Surface-treated metal sheet and automotive member comprising same

Abstract

The present invention provides a surface-treated metal sheet having excellent corrosion resistance while also having excellent weldability for continuous spot welding, and an automotive member comprising the same. Provided are: a surface-treated metal sheet comprising a metal sheet and a coating film having a thickness of 0.5 to 5.0 μm disposed on the surface of the metal sheet, wherein the coating film contains doped oxide particles, an anti-corrosion pigment, and a binder resin, the anti-corrosion pigment contains a Si-containing compound, and the ratio (A / B) of the amount (vol%) (A) of the doped oxide particles to the amount (vol%) (B) of the Si-containing compound is 2.80 to 6.00; and an automotive member comprising the same.

Description

Surface-treated metal sheet and automotive component having the same

[0001] The present invention relates to a surface-treated metal sheet and an automotive component having the same.

[0002] Surface-treated metal sheets are sometimes used as components in automobiles and other vehicles to improve corrosion resistance. Such surface-treated metal sheets may be assembled into a desired shape by, for example, spot welding, and then electrodeposited. Therefore, in such surface-treated metal sheets, it is necessary to impart corrosion resistance while making the coating conductive so that spot welding and / or electrodeposition coating can be performed.

[0003] In this regard, Patent Document 1 provides a metal plate and a coating film disposed on at least one main surface of the metal plate, wherein the coating film comprises oxide particles, a binder resin, and conductive particles, the content of the conductive particles is 5 to 30% by mass relative to the coating film, the oxide particles include undoped oxide particles and / or doped oxide particles, the undoped oxide particles include at least one selected from the group consisting of zinc oxide particles, tin oxide particles, magnesium oxide particles, calcium oxide particles, and strontium oxide particles, the doped oxide particles include at least one selected from the group consisting of doped zinc oxide particles and doped tin oxide particles, the content of the oxide particles is 1 to 30% by mass relative to the coating film when the oxide particles include the doped oxide particles, and 1 to 10% by mass relative to the coating film when the oxide particles do not include the doped oxide particles, and the amount of the coating film adhering to the main surface is 2 to 20 g / m² ２ A surface-treated metal sheet is disclosed. Patent Document 1 teaches that, according to the above configuration, a surface-treated metal sheet is provided that has excellent adhesion to the painted film after painting and excellent weldability.

[0004] International Publication No. 2016 / 159138

[0005] As described above, surface-treated metal sheets may be assembled into desired shapes by spot welding or other methods. In such spot welding, welding may be performed repeatedly with a single electrode. When spot welding is performed continuously, the tip diameter of the welding electrode may be crushed and gradually increase, resulting in insufficient pressure per unit area, making it difficult to secure a conductive path, and consequently, welding defects may occur.

[0006] Therefore, the present invention aims to provide a surface-treated metal sheet that has excellent corrosion resistance and excellent weldability even in continuous spot welding, and an automotive component having the same.

[0007] To achieve the above objective, the inventors focused on and investigated coating films on surface-treated metal plates. Specifically, the inventors first found that by configuring the coating film to contain doped oxide particles and a rust-preventive pigment, and that the rust-preventive pigment contains a Si-containing compound, the desired corrosion resistance can be achieved while the coating film becomes conductive, improving weldability in spot welding. Furthermore, the inventors found that by controlling the ratio of the Si-containing compound to the doped oxide particles to an appropriate ratio, or more specifically, by controlling the ratio (A / B) of the doped oxide particle content (volume %) to the Si-containing compound content (volume %) (B), it is possible to significantly improve weldability in continuous spot welding while maintaining corrosion resistance, thus completing the present invention.

[0008] The present invention, which has achieved the above objective, is as follows: (1) A surface-treated metal plate comprising: a metal plate; and a coating film having a thickness of 0.5 to 5.0 μm disposed on the surface of the metal plate, wherein the coating film comprises doped oxide particles, a rust-preventive pigment, and a binder resin; the rust-preventive pigment comprises a Si-containing compound; and the ratio (A / B) of the content of doped oxide particles (volume %) (A) to the content of Si-containing compound (volume %) (B) is 2.80 to 6.00. (2) The surface-treated metal plate according to (1), wherein the ratio (A / B) of the content of doped oxide particles (volume %) (A) to the content of Si-containing compound (volume %) (B) is 3.00 to 4.50. (3) The surface-treated metal sheet according to (2) above, wherein the ratio (A / B) of the content (volume %) (A) of the doped oxide particles to the content (volume %) (B) of the Si-containing compound is 3.00 to less than 4.00. (4) The surface-treated metal sheet according to any one of (1) to (3) above, wherein the Si-containing compound is amorphous silica, a silicate compound, or a combination thereof. (5) The surface-treated metal sheet according to (4) above, wherein the Si-containing compound is amorphous silica. (6) The surface-treated metal sheet according to any one of (1) to (5) above, wherein the doped oxide particles include zinc oxide particles doped with Al, Ga, In, or a combination thereof. (7) The surface-treated metal sheet according to any one of (1) to (6) above, wherein the ratio of the average particle size (μm) of the Si-containing compound to the thickness (μm) of the coating film is less than 0.50. (8) A surface-treated metal sheet according to any one of (1) to (7) above, wherein the average particle size of the doped oxide particles is 1.0 to 4.0 μm. (9) A surface-treated metal sheet according to any one of (1) to (8) above, wherein the ratio of the average particle size (μm) of the doped oxide particles to the average particle size (μm) of the Si-containing compound is 0.75 to 4.00. (10) A surface-treated metal sheet according to any one of (1) to (9) above, wherein the rust-preventive pigment further comprises a phosphate compound, a vanadate compound, or a combination thereof. (11) A surface-treated metal sheet according to any one of (1) to (10) above, wherein the binder resin is a water-soluble or water-dispersible aqueous resin.(12) A surface-treated metal sheet according to any one of (1) to (11) above, wherein the binder resin contains an epoxy resin. (13) An automotive component comprising a painted metal sheet, wherein the painted metal sheet has a surface-treated metal sheet according to any one of (1) to (12) above and an electrodeposited coating film.

[0009] According to the present invention, it is possible to provide a surface-treated metal sheet that has excellent corrosion resistance and excellent weldability even in continuous spot welding, and an automotive component having the same.

[0010] <Surface-treated metal sheet> The surface-treated metal sheet according to an embodiment of the present invention comprises a metal sheet and a coating film having a thickness of 0.5 to 5.0 μm disposed on the surface of the metal sheet, wherein the coating film contains doped oxide particles, a rust-preventive pigment, and a binder resin, the rust-preventive pigment contains a Si-containing compound, and the ratio (A / B) of the content of doped oxide particles (volume %) (A) to the content of the Si-containing compound (volume %) (B) is 2.80 to 6.00.

[0011] As mentioned earlier, surface-treated metal sheets are sometimes used as components in automobiles and other vehicles to improve corrosion resistance. Such surface-treated metal sheets may be assembled into desired shapes by spot welding or other methods. Therefore, it is necessary to impart conductivity to the coating film of such surface-treated metal sheets to enable spot welding while also providing corrosion resistance. Accordingly, the inventors focused on the coating film of surface-treated metal sheets and conducted research. To explain in more detail, the inventors first found that by configuring the coating film to include doped oxide particles and rust-preventive pigments, and that the rust-preventive pigments include a Si-containing compound, the desired corrosion resistance could be achieved while improving weldability in spot welding. Although we do not intend to be bound by any particular theory, it is presumed that, in addition to the high corrosion resistance of the Si-containing compound, the Si-containing compound has a relatively high melting point, which suppresses the diffusion of plating components, such as zinc which has a relatively low melting point, into the welding electrode, thereby enabling the acquisition of superior corrosion resistance. Furthermore, by configuring the coating to include both conductive doped oxide particles and insulating Si-containing compounds, the coating becomes conductive, while the areas where the Si-containing compounds are present become insulated. This creates resistance in spot welding, generating heat and thereby improving weldability.

[0012] However, simply configuring the coating film to contain doped oxide particles and rust-preventive pigments, and such that the rust-preventive pigments contain Si-containing compounds, sometimes resulted in welding defects during continuous spot welding. As mentioned earlier, during continuous spot welding, the tip diameter of the welding electrode gradually increases due to deformation, resulting in insufficient pressure per unit area, making the coating film less deformable and making it difficult to secure a current path. In addition, simply configuring the coating film to contain Si-containing compounds results in a hard coating film because the rust-preventive pigments, especially Si-containing compounds, are relatively hard pigments. This makes the coating film less deformable (less likely to be crushed) under the pressure of spot welding, and makes it even more difficult to secure a current path. As a result, welding defects are more likely to occur during continuous spot welding. Therefore, the inventors then focused on and investigated the ratio of doped oxide particles to rust-preventive pigments in the coating film. More specifically, we found that by controlling the ratio (A / B) of the content of doped oxide particles (volume %) to the content of Si-containing compound (volume %) (B) to 2.80 to 6.00, we can significantly improve weldability in continuous spot welding while maintaining corrosion resistance. Although we do not intend to be bound by any particular theory, controlling A / B to 2.80 to 6.00 suppresses the increase in coating hardness, thereby making it possible to significantly improve weldability in continuous spot welding while maintaining corrosion resistance.

[0013] As described above, the surface-treated metal sheet according to the embodiment of the present invention can achieve excellent corrosion resistance and excellent weldability in continuous spot welding. Therefore, the surface-treated metal sheet according to the embodiment of the present invention is particularly useful in applications in the automotive field where these properties are required.

[0014] The surface-treated metal plates according to embodiments of the present invention will be described in more detail below. In this specification, unless otherwise specified, the numerical range indicated by "~" includes the numerical values ​​before and after it as the lower limit and upper limit.

[0015] The following describes the various components of surface-treated metal sheets.

[0016] [Metal Sheets] The type of metal sheet is not particularly limited and can be appropriately selected depending on the application. Examples of metal sheets include steel sheets (iron-based alloy sheets), aluminum sheets, aluminum alloy sheets, magnesium sheets, and magnesium alloy sheets.

[0017] The steel sheet mentioned above may be an ordinary steel sheet or a special steel sheet containing additive elements such as chromium. It is preferable that the type and amount of additive elements, as well as the metal structure, are appropriately controlled so that the steel sheet has the desired formability.

[0018] The above-mentioned steel sheet may be a plated steel sheet having a plating layer on its surface. Examples of plated steel sheets include zinc-based plated steel sheets and aluminum-based plated steel sheets. Specifically, examples of zinc-based plated steel sheets include alloyed hot-dip galvanized steel sheets, hot-dip galvanized steel sheets, and electro-galvanized steel sheets.

[0019] A zinc-plated steel sheet has a zinc-plated layer on its surface. Examples of zinc-plated layers include a zinc-plated layer made of zinc; an alloy-plated layer containing zinc and at least one selected from the group consisting of aluminum, cobalt, tin, nickel, iron, chromium, titanium, magnesium, and manganese; and a zinc-alloy-plated layer further containing other metallic or non-metallic elements in addition to the zinc alloy-plated layer (for example, a zinc-alloy-plated layer containing zinc, aluminum, magnesium, and silicon). In the zinc-plated layer, the alloy components other than zinc are not particularly limited. The zinc-plated layer may contain small amounts of dissimilar metallic elements or impurities such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, arsenic, etc., and may also contain inorganic substances such as silica, alumina, titania, etc.

[0020] Aluminum-plated steel sheets have an aluminum-plated layer on the surface of the steel sheet. Examples of aluminum-plated layers include an aluminum-plated layer made of aluminum; and an alloy-plated layer containing aluminum and at least one selected from the group consisting of silicon, zinc, and magnesium (for example, an alloy-plated layer containing aluminum and silicon, an alloy-plated layer containing aluminum and zinc, or an alloy-plated layer containing aluminum, silicon, and magnesium).

[0021] Zinc-plated steel sheets and aluminum-plated steel sheets may also be multi-layered steel sheets formed by combining them with other types of plating layers (e.g., iron plating layer, iron and phosphorus alloy plating layer, nickel plating layer, cobalt plating layer, etc.).

[0022] The method for forming these plating layers is not particularly limited. Examples of methods for forming these plating layers include electroplating, electroless plating, hot-dip plating, vapor deposition plating, and dispersion plating. These plating layers can be formed by continuous or batch processes. Furthermore, after forming these plating layers, treatments such as zero-spangle treatment for uniform appearance, annealing treatment for modifying these plating layers, and temper rolling for surface condition or material adjustment may be performed.

[0023] [Coating] The coating is formed on the surface of the metal plate described above, more specifically, on at least one main surface (i.e., at least one side) of the metal plate described above. "Main surface" refers to two relatively large surfaces of the metal plate (the front surface and the back surface). Depending on the application, the coating may be formed on both sides of the metal plate (both main surfaces) or on only one side of the metal plate (one main surface). Furthermore, the coating may be formed on only a part of the surface of the metal plate or on the entire surface of the metal plate.

[0024] The coating contains doped oxide particles, rust-preventive pigments, and a binder resin. The coating may also contain other additives as needed.

[0025] [Doped Oxide Particles] Doped oxide particles are particles composed of metal oxides containing at least doped elements (impurities). Doped oxide particles are conductive and impart conductivity to coatings.

[0026] The metal oxides that constitute the doped oxide particles (metal oxides to which doped elements are doped) are not particularly limited, but examples include zinc oxide (ZnO) and tin oxide (SnO). ２ ), indium oxide (In ２ O ３ ) etc. are also acceptable.

[0027] Doped oxide particles may be composed entirely of a metal oxide containing a doped element, or only the surface layer of the particle may be composed of a metal oxide containing a doped element. Examples of doped oxide particles include zinc oxide particles doped with a doped element, tin oxide particles doped with a doped element, and indium oxide particles doped with a doped element. Furthermore, doped oxide particles may be particles composed of other metal oxides coated with zinc oxide, tin oxide, or indium oxide doped with a doped element. Examples of other metal oxides include titanium oxide, and specifically, examples include titanium oxide particles coated with tin oxide doped with a doped element.

[0028] As doping elements, elements with a different number of valence electrons from the metal elements contained in the metal oxide (e.g., Zn, Sn, or In) may be selected. For zinc oxide (ZnO), it is preferable to select at least one element selected from the group consisting of elements from Group 13 or Group 15 of the periodic table as doping elements. Among these, Al, Ga, In, or combinations thereof, which are Group 13 elements, are more preferable, and Al, Ga, or combinations thereof are particularly preferable. Also, tin oxide (SnO) ２ It is preferable to select at least one element selected from Group 15 of the periodic table as the doping element. Among these, P, Sb, As, or a combination thereof is more preferable, and P, Sb, or a combination thereof is particularly preferable. In addition, indium oxide (In ２ O ３It is preferable to select at least one element from Group 14 of the periodic table as the doping element. Among these, Sn, Ge, or a combination thereof are more preferable, and Sn is particularly preferred. By combining a metal oxide and a doping element as described above, conductivity can be imparted to the metal oxide.

[0029] The doped oxide particles may include, for example, at least one selected from the group consisting of zinc oxide particles doped with Al, Ga, In or a combination thereof; tin oxide particles doped with P, Sb, As or a combination thereof; indium oxide particles doped with Sn, Ge or a combination thereof; titanium oxide particles coated with zinc oxide doped with Al, Ga, In or a combination thereof; titanium oxide particles coated with tin oxide doped with P, Sb, As or a combination thereof; and titanium oxide particles coated with indium oxide doped with Sn, Ge or a combination thereof. Among these, it is preferable to include zinc oxide particles doped with Al, Ga, In or a combination thereof.

[0030] From the viewpoint of improving conductivity, the doping element content is preferably 0.05 to 5.00 atom%, and more preferably 0.10 to 5.00 atom%, relative to the undoped metal oxide.

[0031] The shape of the doped oxide particles is not particularly limited, but may be spherical, pseudospherical (e.g., elongated sphere, ellipsoid, egg-shaped, rugby ball-shaped, etc.), or polyhedral (e.g., soccer ball-shaped (truncated icosahedron), cube-shaped (cube-shaped), brilliant-cut shapes of various gemstones, etc.), with spherical being preferred. Spherical doped oxide particles tend to disperse uniformly throughout the coating film, making it easier to uniformly form effective electrical pathways that penetrate the coating film in the thickness direction, thereby further improving the conductivity of the coating film.

[0032] The average particle size of the doped oxide particles is not particularly limited, but the lower limit is preferably 0.1 μm or more, more preferably 0.4 μm or more, and particularly preferably 1.0 μm or more. The upper limit of the average particle size of the doped oxide particles is preferably 7.0 μm or less, more preferably 5.0 μm or less, and particularly preferably 4.0 μm or less. By keeping the average particle size of the doped oxide particles within the above range, it is possible to further improve the conductivity of the coating film. Furthermore, the ratio of the average particle size of the doped oxide particles (μm) to the average particle size of the Si compound (μm), which will be explained in detail later, is preferably 0.75 to 4.00 from the viewpoint of further improving the conductivity of the coating film. The ratio of the average particle size of the doped oxide particles (μm) to the average particle size of the Si-containing compound (μm) may be, for example, 0.75 or more, 0.85 or more, or 1.00 or more, and / or 3.80 or less, or 3.50 or less.

[0033] In this specification, the "average particle size" of doped oxide particles refers to the average primary particle size when doped oxide particles exist individually in the coating film, and the average secondary particle size, which represents the particle size of the doped oxide particles at the time of aggregation, when doped oxide particles exist aggregated in the coating film. The average particle size of doped oxide particles is calculated by the following cross-sectional observation. The cross-section in the thickness direction of the surface-treated metal plate is mirror-polished, and the cross-section of the coating film is photographed at 5000x magnification using a scanning electron microscope (JEOL Ltd., "JSM-7100F", acceleration voltage: 15kV) (field of view: 24 μm × 18 μm). In addition, the elements are identified by energy-dispersive X-ray spectroscopy to distinguish the doped oxide particles. The particle sizes of all doped oxide particles with a particle size of 0.50 μm or larger are calculated from the backscattered electron image of the observed field of view. Here, the particle size of each particle is obtained by calculating the average value of the length of the long side and the length of the short side measured using image processing software (Image J). The average particle size is determined by calculating the arithmetic mean of the particle sizes of all particles in the observed field of view. The same measurement is performed on 10 backscattered electron images, and the arithmetic mean of each backscattered electron image is taken as the average particle size of the doped oxide particles.

[0034] The content of doped oxide particles is not particularly limited, but is preferably 5.0 to 30.0 volume%, and more preferably 10.0 to 20.0 volume%, relative to the coating film (total solid content of the coating film). From the viewpoint of imparting conductivity to the coating film, the content of doped oxide particles may be 5.0 volume% or more, 10.0 volume% or more, or 15.0 volume% or more, relative to the coating film (total solid content of the coating film). On the other hand, from the viewpoint of processability of the coating film and adhesion to the electrodeposited coating film when an electrodeposited coating film is formed on top, the content of doped oxide particles may be 30.0 volume% or less, 25.0 volume% or less, or 20.0 volume% or less, relative to the coating film (total solid content of the coating film).

[0035] The content of doped oxide particles in the coating film is calculated by the following cross-sectional observation. Using image processing software (Image J), ​​the area occupied by the coating film and the area occupied by the doped oxide particles are measured from the backscattered electron image obtained in the same manner as the method for measuring the average particle size of doped oxide particles described above. Since the volume ratio of each component in the coating film roughly corresponds to the area ratio of each component when the coating film is observed in cross-section, the measured area ratio of the doped oxide particles is taken as the volume ratio of the doped oxide particles. The same measurement is performed on 10 backscattered electron images, and the arithmetic mean is taken as the content (volume %) of the doped oxide particles.

[0036] [Rust-preventive pigments] Rust-preventive pigments improve the corrosion resistance of surface-treated metal plates, especially the metal plate surface adjacent to the coating.

[0037] [Rust-preventive pigment - Si-containing compound] The rust-preventive pigment contains a Si-containing compound. The Si-containing compound is preferably amorphous silica, a silicate compound, or a combination thereof, more preferably amorphous silica. In addition to the high corrosion resistance of the Si-containing compound, since the Si-containing compound has a relatively high melting point, it prevents plating components such as zinc having a relatively low melting point from diffusing into the electrodes for spot welding, thereby obtaining excellent corrosion resistance. Further, by configuring the coating film to contain the insulating Si-containing compound, the coating film is made conductive, and at the locations where the Si-containing compound is present, it is insulated, and the locations become resistive and generate heat during spot welding, thereby enabling good spot welding.

[0038] Amorphous silica includes, for example, amorphous silicon dioxide and the like. The oil absorption amount of amorphous silica is not particularly limited, and may be, for example, 100 to 1000 ml / 100 g. The lower limit of the oil absorption amount of amorphous silica may be, for example, 200 ml / 100 g or more, 300 ml / 100 g or more, or 400 ml / 100 g or more, and the upper limit of the oil absorption amount of amorphous silica may be, for example, 900 ml / 100 g or less, 800 ml / 100 g or less, or 700 ml / 100 g or less. The oil absorption amount of silica is measured according to JIS K 5101-13-2; 2004. The specific surface area of amorphous silica is not particularly limited, and may be, for example, 200 to 1000 m ２ / g. The lower limit of the specific surface area of amorphous silica may be, for example, 250 m ２ / g or more, 300 m ２ / g or more, or 350 m ２ / g or more, and the upper limit of the specific surface area of amorphous silica may be, for example, 950 m ２ / g or less, 900 m ２ / g or less, 850 m ２ / g or less. Also, the specific surface area of silica is measured by the BET method.

[0039] Examples of silicate compounds include silicates of alkaline earth metals such as magnesium silicate and calcium silicate; silicates of alkali metals such as lithium silicate, sodium silicate, and potassium silicate; and aluminum silicate.

[0040] Examples of alkali metal silicates include silicon dioxide (SiO₂). ２ ) and lithium oxide (Li ２ The molar ratio of O) is 0.5 ≤ (SiO ２ / Li ２ Lithium silicate and silicon oxide (SiO) ≤ 8 ２ ) and sodium oxide (Na ２ The molar ratio of O) is 0.5 ≤ (SiO ２ / Na ２ Sodium silicate and silicon dioxide (SiO₂) ≤ 4 ２ ) and potassium oxide (K ２ The molar ratio of O) is 0.5 ≤ (SiO ２ / K ２ Examples include potassium silicate with O) ≤ 4, and hydrates of these silicates. Specific examples include lithium orthosilicate (Li ４ SiO ４ ;2Li ２ O.Sio ２ ), hexalithium orthonisilicate (Li ６ Si ２ O ７ ;3Li ２ O・2SiO ２ ), lithium metasilicate (Li ２ SiO ３ Li ２ O.Sio ２ ), lithium disilicate (Li ２ Si ２ O ５ Li ２ O・2SiO ２ ), tetralithium heptasilicate (2Li ２ O・7SiO ２ ), lithium tetrasilicate (Li ２ Si ４ O ９ Li ２ O・4SiO ２), lithium orthosilicate (2Li ２ O·9SiO ２ ), lithium pentasilicate (2Li ２ O·15SiO ２ ), sodium orthosilicate (Na ４ SiO ４ ; 2Na ２ O·SiO ２ ), sodium metasilicate (Na ２ SiO ３ ; Na ２ O·SiO ２ ), sodium disilicate (Na ２ Si ２ O ５ ; Na ２ O·2SiO ２ ), sodium tetrasilicate (Na ２ Si ４ O ９ ; Na ２ O·4SiO ２ ), potassium orthosilicate (K ４ SiO ４ ; 2K ２ O·SiO ２ ), potassium metasilicate (K ２ SiO ３ ; K ２ O·SiO ２ ), potassium disilicate (K ２ Si ２ O ５ ; K ２ O·2SiO ２ ), potassium tetrasilicate (K ２ Si ４ O ９ ; K ２ O·4SiO ２ ), and hydrates of these silicates. Many of these silicate hydrates can easily gel while remaining in a hydrated state due to environmental changes such as pH and temperature, and some may polymerize into polysilicates. The silicate compounds applicable to the present invention include such polysilicates.

[0041] The Si-containing compound content is not particularly limited, but is preferably 1.0 to 20.0 volume percent relative to the coating film (total solid content of the coating film). From the viewpoint of corrosion resistance, the Si-containing compound content may be 1.0 volume percent or more, 2.0 volume percent or more, 4.0 volume percent or more, or 6.0 volume percent or more relative to the coating film (total solid content of the coating film). On the other hand, from the viewpoint of hardness and workability of the coating film, the Si-containing compound content may be 20.0 volume percent or less, 15.0 volume percent or less, or 10.0 volume percent or less relative to the coating film (total solid content of the coating film). Furthermore, if the Si-containing compound content is high, there is a risk of deterioration in continuous spot weldability, so the Si-containing compound content may be 10.0 volume percent or less relative to the coating film (total solid content of the coating film).

[0042] The Si-containing compound content in the coating film is calculated by the following cross-sectional observation. Using image processing software (Image J), ​​the area occupied by the coating film and the area occupied by the Si-containing compound are measured from the backscattered electron image obtained in the same manner as the method for measuring the average particle size of the doped oxide particles described above. Since the volume ratio of each component in the coating film roughly corresponds to the area ratio of each component when the coating film is observed in cross-section, the measured area ratio of the Si-containing compound is taken as the volume ratio of the Si-containing compound. The same measurement is performed on 10 backscattered electron images, and the arithmetic mean is taken as the Si-containing compound content (volume %).

[0043] The average particle size of the Si-containing compound is not particularly limited, but preferably 0.02 μm or more, and more preferably 0.05 μm or more. Furthermore, while the average particle size of the Si-containing compound is not particularly limited, preferably 3.0 μm or less, more preferably 2.0 μm or less, and particularly preferably 1.0 μm or less. By keeping the average particle size of the Si-containing compound within the above range, the conductivity of the coating film can be more easily improved. Also, the ratio of the average particle size (μm) of the Si-containing compound to the thickness (μm) of the coating film may be, for example, less than 0.50, less than 0.45, or less than 0.30, and / or 0.001 or more, or 0.01 or more.

[0044] In this specification, the "average particle size" of a Si-containing compound refers to the average primary particle size when the Si-containing compound exists alone in the coating film, and the average secondary particle size, which represents the particle size of the Si-containing compound at the time of aggregation, when Si-containing compounds exist aggregated in the coating film. The average particle size of a Si-containing compound is calculated by the following cross-sectional observation. In the backscattered electron image obtained in the same manner as the measurement method for the average particle size of doped oxide particles described above, the particle sizes of all Si-containing compounds with a particle size of 0.10 μm or larger are calculated. Here, the Si-containing compound is identified by identifying the element using energy-dispersive X-ray spectroscopy. The particle size of each particle is obtained by calculating the average of the length of the long side and the length of the short side measured using image processing software (Image J). The arithmetic mean of the particle sizes of all particles in the observed field of view is calculated to determine the average particle size. The same measurement is performed on 10 backscattered electron images, and the arithmetic mean of each backscattered electron image is taken as the average particle size of the Si-containing compound.

[0045] [Rust-preventive pigments - Other rust-preventive pigments] From the viewpoint of improving corrosion resistance, rust-preventive pigments may further contain phosphate compounds, vanadate compounds, Mg-containing compounds, or combinations thereof, and among these, it is preferable to further contain phosphate compounds, vanadate compounds, or combinations thereof.

[0046] Phosphate compounds and vanadate compounds can release phosphate ions, vanadate ions, or countercations of these anions (e.g., alkaline earth metal ions, Zn ions, Al ions, etc.) in coatings and other applications in response to changes in the surrounding environment. For example, phosphate ions react with metal ions on metal plates to form a sparingly soluble film, thereby suppressing corrosion. Vanadate ions, like phosphate ions, form a film on the surface of metal plates and have a corrosion-suppressing effect. Furthermore, oxidizing ions such as vanadate ions are thought to further suppress corrosion by promoting the formation of the aforementioned sparingly soluble film. In addition, it is presumed that Mg-containing compounds can improve corrosion resistance by reacting with doped oxide particles and Mg to form a sparingly soluble composite oxide. Adding these rust-preventive pigments individually can improve corrosion resistance, but adding multiple types in combination can exert a combined effect and further improve corrosion resistance.

[0047] Examples of phosphate compounds include metal salts such as orthophosphate and polyphosphate (single linear polymers of orthophosphate up to degree of polymerization 6, or mixtures of two or more thereof), metaphosphate (single cyclic polymers of orthophosphate from degree of polymerization 3 to 6, or mixtures of two or more thereof), tetrametaphosphate, and hexametaphosphate; phosphorus pentoxide; phosphate minerals such as monetite, torphyrite, witlockite, xenotime, sturcolite, struubite, and lanmetallic ore; commercially available composite phosphate pigments such as silica polyphosphate and tripolyphosphate; metal salts such as phytic acid, phosphonic acid (phosphorous acid), and phosphinic acid (hypophosphorous acid); and mixtures of two or more thereof. Specific examples of commercially available composite phosphate pigments such as silica polyphosphate and tripolyphosphate include Mg-containing aluminum dihydrogen tripolyphosphate (K-WHITEG105 manufactured by Teika Co., Ltd.). Orthophosphates include their monohydrogen salts (HPO ４ ２－ ), dihydrogen salt (H ２ PO ４ － ) are included. Furthermore, the polyphosphate contains hydrogen salts. The cation species that form the phosphate are not particularly limited, and examples include metal ions such as Co, Cu, Fe, Mn, Nb, Ni, Sn, Ti, V, Y, Zr, Al, Ba, Ca, Mg, Sr, and Zn; and oxocations such as vanadyl, titanyl, and zirconyl. Among these, Al, Ca, Mg, Mn, and Ni are preferred as cation species that form the phosphate. The phosphate compound may be used alone or in combination of two or more types.

[0048] Vanadate compounds are complex compounds in which the valence of vanadium is any one of 0, 2, 3, 4, or 5, or a composite compound having two or more valences. For example, these include oxides, hydroxides, oxygen acid salts of various metals, vanadyl compounds, halides, sulfates, metal powders, etc. These decompose upon heating or in the presence of water and react with coexisting oxygen. For example, metal powders or divalent compounds of vanadium ultimately change into compounds with valences of 3, 4, or 5. Pentavalent vanadium compounds have vanadate ions and easily form heteropolymers that contribute to rust prevention through a heating reaction with phosphate ions. Therefore, it is preferable to include a pentavalent vanadium compound as one component.

[0049] The vanadate compounds are not particularly limited, and examples thereof include vanadium (II) compounds, vanadium (III) compounds, vanadium (IV) compounds, vanadium (V) compounds, or mixtures thereof. Examples of vanadium (II) compounds include vanadium oxide (VO) and vanadium hydroxide (V(OH) ２ ). Examples of vanadium (III) compounds include vanadium trioxide (V ２ O ３ ). Examples of vanadium (IV) compounds include vanadium dioxide (VO ２ ). Examples of vanadium (V) compounds include vanadium pentoxide (V ２ O ５ ), vanadates (orthovanadates, metavanadates, pyrovanadates, etc. containing various metals). Here, the preferred metal species constituting the vanadate are the same as those indicated by the phosphates.

[0050] Examples of the Mg-containing compounds include magnesium oxide, magnesium hydroxide, etc.

[0051] The content of the rust-preventive pigment is not particularly limited, but is preferably 5.0 to 50.0 volume percent relative to the coating film (total solid content of the coating film). When two or more types of rust-preventive pigments are used in combination, the "content of rust-preventive pigment" is the sum of the individual contents. From the viewpoint of corrosion resistance, the content of the rust-preventive pigment may be 5.0 volume percent or more, 10.0 volume percent or more, 15.0 volume percent or more, 20.0 volume percent or more, or 25.0 volume percent or more, relative to the coating film (total solid content of the coating film). On the other hand, from the viewpoint of the processability of the coating film and, if an electrodeposited coating film is formed on the upper layer, the content of the rust-preventive pigment may be 50.0 volume percent or less, 45.0 volume percent or less, 40.0 volume percent or less, 35.0 volume percent or less, or 30.0 volume percent or less, relative to the coating film (total solid content of the coating film).

[0052] The content of rust-preventive pigment in the coating film is calculated by the following cross-sectional observation. Using image processing software (Image J), ​​the area occupied by the coating film and the area occupied by the rust-preventive pigment are measured from the backscattered electron image obtained in the same manner as the method for measuring the average particle size of doped oxide particles described above. Since the volume ratio of each component in the coating film roughly corresponds to the area ratio of each component when the coating film is observed in cross-section, the measured area ratio of the rust-preventive pigment is taken as the volume ratio of the rust-preventive pigment. The same measurement is performed on 10 backscattered electron images, and the arithmetic mean is taken as the content (volume %) of the rust-preventive pigment.

[0053] The average particle size of the rust-preventive pigments other than the Si-containing compound is not particularly limited, but the lower limit is preferably 0.2 μm or more, more preferably 0.5 μm or more, and particularly preferably 1.0 μm or more. Furthermore, the upper limit of the average particle size of the rust-preventive pigments other than the Si-containing compound is preferably 5.0 μm or less, more preferably 4.0 μm or less, and particularly preferably 2.0 μm or less. By keeping the average particle size of the rust-preventive pigments other than the Si-containing compound within the above range, it is possible to further improve the conductivity of the coating film.

[0054] In this specification, the "average particle size" of anti-corrosion pigments other than Si-containing compounds refers to the average primary particle size when the anti-corrosion pigment exists alone in the coating film, and the average secondary particle size, which represents the particle size of the anti-corrosion pigment at the time of aggregation, when the anti-corrosion pigments exist aggregated in the coating film. The average particle size of the anti-corrosion pigment is calculated by the following cross-sectional observation. In the backscattered electron image obtained in the same manner as the measurement method for the average particle size of doped oxide particles described above, the particle size of all anti-corrosion pigments with a particle size of 0.20 μm or larger is calculated. Here, the anti-corrosion pigment is identified by identifying the element using energy-dispersive X-ray spectroscopy. The particle size of each particle is obtained by calculating the average of the length of the long side and the length of the short side measured using image processing software (Image J). The arithmetic mean of the particle sizes of all particles in the observed field of view is calculated to determine the average particle size. The same measurement is performed on 10 backscattered electron images, and the arithmetic mean of each backscattered electron image is taken as the average particle size of the anti-corrosion pigment.

[0055] [Ratio of the content of doped oxide particles (volume %) (A) to the content of Si-containing compound (volume %) (B) (A / B): 2.80 to 6.00] In the surface-treated metal plate according to the embodiment of the present invention, the ratio of the content of doped oxide particles (volume %) (A) to the content of Si-containing compound (volume %) (B) (A / B) is 2.80 to 6.00, preferably 3.00 to 4.50. Furthermore, the ratio of the content of doped oxide particles (volume %) (A) to the content of Si-containing compound (volume %) (B) (A / B) may be, for example, 3.00 to less than 4.00 or 2.80 to less than 4.00, and / or greater than 4.00 to 6.00 or greater than 4.00 to 4.50. As explained earlier, since Si-containing compounds are relatively hard pigments, simply constructing a coating film to include Si-containing compounds will result in a hard coating film that is less likely to deform (crush) under pressure during spot welding, making it difficult to ensure a proper electrical path. As a result, welding defects are more likely to occur in continuous spot welding. For example, if the A / B ratio is less than 2.80, the Si-containing compound content will be relatively high, the coating film will become hard, and the weldability may deteriorate in continuous spot welding. Therefore, the A / B ratio should be 2.80 or higher, and may also be 3.00 or higher, 3.20 or higher, 3.40 or higher, 3.60 or higher, 3.80 or higher, 4.00 or higher, greater than 4.00, 4.10 or higher, 4.20 or higher, or 4.40 or higher. On the other hand, if the A / B ratio is greater than 6.0, the Si-containing compound content will be relatively low, and plating components, such as zinc with a relatively low melting point, may easily diffuse into the welding electrode. In addition, the electrical resistance of the coating itself decreases, which can cause resin components that should adhere to the welding electrode and evaporate to remain. As a result, wear on the welding electrode can become severe, and weldability may deteriorate during continuous spot welding. Therefore, A / B should be 6.00 or less, but may also be 5.70 or less, 5.40 or less, 5.10 or less, 4.80 or less, 4.50 or less, 4.20 or less, 4.00 or less, less than 4.00, 3.90 or less, 3.80 or less, or 3.60 or less.

[0056] [Binder Resin] The binder resin functions as a binder that binds the various components in the coating film together.

[0057] Examples of binder resins include epoxy resins, urethane resins, polyester resins, acrylic resins, phenolic resins, and mixed resins of two or more of these resins. Among these, it is preferable that the binder resin contains epoxy resin.

[0058] Furthermore, the binder resin may be a water-soluble or water-dispersible water-based resin, or a solvent-based resin that dissolves or disperses in an organic solvent. From the viewpoint of manufacturing cost and environmental suitability, the binder resin is preferably a water-soluble or water-dispersible water-based resin.

[0059] The type of water-based resin is not particularly limited. Examples of water-based resins include water-soluble or water-dispersible resins such as epoxy resins, urethane resins, polyester resins, acrylic resins, phenolic resins, and mixed resins of two or more of these resins.

[0060] When using an aqueous epoxy resin, the number average molecular weight (Mn) of the epoxy resin is not particularly limited, but is preferably 1,400 to 20,000, more preferably 2,000 to 10,000, and particularly preferably 2,000 to 4,000. That is, the lower limit of the number average molecular weight (Mn) of the epoxy resin is preferably 1,400 or more, and more preferably 2,000 or more. The upper limit of the number average molecular weight (Mn) of the epoxy resin is preferably 20,000 or less, more preferably 10,000 or less, and particularly preferably 4,000 or less. When the number average molecular weight of the epoxy resin is 1,400 to 20,000, the crosslinking reaction proceeds sufficiently when the epoxy resin is crosslinked, improving the corrosion resistance of the surface-treated metal plate. In addition, it is possible to suppress the crosslinking density of the coating film from becoming too high, and the processability of the coating film can be maintained. In this specification, when simply referred to as epoxy resin, it means that it includes at least one selected from the group consisting of epoxy resin and modified epoxy resins. Furthermore, in this specification, the number-average molecular weight (Mn) of the resin refers to the number-average molecular weight on a polystyrene basis, measured by gel permeation chromatography (GPC).

[0061] The glass transition temperature (Tg) of the epoxy resin is not particularly limited, but may be, for example, 120°C or lower, 115°C or lower, or 110°C or lower. The glass transition temperature (Tg) of the epoxy resin may also be, for example, 50°C or higher, or 55°C or higher. From the viewpoint of improving the corrosion resistance of the surface-treated metal plate without excessively increasing the moisture permeability of the coating film, the glass transition temperature (Tg) of the epoxy resin is preferably 50 to 120°C. The glass transition temperature (Tg) is measured using a thermal analyzer TMA7100 (Hitachi High-Tech Science Corporation), etc.

[0062] The acid value of epoxy resin (including its modified products) is not particularly limited, but is, for example, 0 to 30 mg KOH / g. The oxidation may be 0 mg KOH / g or more, 1 mg KOH / g or more, or 5 mg KOH / g or more, and / or 30 mg KOH / g or less, 25 mg KOH / g or less, or 20 mg KOH / g or less. In this specification, the acid value refers to the solid content acid value and is measured in accordance with the provisions of JIS K 0070;1992.

[0063] The epoxy resin is preferably an epoxy resin emulsion, and more preferably an epoxy resin emulsion with an emulsion particle size of 10 to 100 nm (preferably 20 to 60 nm). If the emulsion particle size is excessively small, manufacturing costs may increase. On the other hand, if the emulsion particle size is excessively large, the gaps between the emulsion particles become larger when a coating film is formed, which may reduce the barrier properties of the coating film.

[0064] The type of epoxy resin is not particularly limited. The epoxy resin may be a hydroxyl group-containing epoxy resin (including modified hydroxyl group-containing epoxy resins). Examples of epoxy resins include resins obtained by condensing epichlorohydrin and bisphenol to a high molecular weight in the presence of a catalyst such as an alkaline catalyst as needed; bisphenol-type epoxy resins such as bisphenol A type and bisphenol F type; and novolac-type epoxy resins. Examples of modified epoxy resins include modified epoxy resins such as acrylic-modified epoxy resins, urethane-modified epoxy resins, and amine-modified epoxy resins. For example, an acrylic-modified epoxy resin can be prepared by reacting the above-mentioned bisphenol-type epoxy resin or novolac-type epoxy resin with a polymerizable unsaturated monomer component containing acrylic acid or methacrylic acid. A urethane-modified epoxy resin can be prepared by reacting the above-mentioned bisphenol-type epoxy resin or novolac-type epoxy resin with a polyisocyanate compound. These epoxy resins may be used individually or in combination.

[0065] When using polyester resin as the water-based resin, the number-average molecular weight (Mn) of the polyester resin is not particularly limited, but is preferably between 10,000 and 30,000. If the number-average molecular weight of the polyester resin is less than 10,000, it may be difficult to ensure sufficient processability. On the other hand, if the number-average molecular weight of the polyester resin exceeds 30,000, the adhesion between the coating film and the electrodeposited coating film formed thereon may decrease. Furthermore, when crosslinking is performed using a curing agent such as melamine, the crosslinking reaction may not be sufficient, resulting in a decrease in the performance of the coating film.

[0066] The polyester resin is preferably a polyester resin emulsion, and more preferably a polyester resin emulsion with an emulsion particle size of 10 to 100 nm (preferably 20 to 60 nm). If the emulsion particle size is excessively small, manufacturing costs may increase. On the other hand, if the emulsion particle size is excessively large, the gaps between the emulsion particles become larger when a coating film is formed, which may reduce the barrier properties of the coating film.

[0067] When using a urethane resin as the water-based resin, the urethane resin is preferably a urethane resin emulsion, and more preferably a urethane resin emulsion with a particle size of 10 to 100 nm (preferably 20 to 60 nm). If the emulsion particle size is excessively small, the cost may increase. On the other hand, if the emulsion particle size is excessively large, the gaps between the emulsion particles may become large when a coating film is formed, which may reduce the barrier properties of the coating film. The type of urethane resin is not particularly limited. Examples of urethane resins include polyether-based urethane resins, polycarbonate-based urethane resins, and polyester-based urethane resins. These may be used alone or in combination.

[0068] The type of solvent-based resin is not particularly limited. The solvent-based resin may be, for example, an epoxy resin, polyester resin, acrylic resin, or a mixed resin of two or more of these resins, which dissolves or disperses in an organic solvent.

[0069] The binder resin may be a crosslinked resin having a crosslinked structure, or it may be a non-crosslinked resin not having a crosslinked structure.

[0070] As a crosslinking agent (curing agent) to impart a crosslinked structure to the binder resin, a water-soluble crosslinking agent is preferred. Specifically, the crosslinking agent is preferably a compound having a melamine or isocyanate group. The amount of crosslinking agent added is not particularly limited, but is preferably 5 to 30 parts by mass per 100 parts by mass of resin solids. If the amount of crosslinking agent added is less than 5 parts by mass, the crosslinking reaction with the resin may not proceed sufficiently, and the performance of the coating film may be insufficient. On the other hand, if the amount of crosslinking agent added is more than 30 parts by mass, the crosslinking reaction may proceed too much, causing the coating film to become excessively hard and reducing its processability.

[0071] The binder resin content is not particularly limited, but is preferably 20 to 80% by mass relative to the coating film (total solid content of the coating film). More preferably, the binder resin content is 25 to 70% by mass relative to the coating film (total solid content of the coating film), and even more preferably 30 to 60% by mass, from the viewpoint of exhibiting binder function and achieving both conductivity, corrosion resistance, and adhesion. That is, the lower limit of the binder resin content may be 20% by mass or more, 25% by mass or more, or 30% by mass or more relative to the coating film (total solid content of the coating film). The upper limit of the binder resin content may be 80% by mass or less, 70% by mass or less, or 60% by mass or less relative to the coating film (total solid content of the coating film).

[0072] The binder resin content is calculated using the following mass spectrometry method. A sample is prepared by scraping the coating from a surface-treated metal plate, and the obtained sample is analyzed using pyrolysis gas chromatography-mass spectrometry (GC-MS). Specifically, a fixed amount of polystyrene is added to the obtained sample as a standard substance, and it is heated to 600°C in a GC-MS instrument (for example, Agilent's GC system "7890B") to perform thermal decomposition. The decomposition products obtained by thermal decomposition are analyzed by GC-MS, and the type and amount of decomposition products are identified by peak analysis. From the analyzed peaks, the amount of binder resin can be determined by comparing the peak area of ​​styrene monomer, which corresponds to the known mass (fixed amount) of polystyrene added as a standard substance, with the peak area of ​​all remaining peaks, which correspond to the binder resin. The binder resin content (mass %) in the coating can be obtained by calculating the ratio of the amount of binder resin to the mass of the scraped sample (coating).

[0073] [Other Additives] The coating film may further contain other additives. Examples of other additives include well-known additives such as extender pigments, solid lubricants, and leveling agents.

[0074] Examples of extender pigments include titania and zirconia.

[0075] Solid lubricants can provide excellent lubrication to coatings and improve powdering resistance.

[0076] Examples of solid lubricants include polyolefin waxes or paraffin waxes such as polyethylene wax, synthetic paraffin, natural paraffin, microwax, and chlorinated hydrocarbons; and fluororesin-based waxes such as polyfluoroethylene resin (polytetrafluoroethylene resin, etc.), polyvinyl fluoride resin, and polyvinylidene fluoride resin.

[0077] The average particle size of the solid lubricant is not particularly limited, but is preferably 0.05 to 4.00 μm. From the viewpoint of obtaining paint adhesion, corrosion resistance, lubricity, and powdering resistance, the average particle size of the solid lubricant is more preferably 0.10 to 3.00 μm, and even more preferably 0.30 to 2.00 μm.

[0078] The softening point of the solid lubricant is preferably 100°C to 135°C, more preferably 110°C to 130°C. When the softening point of the solid lubricant is 100°C to 135°C, the lubricity and powdering resistance are further improved.

[0079] The solid lubricant content is preferably 0.1 to 10.0% by mass relative to the coating film (total solid content of the coating film). More preferably, the solid lubricant content is 0.2 to 5.0% by mass relative to the coating film (total solid content of the coating film), and even more preferably 0.5 to 2.5% by mass, from the viewpoint of adhesion between the coating film and the paint film, lubricity, and corrosion resistance.

[0080] [Coating Film Thickness] In the surface-treated metal plate according to this embodiment, the coating film thickness is 0.5 to 5.0 μm, from the viewpoint of enabling spot welding while ensuring corrosion resistance. Here, if doped oxide particles and / or rust-preventive pigments protrude from the surface of the coating film, the coating film thickness is the thickness of the portion where the doped oxide particles and / or rust-preventive pigments do not protrude from the surface of the coating film. If the coating film thickness is less than 0.5 μm, sufficient adhesion and corrosion resistance between the coating film and the electrodeposited coating film formed on its surface may not be obtained. Therefore, the coating film thickness should be 0.5 μm or more. The coating film thickness may be 1.0 μm or more, 1.5 μm or more, or 2.0 μm or more. On the other hand, if the coating film thickness exceeds 5.0 μm, the conductivity of the coating film decreases, making spot welding difficult, and the cohesive force of the coating film may decrease. Therefore, the coating film thickness should be 5.0 μm or less. The thickness of the coating film may be 4.5 μm or less, 4.0 μm or less, 3.5 μm or less, or 3.0 μm or less.

[0081] The thickness of the coating film is measured by the following cross-sectional observation. The cross-section of the surface-treated metal plate in the thickness direction is mirror-polished, and the cross-section of the coating film is photographed at 5000x magnification using a scanning electron microscope (JEOL Ltd., "JSM-7100F", acceleration voltage: 15kV) (field of view: 24μm × 18μm). From the multiple backscattered electron images obtained, 10 locations are arbitrarily selected so that there is a gap of 5μm or more between each location for measuring the film thickness. Note that the 10 locations to be selected may be from a single image or from multiple images measured in different observation areas (fields of view). The average value of the film thickness measured at the 10 locations is calculated using image processing software (Image J), ​​and this is taken as the thickness of the coating film. Here, the thickness of the coating film is the length of the coating film in the direction perpendicular to the surface of the surface-treated metal plate. The surface of the surface-treated metal plate referred to here does not mean a microscopic area on the order of a few micrometers, but rather the surface (main surface) that extends over the entire surface-treated metal plate being measured.

[0082] [Method for Forming a Coating Film] The method for forming the coating film is not particularly limited, and well-known methods can be used. Specifically, for example, a coating film-forming composition is prepared by mixing doped oxide particles, rust-preventive pigments, binder resin, and other additives as needed in a solvent. The solvent may be water or an organic solvent, but water is preferred from the viewpoint of manufacturing cost and environmental suitability. In other words, the coating film-forming composition is preferably an aqueous composition. Next, the coating film-forming composition can be applied to at least one side of a metal plate and dried to form a coating film. The surface of the metal plate to which the coating film-forming composition is applied may be degreased with an alkaline degreasing agent as needed. A method for applying the coating film-forming composition may be, for example, application by a bar coater.

[0083] As described above, the surface-treated metal sheet according to the embodiment of the present invention has excellent corrosion resistance and excellent weldability even in continuous spot welding. Therefore, the surface-treated metal sheet according to the embodiment of the present invention is particularly useful for use in technical fields where these properties are required, especially in automotive components. In a preferred embodiment, automotive components, particularly automobile bodies and undercarriage components, are provided that include the surface-treated metal sheet according to the embodiment of the present invention. These automotive components, particularly automobile bodies and undercarriage components, may include the surface-treated metal sheet according to the embodiment of the present invention in at least a portion of these components. In another preferred embodiment, mechanical components (such as housings), home appliance components (such as housings), and building materials (such as roofs and walls) are provided, and these components may include the surface-treated metal sheet according to the embodiment of the present invention in at least a portion of these components.

[0084] <Automotive Components> Next, the automotive components according to this embodiment will be described.

[0085] The automotive component according to this embodiment is an automotive component that includes a painted metal plate, wherein the painted metal plate has the surface-treated metal plate described above and an electrodeposited coating film. The automotive component is, for example, a component of the automobile body or a component of the undercarriage.

[0086] [Painted metal sheet] [Surface-treated metal sheet] Surface-treated metal sheets may be formed into a predetermined shape depending on the application. Also, multiple surface-treated metal sheets may be joined together by welding, adhesive, etc. The surface-treated metal sheets described above have excellent conductivity of the coating film, making them less prone to defects such as cracks caused by welding, and an electrodeposited coating film can be formed by electrodeposition coating.

[0087] [Chemical Conversion Layer] The above-mentioned painted metal sheet may or may not have a chemical conversion layer on the surface of the surface-treated metal sheet. The chemical conversion layer is located on the surface of the coating film contained in the surface-treated metal sheet and is formed by performing a chemical conversion treatment on the surface of the coating film. The chemical conversion layer may be a continuous layer that covers the surface of the surface-treated metal sheet without gaps, or it may be a discontinuous layer that covers the surface of the surface-treated metal sheet intermittently.

[0088] The chemical treatment layer is not particularly limited, but may contain either zinc phosphate or zirconium oxide.

[0089] [Electrodeposition Coating Film] The electrodeposition coating film is placed on the surface-treated metal plate and may be placed via a chemical conversion treatment layer if necessary. The electrodeposition coating film is a film formed by electrodeposition coating. The electrodeposition coating film may be a single layer or a multi-layered film (for example, a coating film consisting of a primer layer, an intermediate coat layer, and a top coat layer). In the automotive component according to the embodiment of the present invention, the painted metal plate has at least an electrodeposition coating film and may further have a coating film formed by other coating treatments such as powder coating or solvent coating.

[0090] [Manufacturing Method for Automotive Components] Automotive components according to the embodiment of the present invention can be manufactured, for example, by forming an electrodeposited coating film on the surface of a surface-treated metal plate or a chemical conversion coating layer. If necessary, the process may also include forming a chemical conversion coating layer on the surface of the coating film on the surface-treated metal plate.

[0091] First, prepare the surface-treated metal sheet described above. The surface-treated metal sheet may be formed into a predetermined shape. The surface-treated metal sheet can be formed using well-known forming techniques such as cutting or press forming. Alternatively, multiple surface-treated metal sheets may be joined together by welding (e.g., spot welding). Furthermore, the surface-treated metal sheet may undergo known pre-treatments such as degreasing or surface adjustment.

[0092] In the process of forming an electrodeposited coating film on the surface of a surface-treated metal plate or the chemical conversion treatment layer, the conditions for electrodeposition coating are not particularly limited, but can be appropriately selected depending on the state and composition of the electrodeposited coating film to be formed. Multiple layers of electrodeposited coating films may be formed by performing electrodeposition coating multiple times.

[0093] In the process of forming a chemical conversion treatment layer on the surface of a coating film on a surface-treated metal plate, the chemical conversion treatment liquid and treatment conditions used for the chemical conversion treatment can be appropriately selected according to the state and composition of the chemical conversion treatment layer to be formed.

[0094] By these processes, the automotive component according to this embodiment can be manufactured.

[0095] When taking samples from automotive components for various measurements and analyses, the following locations (i) to (iv) should be avoided: (i) Welded areas: Spot / arc / laser welded areas and areas within 20 mm of the weld toe. (ii) Machined areas: Machined areas with a radius of curvature of less than 15 mm, and areas within 5 mm of the said machined areas. (iii) Ends: Ends within 5 mm of the cut end face of the part. (iv) Red rust: Areas within 5 mm of areas where red rust is visible.

[0096] The present invention will be described in detail below with reference to examples, but the present invention is not limited in any way to these examples.

[0097] [Manufacturing of Surface-Treated Metal Sheets] 1. Preparation of Metal Sheets Alloyed hot-dip galvanized steel sheet (GA) (Zn-10 mass%Fe, sheet thickness 0.8 mm, plating adhesion 45 g / m²) ２ The substrate was prepared by immersing it in a 2.5% by mass aqueous solution of water-based alkaline degreasing agent (FC-301, Nippon Parkerizing Co., Ltd.) at 40°C for 2 minutes to degrease the surface, then washing with water and drying to prepare it as a coating substrate.

[0098] 2. Preparation of Aqueous Compositions In order to form coating films with the compositions shown in Tables 1 and 2, aqueous compositions for coating film formation were prepared by mixing each component to have the same content as in Tables 1 and 2. In Tables 1 and 2, the content of each component is indicated as the ratio (unit: volume %) of the solid content (non-volatile content) of each component to the total solid content (non-volatile content) of the aqueous composition.

[0099] The details of each component (symbol) in Tables 1 and 2 are as follows.

[0100] [Binder Resins] ・E: Epoxy resin emulsion (ADEKA Resin® EM-0718, ADEKA Corporation) ・U: Urethane resin emulsion (Superflex® E-2000, Daiichi Kogyo Seiyaku Co., Ltd.) ・P: Polyester resin emulsion (Vyronal® MD-2000, Toyobo Co., Ltd.)

[0101] [Doped Oxide Particles] ・Zn1: Al-doped zinc oxide (ZnO) particles (23-K, Hakusui Tech Co., Ltd.) ・Zn2: Ga-doped zinc oxide (ZnO) particles (Pazet GK-40, Hakusui Tech Co., Ltd.) ・Sn: P-doped tin oxide (SnO) ２ ) Particles (SP-2, Mitsubishi Materials Electronic Chemicals Co., Ltd.) ・Ti:Sb-doped tin oxide (SnO ２ Titanium oxide (TiO) coated with ) ２ ) Particles (EC-210, Titanium Industry)

[0102] [Rust-preventive pigments - Si-containing compounds] ・Si1: Silicon dioxide (amorphous silica) (Snowtex® ZL, Nissan Chemical Corporation) ・Si2: Magnesium silicate (Fujifilm Wako Pure Chemical Corporation)

[0103] [Rust-preventive pigments - Other rust-preventive pigments] ・PAM: Mg-containing aluminum dihydrogen tripolyphosphate (K-WHITEG105, Teika Co., Ltd.) ・MgO: Magnesium oxide (Fujifilm Wako Pure Chemical Corporation) ・V: Vanadium pentoxide (Kanto Chemical Co., Ltd.)

[0104] The various doped oxide particles described above were dispersed in water with a binder resin added and then ground using a ball mill.

[0105] 3. Manufacturing of Surface-Treated Metal Plates A water-based composition was applied to the metal plate using a bar coater to create the configurations shown in Tables 1 and 2. A coating film was formed by drying in an oven under conditions where the maximum temperature reached was 140°C and held for 8 seconds. The film thickness of the coating film was adjusted by diluting the water-based composition and changing the grit size of the bar coater to achieve the values ​​shown in Tables 1 and 2. The film thickness of the coating film was measured by the following method: The cross-section of the surface-treated metal plate in the thickness direction was mirror-polished, and the cross-section of the coating film was photographed at 5000x magnification using a scanning electron microscope (JEOL Ltd., "JSM-7100F", acceleration voltage: 15kV) (field of view: 24μm × 18μm). From the obtained backscattered electron images, 10 locations were selected for film thickness measurement, with an interval of 5μm or more between each location. The average value of the film thickness at the 10 measured locations was calculated using image processing software (Image J) and was determined as the film thickness of the coating film.

[0106] After manufacturing the surface-treated metal plate, the content (volume %) of doped oxide particles and rust-preventive pigments in the coating film was calculated using the following procedure, and the values ​​were substantially the same as the content (volume %) of doped oxide particles and rust-preventive pigments shown in Tables 1 and 2. The cross-section of the surface-treated metal plate in the thickness direction was mirror-polished, and the cross-section of the coating film was photographed at 5000x magnification using a scanning electron microscope (JEOL Ltd., "JSM-7100F", acceleration voltage: 15kV) (field of view: 24μm × 18μm). In addition, the elements were identified using energy-dispersive X-ray spectroscopy with the same apparatus to distinguish between doped oxide particles and rust-preventive pigments. The obtained backscattered electron images were used with image processing software (Image J) to measure the area occupied by the coating film, the area occupied by doped oxide particles, and the area occupied by rust-preventive pigments. Since the volume ratio of each component in a coating film roughly corresponds to the area ratio of each component when the coating film is observed in cross-section, the measured area ratio of doped oxide particles and the area ratio of rust-preventive pigment were defined as the volume ratio of doped oxide particles and the volume ratio of rust-preventive pigment, respectively. The same measurement was performed on 10 backscattered electron images, and the arithmetic mean values ​​were defined as the content of doped oxide particles (volume %) and the content of rust-preventive pigment (volume %).

[0107] [Evaluation Test] 1. Evaluation of Weldability (Continuous Spot Welding Test) A continuous spot welding test was performed on a surface-treated metal plate using a CF-type Cr-Cu electrode with a tip diameter of 5 mm and radius of R40, with a pressing force of 1.96 N, a welding current of 8 kA, and an energizing time of 12 cycles / 50 Hz. The number of spots just before the nugget diameter fell below 3√t (t: plate thickness) was determined. The following evaluation points were used to evaluate the quality of weldability in the continuous spot welding test. 1: The number of spots was less than 200. 2: The number of spots was 200 or more but less than 1000. 3: The number of spots was 1000 or more but less than 3000. 4: The number of spots was 3000 or more but less than 5000. 5: The number of spots was 5000 or more.

[0108] 2. Evaluation of Corrosion Resistance A corrosion cycle compliant with JASO M 609;91 was performed 90 times on the surface-treated metal sheets. Afterward, the occurrence of red rust was measured on each surface-treated metal sheet, and the area percentage of red rust was calculated. The corrosion resistance of the surface-treated metal sheets was evaluated based on the area percentage of red rust according to the following criteria: AA: No red rust occurred. A: The area percentage of red rust was greater than 0% and less than 10%. B: The area percentage of red rust was 10% or more and less than 20%. C: The area percentage of red rust was 20% or more.

[0109] Surface-treated metal sheets with weldability of 3, 4, and 5 in continuous spot welding tests, and corrosion resistance of AA, A, and B, were evaluated as having excellent corrosion resistance while also exhibiting excellent weldability in continuous spot welding. The evaluation results are shown in Tables 1 and 2.

[0110]

[0111]

[0112] Referring to Tables 1 and 2, Comparative Example 1 had no coating and exhibited high weldability but low corrosion resistance. In Comparative Examples 2 to 4, the surface-treated metal sheets had a ratio (A / B) of doped oxide particle content (volume %) (A) to Si-containing compound content (volume %) (B) that was less than 2.80, suggesting a relatively high Si-containing compound content and a hard coating. As a result, despite good corrosion resistance, weldability was poor in continuous spot welding. On the other hand, in Comparative Example 5, the surface-treated metal sheet had a ratio (A / B) of doped oxide particle content (volume %) (A) to Si-containing compound content (volume %) (B) that was greater than 6.00, indicating a relatively low Si-containing compound content. In this case, the plating components easily diffuse to the welding electrode. In addition, the electrical resistance of the coating itself is also reduced, making it easier for resin components that should normally evaporate to remain on the welding electrode. For these reasons, welding electrodes wore out quickly, resulting in poor weldability during continuous spot welding.

[0113] In contrast, in all the surface-treated metal sheets according to the embodiments, the metal sheet and a coating of a predetermined thickness are disposed on the metal sheet, the coating containing doped oxide particles, a rust-preventive pigment and a binder resin, the rust-preventive pigment containing a Si-containing compound, and the ratio (A / B) of the content of doped oxide particles (volume %) (A) to the content of Si-containing compound (volume %) (B) is controlled to be between 2.80 and 6.00. As a result, it exhibited excellent corrosion resistance while also having excellent weldability even in continuous spot welding. Furthermore, in all the surface-treated metal sheets according to the embodiments, the binder content was 20 to 80% by mass relative to the coating (total solid content of the coating).

Claims

1. A surface-treated metal plate comprising: a metal plate; and a coating film having a thickness of 0.5 to 5.0 μm disposed on the surface of the metal plate, wherein the coating film contains doped oxide particles, a rust-preventive pigment, and a binder resin; the rust-preventive pigment contains a Si-containing compound; and the ratio (A / B) of the content of the doped oxide particles (volume %) to the content of the Si-containing compound (volume %) (B) is 2.80 to 6.

00.

2. The surface-treated metal sheet according to claim 1, wherein the ratio (A / B) of the content (volume %) of the doped oxide particles to the content (volume %) of the Si-containing compound (B) is 3.00 to 4.

50.

3. The surface-treated metal sheet according to claim 2, wherein the ratio (A / B) of the content (volume %) of the doped oxide particles (A) to the content (volume %) of the Si-containing compound (B) is 3.00 to less than 4.

00.

4. The surface-treated metal sheet according to any one of claims 1 to 3, wherein the Si-containing compound is amorphous silica, a silicate compound, or a combination thereof.

5. The surface-treated metal plate according to claim 4, wherein the Si-containing compound is amorphous silica.

6. The surface-treated metal sheet according to any one of claims 1 to 5, wherein the doped oxide particles include zinc oxide particles doped with Al, Ga, In, or a combination thereof.

7. The surface-treated metal sheet according to any one of claims 1 to 6, wherein the ratio of the average particle size (μm) of the Si-containing compound to the thickness (μm) of the coating film is less than 0.

50.

8. The surface-treated metal sheet according to any one of claims 1 to 7, wherein the average particle size of the doped oxide particles is 1.0 to 4.0 μm.

9. The surface-treated metal sheet according to any one of claims 1 to 8, wherein the ratio of the average particle size (μm) of the doped oxide particles to the average particle size (μm) of the Si-containing compound is 0.75 to 4.

00.

10. The surface-treated metal sheet according to any one of claims 1 to 9, wherein the rust-preventive pigment further comprises a phosphate compound, a vanadate compound, or a combination thereof.

11. The surface-treated metal sheet according to any one of claims 1 to 10, wherein the binder resin is a water-soluble or water-dispersible aqueous resin.

12. The surface-treated metal sheet according to any one of claims 1 to 11, wherein the binder resin comprises an epoxy resin.

13. An automotive component comprising a painted metal plate, wherein the painted metal plate has a surface-treated metal plate according to any one of claims 1 to 12 and an electrodeposited coating film.

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