Cooling structure

Abstract

To provide a cooling structure which is excellent in corrosion resistance to cooling liquid (cooling liquid corrosion resistance), corrosion resistance to an external environment (external corrosion resistance), and cooling capability.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 and having a rectangular shape has a flow channel formation part whose internal space is the flow channel for the water cooling medium, and a flow channel upper lid covering the flow channel formation part, wherein the flow channel formation part and the flow channel upper lid are composed of steel plates 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 upper lid and the flow channel formation part are bonded to each other by an adhesive, and at least two sides of the outer edge part of the flow channel upper lid and the outer edge part of the flow channel formation part are caulked and joined to each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In the automotive industry, the shift to electric vehicles (EVs) is progressing in order to reduce CO2 emissions. Among the components used in EVs, battery packs that house the battery cells that serve as the power source require a cooling structure to prevent battery deterioration due to temperature rise. Until now, air-cooled cooling structures have been the mainstream, but in recent years, as battery capacities have increased, water-cooled structures with their high cooling capacity have increasingly been adopted. Components in water-cooled battery packs are generally made of iron or aluminum. 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] Iron is superior to aluminum in terms of strength and cost, but is inferior in corrosion resistance. Because the water coolant flow path uses an aqueous solution of LLC (long-life coolant) containing organic components, the components that make up the water coolant flow path must have high corrosion resistance against the coolant (coolant corrosion resistance). Furthermore, if the components that make up the water coolant flow path are installed on the outside of the battery pack, they will be located on the underside of the vehicle, so corrosion resistance is also required on the exterior (external corrosion resistance). While electrodeposition coating is commonly used to improve external corrosion resistance, avoiding it is recommended to reduce CO2 emissions during the electrodeposition coating process. When welding plated steel sheets, the steel is exposed at the weld, so corrosion resistance cannot be guaranteed without electrodeposition coating. Furthermore, without electrodeposition coating, the steel edge is exposed, making corrosion resistance unsatisfactory.

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

[0006] In order to solve the above problems, the present disclosure employs the following means. (1) A cooling structure according to one embodiment of the present disclosure is a rectangular cooling structure having a water coolant flow path formed on the outside of a bottom surface portion of a battery pack, the cooling structure having a flow path forming portion whose internal space is the water coolant flow path, and a flow path upper lid covering the flow path forming portion, the flow path forming portion and the flow path upper lid 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 upper lid and the flow path forming portion being joined with an adhesive, and at least two sides of the outer edge of the flow path upper lid and the outer edge of the flow path forming portion being crimped. (2) In the cooling structure described in (1) above, the water coolant flow paths may be spaced apart by 20 mm or less. (3) 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 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 of 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-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-preventing 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 an Si-O bond, an Si-C bond, and an Si-OH bond. (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 resin coating may contain a resin, an anti-rust pigment, and a conductive pigment. (14) In the cooling structure described in (1) above, the resin coating contains at least one conductive pigment selected from the group consisting of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles, and the conductive pigment has a powder resistivity of 7.0×10 Ωcm or less at 23 to 27°C and may contain at least one element selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W. (15) In the cooling structure described in (13) or (14) above, the resin film may contain the conductive pigment in a proportion of 1.0 mass % or more and 30 mass % or less. (16) In the cooling structure described in (1) above, the adhesive may contain 10% or more of any of epoxy resin, silicone resin, acrylic resin, and urethane resin. (17) In the cooling structure described in (1) above, the end faces of the flow path forming portion and the end faces of the flow path upper cover may be covered with Al-based plating or Zn-based plating at the outer edge of the side of the cooling structure that is not crimped and joined. (18) The cooling structure described in (1) above may have the end faces of the flow path forming portion and the end faces of the flow path upper cover covered with the adhesive at the outer edge of the side of the cooling structure that is not crimped and joined. (19) The cooling structure described in (1) above may have the end faces of the flow path forming portion and the end faces of the flow path upper cover painted at the outer edge of the side of the cooling structure that is not crimped and joined. (20) In the cooling structure described in (1) above, the thickness of the steel sheet on which an inorganic coating or a resin coating is formed as a chemical conversion coating on the Al-based plated steel sheet or the Zn-based plated steel sheet may be 0.4 mm or more and 1.2 mm or less. [Effects of the Invention]

[0007] According to the above-described aspects of the present invention, it is possible to provide a cooling structure that is excellent in corrosion resistance against a coolant (coolant corrosion resistance), corrosion resistance against the external environment (external corrosion resistance), and cooling capacity. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view illustrating a cooling structure according to an embodiment of the present disclosure. [Figure 2] FIG. 10 is a cross-sectional view showing another example of the cooling structure according to the embodiment. [Figure 3] FIG. 10 is a cross-sectional view showing another example of the cooling structure according to the embodiment. [Figure 4] 2 is a cross-sectional view illustrating one end of the cooling structure of FIG. 1. FIG. [Figure 5A] FIG. 3 is a cross-sectional view showing an example of one end portion of the cooling structure according to the embodiment. [Figure 5B] FIG. 3 is a cross-sectional view showing an example of one end portion of the cooling structure according to the embodiment. [Figure 5C] FIG. 3 is a cross-sectional view showing an example of one end portion of the cooling structure according to the embodiment. [Figure 5D] FIG. 3 is a cross-sectional view showing an example of one end portion of the cooling structure according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[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 designated by the same reference numerals, and their repeated description may be omitted. However, the present disclosure is not limited to the configuration disclosed in this embodiment, and various modifications are possible without departing from the spirit of the present disclosure. In the following description, the direction perpendicular to the plane of FIG. 1 may be referred to as the Y direction, the direction in which multiple flow path forming sections 21 (described later) are arranged may be referred to as the X direction, and the direction perpendicular to both the X and Y directions may be referred to as the Z direction. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" do not fall within the numerical range.

[0010] <1. Overall configuration of the cooling structure> First, the overall configuration of the 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 the bottom surface 10a of the 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. Because an LLC (long life coolant) solution containing organic components flows as a coolant through the water coolant flow paths 25 of the cooling structure 1, the cooling structure 1 is required to have high coolant corrosion resistance. The cooling structure 1 is also required to have external corrosion resistance against the external environment by suppressing exposure of the end faces of the steel plate. Furthermore, the cooling structure 1 is required to improve cooling capacity by narrowing the flow path spacing of the water coolant flow paths 25 to increase the liquid surface area. In the present disclosure, the term "exposed end face of a steel sheet" means that the end face of a steel substrate that has not been treated with electrodeposition coating or the like is exposed to the outside. In the present disclosure, the end face that has not been treated with electrodeposition coating or the like may be referred to as a "substrate end face."

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

[0013] The cooling structure 1 has a flow path forming section 21 whose internal space is a water refrigerant flow path 25, and a flow path upper lid 26 that covers the flow path forming section 21. The cooling structure 1 has a plurality of water refrigerant flow paths 25. The plurality of water refrigerant flow paths 25 are aligned in the X direction to form a plurality of flow path forming sections 21. When viewed from the Y direction, adjacent flow path forming sections 21 are connected via joints 22. The joints 22 are sections between adjacent flow path forming sections 21. The joints 22 are joined to the flow path upper lid 26 via adhesive 30. In this embodiment, as shown in FIG. 1 , the flow path forming section 21 has a rectangular cross section when viewed from the Y direction, and the interior is a space. This space is the water refrigerant flow path 25.

[0014] The flow path upper lid 26 is disposed between the flow path forming portion 21 and the battery pack 10. The flow path upper 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 upper lid 26.

[0015] 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.

[0016] In this embodiment, the water refrigerant 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 refrigerant flow path 25 is not limited to this example, and it may extend in the X direction. Furthermore, the water refrigerant flow path 25 may be curved or may be U-shaped in a plan view.

[0017] The flow path forming portion 21 and the flow path lid 26 are made of a steel sheet on which an inorganic coating or a resin coating 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% by mass Si-plated steel sheet. An example of a Zn-plated steel sheet is a Zn-0.2% by mass Al-plated steel sheet, a Zn-0.09% by mass Al-plated steel sheet, a Zn-6% by mass Al-3% by mass Mg-plated steel sheet, or a Zn-11% by mass Al-3% by mass Mg-0.2% by mass Si-plated steel sheet. A particularly preferred material among Zn-plated steel sheets is a zinc (Zn)-aluminum (Al)-magnesium (Mg)-based alloy-plated steel sheet. Note that, hereinafter, a "steel sheet on which an inorganic coating or a resin coating is formed as a chemical conversion coating" may be referred to as a "chemically treated steel sheet." Chemically treated Al- and Zn-plated steel sheets have high corrosion resistance to coolants. In particular, chemically treated Al- and Zn-plated steel sheets have excellent corrosion resistance to LLC aqueous solutions.

[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 drain pipe are connected to approximately both ends of the water refrigerant flow path 25, respectively, or are arranged according to the 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. After being cooled by a cooling device (not shown), the refrigerant is supplied again from the supply pipe to the water refrigerant flow path 25. In this manner, the coolant flows through the circulation path and the water coolant flow path 25. After being cooled in the circulation path, the coolant flows through the water coolant flow path 25. The coolant absorbs heat from the battery pack 10 while flowing through the water coolant flow path 25. The coolant is then introduced into the circulation path again. That is, the coolant 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 flow path forming portion 21 and the flow path lid 26 are required to have not only external corrosion resistance but also coolant corrosion resistance. In this embodiment, the flow path forming portion 21 and the flow path lid 26 are made of Al-based plated steel sheet or Zn-based plated steel sheet that has been chemically treated. Al-based plated steel sheet and Zn-based 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, which makes it possible to suppress a decrease in thermal conductivity and the elution of components of the battery pack 10 or the cooling structure 1 into the coolant.

[0020] The flow path upper lid 26 and the flow path forming portion 21 are joined by an adhesive 30. More specifically, the flow path upper lid 26 and the joint portion 22 are joined by the adhesive 30. 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 50% or more of any one of these main resin components, and more preferably 10% or more. An adhesive 30 having such a main component can suppress deterioration of the adhesive 30 and corrosion of the joint portion 22 due to coolant liquid, and ensure watertightness. The content of the resin main component of the adhesive 30 is measured by a thermogravimetric analyzer.

[0021] At least two sides of the outer edge 42 of the flow path upper cover 26 and the outer edge 27 of the flow path forming portion 21 are crimped together. The crimped joint is provided over the entire length of each side. In this embodiment, as shown in FIG. 1, the outer edge portions 42, 27 on both sides are crimped together when viewed from the Y direction. The crimped joint may be, for example, the outer edge portions 42, 27 on both sides when viewed from the X direction. FIG. 4 shows an example of a crimping method for one end of the cooling structure 1. In this example, the battery pack 10 (not shown in FIG. 4) is disposed inside the portion to be crimped. FIG. 4A shows a state in which the outer edge 42 of the flow path upper lid 26 and the outer edge 27 of the flow path forming portion 21 are joined with the adhesive 30. FIG. 4B shows a state in which the outer edge 42 of the flow path upper lid 26 is folded from the state shown in FIG. 4A so as to enclose the outer edge 27 of the flow path forming portion 21. At this time, the outer edge 42 may be folded along with the adhesive 30. FIG. 4C shows a state in which the outer edge 42 is further folded to complete the crimping. In this way, at least two sides of the outer edge 42 of the flow path upper lid 26 and the outer edge 27 of the flow path forming portion 21 are crimped, and a crimped joint 71 is formed in the cooling structure 1. The crimping method is not limited to the crimping method shown in FIG. 4, as long as it is a method of joining outer edge portions together by utilizing plastic deformation.

[0022] The cooling structure 1 according to this embodiment is configured such that at least two sides of the outer edge 42 of the flow path lid 26 and the outer edge 27 of the flow path forming portion 21 are crimped together. This results in the cooling structure 1 being configured to prevent exposure of the end face 44 of the flow path lid 26 and the end face 43 of the flow path forming portion 21. The cooling structure 1 is configured to prevent exposure of the base end faces of the flow path lid 26 and the flow path forming portion 21. Therefore, the cooling structure 1 can prevent exposure of the end faces (43, 44) of the steel plate even without electrocoating, ensuring external corrosion resistance to the external environment.

[0023] 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 portions 21 is rectangular, so the distance between the ends of the flow path forming portions 21 in the width direction (flow path interval) w is the distance between the side portions 21b of adjacent flow path forming portions 21. In the examples shown in FIGS. 2 and 3, the boundary portions between the flow path forming portions 21 and the joint portions 22 are the ends of the flow path forming portions 21 in the width direction. By setting the flow path spacing w between the water coolant flow paths 25 to 20 mm or less, the width of the water coolant flow paths 25 can be increased, thereby increasing the contact area between the water coolant flow paths 25 and the bottom surface portion 10a, i.e., the contact area between the coolant and the battery pack 10. Therefore, in this embodiment, the cooling efficiency of the battery pack 10 can be improved. In particular, in this embodiment, the flow path forming portion 21 and the flow path upper cover 26 are made of a steel plate that has been subjected to chemical conversion treatment on an Al-based plated steel plate or a Zn-based plated steel plate. The heat transfer characteristics of a steel plate that has been subjected to chemical conversion treatment on an Al-based plated steel plate or a Zn-based plated steel plate include the fact that heat is easily absorbed by the coolant in the portions of the flow path forming portion 21 and the flow path upper cover 26 directly above the portions that are in contact with the coolant. Therefore, by increasing the contact area between the coolant and the flow path forming portion 21 and the flow path upper cover 26, the area to which heat is transferred can be increased, thereby improving cooling efficiency.

[0024] The passage spacing w between the water coolant passages 25 is preferably 1 mm or more, and preferably 15 mm or less. By setting the passage spacing w between the water coolant passages 25 to 1 mm or more, the width (length in the X direction) of the joint 22 can be ensured, making it easier to ensure the joint strength with the passage lid 26. By setting the passage spacing w between the water coolant passages 25 to 15 mm or less, the contact area between the coolant and the battery pack 10 can be increased, and cooling efficiency can be further improved. The flow path interval w is measured at the longest and shortest points of the flow path interval w in the water coolant flow path 25 using a vernier caliper.

[0025] To efficiently cool the battery pack 10, it is necessary to increase the area ratio of the flow path that contacts 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, and more preferably 0.40 or more. This increases the contact area between the coolant and the battery pack 10, thereby improving the cooling efficiency of the battery pack 10.

[0026] The ratio of the contact area between the water coolant flow path 25 and the bottom surface portion 10a can be increased by increasing 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, i.e., the distance between the side surface portions 21b of the flow path forming portion 21. In the example shown in FIGS. 2 and 3, the boundary portions between the flow path forming portion 21 and the joint portion 22 are the widthwise ends of the flow path forming portion 21, and the flow path width L is the distance between the widthwise ends of the flow path forming portion 21. If the flow path width L is too wide, the stress applied to the joint portion 22 will be large, or the flow of the coolant will not be limited to the longitudinal direction of the flow path and will be unstable. 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 this is the range in which the coolant can flow stably. To further stabilize the flow of the coolant, 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 longest and shortest points of the flow path width L in the water coolant flow path 25.

[0027] If the portion not in contact with the coolant is too far from the end of the channel in the X direction, the cooling effect of the coolant is reduced. Therefore, it is preferable that the end of the water coolant channel 25 that is not in contact with the coolant be short. Specifically, in FIG. 1 , the longest distance D in the X direction from the end of the water coolant channel 25 to the portion of the bottom surface 10a of the battery pack 10 that is not in contact with the water coolant channel 25 is short. The longest distance D is the distance from the end of the water coolant channel 25 to the nearest water coolant channel 25. Specifically, this longest distance is 10 mm or less, more preferably 7.5 mm or less. Therefore, to improve the contact area ratio of the water coolant channel 25 without excessively increasing the channel width L and to shorten the distance between the portion not in contact with the coolant and the water coolant channel 25, it is necessary to narrow the channel spacing w. In other words, the channel spacing w is preferably 20 mm or less, more preferably 15 mm or less. To satisfy the shape of the water coolant channel 25, it is suitable to bond the water coolant channel 25 with an adhesive. By bonding with an adhesive, the flow path interval w can be made the same as the bonded portion. The longest distance D is measured at one point of the longest distance in the water coolant flow path 25 using a vernier caliper.

[0028] The height of the water refrigerant flow path 25, i.e., the distance h in the thickness direction (Z direction) of the water refrigerant 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 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 refrigerant 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 processability for forming the flow path. The distance h is measured by using a vernier caliper to measure the longest and shortest distances in the water coolant flow path 25.

[0029] The flow path forming portion 21 is manufactured 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, for example, on a single Al-based plated steel sheet or a Zn-based plated steel sheet. Therefore, the flow path forming portion 21 can be manufactured inexpensively and easily. The thickness of the steel plate on which the inorganic coating or resin coating is formed as a chemical conversion coating on the Al-plated or Zn-plated steel plate constituting the flow path forming portion 21 and the flow path top cover 26 is not particularly limited, but is preferably 0.4 mm to 1.2 mm, and more preferably 0.4 mm to 1.0 mm. In this case, the strength of the cooling structure 1 can be increased while improving workability (the 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 or Zn-plated steel plates that have been chemically treated for each water refrigerant flow path 25. In this example, the chemically treated Al-plated or Zn-plated steel plates are processed (e.g., bent, drawn, etc.) to form the flow path forming portions 21 corresponding to each water refrigerant flow path 25, and these are then joined to the battery pack 10. The thickness of the steel plate is measured at three locations using a vernier caliper and calculated from the maximum and minimum values ​​of the three locations.

[0030] The bottom surface portion 10a of the battery pack 10 may be made of a steel plate that has been chemically treated with an Al-based plated steel plate or a Zn-based plated steel plate. The thickness of the plate is not particularly limited, but is preferably 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 made thin while maintaining its strength. This reduces the distance between the coolant and the battery pack 10, thereby improving the cooling efficiency of the battery pack 10 and also improving the cooling responsiveness of the battery pack 10. 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 deriving the maximum and minimum values ​​at the three locations. Although there are no particular limitations on the materials for 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 chemically treated, 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 chemically treated, similar to the bottom surface portion 10a.

[0031] In this embodiment, the cooling structure 1, which is exposed to the external environment and coolant, is made of a steel plate that has been chemically treated with an Al-based plated steel plate or a Zn-based plated steel plate, 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.

[0032] <2. Composition of Al-based coated steel sheets> Next, an example of an Al-based plated steel sheet that constitutes the battery pack 10 and the flow path forming portion 21 will be described in detail.

[0033] An 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% by mass or more and 15% by 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% by mass or more, an Al content of 70 to 98% by mass, and a Si content of 2.0% by mass or more and 15% by mass or less. A more preferred range for the Si content is 3.0% by mass or more and 15% by mass or less. By keeping 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 it is preferably formed on both sides.

[0034] Trace amounts of Fe, Ni, Co, etc. may be present as impurity elements in the plating layer. Furthermore, Mg, Sn, misch metal, Sb, Zn, Cr, W, V, Mo, etc. may be added as necessary. There are no particular restrictions 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.

[0035] The composition of the base steel used for the Al-based plated steel sheet is not limited, 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, and alloy steel.

[0036] 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.

[0037] To further enhance the external corrosion resistance and coolant corrosion resistance of the Al-based plated steel sheet, a chemical conversion 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) is preferably formed on the surface (either one side or both sides may be used) of the Al-based plated steel sheet. The coating may also contain an organic component.

[0038] Examples of chemical conversion treatment films are listed 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 treatment films listed in these publications can be suitably used as the chemical conversion treatment film of this embodiment. Here, an overview of the chemical conversion treatment film will be described.

[0039] The first example of the chemical conversion coating is an example of a coating containing a Zr-based component as the main component, consisting only of Zr, F, P, C, O, N, and H, and containing no organic substances with a number-average molecular weight of 200 or more. The components of the chemical conversion coating are adjusted so that the mass ratio of Zr to F, Zr / F, is 1.0 to 10.0, the mass ratio of Zr to P, Zr / 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 sources of each component of the chemical conversion coating are one or more inorganic acids and / or their ammonium salts selected from the group consisting of carbonic acid, phosphoric acid, and hydrofluoric acid, and zirconium-containing complex compounds excluding zirconium hydrofluoric acid.

[0040] The second example of the chemical conversion coating is 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 with 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.

[0041] 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.

[0042] Examples of the zirconium compound include zirconyl nitrate, zirconyl acetate, zirconyl sulfate, ammonium zirconyl carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and zirconium acetate.

[0043] Examples of 2- to 6-linked phosphate esters of myo-inositol include myo-inositol diphosphate ester, myo-inositol triphosphate ester, myo-inositol tetraphosphate ester, myo-inositol pentanephosphate ester, and myo-inositol hexanephosphate ester.

[0044] 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 examples include Snowtex C, Snowtex O, Snowtex N, Snowtex S, Snowtex UP, Snowtex PS-M, Snowtex PS-L, Snowtex 20, Snowtex 30, and Snowtex 40 (all manufactured by Nissan Chemical Industries, Ltd.), Adelite AT-20N, Adelite AT-20A, and Adelite AT-20Q (all manufactured by Asahi Denka Kogyo Co., Ltd.).

[0045] The vapor 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).

[0046] The third example of the chemical conversion coating is 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 / m of zirconium per side of the Al-based plated steel sheet. 2 , vanadium 0.1 to 300 mg / m², phosphate compounds 0.3 to 450 mg / m² (PO₄ equivalent) 2 Furthermore, the content of chromium or chromium compounds in the chemical conversion coating film is 0.1 mg / m 2 The following substances contain fluorine or fluorine compounds with a fluorine content of 0.1 mg / m 2 The details are as follows.

[0047] Examples of the zirconium compound include zirconyl nitrate, zirconyl acetate, zirconyl sulfate, ammonium zirconyl carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and zirconium acetate.

[0048] 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.

[0049] 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).

[0050] The vapor 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).

[0051] The phosphate compound may contain phosphate ions, and 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.

[0052] 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, lignosulfonic acid, and polyphenols; and synthetic polymers such as polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, polyethyleneimine, and water-soluble nylon.

[0053] The chemical conversion coating may contain, as an additional component, a lubricity-imparting component made of at least one of polyolefin wax and paraffin wax.

[0054] A fourth example of a chemical conversion coating is a coating containing a Ti-based component as the main component, 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 coatings with excellent properties. Examples of coatings containing a Ti-based component as the main component include a coating containing a composite of an oxide (TiO2) and a hydroxide (Ti(OH)4). In these coatings, a fluoride of Ti, such as XnTiF6 (X: alkali metal, alkaline earth metal, or NH4, n = 1 or 2), TiF4, or another fluoride, coexists.

[0055] A fifth example of a chemical conversion coating is a coating primarily containing a silicon-based component, specifically an organosilicon compound (silane coupling agent). The organosilicon compound is obtained by blending a silane coupling agent (A) containing one amino group in its molecule with a silane coupling agent (B) containing one glycidyl group in its molecule in a solids 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 (where R1, R2, and R3 each independently represent an alkoxy group or a hydroxyl group, with at least one representing an alkoxy group), and one or more hydrophilic functional groups (b) selected from the group consisting of a hydroxyl group (different from those that may be contained in functional group (a)) and an amino group, and has an average molecular weight of 1,000 to 10,000.

[0056] A sixth example of a chemical conversion coating is an example of a coating containing a silicon-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 within its structure. Here, "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 Si and O bonds, with 3 to 8 Si-O repeating units.

[0057] 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 solids mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound (W) thus obtained preferably 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 of R1, R2, and R3 represents an alkoxy group) and one or more hydrophilic functional groups (b) selected from the group consisting of a hydroxyl group (if the functional group (a) contains a hydroxyl group, the functional group (a) is separate from the hydroxyl group) and an amino group, and has an average molecular weight of 1,000 to 10,000.

[0058] Of course, examples of the chemical conversion coating of this embodiment are not limited to those described above, and for example, the chemical conversion coatings listed in the examples described below can also be suitably used.

[0059] 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.

[0060] <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.

[0061] Zn-based plated steel sheets are steel sheets 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 the plating layer, or Zn-based plated steel sheets with inorganic substances such as silica, alumina, and titania dispersed therein, 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.

[0062] Furthermore, an inorganic coating or a resin coating is formed on the surface of the Zn-plated steel sheet (it may be on one side only, but preferably on both sides) as a chemical conversion coating. The inorganic coating contains a Si-based component or a Zr-based component as the main component (for example, 50 mass % or more). The inorganic coating may also contain an organic component.

[0063] The inorganic coating is preferably composed of a compound phase containing one or more of Si-O bonds, Si-C bonds, and Si-OH bonds. The compound phase preferably contains an acrylic resin, as described below. When these requirements are met, the adhesion of the chemical conversion coating can be improved, thereby improving the external corrosion resistance and coolant corrosion resistance of the processed portion of the Zn-based plated steel sheet. The inorganic coating also preferably contains at least one of V, P, and Co as a rust-preventing component. The rust-preventing component of the inorganic coating is preferably one or more of vanadium oxide, phosphoric acid, and cobalt nitrate. The thickness of the inorganic coating is preferably greater than 0 μm and less than or equal to 1.5 μm. In this case, the adhesion of the chemical conversion coating can be further improved.

[0064] The resin coating preferably contains a resin, an anti-rust pigment, and a conductive pigment. Furthermore, the resin coating preferably contains one or more conductive pigments selected from the group consisting of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles. The conductive pigment preferably has a powder resistivity of 7.0 × 10 Ωcm or less at 23 to 27°C and contains one or more constituent elements selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W. Furthermore, the resin coating preferably contains the conductive pigment in a proportion of 1.0 mass% to 30 mass%. Furthermore, the average thickness of the resin coating 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 coating. When any one or more of these requirements are satisfied, the external corrosion resistance and coolant corrosion resistance of the Zn-based plated steel sheet can be further improved.

[0065] 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.

[0066] The first example of the chemical conversion coating is an inorganic coating, and is a chemical conversion coating containing an organosilicon compound (silane coupling agent) as the 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 solids 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, with at least one representing an alkoxy group), and one or more hydrophilic functional groups (b) selected from hydroxyl groups (other than those that may be contained in functional group (a)) and amino groups, and has an average molecular weight of 1,000 to 10,000.

[0067] In a 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 contained in the chemical conversion coating as at least one component selected from the group consisting of cobalt sulfate, cobalt nitrate, and cobalt carbonate. Examples of vanadium compounds include vanadium pentoxide (VO), metavanadate (HVO), ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride (VOCl), vanadium trioxide (VO), vanadium dioxide (VO), vanadium oxide, vanadium oxysulfate (VOSO), vanadium oxyacetylacetonate (VO(OC(=CH)CHCOCH)), vanadium acetylacetonate (V(OC(=CH)CHCOCH)), vanadium trichloride (VCl), and phosphorus vanadomolybdic acid. It is also possible to use a pentavalent vanadium compound reduced to a tetravalent or divalent vanadium compound 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 phosphate group, and a phosphonate group.

[0068] A second example of a chemical conversion coating is an inorganic coating, which contains an organosilicon compound (silane coupling agent) as a main component. The organosilicon compound has a cyclic siloxane structure within its structure. Here, "cyclic siloxane bond" refers to a cyclic structure having a continuous Si-O-Si bond, composed only of Si and O bonds, with 3 to 8 Si-O repeating units.

[0069] 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 solids mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound (W) thus obtained preferably 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 of R1, R2, and R3 represents an alkoxy group) and one or more hydrophilic functional groups (b) selected from the group consisting of a hydroxyl group (if the functional group (a) contains a hydroxyl group, the functional group (a) is separate from the hydroxyl group) and an amino group, and has an average molecular weight of 1,000 to 10,000.

[0070] In a second example, the Zr-based component is contained in the chemical conversion coating as a zirconium compound. Examples of zirconium compounds include zirconium hydrofluoric acid, zirconium ammonium fluoride, zirconium sulfate, zirconium oxychloride, zirconium nitrate, and zirconium acetate. Among these, zirconium compounds are preferably zirconium hydrofluoric acid. When zirconium hydrofluoric acid is used, better corrosion resistance and paintability can be obtained.

[0071] 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, and is contained in the chemical conversion coating. Examples of vanadium compounds include vanadium pentoxide VO, metavanadate HVO, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl, vanadium trioxide VO, vanadium dioxide VO, vanadium oxide, vanadium oxysulfate VOSO, vanadium oxyacetylacetonate VO(OC(=CH)CHCOCH), vanadium acetylacetonate V(OC(=CH)CHCOCH), vanadium trichloride VCl, and phosphorus vanadomolybdic acid. It is also possible to use a pentavalent vanadium compound reduced 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 phosphate group, and a phosphonate group.

[0072] Examples of the phosphate compound include phosphoric acid, ammonium phosphate, potassium phosphate, and sodium phosphate. Among these, phosphoric acid is more preferable as the phosphate compound. When phosphoric acid is used, better corrosion resistance can be obtained.

[0073] A third example of a chemical conversion coating is an inorganic coating, and contains an acrylic resin, zirconium, vanadium, phosphorus, and cobalt. More specifically, the chemical conversion coating contains particulate acrylic resin (resin particles) and an inhibitor phase. The acrylic resin is preferably a resin containing a polymer of a (meth)acrylic acid alkyl ester, and may be a polymer obtained by polymerizing only a (meth)acrylic acid alkyl ester, or a copolymer obtained by polymerizing a (meth)acrylic acid alkyl ester with other monomers. "(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.

[0074] The fourth example of the chemical conversion 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.

[0075] 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 all the monomer components 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 chemical conversion treatment film.

[0076] Examples of the vanadium compound include vanadium compounds with a valence of 2 to 4. More specifically, for example, vanadium pentoxide (V2O5), metavanadic acid (HVO3), ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride (VOCl3) and other vanadium compounds with a valence of 5 reduced to 2 to 4 with a reducing agent, vanadium trioxide (V2O3), vanadium dioxide (VO2), vanadium oxy sulfate (VOSO4), vanadium oxy 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 4 to 2.

[0077] Examples of phosphorus compounds include inorganic acid anions having an acid group containing phosphorus, and organic acid anions having an acid group containing phosphorus. Examples of 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.

[0078] Examples of organic acid anions having a phosphorus-containing acid group 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.

[0079] Examples of the cobalt compound include cobalt sulfate, cobalt nitrate, and cobalt carbonate.

[0080] A fifth example of the chemical conversion coating is a resin coating, which contains at least one conductive pigment selected from the group consisting 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 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.

[0081] Examples of intermetallic compounds include ferrosilicon and ferromanganese. Examples of conductive oxide particles that can be used include materials that are conductive by doping impurities into the oxide crystal lattice (doped conductive oxides) or oxides whose surfaces are modified with a conductive substance. Examples of the former include commonly 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.). Examples of the latter include commonly known zinc oxide or silica modified with SnO2, which has conductivity. Doped conductive oxides are preferred as conductive oxides, and Al-doped zinc oxide is a preferred doped conductive oxide.

[0082] Conductive non-oxide ceramic particles are composed of ceramics made of oxygen-free elements or compounds. Examples of conductive non-oxide ceramic particles include boride ceramics, carbide ceramics, nitride ceramics, and silicide ceramics. Boride ceramics, carbide ceramics, nitride ceramics, and silicide ceramics are non-oxide ceramics whose main non-metallic constituent elements are boron (B), carbon (C), nitrogen (N), and silicon (Si), respectively. These commonly known non-oxide ceramics may contain one or more elements selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, and W. Furthermore, the following non-oxide ceramics are more preferred as non-oxide ceramic particles in terms of availability as industrial products, stable distribution in domestic and international markets, price, electrical resistivity, and other factors. 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.

[0083] A sixth example of the chemical conversion coating is a resin coating, which contains a resin having urethane bonds and conductive particles (conductive pigments). The resin having urethane bonds is an organic resin obtained from a film-forming resin raw material that includes (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.

[0084] (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.

[0085] 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.

[0086] 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 hydroxydivalinic 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, and polypropylene glycol. Examples of the polyol include aliphatic ones 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 ones 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.

[0087] Examples of polyols having at least three OH groups include glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, pentaerythritol, diglycerin, and ethylene oxide adducts, propionoxide adducts, and ε-caprolactone adducts using these polyols as initiators.

[0088] 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 methyl 2,4-cyclohexane diisocyanate, methyl 2,6-cyclohexane diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 1,3 ... 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'-tetramethylmetaxylylene diisocyanate, 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 compounds include triisocyanates such as 6-diisocyanatocaproate, blocked tetraisocyanates such as 4,4'-diphenylmethylmethane-2,2',5,5'-tetraisocyanate, blocked derivatives of isocyanate compounds such as dimers, trimers, biurets, allophanates, carbodiimides, polymethylene polyphenyl polyisocyanates (crude MDI, c-MDI, polymeric MDI), and crude TDI, as well as blocked prepolymers having NCO groups at their terminals obtained by reacting these compounds with active hydrogen compounds.

[0089] The conductive particles are corrosion-resistant particles made of an alloy or compound containing 50% or more by mass of Si, or a composite thereof. The conductive particles are preferably ferrosilicon. Anti-rust pigments may also be added to the chemical conversion coating. Examples of anti-rust pigments include well-known anti-rust pigments, such as hexavalent chromates such as strontium chromate and calcium chromate. 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.

[0090] Of course, examples of the chemical conversion coating of this embodiment are not limited to those described above, and for example, the chemical conversion coatings listed in the examples described below can also be suitably used.

[0091] The method for forming the above-mentioned chemical conversion coating is not particularly limited, and it is sufficient to apply a chemical conversion treatment solution (coating treatment solution) corresponding to each of the above compositions to a Zn-based plated steel sheet by a known method, and then bake and dry it. Note that one example of a preferred combination of a Zn-based plated steel sheet and a chemical conversion coating is the combination of a Zn-Al-Mg plated steel sheet and an inorganic coating containing a Si-based component as a main component.

[0092] In the above description, a configuration has been described in which at least two sides of the outer edge 42 of the flow path upper cover 26 and the outer edge 27 of the flow path forming portion 21 are crimped together. Below, the outer edge of the side that is not crimped together will be described. Examples of suppressing exposure of the base end surface of the steel sheet are shown in Figures 5A to 5D.

[0093] As shown in FIGS. 5A and 5B, the end faces 43 of the flow path forming portion 21 and the end faces 44 of the flow path upper covers 26 at the outer edges of the cooling structure 1 that are not crimped may be covered with an Al-based plating 51 or a Zn-based plating 52. FIG. 5A shows the state in which the Al-based plating 51 or the Zn-based plating 52 is thickly applied to the surfaces of the end faces 43 and 44. The thickness of the Al-based plating 51 or the Zn-based plating 52 applied to the surfaces of the end faces 43 and 44 is preferably 0.02 mm to 0.1 mm, more preferably 0.03 mm to 0.08 mm. FIG. 5B shows the state in which the Al-based plating 51 or the Zn-based plating 52 is applied in a planar manner to the surfaces of the end faces 43 and 44. The Al-based plating 51 or the Zn-based plating 52 preferably covers 10% or more of the end faces 43 and 44. The plating applied to the end face 43 of the flow path forming part 21 is preferably a plating that has been chemically treated in the flow path forming part 21. The plating applied to the end face 44 of the flow path upper cover 26 is preferably a plating that has been chemically treated in the flow path upper cover 26.

[0094] 5C , the end face 43 of the flow path forming portion 21 and the end face 44 of the flow path lid 26 may be covered with adhesive 30 at the outer edge of the side of the cooling structure 1 that is not crimped. In this example, the adhesive 30 that bonds the flow path forming portion 21 and the flow path lid 26 overflows onto the end face 43 of the flow path forming portion 21 and the end face 44 of the flow path lid 26, thereby covering the end faces 43, 44. The thickness of the adhesive 30 applied to the surfaces of the end faces 43, 44 is preferably 5 μm or more and 5 mm or less, and more preferably 10 μm or more and 3 mm or less. It is preferable that the adhesive 30 cover the entire end faces 43, 44.

[0095] As shown in FIG. 5D, the end face 43 of the flow path forming portion 21 and the end face 44 of the flow path lid 26 may be painted at the outer edge of the side of the cooling structure 1 that is not crimped. In this example, the end face 43 of the flow path forming portion 21 and the end face 44 of the flow path lid 26 are painted with a coating agent 52. As shown in FIG. 5D, the coating agent 52 may also be applied to the adhesive 30 between the flow path forming portion 21 and the flow path lid 26. The coating agent 52 may be, for example, rust-proof fine urethane U100 (manufactured by Nippon Paint Co., Ltd.). The thickness of the coating agent 52 applied to the surfaces of the end faces 43, 44 is preferably 5 μm to 1 mm, more preferably 10 μm to 600 μm. It is preferable that the coating agent 52 completely covers the end faces 43, 44.

[0096] 5A to 5D, the cooling structure 1 is configured to prevent exposure of the end surface 44 of the flow path upper cover 26 and the end surface 43 of the flow path forming portion 21. Therefore, even without electrocoating, the cooling structure 1 can prevent exposure of the base end surfaces (43, 44) of the steel plate, ensuring external corrosion resistance against the external environment. The configuration for suppressing exposure of the base end surface of the steel sheet is not limited to the configurations exemplified in FIGS. 5A to 5D. [Example]

[0097] 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.

[0098] <Material preparation> A steel having the steel composition shown in Table 1 (the balance being iron and impurities) as an ultra-low carbon steel with excellent workability was hot-rolled, pickled, and cold-rolled to a thickness of 0.6 mm to prepare a cold-rolled steel sheet. The cold-rolled steel sheet was then subjected to hot-dip aluminization in a non-oxidation furnace type continuous hot-dip galvanizing line to obtain an aluminized steel sheet. The galvanizing line used was a non-oxidation furnace-reducing furnace type line, and annealing was also performed in this hot-dip galvanizing line. The annealing temperature was 850°C.

[0099] [Table 1]

[0100] After plating, the plating thickness is reduced to approximately 40 g / m on both sides using the gas wiping method. 2 The bath temperature of the coating bath during hot-dip coating was 660°C. A molten Al bath with Si added as needed was used as the coating bath. In the present examples, a steel sheet coated in a molten Al bath without Si added will be referred to as a "pure Al-coated steel sheet," a steel sheet coated in a molten Al bath with 2 mass% Si added will be referred to as an "Al-2%Si-coated steel sheet," a steel sheet coated in a molten Al bath with 9 mass% Si added will be referred to as an "Al-9%Si-coated steel sheet," a steel sheet coated in a molten Al bath with 15 mass% Si added will be referred to as an "Al-15%Si-coated steel sheet," and a steel sheet coated in a molten Al bath with 20 mass% Si added will be referred to as an "Al-20%Si-coated steel sheet."

[0101] Next, the surface of the Al-plated steel sheet was coated with a chemical conversion treatment solution using a roll coater as needed. 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 applied chemical conversion treatment solution was 500 mg / m2 on each 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 80°C. The chemical conversion treatment was applied to both sides of the Al-based plated steel sheet.

[0102] The chemical conversion treatment solutions used for painting were three types: an aqueous solution containing 2.5 g / L of gamma-aminopropyltriethoxysilane, a Si-based chemical conversion treatment solution; an aqueous solution containing 3 g / L of ammonium zirconium carbonate, a Zr-based chemical conversion treatment solution; and an aqueous solution containing 40 g / L of ammonium titanium (IV) fluoride, a Ti-based chemical conversion treatment solution. Details of the Al-based plated steel sheets produced are shown in Tables 4 and 5.

[0103] Furthermore, the cold-rolled steel sheets were annealed in a continuous hot-dip galvanizing apparatus capable of annealing under conditions where the maximum sheet temperature reached 820°C, followed by hot-dip galvanizing to prepare hot-dip galvanized steel sheets. Here, the gas atmosphere in the annealing furnace in the annealing step was an N2 atmosphere containing 1.0 volume % H2. Four types of coating bath components were used in the coating step: Zn-0.2 mass% Al (hereinafter also referred to as "GI"), Zn-0.09 mass% Al (hereinafter also referred to as "GA"), Zn-6 mass% Al-3 mass% Mg (hereinafter also referred to as "Zn-Al-Mg"), and Zn-11 mass% Al-3 mass% Mg-0.2 mass% Si (hereinafter also referred to as "Zn-Al-Mg-Si").

[0104] In addition, hot-dip galvanizing using a hot-dip galvanizing bath containing Zn-0.09% by mass Al (GA) was performed using the following process: The steel sheet was immersed in the hot-dip galvanizing bath. Next, while the steel sheet was being withdrawn from the bath, N2 gas was sprayed onto the steel sheet from a slit nozzle to perform gas wiping, thereby adjusting the coating weight. The steel sheet was then 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.

[0105] The coating weight of the plated steel sheet is 45 g / m2 per side of the steel sheet. 2 , 60g / m for plating other than GA 2 For comparison, a cold-rolled steel sheet was also prepared that was not plated but was only annealed in a continuous annealing line.

[0106] Next, a chemical conversion treatment solution (film treatment solution) was applied to the surface of the plated steel sheet prepared in the above process using a roll coater, as needed. The amount of chemical conversion treatment solution 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 (commonly called nip pressure). In this way, a chemical conversion treatment film of the desired film thickness was formed on the plated steel sheet.

[0107] When the chemical conversion coating was an inorganic coating, the chemical conversion solution was applied and then dried in a hot air oven at a temperature of 80°C. When the chemical conversion coating was a resin coating, Palcoat E200 (manufactured by Nippon Parkerizing Co., Ltd.) was applied to the plated steel sheet using a roll coater as a pretreatment to improve adhesion to the plated steel sheet before applying the chemical conversion coating solution to the plated steel sheet, and then dried in a hot air oven at a temperature of 80°C. The chemical conversion coating was then applied to both sides of the plated steel sheet using a roll coater, and the plated steel sheet was then dried at a temperature of 200°C. The chemical conversion coating was applied to both sides of the plated steel sheet. The thickness of the various coatings after application and drying was measured by embedding the coated steel sheet in resin, polishing it, and observing it with a scanning electron microscope so that its vertical cross section could be observed. The magnification of the scanning electron microscope was selected appropriately depending on the film thickness.

[0108] In addition, samples prepared with inorganic coatings having a thickness exceeding 1.5 μm after application and drying showed cracks and detachment in the coatings in all treatment solutions, making it impossible to obtain uniformly formed coatings, and it was therefore concluded that it was difficult to produce inorganic coatings with a thickness exceeding 1.5 μm. Details of the steel sheets prepared by coating various plated steel sheets with coatings are shown in Tables 4 and 5.

[0109] <How to make inorganic conversion treatment solution> An inorganic chemical conversion treatment solution (chemical conversion treatment solution for forming an inorganic coating) was prepared using the following process. Specifically, an aqueous solution containing 10 g / L of γ-aminopropyltriethoxysilane was prepared as an inorganic chemical conversion treatment solution primarily composed of silicon-based components. Furthermore, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of cobalt nitrate were added to the prepared γ-aminopropyltriethoxysilane aqueous solution as needed to prepare an inorganic chemical conversion treatment solution.

[0110] Furthermore, an aqueous solution containing 3.0 g / L of ammonium zirconium carbonate was prepared as an inorganic chemical conversion treatment solution containing a Zr-based component as the main component. Furthermore, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of cobalt nitrate were added to the prepared ammonium zirconium carbonate aqueous solution as needed to prepare an inorganic chemical conversion treatment solution. Details of the inorganic chemical conversion treatment solution prepared are listed in Table 2.

[0111] Furthermore, an aqueous solution containing 40 g / L of ammonium titanium (IV) fluoride, a Ti-based chemical conversion treatment solution, was prepared. Furthermore, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of cobalt nitrate were added to the prepared ammonium zirconium carbonate aqueous solution as needed to prepare an inorganic chemical conversion treatment solution. Details of the inorganic chemical conversion treatment solution prepared are listed in Table 2.

[0112] [Table 2]

[0113] The presence or absence of Si-O bonds in the inorganic coating was confirmed by the following method. That is, the prepared inorganic conversion treatment solution was applied to one 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 coating was determined to contain 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 Around 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 determined that the inorganic coating contained one or more of the Si-O bond, Si-C bond, and Si-OH bond. The determination results are shown in Table 2.

[0114] <Method for preparing resin-based chemical conversion treatment solution> A resin-based chemical conversion treatment solution (chemical conversion treatment solution for forming a resin film) was prepared using the following process. Specifically, a 30% by mass solution of Toyobo Co., Ltd.'s "Vylon® 300" polyester resin was prepared in cyclohexanone solvent. 20 parts by mass of Allnex Corporation's melamine resin "CYMEL® 303" was added to 100 parts by mass of the solid content of this solution and mixed. Furthermore, 5% by mass of Allnex Corporation's curing catalyst "CYCAT® 600" was added to the total solid content of the prepared mixture and mixed. In this way, a base treatment solution for obtaining a resin film was prepared.

[0115] Next, the particles shown below were mixed with the prepared base treatment liquid to prepare a resin-based chemical conversion treatment liquid. The amount of particles added was adjusted in the following manner. Specifically, the mass ratio of the solid content of the particles added to the base treatment liquid in the resin film (mass ratio to the solid content other than the particles) was determined, and the volume ratio was calculated from the specific gravity of the solid content of the resin film and the specific gravity of the particles. Next, the amount of particles added was adjusted so that the calculated volume ratio was the volume ratio listed in Table 3. The specific gravity was determined from the catalog value or literature value for each substance. Details of the resin-based treatment liquid are shown in Table 3.

[0116] [Table 3]

[0117] Vanadium boride: "VB2-O" manufactured by Nippon Shinkinzoku Co., Ltd. was sieved to an average particle size of 3.1 μm. This will be referred to as "VB2" below. 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 sieved to 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 crusher and then classified using a sieve to obtain an average particle size of 3.5 μm. Hereinafter, this will be referred to as "Fe-Si." Ferromanganese: Ferro-silicon manufactured by Marubeni Tetsugen Co., Ltd. was crushed into fine particles using a crusher and then classified using a sieve to obtain an average particle size of 3.5 μm. Hereinafter, this will also be referred to as "Fe-Mn." Zirconium boride: "ZrB2-O" manufactured by Nippon New Metals Co., Ltd. was used, which was classified using a sieve to have an average particle size of 2 μm. Hereinafter, this will also be referred to as "ZrB2". Molybdenum silicide: "MoSi2-F" manufactured by Nippon Shinkinzoku Co., Ltd. was used, which was classified using a sieve to have an average particle size of 3.5 μm. Hereinafter, this will also be referred to as "MoSi2." Chromium boride: "CrB2-O" manufactured by Nippon Shinkinzoku Co., Ltd. was used, which was classified using a sieve to have an average particle size of 5 μm. Hereinafter, this will also be referred to as "CrB2." Tungsten silicide: "B2-O" manufactured by Nippon Shinkinzoku Co., Ltd. was sieved to an average particle size of 2 μm. Hereinafter, this will also be referred to as "WSi2." Nickel: Reagent nickel powder was sieved to an average particle size of 5 μm. Hereinafter, this will be referred to as "Ni." Conductive titanium oxide: Sn-doped titanium oxide "ET-500W" manufactured by Ishihara Sangyo Kaisha, Ltd., with an average particle size of 2 to 3 μm (catalog value), was used. Hereinafter, this will also be referred to as "conductive Ti." Alumina: Showa Denko 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: "Tipake(R) CR-95" manufactured by Ishihara Sangyo Kaisha, Ltd., with an average particle size of 0.28 μm (catalog value). Hereinafter, this will also 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 also be referred to as "AlN."

[0118] 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.

[0119] <Evaluation of the created metal plate> (1. Evaluation of coolant corrosion resistance) The coolant corrosion resistance of the steel sheets was investigated when they were used in the cooling structure (cooling device) of a battery unit. Specifically, the aluminum-plated steel sheets were processed using the Erichsen process to create a cup-shaped cylindrical workpiece with a diameter of 50 mm and a drawing height of 40 mm. 30 mL of coolant was poured into the inside of the cylindrical workpiece, which was then sealed with a lid. The coolant used was an aqueous solution of Nissan Motor Co., Ltd.'s long-life coolant diluted to 30% by weight with water. These were placed in a constant-temperature bath at 90°C for 1,000 hours to accelerate the deterioration of the steel sheet in the coolant-immersed area. To simulate the deterioration of the coolant, a similar test was also conducted using a 30% by weight aqueous solution of the long-life coolant, to which 800 ppm of formic acid had been added. After the test, the coolant immersed in the cylindrical workpiece was removed, the cylindrical workpiece was dried, and the corrosion condition of the coolant-immersed area was observed. 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. 3 points: White rust has occurred, but the area of ​​white rust in the coolant-immersed area is less than 20% of the total area of ​​the coolant-immersed area. 2 points: White rust occurrence rate is 20% or more but less than 80%. 1 point: White rust is present at 80% or more, or red rust is present.

[0120] (2. External corrosion resistance test) An external corrosion resistance test was conducted to evaluate the external corrosion resistance of the battery unit (including the cooling structure) in areas exposed to the outside air.

[0121] Specifically, the prepared steel plates etc. were cut into pieces measuring 70 mm wide x 150 mm long, and the end faces of the pieces were painted and sealed to prepare test pieces for evaluating the external corrosion resistance of the flat surface.

[0122] In addition, two of the same steel plates were joined by crimping along all four sides to prepare test pieces for evaluating the external corrosion resistance of the crimped joints.

[0123] In addition, two of the same steel plates were painted and sealed on all four sides to prepare test specimens for evaluating the external corrosion resistance of the substrate edge surface.

[0124] In addition, two of the same steel plates were sealed on all four sides with adhesive to prepare test specimens for evaluating the external corrosion resistance of the substrate edge surface.

[0125] A cyclic corrosion test (CCT) was conducted using the prepared test specimens. The CCT mode was conducted in accordance with the automotive industry standard JASO-M609. The flat side and the crimped side were used as the evaluation surfaces, and the specimens were placed in a testing machine so that salt water was sprayed onto the evaluation surfaces.

[0126] The test was carried out for 120 cycles (1 cycle lasting 8 hours), and the corrosion state of the flat surface was observed and the corrosion resistance was evaluated according to the following criteria. A case in which no red rust was observed was rated "Good," and a case in which red rust was observed was rated "Bad." The results are shown in Tables 4 to 9.

[0127] (3. Processability evaluation) A bending test was conducted using the prepared Al-plated steel sheets. 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, depending on the processed shape, corrosion may be more likely to occur from the processed area, so workability was evaluated. Specifically, the prepared Al-plated steel sheets were bent at 180°, and the processed area was inspected with a 20x magnifying glass to visually evaluate the workability. 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 performed because the steel sheet was Zn-plated.

[0128] [Table 4]

[0129] [Table 5]

[0130] [Table 6]

[0131] [Table 7]

[0132] [Table 8]

[0133] [Table 9]

[0134] <Evaluation of cooling characteristics and adhesive durability in battery packs> (1. Creating a battery pack) A battery pack was fabricated using the steel sheets. Specifically, the flat material that had only been cut was used to form the case top cover (top surface) and the channel top cover. Separately, Al-plated steel sheets were prepared and deep-drawn into square cylinders using a press. After processing, the flanges were cut off to form the other parts of the battery pack (bottom and side surfaces). The bottom of the battery pack was fabricated to a width of 375 mm and a length of 2060 mm. Anti-rust oil was applied to the Al-plated steel sheets during processing, and the oil was removed by alkaline degreasing after processing. The punch shoulder R, die shoulder R, and corner R of the square cylinder were all 20 mm. The cooling structure was also fabricated by press processing. Each R in the cooling structure was 10 mm, and the number of channels, channel width (L), and channel spacing (w) were fabricated to the values ​​shown in Table 10.

[0135] Next, adhesive was applied to the joints of the cooling structure, and the cooling structure and the upper lid of the channel 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 four-side joints of the channel and the upper lid of the channel were joined by crimping 50 mm on each side, as shown in Figure 4. The adhesive was then cured according to the curing conditions for each adhesive.

[0136] Next, Shin-Etsu Silicone's "SDP-3540-A" was applied to the entire outer surface of the flow path upper cover, and the bottom part of the battery pack was attached on top of it as shown in Figure 1. The gap filler was hardened by leaving it at room temperature for one week. Through these steps, the battery unit shown in Figure 1 was manufactured.

[0137] Next, rubber heaters were placed inside the battery pack on the bottom surface as substitutes for heat-generating battery cells, and the case was then covered with a lid. When the lid was closed, a sealant was applied to the case flange to seal it. The sealant used was "Sealant 45N" manufactured by Shin-Etsu Silicone Co., Ltd. The metal material that made up the battery pack and the cooling structure was the same. In other words, the battery pack, the flow path lid, and the cooling structure were all made from the same metal material.

[0138] (2. Battery pack cooling characteristic evaluation test) The battery pack was heated by passing a current through the rubber heater. The current value at which the surface temperature of the rubber heater reached 50°C was determined in advance, and this current value was set as a fixed value and passed through the rubber heater. Next, a coolant was passed through the water coolant flow path. The coolant was an aqueous solution prepared by diluting Nissan Motor's long-life coolant liquid with water to 30% by mass. Hoses, pumps, and chillers were attached to the ends of the flow paths on both sides of the cooling structure to form a circulation path, through which the coolant was circulated. The chiller was controlled to maintain the coolant temperature at 25-30°C. The surface temperature of the rubber heater inside the case, directly above the midpoint between the cooling paths, was measured one hour after the start of the coolant circulation. A temperature drop of 8°C or more compared to when coolant was not circulating was evaluated as "A," a temperature drop of 2°C or more but less than 8°C was evaluated as "B," and a temperature drop of less than 2°C was evaluated as "C." The battery pack cooling performance evaluation test was conducted in an air-conditioned room maintained at 25°C. The results are shown in Table 10.

[0139] [Table 10]

[0140] As shown in Tables 4 to 10, the examples of the present invention that met 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), corrosion resistance against the external environment (external corrosion resistance), and cooling capacity.

[0141] In contrast, comparative examples that do not satisfy the requirements of this embodiment, such as those that are not plated, those that have narrow flow path spacing and cause deflection in the flow paths, etc., obtained poor results in some of the evaluation items.

[0142] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0143] 1 Cooling structure 10 Battery Pack 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 rectangular shape and a water coolant passage formed on an outer side of a bottom surface of a battery pack, The cooling structure includes a flow path forming portion, the internal space of which is the water coolant flow path, and a flow path upper cover that covers the flow path forming portion, the flow passage forming portion and the flow passage upper cover are 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 upper cover and the flow path forming portion are joined by an adhesive, A cooling structure, characterized in that at least two sides of an outer edge of the flow passage upper cover and an outer edge of the flow passage forming portion are joined by crimping.

2. 2. The cooling structure according to claim 1, wherein the water coolant passages are spaced apart from one another by a distance of 20 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 resin coating contains a resin, an anti-rust pigment, and a conductive pigment.

14. 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 13,

15. 15. The cooling structure according to claim 13, wherein the resin film contains the conductive pigment in an amount of 1.0 mass % or more and 30 mass % or less.

16. 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.

17. The cooling structure according to claim 1, characterized in that, at the outer edge of the side of the cooling structure that is not crimped, the end face of the flow path forming portion and the end face of the flow path upper cover are covered with Al-based plating or Zn-based plating.

18. The cooling structure according to claim 1, characterized in that, at the outer edge of the side of the cooling structure that is not crimped, the end face of the flow path forming portion and the end face of the flow path upper cover are covered with the adhesive.

19. The cooling structure according to claim 1, wherein an end face of the flow passage forming portion and an end face of the flow passage upper cover are painted at an outer edge portion of an edge of the cooling structure that is not crimped.

20. 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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