JP2009107311A - Zinc-aluminum alloy plated steel sheet with which lubricating plastic was coated - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zinc-aluminum alloy plated steel sheet superior in adhesion with upper coating paint and corrosion resistance, and further excellent in molding processability and black denaturation resistance. <P>SOLUTION: As the upper layer of a plated layer, a lubricating resin layer having mean thickness of 0.5 μm to 4 μm is incorporated on at least one surface of the zinc-aluminum alloy plated steel sheet. The lubricating resin layer includes 50 mass% to 95 mass% of a polyurethane resin of a principal ingredient, includes 5 mass% to 50 mass% of resin of one type or two types or more selected from acrylic-styrene resin, phenol resin and epoxy resin by the total amount having less than 10 of an acid value, and further preferably includes 0.5% to 10% in terms of Zr by mass% to the total amount of lubricating resin layer. Incidentally, the glass transition point of the polyurethane resin is set preferably to 30°C to 60°C, and the glass transition point of the acrylic-styrene resin is set preferably to 30°C to 60°C. The hydroxyl value of the phenol resin is set preferably to 10 to 50, and the epoxy equivalent of the epoxy resin is set preferably to 200 to 400. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a zinc-aluminum alloy-plated steel sheet, and particularly contains no trivalent or hexavalent chromium, has excellent adhesion to a top coat, and is excellent in roll formability, blackening resistance, and corrosion resistance. The present invention relates to a zinc-aluminum alloy-plated steel sheet coated with a lubricating resin of a mold.

  Zinc-aluminum alloy-plated steel sheet is particularly excellent in corrosion resistance, so it can be used in a wide range of fields as building materials such as roofing materials and wall materials, civil engineering materials such as soundproof walls, and automobiles, home appliances and industrial equipment. It is being done. However, since the zinc-aluminum alloy plated steel sheet contains aluminum in the plated layer, the plated layer hardness is higher than that of the hot dip galvanized steel sheet. Therefore, the zinc-aluminum alloy-plated steel sheet has poor lubricity between the plated steel sheet and the forming roll or the press die during processing such as roll forming or press forming, and the plating layer may be destroyed. When the plating layer is destroyed, the resulting plating powder adheres to the molding rolls and press dies, and as a result, flaws are formed on the molded product, and the appearance of the product is impaired. Durability will be significantly reduced.

  Conventionally, when forming a zinc-aluminum alloy plated steel sheet, lubricating oil is applied to the surface of the plated steel sheet (plating layer surface) or the surface of the forming roll or press die that contacts the plating layer. It was applied to improve the lubricity between the plated steel sheet and the forming roll or press die. However, if the lubricating oil remains on the surface of the plated steel sheet, for example, when used as a roofing material, there is a risk that the operator may slip his feet during construction, and when the top coat is applied after the forming process. However, it is necessary to completely remove the adhering lubricating oil, which causes problems such as complicated processes. For this reason, recently, instead of applying lubricating oil to the surface of the plated steel sheet, it has become mainstream to perform a lubrication treatment for forming a resin film rich in lubricity on the surface of the plated steel sheet.

  In addition, in zinc-aluminum alloy plated steel sheets, when the plated steel sheets are stored in the air or in a humid environment, rust is generated, the metallic luster is lost and the appearance of grayish black is exhibited, and the commercial value is significantly reduced. There is a problem. Therefore, in order to improve the corrosion resistance, the chromate treatment is often applied to the surface of the zinc-aluminum alloy plated steel sheet. However, when the chromate-treated zinc-aluminum alloy-plated steel sheet is lubricated with a water-soluble lubricating oil during the forming process, there is a problem that chromate elutes and causes environmental pollution. In particular, hexavalent chromium is a harmful element, and there are concerns about soil contamination and adverse effects on the human body, and there is an increasing demand for surface-treated steel sheets that do not contain trivalent chromium as well as hexavalent chromium. For this reason, recently, there is a demand for a non-chromium zinc-aluminum alloy plated steel sheet having lubricity and excellent corrosion resistance without subjecting the surface of the plated steel sheet to chromate treatment.

In response to such a demand, a lubricating coating treatment for a plated steel sheet has been proposed for the purpose of imparting lubricity during forming and suppressing rusting.
For example, Patent Document 1 discloses that acrylic copolymer fine particles 10 to 99% by weight, urethane resin fine particles 0 to 50% by weight, olefin copolymer fine particles 0 to 40% by weight, colloidal silica fine particles 1 to 40% by weight. A surface treatment method for a zinc-based plated steel sheet is described in which a zinc-based plated steel sheet is treated with an aqueous solution containing the essential component and dried without being washed with water to form a film. In the method described in Patent Document 1, fine particles of the wax component may be contained in the aqueous solution in order to prevent wrinkling of the film when used in applications that undergo severe processing. According to the method described in Patent Document 1, a zinc-based plated steel sheet having the same corrosion resistance and paint adhesion as a chromate-treated steel sheet can be produced without containing hexavalent chromium and without discharging it.

  Patent Document 2 contains a water-based resin as a main component, and contains a thiocarbonyl group-containing compound, organic phosphoric acid and / or a compound thereof, further inorganic phosphoric acid and / or a compound thereof, or further water-dispersible silica. A highly corrosion-resistant aluminum-based plated steel sheet formed by applying a composition liquid to form a resin film is described. In addition, in the aluminum-plated steel plate described in patent document 2, when it receives severe processing, it is said that a lubricant may be contained in the composition liquid. The aluminum-based plated steel sheet described in Patent Document 2 is a non-chromium type, and has better corrosion resistance than a conventional chromate-treated steel sheet, and ensures good press workability by adding a lubricant. I can do it.

  Patent Document 3 discloses that a plating surface layer is mainly composed of an aqueous resin and water, a thiocarbonyl group-containing compound as an essential component, and one or two of phosphate ion, vanadate compound and water-dispersible silica. A galvanized steel material having an organic resin coating layer formed by applying a coating containing at least seeds is described. The galvanized steel material described in Patent Document 3 is a non-chromium type, and exhibits rust prevention superior to conventional chromate-containing aqueous resin-based rust prevention plating materials.

  Patent Document 4 includes, in the upper layer of the metal material, a phosphate compound and a solid lubricant, or a film containing fine silica, or an organic resin, a thiocarbonyl group-containing compound and a solid lubricant, Or a film containing at least one of phosphoric acid compound and fine silica, or an organic resin, vanadate compound, solid lubricant, or further containing at least one of thiocarbonyl group-containing compound, phosphoric acid compound and fine silica Non-chromium type surface-treated metal materials having a coating containing one or more are described. These coatings may contain a silane coupling agent to improve adhesion. The non-chromium type surface-treated metal material described in Patent Document 4 does not use press oil, and does not contain hexavalent chromium, and is a surface-treated metal material having corrosion resistance and galling resistance.

Further, Patent Document 5 discloses a non-chromium formed by forming a lubricant film on the surface of a zinc-based plated steel sheet, in which a urethane elastomer is a main component and an aluminum phosphomolybdate rust inhibitor, a silane coupling agent, and a lubricant are blended. A type lubricating coating-treated galvanized steel sheet is described. The zinc-based plated steel sheet described in Patent Document 5 can form a lubricating coating without using harmful chromium compounds, is excellent in press workability and roll formability, and has a surface appearance after processing, corrosion resistance, blackening resistance, The galvanized steel sheet is also excellent in top coatability.
JP 2000-218230 A JP 2000-297384 A JP 2000-234176 A JP 2000-248384 A JP 2000-225178 A

  According to the techniques described in Patent Documents 1 to 5 described above, it can be said that the lubricity and blackening resistance at the time of roll forming and press forming of the zinc-aluminum alloy plated steel sheet have been improved. However, even with the techniques described in Patent Documents 1 to 5, the level of adhesion and corrosion resistance with the top coat is still not satisfactory, and further improvements have been desired. In addition, there has been a problem of peeling of the top coating resulting from the composition of the treating agent used when forming the lubricating coating.

  The present invention solves the problems of the prior art, and is excellent in adhesion and corrosion resistance with a top coating, and also excellent in lubricity and blackening resistance during molding, and is coated with a non-chromium type lubricating resin. An object is to provide an alloy-plated steel sheet.

  In order to achieve the above-mentioned object, the present inventors diligently studied the influence of the type of lubricating coating (lubricating resin layer) formed on the surface of the plated steel sheet on the adhesion to the top coat and the corrosion resistance. As a result, one or two or more kinds of resins selected from a low acid value acrylic-styrene resin, a phenol resin and an epoxy resin were mixed with the polyurethane resin as a main component. It has been found that by forming a resin coating (lubricating resin layer), the adhesiveness with the top coating can be greatly improved, and at the same time, a zinc-aluminum alloy plated steel sheet having excellent forming processability can be obtained. It has also been found that the corrosion resistance can be improved by blending a relatively small amount of a zirconium compound into the resin coating (lubricating resin layer).

The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) A zinc-aluminum alloy-plated steel sheet having a lubricating resin layer with an average thickness of 0.5 to 4 μm as an upper layer of a plating layer on at least one surface, wherein the lubricating resin layer is a polyurethane resin as a main component. Lubricating resin containing a total of 5 to 50% by mass of one or more resins selected from acrylic-styrene resins, phenolic resins and epoxy resins having an acid value of less than 10 and containing 50 to 95% by mass A zinc-aluminum alloy plated steel sheet, wherein the lubricating resin layer further contains a zirconium compound.

(2) The zinc-aluminum alloy plated steel sheet according to (1), wherein the content of the zirconium compound is 0.5% to 10% in terms of Zr in terms of mass% with respect to the total amount of the lubricating resin layer.
(3) The zinc-aluminum alloy plated steel sheet according to (1) or (2), wherein the polyurethane resin has a glass transition point of 30 to 60 ° C.

(4) The zinc-aluminum alloy plated steel sheet according to any one of (1) to (3), wherein the acrylic-styrene resin has a glass transition point of 30 to 60 ° C.
(5) The zinc-aluminum alloy plated steel sheet according to any one of (1) to (4), wherein the phenol resin has a hydroxyl value of 10 to 50.
(6) The zinc-aluminum alloy plated steel sheet according to any one of (1) to (5), wherein an epoxy equivalent of the epoxy resin is 200 to 400.

  According to the present invention, a zinc-aluminum alloy plating having a lubricating resin layer, which does not contain a chromium compound, is excellent in adhesion with a top coating material, and is excellent in moldability, and further excellent in blackening resistance and corrosion resistance. Steel plates can be manufactured, and it has a remarkable industrial effect. In addition, according to the present invention, it becomes possible to form a product having a complicated shape without containing a chromium compound, and a product having high design characteristics utilizing the unique appearance of a zinc-aluminum alloy-plated steel sheet. It can be applied to wearing building materials, home appliances, kitchen equipment, etc., and has an effect of expanding the application field.

  The zinc-aluminum alloy plated steel sheet of the present invention has a lubricating resin layer on at least one surface as an upper layer of the plating layer. In addition, as a plating layer formed in the zinc-aluminum alloy plating steel plate of this invention, 5 mass% Al-Zn type | system | group based on zinc, 8 mass% Al-Zn type, 15 mass% Al-Zn type, etc. Al-Zn alloy system, Al-Mg-Zn alloy system such as 6 mass% Al-3 mass% Mg-Zn system, 11 mass% Al-3 mass% Mg-Zn system, and Al. Examples of the plating layer include an Al-Zn alloy such as 55% by mass Al-Zn and 75% by mass Al-Zn. Needless to say, the present invention is not limited to these plating layers. Further, the zinc-aluminum alloy plating layer may contain alloy elements such as Mg, Mn, Si, Ti, Ni, Co, Mo, Pb, Sn, Cr, La, Ce, Y, and Nb.

  In the present invention, the lubricating resin layer formed as the upper layer of the plating layer has an average thickness of 0.5 to 4 μm. When the thickness of the lubricating resin layer is less than 0.5 μm, it is difficult to coat with a uniform film thickness due to the unevenness of the plating layer surface, and lubricity and corrosion resistance may be reduced at a thin portion. On the other hand, if the thickness exceeds 4 μm, weldability and solderability may deteriorate. For this reason, the thickness of the lubricating resin layer was limited to 0.5 to 4 μm on average.

  The lubricating resin layer in the present invention formed as an upper layer of the plating layer has a polyurethane resin as a main component. The “main component” as used herein refers to a case where the mass% is 50% or more with respect to the entire lubricating resin layer. The upper limit of the polyurethane-based resin as the main component is 95%. By using a polyurethane-based resin as a main component, the adhesion to the top coat is improved. The polyurethane resin exhibits the effect of enhancing the adhesion between the top coating and the lubricating resin layer.

The term “polyurethane resin” as used herein means a polymer compound obtained by repeating urethane bonds between a polyisocyanate and a polyalcohol (hereinafter referred to as polyol), and the urethane elastomer of the crosslinked structure is submerged in water. It is a dispersed water-based urethane resin.
As polyisocyanate,
(1) aromatic polyisocyanates such as p-phenylene diisocyanate, 2,4-toluylene diisocyanate, 4,4-diphenylmethane diisocyanate, triisocyanate, xylylene diisocyanate, naphthalene 1,5-diisocyanate, polymethylene phenyl isocyanate;
(2) Non-yellowing polyisocyanates such as hexamethylene diisocyanate, lysine diisocyanate, xylylene diisocyanate, hydrogenated toluylene diisocyanate, hydrogenated methylene diisocyanate, dicyclohexyl dimethylmethane, p, p'-diisocyanate, diethyl fumarate diisocyanate;
In particular, non-yellowing polyisocyanate is preferable from the viewpoint of weather resistance.

As a polyol,
(1) Diols such as ethylene glycol, propylene glycol, butylene glycol, hexamethylene glycol;
(2) Single polyol type such as glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol;
(3) A dicarboxylic acid such as adipic acid, sebacic acid, maleic acid or dimer acid bonded with a polyhydric alcohol such as ethylene glycol, propylene glycol, butylene glycol or trimethylolpropane to form a hydroxyl group;
(4) Polyester type such as polymerized lactone glycol ester or castor oil;
(5) A polyether type obtained by ring-opening polymerization of an alkylene oxide such as ethylene oxide, propylene oxide or tetrahydrofuran, or added to a polyhydric alcohol such as glycerin or trimethylolpropane;
(6) Composite type of the above polyester type and polyether type;
The polyester type is preferable from the viewpoints of adhesion to a zinc-aluminum alloy plated steel sheet and long-term weather resistance.

  In the present invention, the polyurethane resin constituting the lubricating resin layer preferably has a glass transition point in the range of 30 to 60 ° C. When the glass transition point of the polyurethane-based resin is less than 30 ° C., the lubricating resin layer is crushed during molding and wrinkles are generated on the plated layer surface, or when the coated steel plates are laminated, blocking may occur. On the other hand, if the glass transition point of the polyurethane resin is higher than 60 ° C., damage to the plating layer surface is suppressed, but the lubricating resin layer cannot follow the deformation and elongation of the steel plate during forming, and the lubricating resin layer Fine cracks and peeling may occur. Therefore, the corrosion resistance of the zinc-aluminum alloy plated steel sheet is reduced due to exposure and damage of the plating layer. For this reason, in the present invention, the polyurethane resin constituting the lubricating resin layer preferably has a glass transition point in the range of 30 to 60 ° C.

If the glass transition point of the polyurethane resin constituting the lubricating resin layer is in the range of 30 to 60 ° C., the formability of the zinc-aluminum alloy plated steel sheet having the lubricating resin layer can be significantly improved.
Generally, when the lubricating resin layer is subjected to wear or friction by molding, the temperature of the lubricating resin layer rises. In particular, the higher the pulling speed of the steel sheet during forming, the greater the temperature rise of the lubricating resin layer. The zinc-aluminum alloy-plated steel sheet of the present invention is mainly applied to applications where the shape of the forming process such as roofing material is relatively gentle, so that the steel sheet drawing speed at the time of forming process is relatively slow, so that the temperature of the lubricating resin layer increases. Is small, and even if the change in temperature is taken into consideration, it is generally in the range of about 25 to 45 ° C. In the present invention, the glass transition point of the lubricating resin layer (the temperature at which the resin transitions to a rubbery state) is about 5 to 15 ° C. higher than the lubricating resin layer temperature at the time of molding, that is, within the range of 30 to 60 ° C. It is desirable to set as follows. Thereby, the lubricating resin layer slides most during the forming process, and the lubricating resin layer is not damaged by wear or friction, and the forming processability of the zinc-aluminum alloy plated steel sheet is remarkably improved.

  The lubricating resin layer in the present invention is one or two or more kinds selected from acrylic-styrene resins, phenol resins and epoxy resins having an acid value of less than 10 in addition to the above-described polyurethane resin as a main component. The resin is contained in a total amount of 5 to 50% by mass. When the total amount of the above-described resins blended in the polyurethane-based resin as the main component is less than 5% by mass, the alkali resistance is lowered. On the other hand, if it exceeds 50% by mass, the formed resin layer has insufficient corrosion resistance and adhesion to the top coating. For this reason, in the lubricating resin layer, the total content of one or more resins selected from acrylic-styrene resins, phenol resins and epoxy resins having an acid value of less than 10 is 5 to 50% by mass. Limited to.

The term “acryl-styrene resin” used herein refers to a copolymer resin containing an acrylic monomer and a styrene monomer in the molecule. As an acrylic monomer,
(A) butyl acrylate, ethyl acrylate, methyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, methacrylonitrile, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, carbitol acrylate, etc. Monofunctional acrylic monomer;
(B) Acrylic acid ester, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, pentaerythritol Bifunctional acrylic esters such as diacrylate;
(C) trifunctional acrylic acid ester such as trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythrol triacrylate, dipentaerythrole hexaacrylate, tetramethylolmethane tetraacrylate;
Etc. can be exemplified. On the other hand, examples of the styrene monomer include α-methylstyrene, styrene, p-methoxystyrene, o-chlorostyrene, and p-chlorostyrene.

  Such an acrylic-styrene resin may be either a thermoplastic resin or a thermosetting resin. The acrylic-styrene resin used for forming the resin layer is a resin having an acid value of less than 10 in order to develop compatibility with the polyurethane resin and high moldability. If the acid value of the acrylic-styrene resin is 10 or more, the long-term stability of the acrylic-styrene resin may be reduced. In addition, Preferably, the acid value of acrylic-styrene resin is 2 or less.

In addition, the “phenolic resin” used for forming the resin layer is one having a phenolic hydroxyl group such as phenol, cresol, xylenol, p-alkylphenol, p-phenylphenol, chlorophenol, bisphenol A, phenolsulfonic acid, resorcin. , A polymer obtained by adding and condensing aldehydes such as formalin and furfural.
Examples of the phenol resin include resole-type alcohol-soluble phenol resin, oil-soluble phenol resin, rosin-type phenol resin, and 100% phenol resin. Among these, a resol-type alcohol-soluble phenol resin is preferable from the viewpoint of compatibility.

The phenolic resin preferably has a hydroxyl value in the range of 10-50. When the hydroxyl value is less than 10, the compatibility with the polyurethane-based resin decreases, and when it exceeds 50, the coating becomes hard and brittle, and the workability decreases.
The “epoxy resin” used for forming the resin layer is preferably a resin having an epoxy equivalent in the range of 200 to 400 from the viewpoint of compatibility with the polyurethane resin. When the epoxy equivalent is less than 200, the coating becomes soft and wrinkles are likely to occur. On the other hand, if it exceeds 400, it becomes too hard and the workability deteriorates. As an epoxy resin,
Glycidyl type such as bisphenol, novolac, alkylphenol, polyglycol, ester, N-glycidylamine;
Non-glycidyl type such as cycloaliphatic epoxy side, epoxidized butadiene, epoxidized glyceride, reactive low viscosity epoxy side;
Etc. can be exemplified. Of these, bisphenol-based epoxy resins are preferred from the viewpoint of corrosion resistance.

The above-mentioned polyurethane resin and one or more of the above-mentioned resins selected from acrylic-styrene resins, phenol resins and epoxy resins having an acid value of less than 10 are the lubricating resin layer obtained. It is preferable to blend so that the glass transition point of the mixture becomes 30 to 60 ° C.
In the present invention, the lubricating resin layer contains a zirconium compound. In addition to the resin composition described above, by containing a zirconium compound, the lubricating resin layer has excellent adhesion to the top coating, and further has excellent molding processability, excellent blackening resistance, and excellent corrosion resistance. In addition, a zinc-aluminum alloy plated steel sheet can also be provided. In order to obtain such an effect, the zirconium compound is preferably contained in the lubricating resin layer in an amount of 0.5% or more in terms of Zr, based on the total amount of the lubricating resin layer. On the other hand, when the content of the zirconium compound exceeds 10% by mass, the resin layer forming coating for forming the lubricating resin layer becomes unstable and lacks long-term stability, and zirconium is eluted when the plated steel sheet is used for a long time. There is a risk that the corrosion resistance will be reduced. For this reason, it is preferable to limit the zirconium compound content in the lubricating resin layer to a range of 0.5 to 10% in terms of Zr in terms of mass% with respect to the total amount of the lubricating resin layer. In addition, More preferably, it is 1 to 7% in terms of Zr in terms of mass% with respect to the total amount of the lubricating resin layer. In the present invention, since the lubricating resin layer has the above-described resin composition, the desired excellent moldability, excellent blackening resistance, and excellent corrosion resistance can be ensured by containing such a small amount of zirconium compound. .

In addition, as a zirconium compound to be used,
Oxides such as zirconium oxide, zircon oxide hydrate, potassium zirconate, ammonium zirconate and related substances;
Halides such as zirconium chloride, zirconium bromide, zirconium iodide, zirconium chlorate;
Oxyacid salts such as zirconium nitrate, zirconium sulfate, zirconium phosphate, zirconium silicate;
Organic acid salts such as zirconium carbonate;
Can be illustrated. Of these, water-soluble zirconium phosphate is preferable from the viewpoint of compatibility with the lubricating resin.

Below, the preferable manufacturing method of the zinc-aluminum alloy plating steel plate which has a lubricating resin layer of this invention is demonstrated.
A plated steel sheet having a zinc-aluminum alloy plating layer on the surface is prepared as a substrate. In addition, one or two or more resins selected from acrylic-styrene resins, phenol resins, and epoxy resins are blended with the polyurethane resin described above, and the mixed resin is mixed in a solvent, preferably water. An emulsified paint or an aqueous solution in which a mixed resin is dissolved in water as a water-soluble resin is prepared, and a zirconium compound is blended with the paint or the aqueous solution to obtain a paint for forming a lubricating resin layer. In addition, the resin for forming the lubricating resin layer can be blended with, for example, other resins, fillers, surfactants, antifoaming agents, wax particles and the like as long as the object of the present invention is not impaired. In addition, additive components conventionally used as additives for paints, for example, color pigments such as titanium white, iron oxide, and carbon black, extender pigments such as calcium carbonate, ultraviolet absorbers, anti-scratch agents, and antifungal agents An antioxidant, an antistatic agent, and the like can be added. Furthermore, a leveling agent, a dispersant, a repellency inhibitor, a color separation inhibitor, an anti-settling agent, and the like can be added to the lubricating resin layer forming coating as necessary as known additives.

  Such a coating for forming a lubricating resin layer is applied to at least one of the above-described substrates (zinc-aluminum alloy plated steel plate). In application, it is preferable to adjust the application amount to 0.5 to 4 μm in average thickness after dry baking. As the coating method, any conventionally known method such as dipping, spraying, brush coating, roll coater, air knife, electrostatic coating, etc. can be used.

  The applied paint is then dried and baked to form a lubricating resin layer. Any known hot-air drying device, far-infrared heating device, induction heating device, etc. can be applied to the drying and baking of the paint. In addition, it is preferable to perform drying and baking at the temperature of the range of 40-200 degreeC.

The coating material for forming the lubricating resin layer shown in Table 1 is applied to both surfaces of a zinc-aluminum alloy plated steel sheet (plating layer: 55% by mass Al—Zn alloy) so as to have a predetermined dry thickness (lubricating resin layer thickness) with a roll coater And dried and baked under the conditions of the maximum temperature reached: 90 ° C. and the treatment time: 7 seconds to obtain a zinc-aluminum alloy plated steel sheet having a lubricating resin layer with an average thickness shown in Table 1. The obtained plated steel sheet was subjected to an adhesion test with a top coating, a formability test, a blackening resistance test, and a corrosion resistance test. The test method was as follows.
(1) Adhesion test with top coat paint Samples are taken from each of the obtained plated steel sheets and coated with urethane acrylic room temperature dry paint (trade name: Retan PG-80, manufactured by Kansai Paint Co., Ltd.). Thickness: 50 μm was applied, dried at room temperature for 72 hours, and overcoated.

As a primary test, a cross cellophane tape peeling test was performed on these test pieces that had been overcoated in accordance with JIS K 5400.
In addition, as a secondary test, these test pieces that have been overcoated are further treated by immersing them in boiling water for 2 hours, and then, similar to the primary test, in accordance with the JIS K 5400 rules, A tape peel test was performed.

In the cross-cut cellophane tape peel test, a 1 mm square crosscut is applied to the top-coated surface of the specimen (range: 70 mm x 150 mm) with a cutter knife, and then the cellophane tape is crimped to the area where the crosscut is applied. After peeling off, the number of grids on which the coating film remained was measured, and the adhesion with the top coating was evaluated.
Evaluation is no abnormality (remaining number of grids: 100) ◎, remaining number of grids 90 or more ○, remaining number of grids 89-60, △, remaining number of grids Less than 60 pieces were set as x.
(2) Formability test A test piece was collected from each of the obtained plated steel sheets and roll-formed into a right-angle shape at a processing speed corresponding to 30 m / min. After roll forming, the degree of occurrence of the metal mark was observed in the portion bent at a right angle, and the forming processability was evaluated. In the evaluation, the occurrence of a metal mark was evaluated as “◯”, the occurrence of a metal mark as a portion was Δ, and the occurrence of a metal mark as an entire surface was evaluated as “X”.
(3) Blackening resistance test A test piece was collected from each of the obtained plated steel sheets and subjected to a cylindrical drawing with a diameter of 50 mm and a depth of 5 mm using a deep drawing tester to obtain a blackness resistance test specimen. These test pieces were superposed in a desiccator filled with distilled water and immersed at 20 ° C. for 7 days, the degree of discoloration on the surface of the test piece was observed, and blackening resistance was evaluated. The evaluation was ◯ when no discoloration was observed, Δ when a black spot was found in a part of the die contact portion, and x when a black spot was found on the entire surface of the die contact portion.
(4) Corrosion resistance test A test piece was collected from each of the obtained plated steel sheets and subjected to a salt spray test in accordance with the provisions of JIS Z 2371. The spray solution was 5% saline (temperature: 35 ° C.), and the spray time was 240 hours. After the test, the state of occurrence of white rust on the surface of the test piece was investigated to evaluate the corrosion resistance. The white rust expression area was 0%, the white rust expression area was 0% to 20% or less, and the white rust expression area was 20% or more.

  The obtained results are shown in Table 1.

  Each of the examples of the present invention is a zinc-aluminum alloy-plated steel sheet that is excellent in adhesion to the top coat and excellent in processability, blackening resistance, and corrosion resistance. On the other hand, in comparative examples that are outside the scope of the present invention, the adhesion to the top coating is reduced, or any of molding processability, blackening resistance, corrosion resistance, some of them, or all of them are reduced. ing.

Claims (6)

  A zinc-aluminum alloy plated steel sheet having a lubricating resin layer having an average thickness of 0.5 to 4 μm as an upper layer of the plating layer on at least one surface, wherein the lubricating resin layer comprises 50 to 95 polyurethane resin as a main component. It is a lubricating resin layer containing 5 to 50% by mass in total of one or more resins selected from acrylic-styrene resins, phenolic resins and epoxy resins having a mass% of less than 10 The zinc-aluminum alloy plated steel sheet, wherein the lubricating resin layer further contains a zirconium compound.   2. The zinc-aluminum alloy plated steel sheet according to claim 1, wherein the content of the zirconium compound is 0.5% to 10% in terms of Zr in terms of mass% with respect to the total amount of the lubricating resin layer.   3. The zinc-aluminum alloy plated steel sheet according to claim 1, wherein the polyurethane resin has a glass transition point of 30 to 60 ° C. 3.   The zinc-aluminum alloy plated steel sheet according to any one of claims 1 to 3, wherein the acrylic-styrene resin has a glass transition point of 30 to 60 ° C.   The zinc-aluminum alloy plated steel sheet according to any one of claims 1 to 4, wherein the phenol resin has a hydroxyl value of 10 to 50. The zinc-aluminum alloy plated steel sheet according to any one of claims 1 to 6, wherein an epoxy equivalent of the epoxy resin is 200 to 400.