gasoline may decrease, which is not preferred. This is because, as will be described later, in the 5 PCT/JP2016/051559 10/33 case where the n-hexadecane contact angle exceeds 70 degrees, oil-repellency becomes remarkable, so that the press workability lowers, and damage in the coating film and the plating may become severe. [0018] On the other hand, in the steel sheet according to the present invention, since the n-hexadecane contact angle on the surface to be the inner surface of the fuel tank is more than or equal to 30 degrees and less than or equal to 70 degrees, the steel sheet repels oil to a certain extent during the press working, but it does not pose a problem on practical use of the press working. Moreover, in the present invention, 10 in the case where the surface to be the outer surface of the fuel tank is the Zn plated surface or the Zn-Ni alloy plated surface, or the non-plated surface, since those surfaces do not repel the oil, the press workability further improves. In this way, the press workability of the steel sheet according to the present invention can be further enhanced by making the surface to be the inner surface of the fuel tank 15 different from the surface to be the outer surface of the fuel tank. [0019] Here, in the steel sheet according to the present invention, the steel sheet (base metal) used as a base material is not particularly limited, and any steel sheet is usable as long as it is a steel sheet that is generally used as a base material of a zinc- 20 based plated steel sheet. [0020] The Zn plated layer or the Zn-Ni alloy plated layer formed on at least one surface of the steel sheet (base metal) according to the present invention is an alloy plated layer containing at least zinc or an alloy of zinc and nickel. The Zn plated 25 layer or the Zn-Ni alloy plated layer can be formed by a known plating method such as an electroplating method. [0021] The deposition amount of the Zn plated layer or the Zn-Ni alloy plated layer in the steel sheet according to the present invention is preferably 5 to 40 g/m2 per 30 surface. In the case where the deposition amoimt of the Zn plated layer or the ZnNi alloy plated layer per surface is less than 5 g/m2 , it is not preferred because the 5 PCT/JP2016/051559 11133 corrosion resistance with respect to deteriorated gasoline is likely to be insufficient. Further, in the case where the deposition amount of the Zn plated layer or the Zn-Ni alloy plated layer per surface exceeds 40 g/m2 , it is not preferred because it is disadvantageous in terms of cost. Moreover, the Ni content in the Zn-Ni alloy plated layer is preferably 9 to 14 mass% with respect to a total mass of the Zn-Ni alloy plated layer. In the case where the Ni content is in this range, the corrosion resistance with respect to deteriorated gasoline in particular becomes satisfactory. Note that the Zn plated layer or the Zn-Ni alloy plated layer may contain a known third component (for 10 example, metal such as Fe, Co, Sn, and Cr), and the underneath the Zn plated layer or the Zn-Ni alloy plated layer may be subjected to known pre-plating (for example, pre-plating of Fe and Ni). [0022] The steel sheet for a fuel tank according to the present invention includes 15 the chromate-free chemical conversion coating layer (hereinafter, also referred to as chemical conversion coating layer) containing a water-and-oil repellent, the chemical conversion coating layer being placed over the Zn plated layer or the Zn-Ni alloy plated layer on the surface to be the inner surface of the fuel tank. The deposition amount of the chromate-free chemical conversion coating layer in the steel sheet 20 according to the present invention is preferably 0.1 to 2 g/m2 . In the case where the deposition amount of the chromate-free chemical conversion coating layer is less than 0.1 g/m2 , it is not preferred because the corrosion resistance with respect to deteriorated gasoline is likely to be insufficient. In the case where the deposition amount of the chromate-free chemical conversion coating layer exceeds 2 g/m2 , it is 25 not preferred because the workability and weldability may deteriorate. [0023] In order to achieve the water contact angle and the n-hexadecane contact angle on the surface to be the inner surface of the fuel tank in the steel sheet according to the present invention, it is necessary that the chromate-free chemical 30 conversion coating layer contain a water-and-oil repellent. In particular, it is preferred that the chromate-free chemical conversion coating layer contain a PCT/JP20 16/051559 12/33 fluorine-based water-and-oil repellent. Any fluorine-based resin having a C-F bond may be used as the fluorine-based water-and-oil repellent, and examples thereof include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polychlorotrifluoro 5 ethylene, polyvinylidene fluoride, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, and perfluoroalkyl groupcontaining polymer. The content of the fluorine-based water-and-oil repellent in the chromate-free chemical conversion coating layer is preferably more than or equal to 0.1 mass% and less than or equal to 10 mass% with respect to the total solid 10 content of the chemical conversion coating layer, and is more preferably more than or equal to 1 mass% and less than or equal to 5 mass% with respect to the total solid content of the chemical conversion coating layer. [0024] Further, the chromate-free chemical conversion coating layer of the steel 15 sheet according to the present invention may further contain a polyolefin lubricant. In such a case, slidability while press working is performed on the steel sheet can be reduced. The content of the polyolefm lubricant in the chromate-free chemical conversion coating layer is preferably more than or equal to 0.1 mass% and less than or equal to 10 mass% with respect to the total solid content of the chemical 20 conversion coating layer, and is more preferably more than or equal to 1 mass% and less than or equal to 5 mass% with respect to the total solid content of the chemical conversion coating layer. [0025] The chromate-free chemical converswn coating layer of the steel sheet 25 according to the present invention may be an organic coating layer or may also be an inorganic coating film layer. However, in the case where higher corrosion resistance with respect to deteriorated gasoline is demanded, it is desired that the chromate-free chemical conversion coating layer do not contain an organic resin component or contain an organic resin component the amount of which is minimized. 30 This is because it is estimated that the organic resin component contained in the chromate-free chemical conversion coating layer lowers the corrosion resistance PCT/JP2016/051559 13/33 since the organic resin component is swelled by the fuel. Specific examples of the organic resin component contained in the chromate-free chemical conversion coating layer include an acrylic resin, an olefin resin, a urethane resin, an epoxy resin, and a polyester resin. The content of those organic resin components in the chromate-free 5 chemical conversion coating layer is preferably less than or equal to 50 mass%, more preferably less than or equal to 30 mass%, and most preferably 0 mass% with respect to the total solid content of the chemical conversion coating layer. [0026] Moreover, the chromate-free chemical conversion coating layer of the steel 10 sheet according to the present invention may contain, as an inorganic component, a silane coupling agent, a condensation polymer of a silane coupling agent, silica, silicate, phosphoric acid, and phosphate. The chromate-free chemical conversion coating layer of the steel sheet according to the present invention may be formed by containing one of those components or two or more of those components in 15 combination, or by being mixed with the above-mentioned organic resin components. 20 Note that, the chromate-free chemical conversion coating layer may be blended with other components including the above-mentioned polyolefin lubricant, in a range that does not deteriorate the characteristics. [0027] Note that the chromate-free chemical conversion coating film of the steel sheet according to the present invention can be formed through a known method. For example, the method involves preparing application liquid containing predetermined component(s) described above, applying the prepared application liquid over the Zn plated layer or the Zn-Ni alloy plated layer through a known 25 method such as bar coater and roll coater, and then heating at predetermined heating temperature and drying the applied film. [0028] As described above, in order to make the weldability of the steel sheet satisfactory, or, in order to make the external appearance of the coating of the surface 30 to be the outer surface of the fuel tank satisfactory, it is preferred that the surface to be the outer surface of the fuel tank do not have the plated layer. In order to make PCT/JP2016/051559 14/33 the outer surface into a state that does not have the plated layer, there can be employed a method not involving applying electric current to the side of the nonplated surface during electroplating. Alternatively, there can be employed a method involving performing plating, and then removing the plating on the side of the non- 5 plated surface through an electrochemical method (for example, anode electrolytic treatruent) or a mechanical method (for example, grinding with a brush). Further, the above-mentioned methods can be used in combination. [0029] Owing to the above methods, the non-plated surface (outer surface of the 10 fuel tank) of the steel sheet according to the present invention can be completely prevented from having Zn and/or Ni being deposited thereon. In that case, the deposition amount of Zn and/or Ni is 0. As described above, this is for improving the weldability and the coating property of the steel sheet. It is desirable that the deposition amount be 0.01 to 0.5 g/m2 , preferably 0.01 to 0.3 g/m2 , more preferably 15 0.01 to 0.1 g/m2 • [0030] The contact angle on the non-plated surface (outer surface) formed through those methods is preferably less than 10 degrees and more preferably less than 5 degrees in the n-hexadecane contact angle. In this way, the press workability and 20 the coating property are improved. In order to ensure the above contact angle, it is effective to suppress oxidation on the surface of the steel sheet, and in this point, it is desirable that a trace amount of Zn and/or Ni is present also on the non-plated surface side. The deposition amount is desirably 0.01 to 0.5 g/m2 . [Examples] 25 [0031] Next, the present invention will be described further specifically with reference to Examples and Comparative Examples. [0032] First, using a non-plated steel sheet, one-surface plated steel sheets, and 30 both-surfaces plated steel sheets shown in Table 1 as original sheets, surface treated steel sheets for a fuel tank were produced. Note that the steel sheets shown in Table PCT/JP2016/051559 15/33 1 were each a Ti-added extra-low carbon steel sheet for deep drawing having a thickness of 0.8 mm, and each chemical conversion coating layer was formed only on one surface (the surface to be the inner surface of the fuel tank) of the original sheet or on both surfaces of the original sheet. Note that the compositions of the 5 base coating films that constitute the respective chemical conversion coating layers are shown in Table 2. Further, to the base coating films shown in Table 2, polyolefm lubricants shown in Table 3 and fluorine-based water-and-oil repellents shown in Table 4 were each added in a proportion shown in Table 5, and the chemical conversion coating layers were formed. 10 [0033] [Table I] Symbol Content S/S non-plated steel sheet S/5 Zn-Ni alloy plating (coating weight: 5 gim2 , Ni: 12.5%) on only one surface (surface to be inner surface) S/15 Zn-Ni alloy plating (coating weight: 15 gim2 , Ni: 11%) on only one surface (surface to be inner surface) S/20 Zn-Ni alloy plating (coating weight: 20 gim2 , Ni: 10.5%) on only one surface (surface to be inner surface) S/30 Zn-Ni alloy plating (coating weight: 30 gim2 , Ni: 10.6%) on only one surface (surface to be inner surface) S/40 Zn-Ni alloy plating (coating weight: 40 gim2 , Ni: 10.1%) on only one surface (surface to be inner surface) 20/20 Zn-Ni alloy plating (coating weight: 20 gim2 , Ni:10.5%) on both surfaces S/EG40 Zn plating (coating weight: 40 gim2 ) on only one surface (surface to be imler surface) EG Zn plated steel sheet (coating weight: 30 gim2 ) on both surfaces 15 [0034] 5 PCT/JP2016/051559 16/33 [Table 2] Composition ofbase coating film {solid content, nnss%) a b c d e f g h i Orga.ni: Urethane resin (*I) 75 - - - - - 50 30 10 resin lono:rrer resin (*2) - 60 - - - - - - Silica 20 30 - lO - 20 - - Silane coupling agent (*3) 2 8 - 9 - 2 - - - Silare coupling agent oligo:rrer (*4) - - 89 - - - 44.5 62.3 80.1 Lithium silicate - - - 75 - - - - Phosphori: acrl - - 5 - - - 2. 5 3. 5 4. 5 Other than Aluminum primary pb:lsphate - - - - 55 - - - - 0.".".."." Magnesiwn primary phosphate - - - - 40 - - - An::u:ronium phosphate I 2 I - - - - PhospOOrOC acid (*5) - - - - 30 30 - - - V anadyl acetylacetonate 2 - 3 2 - - 1.5 2. I 2. 7 Ammonium vanadate - - - 5 4 - - - Amm:mium bexafiuorotitana1e - - I I 5 4 0.5 0.7 0.9 Tetra-n-butoxy titanate - - - - 5 - - Zirconim:n oxycarbonate - - 2 2 - - I 1.4 1.8 Total 100 100 100 100 100 100 100 100 100 [0035] Note that, in Table 2, "urethane resm (*1)" represents an ester-based urethane resin, "ionomer resin (*2)" represents a Na neutralized ionomer resin, "silane coupling agent (*3)" represents 3-glycidoxypropyl trimethoxy silane, "silane coupling agent oligomer (*4)" represents a condensation polymer of 3- glycidoxypropyl trimethoxy silane and 3-aminopropyltriethoxysilane in a ratio of 1:1 10 (molecular weight of approximately 3000), and "phosphonic acid (*5)" represents 1- 15 hydroxy-ethylidene-1,1'-diphosphonic acid. Further, "-" in Table 2 shows that no corresponding component is blended. [0036] [Table 3] Symbol Content PE Polyethylene wax pp Polypropylene wax [0037] [Table 4] . I' ! Symbol Fl F2 F3 F4 [0038] [Table 5] PCT/JP2016/051559 17/33 Content Polytetrafluoroethylene Tetrailuoroethylene - bexailuoropropylene copolymer Tetrailuoroethylene- perfluoroalkyl vinyl ether copolymer Perfluoroalkyl vinyl ether - methacrylate copolymer PCT/JP2016/051559 18/33 Mass ratio (solid content) Base with respect to solid content 100 ofbase coating fihn Coating coating fihnNo. Polyolefin lubricant Fluorine-based water-and-oil repellent fihn PE pp F1 F2 F3 F4 AI a 1 - - - - - A2 a 5 - - - - - A3 a 10 - - - - - A4 a - 5 - - - 5 Bl b 5 - - - - - B2 b - - - - - 5 B3 b 5 - 5 - - - B4 b 5 - 5 - - 3 C1 c 5 - - - - - C2 c - - - - - 0.1 C3 c - - - - - 0.5 C4 c - - - - - 1 C5 c - - - - - 5 C6 c - - - - - 10 C7 c - - 5 - - 10 C8 c 3 - - - - 5 Dl d - - 2 - - - D2 d - - - 3 - - D3 d - - - - 3 - El e - - - - - 3 E2 e - 2 - - - 3 E3 e 2 - - - - 3 Fl f - - - 3 - - F2 f - - - - 3 - Gl g - - - - - 5 Hl h - - - - - 5 II I - - - - - 5 [0039] Note that"-" in Table 5 shows that no corresponding component is blended. PCT/JP2016/051559 19/33 [0040] Subsequently, Tables 6 to 8 each show sample preparation conditions, and performance evaluation results of the prepared steel sheets. Here, the contact angle of the surface to be the inner surface ofthe fuel tank was measured as follows. 5 [0041] (Water contact angle) A contact angle meter (DM-901 manufactured by Kyowa Interface Science Co., Ltd) was used, 3 f.ll of ion exchanged water were dripped under 25°C atmosphere, and a static contact angle after 60 seconds was measured. 10 [0042] (n-hexadecane contact angle) A contact angle meter (DM-901 manufactured by Kyowa Interface Science Co., Ltd) was used, 3 J.tl of n-hexadecane were dripped under 25°C atmosphere, and a static contact angle after 60 seconds was measured. 15 [0043] Performance evaluation was carried out as follows. [0044] (Primary rust resistance) To the prepared sample, rust-resistant oil (NOX-RUST 530, manufactured 20 by Parker Industries, Inc.) was applied extremely slightly (approximately 0.1 g/m2 ), and then the resultant was packed in a manner that the surface to be the inner surface and the surface to be the outer surface came into contact with each other so that the state looked like a coil. After stored in 50°C 98%RH enviromnent for one month, the resultant was unpacked, and a rust state on the surface to be an outer surface of a 25 fuel tank was observed. Note that the observation results were evaluated using the following criteria. 30 [0045] Satisfactory: no rust or discoloration Unsatisfactory: occurrence of white rust or discoloration Poor: occurrence of red rust (Coating property) PCT/JP2016/051559 20/33 The coating property of the surface to be the outer surface was evaluated. Since the outer surface of the fuel tank for an automobile or a motorcycle is normally coated after being subjected to chemical conversion treatment for pre-coating treatment, the external appearance of the coating is dominated by an external 5 appearance after being subjected to the chemical conversion treatment for precoating treatment. Accordingly, a steel sheet after being subjected to the chemical conversion treatment for pre-coating treatment was evaluated for the external appearance of the surface to be the outer surface. Note that the chemical conversion treatment for pre-coating treatment was carried out as follows. 10 [0046] A chemical conversion coating layer was formed through P-free chemical conversion treatment (Example 1 in JP 5274560B) consisting of hexafluorozirconic acid, aluminum nitrate, and polyethyleneimine. After that, the steel sheet over which the chemical conversion coating layer had been formed was evaluated by 15 visual observation (however, in the case where it was difficult to perform evaluation by visual observation, the observation was performed using a scanning electron microscope (SEM) ), and the evaluation was performed using the following criteria. Excellent: uniform external appearance Satisfactory: slight unevenness of an acceptable level 20 Unsatisfactory: remarkable unevenness Poor: occurrence oflack of hiding (no chemical conversion coating layer) [0047] (Coating property after storage) A sample stored for one month was used in the same manner as the above- 25 mentioned evaluation of primary rust resistance, the same chemical conversion treatment for pre-coating treatment as the above-mentioned evaluation of coating property was performed, and the evaluation was performed using the same criteria. [0048] (Workability (slidability)) 30 Evaluation was performed by a draw bead test. Using a die having a convex bead end of 5R and a concave shoulder of 3R, a sample (to which rustPCT/ JP2016/051559 21/33 resistant oil (NOX-RUST 530, manufactured by Parker Industries, Inc.) was applied) which was cut to a width of 30 mm was drawn out 100 mm at a rate of 200 rnrn!min in a range of 500 kg to 1200 kg in terms of press bonding load. After that, a coefficient of friction was determined using the relationship between the press 5 bonding load and a drawing load. Note that the surface to be the inner surface of the fuel tank was set on the convex bead side. Further, no oil was applied to the bead die, and the test was performed by wiping off the oil on the die for every test. The coefficient of friction was evaluated using the following criteria. 10 [0049] Excellent: coefficient of friction :S 0.13 Satisfactory: 0.13 2 S/20 E=np>3 sao E=np>4 S/20 E=np> 5 S/20 E=np>6 S/20 E=np>7 S/20 E=np>8 S/20 E=nple9 S/20 Example 10 S/20 Example 11 S/20 Example 12 S/20 Example 13 S/20 Example 14 S/20 Example 15 S/20 Example 16 S/20 Example 17 S/20 Example 18 S/20 Example 19 S/20 Example 20 20/20 Example21 20/20 Example22 20/20 Example 23 20/20 Example24 20120 Example 25 20/20 Example26 20120 Example27 20/20 Example28 20120 Example29 20120 Example 30 20/20 Example 31 20/20 Example 32 20/20 Example 33 20/20 [0051] [Table 7] Coating fihnNo A4 B2 C3 C4 C5 C6 C7 C8 D1 D2 D3 El E2 El Fl F2 Gl HI II A4 B2 CJ C4 cs C6 C7 C8 D1 D2 D3 El E2 E3 Amnmtof Coating film coating fihn funnod """"' [gim'J hmer ~urfuce 0.6 -·"o"ru"y "" 0.6 -·"o"ow" "" 0.6 hmero~~ 0.6 hmeron~ 0.6 -·""""" 0.6 ""' ~~e 0.6 -"'"""· 0.6 '"" ~~ 0.6 ~~ 0.6 -""oru"y "' 0.6 ~~ 0.6 In=•""= 0.6 -·"'"""' = '""' 0.6 Inre~:~ 0.6 -·"o"ruy" "' 0.6 lniE~:~ 0.6 Inner swftce 0.6 oow -·""""' '""' 0.6 lure:.:~ 0.4 00 -""""' 0.4 '"" !mE~~ 0.4 -·""'= 0.4 -""'"""" " 0.4 oow -·""'= oruy 0.4 In='""""' 0.4 '"" Inrm~:~ OA Inrmr surface 0.4 -·"'"""" "' '""' 0.4 -·""'= OoN 0.4 -""""' 0.4 om, ~:~ 0.4 -""""" 0.4 '"" PCT/JP2016/051559 22/33 Comact- Podb~ on imler surfilce w- l'rim>yrum c"""' c"""' Corrosion ~""""'~ property after Workability "'""'""" property "'"""' """""""' 90 69 Satisfilctory -- """"""' E>roclioro"""' F=Oem Satisfitelmy F=llem 105 70 Satisfactory E>rooJ>ot -- Satisfactory - 91 67 Satisfactory ""'"""' -- E>roollot F=llem 85 55 Satisiactory E>roolkmt """'""' Satisfuctory "=""' 85 62 Satisfactory """'""' F=Oem Satislictmy """'""' 87 63 Satisfactory Excellent F=Oem Satisfactory F=el>m 89 64 ,_ ~'=""' """'""' Satisfuctory """'""' 92 65 Satisfactory -""' "=""' ""'""' - 91 65 Satis:fuctory """'""' E=I>m """"""' E>root>m 89 63 Satisfuctory ""'"" """"""' Satisfactory ""''""' 90 64 Satisfuctmy F=Dool -- Satisfactory """'"""' 95 67 Satisfuctory """"""' &ooh ,_ Satisfuctory 93 66 Satis:fuctory F=eh ~'=""""' Satisfitctmy Satisfactory 92 66 Satisfactory """"""' """'""" Satisfuctory Satisfuctory 90 69 Satis:fuctory -- Satisfitctmy ~'='""" Satisfuctory 99 70 Satis:fuctory """"""' Satisfuctory Satisfuctmy Satisfuctory 70 30 Satis:fuctory -- Satis:fuctocy Satisfactory Satisfuctory 90 60 Satis:fuctory """"""' Satis:fuctory Satisfitctory F=IIom 95 65 Satis:fuctory """'""' Satis:fuctory Satisfactory - 99 69 Satis:fuctory &oollom Satisfactmy Satilrl3ctnry -- 105 70 Satmactory &rellom Satisfuctory Satisfactory -- 91 67 Satisfitctory "'""'"'" Satisfitctory """"""' mollont 85 55 Satisfuctory F=elro"""" -- PCT/JP2016/051559 23/33 Contact angle Perfuflllm:e Armuntof on inner sudiwe Original Coating Coating fihn coating film """' film No limnOO '"""" [g/m2] Prirmry !lEt Coating Coating w,., Corrosion ~h=d~ property afler Workability resistance property - resistance E-k 34 20/20 Fl -·""""" mdy 0.4 "' 63 Satisfactory """"""' Sat:Sfuctory Satisfuctory furelkmt -35 20/20 F2 lll!lersudilce mdy 0.4 90 64 Safufuctory """""'"' SaWfuctmy Safufrwtory E=ll"" """""' 36 zoao Gl "'""'""""" 0.4 """ 95 67 Sa!Efuctory fuoolkmi Satisfuctory Sati;fuctory SatSfuctmy """""' 37 20/20 HI Inoersurfuce 0.4 ooly 93 66 Satisfuctory Excelleni Satisfu.ctoty Sati>fuctory Samfuctory """""' 38 zoao II ~rsurfuce oruy 0.4 92 66 SatEfuctory E=lkmt Satisfuctmy Satrictory Sat:Sfitctmy """""' 39 S/5 C5 --oruy~ 0.6 95 65 Sati<;fuctory fuoolkmt """""'" SatEfuctory SaWfuctory """""' 40 S/5 D2 Inner surface """ 0.6 85 62 Satisfuctory fuoolkmt """""'" Satisfuctory Satisfuctory """""' 41 S/5 El -·"o"ru"y "" 0.6 "' 64 Satisfactory """'""' E=M Salisfuctory Satisfuctory """""' 42 S/5 Fl "'""o'ru"y" "" 0.6 "' 63 Sat:Sfitctmy fuoolkmi E=llm Satisfactory Satisfuctory """""' 43 S/15 C5 -·"""" """ 0.6 95 65 Sati>factmy fuoolkm! F=om SaWfuctmy """''"'" """""' 44 S/15 D2 -·"""" 0.6 """ 85 62 Satisfuctory E=U, """""" Satisfuctnry E=llom """""' 45 S/15 El -·"""" 0.6 89 64 Satisfactory """""' E=Ifuctory """'""' """""' 57 sao C5 -""""" 0.8 95 65 Sat:Bfuctory E•o.U, E=lkml Satisllli:tory Excellent """' """""' 58 S/20 C5 Inner surfuce oruy L2 95 65 SatEfuctory """'""" _., Satisfilctmy """'""' """""' 59 S/20 C5 Inner surface oruy 1.5 95 65 SatEfuctory """'""' """"'" Sat:isfumory """""" """""' 60 S/20 C5 -·""""' """' 2 95 65 Satisfuctmy _.., """'"'" Sat:isfilctory """'"" """""' 6! S/20 D2 lll!leT surfilce """ 0.3 85 62 Satilfilctory """'"'" """'""' Sat5f.wtory """'""" """""' 62 S/20 D2 -·""""' L2 """ 85 62 Sallifuctory """'""" _.,., SatEfactory """'""' """""' 63 S/20 El -·""""" 03 89 64 Sati>fuctory """'"""' E=Ifuctory Excellent _., Sali<>fuctory """"""" """""' 67 S/EG40 Fl Inner surfuce """ 0.3 89 63 Sa!Efuctory """'"" E=lkore 0.6 75 25 Satisfuctnry ""''""" &oob """""" - """""' oojy CoiqJarative S/20 B3 ............ 0.6 10& 75 Poo; - Poo; Unsatl;Jilctmy Satis:fu:tory """""' oojy COJl1>3Ialive sno B4 """'""""' 0.6 115 80 Poo; E=O.m Poo• Poo; u- ...;.,oo oojy Colq)aratiw sno Cl -""""' 0.6 50 0 Satisfuctmy - &rellom Excellcnt Poo; I> "' arative 20/20 Cl """'""""' 04 50 0 Satisfilctory - ""'"""" &l:ellent Poo• Exarrple 15 "oiY Corrpaniliw 20/20 C2 r-"""" 0.4 40 25 Satisfuctmy - ""'- Satisfuctory Poo• &arqlle 16 oojy Co~ 20/20 Al Bothsurfuces 06 50 10 Satisfuctmy Poor Poo; ""''""" Poo• Exarrple 17 c""""""" 20/20 B2 """ '""""' 0.6 99 70 Satisfuctm:y Poor Poo• Poo; - &a!qlle 18 CoJlllaratiw 20/20 B3 """'"""""' 0.6 108 75 Satisfuctmy Poor Poo; Poo; Poo; C"o"iq"Ja"ra"ti9 w 20/20 C2 """ '""""' 0.6 40 25 ,_ Poor p~ ,_ p~ Exarrple20 Con:parntiw 20!20 C3 """"""""' 0.6 70 30 Samfuctory Pom Poo; ~ry - Exarrple21 Colqlarative 20/20 C4 Bodt surilu:es 0.6 90 60 Satisfur:tory Poo; Poo• Poo; u- fuarrple22 Con:parativc s~ cs -""""" I 93 63 Satisfuctory - - Sati Exarrple24 oojy [0053] As shown in the results in Tables 6 to 8, Examples according to the present invention showed evaluations of "Satisfactory" or higher in every evaluation item, and had satisfactory characteristics. To be specific, regarding the primary rust resistance, rust occurred in Comparative Examples 5, 6, 13, and 14 in which the nhexadecane contact angles exceeded the upper limit of the present invention. 10 Further, regarding the coating property, Examples and Comparative Examples other than Comparative Examples 17 to 22, each of which had the chemical conversion coating layer formed on the surface to be the outer surface, showed satisfactory PCT/JP2016/051559 25/33 evaluations of "Excellent", however, regarding the coating property after storage, evaluation results remarkably deteriorated in each of Comparative Examples 5, 6, 13, and 14 in which rust occurred in the primary rust. In addition, as shown in Table 9, regarding the coating property after storage, slight unevenness of an acceptable level 5 occurred in each of Examples 20 to 38 in which the Zn-Ni alloy plated layer was also provided on the surface to be the outer surface. Therefore, it was found that it is more preferred that the steel sheet according to the present invention have a nonplated outer surface. Note that, although each of Comparative Examples 9 to 12, 15, and 16 had the Zn-Ni alloy plated layer on the surface to be the outer surface, the 10 coating property after storage was "Excellent", since the n-hexadecane contact angle on the inner surface was less than the lower limit according to the present invention. However, because the n-hexadecane contact angle on the inner surface was less than the lower limit according to the present invention, the corrosion resistance deteriorated. Regarding the workability (slidability), the workability remarkably 15 deteriorated in each of Comparative Examples 5, 6, 13, and 14 in which the nhexadecane contact angle exceeded the upper limit of the present invention and in each of Comparative Examples 18, 19, 21, and 22 in which, although the nhexadecane contact angle was within the range of the present invention, the chemical conversion coating layers were formed on both inner and outer surfaces. Moreover, 20 comparing Examples according to the present invention with each other, evaluations were more satisfactory in each of Examples 1, 8, 13, 14, 20, 27, 32, and 33 to which po1yolefin wax was added. Regarding the corrosion resistance with respect to deteriorated gasoline, Examples according to the present invention showed satisfactory evaluations, and in particular, Examples 3 to 16, 22 to 35, and 43 to 66, 25 each of which used, as the chromate-free chemical conversion coating layer, an inorganic coating film not containing an organic resin component other than polyolefin wax and a fluorine-based resin, showed more preferable evaluations. Further, it was found that Examples 4 to 16, 23 to 35, and 43 to 66, each of which had the n-hexadecane contact angle of more than or equal to 55 degrees, showed 30 more preferable evaluations. Still further, referring to Examples 55 to 60, in the case where the deposition amount of the chemical conversion coating layer was more PCT/JP2016/051559 26/33 than or equal to 0.3 g/m2 , it was found that the corrosion resistance was more preferable. In addition, referring to Examples 39 to 42, in the case where the deposition amount of the Zn-Ni alloy plated layer per surface is more than or equal to 15 g/m2 , it was found that the corrosion resistance was more preferable. 5 [0054] 10 [Table 9] E=nple 5 E=nple 24 E=nplo 58 E=nple 59 - 67 E=nple 69 E=nple 70 E=nplo 71 E=nplo 72 E=nplo 73 E=nplo 74 E=nplo 75 E=nplo 76 E=nplo 77 COIIJimatiw 22 ExmopJe [0055] Deposition Contact angle Ammmtof amourd: on outer on outer OTig;rnl Coating Coating fihn ooatmgfihn """"" lo'm'l """"" &reel fihnNo funo