JPH04313367A - Galvanized steel sheet with excellent lubricity and formability - Google Patents

Abstract

PURPOSE:To give excellent lubricating property and formability to a galvanized steel sheet without applying a lubricant oil and the like on the surface by applying a coating material obtd. by compounding a solvent-base thermosetting resin and a specified polyethylene fine powder by a specified proportion on the plating layer of the galvanized steel sheet, and heating the coating material to cure. CONSTITUTION:A coating material is applied on at least one galvanized layer of a galvanized steel sheet or a zinc-alloy plated steel sheet, and then cured by heating. This coating material consists of a solvent-base thermosetting resin containing a lubricant, and a polyethylene fine powder having <=120 deg.C melting point and <=5000 average mol.wt. The amt. of polyethyelene fine powder ranges from 5 to 30 pts.wt. to 100 pts.wt. of the solid content of the solvent-base thermosetting resin. The resin film comprising this coating material is 0.3-3.0mum thick per one surface of the steel sheet. The solvent-base thermosetting resin consists of a compsn. of combination of a bisphenol epoxy resin and the like and an amine compd. and the like which can be cured by heating.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a galvanized steel sheet or a zinc-based alloy coated steel sheet (
(Hereinafter, it will be abbreviated as "zinc-based plated steel sheet").

0002

BACKGROUND OF THE INVENTION Zinc-based plated steel sheets are widely used in various industrial fields because of their excellent corrosion resistance. When such galvanized steel sheets are used as materials for office equipment such as copying machines, audio equipment, home appliances, etc., various press forming processes are applied to the galvanized steel sheets. When used as a material for , motor covers, cartridge-type tanks, etc., a drawing process is performed on the zinc-based plated steel sheet.

[0003] The formability of galvanized steel sheets is inferior to that of cold-rolled steel sheets. The reason for this is that the sliding resistance of the zinc-based plated steel sheet with respect to the mold during forming using a press or the like is greater than that of the cold-rolled steel sheet. Therefore, in order to improve the formability of zinc-based coated steel sheets and improve their appearance after forming, lubricating oil or anti-corrosion oil is generally applied to the surface of zinc-based coated steel sheets. It is being said. However, applying lubricating oil or the like on the surface of galvanized steel sheets complicates the manufacturing process, and
Deteriorate the working environment. In addition, even when molding is performed with the application of lubricating oil or the like, if the molding 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 zinc-based plated steel sheets, chromate-treated zinc-based plated steel sheets are known in which a chromate film or a chromate film and a resin film are formed on the surface of the zinc-based plating layer. It is being The corrosion resistance of such a chromate-treated zinc-plated steel sheet in the form of a flat plate without forming is good. However, if molding is performed without applying lubricating oil or the like, the chromate film will peel or darken, resulting in deterioration of corrosion resistance and surface quality. Therefore, even in the case of a chromate-treated zinc-plated steel sheet, it is necessary to apply lubricating oil or the like on the surface when forming the sheet.

[0005] To solve the above-mentioned problems, it has been necessary to develop a surface-treated steel sheet that has excellent lubricity and formability without applying lubricating oil or the like on the surface, and has good corrosion resistance. For example, the following surface-treated steel sheets have been proposed. ■ JP-A 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 the steel plate, which has excellent lubricity. surface-treated steel sheet (hereinafter referred to as prior art 1).

[0006]■ JP-A No. 62-289275 A thermosetting powder coating containing a fluorine-based resin powder with a high melting point as a lubricant is applied onto the surface of the steel plate, and then a thermosetting powder coating containing a fluorine-based resin powder with a high melting point as a lubricant is applied. A surface-treated steel sheet (hereinafter referred to as prior art 2) on which a film is formed on the surface of which a fluororesin powder is exposed by baking at a temperature.

[0007]■ JP-A-1-110140 contains an inorganic solid lubricant such as graphite, molybdenum disulfide, etc., and colloidal silica, which has been previously subjected to titanate coupling treatment on the surface of a zinc-based plated steel sheet. A surface-treated steel sheet on which a water-soluble or water-dispersible acrylic/epoxy resin coating is formed (hereinafter referred to as prior art 3).

[0008]■ JP-A-2-140294 A surface-treated steel sheet (hereinafter referred to as "a surface-treated steel sheet") in which a thin film of montan wax oxide is formed on the surface of a zinc-plated steel sheet in order to suppress the blackening phenomenon during press forming. prior art 4).

[0009]

[Problems to be Solved by the Invention] The above-mentioned prior art has the following problems. (2) In the case of the surface-treated steel sheet of Prior Art 1, some improvement in lubricity and moldability is observed due to the lubricant contained in the water-based acrylic resin coating. However, when the molding conditions are severe, the acrylic resin coating deteriorates due to frictional heat during the molding process, resulting in burning onto the die and blackening of the coating. Therefore, the lubricity and formability are inferior to conventional galvanized steel sheets whose surfaces are coated with lubricating oil or the like. This is considered to be a limitation due to the combination of water-based acrylic resin and inorganic solid lubricant. Furthermore, since the coating contains graphite and/or molybdenum disulfide as a lubricant, the coating has a dark tone and cannot have a white appearance.

[0010] In the case of the surface-treated steel sheet of Prior Art 2, since a powder coating is used as the resin composition constituting the coating, it is difficult to form a coating of uniform thickness; In particular, it is not possible to form a thin film of several μm or less. Furthermore, since it is difficult to make the fluororesin powder added as a lubricant into fine particles of 1 μm or less, the fluororesin powder is exposed in the coating and on the coating surface. As a result, the fluororesin powder does not necessarily contribute to improving lubricity during molding, and on the contrary, the fluororesin powder detaches from the coating, causing the problem of pinholes.

[0011] In the case of the surface-treated steel sheet of Prior Art 3, the affinity and adhesion between the resin component and the inorganic solid lubricant such as graphite or molybdenum disulfide are improved to some extent. However, if the molding conditions are severe,
Similar to Prior Art 1, the lubricity and formability are inferior to conventional galvanized steel sheets whose surfaces are coated with lubricating oil or the like.

[0012] 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 the forming process, the surface temperature decreases to 1
When the temperature reaches a high temperature of 00 to 150°C, the film becomes sticky and falls off, making it impossible to obtain good corrosion resistance.

[0013] In addition to the above-mentioned prior art, a surface-treated steel sheet having a lubricating coating formed by adding an arbitrary lubricant to a specific resin has been proposed. However, such surface-treated steel sheets vary depending on the properties of the base resin (e.g., water-based, powder, thermoplastic, thermosetting, etc.) and the coating formation method (e.g., drying at room temperature, baking at high temperature, etc.). , the lubricity improvement effect is limited. In other words, the effect of improving lubricity cannot be obtained no matter what kind of lubricant is used; satisfactory lubricity and moldability can only be achieved by combining a specific lubricant that is suitable for the performance of the base resin. However, its performance is limited.

Therefore, an object of the present invention is to solve the above-mentioned problems, to exhibit excellent lubricity and moldability without applying lubricating oil to the surface, and to mold under severe conditions where frictional heat is generated. It is an object of the present invention to provide a zinc-based plated steel sheet that does not cause damage or blackening to the coating even when processed, and has excellent lubricity and formability.

[0015]

[Means for Solving the Problems] The present inventors have conducted extensive research in order to solve the above-mentioned problems. As a result, a paint containing a solvent-based thermosetting resin and polyethylene fine powder having a predetermined melting point and molecular weight in a predetermined ratio is applied onto at least one surface of the zinc-based plating layer, and then heated. It has been found that by forming a hardened resin film, a zinc-based plated steel sheet with excellent lubricity and formability can be obtained. [0016] This invention was made based on the above-mentioned knowledge, and this invention provides a resin containing a lubricant on at least one zinc-based plating layer of a galvanized steel sheet and a zinc-based alloy-plated steel sheet. A zinc-based plated steel sheet in which a resin film is formed on the surface of at least one zinc-based plating layer of the steel sheet by applying a paint consisting of the following, and then heating and curing the paint. The paint consists of a solvent-based thermosetting resin and 120
The polyethylene fine powder has a melting point of 5,000 or less and has a melting point of 5,000 or less, and the content of the polyethylene fine powder is 5 parts by weight per 100 parts by weight of the solid content of the solvent-based thermosetting resin. ~30 parts by weight, and the thickness of the resin coating made of such a paint is within the range of 0.3 ~ 3.0 μm per one side of the steel plate. It is.

[0017]

[Operation] In the present invention, the reason why a solvent-based thermosetting resin is used as the base resin in the paint for the resin film formed on the surface of the zinc-based plating layer is as follows. ■ Solvent-based thermosetting resins are superior to water-based resins in their compatibility with additives such as lubricants and rust preventives added to the resin, and in their long-term stability as paints. . ■ Unlike thermoplastic resins, thermosetting resins have no melting point, so they have high mechanical strength at high temperatures. Therefore, if a coating is formed using a paint made of such a resin, the coating will be less likely to peel off or deform even if the temperature of the steel plate increases due to frictional heat during press molding.

Solvent-based thermosetting resins include bisphenol-type epoxy resins, multifunctional epoxy resins, ester resins such as oil-free alkyd resins, acrylic resins, urethane resins (polyols), or modified derivatives of the above-mentioned resins. It consists of a heat-curable composition in which at least one of these and at least one of various amine compounds, amino resins, and isocyanate compounds are combined. A resin having such a composition is crosslinked and cured by applying a paint diluted with a predetermined solvent onto the surface of the zinc-based plating layer and heating.

[0019] The polyethylene fine powder prevents galling and breakage of the steel plate caused by continuous press forming, etc., provides resistance to sliding, deformation, and wear to the steel plate, and prevents damage to the steel plate and mold. It has the effect of preventing Therefore, it is added to paints as a lubricant.

[0020] Polyethylene is generally a crystalline thermoplastic resin with an average molecular weight of several hundred to several million, and its glass transition point is approximately -100°C, which is lower than room temperature.
Its melting point is 90 to 140°C, and it is flexible at room temperature. Furthermore, its critical surface tension is about 30d
yne/cm 2 and has low surface energy and low wettability and adhesion, so it has a lubricating effect. However, when it is included as a lubricant in a paint for a resin film formed on the surface of a zinc-based plating layer as in the present invention, it is difficult to incorporate the lubricant from the viewpoint of paint dispersibility and thin film formation. It is necessary that the polyethylene is a fine powder with a particle size of 20 μm or less, preferably 10 μm or less, more preferably about 5 μm. If polyethylene is not such a fine powder, the initial effect cannot be obtained.

[0021] The melting point of the polyethylene fine powder affects the lubricity. That is, the higher the melting point, the higher the mechanical strength, that is, the deformation resistance near room temperature, and the lower the lubricity (slidability) of the resin coating containing fine polyethylene powder. Therefore, the melting point of the fine polyethylene powder used as a lubricant in this invention is 120°C or less, preferably
It is necessary that the temperature be within the range of 90 to 110°C.

The molecular weight and melt viscosity of polyethylene fine powder are closely related, and the higher the molecular weight, the higher the melt viscosity, making it difficult to obtain sufficient flow when forming a resin film by heating and baking. Therefore, a polyethylene fine powder with a high molecular weight cannot form a smooth resin coating, resulting in decreased lubricity and coating damage resistance during press molding. Paints based on solvent-based thermosetting resins are
150 to 250 for crosslinking during resin film formation
During heating, the fine polyethylene powder in the resin coating flows and becomes amorphous or disc-shaped, which improves the lubricity and press moldability of the resin coating. preferred from the viewpoint of

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 within the range of 140 to 150°C. It has been found that polyethylene fine powder having a melt viscosity in the range of 100 to 1,000 cps at a temperature of 140 to 150°C has optimal flow properties. That is, if the melt viscosity is less than 100 cps, a problem arises in that the formed film becomes sticky and promotes the formation of voids. On the other hand, the melt viscosity is 1,000c
If it exceeds ps, crosslinking and curing of the base resin will proceed without sufficient flow. As a result, a smooth resin film surface cannot be obtained, leading to problems such as increased resistance during press molding, detachment of lubricant, and generation of voids.

The content of the polyethylene fine powder as a lubricant should be within 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. If the content of the polyethylene fine powder is less than 5 parts by weight based on 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 it exceeds 30 parts by weight,
As a result of the decrease in the cohesive force and strength of the resin coating itself, a problem arises in that the resin coating increases in peeling during molding. A more preferable content of the polyethylene fine powder is within 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.

In addition to the above-mentioned base resin and polyethylene fine powder, the paint may contain other components as necessary, such as colorants such as pigments and dyes, surfactants, stabilizers, etc. good. As mentioned above, in this invention, the resin coating contains polyethylene fine powder as a lubricant, so the zinc-plated steel sheet of this invention can be press-formed without applying lubricating oil or the like. Even when applied, the resin coating remains intact with almost no damage. Therefore, the rust prevention effect of the resin film itself can be fully exhibited.

In the present invention, the steel sheet on which the resin coating for lubrication is to be formed is a galvanized steel sheet having a galvanized layer on at least one surface thereof, in addition to zinc,
A zinc alloy-plated steel sheet having a zinc alloy plating layer containing at least one component of nickel, iron, manganese, molybdenum, cobalt, aluminum, chromium, silicon, etc., or the above-mentioned zinc plating layer or zinc alloy plating layer. It may be a multilayer zinc-based plated steel sheet having multiple layers.

In the present invention, a chromate film is formed as an intermediate layer on the zinc-based plating layer of the above-mentioned zinc-based plated steel sheet, and the above-mentioned resin film is formed as an uppermost layer on the chromate film. For example, corrosion resistance is improved and the formation of a resin film is also improved. The chromate film may be formed by any known means such as coating, electrolytic treatment, reaction treatment, etc.

The amount of the chromate film deposited is preferably within the range of 5 to 200 mg/m 2 per side of the steel sheet in terms of metallic chromium. If the amount of the chromate film is less than 5 mg/m 2 per side of the steel sheet in terms of metallic chromium, the effect of improving corrosion resistance cannot be obtained. On the other hand, the amount of chromate film is 200mg/metal chromium per side of the steel plate.
If it exceeds m2, the effect of improving corrosion resistance commensurate with the amount cannot be obtained. In addition, cohesive failure of the chromate coating occurs when the steel sheet is subjected to bending or press forming that involves deformation. A more preferable amount of the chromate film is 10 to 150 mg per side of the steel plate in terms of metallic chromium.
/m2.

In addition to the above-mentioned chromate film, another resin film not containing a lubricant may be formed between the zinc-based alloy plating layer and the uppermost resin film. In this case, the total amount including the top layer resin coating is 5 μm, preferably 3 μm.
It is necessary that it is within a range not exceeding μm. If the total amount including the uppermost resin film exceeds 5 μm, joining by welding becomes difficult.

Formation of a resin film on at least one surface of a zinc-based plated steel sheet is carried out as follows. That is, on at least one surface of the zinc-based plating layer or on at least one 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. After applying a paint having the above-mentioned composition or immersing a galvanized steel sheet in a paint having the above-mentioned composition, the sheet is squeezed by a roll or by blowing air to form a coating of a predetermined amount. Next, this is heated for 1 minute using a hot air stove or induction heating device.
By heating to a temperature of 50 to 250°C, the solvent is evaporated and the resin is crosslinked and cured. In this way, a resin coating is formed on at least one surface of the zinc-based plated steel sheet.

[0031] The thickness of the resin coating formed on at least one surface of the galvanized steel sheet is 0.
．． It should be within 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 sheet, damage to the zinc-based plating layer during molding cannot be prevented. On the other hand, if the thickness of the resin film exceeds 3.0 μm per side of the steel plate, weldability will deteriorate, and if the molding conditions are particularly severe, the amount of resin film peeled off will increase, causing mold damage. Problems such as adhesion to the surface and burn-in may occur.

[0032] Next, the present invention will be explained using examples and in comparison with comparative examples.

[Example 1] The following materials were prepared as paint materials for manufacturing 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-curing polyester resin ■ Isocyanate-curing polyurethane resin ■ Urea resin-curing epoxy resin ■ Water-based acrylic emulsion resin

[0034]
(2) Lubricant A Melting point: 105°C, melt viscosity at 150°C: 20
0 cps, molecular weight: 1,500 polyethylene fine powder B Melting point: 115°C, melt viscosity at 150°C: 70
0 cps, molecular weight: 3,000 polyethylene fine powder C Melting point: 130°C, melt viscosity at 150°C: 3,
000 cps, molecular weight: 5,000 polyethylene fine powder D Melting point: 133°C, melt viscosity at 150°C: 30
,000cps, molecular weight: 10,000 Polypropylene fine powder E Melting point: 160℃ Paraffin wax G Melting point: 70℃ Polytetrafluoroethylene powder H Melting point: 325℃ Fine graphite powder I Molybdenum disulfide fine powder

[0035] Plate thickness 0.8 mm, plating amount 20 g/m2
Both sides of the galvanized layer of the electrogalvanized steel sheet are degreased with alkali, and then a chromate treatment solution is applied on the galvanized layer by roll coating, heated and dried, and the galvanized layer is coated on top of the galvanized layer. 5 in terms of metallic chromium
A chromate coating was applied in an amount of 0 mg/m2.

A coating consisting of the above-mentioned resins (1) to (2) and lubricant A or B in an amount of 10 parts by weight per 100 parts by weight of the solid content of the resin was applied to both sides of the electrogalvanized steel sheet. It was applied onto the chromate film by a roll coating method. Next, this was heated to a temperature of 200° C. using an induction heating device to form a resin film with a thickness of about 1.5 μm on the chromate film. In this way, zinc-based plated steel sheet within the scope of the present invention (hereinafter referred to as "invention steel sheet") No. 1 shown in Table 1 was prepared.
1 to 4 were prepared. In addition, a resin film was formed directly on the galvanized layer by the method described above without forming a chromate film, and steel sheet No. 1 of the present invention shown in Table 1 was prepared.
5 and 6 were prepared.

For comparison, a resin or a lubricant outside the scope of the present invention was used in the same manner as above using a paint containing 10 parts by weight of the lubricant per 100 parts by weight of solid content of the resin. A resin coating with a thickness of about 1.5 μm is formed on the chromate coating or directly on the galvanized layer, and a zinc-plated steel sheet (hereinafter referred to as "comparative steel sheet") No. ．． 1 to 10, and 2 g/m of press oil on the chromate film without resin coating.
2 Coated comparative steel plate No. No. 11 was prepared as shown in Table 1.

Regarding each of the above-mentioned steel sheets of the present invention and steel sheets for comparison, the lubricity, press formability, and scratch/
The blackening property was evaluated by the performance test described below. The evaluation results are also shown in Table 1.

(1) A flat test piece was pulled out using a lubricity tensile tester at a surface pressure of 50 kg/cm2 and a pulling speed of 100 mm/min, and the coefficient of dynamic friction at that time was examined to determine the lubricity. evaluated. The evaluation criteria are as follows. ○: Dynamic friction coefficient less than 0.10, ◇: Dynamic friction coefficient 0.10 to 0.30, ×: Dynamic friction coefficient 0.30 or more.

(2) Press formability A disk-shaped test piece was pressed using a punch and a die under the following conditions: blank diameter: 120 mm, punch diameter: 50 mm, die diameter: 51.91 mm, wrinkle suppressing force: 1 ton. Press formability was evaluated by examining the rate of change in the outer diameter of the test piece when it was molded into a cup shape by passing through it. The evaluation criteria are as follows. ○: 10% or more, ◇: 5-10%,
×: Less than 5%.

(3) Scratches and blackening A disc-shaped test piece was punched using a punch under the following conditions: blank diameter: 100 mm, punch diameter: 50 mm, die diameter: 51.91 mm, wrinkle suppressing force: 1 ton. The appearance of the test piece, which was molded into a cup shape by passing through a die, was visually inspected to evaluate scratching and blackening properties. The evaluation criteria are as follows. ○: Good with almost no change, ◇: Slight scratches and blackening occurred, ×: Severe scratches and blackening.

[0042]

As is clear from Table 1, comparative steel plate No. 1 was coated with a water-based resin paint. Sample No. 1 had poor press moldability and scratch/blackening properties. Comparative steel plate No. 1 used a paint containing fine polyethylene powder whose melting point exceeds the range of the present invention as a lubricant. Samples Nos. 2 and 3 had poor lubricity and press moldability. Comparative steel plate No. 1 using a paint containing a lubricant other than the lubricant of the present invention. Steel sheets No. 4 to No. 8 had poor lubricity, press formability, and scratch/blackening resistance, and in particular, comparative steel sheet No.
The lubricity and press formability of Nos. 7 and 8 were compared with conventional comparative steel sheet No. 7 and No. 8 coated with lubricating oil. It was worse than 9. Comparative steel plate No. 1 using paint that does not contain lubricant. 9 and 10 have poor lubricity and press formability, and are prone to scratches and
In the blackening test, the test piece could not be molded because it was broken, so the test could not be conducted. On the other hand, steel plate No. of the present invention. Nos. 1 to 6 were excellent in all of the lubricity, press moldability, and scratch blackening property.

[0044]

[Example 2] A steel plate having a chromate film similar to that in Example 1 formed on both sides thereof was coated with the above-mentioned resin (1), that is, a melamine-curing polyester resin, on top of the chromate film.
Based on 100 parts by weight of the solid content, a coating material containing lubricant A in a proportion within the range of this invention is applied in the same manner as in Example 1, and then heated to form a resin film on the chromate film. did. In this way, the steel sheet No. of the present invention shown in Table 2. 7 to 10 were prepared.

For comparison, comparative steel plate No. 1 was prepared using a paint containing no lubricant. 12. Comparative steel plate No. 1 using a paint with a lubricant A content outside the range of the present invention.
13, 14, Comparative steel plate No. 1 whose coating thickness is outside the range of the present invention. No. 15, No. 16, and comparative steel sheet No. 1, in which the amount of chromate film is outside the range of the present invention. 17,
It was prepared as shown in Table 2.

Regarding each of the above-mentioned steel sheets of the present invention and steel sheets for comparison, lubricity, press formability, scratching/blackening resistance,
And the corrosion resistance was evaluated by the performance test described above. The corrosion resistance was evaluated by measuring the time required for white rust to occur by a salt spray test based on JIS Z 2371. The evaluation results are shown in Table 3.

[0047]

[0048]

As is clear from Tables 2 and 3,
Comparative steel plate No. 1 using paint that does not contain lubricant.
No. 12, and comparative steel sheet No. 1 using a paint with a lubricant content that is outside the range of the present invention. No. 13 had poor lubricity, press formability, and scratch/blackening properties. Comparative steel plate No. 1 using a paint with a lubricant content exceeding the range of the present invention. No. 14 had poor scratch/blackening resistance and poor corrosion resistance due to an increase in the amount of peeling due to a decrease in the cohesive force of the coating.

[0050] Comparative steel plate No. 1 whose resin coating amount was outside the range of the present invention. Sample No. 15 had poor lubricity, press moldability, scratch/blackening resistance, and workability. Comparative steel plate No. 1 has a large amount of resin coating outside the range of the present invention. 16
had poor press formability and scratch/blackening properties. Comparative steel plate No. 1 has a large amount of chromate film outside the range of the present invention. No. 17 had poor press moldability and scratch/blackening properties.

On the other hand, steel sheet No. of the present invention. 7-1
No. 0 was excellent in all of lubricity, press formability, scratch/blackening resistance, and corrosion resistance.

[0052]

[Effects of the Invention] As described above, according to the galvanized steel sheet of the present invention, even without applying lubricating oil etc. to the surface,
It exhibits excellent lubricity and moldability, and even when molded under harsh conditions that generate frictional heat, the coating does not damage or blacken, and it also has good corrosion resistance.It is an industrially useful product. The effect is demonstrated.

Claims (4)

[Claims] Claim 1: By applying a paint made of a resin containing a lubricant onto at least one zinc-based plating layer of a galvanized steel sheet and a zinc-based alloy-plated steel sheet, and then heating and curing the paint, In the galvanized steel sheet in which a resin film is formed on the surface of at least one zinc-based plating layer of the steel sheet, the paint for the resin film comprises a solvent-based thermosetting resin and a melting point of 120 °C or less. The polyethylene fine powder has an average molecular weight of 5,000 or less, and the content of the polyethylene fine powder is 100% of the solid content of the solvent-based thermosetting resin.
The amount is within the range of 5 to 30 parts by weight, and the thickness of the resin coating made of such a paint is within the range of 0.3 to 3.0 μm per side of the steel plate. A zinc-plated steel sheet with excellent lubricity and formability. 2. A chromate film is formed on the zinc-based plating layer in an amount in the range of 5 to 200 mg/m2 per side of the steel sheet in terms of metallic chromium, and the resin film is formed on the chromate film. The galvanized steel sheet according to claim 1, wherein the galvanized steel sheet is formed. 3. 140 of the polyethylene fine powder
Melt viscosity at ~150°C is 100 ~1,000
The galvanized steel sheet according to claim 1 or 2, which is within the range of cps. 4. The solvent-based thermosetting resin is an ester resin such as a bisphenol epoxy resin, a multifunctional epoxy resin, an oil-free alkyd resin, an acrylic resin, a urethane resin (polyol), or one of the above-mentioned resins. The zinc-based plating according to claim 1 or 2, comprising a heat-curable composition that combines at least one of the modified derivatives and at least one of various amine compounds, amino resins, and isocyanate compounds. steel plate.