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

Abstract

To provide a surface treatment liquid for galvanized steel sheets, which has excellent storage stability and is capable of producing a galvanized steel sheet with a surface treatment coating film excellent in terms of long-term perspiration resistance, flat plate part corrosion resistance, and the like.SOLUTION: A surface treatment liquid for galvanized steel sheets is characterized by including a first surface treatment liquid (X) and a second surface treatment liquid (Y), and is also characterized in that: the first surface treatment liquid (X) contains a silane coupling agent (A) which has a glycidyl group, 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 satisfy a specific relationship; and the second surface treatment liquid (Y) contains sodium silicate (D2), an anionic polyurethane resin (G), and water, and the contents of the components satisfy a specific relationship.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a surface treatment liquid for a zinc-based plated steel sheet, a method for producing a zinc-based plated steel sheet with a surface treatment film, and a zinc-based plated steel sheet with a surface treatment film. [Background technology]

[0002] Zinc-plated steel sheets, which have a zinc-based plating layer on the surface of a base steel sheet, have excellent corrosion resistance and are therefore used in a variety of applications, such as automobiles, home appliances, office automation equipment, building materials, etc. It is also known that when a zinc-based plating layer contains aluminum and / or magnesium as components other than zinc, it exhibits superior corrosion resistance to a zinc-plated layer made of zinc.

[0003] However, it has been confirmed that when a person's hand directly touches the surface of a zinc-based plating layer, the part touched by the hand turns black over time (black discoloration phenomenon). This is believed to be due to oxidation of the surface of the zinc-based plating layer caused by the adhesion of sweat components, and is known to be particularly likely to occur in the case of a zinc-based plating layer that contains aluminum and / or magnesium. Therefore, there is a demand for a zinc-based plated steel sheet that does not cause the black discoloration phenomenon even when sweat adheres to it, i.e., has excellent sweat resistance.

[0004] Patent Document 1 describes a method for producing a zinc-based plated steel sheet with a surface treatment film, which comprises forming a surface treatment film on the surface of a zinc-based plated steel sheet using a surface treatment liquid for zinc-based plated steel sheet that contains a silane coupling agent having a glycidyl group, a tetraalkoxysilane, sodium silicate, a zirconium carbonate compound, an anionic polyurethane resin having a glass transition point (Tg) of 80 to 130° C., a vanadium compound, a molybdic acid compound, and water, has a pH of 8.0 to 10.0, and the contents of the respective components satisfy a predetermined relationship. This production method makes it possible to produce a zinc-based plated steel sheet with a surface treatment film that is excellent in all of heat discoloration resistance, heat cracking resistance, flat plate corrosion resistance, corrosion resistance after alkaline degreasing, blackening resistance, water stain resistance, solvent resistance, sweat resistance, and paint adhesion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-62710 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the inventors of the present invention examined the zinc-based plated steel sheet with a surface treatment film proposed in Patent Document 1, it became clear that the sweat resistance over a long period of time (long-term sweat resistance) was insufficient and there was room for improvement in the long-term sweat resistance.

[0007] In view of the above problems, the present invention aims to provide a surface treatment liquid for zinc-based plated steel sheet, which is capable of producing a zinc-based plated steel sheet with a surface treatment film excellent in all of heat discoloration resistance, heat cracking resistance, flat plate corrosion resistance, processed plate corrosion resistance, corrosion resistance after alkaline degreasing, blackening resistance, water stain resistance, solvent resistance, long-term sweat resistance, and paint adhesion, and which has excellent storage stability. Another aim of the present invention is to provide a method for producing a zinc-based plated steel sheet with a surface treatment film using the surface treatment liquid for zinc-based plated steel sheet, and a zinc-based plated steel sheet with a surface treatment film produced by the production method. [Means for solving the problem]

[0008] The present inventors have made intensive studies to solve the above problems, and have found the following. By forming the surface treatment film into a laminated structure, the penetration of sweat components can be significantly suppressed. Specifically, a first film having film components that satisfy at least conventional characteristics other than long-term sweat resistance is formed on the surface of a zinc-based plated steel sheet. The first film contains sodium silicate in addition to a silane coupling agent having a glycidyl group, a tetraalkoxysilane, and a zirconium carbonate compound, which promotes the formation of a Si-enriched layer on the surface layer and improves long-term sweat resistance. Then, a second film having film components specialized for barrier properties against sweat components is formed on the first film. The second film contains an anionic polyurethane resin, which provides high barrier properties against sweat components, and contains sodium silicate, which provides strong adhesion to the first film having a Si-enriched layer, thereby enabling a significant improvement in long-term sweat resistance.

[0009] That is, the gist and configuration of the present invention are as follows.

[0010] [1] 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) having a glycidyl group, 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 respective components satisfy the following (1) to (6), The second surface treatment liquid (Y) contains sodium silicate (D2), an anionic polyurethane resin (G), and water, and the contents of each component satisfy the following (7) and (8). (1) Solid content mass of silane coupling agent (A) having a glycidyl group (A S ) of the solid content of the silane coupling agent (A) having a glycidyl group (A S ), the solid content of tetraalkoxysilane (B) (B S ), and ZrO in zirconium carbonate compounds (C) 2 Converted mass (C Z ) total mass (X S ) to mass ratio (AS / X S ) is 0.050 to 0.450 (2) Solid content mass of tetraalkoxysilane (B) (B S ) of the total mass (X S ) to mass ratio (B S / X S ) is 0.010 to 0.190 (3) ZrO in zirconium carbonate compounds (C) 2 Converted mass (C Z ) of the total mass (X S ) to the mass ratio (C Z / X S ) is 0.460 to 0.910 (4) Solid content of sodium silicate (D1) (D1 S ) of the total mass (X S ) to mass ratio (D1 S / X S ) is 0.040 to 0.630 (5) The converted mass of vanadium in vanadium compounds (E) (E V ) of the total mass (X S ) and the solid content of sodium silicate (D1) (D1 S ) and the total mass (X S +D1 S ) to mass ratio (E V / (X S +D1 S )) is 0.006 to 0.094 (6) Mo equivalent mass in molybdate compound (F) (F M ) of the total mass (X S ) and the solid content of sodium silicate (D1) (D1 S ) and the total mass (X S +D1 S ) to mass ratio (F M / (X S +D1 S )) is 0.030 to 0.280 (7) Solid content of sodium silicate (D2) (D2 S ) of the solid content of the anionic polyurethane resin (G) (G S ) to mass ratio (D2 S / G S) is 0.010 to 0.100 (8) Solid content mass of anionic polyurethane resin (G) (G S ) of the solid content mass (Y S ) to mass ratio (G S / Y S ) is 0.900~0.980

[0011] [2] The surface treatment liquid for zinc-based plated steel sheet according to the above [1], wherein in the second surface treatment liquid (Y), the anionic polyurethane resin (G) contains an anionic polyurethane resin having a carbonate skeleton, and the content thereof satisfies the following (9). (9) The solid content mass of the anionic polyurethane resin (G) having the carbonate skeleton is S ) mass ratio is 0.20 to 0.80

[0012] [3] The surface treatment liquid for zinc-based plated steel sheet according to the above [1] or [2], wherein the second surface treatment liquid (Y) further contains a silicone resin (H) and the content thereof satisfies the following (10). (10) Solid content mass of silicone resin (H) S ) of the solid content of the anionic polyurethane resin (G) (G S ) to the mass ratio (H S / G S ) is 0.0030 to 0.0400

[0013] [4] The second surface treatment liquid (Y) further contains a crosslinking agent (I) whose content satisfies the following (11). (11) Solid content mass of crosslinking agent (I) S ) of the solid content of the anionic polyurethane resin (G) (G S ) to the mass ratio (I S / G S ) is 0.0030 to 0.0400

[0014] [5] The second surface treatment liquid (Y) further contains a wax (L), the content of which satisfies the following (12). (12) Solid mass of wax (L) S ) of the solid content mass (Y S ) to mass ratio (L S / Y S ) is 0.010 to 0.120

[0015] [6] The surface treatment liquid for zinc-based plated steel sheet according to any one of the above [1] to [5], wherein the first surface treatment liquid (X) further contains a phosphate compound (J), the content of which satisfies the following (13). (13) Solid content mass of phosphoric acid compound (J) (J S ) of the total mass (X S ) to mass ratio (J S / X S ) is 0.140 to 0.770

[0016] [7] The surface treatment liquid for zinc-based plated steel sheet according to any one of the above [1] to [6], wherein the first surface treatment liquid (X) further contains a fluorine compound (K) and the content thereof satisfies the following (14). (14) Solid mass of fluorine compound (K) (K S ) of the total mass (X S ) to mass ratio (K S / X S ) is 0.040 to 0.610

[0017] [8] A method for producing a zinc-based plated steel sheet having a surface treatment film using the surface treatment solution for zinc-based plated steel sheet according to any one of [1] to [7] above, applying the first surface treatment liquid (X) to a surface of a zinc-based plated steel sheet; Thereafter, a step of drying the applied first surface treatment liquid (X) to form a first coating; Thereafter, applying the second surface treatment liquid (Y) to the surface of the first coating; Thereafter, a step of drying the applied second surface treatment liquid (Y) to form a second coating; A method for producing a zinc-based plated steel sheet having a surface treatment film, comprising the steps of:

[0018] [9] The coating weight of the first coating is 0.010 to 0.400 g / m 2 and the coating weight of the second coating is 0.20 to 3.00 g / m 2 The method for producing a zinc-based plated steel sheet having a surface treatment film according to the above [8].

[0019]

[10] A zinc-based plated steel sheet having a surface treatment film, produced by the method for producing a zinc-based plated steel sheet having a surface treatment film according to [8] or [9] above.

[0020]

[11] The zinc-based plated steel sheet with a surface treatment film according to the above item

[10] , wherein the zinc-based plated steel sheet is a hot-dip Zn-Al-based alloy plated steel sheet having a hot-dip Zn-Al-based alloy plating layer having a composition, in mass%, of Al: 3.0 to 12.0%, Mg: 0.2 to 6.0%, Ni: 0.0 to 0.1%, with the balance being Zn and unavoidable impurities, on at least one surface of a base steel sheet serving as a substrate. Effect of the Invention

[0021] According to the present invention, it is possible to provide a surface treatment liquid for a zinc-based plated steel sheet, which is capable of producing a zinc-based plated steel sheet with a surface treatment film excellent in all of heat discoloration resistance, heat cracking resistance, flat plate corrosion resistance, processed plate corrosion resistance, corrosion resistance after alkaline degreasing, blackening resistance, water stain resistance, solvent resistance, long-term sweat resistance, and paint adhesion, and which has excellent storage stability. Also, according to the present invention, it is possible to provide a method for producing a zinc-based plated steel sheet with a surface treatment film using the surface treatment liquid for a zinc-based plated steel sheet, and a zinc-based plated steel sheet with a surface treatment film produced by the production method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, embodiments of the surface treatment solution for zinc-based plated steel sheet, the method for producing a zinc-based plated steel sheet with a surface treatment film, and the zinc-based plated steel sheet with a surface treatment film according to the present invention will be described. Note that the embodiment described below is one example of the present invention, and the configuration of the present invention is not limited to this specific example.

[0023] (Surface treatment solution for zinc-based plated steel sheets) A surface treatment liquid for a zinc-based plated steel sheet according to one embodiment of the present invention comprises a first surface treatment liquid (X) and a second surface treatment liquid (Y). The first surface treatment liquid (X) is used for forming a first coating on the zinc-based plated steel sheet by applying it to the surface of the zinc-based plated steel sheet and drying it. The second surface treatment liquid (Y) is used for forming a second coating on the first coating by applying it to the first coating and drying it.

[0024] [First surface treatment liquid (X)] The first surface treatment liquid (X) contains a silane coupling agent having a glycidyl group (A), a tetraalkoxysilane (B), a zirconium carbonate compound (C), sodium silicate (D1), a vanadium compound (E), a molybdic acid compound (F), and water, and may further contain one or both of a phosphate compound (J) and a fluorine compound (K) as necessary.

[0025] <Silane coupling agent having a glycidyl group (A)> The first surface treatment liquid (X) contains a silane coupling agent (A) having a glycidyl group. The silane coupling agent (A) is not particularly limited as long as it is a glycidyl group and a lower alkoxy group having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms as a hydrolyzable group, which is directly bonded to a Si element, and examples thereof include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane. Among them, 3-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane are preferred from the viewpoint that more condensation points between silane coupling agents (A) having a glycidyl group, or more condensation points with a tetraalkoxysilane (B) or a zirconium carbonate compound (C) described later are easily generated, thereby obtaining high barrier properties after film formation.

[0026] The silane coupling agent (A) having a glycidyl group has an alkoxy group directly bonded to the Si element in the compound, and the alkoxy group reacts with water in an aqueous solution to form a silanol group. This silanol group reacts with the surface of the zinc-based plated steel sheet, or undergoes a complex condensation reaction with the tetraalkoxysilane (B) and the zirconium carbonate compound (C) described below.

[0027] Solid content mass of silane coupling agent (A) having a glycidyl group (A S ) of the solid content of the silane coupling agent (A) having a glycidyl group (A S ), the solid content of tetraalkoxysilane (B) (B S ), and ZrO in zirconium carbonate compounds (C) 2 Converted mass (C Z ) total mass (X S ) to mass ratio (A S / X S The mass ratio (A S / X SIf the mass ratio (A) is less than 0.050, the corrosion resistance of the flat plate, the corrosion resistance of the processed part, and the corrosion resistance after alkaline degreasing are poor. S / X S The mass ratio (A) is 0.050 or more, preferably 0.060 or more, and more preferably 0.090 or more. S / X S If the mass ratio (A) exceeds 0.450, the heat cracking resistance is poor. S / X S ) is 0.450 or less, preferably 0.380 or less, and more preferably 0.290 or less.

[0028] <Tetraalkoxysilane (B)> When the above component (A) is used alone, the thermal cracking resistance is poor, so the first surface treatment liquid (X) contains tetraalkoxysilane (B). Without component (B), the carbon-carbon bonds of component (A) undergo thermal oxidative decomposition in a heated atmosphere of 500°C or higher, which causes large cracks to occur. In contrast, when an appropriate amount of component (B) is added, a dense film with high barrier properties can be obtained while keeping the amount of component (A) added to an acceptable level of thermal cracking resistance. The film obtained from components (A) and (B) is dense, so cracks during heating can be made fine, and no cracks visible to the naked eye occur, resulting in excellent thermal cracking resistance.

[0029] Tetraalkoxysilane (B) has four lower alkoxy groups as hydrolyzable groups directly bonded to the Si element, and has the general formula Si(OR) 4 (wherein R is the same or different alkyl group having 1 to 5 carbon atoms), there is no particular limitation, and examples include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, etc., and one or more of these can be used. Among these, tetraethoxysilane and tetramethoxysilane are preferred from the viewpoint that more condensation points are easily generated between the tetraalkoxysilanes (B) themselves, or between the component (A) and the component (C) described below, thereby obtaining high barrier properties after film formation.

[0030] Tetraalkoxysilane (B) has an alkoxy group directly bonded to the Si element in the compound, and the alkoxy group reacts with water in an aqueous solution to form a silanol group. This silanol group reacts with the surface of the zinc-based plated steel sheet or undergoes a complex condensation reaction with component (A) or component (C) described below.

[0031] Solid content of tetraalkoxysilane (B) (B S ) of the total mass (X S ) to mass ratio (B S / X S ) is 0.010 to 0.190. Mass ratio (B S / X S If the mass ratio (B) is less than 0.010, the corrosion resistance of the flat plate portion, the corrosion resistance of the processed portion, and the corrosion resistance after alkaline degreasing are reduced. S / X S ) is 0.010 or more, preferably 0.020 or more, and more preferably 0.030 or more. S / X S If the mass ratio (B) exceeds 0.190, the thermal cracking resistance decreases. S / X S ) is 0.190 or less, preferably 0.150 or less, and more preferably 0.110 or less.

[0032] Although each of components (A) and (B) may be used alone, it is preferable to add components (A) and (B) to the first surface treatment liquid (X) after subjecting them to a condensation reaction to form a low condensate, which provides higher barrier properties after film formation. This low condensate has a polysiloxane bond formed by a condensation reaction between the silanol groups of components (A) and (B) as its main skeleton, and all of the terminal groups bonded to the Si element may be alkoxy groups, or some of the groups directly bonded to the Si element may be alkoxy groups.

[0033] The low condensate obtained by the condensation reaction of component (A) and component (B) preferably has a condensation degree of 2 to 30, more preferably 2 to 10. If the condensation degree is 30 or less, the component (A) and the component (B) can be used stably without generating white precipitate in an aqueous solution. This low condensate can be obtained by reacting the component (A), the component (B), and a chelating agent described below at a reaction temperature of 1 to 70°C for about 10 minutes to 20 hours, and then performing an autoclave treatment. Examples of the chelating agent 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, and one or more of these can be used.

[0034] The condensation state of this low condensate can be measured by gel permeation chromatography (GPC), NMR, and FT-IR as described in JIS-K7252-4.

[0035] The chelating agent that acts to stabilize the low condensation product acts when the alkoxy group of component (A) and the alkoxy group of component (B) undergo a hydrolysis reaction with water and the chelating agent. The reason for the stabilizing effect of the chelating agent is unclear, but it is thought to be obtained by the chelating agent being appropriately coordinated to the silanol groups derived from components (A) and (B) generated by the hydrolysis reaction. In other words, the appropriate coordination effect of the chelating agent to the silanol groups suppresses excessive condensation of components (A) and (B), so that a first surface treatment liquid (X) with excellent storage stability can be obtained. Furthermore, a first coating with stable quality can be obtained even after the first surface treatment liquid (X) is stored for a long period of time.

[0036] The chelating agent is effective in ensuring the corrosion resistance of the first coating, in addition to the storage stability. Although the reason is unclear, it is thought that the chelating agent also coordinates with the vanadium compound (E) described below. When the first coating is exposed to a corrosive environment, the chelating agent coordinated to the vanadium compound (E) is eluted together with the vanadium compound (E). This causes condensation of the components (A) and (B) that have lost their ligands in the first coating, which is thought to further improve the barrier properties of the first coating and contribute to improving the corrosion resistance.

[0037] <Zirconium carbonate compound (C)> The first surface treatment liquid (X) contains a zirconium carbonate compound (C). When the first surface treatment liquid (X) contains the zirconium carbonate compound (C), a first coating film that is difficult to dissolve in water is obtained, and therefore the corrosion resistance and water stain resistance of the flat plate portion can be improved. In addition, by using the zirconium carbonate compound (C) in combination with sodium silicate (D1) described later, a first coating film that is particularly excellent in long-term sweat resistance can be obtained.

[0038] The first coating containing the above components (A) to (C) usually has moderate hardness and flexibility, high barrier properties, and excellent flat part corrosion resistance, processed part corrosion resistance, and corrosion resistance after alkaline degreasing. The reason for the high barrier properties is that the zirconium carbonate compound (C) has a hydroxyl group that serves as a condensation point with the silanol group. Furthermore, since the zirconium carbonate compound (C) produces zirconium oxide and zirconium hydroxide when dried, even when heated to over 500°C, the dense coating of the tetraalkoxysilane (B) and the zirconium carbonate compound (C) does not cause visually noticeable cracks, and the coating has excellent heat cracking resistance. Examples of the zirconium carbonate compound (C) include salts of sodium, potassium, lithium, and ammonium of zirconium carbonate compounds, and one or more of these can be used. Among them, ammonium zirconium carbonate and potassium zirconium carbonate are preferred in terms of film-forming properties and water stain resistance.

[0039] ZrO in zirconium carbonate compounds (C) 2 Converted mass (C Z) of the total mass (X S ) to the mass ratio (C Z / X S ) is 0.460 to 0.910. Mass ratio (C Z / X S When the mass ratio (C) is less than 0.460, the barrier properties derived from the zirconium carbonate compound (C) are insufficient, and the corrosion resistance after alkaline degreasing is reduced. Z / X S ) is 0.460 or more, preferably 0.580 or more, and more preferably 0.630 or more. Z / X S If the mass ratio (C) exceeds 0.910, the content of hard components derived from zirconium carbonate compounds is high, and good paint adhesion cannot be obtained. Z / X S ) is 0.910 or less, preferably 0.900 or less, and more preferably 0.870 or less.

[0040] <Sodium silicate (D1)> The first surface treatment liquid (X) contains sodium silicate (D1). The sodium contained in the sodium silicate (D1) is converted by heat into SiO 4 SiO separated from the network 4 It bonds to the tetrahedral oxygen atoms. Therefore, SiO 4 The recombination of the interconnecting network is prevented. This action gives fluidity to the silicate glass, lowering the softening temperature of the silicate glass from 1700°C or higher to 500°C to 700°C. In the present invention, it is believed that by utilizing this action, when the first coating which is hard and has a small thermal expansion coefficient and contains components (A) to (C) is heated to 500°C or higher, the first coating is given fluidity, thereby obtaining excellent thermal cracking resistance.

[0041] Although the sodium silicate (D1) used in the present invention is a highly water-soluble component, it has an etching property for zinc, so that when the first surface treatment liquid (X) comes into contact with the surface of the zinc-based plating layer and dries, the zinc ions dissolved in the first surface treatment liquid (X) are fixed as poorly soluble metal silicate salts, which contribute to the adhesion of the first coating. Furthermore, the inventors have discovered that when sodium silicate (D1) is contained in the first surface treatment liquid (X) in combination with the components (A) to (C), the formation of a Si-enriched layer on the surface of the first coating is promoted. Furthermore, the inventors have discovered that the presence of this Si-enriched layer improves long-term sweat resistance. This is believed to be due to the condensation of the silanol groups of the sodium silicate (D1), the silane coupling agent (A), the silanol groups of the tetraalkoxysilane (B), and the hydroxyl groups of the zirconium carbonate compound (C), which incorporates the sodium silicate (D1) and forms a denser network. In addition, in a corrosive environment, the sodium silicate (D1) fixed in the first coating as described above dissolves appropriately, and by manipulating the pH of the surface of the zinc-based plating layer to the alkaline side, it also contributes to delaying and suppressing the anodic reaction of zinc.

[0042] The sodium silicate (D1) used in the present invention is SiO 2 and Na 2 O, the molar ratio of which is SiO 2 / Na 2 It is preferable that O is 1 to 4. SiO 2 / Na 2 By making the O content 4 or less, the effect on thermal cracking resistance can be favorably obtained. 2 / Na 2 By making O 1 or more, the sodium silicate (D1) can be preferably fixed in the first coating while ensuring the effect on thermal cracking resistance, and the deterioration of blackening resistance, water stain resistance, and long-term sweat resistance can be preferably suppressed. 2 / Na 2O is preferably at least 1, and more preferably at least 2. Examples of the sodium silicate (D1) that satisfies the above include sodium silicate No. 2 and sodium silicate No. 3, and one or more of these can be used.

[0043] Solid content of sodium silicate (D1) (D1 S ) of the total mass (X S ) to mass ratio (D1 S / X S ) is 0.040 to 0.630. Mass ratio (D1 S / X S When the mass ratio (D1) is less than 0.040, the corrosion resistance of the flat plate portion, the corrosion resistance of the processed portion, and the corrosion resistance after alkaline degreasing are reduced. S / X S The mass ratio (D1 S / X S When the mass ratio (D1) exceeds 0.630, sodium silicate becomes excessive, which makes it difficult to fix it in the first film, and therefore the blackening resistance, water stain resistance, and long-term sweat resistance are deteriorated. Furthermore, since a large amount of Na ions is present in the first surface treatment liquid (X), the storage stability of the first surface treatment liquid (X) is deteriorated. Therefore, when the mass ratio (D1 S / X S ) is not more than 0.630, and preferably not more than 0.470.

[0044] <Vanadium Compounds (E)> The first surface treatment liquid (X) contains a vanadium compound (E). The vanadium compound (E) is uniformly dispersed in the first film, but dissolves moderately in a corrosive environment, and combines with the zinc ions dissolved in the corrosive environment to form a dense passive film, thereby improving the corrosion resistance of the flat plate portion, the corrosion resistance of the processed portion, and the corrosion resistance after alkaline degreasing. Examples of the vanadium compound (E) include ammonium metavanadate, sodium metavanadate, vanadium acetylacetonate, and metavanadyl acetylacetonate, and one or more of these can be used.

[0045] The converted mass of vanadium in vanadium compounds (E) (E V ) of the total mass (X S ) and the solid content of sodium silicate (D1) (D1 S ) and the total mass (X S +D1 S ) to mass ratio (E V / (X S +D1 S The mass ratio (E V / (X S +D1 S If the mass ratio (E) is less than 0.006, the effect of forming a passive film with zinc ions is insufficient, and the corrosion resistance of the flat plate portion, the corrosion resistance of the processed portion, and the corrosion resistance after alkaline degreasing are reduced. V / (X S +D1 S The mass ratio (E V / (X S +D1 S If the mass ratio (E ) exceeds 0.094, good resistance to blackening and water stains cannot be obtained. Furthermore, when heated to above 500°C, the vanadium undergoes oxidation and discoloration, which reduces the heat discoloration resistance. V / (X S +D1 S ) is 0.094 or less, preferably 0.071 or less, and more preferably 0.047 or less.

[0046] <Molybdic acid compounds (F)> The first surface treatment liquid (X) contains a molybdic acid compound (F). The inclusion of the molybdic acid compound (F) improves the blackening resistance. Examples of the molybdic acid compound (F) include molybdic acid, ammonium molybdate, sodium molybdate, potassium molybdate, magnesium molybdate, and zinc molybdate. In the present invention, it is preferable to use one or more selected from these.

[0047] The blackening phenomenon of zinc-based plating layers is believed to be due to the formation of oxygen-deficient zinc oxide when the zinc-based plating layer is exposed to a high-temperature, high-humidity atmosphere. Molybdenum is a second transition metal with various valences, and in air it combines with oxygen to form MoO 2 Or MoO 3 In the present invention, MoO 4 2- This molybdate is added uniformly to the first coating, and then heated in a high-temperature, high-humidity atmosphere to form a molybdate such as MoO 3 It is believed that molybdenum oxide such as molybdenum oxide is reduced to molybdenum oxide such as molybdenum oxide and molybdenum oxide oxide. This action is believed to provide an appropriate amount of oxygen to the zinc on the surface of the zinc-based plating layer, thereby suppressing the formation of oxygen-deficient zinc oxide. On the other hand, if molybdate is added in excess, the corrosion resistance of flat parts, corrosion resistance of processed parts, and corrosion resistance after alkaline degreasing cannot be obtained.

[0048] Mo equivalent mass in molybdate compound (F) M ) of the total mass (X S ) and the solid content of sodium silicate (D1) (D1 S ) and the total mass (X S +D1 S ) to mass ratio (F M / (X S +D1 S The mass ratio (F M / (X S +D1 S When the mass ratio (F M / (X S +D1 S The mass ratio (F) is 0.030 or more, preferably 0.040 or more, and more preferably 0.050 or more. M / (X S +D1 S When the mass ratio (F ) exceeds 0.280, good corrosion resistance of the flat plate portion, corrosion resistance of the processed portion, and corrosion resistance after alkaline degreasing cannot be obtained. M / (X S +D1 S) is 0.280 or less, preferably 0.240 or less, and more preferably 0.190 or less.

[0049] <Phosphate Compound (J)> The first surface treatment liquid (X) may contain a phosphate compound (J) for the purpose of further improving the corrosion resistance of the first coating. The phosphate compound (J) dissolves moderately in a corrosive environment, bonds with the zinc ions dissolved in the corrosive environment, forms a poorly soluble zinc phosphate coating, and covers coating defects, thereby improving the corrosion resistance of the flat plate portion, the corrosion resistance of the processed portion, and the corrosion resistance after alkaline degreasing.

[0050] The phosphoric acid compound (J) may be at least one selected from inorganic phosphoric acid compounds and organic phosphoric acid compounds. Examples of inorganic phosphoric acid compounds include phosphoric acid, primary phosphates, secondary phosphates, and tertiary phosphates; condensed phosphates such as pyrophosphoric acid, pyrophosphates, tripolyphosphoric acid, and tripolyphosphates; phosphorous acid, phosphites, hypophosphorous acid, and hypophosphites. Examples of organic phosphoric acid compounds include phosphonic acid, diphosphonic acid, phosphonobutane tricarboxylic acid, ethylenediaminetetramylenephosphonic acid, methyldiphosphonic acid, methylenephosphonic acid, ethylidene diphosphonic acid, and ammonium salts and alkali metal salts thereof. For resistance to flaky plating peeling, it is preferable to use inorganic phosphoric acid compounds such as phosphoric acid or ammonium dihydrogen phosphate, from the viewpoint of easier formation of poorly soluble metal salts, and when using an organic phosphoric acid compound, it is preferable to use diphosphonic acid from the viewpoint of better water stain resistance and storage stability of the first surface treatment liquid (X).

[0051] Solid mass of phosphoric acid compound (J) (J S ) of the total mass (X S ) to mass ratio (J S / X S The mass ratio (J) is preferably 0.140 to 0.770. S / X S By making the mass ratio (J) 0.140 or more, the corrosion resistance of the flat plate portion, the corrosion resistance of the processed portion, and the corrosion resistance after alkaline degreasing can be suitably obtained.S / X S ) is preferably 0.140 or more, more preferably 0.180 or more, and even more preferably 0.280 or more. S / X S By making the mass ratio (J) 0.770 or less, heat discoloration resistance, blackening resistance, water stain resistance, long-term sweat resistance, and paint adhesion can be suitably obtained. S / X S ) is preferably 0.770 or less, more preferably 0.720 or less, and even more preferably 0.660 or less.

[0052] <Fluorine compounds (K)> 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 zinc-based plated steel sheet. The fluorine compound (K) slightly etches the zinc-based plated surface and forms fine irregularities on the surface of the zinc-based plated layer, thereby improving the adhesion by an anchor effect.

[0053] From the viewpoint of suppressing excessive dissolution of the plating, the fluorine compound (K) may include hydrofluoric acid, hydrofluoric acid, ammonium fluoride, lithium fluoride, sodium fluoride, potassium fluoride, ammonium acid fluoride, sodium acid fluoride, potassium acid fluoride, fluorotitanic acid, ammonium fluorotitanate, fluorozirconic acid, ammonium fluorozirconate, and the like, and in the present invention, it is preferable to use one or more selected from these.

[0054] Solid mass of fluorine compound (K) (K S ) of the total mass (X S ) to mass ratio (K S / X S The mass ratio (K S / X S By making the mass ratio (K ) 0.040 or more, it is possible to obtain good long-term sweat resistance and paint adhesion. S / X S) is preferably 0.040 or more, more preferably 0.050 or more, and even more preferably 0.080 or more. S / X S By making the mass ratio (K ) 0.610 or less, the corrosion resistance of the flat plate portion, the corrosion resistance of the processed portion, the corrosion resistance after alkaline degreasing, the blackening resistance, and the water stain resistance can be suitably obtained. S / X S ) is preferably 0.610 or less, more preferably 0.450 or less, and even more preferably 0.300 or less.

[0055] <pHが8.0~10.0> The first surface treatment liquid (X) is obtained by mixing the above-mentioned components in water such as deionized water or distilled water. The solid content of the first surface treatment liquid (X) may be appropriately selected, but is preferably 5 to 20 mass %. The pH of the first surface treatment liquid (X) is preferably 8.0 to 10.0. When the pH of the first surface treatment liquid (X) is 8.0 or more, the storage stability of the first surface treatment liquid (X) is preferably obtained. Therefore, the pH of the first surface treatment liquid (X) is preferably 8.0 or more, and more preferably 8.5 or more. On the other hand, when the pH of the first surface treatment liquid (X) is 10.0 or less, the storage stability of the first surface treatment liquid (X) is preferably obtained, and further, etching of the zinc-based plating layer is suitable, and the corrosion resistance of the flat plate portion, the corrosion resistance of the processed portion, and the corrosion resistance after alkaline degreasing are preferably obtained. Therefore, the pH of the first surface treatment liquid (X) is preferably 10.0 or less, and more preferably 9.5 or less. In addition, when adjusting the pH, ammonia or a salt thereof, and one or more of the above-mentioned chelating agents may be appropriately used.

[0056] Furthermore, additives such as alcohols, ketones, cellosolves, amine-based water-soluble solvents, antifoaming agents, antibacterial and antifungal agents, colorants, wettability improvers for uniform coating, resins, surfactants, etc. may be added to the first surface treatment liquid (X) as necessary. However, it is important to add these additives to an extent that does not impair the quality obtained by the present invention, and the amount added is preferably less than 5 mass % at most based on the total solid content of the first surface treatment liquid (X).

[0057] Furthermore, the first surface treatment liquid (X) may contain a small amount 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) described later. In this case, the quality obtained by the present invention is not impaired if the total solid content mass of these is 30 mass% or less based on the total solid content of the first surface treatment liquid (X). Therefore, when the first surface treatment liquid (X) contains one or more of the anionic polyurethane resin (G), silicone resin (H), crosslinking agent (I), and wax (L), the total solid content mass of these is preferably 30 mass% or less based on the total solid content of the first surface treatment liquid (X), more preferably 20 mass% or less, even more preferably 10 mass% or less, and most preferably 5 mass% or less.

[0058] [Second surface treatment liquid (Y)] The second surface treatment liquid (Y) contains sodium silicate (D2), an anionic polyurethane resin (G), and water, and may further contain, as necessary, one or more selected from the group consisting of a silicone resin (H), a crosslinking agent (I), and a wax (L).

[0059] <Sodium silicate (D2)> The second surface treatment liquid (Y) contains sodium silicate (D2). The silanol groups contained in sodium silicate (D2) strengthen the adhesion of the second coating to the first coating, contributing to long-term sweat resistance. When used in combination with the anionic polyurethane resin (G) described below, the high coagulation properties of the urethane bonds in the anionic polyurethane resin (G) allow sodium silicate (D2) to be incorporated into the dense polyurethane resin coating with high barrier properties. In a corrosive environment, the sodium silicate (D2) fixed in the second coating as described above is appropriately dissolved, and the pH of the surface of the zinc-based plating layer is manipulated to the alkaline side, which contributes to delaying and suppressing the anodic reaction of zinc.

[0060] The sodium silicate (D2) used in the present invention is SiO 2 and Na 2 O, the molar ratio of which is SiO 2 / Na2 It is preferable that O is 1 to 4. SiO 2 / Na 2 By making the O content 4 or less, the effect on thermal cracking resistance can be favorably obtained. 2 / Na 2 By making O 1 or more, the sodium silicate (D2) can be preferably fixed in the second coating while ensuring the effect on thermal cracking resistance, and the deterioration of blackening resistance, water stain resistance, and long-term sweat resistance can be preferably suppressed. 2 / Na 2 O is preferably at least 1, and more preferably at least 2. Examples of the sodium silicate (D2) that satisfies the above include sodium silicate No. 2 and sodium silicate No. 3, and one or more of these can be used.

[0061] The sodium silicate (D1) blended in the first surface treatment liquid (X) and the sodium silicate (D2) blended in the second surface treatment liquid (Y) may be the same or different. Since laminating films having different components is effective for effectively improving long-term sweat resistance, it is preferable that the sodium silicate (D1) blended in the first surface treatment liquid (X) and the sodium silicate (D2) blended in the second surface treatment liquid (Y) are different.

[0062] Solid content of sodium silicate (D2) (D2 S ) of the solid content of the anionic polyurethane resin (G) (G S ) to mass ratio (D2 S / G S ) is 0.010 to 0.100. Mass ratio (D2 S / G S If the mass ratio (D2 S / G S ) must be 0.010 or more. On the other hand, the mass ratio (D2 S / G SWhen the mass ratio (D2) exceeds 0.100, the sodium silicate (D2) becomes excessive, which makes it difficult to fix it in the second film, and therefore the blackening resistance, water stain resistance, and long-term sweat resistance are deteriorated. Furthermore, since a large amount of Na ions is present in the second surface treatment liquid (Y), the storage stability of the second surface treatment liquid (Y) is reduced. Therefore, the mass ratio (D2 S / G S ) is 0.100 or less, preferably 0.070 or less, and more preferably 0.050 or less.

[0063] <Anionic polyurethane resin (G)> The second surface treatment liquid (Y) contains an anionic polyurethane resin (G) that has excellent barrier properties against sweat components. This makes the second film denser, contributing to improved long-term sweat resistance. The polyurethane resin has a high molecular weight and the urethane bonds have high intermolecular cohesive force, so it is dense and has high barrier properties, and it also has high adhesion to the first film, so a second film with the above-mentioned excellent performance can be obtained.

[0064] The types of polyols, which are the basic skeleton that determines the properties of the urethane resin, include polyether polyols, polyester polyols, and polycarbonate polyols. Polyester polyols and polycarbonate polyols have polar groups, so that a strong second coating can be obtained by intermolecular interactions. Polycarbonate polyols are expensive, but have excellent mechanical strength. Polyether polyols do not have polar groups, so they are somewhat inferior in mechanical strength, but are chemically stable, such as in terms of hydrolysis resistance. Anionic polyurethane resins (G) can be used alone or in combination of two or more types in the second surface treatment liquid (Y).

[0065] The weight-average molecular weight of the anionic polyurethane resin (G) is not particularly limited, but is preferably about 5,000 to 500,000, and more preferably about 10,000 to 300,000, as measured by gel permeation chromatography as described in JIS-K7252-4. Increasing the weight-average molecular weight can increase the Tg and mechanical properties of the urethane resin, thereby improving the barrier properties of the second coating and further improving the flat plate corrosion resistance, corrosion resistance after alkaline degreasing, water stain resistance, long-term sweat resistance, solvent resistance, and the like.

[0066] The anionic polyurethane resin (G) is obtained by a general synthesis method using a polyol such as polyester polyol, polyether polyol, polycarbonate polyol, etc., and a polyisocyanate as raw materials. Although not limited to the above, a more specific synthesis method is, for example, to produce a urethane prepolymer having isocyanato groups at both ends from a polyol and a polyisocyanate, to which a carboxylic acid having two hydroxyl groups or a reactive derivative thereof is reacted in a solvent to obtain a derivative having isocyanato groups at both ends, and then to which triethanolamine or the like is added as a counter cation, and then to which water is added to form an emulsion, thereby obtaining an anionic polyurethane resin. After this, if necessary, a diamine may be further added to perform chain extension.

[0067] The polyisocyanate used in producing the anionic polyurethane resin (G) may be any of aliphatic, alicyclic and aromatic polyisocyanates. Specific examples include tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, hydrogenated xylylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, phenylene diisocyanate, xylylene diisocyanate, and tetramethylxylylene diisocyanate. Among these, the use of 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, isophorone diisocyanate, etc. is preferred because it gives a second coating that is excellent not only in corrosion resistance of the flat plate portion, corrosion resistance after alkaline degreasing, and solvent resistance, but also in heat discoloration resistance.

[0068] Examples of polyester polyols used in producing the anionic polyurethane resin (G) include various polyester polyols obtained by a dehydration condensation reaction between a glycol or triol, such as ethylene glycol, diethylene glycol, or trimethylolpropane, and a dibasic acid, such as adipic acid or phthalic anhydride; and lactone-based polyester polyols obtained by ring-opening polymerization of ε-caprolactam.

[0069] Examples of polyether polyols used in producing the anionic polyurethane resin (G) include low molecular weight polyols such as 1,2-propanediol, 1,3-propanediol, trimethylolpropane, glycerin, polyglycerin, and pentaerythritol, as well as ethylene oxide and / or propylene oxide adducts of amine compounds such as bisphenol A and ethylenediamine, and polytetramethylene ether glycol.

[0070] Examples of polycarbonate polyols used in producing the anionic polyurethane resin (G) include those obtained by reacting glycols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, methylpentanediol, dimethylbutanediol, butylethylpropanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,4-butanediol, 1,4-cyclohexanediol, and 1,6-hexanediol with diphenyl carbonate, phosgene, or the like.

[0071] The carboxylic acid or its reactive derivative having two or more, preferably two, hydroxyl groups used in producing the anionic polyurethane resin (G) is used to introduce acidic groups into the component (G) and to make the component (G) water-dispersible. Examples of the carboxylic acid include dimethylolalkanoic acids such as dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolpentanoic acid, and dimethylolhexanoic acid. Examples of the reactive derivative include acid anhydrides. By making the component (G) self-dispersible in water in this way and using as little or no emulsifier as possible, a second coating film with excellent water stain resistance can be obtained.

[0072] When producing the anionic polyurethane resin (G), polyamine or water is used. The polyamine or water is used to extend the chain of the prepared prepolymer. Examples of polyamines used in producing the anionic polyurethane resin (G) include hydrazine, ethylenediamine, propylenediamine, 1,6-hexanediamine, tetramethylenediamine, isophoronediamine, xylylenediamine, piperazine, 1,1'-bicyclohexane-4,4'-diamine, diphenylmethanediamine, ethyltolylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, and tetraethylenepentamine, which can be used alone or in combination.

[0073] In order to improve the stability of the resin during synthesis of the anionic polyurethane resin (G) and further the film-forming property when the surrounding environment during film formation is a low-temperature dry environment, it is preferable to add a film-forming assistant during synthesis. Examples of the film-forming assistant include butyl cellosolve, N-methyl-2-pyrrolidone, butyl carbitol, and Texanol, and N-methyl-2-pyrrolidone is preferable.

[0074] The glass transition point (Tg) of the anionic polyurethane resin (G) is preferably 30 to 130°C. If the glass transition point (Tg) is 30°C or higher, the degradation of the barrier property of the second coating can be suppressed, and sufficient solvent resistance can be obtained. Therefore, the glass transition point (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 point (Tg) of the anionic polyurethane resin (G) is 130°C or lower, the second coating can be prevented from becoming excessively hard, and the second coating is less likely to crack during processing, so that excellent paint adhesion can be obtained. Therefore, the glass transition point (Tg) of the anionic polyurethane resin (G) is preferably 130°C or lower, more preferably 110°C or lower. The glass transition point can be adjusted by the molecular weight of the polyol used, etc.

[0075] The glass transition point (Tg) of the anionic polyurethane resin (G) can be determined from the maximum value of tan δ by measuring the dynamic viscoelasticity using a dynamic viscoelasticity measuring device (RSAG2, TA Instrument) using a film prepared by drying at room temperature for 24 hours, then at 80°C for 6 hours and then at 120°C for 20 minutes as a measurement sample.

[0076] Solid content of anionic polyurethane resin (G) (G S ) of the solid content mass of the second surface treatment liquid (Y) (Y S ) to mass ratio (G S / Y S ) is 0.900 to 0.980. Mass ratio (G S / Y S If the mass ratio (G) is less than 0.900, the amount of the anionic polyurethane resin (G) is small, resulting in poor long-term sweat resistance, and also poor resistance to blackening and water stains. S / Y S ) is 0.900 or more, preferably 0.930 or more, and more preferably 0.950 or more. S / Y S If the mass ratio (G) exceeds 0.980, the amount of sodium silicate (D2) decreases relatively, so the adhesion between the second coating and the first coating decreases, and the corrosion resistance of the processed part and the corrosion resistance after alkaline degreasing also decrease. S / Y S ) shall be less than or equal to 0.980.

[0077] In the second surface treatment liquid (Y), the anionic polyurethane resin (G) preferably contains an anionic polyurethane resin having a carbonate skeleton. The anionic polyurethane resin having a carbonate skeleton has a high cohesive force of carbonate bonds, and therefore has small gaps in the resin, which provides excellent barrier properties that suppress the penetration of sweat components or corrosive factors, and is also less prone to hydrolysis, so that a second coating is obtained that is less prone to deterioration in high-temperature and high-humidity environments and can maintain excellent long-term sweat resistance and corrosion resistance for a long period of time. In particular, from the viewpoint of improving long-term sweat resistance, it is preferable to combine a polyether-based polyol with a polycarbonate-based polyol.

[0078] The solid content mass of the anionic polyurethane resin (G) having a carbonate skeleton is S ) is preferably 0.20 to 0.80. By setting the mass ratio to 0.20 or more, long-term sweat resistance can be suitably obtained. Therefore, the mass ratio is preferably 0.20 or more, and more preferably 0.30 or more. On the other hand, by setting the mass ratio to 0.80 or less, solvent resistance can be suitably obtained. Therefore, the mass ratio is preferably 0.80 or less, and more preferably 0.70 or less.

[0079] <Silicone resin (H)> The second surface treatment liquid (Y) may further contain a silicone resin (H). This makes it possible to obtain a second film with better water stain resistance and long-term sweat resistance. The silicone resin (H) is not particularly limited as long as it has a plurality of siloxane bonds and has an organopolysiloxane structure in which an organic group is bonded to silicon (Si), but is preferably an organopolysiloxane structure having at least two organic groups bonded to Si in one molecule. The position at which the organic group is bonded is not particularly limited, and it may be bonded to the main chain, side chain, or end. The silicone resin (H) may be a monopolymer having the above-mentioned organopolysiloxane structure, a mixture of a monopolymer having the above-mentioned organopolysiloxane structure and a monopolymer having a polysiloxane structure, or a copolymer (block copolymer or graft polymer) having the above-mentioned organopolysiloxane structure and a polysiloxane structure. The silicone resin (H) may be an addition type or a condensation type. Furthermore, the silicone resin (H) may be any of a heat curing type, a room temperature curing type (RTV) and a UV curing type.

[0080] Solid content of silicone resin (H) (H S ) of the solid content of the anionic polyurethane resin (G) (G S ) to the mass ratio (H S / G S The mass ratio (H S / GS By making the mass ratio (H ) 0.0030 or more, excellent water repellency and oil repellency can be obtained, and the effect of improving water stain resistance and long-term sweat resistance can be suitably obtained. S / G S ) is preferably 0.0030 or more, more preferably 0.0040 or more. On the other hand, the mass ratio (H S / G S By making the mass ratio (H S / G S ) is preferably 0.0400 or less, more preferably 0.0320 or less.

[0081] <Crosslinking agent (I)> The second surface treatment liquid (Y) may contain a crosslinking agent (I) that reacts with a carboxyl group in order to further improve the corrosion resistance of the processed portion of the second film. The second film contains a carboxyl group possessed by the anionic polyurethane resin (G), and the crosslinking agent (I) crosslinks with the carboxyl group to modify the organic components of the second film. That is, a second film having high barrier properties and flexibility is formed, and cracks in the second film are suppressed even when bending is performed, thereby improving the corrosion resistance of the bent portion. As the crosslinking agent (I), a compound having two or more functional groups capable of reacting with a carboxyl group in one molecule is preferable. Examples of the functional group capable of reacting with a carboxyl group include an epoxy group, a carbodiimide group, and an oxazoline group. Examples of the crosslinking agent (I) include an epoxy resin, a carbodiimide resin, and an oxazoline group-containing polymer, and it is preferable to use one or more selected from these.

[0082] Solid content of crosslinker (I) S ) of the solid content of the anionic polyurethane resin (G) (G S ) to the mass ratio (I S / G S The mass ratio (I S / G S By making the mass ratio (I) 0.0030 or more, the effect of improving the corrosion resistance and solvent resistance of the processed part can be suitably obtained.S / G S ) is preferably 0.0030 or more, more preferably 0.0040 or more. S / G S By making the mass ratio (I) 0.0400 or less, the corrosion resistance of the flat plate portion, the corrosion resistance of the processed portion, the corrosion resistance after alkaline degreasing, and the solvent resistance can be suitably obtained. S / G S ) is preferably 0.0400 or less, more preferably 0.0320 or less.

[0083] <Wax (L)> The second surface treatment liquid (Y) may contain a wax (L) to improve the lubricity of the second coating surface. The wax (L) is not particularly limited as long as it is compatible with the second surface treatment liquid (Y), and examples of the wax include polyolefin waxes such as polyethylene, montan wax, paraffin wax, microcrystalline wax, carnauba wax, lanolin-based wax, silicon-based wax, and fluorine-based wax, and one or more of these can be suitably used. In addition, examples of the polyolefin wax include polyethylene wax, oxidized polyethylene wax, and polypropylene wax, and one or more of these can be used.

[0084] Solid mass of wax (L) S ) of the solid content mass of the second surface treatment liquid (Y) (Y S ) to mass ratio (L S / Y S The mass ratio (L S / Y S By making the mass ratio (L) equal to or greater than 0.010, the lubricity of the surface of the second coating film can be improved. S / Y S ) is preferably 0.010 or more. On the other hand, the mass ratio (L S / Y SBy making the mass ratio (L) 0.120 or less, the lubricity is not too high, and the coil crushing during the winding process during coil production can be suitably prevented. Furthermore, the corrosion resistance and paint adhesion of the processed part can be suitably obtained. Therefore, S / Y S ) is preferably 0.120 or less, more preferably 0.090 or less.

[0085] The second surface treatment liquid (Y) is obtained by mixing the above-mentioned components in water such as deionized water, distilled water, etc. The solid content of the second surface treatment liquid (Y) may be appropriately selected, but is preferably 5 to 20 mass %. The pH of the second surface treatment liquid (Y) is not particularly limited, but is preferably 9.8 to 10.8.

[0086] Furthermore, additives such as alcohols, ketones, cellosolves, amine-based water-soluble solvents, antifoaming agents, antibacterial and antifungal agents, colorants, wettability improvers for uniform coating, resins, surfactants, etc. may be added to the second surface treatment liquid (Y) as necessary. However, it is important to add these additives to an extent that does not impair the quality obtained by the present invention, and the amount added is preferably less than 5 mass % at most based on the total solid content of the second surface treatment liquid (Y).

[0087] (Method of manufacturing zinc-based coated steel sheet with surface treatment film) A method for producing a zinc-based plated steel sheet with a surface treatment film according to one embodiment of the present invention is a method for producing a zinc-based plated steel sheet with a surface treatment film using the above-mentioned surface treatment liquid for zinc-based plated steel sheet, and includes the steps of applying a first surface treatment liquid (X) to the surface of the zinc-based plated steel sheet, drying the applied first surface treatment liquid (X) to form a first film, applying a second surface treatment liquid (Y) to the surface of the first film, and drying the applied second surface treatment liquid (Y) to form a second film. The conditions and methods for forming the first film and the second film are described in detail below.

[0088] Before applying the first surface treatment liquid (X) to the surface of the zinc-based plated steel sheet, the zinc-based plated steel sheet may be subjected to a pretreatment for removing oil or dirt from the surface of the zinc-based plated steel sheet, if necessary. The surface of the zinc-based plated steel sheet is often coated with an anti-rust oil for rust prevention, and even if it is not coated with an anti-rust oil, there is oil or dirt attached during the work. By carrying out the above pretreatment, the surface of the zinc-based plated steel sheet is cleaned and easily wetted uniformly. If there is no oil or dirt on the surface of the zinc-based plated steel sheet and the first surface treatment liquid (X) is uniformly wetted, there is no particular need for a pretreatment step. The method of pretreatment is not particularly limited, and examples thereof include hot water washing, organic solvent washing, and alkaline degreasing washing.

[0089] As a method for applying the first surface treatment liquid (X) to the surface of the zinc-based plated steel sheet and a method for applying the second surface treatment liquid (Y) to the surface of the first coating, an appropriate method may be selected according to the shape of the zinc-based plated steel sheet to be treated, and examples of the method include roll coating, bar coating, immersion, spray coating, etc. After application, it is also possible to adjust the amount of coating, uniform the appearance, and uniform the film thickness by an air knife method or roll squeezing method.

[0090] As a means for drying the applied first surface treatment liquid (X) after the first surface treatment liquid (X) has been applied to the surface of a zinc-based plated steel sheet, in addition to a dryer, a drying oven such as a hot air oven, a high-frequency induction heating oven, or an infrared oven can be used.

[0091] The peak metal temperature (PMT) during drying of the first surface treatment liquid (X) is preferably 40 to 100° C. By setting the peak metal temperature at 40° C. or higher, the condensation reaction of the Si component contained in the first surface treatment liquid (X) can be favorably advanced to form a denser Si-enriched layer. On the other hand, by setting the peak metal temperature at 100° C. or lower, cracks in the first coating can be favorably suppressed.

[0092] The heating time when drying the first surface treatment liquid (X) is appropriately selected according to the composition of the zinc-based plated steel sheet used, the process and configuration of the production line, etc. From the viewpoint of productivity, etc., the heating time is preferably 0.1 to 60 seconds, and more preferably 1 to 30 seconds.

[0093] The amount of the first coating after drying is 0.010 to 0.400 g / m per side. 2 is preferably 0.030 to 0.250 g / m 2 It is more preferable that the coating weight of the first coating is 0.010 g / m 2 By setting the coating weight of the first coating to 0.400 g / m or more, the barrier property is favorably obtained, and the corrosion resistance of the flat plate portion, the corrosion resistance after alkaline degreasing, the blackening resistance, the long-term sweat resistance, and the water stain resistance are favorably obtained. 2 By setting the thickness as described below, the first coating has an appropriate thickness, and favorable resistance to thermal discoloration and thermal cracking can be obtained.

[0094] After the second surface treatment liquid (Y) is applied to the surface of the first coating, a drying oven such as a hot air oven, a high-frequency induction heating oven, or an infrared oven can be used as a means for drying the applied second surface treatment liquid (Y) in addition to a dryer.

[0095] Here, the maximum sheet temperature reached when drying the second surface treatment liquid (Y) is preferably 60 to 200° C., more preferably 80 to 180° C. If the maximum sheet temperature is 60° C. or higher, bonding between the components of the second coating is obtained, and the various properties required by the present invention are preferably obtained. On the other hand, if the maximum sheet temperature is 200° C. or lower, cracks in the second coating or thermal decomposition of the coating components is unlikely to occur, and the various properties required by the present invention are preferably obtained.

[0096] The heating time when drying the second surface treatment liquid (Y) is appropriately selected under optimal conditions depending on the composition of the zinc-based plated steel sheet used, the process and configuration of the production line, etc., and from the viewpoint of productivity, etc., it is preferably 0.1 to 60 seconds, and more preferably 1 to 30 seconds.

[0097] The amount of the second coating applied after drying is 0.20 to 3.00 g / m per side. 2It is preferable that the thickness is 0.40 to 2.00 g / m 2 It is more preferable that the coating weight of the second coating is 0.20 g / m 2 By setting the coating weight of the second coating to 3.00 g / m or more, sufficient barrier properties are obtained, and the flat plate corrosion resistance, corrosion resistance after alkaline degreasing, long-term sweat resistance, and water stain resistance are favorably obtained. 2 By setting the content as below, resistance to heat discoloration, resistance to heat cracking, and paint adhesion can be suitably obtained.

[0098] Regarding steps and conditions not described in the present invention, conventional methods can be used.

[0099] (Zinc-plated steel sheet with surface treatment film) A zinc-based plated steel sheet with a surface treatment film according to one embodiment of the present invention is a zinc-based plated steel sheet with a surface treatment film produced by the above-mentioned production method, and has a zinc-based plated steel sheet and a surface treatment film formed on at least one side of the zinc-based plated steel sheet.

[0100] [Zinc-plated steel sheet] The zinc-based plated steel sheet used in the present invention may be an electrolytic zinc-plated steel sheet, a hot-dip zinc-plated steel sheet, a zinc-aluminum alloy-plated steel sheet, a zinc-iron alloy-plated steel sheet, a zinc-magnesium alloy-plated steel sheet, a zinc-aluminum-magnesium alloy-plated steel sheet, or the like.

[0101] More preferably, a hot-dip Zn-Al alloy-plated steel sheet can be used, which has a hot-dip Zn-Al alloy plating layer containing, in mass%, Al: 3.0 to 12.0%, Mg: 0.2 to 6.0%, Ni: 0.0 to 0.1%, and the balance being Zn and unavoidable impurities, on at least one surface of a base steel sheet as a substrate. The use of this hot-dip Zn-Al alloy-plated steel sheet has the advantage of being superior in red rust resistance compared to the use of other plated steel sheets. This is advantageous when used in more severe corrosive environments such as outdoors. The hot-dip Zn-Al alloy plating layer does not need to contain Ni, but is preferably one containing 0.1 mass% or less Ni, since blackening resistance can be suitably obtained. It is more preferable that this hot-dip Zn-Al alloy-plated steel sheet contains a Zn-Al-Mg ternary eutectic in the hot-dip Zn-Al alloy plating layer. The Zn-Al-Mg ternary eutectic is preferably contained in an area ratio of 1 to 50% on the plating layer surface.

[0102] [Surface treatment film] The surface treatment film in the present invention includes a first film on a zinc-based plated steel sheet and a second film on the first film. The first film is obtained by applying the above-mentioned first surface treatment liquid (X) to the surface of the zinc-based plated steel sheet and drying it. The second film is obtained by applying the above-mentioned second surface treatment liquid (Y) to the surface of the first film and drying it. The zinc-based plated steel sheet with a surface treatment film of this embodiment is excellent in all of heat discoloration resistance, heat cracking resistance, corrosion resistance of flat plate parts, corrosion resistance of processed parts, corrosion resistance after alkaline degreasing, blackening resistance, water stain resistance, solvent resistance, long-term sweat resistance, and paint adhesion.

[0103] It is important that the surface treatment film has a silicon-enriched layer on the outermost surface of the first film, and a second film mainly made of resin. In the drying stage of the first film, the Zr component bonds faster than the Si component, so there are areas where the Si component is incorporated into the network structure of the Zr component, and areas where the Si component is concentrated. The anionic polyurethane resin itself of the second film has high barrier properties against sweat components, and the inclusion of sodium silicate provides strong adhesion to the first film with the silicon-enriched layer, making it possible to significantly improve long-term sweat resistance. EXAMPLES

[0104] The effects of the present invention will be described below with reference to examples and comparative examples. However, these examples are merely examples for explaining the present invention and do not limit the present invention.

[0105] (1) Test board The various zinc-based plated steel sheets used as test sheets are shown in Table 1. The zinc-based plated layers were formed on both sides of the steel sheet (base steel sheet), and the coating weights in Table 1 refer to the coating weight of the zinc-based plated layer per side.

[0106] [Table 1]

[0107] (2) Pretreatment (cleaning) The surface of the above-mentioned test plate was treated with Fine Cleaner E6406 manufactured by Nippon Parkerizing Co., Ltd. to remove oil or dirt from the surface. Next, the test plate was washed with tap water to confirm that the surface of the test plate was 100% wetted with water, and then pure water (deionized water) was poured over it, and the water was dried in an oven at 100°C.

[0108] (3) Preparation of surface treatment solution The components shown in Table 2 were mixed in water at the respective blending ratios (mass ratios) shown in Table 2 to obtain a first surface treatment liquid (X) having a solid content of 6 mass%. The components shown in Table 3 were mixed in water at the respective blending ratios (mass ratios) shown in Table 3 to obtain a second surface treatment liquid (Y) having a solid content of 15 mass%.

[0109] The components shown in Table 4 were mixed in water in the respective blending ratios (mass ratios) shown in Table 4 to obtain first surface treatment liquids X48 to X50 with a solid content of 6 mass%. The first surface treatment liquids X48 and X49 are assumed to be obtained by incorporating the components contained in the first surface treatment liquid (X) and the second surface treatment liquid (Y) of the present invention into one surface treatment liquid. In particular, X49 has the same composition as the surface treatment liquid disclosed in Patent Document 1. X50 is obtained by incorporating 30 mass% of anionic polyurethane resin (G4) into the first surface treatment liquid X1 in Table 2 with respect to the total solid content of X50. In Table 4, the total mass (X S ) of the solid content of the anionic polyurethane resin (G) (G S ) to mass ratio (X S / G S ) is stated.

[0110] [Table 2]

[0111] [Table 3]

[0112] [Table 4]

[0113] The compounds used in Tables 2 to 4 are explained below.

[0114] <Silane coupling agent having a glycidyl group (A)> A1: 3-glycidoxypropyltriethoxysilane A2: 3-glycidoxypropyltrimethoxysilane

[0115] <Tetraalkoxysilane (B)> B1: Tetraethoxysilane B2: Tetramethoxysilane

[0116] <Zirconium carbonate compound (C)> C1: Ammonium zirconium carbonate (ZrO 2 :20.0 mass%) C2: Potassium zirconium carbonate (ZrO 2 :20.0 mass%)

[0117] <Sodium silicate (D1, D2)> D-1: No. 3 sodium silicate (solid content: 38.5% by mass) D-2: No. 2 sodium silicate (solid content: 40.6% by mass)

[0118] <Vanadium Compounds (E)> E1: Metavanadyl acetylacetonate (V: 19.2% by mass) E2: Ammonium metavanadate (V: 43.5% by mass)

[0119] <Molybdic acid compounds (F)> F1: Ammonium molybdate (Mo: 54.4% by mass) F2: Sodium molybdate (Mo: 43.8% by mass)

[0120] <Anionic polyurethane resin (G)> Manufacturing method of anionic polyurethane resin (G1) 100 parts by mass of polyether polyol having 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 having a free isocyanato group content of 5% relative to the solid 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 urethane prepolymer was added and emulsified while stirring with a homomixer. Finally, deionized water was added to obtain a water-dispersible anionic polyurethane resin (G1) having a solid content of 25% by mass. In the anionic polyurethane resin (G1), the solid content mass of the anionic polyurethane resin having a carbonate skeleton was calculated based on the solid content mass (G S ) was 0.4. The glass transition point (Tg) of the resulting anionic polyurethane resin (G1) was 95° C. as measured using a dynamic viscoelasticity measuring device.

[0121] Manufacturing method of anionic polyurethane resin (G2) A water-dispersible anionic polyurethane resin (G2) having a solid content of 25% by mass was obtained in the same manner as in the production method for anionic polyurethane resin (G1), except that 20 parts by mass of 1,4-butanediol-2-sulfonic acid was used in the reactor instead of 20 parts by mass of 2,2-dimethylolpropionic acid. S ) was 0.3 by mass. The glass transition point (Tg) of the resulting anionic polyurethane resin (G2) was 95° C. as measured by a dynamic viscoelasticity measuring device.

[0122] Manufacturing method of anionic polyurethane resin (G3) A water-dispersible anionic polyurethane resin (G3) having a solid content of 25% by mass was obtained in the same manner as in the production method for anionic polyurethane resin (G1), except that 100 parts by mass of a polyester polyol having a number average molecular weight of 2220 obtained from 1,6-hexanediol and adipic acid was used in the reactor instead of 100 parts by mass of a polyether polyol having a number average molecular weight of 5000 obtained from polyethylene glycol and polypropylene glycol. S ) was 0.5 by mass. The glass transition point (Tg) of the resulting anionic polyurethane resin (G3) was 70° C. as measured by a dynamic viscoelasticity measuring device.

[0123] Manufacturing method of anionic polyurethane resin (G4) A water-dispersible anionic polyurethane resin (G4) having a solid content of 25% by mass was obtained in the same manner as in the production method for anionic polyurethane resin (G1), except that 100 parts by mass of a polyether polyol having a number average molecular weight of 1560 obtained from polyethylene glycol and polypropylene glycol was used in the reactor instead of 100 parts by mass of a polyether polyol having a number average molecular weight of 5000 obtained from polyethylene glycol and polypropylene. S ) was 0.4. The glass transition point (Tg) of the resulting anionic polyurethane resin (G4) was 105° C. as measured using a dynamic viscoelasticity measuring device.

[0124] Manufacturing method of anionic polyurethane resin (G5) A water-dispersible anionic polyurethane resin (G5) having a solid content of 25% by mass was obtained in the same manner as in the production method for anionic polyurethane resin (G1), except that 100 parts by mass of a polyester polyol having a number average molecular weight of 1,320 obtained from 1,6-hexanediol and adipic acid was used in place of 100 parts by mass of a polyether polyol having a number average molecular weight of 5,000 obtained from polyethylene glycol and polypropylene glycol in the reactor. S ) was 0.3 by mass. The glass transition point (Tg) of the resulting anionic polyurethane resin (G5) was 120° C. as measured by a dynamic viscoelasticity measuring device.

[0125] Manufacturing method of anionic polyurethane resin (G6) A water-dispersible anionic polyurethane resin (G6) having a solid content of 25% by mass was obtained in the same manner as in the production method for anionic polyurethane resin (G1), except that 100 parts by mass of a polyester polyol having a number average molecular weight of 1000 obtained from 1,6-hexanediol and adipic acid was used in place of 100 parts by mass of a polyether polyol having a number average molecular weight of 5000 obtained from polyethylene glycol and polypropylene glycol in the reactor. S ) was 0.4. The glass transition point (Tg) of the resulting anionic polyurethane resin (G6) was measured using a dynamic viscoelasticity measuring device and was found to be 140°C.

[0126] Manufacturing method of anionic polyurethane resin (G7) A water-dispersible anionic polyurethane resin (G7) having a solid content of 25% by mass was obtained in the same manner as in the production method for anionic polyurethane resin (G1), except that 100 parts by mass of a polyether polyol having a number average molecular weight of 5,900 obtained from polyethylene glycol and polypropylene was used in the reactor instead of 100 parts by mass of a polyether polyol having a number average molecular weight of 5,000 obtained from polyethylene glycol and polypropylene. S ) was 0.5 by mass. The glass transition point (Tg) of the resulting anionic polyurethane resin (G7) was 40° C. as measured by a dynamic viscoelasticity measuring device.

[0127] Manufacturing method of anionic polyurethane resin (G8) A water-dispersible anionic polyurethane resin (G8) having a solid content of 25% by mass was obtained in the same manner as in the production method for anionic polyurethane resin (G1), except that 100 parts by mass of a polycarbonate polyol having a number average molecular weight of 6600 obtained from 1,6-hexanediol and phosgene was used in place of 100 parts by mass of a polyether polyol having a number average molecular weight of 5000 obtained from polyethylene glycol and polypropylene glycol in the reactor. S ) was 0.6. The glass transition point (Tg) of the resulting anionic polyurethane resin (G8) was measured using a dynamic viscoelasticity measuring device and was found to be 20°C.

[0128] Manufacturing method of anionic polyurethane resin (G9) A water-dispersible anionic polyurethane resin (G9) having a solid content of 25% by mass was obtained in the same manner as in the production method for anionic polyurethane resin (G1), except that 100 parts by mass of a polycarbonate polyol having a number average molecular weight of 5,300 obtained from 1,6-hexanediol and phosgene was used in place of 100 parts by mass of a polyether polyol having a number average molecular weight of 5,000 obtained from polyethylene glycol and polypropylene glycol in the reactor. S ) was 0.7. The glass transition point (Tg) of the resulting anionic polyurethane resin (G9) was 60° C. as measured using a dynamic viscoelasticity measuring device.

[0129] <Silicone resin (H)> H1: Silicone resin emulsion (solid content: 37% by mass, Shin-Etsu Chemical Co., Ltd. KM-9782 (registered trademark)) H2: Silicone resin emulsion (solid content: 15% by mass, WACKERHC321 (registered trademark) manufactured by Asahi Kasei Wacker Silicone Co., Ltd.)

[0130] <Crosslinking agent (I)> I1: Epoxy resin (solid content: 100% by mass, Denacol (registered trademark) EX-313 manufactured by Nagase ChemteX Corporation) I2: Carbodiimide resin (solid content: 40% by mass, Carbodilite (registered trademark) SV-02, manufactured by Nisshinbo Chemical Inc.) I3: Oxazoline group-containing polymer (solid content: 40% by mass, Epocross (registered trademark) K-2020 manufactured by Nippon Shokubai Co., Ltd.)

[0131] <Phosphate Compound (J)> J1: Diphosphonic acid (C 2 H 8 P 2 O 7 ) J2: Ammonium dihydrogen phosphate (NH 4 (H 2PO 4 )) J3: Phosphate (H 3 PO 4 )

[0132] <Fluorine compounds (K)> K1: Ammonium fluoride K2: Potassium fluoride

[0133] <Wax (L)> L1: Polyethylene wax (solid content: 40.0 mass%, Mitsui Chemicals, Inc., Chemipearl (registered trademark) W900) L2: Microcrystalline wax (solid content: 46.0% by mass, Nopco (registered trademark) 1245-M-SN manufactured by San Nopco Ltd.)

[0134] (4) Treatment method The various first surface treatment liquids (X) in Table 2 or Table 4 were applied to various test sheets that had been pretreated for each steel sheet shown in Table 1 (the steel sheet numbers are shown in the "plated steel sheet" column in Table 5) using a bar coater, and then, without washing with water, the sheets were placed in an oven as they were, and dried at the maximum sheet temperature shown in the "PMT" column in Table 5, to form a first film on both sides with the adhesion amount (per side) shown in Table 5. Next, the various second surface treatment liquids (Y) in Table 3 were applied to the surface of the first film using a bar coater, and then, without washing with water, the sheets were placed in an oven as they were, and dried at the maximum sheet temperature shown in the "PMT" column in Table 5, to form a second film on both sides with the adhesion amount (per side) shown in Table 5. The adhesion amounts of the first film and the second film were determined by measuring the two-layer film consisting of the first film and the second film using a fluorescent X-ray analyzer. First, the Zr contained in the two-layer film was quantified using a fluorescent X-ray analyzer to determine the Zr adhesion amount. Since the Zr contained in the two-layered film is Zr of the zirconium carbonate compound (C) contained in the first film, the Zr adhesion amount of the two-layered film was calculated by converting the adhesion amount of the first film. Next, the Si contained in the two-layered film was quantified by a fluorescent X-ray analyzer to calculate the Si adhesion amount of the two-layered film. In addition, the Si adhesion amount due to the Si of the silane coupling agent (A) having a glycidyl group and the tetraalkoxysilane (B) contained in the first film was calculated from the adhesion amount of the above-mentioned first film. The Si adhesion amount of the second film was calculated by subtracting the Si adhesion amount of the first film from the Si adhesion amount of the two-layered film. The Si adhesion amount of the second film is due to the Si of the sodium silicate (D2) and silicone resin (H) contained in the second film, and was calculated by converting the Si adhesion amount of the second film from the Si adhesion amount of the second film.

[0135] [Table 5] TIFF2025070283000006.tif245129TIFF2025070283000007.tif245129

[0136] (5) Evaluation test method The following evaluations (5-1) to (5-11) were performed on samples taken from the obtained zinc-based plated steel sheets with surface treatment films, and the following evaluation (5-12) was performed on the first surface treatment liquid (X) and the second surface treatment liquid (Y) are shown in Table 5. The evaluation criteria △ and × are undesirable due to insufficient performance.

[0137] (5-1) Heat resistance Each sample was heated to a sheet temperature of 500°C in 30 seconds in an infrared image furnace, held for 5 minutes, and then allowed to cool naturally to room temperature. The surface appearance was visually observed. The evaluation criteria were as follows: (Evaluation Criteria) ◎: No discoloration ○: Very slightly brownish ○-: Slightly brownish △: Turned brown ×: Discolored to brown

[0138] (5-2) Heat cracking resistance Each sample was heated to a sheet temperature of 500°C in an infrared image furnace for 30 seconds, held for 5 minutes, and then allowed to cool naturally to room temperature, after which the surface appearance was visually observed. If no cracks were visible, they were observed at 1000x magnification using an optical microscope. The evaluation criteria were as follows: (Evaluation Criteria) ◎: No cracks ○: Very slight cracks ○-: Slight cracks △: Thin cracks on the entire surface ×: There are wide cracks in addition to narrow cracks on the entire surface.

[0139] (5-3) Corrosion resistance of flat plate A salt spray test (SST) was conducted for each sample in the flat plate state in accordance with JIS-Z-2371-2000. The corrosion resistance of the flat plate was evaluated based on the area ratio of white rust after 240 hours. The evaluation criteria were as follows: (Evaluation Criteria) ◎: White rust area rate less than 5% ○: White rust area ratio is 5% or more and less than 10% ○-: White rust area ratio is 10% or more and less than 25% △: White rust area ratio is 25% or more and less than 50% ×: White rust area ratio 50% or more and 100% or less

[0140] (5-4) Corrosion resistance of processed parts Each sample was bent 90° at 3R and subjected to a salt spray test (SST) in accordance with JIS-Z-2371-2000. The corrosion resistance of the bent part was evaluated based on the area ratio of white rust on the top of the bent part after 144 hours. The evaluation criteria are as follows: (Evaluation Criteria) ◎: White rust area rate of bent part is less than 5% ○: White rust area rate of bent part is 5% or more and less than 10% ○-: White rust area rate of bent part is 10% or more and less than 25% △: White rust area rate of bent part is 25% or more but less than 50% ×: White rust area rate of bent part is 50% or more and 100% or less

[0141] (5-5) Corrosion resistance after alkaline degreasing Alkaline degreaser 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 this alkaline solution for 2 minutes, removed, washed with water, and dried. A salt spray test (JIS-Z-2371-2000) was conducted on each sample, and the white rust occurrence area rate after 120 hours was evaluated. The evaluation criteria were as shown in (5-3) Evaluation of corrosion resistance of flat plate part above.

[0142] (5-6) Resistance to blackening Each sample was left for 24 hours in a thermohygrostat controlled at a temperature of 80°C and a relative humidity of 98%, and the change in luminosity (L value) (ΔL = L value after test - L value before test) was calculated. The evaluation criteria are as follows. The L value was measured in SCI mode (specular reflection included) using an SR2000 made by Nippon Denshoku Industries Co., Ltd. (Evaluation Criteria) ◎: -6<△L, and uniform appearance without unevenness ○: -10<△L≦-6, and uniform appearance without unevenness ○-: -14<△L≦-10, and uniform appearance without unevenness △: -14<△L≦-10, and there are minute black spots ×: △L≦-14, or appearance unevenness

[0143] (5-7) Water stain resistance For each sample, 100 μL of deionized water was dropped onto the surface of the flat plate, and the plate was placed in a hot air oven at 100° C. for 10 minutes. After removing the plate from the oven, the water droplets were visually observed to evaluate the water stain resistance. The evaluation criteria were as follows: (Evaluation Criteria) ◎: The water droplet boundary is not visible regardless of the viewing angle. ○: The water droplet boundary is slightly visible depending on the viewing angle. ○-: Water droplet boundaries are slightly visible regardless of viewing angle. △: The water droplet boundary is clearly visible regardless of the viewing angle. ×: The boundary of the water droplet is clearly visible beyond the drop area.

[0144] (5-8) Solvent resistance A gauze soaked in ethanol was pressed against the surface of each sample with a load of 4.90 N (500 gf), and the surface was rubbed back and forth 10 times while maintaining the load. The rubbed marks were visually evaluated. The evaluation criteria were as follows: (Evaluation Criteria) ◎: No trace ○: No traces are visible when viewed from above, but they are clearly visible when viewed from an angle. ○-: Slight traces are visible when viewed from above. △: Traces are clearly visible when viewed from above. ×: The coating is peeled off.

[0145] (5-9) Long-term sweat resistance 10μL of artificial sweat conforming to JIS-B7001-1995 was dropped onto the surface of each sample, and a silicone rubber stopper was pressed onto the drop to create a certain area of ​​soiled with artificial sweat. The test piece was left to stand for 8 days in a thermo-hygrostat controlled at a temperature of 40℃ and a relative humidity of 80%, after which the appearance change of the soiled area was evaluated. The evaluation criteria were as follows: (Evaluation Criteria) ◎: No discoloration ○: Very slight discoloration ○-: Slight discoloration △: Slightly blackened ×: Clearly blackened

[0146] (5-10) Paint adhesion Each sample was painted with Delicon (registered trademark) #700 (manufactured by Dai Nippon Toryo Co., Ltd.), a melamine alkyd paint, and baked at 130°C for 30 minutes to form a coating film with a thickness of 30 μm. The sample was then immersed in boiling water for 2 hours, and immediately cut into the steel substrate in a grid pattern (10 × 10 pieces, 1 mm intervals). The sample was then extruded 5 mm using an Erichsen extruder so that the cut parts were on the outer (front) side, and the coating was attached and peeled off using an adhesive tape, and the peeled area of ​​the coating film was measured. The evaluation criteria were as follows. The Erichsen extrusion conditions were in accordance with JISZ-2247-2006, with a punch diameter of 20 mm, a die diameter of 27 mm, and a drawing width of 27 mm. (Evaluation Criteria) ◎: No peeling ○: Peeling area less than 3% ○-: Peeling area 3% or more, less than 10% △: Peeling area 10% or more, less than 30% ×: Peeling area 30% or more

[0147] (5-11) Lubricity A disk-shaped test piece with a diameter of 100 mm was cut out from each sample and molded into a cup shape under the following conditions: punch diameter: 50 mm, die diameter: 51.91 mm, and blank holding force: 1 ton. The appearance of the drawn surface of the molded product (the outer side of the cup) was visually inspected and the degree of scratches and blackening was evaluated. The evaluation criteria were as follows: (Evaluation Criteria) ◎: Almost no change across the entire surface, and the appearance is uniform ○: Slight scratches and blackening occurred, and the appearance was obviously uneven. ○-: Localized scratches and blackening, with a clearly uneven appearance △: Severe scratches and blackening occurred mainly in the corners ×: Unable to mold and cracked

[0148] (5-12) Storage stability Each surface treatment solution shown in Table 2 was stored in a thermostatic chamber at 40° C. for 30 days. After removal, the appearance of each surface treatment solution was visually inspected and evaluated. The evaluation criteria were as follows: (Evaluation Criteria) ◎: No change ○: A very small amount of precipitation is observed ○-: A small amount of precipitation is observed △: A small amount of precipitation was observed and the viscosity increased slightly. ×: A large amount of precipitation was observed or gelation occurred.

[0149] As shown in Table 3, the examples of the present invention are excellent in heat discoloration resistance, heat cracking resistance, flat plate corrosion resistance, processed part corrosion resistance, corrosion resistance after alkaline degreasing, blackening resistance, water stain resistance, solvent resistance, long-term sweat resistance, paint adhesion, and storage stability. In addition, the examples of the present invention containing wax were particularly excellent in lubricity. In contrast, the comparative examples, in which any of the requirements deviate from the appropriate range of the present invention, are unable to fully obtain any of the above characteristics. [Industrial Applicability]

[0150] According to the present invention, it is possible to produce a zinc-based plated steel sheet with a surface treatment film that is excellent in all of heat discoloration resistance, heat cracking resistance, corrosion resistance in flat parts, corrosion resistance in processed parts, corrosion resistance after alkaline degreasing, blackening resistance, water stain resistance, solvent resistance, long-term sweat resistance, and paint adhesion.

Claims

1. 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) having a glycidyl group, 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 respective components satisfy the following (1) to (6); The second surface treatment solution (Y) contains sodium silicate (D2), an anionic polyurethane resin (G), and water, and the contents of each of the components satisfy the following (7) and (8). (1) The solid content mass of the silane coupling agent (A) having a glycidyl group (A Ｓ ) the solid content mass (A) of the silane coupling agent (A) having a glycidyl group Ｓ ), the solid content mass of tetraalkoxysilane (B) (B Ｓ ), and ZrO in the zirconium carbonate compound (C) ２ Converted mass (C Ｚ ) total mass (X Ｓ ) to mass ratio (A Ｓ / X Ｓ ) is 0.050 to 0.450 (2) Solid content mass of tetraalkoxysilane (B) (B Ｓ ) of the total mass (X Ｓ ) to the mass ratio (B Ｓ / X Ｓ ) is 0.010 to 0.190 (3) ZrO in the zirconium carbonate compound (C) ２ Converted mass (C Ｚ ) of the total mass (X Ｓ ) to the mass ratio (C Ｚ / X Ｓ ) is 0.460 to 0.910 (4) Solid content mass of sodium silicate (D1) (D1 Ｓ ) of the total mass (X Ｓ ) to mass ratio (D1 Ｓ / X Ｓ ) is 0.040 to 0.630 (5) Vanadium compound (E) converted to V mass (E Ｖ ) of the total mass (X Ｓ ) and the solid content mass of sodium silicate (D1) (D1 Ｓ ) and the total mass (X Ｓ +D1 Ｓ ) to the mass ratio (E Ｖ / (X Ｓ +D1 Ｓ ) is 0.006 to 0.094 (6) Mo-equivalent mass (F) of the molybdic acid compound (F) Ｍ ) of the total mass (X Ｓ ) and the solid content mass of sodium silicate (D1) (D1 Ｓ ) and the total mass (X Ｓ +D1 Ｓ ) to the mass ratio (F Ｍ / (X Ｓ +D1 Ｓ )) is 0.030 to 0.280 (7) Solid content mass of sodium silicate (D2) (D2 Ｓ ) the solid content mass of the anionic polyurethane resin (G) (G Ｓ ) to mass ratio (D2 Ｓ / G Ｓ ) is 0.010 to 0.100 (8) Solid content mass of anionic polyurethane resin (G) (G Ｓ ) of the solid content mass (Y) of the second surface treatment liquid (Y Ｓ ) to mass ratio (G Ｓ / Y Ｓ ) is between 0.900 and 0.980

2. 2. The surface treatment solution for zinc-based plated steel sheet according to claim 1, wherein in the second surface treatment solution (Y), the anionic polyurethane resin (G) contains an anionic polyurethane resin having a carbonate skeleton, and the content thereof satisfies the following (9). (9) The solid content mass of the anionic polyurethane resin having a carbonate skeleton is the solid content mass of the anionic polyurethane resin (G) (G Ｓ ) mass ratio is 0.20 to 0.80

3. 2. The surface treatment solution for zinc-based plated steel sheet according to claim 1, wherein the second surface treatment solution (Y) further contains a silicone resin (H), the content of which satisfies the following (10). (10) Solid content mass of silicone resin (H) (H Ｓ ) the solid content mass of the anionic polyurethane resin (G) (G Ｓ ) to the mass ratio (H Ｓ / G Ｓ ) is 0.0030 to 0.0400

4. 2. The surface treatment solution for zinc-based plated steel sheet according to claim 1, wherein the second surface treatment solution (Y) further contains a crosslinking agent (I) whose content satisfies the following (11). (11) Solid content mass of crosslinking agent (I) Ｓ ) the solid content mass of the anionic polyurethane resin (G) (G Ｓ ) to the mass ratio (I Ｓ / G Ｓ ) is 0.0030 to 0.0400

5. 2. The surface treatment solution for zinc-based plated steel sheet according to claim 1, wherein the second surface treatment solution (Y) further contains a wax (L), the content of which satisfies the following (12). (12) Solid mass of wax (L) (L Ｓ ) of the solid content mass (Y) of the second surface treatment liquid (Y Ｓ ) to mass ratio (L Ｓ / Y Ｓ ) is 0.010 to 0.120

6. 2. The surface treatment solution for zinc-based plated steel sheet according to claim 1, wherein the first surface treatment solution (X) further contains a phosphate compound (J), the content of which satisfies the following (13). (13) Solid content mass of phosphoric acid compound (J) (J Ｓ ) of the total mass (X Ｓ ) to mass ratio (J Ｓ / X Ｓ ) is 0.140 to 0.770

7. 2. The surface treatment solution for zinc-based plated steel sheet according to claim 1, wherein the first surface treatment solution (X) further contains a fluorine compound (K) and the content thereof satisfies the following (14). (14) Solid content mass of fluorine compound (K) (K Ｓ ) of the total mass (X Ｓ ) to mass ratio (K Ｓ / X Ｓ ) is 0.040 to 0.610

8. A method for producing a zinc-based plated steel sheet having a surface treatment film using the surface treatment liquid for zinc-based plated steel sheet according to any one of claims 1 to 7, comprising the steps of: applying the first surface treatment liquid (X) to a surface of a zinc-based plated steel sheet; Thereafter, a step of drying the applied first surface treatment liquid (X) to form a first coating; thereafter, applying the second surface treatment liquid (Y) to the surface of the first coating; Thereafter, a step of drying the applied second surface treatment liquid (Y) to form a second coating; A method for producing a zinc-based plated steel sheet having a surface treatment film, comprising the steps of:

9. The coating weight of the first coating is 0.010 to 0.400 g / m ２ and the coating weight of the second coating is 0.20 to 3.00 g / m ２ The method for producing a zinc-based plated steel sheet having a surface treatment film according to claim 8,

10. A zinc-based plated steel sheet having a surface treatment film, produced by the method for producing a zinc-based plated steel sheet having a surface treatment film according to claim 8.

11. 11. The zinc-based plated steel sheet with a surface treatment film according to claim 10, wherein the zinc-based plated steel sheet has a hot-dip Zn-Al-based alloy plating layer having a component composition containing, in mass %, 3.0 to 12.0% Al, 0.2 to 6.0% Mg, 0.0 to 0.1% Ni, and the balance consisting of Zn and unavoidable impurities, on at least one surface of a base steel sheet as a substrate.

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