JPH06344499A - Zinc plated steel panel excellent in press moldability, appearance after press molding and corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a zinc plated steel panel improved in lubricity, press moldability, appearance after press molding and corrosion resistance by specifying the amt. of a chromate film, the thickness of a resin film and the components of the resin film. CONSTITUTION:A zinc plated steel panel is obtained by forming a resin film on the surface of the chromate film on the zinc plating layer provided on a steel panel. Herein, the amt. of the chromate film is set to 5-200mg/m<2> per the single surface of the steel panel in terms of metal chromium and the thickness thereof is set to 3-10mum per the single surface of the steel panel. The resin film consists of 100 pts.wt. of a solvent type thermosetting resin, 1-30 pts.wt. of a polyethylene resin with an average mol.wt. of 5000 or less being a solid lubricant and 3-30 pts.wt. of rust-proof pigment. The solvent type thermosetting resin consists of a hydroxyl group-containing urethane prepolymer consisting of polyol, an isocyanate compd. and dihydric alcohol and a curing agent composed of a block polyisocyanate polymer or an amino resin.

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 zinc which has excellent lubricity, press formability, appearance after press forming and corrosion resistance, even if the surface thereof is not coated with lubricating oil or the like. System alloy plated steel sheet (hereinafter, abbreviated as “zinc 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.
Office equipment such as copying machines
When used as a material for audio equipment, home appliances, etc., various press forming is applied to zinc-based plated steel sheets, and when used as a material for motor covers, cartridge tanks, etc., The zinc-plated steel sheet is drawn.

The press formability of galvanized steel sheet is inferior to that of cold rolled steel sheet. The reason is that the friction resistance of the zinc-based plated steel sheet against the forming die during press forming is larger than that of the cold-rolled steel sheet. Therefore,
In order to improve the press formability of the zinc-based plated steel sheet and to make the appearance after press forming good, it is common to apply lubricating oil or rust preventive oil on the surface of the zinc-based plated steel sheet. There is. However, applying the lubricating oil or the like on the surface of the zinc-based plated steel sheet complicates the manufacturing process and deteriorates the working environment. Not only that, even when the lubricant is applied and press-molded, if the molding conditions are severe, galling may occur in the steel sheet to be press-molded 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. Such chromate-treated zinc-based plated steel sheet has good flat plate-shaped corrosion resistance. However, if press forming is performed without applying a lubricating oil or the like, the chromate film peels off or the plating film is damaged, so that the corrosion resistance and surface quality of the zinc-based plated steel sheet deteriorate. 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 performing press forming.

In order to solve the above-mentioned problems and to develop a surface-treated steel sheet having excellent corrosion resistance and excellent lubricity and press formability without applying a 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-61-60886 A thickness of 0.3 to 3 μm per one side of a steel sheet, which is composed of a water-based acrylic copolymer containing a water-dispersible lubricating additive on a chromate film formed on the surface of the steel sheet. A surface-treated steel sheet excellent in lubricity and corrosion resistance, which is formed with the organic composite silicate coating of (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 the prior art 2) on which a coating in which the fluororesin powder is exposed is formed by baking.

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 water-dispersible surface-treated steel sheet having an acrylic / epoxy resin coating film in an amount of 0.2 to ² g / m ² (hereinafter referred to as Prior Art 3).

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 press formability is recognized by the lubricant contained in the organic composite silicate coating film made of the water-based acrylic copolymer. However, when the press molding conditions are strict, the organic composite silicate coating made of the water-based acrylic copolymer deteriorates and is destroyed by frictional heat and vigorous sliding generated during press molding, resulting in seizure on the die and surface. Blackening is unavoidable. Therefore, the appearance after press forming, especially the blackening resistance, may be inferior as compared with a conventional zinc-based plated steel sheet having a surface coated with a lubricating oil or the like. This is due to the combination of the water-based acrylic copolymer and the water-dispersible lubricant, and the thin coating having a thickness of 0.3 to 3 μm.

In the case of the surface-treated steel sheet of Prior Art 2, it is difficult to form a resin coating film having a uniform thickness because the powder coating material is used as the resin forming the resin coating film. In particular, it is impossible to form a thin film of about several μm. Further, since it is difficult to make the fluororesin powder added as a lubricant into fine particles of several μm or less, the fluororesin powder exists in the resin coating and on the surface of the resin coating in an exposed state. . As a result, the fluororesin powder does not contribute to the improvement of lubricity at the time of press molding, and 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, when the press forming conditions are severe, the appearance after press forming, especially the blackening resistance, is inferior to that of the conventional zinc-based plated steel sheet on the surface of which lubricating oil or the like is applied, as in the case of Prior Art 1. . This is due to the limit of inorganic lubricants or thin coatings in amounts of 0.2-2 g / m ² .

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, when the surface temperature rises to a high temperature of 100 to 150 ° C. due to the frictional heat during press molding, the film becomes sticky or falls off, and good corrosion resistance cannot be obtained.

In addition to the above-mentioned prior arts 1 to 4, there has been proposed a surface-treated steel sheet having a resin coating having a thickness of about 1 to 2 μm, in which an arbitrary lubricant is added to a specific resin.
However, in such a surface-treated steel sheet, since the resin coating is thin, it is not possible to suppress the occurrence of blackening due to damage to the plating coating during press forming, and further, the properties of the base resin (for example, water-based, The effect of improving the lubricity is limited by the powder, thermoplasticity, thermosetting property, etc.) and the method of forming the film (for example, room temperature drying, high temperature baking, etc.).
That is, no matter what kind of lubricant is used, the effect of improving the press moldability and the appearance after press molding is not obtained, and a specific lubricant suitable for the performance of the resin as the base is combined to obtain a predetermined lubricant. By forming the film to a film thickness, it is possible to obtain a satisfactory effect of improving press moldability and appearance after press molding for the first time.

Therefore, an object of the present invention is to solve the above-mentioned problems, to exert excellent lubricity and press formability without applying lubricating oil or the like on the surface, and to perform press forming under severe conditions. It is an object of the present invention to provide a zinc-based plated steel sheet in which the resin film is not damaged, and which has excellent appearance and corrosion resistance after press forming and can suppress the blackening phenomenon accompanied by plating damage.

[0015]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems. As a result, the following findings were obtained. (1) A hydroxyl group-containing urethane prepolymer having a specific structure and physical properties, and a crosslinked structure of a polyisocyanate compound or an amino compound have excellent performance as a base resin for a coating, and thus such a solvent is used. On the chromate film formed on the surface of the zinc-based plating layer of the zinc-based plated steel sheet, a paint in which a thermosetting resin, a solid lubricant, and an antirust pigment are mixed in a predetermined ratio By applying and heating and curing this to form a resin film with a thickness within a predetermined range, press moldability and appearance after press molding are improved, and in particular the blackening phenomenon due to damage to the plating film is suppressed. In addition, the corrosion resistance can be improved.

(2) As a solvent-based thermosetting resin, a composite crosslinked structure comprising two or more hydroxyl group-containing urethane prepolymers of specific components and at least one of a polyisocyanate compound and an amino compound is a base resin. , Which has a further excellent performance, and zinc-plated a paint in which two or more kinds of the above solvent-based thermosetting resins having different glass transition temperatures, a solid lubricant, and a rust preventive pigment are mixed in a predetermined ratio. Apply on the chromate film formed on the surface of the zinc-based plating layer of the steel sheet, heat and cure this, to form a resin film of a predetermined range on the chromate film, press, The moldability and the appearance after press molding are further improved, especially the blackening phenomenon due to damage to the plating film is further suppressed, and the corrosion resistance can be improved.

The present invention has been made based on the above findings, and a chromate film is formed on at least one zinc-based plating layer of a zinc-plated steel plate or a zinc-based alloy-plated steel plate, and A zinc-based plated steel sheet on which a resin coating is formed by applying a coating material and heat-curing the coating material, wherein the amount of the chromate coating is 5 in terms of metallic chrome per one side of the steel sheet. The thickness of the resin coating is more than 3 μm per one side of the steel plate, and 10 to 200 mg / m ^2.
within a range of μm or less, the resin coating has a melting point of 130 ° C. or less in terms of solid content: (A) solvent-based thermosetting resin: 100 parts by weight, (B) solid lubricant, and Polyethylene resin with an average molecular weight of 5000 or less:
1 to 30 parts by weight, and (C) an anticorrosive pigment: 3 to 30 parts by weight, and the solvent-based thermosetting resin is (A) a hydroxyl group-containing urethane prepolymer having the following chemical components: , (A) at least one polyol selected from the group consisting of polyether polyols, polyester polyols and polyether polyester polyols, (b)
It is characterized by comprising an isocyanate compound, (c) a dihydric alcohol, and (B) at least one of a block polyisocyanate prepolymer as a curing agent and an amino resin.

[0018]

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 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 has stable performance for a long time. Since the thermosetting resin has no melting point as compared with the thermoplastic resin, the mechanical strength at high temperature is high. Therefore,
When the coating film made of such a resin is used, the resin coating film is less likely to be peeled off or damaged by frictional heat during press molding.

As described above, the solvent-based thermosetting resin is selected from the group consisting of (A) a hydroxyl group-containing urethane prepolymer having the following chemical components, (a) a polyether polyol, a polyester polyol and a polyether polyester polyol. At least one polyol, (b)
It is necessary to comprise an isocyanate compound, and (c) a dihydric alcohol, and (B) at least one of a blocked polyisocyanate prepolymer as a curing agent and an amino resin. The specific composition will be described below.

As the polyether polyol, for example,
Polyethylene glycol, polypropylene glycol,
A linear polyalkylene polyol such as an ethylene oxide or propylene oxide adduct of glycerin is used.

As the polyester polyol, for example,
Obtained by reacting a dibasic acid with a low molecular weight polyol,
A linear polyester having OH groups in the molecular chain is used. Then, as the dibasic acid, for example, adipic acid, azelaic acid, dodecanedioic acid, dimer acid, isophthalic acid, hexahydrophthalic anhydride, terephthalic acid, dimethyl terephthalate, itaconic acid, fumaric acid, maleic anhydride, or the above Esters of each acid are used.

As the polyether polyester polyol, a mixture of a dibasic acid and a polyether polyol or a mixture of a dibasic acid and a low molecular weight polyol is obtained by an esterification reaction and has an OH group in the molecular chain. A polyether obtained by an addition reaction of a linear polyester or a polyester having a carboxyl group and / or a hydroxyl group at the terminal with an alkylene oxide (for example, ethylene oxide, propylene oxide, etc.) is used.

Examples of the isocyanate compound include hexamethylene diisocyanate, o-, m-, or p-phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate, and 2,4-aromatic ring hydrogenated. Or 2,6-
Tolylene diisocyanate, diphenylmethane-4,4'-
Diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, dicyclohexylmethane-4,4 '
-Diisocyanate, ω, ω'-diisocyanate-1.
4-dimethylbenzene, ω, ω'-diisocyanate-1,
An isocyanate compound having an aromatic ring, such as 3-dimethylbenzene, is used alone or in combination of two or more.

As the dihydric alcohol, for example, diols such as ethylene glycol, butylene glycol, diethylene glycol and hydrogenated bisphenol A are used.

Typical examples of the blocked polyisocyanate prepolymer as a curing agent include a block polyisocyanate prepolymer obtained by blocking polyisocyanate with a known blocking agent, for example,
"Burnock D-550", "Burnock D-500",
"Barnock B7-887" (all manufactured by Dainippon Ink and Chemicals, Inc.), "Takenate N-815-N" (manufactured by Takeda Pharmaceutical Co., Ltd.), "ADDITOL VXL-80" (Hoechst Synthesis Co., Ltd.) Manufactured) etc.

As an amino resin as a curing agent, an amino component such as melamine urea acetoguanamine, benzoguanamine, steroganamin or spiroguanamine, an aldehyde component such as formaldehyde, paraform, acetaldehyde, glyoxal, and methanol, ethanol, Isopropanol, n-
A resin obtained by reacting with an alcohol component such as butanol, iso-butanol, sec-butanol is used.

The reason why polyethylene resin is used as the solid lubricant added to the paint is that the polyethylene resin prevents galling and breakage of the steel sheet caused by continuous press molding, etc. This is because it has a function of imparting resistance to movement, deformation and wear and preventing damage to the steel plate and the molding die.

Polyethylene resin is generally a crystalline thermoplastic resin having an average molecular weight of several hundreds to several millions, and its glass transition point is about -100 ° C, which is lower than room temperature.
Its melting point is 90-140 ° C. and its critical surface tension is about 30 dyne / cm 2. Therefore, polyethylene resin
It has a soft property at room temperature and has low wettability and adhesiveness, and thus has excellent lubricity. From the viewpoint of dispersibility in the resin film and film-forming property, it is desirable that the particle size of the polyethylene resin is 20 μm or less, preferably 10 μm or less, more preferably about 5 μm.

The melting point of the polyethylene resin 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 lubricity (sliding property) of the resin coating containing the polyethylene resin decreases.
Therefore, the melting point of the polyethylene resin used as a lubricant in this invention must be 130 ° C. or less. For polyethylene resins with melting points above 130 ° C,
Since the deformation resistance near room temperature is high, the lubricity of the resin coating is reduced. The preferred melting point of the polyethylene resin is in the range of 90 to 130 ° C. The average molecular weight of the polyethylene resin needs to be 5,000 or less from the viewpoint of coating property and lubricity of the resin film. In addition,
Two or more polyethylene resins having a melting point, an average molecular weight and a particle diameter within the ranges described above may be used.

The content of polyethylene resin as a lubricant is 100 parts by weight of the solid content of the solvent-based thermosetting resin,
It should be in the range of 1 to 30 parts by weight. If the content of the polyethylene resin is less than 1 part by weight with respect to 100 parts by weight of the solid content of the solvent-based thermosetting resin, 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 the resin coating is likely to peel off during press molding. The more preferable content of the polyethylene resin is 10% of the solid content of the solvent-based thermosetting resin.
It is in the range of 5 to 20 parts by weight with respect to 0 parts by weight.

At least one of a chromate compound and silica is used as a rust preventive pigment added to a paint together with a lubricant. Chromate-based compounds and silica are corrosion-resistant pigments that improve the corrosion resistance of zinc-based plated steel sheets.
It has a further improving effect. As described above, at least one of the chromate compound and silica is contained in the resin coating.
By containing a rust preventive pigment consisting of seeds, not only the corrosion resistance in the flat plate shape which has not been press molded is improved, but even if the resin film is deformed by press molding, the corrosion resistance of the resin film is It does not deteriorate. In particular, in this invention, the resin coating is less likely to be damaged by flaws or the like during press molding, so the effect of the rust-preventive pigment contained in the resin coating is extremely large.

As chromate compounds, calcium chromate, strontium chromate, barium chromate,
Lead chromate, zinc chromate, zinc potassium chromate, silver chromate, etc. are used. Further, as silica, hydrophobic silica, hydrophilic silica or the like is used.

The content of the rust preventive pigment should be in the range of 3 to 30 parts by weight based on 100 parts by weight of the solid content of the solvent-based thermosetting resin. If the content of the rust preventive pigment 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 it exceeds 30 parts by weight, not only the effect of improving the corrosion resistance is not further obtained, but also the cohesive force of the resin in the resin coating is reduced, which causes a problem that the resin coating easily peels off during press molding. . The more preferable content of the rust preventive pigment is in the range of 5 to 20 parts by weight based on 100 parts by weight of the solid content of the solvent-based thermosetting resin.

In the coating material, in addition to the above-mentioned solvent-based thermosetting resin, solid lubricant and rust preventive pigment, if necessary, other components, for example, colorants such as pigments and dyes, solvents and interfaces. You may include an activator, a stabilizer, etc.

By coating the surface of a zinc-based plated steel sheet with a coating composition of the above-described solvent-based thermosetting resin, solid lubricant and rust preventive pigment diluted with a predetermined solvent, and heating to cross-link and harden it. , A resin film is formed.

The resin coating formed as described above is
It is necessary to form it on the chromate film formed on the zinc-based plating layer of the zinc-based plated steel sheet. As described above, by forming the resin film on the chromate film, the passivation effect of Cr ⁶⁺ contained in the chromate film by the chromate ion occurs. Furthermore, since the surface of the zinc-based plating layer is covered with the chromium hydrate oxide film of Cr ³⁺ , which is a reduction product of chromate ions, the area of the anode is reduced, and Ingress of water and oxygen is prevented. Therefore, the corrosion resistance of the zinc-based plated steel sheet is improved, and the resin film is formed well. In addition,
The formation of the chromate film may be performed by any known means such as coating treatment, electrolytic treatment and reaction treatment.

The amount of the chromate coating, converted to metallic chromium, should be within the range of 5 to 200 mg / m ² per side of the steel sheet. If the amount of the chromate coating, converted to metallic chromium, is less than 5 mg / m ² per side of the steel sheet, the effect of improving corrosion resistance cannot be obtained. On the other hand, if the amount of the chromate coating, converted to metallic chromium, exceeds 200 mg / m ² per side of the steel sheet, not only a further corrosion resistance improvement effect cannot be obtained, but also severe press forming accompanied by deformation of the steel sheet. When applied, the problem of breaking the chromate coating occurs. A more preferable amount of the chromate film is converted into metallic chromium,
It is in the range of 10 to 150 mg / m ² per side of the steel sheet.

In the present invention, the steel sheet on which the resin coating for lubrication is to be formed is a zinc-plated steel sheet having a galvanized layer on at least one surface thereof, in addition to zinc, nickel, iron, Even a zinc alloy plated steel sheet having a zinc alloy plated layer containing at least one component of manganese, molybdenum, cobalt, aluminum, chromium, silicon, or the like, or a plurality of layers of the above zinc plated layer or zinc alloy plated layer It may be a multi-layer zinc-based plated steel sheet. The steel sheet on which the zinc-based plating layer should be formed on at least one surface thereof may be a cold-rolled steel sheet, a hot-rolled steel sheet, a stainless steel sheet or the like, or a metal plate other than steel, such as aluminum or copper. Good. Needless to say, the above metal plate without the zinc-based plating layer is also applicable.

The resin coating film is formed on at least one surface of the zinc-based plated steel sheet as follows.
That is, on the surface of the chromate film formed on the zinc-based plating layer, by a known method such as a roll coater, curtain flow coater or spray coating, or a coating composition having the above-mentioned composition is applied, or A zinc-based plated steel sheet having a chromate film formed on its surface is dipped in the coating material, and then the attached coating material is squeezed by a roll or air blow to form a predetermined amount of the coating film. Next, this is heated to 150-250 by a hot air stove or induction heating device.
It is heated to a temperature of ℃ to evaporate the solvent in the paint and cure the resin. Thus, the resin film is formed on the chromate film formed on the surface of the zinc-based plated steel sheet.

The thickness of the resin coating formed as described above should be within the range of more than 3 μm and 10 μm or less per one side of the steel sheet. If the thickness of the resin coating is 3 μm or less per one side of the steel sheet, it is not possible to completely prevent damage to the zinc-based plating layer during press forming, especially during severe press forming that requires high precision. Further, since the sliding resistance is added, the blackening phenomenon cannot be suppressed. On the other hand, the thickness of the resin coating is 10 μm per steel plate
If the value exceeds the above range, the amount of the resin film itself is destroyed or peeled off during press molding, and the adhesion or deposition on the mold becomes unavoidable, which causes a problem that stable press molding cannot be performed continuously. .

As the solvent-based thermosetting resin in the resin coating,
When a solvent-based thermosetting resin composed of two or more kinds having different glass transition temperatures is used, press moldability and appearance after press molding can be further improved. The reason is as follows.

That is, the solvent-based thermosetting resin having a low glass transition temperature is excellent in flexibility at low temperature. Therefore, when press-molding a zinc-based plated steel sheet on which a resin film made of such a resin as a base resin is formed, when the press-molding conditions are gentle or at a gentle portion, solvent-based heat with a low glass transition temperature is used. The use of the curable resin improves the press moldability and the appearance after the press molding. However, in the case where the press molding conditions are severe such that the surface becomes hot, or in a severe part, the resin coating softens and peels off due to frictional heat generated during press molding. As a result of being attached to the mold, the press moldability and the appearance after press molding are likely to deteriorate.

On the other hand, the solvent-based thermosetting resin having a high glass transition temperature is excellent in high temperature strength. Therefore, when press-molding a zinc-based plated steel sheet on which a resin coating having such a resin as a base resin is formed, the press-forming conditions are:
Even in a severe case where the surface becomes hot or in a severe part, the resin coating does not soften and peel off from the plated steel sheet.

However, the solvent-based thermosetting resin having a high glass transition temperature has the following problems. That is, since the flexibility at low temperature is poor, the resin coating is powdered and peeled off when the press molding conditions are gentle or in a gentle portion, and the peeled resin coating adheres to the molding die. This causes deterioration in formability and appearance after press forming. From the above, if two or more solvent-based thermosetting resins having different glass transition temperatures are used as the solvent-based thermosetting resin in the resin coating, the flexibility at low temperature during the above-described press molding will be obtained. The strength at high temperature can be imparted to the resin coating.

Preferred solvent-based thermosetting resins include a solvent-based thermosetting resin having a low glass transition temperature of 50 ° C. or lower after curing and a high glass transition temperature of 50 ° C. or higher after curing. It is a resin composed of a temperature-based solvent-based thermosetting resin. Solvent-based thermosetting resin having a low glass transition temperature described above, a more preferable glass transition temperature is 10 to 50.
C., and the more preferable glass transition temperature of the above-mentioned high glass transition temperature solvent-based thermosetting resin is in the range of more than 50.degree. C. to 100.degree.

The preferred compounding ratio of the solvent-type thermosetting resin having a low glass transition temperature and the solvent-type thermosetting resin having a high glass transition temperature is in the range of 9: 1 to 1: 9. If the compounding ratio is more than 9: 1 and less than 1: 1, during press forming of a zinc-based plated steel sheet on which a resin coating having such a resin as a base resin is formed, the forming conditions are so severe that the surface of the steel sheet becomes hot. In this case, there arises a problem that the resin coating film is softened and separated from the plated steel sheet. On the other hand, if the compounding ratio is less than 1: more than 9, there is a problem that the resin coating is powdered and peeled off from the plated steel sheet when the molding conditions are gentle such that the steel sheet surface does not reach such a high temperature. A more preferable compounding ratio of the solvent thermosetting resin having a low glass transition temperature and the solvent thermosetting resin having a high glass transition temperature is within a range of 9: 1 to 5: 5.

The above-mentioned solvent type thermosetting resin having a low glass transition temperature of 50 ° C. or lower and the solvent type thermosetting resin having a high glass transition temperature of more than 50 ° C. are chemical components of a hydroxyl group-containing urethane prepolymer. Can be obtained by adjusting.

[0048]

EXAMPLES Next, the present invention will be described by way of Examples in comparison with Comparative Examples. Example 1 As a hydroxyl group-containing urethane prepolymer in a solvent-based thermosetting resin that constitutes 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, Table 1 No. 1 to 8 of the composition shown in 8
Various types of hydroxyl group-containing urethane prepolymers were prepared.

[0049]

[Table 1]

The production examples of the No. 1 hydroxyl group-containing urethane prepolymer in Table 1 will be described below. Using a reactor equipped with a heating device, stirrer, water separator and thermometer,
Aromatic polyester polyol (AR) as polyester polyol: 915 parts by weight and aliphatic polyester polyol (AL): 915 parts by weight were fed into the apparatus, which were heated and melted under an inert atmosphere. While stirring the molten polyester polyol
It was heated to a temperature of 100 ° C. and kept at that temperature for 30-60 minutes and then dehydrated.

Then, the temperature of the melted raw material is cooled to 70 ° C., and at that temperature, the divalent alcohol
1,4-butanediol: 28 parts by weight, diphenylmethane-4,4'-diisocyanate as an isocyanate compound: 31
3 parts by weight, dibutyltin laurylate as a reaction catalyst: 0.55 parts by weight and cyclohexanone as a solvent: 9
40 parts by weight each were added and mixed and allowed to react for 5-10 hours. After the above mixture had a predetermined viscosity, 10 parts by weight of 1,3-butanediol as a dihydric alcohol was added to terminate the reaction. Further, cyclohexanone as a solvent: 4,150 parts by weight was added, and thus, nonvolatile content: 30%
A urethane prepolymer containing hydroxyl groups having a viscosity of 1,400 cps was prepared.

No. 2 to 8 hydroxyl group-containing urethane prepolymers shown in Table 1 were also prepared by the same method as described above. To each of the hydroxyl group-containing urethane prepolymers Nos. 1 to 8 prepared as described above, hexamethylene diisocyanate trimer was added as a block polyisocyanate prepolymer as a curing agent, and NCO / ON = 1/1. Added in equal proportions. Thus, eight kinds of solvent-based thermosetting resins each consisting of each of the hydroxyl group-containing urethane prepolymer Nos. 1 to 8 and the block polyisocyanate prepolymer as the curing agent were prepared. 8 thus obtained
The glass transition temperature of each type of solvent-based thermosetting resin,
It is also shown in Table 1.

On the other hand, six kinds of solid lubricants a to f having the composition shown in Table 2 were prepared.

[0054]

[Table 2]

Both sides of the galvanized layer of an electrogalvanized steel sheet having a plate thickness of 0.8 mm and a plating amount of 20 g / m ² or a hot-dip galvanized steel sheet having a plate thickness of 0.8 mm and a plating amount of 90 g / m ² were degreased with alkali. , Then, on the galvanized layer, after applying a chromate treatment liquid containing silica sol by a roll coating method, heated and dried, on the galvanized layer,
A chromate film was formed in an amount of 50 mg / m ² in terms of metallic chromium.

From each of the solvent type thermosetting resins consisting of the hydroxyl group-containing urethane pretan polymer Nos. 1 to 8 shown in Table 1, the lubricant a shown in Table 2, and silica as a rust preventive pigment. The coating composition was applied by a roll coating method on the chromate coating formed on both sides of the electrogalvanized steel sheet. Then, this was heated to a temperature of 200 ° C. in an induction heating furnace to form a resin film having a thickness of about 4 μm 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 9 shown in Table 3 within the scope of the present invention were prepared.

For comparison, a coating using a resin outside the scope of the present invention was used to form a resin coating having a thickness of about 4 μm on the chromate coating in the same manner as described above, and the resin coating outside the scope of the present invention was used. Zinc-based plated steel sheet (hereinafter referred to as "comparative steel sheet") Nos. 1 to 3 and a comparative steel sheet N that does not have a resin film and is coated with ² g / m ² of press oil on the chromate film
o.4 was prepared as also shown in Table 3. In Table 3, "a" indicates an electrogalvanized steel sheet, and "a" indicates a hot-dip galvanized steel sheet.

[0058]

[Table 3]

With respect to each of the above-described steel sheet of the present invention and the comparative steel sheet, the lubricity, press formability, blackening resistance (appearance after press forming) and corrosion resistance after press forming were evaluated by the performance tests described below. . The evaluation results are shown in Table 4.

[0060]

[Table 4]

(1) Lubricity The tester shown in the schematic front view of FIG. 1 was used. The testing machine is
As shown in FIG. 1, it has a female die 1 having a flat surface fixed to one side 2a of a box-shaped frame 2 and a substantially horizontal projection 3 facing the female die 1 and having a predetermined height. It comprises a male die 4 and a hydraulic cylinder 5 which is fixed to the other side 2b of the frame 2 for supporting the male die 4 and horizontally moving the male die 4 toward the female die 1. The male die 4 is fixed to the rod 5a of the hydraulic cylinder 5 via the load cell 6. The width of the ridge 3 of the male die 4 is
The length of the tip is 1 mm.

The test piece 7 cut out from the steel sheet of the present invention and the steel sheet for comparison was vertically inserted into the gap between the female die 1 and the male die 4, and the hydraulic cylinder 5 was operated to operate the female die 1. And test piece 7 with male die 4 at 50Kgf
It was pressed at a pressure of (500 Kgf / cm ² ). Next, test piece 7
As indicated by the arrow, the upper part was pulled out at a speed of 100 mm / min, the dynamic friction coefficient at that time was investigated, and the lubricity was evaluated by this. In addition to the test piece at room temperature (20 ℃), the test was performed at 120 ℃ considering the rise in plate temperature during the actual press work.
A high-temperature test piece having a temperature of 1 was also performed.

(2) Press-formability A circular test piece was used for punch diameter: 50 mm, die diameter: 51.84 m.
m, wrinkle holding force: Under the conditions of 1 ton, the limit drawing ratio when forming into a cup shape was investigated, and the press formability was evaluated by this.

(3) Blackening resistance In advance, a slit flaw reaching the plated surface in the width direction of the test piece was provided by a cutter, and the test piece shown in FIG. 1 was used for that portion 20 times under the same conditions. After repeated sliding, the appearance was examined and the blackening resistance was evaluated by this. The evaluation criteria are as follows. ⊚: No blackening occurred, ○: Some blackening occurred in the vicinity of the slit flaw, Δ: Clear blackening occurred in the vicinity of the slit flaw, ×: Extremely blackening occurred over the entire surface.

(4) Corrosion resistance after press molding A circular test piece was blanked with a diameter of 100 mm and a punch diameter of 50 m.
m, die diameter: 51.84 mm, wrinkle holding force: 1 ton, formed into a cup shape, and then the edge was sealed with tar epoxy paint, then salt spray test based on JIS Z 2371 for 240 hours The white rust occurrence rate was examined after 240 hours, and the corrosion resistance after press molding was evaluated. The evaluation criteria are as follows. ◎: White rust occurrence rate of less than 5%, ◯: White rust occurrence rate of 5 to less than 20%, △: White rust occurrence rate of 20 to less than 40%, ×: White rust occurrence rate of 40% or more.

As is clear from Tables 3 and 4, Comparative Steel Sheet No. 1 using a coating material made of a resin other than the present invention
No. 3 to 3 had poor lubricity at high temperature. Furthermore, the comparative steel sheet No. 1 has poor corrosion resistance after press forming, the comparative steel sheet No. 2 has poor blackening resistance, and the comparative steel sheet No. 3 has blackening resistance and corrosion resistance after press forming. Both were bad.
Further, Comparative Steel Sheet No. 4 coated with press oil had poor lubricity, press formability, blackening resistance, and corrosion resistance after press forming. On the other hand, the present invention steel plate No.
Nos. 1 to 9 were excellent in all of lubricity, press moldability, blackening resistance, and corrosion resistance after press molding.

Example 2 The same chromate coating as in Example 1 was formed on both sides of the chromate coating on a steel sheet, and the lubricant a or b was added to 100 parts by weight of the solid content of the resin No. 1 described above. A coating material containing a rust preventive pigment 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. In this way
Inventive steel sheets Nos. 10 to 20 shown in Table 5 were prepared.

For comparison, Comparative Steel Sheets Nos. 5 to 8 using a lubricant outside the scope of the present invention, which is also shown in Table 5, a coating material containing less lubricant than the scope of the present invention Steel plate for comparison No. 9 using the above, the content of the lubricant is out of the range of the present invention, and the steel plate for comparison using the coating material No. 10 and the content of the rust preventive pigment are out of the range of the present invention Comparative steel plate No. 11 using the paint, the content of the rust preventive pigment is outside the scope of the present invention Comparative steel plate No. 12 using the paint, the content of the rust preventive pigment is outside the scope of the present invention Comparative steel plate No. 13 with a large amount of chromate coating outside the scope of the present invention
, And a comparative steel plate No. 14 in which the content of the rust preventive pigment was large outside the range of the present invention and the amount of the resin coating was small outside the range of the present invention was prepared. In addition, in Table 5,
“A” indicates an electrogalvanized steel sheet.

[0069]

[Table 5]

With respect to each of the steel sheets Nos. 10 to 20 of the present invention and the steel sheets No. 5 to 14 for comparison described above, the lubricity, press formability, blackening resistance and corrosion resistance after press forming were evaluated by the above performance test. evaluated. The evaluation results are shown in Table 6.

[0071]

[Table 6]

As is clear from Tables 5 and 6, comparative steel sheets Nos. 5 to 8 using lubricants outside the scope of the present invention.
Had poor lubricity, press moldability, blackening resistance, and corrosion resistance after press molding. Comparative Steel Sheet No. 9, which used a coating material having a lubricant content outside the range of the present invention, was poor in lubricity, press formability, blackening resistance, and corrosion resistance after press forming. Steel sheet for comparison using a coating material containing a large amount of lubricant outside the range of the present invention
In No. 10, the corrosion resistance after press molding was poor because the amount of peeling increased due to the decrease in the cohesive force of the coating.

Comparative Steel Sheet No. 11 using a coating material containing a small amount of rust preventive pigment outside the range of the present invention had poor corrosion resistance after press forming. Comparative steel sheet No. 12 using a paint whose content of the rust preventive pigment is out of the range of the present invention, the content of the rust preventive pigment is out of the range of the present invention and the amount of the chromate film of the present invention is No. 1 for comparison steel plate that is out of range
3, and the comparative steel sheet No. 14 in which the content of the rust-preventive pigment is out of the range of the present invention and the amount of the resin coating is out of the range of the present invention is low, lubricity and press formability are all , Blackening resistance and corrosion resistance after press molding were all poor.

On the other hand, the steel sheets Nos. 10 to 20 of the present invention are
It was excellent in lubricity, press formability, blackening resistance, and corrosion resistance after press forming.

Example 3 As the solvent-based thermosetting resin, the hydroxyl group-containing urethane prepolymer shown in Table 1 was used, and as shown in Table 7, two types having different glass transition temperatures were specified. 9 kinds of solvent-based thermosetting resins A to I were prepared in combination with each other.

[0076]

[Table 7]

As in Example 1, the plate thickness was 0.8 mm and the plating amount was
20 g / m ² electrogalvanized steel sheet, or a plate thickness 0.8 mm, on the galvanized layer of the galvanized steel sheet having a plating amount of 90 g / m ² , a chromate coating within the scope of the present invention is formed, and then, A resin coating having a thickness of about 4 μm, which is composed of the solvent-based thermosetting resin shown in Table 7, the solid lubricant a shown in Table 2, and silica as a rust preventive pigment on the chromate coating. Was formed. In this way, the steel sheets Nos. 21 to 30 of the present invention shown in Table 8 were prepared. In addition, in Table 8,
“A” indicates an electrogalvanized steel sheet, and “a” indicates a hot-dip galvanized steel sheet.

[0078]

[Table 8]

With respect to each of the steel sheets Nos. 21 to 30 of the present invention described above, the lubricity, press formability, blackening resistance, and corrosion resistance after press forming were evaluated by the above-mentioned performance test.
The evaluation results are shown in Table 9.

[0080]

[Table 9]

As is clear from comparison between Table 9 and Table 4 of Example 1 described above, two kinds of resins having different glass transition temperatures are used in combination as the solvent-based thermosetting resin in the resin coating. Of the present invention steel sheets No. 21 to 30, lubricity,
The press moldability, blackening resistance, and corrosion resistance after press molding were much better.

[0082]

As described above, according to the zinc-plated steel sheet of the present invention, excellent lubricity and press formability are exhibited without applying lubricating oil or the like on the surface, and press forming is performed under severe conditions. Does not damage the resin coating,
And, it is excellent in appearance and corrosion resistance after press molding, and in particular, it is possible to suppress the blackening phenomenon accompanied by plating damage,
Industrially useful effects are provided.

[Brief description of drawings]

FIG. 1 is a schematic front view of a tester for evaluating the lubricity of a test piece.

[Explanation of symbols]

 1 female die, 2 frames, 3 ridges, 4 male dies, 5 hydraulic cylinders, 6 load cells, 7 test pieces.

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C23F 11/00 F 8414-4K (72) Inventor Norio Kosaka 3-3-3 Higashisukematsucho, Izumiotsu City, Osaka Prefecture

Claims (6)

[Claims] 1. A chromate film is formed on at least one zinc-based plating layer of a galvanized steel plate or a zinc-based alloy-plated steel plate, and a paint is applied on the chromate film and heat-cured. A zinc-based plated steel sheet having a resin coating formed thereon by the method, wherein the amount of the chromate coating is in the range of 5 to 200 mg / m ² per one side of the steel sheet, in terms of metal chromium, The thickness of the resin coating is 3μm per one side of the steel plate
Within the range of 10 μm or less, the resin coating has a melting point of 130 ° C. or less in terms of solid content: (A) solvent-based thermosetting resin: 100 parts by weight, (B) solid lubricant. And a polyethylene resin having an average molecular weight of 5000 or less:
1 to 30 parts by weight, and (C) a rust preventive pigment: 3 to 30 parts by weight, and the solvent-based thermosetting resin is (A) a hydroxyl group-containing urethane prepolymer having the following chemical components: , (A) at least one polyol selected from the group consisting of polyether polyols, polyester polyols and polyether polyester polyols, (b)
Press moldability, comprising an isocyanate compound, (c) a dihydric alcohol, and (B) at least one of a blocked polyisocyanate prepolymer as a curing agent and an amino resin. , Zinc-based plated steel sheet with excellent appearance and corrosion resistance after press forming. 2. The solvent-based thermosetting resin is composed of two or more kinds of resins having different glass transition temperatures.
The zinc-based plated steel sheet described. 3. The two or more solvent-based thermosetting resins having different glass transition temperatures have a glass transition temperature after curing of 50 ° C.
The following, solvent-based thermosetting resin of low glass transition temperature,
The zinc-based plated steel sheet according to claim 2, which is composed of a solvent-based thermosetting resin having a high glass transition temperature and having a glass transition temperature after curing of more than 50 ° C. 4. The compounding ratio of the solvent-type thermosetting resin having the low glass transition temperature and the solvent-type thermosetting resin having the high glass transition temperature is in the range of 9: 1 to 1: 9. Claim 2
Or the zinc-based plated steel sheet according to 3. 5. The melting point of the polyethylene resin as the solid lubricant is in the range of 90 to 130 ° C., and the particle size thereof is 20 μm or less, according to any one of claims 1 to 4. Galvanized steel sheet. 6. The zinc-based plated steel sheet according to claim 1, wherein the rust-preventive pigment comprises at least one of a chromate-based compound and silica.