WO2016208621A1 - Coated steel plate - Google Patents

Abstract

This coated steel plate is provided with: a base steel plate; a galvanization layer formed on the base steel plate; a zinc phosphate film formed on the galvanization layer and containing zinc phosphate crystals, the zinc phosphate film being deposited in the amount of 0.4-2.5 g/m²; a lower-layer film which is an inorganic film or an organic/inorganic composite film, formed on the zinc phosphate film and deposited in the amount of 50-2000 mg/m²; and an upper-layer film formed on the lower-layer film, the upper-layer film having a film thickness of 2.0-10.0 µm and containing 5-25% by mass of a first carbon black; the maximum gap between the zinc phosphate crystals at the interface of the galvanization layer and the zinc phosphate film being 0.2 µm or less.

Description

Painted steel plate

The present invention relates to a coated steel sheet suitable for a housing for AV equipment represented by a thin display such as a liquid crystal television, an organic EL television, and a plasma television.
This application claims priority based on Japanese Patent Application No. 2015-128016 filed in Japan on June 25, 2015, the contents of which are incorporated herein by reference.

When manufacturing a coated steel plate (also referred to as a pre-coated steel plate or PCM), first, the base steel plate is painted and baked to form a coating film on the base steel plate. After the coating is formed, the coated steel sheet is wound into a coil and delivered to the user in that state. The user unwinds the coil and performs punching, bending, drawing, or a combination thereof to produce a product.
Such a coated steel sheet is applied to many fields because it does not cause deterioration of the working environment on the user side and it is not necessary to perform the painting work on the user side.

In general, the production of the coated steel sheet is performed by a 2-coat 2-bake method. In the 2-coat 2-bake method, first, a base steel plate (typically a galvanized steel plate including zinc plating and zinc alloy plating) is subjected to chemical conversion treatment as a pretreatment. Next, an undercoat paint (primer) is applied and baked. Finally, the top coat is applied and baked.
However, the back surface opposite to the front surface which is the outer side of the final product may be coated by a 1-coat 1-bake method using a paint developed for the back surface after the pretreatment.

Painted steel sheet has many performances such as corrosion resistance (suppression of white rust and / or red rust at the edge of the coating), workability, coating hardness (scratch resistance), stain resistance, chemical resistance, weather resistance, etc. Must be achieved at a high level. However, in recent years, from the viewpoint of cost reduction, environmental measures, and rationalization of painting work, it is also possible to reduce the film thickness (thinner film thickness) even for coatings that provide quality assurance that requires the design of coated steel sheets. It has been demanded.
For example, in a coated steel sheet used on the back side of the final product such as a coated steel sheet used for a back panel of a thin display, it may be required to limit the coating thickness to less than 10 μm. This level of coating thickness is the level of coating thickness required for chemical conversion treated steel plates and fingerprint-resistant steel plates, and this level of coating thickness was not required for conventional coated steel plates.

When the coating film thickness is reduced, it is possible to reduce the burden on the insulator used to burn the organic solvent generated during baking of the coating film, and to reduce the CO ₂ emitted therefrom. It becomes possible. In addition, the amount of organic solvent discharged during coating baking depends on the coating thickness, so when the coating thickness is reduced, the line speed can be increased within the capacity of the incinator, and the painting work can be performed. It becomes possible to rationalize.

However, when the coating thickness is reduced, for example, the surface brightness of the coated steel sheet is deteriorated, the color tone of the coated steel sheet varies due to the coating film, and it is difficult to conceal the wrinkles of the base steel sheet. It is usually difficult to obtain a good appearance as a steel plate. An invention aimed at improving this point is disclosed in Patent Document 1. In addition, Patent Document 2 discloses an invention aimed at improving the corrosion resistance reduction of the coated steel sheet accompanying the thinning of the coating film.

In addition, water-based paints that are free from trace amounts of solvents contained in paints are being studied as a way to reduce the burden on the insulator used to burn organic solvents generated during coating baking. Patent Document 3 discloses an invention aimed at achieving both corrosion resistance as a back panel application for a thin display.

On the other hand, many surface-treated steel sheets (for example, so-called fingerprint-resistant steel sheets) in which a thin film of about several μm is formed on the surface of a base steel sheet using an aqueous chemical solution have been developed.
For example, Patent Document 4 discloses a surface-treated steel sheet intended to have corrosion resistance, thermal radiation, and conductivity. The surface-treated steel sheet of Patent Document 4 has two chemical conversion treatment coating layers, and at least the upper chemical conversion treatment coating layer of the two chemical conversion treatment coating layers contains a color pigment.
Patent Document 5 discloses a surface-treated steel sheet for the purpose of stabilizing the appearance. The surface-treated steel sheet of Patent Document 5 has two chemical conversion coating layers, and both chemical conversion coating layers contain a color pigment.
Patent Document 6 discloses a surface-treated steel sheet intended to have fingerprint resistance, corrosion resistance, and the like. The surface-treated steel sheet of Patent Document 6 has a silica-organic resin composite film formed on the steel sheet surface.

Japanese Unexamined Patent Publication No. 2008-55774 Japanese Unexamined Patent Publication No. 2010-115902 Japanese Unexamined Patent Publication No. 2010-247396 Japanese Unexamined Patent Publication No. 2009-220511 Japanese Unexamined Patent Publication No. 2013-18192 Japanese Unexamined Patent Publication No. 2000-263695

The coated steel sheets described in Patent Documents 1, 2 and 3 all require a coating film thickness of 2.0 μm or more in order to ensure designability (overcoat). At least one of the undercoating film is provided. Therefore, it is difficult to reduce the coating thickness in the coated steel sheets described in Patent Documents 1, 2, and 3.
The surface-treated steel sheets described in Patent Documents 4 and 5 are provided with a chemical conversion treatment film having at least one layer of a color pigment on the steel sheet surface, and depending on the color pigment, there is a possibility of affecting the corrosion resistance of the steel sheet. .
In the surface-treated steel sheet of Patent Document 6, the silica-organic resin composite film formed on the steel sheet surface is basically a transparent film. Therefore, the surface-treated steel sheet of Patent Document 6 may be greatly affected by the appearance (color tone and wrinkles) of the surface of the base steel sheet.

The present invention has been made in view of the above circumstances, and provides a coated steel sheet having excellent scratch resistance and corrosion resistance even though the film thickness of the coating film formed on the steel sheet surface is thin. With the goal. In the present invention, the term “scratch resistance” means that when a predetermined brazing test is performed and wrinkles are imparted to the surface of the coated steel sheet, it is difficult to visually distinguish the wrinkles. .

The present invention adopts the following means in order to solve the above problems and achieve the object.

(1) A coated steel sheet according to an aspect of the present invention is a base steel sheet, a galvanized layer formed on the base steel sheet, formed on the galvanized layer, and containing zinc phosphate crystals, A zinc phosphate coating having an adhesion amount of 0.4 to 2.5 g / m ² and an inorganic coating or an organic-inorganic composite formed on the zinc phosphate coating and having an adhesion amount of 50 to 2000 mg / m ² A lower film that is a film, and an upper film that is formed on the lower film and has a film thickness of 2.0 to 10.0 μm and contains 5 to 25 mass% of the first carbon black, At the interface between the zinc plating layer and the zinc phosphate film, the maximum gap between the zinc phosphate crystals is 0.2 μm or less.

(2) In the coated steel sheet described in (1) above, a configuration in which the lower layer film contains 10 to 50% by mass of a color pigment may be employed.

(3) In the coated steel sheet described in (2) above, a configuration in which the lower layer film contains 10 to 30% by mass of a color pigment may be employed.

(4) In the coated steel sheet according to (2) or (3) above, a configuration in which the color pigment is second carbon black may be adopted.

(5) In the coated steel sheet described in (4) above, a configuration in which the particle size of the second carbon black is more than 100 nm may be adopted.

(6) In the coated steel sheet according to (4) or (5), a configuration in which a primary particle diameter of the first carbon black is smaller than a primary particle diameter of the second carbon black may be adopted. .

(7) In the coated steel sheet according to any one of the above (1) to (6), the lower layer film has an electrical resistivity of 0.1 × 10 ⁻⁶ to 185 × 10 ^{− at} a temperature of 25 ° C. A configuration containing 5 to 15% by mass of one or more non-oxide ceramic particles selected from the group consisting of boride, carbide, nitride, and silicide of ⁶ Ωcm may be employed.

According to each of the above aspects, it is possible to provide a coated steel sheet having excellent scratch resistance and corrosion resistance even though the coating film formed on the steel sheet surface is thin.

It is a schematic diagram showing the layer structure of the coated steel plate which concerns on this embodiment. It is a schematic diagram showing the measuring method of the largest space | gap between zinc phosphate crystals. It is a schematic diagram showing the measuring method of the largest space | gap between zinc phosphate crystals. It is a schematic diagram showing the particle size of the carbon black contained in the lower layer membrane | film | coat which concerns on this embodiment, and the particle size of the carbon black contained in an upper layer membrane | film | coat.

Hereinafter, the coated steel plate 1 and the manufacturing method thereof according to the embodiment will be described with reference to the drawings.
(Coated steel sheet 1)
First, the coated steel plate 1 will be described.
FIG. 1 is a schematic diagram showing a layer structure of a coated steel sheet 1 according to this embodiment. As shown in FIG. 1, a coated steel plate 1 includes a base steel plate 2, a galvanized layer 3 formed on the base steel plate 2, formed on the galvanized layer 3, contains zinc phosphate, and is attached. A zinc phosphate film 4 having an amount of 0.4 to 2.5 g / m ² and a maximum gap of 0.2 μm or less, and a zinc phosphate film 4 formed on the zinc phosphate film 4 and having an adhesion amount of 50 to 2000 mg / m ² A first carbon black formed on the lower layer film 5 and having a film thickness of 2.0 to 10.0 μm and having a thickness of 5 to 25% by mass. And an upper layer film 6 containing 7.

[Substrate steel plate 2]
The base steel plate 2 is not particularly limited, and various steel plates having known characteristics and chemical compositions can be used. Moreover, the chemical composition of the base steel plate 2 is not particularly limited.

[Zinc plating layer 3]
The galvanized layer 3 is not particularly limited, and a generally known galvanized layer 3 can be used.

The adhesion amount of the galvanized layer 3 is preferably 3 to 100 g / m ² per side. When the adhesion amount of the galvanized layer 3 is less than 3 g / m ² per side, the corrosion resistance becomes insufficient, which is not preferable. Moreover, since the workability of the zinc plating layer 3 and the adhesiveness with respect to the base-material steel plate 2 will fall when the adhesion amount of the zinc plating layer 3 is more than 100 g / m < ² > per one side, it is unpreferable.
A more preferable coating amount of the galvanized layer 3 is 5 to 70 g / m ² per side.

[Zinc phosphate coating 4]
A zinc phosphate film 4 containing zinc phosphate crystals is formed on the galvanized layer 3.
The thickness of the zinc phosphate coating 4 is preferably less than 1.0 μm, which further improves the design and scratch resistance of the processed part. In addition, although the minimum of thickness is not specifically limited, For example, 0.3 micrometer is mentioned.

The adhesion amount of the zinc phosphate film 4 is 0.4 to 2.5 g / m ² . When the adhesion amount of the zinc phosphate coating 4 is less than 0.4 g / m ² , many crystal scales (flakes) of the zinc phosphate coating 4 are formed on the surface of the galvanized layer 3, and sufficient scratch resistance is obtained. This is not preferable because On the other hand, when the adhesion amount of the zinc phosphate coating 4 exceeds 2.5 g / m ² , the cohesive force of the zinc phosphate coating 4 decreases, and the possibility that the zinc phosphate coating 4 peels during processing increases. When the conductive pigment is added to the upper layer film 6 (colored coating film), it is difficult to obtain excellent conductivity, which is not preferable.
From the viewpoint of scratch resistance, adhesion during processing, and conductivity, the amount of zinc phosphate coating 4 attached is more preferably 0.6 to 2.0 g / m ² .

At the interface between the galvanized layer 3 and the zinc phosphate coating 4, the maximum gap between the zinc phosphate crystals is 0.2 μm or less. When the maximum gap between the zinc phosphate crystals is 0.2 μm or less, the zinc plating layer 3 having a high L value can be concealed, the L value is lowered, and wrinkles and the like can be made inconspicuous. is there. On the other hand, when the maximum gap between the zinc phosphate crystals is more than 0.2 μm, the zinc plating layer 3 cannot be concealed and it is difficult to lower the L value, which is not preferable.
The maximum gap between zinc phosphate crystals is more preferably 0.15 μm or less. Thereby, the L value can be further reduced.

2 and 3 are schematic views showing a method for measuring the maximum gap between zinc phosphate crystals.
As shown in FIGS. 2 and 3, when measuring the maximum gap between the zinc phosphate crystals, it is preferable to obtain by the following method. First, the base steel plate 2 on which the galvanized layer 3 and the zinc phosphate coating 4 are formed is cut to expose the cross section, and the cross section is further polished. The cross section thus obtained is observed with an electron microscope, and an observation image of the cross section in the vicinity of the interface between the galvanized layer 3 and the zinc phosphate coating 4 is obtained. The maximum gap between the zinc phosphate crystals at the interface between the galvanized layer 3 and the zinc phosphate coating 4 existing in the field of the observed image is measured.

When the observation image of the cross section in the vicinity of the interface between the zinc plating layer 3 and the zinc phosphate coating 4 is in the state shown in FIG. 2, first, the point A that is a contact point between the zinc phosphate crystal and the zinc plating layer 3. ˜H is detected. Next, the lengths of the line segments AB, CD, EF, and GH are obtained, and the length of the line segment having the maximum length is set as the maximum gap length between the zinc phosphate crystals. In the case shown in FIG. 2, the length of the line segment AB is the length of the maximum gap between the zinc phosphate crystals.
FIG. 2 shows the case where the interface between the galvanized layer 3 and the zinc phosphate film 4 is a straight line, but the case where the interface between the galvanized layer 3 and the zinc phosphate film 4 is not a straight line as shown in FIG. The maximum gap between zinc phosphate crystals is obtained as follows. First, as in the case of FIG. 2, points A ′ to H ′, which are contact points between the zinc phosphate crystal and the zinc plating layer 3, are detected. Next, the lengths of the line segments A′B ′, C′D ′, E′F ′, and G′H ′ are obtained. At this time, the distances between A′B ′, C′D ′, E′F ′ and G′H ′ along the interface between the zinc phosphate crystal and the zinc plating layer 3 are not obtained. Find the length of the line directly connecting the two points. Similar to the case of FIG. 2, the length of the line segment having the maximum length is the length of the maximum gap between the zinc phosphate crystals. In the case shown in FIG. 3, the length of the line segment A′B ′ is the maximum gap length between the zinc phosphate crystals.

[Undercoat 5]
A lower layer film 5 is formed on the zinc phosphate film 4. The lower layer film 5 is formed for the purpose of improving the adhesion and corrosion resistance between the zinc phosphate film 4 and the upper layer film 6.
The lower layer film 5 is an inorganic film or an organic-inorganic composite film. Examples of the main film component of the lower layer film 5 include silicon compounds such as liquid phase silica, gas phase silica and silicate, and zircon compounds. The lower layer film 5 may contain an organic resin in addition to the main film component.
The lower layer film 5 preferably does not substantially contain chromium from the viewpoint of environmental protection.

The adhesion amount of the lower layer film 5 is preferably in the range of 50 to 2000 mg / m ² . If the adhesion amount of the lower layer film 5 is less than 50 mg / m ^2, it is not preferable because sufficient corrosion resistance cannot be obtained. When the adhesion amount of the lower layer film 5 exceeds 2000 mg / m ² , the cohesive force of the lower layer film 5 itself is reduced, and the possibility that the lower layer film 5 is peeled off during processing increases, and when the conductive pigment is added to the upper layer film 6 It is not preferable because it is difficult to obtain excellent conductivity.
From the viewpoint of corrosion resistance, adhesion during processing, and conductivity, a more preferable adhesion amount of the lower layer film 5 is 100 to 1000 mg / m ² .

The lower layer film 5 preferably further contains a color pigment from the viewpoint of making wrinkles less noticeable. The lower layer film 5 is formed so as to enter the recess of the zinc phosphate film 4 and cover the zinc phosphate film 4, but the lower layer film 5 contains a color pigment, so that wrinkles generated on the surface of the upper layer film 6 are more conspicuous. It is possible to eliminate.
The color pigment contained in the lower layer film 5 is preferably more than 10% by mass and 50% by mass or less with respect to the weight of the lower layer film 5. If the amount of the color pigment contained in the lower layer film 5 is 10% by mass or less, the effect of making the wrinkles less noticeable is not sufficient, which is not preferable. If the amount of the color pigment contained in the lower layer film 5 is more than 50% by mass, the ratio of the base chemical solution is relatively decreased, and sufficient corrosion resistance may not be obtained.

Examples of the color pigments contained in the lower layer film 5 include organic color pigments.
A preferable example of the color pigment contained in the lower layer film 5 is carbon black (second carbon black 8). When the lower layer film 5 contains the second carbon black 8, the content thereof is preferably more than 10% by mass and 30% by mass or less with respect to the total weight of the lower layer film 5. If the amount of the second carbon black 8 contained in the lower layer film 5 is 10% by mass or less, the effect of making wrinkles less noticeable is not sufficient, which is not preferable. If the amount of the second carbon black 8 contained in the lower layer film 5 exceeds 30% by mass, the possibility of different metal contact corrosion between the second carbon black 8 and the galvanized layer 3 increases, and both corrosion resistance can be achieved. Since it becomes difficult, it is not preferable.

When the lower layer film 5 contains the second carbon black 8, the particle diameter of the second carbon black 8 is preferably more than 100 nm. When the particle diameter of the second carbon black 8 exceeds 100 nm, the possibility that the second carbon black 8 enters the gaps in the zinc phosphate coating 4 is reduced. This is preferable because it can prevent the contact corrosion of different metals.
The term “particle size” as used herein refers to the average primary particle size when the carbon black particles present in the film are present alone, and the particle size at the time of aggregation when the carbon black particles are present in an aggregated state. This means the average secondary particle size, which can be determined by the following measurement method. First, the coated steel sheet 1 on which the lower layer film 5 is formed is cut to expose the cross section, and the cross section is further polished. The cross section thus obtained is observed with an electron microscope, and an observation image of the cross section of the lower layer film 5 is obtained. Several are selected from the second carbon blacks 8 existing in the field of view of the observed image. Then, the long side length and the short side length of each second carbon black 8 are measured, the average value of the long side lengths and the average value of the short side lengths are calculated, and these are averaged to obtain particles. Calculate the diameter.
If the above-described method is used, the particle diameter of the second carbon black 8 can be obtained even if the upper film 6 is formed on the lower film 5.
In addition, it is also possible to obtain | require the particle diameter of the 1st carbon black 7 using the above-mentioned method.

The second carbon black 8 may be secondarily aggregated in the lower layer film 5. Therefore, the surface treatment for the second carbon black 8 is not essential, and the second carbon black 8 not subjected to the surface treatment may be used.

[Upper layer film 6]
The upper film 6 is formed on the above-described lower film 5 and becomes the outermost layer of the coated steel sheet 1. The upper layer film 6 contains 5 to 25% by mass of carbon black (first carbon black) 7 with respect to the total weight of the upper layer film 6.

The particle diameter of the first carbon black 7 in the upper film 6 is preferably smaller than the particle diameter of the second carbon black 8 in the lower film 5.
FIG. 4 is a schematic diagram showing the particle size of the second carbon black 8 included in the lower layer film 5 and the particle size of the first carbon black 7 included in the upper layer film 6.
As shown in FIG. 4, even when the particle size of the second carbon black 8 is large or small, it cannot penetrate into the gap of the zinc phosphate coating 4 due to secondary aggregation. Thereby, dissimilar metal contact between the galvanized layer 3 and the second carbon black 8 can be prevented. On the other hand, it is preferable that the particle diameter of the first carbon black 7 is small so that blackness can be expressed even when the thickness of the upper film 6 is thin.

More preferably, the particle diameter of the first carbon black 7 and the particle diameter of the second carbon black 8 satisfy the following formula (1). When the particle diameter of the first carbon black 7 and the particle diameter of the second carbon black 8 satisfy the following formula (1), the above-described effect can be more reliably exhibited.
(Particle diameter of the first carbon black) / (Particle diameter of the second carbon black) <0.5 (1)

The film thickness of the upper layer film 6 is 2.0 to 10.0 μm. When the film thickness of the upper layer film 6 is less than 2.0 μm, it is not preferable because the scratch resistance and the corrosion resistance cannot be sufficiently obtained. When the film thickness of the upper layer film 6 exceeds 10.0 μm, it is not preferable because when the conductive pigment is added, the conductivity is lowered and the economical efficiency is deteriorated.
The particle diameter of the first carbon black 7 is preferably 50 nm or less. When the particle diameter of the first carbon black 7 is 50 nm or less, a sufficient color tone can be exhibited even when the film thickness of the upper film 6 is 2.0 to 10.0 μm.
The film thickness of the upper layer film 6 is preferably 3.0 to 8.0 μm from the viewpoint of scratch resistance, corrosion resistance, weldability and economy.

The upper layer film 6 may contain a coloring pigment other than the first carbon black 7. Specific examples of the color pigment other than the first carbon black 7 include known organic pigments, barium sulfate, titania and the like. When the upper layer film 6 contains a color pigment other than the first carbon black 7, the content is preferably 25% by mass or less with respect to the solid content mass of the upper layer film 6. If the content of the color pigment other than the first carbon black 7 in the upper layer film 6 exceeds 25% by mass, the chemical resistance and the barrier property are deteriorated, which is not preferable.

The upper film 6 may include non-oxide ceramic particles selected from borides, carbides, nitrides, and silicides having an electrical resistivity at 25 ° C. of 0.1 × 10 ⁻⁶ to 185 × 10 ⁻⁶ Ωcm.
Since non-oxide ceramic particles are unlikely to deteriorate in water, even if the composition for forming the upper layer film 6 is an aqueous composition, it is possible to maintain high electrical conductivity. Therefore, when the upper film 6 contains non-oxide ceramic particles, the coated steel sheet 1 can maintain excellent conductivity for a long period of time.

Here, the non-oxide ceramic represents a ceramic made of an element or compound not containing oxygen. Boride ceramics, carbide ceramics, nitride ceramics, and silicide ceramics have boron (B), carbon (C), nitrogen (N), and silicon (Si) as main nonmetallic constituent elements, respectively. Represents non-oxide ceramics. All of these have an electrical resistivity at 25 ° C. of 0.1 × 10 ⁻⁶ to 185 × 10 ⁻⁶ Ωcm.

Non-oxide ceramic particles have high conductivity in a small amount. Therefore, even if the content of non-oxide ceramic particles in the upper layer film 6 is small, the coated steel sheet 1 can obtain suitable conductivity. If the content of the non-oxide ceramic particles in the upper layer film 6 is small, the deterioration of corrosion resistance and formability due to the upper layer film 6 containing the non-oxide ceramic particles will not be a problem.
The electric resistivity of pure metal is 1.6 × 10 ⁻⁶ Ωcm (Ag simple substance) to 185 × 10 ⁻⁶ Ωcm (Mn simple substance). On the other hand, the electrical resistivity of the non-oxide ceramic is 0.1 × 10 ⁻⁶ to 185 × 10 ⁻⁶ Ωcm. From this, it can be seen that non-oxide ceramics have excellent conductivity equivalent to that of pure metal.

The content of non-oxide ceramic particles in the upper film 6 is preferably 0.5 to 20% by mass with respect to the total mass of the upper film 6. When the content of the non-oxide ceramic particles is less than 0.5% by mass, it is not preferable because preferable weldability may not be obtained even when other conductive particles are used in combination. When the content of the non-oxide ceramic particles exceeds 20% by mass, a phenomenon in which the non-oxide ceramic particles are stuck into the electrode during continuous welding is likely to occur, and welding failure may occur, which is not preferable.
The lower limit of the content of non-oxide ceramic particles is preferably 1% by mass, more preferably 5% by mass, and the upper limit is preferably 15% by mass, more preferably 10% by mass.

Examples of the non-oxide ceramic particles include the following.
As boride ceramic particles, Group IV (Ti, Zr, Hf), Group V (V, Nb, Ta), Group VI (Cr, Mo, W) transition metals of the periodic table, Mn, Examples include Fe, Co, Ni, rare earth elements, or Group II (Ca, Sr, Ba) boride ceramic particles other than Be and Mg.
However, among the boride ceramic particles of Be, ceramic particles (for example, Be ₂ B, BeB ₆ etc.) whose electrical resistivity at 25 ° C. exceeds 185 × 10 ⁻⁶ Ωcm have low electrical conductivity and weldability. Is not preferred because it may decrease. Further, Mg boride ceramics (Mg ₃ B ₂ , MgB _2, etc.) particles are not preferable because they have low stability against water or acid and may deteriorate weldability.

As the carbide ceramic particles, transition metals of Group IV (Ti, Zr, Hf), Group V (V, Nb, Ta), Group VI (Cr, Mo, W) of the periodic table, or Mn, Examples are Fe, Co, Ni carbide ceramic particles.
However, rare earth elements and Group II carbide ceramics (for example, YC ₂ , LaC ₂ , CeC ₂ , PrC ₂ , Be ₂ C, Mg ₂ C ₃ , SrC _2, etc.) particles are easily hydrolyzed in a humid atmosphere. This is not preferable because weldability may be deteriorated.

As nitride ceramic particles, transition metals of Group IV (Ti, Zr, Hf), Group V (V, Nb, Ta), Group VI (Cr, Mo, W) of the periodic table, or Examples thereof include nitride ceramic particles of Mn, Fe, Co, and Ni.
However, rare earth elements and Group II nitride (eg, LaN, Mg ₃ N ₂ , Ca ₃ N _2, etc.) particles are not preferable because they are easily hydrolyzed in a wet atmosphere and the weldability may be reduced. .

Silicide ceramic particles include transition metals of Group IV (Ti, Zr, Hf), Group V (V, Nb, Ta) and Group VI (Cr, Mo, W) of the periodic table, or Mn, Fe Co, Ni silicide particles are exemplified.
However, rare earth elements and Group II silicides (eg, LaSi, Mg ₂ Si, SrSi ₂ , BaSi _2, etc.) particles easily react with water in a humid atmosphere to generate hydrogen, resulting in poor weldability. This is not preferable.

In addition, as non-oxide ceramic particles, particles of two or more kinds of mixtures selected from the group consisting of these boride ceramics, carbide ceramics, nitride ceramics, and silicide ceramics, these ceramics as metal binders The cermet particle | grains etc. which were mixed and sintered are illustrated.

When the upper layer film is prepared from an aqueous composition, it is preferable that the standard electrode potential of the metal constituting a part of the cermet particles is −0.3 V or more and is water-resistant. When the standard electrode potential of the metal constituting a part of the cermet particles is less than −0.3 V, if the cermet particles are present in the aqueous composition for a long time, a rust layer or a thick oxide insulating layer is likely to be formed on the surface of the particles. This is because the conductivity of the particles may be lost. Examples of water-resistant cermet particles include WC-12Co, WC-12Ni, TiC-20TiN-15WC-10Mo2C-5Ni, and the like. The standard electrode potentials of Co and Ni are −0.28 V and −0.25 V, respectively, which are nobler than −0.3 V, and both metals are resistant to water.

Among non-oxide ceramics, Cr-based ceramics (CrB, CrB ₂ , Cr ₃ C ₂ , Cr ₂ N, CrSi, etc.) are not preferable from the viewpoint of environmental properties. Many of Hf ceramics (HfB ₂ , HfC, HfN, etc.) and rare earth ceramics on the rare earth side of Tb are not preferable from the viewpoints of economy and availability.
Therefore, the non-oxide ceramics added to the upper layer film 6 include Cr-based ceramics, Hf-based ceramics, and non-oxide ceramic particles excluding rare earth element-based ceramics on the heavy rare earth side from Tb, or these ceramics are excluded. Also preferred are particles of a mixture of two or more non-oxide ceramics.

Further, the non-oxide ceramic particles are more preferably non-oxide ceramics exemplified below from the viewpoints of the presence or absence of industrial products, stable distribution in domestic and overseas markets, price, electrical resistivity, and the like.
That is, non-oxide ceramic particles include BaB ₆ (electric resistivity 77 × 10 ⁻⁶ Ωcm), CeB ₆ (30 × 10 ⁻⁶ Ωcm), Co ₂ B (33 × 10 ⁻⁶ Ωcm), CoB ( 76 × 10 ⁻⁶ Ωcm), FeB (80 × 10 ⁻⁶ Ωcm), GdB ₄ (31 × 10 ⁻⁶ Ωcm), GdB ₆ (45 × 10 ⁻⁶ Ωcm), LaB ₄ (12 ×) 10 ^-6 Ωcm), LaB ₆ (same _{^{15 × 10 -6 Ωcm), Mo}} 2 B ( the ^{40 × 10 -6 Ωcm), MoB} ( the ^{35 × 10 -6 Ωcm), MoB} 2 ( same 45 × 10 ^{- 6} Ωcm), Mo ₂ B ₅ (26 × 10 ⁻⁶ Ωcm), Nb ₃ B ₂ (45 × 10 ⁻⁶ Ωcm), NbB (6.5 × 10 ⁻⁶ Ωcm), Nb ₃ B ₄ ( the ^{34 × 10 -6 Ωcm), NbB} 2 ( same 10 × ^{10 -6} cm), NdB ₄ (the ^{39 × 10 -6 Ωcm), NdB} 6 ( same ^{20 × 10 -6 Ωcm), PrB} 4 ( the ^{40 × 10 -6 Ωcm), PrB} 6 ( same 20 × ^{10 -6} Ωcm) , SrB ₆ (77 × 10 ⁻⁶ Ωcm), TaB (100 × 10 ⁻⁶ Ωcm), TaB ₂ (100 × 10 ⁻⁶ Ωcm), TiB (40 × 10 ⁻⁶ Ωcm), TiB ₂ ( 28 × 10 ⁻⁶ Ωcm), VB (35 × 10 ⁻⁶ Ωcm), VB ₂ (150 × 10 ⁻⁶ Ωcm), W ₂ B ₅ (80 × 10 ⁻⁶ Ωcm), YB ₄ (same as above) 29 × 10 ⁻⁶ Ωcm), YB ₆ (40 × 10 ⁻⁶ Ωcm), YB ₁₂ (95 × 10 ⁻⁶ Ωcm), ZrB ₂ (60 × 10 ⁻⁶ Ωcm), MoC (97 × 10) ⁻⁶ Ωcm), Mo ₂ C (100 × 10 ⁻⁶ Ωcm) Nb ₂ C (144 × 10 ⁻⁶ Ωcm), NbC (74 × 10 ⁻⁶ Ωcm), Ta ₂ C (49 × 10 ⁻⁶ Ωcm), TaC (30 × 10 ⁻⁶ Ωcm), TiC (180 × 10 ⁻⁶ Ωcm), V ₂ C (140 × 10 ⁻⁶ Ωcm), VC (150 × 10 ⁻⁶ Ωcm), WC (80 × 10 ⁻⁶ Ωcm), W ₂ C (same) 80 × 10 ⁻⁶ Ωcm), ZrC (70 × 10 ⁻⁶ Ωcm), Mo ₂ N (20 × 10 ⁻⁶ Ωcm), Nb ₂ N (142 × 10 ⁻⁶ Ωcm), NbN (54 ×) 10 ⁻⁶ Ωcm), ScN (25 × 10 ⁻⁶ Ωcm), Ta ₂ N (135 × 10 ⁻⁶ Ωcm), TiN (22 × 10 ⁻⁶ Ωcm), ZrN (14 × 10 ⁻⁶ Ωcm). ), CoSi ₂ (same _{^{18 × 10 -6 Ωcm), Mo}} 3 Si ( same 22 _{^{10 -6 Ωcm), Mo 5 Si}} 3 ( the ^{46 × 10 -6 Ωcm), MoSi} 2 ( same ^{22 × 10 -6 Ωcm), NbSi} 2 ( same _{^{6.3 × 10 -6 Ωcm), Ni}} 2 Si ( 20 × 10 ⁻⁶ Ωcm), Ta ₂ Si (124 × 10 ⁻⁶ Ωcm), TaSi ₂ (8.5 × 10 ⁻⁶ Ωcm), TiSi (63 × 10 ⁻⁶ Ωcm), TiSi ₂ ( 123 × 10 ⁻⁶ Ωcm), V ₅ Si ₃ (115 × 10 ⁻⁶ Ωcm), VSi ₂ (9.5 × 10 ⁻⁶ Ωcm), W ₃ Si (93 × 10 ⁻⁶ Ωcm), Particles of WSi ₂ (33 × 10 ⁻⁶ Ωcm), ZrSi (49 × 10 ⁻⁶ Ωcm), ZrSi ₂ (76 × 10 ⁻⁶ Ωcm), and a mixture of two or more kinds selected from these preferable.

Among these, non-oxide ceramic particles having an electrical resistivity at 25 ° C. of 0.1 to 100 × 10 ⁻⁶ Ωcm are particularly preferable. This is because the non-oxide ceramic particles have an electric resistivity at 25 ° C. of 0.1 to 100 × 10 ⁻⁶ Ωcm, whereby the content of the non-oxide ceramic particles in the upper film 6 can be further reduced. By reducing the content of the non-oxide ceramic particles in the upper layer film 6, formation of a conduction path of a corrosion current that penetrates the upper layer film 6 is suppressed, and a decrease in corrosion resistance is preferably suppressed. In addition to this, it is preferable to reduce the content of non-oxide ceramic particles in the upper layer film 6, thereby suppressing the peeling or galling of the upper layer film 6 during press molding and suppressing the decrease in formability.

The upper film 6 may contain a rust preventive pigment. The rust preventive pigment is not particularly limited, but is aluminum tripolyphosphate, phosphoric acid and phosphorous acid Zn, Mg, Al, Ti, Zr and Ce salts, hydrocalumite-treated phosphate compound (for example, zinc phosphate EXPERT NP-530 N5) manufactured by Toho Pigment, which is a hydrocalumite treatment, and Ca ion-exchanged silica, and an amorphous oil having an oil absorption of 100 to 1000 ml / 100 g, a specific surface area of 200 to 1000 m ² / g, and an average particle size of 2 to 30 μm At least one rust preventive pigment selected from the group consisting of porous silica is preferred.
Among these, preferable rust preventive pigments are phosphate-based rust preventive pigments (aluminum tripolyphosphate, a phosphate compound treated with hydrocalumite, etc.), silica, from the viewpoint of improving the corrosion resistance of both the heel portion and the flat portion. It is a system antirust pigment, or a combination of both. Particularly preferred anti-rust pigments are aluminum tripolyphosphate, hydrocalumite-treated phosphate compound, Ca-exchanged silica, oil absorption of 100 to 1000 ml / 100 g, specific surface area of 200 to 1000 m ² / g, and average particle size of 2 to 30 μm. It is at least one selected from the group consisting of amorphous silica.

Silica oil absorption can be measured according to JIS K 5101-13-2: 2004. The specific surface area of silica can be measured by the BET method. The average particle diameter of silica can be measured by the same method as the average particle diameter of conductive particles.

The content of the rust preventive pigment is preferably 2.5 to 20% by mass relative to the total solid mass of the upper layer film 6.
When the content of the rust preventive pigment is less than 2.5% by mass, corrosion resistance may not be sufficiently obtained, which is not preferable. When the content of the rust preventive pigment exceeds 20% by mass, the processability and cohesive force of the upper layer film 6 may be lowered, which is not preferable.
The content of the rust preventive pigment is more preferably 5 to 15% by mass with respect to the total solid mass of the upper film 6 from the viewpoint of corrosion resistance and processability.

The upper layer film 6 may contain other additives. Examples of the additive include well-known additives such as extender pigments, solid lubricants, and leveling agents.
Examples of extender pigments include silica (including colloidal silica), titania, zirconia, and the like. The content of the extender is preferably 0.1 to 20% by mass relative to the total solid mass of the upper layer film 6. When the content of the extender is less than 0.1% by mass, the effect of adding the extender may not be sufficiently obtained, which is not preferable. The upper limit of the content of the extender pigment is not particularly limited, but if the content is excessively large, the content of other components in the upper layer film 6 may decrease, and the desired effect may not be obtained. Therefore, it is preferably about 20% by mass or less.

It is preferable to add a solid lubricant to the upper film 6 because it can impart excellent lubricity to the upper film 6 and improve powdering resistance. Examples of the solid lubricant include polyolefin wax, paraffin wax, and fluororesin wax.
Examples of the polyolefin wax and paraffin wax include polyethylene wax, synthetic paraffin, natural paraffin, micro wax, chlorinated hydrocarbon, and the like. Examples of the fluororesin wax include polyfluoroethylene resin (polytetrafluoroethylene resin, etc.), polyvinyl fluoride resin, and polyvinylidene fluoride resin.

The average particle size of the solid lubricant is preferably 0.05 to 25 μm. When the average particle size of the solid lubricant is less than 0.05 μm, the area occupied by the lubricant in the surface layer of the upper film 6 is increased due to the surface concentration of the lubricant, and the adhesion between the upper film 6 and the lower film 5 is increased. Is not preferred because it may decrease. In addition, when the average particle size of the solid lubricant is less than 0.05 μm and when further coating (post-coating) is applied to the upper layer of the upper film 6, the adhesion between the upper film 6 and the film formed by the post-coating Is also not preferable. On the other hand, when the average particle size of the solid lubricant exceeds 25 μm, it is difficult to obtain the predetermined lubricity due to the lubricant being easily removed from the upper layer film 6, and the corrosion resistance may be lowered. .
The average particle size of the solid lubricant is more preferably from 1 to 15 μm, and even more preferably from 3 to 10 μm from the viewpoint of obtaining excellent paint adhesion, corrosion resistance, lubricity and powdering resistance.

The softening point of the solid lubricant is preferably 100 ° C to 135 ° C, more preferably 110 to 130 ° C. When the softening point of the solid lubricant is 100 ° C. to 135 ° C., the lubricity and the powdering resistance are further improved.

The content of the solid lubricant is preferably 0.1 to 10% by mass with respect to the total solid mass of the upper film 6. When the content of the solid lubricant is less than 0.1% by mass, it is not preferable because sufficient lubricity may not be obtained. When the content of the solid lubricant exceeds 10% by mass, the adhesion and corrosion resistance between the upper layer film 6 and the lower layer film 5 may be lowered, which is not preferable.
The content of the solid lubricant is more preferably 0.2 to 5% by mass with respect to the total solid mass of the upper layer film 6 in terms of adhesion between the upper layer film 6 and the lower layer film 5, lubricity and corrosion resistance. More preferably, it is 0.5 to 2.5% by mass.

Since the upper layer film 6 includes the first carbon black 7, the L value is generally small. On the other hand, the base steel plate 2 and the galvanized layer 3 are generally silver white and have a relatively large L value. When wrinkles occur in the upper layer film 6, when the appearance of the coated steel sheet 1 is observed, the lower base steel sheet 2 or the galvanized layer 3 may be visible. In that case, there was a problem that the color difference (difference in L value) between the portion of the upper film 6 without wrinkles and the base steel plate 2 or the galvanized layer 3 was large, and wrinkles were conspicuous.
The coated steel sheet 1 has a zinc phosphate film 4 containing 0.4 to 2.5 g / m ² of zinc phosphate on the galvanized layer 3 as an adhesion amount. The L value of the zinc phosphate coating 4 is smaller than that of the base steel plate 2 and the galvanized layer 3. That is, the color tone difference between the upper film 6 and the zinc phosphate film 4 is smaller than the color difference between the upper film 6 and the base steel plate 2 or the galvanized layer 3. Therefore, the formation of the zinc phosphate film 4 on the galvanized layer 3 makes the wrinkles less noticeable.
By forming the zinc phosphate film 4 on the galvanized layer 3, irregularities on the order of several μm are formed on the surface of the galvanized layer 3. It is considered that the L value of the zinc phosphate coating 4 is small because the irregularities cause irregular reflection of light.

In addition, when the wrinkle is formed on the surface of the upper layer film 6 and the adhesion between the lower layer film 5 and the galvanized layer 3 is not good, the lower layer film 5 is easily peeled off, and the wrinkle is the base steel plate 2 or the galvanized plate. Easy to reach layer 3.
On the other hand, by forming the zinc phosphate coating 4 on the zinc plating layer 3, the unevenness of the zinc phosphate coating 4 as described above improves the adhesion between the zinc plating layer 3 and the lower coating 5. Thereby, since the lower layer film 5 becomes difficult to peel off, it becomes difficult for the wrinkles to reach the base steel plate 2 or the galvanized layer 3.

Furthermore, when wrinkles occur in the upper layer film 6, the shaved portion of the upper layer film 6 enters the irregularities of the zinc phosphate film 4. Since the scraped portion of the upper layer film 6 includes the first carbon black 7, even if wrinkles occur, the concave portions of the zinc phosphate film 4 become black, and the wrinkles are less noticeable.
Further, a color pigment such as carbon black has a large potential difference from zinc or iron contained in the plating, and the corrosion resistance of the coated steel sheet 1 may be lowered. However, the coated steel sheet 1 is configured such that the pigment (carbon black or the like) in the upper layer film 6 is not in direct contact with the galvanized layer 3 by the zinc phosphate film 4. Therefore, the coated steel sheet 1 has good corrosion resistance.

In the coated steel sheet 1, an upper layer film 6 is not directly formed on the zinc phosphate film 4, but a lower layer film 5 is formed between the zinc phosphate film 4 and the upper layer film 6. Thereby, compared with the case where the upper layer film | membrane 6 is directly formed on the zinc phosphate film | membrane 4, it is possible to reduce the thickness as the coated steel plate 1 whole.

[Back coating]
In the coated steel sheet 1, the configuration of the back film formed on the back side of the product is not particularly limited.

[Usage]
The coated steel plate 1 can be suitably used for a housing for home appliances. Since the coated steel sheet 1 has a thin film, it can be manufactured at low cost. Therefore, the coated steel sheet 1 is suitable for a back panel of an AV device such as a thin display that is particularly required to be manufactured at a low cost.

(Manufacturing method of the coated steel plate 1)
Next, the manufacturing method of the coated steel plate 1 is demonstrated.

[Zinc plating process]
First, the galvanized layer 3 is formed on the base steel plate 2 by subjecting the base steel plate 2 to a galvanizing step.
The specific method of the galvanizing process is not particularly limited, but is electro-Zn plating, electro-Zn—Ni plating, electro-Zn—Co plating, hot-dip Zn plating, alloyed hot-dip Zn plating, hot-zinc-55% Al-1.6. % Si plating, hot-dip Zn-11% Al plating, hot-melting Zn-11% Al-3% Mg plating, hot-melting Zn- ⁶ % Al-3% Mg plating, hot-melting Zn-11% Al-3% Mg-0.2 % Si plating and the like. Moreover, you may coat | cover plating of the said component by methods, such as vapor deposition.

When using an electroplating method in a galvanization process, it electrolyzes between the counter electrode by using the base-material steel plate 2 as a negative electrode in the electrolyte solution containing Zn ion. By controlling the electrolyte composition, current density, and electrolysis time, the amount of plating adhered to the base steel sheet 2 is controlled.

When the hot dip plating method is used in the galvanizing process, the base steel plate 2 is immersed in a plating bath in which Zn or Zn alloy in a molten state is held, and the base steel plate 2 is pulled up from the plating bath. By adjusting the pulling speed of the base steel plate 2, the flow rate of the wiping gas ejected from the wiping nozzle provided above the plating bath, the flow rate adjustment, and the like, the amount of plating adhered to the base steel plate 2 is controlled.
The alloying process is performed by heating the base steel sheet 2 after the galvanized layer 3 is formed in a gas furnace, an induction heating furnace, a heating furnace using a combination thereof, or the like after the plating process as described above.
As for the plating operation, plating may be performed by either a continuous plating method of a coil or a plating method of a single cut plate.

[Zinc phosphate treatment process]
A zinc phosphate coating 4 is formed on the zinc plating layer 3 by performing a zinc phosphate treatment step after the zinc plating step. The specific method of the zinc phosphate treatment is not particularly limited, and any zinc phosphate treatment of reaction type treatment, coating type treatment, and electrolytic type treatment may be used.
In the reactive zinc phosphate treatment, the base steel plate 2 on which the galvanized layer 3 is formed is degreased, washed with water and subjected to surface conditioning treatment, and then contacted with a reactive treatment solution, washed with water and dried. be able to. The reactive processing solution contains at least one selected from iron ions, cobalt ions, and calcium ions in an aqueous solution mainly composed of phosphate ions, nitrate ions, and zinc ions. The reactive processing liquid may further contain at least one selected from peroxides, fluoride ions, complex fluoride ions, and nitrite ions.

In the coating type zinc phosphate treatment, a zinc phosphate treatment liquid mainly composed of phosphate ions, nitrate ions and zinc ions is applied to at least one surface of the base steel plate 2 on which the galvanized layer 3 is formed.
The coating method is arbitrary. In addition to coating by a roll coater method, the coating amount can be adjusted by an air knife method or a roll squeezing method after coating by a dipping method or a spray method. After the zinc phosphate treatment liquid is applied to the surface of the base steel plate 2, the zinc phosphate coating 4 can be formed by drying using a dryer, hot air furnace, high frequency induction heating furnace, or infrared furnace.

As a drying method for forming the zinc phosphate coating 4 by the coating type treatment, it is preferable to dry the base steel plate 2 so that the ultimate plate temperature is 70 ° C. to 400 ° C. When the ultimate plate temperature during drying is lower than 70 ° C., the zinc phosphate film 4 is not sufficiently dried, the zinc phosphate film 4 becomes sticky, and not only the paint adhesion is deteriorated, but also the upper layer of the zinc phosphate film 4. This is not preferable because unevenness occurs in the film formed. Further, if the ultimate plate temperature exceeds 400 ° C., not only is the effect not obtained, it is not economical, but also defects in the zinc phosphate film 4 are likely to occur and the corrosion resistance is inferior.
From such a viewpoint, the ultimate temperature of the base steel sheet 2 during drying is more preferably 100 to 300 ° C, and further preferably 120 to 170 ° C.

The zinc phosphate treatment liquid may contain at least one selected from nickel ions, manganese ions, and magnesium ions in addition to zinc ions. Among them, in order to further improve the design and scratch resistance of the processed part, it is preferable that the zinc phosphate treatment liquid contains both magnesium ions and nickel ions in addition to zinc ions. The magnesium ion content in the zinc phosphate treatment solution is preferably 5.0 to 40.0 g / l, more preferably 10.0 to 25.0 g / l. The content of nickel ions in the zinc phosphate treatment solution is preferably 0.05 to 2.00 g / l, more preferably 0.10 to 1.50 g / l.
The content of phosphate ions in the zinc phosphate treatment solution is preferably 1 to 20 g / l, more preferably 3 to 10 g / l. The content of Zn ions in the zinc phosphate treatment solution is preferably 0.1 to 10 g / l, more preferably 1 to 5 g / l.

As the electrolytic treatment, the electrolytic treatment is performed between the counter electrode using the base steel plate 2 as a negative electrode in an electrolytic treatment liquid containing phosphate ions, nitrate ions and zinc ions as main components. The amount of the zinc phosphate coating 4 attached to the base steel plate 2 on which the galvanized layer 3 is formed is controlled by adjusting the electrolyte composition, current density, and electrolysis time.

[Lower layer 5 forming step]
The lower layer film 5 is formed on the zinc phosphate film 4 by performing the lower layer film 5 forming step after the zinc phosphate treatment step. In the lower layer coating 5 forming step, the lower layer coating 5 is formed by applying and baking the base chemical on the zinc phosphate coating 4. The application and baking method is not particularly limited, and a known method can be used.
As the base chemical, E300 series manufactured by Nippon Parkerizing Co., Ltd., Surfcoat series manufactured by Nippon Paint Co., Ltd., or the like can be used. In consideration of the environmental load and the like, the base chemical solution preferably does not contain chromium.
In addition, what is necessary is just to add a color pigment to a base chemical | medical solution suitably, when the lower layer membrane | film | coat 5 contains a color pigment.

[Upper layer 6 forming step]
The upper film 6 is formed on the lower film 5 by performing the upper film 6 forming process after the lower film 5 forming process. In the upper layer coating 6 forming step, the upper layer coating 6 is formed by applying and baking the base chemical on the lower layer coating 5. The application and baking method is not particularly limited, and a known method can be used.
For the formation of the upper layer film 6, for example, a known base chemical solution used for forming a surface film of a commercially available fingerprint-resistant steel sheet can be used. The fingerprint-resistant steel plate is a base steel plate (usually a plated steel plate) formed with a thin film based on polyester resin, urethane resin, acrylic resin, epoxy resin, or the like. A treatment liquid is prepared by appropriately adding carbon black to such a base chemical.

Hereinafter, the present invention will be described more specifically with reference to examples. However, these examples do not limit the present invention.

[Pretreatment process]
The following nine types of galvanized steel sheets were degreased by immersing them in an aqueous solution containing 2.5% by mass of an aqueous alkaline degreasing agent (FC-301 manufactured by Nihon Parkerizing Co., Ltd.) at a temperature of 40 ° C. for 2 minutes. . Thereafter, the galvanized steel sheet was washed with water and dried.
EG2: Electrogalvanized steel sheet (plate thickness 0.8 mm, plating adhesion 2 g / m ² )
EG5: Electrogalvanized steel sheet (plate thickness 0.8 mm, plating adhesion 5 g / m ² )
EG10: electrogalvanized steel sheet (plate thickness 0.8 mm, plating adhesion 10 g / m ² )
EG20: electrogalvanized steel sheet (plate thickness 0.8 mm, plating adhesion 20 g / m ² )
EG40: electrogalvanized steel sheet (plate thickness 0.8 mm, plating adhesion 40 g / m ² )
ZL: Electric Zn-10 mass% Ni alloy plated steel sheet (plate thickness 0.8 mm, plating adhesion 10 g / m ² )
GI: hot dip galvanized steel sheet (plate thickness 0.8 mm, plating adhesion 60 g / m ² )
SD: Molten Zn-11 mass% Al-3 mass% Mg-0.2 mass% Si alloy-plated steel sheet (plate thickness 0.8 mm, plating adhesion 60 g / m ² )
GA: Alloyed hot-dip galvanized steel sheet (plate thickness 0.8 mm, 10 mass% Fe, plating adhesion 45 g / m ² )

[Zinc phosphate treatment process]
The surface of the galvanized steel sheet after the pretreatment step was subjected to spray treatment using a titanium colloidal surface treatment agent (preparene Z) manufactured by Nihon Parkerizing Co., Ltd. at room temperature for a predetermined time.
Next, the surface of the galvanized steel sheet was subjected to spray treatment using a zinc phosphate chemical (Palbond 3312) manufactured by Nippon Parkerizing Co., Ltd. at a temperature of 60 ° C. In addition, the immersion treatment time in the zinc phosphate chemical conversion solution was adjusted at each level so that the adhesion amount of each level of the zinc phosphate film became a desired adhesion amount.
Thereafter, the galvanized steel sheet was transferred to a hot air oven, and dried at a surface temperature of 70 ° C. to form a zinc phosphate film having a predetermined adhesion amount.

[Formation of lower layer film]
In forming the lower layer film, two types of base chemical solutions p and q were prepared.
The base chemical p is composed of a silane coupling agent (3-glycidoxypropyltrimethoxysilane), silica fine particles (colloidal silica (Snowtex N manufactured by Nissan Chemical Co., Ltd.)), Zr compound (ammonium zirconium carbonate) and urethane resin (water dispersion). An aqueous coating composition comprising a urethane resin (Superflex E-2000 manufactured by Daiichi Kogyo Co., Ltd.).
The base chemical solution q is composed of a silane coupling agent (3-glycidoxypropyltrimethoxysilane), silica fine particles (colloidal silica (Snowtex O manufactured by Nissan Chemical Co., Ltd.)) and polyester resin (water-dispersed polyester resin (Toyobo Co., Ltd., Bironal MD). -1200)).
The contents of each component in the base chemical solutions p and q are as shown in Table 1.

A treatment liquid for forming a lower layer film was prepared by adding a pigment to the base chemical liquids p and q. Except for the level p1, the treatment solutions for forming the lower layer film include C1 (carbon black dispersion (manufactured by Toyo Ink Industries)), C2 (carbon black (MA-100, manufactured by Mitsubishi Chemical Corporation)), P (benzimidazolone (Toyo Ink) Ink Industries)) or B (Copper Phthalocyanine (Toyo Ink Industries)) was added.
Table 2 shows the types and contents of the base chemicals and pigments used in each of the lower layer film forming treatment liquids, and the carbon black particle diameter when carbon black is used as the pigment.

The processing liquid for lower layer film formation shown in Table 2 was applied to the surface of the galvanized steel sheet by the bar coat method. Thereafter, the galvanized steel sheet was transferred to a hot air furnace and dried and air-dried so that the temperature reached on the surface of the galvanized steel sheet was 70 ° C., thereby forming a lower layer film on the surface of the galvanized steel sheet. When forming the lower layer film, the dilution conditions and the bar count were adjusted so that the adhesion amounts shown in Tables 5 to 7 were obtained.
At level 120, NRC300 manufactured by Nippon Paint Surf Chemicals Co., Ltd. was applied so as to be 50 mg / m ^{2 in} terms of Cr, and baked at 130 ° C. and chromated (Cr ) A film was prepared.

[Formation of upper layer film]
In forming the upper layer film, the resins shown in Table 3 and the curing agent were mixed in the ratios shown in Table 3 to prepare upper layer binders B1 to B8.

Carbon black, conductive pigment, rust preventive pigment, colloidal silica and lubricant were added to the upper layer binder to prepare an upper layer film forming treatment liquid. Table 4 shows the composition of the treatment liquid for forming the upper layer film at each level.

Apply the treatment solution for forming the upper layer film shown in Table 4 on the galvanized steel sheet on which the lower layer film is formed with a bar coater, and dry using an oven under heating conditions such that the maximum temperature reaches 200 ° C. in 30 seconds. Thus, an upper film was formed. The coating amount of the upper layer film was adjusted by dilution of the coating composition and the count of the bar coater so that the total coating amount of the solid content (nonvolatile content) in the coating composition became the deposition amount shown in Table 4.
In Table 4, the solid content concentration of each component was described as the ratio (mass%, value per side) of the solid content (nonvolatile content) of each component to the solid content (nonvolatile content) of the entire coating composition.

Each compound used in Table 4 is specifically shown below.
(Carbon black)
C1: Carbon black dispersion (manufactured by Toyo Ink Industries)

(Conductive pigment)
VB: vanadium diboride particles (average particle size of 1 to 3 μm)
VC: Vanadium carbide particles (average particle size of 1 to 3 μm)
VN: Vanadium nitride particles (average particle size of 1 to 3 μm)
・ ZS: Zirconium disilicide particles (average particle size 1 to 3 μm)
ZN: zirconium nitride particles (average particle size of 1 to 3 μm)
TN: Titanium nitride particles (average particle size of 1 to 3 μm)
SUS: SUS particles (average particle size 3-7 μm)
Ni: Ni particles (average particle size 3-7 μm) (rust preventive pigment)
PA: aluminum tripolyphosphate (average particle size of 1 to 2 μm)
・ PM: Magnesium phosphate (average particle size 1 ~ 2μm)
SC: Calcium ion exchanged silica (average particle size of 1 to 2 μm)
Si: Silica (Amorphous silica having an oil absorption of 100 to 1000 ml / 100 g, a specific surface area of 200 to 1000 m ² / g, and an average particle size of 1 to 30 μm) (Fuji Silysia silo mask 02)

(Colloidal silica)
T: Colloidal silica (average particle size: 10 to 15 nm) (Snowtex N manufactured by Nissan Chemical Co., Ltd.)
(lubricant)
PE: polyethylene wax (average particle size 1 μm, softening point 132 ° C.) (Chemical Pearl W700 manufactured by Mitsui Chemicals)

[Performance evaluation]
The performance evaluation of the test plate produced by the above-described method was performed according to the following methods and standards. Tables 5 to 7 show the conditions for producing the test plates of the examples and comparative examples, and Tables 8 to 10 show the performance evaluation results of the test plates of the examples and comparative examples.

(Scratch resistance)
Cold-rolled steel plate (0.8mm thickness) is punched into a 40mmφ disk, and the disk is tilted at an elevation angle of 45 ° with the test plate, and a load of 0.5kg is applied in a direction perpendicular to the disk surface and 50mm at a speed of 10mm / sec. I scratched it. The black appearance of the scratched buttocks was visually observed and evaluated according to the following criteria.
When the score was 3 or more, it was judged that the scuff resistance was excellent.

5: No difference in black appearance between the normal part and the buttocks. Appears to have a uniform black appearance, including the buttocks.
4: There is no difference in the black appearance of the buttocks, but the glossiness appears to change slightly.
3: A slight change is seen in the black appearance of the buttocks, but there is no exposure of the base.
2: A change is seen in the black appearance of a collar part, and there exists exposure of a foundation | substrate.
1: A noticeable change is seen in the black appearance of the buttocks, and there is a remarkable exposure of the groundwork.

(Corrosion resistance)
The back and edges of the unprocessed flat plate were tape-sealed, and a salt spray test (JIS-Z-2371: 2000) was conducted for 120 hours. The appearance was observed after 120 hours, and the corrosion resistance was evaluated by the corrosion status and the corrosion area ratio.
When the score was 3 or more, it was judged that the corrosion resistance was excellent.

5: White rust is less than 2% 4: White rust is 2% or more and less than 5% 3: White rust is 5% or more and less than 10% 2: No red rust is generated, White rust is 10% or more 1: Red rust is generated, white rust 10% or more

(Adhesion)
After 0T bending (180 ° bending) processing was performed and the outer side of the bent portion was peeled off from the tape, the state of adhesion of the coating film to the tape side was observed and evaluated according to the following evaluation criteria.
When the score was 2 or more, it was judged that the adhesion was excellent.

3: No film adhesion on the tape side 2: Several peelings on the tape side were observed, peeling on the steel sheet side was less than 10% 1: Coating film peeling on the tape side, peeling on the steel sheet side was 10 %more than

(Conductivity)
Using a Lorester 4-end needle, 20 points were measured and the conductivity was measured. Of the 20 points where the conductivity was measured, the conductivity was evaluated by the number of points that were below a predetermined resistance value.
When the following score was 2 or 3, it was judged that it was excellent in electroconductivity.

3: Less than a predetermined resistance value at all 20 points 2: Below a predetermined resistance value at 10 to 19 points out of 20 1: Below a predetermined resistance value at 0 to 9 out of 20 points

As shown in Tables 8 to 10, the test plates according to the examples had suitable scratch resistance, corrosion resistance, adhesion, and conductivity. On the other hand, the test plate according to the comparative example was inferior in performance.
As a result, according to the present invention, even if the coating formed on the surface of the base steel sheet is thin, wrinkles from the coating surface that occurs during handling and processing are not noticeable, and the surface has relatively good corrosion resistance. It was found that a treated steel plate can be obtained.

According to the above-described embodiment, it is possible to provide a coated steel sheet having excellent scratch resistance and corrosion resistance even though the coating film formed on the steel sheet surface is thin.

DESCRIPTION OF SYMBOLS 1 Coated steel plate 2 Base steel plate 3 Zinc plating layer 4 Zinc phosphate coating 5 Lower layer coating 6 Upper layer coating 7 First carbon black 8 Second carbon black

Claims (7)

1. A base steel plate;
   A galvanized layer formed on the base steel sheet;
   A zinc phosphate coating formed on the galvanized layer and containing zinc phosphate crystals and having an adhesion amount of 0.4 to 2.5 g / m ² ;
   A lower layer film formed on the zinc phosphate film and having an adhesion amount of 50 to 2000 mg / m ² and being an inorganic film or an organic-inorganic composite film;
   An upper film formed on the lower film and having a film thickness of 2.0 to 10.0 μm and containing 5 to 25% by mass of the first carbon black;
   With
   A coated steel sheet, wherein a maximum gap between the zinc phosphate crystals is 0.2 μm or less at an interface between the zinc plating layer and the zinc phosphate film.
2. The coated steel sheet according to claim 1, wherein the lower layer film contains 10 to 50% by mass of a coloring pigment.
3. The coated steel sheet according to claim 2, wherein the lower layer film contains 10 to 30% by mass of a coloring pigment.
4. The coated steel sheet according to claim 2 or 3, wherein the colored pigment is second carbon black.
5. The coated steel sheet according to claim 4, wherein the particle size of the second carbon black is more than 100 nm.
6. The coated steel sheet according to claim 4 or 5, wherein a primary particle diameter of the first carbon black is smaller than a primary particle diameter of the second carbon black.
7. The lower layer film has at least one selected from the group consisting of borides, carbides, nitrides and silicides having an electrical resistivity of 0.1 × 10 ⁻⁶ to 185 × 10 ⁻⁶ Ωcm at a temperature of 25 ° C. The coated steel sheet according to any one of claims 1 to 6, comprising 5 to 15% by mass of non-oxide ceramic particles.

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