JP7287756B2 - Painted plated steel sheet, its manufacturing method and building material - Google Patents

Description

TECHNICAL FIELD The present disclosure generally relates to a painted plated steel sheet and building materials, and more specifically, a painted plated steel sheet provided with an undercoat layer and a topcoat layer on a plating layer, and a building material including a metal member made of the painted plated steel sheet. Regarding.

BACKGROUND ART Conventionally, there has been known a coated steel sheet in which a coating layer is provided on a coating layer. For example, Patent Literature 1 discloses a coated steel sheet in which an undercoat layer and a topcoat layer are laminated on a zinc-based plating layer.

Japanese Patent Laid-Open No. 2004-34591

When producing a building material from a coated steel sheet, the coated steel sheet may be bent. When a painted plated steel sheet is subjected to bending or the like, cracks may occur in the paint layer as the plated layer cracks. In this case, the paint layer tends to crack, and the corrosion resistance of the processed portion tends to be lower than that of the flat portion. By lowering the glass transition temperature (Tg) of the paint layer, the flexibility of the paint layer can be improved and cracks can be suppressed. However, when the glass transition temperature of the coating layer is lowered, the coating layer becomes more susceptible to scratches, ie, the scratch resistance tends to decrease.

An object of the present disclosure is to provide a painted plated steel sheet with excellent workability and scratch resistance, and a building material including a metal member made of this painted plated steel sheet.

The painted plated steel sheet according to the present disclosure includes a steel sheet, a plating layer covering the steel sheet and containing aluminum and zinc, an undercoat layer covering the plating layer, a topcoat layer covering the undercoat layer, including. The undercoat layer contains a crosslinked first polyester resin and a first soft resin that is a polyester polyol, and has a glass transition temperature of 50° C. or higher. The overcoat layer comprises a crosslinked second polyester resin, a second soft resin that is a polyester polyol, and particulate wax.

A building material according to the present disclosure includes a metal member, and the metal member is made of the above-described coated steel plate.

According to the present disclosure, it is possible to provide a coated steel sheet with excellent workability and scratch resistance, and a building material including a metal member made of this coated coated steel sheet.

FIG. 1 is a schematic cross-sectional view showing a coated steel sheet according to one aspect of the present disclosure. FIG. 2 is an explanatory view showing how a coated steel sheet is leveled. 3A and 3B are schematic cross-sectional views showing examples of building materials according to one aspect of the present disclosure.

1. Outline of the Present Disclosure A painted plated steel sheet 1 according to the present embodiment, as shown in FIG. It includes a coating layer 4 and a topcoat layer 5 covering the basecoat layer 4 . The undercoat layer 4 contains a crosslinked first polyester resin and a first soft resin that is a polyester polyol, and has a glass transition temperature of 50° C. or higher. The overcoat layer 5 contains a crosslinked second polyester resin, a second soft resin that is a polyester polyol, and particulate wax.

In this embodiment, since the undercoat layer 4 contains the first soft resin and the topcoat layer 5 contains the second soft resin, the flexibility of the undercoat layer 4 and the topcoat layer 5 can be improved. Therefore, it is possible to suppress the occurrence of cracks in the undercoat layer 4 and the topcoat layer 5 when the coated steel sheet 1 is processed such as bending. Moreover, since the topcoat layer 5 contains particulate wax, the surface of the undercoat layer 4 can be made slippery, and the scratch resistance of the topcoat layer 5 can be improved. Moreover, since the glass transition temperature of the undercoat layer 4 is 50° C. or higher, the scratch resistance of the undercoat layer 4 can be improved. That is, in this embodiment, the scratch resistance of the coated steel sheet 1 can be improved by the slipperiness of the surface of the topcoat layer 4 and the glass transition temperature of the undercoat layer 4 .

A building material 100 according to the present embodiment includes a metal member 10 made of the coated steel sheet 1 described above.

When manufacturing the building material 100 using the coated steel sheet 1, the coated coated steel sheet 1 is processed such as bending. In the coated steel sheet 1 of the present embodiment, cracks are less likely to occur in the undercoat layer 4 and the topcoat layer 5 even when working such as bending is performed. Therefore, the undercoat layer 4 and the topcoat layer 5 of the metal member 10 included in the building material 100 are less likely to crack.

2. Details of Coated Steel Sheet The configuration of the coated steel sheet 1 of the present embodiment will be described in more detail below. The paint-plated steel sheet 1 includes the steel sheet 2, the plating layer 3, the undercoat layer 4, and the topcoat layer 5 as described above.

2-1. Steel plate The steel plate 2 is not particularly limited. The steel plate 2 is, for example, a low-carbon steel plate, a high-carbon steel plate, or a high-tensile steel plate.

2-2. Plating Layer The plating layer 3 covers the steel plate 2 as described above. As a method for producing the plating layer 3, for example, a hot-dip plating method can be adopted.

The plating layer 3 contains aluminum and zinc. The plated layer 3 may further contain components other than aluminum and zinc. The plating layer 3 may contain, for example, one or both of magnesium and silicon. The plating layer 3 may contain one or more components selected from the group consisting of strontium, iron, alkaline earth elements, scandium, yttrium, lanthanide elements, titanium, and boron. Examples of alkaline earth elements include beryllium, calcium, barium, and radium. Examples of lanthanide elements include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium. The plating layer 3 may contain one or more of these components. The plating layer 3 may or may not contain chromium.

The amount of aluminum contained in the plating layer 3 is preferably 25% by mass or more and 75% by mass or less, more preferably 45% by mass or more and 65% by mass or less.

When the plating layer 3 contains magnesium, the amount of magnesium contained in the plating layer 3 is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 3% by mass or less. In this case, the end face corrosion resistance of the coated steel sheet 1 can be improved. When the plating layer 3 contains magnesium, the flexibility of the plating layer 3 tends to be low, and the workability of the coated steel sheet 1 tends to be low. On the other hand, in the coated steel sheet 1 of the present embodiment, the first soft resin contained in the undercoat layer 4 and the second soft resin contained in the topcoat layer 5 make the undercoat layer 4 and the topcoat layer 5 flexible. can improve sexuality. Therefore, even if the plating layer 3 contains magnesium, the workability of the coated steel sheet 1 can be improved.

When the plating layer 3 contains silicon, the amount of silicon relative to the amount of aluminum contained in the plating layer 3 is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1.0% by mass or more5. It is 0% by mass or less.

2-3. Undercoat Layer The undercoat layer 4 covers the plating layer 3 as described above. In this embodiment, the undercoat layer 4 is in direct contact with the plating layer 3 . The undercoat layer 4 is preferably a cured undercoat paint. The primer coating contains a polyester resin (hereinafter also referred to as polyester resin (A)) and a cross-linking agent (hereinafter also referred to as cross-linking agent (B)). The primer further contains a first soft resin.

The polyester resin (A) may include polyester resins contained in known polyester resin paints. The polyester resin (A) may contain, for example, a polycondensate of polyvalent carboxylic acid and polyol. In this embodiment, the polyester resin (A) preferably contains a polyester resin having a hydroxyl group. This hydroxyl group can be used for reaction with a cross-linking agent (B) described below.

The polyester resin (A) preferably contains 10% by weight or more of a hydroxyl group-containing polyester resin (A1) having a glass transition temperature of 60° C. or higher. In this case, it is possible to prevent the glass transition temperature of the undercoat layer 4 from becoming too low. Therefore, the scratch resistance of the undercoat layer 4 can be improved. More preferably, the polyester resin (A1) contains 15% by weight or more and 30% by weight or less of a hydroxyl-containing polyester resin (A2) having a glass transition temperature of 65°C or more and 75°C or less. In this case, the glass transition temperature of the undercoat layer 4 can be particularly prevented from becoming too low, and the scratch resistance of the undercoat layer 4 can be particularly improved. Furthermore, it is easy to ensure the curability of the undercoat. The number average molecular weight of the polyester resin (A1) is preferably 10,000 or more and 30,000 or less, more preferably 17,000 or more and 25,000 or less. The hydroxyl value of the polyester resin (A1) is preferably 5 mgKOH/g or more and 15 mgKOH/g or less, more preferably 7 mgKOH/g or more and 13 mgKOH/g or less.

The polyester resin (A) can contain 90% by weight or less of a hydroxyl group-containing polyester resin (A3) having a glass transition temperature of less than 60°C. For example, the polyester resin (A) preferably contains a polyester resin (A4) having a hydroxyl group having a glass transition temperature of 40° C. or more and less than 60° C., and a hydroxyl group having a glass transition temperature of 45° C. or more and 55° C. or less. It is preferable to contain the polyester resin (A5) having. In this case, it is possible to prevent the glass transition temperature of the undercoat from becoming too high. Therefore, the flexibility of the undercoat layer 4 and the curability of the undercoat can be ensured. The number average molecular weight of the polyester resin (A3) is preferably 1500 or more and 6000 or less, more preferably 2000 or more and 5000 or less. The hydroxyl value of the polyester resin (A3) is preferably 20 mgKOH/g or more and 60 mgKOH/g or less, more preferably 30 mgKOH/g or more and 50 mgKOH/g or less.

The crosslinking agent (B) is not particularly limited as long as it can be crosslinked with hydroxyl groups derived from the polyester resin (A). Examples of the cross-linking agent (B) include isocyanate compounds such as blocked isocyanate and melamine resins such as methylated melamine. The cross-linking agent may contain only the isocyanate compound, may contain only the melamine resin, or may contain the isocyanate compound and the melamine resin.

In this embodiment, the cross-linking agent preferably contains a blocked isocyanate. In this case, a urethane bond (--NHCOO--) can be formed by the reaction between the hydroxyl group (--OH) derived from the polyester resin (A) and the isocyanate group (--NCO) derived from the blocked isocyanate. Thereby, the scratch resistance of the undercoat layer 4 can be improved.

A blocked isocyanate can be obtained, for example, by reacting an isocyanate group of a polyisocyanate with a blocking agent. The polyisocyanate and blocking agent are reacted by known methods.

The polyisocyanate can contain, for example, one or more selected from the group consisting of tolylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, and tolidine diisocyanate. The polyisocyanate may be a monomer, or a derivative such as a prepolymer, an adduct (an adduct of trimethylolpropane or the like), an isocyanurate, or a biuret.

The blocking agent can contain, for example, one or more selected from the group consisting of active methylene-based blocking agents, amine-based blocking agents, oxime-based blocking agents, and caprolactam-based blocking agents.

A commercial product may be used as the blocked isocyanate. Examples of commercially available blocked isocyanates may include Sumidule BL3175 and Desmodur BL4265 manufactured by Sumika Bayer Urethane Co., Ltd., and VESTANAT B1358A manufactured by Evonik.

The undercoat preferably contains blocked isocyanate so that the content of isocyanate groups (--NCO) is 5% by weight or more and 15% by weight or less with respect to the total amount of the undercoat. In this case, the hydroxyl group derived from each component contained in the undercoat can be effectively reacted with the isocyanate group derived from the blocked isocyanate, and the scratch resistance of the undercoat layer 4 can be improved.

The primer contains a first soft resin. That is, the undercoat layer 4 contains the first soft resin. This first soft resin is a polyester polyol. The first soft resin can impart flexibility to the undercoat layer 4 and improve workability of the coated steel sheet 1 . In addition, the scratch resistance of the undercoat layer 4 is also improved. A possible reason for this is that when the cross-linking agent (B) contains a blocked isocyanate, the hydroxyl group derived from the polyester polyol reacts with the isocyanate group of the above-described blocked cyanate.

Polyester polyols are obtained, for example, by direct esterification reaction and/or transesterification reaction between a low-molecular-weight polyol and a polyvalent carboxylic acid or an ester-forming derivative thereof. Polyester polyols can be produced, for example, by condensation polymerization of lactones or hydroxycarboxylic acid compounds.

Low molecular weight polyols are, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, neopentyl glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1 ,4-butylene glycol, hexamethylene glycol, bisphenol A, hydrogenated bisphenol A, trimethylolpropane, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl -2-ethyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-2,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 3- methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 3,5 -aliphatic diols such as heptanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol; trimethylolethane, trimethylolpropane, hexitol , pentitols, glycerin, diglycerin, polyglycerin, pentaerythritol, dipentaerythritol, and one or more components selected from the group consisting of trihydric or higher aliphatic or alicyclic alcohols such as tetramethylolpropane can be contained.

Polycarboxylic acids include, for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2-methylsuccinic acid, 2-methyladipic acid, Aliphatic dicarboxylic acids such as 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecanedioic acid, dimer acid, and hydrogenated dimer acid Acids; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid and naphthalene dicarboxylic acid; tricarboxylic acids such as trimellitic acid, trimesic acid and castor oil fatty acid trimers; and one or more components selected from the group consisting of tetracarboxylic acids or higher polycarboxylic acids such as pyromellitic acid.

Lactones can contain, for example, one or more components selected from the group consisting of γ-caprolactone, δ-caprolactone, ε-caprolactone, γ-valerolactone, and δ-valerolactone.

The number average molecular weight of the first soft resin is preferably 500 or more and 3000 or less, more preferably 1000 or more and 2000 or less. The hydroxyl value of the first soft resin is preferably 30 mgKOH/g or more and 200 mgKOH/g or less, more preferably 50 mgKOH/g or more and 110 mgKOH/g or less.

The ratio of the first soft resin contained in the undercoat is preferably 10% by weight or more and 30% by weight or less, more preferably 10% by weight or more and 18% by weight or less, relative to the total amount of the polyester resin (A). preferable. In this case, the flexibility of the undercoat layer 4 can be effectively improved, and the workability of the coated steel sheet 1 can be effectively improved.

The undercoat can contain antirust pigments, coloring pigments, solvents, additives, etc., as required. Examples of rust preventive pigments include phosphoric acid-based rust preventive pigments such as zinc phosphate, iron phosphate, aluminum phosphate, and magnesium phosphate; Rust preventive pigments, vanadium-based rust preventive pigments such as vanadium oxide, fine-grained silica such as water-dispersed silica, calcium ion-exchanged silica, and fumed silica, chromate-based rust preventives such as strontium chromate, zinc chromate, calcium chromate, and barium chromate Contains pigments. The undercoat paint can contain one or more of these antirust pigments.

Examples of color pigments include inorganic pigments such as titanium oxide, carbon black, iron oxide, chromates and calcium carbonate, and organic pigments such as cyanine green and cyanine blue.

Examples of solvents include hydrocarbon solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; ethyl solvents such as cellosolves; and ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone and cyclohexanone. be The primer can contain one or more of these solvents.

Examples of additives include defoamers, pigment dispersants, anti-sagging agents, leveling agents, silane coupling agents, extenders. Examples of extender pigments include silica, alumina, talc, calcium carbonate, titania. The primer can contain one or more of these additives.

The undercoat can be prepared by mixing the above polyester resin (A), a cross-linking agent, a first soft resin, and, if necessary, a pigment, a solvent, and additives.

The undercoat layer 4 can be produced, for example, by applying an undercoat paint onto the plating layer 3 and then heating and curing the paint. As a method for applying the undercoat paint onto the plating layer 3, an appropriate coating method such as roll coating, curtain flow coating, or spray coating can be employed. As for the heating temperature of the undercoat, it is preferable that the maximum temperature reached is 200° C. or more and 260° C. or less. The heating time of the undercoat paint film is preferably 15 seconds or more and 90 seconds or less.

The undercoat layer 4 thus produced contains a first polyester resin and a first soft resin. The first polyester resin contains a reaction product of polyester resin (A) and a cross-linking agent. Therefore, the first polyester resin has crosslinks. When the cross-linking agent contains blocked isocyanate, the first polyester resin has urethane bonds as cross-links.

The glass transition temperature of the undercoat layer 4 is 50° C. or higher, more preferably 60° C. or higher. In this case, the undercoat layer 4 is less likely to be scratched, and the scratch resistance of the undercoat layer 4 can be improved. The glass transition temperature of the undercoat layer 4 is preferably 80° C. or lower, more preferably 75° C. or lower. In this case, the flexibility of the undercoat layer 4 can be ensured. That is, in the present embodiment, since the glass transition temperature of the undercoat layer 4 is 50° C. or more and 80° C. or less, both scratch resistance and flexibility of the undercoat layer 4 can be achieved.

The thickness of the undercoat layer 4 is preferably in the range of 3 μm or more and 10 μm or less. In this case, the flexibility and scratch resistance of the undercoat layer 4 can be effectively improved.

2-4. Topcoat Layer The topcoat layer 5 covers the basecoat layer 4 as described above. In this embodiment, the topcoat layer 5 is in direct contact with the basecoat layer 4 . The topcoat layer 5 is a cured product of a topcoat. The topcoat paint of the present embodiment contains a polyester resin having a hydroxyl group (hereinafter also referred to as a polyester resin (C)) and a cross-linking agent having an isocyanate group (hereinafter also referred to as a cross-linking agent (D)). The topcoat further contains a second soft resin.

The polyester resin (C) may contain a polyester resin having a hydroxyl group among polyester resins contained in known polyester resin paints.

The polyester resin (C) preferably contains, for example, 10% by weight or more and 50% by weight or less of a hydroxyl group-containing polyester resin (C1) having a glass transition temperature of 10° C. or more and 50° C. or less. In this case, the scratch resistance, flexibility, and weather resistance of the topcoat layer 5 can be improved. The number average molecular weight of the polyester resin (C1) is preferably within the range of 1,000 or more and 6,000 or less. The hydroxyl value of the polyester resin (C1) is preferably 40 mgKOH/g or more and 150 mgKOH/g or less, and preferably 60 mgKOH/g or more and 120 mgKOH/g or less.

The cross-linking agent (D) is not particularly limited as long as it can be cross-linked with the hydroxyl-containing polyester resin (C) and has an isocyanate group. A urethane bond (--NHCOO--) can be formed by a reaction between a hydroxyl group (--OH) derived from the polyester resin (C) and an isocyanate group (--NCO) derived from the cross-linking agent (D). Thereby, the scratch resistance of the topcoat layer 5 can be improved. The crosslinker (D) can contain, for example, blocked isocyanates. When the topcoat contains blocked isocyanate, the blocked isocyanate in the topcoat may be the same as or different from the blocked isocyanate in the undercoat.

The topcoat preferably contains blocked isocyanate so that the content of isocyanate groups (--NCO) in the topcoat is 5% by weight or more and 15% by weight or less. In this case, the hydroxyl group derived from each component contained in the topcoat can be effectively reacted with the isocyanate group derived from the blocked isocyanate, and the scratch resistance of the topcoat layer 5 can be improved.

The topcoat contains a second soft resin. That is, the overcoat layer 5 contains the second soft resin. This second soft resin is a polyester polyol. The second soft resin can impart flexibility to the topcoat layer 5 and improve the workability of the coated steel sheet 1 . In addition, the scratch resistance of the topcoat layer 5 is also improved. A possible reason for this is that the hydroxyl group derived from the polyester polyol reacts with the isocyanate group of the above-described block cyanate. As the second soft resin, the same material as polyester polyol, which is the first soft resin contained in the undercoat, can be used.

The number average molecular weight of the second soft resin is preferably 500 or more and 3000 or less, more preferably 1000 or more and 2000 or less. The hydroxyl value of the second soft resin is preferably 30 mgKOH/g or more and 200 mgKOH/g or less, more preferably 50 mgKOH/g or more and 110 mgKOH/g or less.

The ratio of the second soft resin to the topcoat is preferably 5% by weight or more and 20% by weight or less, and preferably 10% by weight or more and 18% by weight or less, relative to the total amount of the polyester resin (B). In this case, the flexibility of the topcoat layer 5 can be effectively improved, and the workability of the coated steel sheet 1 can be effectively improved.

The topcoat contains particulate wax. In this case, part of the particulate wax can be exposed on the surface of the topcoat layer 5 . Thereby, the slipperiness|lubricacy of the surface of the topcoat layer 5 is improved, and the scratch resistance of the topcoat layer 5 is improved. If the topcoat layer 5 does not contain particulate wax, when the coated steel sheet 1 is subjected to a molding process such as continuous roll forming, the topcoat layer 5 may be ripped, scratched, or the like. This is because the frictional resistance between the working rolls and the overcoat layer 5 is large. On the other hand, in the topcoat layer 5 of the present embodiment, part of the particulate wax is exposed on the surface, and the slipperiness of the surface of the topcoat layer 5 is improved. etc. is unlikely to occur.

Particulate waxes include vegetable waxes such as carnauba wax, candelilla wax and rice wax, animal waxes such as beeswax and lanolin, mineral waxes such as montan wax and ceresin wax, and petroleum waxes such as paraffin wax and microcrystalline wax. Containing one or more components selected from the group consisting of waxes and synthetic hydrocarbon waxes such as Fischer-Tropsch wax, polyethylene wax, oxidized polyethylene wax, polypropylene wax, oxidized polypropylene wax, and polytetrafluoroethylenex. can be done. In this embodiment, the particulate wax is preferably polytetrafluoroethylene wax. In this case, the slipperiness of the surface of the topcoat layer 5 can be particularly improved, and the scratch resistance of the topcoat layer 5 can be particularly improved. The topcoat paint of the present embodiment preferably contains only polytetrafluoroethylene wax as the particulate wax.

The 90% diameter (D ₉₀ ) of the particulate wax is preferably 5 μm or less, more preferably 4 μm or less. In this case, it is possible to make it difficult for the particulate wax to drop off from the surface of the topcoat layer 5 . The painted plated steel sheet 1 after production is rolled up, for example, into a cylindrical shape (see FIG. 2). When flattening the coated steel sheet 1 , it is pressed by a plurality of rolls 10 provided in a leveler 100 . If the 90% diameter (D ₉₀ ) of the particulate wax is larger than 5 μm, the wax may fall off from the surface of the topcoat layer 5 and may adhere and deposit on the surface of the roll 10 . If the coated steel sheet 1 is continuously pressed while the wax adheres and accumulates on the surface of the roll 10, surface contamination of the coated coated steel sheet 1, indentation damage due to hardened wax, and the like may occur. Frequent cleaning of the roll 10 can control these, but reduces production efficiency. On the other hand, in the present embodiment, since the 90% diameter (D ₉₀ ) of the particulate wax is 5 μm or less, the detachment of the particulate wax is suppressed. Indentation damage and the like can be suppressed. Moreover, since the cleaning frequency of the roll 10 is reduced, production efficiency can be improved. Also, the 50% diameter ( _D50 ) of the particulate wax is preferably 3 μm or less. The 90% diameter (D ₉₀ ) and 50% diameter (D ₅₀ ) of the particulate wax are the 90% diameter and 50% diameter in the volume-based integrated fraction in the laser diffraction/scattering method particle diameter distribution of the particulate wax, respectively. It can be measured by, for example, a laser diffraction/scattering particle size distribution analyzer (product number Microtrac FRA manufactured by Microtrac Bell Co., Ltd.).

The top coating preferably contains 0.3 to 2.0% by weight of particulate wax, preferably 0.7 to 1.5% by weight. In this case, the slipperiness of the surface of the topcoat layer 5 can be effectively improved, and the scratch resistance of the topcoat layer 5 can be effectively improved.

The topcoat can contain pigments, solvents, additives, etc., as required.

As the pigment, a general coloring pigment contained in the topcoat layer of the coated steel sheet can be used. Examples of such colored pigments include titanium oxide ( _TiO2 ), zinc oxide (ZnO), zirconium oxide ( _ZrO2 ), calcium carbonate ( _CaCO3 ), barium sulfate ( _BaSO4 ), alumina ( _{Al2O3 )} . ), kaolin clay, carbon black, iron oxide (Fe ₂ O ₃ , Fe ₃ O ₄ ) and other inorganic coloring pigments, and Hansa yellow, pyrazolone orange, azo pigments and other organic coloring pigments. The topcoat can contain one or more of these color pigments.

Examples of solvents include water; hydrocarbons such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; ethyl solvents such as cellosolves; ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone and cyclohexanone. is included. The primer can contain one or more of these solvents,
Examples of additives that can be used include inorganic fillers, organic fillers, and extender pigments. Examples of inorganic fillers that can be used include glass fiber, alumina fiber, and boron nitride. Examples of organic fillers include thermoplastic resin beads such as acrylic resin beads and nylon beads having an average particle size of 1 μm or more and 50 μm or less.

The topcoat can be prepared by mixing the above polyester resin (B), a cross-linking agent, a second soft resin, particulate wax, and optionally pigments, solvents, and additives.

The topcoat layer 5 can be produced, for example, by applying a topcoat paint on the undercoat layer 4 and then heating and curing the paint. As a method for applying the topcoat paint onto the undercoat layer 4, an appropriate coating method such as roll coating, curtain flow coating, or spray coating can be employed. It is preferable that the heating temperature of the top coat is 200° C. or higher and 250° C. or lower. The heating time of the coating film is preferably 20 seconds or more and 90 seconds or less.

The topcoat layer 5 thus produced contains the second polyester resin, the second soft resin, and the particulate wax. The second polyester resin contains a reaction product of polyester resin (B) and a cross-linking agent. Therefore, the second polyester resin has crosslinks. When the cross-linking agent contains a blocked isocyanate, the second polyester resin has urethane bonds as cross-links.

The glass transition temperature of the topcoat layer 5 is preferably 10° C. or higher and 60° C. or lower, and more preferably 20° C. or higher and 50° C. or lower. In this case, scratch resistance, flexibility and weather resistance of the topcoat layer 5 can be ensured.

The thickness of the overcoat layer 5 is preferably in the range of 10 μm or more and 25 μm or less. In this case, the flexibility, scratch resistance and weather resistance of the topcoat layer 5 can be effectively improved.

2-5. Painted plated steel sheet As described above, the painted plated steel sheet 1 of the present embodiment is produced by providing the undercoat layer 4 on the plating layer 3 covering the steel sheet 2 and further providing the topcoat layer 5 on the undercoat layer 4. can be done.

2-6. Modification The configuration of the coated steel sheet 1 is not limited to the configuration described above.

For example, FIG. A layer 4 and a topcoat layer 5 may be provided. That is, the plating layer 3 , the undercoat layer 4 and the topcoat layer 5 may be provided on both surfaces of the steel sheet 2 .

For example, the coated plated steel sheet 1 may include layers other than the steel sheet 2 , the plating layer 3 , the undercoat layer 4 and the topcoat layer 5 . For example, between the plating layer 3 and the undercoat layer 4, a chemical conversion treatment film produced by chemically converting the plating layer 3 may be provided. For example, an alloy layer may be provided between the steel plate 2 and the plating layer 3 . For example, an intermediate coat layer may be provided between the undercoat layer 4 and the topcoat layer 5 . The intermediate coating layer can be formed from known paints such as epoxy resin-based paints and polyester resin-based paints. The intermediate coating layer may be formed from a paint other than the epoxy resin-based paint and the polyester resin-based paint.

Further, in the method of manufacturing the above-described coated steel sheet 1, after the coating film of the undercoat paint formed on the plating layer 3 is heated and cured to form the undercoat layer 4, the topcoat paint formed on the undercoat layer 4 is applied. Although the coating film is heat-cured to form the topcoat layer 5, it is not limited to this. For example, after forming a coating film of the undercoat paint on the plating layer 3, a coating film of the topcoat paint is formed on the coating film of the undercoat paint, and the coating film of the undercoat paint and the topcoat paint are heated and cured at the same time. Thus, the undercoat layer 4 and the topcoat layer 5 may be produced at the same time.

3. Details of Building Material The building material 100 of the present embodiment includes the metal member 10 as described above. The metal member 10 is made of the coated steel plate 1 described above. That is, the coated steel sheet 1 is for building materials.

Examples of the building material 100 include processed building materials such as storm shutters, doors, storerooms and rain gutters, exterior wall materials such as siding and sandwich panels, and roof materials.

FIG. 3A shows a building material 100 that is a sandwich panel. This building material 100 includes a pair of metal skins made of metal members 10 and a core material 11 between the pair of metal skins. A metal member 10 is produced from a coated steel sheet 1 . As shown in FIG. 3A, the metal skin has a working portion 12 . The processed portion 12 is produced by bending the coated steel sheet 1. More specifically, the processed portion 12 is produced by bending the coated steel sheet 1 at an acute angle (bending of 90 degrees or more). be.

FIG. 3B shows a building material 100 that is a roofing material. This building material 100 is composed of a metal member 10 made from a coated steel sheet 1 . That is, the building material 100 itself may be made of the coated steel plate 1 . As shown in FIG. 3B, the metal member 10 has a processed portion 12 . The processed portion 12 is produced by bending the coated steel sheet 1. More specifically, the processed portion 12 is produced by bending the coated steel sheet 1 at an acute angle (bending of 90 degrees or more). be.

In the process of producing the building material 100 shown in FIGS. 3A and 3B, the coated plated steel sheet 1 is subjected to various bending processes such as sharp bending. Since the coated steel sheet 1 of the present embodiment has excellent workability, cracks are less likely to occur in the undercoat layer 4 and the topcoat layer 5 even when the coated steel sheet 1 is subjected to bending. Therefore, the undercoat layer 4 and the topcoat layer 5 of the metal member 10 included in the building material 100 can be made less likely to crack.

EXAMPLES The present disclosure will be specifically described below with reference to examples.

(Examples 1 to 8, Comparative Examples 1 to 3)
As a steel sheet and a plated steel sheet having a plating layer, "SGL (registered trademark)" (manufactured by Nippon Steel & Sumikin Steel Sheet Co., Ltd., plate thickness: 0.5 mm, double-sided adhesion amount: 150 g / m ² ) (hereinafter, SGL) was prepared. .

An undercoat paint and a topcoat paint having the compositions shown in Table 1 below were prepared.

On the plating layer, the undercoat paint was applied with a bar coater to form a coating film, and the coating film was cured by heating for 40 seconds so that the maximum temperature reached 235 ° C., and the thickness was 5 μm. A primer layer was formed.

A top coat was applied onto the undercoat layer with a bar coater to form a coating film. The coating film was cured by heating for 50 seconds so that the highest temperature reached 235° C. to form a topcoat layer having a thickness of 20 μm.

Thus, the coated steel sheets of Examples 1 to 8 and Comparative Examples 1 to 3 were produced.

The details of each component contained in the undercoat paint and topcoat paint described in Table 1 are as follows.
· Polyester resin 1: LH822-01 (trade name, manufactured by Evonik) (glass transition temperature: 17°C, hydroxyl value: 50 mgKOH/g, number average molecular weight: 5,000).
- Polyester resin 2: VYLON29XS (trade name, manufactured by Toyobo Co., Ltd.) (glass transition temperature: 72°C, hydroxyl value: 7 mgKOH/g, number average molecular weight: 22,000).
· Polyester resin 3: LH820-16 (trade name, manufactured by Evonik) (glass transition temperature: 55°C, hydroxyl value: 20 mgKOH/g, number average molecular weight: 5,000).
- Polyester resin 4: ALKYNOL TPLS2013 (hydroxyl value: 94 mgKOH/g, number average molecular weight: 2,350).
- Epoxy resin: jER1004 (trade name, manufactured by Mitsubishi Chemical Corporation) epoxy equivalent: 925, number average molecular weight: 1,650).
• Cross-linking agent: blocked isocyanate.
· Soft resin 1: DESMOPHEN C1200 (trade name, manufactured by Covestro) (hydroxyl value: 56.1 mgKOH/g).
· Soft resin 2: DESMOPHEN C1100 (trade name, manufactured by Covestro) (hydroxyl value: 109 mgKOH/g).
Wax 1: KTL-1N (trade name, manufactured by Kitamura Co., Ltd.) (90% diameter (D90): 3.3 μm).

(evaluation)
The coated steel sheets of Examples 1 to 8 and Comparative Examples 1 to 3 were evaluated for glass transition temperature, workability, scratch resistance, leveler contamination, and weather resistance of the undercoat layer and topcoat layer. The evaluation method and evaluation criteria for each evaluation are as follows.

(Glass-transition temperature)
From the coated steel sheets of Examples 1 to 8 and Comparative Examples 1 to 3, the undercoat layer and the topcoat layer were peeled off, and the glass transition temperatures of the undercoat layer and the topcoat layer were measured by TMA (Thermomechanical Analysis). It was measured by the method. The results are shown in Table 1 below.

(workability)
Test pieces of 50 mm×150 mm were cut out from the coated steel sheets of Examples 1 to 8 and Comparative Examples 1 to 3. This test piece was bent 180 degrees with the coating film (topcoat layer and undercoat layer) facing outward, sandwiching n steel plates with a thickness of 0.5 mm. The coating film of the test piece after bending was visually observed with a 10x loupe. The number of steel sheets at which cracks no longer occur (no-crack T number) was measured and evaluated according to the following criteria. The results are shown in Table 1 below.
A: The no-crack T number is 6 or less.
B: No crack T number is 7 or more.

(Scratch resistance)
The surfaces of the coated steel sheets of Examples 1 to 8 and Comparative Examples 1 to 3 were scratched with a continuous load type scratch strength tester manufactured by Sintokagaku Co., Ltd. (using a diamond needle with a tip diameter of 0.3 mm). scratched. The load required to expose the undercoat layer was measured and evaluated according to the following criteria. The results are shown in Table 1 below.
A: The load required to expose the undercoat layer is 900 g or more.
B: The load required to expose the undercoat layer is less than 900 g.

(Leveler contamination)
On the surfaces of the coated steel sheets of Examples 1 to 8 and Comparative Examples 1 to 3, a stainless steel ball was slid so that the trajectory was spiral using a friction player manufactured by Lesca. The sliding distance was 20 m. The state of the stainless ball after sliding was confirmed and evaluated according to the following criteria. The results are shown in Table 1 below.
A: Almost no wax, dust, etc. adhere to the stainless ball.
B: Wax, debris, etc. adhere to the stainless ball.

(Weatherability)
For the coated steel sheets of Examples 1 to 8 and Comparative Examples 1 to 3, a super accelerated weathering tester (manufactured by Iwasaki Electric, model number SUV-F2) and a moisture resistance tester (manufactured by Suga Test Instruments Co., Ltd., model number CT-3) UV irradiation test under the conditions of irradiation time 24 hours, black panel temperature 63 ° C, ultraviolet intensity 100 mW / cm2, and test time 24 hours, chamber temperature 50 ° C, chamber humidity 98% or more Humidity. A test cycle was repeated for 10 cycles.

After sticking a cellophane adhesive tape to the topcoat layer of the painted plated steel sheet after the test, it was peeled off.
A: Peeling of the topcoat layer is not observed.
B: Peeling of the topcoat layer is observed in an area of less than 5% of the topcoat layer.
C: Peeling of the topcoat layer is observed in a region of 5% or more and less than 30% of the topcoat layer.
D: Peeling of the topcoat layer is observed in an area of 30% or more of the topcoat layer.

Further, the gloss and hue of the overcoat layer were measured before and after the accelerated weather resistance test, respectively, and the gloss retention rate and hue change were derived based thereon. The results were evaluated according to the following criteria. Gloss and color difference were measured using a color difference meter (SM45 type color difference meter manufactured by Suga Test Instruments Co., Ltd.). Gloss retention (%) is a value derived based on the 60° specular gloss after testing. Hue change is the color change (ΔE) before and after the test derived from the Hunter color difference formula.

Gloss retention rate A: 70% or more.
B: 50% or more and less than 70%.
C: 30% or more and less than 50%.
D: Less than 30%.

Hue change A: 3.0 or less.
B: greater than 3.0 and less than or equal to 6.0.
C: greater than 6.0 and less than or equal to 9.0.
D: Greater than 9.0.

REFERENCE SIGNS LIST 1 painted plated steel sheet 2 steel sheet 3 plating layer 4 undercoat layer 5 topcoat layer 100 building material

Claims (9)

steel plate;
A coating layer covering the steel plate and containing aluminum and zinc;
an undercoat layer covering the plating layer;
and a topcoat layer covering the undercoat layer,
The undercoat layer is a cured product of an undercoat paint containing a polyester resin (A) containing a polyester resin having a hydroxyl group, a crosslinking agent (B) containing an isocyanate compound, and a polyester polyol, and has a glass transition The temperature is 50° C. or higher,
The topcoat layer is a cured topcoat paint containing a polyester resin (C) having a hydroxyl group, a cross-linking agent (D) having an isocyanate group, a polyester polyol, and particulate wax ,
The polyester polyol contained in the topcoat is 5% by weight or more and 20% by weight or less with respect to the total amount of the polyester resin (C) having a hydroxyl group.
Painted plated steel sheet. The polyester resin (A) contains 10% by weight or more of a polyester resin (A1) having a hydroxyl group with a glass transition temperature of 60° C. or higher.
The paint plated steel sheet according to claim 1. The cross-linking agent (B) contains a blocked isocyanate,
The paint plated steel sheet according to claim 1 or 2. The particulate wax is polytetrafluoroethylene wax,
The paint plated steel sheet according to any one of claims 1 to 3. 90% diameter (D90) of the particulate wax is 5 μm or less,
The paint plated steel sheet according to claim 4. The glass transition temperature of the topcoat layer is 10 ° C. or higher and 60 ° C. or lower.
The paint plated steel sheet according to any one of claims 1 to 5. for building materials,
The paint plated steel sheet according to any one of claims 1 to 6. including metal members,
The metal member is made of the coated steel sheet according to any one of claims 1 to 7,
building material. steel plate;
A coating layer covering the steel plate and containing aluminum and zinc;
An undercoat layer covering the plating layer and having a glass transition temperature of 50° C. or higher;
A method for producing a coated steel sheet, comprising a topcoat layer covering the undercoat layer,
A polyester resin (A) containing a polyester resin having a hydroxyl group, a cross-linking agent (B) containing an isocyanate compound, and an undercoat paint containing a polyester polyol are applied onto the plating layer, and then cured by heating. Create a coating layer,
A polyester resin (C) having a hydroxyl group, a cross-linking agent (D) having an isocyanate group, a polyester polyol, and a topcoat containing particulate wax are applied on the undercoat layer, and then heat-cured. Create a topcoat layer ,
The polyester polyol contained in the topcoat is 5% by weight or more and 20% by weight or less with respect to the total amount of the polyester resin (C) having a hydroxyl group.
A method for producing a coated steel sheet.

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