[0001]The present invention, as a material for a fuel tank of an automobile and a motorcycle, excellent strength, corrosion resistance, press formability, and to a surface treated steel sheet having a resistance weldability.
Background technique
[0002]
　The fuel tank of an automobile and a motorcycle having a complicated shape, the fuel tank materials are excellent processability (deep drawability) is required. Further, fuel tank, since it is important safety parts in automotive and motorcycles, in its material, without corrosion products occur causing clogging of the filter, there is no fear of the perforated corrosion, moreover, stable it is important that the material that can be easily welded to the.
[0003]
　As a material having these various properties, Pb-Sn alloy plated steel sheet has been widely used as materials for automobile fuel tank (Patent Document 1, reference). Pb-Sn alloy plated steel sheet has a stable chemical properties against gasoline and plating excellent press formability is excellent in lubricating properties and also the resistance weldability such a spot welding or seam welding Are better. However, in recent years, in terms of the impact on the environment, materials that do not use lead has been demanded.
[0004]
　Without the use of Pb, one of the material having good corrosion resistance and workability, a Zn-plated steel sheet. Zn, compared steel, so forming a stable sacrificial protection effect, Zn-plated steel sheet, other gasoline, to alcohol or organic acid produced gasoline is deteriorated, and has good corrosion resistance.
[0005]
　Therefore, conventionally, as a fuel tank material subjected to Zn-based plating, various techniques have been proposed. For example, Patent Documents 2 and 3, the Zn-plated steel sheet, further, for the purpose of improving the corrosion resistance, be subjected to a chromate treatment mainly comprising chromic acid and silica is disclosed. However, these methods, coating of chromate principal, because it contains hexavalent Cr high environmental impact unfavorably.
[0006]
　Patent Document 4 does not contain Pb and hexavalent Cr, although surface treatment plated steel sheet having a single layer coating type coating is disclosed, the film is a film mainly composed of resin, the moldability can be expected by resistance heating of the film during welding, there is a concern that continuous operation is lowered.
[0007]
　Patent Document 5, in an organic resin film containing a metal pigment, although weldable zinc-plated steel sheet is disclosed, since the organic film is applied, a load is applied to resistance welding, a weldable although, the low that the productivity and corrosion resistance have problems such as higher cost of what is good.
[0008]
　After all, in the prior art, continuous workability required when the fuel tank manufacturing, satisfying the workability and corrosion resistance is required as a fuel tank characteristics, and, what is difficult to produce at low cost at present.
[0009]
　Recently, the need for weight reduction of the fuel tank, the application of high-strength steel sheet has been studied. For example, Patent Document 6, a tensile strength of more than 440 MPa, in r value of 2.0 or more, excellent strength -r value balance, also excellent in corrosion resistance of the tank outer surface, further, the spot weldability and press working excellent steel sheet for fuel tank is also disclosed in sex.
[0010]
　However, Patent Document 6, there is description about coating treatment of the steel sheet surface, suitable steel sheet strength and surface morphology relative to workability, and the condition of the plating layer, since there is no description regarding surface film, Patent Document 6 in the steel sheet for fuel tank, the workability is a concern not sufficiently obtained.
[0011]
　Patent Document 7, Ni, Co, Cr, is a zinc-based alloy plating layer to shift one or more alloy components of Fe formed, thereon, a fuel tank for surface treatment Ni plating layer is formed steel plate have been disclosed. And a Ni plating layer is formed on the Zn-based plating layer, although increasing the corrosion resistance to fuels, study and of the steel sheet strength, without consideration of the surface morphology or surface film is not made sufficiently, the fuel tank of patent document 7 in use the surface treated steel sheet, workability is a concern not sufficiently obtained.
[0012]
　In Patent Document 8, by controlling the number and total area of ​​the recesses of the steel sheet surface, during molding, surface fuel tank having excellent press workability which suppresses oiling out of the working oil to be oiled steel plate treated steel sheet is disclosed. However, in the control of the surface morphology due to the total area and the number of the recesses of the steel sheet surface, not is sufficient retention of oiling, there is press workability is sufficiently obtained without concern.
CITATION
Patent Literature
[0013]
Patent Document 1: JP-B 57-061833 Patent Publication
Patent Document 2: JP 2011-021279 Patent Publication
Patent Document 3: JP 2008-248360 Patent Publication
Patent Document 4: JP 2006-291246 Patent Publication
Patent Document 5: JP 2001-279470 JP
Patent Document 6: JP 2005-314737 Patent Publication
Patent Document 7: JP-A 11-310897 JP
Patent Document 8: Japanese Patent Application No. 2015-169734
Summary of the Invention
Problems that the Invention is to Solve
[0014]
　The present invention provides a surface treated steel sheet of the material of the fuel tank of a motor vehicle and motorcycle, as well as improve the balance of the corrosion resistance and resistance weldability, and an object thereof is to ensure a good press formability, the solution to the problem, excellent press formability, material strength, corrosion resistance, and aims to provide a surface treated steel sheet having a resistance weldability.
Means for Solving the Problems
[0015]
　The present inventors have found that in order to solve the above problems, as a material for a fuel tank, corrosion resistance, formability, and excellent weldability, various studies the coating aspect of the Zn-plated steel sheet.
[0016]
　As a result, the surface of the steel sheet of the required chemical composition, to form a recess at a specific area ratio, after the recess formed, to form a Zn-Ni alloy plating layer, thereon, to form the desired resin film layer, press formability, corrosion resistance, and resistance weldability was found that improved. On the surface the outermost layer of the steel sheet of the required chemical composition, a recess, formed matches the sum of the volume of the recesses of the desired depth (total volume) within the required range, after the recess formation, Zn-Ni alloy the plating layer is formed, thereon, was found to form the desired resin film layer, press formability, corrosion resistance, and, that the resistance weldability is remarkably improved.
[0017]
　Further, on the Zn-Ni alloy plating layer with increased surface layer of Ni amount, to form the desired resin film layer, various characteristics as a material for a fuel tank has been found to be improved.
[0018]
　When the steel sheet contains a large amount of Si, since the Si-concentrated layer on the surface of the steel sheet is formed, in the case of applying the surface treatment to the steel sheet, it is necessary to pay attention to the method of surface treatment. That is, when plating the steel sheet surface, it is necessary to consider the adhesiveness of the steel sheet surface and the plating layer. In particular, by containing a large amount of Si, when the likely steel oxide film is formed on the surface, in the deep drawing processing the fuel tank, it is necessary to perform a surface treatment peeling of the plating layer does not occur.
[0019]
　Furthermore, in the material of the fuel tank, it is necessary it is possible to spot welding or seam welding, the present inventors have the form of a steel sheet surface appropriately adjusted, thereon, a Zn-Ni alloy plating layer formed, thereon, by forming the required film contributes to the improvement of adhesion of the plating layer, workability to withstand severe working of processing the fuel tank, further, that it is possible to enhance the weldability found it was.
[0020]
　The present invention has been made based on the findings, the gist is as follows.
[0021]
　[1]
　on one or both sides of the steel sheet, Zn-Ni alloy plating layer, thereon, a surface treated steel sheet for fuel tanks having a trivalent chromate film layer or chromate-free coating layer,
　the steel sheet contains, by mass% ,
　C:
　0.0005 ~
　0.0050%, Si: 0.01 ~ 1.00%, Mn: 0.70
　~ 2.00%, P: 0.060% or
　less, S: 0.010% or less,
　al:
　0.01
　~ 0.30%, N: 0.001
　~ 0.010%, Ti: 0.010 ~ 0.050%, Nb: 0.010
　~ 0.040%, B: 0.0005 ~ 0.0030% or
contain, comprises a component comprising the balance of Fe and unavoidable impurities,
(i) the surface outermost layer of the trivalent chromate coating layer or the chromate-free coating layer, the surface of the uppermost layer of the cross section curve depth from the arithmetic average height of more than 0.1μm Parts is 50 to 1000 / mm 2 , is present at an area ratio of 20-80% with respect to the surface area of the steel sheet
for fuel tank surface treated steel sheet, characterized in that.
[0022]
　[2]
　instead of the (i),
(i ') to the surface the outermost layer of the trivalent chromate coating layer or the chromate-free coating layer, the depth of the arithmetic average height of the surface outermost layer of the cross section curve 0.1μm or more recesses, the surface layer morphology index Z which is defined by the following equation (a), 1.0 × 10 4 ~ 1.0 × 10 6 is present in the range of
described, characterized in that [1] surface-treated steel sheet for a fuel tank.
　Z ([mu] m 3 / mm 2 ) = surface total depth from the arithmetic average height of the outermost layer of the cross section curve of the volume of or more recesses 0.1 [mu] m (total volume) / surface uppermost layer of the unit area.. ( a)
[0023]
　[3]
　the place of the
(i), (i ") trihydric the surface of the chromate film layer or the chromate-free coating layer, four sides arithmetic average roughness in the rectangular region of 5 [mu] m (Ra) is 5 ~ 200 nm, maximum section height of the roughness curve (Rt) is 100 ~ 1000 nm
fuel tank for surface treated steel sheet according to, characterized in that [1].
[0024]
　[4]
　The Zn-Ni alloy plating layer, and mainly Zn, an alloy plating layer containing 5-15 wt% of Ni, and the deposited amount 3 ~ 50 g / m 2 , the said Zn-Ni alloy Ni content of the surface layer of layer thickness 1/10 of the plating layer is, in any one of the characterized in that is Zn-Ni more than 120% of the average amount of Ni alloy plating layer [1] to [3] fuel tank for surface treated steel sheet according.
[0025]
　[5]
　The chromate-free coating layer, (A) a silicon compound and containing phosphorus acid compound, further, Zr, V, Ti, coating layer containing one or more compounds of Co, (B) coating layer of urethane resin, or, (C) crosslinked epoxy - and urethane resin, characterized in that it is a coating layer containing at least one polyolefin resin and fluorine resin [1] - [4 fuel tank for surface treated steel sheet according to any one of.
[0026]
　[6]
　on the trivalent chromate coating layer, (B) coating layer of urethane resin, and, (C) crosslinked epoxy - containing at least one urethane resins, polyolefin resins and fluorine-based resin fuel tank for surface treated steel sheet according to any one of [1] to [4], characterized in that it comprises at least one layer of the coating layer.
[0027]
　[7]
　The containing (A) a silicon compound and a phosphoric acid compound, further, Zr, V, Ti, the compound of Co over the coating layer containing one or two or more, (B) a urethane resin coating layer, and, (C) crosslinked epoxy - according to the urethane resin, and having at least one layer of the coating layer containing at least one polyolefin resin and fluorine resin [5] surface-treated steel sheet for a fuel tank.
[0028]
　[8]
　The chemical conversion treatment film (B) is 0.6 to 10 mass% urethane groups and urea groups in N terms of the total coating solids, and 5 to calculated as Si content in the whole film to Si has a resin film layer containing 20% by weight and,
　the layer thickness is 0.5 ~ 2.0 .mu.m of the resin coating layer, the dynamic friction coefficient of the surface is characterized in that 0.06 to 0.25 1] ~ fuel tank for surface treated steel sheet according to any one of [4].
[0029]
　[9]
　on the trivalent chromate film layer or the chromate-free coating layer, 0.6-10 wt% of the urethane groups and urea groups in N terms of the total coating solids, and the entire film in Si in the terms of Si content of 5 to have a resin coating layer containing 20 wt%, and
　the layer thickness is 0.5 ~ 2.0 .mu.m of the resin coating layer, with the coefficient of dynamic friction of 0.06 ~ 0.25 surface fuel tank for surface treated steel sheet according to any one of [1] to [4], characterized in that there.
[0030]
　[10]
　on the trivalent chromate film layer or the chromate-free coating layer, a resin having a urethane bond, one or more polyolefin resin and fluorine resin, and an organic coating layer containing the conductive pigment, 3 has a thickness of ~ 20 [mu] m,
the resin having a urethane bond (iii), and (i) functional groups of at least 3 polyester polyol, and, (ii) an organic polyisocyanate blocked product, or, an organic polyisocyanate the terminal obtained by reacting the active hydrogen compound is an organic resin obtained from film forming resin material containing a blocked product of a prepolymer having an NCO group
, characterized in that any one of [1] to [4] 1 fuel tank for surface treated steel sheet according to item.
[0031]
　[11]
　wherein the conductive pigment is stainless steel, Zn, Al, Ni, ferrosilicon, consists one or more of iron phosphide, and the content of the conductive pigment, 5 on a solid basis fuel tank for surface treated steel sheet according to [10], characterized in that a ~ 50% by volume.
[0032]
　[12]
　The organic coating layer further anticorrosive pigments contain 1-40% by volume in terms of solid content, and a rustproof pigment, in total, containing 5 to 70 volume% in terms of solid content fuel tank for surface treated steel sheet according to any one of, wherein [10] or [11] that.
[0033]
　[13]
　on one side or both sides of the surface of the steel sheet, Zn-Ni alloy plating layer, thereon, a trivalent chromate coating layer on top of the trivalent chromate film layer, the chemical conversion film (C), crosslinked epoxy - urethane resin, and a polyolefin resin, a second resin film layer containing at least one fluorine-based resin,
the amount of Cr (iv) the trivalent chromate film, Cr equivalent amount in 5 ~ 200 mg / m 2 and,
they said the (v) the layer thickness of the second resin film layer is 0.3 ~ 2.0 .mu.m, dynamic friction coefficient of the surface is from 0.06 to 0.25 [1] ~ fuel tank for surface treated steel sheet according to any one of [4].
Effect of the invention
[0034]
　According to the present invention, as a material for a fuel tank of an automobile and a motorcycle, excellent press formability, material strength, corrosion resistance, and can provide a surface-treated steel sheet having a resistance weldability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035]
It shows the embodiment of FIG. 1 surface treatment depth 0.1μm or more recesses in the surface outermost layer of the steel sheet. (A) shows a three-dimensional image of the surface the uppermost layer of the surface treated steel sheet was observed with a laser microscope, (b) show an image obtained by binarizing a three-dimensional image of (a).
It is a diagram illustrating an example of FIG. 2 surface morphology index and results of the examination of pressing of the relationship.
[Figure 3] shows a portion of an AFM image of the surface outermost layer of the three-dimensional image of the surface treated steel sheet.
[4] at a different angle than FIG. 3 is a diagram showing an example of an image of the surface of the imaging surface treated steel sheet with an atomic force microscope (AFM).
5 is a diagram showing the shape of a test piece for testing the seam weld.
DESCRIPTION OF THE INVENTION
[0036]
　Fuel tank for surface-treated steel sheet of the present invention (hereinafter sometimes referred to as "the present invention steel sheet".) Is, on one or both sides of the steel sheet, Zn-Ni alloy plating layer, thereon, trivalent chromate film layer or the chromate-free be one having a coating layer,
　wherein the steel sheet contains, by
　mass%, C:
　0.0005 ~ 0.0050%,
　Si: 0.01 ~ 1.00%, Mn: 0.70 ~ 2.00%,
　P: 0.060% or
　less, S: 0.010% or
　less,
　Al: 0.01 ~
　0.30%, N: 0.001 ~ 0.010%, Ti: 0.010 ~ 0.050%,
　Nb : 0.010
　~ 0.040%, B: 0.0005 ~ 0.0030%
contained, has a component the balance Fe and unavoidable
impurities, (i) the trivalent chromate film layer or the chromate-free the surface outermost layer of the coating layer, the surface outermost layer Recess depth is more than 0.1μm from the arithmetic average height of the profile curve is 50 to 1000 / mm 2 and being present in an area ratio of 20-80% with respect to the surface area of the steel sheet.
[0037]
　The present invention steel sheet, on the surface of the steel sheet of the required chemical composition, to form a Zn-Ni alloy plating layer, further thereon, to form a suitable coating layer, press formability, material strength and, an excellent surface-treated steel sheet corrosion resistance. Further, the present invention steel sheet, is made higher than the average amount of Ni the Ni content of the surface layer of Zn-Ni alloy plating layer, a surface-treated steel sheet Various characteristics of the material of the fuel tank is improved.
[0038]
　First, a description will be given reasons for limiting the chemical composition of the steel sheet of the present invention. Hereinafter,% of the component composition means mass%.
[0039]
　The chemical composition, in mass%, C: 0.0005 ~ 0.0050%, Si: 0.01 ~ 1.00%, Mn: 0.70 ~ 2.00%, P: 0.060% or less, S 0.010% or less, Al: 0.01 ~ 0.30%, N: 0.001 ~ 0.010%, Ti: 0.010 ~ 0.050%, Nb: 0.010 ~ 0.040% , B: made from 0.0005 to 0.0030% and the balance is Fe and unavoidable impurities.
[0040]
　C: 0.0005 ~ 0.0050%
　C combines with Nb and Ti to form carbides, a very effective element to achieve high strength. C even small amounts, can make up for the strength in other ways, the C is less than 0.0005%, with decarburization costs at the time of steelmaking rises dramatically, the strength securing using other methods since it is difficult, C is 0.0005% or more. Preferably is 0.0010% or more.
[0041]
　On the other hand, when C exceeds 0.0050%, the increasing amount of Ti and Nb required for fixing the C, together with the workability is decreased, since the welded portion toughness is reduced, C is a 0.0050% or less to. If very high workability and weld zone toughness are required, C is preferably 0.0030% or less.
[0042]
　Si: 0.01 ~
　1.00% Si is by solid solution strengthening, an element which contributes to the improvement of the strength of the steel sheet. When Si is less than 0.01%, the addition effect is not sufficiently obtained, Si is 0.01% or more. Preferably 0.10% or more.
[0043]
　On the other hand, when the Si is more than 1.00%, since the workability is deteriorated, Si is not more than 1.00%. Hot rolling, in terms of suppressing the generation of causative Si scale scale defects, Si is preferably 0.80% or less, more preferably 0.60% or less.
[0044]
　Mn: 0.70 ~
　2.00% Mn, like Si, the solid solution strengthening, an element which contributes to the improvement of the strength of the steel sheet. When Mn is less than 0.70%, the addition effect is insufficient, be supplemented with other elements, since the weld zone toughness and a required secondary work embrittlement resistance can not be obtained, Mn 0. to 70% or more. In hot rolling finishing temperature of 910 ° C. or less, in terms of capable of ensuring the required steel sheet microstructure, Mn is preferably at least 1.00%.
[0045]
　On the other hand, when the Mn exceeds 2.00%, the deep drawability plane anisotropy of r value which is an index becomes large, since press formability is lowered, Mn is not more than 2.00%. Preferably not more than 1.70%.
[0046]
　P: 0.060% or less
　P is a solid solution strengthening, an element which contributes to the improvement of the strength of the steel sheet. Also, P is is segregated in the grain boundary, thereby inhibiting secondary work embrittlement resistance, and solidification segregation in welds, even an element inhibiting the weld zone toughness.
[0047]
　If P is more than 0.060% said segregation occurs, since the weld zone toughness and secondary work embrittlement resistance is deteriorated, P is not more than 0.060%. The lower limit includes 0% and to reduce P to less than 0.005%, the production cost is greatly increased, practically steel, 0.005%, which is substantially the lower. In terms of securing strength, P is preferably 0.020% or more.
[0048]
　S: 0.010% or less
　S is an impurity unavoidably mixed from iron material, to form precipitates with Mn and Ti, is an element that inhibits workability.
[0049]
　If S exceeds 0.010%, since significantly reduced workability, S is 0.010% or less. Preferably not more than 0.005%. The lower limit includes 0% and reduces the S to less than 0.0001%, the manufacturing cost is greatly increased, practically steel, 0.0001%, which is substantially the lower.
[0050]
　Al: 0.01 ~
　0.30% Al, at the time of refining the steel, is an element added as a deoxidizer. If Al is less than 0.01%, the deoxidizing effect is not sufficiently obtained, Al is 0.01% or more. Preferably 0.10% or more. On the other hand, when the Al exceeds 0.30%, since the weld zone toughness and workability is lowered, Al is not more than 0.30%. Preferably not more than 0.25%.
[0051]
　N: 0.001 ~ 0.010%
　N is unavoidably mixed during refining of the steel, Ti, Al, and / or, by forming a Nb and nitrides, but does not adversely affect the processability, is an element that inhibits weld toughness.
[0052]
　Reducing the N to less than 0.001%, the production cost rises dramatically, N is 0.001% or more. Preferably 0.003% or more. On the other hand, when N exceeds 0.010%, the weld zone toughness is remarkably lowered, N is 0.010% or less. Preferably 0.007% or less.
[0053]
　Ti: 0.010 ~
　0.050% Ti has a strong affinity with C and N, carbonitrides formed during solidification or during hot rolling, to reduce the solute C and solute N, processability an element which contributes to the improvement of.
[0054]
　When Ti is less than 0.010%, because the addition effect is not sufficiently obtained, Ti is set to 0.010% or more. Preferably 0.015% or more. On the other hand, when the Ti exceeds 0.050%, the strength and toughness of the weld is reduced, Ti is set to 0.050% or less. Preferably not more than 0.045%.
[0055]
　Nb: 0.010 ~
　0.040% Nb, like Ti, strong affinity with C and N, carbonitrides formed during solidification or during hot rolling, reducing the solid solution C and solid solution N to an element which contributes to the improvement of workability.
[0056]
　If Nb is less than 0.010%, because the addition effect is not sufficiently obtained, Nb is 0.010% or more. Preferably 0.015% or more. On the other hand, when Nb exceeds 0.040%, the recrystallization temperature rises, high-temperature annealing with is required, since the weld zone toughness is lowered, Nb is set to 0.040% or less. Preferably not more than 0.035%.
[0057]
　B: 0.0005 ~ 0.0030%
　B is segregated at the grain boundaries, increasing the grain boundary strength, which is an element contributing to the improvement of the secondary work embrittlement resistance. When B is less than 0.0005%, the addition effect is not sufficiently obtained, B is 0.0005% or more. Preferably it is greater than or equal to 0.0008%.
[0058]
　On the other hand, when the content of B exceeds 0.0030%, (a) segregation to ferrite transformation is suppressed in the γ grain boundaries during welding, weld and heat-affected zone of tissue becomes low temperature transformation structure, the weld and heat-affected zone toughness is lowered and is hardened, as a result, lowers the toughness of the coach peel seam weld zone, (b) ferrite transformation during hot rolling is suppressed, it becomes high-strength hot-rolled steel sheet of a low temperature transformation structure, cold load is increased during rolling, also by (c) recrystallization temperature rises, high-temperature annealing is is necessary, the manufacturing cost is increased, in-plane anisotropy of r value is deep drawability index sex is increased, since the press formability is degraded, B is set to 0.0030% or less. Preferably is 0.0020%.
[0059]
　Next, the surface outermost layer of the steel sheet of the present invention will be described recess is present in the required area ratio.
[0060]
　The surface outermost layer of the steel sheet of the present invention, the recess of the required number is present in the required area ratio to the surface area. The surface outermost layer, a outermost layer which is exposed on the surface of the surface treated steel sheet, if having a trivalent chromate film layer on the Zn-Ni alloy plating layer, and the outermost surface layer of the trivalent chromate film layer, Zn If having a chromate-free coating layer on top of -Ni alloy plated layer is the outermost layer of chromate-free coating layer. Note that recesses are present on the surface outermost layer, by forming a concave portion on the surface of the front of the Zn-Ni alloy plating layer trivalent chromate film layer or the chromate-free coating layer is formed, the trivalent chromate coating layer It is formed on the uppermost layer of the or chromate-free coating layer. Also, by the By forming the recesses in the surface of the front of the steel sheet forming the Zn-Ni alloy plating layer, it is possible to form the recesses in the outermost layer of the trivalent chromate film layer and chromate-free coating layer . Recesses formed in the surface of the Zn-Ni alloy plating layer, be laminated film layer one or more layers on a Zn-Ni alloy plating layer, remaining on the surface outermost layer of the coating layer. Similarly, recess formed on the surface of the steel sheet, be laminated plating layer and coating layer at least one layer on the steel plate, remaining on the surface outermost layer of the coating layer.
[0061]
　The recess formed in the surface outermost layer of the steel sheet of the present invention, a recess from the arithmetic average height of the surface outermost layer of the cross section curve has a depth of at least 0.1 [mu] m. Here, the arithmetic average height of the profile curve, which corresponds to a Pa defined by JIS B 0601 (2001). Is the number of recess 50 to 1000 / mm 2 is. The total area of the recesses is 20 to 80% area ratio with respect to the entire area of the surface of the surface treated steel sheet.
[0062]
　When the depth of the recess is less than 0.1 [mu] m, when deep drawing, since oiling out of processing oil coated on the surface of the steel sheet is likely to occur, the depth of the recess is not less than 0.1 [mu] m. Preferably is 0.3μm or more. Incidentally, the recesses, as will be described later, are formed in the cell cut in the formation process of the Zn-Ni alloy plating layer, in addition to this, in the manufacturing process of the steel sheet, skin pass rolling Ya by rolls having a certain roughness , etching of the surface due to pickling, by adding a brushing degreasing-pickling step may be a recess in the surface of the steel sheet. By forming a Zn-Ni predetermined recesses in the surface of the surface and the steel sheet of the alloy plating layer, is taken over the recess, the recess on the outermost surface of the surface layer of the surface treated steel sheet appears remained. The upper limit of the depth of the recess is not particularly limited.
[0063]
　The number of recesses 50 / mm 2 , or less than, the total area of the concave portion is less than 20% by area, especially during deep drawing of the press working, similarly, oiling out of the working oil is likely to occur since, the number of recesses 50 / mm 2 and more, the total area of the recesses, and an area ratio of 20% or more. Preferably, the number of recesses 100 / mm 2 or more, the total area of the recess area ratio is 30% or more. More preferably, the number of recesses 120 / mm 2 or more, the total area of the recess is an area ratio of 40% or more.
[0064]
　On the other hand, the number of recesses 1000 / mm 2 exceeded, or, if more than 80% the total area the area ratio of the recesses, especially at deep drawing of press work, the frictional resistance of the steel sheet surface is increased, the molding because sex there be deteriorated, the number of recesses 1000 / mm 2 and less, the total area of the recesses is 80% or less in area ratio. Preferably, the number of recesses 700 / mm 2 or less, the total area of the recesses is 70% or less in area ratio. More preferably, the number of recesses 400 / mm 2 or less, the total area of the recesses is 60% or less by area ratio.
[0065]
　The number and area of ​​the recess (or volume) can be measured as follows. That is, using a laser microscope VK-9710 of KEYENCE Corporation, the roughness information acquired in the field of view of 500 [mu] m × 500 [mu] m in the surface of the surface treated steel sheet, on the basis of the roughness information, the arithmetic mean height of the cross section curve in the measurement field of view It is calculated, and the depth of the recess of the calculated arithmetic average height than 0.1μm or more depth binarized analyzes the binarized image, and calculates the number of recesses and area (volume). Furthermore, KEYENCE Corporation be used analysis software VKAnalyzer, it calculates the volume of the recess.
[0066]
　Figure 1 shows an embodiment of a depth 0.1μm or more recesses in the surface the uppermost layer of the surface treated steel sheet. In FIG. 1 (a), shows a three-dimensional image of the surface outermost layer of the steel sheet was observed with a laser microscope, in FIG. 1 (b), shows an image obtained by binarizing a three-dimensional image of FIG. 1 (a).
[0067]
　Area ratio of the concave portion (%) is calculated by × 100 {the total area of ​​the recesses (x) / (total area of ​​the total area (x) + smooth surface portion of the recess (y))}.
[0068]
　Further, the surface outermost layer of the steel sheet of the present invention, the surface outermost layer of the trivalent chromate coating layer or the chromate-free coating layer, the depth of the arithmetic average height of the surface outermost layer of the cross section curve 0.1μm more recesses, the surface layer morphology index Z which is defined by the following equation (a), 1.0 × 10 4 ~ 1.0 × 10 6 is present in the range of.
　Z ([mu] m 3 / mm 2 ) = surface total depth from the arithmetic average height of the outermost layer of the cross section curve of the volume of or more recesses 0.1 [mu] m (total volume) / surface uppermost layer of the unit area.. ( a)
[0069]
　Surface morphology index Z is the surface-treated steel sheet to form a predetermined resin film layer on the Zn-Ni alloy plating layer, to increase the press formability significantly, in order to evaluate the novel which we have introduced it is such an index.
[0070]
　When pressing the surface treated steel sheet, but to apply the processing oil on the surface of the steel sheet, coated processing oil is held by a recess existing on the surface the outermost layer of the steel sheet, during processing, it functions as a lubricant. The present inventors have found that the holding amount of the processing oil on the surface the uppermost layer of the surface treated steel sheet, since that depends on the sum of the volume of the recesses in the surface outermost layer, by adjusting the said total sum in the appropriate range, press workability Ya deep drawability conceived with significantly improved by introducing the surface morphology index Z as defined above formula (a), was intensively investigated the relationship between press formability and deep drawability.
[0071]
　2 shows an example of a result of the examination of the surface morphology index Z and pressing of the relationship. The present inventors have based on the results shown in FIG. 2, the surface morphology index Z ([mu] m 3 / mm 2 a) 1.0 × 10 4 ~ 1.0 × 10 6 to.
[0072]
　Since depth is less ability recess below 0.1μm is for holding a processing oil were excluded from recess for calculating the total volume of the recess. Target recess for calculating the surface morphology index Z is depth and 0.1μm or more recesses. Preferably a recess above 0.3 [mu] m.
[0073]
　Surface morphology index Z is 1.0 × 10 4 is less than, during press working, since oiling out of the working oil is likely to occur, the surface morphology index Z ([mu] m 3 / mm 2 ) is 1.0 × 10 4 and more. Preferably 3.0 × 10 4 or more, more preferably 5.0 × 10 4 is more. On the other hand, the surface morphology index Z ([mu] m 3 / mm 2 ) is 1.0 × 10 6 exceeds, during press working, increased frictional resistance of the steel sheet surface, since the press workability is a concern to decrease, the surface morphology index Z ([mu] m 3 / mm 2 ) is 1.0 × 10 6 or less. Preferably 0.7 × 10 6 or less, more preferably 0.5 × 10 6 or less.
[0074]
　Figure 3 shows a portion of the AFM image of the surface outermost layer of the three-dimensional image of the surface treated steel sheet. AFM image shown in FIG. 3 is a three-dimensional part of the 5 [mu] m × 5 [mu] m range more microscopically observed image of the image of FIG. 1 (a). From this image, on the surface the uppermost layer of the surface treated steel sheet, it can be seen that the different recesses depths exist in disordered state. The present inventors, from the image, in order to improve the press formability of the surface-treated steel plate is three-dimensional surface properties of steel sheet greatly affects the surface properties of the surface-treated steel sheet, i.e., the outermost layer of the form reaches the idea that there is a need to consider, was introduced surface morphology index Z.
[0075]
　Further, the present invention steel sheet, the surface of the trivalent chromate coating layer or the chromate-free coating layer, the arithmetic average roughness of the rectangular region of the four sides 5 [mu] m (Ra) is 5 ~ 200 nm, the maximum section height of the roughness curve ( Rt) is 100 ~ 1000nm.
[0076]
　When the arithmetic average roughness (Ra) is less than 5 nm, working oil oiled during press molding, since hardly remains in the mold crimping surface, the arithmetic average roughness (Ra) is not less than 5 nm. Preferably 10nm or more, and more preferably 15nm or more.
[0077]
　On the other hand, if the arithmetic average roughness (Ra) is more than 200nm greater, the concern that corrosion resistance of a surface treated steel sheet is degraded, the arithmetic mean roughness (Ra) is set to 200nm or less. Preferably 150nm or less, more preferably 120nm or less.
[0078]
　When the maximum section height of the roughness curve (Rt) is less than 100 nm, similarly, processing oil oiled during press molding, since hardly remains in the mold crimping surfaces, the maximum section height of the roughness curve (Rt) is equal to or greater than 100nm. Preferably 200nm or more, and more preferably 250nm or more.
[0079]
　On the other hand, when the maximum section height of the roughness curve (Rt) exceeds 1000nm, similarly, since the concern that corrosion resistance of a surface treated steel sheet is degraded, the maximum section height of the roughness curve (Rt) is 1000nm or less and to. Preferably 800nm ​​or less, more preferably 700nm or less.
[0080]
　Surface roughness of the surface treated steel sheet is usually varies depending the measuring method, the arithmetic mean roughness of the steel sheet of the present invention (Ra) and the maximum section height of the roughness curve (Rt) is between the surface of the surface treated steel sheet atoms captured by force microscope (AFM), a value calculated on the basis of the roughness curve measured in the image obtained.
[0081]
　Here, in FIG. 4, at a different angle than FIG. 3 shows an example of an image of the surface of the imaging surface treated steel sheet with an atomic force microscope (AFM). Captured by atomic force microscopy (AFM), the arithmetic mean roughness calculated based on the image of the surface of the coated steel sheets (Ra) and the maximum section height of the roughness curve (Rt), the surface morphology of the coated steel sheets which is an index to describe accurately.
[0082]
　Arithmetic mean roughness defined in the invention (Ra) is 5 ~ 200 nm, and the maximum section height (Rt) of 100 ~ 1000 nm surface roughness curve, for example, continuous electro-galvanized composed of a plurality of plating tanks in line, by which stops the energization part of the plating tank (cell cut), the step of dissolving a portion of the electrodeposited zinc was plated layer so far, it can be realized. Note that, the recess of the required number described above, also predetermined surface morphology index Z Similarly, it is possible to realize by the cell cuts.
[0083]
　As an example, the case of zinc electroplating using an acidic aqueous solution, the following reaction formula (1-1) proceeds in (1-2).
　　Zn 2Tasu　Tasu 2E -　￫ Zn · · · (1-1)
　　2H Tasu　Tasu 2E -　￫ H 2　　　· · · (1-2)
[0084]
　Immersing the substrate and the electrodes in a plating solution, whereupon the electrolyte so the zinc is electrodeposited (cathode electrolysis), it proceeds as in equation (1-1) and (1-2). On the other hand, it stops the energization while immersed (cell cut), the stop electrolytic corrosion reaction of Zn with the formula (1-2) by the equation (1-3) proceeds (Formula (1-4)).
　　￫ Zn Zn 2Tasu　Tasu 2E -　　　· · · (1-3)
　　Zn Tasu 2H Tasu　￫ Zn 2Tasu　Tasu H 2　　　· · · (1-4)
[0085]
　Zinc elution progresses the case of zinc-nickel electroplating stop electrolysis while immersed. This is due to the high standard electrode potential nickel compared to zinc. In other words, by immersion conditions after electrolysis, it is possible to galvanized amount control. Further, since also changes the surface roughness with the zinc dissolution, it is also possible the control. By adjusting the surface roughness by the zinc dissolution, implementing the arithmetic average roughness (Ra) and the maximum section height of the roughness curve (Rt). Forming recess, discontinuation of energization of the second half of the galvanizing line process (cell cut), or may be carried out either remains immersed in the process after the plating. The surface roughness adjustment and a predetermined arithmetic average roughness (Ra) and the maximum section height of the roughness curve (Rt) may be defined by the surface Ni concentrations.
[0086]
　It will now be described plating layer and the film layer formed on the steel plate.
[0087]
　Zn-Ni alloy plating layer
　on one or both sides of the steel sheet, Zn-Ni alloy plating layer (hereinafter, simply referred to as "plating layer".) To form a. Zn-Ni alloy plating layer, the Ni content of the surface layer, the average amount of Ni greater than Zn-Ni alloy plating layer of the plated layer, press formability, material strength, corrosion resistance, and is preferable in terms of improving the weldability.
[0088]
　Adhesion amount of Zn-Ni alloy plating 3 ~ 50 g / m 2 preferably. Adhesion amount of Zn-Ni alloy plating is 3 g / m 2 by weight, since no sufficient corrosion resistance is obtained, it said adhesion amount 3 g / mm 2 or more. More preferably 5 g / m 2 is at least. Meanwhile, the amount of adhered 50 g / m 2 by weight, the corrosion resistance is improved, since the plating adhesion and weldability is decreased, the coating weight 50 g / mm 2 or less. More preferably 40 g / m 2 or less.
[0089]
　Ni content of Zn-Ni alloy plating layer is preferably 5 to 15 wt%. When alloying Ni in Zn, but improves the workability and weldability of the plated layer, the Ni content of Zn-Ni alloy plating layer is less than 5 wt%, since the improving effect is not sufficiently obtained, the Ni content is preferably at least 5 mass%. More preferably 8 mass% or more.
[0090]
　On the other hand, when the Ni content exceeds 15 mass%, and the hardness of the plating layer is increased, cracks are in the plating layer, since the plating layer is easily peeled off, the Ni content is preferably 15 mass% or less. More preferably at most 13 mass%.
[0091]
　Ni content of the surface layer of layer thickness 1/10 of the plating layer is more than 120% of the average amount of Ni plating layer. The surface layer of Ni of thickness 1/10 of the plating layer, when more than 120% of the average amount of Ni plating layer, so improving the plated surface hardness and corrosion resistance, improved properties as a fuel tank. More preferably 130% or more.
[0092]
　The surface layer of the Ni amount is high plating layer, the second half of the successive electroplating, and a method of changing the electrolyte composition and electrolysis conditions, after the Zn-Ni plating, can be formed by a method of dissolving the surface layer Zn by etching . Further, in the continuous electrolytic zinc plating line comprising a plurality of the plating bath described above, by ceasing the energization part of the plating tank (cell cut), the surface Zn is eluted, Ni amount of the surface layer is relatively It is enhanced. Incidentally, Ni amount of the surface layer, glow discharge optical emission spectroscopy, Auger electron spectroscopy or the like, to analyze the depth direction of the plated layer can be measured.
[0093]
　Trivalent chromate coating and chromate-free coating layer
　on top of the Zn-Ni alloy plating layer, trivalent chromate film layer, or, to form a chromate-free coating layer. Incidentally, on the Zn-Ni alloy plating layer, trivalent chromate film layer, or it may be formed either the chromate-free coating layer, or, on the Zn-Ni alloy plating layer, trivalent chromate forming a coating layer may be further formed chromate-free coating layer on top of the trivalent chromate coating layer.
[0094]
　(Trivalent chromate film)
　trivalent chromate film layer formed on the Zn-Ni alloy plating layer may be a single coating layer of trivalent chromate, the trivalent chromate, Si, Ti, Zr, P it may be a coating layer formed by mixing one or more oxides of V.
[0095]
　Adhesion amount of the trivalent chromate coating layer, 5 ~ 200mg / m of Cr equivalent amount 2 preferably. Adhesion amount of the trivalent chromate film layer is 5mg / m 2 by weight, can not be obtained sufficient corrosion resistance, there is a concern that develops corrosion from crack of the plating layer, the adhesion amount of the trivalent chromate coating layer 5mg / m 2 or more. In terms of reliably ensuring the corrosion resistance of the fuel tank, the adhesion amount of the trivalent chromate film layer is 10 mg / m 2 and more preferably at least, 15 mg / m 2 or more is more preferable.
[0096]
　On the other hand, the adhesion amount of the trivalent chromate film layer is 200mg / m 2 by weight, the corrosion resistance is improved, since reduction of the continuous dotting property during spot welding is concerned, the adhesion amount of the trivalent chromate film layer is 200mg / m 2 or less. In terms of obtaining reliably corrosion resistance and continuous dotting property during spot welding as a fuel tank, the adhesion amount of the trivalent chromate film layer, 100 mg / m 2 and more preferably less, 70 mg / m 2 or less is more preferred.
[0097]
　Chromate treatment, using conventional chromate treatment liquid may be performed in a conventional chromate treatment, and certain chromate treatment liquid is not limited to the specific chromate treatment method.
[0098]
　(Chromate-free coating layer)
　chromate-free coating layer formed on the Zn-Ni alloy plating layer contains (A) a silicon compound and a phosphoric acid compound, further, Zr, V, Ti, the compound of Co 1 or or coating layer containing two or more, (B) coating layer of urethane resin, or, (C) crosslinked epoxy - coating layer containing at least one of the urethane resin, polyolefin resin and fluorine resin It is preferred.
[0099]
　Hereinafter, (A), (B), and will be described chromate-free coating layer (C).
[0100]
　[Containing (A) a silicon compound and a phosphoric acid compound, further, Zr, V, Ti, coating layer containing one or more compounds of Co]
　
　silicon compound, an organic silicon compound preferable. The organosilicon compounds can be used alone, one containing silane coupling agent of amino group in the molecule and (a), one containing silane coupling agent a glycidyl group in the molecule (b) , is blended in a specific ratio, more preferred properties are obtained.
[0101]
　Mixing ratio of the silane coupling agent (a) and the silane coupling agent (b) is preferably 0.5-1.7 in terms of solid content mass ratio [(a) / (b)]. When the solid content mass ratio [(a) / (b)] is less than 0.5, since the effect of improving the processability is not sufficiently obtained, the solid content mass ratio [(a) / (b)] is 0 .5 or more. More preferably 0.7 or more, still more preferably 0.9 or more.
[0102]
　On the other hand, the solid content mass ratio when [(a) / (b)] is more than 1.7, water resistance is significantly reduced, since an adverse effect on corrosion resistance, solid mass ratio [(a) / (b)] It is preferably 1.7 or less. More preferably 1.4 or less, more preferably 1.1 or less.
[0103]
　One-containing silane coupling agent of amino group in the molecule (a) it is particularly, but not limited to the specific silane coupling agent, 3-aminopropyltriethoxysilane, and the like 3-aminopropyltrimethoxysilane be able to.
[0104]
　One-containing silane coupling agent a glycidyl group in the molecule (b) is particularly, but not limited to the specific silane coupling agent, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyl triethoxy silane, and the like.
[0105]
　
　phosphoric acid compound include phosphoric acid, ammonium salt compound of phosphoric acid, Na salt compound phosphate, K salt compounds of phosphoric acid, mention may be made of magnesium phosphate compound.
[0106]
　Specifically, for example, phosphoric acid, trisodium phosphate, ammonium phosphate dibasic, ammonium dihydrogen phosphate, potassium phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, phosphoric acid sodium dihydrogen phosphate dihydrogen calcium, magnesium hydrogen phosphate, phosphoric acid dihydrogen magnesium can be mentioned.
[0107]
　The amount of phosphoric acid compound is a solid mass ratio of phosphoric acid compound and an organic silicon compound (phosphoric acid compound / organic silicon compound) is preferably from 0.03 to 0.12. When the solid content mass ratio of the phosphoric acid compound and an organic silicon compound is less than 0.03, because the addition effect is not sufficiently obtained, solid content mass ratio is preferably 0.03 or more. More preferably 0.05 or more, further preferably 0.09 or more.
[0108]
　On the other hand, when the solid content weight ratio of phosphoric acid compound and an organic silicon compound is more than 0.12, because undesirable water soluble markedly increased by the coating layer, solid content mass ratio is preferably 0.12 or less. More preferably 0.11 or less, more preferably 0.10 or less.
[0109]
　
　amount of V compounds, solid mass ratio of V compound and a silicon compound [V compound / silicon compound] is preferably 0.05 to 0.17. When the solid content mass ratio [V compound / silicon compound] is less than 0.05, since the effect of the addition of V compound is not sufficiently obtained, the solid content mass ratio [V compound / silicon compound] is 0.05 or more preferable. More preferably 0.07 or more, more preferably 0.0 9 or more, and most preferably 0.11 or more.
[0110]
　On the other hand, when the solid mass ratio [V compound / silicon compound] is more than 0.17, the stability of the coating layer is extremely lowered, solid mass ratio [V compound / silicon compound] is preferably 0.17 or less . More preferably 0.15 or less, more preferably 0.14 or less.
[0111]
　The amount of Ti compound, solid content mass ratio of Ti compound and a silicon compound [Ti compound / silicon compound] is preferably from 0.02 to 0.07. When the solid content mass ratio [Ti compound / silicon compound] is less than 0.02, since the effect of the addition of Ti compound is not sufficiently obtained, the solid content mass ratio [Ti compound / silicon compound] is 0.02 or more preferable. More preferably 0.03 or more, more preferably 0.04 or more.
[0112]
　On the other hand, when the solid mass ratio [Ti compound / silicon compound] is more than 0.07, since the conductive coating is reduced, solid mass ratio [Ti compound / silicon compound] is preferably 0.07 or less. More preferably 0.06 or less, more preferably 0.05 or less.
[0113]
　The amount of Zr compound, solid content mass ratio of Zr compound and a silicon compound [Zr compound / silicon compound], likewise, preferably from 0.02 to 0.07. When the solid content mass ratio [Zr compound / silicon compound] is less than 0.02, since the effect of the addition of Zr compound is not sufficiently obtained, the solid content mass ratio [Zr compound / silicon compound] is 0.02 or more preferable. More preferably 0.03 or more, more preferably 0.04 or more.
[0114]
　On the other hand, when the solid mass ratio [Zr compound / silicon compound] is more than 0.07, since the conductive coating is reduced, solid mass ratio [Zr compound / silicon compound] is preferably 0.07 or less. More preferably 0.06 or less, more preferably 0.05 or less.
[0115]
　V compounds, particularly, but not limited to a particular V compound, vanadium pentoxide V 2 O 5 , metavanadate HVO 3 , ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl 3 , vanadium trioxide V 2 O 3 , vanadium dioxide VO 2 , vanadium oxysulfate VOSO 4 , vanadium oxy acetylacetonate VO (OC (= CH 2 ) CH 2 COCH 3 )) 2 , vanadium acetylacetonate V (OC (= CH 2 ) CH 2 COCH 3 ) ) 3 , vanadium trichloride VCl 3 , and the like phosphovanadomolybdic acid. Moreover, the pentavalent vanadium compound, a hydroxyl group, a carbonyl group, a carboxyl group, primary to tertiary amino group, an amide group, phosphate group, and, in an organic compound having one or more phosphonic acid groups, 4 V compound was reduced to ~ divalent may also be used.
[0116]
　Ti compounds, hexafluoro titanic acid, or a salt thereof, for example, may be mentioned ammonium salts, potassium salts, such as sodium salt.
[0117]
　Zr compounds, hexafluorozirconate, or a salt thereof, for example, may be mentioned ammonium salts, potassium salts, such as sodium salt.
[0118]
　Solid weight ratio of the V compound and the Ti compound [V compound / Ti compound] is preferably 1.3 to 6.0. When the solid content mass ratio [V compound / Ti compound] is less than 1.3, since the effect of the addition of V compound is not sufficiently obtained, the solid content mass ratio [V compound / Ti compound] is 1.3 or more preferable. More preferably 2.5 or more, more preferably 2.8 or more.
[0119]
　On the other hand, when the solid mass ratio [V compound / Ti compound] is more than 6.0, since the stability and workability of the coating layer is lowered, solid mass ratio [V compound / Ti compound] is 6.0 or less It is preferred. More preferably 4.5 or less, more preferably 3.3 or less.
[0120]
　Solid weight ratio of the V compound and Zr compound [V compound / Zr compound] is preferably 1.3 to 6.0. When the solid content mass ratio [V compound / Zr compound] is less than 1.3, since the effect of the addition of V compound is not sufficiently obtained, the solid content mass ratio [V compound / Zr compound] is 1.3 or more preferable. More preferably 2.5 or more, more preferably 2.8 or more.
[0121]
　On the other hand, when the solid mass ratio [V compound / Zr compound] is more than 6.0, since the stability and workability of the coating layer is lowered, solid mass ratio [V compound / Zr compound] is 6.0 or less It is preferred. More preferably 4.5 or less, more preferably 3.3 or less.
[0122]
　Solid mass ratio of Co compound and a silicon compound [Co compound / silicon compound] is preferably 0.01-0.10. When the solid content mass ratio [Co compound / silicon compound] is less than 0.01, since the effect of adding the Co compound is not sufficiently obtained, the solid content mass ratio [Co compound / silicon compound] is at least 0.01 preferable. More preferably 0.02 or more, more preferably 0.03 or more.
[0123]
　On the other hand, when the solid mass ratio [Co compound / silicon compound] is more than 0.10, since the corrosion resistance is lowered, solid mass ratio [Co compound / silicon compound] is preferably 0.10 or less. More preferably 0.08 or less, more preferably 0.06 or less.
[0124]
　Co compound, cobalt sulfate, cobalt nitrate, and can include at least one cobalt compound of cobalt carbonate.
[0125]
　(A) containing a silicon compound and a phosphoric acid compound, further, Zr, V, Ti, coating weight of the coating layer of the compound of Co containing one or more than 0.05 ~ 2.0 g / m 2 It is preferred. Deposition amount of the coating layer is 0.05 g / m 2 by weight, can not be sufficiently cover the surface of the plated steel sheet, since the corrosion resistance is significantly decreased, the coating weight 0.05 g / m 2 or more preferable. More preferably 0.10 g / m 2 or more, more preferably 0.30 g / m 2 is at least.
[0126]
　Meanwhile, the amount of adhered 2.0 g / m 2 by weight, since the workability of the coating layer decreases, the deposition amount of 2.0 g / m 2 or less. More preferably 1.6 g / m 2 or less, more preferably 1.2 g / m 2 is less.
[0127]
　The coating layer on the surface of the plated steel sheet, a silane coupling agent blended in a predetermined solid content mass ratio (a) and the silane coupling agent (b), phosphoric acid compounds, and, Zr, V, Ti, the Co the aqueous metal surface treatment agent containing one or two or more compounds is applied, it can be dried in less than 50 ~ 250 ° C. temperature reached to form.
[0128]
　When reaching temperature is less than 50 ° C., the solvent of the aqueous metal surface treatment agent is not completely volatilized, because the required coating layer is not formed, reaching temperature is preferably at least 50 ° C.. More preferably 70 ° C. or higher, further preferably 100 ° C. or higher. On the other hand, when the temperature reached is 250 ° C. or higher, to decompose a portion of the organic chain forming a coating layer, since the coating layer is deteriorated, reaching temperature is preferably lower than 250 ° C.. More preferably 220 ° C. or less, more preferably 200 ° C. or less.
[0129]
　[(B) coating layer of urethane resin]
　urethane resin coating layer comprises a polyurethane resin containing a silanol group, a polyester resin containing a sulfonic acid group, a phenol resin, a polyolefin resin, and at least one acrylic resin, as a crosslinking agent, a water-soluble isocyanate compound, a carbodiimide group-containing compounds, oxazoline group-containing compound, it contains one or more organic titanate compound, further coating layer containing silicon oxide or phosphate compound.
[0130]
　Polyurethane resin containing a silanol group, for example, by reacting a hydrolyzable silicon group-containing compound and the polyurethane prepolymer having at least one or more active hydrogen groups in the molecule, then, dispersed or dissolved in water, hydrolysis is allowed can be formed.
[0131]
　Hydrolyzable silicon group is a group hydrolyzable group undergoes hydrolysis is bonded to a silicon atom, specifically, a hydrogen atom, a halogen atom, an alkoxy group, an acyloxy group, an amino group, an amide group, aminooxy group, and a mercapto group. Alkoxy groups, hydrolyzable relatively low, because the handling is easy, which is preferable. Hydrolyzable group is usually attached 1-3 to one silicon atom, the reactivity of the hydrolyzable silyl group after application, water resistance, and, in terms of solvent resistance, 2- those three bonds to is preferred.
[0132]
　The hydrolyzable silicon group-containing compound having at least one or more active hydrogen groups in the molecule, .gamma. (2-aminoethyl) aminopropyl trimethoxysilane, .gamma. (2-aminoethyl) aminopropyl triethoxysilane , .gamma. (2-aminoethyl) aminopropyl dimethoxysilane, .gamma. (2-aminoethyl) aminopropyl diethoxysilane, .gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltriethoxysilane, .gamma.-aminopropyl dimethoxysilane , .gamma.-aminopropyl diethoxy silane, .gamma.-mercaptopropyltrimethoxysilane, .gamma.-mercaptopropyl methyl dimethoxy silane, .gamma.-mercaptopropyl triethoxysilane, mention may be made of .gamma.-mercaptopropyl diethoxy silane. In contributing point by film formation, it is preferable to introduce silanol groups between molecules constituting a polyurethane resin, hydrolyzable silicon group-containing compound having two or more active hydrogen groups are preferred.
[0133]
　The content of silanol groups or Si-O bonds, in order to impart crosslinking reactivity and performance superior to the polyurethane resin relative to the total solids content of the polyurethane resin, 0.1 to 10 wt% of silicon content is preferred. If the content of silanol groups or Si-O bonds is less than 0.1 wt%, without properly contribute to the crosslinking reaction, because the addition effect is not sufficiently obtained, the content is more than 0.1 mass% It is preferred. More preferably not less than 0.5 mass%.
[0134]
　On the other hand, when the content of silanol groups or Si-O bond is more than 10 wt%, the effect of addition is saturated, the stability of the processing solution is lowered, the content is preferably 10 mass% or less. More preferably not more than 5 wt%.
[0135]
　The polyurethane prepolymers, for example, polycarbonate polyols, polyester polyols, polyether polyols, polyesteramide polyols, acrylic polyols, polyurethane polyols, or can include mixtures thereof. Among these, polycarbonate polyol, polyester polyol, polyether polyol, ensuring workability, and is preferred in terms of ensuring a high elastic modulus.
[0136]
　Polyurethane prepolymers can be obtained a compound having two active hydrogen groups per molecule, it is reacted with a polyisocyanate compound having two isocyanate per molecule, by dissolving or dispersing in water.
[0137]
　Examples of the compound having per molecule at least two active hydrogen groups that constitute the polyurethane prepolymer, for example, as a compound having an active hydrogen group, an amino group, a hydroxyl group, there may be mentioned a compound having a mercapto group, an isocyanate considering the reactivity with the group, the compound having a hydroxyl group, the reaction rate faster preferred. The compound having at least two active hydrogen groups per molecule, polycarbonate polyols, polyester polyols, polyether polyols, polyesteramide polyols, acrylic polyols, polyurethane polyols, or can include mixtures thereof.
[0138]
　The compound having at least two isocyanate groups per molecule, for example, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3 - butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, and aliphatic isocyanates such as 2,6-diisocyanate methyl caproate, for example, 1,3 - cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethyl-cyclohex Le isocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,2-bis (isocyanatomethyl) cyclohexane, 1,4-bis ( isocyanatomethyl) cyclohexane, 1,3-bis (and alicyclic diisocyanates such as isocyanatomethyl) cyclohexane, for example, m- xylene diisocyanate, m- phenylene diisocyanate, p- phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4- or 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, dianisidine Isocyanates, and aromatic diisocyanates such as 4,4'-diphenyl ether diisocyanate, for example, omega, omega .'- diisocyanate-1,3-dimethylbenzene, omega, omega .'- diisocyanate-1,4-dimethylbenzene, omega, omega ' - or araliphatic diisocyanates diisocyanate-1,4-diethylbenzene, for example, triphenylmethane-4,4'-4 '' - triisocyanate, 1,3,5-triiso Cyanate benzene, or triisocyanate such as 2,4,6-triisocyanate toluene, for example, 4,4'-diphenyl-dimethyl methane-2,2 ', and polyisocyanate monomers such as 5,5' isocyanate, the polyisocyanate monomers derived from dimer, trimer, biuret, allophanate, carbodiimide, the or polyisocyanate derivatives resulting from the polyisocyanate monomers, such as ethylene glycol, propylene glycol, less than butylene glycol molecular weight 200 adducts or to the polyisocyanate monomer of low molecular weight polyols, polyester polyols, polyether polyols, polycarbonate polyols, polyesteramide polyols, acrylic polyols, polyurethane Po It can be mentioned adduct to the polyisocyanate monomer ol.
[0139]
　In order to disperse the polyurethane resin in water, introducing a hydrophilic group into the polyurethane prepolymer. To introduce a hydrophilic group, for example, it has at least one or more active hydrogen groups in the molecule, and containing a carboxyl group, a sulfonic acid group, a sulfonate group, a hydrophilic group such as polyoxyethylene groups the compound, at least one or more, it is sufficient to copolymerized during the polyurethane prepolymer production.
[0140]
　The hydrophilic group-containing compounds, e.g., 2,2-dimethylolpropionic acid, 2,2-dimethylol butyric acid, 2,2-dimethylol valeric acid, dioxy maleic acid, 2,6-dioxy benzoic acid, 3,4 - carboxyl group-containing compound or a derivative thereof such as diaminobenzoic acid, or their co-polymerized to a polyester polyol obtained, maleic anhydride, phthalic anhydride, succinic anhydride, trimellitic anhydride, pyromellitic anhydride compound and the active hydrogen group a carboxyl group-containing compound or a derivative thereof obtained by reacting a compound having having anhydride groups, such as 2-oxyethanesulfonic acid, phenolsulfonic acid, sulfobenzoic acid, sulfosuccinic acid, 5-sulfoisophthalic acid, sulfonic acid-containing compounds and derivatives thereof, such as sulfanilic acid or this, And polyester polyols obtained by copolymerizing al.
[0141]
　In the polyurethane resin, in order to satisfactorily dissolve or disperse in water, using a neutralizing agent. Examples of the neutralizing agent, for example, ammonia, triethylamine, triethanolamine, triisopropanolamine, trimethylamine, tertiary amines dimethylethanolamine such as sodium hydroxide, potassium hydroxide, alkali metals, alkaline earth such as calcium hydroxide Although basic substances such as hydroxides of classes metals, weldability, solvent resistance, the odor at the time of welding, boiling point 120 ° C. or more tertiary amines are preferred.
[0142]
　Neutralizing agent, either alone or may be used in mixture of two or more. The method of adding the neutralizing agent may be added directly to the polyurethane prepolymer or may be added to the water when dissolving or dispersing in water. The addition amount of the neutralizing agent is preferably 0.1 to 2.0 equivalents to the carboxyl group, and more preferably 0.3 to 1.3 equivalents.
[0143]
　Polyolefin resin contained in the urethane-based coating layer, ethylene - alkali metal neutralization product of an unsaturated carboxylic acid copolymer. Here, a polyolefin resin is an ethylene - the alkali metal neutralization product of an unsaturated carboxylic acid copolymer, ethylene - part of the carboxyl groups contained in the unsaturated carboxylic acid copolymer, KOH, NaOH, It means that which has been neutralized by an alkali metal supplied by a metal compound such as LiOH.
[0144]
　Ethylene - alkali metal neutralization product of an unsaturated carboxylic acid copolymer, neutralization rate, the lower limit of 30%, the upper limit 90% is preferable. Neutralization rate lower 30%, the upper limit of 90%, an ethylene - means that 30-90% of the carboxyl groups contained in the unsaturated carboxylic acid copolymer are neutralized. When neutralization ratio is less than 30%, the adhesion to the intermediate layer film (C) of the resultant coating layer is not sufficient, the neutralization ratio is preferably 30% or more. More preferably 40% or more.
[0145]
　On the other hand, when the neutralization ratio exceeds 90%, the adhesion between the film and the intermediate layer (C) may be reduced, neutralization ratio is preferably 90% or less. More preferably 80% or less.
[0146]
　Ethylene - unsaturated carboxylic acid copolymer, and ethylene, methacrylic acid, acrylic acid, maleic acid, fumaric acid, itaconic acid, a copolymer obtained by radical polymerization of unsaturated carboxylic acid under a pressure of crotonic acid .
[0147]
　Olefin resins, ethylene - unsaturated carboxylic acid copolymer, an amine (e.g., triethylamine, water-soluble amines such as ethanolamine, etc.), may be obtained by neutralization with ammonia. Amine may be used alone or in combination of two or more thereof. Olefin resins, ethylene - in the neutralization of the unsaturated carboxylic acid copolymer, ammonia with an alkali metal, may be used in combination amine.
[0148]
　The phenol resin contained in the urethane resin coating layer, can be exemplified phenol resin composition which impart water solubility, for example, phenol, resorcinol, cresol, bisphenol A, and aromatics such as p-xylylene dimethyl ether a formaldehyde diethanolamine phenolic resins such as methylolated phenolic resin obtained by addition reaction in the presence of a reaction catalyst, is reacted with an amine compound such as N- methyl ethanolamine, obtained by neutralization with organic or inorganic acid mention may be made of things like.
[0149]
　Crosslinking agent contained in the urethane resin coating layer, it performs efficiently at a lower baking temperature crosslinking reaction, is used as a means for adding the characteristic of the crosslinkable agent itself coatings. Crosslinking agent, if water-soluble or water-dispersible, but both can be used, among others, water-soluble isocyanate compound, a carbodiimide group-containing compounds, oxazoline group-containing compounds, one or more is preferably selected from organic titanate compound .
[0150]
　The water-soluble isocyanate compound, mention may be made of a polyisocyanate compound imparting water-dispersibility, mainly, to form a crosslinked structure by reacting with the hydroxyl groups of silanol groups. For example, Burnock 5000 (manufactured by Dainippon Ink and Chemicals, Inc.), and the like.
[0151]
　The carbodiimide group-containing compound, an aromatic carbodiimide compound, mention may be made of an aliphatic carbodiimide compound, mainly carboxyl groups, to form an active hydrogen group and a crosslinking structure such as a hydroxyl group. For example, Carbodilite V-02, the V-02-L2, the E-01, the E-02, the E-03A, the E-04 (manufactured by Nisshinbo Co.) is.
[0152]
　The oxazoline group-containing compounds include, for example, EPOCROS K-2010E, the same K-2020E, the same K-2030E, the WS-500, the WS-700 (manufactured by Nippon Shokubai Co., Ltd.). Oxazoline group-containing compound, primarily, to form a crosslinked structure by reacting with the carboxyl group.
[0153]
　The organic titanate compounds, for example, Orgatics TC-300 (dihydroxy bis (ammonium lactate) titanium, manufactured by Matsumoto Chemical Industry Co., Ltd.), TC-400 (diisopropoxy titanium bis (triethanolaminate), manufactured by Matsumoto Chemical Industry Co., Ltd.) and the like. Organotitanate compounds are primarily carboxyl groups, to form an active hydrogen group and a crosslinking structure such as a hydroxyl group.
[0154]
　The preferred amount of crosslinking agent varies depending on the acid value of the resin, elongation and curing of the coating layer, the balance of the physical properties such as hardness, 5 to 50 mass in solid content ratio of the crosslinking agent the total amount for the main resin It is preferred.
[0155]
　Urethane resin coating layer phosphoric acid compound to be contained in, for example, a three-ammonium phosphate, ammonium phosphate dibasic, ammonium dihydrogen phosphate, potassium phosphate, potassium dihydrogen phosphate, trisodium phosphate, phosphoric disodium hydrogen, sodium dihydrogen phosphate, calcium dihydrogen phosphate, magnesium hydrogen phosphate, can be mentioned magnesium dihydrogen phosphate or the like.
[0156]
　Among them, triammonium phosphate, ammonium phosphate dibasic, ammonium phosphate compound of ammonium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium phosphate compound in sodium dihydrogen phosphate, calcium compounds such as calcium dihydrogen phosphate, magnesium hydrogen phosphate, among magnesium phosphate compounds such as magnesium dihydrogen phosphate, at least one compound, remarkable effect of improving the solvent resistance and corrosion resistance because, preferable.
[0157]
　These compounds are water-soluble, or, if soluble in acid or alkali, it is possible to use depending on the pH of the treatment bath, either can be used, such as a pure compound or hydrate .
[0158]
　Content of the phosphoric acid compound is based on the solid coating amount of 0.1 to 10 mass% in the phosphorus content is preferred. When the content of the phosphoric acid compound is less than 0.1 wt%, the addition effect is not sufficiently obtained, the content of the phosphate compound is preferably at least 0.1 wt%. On the other hand, when the content of the phosphoric acid compound is more than 10 wt%, wettability is increased to coating, since corrosion resistance may be decreased, the content of the phosphate compound is preferably 10 mass% or less .
[0159]
　Silicon oxide contained in the urethane resin coating layer, for example, a silicon dioxide, and the like. The silicon oxide may be any non stably dispersed precipitated compounds in water, among others, colloidal silica, because the effect of improving the solvent resistance and corrosion resistance remarkably appears preferable.
[0160]
　For example, "Snow Tex O", "Snowtex OS", "SNOWTEX OXS", "Snowtex N", "SNOWTEX NS", "Snowtex NXS" (both manufactured by Nissan Chemical Industries, Inc.) of commercially available colloidal silica particles, "SNOWTEX UP", the fibrous colloidal silica such as "Snowtex PS" (manufactured by Nissan Chemical Industries, Ltd.), can be used depending on the pH of the treatment liquid.
[0161]
　The content of silicon oxide, relative to the solid coating amount is preferably 2-20% by weight of silicon content. If the content of silicon oxide is less than 2 wt%, the addition effect is not sufficiently obtained, the content of silicon oxide is more than 2% by mass. On the other hand, when the content of silicon oxide is more than 20 wt%, the effect of addition is saturated, the workability and the corrosion resistance may be lowered, the content of silicon oxide is preferably 20 wt% or less.
[0162]
　To improve the corrosion resistance, further, inorganic rust inhibitor niobium compound and a zirconium compound, guanidino group-containing compound, biguanidino group-containing compound, and, it is preferable to add an organic corrosion inhibitor such as thiocarbonyl group-containing compounds as appropriate. The addition amount of the rust inhibitor, the solid content of 100% of the coating layer, when the inorganic anticorrosive agents, 1.0-15% by mass in a total amount in the case of the organic corrosion inhibitor, 0.1 to 10 mass in total % is preferred.
[0163]
　Inorganic corrosion inhibitor is less than 1.0 wt%, or, when the organic corrosion inhibitor is less than 0.1 wt%, the addition effect is not sufficiently obtained, inorganic rust inhibitor 1.0 wt% preferably, the organic rust is preferably at least 0.1 wt%. On the other hand, the inorganic corrosion inhibitor is more than 15 wt%, or, when the organic corrosion inhibitor is more than 10 wt%, the effect of addition is saturated, the workability and the corrosion resistance may be lowered, inorganic corrosion inhibitor preferably 15 wt% or less, the organic rust is preferably 10 mass% or less.
[0164]
　Urethane resin, a polyurethane resin containing a silanol group, in terms of promoting the crosslinking reaction, preferably. In order to enhance the strength of the coating layer, it is preferable to blend a silicon oxide. The content of silanol groups and Si compounds, based on the solid content of the coating layer is preferably 5 to 20 mass% of silicon conversion. If the content of silanol groups and Si compound is less than 5 mass%, because the addition effect is not sufficiently obtained, the content is preferably at least 5 mass%.
[0165]
　On the other hand, when the content of silanol groups and Si compound is more than 20 wt%, the effect of addition is saturated, the workability and the corrosion resistance may be lowered, the content is preferably 20 mass% or less.
[0166]
　Resin film layer having a urethane bond + urea bond and Si, polyurethane resin (urethane group, urea group-containing) that was bound to silanol groups on the resin backbone is dispersed or dissolved in water, further, the surface treatment of a mixture of silicon oxide to produce a material, the surface treatment agent was coated on the surface of the steel sheet is formed by baking and drying or natural drying. Further, a polyurethane resin obtained by binding silanol groups in the resin skeleton, a solution obtained by mixing another resin, further, to prepare a surface treating agent obtained by mixing silicon oxide was applied on the surface of the steel sheet, and baking and drying formed to.
[0167]
　The resin coating layer, by adding a lubricity imparting agent as appropriate, while maintaining good performance, low dynamic friction coefficient of the surface, it is possible to obtain an excellent surface-treated steel sheet in workability. Lubricity imparting agent, as a representative and water-dispersible polyethylene resin, tetrafluoroethylene resin, stearic acid compounds include natural paraffin wax. Among them, polyethylene resin, tetrafluoroethylene resin, because lubricity reduction effect conspicuous, preferred.
[0168]
　The addition amount of the lubricity imparting agent, 1-40% by mass in terms of solid content of the resin film layer is preferred. If the amount of the lubricity providing material is less than 1 wt%, the addition effect is not sufficiently obtained, the amount added 1% by mass or more is preferable. On the other hand, when the amount of the lubricant imparting agent exceeds 40 wt%, with a decrease effect is saturated coefficient of dynamic friction, and reduced film-forming ability, there is a dance corrosion resistance decreases, the amount added is 40 wt% the following are preferred.
[0169]
　[(C) crosslinked epoxy - urethane resin, coating layer contains at least one polyolefin resin and fluorine resin]
　crosslinked epoxy - and urethane resins, at least one polyolefin resin and fluorine resin It explained coating layer containing.
[0170]
　The upper layer of the coating layer of the steel sheet of the present invention, crosslinked epoxy - and urethane resin, a coating layer containing at least one polyolefin resin and fluorine resin. By cross-linking the specific resin, it is possible to form an excellent coating layer gasoline resistance.
[0171]
　
　crosslinked epoxy - urethane resin, the binder resin and the crosslinking agent consists of (b), gasoline resistance, water resistance, alkali resistance is good, adhesion to a base material, adhesion to the topcoat paint film is particularly good organic solvent-soluble resins. The binder resin had a number average molecular weight of 300 to 100,000 bisphenol epoxy resin (a) is preferred.
[0172]
　For example, it is possible to use a resin represented by the following formula (1).
[0173]
[Number 1]

[0174]
　In the formula, R represents, H, or CH 3 , A is C (CH 3 ) 2 , CH 2 , O, SO 2 represents or S, X represents a p- phenylene group. N in the formula (1) is 2 to 9 are preferred. A is C (CH 3 ) 2 For, it is possible to obtain a particularly favorable results.
[0175]
　When the number average molecular weight of the bisphenol type epoxy resin (a) is less than 300, polymerization reaction does not proceed sufficiently, because insufficient anticorrosive ability of the coating layer, the number average molecular weight is preferably 300 or more. On the other hand, if the number average molecular weight of the bisphenol type epoxy resin exceeds 100,000, the crosslinking reaction does not proceed sufficiently, decreased solvent resistance of the coating layer, since no sufficient corrosion resistance can not be obtained, the said number-average molecular weight of 100,000 the following are preferred.
[0176]
　The amount of bisphenol type epoxy resin (a) is more than 30 mass% in solid content is preferable. When the amount of the bisphenol type epoxy resin is less than 30 wt%, the brittle coating layer, since the film adhesion during processing is lowered, the amount is preferably at least 30 mass%.
[0177]
　Curing agent (b) consists of a polyisocyanate compound and / or a blocked polyisocyanate compound. As the polyisocyanate compound, for example, aliphatic or alicyclic diisocyanate compounds (hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, etc.), aromatic diisocyanate compounds (tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate) , triisocyanate compound (1 mole of trimethylol propane and the diisocyanate 3 mole adducts, trimers of diisocyanates such as hexamethylene diisocyanate and tolylene diisocyanate, etc.) and the like can be mentioned, one or more of these it can be used.
[0178]
　Blocked polyisocyanate compound, for example, those obtained by blocking an isocyanate with a blocking agent. The blocking agent, a stable adduct produced by adding the isocyanate groups at room temperature, and it is necessary that those dissociated during coating baking allowed to regenerate free isocyanate groups.
[0179]
　The blocking agent, for example, lactam type blocking agents (.epsilon.-caprolactam, .gamma.-butyrolactam, etc.), oxime type blocking agents (methyl ethyl ketoxime, hexa oxime like cyclohexane), alcohols blocking agents (methanol, ethanol, isobutyl alcohol, etc. ), phenol type blocking agents (phenol, p-tertiary-butylphenol, cresol and the like), and ester-based blocking agents (ethyl acetoacetate, methyl acetoacetate). In particular, dissociates at low temperature, the paint storage conditions and stable methyl ethyl ketoxime, ethyl acetoacetate, and the like are preferable.
[0180]
　The amount of the curing agent (b), based on the solid content of the bisphenol type epoxy resin (a), the weight ratio (a) / (b) at preferably 10 / 1-1 / 1.
[0181]
　The mass ratio of the bisphenol epoxy resin (a) and the curing agent (b), low temperature, short-time baking conditions, for example, below the highest temperature 160 ° C., the reaction in baking conditions of baking time of 5 to 60 seconds sufficient it is in progress, to form a suitable resin film layer be in.
[0182]
　When the mass ratio (a) / (b) is more than 10/1, the progress of the crosslinking reaction is insufficient, because the lack of corrosion resistance of the coating layer, the mass ratio (a) / (b) is 10/1 the following are preferred. More preferably 7/1 or less. On the other hand, when the mass ratio (a) / (b) is less than 1/1, with water resistance and alkali resistance of the coating layer is lowered, since the film adhesion during processing is lowered, the weight ratio (a ) / (b) is 1/1 or more. More preferably 3/1 or more.
[0183]
　
　least one resin of the polyolefin resin and fluorine resin is a resin component which gives processability and lubricity to the coating layer. As the polyolefin resin, polyethylene, may be mentioned polypropylene, a fluorine resin, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, it may be mentioned polyvinyl fluoride and the like. Resin containing one or more thereof are preferred.
[0184]
　The polyolefin resin and / or fluororesin, by reducing the dynamic friction coefficient of the surface of the coating layer, to impart lubricity to the coating layer, to prevent galling at the time of processing, press formability and ironing workability of the coating layer It contributes to the improvement of, crosslinked epoxy - and combined with a urethane resin film, a resin forming the effect of maintaining the flexibility of the entire coating layer.
[0185]
　The amount of polyolefin resin and at least one resin of the fluorine resin, crosslinked epoxy - relative weight of the total resin ingredient plus urethane resin is preferably 0.5 to 15 weight%. If the amount of at least one resin of the polyolefin resin and fluorine resin is less than 0.5 mass%, the effect of imparting lubricity to the coating layer is not sufficiently obtained, the amount is 0.5 mass% or more. More preferably 3 mass% or more.
[0186]
　On the other hand, if the amount of at least one resin of the polyolefin resin and fluorine resin exceeds 15 wt%, continuity and uniformity of the coating layer is lost, the adhesion between the undercoat decreases, also the coating composition since the storage stability of the drops, the amount is preferably 15 mass% or less. More preferably 10 wt% or less.
[0187]
　
　coating layer of the steel sheet of the present invention, degreasing, without eluting the harmful substances in the film-forming bath, to ensure excellent corrosion corrosion, silica particles having an average particle size of 0.10 ~ 100 [mu] m (the Hiyumudoshirika) it may contain 5 to 50 wt% in solid content.
[0188]
　When the average particle diameter of the silica particles is less than 0.10 .mu.m, alkali resistance and, since adhesion between the top coat is reduced, it said average particle size is preferably at least 0.10 .mu.m. On the other hand, when the average particle size of the silica particles exceeds 100 [mu] m, since the reduced corrosion resistance of the coating layer, the average particle diameter is preferably 100 [mu] m or less.
[0189]
　The amount of the silica particles (Hiyumudoshirika) is preferably 5 to 50% by mass relative to paint solids. When the amount of silica particles (Hiyumudoshirika) is 5 wt% or less, since the anticorrosive ability of the coating layer is insufficient, the amount is preferably at least 5 mass%. More preferably at least 10 wt%.
[0190]
　On the other hand, if the amount of the silica particles (Hiyumudoshirika) exceeds 50 mass%, since the film adhesion during processing is lowered, the amount is preferably 50 mass% or less. More preferably not more than 30 wt%.
[0191]
　To formulate a large amount of silica particles (Hiyumudoshirika) in coating layer, it is preferred to use a ketone organic solvent. A large amount of silica particles (fumed silica) is to increase the viscosity of the paint for coating layer formation, when there is a risk of difficulty in uniform application of the paint to disperse the silica particles in a ketone organic solvent, wherein the coating material the thin, it is possible to uniformly apply.
[0192]
　Ketone-based organic solvents, the additional inclusion least 40 wt% of the coating mass, and, by adjusting the solid content concentration of 10 to 50 wt%, it is possible to easily form a uniform thin film. When paint solids concentration is less than 10 wt%, the solvent content is too much, because it is not economical, paint solids concentration is preferably at least 10 mass%.
[0193]
　On the other hand, when the solid content concentration exceeds 50 mass%, the coating workability is lowered since it becomes difficult to thin film uniformly formed, paint solids concentration is preferably 50 wt% or less.
[0194]
　Examples of the ketone-based organic solvents, methyl isobutyl ketone, acetone and cyclohexanone, isophorone and the like, may be mentioned as being particularly preferred. Although other solvents may also be used, for example, as such as water and alcohol, the solvent reacts with the polyisocyanate compound should be avoided.
[0195]
　Baking conditions of the coating composition for forming the coating layer is attained temperature of the steel sheet is preferably 120 ~ 250 ° C.. When temperature reached of the steel sheet is less than 120 ° C., a short time the crosslinking reaction is difficult to cure to proceed, since the gasoline resistance is lowered, achieving temperature of the steel sheet is preferably at least 120 ° C.. More preferably 140 ° C. or higher.
[0196]
　On the other hand, when the temperature reached of the steel sheet exceeds 250 ° C., and the coating layer begins to thermally decompose, since the coating performance is lowered, achieving temperature of the steel sheet is preferably 250 ° C. or less. More preferably 200 ° C. or less.
[0197]
　Coating method, a roll coating method may be a known method such as a curtain flow coating method, baking method also, hot air drying, high frequency induction heating may be used a known method such as near-infrared heating.
[0198]
　In the present invention the steel sheet, the thickness of the whole coating layer 0.3 ~ 2.0 .mu.m, the dynamic friction coefficient of the surface of the coating layer preferably 0.07 to 0.15. When the thickness is less than 0.3 [mu] m coating layer, depending on the combination of the surface-treated steel sheets and surface treatment film, since anticorrosive effect is not sufficiently obtained, the thickness of the coating layer is preferably at least 0.3 [mu] m. Stable corrosion resistance, workability, in order to increase the weldability, and more preferably not less than 0.5 [mu] m.
[0199]
　On the other hand, if the thickness of the coating layer is more than 2.0 .mu.m, with a thickness effect is saturated, since the weldability decreases, the thickness of the coating layer is preferably 2.0 .mu.m or less. Stable corrosion resistance, workability, in order to increase the weldability, and more preferably not more than 1.5 [mu] m.
[0200]
　Dynamic friction coefficient of the surface of the coating layer is preferably 0.07 to 0.25 absence of oiling. When the dynamic friction coefficient of the surface of the coating layer is less than 0.07, with a friction coefficient reducing effect by dynamic friction coefficient is too low is saturated, there is a concern that wrinkles are likely to occur during press molding, wherein the dynamic friction coefficient is 0 .07 or more. In terms of obtaining a stable workability, more preferably 0.08 or more.
[0201]
　On the other hand, the the dynamic friction coefficient exceeds 0.25, depending on the state of the state and mold oiling, since the workability in the course machining there is a concern that lowers the dynamic friction coefficient is preferably 0.25 or less. In terms of obtaining a stable workability, more preferably 0.20 or less.
[0202]
　The present invention steel sheet, instead of the trivalent chromate coating layer or chromate-free coating layer, 0.6-10 wt% of the urethane groups and urea groups in N terms of the total coating solids, and the entire film in Si it may have a resin film layer containing at the Si equivalent amount 5-20% by weight. In that case, for example, the thickness of the resin film layer is 0.5 ~ 2.0 .mu.m, the dynamic friction coefficient of the surface is 0.06 to 0.25.
[0203]
　The steel sheet of the present invention, trivalent chromate on the coating layer or the chromate-free coating layer, 0.6-10 wt% of the urethane groups and urea groups in N terms of the total coating solids, and the Si total film 5 ~ may have a resin film layer containing 20 wt% in terms of Si content in. In that case, for example, the thickness of the resin film layer is 0.5 ~ 2.0 .mu.m, the dynamic friction coefficient of the surface is 0.06 to 0.25.
[0204]
　The present invention steel sheet also, on the trivalent chromate coating layer or chromate-free coating layer, a resin having a urethane bond, one or more polyolefin resin and fluorine resin, and an organic coating layer containing the conductive pigment, 3 may have a film thickness of ~ 20μm. In that case, for example,
a resin having a urethane bond (iii), and (i) functional groups of at least 3 polyester polyol, and, (ii) an organic polyisocyanate blocked product, or organic polyisocyanate with an active hydrogen compound an organic resin obtained from film forming resin material containing a blocked product of a prepolymer having an NCO group at the end obtainable by reaction.
　Further, for example, conductive pigments of the organic coating layer is, stainless steel, Zn, Al, Ni, ferrosilicon, consists one or more of iron phosphide, and conductive pigment content of solid 5 to 50% by volume in minutes conversion.
　Further, for example, an organic film layer further anticorrosive pigments contain 1-40% by volume in terms of solid content, and a conductive pigment and anticorrosive pigment, in total, 5 to 70 volume on a solid basis %contains.
[0205]
　The steel sheet of the present invention, on one or both sides of the surface of the steel sheet, Zn-Ni alloy plating layer, thereon, a trivalent chromate coating layer on top of the trivalent chromate film layer, crosslinked epoxy - urethane system resin, and a polyolefin resin, a second resin film layer containing at least one fluorine-based resin,
(iv) Cr amount of the trivalent chromate coating, with Cr equivalent amount 5 ~ 200 mg / m 2 , and,
(v) the layer thickness of the second resin film layer is 0.3 ~ 2.0 .mu.m, dynamic friction coefficient of the surface may be from 0.06 to 0.25.
Example
[0206]
　Next, a description will be given of an embodiment of the present invention, conditions in examples are an example of conditions adopted for confirming the workability and effects of the present invention, the present invention is, in this single condition example the present invention is not limited. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various conditions.
[0207]
　The steel compositions shown in Table 1 was melted, heated held at 1240 ° C., hot rolling finishing temperature 860 ~ 910 ° C., hot rolled at a coiling temperature 630 ~ 670 ° C., the plate thickness 3.7mm heat It was rolled sheet. Next, pickled hot rolled sheet, pickling, and cold rolled to a cold-rolled sheet having a thickness of 1.0 mm.
[0208]
[Table 1]

[0209]
　The cold-rolled sheet was subjected to cycles annealing for holding 60 seconds at 760 ~ 820 ° C.. Some annealed steel sheet, a roll with a large number of convex portions is subjected to skin pass rolling to form a recess on the surface of the steel sheet. Degreased steel sheet, pickling, electroplating method, was subjected to Zn-11% Ni alloy plating. Some of the steel sheet, a Zn-11 ~ 20% Ni alloy plating 100 mg / m 2 after subjected to enhanced the Ni content of the surface by holding in a state of being immersed in it a plating solution (cell cut) the plated steel sheet was produced. Thereafter, using a surface treatment agent shown in Tables 2 to 5, and the test materials subjected to coating treatment in the plated steel sheet. Incidentally, the coating process was set to one layer or two layers of film 1 and 2 of the film 1. Kinds of codes of Tables 6 to coating of 17 1 and 2 show a coating process, lowercase c show a trivalent chromate treatment.
[0210]
　Table 2 shows the embodiment of the trivalent chromate treatment. Table 3 shows the surface treatment agent (A), shown in Table 4, surface treatment agent (B). Table 5 shows the surface treatment agent (C).
[0211]
[Table 2]

[0212]
[table 3]

[0213]
[Table 4]

[0214]
[table 5]

[0215]
　Then, the corrosion resistance of the test material, the press formability, weldability, and secondary processability, and was evaluated paintability. Press forming test, and, when performing the weldability test was tested while applying a lubricating rust preventive oil.
[0216]
　(1) Evaluation 1 of the corrosion resistance
　was evaluated the corrosion resistance to gasoline. Hydraulic molding tester, flange width 20 mm, diameter 50 mm, the sample was subjected to flat-bottomed cylindrical deep drawing depth 25 mm, put test solution and capped with a glass through a silicone rubber ring. Corrosion status after the test was visually observed.
[0217]
　(Test conditions)
　　Test solution: gasoline + distilled water 10% + formic acid 100ppm
　　test period: 3 months standing at 40 ° C.
　(Evaluation
　　criteria) 4: No change
　　3: white rust than 0.1%
　　2: red rust 5% or white rust from 0.1 to
　　50% 1: Red rust occurrence than 5%, or, white rust markedly
[0218]
　(2) Evaluation 2 of corrosion resistance
　as simulated the acceleration test the outer surface side, subjected to salt spray test was evaluated corrosion resistance to salt water. A test piece of 70 × 150 mm, was tested in accordance with JIS Z 2371, 5% saline was evaluated by rust incidence was sprayed for 120 hours.
　(Evaluation
　　criteria) 4: rust of less than 3%
　　3: rust 3% to 10% less than
　　2: rust 10% or more and less than 30%
　　1: rust over 30%
[0219]
　(3) Press workability evaluation
　hydraulic molding tester with a cylindrical punch having a diameter of 50 mm, were molded test drawing ratio 2.2. Blank holder pressure as 1000 kg, was evaluated moldability.
　(Evaluation criteria)
　　4: moldable, no defects in the plating layer
　　3: moldable, plating layer slightly scratches occurred
　　2: moldable, peeling occurs in the plating layer
　　1: molding impossible
[0220]
　(4) Weldability Evaluation
　weldability was evaluated spot welding continuous dotting property and seam weldability.
　(Spot Welding continuous dotting property)
　using an electrode having a diameter of 6 mm, welding current 10 kA, applied pressure 200 kg, subjected to spot welding in welding time 12 cycles were evaluated in a continuous dotting number up to the point where the nugget diameter was cut 4√t .
　(Evaluation
　　criteria) 5: more consecutive RBI 1500 points
　　4: Continuous RBI 1000 points and 1500 points less than
　　3: Continuous RBI 500-1000 points less than
　　2: less than the continuous dotting 250-500 points
　　less than 1: Continuous Dot 250 dot
[0221]
　(Seam welding
　property) using an electrode wheels R6mm-φ250mm, welding current 13 kA, applied pressure 400 kg, and seam welding energization 2on-2off, bending to form a flange portion, to produce a test piece shown in FIG. 5 . The horizontal portion 1a and 1b of the test piece were fixed with chucks, a tensile test at 200 mm / min is performed at different temperatures to investigate the fracture surface after fracture, brittle fracture and ductile fracture is 50/50 the temperature at which was obtained as ductile brittle transition temperature. Was passed ductile brittle transition temperature -40 ℃ less (pass = rating of 5, failed = score 1).
[0222]
　(5) Evaluation of resistance to secondary work embrittlement
　of the sample material, after blanking the diameter 95 mm, subjected to cylindrical aperture in a punch having an outer diameter is 50 mm, the drawn cup is placed on the truncated cone of 30 °, various under the temperature conditions, by dropping a weight weighing 5kg from 1m high position, to determine the lowest temperature at which cracking cup does not occur (secondary work embrittlement resistance temperature).
[0223]
　Secondary work embrittlement resistance temperature will vary with the thickness and test methods of the steel sheet in the plate thickness of the cold-rolled steel sheet is 1.2mm were evaluated as acceptable -50 ° C. or less (pass = score 5, fail = score 1).
[0224]
　(6) coating Evaluation
　melamine alkyd paint, as the film thickness after drying by baking becomes 25 [mu] m, was applied by bar coating, after baking 20 minutes at 120 ° C., cut into 1mm crosscut, the evaluation of adhesiveness, remaining number ratio was carried out by (remaining number / number of cuts 100).
　(Evaluation
　　criteria) 4 =
　　100% 3 = more than 95%
　　2 = 90% or more and less than 95%
　　1 = less than 90%
[0225]
　These evaluation results, Tables 6-8 (Example of the present invention), and Table 9 (Comparative Example) (Example of the present invention) Tables 10 to 12 and Table 13 (Comparative Example) Table 14 ~ 16 (example of the present invention), and it is shown in Table 17 (Comparative example). Incidentally, (Example of the present invention) Table 6-8, and, in Table 9 (Comparative Example), steel composition, and a recess 50 to 1000 / mm 2 , with respect to the surface area of the surface treated steel sheet 20% to 80% shown by comparison the provision of the area ratio. Tables 10-12 (Examples of the present invention), and, Table 13 (Comparative Example), steel composition, and, in the surface morphology index Z as defined in formula (a), 1.0 × 10 4 ~ 1.0 10 × 6 shows in comparison the provision of a range of. Table 14-16 (Examples of the present invention), and, Table 17 (Comparative Example), steel composition, and, four sides arithmetic average roughness in the rectangular region of 5 [mu] m (Ra) is 5 ~ 200 nm, the roughness curve maximum section height (Rt) is shown in comparison the provision of 100 ~ 1000 nm.
[0226]
[Table 6]

[0227]
[Table 7]

[0228]
[Table 8]

[0229]
[Table 9]

[0230]
[Table 10]

[0231]
[Table 11]

[0232]
[Table 12]

[0233]
[Table 13]

[0234]
[Table 14]

[0235]
[Table 15]

[0236]
[Table 16]

[0237]
[Table 17]

[0238]
　Table 6-8, Table 9-12, as shown in Table 13-16, embodiments of the present invention are all, have a strength of the steel sheet exhibiting excellent press formability and durability, and good corrosion resistance , weldability, resistance to secondary work embrittlement, and show the paintability shows a performance capable of withstanding sufficiently used as a fuel tank material.
Industrial Applicability
[0239]
　As described above, according to the present invention, as a material for a fuel tank of an automobile and a motorcycle, it is possible to provide excellent press formability, material strength, corrosion resistance, and, the surface-treated steel sheet having a resistance weldability. Accordingly, the present invention has high applicability in the steel sheet manufacturing industry and automotive industry.
DESCRIPTION OF SYMBOLS
[0240]
　1a, the horizontal portion of the 1b specimen
　2 weld

claims

[Claim 1]On one or both sides of the steel sheet, Zn-Ni alloy plating layer, thereon, a surface treated steel sheet for fuel tanks having a trivalent chromate film layer or chromate-free coating layer,
　the steel sheet is a mass%,
　C:
　~
　0.0050% 0.0005, Si: 0.01 ~ 1.00%, Mn: 0.70
　~ 2.00%, P: 0.060% or
　less, S: 0.010% or
　less, Al: 0
　~
　0.30% .01,
　N: 0.001 ~ 0.010%, Ti: 0.010 ~
　0.050%, Nb: 0.010 ~ 0.040%, B: 0.0005 ~ 0.0030 %
containing, having a component comprising the balance of Fe and unavoidable impurities,
(i) the on the surface outermost layer of the trivalent chromate coating layer or the chromate-free coating layer, the surface arithmetic mean height of the uppermost layer of the cross section curve a recess depth is more than 0.1μm from the 50-1000 pieces / mm 2 , is present in 20-80% of the area ratio with respect to the surface area of the steel sheet
for fuel tank surface treated steel sheet, characterized in that.
[Claim 2]
　Wherein instead of (i),
(i ') the trivalent to the surface outermost layer of the chromate film layer or the chromate-free coating layer, 0.1 [mu] m depth from the arithmetic average height of the surface outermost layer of the cross section curve more recesses, the surface layer morphology index Z which is defined by the following equation (a), 1.0 × 10 4 ~ 1.0 × 10 6 is present in the range of
the fuel tank according to claim 1, characterized in that use surface-treated steel sheet.
　Z ([mu] m 3 / mm 2 ) = surface total depth from the arithmetic average height of the outermost layer of the cross section curve of the volume of or more recesses 0.1 [mu] m (total volume) / surface uppermost layer of the unit area.. ( a)
[Claim 3]
　Wherein instead of
(i), (i ") at the surface of the trivalent chromate coating layer or the chromate-free coating layer, four sides arithmetic average roughness in the rectangular region of 5 [mu] m (Ra) is 5 ~ 200 nm, the roughness curve maximum section height (Rt) is 100 ~ 1000 nm
fuel tank for surface treated steel sheet according to claim 1, characterized in that.
[Claim 4]
　The Zn-Ni alloy plating layer, and mainly Zn, an alloy plating layer containing 5-15 wt% of Ni, and the deposited amount 3 ~ 50 g / m 2 , the of the Zn-Ni alloy plating layer Ni content of the surface layer of layer thickness 1/10, fuel tank according to any one of claims 1 to 3, characterized in that said at Zn-Ni more than 120% of the average amount of Ni alloy plating layer surface-treated steel sheet.
[Claim 5]
　The chromate-free coating layer, (A) containing a silicon compound and a phosphoric acid compound, further, Zr, V, Ti, coating layer containing one or more compounds of Co, (B) a urethane resin coating layer, or, (C) crosslinked epoxy - and urethane resin, any one of claims 1 to 4, characterized in that a coating layer containing at least one polyolefin resin and fluorine resin 1 fuel tank for surface treated steel sheet according to item.
[Claim 6]
　On the trivalent chromate coating layer, (B) coating layer of urethane resin, and, (C) crosslinked epoxy - coating layer containing at least one of the urethane resin, polyolefin resin and fluorine resin fuel tank for surface treated steel sheet according to any one of claims 1 to 4, characterized in that it comprises at least one layer of.
[Claim 7]
　Said containing (A) a silicon compound and a phosphoric acid compound, further, Zr, V, Ti, the compound of Co over the coating layer containing one or two or more, (B) coating layer of urethane resin and, (C) crosslinked epoxy - and urethane resins, a fuel tank according to claim 5, characterized in that it comprises at least one layer of the coating layer containing at least one polyolefin resin and fluorine resin use surface-treated steel sheet.
[8.]
　The trivalent chromate film layer or in place of the chromate-free coating layer, 0.6-10 wt% of the urethane groups and urea groups in N terms of the total coating solids, and, Si in terms of the total coating an Si has a resin film layer containing 5 to 20 wt% in an amount, and
　the layer thickness is 0.5 ~ 2.0 .mu.m of the resin coating layer, the dynamic friction coefficient of the surface is 0.06 to 0.25 fuel tank for surface treated steel sheet according to any one of claims 1 to 4, wherein.
[Claim 9]
　On the trivalent chromate film layer or the chromate-free coating layer, 0.6-10 wt% of the urethane groups and urea groups in N terms of the total coating solids, and, Si in terms of the total coating an Si has a resin film layer containing 5 to 20 wt% in an amount, and
　the layer thickness is 0.5 ~ 2.0 .mu.m of the resin coating layer, the dynamic friction coefficient of the surface is 0.06 to 0.25 wherein, the fuel tank for surface treated steel sheet according to any one of claims 1-4.
[Claim 10]
　On the trivalent chromate film layer or the chromate-free coating layer, a resin having a urethane bond, one or more polyolefin resin and fluorine resin, and an organic coating layer containing a conductive pigment, for 3 ~ 20 [mu] m has a thickness,
(iii) a resin having a urethane bond, (b) functional groups of at least 3 polyester polyol, and, (ii) an organic polyisocyanate blocked product, or organic polyisocyanate with an active hydrogen compound the terminal obtained by reacting an organic resin obtained from film forming resin material containing a blocked product of a prepolymer having an NCO group with
fuel according to any one of claims 1 to 4, that wherein surface-treated steel sheet for the tank.
[Claim 11]
　Conductive pigments of the organic coating layer is, stainless steel, Zn, Al, Ni, ferrosilicon, consists of one or more of iron phosphide, and conductive pigment content of, in terms of solid content fuel tank for surface treated steel sheet according to claim 10, characterized in that 5 to 50% by volume.
[Claim 12]
　The organic coating layer further anticorrosive pigments contain 1-40% by volume in terms of solid content, and a conductive pigment and anticorrosive pigment, in total, containing 5 to 70 volume% in terms of solid content fuel tank for surface treated steel sheet according to any one of claims 10 or 11, characterized in that.
[Claim 13]
　On one or both sides of the surface of the steel sheet, Zn-Ni alloy plating layer, thereon, a trivalent chromate coating layer on top of the trivalent chromate film layer, crosslinked epoxy - urethane resin, and , a polyolefin resin, a second resin film layer containing at least one fluorine-based
resin, (iv) Cr amount of the trivalent chromate coating film, Cr equivalent amount in 5 ~ 200 mg / m 2 and,
(v) said second layer thickness of the resin film layer is 0.3 ~ 2.0 .mu.m, any one of claims 1 to 4, dynamic friction coefficient of the surface is characterized in that 0.06 to 0.25 to 1. fuel tank for surface treated steel sheet according to item.