AU2021363219B2

AU2021363219B2 - Plated steel sheet for precoated steel sheet, precoated plated steel sheet, and molded article

Info

Publication number: AU2021363219B2
Application number: AU2021363219A
Authority: AU
Inventors: Takashi Fujii; Hiroyasu Furukawa; Akira Nakagawa; Fumio Shibao; Kohei Ueda
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2020-10-23
Filing date: 2021-10-05
Publication date: 2024-05-30
Anticipated expiration: 2041-10-05
Also published as: KR102781055B1; KR20230085182A; JPWO2022085434A1; AU2021363219A1; JP7401828B2; WO2022085434A1

Abstract

[Problem] To more reliably suppress the generation of coating film blistering even when drawing is carried out. [Solution] A plated steel sheet for precoated steel sheet according to the present invention has a steel sheet and, disposed on one or both sides of the steel sheet, a plating layer comprising 0.5-60.0 mass% aluminum and 0.5-15.0 mass% magnesium, with the remainder being zinc and impurities. At a depth of 10 nm from the surface of the plating layer, the proportion of magnesium oxide and hydroxide is at least 2.0 that of the proportion of magnesium metal or the proportion of zinc oxide and hydroxide is at least 7.0 that of the proportion of zinc metal.

Description

[Name of Document] DESCRIPTION

[Title of the Invention] PLATED STEEL SHEET FOR PRE-PAINTED STEEL SHEET,

PRE-PAINTED PLATED STEEL SHEET, AND MOLDED PRODUCT

[Technical Field]

[0001]

The present invention relates to a plated steel sheet for pre-painted steel sheet, a

pre-painted plated steel sheet, and a molded product.

[Background Art]

[0002]

Pre-painted steel sheets, which are pre-painted plated steel sheets, are required to

have many properties such as corrosion resistance, formability, paint film hardness (scratch

resistance), stain resistance, chemical resistance, and weather resistance. The order of

these required performances differs according to the use of the pre-painted plated steel

sheet. For example, in the pre-painted plated steel sheets that are mainly used for outdoor

applications such as air conditioner outdoor units and water heaters, the formability and the

corrosion resistance are particularly important among the above performances.

[0003]

In such a pre-painted plated steel sheet, many techniques have been

conventionally studied as a method for improving the adhesion between the plated steel

sheet and the paint film.

[0004]

For example, Patent Document 1 below discloses a pre-painted metal sheet

excellent in press formability in which a paint film at a drawn molded portion is not

damaged or peeled off during drawing. Patent Document 1 discloses that in order to

obtain a pre-painted metal sheet with excellent press formability that does not peel off, the

paint film has a specific viscoelastic curve, the number average molecular weight of a paint resin is 10000 or more, and the glass transition point (Tg) of the paint resin is 25°C or more, preferably.

[0005]

Further, Patent Document 2 below discloses a pre-painted metal sheet that is

excellent in continuous press formability and excellent in outdoor corrosion resistance at

an end face portion of a drawn portion. Patent Document 2 discloses that in order to

obtain a pre-painted metal sheet excellent in continuous press formability, it is important

that as such paint film physical properties, a paint film has a Tg of 40 to 120°C, the

minimum value of the storage elastic modulus in a rubbery elastic region of the paint film

measured in a dynamic viscoelasticity measuring device is 2 x 107 Pa or less, the surface

tension of the paint film is 28 mN/m or less, and the kinematic friction coefficient of the

surface of the paint film is 0.15 or less.

[0006]

Further, Patent Document 3 below discloses a high-gloss pre-painted metal sheet

that includes one or two paint film layers on one side or both sides of the metal sheet, the

uppermost paint film has physical properties in which Tg is 5 to 30°C, the hardness at

23°C is 2.5 N/mm2 or more as a universal hardness under a load of 5 mN and the fracture

elongation at 23°C is 100% or more, and the specular gloss of the uppermost paint film is

60% or more when measured under a condition that an incident angle and an acceptance

angle are 60°. Regarding such a pre-painted metal sheet, there is a description in Patent

Document 3 to the effect that a painted metal molded product with excellent press

formability is provided, in which gloss degradation of the paint film does not occur easily

at a worked portion even when deep drawing is performed.

[Prior Art Document]

[Patent Document]

[0007]

Patent Document 1: Japanese Laid-open Patent Publication No. 02-217500

Patent Document 2: Japanese Laid-open Patent Publication No. 08-253883

Patent Document 3: Japanese Laid-open Patent Publication No. 2007-44922

[Disclosure of the Invention]

[Problems to Be Solved by the Invention]

[0008]

The present inventors conducted studies in order to further improve the

formability and the corrosion resistance of the pre-painted plated steel sheet as described

above. As a result, it was newly found out that when the pre-painted plated steel sheet is

used to be subjected to drawing for a top plate of an air conditioner outdoor unit, or the like, a phenomenon called "paint film floating" (a phenomenon in which the paint film becomes

rough due to aggregates of minute point-like blisters) occurs in a drawn portion.

Hereinafter, the portion where these phenomena occur is referred to as a "paint film

floating portion." The cross-sectional observation of the paint film floating portion

revealed that the paint film was detached upward in portions where the paint film failed to

follow deformation (compression) of the plated steel sheet during draw molding of the

pre-painted plated steel sheet and became redundant, resulting in insufficient adhesion to

the plated steel sheet.

[0009] The technique of Patent Document 1 described above aims to inhibit the buckling

of the paint film due to the compressive strain of the drawn molded portion, which occurs

during drawing, by specifying the paint film physical properties. However, as a result of

studies by the present inventors, in order to inhibit the buckling of the paint film, in

addition to the paint film physical properties, the hardness of plating, the uniformity of

plating, the physical properties of a chemical treatment film, the worked shape, and so on

are also assumed to be non-negligible influencing factors. Patent document 1 does not describe any influencing factors other than these paint film physical properties. Therefore,

Patent Document 1 still has room for improvement with respect to the inhibition of buckling of

the paint film at the paint film floating portion that occurs during drawing, which the present

inventors focused on.

[0010]

Further, the technique of Patent Document 2 described above is the same as the

invention of Patent Document 1 described above in that the paint film physical properties are

specified to inhibit the buckling of the paint film due to the compressive strain during drawing.

Therefore, Patent Document 2 still has room for improvement with respect to the inhibition of

buckling of the paint film at the paint film floating portion that occurs during drawing, which the

present inventors focused on.

[0011]

Furthermore, the technique of Patent Document 3 described above is the same as Patent

Documents 1 and 2 in that the buckling of the paint film due to the compressive strain is

inhibited only by specifying the paint film physical properties. Therefore, Patent Document 3

still has room for improvement with respect to the inhibition of buckling of the paint film at the

paint film floating portion that occurs during drawing, which the present inventors focused on.

[0012] Thus, the present invention has been made in consideration of the above-described problems, and an object of the present invention in at least one preferred form is to provide a plated steel sheet for pre-painted steel sheet, a pre-painted plated steel sheet, and a molded product, which are capable of more reliably inhibiting the occurrence of paint film floating portions even when drawing is performed.

[0012a] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

4a

[0012b] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[Means for Solving the Problems]

[0012c] According to a first aspect, the present invention provides a plated steel sheet for pre painted steel sheet, comprising: a steel sheet; and a plating layer located on one side or both sides of the steel sheet, the plating layer containing 0.5 mass% or more and 60.0 mass% or less of aluminum, 0.5 mass% or more and 15.0 mass% or less of magnesium, and the balance being composed of zinc and impurities, wherein at a depth of 10 nm from the surface of the plating layer, the ratio of oxide and hydroxide of magnesium is 2.0 or more with respect to the ratio of metal magnesium, or the ratio of oxide and hydroxide of zinc is 7.0 or more with respect to the ratio of metal zinc.

[0012d] According to a second aspect, the present invention provides a pre-painted plated steel sheet, comprising: a steel sheet, a plating layer located on one side or both sides of the steel sheet, the plating layer containing 0.5 mass% or more and 60.0 mass% or less of aluminum, 0.5 mass% or more and 15.0 mass% or less of magnesium, and the balance being composed of zinc and impurities, a chemical treatment film located on the plating layer; and a paint film located on the chemical treatment film, wherein at a depth of 10 nm from the interface between the chemical treatment film and the plating layer toward the inside of the plating layer, the ratio of oxide and hydroxide of magnesium is 0.30 or less with respect to the ratio of metal magnesium, or the ratio of oxide and hydroxide of zinc is 7.0 or more with respect to the ratio of metal zinc.

[0012e] According to a third aspect, the present invention provides a molded product being a molded product formed of the pre-painted plated steel sheet according to the second aspect of the invention, wherein at a portion where the thickness of the plated steel sheet in the molded product has increased by 5% or more compared to the thickness of a non-molded portion, a peel strength measured by cutting the interface between the chemical treatment film and the paint film by a SAICAS method is 1.00 kN/m or more on average, 20% or less of a cut area is in the form of interfacial peeling, and the remaining cut area is in the form of cohesive failure within the paint film.

4b

[0012f] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

[0013]

In order to solve the above-described problems, the present inventors have

earnestly conducted studies, and then learned that the surface oxidation state of the plated

steel sheet, which is a painting base sheet for the pre-painted plated steel sheet, affects the

adhesion of the paint film at a worked portion of the molded product, as will be described

in detail below.

The gist of the present invention, which has been completed as a result of further

studies based on these findings, is as follows.

[0014]

(1) A plated steel sheet for pre-painted steel sheet includes: a steel sheet; an a

plating layer located on one side or both sides of the steel sheet, the plating layer

containing 0.5 mass% or more and 60.0 mass% or less of aluminum, 0.5 mass% or more

and 15.0 mass% or less of magnesium, and the balance being composed of zinc and

impurities, in which at a depth of 10 nm from the surface of the plating layer, the ratio of

oxide and hydroxide of magnesium is 2.0 or more with respect to the ratio of metal

magnesium, or the ratio of oxide and hydroxide of zinc is 7.0 or more with respect to the

ratio of metal zinc.

(2) The plated steel sheet for pre-painted steel sheet according to (1), in which at a

depth of 10 nm from the surface of the plating layer, the ratio of oxide and hydroxide of

magnesium is 2.0 or more with respect to the ratio of metal magnesium, and the ratio of

oxide and hydroxide of zinc is 7.0 or more with respect to the ratio of metal zinc.

(3) The plated steel sheet for pre-painted steel sheet according to (1) or (2), in

which at a depth of 10 nm from the surface of the plating layer, the ratio of oxide and

hydroxide of aluminum is 1.3 or more with respect to the ratio of metal aluminum.

(4) The plated steel sheet for pre-painted steel sheet according to any one of (1) to

(3), in which the plating layer is Zn-11IAl-3%Mg-0.2%Si alloy plating.

(5) A pre-painted plated steel sheet includes: a chemical treatment film located on the plating layer in the plated steel sheet according to any one of (1) to (4); and a paint film located on the chemical treatment film, in which at a depth of 10 nm from the interface between the chemical treatment film and the plating layer toward the inside of the plating layer, the ratio of oxide and hydroxide of magnesium is 0.30 or less with respect to the ratio of metal magnesium, or the ratio of oxide and hydroxide of zinc is 7.0 or more with respect to the ratio of metal zinc.

(6) The pre-painted plated steel sheet according to (5), in which at a depth of 10

nm from the interface between the chemical treatment film and the plating layer toward the

inside of the plating layer, the ratio of oxide and hydroxide of magnesium is 0.30 or less

with respect to the ratio of metal magnesium, and the ratio of oxide and hydroxide of zinc

is 7.0 or more with respect to the ratio of metal zinc.

(7) The pre-painted plated steel sheet according to (5) or (6), in which at a depth

of 10 nm from the interface between the chemical treatment film and the plating layer

toward the inside of the plating layer, the ratio of oxide and hydroxide of aluminum is 0.30

or less with respect to the ratio of metal magnesium.

(8) A molded product being a molded product formed of the pre-painted plated

steel sheet according to any one of (5) to (7), in which at a portion where the thickness of

the plated steel sheet in the molded product has increased by 5% or more compared to the

thickness of a non-molded portion, a peel strength measured by cutting the interface

between the chemical treatment film and the paint film by a SAICAS method is 1.00 kN/m

or more on average, 20% or less of a cut area is in the form of interfacial peeling, and the

remaining cut area is in the form of cohesive failure within the paint film.

(9) The molded product according to (8), in which 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.

[Effect of the Invention]

[0015]

As explained above, according to the present invention, it becomes possible to

provide a plated steel sheet for pre-painted steel sheet, a pre-painted plated steel sheet, and

a molded product, which are capable of more reliably inhibiting the occurrence of paint

film floating portions even when drawing is performed.

[Brief Description of the Drawings]

[0016]

[FIG. 1A] FIG. 1A is an explanatory view schematically illustrating one example

of a structure of a plated steel sheet for pre-painted steel sheet according to each

embodiment of the present invention.

[FIG.iB] FIG. lB is an explanatory view schematically illustrating another one

example of the structure of the plated steel sheet for pre-painted steel sheet according to

each embodiment of the present invention.

[FIG. 2] FIG. 2 is an explanatory view for explaining a plating layer in the plated

steel sheet for pre-painted steel sheet according to each embodiment of the present

invention.

[FIG. 3A] FIG. 3A is an explanatory view schematically illustrating one example

of a structure of a pre-painted plated steel sheet according to each embodiment of the

present invention.

[FIG. 3B] FIG. 3B is an explanatory view schematically illustrating another one

example of the structure of the pre-painted plated steel sheet according to each

embodiment of the present invention.

[FIG. 4] FIG. 4 is an explanatory view for explaining a plating layer in the

pre-painted plated steel sheet according to each embodiment of the present invention.

[FIG. 5] FIG. 5 is an explanatory view schematically illustrating one example of a

structure of a molded product according to each embodiment of the present invention.

[Embodiments for Carrying out the Invention]

[0017] There will be explained in detail preferred embodiments of the present invention

below with reference to the accompanying drawings. Incidentally, in this description and

the drawings, components having substantially the same functional configuration are

denoted by the same reference numerals, thereby omitting their redundant explanations.

[0018]

(Regarding the studies conducted by the present inventors)

In the following, before explaining a plated steel sheet for pre-painted steel sheet,

a pre-painted plated steel sheet, and a molded product according to the embodiment of the

present invention, there will be explained in detail the contents of various studies

conducted on the paint film floating portion as described above.

[0019]

When the present inventors observed the cross section of the paint film floating

portion of a molded product obtained by drawing the pre-painted plated steel sheet, it was

observed that the paint film was compressed due to deformation (compression) of the

plated steel sheet, and the redundant paint film was detached upward. When the sheet

thickness of the plated steel sheet of this portion was measured, the sheet thickness

increased from the sheet thickness before molding, which reveals that the paint film

floating portion that the present inventors focused on is the portion where the plated steel

sheet was compressed.

[0020]

On the other hand, in the portion where the paint film was peeled off due to

rubbing against a mold during drawing (namely, a portion where peeling occurred due to a

mechanical abrasion) and the portion where the paint film stretched along with a painting

base sheet but the adhesion decreased as a result of stress concentration at the interface between the plating and the paint film caused by elongation and then the paint film was peeled off due to sliding of a mold (namely, a portion where peeling occurred due to stress concentration), the sheet thickness of the plated steel sheet decreased from the sheet thickness before molding. These results revealed that these portions where the paint film was peeled off are portions where the plated steel sheet was elongated. However, in the drawing, compression and elongation of the plated steel sheet do not occur independently of each other, but occur simultaneously, and the degree of compression and elongation only differs depending on the worked portion. The thickness of the plated steel sheet is greater than that before molding at the portion where compression exceeds elongation. On the other hand, the thickness of the plated steel sheet is smaller than that before molding at the portion where elongation exceeds compression.

[0021]

Generally, when the adhesion strength (peel strength) between the paint film and

the plating interface decreases with deformation of the plated steel sheet during molding,

paint film floating or paint film peeling occurs.

[0022]

As a result of studies by the present inventors, they came to the conclusion that the

following three influencing factors (1) to (3) should be considered as factors that determine

the presence or absence of the occurrence of paint film floating or paint film peeling. If

these influencing factors are in a good state overall, it is believed that paint film floating

and paint film peeling will be inhibited.

[0023]

(1) Soundness of a plated surface after working with compression and elongation

(presence or absence of irregularities or cracks)

(2) Adhesion between plating and a primer paint film through a chemical

treatment film after working with compression and elongation

(3) State of the entire paint film including a top paint film deformed by working

with compression and elongation (presence or absence of cracks and internal stress)

[0024]

Since the phenomenon of paint film floating as described above is likely to occur

in pre-painted plated steel sheets that use zinc-based plated steel sheets (particularly,

zinc-based alloy plated steel sheets containing aluminum and magnesium) as the painting

base sheet, the present inventors focused on the plated surface of the painting base sheet, as

described in (1) and (2) above, and conducted further studies.

[0025]

As a result, the present inventors found out that the surface oxidation state of the

plated steel sheet of the painting base sheet affects the adhesion of the paint film at a

molded portion. Here, the surface oxidation state of the plated steel sheet that the present

inventors focused on includes two types mainly: (a) the state of oxides and hydroxides of

aluminum and magnesium on the surface of the plated steel sheet; and (b) the state of oxide

and hydroxide of zinc on the surface of the plated steel sheet.

[0026]

First, there is described (a) the state of oxides and hydroxides of aluminum and

magnesium on the surface of the plated steel sheet.

[0027]

As a result of studies by the present inventors, they learned that as the

concentration of oxides and hydroxides of aluminum and magnesium on the surface of the

plated steel sheet is lower, the paint film adhesion at the molded portion becomes higher.

This is presumably because oxides and hydroxides of aluminum and magnesium, which

are easily oxidizable elements, are formed on the surface of the zinc-based alloy plated

steel sheet containing aluminum and magnesium, to thereby reduce wettability to a

degreasing liquid or a chemical treatment solution, resulting in a decrease in the paint film adhesion at the molded portion.

[0028] Furthermore, the present inventors earnestly studied the correlation between the

oxidation state of the plated surface of the painting base sheet and the paint film adhesion

at the molded portion. As a result, it became clear that regarding magnesium, when the

presence ratio of oxide and hydroxide of magnesium is 2.0% or more with respect to the

presence ratio of metal of magnesium (in other words, magnesium in a metallic state) at a

depth of 10 nm below the surface of the plating layer, good paint film adhesion is obtained

at the molded portion.

[0029]

Despite the fact that the surface concentration of surface oxides of magnesium

should be smaller, it is still not clear why the ratio of oxide and hydroxide should be above

a certain level with respect to the ratio of metal in magnesium in the vicinity of the surface

of the plating layer, as described above. However, in order to obtain good paint film

adhesion at the molded portion, it is presumed that it is necessary to dissolve both metal of

magnesium and oxide and hydroxide of magnesium by an acid treatment, alkaline

degreasing, or the like, but a higher ratio of oxide and hydroxide of magnesium is better for

magnesium itself due to the difference in dissolution rate, deposition after dissolution, or

other factors.

[0030] Further, as a result of studies by the present inventors, it also became clear that

when the zinc-based alloy plated steel sheet containing aluminum and magnesium as

described above is subjected to a chemical treatment and painting to form a pre-painted

steel sheet, in order to exhibit good paint film adhesion at the molded portion, the ratio of

oxides and hydroxides of aluminum and magnesium should be lower than the ratio of

metal of those elements by a certain level or more at the interface between the plating layer and the chemical treatment film.

[0031]

This is presumably because aluminum and magnesium on the surface of the

plating layer are dissolved by the chemical treatment and some of aluminum and

magnesium are introduced into the chemical treatment film, and thereby, the surface ratio

of oxides and hydroxides, which are presumed to adversely affect the paint film adhesion,

should be small. Incidentally, although the details of how aluminum and magnesium are

introduced into the chemical treatment film are unknown, it is presumed that there are two

types of aluminum and magnesium: one is introduced as oxides - hydroxides; and the other

is introduced as metal.

[0032]

Next, there is described (b) the state of oxide and hydroxide of zinc on the surface

of the plated steel sheet.

[0033]

As a result of studies by the present inventors, they learned that as the

concentration of oxide and hydroxide of zinc on the surface of the plated steel sheet is

lower, the paint film adhesion at the molded portion becomes higher. This is presumably

because the oxide and hydroxide of zinc have higher wettability to a degreasing liquid or a

chemical treatment solution than metal zinc, and the oxide and hydroxide cover the surface

of the plating, to thereby improve the adhesion to the chemical treatment film, and as a

result, the paint film adhesion after molding is improved when the amount of oxide and

hydroxide of zinc is larger.

[0034]

Thus, it is still not clear why a higher ratio of oxide and hydroxide of zinc is better

with respect to the ratio of metal zinc on the surface of the plated steel sheet, which is the

painting base sheet. However, in order to obtain good paint film adhesion at the molded portion, it is presumed that it is necessary to dissolve both zinc of metal and oxide and hydroxide of zinc by an acid treatment, alkaline degreasing, or the like, but a higher ratio of oxide and hydroxide of zinc is better for zinc itself due to the difference in dissolution rate, deposition after dissolution, or other factors.

[0035] Further, it was also inferred that in the zinc-based plated steel sheet containing

aluminum and magnesium among zinc-based plated steel sheets, the dissolution of

aluminum and magnesium relatively affects the surface concentration of zinc.

[0036] Further, as a result of studies by the present inventors, it also became clear that

when the zinc-based plated steel sheet as described above is subjected to a chemical

treatment and painting to form a pre-painted steel sheet, in order to exhibit good paint film

adhesion at the molded portion, the ratio of oxide and hydroxide of zinc should be higher

than the ratio of metal zinc by a certain level or more at the interface between the plating

layer and the chemical treatment film.

[0037] As a result that the present inventors conducted earnest studies based on the above

findings, it was possible to find out the conditions for the acid treatment and the alkaline

degreasing to achieve appropriate states of oxides and hydroxides, as described in detail

below.

[0038] Further, the present inventors studied the peel strength and the peel form at the

interface between the chemical treatment film or paint film (for example, the primer paint

film when the paint film is composed of a plurality of layers) and the plating layer of a

molded body obtained by molding the above-described pre-painted plated steel sheet. In

a conventional peel test, it was possible to measure the peel strength of the paint film of the pre-painted steel sheet, but it was not possible to accurately measure the peel strength and the peel form of a compressed portion and an elongated portion of the plated steel sheet forming the molded body. The present inventors evaluated the peel strength and the peel form using the SAICAS method (Surface and Interfacial Cutting Analysis System) as a technique capable of simultaneously measuring these portions.

[0039]

The SAICAS method is a method in which a sharp blade is used to perform

cutting from the surface of a sample to the adhesive interface between a base and an

adherend at an ultra-low speed to measure the peel strength. Therefore, it is possible to

observe the peel strength and the peel state at the interface between specific layers of a

laminated multilayer film, which was difficult to measure them by the conventional

method.

[0040]

It is impossible to prepare samples of the compressed portion and the elongated

portion of the plated steel sheet of the molded body independently of each other.

Therefore, the present inventors performed cylindrical cup drawing using the pre-painted

steel sheet, and focused on the portion where the thickness increased compared to the

thickness of the plated steel sheet before molding as a compression-dominant molded

portion, and at the same time, focused on the portion where the thickness decreased

compared to the thickness of the plated steel sheet before molding as an

elongation-dominant molded portion. They learned the following findings by measuring

both of these portions using the SAICAS method.

[0041]

That is, it was found out that in the molded body formed of the pre-painted plated

steel sheet that does not cause paint film floating or paint film peeling as described above,

the peel form of the paint film is not in the form of interfacial peeling at the interface between the chemical treatment film or the paint film (for example, the primer paint film when the paint film is composed of a plurality of layers) and the plating layer, but in the form of cohesive failure of the paint film (for example, the primer paint film when the paint film is composed of a plurality of layers).

[0042]

As a result, it became clear that when both the following two conditions (i) and

(ii) are satisfied, the molded product formed of the pre-painted plated steel sheet that does

not cause paint film peeling can be obtained.

[0043]

(i) Peel strength of the compressed portion of the plated steel sheet by the

SAICAS method (that is, the portion where the thickness of the plated steel sheet of the

molded product has increased by 5% or more compared to that before molding, (which can

be considered as a non-molded portion),) is 1.00 kN/m or more on average.

(ii) Twenty percent or less of a cut area is in the form of interfacial peeling, and

the remaining cut area is in the form of cohesive failure within the paint film (for example,

within the primer paint film when the paint film is composed of a plurality of layers).

[0044]

Here, the form of interfacial peeling refers to any of cohesive failure of the

chemical treatment film, interfacial peeling between the chemical treatment film and the

paint film (for example, the primer paint film when the paint film is composed of a

plurality of layers), and interfacial peeling between the chemical treatment film and the

plating layer, or a combined form of these states. However, the film thickness of the

chemical treatment film is extremely thin, and thus, the chemical treatment film is

integrated with the plating layer or the paint film (the primer paint film when the paint film

is composed of a plurality of layers, for example), failing to visually distinguish the above

peel form.

[0045]

Hereinafter, there will be explained in detail the plated steel sheet for pre-painted

steel sheet, the pre-painted plated steel sheet, and the molded product according to each of

the embodiments of the present invention, which have been completed based on the above

findings.

[0046]

The first embodiment of the present invention described below is an embodiment

focusing on the state of oxides and hydroxides of aluminum and magnesium on the surface

of the plated steel sheet, which was mentioned as (a) described above. Further, the

second embodiment of the present invention described below is an embodiment focusing

on the state of oxide and hydroxide of zinc on the surface of the plated steel sheet, which

was mentioned as (b) described above. Further, the third embodiment of the present

invention described below is an embodiment focusing on the state of oxides and

hydroxides of zinc, aluminum, and magnesium on the surface of the plated steel sheet.

[0047] «First embodiment>>

(Regarding the plated steel sheet for pre-painted steel sheet)

There is first explained in detail a plated steel sheet for pre-painted steel sheet

according to the first embodiment of the present invention with reference to FIG. 1A to

FIG. 2.

[0048]

As schematically illustrated in FIG. 1A, a plated steel sheet 10 according to this

embodiment includes a steel sheet 101 serving as a base material and a plating layer 103

located on one side of the steel sheet. Further, in the plated steel sheet 10 according to

this embodiment, as schematically illustrated in FIG. 1B, the plating layers 103 may be

located on both sides of the steel sheet 101 serving as the base material.

[0049]

Various steel sheets can be used for the steel sheet 101 used as the base material of

the plated steel sheet 10 according to this embodiment, depending on the mechanical

strength, or the like required for the plated steel sheet 10. As such a steel sheet 101, there

can be cited various steel sheets such as, for example, Al-killed steel, ultralow carbon steel

containing Ti, Nb, and the like, and high-strength steel further containing strengthening

elements such as P, Si, and Mn in the ultralow carbon steel.

[0050]

Further, the thickness of the steel sheet 101 according to this embodiment (a

thickness dO in FIG. 1A and FIG. 1B) may be appropriately set according to the

mechanical strength, or the like required for the plated steel sheet 10, and can be set to

about 0.2 mm to 2.0 mm, for example.

[0051]

The plating layer 103 according to this embodiment is a layer to be formed on at

least one surface of the steel sheet 101, as schematically illustrated in FIG. 1A and FIG. 1B,

and is provided to improve the corrosion resistance of the plated steel sheet 10. First, the

chemical composition of the plating layer 103 according to this embodiment will be

explained below.

[0052]

The plating layer 103 according to this embodiment is a plating layer containing:

in mass%, aluminum (Al): 0.5% or more and 60.0% or less; magnesium (Mg): 0.5% or

more and 15.0% or less; and the balance being composed of zinc (Zn) and impurities. In

other words, the plating layer 103 according to this embodiment is an Al-Mg Zn-based

ternary plating layer.

[0053]

[Al: 0.5 to 60.0 mass%]

The Zn alloy plating layer 103 according to this embodiment contains 0.5 mass%

or more and 60.0 mass% or less of Al. By setting the content of Al to 0.5 mass% or more and 60.0 mass% or less, the corrosion resistance of the plated steel sheet 10 according to

this embodiment improves, and the adhesion of the plating layer 103 (more precisely, the

adhesion to the steel sheet 101) can be ensured. When the content of Al is less than 0.5

mass%, the plating layer 103 becomes brittle and the adhesion of the plating layer 103

decreases. The content of Al is preferably 5.0 mass% or more. On the other hand, when

the content of Al exceeds 60.0 mass%, the effect of improving the corrosion resistance of

the plated steel sheet 10 is saturated. The content of Al is preferably 15.0 mass% or less.

[0054]

[Mg: 0.5 to 15.0 mass%]

The plating layer 103 according to this embodiment contains 0.5 mass% or more

and 15.0 mass% or less of Mg. By setting the content of Mg to 0.5 mass% or more and

15.0 mass% or less, the corrosion resistance of the plated steel sheet according to this

embodiment improves, and the adhesion of the plating layer 103 (more precisely, the

adhesion to the steel sheet 101) can be ensured. When the content of Mg is less than 0.5

mass%, the effect of improving the corrosion resistance of the plated steel sheet 10

becomes insufficient. The content of Mg is preferably 2.0 mass% or more. On the other

hand, when the content of Mg exceeds 15.0 mass%, the plating layer 103 becomes brittle

and the adhesion of the plating layer 103 decreases. The content of Mg is preferably 4.0

mass% or less.

[0055]

[Balance: Zn and impurities]

In the plating layer 103 according to this embodiment, the balance other than the above components is Zn and impurities. Further, the plating layer 103 according to this embodiment may contain silicon (Si) in a content of 0 mass% or more and 2.0 mass% or less in place of a part of Zn of the balance.

[0056]

[Si: 0 to 2.0 mass%]

The plating layer 103 according to this embodiment may contain 0 mass% or

more and 2.0 mass% or less of Si in place of a part of Zn of the balance. By setting the

content of Si to 0 mass% or more and 2.0 mass% or less, the adhesion of the plating layer

103 can be ensured more reliably. When the content of Si exceeds 2.0 mass%, the effect

of improving the adhesion of the plating layer 103 may be saturated. The content of Si is

more preferably 1.6 mass% or less.

[0057] Further, in the plating layer 103 according to this embodiment, 1 mass% or less of

elements such as Fe, Sb, and Pb may be contained alone or in combination in place of a

part of Zn of the balance.

[0058] As the plated steel sheet 10 for pre-painted steel sheet provided with the plating

layer 103 having the chemical composition as described above, there can be cited, for

example, such a hot-dip zinc-aluminum-magnesium-silicon alloy plated steel sheet as a

plated steel sheet including a Zn-1%Al-3%Mg-0.2%Si alloy plating layer (for example, "SuperDyma (registered trademark)" and "ZAM (registered trademark)" manufactured by

Nippon Steel Corporation), and so on.

[0059]

[Regarding the average film thickness of the plating layer 103]

In the plated steel sheet 10 for pre-painted steel sheet according to this

embodiment, the average film thickness (a thickness d in FIG. 1A and FIG. 1B) of the plating layer 103 is preferably 6 m or more and more preferably 9 m or more, for example. With the plating layer 103 having such an average film thickness, the corrosion resistance of the plated steel sheet 10 for pre-painted steel sheet can be more reliably ensured. Incidentally, when the average film thickness dl of the plating layer 103 exceeds 45 tm, the influence of the increase in plating cost is greater than the improvement in corrosion resistance. Therefore, from an economic point of view, the average film thickness dl of the plating layer 103 is preferably 45 m or less.

[0060]

Incidentally, the average flm thickness dl of the plating layer 103 can be

calculated by the following gravimetric method, for example. That is, a plated steel sheet

having a predetermined area (for example, 50 mm x 50 mm) is dissolved in hydrochloric

acid containing an inhibitor, and the dissolved weight is calculated by the difference in

weight before and after dissolution. The weight ratio of elements such as Al, Zn, and Fe

separately contained in a solution is measured and calculated by high-frequency

inductively coupled plasma (Inductively Coupled Plasma: ICP) emission spectrometry, and

the average specific gravity of the plating layer is calculated from the ratio. The average

film thickness dl of the plating layer 103 is calculated by dividing the dissolved weight by

the average specific gravity and then dividing the resultant by the area (or the area x 2 in

the case of double-sided plating).

[0061]

Based on the findings explained previously, in the plating layer 103 according to

this embodiment, the state of metals, oxides, and hydroxides of magnesium and aluminum

on the surface of the plating layer 103 is defined.

[0062]

Here, on the surface of the plating layer 103, various unintended impurities may exist in addition to the metals, oxides, hydroxides, and the like of magnesium and aluminum. Therefore, in this embodiment, as schematically illustrated in FIG. 2, at a

"position A," which is located at a depth of 10 nm from the surface of the plating layer 103,

the state of metals, oxides, and hydroxides of magnesium and aluminum is specified and

the state of these substances on the surface of the plating layer 103 is determined.

[0063] The state analysis of metals, oxides, and hydroxides of magnesium and aluminum

is specified by X-ray Photoelectron Spectroscopy (XPS). The XPS analysis is performed

by using Quantum 2000 manufactured by ULVAC-PHI, Inc., with X-ray source: Al Ka,

X-ray output 15 kV, 25 W, measurement region: 300 x 300 m square, degree of vacuum:

1.5 x 10-9 Torr (1 Torr being about 133.3 Pa), and detection accuracy: 45. Further,

sputtering for a depth profile analysis is performed with ion species: Ar*, acceleration

voltage: 1 kV, region: 1 x 1 mm, and sputtering rate: 2.7 nm/min (in terms of SiO 2 ). The

sputtering is performed based on the above-described sputtering rate, and the position

specified by this sputtering is regarded as the "position A" described above.

[0064]

Here, the separation of attributions of the ratio (presence ratio) between oxide and

hydroxide of magnesium and metal magnesium is calculated from the intensity ratio of the

peaks attributed to the respective substances (oxide, hydroxide, and metal) from a narrow

spectrum in the region of 295 to 325 cm-1 by Mg KLL. Similarly, the separation of

attributions of the ratio (presence ratio) between oxide and hydroxide of aluminum and

metal aluminum is calculated from the intensity ratio of the peaks attributed to the

respective substances (oxide, hydroxide, and metal) from a narrow spectrum in the region

of 68 to 84 cm-1 by Al 2p.

[0065]

In the plating layer 103 in this embodiment, the ratio of oxide and hydroxide of magnesium at a depth of 10 nm from the surface of the plating layer (position A in FIG. 2) specified as described above is 2.0 or more with respect to the ratio of metal magnesium.

The presence ratio of oxide and hydroxide of magnesium to metal magnesium is 2.0 or

more, and thereby, good paint film adhesion at the molded portion can be achieved to

inhibit the occurrence of paint film floating portions even when the pre-painted plated steel

sheet using the plated steel sheet 10 for pre-painted steel sheet including the plating layer

103 according to this embodiment is drawn. On the other hand, when the

above-described presence ratio of oxide and hydroxide of magnesium is less than 2.0, good

paint film adhesion at the molded portion cannot be exhibited, failing to inhibit the

occurrence of paint film floating portions. The presence ratio of oxide and hydroxide of

magnesium to metal magnesium is preferably 4.0 or more and more preferably 6.0 or more.

Further, the upper limit value of the presence ratio of oxide and hydroxide of magnesium

to metal magnesium is substantially 10.0 or so.

[0066]

Further, in the plating layer 103 according to this embodiment, the ratio of oxide

and hydroxide of aluminum at a depth of 10 nm from the surface of the plating layer

(position A in FIG. 2) specified as described above is preferably 1.3 or more with respect to

the ratio of metal aluminum. The presence ratio of oxide and hydroxide of aluminum to

metal aluminum is 1.3 or more, and thereby, good paint film adhesion at the molded

portion can be achieved to more reliably inhibit the occurrence of paint film floating

portions even when the pre-painted plated steel sheet using the plated steel sheet 10

including the plating layer 103 according to this embodiment is drawn. On the other hand,

when the above-described presence ratio of oxide and hydroxide of aluminum is less than

1.3, good paint film adhesion at the molded portion cannot be exhibited in some cases.

The presence ratio of oxide and hydroxide of aluminum to metal aluminum is more

preferably 1.4 or more and further preferably 2.0 or more. Further, the upper limit value of the presence ratio of oxide and hydroxide of aluminum to metal aluminum is substantially 10.0 or so.

[0067]

Here, the measurements by XPS are performed on a region having a size of 300

m x 300 [m. Further, the presence ratio calculated as described above means an average

value in the measurement region as described above.

[0068] Incidentally, in the plated steel sheet 10 according to this embodiment, the

establishment of the above relationship regarding magnesium in the plating layer 103

makes it possible to exhibit good paint film adhesion at the molded portion. This is

because magnesium has a lower standard electrode potential than aluminum, which is more

prone to corrosion, and more inhibition of corrosion of magnesium is effective in

improving the paint film adhesion at the molded portion.

[0069]

As above, the plated steel sheet 10 for pre-painted steel sheet according to this

embodiment has been explained in detail with reference to FIG. 1A to FIG. 2.

[0070]

The plated steel sheet 10 for pre-painted steel sheet according to this embodiment

as explained above can be manufactured as follows, for example. First, pretreatments

such as washing and degreasing are performed on the surface of the prepared steel sheet

101 as necessary. Thereafter, an ordinary non-oxidizing furnace type hot-dip plating

method is applied to the steel sheet 101 that has undergone the pretreatments as necessary,

and thereby a plating layer is formed.

[0071]

Then, a posttreatment step by at least any of an acid treatment, an alkali treatment,

and mechanical cutting is performed on the steel sheet on which the plating layer is formed.

This modifies the surface of the plating layer or removes the surface of the plating layer, to

thereby satisfy the conditions regarding the XPS spectrum mentioned previously.

[0072]

Here, a hot-dip galvanizing bath containing desired chemical components (that is,

a hot-dip galvanizing bath containing at least Al: 0.5 to 60.0 mass% and Mg: 0.5 to 15.0

mass%, and the balance being composed of Zn and impurities) is prepared, and the bath

temperature of such a plating bath is controlled to about 450°C. Then, the obtained steel

sheet 101 is immersed in the plating bath to apply hot-dip galvanization to the surface of

the steel sheet so as to obtain a desired average film thickness. Thereafter, the cooling

rate after plating is controlled to 10°C/second or more. Thereby, the plating layer can be

formed.

[0073]

While measuring the XPS spectrum of the plating layer obtained in the above

manner using an XPS analyzer set to the above measurement conditions, the surface of the

plating layer is modified or removed by various methods such as an acid treatment, an

alkali treatment, and mechanical cutting, until the previously mentioned conditions

regarding the XPS spectrum are satisfied. As a result, the plated steel sheet 10 for

pre-painted steel sheet according to this embodiment, which includes the plating layer 103

as described above, can be manufactured.

[0074]

Here, any alkali treatment, acid treatment, or mechanical cutting to be applied

may be performed, and these treatments may be combined in various ways.

[0075]

For example, in the case of performing the alkali treatment, the higher the alkali

concentration and the longer the treatment time, the higher the presence ratio of oxide and

hydroxide of magnesium on the surface of the plating layer tends to be. For example, when spraying is performed at 50°C using a commercially available standard sodium orthosilicate-based (medium alkaline type) degreasing solution as the alkali treatment, if the spray time is about 10 seconds or less, the presence ratio of oxide and hydroxide of magnesium on the surface of the plating layer cannot satisfy the specified conditions, but if the spray time is prolonged, the conditions will be satisfied, and if it is prolonged to about

2 minutes, the conditions will be satisfied reliably. Further, if the concentration of this

degreasing solution is doubled, the conditions will be reliably satisfied in about 30 seconds.

Although the reason is not clear, it is conceivable that by performing the alkali treatment,

the component of metal magnesium may be dissolved to be transformed into oxide or

hydroxide and redeposited on the plated surface.

[0076]

Further, for example, in the case of performing the acid treatment, such a

treatment exhibits the effect of removing oxide and hydroxide of magnesium on the surface

of the plating layer, unlike the alkali treatment. Therefore, the specified conditions can be

obtained by performing the treatment under mild conditions to the extent of removing

contaminant components adhering to the plated surface. For example, when spraying at

50°C using 5% sulfuric acid, by setting the spray time to about 5 seconds to 10 seconds,

the presence ratio of oxide and hydroxide of magnesium on the surface of the plating layer

can satisfy the specified conditions. However, spraying for a longer time does not satisfy

the conditions.

[0077]

Further, for example, in the case of performing the mechanical cutting, such

cutting exhibits the effect of removing all of metal magnesium and oxide and hydroxide on

the surface of the plating layer. Therefore, it is preferable to use a nylon brush, a

grindstone with an appropriate grain size, or the like, and perform the cutting under mild

conditions to the extent of removing contaminant components adhering to the plated surface. After the mechanical cutting, the surface is washed with water to remove cutting contaminants.

[0078]

Examples of the various treatment methods have been described above, but the

conditions for each treatment also vary depending on the initial oxidation state of the

plating layer of the steel sheet to be used. Therefore, the plated steel sheet 10 for

pre-painted steel sheet according to this embodiment may be manufactured by

appropriately selecting optimum conditions.

[0079]

(Regarding the pre-painted plated steel sheet)

Then, the pre-painted plated steel sheet using the plated steel sheet 10 for

pre-painted steel sheet as explained above will be explained in detail with reference to FIG.

3A to FIG. 4.

[0080]

As schematically illustrated in FIG. 3A, a pre-painted plated steel sheet 20

according to this embodiment is one using the plated steel sheet 10 for pre-painted steel

sheet explained previously as the base material. Such a pre-painted plated steel sheet 20

includes a steel sheet 101, a plating layer 201 located on one side of the steel sheet 101, a

chemical treatment film 203 located on the plating layer 201, and a paint film 205 located

on the chemical treatment film 203. Further, the pre-painted plated steel sheet 20

according to this embodiment may include the plating layers 201, the chemical treatment

films 203, and the paint films 205 formed on both sides of the steel sheet 101, as

schematically illustrated in FIG. 3B.

[0081]

Here, the steel sheet 101 in the pre-painted plated steel sheet 20 according to this

embodiment has the same configuration as the steel sheet 101 in the plated steel sheet 10 for pre-painted steel sheet explained previously, and exhibits the same effect. Therefore, its detailed explanation is omitted below.

[0082]

Further, regarding the plating layer 201 in the pre-painted plated steel sheet 20

according to this embodiment, along with the formation of the chemical treatment film 203

described later, interdiffusion or the like of atoms or the like contained in each layer occurs

in the vicinity of the interface between the plating layer 201 and the chemical treatment

film 203. 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-painted steel sheet

explained previously, and the same effect is exhibited. Therefore, its detailed explanation

is omitted below.

[0083] Incidentally, there is explained the state of metals, oxides, and hydroxides of

magnesium and aluminum exhibited by the plating layer 201 of the pre-painted plated steel

sheet 20 according to this embodiment below.

[0084]

The chemical treatment film 203 according to this embodiment is a film layer

located on the plating layer 201, and is a layer formed by a chemical treatment after

removing impurities such as oil and surface oxides adhering to the surface of the plated

steel sheet 10 for pre-painted steel sheet by a well-known degreasing step and washing

step.

[0085]

The chemical treatment film 203 according to this embodiment may contain any

one or more selected from the group consisting of resin, a silane coupling agent, a

zirconium compound, silica, phosphoric acid and its salt, fluoride, a vanadium compound, and tannin or tannic acid. These substances are contained, to thereby further improve the film formability obtained after applying a chemical treatment solution, the barrier property

(denseness) of the film against corrosion factors such as moisture and corrosive ions, the

film adhesion to the plated surface, and the like, resulting in contribution to the

improvement in the corrosion resistance of the film.

[0086] In particular, when the chemical treatment film 203 contains one or more of a

silane coupling agent and a zirconium compound, a crosslinked structure is formed within

the film 203 to strengthen bonding with the plated surface. As a result, it becomes

possible to further improve the adhesion and the barrier property of the film.

[0087]

Further, when the chemical treatment film 203 contains any one or more of silica,

phosphoric acid and its salt, fluoride, and a vanadium compound, these compounds

function as inhibitors and form a precipitation film or passive film on the plating or steel

surface. As a result, it becomes possible to further improve the corrosion resistance.

[0088] In the following, there will be explained details of each component that can be

contained in the chemical treatment film 203 described above with reference to examples.

[0089]

[Resin]

As the resin, well-known organic resins such as a polyester resin, a polyurethane

resin, an epoxy resin, a phenol resin, an acrylic resin, and a polyolefin resin, for example,

can be used. To further improve the adhesion to the plated steel sheet for pre-painted

steel sheet, it is preferable to use at least one of the resins (polyester resin, urethane resin,

epoxy resin, acrylic resin, and so on) having a forced site or polar functional group in a

molecular chain. The resins may be used alone or in combination of two or more resins.

[0090] The content of the resin in the chemical treatment film 203 is preferably, for

example, 0 mass% or more and 85 mass% or less with respect to the solid content of the

film. The content of the resin is more preferably 0 mass% or more and 60 mass% or less,

and further preferably 1 mass% or more and 40 mass% or less. When the content of the

resin exceeds 85 mass%, the ratio of the other film components may decrease and the

performance required as the film other than corrosion resistance may decrease.

[0091]

[Silane coupling agent]

As the silane coupling agent, there can be cited, for example,

y-(2-aminoethyl)aminopropyltrimethoxysilane,

y-(2-aminoethyl)aminopropylmethyldimethoxysilane,

y-(2-aminoethyl)aminopropyltriethoxysilane,

y-(2-aminoethyl)aminopropylmethyldiethoxysilane,

y-(2-aminoethyl)aminopropylmethyldimethoxysilane,

y-methacryloxypropyltrimethoxysilane, y-methacryloxypropylmethyldimethoxysilane, y

methacryloxypropyltriethoxysilane, y-methacryloxypropylmethyldiethoxysilane,

N-j-(N-vinylbenzylaminoethyl)-y-aminopropyltrimethoxysilane,

N-j-(N-vinylbenzylaminoethyl)-y-aminopropylmethyldimethoxysilane,

N-j-(N-vinylbenzylaminoethyl)-y-aminopropyltriethoxysilane,

N-j-(N-vinylbenzylaminoethyl)-y-aminopropylmethyldiethoxysilane,

y-glycidoxypropyltrimethoxysilane, y-glycidoxypropylmethyldimethoxysilane,

y-glycidoxypropyltriethoxysilane, y-glycidoxypropylmethyldiethoxysilane,

y-mercaptopropyltrimethoxysilane, y-mercaptopropylmethyldimethoxysilane,

y-mercaptopropyltriethoxysilane, y-mercaptopropylmethyldiethoxysilane,

methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, vinyltriacetoxysilane, y-chloropropyltrimethoxysilane, y-chloropropylmethyldimethoxysilane, y-chloropropyltriethoxysilane, y-chloropropylmethyldiethoxysilane, hexamethyldisilazane, y-anilinopropyltrimethoxysilane, y-anilinopropylmethyldimethoxysilane, y-anilinopropyltriethoxysilane, y-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-(methyldiethoxysilyl)propyl]ammonium chloride, y-chloropropylmethyldimethoxysilane, y-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, and so on. The added amount of the silane coupling agent in a chemical treatment agent for forming the chemical treatment film 203 can be, for example, 2 to 80 g/L. When the added amount of the silane coupling agent is less than 2 g/L, the adhesion to the plated surface may be insufficient, leading to a decrease in the work adhesion of the paint film. Further, when the added amount of the silane coupling agent exceeds 80 g/L, the cohesive force of the chemical treatment film may be insufficient, leading to a decrease in the work adhesion of the paint film. The silane coupling agents as described as examples above may be used alone or in combination of two or more.

[0092]

[Zirconium compound]

As the zirconium compound, there can be cited, for example, zirconium normal

propylate, zirconium normal butyrate, zirconium tetraacetylacetonate, zirconium

monoacetylacetonate, zirconium bisacetylacetonate, zirconium monoethylacetoacetate, zirconium acetylacetonate bisethylacetoacetate, zirconium acetate, zirconium monostearate, zirconium carbonate, zirconium ammonium carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and so on. The added amount of the zirconium compound in the chemical treatment agent for forming the chemical treatment film 203 can be, for example, 2 to 80 g/L. When the added amount of the zirconium compound is less than 2 g/L, the adhesion to the plated surface may be insufficient, leading to a decrease in the work adhesion of the paint film. Further, when the added amount of the zirconium compound exceeds 80 g/L, the cohesive force of the chemical treatment film may be insufficient, leading to a decrease in the work adhesion of the paint film. Such zirconium compounds may be used alone or in combination of two or more.

[0093]

[Silica]

As the silica, there can be used, for example, commercially available silica gels

such as "SNOWTEX N," "SNOWTEX C," "SNOWTEX UP," and "SNOWTEX PS"

manufactured by Nissan Chemical Corporation, and "ADELITE AT-20Q" manufactured by

ADEKA CORPORATION, or powdered silica such as AEROSIL #300 manufactured by NIPPON AEROSIL CO., LTD.. Silica can be appropriately selected according to the

required performance of the pre-painted plated steel sheet. The added amount of the

silica in the chemical treatment agent for forming the chemical treatment film 203 is

preferably set to 1 to 40 g/L. When the added amount of the silica is less than 1 g/L, the

work adhesion of the paint film may decrease, and when the added amount of the silica

exceeds 40 g/L, the effects of work adhesion and corrosion resistance are likely to be

saturated, which is uneconomical.

[0094]

[Phosphoric acid and Its salt]

As the phosphoric acid and its salt, there can be cited, for example, phosphoric

acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid and salts thereof, 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), and diethylenetriaminepenta(methylenephosphonic acid) and salts thereof, organic phosphoric acids such as phytic acid and salts thereof, and so on. Incidentally, as salts of phosphoric acid other than ammonium salts, there can be cited metal salts with Na, Mg, Al, K, Ca, Mn,

Ni, Zn, Fe, and so on. The phosphoric acid and its salt may be used alone or in

combination of two or more.

[0095]

Incidentally, the content of the phosphoric acid and its salt is preferably 0 mass%

or more and 20 mass% or less with respect to the solid content of the film. When the

content of the phosphoric acid and its salt exceeds 20 mass%, the film becomes brittle and

the work adhesion of the film may decrease when the pre-painted plated steel sheet is

molded. The content of the phosphoric acid and its salt is more preferably 1 mass% or

more and 10 mass% or less.

[0096]

[Fluoride]

As the fluoride, there can be cited, for example, Ammonium hexaflorozirconate,

Diammonium hexafluorosilicate, Ammonium Hexafluorotitanate(IV), sodium fluoride,

potassium fluoride, calcium fluoride, lithium fluoride, Hexafluorotitanic acid,

Hexafluorozirconic acid, and so on. Such fluorides may be used alone or in combination

of two or more.

[0097]

Incidentally, the content of the fluoride is preferably 0 mass% or more and 20

mass% or less with respect to the solid content of the film. When the content of the fluoride exceeds 20 mass%, the film becomes brittle and the work adhesion of the film may decrease when the pre-painted plated steel sheet is molded. The content of the fluoride is more preferably 1 mass% or more and 10 mass% or less.

[0098]

[Vanadium compound]

As the vanadium compound, there can be cited, for example, vanadium

compounds obtained by reducing pentavalent vanadium compounds such as vanadium

pentoxide, metavanadic acid, ammonium metavanadate, sodium metavanadate, and

vanadium oxytrichloride to 2 to 4 valences with a reducing agent, vanadium compounds

with oxidation numbers of 4 to 2 valences, such as vanadium trioxide, vanadium dioxide, vanadium oxysulfate, vanadium oxyoxalate, vanadium oxyacetylacetonate, vanadium

acetylacetonate, vanadium trichloride, phosphovanadomolybdic acid, vanadium sulfate,

vanadium dichloride, and vanadium oxide, and so on. Such vanadium compounds may

be used alone or in combination of two or more.

[0099] Incidentally, the content of the vanadium compound is preferably 0 mass% or

more and 20 mass% or less with respect to the solid content of the film. When the

content of the vanadium compound exceeds 20 mass%, the film becomes brittle and the

work adhesion of the film may decrease when the pre-painted plated steel sheet is molded.

The content of the vanadium compound is more preferably 1 mass% or more and 10

mass% or less.

[0100]

[Tannin or tannic acid]

As the tannin or tannic acid, hydrolyzable tannin and condensed tannin both can

be used. As examples of tannin and tannic acid, there can be cited hamamelitannin, gall

tannin, gallnut tannin, myrobalan tannin, divi-divi tannin, algarovilla tannin, valonia tannin, catechin, and so on. The added amount of the tannin or tannic acid in the chemical treatment agent for forming the chemical treatment film 203 can be set to 2 to 80 g/L.

When the added amount of the tannin or tannic acid is less than 2 g/L, the adhesion to the

plated surface may be insufficient, leading to a decrease in the work adhesion of the paint

film. Further, when the added amount of the tannin or tannic acid exceeds 80 g/L, the

cohesive force of the chemical treatment film may be insufficient, leading to a decrease in

the work adhesion of the paint film.

[0101]

Further, an acid, an alkali, or the like may be added to the chemical treatment

agent for forming the chemical treatment film 203 in order to adjust pH within a range that

does not impair the performance.

[0102]

The chemical treatment agent containing various components as described above

is applied to one side or both sides of the plated steel sheet 10 for pre-painted steel sheet,

and then dried to form the chemical treatment film 203. In the pre-painted steel sheet

according to this embodiment, it is preferable to form a chemical treatment film of 10 to

1000 mg/m2 per side on the plated steel sheet for pre-painted steel sheet. The amount of

the chemical treatment film 203 is more preferably 20 to 800 mg/m2 and most preferably

50 to 600 mg/m2 . Incidentally, the film thickness (a thickness d2 in FIG. 3A and FIG.

3B) of the chemical treatment film 203 corresponding to such an amount is approximately

0.01 to 1 m, depending on the components contained in the chemical treatment agent.

[0103]

The paint film 205 according to this embodiment is a layer formed on the

chemical treatment film 203 as described above. Such a paint film 205 may be composed

of a single layer, as schematically illustrated in FIG. 3A and FIG. 3B, or may be composed of two or more layers.

[0104]

Here, when the paint film 205 is composed of two or more layers, the paint film in

contact with the chemical treatment film 203 is also called a primer paint film, and is often

provided to ensure the adhesion and corrosion resistance of the entire paint film 205 and

the chemical treatment film 203. On the other hand, the paint film located above such a

primer paint film is also called a top paint film, and is often provided to ensure design,

barrier properties, and other surface functionality through coloring.

[0105]

Further, when the paint film 205 is composed of a single layer, such a paint film

205 is often provided so as to exhibit at least any of the functions exhibited by the primer

paint film and the top paint film described above.

[0106]

Such a paint film 205 contains at least resin. Moreover, such a paint film 205

preferably further contains a pigment. In addition to these components, the paint film 205

may contain various additives such as a leveling agent, an antifoaming agent, a coloring

agent, a viscosity modifier, and an ultraviolet absorber. Incidentally, a painting solution

for forming the paint film 205 is preferably obtained by dispersing or dissolving each of

the above components in a solvent.

[0107]

In the following, in order to explain the configuration of the paint film 205

according to this embodiment in more detail, for convenience, there is explained in detail

the case where the paint film 205 is composed of a primer paint film and a top paint film as

an example.

[0108]

[Primer paint film]

An appropriate base paint for the primer paint film may be selected according to

the usage environment and application of the pre-painted plated steel sheet. As the type

of resin for the base paint, generally well-known ones can be used. As such a resin, there can be cited, for example, a polyacrylic-based resin, a polyolefin-based resin, a

polyurethane-based resin, an epoxy-based resin, a polyester-based resin, a

polybutyral-based resin, a melamine-based resin, a silicon resin, a fluorocarbon resin, an

acrylic resin, and so on, and these resins can be used as they are or in combination.

Further, these resins can be cured with any curing agent. The base paint can be used in

any form such as an organic solvent-based form, water-based form, or powder-based form.

[0109]

Such a base paint preferably contains an anti-corrosive pigment, and more

preferably contains a chromate-free anti-corrosive pigment in particular. As the

chromate-free anti-corrosive pigment in the base paint, there can be used calcium

ion-exchanged silica (commonly called calcium silicate in some cases), aluminum

tripolyphosphate, phosphorus and vanadium pigment (PV pigment), zinc phosphate, iron

phosphate, aluminum phosphate, calcium molybdate, aluminum molybdate, barium

molybdate, vanadium oxide, water-dispersible silica, fumed silica, orthophosphoric acid,

pyrophosphoric acid, metaphosphoric acid, hypophosphoric acid, phosphorous acid,

hypophosphorous acid and salts thereof, and so on. The content of such an anti-corrosive

pigment is preferably, for example, 5 to 70 mas% with respect to the solid content of the

paint film. When the content of the anti-corrosive pigment is less than 5 mass%, in

addition to the possibility that the effect of corrosion resistance cannot be sufficiently

ensured, the rigidity and cohesive force of the paint film decrease, resulting in that paint

film peeling (namely, paint film scuffing as physical peeling) is likely to occur in some

cases when the surface of the paint film rubs against a mold during pressing of the painted

plated steel sheet. Further, when the content of the anti-corrosive pigment exceeds 70 mass%, workability sometimes decreases. From the viewpoint of the balance between corrosion resistance, chemical resistance, and workability, the content of the anti-corrosive pigment is more preferably 15 to 70 mass%, and still more preferably 20 to 50 mass%.

[0110]

As the curing agent, it is preferable to use an amino resin such as a melamine resin,

a urea resin, or a benzoguanamine resin, or an isocyanate compound and its block. The

mass ratio of the curing agent and the resin in the dry paint film is preferably 5 to 30 parts

by mass of the curing agent with respect to 100 parts by mass of the total amount of the

resin and the curing agent. When the amount of the curing agent is 5 parts by mass or

less, adhesion and corrosion resistance may not be sufficiently exhibited, and when it is 30

parts by mass or more, workability and chemical resistance may decrease.

[0111]

The film thickness of the primer paint film before molding is generally 2 m or

more and 10 m or less as the pre-painted plated steel sheet. In this embodiment as well,

the film thickness of the primer paint film is preferably 2 to 10 m. When the film

thickness of the primer paint film is less than 2 m, the functions such as corrosion

resistance required as the pre-painted plated steel sheet may not be exhibited sufficiently.

On the other hand, when the film thickness of the primer paint film exceeds 10 m, the

workability of the paint film may decrease.

[0112]

After applying a primer paint component containing the components forming the

primer paint film as described above, the primer paint component is baked at a temperature

of 150°C or more and less than 300°C to be cured and dried. When the baking

temperature is less than 150°C, adhesion may not be sufficiently ensured, and when the

baking temperature is 300°C or more, thermal degradation of the resin component may

occur, resulting in a decrease in the workability.

[0113] Incidentally, the application of the primer paint component as described above can

be performed by generally well-known coating methods such as roll coating, curtain flow

coating, air spray, airless spray, immersion, bar coating, or brush coating, for example.

[0114]

[Top paint film]

An appropriate base paint for the top paint film may be selected according to the

usage environment and application of the pre-painted plated steel sheet. As the type of

resin for the base paint, generally well-known ones can be used. As such a resin, there

can be cited, for example, a polyacrylic-based resin, a polyolefin-based resin, a

polyurethane-based resin, an epoxy-based resin, a polyester-based resin, a

Incidentally, the resin contained in the base paint of the top paint film may be of the same

type as or different from that contained in the base paint film of the primer paint film.

However, considering the adhesion between the primer paint film and the top paint film, it

is preferable to use the same type of base paint as each other,

[0115] For use applications with more demanding formability, the base paint preferably

contains a high-molecular polyester resin and a curing agent. The high-molecular

polyester resin can be selected according to the application of the pre-painted plated steel

sheet, and any high-molecular polyester-based resin that is usually used as a solvent-based

paint can also be used. Such a high-molecular polyester-based resin is preferably a

high-molecular polyester resin in which the main resin is composed of ester bonds of two or more resin monomers.

[0116] As a curing agent used to form a thermosetting resin paint film by reaction with

the above-described high-molecular polyester resin, it is possible to use an amino resin

such as a melamine resin, a urea resin, or a benzoguanamine resin, or an isocyanate

compound and its block. The mass ratio of the curing agent and the resin in the dry paint

film is preferably 10 to 35 parts by mass of the curing agent with respect to 100 parts by

mass of the total amount of the resin and the curing agent. When the amount of the

curing agent is less than 10 parts by mass, adhesion, corrosion resistance, solvent

resistance, or the like may not be sufficiently exhibited, and when it exceeds 35 parts by

mass, workability, chemical resistance, and impact resistance may decrease.

[0117] Further, the top paint film can further contain additives such as a pigment,

surface-modified metal powders or glass powders, a dispersing agent, a leveling agent, a

wax, an aggregate, and fluorocarbon resin beads, a diluting solvent, and so on as needed.

[0118]

The film thickness of the top paint film before molding is preferably in the range

of 5 to 25 m, for example. When the top paint film is composed of a plurality of layers, the total thickness is preferably within the range of 5 to 25 m.

[0119]

After applying the paint component for the top paint film, the paint component is

baked at a temperature of 150°C or more and less than 300°C to be cured and dried.

When the baking temperature is less than 150°C, adhesion of each paint film may not be

sufficiently ensured, and when the baking temperature is 300°C or more, thermal

degradation of the resin component such as a polyester resin component may occur, resulting in a decrease in the workability.

[0120]

Incidentally, the application of the top paint can be performed by a generally

well-known application method such as roll coating, curtain flow coating, air spray, airless

spray, immersion, bar coating, or brush coating, for example.

[0121]

The chemical treatment film, the primer paint film, and the top paint film

according to this embodiment have been explained above with reference to the chemical

treatment agent and the paint components used to form the respective films. Ordinary,

when these treatment agents and components are applied to plated steel sheets, these

components are usually different from the composition of the film formed. For example,

with the chemical treatment agent, the composition of the chemical treatment agent and the

composition of the chemical treatment film after application are different due to the

reaction with the plated steel sheet, volatilization of volatile components in the chemical

treatment agent, or the like, and it is usually technically difficult to determine the

composition of the formed chemical treatment film. Further, it is also technically difficult

in reality to specify the composition of such a chemical treatment film by instrumental

analysis or the like. This is also true for the primer paint film and the top paint film.

Thus, in this embodiment, the chemical treatment film, the primer paint film, and the top

paint film that are formed are specified by specifying the compositions of the chemical

treatment agents and the paint components.

[0122]

Based on the previously explained findings, in the pre-painted plated steel sheet

20 according to this embodiment, the state of metals, oxides, and hydroxides of magnesium

and aluminum at the interface of the plating layer 201 (more precisely, the interface

between the plating layer 201 and the chemical treatment film 203) is specified.

[0123]

Here, in this embodiment, as schematically illustrated in FIG. 4, at a "position B"

located at a depth of 10 nm from the interface between the plating layer 201 and the

chemical treatment film 203 toward the inside of the plating layer 201, the state of metals,

oxides, and hydroxides of magnesium and aluminum is specified, and the state of these

substances at the interface of the plating layer 201 is determined.

[0124]

In this embodiment, the position of the interface between the plating layer 201 and

the chemical treatment film 203 can be specified from the element profile in the depth

direction of the pre-painted plated steel sheet, which is obtained by analyzing the

pre-painted plated steel sheet by XPS. That is, in this embodiment, an element contained

in the chemical treatment film 203 is used as a marker, and the place where the strength of

the marker element decreases by half in the depth direction is defined as the interface

between the plating layer 201 and the chemical treatment film 203.

[0125]

Here, the measurement conditions of XPS for the depth profile analysis and the

measurement conditions for the state analysis of metals, oxides, and hydroxides of

magnesium and aluminum are the same as those of XPS in the plated steel sheet 10 for

pre-painted steel sheet described previously.

[0126]

That is, the state analysis of metals, oxides, and hydroxides of magnesium and

aluminum are specified by XPS. The XPS analysis is performed by Quantum 2000

manufactured by ULVAC-PHI, Inc. with X-ray source: Al Ka, X-ray output 15 kV, 25 W,

measurement region: 300 x 300 m square, degree of vacuum: 1.5 x 10-9 Torr, detection

accuracy: 45°. Further, sputtering for the depth profile analysis is performed with ion

species: Ar, acceleration voltage: 1 kV, region: 1 x 1 mm, and sputtering rate: 2.7 nm/min

(in terms of SiO 2 ). The sputtering is performed based on the above-described sputtering

rate, and the position specified by this sputtering is regarded as the "position B" described

above.

[0127]

spectrum in the region of 295 to 325 cm-1 by Mg KLL. The separation of attributions of

the ratio (presence ratio) between oxide and hydroxide of aluminum and metal aluminum

is calculated from the intensity ratio of the peaks attributed to the respective substances

(oxide, hydroxide, and metal) from a narrow spectrum in the region of 68 to 84 cm-' by Al

2p in the same manner.

[0128]

At the interface of the plating layer 201 according to this embodiment, the ratio of

oxide and hydroxide of magnesium at a depth of 10 nm from the interface of the plating

layer (position B in FIG. 4) specified as described above is 0.30 or less with respect to the

ratio of metal magnesium. When the presence ratio of oxide and hydroxide of

magnesium to metal magnesium is 0.30 or less, good paint film adhesion at the molded

portion is achieved, thereby making it possible to inhibit the occurrence of paint film

floating portions even when the pre-painted plated steel sheet 20 according to this

embodiment is drawn. On the other hand, when the above-described presence ratio of

oxide and hydroxide of magnesium exceeds 0.30, good paint film adhesion at the molded

portion cannot be exhibited, failing to inhibit the occurrence of paint film floating portions.

The presence ratio of oxide and hydroxide of magnesium to metal magnesium is preferably

0.25 or less and more preferably 0.20 or less. Further, the lower limit value of the

presence ratio of oxide and hydroxide of magnesium to metal magnesium is substantially

0.01 or so.

[0129]

Further, at the interface of the plating layer 201 according to this embodiment, the

ratio of oxide and hydroxide of aluminum at a depth of 10 nm from the interface of the

plating layer (position B in FIG. 4) specified as described above is preferably 0.30 or less

with respect to the ratio of metal aluminum. When the presence ratio of oxide and

hydroxide of aluminum to metal aluminum is 0.30 or less, good paint film adhesion at the

molded portion is achieved, thereby making it possible to more reliably inhibit the

occurrence of paint film floating portions even when the pre-painted plated steel sheet 20

according to this embodiment is drawn. On the other hand, when the above-described

presence ratio of oxide and hydroxide of aluminum exceeds 0.30, good paint film adhesion

at the molded portion cannot be achieved in some cases. The presence ratio of oxide and

hydroxide of aluminum to metal aluminum is more preferably 0.25 or less and still more

preferably 0.20 or less. Further, the lower limit value of the presence ratio of oxide and

hydroxide of aluminum to metal aluminum is substantially 0.01 or so.

[0130]

Here, the measurement by XPS is performed on a region having a size of 300 m

x 300 [m, and the presence ratio calculated as described above means an average value in

the measurement region as described above.

[0131]

The pre-painted plated steel sheet 20 according to this embodiment has been

explained in detail above with reference to FIG. 3A to FIG. 4.

[0132]

(Regarding the molded product)

Next, there is explained in detail a molded product using the pre-painted plated

steel sheet 20 as explained above with reference to FIG. 5.

[0133]

As schematically illustrated in FIG. 5 as an example, a molded product 30

according to this embodiment is one formed in a manner that the pre-painted plated steel

sheet 20 as explained above is subjected to various workings such as deep drawing and

square cylinder pressing to be molded into a desired shape.

[0134]

Here, the average composition of a plating layer included in the molded product

30 according to this embodiment is the same as that of the plating layer 201 included in the

pre-painted plated steel sheet 20 serving as a base, and thus, the plating layer included in

the molded product 30 contains 0.5 to 60.0 mass% of aluminum and 0.5 to 15.0 mass% of

magnesium. Of the plating layers, the plating layer included in the molded product 30

according to this embodiment preferably contains 5 mass% or more and 15 mass% or less

of aluminum and 2 mass% or more and 4 mass% or less of magnesium. The plating layer

of the molded product 30 contains aluminum and magnesium in the above-described

contents, thereby making it possible to achieve desired corrosion resistance more reliably.

Incidentally, in the plating layer in the molded product 30, the balance other than the

above-described aluminum and magnesium is elements derived from the external

environment, zinc, and impurities.

[0135]

Examples of a specific shape of the molded product 30 according to this

embodiment include various shapes that various parts have, including articles mainly used

outdoors such as air conditioner outdoor units and water heaters.

[0136]

Various well-known methods can be employed as a working method used for

working the pre-painted plated steel sheet 20 according to this embodiment to form a

molded product. Further, the working conditions may be appropriately set according to the working method to be used, the shape of the molded product, or the like.

[0137]

It can be said that working the top plate of an air conditioner outdoor unit, which

is an example of the above molded product, is a severe molding work for the pre-painted

plated steel sheet 20. Although the degree of working differs among air conditioner

companies, in each of the companies, one type of high-speed square cylinder pressing is

performed to form the top plate of the outdoor unit. At each of four comers of the top

plate, a compressed portion and an elongated portion are made. When a general

pre-painted plated steel sheet is used, paint film floating frequently occurs at the

compressed portions, and paint film peeling frequently occurs at the elongated portions.

[0138]

However, when the pre-painted plated steel sheet 20 according to this embodiment

is used as a material, it is possible to inhibit the occurrence of paint film floating portions

and paint film peeling more reliably because at the interface of the plating layer of the

pre-painted plated steel sheet 20, the state of metals, oxides, and hydroxides of magnesium

and aluminum is appropriately controlled.

[0139]

[Regarding measured values by the SAICAS method>

In the molded product formed of the pre-painted plated steel sheet according to

this embodiment, the peel strength obtained by measuring a specific portion by the

SAICAS method and the peel state of this portion are specified.

[0140]

In the molded product according to this embodiment, which is schematically

illustrated in FIG. 5 as an example, the portion where the thickness of the pre-painted

plated steel sheet of the molded product has increased by 5% or more (in FIG. 5, for

example, a portion surrounded by a dotted line, and a portion where the relationship of (d' - d)/d > 0.05 is established when the thickness is d') compared to a thickness d of the pre-painted plated steel sheet before molding, (which can also be regarded as a non-molded portion), is a portion where the plated steel sheet is compressed and elongated by working, and the compression exceeds the elongation. Hereinafter, such a portion where the thickness has increased by 5% or more is referred to as a "compressed portion." Such a compressed portion is a portion where the paint film tends to float in the molded product.

[0141]

In the molded product according to this embodiment, in the portion where the

thickness of the pre-painted plated steel sheet has increased by 5% or more compared to

that before molding (namely, the compressed portion), the peel strength between the

chemical treatment film and the paint film (or the primer paint film when the paint film is

composed of a plurality of layers) is measured by the SAICAS method and is 1.00 kN/m or

more on average. In addition, when such a compressed portion is cut by the SAICAS

method, 20% or less of a cut area is in the form of interfacial peeling, and the remaining

cut area is in the form of cohesive failure within the paint film (the primer paint film when

the paint film is composed of a plurality of layers). When the compressed portion does

not satisfy all of the above-described conditions regarding the peel strength and the peeled

area, the chemical treatment film is destroyed by working with compression, resulting in a

decrease in the adhesion. In addition, an internal stress of the paint film concentrates at

the interface between the chemical treatment film and the paint film (the primer paint film

when the paint film is composed of a plurality of layers) or the interface between the

chemical treatment film and the plating layer, resulting in that the paint film adhesion

during compression is insufficient at the portion with the lowest adhesion strength, causing

the paint film to float.

[0142]

Incidentally, if the thickness of the pre-painted plated steel sheet in the molded product has increased by 5% or more compared to that before molding, no significant difference due to the difference in % is observed in the measurement results by the

SAICAS method.

[0143]

In the molded product according to this embodiment, the above-described peel

strength according to the SAICAS method is preferably an average of 1.10 kN/m or more

and more preferably 1.20 kN/m or more. Incidentally, a higher upper limit value of the

peel strength is better. The upper limit of the above-described peel strength is

substantially 1.5 kN/m or so.

[0144]

Further, regarding the cut area of the compressed portion of the molded product

according to this embodiment by the SAICAS method, the ratio of the portion that is in the

form of interfacial peeling is preferably 15% or less and more preferably 10% or less.

Incidentally, a smaller lower limit value of the ratio of the portion that is in the form of

interfacial peeling is better. The lower limit of the ratio of the portion that is in the form

of interfacial peeling is substantially 0%.

[0145]

[Method of measuring the peel strength and the peel form by the SAICAS method]

The peel strength and the peel form by the SAICAS method for the focused

molded product using the pre-painted plated steel sheet are measured as follows.

First, three or more flat portions of the focused molded product, which are

considered to be non-molded portions, are specified, and the total thickness of each of the

flat portions (including the plated steel sheet of the base and the paint films on the front

and back surfaces) is measured three times with a microgauge, to calculate the average

value of the measured thicknesses. Such measurements are performed at a plurality of

specified positions, and an average value at each of the positions is further calculated.

The average value of the obtained values at a plurality of positions is set to the thickness of

the pre-painted plated steel sheet before molding (for example, the thickness d in FIG. 5) in

the focused molded product.

[0146]

Further, a measurement sample (having a size of roughly 20 mm x 20 mm or

more) is cut out from a portion that seems to have been subjected to various moldings such

as deep drawing, and is smoothed with a steel plate straightener (leveler). Of the obtained

measurement sample, the total thickness (including the plated steel sheet of the base and

the paint films on the front and back surfaces) is measured with a microgauge, and the

increase ratio is calculated based on the obtained measured value and the thickness of the

pre-painted plated steel sheet before molding, which is obtained as described above. The

portion exhibiting a value of 5% or more in terms of the increase ratio obtained in this

manner is defined as the compressed portion of the molded product. Incidentally, in

various moldings such as deep drawing, the upper limit of the increase ratio described

above is about 11%.

[0147]

The peel strength and the peel form of the paint film are measured by cutting the

compressed portion specified as above while using a measuring device that can utilize the

SAICAS method (for example, DN-GS model manufactured by DAIPLA WINTES CO.,

LTD.). Incidentally, the cutting direction in the SAICAS method is set to be parallel to

the edge line of the steel sheet after drawing.

[0148]

Incidentally, it is possible to confirm that there is no difference in the value of the

increase ratio calculated by the above method within the above range, as compared to the

value calculated from the thickness of the base measured in a state where pre-painted

plated steel sheets before and after molding are prepared and paint films are removed from the front and back surfaces of the pre-painted plated steel sheets before and after molding with a paint film remover.

[0149]

The cutting conditions for the SAICAS method are as follows.

A diamond blade (0.3 mm in width) is used as a cutting blade, and oblique cutting

is performed in a constant speed mode with a horizontal velocity of 1 m/sec. and a

vertical velocity of 0.1 m/sec. and then near the interface, the cutting is switched to only

the horizontal movement to cut a length of 200 m, and the average peel strength during

the horizontal movement is measured. The depth position at which to switch to

horizontal movement is set by specifying the interface position (a position at the very limit

where the plating is not cut) through a preliminary experiment. When the plated surface

is cut due to the unevenness of the plating during the horizontal movement of the cutting

blade, the peel strength can be discriminated because it momentarily increases abnormally.

Such a case is excluded as an abnormal value, and the average peel strength is calculated.

Incidentally, the number of measurements n = 3 is set, and the average value of the three

values of the average peel strength is taken as the peel strength.

[0150]

The method of measuring the ratio of the interfacial peeling form and the cohesive

failure form in the cut portion during horizontal movement is as follows.

Observation of the surface of the cut portion by the SAICAS method with an

optical microscope makes it possible to clearly distinguish the difference in peel form for

each portion. (A) When an extremely thin paint film remains on the cut portion, it is

possible to determine that the peel form is thin-layer cohesive failure within the paint film

because coloration due to the resin and pigment in the paint film is observed. (B) When

the cut portion is interfacial peeling, the appearance of the plated surface of the base is

observed. No strong reflection is seen even when such a portion is irradiated with light, resulting in a blackish appearance. Further, in the case of interfacial peeling, the fact that the peel strength by the SAICAS method decreases locally is also a determining factor.

This is because although the moving position of the cutting blade is within the paint film

immediately above the interface, interfacial peeling occurs as a result of the peeling

position shifting to the interface because the adhesion force of the interface is lower than

the cohesive force of the paint film. (C) When the cut portion is cohesive failure of the

plating layer, a metallic luster is observed, and when such a portion is irradiated with light,

the light is strongly reflected, resulting in that distinguishing from interfacial peeling is

easy. Further, the fact that the peel strength by the SAICAS method increases locally is

also a determining factor.

[0151]

An optical micrograph of a horizontal cut range (having a size of 300 pm x 200

m) by the SAICAS method is taken, portions of the paint film cohesive failure, the

interfacial peeling, and the plating layer cohesive failure within the same range are

specified according to the above criteria, and areas of the portions are measured using

image processing software or transparent graph paper. Then, the ratio of the interfacial

peeling area to the area excluding the plating layer cohesive failure is calculated from the

horizontal cut range by the SAICAS method.

[0152]

The molded product according to this embodiment has been explained in detail

above with reference to FIG. 5.

[0153]

As explained above, according to this embodiment, by using the plated steel sheet

for pre-painted steel sheet according to this embodiment, it is possible to obtain a molded

body formed of the pre-painted plated steel sheet and the pre-painted steel sheet that does

not cause paint film floating portions or paint film peeling at the portion worked by drawing or the like.

[0154]

«Second embodiment>>

(Regarding the plated steel sheet for pre-painted steel sheet)

First, there is explained a plated steel sheet for pre-painted steel sheet according to

the second embodiment of the present invention in detail with reference to FIG. 1A to FIG.

2.

[0155]

As has been schematically illustrated in FIG. 1A, a plated steel sheet 10 for

pre-painted steel sheet according to this embodiment includes a steel sheet 101 serving as a

base material and a plating layer 103 located on one side of the steel sheet. Further, in the

plated steel sheet 10 for pre-painted steel sheet according to this embodiment, as has been

schematically illustrated in FIG. 1B, the plating layers 103 may be located on both sides of

the steel sheet 101 serving as the base material.

[0156]

The steel sheet 101 used as the base material of the plated steel sheet 10 for

pre-painted steel sheet according to this embodiment has the same configuration as the

steel sheet 101 in the plated steel sheet 10 for pre-painted steel sheet according to the first

embodiment, and exhibits the same effect. Therefore, its detailed explanation is omitted

below.

[0157]

least one surface of the steel sheet 101, as has been schematically illustrated in FIG. 1A

and FIG. 1B, and is provided to improve the corrosion resistance of the plated steel sheet

10 for pre-painted steel sheet. Here, the plating layer 103 according to this embodiment

has the same configuration of the chemical composition as the plating layer 103 in the

plated steel sheet 10 for pre-painted steel sheet according to the first embodiment, and

exhibits the same effect. Therefore, its detailed explanation is omitted below.

[0158]

[Regarding the average film thickness of the plating layer 103]

Further, in the plated steel sheet 10 for pre-painted steel sheet according to this

embodiment, the average film thickness of the plating layer 103 (the thickness dl in FIG.

1A and FIG. 1B) is also the same as that in the first embodiment, and therefore, its detailed

explanation is omitted below.

[0159]

this embodiment, the state of metal, oxide, and hydroxide of zinc on the surface of the

plating layer 103 is defined.

[0160]

Here, on the surface of the plating layer 103, various unintended impurities may

exist in addition to the metal, oxide, and hydroxide of zinc, and the like. Therefore, in

this embodiment as well, as has been schematically illustrated in FIG. 2, the state of metal,

oxide, and hydroxide of zinc is specified at the "position A," which is located at a depth of

10 nm from the surface of the plating layer 103, and the state of these substances on the

surface of the plating layer 103 is determined.

[0161]

The state analysis of metal, oxide, and hydroxide of zinc is specified by XPS.

The XPS analysis is performed by Quantum 2000 manufactured by ULVAC-PHI, Inc. with

X-ray source: Al Ka, X-ray output 15 kV, 25 W, measurement region: 300 x 300 m square, degree of vacuum: 1.5 x 10-9 Torr, detection accuracy: 45°. Further, sputtering for the depth profile analysis is performed with ion species: Ar*, acceleration voltage: 1 kV, region: 1 x 1 mm, and sputtering rate: 2.7 nm/min (in terms of SiO 2 ). The sputtering is performed based on the above-described sputtering rate, and the position specified by this sputtering is regarded as the "position A" described above.

[0162]

hydroxide of zinc and metal zinc is calculated from the intensity ratio of the peaks

attributed to the respective substances (oxide, hydroxide, and metal) from a narrow

spectrum in the region of 480 to 515 cm-1 by Zn 2p.

[0163]

In the plating layer 103 in this embodiment, the ratio of oxide and hydroxide of

zinc at a depth of 10 nm from the surface of the plating layer (position A in FIG. 2)

specified as described above is 7.0 or more with respect to the ratio of metal zinc. The

presence ratio of oxide and hydroxide of zinc to metal zinc is 7.0 or more, and thereby,

good paint film adhesion at the molded portion can be achieved to inhibit the occurrence of

paint film floating portions even when the pre-painted plated steel sheet using the plated

steel sheet 10 for pre-painted steel sheet including the plating layer 103 according to this

oxide and hydroxide of zinc is less than 7.0, good paint film adhesion at the molded

The presence ratio of oxide and hydroxide of zinc to metal zinc is preferably 8.0 or more

and more preferably 9.0 or more. Further, the upper limit value of the presence ratio of

oxide and hydroxide of zinc to metal zinc is substantially 20.0 or so.

[0164]

Here, the measurement by XPS is performed on a region having a size of 300 m x 300 [m, and the presence ratio calculated as described above means an average value in the measurement region as described above.

[0165]

has been explained in detail above with reference to FIG. 1A to FIG. 2.

[0166]

101 as necessary. Thereafter, a non-oxidizing furnace type hot-dip plating method is

applied to the steel sheet 101 that has undergone the pretreatments as necessary, and

thereby a plating layer is formed.

[0167]

thereby satisfy the conditions regarding the XPS spectrum mentioned previously.

[0168]

formed.

[0169]

While measuring the XPS spectrum of the plating layer obtained in the above

as described above, can be manufactured.

[0170]

Here, any alkali treatment, acid treatment, or mechanical cutting to be applied

may be performed, and these treatments may be combined in various ways.

[0171]

hydroxide of zinc on the surface of the plating layer tends to be. For example, as the

alkali treatment, when spraying is performed at 50°C using a commercially available

standard sodium orthosilicate-based (medium alkaline type) degreasing solution, if the

spray time is about 10 seconds or less, the presence ratio of oxide and hydroxide of zinc on

the surface of the plating layer cannot satisfy the specified conditions, but if the spray time

is prolonged, the conditions will be satisfied, and if it is prolonged to about 2 minutes, the

conditions will be satisfied reliably. Further, if the concentration of this degreasing

solution is doubled, the conditions will be reliably satisfied in about 30 seconds.

the component of metal zinc may be dissolved to be transformed into oxide or hydroxide

and redeposited on the plated surface.

[0172]

Further, for example, in the case of performing the acid treatment, such a

treatment exhibits the effect of removing oxide and hydroxide of zinc on the surface of the

plating layer, unlike the alkali treatment. Therefore, the specified conditions can be

the presence ratio of oxide and hydroxide of zinc on the surface of the plating layer can

satisfy the specified conditions. However, spraying for a longer time does not satisfy the

conditions.

[0173]

Further, for example, in the case of performing the mechanical cutting, such

cutting exhibits the effect of removing all of metal zinc and oxide and hydroxide on the

surface of the plating layer. Therefore, it is preferable to use a nylon brush, a grindstone

with an appropriate grain size, or the like, and perform the cutting under mild conditions to

the extent of removing contaminant components adhering to the plated surface. After the

mechanical cutting, the surface is washed with water to remove cutting contaminants.

[0174]

Examples of the various treatment methods have been described above, but the

pre-painted steel sheet according to this embodiment may be manufactured by

appropriately selecting optimum conditions.

[0175]

(Regarding the pre-painted plated steel sheet)

Then, the pre-painted plated steel sheet using the plated steel sheet 10 for

3A to FIG. 4.

[0176]

As has been schematically illustrated in FIG. 3A, a pre-painted plated steel sheet

20 according to this embodiment uses the plated steel sheet 10 for pre-painted steel sheet

explained previously as the base material. Such a pre-painted plated steel sheet 20

films 203, and the paint films 205 formed on both sides of the steel sheet 101, as has been

schematically illustrated in FIG. 3B.

[0177]

embodiment has the same configuration as the steel sheet 101 in the plated steel sheet 10

for pre-painted steel sheet explained previously, and exhibits the same effect. Therefore,

its detailed explanation is omitted below.

[0178]

is omitted below.

[0179]

Incidentally, there is explained the state of metal, oxide, and hydroxide of zinc

exhibited by the plating layer 201 of the pre-painted plated steel sheet 20 according to this

embodiment below.

[0180]

The chemical treatment film 203 according to this embodiment is a film layer

step.

[0181]

The detailed configuration of the chemical treatment film 203 according to this

embodiment is the same as that of the first embodiment, and the same effect is exhibited.

Therefore, its detailed explanation is omitted below.

[0182]

The paint film 205 according to this embodiment is a layer formed on the

of a single layer, as has been schematically illustrated in FIG. 3A and FIG. 3B, or may be

composed of two or more layers. Here, the detailed configuration of the paint film 205

according to this embodiment is the same as that of the first embodiment, and the same

effect is exhibited. Therefore, its detailed explanation is omitted below.

[0183]

Based on the findings explained previously, in the pre-painted plated steel sheet

20 according to this embodiment, the state of metal, oxide, and hydroxide of zinc at the interface of the plating layer 201 (more precisely, the interface between the plating layer

201 and the chemical treatment film 203) is specified.

[0184]

Here, in this embodiment, as has been schematically illustrated in FIG. 4, at the

"position B" located at a depth of 10 nm from the interface between the plating layer 201

and the chemical treatment film 203 toward the inside of the plating layer 201, the state of

metal, oxide, and hydroxide of zinc is specified, and the state of these substances at the

interface of the plating layer 201 is determined.

[0185]

between the plating layer 201 and the chemical treatment film 203.

[0186]

Here, the measurement conditions of XPS for the depth profile analysis and the

measurement conditions for the state analysis of metal, oxide, and hydroxide of zinc are

the same as those of XPS in the plated steel sheet 10 for pre-painted steel sheet described

previously.

[0187]

That is, the state analysis of metal, oxide, and hydroxide of zinc is specified by

XPS. The XPS analysis is performed by Quantum 2000 manufactured by ULVAC-PHI,

Inc. with X-ray source: Al Ka, X-ray output 15 kV, 25 W, measurement region: 300 x 300

pm square, degree of vacuum: 1.5 x 10-9 Torr, detection accuracy: 45°. Further, sputtering for the depth profile analysis is performed with ion species: Ar*, acceleration voltage: 1 kV, region: 1 x 1 mm, and sputtering rate: 2.7 nm/min (in terms of Si 2 ). The sputtering is performed based on the above-described sputtering rate, and the position specified by this sputtering is regarded as the "position B" described above.

[0188] Here, the separation of attributions of the ratio (presence ratio) between oxide and

spectrum in the region of 480 to 515 cm-1 by Zn 2p.

[0189]

oxide and hydroxide of zinc at a depth of 10 nm from the interface of the plating layer

(position B in FIG. 4) specified as described above is 7.0 or more with respect to the ratio

of metal zinc. When the presence ratio of oxide and hydroxide of zinc to metal zinc is 7.0

or more, good paint film adhesion at the molded portion is achieved, thereby making it

possible to inhibit the occurrence of paint film floating portions even when the pre-painted

plated steel sheet 20 according to this embodiment is drawn. On the other hand, when the

above-described presence ratio of oxide and hydroxide of zinc is less than 7.0, good paint

film adhesion at the molded portion cannot be exhibited, failing to inhibit the occurrence of

paint film floating portions. The presence ratio of oxide and hydroxide of zinc to metal

zinc is preferably 8.0 or more and more preferably 9.0 or more. Further, the upper limit

value of the presence ratio of oxide and hydroxide of zinc to metal zinc is substantially

20.0 or so.

[0190]

Here, the measurement by XPS is performed on a region having a size of 300 m

x 300 [m, and the presence ratio calculated as described above means an average value in the measurement region as described above.

[0191]

The pre-painted plated steel sheet 20 according to this embodiment has been

explained in detail above with reference to FIG. 3A to FIG. 4.

[0192] (Regarding the molded product)

steel sheet 20 as explained above with reference to FIG. 5.

[0193]

As has been schematically illustrated in FIG. 5 as an example, a molded product

30 according to this embodiment is one formed in a manner that the pre-painted plated

steel sheet 20 as explained above is subjected to various workings such as deep drawing

and square cylinder pressing to be molded into a desired shape.

[0194]

Here, the average composition of a plating layer included in the molded product 30 according to this embodiment is the same as that of the plating layer 201 included in the

of the molded product 30 contains aluminum and magnesium in the above-described

above-described aluminum and magnesium is elements derived from the external

environment, zinc, and impurities.

[0195]

Examples of a specific shape of the molded product 30 according to this

outdoors such as air conditioner outdoor units and water heaters.

[0196]

Various well-known methods can be employed as a working method used for

molded product. Further, the working conditions may be appropriately set according to

the working method to be used, the shape of the molded product, or the like.

[0197]

performed to form the top plate of the outdoor unit. At each of four corners of the top

plate, a compressed portion and an elongated portion are made. When a general

[0198]

is used as a material, at the interface of the plating layer of the pre-painted plated steel

sheet 20, the state of metal, oxide, and hydroxide of zinc is appropriately controlled, thus

making it possible to inhibit the occurrence of paint film floating portions and paint film

peeling more reliably.

[0199]

[Regarding measured values by the SAICAS method>

In the molded product formed of the pre-painted plated steel sheet according to

SAICAS method and the peel state of this portion are specified. Here, the measurement

method by the SAICAS method and the conditions required for the obtained measurement

values are the same as those described in thefirst embodiment, and thus, their detailed

explanations are omitted below.

[0200]

not cause paint film floating portions or paint film peeling at the portion worked by

drawing or the like.

[0201]

«Third embodiment>>

The third embodiment of the present invention described below is an embodiment focusing on both the state of oxide and hydroxide of zinc on the surface of the plated steel

sheet and the state of oxides and hydroxides of aluminum and magnesium on the surface of

the plated steel sheet.

[0202]

(Regarding the plated steel sheet for pre-painted steel sheet)

As has been schematically illustrated in FIG. 1A, a plated steel sheet 10 for

the steel sheet 101 serving as the base material.

[0203]

Here, the steel sheet 101 used as the base material of the plated steel sheet 10 for

steel sheets 101 in the plated steel sheets 10 for pre-painted steel sheet according to the

first embodiment and the second embodiment, and exhibits the same effect. Therefore, its

detailed explanation is omitted below.

[0204]

Further, the plating layer 103 also has the same configuration as the plating layers

103 in the plated steel sheets 10 for pre-painted steel sheet according to the first

embodiment and the second embodiment, except that attention is paid to both the state of

oxide and hydroxide of zinc and the state of oxides and hydroxides of aluminum and

magnesium on the surface of the plated steel sheet, and exhibits the same effect.

Therefore, its detailed explanation is omitted below.

[0205]

Incidentally, the methods of state analysis of metals, oxides, and hydroxides of

aluminum and magnesium and state analysis of metal, oxide, and hydroxide of zinc, and

the conditions to be met by the obtained analysis results, are as explained in the first

embodiment and the second embodiment.

[0206]

However, in this embodiment, at a depth of 10 nm from the surface of the plating

layer 103 (that is, the position A in FIG. 2), the ratio of oxide and hydroxide of magnesium

is 2.0 or more with respect to the ratio of metal magnesium, and the ratio of oxide and

hydroxide of zinc is 7.0 or more with respect to the ratio of metal zinc.

[0207]

By achieving the above states, better paint film adhesion at the molded portion is

achieved, thereby making it possible to more reliably inhibit the occurrence of paint film floating portions even when the pre-painted plated steel sheet using the plated steel sheet

10 for pre-painted steel sheet including the plating layer 103 according to this embodiment

is drawn.

[0208]

Further, it is more preferable that the states of oxides and hydroxides of

magnesium and zinc are made as described above, and further that the ratio of oxide and

hydroxide of aluminum is 1.3 or more with respect to the ratio of metal aluminum. By

achieving such states, much better paint film adhesion at the molded portion is achieved,

thereby making it possible to much more reliably inhibit the occurrence of paint film

floating portions even when the pre-painted plated steel sheet using the plated steel sheet

is drawn.

[0209]

has been explained in detail above with reference to FIG. 1A to FIG. 2.

[0210]

Such a plated steel sheet 10 for pre-painted steel sheet can be manufactured by

such a manufacturing method as explained in the first embodiment and the second

embodiment.

[0211]

Here, in particular, by performing the alkali treatment after performing the

mechanical cutting or the acid treatment, the state of the plating layer in this embodiment

can be achieved more reliably. This is thought to be because the mechanical cutting or

the acid treatment is first performed, and thereby, the plated surface is removed to create a

fresh new surface, and then the alkali treatment is performed in this state, to thereby

achieve more efficient redeposition of oxides or hydroxides of zinc and magnesium on the plated surface.

[0212]

Further, the mechanical cutting is first performed under light pressure conditions

to selectively cut convex portions of uneven portions of the plating, and then the alkali

treatment is performed, thereby making it possible to relatively increase the presence ratio

of oxide or hydroxide of aluminum. This is thought to be because the surface of the

convex portion of the plating is high in content ratio of aluminum, and thus when the alkali

treatment of the fresh new surface of such a portion is performed, elution of aluminum

increases, resulting in an increase in the presence ratio of oxide or hydroxide of aluminum.

[0213] Not limited to this example, by changing the order or conditions of mechanical

cutting, acid treatment, and alkali treatment, it is possible to variously vary the presence

ratios of oxides or hydroxides of zinc, magnesium, and aluminum.

[0214]

(Regarding the pre-painted plated steel sheet)

Then, the pre-painted plated steel sheet using the plated steel sheet 10 for

pre-painted steel sheet as explained above will be explained with reference to FIG. 3A to

FIG. 4.

[0215]

according to this embodiment may include the plating layers 201, the chemical treatment films 203, and the paint films 205 formed on both sides of the steel sheet 101, as has been schematically illustrated in FIG. 3B.

[0216]

its detailed explanation is omitted below.

[0217]

is omitted below.

[0218]

The states of metals, oxides, and hydroxides of magnesium, aluminum, and zinc

embodiment, and the methods for measuring the states are as described in the first

embodiment and the second embodiment.

[0219]

The chemical treatment film 203 and the paint film 205 are located above such a

plating layer 201. The detailed configuration of the chemical treatment film 203

according to this embodiment is the same as that in the first embodiment and the second

embodiment, and the same effect is exhibited. Therefore, its detailed explanation is omitted below. Further, the detailed configuration of the paint film 205 according to this embodiment is the same as that in the first embodiment and the second embodiment, and the same effect is exhibited. Therefore, its detailed explanation is omitted below.

[0220]

The pre-painted plated steel sheet 20 according to this embodiment has been explained above with reference to FIG. 3A to FIG. 4.

[0221]

(Regarding the molded product)

Next, there is explained a molded product using the pre-painted plated steel sheet

20 as explained above with reference to FIG. 5.

[0222]

As has been schematically illustrated in FIG. 5 as an example, a molded product

and square cylinder pressing to be molded into a desired shape. Here, the details of the

molded product 30 are as explained in the first embodiment and the second embodiment,

and therefore, its detailed explanation is omitted below.

[0223]

As explained above, in this embodiment as well, by using the plated steel sheet for

pre-painted steel sheet according to this embodiment, it is possible to obtain a molded body

formed of the pre-painted plated steel sheet and the pre-painted steel sheet that does not

cause paint film floating portions or paint film peeling at the portion worked by drawing or

the like.

[Example]

[0224]

Hereinafter, the plated steel sheet for pre-painted steel sheet, the pre-painted plated steel sheet, and the molded product according to the present invention will be specifically explained while describing examples and comparative examples. Incidentally, the examples described below are merely examples of the plated steel sheet for pre-painted steel sheet, the pre-painted plated steel sheet, and the molded product according to the present invention, and the plated steel sheet for pre-painted steel sheet, the pre-painted plated steel sheet, and the molded product according to the present invention are not limited to the following examples.

[0225]

«First test example>>

A first test example described below is a test example relating to the plated steel

sheet for pre-painted steel sheet, the pre-painted plated steel sheet, and the molded product

according to the above-described first embodiment.

[0226]

(1. Plated steel sheet for pre-painted steel sheet)

As the plated steel sheet for pre-painted steel sheet, the following five types of zinc-based plated steel sheets commercially available were used. Plating layers of the

following zinc-based plated steel sheets were treated with various acid solutions and

alkaline solutions while changing the treatment time, and thereby the ratio of oxides and

hydroxides of magnesium and aluminum on the surface of the plating layer (more

specifically, at a depth of 10 nm from the surface) was controlled.

[0227]

Al: Zn-1%Al-3%Mg-0.2%Si hot-dip galvanized steel sheet (sheet thickness 0.60

mm, plating amount 40 g/m2 )

A2: Zn-6%Al-3%Mg hot-dip galvanized steel sheet (sheet thickness 0.60 mm,

plating amount 40 g/m 2 )

A3: Zn-55%Al-2%Mg-1.6%Si hot-dip galvanized steel sheet (sheet thickness 0.35 mm, plating amount 75 g/m2

) A4: hot-dip zinc plated steel sheet (sheet thickness 0.60 mm, plating amount 40

g/m 2 )

A5: Zn-55%Al-1.6%Si hot-dip galvanized steel sheet (sheet thickness 0.35 mm,

plating amount 75 g/m 2 )

[0228]

(2. Chemical treatment film film formation)

As a painting component intended for forming the chemical treatment film, the

following was used. Incidentally, an added amount of each component in each of the

painting components was adjusted so as to be within the range of the added amount

explained previously.

[0229]

SI: Water-based painting component composed of tannic acid, a silane coupling

agent, fine silica particles, and a polyester resin

S2: Water-based painting component composed of a silane coupling agent,

phosphate, and an acrylic resin

S3: Water-based painting component composed of a silane coupling agent,

fluorotitanic acid, fluorozirconic acid, and a urethane resin

[0230]

The above-described painting components SI to S3 were bar-coated on the

above-described plated steel sheets for pre-painted steel sheet so as to have a

predetermined amount when dried, and then dried in an air-heating furnace at a peak metal

temperature of 70°C and air-dried.

[0231]

In this test example, a two-layer paint film composed of a primer paint film and a

top paint film was mainly prepared, and a single-layer paint film composed of only a top paint film without including a primer paint film was also formed.

[0232]

(3-1. Primer paint film film formation)

As a painting component intended for forming the primer paint film, the following

was used.

[0233]

P1: Polyester/melamine resin curing system composition (FLC641 manufactured

by Nippon Paint Industrial Coatings Co., Ltd.)

P2: Polyester/isocyanate resin curing system composition (FLC690 manufactured

by Nippon Paint Co., Ltd.)

P3: Epoxy/melamine resin curing system composition

[0234]

The above-described P1 to P3 were bar-coated on the plated steel sheets for

pre-painted steel sheet on which the above-described chemical treatment was performed so

as to have a predetermined film thickness when dried (1 to 12 m), and then dried in an

air-heating furnace at a peak metal temperature of 215°C.

[0235]

(3-2. Top paint film film formation)

As a painting component intended for forming the top paint film, the following

was used.

[0236]

TI: Polymer polyester/melamine resin curing system composition (FLC7000

manufactured by Nippon Paint Co., Ltd.)

T2: Polyester/melamine resin curing system composition (FLC100HQ

manufactured by Nippon Paint Co., Ltd.)

[0237]

The above-described TI or T2 was bar-coated on the plated steel sheets for

pre-painted steel sheet on which the above-described chemical treatment film was formed

so as to have a predetermined film thickness when dried (4 to 30 m), and then dried in an

air-heating furnace at a peak metal temperature of 230°C.

[0238]

(4. Ratio of oxide content and hydroxide content to metal of magnesium and aluminum)

The surface of the plated steel sheet for pre-painted steel sheet before chemical

treatment and the interface of the plated steel sheet for pre-painted steel sheet after paint

film formation were observed by X-ray photoelectron spectroscopy (XPS), and from the

ratio of the sum of peak intensities of the oxide content and the hydroxide content of

magnesium (in the region of 295 to 325 cm-1 by Mg KLL) and aluminum (in the region of

68 to 84 cm-1 by Al 2p) at a position where sputter etching was performed for 10 nm from

the surface or interface to the peak intensity of the metal content, the ratio was calculated.

[0239]

Here, the measurement conditions of XPS and the sputtering rate in the depth

profile measurement were set as previously described.

[0240]

Incidentally, the position of the interface between the chemical treatment film and

the plating layer was determined by focusing on the depth profile of silicon in the depth

direction of the pre-painted plated steel sheet by X-ray photoelectron spectroscopy, and

specifying the position where the intensity of silicon decreases by half with respect to the

depth direction.

[0241]

(5. Performance evaluation)

The pre-painted zinc plated steel sheet manufactured by the above-described

method was used to be subjected to cylindrical cup drawing. Cutting was performed by the SAICAS method on the interface between the chemical treatment film and the primer paint film or the interface between the chemical treatment film and the plating layer of the portion where the thickness of the plated steel sheet for pre-painted steel sheet increased by

5% or more compared to that before molding, and the peel strength and the interfacial

peeling form were measured. The device used for the SAICAS method is DN-GS model

manufactured by DAIPLA WINTES CO., LTD..

[0242]

Incidentally, the cylindrical cup drawing was performed as follows.

The pre-painted plated steel sheet obtained as described above was subjected to

cylindrical cup drawing at a drawing ratio of 2.0 so that the surface to be measured was

located on the outside and a portion near the steel sheet end portion of a cylindrical body

portion was cut into a sufficient size (approximately 20 x 20 mm or more) with metal

shears or the like, and then the steel sheet was smoothed with a steel plate straightener

(leveler). Of the obtained steel sheet piece, the portion where the thickness increased by

5% or more compared to that before molding was specified by the method described

previously, and the peel strength and the peel form of the paint film at the specified portion

were measured by cutting with the SAICAS method. Incidentally, the cutting direction

was set to the direction parallel to the edge line of the steel sheet after drawing.

[0243]

The cutting conditions by SAICAS are as follows.

A diamond blade (0.3 mm in width) was used, and oblique cutting was performed

in a constant speed mode with a horizontal velocity of 1 m/second and a vertical velocity

of 0.1 m/second and then near the interface, the cutting was switched to only the

horizontal movement to cut a length of 200 [m, and the average peel strength during the

horizontal movement was measured. The depth position at which to switch to horizontal movement was set by specifying the interface position (a position at the very limit where the plating is not cut) through a preliminary experiment. When the plated surface is cut due to the unevenness of the plating during the horizontal movement of the cutting blade, the peel strength can be discriminated because it momentarily increases abnormally.

Such a case was excluded as an abnormal value, and the average peel strength was

calculated. The number of measurements was set to n = 3, and the average value of the

three values of the average peel strength was taken as the peel strength.

[0244]

An optical micrograph of a horizontal cut range (300 pm x 200 im) by SAICAS

was taken, portions of the primer cohesive failure, the interfacial peeling, and the plating

cohesive failure within the same range were specified according to the above criteria, and

areas of the portions were measured using transparent graph paper. Then, the ratio of the

interfacial peeling area to the area excluding the plating cohesive failure was calculated

from the horizontal cut range by SAICAS.

[0245]

«Contents of aluminum and magnesium in the plating layer of the molded product>>

The contents of aluminum and magnesium in the plating layer of the molded

product obtained as described above were measured by XPS (Quantum 2000 manufactured

by ULVAC-PHI, Inc.).

[0246]

Further, the presence or absence of paint film peeling and the state of paint film

floating were confirmed at corner portions obtained by separately actual-pressing the

obtained pre-painted plated steel sheet in a mold for the top plate of an air conditioner

outdoor unit.

[0247]

Regarding the evaluation, the compressed portion of the comer portion of the top

plate was observed with a loupe at four positions to confirm the presence or absence of

paint film peeling, and the state of paint film floating was evaluated based on the average

value of the four positions with the following scores. Incidentally, the following scores

are given per corner.

[0248]

5: No paint film floating portion

4: Several paint film floating portions

3: 10 or more paint film floating portions

2: 20 or more paint film floating portions

1: 20 or more paint film floating portions and the presence of peeling due to

connection of paint film floating portions

[0249]

Obtained results are illustrated in Table 1 collectively below.

[0250]

[Table 1] a 0

0 0 ZO < z j 0C 0 0w 0w 0w 0w0 00 0 0 0 0 00w 00 0 0 0 0 0

< 0 ~< << a a a << <<< a < << a < << a <<< a< << < < <

0

a Ha 0 0

o H

<<

. 00

00 0

0H1 0

z a0 0 0 0

0 0

I

a H

Li L

z- a a a a a a a a a a a a a a a a a a a a a Li H

H- z - 000 E 0 -000-000- 000 - - -00 -0000--00 ---

22 i~ < < <

> > >>>>>> 0 2

0000 0 0 0 0

[025 1]

In each ofthe examples, the ratio ofoxide content andhydroxide content tometal content ofmagnesium and aluminum onthe surface of the plated steelsheet before molding and at the interface of the plated steel sheetafter paintingand thepeel strength and the peel form of the compressed portion of the molded product by SAICAS satisfied the criteria, and thus, no occurrence of paint film floating or paint film peeling was observed in the actual working of the top plate of the air conditioner outdoor unit.

[0252]

On the other hand, in each of the comparative examples, the ratio of oxide content

and hydroxide content to metal content of magnesium and aluminum on the surface of the

plated steel sheet before molding and at the interface of the plated steel sheet after painting

and the peel strength and the peel form of the compressed portion of the molded product by

SAICAS did not satisfy the criteria, and thus, occurrences of paint film floating and paint

film peeling were observed in the actual working of the top plate of the air conditioner

outdoor unit.

[0253]

«Second test example>>

The second test example described below is a test example relating to the plated

steel sheet for pre-painted steel sheet, the pre-painted plated steel sheet, and the molded

product according to the above-described second embodiment.

[0254]

(1. Plated steel sheet for pre-painted steel sheet)

Plated steel sheets for pre-painted steel sheet were prepared in the same manner as

in the first test example.

[0255]

(2. Chemical treatment film form formation)

A chemical treatment film was formed on the obtained plated steel sheet for

pre-painted steel sheet in the same manner as in the first test example.

[0256]

In this test example as well, a two-layer paint film composed of a primer paint film and a top paint film was mainly prepared, and a single-layer paint film composed of only a top paint film without including a primer paint film was also formed.

[0257]

(3-1. Primer paint film film formation)

A primer paint film was formed in the same manner as in the first test example.

[0258]

(3-2. Top paint film film formation)

A top paint film was formed in the same manner as in thefirst test example.

[0259]

(4. Ratio of oxide content and hydroxide content to zinc metal)

ratio of the sum of peak intensities of the oxide content and the hydroxide content of zinc

(in the region of 480 to 515 cm-1 by Zn 2p) at a position where sputter etching was

performed for 10 nm from the surface or interface to the peak intensity of the metal content,

the ratio was calculated.

[0260]

Here, the measurement conditions of XPS and the sputtering rate in the depth

profile measurement were set as previously described.

[0261]

depth direction.

[0262]

(5. Performance evaluation)

Performance evaluation was performed in the same manner as in the first test

example. The evaluation method and the evaluation criteria are the same as those in the

first test example.

[0263]

Obtained results are illustrated in Table 2 collectively below.

[0264]

[Table 2]

0 CD 0

~~j 500 U0 CZO 00 00 0020 00 00 00 00 00 00 0

2 w 7!0

0 0 w ~ 0 0-0 0

0 Z 0 M IZ w 'V 0] 'V P f.V'' 'V 0] qVINrV 0] 'T V' P? 'V fVVIN INVr 'V P

0 H

0

0 H w~ 0

0H

Li.Q~~ Eo~"i404c

HtIH

E V H -V -V -V -VV - -HH - H- H-I- --H- HH-- -H --

i E ZZ

~~~~~~ 00 0 Pi0 P0 0 0 0 0 0 0 0 0 0 0 0 L 0 0 0

w H) 0C )wwwwwC wwwww0wwwww0wwwwwwwC

O E E E o 0 0 0 0 0 0 0 0 1 0 0 0 0 000 02 0" 0" w" 00 0" 000 0A 000 0 000 0w00 0 0 0

00[0206510 0 0 00 0 0 0 00 0 0 00 0 0 0

H n of000h th exm ls 000 00 rai 000 oxd 0000en an 0000xid cotn 00 00 met00

otnto in nte ufceo h pae selshe eor odigadatteinefc

oftepaedselset-feianinn h pe tegh n h e- omo h

copesdprino0h0ode0rdc ySIA aifedtecieiadtun occurrence of paint film floating or paint film peeling was observed in the actual working of the top plate of the air conditioner outdoor unit.

[0266]

and hydroxide content to metal content of zinc on the surface of the plated steel sheet

before molding and at the interface of the plated steel sheet after painting and the peel

strength and the peel form of the compressed portion of the molded product by SAICAS

did not satisfy the criteria, and thus, occurrences of paint film floating and paint film

peeling were observed in the actual working of the top plate of the air conditioner outdoor

unit.

[0267]

«Third test example>>

The third test example described below is a test example relating to the plated

product according to the above-described third embodiment.

[0268]

Plated steel sheets for pre-painted steel sheet, pre-painted plated steel sheets, and

molded products 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 sheet, pre-painted plated steel sheets, and molded products were similarly evaluated according to the measurement method and the evaluation method described in the first test example and

the second test example.

[0269]

Obtained results are illustrated in Table 3 collectively below.

[0270]

[Table 3]

0 0

H 0 09 0 0 0 0 0 0 0 S0 US0 0 00 0 0 00 0 0 0

O aaz zzz z zz zz zz zz zz zz zz zz zz zz zz zz zz zz zz zz zz zz zz z

0a ww

0 9 Hz

H2 SZU 00 00 0 0> 00 0 !2 00 0> >0>0> 000 N 2 0>00 0>0 Oo a E0 oa eo nm

z O I a

00H 0 O w z I

H Wa LL

z LL I|-c! I

a x Ow H

0 0< 0 E 0 a N

zf In

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[0271]

In each of the examples, the ratio of oxide content and hydroxide content to metal content of zinc on the surface of the plated steel sheet before molding and at the interface of the plated steel sheet after painting and the peel strength and the peel form of the compressed portion of the molded product by SAICAS satisfied the criteria, and thus, no occurrence of paint film floating or paint film peeling was observed in the actual working of the top plate of the air conditioner outdoor unit.

[0272] The preferred embodiments of the present invention have been described in detail

above with reference to the attached drawings, but the present invention is not limited to

such examples. It is apparent that a person having common knowledge in the technical field to which the present invention belongs is able to devise various variation or

modification examples within the range of technical ideas described in the claims, and it

should be understood that such examples belong to the technical scope of the present

invention as a matter of course.

[Explanation of Codes]

[0273] 10 plated steel sheet for pre-painted steel sheet

2 pre-painted plated steel sheet

30 molded product

101 steel sheet

103, 201 plating layer

203 chemical treatment film

205 paint film

Claims

[Claim 1] A plated steel sheet for pre-painted steel sheet, comprising: a steel sheet; and a plating layer located on one side or both sides of the steel sheet, the plating layer containing 0.5 mass% or more and 60.0 mass% or less of aluminum, 0.5 mass% or more and 15.0 mass% or less of magnesium, and the balance being composed of zinc and impurities, wherein at a depth of 10 nm from the surface of the plating layer, the ratio of oxide and hydroxide of magnesium is 2.0 or more with respect to the ratio of metal magnesium, or the ratio of oxide and hydroxide of zinc is 7.0 or more with respect to the ratio of metal zinc.
[Claim 2] The plated steel sheet for pre-painted steel sheet according to claim 1, wherein at a depth of 10 nm from the surface of the plating layer, the ratio of oxide and hydroxide of magnesium is 2.0 or more with respect to the ratio of metal magnesium, and the ratio of oxide and hydroxide of zinc is 7.0 or more with respect to the ratio of metal zinc.
[Claim 3] The plated steel sheet for pre-painted 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 oxide and hydroxide of aluminum is 1.3 or more with respect to the ratio of metal aluminum.
[Claim 4] The plated steel sheet for pre-painted steel sheet according to any one of claims I to 3, wherein the plating layer is Zn-11%Al-3%Mg-0.2%Si alloy plating.
[Claim 5] A pre-painted plated steel sheet, comprising: a steel sheet, a plating layer located on one side or both sides of the steel sheet, the plating layer containing 0.5 mass% or more and 60.0 mass% or less of aluminum, 0.5 mass% or more and 15.0 mass% or less of magnesium, and the balance being composed of zinc and impurities, a chemical treatment film located on the plating layer; and a paint film located on the chemical treatment film, wherein at a depth of 10 nm from the interface between the chemical treatment film and the plating layer toward the inside of the plating layer, the ratio of oxide and hydroxide of magnesium is 0.30 or less with respect to the ratio of metal magnesium, or the ratio of oxide and hydroxide of zinc is 7.0 or more with respect to the ratio of metal zinc.
[Claim 6] The pre-painted plated steel sheet according to claim 5, wherein at a depth of 10 nm from the interface between the chemical treatment film and the plating layer toward the inside of the plating layer, the ratio of oxide and hydroxide of magnesium is 0.30 or less with respect to the ratio of metal magnesium, and the ratio of oxide and hydroxide of zinc is 7.0 or more with respect to the ratio of metal zinc.
[Claim 7] The pre-painted plated steel sheet according to claim 5 or 6, wherein at a depth of 10 nm from the interface between the chemical treatment film and the plating layer toward the inside of the plating layer, the ratio of oxide and hydroxide of aluminum is 0.30 or less with respect to the ratio of metal magnesium.
[Claim 8] A molded product being a molded product formed of the pre-painted plated steel sheet according to any one of claims 5 to 7, wherein at a portion where the thickness of the plated steel sheet in the molded product has increased by 5% or more compared to the thickness of a non-molded portion, a peel strength measured by cutting the interface between the chemical treatment film and the paint film by a SAICAS method is 1.00 kN/m or more on average, 20% or less of a cut area is in the form of interfacial peeling, and the remaining cut area is in the form of cohesive failure within the paint film.
[Claim 9] 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.