JP2017203192A - Coating plated sheet steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating plated sheet steel excellent in end face corrosion resistance without requiring a chromate treatment and a chromate-based pigment in a primer layer.SOLUTION: A coating plated sheet steel 1 includes a steel sheet 11, plating layers 12, 13 containing magnesium, primer layers 30, 60 containing vanadium, and top layers 40, 70. The coating plated sheet steel, in which plating is expressed as 55 mass% Al-2 mass% Mg-1.6 mass% Si-Zn or the like, can show excellent end face corrosion resistance by synergic effect between magnesium and vanadium.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a coated plated steel sheet.

  Conventionally, a coated plated steel sheet obtained by coating a plated steel sheet has been widely used for building materials. Such a coated plated steel sheet is often cut and molded and applied with the end face exposed. The corrosion resistance of this end face is inferior to the corrosion resistance of other parts of the coated plated steel sheet, and edge creep may progress from the end face when exposed to the outdoors for a long period of time. Edge creep is a phenomenon in which the plated steel sheet under the coating is corroded and the coating is swollen.

  In order to improve the corrosion resistance of the end face, a chromate treatment is performed on the plated steel plate as a coating base treatment during the production of the coated steel plate.

  In recent years, since there is a concern about the adverse effects on the environment caused by elution of chromium, a coated plated steel sheet having high end surface corrosion resistance has been studied without requiring chromate treatment and a chromate pigment in the primer layer.

For example, Patent Document 1 discloses a coating film obtained by coating a chromate-free coating composition containing an amorphous MgO—V ₂ O ₅ based compound on an aluminum / zinc alloy plated steel sheet (Al 55%). A precoated steel sheet provided is specifically disclosed. Patent Document 2 specifically discloses a coated steel sheet provided with a chromate-free rust-proof coating film containing vanadium pentoxide and magnesium carbonate on the surface of an aluminum galvanized steel sheet.

  However, it is necessary to further improve the corrosion resistance of the end face of the coated plated steel sheet that does not require chromate treatment as disclosed in Patent Documents 1 and 2.

JP 2014-111785 A Japanese Patent Laying-Open No. 2015-209443

  An object of the present invention is to provide a coated steel sheet having excellent end face corrosion resistance without requiring chromate treatment and a chromate pigment in a primer layer.

  The coated plated steel sheet according to an aspect of the present invention includes a plated steel sheet including a steel sheet and a plated layer covering the steel sheet, a primer layer covering the plated layer, and a top layer covering the primer layer, And magnesium, and the primer layer contains a vanadium compound.

  1 aspect of this invention WHEREIN: It is preferable that the said plating layer contains aluminum and zinc.

  1 aspect of this invention WHEREIN: It is preferable that the quantity of the said magnesium with respect to the said plating layer exists in the range of 0.5-10 mass%.

1 aspect of this invention WHEREIN: It is preferable that the double-sided adhesion amount of the said plating layer exists in the range of 50-300 g / m < ² >.

In one aspect of the present invention, the total elution amount of magnesium and vanadium per end face length from the end face of the coated steel sheet into the ion exchange water increases in proportion to the square root of the elapsed time, The coefficient A1 is preferably greater than 1.35 (μg / m) / (hour) ^0.5 .

In one aspect of the present invention, the total amount of vanadium eluted from the end face of the coated steel sheet into the ion-exchanged water per length of the end face increases in proportion to the square root of the elapsed time, and its proportionality factor A2 Is preferably greater than 0.3 (μg / m) / (hour) ^0.5 .

  In one embodiment of the present invention, the vanadium compound preferably contains at least one compound selected from the group consisting of calcium vanadate, vanadium pentoxide, and ammonium metavanadate.

  In one aspect of the present invention, the primer layer includes a urea resin formed from a reaction product of a polyamine and a polyisocyanate, a polyester resin crosslinked with a melamine resin, a polyester resin crosslinked with an isocyanate resin, a melamine resin, and an isocyanate. It is preferable to contain at least one resin selected from the group consisting of a polyester resin crosslinked with a resin, an epoxy resin, and an aqueous polymer.

  According to the present invention, a coated plated steel sheet having excellent end surface corrosion resistance can be obtained without requiring chromate treatment and a chromate pigment in the primer layer.

It is sectional drawing of the coating plating steel plate which concerns on 1st embodiment of this invention. It is a graph which shows the relationship between the elution amount of vanadium per the length of the end surface of the sample of Example 1 and the comparative example 1 obtained in the elution evaluation, and elapsed time. It is a graph which shows the relationship between the elution amount of magnesium per length of the end surface of the sample of Example 1 and Comparative Example 1 obtained in the dissolution property evaluation and the elapsed time. It is a graph which shows the relationship between the elution amount of chromium per length of the end surface of the sample of Comparative Example 2 and Comparative Example 3, and elapsed time obtained in the elution property evaluation. It is a graph which shows the relationship between the total elution amount of magnesium and vanadium per length of the end surface of the sample of Example 1 and Comparative Example 1, and the square root of elapsed time obtained in the elution evaluation. It is a graph which shows the relationship between the elution amount of vanadium per the length of the end surface of the sample of Example 1 and Comparative Example 1 obtained in the dissolution property evaluation, and the square root of the elapsed time. It is a graph which shows the relationship between the elution amount of chromium per the length of the end surface of the sample of the comparative example 2 and the comparative example 3, and the square root of elapsed time obtained in the dissolution property evaluation.

  Embodiments of the present invention will be described below.

[First embodiment of the present invention]
As shown in FIG. 1, the coated plated steel sheet 1 according to the first embodiment of the present invention has a first plating layer 12, a first chemical conversion coating 20, a first primer layer 30, and a first surface of a steel sheet 11. The first top layer 40 is laminated in this order, and on the second surface opposite to the first surface of the steel plate 11, the second plating layer 13, the second chemical conversion coating 50, and the second primer layer 60 are provided. , And the second top layer 70 are laminated in this order. Hereinafter, the first plating layer 12 and the second plating layer 13 are simply the plating layers 12 and 13, the first chemical conversion coating 20 and the second chemical conversion coating 50 are simply the chemical conversion coatings 20 and 50, and the first primer layer 30. In some cases, the second primer layer 60 is simply referred to as the primer layers 30 and 60, and the first top layer 40 and the second top layer 70 are simply referred to as the top layers 40 and 70.

  The first plating layer 12 covers the first surface of the steel plate 11. The first chemical conversion coating 20 covers the first plating layer 12. The first primer layer 30 covers the first chemical conversion treatment film 20. That is, the first primer layer 30 covers the first plating layer 12. The first top layer 40 covers the first primer layer 30. The second plating layer 13 covers the second surface of the steel plate 11. The second chemical conversion treatment film 50 covers the second plating layer 13. The second primer layer 60 covers the second chemical conversion treatment film 50. That is, the second primer layer 60 covers the second plating layer 13. The second top layer 70 covers the second primer layer 60. The coated steel sheet 1 is used with the surface on the first top layer 40 side as the front surface and the surface on the second top layer 70 side as the back surface.

  In the first embodiment, the plating layers 12 and 13 contain magnesium, and the primer layers 30 and 60 contain a vanadium compound. Thereby, compared with the case where the plating layers 12 and 13 do not contain magnesium, the end surface corrosion resistance of the coated plated steel sheet 1 is remarkably improved. This remarkable improvement in the end face corrosion resistance is not exhibited only by magnesium, but is exhibited only by the synergistic effect of magnesium in the plating layers 12 and 13 and the vanadium compound in the primer layers 30 and 60. This can be confirmed from the elution amount of vanadium from the end face in ion-exchanged water or salt water (hereinafter sometimes referred to as water). The plating layers 12 and 13 contain magnesium. Therefore, compared with the case where the plating layers 12 and 13 do not contain magnesium, the elution amount of vanadium from the end face is remarkably increased. From this, it can be seen that magnesium in the plating layers 12 and 13 promotes the elution of the vanadium compound from the end face. The eluted vanadium suppresses the progress of edge creep as an inhibitor (corrosion inhibitor). Thereby, the end surface corrosion resistance of the coated plated steel sheet 1 is remarkably improved.

  Thus, when the plating layers 12 and 13 contain magnesium, it exists in the tendency for vanadium to elute in water easily compared with the case where the plating layers 12 and 13 do not contain magnesium. Regarding the effect of promoting magnesium in the plating film on the elution rate of vanadium in the coating film, the details of the mechanism are unclear, but vanadium has the property of forming an amorphous oxide with magnesium. It seems to be related.

  The elution rate of vanadium and magnesium per length of the end face from the primer layers 30 and 60 on the end face of the coated plated steel sheet 1 decreases with time, but the type of plating and the vanadium compound in the coating film, The behavior varies depending on the combination of the types of anticorrosive pigments. For example, the coated plated steel sheet 1 has a higher elution rate of magnesium and vanadium than a plated steel sheet in which a plated layer such as a Galvalume steel sheet (registered trademark) does not contain magnesium. As a result, the progress of corrosion of aluminum or zinc can be suppressed. The end surface includes a cut surface when the coated plated steel sheet 1 is cut. The length of the end face is the length of the end face along the direction orthogonal to the thickness direction of the coated plated steel sheet 1.

The elution rate of magnesium and vanadium is based on the change over time of the total elution amount of magnesium and vanadium per end length of a strip-shaped sample having a size of 5 mm × 50 mm in plan view obtained by cutting the coated plated steel sheet 1. I can know. The total elution amount of magnesium and vanadium per length of the end face of the sample is a value measured for the coated plated steel sheet 1 before being installed in a building or the like. In measuring the total elution amount of magnesium and vanadium per end face length of this sample, the coated plated steel sheet 1 was cut to obtain strip-shaped samples having a size of 5 mm × 50 mm in plan view, and 25 pieces obtained. Are immersed in ion-exchanged water having a temperature of 20 ° C. and a volume of 100 cm ³ . As a result, magnesium and vanadium are eluted from the primer layers 30 and 60 into the ion-exchanged water at the end face of the sample, and dissolved water containing magnesium and vanadium is obtained. Subsequently, the total amount of magnesium and vanadium in the dissolved water is measured. In measuring the total amount of magnesium and vanadium, for example, based on ICP (inductively coupled plasma) mass spectrometry, the amount of magnesium and the amount of vanadium in the dissolved water are determined by a calibration curve method. The total amount of vanadium is derived. Then, the sum of the derived amounts of magnesium and vanadium is divided by the length of the end surface of the sample to derive the total amount of magnesium and vanadium per length of the end surface of the sample in the dissolved water. Thereby, the obtained value corresponds to the total elution amount of magnesium and vanadium per length of the end face of the sample. Here, the length of the end face of the sample is the length obtained by multiplying the length of the end face per sample, that is, the length of the outer periphery in plan view of the sample by the number of samples. 2750 mm (110 mm × 25). And the elution rate of magnesium and vanadium can be calculated | required by calculating | requiring the total variation | change_quantity of the elution amount of magnesium and vanadium with respect to the elapsed time from the time the sample was immersed in ion-exchange water.

  Further, the total elution amount of magnesium and vanadium per end face length from the end face of the coated plated steel sheet 1 into the ion-exchanged water increases with the elapsed time and is proportional to the square root of the elapsed time. This is because a series of reactions that dissolve in the ion exchange water from the end face of the coated galvanized steel sheet 1 is limited by the diffusion of metal atoms from the coated galvanized steel sheet 1 to the solid-liquid interface between the coated galvanized steel sheet 1 and the ion exchange water. It is estimated that.

The total elution amount of magnesium and vanadium per end face length from the end face of the coated steel sheet 1 into the ion-exchanged water increases in proportion to the square root of the elapsed time, and the proportionality factor A1 is 1.35 (μg / M) / (hour) is preferably greater than ^0.5, more preferably 15 (μg / m) / (hour) greater than ^0.5 , and 18 (μg / m) / (hour) from ^0.5 More preferably, it is large. The greater the proportionality coefficient A1, the greater the total dissolution rate of magnesium and vanadium in the measurement range. If proportionality coefficient A1 is in the said range, the end surface corrosion resistance of the coating plating steel plate 1 will be more excellent.

  The proportionality coefficient A1 is, for example, the total amount of magnesium and vanadium in the dissolved water when the elapsed time from the time when the sample is immersed in ion-exchanged water is 0 hours, 2 hours, 7 hours, 13 hours, and 25 hours. Can be obtained from these measurement results by the method of least squares.

  Further, the total amount of vanadium eluted from the end face of the coated plated steel sheet 1 into the ion-exchanged water per end face length increases with the elapsed time, and is proportional to the square root of the elapsed time. Again, a series of reactions that dissolve into the ion exchange water from the end face of the coated plated steel sheet 1 is limited by the diffusion of metal atoms from the coated plated steel sheet 1 to the solid-liquid interface between the coated plated steel sheet 1 and the ion exchange water. It is estimated that.

The elution amount of vanadium per end face length from the end face of the coated plated steel sheet 1 into the ion exchange water increases in proportion to the square root of the elapsed time, and the proportionality coefficient A2 is 0.3 (μg / m) / (Hour) It is preferably larger than ^0.5, more preferably 0.5 (μg / m) / (hour) More preferably larger than ^0.5 , 1.0 (μg / m) / (hour) From ^0.5 More preferably, it is large. When the proportionality coefficient A2 is within the above range, the end face corrosion resistance of the coated plated steel sheet 1 is more excellent.

  The proportionality factor A2 is measured, for example, by measuring the amount of vanadium in the dissolved water when the elapsed time from the time when the sample is immersed in ion-exchanged water is 0 hours, 2 hours, 7 hours, 13 hours, and 25 hours, What is necessary is just to obtain | require by the least squares method from these measurement results.

  In order to set the proportionality coefficient A1 or A2 within the above range, for example, the adhesion amount of the plating layers 12 and 13, the amount of magnesium to the plating layers 12 and 13, the adhesion amount of the primer layers 30 and 60, and the primer layers 30 and 60 What is necessary is just to adjust the quantity etc. of a vanadium compound suitably.

  The plate thickness of the coated plated steel sheet 1 is preferably in the range of 0.25 to 2.3 mm.

  Hereinafter, the plated steel sheet 10, the chemical conversion coatings 20 and 50, the primer layers 30 and 60, and the top layers 40 and 70 constituting the coated plated steel sheet 1 will be described in detail.

(Plated steel plate 10)
The coated plated steel sheet 1 includes a plated steel sheet 10. As shown in FIG. 1, the plated steel plate 10 includes a steel plate 11, a first plating layer 12 that covers the first surface of the steel plate 11, and a second plating layer 13 that covers the second surface of the steel plate 11. The plating layers 12 and 13 may have the same configuration or different configurations.

  As the steel plate 11, for example, a low carbon steel plate, a high carbon steel plate, a high tensile steel plate, or the like can be used.

  The plating layers 12 and 13 contain magnesium as a constituent element, for example, preferably contain magnesium, aluminum, and zinc, and more preferably contain magnesium, aluminum, zinc, and silicon. Furthermore, the plating layers 12 and 13 may further contain strontium, iron, an alkaline earth element, scandium, yttrium, a lanthanoid element, titanium, boron or the like as a constituent element. As the alkaline earth element, beryllium, calcium, barium, or radium can be used. As the lanthanoid element, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium and the like can be used. Moreover, the plating layers 12 and 13 may further contain chromium as a constituent element.

  The amount of magnesium with respect to the plating layers 12 and 13 is preferably in the range of 0.5 to 10% by mass, more preferably in the range of 1 to 3% by mass. If the amount of magnesium is within the above range, the end face corrosion resistance of the coated plated steel sheet 1 is more excellent.

  The amount of aluminum with respect to the plating layers 12 and 13 is preferably in the range of 25 to 75 mass%, more preferably in the range of 45 to 65 mass%. The amount of silicon with respect to aluminum is preferably in the range of 0.5 to 10% by mass, more preferably in the range of 1.0 to 5.0% by mass.

The adhesion amount on both surfaces of the plating layers 12 and 13 may be adjusted as appropriate according to the amount of magnesium with respect to the plating layers 12 and 13, and is preferably in the range of 50 to 300 g / m ² , more preferably 100 to 200 g / m. Within the range of ² . If the adhesion amount on both surfaces of the plating layers 12 and 13 is within the above range, in the water, vanadium from the end surface is easily eluted in the water, the progress of edge creep is further suppressed, and the end surface corrosion resistance of the coated plated steel sheet 1 is further improved. Excellent. Furthermore, if the adhesion amount on both surfaces of the plating layers 12 and 13 is within the above range, the amount of zinc elution from the end surface is further suppressed in water, the occurrence of white rust is further suppressed, and the end surface corrosion resistance of the coated plated steel sheet 1 is reduced. Is better.

  The formation method of the plating layers 12 and 13 is not particularly limited, and a hot dipping method is preferable.

(Chemical conversion coating 20, 50)
The coated galvanized steel sheet 1 includes chemical conversion coatings 20 and 50. The chemical conversion treatment films 20 and 50 are layers formed by a known chemical conversion treatment. The chemical conversion coatings 20 and 50 may have the same configuration or different configurations.

  Examples of the treatment agent for forming the chemical conversion treatment layer (hereinafter referred to as chemical conversion treatment agent) include, for example, phosphate treatment agents such as zinc phosphate treatment agent and iron phosphate treatment agent; cobalt, nickel, tungsten, zirconium, etc. Oxide treatment agent containing metal oxides alone or in combination; Treatment agent containing inhibitor component to prevent corrosion; Treatment that combines binder component (organic, inorganic, organic-inorganic composite, etc.) and inhibitor component An agent; a treatment agent in which an inhibitor component and a metal oxide are combined; a treatment agent in which a binder component and a sol such as silica, titania, and zirconia are combined; a treatment agent that further combines the components of the exemplified treatment agent, etc. Can do.

  Examples of the oxide treating agent containing zirconium oxide include water and water-dispersible polyester urethane resin, water-dispersible acrylic resin, zirconium compound such as sodium zirconium carbonate, and hindered amines. The treating agent prepared in this manner can be used. The water-dispersible polyester-based urethane resin is synthesized, for example, by reacting a polyester polyol with hydrogenated isocyanate and self-emulsifying by copolymerizing dimethylol alkyl acid. Such a water-dispersible polyester-based urethane resin imparts high water resistance to the chemical conversion treatment layers 20 and 50 without using an emulsifier, leading to improvement in end face corrosion resistance and alkali resistance of the plated steel sheet 10. Moreover, it is preferable that a chemical conversion treatment agent does not contain a chromium compound. The phrase “not containing a chromium compound” means intentionally not containing a chromium compound, and may contain a chromium compound as an unavoidable impurity.

  Between the chemical conversion treatment layers 20 and 50 and the plating layers 12 and 13, nickel plating treatment, cobalt plating treatment, or the like may be performed.

  The chemical conversion treatment layers 20 and 50 may be formed by a known method such as a roll coating method, a spray method, a dipping method, an electrolytic treatment method, or an air knife method using a chemical conversion treatment agent. After application of the chemical conversion treatment agent, a step such as standing at room temperature or drying or baking with a heating device such as a hot air furnace, an electric furnace, or an induction heating furnace may be added as necessary. A curing method using energy rays such as infrared rays, ultraviolet rays and electron beams may be applied. The temperature and drying time during drying are appropriately determined according to the type of chemical conversion treatment agent used and the required productivity. The thickness of the chemical conversion treatment layers 20 and 50 is appropriately determined according to the type of treatment, required performance, and the like.

(Primer layers 30, 60)
The coated plated steel sheet 1 includes primer layers 30 and 60. The primer layers 30 and 60 are layers formed of an undercoat paint containing a vanadium compound and containing a vanadium compound. The vanadium compound contributes to the end surface corrosion resistance of the coated plated steel sheet 1 as an elution inhibitor. The primer layers 30 and 60 may have the same configuration or different configurations.

The adhesion amount of the first primer layer 30 is preferably larger than the adhesion amount of the second primer layer 60. The adhesion amount of the first primer layer 30 is preferably in the range of 3 to ²⁰ g / m ² , more preferably in the range of 5 to 15 g / m ² . The adhesion amount of the second primer layer 60 is preferably in the range of 1 to 10 g / m ² , more preferably in the range of ^{2 to 5} g / m ² .

  The undercoat paint contains a vanadium compound, resins and a solvent, and may further contain a rust preventive pigment and an additive.

  The undercoat paint contains a vanadium compound. Examples of the vanadium compound include vanadium pentoxide, metavanadate, calcium vanadate, magnesium vanadate, ammonium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, vanadium oxysulfate, vanadium oxyacetylacetonate, vanadium acetyl. Acetonate, vanadium trichloride, or the like can be used. Especially, since it is easy to elute in water from an end surface, it is preferable that a vanadium compound contains at least 1 type of compound chosen from the group which consists of calcium vanadate, vanadium pentoxide, and ammonium metavanadate. Further, it is preferable that the base treatment and the undercoat paint do not contain a chromium compound.

The vanadium compound content per area in the primer layers 30 and 60 is preferably in the range of 0.1 to 20 g / m ² , more preferably in the range of 0.5 to 10 g / m ² . If content of a vanadium compound is in the said range, the end surface corrosion resistance of the coating plating steel plate 1 will be more excellent.

  The undercoat paint may contain a rust preventive pigment different from the vanadium compound. As the rust preventive pigment, generally known chromate-free rust preventive pigments, for example, phosphate phosphate rust preventive pigments such as zinc phosphate, iron phosphate, aluminum phosphate, magnesium phosphate; calcium molybdate, aluminum molybdate, Molybdic acid-based defense pigments such as barium molybdate; finely divided silica such as water-dispersible silica and fumed silica can be used.

  The undercoat paint contains resins. As the resins, for example, epoxy resin-based paints, urea resin-based paints, polyester resin-based paints containing a crosslinking agent, polyvinyl chloride-based resins, aqueous polymers, and the like can be used. Among them, a urea resin made of a reaction product of polyamine and polyisocyanate, which will be described later, a polyester resin crosslinked with a melamine resin, a polyester resin crosslinked with an isocyanate resin, a melamine resin and an isocyanate resin are crosslinked. It is preferable to contain at least one resin selected from the group consisting of a polyester resin, an epoxy resin, and an aqueous polymer.

  The urea resin-based paint preferably contains a blocked isocyanate and a polyamine. The urea resin-based paint makes it easy to increase the thickness of the primer layers 30 and 60. With this paint, the thick primer layers 30 and 60 can be formed without generating bubbles (bubbles). By using a blocked isocyanate, it becomes possible to make the paint one component.

When the urea resin-based paint is heated, the blocking agent is dissociated from the blocked isocyanate, and the isocyanate group (—NCO) is regenerated. Polymerization occurs when this isocyanate group reacts with an amino group (—NH ₂ ) in the polyamine to form a urea bond (—NHCONH—). For this reason, the primer layers 30 and 60 formed from a urea resin-based paint have a configuration in which a vanadium compound is dispersed in a urea resin made of a reaction product of a polyamine and a polyisocyanate.

  The urea resin-based paint preferably contains a urea resin and a polyester resin crosslinked with a melamine resin. In this case, vanadium is particularly easily eluted from the primer layers 30 and 60.

  The blocked isocyanate constituting the urea resin-based paint is a compound obtained by reacting an isocyanate group of polyisocyanate with a blocking agent to block.

  As the polyisocyanate, aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, and tolidine diisocyanate can be used. Of these, tolylene diisocyanate is preferred from the viewpoint of performance and economy. The polyisocyanate is not a monomer but may be a derivative such as a prepolymer, an adduct (adduct such as trimethylolpropane), an isocyanurate body, and a biuret body. Moreover, you may use combining 2 or more types of polyisocyanate or its derivative (s).

  As the polyisocyanate blocking agent, it is preferable that the dissociation temperature, which is the temperature at which the blocking agent is dissociated from the blocked isocyanate, is 150 ° C. or higher in order to increase the thickness of the primer layers 30 and 60. When a blocking agent having a dissociation temperature lower than 150 ° C. (for example, cresol having a dissociation temperature of 120 ° C. or methyl ethyl ketone oxime having a dissociation temperature of 140 ° C.), a bubble (bubbles) is likely to be generated during baking after coating. Film coating may be difficult. On the other hand, if the dissociation temperature is too high, it is necessary to increase the baking temperature or to increase the baking time. Therefore, the dissociation temperature is preferably 200 ° C. or lower, particularly 180 ° C. or lower. In particular, the dissociation temperature of the blocking agent is preferably in the range of 150 to 200 ° C, more preferably in the range of 160 to 180 ° C. As a particularly preferable blocking agent, ε-caprolactam having a dissociation temperature of 170 ° C. can be used.

  The polyisocyanate and the blocking agent can be reacted by a known method. In general, a polyisocyanate in a solvent and a stoichiometric amount or a slightly excess amount of a blocking agent can be reacted under heating. The number average molecular weight of the blocked isocyanate is preferably in the range of 1000 to 4000. Since various products are commercially available as the blocked isocyanate, an appropriate one can be selected from commercially available products.

  As the polyamine constituting the urea resin-based paint, aliphatic (including alicyclic) polyamines, aromatic polyamines, and the like can be used, and among them, alicyclic polyamines are preferably used. As the alicyclic polyamine, for example, an alicyclic polyamine used as a curing agent for an epoxy resin can be used. Examples of the alicyclic polyamine include 1-cyclohexylamino-3-aminopropane, diaminocyclohexanes, bis (4-aminocyclohexyl) methane, bis (4-aminocyclohexyl) sulfone, 3,3′-dimethyl-4, 4′-diaminodicyclohexylmethane, isophoronediamine and the like can be used. Of these, 3,3′-dimethyl-4,4′-diaminodicyclohexylmethane is preferably used. One or more polyamines can also be used.

  In the urea resin-based paint, the blending ratio of blocked isocyanate and polyamine is such that the molar ratio of isocyanate group / amino group is preferably in the range of 0.6 to 2.0, more preferably in the range of 0.8 to 1.2. Is within.

  When preparing the undercoat paint, for example, a vanadium compound is further added to a resin liquid obtained by dissolving blocked isocyanate and polyamine in an appropriate solvent, and the vanadium compound is uniformly dispersed in the resin liquid. By doing so, an undercoat paint is obtained.

  As the polyester resin-based paint, except that a vanadium compound is added, the same paint as the polyester resin-based paint used as a top coat described later can be used. Especially, it is preferable that a polyester resin type coating material contains the polyester resin bridge | crosslinked with the melamine resin, the polyester resin bridge | crosslinked with the isocyanate resin, the melamine resin, and the polyester resin bridge | crosslinked with the isocyanate resin. As the melamine resin, methylated melamine, butylated melamine or the like can be used. Isocyanate resin is a crosslinking agent formed of a resin made of a compound having an isocyanate group.

  As an epoxy resin-type coating material, the appropriate thing currently used for the conventional coating plating steel plate can be used.

  As an aqueous polymer which comprises an aqueous polymer coating material, acrylic resin-type resin, urethane resin-type resin, polyester resin-type resin etc. can be used, for example. As an aqueous polymer paint containing an acrylic resin, trade name Almatex manufactured by Mitsui Chemicals, Inc. may be mentioned. As a water-based polymer paint containing a urethane resin, trade name Superflex manufactured by Daiichi Kogyo Seiyaku Co., Ltd. and the like can be mentioned. As a water-based polymer paint containing a polyester resin, trade name “Hardlen” manufactured by Toyobo Co., Ltd. may be mentioned.

  When such an aqueous polymer paint contains a vanadium compound, at least a part of the vanadium compound is dissolved in water in the aqueous polymer paint. A part of the rust preventive pigment is dissolved in water in the state of the paint before drying from this aqueous polymer paint, and the vanadium compound has water solubility even in the dry paint film formed from this aqueous polymer paint, For this reason, the elution rate of vanadium can be improved.

  For example, when a resin other than a urea resin-based paint is used as the resin constituting the undercoat paint, the thickness of the coating film that can be formed without generating a crack by one coating is about 20 μm, compared with the case of a urea resin-based paint. As a result, the thickness of the coating is reduced. Therefore, in order to adjust the amount of the vanadium compound in the primer layers 30 and 60 to a desired amount, the primer coating may be applied twice or more as necessary.

  The undercoat paint contains a solvent. Examples of the solvent include water; hydrocarbon solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; ethyl solvents such as cellosolves; ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone, and cyclohexanone. Etc. can be used.

  The undercoat paint may contain an additive. Examples of additives include extenders, antifoaming agents, pigment dispersants, anti-sagging agents, leveling agents, silane coupling agents, and other additives, catalysts for the reaction of polyisocyanates and polyamides (eg, organotin compounds) ) Etc. can be used. Examples of extender pigments that can be used include silica, alumina, talc, calcium carbonate, and titania.

  As a method for applying the undercoat paint, an appropriate application method such as roll coating, curtain flow coating, spray coating or the like can be employed. When continuous coating is applied to the plated steel sheet 10 having the coiled chemical conversion coatings 20 and 50, roll coating is generally employed. If the thickness of the coating film does not reach the required thickness after one application, the undercoat may be applied twice or more. When the undercoat paint is applied twice or more, two or more undercoat paints having different compositions may be used.

  After the primer coating is applied onto the chemical conversion coatings 20 and 50, the primer layers 30 and 60 are formed when the coating of the primer coating is heated as necessary. As for the heating temperature of the coating film, the highest temperature is preferably in the range of 180 to 240 ° C., and the heating time of the coating film is preferably in the range of 30 to 70 seconds. If the heating temperature is too low, the resin in the undercoat paint may not be sufficiently cured, and if the heating temperature is too high, the resin in the undercoat paint may be decomposed to deteriorate film properties such as workability. It is particularly preferable that the maximum temperature reached during heating is in the range of 200 to 220 ° C.

(Top layers 40, 70)
The coated plated steel sheet 1 includes top layers 40 and 70. The top layers 40 and 70 are layers formed from a top coat. The top layers 40 and 70 may have the same configuration or different configurations.

The adhesion amount of the first top layer 40 is preferably larger than the adhesion amount of the second top layer 70. The adhesion amount of the first top layer 40 is preferably in the range of ^{20 to} 50 g / m ² , more preferably in the range of 25 to 45 g / m ² . The adhesion amount of the second top layer 70 is preferably in the range of 5 to ²⁰ g / m ² , more preferably in the range of 3 to 15 g / m ² . If the adhesion amount of the top layers 40 and 70 is within the above range, the hue of the top layers 40 and 70 is stabilized, and the coated plated steel sheet 1 is more excellent in end face corrosion resistance, weather resistance and workability.

  The top coat contains a resin and a solvent, and may further contain an additive. It is preferable that the top coating does not contain a chromium compound.

  The top coat paint contains resins. As the resins, polyurethane paints, polyester paints, and the like can be used.

  The polyurethane paint is a paint containing polyisocyanate and polyol. The polyurethane-based paint used as the top coat is also preferably a one-component paint in which polyisocyanate is reacted with a blocking agent and contained in the form of blocked isocyanate.

  As polyisocyanate which comprises a polyurethane-type coating material, aliphatic polyisocyanate also including an alicyclic type, hydrogenated diphenylmethane diisocyanate, etc. can be used, for example. Especially, it is preferable to use hydrogenated diphenylmethane diisocyanate at the point which can form the coating film excellent in workability.

  When an aliphatic polyisocyanate including an alicyclic type is used, the top layers 40 and 70 which are excellent in weather resistance and hardly yellow can be formed. Examples of such aliphatic polyisocyanates include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and the like. As the polyisocyanate, a prepolymer, an adduct, an isocyanurate body, a biuret body, or the like can be used.

  Examples of the polyol constituting the polyurethane-based paint include polyesters and polyethers (eg, those obtained by ring-opening polymerization of ethylene oxide or propylene oxide using a polyhydric alcohol as an initiator). These 1 type (s) or 2 or more types can be used.

  Especially, it is preferable to use a polyester resin as a polyol. As this polyester resin, it is preferable to use a high molecular weight saturated polyester resin. The polyester resin may be a linear polyester obtained by polycondensation of one or two or more saturated aliphatic (including alicyclic) or aromatic dicarboxylic acids and glycol. As the saturated aliphatic dicarboxylic acid, for example, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, 1,4-cyclohexanedicarboxylic acid and the like can be used. As the aromatic dicarboxylic acid, for example, phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid and the like can be used. Examples of the glycol include ethylene glycol, propylene glycol, butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, hydroquinone and the like. Can be used. The saturated polyester resin is a group consisting of a trivalent or higher carboxylic acid (eg, trimellitic acid) and a trivalent or higher alcohol (eg, glycerin, trimethylolpropane, pentaerythritol, sorbitol, etc.) in addition to the above reaction components. A branched polyester obtained by copolymerizing at least one selected from the above may also be used.

  The polyester resin used as the polyol constituting the polyurethane paint preferably has a weight average molecular weight in the range of 5000 to 20000, more preferably in the range of 8000 to 15000, and a hydroxyl group content of 1.0 to 4.0% by mass. In the range, more preferably in the range of 2.0 to 3.0% by mass, and the glass transition temperature in the range of −30 ° C. to 0 ° C. Thereby, a top-coated polyurethane coating film excellent in both weather resistance and processability is formed.

  A preferred polyurethane paint is a blocked isocyanate containing at least 20% by mass of a blocked isocyanate obtained by blocking hydrogenated diphenylmethane diisocyanate with a suitable blocking agent, and a polyester having the above preferred molecular weight, hydroxyl group content and glass transition temperature as a polyol component. And a resin. The molar ratio of isocyanate group / hydroxyl group in the polyurethane paint is preferably in the range of 0.6 to 2.0, particularly in the range of 0.8 to 1.2.

  It is preferable that the polyester-type paint which comprises top coat paint contains the polyester resin illustrated as a polyol which comprises the said polyurethane-type paint, for example, and the melamine resin as a crosslinking agent. The melamine resin is particularly preferably alcohol-modified. Polyester paints are slightly more workable than polyurethane paints, but are economically more advantageous than polyurethane paints.

  The top coat contains a solvent. Examples of the solvent include water; hydrocarbon solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; ethyl solvents such as cellosolves; ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone, and cyclohexanone. A solvent or the like can be used.

  The top coat may contain additives. As the additive, for example, an inorganic filler, an organic filler, a color pigment, an extender pigment, and the like can be used. As the inorganic filler, for example, glass fiber, alumina fiber, boron nitride and the like can be used. As the organic filler, thermoplastic resin beads (eg, acrylic resin or nylon beads, preferably having an average particle diameter in the range of 1 to 50 μm) can be used. You may contain an organic filler in the quantity of 10 mass% or less. Thereby, unevenness is formed on the surface of the coating film, the wear resistance of the coating film is improved, and it becomes difficult to be damaged. In particular, in the case of resin beads, the appearance is reduced in gloss and design is imparted.

  After the top coat is applied on the first primer layer 30, the top coat is heated as necessary to form the first top layer 40, and the top coat is applied on the second primer layer 60. After the application, the second top layer 70 is formed by heating the coating film of the top coat as necessary. As for the heating temperature of a coating film, it is preferable that the highest achieved temperature is in the range of 200 to 240 ° C., and the heating time of the coating film is preferably in the range of 40 to 90 seconds. If the heating temperature is too low, the resin in the top coating material may not be sufficiently cured, and if the heating temperature is too high, the resin in the top coating material may be decomposed to deteriorate film properties such as workability. It is particularly preferable that the maximum temperature reached during heating is in the range of 200 to 220 ° C.

  The top coat can also be applied in the same manner as the undercoat.

[Other Embodiments of the Present Invention]
As another embodiment of the present invention, a coated plated steel sheet having the same configuration as the coated plated steel sheet 1 except that the second chemical conversion film 50, the second primer layer 60 and the second top layer 70 are not provided; The coated plated steel sheet having the same structure as the coated plated steel sheet 1 except that the primer layers 30 and 60 cover the plated layers 12 and 13 without the chemical conversion coatings 20 and 50. A coated plated steel sheet having the same configuration as that of the coated plated steel sheet 1 except that a first coating layer is formed between the primer layer 30 and the first chemical conversion coating 20; the first primer layer 30 and the first top layer 40 A coated plated steel sheet having the same structure as the coated plated steel sheet 1 except that a second coated layer is formed between the second coated layer and the third coated layer between the second primer layer 60 and the second plated layer 13. (Not shown) is formed Painted steel sheet having the same configuration as the plated steel sheet 1; Coating having the same structure as the coated steel sheet 1 except that the fourth coating layer is formed between the second primer layer 60 and the second top layer 70. Examples thereof include plated steel sheets. However, the top layers 40 and 70 are disposed on the outermost layer of the coated plated steel sheet 1. The first to fourth coating layers may be formed from an appropriate resin paint such as an epoxy resin paint.

  Hereinafter, the present invention will be specifically described by way of examples.

[Example 1]
As the plated steel sheet 10, “SG (registered trademark)” (manufactured by Nippon Steel & Sumikin Steel Co., Ltd., plate thickness: 0.8 mm, double-sided adhesion amount: 150 g / m ² ) (hereinafter, SGL) was prepared. The plated steel plate 10 includes a steel plate 11, a first plating layer 12 that covers the first surface of the steel plate 11, and a second plating layer 13 that covers the second surface of the steel plate 11. The composition of the plating layers 12 and 13 was 55 mass% Al-2 mass% Mg-1.6 mass% Si-Zn.

A chromate-free treatment agent was applied onto the plating layers 12 and 13 with a bar coater, and further heated for about 10 seconds so that the maximum plate temperature reached 100 ° C. Thereby, the 1st chemical conversion treatment film 20 which covers the 1st plating layer 12, and the 2nd chemical conversion treatment film 50 which covers the 2nd plating layer 13 were formed, respectively. The adhesion amount per one side of the chemical conversion treatment films 20 and 50 was 100 mg / m ² .

On the first chemical conversion coating 20, an epoxy paint (vanadium compound: calcium vanadate, rust preventive pigment: magnesium phosphate, vanadium compound content ratio: the total mass of the epoxy paint as an undercoat paint for forming the first primer layer 30% by mass with respect to the total mass of the epoxy paint and 20% by mass with respect to the total mass of the epoxy paint, and 50% by mass with respect to the total mass of the epoxy paint). Further, heating was performed for 60 seconds so that the maximum plate temperature reached 200 ° C. Thereby, the 1st primer layer 30 which covers the 1st chemical conversion treatment film 20 was formed. The adhesion amount of the first primer layer 30 was 7 g / m ² .

An epoxy paint (vanadium compound: calcium vanadate, rust preventive pigment: magnesium phosphate, vanadium compound content ratio: the total mass of the epoxy paint on the second chemical conversion coating 50 as an undercoat paint for forming the second primer layer. 30% by mass with respect to the total mass of the epoxy paint and 20% by mass with respect to the total mass of the epoxy paint, and 50% by mass with respect to the total mass of the epoxy paint). Further, heating was performed for 60 seconds so that the maximum plate temperature reached 200 ° C. Thereby, the 2nd primer layer 60 which covers the 2nd chemical conversion treatment film 50 was formed. The adhesion amount of the second primer layer 60 was 2 g / m ² .

As the first top layer forming top coat, this first top layer forming top coat (polyester-based paint, black, matte) is applied onto the first primer layer 30 with a bar coater. Heated to 60 ° C. for 60 seconds. Thereby, the first top layer 50 covering the first primer layer 30 was formed. The adhesion amount of the first top layer 50 was 24 g / m ² .

As the second top layer forming top coating, this second top layer forming top coating (polyester paint, ocher) was applied onto the second primer layer 60 by a bar coater, and the maximum temperature reached 220 ° C. For 60 seconds. Thereby, the 2nd top layer 70 which covers the 2nd primer layer 60 was formed. The adhesion amount of the second top layer 70 was 6 g / m ² .

  Thus, the coating plating steel plate 1 (henceforth a SGL vanadium steel plate) was obtained.

[Comparative Example 1]
Other than using “Galbarium steel plate (registered trademark)” (manufactured by Nippon Steel & Sumikin Steel Co., Ltd., plate thickness: 0.8 mm, double-sided adhesion amount: 150 g / m ² ) (hereinafter referred to as GL) In the same manner as in Example 1, a coated plated steel sheet 1 (hereinafter referred to as GL vanadium steel sheet) was obtained. The plated steel plate 10 includes a steel plate 11, a first plating layer 12 that covers the first surface of the steel plate 11, and a second plating layer 13 that covers the second surface of the steel plate 11. This steel plate 11 was the same as the steel plate 11 used in Example 1. Moreover, the composition of this plating layer 12 and the plating layer 13 was 55 mass% Al-1.6 mass% Si-Zn.

[Comparative Example 2]
As the plated steel plate 10, “SG® (registered trademark)” (manufactured by Nippon Steel & Sumikin Steel Co., Ltd., plate thickness: 0.8 mm, double-sided adhesion amount: 150 g / m ² ) was prepared.

A chromate treatment agent (manufactured by Nihon Parkerizing Co., Ltd., product number “ZM1300AN”) was applied to the plated layers 12 and 13 of the plated steel sheet 10 with a bar coater, and further heated for about 10 seconds so that the maximum plate temperature reached 100 ° C. . The chromium adhesion amount per one side of the chemical conversion treatment films 20 and 50 was 40 mg / m ² .

On the first chemical conversion coating 20, an epoxy-based paint (rust preventive pigment: strontium chromate) is applied by a bar coater as an undercoat for forming the first primer layer, and further, the maximum reached plate temperature is 200 ° C. Heated for 2 seconds. Thereby, the 1st primer layer 30 which covers the 1st chemical conversion treatment film 20 was formed. The adhesion amount of the first primer layer 30 was 6 g / m ² .

On the second chemical conversion coating 50, an epoxy-based paint (rust-preventive pigment: strontium chromate) is applied by a bar coater as an undercoat paint for forming the second primer layer, and further, the maximum plate temperature is set to 200 ° C. Heated for 2 seconds. Thereby, the 2nd primer layer 60 which covers the 2nd chemical conversion treatment film 50 was formed. The adhesion amount of the second primer layer 60 was 2 g / m ² .

  In the same manner as in Example 1, the first top layer 40 and the second top layer 70 were formed on the first primer layer 30 and the second primer layer 60, respectively.

  Thus, a coated plated steel sheet 1 (hereinafter referred to as SGL chromate steel sheet) was obtained.

[Comparative Example 3]
As the plated steel plate 10, instead of “SG” (registered trademark), “Galbarium steel plate (registered trademark)” (manufactured by Nippon Steel & Sumikin Steel Co., Ltd., plate thickness: 0.8 mm, double-sided adhesion amount: 150 g / m ² ) A coated plated steel sheet 1 (hereinafter referred to as GL chromated steel sheet) was obtained in the same manner as in Comparative Example 1 except that it was used.

[Evaluation test]
(Elution evaluation)
The coated steel sheet 1 obtained in each example and comparative example was cut with a shear cutter to obtain a strip-shaped sample having a size of 5 mm × 50 mm in plan view. With respect to the thickness of the coated plated steel sheet 1, the cutting clearance is 60% of the length in the thickness direction of the coated plated steel sheet 1 from the top (first top layer 40 side) to the sheared surface. It cut | disconnected (halved) so that the length of the thickness direction might be 40%. The rest was cut in the same way from below (second top layer 70 side). 25 samples were immersed in ion-exchanged water having a temperature of 20 ° C. and a volume of 100 cm ³ for 2 hours to obtain dissolved water.

  Subsequently, all 25 samples were taken out of the dissolved water, and the amount of each element in the dissolved water was further analyzed by ICP (inductively coupled plasma) mass spectrometry using a spectrophotometer (product number “7700X” manufactured by Agilent Technologies, Inc.). Measured based on Similarly, dissolved water immersed for 7 hours, dissolved water immersed for 13 hours, and dissolved water immersed for 25 hours were obtained, and the amount of each element in each dissolved water was measured. The ion-exchanged water contained less than 1 ppb impurities such as V, Mg, and Cr.

  In Example 1 and Comparative Example 1, the amount of vanadium and the amount of magnesium in the dissolved water were measured. The amount of each element was determined simultaneously with multiple elements. In any case, each element was quantitatively analyzed using a calibration curve prepared in advance.

  In Comparative Examples 2 and 3, the amount of chromium in the dissolved water was measured. The amount of chromium was measured based on a spectrophotometer (manufactured by Shimadzu Corporation, product number “UV3600”). As with other elements, the amount of chromium was quantified based on a calibration curve prepared in advance.

  From the measurement results, the elution amount of the element per length of the end face of the sample was derived. The results are shown in Table 1. Furthermore, the graph which shows the relationship between the elution amount of vanadium per the length of the end surface of the sample of Example 1 and the comparative example 1, and elapsed time obtained in the elution evaluation is shown in FIG. The graph which shows the relationship between the elution amount of magnesium per length of the end surface of the sample of Example 1 and Comparative Example 1 and elapsed time is shown in FIG. A graph showing the relationship between the elution amount of chromium per end face length of the samples of Comparative Example 2 and Comparative Example 3 and the elapsed time is shown in FIG. FIG. 5 is a graph showing the relationship between the total elution amount of magnesium and vanadium per end face length of the samples of Example 1 and Comparative Example 1 and the square root of the elapsed time. The graph which shows the relationship between the elution amount of vanadium per the length of the end surface of the sample of Example 1 and Comparative Example 1 and the square root of elapsed time is shown in FIG. FIG. 7 is a graph showing the relationship between the elution amount of chromium per end face length of the samples of Comparative Example 2 and Comparative Example 3 and the square root of the elapsed time. The straight line in FIGS. 5 to 7 is a correlation straight line obtained by the least square method from the elution amount of the element per the length of the end face of each sample with respect to the square root of the elapsed time.

(End surface corrosion resistance evaluation)
The coated plated steel sheet 1 obtained in each example and comparative example is alternately turned from the first top layer 40 (evaluation surface) side and from the second top layer 70 (surface opposite to the evaluation surface) side by a shearing machine. A sample having a size of 70 mm × 150 mm in plan view was cut out. The cutting was performed so that the sheared portion was 60% and the fragile portion was 40% from the top with respect to the thickness of the coated plated steel sheet 1. A lower burr is formed on one long side (side of 150 mm in length) of the sample (hereinafter referred to as a lower burr portion), and an upper burr is formed on the other long side edge (hereinafter referred to as an upper burr portion). It was. The upper burr means that a burr (burr) is generated on the first top layer 40 side which is the evaluation surface, and the lower burr means the second top layer 70 side which is the side opposite to the evaluation surface. This means that burrs have occurred. And the end surface in each short side (side of length 70mm) of this sample was sealed, and the sample for end surface corrosion resistance evaluation was obtained.

  A combined cycle test (CCT) was performed using the obtained sample for evaluation of end face corrosion resistance, and end face corrosion resistance in the lower burr portion was evaluated. Specifically, the combined cycle test (CCT) consists of SST (5% NaCl salt spray: 35 ° C .; 2 hours), dry (60 ° C., 4 hours) and wet (constant temperature wet: 50 ° C., 95% RH; 2 Time) was taken as one cycle, and 100 cycles were carried out.

  About the sample after a test, the "blowing (mm)" in a lower burr | flash part was measured. The measurement results are shown in Table 1.

  For the sample after the test, “white rust length (mm)” generated from the edge of the first top layer 40 toward the upper burr portion in the lower burr portion was measured. The measurement results are shown in Table 1.

  As shown in Table 1, the GL vanadium steel sheet of Comparative Example 1 contains the vanadium compound in the primer layers 30 and 60, but did not contain magnesium in the plating layers 12 and 13, so both swelling and white rust length were observed. It was big.

  As shown in Table 1, the SGL chromate steel sheet of Comparative Example 2 did not contain the vanadium compound in the primer layers 30 and 60, but the plating layers 12 and 13 contained magnesium, and the primer layers 30 and 60 were rust-proof. Since strontium chromate was contained as a pigment, both swelling and white rust length were small.

  As shown in Table 1, in the GL chromate steel sheet of Comparative Example 3, the plating layers 12 and 13 did not contain magnesium, and the primer layers 30 and 60 did not contain a vanadium compound. Since strontium chromate was contained as a rust pigment, both swelling and white rust length were large.

  On the other hand, as shown in Table 1, the SGL vanadium steel sheet of Example 1 contained magnesium in the plating layers 12 and 13 and the calcium oxide vanadate as the vanadium compound in the primer layers 30 and 60. Both white rust lengths were small.

  As mentioned above, it turned out that the SGL vanadium steel plate of Example 1 is more excellent in end surface corrosion resistance than the GL vanadium steel plate of the comparative example 1 equivalent to the conventional coating plating steel plate which does not require chromate treatment. Further, the SGL vanadium steel sheet of Example 1 is superior in end face corrosion resistance to the GL chromate steel sheet of Comparative Example 3 corresponding to a conventional coated steel sheet requiring chromate treatment, and Comparative Example 2 corresponding to a paint plated steel sheet requiring chromate treatment. It was found that the end face corrosion resistance was equivalent to that of the SGL chromate steel sheet. That is, it was found that the SGL vanadium steel sheet of Example 1 was excellent in end face corrosion resistance even without the chromate treatment and the chromate pigment in the primer layer.

  Moreover, as shown in Table 1, the elution amount of vanadium per length of the end face of the sample was 1.1 to 1.2 μg / m in Comparative Example 1, whereas in Example 1, it was 5.6 to It was 9.1 μg / m. The elution amount of magnesium per length of the end face of the sample was 1.9 to 4.9 μg / m in Comparative Example 1, whereas it was 30.4 to 90.9 μg / m in Example 1. . From these results, the elution of the vanadium compound in the primer layers 30 and 60 can be greatly promoted by containing magnesium in the plating layers 12 and 13 and elution of the magnesium in the plating layers 12 and 13 in water. all right.

  Further, as shown in Table 1, the elution amount of chromium per end face length of the sample was 180 to 480 μg / m in Comparative Example 2, whereas it was 200 to 510 μg / m in Comparative Example 3. It was. From these results, it was found that the elution amount of chromium per end face length of the sample did not depend on the magnesium content of the plating layers 12 and 13.

  Thus, when the plating layers 12 and 13 contained magnesium, the tendency for the vanadium to elute in water easily was seen compared with the case where the plating layers 12 and 13 do not contain magnesium. In addition, the SGL vanadium steel sheet with the chromate-free coating applied to the SGL of Example 1 clearly had a higher elution rate of magnesium and vanadium than the GL vanadium steel sheet with the chromate-free coating applied to the GL of Comparative Example 1. . It has been found that the progress of corrosion of aluminum and zinc can be suppressed.

From FIG. 5, it was found that the total elution amount of magnesium and vanadium per end face length from the end face of the sample into the ion-exchanged water increased with the elapsed time and was proportional to the square root of the elapsed time. Further, with respect to the total amount of magnesium and vanadium per length of the end face of the sample, the proportionality coefficient A1 of the correlation line in Comparative Example 1 shown in FIG. 5 is 1.35 (μg / m) / (hour) ^0.5 . In contrast, the proportionality coefficient A1 of the correlation line of Example 1 was 20.6 (μg / m) / (hour) ^0.5 . That is, the proportionality coefficient A1 of Example 1 was about 15 times larger than the proportionality coefficient A1 of Comparative Example 1. From this, it was found that when the plating layers 12 and 13 contain magnesium, the element amounts of magnesium and vanadium increase compared to the case where the plating layers 12 and 13 do not contain magnesium.

From FIG. 6, it was found that the elution amount of vanadium per end face length from the end face of the sample into the ion exchange water increased with the elapsed time and was proportional to the square root of the elapsed time. Further, regarding the amount of vanadium per length of the end face of the sample, the proportionality coefficient A2 of the correlation line of Comparative Example 1 shown in FIG. 6 was 0.3 (μg / m) / (hour) ^0.5. On the other hand, the proportionality coefficient A2 of the correlation line of Example 1 was 2.0 (μg / m) / (hour) ^0.5 . That is, the proportionality coefficient A2 of Example 1 was about 7 times larger than the proportionality coefficient A2 of Comparative Example 1. From this, it was found that when the plating layers 12 and 13 contain magnesium, the amount of vanadium element is increased as compared with the case where the plating layers 12 and 13 do not contain magnesium.

  In addition, the SGL vanadium steel sheet of Example 1 in which the plating layers 12 and 13 contain magnesium and the primer layers 30 and 60 contain calcium vanadate and magnesium phosphate, the plating layers 12 and 13 do not contain magnesium, Compared with the GL vanadium steel sheet of Comparative Example 1 in which the primer layers 30 and 60 contain calcium vanadate and magnesium phosphate, the elution amount of vanadium per length of the end face of the sample was large. Therefore, it is considered that magnesium in the plating layers 12 and 13 works effectively for elution of vanadium in the primer layers 30 and 60.

Claims (8)

A plated steel sheet comprising a steel sheet and a plating layer covering the steel sheet;
A primer layer covering the plating layer;
A top layer covering the primer layer,
The plating layer contains magnesium,
The primer layer is a coated plated steel sheet containing a vanadium compound.   The said plating layer is the coating plating steel plate of Claim 1 containing aluminum and zinc.   The coated steel sheet according to claim 1 or 2, wherein a content of the magnesium with respect to the plating layer is in a range of 0.5 to 10 mass%. Coated plated steel sheet according to any one of claims 1 to 3 duplex adhesion amount is in the range of 50 to 300 g / m ² of the plating layer. The total elution amount of magnesium and vanadium per end face length from the end face of the coated steel sheet into the ion-exchanged water increases in proportion to the square root of the elapsed time, and the proportionality coefficient A1 is 1.35 ( The coated galvanized steel sheet according to any one of claims 1 to 4, wherein μg / m) / (hour) is greater than ^0.5 . The total elution amount of vanadium per length of the end face from the end face of the coated plated steel sheet into the ion-exchanged water increases in proportion to the square root of the elapsed time, and the proportionality coefficient A2 is 0.3 (μg / m) / (hours) The coated plated steel sheet according to any one of claims 1 to 5, which is larger than ^0.5 .   The coated vane steel sheet according to any one of claims 1 to 6, wherein the vanadium compound contains at least one compound selected from the group consisting of calcium vanadate, vanadium pentoxide, and ammonium metavanadate.   The primer layer includes a urea resin made of a reaction product of polyamine and polyisocyanate, a polyester resin crosslinked with a melamine resin, a polyester resin crosslinked with an isocyanate resin, a polyester crosslinked with a melamine resin and an isocyanate resin. The coated plated steel sheet according to any one of claims 1 to 7, comprising at least one resin selected from the group consisting of a resin, an epoxy resin, and an aqueous polymer.

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