Cooling structure and battery unit

Abstract

Provided is a cooling structure (1) having water-cooling medium flow paths (25) formed so as to be in contact with a bottom surface portion (10a) of a battery pack (10). The cooling structure (1) has a flow path formation part (21) that forms a portion of the water-cooling medium flow paths (25). The flow path formation part (21) is joined to an adherend member by an adhesion part (30). The adherend member is made of a steel sheet obtained by forming an inorganic coating or a resin coating as a chemical conversion coating on an Al-based plated steel sheet or a Zn-based plated steel sheet. The flow path formation part (21) is made of an aluminum alloy. The thickness of the adhesion part (30) is at least 0.0005 mm. The adhesion part (30) protrudes by at least 0.1 mm toward the water-cooling medium flow paths (25). The flow path interval between the water-cooling medium flow paths (25) is at most 20 mm. The width of the water-cooling medium flow paths (25) is at most 60 mm.

Description

[Technical Field]

[0001] The present invention relates to a cooling structure and a battery unit. This disclosure claims priority under Japanese Patent Application No. 2023-191328, filed in Japan on November 9, 2023, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] In the automotive sector, the shift to electric vehicles (EVs) is progressing in order to reduce CO2 emissions. Among the components used in EV vehicles, the battery pack, which houses the battery cells that serve as the power source, requires a cooling structure to prevent battery degradation due to temperature rise. Until now, air cooling was the mainstream method for cooling structures, but in recent years, with the increase in battery capacity, there has been an increase in the adoption of water cooling, which has a higher cooling capacity. Iron and aluminum are generally used for the components of water-cooled battery packs. For example, Patent Document 1 discloses the use of adhesive to join aluminum cooling plates. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2022-514223 [Overview of the project] [Problems that the invention aims to solve]

[0004] Iron is superior to aluminum in terms of strength and cost, but inferior in corrosion resistance. A cooling channel combining iron and aluminum can provide the strength and cost advantages of iron, while retaining the high corrosion resistance of aluminum. However, because it is a combination of dissimilar metals, contact corrosion between the iron and aluminum and distortion due to differences in thermal expansion coefficients become challenges at the contact points. Furthermore, since the inside of the channel is an environment where a coolant such as a liquid flows, corrosion resistance is required in addition to strength at the joint.

[0005] This invention has been made in view of the above problems, and aims to provide a cooling structure that is excellent in strength and corrosion resistance at the joint portion of dissimilar metals. [Means for solving the problem]

[0006] To solve the aforementioned problems, this disclosure employs the following means. (1) A cooling structure according to one aspect of the present disclosure is a cooling structure having a water coolant channel formed to contact the bottom surface of a battery pack, wherein the cooling structure has a channel forming portion that constitutes a part of the water coolant channel, the channel forming portion is joined to a member by an adhesive portion, the member to be joined is either the bottom surface or a channel cover that covers the channel forming portion, the member to be joined is made of a steel plate on which an inorganic film or resin film is formed as a chemical conversion treatment film on an Al-plated steel plate or a Zn-plated steel plate, the channel forming portion is made of an aluminum alloy, the thickness of the adhesive portion is 0.0005 mm or more, the adhesive portion protrudes 0.1 mm or more towards the water coolant channel, the channel spacing between the water coolant channels is 20 mm or less, and the width of the water coolant channels is 60 mm or less. (2) The cooling structure described in (1) above may contain Si in the plating layer of the Al-based plated steel sheet. (3) The cooling structure described in (2) above may have a Si content of 2.0% by mass or more and 15% by mass or less in the plating layer of the Al-based plated steel sheet. (4) The cooling structure described in (1) or (2) above may have a coating formed on the surface of the Al-plated steel sheet as a chemical conversion coating, the coating mainly consisting of a Zr-based component, a Ti-based component, or a Si-based component. (5) The cooling structure described in (1) above may have an inorganic film on the surface of the Zn-plated steel sheet that mainly contains a Si-based component or a Zr-based component. (6) The cooling structure described in (1) above may have an inorganic film on the surface of the Zn-plated steel sheet containing at least one of the following as rust-preventive components: V, P, and Co. (7) The cooling structure described in (6) above may have one or more of the following rust-preventive components: vanadium oxide, phosphoric acid, and Co nitrate. (8) The cooling structure described in (1) above may be composed of a compound phase in which the inorganic film on the surface of the Zn-plated steel sheet contains one or more of the following: Si-O bonds, Si-C bonds, and Si-OH bonds. (9) The cooling structure described in (1) above may have an inorganic film thickness greater than 0 μm and less than or equal to 1.5 μm. (10) The cooling structure described in (1) above may have an inorganic coating or a resin coating that is electrically conductive. (11) The cooling structure described in (1) above may include a resin coating, a rust-preventive pigment, and a conductive pigment. (12) The cooling structure described in (11) above, wherein the resin film contains one or more of the following as conductive pigments: 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 × 10⁷ Ωcm or less at 23 to 27°C, and may contain one or more elements selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W as constituent elements. (13) The cooling structure described in (11) or (12) above may have the resin film containing the conductive pigment in a proportion of 1.0% by mass or more and 30% by mass or less. (14) The cooling structure described in (1) above may contain 10% or more of any of epoxy resin, silicone resin, acrylic resin, or urethane resin in the adhesive portion. (15) The cooling structure described in (1) above may have a hardness of A15 or more and D90 or less for the adhesive portion. (16) A battery unit according to one aspect of the present disclosure is characterized by comprising the cooling structure described in (1) or (2) above and a battery pack. [Effects of the Invention]

[0007] According to the above aspects of the present invention, it is possible to provide a cooling structure that is excellent in strength and corrosion resistance at the joint portion of dissimilar metals.

Brief Description of the Drawings

[0008] [Figure 1] It is a schematic cross-sectional view showing a cooling structure according to an embodiment of the present disclosure. [Figure 2] It is a schematic cross-sectional view showing another example of the cooling structure according to the embodiment. <00000​​​​​​​​​​​​​​​​​​​​​​​​​​​​The cooling structure 1 according to this embodiment is installed, for example, on the outside (bottom) of the underside of an automobile. Since an aqueous solution of LLC (long-life coolant) containing organic components flows as the coolant (water coolant) through the water coolant flow path 25 of the cooling structure 1, the cooling structure 1 is required to have high coolant corrosion resistance. Furthermore, the cooling structure 1 is required to improve its cooling capacity by narrowing the flow path spacing of the water coolant flow path 25 and increasing the liquid surface area.

[0013] The cooling structure 1 has a water coolant channel 25. The coolant flowing through the water coolant channel 25 cools the battery pack 10 by coming into direct contact with the bottom surface 10a of the battery pack 10, or via a channel cover 26 described later. Battery cells (not shown) are housed in the battery pack 10. Inside the battery pack 10, the battery cells are arranged in close contact with the bottom surface 10a.

[0014] The cooling structure 1 has a flow path forming section 21. The flow path forming section 21, together with a member to be joined later, forms a flow path 25 for the water refrigerant. That is, the flow path forming section 21 constitutes a part of the flow path 25 for the water refrigerant. In the cooling structure 1, in a cross-sectional view as shown in Figure 1, multiple water refrigerant flow paths 25 appear to be lined up. The flow path forming section 21, together with a member to be joined later, forms multiple water refrigerant flow paths 25 extending in the Y direction. Along the X direction, adjacent water refrigerant flow paths 25 are connected to each other via a joint 22 of the flow path forming section 21. The joint 22 is the portion between adjacent water refrigerant flow paths 25.

[0015] The flow path forming portion 21 is joined to the member to be joined by the adhesive portion 30. The member to be joined is either the bottom surface portion 10a of the battery pack 10 or the flow path upper cover 26 that covers the flow path forming portion 21. Either the bottom surface portion 10a of the battery pack 10 or the flow path upper cover 26 that covers the flow path forming portion 21 is joined to the flow path forming portion 21 by the adhesive portion 30. Here, the statement that the flow path cover 26 covers the flow path forming section 21 means that the flow path cover 26 is positioned on the battery pack 10 side in at least the portion of the flow path forming section 21 that constitutes the water refrigerant flow path 25.

[0016] As shown in the example in Figure 1, when the cooling structure 1 has a flow path cover 26, the member to be joined is the flow path cover 26, and the flow path forming part 21 and the flow path cover 26 are joined by the adhesive part 30. When the cooling structure 1 does not have a flow path cover 26, the member to be joined is the bottom surface 10a of the battery pack 10, and the flow path forming part 21 and the bottom surface 10a of the battery pack 10 are joined by the adhesive part 30. The joining part 22 is joined to the bottom surface 10a of the battery pack 10, or the flow path cover 26, via the adhesive part 30. In this embodiment, as shown in Figure 1, the flow path cover 26, which covers at least the water refrigerant flow path 25, and the flow path forming part 21 are joined by the adhesive part 30. In detail, the flow path cover 26 is joined to the joining part 22 by the adhesive part 30.

[0017] In this embodiment, the water refrigerant flow path 25 is a space that has a rectangular shape when viewed from the Y direction, as shown in Figure 1.

[0018] As shown in Figure 1, the cooling structure 1 according to this embodiment has a flow path cover 26 that covers the upper part of the flow path forming section 21. In this case, the flow path cover 26 is positioned between the flow path forming section 21 and the battery pack 10. The battery pack 10 is provided on the side opposite the flow path forming section 21, with the flow path cover 26 in between.

[0019] The flow path cover 26 is made of a steel sheet that has an inorganic film or resin film formed as a chemical conversion treatment coating on an Al (aluminum) plated steel sheet or a Zn (zinc) plated steel sheet. In the following, "a steel sheet that has an inorganic film or resin film formed as a chemical conversion treatment coating" may be referred to as "a steel sheet that has undergone chemical conversion treatment."

[0020] If the cooling structure 1 does not have a flow path cover 26, the bottom portion 10a of the battery pack 10 is joined to the flow path forming portion 21, and a flow path 25 for the water coolant is formed by a part of the bottom portion 10a of the battery pack 10 and a part of the flow path forming portion 21. In this case, the flow path 25 for the water coolant is in direct contact with the bottom portion 10a of the battery pack 10. In this case, the bottom portion 10a of the battery pack 10 is made of a steel plate on which an inorganic film or resin film is formed as a chemical conversion treatment film on an Al-plated steel plate or a Zn-plated steel plate. If the cooling structure 1 has a flow path cover 26, the bottom portion 10a does not necessarily have to be made of a steel plate on which an Al-plated steel plate or a Zn-plated steel plate has been chemically treated, because the bottom portion 10a does not come into contact with the coolant.

[0021] An example of an Al-based plated steel sheet is an Al-9 mass%Si plated steel sheet. Examples of Zn-based plated steel sheets include Zn-0.2 mass%Al plated steel sheet, Zn-0.09 mass%Al plated steel sheet, Zn-6 mass%Al-3 mass%Mg plated steel sheet, and Zn-11 mass%Al-3 mass%Mg-0.2 mass%Si plated steel sheet. Among Zn-based plated steel sheets, a particularly preferred material is a zinc (Zn)-aluminum (Al)-magnesium (Mg) alloy plated steel sheet.

[0022] Steel sheets that have undergone chemical conversion treatment on aluminum-plated steel sheets and zinc-plated steel sheets exhibit high corrosion resistance to coolants. In particular, steel sheets that have undergone chemical conversion treatment on aluminum-plated steel sheets and zinc-plated steel sheets have excellent corrosion resistance to LLC aqueous solutions.

[0023] The shape of the cross-section perpendicular to the extension direction of the water refrigerant flow path 25 is not limited to a rectangular shape, but may be, for example, a trapezoidal shape as shown in Figure 2, a semicircular shape as shown in Figure 3, or any other shape.

[0024] In this embodiment, the water refrigerant channel 25 extends in the Y direction (for example, in a direction parallel to or perpendicular to the longitudinal direction of the bottom surface 10a of the battery pack 10). The direction of extension of the water refrigerant channel 25 is not limited to this example, and it may also extend in the X direction. The water refrigerant flow path 25 may have not only straight sections but also curved sections when viewed in plan in a direction perpendicular to the surface of the bottom portion 10a. Furthermore, as illustrated in Figure 4, the water refrigerant flow path 25 may have a U-shaped portion when viewed in plan in a direction perpendicular to the plate surface of the bottom portion 10a. The U-shaped portion may be provided for the purpose of folding back the straight section, and for example, adjacent straight sections may be connected by these portions. Figure 4(a) illustrates a schematic shape of the water refrigerant flow path 25 in which a straight section 25a extending in the Y direction is folded back by a U-shaped folded section 25b. Figure 4(b) illustrates a schematic shape of the water refrigerant flow path 25 in which a similar straight section 25a is folded back by a U-shaped folded section 25b.

[0025] The water refrigerant flow path 25 is connected to a circulation path not shown. For example, the water refrigerant flow path 25 is connected to a supply pipe (not shown) that supplies the water refrigerant and a drain pipe (not shown) that drains the water refrigerant. The supply pipe and the drain pipe may be connected to the flow path forming section 21 at approximately both ends of the water refrigerant flow path 25, respectively. Alternatively, the supply pipe may be positioned approximately in the middle of the water refrigerant flow path 25, and multiple drain pipes may be provided at both ends of the water refrigerant flow path 25, or arranged according to the cooling design. The water refrigerant supplied from the supply pipe flows through the water refrigerant flow path 25 and is drained from the drain pipe. After the water refrigerant is cooled by a cooling device (not shown), it is supplied again from the supply pipe to the water refrigerant flow path 25.

[0026] In this manner, the coolant, which is a water-based coolant, flows through the circulation path and the water-based coolant channel 25. After being cooled in the circulation path, the coolant flows through the water-based coolant channel 25. While flowing through the water-based coolant channel 25, the coolant absorbs heat from the battery pack 10. Subsequently, the coolant is reintroduced into the circulation path. That is, the coolant repeatedly flows through the circulation path and the water-based coolant channel 25, thereby repeatedly absorbing heat from the battery pack 10.

[0027] Therefore, the material of the channel forming section 21 that forms the water coolant channel 25 is required to have resistance to coolant corrosion. In this embodiment, the channel forming section 21 is made of an aluminum alloy. As an example, the aluminum alloy is a 3000 series or 6000 series aluminum alloy. Since the channel forming section 21 is made of an aluminum alloy, it has high resistance to coolant corrosion, and a cooling structure 1 that is lighter compared to a cooling structure that uses a steel channel can be obtained. The channel forming portion 21 may be an Al alloy plate having the same composition as the plating layer described above.

[0028] If the cooling structure 1 has a flow path cover 26, the flow path forming portion 21 is joined to the flow path cover 26 by an adhesive portion 30. If the cooling structure 1 does not have a flow path cover 26, the flow path forming portion 21 is joined to the bottom surface portion 10a of the battery pack 10 by an adhesive portion 30. The thickness (length in the Z direction) D30 of the adhesive portion 30 formed by the above joining is 0.0005 mm or more.

[0029] In this embodiment, as shown in Figure 5, the thickness D30 of the adhesive portion 30 is the distance between the opposing surfaces of the joined members, namely the upper flow channel cover 26 and the joint portion 22 of the flow channel forming portion 21, in a direction perpendicular to the surface of the joined members (the Z direction in the example of Figure 5). If the cooling structure 1 does not have an upper flow channel cover 26, the thickness D30 of the adhesive portion 30 is the distance between the opposing surfaces of the joined members, namely the bottom surface portion 10a of the battery pack 10 and the joint portion 22 of the flow channel forming portion 21, in a direction perpendicular to the surface of the joined members (the Z direction in the example of Figure 5).

[0030] Since the distance (D30) between the flow channel forming portion 21 and the member to be joined is 0.0005 mm or more, even in the joining of dissimilar metals, such as a member to be joined that has undergone chemical conversion treatment on an Al-plated steel sheet or a Zn-plated steel sheet and a flow channel forming portion 21 made of an aluminum alloy, contact corrosion between the dissimilar metals and distortion due to differences in thermal expansion coefficients can be suppressed. If the thickness D30 of the adhesive portion 30 is too large, the joining strength will decrease, so it is preferably 10 mm or less, more preferably 5 mm or less.

[0031] The thickness D30 of the bonded portion 30 can be controlled by including fillers and spacers in the adhesive that forms the bonded portion 30. Common materials can be used as fillers and spacers. There are no particular restrictions on the particle size of the fillers and spacers; they may be equal to or smaller than the desired thickness D30.

[0032] The thickness D30 of the adhesive portion 30 can be measured as follows. A sample is prepared by cutting out the channel forming portion 21 along the Z direction so as to include the adhesive portion 30. This sample is observed using an optical microscope or SEM (scanning electron microscope), and the thickness D30 of the adhesive portion 30 in the direction perpendicular to the surface of the joined members is measured from the captured image (photograph) and scale bar. In this case, the arithmetic mean of 5 points obtained from 5 fields of view is taken as the thickness D30.

[0033] Generally, adhesive is applied within the width (X direction) of the joint 22. In other words, the adhesive is applied in a way that prevents it from spilling out of the joint 22. This is because spillage of adhesive increases the amount of adhesive used, which is thought to increase costs. In contrast, this embodiment has an overhang portion 23 that extends from the joint portion 22 into the water refrigerant flow path 25. That is, the overhang portion 23 is configured to protrude from the joint portion 22 towards the water refrigerant flow path 25 in the X direction. Specifically, the overhang portion 23 protrudes by 0.1 mm or more towards the water refrigerant flow path 25.

[0034] The protruding portion 23 is a part formed by the hardening of the adhesive, similar to the bonded portion 30 (adhesive hardened portion), and therefore has the same chemical composition as the bonded portion 30. In the protruding portion 23, the material constituting the protruding portion 23 is in contact with the member to be joined, but on the water refrigerant flow path 25 side, it is not in contact with other members. Alternatively, in the protruding portion 23, there are areas that are in contact with the flow path forming portion 21 without contacting the member to be joined. Therefore, the protruding portion 23 does not have the function of bonding other members together.

[0035] Figure 5 shows an example of the shape of the protruding portion 23. As shown in Figure 5, the protruding portion 23 that extends into the water refrigerant flow path 25 has a rounded shape. In the width direction of the water refrigerant flow path 25 (the X direction in the example of Figure 5), when the distance between the point P (the boundary between the water refrigerant flow path 25 and the joint 22) closest to the joint 22 among the inner surfaces of the side surface 21b of the flow path forming portion 21 (the surfaces constituting the water refrigerant flow path 25) and the end of the protruding portion 23 is defined as the protruding length L23, the protruding length L23 is 0.1 mm or more. By having the protruding portion 23 extend 0.1 mm or more into the water refrigerant flow path 25, it is possible to secure a wear allowance for the adhesive portion 30 due to erosion, thereby improving the bonding strength. The protruding length L23 is preferably 0.2 mm or more. If the overhang length L23 is too large, it will hinder heat exchange between the water coolant and the bottom surface of the battery pack, resulting in reduced cooling performance and no significant improvement in bonding strength. Therefore, it is preferably 1 mm or less, and more preferably 0.8 mm or less. Here, the end of the protruding portion 23 refers to the point furthest from point P along the width direction of the water refrigerant flow path 25 (the X direction in the example of Figure 5) within the interface between the protruding portion 23 and the member to be joined.

[0036] The protruding portion 23 is preferably arranged on both sides in the width direction of the joint portion 22, but it may also be arranged on only one side in the width direction of the joint portion 22.

[0037] The overhang length L23 can be measured as follows: A sample is prepared by cutting out the channel forming section 21, including the adhesive section 30, in a cross-section perpendicular to the extension direction (Y direction above) of the water refrigerant channel 25. This sample is observed using an optical microscope, and the overhang length L23 is measured from the captured image (photograph) and scale bar. In this case, the arithmetic mean of 5 points obtained from 5 fields of view is taken as the overhang length L23.

[0038] The means for applying the adhesive that constitutes the bonded portion 30 and the overflow portion 23 are not particularly limited, but it is preferable to apply the adhesive in a way that does not result in uneven application. For example, a method that can apply the adhesive at a constant discharge rate and speed (for example, a method in which a robot moves while discharging adhesive from a gun) results in an even application and good quality.

[0039] It is more preferable that there are no welded or brazed joints between the member to be joined and the joint 22, and only an adhesive joint 30 exists. For example, if a steel sheet that has an inorganic film or resin film formed as a chemical conversion treatment film on an Al-based plated steel sheet or a Zinc-based plated steel sheet is subjected to high-temperature treatment such as spot welding or brazing, the plating layer, inorganic film, or resin film may be damaged. However, by employing bonding using an adhesive, as in the cooling structure 1 according to this embodiment, such damage problems do not occur, and thus oxidation resistance can be ensured.

[0040] The channel spacing w between water refrigerant channels 25 is 20 mm or less. In other words, this channel spacing w is the distance between the ends of adjacent water refrigerant channels 25 in the width direction (X direction). In the example shown in Figure 1, since the cross-sectional shape of the water refrigerant channels 25 is rectangular, the distance between the ends of the water refrigerant channels 25 in the width direction (channel spacing) w is the distance between the side surfaces 21b of the channel forming section 21 that forms adjacent water refrigerant channels 25. In the examples shown in Figures 2 and 3, the boundary between the water refrigerant channel 25 and the joint section 22 is the end of the water refrigerant channel 25 in the width direction. For example, in order to join members together by spot welding, a joining surface of a predetermined area is required to provide the spot weld. If the cooling structure according to this embodiment is to be fabricated using spot welding instead of the adhesive joint 30, the spot weld will exceed the flow path spacing, making proper joining impossible. Furthermore, if the flow path spacing is secured in order to properly form the spot weld, the flow path width, which will be described later, will be narrowed, which is undesirable.

[0041] By setting the spacing w between the water coolant flow channels 25 to 20 mm or less, the width of the water coolant flow channels 25 can be increased, thereby increasing the contact area between the water coolant flow channels 25 and the bottom surface 10a, in other words, 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 increased. In particular, in this embodiment, the flow channel upper cover 26 or the bottom surface 10a of the battery pack 10 is made of a steel plate that has been chemically treated from an Al-plated steel plate or a Zn-plated steel plate. As a heat transfer characteristic of a steel plate that has been chemically treated from an Al-plated steel plate or a Zn-plated steel plate, the heat in the portion of the flow channel upper cover 26 or the bottom surface 10a of the battery pack 10 that is directly above the portion in contact with the coolant is easily absorbed by the coolant. Therefore, by increasing the contact area between the coolant and the flow channel upper cover 26 or the battery pack 10, the area over which heat is transferred can be increased, and consequently, the cooling efficiency can be increased. The material of the side portion 10b and the top portion 10c of the battery pack 10 is not particularly limited, but it is preferable that they be made of Al-plated steel sheet or Zn-plated steel sheet that has undergone chemical conversion treatment, similar to the bottom portion 10a. In particular, since the side portion 10b is exposed to the external environment, it is preferable that it be made of Al-plated steel sheet or Zn-plated steel sheet that has undergone chemical conversion treatment, similar to the bottom portion 10a.

[0042] The spacing w between the water refrigerant flow channels 25 is preferably 1 mm or more, and preferably 15 mm or less. By setting the spacing w between the water refrigerant flow channels 25 to 1 mm or more, the width (length in the X direction) of the joint portion 22 can be secured, making it easier to secure the joint strength with the bottom portion 10a of the battery pack 10 or the upper cover 26 of the flow channel. By setting the spacing w between the water refrigerant flow channels 25 to 15 mm or less, the contact area between the coolant and the battery pack 10 can be increased, thereby further improving the cooling efficiency. To improve the area ratio of the water refrigerant flow path 25 without excessively expanding the flow path width L, and to shorten the distance between the water refrigerant flow path 25 and the areas that do not come into contact with the coolant, it is necessary to narrow the flow path spacing w. To satisfy the shape of the water refrigerant flow path 25, it is suitable to join the water refrigerant flow path 25 with an adhesive. By joining with an adhesive, the flow path spacing w can be made equivalent to that of the joined portion.

[0043] The channel spacing w in the water refrigerant channel 25 is measured using a caliper. The channel spacing w is determined by cutting out 10 arbitrary locations from the channel forming section 21, measuring the channel spacing w at each cut-out location using a caliper, and calculating the average of the maximum and minimum values ​​measured at the 10 locations. Note that the flow path spacing w refers to the flow path spacing w in the range where multiple water refrigerant flow paths 25 are arranged side by side and joints 22 are provided between the water refrigerant flow paths 25, as illustrated in Figure 1, etc. Therefore, as described above, flow path bends that form a U-shape, V-shape, U-shape, etc. when viewed in plan in a direction perpendicular to the plate surface of the bottom surface 10a are excluded from the measurement position of the flow path spacing w.

[0044] To efficiently cool the battery pack 10, it is necessary to increase the area ratio of the water coolant flow path 25 that contacts the battery pack 10. When viewed from a plane perpendicular to the surface of the bottom portion 10a (for example, the plane view shown in Figure 4), the ratio of the area occupied by the water coolant flow path 25 to the area of ​​the bottom 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. There is no particular upper limit to the above ratio, but it may be 0.80 as it is preferable to ensure a certain degree of bonding strength between the joint portion 22 and the bottom portion 10a. From the perspective of balancing bonding strength and cooling efficiency, the above ratio is more preferably 0.23 to 0.71. In other words, the cooling performance of the cooling structure 1 improves as the above ratio increases, but it is also preferable to consider the bonding strength with the battery pack 10. From this viewpoint, the above ratio is preferably 0.23 to 0.71.

[0045] The ratio of the area occupied by the water refrigerant flow path 25 to the area of ​​the bottom surface 10a can be increased by widening the flow path width L. As shown in Figure 1, the flow path width L is the length of the water refrigerant flow path 25 in the X direction, that is, the distance between the outer surfaces of the side surfaces 21b of the flow path forming section 21 that forms the water refrigerant flow path 25. In the example shown in Figures 2 and 3, the boundary between the flow path forming section 21 and the joint section 22 becomes the end in the width direction of the flow path forming section 21, and the flow path width L is the distance between the ends in the width direction of the water refrigerant flow path 25. If the flow path width L is too wide, the stress applied to the joint section 22 will increase, or the flow of the coolant will not be limited to the longitudinal direction of the flow path and will not be stable. Therefore, the flow path width L is 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 in the water refrigerant flow path 25 is measured using calipers. The flow path width L is determined by cutting out any 10 locations from the flow path forming section 21, measuring the flow path width L at each cut-out location using calipers, and calculating the average of the maximum and minimum values ​​measured at the 10 locations. Furthermore, as described above, any turning points in the flow path that form a U-shape, V-shape, or U-shape when viewed in a plan view perpendicular to the surface of the bottom portion 10a are excluded from the measurement position of the flow path width L.

[0046] As shown in Figure 1, etc., there is an area on the outer edge 27 of the flow path forming section 21 where the water coolant flow path 25 is not formed. If the area where the water coolant flow path 25 is not provided is too large, the cooling effect by the coolant will be reduced, so it is preferable that the length of the end of the water coolant flow path 25 that does not come into contact with the coolant is short. Specifically, as shown in Figure 1, etc., it is preferable that the distance D in the X direction of the area on the bottom surface 10a of the battery pack 10 where the water coolant flow path 25 does not exist, from the end of the flow path forming section 21 to the nearest water coolant flow path 25, be short. Distance D is the distance in the width direction of the water coolant flow path 25 from the end of the water coolant flow path 25 to the nearest water coolant flow path 25. Specifically, this distance is 10 mm or less, and more preferably 7.5 mm or less. The distance D from the end of the flow path forming section 21 to the start of the cavity in the nearest water refrigerant flow path 25 is measured using a caliper. To determine the distance D, ten arbitrary locations are cut out from the outer edge 27 of the flow path forming section 21, including the water refrigerant flow path 25 closest to the outer edge 27. The distance D in the width direction of the water refrigerant flow path 25 at these cut-out locations is measured using a caliper, and the average of the maximum and minimum values ​​of the measurements at the ten locations is calculated.

[0047] The height of the water refrigerant flow path 25, that is, the distance h in the thickness direction (Z direction) of the water refrigerant flow path 25 from the bottom surface 21a of the flow path forming section 21 (the lower end portion 21a-1 of the flow path forming section 21 in the example of Figure 3) to the joint 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 flow path formation, 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 better balance the cooling efficiency of the battery pack 10 with processability for flow path formation. The distance h is measured using a caliper. To determine the distance h, ten arbitrary locations are cut out of the flow path forming section 21, the distance h at each cut-out location is measured using a caliper, and the average of the maximum and minimum measured values ​​at the ten locations is calculated.

[0048] The main resin component of the adhesive portion 30 is preferably one of epoxy resin, silicone resin, acrylic resin, or urethane resin. The adhesive portion 30 preferably contains 10% or more of any of these main resin components, and more preferably 20% or more. The adhesive portion 30 having such a main component suppresses deterioration of the adhesive portion 30 and corrosion of the joint portion 22 due to the water refrigerant, and ensures watertightness. The content of the main resin component in the adhesive portion 30 is measured using a thermogravimetric analyzer.

[0049] Even at the outer edge of the cooling structure 1, the flow path forming portion 21 is joined to the member to be joined by an adhesive portion 30. Specifically, the outer edge portion 27 of the flow path forming portion 21 is joined to the outer edge portion 42 of the flow path upper cover 26 by an adhesive portion 30. The outer edge portion 27 of the flow path forming portion 21 and the outer edge portion 42 of the flow path upper cover 26 are joined (watertight joint), forming a watertight joint portion 70. A watertight joint is a joint that seals in water and prevents leakage even under water pressure. If the cooling structure 1 does not have a flow path upper cover 26, the outer edge portion 11 of the bottom portion 10a of the battery pack 10 is joined to the outer edge portion 42 of the flow path upper cover 26 by an adhesive portion 30, forming a watertight joint portion 70. In this way, by sealing the outer edge of the cooling structure 1 in a watertight manner, leakage of the coolant can be prevented and watertightness can be ensured.

[0050] The flow channel forming section 21 is manufactured, for example, by processing a single sheet of aluminum alloy (e.g., bending, drawing, casting, etc.). The thickness of the aluminum alloy plate constituting the channel forming section 21 is not particularly limited, but is preferably 0.4 mm to 10.0 mm, and more preferably 0.4 mm to 5.0 mm. In this case, the strength of the channel forming section 21 can be increased. The manufacturing method of the channel forming section 21 is not limited to this example. For example, the channel forming section 21 may be manufactured using a die-casting method. The thickness of the aluminum alloy plate is determined by cutting out a portion of the flow channel forming section 21, measuring the plate thickness at 10 locations using calipers, and calculating the average of the maximum and minimum values ​​measured at the 10 locations.

[0051] The thickness of the steel plate constituting the bottom surface 10a of the battery pack 10 is not particularly limited, but is preferably 0.4 mm or more and 1.2 mm or less, and more preferably 0.4 mm or more and 1.0 mm or less. In this case, the bottom surface 10a of the battery pack 10 can be made thinner while maintaining the strength of the bottom surface 10a. Therefore, the distance between the coolant and the battery cells inside the battery pack 10 can be narrowed, thereby increasing the cooling efficiency of the battery pack 10 and improving the cooling responsiveness of the battery pack 10. Furthermore, the thickness of the flow path cover 26 is not particularly limited, but is preferably 0.4 mm or more and 1.2 mm or less, and more preferably 0.4 mm or more and 1.0 mm or less. The thickness of the steel plate is determined by cutting out a portion of the bottom surface 10a of the battery pack 10 or a part of the flow path cover 26, measuring the thickness of the plate at 10 locations using calipers, and calculating the average of the maximum and minimum values ​​measured at the 10 locations.

[0052] In this embodiment, the member to be joined (the bottom surface 10a of the battery pack 10 or the upper cover 26 of the flow path) is made of an Al-plated steel sheet or a Zn-plated steel sheet that has undergone chemical conversion treatment, and the flow path forming part 21 is made of an aluminum alloy. Since these different types of metals are joined by the adhesive part 30, and the thickness of the adhesive part 30 formed by the joining is 0.0005 mm or more, contact corrosion between dissimilar metals and distortion due to differences in thermal expansion coefficients can be suppressed. In addition, since the protruding part 23 is configured to protrude 0.1 mm or more towards the water refrigerant flow path 25 side, it is possible to ensure that the adhesive part 30 is worn down by erosion, and the joint strength is improved.

[0053] The hardness of the adhesive portion 30 is preferably between A15 and D90. The hardness of the adhesive portion 30 refers to the hardness of the adhesive portion 30 after the adhesive constituting the adhesive portion 30 has hardened. This ensures that the adhesive does not wear down in an environment where cooling water circulates, and that it has high erosion resistance. The hardness of the adhesive portion 30 is measured using a durometer hardness tester. Specifically, ten arbitrary locations are cut out, the hardness of each cut-out location is measured according to JIS K 7215 "Durometer Hardness Test Method for Plastics," and the average of the maximum and minimum measured values ​​at the ten locations is calculated.

[0054] Furthermore, the cooling structure 1 according to this embodiment may be provided on the inside (above) of the bottom surface of the automobile battery unit. In this case, the cooling structure 1 is housed inside the battery pack 10 together with the battery cells, and the battery cells are positioned above the cooling structure 1.

[0055] <2. Composition of Al-plated steel sheet> Next, we will describe in detail an example of an Al-plated steel sheet that constitutes the member to be joined.

[0056] Al-plated steel sheets are steel sheets on which a plating layer containing Al is formed. Preferably, the plating layer of Al-plated steel sheets contains Si. For example, the Si content is 2.0% by mass or more and 15% by mass or less. Preferably, the plating layer of Al-plated steel sheets has an Al content of 70% by mass or more, and is a two-component or multi-component plating with an Al content of 70-98% by mass and a Si content of 2.0% by mass or more and 15% by mass or less. A more preferable range for the Si content is 3.0% by mass or more and 15% by mass or less. By setting the Si content within the above range, the workability and corrosion resistance of the Al-plated steel sheets can be improved. The chemical composition of the plating layer may include Al and Si, as well as Zn at 15% by mass or less, Mg at 5% by mass or less, with the remainder being Fe. The plating layer may be formed on only one side of the steel sheet, but it is preferable that it be formed on both sides.

[0057] Furthermore, trace amounts of impurity elements such as Fe, Ni, and Co may be present in the plating layer. Additionally, Mg, Sn, mischmetal, Sb, Zn, Cr, W, V, Mo, etc., may be added as needed. There are no particular restrictions on the manufacturing method of the aluminum-plated steel sheet, but hot-dip flux plating, hot-dip plating by the Zenzimer method, all-radiant method, electroplating, and vapor deposition plating are preferred.

[0058] While there are no limitations on the composition of the base steel used in Al-plated steel sheets, examples of steel types 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.

[0059] To further enhance the external corrosion resistance and coolant corrosion resistance of Al-plated steel sheets, it is preferable that a chemical conversion coating is formed on the surface of the Al-plated steel sheet (either on one side or both sides, but preferably on both sides) as a chemical conversion coating, with a Zr-based component, a Ti-based component, or a Si-based component as the main component (for example, 50% by mass or more). The coating may also contain organic components.

[0060] Examples of chemical conversion coatings are cited in, for example, Japanese Patent Publication No. 2008-115442, Japanese Patent Publication No. 2013-7108, Japanese Patent Publication No. 2004-232040, Japanese Patent Publication No. 3302676, Japanese Patent Publication No. 4776458, Japanese Patent Publication No. 5336002, etc. Therefore, the chemical conversion coatings cited in these publications can be suitably used as the chemical conversion coatings in this embodiment. Hereinafter, an overview of the chemical conversion coatings will be described.

[0061] The first example of a chemical conversion coating is a coating mainly composed of Zr-based components, consisting only of Zr, F, P, C, O, N, and H, and not containing any 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% to 48.0% by mass. The sources of each component of the chemical conversion coating consist of 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.

[0062] The second example of a chemical conversion coating is a coating mainly composed of Zr-based components, and contains (A) at least one of titanium compounds and zirconium compounds, (B) at least one of 2-6 bonded phosphate esters of myo-inositol, and its alkali metal salts, alkaline earth metal salts, and ammonium salts, and (C) silica. In this chemical conversion coating, the mass ratio of the metal equivalent amounts of (A) (Zr+Ti):(B):(C) is 1:0.2-1.7:0.2-5.

[0063] 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, and titania sol.

[0064] Examples of zirconium compounds include zirconyl nitrate, zirconyl acetate, zirconyl sulfate, ammonium zirconyl carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and zirconium acetate.

[0065] Examples of myo-inositol phosphate esters with 2 to 6 bonded molecules include myo-inositol diphosphate, myo-inositol triphosphate, myo-inositol tetraphosphate, myo-inositol pentane phosphate, and myo-inositol hexane phosphate.

[0066] Examples of silica include water-dispersible silica compounds. Water-dispersible silica compounds include liquid-phase colloidal silica and gas-phase silica. Examples of liquid-phase colloidal silica, though not particularly limited, include Snowtex C, Snowtex O, Snowtex N, Snowtex S, Snowtex UP, Snowtex PS-M, Snowtex PS-L, Snowtex 20, Snowtex 30, Snowtex 40 (all manufactured by Nissan Chemical Industries), Adelite AT-20N, Adelite AT-20A, and Adelite AT-20Q (all manufactured by Asahi Denka Kogyo).

[0067] Examples of gas-phase silica include, but are not limited to, Aerosil 50, Aerosil 130, Aerosil 200, Aerosil 300, Aerosil 380, Aerosil TT600, Aerosil MOX80, and Aerosil MOX170 (all manufactured by Nippon Aerosil).

[0068] A third example of a chemical conversion coating is a coating mainly composed of a Zr-based component, and is a composite coating consisting of a zirconium compound, a vanadium compound, a silica compound, a phosphoric acid compound, and an organic compound having at least one functional group from among a hydroxyl group, a carbonyl group, and a carboxyl group. This chemical conversion coating contains 2 to 1200 mg / m² of zirconium per side of an Al-plated steel sheet. 2 , vanadium 0.1~300 mg / m³ 2 Phosphate compounds, expressed as PO4 equivalent, 0.3-450 mg / m² 2 , contains. Furthermore, the content of chromium or chromium compounds in the chemical conversion treated film is 0.1 mg / m² as chromium. 2 The following refers to a fluorine or fluorine compound content of 0.1 mg / m³ as fluorine. 2 It is as follows:

[0069] Examples of zirconium compounds include zirconyl nitrate, zirconyl acetate, zirconyl sulfate, ammonium zirconyl carbonate, potassium zirconium carbonate, sodium zirconium carbonate, and zirconium acetate.

[0070] 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, phosphovanadomolybdate, vanadium sulfate, vanadium dichloride, and vanadium oxide.

[0071] Examples of silica compounds include water-dispersible silica compounds. Water-dispersible silica compounds include colloidal silica and gas-phase silica. Examples of colloidal silica, though not particularly limited, include 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).

[0072] Examples of gas-phase silica include, but are not limited to, Aerosil 50, Aerosil 130, Aerosil 200, Aerosil 300, Aerosil 380, Aerosil TT600, Aerosil MOX80, and Aerosil MOX170 (all manufactured by Nippon Aerosil).

[0073] Phosphate compounds only need to contain phosphate ions. Examples of phosphate compounds include orthophosphate (phosphoric acid), metaphosphate, pyrophosphate, and salts such as ammonium salts, sodium salts, calcium salts, and potassium salts in which some or all of the hydrogen ions of these substances are replaced, which can be used individually or in combination.

[0074] Examples of organic compounds having at least one functional group among hydroxyl groups, carbonyl groups, and carboxyl groups include alcohols such as methanol, ethanol, isopropanol, and ethylene glycol; carbonyl compounds such as formaldehyde, acetaldehyde, furfural, acetylacetone, ethyl acetoethyl acetate, 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, ligninsulfonic acid, and polyphenols; and synthetic polymers such as polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, polyethyleneimine, and water-soluble nylon.

[0075] The chemical conversion coating may also contain, as an additional component, a lubricating component consisting of at least one of polyolefin-based waxes and paraffin-based waxes.

[0076] A fourth example of a chemical conversion coating is a coating mainly composed of Ti-based components, in which oxides or hydroxides of valve metal and fluorides 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 mainly composed of Ti-based components include coatings that are composites of oxides [TiO2] and hydroxides [Ti(OH)4]. In this coating, fluorides of Ti, such as XnTiF6 (X: alkali metal, alkaline earth metal, or NH4, n=1 or 2), TiF4, etc., coexist.

[0077] The fifth example of a chemical conversion coating is an example of a coating mainly composed of Si-based components, and is a chemical conversion coating mainly composed of 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 and a silane coupling agent (B) containing one glycidyl group in its molecule in a solid content mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound contains two or more functional groups (a) represented by the formula -SiR1R2R3 (wherein R1, R2, and R3 independently represent an alkoxy group or a hydroxyl group, and at least one represents an alkoxy group) and one or more hydrophilic functional groups (b) selected from a hydroxyl group (different from those that may be included in functional group (a)) and an amino group, and has an average molecular weight of 1000 to 10000.

[0078] The sixth example of a chemical conversion coating is a coating that mainly contains Si-based components, specifically an organosilicon compound (silane coupling agent). Organosilicon compounds have a cyclic siloxane structure in their structure. Here, "cyclic siloxane bond" refers to a cyclic structure that has a continuous Si-O-Si bond configuration and is composed only of Si and O bonds, with 3 to 8 Si-O repeats.

[0079] The organosilicon compound is obtained by blending a silane coupling agent (A) containing at least one amino group in its molecule and a silane coupling agent (B) containing at least one glycidyl group in its molecule in a solid content 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 independently represent an alkoxy group or a hydroxyl group, and at least one of R1, R2, and R3 represents an alkoxy group), and at least one hydrophilic functional group (b) selected from the group consisting of a hydroxyl group (however, if functional group (a) contains a hydroxyl group, the hydroxyl group (b) is separate from that hydroxyl group) and an amino group, and has an average molecular weight of 1000 to 10000.

[0080] Of course, the examples of chemical conversion treated coatings in this embodiment are not limited to those described above, and chemical conversion treated coatings listed in the examples described later can also be suitably used.

[0081] The method for forming the chemical conversion coating described above is not particularly limited; the chemical conversion solution (coating solution) corresponding to each of the above compositions can be applied to the Al-plated steel sheet by a known method and then baked and dried.

[0082] <3. Composition of Zn-plated steel sheet> Next, we will describe in detail an example of a Zn-plated steel sheet that constitutes the member to be joined.

[0083] Zn-plated steel sheets are steel sheets on which a plating layer containing Zn has been formed. The plating layer may be formed on only one side of the steel sheet, but it is preferable that it be formed on both sides. Examples of Zn-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-plated steel sheets can also be used that contain small amounts of dissimilar metal elements or impurities in the plating layer, such as cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, arsenic, etc., or that have inorganic substances such as silica, alumina, and titania dispersed in them. Furthermore, the above-mentioned plating can be combined with other types of plating; for example, multi-layer plating combining iron plating, iron-phosphorus plating, nickel plating, cobalt plating, etc., is also applicable. The plating method is not particularly limited and any known method such as electroplating, hot-dip plating, vapor deposition, dispersion plating, or vacuum plating may be used.

[0084] Furthermore, an inorganic film or resin film is formed on the surface of the Zn-plated steel sheet (either one side or both sides, but preferably both sides) as a chemical conversion treatment film. The inorganic film mainly contains Si-based or Zr-based components (for example, 50% by mass or more). The inorganic film may also contain organic components.

[0085] The inorganic film or resin film is preferably electrically conductive. In this case, the electrodeposition coating properties of the Zn-plated steel sheet can be improved. Furthermore, the inorganic film is preferably composed of a compound phase containing one or more of Si-O bonds, Si-C bonds, and Si-OH bonds. It is also preferable that the compound phase contains an acrylic resin, which will be described later. When these requirements are met, the adhesion of the chemical conversion treatment film can be improved, thereby improving the external corrosion resistance and coolant corrosion resistance of the processed part of the Zn-plated steel sheet. Furthermore, the inorganic film is preferably composed of at least one of the V, P, and Co components as a rust-preventive component. The rust-preventive component of the inorganic film is preferably one or more of vanadium oxide, phosphoric acid, and Co nitrate. Furthermore, the thickness of the inorganic film is preferably greater than 0 μm and less than or equal to 1.5 μm. In this case, the conductivity or adhesion of the chemical conversion treatment film described above can be further improved.

[0086] The resin coating preferably contains a resin, a rust-preventive pigment, and a conductive pigment. Furthermore, the resin coating preferably contains one or more of the following as conductive pigments: 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 × 10⁷ Ωcm or less at 23-27°C and preferably contains one or more 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% to 30% by 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. If one or more of these requirements are met, the external corrosion resistance and coolant corrosion resistance of the Zn-plated steel sheet can be further improved.

[0087] Examples of chemical conversion coatings are cited in, for example, Japanese Patent Publication No. 4776458, Japanese Patent Publication No. 5336002, Japanese Patent Publication No. 6191806, Japanese Patent Publication No. 6263278, International Publication No. 2020 / 202461, Japanese Patent Publication No. 4084702, and others. Therefore, the chemical conversion coatings cited in these publications can be suitably used as the chemical conversion coatings in this embodiment. Hereinafter, an overview of the chemical conversion coatings will be described.

[0088] The first example of a chemical conversion coating is an example of an inorganic coating, which is a chemical conversion coating mainly composed of 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 and a silane coupling agent (B) containing one glycidyl group in its molecule in a solid content mass ratio [(A) / (B)] of 0.5 to 1.7. The organosilicon compound contains two or more functional groups (a) represented by the formula -SiR1R2R3 (wherein R1, R2, and R3 independently represent an alkoxy group or a hydroxyl group, and at least one represents an alkoxy group) and one or more hydrophilic functional groups (b) selected from a hydroxyl group (different from those that may be included in functional group (a)) and an amino group, and has an average molecular weight of 1000 to 10000.

[0089] In the first example, the Zr component is included in the chemical conversion coating as zirconium hydrofluoric acid. The V component is a vanadium compound, the P component is phosphoric acid, and the Co component is at least one selected from the group consisting of cobalt sulfate, cobalt nitrate, and cobalt carbonate. Examples of vanadium compounds include vanadium pentoxide V2O5, metavanadate HVO3, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl3, vanadium trioxide V2O3, vanadium dioxide VO2, vanadium oxide, vanadium oxysulfate VOSO4, vanadium oxyacetylacetonate VO(OC(=CH2)CH2COCH3))2, vanadium acetylacetonate V(OC(=CH2)CH2COCH3))3, vanadium trichloride VCl3, and phosphovanadomolybdic acid. Furthermore, pentavalent vanadium compounds can also be used that have been reduced to tetravalent or divalent using an organic compound having at least one functional group selected from the group consisting of hydroxyl groups, carbonyl groups, carboxyl groups, primary to tertiary amino groups, amide groups, phosphate groups, and phosphonic acid groups.

[0090] The second example of a chemical conversion coating is an example of an inorganic coating, which is a chemical conversion coating mainly composed of an organosilicon compound (silane coupling agent). Organosilicon compounds have a cyclic siloxane structure in their structure. Here, "cyclic siloxane bond" refers to a cyclic structure that has a continuous Si-O-Si bond configuration and is composed only of Si and O bonds, with 3 to 8 Si-O repeats.

[0091] The organosilicon compound is obtained by blending a silane coupling agent (A) containing at least one amino group in its molecule and a silane coupling agent (B) containing at least one glycidyl group in its molecule in a solid content 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 independently represent an alkoxy group or a hydroxyl group, and at least one of R1, R2, and R3 represents an alkoxy group), and at least one hydrophilic functional group (b) selected from the group consisting of a hydroxyl group (however, if functional group (a) contains a hydroxyl group, the hydroxyl group (b) is separate from that hydroxyl group) and an amino group, and has an average molecular weight of 1000 to 10000.

[0092] In the second example, the Zr-based component is included 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 hydrofluoric acid is more preferable. When zirconium hydrofluoric acid is used, better corrosion resistance and paintability can be obtained.

[0093] The chemical conversion coating contains a vanadium compound as component V, a phosphoric acid compound as component P, and at least one selected from the group consisting of cobalt sulfate, cobalt nitrate, and cobalt carbonate as component Co. Examples of vanadium compounds include vanadium pentoxide V2O5, metavanadate HVO3, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride VOCl3, vanadium trioxide V2O3, vanadium dioxide VO2, vanadium oxide, vanadium oxysulfate VOSO4, vanadium oxyacetylacetonate VO(OC(=CH2)CH2COCH3)2, vanadium acetylacetonate V(OC(=CH2)CH2COCH3)3, vanadium trichloride VCl3, and phosphovanadomolybdic acid. Furthermore, a pentavalent vanadium compound can also be used if it has been reduced to a tetravalent or divalent state by an organic compound having at least one functional group selected from the group consisting of hydroxyl groups, carbonyl groups, carboxyl groups, primary to tertiary amino groups, amide groups, phosphate groups, and phosphonic acid groups.

[0094] Examples of phosphate compounds include phosphoric acid, ammonium phosphate, potassium phosphate, and sodium phosphate. Among these, phosphoric acid is more preferable. When phosphoric acid is used, superior corrosion resistance can be obtained.

[0095] A third example of a chemical conversion coating is an inorganic coating, which includes an acrylic resin, zirconium, vanadium, phosphorus, and cobalt. More specifically, the chemical conversion coating includes particulate acrylic resin (resin particles) and an inhibitor phase. The acrylic resin is preferably a resin containing a polymer of (meth)acrylate alkyl ester, which may be a polymer obtained by polymerizing only (meth)acrylate alkyl ester, or a copolymer obtained by polymerizing (meth)acrylate alkyl ester and other monomers. "(meth)acrylic" means "acrylic" or "methacrylic". The inhibitor phase includes zirconium, vanadium, phosphorus, and cobalt. The zirconium forms a crosslinked structure with the acrylic resin.

[0096] The fourth example of the formation treatment film is an example of an inorganic film, and includes a zirconium carbonate compound, an acrylic resin, a vanadium compound, a phosphorus compound, and a cobalt compound. Examples of the zirconium carbonate compound include zirconium carbonate, ammonium zirconium carbonate, potassium zirconium carbonate, sodium zirconium carbonate, etc., and one or more of these can be used. Among them, zirconium carbonate and ammonium zirconium carbonate are preferable in terms of excellent corrosion resistance.

[0097] 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 formation treatment film.

[0098] Examples of the vanadium compound include divalent to tetravalent vanadium compounds. More specifically, for example, vanadium pentoxide (V2O5), metavanadic acid (HVO3), ammonium metavanadate, sodium metavanadate, vanadium oxychloride (VOCl3) and other pentavalent vanadium compounds reduced to divalent to tetravalent with a reducing agent, vanadium trioxide (V2O3), vanadium dioxide (VO2), vanadium oxy sulfate (VOSO4), vanadium oxy oxalate [VO(COO)2], vanadium oxyacetylacetonate [VO(OC(CH3)=CHCOCH3))2], vanadium acetylacetonate [V(OC(CH3)=CHCOCH3))3], vanadium trichloride (VCl3), phosphovanadomolybdic acid {H 15 -X[PV 12 -xM ox O 40Vanadium compounds with oxidation numbers of 4 to 2, such as ·nH2O (6 < x < 12, n < 30), vanadium sulfate (VSO4·8H2O), vanadium dichloride (VCl2), vanadium oxide (VO), etc., can be mentioned.

[0099] 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 of inorganic acids such as orthophosphoric acid, metaphosphoric acid, condensed phosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetraphosphoric acid, hexametaphosphoric acid, etc. is free and salts thereof.

[0100] Examples of organic acid anions having an acid group containing phosphorus include, for example, 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-phosphonobutane-1,2,4-tricarboxylic acid, inositol hexaphosphonic acid, phytic acid, etc. Organic acid anions in which at least one hydrogen of organic phosphonic acids, organic phosphoric acids, etc. is free and salts thereof can be mentioned.

[0101] Examples of cobalt compounds include cobalt sulfate, cobalt nitrate, and cobalt carbonate.

[0102] The fifth example of the formation treatment film is an example of a resin film, which contains any one or more of metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles as conductive pigments. The conductive pigment has a powder resistivity of 7.0×10 at 23 to 27 °C 7It has a density of Ωcm or less and contains one or more elements selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W.

[0103] Examples of intermetallic compounds include ferrosilicon and ferromanganese. Conductive oxide particles can be, for example, substances that have conductivity by doping impurities into the crystal lattice of an oxide (doped conductive oxides) or types in which the oxide surface is modified with a conductive substance. As for the former, generally known materials can be used, such as 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.). As for the latter, generally known materials can be used, such as zinc oxide or silica modified with conductive SnO2. Doped conductive oxides are preferred as conductive oxides, and Al-doped zinc oxide is preferred as a doped conductive oxide.

[0104] Conductive non-oxide ceramic particles are composed of ceramics made of elements or compounds that do not contain oxygen. 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 in which boron (B), carbon (C), nitrogen (N), and silicon (Si) are the main non-metallic constituent elements, respectively. These are generally known non-oxide ceramics, and any one or more selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, and W can be used. Furthermore, from the viewpoint of whether or not they are used in industrial products, as well as stable distribution in domestic and international markets, price, and electrical resistivity, the non-oxide ceramics exemplified below are more preferred. 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, or a mixture of two or more of these particles is more preferred.

[0105] The sixth example of a chemical conversion treatment film is a resin film, which includes 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 3 functional groups, and (b) a blocked organic polyisocyanate or a blocked prepolymer having NCO groups at the ends obtained by the reaction of an organic polyisocyanate with an active hydrogen compound.

[0106] (i) A polyester polyol having at least three functional groups can be obtained by esterifying a dicarboxylic acid, a glycol, and a polyol having at least three OH groups.

[0107] Examples of dicarboxylic acids used in the production of polyester polyols include aliphatic acids such as succinic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, dodecane diacitic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, and dimer acid, as well as aromatic and alicyclic acids such as phthalic acid, phthalic anhydride, isophthalic acid, dimethyl isophthalate, terephthalic acid, dimethyl terephthalate, 2,6-naphthalenedicarboxylic acid, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, cyclohexanedicarboxylic acid, dimethyl cyclohexanedicarboxylic acid, methylhexahydrophthalic anhydride, hymic anhydride, and methylhymic anhydride.

[0108] 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 hydroxydivalic 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, polycaprolactonediol, polypropylene glycol. Examples include aliphatic compounds such as polytetramethylene ether glycol, polycarbonate diol, 2-n-butyl-2-ethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol, as well as aliphatic or aromatic compounds such as cyclohexanedimethanol, cyclohexanediol, 2-methyl-1,1-cyclohexanedimethanol, xylylene glycol, bishydroxyethyl terephthalate, 1,4-bis(2-hydroxyethoxy)benzene, hydrogenated bisphenol A, ethylene oxide adducts of bisphenol A, and propylene oxide adducts of bisphenol A.

[0109] Examples of polyols having at least three OH groups include glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, pentaerythritol, diglycerin, and ethylene oxide adducts, propion oxide adducts, or ε-caprolactane adducts derived from these polyols as initiators.

[0110] (b) Blocked compounds include, for example, compounds having at least two NCO groups, 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, 2,6-diisocyanate methyl caproate, and other aliphatic diisocyanates. For example, 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanate methyl-3,5,5-trimethylhexyl isocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,2-bis(isocyanate methyl)cyclohexane, 1,4-bis(isocyanate methyl)cyclohexane, 1,3-bis(isocyanate Cycloalkylene diisocyanates such as trans-methyl)cyclohexane and trans-cyclohexane-1,4-diisocyanate, as well as, for example, 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-tole diisocyanate, 4,4'-toluidine diisocyanate, dianisidine diisocyanate, and 4,4'-diphenyl ether di Aromatic diisocyanates such as isocyanates, and aliphatic diisocyanates such as ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, α,α,α',α'-tetramethylmetaxylylenediisocyanate, and triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatebenzene, 2,4,6-triisocyanatetoluene, ω-isocyanateethyl-2,Examples include blocked triisocyanates such as 6-diisocyanate caproate, blocked tetraisocyanates such as 4,4'-diphenylmethylmethane-2,2',5,5'-tetraisocyanate, blocked derivatives of isocyanate compounds such as dimers, trimers, biuret, allophanate, carbodiimide, polymethylene polyphenyl polyisocyanate (crude MDI, c-MDI, polymeric MDI), crude TDI, or blocked prepolymers having NCO groups at the terminals obtained by reaction of these with active hydrogen compounds.

[0111] The conductive particles are corrosion-resistant particles that are alloys or compounds containing 50% or more by mass of Si, or composites thereof. The conductive particles are preferably ferrosilicon. Furthermore, rust-preventive pigments may be added to the chemical conversion coating. Examples of known rust-preventive pigments include hexavalent chromates such as strontium chromate and calcium chromate. If the use of hexavalent chromium compounds as rust inhibitors is to be avoided, those that release one or more of silicate ions, phosphate ions, or vanadate ions can be used.

[0112] Of course, the examples of chemical conversion treated coatings in this embodiment are not limited to those described above, and chemical conversion treated coatings listed in the examples described later can also be suitably used.

[0113] The method for forming the chemical conversion coating described above is not particularly limited; a chemical conversion solution (coating solution) corresponding to each of the above compositions can be applied to the Zn-plated steel sheet by a known method and then baked and dried. As an example of a preferred combination of Zn-plated steel sheet and chemical conversion coating, a combination of Zn-Al-Mg plated steel sheet and an inorganic coating mainly composed of Si components can be mentioned. [Examples]

[0114] The present disclosure will be further described below with reference to examples. The examples described below are merely examples of the present disclosure and do not limit it.

[0115] <Preparing the materials> As an extremely low-carbon steel with excellent workability, steel having the steel composition shown in Table 1 (the remainder being iron and impurities) was hot-rolled, pickled, and cold-rolled to a thickness of 0.6 mm to prepare a cold-rolled steel sheet. Next, the cold-rolled steel sheet was subjected to hot-dip aluminum plating in a continuous hot-dip galvanizing line of the non-oxidizing furnace type to obtain an aluminum-plated steel sheet. The plating line used was a non-oxidizing furnace-reducing furnace type line, and annealing was also performed in this hot-dip galvanizing line. The annealing temperature was 850°C.

[0116] [Table 1]

[0117] After plating, the plating thickness is reduced to approximately 40g / m² on both sides using the gas wiping method. 2 The temperature was adjusted accordingly. The bath temperature for the molten plating was set to 660°C. The plating bath used was a molten aluminum bath with silicon added as needed.

[0118] In this embodiment, a steel sheet plated in a molten Al bath without added Si is also referred to as a "pure Al plated steel sheet," a steel sheet plated in a molten Al bath with 2% by mass of Si added is also referred to as an "Al-2%Si plated steel sheet," a steel sheet plated in a molten Al bath with 9% by mass of Si added is also referred to as an "Al-9%Si plated steel sheet," a steel sheet plated in a molten Al bath with 15% by mass of Si added is also referred to as an "Al-15%Si plated steel sheet," and a steel sheet plated in a molten Al bath with 20% by mass of Si added is also referred to as an "Al-20%Si plated steel sheet."

[0119] Next, the surface of the Al-plated steel sheet was coated with a chemical conversion solution using a roll coater as needed. The amount of chemical conversion solution applied was adjusted by adjusting the rotation speed of the roll coater and the pressure between the rolls (generally called nip pressure). The amount applied was 500 mg / m² per side by dry weight. 2 The chemical conversion treatment solution was applied, and then dried in a hot air oven under conditions that the final plate temperature reached 80°C. The chemical conversion treatment was applied to both sides of the aluminum-plated steel sheet.

[0120] The chemical conversion treatment solutions used for painting were three types: an aqueous solution containing 2.5 g / L of γ-aminopropyltriethoxysilane, a Si-based chemical conversion treatment solution; an aqueous solution containing 3 g / L of zirconium ammonium carbonate, a Zr-based chemical conversion treatment solution; and an aqueous solution containing 40 g / L of titanium(IV) ammonium fluoride, a Ti-based chemical conversion treatment solution. Details of the prepared Al-plated steel sheets are shown in Table 4.

[0121] Furthermore, after the cold-rolled steel sheets, which had undergone the cold-rolling process described above, were annealed in a continuous hot-dip galvanizing apparatus capable of annealing under conditions where the maximum achievable sheet temperature was 820°C, and then hot-dip galvanized steel sheets (Zn-based plated steel sheets) were also prepared. Here, the gas atmosphere in the annealing furnace during the annealing process was an N2 atmosphere containing 1.0 volume% H2. Four types of plating bath components were used in the plating process: 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").

[0122] Furthermore, in hot-dip galvanizing using a Zn-0.09 mass%Al plating (GA) molten plating bath, alloying hot-dip galvanizing was performed by the following process. Specifically, the steel plate was immersed in the molten plating bath. Then, while withdrawing the steel plate from the plating bath, the amount of coating was adjusted by gas wiping with N2 gas blown from a slit nozzle. Next, the plate was heated to a temperature of 480°C using an induction heater to alloy it and diffuse the Fe in the steel plate into the plating layer.

[0123] Furthermore, the amount of plating adhering to the plated steel sheet is 45 g / m² per side of the steel sheet for GA. 2 Plating other than GA is 60g / m 2 For comparison, cold-rolled steel sheets that had only been annealed on a continuous annealing line without plating were also prepared.

[0124] Next, a chemical conversion treatment solution (film treatment solution) was applied to the surface of the Zn-plated steel sheet produced in the above process using a roll coater as needed. The amount of chemical conversion treatment solution applied (i.e., the thickness of the chemical conversion treatment film) was adjusted by controlling the rotation speed of the roll coater and the pressure between the rolls (generally called nip pressure). This formed a chemical conversion treatment film of a predetermined thickness on the plated steel sheet.

[0125] In this process, when the chemical conversion treatment film was an inorganic film, the chemical conversion treatment solution was applied and then dried in a hot air oven under conditions that resulted in a plate temperature of 80°C. When the chemical conversion treatment film was a resin film, before applying the chemical conversion treatment solution to the plated steel sheet, Palcoat E200, a chemical conversion treatment product 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, and then dried in a hot air oven under conditions that resulted in a plate temperature of 80°C. After that, the chemical conversion treatment solution was applied to a predetermined film thickness using a roll coater, and then dried in a hot air oven under conditions that resulted in a plate temperature of 200°C. The chemical conversion treatment film was applied to both sides of the plated steel sheet. The film thickness after each type of film was applied and dried was measured by embedding the coated steel sheet in resin so that the vertical cross-section could be observed, polishing it, and then observing it with a scanning electron microscope. The magnification used for observation with the scanning electron microscope was appropriately selected according to the film thickness.

[0126] Furthermore, in samples prepared with a film thickness exceeding 1.5 μm after coating and drying the inorganic film, uniform film formation was not achieved with any processing solution, resulting in cracks or delamination of the film. Therefore, it was determined that it is difficult to manufacture inorganic films with a film thickness exceeding 1.5 μm. Details of the steel sheets prepared by coating various plated steel sheets with the film are shown in Table 4.

[0127] <Method for preparing inorganic chemical treatment solution> An inorganic chemical treatment solution (a chemical treatment solution for forming an inorganic film) was prepared using the following procedure. Specifically, an aqueous solution was prepared by adding 10 g / L of γ-aminopropyltriethoxysilane as an inorganic chemical treatment solution mainly composed of Si components. Furthermore, to the prepared γ-aminopropyltriethoxysilane aqueous solution, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of Co nitrate were added as needed to prepare an inorganic chemical treatment solution.

[0128] Furthermore, an aqueous solution containing 3.0 g / L of zirconium ammonium carbonate was prepared as an inorganic chemical treatment solution mainly composed of Zr-based components. To this prepared zirconium ammonium carbonate aqueous solution, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of cobalt nitrate were added as needed to prepare further inorganic chemical treatment solutions. Details of the prepared inorganic chemical treatment solutions are shown in Table 2.

[0129] Furthermore, an aqueous solution was prepared by adding 40 g / L of titanium(IV) ammonium fluoride, a Ti-based chemical conversion treatment solution. Then, to the prepared ammonium zirconium carbonate aqueous solution, 1.3 g / L of vanadium oxide, 0.7 g / L of phosphoric acid, and 0.5 g / L of cobalt nitrate were added as needed to prepare an inorganic chemical conversion treatment solution. Details of the prepared inorganic chemical conversion treatment solutions are shown in Table 2.

[0130] [Table 2]

[0131] The presence or absence of Si-O bonds, etc., in the inorganic film was confirmed by the following method. Specifically, the prepared inorganic chemical 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 plate temperature of 80°C. This formed an inorganic film on the plated steel sheet. Next, the film surface was measured using an IRT-5200 manufactured by JASCO Corporation, and the presence or absence of one or more Si-O bonds, Si-C bonds, and Si-OH bonds in the inorganic film was determined from the assignment of observed peaks originating from the resin component in the infrared absorption spectrum of the obtained inorganic film. Specifically, at 3250 cm², -1 Nearby, 1080-1020cm -1 Nearby, 500-300cm -1 Nearby, 900-700cm -1 If a peak was observed in at least one of the surrounding areas, it was determined that the inorganic film contained one or more of the following: Si-O bonds, Si-C bonds, or Si-OH bonds. The results are shown in Table 2.

[0132] <Method for preparing resin-based chemical conversion treatment solution> A resin-based chemical conversion treatment solution (a chemical conversion treatment solution for forming a resin film) was prepared using the following procedure. Specifically, a solution was prepared by dissolving Toyobo's "Byron(R) 300" polyester resin in cyclohexanone as a solvent at a concentration of 30% by mass. To 100 parts by mass of the solid content of this solution, 20 parts by mass of Ornex's melamine resin "CYMEL(R) 303" was added and mixed. Furthermore, 5% by mass of Ornex's curing catalyst "CYCAT(R) 600" was added and mixed to the total solid content of the prepared mixture. In this way, a base treatment solution for obtaining a resin film was prepared.

[0133] Next, a resin-based chemical conversion treatment solution was prepared by mixing the following particles into the prepared base treatment solution. The amount of particles added was adjusted using the following method. Specifically, the mass ratio of the particles added to the base treatment solution to the solid content in the resin film (mass ratio to solid content other than particles) was determined, and the volume fraction was calculated from the specific gravity of the solid content in the resin film and the specific gravity of the particles. Then, the amount of particles added was adjusted so that the calculated volume ratio matched the volume fractions listed in Table 3. The specific gravity used was the catalog value or literature value for each substance. Details of the resin-based treatment solution are shown in Table 3.

[0134] [Table 3]

[0135] • Vanadium boride: "VB2-O" manufactured by Nippon Shinkinzoku Co., Ltd. was classified using a sieve to obtain an average particle size of 3.1 μm. Hereafter, it will also be referred to as "VB2". The average particle size was calculated based on the mass percentage of each particle size category after classification. • Al-doped zinc oxide: Conductive zinc oxide (Al-Doped ZnO) "23-K" manufactured by Hakusui Tech Co., Ltd., with a primary particle size of 120-250 nm (catalog value) was used. Hereafter, it will also be referred to as "Al-ZnO". • Metallic zinc: Reagent zinc granules were classified using a sieve to obtain an average particle size of 10 μm. Hereafter, this will also be referred to as "Zn". • Ferrosilicon: Ferrosilicon manufactured by Marubeni Tetsugen Co., Ltd. was pulverized into fine particles using a pulverizer, classified using a sieve to obtain an average particle size of 3.5 μm. Hereinafter referred to as "Fe-Si". • Ferromanganese: Ferrosilicon manufactured by Marubeni Tetsugen Co., Ltd. was pulverized into fine particles using a pulverizer, 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 Shinkinzoku Co., Ltd., was classified using a sieve to obtain an average particle size of 2 μm. Hereafter, it will also be referred to as "ZrB2". • Molybdenum silicide: "MoSi2-F" manufactured by Nippon Shinkinzoku Co., Ltd. was classified using a sieve to obtain an average particle size of 3.5 μm. Hereafter, it will also be referred to as "MoSi2". • Chromium boride: "CrB2-O" manufactured by Nippon Shinkinzoku Co., Ltd. was classified using a sieve to obtain an average particle size of 5 μm. Hereafter, it will also be referred to as "CrB2". • Tungsten silicide: "WSi2-F" manufactured by Nippon Shinkinzoku Co., Ltd. was classified using a sieve to obtain an average particle size of 2 μm. Hereafter, it will also be referred to as "WSi2". Nickel: Reagent nickel powder was used, classified using a sieve to obtain an average particle size of 5 μm. Hereafter, it will also be referred to as "Ni". • Conductive titanium oxide: Sn-doped titanium oxide "ET-500W" manufactured by Ishihara Sangyo Co., Ltd., with an average particle size of 2-3 μm (catalog value), was used. Hereinafter referred to as "conductive Ti". • Alumina: Showa Denko's fine-grained alumina "A-42-2" with an average particle size (center diameter of particle size distribution) of 4.7 μm (catalog value) was used. Hereafter, it will also be referred to as "alumina". Titanium dioxide: "Typake(R) CR-95" manufactured by Ishihara Sangyo Co., Ltd., with an average particle size of 0.28 μm (catalog value), was used. Hereafter, it will also be referred to as "TiO2". • Aluminum nitride: Aluminum nitride powder for fillers manufactured by Tokuyama Corporation, particle size 1 μm (catalog value) was used. Hereafter referred to as "AlN".

[0136] The powder resistivity of the particles in Table 3 was determined using the MCP-PD51 powder resistance measurement system manufactured by Mitsubishi Chemical Analytec Co., Ltd., as the resistance value when each powder was compressed to 10 MPa at 25°C.

[0137] <Evaluation of the fabricated metal plate> (1. Evaluation of coolant corrosion resistance) The corrosion resistance of the fabricated steel plates to coolant when used in the cooling structure (cooling device) of a battery unit was investigated. Specifically, cylindrical parts with a diameter of Φ50 mm and a draw height of 40 mm were fabricated by Erichsen processing of the fabricated Al-plated steel plates and Zn-plated steel plates. 30 mL of coolant was added to the inside of these cylindrical parts, and then the lid was closed to seal it. The coolant used was an aqueous solution of Nissan Motor Co., Ltd.'s Long Life Coolant diluted to 30% by mass with water. These were left standing in a constant temperature bath at 90°C for 1000 hours to accelerate the deterioration of the steel plates in the coolant-immersed area. In addition, a similar test was conducted using a deteriorated solution prepared by adding 800 ppm of formic acid to a 30% by mass aqueous solution of the Long Life Coolant, simulating the case where the coolant deteriorated. After the test, the coolant immersion in the cylindrical parts was removed, the cylindrical parts were dried, and the corrosion status 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.

[0138] The evaluation of coolant corrosion resistance in Tables 4 and 5 is as follows: 5 points: No change in appearance. 4 points: Discolored to black, or showing spotty white rust. 3. White rust is present, but the area affected by white rust in the coolant-immersed portion is less than 20% of the total area of ​​the coolant-immersed portion. 2. The rate of white rust occurrence is between 20% and 80%. 1. The rate of white rust occurrence is 80% or higher, or red rust is present.

[0139] (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. Since electrodeposition coating is commonly applied to areas exposed to the outside air, this disclosure evaluates the external corrosion resistance after electrodeposition coating.

[0140] Specifically, steel sheets cut to a size of 70 mm wide x 150 mm long were degreased, surface-treated, treated with zinc phosphate, and then electrodeposited. Specifically, degreasing was performed by immersing the steel sheets in Nippon Parkerizing Co., Ltd.'s degreasing agent "Fine Cleaner E6408" at 60°C for 5 minutes. Surface treatment was performed by immersing the degreased steel sheets in Nippon Parkerizing Co., Ltd.'s "Preparen X" at 40°C for 5 minutes. After that, zinc phosphate treatment was performed by immersing the steel sheets in Nippon Parkerizing Co., Ltd.'s zinc phosphate chemical agent "Palbond L3065" at 35°C for 3 minutes. After zinc phosphate treatment, the steel sheets were washed with water and dried in an oven at a 150°C atmosphere. Then, Nippon Paint's electrodeposition paint "Power Float 1200" was electrodeposited onto the steel sheets to a thickness of 15 μm per side, and baked in an oven at a 170°C atmosphere for 20 minutes. The electrodeposited steel billet prepared using the above process was cut with a utility knife to create a test specimen.

[0141] A cycle corrosion test (CCT) was performed using the prepared test specimens. The CCT mode was performed in accordance with the automotive industry standard JASO-M609. The side of the electrodeposited coating with cuts was used as the evaluation surface, and the test machine was set up so that salt water was sprayed onto the evaluation surface for the cycle corrosion test.

[0142] The test was conducted for 120 cycles (8 hours per cycle), and the corrosion status from the cut area was observed to evaluate the external corrosion resistance according to the following criteria. The results are shown in Tables 4 and 5. The evaluation of external corrosion resistance in Tables 4 and 5 is as follows: 5 points: If the paint film blister width from the cut area is 15 mm or less and no red rust occurs. 4 points: If the paint film blister width from the cut area is more than 15 mm but within 20 mm, and no red rust has occurred. 3 points: If the paint film blister width from the cut area is more than 20 mm, and no red rust has occurred. 2. If a small amount of red rust is present at the cut area. 1 point: If red rust is present across the entire cut surface.

[0143] (3. Processability evaluation) Bending tests were conducted using the fabricated aluminum-plated steel sheets and zinc-plated steel sheets. In particular, when cracks occur on the surface of the plated steel sheets during processing, the plating layer breaks and the iron substrate is exposed to the air. Therefore, depending on the processed shape, there is a risk of corrosion occurring from the processed area, so the processability was evaluated. Specifically, the fabricated Al-plated steel sheets were subjected to a 180° tight-fitting bend, and the processed area was examined with a 20x magnifying glass to visually evaluate the processability. Specifically, the processability was evaluated based on whether or not cracks occurred on the surface. The results are shown in Tables 4 and 5. A "-" in Tables 4 and 5 indicates that this evaluation was not performed because the plated material was Zn-plated.

[0144] [Table 4]

[0145] [Table 5]

[0146] <Evaluation of cooling characteristics and adhesive durability in battery packs> (1. Creating a battery pack) A battery unit was fabricated using the manufactured steel plate (steel plate No. 4 in Table 4) and A6063 aluminum alloy. Specifically, flat plates cut from this steel plate were used as the top cover (top surface) 10c of the battery pack case and the aforementioned flow path top cover 26. Separately, a prepared steel plate was deep-drawn into a rectangular tube using a press machine, and the flange portion was cut after processing to create the other parts of the battery pack (bottom and side surfaces). The bottom surface of the battery pack was also processed to be 375 mm wide x 1060 mm long. During processing, rust-preventive oil was applied to the Al-plated steel plate, and after processing, the oil was removed by alkaline degreasing.

[0147] Furthermore, the cooling structure was fabricated by die-casting A6063 aluminum to create the flow channel formation section. The cooling structure was manufactured so that the number of flow channels, flow channel width (L), and distance between flow channels (w) matched the values ​​shown in Tables 7 and 8.

[0148] Next, adhesive was applied to the joints of the cooling structure, and the cooling structure and the flow path cover were placed on top of each other. The adhesives used were "ThreeBond 2249G" (manufactured by ThreeBond Fine Chemicals Co., Ltd.) for epoxy adhesive, "ThreeBond 1207B" (manufactured by ThreeBond Fine Chemicals Co., Ltd.) for silicone adhesive, "Metal Grip" (manufactured by 3M Japan Limited) for acrylic adhesive, and "ThreeBond 1539" (manufactured by ThreeBond Fine Chemicals Co., Ltd.) for urethane adhesive. After joining, adhesive was applied to achieve the thickness (D30) and overhang length (L23) shown in Tables 7 and 8, and the parts were joined. Subsequently, the adhesives were cured according to the curing conditions of each adhesive. The main component resin content and hardness after curing of each adhesive are shown in Table 6.

[0149] [Table 6]

[0150] Next, rubber heaters were laid on the bottom of the inside of the battery pack as a substitute for the heat-generating battery cells, and the case was then covered with a lid. When covering the case, sealant was applied to the flange to create a tight seal. The sealant used was "Sealant 45N" manufactured by Shin-Etsu Silicone Co., Ltd.

[0151] (2. Battery pack cooling characteristics evaluation test) The fabricated battery pack was heated by passing an electric current through its rubber heater. Here, the current value that would raise the rubber heater's surface temperature to 50°C was determined beforehand, and this fixed current value was then applied to the rubber heater. Next, coolant was flowed through the water refrigerant channel. As the coolant, an aqueous solution of Nissan Motor's Long Life Coolant diluted with water to 30% by mass was used. Hoses, a pump, and a chiller were attached to the ends of the channel on both sides of the cooling structure to form a circulation path, and the coolant was circulated within this path. The chiller was controlled so that the temperature of the coolant was 25-30°C. Then, the temperature of the rubber heater surface inside the case, directly above the intermediate section between the cooling channels, was measured one hour after the start of coolant circulation. In the "cooling capacity" category, a temperature decrease of 8°C or more compared to when the coolant was not circulating was evaluated as "A", a temperature decrease of 2°C or less but less than 8°C was evaluated as "B", and a temperature decrease of less than 2°C was evaluated as "C". The battery pack cooling characteristic evaluation test was conducted in a room maintained at 25°C by air conditioning. The results are shown in Tables 7 and 8. In Tables 7 and 8, "-" indicates a level where the channel was not established due to insufficient bonding strength.

[0152] [Table 7]

[0153] [Table 8]

[0154] (3. Battery pack bonding strength evaluation test) To evaluate the joint strength of the battery pack, the joint portion of the cooling structure was cut out and subjected to a peel tensile test. In the "joint strength" category, a peel tensile strength of 1.0 kN / m or more was classified as "A", 0.2 kN / m or more but less than 1.0 kN / m was classified as "B", and less than 0.2 kN / m was classified as "C".

[0155] Furthermore, after circulating cooling water through the fabricated cooling structure for 1000 hours, the joint portion of the cooling structure was cut out and subjected to a peel tensile test. In the "Joint Strength Retention Rate" category, a retention rate of 60% or more in the peel tensile strength of the joint before and after cooling water circulation was classified as "A," 60% or more but less than 20% as "B," and less than 20% as "C." The results are shown in Tables 7 and 8. In Table 8, "-" indicates a level where the flow path was not established due to insufficient joint strength.

[0156] As shown in Tables 4, 5, 7, and 8, the present invention example that satisfies the requirements of this embodiment obtained excellent results in all evaluation items. Therefore, it was found that the cooling structure according to this embodiment has excellent strength and corrosion resistance at the joint portion of dissimilar metals.

[0157] In contrast, comparative examples that did not meet the requirements of this embodiment, such as those without plating, yielded poor results in at least one of the evaluation items.

[0158] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention. [Industrial applicability]

[0159] The cooling structure and battery unit described herein are extremely useful in industry because they provide a cooling structure with excellent strength and corrosion resistance at the joints of dissimilar metals. [Explanation of symbols]

[0160] 1 Cooling structure 10 Battery Packs 21 Flow channel forming section 22 Joint 23. Protruding part 25 Water cooling medium channel 26 Flow channel upper cover 30 Adhesive part

Claims

1. A cooling structure having a water coolant channel formed to contact the bottom surface of a battery pack, The cooling structure has a flow path forming portion which constitutes a part of the flow path for the water refrigerant, The aforementioned flow path forming portion is joined to the member to be joined by an adhesive portion. The member to be joined is either the bottom surface portion or the upper cover of the flow path that covers the flow path forming portion. The member to be joined is made of a steel sheet on which an inorganic film or resin film is formed as a chemical conversion treatment film on an Al-plated steel sheet or a Zn-plated steel sheet. The aforementioned flow channel forming portion is made of aluminum alloy. The thickness of the adhesive portion is 0.0005 mm or more, and the adhesive portion protrudes 0.1 mm or more towards the water refrigerant flow path side. The distance between the flow paths for the water refrigerant is 20 mm or less. The width of the water refrigerant flow path is 60 mm or less. A cooling structure characterized by the following features.

2. The cooling structure according to claim 1, characterized in that the plating layer of the Al-based plated steel sheet contains Si.

3. The cooling structure according to claim 2, characterized in that the Si content of the plating layer of the Al-based plated steel sheet is 2.0% by mass or more and 15% by mass or less.

4. The cooling structure according to claim 1 or 2, characterized in that a film containing a Zr-based component, a Ti-based component, or a Si-based component as the main component is formed on the surface of the Al-based plated steel sheet as a chemical conversion treatment film.

5. The cooling structure according to claim 1, characterized in that the inorganic film on the surface of the Zn-plated steel sheet mainly contains a Si-based component or a Zr-based component.

6. The cooling structure according to claim 1, characterized in that the inorganic film on the surface of the Zn-plated steel sheet contains at least one of the following components as a rust inhibitor: V, P, and Co.

7. The cooling structure according to claim 6, characterized in that the rust-preventive component is one or more of vanadium oxide, phosphoric acid, and Co nitrate.

8. The cooling structure according to claim 1, characterized in that the inorganic film on the surface of the Zn-plated steel sheet is composed of a compound phase containing one or more of Si-O bonds, Si-C bonds, and Si-OH bonds.

9. The cooling structure according to claim 1, characterized in that the thickness of the inorganic film is greater than 0 μm and less than or equal to 1.5 μm.

10. The cooling structure according to claim 1, characterized in that the inorganic film or the resin film is electrically conductive.

11. The cooling structure according to claim 1, characterized in that the resin coating comprises a resin, a rust-preventive pigment, and a conductive pigment.

12. The resin film contains one or more of the following as conductive pigments: metal particles, intermetallic compound particles, conductive oxide particles, and conductive non-oxide ceramic particles. The cooling structure according to claim 11, characterized in that the conductive pigment has a powder resistivity of 7.0 × 10⁷ Ωcm or less at 23 to 27°C, and contains one or more elements selected from the group consisting of Zn, Si, Zr, V, Cr, Mo, Mn, Fe, and W as constituent elements.

13. The cooling structure according to claim 11 or 12, characterized in that the resin film contains the conductive pigment in a proportion of 1.0% by mass or more and 30% by mass or less.

14. The cooling structure according to claim 1, characterized in that the adhesive portion contains 10% or more of any of epoxy resin, silicone resin, acrylic resin, or urethane resin.

15. The cooling structure according to claim 1, characterized in that the hardness of the adhesive portion is A15 or more and D90 or less.

16. A battery unit comprising a cooling structure according to claim 1 or 2 and a battery pack.

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