JPH09184090A - Electrolytic organic coated steel sheet excellent in corrosion resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel sheet excellent in all of corrosion resistance, adhesion to coating material and weldability and particularly excellent as the stock for an automobile body and to provide a method for economically producing the steel sheet with simple equipment. SOLUTION: This electrolytic organic coated steel sheet excellent in corrosion resistance is the one in which at least one surface of a steel sheet is applied with a plating layer selected from a galvanizing layer, a galvannealing layer and a zinc base composite dispersed plating layer, the upper layer is applied with a Cr plating layer with 10 to 1000mg/m<2> coating weight by the total Cr content, and the upper layer is applied with an organic film with 0.01 to 3g/m<2> coating weight formed by anode oxidizing polymerization. Furthermore, the method for producing the electrolytic organic coated steel sheet excellent in corrosion resistance in which a galvanizing layer and a Cr plating layer are formed on the surface of at least one surface of a steel sheet, and, after that, anode oxidizing polymerization is executed without drying the surface of the plated steel sheet to form an organic film with 0.01 to 3g/m<2> coating weight is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a surface-treated steel sheet having excellent corrosion resistance, particularly as a steel sheet for automobile bodies, which is particularly excellent in corrosion resistance and also has excellent paint adhesion and weldability, and a method for producing the same. To do.

[0002]

2. Description of the Related Art In recent years, the application of various surface-treated steel sheets has expanded year by year in response to the social demand for high corrosion resistance of automobile bodies. Examples of such a surface-treated steel sheet include a galvanized steel sheet and a zinc alloy plated steel sheet. In addition to this, in the case of steel sheets for automobile bodies, in the coating performed after the vehicle body is assembled, it is difficult to spread the coating sufficiently, and in the bag structure portion and bending portion (hemming portion) on the inner surface of the vehicle body exposed to high humidity, High corrosion resistance has been required.

As a steel plate that meets such requirements, for example, JP-A-3-130141 and JP-A-2-258335 have been proposed. These technologies are an organic composite coated steel sheet in which a chromate layer is coated on a zinc or zinc-based alloy plated steel sheet and an organic polymer resin layer containing silica with a thickness of a few μm or less. Since it has very good corrosion resistance even in the state, the organic composite-coated steel sheet is often used for the inner surface of the vehicle body.

However, in recent years, the cost of the automobile industry has been further reduced as the economic environment deteriorates. The above-mentioned organic composite coated steel sheet requires a coating coater and a baking furnace in each step in order to form a chromate film by a coating type chromate and an organic film by a coating method after Zn-based plating.

In this case, since the structure of the plating equipment is different from that of the coating coater and the baking furnace, and therefore the line speed and control items are different, the general production equipment is
After the Zn-based plating, the coil is temporarily coiled up, and the coating coater and the baking furnace, which have been constructed separately, are used for processing. As a result, in the case of the above-mentioned method, it is necessary to construct various equipments, and the cost is considerably increased in operation, and both the automobile manufacturer and the steel manufacturer are burdened with management.

According to the electrolytic polymerization method of the present invention, an organic coated steel sheet can be produced without using a new construction cost by using a Zn-based plating preliminary tank and a post-treatment facility, and a product can be produced only by a plating line. Yes (can coil up)
Therefore, the cost will be considerably reduced in terms of operation. That is, if it is an electrolytic polymerization method according to the present invention, if it has a Zn-based plating equipment, it can be switched to the production of an organic coated steel sheet having excellent corrosion resistance by using the existing equipment without adding it. You can

As a method for forming an organic film on the surface of a steel sheet by electrolysis, electrodeposition coating is generally performed.
Electrodeposition coating is a method in which an aqueous solution containing an aqueous or emulsified resin (polymer) and a pigment is charged to migrate and precipitate the polymer and the pigment. However, in the case of electrodeposition coating, the uniformity of the film formed on the surface of the steel sheet is poorer than that in coater coating.

In the case of forming an organic film having a film thickness of several tens of μm or more, there is no problem even if there is some unevenness in the film thickness, but the steel sheet for automobiles, which is the main object of the present invention, has a weldability. In order to secure the thickness, the organic film needs to be a thin film having a thickness of several μm or less. In such a thin film, the uniformity greatly affects the corrosion resistance, and therefore electrodeposition coating is not suitable. Further, since it is necessary to perform baking after the electrodeposition coating and high-voltage electrolytic treatment is required, the cost becomes high.

As another means for forming an organic film by electrolysis, there is an electrolytic polymerization method. In the electrolytic polymerization method, starting from a monomer, polymerization and film formation are simultaneously performed by electrolysis to form an organic film on a material to be treated. The electrolytic polymerization method has been rapidly used in recent years mainly in the fields of capacitors and electronic materials (Japanese Patent Publication No. 3-6500).
No. 8, Japanese Patent Publication No. 3-61314, and Japanese Patent Publication No. 4-7521).

In this case, the required characteristic of the film is mainly conductivity, and the corrosion resistance of the material to be treated has not been studied at all. As a method for directly treating the surface of a metal body by directly forming an electrolytic polymerized film on the metal surface, Japanese Patent Publication No.
JP-A-55-16075. These are proposed as alternatives to electrodeposition coating, and are aimed at cost merit by omitting baking and reducing the amount of electricity (low voltage).

When an organic film is formed on the surface of a conductive object to be processed by electrodeposition coating or a coater, most of the purpose is corrosion resistance (rust prevention), which is electric insulation, water and oxygen non-resistance. The thickness of the organic coating is required to be several tens of μm or more because it is achieved by the transparency. In such a case, when the organic film formation is performed by an electrolytic polymerization method, for example, Japanese Patent Publication No. 50-1548.
As described in Japanese Patent No. 5, in order to secure rust prevention by electrical insulation, that is, in order to secure rust prevention by increasing the organic film thickness, not only the electrolysis time becomes longer, but also
As the film becomes thicker, the voltage increases due to its resistance, the film is less likely to be formed, the amount of electricity required also increases, and the cost merit due to omission of baking is almost eliminated.

Further, in the case of electrolytic polymerization, there are drawbacks that the monomers to be used are limited (the monomers that can be electrolytically polymerized are limited) and that the chemical structures such as modification and cross-linking which are possible with polymers cannot be adopted. However, at present, it has not been put into practical use as a substitute for a general organic film for the purpose of ensuring rust prevention by electrical insulation.

[0013]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a steel sheet excellent in corrosion resistance, paint adhesion and weldability, particularly a steel sheet excellent as a material for automobile bodies. And to provide a method capable of economically producing the steel sheet with simple equipment.

[0014]

According to a first aspect of the present invention, any one of a zinc plating layer, a zinc alloy plating layer, and a zinc composite dispersion plating layer having an adhesion amount of 10 to 40 g / m ² is formed on at least one surface of a steel sheet. It has a plating layer selected from the above, the adhesion amount in the upper layer has a Cr plating layer of 10 to 1000 mg / m ^{2 in} total Cr amount, and the adhesion amount formed by anodic oxidation polymerization in the upper layer is 0.
It is an electrolytic organic coated steel sheet having excellent corrosion resistance, which is characterized by having an organic coating of 01 to 3 g / m ² .

In a second aspect of the present invention, at least one surface of the steel sheet is coated with zinc-based plating selected from zinc coating with a deposition amount of 10 to 40 g / m ² , zinc-based alloy plating, and zinc-based composite dispersion plating. After that, the adhesion amount is 10 to 1000 mg in total Cr amount
/ m ² Cr plating is applied, and the surface of the plated steel sheet after Cr plating is subjected to anodizing polymerization treatment without drying, and the adhesion amount is 0.01.
It is a method for producing an electrolytic organic coated steel sheet having excellent corrosion resistance, which is characterized by forming an organic film of ³ g / m ² .

In the above first and second inventions, the Cr plating layer may be formed by a chromate method, and the chromate method is preferably an electrolytic chromate method.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. Since the electrolytic organic coated steel sheet of the present invention is mainly used for automobile steel sheets, the organic coating on the steel sheet surface must have the weldability and electrodeposition coatability as described above,
The organic film must be very thin, a few μm or less,
Therefore, it has water and oxygen permeability, and rust prevention becomes a problem.

In the present invention, the anticorrosive property is mainly due to the sacrificial anticorrosive action of the Zn plating, and thus the elution rate of Zn greatly affects the life of the steel sheet. Since the elution rate of Zn is greatly delayed by stably retaining the corrosion product of Zn formed on the surface of the underlying Zn plating layer, the role of the organic film is to retain the corrosion product of Zn. Is the most important.

Such an ultra-thin organic film exhibits its rust preventive property only when it is used together with the Zn-based plating of the base, and in order to stably hold the corrosion product of Zn, the upper layer thereof is required. It is important that the organic film of the ultra-thin film in 1) be uniform. FIG. 1 schematically shows a cross section of a steel plate surface when an ultrathin organic film is formed on the steel plate by coater coating.

FIG. 2 schematically shows a cross section of the surface of a steel sheet when an ultrathin organic film is formed on the steel sheet by electrolytic polymerization. Originally, it is very difficult to control the thin film thickness with a coater, but even if the film thickness can be controlled, it does not follow the unevenness of the surface existing on the base plated steel sheet 1 as shown in FIG. Since the organic film 2 is formed in such a manner that a large amount is accumulated in the recesses, it is unavoidable that the film thickness becomes microscopically non-uniform.

As a result, the thickness of the organic coating becomes large at the concave portion of the base, which adversely affects the electrodeposition coating property, while the thickness of the organic coating becomes extremely small at the convex portion of the base,
The corrosion product of Zn cannot be stably held, the dissolution of Zn proceeds, and it tends to become a point of corrosion occurrence. However, if the electrolytic polymerization method is used, not only the control of the film thickness by the electrolysis time or the amount of electricity is easy, but also the organic film 3 is formed following the irregularities on the surface of the base plated steel sheet 1 as shown in FIG. Therefore, as the obtained organic coated steel sheet, one having stable electrodeposition coating property, weldability and corrosion resistance can be obtained.

As described above, the inventors of the present invention, by forming an organic film by the electrolytic polymerization method, have characteristics different from the electrically insulating property and the impermeability of water and oxygen expected in the conventionally considered organic film. The present invention has been completed by finding out the uniformity of thin film and the retention of Zn corrosion products. Therefore, in the present invention, it is very important to have a zinc-based plating layer under the electrolytic polymerization film, and the effect of forming an organic film by the electrolytic polymerization method appears only when the zinc-based plating layer is present.

Further, according to the present invention, it has been clarified that the organic film formation by the short-time electrolysis and the baking furnace are not required, so that the cost can be largely reduced. As described above, the present inventors diligently investigated the rust prevention mechanism of the organic composite coated steel sheet that has been conventionally used as a rust preventive steel sheet for automobiles, and also examined a method for manufacturing with facility-saving and cost-saving. , Furthermore, as a result of investigating the characteristics of the coating formed by the electrolytic polymerization method and the characteristics of the formed coating, and as a result of repeated studies, a steel sheet excellent in both corrosion resistance, paint adhesion and weldability that could not be achieved by the conventional technology, especially The inventors have found a steel sheet suitable for automobiles, and a method for producing the steel sheet which is excellent in economics, in which large capital investment is not required even when applied to existing equipment, and operating cost hardly increases.

In the present invention, the lowermost layer of the steel sheet surface coating layer has a zinc-based plating layer selected from a zinc-plating layer, a zinc-based alloy plating layer and a zinc-based composite dispersion plating layer. In the present invention, the zinc plating layer, the type of plating of the zinc-based alloy plating layer or the zinc-based composite dispersion plating layer, pure Zn plating, Zn-Ni alloy plating, Zn-Fe alloy plating, Zn-Cr alloy plating, Zn Binary Zn alloy plating such as -Co alloy plating, Zn-Ni-Cr alloy plating, Zn-Co-Cr
Ternary Zn alloy plating such as alloy plating can be used, and zinc-based composite dispersion plating such as Zn—SiO ₂ plating and Zn—Co—Cr—Al ₂ O ₃ plating can also be used.

The zinc-based composite dispersion plating in the present invention refers to composite plating in which oxide particles such as silica and alumina are dispersed and co-deposited on zinc plating or zinc-based alloy plating. Further, the above-mentioned zinc-based plating layer in the present invention is Cu, Sn, A within a range not impairing the object of the present invention.
It may contain elements such as s and Pb.

The zinc-based plating described above is an electroplating method,
It is performed by hot dip plating, alloy hot dip plating, or vapor plating. The above-mentioned zinc plating layer, the zinc-based alloy plating layer or the zinc-based composite dispersion plating layer, the plating amount per one side of the steel plate, 10 ~ 40 g / m ²
It is preferable that This is because if it is less than 10 g / m ² , sufficient corrosion resistance cannot be obtained, and if it exceeds 40 g / m ² , the contribution to corrosion resistance due to an increase in the amount of plating is reduced, which is economically disadvantageous. .

In the present invention, a Cr plating layer is formed as an intermediate layer between the above-mentioned first zinc-based plating layer and the anodic oxidation polymerization coating layer above it. According to the present invention, by forming the anodized polymerized film layer and the Cr plating layer, it is possible to improve the corrosion resistance, but it is economically disadvantageous. Therefore, depending on the required degree of corrosion resistance, the Cr plating layer Are preferably formed.

The amount of Cr plating deposited is preferably 10 to 1000 mg / m ² per one side of the steel sheet as the total Cr amount. If it is less than 10 mg / m ² , the effect of improving the corrosion resistance due to the formation of the Cr plating layer is not observed, and if it exceeds 1000 mg / m ² , the effect of increasing the Cr plating amount on the corrosion resistance becomes small, which is economically disadvantageous. The adhesion amount was limited. The form of Cr in the Cr plating layer is not particularly limited, but in order to have an effect as a barrier of the Zn-based plating layer shown in [A] described below, metal Cr should have 50 mg / m ² or more per one side of the steel plate. Is preferred. The amount of Cr oxide is not particularly limited and may be in the range of the above total Cr amount.

Next, the organic film formed by anodic oxidation polymerization in the present invention will be described. Electrolytic polymerized coatings can be roughly classified into anodized polymerized coatings and cathodic reduction polymerized coatings.In the case of anodized polymerized coatings, the time until the occurrence of white rust is almost the same as that of cathodic reduction polymerized coatings, but the progress of red rust Slow and a good corrosion resistant film is formed. The reason for this is not clear, but it is presumed that an oxide of the underlying metal (Zn) is also formed during the anodizing treatment, which serves as a barrier film and delays the progress of the dissolution reaction (anodic reaction) of Zn during the corrosion resistance test.

It is necessary that the amount of the anodized polymerized film deposited is 0.01 to 3 g / m ² per one side of the steel sheet. Adhesion amount 0.01g / m ²
When the amount is less than the above, the effect of improving the corrosion resistance cannot be sufficiently obtained, and when it exceeds 3 g / m ² , the effect of increasing the amount of adhesion on the corrosion resistance becomes small, which is economically disadvantageous. If the adhesion amount is large, the spot weldability deteriorates, so the amount was limited to the amount shown above.

From the viewpoints of corrosion resistance and paint adhesion, it is more desirable that the amount of the anodized polymerized film deposited is per one side of the steel sheet.
It is good to set it to 0.1-3 g / m ² . The monomer used for the anodic oxidation polymerization is preferably one or more selected from pyrrole, thiophene, phenol, azulene, aniline and the like, but is not particularly limited.

As the electrolyte of the electrolytic solution, preferably, one or more basic substances selected from sodium oxalate, potassium oxalate, sodium hydroxide, potassium hydroxide and the like are exemplified, and the solvent is used. Is preferably an aqueous solution composed of water or, in addition, an organic solvent having a polarity other than water. The current density in anodic oxidation polymerization is preferably 1 A / dm ² or more,
More preferably, it is 1 to 100 A / dm ² .

Conventionally, electrolytic polymerization has generally been carried out at a current density of less than 1 A / dm ² . However, when the current density is as low as less than 1 A / dm ² , it is rather not preferable because an uneven film, that is, film unevenness, is likely to occur on the surface of the steel sheet.
Further, when the current density is less than 1 A / dm ² , it is necessary to prolong the electrolysis time in order to obtain a sufficient amount of coating, which requires a large number of electrolytic baths, which is economically disadvantageous, so that 1 A / dm ² or more. It is preferable to carry out the electrolysis at a current density of 10 seconds or less.

The anodic oxidation polymerized film has been described above,
In the present invention, when the anodized polymerized film is formed on the surface of the Cr plating, the monomers are directly bonded to the surface of the Cr plating by electrolysis, and the organic film obtained by polymerizing them also has a strong bonding force with the surface of the Cr plating. However, good adhesion of the organic film was obtained, and as a result, in combination with the uniformity of the organic film thickness,
Excellent performance in terms of both corrosion resistance and paint adhesion.

As a result of further study by the present inventors, the following findings [A] and [B] were obtained. [A] The effect of forming the Cr plating layer is not limited to the effect of improving the corrosion resistance described above.
The Cr plating layer also has an effect as a barrier of the system plating layer, that is, the Cr plating layer also has an effect of preventing dissolution of the Zn system plating layer during formation of the anodized polymerized film.

[B] After Cr plating, a sufficient amount of organic coating layer can be formed on the surface of the Cr plating layer by continuously performing anodizing polymerization treatment in a wet state without drying the surface of the plating layer. The process leading to this finding will be described below. As described above, with respect to the electrolytic polymerization, there have been few studies to improve the corrosion resistance of metals, and no studies have been particularly made on the formation of an anodized polymerization film on the Zn-based plating layer.

On the other hand, in the examination process of the present invention, when an anodized polymerized film is formed on a Zn-plated steel sheet,
It was found that the dissolution of the Zn-based plating layer (particularly Zn) is prioritized, and a sufficient amount of organic film may not be obtained. Therefore, the present inventors tried and investigated a method capable of forming an organic film with priority over dissolution of a base metal without impairing corrosion resistance, such as selection of an electrolyte in an electrolytic polymerization solution and formation of a barrier for a plating layer.

As a result, as described above, the effect of forming the Cr plating layer is not only the effect of improving the corrosion resistance, but also the effect as the barrier of the Zn-based plating layer at the time of forming the anodic oxidation polymerized film, that is, the Cr plating layer is When forming anodically polymerized film
It was found that it also has an effect of preventing dissolution of the Zn-based plating layer. As described above, it was found that both the corrosion resistance improvement and the barrier effect of the Zn-based plating layer are satisfied by plating with Cr, but by anodic oxidation polymerization after Cr plating,
It was difficult to form a sufficient amount of organic film.

As a cause of this, formation of a passive film by the Cr oxide layer on the surface of Cr plating was considered. That is,
The Cr oxide layer formed during Cr plating is present as a gel-like precipitate on the surface of the metallic Cr at the time of formation, but it is then dehydrated and condensed by drying to form a passive film, which inhibits subsequent anodic oxidation polymerization. I thought. Therefore, Cr is plated on the upper layer of the zinc-based plating layer of the first layer, and then the surface is kept in a wet state without drying, that is, the anodizing polymerization treatment is continuously performed while the Cr-plated surface is kept in a water-containing state. As a result, a sufficient amount of organic coating layer could be formed on the surface of the Cr plating layer.

In the present invention, when Cr plating is applied as a barrier of the Zn-based plating layer at the time of forming the anodic oxidation polymerized film, the adhesion amount of metallic Cr is preferably 50 mg / m ² or more per one side of the steel sheet. . The Cr plating method is not particularly limited, and the commonly known Sargent Cr
Electroplating may be performed using plating or a bath in which sulfuric acid and a fluoride are added to chromium trioxide as an auxiliary agent, a bath in which one or several kinds of fluorides are added to chromium trioxide as an auxiliary agent, and the like.

When Cr plating is applied as a barrier of the Zn-based plating layer when forming the anodized polymerized film, the Cr of the Cr plating layer is
As for the form, it is preferable to have metal Cr and Cr oxide, and the adhesion amount of metal Cr is 50 per one side of the steel plate as described above.
It is preferably at least mg / m ² . This is because when the amount of metallic Cr is large, dissolution of the Zn-based plating layer at the time of forming the anodic oxidation polymerized film is prevented.

Further, in order to form a sufficient amount of the organic coating layer on the surface of the Cr plating layer, when the anodizing polymerization treatment is continuously performed in a wet state without drying the surface of the plated steel sheet after Cr plating, the water content of the plated steel sheet surface after plating, preferably steel sheet per surface 0.5 g / m ² or more, more preferably be carried out subsequently anodic oxidation polymerization process remains held in the steel sheet per side 2 g / m ² or more preferable. The amount of water on the surface of the plated steel sheet in this case can be determined from the measurement of the amount of evaporated water when the plated steel sheet after Cr plating is dried at 100 ° C.

According to the present invention, [a] zinc-based plating, [b]
Cr plating and [c] organic film formation can be performed with a simple set of equipment (one row) in series with the corresponding electrolytic cells in series, enabling in-line processing, that is, processing on the same line. It was Therefore, conventional [d] electroplating, chromate formation by [e] coating type chromate, [f]
The coating coater and baking oven for each of the [e] and [f] steps in the process of forming an organic film by the coating method are not required. Furthermore, in these conventional methods, the electroplating line, the chromate coating line, and the organic film coating line are not required. It eliminates the need for cutting steel strips (strips), coiling, coil transportation, and coil welding, which were required for each process in between, and the present invention provides excellent corrosion resistance, paint adhesion, and weldability. It has become possible to manufacture surface-treated steel sheets with a highly productive method.

[0044]

EXAMPLES Next, the present invention and the effects obtained by the present invention will be specifically described based on Examples. (Example 1) After pickling and degreasing a low carbon steel plate having a plate thickness of 0.75 mm,
Zn-Ni alloy electroplating (Ni: 12% by weight) was applied.

Next, the obtained Zn-Ni alloy electroplating upper layer is further subjected to Cr plating treatment, and then the plated steel sheet is used as an anode to form an organic film by anodic oxidation polymerization under the conditions shown below to perform electrolysis. An organic coated steel sheet was prototyped (Invention Examples 1 to 11 and Comparative Example 9). Various tests such as a corrosion resistance test, a paint adhesion test and a spot weldability test were conducted on the obtained electrolytic organic coated steel sheet.

In this case, after the Cr plating treatment, (1) a treatment method of continuously forming an organic film by anodic oxidation polymerization while the surface of the plated steel sheet is in a wet state (wet state) without drying the surface; 2) The test was conducted by two treatment methods, that is, the surface was dried at room temperature and then the organic film was formed by anodic oxidation polymerization. Further, as comparative materials, various tests such as a corrosion resistance test, a paint adhesion test and a spot weldability test were conducted on the following steel plates.

Steel plates (Comparative Examples 1 to 5) on which an organic film was formed directly by anodic oxidation polymerization on the above-mentioned Zn-Ni alloy electroplating layer. : Zn-Ni alloy electroplated steel sheet itself (Comparative Example 6). : Surface-treated steel sheets obtained by coating the above Zn-Ni alloy electroplated steel sheet with an epoxy resin using a coating coater (Comparative Examples 7 and 8).

An electrolytic organic coated steel sheet (Comparative Example 10) obtained by Cr-plating the above-mentioned low carbon steel sheet and anodic oxidation polymerization on the upper layer thereof under the conditions shown below. : An electrolytic organic coated steel sheet obtained by anodizing polymerization of the above-mentioned low carbon steel sheet directly under the conditions shown below (Comparative Example 11). The conditions for Cr plating and anodic oxidation polymerization are as follows.

[Cr plating] Plating bath composition: CrO ₃ 60 g / l, H ₂ SO ₄ 0.1 to 0.6 g / l Plating bath temperature: 40 ° C. Current density: 50 A / dm ² [anodic oxidation polymerization] Monomer used: pyrrole, Thiophene, phenol, azulene Charged monomer concentration in electrolyte: 0.1 to 1 mol / l Electrolyte in electrolyte: sodium oxalate Sodium oxalate concentration in electrolyte: 0.05 to 0.5 mol / l Solvent for electrolyte: water 100% ~ Water 50% -Methanol 50% Electrolyte temperature: 40 ° C Current density: 5-50A / dm ² Electrolysis time: 0.1-5 seconds The test results obtained are shown in Table 1 together with the plating and organic film formation conditions. Show.

Table 1 also shows the evaluation results of facility and operation simplicity with respect to the respective inventive examples and comparative examples.
In addition, various test methods, evaluation methods, and evaluation criteria thereof are as follows. (Amount of Zn-Ni alloy plating deposited) The amount was determined from the Zn and Ni counts in the fluorescent X-ray analysis.

(Total Cr amount) Obtained from the Cr count number in the fluorescent X-ray analysis. (Amount of metallic Cr) Cr is similarly plated on mild steel (preparation of tin-free steel) and analyzed in the depth direction by ESCA (X-ray photoelectron spectroscopy). A calibration curve was created from the quantification. Based on this calibration curve, the amount of metallic Cr on the Zn-Ni alloy plating was determined by ESCA.

(Amount of Organic Film Adhesion) It was obtained from the C count number in the fluorescent X-ray analysis. (CCT test: Cycle corrosion test) Spray salt water (5% NaCl solution) for 4 hours at 35 ° C → 60 ° C
Then, a cycle corrosion test was carried out, in which drying was performed for 2 hours and then left at 50 ° C. in a 45% RH (wet) atmosphere for 2 hours as one cycle, and the occurrence of red rust was observed. The evaluation is shown by the number of cycles until red rust occurs.

(Paint adhesion test) Film thickness of 20 μm on sample surface
After the electrodeposition coating of No. 1 was applied, the DuPont impact test shown below was performed, and then the sample surface was peeled off with a tape to check the adhesion by the presence or absence of peeling of the coating film. DuPont Impact Test: 1 using a 1/4 inch diameter shotgun
A weight of kg was dropped from the height of 50 cm on the back surface of the sample.

(Spot Weldability) In order to evaluate the spot weldability, a welding tip made of an Al ₂ O ₃ dispersed copper alloy having a tip of 6 mmφ was used, a pressing force of 200 kgf, a welding current of 9 kA and a welding time of 10
Continuous welding was performed at Hz, and the number of continuous welding points until the nugget diameter fell below the reference diameter was measured. The evaluation criteria are shown below.

◎: 3000 points or more ○: 2000 points or more and less than 3000 points △: 1000 points or more, less than 2000 points ×: Less than 1000 points (simpleness in terms of equipment and operation) (a) Simple in terms of equipment Property: It was evaluated whether or not it is possible to manufacture by using the spare tank and the post-treatment equipment of the usual Zn-based plating equipment.
The specific evaluation criteria are shown below.

⊚: When electrolyzing at the same line speed as Zn-based plating, it can be judged that it can be manufactured with equipment within 3 plating tanks (basically expected to be manufactured without expansion). ○: When electrolyzing at the same line speed as Zn-based plating, it can be judged that it can be produced with equipment within 5 plating tanks (those that are expected to be producible with or without small expansion).

X: It can be judged that it is necessary to construct new equipment completely separately. (b) Operational simplicity: ◎: It is judged that the normal Zn-based plating equipment can be operated continuously and there are few management items. ○: It is possible to operate continuously with normal Zn-based plating equipment, but it is judged that the management items will increase.

X: It is judged that it is necessary to temporarily coil up after normal Zn-based plating, transport the coil to another facility, process it again, and manufacture it. As shown in Examples 1 to 11 of the present invention in Table 1, according to the present invention, a surface-treated steel sheet excellent in both corrosion resistance, paint adhesion and spot weldability is an electrolytic bath corresponding to plating and anodizing polymerization. It was obtained at a low cost, which cannot be obtained by the conventional method, with a simple equipment consisting of.

In Comparative Example 1, no Cr plating was applied and the amount of the anodized polymerized film deposited was as small as 0.005 g / m ^2, and the corrosion resistance was poor, and the effect of contributing to the corrosion resistance of the anodized polymerized film and the paint adhesion was revealed. There wasn't. In Comparative Examples 2 to 4 in which the anodized polymerized film was formed, the corrosion resistance and the paint adhesion were improved as compared with Comparative Example 1, but as a result of not performing the Cr plating, the effect of improving the corrosion resistance was compared with the above-mentioned inventive examples. Was few.

In Comparative Example 5, the Zn-Ni plating amount was as small as 5 g / m ² , the plating effect was not sufficient and the corrosion resistance was poor. Further, in Comparative Examples 10 and 11 which were not subjected to Zn-Ni plating, similarly to Comparative Example 5, even though the organic film was formed by anodic oxidation polymerization, the corrosion resistance was extremely poor.

Comparative Example 6 is a conventionally used Zn-Ni plated steel sheet, which shows corrosion resistance in the absence of Cr plating and an anodic oxidation polymerized film. In this case, in the CCT test, 60
Red rust occurred in the cycle. On the other hand, in the present invention examples 1, 2, 4 to 7 and 9 which have Cr plating and an anodized polymerized film on the plated steel sheet of Comparative Example 6, the time until red rust is generated is 150 to 250 cycles. The life of the surface-treated steel sheet can be greatly extended and the paint adhesion is also improved.

In Comparative Examples 7 and 8, the epoxy resin film was formed by coating with a coater, and the adhesion to the Zn-Ni plating was not sufficient. For this reason, the corrosion resistance of the formed organic film was increased. Was hardly seen. In Comparative Example 9, the amount of the anodized polymerized film deposited was large, and the spot weldability was significantly reduced.

[0063]

[Table 1]

[0064]

[Table 2]

Example 2 A low carbon steel plate having a plate thickness of 0.75 mm was pickled and degreased, then pure Zn plating (Zn: 100% by weight), Zn-Cr plating (Cr: 10% by weight), Zn-Cr- Co-Al ₂ O ₃ plating (C
r: 7% by weight, Co: 0.7% by weight, Al ₂ O ₃ : 1% by weight (Al
As))). Next, the upper layer of the obtained zinc-based plating was further subjected to Cr plating treatment by the same method as in Example 1, and then the plated steel sheet was used as an anode to form an organic film by anodic oxidation polymerization under the following conditions. Then, an electrolytic organic coated steel sheet was produced as a prototype (Invention Examples 12 to 18).

Various tests such as a corrosion resistance test, a paint adhesion test and a spot weldability test were conducted on the obtained electrolytic organic coated steel sheet in the same manner as in Example 1. [Anodic oxidation polymerization] Monomers used: pyrrole, thiophene, phenol Charged monomer concentration in electrolyte: 0.1-1 mol / l Electrolyte in electrolyte: sodium oxalate, potassium hydroxide Electrolyte concentration in electrolyte: 0.05-0.5 mol / l Electrolyte solvent: water 100% to water 50% -ethyl cellosolve 50
% Electrolyte temperature: 40 ° C. Current density: 5 to 50 A / dm ² Electrolysis time: 0.1 to 5 seconds The test results obtained are shown in Table 2 together with the plating and organic film formation conditions.

Table 2 also shows the evaluation results of the facility and operation of each of the examples of the present invention. The evaluation method and evaluation criteria are the same as in Example 1. As shown in Table 2, from this example, by having three layers of a zinc-based plating layer, a Cr plating layer, and an organic film formed by anodic oxidation polymerization, due to the synergistic effect of each layer, excellent corrosion resistance and paint adhesion, and It was found that a surface-treated steel sheet having excellent spot weldability was obtained.

[0068]

[Table 3]

[0069]

According to the present invention, a surface-treated steel sheet excellent in corrosion resistance, paint adhesion and weldability can be obtained.
In particular, it is possible to provide an excellent steel plate as a material for an automobile body. Further, according to the present invention, the steel sheet can be manufactured by a simple facility that is not required in the conventional method and by a method excellent in economic efficiency, and not only the industrial effect is great, but the present invention is It contributes to the improvement of durability and eventually to the saving of global resources.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of a steel sheet surface when an ultrathin organic film is formed on the steel sheet by coater coating.

FIG. 2 is a schematic view showing a cross section of a steel plate surface when an ultrathin organic film is formed on the steel plate by electrolytic polymerization.

[Explanation of symbols]

 1 Underplated steel plate 2, 3 Organic film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomokatsu Katagiri 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Institute (72) Inventor Shuichi Asahina 1 Kawasaki-cho, Chuo-ku, Chiba (72) Inventor Kazuo Mochizuki, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Inside Kawasaki Steel Co., Ltd.

Claims (2)

[Claims] 1. A steel sheet has a plating layer selected from any one of a zinc plating layer, a zinc alloy plating layer, and a zinc composite dispersion plating layer on at least one surface of the steel sheet, and an amount of the total amount of Cr deposited on the plating layer is an upper layer. Electrolytic organic material with excellent corrosion resistance, characterized in that it has a Cr plating layer of 10 to 1000 mg / m ² and further has an organic coating of 0.01 to 3 g / m ² deposited thereon by anodic oxidation polymerization. Coated steel sheet. 2. A zinc-based plating selected from zinc plating, a zinc-based alloy plating, and a zinc-based composite dispersion plating is applied to at least one surface of a steel sheet, and then the adhesion amount is 10 to 1000 mg in terms of the total Cr amount. / subjected to Cr plating m ^2, excellent corrosion resistance, characterized in that to form the organic coating adhesion amount 0.01 to 3 g / m ² performs anodic oxidation polymerization process without drying the plated steel sheet surface after the Cr plating Method for producing electrolyzed organic coated steel sheet.