JPH0811214B2 - Galvanized steel sheet with excellent lubricity, formability and corrosion resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvanized steel sheet or a zinc-based steel sheet which has excellent lubricity and forming processability and has good corrosion resistance even if the surface thereof is not coated with lubricating oil or the like. The present invention relates to an alloy-plated steel sheet (hereinafter abbreviated as "zinc-based plated steel sheet").

[0002]

2. Description of the Related Art Zinc-based plated steel sheets are widely used in various industrial fields because of their excellent corrosion resistance. When such a zinc-based plated steel sheet is used as a material for office equipment such as copying machines, audio equipment, household electric appliances, etc., the zinc-based plated steel sheet is subjected to various press forming processes. When used as a material for a motor cover, a cartridge type tank, etc., a zinc-based plated steel sheet is subjected to a drawing process.

Formability of galvanized steel sheet is inferior to that of cold rolled steel sheet. The reason is that the sliding resistance of the zinc-based plated steel sheet with respect to the die during forming by pressing or the like is larger than that of the cold-rolled steel sheet. Therefore, in order to improve the formability of the galvanized steel sheet and to improve the appearance after the forming, it is common practice to apply lubricating oil or rust preventive oil on the surface of the galvanized steel sheet. It is being appreciated. However, applying a lubricating oil or the like on the surface of the zinc-based plated steel sheet complicates the manufacturing process, and
It worsens the working environment. Not only that, even when lubricating oil or the like is applied for molding, if the molding processing conditions are severe, galling may occur in the molded product and the corrosion resistance may deteriorate.

On the other hand, in order to further improve the corrosion resistance of the zinc-based plated steel sheet, there is known a chromate-treated zinc-based plated steel sheet in which a chromate film or a chromate film and a resin film are formed on the surface of the zinc-based plated layer. Has been. Corrosion resistance of such a chromate-treated zinc-based plated steel sheet in a flat plate shape without forming is good. However, when the molding process is performed without applying the lubricating oil or the like, the chromate film is peeled or blackened, and the corrosion resistance and the surface properties are deteriorated. Therefore, even in the case of a chromate-treated zinc-based plated steel sheet, it is necessary to apply a lubricating oil or the like on the surface when forming is performed.

In order to solve the above-mentioned problems and to develop a surface-treated steel sheet which has excellent lubricity and formability and which has good corrosion resistance without applying lubricating oil or the like on the surface, This has been demanded, and for example, the following surface-treated steel sheets have been proposed. JP-A-61-227178 Japanese Patent Application Laid-Open No. 61-227178 A water-based acrylic resin film containing graphite and / or molybdenum disulfide as a solid lubricant is formed on the chromate film formed on the surface of a steel sheet, which has excellent lubricity. Surface-treated steel sheet (hereinafter referred to as Prior Art 1).

JP-A-62-289275 A thermosetting powder coating containing a high melting point fluororesin powder as a lubricant is applied on the surface of a steel sheet, and then a temperature below the melting point of the fluororesin is applied. A surface-treated steel sheet (hereinafter referred to as Prior Art 2) having a coating film on which the fluorine-based resin powder is exposed, which is formed by baking the surface-treated steel sheet.

Japanese Laid-Open Patent Publication No. 1-110140 A water-soluble zinc-plated steel sheet containing an inorganic solid lubricant such as graphite and molybdenum disulfide, which has been previously subjected to titanate coupling treatment, and colloidal silica. -Treated or steel-coated steel sheet with water-dispersible acrylic / epoxy resin coating (hereinafter referred to as Prior Art 3).
That).

Japanese Unexamined Patent Publication No. 2-140294 A surface-treated steel sheet on which a thin film of montan wax oxide is formed on the surface of a zinc-based plated steel sheet in order to suppress a blackening phenomenon during press forming Technology 4).

[0009]

The above-mentioned prior art has the following problems. In the case of the surface-treated steel sheet of Prior Art 1, some improvement in lubricity and moldability is recognized by the lubricant contained in the water-based acrylic resin coating. However, when the molding processing conditions are severe, the acrylic resin film deteriorates due to frictional heat during the molding process, and seizure on the die and blackening of the film cannot be avoided. Therefore, the lubricity and the formability are inferior to those of the conventional zinc-based plated steel sheet on the surface of which lubricating oil or the like is applied. This is considered to be the limit due to the combination of the water-based acrylic resin and the inorganic solid lubricant. Furthermore, since the coating contains graphite and / or molybdenum disulfide as a lubricant, the color tone of the coating becomes dark and a white appearance cannot be obtained.

In the case of the surface-treated steel sheet of Prior Art 2, it is difficult to form a coating film having a uniform thickness because powder coating is used as the resin composition forming the coating film. However, it is not possible to form a thin film of several μm or less. Further, since it is difficult to make the fluororesin powder added as a lubricant into fine particles of 1 μm or less, the fluororesin powder exists in the film and the surface of the film in an exposed state. As a result, not only does the fluororesin powder not contribute to the improvement of lubricity during the molding process, but conversely, the fluororesin powder is detached from the coating film, causing a problem of pinholes.

In the case of the surface-treated steel sheet of Prior Art 3, the affinity and adhesion between the inorganic solid lubricant such as graphite and molybdenum disulfide and the resin component are slightly improved. However, if the molding conditions are severe,
Similar to the prior art 1, the lubricity and the formability are inferior to those of the conventional zinc-based plated steel sheet whose surface is coated with lubricating oil or the like.

In the case of the surface-treated steel sheet of Prior Art 4, the softening point of the montan wax that imparts lubricity is low. Therefore, due to the frictional heat during molding, the surface temperature is
At high temperatures of 100 to 150 ° C, the film becomes sticky and falls off, and good corrosion resistance cannot be obtained.

In addition to the above-mentioned prior art, there has been proposed a surface-treated steel sheet having a lubricating coating in which an arbitrary lubricant is added to a specific resin. However, such a surface-treated steel sheet depends on the properties of the base resin (for example, water-based, powder, thermoplastic, thermosetting, etc.) and the method for forming the coating (for example, room temperature drying, high temperature baking, etc.). ,
Lubricity improvement effect is limited. That is, no matter what kind of lubricant is used, the effect of improving the lubricity cannot be obtained. Only by combining a specific lubricant suitable for the performance of the base resin, can the lubricity and molding processability satisfying Is obtained, and its performance is limited.

Therefore, an object of the present invention is to solve the above-mentioned problems and to achieve excellent lubricity and molding processability without applying lubricating oil or the like on the surface, and to form under severe conditions where frictional heat is generated. It is an object of the present invention to provide a zinc-plated steel sheet which has excellent lubricity and formability without causing damage or blackening of the coating film even if processed, and has good corrosion resistance.

[0015]

Means for Solving the Problem] The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems. As a result, a solvent-based thermosetting resin, a polyethylene fine powder having a predetermined melting point and a predetermined molecular weight, and a chromate compound are mixed in a predetermined ratio on at least one surface of the zinc-based plating layer. It was found that a zinc-based plated steel sheet having excellent lubricity and forming processability and good corrosion resistance can be obtained by applying the above-mentioned material and forming a resin film by heating and curing the material. The present invention has been made based on the above findings, and the present invention provides a resin containing a lubricant on at least one zinc-based plating layer of a zinc-plated steel sheet and a zinc-based alloy-plated steel sheet. In a zinc-based plated steel sheet in which a resin coating is formed on the surface of at least one zinc-based plating layer of the steel sheet by applying a coating composition consisting of Is composed of a solvent-based thermosetting resin, a polyethylene fine powder having a melting point of 120 ° C. or less and an average molecular weight of 5,000 or less, and a chromate compound. The amount is within the range of 5 to 30 parts by weight with respect to 100 parts by weight of the solid content of the solvent-based thermosetting resin, and the content of the chromate compound is the solvent-based thermosetting resin. It is in the range of 3 to 20 parts by weight with respect to 100 parts by weight of solids of fat, and the thickness of the resin coating made of such a coating is 0.3 to 10 parts per side.
It is characterized by being in the range of 3.0 μm.

[0017]

In the present invention, the reason why the solvent-based thermosetting resin is used as the base resin in the coating material for the resin coating formed on the surface of the zinc-based plating layer is as follows. The solvent-based thermosetting resin is superior to the water-based resin in compatibility with additives such as a lubricant and a rust preventive added to the resin and long-term stability as a paint. Unlike a thermoplastic resin, a thermosetting resin has no melting point, so that it has high mechanical strength at high temperatures. Therefore, if a coating film made of such a resin is used, peeling or deformation of the coating film is unlikely to occur even if the temperature of the steel sheet rises due to frictional heat during press forming.

The solvent type thermosetting resin is a bisphenol type epoxy resin, a polyfunctional type epoxy resin, an ester resin such as an oil-free alkyd resin, an acrylic resin, a urethane resin (polyol), or a modified derivative of each of the above resins. At least one of them is combined with at least one of various amine compounds, amino resins, and isocyanate compounds to form a heat-curable composition. The resin having such a composition is cross-linked and cured by applying a paint obtained by diluting the resin with a predetermined solvent onto the surface of the zinc-based plating layer and heating.

The fine polyethylene powder prevents galling, breakage of the steel plate, etc., which are caused by continuous press molding, etc., and imparts resistance to sliding, deformation and wear to the steel plate, and damages the steel plate and the mold. It has a preventive action. Therefore, it is added as a lubricant in the paint.

Polyethylene is generally a crystalline thermoplastic resin having an average molecular weight of several hundreds to several millions, its glass transition temperature is about -100 ° C, which is lower than room temperature, and its melting point is 90-140. It has a soft property at room temperature. Furthermore, its critical surface tension is about 30 dyne / cm 2, and since it has low surface energy, it has low wettability and adhesion, and therefore has a lubricating action. However,
As in the present invention, in the case where it is contained as a lubricant in the paint for the resin coating formed on the surface of the zinc-based plating layer, the particle size thereof is taken into consideration from the viewpoint of dispersibility and thin film formability of the paint. However, it is necessary that the fine powder has a particle size of 20 μm or less, preferably 10 μm or less, and more preferably about 5 μm, and polyethylene which is not such a powder cannot obtain the initial effect.

The melting point of polyethylene fine powder affects the lubricity. That is, the higher the melting point, the higher the mechanical strength near room temperature, that is, the deformation resistance, and the lower the lubricity (sliding property) of the resin film containing the fine polyethylene powder. Therefore, the melting point of the polyethylene fine powder as a lubricant used in the present invention is 120 ° C. or lower, preferably 90 to
It must be in the range of 110 ° C.

The molecular weight of polyethylene fine powder is closely related to the melt viscosity. The higher the molecular weight is, the higher the melt viscosity is, and a sufficient flow cannot be obtained at the time of forming a resin film by heating and baking. Therefore, with a polyethylene fine powder having a high molecular weight, a smooth resin film cannot be formed, and the lubricity and the film damage resistance during press molding are reduced. Paint based on solvent-based thermosetting resin
The resin is heated to a temperature in the range of 150 to 250 ° C to crosslink it when it is formed. During this heating, the polyethylene fine powder in the resin film is allowed to flow to make it amorphous or disc-shaped. Are preferable from the viewpoints of lubricity of the resin coating and press workability.

As a result of research conducted by the present inventors, the flowability of polyethylene fine powder as a lubricant dispersed in a thermosetting resin is closely related to the melt viscosity at a temperature in the range of 140 to 150 ° C., Melt viscosity at temperatures of 140 to 150 ° C
Polyethylene fine powder within the range of 100 to 1,000 cps,
It was found to have an optimum flow property. That is, when the melt viscosity is less than 100 cps, the formed film becomes sticky,
The problem arises of promoting void formation. On the other hand, if the melt viscosity exceeds 1,000 cps, sufficient flow is not performed,
Crosslinking and curing of the base resin proceeds. As a result, a smooth resin film surface could not be obtained, resulting in increased resistance during press molding,
This causes problems such as lubricant desorption and void generation.

The content of polyethylene fine powder as a lubricant should be in the range of 5 to 30 parts by weight based on 100 parts by weight of the solid content of the solvent-based thermosetting resin. The content of polyethylene fine powder is 100% solid content of solvent-based thermosetting resin.
If the amount is less than 5 parts by weight, the effect of improving lubricity cannot be obtained. On the other hand, if the amount exceeds 30 parts by weight, the cohesive force and strength of the resin coating itself decrease, resulting in a problem that peeling of the resin coating increases during molding. The more preferable content of the polyethylene fine powder is in the range of 10 to 20 parts by weight based on 100 parts by weight of the solid content of the solvent-based thermosetting resin.

The chromate-based compound added together with the fine polyethylene powder has a function as a rust preventive to further improve the corrosion resistance of the zinc-plated steel sheet. As described above, by containing the chromate-based compound in the resin coating, not only the corrosion resistance in the case of a flat plate that has not been molded is improved, but also the resin coating is deformed by the molding. Even if damage occurs, it is possible to prevent deterioration of corrosion resistance.

As the chromate compound, barium chromate and / or strontium chromate having a low water-soluble content is used. The content of the chromate compound is 100 parts by weight of the solid content of the solvent-based thermosetting resin,
It should be in the range of 3 to 20 parts by weight. If the content of the chromate-based compound is less than 3 parts by weight based on 100 parts by weight of the solid content of the solvent-based thermosetting resin, the effect of improving the corrosion resistance cannot be obtained. On the other hand, even if the amount exceeds 20 parts by weight, not only the effect of improving the corrosion resistance is not further obtained, but also the cohesive force of the resin coating is lowered, so that the problem of increasing the peeling of the resin coating during molding occurs.

In the paint, in addition to the above-mentioned base resin, polyethylene fine powder and chromate compound, if necessary, other components, for example, colorants such as pigments and dyes, surfactants, stabilizers, stabilizers, stabilizers, etc. You may also contain an agent.

As described above, in the present invention, since the resin coating contains polyethylene fine powder as a lubricant and a rust preventive, the zinc-based plated steel sheet of the present invention is Even if the press molding process is performed without applying the lubricating oil or the like, the resin film is present without any damage. Therefore, the rust preventive effect of the resin film itself can be sufficiently exerted.

In the present invention, the steel sheet on which the resin coating for lubrication and rust prevention is to be formed is a galvanized steel sheet having a galvanized layer on at least one surface thereof, in addition to zinc, nickel, iron, manganese, Molybdenum, cobalt,
Zinc alloy plated steel sheet having a zinc alloy plated layer containing at least one component of aluminum, chromium, silicon, etc., or multi-layer zinc-based plated steel sheet having a plurality of the above-mentioned zinc plated layers or zinc alloy plated layers May be

In the present invention, when a chromate film is formed on the zinc-based plated layer of the above-mentioned zinc-based plated steel sheet and the above-mentioned resin film is formed on such a chromate film, more excellent corrosion resistance is obtained. The obtained resin film can be formed well. The formation of the chromate film may be performed by any known means such as coating, electrolytic treatment and reaction treatment.

The amount of the chromate coating adhered is preferably in the range of 5 to 200 mg / m ² per one side of the steel plate, in terms of metallic chromium. If the amount of the chromate coating, calculated as metal chromium, is less than 5 mg / m ^{2 on} one side of the steel sheet, a more excellent effect of improving corrosion resistance cannot be obtained. On the other hand, when the amount of chromate coating, calculated as metallic chromium, exceeds 200 mg / m ² on one side of the steel plate, not only the corrosion resistance improvement effect commensurate with that amount cannot be obtained, but also bending and press forming accompanied by deformation of the steel plate. When processed, cohesive failure of the chromate film occurs. The more preferable amount of the chromate film is in the range of 10 to 150 mg / m ² per one side of the steel plate, in terms of metallic chromium.

In addition to the chromate film described above, another resin film containing no lubricant may be formed between the zinc-based alloy plating layer and the uppermost resin film for anti-lubrication. In this case, the total amount with the uppermost resin coating is 5μ.
m It is necessary that it is preferably within a range not exceeding 3 μm. If the total amount with the uppermost resin coating exceeds 5 μm, joining by welding becomes difficult.

The resin coating film is formed on at least one surface of the zinc-based plated steel sheet as follows.
That is, on at least one surface of the zinc-based plating layer, or on at least one surface of the chromate coating formed on the zinc-based plating layer, by a known method such as a roll coater, a curtain flow coater, or spray coating. After applying the coating composition having the above-mentioned composition or immersing the zinc-based plated steel sheet in the coating composition having the above-described composition, the coating film is formed in a predetermined amount by squeezing it to a predetermined amount by blowing a roll or air. Then, this is heated to a temperature of 150 to 250 ° C. by a hot air oven or an induction heating device to remove the solvent and crosslink and cure the resin. Thus, the resin coating is formed on at least one surface of the zinc-based plated steel sheet.

The thickness of the resin coating formed on at least one surface of the zinc-based plated steel sheet is 0.
It should be in the range of 3 to 3.0 μm. If the thickness of the resin coating is less than 0.3 μm per side of the steel plate,
It is not possible to prevent damage to the zinc-based plating layer. On the other hand, the thickness of the resin coating is 3.0 μm per side of the steel plate.
If it exceeds, weldability deteriorates, and if the molding processing conditions are particularly severe, the amount of peeling of the resin film increases, and problems such as adhesion to the mold and baking occur.

Next, the present invention will be described by way of Examples in comparison with Comparative Examples.

Example 1 The following materials were prepared as materials for a coating material for producing a zinc-based plated steel sheet within the scope of the present invention and a zinc-based plated steel sheet outside the scope of the present invention.

(1) Resin Melamine-curable polyester resin Isocyanate-curable polyurethane resin Urea resin-curable epoxy resin Aqueous acrylic emulsion resin

(2) Lubricant A Melting point: 105 ° C, melt viscosity at 150 ° C: 200 cps, molecular weight: 1,500 polyethylene fine powder B Melting point: 115 ° C, melt viscosity at 150 ° C: 700 cps, molecular weight: 3,000 polyethylene Fine powder C Melting viscosity at melting point: 130 ° C, 150 ° C: 3,000cps, molecular weight: 5,000 Polyethylene fine powder D Melting point: 133 ° C, melt viscosity at 150 ° C: 30,000cps, Polyethylene fine powder with molecular weight: 10,000 E Melting point: 160 ° C polypropylene fine powder F Melting point: 70 ° C paraffin wax G Melting point: 325 ° C polytetrafluoroethylene powder H Graphite fine powder I Molybdenum disulfide fine powder

Both sides of the galvanized layer of a galvanized steel sheet having a plate thickness of 0.8 mm and a plating amount of 20 g / m ² were degreased with alkali,
Then, on the galvanized layer, after applying a chromate treatment liquid by a roll coating method, heating and drying,
A chromate film was formed on the galvanized layer in an amount of 50 mg / m ^{2 in} terms of metallic chromium.

The above resins ~, lubricant A or B,
And a coating material comprising barium chromate as a chromate compound was applied by a roll coating method onto the chromate coating formed on both surfaces of the electrogalvanized steel sheet. Then, this is heated by an induction heating device to 20
By heating to a temperature of 0 ° C., a resin film having a thickness of about 1.5 μm was formed on the chromate film. In this way, the zinc-based plated steel sheets (hereinafter referred to as "the steel sheet of the present invention") Nos. 1 to 4 shown in Table 1 within the scope of the present invention were prepared.

For comparison, a paint containing no lubricant or chromate compound, or containing a lubricant or chromate compound outside the scope of this invention was chromated in the same manner as above. A resin coating with a thickness of about 1.5 μm is formed on the coating, and zinc-based plated steel sheets (hereinafter referred to as “comparative steel sheets”) Nos. 1 to 10 that do not have a resin coating A comparative steel plate No. 11 in which pressing oil was applied on the chromate film at 2 g / m ² was prepared as shown in Table 1 together.

With respect to each of the above-mentioned steel sheet of the present invention and the comparative steel sheet, lubricity, press formability, scratch / blackening property,
The flat plate corrosion resistance and the post-processing corrosion resistance were evaluated by the performance tests described below. The evaluation results are shown in Table 2.

(1) Lubricity A flat test piece was pulled out by a tensile tester under the conditions of a surface pressure of 50 kg / cm ² and a drawing speed of 100 mm / min.
The dynamic friction coefficient at that time was examined to evaluate the lubricity. The evaluation criteria are as follows. ○: Dynamic friction coefficient less than 0.10, ◇: Dynamic friction coefficient 0.10 ~
0.30, x: Dynamic friction coefficient of 0.30 or more.

(2) Press-moldability A disc-shaped test piece was blanked with a diameter of 120 mm and a punch diameter of 50 mm.
, Die diameter: 51.91 mm, Wrinkle holding force: 1 ton, check the outer diameter change rate of the test piece when molded into a cup shape by passing through the die using a punch,
The press formability was evaluated. The evaluation criteria are as follows. ○: 10% or more, ◇: 5 to 10%, ×: less than 5%.

(3) Scratch / blackening A disc-shaped test piece was blanked with a diameter of 100 mm and a punch diameter of 50 mm.
, Die diameter: 51.91 mm, Wrinkle holding force: 1 ton, scratches and blackening by visually inspecting the appearance of the test piece when it is molded into a cup shape by passing it through a die using a punch Was evaluated. The evaluation criteria are as follows. ◯: Good with almost no change, ◇: Slight scratches and blackening occurred, X: Scratches and blackening occurred severely.

(4) Flat plate corrosion resistance A test piece was subjected to a salt spray test based on JIS Z 2371, and the time until the occurrence of white rust was examined and evaluated.

(5) Corrosion resistance after processing After the edge portion of the test piece formed into a cup shape by the method of (3) above was sealed with tar epoxy coating, 12
A salt spray test was carried out by salt spray for 0 hours, the occurrence rate of white rust was investigated, and the corrosion resistance after processing was evaluated. The evaluation standard is
It is as follows. ○: White rust occurrence rate is less than 20%, ◇: White rust occurrence rate is 20-40%
, ×: White rust occurrence rate of 40% or more.

[0047]

[0048]

As is clear from Tables 1 and 2,
The comparative steel plate No. 1 that uses a paint made of water-based resin is
Poor press formability, scratch / blackening, and corrosion resistance after processing. Comparative steel plate No. 2, which uses a paint that does not contain barium chromate, has poor flat plate corrosion resistance and post-processing corrosion resistance. Comparative steel plate No. using a paint containing no lubricant
Sample No. 3 was poor in lubricity and press formability, and could not be tested for scratching / blackening and corrosion resistance after processing because the test piece broke and therefore could not be formed. As a lubricant, a comparative steel sheet N using a paint containing polyethylene fine powder whose melting point is higher than the range of the present invention.
o.4 and 5 are poor in lubricity and press formability.

Comparative Steel Sheets Nos. 6 to 10 using the coating material containing a lubricant other than the lubricant of the present invention have any of lubricity, press formability, scratch blackening property, flat plate corrosion resistance and post-processing corrosion resistance. In particular, the lubricity and press formability of the comparative steel sheets Nos. 9 and 10 were worse than those of the conventional comparative steel sheet No. 11 coated with lubricating oil. On the other hand, the steel sheet of the present invention
No. 1 to 4 are lubricity, press moldability, scratch blackening,
It was excellent in both flat plate corrosion resistance and post-processing corrosion resistance.

[0051]

Example 2 A steel sheet having the same chromate film as that of Example 1 formed on both sides thereof was lubricated on the chromate film with respect to 100 parts by weight of the solid content of the resin, that is, the melamine-curable polyester resin. A coating material containing the agent A and barium chromate in a ratio within the range of the present invention was applied in the same manner as in Example 1 and then heated to form a resin film on the chromate film. Thus, the steel sheets Nos. 5 to 12 of the present invention shown in Table 3 were prepared.

For comparison, comparative steel sheets Nos. 12 to 15 using paints in which the contents of lubricant A and barium chromate are outside the range of the present invention, and the amount of chromate coating outside the range of the present invention A comparative steel plate No. 16 and comparative steel plates No. 17, 18 having coating thicknesses outside the scope of the present invention were prepared as shown in Table 3 together. For each of the present invention steel sheet and comparative steel sheet described above, lubricity, press formability,
Scratch and blackening properties, flat plate corrosion resistance and post-processing corrosion resistance were evaluated by the above-mentioned performance test. The evaluation results are shown in Table 4.

[0053]

[0054]

As is apparent from Tables 3 and 4,
Comparative steel sheet No. 12, which uses a paint having a lubricant content outside the range of the present invention, has poor lubricity, press formability, scratch / blackening property, and corrosion resistance after working. The comparative steel plate No. 13 using a coating material containing a large amount of lubricant outside the range of the present invention has an increase in the amount of peeling due to a decrease in the cohesive strength of the coating, resulting in scratching / blackening and corrosion resistance after processing. bad.

Comparative Steel Sheet No. 14 using a coating material having a small barium chromate content outside the range of the present invention has poor flat plate corrosion resistance and post-processing corrosion resistance. Comparative steel sheet No. 15 using a paint having a large barium chromate content outside the range of the present invention has poor press formability, scratch / blackening property, and post-processing corrosion resistance. Comparative steel sheet No. 16 in which the amount of the chromate film is out of the range of the present invention is press formability,
Scratch / blackening property and poor corrosion resistance after processing.

The comparative steel sheet No. 17 in which the amount of the resin coating was out of the range of the present invention was lubricity, press formability, scratching,
Blackness, flat plate corrosion resistance and post-processing corrosion resistance are all poor.
A comparative steel plate with a large amount of resin coating outside the scope of the present invention No.
No. 18 has poor press formability, scratch and blackening properties, and corrosion resistance after processing.

On the other hand, the steel sheets Nos. 5 to 12 of the present invention are
It was excellent in lubricity, press formability, scratch / blackening, flat plate corrosion resistance and post-processing corrosion resistance.

[0059]

As described above, according to the zinc-based plated steel sheet of the present invention, even if the surface is not coated with lubricating oil or the like,
Excellent lubricity and moldability are exhibited, and even if the molding process is performed under severe conditions where frictional heat is generated, the coating is not damaged or blackened, and excellent corrosion resistance is obtained. Industrially useful. The effect is exhibited.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location B05D 7/24 U 7415-4F V 7415-4F 303 E 7415-4F C23C 22/24 (72) Invention Tatsuya Miyoshi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (56) Reference JP-A-2-263633 (JP, A)

Claims (5)

[Claims] 1. A paint comprising a resin containing a lubricant is applied onto at least one zinc-based plating layer of a zinc-plated steel plate and a zinc-based alloy-plated steel plate, and then this is heated and cured, In a zinc-based plated steel sheet in which a resin coating is formed on the surface of at least one zinc-based plated layer of the steel sheet, the coating material for the resin coating has a solvent-based thermosetting resin and a melting point of 120 ° C. or less. It has a polyethylene fine powder having an average molecular weight of 5,000 or less, and a chromate-based compound. The content of the polyethylene fine powder is 100 parts by weight of the solid content of the solvent-based thermosetting resin. 5 to 30 parts by weight, and the content of the chromate compound is 3 to 20 parts by weight with respect to 100 parts by weight of the solid content of the solvent-based thermosetting resin. And It is the thickness of the resin film, such consisting paint as per one surface of steel sheet, 0.3 to 3.0 mu
A zinc-based plated steel sheet excellent in lubricity, formability and corrosion resistance, characterized by being in the range of m. ^2. A chromate coating is formed on the zinc-based plating layer in an amount of 5 to 200 mg / m ² per one side of the steel sheet in terms of metallic chromium, and the resin coating is formed on the chromate coating. The zinc-based plated steel sheet according to claim 1, wherein 3. The polyethylene fine powder, 140-150.
Melt viscosity at ℃ is in the range of 100-1,000cps,
The zinc-based plated steel sheet according to claim 1 or 2. 4. The chromate compound is barium chromate and / or strontium chromate,
The zinc-based plated steel sheet according to claim 1 or 2. 5. The solvent-based thermosetting resin is a bisphenol type epoxy resin, a polyfunctional type epoxy resin, an ester resin such as an oil-free alkyd resin, an acrylic resin,
It is composed of a urethane resin (polyol), or at least one of the modified derivatives of each of the above-mentioned resins, and at least one of various amine compounds, amino resins and isocyanate compounds, which is heat-curable. The zinc-based plated steel sheet according to claim 1 or 2.