JP2017155261A - Surface treatment galvanized steel sheet excellent in appearance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment galvanized steel sheet excellent in appearance.SOLUTION: The surface treatment galvanized steel sheet comprises a galvanized steel sheet, a first layer formed on at least one surface of the galvanized steel sheet and a second layer formed on the first layer. The first layer includes a zinc phosphate crystal; the coating weight of the zinc phosphate crystal is 0.04 -0.4 g/m; and the major axis of the zinc phosphate crystal is 2.5 μm or less. The second layer includes a resin, and the coating weight of the second layer is 0.35-0.85 g/m.SELECTED DRAWING: None

Description

  The present invention relates to a surface-treated galvanized steel sheet excellent in appearance.

Conventionally, it is known that a blackening phenomenon occurs on the surface of a galvanized steel sheet. The blackening phenomenon of galvanized steel sheets is a phenomenon in which the galvanized surface turns blackish. Specifically, it is a corrosion phenomenon seen in the early stage of the corrosive environment before white rust occurs, and it is relatively mild. It occurs in a corrosive environment. The reason why the plating surface looks black is that an amorphous oxide deviating from the stoichiometric composition of Zn _x O _1-x is formed during the oxidation reaction (corrosion reaction) of Zn. Blackening is said to occur because the oxidation reaction of Zn ends halfway. To prevent blackening, the oxidation reaction may be promoted to some extent, but if it is promoted too much, the corrosion resistance will be significantly degraded. And white rust occurs.

  Therefore, it is conceivable to add Ni, Co, In, or the like as an element that appropriately promotes the oxidation reaction to the galvanized layer. However, it is necessary to consider the balance with elements that degrade the corrosion resistance, such as Pb, Cu, and Ag, present as impurities in the galvanized layer.

  Patent documents 1-4 are mentioned as conventional technology which added elements, such as Ni, Co, and In, and adjusted the balance in a Zn plating layer.

  As a method other than the above, Patent Document 5 discloses a metal layer formed by depositing at least one of Ni and Co on the surface of an electrogalvanized layer, and a chromate film formed on the metal layer. A steel plate provided with is disclosed.

  Furthermore, as a method for improving blackening resistance without deteriorating the corrosion resistance of the chromate-free steel sheet, Patent Document 6 includes Si, P, As, S, Fe, Co, B, Ge, Mn, Cu, and Zn. Containing at least one selected first element (heteroelement) and at least one second element (polyelement) selected from Mo, W, V, and Nb, and the second element as a heteropoly A zinc-based plated steel sheet that is present in the chemical conversion coating as an acid is disclosed.

Japanese Patent Laid-Open No. 2-8374 Japanese Patent Laid-Open No. 1-129991 Japanese Unexamined Patent Publication No. 60-77788 JP 2000-355790 A JP-A-10-219494 JP 2012-167326 A

  By adding a metal element such as Ni or Co to the zinc plating solution or providing a layer containing a metal element such as Ni or Co on the steel plate, the resistance to blackening can be improved, but the metal element in a corrosive environment can be improved. Discoloration unevenness due to valence change or metal elution may occur, resulting in poor appearance.

  Further, considering the balance of corrosion resistance, blackening resistance, adhesion to the galvanized surface, and electrical conductivity of the steel sheet, an inorganic rich film or an organic rich film is further added on the steel sheet described in each of the above patent documents. It is also conceivable to form a thin film of about 5 to 1 μm. However, the corrosion resistance (barrier property) is improved halfway due to the difference in barrier properties (oxygen permeability, water permeability) between the existing coating or plating surface and the newly provided coating. An oxidation reaction occurs in a state where oxygen supply to the surface is insufficient, and an amorphous oxide is generated, resulting in a blackening phenomenon on the galvanized surface. In particular, in a steel sheet provided with an inorganic rich film having poor barrier properties, not only the blackening phenomenon is likely to occur, but also stain-like (black brown) unevenness (hereinafter referred to as stain stain) is likely to occur.

  The present invention has been made in view of the circumstances as described above, and the object thereof is a surface-treated zinc-based plated steel sheet that is excellent in blackening resistance and suppresses the occurrence of stain stains, that is, surface-treated zinc that is excellent in appearance. It is to provide a galvanized steel sheet.

The surface-treated zinc-based plated steel sheet that can solve the above problems is a zinc-based plated steel sheet, a first layer formed on at least one surface of the zinc-based plated steel sheet, and a second layer formed on the first layer. A surface-treated zinc-based plated steel sheet, wherein the first layer includes zinc phosphate crystals, and the amount of zinc phosphate crystals deposited is 0.04 to 0.4 g / m ^2. The major axis of the zinc phosphate crystal is 2.5 μm or less, the second layer contains a resin, and the adhesion amount of the second layer is 0.35 to 0.85 g / m ² . It is characterized by that.

  The first layer preferably further contains colloidal silica.

  The second layer forming composition for forming the second layer preferably contains a binder resin, colloidal silica, an external crosslinking agent, and a lubricant.

  The composition for forming the second layer has a content of the binder resin of 54 to 79 parts by mass in a total of 100 parts by mass of the binder resin, the colloidal silica, the external crosslinking agent, and the lubricant, and the colloidal More preferably, the silica content is 10 to 35 parts by mass, the external cross-linking agent content is 5 to 8.5 parts by mass, and the lubricant content is 2 to 5 parts by mass.

  According to the present invention, the amount of zinc phosphate crystals attached to the first layer and the major axis of the zinc phosphate crystals are adjusted, and further, the amount of adhesion of the second layer is adjusted to provide a surface-treated zinc-based material with excellent appearance. It can be set as a plated steel plate. The surface-treated galvanized steel sheet of the present invention can be used for casings and interior / exterior parts of automobiles and household electrical appliances, outer plate materials such as steel furniture, and building materials.

FIG. 1 is a schematic view of a spray device. FIG. 2 is a schematic view of a crank press device. FIG. 3 is a view showing a steel plate after pressing.

  A surface-treated galvanized steel sheet (hereinafter referred to as a surface-treated steel sheet) according to the present invention is formed on a galvanized steel sheet, a first layer formed on at least one surface of the galvanized steel sheet, and the first layer. And a second layer. The first layer is a film containing zinc phosphate crystals, and the second layer is a film containing resin.

[Zinc-based plated steel sheet]
The steel plate used in the present invention is not particularly limited as long as it is a zinc-based plated steel plate. For example, a hot-dip galvanized steel plate (GI), an alloyed molten Zn-Fe plated steel plate (GA), and an alloyed molten Zn-5% Examples thereof include an Al-plated steel sheet (GF), an electrogalvanized steel sheet (EG), and a Zn—Ni alloy electroplated steel sheet. Among these, an electrogalvanized steel sheet (EG) is preferable.

[First layer]
The first layer is a phosphorus-containing film formed by a phosphorus-containing treatment liquid (first layer forming composition). By providing the phosphorus-containing film on the surface of the galvanized steel sheet, blackening resistance can be suppressed. In addition, by providing a uniform phosphorus-containing coating on the surface of the galvanized steel sheet, dirt (uneven appearance on the galvanized surface) derived from the original sheet (galvanized steel sheet) is concealed and the appearance is beautiful. It can be set as a surface treatment steel plate. Moreover, the corrosion resistance of the surface-treated steel sheet can be improved. The first layer may be provided only on one side of the galvanized steel sheet or may be provided on both sides.

  The first layer forming composition only needs to contain zinc phosphate crystals. Moreover, it is preferable that the composition for 1st layer formation contains phosphoric acid, and the composition for 1st layer formation uses a hydrofluoric acid and the zinc nitrate of an accelerator as an etching agent of the zinc plating surface. It is preferable to contain.

  As the first-layer forming composition, a commercially available phosphorus-containing treatment solution may be used. Commercially available products include, for example, Palbond (registered trademark) 3312, Palbond (registered trademark) 3300, Palbond (registered trademark) 3140, Palbond (registered trademark) 3100, Palbond (registered trademark) 3308, and Enares (registered) manufactured by Nippon Parkerizing Co., Ltd. (Trademark) 20, SurfDyne (registered trademark) select 1000 series manufactured by Nippon Paint Surf Chemicals.

Adhesion amount of the zinc phosphate crystals (the amount of zinc phosphate crystals contained in the first layer) is ^{0.04~0.4g / m 2 (2.7~27mg / m} 2 at P conversion), more preferably ^{0.06~0.39g / m 2 (4.0~26.3mg / m} 2 at P conversion), 6.1 more preferably 0.09~0.28g / m ² (P terms ˜18.9 mg / m ² ). When the adhesion amount of the zinc phosphate crystal is within the above range, the tape peeling resistance is improved due to the anchor effect. The amount of zinc phosphate crystals attached can be adjusted by adjusting the concentration and temperature of the phosphorus-containing treatment liquid, the plate passing speed, and the like. A specific method for adjusting the adhesion amount of zinc phosphate crystals will be described later.

When the adhesion amount of zinc phosphate crystals exceeds 0.4 g / m ² , the tape peel resistance is good due to the anchor effect, but it becomes difficult to cover the surface of the first layer with the second layer, and the corrosion resistance and Blackening resistance deteriorates. In addition, since zinc phosphate crystals have high insulating properties, conductivity is also greatly deteriorated. Furthermore, since the zinc phosphate crystal is hard and brittle, the bendability of the surface-treated steel sheet deteriorates as the amount of adhesion increases. On the other hand, if the adhesion amount of zinc phosphate crystals is less than 0.04 g / m ² , the tape peel resistance is greatly deteriorated.

By coating and drying the second layer on the first layer, the hydroxy groups present in the zinc phosphate crystals (Zn ₃ (PO ₄ ) ₂ .4H ₂ O) contained in the first layer and the second layer Since the ester bond is generated by dehydration condensation with the existing carboxyl groups, the anchor effect makes the first layer and the second layer excellent in adhesion, that is, excellent in tape peel resistance. Become. Therefore, in order to improve the adhesion between the first layer and the second layer by the anchor effect, the growth of the zinc phosphate crystal is suppressed, the crystal is made as small as possible, and the zinc phosphate is formed on the surface of the zinc-based plated steel sheet. It is necessary to disperse the crystals uniformly.

  The major axis of the zinc phosphate crystal is 2.5 μm or less, preferably 2.2 μm or less, more preferably 1.56 μm or less. Further, the lower limit of the major axis of the zinc phosphate crystal is not particularly limited, but is preferably 0.5 μm or more from the viewpoint of adhesion to the film. When the long diameter of the zinc phosphate crystal exceeds 2.5 μm, the tape peel resistance is improved due to the anchor effect, but it becomes difficult to cover the surface of the first layer with the second layer, and the corrosion resistance and blackening resistance are reduced. to degrade. In addition, since zinc phosphate crystals have high insulating properties, conductivity is also greatly deteriorated. Furthermore, since the zinc phosphate crystal is hard and brittle, the bendability of the surface-treated steel sheet deteriorates as the crystal increases. On the other hand, when the major axis of the zinc phosphate crystal is less than 0.5 μm, the tape peel resistance may be deteriorated.

  The major axis of the zinc phosphate crystal correlates with the adhesion amount of the zinc phosphate crystal, and the major axis of the zinc phosphate crystal becomes longer as the adhesion amount of the zinc phosphate crystal increases. The major axis of the zinc crystal can be adjusted by adjusting the concentration and temperature of the phosphorus-containing treatment liquid, the plate passing speed (plating time), and the like, similarly to the amount of zinc phosphate crystal attached.

  The formation method and conditions of the first layer are not particularly limited, and can be formed by a known coating method. For example, a bar coater method, a curtain flow coater method, a roll coater method, a spray method, a spray ringer method and the like can be mentioned. Among these, the bar coater method and the spray ringer method are preferable from the viewpoint of cost and the like, and the spray ringer method Is particularly preferred. Details of the spray ringer method will be described later. In addition, there is no limitation in particular about the conditions of the heat drying of the 1st layer after application | coating, For example, it can heat dry at 200-300 degreeC.

<Colloidal silica>
The composition for forming the first layer may further contain colloidal silica. By containing colloidal silica, it is possible to prevent the occurrence of a site (repel portion) where the first layer does not exist during application / drying of the first layer forming composition, and the first layer can be uniformly applied. . The colloidal silica in the first layer forming composition is preferably 0.2 to 2.0 g / L, more preferably 0.5 to 1.5 g / L in terms of SiO ₂ . Since the composition for forming the first layer does not contain a resin as a binder, it is considered that the colloidal silica in the film exists in a form that is taken in between the zinc phosphate crystals. Therefore, when the content of colloidal silica exceeds 2.0 g / L, the adhesion between the first layer and the second layer is lowered, and the tape peel resistance may be lowered. On the other hand, when the content of colloidal silica is less than 0.2 g / L, tape peel resistance, corrosion resistance, and blackening resistance of the surface-treated steel sheet may be reduced.

  The colloidal silica is not particularly limited, and specifically, colloidal silica having an average particle diameter of 4 to 6 nm (in a commercial product, for example, “Snowtex (registered trademark) XS” manufactured by Nissan Chemical Industries, Ltd., “Snowtex (registered trademark) NXS”, “Snowtex (registered trademark) OXS”, “Snowtex (registered trademark) CXS”), colloidal silica having an average particle diameter of 10 to 15 nm (commercially available products such as Nissan Chemical Industries, Ltd.) "Snowtex (registered trademark) 30", "Snowtex (registered trademark) 40", "Snowtex (registered trademark) N30G", "Snowtex (registered trademark) N", "Snowtex (registered trademark)" O ”,“ Snowtex (registered trademark) C ”, etc.), colloidal silica having an average particle diameter of 20 to 25 nm (commercially available products such as Nissan “Snowtex (registered trademark) 50”, “Snowtex (registered trademark) N-40”, “Snowtex (registered trademark) O-40”, etc.) manufactured by Kogyo Co., Ltd., colloidal silica having an average particle diameter of 8 to 11 nm ( Examples of commercially available products include “Snowtex (registered trademark) S”, “Snowtex (registered trademark) NS”, and “Snowtex (registered trademark) OS” manufactured by Nissan Chemical Industries, Ltd.). From the viewpoint of the dispersibility of colloidal silica in the composition for forming the first layer, the effect of improving the corrosion resistance and blackening resistance of the surface-treated steel sheet, "Snowtex (registered trademark) OXS", "Snowtex (registered trademark)" Acid colloidal silica having a pH of 2.0 to 4.0, such as “OS”, “Snowtex (registered trademark) O”, “Snowtex (registered trademark) O-40”, is preferable, and “Snowtex (registered trademark) OXS” Acid colloidal silica having a pH of 2.0 to 4.0 and an average particle diameter of 4 to 15 nm, such as “Snowtex (registered trademark) OS” and “Snowtex (registered trademark) O”, is more preferable. When the average particle diameter of the colloidal silica in the composition for forming the first layer is larger than 15 nm, the adhesion between the first layer and the second layer is lowered, and the tape peel resistance may be lowered. In addition, colloidal silica having an average particle diameter of less than 4 nm is not commercially available at present, and the particle surface of colloidal silica having an average particle diameter of less than 4 nm is activated, so that the liquid stability of the composition for forming the first layer is increased. May be deteriorated, and the agglomeration of colloidal silica and the gelation of the solution may be promoted.

  The average particle size of colloidal silica in the present specification is a value measured by the Sears method when the average particle size is about 1 to 10 nm and by the BET method when the average particle size is about 10 to 100 nm. Moreover, when a notary value is described in the manufacturer's pamphlet, the notarized value is defined as an average particle diameter.

[Second layer]
The 2nd layer contains resin, ie, the composition for 2nd layer formation which forms the 2nd layer contains resin. The composition for forming the second layer preferably contains a resin, colloidal silica, an external cross-linking agent, and a lubricant, and the resin preferably serves as a binder resin. The composition for forming the second layer is such that the binder resin content is 54 to 79 parts by mass in a total of 100 parts by mass of the binder resin, the colloidal silica, the external crosslinking agent, and the lubricant. The colloidal silica content is 10 to 35 parts by mass, the external cross-linking agent content is 5 to 8.5 parts by mass, and the lubricant content is 2 to 5 parts by mass. More preferred. By using such a composition for forming a second layer, the corrosion resistance of the surface-treated steel sheet can be increased. Moreover, by using such a composition for forming a second layer, the second layer can be made thin, and a surface-treated steel sheet having excellent conductivity can be obtained.

<Binder resin>
By containing a binder resin, colloidal silica can be fixed to the second layer. As long as the colloidal silica can be fixed as the binder resin, the kind thereof is not particularly limited, and acrylic resin, urethane resin, polyolefin resin, polyester resin, fluorine resin, silicone resin, And mixed or modified resins thereof can be used as appropriate. Of these, polyolefin resins are preferred. Binder resin may be used independently or may be used in combination of 2 or more type. Moreover, resin other than binder resin may be contained.

  The polyolefin resin preferably contains an olefin-α, β-unsaturated carboxylic acid copolymer (hereinafter sometimes referred to as “olefin-acid copolymer”). By having an olefin-acid copolymer, the dispersion stability of the colloidal silica in the composition for forming the second layer is not impaired, and the barrier property is excellent, so that the penetration of water into the first layer is suppressed, and the corrosion resistance is improved. Can be improved.

(Olefin-α, β-unsaturated carboxylic acid copolymer)
The olefin-α, β-unsaturated carboxylic acid copolymer (hereinafter referred to as olefin-acid copolymer) in the present invention is a copolymer of an olefin and an α, β-unsaturated carboxylic acid, This means that the structural unit derived from the copolymer is 50% by mass or more (that is, the structural unit derived from the α, β-unsaturated carboxylic acid is 50% by mass or less).

  The olefin-acid copolymer can be produced by copolymerizing an olefin and an α, β-unsaturated carboxylic acid by a known method, and is commercially available. 1 type (s) or 2 or more types can be used for an olefin-acid copolymer.

  Although there is no limitation in particular as an olefin which can be used for manufacture of an olefin-acid copolymer, ethylene, propylene, etc. are preferable and ethylene is more preferable. The olefin-acid copolymer may be one in which the olefin structural unit is derived from only one olefin, or may be derived from two or more olefins.

  The α, β-unsaturated carboxylic acid that can be used for the production of the olefin-acid copolymer is not particularly limited, and examples thereof include monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and isocrotonic acid; maleic acid, fumaric acid, Examples thereof include dicarboxylic acids such as itaconic acid, and one kind or a mixture of two or more kinds can be used. Among these, acrylic acid or methacrylic acid is preferable, and acrylic acid is more preferable. In the olefin-acid copolymer, the constituent unit of α, β-unsaturated carboxylic acid may be derived from only one α, β-unsaturated carboxylic acid, or two or more α, β, It may be derived from a β-unsaturated carboxylic acid.

  The α, β-unsaturated carboxylic acid unit in the olefin-acid copolymer serves to improve the adhesion between the first layer and the second layer. The amount of α, β-unsaturated carboxylic acid units in the copolymer is preferably 5% by mass or more, and more preferably 10% by mass or more. On the other hand, the upper limit of the amount of α, β-unsaturated carboxylic acid units in the copolymer is 50% by mass as described above, but is preferably 30% by mass or less, more preferably 25% by mass from the viewpoint of corrosion resistance. % Or less.

  The olefin-acid copolymer may have structural units derived from other monomers within a range that does not adversely affect corrosion resistance, blackening resistance, and the like. In the olefin-acid copolymer, the structural unit amount derived from other monomers is preferably 10% by mass or less, more preferably 5% by mass or less, and the most preferable olefin-acid copolymer is other Is a copolymer composed only of olefin- and α, β-unsaturated carboxylic acid. Moreover, an ethylene-acrylic acid copolymer is mentioned as a preferable olefin-acid copolymer.

(Amine with a boiling point of 100 ° C or lower)
Since the olefin-acid copolymer has a carboxyl group, it is possible to emulsify (form an aqueous dispersion) the composition for forming the second layer by neutralizing with an organic base or a metal ion. Become. It is preferable to use an amine having a boiling point of 100 ° C. or lower as the organic base. An amine having a boiling point exceeding 100 ° C. tends to remain on the steel sheet when the resin coating film is dried, and the water absorption of the resin coating film increases, which may reduce the corrosion resistance.

  Specific examples of amines having a boiling point of 100 ° C. or less include tertiary amines such as triethylamine, N, N-dimethylbutylamine, N, N-dimethylallylamine, N-methylpyrrolidine, tetramethyldiaminomethane, trimethylamine; N-methylethylamine, Secondary amines such as diisopropylamine and diethylamine; primary amines such as propylamine, t-butylamine, sec-butylamine, isobutylamine, 1,2-dibutylpropylamine, and 3-pentylamine, and the like. A mixture of seeds or more can be used. Of these, tertiary amines are preferred, and triethylamine is the most preferred.

  The amount of the amine having a boiling point of 100 ° C. or less is preferably 0.2 to 0.8 mol (20 to 80 mol%) with respect to 1 mol of the carboxyl group in the olefin-acid copolymer. This is because within this range, the surface-treated steel sheet has good corrosion resistance and tape peel resistance. When the amount of the amine is less than 0.2 mol, the particle size of the resin particles in the composition for forming the second layer is increased, and thus the above effect may not be exhibited. Moreover, when the said amine exceeds 0.8 mol, there exists a possibility that the composition for 2nd layer formation may thicken and gelatinize. The upper limit of the amount of the amine is more preferably 0.6 mol or less, and further preferably 0.5 mol or less. About the minimum of the quantity of the said amine, it is more preferable that it is 0.3 mol or more.

(Compound containing monovalent metal)
From the viewpoint of improving the film hardness, it is preferable to add a monovalent metal ion to the olefin-acid copolymer for neutralization. The monovalent metal preferably contains one or more metals selected from sodium, potassium, and lithium, and the compound containing a monovalent metal (hereinafter simply referred to as a compound) Hydroxides, carbonates or oxides are preferred. Among these, NaOH, KOH, LiOH and the like are preferable, and NaOH is more preferable.

  The amount of the compound is in the range of 0.02 to 0.4 mol (2 to 40 mol%) with respect to 1 mol of the carboxyl group in the olefin-acid copolymer. When the amount of the compound is less than 0.02 mol, the emulsion stability becomes insufficient, but when it exceeds 0.4 mol, the corrosion resistance may be deteriorated. The upper limit of the amount of the compound is more preferably 0.2 mol or less. The lower limit of the amount of the compound is more preferably 0.03 mol or more, and further preferably 0.1 mol or more.

  The preferred ranges of the amounts used of the amine having a boiling point of 100 ° C. or less and the compound are as described above, and these are all formed by neutralizing the carboxyl group in the olefin-acid copolymer to form a second layer. Used to emulsify the composition. Accordingly, if the total amount (neutralization amount) is too large, the viscosity of the composition for forming the second layer may rapidly increase and solidify, and excessive alkali content may cause corrosion resistance deterioration. Therefore, a large amount of energy is required for volatilization, which is not preferable. However, if the amount of neutralization is too small, the emulsifiability may be insufficient. Therefore, the total amount of the amine having the boiling point of 100 ° C. or less and the compound is 0.3 to 1.0 mol (30 to 100 mol%) with respect to 1 mol of the carboxyl group in the olefin-acid copolymer. It is preferable.

(Internal crosslinking agent)
An olefin-acid copolymer having a carboxyl group neutralized by an amine having a boiling point of 100 ° C. or less and a monovalent metal ion forms an intermolecular association by an ion cluster (ionomerization), and is resistant to corrosion and tape peeling. Forms an excellent resin film. However, in order to form a tougher film, it is desirable to crosslink the polymer chains by chemical bonding utilizing a reaction between functional groups. Therefore, the second layer forming composition preferably has a crosslinking agent having two or more functional groups capable of reacting with a carboxyl group. In addition, let the crosslinking agent used for binder resin formation as described in this paragraph be an internal crosslinking agent, and let the below-mentioned crosslinking agent used for formation of a 2nd layer be an external crosslinking agent. The amount of the internal crosslinking agent is preferably 1 to 20% by mass (more preferably 5 to 10% by mass) out of 100% by mass of the solid content in the binder resin component. When the amount is less than 1% by mass, the effect of crosslinking by chemical bonding becomes insufficient, and the effect of improving the corrosion resistance and tape peel resistance is hardly exhibited. On the other hand, if it exceeds 20% by mass, the crosslink density of the second layer becomes excessively high, the hardness increases, and cracks are generated because it becomes impossible to follow the deformation at the time of press working, resulting in a decrease in corrosion resistance. There is a fear.

  The internal crosslinking agent having two or more functional groups capable of reacting with a carboxyl group is not particularly limited, but sorbitol polyglycidyl ether, (poly) glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, trimethylolpropane poly Polyglycidyl ethers such as glycidyl ether, neopentyl glycol diglycidyl ether, (poly) ethylene glycol diglycidyl ether, and glycidyl group-containing crosslinking agents such as polyglycidyl amines; 4,4′-bis (ethyleneiminocarbonylamino) Diphenylmethane, N, N′-hexamethylene-1,6-bis (1-aziridinecarboxamide), N, N′-diphenylmethane-4,4′-bis (1-aziridinecarboxamide), toluenebi Bifunctional aziridine compounds such as aziridinecarboxamide; tri-1-aziridinylphosphine oxide, tris [1- (2-methyl) aziridinyl] phosphine oxide, trimethylolpropane tris (β-aziridinylpropionate), tris An aziridinyl group-containing crosslinking agent such as a tri- or higher functional aziridine compound such as 2,4,6- (1-aziridinyl) -1,3,5-triazine, tetramethylpropanetetraaziridinylpropionate, or a derivative thereof. Of these, one or more of these can be used. Among them, bifunctional or higher functional aziridine compounds are preferable, bifunctional aziridine compounds are more preferable, and 4,4′-bis (ethyleneiminocarbonylamino) diphenylmethane is further preferable.

<Colloidal silica>
It is preferable that the composition for forming a second layer further contains colloidal silica. The colloidal silica (solid content) is preferably contained in an amount of 5 to 40% by mass, more preferably 10 to 37% by mass, and further preferably 20 to 35% by mass in 100% by mass of the total solid content. In the present specification, the total solid content (solid content: 100% by mass) refers to the total solid content of the binder resin, colloidal silica, external cross-linking agent, and lubricant. If the colloidal silica content is less than 5% by mass, the corrosion resistance, blackening resistance, tape peel resistance and the like of the surface-treated steel sheet may be reduced. Moreover, since binder resin increases relatively, the film thickness of a film | membrane becomes thick and electroconductivity also deteriorates. On the other hand, if the colloidal silica content exceeds 40% by mass, the film-forming property is lowered, and the film is cracked or the film becomes brittle. Therefore, the corrosion resistance, blackening resistance and bending workability of the surface-treated steel sheet are reduced. May decrease. The reason why the corrosion resistance and blackening resistance are improved is presumed to be that colloidal silica is dissolved and eluted in a corrosive environment to cause a pH buffering action and a passive film forming action. Furthermore, by containing colloidal silica, it is possible to prevent the occurrence of a site (repellent portion) where the second layer does not exist when the second layer forming composition is applied and dried. The mass ratio of the colloidal silica and the binder resin is preferably 5:84 to 40:49, more preferably 20:69 to 35:54, in terms of solid ratio.

  The colloidal silica is not particularly limited, and examples thereof include the same type as the colloidal silica used in the above-described first layer forming composition. Colloidal silica having an average particle diameter of 4 to 15 nm is particularly preferable from the viewpoints of dispersibility in the composition for forming the second layer, the corrosion resistance of the surface-treated steel sheet, and the effect of improving blackening resistance. Trademark) XS "is preferred.

<External crosslinking agent>
In order to crosslink the binder resin, the second layer forming composition preferably contains an external crosslinking agent. By including an external crosslinking agent, the corrosion resistance and blackening resistance of the surface-treated steel sheet can be enhanced. The external cross-linking agent is preferably contained in an amount of 5 to 8.5% by mass, more preferably 6 to 8% by mass, and still more preferably 6 to 100% by mass of the total solid content of the composition for forming the second layer. 5 to 7.5% by mass. By setting the external cross-linking agent to 5% by mass or more, the cross-linking proceeds sufficiently to further improve the corrosion resistance and blackening resistance. On the other hand, by setting the external cross-linking agent to 8.5% by mass or less, self-crosslinking of the surplus cross-linking agent is prevented, and the corrosion resistance and blackening resistance are further improved. The mass ratio of the external cross-linking agent and colloidal silica is preferably 5: 32.5 to 8.5: 29, more preferably 6.5: 31 to 7.5: 30 in terms of solid ratio. preferable.

  The external cross-linking agent is preferably an epoxy cross-linking agent from the viewpoint of reactivity. Sorbitol polyglycidyl ether, (poly) glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, trimethylolpropane polyglycidyl ether, neopentyl glycol diglycidyl ether And polyglycidyl ethers such as (poly) ethylene glycol diglycidyl ether, and polyglycidyl amines. As such an epoxy-based crosslinking agent, Epicron (registered trademark) CR5L, CR75, and the like manufactured by DIC are available.

<Lubricant>
The composition for forming the second layer preferably contains a lubricant. By including the lubricant, the friction on the surface of the second layer is reduced, and it becomes difficult to cause wrinkles. The lubricant is preferably contained in an amount of 2 to 5% by mass in 100% by mass of the total solid content, more preferably 3 to 4.7% by mass, and further preferably 3.5 to 4.5% by mass. . When the content of the lubricant is less than 2% by mass, the lubricity of the obtained second layer is not sufficient, and the bendability of the surface-treated steel sheet may be lowered. If the lubricant exceeds 5% by mass, the film-forming property of the second layer is lowered, so that the corrosion resistance of the surface-treated steel sheet may be lowered. When a lubricant such as spherical polyethylene wax is used, if the lubricant exceeds 5% by mass, the corrosion resistance may be deteriorated due to hydrolysis of the lubricant or the like. The mass ratio between the lubricant and the binder resin is preferably 2: 60.5 to 5: 57.5, more preferably 3.5: 59 to 4.5: 58, in terms of solid ratio.

  As the lubricant, polyolefin waxes such as polyethylene, polyethylene oxide, and polypropylene; fluorine resins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and tetrafluoroethylene; organic modified polysiloxanes; paraffin wax, etc. are used. Is possible. Among these, polyolefin wax is preferable, and polyethylene wax is more preferable.

  The polyethylene wax particles are preferably spherical and have an average particle diameter of 0.1 to 3 μm, more preferably an average particle diameter of 0.3 to 1.0 μm. When the average particle diameter exceeds 3 μm, it is difficult to uniformly disperse the lubricant in the composition for forming the second layer, and the corrosion resistance tends to be lowered because the film forming property is inhibited. On the other hand, when the average particle diameter of the polyethylene wax particles is smaller than 0.1 μm, the lubricity of the second layer may not be improved. The average particle diameter of the polyethylene wax particles can be measured by a Coulter counter method.

  By using such a polyethylene wax, the second layer exists in a spherical shape, and friction on the surface of the second layer can be effectively reduced, which is effective in suppressing the occurrence of wrinkles. Examples of the spherical polyethylene wax include “Chemipearl (registered trademark) W640”, “Chemipearl (registered trademark) W700”, “Chemipearl (registered trademark) W950”, and “Chemical (registered trademark) W900” manufactured by Mitsui Chemicals. .

<Adhesion amount>
The adhesion amount of the second layer is preferably 0.35 to 0.85 g / m ² after drying, more preferably 0.4 to 0.8 g / m ² , and 0.4 to 0.7 g / m ^2. m ² is more preferable, and 0.45 to 0.6 g / m ² is most preferable. By forming a film containing a resin on the first layer as the second layer, the second layer can be made thinner. Moreover, by achieving a thin film, a surface-treated steel sheet having conductivity can be obtained. When the adhesion amount is less than 0.35 g / m ² , it is difficult to uniformly apply the second layer onto the first layer, and the corrosion resistance, blackening resistance, tape peeling resistance, and bending workability of the surface-treated steel sheet are difficult. May deteriorate. On the other hand, when the adhesion amount exceeds 0.85 g / m ² , the conductivity of the surface-treated steel sheet may be lowered.

<Other ingredients>
In the aqueous black resin composition, within the range that does not impair the effects of the present invention, dilution solvent, anti-skinning agent, leveling agent, antifoaming agent, penetrating agent, emulsifying agent, film-forming aid, coloring pigment, thickener, Silane coupling agents, other resins, etc. may be added as appropriate.

<Method for forming second layer>
The composition for forming the second layer can be prepared by mixing the above-described components at a predetermined ratio. The mixing order is not particularly limited.

  The method for applying and drying the second layer forming composition when forming the second layer on the first layer is not particularly limited, and known methods can be appropriately employed. Examples of the method for applying the composition for forming the second layer include a bar coater method, a roll coater method, a curtain flow coater method, a spray method, a spray ringer method, and the like. A coater method, a roll coater method and a spray ringer method are preferred. Moreover, as drying temperature, it should just be a grade which a 2nd layer does not deteriorate with a heat | fever, For example, about 50-160 degreeC is preferable, More preferably, it is about 70-140 degreeC.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention. In the following, “%” may indicate “mass%” and “part” may indicate “mass part”.

  First, the measurement / evaluation methods used in the examples will be described below.

(1) Zinc phosphate crystal (1-1) Long diameter of zinc phosphate crystal The long diameter of the zinc phosphate crystal in the first layer was photographed at a magnification of 5000 times using a scanning electron microscope (SUPRA35 manufactured by Carl Zeiss). And measured.

(1-2) Amount of Zinc Phosphate Crystal First, the content of P element per 1 m ² in the first layer (unit: g / m) using a fluorescent X-ray analyzer (MXF-2100 manufactured by Shimadzu Corporation). ² ) measured. And the adhesion amount of the zinc phosphate crystal (molecular weight: 458.05) in the first layer was calculated from the measured content of P element (molecular weight: 65.37). That is, the value obtained by multiplying the content of P element per 1 m ² by 458.05 / 65.37 was defined as the amount of zinc phosphate crystals deposited per 1 m ² in the first layer (unit: g / m ² ). .

(2) Corrosion resistance A cross-cut was made on the surface of the test material with a cutter knife, and a 5% NaCl solution was sprayed in a 35 ° C. atmosphere in accordance with JIS Z2371, and a salt spray test was performed. The time until the white rust occurrence rate reached 5% (SST time) was measured, evaluated according to the following criteria, A and B evaluations passed, and C and D evaluations rejected.
A: SST time is 240 hours or more B: SST time is 168 hours or more and less than 240 hours C: SST time is 120 hours or more and less than 168 hours D: SST time is less than 120 hours

(3) Appearance (3-1) Quantitative Analysis First, the L value of the test material was measured using a color difference meter (Nippon Denshoku Industries SZS-Σ90). The sample material was stored in a constant temperature and humidity tester at 50 ° C. and 98% humidity for 168 hours, and then the L value of the sample material was measured again. A difference ΔL between the L values before and after storage for 168 hours was calculated, and quantitatively evaluated according to the following criteria. A and B evaluations passed, and C and D evaluations failed.
A: ΔL is less than 1 B: ΔL is 1 or more and less than 2 C: ΔL is 2 or more and less than 3 D: ΔL is 3 or more

(3-2) Qualitative Analysis First, the appearance of the test material was confirmed. The specimen was stored in a constant temperature and humidity tester at 50 ° C. and a humidity of 98% for 168 hours, and then the appearance of the specimen was confirmed again. The difference in appearance before and after storage for 168 hours was evaluated according to the following criteria, and A and B evaluations passed, and C and D evaluations failed.
A: No change before and after the test B: The test material after the test has a slight blackening, but there is no stain stain C: The test material after the test has a slight blackening, the stain There is also dirt. D: The test material after the test has blackening and stains.

(4) Conductivity Using a surface resistance measuring device (Loresta (registered trademark) -EP manufactured by Dia Instruments Co., Ltd.), a two-probe method (two-probe AP probe (type A), pin-to-pin distance: 10 mm, pin tip diameter: 2 mmφ, spring pressure during measurement: 240 g / piece, no copper plate), the surface resistance value (conductivity) of the test material was measured by bringing the terminal directly into contact with the steel plate surface, and passed A and B evaluations, C and D Evaluation was rejected.
A: Surface resistance value is less than 0.05Ω B: Surface resistance value is from 0.05Ω to less than 0.50Ω C: Surface resistance value is from 0.50Ω to less than 1.00Ω D: Surface resistance value 1.00Ω or more

(5) Tape peeling resistance Filament tape (Flax tape # 9510 manufactured by Maxell Sliontec Co., Ltd.) is attached to the surface of the test material, and stored in a constant temperature and humidity test apparatus at a temperature of 40 ° C. and a humidity of 98% for 120 hours. After that, a tape peeling test was performed according to JIS K5400, and the ratio of the remaining area of the film (residual rate) was measured and evaluated according to the following criteria. Adhesive tape is applied to the surface of the test material, and the adhesive tape plasticizer is infiltrated into the film under high temperature and high humidity conditions to promote the deterioration of the adhesion between the film and the metal plate. Adhesion can be evaluated.
A: Residual rate is 95% or more B: Residual rate is 90% or more and less than 95% C: Residual rate is 80% or more and less than 90% D: Residual rate is less than 80%

(6) Bending workability (90 ° bending test)
About the obtained test material, about the test material 5 like FIG. 2 on the press molding conditions described below using the 80-ton crank press apparatus (Aida Engineering Co., Ltd. 80TON crank press) shown in FIG. 90 ° L bending was performed. After processing, the appearance of the sliding portion of the specimen (sliding portion 6 in FIG. 3) was visually observed according to the following evaluation criteria and evaluated according to the following criteria.
A: No film damage B: Slight film peeling / scratching C: Slight film peeling / scratching D: Film peeling / scratching

<Press molding conditions>
Die shoulder radius R1: 0.5mm
Punch shoulder radius R2: 0.5mm
Punch-die clearance CL: Plate thickness -10 μm, ± 0
Wrinkle holding pressure: 0.2MPa
Molding speed: 40 spm (stroke / min)
Note that no lubricant is used.

(Examples 1-4, Comparative Examples 1-5)
[Method for producing first layer]
Palbond (registered trademark) 3312 manufactured by Nippon Parkerizing Co., Ltd. (zinc phosphate crystals: 10 to 20% by mass, phosphoric acid: 1 to 10% by mass, hydrofluoric acid: 1 to 10% by mass, zinc nitrate: 0.2% by mass) %) Was diluted with pure water to prepare a composition for forming a first layer. Then, the 1st layer was formed with the spray ringer method on both surfaces of the electrogalvanized steel plate (Zn adhesion amount 20g / m < ² >) using the spray apparatus shown in FIG.

  The spray device shown in FIG. 1 will be specifically described. The spray device 1 includes an upstream zone 2 for spray-coating the first layer forming composition in a direction in which the steel plate is fed, a midstream zone 3 for washing the steel plate with pure water, and a downstream zone 4 for washing the steel plate with pure water. In order. Each zone is provided with a ringer roll that sandwiches the steel plate from above and below. First, in the upstream zone 2, the composition for forming the first layer is applied to the steel plate at a spray pressure of 0.08 MPa, and after the composition for forming the first layer is squeezed with a ringer roll in the upstream zone 2, 3, using a water spray, the steel sheet is washed with a spray pressure of 0.05 MPa, and the remaining water is squeezed with a ringer roll in the midstream zone 3. Thereafter, in the downstream zone 4, the water spray is used again to wash the steel sheet with a spray pressure of 0.02 MPa, and the remaining water is squeezed with the ringer roll in the downstream zone 4. Finally, the steel plate was dried for 10 seconds at a hot air temperature of 250 ° C. and a wind speed of 10 m / sec so that the ultimate plate temperature was 90 ° C.

The amount of zinc phosphate crystals attached was adjusted by adjusting the following conditions. In addition, adjustment of each condition was performed based on the relationship between the conditions of the concentration and temperature of the phosphorus-containing treatment liquid described in Table 1 below, the condition of the plate feeding speed, and the amount of zinc phosphate crystals attached. By appropriately adjusting these conditions, the amount of zinc phosphate crystals attached can be adjusted. Table 1 shows the relationship between these conditions and the amount of zinc phosphate crystals deposited.
Concentration of phosphorus-containing treatment solution: 6% or 3%
Temperature of phosphorus-containing treatment solution: 40 ° C. or 20 ° C.
Plate speed: 5-30m / min

  In addition to the above method, zinc phosphate crystals can be attached by immersing the steel sheet in a phosphorus-containing treatment solution.

[Method for producing second layer]
An autoclave having an emulsification facility equipped with a stirrer, a thermometer and a temperature controller (internal capacity 0.8 L), water 626 parts, ethylene-acrylic acid copolymer (acrylic acid 20% by mass, melt index (MI) 300) ) 160 parts, and 0.4 mol of triethylamine (boiling point: 89.5 ° C.) and 0.15 mol of sodium hydroxide are added to 1 mol of the carboxyl group of the ethylene-acrylic acid copolymer. The mixture was stirred at 150 ° C. and 0.5 MPa for 3 hours at high speed, and then cooled to 40 ° C. Thereafter, 4,100′-bis (ethyleneiminocarbonylamino) diphenylmethane (Nippon Catalyst Chemitite (registered trademark)) was used as an internal crosslinking agent for 100 parts of the non-volatile resin component of the ethylene-acrylic acid copolymer. ) 5 parts of DZ-22E) was added and stirred for 10 minutes to obtain an aqueous dispersion in which the polyethylene resin was dispersed.

  Next, 30 parts by mass of colloidal silica having an average particle diameter of 4 to 6 nm (Snowtex (registered trademark) XS manufactured by Nissan Chemical Industries, Ltd.) is added to 59 parts by mass of the polyethylene-based resin, and a glycidyl group as an external crosslinking agent. 7.5 parts by mass of an epoxy resin compound (Epiclon (registered trademark) CR5L manufactured by DIC) was added, and finally, spherical polyethylene wax (Chemical (registered trademark) W640 manufactured by Mitsui Chemicals, particle size: 1.0 μm) as a lubricant. Was added to prepare a second layer forming composition.

[Method for producing surface-treated steel sheet]
On the first layer, the composition for forming the second layer is applied and dried so that the coating amount is 0.60 g / m ² (film thickness is about 0.5 μm) with a bar coater. A surface-treated steel sheet with two layers was obtained.

  Table 2 shows the structure of the first layer and the evaluation results of the obtained surface-treated steel sheet.

(Examples 5-8, Comparative Examples 6-7)
Dilute with pure water so that the stock solution of Palbond (registered trademark) 3312 manufactured by Nippon Parkerizing Co., Ltd. is 6% by mass, and add 0.5 g / L of Snowtex (registered trademark) O manufactured by Nissan Chemical Industries, Ltd. A forming composition was obtained. After spray-coating the composition for forming the first layer on the electrogalvanized steel sheet (Zn adhesion amount 20 g / m ² ) at a liquid temperature of about 40 ° C. with a spray ringer facility, A first layer having an adhesion amount of 0.09 g / m ² and a zinc phosphate crystal major axis of 1.30 μm was formed on the surface of the electrogalvanized steel sheet. That is, about the 1st layer, it manufactured on the same manufacturing conditions as Example 3 except having added Snowtex (trademark) O (average particle diameter of 10-15 nm) by Nissan Chemical Industries. Subsequently, for the second layer, a surface-treated steel sheet was obtained in the same manner as in Example 3 except that the adhesion amount of the composition for forming the second layer was 0.35 to 0.90 g / m ^2. It was. Table 3 shows the structure of the first layer and the evaluation results of the obtained surface-treated steel sheet.

(Examples 9 to 14)
In the composition for forming the first layer, Example except that Snowtex (registered trademark) O (average particle diameter: 10 to 15 nm) manufactured by Nissan Chemical Industries, Ltd. was added so as to be 0.2 to 2.2 g / L. In the same manner as in No. 3, a surface-treated steel sheet was obtained. Table 4 shows the structure of the first layer and the evaluation results of the obtained surface-treated steel sheet.

(Examples 15 to 21)
A surface-treated steel sheet was obtained in the same manner as in Example 3 except that the colloidal silica described below was added at 0.5 g / L or 1.0 g / L in the first layer formation composition. In Examples 15 to 21, as colloidal silica, Snow Chemicals (registered trademark) OXS (average particle diameter 4 to 6 nm) manufactured by Nissan Chemical Industries, Ltd., Snow Snow (registered trademark) OS (average particle diameter) manufactured by Nissan Chemical Industries, Ltd. 8-11 nm), Nissan Chemical Industries Snowtex (registered trademark) O (average particle diameter 10-15 nm), Nissan Chemical Industries Snowtex (registered trademark) O-40 (average particle diameter 20-25 nm) It was. Table 5 shows the structure of the first layer and the evaluation results of the obtained surface-treated steel sheet.

(Examples 22 to 26)
In the composition for forming the second layer, examples were obtained except that the binder resin was blended so as to be 49.0 to 84.0 parts by mass and colloidal silica was 5.0 to 40.0 parts by mass in terms of solid content. In the same manner as in No. 7, a surface-treated steel sheet was obtained. Table 6 shows the structure of the second layer and the evaluation results of the obtained surface-treated steel sheet.

(Examples 27 to 29)
In the composition for forming the second layer, it was carried out except that it was blended so that the colloidal silica was 29.0 to 32.5 parts by mass and the external crosslinking agent was 5.0 to 8.5 parts by mass in terms of solid content. A surface-treated steel sheet was obtained in the same manner as in Example 7. Table 7 shows the structure of the second layer and the evaluation results of the obtained surface-treated steel sheet.

(Examples 30 to 32)
In the composition for forming the second layer, examples were obtained except that the binder resin was blended in an amount of 57.5 to 60.5 parts by mass and the lubricant was 2.0 to 5.0 parts by mass in terms of solid content. In the same manner as in No. 7, a surface-treated steel sheet was obtained. Table 8 shows the structure of the second layer and the evaluation results of the obtained surface-treated steel sheet.

  From Tables 2 to 8, it can be considered as follows.

  The surface-treated steel sheets of Examples 1 to 32 that satisfy the constituent requirements of the present invention were excellent in appearance. Furthermore, it was excellent in corrosion resistance, conductivity, tape peel resistance, and bending workability.

  On the other hand, as described in detail below, the steel sheets other than the above did not satisfy the constituent requirements of the present invention, and the desired characteristics were not obtained.

  In Comparative Examples 1 to 3, in which the amount of zinc phosphate crystals attached was too large and the major axis of the zinc phosphate crystals was too long, the appearance was poor, and the corrosion resistance, conductivity, and bending workability were also poor.

  In Comparative Examples 4 to 5 in which the amount of zinc phosphate crystals attached was too small, the appearance was poor and the tape peel resistance was also poor.

  In Comparative Example 6 in which the amount of the second layer attached was too small, the appearance was inferior, and the corrosion resistance and tape peel resistance were also inferior. In Comparative Example 7 in which the amount of adhesion of the second layer was too large, the conductivity was inferior.

Claims (4)

Galvanized steel sheet,
A first layer formed on at least one side of the galvanized steel sheet;
A surface-treated galvanized steel sheet provided with a second layer formed on the first layer,
The first layer includes zinc phosphate crystals;
The amount of zinc phosphate crystals deposited is 0.04 to 0.4 g / m ² ,
The major axis of the zinc phosphate crystal is 2.5 μm or less,
The second layer contains a resin,
The adhesion amount of said 2nd layer is 0.35-0.85 g / m < ² >. The surface treatment zinc-based plated steel plate characterized by the above-mentioned.   The surface-treated zinc-based plated steel sheet according to claim 1, wherein the first layer further contains colloidal silica.   The surface-treated galvanized steel sheet according to claim 1 or 2, wherein the composition for forming the second layer forming the second layer contains a binder resin, colloidal silica, an external crosslinking agent, and a lubricant.   In the second layer forming composition, the binder resin content is 54 to 79 parts by mass in a total of 100 parts by mass of the binder resin, the colloidal silica, the external crosslinking agent, and the lubricant, The content of colloidal silica is 10 to 35 parts by mass, the content of the external cross-linking agent is 5 to 8.5 parts by mass, and the content of the lubricant is 2 to 5 parts by mass. The surface-treated zinc-based plated steel sheet described.

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