Cooling structure

Abstract

To provide a cooling structure which is excellent in corrosion resistance to cooling liquid, cooling capability, and water rightness.SOLUTION: A cooling structure having a flow channel for a water cooling medium formed in outside of a bottom face part of a battery pack has a flow channel formation part whose internal space is the flow channel for the water cooling medium, wherein the flow channel formation part is composed of a steel plate in which an inorganic film or a resin film is formed as a chemical conversion film on an Al-based plated steel sheet or a Zn-based plated steel sheet, the flow channel formation part is joined to a joined member by an adhesive, the joined member is any one of the bottom face part and a flow channel upper lid covering the flow channel formation part, the outer edge part of the joined member is directly and continuously joined to the outer edge part of the cooling structure, by an adhesive or mechanical joint to the adhesive, and the interval between the flow channels for the water cooling medium is 20 mm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cooling structure. [Background technology]

[0002] In the automotive sector, CO 2 To reduce power consumption, the shift to electric vehicles is progressing. Among the components used in EVs, the battery pack that houses the battery cells that serve as the power source needs to be provided with a cooling structure to prevent deterioration of the batteries due to temperature rise. Until now, air-cooled cooling structures have been the mainstream, but in recent years, as the capacity of batteries has increased, there have been an increasing number of cases where water-cooled structures with high cooling capacity are being adopted. Iron and aluminum are generally used for components of water-cooled battery packs. For example, Patent Document 1 discloses the use of adhesives to bond aluminum cooling plates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2022-514223 Summary of the Invention [Problem to be solved by the invention]

[0004] Although iron is superior to aluminum in terms of strength and cost, it is inferior in corrosion resistance. Since an aqueous solution of LLC (long life coolant) containing organic components flows as a coolant in the water coolant flow path, the components constituting the water coolant flow path are required to have high corrosion resistance against the coolant (coolant corrosion resistance). In addition, when the components constituting the water coolant flow path are provided on the outside of the battery pack, they are placed on the bottom surface of the car, so corrosion resistance (external corrosion resistance) is also required on the outside surface. Furthermore, the cooling structure needs to increase the liquid surface area by narrowing the flow path interval of the water coolant flow path to improve cooling capacity, and to ensure watertightness to prevent coolant leakage.

[0005] The inventors have conducted extensive research into materials with different corrosion resistances, and have found that chemically treated Al-based plated steel sheets or Zn-based plated steel sheets have corrosion resistance to an LLC aqueous solution. The present invention has been made in consideration of the above problems, and has an object to provide a cooling structure that is excellent in corrosion resistance against a coolant (coolant corrosion resistance), cooling capacity, and watertightness. [Means for solving the problem]

[0006] In order to solve the above problems, the present disclosure employs the following measures. (1) A cooling structure according to one embodiment of the present disclosure is a cooling structure having a water coolant flow path formed on the outside of a bottom surface of a battery pack, the cooling structure having a flow path forming portion whose internal space is the water coolant flow path, the flow path forming portion being made of a steel plate having an inorganic coating or a resin coating formed as a chemical conversion coating on an Al-based plated steel plate or a Zn-based plated steel plate, the flow path forming portion being joined to a member to be joined with an adhesive, the member to be joined being either the bottom surface or a flow path top cover covering the flow path forming portion, an outer edge portion of the member to be joined being directly and continuously joined to an outer edge portion of the cooling structure by an adhesive or by a combination of an adhesive and mechanical joining, and a flow path spacing between the water coolant flow paths is 20 mm or less. (2) In the cooling structure described in (1) above, the passage interval may be 1 mm or more and 15 mm or less. (3) In the cooling structure described in (1) above, the water coolant flow path may have a width of 6 mm or more and 60 mm or less. (4) In the cooling structure described in (1) or (2) above, the water coolant flow path may have a width of 6 mm or more and 20 mm or less. (5) In the cooling structure described in (1) or (2) above, the plating layer of the Al-based plated steel sheet may contain Si. (6) In the cooling structure described in (5) above, the Si content in the plating layer of the Al-based plated steel sheet may be 2.0 mass % or more and 15 mass % or less. (7) In the cooling structure described in (1) or (2) above, a coating containing a Zr-based component, a Ti-based component, or a Si-based component as a main component may be formed on the surface of the Al-based plated steel sheet as a chemical conversion coating. (8) In the cooling structure described in (1) above, the inorganic coating on the surface of the Zn-based plated steel sheet may contain a Si-based component or a Zr-based component as a main component. (9) In the cooling structure described in (1) above, the inorganic coating on the surface of the Zn-based plated steel sheet may contain at least one of a V component, a P component, and a Co component as an anti-rust component. (10) In the cooling structure described in (9) above, the rust-preventive component may be at least one of vanadium oxide, phosphoric acid, and cobalt nitrate. (11) In the cooling structure described in (1) above, the inorganic coating on the surface of the Zn-based plated steel sheet may be composed of a compound phase containing one or more of Si-O bonds, Si-C bonds, and Si-OH bonds. (12) In the cooling structure described in (1) above, the inorganic coating may have a thickness of more than 0 μm and not more than 1.5 μm. (13) In the cooling structure described in (1) above, the inorganic coating or the resin coating may be electrically conductive. (14) In the cooling structure described in (1) above, the resin coating may contain a resin, an anti-rust pigment, and a conductive pigment. (15) In the cooling structure described in (14) above, the resin coating contains at least one of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles as the conductive pigment, and the conductive pigment may have a powder resistivity of 7.0×10 Ω cm or less at 23 to 27° C. and contain at least one element selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W. (16) In the cooling structure according to (14) or (15) above, the resin film may contain the conductive pigment in a proportion of 1.0 mass % or more and 30 mass % or less. (17) In the cooling structure described in (1) above, the adhesive may contain 10% or more of any one of an epoxy resin, a silicone resin, an acrylic resin, and a urethane resin. (18) In the cooling structure described in (1) above, the thickness of the Al-based plated steel sheet or the Zn-based plated steel sheet on which an inorganic coating or a resin coating is formed as a chemical conversion coating may be 0.4 mm or more and 1.2 mm or less. Effect of the Invention

[0007] According to the above-mentioned aspects of the present invention, it is possible to provide a cooling structure having excellent corrosion resistance against a coolant (coolant corrosion resistance), cooling capacity, and watertightness. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a cross-sectional view illustrating a cooling structure according to an embodiment of the present disclosure. [Diagram 2] FIG. 4 is a cross-sectional view showing another example of the cooling structure according to the embodiment. [Diagram 3] FIG. 4 is a cross-sectional view showing another example of the cooling structure according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A cooling structure according to an embodiment of the present disclosure will be described with reference to the drawings. In the following description, common components may be assigned the same reference numerals and their repeated description may be omitted. However, the present disclosure is not limited to the configuration disclosed in the present embodiment, and various modifications may be made without departing from the spirit of the present disclosure. In the following description, the direction perpendicular to the paper surface of FIG. 1 may be referred to as the Y direction, the direction in which a plurality of flow path forming parts 21, which will be described later, are arranged may be referred to as the X direction, and the direction perpendicular to both the X direction and the Y direction may be referred to as the Z direction. A numerical range represented by "~" means a range including the numerical values ​​described before and after "~" as the lower and upper limits. A numerical value indicated as "greater than" or "less than" does not fall within the numerical range.

[0010] <1. Overall configuration of the cooling structure> First, the overall configuration of a cooling structure 1 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view (a cross-sectional view perpendicular to a bottom surface portion 10a of a battery pack 10) showing an overview of the cooling structure 1 according to this embodiment.

[0011] The cooling structure 1 according to this embodiment is provided on the outside (below) of the bottom surface of the automobile. Since an aqueous solution of LLC (long life coolant) containing organic components flows as a coolant in the water coolant flow passage 25 of the cooling structure 1, the cooling structure 1 is required to have high coolant corrosion resistance. In addition, the cooling structure 1 is required to improve the cooling performance by narrowing the flow passage interval of the water coolant flow passage 25 to increase the liquid area. Furthermore, the cooling structure 1 needs to ensure watertightness to prevent leakage of the coolant.

[0012] The cooling structure 1 has a water coolant flow path 25 formed on the outer side (below) of the bottom surface portion 10a of the battery pack 10. Battery cells (not shown) are housed in the battery pack 10. The battery cells are arranged in close contact with the bottom surface portion 10a of the battery pack 10.

[0013] The cooling structure 1 has a flow path forming portion 21 whose internal space is a water coolant flow path 25. The cooling structure 1 has a plurality of water coolant flow paths 25. The plurality of water coolant flow paths 25 are arranged in the X direction to form a plurality of flow path forming portions 21. When viewed from the Y direction, adjacent flow path forming portions 21 are connected via joint portions 22. The joint portions 22 are portions between adjacent flow path forming portions 21. The flow path forming portions 21 are joined to a member to be joined with an adhesive 30. The member to be joined is either the bottom surface portion 10a of the battery pack 10 or a flow path upper lid covering the flow path forming portion 21. Either the bottom surface portion 10a of the battery pack 10 or a flow path upper lid 26 covering the flow path forming portion 21 is joined to the flow path forming portion 21 with an adhesive 30. When the cooling structure 1 has the flow path upper lid 26, the member to be joined is the flow path upper lid 26, and the flow path forming portion 21 is joined to the flow path upper lid 26 with an adhesive 30. When the cooling structure 1 does not have the flow path lid 26, the joined member is the bottom surface portion 10a of the battery pack 10, and the flow path forming portion 21 is joined to the bottom surface portion 10a of the battery pack 10 with an adhesive 30. The joining portion 22 is joined to the bottom surface portion 10a of the battery pack 10 or the flow path lid 26 via the adhesive 30. In this embodiment, as shown in FIG. 1 , the flow path lid 26 covering the water coolant flow path 25 is joined to the flow path forming portion 21 with the adhesive 30. In detail, the flow path lid 26 is joined to the joining portion 22 with the adhesive 30. 1, in this embodiment, the flow path forming portion 21 has a rectangular cross section as viewed from the Y direction, and has a space therein. This space is a flow path 25 for a water coolant.

[0014] As shown in FIG. 1, the cooling structure 1 according to this embodiment has a flow path lid 26 that covers the upper side of the flow path forming portion 21. In this case, the flow path lid 26 is disposed between the flow path forming portion 21 and the battery pack 10. The flow path lid 26 covers the upper side of the water coolant flow path 25, i.e., covers the upper side of the flow path forming portion 21. The battery pack 10 is provided above the flow path lid 26. The flow path lid 26 is made of a steel plate in which an inorganic film or a resin film is formed as a chemical conversion coating on an Al-based plated steel plate or a Zn-based plated steel plate. Hereinafter, the "steel plate in which an inorganic film or a resin film is formed as a chemical conversion coating" may be referred to as a "chemically treated steel plate." When the cooling structure 1 does not have the flow path upper cover 26, the bottom surface portion 10a of the battery pack 10 covers the upper side of the water coolant flow path 25, i.e., covers the upper side of the flow path forming portion 21. In this case, the water coolant flow path 25 is in direct contact with the bottom surface portion 10a of the battery pack 10. In this case, the bottom surface portion 10a of the battery pack 10 is made of an Al-based plated steel sheet or a Zn-based plated steel sheet that has been subjected to chemical conversion treatment. When the cooling structure 1 has the flow path upper cover 26, the bottom surface portion 10a does not necessarily have to be made of an Al-based plated steel sheet or a Zn-based plated steel sheet that has been subjected to chemical conversion treatment. This is because the bottom surface portion 10a does not come into contact with the coolant.

[0015] The flow passage forming section 21 is composed of a steel sheet in which an inorganic film or a resin film is formed as a chemical conversion coating on an Al (aluminum)-plated steel sheet or a Zn (zinc)-plated steel sheet. An example of an Al-plated steel sheet is an Al-9 mass% Si-plated steel sheet. An example of a Zn-plated steel sheet is a Zn-0.2 mass% Al-plated steel sheet, a Zn-0.09 mass% Al-plated steel sheet, a Zn-6 mass% Al-3 mass% Mg-plated steel sheet, and a Zn-11 mass% Al-3 mass% Mg-0.2 mass% Si-plated steel sheet. A particularly preferred material among the Zn-plated steel sheets is a zinc (Zn)-aluminum (Al)-magnesium (Mg)-based alloy-plated steel sheet. Chemically treated Al-based and Zn-based plated steel sheets have high corrosion resistance to coolants. In particular, chemically treated Al-based and Zn-based plated steel sheets have excellent corrosion resistance to LLC aqueous solutions.

[0016] The cross-sectional shape of the flow path forming portion 21 is not limited to a rectangular shape, and may be, for example, a trapezoidal shape as shown in FIG. 2, a semicircular shape as shown in FIG. 3, or another shape.

[0017] In this embodiment, the water coolant flow path 25 extends in the Y direction (for example, a direction parallel to or perpendicular to the longitudinal direction of the bottom surface portion 10a of the battery pack 10). The extension direction of the water coolant flow path 25 is not limited to this example, and it may extend in the X direction. The water coolant flow path 25 may be curved, or may be U-shaped in a plan view.

[0018] The water refrigerant flow path 25 is connected to a circulation path not shown. For example, the water refrigerant flow path 25 is provided with a supply pipe (not shown) for supplying the refrigerant and a drain pipe (not shown) for draining the refrigerant. The supply pipe and the drain pipe are connected to approximately both ends of the water refrigerant flow path 25, respectively, or are arranged according to a cooling design, such as by positioning the supply pipe approximately in the middle of the water refrigerant flow path 25 and providing multiple or more drain pipes at both ends of the water refrigerant flow path 25. The refrigerant supplied from the supply pipe flows through the water refrigerant flow path 25 and is drained from the drain pipe, and is cooled by a cooling device (not shown) and then supplied again from the supply pipe to the water refrigerant flow path 25. In this manner, the cooling liquid flows through the circulation path and the water coolant flow path 25. After being cooled in the circulation path, the cooling liquid flows through the water coolant flow path 25. The cooling liquid absorbs heat from the battery pack 10 while flowing through the water coolant flow path 25. The cooling liquid is then introduced into the circulation path again. That is, the cooling liquid repeatedly flows through the circulation path and the water coolant flow path 25, thereby repeatedly absorbing heat from the battery pack 10.

[0019] Therefore, the members constituting the water coolant passage 25, i.e., the cooling structure 1, are required to have not only external corrosion resistance but also coolant corrosion resistance. In this embodiment, the passage forming portion 21 is made of an Al-plated steel sheet or a Zn-plated steel sheet that has been chemically treated. The Al-plated steel sheet and the Zn-plated steel sheet that has been chemically treated have high external corrosion resistance and coolant corrosion resistance. Therefore, the cooling structure 1 has high external corrosion resistance and coolant corrosion resistance. Therefore, in this embodiment, corrosion of the battery pack 10 and the cooling structure 1 by the coolant is suppressed, so that it is possible to suppress a decrease in thermal conductivity and elution of components of the battery pack 10 or the cooling structure 1 into the coolant.

[0020] The flow path interval w between the water coolant flow paths 25 is 20 mm or less. In other words, the flow path interval w is the distance between the ends of adjacent flow path forming portions 21 in the width direction (X direction). In the example shown in FIG. 1, the cross-sectional shape of the flow path forming portion 21 is rectangular, so the distance between the ends (flow path interval) w in the width direction of the flow path forming portions 21 is the distance between the side portions 21b of adjacent flow path forming portions 21. In the example shown in FIGS. 2 and 3, the boundary portion between the flow path forming portion 21 and the joint portion 22 becomes the end of the flow path forming portion 21 in the width direction. By setting the flow passage interval w between the water coolant flow passages 25 to 20 mm or less, the width of the water coolant flow passages 25 can be increased, and therefore the contact area between the water coolant flow passages 25 and the bottom surface portion 10a, in other words, the contact area between the coolant and the battery pack 10, can be increased. Therefore, in this embodiment, the cooling efficiency of the battery pack 10 can be improved. In particular, in this embodiment, the flow passage upper cover 26 or the bottom surface portion 10a of the battery pack 10 is made of a steel plate that has been chemically treated to be an Al-based plated steel plate or a Zn-based plated steel plate. The heat transfer characteristics of the Al-based plated steel plate or the Zn-based plated steel plate that has been chemically treated include that the heat of the part of the flow passage upper cover 26 or the bottom surface portion 10a of the battery pack 10 directly above the part that is in contact with the coolant is easily absorbed by the coolant. Therefore, by increasing the contact area between the coolant and the flow passage upper cover 26 or the battery pack 10, the part to which heat is transferred can be increased, and thus the cooling efficiency can be improved.

[0021] The passage interval w between the water coolant flow paths 25 is preferably 1 mm or more, and is preferably 15 mm or less. By setting the passage interval w between the water coolant flow paths 25 to 1 mm or more, the width (length in the X direction) of the joint 22 can be ensured, and it becomes easier to ensure the joint strength with the joined member (the bottom surface portion 10a of the battery pack 10 or the passage upper cover 26). By setting the passage interval w between the water coolant flow paths 25 to 15 mm or less, the contact area between the coolant and the battery pack 10 can be made wider, and the cooling efficiency can be improved. The flow passage interval w is measured at the longest point and the shortest point of the flow passage interval w in the water coolant flow passage 25 using a vernier caliper.

[0022] In order to efficiently cool the battery pack 10, it is necessary to increase the area ratio of the flow path in contact with the battery pack 10. The ratio of the contact area between the water coolant flow path 25 and the bottom surface portion 10a to the area of ​​the bottom surface portion 10a is preferably 0.23 or more, more preferably 0.40 or more. This allows the contact area between the coolant and the battery pack 10 to be widened, and thus the cooling efficiency of the battery pack 10 can be improved. The upper limit of the ratio is not particularly limited, but since it is preferable to ensure a certain degree of bonding strength between the bonding portion 22 and the bottom surface portion 10a, it may be 0.80. From the perspective of the balance between the bonding strength and the cooling efficiency, the ratio is more preferably 0.23 to 0.71. In other words, the cooling performance of the cooling structure 1 improves as the ratio increases, but it is also preferable to consider the bonding strength with the battery pack 10. From this perspective, the ratio is preferably 0.23 to 0.71.

[0023] The ratio of the contact area between the water coolant flow path 25 and the bottom surface portion 10a can be increased by enlarging the flow path width L. As shown in FIG. 1, the flow path width L is the length of the flow path forming portion 21 in the X direction, that is, the distance between the side portions 21b of the flow path forming portion 21. In the example shown in FIG. 2 and FIG. 3, the boundary portion between the flow path forming portion 21 and the joint portion 22 becomes the end portion in the width direction of the flow path forming portion 21, and the flow path width L is the distance between the end portions in the width direction of the flow path forming portion 21 in the flow path forming portion 21. If the flow path width L is too wide, the stress applied to the joint portion 22 becomes large, or the flow of the cooling liquid is not limited to the longitudinal direction of the flow path and is not stable. Therefore, the flow path width L is preferably 60 mm or less. The lower limit of the flow path width is preferably 6 mm or more as a range in which the cooling liquid can flow stably. In order to make the flow of the cooling liquid more stable, the flow path width L is more preferably 6 mm or more and 30 mm or less, and even more preferably 6 mm or more and 20 mm or less. The flow path width L is measured by using a vernier caliper at the maximum and minimum points of the flow path width L in the water coolant flow path 25.

[0024] If the portion not in contact with the coolant is too far from the end of the flow path in the X direction, the cooling effect of the coolant is reduced, so it is preferable that the length of the end of the water coolant flow path 25 that is not in contact with the coolant is short. Specifically, in FIG. 1, it is preferable that the maximum distance D in the X direction from the end of the water coolant flow path 25 to the portion of the bottom surface portion 10a of the battery pack 10 that is not in contact with the water coolant flow path 25 is short. The maximum distance D is the distance from the end of the water coolant flow path 25 to the nearest water coolant flow path 25. Specifically, the maximum distance D is 10 mm or less, more preferably 7.5 mm or less. Therefore, in order to improve the contact area ratio of the water coolant flow path 25 without excessively expanding the flow path width L and to shorten the distance between the portion not in contact with the coolant and the water coolant flow path 25, it is necessary to narrow the flow path interval w. In other words, the flow path interval w is preferably 20 mm or less, more preferably 15 mm or less. In order to satisfy the shape of the water coolant flow passage 25, it is suitable to bond the water coolant flow passage 25 with an adhesive. By bonding with an adhesive, the flow passage interval w can be made the same as that of the joint portion. The maximum distance D is measured at one point of the maximum distance in the water coolant flow path 25 using a vernier caliper.

[0025] The height of the water coolant flow path 25, i.e., the distance h in the thickness direction (Z direction) of the water coolant flow path 25 from the bottom surface portion 21a of the flow path forming portion 21 (the lower end portion 21a-1 of the flow path forming portion 21 in the example of FIG. 3) to the joint portion 22 is not particularly limited, but is preferably 1 mm to 10 mm from the viewpoint of the cooling efficiency of the battery pack 10. From the viewpoint of the processability for forming the flow path, the upper limit of the distance h is preferably 8 mm. By setting the height (distance h) of the water coolant flow path 25 to 1 mm to 8 mm, it is possible to achieve a better balance between the cooling efficiency of the battery pack 10 and the processability for forming the flow path. The distance h is the longest distance and the shortest distance in the water coolant flow path 25, which are measured using a vernier caliper.

[0026] The main resin component of the adhesive 30 is preferably any one of epoxy resin, silicone resin, acrylic resin, and urethane resin. The adhesive 30 preferably contains any one of these main resin components at 10% or more, more preferably 20% or more. The adhesive 30 having such a main component can suppress deterioration of the adhesive 30 and corrosion of the joint 22 due to coolant liquid, and ensure watertightness. The content of the main resin component in the adhesive 30 is measured using a thermogravimetric analyzer.

[0027] The outer edge 42 of the flow path lid 26 (joined member) is directly and continuously joined (watertightly joined) to the outer edge 27 of the cooling structure 1 by (1) an adhesive or (2) an adhesive and mechanical joining, forming a watertight joint 70. Direct and continuous joining is a joining that seals water and does not leak even when water pressure is applied. When the cooling structure 1 does not have the flow path lid 26, the outer edge 11 of the bottom portion 10a (joined member) of the battery pack 10 is directly and continuously joined (watertightly joined) to the outer edge of the cooling structure 1 by (1) an adhesive or (2) an adhesive and mechanical joining, forming a watertight joint 70. The mechanical joining (mechanical joining means) is, for example, joining by riveting, screw joining, press fitting, rolling, seaming, etc. Mechanical joining forms the mechanical joint 50. For example, TOX (registered trademark) manufactured by Toxpressotechnik is used as the mechanical joining means. In this way, the cooling structure 1 is directly and continuously joined, thereby preventing leakage of the coolant and ensuring watertightness. In addition, the outer edge 11 of the bottom surface portion 10a of the battery pack 10 or the outer edge 42 of the flow path upper cover 26 is directly and continuously joined by both an adhesive and a mechanical joint, thereby ensuring better watertightness. The adhesive used to bond to the outer edge portion 42 of the member to be joined (the bottom surface portion 10a of the battery pack 10, or the flow path upper cover 26 covering the flow path forming portion 21) may be the same adhesive as the adhesive 30 used to bond to the member to be joined, or may be a different adhesive.

[0028] The cooling structure 1 is manufactured, for example, by processing (e.g., bending, drawing, etc.) a steel sheet on which an inorganic coating or a resin coating is formed as a chemical conversion coating on a single Al-based plated steel sheet or a Zn-based plated steel sheet. Therefore, the cooling structure 1 can be manufactured cheaply and easily. The thickness of the steel plate on which the inorganic film or resin film is formed as a chemical conversion coating on the Al-plated steel plate or Zn-plated steel plate constituting the cooling structure 1 is not particularly limited, but is preferably 0.4 mm or more and 1.2 mm or less, and more preferably 0.4 mm or more and 1.0 mm or less. In this case, the strength of the cooling structure 1 can be increased while improving the workability (workability when manufacturing the cooling structure 1). The manufacturing method of the cooling structure 1 is not limited to this example. For example, the cooling structure 1 may be manufactured using different Al-plated steel plates or Zn-plated steel plates that have been chemically treated for each water coolant flow path 25. In this example, the flow path forming parts 21 corresponding to each water coolant flow path 25 may be formed by processing (for example, bending, drawing, etc.) each Al-plated steel plate or Zn-plated steel plate that has been chemically treated, and these may be joined to the battery pack 10. The thickness of the steel plate is determined by cutting out a part of the cooling structure 1, measuring the thickness at three points using a vernier caliper, and deriving the maximum and minimum values ​​at the three points.

[0029] The thickness of the steel plate constituting the bottom surface portion 10a of the battery pack 10 is not particularly limited, but is preferably, for example, 0.4 mm to 1.2 mm, and more preferably 0.4 mm to 1.0 mm. In this case, the bottom surface portion 10a of the battery pack 10 can be formed thin while maintaining the strength of the bottom surface portion 10a. Therefore, the distance between the coolant and the battery pack 10 can be narrowed, and the cooling efficiency of the battery pack 10 can be improved, and the cooling responsiveness of the battery pack 10 can be improved. The thickness of the steel plate is determined by cutting out a portion of the battery pack 10, measuring the thickness at three locations using a vernier caliper, and calculating the maximum and minimum values ​​at the three locations. Although there are no particular limitations on the materials of the side surface portion 10b and the top surface portion 10c of the battery pack 10, they are preferably made of an Al-based plated steel sheet or a Zn-based plated steel sheet that has been subjected to a chemical conversion treatment, similar to the bottom surface portion 10a. In particular, since the side surface portion 10b is exposed to the external environment, it is preferably made of an Al-based plated steel sheet or a Zn-based plated steel sheet that has been subjected to a chemical conversion treatment, similar to the bottom surface portion 10a.

[0030] In this embodiment, the cooling structure 1, which is exposed to the external environment and the coolant, is made of an Al-based plated steel plate or a Zn-based plated steel plate that has been chemically treated, which has excellent external corrosion resistance and coolant corrosion resistance, thereby improving the external corrosion resistance and coolant corrosion resistance of the cooling structure 1.

[0031] <2. Composition of Al-based plated steel sheets> Next, an example of the Al-based plated steel sheet that constitutes the battery pack 10 will be described in detail.

[0032] The Al-based plated steel sheet is a steel sheet on which a plating layer containing Al is formed. The plating layer of the Al-based plated steel sheet preferably contains Si. The Si content is, for example, 2.0 mass% or more and 15 mass% or less. The plating layer of the Al-based plated steel sheet is preferably a two-component or multi-component plating having an Al content of 70 mass% or more, an Al content of 70 to 98 mass%, and a Si content of 2.0 mass% or more and 15 mass% or less. A more preferable range of the Si content is 3.0 mass% or more and 15 mass% or less. By setting the Si content within the above range, the workability and corrosion resistance of the Al-based plated steel sheet can be improved. The plating layer may be formed on only one side of the steel sheet, but is preferably formed on both sides.

[0033] Impurity elements in the plating layer may include trace amounts of Fe, Ni, Co, etc. Furthermore, Mg, Sn, misch metal, Sb, Zn, Cr, W, V, Mo, etc. may be added as necessary. There are no particular limitations on the method for producing the aluminum-plated steel sheet, but hot-dip flux plating, hot-dip plating by the Sendzimir method, all-radiant method, etc., electroplating, and vapor deposition plating are preferred.

[0034] There are no limitations on the components of the base steel used in the Al-based plated steel sheet, but examples of the steel type include IF steel with added Ti, Nb, B, etc., Al-k steel, Cr-added steel, stainless steel, high tensile steel, low carbon steel, medium carbon steel, high carbon steel, alloy steel, etc.

[0035] The Al plate may be made of pure Al, or may be an Al alloy plate having the same composition as the above-mentioned plating layer.

[0036] In order to further improve the external corrosion resistance and coolant corrosion resistance of the Al-based plated steel sheet, a coating containing a Zr-based component, a Ti-based component or a Si-based component as a main component (for example, 50 mass % or more) as a chemical conversion coating is preferably formed on the surface (which may be only one side, but preferably both sides) of the Al-based plated steel sheet. The coating may contain an organic component.

[0037] Examples of chemical conversion coatings are given in, for example, JP 2008-115442 A, JP 2013-7108 A, JP 2004-232040 A, Japanese Patent No. 3302676 A, Japanese Patent No. 4776458 A, and Japanese Patent No. 5336002 A. Therefore, the chemical conversion coatings given in these publications can be suitably used as the chemical conversion coating of this embodiment. Here, an overview of the chemical conversion coating will be given.

[0038] The first example of the chemical conversion coating is an example of a coating containing a Zr-based component as the main component, which is composed only of Zr, F, P, C, O, N, and H, and does not contain any organic matter with a number average molecular weight of 200 or more. The components of the chemical conversion coating are adjusted so that the mass ratio Zr / F of Zr to F is 1.0 to 10.0, the mass ratio Zr / P of Zr to P is 8.5 to 18.0, and the Zr content in the chemical conversion coating is 23.0 mass% to 48.0 mass%. The supply sources of each component of the chemical conversion coating are one or more inorganic acids selected from the group consisting of carbonic acid, phosphoric acid, and hydrofluoric acid and / or their ammonium salts, and zirconium-containing complex compounds excluding zirconium hydrofluoric acid.

[0039] The second example of the chemical conversion coating is an example of a coating containing a Zr-based component as the main component, and contains (A) at least one of titanium compounds and zirconium compounds, (B) at least one of myo-inositol phosphate esters having 2 to 6 bonds and their alkali metal salts, alkaline earth metal salts, and ammonium salts, and (C) silica. In this chemical conversion coating, the mass ratio of the metal equivalents of (A) (Zr+Ti):(B):(C) is 1:0.2-1.7:0.2-5.

[0040] Examples of titanium compounds include potassium titanium oxalate, titanyl sulfate, titanium chloride, titanium lactate, titanium isopropoxide, isopropyl titanate, titanium ethoxide, titanium 2-ethyl-1-hexanolate, tetraisopropyl titanate, tetra-n-butyl titanate, titania sol, and the like.

[0041] Examples of the zirconium compound include zirconyl nitrate, zirconyl acetate, zirconyl sulfate, ammonium zirconyl carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and zirconium acetate.

[0042] Examples of 2- to 6-linked phosphate ester of myo-inositol include myo-inositol diphosphate ester, myo-inositol triphosphate ester, myo-inositol tetraphosphate ester, myo-inositol pentane phosphate ester, and myo-inositol hexane phosphate ester.

[0043] Examples of silica include water-dispersible silica compounds. Water-dispersible silica compounds include liquid-phase colloidal silica and gas-phase silica. Liquid-phase colloidal silica is not particularly limited, but includes Snowtex C, Snowtex O, Snowtex N, Snowtex S, Snowtex UP, Snowtex PS-M, Snowtex PS-L, Snowtex 20, Snowtex 30, Snowtex 40 (all manufactured by Nissan Chemical Industries), Adelite AT-20N, Adelite AT-20A, and Adelite AT-20Q (all manufactured by Asahi Denka Kogyo).

[0044] The gas phase silica is not particularly limited, but examples thereof include Aerosil 50, Aerosil 130, Aerosil 200, Aerosil 300, Aerosil 380, Aerosil TT600, Aerosil MOX80, and Aerosil MOX170 (all manufactured by Nippon Aerosil).

[0045] The third example of the chemical conversion coating is an example of a coating containing a Zr-based component as the main component, and is a composite coating made of a zirconium compound, a vanadium compound, a silica compound, a phosphate compound, and an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, and a carboxyl group. This chemical conversion coating contains 2 to 1200 mg / m2 of zirconium per side of the Al-based plated steel sheet. 20.1-300mg / m2 of vanadium, 0.3-450mg / m2 of phosphate compounds calculated as PO4 2 Furthermore, the content of chromium or chromium compounds in the chemical conversion coating is 0.1 mg / m 2 The following substances contain 0.1 mg / m fluorine or fluorine compounds: 2 The details are as follows.

[0046] Examples of the zirconium compound include zirconyl nitrate, zirconyl acetate, zirconyl sulfate, ammonium zirconyl carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and zirconium acetate.

[0047] Examples of vanadium compounds include vanadium pentoxide, metavanadic acid, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, vanadium oxysulfate, vanadium oxyacetylacetonate, vanadium acetylacetonate, vanadium trichloride, phosphovanadomolybdic acid, vanadium sulfate, vanadium dichloride, and vanadium oxide.

[0048] Examples of silica compounds include water-dispersible silica compounds. Examples of water-dispersible silica compounds include colloidal silica and gas-phase silica. Examples of colloidal silica include, but are not limited to, Snowtex C, Snowtex O, Snowtex N, Snowtex S, Snowtex UP, Snowtex PS-M, Snowtex PS-L, Snowtex 20, Snowtex 30, Snowtex 40 (all manufactured by Nissan Chemical Industries), Adelite AT-20N, Adelite AT-20A, Adelite AT-20Q (all manufactured by Asahi Denka Kogyo Co., Ltd.) and the like.

[0049] The gas phase silica is not particularly limited, but examples thereof include Aerosil 50, Aerosil 130, Aerosil 200, Aerosil 300, Aerosil 380, Aerosil TT600, Aerosil MOX80, and Aerosil MOX170 (all manufactured by Nippon Aerosil).

[0050] The phosphate compound may contain phosphate ions. Examples of the phosphate compound include orthophosphoric acid (phosphoric acid), metaphosphoric acid, pyrophosphoric acid, and salts of these substances in which some or all of the hydrogen ions have been replaced, such as ammonium salts, sodium salts, calcium salts, and potassium salts, which can be used alone or in combination.

[0051] Examples of organic compounds having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, and a carboxyl group include alcohols such as methanol, ethanol, isopropanol, and ethylene glycol; carbonyl compounds such as formaldehyde, acetaldehyde, furfural, acetylacetone, ethyl acetoacetate, dipivaloylmethane, and 3-methylpentanedione; organic acids such as formic acid, acetic acid, propionic acid, tartaric acid, ascorbic acid, gluconic acid, citric acid, and malic acid; monosaccharides such as glucose, mannose, and galactose; oligosaccharides such as maltose and sucrose; natural polysaccharides such as starch and cellulose; aromatic compounds such as tannic acid, humic acid, lignin sulfonic acid, and polyphenols; and synthetic polymers such as polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, polyethyleneimine, and water-soluble nylon.

[0052] The chemical conversion coating may contain, as an additional component, a lubricity-imparting component made of at least one of polyolefin-based wax and paraffin-based wax.

[0053] The fourth example of the chemical conversion coating is an example of a coating containing a Ti-based component as the main component, and is a coating in which an oxide or hydroxide of a valve metal and a fluoride coexist. Examples of valve metals include Ti and V. Among these, tetravalent compounds of Ti are preferred because they are stable compounds and can form a coating with excellent properties. Examples of coatings containing a Ti-based component as the main component include coatings in which oxides [TiO2] and hydroxides [Ti(OH)4] are combined. In this coating, fluorides of Ti, such as XnTiF6 (X: alkali metal, alkaline earth metal, or NH4, n=1 or 2), TiF4, and other fluorides coexist.

[0054] The fifth example of the chemical conversion coating is an example of a coating containing a Si-based component as a main component, and is a chemical conversion coating containing an organosilicon compound (silane coupling agent) as a main component. The organosilicon compound is obtained by blending a silane coupling agent (A) containing one amino group in the molecule with a silane coupling agent (B) containing one glycidyl group in the molecule in a solid content mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound contains two or more functional groups (a) represented by the formula -SiR1R2R3 (wherein R1, R2, and R3 each independently represent an alkoxy group or a hydroxyl group, and at least one represents an alkoxy group) in the molecule, and one or more hydrophilic functional groups (b) selected from a hydroxyl group (different from those that may be contained in the functional group (a)) and an amino group, and has an average molecular weight of 1000 to 10000.

[0055] The sixth example of the chemical conversion coating is an example of a coating containing a Si-based component as a main component, that is, a chemical conversion coating containing an organosilicon compound (silane coupling agent) as a main component. The organosilicon compound has a cyclic siloxane structure in its structure. Here, the "cyclic siloxane bond" refers to a cyclic structure having a structure in which Si-O-Si bonds are continuous, and which is composed only of bonds between Si and O, with the number of Si-O repeats being 3 to 8.

[0056] The organosilicon compound is obtained by blending a silane coupling agent (A) containing at least one amino group in the molecule with a silane coupling agent (B) containing at least one glycidyl group in the molecule in a solid content mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound (W) thus obtained preferably contains in the molecule two or more functional groups (a) represented by the formula -SiR1R2R3 (wherein R1, R2 and R3 each independently represent an alkoxy group or a hydroxyl group, and at least one of R1, R2 and R3 represents an alkoxy group), one or more hydrophilic functional groups (b) selected from the group consisting of a hydroxyl group (however, when the functional group (a) contains a hydroxyl group, the functional group is separate from the hydroxyl group) and an amino group, and has an average molecular weight of 1000 to 10000.

[0057] Of course, examples of the chemical conversion coating of this embodiment are not limited to those mentioned above, and for example, the chemical conversion coatings given in the examples described below can also be suitably used.

[0058] The method for forming the above-mentioned chemical conversion coating is not particularly limited, and a chemical conversion solution (coating solution) corresponding to each of the above compositions may be applied to a Zn-based plated steel sheet by a known method, followed by baking and drying.

[0059] <3. Composition of Zn-based coated steel sheets> Next, an example of the Zn-based plated steel sheet that constitutes the cooling structure 1 will be described in detail.

[0060] The Zn-based plated steel sheet is a steel sheet on which a plating layer containing Zn is formed. The plating layer may be formed on only one side of the steel sheet, but is preferably formed on both sides. Examples of Zn-based plated steel sheets include zinc-plated steel sheets, zinc-nickel-plated steel sheets, zinc-iron-plated steel sheets, zinc-chromium-plated steel sheets, zinc-aluminum-plated steel sheets, zinc-titanium-plated steel sheets, zinc-magnesium-plated steel sheets, zinc-manganese-plated steel sheets, zinc-aluminum (Al)-magnesium (Mg)-plated steel sheets, and zinc-aluminum-magnesium-silicon-plated steel sheets. Furthermore, Zn-based plated steel sheets containing small amounts of different metal elements or impurities such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, and arsenic in these plating layers, and Zn-based plated steel sheets in which inorganic substances such as silica, alumina, and titania are dispersed can also be used. Furthermore, the above plating can be combined with other types of plating, and for example, multi-layer plating can be applied by combining it with iron plating, iron-phosphorus plating, nickel plating, cobalt plating, etc. The plating method is not particularly limited, and any of the known methods such as electroplating, hot-dip plating, vapor deposition plating, dispersion plating, and vacuum plating can be used.

[0061] Furthermore, an inorganic coating or a resin coating is formed as a chemical conversion coating on the surface (which may be only one side, but preferably both sides) of the Zn-based plated steel sheet. The inorganic coating contains a Si-based component or a Zr-based component as a main component (for example, 50 mass% or more by mass). The inorganic coating may also contain an organic component.

[0062] The inorganic film or resin film is preferably conductive. In this case, the electrodeposition coating property of the Zn-plated steel sheet can be improved. Furthermore, the inorganic film is preferably composed of a compound phase containing one or more of Si-O bonds, Si-C bonds, and Si-OH bonds. In addition, it is preferable that the compound phase contains an acrylic resin described later. When these requirements are satisfied, the adhesion of the chemical conversion coating can be improved, so that the external corrosion resistance and coolant corrosion resistance of the processed part of the Zn-plated steel sheet can be improved. In addition, it is preferable that the inorganic film contains at least one of V, P, and Co components as a rust-preventive component. The rust-preventive component of the inorganic film is preferably one or more of vanadium oxide, phosphoric acid, and Co nitrate. In addition, the thickness of the inorganic film is preferably more than 0 μm and 1.5 μm or less. In this case, the conductivity or adhesion of the above-mentioned chemical conversion coating can be further improved.

[0063] The resin film preferably contains a resin, an anti-rust pigment, and a conductive pigment. Furthermore, the resin film preferably contains at least one of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles as a conductive pigment. The conductive pigment preferably has a powder resistivity of 7.0×107 Ωcm or less at 23 to 27° C. and contains at least one selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W as a constituent element. Furthermore, the resin film preferably contains the conductive pigment in a ratio of 1.0 mass % to 30 mass %. Furthermore, the average thickness of the resin film is preferably 1.0 μm to 15 μm. Furthermore, the average particle size of the conductive pigment is preferably 0.5 to 1.5 times the average thickness of the resin film. When at least one of these requirements is satisfied, the external corrosion resistance and coolant corrosion resistance of the Zn-based plated steel sheet can be further improved.

[0064] Examples of chemical conversion coatings are listed in, for example, Japanese Patent No. 4776458, Japanese Patent No. 5336002, Japanese Patent No. 6191806, Japanese Patent No. 6263278, International Publication No. 2020 / 202461, and Japanese Patent No. 4084702. Therefore, the chemical conversion coatings listed in these publications can be suitably used as the chemical conversion coating of this embodiment. Here, an overview of the chemical conversion coating will be described.

[0065] The first example of the chemical conversion coating is an example of an inorganic coating, and is a chemical conversion coating containing an organosilicon compound (silane coupling agent) as a main component. The organosilicon compound is obtained by blending a silane coupling agent (A) containing one amino group in the molecule with a silane coupling agent (B) containing one glycidyl group in the molecule in a solid content mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound contains two or more functional groups (a) represented by the formula -SiR1R2R3 (wherein R1, R2, and R3 each independently represent an alkoxy group or a hydroxyl group, and at least one represents an alkoxy group) in the molecule, and one or more hydrophilic functional groups (b) selected from a hydroxyl group (different from those that may be contained in the functional group (a)) and an amino group, and has an average molecular weight of 1000 to 10000.

[0066] In the first example, the Zr-based component is contained in the chemical conversion coating as zirconium hydrofluoric acid. The V component is a vanadium compound, the P component is phosphoric acid, and the Co component is at least one selected from the group consisting of cobalt sulfate, cobalt nitrate, and cobalt carbonate. Examples of vanadium compounds include vanadium pentoxide V2O5, metavanadate HVO3, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl3, vanadium trioxide V2O3, vanadium dioxide VO2, vanadium oxide, vanadium oxysulfate VOSO4, vanadium oxyacetylacetonate VO(OC(=CH2)CH2COCH3))2, vanadium acetylacetonate V(OC(=CH2)CH2COCH3))3, vanadium trichloride VCl3, and phosphorus vanadomolybdic acid. Also usable are pentavalent vanadium compounds reduced to tetravalent or divalent vanadium compounds by an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, a carboxyl group, a primary to tertiary amino group, an amide group, a phosphoric acid group, and a phosphonic acid group.

[0067] The second example of the chemical conversion coating is an example of an inorganic coating, which is a chemical conversion coating containing an organosilicon compound (silane coupling agent) as a main component. The organosilicon compound has a cyclic siloxane structure in its structure. Here, the "cyclic siloxane bond" refers to a cyclic structure having a structure in which Si-O-Si bonds are continuous, and which is composed only of bonds between Si and O, with the number of Si-O repeats being 3 to 8.

[0068] The organosilicon compound is obtained by blending a silane coupling agent (A) containing at least one amino group in the molecule with a silane coupling agent (B) containing at least one glycidyl group in the molecule in a solid content mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound (W) thus obtained preferably contains in the molecule two or more functional groups (a) represented by the formula -SiR1R2R3 (wherein R1, R2 and R3 each independently represent an alkoxy group or a hydroxyl group, and at least one of R1, R2 and R3 represents an alkoxy group), one or more hydrophilic functional groups (b) selected from the group consisting of a hydroxyl group (however, when the functional group (a) contains a hydroxyl group, the functional group is separate from the hydroxyl group) and an amino group, and has an average molecular weight of 1000 to 10000.

[0069] In the second example, the Zr-based component is contained in the chemical conversion coating as a zirconium compound. Examples of the zirconium compound include zirconium hydrofluoric acid, zirconium ammonium fluoride, zirconium sulfate, zirconium oxychloride, zirconium nitrate, and zirconium acetate. Among these, the zirconium compound is more preferably zirconium hydrofluoric acid. When zirconium hydrofluoric acid is used, better corrosion resistance and paintability can be obtained.

[0070] The V component is a vanadium compound, the P component is a phosphate compound, and the Co component is at least one selected from the group consisting of cobalt sulfate, cobalt nitrate, and cobalt carbonate, contained in the chemical conversion coating. Examples of vanadium compounds include vanadium pentoxide V2O5, metavanadate HVO3, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl3, vanadium trioxide V2O3, vanadium dioxide VO2, vanadium oxide, vanadium oxysulfate VOSO4, vanadium oxyacetylacetonate VO(OC(=CH2)CH2COCH3)2, vanadium acetylacetonate V(OC(=CH2)CH2COCH3)3, vanadium trichloride VCl3, and phosphorus vanadomolybdic acid. Also usable is a compound obtained by reducing a pentavalent vanadium compound to a tetravalent or divalent vanadium compound using an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, a carboxyl group, a primary to tertiary amino group, an amide group, a phosphoric acid group, and a phosphonic acid group.

[0071] Examples of the phosphate compound include phosphoric acid, ammonium phosphate, potassium phosphate, and sodium phosphate. Among these, the phosphate compound is preferably phosphoric acid. When phosphoric acid is used, better corrosion resistance can be obtained.

[0072] The third example of the chemical conversion coating is an example of an inorganic coating, and contains an acrylic resin, zirconium, vanadium, phosphorus, and cobalt. More specifically, the chemical conversion coating contains a particulate acrylic resin (resin particles) and an inhibitor phase. The acrylic resin is preferably a resin containing a polymer of an alkyl (meth)acrylate ester, and may be a polymer obtained by polymerizing only an alkyl (meth)acrylate ester, or may be a copolymer obtained by polymerizing an alkyl (meth)acrylate ester and another monomer. "(Meth)acrylic" means "acrylic" or "methacrylic". The inhibitor phase contains zirconium, vanadium, phosphorus, and cobalt. The zirconium forms a crosslinked structure with the acrylic resin.

[0073] The fourth example of the formation treatment film is an example of an inorganic film, and includes a zirconium carbonate compound, an acrylic resin, a vanadium compound, a phosphorus compound, and a cobalt compound. Examples of the zirconium carbonate compound include zirconium carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, sodium zirconium carbonate, etc., and one or more of these can be used. Among them, zirconium carbonate and ammonium zirconium carbonate are preferable in terms of excellent corrosion resistance.

[0074] The acrylic resin is a resin obtained by copolymerizing a monomer component containing at least styrene (b1), (meth)acrylic acid (b2), (meth)acrylic acid alkyl ester (b3), and acrylonitrile (d4), and the amount of acrylonitrile (b4) is 20 to 38% by mass based on the solid content mass of the total monomer component of the resin, and it is a water-soluble resin and an aqueous emulsion resin having a glass transition temperature of -12 to 15°C. That is, the acrylic resin exists in the form of resin particles in the formation treatment film.

[0075] Examples of the vanadium compound include divalent to tetravalent vanadium compounds. More specifically, for example, vanadium pentoxide (V2O5), metavanadic acid (HVO3), ammonium metavanadate, sodium metavanadate, vanadium oxychloride (VOCl3) and other pentavalent vanadium compounds reduced to divalent to tetravalent with a reducing agent, vanadium trioxide (V2O3), vanadium dioxide (VO2), vanadium oxy sulfate (VOSO4), vanadium oxalate [VO(COO)2], vanadium oxyacetylacetonate [VO(OC(CH3)=CHCOCH3))2], vanadium acetylacetonate [V(OC(CH3)=CHCOCH3))3], vanadium trichloride (VCl3), phosphovanadomolybdic acid {H15-X[PV12-xMoxO40]·nH2O(6<x<12,n<30)}, vanadium sulfate (VSO4·8H2O), vanadium dichloride (VCl2), vanadium oxide (VO) and other vanadium compounds with an oxidation number of tetravalent to divalent, etc. can be mentioned.

[0076] Examples of the phosphorus compound include inorganic acid anions having an acid group containing phosphorus, and organic acid anions having an acid group containing phosphorus. Examples of the inorganic acid anions having an acid group containing phosphorus include inorganic acid anions in which at least one hydrogen atom of inorganic acids such as orthophosphoric acid, metaphosphoric acid, condensed phosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetraphosphoric acid, and hexametaphosphoric acid is liberated, and salts thereof.

[0077] Examples of organic acid anions having an acid group containing phosphorus include organic acid anions having at least one free hydrogen atom, such as organic phosphonic acids such as 1-hydroxymethane-1,1-diphosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, 1-hydroxypropane-1,1-diphosphonic acid, 1-hydroxyethylene-1,1-diphosphonic acid, 2-hydroxyphosphonoacetic acid, aminotri(methylenephosphonic acid), ethylenediamine-N,N,N',N'-tetra(methylenephosphonic acid), hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic acid), diethylenetriamine-N,N,N',N'',N''-penta(methylenephosphonic acid), 2-phosphonic acid butane-1,2,4-tricarboxylic acid, inositol hexaphosphonic acid, and phytic acid, and organic phosphoric acid, and salts thereof.

[0078] Examples of the cobalt compound include cobalt sulfate, cobalt nitrate, and cobalt carbonate.

[0079] A fifth example of the chemical conversion coating is an example of a resin coating, and contains at least one of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles as a conductive pigment. The conductive pigment has a powder resistivity of 7.0×107 Ωcm or less at 23 to 27°C, and contains at least one element selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W.

[0080] Examples of intermetallic compounds include ferrosilicon and ferromanganese. Examples of conductive oxide particles include materials that have conductivity by doping impurities into the crystal lattice of the oxide (doped conductive oxides) or oxides whose surfaces are modified with conductive materials. The former can be generally known metal oxides doped with one or more metal elements selected from Al, Nb, Ga, Sn, etc. (e.g., Al-doped zinc oxide, Nb-doped zinc oxide, Ga-doped zinc oxide, Sn-doped zinc oxide, etc.). The latter can be generally known zinc oxide or silica modified with SnO2, which has conductivity in the oxide. The conductive oxide is preferably a doped conductive oxide, and the doped conductive oxide is preferably Al-doped zinc oxide.

[0081] The conductive non-oxide ceramic particles are composed of ceramics made of elements or compounds that do not contain oxygen. Examples of the conductive non-oxide ceramic particles include boride ceramics, carbide ceramics, nitride ceramics, and silicide ceramics. In addition, boride ceramics, carbide ceramics, nitride ceramics, and silicide ceramics are non-oxide ceramics that have boron (B), carbon (C), nitrogen (N), and silicon (Si) as major non-metallic constituent elements, respectively, and these generally known non-oxide ceramics that contain one or more selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, and W can be used. Furthermore, the non-oxide ceramic particles are more preferably the non-oxide ceramics exemplified below in terms of the presence or absence of industrial products, stable distribution in domestic and overseas markets, price, electrical resistivity, and the like. For example, particles of Mo2B, MoB, MoB2, Mo2B5, NbB2, VB, VB2, W2B5, ZrB2, Mo2C, V2C, VC, WC, W2C, ZrC, Mo2N, VN, ZrN, Mo3Si, Mo5Si3, MoSi2, NbSi2, Ni2Si, Ta2Si, TaSi2, TiSi, TiSi2, V5Si3, VSi2, W3Si, WSi2, ZrSi, ZrSi2, CrB, CrB2, Cr3C2, Cr2N, CrSi, and particles of a mixture of two or more selected from these are more preferred.

[0082] The sixth example of the chemical conversion coating is an example of a resin coating, which contains a resin having a urethane bond and conductive particles (conductive pigments). The resin having a urethane bond is an organic resin obtained from a film-forming resin raw material that contains (a) a polyester polyol having at least three functional groups, and (b) a blocked product of an organic polyisocyanate or a blocked product of a prepolymer having NCO groups at its terminals, which is obtained by reacting an organic polyisocyanate with an active hydrogen compound.

[0083] (a) The polyester polyol having a functionality of at least 3 can be obtained by esterifying a dicarboxylic acid, a glycol, and a polyol having at least 3 OH groups.

[0084] Examples of dicarboxylic acids used in the production of polyester polyols include aliphatic dicarboxylic acids such as succinic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, dodecanoic diacid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, and dimer acid; and aromatic and alicyclic dicarboxylic acids such as phthalic acid, phthalic anhydride, isophthalic acid, isophthalic acid dimethyl ester, terephthalic acid, terephthalic acid dimethyl ester, 2,6-naphthalenedicarboxylic acid, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, cyclohexanedicarboxylic acid, cyclohexanedicarboxylic acid dimethyl ester, methylhexahydrophthalic anhydride, himic anhydride, and methyl himic anhydride.

[0085] Examples of glycols include ethylene glycol, diethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, dipropylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, neopentyl glycol ester of hydroxydivalanic acid, triethylene glycol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,4-diethyl-1,5-pentanediol, polycaprolactone diol, polypropylene glycol, Examples of the polyphenols include aliphatic polyphenols such as glycol, polytetramethylene ether glycol, polycarbonate diol, 2-n-butyl-2-ethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol; and aliphatic or aromatic polyphenols such as cyclohexanedimethanol, cyclohexanediol, 2-methyl-1,1-cyclohexanedimethanol, xylylene glycol, bishydroxyethyl terephthalate, 1,4-bis(2-hydroxyethoxy)benzene, hydrogenated bisphenol A, an ethylene oxide adduct of bisphenol A, and a propylene oxide adduct of bisphenol A.

[0086] Examples of polyols having at least three OH groups include glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, pentaerythritol, diglycerin, and ethylene oxide adducts, propionate adducts, and ε-caprolactone adducts using these polyols as initiators.

[0087] Examples of the blocked compounds of (b) include compounds having at least two NCO groups, such as aliphatic diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, and 2,6-diisocyanatomethyl caproate. and other isocyanates such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylhexyl isocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane, Cycloalkylene diisocyanates such as (methyl)cyclohexane and trans-cyclohexane-1,4-diisocyanate, and diisocyanates such as m-xylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4- or 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, aromatic diisocyanates such as isocyanate, for example, ω,ω'-diisocyanato-1,3-dimethylbenzene, ω,ω'-diisocyanato-1,4-dimethylbenzene, ω,ω'-diisocyanato-1,4-diethylbenzene, α,α,α',α'-tetramethylmetaxylylenediisocyanate, and aromatic aliphatic diisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, ω-isocyanatoethyl-2,Examples of such blocked products include triisocyanates such as 6-diisocyanatocaproate, tetraisocyanates such as 4,4'-diphenylmethylmethane-2,2',5,5'-tetraisocyanate, and derivatives of isocyanate compounds such as dimers, trimers, biuret, allophanates, carbodiimides, polymethylene polyphenyl polyisocyanates (crude MDI, c-MDI, polymeric MDI), and crude TDI, as well as blocked products of prepolymers having NCO groups at their ends obtained by reacting these with active hydrogen compounds.

[0088] The conductive particles are corrosion-resistant particles that are alloys or compounds containing 50% or more by mass of Si, or composites thereof. The conductive particles are preferably ferrosilicon. Anti-rust pigments may be added to the chemical conversion coating. Examples of the anti-rust pigments include known anti-rust pigments such as hexavalent chromates, such as strontium chromate and calcium chromate. When it is desired to avoid using hexavalent chromium compounds as anti-rust agents, it is possible to use those that release one or more of silicate ions, phosphate ions, and vanadate ions.

[0089] Of course, examples of the chemical conversion coating of this embodiment are not limited to those mentioned above, and for example, the chemical conversion coatings given in the examples described below can also be suitably used.

[0090] The method for forming the above-mentioned chemical conversion coating is not particularly limited, and a chemical conversion solution (coating solution) corresponding to each of the above compositions may be applied to a Zn-based plated steel sheet by a known method, followed by baking and drying. An example of a preferred combination of a Zn-based plated steel sheet and a chemical conversion coating is a combination of a Zn-Al-Mg plated steel sheet and an inorganic coating containing a Si-based component as a main component. EXAMPLES

[0091] The present disclosure will be described in more detail below with reference to examples. Note that the examples described below are merely examples of the present disclosure and are not intended to limit the present disclosure.

[0092] <Material preparation> Steel having the steel composition shown in Table 1 as an extremely low carbon steel with excellent workability (the balance being iron and impurities) was hot-rolled, pickled, and cold-rolled to prepare a cold-rolled steel sheet with a thickness of 0.6 mm. The cold-rolled steel sheet was then subjected to hot-dip Al plating in a non-oxidation furnace type continuous hot-dip plating line to obtain an aluminized steel sheet. A non-oxidation furnace-reducing furnace type plating line was used, and annealing was also performed in this hot-dip plating line. The annealing temperature was 850°C.

[0093] [Table 1]

[0094] After plating, the plating thickness is reduced to approximately 40g / m on both sides using the gas wiping method. 2 The bath temperature of the plating bath during hot-dip plating was 660°C. A molten Al bath with Si added as necessary was used as the plating bath. In this embodiment, a steel sheet plated in a molten Al bath with no Si added thereto is also called "pure Al plated steel sheet", a steel sheet plated in a molten Al bath with 2 mass% Si added thereto is also called "Al-2%Si plated steel sheet", a steel sheet plated in a molten Al bath with 9 mass% Si added thereto is also called "Al-9%Si plated steel sheet", a steel sheet plated in a molten Al bath with 15 mass% Si added thereto is also called "Al-15%Si plated steel sheet", and a steel sheet plated in a molten Al bath with 20 mass% Si added thereto is also called "Al-20%Si plated steel sheet".

[0095] Next, the surface of the Al-plated steel sheet was coated with a chemical conversion treatment solution using a roll coater as required. The amount of chemical conversion treatment solution applied was adjusted by adjusting the rotation speed of the roll coater and the pressure between the rolls (commonly called nip pressure). The amount of application was 500 mg / m2 per side in dry weight. 2 After the chemical conversion treatment solution was applied, it was dried in a hot air oven under conditions that the sheet temperature reached was 80° C. The chemical conversion treatment was applied to both sides of the Al-based plated steel sheet.

[0096] The chemical conversion treatment solutions used for painting were three types: an aqueous solution containing 2.5 g / L of gamma-aminopropyltriethoxysilane, which is a Si-based chemical conversion treatment solution, an aqueous solution containing 3 g / L of ammonium zirconium carbonate, which is a Zr-based chemical conversion treatment solution, and an aqueous solution containing 40 g / L of ammonium titanium (IV) fluoride, which is a Ti-based chemical conversion treatment solution. Details of the Al-based plated steel sheets that were created are shown in Table 4.

[0097] Furthermore, the cold-rolled steel sheet was annealed under conditions where the maximum sheet temperature reached was 820°C using a continuous hot-dip galvanizing device capable of annealing, and then hot-dip galvanized to prepare a hot-dip galvanized steel sheet. Here, the gas atmosphere in the annealing furnace in the annealing process was 1.0% by volume H 2 Including N 2 The plating bath used in the plating step had four components: Zn-0.2% by mass Al (hereinafter also referred to as "GI"), Zn-0.09% by mass Al (hereinafter also referred to as "GA"), Zn-6% by mass Al-3% by mass Mg (hereinafter also referred to as "Zn-Al-Mg"), and Zn-11% by mass Al-3% by mass Mg-0.2% by mass Si (hereinafter also referred to as "Zn-Al-Mg-Si").

[0098] In the case of hot-dip galvanizing using a hot-dip galvanizing bath of Zn-0.09 mass% Al coating (GA), alloyed hot-dip galvanizing was performed by the following steps: The steel sheet was immersed in the hot-dip galvanizing bath. Next, while the steel sheet was being pulled out of the coating bath, N 2 The amount of coating was adjusted by gas wiping using gas blowing.Then, the steel sheet was alloyed by heating it to a sheet temperature of 480°C using an induction heater, and the Fe in the steel sheet was diffused into the coating layer.

[0099] The coating weight of the plated steel sheet is 45 g / m2 for GA per side of the steel sheet. 2 , 60g / m for plating other than GA 2 For comparison, cold-rolled steel sheets that were not plated but only annealed in a continuous annealing line were also prepared.

[0100] Next, a chemical conversion treatment liquid (film treatment liquid) was applied to the surface of the plated steel sheet prepared in the above process using a roll coater as necessary. The amount of chemical conversion treatment liquid applied (i.e., the film thickness of the chemical conversion treatment film) was controlled by adjusting the rotation speed of the roll coater and the pressure between the rolls (generally called nip pressure). In this way, a chemical conversion treatment film of a specified film thickness was formed on the plated steel sheet.

[0101] Here, when the chemical conversion coating is an inorganic coating, the chemical conversion coating solution was applied and then dried in a hot air oven under conditions where the ultimate sheet temperature was 80°C. When the chemical conversion coating is a resin coating, before the chemical conversion coating solution was applied to the plated steel sheet, the plated steel sheet was coated with Palcoat E200, a chemical conversion coating made by Nippon Parkerizing Co., Ltd., using a roll coater as a pretreatment to enhance adhesion to the plated steel sheet, and then dried in a hot air oven under conditions where the ultimate sheet temperature was 80°C. Thereafter, the chemical conversion coating solution was applied to a predetermined film thickness using a roll coater, and then dried in a hot air oven under conditions where the ultimate sheet temperature was 200°C. The chemical conversion coating was applied to both sides of the plated steel sheet. The film thickness after the coating and drying of each coating was measured by embedding the coated steel sheet in resin and polishing it so that the vertical cross section could be observed, and observing it with a scanning electron microscope. The magnification of the observation with the scanning electron microscope was appropriately selected optimally according to the film thickness of the coating.

[0102] In addition, in the samples where the inorganic film was created with a thickness exceeding 1.5 μm after coating and drying, cracks occurred in the film or the film came off in any of the treatment solutions, and it was not possible to obtain a uniformly formed film, so it was determined that it is difficult to produce an inorganic film with a thickness exceeding 1.5 μm. Details of the steel sheets created by coating various plated steel sheets with films are shown in Tables 4 and 5.

[0103] <How to make inorganic conversion treatment solution> An inorganic conversion treatment liquid (chemical conversion treatment liquid for forming an inorganic coating) was prepared by the following process. That is, an aqueous solution containing 10 g / L of γ-aminopropyltriethoxysilane was prepared as an inorganic conversion treatment liquid mainly composed of a Si-based component. Furthermore, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of Co nitrate were added to the prepared γ-aminopropyltriethoxysilane aqueous solution as required to prepare an inorganic conversion treatment liquid.

[0104] Furthermore, an aqueous solution containing 3.0 g / L of ammonium zirconium carbonate was prepared as an inorganic conversion treatment solution mainly composed of Zr-based components. Furthermore, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of Co nitrate were added to the prepared aqueous solution of ammonium zirconium carbonate as required to prepare an inorganic conversion treatment solution. Details of the inorganic conversion treatment solution prepared are shown in Table 2.

[0105] Furthermore, an aqueous solution was prepared by mixing 40g / L of ammonium titanium (IV) fluoride, which is a Ti-based chemical conversion treatment solution. Furthermore, 1.3g / L of vanadium oxide, 0.7g / L of phosphoric acid, and 0.5g / L of cobalt nitrate were mixed into the prepared aqueous solution of ammonium zirconium carbonate as required to prepare an inorganic chemical conversion treatment solution. Details of the inorganic chemical conversion treatment solution prepared are shown in Table 2.

[0106] [Table 2]

[0107] The following method was used to confirm whether the inorganic coating contained Si-O bonds or the like. That is, the prepared inorganic conversion treatment solution was applied to any of the plated steel sheets prepared above using a wire bar, and dried under conditions that resulted in a sheet temperature of 80°C. In this way, an inorganic coating was formed on the plated steel sheet. Next, the coating surface was measured using an IRT-5200 manufactured by JASCO Corporation, and it was determined whether the inorganic coating contained one or more of Si-O bonds, Si-C bonds, and Si-OH bonds based on the assignment of observed peaks derived from resin components in the infrared absorption spectrum of the obtained inorganic coating. Specifically, the inorganic conversion treatment solution was applied to any of the plated steel sheets prepared above using a wire bar, and dried under conditions that resulted in a sheet temperature of 80°C. In this way, an inorganic coating was formed on the plated steel sheet. Next, the coating surface was measured using an IRT-5200 manufactured by JASCO Corporation, and it was determined whether the inorganic coating contained one or more of Si-O bonds, Si-C bonds, and Si-OH bonds based on the assignment of observed peaks derived from resin components in the infrared absorption spectrum of the obtained inorganic coating. -1 Near, 1080~1020cm -1 Near, 500~300cm -1 Near, 900~700cm -1 When a peak was observed in at least one of the vicinity, it was judged that the inorganic coating contained one or more of the Si-O bond, the Si-C bond, and the Si-OH bond. The judgment results are shown in Table 2.

[0108] <How to prepare resin-based conversion treatment solution> A resin-based chemical conversion treatment liquid (chemical conversion treatment liquid for forming a resin film) was prepared in the following steps. That is, a polyester resin "Vylon(R) 300" manufactured by Toyobo Co., Ltd. was dissolved in cyclohexanone as a solvent at 30 mass %, and 20 mass parts of solid content of melamine resin "CYMEL(R) 303" manufactured by Allnex Co., Ltd. was added to 100 mass parts of solid content of this solution and mixed. In addition, 5 mass % of hardening catalyst "CYCAT(R) 600" manufactured by Allnex Co., Ltd. was added to the total solid content of the prepared mixture and mixed. In this way, a base treatment liquid for obtaining a resin film was prepared.

[0109] Next, the particles shown below were mixed into the prepared base treatment liquid to prepare a resin-based chemical conversion treatment liquid. The amount of particles added was adjusted by the following method. That is, the solid mass ratio (mass ratio to solids other than particles) of the particles added to the base treatment liquid in the resin film was obtained, and the volume ratio was calculated from the specific gravity of the solids in the resin film and the specific gravity of the particles. Next, the amount of particles added was adjusted so that the calculated volume ratio became the volume ratio shown in Table 3. The specific gravity was used from the catalog value or literature value of each substance. Details of the resin-based treatment liquid are shown in Table 3.

[0110] [Table 3]

[0111] Vanadium boride: "VB2-O" manufactured by Japan New Metals Co., Ltd. was sieved to obtain an average particle size of 3.1 μm. Hereinafter, this is also referred to as "VB2". The average particle size was calculated based on the mass percentage of each particle size fraction. Al-doped zinc oxide: Conductive zinc oxide (Al-doped ZnO) "23-K" manufactured by Hakusui Tech Co., Ltd., with a primary particle size of 120 to 250 nm (catalog value) was used. Hereinafter, this will also be referred to as "Al-ZnO". Metallic zinc: Reagent zinc particles were classified using a sieve to have an average particle size of 10 μm. Hereinafter, this will be referred to as "Zn." Ferrosilicon: Ferrosilicon manufactured by Marubeni Tetsugen Co., Ltd. was crushed into fine particles using a grinder and classified using a sieve to obtain an average particle size of 3.5 μm. Hereinafter, this is also referred to as "Fe-Si." Ferromanganese: Ferro-silicon manufactured by Marubeni Tetsugen Co., Ltd. was crushed into fine particles using a grinder and classified using a sieve to obtain an average particle size of 3.5 μm. Hereinafter, this is also referred to as "Fe-Mn." Zirconium boride: "ZrB2-O" manufactured by Japan New Metals Co., Ltd. was classified with a sieve to have an average particle size of 2 μm. Hereinafter, this will be referred to as "ZrB2". Molybdenum silicide: "MoSi2-F" manufactured by Nippon Shinkinzoku Co., Ltd. was classified with a sieve to obtain an average particle size of 3.5 μm. Hereinafter, this will be referred to as "MoSi2". Chromium boride: "CrB2-O" manufactured by Nippon Shinkinzoku Co., Ltd. was classified with a sieve to have an average particle size of 5 μm. Hereinafter, this will be referred to as "CrB2". Tungsten silicide: "B2-O" manufactured by Japan New Metals Co., Ltd. was classified with a sieve to have an average particle size of 2 μm. Hereinafter, this will be referred to as "WSi2". Nickel: Nickel powder was used as a reagent, which was sieved to have an average particle size of 5 μm. Hereinafter, this will be referred to as "Ni." Conductive titanium oxide: Ishihara Sangyo Kaisha's Sn-doped titanium oxide "ET-500W" with an average particle size of 2 to 3 μm (catalog value) was used. Hereinafter, this will be referred to as "conductive Ti." Alumina: Showa Denko Co., Ltd. fine alumina "A-42-2" with an average particle size (median particle size distribution diameter) of 4.7 μm (catalog value) was used. Hereinafter, this will also be referred to as "alumina". Titanium oxide: "Tipaque(R) CR-95" manufactured by Ishihara Sangyo Kaisha, Ltd., with an average particle size of 0.28 μm (catalog value). Hereinafter, this will be referred to as "TiO2". Aluminum nitride: Tokuyama Corporation's aluminum nitride powder for filler, particle size 1 μm (catalog value), was used. Hereinafter, this will be referred to as "AlN".

[0112] The powder resistivity of the particles in Table 3 was determined as the resistance value when each powder was compressed at 10 MPa at 25°C using a powder resistivity measurement system MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd.

[0113] <Evaluation of the created metal plate> (1. Evaluation of coolant corrosion resistance) The corrosion resistance of the steel sheet to coolant was investigated when it was used in the cooling structure (cooling device) of a battery unit. Specifically, the Al-plated steel sheet was processed by Erichsen to produce a cylindrical cup-shaped product with a diameter of 50 mm and a drawing height of 40 mm. 30 mL of coolant was added to the inside of this cylindrical product, and then the product was sealed with a lid. The coolant used was an aqueous solution of Nissan Motor Co., Ltd.'s long-life coolant diluted with water to 30% by mass. These were left in a thermostatic bath at 90°C for 1000 hours to promote the deterioration of the steel sheet in the coolant-immersed area. In addition, assuming the deterioration of the coolant, a similar test was also conducted using a deteriorated solution in which 800 ppm of formic acid was added to a 30% by mass aqueous solution of the long-life coolant. After the test, the coolant immersed in the cylindrical product was removed and the cylindrical product was dried, and the corrosion state of the coolant-immersed area was observed, and the coolant corrosion resistance was evaluated according to the following criteria. The results are shown in Tables 4 and 5. 5 points: No change in appearance. 4 points: Black discoloration or white rust spots have appeared. 3 points: White rust has occurred, but the area of ​​the part immersed in the coolant where the white rust has occurred is less than 20% of the total area immersed in the coolant. 2 points: White rust occurrence rate is 20% or more but less than 80%. 1 point: White rust occurrence is 80% or more, or red rust has occurred.

[0114] (2. External corrosion resistance test) An external corrosion resistance test was carried out to evaluate the external corrosion resistance of the battery unit (including the cooling structure) at the portion exposed to the outside air. Since electrodeposition coating is generally applied to the portion exposed to the outside air, in the present invention, the external corrosion resistance after electrodeposition coating was evaluated.

[0115] Specifically, the prepared steel plate was cut into pieces measuring 70 mm wide x 150 mm long, and the pieces were degreased, surface-conditioned, and zinc phosphate-treated, and then electrocoated. Specifically, the pieces were degreased by immersing them in a degreaser "Fine Cleaner E6408" manufactured by Nippon Parkerizing Co., Ltd. for 5 minutes at 60°C. The degreased pieces were surface-conditioned by immersing them in "Preparen X" manufactured by Nippon Parkerizing Co., Ltd. for 5 minutes at 40°C. Thereafter, the pieces were immersed in a zinc phosphate conversion agent "Palbond L3065" manufactured by Nippon Parkerizing Co., Ltd. for 3 minutes at 35°C to perform zinc phosphate treatment. The pieces after the zinc phosphate treatment were washed with water and dried in an oven at 150°C. Then, the pieces were electrocoated with an electrocoating paint "Power Float 1200" manufactured by Nippon Paint Co., Ltd. at a thickness of 15 μm per side, and baked in an oven at 170°C for 20 minutes. The electrocoated steel pieces prepared by the above steps were cut with a cutter knife to prepare test pieces.

[0116] A cyclic corrosion test (CCT) was conducted using the prepared test pieces. The CCT mode was conducted in accordance with the automotive industry standard JASO-M609. The surface with cut scratches in the electrocoating film was used as the evaluation surface, and the test piece was placed in a testing machine so that salt water was sprayed on the evaluation surface, and a cyclic corrosion test was conducted.

[0117] The test was carried out for 120 cycles (1 cycle lasting 8 hours), and the state of corrosion from the cut portion was observed to evaluate the external corrosion resistance according to the following criteria. The results are shown in Tables 4 and 5. 5 points: The paint bulge width from the cut part is within 15 mm and there is no red rust. 4 points: The paint bulge width from the cut part is more than 15mm but not more than 20mm, and there is no red rust. 3 points: The paint blister width from the cut part is more than 20 mm and there is no red rust. 2 points: A small amount of red rust has formed on the cut area. 1 point: Red rust has developed on the entire cut area.

[0118] (3. Processability Evaluation) A bending test was conducted using the prepared Al-plated steel sheet. In particular, if cracks occur on the surface when the plated steel sheet is processed, the plating layer breaks and the iron base is exposed to the outside air. Therefore, since there is a concern that corrosion may occur easily from the processed part depending on the processed shape, the workability was evaluated. Specifically, the prepared Al-plated steel sheet was subjected to 180° close bending, the processed part was checked with a 20x magnifying glass, and the workability was evaluated visually. Specifically, the workability was evaluated based on whether or not cracks occurred on the surface. The results are shown in Tables 4 and 5. "-" in Tables 4 and 5 indicates that this evaluation was not conducted because the steel sheet was Zn-plated.

[0119] [Table 4]

[0120] [Table 5]

[0121] <Evaluation of cooling characteristics and adhesive durability in battery packs> (1. Creating a battery pack) A battery pack was produced using the prepared steel sheet. Specifically, the flat plate material that had only been cut was used as the case top cover (top surface) and the flow path top cover. Separately, an Al-plated steel sheet was deep-drawn into a square cylinder by a press machine, and the flange portion was cut after processing to produce the other parts of the battery pack (bottom surface and side surface). The bottom surface of the battery pack was processed to have a width of 375 mm and a length of 2060 mm. During processing, rust-preventive oil was applied to the Al-plated steel sheet, and the oil was removed by alkaline degreasing after processing. The punch shoulder R, die shoulder R, and corner R of the square cylinder shape were all 20 mm. The cooling structure was also produced by pressing. Each R in the cooling structure was 10 mm, and the number of flow paths, flow path width (L), and flow path interval (w) were produced to the values ​​shown in Table 5.

[0122] Next, adhesive was applied to the joints of the cooling structure, and the cooling structure and the upper lid of the flow path were overlapped. The adhesives used were "ThreeBond 2249G" (manufactured by ThreeBond Fine Chemical Co., Ltd.) for the epoxy adhesive, "ThreeBond 1207B" (manufactured by ThreeBond Fine Chemical Co., Ltd.) for the silicone adhesive, "Metal Grip" (manufactured by 3M Japan Ltd.) for the acrylic adhesive, and "ThreeBond 1539" (manufactured by ThreeBond Fine Chemical Co., Ltd.) for the urethane adhesive. Next, the joints on the four sides of the flow path and the upper lid of the flow path were spot welded together at 30 mm on each side. After that, the adhesive was cured according to the curing conditions of each adhesive.

[0123] Next, Shin-Etsu Silicone's "SDP-3540-A" was applied to the entire outer surface of the flow path top cover, the bottom part of the battery pack was attached on top of it as shown in Figure 1, and the gap filler was hardened by leaving it at room temperature for one week. Through the above process, the battery unit shown in Figure 1 was manufactured.

[0124] Next, rubber heaters were laid on the bottom inside the battery pack as a substitute for heat-generating battery cells, and the case was covered with a lid. When the lid was closed, a sealant was applied to the case flange to seal it. Shin-Etsu Silicone's "Sealant 45N" was used as the sealant. The battery pack and the cooling structure were made of the same metal material. In other words, the battery pack, the flow path lid, and the cooling structure were made of the same metal material.

[0125] (2. Battery pack cooling characteristic evaluation test) The battery pack was heated by passing a current through the rubber heater of the battery pack. Here, the current value at which the surface temperature of the rubber heater becomes 50°C was searched in advance, and the current value was passed through the rubber heater as a fixed value. Next, the coolant was passed through the water coolant flow path. The coolant was an aqueous solution obtained by diluting Nissan Motor's long-life coolant liquid with water to 30% by mass. In addition, a hose, a pump, and a chiller were attached to the end of the flow path on both sides of the cooling structure to form a circulation path, and the coolant was circulated within this circulation path. Here, the chiller was controlled so that the temperature of the coolant was 25 to 30°C. Then, the temperature of the rubber heater surface in the case directly above the middle part between the cooling flow paths was measured one hour after the start of the cooling water circulation, and the case where the temperature was 8°C or more lower than when the cooling water was not circulating was evaluated as "A", the case where the temperature drop was less than 8°C and 2°C or more was evaluated as "B", and the case where the temperature drop was less than 2°C was evaluated as "C". The cooling characteristic evaluation test of the battery pack was performed in a room kept at 25°C by air conditioning. The results are shown in Table 6.

[0126] [Table 6]

[0127] (3. Battery pack watertightness evaluation test) A hose, a pump, and a chiller were attached to the end of the flow path of the cooling structure of the battery pack thus fabricated to form a circulation path, and the coolant was circulated in this circulation path. The coolant was an aqueous solution obtained by diluting Nissan Motor's long-life coolant liquid with water to 30% by mass. The chiller was controlled so that the temperature of the coolant was 25 to 30°C. The coolant was circulated for 2000 hours from the start of circulation, during which time the presence or absence of leakage of the coolant from the flow path was confirmed, and watertightness was evaluated. In this example, no leakage of the coolant was confirmed even once during circulation. In Table 6, cases where there was no leakage of the coolant are indicated by "◯".

[0128] As shown in Tables 4 to 6, the examples of the present invention that satisfied the requirements of this embodiment achieved excellent results in all evaluation items. Therefore, it was found that the cooling structure according to this embodiment has excellent corrosion resistance against the coolant (coolant corrosion resistance), cooling capacity, and watertightness, and also has excellent corrosion resistance against the external environment (external corrosion resistance).

[0129] In contrast, in comparative examples that do not satisfy the requirements of this embodiment, such as those that were not plated or those in which the flow passage spacing was narrow and deflection occurred in the flow passages, poor results were obtained in some of the evaluation items.

[0130] Although the preferred embodiment of the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to such an example. It is clear that a person having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention. [Explanation of symbols]

[0131] 1 Cooling structure 10 Battery Pack 10a Bottom part 21 Flow path forming section 22 Joint 25 Water cooling medium channel 26 Flow channel cover 30 Adhesive

Claims

1. A cooling structure having a water coolant passage formed on an outer side of a bottom surface of a battery pack, The cooling structure has a flow path forming portion whose internal space is a flow path for the water coolant, the flow passage forming portion is made of a steel plate having an inorganic coating or a resin coating formed as a chemical conversion coating on an Al-based plated steel plate or a Zn-based plated steel plate, The flow path forming portion is bonded to a bonded member by an adhesive, the member to be joined is either the bottom surface portion or a flow path upper lid that covers the flow path forming portion, the outer edge of the joined member is directly and continuously joined to the outer edge of the cooling structure by an adhesive or an adhesive and a mechanical joint; The distance between the water coolant passages is 20 mm or less. A cooling structure comprising:

2. The cooling structure according to claim 1 , wherein the passage interval is 1 mm or more and 15 mm or less.

3. 3. The cooling structure according to claim 1, wherein the water coolant flow path has a width of 6 mm or more and 60 mm or less.

4. 3. The cooling structure according to claim 1, wherein the water coolant flow path has a width of 6 mm or more and 20 mm or less.

5. 3. The cooling structure according to claim 1, wherein the plating layer of the Al-based plated steel sheet contains Si.

6. The cooling structure according to claim 5 , wherein the Si content of the plating layer of the Al-based plated steel sheet is 2.0 mass % or more and 15 mass % or less.

7. 3. The cooling structure according to claim 1, wherein a coating containing a Zr-based component, a Ti-based component or a Si-based component as a main component is formed on a surface of the Al-based plated steel sheet as a chemical conversion coating.

8. 2. The cooling structure according to claim 1, wherein the inorganic coating on the surface of the Zn-based plated steel sheet contains a Si-based component or a Zr-based component as a main component.

9. 2. The cooling structure according to claim 1, wherein the inorganic coating on the surface of the Zn-based plated steel sheet contains at least one of a V component, a P component, and a Co component as an anti-rust component.

10. The cooling structure according to claim 9, wherein the rust-preventive component is at least one of vanadium oxide, phosphoric acid, and cobalt nitrate.

11. 2. The cooling structure according to claim 1, wherein the inorganic coating on the surface of the Zn-based plated steel sheet is composed of a compound phase containing at least one of a Si—O bond, a Si—C bond, and a Si—OH bond.

12. The cooling structure according to claim 1 , wherein the inorganic coating has a thickness of more than 0 μm and not more than 1.5 μm.

13. The cooling structure according to claim 1 , wherein the inorganic film or the resin film is electrically conductive.

14. The cooling structure according to claim 1 , wherein the resin coating contains a resin, an anti-rust pigment, and a conductive pigment.

15. The resin coating contains, as the conductive pigment, at least one of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles; The conductive pigment has a powder resistivity of 7.0×10 Ω cm or less at 23 to 27° C., and contains at least one element selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W. The cooling structure according to claim 14,

16. 16. The cooling structure according to claim 14, wherein the resin film contains the conductive pigment in a proportion of 1.0 mass % or more and 30 mass % or less.

17. 2. The cooling structure according to claim 1, wherein the adhesive contains at least 10% of any one of an epoxy resin, a silicone resin, an acrylic resin, and a urethane resin.

18. 2. The cooling structure according to claim 1, wherein the thickness of the Al-based plated steel sheet or the Zn-based plated steel sheet on which an inorganic coating or a resin coating is formed as a chemical conversion coating is 0.4 mm or more and 1.2 mm or less.

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