JP2002172363A - Organic coating-bearing surface treated steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pre-primed steel plate made of a zinc base plating-plated steel as a mother material, subjected to under coating treatment, coated with an under coating, and excellent in weldability to such as spot welding and seam welding and corrosion resistance in the cut end face. SOLUTION: The organic coating-bearing surface treated steel plate is a zinc or zinc-based alloy-plated steel plate subjected to an under coating treatment and further coated with an organic resin coating containing 10-70% by mass of ferrosilicon with a particle size of 0.5-10 μm in 2.5-8 μm thickness. In this case, ferrosilicon with 15-95% by mass of Si content is preferable. The under coating treatment may be a layer of a thermosetting type resin containing 20-95% by mass of colloidal silica in a thickness of 0.05-0.5 g/m3 or the plating layer may be an alloy plating containing 0.2-10% by mass of cobalt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic-coated surface-treated steel sheet which is obtained by applying an organic coating to a pure galvanized steel sheet or a zinc-based alloy-plated steel sheet, and then welding after press working.

[0002]

2. Description of the Related Art In consideration of improvement of corrosion resistance and design of appearance,
Zinc-based plated steel sheets are often used with their surfaces painted.
Such a steel sheet whose surface is coated with a paint at the stage of flat plate shipment at the factory is generally referred to as an organic-coated surface-treated steel sheet. This steel sheet is formed into required parts,
When the surface is shipped from the factory and used as an outer panel of a product, it is called a pre-coated steel sheet, and has been used for roofing materials and wall materials in the field of building materials. In addition, since it is omitted in the painting process, it is widely used for home appliances and outer panels of indoor equipment.

[0003] However, the precoated steel sheet has no electrical conductivity in the surface coating film, making it difficult to perform electric resistance welding, which is often used in automobile production, etc., and the design of the surface remains as it is when shipped from the steel sheet factory. For this reason, the field of application is often limited. On the other hand, there has been considered a method of simplifying the coating process by performing forming and welding using a steel sheet that has already been subjected to base treatment and undercoating, and applying only coating that determines the final appearance. . A steel sheet which has been subjected to the base treatment and the coating of the lower layer and which can achieve the desired appearance by coating only the upper or middle layer and the upper layer is called a pre-primed steel sheet.

[0004] When a surface-treated steel sheet is used for an outer panel of an automobile for the purpose of corrosion resistance, in the manufacturing process of the automobile, usually, press working, assembly by spot welding or seam welding are performed.
An undercoat is applied to the lowermost layer by electrodeposition coating, and then the middle and upper layers are applied. Such surface-treated steel sheets for automobiles include zinc-plated steel sheets mainly on the inner surface and zinc-cloth metal coated with an organic coating film containing zinc powder (trade name of Diamond Shamrock Co., Ltd.)
Also, a thin-film organic composite plated steel sheet in which a thin organic film is applied on a zinc alloy plating has been used.

[0005] All of these surface-treated steel sheets are premised on carrying out electric resistance welding and electrodeposition coating. For this reason, when an organic coating film is provided, the coating film must be electrically conductive to have conductivity. In the case where particles are contained or the conductive particles are not contained, a thin film is formed so as not to hinder energization. And many inventions have been proposed regarding the organic composite plated steel sheet having both such electrodeposition coating property and weldability.

[0006] The pre-primed steel sheet has almost the same structure as the above-mentioned thin film organic composite coated steel sheet. The pre-primed steel sheet is subjected to a base treatment on a zinc or zinc-based alloy coated steel sheet, and an organic coating film containing conductive particles is formed thereon. Cover with. However, in the case of thin-film organic composite plated steel sheets, it is assumed that electrodeposition coating is performed on the side where the steel sheet is used, whereas pre-primed steel sheets do not undercoat electrodeposition coating or middle layer coating That is, these steps are omitted, and the product manufacturing process is rationalized.

It is needless to say that such a steel sheet requires a certain plating thickness for ensuring corrosion resistance, in addition to characteristics such as excellent workability and high strength of the base steel sheet depending on the use. Absent. Although electrodeposition coating is not particularly necessary, spot welding, seam welding, etc.
It is essential that resistance welding can be performed with the surface film as it is, and these weldability must be good. Also,
When electrodeposition coating is performed, the cut end face is well coated with paint, and the corrosion resistance of that part is good, but in the case of pre-primed steel sheet, the middle layer and the upper layer or only the upper layer is painted or used as it is, so cut it The corrosion resistance of the end face becomes a problem.

Several proposals have been made for such a pre-primed steel sheet. For example, JP 9-2767
No. 88 discloses a chemical treatment (chromate treatment) of a chromium compound as a base treatment on the surface of a zinc-based alloy plated steel sheet of zinc-iron, zinc-nickel, or zinc-chromium.
The invention of a steel sheet in which an organic film composed of 40 to 90% by volume of an organic resin, 3 to 59% by volume of a conductive pigment and 1 to 57% by volume of a rust preventive pigment is formed thereon to a thickness of 0.5 to 20 μm is disclosed. ing.

Japanese Patent Application Laid-Open No. 10-43677 discloses that a zinc-coated steel sheet is subjected to a chromate treatment, and a resin obtained by blending 5 to 80 parts by weight of an isocyanate compound with 100 parts by weight of an epoxy resin is used as a base. The conductive pigment and the amount of the solid lubricant were each regulated and added, and the thickness was 1.0 to 30 μm.
The invention of a steel sheet coated with a resin film is proposed.

Further, the invention disclosed in Japanese Patent Application Laid-Open No. H11-5269 discloses that a zinc-plated or aluminum-plated metal plate subjected to a base treatment contains iron phosphide as a main component depending on the thickness to be coated. The present invention relates to a weldable resin-coated steel sheet having a resin film to which a conductive pigment is added.

In each of the above-mentioned inventions, a chromate treatment is applied as a base treatment on zinc or zinc alloy-based plating, and a resin to which a conductive pigment and a rust-preventive pigment are added is coated while regulating the film thickness. In common. The conductive pigment makes the resin conductive and facilitates welding, and the rust preventive pigment mainly improves the corrosion resistance of the cut end face.

However, in order to ensure weldability, it is preferable that the thickness of the resin film is thinner, although it has conductivity. On the other hand, from the viewpoint of rust prevention at the cut end surface, it is preferable that the resin thickness is thicker. Therefore, it is difficult to say that a steel sheet having these two contradictory characteristics sufficiently compatible is obtained.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a zinc-plated steel sheet having excellent spot weldability and seam weldability and excellent corrosion resistance at a cut end face as a base material, and to perform a base treatment and a lower layer coating. In providing pre-primed steel sheets.

[0014]

Means for Solving the Problems The present inventors have conducted various studies mainly on pre-primed steel sheets applicable to automobile parts in order to improve the practicality thereof. In the case of automobiles, spot welding and seam welding are frequently used, and therefore, their weldability is particularly important. This weldability means early wear of the electrode due to repeated use, contamination of the electrode by plating and decomposition products such as resin, and consequent impairment of nugget formation. It is considered that the case approaches a case of a bare steel plate without a surface coating layer.

First, the base material of the steel sheet is excluded from the study because the material is determined depending on whether the use of the part requires strength or deep drawing is required. It is considered that the plating layer is preferably thin and hard from the viewpoint of weldability, but is often selected in terms of corrosion resistance and peeling during processing, and cannot be limited only by weldability. However, in general, zinc alloy-based plating is preferable for pre-primed steel sheets because the same corrosion resistance is obtained even when it is thin, and the plating layer tends to be harder. Next, as the organic film for coating the plating layer, various kinds of materials are applied from the performance required as a coating material for the base resin, and various organic additives are mixed in to improve the performance. You. However, most of these components are decomposed and diffused at a high temperature during welding, except for inorganic pigments, so that it is considered that they have no direct effect on weldability except for the thickness related to the amount.

In view of the above, conductive pigments or conductive powders which are added for the purpose of imparting conductivity to the resin film for welding and which are considered to remain even during heating at a high temperature during welding are particularly suitable for welding. Investigations were conducted with emphasis on the effects on the environment. As the conductor powder,
There were metals, alloys, carbon, other conductive compounds, and the like, and as a result of various tests on those which could be adjusted, it was found that ferrosilicon, that is, Fe-Si alloy powder showed the best results. However, it is not always clear why ferrosilicon powders give good results.

Generally, iron phosphide powder is often used to impart conductivity to the coating resin. However, phosphorus causes embrittlement by a small amount when entering steel,
Once in the copper used for welding electrodes, it also tends to be hard and brittle. Since phosphorus evaporates at a temperature much lower than the melting point of steel or copper and is thought to enter steel or copper, it was thought that this would promote a reduction in the strength of the weld and deformation of the electrode.

On the other hand, in the case of silicon, such embrittlement does not occur even in a small amount, and it is not easily vaporized like phosphorus. Silicon has a large deoxidizing effect on molten iron, and especially in seam welding, etc., blowholes may be formed in the weld near the melting point of steel, but it is also effective in suppressing such blowholes There seems to be. Ferrosilicon itself is hard and brittle, and it is easy to obtain fine and uniform powder, so that it is well dispersed in resin. As a result, in spot welding or seam welding in which pressure is applied and electricity is generated to generate heat, it is speculated that current may flow evenly in the pressurized portion and uneven wear of the electrodes may be suppressed, resulting in excellent weldability. .

There are different types of ferrosilicon materials depending on the silicon content, but those with a lower silicon content are particularly excellent. This is because if the amount of silicon increases, the electric resistance increases, and furthermore, it becomes too brittle, so that it is difficult to form a uniform energizing path at the time of welding, and it is thought that electrode wear is increased.
Regarding the particle size and amount of ferrosilicon to be added,
It was confirmed that there was an optimum content range for maintaining not only weldability but also properties as a paint.

As described above, since it was expected that an organic resin layer having excellent weldability could be obtained, the corrosion resistance of the cut end face when the surface was coated with this paint was examined. The corrosion resistance of the cut end face is improved by the presence of a plating layer that is base to iron such as zinc. Then, it is considered that the presence of the organic film covers the cut end surface due to the infiltration of the film at the time of cutting, and the corrosion resistance of that portion is further improved. Such an effect cannot be expected much when the plate thickness is large, but is very effective when the plate thickness is about 1 mm or less, such as for an automobile.

As a result of the investigation, it was confirmed that the effect of improving the end face corrosion resistance was obtained if the organic film had a certain thickness or more, and that the thicker the organic film, the better. However, when the thickness is increased, there is a limit because the weldability deteriorates even with a film having improved conductivity. In addition, the addition of a pigment having a rust-preventing effect to the organic film was also effective for end-surface rust prevention.

In the process of studying the improvement of the weldability and the corrosion resistance of the cut end face, the influence of the composition of the plating layer was also investigated, and it was confirmed that alloy plating was preferable to pure zinc plating. Above all, it was found that the Zn-Co alloy plating had better corrosion resistance on the end face and good weldability if the basis weight was the same. This is Zn
This is because the -Co alloy is more base than other zinc-based alloys, and thus has a large effect of suppressing the generation of red rust. In addition, it is considered that the -Co alloy has an effect of increasing the hardness of the plating layer.

An undercoating treatment is performed to sufficiently adhere an organic coating material to a metal surface such as plating and to improve corrosion resistance. As a base treatment, chromate treatment is widely performed on zinc-based plating, and phosphate treatment is also performed. After performing the undercoating, an organic coating containing the above-described ferrosilicon pigment is applied. If a commonly used undercoating is employed, a steel sheet having the features of the present invention can be manufactured.

A more effective undercoating method for the organic film containing the ferrosilicon pigment was examined. As a result, it has been found that by applying and drying a liquid composed of colloidal silica and a thermosetting resin, a film adhesion and a corrosion resistance of a cut end surface equivalent to or higher than that of a chromate treatment can be obtained. The colloidal silica acts together with the thermosetting resin to strengthen the adhesion to the plating surface, and the thermosetting resin is considered to be involved in the adhesion with the coating resin thereon, that is, the secondary adhesion. The weldability also appeared to be superior to the chromate treatment. This suggests that the conductive material of the film contains silicon, and that the compatibility with the silica for the base treatment is good. The ability to carry out a process that does not contain chromium in this way is
It is considered preferable because chromium (VI) is not treated.

From the above examination results, it was found that a pre-primed steel sheet excellent in spot welding and seam welding and excellent in corrosion resistance of the cut end face was obtained. The present invention was completed by confirming the respective limit ranges of the composition, thickness, and the like. The gist of the present invention is as follows.

(1) At least one surface of a zinc or zinc-based alloy-plated steel sheet has a base treatment, and a grain size of 0.5
An organic-coated surface-treated steel sheet characterized in that an organic resin film containing 10 to 70% by mass of ferrosilicon of 10 to 70 μm is coated with a thickness of 2.5 to 8 μm.

(2) Ferrosilicon containing 15 to 95% by mass of Si
The organic-coated surface-treated steel sheet according to the above (1), comprising:

(3) The plating layer of a zinc-based alloy-plated steel sheet contains 0.2 to 10% by mass of cobalt.
The organic-coated surface-treated steel sheet according to (1) or (2).

(4) The base treatment layer is made of colloidal silica
The organic-coated surface-treated steel sheet according to (1), (2) or (3), which is a layer of 0.05 to 0.5 g / m ^{2 made} of a thermosetting resin containing up to 95% by mass.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION The steel sheet of the present invention has a structure in which a base material belonging to a general cold-rolled steel sheet has metal plating on the surface thereof, is subjected to a base treatment, and is further coated with an organic resin. is there. The base steel sheet used may be the same as a normal cold-rolled steel sheet. Cold-rolled steel sheets have excellent drawability, high strength, low yield ratio, baking hardenability, etc., depending on the purpose of use, but any of them may be used.
There is no particular limitation.

The metal plating may be zinc or a zinc-based alloy which is generally used, and zinc plating of an alloy is preferable from the viewpoint that the corrosion resistance is good even if the amount is small. For alloy zinc plating, Zn-Al, Zn-Co,
There are various types such as Zn-Cr, Zn-Fe, Zn-Mg, and Zn-Ni, and any plating may be used.

However, Z containing 0.2 to 10% by mass of Co
The n-Co alloy plating has particularly excellent corrosion resistance and good weldability when the surface is further covered with an organic resin containing a conductive pigment of ferrosilicon. in this case,
When the Co content of the plating layer is less than 0.2% by mass, the effect of improving both the corrosion resistance and the weldability is small, and when the content exceeds 10% by mass, the corrosion resistance of the cut end face deteriorates.

The amount of plating must be 10 g / m ² or more per side to ensure the corrosion resistance of the steel sheet. From the viewpoint of corrosion resistance, the larger the amount of adhesion, the better, but it is preferably 80 g / m ² or less so as not to deteriorate the weldability.

The undercoating treatment applied between the plating layer and the organic coating may be directly applied to a chromate treatment or a phosphate treatment, which is generally performed for the purpose of improving the adhesion and corrosion resistance of the coating on the metal surface. However, in the case of the pre-primed steel sheet of the present invention, an effect of improving both weldability and corrosion resistance can be obtained by using a base treatment made of colloidal silica and a thermosetting resin.

In this case, a thermosetting resin is dissolved or mixed in an emulsion form in water or an organic solvent in which colloidal silica is dispersed, and the mixture is applied to the plating surface and dried to form a treated layer. The colloidal silica may be spherical, string-shaped or pearl necklace-shaped, and any of them can be applied. However, string-shaped or pearl necklace-shaped colloidal silica is preferable in terms of adhesion and corrosion resistance of the organic film. Examples of the thermosetting resin include thermosetting polyester resins, epoxy resins, urethane resins, phenol resins, melamine resins, benzoguanamine resins, and the like. It is preferable to avoid using the resin because the adhesion may not be good depending on the type of resin used for coating.

The mixing ratio between the colloidal silica and the thermosetting resin is 20/80 to 95/5 in terms of mass ratio, that is, the colloidal silica in the solid component is effective in the range of 20 to 95%. 20%
If it is less than, the corrosion resistance of the organic coated steel sheet is inferior, and if it exceeds 95%, the secondary adhesion of the organic film becomes poor, and the corrosion resistance of the cut end face becomes inferior. Desirable is in the range of 40-90%.

In any of the above-mentioned chromate treatments, phosphate treatments, or base treatments of colloidal silica and thermosetting resin, the amount of adhesion is preferably 0.05 to 0.5 g / m ² . If the amount exceeds 0.5 g / m ² , the weldability will be poor.
This has little effect on the electric conductivity because the thickness of the underlayer treatment is thin. However, when the thickness is too large, the electric conductivity is hindered due to the lack of electric conductivity, and the weldability may be deteriorated. Further, since the coating weight is too small no effect of surface treatment is required at least 0.05 g / m ² or more. Desirably, the content is 0.08 or more and 0.4 g / m ² or less.

The organic resin film contains a conductive pigment of ferrosilicon in an organic resin serving as a base. If necessary, a rust-preventive pigment, an extender pigment, a coloring pigment, a solid lubricant, or a film-forming auxiliary is used. Agents and the like may be included.

It is assumed that a film having such a composition has a thickness of 2.5 to 8 μm and is formed on the undercoat layer. When the thickness of the organic resin film is less than 2.5 μm, the coating on the cut end face becomes insufficient at the time of cutting such as blanking in press working, and the end face corrosion resistance may be insufficient.
However, when the thickness exceeds 8 μm, the weldability deteriorates due to gas generation during spot welding and seam welding and a decrease in conductivity. It is preferably in the range of 3 to 7 μm, more preferably 3 to 5 μm.

The organic resin serving as a base of the film is not particularly limited, since the film plays a role as an undercoat, and those generally used for such purposes may be used. For this purpose, a thermosetting resin is more suitable than a thermoplastic resin, and specific examples thereof include epoxy-based, acrylic-based, urethane-based, polyester-based, and phenol-based resins. From the viewpoint of compatibility between weldability and end face corrosion resistance, the epoxy resin is bonded with an aliphatic dibasic acid,
Further, it is preferable to use a urethane-modified epoxy resin in which the terminal of the resin is modified with a urethane-based resin.

The molecular weight of the base resin before forming the film is preferably in the range of 5,000 to 50,000. If the molecular weight is lower than this range, the end face corrosion resistance is inferior, and if the molecular weight is high, the coating material has a high viscosity, making coating difficult.

The film contains various additives described below. In order to sufficiently retain the function as a lower layer paint on which a film is further formed, for example, secondary adhesion, etc. It is desirable that at least 30% by mass of the film is the organic base.

Ferrosilicon materials to be contained in the film as conductive pigments are classified into No. 1, No. 2, No. 3 and No. 6 according to the amount of Si contained in JIS-G-2302. May be used. However, if the Si content is too large or too small, the weldability tends to be inferior, and if the Si content can be arbitrarily selected, a good result is obtained if the Si content is 15 to 95% by mass. . This is because, if the content of Si in ferrosilicon is less than 15% by mass, uniform dispersion in the organic resin becomes slightly difficult, and it is difficult to obtain a uniform energizing path in the formed film, thereby deteriorating the weldability. It has been estimated that when Si exceeds 95% by mass, the electric resistance of the ferrosilicon particles themselves increases, which may also reduce the weldability. A particularly preferable amount of Si in ferrosilicon is 40 to 80% by mass, and a Si content of No. 2 or No. 3 specified by the above JIS is suitable.

The particle size of the ferrosilicon to be contained is 0.
5 to 10 μm. This is because if the particle diameter is less than 0.5 μm, not only does the raw material price increase, but also the weldability is poor. It is considered that when the particle diameter is small, the particles easily aggregate in the organic resin layer, and a uniform current-carrying path cannot be obtained, and the electrode is worn. On the other hand, if it is larger than 10 μm, the ferrosilicon particles may be exposed from the organic resin layer and fall off during press molding to damage the surface, or a local energization path may be formed at the time of welding to increase the deformation of the electrode. The particle size is
Within the range of 0.5 μm or more, it is considered that the smaller the diameter, the more uniform energization can be obtained at the position of the pressurized electrode, and the better the weldability. That is, the preferred range of the particle size is 0.5 to 5 μm
And desirably 0.5 to 3 μm.

It is assumed that the above-mentioned ferrosilicon is contained in the organic film in an amount of 10 to 70% by mass of its dry mass. This is because if the content of the conductive pigment is less than 10% by mass, the conductivity is insufficient, and the weldability is deteriorated. If the content exceeds 70% by mass, the corrosion resistance of the steel sheet is reduced, and the secondary adhesion is also reduced. Because it gets worse.

It is preferable that the organic film contains not more than 20% by mass of a rust-preventive pigment in addition to the above ferrosilicon. The addition of the rust preventive pigment improves the corrosion resistance of the coated steel sheet, but is more effective in improving the corrosion resistance of the cut end face. As the rust-preventive pigment, a chromate-based rust-preventive pigment such as strontium chromate, zinc chromate and ammonium chromate which is generally used may be used.

However, when a chromium component is not used in the organic film together with the undercoating treatment, a borate such as calcium borate and zinc borate, a phosphate such as calcium phosphate, zinc phosphate and vanadium phosphate, zinc phosphite, A phosphite such as aluminum phosphite, a polyphosphate such as aluminum polyphosphate and vanadium polyphosphate, or a non-chromate rust preventive pigment such as basic zinc cyanamide may be selected.

In addition, colored pigments for coloring paints, extenders such as silica and titania, molding aids such as polyolefin wax and natural wax, and solids such as molybdenum disulfide and graphite for improving the performance of organic films. The addition of a lubricant, a silane coupling agent for assisting film formation, etc. does not reduce the characteristics of the organically coated surface-treated steel sheet of the present invention. However, in order to ensure the desired weldability and end face corrosion resistance, the total content of the components other than the organic resin and ferrosilicon pigment, which are essential components of the organic film,
It is desirable that the content be 25% by mass or less based on the entire coating.

The undercoat treatment or the formation of the organic film of the steel sheet of the present invention may be carried out under conditions generally selected depending on the resin or paint used, and is not particularly limited.

[0050]

[Example 1] A Zn-13% Ni electroplated steel sheet having a thickness of 0.8 mm and a coating weight of 30 g / m ^{2 on} each of the front and back sides was used, and the following undercoating and organic resin coating were performed on both sides. Was.

Base treatment: Aqueous epoxy resin (Watersol CD540, manufactured by Dainippon Ink) and colloidal silica (Snowtex UP, manufactured by Nissan Chemical Co., Ltd.) were mixed so that the colloidal silica was 70% by mass on a dry basis. Then, the composition was coated and dried so that the amount of adhesion during drying was 0.1 g / m ² .

Organic resin coating: Based on a thermosetting urethane-modified epoxy resin having a number average molecular weight of 30,000 (containing 20% by mass of a resol type phenol curing agent), which has a Si content of 75% by mass and a different particle size Ferrosilicon was added varying its content. These organic resin paints were applied on the above-mentioned undercoating treatment in different thicknesses and baked at 230 ° C. for 50 seconds. Table 1 shows the particle size of ferrosilicon, the content in the film, and the coating thickness after baking.

[0053]

[Table 1]

Regarding the prepared organic-coated surface-treated steel sheet,
Evaluation of weldability by continuous spot welding or continuous seam welding and evaluation of end face corrosion resistance as described below were performed. 1) Spot welding Electrode diameter: 6 mm (Cu-Cr electrode) Pressurization: 250 kgf (2452 N) Electricity: 12 cycles Holding: 5 cycles Current: 9000 A Evaluation method: Perform continuous 5000 spot welding, and nugget diameter every 100 points 2) Seam welding Electrode R: 5mm Pressurization: 300kgf (2942N) Energization: 2 cycles Pause: 2 cycles Current: 13kA Speed: 2.5m / min Evaluation method: Perform 300m continuous seam welding Observation and investigation of working conditions 3) Corrosion resistance of end face Test piece: punched circular blank with a diameter of 100 mm Test condition: wet / dry ratio including salt spray test for 1 hour 3
60 cycles of a combined cycle test of 0%, 8 hours per cycle Evaluation method: Visual measurement of the length of occurrence of red rust + white rust on the cut end surface The evaluation criteria were the five stages shown in Table 2 for each test. In this case, ○-or more is a pass. The evaluation results after the test are also shown in Table 1.

[0055]

[Table 2]

As is clear from the results in Table 1, the sample No. 3 in which the thickness of the organic film, the resin content, the particle size of the ferrosilicon pigment and the content in the film are within the range defined by the present invention.
-9, Test Nos. 14-18 and Test Nos. 23-26 both have excellent weldability and end face corrosion resistance, indicating that good pre-primed steel sheets can be obtained. On the other hand, any one of the above-mentioned items deviates from the range defined by the present invention, test numbers 1-2,
Test Nos. 10 to 13, Test Nos. 19 to 22, and Test Nos. 27 to 29 do not show sufficient performance.

Example 2 Zn-1% Co electroplated steel sheet, Zn-13% Ni electroplated steel sheet and galvannealed hot-dip galvanized steel sheet having a thickness of 0.8 mm and a coating weight of 30 g / m ² on both sides. Using the three types of steel sheets, the same undercoating treatment as in Example 1 was performed so that the adhesion amount during drying was 0.15 g / m ² . Based on the thermosetting urethane-modified epoxy resin having a number average molecular weight of 30,000 used in Example 1, the resin was 45% by mass, the Si concentration was 75% by mass, and the particle size was 1.0%.
μm ferrosilicon at 30% by mass and the remaining 25%
An organic coating composition was prepared in which the content by mass of colloidal silica and various rust preventive pigments was changed. Table 3 shows the amount of colloidal silica and the type and content of the rust preventive pigment.

[0058]

[Table 3]

This paint was applied to a steel sheet after the base treatment so that the thickness after drying was 3 μm, and baked at 230 ° C. for 45 seconds. Using the steel sheet thus produced, the weldability and the end face corrosion resistance were evaluated in the same manner as in Example 1. The evaluation was performed in the same manner as in Example 1, and Table 2 shown above was used.
According to the criteria. The results are also shown in Table 3. These results show that the addition of the rust preventive pigment is effective in improving the corrosion resistance of the cut end face. In addition, for example, when comparing Nos. 35, 42, and 44 containing no rust-preventive pigment, Zn-Co plating tends to have better end face corrosion resistance than Zn-Ni or Zn-Fe alloy plating.

Example 3 A Zn-1% Co electroplated steel sheet having a thickness of 0.8 mm and a plating adhesion amount of 30 g / m ² on both sides was used, and a base treatment was performed by a coating type zinc phosphate treatment (Prefos Fate treatment) or a treatment by mixing the colloidal silica used in Example 1 with an epoxy resin, and the amount of adhesion of these base treatments was variously changed. Table 4 shows the base treatment and the amount of the base treatment.

The organic resin layer for the surface coating contained 50% by mass of the organic resin, and was made of a urethane-modified epoxy resin, an amine-modified epoxy resin, a high-molecular polyester resin, a methyl methacrylate resin or a methyl-modified silicone resin. 35% by mass of ferrosilicon having a Si concentration of 75% by mass and a particle diameter of 1.0 μm, 5% by mass of colloidal silica, and 10% by mass of zinc borate as a rust-preventive pigment. . This paint was applied on both sides to a coating layer thickness of 3.5 μm and baked at 240 ° C. for 40 seconds.
The prepared organic-coated surface-treated steel sheet was evaluated for weldability and corrosion resistance of the cut end face in the same manner as in Example 1. The results are shown in Table 4.

[0062]

[Table 4]

By coating the surface with an organic resin to which ferrosilicon powder is added as a conductive pigment, good weldability and end face corrosion resistance can be obtained. However, comparing the sample numbers 45, 52, 56-59 with the same amount of undercoat treatment,
It can be seen that the steel sheet No. 52 in which the surface was coated with the urethane-modified epoxy resin by the base treatment with the colloidal silica and the epoxy resin showed excellent tendency in both the weldability and the end face corrosion resistance.

Example 4 A Zn-13% Ni electroplated steel sheet having a thickness of 0.8 mm and a coating weight of 30 g / m ^{2 on} each of the front and back surfaces was used. It was applied so that the amount was 0.15 g / m ² . On the basis of the thermosetting type urethane modified epoxy resin having a number average molecular weight of 30,000 used in Example 1, 50% by mass of resin was used as a coating layer composition.
Then, 30% by mass of ferrosilicon having an average particle diameter of 1.0 μm having different Si contents and 10% by mass of aluminum polybutenoate as a rust preventive pigment, and 10% by mass of colloidal silica, respectively, were dried, and then dried. It was applied to a thickness of 3 μm and baked at 230 ° C. for 45 seconds. Table 5 shows the Si content in ferrosilicon.

Using the obtained steel sheet in the same manner as in Example 1,
The weldability was evaluated. The results are shown in Table 5, and the evaluation criteria were in accordance with Table 2.

From these results, it was found that S in ferrosilicon
The weldability varies depending on the i content, and the Si content is 15% by mass.
If it is less than 95% or more than 95% by mass, the weldability is slightly inferior.

[0067]

[Table 5]

[0068]

The pre-primed steel sheet of the present invention is particularly excellent in weldability and corrosion resistance of the cut end face. This steel plate can be easily spot-welded or seam-welded after processing with a press or the like, and the upper layer or middle layer and upper layer can be coated without performing lower layer coating such as electrodeposition coating.
It can be used to omit the manufacturing process of painted parts.
In addition, a manufacturing process that does not contain chromium is also possible, which is effective for pollution control.

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[Procedure amendment]

[Submission date] December 7, 2000 (200.12.
7)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction contents]

[0053]

[Table 1]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0067

[Correction method] Change

[Correction contents]

[0067]

[Table 5]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C09D 5/00 C09D 5/00 D 7/12 7/12 201/00 201/00 C23C 22/00 C23C 22 / 00 Z 22/02 22/02 28/00 28/00 C (72) Inventor Kazuhito Imai 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (72) Inventor Kiyoshi Fukui No. 4-5-33 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture F-term (reference) 4D075 DB05 EC03 4F100 AA20C AB03A AB15A AB18A AB31A AH06B AH08B AK01B AK01C AK51B AK53B AK53C BA03 BA07 BA10A BAA DEB GB08 GB48 JB02 JB13B JB13C 4J038 CD091 CG141 DA041 DB001 DB481 DD001 DG001 DL031 EA011 HA066 HA446 KA12 KA20 NA03 NA12 NA20 PA08 PA12 PA19 PC02 4K026 AA02 AA12 AA22 BB08 BB10 CA02 A04 AE04 AB02 BA06 BA10 BA12 BA19 BA21 BB04 BC02 BC08 CA16 CA18 CA53

Claims (4)

[Claims] 1. A zinc or zinc-based alloy-plated steel sheet having a base treatment layer on at least one surface thereof, and a grain size of 0.5 to 1
An organic-coated surface-treated steel sheet, which is coated with an organic resin film containing 10 to 70% by mass of 0 μm ferrosilicon in a thickness of 2.5 to 8 μm. 2. The organic-coated surface-treated steel sheet according to claim 1, wherein the ferrosilicon contains 15 to 95% by mass of Si. 3. The organic-coated surface-treated steel sheet according to claim 1, wherein the plating layer of the zinc-based alloy-plated steel sheet contains 0.2 to 10% by mass of cobalt. 4. An undercoating layer comprising colloidal silica of 20 to 95
3. The organic-coated surface-treated steel sheet according to claim 1, wherein the layer is a 0.05 to 0.5 g / m ² layer made of a thermosetting resin containing 3% by mass.