JPH0525679A - Highly corrosion-resistant surface-treated steel sheet with excellent impact resistance and adhesion - Google Patents

Abstract

(57) [Summary] [Purpose] To realize a highly corrosion-resistant surface-treated steel sheet with excellent perforation resistance, outer surface rust resistance, press workability, electrodeposition paintability, impact resistance, etc. [Constitution] Adjacent to the steel plate surface, crack width: 0.01-0.5μ
m, crack density: It has a Zn-Ni alloy plating thin underlayer with minute cracks that have no directionality of 10 to 60% in terms of crack area fraction, and A) on one side of the steel sheet.
Zn plating layer or Ni content less than 10% by weight and η phase
Zn-Ni alloy plating layer: 10 to 50 g / m ² , B) Zinc phosphate coating layer: 0.1 to 5 g / m ² or film-removable solid lubricating coating layer: 0.5 to
3.0 μm multi-layers in this order and on the other side
a) Zn plating layer or Z with Ni content of 10% or less and η phase
n-Ni alloy plating layer: 10 to 50 g / m ² , b) Zinc phosphate coating layer: 0.1 to 5 g / m ² (optional), c) Chrome
G) Treated layer: Cr is 30 to 300 mg / m ² , d) Protective resin film layer: 0.2 to 2.0 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly corrosion-resistant surface-treated steel sheet having excellent impact resistance, working adhesion and corrosion resistance of a plating film and exhibiting excellent performance when applied to, for example, automobile steel sheets. is there.

[0002]

2. Description of the Related Art In recent years, the requirements for corrosion resistance (perforation corrosion resistance, outer surface rust resistance) of automobile steel sheets have become more and more advanced year by year, and "simple cold rolled steel sheets" that have been used in the past have been used. There is a general tendency to use “galvanized steel sheet” or “zinc alloy plated steel sheet” instead of.

However, in an environment where it is liable to come into contact with corrosive substances such as areas where rock salt is sprayed in order to prevent freezing of roads in winter, even when the above-mentioned plated steel sheet is used, the plating adheres. It has been pointed out that sufficient corrosion resistance cannot be obtained unless the amount is excessive. However, if the amount of plating adhered is increased, powder-like peeling (powdering) and flaky peeling (flaking) of the plating layer during press working are likely to occur, and there is a problem that press workability is significantly impaired. .

Therefore, in order to deal with such a problem, a metal-organic multi-layer coated steel sheet has been devised in which a plated steel sheet is subjected to chromate treatment and rust preventive coating. However, the proposal in the initial stage relates to "corrosion-resistant steel plate coated with zinc rich coating" as shown in Japanese Patent Publication No. 45-24230, and the level of improvement in corrosion resistance is not yet sufficient, and the coating film There was a problem that the Zn powder contained therein peeled off during press working, and the powdering resistance could not be improved to a desired level.

Therefore, subsequently, a multi-layer coated steel sheet was proposed in which two layers, a chrome coating and an organic composite silicate coating, were applied on a zinc-based plated steel sheet (JP-A-57-1).
08212, JP-A-58-224174, JP-A-6
0-174879). However, although these multi-layer coated steel sheets do not contain metal powder such as Zn powder in the coating film, the powdering resistance is greatly improved, but still the corrosion resistance required for the current steel sheets for automobiles is improved. I didn't reach the level.

[0006] Therefore, recently, of course, in addition to the research on the improvement of the properties of the chromate film and the organic film, various studies have been made for the further improvement of the properties of the lowermost zinc-based plated steel sheet itself. It has come to be done from a viewpoint. As a result, for example, the Ni content is 9
~ 20% (Hereafter,% representing the component ratio shall be% by weight)
A surface-treated steel sheet having a Ni-Zn (γ layer) alloy plating layered with a chromate treatment layer and a conductive paint layer (JP-A-58-21).
No. 0192), the Fe content on the γ-phase Ni-Zn alloy plating layer is
A surface-treated steel sheet having a 10 to 40% Fe-Zn alloy plating layer, a chromate treatment layer, and a conductive pigment layer as a multilayer (JP-A-58-58).
No. 210190), and a surface-treated steel sheet (JP-A-61-84381) in which a chromium-treated layer and a polymer coating layer are laminated on a Ni-Zn alloy plated layer having a Ni content of 1 to 3%. Each has been proposed.

Further, for example, as disclosed in Japanese Patent Laid-Open No. 63-203778, fine particles of 5 μm or less such as oxides, carbides and nitrides of Si, Al and the like are dispersed in Zn or Zn alloy plating to form the plating film itself. Along with improving the characteristics,
A surface-treated steel sheet in which a chromate-treated layer and an organic coating film are formed on the plated surface is also proposed.

Certainly, these techniques have made it possible to secure steel sheets exhibiting even more excellent corrosion resistance, but the "corrosion resistance" improved by the above-mentioned technologies is mainly "perforation resistance". According to the study by the present inventors, it has been clarified that each of the surface-treated steel sheets does not always have sufficient performance as an automobile steel sheet in terms of "outer surface rust resistance". Here, "outer surface rust resistance" is a performance that indicates "difficulty in blistering of the coating film" that occurs when the coating film on the outer surface of the automobile exterior is damaged by stones, scratches, etc. Needless to say.

Of course, various proposals have been made for plated steel sheets aimed at the outer surface rust resistance, but even in that case, both the outer surface rust resistance and the perforation resistance, and in addition to these, press working The current situation is that no surface-treated steel sheet that also fully satisfies the requirements has been found.

In view of the above, the present invention aims not only to exhibit sufficient "perforation resistance", but also to resistance to peeling of the plating due to stone chips (low temperature chipping resistance: It is to realize a highly corrosion-resistant surface-treated steel sheet that is excellent in "outer surface rust resistance" including impact resistance (adhesion resistance) and also has good "press workability", which is sufficiently satisfactory as a steel sheet for automobiles. It was

[0011]

The present invention has been completed based on the results of research conducted by the present inventors, which have been repeated while repeating many experiments to achieve the above object.
"As shown in Fig. 1, adjacent to the steel plate surface, crack width: 0.01 to 0.5 µm, crack density: crack area fraction 10 to 60%, and there are non-directional" fine cracks "Zn-Ni
It has a system alloy plating thin underlayer, and A) a Zn plating layer on one surface of the steel sheet, or the Ni content is 10% or less (hereinafter,% representing the component ratio is% by weight) and the η phase Zn with
-Ni-based alloy plating layer: 10 to 50 g / m ² , B) Zinc phosphate coating layer: 0.1 to 5 g / m ² , multiple layers in this order, and a) Zn plating layer on the other side, Alternatively, a plating layer of Zn-Ni alloy having a Ni content of 10% or less and having an η phase: 10 to 50 g / m ² , b) Zinc phosphate coating layer: 0.1 to 5 g / m ² , c) Chrome G) Treated layer: Cr content of 30-300 mg / m ² , d) Protective resin film layer: 0.2-2.0 μm, provided in this order as multiple layers to protect the outer surface from rust and puncture. The major feature is that "a surface-treated steel sheet that has both excellent openability and press workability has been realized." Also, as shown in Fig. 2, crack width: 0.01 to 0.5 μm, crack density: cracks adjacent to the steel sheet surface Area fraction of 10-60%, Zn-Ni with non-directional "fine cracks"
A alloy-plated thin underlayer, and A) a Zn-plated layer on one surface of the steel sheet, or a Zn-Ni-based alloy plated layer having a η phase with a Ni content of 10% or less: 10 to 50 g / m ² , B) Detachable solid lubricating coating layer: 0.5 to 3.0 μm, in this order, and a) a Zn plating layer on the other side, or a Ni content of 10% or less Zn-Ni alloy plating layer having η phase: 10 to 50 g / m ² , b) Chromate treatment layer: Cr content of 30 to 300 mg / m ² , c) Protective resin film layer: 0.2 to 2.0 μm, By providing multiple layers in this order, we have achieved a surface-treated steel sheet that is excellent in both external rust resistance including impact adhesion, perforation resistance and press workability ”.

Here, the "Zn plating" and the "Zn-Ni alloy plating" (both of which form a thin underlayer having microcracks and which form a plating layer having a Ni content of 10% or less) Means not only "pure Zn plating" and "Zn-Ni alloy plating" but also Co, which is a well-known corrosion resistance improving element.
It also means inclusion in the range of 0.3% or less.

The "zinc phosphate coating layer" is sufficient if it is formed by a known zinc phosphate treatment. In forming the zinc phosphate coating layer, for example, a dipping type or spray type method may be appropriately adopted. good.

Further, the "film removal type solid lubricating film layer" is
Fatty acids, fatty acid esters, fatty acid soaps, metal soaps, alcohols as lubricants for conventionally known dry or bake-curable coating film forming components such as acrylic resins, epoxy resins, melamine resins, phenol resins, etc. It can be formed by coating and drying a mixture of one or more of fine powder, polyethylene fine powder, graphite, molybdenum disulfide, fluororesin powder and the like.

Further, the "chromate-treated layer" may be formed by a known chromate treatment, and the formation thereof may be performed by, for example, electrolytic chromate treatment or coating type chromate treatment. Alternatively, the immersion chromate treatment method may be appropriately adopted.

The resin composition of the "protective resin film layer" may be epoxy resin, polyester resin, melamine resin, vinyl resin, styrene resin, acrylic resin, polyurethane resin, phthalic acid resin, etc., alone or modified. Known materials such as rust-preventive pigments such as BaCrO ₄ and coloring pigments such as Fe ₂ O ₃ or pigments such as SiO ₂ are optionally included.

The high-corrosion-resistant surface-treated steel sheet according to the present invention can be manufactured as follows. That is,
First, the surface of the degreased and pickled steel sheet is plated with Zn-Ni alloy (preferably Zn-Ni alloy with Ni content of 10% or less) 0.1-5 g /
It is applied with an extremely thin thickness of m ² , and then electrolessly dipped in an acid solution such as a Zn-Ni alloy plating solution or subjected to anodic electrolysis in the electrolytic solution to preferentially dissolve Zn in the plating film. As a result, minute cracks having no directivity are generated in the ultrathin plating film, and the plating undercoat layer having a relatively high Ni content is obtained. Next, electroplating is performed by the same electrolytic treatment operation as in the production of a normal Zn-Ni alloy plated steel sheet.

Thereafter, one surface is coated with a zinc phosphate treatment or a film-removing type solid lubricating coating in a conventional manner, and the other surface is subjected to a conventional chrome treatment and a protective resin coating. Is applied. In this case, the zinc phosphate treatment is applied to the one surface at the same time as the zinc phosphate treatment on the other surface, and the other surface is treated with chrome on the zinc phosphate treated layer.
The workability is to provide a coating film and a protective resin film,
It is advantageous in terms of performance.

Next, the reason why the component composition of the plating layer, the coating weight, etc. in the highly corrosion-resistant surface-treated steel sheet of the present invention are numerically limited as described above will be described in detail together with its action.

[Function] [A] Zn-Ni alloy plating underlayer Zn-Ni alloy plating thin underlayer is applied to improve the plating adhesion and to improve the impact resistance and processing adhesion of the plating film. To be done. The fine cracks in the thin underlayer play an extremely important role in improving the adhesion of the plating through the anchor effect (anchoring effect).
When the thickness is less than μm, even when the Zn-Ni alloy is overplated, the cracks are not plated even in the interior and good plating adhesion cannot be obtained. On the other hand, when the width of the microcracks exceeds 0.5 μm, the above-described effect as the underlayer cannot be obtained, and improvement in plating adhesion cannot be expected. Therefore, the width of the microcracks in the underlayer was set to 0.01 to 0.5 μm.

The fine crack width can be easily adjusted by adjusting the time for immersing it in an acid solution (plating solution or the like) after the initial thin plating or the time for anodic electrolytic treatment in the acid solution. .

Further, the existence density of microcracks in the underlayer also has a great influence on the improvement of the plating adhesion, but if the density is less than 10% in area fraction, the Zn-
Since the area where the Ni-based alloy plating penetrates into the cracks is small, a sufficient anchoring effect cannot be obtained, and the desired impact resistance improving effect cannot be obtained. On the other hand, even when the density of the minute cracks exceeds 60% in terms of area fraction, the effect of the base treatment cannot be obtained, and it does not contribute to the improvement of the adhesion. Therefore, the density of the microcracks is 10 to 10.
It was set at 60%.

This fine crack density also increases as the time for immersing it in the acid solution (plating solution or the like) after the initial thin plating or for the time of anodic electrolytic treatment in the acid solution increases, so the density is 10 to 60. In order to control the ratio to%, the amount of dissolution of the initial plating film may be adjusted during immersion in an acid solution or during anodic electrolysis in the acid solution.

In order to secure a better plating adhesion, the length of the microcracks is adjusted to 10 μm by adjusting the processing conditions such as the dissolution time of the initial plating.
It is preferable to regulate as follows (however, since cracks are generally branched, “crack length” here means “length along the crack between crack branch points”. ).

Furthermore, since the width and density of the microcracks in the underlayer are closely related to the "dissolved amount of Zn by non-electric current immersion", in other words, "the Ni content of the film after non-electric current immersion",
Even if the crack condition is not directly controlled, the impact resistance can be improved as a result by controlling the Ni content of the thin underlayer.

The Ni content of this thin underlayer also affects the plating adhesion in relation to the "Ni content of the plating layer immediately above", so that from the viewpoint of ensuring better adhesion, "Ni content of the base layer" is "Ni of the plating layer immediately above
It can be said that it is preferable that the content ratio is 1.2 to 5 times.

[B] Each treatment layer on the "one side" side (a) Plating layer The "one side" side of the multilayer surface-treated steel sheet according to the present invention is applied, for example, as a steel sheet for automobiles, etc. The outer surface side has a particularly remarkable effect. However, in order to ensure sufficient outer surface rust resistance, the plating layer applied to this "one surface" side has "Zn plating or Ni content Zn-Ni alloy plating with η phase of 10% or less "or 0.3
Alloy plating containing less than 50% Co is applied.
-In the case of Ni-based alloy plating, the Ni content exceeds 10% and η
When the phases disappear, the external surface rust resistance becomes poor. this is,
It is considered that the corrosion of the steel sheet as the base material is promoted by the local battery action of the Ni residue that accompanies the progress of corrosion. As is clear from the results of Examples described later, the Ni residue has a large effect when the coating film is scratched to reach the steel sheet with a considerably wide width (about 0.8 mm).

Further, if the coating weight of the plating is less than 10 g / m ² , the effect of improving the external surface rust resistance is not sufficient, while if the coating weight of more than 50 g / m ² , the improvement effect is commensurate with the cost increase. Cannot be secured. Therefore, the coating weight of the "one surface" side is limited to 10 to 50 g / m ² .

(B) Zinc Phosphate Coating Layer As described above, good performance can be secured for the outer surface rust resistance by adjusting the plating composition. However, for press workability, the Ni content is within the above range. (0 to 10%) is not preferable because the η phase is precipitated in the plating layer. That is, when the η phase is deposited, the hardness of the plating layer becomes soft,
For this reason, there arises a problem that the surface sliding resistance during press working becomes high and cracks occur. However, by providing the zinc phosphate coating layer on the plating layer, it is possible to effectively solve this problem.

Here, the amount of zinc phosphate film formed is 0.1 g /
If it is less than m ^2, it is not possible to secure a sufficient effect of lowering the surface sliding resistance. On the other hand, if the coating amount of the coating layer exceeds 5 g / m ² , the effect commensurate with the cost increase cannot be expected. . Therefore, the amount of the zinc phosphate coating layer provided on the plating layer is limited to 0.1 to 5 g / m ² .

(C) De-filming type solid lubricating coating layer "Zn plating" or having a η phase with a Ni content of 10% or less
Regarding the press workability of "Zn-Ni alloy plated steel sheet",
It is also possible to effectively solve the problem by providing a "film removal type solid lubricating film layer" instead of the above-mentioned "formation of zinc phosphate film layer". In the case of zinc phosphate treatment, it was advantageous to form a coating layer on both sides of the plated steel sheet from the viewpoint of workability as well, but in the case of a de-filming type solid lubricating coating layer, formation on only one side Is also easy,
"External surface side" where lubricity during pressing is a particular problem,
It can be said that it is advantageous to provide it on only one side.

As the coating material for forming the film-removing type solid lubricating film, as described above, acrylic resin, epoxy resin,
In addition to conventionally known dry or bake-curable coating film forming components such as melamine resins and phenol resins, fatty acids, fatty acid esters, fatty acid soaps, metal soaps, alcohols, polyethylene Powder, graphite,
A mixture of molybdenum disulfide, fluorine resin powder, etc. is used, but if the thickness of the coating layer formed by this is less than 0.5 μm, a sufficient reduction effect of surface sliding resistance is secured. No, on the other hand, the thickness of the film layer is 3.0
If the thickness exceeds μm, it cannot be expected to improve the effect commensurate with the cost increase. Therefore, when a film-removing solid lubricating film layer is provided on the plating layer on the "one surface" side (a side suitable as an outer surface) instead of the zinc phosphate film layer, the film-removing solid lubricating film layer It was decided to adjust the thickness to 0.5 to 3.0 μm. When the zinc phosphate treatment is performed in the coating process after the press working, the defilming type solid lubricating coating layer needs to be completely removed in the degreasing process.

[0032] [C] wherein the "other face" side of the treated layer of the "other side of the face" side (a) multi-layer surface-treated steel sheet according to the plating layer present invention, for example when applied as automotive steel sheets It is preferable that the inner surface side is the same as the "other surface" side, but the "other surface" side has the same composition as that of the "one surface" side, namely "Zn plating," or "Ni content is 10% or less and η A Zn-Ni alloy plating layer having a layer or an alloy plating layer containing 0.3% or less of Co is provided. This of course ensures corrosion resistance such as perforation resistance, but it is also very advantageous in terms of plating workability because the plating layers provided on both sides have the same composition. And, the coating weight at this time is the same as the case of the "one side" side.
Adjusted to 10-50g / m ₂ .

(B) Zinc phosphate coating layer When a zinc phosphate coating layer is provided on the plating layer on the "one side" side to improve the press workability, the "other side" is considered from the workability side. It is advantageous to provide a similar zinc phosphate coating layer on the plating layer on one side, which does not have a particularly adverse effect on the characteristics on the "other surface" side, but also on the "one surface" side. It can be said that it is also effective in terms of press workability as in the side. The amount of zinc phosphate film formed here is also adjusted to 0.1 to 5 g / m ₂ for the same reason as in the case of the "one surface" side.

(C) Chromate treated layer As described above, in the present invention, "Zn plating" on the "other surface" side of the steel sheet, or "Zn having a Ni content of 10% or less and an η layer" is also used. -Ni alloy plating "or Co less than 0.3%
`` Alloy plating containing the '' layer is provided to ensure corrosion resistance such as puncture resistance, but in the case of Zn-Ni alloy plating, if the Ni content is 10% or less, In terms of sex, there are some cases in which some difficulties are not recognized. Therefore, in the present invention, in order to further improve the perforation resistance, the "chromate treatment layer" and the "protective resin" are provided on the plating layer on the "other surface" side or the zinc phosphate coating layer provided thereon. A film layer "is formed.

Here, if the amount of formation of the chromate treatment layer is less than 30 mg / m ^{2 based on the} amount of Cr, the desired perforation resistance cannot be ensured, while the amount of formation is 300 mg in terms of Cr amount. / m
^If it exceeds ² , the coatability of the electrodeposition will be deteriorated, so the amount of formation of the chromate layer is 30 to 300 mg / m ² in terms of Cr amount.
Limited.

(D) Protective resin coating layer The resin coating material for the protective coating is epoxy resin, polyester resin, melamine resin, vinyl resin, styrene resin, acrylic resin, polyurethane resin, phthalic acid resin, etc., alone or modified. And rust preventive pigments such as BaCrO _{4 and} Fe ₂
A known pigment containing a coloring pigment such as O ₃ or a pigment such as SiO ₂ is optionally used, but if the thickness of the protective resin film layer is less than 0.2 μm, sufficient perforation resistance is secured. On the other hand, if the thickness exceeds 2.0 μm, the electrodeposition coatability and spot weldability deteriorate, so the thickness of the protective resin film layer was limited to 0.2 to 2.0 μm.

Next, the effects of the present invention will be described more specifically by way of examples.

EXAMPLES Example 1 A steel plate having a plate thickness of 0.8 mm was prepared and treated as follows to obtain a multi-layer surface-treated steel plate. That is, first, after performing alkaline degreasing and pickling of the steel sheet, initial plating was performed using the sulfuric acid bath shown in Table 1 (for some of them, Co ions were also added), and subsequently the same plating as that used for initial plating The substrate was immersed in a plating solution without electricity to form a base treatment layer having cracks of a predetermined width and a predetermined density.

Then, a plating solution of Zn with a predetermined thickness is similarly used.
-Ni alloy plating was applied. The Ni content in the plating film is adjusted by controlling the concentration of Zn ²⁺ and Ni ²⁺ for electroplating, and the coating weight is adjusted by controlling the amount of electricity. It was

[0039]

Next, this plated steel sheet was washed with water and dried, and then spray-process zinc phosphate treatment was performed to form a zinc phosphate coating layer on both surfaces. Next, the steel sheet on which the zinc phosphate coating layer is formed is washed again with water and dried,
On the side supposed to be the inner surface, a coating type chromate treatment liquid was applied, baked and dried. During application of the chromate treatment liquid, the peripheral speed ratio and touch pressure of the roll coater roll and the applicator roll were changed, and the concentration of the chromate treatment liquid was also changed. The formation amount of the chromate-treated layer (Cr deposition amount) was adjusted.

Further, in order to form a protective resin film on the surface of the steel sheet after the chromate treatment, a clear coating was applied by the roll coater method. In addition, the film thickness control of the protective resin film,
It was performed by adjusting the amount of solvent in the resin and adjusting the peripheral speed ratio of the applicator roll and the pickup roll.

Then, with respect to the multi-layer surface-treated steel sheet produced in this manner, the outer surface rust resistance, perforation resistance, press slidability, electrodeposition coating property, and impact resistance were investigated. The results are shown in Tables 2 and 3.

[0043]

[Table 2]

[0044]

[Table 3]

Here, each of the above investigations was carried out in the following manner. External rust resistance evaluation procedure A) Preparation of painted plate test pieces. Zinc phosphate treatment {PBL-3020 (trade name of Nippon Parkerizing Co., Ltd.)} → Cationic electrodeposition coating {U-600 (trade name of Nippon Paint Co., Ltd.): 20 μm} → Medium / top coating: 35 μm of melamine alkyd resin, respectively. B) Put a cross cut using a saw blade as shown in Fig. 3 on the coated plate test piece. C) Outdoor exposure test (performed for 1 year while spraying 5% NaCl twice a week). D) The blistering width of the coating film (maximum creep width on one side from the cross cut shown in FIG. 3) was measured to evaluate the outer surface rust resistance. The defilming type solid lubricating film layer formed on the side supposed to be the outer surface for improving lubricity was completely removed in the degreasing step in the zinc phosphate treatment step.

Evaluation of perforation resistance The uncoated plate test pieces after degreasing with alkali were sealed with polyester tape on the back surface and the edge part, and the following cycle of "corrosion accelerated test (1 cycle: 24 hr)" The maximum corrosion depth of the corroded part after 200 cycles.
Evaluate by measuring with a tar. Salt spray (6hr) → Dry (2hr at 50 ℃) → Wet (95% at 50 ℃)
16hr).

Evaluation of press slidability In order to investigate slidability between the plated surface and the tool surface, a method of determining the friction coefficient of the plated surface by the "improved Bowden test method" which is an improvement of the Bowden test as shown in FIG. It was adopted and the sliding characteristics were evaluated by it.

Evaluation of Electrodeposition Paintability For example, even when the inside of equipment such as a trunk lid or bonnet of an automobile is opened, the paint finish leads to the evaluation of the product visually. Therefore, the finish of electrodeposition coating was visually observed on both sides of the surface-treated steel sheet according to the example, and five levels (◎ ... excellent, ○ ... good, △ ... acceptable,
It was evaluated as “Poor”, “Poor”, and “Poor”.

Impact Resistance Adhesion Evaluation After a test piece of 70 mm × 150 mm was coated with 3 coats for automobile (total film thickness 100 μm), ASTM D- was used at a low temperature of −20 ° C. using a gravelometer. The chipping test specified in 3170-74 was performed, and the plating peeling area ratio at that time was evaluated according to the following criteria. 4 ... No plating peeling, 3 ... Plating peeling area ratio is less than 0.2%, 2 ... Plating peeling area ratio is 0.2% or more and less than 1%, 1 ... Plating peeling area ratio is 1% or more.

As is clear from the results shown in Tables 2 and 3, the surface-treated steel sheet according to the present invention shows excellent results in any property investigation, and the recent anticorrosion steel sheet for automobiles, etc. It can be seen that the comparative steel sheet, which does not satisfy the conditions specified in the present invention, does not have sufficient characteristics, while the strict requirements for the above are sufficiently satisfied.

Example 2 A steel plate and a sulfuric acid bath (composition shown in Table 1) similar to those in Example 1 were prepared, and these were used to electroplating Zn with different Ni contents in the same manner as in Example 1. Steel plate or Zn-
A Ni-based alloy electroplated steel sheet was obtained.

Next, this plated steel sheet was washed with water and dried, and then the coating type chromate treatment liquid was applied to the side supposed to be the inner surface and baked and dried. When the chromate treatment liquid is applied, the peripheral speed ratio and touch pressure of the roll coater roll and the applicator roll are changed in the same manner as in Example 1, and the chromate is applied. The concentration of the chromate treatment layer (Cr adhesion amount) was adjusted by changing the concentration of the treatment liquid. Then, in order to form a protective resin film on the steel plate surface after the chromate treatment, the clear paint was applied by the same method as in Example 1.

On the other hand, a film-removal type solid lubricating film layer was formed on the plating layer on the side supposed to be the outer surface. The film-removing type solid lubricating film layer was formed by a roll coater method. Paint (melamine alkyd resin mixed with fluororesin powder)
Was applied and baked to dry. When applying the film-removing solid lubricant paint, the roll coat
Amount of de-filming type solid lubricating film layer formed by changing the peripheral speed ratio and touch pressure of the water pickup roll and the applicator roll, and also changing the concentration of the solid lubricant (fluorine resin powder) Was adjusted.

Then, with respect to the multi-layer surface-treated steel sheet produced in this way, outer surface rust resistance, perforation resistance, press slidability, and electrodeposition paintability were investigated. Each of these investigations was carried out. The procedure was the same as in Example 1. The results are shown in Tables 4 and 5.

[0055]

[Table 4]

[0056]

[Table 5]

From the results shown in Tables 4 and 5, the surface-treated steel sheet according to the present invention has excellent performances in all of outer surface rust resistance, perforation resistance, press slidability and electrodeposition coating property. It can be confirmed that it has.

[0058]

[Summary of Effects] As described above, according to the present invention, not only the corrosion resistance such as the perforation resistance and the outer surface rust resistance but also the
We can provide surface-treated steel sheets with excellent properties such as press workability, electrodeposition paintability, and impact adhesion resistance, and further improve their performance by applying them to rust-preventing steel sheets for automobiles and home appliances. It is possible to bring about an extremely useful effect in the industry such that it can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of a surface-treated steel sheet according to the present invention.

FIG. 2 is a schematic configuration diagram of another example of the surface-treated steel sheet according to the present invention.

FIG. 3 is an explanatory diagram of an evaluation method of outer surface rust resistance.

FIG. 4 is a schematic explanatory view of an improved Bowden test method.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Reference number within the agency FI Technical indication C25D 5/48 6919-4K 11/34 303 7179-4K 11/38 C 7179-4K

Claims (3)

[Claims] 1. A Zn-Ni which has a non-directional "micro crack" having a crack width: 0.01 to 0.5 μm, a crack density: a crack area fraction of 10 to 60% adjacent to a steel plate surface.
Having a thin base alloy-plated base layer, and A) a Zn-plated layer on one surface of the steel plate, or a Zn-Ni-based alloy plated layer having a η phase with a Ni content of 10% by weight or less: 10 to 50 g / m ² , B) Zinc phosphate coating layer: 0.1 to 5 g / m ² , multiple layers in this order, and a) Zn plating layer on the other side, or Ni content of 10 wt% or less Zn-Ni alloy plating layer having η phase: 10 to 50 g / m ² , b) Zinc phosphate coating layer: 0.1 to 5 g / m ² , c) Chromate treatment layer: 30 to 30 in terms of Cr amount 300 mg / m ² , d) Protective resin film layer: A high corrosion-resistant surface-treated steel sheet excellent in impact adhesion, characterized by comprising a plurality of layers of 0.2 to 2.0 μm in this order. 2. A Zn-Ni which has a non-oriented "fine crack" having a crack width: 0.01 to 0.5 μm, a crack density: a crack area fraction of 10 to 60%, adjacent to the steel plate surface.
Having a thin base alloy-plated base layer, and A) a Zn-plated layer on one surface of the steel plate, or a Zn-Ni-based alloy plated layer having a η phase with a Ni content of 10% by weight or less: 10 to 50g / m ² , B) Detachable solid lubricant film layer: 0.5 to 3.0 μm, in this order, and a) a Zn plating layer on the other surface, or a Ni content of 10 wt% or less. Zn-Ni alloy plating layer having η phase: 10 to 50 g / m ² , b) Chromate treatment layer: 30 to 300 mg / m ^{2 in} Cr amount, c) Protective resin film layer: 0.2 to 2.0 A high-corrosion-resistant surface-treated steel sheet having excellent impact resistance and adhesion, which is characterized by comprising multiple layers of μm, in this order. 3. The impact resistance according to claim 1, wherein the "Ni content of the Zn-Ni alloy plating thin underlayer" is 1.2 to 5 times the "Ni content of the plating layer immediately above". Highly corrosion-resistant surface-treated steel sheet with excellent adhesion.