Surface treatment liquid for galvanized steel sheet, method for producing galvanized steel sheet with surface treatment coating, and galvanized steel sheet with surface treatment coating

Abstract

Provided is a surface treatment liquid for a zinc-plated steel sheet, which is capable of producing a zinc-plated steel sheet with a surface treatment coating having excellent long-term perspiration resistance, corrosion resistance in a flat plate section, and the like, and which has excellent storage stability. A surface treatment liquid for a zinc-plated steel sheet according to the present invention is characterized by comprising a first surface treatment liquid (X) and a second surface treatment liquid (Y), the first surface treatment liquid (X) containing a glycidyl group-containing silane coupling agent (A), a tetraalkoxysilane (B), a zirconium carbonate compound (C), sodium silicate (D1), a vanadium compound (E), a molybdic acid compound (F) and water, and the contents of the components satisfying a predetermined relationship. The second surface treatment liquid (Y) contains sodium silicate (D2), an anionic polyurethane resin (G), and water, and the content of each component satisfies a predetermined relationship.

Description

Technical Field

[0001] This invention relates to a surface treatment liquid for galvanized steel sheets, a method for manufacturing galvanized steel sheets with a surface treatment coating, and galvanized steel sheets with a surface treatment coating. Background Technology

[0002] Galvanized steel sheets with a galvanized coating on the surface of the base steel sheet are used in various applications such as automobiles, home appliances, office equipment, and building components due to their excellent corrosion resistance. Furthermore, it is known that when the galvanized coating includes aluminum and / or magnesium as components other than zinc, it exhibits even better corrosion resistance than a zinc-based galvanized layer.

[0003] However, it has been confirmed that when a person directly touches the surface of a galvanized steel coating, the area touched by the hand will turn black over time (blackening). This is believed to be due to the oxidation of the galvanized surface caused by the adhesion of sweat, a phenomenon known to occur particularly easily in galvanized coatings containing aluminum and / or magnesium. Therefore, there is a demand for galvanized steel sheets that do not blacken even when covered by sweat, i.e., those with excellent sweat resistance.

[0004] Patent Document 1 discloses a method for manufacturing a galvanized steel sheet with a surface-treated film formed on its surface using a surface treatment solution for galvanized steel sheets. This surface treatment solution contains a glycidyl silane coupling agent, tetraalkoxysilane, sodium silicate, zirconium carbonate compound, an anionic polyurethane resin with a glass transition temperature (Tg) of 80–130°C, a vanadium compound, a molybdate compound, and water, with a pH of 8.0–10.0, and the content of each component meets a specified relationship. According to this manufacturing method, a galvanized steel sheet with a surface-treated film exhibiting excellent heat resistance, heat crack resistance, corrosion resistance of the flat portion, corrosion resistance after alkali degreasing, blackening resistance, water stain resistance, solvent resistance, perspiration resistance, and coating adhesion can be manufactured.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-62710 Summary of the Invention

[0008] However, the inventors studied the galvanized steel sheet with a surface treatment coating proposed in Patent Document 1, and the results showed that its long-term sweat resistance (long-term sweat resistance) was insufficient, and there was room for improvement in long-term sweat resistance.

[0009] In view of the above-mentioned problems, the object of the present invention is to provide a surface treatment liquid for galvanized steel sheets with a surface treatment coating that exhibits excellent heat resistance to discoloration, heat cracking resistance, corrosion resistance of the flat portion, corrosion resistance of the processed portion, corrosion resistance after alkali degreasing, blackening resistance, water stain resistance, solvent resistance, long-term sweat resistance, and coating adhesion, and also has excellent storage stability. Furthermore, the object of the present invention is to provide a method for manufacturing a galvanized steel sheet with a surface treatment coating using the surface treatment liquid for galvanized steel sheets, and a galvanized steel sheet with a surface treatment coating manufactured by the same method.

[0010] To address the aforementioned issues, the inventors conducted in-depth research and obtained the following insights. By constructing a layered structure for the surface-treated coating, the penetration of sweat components can be significantly suppressed. Specifically, a first coating with coating components possessing conventional properties beyond at least long-term sweat resistance is formed on the surface of a galvanized steel sheet. The first coating, in addition to a silane coupling agent with glycidyl groups, tetraalkoxysilane, and a zirconium carbonate compound, also contains sodium silicate, which promotes the formation of a Si-rich layer on the surface, thus improving long-term sweat resistance. Then, a second coating with coating components specifically designed to block sweat components is formed on the first coating. The second coating, containing anionic polyurethane resin, exhibits high barrier properties against sweat components, and by containing sodium silicate, it can firmly adhere to the first coating with the Si-rich layer, significantly improving long-term sweat resistance.

[0011] That is, the main structure of the present invention is as follows.

[0012] [1] A surface treatment liquid for galvanized steel sheets, characterized in that it comprises a first surface treatment liquid (X) and a second surface treatment liquid (Y).

[0013] The first surface treatment liquid (X) contains a silane coupling agent (A) with glycidyl group, a tetraalkoxysilane (B), a zirconium carbonate compound (C), sodium silicate (D1), a vanadium compound (E), a molybdate compound (F) and water, and the content of each component satisfies the following (1) to (6).

[0014] The second surface treatment liquid (Y) mentioned above contains sodium silicate (D2), anionic polyurethane resin (G) and water, and the content of each component satisfies the following (7) and (8).

[0015] (1) Mass of solid components (A) of silane coupling agent (A) with glycidyl groups S The mass of solid components relative to the silane coupling agent (A) with glycidyl groups (A) S Solid composition mass of tetraalkoxysilane (B) S The equivalent mass of ZrO2 in zirconium carbonate (C) and zirconium carbonate compound (C) ZThe total mass (X) S The mass ratio of (A) S / X S The value ranges from 0.050 to 0.450.

[0016] (2) Mass of solid components of tetraalkoxysilane (B) (B) S ) relative to the total mass (X) mentioned above S The mass ratio of (B) S / X S The value ranges from 0.010 to 0.190.

[0017] (3) The equivalent mass of ZrO2 in zirconium carbonate compound (C) (C Z ) relative to the total mass (X) mentioned above S The mass ratio of (C) Z / X S The value ranges from 0.460 to 0.910.

[0018] (4) Mass of solid components of sodium silicate (D1) S ) relative to the total mass (X) mentioned above S The mass ratio of (D1) S / X S The value ranges from 0.040 to 0.630.

[0019] (5) The equivalent mass of V in vanadium compound (E) (E) V ) relative to the total mass (X) mentioned above S The solid composition mass of sodium silicate (D1) and sodium silicate (D1) S The total mass (X) S +D1 S The mass ratio of (E) V / (X) S +D1 S The value ranges from 0.006 to 0.094.

[0020] (6) The equivalent mass of Mo in molybdate compound (F) M ) relative to the total mass (X) mentioned above S The solid composition mass of sodium silicate (D1) and sodium silicate (D1) S The total mass (X) S +D1 S The mass ratio of (F) M / (X) S +D1 S The value ranges from 0.030 to 0.280.

[0021] (7) Mass of solid components of sodium silicate (D2) S The mass of solids relative to anionic polyurethane resin (G) (G)S The mass ratio of (D2) S / G S The value ranges from 0.010 to 0.100.

[0022] (8) Mass of solids component of anionic polyurethane resin (G) (G) S The solid content mass relative to the second surface treatment liquid (Y) mentioned above (Y) S The mass ratio of (G) S / Y S The value ranges from 0.900 to 0.980.

[0023] [2] According to the surface treatment liquid for galvanized steel sheet described in [1] above, wherein in the second surface treatment liquid (Y), the anionic polyurethane resin (G) contains anionic polyurethane resin having a carbonate backbone, and its content satisfies the following (9):

[0024] (9) The solid content mass of the above-mentioned anionic polyurethane resin with a carbonate backbone relative to the solid content mass of the anionic polyurethane resin (G) (G S The mass ratio is 0.20 to 0.80.

[0025] [3] The surface treatment liquid for galvanized steel sheet according to [1] or [2] above, wherein the second surface treatment liquid (Y) further contains an organosilicon resin (H) in a content that satisfies the following (10):

[0026] (10) Mass of solid components of organosilicon resin (H) (H) S The mass of solids relative to anionic polyurethane resin (G) (G) S The mass ratio of (H) S / G S The range is 0.0030 to 0.0400.

[0027] [4] The surface treatment liquid for galvanized steel sheet according to any one of [1] to [3] above, wherein the second surface treatment liquid (Y) further contains a crosslinking agent (I) whose content satisfies the following (11):

[0028] (11) Mass of solid components of crosslinking agent (I) S The mass of solids relative to anionic polyurethane resin (G) (G) S The mass ratio of (I) S / G S The range is 0.0030 to 0.0400.

[0029] [5] The surface treatment liquid for galvanized steel sheet according to any one of [1] to [4] above, wherein the second surface treatment liquid (Y) further contains wax (L) in a content satisfying the following (12):

[0030] (12) Mass of solid components of wax (L) S The solid content mass relative to the second surface treatment liquid (Y) mentioned above (Y) S The mass ratio of (L) S / Y S The range is 0.010 to 0.120.

[0031] [6] The surface treatment liquid for galvanized steel sheet according to any one of [1] to [5] above, wherein the first surface treatment liquid (X) further contains a phosphate compound (J) whose content satisfies the following (13):

[0032] (13) Solid content mass of phosphoric acid compound (J) S ) relative to the total mass (X) mentioned above S The mass ratio of (J) S / X S The range is 0.140 to 0.770.

[0033] [7] The surface treatment liquid for galvanized steel sheet according to any one of [1] to [6] above, wherein the first surface treatment liquid (X) further contains a fluorine compound (K) in a content satisfying the following (14):

[0034] (14) Mass of solid components of fluorine compound (K) S ) relative to the total mass (X) mentioned above S The mass ratio of (K) S / X S The range is 0.040 to 0.610.

[0035] [8] A method for manufacturing a galvanized steel sheet with a surface treatment coating, comprising the following steps: (1) manufacturing a galvanized steel sheet with a surface treatment coating using the surface treatment liquid for galvanized steel sheets described in any one of [1] to [7] above.

[0036] The process of applying the first surface treatment liquid (X) to the surface of a galvanized steel sheet;

[0037] Then the process of drying the coated first surface treatment liquid (X) to form a first film;

[0038] Then, the process of coating the surface of the first film with the second surface treatment liquid (Y); and

[0039] The process of drying the applied second surface treatment liquid (Y) to form a second film.

[0040] [9] According to the manufacturing method of the galvanized steel sheet with surface treatment coating described in [8] above, wherein the amount of the first coating is 0.010 to 0.400 g / m 2 The amount of the second coating applied is 0.20–3.00 g / m³. 2 .

[0041]

[10] A galvanized steel sheet with a surface treatment coating is manufactured by the manufacturing method of the galvanized steel sheet with a surface treatment coating described in [8] or [9] above.

[0042]

[11] According to

[10] above, the galvanized steel sheet with a surface-treated coating is a hot-dip Zn-Al alloy steel sheet having a hot-dip Zn-Al alloy coating on at least one surface of a base steel sheet as a substrate. The hot-dip Zn-Al alloy coating has a composition containing, by mass %: Al: 3.0 to 12.0%, Mg: 0.2 to 6.0%, Ni: 0.0 to 0.1%, and the remainder being composed of Zn and unavoidable impurities.

[0043] According to the present invention, a surface treatment liquid for galvanized steel sheets with a surface treatment coating that exhibits excellent resistance to heat discoloration, heat cracking, corrosion resistance of the flat portion, corrosion resistance of the processed portion, corrosion resistance after alkali degreasing, resistance to blackening, water stain resistance, solvent resistance, long-term sweat resistance, and coating adhesion, as well as excellent storage stability, can be provided. Furthermore, according to the present invention, a method for manufacturing a galvanized steel sheet with a surface treatment coating using the surface treatment liquid for galvanized steel sheets, and a galvanized steel sheet with a surface treatment coating manufactured by the same method, can be provided. Detailed Implementation

[0044] The following describes the surface treatment liquid for galvanized steel sheets, the manufacturing method of galvanized steel sheets with surface treatment coatings, and embodiments of galvanized steel sheets with surface treatment coatings according to the present invention. It should be noted that the embodiments described below are examples embodying the present invention and are not intended to limit the scope of the invention to these specific examples.

[0045] (Surface treatment liquid for galvanized steel sheets)

[0046] One embodiment of the present invention provides a surface treatment liquid for galvanized steel sheets, comprising a first surface treatment liquid (X) and a second surface treatment liquid (Y). The first surface treatment liquid (X) is applied to the surface of the galvanized steel sheet and dried to form a first coating on the galvanized steel sheet. The second surface treatment liquid (Y) is applied to the first coating and dried to form a second coating on the first coating.

[0047] [First surface treatment liquid (X)]

[0048] The first surface treatment liquid (X) contains a silane coupling agent (A) with a glycidyl group, a tetraalkoxysilane (B), a zirconium carbonate compound (C), sodium silicate (D1), a vanadium compound (E), a molybdate compound (F), and water, and may also contain one or both of a phosphate compound (J) and a fluorine compound (K) as needed.

[0049] <Silane coupling agent with glycidyl group (A)>

[0050] The first surface treatment liquid (X) contains a silane coupling agent (A) having a glycidyl group. This silane coupling agent (A) is not particularly limited as long as it is a silane coupling agent in which a glycidyl group and a lower alkoxy group having 1 to 5 carbon atoms, preferably 1 to 3, as the hydrolyzable group are directly bonded to the Si element. Examples include 3-epoxypropoxypropyltrimethoxysilane, 3-epoxypropoxypropyltriethoxysilane, 3-epoxypropoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane. From the viewpoint that it is easier to generate more condensation points between the silane coupling agents (A) having glycidyl groups or with the tetraalkoxysilane (B) and zirconium carbonate compound (C) described later, thereby obtaining high barrier properties after film formation, 3-epoxypropoxypropyltrimethoxysilane and 3-epoxypropoxypropyltriethoxysilane are preferred.

[0051] In the silane coupling agent (A) with a glycidyl group, the alkoxy group is directly bonded to the Si element in the compound. This alkoxy group reacts with water in an aqueous solution to form a silanol group. This silanol group reacts with the surface of galvanized steel sheet or undergoes a complex condensation reaction with the tetraalkoxysilane (B) and zirconium carbonate compound (C) described later.

[0052] Solid composition mass (A) of silane coupling agent (A) with glycidyl group S The mass of solid components relative to the silane coupling agent (A) with glycidyl groups (A) S Solid composition mass of tetraalkoxysilane (B) S The equivalent mass of ZrO2 in zirconium carbonate (C) and zirconium carbonate compound (C) Z The total mass (X) SThe mass ratio of (A) S / X S The mass ratio (A) is 0.050–0.450. S / X S When the mass ratio (A) is less than 0.050, the corrosion resistance of the plate section, the machined section, and the corrosion resistance after alkali degreasing are poor. Therefore, the mass ratio (A) S / X S The mass ratio (A) is 0.050 or higher, preferably 0.060 or higher, and more preferably 0.090 or higher. On the other hand, the mass ratio (A) S / X S When the ratio (A) exceeds 0.450, the heat cracking resistance is poor. Therefore, the mass ratio (A) S / X S The value is 0.450 or less, preferably 0.380 or less, and more preferably 0.290 or less.

[0053] <Tetraalkoxysilane (B)>

[0054] If component (A) is used alone, the heat cracking resistance is poor; therefore, the first surface treatment solution (X) contains tetraalkoxysilane (B). Without component (B), in a heating atmosphere above 500°C, the carbon-carbon bonds of component (A) undergo thermal oxidation and decomposition, leading to large cracks. In contrast, by adding an appropriate amount of component (B), the amount of component (A) can be controlled to a level acceptable for heat cracking resistance, while simultaneously obtaining a dense and highly barrier film. Because the film obtained from components (A) and (B) is dense, cracks during heating can be minimized, preventing the formation of visually detectable cracks and resulting in excellent heat cracking resistance.

[0055] Tetraalkoxysilane (B) has four lower alkoxy groups that are hydrolyzable groups directly bonded to the Si element. There are no particular limitations as long as the compound is represented by the general formula Si(OR)4 (where R represents an alkyl group with 1 to 5 carbon atoms, either the same or different). Examples of tetraalkoxysilane (B) include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane, and more than one of them may be used. From the viewpoint that it is easier to generate more condensation points between tetraalkoxysilanes (B) and with components (A) and (C) described later, thereby obtaining high barrier properties after film formation, tetraethoxysilane and tetramethoxysilane are preferred.

[0056] In tetraalkoxysilane (B), the alkoxy group is directly bonded to the Si element in the compound. This alkoxy group reacts with water in an aqueous solution to form a silanol group. This silanol group reacts with the surface of galvanized steel sheet or undergoes a complex condensation reaction with component (A) or component (C) described later.

[0057] The solid composition mass of tetraalkoxysilane (B) (B S ) relative to the total mass (X) mentioned above S The mass ratio of (B) S / X S The value ranges from 0.010 to 0.190. In the mass ratio (B... S / X S When the mass ratio (B) is less than 0.010, the corrosion resistance of the plate section, the corrosion resistance of the machined section, and the corrosion resistance after alkali degreasing decrease. Therefore, the mass ratio (B) S / X S The mass ratio (B) is 0.010 or higher, preferably 0.020 or higher, and more preferably 0.030 or higher. On the other hand, the mass ratio (B) S / X S When the mass ratio (B) exceeds 0.190, the heat crack resistance decreases. Therefore, the mass ratio (B) S / X S The value is 0.190 or less, preferably 0.150 or less, and more preferably 0.110 or less.

[0058] Components (A) and (B) can be used separately as monomers, but it is preferable to add them to the first surface treatment solution (X) after a condensation reaction to form a low-condensation compound, which results in higher barrier properties after film formation. This low-condensation compound uses polysiloxane bonds formed by the condensation reaction of the silanol groups of components (A) and (B) as its main framework. These bonds can be composed entirely of alkoxy groups at the ends of the Si element, or a subset of the groups directly bonded to the Si element can be alkoxy groups.

[0059] The low-condensation compound obtained by the condensation reaction of components (A) and (B) preferably has a degree of condensation of 2 to 30, more preferably 2 to 10. If the degree of condensation is below 30, no white precipitate will form in the aqueous solution, and components (A) and (B) can be used stably. This low-condensation compound can be obtained by autoclaving components (A), (B), and the chelating agent described later at a reaction temperature of 1 to 70°C for about 10 minutes to 20 hours. Examples of chelating agents include hydroxycarboxylic acids such as malic acid, acetic acid, and tartaric acid; monocarboxylic acids; polycarboxylic acids such as dicarboxylic acids or tricarboxylic acids such as oxalic acid, malonic acid, succinic acid, citric acid, and adipic acid; and aminocarboxylic acids such as glycine, etc., and one or more of them can be used.

[0060] The condensation state of this low condensate can be determined using gel permeation chromatography (GPC), NMR, and FT-IR as described in JIS-K7252-4.

[0061] The chelating agent that stabilizes the low-condensation product functions during the hydrolysis reaction of the alkoxy groups of component (A) and component (B) via water and the chelating agent. While the rationale for the stabilizing effect of the chelating agent is not yet clear, it is believed to be achieved through the appropriate coordination of the chelating agent with the silanol groups generated by the hydrolysis reaction from components (A) and (B). That is, the appropriate coordination of the chelating agent with the silanol groups inhibits excessive condensation of components (A) and (B), thus resulting in a first surface treatment solution (X) with excellent storage stability. Furthermore, a stable first coating quality is also obtained after long-term storage of the first surface treatment solution (X).

[0062] Besides ensuring storage stability, chelating agents are also effective in ensuring the corrosion resistance of the first coating. The reason for this is not yet clear, but it is believed that the chelating agent is also ligated to the vanadium compound (E), which will be described later. If the first coating is exposed to a corrosive environment, the chelating agent ligated to the vanadium compound (E) dissolves along with the vanadium compound (E). It is thus believed that the condensation of components (A) and (B) without ligands occurs within the first coating, thereby further enhancing the barrier properties of the first coating and contributing to improved corrosion resistance.

[0063] <Zirconium carbonate compound (C)>

[0064] The first surface treatment solution (X) contains a zirconium carbonate compound (C). If the first surface treatment solution (X) contains a zirconium carbonate compound (C), a first coating that is not easily soluble in water can be obtained, improving the corrosion resistance and water stain resistance of the flat surface. Furthermore, by using it in combination with sodium silicate (D1) as described later, a first coating with particularly excellent long-term sweat resistance can be obtained.

[0065] The first coating containing the above components (A) to (C) typically possesses moderate hardness and flexibility, high barrier properties, and excellent corrosion resistance in the flat portion, the processed portion, and after alkali degreasing. The high barrier properties are due to the presence of hydroxyl groups in the zirconium carbonate compound (C) that form condensation points with silanol groups. Furthermore, the zirconium carbonate compound (C) generates zirconium oxide and zirconium hydroxide upon drying; therefore, even at temperatures exceeding 500°C, no visually detectable cracks are formed due to the dense coating of tetraalkoxysilane (B) and the zirconium carbonate compound (C), resulting in excellent resistance to heat cracking. Examples of zirconium carbonate compound (C) include salts of sodium, potassium, lithium, and ammonium zirconium carbonate, and one or more of these can be used. Among these, ammonium zirconium carbonate and potassium zirconium carbonate are preferred from the perspectives of film formation and water resistance.

[0066] The equivalent mass of ZrO2 in zirconium carbonate (C) Z ) relative to the total mass (X) mentioned above S The mass ratio of (C) Z / XS The mass ratio (C) is 0.460–0.910. Z / X S When the ratio (C) is less than 0.460, the barrier properties from zirconium carbonate compounds (C) are insufficient, and corrosion resistance decreases after alkali degreasing. Therefore, the mass ratio (C) Z / X S The mass ratio (C) is 0.460 or higher, preferably 0.580 or higher, and more preferably 0.630 or higher. On the other hand, the mass ratio (C) Z / X S When the mass ratio (C) exceeds 0.910, the hard component from the zirconium carbonate compound is excessive, resulting in poor coating adhesion. Therefore, the mass ratio (C) Z / X S The value is 0.910 or less, preferably 0.900 or less, and more preferably 0.870 or less.

[0067] <Sodium silicate (D1)>

[0068] The first surface treatment liquid (X) contains sodium silicate (D1). The sodium in sodium silicate (D1) is bonded to oxygen atoms in the SiO4 tetrahedra that break from the SiO4 network due to heat. Therefore, the recombination of the SiO4 network is prevented. Through this effect, the glass silicate is given fluidity, reducing its softening temperature from above 1700°C to 500°C to 700°C. In this invention, utilizing this effect, it is believed that when the first coating, containing components (A) to (C), which is hard and has a low coefficient of thermal expansion, is heated to above 500°C, the first coating is given fluidity, thereby achieving excellent heat crack resistance.

[0069] Although sodium silicate (D1) used in this invention is a highly water-soluble component, it has the ability to etch zinc. Therefore, during the process of the first surface treatment solution (X) contacting and drying the surface of the zinc-plated layer, the zinc ions dissolved in the first surface treatment solution (X) are immobilized into insoluble metal silicate salts, which helps to improve the adhesion of the first coating. Furthermore, the inventors discovered that if sodium silicate (D1) is used in conjunction with components (A) to (C) in the first surface treatment solution (X), it promotes the formation of a Si-enriched layer on the surface of the first coating. Moreover, the inventors found that long-term sweat resistance is improved by having this Si-enriched layer. This is presumably because the silanol groups in sodium silicate (D1), the silane coupling agent (A), the silanol groups in tetraalkoxysilane (B), and the hydroxyl groups in the zirconium carbonate compound (C) undergo condensation, incorporating sodium silicate (D1) and forming a denser network. In addition, under corrosive conditions, the sodium silicate (D1) immobilized in the first coating as described above dissolves moderately, and the pH operation that moves the surface of the zinc plating layer toward the alkaline side also helps to delay and inhibit the anodic reaction of zinc.

[0070] The sodium silicate (D1) used in this invention comprises SiO2 and Na2O, and the molar ratio of SiO2 / Na2O is preferably 1 to 4. By making the SiO2 / Na2O ratio 4 or less, an effect on heat crack resistance can be appropriately obtained. On the other hand, by making the SiO2 / Na2O ratio 1 or more, an effect on heat crack resistance can be ensured, and at the same time, the immobilization of sodium silicate (D1) in the first coating can be appropriately suppressed, thereby appropriately inhibiting the decrease in resistance to blackening, water stains, and long-term perspiration. Therefore, the SiO2 / Na2O ratio is preferably 1 or more, and more preferably 2 or more. Examples of sodium silicate (D1) satisfying the above requirements include, for example, sodium silicate No. 2, sodium silicate No. 3, etc., and one or more of them can be used.

[0071] Sodium silicate (D1) solid composition mass (D1) S ) relative to the total mass (X) mentioned above S The mass ratio of (D1) S / X S The ratio is 0.040 to 0.630. In the mass ratio (D1) S / X S When the coefficient of corrosion resistance (D1) is less than 0.040, the corrosion resistance of the plate section, the machined section, and the corrosion resistance after alkali degreasing decrease. Therefore, the mass ratio (D1) S / X S The mass ratio (D1) is 0.040 or higher, preferably 0.050 or higher. On the other hand, the mass ratio (D1) is... S / X S When the sodium silicate content exceeds 0.630, it becomes excessive, making immobilization in the first coating difficult, resulting in poor resistance to blackening, water staining, and long-term perspiration. Furthermore, the presence of a large amount of Na ions in the first surface treatment solution (X) reduces its storage stability. Therefore, the mass ratio (D1) S / X S The value should be 0.630 or less, preferably 0.470 or less.

[0072] <vanadium compounds (E)>

[0073] The first surface treatment solution (X) contains a vanadium compound (E). The vanadium compound (E) is uniformly dispersed in the first coating, but dissolves moderately under corrosive conditions, combining with zinc ions dissolved under corrosive conditions to form a dense passivation coating, thereby improving the corrosion resistance of the flat surface, the processed surface, and the corrosion resistance after alkali degreasing. Examples of the vanadium compound (E) include ammonium metavanadate, sodium metavanadate, vanadium acetylacetone, and vanadium acetylacetone oxide; one or more of these can be used.

[0074] The equivalent mass of V in vanadium compounds (E) V ) relative to the total mass (X) mentioned aboveS The solid composition mass of sodium silicate (D1) and sodium silicate (D1) S The total mass (X) S +D1 S The mass ratio of (E) V / (X) S +D1 S The ratio is 0.006 to 0.094. In the mass ratio (E... V / (X) S +D1 S When the ratio of zinc ions to zinc ions is less than 0.006, the passivation film formation effect is insufficient, thus reducing the corrosion resistance of the flat section, the processed section, and the corrosion resistance after alkali degreasing. Therefore, the mass ratio (E) V / (X) S +D1 S The mass ratio (E) is 0.006 or more, preferably 0.008 or more, and more preferably 0.012 or more. On the other hand, the mass ratio (E) V / (X) S +D1 S When the content exceeds 0.094, good resistance to blackening and water staining cannot be obtained. Furthermore, vanadium oxidation and discoloration occur when heated above 500°C, thus reducing heat resistance to discoloration. Therefore, the mass ratio (E) V / (X) S +D1 S The value is 0.094 or less, preferably 0.071 or less, and more preferably 0.047 or less.

[0075] <Molybdate compound (F)>

[0076] The first surface treatment liquid (X) contains a molybdate compound (F). The presence of the molybdate compound (F) improves resistance to blackening. Examples of molybdate compound (F) include molybdic acid, ammonium molybdate, sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate; in this invention, it is preferred to use one or more selected from these compounds.

[0077] The blackening phenomenon in galvanized coatings is believed to be due to the formation of oxygen-deficient zinc oxide when the coating is exposed to a high-temperature, high-humidity atmosphere. Molybdenum is a second transition metal with various valences, existing in the air as MoO2 or MoO3 by combining with oxygen. In this invention, MoO4 is used. 2－ Molybdates are used. It is believed that when molybdates are uniformly added to the first coating, they are reduced to molybdenum oxides such as MoO3 under a high-temperature, high-humidity atmosphere. This process is thought to moderately supply oxygen to the zinc on the zinc-plated surface, thus inhibiting the formation of oxygen-deficient zinc oxide. On the other hand, if excessive molybdates are added, corrosion resistance of the flat section, the machined section, and the post-alkali degreasing corrosion resistance cannot be obtained.

[0078] Mo equivalent mass (F) in molybdate compound (F) M ) relative to the total mass (X) mentioned above S The solid composition mass of sodium silicate (D1) and sodium silicate (D1) S The total mass (X) S +D1 S The mass ratio of (F) M / (X) S +D1 S The ratio is 0.030 to 0.280. (In the mass ratio (F)) M / (X) S +D1 S When the mass ratio (F) is less than 0.030, excellent resistance to blackening cannot be obtained. Therefore, the mass ratio (F) M / (X) S +D1 S The mass ratio (F) is 0.030 or higher, preferably 0.040 or higher, and more preferably 0.050 or higher. On the other hand, the mass ratio (F) M / (X) S +D1 S When the mass ratio (F) exceeds 0.280, good corrosion resistance of the flat section, the machined section, and the post-alkali degreasing corrosion resistance cannot be obtained. Therefore, the mass ratio (F) M / (X) S +D1 S The value is 0.280 or less, preferably 0.240 or less, and more preferably 0.190 or less.

[0079] <Phosphoric Acid Compounds (J)>

[0080] The first surface treatment solution (X) may contain a phosphate compound (J) to further improve the corrosion resistance of the first coating. The phosphate compound (J) dissolves moderately in a corrosive environment and combines with zinc ions dissolved in the corrosive environment to form a poorly soluble zinc phosphate coating, which covers coating defects, thereby improving the corrosion resistance of the flat part, the corrosion resistance of the machined part, and the corrosion resistance after alkali degreasing.

[0081] The phosphoric acid compound (J) can be at least one selected from inorganic phosphoric acid compounds and organic phosphoric acid compounds. Examples of inorganic phosphoric acid compounds include phosphoric acid, dihydrogen phosphate, hydrogen phosphate, phosphate; condensed phosphates such as pyrophosphate, pyrophosphate, tripolyphosphate, and tripolyphosphate; and phosphorous acid, phosphite, hypophosphoric acid, and hypophosphite. Examples of organic phosphoric acid compounds include phosphonic acid, diphosphonic acid, phosphonobutane tricarboxylic acid, ethylenediaminetetramethylenephosphonic acid, methyldiphosphonic acid, methylenephosphonic acid, ethylidene diphosphonic acid, and their ammonium salts and alkali metal salts. From the viewpoint that it is easier to form insoluble metal salts, inorganic phosphoric acid compounds such as phosphoric acid or ammonium dihydrogen phosphate are preferred for resistance to peeling of thin-film coatings. When using organic phosphoric acid compounds, from the viewpoint that they offer better resistance to water staining and storage stability of the first surface treatment solution (X), diphosphonic acid is preferred.

[0082] Solid content mass of phosphoric acid compound (J) S ) relative to the total mass (X) mentioned above S The mass ratio of (J) S / X S The preferred value is 0.140 to 0.770. This is achieved by adjusting the mass ratio (J) S / X S With a mass ratio (J) of 0.140 or higher, appropriate corrosion resistance can be obtained for the plate section, the machined section, and the section after alkali degreasing. Therefore, the mass ratio (J) S / X S The mass ratio (J) is preferably 0.140 or higher, more preferably 0.180 or higher, and even more preferably 0.280 or higher. On the other hand, by making the mass ratio (J) S / X S With a mass ratio (J) below 0.770, suitable properties such as heat resistance to discoloration, resistance to blackening, water resistance, long-term sweat resistance, and coating adhesion can be obtained. Therefore, the mass ratio (J) S / X S Preferably, the value is 0.770 or less, more preferably 0.720 or less, and even more preferably 0.660 or less.

[0083] <Fluorine compounds (K)>

[0084] The first surface treatment liquid (X) may contain a fluorine compound (K) for the purpose of further improving the adhesion between the first coating and the surface of the galvanized steel sheet. The fluorine compound (K) slightly etches the galvanized surface, forming fine irregularities on the surface of the galvanized layer, thereby improving adhesion through an anchoring effect.

[0085] From the viewpoint of suppressing excessive dissolution of the coating, examples of fluorine compounds (K) include hydrofluoric acid, fluorosilicic acid, ammonium fluoride, lithium fluoride, sodium fluoride, potassium fluoride, acidic ammonium fluoride, acidic sodium fluoride, acidic potassium fluoride, fluorotitanic acid, ammonium fluorotitanate, fluorozirconic acid, ammonium fluorozirconate, etc. In this invention, it is preferred to use one or more of them.

[0086] Mass of solid components of fluorine compound (K) S ) relative to the total mass (X) mentioned above S The mass ratio of (K) S / X S The preferred value is 0.040 to 0.610. This is achieved by adjusting the mass ratio (K) S / X S A K0.040 or higher can adequately achieve long-term perspiration resistance and coating adhesion. Therefore, a mass ratio (K0.040) is suitable. S / X S The mass ratio (K) is preferably 0.040 or higher, more preferably 0.050 or higher, and even more preferably 0.080 or higher. On the other hand, by making the mass ratio (K)... S / X S With a mass ratio (K) below 0.610, appropriate corrosion resistance of the plate section, corrosion resistance of the machined section, corrosion resistance after alkali degreasing, resistance to blackening, and resistance to water stains can be obtained. Therefore, the mass ratio (K) S / X S Preferably, the content is 0.610 or less, more preferably 0.450 or less, and even more preferably 0.300 or less.

[0087] <pH 8.0–10.0>

[0088] The first surface treatment solution (X) can be obtained by mixing the above-mentioned components in water such as deionized water or distilled water. The solid component ratio of the first surface treatment solution (X) can be appropriately selected, preferably 5 to 20% by mass. In addition, the pH of the first surface treatment solution (X) is preferably 8.0 to 10.0. If the pH of the first surface treatment solution (X) is 8.0 or higher, the storage stability of the first surface treatment solution (X) can be appropriately obtained. Therefore, the pH of the first surface treatment solution (X) is preferably 8.0 or higher, more preferably 8.5 or higher. On the other hand, if the pH of the first surface treatment solution (X) is 10.0 or lower, the storage stability of the first surface treatment solution (X) can be appropriately obtained, and the etching of the zinc plating layer is appropriate, and the corrosion resistance of the plate portion, the corrosion resistance of the processed portion, and the corrosion resistance after alkali degreasing can be appropriately obtained. Therefore, the pH of the first surface treatment solution (X) is preferably 10.0 or lower, more preferably 9.5 or lower. It should be noted that when adjusting the pH, ammonia or its salt and any one or more of the above-mentioned chelating agents can be appropriately used.

[0089] Furthermore, alcohols, ketones, cellosolves, amine-based water-soluble solvents, defoamers, antibacterial and antifungal agents, colorants, wettability improvers for uniform coating, resins, surfactants, and other additives may be added to the first surface treatment liquid (X) as needed. However, it is important that these additives be added to a degree that does not impair the quality obtained in this invention, and the amount added is preferably no more than 5% by mass relative to the total solid content of the first surface treatment liquid (X).

[0090] Furthermore, the first surface treatment liquid (X) may contain trace amounts of at least one of the anionic polyurethane resin (G), silicone resin (H), crosslinking agent (I), and wax (L) contained in the second surface treatment liquid (Y), which will be described later. In this case, if the total mass of their solid components is 30% by mass or less relative to the total solid content of the first surface treatment liquid (X), the quality obtained in the present invention will not be impaired. Therefore, when the first surface treatment liquid (X) contains any one or more of the anionic polyurethane resin (G), silicone resin (H), crosslinking agent (I), and wax (L), the total mass of their solid components is preferably 30% by mass or less relative to the total solid content of the first surface treatment liquid (X), more preferably 20% by mass or less, further preferably 10% by mass or less, and most preferably 5% by mass or less.

[0091] [Second surface treatment liquid (Y)]

[0092] The second surface treatment liquid (Y) contains sodium silicate (D2), anionic polyurethane resin (G) and water, and may further contain one or more selected from silicone resin (H), crosslinking agent (I) and wax (L) as needed.

[0093] <Sodium silicate (D2)>

[0094] The second surface treatment solution (Y) contains sodium silicate (D2). Sodium silicate (D2) enhances the adhesion between the second and first coatings through its silanol groups, contributing to long-term sweat resistance. Furthermore, when used in conjunction with the anionic polyurethane resin (G) described later, the high cohesiveness of the urethane bonds in the anionic polyurethane resin (G) introduces sodium silicate (D2) into a dense and highly barrier polyurethane resin coating. Under corrosive conditions, the sodium silicate (D2) immobilized in the second coating as described above dissolves moderately, and the pH operation, which shifts the surface of the zinc plating layer towards the alkaline side, also helps to delay and inhibit the anodic reaction of zinc.

[0095] The sodium silicate (D2) used in this invention comprises SiO2 and Na2O, and the molar ratio of SiO2 / Na2O is preferably 1 to 4. By making the SiO2 / Na2O ratio 4 or less, an effect on heat crack resistance can be appropriately obtained. On the other hand, by making the SiO2 / Na2O ratio 1 or more, an effect on heat crack resistance can be ensured, and at the same time, the immobilization of sodium silicate (D2) in the second coating can be appropriately suppressed, thereby appropriately inhibiting the decrease in resistance to blackening, water stains, and long-term perspiration. Therefore, the SiO2 / Na2O ratio is preferably 1 or more, and more preferably 2 or more. Examples of sodium silicate (D2) satisfying the above requirements include sodium silicate No. 2 and sodium silicate No. 3, and one or more of them can be used.

[0096] It should be noted that the sodium silicate (D1) in the first surface treatment solution (X) and the sodium silicate (D2) in the second surface treatment solution (Y) can be the same or different. In order to effectively improve long-term sweat resistance, it is effective to laminate films with different constituent components. Therefore, it is preferable that the sodium silicate (D1) in the first surface treatment solution (X) and the sodium silicate (D2) in the second surface treatment solution (Y) are different.

[0097] Sodium silicate (D2) solid composition mass (D2) S The mass of solids relative to anionic polyurethane resin (G) (G) S The mass ratio of (D2) S / G S The value is 0.010 to 0.100. In the mass ratio (D2) S / G S When the ratio (D2) is less than 0.010, the corrosion resistance of the plate section and its corrosion resistance after alkali degreasing decrease. Therefore, the mass ratio (D2) S / G S The value is 0.010 or higher. On the other hand, the mass ratio (D2) is... S / G S When the concentration of sodium silicate (D2) exceeds 0.100, excess sodium silicate (D2) makes immobilization in the second coating difficult, resulting in poor resistance to blackening, water stains, and long-term perspiration. Furthermore, the presence of a large amount of Na ions in the second surface treatment solution (Y) reduces its storage stability. Therefore, the mass ratio (D2)... S / G S The value is 0.100 or less, preferably 0.070 or less, and more preferably 0.050 or less.

[0098] <Anionic polyurethane resin (G)>

[0099] The second surface treatment liquid (Y) contains anionic polyurethane resin (G) with excellent barrier properties against sweat components. This results in a denser second coating, contributing to improved long-term sweat resistance. The polyurethane resin has a high molecular weight, and the urethane bonds exhibit high intermolecular cohesion, thus resulting in a dense and highly barrier material. Furthermore, it exhibits excellent adhesion to the first coating, thereby yielding a second coating with the aforementioned superior properties.

[0100] The types of polyols that form the basic framework and influence the properties of urethane resins include polyether polyols, polyester polyols, and polycarbonate polyols. Polyester and polycarbonate polyols possess polar groups, thus achieving a strong and tough second coating through intermolecular interactions. Polycarbonate polyols are expensive but offer excellent mechanical strength. Polyether polyols lack polar groups, resulting in slightly lower mechanical strength, but they are chemically stable, exhibiting good hydrolysis resistance. The second surface treatment solution (Y) can use anionic polyurethane resin (G) alone or in combination of two or more types.

[0101] The weight-average molecular weight of the anionic polyurethane resin (G) is not particularly limited, but when determined by gel permeation chromatography as described in JIS-K7252-4, it is preferably around 5,000 to 500,000, and more preferably around 10,000 to 300,000. Increasing the weight-average molecular weight can improve the Tg and mechanical properties of the urethane resin, thus improving the barrier properties of the second film and further enhancing the corrosion resistance of the plate portion, corrosion resistance after alkali degreasing, water stain resistance, long-term perspiration resistance, and solvent resistance.

[0102] Anionic polyurethane resin (G) is obtained from polyols such as polyester polyols, polyether polyols, and polycarbonate polyols, and polyisocyanates, through conventional synthetic methods. This is not a limiting explanation, but a more specific synthesis can be achieved by producing a urethane prepolymer with isocyanate groups at both ends from polyols and polyisocyanates, reacting it with a carboxylic acid with two hydroxyl groups or its reactive derivative in a solvent to produce a derivative with isocyanate groups at both ends, then adding triethanolamine or similar antications, and finally adding it to water to form an emulsion, thus obtaining the anionic polyurethane resin. Then, if necessary, diamine can be added for chain extension.

[0103] Polyisocyanates used in the manufacture of anionic polyurethane resins (G) include aliphatic, alicyclic, and aromatic polyisocyanates. Specifically, examples include tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, hydrogenated xylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, benzene diisocyanate, xylene diisocyanate, and tetramethylxylene diisocyanate. Among them, when using aliphatic or alicyclic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, hydrogenated xylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, and isophorone diisocyanate, a second coating film with excellent corrosion resistance of the flat part, corrosion resistance after alkali degreasing, solvent resistance, and heat discoloration resistance can be obtained, which is therefore preferred.

[0104] Examples of polyester polyols used in the manufacture of anionic polyurethane resins (G) include various polyester polyols obtained by the dehydration condensation reaction of diols or triols such as ethylene glycol, diethylene glycol, and trimethylolpropane with dicarboxylic acids such as adipic acid and phthalic anhydride; and lactone-based polyester polyols obtained by the ring-opening polymerization of ε-caprolactam.

[0105] Examples of polyether polyols used in the manufacture of anionic polyurethane resins (G) include low molecular weight polyols such as 1,2-propanediol, 1,3-propanediol, trimethylolpropane, glycerol, polyglycerol, and pentaerythritol. Other examples include ethylene oxide and / or propylene oxide adducts of amine compounds such as bisphenol A and ethylenediamine, and polytetramethylene ether glycol.

[0106] Examples of polycarbonate polyols used in the manufacture of anionic polyurethane resins (G) include substances obtained by reacting diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, methylpentyl glycol, dimethylbutanediol, butyl ethyl propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,4-butanediol, 1,4-cyclohexanediol, and 1,6-hexanediol with diphenyl carbonate, phosgene, etc.

[0107] In the manufacture of anionic polyurethane resin (G), a carboxylic acid having two or more, preferably two hydroxyl groups, or a reactive derivative thereof, is used to introduce an acidic group into component (G) and to make component (G) water-dispersible. Examples of such carboxylic acids include dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvalerate, dimethylolhexanoic acid, and other dimethylolalkyl acids. Examples of reactive derivatives include acid anhydrides. In this way, by making component (G) self-dispersible in water and minimizing or completely eliminating the use of emulsifiers, a second film with excellent water resistance can be obtained.

[0108] Polyamines or water are used in the manufacture of anionic polyurethane resin (G). These polyamines or water are used to extend the chains of the modified prepolymer. Examples of polyamines used in the manufacture of anionic polyurethane resin (G) include hydrazine, ethylenediamine, propylenediamine, 1,6-hexanediamine, tetramethylenediamine, isophoronediamine, xylenediamine, piperazine, 1,1'-bicyclohexane-4,4'-diamine, diphenylmethanediamine, ethyltoluenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, etc., and they can be used alone or in combination.

[0109] To improve the stability of the anionic polyurethane resin (G) during synthesis and its film-forming properties when the surrounding environment is under low-temperature drying conditions, it is preferable to incorporate a film-forming aid during synthesis. Examples of film-forming aids include butyl cellosolve, N-methyl-2-pyrrolidone, butyl carbitol, and Texanol, with N-methyl-2-pyrrolidone being the most preferred.

[0110] The glass transition temperature (Tg) of the anionic polyurethane resin (G) is preferably 30 to 130°C. If the glass transition temperature (Tg) is 30°C or higher, the reduction in the barrier properties of the second coating can be suppressed, resulting in sufficient solvent resistance. Therefore, the glass transition temperature (Tg) of the anionic polyurethane resin (G) is preferably 30°C or higher, more preferably 50°C or higher. On the other hand, if the glass transition temperature (Tg) of the anionic polyurethane resin (G) is 130°C or lower, the second coating is prevented from becoming too hard, and cracks are less likely to occur during processing, thus achieving excellent coating adhesion. Therefore, the glass transition temperature (Tg) of the anionic polyurethane resin (G) is preferably 130°C or lower, more preferably 110°C or lower. It should be noted that the glass transition temperature can be adjusted according to the molecular weight, etc., of the polyol used.

[0111] It should be noted that the glass transition temperature (Tg) of anionic polyurethane resin (G) can be determined using a dynamic viscoelasticity measuring device (RSAG2, TA Instrument). The test sample is a film prepared by drying at room temperature for 24 hours, drying at 80°C for 6 hours, and then drying at 120°C for 20 minutes. The dynamic viscoelasticity is then measured and determined from the maximum value of tanδ.

[0112] Solid content mass of anionic polyurethane resin (G) S The mass of solid components relative to the second surface treatment liquid (Y) S The mass ratio of (G) S / Y S The mass ratio (G) is 0.900–0.980. S / Y S When the mass ratio (G) is less than 0.900, the amount of anionic polyurethane resin (G) is low, resulting in poor long-term perspiration resistance, reduced resistance to blackening, and decreased resistance to water stains. Therefore, the mass ratio (G) S / Y S The mass ratio (G) is 0.900 or higher, preferably 0.930 or higher, and more preferably 0.950 or higher. On the other hand, the mass ratio (G) S / Y S When the mass ratio (G) exceeds 0.980, the amount of sodium silicate (D2) decreases relatively, thus reducing the adhesion between the second and first films, and also reducing the corrosion resistance of the processed part and the corrosion resistance after alkali degreasing. Therefore, the mass ratio (G) S / Y S The value is below 0.980.

[0113] In the second surface treatment liquid (Y), the anionic polyurethane resin (G) preferably contains an anionic polyurethane resin with a carbonate backbone. Anionic polyurethane resins with a carbonate backbone have small interstitial spaces due to the high cohesive force of the carbonate bonds, thus exhibiting excellent barrier properties against the permeation of sweat components or corrosive agents, and are less prone to hydrolysis. Therefore, a second coating is obtained that is not easily degraded in high-temperature and high-humidity environments and can maintain excellent long-term sweat resistance and corrosion resistance. Particularly from the viewpoint of improving long-term sweat resistance, a combination of polyether-based polyols and polycarbonate-based polyols is preferred as the anionic polyurethane resin (G).

[0114] The solids content mass of anionic polyurethane resin with a carbonate backbone relative to the solids content mass of anionic polyurethane resin (G) (G) SThe mass ratio of the components is preferably 0.20 to 0.80. By setting the mass ratio to 0.20 or higher, suitable long-term sweat resistance can be obtained. Therefore, the mass ratio is preferably 0.20 or higher, more preferably 0.30 or higher. On the other hand, by setting the mass ratio to 0.80 or lower, suitable solvent resistance can be obtained. Therefore, the mass ratio is preferably 0.80 or lower, more preferably 0.70 or lower.

[0115] <Organosilicon resin (H)>

[0116] The second surface treatment liquid (Y) may further contain silicone resin (H). This results in a second coating with superior resistance to water stains and long-term perspiration. The silicone resin (H) is not particularly limited as long as it has multiple siloxane bonds and an organopolysiloxane structure with organic groups bonded to silicon (Si), but preferably has an organopolysiloxane structure with at least two organic groups bonded to Si in one molecule. It should be noted that there are no particular limitations on the position of the organic groups; they can be bonded to the main chain, side chain, or end. The silicone resin (H) can be a monomer with the above-mentioned organopolysiloxane structure, a mixture of a monomer with the above-mentioned organopolysiloxane structure and a monomer with a polysiloxane structure, or a copolymer (block copolymer or graft polymer) with the above-mentioned organopolysiloxane structure and a polysiloxane structure. Furthermore, the silicone resin (H) can be addition-type or condensation-type. Additionally, the silicone resin (H) can be any one of thermosetting, room temperature curing (RTV), or UV curing types.

[0117] Mass of solids component of silicone resin (H) S The mass of solids relative to anionic polyurethane resin (G) (G) S The mass ratio of (H) S / G S The preferred value is 0.0030 to 0.0400. This is achieved by adjusting the mass ratio (H) S / G S A mass ratio (H) of 0.0030 or higher yields excellent water and oil resistance, and can appropriately improve resistance to water stains and long-term sweat resistance. Therefore, the mass ratio (H) S / G S The mass ratio (H) is preferably 0.0030 or higher, more preferably 0.0040 or higher. On the other hand, by making the mass ratio (H)... S / G S When the concentration is below 0.0400, the oil resistance will not be too high, and appropriate coating adhesion can be achieved. Therefore, the mass ratio (H) S / G S The value is preferably 0.0400 or less, and more preferably 0.0320 or less.

[0118] <Crosslinking agent (I)>

[0119] The second surface treatment liquid (Y) may contain a crosslinking agent (I) that reacts with carboxyl groups to further improve the corrosion resistance of the processed portion of the second coating. The second coating contains carboxyl groups present in the anionic polyurethane resin (G), and the crosslinking agent (I) undergoes a crosslinking reaction with them, thereby modifying the organic components of the second coating. That is, a second coating with high barrier and flexibility is formed, suppressing cracks in the second coating even during bending processes, thereby improving the corrosion resistance of the bent portion. As the crosslinking agent (I), it is preferably a compound having two or more functional groups capable of reacting with carboxyl groups in one molecule. Examples of functional groups capable of reacting with carboxyl groups include epoxy groups, carbodiimide groups, etc. Azoline group. Examples of crosslinking agents (I) include epoxy resins, carbodiimide resins, and resins containing... Polymers with zoline groups are preferred, preferably selected from one or more of them.

[0120] The mass of solid components of crosslinking agent (I) S The mass of solids relative to anionic polyurethane resin (G) (G) S The mass ratio of (I) S / G S The preferred value is 0.0030 to 0.0400. This is achieved by adjusting the mass ratio (I...) S / G S When the mass ratio (I) is above 0.0030, the corrosion resistance and solvent resistance of the processed parts can be appropriately improved. Therefore, the mass ratio (I) S / G S The mass ratio (I) is preferably 0.0030 or higher, more preferably 0.0040 or higher. On the other hand, by making the mass ratio (I) S / G S When the concentration is below 0.0400, appropriate corrosion resistance can be obtained for the plate section, the machined section, the corrosion resistance after alkali degreasing, and the solvent resistance. Therefore, the mass ratio (I) S / G S The value is preferably 0.0400 or less, and more preferably 0.0320 or less.

[0121] <Wax (L)>

[0122] To improve the lubricity of the second coating surface, the second surface treatment liquid (Y) may contain a wax (L). There are no particular limitations on the type of wax (L) as long as it is compatible with the second surface treatment liquid (Y). Examples of suitable waxes include polyolefin waxes such as polyethylene, lignite wax, paraffin wax, microcrystalline wax, carnauba wax, lanolin wax, silicone wax, and fluorinated wax; one or more of these can be used appropriately. Furthermore, examples of polyolefin waxes include polyethylene wax, oxidized polyethylene wax, and polypropylene wax; one or more of these can be used.

[0123] Mass of solid components of wax (L) S The mass of solid components relative to the second surface treatment liquid (Y) S The mass ratio of (L) S / Y S The preferred value is 0.010 to 0.120. This is achieved by adjusting the mass ratio (L...) S / Y S When the mass ratio (L) is 0.010 or higher, the lubricity of the second film surface can be appropriately improved. Therefore, the mass ratio (L) S / Y S The preferred value is 0.010 or higher. On the other hand, by making the mass ratio (L...)... S / Y S With a viscosity of 0.120 or less, the lubricity is not excessive, which can appropriately prevent the steel coil from being flattened during the coiling process in steel coil manufacturing. Furthermore, appropriate corrosion resistance of the processed parts and coating adhesion can be obtained. Therefore, the mass ratio (L) S / Y S Preferably, the value is 0.120 or less, and more preferably 0.090 or less.

[0124] The second surface treatment solution (Y) can be obtained by mixing the above components in water such as deionized water or distilled water. The proportion of solid components in the second surface treatment solution (Y) can be appropriately selected, preferably 5% to 20% by mass. In addition, the pH of the second surface treatment solution (Y) is not particularly limited, but preferably 9.8 to 10.8.

[0125] Furthermore, alcohols, ketones, cellosolves, amine-based water-soluble solvents, defoamers, antibacterial and antifungal agents, colorants, wettability improvers for uniform coating, resins, surfactants, and other additives may be added to the second surface treatment liquid (Y) as needed. However, it is important that these additives be added to a degree that does not impair the quality obtained in this invention, and the amount added is preferably no more than 5% by mass relative to the total solid content of the second surface treatment liquid (Y).

[0126] (Manufacturing method of galvanized steel sheet with surface treatment coating)

[0127] A method for manufacturing a galvanized steel sheet with a surface-treated coating according to one embodiment of the present invention is a method for manufacturing a galvanized steel sheet with a surface-treated coating using the above-described surface treatment liquid for galvanized steel sheets. The method includes: a step of coating a first surface treatment liquid (X) onto the surface of the galvanized steel sheet; a step of drying the coated first surface treatment liquid (X) to form a first coating; a step of coating a second surface treatment liquid (Y) onto the surface of the first coating; and a step of drying the coated second surface treatment liquid (Y) to form a second coating. The formation conditions and methods for the first and second coatings will be described in detail below.

[0128] Before applying the first surface treatment liquid (X) to the surface of the galvanized steel sheet, a pretreatment can be performed as needed to remove oil or dirt from the surface of the galvanized steel sheet. Most galvanized steel sheets are coated with rust-preventive oil for rust prevention; however, even without rust-preventive oil, oil or dirt may adhere during operation. By performing the aforementioned pretreatment, the surface of the galvanized steel sheet is cleaned and easily and evenly wetted. If the surface of the galvanized steel sheet is free of oil or dirt and is evenly wetted by the first surface treatment liquid (X), a pretreatment step is not particularly necessary. It should be noted that the pretreatment method is not particularly limited; for example, hot water washing, organic solvent cleaning, and alkaline degreasing cleaning can be used.

[0129] As for the methods of applying the first surface treatment liquid (X) to the surface of the galvanized steel sheet and applying the second surface treatment liquid (Y) to the surface of the first coating, the optimal method can be selected appropriately according to the shape of the galvanized steel sheet being treated. Examples include roller coating, bar coating, dipping, and spraying. In addition, the coating amount, appearance uniformity, and film thickness uniformity can be achieved after coating by air knife method or roller pressing method.

[0130] As a means of drying the first surface treatment liquid (X) after it has been applied to the surface of a galvanized steel sheet, in addition to a dryer, a drying oven such as a hot air furnace, a high-frequency induction heating furnace, and an infrared furnace can also be used.

[0131] The peak metal temperature (PMT) during drying of the first surface treatment solution (X) is preferably 40–100°C. By setting the peak metal temperature to 40°C or higher, the condensation reaction of the Si component contained in the first surface treatment solution (X) proceeds appropriately, resulting in a denser Si-enriched layer. On the other hand, by setting the peak metal temperature to 100°C or lower, cracks in the first coating can be appropriately suppressed.

[0132] The heating time during the drying of the first surface treatment liquid (X) is selected according to the composition of the galvanized steel sheet used, the process and structure of the production line, etc., and the optimal conditions are appropriately selected. From the viewpoint of productivity, it is preferably 0.1 to 60 seconds, and more preferably 1 to 30 seconds.

[0133] The preferred amount of the first film after drying is 0.010–0.400 g / m² per single side. 2 More preferably, it is 0.030–0.250 g / m 2 By making the amount of the first coating 0.010 g / m 2 The above provides appropriate barrier properties, corrosion resistance of the flat portion, corrosion resistance after alkali degreasing, resistance to blackening, long-term sweat resistance, and water stain resistance. On the other hand, by setting the adhesion amount of the first coating to 0.400 g / m... 2 The following applies: if the thickness of the first coating is appropriate, heat resistance to discoloration and heat resistance to cracking can be obtained appropriately.

[0134] As a means of drying the second surface treatment liquid (Y) after it has been applied to the surface of the first film, in addition to a dryer, a drying oven such as a hot air furnace, a high-frequency induction heating furnace, and an infrared furnace can also be used.

[0135] Here, the maximum plate temperature reached during the drying of the second surface treatment liquid (Y) is preferably 60–200°C, more preferably 80–180°C. If the maximum plate temperature reaches 60°C or higher, bonding between the components of the second coating can be achieved, and the various properties required by the present invention can be appropriately obtained. On the other hand, if the maximum plate temperature reaches 200°C or lower, cracks in the second coating or thermal decomposition of the coating components are less likely to occur, and the various properties required by the present invention can be appropriately obtained.

[0136] The heating time during the drying of the second surface treatment liquid (Y) is selected according to the composition of the galvanized steel sheet used, the process and structure of the production line, etc., and the optimal conditions are appropriately selected. From the viewpoint of productivity, it is preferably 0.1 to 60 seconds, and more preferably 1 to 30 seconds.

[0137] The amount of the second film after drying is preferably 0.20–3.00 g / m² per single side. 2 More preferably, it is 0.40–2.00 g / m 2 By making the amount of the second film attached 0.20 g / m 2 The above provides sufficient barrier properties, appropriately achieving good corrosion resistance of the flat portion, corrosion resistance after alkali degreasing, long-term sweat resistance, and water stain resistance. On the other hand, by achieving an adhesion amount of 3.00 g / m² for the second coating... 2 The following properties can be appropriately obtained: heat resistance to discoloration, heat resistance to cracking, and coating adhesion.

[0138] It should be noted that conventional methods can be used for any steps or conditions not described in this invention.

[0139] (Galvanized steel sheet with surface treatment coating)

[0140] One embodiment of the present invention provides a galvanized steel sheet with a surface treatment coating, which is a galvanized steel sheet with a surface treatment coating manufactured by the above-described manufacturing method, having a galvanized steel sheet and a surface treatment coating formed on at least one side of the galvanized steel sheet.

[0141] [Galvanized steel sheet]

[0142] The galvanized steel sheet used in this invention can be electro-galvanized steel sheet, hot-dip galvanized steel sheet, zinc-aluminum alloy coated steel sheet, zinc-iron alloy coated steel sheet, zinc-magnesium alloy coated steel sheet, zinc-aluminum-magnesium alloy coated steel sheet, etc.

[0143] Further preferred is a hot-dip Zn-Al alloy steel sheet having a hot-dip Zn-Al alloy coating on at least one surface of a base steel sheet serving as a substrate. This hot-dip Zn-Al alloy coating contains, by mass percent, Al: 3.0–12.0%, Mg: 0.2–6.0%, and Ni: 0.0–0.1%, with the remainder consisting of Zn and unavoidable impurities. Using this hot-dip Zn-Al alloy steel sheet offers superior resistance to red rust compared to other coated steel sheets. Therefore, it is advantageous for use in harsher corrosive environments such as outdoors. It should be noted that the hot-dip Zn-Al alloy coating may not contain Ni, but by containing less than 0.1% by mass of Ni, suitable resistance to blackening can be obtained, and this is therefore preferred. More preferably, the hot-dip Zn-Al alloy steel sheet contains a Zn-Al-Mg ternary eutectic in the hot-dip Zn-Al alloy coating. The Zn-Al-Mg ternary eutectic preferably contains 1-50% by the area ratio of the coating surface.

[0144] [Surface treatment coating]

[0145] The surface treatment coating of the present invention comprises a first coating on a galvanized steel sheet and a second coating on the first coating. The first coating is obtained by applying the first surface treatment liquid (X) to the surface of the galvanized steel sheet and drying it. The second coating is obtained by applying the second surface treatment liquid (Y) to the surface of the first coating and drying it. The galvanized steel sheet with the surface treatment coating of this embodiment exhibits excellent heat resistance to discoloration, heat resistance to cracking, corrosion resistance of the flat portion, corrosion resistance of the processed portion, corrosion resistance after alkali degreasing, resistance to blackening, water stain resistance, solvent resistance, long-term sweat resistance, and coating adhesion.

[0146] Importantly, the surface-treated coating has a Si-enriched layer on the outermost layer of the first coating and a second coating mainly composed of resin. During the drying stage, the Zr component of the first coating bonds earlier than the Si component, thus creating regions where the Si component enters the network structure of the Zr component and regions where the Si component is enriched. Because the anionic polyurethane resin itself has high barrier properties against sweat components and contains sodium silicate, the second coating bonds firmly to the first coating with the Si-enriched layer, thus significantly improving long-term sweat resistance.

[0147] Example

[0148] The effects of the present invention will be illustrated below through examples and comparative examples. However, these examples are merely illustrative of the present invention and do not limit the present invention.

[0149] (1) Test plate

[0150] Table 1 shows the various galvanized steel sheets used as test plates. It should be noted that the galvanized coating is formed on both sides of the steel sheet (base steel sheet), and the adhesion amount in Table 1 refers to the adhesion amount of the galvanized coating on each single side.

[0151]

[0152] (2) Pretreatment (cleaning)

[0153] The surface of the test panels was treated with Finecleaner E6406 (manufactured by Nihon Parkerizing Co., Ltd.) to remove oil or dirt. Next, the panels were rinsed with tap water until 100% wet, then rinsed with deionized water and dried in an oven at 100°C.

[0154] (3) Preparation of surface treatment solution

[0155] The components shown in Table 2 were mixed in water at their respective proportions (mass ratios) as shown in Table 2 to obtain a first surface treatment solution (X) with a solid content of 6% by mass. The components shown in Table 3 were mixed in water at their respective proportions (mass ratios) as shown in Table 3 to obtain a second surface treatment solution (Y) with a solid content of 15% by mass.

[0156] The components shown in Table 4 were mixed in water at their respective proportions (mass ratios) as shown in Table 4 to obtain first surface treatment liquids X48 to X50 with a solid content of 6% by mass. It should be noted that first surface treatment liquids X48 and X49 assume that the components contained in the first surface treatment liquid (X) and the second surface treatment liquid (Y) of the present invention are contained in one surface treatment liquid. In particular, X49 has the same composition as the surface treatment liquid disclosed in Patent Document 1. Furthermore, X50 contains 30% by mass of anionic polyurethane resin (G4) relative to the total solid content of X50 in the first surface treatment liquid X1 in Table 2. It should be noted that in Table 4, the total mass (X) is as described in Patent Document 1. S The mass of solids relative to anionic polyurethane resin (G) (G) S The mass ratio of (X) S / G S ).

[0157] The compounds used in Tables 2 to 4 are described below.

[0158] <Silane coupling agent with glycidyl group (A)>

[0159] A1: 3-Epoxypropoxypropyltriethoxysilane

[0160] A2: 3-Epoxypropoxypropyltrimethoxysilane

[0161] <Tetraalkoxysilane (B)>

[0162] B1: Tetraethoxysilane

[0163] B2: Tetramethoxysilane

[0164] <Zirconium carbonate compound (C)>

[0165] C1: Ammonium zirconium carbonate (ZrO2: 20.0% by mass)

[0166] C2: Potassium zirconium carbonate (ZrO2: 20.0% by mass)

[0167] <Sodium silicate (D1, D2)>

[0168] D-1: Sodium silicate No. 3 (solid content: 38.5% by mass)

[0169] D-2: Sodium silicate No. 2 (solid content: 40.6% by mass)

[0170] <vanadium compounds (E)>

[0171] E1: Vanadyl acetylacetone (V: 19.2% by mass)

[0172] E2: Ammonium metavanadate (V: 43.5% by mass)

[0173] <Molybdate compound (F)>

[0174] F1: Ammonium molybdate (Mo: 54.4% by mass)

[0175] F2: Sodium molybdate (Mo: 43.8% by mass)

[0176] <Anionic polyurethane resin (G)>

[0177] Method for manufacturing anionic polyurethane resin (G1)

[0178] 100 parts by mass of a polyether polyol with a number average molecular weight of 5000 obtained from polyethylene glycol and polypropylene glycol, 5 parts by mass of 2,2-dimethyl-1,3-propanediol, 100 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 20 parts by mass of 2,2-dimethylolpropionic acid, and 120 parts by mass of N-methyl-2-pyrrolidone were added to a reactor to obtain a urethane prepolymer with a free isocyanate group content of 5% relative to the solids content. Next, 16 parts by mass of tetramethylenediamine and 10 parts by mass of triethylamine were added to 500 parts by mass of deionized water, and the above urethane prepolymer was emulsified and dispersed while stirring with a homogenizer. Finally, deionized water was added to obtain a water-dispersible anionic polyurethane resin (G1) with a solids content of 25% by mass. In the anionic polyurethane resin (G1), the solids content of the anionic polyurethane resin with a carbonate backbone is relative to the solids content of the anionic polyurethane resin (G1) (G S The mass ratio of ) is 0.4. It should be noted that the glass transition temperature (Tg) of the obtained anionic polyurethane resin (G1) was determined using a dynamic viscoelasticity measuring device, and the result was 95℃.

[0179] Method for manufacturing anionic polyurethane resin (G2)

[0180] In the reactor, 20 parts by mass of 1,4-butanediol-2-sulfonic acid were used instead of 20 parts by mass of 2,2-dimethylolpropionic acid. Otherwise, an anionic polyurethane resin (G2) with a solid content of 25% by mass was obtained in the same manner as that used to manufacture the anionic polyurethane resin (G1). In the anionic polyurethane resin (G2), the solid content mass of the anionic polyurethane resin having a carbonate backbone relative to the solid content mass of the anionic polyurethane resin (G2) (G... S The mass ratio of ) is 0.3. It should be noted that the glass transition temperature (Tg) of the obtained anionic polyurethane resin (G2) was determined using a dynamic viscoelasticity measuring device, and the result was 95℃.

[0181] Method for manufacturing anionic polyurethane resin (G3)

[0182] In the reactor, 100 parts by mass of a polyester polyol with a number-average molecular weight of 2220, obtained from 1,6-hexanediol and adipic acid, were used instead of 100 parts by mass of a polyether polyol with a number-average molecular weight of 5000, obtained from polyethylene glycol and polypropylene glycol. Otherwise, a water-dispersible anionic polyurethane resin (G3) with a solids content of 25% by mass was obtained in the same manner as that used in the manufacture of anionic polyurethane resin (G1). In the anionic polyurethane resin (G3), the solids content of the anionic polyurethane resin having a carbonate backbone is relative to the solids content of the anionic polyurethane resin (G3) (G... S The mass ratio of the two components is 0.5. It should be noted that the glass transition temperature (Tg) of the obtained anionic polyurethane resin (G3) was determined using a dynamic viscoelasticity measuring device, and the result was 70°C.

[0183] Method for manufacturing anionic polyurethane resin (G4)

[0184] In the reactor, 100 parts by mass of a polyether polyol with a number average molecular weight of 1560 obtained from polyethylene glycol and polypropylene glycol were used instead of 100 parts by mass of a polyether polyol with a number average molecular weight of 5000 obtained from polyethylene glycol and polypropylene glycol. Otherwise, a water-dispersible anionic polyurethane resin (G4) with a solid content of 25% by mass was obtained in the same manner as the manufacturing method of the anionic polyurethane resin (G1). In the anionic polyurethane resin (G4), the solid content mass of the anionic polyurethane resin having a carbonate backbone is relative to the solid content mass of the anionic polyurethane resin (G4) (G... S The mass ratio of the two components is 0.4. It should be noted that the glass transition temperature (Tg) of the obtained anionic polyurethane resin (G4) was determined using a dynamic viscoelasticity measuring device, and the result was 105℃.

[0185] Method for manufacturing anionic polyurethane resin (G5)

[0186] In the reactor, 100 parts by mass of a polyester polyol with a number-average molecular weight of 1320, obtained from 1,6-hexanediol and adipic acid, were used instead of 100 parts by mass of a polyether polyol with a number-average molecular weight of 5000, obtained from polyethylene glycol and polypropylene glycol. Otherwise, a water-dispersible anionic polyurethane resin (G5) with a solids content of 25% by mass was obtained in the same manner as that used in the manufacture of anionic polyurethane resin (G1). In the anionic polyurethane resin (G5), the solids content of the anionic polyurethane resin having a carbonate backbone is relative to the solids content of the anionic polyurethane resin (G5) (G... SThe mass ratio of ) is 0.3. It should be noted that the glass transition temperature (Tg) of the anionic polyurethane resin (G5), measured using a dynamic viscoelasticity measuring device, is 120°C.

[0187] Method for manufacturing anionic polyurethane resin (G6)

[0188] In the reactor, 100 parts by mass of a polyester polyol with a number average molecular weight of 1000, obtained from 1,6-hexanediol and adipic acid, were used instead of 100 parts by mass of a polyether polyol with a number average molecular weight of 5000, obtained from polyethylene glycol and polypropylene glycol. Otherwise, a water-dispersible anionic polyurethane resin (G6) with a solid content of 25% by mass was obtained in the same manner as that used in the manufacture of anionic polyurethane resin (G1). In the anionic polyurethane resin (G6), the solid content mass of the anionic polyurethane resin having a carbonate backbone relative to the solid content mass of the anionic polyurethane resin (G6) (G... S The mass ratio of the two components is 0.4. It should be noted that the glass transition temperature (Tg) of the obtained anionic polyurethane resin (G6) was determined using a dynamic viscoelasticity measuring device, and the result was 140℃.

[0189] Method for manufacturing anionic polyurethane resin (G7)

[0190] In the reactor, 100 parts by mass of a polyether polyol with a number average molecular weight of 5900 obtained from polyethylene glycol and polypropylene glycol were used instead of 100 parts by mass of a polyether polyol with a number average molecular weight of 5000 obtained from polyethylene glycol and polypropylene glycol. Otherwise, a water-dispersible anionic polyurethane resin (G7) with a solid content of 25% by mass was obtained in the same manner as the manufacturing method of the anionic polyurethane resin (G1). In the anionic polyurethane resin (G7), the solid content mass of the anionic polyurethane resin having a carbonate backbone is relative to the solid content mass of the anionic polyurethane resin (G7) (G... S The mass ratio of the two components is 0.5. It should be noted that the glass transition temperature (Tg) of the obtained anionic polyurethane resin (G7) was determined using a dynamic viscoelasticity measuring device, and the result was 40°C.

[0191] Method for manufacturing anionic polyurethane resin (G8)

[0192] In the reactor, 100 parts by mass of a polycarbonate polyol with a number-average molecular weight of 6600, obtained from 1,6-hexanediol and phosgene, were used instead of 100 parts by mass of a polyether polyol with a number-average molecular weight of 5000, obtained from polyethylene glycol and polypropylene glycol. Otherwise, a water-dispersible anionic polyurethane resin (G8) with a solids content of 25% by mass was obtained in the same manner as that used in the manufacture of anionic polyurethane resin (G1). In the anionic polyurethane resin (G8), the solids content of the anionic polyurethane resin having a carbonate backbone is relative to the solids content of the anionic polyurethane resin (G8) (G... S The mass ratio of the two components is 0.6. It should be noted that the glass transition temperature (Tg) of the obtained anionic polyurethane resin (G8) was determined using a dynamic viscoelasticity measuring device, and the result was 20°C.

[0193] Method for manufacturing anionic polyurethane resin (G9)

[0194] In the reactor, 100 parts by mass of a polycarbonate polyol with a number average molecular weight of 5300, obtained from 1,6-hexanediol and phosgene, were used instead of 100 parts by mass of a polyether polyol with a number average molecular weight of 5000, obtained from polyethylene glycol and polypropylene glycol. Otherwise, a water-dispersible anionic polyurethane resin (G9) with a solid content of 25% by mass was obtained in the same manner as that used in the manufacture of anionic polyurethane resin (G1). In the anionic polyurethane resin (G9), the solid content mass of the anionic polyurethane resin having a carbonate backbone relative to the solid content mass of the anionic polyurethane resin (G9) (G... S The mass ratio of ) is 0.7. It should be noted that the glass transition temperature (Tg) of the obtained anionic polyurethane resin (G9) was determined using a dynamic viscoelasticity measuring device, and the result was 60°C.

[0195] <Organosilicon resin (H)>

[0196] H1: Organosilicon resin emulsion (solid content: 37% by mass, manufactured by Shin-Etsu Chemical Co., Ltd., KM-9782 (registered trademark))

[0197] H2: Organosilicon resin emulsion (solid content: 15% by weight, manufactured by Wacker Asahikasei Silicone Co., Ltd., WACKERHC321 (registered trademark))

[0198] <Crosslinking agent (I)>

[0199] I1: Epoxy resin (solid content: 100% by weight, manufactured by Nagase ChemteX Corporation, Denacol (registered trademark) EX-313)

[0200] I2: Carbodiimide resin (solid content: 40% by mass, manufactured by Nisshinbo Chemical Co., Ltd. CARBODILITE (registered trademark) SV-02)

[0201] I3: includes Polymers with zoline groups (solid content: 40% by mass, manufactured by Nippon Shokubai Co., Ltd. EPOCROS (registered trademark) K-2020)

[0202] <Phosphoric Acid Compounds (J)>

[0203] J1: Diphosphonic acid (C2H8P2O7)

[0204] J2: Ammonium dihydrogen phosphate (NH4(H2PO4))

[0205] J3: Phosphoric acid (H3PO4)

[0206] <Fluorine compounds (K)>

[0207] K1: Ammonium fluoride

[0208] K2: Potassium fluoride

[0209] <Wax (L)>

[0210] L1: Polyethylene wax (Solids: 40.0% by weight, manufactured by Mitsui Chemicals, Inc., Chemipearl (registered trademark) W900)

[0211] L2: Microcrystalline wax (solid content: 46.0% by weight, manufactured by San Nopco Ltd., NOPCO (registered trademark) 1245-M-SN)

[0212] [Table 2]

[0213]

[0214]

[0215] [Table 3]

[0216]

[0217]

[0218] [Table 4]

[0219]

[0220] (4) Treatment methods

[0221] Various test plates pretreated with the steel plates shown in Table 1 (the steel plate numbers are shown in the "Coated Steel Plate" column of Table 5) were coated with the various first surface treatment solutions (X) from Table 2 or Table 4 using a bar coater. Then, without washing, they were placed directly into an oven and dried at the highest plate temperature reached as shown in the "PMT" column of Table 5, forming a first coating on both sides with the adhesion amount (per side) shown in Table 5. Next, the various second surface treatment solutions (Y) from Table 3 were coated onto the surface of the first coating using a bar coater, and then, without washing, they were placed directly into an oven and dried at the highest plate temperature reached as shown in the "PMT" column of Table 5, forming a second coating on both sides with the adhesion amount (per side) shown in Table 5. It should be noted that the adhesion amount of the first and second coatings was determined by measuring the double coating composed of the first and second coatings using a fluorescence X-ray analysis device. First, the Zr content in the double coating was quantified using a fluorescence X-ray analysis device to determine the Zr adhesion amount. The Zr contained in the double-layer coating is the Zr from the zirconium carbonate compound (C) contained in the first coating; therefore, the amount of Zr attached to the first coating is calculated from the amount of Zr attached to the double-layer coating. Next, the Si contained in the double-layer coating is quantified using a fluorescence X-ray analysis device to determine the amount of Si attached to the double-layer coating. Furthermore, the amount of Si attached to the first coating, resulting from the Si of the glycidyl silane coupling agent (A) and tetraalkoxysilane (B) containing glycidyl groups, is determined from the amount of Si attached to the first coating. The amount of Si attached to the second coating is obtained by subtracting the amount of Si attached to the first coating from the amount of Si attached to the double-layer coating. The amount of Si attached to the second coating originates from the Si of sodium silicate (D2) and organosilicon resin (H) contained in the second coating; the amount of Si attached to the second coating is calculated from the amount of Si attached to the second coating.

[0222] (5) Evaluation methods

[0223] Table 5 shows the results of evaluations (5-1) to (5-11) for samples taken from galvanized steel sheets with the obtained surface treatment coating, and the results of evaluations (5-12) for the first surface treatment liquid (X) and the second surface treatment liquid (Y). It should be noted that the evaluation criteria △ and × represent insufficient performance and are therefore not preferred.

[0224] (5-1) Heat resistance and color change

[0225] Each sample was heated to 500°C using an infrared imaging furnace for 30 seconds, held for 5 minutes, and then allowed to cool naturally to room temperature. The surface appearance was then visually observed. The evaluation criteria are as follows.

[0226] (Evaluation Criteria)

[0227] ◎: No color change

[0228] ○: Very slight brownish tint

[0229] ○-: Slightly brownish in tone

[0230] △: Changes color to brown

[0231] ×: The color changes to brownish-red.

[0232] (5-2) Heat cracking resistance

[0233] Each sample was heated to 500°C in an infrared imaging furnace for 30 seconds, held for 5 minutes, and then allowed to cool naturally to room temperature. The surface appearance was then visually observed. When cracks could not be confirmed visually, they were observed using an optical microscope at 1000x magnification. The evaluation criteria are as follows.

[0234] (Evaluation Criteria)

[0235] ◎: No cracks

[0236] ○: There is a very slight crack.

[0237] ○-: There are slight cracks

[0238] △: The entire surface has narrow cracks.

[0239] ×: The entire surface has both narrow and wide cracks.

[0240] (5-3) Corrosion resistance of plate section

[0241] For each sample, a salt spray test (SST) according to JIS-Z-2371-2000 was performed on a flat plate. The corrosion resistance of the plate section was evaluated by the area ratio of white rust formation after 240 hours. The evaluation criteria are as follows.

[0242] (Evaluation Criteria)

[0243] ◎: White rust area ratio is less than 5%

[0244] ○: White rust area rate is 5% or more but less than 10%

[0245] ○-: The area of ​​white rust is 10% or more but less than 25%.

[0246] △: White rust area rate is 25% or more but less than 50%

[0247] ×: White rust area rate is 50%–100%.

[0248] (5-4) Corrosion resistance of the machined parts

[0249] For each sample, a salt spray test (SST) according to JIS-Z-2371-2000 was performed with the sample bent at 90° using a 3R configuration. The corrosion resistance of the bent section was evaluated by the area percentage of white rust formation on the top after 144 hours. The evaluation criteria are as follows.

[0250] (Evaluation Criteria)

[0251] ◎: The area of ​​white rust on the bending section is less than 5%.

[0252] ○: The area of ​​white rust on the bending section is 5% or more but less than 10%.

[0253] ○-: The area of ​​white rust on the bending section is 10% or more but less than 25%.

[0254] △: The area of ​​white rust on the bending section is 25% or more but less than 50%.

[0255] ×: The area of ​​white rust on the bending section is 50%–100%.

[0256] (5-5) Corrosion resistance after alkali degreasing

[0257] Alkali degreasing agent FC-E6406 (manufactured by Nihon Parkerizing Co., Ltd.) was dissolved in pure water at a concentration of 20 g / L and heated to 60°C. Each sample was immersed in the alkaline solution for 2 minutes, then removed, washed with water, and dried. A salt spray test (JIS-Z-2371-2000) was performed on each sample, and the evaluation was based on the area percentage of white rust formation after 120 hours. The evaluation criteria were as shown in the corrosion resistance evaluation of the plate section in section (5-3) above.

[0258] (5-6) Resistance to blackening

[0259] The change in lightness (L value) of each sample after standing for 24 hours in a constant temperature and humidity chamber at a controlled temperature of 80°C and a relative humidity of 98% (ΔL = L value after test - L value before test) was calculated. The evaluation criteria are as follows. The L value was measured using an SR2000 manufactured by Nippon Denshoku Kogyo Co., Ltd. in SCI mode (including positive reflection light).

[0260] (Evaluation Criteria)

[0261] ◎ : -6 < △L, and has a uniform appearance without any inconsistencies.

[0262] ○: -10 < △L ≤ -6, and has a uniform appearance without any inconsistencies.

[0263] ○-:-14<△L≤-10,and has a uniform appearance without any inconsistencies.

[0264] △: -14 < △L ≤ -10, and has fine black dots.

[0265] ×: △L≤-14, or there may be uneven appearance.

[0266] (5-7) Water resistance

[0267] For each sample, 100 μL of deionized water was dropped onto the sample surface in a flat plate state, and the sample was placed in a hot air oven at 100°C for 10 minutes. After removing the sample from the oven, the water droplet marks were visually observed to evaluate its water resistance. The evaluation criteria are as follows.

[0268] (Evaluation Criteria)

[0269] ◎ : No matter what angle you look at it from, you can't confirm the boundary of the water droplet.

[0270] ○: Based on the angle of observation, the boundary of the water droplet can be roughly confirmed.

[0271] ○-: The boundary of the water droplet can be roughly confirmed from any angle.

[0272] △: The boundary of the water droplet can be clearly identified from any angle.

[0273] ×: Clearly confirmed to be at the water droplet boundary, exceeding the dripping range.

[0274] (5-8) Solvent resistance

[0275] Apply a load of 4.90 N (500 gf) to the surface of each sample using gauze soaked in ethanol, and rub back and forth 10 times while maintaining this load. Visually evaluate the wiping marks. The evaluation criteria are as follows.

[0276] (Evaluation Criteria)

[0277] ◎: No trace

[0278] ○: The trace is not visible when viewed from above, but it is clearly visible when viewed from an angle.

[0279] ○-: Slight traces can be seen when viewed from above.

[0280] △: The traces are clearly visible when viewed from above.

[0281] ×: Film peeling.

[0282] (5-9) Long-term sweat resistance

[0283] 10 μL of artificial sweat according to JIS-B7001-1995 was dropped onto the surface of each sample. A silicone rubber plug was pressed into the dropping area to create a region contaminated with artificial sweat. The test piece was then placed in a constant temperature and humidity chamber at 40℃ and 80% relative humidity for 8 days, and the appearance changes of the contaminated area were evaluated. The evaluation criteria are as follows.

[0284] (Evaluation Criteria)

[0285] ◎: No color change

[0286] ○: Very slight discoloration

[0287] ○-: Slight discoloration

[0288] △: Slightly darkened

[0289] ×: Obvious blackening

[0290] (5-10) Coating adhesion

[0291] Delicon (registered trademark) #700 (manufactured by Dai Nippon Paint Co., Ltd.) as a melamine alkyd coating was applied to each sample and sintered at 130°C for 30 minutes to form a film with a thickness of 30 μm. Then, the samples were immersed in boiling water for 2 hours, and immediately 10 × 10 checkerboard cuts (1 mm intervals) were made extending to the steel substrate. Further extrusion was performed using an Ericsson extruder with the cut areas as the outer (surface) side, and the coating was then bonded and peeled using adhesive tape. The peel area of ​​the coating was measured. The evaluation criteria are as follows. It should be noted that the Ericsson extrusion conditions were based on JISZ-2247-2006, with a punch diameter of 20 mm, a die diameter of 27 mm, and a drawing width of 27 mm.

[0292] (Evaluation Criteria)

[0293] ◎: No peeling

[0294] ○: Peeling area less than 3%

[0295] ○-: The area of ​​peeling is more than 3% but less than 10%.

[0296] △: The area of ​​peeling is more than 10% but less than 30%.

[0297] ×: Peeling area of ​​more than 30%

[0298] (5-11) Lubricity

[0299] 100mm diameter circular test pieces were cut from each sample and formed into cup shapes under the conditions of a punch diameter of 50mm, a die diameter of 51.91mm, and a folding pressure of 1 ton. The appearance of the deep-drawn surface (outer side of the cup) of the molded product was visually examined to evaluate the degree of scratches and blackening. The evaluation criteria are as follows.

[0300] (Evaluation Criteria)

[0301] ◎: The entire surface shows almost no change, with a uniform appearance.

[0302] ○: Slight scratches and blackening, with noticeably uneven appearance.

[0303] ○-: Localized scratches and blackening, resulting in an uneven appearance.

[0304] △: Severe scratches and blackening occur centered around the corner.

[0305] ×: Failed to form and broke

[0306] (5-12) Storage stability

[0307] Each surface treatment solution shown in Table 2 was stored in a constant temperature bath at 40°C for 30 days. The solutions were then removed and their appearance was visually inspected and evaluated. The evaluation criteria are as follows.

[0308] (Evaluation Criteria)

[0309] ◎: No change

[0310] ○: A very small amount of precipitate can be seen.

[0311] ○-: A trace amount of sediment can be seen.

[0312] △: A trace amount of sediment can be seen, and the viscosity has increased slightly.

[0313] ×: A large amount of sediment or gelation may be observed.

[0314] [Table 5]

[0315]

[0316]

[0317]

[0318] As shown in Table 5, the embodiments of the present invention exhibit excellent heat resistance to discoloration, heat resistance to cracking, corrosion resistance of the flat portion, corrosion resistance of the processed portion, corrosion resistance after alkali degreasing, resistance to blackening, water stain resistance, solvent resistance, long-term sweat resistance, coating adhesion, and storage stability. Furthermore, the embodiments containing wax exhibit particularly excellent lubricity. In contrast, comparative embodiments that deviate from the appropriate scope of the present invention fail to adequately achieve any of the aforementioned properties.

[0319] Industrial availability

[0320] According to the present invention, it is possible to manufacture galvanized steel sheets with surface-treated coatings that exhibit excellent heat resistance to discoloration, heat resistance to cracking, corrosion resistance of flat sections, corrosion resistance of processed sections, corrosion resistance after alkali degreasing, resistance to blackening, water stain resistance, solvent resistance, long-term sweat resistance, and coating adhesion.

Claims

1. A surface treatment liquid for galvanized steel sheets, characterized in that, It has a first surface treatment liquid X and a second surface treatment liquid Y. The first surface treatment liquid X contains a silane coupling agent A with glycidyl groups, a tetraalkoxysilane B, a zirconium carbonate compound C, sodium silicate D1, a vanadium compound E, a molybdate compound F, and water, and the content of each component satisfies the following (1) to (6). The second surface treatment liquid Y contains sodium silicate D2, anionic polyurethane resin G and water, and the content of each component satisfies the following (7) and (8). (1) Mass of solid component A of silane coupling agent A with glycidyl group S The solid component mass A relative to silane coupling agent A with glycidyl groups S The solid composition mass of tetraalkoxysilane B S The equivalent mass C of ZrO2 in zirconium carbonate compound C Z Total mass X S mass ratio of A S / X S The range is 0.050 to 0.

450. (2) The solid component mass B of tetraalkoxysilane B S Relative to the total mass X S The mass ratio of B S / X S The range is 0.010 to 0.

190. (3) The equivalent mass C of ZrO2 in zirconium carbonate compound C Z Relative to the total mass X S mass ratio of C Z / X S The range is 0.460 to 0.

910. (4) Mass of solid components of sodium silicate D1 S Relative to the total mass X S The mass ratio of D1 S / X S The range is 0.040 to 0.

630. (5) The equivalent mass E of V in vanadium compound E V Relative to the total mass X S The solid composition mass of sodium silicate D1 S Total mass X S +D1 S quality E V / (X) S +D1 S The value ranges from 0.006 to 0.

094. (6) The equivalent mass of Mo in molybdate compound F M Relative to the total mass X S The solid composition mass of sodium silicate D1 S Total mass X S +D1 S mass ratio F M / (X) S +D1 S The value ranges from 0.030 to 0.

280. (7) Mass of solid components of sodium silicate D2 S The solid component mass G relative to the anionic polyurethane resin G S The mass ratio of D2 S / G S The range is 0.010 to 0.

100. (8) Mass of solid components of anionic polyurethane resin G S The solid component mass Y relative to the second surface treatment liquid Y S The quality is higher than G S / Y S It ranges from 0.900 to 0.

980.

2. The surface treatment liquid for galvanized steel sheets according to claim 1, wherein, In the second surface treatment liquid Y, the anionic polyurethane resin G contains anionic polyurethane resin with a carbonate backbone, the content of which satisfies the following (9): (9) The solid content mass of the anionic polyurethane resin with a carbonate backbone relative to the solid content mass G of the anionic polyurethane resin G. S The mass ratio is 0.20 to 0.

80.

3. The surface treatment liquid for galvanized steel sheets according to claim 1 or 2, wherein, The second surface treatment liquid Y further contains organosilicon resin H, the content of which satisfies the following (10): (10) Mass of solid components of organosilicon resin H S The solid component mass G relative to the anionic polyurethane resin G S mass ratio of H S / G S The range is 0.0030 to 0.0400.

4. The surface treatment liquid for galvanized steel sheets according to any one of claims 1 to 3, wherein, The second surface treatment liquid Y further contains crosslinking agent I, the content of which satisfies the following (11): (11) Mass of solid component I of crosslinking agent I S The solid component mass G relative to the anionic polyurethane resin G S mass ratio I S / G S The range is 0.0030 to 0.0400.

5. The surface treatment liquid for galvanized steel sheets according to any one of claims 1 to 4, wherein, The second surface treatment liquid Y further contains wax L, the content of which satisfies the following (12): (12) Mass of solid component L of wax L S The solid component mass Y relative to the second surface treatment liquid Y S mass ratio L S / Y S The value ranges from 0.010 to 0.

120.

6. The surface treatment liquid for galvanized steel sheets according to any one of claims 1 to 5, wherein, The first surface treatment liquid X further contains a phosphoric acid compound J, the content of which satisfies the following (13): (13) The solid mass of phosphoric acid compound J S Relative to the total mass X S mass ratio J S / X S The range is 0.140 to 0.

770.

7. The surface treatment liquid for galvanized steel sheets according to any one of claims 1 to 6, wherein, The first surface treatment liquid X further contains a fluorine compound K, the content of which satisfies the following (14): (14) The solid mass of fluorine compound K S Relative to the total mass X S mass ratio K S / X S The range is 0.040 to 0.

610.

8. A method for manufacturing a galvanized steel sheet with a surface treatment coating, comprising a method for manufacturing a galvanized steel sheet with a surface treatment coating using the surface treatment liquid for galvanized steel sheets according to any one of claims 1 to 7, characterized in that, It has the following processes: The process of applying the first surface treatment liquid X to the surface of a galvanized steel sheet; The process of drying the coated first surface treatment liquid X to form a first film; Then, the process of coating the surface of the first film with the second surface treatment liquid Y; and The process of drying the coated second surface treatment liquid Y to form a second film.

9. The method for manufacturing galvanized steel sheet with a surface-treated coating according to claim 8, wherein, The amount of the first film attached is 0.010–0.400 g / m³. 2 The amount of the second coating is 0.20–3.00 g / m³. 2 .

10. A galvanized steel sheet with a surface treatment coating, manufactured by the method for manufacturing a galvanized steel sheet with a surface treatment coating as described in claim 8 or 9.

11. The galvanized steel sheet with a surface-treated coating according to claim 10, wherein, The galvanized steel sheet is a hot-dip Zn-Al alloy steel sheet having a hot-dip Zn-Al alloy coating on at least one surface of a base steel sheet serving as a substrate. The hot-dip Zn-Al alloy coating has a composition, by mass%, containing Al: 3.0-12.0%, Mg: 0.2-6.0%, Ni: 0.0-0.1%, with the remainder consisting of Zn and unavoidable impurities.

Images