JPH0478529A - Highly corrosion-resistant surface-treated steel sheet - Google Patents

Abstract

PURPOSE:To improve corrosion resistance against hole-producing, outer face corrosion resistance and press processing by providing a Zn plating layer or a specified Zn-Ni alloy plating layer and a demembrane-type solid lubricating film layer on one face of a steel sheet in this order and providing a specified Zn-Ni alloy plating layer, a chromate treatment layer and a protective resin film layer on another face in this order. CONSTITUTION:A highly corrosion-resistant surface treatment steel sheet provides a double layer consisting of a Zn plating layer or a Zn-Ni alloy plating layer (10-50 g/m<2>) with an Ni content of 10 wt.% or less and a demembrane-type solid lubricating film layer (0.5-3.0mum) on one of a steel sheet in this order and provides a multi-layer consisting of a Zn-Ni alloy plating layer (10-50 g/m<2>) with an Ni content of 10-40 wt.%, a chromate treatment layer (30-300 gm/m<2> in terms of Cr content) and a protective resin film layer (0.2-2.0mum) on another face in this order. A highly corrosion-resistant surface treatment steel sheet with both excellent drilling resistance and outer face corrosion resistance and good press processing.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a highly corrosion-resistant surface-treated steel sheet suitable for use in automobiles, home appliances, etc.

<Conventional technology and its issues> In recent years, corrosion resistance (porous corrosion resistance) of automotive steel sheets has been improved.

The requirements for exterior rust resistance (external rust resistance) have become more sophisticated over the years, and the conventionally used "simple cold-rolled steel sheets" have been replaced by "galvanized steel sheets" and "zinc-based alloy plated steel sheets."
The trend of using .

However, in environments where there is a tendency to come into contact with corrosive substances, such as areas where rock salt is sprayed to prevent roads from freezing in winter, even if plated steel sheets such as those mentioned above are used, the amount of coating may be excessive. It was pointed out that sufficient corrosion resistance could not be obtained unless the However, when the amount of plating deposited is increased, the plating layer becomes more likely to peel off in powder form (powdering) and peel off (flaking) during press working, so there is a problem that press workability is significantly inhibited.

Therefore, in order to deal with such problems, a metal-organic multilayer coated steel sheet has been devised in which a plated steel sheet is subjected to chromate treatment and anti-rust coating.

However, the proposal in the initial process was
This issue relates to "rust-proof steel sheets coated with zinc clinch coating" as seen in Publication No. 30, and the problem is that the level of improvement in corrosion resistance is not yet sufficient, and that the Zn powder contained in the coating film peels off during press working. Therefore, the powdering resistance could not be improved to the desired level.

Therefore, a multi-layer coated steel sheet was proposed, which was made by applying two layers of a chromate film and an organic composite silicate film on a zinc-plated steel sheet (Japanese Unexamined Patent Publication No. 57-108212).
No., JP-A-58-224174, JP-A-601748
No. 79, etc.). However, these multilayer wave rf! Although the powdering resistance of steel sheets is greatly improved because they do not contain metal powders such as Zn powder in the coating, the corrosion resistance still does not reach the level of corrosion resistance required of current automotive steel sheets. .

For this reason, recently, in addition to research on improving the properties of chromate films and organic films, studies have been conducted from various perspectives to further improve the properties of the bottom layer zinc-based plating itself. It has become. As a result, for example, the Ni content is 9 to 20%.
(Hereinafter, % representing the component ratio is expressed as weight %)
Surface-treated steel sheet with multiple layers of chromate treatment layer and conductive paint layer on Zn (single layer) alloy plating (Japanese Patent Laid-Open No. 58-210
No. 192), a surface-treated steel sheet in which a Fe-Zn alloy plating layer with an Fe content of 10 to 40%, a chromate treatment layer, and a conductive pigment layer are multilayered on a γ-phase Ni-Zn alloy plating layer (Japanese Patent Application Laid-Open No. No. 58-210190).

A surface-treated steel sheet (JP-A-61-84381) has been proposed in which a chromate treatment layer and a polymer coating layer are multilayered on a Ni--Zn alloy plating layer with an Nj content of 1 to 3%.

Furthermore, for example, as JP-A No. 63-203778, etc., Z
By dispersing microparticles of 5 or less particles of oxides such as Sit Ai, carbides, nitrides, etc. during n or Zn alloy plating, we aim to improve the characteristics of the plating film itself, and also add a chromate treatment layer and organic A surface-treated steel sheet with a coating film has also been proposed.

It is true that these technologies have made it possible to secure steel sheets that exhibit even better corrosion resistance, but the "corrosion resistance" improved by the above-mentioned technologies is primarily "porosity resistance." According to the studies conducted by the present inventors, it has become clear that each of the above-mentioned surface-treated steel sheets does not necessarily have sufficient performance as a steel sheet for automobiles in terms of "external surface rust resistance."

Here, "external rust resistance" refers to the performance that indicates the "resistance of the paint film to blistering, etc." that occurs when the paint film on the outside of the automobile exterior is damaged by stone chips, scratches, etc. Needless to say.

Of course, various proposals have been made for plated steel sheets that aim for external rust resistance, but even in these cases, there is still no surface-treated steel sheet that fully satisfies both external rust resistance and pitting resistance. The current situation was that it had not been discovered.

Therefore, the purpose of the present invention is to provide a highly corrosion-resistant surface treatment that is excellent in both pitting resistance and external rust resistance, and also has good press workability, and is sufficiently satisfactory for use as steel sheets for automobiles, etc. The goal was to realize steel plates.

Means for Solving the Problems> The present invention has been completed based on the research results of the present inventors through repeated numerous experiments in order to achieve the above object. a) Zn plating layer or plating layer of Zn-Ni alloy with Ni content of 10% or less: 10 to 50 g/m
.

b) Removable solid lubricant film layer: has multiple layers of 0.5 to 3.0 μm in this order, and the other surface has () a Ni content of 1
0-40% Zn-Ni alloy plating layer: 10-5
0g/rd.

0) Chromate treatment layer = Cr amount of 30 to 300 mg/
rr? c) Protective resin film layer: 0.2 to 2.0 mark multilayer,
Or a) Zn plating layer or Zn-Ni alloy plating layer with Ni content of 10% or less: 10 to 50 g/n (
.

o) Zn-Ni alloy plating layer with Ni content of 10-40%: 0.5-20 g/n (.

c) Chromate treatment layer 2 Cr amount: 30 to 300 mg/
n(.

2) By constructing a surface-treated steel sheet by providing multiple layers of protective resin film layer = 0.2 to 2.0 μm in this order,
It is characterized by significantly improved hole resistance, external rust resistance, and press workability.

In addition, FIG. 1 is a conceptual diagram explaining the structure of a highly corrosion-resistant surface-treated copper plate according to the present invention, and FIG.
b) shows different embodiments.

Here, the term "rZn or Zn-Ni alloy (both with Ni content of 10% or less and 10-40%)" refers to not only pure Zn and Zn-Ni alloy, but also those with improved corrosion resistance. It also means those containing the element Co in a range of 0.3% or less.

Further, the "chromate treatment layer" may be formed by any of the known electrolytic chromate treatment, coating type chromate treatment, or immersion type chromate treatment.

The resin composition of the "protective resin film layer" is as follows:
BaCr is added to epoxy resins, polyester resins, melamine resins, vinyl resins, 5-styrene resins, acrylic resins, polyurethane resins, phthalate resins, etc. alone or in modified form.
Rust preventive pigments such as O4, colored pigments such as FezO:+, or S
A known material containing a pigment such as iO2, if necessary, can be used.

Further, the "removable solid lubricating film layer" is made of acrylic resin, epoxy resin, or melamine resin.

In addition to conventionally known drying or baking-curing coating forming components such as phenolic resins, fatty acids, fatty acid esters, fatty acid soaps, and metal soaps are used as lubricants.

Alcohol, polyethylene fine powder, graphite.

It can be formed by applying and drying a mixture of one or more of molybdenum disulfide, fluororesin powder, and the like.

Next, the reason why the composition of the plating layer, the plating weight, etc. in the highly corrosion-resistant surface-treated steel sheet of the present invention is numerically limited as described above will be explained in detail together with the effect thereof.

<Operation> mμ] L times (8) Plated layer The "one surface" side of the multilayer surface-treated steel sheet according to the present invention is the outer surface side when it is applied as a steel sheet for automobiles, for example. However, in order to ensure sufficient external rust resistance, the plating layer applied to one side J is coated with Zn plating or Ni content of 10%.
Zn-Ni alloy plating below or 0.3% on these
The following alloy plating containing CO is applied, but Z
In the case of n-Ni alloy plating, the Ni content is 10%.
Exceeding this value will result in poor external rust resistance. This is thought to be because the corrosion of the steel plate, which is the base material, is accelerated by the local battery action of the Ni residue that occurs as the corrosion progresses. As is clear from Fig. 2, which summarizes the results of the examples described later, when the coating film is scratched with a fairly wide width (approximately 0.8w) reaching the steel plate, the Ni residue is removed. has a large influence. Here, the symbols (numbers and alphabets) in FIG. 2 correspond to the type symbols of the sample materials in Table 2, which will be described later.

Furthermore, if the basis weight of plating is less than 10g/rd, the effect of improving the external rust resistance will not be sufficient;
If r4 is exceeded, it will not be possible to secure an improvement effect commensurate with the cost increase. Therefore, the plating weight on the "one side" side was limited to 10 to 50 g/n.

(b) Removable solid lubricant film layer As mentioned above, good performance can be ensured with respect to external rust resistance by adjusting the plating composition, but with regard to press workability, the above Ni content range ( 0-10%
) is not preferable because the η phase precipitates in the plating layer.

That is, when the η phase precipitates, the hardness of the plating layer becomes softer, which causes problems such as increased surface sliding resistance during press working and generation of cracks. However, this problem can be effectively solved by providing a removable solid lubricant film layer on the plated layer.

Here, as the paint for forming a removable solid lubricating film, as mentioned above, conventionally known drying or baking hardening type paint film forming components such as acrylic resin, epoxy resin, melamine resin, phenol resin, etc. and fatty acids and fatty acid esters as lubricants.

Fatty acid soap, metal soap, alcohol 1 polyethylene fine powder, graphite, molybdenum disulfide.

A mixture of one or more types of fluororesin powder etc. is applied, but the thickness of the film layer formed by this is 0.5
If the thickness is less than μm, a sufficient effect of lowering the surface sliding resistance cannot be ensured, while if the thickness of the film layer exceeds 3.0 m+, an improvement in effect commensurate with the increase in cost cannot be expected. Therefore, the thickness of the removable solid lubricant film layer provided on the plating layer on the "one surface" side (the side suitable as the outer surface) was limited to 0.5 to 3.0 knots.

Note that this removable solid lubricant film layer needs to be completely removed in the degreasing process when the zinc phosphate treatment is performed in the painting process after press working.

The "other surface" side of the multilayer surface-treated steel sheet according to the present invention is preferably the inner surface side when it is applied as a steel sheet for automobiles, etc. The plating layer applied to this "other surface" side is coated with "Zn-Ni alloy plating with a Ni content of 10 to 40%" or 0.3% to this in order to ensure sufficient porosity resistance. % or less, or [Zn plating with the same composition as the one side, or Zn-Ni with a Ni content of 10% or less.
On the lower layer consisting of "alloy plating" or alloy plating containing 0.3% or less of Go,
0-40% ZnNi alloy plating” or 0.3% to this
The following multi-layer coating containing Co-containing alloy plating as an upper layer is applied.

Here, it is better to provide "Zn-based plating or a Zn-Ni-based alloy plating layer with Ni content of 10% or less" as a lower layer of "Zn-Ni-based alloy plating layer with Ni content of 10 to 40%." This is a good method when you want to ensure good corrosion resistance, but in this case, the Ni content of the lower layer plating is 10%.
If the coating weight of the lower layer plating is less than 10 g/m, it will not be possible to secure the desired corrosion resistance improvement effect. Further, even if the basis weight of the lower layer plating exceeds 50 g/rd, it is not possible to obtain an effect of improving corrosion resistance commensurate with the increase in cost.

On the other hand, a "Zn-Ni alloy plating layer with a Ni content of 10 to 40%" is essential to ensure the desired porosity resistance, but the mechanism by which the Ni content affects the porosity resistance is unknown. is still not fully clear. However, it is speculated that this may be related to the reactivity with the chromate applied as an upper layer of the plating layer. As is clear from FIG. 3, which summarizes the results of the examples described later, this plating layer can withstand even if the Ni content is less than 10% or exceeds 40%. The porosity deteriorates, making it impossible to secure the desired performance. Here, the symbols (numbers and alpha vents) in FIG. 3 correspond to the type symbols of the sample materials in Table 2, which will be described later.

The basis weight of the "Zn-Ni alloy plating layer with a Ni content of 10 to 40%" is less than 10 g/rd when there is no lower layer plating, and 0.0 g/rd when there is a lower layer plating. If it is less than 5 g/%, the desired effect of improving porosity resistance cannot be ensured. On the other hand, even if the basis weight exceeds 50 g/rd when there is no lower layer plating, or 20 g/rd when there is a lower layer plating, the effect of improving the perforation resistance is commensurate with the cost increase. I can't. Therefore, the basis weight of the "Zn-Ni alloy plating layer with a Ni content of 10 to 40%" on the "other surface" side is 10 to 50 g when there is no lower layer plating (in the case of single layer plating). /rd and 0.5 to 20 if there is a lower layer plating (in the case of two-layer plating)
g/i, respectively.

(b) Chromate treatment layer The amount of chromate treatment layer formed is 30 m based on the amount of Cr.
If it is less than g/rrr, the desired perforation resistance cannot be secured;
On the other hand, the amount of Cr formed is 300 mg/n? If the chromate treatment layer exceeds 30 to 300 mg/r, the amount of chromate treatment layer should be 30 to 300 mg/r.
It was limited to rr.

(C1 Protective Resin Film Layer As mentioned above, resin coatings for the protective film include epoxy resin, polyester resin, melamine resin, vinyl resin, styrene resin, and acrylic resin.

Known materials such as polyurethane resins, phthalic acid resins, etc., alone or modified, containing anticorrosion pigments such as BaCrO4, coloring pigments such as Fe, 03, or pigments such as Sing, etc., can be used. If the thickness of the protective resin film layer is less than 0.21 rm, sufficient porosity resistance cannot be ensured, while if the thickness exceeds 260 μm, it will lead to deterioration of electrodeposition coating properties and spot weldability. The thickness of the resin film layer is 0.2 to 2. It was limited to OIrm.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

<Example> A steel plate having a plate thickness of 0.8 nm was prepared and treated as follows to obtain a multilayer surface-treated steel plate.

That is, first, a steel plate is degreased and pickled, and then Zn''+ and Ni are removed by an electroplating process using a sulfuric acid bath shown in Table 1.
By controlling the concentration of ``, the Ni content rate of the ``first plating layer'' and the ``second plating layer'' is changed, and by controlling the amount of electricity, the basis weight is changed, and Ni One or two layers of Zn- with different contents
A Ni alloy electroplated steel sheet was obtained.

Next, this one-layer or two-layer plated steel plate was washed with water and dried, and then a coated chromate treatment liquid was applied to the side intended for the inner surface, and baked and dried. When applying the chromate treatment liquid, the peripheral speed ratio and touch pressure of the pickup roll and applicator roll of the roll coater are changed, and the concentration of the chromate treatment liquid is also changed to determine the amount of chromate treatment layer formed (Cr adhesion). adjusted.

Next, in order to form a protective resin film on the surface of the steel sheet after the chromate treatment, a clear paint was applied using a roll coater method. The thickness of the protective resin film was controlled by adjusting the amount of solvent in the resin and the peripheral speed ratio of the applicator roll and pickup roll.

On the other hand, a removable solid lubricant film layer was formed on the plating layer on the side intended for the external surface. It was formed by applying a mixture of In addition, when applying the film-removable solid lubricant paint, the peripheral speed ratio and touch pressure of the pink-up roll and applicator roll of the roll coater were changed, and the concentration of the solid lubricant (fluororesin powder) was also changed. The amount of the removable solid lubricant film layer was adjusted using

Then, the multilayer surface-treated steel sheets produced in this manner were investigated for external surface clogging resistance, puncture resistance, press sliding properties, and electrodeposition coating properties.

These results are shown in Table 2.

Here, each of the above-mentioned investigations was conducted in the following manner.

1) I A) Preparation of painted plate test piece.

Zinc phosphate treatment (PBL-3020 (product name of Nihon Baru Ising Co., Ltd.)) - Cationic electrodeposition coating (U-600
(Nippon Paint Co., Ltd. product name): 20 μm) - Medium/top coat:
Each contains 35 pieces of melamine alkyd resin.

B) Make a cross cut using a saw blade as shown in Figure 4 on the painted plate test piece.

C) Outdoor exposure test (conducted for 1 year with twice weekly 5χ NaCl spraying).

D) Measure the blistering width of the two films (the maximum creep width on one side from the crosscant shown in Figure 4) to evaluate the external rust resistance.

Note that the removable solid lubricant film layer formed on the assumed outer surface to improve lubricity was completely removed in the degreasing step in the zinc phosphate treatment step.

I ball, h @ ('l) After sealing the back side and edges of the unpainted board test piece after alkaline degreasing with a polyester tube, the following cycle of "accelerated perforation corrosion test (1 cycle: 24 hr)" was performed.
The maximum erosion depth of the corroded area after 0 cycles was measured and evaluated using a point micrometer.

Salt spray (6 hr) - Dry (2 hr at 50°C) - Wet (
952, 16 hours at 50°C).

12th Old Hair 1 ■ Review To investigate the sliding properties between the plated surface and the tool surface, the method of determining the friction coefficient of the plated surface using the "improved Bauden test method", which is an improved version of the Bowden test, as shown in Figure 5, is used. The sliding characteristics were evaluated using this method.

Even if it is inside equipment such as the trunk lid or bonnet of a car, the finish quality of the paint will be noticed by the public when it is opened, and this will also lead to the evaluation of the product. Therefore, the finish condition of the electrodeposition coating was visually observed on both sides of the surface-treated steel sheet according to the example, and the results were graded into 5 grades (◎...Excellent, ○...Good, △・
..fair, ×...poor, XX...unsatisfactory).

As is clear from the results shown in Table 2 above, the surface-treated steel sheet according to the present invention has shown excellent results in all property tests, and has met the strict requirements for recent automotive rust-proof steel sheets. It can be seen that the comparative steel sheets, which do not meet the conditions specified in the present invention, do not have sufficient properties.

<Summary of Effects> As explained above, according to the present invention, not only corrosion resistance such as 4-hole perforation and external rust resistance, but also excellent properties such as press workability and electrodeposition coating properties are achieved. It is possible to provide a surface-treated steel sheet, and it can be applied to rust-proof copper sheets for automobiles, home appliances, etc. to further improve their performance, which brings about extremely useful effects industrially.

[Brief explanation of drawings]

1 is a schematic configuration diagram of an example of a surface-treated steel sheet according to the present invention, and FIG. 1 fal and FIG. 1 (b) each show different examples. FIG. 2 is a graph showing the relationship between the Ni content of the plating layer and the maximum creep width from cross-cut, and the symbols in the figure correspond to the type symbols of the sample materials in Table 2. FIG. 3 is a graph showing the relationship between the Ni content of the plating layer and the maximum erosion depth, and the symbols in the figure correspond to the type symbols of the sample materials in Table 2. FIG. 4 is an explanatory diagram of a method for evaluating external rust resistance. FIG. 5 is a schematic explanatory diagram of the improved Bowden test method. Fig. 2 Fig. 3 N1 content in plating (%) 1. Trouble on the other side (inner side) Trouble on the other side (inner side) 4. 5.

Claims (2)

[Claims] (1) On one side of the steel plate: a) Zn plating layer or plating layer of Zn-Ni alloy with Ni content of 10% by weight or less: 10 to 50 g/m^2
, b) Removable solid lubricant film layer: multiple layers of 0.5 to 3.0 μm in this order, and on the other side a) Zn-Ni alloy plating with a Ni content of 10 to 40% by weight Layer: 10 to 50 g/m^2, b) Chromate treated layer: 30 to 300 mg/m in Cr content
^2, c) Protective resin film layer: A highly corrosion-resistant surface-treated steel sheet comprising multiple layers of 0.2 to 2.0 μm in this order. (2) On one side of the steel plate: a) Zn plating layer or plating layer of Zn-Ni alloy with Ni content of 10% by weight or less: 10 to 50 g/m^2
, b) Removable solid lubricant film layer: multiple layers of 0.5 to 3.0 μm in this order, and on the other side a) Zn plating layer or Zn- with Ni content of 10% by weight or less. Ni-based alloy plating layer: 10-50g/m^2
, b) Zn-Ni alloy plating layer with Ni content of 10 to 40% by weight: 0.5 to 20 g/m^2, c) Chromate treatment layer: Cr amount of 30 to 300 mg/m
^2, d) Protective resin film layer: A highly corrosion-resistant surface-treated steel sheet comprising multiple layers of 0.2 to 2.0 μm in this order.