JP7401828B2 - Plated steel sheets for pre-painted steel sheets, pre-painted plated steel sheets and molded products - Google Patents

Description

The present invention relates to a plated steel sheet for pre-painted steel sheets, a pre-painted plated steel sheet, and a molded product.

Pre-coated steel sheets, which are coated steel sheets that have been coated in advance, are required to have many properties such as corrosion resistance, formability, coating hardness (scratch resistance), stain resistance, chemical resistance, and weather resistance. The order of these required performances differs depending on the use of the prepainted plated steel sheet. For example, among the above-mentioned performances, formability and corrosion resistance are particularly important for pre-coated plated steel sheets used mainly in outdoor applications such as outdoor units of air conditioners and water heaters.

In such a pre-coated plated steel sheet, many techniques have been studied in the past as methods for increasing the adhesion between the plated steel sheet and the coating film.

For example, the following Patent Document 1 discloses a precoated metal plate with excellent press formability, in which the coating film on the drawn portion is not damaged or peeled off during drawing processing. In Patent Document 1, in order to obtain a precoated metal plate with excellent press formability that does not peel off, the coating film has a specific viscoelastic curve, the number average molecular weight of the coating resin is 10,000 or more, and the coating film has a specific viscoelastic curve. It is disclosed that the glass transition point (Tg) of the resin is preferably 25° C. or higher.

Moreover, the following Patent Document 2 discloses a precoated metal plate that has excellent continuous press formability and excellent outdoor corrosion resistance at the end face portion of the drawn portion. In Patent Document 2, in order to obtain a pre-coated metal plate with excellent continuous press formability, the physical properties of the coating film are such that the Tg of the coating film is 40 to 120°C, and the coating film measured with a dynamic viscoelasticity measuring device is The minimum value of the storage modulus in the rubber- ^like elastic region of It is disclosed that it is important.

Furthermore, in Patent Document 3 below, a metal plate has one or more coating layers on one or both sides, and the outermost coating has a Tg of 5 to 30°C and a temperature of 23°C. The hardness is 2.5 N/mm2 ^or more in terms of universal hardness under a load of 5 mN, the elongation at break at 23°C is 100% or more, and the specular gloss of the outermost coating film is within the angle of incidence. A high gloss precoated metal plate is disclosed which has a gloss of 60% or more when measured under the condition of a light receiving angle of 60°. Regarding such a pre-coated metal plate, Patent Document 3 describes that it provides a coated metal molded product with excellent press formability, in which the gloss of the coating film is unlikely to deteriorate in the processed area even when deep drawing is performed. There is.

Japanese Patent Application Publication No. 2-217500 Japanese Patent Application Publication No. 8-253883 Japanese Patent Application Publication No. 2007-44922

The present inventors conducted studies in order to further improve the formability and corrosion resistance of the pre-coated plated steel sheet as described above. As a result, when a pre-coated plated steel sheet is used to draw the top plate of an air conditioner outdoor unit, etc., a phenomenon called paint film lifting occurs in the drawn part (a phenomenon in which the paint film becomes rough due to an aggregate of minute blisters). It has been newly discovered that this occurs. Hereinafter, the area where these phenomena occur will be referred to as a "paint film floating area." From the cross-sectional observation of the floating parts of the coating film, it was found that during drawing forming of the pre-coated plated steel plate, the coating film could not follow the deformation (compression) of the plated steel plate, resulting in a surplus of coating film, and the coating film did not adhere properly to the plated steel plate in places where it was not able to follow the deformation (compression) of the plated steel plate. It became clear that the layer had peeled off upward.

The technique disclosed in Patent Document 1 is intended to control the buckling of the coating film due to compressive strain in the drawn portion that occurs during drawing processing by regulating the physical properties of the coating film. However, as a result of studies conducted by the present inventors, in order to suppress buckling of the coating film, in addition to the physical properties of the coating film, it is actually necessary to check the hardness of the plating, the uniformity of the plating, the physical properties of the chemical conversion film, the processed shape, etc. It is assumed that this is an influential factor that cannot be ignored. Patent Document 1 does not include any description regarding influencing factors other than these physical properties of the coating film. Therefore, there is still room for improvement in Patent Document 1 with regard to suppressing the buckling of the coating film in the coating film floating portion that occurs due to the drawing process, which is the focus of the present inventors.

Further, the technique of Patent Document 2 is not different from the invention of Patent Document 1 in that it attempts to suppress buckling of the coating film due to compressive strain during drawing by regulating the physical properties of the coating film. Therefore, there is still room for improvement in Patent Document 2 with regard to suppressing buckling of the coating film in the coating film floating portion that occurs due to the drawing process, which is the focus of the present inventors.

Furthermore, the technique of Patent Document 3 is also similar to Patent Documents 1 and 2 in that it attempts to suppress buckling of the coating film due to compressive strain only by specifying the physical properties of the coating film. Therefore, there is still room for improvement in Patent Document 3 with regard to suppressing buckling of the coating film in the coating film floating portion that occurs due to the drawing process, which is the focus of the present inventors.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to more reliably suppress the occurrence of floating parts of the paint film even when drawing is performed. The purpose of the present invention is to provide a plated steel sheet for pre-painted steel sheets, a pre-painted plated steel sheet, and a molded product.

In order to solve the above-mentioned problems, the inventors of the present invention have conducted extensive studies and found that the surface oxidation state of the plated steel sheet, which is the original plate for pre-coated plated steel sheet, is such that the coating film in the processed part of the molded product is It was found that the adhesion of
The gist of the present invention, which was completed as a result of further studies based on this knowledge, is as follows.

(1) A steel plate, located on one or both sides of the steel plate, containing 0.5% by mass or more and 60.0% by mass or less of aluminum, 0.5% by mass or more and 15.0% by mass or less of magnesium, and the remainder being a plating layer consisting of zinc and impurities, and at a depth of 10 nm from the surface of the plating layer, the ratio of magnesium oxide and hydroxide to the ratio of metallic magnesium is 2.0 or more. or a plated steel sheet for pre-coated steel sheet, wherein the ratio of zinc oxide and hydroxide to the ratio of metal zinc is 7.0 or more.
(2) At a depth of 10 nm from the surface of the plating layer, the ratio of the magnesium oxide and hydroxide to the ratio of metal magnesium is 2.0 or more, and the zinc oxide and The plated steel sheet for pre-coated steel sheet according to (1), wherein the ratio of hydroxide is 7.0 or more to the ratio of metal zinc.
(3) In (1) or (2), the ratio of aluminum oxide and hydroxide is 1.3 or more to the ratio of metal aluminum at a depth of 10 nm from the surface of the plating layer. The plated steel sheet for the prepainted steel sheet described above.
(4) The plated steel sheet for pre-coated steel sheet according to any one of (1) to (3), wherein the plating layer is a Zn-11%Al-3%Mg-0.2%Si alloy plating.
(5) A steel plate, located on one or both sides of the steel plate, containing 0.5% by mass or more and 60.0% by mass or less of aluminum, 0.5% by mass or more and 15.0% by mass or less of magnesium, and the remainder being It has a plating layer made of zinc and impurities, a chemical conversion film located on the plating layer, and a coating film located on the chemical conversion film, and the combination of the chemical conversion film and the plating layer is At a depth of 10 nm from the interface toward the inside of the plating layer, the ratio of magnesium oxide and hydroxide to the ratio of metallic magnesium is 0.30 or less, or zinc oxide A pre-coated plated steel sheet in which the ratio of metal zinc and hydroxide is 7.0 or more to the ratio of metal zinc.
(6) At a depth of 10 nm from the interface between the chemical conversion film and the plating layer toward the inside of the plating layer, the ratio of the magnesium oxide and hydroxide to the ratio of metallic magnesium 0.30 or less, and the ratio of the zinc oxide and hydroxide is 7.0 or more with respect to the ratio of metal zinc.
(7) At a depth of 10 nm from the interface between the chemical conversion coating and the plating layer toward the inside of the plating layer, the ratio of aluminum oxide and hydroxide to the ratio of metallic aluminum is The pre-coated plated steel sheet according to (5) or (6), which has a particle diameter of 0.30 or less.
(8) A molded product made of the pre-coated plated steel sheet according to any one of (5) to (7), wherein the thickness of the plated steel sheet in the molded product is increased by 5% or more compared to the non-formed part. The peel strength measured by cutting the interface between the chemical conversion coating film and the coating film using the SAICAS method is 1.00 kN/m or more on average, and 20% or less of the cutting area is A molded article which has an interfacial peeling pattern and the remaining cut area has a cohesive failure pattern within the coating film.
(9) The molded product according to (8), wherein the plating layer in the molded product contains 5% to 15% aluminum and 2% to 4% magnesium.

As explained above, the present invention provides a plated steel sheet for pre-painted steel sheets, a pre-painted plated steel sheet, and a molded product that can more reliably suppress the occurrence of coating film floating parts even when drawing is performed. It becomes possible to provide

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram schematically showing an example of the structure of a plated steel sheet for prepainted steel sheets according to each embodiment of the present invention. FIG. 3 is an explanatory diagram schematically showing another example of the structure of a plated steel sheet for pre-coated steel sheets according to each embodiment of the present invention. It is an explanatory view for explaining a plating layer in a plated steel sheet for prepainted steel sheets concerning each embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram schematically showing an example of the structure of a pre-coated plated steel sheet according to each embodiment of the present invention. FIG. 2 is an explanatory diagram schematically showing another example of the structure of a pre-coated plated steel sheet according to each embodiment of the present invention. It is an explanatory view for explaining a plating layer in a precoat plated steel plate concerning each embodiment of the present invention. FIG. 1 is an explanatory diagram schematically showing an example of the structure of a molded product according to each embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that, in this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals and redundant explanation will be omitted.

(Regarding studies conducted by the inventors)
Below, before explaining the plated steel plate for pre-coated steel plate, pre-coated plated steel plate, and molded product according to the embodiments of the present invention, various studies conducted on the above-mentioned coating film floating portion will be explained in detail.

When the present inventors observed the cross section of the floating part of the coating film in a molded product made by drawing and forming a pre-coated plated steel plate, the coating film was compressed due to the deformation (compression) of the plated steel plate, and the excess coating film was pushed upward. Peeling was observed. When we measured the thickness of the plated steel plate in this area, we found that it had increased compared to the thickness before forming, which revealed that the coating film floating part we were looking at was the part where the plated steel plate was compressed. .

On the other hand, areas where the paint film peeled off due to friction with the mold during the drawing process (i.e., areas where peeling occurred due to mechanical abrasion), and areas where the paint film expanded following the painted base plate, As a result of stress concentration at the interface between the plating and the coating film, adhesion deteriorates, and areas where coating peeling occurs due to mold sliding (i.e., areas where peeling occurs due to stress concentration) are removed from the plated steel plate. The thickness was smaller than before molding. These results revealed that the areas where the coating film peeled off were the areas where the plated steel sheet was elongated. However, in the drawing process, the compression and expansion of the plated steel sheet do not occur independently, but occur simultaneously, and the extent of compression and expansion differs depending on the processed area. In areas where compression exceeds elongation, the thickness of the plated steel sheet is greater than before forming. Conversely, in areas where elongation exceeds compression, the thickness of the plated steel sheet is smaller than before forming.

Generally, when the adhesion strength (peel strength) between the coating film and the plating interface decreases due to deformation of the plated steel sheet during forming processing, coating lifting and coating peeling occur.

As a result of the studies conducted by the present inventors, we came up with the knowledge that the following three influencing factors (1) to (3) should be considered as factors that determine whether paint film lifting or peeling occurs. did. If these influencing factors are in overall good condition, it is thought that lifting of the paint film and peeling of the paint film will be suppressed.

(1) Healthiness of the plating surface after processing that involves compression and expansion (presence of unevenness and cracks)
(2) Adhesion between the plating and primer coating through the chemical conversion coating after processing that involves compression and stretching (3) Condition of the entire coating film, including the top coating that has been deformed due to processing that involves compression and stretching ( presence of cracks and internal stress)

The present inventors discovered that the above-mentioned phenomenon of paint film lifting is likely to occur on pre-coated steel sheets using zinc-based coated steel sheets (particularly zinc-based alloy-plated steel sheets containing aluminum and magnesium) as the base plate for coating. Further studies were conducted focusing on the plating surface as a painted base plate as shown in (1) and (2) above.

As a result, the present inventors found that the surface oxidation state of the plated steel plate used as the original plate for painting affects the adhesion of the coating film in the formed part. Here, the surface oxidation state of the plated steel sheet that the inventors focused on is (a) the state of aluminum and magnesium oxides and hydroxides on the surface of the plated steel sheet, and (b) the oxidation of zinc on the surface of the plated steel sheet. There are mainly two types: solid state and hydroxide state.

First, (a) the state of aluminum and magnesium oxides and hydroxides on the surface of a plated steel sheet will be mentioned.

As a result of studies conducted by the present inventors, it was found that the lower the concentration of aluminum and magnesium oxides and hydroxides on the surface of the plated steel sheet, the higher the coating film adhesion of the formed part. This is because oxides and hydroxides of aluminum and magnesium, which are easily oxidized elements, are formed on the surface of zinc-based alloy coated steel sheets containing aluminum and magnesium, which reduces wettability with degreasing liquids and chemical conversion treatment liquids. It is estimated that this caused the coating film adhesion in the processed area to deteriorate.

Furthermore, the present inventors have conducted extensive studies on the correlation between the oxidation state of the plating surface of the original plate and the adhesion of the coating in the molded area. As a result, regarding magnesium, at a depth of 10 nm below the surface of the plating layer, the abundance ratio of magnesium oxides and hydroxides was 2.0% relative to the abundance ratio of magnesium metal (in other words, magnesium in a metallic state). It has become clear that when the value is 0 or more, good coating film adhesion in the molded part can be obtained.

Although it is better to have a smaller surface concentration of oxides on the surface of magnesium, as mentioned above, in magnesium near the surface of the plating layer, the ratio of oxides and hydroxides is constant relative to the ratio of metal. The reason why the above is better is still not clear. However, in order to have good paint film adhesion in the molded part, it is necessary to dissolve both the magnesium metal and the magnesium oxides and hydroxides by acid treatment, alkaline degreasing, etc. It is presumed that this is because, due to differences in dissolution rates and deposition after dissolution, it would have been better to have a higher proportion of oxides and hydroxides in magnesium itself.

Furthermore, as a result of studies by the present inventors, when a zinc-based alloy plated steel sheet containing aluminum and magnesium is subjected to chemical conversion treatment and painting to make it into a pre-painted steel sheet, as described above, In order to exhibit good film adhesion, the ratio of aluminum and magnesium oxides and hydroxides at the interface between the plating layer and the chemical conversion film should be lower than a certain level relative to the metal ratio of these elements. It has also become clear that

This is because chemical conversion treatment also dissolves aluminum and magnesium on the surface of the plating layer, and some of the aluminum and magnesium are also incorporated into the chemical conversion treatment film, which is presumed to have a negative effect on paint film adhesion. This is presumably because it is better for the surface ratio of oxides and hydroxides to be small. Although the details of the form in which aluminum and magnesium are incorporated into the chemical conversion coating are unknown, both are incorporated as oxides/hydroxides and as metals. It is assumed that it exists.

Next, (b) the state of zinc oxides and hydroxides on the surface of the plated steel sheet will be mentioned.

As a result of studies conducted by the present inventors, it was found that the lower the concentration of zinc oxides and hydroxides on the surface of the plated steel sheet, the higher the coating adhesion of the formed part. This is because zinc oxides and hydroxides have higher wettability with degreasing liquids and chemical conversion treatment liquids than metal zinc, so these oxides and hydroxides cover the surface of the plating, causing chemical conversion. It is estimated that the adhesion with the treated film layer improves, and as a result, the larger the amount of zinc oxide and hydroxide, the better the adhesion of the film after molding.

Thus, the reason why it is better to have a higher ratio of zinc oxides and hydroxides than the ratio of metallic zinc on the surface of a plated steel sheet, which is an original plate for painting, is still not clear. However, in order to have good coating adhesion in the molded part, it is necessary to dissolve both the zinc metal and the zinc oxides and hydroxides by acid treatment, alkaline degreasing, etc. It is presumed that this is because the higher the proportion of oxides and hydroxides in zinc itself, the better, due to the difference in dissolution rate and the deposition after dissolution.

Furthermore, among zinc-based plated steel sheets, it was also inferred that in zinc-based plated steel sheets containing aluminum and magnesium, the surface concentration of zinc was relatively affected by the dissolution of aluminum and magnesium.

Furthermore, as a result of studies by the present inventors, when the above-mentioned zinc-based plated steel sheet is subjected to chemical conversion treatment and painting to make it into a pre-coated steel sheet, in order to show good paint film adhesion at the forming part. It was also revealed that the ratio of zinc oxide and hydroxide at the interface between the plating layer and the chemical conversion coating should be higher than a certain level relative to the ratio of metal zinc.

Based on the above knowledge, the present inventors conducted intensive studies and found that the conditions for acid treatment and alkaline degreasing to achieve appropriate oxide and hydroxide states were determined as detailed below. I was able to find out.

Furthermore, the present inventors have determined that the molded product obtained by forming the above-mentioned pre-coated plated steel sheet has a chemical conversion film or a coating film (for example, a primer coating film when the coating film consists of multiple layers). The peel strength and peel form at the interface with the plating layer were investigated. Conventional peel tests can measure the peel strength of the coating film on pre-coated steel sheets, but it has not been possible to accurately measure the peel strength and peel form of the compressed and stretched parts of the plated steel sheet that makes up the compact. The present inventors evaluated the peel strength and peel form using the SAICAS method (Surface and Interfacial Cutting Analysis System) as a method that can measure these parts simultaneously.

The SAICAS method is a method of measuring peel strength by cutting at an extremely low speed from the sample surface to the adhesive interface between the substrate and the adherend using a sharp blade. Therefore, it is possible to observe the peel strength and peel state at the interface between specific layers of a laminated multilayer film, which has been difficult to measure using conventional methods.

It is impossible to prepare samples of the compression part and the extension part of the plated steel sheet of the molded body individually. Therefore, the present inventors performed cylindrical cup drawing using a pre-painted steel sheet, and focused on the part where the thickness is increased compared to the thickness of the plated steel sheet before forming, as the forming part where compression is dominant. As the formed part where elongation is dominant, we focused on the part where the thickness is reduced compared to the thickness of the plated steel sheet before forming. The following findings were obtained by measuring both of these parts using the SAICAS method.

In other words, for molded bodies made of pre-coated steel sheets that do not cause the above-mentioned coating lifting or peeling, the peeling form of the coating film may be due to chemical conversion coatings or coatings (for example, coatings with multiple layers). It has been found that cohesive failure of the paint film (for example, the primer paint film if the paint film consists of multiple layers) occurs, rather than interfacial peeling at the interface between the primer paint film and the plating layer. Ta.

As a result, it has become clear that a molded article made of a pre-coated plated steel sheet without coating peeling can be obtained when the following two conditions (i) and (ii) are both satisfied.

(i) The compressed part of the plated steel sheet by the SAICAS method (i.e., the part where the thickness of the plated steel sheet of the molded product increases by 5% or more compared to before forming (which can also be considered a non-forming part)) The average peel strength is 1.00 kN/m or more.
(ii) 20% or less of the cut area is in the form of interfacial peeling, and the remaining cut area is in the form of cohesive failure within the coating film (for example, within the primer coating when the coating film consists of multiple layers).

Here, the form of interfacial peeling refers to cohesive failure of the chemical conversion coating, interfacial peeling between the chemical conversion coating and the paint film (for example, primer coating if the coating consists of multiple layers), or interfacial peeling of the chemical conversion coating. Refers to interfacial peeling between the surface and the plating layer, or a combination of these conditions. However, since the film thickness of the chemical conversion coating is extremely thin, it is integrated with the plating layer and paint film (for example, if the paint film consists of multiple layers, the primer paint film), and the above peeling pattern can be visually distinguished. I can't.

Below, a plated steel plate for a pre-coated steel plate, a pre-coated plated steel plate, and a molded product according to each embodiment of the present invention, which were completed based on the above knowledge, will be described in detail.

A first embodiment of the present invention described below is an embodiment that focuses on the state of aluminum and magnesium oxides and hydroxides on the surface of a plated steel sheet, referred to as (a) above. Further, the second embodiment of the present invention described below is an embodiment that focuses on the state of zinc oxides and hydroxides on the surface of the plated steel sheet, referred to as (b) above. Further, a third embodiment of the present invention described below is an embodiment that focuses on the state of oxides and hydroxides of zinc, aluminum, and magnesium on the surface of a plated steel sheet.

≪First embodiment≫
(About plated steel sheets for pre-painted steel sheets)
First, a plated steel sheet for pre-painted steel sheet according to a first embodiment of the present invention will be described in detail with reference to FIGS. 1A to 2.

As schematically shown in FIG. 1A, the plated steel plate 10 according to the present embodiment includes a steel plate 101 serving as a base material, and a plating layer 103 located on one side of the steel plate. Further, in the plated steel sheet 10 according to the present embodiment, as schematically shown in FIG. 1B, plating layers 103 may be located on both sides of the steel sheet 101 serving as a base material.

<About steel plate 101>
As the steel plate 101 used as the base material of the plated steel plate 10 according to the present embodiment, various steel plates can be used depending on the mechanical strength etc. required of the plated steel plate 10. Examples of such a steel plate 101 include Al-killed steel, ultra-low carbon steel containing Ti, Nb, etc., and high-strength steel containing ultra-low carbon steel further containing reinforcing elements such as P, Si, and Mn. Various steel plates can be mentioned.

Further, the thickness of the steel plate 101 according to the present embodiment (thickness d0 in FIGS. 1A and 1B) may be appropriately set depending on the mechanical strength required for the plated steel plate 10, and is, for example, 0.2 mm to 2.0 mm. It can be done to a certain extent.

<About the plating layer 103>
As schematically shown in FIGS. 1A and 1B, the plating layer 20 according to the present embodiment is a layer formed on at least one surface of the steel plate 101, and is used to improve the corrosion resistance of the plated steel plate 10. provided. Below, first, the chemical composition of the plating layer 103 according to this embodiment will be explained.

The plating layer 103 according to the present embodiment contains aluminum (Al): 0.5% to 60.0%, magnesium (Mg): 0.5% to 15.0%, and , the remainder is a plating layer consisting of zinc (Zn) and impurities. That is, the plating layer 103 according to this embodiment is an Al--Mg--Zn-based ternary plating layer.

[Al: 0.5 to 60.0% by mass]
The Zn alloy plating layer 103 according to this embodiment contains Al from 0.5% by mass to 60.0% by mass. By setting the Al content to 0.5% by mass or more and 60.0% by mass or less, the corrosion resistance of the plated steel sheet 10 according to the present embodiment improves, and the adhesion of the plating layer 103 (more specifically, the adhesion of the steel sheet 101) can be ensured. If the Al content is less than 0.5% by mass, the plating layer 103 becomes brittle and the adhesion of the plating layer 103 decreases. The content of Al is preferably 5.0% by mass or more. On the other hand, when the Al content exceeds 60.0% by mass, the effect of improving the corrosion resistance of the plated steel sheet 10 is saturated. The Al content is preferably 15.0% by mass or less.

[Mg: 0.5 to 15.0% by mass]
The plating layer 103 according to the present embodiment contains Mg from 0.5% by mass to 15.0% by mass. By setting the Mg content to 0.5% by mass or more and 15.0% by mass or less, the corrosion resistance of the plated steel sheet 10 according to the present embodiment improves, and the adhesion of the plating layer 103 (more specifically, 101) can be ensured. If the Mg content is less than 0.5% by mass, the effect of improving the corrosion resistance of the plated steel sheet 10 will be insufficient. The content of Mg is preferably 2.0% by mass or more. On the other hand, if the Mg content exceeds 15.0% by mass, the plating layer 103 becomes brittle and the adhesion of the plating layer 103 decreases. The Mg content is preferably 4.0% by mass or less.

[Remainder: Zn and impurities]
In the plating layer 103 according to this embodiment, the remaining components other than the above components are Zn and impurities. Furthermore, the plating layer 103 according to the present embodiment may contain silicon (Si) in a content of 0% by mass or more and 2.0% by mass or less in place of a portion of the remaining Zn.

[Si: 0 to 2.0% by mass]
The plating layer 103 according to the present embodiment may contain Si in an amount of 0% by mass or more and 2.0% by mass or less in place of a part of the remaining Zn. By setting the Si content to 0% by mass or more and 2.0% by mass or less, the adhesion of the plating layer 103 can be ensured more reliably. If the Si content exceeds 2.0% by mass, the effect of improving the adhesion of the plating layer 103 may be saturated. The content of Si is more preferably 1.6% by mass or less.

Furthermore, the plating layer 103 according to the present embodiment may contain elements such as Fe, Sb, and Pb alone or in combination in an amount of 1% by mass or less in place of a portion of the remaining Zn.

As the plated steel plate 10 for pre-coated steel plate provided with the plated layer 103 having the above-mentioned chemical composition, for example, a plated steel plate having a Zn-11%Al-3%Mg-0.2%Si alloy plated layer may be used. , hot-dip zinc-aluminum-magnesium-silicon alloy plated steel sheets (for example, "Superdyma (registered trademark)" and "ZAM (registered trademark)" manufactured by Nippon Steel Corporation).

[About the average film thickness of plating layer 103]
In the plated steel sheet 10 for pre-coated steel sheets according to the present embodiment, the average film thickness of the plating layer 103 (thickness d1 in FIGS. 1A and 1B) is, for example, preferably 6 μm or more, more preferably 9 μm or more. . When the plating layer 103 has such an average film thickness, it becomes possible to more reliably ensure the corrosion resistance of the plated steel sheet 10 for pre-coated steel sheet. In addition, when the average film thickness d1 of the plating layer 103 exceeds 45 μm, the effect of increase in plating cost becomes greater than the improvement in corrosion resistance. Therefore, from the viewpoint of economy, the average thickness d1 of the plating layer 103 is preferably 45 μm or less.

Note that the average thickness d1 of the plating layer 103 can be calculated, for example, by the following gravimetric method. That is, a plated steel plate having a predetermined area (for example, 50 mm x 50 mm) is dissolved in hydrochloric acid containing an inhibitor, and the melted weight is calculated from the difference in weight before and after melting. Separately, the weight ratio of elements such as Al, Zn, and Fe contained in the solution is measured and calculated by high-frequency inductively coupled plasma (ICP) emission spectrometry, and the average specific gravity of the plating layer is calculated from the ratio. . The average film thickness d1 of the plating layer 103 is calculated by dividing the melted weight by the average specific gravity and further by the area (or area x 2 in the case of double-sided plating).

<State of magnesium and aluminum on the surface of the plating layer>
Based on the findings described above, in the plating layer 103 according to the present embodiment, the states of metals, oxides, and hydroxides of magnesium and aluminum on the surface of the plating layer 103 are defined.

Here, in addition to metals such as magnesium and aluminum, oxides, hydroxides, and the like, various unintended impurities may exist on the surface of the plating layer 103. Therefore, in this embodiment, as schematically shown in FIG. The state is determined to be the state of these substances on the surface of the plating layer 103.

The state analysis of metals, oxides, and hydroxides of magnesium and aluminum is determined by X-ray Photoelectron Spectroscopy (XPS). For XPS analysis, Quantum 2000 model manufactured by ULVAC-PHI was used, X-ray source: Al Kα, X-ray output 15 kV, 25 W, measurement area: 300 x 300 μm square, degree of vacuum: 1.5 x 10 ^-9 Torr (1 Torr is , approximately 133.3 Pa), detection accuracy: 45 ^o . Further, sputtering for depth profile analysis is performed using ion species: Ar ⁺ , acceleration voltage: 1 kV, area: 1×1 mm, and sputtering rate: 2.7 nm/min (SiO ₂ equivalent). Sputtering is performed based on the above sputtering rate, and the position specified by this sputtering is regarded as the above-mentioned "position A".

Here, the attribution separation of the ratio (abundance ratio) between magnesium oxides and hydroxides and magnesium metal is determined from the narrow spectrum in the region of 295 to 325 cm ^-1 by Mg KLL. Calculated from the intensity ratio of peaks attributed to (oxides, metals). Similarly, the attribution separation of the proportions (abundance ratios) of aluminum oxides and hydroxides and metallic aluminum can be determined from the narrow spectrum of Al 2p in the 68 to 84 cm ^-1 region. Calculated from the intensity ratio of peaks attributed to (oxides, metals).

In the plating layer 103 according to the present embodiment, the ratio of magnesium oxide and hydroxide at a depth of 10 nm from the surface of the plating layer (position A in FIG. 2), which was specified as described above, is The ratio of magnesium is 2.0 or more. When the ratio of magnesium oxide and hydroxide to metal magnesium is 2.0 or more, the pre-coated plated steel plate using the plated steel plate 10 for pre-coated steel plate having the plating layer 103 according to the present embodiment is squeezed. Even during processing, good coating film adhesion is achieved in the molded parts, making it possible to suppress the occurrence of coating film floating parts. On the other hand, if the abundance ratio of the magnesium oxide and hydroxide is less than 2.0, good coating film adhesion cannot be achieved in the molded part, and floating parts of the coating film may occur. cannot be suppressed. The proportion of magnesium oxide and hydroxide relative to magnesium metal is preferably 4.0 or more, more preferably 6.0 or more. Moreover, the upper limit value of the abundance ratio of magnesium oxides and hydroxides to metal magnesium is substantially about 10.0.

Furthermore, in the plating layer 103 according to the present embodiment, the ratio of aluminum oxide and hydroxide at a depth of 10 nm from the surface of the plating layer (position A in FIG. 2), which was specified as described above, is , is preferably 1.3 or more relative to the proportion of metal aluminum. When the pre-coated plated steel plate using the plated steel plate 10 having the plated layer 103 according to the present embodiment is drawn, the ratio of aluminum oxide and hydroxide to metal aluminum is 1.3 or more. Even if it is, better paint film adhesion in the molded part is achieved, and it becomes possible to more reliably suppress the occurrence of paint film floating parts. On the other hand, if the proportion of the aluminum oxide and hydroxide is less than 1.3, it may not be possible to achieve better coating film adhesion in the molded part. The ratio of aluminum oxide and hydroxide to metal aluminum is more preferably 1.4 or more, and even more preferably 2.0 or more. Further, the upper limit of the proportion of aluminum oxides and hydroxides relative to metal aluminum is substantially approximately 10.0.

Here, the measurement by XPS is performed on a region having a size of 300 μm×300 μm. Moreover, the abundance ratio calculated as described above means a value as an average in the measurement area as described above.

In addition, in the plated steel sheet 10 according to the present embodiment, as long as the above relationship regarding magnesium is established in the plating layer 103, it is possible to exhibit good coating film adhesion in the formed portion. This is because magnesium has a lower standard electrode potential than aluminum, so corrosion progresses more easily, and further suppressing corrosion of magnesium is effective in increasing paint film adhesion in molded parts. .

The plated steel sheet 10 for prepainted steel sheets according to the present embodiment has been described in detail above with reference to FIGS. 1A to 2.

The plated steel sheet 10 for pre-painted steel sheet according to the present embodiment as explained above can be manufactured, for example, as follows. First, the surface of the prepared steel plate 101 is subjected to pretreatment such as cleaning and degreasing as necessary. Thereafter, a plating layer is formed by applying a normal non-oxidation furnace hot-dip plating method to the steel plate 101 which has been pretreated as necessary.

Subsequently, the steel plate on which the plating layer has been formed is subjected to a post-treatment step using at least one of acid treatment, alkali treatment, and mechanical cutting treatment. This modifies the surface of the plating layer or removes the surface of the plating layer, thereby satisfying the conditions regarding the XPS spectrum mentioned above.

Here, a hot-dip galvanizing bath having desired chemical components (i.e., contains at least 0.5 to 60.0% by mass of Al, 0.5 to 15.0% by mass of Mg, and the balance is Zn and A hot-dip galvanizing bath (containing impurities) is prepared, and the temperature of the plating bath is controlled to about 450°C. Thereafter, the obtained steel plate 101 is immersed in a plating bath, and hot-dip galvanizing is applied to the surface of the steel plate so as to have a desired average film thickness. Thereafter, the cooling rate after plating is controlled to 10° C./second or more. Thereby, a plating layer can be formed.

The plating layer obtained as described above was subjected to various methods such as acid treatment, alkali treatment, mechanical cutting treatment, etc. while measuring the XPS spectrum with an XPS analyzer set to the above measurement conditions. The surface of the plating layer is modified or removed until the conditions regarding the XPS spectrum mentioned earlier are satisfied. Thereby, the plated steel sheet 10 for pre-coated steel sheet according to this embodiment, which has the plating layer 103 as described above, can be manufactured.

Here, any alkali treatment, acid treatment, or mechanical cutting treatment may be applied, or various combinations of these treatments may be used.

For example, when performing alkali treatment, the higher the alkali concentration and the longer the treatment time, the higher the proportion of magnesium oxides and hydroxides on the surface of the plating layer tends to be. For example, when spraying at 50°C using a commercially available standard sodium orthosilicate degreasing solution (medium alkaline type) as an alkaline treatment, if the spraying time is less than about 10 seconds, magnesium on the surface of the plating layer will oxidize. Although the proportions of substances and hydroxides cannot satisfy the specified conditions, increasing the spraying time will make them meet the conditions, and increasing the spray time to about 2 minutes will definitely satisfy the conditions. Furthermore, if the concentration of this degreasing liquid is doubled, the conditions will be reliably met in about 30 seconds. Although the reason is not clear, it is thought that the metal magnesium component may be dissolved by the alkali treatment, changed to an oxide or hydroxide, and redeposited on the plating surface.

Furthermore, when acid treatment is performed, for example, such treatment exhibits the effect of removing magnesium oxides and hydroxides on the surface of the plating layer, unlike alkali treatment. Therefore, specified conditions can be obtained by processing under conditions that are weak enough to remove dirt components adhering to the plating surface. For example, when using 5% sulfuric acid and spraying at 50°C, by setting the spraying time to about 5 to 10 seconds, the abundance ratio of magnesium oxides and hydroxides on the surface of the plating layer can be adjusted to the specified conditions. can be fulfilled. However, if sprayed for a longer period of time, the conditions will no longer be met.

Furthermore, when mechanical cutting treatment is performed, for example, such treatment exhibits the effect of removing metallic magnesium, oxides, and hydroxides on the surface of the plating layer. Therefore, it is preferable to use a nylon brush or a grindstone with an appropriate particle size to perform the treatment under conditions that are weak enough to remove dirt components attached to the plating surface. After the mechanical cutting process, wash with water to remove cutting dirt.

Examples of various treatment methods have been described above, but the conditions for each treatment also change depending on the initial oxidation state of the plating layer of the steel sheet used. Therefore, the plated steel sheet 10 for pre-painted steel sheet according to the present embodiment may be manufactured by appropriately selecting optimal conditions.

(About pre-painted plated steel sheets)
Next, a prepainted plated steel sheet using the plated steel sheet 10 for prepainted steel sheets as described above will be described in detail with reference to FIGS. 3A to 4.

As schematically shown in FIG. 3A, the prepainted plated steel sheet 20 according to the present embodiment uses the plated steel sheet 10 for prepainted steel sheets as described above as a base material. The pre-coated plated steel sheet 20 includes a steel sheet 101, a plating layer 201 located on one side of the steel sheet 101, a chemical conversion coating 203 located on the plating layer 201, and a coating film 205 located on the chemical conversion coating 203. have. Further, in the pre-coated plated steel sheet 20 according to the present embodiment, a plating layer 201, a chemical conversion film 203, and a coating film 205 may be formed on both sides of the steel sheet 101, as schematically shown in FIG. 3B.

Here, the steel plate 101 in the pre-coated plated steel plate 20 according to the present embodiment has the same configuration as the steel plate 101 in the plated steel plate 10 for pre-coated steel plate described previously, and has the same effects. Therefore, detailed explanation will be omitted below.

Further, regarding the plating layer 201 in the pre-coated plated steel sheet 20 according to the present embodiment, as the chemical conversion film 203 described below is formed, atoms, etc. contained in each layer near the interface between the plating layer 201 and the chemical conversion film 203 are Mutual diffusion etc. may occur. However, the average chemical composition of the plating layer 201 is the same as that of the plating layer 103 in the plated steel sheet 10 for pre-coated steel sheet described above, and the same effect is achieved. Therefore, detailed explanation will be omitted below.

Note that the states of metals, oxides, and hydroxides of magnesium and aluminum, which are represented by the plating layer 201 of the pre-coated plated steel sheet 20 according to the present embodiment, will be described below.

<About chemical conversion coating 203>
The chemical conversion film 203 according to the present embodiment is a film layer located on the plating layer 201, and removes impurities such as oil and surface oxides adhering to the surface of the plated steel sheet 10 for pre-coated steel sheets using a known degreasing process and cleaning process. This is a layer formed by chemical conversion treatment after removal in the process.

The chemical conversion coating 203 according to the present embodiment is made of any one selected from the group consisting of resin, silane coupling agent, zirconium compound, silica, phosphoric acid and its salt, fluoride, vanadium compound, and tannin or tannic acid. It may contain one or more. Containing these substances further improves the film formability after application of the chemical conversion treatment solution, the barrier properties (denseness) of the film against corrosion factors such as moisture and corrosive ions, and the adhesion of the film to the plated surface. This contributes to improving the corrosion resistance of the film.

In particular, when the chemical conversion coating 203 contains one or more of a silane coupling agent or a zirconium compound, a crosslinked structure is formed within the coating 203 to strengthen the bond with the plating surface. As a result, it becomes possible to further improve the adhesion and barrier properties of the film.

Furthermore, if the chemical conversion coating 203 contains one or more of silica, phosphoric acid and its salts, fluoride, or vanadium compounds, these compounds function as an inhibitor, forming a precipitated coating on the plating or steel surface. Forms a passive film. As a result, it becomes possible to further improve corrosion resistance.

Below, details of each component that can be included in the chemical conversion film 203 as described above will be explained while giving examples.

[resin]
As the resin, for example, known organic resins such as polyester resin, polyurethane resin, epoxy resin, phenol resin, acrylic resin, polyolefin resin, etc. can be used. In order to further improve the adhesion with the plated steel sheet for pre-coated steel sheets, use at least one resin (polyester resin, urethane resin, epoxy resin, acrylic resin, etc.) that has a forced moiety or polar functional group in its molecular chain. It is preferable. The resins may be used alone or in combination of two or more.

The content of the resin in the chemical conversion coating 203 is preferably, for example, 0% by mass or more and 85% by mass or less based on the solid content of the coating. The resin content is more preferably 0% by mass or more and 60% by mass or less, and still more preferably 1% by mass or more and 40% by mass or less. When the content of the resin exceeds 85% by mass, the proportions of other coating components may decrease, and the performance required for the coating other than corrosion resistance may deteriorate.

[Silane coupling agent]
Examples of the silane coupling agent include γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, and γ-(2-aminoethyl)aminopropyltriethoxysilane. , γ-(2-aminoethyl)aminopropylmethyldiethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ- Methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl) -γ-aminopropylmethyldimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltriethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropylmethyldiethoxy Silane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane , γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, vinyltriacetoxysilane, γ-Chloropropyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltriethoxysilane, γ-chloropropylmethyldiethoxysilane, hexamethyldisilazane, γ-anilinopropyltrimethoxysilane, γ-aniline Linopropylmethyldimethoxysilane, γ-anilinopropyltriethoxysilane, γ-anilinopropylmethyldiethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, octadecyldimethyl [3 -(trimethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(methyldimethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(triethoxysilyl)propyl]ammonium chloride, octadecyldimethyl[3-(methyldiethoxy) silyl)propyl] ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, and the like. The amount of the silane coupling agent added in the chemical conversion treatment agent for forming the chemical conversion coating 203 can be, for example, 2 to 80 g/L. If the amount of the silane coupling agent added is less than 2 g/L, the adhesion to the plating surface may be insufficient and the processing adhesion of the coating film may be reduced. Furthermore, if the amount of the silane coupling agent added exceeds 80 g/L, the cohesive force of the chemical conversion coating may be insufficient and the processing adhesion of the coating may decrease. The silane coupling agents exemplified above may be used alone or in combination of two or more.

[Zirconium compound]
Examples of the zirconium compound include zirconium normal propylate, zirconium normal butyrate, zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium bisacetylacetonate, zirconium monoethylacetoacetate, zirconium acetylacetonate bisethylacetoacetate, Examples include zirconium acetate, zirconium monostearate, zirconium carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, and sodium zirconium carbonate. The amount of the zirconium compound added to the chemical conversion treatment agent for forming the chemical conversion coating 203 can be, for example, 2 to 80 g/L. If the amount of the zirconium compound added is less than 2 g/L, the adhesion to the plating surface may be insufficient and the processing adhesion of the coating film may be reduced. Further, if the amount of the zirconium compound added exceeds 80 g/L, the cohesive force of the chemical conversion coating may be insufficient, and the processing adhesion of the coating may decrease. Such zirconium compounds may be used alone or in combination of two or more.

[silica]
Examples of commercially available silica include "Snowtex N", "Snowtex C", "Snowtex UP", and "Snowtex PS" manufactured by Nissan Chemical Co., Ltd., and "Adelite AT-20Q" manufactured by ADEKA Co., Ltd. or powdered silica such as Aerosil #300 manufactured by Nippon Aerosil Co., Ltd. can be used. Silica can be selected as appropriate depending on the required performance of the precoated plated steel sheet. The amount of silica added in the chemical conversion treatment agent for forming the chemical conversion coating 203 is preferably 1 to 40 g/L. If the amount of silica added is less than 1 g/L, the processing adhesion of the coating film may decrease, and if the amount of silica added exceeds 40 g/L, the effect of processing adhesion and corrosion resistance may be reduced. It is uneconomical because there is a high possibility that the amount of electricity will be saturated.

[Phosphoric acid and its salts]
Examples of phosphoric acid and its salts include phosphoric acids and their salts such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid; ammonium salts such as triammonium phosphate and diammonium hydrogen phosphate; Phosphonic acids such as aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid) and their salts, organic phosphoric acids such as phytic acid and salts thereof. Note that examples of salts of phosphoric acid other than ammonium salts include metal salts with Na, Mg, Al, K, Ca, Mn, Ni, Zn, Fe, and the like. Phosphoric acid and its salts may be used alone or in combination of two or more.

The content of phosphoric acid and its salts is preferably 0% by mass or more and 20% by mass or less based on the solid content of the film. When the content of phosphoric acid and its salt exceeds 20% by mass, the film becomes brittle, and the processing adhesion of the film when forming the pre-coated plated steel sheet may decrease. The content of phosphoric acid and its salt is more preferably 1% by mass or more and 10% by mass or less.

[Fluoride]
Examples of the fluoride include zircon ammonium fluoride, ammonium silicofluoride, titanium ammonium fluoride, sodium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, titanium hydrofluoride, zircon hydrofluoride, and the like. . Such fluorides may be used alone or in combination of two or more.

The content of fluoride is preferably 0% by mass or more and 20% by mass or less based on the solid content of the film. If the fluoride content exceeds 20% by mass, the coating may become brittle and the processing adhesion of the coating during forming of the pre-coated plated steel sheet may be reduced. The content of fluoride is more preferably 1% by mass or more and 10% by mass or less.

[Vanadium compound]
Examples of vanadium compounds include vanadium compounds obtained by reducing pentavalent vanadium compounds such as vanadium pentoxide, metavanadate, ammonium metavanadate, sodium metavanadate, and vanadium oxytrichloride to divalent to tetravalent vanadium compounds with a reducing agent, and vanadium trioxide. , vanadium dioxide, vanadium oxysulfate, vanadium oxyoxalate, vanadium oxyacetylacetonate, vanadium acetylacetonate, vanadium trichloride, phosphovanadomolybdic acid, vanadium sulfate, vanadium dichloride, vanadium oxide, etc. with an oxidation number of 4 to 2. Examples include vanadium compounds. Such vanadium compounds may be used alone or in combination of two or more.

The content of the vanadium compound is preferably 0% by mass or more and 20% by mass or less based on the solid content of the film. When the content of the vanadium compound exceeds 20% by mass, the coating becomes brittle, and the processing adhesion of the coating when forming the pre-coated plated steel sheet may decrease. The content of the vanadium compound is more preferably 1% by mass or more and 10% by mass or less.

[Tannin or tannic acid]
As the tannin or tannic acid, either a hydrolyzable tannin or a condensed tannin can be used. Examples of tannins and tannic acids include hameta tannin, pentad tannin, gallic tannin, myrobalan tannin, zibijibi tannin, algarobilla tannin, valonia tannin, catechin, and the like. The amount of tannin or tannic acid added in the chemical conversion treatment agent for forming the chemical conversion coating 203 can be 2 to 80 g/L. If the amount of tannin or tannic acid added is less than 2 g/L, the adhesion to the plating surface may be insufficient and the processing adhesion of the coating film may be reduced. In addition, if the amount of tannin or tannic acid added exceeds 80 g/L, the cohesive force of the chemical conversion coating may be insufficient, leading to a decrease in the processing adhesion of the coating. be.

Further, an acid, an alkali, or the like may be added to the chemical conversion treatment agent for forming the chemical conversion coating 203 to adjust the pH within a range that does not impair performance.

The chemical conversion treatment agent containing the various components described above is applied to one or both sides of the plated steel sheet 10 for pre-coated steel sheet, and then dried to form the chemical conversion film 203. In the pre-coated steel sheet according to the present embodiment, it is preferable that a chemical conversion film of 10 to 1000 mg/m ² per side be formed on the plated steel sheet for pre-coated steel sheet. The adhesion amount of the chemical conversion coating 203 is more preferably 20 to 800 mg/m ² , most preferably 50 to 600 mg/m ² . Note that the thickness of the chemical conversion film 203 corresponding to this amount of adhesion (thickness d2 in FIGS. 3A and 3B) is approximately 0.01 to 1 μm, although it depends on the components contained in the chemical conversion agent.

<About the coating film 205>
The coating film 205 according to this embodiment is a layer formed on the chemical conversion treatment film 203 as described above. The coating film 205 may be composed of a single layer as schematically shown in FIGS. 3A and 3B, or may be composed of two or more layers.

Here, when the coating film 205 is composed of two or more layers, the coating film in contact with the chemical conversion coating film 203 is also called a primer coating film, and the coating film 205 as a whole and the chemical conversion coating film 203 are It is often provided to ensure adhesion and corrosion resistance. On the other hand, a coating film located above the primer coating film is also called a top coating film, and is often provided for the purpose of securing design properties, barrier properties, and other surface functionality through coloring.

Further, when the coating film 205 is composed of a single layer, the coating film 205 is often provided so as to exhibit at least one of the functions exhibited by the primer coating film and the top coating film described above.

Such coating film 205 contains at least resin. Moreover, it is preferable that the coating film 205 further contains a pigment. In addition to these components, the coating film 205 may contain various additives such as a leveling agent, an antifoaming agent, a coloring agent, a viscosity modifier, and an ultraviolet absorber. Note that the coating liquid for forming the coating film 205 is preferably obtained by dispersing or dissolving each of the above components in a solvent.

Below, in order to explain in more detail the structure of the coating film 205 according to the present embodiment, for convenience, the case where the coating film 205 is composed of a primer coating film and a top coating film will be taken as an example. Explain.

[Primer coating film]
An appropriate base paint for the primer coating may be selected depending on the usage environment and application of the precoated plated steel sheet. As the type of resin for the base paint, generally known resins can be used. Examples of such resins include polyacrylic resins, polyolefin resins, polyurethane resins, epoxy resins, polyester resins, polybutyral resins, melamine resins, silicone resins, fluororesins, acrylic resins, etc. These resins can be used alone or in combination. Further, these resins can be cured with any curing agent. The base paint can be used in any form such as organic solvent-based, water-based, or powder-based.

It is preferable that such a base paint contains a rust preventive pigment, and it is particularly preferable that it contains a chromate-free rust preventive pigment. The chromate-free antirust pigments in the base paint include calcium ion exchange silica (sometimes referred to as calcium silicate), aluminum tripolyphosphate, phosphorus vanadium pigment (PV pigment), zinc phosphate, iron phosphate, Aluminum phosphate, calcium molybdate, aluminum molybdate, barium molybdate, vanadium oxide, water-dispersed silica, fumed silica, orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, hypophosphoric acid, phosphorous acid, hypophosphorous acid, and these You can use salt, etc. The content of such antirust pigment is preferably, for example, 5 to 70% by mass based on the solid content of the coating film. If the content of the anti-rust pigment is less than 5% by mass, there is a possibility that corrosion-resistant hardening may not be sufficiently ensured, and the rigidity and cohesive force of the coating film will decrease, causing the paint plating to deteriorate. When the coating surface rubs against a mold during press working of a steel plate, coating peeling (that is, coating scratching as physical peeling) may easily occur. Moreover, when the content of the rust-preventing pigment exceeds 70% by mass, processability may decrease. From the viewpoint of the balance between corrosion resistance, chemical resistance, and processability, the content of the rust preventive pigment is more preferably 15 to 70% by mass, and even more preferably 20 to 50% by mass.

As the curing agent, it is preferable to use amino resins such as melamine resins, urea resins, and benzoguanamine resins, or isocyanate compounds and blocks thereof. The mass ratio of the curing agent and the resin in the dry coating film is preferably 5 to 30 parts by mass of the curing agent per 100 parts by mass of the total amount of the resin and the curing agent. If the amount of curing agent is less than 5 parts by mass, adhesion and corrosion resistance may not be sufficiently exhibited, and if it is more than 30 parts by mass, processability and chemical resistance may be reduced. be.

The thickness of the primer coating film before forming is generally 2 μm or more and 10 μm or more for a precoated plated steel sheet. Also in this embodiment, the thickness of the primer coating film is preferably 2 to 10 μm. If the thickness of the primer coating film is less than 2 μm, there is a possibility that functions such as corrosion resistance required for a precoated plated steel sheet cannot be sufficiently exhibited. On the other hand, if the thickness of the primer coating exceeds 10 μm, the processability of the coating may decrease.

After applying a primer coating composition containing the components constituting the primer coating film as described above, it is baked at a temperature of 150° C. or higher and lower than 300° C. to cure and dry. If the baking temperature is less than 150°C, it may not be possible to ensure sufficient adhesion, and if the baking temperature is 300°C or higher, thermal deterioration of the resin component may occur, resulting in reduced workability. There is sex.

The primer coating composition as described above can be applied by generally known coating methods such as roll coating, curtain flow coating, air spraying, airless spraying, dipping, bar coating, and brush coating.

[Top coating]
The base paint for the top coating film may be selected appropriately depending on the usage environment and application of the precoated plated steel sheet. As the type of resin for the base paint, generally known resins can be used. Examples of such resins include polyacrylic resins, polyolefin resins, polyurethane resins, epoxy resins, polyester resins, polybutyral resins, melamine resins, silicone resins, fluororesins, acrylic resins, etc. These resins can be used alone or in combination. Further, these resins can be cured with any curing agent. The base paint can be used in any form such as organic solvent-based, water-based, or powder-based. The resin contained in the base paint of the top coat may be the same type as the resin contained in the base paint of the primer coat, or may be different. However, in consideration of the adhesion between the primer coating film and the top coating film, it is preferable to use the same kind of primer coating film and top coating film.

In applications where moldability is more demanding, the base coating preferably contains a high-molecular polyester resin and a curing agent. The polymeric polyester resin can be selected depending on the use of the precoated plated steel sheet, and any polymeric polyester resin commonly used as a solvent-based paint can be used. It is preferable that such a high-molecular polyester resin is a high-molecular polyester resin in which the main resin is constituted by ester bonds of two or more types of resin monomers.

As the curing agent used to form a thermosetting resin coating film by reaction with the above polymeric polyester resin, amino resins such as melamine resins, urea resins, benzoguanamine resins, or isocyanate compounds and blocks thereof are used. be able to. The mass ratio of the curing agent and the resin in the dry coating film is preferably such that the amount of the curing agent is 10 to 35 parts by mass per 100 parts by mass of the total amount of the resin and the curing agent. If the amount of the curing agent is less than 10 parts by mass, it may not be possible to sufficiently ensure adhesion, corrosion resistance, solvent resistance, etc., and if it exceeds 35 parts by mass, the processability, chemical resistance, impact resistance, etc. performance may decrease.

In addition, the top coating film further contains additives such as pigments, surface-modified metal powders and glass powders, dispersants, leveling agents, waxes, aggregates, fluororesin beads, and diluting solvents, as necessary. be able to.

The thickness of the top coating film before molding is preferably within the range of 5 to 25 μm, for example. When the top coating film is composed of a plurality of layers, the total film thickness is preferably within the range of 5 to 25 μm.

After the coating composition for the top coating film is applied, it is baked at a temperature of 150°C or higher and lower than 300°C to cure and dry. If the baking temperature is less than 150°C, the adhesion of each coating film may not be sufficiently ensured, and if the baking temperature is 300°C or more, the resin components such as polyester resin components may not be fully secured. Heat deterioration may occur and processability may decrease.

The top paint can be applied by generally known coating methods such as roll coating, curtain flow coating, air spraying, airless spraying, dipping, bar coating, and brush coating.

The chemical conversion coating, primer coating, and top coating according to this embodiment have been described above using the chemical conversion treatment agents and coating compositions used to form the respective films. Normally, when these treatment agents and compositions are applied to a plated steel sheet, these components and the composition of the film formed are usually different. For example, with chemical conversion treatment agents, the composition of the chemical conversion treatment film after application differs due to reactions with plated steel sheets, volatilization of volatile components in the chemical conversion treatment agent, etc. Determining the composition of the coating layer is usually technically difficult. Furthermore, it is actually technically difficult to specify the composition of such a chemical conversion film layer by means of instrumental analysis or the like. This also applies to the primer coating and top coating. Therefore, in this embodiment, the chemical conversion coating, primer coating, and top coating to be formed are specified by specifying the composition of the chemical conversion treatment agent and coating composition.

<State of magnesium and aluminum at the plating layer interface>
Based on the knowledge explained above, in the pre-coated plated steel sheet 20 according to the present embodiment, metals such as magnesium and aluminum, oxides and Specifies the state of hydroxide.

Here, in this embodiment, as schematically shown in FIG. 4, "position B" is located at a depth of 10 nm from the interface between the plating layer 201 and the chemical conversion coating 203 toward the inside of the plating layer 201. In this step, the states of metals, oxides, and hydroxides of magnesium and aluminum are specified, and the states of these substances at the interface of the plating layer 201 are determined.

In this embodiment, the position of the interface between the plating layer 201 and the chemical conversion coating 203 can be identified from the element profile in the depth direction of the pre-coated plated steel sheet, which is obtained by analyzing the pre-coated plated steel plate by XPS. That is, in this embodiment, an element contained in the chemical conversion coating 203 is used as a marker, and a point where the intensity of the marker element is halved in the depth direction is defined as the interface between the plating layer 201 and the chemical conversion coating 203. .

Here, the XPS measurement conditions for depth profile analysis and the measurement conditions for state analysis of metals, oxides and hydroxides of magnesium and aluminum are the XPS measurement conditions for the plated steel sheet 10 for pre-painted steel sheet shown previously. The measurement conditions are the same as those for .

That is, the state analysis of metals, oxides, and hydroxides of magnesium and aluminum is specified by XPS. For XPS analysis, Quantum 2000 model manufactured by ULVAC-PHI was used, X-ray source: Al Kα, X-ray output 15 kV, 25 W, measurement area: 300 x 300 μm square, degree of vacuum: 1.5 x 10 ^-9 Torr, detection accuracy. :45 ^o . Further, sputtering for depth profile analysis is performed using ion species: Ar ⁺ , acceleration voltage: 1 kV, area: 1×1 mm, and sputtering rate: 2.7 nm/min (SiO ₂ equivalent). Sputtering is performed based on the above sputtering rate, and the position specified by this sputtering is regarded as the above-mentioned "position B".

Here, the attribution separation of the ratio (abundance ratio) between magnesium oxides and hydroxides and magnesium metal is determined from the narrow spectrum in the region of 295 to 325 cm ^-1 by Mg KLL. Calculated from the intensity ratio of peaks attributed to (oxides, metals). Similarly, the attribution separation of the proportions (abundance ratios) of aluminum oxides and hydroxides and metallic aluminum can be determined from the narrow spectrum of Al 2p in the 68 to 84 cm ^-1 region. Calculated from the intensity ratio of peaks attributed to (oxides, metals).

At the interface of the plating layer 201 according to this embodiment, the ratio of magnesium oxide and hydroxide at a depth of 10 nm from the interface of the plating layer (position B in FIG. 4), which was specified as described above, is , is 0.30 or less relative to the proportion of metallic magnesium. Since the ratio of magnesium oxides and hydroxides to metal magnesium is 0.30 or less, even when the pre-coated plated steel sheet 20 according to the present embodiment is drawn, the formed portion remains in good condition. As a result, excellent paint film adhesion is achieved, making it possible to suppress the occurrence of raised parts of the paint film. On the other hand, if the abundance ratio of the magnesium oxide and hydroxide exceeds 0.30, good coating film adhesion cannot be achieved in the molded part, and the occurrence of coating film floating parts may occur. It cannot be suppressed. The proportion of magnesium oxide and hydroxide relative to magnesium metal is preferably 0.25 or less, more preferably 0.20 or less. Further, the lower limit of the ratio of magnesium oxide and hydroxide to metal magnesium is substantially about 0.01.

Further, at the interface of the plating layer 201 according to the present embodiment, aluminum oxide and hydroxide are present at a depth of 10 nm from the interface of the plating layer (position B in FIG. 4), which was identified as described above. The ratio is preferably 0.30 or less to the ratio of metal aluminum. Since the ratio of aluminum oxides and hydroxides to metal aluminum is 0.30 or less, even when the pre-coated plated steel sheet 20 according to the present embodiment is drawn, the forming part is less Good paint film adhesion is achieved, making it possible to more reliably suppress the occurrence of raised parts of the paint film. On the other hand, if the proportion of the aluminum oxide and hydroxide exceeds 0.30, it may not be possible to achieve better coating film adhesion in the molded part. The ratio of aluminum oxide and hydroxide to metal aluminum is more preferably 0.25 or less, and even more preferably 0.20 or less. Further, the lower limit of the ratio of aluminum oxide and hydroxide to metal aluminum is substantially about 0.01.

Here, the measurement by XPS is carried out on a region of size 300 μm x 300 μm, and the abundance ratio calculated as above is the average value in the measurement region as described above. It means.

The prepainted plated steel sheet 20 according to the present embodiment has been described in detail above with reference to FIGS. 3A to 4.

(About molded products)
Next, with reference to FIG. 5, a molded product using the pre-coated plated steel sheet 20 as described above will be described in detail.

As an example is schematically shown in FIG. 5, the molded product 30 according to the present embodiment is produced by performing various processing such as deep drawing and square cylinder press processing on the pre-coated plated steel sheet 20 as described above. By applying it, it is molded into a desired shape.

Here, the average chemical composition of the plating layer of the molded product 30 according to the present embodiment is the same as that of the plating layer 201 of the original pre-coated plated steel sheet 20, and therefore 0.5 to 60.0 mass % aluminum and 0.5 to 15.0 mass % magnesium. Among these, it is preferable that the plating layer of the molded product 30 according to the present embodiment contains aluminum in an amount of 5% by mass to 15% by mass, and magnesium in a range of 2% by mass to 4% by mass. When the plating layer of the molded product 30 contains aluminum and magnesium in the above-mentioned contents, desired corrosion resistance can be more reliably achieved. Note that the remainder other than the aluminum and magnesium in the plating layer of the molded product 30 is elements derived from the external environment, zinc, and impurities.

Specific examples of the shape of the molded product 30 according to the present embodiment include various shapes of various parts, including articles that are mainly used outdoors, such as outdoor air conditioner units and water heaters. .

Various known methods can be employed as the processing method used to process the pre-coated plated steel sheet 20 according to the present embodiment into a molded product. Further, the processing conditions may be appropriately set depending on the processing method used, the shape of the molded product, etc.

The processing of the top plate of an outdoor unit of an air conditioner, which is an example of the above-mentioned molded product, can be said to be a difficult forming process for the pre-coated plated steel sheet 20. The degree of processing varies depending on the air conditioner manufacturer, but all use a type of high-speed square cylinder press to form the top plate of the outdoor unit. At the four corners of the top plate, there are compressed parts and stretched parts. When a general pre-coated plated steel sheet is used, the coating frequently peels off in the compression processed areas, and the coating often peels off in the stretched areas.

However, when the pre-coated plated steel sheet 20 according to the present embodiment is used as a material, the states of metals, oxides and hydroxides of magnesium and aluminum are appropriately controlled at the plating layer interface of the pre-coated plated steel plate 20. Therefore, it is possible to more reliably suppress the occurrence of paint film floating parts and paint film peeling.

<About measured values by SAICAS method>
In the molded product made of the pre-coated plated steel sheet according to the present embodiment, the peel strength obtained by measuring a specific portion by the SAICAS method and the peeling state in such a portion are defined.

In the molded product according to this embodiment, an example of which is schematically shown in FIG. The area where the increase is 5% or more (for example, the area surrounded by the broken line in Figure 5, where the thickness is d', the relationship (d'-d)/d≧0.05 holds true). This is the area where the plated steel sheet is compressed and expanded during processing, and the compression exceeds the expansion. Hereinafter, such a portion where the thickness increases by 5% or more will be referred to as a “compressed portion”. Such compressed areas are areas where the coating film tends to float in the molded product.

In the molded product according to this embodiment, in the part where the thickness of the pre-coated plated steel sheet has increased by 5% or more compared to before forming (i.e. the compressed part), the chemical conversion film and the paint film (the paint film is made of multiple layers) The peel strength between the primer coating film and the primer coating film is 1.00 kN/m or more on average, as measured by the SAICAS method. In addition, when such a compressed part is cut using the SAICAS method, less than 20% of the cut area becomes interfacial peeling, and the remaining cut area is within the coating film (if the coating film is composed of multiple layers) is a cohesive failure form (within the primer coating). If the compressed portion does not satisfy all of the conditions regarding peel strength and peel area as described above, the chemical conversion coating will be destroyed by the processing accompanied by compression, resulting in a decrease in adhesion. In addition, the internal stress of the paint film is caused by the stress at the interface between the chemical conversion film and the paint film (or the primer paint film if the paint film is composed of multiple layers) or the interface between the chemical conversion film and the plating layer. As a result, the coating film adhesion during compression processing is insufficient at the portion with the lowest adhesion strength, and coating film lifting occurs.

In addition, if the thickness of the pre-coated plated steel sheet in the molded product is increased by 5% or more compared to before molding, no significant difference due to the difference in percentage will be found in the measurement results using the SAICAS method.

In the molded article according to the present embodiment, the peel strength as determined by the SAICAS method is preferably 1.10 kN/m or more on average, and more preferably 1.20 kN/m or more. Note that the higher the upper limit value of the peel strength, the better. The upper limit of the above peel strength is substantially 1.5 kN/m.

In addition, regarding the cutting area of the compressed part of the molded product according to the present embodiment by the SAICAS method, the proportion of the part in an interfacial peeling state is preferably 15% or less, and more preferably 10% or less. . Note that the smaller the lower limit of the ratio of the portion in the interfacial peeling state, the better. The lower limit of the proportion of the portion in the form of interfacial peeling is substantially 0%.

[Measurement method of peel strength and peel form using SAICAS method]
The peel strength and peel form of a molded product of interest using a pre-coated plated steel sheet are measured by the SAICAS method as follows.
First, for the molded product of interest, identify three or more flat parts that are considered to be non-molded parts, and measure the total thickness of each flat part (including the plated steel plate of the substrate and the coating on the front and back surfaces) using a micrometer. Measure three times and calculate the average value. Such measurements are performed at a plurality of identified locations, and the average value between each location is further calculated. The average value between the plurality of locations obtained in this manner is defined as the thickness of the pre-coated plated steel sheet before molding (for example, the thickness d in FIG. 5) in the molded product of interest.

In addition, a measurement sample (approximately 20 mm x 20 mm or more in size) is cut out from a portion that is believed to have been subjected to various forming processes such as deep drawing, and smoothed using a steel plate straightener (leveler). The total thickness of the obtained measurement sample (including the plated steel plate of the substrate and the coating on the front and back surfaces) was measured using a microgauge, and the measured value and the thickness obtained as described above were measured using a microgauge. The increase ratio is calculated based on the thickness of the pre-coated steel sheet before forming. Among the increase ratios obtained in this manner, the portions exhibiting a value of 5% or more are defined as compressed portions of the molded article. In addition, in various molding processes including deep drawing, the upper limit of the value of the increase ratio as described above is about 11%.

For the compressed area identified in this way, the peel strength and peel form of the coating film are measured by cutting using a measuring device that can use the SAICAS method (for example, DN-GS model manufactured by Daipra Wintes). do. Note that the cutting direction in the SAICAS method is parallel to the edge line of the steel plate after drawing.

In addition, the value of the increase ratio calculated by the above method is determined within the above range by preparing a pre-coated plated steel plate before and after forming, and applying a film remover from both sides of the pre-coated plated steel plate before and after forming. It has been confirmed that there is no difference when compared with the value calculated from the thickness of the substrate measured with the film removed.

The cutting conditions according to the SAICAS method are as follows.
A diamond blade (0.3 mm width) was used as a cutting knife, and the horizontal speed was 1 μm/sec. , vertical speed 0.1 μm/sec. After performing diagonal cutting in constant speed mode, switch to only horizontal movement near the interface, cut to a length of 200 μm, and measure the average peel strength during the horizontal movement. The depth position at which to switch to horizontal movement was determined by identifying the interface position (the last possible position without cutting the plating) through preliminary experiments. If the plating surface is cut due to the unevenness of the plating while the cutting knife is moving horizontally, the peel strength can be detected because the peel strength momentarily increases abnormally. Such cases are excluded as abnormal values and the average peel strength is calculated. Note that the number of measurements is n=3, and the average value of the three values of the average peel strength is defined as the peel strength.

The method for measuring the ratio of interfacial separation form and cohesive failure form in the cut portion during horizontal movement is as follows.
When the surface of the part cut by the SAICAS method is observed with an optical microscope, it is possible to clearly distinguish differences in the form of peeling from part to part. (A) If an extremely thin coating film remains on the cut portion, coloring due to the resin and pigment in the coating film can be seen, so it can be determined that the form of peeling is thin layer cohesive failure within the coating film. (B) When the cut portion has interfacial peeling, the appearance of the plated surface of the substrate is observed. Even when such a portion is irradiated with light, no strong reflection is observed, resulting in a blackish appearance. In the case of interfacial peeling, the fact that the peel strength obtained by the SAICAS method becomes locally low can also be used as a determining factor. This is because, although the cutting knife moves within the paint film directly above the interface, the adhesion force at the interface is lower than the cohesive force of the paint film, so the peeling position shifts to the interface, resulting in interfacial peeling. Because it does. (C) When the cut portion is a cohesive failure of the plating layer, a metallic luster is observed, and when light is irradiated to this portion, it is strongly reflected, so it is easy to distinguish it from interfacial peeling. In addition, the fact that the peel strength obtained by the SAICAS method becomes locally high can also be used as a criterion.

An optical microscope photograph was taken of the horizontal cutting area (size 300 μm x 200 μm) using the SAICAS method, and areas of cohesive failure of the coating film, interfacial peeling, and cohesive failure of the plating layer within the same area were identified using the above criteria. Then, measure their area using image processing software or transparent graph paper. Then, the ratio of the interfacial peeling area to the area excluding cohesive failure of the plating layer from the horizontal cutting range of the SAICAS method is calculated.

The molded product according to this embodiment has been described in detail above with reference to FIG.

As explained above, according to the present embodiment, by using the plated steel plate for pre-painted steel sheets according to the present embodiment, the pre-coated plated steel plate does not cause coating film floating portions or coating film peeling in processed parts such as drawing. A molded body made of a pre-coated steel plate can be obtained.

≪Second embodiment≫
(About plated steel sheets for pre-painted steel sheets)
First, a plated steel sheet for pre-painted steel sheet according to a second embodiment of the present invention will be described in detail with reference to FIGS. 1A to 2.

As schematically shown in FIG. 1A, the plated steel plate 10 for pre-coated steel plate according to the present embodiment includes a steel plate 101 serving as a base material, and a plating layer 103 located on one side of the steel plate. Further, in the plated steel plate 10 for pre-coated steel plate according to the present embodiment, the plating layer 103 may be located on both sides of the steel plate 101 serving as the base material, as schematically shown in FIG. 1B.

<About steel plate 101>
The steel plate 101 used as the base material of the plated steel plate 10 for pre-painted steel plate according to the present embodiment has the same configuration as the steel plate 101 in the plated steel plate 10 for pre-painted steel plate according to the first embodiment, and has the same effects. It is something. Therefore, detailed explanation will be omitted below.

<About the plating layer 103>
As schematically shown in FIGS. 1A and 1B, the plating layer 20 according to the present embodiment is a layer formed on at least one surface of the steel plate 101, and improves the corrosion resistance of the plated steel plate 10 for pre-coated steel plate. It is set up to make it happen. Here, the chemical composition of the plating layer 103 according to this embodiment is the same as that of the plating layer 103 in the plated steel sheet 10 for pre-coated steel sheet according to the first embodiment, and has the same effect. Therefore, detailed explanation will be omitted below.

[About the average film thickness of plating layer 103]
In addition, in the plated steel sheet 10 for pre-coated steel sheets according to the present embodiment, the average film thickness of the plating layer 103 (thickness d1 in FIGS. 1A and 1B) is also the same as that in the first embodiment, so a detailed description will be given below. is omitted.

<State of zinc on the surface of the plating layer>
Based on the knowledge explained above, in the plating layer 103 according to the present embodiment, the states of zinc metal, oxide, and hydroxide on the surface of the plating layer 103 are defined.

Here, in addition to zinc metal, oxide, hydroxide, etc., various unintended impurities may be present on the surface of the plating layer 103. Therefore, in this embodiment as well, as schematically shown in FIG. are determined to be the state of these substances on the surface of the plating layer 103.

The state analysis of zinc metal, oxide and hydroxide is determined by XPS. For XPS analysis, Quantum 2000 model manufactured by ULVAC-PHI was used, X-ray source: Al Kα, X-ray output 15 kV, 25 W, measurement area: 300 x 300 μm square, degree of vacuum: 1.5 x 10 ^-9 Torr, detection accuracy. :45 ^o . Further, sputtering for depth profile analysis is performed using ion species: Ar ⁺ , acceleration voltage: 1 kV, area: 1×1 mm, and sputtering rate: 2.7 nm/min (SiO ₂ equivalent). Sputtering is performed based on the above sputtering rate, and the position specified by this sputtering is regarded as the above-mentioned "position A".

Here, the attribution separation of the ratio (abundance ratio) between zinc oxides and hydroxides and metallic zinc is determined from the narrow spectrum of Zn 2p in the region of 480 to 515 cm ^-1 . Calculated from the intensity ratio of peaks attributed to (oxides, metals).

In the plating layer 103 according to the present embodiment, the ratio of zinc oxide and hydroxide at a depth of 10 nm from the surface of the plating layer (position A in FIG. 2), which was specified as described above, is The ratio of zinc is 7.0 or more. When the ratio of zinc oxides and hydroxides to metal zinc is 7.0 or more, the prepainted plated steel sheet using the plated steel sheet 10 for prepainted steel sheets having the plating layer 103 according to the present embodiment is squeezed. Even during processing, good coating film adhesion is achieved in the molded parts, making it possible to suppress the occurrence of coating film floating parts. On the other hand, if the proportion of zinc oxides and hydroxides is less than 7.0, good paint film adhesion cannot be achieved in the molded part, and floating parts of the paint film may occur. cannot be suppressed. The ratio of zinc oxide and hydroxide to metal zinc is preferably 8.0 or more, more preferably 9.0 or more. Further, the upper limit of the proportion of zinc oxide and hydroxide relative to metal zinc is substantially approximately 20.0.

Here, the measurement by XPS is carried out on a region of size 300 μm x 300 μm, and the abundance ratio calculated as above is the average value in the measurement region as described above. It means.

The plated steel sheet 10 for prepainted steel sheets according to the present embodiment has been described in detail above with reference to FIGS. 1A to 2.

The plated steel sheet 10 for pre-painted steel sheet according to the present embodiment as explained above can be manufactured, for example, as follows. First, the surface of the prepared steel plate 101 is subjected to pretreatment such as cleaning and degreasing as necessary. Thereafter, a plating layer is formed by applying a normal non-oxidation furnace hot-dip plating method to the steel plate 101 which has been pretreated as necessary.

Subsequently, the steel plate on which the plating layer has been formed is subjected to a post-treatment step using at least one of acid treatment, alkali treatment, and mechanical cutting treatment. This modifies the surface of the plating layer or removes the surface of the plating layer, thereby satisfying the conditions regarding the XPS spectrum mentioned above.

Here, a hot-dip galvanizing bath having desired chemical components (i.e., contains at least 0.5 to 60.0% by mass of Al, 0.5 to 15.0% by mass of Mg, and the balance is Zn and A hot-dip galvanizing bath (containing impurities) is prepared, and the temperature of the plating bath is controlled to about 450°C. Thereafter, the obtained steel plate 101 is immersed in a plating bath, and hot-dip galvanizing is applied to the surface of the steel plate so as to have a desired average film thickness. Thereafter, the cooling rate after plating is controlled to 10° C./second or more. Thereby, a plating layer can be formed.

The plating layer obtained as described above was subjected to various methods such as acid treatment, alkali treatment, mechanical cutting treatment, etc. while measuring the XPS spectrum with an XPS analyzer set to the above measurement conditions. The surface of the plating layer is modified or removed until the conditions regarding the XPS spectrum mentioned earlier are satisfied. Thereby, the plated steel sheet 10 for pre-coated steel sheet according to this embodiment, which has the plating layer 103 as described above, can be manufactured.

Here, any alkali treatment, acid treatment, or mechanical cutting treatment may be applied, or various combinations of these treatments may be used.

For example, when performing alkali treatment, the higher the alkali concentration and the longer the treatment time, the higher the proportion of zinc oxides and hydroxides on the surface of the plating layer tends to be. For example, when spraying at 50°C using a standard commercially available sodium orthosilicate degreasing solution (medium alkaline type) as an alkali treatment, if the spraying time is less than 10 seconds, the zinc on the surface of the plating layer will oxidize. Although the proportions of substances and hydroxides cannot satisfy the specified conditions, increasing the spraying time will make them meet the conditions, and increasing the spray time to about 2 minutes will definitely satisfy the conditions. Furthermore, if the concentration of this degreasing liquid is doubled, the conditions will be reliably met in about 30 seconds. Although the reason is not clear, it is thought that the metal zinc component may be dissolved by the alkali treatment, changed to an oxide or hydroxide, and redeposited on the plating surface.

Further, when performing acid treatment, for example, such treatment exhibits the effect of removing zinc oxides and hydroxides on the surface of the plating layer, unlike alkali treatment. Therefore, specified conditions can be obtained by processing under conditions that are weak enough to remove dirt components adhering to the plating surface. For example, when spraying 5% sulfuric acid at 50°C, by setting the spraying time to about 5 to 10 seconds, the proportion of zinc oxides and hydroxides on the surface of the plating layer can be adjusted to the specified conditions. can be fulfilled. However, if sprayed for a longer period of time, the conditions will no longer be met.

Furthermore, when mechanical cutting treatment is performed, for example, such treatment exhibits the effect of removing metallic zinc, oxides, and hydroxides on the surface of the plating layer. Therefore, it is preferable to use a nylon brush or a grindstone with an appropriate particle size to perform the treatment under conditions that are weak enough to remove dirt components attached to the plating surface. After the mechanical cutting process, wash with water to remove cutting dirt.

Examples of various treatment methods have been described above, but the conditions for each treatment also change depending on the initial oxidation state of the plating layer of the steel sheet used. Therefore, the plated steel sheet 10 for pre-painted steel sheet according to the present embodiment may be manufactured by appropriately selecting optimal conditions.

(About pre-painted plated steel sheet)
Next, a prepainted plated steel sheet using the plated steel sheet 10 for prepainted steel sheets as described above will be described in detail with reference to FIGS. 3A to 4.

As schematically shown in FIG. 3A, the prepainted plated steel sheet 20 according to the present embodiment uses the plated steel sheet 10 for prepainted steel sheets as described above as a base material. The pre-coated plated steel sheet 20 includes a steel sheet 101, a plating layer 201 located on one side of the steel sheet 101, a chemical conversion coating 203 located on the plating layer 201, and a coating film 205 located on the chemical conversion coating 203. have. Further, in the pre-coated plated steel sheet 20 according to the present embodiment, a plating layer 201, a chemical conversion film 203, and a coating film 205 may be formed on both sides of the steel sheet 101, as schematically shown in FIG. 3B.

Here, the steel plate 101 in the pre-coated plated steel plate 20 according to the present embodiment has the same configuration as the steel plate 101 in the plated steel plate 10 for pre-coated steel plate described previously, and has the same effects. Therefore, detailed explanation will be omitted below.

Further, regarding the plating layer 201 in the pre-coated plated steel sheet 20 according to the present embodiment, as the chemical conversion film 203 described below is formed, atoms, etc. contained in each layer near the interface between the plating layer 201 and the chemical conversion film 203 are Mutual diffusion etc. may occur. However, the average chemical composition of the plating layer 201 is the same as that of the plating layer 103 in the plated steel sheet 10 for pre-coated steel sheet described above, and the same effect is achieved. Therefore, detailed explanation will be omitted below.

Note that the states of zinc metal, oxide, and hydroxide shown in the plating layer 201 of the pre-coated plated steel sheet 20 according to the present embodiment will be explained below.

<About chemical conversion coating 203>
The chemical conversion film 203 according to the present embodiment is a film layer located on the plating layer 201, and removes impurities such as oil and surface oxides adhering to the surface of the plated steel sheet 10 for pre-coated steel sheets using a known degreasing process and cleaning process. This is a layer formed by chemical conversion treatment after removal in the process.

The detailed structure of the chemical conversion coating 203 according to this embodiment is the same as that of the first embodiment, and produces the same effects. Therefore, detailed explanation will be omitted below.

<About the coating film 205>
The coating film 205 according to this embodiment is a layer formed on the chemical conversion treatment film 203 as described above. The coating film 205 may be composed of a single layer as schematically shown in FIGS. 3A and 3B, or may be composed of two or more layers. Here, the detailed structure of the coating film 205 according to the present embodiment is the same as that of the first embodiment, and the same effects can be achieved. Therefore, detailed explanation will be omitted below.

<State of zinc at the plating layer interface>
Based on the knowledge explained above, in the pre-coated plated steel sheet 20 according to the present embodiment, metal, oxide and hydroxide of zinc at the interface of the plating layer 201 (more specifically, the interface between the plating layer 201 and the chemical conversion coating 203). Define the state of things.

Here, in this embodiment, as schematically shown in FIG. 4, "Position B" is located at a depth of 10 nm from the interface between the plating layer 201 and the chemical conversion coating 203 toward the inside of the plating layer 201. In this step, the states of metal, oxide, and hydroxide of zinc are specified, and the states of these substances at the interface of the plating layer 201 are determined.

In this embodiment, the position of the interface between the plating layer 201 and the chemical conversion coating 203 can be identified from the element profile in the depth direction of the pre-coated plated steel sheet, which is obtained by analyzing the pre-coated plated steel plate by XPS. That is, in this embodiment, an element contained in the chemical conversion coating 203 is used as a marker, and a point where the intensity of the marker element is halved in the depth direction is defined as the interface between the plating layer 201 and the chemical conversion coating 203. .

Here, the XPS measurement conditions for depth profile analysis and the measurement conditions for zinc metal, oxide, and hydroxide state analysis are the XPS measurement on the plated steel sheet 10 for prepainted steel sheet shown previously. The conditions are the same.

That is, the state analysis of zinc metal, oxide, and hydroxide is specified by XPS. For XPS analysis, Quantum 2000 model manufactured by ULVAC-PHI was used, X-ray source: Al Kα, X-ray output 15 kV, 25 W, measurement area: 300 x 300 μm square, degree of vacuum: 1.5 x 10 ^-9 Torr, detection accuracy. :45 ^o . Further, sputtering for depth profile analysis is performed using ion species: Ar ⁺ , acceleration voltage: 1 kV, area: 1×1 mm, and sputtering rate: 2.7 nm/min (SiO ₂ equivalent). Sputtering is performed based on the above sputtering rate, and the position specified by this sputtering is regarded as the above-mentioned "position B".

Here, the attribution separation of the ratio (abundance ratio) between zinc oxides and hydroxides and metallic zinc is determined from the narrow spectrum of Zn 2p in the region of 480 to 515 cm ^-1 . Calculated from the intensity ratio of peaks attributed to (oxides, metals).

At the interface of the plating layer 201 according to the present embodiment, the ratio of zinc oxide and hydroxide at a depth of 10 nm from the interface of the plating layer (position B in FIG. 4), which was specified as described above, is , the ratio of metal zinc is 7.0 or more. Since the ratio of zinc oxides and hydroxides to metal zinc is 7.0 or more, even when the pre-coated plated steel sheet 20 according to the present embodiment is drawn, the formed portion is maintained in good condition. As a result, excellent paint film adhesion is achieved, making it possible to suppress the occurrence of raised parts of the paint film. On the other hand, if the proportion of zinc oxides and hydroxides is less than 7.0, good coating film adhesion cannot be achieved in the molded part, and floating parts of the coating film may occur. cannot be suppressed. The ratio of zinc oxide and hydroxide to metal zinc is preferably 8.0 or more, more preferably 9.0 or more. Further, the upper limit of the proportion of zinc oxide and hydroxide relative to metal zinc is substantially approximately 20.0.

Here, the measurement by XPS is carried out on a region of size 300 μm x 300 μm, and the abundance ratio calculated as above is the average value in the measurement region as described above. It means.

The prepainted plated steel sheet 20 according to the present embodiment has been described in detail above with reference to FIGS. 3A to 4.

(About molded products)
Next, with reference to FIG. 5, a molded product using the pre-coated plated steel sheet 20 as described above will be described in detail.

As an example is schematically shown in FIG. 5, the molded product 30 according to the present embodiment is produced by performing various processing such as deep drawing and square cylinder press processing on the pre-coated plated steel sheet 20 as described above. By applying it, it is molded into a desired shape.

Here, the average chemical composition of the plating layer of the molded product 30 according to the present embodiment is the same as that of the plating layer 201 of the original pre-coated plated steel sheet 20, and therefore 0.5 to 60.0 mass % aluminum and 0.5 to 15.0 mass % magnesium. Among these, it is preferable that the plating layer of the molded product 30 according to the present embodiment contains aluminum in an amount of 5% by mass to 15% by mass, and magnesium in a range of 2% by mass to 4% by mass. When the plating layer of the molded product 30 contains aluminum and magnesium in the above-mentioned contents, desired corrosion resistance can be more reliably achieved. Note that the remainder other than the aluminum and magnesium in the plating layer of the molded product 30 is elements derived from the external environment, zinc, and impurities.

Specific examples of the shape of the molded product 30 according to the present embodiment include various shapes of various parts, including articles that are mainly used outdoors, such as outdoor air conditioner units and water heaters. .

Various known methods can be employed as the processing method used to process the pre-coated plated steel sheet 20 according to the present embodiment into a molded product. Further, the processing conditions may be appropriately set depending on the processing method used, the shape of the molded product, etc.

The processing of the top plate of an outdoor unit of an air conditioner, which is an example of the above-mentioned molded product, can be said to be a difficult forming process for the pre-coated plated steel sheet 20. The degree of processing varies depending on the air conditioner manufacturer, but all use a type of high-speed square tube press to form the top plate of the outdoor unit. At the four corners of the top plate, there are compressed parts and stretched parts. When a general pre-coated plated steel sheet is used, the coating frequently peels off in the compression processed areas, and the coating often peels off in the stretched areas.

However, when the pre-coated plated steel sheet 20 according to the present embodiment is used as a material, the states of zinc metal, oxide and hydroxide are appropriately controlled at the plating layer interface of the pre-coated plated steel plate 20. In addition, it becomes possible to more reliably suppress the occurrence of paint film floating parts and paint film peeling.

<About measured values by SAICAS method>
In the molded product made of the pre-coated plated steel sheet according to the present embodiment, the peel strength obtained by measuring a specific portion by the SAICAS method and the peeling state in such a portion are defined. Here, since the measurement method using the SAICAS method and the conditions required for the obtained measurement values are the same as those described in the first embodiment, detailed explanations will be omitted below.

As explained above, according to the present embodiment, by using the plated steel plate for pre-painted steel sheets according to the present embodiment, the pre-coated plated steel plate does not cause coating film floating portions or coating film peeling in processed parts such as drawing. A molded body made of a pre-coated steel plate can be obtained.

≪Third embodiment≫
The third embodiment of the present invention described below focuses on both the state of zinc oxides and hydroxides on the surface of a galvanized steel sheet, and the state of aluminum and magnesium oxides and hydroxides on the surface of a galvanized steel sheet. This is an embodiment.

(About plated steel sheets for pre-painted steel sheets)
As schematically shown in FIG. 1A, the plated steel plate 10 for pre-coated steel plate according to the present embodiment includes a steel plate 101 serving as a base material, and a plating layer 103 located on one side of the steel plate. Further, in the plated steel plate 10 for pre-coated steel plate according to the present embodiment, the plating layer 103 may be located on both sides of the steel plate 101 serving as the base material, as schematically shown in FIG. 1B.

Here, the steel plate 101 used as the base material of the plated steel plate 10 for pre-painted steel plates according to the present embodiment has the same configuration as the steel plate 101 in the plated steel plate 10 for pre-painted steel plates according to the first embodiment and the second embodiment. It has similar effects. Therefore, detailed explanation will be omitted below.

Furthermore, regarding the plating layer 103, the differences from the first embodiment are the same as in the first embodiment, except that attention is paid to both the states of zinc oxides and hydroxides and the states of aluminum and magnesium oxides and hydroxides on the surface of the plated steel sheet. It has the same configuration as the plating layer 103 in the plated steel sheet 10 for pre-coated steel sheet according to the second embodiment, and has the same effects. Therefore, detailed explanation will be omitted below.

The method for analyzing the state of metals, oxides and hydroxides of aluminum and magnesium, and the state of zinc metals, oxides and hydroxides, and the conditions that the obtained analysis results must satisfy are described in Chapter 1. This is as described in the first embodiment and the second embodiment.

However, in this embodiment, at a depth of 10 nm from the surface of the plating layer 103 (i.e., position A in FIG. 2), the ratio of magnesium oxide and hydroxide is 2.0 to the ratio of metallic magnesium. In addition, the ratio of zinc oxide and hydroxide to the ratio of metal zinc is 7.0 or more.

By being in the above state, even when a pre-painted plated steel sheet using the plated steel sheet 10 for pre-painted steel sheet having the plating layer 103 according to the present embodiment is drawn, better coating in the forming part can be achieved. Film adhesion is achieved, making it possible to more reliably suppress the occurrence of floating parts of the paint film.

Further, the states of the oxides and hydroxides of magnesium and zinc are as described above, and the ratio of the oxides and hydroxides of aluminum is 1.3 or more to the ratio of metal aluminum. It is more preferable that By being in such a state, even when a pre-coated plated steel plate using the plated steel plate 10 having the plated layer 103 according to the present embodiment is drawn, even better coating film adhesion in the forming part is achieved. This makes it possible to more reliably suppress the occurrence of floating parts of the paint film.

The plated steel sheet 10 for prepainted steel sheets according to the present embodiment has been described in detail above with reference to FIGS. 1A to 2.

Such a plated steel sheet 10 for pre-painted steel sheet can be manufactured by the manufacturing method as explained in the first embodiment and the second embodiment.

Here, in particular, by performing alkali treatment after mechanical cutting treatment or acid treatment, the state of the plating layer in this embodiment can be more reliably realized. First, by performing mechanical cutting treatment or acid treatment, the plating surface is detached and a fresh new surface is generated. By performing alkali treatment in this state, zinc and magnesium oxides or This is thought to be due to redeposition of hydroxide onto the plating surface.

In addition, by first performing mechanical cutting treatment under light pressure conditions to selectively cut the convex portions of the uneven parts of the plating, and then performing alkali treatment, the proportion of aluminum oxides or hydroxides can be relatively reduced. It is possible to raise the This is because the surface of the convex parts of the plating has a high aluminum content, so the alkali treatment of the new surface of these areas increases the elution of aluminum, resulting in a high proportion of aluminum oxides or hydroxides. it is conceivable that.

Not limited to this example, by changing the order and conditions of mechanical cutting treatment, acid treatment, and alkali treatment, it is possible to vary the abundance ratio of zinc, magnesium, and aluminum oxides or hydroxides. .

(About pre-painted plated steel sheets)
Next, a prepainted plated steel sheet using the plated steel sheet 10 for prepainted steel sheets as described above will be described with reference to FIGS. 3A to 4.

As schematically shown in FIG. 3A, the prepainted plated steel sheet 20 according to the present embodiment uses the plated steel sheet 10 for prepainted steel sheets as described above as a base material. The pre-coated plated steel sheet 20 includes a steel sheet 101, a plating layer 201 located on one side of the steel sheet 101, a chemical conversion coating 203 located on the plating layer 201, and a coating film 205 located on the chemical conversion coating 203. have. Further, in the pre-coated plated steel sheet 20 according to the present embodiment, a plating layer 201, a chemical conversion film 203, and a coating film 205 may be formed on both sides of the steel sheet 101, as schematically shown in FIG. 3B.

Here, the steel plate 101 in the pre-coated plated steel plate 20 according to the present embodiment has the same configuration as the steel plate 101 in the plated steel plate 10 for pre-coated steel plate described previously, and has the same effects. Therefore, detailed explanation will be omitted below.

Further, regarding the plating layer 201 in the pre-coated plated steel sheet 20 according to the present embodiment, as the chemical conversion film 203 described below is formed, atoms, etc. contained in each layer near the interface between the plating layer 201 and the chemical conversion film 203 are Mutual diffusion etc. may occur. However, the average chemical composition of the plating layer 201 is the same as that of the plating layer 103 in the plated steel sheet 10 for pre-coated steel sheet described above, and the same effect is achieved. Therefore, detailed explanation will be omitted below.

Furthermore, the states of the metals, oxides and hydroxides of magnesium, aluminum, and zinc shown in the plating layer 201 of the pre-coated plated steel sheet 20 according to the present embodiment, and the method for measuring the same, are as described in the first embodiment and the second embodiment. As shown in the form.

Above the plating layer 201, a chemical conversion coating 203 and a coating film 205 are located. The detailed structure of the chemical conversion coating 203 according to this embodiment is the same as that of the first embodiment and the second embodiment, and provides the same effects. Therefore, detailed explanation will be omitted below. Moreover, the detailed structure of the coating film 205 according to this embodiment is the same as that of the first embodiment and the second embodiment, and the same effects are achieved. Therefore, detailed explanation will be omitted below.

The prepainted plated steel sheet 20 according to the present embodiment has been described above with reference to FIGS. 3A to 4.

(About molded products)
Next, with reference to FIG. 5, a molded product using the pre-coated plated steel sheet 20 as described above will be described.

As an example is schematically shown in FIG. 5, the molded product 30 according to the present embodiment is produced by performing various processing such as deep drawing and square cylinder press processing on the pre-coated plated steel sheet 20 as described above. By applying it, it is molded into a desired shape. Here, since the details of the molded product 30 are as described in the first embodiment and the second embodiment, detailed explanation will be omitted below.

As explained above, in this embodiment as well, by using the plated steel sheet for pre-painted steel sheet according to this embodiment, the pre-painted plated steel sheet and the plated steel sheet that do not cause coating film floating parts or coating film peeling in the processed parts such as drawing forming etc. A molded body made of a prepainted steel plate can be obtained.

Hereinafter, the plated steel sheet for pre-coated steel plates, the hard and soft pre-coated plated products, and the molded products according to the present invention will be specifically explained while showing Examples and Comparative Examples. The examples shown below are only examples of the plated steel plate for pre-painted steel plate, the pre-painted plated steel plate and the molded product according to the present invention, and the plated steel plate for pre-painted steel plate, the pre-painted plated steel plate and the molded product according to the present invention are as follows: The examples are not limited.

≪First test example≫
The first test example shown below is a test example regarding the plated steel sheet for pre-painted steel sheet, the pre-painted plated steel sheet, and the molded product according to the first embodiment.

(1. Plated steel sheet for pre-painted steel sheet)
The following five types of commercially available zinc-based plated steel plates were used as plated steel plates for pre-coated steel plates. By treating the plating layer of the following zinc-based plated steel sheet with various acid solutions and alkaline solutions while changing the treatment time, magnesium and The proportions of aluminum oxide and hydroxide were controlled.

A1: Zn-11%Al-3%Mg-0.2%Si hot-dip zinc alloy plated steel plate (plate thickness 0.60mm, coating weight 40g/m ² )
A2: Zn-6%Al-3%Mg hot-dip galvanized alloy plated steel plate (plate thickness 0.60mm, coating weight 40g/m ² )
A3: Zn-55%Al-2%Mg-1.6%Si hot-dip zinc alloy plated steel plate (plate thickness 0.35mm, coating weight 75g/m ² )
A4: Hot-dip galvanized steel plate (thickness 0.60 mm, coating weight 40 g/m ² )
A5: Zn-55%Al-1.6%Si hot-dip zinc alloy plated steel plate (plate thickness 0.35mm, coating weight 75g/m ² )

(2. Formation of chemical conversion coating)
The following was used as a coating composition for forming a chemical conversion film. In addition, the amount of each component added in each coating composition was adjusted so that it was within the range of the amount added previously described.

S1: Water-based coating composition consisting of tannic acid, silane coupling agent, silica fine particles, and polyester resin S2: Water-based coating composition consisting of silane coupling agent, phosphate, and acrylic resin S3: Silane coupling agent, fluorine Water-based coating composition consisting of titanic acid fluoride, zirconate fluoride, and urethane resin

The coating compositions S1 to S3 were bar-coated on the plated steel sheet for pre-coated steel sheet so as to have a predetermined dry coating weight, and then dried in a hot air oven at a metal surface temperature of 70° C. and air-dried.

In this test example, a two-layer type coating film consisting of a primer coating film and a top coating film was mainly created, and a single-layer type coating film consisting only of a top coating film without a primer coating film was also formed. .

(3-1. Formation of primer coating film)
The following coating composition was used to form the primer coating.

P1: Polyester/melamine resin curing composition (FLC641 manufactured by Nippon Paint Industrial Coatings Co., Ltd.)
P2: Polyester/isocyanate resin curing composition (FLC690 manufactured by Nippon Paint Co., Ltd.)
P3: Epoxy/melamine resin curing composition

After bar-coating the above P1 to P3 on the plated steel sheet for pre-coated steel sheet which has been subjected to the above chemical conversion treatment so as to have a predetermined dry film thickness (1 to 12 μm), the metal surface reached a temperature of 215°C in a hot air oven. It was dried.

(3-2. Formation of top coating film)
The following coating composition was used to form the top coating film.

T1: High molecular polyester/melamine resin curing composition (FLC7000 manufactured by Nippon Paint Co., Ltd.)
T2: Polyester/melamine resin curing composition (FLC100HQ manufactured by Nippon Paint Co., Ltd.)

The above T1 or T2 is bar coated on the plated steel plate for pre-coated steel plate on which the above primer coating has been formed so as to have a predetermined dry film thickness (4 to 30 μm), and then heated in a hot air oven to achieve a metal surface temperature of 230°C. It was dried.

(4. Ratio of oxides and hydroxides to metals of magnesium and aluminum)
The surface of the plated steel plate for pre-coated steel sheets before chemical conversion treatment and the interface of the plated steel plate for pre-coated steel plates after coating film formation were observed by X-ray photoelectron spectroscopy (XPS), and magnesium (Mg From the ratio of the sum of peak intensities of oxide and hydroxide components of 295 to 325 cm ^-1 region by KLL) and aluminum (68 to 84 cm ^-1 region by Al 2p) and the peak intensity of metal component, the ratio is calculated. was calculated.

Here, the measurement conditions of XPS and the sputtering rate in depth profile measurement were set as shown above.

The interface position between the chemical conversion film and the plating layer was determined by focusing on the depth profile of silicon in the depth direction of the pre-coated steel sheet using X-ray photoelectron spectroscopy, and found that the strength of silicon is halved in the depth direction. The location was determined to be the interface between the chemical conversion coating and the plating layer.

(5. Performance evaluation)
Using the pre-coated galvanized steel sheet produced by the above method, cylindrical cup drawing forming was performed, and the chemical conversion coating and primer coating were applied to the areas where the thickness of the plated steel sheet for pre-coated steel sheet increased by 5% or more compared to before forming. The interface of the film or the interface between the chemical conversion film and the plating layer was cut using the SAICAS method, and the peel strength and interfacial peel form were measured. The apparatus used in the SAICAS method is a DN-GS model manufactured by Daipra Wintes.

Note that the cylindrical cup drawing molding was carried out as follows.
The pre-coated plated steel plate obtained as described above is drawn into a cylindrical cup at a drawing ratio of 2.0 so that the surface to be measured is on the outside, and the vicinity of the end of the steel plate of the cylindrical body is cut with metal scissors or the like. After cutting out the steel plate to a sufficient size (approximately 20×20 mm or more), the steel plate was smoothed using a steel plate straightener (leveler). Among the obtained steel plate pieces, the parts where the thickness has increased by 5% or more compared to before forming were identified by the method explained earlier, and the peel strength and peeling form of the coating film in the identified parts were measured using the SAICAS method. It was cut and measured. Note that the cutting direction was parallel to the edge line of the steel plate after drawing and forming.

<Peel strength>
The cutting conditions according to SAICAS are as follows.
Using a diamond blade (0.3 mm width), perform diagonal cutting in constant speed mode with a horizontal speed of 1 μm/s and a vertical speed of 0.1 μm/s, then switch to only horizontal movement near the interface and cut to a length of 200 μm. Then, the average peel strength during horizontal movement was measured. The depth position at which to switch to horizontal movement was determined by identifying the interface position (the last possible position without cutting the plating layer) through preliminary experiments. If the plating surface is cut due to the unevenness of the plating while the cutting knife is moving horizontally, this can be determined because the peel strength momentarily increases abnormally. Such cases were excluded as abnormal values and the average peel strength was calculated. The number of measurements was n=3 in each case, and the average value of the three values of average peel strength was taken as the peel strength.

<Interfacial peeling form>
An optical microscope photograph of the SAICAS horizontal cutting range (300 x 200 μm) was taken, and the areas of primer cohesive failure, interfacial peeling, and plating cohesive failure within the same area were identified using the criteria described above, and their areas were calculated. Measurements were made using transparent graph paper. Then, from the horizontal cutting range of SAICAS, the ratio of the interfacial peeling area to the area excluding cohesive failure of the plating was calculated.

<Aluminum and magnesium content in the plating layer of the molded product>
The aluminum and magnesium contents of the plating layer of the molded product obtained as described above were measured by XPS (Quantum 2000 model manufactured by ULVAC-PHI).

<Paint film abnormality on the outdoor unit top plate processing area>
In addition, the obtained pre-coated plated steel sheet was separately actually pressed using a mold for the top plate of an outdoor air conditioner unit, and the presence or absence of paint film peeling and the state of paint film lifting were confirmed at the corners.

For evaluation, the compressed part of the processed part of the top plate corner is observed with a magnifying glass at 4 locations to confirm the presence or absence of paint film peeling, and the situation of paint film lifting is evaluated based on the average value of the 4 locations using the following ratings. did. Note that the following scores are for each corner.

5: No floating parts of the paint film 4: Several floating parts of the paint film 3: 10 or more raised parts of the paint film 2: 20 or more raised parts of the paint film 1: 20 or more raised parts of the paint film, and Peeling due to connection

The obtained results are summarized in Table 1 below.

In all examples, the ratio of oxide and hydroxide to the metal content of magnesium and aluminum on the surface of the plated plate before forming and the interface of the plated steel plate after painting, as well as the peel strength and peeling measured by SAICAS of the compressed part of the molded product. Since the shape met the standards, no lifting or peeling of the paint film was observed during actual processing of the top plate of the outdoor unit of the air conditioner.

On the other hand, the comparative examples are all about the ratio of oxide and hydroxide to the metal content of magnesium and aluminum on the surface of the plated plate before forming and the interface of the plated steel plate after painting, and the peeling by SAICAS of the compressed part of the molded product. Because the strength and form of peeling did not meet the standards, lifting and peeling of the paint film was observed during actual processing of the top plate of the outdoor air conditioner unit.

≪Second test example≫
The second test example shown below is a test example regarding the plated steel plate for pre-painted steel plate, the pre-painted plated steel plate, and the molded product according to the second embodiment.

(1. Plated steel sheet for pre-painted steel sheet)
A plated steel plate for pre-painted steel plate was prepared in the same manner as in the first test example.

(2. Formation of chemical conversion coating)
A chemical conversion coating was formed on the obtained plated steel sheet for pre-coated steel sheet in the same manner as in the first test example.

In this test example, a two-layer coating consisting of a primer coating and a top coating was mainly created, and a single-layer coating consisting of only a top coating without a primer coating was also formed. did.

(3-1. Formation of primer coating film)
A primer coating film was formed in the same manner as in the first test example above.

(3-2. Formation of top coating film)
A top coating film was formed in the same manner as in the first test example above.

(4. Ratio of oxide and hydroxide to metal of zinc)
The surface of the plated steel plate for pre-coated steel sheets before chemical conversion treatment and the interface of the plated steel plate for pre-coated steel plates after coating film formation were observed by X-ray photoelectron spectroscopy (XPS), and zinc (Zn The ratio was calculated from the ratio of the sum of the peak intensities of the oxide and hydroxide components (in the region of 480 to 515 cm ^-1 according to 2p) and the peak intensity of the metal component.

Here, the measurement conditions of XPS and the sputtering rate in depth profile measurement were set as shown above.

The interface position between the chemical conversion film and the plating layer was determined by focusing on the depth profile of silicon in the depth direction of the pre-coated steel sheet using X-ray photoelectron spectroscopy, and found that the strength of silicon is halved in the depth direction. The location was determined to be the interface between the chemical conversion coating and the plating layer.

(5. Performance evaluation)
Performance evaluation was performed in the same manner as in the first test example above. The evaluation method and evaluation criteria are the same as in the first test example.

The obtained results are summarized in Table 2 below.

The examples are all about the ratio of oxide and hydroxide to the metal content of zinc on the surface of the plated plate before forming and the interface of the plated steel plate after painting, as well as the peel strength and peeling form by SAICAS of the compressed part of the molded product. Since this meets the standards, no lifting or peeling of the paint film was observed during actual processing of the top plate of the outdoor air conditioner unit.

On the other hand, in the comparative examples, the ratio of oxide and hydroxide to the metal content of zinc on the surface of the plated plate before forming and the interface of the plated steel plate after painting, as well as the peel strength and peel strength measured by SAICAS of the compressed part of the molded product. Because the form of peeling did not meet the standards, lifting and peeling of the paint film was observed during actual processing of the top plate of the outdoor unit of the air conditioner.

≪Third test example≫
The third test example shown below is a test example regarding the plated steel sheet for pre-painted steel sheet, the pre-painted plated steel sheet, and the molded product according to the third embodiment.

A plated steel plate for a pre-painted steel plate, a pre-painted plated steel plate, and a molded product were prepared in the same manner as in the first test example and the second test example. The obtained plated steel sheets for pre-painted steel sheets, pre-painted plated steel sheets, and molded products were evaluated in the same manner according to the measurement method and evaluation method shown in the first test example and the second test example.

The obtained results are summarized in Table 3 below.

In both cases, the ratio of oxides and hydroxides to the metal content of zinc on the surface of the plated plate before forming and the interface of the plated steel plate after painting, as well as the peel strength and form of peeling determined by SAICAS of the compressed part of the molded product, met the standards. As a result, no lifting or peeling of the paint film was observed during actual processing of the top plate of the outdoor air conditioner unit.

Although preferred embodiments of the present invention have been described above in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person with ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea stated in the claims. It is understood that these also naturally fall within the technical scope of the present invention.

10 Plated steel plate for pre-coated steel plate 20 Pre-coated plated steel plate 30 Molded product 101 Steel plate 103,201 Plating layer 203 Chemical conversion film 205 Coating film

Claims (9)

steel plate and
Plating located on one or both sides of the steel plate, containing 0.5% by mass or more and 60.0% by mass or less of aluminum, 0.5% by mass or more and 15.0% by mass or less of magnesium, and the remainder consisting of zinc and impurities. layer and
It has
At a depth of 10 nm from the surface of the plating layer, the ratio of magnesium oxide and hydroxide to the ratio of metal magnesium is 2.0 or more, or A plated steel sheet for pre-coated steel sheet, wherein the ratio is 7.0 or more to the ratio of metal zinc. At a depth of 10 nm from the surface of the plating layer, the ratio of the magnesium oxide and hydroxide to the ratio of metal magnesium is 2.0 or more, and the zinc oxide and hydroxide The plated steel sheet for pre-coated steel sheet according to claim 1, wherein the ratio of 7.0 to the ratio of metal zinc is 7.0 or more. The precoated steel sheet according to claim 1 or 2, wherein at a depth of 10 nm from the surface of the plating layer, the ratio of aluminum oxide and hydroxide is 1.3 or more with respect to the ratio of metal aluminum. Plated steel plate. The plated steel sheet for a prepainted steel sheet according to any one of claims 1 to 3, wherein the plating layer is a Zn-11%Al-3%Mg-0.2%Si alloy plating. steel plate and
Plating located on one or both sides of the steel plate, containing 0.5% by mass or more and 60.0% by mass or less of aluminum, 0.5% by mass or more and 15.0% by mass or less of magnesium, and the remainder consisting of zinc and impurities. layer and
a chemical conversion coating located on the plating layer;
a coating film located on the chemical conversion coating;
It has
At a depth of 10 nm from the interface between the chemical conversion film and the plating layer toward the inside of the plating layer, the ratio of magnesium oxide and hydroxide is 0.30 to the ratio of metallic magnesium. or the ratio of zinc oxide and hydroxide to the ratio of metallic zinc is 7.0 or more. At a depth of 10 nm from the interface between the chemical conversion film and the plating layer toward the inside of the plating layer, the ratio of the magnesium oxide and hydroxide is 0.30 to the ratio of metal magnesium. The pre-coat plated steel sheet according to claim 5, wherein the ratio of the zinc oxide and hydroxide is 7.0 or more with respect to the ratio of metal zinc. At a depth of 10 nm from the interface between the chemical conversion film and the plating layer toward the inside of the plating layer, the ratio of aluminum oxide and hydroxide is 0.30 to the ratio of metal aluminum. The prepainted plated steel sheet according to claim 5 or 6, which is as follows. A molded article made of the prepainted plated steel sheet according to any one of claims 5 to 7,
Peel strength measured by cutting the interface between the chemical conversion treatment film and the coating film using the SAICAS method in a part where the thickness of the plated steel sheet in the molded product is increased by 5% or more compared to the non-forming processed part. is 1.00 kN/m or more on average, and 20% or less of the cut area is in the form of interfacial peeling, and the remaining cut area is in the form of cohesive failure within the coating film. The molded product according to claim 8, wherein the plating layer in the molded product contains 5% or more and 15% or less of aluminum and 2% or more and 4% or less of magnesium.

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