JPH0551788A - Zn-cr-p organic composite plated steel sheet having excellent post-working corrosion resistance, ed coating corrosion resistance and end face rust preventiveness - Google Patents

Abstract

PURPOSE:To provide the Zn-Cr-P org. composite plated steel sheet having excellent post-working corrosion resistance, ED coating corrosion resistance and end face rust preventiveness. CONSTITUTION:The org. composite plated steel sheet having the excellent post-working corrosion resistance, ED coating corrosion resistance and end face rust preventiveness is constituted by having an electroplating layer of a Zn-Cr-P alloy having 5 to 14% Cr concn. and over 0.5 and <=30%P concn., having >=2 and <=20 Cr/P ratio and consisting of the balance Zn and by having a chromate layer thereon and further coating the surface thereof with an org. resin. The extremely dense chromate film is formed by the effect of the Cr and the P if the Zn-Cr-P alloy plating having the specific concns. shown above is subjected to a chromate treatment, by which the corrosion resistance of the Zn-Cr-P alloy is greatly improved. In addition, the chromate film is protected over a long period of time and the overwhelming corrosion resistance is assured if the org. film is formed thereon. The coating corrosion resistance and the end face rust preventiveness are assured by the excellent adhesive strength of the chromate film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic composite plated steel sheet having excellent corrosion resistance after processing, ED coating corrosion resistance and end face rust resistance.

[0002]

2. Description of the Related Art Electrogalvanized steel sheets, hot-dip galvanized steel sheets and various alloy-plated steel sheets are widely used in automobiles, electric appliances for home appliances, building materials and the like. Under these circumstances, there has recently been a strong demand for surface treatment materials having excellent corrosion resistance, and the demand for such steel sheets tends to increase rapidly in the future. For example, in the home electric appliance industry, from the viewpoint of process saving and cost reduction, there is a demand for a steel sheet that has excellent corrosion resistance and can be used naked without painting. Further, in the automobile industry, there is a strong demand for a surface-treated steel sheet having excellent corrosion resistance from the viewpoint of safety against a corrosive environment caused by rock salt sprayed to prevent freezing of roads in North America and Northern Europe, for example.
Further, in the housing industry and other construction industries, due to the demand for extending the life of building structures, it is becoming more and more popular to use surface-treated steel sheets and to apply electrodeposition coating (hereinafter referred to as ED coating) on them. Various studies have been made to solve these problems, and many products have been developed. Conventionally, galvanization has been performed to improve the corrosion resistance of steel sheets. The galvanized steel sheet prevents corrosion of the steel sheet by the sacrificial anticorrosive action of zinc, and the zinc adhesion amount must be increased to obtain corrosion resistance. Therefore, cost increase due to increase in required zinc amount, or workability,
There are some problems such as weldability and reduced productivity. In addition, the paint adhesion of galvanized steel sheets is generally poor. As a method for improving the corrosion resistance of such a galvanized steel sheet, various alloy-plated steel sheets have been studied.
n-Ni system, Zn-Ni-Co system, Zn-Ni-Cr
Examples thereof include a system, a Zn-Fe system, a Zn-Co system, and a Zn-Mn system. It is recognized that these alloy platings improve the bare corrosion resistance by about 3 to 5 times as compared with normal galvanized steel sheets. However, even if it is left outdoors for a long time or sprayed with water or salt water, there is a problem that white rust or red rust easily occurs. There is also a method of performing chromate treatment after plating in order to improve corrosion resistance, which is quite effective, but it is about 100 to 15 under high temperature and high humidity and salt-containing atmosphere.
White rust occurs in 0 hours.

On the other hand, in order to further improve the corrosion resistance, a so-called simple pre-coated steel sheet (hereinafter referred to as an organic composite plated steel sheet) in which various resins are applied to a chromate-treated material of a zinc-based plated steel sheet has been developed. It is used in various fields as a rust steel plate or as a corrosion resistant material for home appliances.
An example of an alloy plated steel sheet is shown. JP, 63-243295, A (1) A rust-preventive steel plate having excellent corrosion resistance, which has an eutectoid plating layer of zinc and chromium having a chromium composition of more than 1% by weight to 70% by weight. (2) Zinc-chromium eutectoid plating layer having a chromium composition of more than 1 wt% to 70 wt% and Zn, Fe, Ni, Co,
Mn, Cr, Al, Mg, Si, Mo, Cu, Pb, S
A rust-preventing steel plate having excellent corrosion resistance, which has a multi-layer plating including a plating layer of one or more elements selected from n, Ti, Sb and P. (3) Zinc containing more than 1% by weight to 70% by weight of chromium and Fe, Ni,
Zinc and chromium containing one or more elements selected from Co, Mn, Mo, Cu, Pb, Sn, Sb and P in a total amount smaller than the weight content of zinc or chromium. A corrosion-resistant steel plate having a corrosion-resistant plated layer mainly containing aluminum. (4) In the eutectoid plating layer mainly containing zinc and chromium containing more than 1% by weight to 70% by weight of chromium, Fe, Ni,
Zinc and chromium containing one or more elements selected from Co, Mn, Mo, Cu, Pb, Sn, Sb and P in a total amount smaller than the weight content of zinc or chromium. An eutectoid plating layer mainly composed of Zn, F
e, Ni, Co, Mn, Cr, Al, Mg, Si, M
1 selected from o, Cu, Pb, Sn, Ti, Sb, P
A rust-preventing steel plate having excellent corrosion resistance, which has a multi-layer plating consisting of one or more plating layers of elements. The above-mentioned alloy-plated steel sheets have improved bare corrosion resistance as compared to conventional alloy-plated steel sheets, but bare corrosion resistance after processing in a severe corrosive environment, corrosion resistance after ED coating, and red rust resistance on the end surface. The sex is insufficient.

An example of a chromate-treated steel sheet will be shown. SUMMARY OF THE INVENTION Zinc containing 5 to 40% of Cr-Zinc characterized in that a chromate film is formed on the surface of a chromium plating layer-
Chromate-based electroplated steel sheet. The above-mentioned chromate-treated steel sheets have further improved bare corrosion resistance compared to alloy-plated steel sheets, but bare corrosion resistance after processing in a severe corrosive environment, ED coating corrosion resistance, scratched parts and red rust resistance etc. Similarly insufficient. Next, an example of an organic composite plated steel sheet is shown. SUMMARY OF THE INVENTION A resin-coated zinc-chromium electroplated steel sheet in which a chromate film is formed on the surface of a zinc-chromium plating layer containing 5 to 40% of Cr, and a resin layer is further formed thereon. The organic composite plated steel sheet exemplified above is further improved in bare corrosion resistance as compared with the above alloy plated steel sheet and the chromate treated steel sheet, and although various characteristics are improved as compared with the conventional organic composite plated steel sheet, it is extremely severe. It cannot be said that the corrosion resistance after processing in a corrosive environment and the red rust resistance of the flawed portion and the end surface are necessarily sufficient, and the ED coating corrosion resistance is remarkably poor.

[0005]

However, as a recent tendency, automobiles are exposed to more and more severe corrosive environments, and the automobile industry has excellent bare corrosion resistance and ED coating corrosion resistance after processing in such environments. In addition, there is a strong demand for body rust-preventive steel sheets that have excellent red rust resistance on the flawed part and the end surface. On the other hand, when manufacturing an organic composite plated steel sheet, it was found that any of the above problems can be overcome by applying a plating layer suitable for the organic composite plated steel sheet to the underlayer.

[0006]

The present invention has a Cr concentration of 5
% To 14% or less, P concentration exceeds 0.5% to 3.0% and Cr / P is 2 to 20 and the balance is Zn.
Z having a Zn-Cr-P-based alloy electroplating layer made of
It is an organic composite plated steel sheet based on an n-Cr-P alloy plated steel sheet, and is excellent in bare corrosion resistance after processing, ED coating corrosion resistance, and red rust resistance of a scratched portion or an end surface.

[0007]

The present invention will be described in detail below along with the operation. The present invention limits Zn and Cr and P to a specific concentration on the surface of a steel sheet and Cr / P to a specific value, and Zn-Cr-P alloy electroplating in which the balance is Zn. An organic composite-plated steel sheet having a layer, chromate-treated thereon, and further coated with an organic film. Here, the amount of Zn—Cr—P alloy plating deposited is not particularly limited, but is preferably 10 to 30 g / m ² . 1
If it is 0 g / m ² or less, the characteristics such as corrosion resistance may not be sufficiently secured in a particularly severe corrosive environment.
^If it is ² or more, it is sufficiently secured, so it is not necessary to attach it further from the economical aspect. Further, the amount of the chromate film attached is preferably 10 to 150 mg / m ² . 10m
If it is less than g / m ² , the coating to the plating layer is insufficient and the adhesion with the organic film is not sufficiently secured. 150m
This is because if the chromate film is more than g / m ^2, it is difficult to form a dense film of the chromate film itself and the chromate film is easily broken, and the adhesion to the organic film is lowered. Further, the organic film above the chromate film is preferably 0.5 to 3.0 g / m ² . 0.5 g /
When it is less than m ² , the coating to the underlayer is insufficient and the function of protecting the chromate film, which is the most important role of the organic film, cannot be sufficiently exhibited. If it is 3.0 g / m ² or more, the characteristics are particularly maintained as it is, so it is not economically necessary to further secure the film thickness.

The details will be described below. 1, 2 and 3 are Zn-Cr-P-based organic composite plated steel sheets in which the basis weight is kept constant at 20 g / m ² and the concentrations of Cr and P and the Cr / P ratio are variously changed. Commercially available coated chromate was treated on the above so as to have a Cr content of 55 mg / m ^2, and the olefin / acrylic acid copolymer resin (1
The following shows the results of evaluation of bare corrosion resistance after processing by applying 1.5 μm of a water-based resin of (00) -colloidal silica (30) (parts by weight) and drying to produce an organic composite plated steel sheet. As for processing, as shown in FIG. 4, a bead processing was performed with a pressing load of 2 t to evaluate the corrosion resistance of the side surface portion. Corrosion resistance is JIS-Z-237
The red rust occurrence rate after 8000 hours was measured by a salt spray test according to 1 (salt water concentration 5%, tank temperature 35 ° C., spray pressure 2.0 psi), and was measured as ◎, ○, △, ×, XX. The grade was evaluated. ◎: Red rust occurrence rate 0% ○: 〃 0 to 1% △: 〃 1 to 10% ×: 〃 10 to 50% × ×: 〃 50% or more

As is clear from FIG. 1, when the Cr concentration is more than 5% to 14% and the P concentration is more than 0.5% to 3% and the Cr / P ratio is more than 2 and less than 20, it is extremely high. There are areas that exhibit excellent corrosion resistance after processing. On the other hand, Cr
Even if the P and P concentrations are the same, if the Cr / P ratio is less than 2 or more than 20, the corrosion resistance after processing gradually decreases. Further, if the Cr concentration is more than 5% to 14% or less and the P concentration is 0.5%,
Below, the corrosion resistance after processing is generally inferior to that in the case of more than 0.5% to 3% or less, and the corrosion resistance after processing gradually decreases as the Cr / P ratio increases. Also, the Cr concentration is 5%
If the P concentration is over 14% or less and the P concentration is over 3%, the P concentration is 0.1.
Compared with the case of more than 5% to 3% or less, the corrosion resistance after working is considerably lowered as a whole, and the corrosion resistance after working is remarkably lowered as the Cr / P ratio is lowered.

Next, when the Cr concentration is 5% or less, the P concentration and Cr
FIG. 2 shows the corrosion resistance after processing when the / P ratio was changed. As is clear from FIG. 2, when the Cr concentration is 5% or less and the P concentration is more than 0.5% to 3% or less, the corrosion resistance after the processing is relatively good, but as the Cr / P ratio decreases, the Corrosion resistance decreases rapidly. Further, when the Cr concentration is 5% or less and the P concentration is 0.5% or less, the Cr / P ratio is 6 or more and 12 or less, which shows a slightly good value, but even if the Cr / P ratio becomes larger than that. Alternatively, even if it is lowered, the corrosion resistance after processing is lowered. Further, when the Cr concentration is 5% or less and the P concentration is more than 3%, the corrosion resistance after working is rapidly reduced as the Cr / P ratio is decreased. Further, as is clear from FIG. 3, the Cr concentration is 14%.
If the P concentration is more than 0.5% and less than 3% and the Cr / P ratio is 5 or more and 20 or less, the corrosion resistance after working is slightly good, but if the Cr / P ratio is more than 20, after working. The corrosion resistance of is gradually reduced. Further, if the P concentration exceeds 3%, the Cr / P ratio becomes 4
Above 20 to below 20 shows a little good corrosion resistance after processing,
It gradually decreases in a region of less than 4 or more than 20.

Next, FIGS. 5, 6 and 7 show Zn-Cr-P.
In the system-based organic composite plated steel sheet, the basis weight was kept constant at 20 g / m ² and the commercially available coating chromate was 60 mg / mL on the plating layer when the Cr and P concentrations and the Cr / P ratio were variously changed. m ² and treated with an olefin / acrylic acid copolymer (100) -colloidal silica (25) (part by weight) aqueous resin of 1.5 μm.
E when applied and dried to produce an organic composite plated steel sheet
The result of D coating corrosion resistance is shown. Regarding the ED coating corrosion resistance, each organic composite plated steel sheet was subjected to ED coating, and the coating film was scratched in a cross shape with a cutter to evaluate the corrosion resistance. Corrosion resistance is JI
According to a salt spray test based on S-Z-2371 (concentration of salt solution 5%, bath temperature 35 ° C, spray pressure 2.0 psi)
Measure the corrosion depth after 8000 hours and check ◎, ○, △, ×,
The evaluation was made in 5 grades of XX. ◎: Maximum corrosion depth 0 to 0.05 mm ○: 〃 0.05 to 0.1 mm △: 〃 0.1 to 0.2 mm ×: 〃 0.2 to 0.5 mm XX: 〃 0.5 mm or more

In FIG. 5, when the Cr concentration exceeds 5% to 14% or less, P
The results of ED coating corrosion resistance when the concentration and the Cr / P ratio are variously changed are shown. As is clear from FIG. 5, the Cr concentration is 5%
In the range of more than 14% or less and P concentration of more than 0.5% to 3% and Cr / P ratio of 2 or more and 20 or less, ED coating corrosion resistance is extremely excellent. On the other hand, similarly, when the Cr concentration is more than 5% to 14% and the P concentration is 0.5% or less, the Cr / P ratio is 10 or more to 18 or less and the ED coating corrosion resistance is slightly excellent. When the ratio exceeds 18, the ED coating corrosion resistance gradually decreases. Also, P concentration is 3%
If it exceeds the above range, the corrosion resistance of the ED coating gradually decreases as the Cr / P ratio decreases. If the P concentration exceeds 3%, the ED coating corrosion resistance decreases as the Cr / P ratio decreases. Next, FIG. 6 shows the results of the ED coating corrosion resistance after processing when the Cr concentration was 5% or less and the P concentration and the Cr / P ratio were changed. As is clear from FIG. 6, when the P concentration exceeds 0.5% to 3% or less, Cr /
The corrosion resistance of the ED coating gradually decreases as the P ratio decreases. Further, when the P concentration is 0.5% or less, there is a region where the ED coating corrosion resistance is slightly good in the Cr / P ratio of 2 or more to 22 or less, but when the Cr / P ratio is less than 2 or more than 22, the ED coating corrosion resistance is low. Sex tends to decrease. Further, when the P concentration exceeds 3%, when the Cr / P ratio is 2 or less, the ED coating corrosion resistance sharply decreases as the Cr / P ratio decreases.

Next, when the Cr concentration exceeds 14%, the P concentration and Cr
The results of the ED coating corrosion resistance when the / P ratio was changed are shown in FIG. As is clear from FIG. 7, the P concentration exceeds 0.5% to 3
% Or less, Cr / P ratio of 5 or more to 16 or less shows slightly good ED coating corrosion resistance, but Cr / P ratio of more than 16 results in C
The corrosion resistance of the ED coating gradually decreases as the r / P ratio increases. When the P concentration is 0.5% or less, the ED coating corrosion resistance gradually decreases as the Cr / P ratio increases. Also,
If the P concentration exceeds 3%, the ED coating corrosion resistance gradually decreases as the Cr / P ratio increases. Next, FIG. 8, FIG. 9 and FIG.
In Zn-Cr-P-based organic composite plated steel sheet, and a constant basis weight to 20 g / m ^2, and, Cr, and form various varied plating layer the concentration and Cr / P ratio of P, commercially available thereon The coated chromate of No. 1 was treated so that the amount of deposited Cr was 55 mg / m ^2, and then the olefin / acrylic acid copolymer resin (100) -colloidal silica (3
5) (part by weight) of the water-based resin is applied in an amount of 1.5 μm and dried to produce an organic composite plated steel sheet, and the results of evaluating the end face rust resistance are shown below.

As shown in FIG. 11, the end surface rust resistance was evaluated by corroding the test piece by punching a test piece into a circle from the forward and reverse directions and then applying ED. Corrosion resistance was determined by a salt spray test according to JIS-Z-2371 (saline concentration 5%, bath temperature 35 ° C, spray pressure 2.0 psi), and the red rust occurrence rate on the inner end face of the circular part after 6000 hours was measured. Measure ◎, ○, △, ×, XX 5
The grade was evaluated. ◎: Red rust occurrence rate 0% ○: 〃 0% to 5% △: 〃 5% to 10% ×: 〃 10% to 50% XX: 〃 50% or more

In FIG. 8, when the Cr concentration exceeds 5% to 14% or less, P
The results of the rust preventive property of the end face when the concentration and the Cr / P ratio are variously changed are shown. As is clear from FIG. 8, the Cr concentration exceeds 5%
14% or less, the P concentration is more than 0.5% to 3% or less, and
In the region where the Cr / P ratio is 2 or more and 20 or less, extremely excellent end face rust resistance is exhibited. In contrast, the Cr concentration is 5%
Cr / P when the P concentration is 0.5% or less and over 14% or less
When the ratio is 10 or more and 18 or less, the end face rust resistance is slightly excellent, but when the Cr / P ratio exceeds 18, the ED coating corrosion resistance gradually decreases as the Cr / P ratio increases. If the P concentration exceeds 3%, Cr /
As the P ratio decreases, the end surface rust resistance gradually decreases. On the other hand, if the P concentration exceeds 3%, the rust preventive property of the end face decreases as the Cr / P ratio decreases. Next, FIG. 9 shows the results of the end surface rust preventive property when the Cr concentration is 5% or less and the P concentration and the Cr / P ratio are changed.
Shown in. As is clear from FIG. 9, the P concentration exceeds 0.5%
If it is 3% or less, the rust preventive property of the end face gradually decreases as the Cr / P ratio decreases. When the P concentration is 0.5% or less, Cr
Although there is a region having a slightly good end surface rust preventive property in the region where the / P ratio is 2 or more and 18 or less, the end face rust preventive property tends to decrease when the Cr / P ratio is less than 2 or exceeds 18. Also, the P concentration is 3
If it exceeds 2% and the Cr / P ratio is 2 or less, the rust preventive property of the end face sharply decreases as the Cr / P ratio decreases.

Next, when the Cr concentration exceeds 14%, the P concentration and Cr
FIG. 10 shows the result of the end surface rust preventive property when the / P ratio was changed. As is clear from FIG. 10, the P concentration exceeds 0.5% to 3
% Or less, a Cr / P ratio of 5 or more to 14 or less shows a slightly good end surface rust resistance, but a Cr / P ratio of more than 14 results in Cr / P
As the P ratio increases, the end face rust resistance gradually decreases. Further, when the P concentration is 0.5% or less, the end face rust preventive property gradually decreases as the Cr / P ratio increases. Further, the P concentration is 0.
If it is 5% or less, the rust preventive property of the end face gradually decreases as the Cr / P ratio increases. On the other hand, if the P concentration exceeds 3%, the rust preventive property of the end face gradually decreases as the Cr / P ratio increases. It is considered as follows that extremely excellent performance can be obtained by producing an organic composite-plated steel sheet using a plating layer having a limited Cr concentration, P concentration and Cr / P ratio as a base.
That is, since the affinity of P and Cr is fairly strong, Zn-
By adding P to the Cr-based alloy, the Cr element is firmly fixed by P, and when both elements have a specific ratio, the affinity between the two becomes particularly strong and becomes stronger, and by suppressing the elution of ions. The corrosion resistance of the plating layer itself is significantly improved. At the same time, it was found that when chromate treatment is performed in a state where Cr and P are alloyed in a specific ratio, an extremely dense and stable chromate film is formed. With this special chromate film formed, Zn-Cr-P
The corrosion resistance of the alloys is greatly improved, and when an organic film is formed on the upper layer, the organic film protects the chromate film for a long time, and the synergistic effect results in overall overwhelming corrosion resistance. all right. In addition, Zn-C
Since the chromate film formed on the r-P alloy is extremely dense and stable, it also has excellent adhesion to the organic film to be applied on top of it, so that the coating film from the cross-cut part in the ED coating corrosion resistance The progress of under-corrosion is also very slow and therefore shows excellent ED coating corrosion resistance. The same applies to the end face rust resistance, and the presence of the excellent chromate film significantly suppresses the progress of under-coat corrosion on the end face portion, whereby the sacrificial anticorrosive action of the Zn-Cr-P alloy is prolonged. It is maintained and exhibits excellent end face rust resistance.

As is clear from the above results, when the organic composite plated steel sheet is manufactured, the Zn-Cr-P alloy plated steel sheet is used as the underlayer and the Cr and P concentrations and the Cr / P ratio are limited to specific ranges. It has been found that an organic composite plated steel sheet excellent in corrosion resistance after processing, ED coating corrosion resistance and end surface rust resistance can be produced by chromate-treating and organic coating on it. From this, in the present invention, when manufacturing the organic composite plated steel sheet, the Cr concentration is more than 5% to 14%,
P concentration is more than 0.5% to 3.0% or less, and Cr / P
Zn-C in which the ratio is 2 to 20 and the balance is Zn
The r-P ternary alloy plating is used as a base, and chromate treatment is performed on the base to coat an organic film. The chromate treatment used when producing the organic composite plated steel sheet may be either coating chromate or electrolytic chromate. Further, the organic film to be coated may be either water-based or solvent-based resin. Examples will be described below.

[0018]

【Example】

Example 1 Zn-Cr-P ternary alloy electroplating with a coating weight of 20 g / m ² , a Cr concentration of 6%, a P concentration of 6%, and Cr / P = 10 was applied on top of it. Cr adhesion amount is 45 mg
/ M ² coating type chromate treatment and further water-based olefin / acrylic acid copolymer resin (1
00) -Colloidal silica (30) (parts by weight) was applied after drying to a thickness of 1.5 μm to produce an organic composite plated steel sheet. Example 2 Plating coverage is 20 g / m ² , Cr concentration is 10%, P
Zn-Cr with a concentration of 0.5% and Cr / P = 20
-P ternary alloy electroplating, and electrolytic chromate treatment on it so that the amount of deposited Cr is 65 mg / m ² .
Further thereon, an aqueous olefin / acrylic acid copolymer resin (100) -colloidal silica (30) (parts by weight)
Was coated to a thickness of 1.3 μm after drying to produce an organic composite plated steel sheet. Example 3 Plating adhesion amount is 20 g / m ² , Cr concentration is 12%, P
Zn-Cr with 0.8% concentration and Cr / P = 15
-P ternary alloy electroplating, and electrolytic chromate treatment on it so that the amount of deposited Cr is 85 mg / m ² .
Further thereon, an aqueous olefin / acrylic acid copolymer resin (100) -colloidal silica (30) (parts by weight)
Was coated to a thickness of 1.3 μm after drying to produce an organic composite plated steel sheet.

Example 4 The coating weight was 20 g / m ² , the Cr concentration was 15%, and P was
Zn- with a concentration of 1.2% and Cr / P = 12.5
Cr-P ternary alloy electroplating, coating type chromate treatment on it so that the amount of deposited Cr was 55 mg / m ^2, and further water-based polyacrylic acid copolymer resin (100)- Colloidal silica (30) (part by weight) was dried and applied so as to have a thickness of 1.8 μm to produce an organic composite plated steel sheet. Example 5 Zn-Cr- having a coating weight of 20 g / m ² , Cr concentration of 9%, P concentration of 0.6%, and Cr / P = 15.
P ternary alloy electroplated with Cr deposition of 5
The coating type chromate treatment was performed so that the concentration became 0 mg / m ^2, and the solvent type epoxy resin (100) -aerosil (30) (part by weight) was further dried and applied so as to have a concentration of 1.0 μm. A composite plated steel sheet was manufactured. Example 6 Plating adhesion amount is 20 g / m ² , Cr concentration is 13%, P
Zn- with a concentration of 0.7% and Cr / P = 18.6.
Cr-P ternary alloy electroplating, electrolytic chromate treatment so that the amount of deposited Cr is 80 mg / m ^2, and a solvent-based epoxy resin (100)
-Aerosil (30) (part by weight) was applied to a dry thickness of 1.2 to produce an organic composite plated steel sheet.

Comparative Example 1 Z having a coating weight of 20 g / m ² and a Cr concentration of 12%
n-Cr binary alloy electroplating, coating type chromate treatment on it so that the amount of deposited Cr is 50 mg / m ^2, and further polyacrylic acid ester copolymer resin (100) -colloidal Silica (30) (parts by weight) was applied after drying to a thickness of 1.5 μm to produce an organic composite plated steel sheet. Comparative Example 2 Zn-Cr- with a coating weight of 20 g / m ² , a Cr concentration of 8%, a P concentration of 0.2%, and Cr / P = 40.
P ternary alloy electroplated with Cr deposition of 5
A coating type chromate treatment was performed so that the concentration was 5 mg / m ^2, and a styrene-acrylic acid copolymer resin (10
0) -Colloidal silica (30) (parts by weight) was dried and applied to a thickness of 1.5 μm to produce an organic composite plated steel sheet. Comparative Example 3 Plating coverage is 20 g / m ² , Cr concentration is 14%, P
Zn-Cr with a concentration of 0.6% and Cr / P = 23
-P ternary alloy electroplating, and coating chromate treatment on it so that the amount of deposited Cr is 58 mg / m ² .
Furthermore, a styrene-acrylic acid copolymer resin (1
00) -colloidal silica (25) (parts by weight) was dried and applied to a thickness of 1.7 μm to produce an organic composite plated steel sheet.

Comparative Example 4 Plating coverage was 20 g / m ² , Cr concentration was 13%, P
Zn-Cr with a concentration of 3.5% and Cr / P = 3.7
-P ternary alloy electroplating, and electrolytic chromate treatment on it so that the amount of deposited Cr is 75 mg / m ² .
Furthermore, an ethylene-acrylic acid copolymer resin (1
00) -Colloidal silica (30) (parts by weight) was applied so as to have a thickness of 1.3 μm after drying to produce an organic composite plated steel sheet. Comparative Example 5 Zn-Cr- with a coating weight of 20 g / m ² , Cr concentration of 3%, P concentration of 0.2%, and Cr / P = 15.
Pt ternary alloy electroplated with a Cr deposit of 8
Electrolyte-type chromate treatment was carried out so as to obtain 5 mg / m ^2, and further ethylene-acrylic acid copolymer resin (10
0) -Colloidal silica (30) (parts by weight) was applied after drying to a thickness of 1.3 μm to produce an organic composite plated steel sheet. Comparative Example 6 Zn-Cr having a coating weight of 20 g / m ² , a Cr concentration of 2%, a P concentration of 0.8%, and Cr / P = 2.5.
-P ternary alloy electroplating, followed by electrolytic chromate treatment so that the amount of deposited Cr is 60 mg / m ² .
Furthermore, an ethylene-acrylic acid copolymer resin (1
00) -Colloidal silica (30) (parts by weight) was applied so as to have a thickness of 1.3 μm after drying to produce an organic composite plated steel sheet.

Comparative Example 7 Zn-Cr having a coating weight of 20 g / m ² , Cr concentration of 4%, P concentration of 2.8% and Cr / P = 1.4.
-P ternary alloy electroplating, followed by electrolytic chromate treatment so that the amount of deposited Cr is 60 mg / m ² .
Furthermore, an ethylene-acrylic acid copolymer resin (1
00) -Colloidal silica (30) (parts by weight) was applied so as to have a thickness of 1.3 μm after drying to produce an organic composite plated steel sheet. Comparative Example 8 Plating coverage is 20 g / m ² , Cr concentration is 17%, P
Zn-Cr with a concentration of 0.2% and Cr / P = 85
-P ternary alloy electroplating, followed by coating type chromate treatment so that the amount of deposited Cr is 45 mg / m ² ,
Furthermore, a styrene-acrylic acid copolymer resin (1
00) -Colloidal silica (30) (parts by weight) was applied so as to have a thickness of 1.3 μm after drying to produce an organic composite plated steel sheet. Comparative Example 9 Plating coverage is 20 g / m ² , Cr concentration is 18%, P
Zn- with a concentration of 0.7% and Cr / P = 25.7
Cr-P ternary alloy electroplating, coating type chromate treatment on it so that the amount of deposited Cr was 50 mg / m ^2, and styrene-acrylic acid copolymer resin (100) -colloidal Silica (30) (parts by weight) was applied after drying to a thickness of 1.3 μm to produce an organic composite plated steel sheet.

Comparative Example 10 Plating adhesion amount is 20 g / m ² , Cr concentration is 20%, P
Zn-Cr-P with a concentration of 3.7% and Cr / P = 5.4
Ternary alloy electroplated with a Cr deposit of 50
Coating-type chromate treatment was carried out so as to obtain mg / m ^2, and then ethylene-acrylic acid copolymer resin (10
0) -Colloidal silica (30) (parts by weight) was applied after drying to a thickness of 1.3 μm to produce an organic composite plated steel sheet. Table 1 shows the results of an examination of the corrosion resistance after processing, the ED coating corrosion resistance and the end surface rust resistance of the organic composite plated steel sheets obtained in Examples 1 to 6 and Comparative Examples 1 to 10. The test methods for the corrosion resistance after processing, the coating corrosion resistance and the end face rust resistance are as described above. As is clear from Table 1, the examples of the present invention are extremely superior to the comparative examples.

[0024]

[Table 1]

[0025]

As described above, according to the present invention, a surface-treated steel sheet having extremely excellent post-working corrosion resistance, ED coating corrosion resistance and end face rust resistance at the same time can be obtained.
It contributes to improving the quality and useful life of home appliances, building materials, etc.

[Brief description of drawings]

FIG. 1 shows bare corrosion resistance of a Zn—Cr—P-based organic composite-plated steel sheet having a Cr concentration of more than 5% to 14% and varying P concentration and Cr / P ratio after processing.

FIG. 2 shows bare corrosion resistance of a Zn—Cr—P-based organic composite-plated steel sheet after processing when the Cr concentration is 5% or less and the P concentration and the Cr / P ratio are changed.

FIG. 3 shows bare corrosion resistance after working of Zn—Cr—P-based organic composite plated steel sheets when the Cr concentration exceeds 14% and the P concentration and the Cr / P ratio are changed.

FIG. 4 shows an evaluation position of a beaded test piece.

FIG. 5 shows ED coating corrosion resistance of Zn—Cr—P-based organic composite plated steel sheets when the Cr concentration is more than 5% to 14% or less and the P concentration and the Cr / P ratio are changed.

FIG. 6 shows ED coating corrosion resistance of a Zn—Cr—P-based organic composite plated steel sheet when the Cr concentration is 5% or less and the P concentration and the Cr / P ratio are changed.

FIG. 7 shows ED coating corrosion resistance of Zn—Cr—P-based organic composite plated steel sheets when the Cr concentration exceeds 14% and the P concentration and the Cr / P ratio are changed.

FIG. 8 shows end face rust preventive properties of Zn—Cr—P-based organic composite plated steel sheets when the Cr concentration is more than 5% to 14% or less and the P concentration and the Cr / P ratio are changed.

FIG. 9 shows end face rust preventive properties of Zn—Cr—P-based organic composite plated steel sheets when the Cr concentration is 5% or less and the P concentration and the Cr / P ratio are changed.

FIG. 10: P concentration and Cr / P when Cr concentration exceeds 14%
The end surface rust preventive property of the Zn-Cr-P type | system | group organic composite plating steel plate when changing a ratio is shown.

FIG. 11 shows a punched state of a test piece for evaluation of end surface rust prevention.

Claims (1)

[Claims] 1. A Cr concentration of more than 5% to 14%, a P concentration of more than 0.5% to 3.0%, and a Cr / P ratio of 2
Zn-Cr-P consisting of Zn with the rest being not less than 20 and not more than 20
Organic alloy with excellent corrosion resistance after processing, ED coating corrosion resistance and end face rust resistance, which has a system alloy electroplating layer, a chromate layer on it, and an organic resin coating on it Composite plated steel sheet