Surface-treated galvanized steel sheet, resin film-coated steel sheet, building panel, method for manufacturing surface-treated galvanized steel sheet, and method for manufacturing resin film-coated steel sheet

Abstract

[PROBLEM] To provide a surface-treated galvanized steel sheet, a resin film-coated steel sheet, and a building panel that have excellent corrosion resistance and processing adhesion to a resin film. [SOLUTION] The surface-treated galvanized steel sheet comprises: a steel sheet; a galvanized layer that is formed on the steel sheet; a first chemically-converted covered film layer that is formed on the galvanized layer and that contains 5 mg / m2 or more and less than 30 mg / m2 of cobalt metal; and a second chemically-converted covered film layer that is formed on the first chemically-converted covered film and that contains (a) a zirconium component, (b) a binding component originating from dehydration condensation of a silanol group, and (c) a urethane binding component.

Description

Surface-treated galvanized steel sheet, resin film-coated steel sheet, architectural panel, method for manufacturing surface-treated galvanized steel sheet, and method for manufacturing resin film-coated steel sheet

[0001] The present disclosure relates to a surface-treated zinc-plated steel sheet and a resin film-coated steel sheet, to a building panel using the surface-treated zinc-plated steel sheet and the resin film-coated steel sheet, and to a method for manufacturing the surface-treated zinc-plated steel sheet and the resin film-coated steel sheet.

[0002] In recent years, there has been a demand for reducing the environmental impact of surface-treated steel sheets used in architectural panels, such as bathroom panels and kitchen panels. Specifically, from the viewpoint of preventing water pollution and soil contamination, there is a demand for surface-treated steel sheets that do not contain chromate coatings.

[0003] For example, Patent Document 1 listed below discloses a method for producing a zinc-based plated steel sheet having excellent flat-plate corrosion resistance and paint adhesion, which comprises forming a first coating on the surface of the zinc-based plated steel sheet using a first surface treatment liquid containing an ion-bonding salt containing a predetermined cation, a predetermined chelating agent, and water, and then forming a second coating on the surface of the first coating using a second surface treatment liquid containing a silane coupling agent having a glycidyl group, a tetraalkoxysilane, a zirconium carbonate compound, a predetermined anionic polyurethane resin, a vanadium compound, a molybdic acid compound, and predetermined amounts of water.

[0004] Patent Document 2 discloses a pre-coated steel sheet having excellent corrosion resistance and workability, in which a chrome-free primer is applied to both sides of a zinc-plated steel sheet, and on one side, which is the front side, an undercoat coating layer is applied on the primer coating, the undercoat coating layer containing a polyester resin and / or an epoxy-modified polyester resin as a binder and at least one of an ion-exchange type oxide rust-preventive pigment or a phosphate-based rust-preventive pigment, and one or more topcoat coating layers are further applied on top of the undercoat coating layer, and on the other side, which is the back side, an undercoat coating layer is applied which contains a polyester resin and / or an epoxy-modified polyester resin as a binder and at least one of an ion-exchange type oxide rust-preventive pigment or a phosphate-based rust-preventive pigment, and one or more topcoat coating layers are further applied on top of the undercoat coating layer.

[0005] Patent Document 3 discloses a chromate-free surface-treated metal material that satisfies requirements such as corrosion resistance and heat resistance. The metal material is coated with a Zn—Co plating film containing a trace amount of Co, and then coated with an aqueous metal surface treatment agent containing an organosilicon compound (W) obtained by blending a silane coupling agent (A) containing one amino group in the molecule and a silane coupling agent (B) containing one glycidyl group in the molecule in a solid content mass ratio [(A) / (B)] of 0.5 to 1.7, at least one fluoro compound (X) selected from titanium hydrofluoric acid and zirconium hydrofluoric acid, phosphoric acid (Y), and a vanadium compound (Z), and then dried to form a composite coating containing each of the components.

[0006] Patent Document 4 describes a coated steel sheet having sufficiently improved corrosion resistance and adhesion of processed parts, which is made of a steel sheet, a zinc-based plating layer, and a total coating amount of Ni and Co of 20 mg / m ２ 100mg / m or more ２ The coating amount of the treatment layer is 2.0 g / m or less. ２ 7.0g / m or more ２ The patent document discloses a coated steel sheet having, in this order: a phosphate treatment layer; a chromium-free sealing coating containing an oxoacid salt of a Group 4 metal and a Group 1 metal or its salt; and an organic coating.

[0007] Patent Document 5 discloses a chemically treated steel sheet having excellent paint film adhesion and film adhesiveness after processing, which uses a zinc-plated steel sheet or a zinc alloy-plated steel sheet as a substrate and has a chemical conversion coating formed on the surface of the plated steel sheet, the chemical conversion coating being made of an oxide or hydroxide of a valve metal, the oxide of which exhibits high insulation resistance, and a fluoride, and a polyhydric phenol resin, with a thickness of 0.01 to 0.5 μm.

[0008] JP 2022-39097 A JP 2007-119858 A JP 2008-184659 A JP 2020-152986 A JP 2008-163364 A

[0009] However, all of the above Patent Documents 1 to 5 have room for improvement in terms of meeting the current demand for materials for architectural panels. That is, in recent years, in the case of surface-treated steel sheets for architectural panel applications, which require a wide variety of appearances, a resin film with design properties is attached onto the surface that has been subjected to chemical conversion treatment.

[0010] Furthermore, surface-treated steel sheets laminated with resin films such as polyester and polyvinyl chloride are often formed into various shapes by press working, etc. Therefore, they are required to have excellent corrosion resistance and high processing adhesion of the resin film so as to be able to withstand harsh environments such as those used in bathrooms.

[0011] As a result of extensive research into the composition of materials for architectural panels that have higher adhesion to resin films during processing, the present invention has been conceived. That is, the present disclosure aims to provide a surface-treated galvanized steel sheet that has corrosion resistance equivalent to that of conventional chromate films and also has good adhesion to resin films during processing.

[0012] In order to solve the above problems, a surface-treated galvanized steel sheet according to one embodiment of the present disclosure comprises a steel sheet, a galvanized layer formed on the steel sheet, and a galvanized layer formed on the galvanized layer, the galvanized layer containing 5 mg / m cobalt metal. ２ 30mg / m or more ２and a second chemical conversion coating layer formed on the first chemical conversion coating and containing (a) a zirconium component, (b) a bonding component formed by dehydration condensation of silanol groups, and (c) a urethane bonding component.

[0013] Furthermore, a resin film-coated steel sheet according to one embodiment of the present disclosure is characterized in that it comprises the above-mentioned surface-treated zinc-plated steel sheet, an adhesive layer formed on the surface-treated zinc-plated steel sheet, and a resin film formed on the adhesive layer.

[0014] Furthermore, a building panel according to one embodiment of the present disclosure is characterized in that it is made using the resin film-coated steel sheet.

[0015] A method for producing a surface-treated galvanized steel sheet according to one embodiment of the present disclosure includes applying an alkaline treatment agent containing a metal chelating agent containing cobalt nitrate and ferric nitrate to the galvanized steel sheet, thereby producing a surface-treated galvanized steel sheet containing 5 mg / m cobalt metal. ２ 30mg / m or more ２ and a second treatment step of applying an aqueous treatment agent containing a coupling agent, a metal oxide, a blocked isocyanurate, and a polyester polyol as constituent components to the first chemical conversion coating layer, followed by drying at 60°C or higher.

[0016] A method for producing a resin film-coated steel sheet in one embodiment of the present disclosure is characterized by comprising: a third treatment step of applying a polyester-based adhesive to the surface-treated zinc-plated steel sheet to a thickness of 1 μm to 4 μm; and a fourth treatment step of heating the surface-treated zinc-plated steel sheet to which the polyester-based adhesive has been applied to 180°C or higher and coating a resin film on top of the polyester-based adhesive.

[0017] According to the present disclosure, it is possible to provide a surface-treated zinc-plated steel sheet, a resin film-coated steel sheet, and an architectural panel that do not contain a chromate film and have excellent corrosion resistance and processing adhesion with a resin film.

[0018] Fig. 1 is a schematic cross-sectional view of a surface-treated zinc-plated steel sheet according to an embodiment. Fig. 2 is a schematic cross-sectional view of a resin film-coated steel sheet according to an embodiment. Fig. 3 is a schematic cross-sectional view of a building panel according to an embodiment. Fig. 4 is a diagram showing a method for manufacturing a surface-treated zinc-plated steel sheet and a resin film-coated steel sheet. Fig. 5 is a diagram showing test evaluation criteria in this embodiment.

[0019] <Surface-treated galvanized steel sheet 100> The surface-treated galvanized steel sheet according to this embodiment will be described in detail below. As shown in Fig. 1 , the surface-treated galvanized steel sheet 100 according to this embodiment includes a galvanized steel sheet 10 and a chemical conversion treatment film 20 coated on at least one surface of the galvanized steel sheet 10. The galvanized steel sheet 10 includes a steel sheet 11 and a galvanized layer 13 formed on the steel sheet 11. The chemical conversion treatment film 20 also includes a first chemical conversion treatment film layer 21 on the galvanized layer 13, and a second chemical conversion treatment film layer 23 that coats both the galvanized layer 13 and the first chemical conversion treatment film layer 21.

[0020] <Galvanized Steel Sheet 10> The galvanized steel sheet 10 used in this embodiment can be a galvanized steel sheet commonly used in laminated metal sheets. Examples include hot-dip galvanized steel sheets, hot-dip zinc alloy-plated steel sheets, alloyed hot-dip galvanized steel sheets, electrogalvanized steel sheets, and electrogalvanized zinc alloy-plated steel sheets. Among these, hot-dip galvanized steel sheets (JIS G3302) are preferably used from the viewpoints of availability and price.

[0021] There are no particular restrictions on the thickness of the galvanized steel sheet 10, but a thickness of 0.10 mm to 1.20 mm is preferable from the viewpoints of ease of application and appearance. If the thickness of the galvanized steel sheet is less than 0.1 mm, it may be difficult to obtain desirable corrosion resistance and weather resistance. On the other hand, if the thickness of the galvanized steel sheet exceeds 1.2 mm, the weight increases, which may cause problems during application, and is undesirable from the viewpoint of cost.

[0022] The steel sheet 11 included in the galvanized steel sheet 10 may be, for example, a cold-rolled ordinary steel sheet having a thickness of about 0.05 mm to 1.20 mm. Among cold-rolled steel sheets, a low-carbon or ultra-low-carbon aluminum-killed steel sheet having a carbon content of less than 0.01 mass % is preferably used as the steel sheet 11 from the viewpoint of workability and the like.

[0023] The amount of zinc coating of the zinc coating layer 13 formed on the steel sheet 11 is not particularly limited, but is, for example, 60 g / m ２ ~600g / m ２ More specifically, when the galvanized steel sheet 10 is a hot-dip galvanized steel sheet, the coating weight indication symbol of the coating weight indicated in JIS G3302:2019 is preferably within the range of Z06 to Z60.

[0024] <Chemical conversion treatment film 20> As described above, the chemical conversion treatment film 20 is formed on at least one surface of the galvanized steel sheet 10. The chemical conversion treatment film 20 includes a first chemical conversion treatment coating layer 21 that covers at least a portion of the surface of the galvanized steel sheet 10, and a second chemical conversion treatment coating layer 23 that is formed on the first chemical conversion treatment coating layer 21 and that covers the entire surface of the galvanized steel sheet 10.

[0025] <First chemical conversion coating layer 21> The first chemical conversion coating layer 21 has a cobalt metal content of 5 mg / m ２ 30mg / m or more ２ As shown in Fig. 1 , the first chemical conversion coating layer 21 is in contact with the surface of the galvanized steel sheet 10. The first chemical conversion coating layer 21 does not need to cover the entire surface of the galvanized steel sheet 10, and it is sufficient that the first chemical conversion coating layer 21 is present on at least a portion of the surface of the galvanized steel sheet 10.

[0026] The effect of the first chemical conversion coating layer 21 on the surface of the galvanized steel sheet 10 is as follows: Cobalt (Co), which has a lower ionization tendency than zinc (Zn), becomes an oxygen reduction reaction site (cathode), and therefore microcells of Co (cathode) and Zn (anode) are formed under the first chemical conversion coating layer 21. As a result, OH under the coating －This reduces the amount of ions produced, thereby suppressing cathodic delamination and corrosion under the coating.

[0027] The method for forming the first chemical conversion coating layer 21 will be described in detail later, but is carried out by applying a cobalt-containing alkaline treatment solution to the surface of the galvanized steel sheet 10. When the alkaline treatment solution is applied to the surface of the galvanized steel sheet 10, zinc (Zn) on the galvanized steel sheet 10 dissolves, and electrons are released at that time, which causes the Co in the alkaline treatment solution to dissolve. 2＋ Ions are reduced (displacement electroless plating).

[0028] <Second chemical conversion coating layer 23> The second chemical conversion coating layer 23 is (a) an organic-inorganic composite coating containing a zirconium component. The coating amount of the second chemical conversion coating layer is 4 mg / m ２ ~600 mg / m ２ It is preferable that the concentration is 30 mg / m ２ ~70 mg / m ２ The dry film weight of the second chemical conversion coating layer can be measured using a known fluorescent X-ray analyzer.

[0029] The thickness of the second chemical conversion coating layer is preferably 1 μm or less. The amount of zirconium contained in the second chemical conversion coating layer 23 is preferably 1.2 mg / m ２ 171.4mg / m ２ Preferably, it is 8.6 mg / m or less. ２ ~20.0 mg / m ２ It is more preferable that the dry coating weight of the second chemical conversion coating layer described above can be calculated from the zirconium content. More specifically, this can be calculated using the following formula: ２ ) = zirconium content (mg / m ２ ) x 3.5

[0030] The second chemical conversion coating layer 23 further includes (b) a bonding component originating from the dehydration condensation of silanol groups and (c) a urethane bonding component. The (b) bonding component originating from the dehydration condensation of silanol groups includes siloxane bonds and the like, and is a silane coupling agent component. The silane coupling agent reacts with the metal surface and resin when cured by heat. That is, the second chemical conversion coating layer 23 is thought to have a structure in which siloxane bonds (-Si-O-Si-) are dispersed in the urethane resin component, and are also bonded (-Si-O-metal-) to the metal oxide and the cobalt metal in the first chemical conversion coating layer or the zinc on the galvanized steel sheet.

[0031] <Resin Film-Coated Steel Sheet 200> As shown in FIG. 2 , the resin film-coated steel sheet 200 in the present disclosure includes an adhesive layer 30 formed on at least one surface of the above-mentioned surface-treated zinc-plated steel sheet 100, and a resin film 40 formed on the adhesive layer 30.

[0032] <Adhesive Layer 30> The adhesive layer 30 is preferably an adhesive containing a polyester resin as a main component, and more preferably a polyester urethane adhesive. The adhesive layer 30 may also be an adhesive containing an acrylic resin as a main component. One type of adhesive may be used, or multiple types may be mixed and used, and a polyester adhesive may be mixed with an acrylic adhesive or an olefin adhesive.

[0033] The thickness of the adhesive layer 30 is preferably 1 μm to 4 μm. In order to improve the adhesion between the second chemical conversion coating layer 23 and the resin film 40 during processing, the adhesive layer 30 may contain an adhesion improver. Examples of the adhesion improver include a silane coupling agent having a trimethoxysilyl group, an amino group, or an epoxy group.

[0034] <Resin Film 40> The resin film 40 may be a film used for construction purposes. Examples of materials for the resin film 40 include polyvinyl chloride film, polyester film, acrylic film, and olefin film. The resin film 40 may be a transparent film or a colored film. The resin film 40 may also be a film with a design, such as an embossed surface. The resin film 40 may also be a laminate of films made of multiple different materials. For example, the resin film 40 may be a film formed by laminating a polyethylene terephthalate film and a polyvinyl chloride film. The thickness of the resin film 40 is preferably 0.06 mm or more. There is no particular upper limit to the thickness of the resin film 40, but from a cost perspective, it is preferably 0.5 mm or less.

[0035] Generally, when a resin film having a thickness of 0.06 mm or more is laminated on a surface-treated steel sheet and then formed, peeling of the resin film may occur due to internal stress. However, the resin film-coated steel sheet of the present disclosure can significantly improve adhesion during processing. The reasons for this are roughly as follows.

[0036] When a steel sheet is stretched during processing, stress is applied to the chemical conversion coating layer, which contains inorganic components. If the chemical conversion coating layer is thicker than a certain thickness, it cannot follow the processing, and stress is concentrated at the interface between the chemical conversion coating layer and the zinc plating. As a result, the chemical conversion coating layer undergoes cohesive failure, causing peeling of the resin film. These are the reasons for peeling of the chemical conversion coating layer on typical resin film-coated steel sheets.

[0037] On the other hand, in the present disclosure, the chemical conversion coating layer has a two-layer structure consisting of a first chemical conversion coating layer containing cobalt metal and a second chemical conversion coating layer containing a coupling agent component, thereby achieving improved processing adhesion.

[0038] <Building Panel 300> Next, the building panel 300 of this embodiment will be described. As shown in FIG. 3 , the building panel 300 of this embodiment is characterized by using the above-mentioned surface-treated zinc-plated steel sheet 100 or resin film-coated steel sheet 200. More specifically, the building panel 300 of this embodiment is provided with a rear paint layer 50 on the surface of the resin film-coated steel sheet 200 opposite the resin film 40. There are no particular restrictions on the thickness of the rear paint layer 50, but it may be, for example, 5 μm to 20 μm. Furthermore, as the type of rear paint layer 50, known paints generally used for building purposes can be applied, such as epoxy-based paints and polyester-based paints.

[0039] Furthermore, the building panel 300 in this embodiment may have a metal layer, a resin layer, a gypsum board layer, a volcanic glass multi-layer board, etc. (not shown) on at least one side of the back paint layer 50.

[0040] The architectural panel 300 of this embodiment can be used as an interior material for bathrooms, kitchens, etc. More specifically, it can be used as an interior material for a modular bathroom, a composite magnetic panel for a kitchen, or a panel that can be attached to an interior wall. It can also be used as an exterior material for a front door, etc.

[0041] <Method for manufacturing surface-treated galvanized steel sheet> Next, a method for manufacturing the surface-treated galvanized steel sheet 100 of this embodiment will be described. As shown in Fig. 4, the method for manufacturing the surface-treated galvanized steel sheet 100 of this embodiment includes the following first and second treatment steps. Note that the method for manufacturing the surface-treated galvanized steel sheet 100 of this embodiment may also include a known degreasing step. Note that, as the step of galvanizing the steel sheet can be performed by any known step, a description thereof will be omitted here.

[0042] <Degreasing step> First, the degreasing step of the galvanized steel sheet will be described. Note that this degreasing step is not an essential step and can be omitted as appropriate. Specifically, the galvanized steel sheet may be subjected to this degreasing step in order to remove an oxide film or oil coating on the surface of the galvanized steel sheet to be used.

[0043] Specifically, the degreasing step can be carried out by applying a known alkaline treatment agent to the surface of the galvanized steel sheet. Specifically, a silicate-type alkaline treatment agent containing 35 to 40% sodium metasilicate and 0.1 to 1.0% potassium hexafluorotitanate in terms of composition concentration can be used. During the degreasing step, this alkaline treatment agent can be adjusted to a concentration of 2.0% or less and a liquid temperature of 60 to 75°C. Known methods, such as spraying and immersion, can be used to apply the alkaline treatment agent to the galvanized steel sheet. The treatment time in the degreasing step can be 9 to 13 seconds when using the spray or immersion method. After treatment, the treatment agent is preferably removed by rinsing the galvanized steel sheet with water.

[0044] <First Treatment Step> The first treatment step can be carried out following the optional degreasing step. The first treatment step is a step of forming a first chemical conversion coating layer on the galvanized steel sheet. The first chemical conversion coating layer contains 5 mg / m of cobalt metal. ２ 30mg / m or more ２ The first chemical conversion coating layer can be formed by applying an alkaline treatment agent containing a cobalt metal component to the galvanized steel sheet. The alkaline treatment agent can include a metal chelating agent containing cobalt nitrate and ferric nitrate.

[0045] More specifically, the alkaline treatment agent used in the first treatment step may contain, in terms of composition concentration, 20 to 25% sodium hydroxide, 1 to 5% cobalt nitrate, and 1 to 5% ferric nitrate. In addition, in the first treatment step, the alkaline treatment agent may be used after adjusting the liquid temperature to 60°C to 75°C.

[0046] In the first treatment step, known methods such as spraying and immersion can be used to apply the alkaline treatment agent to the galvanized steel sheet. The treatment time in the first treatment step can be 8 to 16 seconds in the case of spraying or immersion. After the first treatment step, by-products and treatment solution components remaining on the surface of the galvanized steel sheet can be removed by rinsing with water. Furthermore, by drying the surface of the galvanized steel sheet with hot air after rinsing with water, a cobalt metal coating can be formed on the surface of the galvanized steel sheet as a first chemical conversion coating layer. The cobalt metal contained in the first chemical conversion coating layer is 5 mg / m ２ 30mg / m or more ２ is less than.

[0047] In the first treatment step, the mechanism by which the cobalt metal film is formed as the first chemical conversion coating layer is roughly as follows: On the galvanized steel sheet, zinc (Zn), which is a base metal, dissolves, and the electrons released at that time convert the Co of the alkaline treatment agent into ２＋ The ions are reduced and precipitated on the galvanized steel sheet. In other words, a cobalt metal coating can be formed as the first chemical conversion coating layer by a displacement electroless plating method that utilizes the ionization tendency.

[0048] <Second Treatment Step> In the method for producing a surface-treated galvanized steel sheet according to this embodiment, the second treatment step is carried out after the first treatment step. The second treatment step is a step of forming a second chemical conversion coating layer on the first chemical conversion coating layer. In the second treatment step, the second chemical conversion coating layer can be formed by applying an aqueous treatment agent containing a coupling agent and a metal oxide.

[0049] The coupling agent contained in the aqueous treatment agent used in the second treatment step is preferably a silane coupling agent, and more preferably a silane coupling agent containing an aminoalkylsilane. The aminoalkylsilane is thought to contribute to processing adhesion because the amino group bonds with the ester group in the adhesive layer and the second chemical conversion coating layer described below. More specifically, the aminoalkylsilane is thought to contribute to processing adhesion by forming a siloxane bond (-Si-O-Si-) through dehydration condensation and bonding (-Si-O-metal-) with the metal oxide and the first chemical conversion coating layer described below.

[0050] Specific examples of the aminoalkylsilane include 3-aminopropyldimethoxymethylsilane, 3-aminopropyltrimethoxysilane, 3-aminopropyldiethoxymethylsilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethylamino)propyldimethoxymethylsilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 3-(2-aminoethylamino)propyltriethoxysilane, [3-(6-aminohexaamino)propyl]trimethoxysilane, trimethoxy[3-(methylamino)propyl]silane, [3-(N,N-dimethylamino)propyl]trimethoxysilane, N-[3-(trimethoxysilyl)propyl]-1-butanamine, trimethoxy[3-(phenylamino)propyl]silane, bis[3-(trimethoxysilyl)propyl]amine, trimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, and trimethyl[3-(triethoxysilyl)propyl]ammonium chloride. Of these, 3-aminopropyltriethoxysilane is particularly preferred from the viewpoints of adhesion during processing, weather resistance, and availability.

[0051] The coupling agents contained in the aqueous treatment agent may be used alone or in combination of two or more. Furthermore, the silane coupling agent containing aminoalkylsilane may be partially hydrolyzed or dehydration-condensed.

[0052] The content of the coupling agent in the aqueous treatment agent is not particularly limited, but is preferably 1 to 5 wt %.

[0053] Examples of metal oxides contained in the aqueous treatment agent include zirconium oxide, silicon oxide, and titanium oxide. Examples of zirconium oxide include zirconium oxide. Examples of silicon oxide include silicon dioxide. Examples of titanium oxide include titanium oxide. These metal oxides may be used alone or in combination of two or more.

[0054] These metal oxides are preferably present as particles, and the average particle size is preferably 1 μm or less, and more preferably 10 to 300 nm.

[0055] The metal oxide content of the aqueous treatment agent is not particularly limited, but is preferably 1.0 to 5.0 wt % based on the total weight of the aqueous treatment agent. By setting the metal oxide content to 0.1 wt % or more, the heat resistance and corrosion resistance of the resulting second chemical conversion coating layer tend to be improved. On the other hand, by setting the metal oxide content to 5.0 wt % or less, the working adhesion of the resulting second chemical conversion coating layer to the galvanized steel sheet tends to be improved.

[0056] The aqueous treatment agent in the second treatment step may contain a component that forms a urethane bond. Specifically, the aqueous treatment agent in the second treatment step preferably contains a blocked isocyanurate and a polyester polyol.

[0057] The blocked isocyanurate contained in the aqueous treatment agent is preferably a pyrazole blocked isocyanurate. Specifically, the pyrazole blocked isocyanurate is preferably a trimer of an aliphatic polyisocyanate monomer (e.g., an isocyanurate-modified product) to which a pyrazole compound has been introduced as a blocking agent for isocyanate groups. The blocking agent blocks and inactivates the isocyanate groups, while deblocking them by heating to activate the isocyanate groups.

[0058] Specific examples of the aliphatic polyisocyanate include 1,6-hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, tetramethylene diisocyanate, 3-methyl-1,5-pentane diisocyanate, etc. Among these, it is preferable to use 1,6-hexamethylene diisocyanate from the viewpoints of reactivity and availability.

[0059] On the other hand, specific examples of the pyrazole compound include pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, 3-ethylpyrazole, 3,5-diethylpyrazole, 3-propylpyrazole, etc. Among these, it is more preferable to use 3,5-dimethylpyrazole, which has excellent solubility in solvents and is often used in the production of pyrazole-blocked isocyanurates.

[0060] The polyester polyol contained in the aqueous treatment agent in the second treatment step reacts with the isocyanurate after the blocking agent dissociation to form urethane bonds, thereby improving the processing adhesion of the second chemical conversion coating layer. Specifically, the polyester polyol can be obtained by a condensation reaction between a dibasic acid (single or a mixture of two or more) and a polyhydric alcohol (single or a mixture of two or more). Examples of dibasic acids include succinic acid, adipic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, and carboxylic acids such as 1,4-cyclohexanedicarboxylic acid. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, trimethylpentanediol, cyclohexanediol, trimethylolpropane, glycerin, pentaerythritol, 2-methylolpropanediol, and ethoxylated trimethylolpropane. As the polyester polyol, polycaprolactone polyol obtained by ring-opening polymerization of ε-caprolactone with a low molecular weight polyol can also be used.

[0061] In the aqueous treatment agent in the second treatment step, the content of the component that forms a urethane bond is not particularly limited, but is preferably 0.1 to 0.5 wt %.

[0062] The aqueous treatment agent in the second treatment step may further contain known substances such as a solvent, a catalyst, a stabilizer, a pH adjuster, and the like.

[0063] The pH of the aqueous treatment agent in the second treatment step is preferably 7 or less, and more preferably 5 to 7. By adjusting the pH of the aqueous treatment agent to 7 or less, storage stability is further improved.

[0064] The aqueous treatment agent can be applied to the first chemical conversion coating layer by roll coating. The applied aqueous treatment agent is then dried in a hot air drying oven at a temperature of 80°C to 100°C to form an organic-inorganic composite coating as the second chemical conversion coating layer. The dry coating amount of the second chemical conversion coating layer is 4 mg / m ２ ~600 mg / m ２ It is preferable that the concentration is 30 mg / m ２ ~70 mg / m ２ The dry film weight of the second chemical conversion coating layer can be measured using a known fluorescent X-ray analyzer. The thickness of the second chemical conversion coating layer is preferably 1 μm or less.

[0065] The amount of zirconium contained in the second chemical conversion coating layer after drying was 1.2 mg / m ２ ~171.4mg / m ２ It is preferable that the concentration is 8.6 mg / m ２ ~20.0 mg / m ２ It is more preferable that the dry film weight of the second chemical conversion coating layer is calculated from the zirconium content. More specifically, it can be calculated using the following formula: ２ ) = zirconium content (mg / m ２ ) x 3.5

[0066] <Method for manufacturing resin film-coated steel sheet> Next, a method for manufacturing the resin film-coated steel sheet 200 of this embodiment will be described. As shown in Fig. 4, the method for manufacturing the resin film-coated steel sheet 200 of this embodiment includes the first and second processing steps described above, followed by the following third and fourth processing steps.

[0067] <Third Treatment Step> In the third treatment step, an adhesive layer is formed on the second chemical conversion coating layer described above. The thickness of the formed adhesive layer 30 is preferably 1 μm to 4 μm. In the third treatment step, a known adhesive used in building material applications can be applied to the second chemical conversion coating layer using a known method. For example, a solvent-based adhesive containing a polyester urethane resin and a silane coupling agent consisting of a trimethoxysilyl group and an amino group can be applied with a roll coater and then heated and dried to obtain an adhesive layer with a thickness of 1 μm to 4 μm.

[0068] <Fourth Treatment Step> In the fourth treatment step, a resin film is laminated on the adhesive layer. Specifically, after the third treatment step, the surface-treated zinc-plated steel sheet on which the adhesive layer has been formed is heated to a temperature equal to or higher than the curing temperature of the adhesive, and the adhesive layer and the resin film are brought into contact with each other, and then the sheet is passed between a pair of rolls to laminate the resin film. Alternatively, after the third treatment step, a method of extruding the molten resin may be applied.

[0069] <Fifth Treatment Step> The manufacturing method for a building panel according to the present disclosure may include a step (fifth treatment step) of forming a back paint layer on the surface opposite to the resin film of the resin film-coated steel sheet obtained as described above. A known method can be used to form the back paint layer. The formation of the back paint layer may be carried out simultaneously with the third or fourth treatment step described above.

[0070] The present invention will be described in more detail below with reference to examples.

[0071] <Production of Surface-Treated Galvanized Steel Sheet> Untreated hot-dip galvanized steel sheet (sheet thickness 0.45 mm) specified in JIS G3302 was prepared. When white rust or the like had formed on the surface of the hot-dip galvanized steel sheet due to storage, the steel sheet was subjected to a degreasing treatment by the following known method (degreasing step). The degreasing treatment was performed by spraying and immersing the steel sheet in a silicate-type alkaline treatment agent containing an aqueous solution of sodium metasilicate (concentration 2%, liquid temperature 65±5°C) for 11±2 seconds. After the degreasing treatment, the treatment agent was removed by rinsing with water.

[0072] Next, a first chemical conversion coating layer was formed on the surface of the hot-dip galvanized steel sheet using an alkaline treatment agent having the following composition (first treatment step): Solvent: 25% aqueous solution of sodium hydroxide Metal component: 5 wt % cobalt nitrate Solution temperature: 60 to 75°C pH: 11.5 Electrical conductivity: 115 mS Treatment method: Spray immersion treatment (12±4 seconds) After treatment, the alkaline treatment agent was removed by rinsing with water, and a first chemical conversion coating layer was formed.

[0073] Next, a second chemical conversion coating layer was formed on the first chemical conversion coating layer using an aqueous treatment agent with the following composition (second treatment step): Solvent: 95 wt% water, 1.5 wt% ethanol, Coupling agent (3-aminopropyltriethoxysilane 1.3 wt%), Metal oxides (1.1 wt% zirconium oxide, 0.02 wt% hafnium oxide, 0.6 wt% silicon dioxide), Blocked isocyanurate (0.15 wt% 1,6-hexamethylene diisocyanate, 0.06 wt% 3,5-dimethylpyrazole), Polyester polyol 0.2 wt%, pH: 5-7

[0074] In the second treatment step, the aqueous treatment agent was applied using a roll coater and then dried at 80° C. or higher and 100° C. or lower to form a second chemical conversion coating layer.

[0075] <Production of Resin Film-Coated Steel Sheet> A resin film was laminated onto the surface-treated zinc-plated steel sheet obtained as described above, via an adhesive layer.

[0076] An adhesive layer was formed on the second chemical conversion coating layer (third treatment step). The adhesive used was a solvent-based adhesive containing a polyester urethane resin and a silane coupling agent consisting of a trimethoxysilyl group and an amino group.

[0077] Next, a resin film was laminated on the adhesive layer (fourth treatment step). The following types of resin film (A) or (B) were used: (A) PET / vinyl chloride multilayer resin film (PET / Vinyl chloride) A multilayer film of stretched PET film (0.025 mm) and vinyl chloride (0.10 mm) (B) PET / PBT multilayer resin film (PET / PBT) A multilayer film of stretched PET film (0.025 mm) and PBT (0.075 mm)

[0078] The surface-treated zinc-plated steel sheet on which the adhesive layer was formed was heated to a final sheet temperature and laminated with a resin film to obtain a resin film-coated steel sheet. The final sheet temperature was 200°C for the PET / vinyl chloride multilayer resin film and 230°C for the PET / PBT multilayer resin film.

[0079] <Measurement and Evaluation of Resin Film Adhesion During Processing Depending on the Cobalt Amount in the First Chemical Conversion Coating Layer> For the resin film-coated steel sheets of the Examples and Comparative Examples, the adhesion of the resin film during processing depending on the cobalt amount in the first chemical conversion coating layer was evaluated based on the results of an Igeta-Erichsen stretch test. Specifically, this was performed in accordance with the adhesion test of "JIS K 6744 2019: Polyvinyl Chloride Coated Metal Sheets and Strips, Section 9." The measurement conditions are shown below. The measurement results are also shown in Table 1.

[0080] Test Method: (1) Test specimens measuring approximately 75 x 150 mm or larger were cut from each resin film-coated steel plate in each Example or Comparative Example. (2) Two vertical and horizontal straight cuts were made with a blade, 2.5 mm apart on either side of the centerline of the cut specimen, reaching the steel plate. Each cut was 50 mm long. The intersection of the vertical and horizontal centerlines was referred to as the test position. The cut specimen was placed in an Erichsen tester (JIS B 7729). (3) Specifically, the cut side of the test specimen was placed facing the die of the tester, with the test position aligned with the center of the punch, die, and blank holder. (4) The punch was pressed 8 mm in at as uniform a speed as possible. The pressing speed was within the range of 30 to 120 mm per minute, and the test was conducted at an ambient temperature of 25±5°C.

[0081] Evaluation method (5) After the pressing was completed, the test piece was removed from the Erichsen tester. The cut portion of the test piece was visually inspected for peeling of the resin film. (6) The test piece after the test was evaluated on a 5-point scale based on the following criteria. The evaluation criteria for the test piece after the test are shown schematically in Figure 5. A: No abnormality in the resin film (no lifting) B: Slight lifting at the edge of the resin film C: Clear lifting at the edge of the resin film D: Significant lifting from the edge of the resin film E: Lifting over the entire resin film The above A and B were rated as ○ (suitable for practical use), C as △ (difficult to use in practical use), and D and E as × (impossible to use in practical use), and the results were entered in a table.

[0082] <Testing and Evaluation of Corrosion Resistance of Resin Film-Coated Steel Sheets According to Cobalt Amount in First Chemical Conversion Coating Layer> A salt spray test was conducted to evaluate the corrosion resistance of resin film-coated steel sheets in accordance with JIS Z2371. Test specimens similar to those used in the resin film adhesion test were prepared, and cross-cuts reaching the steel sheet were made on the resin film coating surface. A neutral salt spray test (5% NaCl aqueous solution) was conducted for 1,000 hours. After the test, the blister widths of the cross-cut and flat portions of the test specimens were measured. The results were evaluated as follows: ∘: The resin film peeled off at the cross-cut portion by a maximum of less than 10 mm, and no blisters were observed from the flat portion. Δ: The resin film peeled off at the cross-cut portion by a maximum of 10 mm or more, and no blisters were observed from the flat portion. ×: The resin film peeled off entirely from the cross-cut portion, or blisters were observed throughout the flat portion.

[0083] <Measurement and evaluation of resin film adhesion during processing according to the amount of second chemical conversion coating layer> For the resin film-coated steel sheets of the Examples and Comparative Examples, the adhesion during processing of the resin film according to the amount of second chemical conversion coating layer was evaluated based on the results of an Igeta-Erichsen stretch test. The measurement and evaluation methods were the same as those for the evaluation according to the cobalt content, and the results are shown in Table 2.

[0084] <Measurement and Evaluation of Accelerated Wet and Heat Adhesion According to Adhesion Amount of Second Chemical Conversion Coating Layer> A wet and heat adhesion test was conducted in accordance with JIS K6744 2019: Polyvinyl Chloride Coated Metal Sheets and Metal Strips, Section 9, to evaluate the adhesion of a resin film under wet and heat conditions. The same test specimens as those used in the resin film processing adhesion test were prepared, and cross-cuts reaching the steel plate were made on the resin film-coated surface, followed by immersion in boiling water for 20 hours. After removing and drying the test specimen, the resin film on the test specimen was forcibly peeled off, and the peel length was measured and evaluated as follows: ○: Peel length less than 10 mm △: Peel length more than 10 mm to 20 mm or less ×: Peel length more than 20 mm

[0085] (Examples 1 to 10, Comparative Examples 1 to 6) Resin film-coated steel sheets were produced using the types of resin film shown in Table 1, with the cobalt metal content of the first chemical conversion coating layer being varied. The cobalt deposition amount of the first chemical conversion coating layer was varied by changing the number of seconds of spray immersion treatment and the liquid temperature of the treatment liquid. The liquid temperatures of the treatment liquid are shown in Table 1. When the cobalt metal content in the first chemical conversion coating layer was 5 mg / m ２ 30mg / m or more ２ It was confirmed that when the temperature is less than 1000°C, a resin film-coated steel sheet having both excellent adhesion for processing and excellent corrosion resistance can be obtained.

[0086] (Examples 11 to 19, Comparative Examples 7 to 9) Resin film-coated steel sheets were prepared using the types of resin film shown in Table 2, with the amount of film of the second chemical conversion coating layer varied. Specifically, the amount of film of the second chemical conversion coating layer was varied by changing the size of the coating bar coater used when applying the aqueous treatment agent. When the type of resin film was a PET / vinyl chloride multilayer film, the amount of film of the second chemical conversion coating layer was 4 mg / m². ２ ~600 mg / m ２ It was confirmed that good processing adhesion could be obtained within the range of 10 mg / m. In addition, when the type of resin film was a PET / PBT multilayer film, the coating amount of the second chemical conversion coating layer was 10 mg / m. ２ ~600 mg / m ２ It was confirmed that good processing adhesion could be obtained within this range.

[0087] (Reference Example 1) A hot-dip galvanized steel sheet (sheet thickness: 0.45 mm) conforming to JIS G3302 (basis weight: Z18) was coated with an inorganic chromium-free chemical conversion coating (coating amount: 300 mg / m ２ A surface-treated steel sheet having a surface coated with a 3 μm thick polyester adhesive was prepared. A resin film was laminated onto the surface. The resin film was a multilayer film (total thickness 0.10 mm) of oriented PET and colored vinyl chloride. The Igeta-Erichsen extension test was performed in the same manner as in Example 1, and the results are shown in Table 2.

[0088] (Reference Example 2) The chemical conversion coating was replaced with an organic chromium-free chemical conversion coating (coating amount: 700 mg / m ２The results are shown in Table 2.

[0089] (Reference Example 3) The chemical conversion coating was an organic-inorganic chromium-free chemical conversion coating (coating amount: 700 mg / m ２ The same procedure as in Reference Example 1 was carried out, except that the chemical conversion coating of Reference Example 3 did not include a layer containing cobalt metal. Furthermore, although a Zr-based conversion coating was formed, it did not contain Si. The results are shown in Table 2.

[0090] (Discussion of Reference Examples 1 to 3) In the Igeta-Erichsen stretch test, it was confirmed that the resin film peeled off during processing in all of Reference Examples 1 to 3. The reason for this is thought to be that the chemical conversion coating was unable to follow the processing, resulting in a concentration of stress acting on the interface between the chemical conversion coating and plating in the Erichsen cut portion.

[0091]

[0092]

[0093] The above-described embodiment and examples can be modified in various ways without departing from the spirit of the present invention.

[0094] It can be suitably used as a bathroom wall material such as a unit bath, an exterior material for housing components, an interior magnetic panel, and an interior material for a system kitchen.

[0095] 100: Surface-treated zinc-plated steel sheet 10: Zinc-plated steel sheet 200: Resin film-coated steel sheet 20: Chemical conversion coating film 21: First chemical conversion coating layer 30: Adhesive layer 40: Resin film 300: Building panel

Claims

1. A steel sheet, a zinc plating layer formed on the steel sheet, and a galvanized steel sheet having a cobalt metal content of 5 mg / m2 formed on the zinc plating layer. ２ 30mg / m or more ２ and a second chemical conversion coating layer formed on the first chemical conversion coating and containing (a) a zirconium component, (b) a bonding component formed by dehydration condensation of silanol groups, and (c) a urethane bonding component.

2. The coating amount of the second chemical conversion coating layer is 4 mg / m ２ ~600mg / m ２ The surface-treated zinc-plated steel sheet according to claim 1 .

3. The amount of zirconium contained in the second chemical conversion coating layer is 1.2 mg / m ２ 171.4mg / m ２ The surface-treated galvanized steel sheet according to claim 2, wherein:

4. A resin film-coated steel sheet comprising: a surface-treated galvanized steel sheet according to any one of claims 1 to 3; an adhesive layer formed on the surface-treated galvanized steel sheet; and a resin film formed on the adhesive layer.

5. The resin film-coated steel sheet according to claim 4, wherein the resin film comprises at least one of a polyvinyl chloride film, a polyester film, an acrylic film, and an olefin film, and the thickness of the resin film is 0.06 mm or more.

6. The resin film-coated steel sheet according to claim 5, wherein the adhesive layer is composed mainly of a polyester resin or an acrylic resin.

7. An architectural panel using the resin film-coated steel sheet according to claim 5.

8. An alkaline treatment agent containing a metal chelating agent containing cobalt nitrate and ferric nitrate is applied to a zinc-plated steel sheet, and the cobalt metal is reduced to 5 mg / m ２ 30mg / m or more ２ and a second treatment step of applying an aqueous treatment agent containing a coupling agent, a metal oxide, a blocked isocyanurate, and a polyester polyol as constituent components onto the first chemical conversion coating layer, and drying the aqueous treatment agent at 60° C. or higher.

9. A method for producing a surface-treated zinc-plated steel sheet as described in claim 8, wherein in the first treatment step, the alkaline treatment agent has a pH of 12 or more and is applied to the zinc-plated steel sheet at a liquid temperature of 60°C or more and 75°C or less.

10. The method for producing a surface-treated zinc-plated steel sheet according to claim 9, wherein the aqueous treatment agent has a pH of 5 to 7, the coupling agent contains an aminoalkylsilane, and the blocked isocyanurate is a pyrazole blocked isocyanurate.

11. A method for producing a resin film-coated steel sheet, comprising: a third processing step of applying a polyester-based adhesive to a thickness of 1 μm to 4 μm on the surface-treated zinc-plated steel sheet according to any one of claims 1 to 3; and a fourth processing step of heating the surface-treated zinc-plated steel sheet to which the polyester-based adhesive has been applied to 180°C or higher and coating a resin film on the polyester-based adhesive.

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