JPWO2015075792A1 - Galvanized steel sheet excellent in blackening resistance and corrosion resistance and method for producing the same - Google Patents

Abstract

The present invention relates to a galvanized steel sheet capable of achieving both corrosion resistance and blackening resistance and a method for producing the same. The galvanized steel sheet of the present invention includes a steel sheet, a Zn-Al-Mg-Si alloy plating layer formed on the surface of the steel sheet, and a coating film containing Al formed on the plating layer. Al in the coating containing Al is separated from the plating layer by the presence of an insulating material, and the coating containing Al is observed from a direction perpendicular to the surface, and Al in the coating of the plating layer is observed. The coverage ratio by Al, which is defined as the ratio of the area of the portion concealed by the above to the total area of the observation field, is 75 to 100%. In one embodiment, the galvanized steel sheet of the present invention contains scaly Al particles and an insulating material in a solvent, and has shear rates of 1 s-1 and 10000 s-1 measured by a rotational viscometer at 25 ° C. In an induction heating furnace, a steel sheet coated with a coating having a viscosity adjusted to 150 to 1500 mPa · s and 50 to 150 mPa · s on the plating layer is heated to a final plate temperature of 180 to 230 ° C at a heating rate of 5 to 70 ° C / s. Obtained by heating.

Description

  The present invention relates to a galvanized steel sheet excellent in blackening resistance and corrosion resistance, and relates to a galvanized steel sheet applicable to home appliances, building materials, civil engineering, machinery, automobiles, furniture, containers, and the like. It also relates to the manufacturing method.

  Galvanized steel sheets are widely used as plated steel sheets having excellent corrosion resistance for home appliances, building materials, automobiles, and the like. Further, a Zn—Al—Mg—Si plated steel sheet described in Patent Document 1 is known as a technique for further improving the corrosion resistance of a galvanized steel sheet.

  On the other hand, these galvanized steel sheets are liable to generate white rust due to zinc corrosion, and it is a known technique to perform chemical conversion treatment such as chromate treatment in order to suppress this. The galvanized steel sheet subjected to the chromate treatment is less prone to white rust, but on the other hand, there is a problem that the plating surface turns grayish black when exposed to the atmosphere for a long time. Hereinafter, this discoloration phenomenon may be referred to as black discoloration. In particular, blackening occurs remarkably in Zn-Al alloy-plated steel sheets and Zn-Al-Mg alloy-plated steel sheets to which Al or Mg is added during galvanization.

Techniques described in Patent Documents 2 to 6 are disclosed as techniques for improving the blackening resistance of a galvanized steel sheet. Patent Document 2 discloses a technique for treating a galvanized steel sheet with a solution in which Ni ions or Co ions are mixed. Patent Document 3 discloses a technique for treating a galvanized steel sheet with a chromate treatment liquid having a specific composition containing nitrate ions. In Patent Document 4, 1 to 100 g / l of molybdenum oxyacid ions in terms of Mo, 0.2 to 2 phosphate ions in terms of P / Mo equivalent mass ratio, and 0.03 to 0.00 in terms of Co / Mo equivalent mass ratio. 3 discloses a technique in which an aqueous treatment liquid containing 3 cobalt ions and 1 to 300 g / l oxycarboxylic acid is applied to a zinc-based plated steel sheet at an Mo equivalent deposition amount of 10 to 120 mg / m ² . Furthermore, Patent Document 5 has a zinc phosphate treatment layer on a galvanization layer, and further has an Ni adhesion portion of 0.1 to 500 mg / m ² between the galvanization layer and the phosphate treatment layer. A technique of an intervening plating layer structure is disclosed. In Patent Document 6, a phosphate coating is formed on the surface of a molten Zn—Al—Mg alloy-plated steel sheet, and a chemical conversion coating is formed by crosslinking a specific aqueous fluorine-containing resin on the phosphate coating. It is disclosed that the blackening resistance of a hot-dip Zn—Al—Mg alloy-plated steel sheet can be improved.

  As described later, in the present invention, a coating film containing scaly Al particles is used. In Patent Document 7, in a pre-coated metal plate provided with a metallic appearance by a coating film containing an aluminum pigment, the surface of the aluminum pigment is coated in order to prevent blackening of the pigment due to contact between the aluminum pigment and the base metal plate. It is disclosed.

  On the other hand, although not related to blackening resistance, Patent Document 8 discloses a coating composition containing thin-film scaly aluminum, which is used for coating a steel sheet or the like having a coating-like appearance with excellent design. Things are listed. Patent Document 9 discloses a technique for preventing design deterioration such as discoloration of a coating film by inhibiting aluminum from eluting from the coating film in a strongly alkaline environment in a coated steel sheet in which aluminum particles are dispersed in the coating film. Is described.

Japanese Patent No. 3179446 JP 59-177381 A JP-A-10-18048 JP 2001-158972 A JP 2006-225737 A JP 2012-077332 A International Publication No. 2013/065354 Pamphlet JP 2000-136329 A JP 2011-194472 A

  As described above, in recent years, Zn-Al-Mg alloy-plated steel sheets have been developed as galvanized steel sheets with excellent corrosion resistance. However, these steel sheets in which Al and Mg are added to the galvanizing are called blackening on the other hand. I have a big challenge. In particular, Zn-Al-Mg-Si alloy-plated steel sheets with excellent corrosion resistance are excellent in long-term corrosion resistance and are not prone to white rust. Therefore, there is a need to apply them to parts that can be seen from the outside, such as outer panels, in building material structures and home appliances. Is growing. Particularly in recent years, the design orientation of building structures and home appliances has increased, and the need to suppress blackening of Zn-Al-Mg-Si alloy-plated steel sheets has further increased.

  With the techniques described in Patent Documents 2 to 6, the blackening resistance of Zn—Al—Mg-based alloy plated steel sheets including Zn—Al—Mg—Si alloy plated steel sheets can be improved to some extent. However, these technologies are galvanized during the period in which they are stored or transported in warehouses from the time they are manufactured by steel plate manufacturers until they are used by users such as building material processing manufacturers, home appliance manufacturers, and automobile manufacturers. It is only a technology for suppressing blackening of steel sheets. Therefore, even if these blackening resistance technologies are applied, galvanized steel sheets are incorporated into building material structures, home appliances, automobile parts, etc., and when these products and parts are actually used for a long time, they will turn black. There was a problem that would occur.

  On the other hand, the technique described in Patent Document 7 prevents blackening of the aluminum pigment contained in the coating film in the precoated steel sheet, and prevents blackening of the base galvanized surface of the precoated steel sheet that has been exposed to the atmosphere for a long time. It does not prevent.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a Zn-Al-Mg-Si alloy-plated steel sheet capable of achieving both corrosion resistance and long-term blackening resistance.

  As a result of intensive studies to solve the above problems, the inventors have made a film containing aluminum (Al) on the plating layer on the surface of the Zn-Al-Mg-Si alloy-plated steel sheet, and the Al in the film is a plating layer. It is defined as the ratio of the area of the plating layer part covered with Al in the film to the total area of the observation field when the film containing Al is observed from the direction perpendicular to the surface. It was found that corrosion resistance and long-term blackening resistance can be ensured by making the coverage with Al to be 75 to 100%.

The present invention has been completed based on such knowledge, and the gist of the present invention is as follows.
[1] a steel plate;
Zn-Al-Mg-Si alloy plating layer formed on the surface of the steel plate;
A film containing Al formed on the plating layer;
Including
Al in the film containing Al is separated from the plating layer by the presence of an insulating material;
And by observing the film containing Al from a direction perpendicular to the surface, the area of the portion of the plating layer concealed by Al in the film is defined as a ratio to the total area of the observation field. The coverage is 75-100%,
A galvanized steel sheet with excellent blackening resistance and corrosion resistance.
[2] The film containing Al is made of an insulating material containing scaly Al particles, and the Al particles are within a range of at least 0.5 μm from the interface between the film containing Al and the plating layer. The galvanized steel sheet excellent in blackening resistance and corrosion resistance as described in [1], which does not exist.
[3] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [2], wherein the Al particles have an average particle diameter of 5 to 30 μm and an aspect ratio of 20 or more.
[4] The film according to [1], wherein the film containing Al is composed of at least two layers of an intermediate layer formed of an insulating material and an Al metal layer in order from the plating layer side. Galvanized steel sheet with excellent blackening resistance and corrosion resistance.
[5] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [4], wherein the Al metal layer is composed of an aggregate of scaly Al particles.
[6] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [1], wherein the insulating substance is a resin.
[7] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [6], wherein the resin is a polyester resin crosslinked with a melamine compound.
[8] The galvanized steel sheet having excellent blackening resistance and corrosion resistance according to [7], wherein the polyester resin has a glass transition temperature Tg of −20 to 70 ° C. and a number average molecular weight of 15,000 to 25000. .
[9] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [1], wherein the thickness of the film containing Al is 2 to 10 μm.
[10] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [1], further comprising a clear resin film on the Al-containing film.
[11] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [10], wherein the clear resin film has a thickness of 0.2 to 20 μm.
[12] The galvanized layer contains 0.01 to 60% by mass of Al, 0.001 to 10% by mass of Mg, and 0.001 to 2% by mass of Si, according to [1]. Galvanized steel sheet with excellent blackening resistance and corrosion resistance.
[13] A method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance as described in [2], comprising flaky Al particles and an insulating material in a solvent, measured at 25 ° C. with a rotational viscometer viscosity in terms of shear rate 1s ^-1 is 150~1500mPa · s, and the steel sheet paint viscosity at a shear rate of 10000s ^-1 as measured by a rotational viscometer is 50~150mPa · s at 25 ° C. Then, the steel sheet is heated in an induction furnace to a final plate temperature of 180 to 230 ° C. at a heating rate of 5 to 70 ° C./s to form a film containing Al. A method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance.
[14] The paint is prepared by mixing scale-like Al particles in a solvent together with 100 parts by mass of a water-based emulsion type polyester resin solid content and 10 to 30 parts by mass of a melamine compound solid content as a crosslinking agent. The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [13].
[15] The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [13], wherein the viscosity of the paint is adjusted using a viscosity modifier.
[16] As the viscosity modifier, a surfactant mainly composed of 0.2 to 10 parts by mass of a urethane-modified polyether with respect to 100 parts by mass of the aqueous emulsion type polyester resin dispersion is used. [15] The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [15].
[17] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [13], wherein Al particles having an average particle diameter of 5 to 30 μm and an aspect ratio of 20 or more are used as the Al particles. Production method.
[18] A method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [4],
(A) An intermediate layer of an insulating material is formed on the galvanized layer on the surface of the steel plate, and then an Al metal layer is formed thereon by a plating method, or
(B) Applying a liquid material for forming an intermediate layer of an insulating material on the galvanized layer on the surface of the steel plate, spraying scaly Al particles on the liquid material, and then solidifying the liquid material Forming an intermediate layer of insulating material and an Al metal layer thereon;
A method for producing a galvanized steel sheet having excellent blackening resistance and corrosion resistance.
[19] The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [18], wherein the plating method is a vacuum deposition plating method.

  According to the present invention, there is provided a new Zn-Al-Mg-Si galvanized steel sheet that has long-term blackening resistance in addition to the excellent corrosion resistance inherent in the Zn-Al-Mg-Si galvanized steel sheet. Can be provided.

Hereinafter, embodiments of the present invention will be described.
The galvanized steel sheet of the present invention includes a steel sheet, a Zn-Al-Mg-Si alloy plating layer formed on the surface of the steel sheet, and a coating film containing Al formed on the Zn-Al-Mg-Si alloy plating layer. Are configured.

  It does not specifically limit as a steel plate, General steel plates, such as a hot rolled steel plate and a cold rolled steel plate, can be used. The steel type is not particularly limited, and for example, Al killed steel, ultra-low carbon steel added with Ti, Nb, etc., and high-tensile steel added with elements such as P, Si, Mn, etc. can be used. is there.

  The Zn—Al—Mg—Si alloy plating layer is a plating layer formed on the surface of the steel plate. This plating layer contains 0.01 to 60% by mass of Al, 0.001 to 10% by mass of Mg and 0.001 to 2% by mass of Si, with the balance being Zn and inevitable impurities. It is.

  If the Al content of the Zn-Al-Mg-Si alloy plating layer is less than 0.01%, the effect of improving the corrosion resistance of the plated steel sheet due to the addition of Al is not exhibited, and if it exceeds 60%, the effect of improving the corrosion resistance is saturated. Resulting in. A preferable Al content is 1 to 60% by mass, and more preferably 5 to 60% by mass.

  If the Mg content of the Zn-Al-Mg-Si alloy plating layer is less than 0.001%, the effect of improving the corrosion resistance of the plated steel sheet due to the addition of Mg will not be exhibited, and if it exceeds 10%, Mg will dissolve in the plating bath. It floats as an oxide without being broken (generally called dross), and when galvanized in this plating bath, the oxide adheres to the plating surface layer and causes poor appearance, or a portion that is not plated (generally called non-plating) May occur. A preferable Mg content is 1 to 5% by mass, and more preferably 1 to 4% by mass.

  If the Si content of the Zn—Al—Mg—Si alloy plating layer is less than 0.001%, the corrosion resistance improving effect is hardly exhibited. Further, if the Si content is less than 0.001%, an oxide containing Zn, Mg, or Al (generally called dross) is likely to be generated. On the other hand, if it exceeds 2%, Si does not melt in the plating bath and floats as an oxide (generally referred to as dross), and when galvanized in this plating bath, the oxide adheres to the plating surface layer and causes an appearance defect. There is a possibility that a portion that is not plated (generally referred to as non-plating) may occur. In some cases, dross may be slightly generated even when the Si content is about 1%. Preferable Si content is 0.01-1 mass%, More preferably, it is 0.01-0.5 mass%.

The adhesion amount of the Zn—Al—Mg—Si alloy plating layer on one side of the steel sheet is desirably 10 g / m ² or more from the viewpoint of corrosion resistance, and desirably 350 g / m ² or less from the viewpoint of workability.

  The galvanized steel sheet of the present invention excellent in blackening resistance and corrosion resistance has a coating containing Al on a Zn-Al-Mg-Si alloy plating layer. This film is important for improving blackening resistance.

  It is known that blackening is likely to occur in a plated steel sheet having a Zn—Al—Mg—Si alloy plating layer to which Al and Mg are added. The main cause of blackening is oxidation of the plating layer surface. Covering the Zn-Al-Mg-Si alloy plating layer with a film mainly composed of a film-forming material such as a resin is not sufficient to prevent the permeation of oxygen in the air and is effective in preventing blackening. Absent. In the present invention, the blackening can be effectively prevented by making Al present in the coating covering the plating layer. Since Al forms a stable Al oxide on the surface layer in the air atmosphere, it is a very stable metal. Therefore, by providing an Al-containing film on the surface of the Zn-Al-Mg-Si alloy-plated steel sheet, the Zn-Al-Mg-Si alloy-plated layer is unlikely to discolor over a long period of time. Moreover, the fact that Al in the film blocks the path through which oxygen passes through the film greatly contributes to prevention of blackening of the plating layer.

  From the viewpoint of blocking the oxygen transmission path, it is important that Al in the coating covering the plating layer hides the plating layer surface as much as possible. Therefore, in the present invention, the film containing Al is observed from a direction perpendicular to the surface thereof, and is defined as the ratio of the area of the portion of the plating layer concealed by Al in the film to the total area of the observation field. The coverage with Al is required to be 75 to 100%. The higher the coverage, the better. Therefore, for example, 85% or more, or 95% or more is more preferable.

  Since the surface oxide of Al is a noble substance than Zn contained in the plated layer of the Zn—Al—Mg—Si alloy-plated steel sheet, it is liable to cause different metal contact corrosion when they are in contact. Therefore, in the present invention, in order to prevent contact between Al in the coating and the surface of the plating layer, it is also necessary that Al in the coating and the plating layer be separated by an insulating material. The distance between the Al and the plating layer in the film may be 0.5 μm or more, and more preferably 1.0 μm or more. If the distance is less than 0.5 μm, the insulating effect cannot be obtained. When the interval exceeds 3 μm, not only the insulating effect is saturated, but it is difficult to form such an interval. An interval of about 0.5 to 1.5 μm is most suitable.

  As Al in the film covering the plating layer, scaly Al particles can be used. The scaly Al particles are advantageous because a coating containing Al can be easily formed by applying a coating in which the particles are dispersed on the plating layer. As the scaly Al particles, those having an average particle diameter of 5 to 30 μm and an aspect ratio (average particle diameter / thickness ratio) of 20 or more can be used. If the average particle diameter is less than 5 μm, the coverage with Al tends to be less than 75%, and the concealing effect of the plating layer is weakened. If it exceeds 30 μm, since the Al particles are too large, a part of the Al particles comes out of the coating film after coating, which may result in an uneven appearance and poor appearance. If the aspect ratio is less than 20, the coverage with Al tends to be less than 75%. The upper limit of the aspect ratio is not particularly defined, but is preferably less than 300. Al particles having an aspect ratio exceeding 300 are difficult to produce and difficult to obtain.

  The average particle diameter is determined by measuring the major axis and the minor axis for one of the arbitrary aluminum particles, and calculating the average of the average particle diameter of one Al particle, that is, [average particle diameter of one Al particle] = [( (Major axis + minor axis)] / 2, and the average measured for any 100 Al particles is the average particle size. The average particle diameter of each Al particle can be measured by enlarging with an optical microscope or an electron microscope. Moreover, the average particle diameter can also be calculated | required by calculating | requiring cumulative weight distribution for the Al particle to be used using the laser diffraction type particle size distribution measuring apparatus based on the principle of a laser diffraction method, a sieve, etc. Based on the cumulative weight distribution, the cumulative weight 50% particle diameter (generally called the average particle diameter D50) may be calculated and obtained. In the present invention, either 100 average particle diameters measured with a microscope or 50% cumulative weight particle diameter can be used as the average particle diameter.

  In addition, the average thickness of the Al particles necessary for determining the aspect ratio is determined by observing an arbitrary cross section of the arbitrary Al particles with an optical microscope or an electron microscope (in general, the direction perpendicular to the measurement plane of the major axis and minor axis described above) The average thickness of 100 arbitrary Al particles can be used as the average Al particle thickness defined in the present invention.

  Thus, the aspect ratio is defined by [aspect ratio] = [average particle diameter of Al particles measured above] / [average thickness of Al particles measured above].

  The Al-containing film on the plating layer can be formed by, for example, a paint containing scaly Al particles. In the film thus formed, the Al particles are oriented in a direction parallel or substantially parallel to the lower plating layer, It is dispersed in a continuous phase formed by a film forming component as an insulating material and collected on the upper part of the film. Only the continuous phase exists at the lower part of the film, and the Al particles are isolated from the surface of the plating layer with the above-mentioned interval.

  The film containing Al may be composed of at least two layers of an intermediate layer formed of an insulating material and an Al metal layer in order from the plating layer side.

  In this case, the Al metal layer can be formed as an aggregate of scaly Al particles on an intermediate layer formed using an insulating material on the plating layer, or formed as a continuous Al layer by plating. May be. In the case of an aggregate of scaly Al particles, the above scaly Al particles can be used. The aggregate of the scale-like Al particles is present in the coating formed by the coating containing the scale-like Al particles described above, in which the particles are dispersed in the continuous phase of the resin (the resin exists between adjacent particles). In contrast to the higher particle concentration coating, there is a possibility of particle contact, but in the lower particle concentration particle contact is negligible (if any). The intermediate layer resin is formed using an adhesive or a binder, and adjacent particles are fixed by a resin that fills a gap between them while contacting each other. Therefore, in the present invention, such an aggregate of scaly Al particles is included in the “Al metal layer”.

  When the film containing Al is composed of at least two layers of an insulating material intermediate layer and an Al metal layer, the thickness of the intermediate layer may be 0.5 μm or more, and the thickness of the Al metal layer may be 1.5 to 9.5 μm. If the thickness of the intermediate layer is less than 0.5 μm, the insulating effect cannot be obtained and the corrosion resistance is poor. The thickness of the intermediate layer is more preferably 0.5 to 3 μm, still more preferably 0.5 to 1.5 μm. If it exceeds 3 μm, the insulating effect is saturated, so there is no need to apply more. If the thickness of the Al metal layer is less than 1.5 μm, it is insufficient for concealing the lower plating layer, and if it exceeds 9.5 μm, the workability may be inferior. The thickness of the Al metal layer is preferably 2.5 to 9.5 μm, and more preferably 3.5 to 9.5 μm.

  The Al material in the coating containing Al may be made of pure Al or an Al alloy containing Al as a main component. As the Al alloy, generally known Al alloys can be used.

  A resin is suitable as the insulating substance in the film containing Al. The insulating material plays a role of preventing corrosion of the plating layer due to different metal contact between Al in the coating and the plating layer in order to improve blackening resistance, and preferably has an insulation resistance of 10Ω or more. .

  When the film containing Al is formed of a resin in which scaly Al particles are dispersed, it is preferably a polyester resin crosslinked with a melamine compound. This polyester resin preferably has a glass transition temperature Tg of -20 to 70 ° C and a number average molecular weight of 15000 to 25000. When the glass transition temperature Tg is less than −20 ° C., the adhesion of the processed part of the coating layer containing Al may be lowered. If it exceeds 70 ° C., the workability of the coating layer containing Al is lowered, and there is a risk that the coating layer may crack during processing. More preferable Tg is 0 to 50 ° C. The glass transition temperature Tg can be measured with a differential scanning calorimeter called DSC or a thermomechanical analyzer called TMA. When the number average molecular weight of the polyester resin is less than 15000, the processability of the film is lowered, and there is a risk that the film may crack during processing. If it exceeds 25000, the viscosity is too high when it is used as a coating liquid, so that there may be defects such as streak-like coating defects generally called living at the time of coating, and Al particles are difficult to uniformly disperse and the coverage is reduced. There is. The number average molecular weight can be measured by a generally known method such as a gel permeation chromatography method called GPC.

  The resin of the intermediate layer when the coating containing Al is composed of at least two layers of the intermediate layer and the Al metal layer thereon is not particularly limited, and generally known resins can be used. For example, a polyester resin, an epoxy resin, a urethane resin, an acrylic resin, a melamine resin, or the like can be used. However, since there are many cases in which galvanized steel sheets are molded and used, polyester resins and urethane resins excellent in workability are more suitable. Epoxy resins are also preferred because of their excellent adhesion to metals. When the intermediate layer is formed by dissolving these resins in a solvent or by emulsifying and applying a coating solution dispersed in water or a solvent, the workability at the time of production is improved and it is more efficient. In addition, it is more preferable to add a curing agent such as melamine or isocyanate to these resins to obtain a thermosetting type because adhesion with an Al metal layer or a Zn—Al—Mg—Si alloy plating layer is increased. Since it is excellent in adhesiveness with the film layer containing Al, etc. that it is the same resin as the film layer containing Al, it is more suitable.

  In the case where the coating containing Al is composed of an intermediate layer and an Al metal layer thereon, other layers may be present. For example, when an Al metal layer is formed by a plating method, it is possible to provide a layer effective for promoting adhesion of plating to the intermediate layer between the intermediate layer and the Al metal layer.

  Additives such as pigments, aggregates, and rust preventives can be added to the resin constituting the coating film containing Al, if necessary. Incorporation of pigments and aggregates is more preferable because the strength of the film is increased and the adhesion with the Al and Zn—Al—Mg—Si alloy plating layer is increased. In addition, the addition of a rust preventive agent is more preferable because the corrosion resistance of the Zn—Al—Mg—Si alloy plating layer is improved. What is necessary is just to determine the addition amount of an additive suitably so that it may not become disadvantageous for the membrane | film | coat of this invention.

  The film thickness of the film containing Al is preferably in the range of 2 to 10 μm. If it is less than 2 μm, the plating layer may not be concealed and the coverage may be less than 75%. If it exceeds 10 μm, the workability may be inferior. The film thickness can be measured by observing the cross section with an electron microscope using an optical microscope.

  As already explained, on the side of the coating containing Al that is in contact with the plating layer, the portion where the Al particles dispersed in the continuous phase of the resin are not present (the portion containing only the resin), or independently from the Al metal layer. An intermediate layer made of resin is located. And those thickness is as having demonstrated previously.

  In the galvanized steel sheet of the present invention, a clear resin film can be provided on a film containing Al. The clear resin film can improve the fingerprint resistance particularly when the film containing Al has an Al metal layer. The clear resin film also has an effect of smoothing the surface of the plated steel sheet by filling the unevenness of the film surface containing Al.

  The type of clear resin is not particularly limited, and generally known resins such as polyester resins, epoxy resins, urethane resins, acrylic resins, melamine resins, and the like can be used. However, since there are many cases in which galvanized steel sheets are molded and used, polyester resins and urethane resins excellent in workability are more suitable. Epoxy resins are also preferable because they have excellent adhesion to metal (here, Al exposed on the surface of a film containing Al). It is more preferable to add a curing agent such as melamine or isocyanate to the clear resin to obtain a thermosetting type because the hardness of the film is improved and the scratch resistance is excellent.

  A rust inhibitor may be added to the clear resin as necessary. Addition of a rust inhibitor is preferable because the corrosion resistance of the film containing Al is improved. Furthermore, the addition of pigments and aggregates is more preferable because the strength of the clear resin film increases and the adhesion with the film containing Al increases.

  The thickness of the clear resin film layer is preferably in the range of 0.2 to 20 μm. If the thickness is less than 0.2 μm, the effect on fingerprint resistance may be reduced. If the thickness exceeds 20 μm, it is generally called boiling when applied using a solvent-soluble or emulsion-dispersed resin coating solution and then dried and cured. Film defects may occur.

  When Al particles are used in a film containing Al, depending on the production method, the Al particles may be slightly diffused and dispersed in the upper clear resin film. In this case, the part where Al particles are diffused is regarded as a film containing Al, and the thickness up to that part (distance from the surface of the plating layer) can be the film thickness of the film containing Al. Accordingly, in this case, the film thickness of the clear resin film means the thickness of a portion where no Al particles are present (portion containing only resin).

  In the present invention, the thickness of the plating layer, the coating containing Al, the intermediate layer of the insulating resin, the Al metal layer and the clear resin coating, the distance between the Al and the plating layer in the coating, etc. It can be determined by observing a cross section in the thickness direction that is exposed by embedding and polishing with an electron microscope or the like.

  In the galvanized steel sheet of the present invention, a known chemical conversion treatment may be applied to the surface of the Zn—Al—Mg—Si alloy plating layer. Examples of applicable chemical conversion treatments include chromate treatment, phosphoric acid treatment, silica treatment, Mo treatment, Co treatment, Ni treatment, and Zr treatment. In an embodiment in which an Al metal layer is located on the surface of a film containing Al and a clear resin film is further provided, the above-described chemical conversion treatment can be performed on the Al metal layer.

  Next, the manufacturing method of the galvanized steel sheet of this invention is demonstrated.

Of the galvanized steel sheet of the present invention, the coating containing Al is composed of an insulating material containing scaly Al particles, and the Al particles are within a range of at least 0.5 μm from the interface between the coating containing Al and the plating layer. The non-existing galvanized steel sheet contains scaly Al particles and an insulating substance in a solvent, and has a viscosity of 150 to 1500 mPa · s under the condition of a shear rate of 1 s ⁻¹ measured by a rotational viscometer at 25 ° C., and A paint having a viscosity of 50 to 150 mPa · s at a shear rate of 10000 s ⁻¹ measured by a rotational viscometer at 25 ° C. is applied onto the galvanized layer on the surface of the steel plate, and then the steel plate is heated at a heating rate of 5 to 70 ° C. / It can manufacture by heating in an induction heating furnace to the ultimate plate temperature of 180-230 degreeC by s, and forming the said film | membrane containing Al.

The inventors prepare a solution (hereinafter also referred to as “coating liquid” or “paint”) in which scaly Al particles are dispersed in a resin solution that is an insulating substance, and the viscosity is set to a specific condition. When adjusted, the viscosity is controlled in the drying and baking process of the coating liquid applied to the plated steel sheet of the base material, and the scale-like Al particles are lifted by the convection of the coating liquid, and the lower layer does not contain Al particles. I found that the part was expressed. That is, the inventors measured the viscosity measured by a rotational viscometer at 25 ° C. of a coating liquid containing scaly Al particles and a resin that is an insulating substance or an emulsified resin in a solvent under conditions of a shear rate of 1 s ⁻¹ 150 to 1500 mPa · s at a shear rate of 10000 s ⁻¹ and adjusted to 50 to 150 mPa · s under the conditions of a shear rate of 10000 s ⁻¹ , and the coating solution is directly applied onto the galvanized layer at a heating rate of 5 to 70 ° C./s. When a film is formed by heating in an induction heating furnace to an ultimate plate temperature of 180 to 230 ° C., the Al particles float on the upper layer of the film in the dry baking process after the start of heating, and the film is finally cured in that state. The present inventors have found that a film having a unique structure is formed in which Al particles are not present within the range of at least 0.5 μm from the interface between the film and the plating layer, and are present only in the upper layer.

  In this case, a water-based emulsion type polyester resin can be suitably used as the insulating substance resin. Furthermore, the adhesiveness with a Zn-Al-Mg-Si alloy plating layer can be improved by using a melamine compound as a crosslinking agent and making it a thermosetting resin. As the water-based emulsion-type polyester resin, for example, Bhironal (registered trademark) series manufactured by Toyobo Co., Ltd. can be used. Examples of the melamine compound as a crosslinking agent include CYMEL (trademark) series manufactured by CYTEC. In general, 10 to 30 parts by mass of a melamine cross-linking agent in solid content can be used with respect to 100 parts by mass of solid content of water-based emulsion type polyester resin. The amount of the melamine crosslinking agent used is more preferably 10 to 20 parts by mass with respect to 100 parts by mass of the aqueous emulsion type polyester resin solid content.

  The coating material can be prepared by adding a water-based emulsion type polyester resin, a melamine cross-linking agent, and scaly Al particles (as described above) to an aqueous solvent such as water or alcohol and stirring. . The blending ratio of the water-based emulsion type polyester resin and the melamine crosslinking agent is as described above. What is necessary is just to determine the compounding quantity of scale-like Al particle | grains according to the characteristic of the particle | grains to be used, and the film thickness of the membrane | film | coat to form. In particular, when the film thickness is increased, the blending amount of Al particles is relatively increased (the thickness of the portion where the Al particles are present is relatively larger than the interval between Al and the plating layer in the film). On the other hand, the distance between the Al in the film and the plating layer varies depending on the viscosity condition of the paint and the dry baking condition. Therefore, the blending amount of the scaly Al particles in the paint may be determined by experiment in consideration of these requirements. However, the paint prepared in this way usually does not satisfy the above-mentioned viscosity condition. In order to satisfy the above-mentioned conditions for the viscosity of the paint, a viscosity modifier can be used.

  The phenomenon that a liquid such as a coating liquid has a high viscosity in a low shear rate region and a low viscosity in a high shear rate region is generally called a shear thinning effect. In order to impart a shear thinning effect to a liquid, it is common to use a concentrated dispersion of a liquid to which high-concentration granular fine particles are added. By using a thick dispersion system, it is said that the interparticle distance between the fine particles added to the coating liquid is shortened, the attractive force between the particles is increased, and the shearing effect is exhibited. However, even when scaly metal particles having a relatively high specific gravity are added at a high concentration as in the present invention, the distance between particles is unlikely to be shortened unlike granular fine particles. In addition, since the specific gravity is high, if the amount added is increased in order to further reduce the distance between the particles, the particles are likely to precipitate, which is inappropriate.

  There is known a technique for controlling the viscosity of the same liquid in different shear rate regions by adding a specific additive. In this case, an additive generally called a rheology control agent is used. When such a rheology control agent is added to the coating solution, the rheology control agent slightly reacts with the resin in the coating solution to form a network phase in the coating solution. However, if a general rheology control agent is added to the coating liquid used in the present invention, the required coating liquid viscosity condition described above cannot be satisfied.

  In the present invention, a specific viscosity adjusting agent can be used to make the viscosity of the coating liquid satisfy the above-described conditions. Unlike general rheology control agents, the viscosity modifier used in the present invention does not react with the resin in the coating liquid, and its molecular end chain is bonded to the resin in the coating liquid with a weak binding force such as adsorption. Type of substance. One example thereof is a surfactant mainly composed of urethane-modified polyether. For example, “SN thickener 629N” manufactured by San Nopco can be used. The addition amount of the viscosity modifier in the present invention varies depending on the resin type and solvent type used in the coating liquid, and is appropriately selected as necessary. More specifically, in the present invention, it is necessary to form a coating containing Al so that Al particles do not exist within a range of at least 0.5 μm from the interface between the coating and the plating layer. The amount is determined to satisfy this requirement. In general, the viscosity modifier can be used in an amount of 0.2 to 10 parts by mass with respect to 100 parts by mass of the aqueous emulsion type polyester resin dispersion. If it is less than 0.2 parts by mass, it is difficult to obtain the necessary coating liquid viscosity conditions, and if it exceeds 10 parts by mass, the water-based emulsion type polyester resin may be gelled. A preferable addition amount of the viscosity modifier is 0.2 to 1.0 part by mass with respect to 100 parts by mass of the aqueous emulsion type polyester resin dispersion.

  The coating liquid whose viscosity is adjusted is directly applied on the galvanized layer, and heated to a final plate temperature of 180 to 230 ° C. at a heating rate of 5 to 70 ° C./s to complete the curing of the resin in the coating liquid to form a film. As a result, a film is formed in which Al particles are not present in the range of at least 0.5 μm from the interface between the film and the plating layer, and are present only in the upper layer part. Heating must be performed in an induction heating furnace. The reason for this is that the Al particles floating above the coating solution on the plating layer by Marangoni convection settles down to the surface of the plating layer, as described later, by heating from the base plate steel plate side by induction heating. This is because it is convenient to obtain a film with a structure in which the distribution of Al particles is concentrated on one side (the side far from the plating layer) by suppressing the flow of the solvent evaporating from the surface to the coating liquid surface side. is there. When the heating rate is less than 5 ° C./s, the Marangoni convection that occurs due to the slow heating rate is difficult to occur, or the convection rate is slow, so that the Al particles are difficult to float, and the Al particles are not at the interface between the coating and the plating layer. To 0.5 μm, Al particles may exist and corrosion resistance may be poor. Further, when the heating rate is higher than 70 ° C./s, the heating rate is too high, so that the coating is cured in a state where the coating is boiled in the solvent drying process, and the coating defect (generally, the trace of bubbles due to boiling remains in the film) There is a risk that this will occur). Moreover, since the heating time is short when the heating rate is high, the coating film surface layer tends to be slightly uncured, which causes the coating film to peel off. If the ultimate plate temperature is less than 180 ° C., the film may not be cured and the surface of the film may be undried, and if the surface of the coating film is uncured (undried), the coating film may be peeled off. When the ultimate plate temperature exceeds 230 ° C., the paint is cured in a state where the paint is boiled in the solvent drying process, and there is a risk that a coating defect (generally referred to as boiling) in which traces of bubbles due to boiling remain in the film may occur. . Furthermore, since the coating film is hardened by baking at a high temperature, it becomes hard, and the coating film is easily cracked or peeled off by processing. Since the galvanized steel sheet is generally used after being processed, a processed part where the coating is cracked or peeled off by processing is likely to be a source of corrosion.

  Although the detailed mechanism by which the above-described film having a specific structure is formed has not been elucidated, the inventors presume as follows. In general, the coating solution is applied to the surface of the plated layer of the base-plated steel sheet at room temperature or slightly higher than room temperature (for example, about 30 ° C or 40 ° C), and heating is started for dry baking. In this case, regions having different temperatures are generated, Marangoni convection is generated, and the coating liquid starts to flow. In the initial stage where the coating liquid is flowing, that is, under conditions where the shear rate is relatively high, the coating liquid viscosity is low, so that Al particles float on the upper part of the coating liquid on the plating layer, and the dry baking process proceeds. After the convection has subsided and the shear rate has slowed, the coating liquid viscosity increases and the Al particles do not settle, so a film containing no Al particles is formed in the lower layer.

  Thus, in the present invention, by using a coating liquid whose viscosity is adjusted so as to satisfy the above-mentioned specific conditions, the Al particles generated by Marangoni convection generated in the process of heating and drying and baking the coating liquid applied to the plating surface. The movement is controlled so that the Al particles are concentrated on the upper layer of the coating liquid in the initial stage of heating. By continuing the heating while maintaining this state, the solvent of the coating solution is volatilized and the resin is cured, and a film in which Al particles are not present within the range of at least 0.5 μm from the interface with the plating layer is formed.

  The film having a unique constitution of the present invention in which Al particles are not present within the range of at least 0.5 μm from the interface with the plating layer is brought about by heat treatment in a high temperature region where the ultimate plate temperature is 180 to 230 ° C. On the other hand, in the present invention, the coating liquid for forming such a film is required to use a liquid that satisfies the viscosity conditions defined by the measured values at 25 ° C. (different shear rates). It may seem strange. However, the inventors have used a paint that satisfies this viscosity condition and formed under the above-mentioned dry baking conditions, so that a film in which Al particles are not actually present in the range of at least 0.5 μm from the interface with the plating layer. It was found that it was obtained (see Examples).

According to the present invention, a galvanized steel sheet composed of at least two layers of an intermediate layer formed of an insulating material and an Al metal layer in order from the plating layer side, which contains Al,
(A) An intermediate layer of an insulating material is formed on the galvanized layer on the surface of the steel plate, and then an Al metal layer is formed thereon by a plating method, or
(B) Applying a liquid material for forming an intermediate layer of an insulating material on the galvanized layer on the surface of the steel plate, spraying scaly Al particles on the liquid material, and then solidifying the liquid material, Forming an intermediate layer of insulating material and an Al metal layer thereon;
Can be manufactured.

  In both cases according to (a) and (b), as the insulating material for the intermediate layer, generally known materials can be used. For example, polyester resin, epoxy resin, urethane resin, acrylic resin, melamine resin, etc. are used. be able to. Since there are many cases in which galvanized steel sheets are molded and used, polyester resins and urethane resins having excellent processability are more suitable. Epoxy resins are also preferred because of their excellent adhesion to metals. When the intermediate layer is formed by dissolving these resins in a solvent or by emulsifying and applying a coating solution dispersed in water or a solvent, the workability at the time of production is improved and it is more efficient. Further, when a curing agent such as melamine or isocyanate is added to these resins to form a thermosetting type, the adhesion with the Al metal layer or the Zn—Al—Mg—Si alloy plating layer is increased, which is more preferable.

  The insulation resin intermediate layer is made of a paint in which the insulation resin is dissolved in a solvent such as thinner, or an emulsion type paint dispersed in water, and after this is applied, it is dried and baked or at a temperature lower than the melting point of Zn. It can be easily formed on the Zn-Al-Mg-Si alloy plating layer by melting and coating the Zn-Al-Mg-Si alloy plating layer.

  When an Al metal layer is formed by the above method (a), a generally known plating method, for example, a vacuum deposition plating method, an electroplating method, an electroless plating method, is formed on an intermediate layer of a previously formed insulating resin. The Al metal layer can be formed using such as. Among these, it is preferable to use a vacuum evaporation plating method. The hot dip galvanizing method is not suitable because the plating layer melts because the melting temperature of Al is higher than the melting temperature of Zn, which is the main component of the Zn—Al—Mg—Si alloy plating.

  When the Al metal layer is formed by the method (b) above, a paint for forming an intermediate layer on the galvanized layer (same as described above for the method (a)) is applied. Then, the scaly Al particles are sprayed on the applied paint, and then the intermediate paint is solidified by heating to form an Al metal layer as an aggregate of scaly Al particles. Here, the Al particles can be fixed on the insulating film layer by using the resin of the intermediate layer as an adhesive or a binder.

  In any of the above methods (a) and (b), the ratio of the resin and the cross-linking agent, the heating conditions for dry baking of the paint, etc. are formed by a coating liquid in which Al particles are dispersed. This is the same as that described for the method.

  When a clear resin film is formed on a film containing Al, a general clear resin as described above is dissolved in a solvent such as thinner, or an emulsion type coating liquid in which water is dispersed contains Al. It can be formed by means such as drying and baking after coating on the film, or melting the clear resin at a temperature lower than the melting point of Zn and coating the melt on the film containing Al.

  In the present invention, the method for applying the paint when forming the Al-containing film and the clear resin film is not particularly limited, and a general method used for coating a steel sheet can be used. For example, a coating method using a roll coater or a curtain coater can be suitably used. A general method used for coating a steel sheet can also be used for drying and baking the paint.

  The invention will now be further described by way of examples. Needless to say, the present invention is not limited to the following examples.

(1. Formation of plating layer)
A cold-rolled steel sheet with a thickness of 1 mm is immersed in a 450 ° C. Zn-Al-Mg-Si plating bath with various metals added for 3 seconds to perform hot dipping, and the amount of plating applied is 90 g / m ² on one side by N ₂ wiping. The Zn—Al—Mg—Si plating layer was formed on the steel sheet.

(2. Formation of coating containing Al particles)
Al powder is dispersed in a mixed solution of water emulsion type polymer polyester and melamine resin, and an additive “SN thickener 629N” containing pure water and urethane-modified polyether manufactured by San Nopco is added to the obtained dispersion as appropriate. Thus, a coating liquid was prepared by adjusting the viscosity at 30 ° C. at a shear rate of 1 S ⁻¹ (low shear viscosity) and the viscosity at a shear breaking rate of 10000 S ⁻¹ (high shear viscosity). Water-emulsion-type high molecular polyesters include Vylonal (registered trademark) MD-1480 (number average molecular weight 15000, Tg 20 ° C.), Vylonal (registered trademark) MD-1220 (number average molecular weight 15000, Tg 67 ° C.), manufactured by Toyobo Co., Ltd. (Registered trademark) MD-1100 (number average molecular weight 20000, Tg 40 ° C.), Vylonal® (registered trademark) MD-1985 (number average molecular weight 25000, Tg-20 ° C.), Vylonal® MD-1335 (number average molecular weight 8000) , Tg 4 ° C.), Vironal (registered trademark) MD-1500 (number average molecular weight 8000, Tg 77 ° C.). Cymel (registered trademark) 303 manufactured by Mitsui Cytec was used as the melamine resin. Al particles include “Sap 561PS” (average particle size 16 μm, aspect ratio 20 or more) manufactured by Showa Aluminum Powder, “Sap 2173SW” (average particle size 6 μm, aspect ratio 20 or more) manufactured by Showa Aluminum Powder, Showa Aluminum “Sap 720N” (average particle size 30 μm, aspect ratio 20 or more) manufactured by Powder Co., Ltd., and “Aluminum powder” manufactured by Kanto Chemical Co., Ltd., with the same particle size using different mesh screens, and only fine particles taken out ( An average particle size of 20 μm and an aspect ratio of less than 20) were used. The polyester resin and the melamine resin were blended at a polyester resin solid content: melamine resin solid content mass ratio = 100: 20, and Al particles were added so that the polyester resin: Al particle mass ratio was 100: 15. The coating liquid is applied onto the plating layer of the steel sheet with a curtain coater, heated in an induction heating furnace at a heating rate of 50 ° C./s until reaching a predetermined plate temperature, cured with resin, then cooled with water, and contains Al. A film was formed. Then, the total film thickness of the film, the thickness of the part in which no Al particles existed in the film (part of resin only), and the Al coverage were measured. The film thickness was measured by observing an arbitrary vertical section exposed by embedding a galvanized steel sheet in a resin and polishing it at a magnification of 500 using a traveling electron microscope (SEM). As sought. The Al coverage was determined as an area ratio in which Al in the entire visual field was detected when EPMA analysis was performed on an arbitrary plane of the coating and element mapping was performed on Al with a 100-fold visual field. Hereinafter, this method is referred to as “particle dispersion method”.
Moreover, in the particle dispersion method, samples in which the addition amount of Al particles and the addition amount of melamine resin were changed as necessary were also prepared.

(3. Formation of a film including an Al metal layer by plating)
Byron (registered trademark) 29CS, a cyclohexanone / solvesso mixed organic solvent-soluble amorphous polyester resin manufactured by Toyobo Co., Ltd., and Byronal (registered trademark) MD-, a water-dispersed polymer polyester manufactured by Toyobo Co., Ltd. 1220 were prepared as resin coating solutions, respectively. An insulating layer as an intermediate layer produced using Byron (registered trademark) 29CS is hereinafter referred to as a “solvent type”, and an insulating layer produced using Byronal (registered trademark) MD-1220 is hereinafter referred to as a “water dispersion type”. . In these resin coating solutions, Cymel (registered trademark) 303, which is a melamine resin manufactured by Mitsui Cytec Co., Ltd., is used as a curing agent so that the polyester resin solid content: melamine resin solid content = 100: 20 in the mass ratio of the resin solid content. Added to. Furthermore, for the “solvent type” coating solution, 0.5% by mass of Catalyst TM600, an acidic catalyst manufactured by Mitsui Cytec Co., Ltd., was added to a mixed solution of polyester resin and melamine resin. No catalyst was added to the “water-dispersed” coating solution.

  The resin coating solution is applied on the previously prepared plating layer with a bar coater, dried and cured in a hot air oven under the condition that the ultimate plate temperature is 200 ° C., and then cooled with water, so that the insulating layer is formed on the plating layer. Formed.

  Next, an Al metal layer was formed on the insulating layer by performing vapor deposition plating of Al with a vacuum vapor deposition plating apparatus. Hereinafter, this method is referred to as “evaporation method”.

  About the film | membrane containing the Al metal layer by plating formed in this way, the film thickness and the coverage were measured as mentioned above.

(4. Formation of coating containing Al metal layer made of Al particles)
Scale-like Al particles were sprayed on the insulating layer as the intermediate layer formed as described above to form an Al metal film. For the Al metal layer made of Al particles, apply the coating liquid for the insulating layer prepared as described above on the plating layer with a bar coater, and then sprinkle the Al particles uniformly on the coating film before drying. After that, the coating film was dried and cured in a hot air drying furnace under the condition of a predetermined ultimate plate temperature. In this example, aluminum paste “Sap 561PS” manufactured by Showa Aluminum Powder Co., Ltd. was used as the Al particles, and the particles were formed into particles (average particle size 16 μm). Hereinafter, this method is referred to as “particle spraying method”.

(5. Formation of clear resin film)
On the Al metal layer, the resin coating solution prepared as the coating solution for the insulating layer as the intermediate layer described in the formation of the coating including the Al metal layer by plating is applied with a bar coater, and the ultimate plate temperature 230 is applied in a hot air drying furnace. After drying and curing at a temperature of 0 ° C., a clear resin film layer was formed by cooling with water.

  A galvanized steel sheet was produced as described above. The details of the manufactured galvanized steel sheet are shown in Tables 1-4.

  The following evaluation test was implemented about the manufactured galvanized steel plate. In any test, the test was carried out using the surface having a film containing Al as the evaluation surface.

(I. Workability test)
A cupping test was conducted under the condition of an indentation depth of 8 mm by the method described in JIS K 5600-5-2 “Copping resistance”. The test was performed under conditions such that the evaluation surface was on the outside of the cup, and a test generally referred to as a tape peeling test was performed in which a tape was attached to the processed part after the test and peeled off.

  After completion of the test, the state of damage on the surface of the tape peeled portion was visually observed, and when there was no damage at all, ◎, when the peeling of the Al metal layer at the processed portion was less than 20% by area ratio When the peeling of the Al metal layer at the processed part was 20 to 50% in area ratio, Δ was evaluated, and when the peeling of the Al metal layer at the processed part was more than 50%, the evaluation was x.

(II. Corrosion resistance test)
The produced galvanized steel sheet was cut into a size of 70 mm wide × 150 mm long, cut scratches reaching the steel sheet substrate were provided on the evaluation surface, and the four cut end surfaces were sealed with tape to prepare a sample for corrosion resistance test. . And the salt spray test was implemented by the method of 9.1 of JISK5400. The salt water was sprayed so as to be sprayed on the evaluation surface. The test time was 240 hours.

  After the test, measure the maximum swollen width on one side of the cut wound, ◎ when the swollen width is 3 mm or less ◎ when 3 mm or more and 4 mm or less ◎ ○ when 4 mm or more and 5 mm or less ○ ○ 5 mm or more and 10 mm or less In some cases, the case was evaluated as x if it was more than 10 mm.

(III. Blackening resistance test)
The produced galvanized steel sheet is cut into a size of 70 mm wide × 150 mm long and exposed to the coastal area of Kimitsu City, Chiba Prefecture for 6 months. The color tone of the steel sheet before and after the exposure test is measured with a spectrocolorimeter. The L ^* value representing the brightness of the CIE color system (L ^* a ^* b ^* color system) was measured. Then, when ΔL ^* = [L ^* before test] − [L ^* after test], ΔL ^* ≦ 5 is ◎, 5 <ΔL ^* ≦ 10 is ◯, 10 <ΔL ^* ≦ 15 was evaluated as Δ, and 15 <ΔL ^* ≦ 20 was evaluated as ×.

(IV. Fingerprint resistance)
If the fingerprint is not attached at all after pressing the index finger against the evaluation surface, ◎, if the fingerprint adheres but the fingerprint disappears if wiped off with a cloth, the fingerprint adheres but if wiped off with a cloth The case where the fingerprint remained but it was difficult to visually confirm the remaining fingerprint was evaluated as △, and the case where the fingerprint adhered and wiped off with a cloth was not evaluated at all.
(V. Appearance observation)
The appearance of the evaluation surface was visually observed to evaluate the presence of appearance defects.

  Details of the evaluation results (see Tables 5 to 8) will be described below. As the evaluation criteria of the inventive examples and comparative examples, any of the corrosion resistance and blackening resistance evaluated as “x” was regarded as a comparative example without exception. On the other hand, in all the evaluation results, there was only one “Δ”, and when the other evaluations were “◯” or more, the example of the present invention was obtained. Furthermore, even if the fingerprint resistance is “X” or “Δ”, the present invention example is used if both the corrosion resistance and blackening resistance are “◯” or more.

  Tables 5 and 6 show the evaluation results of the galvanized steel sheets produced by the “particle dispersion method”. No. 1) -1 to 24 and No. 1 2) In the present invention of -1 to 11, excellent evaluation results were shown in all items of workability, corrosion resistance, blackening resistance, and fingerprint resistance.

  Invention Example No. 1) -4 has a tendency for the corrosion resistance to decrease when the area where Al in the lower layer of the coating film is not present is 0.5 μm. Comparative Example No. 1) -26 is 0 μm in the area where Al is not present in the lower layer of the coating film, that is, Al and the plating layer are in contact with each other.

  Invention Example No. In 1) -6, since the Al metal film layer is as thin as 2 μm, the Al coverage is as low as 75% and the blackening resistance tends to decrease. Comparative Example No. 1) -27 is not suitable because the Al metal film layer has a thinner film thickness and the coverage is less than 75%, resulting in poor blackening resistance. Invention Example No. In 1) -8, the film thickness of the Al metal film layer is as thick as 20 μm, so the workability is low.

  Invention Example No. 1) -16 has a large amount of Mg added to the hot dip galvanized layer as 10% by mass, so that poor appearance due to dross where oxides (dross) oxidized without being dissolved in the plating bath adhere to the plated layer. Slightly occurred. Appearance defects due to dross tend to be disliked in places where people can see the eyes (for example, outer panels of home appliances and buildings) from the viewpoint of design and design. . However, since the appearance defect due to dross is simply an oxide adhered to the plating layer, it can be used as a plated steel sheet without any problem if there is no problem in performance.

  Invention Example No. 1) -21 has a large amount of Si added to the hot dip galvanized layer as 2% by mass, so that the appearance defect due to dross where oxide (dross) oxidized without being dissolved in the plating bath adheres to the plated layer. Slightly occurred. In addition, according to the present invention, the Si addition amount is 1% by mass. 1) -20 was also slight, but there was an appearance defect due to dross. Appearance defects due to dross tend to be disliked in places where people can see the eyes (for example, outer panels of home appliances and buildings) from the viewpoint of design and design. . However, since the appearance defect due to dross is simply an oxide adhered to the plating layer, it can be used as a plated steel sheet without any problem if there is no problem in performance.

  Comparative Example No. 1) -25 is not suitable because it does not contain Al or Mg in the galvanized layer, and is inferior in corrosion resistance.

  Comparative Example No. 1) -30 has a heating rate of less than 5 ° C./s when baking the coating liquid to form an Al metal film layer, and the heating rate is slow, so that the Al particles are less likely to float, and the Al particles are plated with the film. Al particles are present within a range of 0.5 μm from the interface with the layer, resulting in poor corrosion resistance. Comparative Example No. 1) -31 has a heating rate of more than 70 ° C./s when baking the coating liquid to form an Al metal film layer, so that the paint is cured while the paint is boiling in the solvent drying process. There was a coating defect called boiling where traces of bubbles due to boiling remained in the film. Furthermore, since the heating rate was fast and the heating time was short, the coating film surface layer was slightly uncured, and when the coating film surface layer was touched with a finger, it was felt that some fingers were sticking to the coating film (sticky feeling). If the surface of the coating film is uncured, the coating film is peeled off, which is not suitable. Comparative Example No. 1) -33 has a final plate temperature of less than 180 ° C. when the coating liquid is baked to form an Al metal film layer, so that the coating surface layer is slightly uncured and slightly touches the coating surface layer with a finger. There was a feeling of sticking to the film (sticky feeling). If the surface of the coating film is uncured, the coating film is peeled off, which is not suitable. Comparative Example No. 1) -35 has a reached plate temperature of more than 230 ° C. when the coating liquid is baked to form an Al metal film layer, so that the paint is cured in a state where the paint boiled in the solvent drying step. There was a coating defect called boiling where traces of bubbles due to boiling remained in the film. Furthermore, since the coating film was cured at a high temperature, the coating film was hardened, and when it was bent 180 degrees, the coating film was cracked or peeled off. Since galvanized steel sheets are generally used after being processed, there is a risk of corrosion from the processed parts where the coating film cracks or peels off due to processing, which is unsuitable because the product value is significantly reduced. .

  Comparative Example No. 2) -12 is not suitable because the aspect ratio of Al particles is less than 20, the Al coverage is low, and the blackening resistance is poor.

  Invention Example No. 2) -4 is Vylonal (registered trademark) MD-1335 (number average molecular weight 8000, Tg 4 ° C.) having a low number average molecular weight. Since 2) -5 uses Vylonal (registered trademark) MD-1500 (number average molecular weight 8000, Tg 77 ° C.) having a high Tg, the workability tends to decrease. In addition, the present invention No. 2) -1 is Vylonal (registered trademark) MD-1220 (number average molecular weight 15000, Tg 67 ° C.) having a higher Tg. 2) -3 has a high number average molecular weight and a low Tg Vylonal (registered trademark) MD-1985 (number average molecular weight 25000, Tg-20 ° C.), so that the processability tends to decrease. .

  Invention Example No. In 2) -11, since the average particle diameter of Al particles was as large as 30 μm, a part of the Al particles came out of the coating film, resulting in a slightly uneven appearance. However, since the uneven appearance is simply that Al particles in the coating film have come out of the coating film, it can be used as a plated steel sheet without any problem in performance.

  Table 7 shows the evaluation results of the galvanized steel sheets produced by the “evaporation method”. As shown in Table 7, no. 3) In the present invention examples of -1 to 25, excellent evaluation results were shown in all items of workability, corrosion resistance, blackening resistance, and fingerprint resistance.

  No. of the example of the present invention. 3) -1 to 13 and 3) -15 to 25 were excellent in workability because the insulating layer (intermediate layer) was a resin.

  No. of the example of the present invention. 3) -14 had a film thickness of the insulating layer (intermediate layer) of more than 1.5 μm, and the insulating film layer was slightly inferior in workability compared to other invention examples of 1.5 μm or less. Other items were good.

  No. of the example of the present invention. 3) -20 has no clear resin film on the Al metal film layer, and was inferior to fingerprint resistance compared to other invention examples having a clear resin film. Excellent results.

  Comparative Example No. 3) No. 21 had a clear resin film thickness of 0.2 μm, and the evaluation result of fingerprint resistance was Δ and the lower limit level.

  No. of the example of the present invention. 3) -24 is good in all evaluations, but the clear resin film is relatively thick, more than 25 μm, and there is a tendency that a coating result called boiling is generated in the film in the process of applying the clear resin film and drying and curing. there were.

  Comparative Example No. 3) -8 has a Si content of less than 0.001% by mass in the hot dip galvanized layer, and has a tendency to be slightly inferior in corrosion resistance to other invention examples in which Si is added in an amount of 0.001% by mass or more. The plating appearance failure due to dross was also severe, so it is not suitable. No. of the present invention. 3) -10 had a Si content of 2% by mass in the hot dip galvanized layer, and a dross appearance was slightly observed. However, since the dross appearance is slight, it is considered that the quality level has no problem in actual use.

  No. of the example of the present invention. 3) -11 has a Si content of more than 2% by mass and the Si addition amount is 2% by mass or less, and the appearance of plating by dross tends to be inferior to that of other invention examples. It was excellent.

  Invention No. of this application. 3) -24 had a clear coating film thickness of 25 μm, and a coating defect called boiling occurred. Boiling is a process of drying and baking the coating film, and is a coating film defect in which a trace of boiling of the solvent remains in a crater form, and is likely to occur when the film thickness is thick. For this reason, in places where people can see it (for example, outer panel panels of home appliances, buildings, etc.), those with poor appearance tend to be disliked from the viewpoint of design and design. It is better not to occur. However, if there is no problem in performance, it looks bad, but it can be used without any problem.

  On the other hand, no. 3) -26 was inferior in blackening resistance because the Al metal film layer was not formed on the Zn-Al-Mg-Si alloy plating layer. Comparative Example No. 3) -27 is not suitable because it does not have an insulating film layer made of an insulating material between the hot-dip galvanized layer and the Al metal layer, and therefore has poor corrosion resistance.

  Table 8 shows the evaluation test results of the galvanized steel sheets produced by the “particle spraying method”. No. of the example of the present invention. 4) -1 to 19 and 21 to 24 were excellent in all of workability, corrosion resistance, blackening resistance, and fingerprint resistance.

  ADVANTAGE OF THE INVENTION According to this invention, the Zn-Al-Mg-Si type galvanized steel plate which made the outstanding corrosion resistance and long-term black-proof property compatible can be provided. As a result, Zn-Al-Mg-Si galvanized steel sheets that do not require painting, are inexpensive, and have excellent corrosion resistance can be used as building materials and outer panels for home appliances. The process can be omitted and the manufacturing cost of the product can be reduced. Therefore, the present invention can be said to be an invention with extremely high industrial value.

The present invention has been completed based on such knowledge, and the gist of the present invention is as follows.
[1] a steel plate;
Zn-Al-Mg-Si alloy plating layer formed on the surface of the steel plate;
A film containing Al formed on the plating layer;
Including
Al in the film containing Al is separated from the plating layer by the presence of an insulating material;
And by observing the film containing Al from a direction perpendicular to the surface, the area of the portion of the plating layer concealed by Al in the film is defined as a ratio to the total area of the observation field. The coverage is 75-100%,
A galvanized steel sheet with excellent blackening resistance and corrosion resistance.
[2] The film containing Al is made of an insulating material containing scaly Al particles, and the Al particles are within a range of at least 0.5 μm from the interface between the film containing Al and the plating layer. The galvanized steel sheet excellent in blackening resistance and corrosion resistance as described in [1], which does not exist.
[3] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [2], wherein the Al particles have an average particle diameter of 5 to 30 μm and an aspect ratio of 20 or more.
[4] The film according to [1], wherein the film containing Al is composed of at least two layers of an intermediate layer formed of an insulating material and an Al metal layer in order from the plating layer side. Galvanized steel sheet with excellent blackening resistance and corrosion resistance.
[5] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [4], wherein the Al metal layer is composed of an aggregate of scaly Al particles.
[6] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [1], wherein the insulating substance is a resin.
[7] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [6], wherein the resin is a polyester resin crosslinked with a melamine compound.
[8] The galvanized steel sheet having excellent blackening resistance and corrosion resistance according to [7], wherein the polyester resin has a glass transition temperature Tg of −20 to 70 ° C. and a number average molecular weight of 15,000 to 25000. .
[9] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [1], wherein the thickness of the film containing Al is 2 to 10 μm.
[10] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [1], further comprising a clear resin film on the Al-containing film.
[11] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [10], wherein the clear resin film has a thickness of 0.2 to 20 μm.
[12] Before SL Me Tsu Ki layer is 0.01 to 60 wt% Al, characterized in that it comprises a 0.001 to 10 mass% of Mg and 0.001 wt% of Si, [1] A galvanized steel sheet excellent in blackening resistance and corrosion resistance as described in 1.
[13] A method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance as described in [2], comprising flaky Al particles and an insulating material in a solvent, measured at 25 ° C. with a rotational viscometer A paint having a viscosity of 150 to 1500 mPa · s at a shear rate of 1 s −1 and a viscosity of 50 to 150 mPa · s at a shear rate of 10000 s −1 measured at 25 ° C. with a rotational viscometer coated on in order Kki layer on the surface of and then heated in an induction heating furnace until reaching plate temperature of 180 to 230 ° C. the steel sheet at a heating rate of 5 to 70 ° C. / s, to form a film containing the Al A method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance.
[14] The paint is prepared by mixing scale-like Al particles in a solvent together with 100 parts by mass of a water-based emulsion type polyester resin solid content and 10 to 30 parts by mass of a melamine compound solid content as a crosslinking agent. The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [13].
[15] The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [13], wherein the viscosity of the paint is adjusted using a viscosity modifier.
[16] As the viscosity modifier, a surfactant mainly composed of 0.2 to 10 parts by mass of a urethane-modified polyether with respect to 100 parts by mass of the aqueous emulsion type polyester resin dispersion is used. [15] The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [15].
[17] The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [13], wherein Al particles having an average particle diameter of 5 to 30 μm and an aspect ratio of 20 or more are used as the Al particles. Production method.
[18] A method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [4],
(A) an intermediate layer of insulating material is formed on the layer Ki Tsu because the surface of the steel sheet, and then either forming the Al metal layer by plating thereon, or,
(B) a liquid material for forming the intermediate layer of insulating material over the layer Ki Tsu because the surface of the steel sheet is coated, sprayed with scaly Al particles on the liquid material, is then solidifying the liquid material Forming an intermediate layer of insulating material and an Al metal layer thereon,
A method for producing a galvanized steel sheet having excellent blackening resistance and corrosion resistance.
[19] The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to [18], wherein the plating method is a vacuum deposition plating method.

Claims (19)

Steel sheet,
Zn-Al-Mg-Si alloy plating layer formed on the surface of the steel plate;
A film containing Al formed on the plating layer;
Including
Al in the film containing Al is separated from the plating layer by the presence of an insulating material;
And by observing the film containing Al from a direction perpendicular to the surface, the area of the portion of the plating layer concealed by Al in the film is defined as a ratio to the total area of the observation field. The coverage is 75-100%,
A galvanized steel sheet with excellent blackening resistance and corrosion resistance.   The film containing Al is made of an insulating material containing scaly Al particles, and the Al particles do not exist within a range of at least 0.5 μm from the interface between the film containing Al and the plating layer. The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 1.   The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 2, wherein the Al particles have an average particle diameter of 5 to 30 μm and an aspect ratio of 20 or more.   2. The blackening resistance according to claim 1, wherein the coating containing Al is composed of at least two layers of an intermediate layer formed of an insulating material and an Al metal layer in order from the plating layer side. Galvanized steel sheet with excellent corrosion resistance.   The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 4, wherein the Al metal layer is composed of an aggregate of scaly Al particles.   The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 1, wherein the insulating substance is a resin.   The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 6, wherein the resin is a polyester resin cross-linked with a melamine compound.   The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 7, wherein the polyester resin has a glass transition temperature Tg of −20 to 70 ° C. and a number average molecular weight of 15000 to 25000.   2. The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 1, wherein a thickness of the film containing Al is 2 to 10 μm.   The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 1, further comprising a clear resin film on the Al-containing film.   The galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 10, wherein the clear resin film has a thickness of 0.2 to 20 μm.   2. The black resistance according to claim 1, wherein the galvanized layer contains 0.01 to 60 mass% Al, 0.001 to 10 mass% Mg, and 0.001 to 2 mass% Si. Galvanized steel sheet with excellent modification and corrosion resistance. A method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 2, comprising scale-like Al particles and an insulating material in a solvent, and a shear rate measured by a rotational viscometer at 25 ° C. viscosity at the conditions of 1s ^-1 is 150~1500mPa · s, and coating the surface of the steel sheet viscosity at a shear rate of 10000s ^-1 as measured by a rotational viscometer at 25 ° C. is 50~150mPa · s It is applied on a galvanized layer, and then the steel sheet is heated in an induction heating furnace at a heating rate of 5 to 70 ° C./s to an ultimate plate temperature of 180 to 230 ° C. to form the Al-containing film. A method for producing a galvanized steel sheet having excellent blackening resistance and corrosion resistance.   14. The coating material is prepared by mixing scale-like Al particles in a solvent together with 100 parts by weight of an aqueous emulsion type polyester resin and 10 to 30 parts by weight of a melamine compound as a crosslinking agent. Of galvanized steel sheet with excellent blackening resistance and corrosion resistance.   The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 13, wherein the viscosity of the paint is adjusted using a viscosity modifier.   The surfactant according to claim 15, wherein a surfactant mainly comprising 0.2 to 10 parts by mass of a urethane-modified polyether is used as the viscosity modifier based on 100 parts by mass of the water-based emulsion type polyester resin. Of galvanized steel sheet with excellent blackening resistance and corrosion resistance.   The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 13, wherein Al particles having an average particle diameter of 5 to 30 μm and an aspect ratio of 20 or more are used as the Al particles. A method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 4,
(A) An intermediate layer of an insulating material is formed on the galvanized layer on the surface of the steel plate, and then an Al metal layer is formed thereon by a plating method, or
(B) Applying a liquid material for forming an intermediate layer of an insulating material on the galvanized layer on the surface of the steel plate, spraying scaly Al particles on the liquid material, and then solidifying the liquid material Forming an intermediate layer of insulating material and an Al metal layer thereon;
A method for producing a galvanized steel sheet having excellent blackening resistance and corrosion resistance.   The method for producing a galvanized steel sheet excellent in blackening resistance and corrosion resistance according to claim 18, wherein the plating method is a vacuum deposition plating method.