JPH07278844A - Organic-coated rustproof steel sheet excellent in spot weldability - Google Patents

Abstract

PURPOSE:To produce an organic-coated rustproof steel sheet with the spot weldability improved while securing the corrosion resistance, deposition coating suitability and press workability. CONSTITUTION:A chromate coating film contg. 10-60mg/m<2> oxide of at least one kind of element selected from a group consisting of Si, Al, Zn, Mg and Co in total is provided on zinc or galvanized steel sheet at the chromium coating weight of 10-100mg/m<2> as a first layer. A resin coating film contg. org. resin silane coupling agent, colloidal silica and the phosphate at least one kind of element selected from a group consisting of Al, Ba, Ca, Co, Mg and Zn is formed on the first layer as a second layer in a range of 0.1-2g/m<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic coated rust-preventive steel sheet having excellent spot weldability, and more specifically, it has excellent spot weldability, corrosion resistance, workability, paintability, etc. The present invention relates to an organic coated rust-preventive steel plate that can be suitably used for electric appliances for construction, walls for buildings and the like.

[0002]

2. Description of the Related Art In recent years, the demand for corrosion resistance has increased in automobile bodies, household electric appliances, walls for buildings, etc., and thus, instead of conventional cold-rolled steel plates and steel plates with plating, corrosion resistance Surface-treated steel sheets, which are even better, have been used. Conventionally, as such a surface-treated steel sheet, a zinc plated steel sheet, Ni, Fe, Mn, Mo, Co, Al,
Zinc or zinc-based plated steel sheet containing one or more kinds of metals such as Cr or oxides thereof, or multi-layered plated steel sheet obtained by applying zinc or zinc-based plating in multiple layers,
Furthermore, organic coated steel sheets in which a chromate layer and an organic resin layer are provided on these plated steel sheets have been developed, and in particular, they are used in large quantities in automobile bodies.

However, these conventional organic coated steel sheets do not satisfy all the properties required as a rust-preventing steel sheet in automobile bodies and other applications.
It is still insufficient in spot weldability. For example,
Japanese Patent Publication No. 45-24230 and Japanese Patent Publication No. 47-8882
Although the zinc-coated steel sheet described in Japanese Patent Publication No. JP-A-2004-242242 can be electrodeposited, it is not sufficient in terms of corrosion resistance, press formability, weldability and the like. Also, Japanese Patent Publication No. 52-44569, Japanese Patent Publication No. 58-138758, and Japanese Patent Publication No. 51-
Japanese Patent Publication No. 79138 discloses a resin-coated steel sheet containing a conductive inorganic pigment in order to improve weldability. Such a resin-coated steel sheet has improved weldability and is also excellent in corrosion resistance, but since the resin coating has a conductive pigment with a relatively large particle size, it lacks surface smoothness, and therefore However, when electrodeposition coating is applied, the coating film surface becomes uneven, and the appearance is significantly impaired.

On the other hand, JP-A-60-33192, JP-A-58-224174, and JP-A-60-1748.
No. 79, etc., the film thickness is 0.3 including no conductive inorganic pigment.
An organically coated steel sheet provided with a thin film of an organic composite silicate having a thickness of up to 3 μm has been proposed. Such an organic composite silicate thin film can be electrodeposited on it, and
Although the corrosion resistance, weldability, press formability, etc. have been improved, unevenness is still observed on the surface of the electrodeposition coating film.

Therefore, in JP-A-4-197473, a chromate film is applied as a first layer on a zinc-based plating layer, and a second layer is formed thereon with colloidal silica or a silane coupling agent. Although an organic coated steel sheet which is formed by applying a resin coating containing the above phosphate and has improved electrodeposition coatability and weldability, there is still room for improvement in weldability.

[0006] For example, steel products are mainly used as a material for car bodies during the manufacture of automobile bodies, and spot welding is an indispensable means for joining them. Here, conventionally, the welding of the car body is usually
Since it is performed by an automatic welding robot, it is said that welding is a major problem. Here, as the welding, not only the severe welding that has been conventionally required to be solved (hereinafter, simply referred to as welding) but also the slight welding between the resin coating on the surface of the organic coated steel sheet and the welding chip. Even when the welding occurs, the automatic welding robot interrupts the work. Therefore, it is required to solve the slight welding (hereinafter referred to as light welding).

Further, in the conventional organic coated rust-preventive steel sheet, external dust caused by applying an organic resin coating which is originally insulative to the surface of the steel sheet is also a problem. Outer dust is, for example, not a normal dust (hereinafter referred to as a dust) generated from a superposed portion of steel plates, but is generated from between a steel plate surface and a welding electrode chip, and is also called a spark. . Conventionally, with respect to this spark, the generation mechanism, the prevention method, and the like have not been clarified at all, so that the generation cannot be suppressed.

[0008]

The present invention has been made to solve the above-mentioned various problems in the conventional organic coated rust-preventive steel sheet, and ensures corrosion resistance, electrodeposition coating property and press workability. At the same time, it is an object of the present invention to provide an organic coated rust-preventive steel sheet having improved spot weldability.

[0009]

An organic coated rust-preventive steel sheet excellent in spot weldability according to the present invention is a group consisting of (A) Si, Al, Zr, Mg and Co on a zinc or zinc-based plated steel sheet. A total of 10 oxides of at least one element selected from
Has a chromate film comprising at range to 60 mg / m ² as a first layer in the range of 10-100 mg / m ² as chromium deposition amount, thereon, with (B) an organic resin, (a) Shirankatsupu Ring agent,
(b) Colloidal silica, and (c) Al, Ba, Ca, C
at least 1 selected from the group consisting of o, Mg and Zn
It is characterized by having a resin coating containing a phosphate of a seed element in the range of 0.1 to ² g / m ² as the second layer.

The organic coated rust-preventive steel sheet excellent in spot weldability according to the present invention is obtained by applying S or S on a zinc or zinc-based plated steel sheet.
The first layer has a chromate film containing an oxide of at least one element selected from the group consisting of i, Al, Zr, Mg and Co (hereinafter referred to as an inorganic oxide). Such a chromate coating improves the corrosion resistance of the steel sheet and the adhesion between the steel sheet and the resin coating. The effect of such a chromate film is a barrier effect by an inorganic polymer film made of Cr ³⁺ formed on a zinc or zinc-based plated steel sheet, and a Cr effect trapped in such an inorganic polymer film. ^It is thought to be due to the self-repairing function of ⁶⁺ .

In the present invention, such a chromate is used.
The coating has a chromium adhesion of 10 to 100 mg.
/ M²It is preferably in the range of. With chromate coating
Adhesion amount is 10 mg / m as chromium adhesion amount²Less than
Is sufficient to improve the corrosion resistance of the steel sheet with the chromate coating.
None, on the other hand, 100 mg / m²When it exceeds the
Cr in coating⁶⁺As the amount increases,
Cr in the environment when handling ⁶⁺Elutes and causes environmental pollution
There is a risk. Particularly preferably, the chromate film
Adhesion amount is 20-80mg / m in terms of chromium adhesion amount²Range of
Is.

In the present invention, the chromate coating is S
It contains an inorganic oxide of at least one element selected from the group consisting of i, Al, Zr, Mg and Co, and these inorganic oxides improve the corrosion resistance and weldability of the steel sheet. The reason is not necessarily clear, but by incorporating these inorganic oxides in the chromate film, which is an inorganic polymer film, to suppress the permeation of water and oxygen, which are substances that promote corrosion. It seems that there is.

Such an inorganic oxide is preferably contained in the chromate coating in a total amount of 10 to 60 mg / m ² so that the resulting organic coated rust-preventive steel sheet has excellent spot weldability. . The effect of the inorganic oxide in the chromate film during welding is not always clear, but it is presumed as follows. The chromate film itself is C
Since it is an inorganic polymer film mainly composed of r ³⁺ , originally,
Although it is insulative, when the inorganic oxide is included, fine particles of the inorganic oxide may adhere to the tip of the chip during spot welding to suppress the wear of the tip of the chip. When the amount of the inorganic oxide compounded in the chromate coating is less than 10 mg / m ² , the effect of suppressing such wear of the tip of the chip is poor, while when it is more than 60 mg / m ² ,
It impedes conductivity and makes the welding current non-uniform, causing light welding during welding.

Particularly in the present invention, the compounding amount of the inorganic oxide in the chromate film is preferably in the range of 30 to 50 mg / m ² .

According to the present invention, a silane coupling agent, phosphoric acid, and a fluorine compound are added to the chromate film in order to suppress corrosion resistance, paintability, weldability, workability, elution of chromium and the like. Also, the suppression of the black color change in the plating,
Co, Ni, Fe for the purpose of improving the adhesion of the coating film
You may add metal ions, such as.

The organic coated rust-preventive steel sheet excellent in spot weldability according to the present invention has the above-mentioned chromate coating as the first layer, and further has a silane coupling agent, colloidal silica, and Al in addition to the organic resin. , Ba, Ca,
It has a resin film containing a phosphate of at least one element selected from the group consisting of Co, Mg and Zn.

Particularly, the resin coating is 2 to 40 parts by weight of a silane coupling agent with respect to 100 parts by weight of the organic resin.
10-60 parts by weight of colloidal silica, and Al, Ba,
It is preferable to contain 15 to 50 parts by weight of a phosphate of at least one element selected from the group consisting of Ca, Co, Mg and Zn.

In the present invention, the resin forming the resin coating is preferably a urethane resin. here,
The urethane-based resin is a polymer obtained by polymerizing an organic polyisocyanate and a polyvalent hydroxy compound in the presence of, for example, a polyvalent amine compound as a curing agent. Usually, an organic polyisocyanate and a polyvalent hydroxy compound are previously reacted to obtain a urethane prepolymer, and this is reacted in the presence of a curing agent to obtain a urethane resin.

The above-mentioned organic polyisocyanate is not particularly limited, but for example, tolylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, hexamethylene diisocyanate, xylylene diisocyanate,
Aliphatic, aromatic and / or alicyclic polyisocyanates such as naphthalene diisocyanate, tolidine diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated dicyclohexylmethane diisocyanate, and further dimers and trimers thereof Used.

The polyhydric hydroxy compound is also not particularly limited, but for example, polyalkylene glycol, polyamine polyol, polymer polyol, polyether polyol such as polytetramethylene glycol, adipate polyol, phthalic acid polyol. ,
Polyester polyols such as polycarbonate polyols, polyhydric alcohols such as trimethylolpropane and butanediol, etc. are used.

Examples of the polyvalent amine compound as a curing agent include methylene orthochloroaniline,
Examples thereof include, but are not limited to, diaminodiphenylmethane, ethylenediamine, diethylenetriamine, hydrazine, isophoronediamine, and triethylenetetramine.

In the present invention, preferably, the urethane resin has a hydrophilic group in its molecule, and an aqueous urethane resin obtained by emulsifying in water with an emulsifier if necessary is preferably used. Various types of water-based resins have been already known. For example, when an epoxy resin or an acrylic resin is used, the resin film obtained is inferior in electrodeposition coating property and corrosion resistance after processing.

In the present invention, the resin coating contains a silane coupling agent and colloidal silica. Examples of the silane coupling agent include γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and γ-methacryloxy. Propyltrimethoxysilane,
β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (aminoethyl)
Examples include -γ-aminopropylmethyldimethoxysilane and the like.

The content of the silane coupling agent in the resin coating is preferably in the range of 2 to 40 parts by weight with respect to 100 parts by weight of the organic resin. When the content of the silane coupling agent in the resin film is less than 2 parts by weight with respect to 100 parts by weight of the organic resin, there is no effect in improving the spot weldability of the obtained organic coated rust-preventive steel sheet, and the resin The corrosion resistance of the coating also does not improve. However, when the amount exceeds 40 parts by weight with respect to 100 parts by weight of the organic resin, a large amount of sparks are generated during spot welding and the effect of improving the corrosion resistance of the resin coating is saturated, which is not economically preferable. . Particularly, in the present invention, from the viewpoint of such corrosion resistance and spot weldability, the content of the silane coupling agent in the resin coating is in the range of 5 to 20 parts by weight with respect to 100 parts by weight of the organic resin. Is preferred.

As the colloidal silica, commercially available products can be preferably used. Examples of such commercially available products include Snowtex SS, Snowtex XS, Snowtex 40, Snowtex O, Snowtex N, Snowtex C (all manufactured by Nissan Kagaku Co., Ltd.).

The content of colloidal silica in the resin coating is preferably 1 with respect to 100 parts by weight of the organic resin.
It is in the range of 0 to 60 parts by weight. The content of colloidal silica in the resin coating is 100 parts by weight of the organic resin,
When the amount is less than 10 parts by weight, the effect of improving the corrosion resistance and paintability of the resin coating is poor. However, the organic resin 10
When the amount exceeds 60 parts by weight with respect to 0 parts by weight, the resin film formed becomes excessively hard, the resin film is not sufficiently removed during spot welding, welding occurs, and corrosion resistance after processing is also increased. to degrade. In particular, in the present invention, in addition to spot weldability, the resulting organic coated rust-preventive steel plate has corrosion resistance,
The content of colloidal silica in the resin coating is preferably in the range of 20 to 40 parts by weight with respect to 100 parts by weight of the organic resin so as to have excellent coatability and processability.

According to the present invention, the spot weldability can be further improved by blending the silane coupling agent and the colloidal silica together in the resin coating.

Further, in the present invention, the resin coating is used together with the above-mentioned colloidal silica and silane coupling agent in order to improve spot weldability and corrosion resistance.
It contains a phosphate of at least one element selected from the group consisting of 1, Ba, Ca, Co, Mg and Zn, and the amount thereof is preferably 15 with respect to 100 parts by weight of the organic resin.
Is in the range of 50 parts by weight. When the content of the phosphate in the resin coating is less than 15 parts by weight with respect to 100 parts by weight of the organic resin, the effect of improving weldability and corrosion resistance is poor, while the content of the phosphate in the resin coating is poor. This is because when the content exceeds 50 parts by weight with respect to 100 parts by weight of the organic resin, the corrosion resistance of the resin coating may deteriorate.

In the organic coated rust-preventing steel sheet according to the present invention, the resin composition containing the aqueous resin is applied onto the chromate film and dried to form a resin film. Since it is poorly soluble, when it is blended in an excessively large amount in the resin composition, in the resin composition,
Agglomeration and precipitation of phosphate occur, which reduces the stability of the resin composition and the workability at the time of coating on a steel sheet. Further, the obtained resin coating film may be non-uniform. Particularly, in the present invention, the content of the phosphate in the resin coating is preferably in the range of 30 to 50 parts by weight with respect to 100 parts by weight of the organic resin.

Generally, in welding an organic coated rustproof steel sheet, the electrical conductivity of the resin coating is important. Therefore, in the conventional organic coated steel sheet, a conductive inorganic pigment is blended in the resin coating to ensure the electrical conductivity. However, as described above, the surface of the resin coating containing the conductive inorganic pigment is inferior in smoothness, so that the surface irregularity of the coating due to electrodeposition coating is remarkable. However, since the resin coating containing no conductive inorganic pigment has a large electric resistance, the electric current at the time of welding is large, the wear of the welding chip is promoted, and the continuous spotting property is deteriorated.

On the other hand, according to the present invention, the resin coating as the second layer contains a phosphate, and
According to the organic coated rust-preventive steel sheet containing an inorganic oxide in the chromate film as a layer, during spot welding, by the phosphate fine particles and the inorganic oxide, the resin film is mechanically destroyed, The electric resistance of the coating itself decreases, thus
It is thought that spot weldability is improved because the current easily flows. The above-mentioned phosphate suppresses chip wear at the time of welding, and has a particularly excellent effect on continuous hitting property.

In the present invention, the adhesion amount of the above resin film is preferably in the range of 0.1 to ² g / m ² . When the amount of the resin film deposited is less than 0.1 g / m ² , it is difficult to give the resin film a stable and high corrosion resistance.
On the other hand, when it exceeds ² g / m ² , there is no particular problem in terms of corrosion resistance, but even if a phosphate is added, the spot weldability is still insufficient. Especially from the point of spot weldability,
According to the present invention, the adhesion amount of the resin coating is 0.3 to 1.0 g /
It is preferably in the range of m ² .

In the present invention, the steel plate may be a generally manufactured zinc plated steel plate or a zinc alloy electroplated steel plate, and the manufacturing method thereof is not limited at all.

The organic coated rust-preventive steel sheet according to the present invention has zinc or zinc-based plating on at least one surface of the steel sheet as described above, and further has a chromate coating and a resin coating in this order. Have.

In the present invention, the base steel sheet is a zinc or zinc-based plated steel sheet from the viewpoints of corrosion resistance and workability, and the zinc-based plated steel sheet is not particularly limited. Preferable examples include alloyed steel sheets of zinc and at least one of iron, chromium, nickel, cobalt, manganese, aluminum and the like.
For example, for car body applications, nickel content of 9-15
A steel plate with a zinc-nickel alloy plating of wt% is preferably used.

The chromate treatment is already well known. The organic coated rust-preventing steel sheet according to the present invention is a chromate-treated solution prepared by mixing an inorganic oxide in a reduced chromic acid solution obtained by reducing a chromic anhydride solution, and using this as a chromate treatment solution, the surface of a zinc or zinc-based plated steel sheet Is applied in a usual manner and dried to form a chromate film. A silane coupling agent, colloidal silica and phosphate are mixed with an aqueous urethane resin to form a coating composition, and the coating composition is applied onto the chromate film and dried to obtain an organic coating according to the present invention. A rustproof steel plate can be obtained.

[0037]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

Example 1 A zinc-nickel alloy was deposited on a cold-rolled steel sheet having a thickness of 0.8 mm which had been degreased and pickled by a conventional method, using a sulfuric acid bath at a deposition amount of 20 g / m ² . I gave a tsuki. An inorganic oxide was added to a reduced chromic acid solution obtained by reducing the chromic anhydride solution to various concentrations to prepare a chromate-treated solution, which was treated with the above zinc-
It was applied onto a nickel alloy plated steel plate, dried, and chromated. Along with 100 parts by weight (solid content) of the urethane resin, 15 parts by weight of a silane coupling agent and 30 parts of colloidal silica are used together with the aqueous urethane resin.
An aqueous resin composition containing 1 part by weight and 40 parts by weight of phosphate was applied so that the coating weight after drying was 1.0 g / m ^2, and dried to obtain an organic coated rust-preventing steel sheet.

The following evaluations were performed on these. The results are shown in Tables 1 to 4. Spot weldability Electrode tip diameter 6 mm FC Applied pressure 200 kgf current 9 kA time 10 cycles Number of dots 1000 dots Under the above conditions, the following items were evaluated. Light welding: The steel plate adheres to the welding chip during continuous welding, but no uniform alloy layer is found on the chip and the steel plate Number of welding occurrences Spark welding Number of dust between resin and resin coating

Corrosion resistance Using a draw bead tester as shown in FIG. 1, after processing at a tensile rate of 300 mm / min and an elongation of 15%, 3
Salt spray at 5 ° C for 4 hours, heat drying at 60 ° C for 2 hours,
Wet for 2 hours at 50 ° C., then cycle to return to salt spray for 1 hour and 8 hours to carry out a cycle test. After 200 cycles, rust was removed and the erosion depth was measured with a dial gauge.

Coatability A cationic electrodeposition coating composition was used to apply electrodeposition coating having a film thickness of 20 μm, and then an intermediate coating and a topcoat coating for automobiles were each spray-coated to a thickness of 35 μm and baked. Then
After immersing in warm water of 50 ° C for 240 hours, put a 2 mm grid with a cutter knife and perform an adhesive tape test.
The amount of remaining coating film / the number of grids (100) was used for display.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

Example 2 On a cold-rolled steel sheet having a thickness of 0.8 mm which was degreased and pickled by a conventional method, a sulfuric acid bath was used to deposit a zinc-nickel alloy at a deposition amount of 20 g / m ² . I gave a tsuki. Then, chromate treatment was performed on the plated steel sheet so that the amount of chromium deposited was 50 mg / m ² and the inorganic oxide in the coating film was 40 mg / m ^2, and further, a silane coupling was performed with the aqueous urethane resin. A resin composition containing an agent, colloidal silica and phosphate is applied so that the coating weight after drying is 1.0 g / m ² .
It was dried to obtain an organic coated rustproof steel plate.

These were evaluated in the same manner as in Example 1. The results are shown in Tables 5 to 8. In the table, the addition amounts (parts) of the silane coupling agent, colloidal silica and phosphate in the column of resin coating are the parts by weight per 100 parts by weight of the resin.

[0048]

[Table 5]

[0049]

[Table 6]

[0050]

[Table 7]

[0051]

[Table 8]

Example 3 Degreasing and pickling by a conventional method to a thickness of 0.8
20 g / m ² on a cold-rolled steel sheet with a sulfuric acid bath
A zinc-nickel alloy plating was applied. Then, a chromate treatment is performed on the plated steel sheet so that the amount of chromium deposited is 50 mg / m ² and the inorganic oxide in the coating film is 40 mg / m ² .
Further, on top of that, together with an aqueous urethane resin, 15 parts by weight of a silane coupling agent, 30 parts by weight of colloidal silica, and various amounts of phosphate per 100 parts by weight (solid content) of the urethane resin. The resin composition was applied with a bar coater and dried to obtain an organic coated rustproof steel plate.

The following evaluations were performed on these. The results are shown in Tables 9 to 16. In the table, the addition amount (parts) of the phosphate is the number of parts by weight with respect to 100 parts by weight of the resin.

[0054]

[Table 9]

[0055]

[Table 10]

[0056]

[Table 11]

[0057]

[Table 12]

[0058]

[Table 13]

[0059]

[Table 14]

[0060]

[Table 15]

[0061]

[Table 16]

[Brief description of drawings]

FIG. 1 is a view showing a draw bead test device used for examining corrosion resistance after processing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Yamaguchi 1 Kanazawa-machi, Kakogawa-shi, Hyogo Kamido Steel Works Kakogawa Works

Claims (3)

[Claims] 1. A total of 10 (A) oxides of at least one element selected from the group consisting of Si, Al, Zr, Mg and Co on a zinc or zinc-based plated steel sheet.
Has a chromate film comprising at range to 60 mg / m ² as a first layer in the range of 10-100 mg / m ² as chromium deposition amount, thereon, with (B) an organic resin, (a) Shirankatsupu Ring agent,
(b) Colloidal silica, and (c) Al, Ba, Ca, C
at least 1 selected from the group consisting of o, Mg and Zn
An organic coated rust-preventing steel sheet having excellent spot weldability, which has a resin coating containing a phosphate of a certain element as a second layer in the range of 0.1 to ² g / m ² . 2. A total of 10 or more oxides of at least one element selected from the group consisting of (A) Si, Al, Zr, Mg and Co on a zinc or zinc-based plated steel sheet.
Has a chromate film comprising at range to 60 mg / m ² as a first layer in the range of 10-100 mg / m ² as chromium deposition amount, thereon, with respect to (B) an organic resin 100 parts by weight, (a) 2 to 40 parts by weight of silane coupling agent, (b) colloidal silica 10
~ 60 parts by weight, and (c) Al, Ba, Ca, Co, Mg
And a resin coating containing 15 to 50 parts by weight of a phosphate of at least one element selected from the group consisting of Zn and Zn.
An organic coated rustproof steel sheet having excellent spot weldability, which has a second layer in the range of g / m ² . 3. The organic resin is a urethane resin.
Alternatively, the organic coated rust-preventing steel sheet according to 2 above.